Clinically Oriented Anatomy

Table of Contents Authors Editors Dedication Preface Acknowledgments Table of Contents List of Clinical Blue Boxes Int...

Author: Keith L. Moore MSc PhD FIAC FRSM FAAA | Authur F. Dalley | Anne M.R. Agur PhD

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Table of Contents Authors Editors Dedication Preface Acknowledgments Table of Contents

List of Clinical Blue Boxes Introduction to Clinically Oriented Anatomy 1 - Thorax 2 - Abdomen 3 - Pelvis and Perineum 4 - Back 5 - Lower Limb 6 - Upper Limb 7 - Head 8 - Neck 9 - Summary of Cranial Nerves Appendices Abbreviations Figure Credits Index

Authors: Moore, Keith L.; Dalley, Arthur F. Title: Clinically Oriented Anatomy, 5th Edition

Authors Keith L. Moore Ph.D., F.I.A.C., F.R.S.M. Professor Emeritus in Division of Anatomy Department of Surgery; Former Chair of Anatomy and Associate Dean for Basic Medical Sciences; Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Arthur F. Dalley II Ph.D. Professor of Cell and Developmental Biology, Director Medical Gross Anatomy and Anatomical Donations Program, Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee, U.S.A. In collaboration with, and with content provided by

Anne M. R. Agur B.Sc. (OT), M.Sc., Ph.D. Associate Professor in Division of Anatomy Department of Surgery, Department of Physical Therapy and Department of Occupational Therapy, Division of Biomedical Communications, Department of Surgery, Institute of Medical Science; Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada With the developmental assistance and dedication of

Marion E. Moore B.A.

Secondary Editors Betty Sun Acquisitions Editor Kathleen H. Scogna Developmental Editor Joe Schott Marketing Manager Jennifer Glazer Production Editor Christiane Odyniec Production Editor Doug Smock Designer Maryland Composition Company, Inc. Compositor R. R. Donnelly & Sonsâ€”Willard Printer


Dedication To Marion My best friend, wife, colleague, and mother of our five children for her love, unconditional support, and understanding, and in loving memory of our son Warren, who is sadly missed. K L M To Muriel My bride, best friend, counselor, and mother of our boys; and to our family—Tristan, Lana, and Elijah Gray, Denver, and Skyler—with love and great appreciation for their support, understanding, good humor, and—most of all—patience A F D To Our Students You will remember some of what you hear, much of what you read, more of what you see, and almost all of what you experience and understand fully.


Preface A quarter century has passed since the first edition of Clinically Oriented Anatomy appeared on bookstore shelves; six years have passed since the fourth edition was published. The relatively long interval between editions results from efforts to continue to make this book even more student friendly and authoritative. This fifth edition has therefore been thoroughly revised with significant new changes and updates.

Key Features Clinically Oriented Anatomy has been widely acclaimed for the relevance of its clinical correlations. As in previous editions, the fifth edition places clinical emphasis on anatomy that is important in general practice, diagnostic radiology, emergency medicine, and general surgery. Special attention has been directed toward assisting students in learning the anatomy they will need to know in the twenty‐first century, and to this end new features have been added and existing features updated. Clinical correlations. Popularly known as “blue boxes,” the clinical information sections have grown, and many of them are now supported by photographs and/or dynamic color illustrations to help with understanding the practical value of anatomy. Bottom Line summaries. A new feature in this edition, frequent Bottom Line boxes summarize the preceding information, ensuring that primary concepts do not become lost in the many details necessary for thorough understanding. These summaries provide a convenient means of ongoing review. Anatomy described in a practical, functional context. A more realistic approach to the musculoskeletal system emphasizes the action and use of muscles and muscle groups in daily activities. New material has been added to address gait and grip. The eccentric contraction of muscles, which accounts for much of their activity, is now discussed along with the concentric contraction that is typically the sole focus in anatomy texts. This perspective is important to most health professionals, including the growing number of physical and occupational therapy students using this book. Surface anatomy. Surface anatomy sections, identified by their yellow‐screened background, feature all‐new color photographs, clearly demonstrating anatomy's relationship to physical examination and diagnosis. Both natural views of unobstructed surface anatomy and illustrations superimposing anatomical structures on surface anatomy photographs are components of each regional chapter. Medical imaging. Each regional chapter ends with sections on medical imaging, identified by their green‐screened backgrounds. These sections provide various combinations of plain and contrast radiographic, MRI, CT, and ultrasonography

studies, often with correlative line art as well as explanatory text, to help prepare future professionals who need to be familiar with diagnostic images. Case studies, accompanied by clinicoanatomical problems and 105 new USMLE‐style multiple‐choice questions. These interactive case studies and multiple‐choice questions are included on an accompanying CD, providing a convenient and comprehensive means of self‐testing and review. Extensive new art program. The extensive new art program implemented in the fourth edition has been extended and revised. An effort has been made to ensure that all the anatomy presented and covered in the text is also illustrated. The text and illustrations have been developed to work together for optimum pedagogical effect, aiding the learning process and reducing the amount of searching required to find structures. The great majority of the clinical conditions are now supported by photographs and/or color illustrations; multipart illustrations often combine dissections, line art, and medical images; most tables appear in color and are illustrated to aid the student's understanding of the structures described. Terminology. The terminology fully adheres to the new Terminologia Anatomica (1998), approved by the International Federation of Associations of Anatomists (IFAA). Although the official English‐equivalent terms are used throughout the book, when new terms are introduced, the Latin form, used in Europe, Asia, and other parts of the world, is also provided. The roots and derivations of terms are provided to help students understand meaning and increase retention. Eponyms, although not endorsed by the IFAA, appear in parentheses in this edition—for example, sternal angle (angle of Louis) —to assist students who will hear eponymous terms during their clinical studies.

Retained and Improved Features Students and faculty have told us what they want and expect from Clinically Oriented Anatomy, and we listened: 

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A comprehensive text enabling students to fill in the blanks, as time allotted for lectures continues to decrease, laboratory guides become exclusively instructional, and multiauthored lecture notes develop inconsistencies in comprehension, fact, and format. A resource capable of supporting areas of special interest and emphasis within specific anatomy courses that serves the anatomy needs of students during both the basic science and the clinical phases of their studies. A thorough Introduction that covers important systemic information and concepts basic to the understanding of the anatomy presented in the subsequent regional chapters. Students from many countries and backgrounds have written to express their views of this book—gratifyingly, most are congratulatory. Health professional students have more diverse backgrounds and experiences than ever before. Curricular constraints often result in unjustified assumptions concerning the prerequisite information necessary for many students to understand the presented material. The Introduction includes efficient summaries of functional systemic anatomy. Student comments specifically emphasized the need for a systemic description of the nervous

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system and the peripheral autonomic nervous system (ANS) in particular. The increased coverage of the ANS implemented in the fourth edition has been strengthened and further supported with new illustrations in this edition. Routine facts (such as muscle attachments, innervations, and actions) presented in tables organized to demonstrate shared qualities and illustrated to demonstrate the provided information. Clinically Oriented Anatomy provides more tables than any other anatomy textbook. Illustrated clinical correlations that not only describe but also show anatomy as it is applied clinically. Illustrations that facilitate orientation. Many orientation figures have been added, along with arrows to indicate the locations of the inset figures (areas shown in close‐up views) and viewing sequences. Almost all illustrations have been completely relabeled, moving the viewpoint out of the legend and next to each part of every illustration. Labels have been placed to minimize the distance between label and object, with leader lines running the most direct course possible. Case studies with practice questions that review and underscore important aspects of clinically applied anatomy are useful in preparation for internal and external examinations, such as the USMLE.

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More than 130 new full‐color illustrations, including many multipart illustrations combining dissections, line art, and medical images such as CTs and MRIs have been added to this edition. Boldface type indicates the main entries of anatomical terms when they are introduced and defined; italic type indicates anatomical terms important to the topic and region of study. Boldface is also used in the surface anatomy (yellow) boxes to indicate visible or palpable features and to introduce clinical terms in the clinical correlation (blue) boxes. Useful content outlines appear at the beginning of every chapter. Instructor's resources and supplemental materials, including images exportable for Power Point presentation, are available—both specific to COA and through the institutional version of Dynamic Human Anatomy, which includes many resources from the LWW portfolio of anatomy products.

Commitment to Educating Students This book is written for health science students, keeping in mind those who may not have had a previous acquaintance with anatomy. We have tried to present the material in an interesting way so that it can be easily integrated with what will be taught in more detail in other disciplines such as physical diagnosis, medical rehabilitation, and surgery. We hope this text will serve two purposes: to educate and to excite. If students develop enthusiasm for clinical anatomy, the goals of this book will have been fulfilled. Keith L. Moore University of Toronto, Faculty of Medicine Arthur F. Dalley II Vanderbilt University, School of Medicine


Acknowledgments We wish to thank the following colleagues who were invited by the publisher to assist with the development of this fifth edition through their critical analysis and review of an initial draft of the manuscript.    

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Patricia A. Brewer, Ph.D., Assistant Professor, Department of Physical Therapy, University of Texas Health Science Center at San Antonio, San Antonio, Texas. Matthew Davey, M.D., Registrar, Intensive Care Unit, The Canberra Hospital, Canberra, ACT, Australia. Duane E. Haines, Ph.D., Professor and Chairman, Department of Anatomy, The University of Mississippi Medical Center, Jackson, Mississippi. Kenneth H. Jones, Ph.D., Assistant Professor, Department of Anatomy and Medical Education, Ohio State University, College of Medicine and Public Health, Columbus, Ohio. William A. Roy, Ph.D., Associate Professor of Anatomy, The University of Mississippi Medical Center, Jackson, Mississippi. Joel A. Vilensky, Ph.D., Professor of Anatomy, Department of Anatomy and Cell Biology, Indiana University School of Medicine, Fort Wayne, Indiana. Michael P. Zumpano, Ph.D., Associate Professor, Department of Anatomy, New York Chiropractic College, Seneca Falls, New York.

Several students, who have since graduated, were also invited by the publisher to review an initial draft of the manuscript:  

Renee Hsia, M.D., M.Sc., Emergency Medicine Resident, Stanford University Hospital, Stanford, California. John C. Teeters, M.D., Resident, University of Rochester Medical Center, Rochester, New York.

In addition to reviewers, many people—some of them unknowingly—helped us by perusing, discussing, or contributing to parts of the manuscript and/or providing constructive criticism of the text and illustrations in this and previous editions:  Dr. Peter Abrahams, Consultant Clinical Anatomist, University of Cambridge and examiner to the Royal College of Surgeons of Edinburgh, Cambridge, United Kingdom.  Dr. Robert D. Acland, Professor of Surgery/Microsurgery, Division of Plastic and Reconstructive Surgery, University of Louisville, Louisville, Kentucky.  Dr. Oloruntosin Akindele, Tofunmi Medical Center, Igbogbo, Lagos State, Nigeria.  Dr. Julian J. Baumel, Professor Emeritus of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska.  Dr. Edna Becker, Associate Professor of Medical Imaging, University of Toronto Faculty of Medicine, Toronto, Ontario, Canada.  Dr. Donald R. Cahill, Professor of Anatomy (retired; former Chair), Mayo Medical School; former Editor‐in‐Chief of Clinical Anatomy, Rochester, Minnesota.  Dr. Joan Campbell, Assistant Professor of Medical Imaging, University of Toronto Faculty of Medicine, Toronto, Ontario, Canada.

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Dr. Stephen W. Carmichael, Professor and Chair of Anatomy, Mayo Medical School, Editor‐in‐Chief of Clinical Anatomy, Rochester, Minnesota. Dr. Carmine D. Clemente, Professor of Anatomy and Orthopedic Surgery, University of California, Los Angeles School of Medicine, Los Angeles, California. Dr. James D. Collins, Professor of Radiological Sciences, University of California, Los Angeles School of Medicine/Center for Health Sciences, Los Angeles, California. Dr. Raymond F. Gasser, Professor of Anatomy, Louisiana State University School of Medicine, New Orleans, Louisiana. Dr. Ralph Ger, Professor of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York; Associate Chairman, Department of Surgery, Nassau County Medical Center, East Meadow, New York. Dr. Douglas J. Gould, Associate Professor, University of Kentucky, Lexington, Kentucky. Dr. Daniel O. Graney, Professor of Biological Structure, University of Washington School of Medicine, Seattle, Washington. Dr. David G. Greathouse, Professor and Chair, Belmont University School of Physical Therapy, Nashville, Tennessee. Dr. Masoom Haider, Assistant Professor of Medical Imaging, University of Toronto Faculty of Medicine, Toronto, Ontario, Canada. Dr. John S. Halle, Professor, Belmont University School of Physical Therapy, Nashville, Tennessee. Dr. Jennifer L. Halpern, Resident in Orthopedic Surgery and Rehabilitation, Vanderbilt University School of Medicine, Nashville, Tennessee. Dr. Walter Kuchareczyk, Professor and Chair of Medical Imaging, University of Toronto Faculty of Medicine; Clinical Director of Tri‐Hospital Magnetic Resonance Centre, Toronto, Ontario, Canada. Dr. Nirusha Lachman, Program Chair, Anatomy, Durban Institute of Technology, Durban, South Africa. Dr. H. Wayne Lambert, Instructor, Cell and Developmental Biology and Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee. Dr. Michael von LÃ¼dinghausen, University Professor, Anatomy Institute, University of WÃ¼rzburg, WÃ¼rzburg, Germany. Dr. Shirley McCarthy, Director of MRI, Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut. Dr. Lillian Nanney, Professor of Plastic Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee. Dr. Todd R. Olson, Professor of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York. Dr. Wojciech Pawlina, Professor of Anatomy, Mayo Medical School, Rochester, Minnesota. Dr. David Peck, Associate Professor of Anatomy and Neurobiology (retired), University of Kentucky School of Medicine, Lexington, Kentucky. Dr. T. V. N. Persaud, Professor of Human Anatomy and Cell Science Faculties of Medicine and Dentistry, University of Manitoba, Winnipeg, Manitoba, Canada. Dr. Cathleen C. Pettepher, Associate Professor of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee. Dr. Thomas H. Quinn, Professor of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska. Dr. George E. Salter, Professor of Anatomy, Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama.

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Dr. Tatsuo Sato, Professor and Head (retired), Second Department of Anatomy, Tokyo Medical and Dental University Faculty of Medicine, Tokyo, Japan. Professor Colin P. Wendell‐Smith, Department of Anatomy and Physiology, University of Tasmania, Hobart, Tasmania, Australia. Dr. Andreas H. Weiglein, Associate Professor, Institut fur Anatomie, Medical University Graz, Graz, Austria. Dr. David G. Whitlock, Professor of Anatomy, University of Colorado Medical School, Denver, Colorado.

Our grateful appreciation is extended to Marion Moore, the senior author's wife (of 55 years), for her friendly help and patience with the preparation of the manuscript. She prepared many drafts of each chapter and provided tactful, constructive criticism as the “polishing” process progressed. We also wish to acknowledge the excellent work of Kathleen Scogna, the Senior Developmental Editor. Her great efforts cannot be overstated. The quality of this edition is the result in no small part of her critical perspective, keen observations and insights, encouragement, advocacy, great attention to detail, and detailed text—art coordination. Art plays a major role in facilitating learning. We extend our sincere gratitude and appreciation for the skills, talents, and timely work of our medical illustrators for this edition, Rob Duckwall of Dragonfly Media Group and Valerie Oxorn, who contributed many new and modified illustrations. David Rini also contributed to the art program in this edition. Wayne Hubble at LWW did a masterful job of labeling, relabeling, and resizing artwork. E. Anne Rayner, Senior Photographer, Vanderbilt Medical Art Group did an excellent job photographing the surface anatomy models, working in association with Dr. Anne Agur and the junior author (AFD). We greatly appreciate the contribution our models made to the quality of this edition. Much of the art was originally prepared for the fourth edition by Craig Durant and colleagues at J/B Woolsey Associates, Elkins Park, Pennsylvania. Although the number of illustrations from Grant's Atlas of Anatomy continues to be reduced and replaced by new art, we gratefully acknowledge the excellent art done by the following: Dorothy Foster Chubb, Elizabeth Blackstock, Nancy Joy, Nina Kilpatrick, David Mazierski, Stephen Mader, Bart Vallecoccia, Sari O'Sullivan, Kam Yu, and Caitlin Duckwall. Many thanks also to those at Lippincott Williams & Wilkins who participated in the development of this edition: Betty Sun, Executive Editor; Crystal Taylor, Acquisitions Editor; and Jennifer Glazer and Christiane Odyniec, Production Editors. We would like to thank Joe Schott and his marketing colleagues for their imaginative and informative marketing and promotion of the previous and current editions. Finally, thanks is due to the sales division at LWW, which has played a key role in the continued success of this book. Keith L. Moore Arthur F. Dalley II


List of Clinical Blue Boxes Introduction to Clinically Oriented Anatomy Skin Incisions and Scarring / 14 Stretch Marks in Skin / 14 Skin Injuries and Their Classification / 15 Lacerations / 15 Burns / 15 Fascial Planes / 18 Accessory Bones / 21 Heterotopic Bones / 21 Trauma to Bone and Bone Changes / 21 Osteoporosis / 22 Sternal Puncture / 22 Bone Growth and the Assessment of Bone Age / 24 Effects of Disease and Diet on Bone Growth / 25 Displacement and Separation of Epiphyses / 25 Avascular Necrosis / 26 Joints of the Newborn Cranium / 29 Degenerative Joint Disease / 29 Arthroscopy / 30 Muscle Dysfunction and Paralysis / 37 Absence of Muscle Tone / 37 Muscle Soreness and â€œPulledâ€ Muscles / 37 Growth and Regeneration of Skeletal Muscle / 37 Muscle Testing / 37 Hypertrophy of the Myocardium and Myocardial Infarction / 38 Hypertrophy and Hyperplasia of Smooth Muscle / 39 Arteriosclerosis: Ischemia and Infarction / 41 Varicose Veins / 43 The Spread of Cancer / 46 Lymphangitis, Lymphadenitis, and Lymphedema / 46 Damage to the CNS / 47 Rhizotomy / 58 Peripheral Nerve Degeneration and Ischemia of Nerves / 58

1: Thorax Chest Pain / 77 Rib Fractures / 79 Flail Chest / 80 Thoracotomy, Intercostal Space Incisions, Rib Excision, and Bone Grafting / 80 Supernumerary Ribs / 81 Protective Function and Aging of Costal Cartilages / 81 Ossified Xiphoid Processes / 84 Sternal Fractures / 84

Median Sternotomy / 84 Sternal Biopsy / 84 Sternal Anomalies / 84 Thoracic Outlet Syndrome / 85 Dislocation of Ribs / 90 Separation of Ribs / 90 Paralysis of the Diaphragm / 90 Dyspnea: Difficult Breathing / 98 Extrapleural Intrathoracic Surgical Access / 98 Herpes Zoster Infection of the Spinal Ganglia / 101 Intercostal Nerve Block / 102 Changes in the Breasts / 106 Breast Quadrants / 106 Carcinoma of the Breast / 109 Polymastia, Polythelia, and Amastia / 110 Breast Cancer in Men / 111 Gynecomastia / 111 Injuries to the Cervical Pleura and Apex of Lung / 117 Injury to Other Parts of the Pleurae / 117 Pulmonary Collapse / 117 Pneumothorax, Hydrothorax, and Hemothorax / 118 Thoracentesis / 118 Insertion of a Chest Tube / 119 Thoracoscopy / 119 Pleuritis (Pleurisy) / 119 Pleurectomy and Pleurodesis / 120 Variations in the Lobes of the Lung / 123 Appearance of the Lungs and Inhalation of Carbon Particles and Irritants / 123 Auscultation of the Lungs and Percussion of the Thorax / 123 Lung Cancer and Mediastinal Nerves / 124 Aspiration of Foreign Bodies / 126 Bronchoscopy / 126 Lung Resections / 128 Segmental Atelectasis / 128 Pulmonary Embolism / 131 Lymphatic Drainage after Pleural Adhesion / 132 Bronchogenic Carcinoma / 132 Pleural Pain / 132 Levels of the Viscera Relative to the Mediastinal Divisions / 136 Mediastinoscopy and Mediastinal Biopsies / 136 Widening of the Mediastinum / 137 Surgical Significance of the Transverse Pericardial Sinus / 140 Exposure of the IVC and SVC / 140 Pericarditis, Pericardial Rub, and Pericardial Effusion / 140 Cardiac Tamponade / 140 Pericardiocentesis / 141 Positional Abnormalities of the Heart / 145 Percussion of the Heart / 145 Embryology of the Right Atrium / 147

Septal Defects / 150 Stroke or Cerebrovascular Accident / 151 Basis for Naming the Cusps of the Aortic and Pulmonary Valves / 154 Valvular Heart Disease / 154 Coronary Artery Disease or Coronary Heart Disease / 159 Angina Pectoris / 160 Coronary Bypass Graft / 161 Coronary Angioplasty / 161 Collateral Circulation via the Smallest Cardiac Veins / 162 Electrocardiography / 165 Coronary Occlusion and the Conducting System of the Heart / 165 Artificial Cardiac Pacemaker / 166 Restarting the Heart / 166 Fibrillation of the Heart / 166 Defibrillation of the Heart / 166 Cardiac Referred Pain / 166 Age Changes in the Thymus / 170 Aneurysm of the Ascending Aorta / 173 Variations in the Great Arteries / 174 Coarctation of the Aorta / 175 Injury to the Recurrent Laryngeal Nerves / 176 Blockage of the Esophagus / 180 Laceration of the Thoracic Duct / 181 Variations of the Thoracic Duct / 182 Alternate Venous Routes to the Heart / 184

2: Abdomen Clinical Significance of Fascia and Fascial Spaces of Abdominal Wall / 198 Protuberance of the Abdomen / 205 Abdominal Hernias / 205 Palpation of the Anterolateral Abdominal Wall / 206 Superficial Abdominal Reflexes / 206 Injury to Nerves of the Anterolateral Abdominal Wall / 208 Abdominal Surgical Incisions / 208 Reversal of Venous Flow and Collateral Pathways of Superficial Abdominal Veins / 212 External Supravesical Hernia / 214 Postnatal Patency of the Umbilical Vein / 214 Maldescent of Testis / 220 Cancer of the Uterus and Labium Majus / 220 Inguinal Hernias / 223 Cremasteric Reflex / 225 Cysts and Hernias of the Canal of Nuck / 225 Hydrocele / 225 Hematocele / 226 Torsion of the Spermatic Cord / 226 Anesthetizing the Scrotum / 227 Spermatocele and Epididymal Cyst / 228 Vestigial Remnants of Embryonic Genital Ducts / 228

Varicocele / 228 Cancer of the Testis and Scrotum / 229 Patency and Blockage of the Uterine Tubes / 232 The Peritoneum and Surgical Procedures / 232 Peritonitis and Ascites / 233 Peritoneal Adhesions and Adhesiotomy / 233 Abdominal Paracentesis / 233 Intraperitoneal Injection and Peritoneal Dialysis / 233 Functions of the Greater Omentum / 238 Abscess Formation / 238 Spread of Pathological Fluids / 238 Flow of Ascitic Fluid and Pus / 238 Fluid in the Omental Bursa / 239 Intestine in the Omental Bursa / 239 Severance of the Cystic Artery / 241 Esophageal Varices / 247 Pyrosis / 248 Displacement of the Stomach / 250 Hiatal Hernia / 250 Congenital Diaphragmatic Hernia / 252 Pylorospasm / 256 Congenital Hypertrophic Pyloric Stenosis / 256 Carcinoma of the Stomach / 256 Gastrectomy / 256 Gastric Ulcers, Helicobacter pylori, and Vagotomy / 257 Visceral Referred Pain / 257 Duodenal Ulcers / 264 Developmental Changes in the Mesoduodenum / 264 Paraduodenal Hernias / 264 Brief Review of the Embryological Rotation of the Midgut / 268 Navigating the Small Intestine / 268 Ischemia of the Intestine / 268 Ileal Diverticulum / 270 Position of the Appendix / 275 Appendicitis / 275 Appendectomy / 275 Laparoscopy / 275 Mobile Ascending Colon / 277 Colitis, Colectomy, Ileostomy, and Colostomy / 279 Colonoscopy / 279 Diverticulosis / 280 Rupture of the Spleen / 284 Splenectomy and Splenomegaly / 285 Accessory Spleen(s) / 285 Splenic Needle Biopsy and Splenoportography / 286 Blockage of the Hepatopancreatic Ampulla and Pancreatitis / 287 Accessory Pancreatic Tissue / 287 Pancreatectomies / 288 Rupture of the Pancreas / 288

Pancreatic Cancer / 288 Subphrenic Abscesses / 292 Hepatic Lobectomies and Segmentectomy / 293 Rupture of the Liver / 294 Aberrant Hepatic Arteries / 297 Variations in the Relationships of the Hepatic Arteries / 297 Unusual Formation of the Portal Vein / 298 Hepatomegaly / 298 Cirrhosis of the Liver / 298 Liver Biopsy / 300 Infundibulum of the Gallbladder / 303 Mobile Gallbladder / 303 Variations in the Cystic and Hepatic Ducts / 303 Accessory Hepatic Ducts / 304 Gallstones / 304 Gallstones in the Duodenum / 305 Cholecystectomy / 305 Portosystemic Shunts / 307 Portal Hypertension / 307 Perinephric Abscess / 308 Nephroptosis / 308 Renal Transplantation / 311 Renal Cysts / 312 Pain in the Pararenal Region / 312 Accessory Renal Vessels / 314 Congenital Anomalies of the Kidneys and Ureters / 314 Renal and Ureteric Calculi / 319 Hiccups / 328 Section of a Phrenic Nerve / 330 Referred Pain from the Diaphragm / 330 Rupture of the Diaphragm and Herniation of Viscera / 330 Congenital Diaphragmatic Hernia / 330 Psoas Abscess / 333 Posterior Abdominal Pain / 335 Partial Lumbar Sympathectomy / 337 Pulsations of the Aorta and Abdominal Aortic Aneurysm / 338 Collateral Routes for Abdominopelvic Venous Blood / 341

3: Pelvis and Perineum Variations in the Male and Female Pelves / 362 Pelvic Diameters (Conjugates) / 362 Pelvic Fractures / 363 Spondylolysis and Spondylolisthesis / 366 Relaxation of Pelvic Ligaments and Increased Joint Mobility during Pregnancy / 367 Injury to the Pelvic Floor / 373 Prenatal â€œRelaxationâ€ Training for Participatory Childbirth / 373 Injury to the Pelvic Nerves / 382 Iatrogenic Injury of the Ureters during Ligation of Uterine Artery / 387

Ligation of the Internal Iliac Artery and Collateral Circulation in the Pelvis / 388 Iatrogenic Injury of the Ureters during Ligation of Ovarian Artery / 389 Iatrogenic Compromise of the Ureteric Blood Supply / 394 Ureteric Calculi / 394 Cystoceleâ€”Hernia of the Bladder / 400 Suprapubic Cystotomy / 400 Rupture of the Bladder / 400 Cystoscopy / 401 Clinically Significant Differences between Male and Female Urethrae / 405 Male Sterilization / 405 Abscesses in the Seminal Glands / 406 Hypertrophy of the Prostate / 409 Distension of the Vagina / 412 Digital Examination through the Vagina / 413 Vaginal Fistulae / 413 Culdoscopy and Culdocentesis / 413 Cervical Cancer, Cervical Examination, and Pap Smear / 418 Examination of the Uterus / 418 Lifetime Changes in the Normal Anatomy of the Uterus / 418 Disposition of the Uterus and Uterine Prolapse / 419 Hysterectomy / 421 Anesthesia for Childbirth / 422 Infections of the Female Genital Tract / 426 Patency of the Uterine Tubes / 426 Ligation of the Uterine Tubes / 426 Ectopic Tubal Pregnancy / 426 Remnants of the Embryonic Ducts / 427 Laparoscopic Examination of Pelvic Viscera / 428 Rectal Examination / 433 Resection of the Rectum / 433 Disruption of the Perineal Body / 435 Episiotomy / 436 Rupture of the Urethra in Males and Extravasation of Urine / 441 Starvation and Rectal Prolapse / 445 The Pectinate Lineâ€”A Clinically Important Landmark / 449 Anal Fissures and Perianal Abscesses / 449 Hemorrhoids / 450 Anorectal Incontinence / 451 Urethral Catheterization / 452 Distension of the Scrotum / 453 Palpation of the Testes / 453 Hypospadias / 458 Phimosis, Paraphimosis, and Circumcision / 458 Female Circumcision / 464 Vulvar Trauma / 464 Infection of the Greater Vestibular Glands / 464 Administration of Pudendal and Ilioinguinal Nerve Blocks / 465 Kegel Exercises for Increased Development of Female Perineal Muscles / 467 Vaginismus / 467

4: Back Backache and Back Pain / 478 Laminectomy / 482 Dislocation of the Cervical Vertebrae / 485 Fracture and Dislocation of the Atlas / 485 Fracture and Dislocation of the Axis / 486 Lumbar Spinal Stenosis / 489 Caudal Epidural Anesthesia / 493 Abnormal Fusion of Vertebrae / 494 Injury of the Coccyx / 494 Cervical Ribs / 495 Effect of Aging on Vertebrae / 495 Anomalies of the Vertebrae / 496 Aging of the Intervertebral Discs / 502 Herniation of the Nucleus Pulposus / 502 Injury and Disease of Zygapophysial Joints / 504 Fracture of the Dens / 509 Rupture of the Transverse Ligament of the Atlas / 509 Rupture of the Alar Ligaments / 510 Compression of C2 Spinal Ganglion / 510 Fractures and Dislocations of the Vertebrae / 512 Abnormal Curvatures of the Vertebral Column / 514 Back Pain / 519 Compression of the Lumbar Spinal Nerve Roots / 523 Development of the Meninges and Subarachnoid Space / 526 Lumbar Spinal Puncture / 526 Spinal Block / 527 Epidural Blocks / 527 Ischemia of the Spinal Cord / 530 Spinal Cord Injuries / 530 Back Strains and Sprains / 543 Reduced Blood Supply to the Brainstem / 547

5: Lower Limb Lower Limb Injuries / 556 Injuries of the Hip Bone (Pelvic Injuries) / 563 Coxa Vara and Coxa Valga / 565 Dislocated (â€œSlippedâ€ ) Epiphysis of the Femoral Head / 565 Femoral Fractures / 566 Tibial Fractures / 568 Fractures Involving the Epiphysial Plates / 568 Fibular Fractures / 569 Bone Grafts / 570 Calcaneal Fractures / 576 Fractures of the Talar Neck / 576 Fractures of the Metatarsals / 576 Os Trigonum / 577 Fracture of the Sesamoid Bones / 578

Varicose Veins, Thrombosis, and Thrombophlebitis / 583 Saphenous Vein Grafts / 584 Saphenous Cutdown and Saphenous Nerve Injury / 584 Enlarged Inguinal Lymph Nodes / 584 Regional Anesthetic Nerve Blocks of the Lower Limbs / 587 Variations of the Cutaneous Nerves / 588 Abnormalities of Sensory Function / 588 Absence of Plantarflexion in Walking / 589 Hip and Thigh Contusions / 596 Psoas Abscess / 596 Paralysis of the Quadriceps / 596 Chondromalacia Patellae / 596 Patellar Fractures / 596 Abnormal Ossification of the Patella / 597 Patellar Tendon Reflex / 597 Transplantation of the Gracilis / 600 Groin Pull / 600 Injury to the Adductor Longus / 600 Palpation, Compression, and Cannulation of the Femoral Artery / 603 Laceration of the Femoral Artery / 604 Replaced or Accessory Obturator Artery / 604 Potentially Lethal Misnomer / 606 Saphenous Varix / 606 Location of the Femoral Vein / 606 Cannulation of the Femoral Vein / 606 Femoral Hernia / 607 Ischial Bursitis / 616 Trochanteric Bursitis / 616 Hamstring Injuries / 619 Injury to the Superior Gluteal Nerve / 621 Anesthetic Block of the Sciatic Nerve / 622 Injury to the Sciatic Nerve / 623 Intragluteal Injections / 623 Popliteal Abscesses and Tumors / 636 Popliteal Pulse / 636 Popliteal Aneurysm and Hemorrhage / 636 Injury to the Tibial Nerve / 636 Compartment Infections and Syndromes in the Leg / 636 Tibialis Anterior Strain (Shin Splints) / 642 Deep Fibular Nerve Entrapment / 642 The Fibularis Muscles and Evolution of the Human Foot / 645 Injury to the Common Fibular Nerve and Footdrop / 646 Superficial Fibular Nerve Entrapment / 646 Avulsion of the Tuberosity of the 5th Metatarsal / 646 Fabella in the Gastrocnemius / 649 Calcaneal Tendinitis / 649 Ruptured Calcaneal Tendon / 652 Calcaneal Tendon Reflex / 652 Gastrocnemius Strain / 652

Calcaneal Bursitis / 652 Venous Return from the Leg / 652 Accessory Soleus / 653 Posterior Tibial Pulse / 656 Plantar Fasciitis / 663 Infections of the Foot / 666 Contusion of the Extensor Digitorum Brevis / 668 Sural Nerve Grafts / 669 Anesthetic Block of the Superficial Fibular Nerve / 669 Plantar Reflex / 669 Medial Plantar Nerve Entrapment / 669 Palpation of the Dorsalis Pedis Pulse / 670 Hemorrhaging Wounds of the Sole of the Foot / 671 Lymphadenopathy / 672 Bipedalism and Congruity of the Articular Surfaces of the Hip Joint / 675 Fractures of the Femoral Neck (â€œHip Fracturesâ€ ) / 682 Surgical Hip Replacement / 682 Necrosis of the Femoral Head in Children / 682 Dislocation of the Hip Joint / 683 Genu Valgum and Genu Varum / 687 Patellar Dislocation / 689 Patellofemoral Syndrome / 690 Knee Joint Injuries / 695 Arthroscopy of the Knee Joint / 699 Aspiration of the Knee Joint / 699 Bursitis in the Knee Region / 700 Popliteal Cysts / 700 Knee Replacement / 700 Ankle Injuries / 706 Tibial Nerve Entrapment / 706 Hallux Valgus / 712 Hammer Toe / 712 Claw Toes / 713 Pes Planus (Flatfeet) / 713 Clubfoot (Talipes) / 714

6: Upper Limb Upper Limb Injuries / 726 Variations of the Clavicle / 729 Fracture of the Clavicle / 729 Ossification of the Clavicle / 730 Fracture of the Scapula / 732 Fractures of the Humerus / 733 Fractures of the Radius and Ulna / 736 Fracture of the Scaphoid / 738 Fracture of the Hamate / 738

Fracture of the Metacarpals / 738 Fracture of the Phalanges / 738 Absence of the Pectoral Muscles / 750 Paralysis of the Serratus Anterior / 751 Triangle of Auscultation / 757 Injury of the Accessory Nerve (CN XI) / 757 Injury of the Thoracodorsal Nerve / 757 Injury to the Dorsal Scapular Nerve / 759 Injury to the Axillary Nerve / 760 Fractureâ€“Dislocation of the Proximal Humeral Epiphysis / 762 Rotator Cuff Injuries and the Supraspinatus / 763 Compression of the Axillary Artery / 766 Arterial Anastomoses around the Scapula / 767 Aneurysm of the Axillary Artery / 767 Injuries to the Axillary Vein / 770 The Role of the Axillary Vein in Subclavian Vein Puncture / 771 Enlargement of the Axillary Lymph Nodes / 773 Dissection of the Axillary Lymph Nodes / 773 Variations of the Brachial Plexus / 775 Brachial Plexus Injuries / 778 Brachial Plexus Block / 781 Bicipital Myotatic Reflex / 786 Biceps Tendinitis / 787 Dislocation of the Tendon of the Long Head of the Biceps / 787 Rupture of the Tendon of the Long Head of the Biceps / 789 Interruption of Blood Flow in the Brachial Artery / 793 Fracture of the Humeral Shaft / 793 Injury to the Musculocutaneous Nerve / 794 Injury to the Radial Nerve in the Arm / 795 Venipuncture in the Cubital Fossa / 799 Variation of Veins in the Cubital Fossa / 799 Elbow Tendinitis or Lateral Epicondylitis / 813 Mallet or Baseball Finger / 813 Fracture of the Olecranon / 813 Synovial Cyst of the Wrist / 813 High Division of the Brachial Artery / 817 Superficial Ulnar Artery / 817 Measuring the Pulse Rate / 818 Variations in the Origin of the Radial Artery / 818 Median Nerve Injury / 819 Pronator Syndrome / 822 Communications between the Median and the Ulnar Nerves / 822 Ulnar Nerve Injury / 822 Cubital Tunnel Syndrome / 823 Radial Nerve Injury in the Forearm / 824 Dupuytren Contracture of Palmar Fascia / 830 Hand Infections / 830 Tenosynovitis / 836 Laceration of the Palmar Arches / 838

Ischemia of the Fingers / 838 Lesions of the Median Nerve / 839 Carpal Tunnel Syndrome / 840 Trauma to the Median Nerve / 843 Ulnar Canal Syndrome (Guyon Tunnel Syndrome) / 844 Handlebar Neuropathy / 844 Radial Nerve Injury and the Hand / 844 Dermatoglyphics / 848 Palmar Wounds and Surgical Incisions / 848 Dislocation of the Sternoclavicular Joint / 851 Ankylosis of the Sternoclavicular Joint / 851 Dislocation of the Acromioclavicular Joint / 852 Calcific Supraspinatus Tendinitis / 856 Rotator Cuff Injuries / 857 Dislocation of the Glenohumeral Joint / 858 Axillary Nerve Injury / 858 Glenoid Labrum Tears / 859 Adhesive Capsulitis of the Glenohumeral Joint / 859 Bursitis of the Elbow / 862 Avulsion of the Medial Epicondyle / 862 Dislocation of the Elbow Joint / 862 Subluxation and Dislocation of Radial Head / 865 Wrist Fractures / 870 Bull Rider's Thumb / 874 Skier's Thumb / 874

7: Head Head Injuries / 886 Headaches and Facial Pain / 886 Injury to the Superciliary Arches / 891 Malar Flush / 891 Fractures of the Maxillae and Associated Bones / 891 Fractures of the Mandible / 891 Resorption of Alveolar Bone / 892 Fractures of the Calvaria / 893 Fracture of the Pterion / 893 Development of the Cranium / 902 Age Changes in the Face / 903 Obliteration of the Cranial Sutures / 904 Age Changes in the Cranium / 904 Craniosynostosis and Cranial Malformations / 904 Scalp Wounds / 906 Scalp Infections / 906 Sebaceous Cysts / 906 Cephalhematoma / 906 Bone Flaps / 908 Blunt Trauma to the Head / 911 Tentorial Herniation / 912

Bulging of the Sellar Diaphragm / 912 Occlusion of Cerebral Veins and Dural Venous Sinuses / 915 Metastasis of Tumor Cells to the Dural Sinuses / 915 Fractures of the Cranial Base / 915 Dural Origin of Headaches / 917 Leptomeningitis / 919 Head Injuries and Intracranial Hemorrhage / 919 Cerebral Injuries / 921 Cisternal Puncture / 925 Hydrocephalus / 925 Leakage of Cerebrospinal Fluid / 925 Anastomoses of Cerebral Arteries and Cerebral Embolism / 930 Variations of the Cerebral Arterial Circle / 930 Strokes / 930 Brain Infarction / 931 Transient Ischemic Attacks / 931 Facial Lacerations and Incisions / 933 Flaring of the Nostrils / 938 Paralysis of Facial Muscles / 938 Infraorbital Nerve Block / 943 Mental and Incisive Nerve Blocks / 944 Buccal Nerve Block / 944 Trigeminal Neuralgia / 944 Lesions of the Trigeminal Nerve / 944 Herpes Zoster Infection of the Trigeminal Ganglion / 944 Testing the Sensory Function of CN V / 945 Injuries to the Facial Nerve / 945 Compression of the Facial Artery / 950 Pulses of the Arteries of the Face / 951 Stenosis of the Internal Carotid Artery / 951 Scalp Lacerations / 951 Scalp Injuries / 951 Thrombophlebitis of the Facial Vein / 952 Squamous Cell Carcinoma of the Lip / 952 Parotidectomy / 955 Infection of the Parotid Gland / 955 Abscess in the Parotid Gland / 955 Sialography of the Parotid Duct / 955 Blockage of the Parotid Duct / 955 Accessory Parotid Gland / 955 Periorbital Ecchymosis / 958 Fractures of the Orbit / 958 Orbital Tumors / 961 Injury to the Nerves Supplying the Eyelids / 963 Inflammation of the Palpebral Glands / 963 Hyperemia of the Conjunctiva / 963 Subconjunctival Hemorrhages / 963 Pupillary Light Reflex / 964 Uveitis / 966

Development of the Retina / 966 Ophthalmoscopy / 966 Retinal Detachment / 966 Papilledema / 967 Corneal Abrasions and Lacerations / 968 Presbyopia and Cataracts / 968 Hemorrhage into the Anterior Chamber / 968 Artificial Eye / 972 Corneal Reflex / 973 Corneal Ulcers and Transplants / 973 Oculomotor Nerve Palsy / 973 Horner Syndrome / 973 Paralysis of the Extraocular Muscles / 973 Glaucoma / 975 Blockage of the Central Artery of the Retina / 975 Blockage of the Central Vein of the Retina / 976 Mandibular Nerve Block / 981 Inferior Alveolar Nerve Block / 981 Dislocation of the TMJ / 986 Arthritis of the TMJ / 987 Cleft Lip / 990 Cyanosis of the Lips / 990 Large Labial Frenula / 991 Gingivitis / 992 Dental Caries, Pulpitis, and Tooth Abscesses / 995 Extraction of the Teeth / 996 Nasopalatine Block / 1000 Greater Palatine Block / 1000 Cleft Palate / 1000 Gag Reflex / 1007 Paralysis of the Genioglossus / 1007 Injury to the Hypoglossal Nerve / 1007 Sublingual Absorption of Drugs / 1007 Lingual Carcinoma / 1007 Frenectomy / 1007 Thyroglossal Duct Cyst / 1007 Aberrant Thyroid Gland / 1007 Excision of the Submandibular Gland and Removal of a Calculus / 1009 Sialography of the Submandibular Ducts / 1010 Transantral Approach to the Pterygopalatine Fossa / 1011 Nasal Fractures / 1014 Deviation of the Nasal Septum / 1014 Rhinitis / 1019 Epistaxis / 1019 Sinusitis / 1019 Variation of the Frontal Sinuses / 1019 Infection of the Ethmoidal Cells / 1019 Infection of the Maxillary Sinuses / 1022 Relationship of the Teeth to the Maxillary Sinus / 1022

Transillumination of the Sinuses / 1022 External Ear Injury / 1025 Otoscopic Examination / 1025 Acute Otitis Externa / 1026 Otitis Media / 1029 Perforation of the Tympanic Membrane / 1029 Mastoiditis / 1029 Blockage of the Pharyngotympanic Tube / 1030 Paralysis of the Stapedius / 1032 Motion Sickness / 1036 Dizziness and Hearing Loss / 1036 MÃ©niÃ¨re Syndrome / 1036 High Tone Deafness / 1036 Otic Barotrauma / 1036

8: Neck Cervical Pain / 1046 Fracture of the Hyoid / 1048 Paralysis of the Platysma / 1049 Spread of Infections in the Neck / 1053 Congenital Torticollis / 1055 Spasmodic Torticollis / 1055 Subclavian Vein Puncture / 1060 Right Cardiac Catheterization / 1060 Prominence of the External Jugular Vein / 1060 Severance of the External Jugular Vein / 1060 Lesions of the Spinal Accessory Nerve (CN XI) / 1061 Severance of the Phrenic Nerve, Phrenic Nerve Block, and Phrenic Nerve Crush / 1064 Nerve Blocks in the Lateral Cervical Region / 1064 Injury to the Suprascapular Nerve / 1065 Ligation of the External Carotid Artery / 1071 Surgical Dissection of the Carotid Triangle / 1071 Carotid Occlusion and Endarterectomy / 1071 Carotid Pulse / 1071 Carotid Sinus Hypersensitivity / 1071 Role of the Carotid Bodies / 1072 Internal Jugular Pulse / 1072 Internal Jugular Vein Puncture / 1072 Cervicothoracic Ganglion Block / 1083 Lesion of the Cervical Sympathetic Trunk / 1083 Thyroid Ima Artery / 1084 Thyroglossal Duct Cysts / 1084 Ectopic Thyroid Gland / 1084 Accessory Thyroid Glandular Tissue / 1085 Pyramidal Lobe of the Thyroid Gland / 1085 Enlargement of the Thyroid Gland / 1085 Thyroidectomy / 1086 Injury to the Recurrent Laryngeal Nerves / 1086

Inadvertent Removal of the Parathyroid Glands / 1088 Fractures of the Laryngeal Skeleton / 1091 Laryngoscopy / 1095 Valsalva Maneuver / 1095 Aspiration of Foreign Bodies and the Heimlich Maneuver / 1095 Injury to the Laryngeal Nerves / 1098 Superior Laryngeal Nerve Block / 1099 Cancer of the Larynx / 1099 Age Changes in the Larynx / 1099 Tracheostomy / 1100 Foreign Bodies in the Laryngopharynx / 1109 Sinus Tract from the Piriform Recess / 1110 Tonsillectomy / 1110 Adenoiditis / 1110 Branchial Fistula / 1110 Branchial Sinuses and Cysts / 1111 Esophageal Injuries / 1112 Tracheoesophageal Fistula / 1112 Esophageal Cancer / 1113 Zones of Penetrating Neck Trauma / 1113 Radical Neck Dissections / 1115

9: Summary of Cranial Nerves Cranial Nerve Injuries / 1124 Anosmiaâ€”Loss of Smell / 1130 Olfactory Hallucinations / 1131 Demyelinating Diseases and the Optic Nerve / 1135 Optic Neuritis / 1135 Visual Field Defects / 1135 Injury to the Oculomotor Nerve / 1137 Compression of the Oculomotor Nerve / 1137 Aneurysm of the Posterior Cerebral or Superior Cerebellar Artery / 1137 Injury to the Trochlear Nerve / 1137 Injury to the Trigeminal Nerve / 1139 Dental Anesthesia / 1141 Injury to the Abducent Nerve / 1142 Injury to the Facial Nerve / 1143 Injuries of the Vestibulocochlear Nerve / 1146 Deafness / 1146 Acoustic Neuroma / 1146 Trauma and Vertigo / 1146 Lesions of the Glossopharyngeal Nerve / 1149 Glossopharyngeal Neuralgia / 1149 Lesions of the Vagus Nerve / 1151 Injury to the Spinal Accessory Nerve / 1153 Injury to the Hypoglossal Nerve / 1154


Introduction to Clinically Oriented Anatomy A Brief History of Anatomy Anatomy—the study of the structure of the body—is one of the oldest basic medical sciences; it was first studied formally in Egypt (approximately 500 B.C.E. [B.C.]). The earliest descriptions of anatomy were written on papyruses (paper reed) between 3000 and 2500 B.C.E. (Persaud, 1984). Much later, human anatomy was taught in Greece by Hippocrates (460—377 B.C.E.), who is regarded as the Father of Medicine and a founder of the science of anatomy. In addition to the Hippocratic Oath, Hippocrates wrote several books on anatomy. In one he stated, “The nature of the body is the beginning of medical science.” Aristotle (384—322 B.C.E.) was the first person to use the term anatome, a Greek word meaning “cutting up or taking apart.” The Latin word dissecare has a similar meaning. Andreas Vesalius's (1514—1564 C.E [A.D.]) masterpiece De Humani Corporis Fabrica, published in 1543, marked a new era in the history of medicine. At that time, the study of anatomy became an objective discipline based on direct observations as well as scientific principles. Vesalius recognized anatomy “as the firm foundation of the whole art of medicine and its essential preliminary.” Hieronymus Fabricius (1537— 1619) was responsible for the construction in 1594 of the famous anatomical theater at Padua. He was one of the teachers of William Harvey, and it is believed that Fabricius's discovery of the valves in the veins led Harvey to the discovery of the circulation of blood. The publication in 1628 of Harvey's book Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, on the movements of the heart and the circulation of blood in animals, represents a milestone in the history of medicine (Persaud, 1997). By the 17th century, human dissections became an important feature in European medical schools, and anatomical museums were established in many cities. During the 18th and 19th centuries, anatomists published impressive treatises and lavish atlases with illustrations that introduced new standards for depicting the human body. The shortage of cadavers for dissection and anatomical demonstrations led to illegal means of obtaining human bodies. Professional grave robbers supplied anatomy schools with corpses, in some cases by murdering their victims. Medical students and their teachers had also been involved in body snatching (Persaud, 1997). In Britain, the Anatomy Act was passed by Parliament in 1832. It made legal provisions for medical schools to receive unclaimed and donated bodies for anatomical studies. This paved the way for similar legislation in other countries.

Approaches to Studying Anatomy Anatomy is the setting (structure) in which the events (functions) of life occur. Although historically and strictly speaking the primary concern of anatomy is structure, true understanding results when structure and function are considered together. Modern anatomy is functional anatomy. This book deals mainly with functional human gross anatomy—the examination of structures of the human that can be seen without a microscope. The three main approaches to studying anatomy

Introduction to Clinically Oriented Anatomy

are regional, systemic, and clinical (applied), reflecting the body's organization and the priorities and purposes for studying it. Regional Anatomy Regional anatomy (topographical anatomy) considers the organization of the human body as segments or major parts based on form and mass (Fig. I.1): a main body, consisting of the head, neck, and trunk (subdivided into thorax, abdomen, back, and pelvis/perineum), and paired upper limbs and lower limbs. All the major parts may be further subdivided into regions and zones. Regional anatomy is the method of studying the body's structure by focusing attention on a specific part (e.g., the head), region (the face), or subregion (the orbit); examining the arrangement and relationships of the various systemic structures (muscles, nerves, arteries, etc.) within it; and then usually continuing to study adjacent regions in an ordered sequence. It is the approach followed in this book, with each chapter addressing the anatomy of a major part of the body, and the approach usually taken in advanced anatomy courses that have a laboratory component involving dissection. When studying anatomy by this approach, it is important to make the effort routinely to put the regional anatomy into the context of that of adjacent regions and of the body as a whole. Regional anatomy also recognizes the body's organization by layers: skin, subcutaneous tissue, and deep fascia covering the deeper structures of muscles, skeleton, and cavities, which contain viscera (internal organs). Many of these deeper structures are partially evident beneath the body's outer covering and may be studied and examined in living individuals via surface anatomy. Surface anatomy is an essential part of the study of regional anatomy. It is specifically addressed in this book in “surface anatomy sections” (orange background) that provide knowledge of what lies under the skin and what structures are perceptible to touch (palpable) in the living body at rest and in action. We can learn much by observing the external form and surface of the body and observing or feeling the superficial aspects of structures beneath its surface. The aim of this method is to visualize (recall distinct mental images of) structures that confer contour to the surface or are palpable beneath it and, in clinical practice, to distinguish any unusual or abnormal findings. In other words, surface anatomy requires a thorough understanding of the anatomy of the structures beneath the surface. In people with stab wounds, for example, a physician must be able to visualize the deep structures that might be injured. Knowledge of surface anatomy can also decrease the need to memorize facts because the body is always available to observe and palpate.

Clinically Oriented Anatomy, 5th Edition By Keith Moore

Figure I.1. Major parts of the body as studied by regional anatomy. Anatomy is described relative to the anatomical position illustrated.

Physical examination is the clinical application of surface anatomy. Palpation is a clinical technique for examining living anatomy. Palpation of arterial pulses, for instance, is part of routine physical examinations. Students of many of the health sciences will learn to use instruments to facilitate examination of the body (such as an ophthalmoscope to observe features of the eyes) and to listen to functioning parts of the body (a stethoscope to listen to the heart and lungs). A reflex hammer may be used to examine the functional state of nerves and muscles. When reading the surface anatomy sections in this text, make an effort to associate living anatomy with the anatomy you learn from lectures, dissection, and/or demonstrations. Regional study of deep structures and abnormalities in a living person is now also possible by means of radiological imaging. Radiographic anatomy provides useful information about normal structures in living individuals, as affected by muscle tone, body fluids and pressures, and gravity; diagnostic radiology reveals the effects of trauma, pathology, and aging on normal structures. In this book, the “medical imaging sections” (green background) at the end of each chapter provide an introduction to radiographic anatomy. However, the detailed and thorough learning of the three‐dimensional anatomy of deep structures and their relationships is best accomplished by transecting or by removing the body's outer cover to observe the structures directly through the process of dissection. In clinical practice, surface anatomy, radiographic images, and your experience from studying anatomy will combine to provide you with knowledge of each patient's anatomy. The computer is a useful adjunct in teaching regional anatomy (Cahill and Leonard, 1997) because it facilitates certain aspects of instruction and review. Computers aid learning by allowing interactivity and manipulation of two‐ and three‐dimensional


anatomical renderings; the sequential or side‐by‐side display of planar images, such as anatomical serial sections, computed tomography (CT), and magnetic resonance imaging (MRI); and layer separations of tissues in mock dissection. Prosections, carefully prepared dissections for the demonstration of anatomical structures, are also useful. However, learning is most efficient and retention is highest when didactic study is combined with the experience of actual dissection—that is, learning by doing (Amadio, 1996; Mutyala and Cahill, 1996). During dissection you observe, palpate, move, and sequentially reveal parts of the body. In 1770, Dr. William Hunter, a distinguished Scottish anatomist and obstetrician, stated: “Dissection alone teaches us where we may cut or inspect the living body with freedom and dispatch.” Systemic Anatomy Systemic anatomy recognizes the organization of the body's organs into systems or collective apparatuses that work together to carry out complex functions; thus it is a sequential study of the functional systems of the body. The basic systems and the field of study or treatment of each (in parentheses) are 

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The integumentary system (dermatology) consists of the skin (L. integumentum, a covering) and its appendages—hair, nails, and sweat glands, for example— and the subcutaneous tissue just beneath it. The skin, an extensive sensory organ, forms the body's outer, protective covering and container. The skeletal system (osteology) consists of bones and cartilage; it provides our basic shape and support for the body and is what the muscular system acts on to produce movement. It also protects vital organs such as the heart, lungs, and pelvic organs. The articular system (arthrology) consists of joints and their associated ligaments, connecting the bony parts of the skeletal system and providing the sites at which movements occur. The muscular system (myology) consists of muscles that act (contract) to move or position parts of the body (e.g., the bones that articulate at joints). The nervous system (neurology) consists of the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves and ganglia, together with their motor and sensory endings). The nervous system controls and coordinates the functions of the organ systems, enabling the body's responses to and activities within its environment. The circulatory system (angiology) consists of the cardiovascular and lymphatic systems, which function in parallel to transport the body's fluids. o The cardiovascular system (cardiology) consists of the heart and blood vessels that propel and conduct blood through the body, delivering oxygen, nutrients, and hormones to cells and removing their waste products. o The lymphatic system is a network of lymphatic vessels that withdraws excess tissue fluid (lymph) from the body's interstitial (intercellular) fluid compartment, filters it through lymph nodes, and returns it to the bloodstream. The digestive or alimentary system (gastroenterology) consists of the organs and glands associated with ingestion, mastication (chewing), deglutition




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(swallowing), digestion, and absorption of food and the elimination of feces (solid waste) remaining after the nutrients have been absorbed. The respiratory system (pulmonology) consists of the air passages and lungs that supply oxygen to the blood for cellular respiration and eliminate carbon dioxide from it. The diaphragm and larynx control the flow of air through the system, which may also produce tone in the larynx that is further modified by the tongue, teeth, and lips into speech. The urinary system (urology) consists of the kidneys, ureters, urinary bladder, and urethra, which filter blood and subsequently produce, transport, store, and intermittently excrete urine (liquid waste). The reproductive or genital system (gynecology for females; andrology for males) consists of the gonads (ovaries and testes) that produce oocytes (eggs) and sperms, the ducts that transport them, and the genitalia that enable their union. After conception, the female reproductive tract nourishes and delivers the fetus. The endocrine system (endocrinology) consists of discrete ductless glands (such as the thyroid gland) as well as isolated and clustered cells of the gut and blood vessel walls and specialized nerve endings that secrete hormones. Hormones are organic molecules that are carried by the circulatory system to distant effector cells in all parts of the body. The influence of the endocrine system is thus as broadly distributed as that of the nervous system. These glands influence metabolism and other processes, such as the menstrual cycle.

The passive skeletal and articular systems and the active muscular system collectively constitute a supersystem, the locomotor apparatus or system (orthopedics), because they must work together to produce locomotion of the body. And although the structures directly responsible for locomotion are the muscles, bones, joints, and ligaments of the limbs, other systems are indirectly involved as well: the arteries and veins of the circulatory system supply oxygen and nutrients to and remove waste from these structures and the nerves of the nervous system stimulate them to act. In fact, none of the systems functions in isolation. Systemic anatomy is the approach taken by most survey (introductory) courses not involving dissection and when the overall curriculum follows a systemic approach. Clinical Anatomy Clinical (applied) anatomy emphasizes aspects of bodily structure and function important in the practice of medicine, dentistry, and the allied health sciences. It incorporates the regional and systemic approaches to studying anatomy and stresses clinical application. Endoscopic and imaging techniques (e.g., examination of the interior of the stomach) also demonstrate living anatomy. Clinical anatomy often involves inverting or reversing the thought process typically followed when studying regional or systemic anatomy. For example, instead of thinking, “The action of this muscle is to ‐‐” clinical anatomy asks, “How would the absence of this muscle's activity be manifest?” Instead of noting, “The ‐‐ nerve provides innervation to this area of skin,” clinical anatomy asks, “Numbness in this area indicates a lesion of which nerve?” Clinical anatomy is exciting to learn because of its role in solving clinical problems. The “clinical correlation (blue) boxes” (blue background) in this book describe practical applications of anatomy.


“Case studies,” such as those on the accompanying CD, are integral parts of the clinical approach to studying anatomy. The Bottom Line Anatomy is the study of the structure of the human body. Regional anatomy considers the body as organized into segments or parts; systemic anatomy sees the body as organized into organ systems. Surface anatomy provides information about structures that may be observed or palpated beneath the skin, and radiographic anatomy allows appreciation of structures in the living, as they are affected by muscle tone, body fluids and pressures, and gravity. Clinical anatomy emphasizes application of anatomical knowledge to the practice of medicine. Anatomicomedical Terminology An international vocabulary has been established for anatomy and medicine. Although you are familiar with common terms for parts and regions of the body, you must learn the correct nomenclature (e.g., axillary fossa instead of armpit and clavicle instead of collarbone) that enables precise communication among healthcare professionals worldwide as well as among scholars in basic and applied health sciences. You must also know the common and colloquial terms people are likely to use when they describe their complaints. Furthermore, you must be able to use terms people will understand when explaining their medical problems to them. The terminology in this book conforms to the new Terminologia Anatomica: International Anatomical Terminology (Federative Committee on Anatomical Terminology, 1998)—the authorized international reference guide on anatomical language. Terminologia Anatomica (TA) lists anatomical terms both in Latin and as English equivalents (e.g., the common shoulder muscle is musculus deltoideus in Latin and deltoid in English). Most terms in this book are English equivalents. Unfortunately, the terminology commonly used in the clinical arena may differ from the official terminology. Because this discrepancy may be a source of confusion, this text clarifies commonly confused terms by placing the unofficial designations in parentheses when the terms are first used—for example, pharyngotympanic tube (auditory tube, eustachian tube) and internal thoracic artery (internal mammary artery). Eponyms, terms incorporating the names of people, are not used in the new terminology because they give no clue about the type or location of the structures involved. In addition, some eponyms are historically inaccurate—for example, Poupart was not the first anatomist to describe the inguinal ligament (Poupart ligament). Notwithstanding, commonly used eponyms appear in parentheses throughout the book when these terms are first used—such as sternal angle (angle of Louis)—since you will surely encounter them. Note that the eponymous term does not indicate that the angle is in the sternum. Anatomical terminology introduces and makes up a large part of medical terminology. To be understood, you must express yourself clearly, using the proper terms in the correct way. Because most terms are derived from Latin and Greek, medical language may seem difficult at first; however, as you learn the origin of terms, the words make sense. For example, the term decidua, used to describe the lining of the pregnant uterus, is derived from Latin and means “a falling off.” This term is appropriate because the endometrium “falls off” or is expelled after the baby is born, ending the pregnancy, just as the leaves of deciduous trees fall at the end of summer.


To describe the body clearly and to indicate the position of its parts and organs relative to each other, anatomists worldwide have agreed to use the same descriptive terms of position and direction. Because clinicians also use these terms, it is important to master the use of this vocabulary. Practice using proper terminology as you study and review so that your meaning will be clear when you describe parts of the body in patient histories or during discussions of patients with clinicians. Anatomical Position All anatomical descriptions are expressed in relation to one consistent anatomical position, ensuring that descriptions are not ambiguous (Figs. I.1 and I.2). The anatomical position refers to the body position as if the person were standing upright, regardless of the actual posture or position, with the:   

Head, gaze (eyes), and toes directed anteriorly (forward). Arms adjacent to the sides with the palms facing anteriorly. Lower limbs close together with the feet parallel and the toes directed anteriorly.

This anatomical position is adopted globally for anatomicomedical descriptions. By using this position and appropriate terminology, you can relate any part of the body precisely to any other part. Although gravity causes a downward shift of internal organs when the upright position is assumed, it is often necessary to describe the position of organs in the recumbent or supine position because this is the posture in which people are typically examined. Visualize the anatomical position in your mind's eye when describing patients (or cadavers), whether they are lying on their sides, supine (recumbent, lying down, face upward), or prone (face downward). Anatomical Planes Anatomical descriptions are based on four imaginary planes (median, sagittal, frontal, and transverse) that intersect the body in the anatomical position (Fig. I.2): 





The median plane, the vertical plane passing longitudinally through the body, divides the body into right and left halves. The plane intersects the midlines of the anterior and posterior surfaces of the body. Midline is often erroneously used as a synonym for the median plane. Sagittal planes are vertical planes passing through the body parallel to the median plane. It is helpful to give a point of reference by naming a structure intersected by the plane you are referring to, such as a sagittal plane through the midpoint of the clavicle. The term midsagittal plane is a superfluous term for the median plane (O'Rahilly, 1997). Parasagittal, commonly used by neuroanatomists and neurologists, is also unnecessary because any plane parallel and to either side of the median plane is sagittal by definition. However, a plane parallel and near to the median plane may be referred to as a paramedian plane. Frontal (coronal) planes are vertical planes passing through the body at right angles to the median plane, dividing the body into anterior (front) and posterior (back) parts. Again, a point of reference is necessary to indicate the position of the plane (e.g., a frontal plane through the heads of the mandible).


Figure I.2. Anatomical planes. The main planes of reference in the body are illustrated. 

Transverse planes are planes passing through the body at right angles to the median and frontal planes, dividing the body into superior (upper) and inferior (lower) parts. It is helpful to give a reference point to identify the level of the plane, such as a “transverse plane through the umbilicus” or through a specific vertebra. Radiologists refer to transverse planes as transaxial, which is commonly shortened to axial planes.

Commonly, sections of the body in frontal and transverse planes are symmetrical, passing through both the right and left members of paired structures, allowing some comparison. The number of sagittal, frontal, and transverse planes is unlimited. The main use of anatomical planes is to describe sections. Anatomists create sections of the body and its parts anatomically (Fig. I.3) and clinicians create them by planar imaging technologies, such as CT, to describe and display internal structures. Sections provide views of the body as if cut or sectioned along particular planes.  



Longitudinal sections run lengthwise or parallel to the long axis of the body or of any of its parts, and the term applies regardless of the position of the body. Transverse sections, or cross sections, are slices of the body or its parts that are cut at right angles to the longitudinal axis of the body or of any of its parts; because the long axis of the foot runs horizontally, a transverse section of the foot lies in the frontal plane (Fig. I.2C). Oblique sections are slices of the body or any of its parts that are not cut along one of the previously mentioned anatomical planes. In practice, many radiographic images and anatomical sections do not lie precisely in the sagittal, frontal, or transverse planes; often they are slightly oblique.


Terms of Relationship and Comparison Various adjectives, arranged as pairs of opposites, describe the relationship of parts of the body in the anatomical position and compare the position of two structures relative to each other (Fig. I.4). Superficial, intermediate, and deep describe the position of structures relative to the surface of the body or the relationship of one structure to another underlying or overlying structure. Medial is used to indicate that (in the anatomical position) a structure, such as the 5th digit of the hand (little finger), is nearer to the median plane of the body than the other digits. Conversely, lateral stipulates that a structure, such as the 1st digit of the hand (thumb), is farther away from the median plane. Lateral and medial are not synonymous with the terms external (outer) and internal (inner). External and internal mean farther from and nearer to the center of an organ or cavity, respectively, regardless of direction. Posterior (dorsal) denotes the back surface of the body or nearer to the back. Anterior (ventral) denotes the front surface of the body. Rostral is often used instead of anterior when describing parts of the brain; it means toward the rostrum (L. from beak); however, in humans it denotes nearer the anterior part of the head (e.g., the frontal lobe of the brain is rostral to the cerebellum).

Figure I.3. Sections of the limbs. Sections may be obtained by anatomical sectioning or medical imaging techniques. Inferior refers to a structure that is situated nearer the sole of the foot. Caudal (L. cauda, tail) is a useful directional term that means toward the tail region, represented in humans by the coccyx, the small bone at the inferior (caudal) end of the vertebral column. The term caudal is used in embryology because the human embryo has a tail‐like caudal eminence until the middle of the 8th week (Moore and Persaud, 2003). Superior refers to a structure that is nearer the vertex, the topmost point of the cranium. Cranial relates to the cranium (Mediev. L. skull) and is a useful directional term, meaning toward the head.


Combined terms describe intermediate positional arrangements: inferomedial means nearer to the feet and median plane—for example, the anterior parts of the ribs run inferomedially; superolateral means nearer to the head and farther from the median plane. Proximal and distal are used when contrasting positions nearer to or farther from the attachment of a limb or the central aspect of a linear structure, respectively. Dorsum usually refers to the superior or posterior (back) surface of any part that protrudes anteriorly from the body, such as the dorsum of the tongue, nose, penis, or foot. It is also used to describe the back of the hand. It is easier to understand why these surfaces are considered posterior if one thinks of a quadripedal plantigrade animal that walks on its palms and soles, such as a bear. The sole indicates the inferior aspect or bottom of the foot, much of which is in contact with the ground when standing barefoot. The palm refers to the flat of the hand, exclusive of the thumb and other fingers, and is the opposite of the dorsum of the hand. Terms of Laterality Paired structures having right and left members (e.g., the kidneys) are bilateral, whereas those occurring on one side only (e.g., the spleen) are unilateral. Ipsilateral refers to something occurring on the same side of the body as another structure; the right thumb and right great (big) toe are ipsilateral, for example. Contralateral means occurring on the opposite side of the body relative to another structure; the right hand is contralateral to the left hand. Terms of Movement Various terms describe movements of the limbs and other parts of the body (Fig. I.5). While most movements occur at joints where two or more bones or cartilages articulate with one another, several non‐skeletal structures exhibit movement (e.g., tongue, lips, eyelids). Flexion indicates bending or decreasing the angle between the bones or parts of the body. For most joints (e.g., elbow), flexion generally involves movement in an anterior direction; however, flexion at the knee joint involves posterior movement. Dorsiflexion describes flexion at the ankle joint, as occurs when walking uphill or lifting the toes off the ground. Plantarflexion turns the foot or toes toward the plantar surface (e.g., when standing on your toes). Extension indicates straightening or increasing the angle between the bones or parts of the body. Extension usually occurs in a posterior direction, but extension of the knee joint occurs in an anterior direction. Extension of a limb or part beyond the normal limit—hyperextension (overextension)—can cause injury, such as “whiplash” (i.e., hyperextension of the neck during a rear‐end automobile collision). Note in Figure I.5 that when the foot is extended at the ankle joint, it is plantarflexed (e.g., when standing on your toes). Except for the thumb, from the anatomical position, flexion and extension are movements in the sagittal plane.


Figure I.4. Terms of relationship and comparison. These terms describe the position of one structure relative to another.


Figure I.5. Terms of movement. These terms describe movements of the limbs and other parts of the body; the movements take place at joints, where two or more bones or cartilages articulate with one another.

Abduction means moving away from the median plane in the frontal plane (e.g., when moving an upper limb away from the side of the body). In abduction of the digits (fingers or toes), the term means spreading them apart—moving the other fingers away from the neutrally positioned 3rd (middle) finger or moving the other toes away from the neutrally positioned 2nd toe. The 3rd finger and 2nd toe medially or laterally abduct away from the neutral position. Right and left lateral flexion (lateral bending) are special forms of abduction for only the neck and trunk. The face and upper trunk are directed anteriorly as the head and/or shoulders tilt to the right or left side, causing the midline of the body itself to become bent sideways. This is a compound movement occurring between many adjacent vertebrae. Adduction means moving toward the median plane in a frontal plane (e.g., when moving an upper limb toward the side of the body). In adduction of the digits, the term means reapproximating the spread fingers or toes or moving the other digits toward the neutral position of the 3rd finger or 2nd toe. The medially or laterally abducted 3rd finger or 2nd toe adducts back to the neutral position. As you can see by noticing the way the thumbnail faces (laterally instead of posteriorly in the anatomical position), the thumb is rotated 90Â° relative to the other digits. Therefore, the thumb flexes and extends in the frontal plane, and abducts and adducts in the sagittal plane. Circumduction is a circular movement that is a combination of flexion, extension, abduction, and adduction occurring in such a way that the distal end of the part


moves in a circle. Circumduction can occur at any joint at which all the above‐ mentioned movements are possible (e.g., the hip joint). Rotation involves turning or revolving a part of the body around its longitudinal axis, such as turning one's head to face sideways. Medial rotation (internal rotation) brings the anterior surface of a limb closer to the median plane, whereas lateral rotation (external rotation) takes the anterior surface away from the median plane. Pronation is the rotational movement of the forearm and hand that swings the radius (the lateral long bone of the forearm) medially around its longitudinal axis so that the palm of the hand faces posteriorly and its dorsum faces anteriorly. When the elbow joint is flexed, pronation moves the hand so that the palm faces inferiorly (e.g., placing the palms flat on a table). When applied to the foot, pronation refers to a combination of eversion and abduction that results in lowering of the medial margin of the foot. (The feet of an individual with flat feet are pronated.) Supination is the rotational movement of the forearm and hand that swings the radius laterally around its longitudinal axis so that the dorsum of the hand faces posteriorly and the palm faces anteriorly (i.e., moving them into the anatomical position). When the elbow joint is flexed, supination moves the hand so that the palm faces superiorly. (Memory device: You can hold soup in the palm of your hand when the flexed forearm is supinated but are prone [likely] to spill it if the forearm is then pronated!) When applied to the foot, supination generally implies movements resulting in raising the medial margin of the foot. Opposition is the movement by which the pad of the 1st digit (thumb) is brought to another digit pad. This movement is used to pinch, button a shirt, and lift a teacup by the handle. Reposition describes the movement of the 1st digit from the position of opposition back to its anatomical position. Protrusion is a movement anteriorly (forward) as in protruding the mandible (chin), lips, or tongue. Retrusion is a movement posteriorly (backward), as in retruding the mandible, lips, or tongue. The similar terms protraction and retraction are used most commonly for anterior and posterior movements of the shoulder. Elevation raises or moves a part superiorly, as in elevating the shoulders when shrugging, the upper lid when opening the eye, or the tongue when pushing it up against the palate. Depression lowers or moves a part inferiorly, as in depressing the shoulders when standing at ease, the upper lid when closing the eye, or pulling the tongue away from the palate. Eversion moves the sole of the foot away from the median plane (turning the sole laterally). When the foot is fully everted it is also dorsiflexed. Inversion moves the sole of the foot toward the median plane (facing the sole medially). When the foot is fully inverted it is also plantarflexed. Structure of Terms Anatomy is a descriptive science and necessarily requires names for the many structures and processes of the body. Students beginning their studies in anatomy often feel overwhelmed by the many new anatomicomedical terms. Fortunately, there are resources to help you learn these terms (Mehta et al., 1996; Stedman's Medical Dictionary, 2005; Willis, 1995). Many terms provide information about a structure's shape, size, location, or function or about the resemblance of one structure to another.


Some muscles have descriptive names to indicate their main characteristics—for example, the deltoid muscle, which covers the point of the shoulder, is triangular, like the symbol for delta, the fourth letter of the Greek alphabet. The suffix ‐oid means “like” ; therefore, deltoid means like delta. Biceps means two‐headed and triceps means three‐headed. Some muscles are named according to their shape—the piriformis muscle, for example, is pear shaped (L. pirum, pear + L. forma, shape or form). Other muscles are named according to their location. The temporal muscle is in the temporal region (temple) of the cranium (skull). In some cases, actions are used to describe muscles—for example, the levator scapulae elevates the scapula (L. shoulder blade). Thus there are logical reasons for the names of muscles and other parts of the body, and if you learn their meanings and think about them as you read and dissect, you should have no difficulty remembering their names. Abbreviations of Terms Abbreviations of terms are used for brevity in medical histories and in this and other books, such as in tables of muscles, arteries, and nerves and even in speaking. Clinical abbreviations are used in discussions and descriptions of signs and symptoms. Learning to use these abbreviations also speeds note taking. Common anatomical and clinical abbreviations are provided in this text when the corresponding term is introduced—for example, temporomandibular joint (TMJ). They are also included in the lists of common medical abbreviations found in the appendices of comprehensive medical dictionaries (e.g., Stedman's Medical Dictionary). The Bottom Line Anatomical structural terms used in this book are derived from an international reference guide called Terminologia Anatomica (1998); however, colloquial terminology and eponymous terms are often used in the clinical setting. Anatomical directional terms are based on the body in the anatomical position. Four anatomical planes divide the body, and sections divide the planes into visually useful and descriptive parts. Other anatomic terms describe relationships of parts of the body, compare the positions of structures, and describe laterality and movement. Anatomical Variations Anatomy books describe (initially, at least) the structure of the body as it is usually observed in people—that is, the most common pattern. However, occasionally a particular structure demonstrates so much variation within the normal range that the most common pattern is found less than half the time! Beginning students are frequently frustrated because the bodies they are examining or dissecting do not conform to the atlas or text they are using (Bergman et al., 1988). Often students ignore the variations or inadvertently damage them by attempting to produce conformity. Therefore, you should expect anatomical variations when you dissect or inspect prosected specimens. In a random group of people, individuals differ from each other in physical appearance. The bones of the skeleton vary not only in their basic shape but also in lesser details of surface structure. A wide variation is found in the size, shape, and form of the attachments of muscles. Similarly, considerable variation exists in the patterns of branching of veins, arteries, and nerves. Veins vary the most and nerves


the least. Individual variation must be considered in physical examination, diagnosis, and treatment. Most descriptions in this text assume a normal range of variation. However, the frequency of variation often differs among human groups, and variations collected in one population may not apply to members of another population. Some variations, such as those occurring in the origin and course of the cystic artery to the gallbladder, are clinically important (see Chapter 2), and any surgeon operating without knowledge of them is certain to have problems. In this book, clinically significant variations appear in the clinical correlation (blue) boxes. Apart from racial and sexual differences, humans exhibit considerable genetic variation, such as polydactyly (extra digits). Approximately 3% of newborns show one or more significant congenital anomalies (Moore and Persaud, 2003). Other defects (e.g., atresia or blockage of the intestine) are not detected until symptoms occur. Discovering variations and congenital anomalies in cadavers is actually one of the many benefits of firsthand dissection, because it enables students to develop an awareness of the occurrence of variations and a sense of their frequency. The Bottom Line Anatomical variations are common and students should expect to encounter them during dissection. It is important to know how such variations may influence physical examination, diagnosis, and treatment. Integumentary System Because the skin is readily accessible and is one of the best indicators of general health (Swartz, 2001), careful observation of it is important in physical examinations. It is considered in the differential diagnosis of almost every disease. The skin provides  Protection of the body from environmental effects, such as abrasions, fluid loss, harmful substances, ultraviolet radiation, and invading microorganisms.  Containment for the body's structures (e.g., tissues and organs) and vital substances (especially extracellular fluids), preventing dehydration, which may be severe when extensive skin injuries (e.g., burns) are experienced.  Heat regulation through the evaporation of sweat and/or the dilation or constriction of superficial blood vessels.  Sensation (e.g., pain) by way of superficial nerves and their sensory endings.  Synthesis and storage of vitamin D. The skin, the body's largest organ, consists of the epidermis, a superficial cellular layer, and the dermis, a deep connective tissue layer (Fig. I.6). The epidermis is a keratinized epithelium—that is, it has a tough, horny superficial layer that provides a protective outer surface overlying its regenerative and pigmented deep or basal layer. The epidermis has no blood vessels or lymphatics. The avascular epidermis is nourished by the underlying vascularized dermis, which is supplied by arteries that enter its deep surface to form a cutaneous plexus of anastomosing arteries. The skin is also supplied with afferent nerve endings that are sensitive to touch, irritation (pain), and temperature. Most nerve terminals are in the dermis, but a few penetrate into the epidermis.


Figure I.6. Skin and some of its specialized structures. The layered arrangement of the body's covering and the hairs and glands embedded within the skin and subcutaneous tissue are illustrated.

The dermis is a dense layer of interlacing collagen and elastic fibers. These fibers provide skin tone and account for the strength and toughness of skin. The dermis of animals is removed and tanned to produce leather. Karl Langer, an Austrian anatomist, studied the skin of unembalmed cadavers and observed that, although the bundles of collagen fibers in the dermis run in all directions to produce a tough felt‐ like tissue, in any specific location most fibers run in the same direction. He noted that stab wounds in a cadaver's skin produced by an ice pick are slit‐like rather than rounded because the pick splits the dermis in the predominate direction of the collagen fibers and allows the wound to gape. The predominant pattern of collagen fibers determines the characteristic tension and wrinkle lines in the skin. The tension lines (also called cleavage lines or Langer lines) tend to spiral longitudinally in the limbs and run transversely in the neck and trunk (Fig. I.7). Tension lines at the elbows, knees, ankles, and wrists are parallel to the transverse creases that appear when the limbs are flexed; flex your wrist and you will see several of them. The elastic fibers of the dermis deteriorate with age and are not replaced; consequently, in older people the skin wrinkles and sags as it loses its elasticity. The skin also contains many specialized structures (Fig. I.6). The deep layer of the dermis contains hair follicles, with associated smooth arrector muscles and sebaceous glands. Contraction of the arrector muscles of hairs (L. musculi arrector pili) erects the hairs, causing goose bumps. Hair follicles are generally slanted to one side, and several sebaceous glands lie on the side pointed to by the hair (as the hair appears to “enter” the skin—of course, it is emerging from rather than entering the skin). Thus contraction of the arrector muscles causes the hairs to stand up straighter, thereby compressing the sebaceous glands and helping them secrete their


oily product onto the skin surface. The evaporation of the watery secretion (sweat) of the sweat glands from the skin provides a thermoregulatory mechanism for heat loss (cooling). Also involved in the loss or retention of body heat are the small arteries (arterioles) within the dermis. They dilate to fill superficial capillary beds to radiate heat (skin appears red) or constrict to minimize surface heat loss (skin, especially of lips and fingertips, appears blue). Other integumentary structures or derivatives include the hair, the nails (fingernails, toenails), the mammary glands, and the enamel of teeth. Located between the overlying skin (dermis) and underlying deep fascia, the subcutaneous tissue (superficial fascia) is composed mostly of loose connective tissue and stored fat, and contains sweat glands, superficial blood vessels, lymphatic vessels, and cutaneous nerves (Fig. I.6). The neurovascular structures course in this layer, distributing only their terminal branches to the skin. The subcutaneous tissue provides for most of the body's fat storage, so its thickness varies greatly, depending on nutritional state. Nutritional state aside, the distribution of subcutaneous tissue varies considerably in different sites in the same individual. Compare, for example, the relative abundance of subcutaneous tissue evident by the thickness of the fold of skin that can be pinched at the waist or thighs with the anteromedial part of the leg (the shin, the anterior border of the tibia) or the back of the hand, the latter two being nearly devoid of it. Also consider the distribution of subcutaneous tissue and fat between the sexes: In mature females, it tends to accumulate in the breasts and thighs and in males, in the lower abdominal wall. Subcutaneous tissue participates in thermoregulation, functioning as insulation, retaining heat in the body's core. It also provides padding that protects the skin from compression by bony prominences, such as in the buttocks. Figure I.7. Tension (Langer) lines in the skin. The dashed lines indicate the predominant direction of the collagen fiber bundles in the dermis. Incisions or lacerations running parallel to these lines have less tendency to gape than those crossing them.


Skin ligaments (L. retinacula cutis), numerous small fibrous bands, extend through the subcutaneous tissue and attach the deep surface of the dermis to the underlying deep fascia (Fig. I.6). The length and density of these ligaments determines the mobility of the skin over deep structures. Where skin ligaments are longer and sparse, the skin is more mobile, such as on the back of the hand (Fig. I.8A & C). Where ligaments are short and abundant, the skin is firmly attached to the underlying deep fascia, such as in the palms and soles (Fig. I.8B). Skin ligaments are long but particularly well developed in the breasts, where they form weight‐bearing suspensory ligaments (see Fig. 1.20). Skin Incisions and Scarring The skin is always under tension. In general, lacerations or incisions that parallel the tension lines usually heal well with little scarring because there is minimal disruption of fibers. The uninterrupted fibers tend to retain the cut edges in place. However, a laceration or incision across the tension lines disrupts a greater number of collagen fibers. The disrupted lines of force cause the wound to gape, and it may heal with excessive (keloid) scarring. When other considerations, such as adequate exposure and access or avoidance of nerves, are not of greater importance, surgeons attempting to minimize scarring for cosmetic reasons may use surgical incisions that parallel the tension lines. Stretch Marks in Skin The collagen and elastic fibers in the dermis form a tough, flexible meshwork of tissue. Because the skin can distend considerably, a relatively small incision can be made during surgery compared with the much larger incision required to attempt the same procedure in an embalmed cadaver, which no longer exhibits elasticity. The skin can stretch and grow to accommodate gradual increases in size. However, marked and relatively fast size increases, such as the abdominal enlargement and weight gain accompanying pregnancy, can stretch the skin too far, damaging the collagen fibers in the dermis (Fig. BI.1). Bands of thin wrinkled skin, initially red but later becoming purple, and white stretch marks (L. striae gravidarum) appear on the abdomen, buttocks, thighs, and breasts during pregnancy. Stretch marks (L. striae cutis distensae) also form in obese individuals and result from loosening of the deep fascia and reduced cohesion between the collagen fibers as the skin stretches. Stretch marks generally fade after pregnancy and weight loss; they never disappear completely.

Figure BI.1.


Skin Injuries and Their Classification Lacerations Accidental cuts and skin tears are superficial or deep. Superficial lacerations violate the epidermis and perhaps the superficial layer of the dermis; they bleed but do not interrupt the continuity of the dermis. Deep lacerations penetrate the deep layer of the dermis, extending into the subcutaneous tissue or beyond; they gape and require approximation of the cut edges of the dermis (by suturing, or stitches) to minimize scarring. Burns Burns, common injuries of skin, are caused by thermal trauma, ultraviolet or ionizing radiation, or chemical agents. Burns are classified, in increasing order of severity, based on the depth of skin injury (Fig. BI.2): 



1st‐degree (superficial) burn: damage limited to epidermis; symptoms are erythema (hot red skin), pain, and edema (swelling); desquamation (peeling) of the superficial layer usually occurs several days later, but the layer is quickly replaced from the basal layer without significant scarring; example is sunburn. 2nd‐degree (partial‐thickness) burn: epidermal and superficial dermis are damaged; blistering occurs; nerve endings are damaged, making this variety the most painful; except for their most superficial parts, the sweat glands and hair follicles are not damaged and can provide the source of replacement cells for the basal layer of the epidermis; healing will occur slowly (within 21 days or less), leaving scarring and some contracture, but it is usually complete.

Figure BI.2.

Introduction to Clinically Oriented Anatomy 

3rd‐degree (full‐thickness) burn: the entire thickness of the skin is damaged and perhaps underlying muscle; a minor degree of healing may occur at the edges, but the open, ulcerated portions require skin grafting; dead material (eschar) is removed and replaced with skin harvested (taken) from a non‐ burned location.

The extent of a burn (percent of total body surface affected) is generally more significant than the degree (severity in terms of depth) in estimating the effect on the well‐being of the victim. Figure I.8. Skin ligaments of subcutaneous tissue. A. The thickness of subcutaneous tissue can be estimated as being approximately half that of a pinched fold of skin (i.e., a fold of skin includes a double thickness of subcutaneous tissue). The dorsum of the hand has relatively little subcutaneous tissue. B. Long, relatively sparse skin ligaments allow the mobility of the skin demonstrated in part A. C. The skin of the palm of the hand (like that of the soles of the feet) is firmly attached to the underlying deep fascia.

The Bottom Line The integumentary system (the skin) consists of the epidermis, dermis, and specialized structures (hair follicles, sebaceous glands, and sweat glands). The skin plays important roles in protection, containment, heat regulation, and sensation; it also synthesizes and stores vitamin D. Tension (Langer) lines in the skin have implications in surgery and wound healing. Subcutaneous tissue, located beneath the dermis, contains most of the body's fat stores.


Fascias, Fascial Compartments, Bursae, and Potential Spaces Fascias (L. fasciae) constitute the wrapping, packing, and insulating materials of the deep structures of the body. Underlying the subcutaneous tissue (also called superficial fascia) almost everywhere is the deep fascia (Fig. I.9). The deep fascia is a dense, organized connective tissue layer, devoid of fat, that covers most of the body parallel to (deep to) the skin and subcutaneous tissue. Extensions from its internal surface invest deeper structures, such as individual muscles and neurovascular bundles, as investing fascia (Gartner and Hiatt, 2001). Its thickness varies widely. In the face and ischioanal fossa, distinct layers of deep fascia are absent. In the limbs, groups of muscles with similar functions sharing the same nerve supply are located in compartments, separated by thick sheets of deep fascia, called intermuscular septa, that extend centrally from the surrounding fascial sleeve to attach to the bones. These fascial compartments may contain or direct the spread of an infection or a tumor. In a few places, the deep fascia gives attachment (origin) to the underlying muscles (although it is not usually mentioned in lists or tables of origins and insertions); but in most places, the muscles are free to contract and glide deep to it. However, the deep fascia itself never passes freely over bone; where deep fascia contacts bone, it blends firmly with the periosteum (bone covering). The relatively unyielding deep fascia investing muscles, and especially that surrounding the fascial compartments in the limbs, limits the outward expansion of the bellies of contracting skeletal muscles. Blood is thus pushed out as the veins of the muscles and compartments are compressed. Valves within the veins allow the blood to flow only in one direction (toward the heart), preventing the backflow that might occur as the muscles relax. Thus deep fascia, contracting muscles, and venous valves work together as a musculovenous pump to return blood to the heart, especially in the lower limbs where blood must move against the pull of gravity (Fig. I.25). Near certain joints (e.g., wrist and ankle), the deep fascia becomes markedly thickened, forming a retinaculum (plural = retinacula) to hold tendons in place where they cross the joint during flexion and extension, preventing them from taking a shortcut, or bow stringing, across the angle created (Fig. I.19). Figure I.9. Excavated section of the leg demonstrating the deep fascia and fascial formations. Deep to the skin and subcutaneous tissue, a circumferential layer of deep fascia covers the musculoskeletal structures. Thick intermuscular septa extend centrally from the outer layer, forming fascial compartments containing muscles of similar function. Individual muscles are covered by investing fascia.


Subserous fascia, with varying amounts of fatty tissue, lies between the internal surfaces of the musculoskeletal walls and the serous membranes lining the body cavities. These are the endothoracic, endoabdominal, and endopelvic fascias; the latter two may be referred to collectively as extraperitoneal fascia. Bursae (singular = bursa; Mediev. L., a purse) are closed sacs or envelopes of serous membrane (a delicate connective tissue membrane capable of secreting fluid to lubricate a smooth internal surface) that are collapsed or essentially “empty,” except for a thin layer of lubricating fluid secreted by the membrane. Usually occurring in locations subject to friction, bursae enable one structure to move more freely over another. Subcutaneous bursae occur in the subcutaneous tissue between skin and bony prominences, such as at the elbow or knee; subfascial bursae lie beneath deep fascia; and subtendinous bursae facilitate the movement of tendons over bone. Synovial tendon sheaths are a specialized type of elongated bursae that wrap around tendons, usually enclosing them as they traverse osseofibrous tunnels that anchor the tendons in place (Fig. I.10A). Bursae occasionally communicate with the synovial cavities of joints. Because they are formed only of delicate, transparent serous membrane and are collapsed, bursae are not easily noticed or dissected in the laboratory. It is possible to display bursae by injecting and distending them with colored fluid. In atlases and textbooks, they are typically illustrated as they would appear if injected with (usually blue) latex that has solidified so that it remains in place as a cast of the bursa when the surrounding tissues are removed. As noted, bursae and synovial tendon sheaths are examples of empty, or potential, sacs or spaces, usually lined with or formed of a serous or synovial membrane, and are encountered in the study of anatomy. Unlike three‐dimensional realized or actual spaces, these spaces are collapsed so that they have no depth; their walls are apposed with only a thin film of lubricating fluid between them. When the wall is interrupted at any point or when a fluid is secreted or formed within them in excess, they become realized spaces; however, this condition is abnormal or pathological. Such collapsed bursal sacs surround many important organs (e.g., the heart, lungs, and abdominal viscera) and structures (e.g., portions of tendons). This configuration is much like wrapping a large but empty balloon around a structure, such as a fist (Fig. I.10B). The object is surrounded by the two layers of the empty balloon, but is not inside the balloon; the balloon itself remains empty. For an even more exact comparison, the balloon should first be filled with water and then emptied, leaving the empty balloon wet inside. In exactly this way, the heart is surrounded by—but is not inside—the pericardial sac. Each lung is surrounded by—but is not inside—a pleural sac, and the abdominal viscera are surrounded by—but are not inside—the peritoneal sac. In such cases, the inner layer of the balloon or serous sac (the one adjacent to the fist, viscus, or viscera) is called the visceral layer; the outer layer of the balloon (or the one in contact with the body wall) is called the parietal layer. Such a surrounding double layer of membranes, moistened on their apposed surfaces, confers freedom of movement on the surrounded structure when it is contained within a confined space, such as the heart within the thorax and a tendon traversing an osseofibrous tunnel.


Figure I.10. Synovial tendon sheaths and bursal sacs. A. Synovial tendon sheaths are longitudinal bursae that surround tendons as they pass deep to retinacula or through fibrous digital sheaths. B. Bursal sacs enclose several structures, such as the heart, lungs, digestive tract, and tendons, much like this collapsed balloon encloses the fist. A thin film of lubricating fluid between the parietal and visceral layers confers mobility to the structure surrounded by the bursa within a confined compartment. The double folds of synovial membrane between the parietal and visceral layers surrounding the vessels (and other structures) passing to and from the intraperitoneal structure(s) are called mesenteries. In the case of a synovial tendon sheath, the mesentery is called a mesotendon.

Fascial Planes In living people, fascial planes (interfascial and intrafascial) exist that are potential spaces between adjacent fascias or fascia‐lined structures or within loose areolar fascias, such as the subserous fascias. During operations, surgeons take advantage of these interfascial planes, separating structures to create actual spaces that allow movement and access to deeply placed structures. In some procedures, surgeons use extrapleural or extraperitoneal fascial planes, which allow them to operate outside the membranes lining the body cavities, minimizing the potential for contamination, the spread of infection, and consequent formation of adhesions within the cavities. Unfortunately, these planes are often fused and difficult to establish or appreciate in the embalmed cadaver. The Bottom Line Deep fascia is an organized connective tissue layer that completely envelops the body beneath the subcutaneous tissue of the skin. Extensions of the deep fascia divide muscles into groups (intermuscular septa), invest individual muscles and neurovascular bundles (investing fascia), and lie between musculoskeletal walls and the serous membranes lining body cavities (subserous fascia). Retinacula are thickenings of deep fascia that hold tendons in place during joint movements. Bursae are closed sacs formed of serous membrane that occur in locations subject to friction; they enable one structure to move freely over another.


Skeletal System The skeletal system may be divided into two functional parts (Fig. I.11): 

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The axial skeleton consists of the bones of the head (cranium or skull), neck (hyoid bone and cervical vertebrae), and trunk (ribs, sternum, vertebrae, and sacrum). The appendicular skeleton consists of the bones of the limbs, including those forming the pectoral (shoulder) and pelvic girdles.

Figure I.11. Skeletal system. The skeleton of the head, neck, and trunk forms the axial skeleton; the skeleton of the limbs forms the appendicular skeleton.

Cartilage and Bones The skeleton is composed of cartilages and bones. Cartilage is a resilient, semirigid form of connective tissue that forms parts of the skeleton where more flexibility is required—for example, where the costal cartilages attach the ribs to the sternum. Also, the articulating surfaces of bones participating in a synovial joint are capped with articular cartilages that provide smooth, low‐friction, gliding surfaces for free movement (Fig. I.16). Blood vessels do not enter cartilage (i.e., it is avascular); consequently, its cells obtain oxygen and nutrients by diffusion. The proportion of bone and cartilage in the skeleton changes as the body grows; the younger a person is, the more cartilage her or she has. The bones of a newborn are soft and flexible because they are mostly composed of cartilage. Bone, a living tissue, is a highly specialized, hard form of connective tissue that makes up most of the skeleton. It is the chief supporting tissue of the body. Bones of the adult skeleton provide

Clinically Oriented Anatomy, 5th Edition By Keith Moore     

Support for the body and its vital cavities. Protection for vital structures. The mechanical basis for movement (leverage). Storage for salts (e.g., calcium). A continuous supply of new blood cells (produced by the marrow contained within many bones).

A fibrous connective tissue covering surrounds each skeletal element like a sleeve, except where articular cartilage occurs; that surrounding bones is periosteum (Fig. I.15), whereas that around cartilage is perichondrium. The periosteum and perichondrium nourish the external aspects of the skeletal tissue. They are capable of laying down more cartilage or bone (particularly during fracture healing) and provide the interface for attachment of tendons and ligaments. The two types of bone are compact bone and spongy (trabecular or cancellous) bone. They are distinguished by the relative amount of solid matter and by the number and size of the spaces they contain (Fig. I.12). All bones have a superficial thin layer of compact bone around a central mass of spongy medullary bone, except where the latter is replaced by a medullary (marrow) cavity. Within the medullary cavity of adult bones, and between the spicules (trabeculae) of spongy bone, blood cells and blood platelets are formed (Ross et al., 2003). The architecture and proportion of compact and spongy bone vary according to function. Compact bone provides strength for weight bearing. In long bones designed for rigidity and attachment of muscles and ligaments, the amount of compact bone is greatest near the middle of the shaft where the bones are liable to buckle. In addition, long bones have elevations (e.g., ridges, crests, and tubercles) that serve as buttresses (supports) where large muscles attach. Living bones have some elasticity (flexibility) and great rigidity (hardness). Classification of Bones Bones are classified according to their shape.     

Long bones are tubular (e.g., the humerus in the arm). Short bones are cuboidal and are found only in the ankle (tarsus) and wrist (carpus). Flat bones usually serve protective functions (e.g., those forming the cranium protect the brain). Irregular bones (e.g., in the face) have various shapes other than long, short, or flat. Sesamoid bones (e.g., the patella or knee cap) develop in certain tendons and are found where tendons cross the ends of long bones in the limbs; they protect the tendons from excessive wear and often change the angle of the tendons as they pass to their attachments.


Figure I.12. Transverse sections of the humerus (upper arm bone). The shaft of a living bone is a tube of compact bone that surrounds a medullary cavity, which contains red or yellow bone marrow or a combination of both.

Accessory Bones Accessory (supernumerary) bones develop when additional ossification centers appear and form extra bones. Many bones develop from several centers of ossification, and the separate parts normally fuse. Sometimes one of these centers fails to fuse with the main bone, giving the appearance of an extra bone; but careful study shows that the apparent extra bone is a missing part of the main bone. Circumscribed areas of bone are often seen along the sutures of the cranium where the flat bones abut, particularly those related to the parietal bone (see Chapter 7). These small, irregular, worm‐like bones are sutural bones (wormian bones). It is important to know that accessory bones are common in the foot, to avoid mistaking them for bone fragments in radiographs and other medical images. Heterotopic Bones Bones sometimes form in soft tissues where they are not normally present (e.g., in scars). Horse riders often develop heterotopic bones in their thighs (rider's bones), probably because of chronic muscle strain resulting in small hemorrhagic (bloody) areas that undergo calcification and eventual ossification. Bone Markings and Formations Bone markings appear wherever tendons, ligaments, and fascias are attached or where arteries lie adjacent to or enter bones. Other formations occur in relation to the passage of a tendon (often to direct the tendon or improve its leverage) or to control the type of movement occurring at a joint. The various markings and features of bones are (Fig. I.13)   

Capitulum: small, round, articular head (e.g., the capitulum of the humerus). Condyle: rounded, knuckle‐like articular area, usually occurring in pairs (e.g., the lateral femoral condyle). Crest: ridge of bone (e.g., the iliac crest).

Clinically Oriented Anatomy, 5th Edition By Keith Moore  

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Epicondyle: eminence superior to a condyle (e.g., the lateral epicondyle of the humerus). Facet: smooth flat area, usually covered with cartilage, where a bone articulates with another bone (e.g., the superior costal facet on the body of a vertebra for articulation with a rib). Foramen: passage through a bone (e.g., the obturator foramen). Fossa: hollow or depressed area (e.g., the infraspinous fossa of the scapula). Groove: elongated depression or furrow (e.g., the radial groove of the humerus). Head (L. caput): large, round articular end (e.g., the head of the humerus). Line: linear elevation (e.g., the soleal line of the tibia). Malleolus: rounded process (e.g., the lateral malleolus of the fibula). Notch: indentation at the edge of a bone (e.g., the greater sciatic notch). Protuberance: projection of bone (e.g., the external occipital protuberance). Spine: thorn‐like process (e.g., the spine of the scapula). Spinous process: projecting spine‐like part (e.g., the spinous process of a vertebra). Trochanter: large blunt elevation (e.g., the greater trochanter of the femur). Trochlea: spool‐like articular process or process that acts as a pulley (e.g., trochlea of the humerus). Tubercle: small raised eminence (e.g., the greater tubercle of the humerus). Tuberosity: large rounded elevation (e.g., the ischial tuberosity).

Trauma to Bone and Bone Changes Bones are living organs that hurt when injured, bleed when fractured, remodel in relationship to stresses placed on them, and change with age. Like other organs, bones have blood vessels, lymphatic vessels, and nerves, and they may become diseased. Unused bones, such as in a paralyzed limb, atrophy (decrease in size). Bone may be absorbed, which occurs in the mandible when the teeth are extracted. Bones hypertrophy (enlarge) when they support increased weight for a long period. Trauma to a bone (e.g., during an accident) may break it. For the fracture to heal properly, the broken ends must be brought together, approximating their normal position. This is called reduction of a fracture. During bone healing, the surrounding fibroblasts (connective tissue cells) proliferate and secrete collagen, which forms a collar of callus to hold the bones together (Fig. BI.3). Bone remodeling occurs in the fracture area, and the callus calcifies. Eventually, the callus is resorbed and replaced by bone. After several months, little evidence of the fracture remains, especially in young people. Fractures are more common in children than in adults because of the combination of their slender, growing bones and carefree activities. Fortunately, many of these breaks are greenstick fractures (incomplete breaks caused by bending the bones). Fractures in growing bones heal faster than those in adult bones.


Figure BI.3. Osteoporosis During the aging process, the organic and inorganic components of bone both decrease, often resulting in osteoporosis, a reduction in the quantity of bone, or atrophy of skeletal tissue. (Fig. BI.4) Hence, the bones become brittle, lose their elasticity, and fracture easily. Sternal Puncture Examination of bone marrow provides valuable information for evaluating hematological diseases. Because it lies just beneath the skin (i.e., is subcutaneous) and is easily accessible, the sternum (breast bone) is a commonly used site for harvesting bone marrow. During a sternal puncture, a wide‐bore (large‐diameter) needle is inserted through the thin cortical bone of the sternum into the spongy bone, and a sample of red bone marrow (marrow that produces blood cells) is aspirated with a syringe for laboratory examination. Bone marrow transplantation is sometimes performed in the treatment of leukemia.

Figure BI.4.


The Bottom Line The skeletal system can be divided into the axial (bones of the head, neck, and trunk) and appendicular skeletons (bones of the limbs). The skeleton itself is composed of cartilage, a semirigid connective tissue, and bone, a hard form of connective tissue that provides support, protection, movement, storage (of certain electrolytes), and synthesis of blood cells. Periosteum, which surrounds bones, and perichondrium, which surrounds cartilage, provide nourishment for these tissues and are the sites of new cartilage and bone formation. Two types of bone, spongy and compact, are distinguished by the amount of solid matter and the size and number of spaces they contain. Bones can be classified as long, short, flat, irregular, or sesamoid; standard terms for specific bone markings and features are used when describing the structure of individual bones. Figure I.13. Bone markings and formations. Markings appear on bones wherever tendons, ligaments, and fascia attach. Other formations relate to joints, the passage of tendons, and the provision of increased leverage.


Bone Development Most bones take many years to grow and mature. The humerus (arm bone), for example, begins to ossify at the end of the embryonic period (8 weeks); however, ossification is not complete until age 20. All bones derive from mesenchyme (embryonic connective tissue) by two different processes: intramembranous ossification (directly from mesenchyme) and endochondral ossification (from cartilage derived from mesenchyme). The histology (microscopic structure) of a bone is the same either way (Cormack, 2001; Moore and Persaud, 2003). 

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In intramembranous ossification (membranous bone formation), mesenchymal models of bones form during the embryonic period, and direct ossification of the mesenchyme begins in the fetal period. In endochondral ossification (cartilaginous bone formation), cartilage models of the bones form from mesenchyme during the fetal period, and bone subsequently replaces most of the cartilage.

A brief description of endochondral ossification helps explain how long bones grow (Fig. I.14). The mesenchymal cells condense and differentiate into chondroblasts, dividing cells in growing cartilage tissue, thereby forming a cartilaginous bone model. In the midregion of the model, the cartilage calcifies (becomes impregnated with calcium salts), and periosteal capillaries (capillaries from the fibrous sheath surrounding the model) grow into the calcified cartilage of the bone model and supply its interior. These blood vessels, together with associated osteogenic (bone‐ forming) cells, form a periosteal bud (Fig. I.14A). The capillaries initiate the primary ossification center, so named because the bone tissue it forms replaces most of the cartilage in the main body of the bone model. The shaft of a bone ossified from the primary ossification center is the diaphysis, which grows as the bone develops.

Figure I.14. Development and growth of a long bone. A. The formation of primary and secondary ossification centers is shown. B. Growth in length occurs on both sides of the cartilaginous epiphysial plates (blue arrows). For growth to continue, the bone formed from the primary center in the diaphysis does not fuse with that formed from the secondary centers in the epiphyses until the bone reaches its adult size. When growth ceases, the epiphysial plate is replaced by a synostosis (bone‐to‐bone fusion), seen as an epiphysial line in radiographs.


Most secondary ossification centers appear in other parts of the developing bone after birth; the parts of a bone ossified from these centers are epiphyses. The chondrocytes in the middle of the epiphysis hypertrophy, and the bone matrix (extracellular substance) between them calcifies. Epiphysial arteries grow into the developing cavities with associated osteogenic cells. The flared part of the diaphysis nearest the epiphysis is the metaphysis. For growth to continue, the bone formed from the primary center in the diaphysis does not fuse with that formed from the secondary centers in the epiphyses until the bone reaches its adult size. Thus, during growth of a long bone, cartilaginous epiphysial plates intervene between the diaphysis and epiphyses (Fig. I.14B). These growth plates are eventually replaced by bone at each of its two sides, diaphysial and epiphysial. When this occurs, bone growth ceases, and the diaphysis fuses with the epiphyses. The seam formed during this fusion process (synostosis) is particularly dense and is recognizable in radiographs as an epiphysial line. The epiphysial fusion of bones occurs progressively from puberty to maturity. Ossification of short bones is similar to that of the primary ossification center of long bones, and only one short bone, the calcaneus (heel bone), develops a secondary ossification center. Bone Growth and the Assessment of Bone Age Knowledge of the sites where ossification centers occur, the times of their appearance, the rates at which they grow, and the times of fusion of the sites (times when synostosis occurs) is important in clinical medicine, forensic science, and anthropology. A general index of growth during infancy, childhood, and adolescence is indicated by bone age, as determined from radiographs (negative images on X‐ray films). The age of a young person can be determined by studying the ossification centers in bones (see “Medical Imaging of the Upper Limb” in Chapter 6 for examples). The main criteria are (1) the appearance of calcified material in the diaphysis and/or epiphyses and (2) the disappearance of the dark line representing the epiphysial plate (absence of this line indicates that epiphysial fusion has occurred; fusion occurs at specific times for each epiphysis). The fusion of epiphyses with the diaphysis occurs 1—2 years earlier in girls than in boys. Determining bone age can be helpful in predicting adult height in early‐ or late‐maturing adolescents (Behrman et al., 2004). Assessment of bone age also helps establish the approximate age of human skeletal remains in medicolegal cases. Effects of Disease and Diet on Bone Growth Some diseases produce early epiphysial fusion (ossification time) compared with what is normal for the person's chronological age; other diseases result in delayed fusion. The growing skeleton is sensitive to relatively slight and transient illnesses and to periods of malnutrition. Proliferation of cartilage at the metaphysis slows down during starvation and illness, but the degeneration of cartilage cells in the columns continues, producing a dense line of provisional calcification. These lines later become bone with thickened trabeculae, or lines of arrested growth. Displacement and Separation of Epiphyses Without knowledge of bone growth and the appearance of bones in radiographic and other diagnostic images at various ages, a displaced epiphysial plate could be mistaken for a fracture, and separation of an epiphysis could be interpreted as a


displaced piece of a fractured bone. Knowing the patient's age and the location of epiphyses can prevent these anatomical errors. The edges of the diaphysis and epiphysis are smoothly curved in the region of the epiphysial plate. Bone fractures always leave a sharp, often uneven edge of bone. An injury that causes a fracture in an adult usually causes the displacement of an epiphysis in a child. Vasculature and Innervation of Bones Bones are richly supplied with blood vessels. Most apparent are the nutrient arteries (one or more per bone) that arise as independent branches of adjacent arteries outside the periosteum and pass obliquely through the compact bone of the shaft of a long bone via nutrient foramina. The nutrient artery divides in the medullary cavity into longitudinal branches that proceed toward each end, supplying the bone marrow, spongy bone, and deeper portions of the compact bone (Fig. I.15). However, many small branches from the periosteal arteries of the periosteum are responsible for nourishment of most of the compact bone. Consequently, a bone from which the periosteum has been removed dies. Blood reaches the osteocytes (bone cells) within the compact bone by means of microscopic canal systems (haversian systems or osteons) that house small blood vessels. The ends of the bones are supplied by metaphysial and epiphysial arteries that arise mainly from the arteries that supply the joints; in the limbs, these arteries are typically part of a periarticular arterial plexus, which surrounds the joint, ensuring blood flow distal to the joint regardless of the position assumed by the joint. Figure I.15. Vasculature and innervation of a long bone. The large nutrient artery (or arteries) supplies the marrow, spongy bone, and deeper compact bone of the diaphysis and metaphyses. Small branches from the periosteal arteries supply most of the compact bone from the superficial aspect. The haversian canal systems enable blood to penetrate the compact bone to nourish the osteocytes (bone cells). Epiphysial and metaphysial arteries supply the ends of long bones. The periosteum is also rich in sensory (periosteal) nerves.

Veins accompany arteries through the nutrient foramina. Many large veins also leave through foramina near the articular ends of the bones. Bones containing red bone marrow have numerous large veins. Lymphatic vessels are abundant in the periosteum. Nerves accompany blood vessels supplying bones. The periosteum is richly supplied with sensory nerves—periosteal nerves—that carry pain fibers. The periosteum is


especially sensitive to tearing or tension, which explains the acute pain from bone fractures. Bone itself is relatively sparsely supplied with sensory endings. Within bones, vasomotor nerves cause constriction or dilation of blood vessels, regulating blood flow through the bone marrow. Avascular Necrosis Loss of the arterial supply to an epiphysis or other parts of a bone results in the death of bone tissue, or avascular necrosis (G. nekrosis, deadness). After every fracture, small areas of adjacent bone undergo necrosis. In some fractures, avascular necrosis of a large fragment of bone may occur. A number of clinical disorders of epiphyses in children result from avascular necrosis of unknown etiology (cause). These disorders are referred to as osteochondroses (Salter, 1998). The Bottom Line Bones grow through the processes of intramembraneous ossification, in which mesenchymal bone models are formed during the embryonic and prenatal periods, and endochondral ossification, in which cartilage models are formed during the fetal period, with bone subsequently replacing most of the cartilage after birth. Joints A joint (articulation) is a union or junction between two or more bones or rigid parts of the skeleton. Joints exhibit a variety of forms and functions. Some joints have no movement; others allow only slight movement, and some are freely movable, such as the glenohumeral (shoulder) joint. Classification of Joints Three classes of joints are described based on the manner or type of material by which the articulating bones are united. 

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The articulating bones of synovial joints are united by a joint (articular) capsule (composed of an outer fibrous layer or membrane lined by a serous synovial membrane) spanning and enclosing an articular cavity. The articular cavity of a synovial joint, like the knee, is a potential space that contains a small amount of lubricating synovial fluid, secreted by the synovial membrane. Inside the capsule, articular cartilage covers the articular surfaces (bearing surfaces) of the bones; all other internal surfaces are covered by synovial membrane. The bones in Figure I.16A, normally closely apposed, have been pulled apart for demonstration, and the joint capsule has been inflated. Consequently the normally potential joint cavity is exaggerated. The periosteum investing the participating bones external to the joint blends with the fibrous layer of the joint capsule. The articulating bones of fibrous joints are united by fibrous tissue. The amount of movement occurring at a fibrous joint depends in most cases on the length of the fibers uniting the articulating bones. The sutures of the cranium are examples of fibrous joints (Fig. I.16B). These bones are close together, either interlocking along a wavy line or overlapping. A syndesmosis type of fibrous joint unites the bones with a sheet of fibrous tissue, either a ligament or a fibrous membrane. Consequently, this type of joint is partially movable. The interosseous membrane in the forearm is a sheet of fibrous tissue that


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joins the radius and ulna in a syndesmosis. A gomphosis (socket), or dentoalveolar syndesmosis, is a fibrous joint in which a peg‐like process fits into a socket articulation between the root of the tooth and the alveolar process of the jaw. Mobility of this joint (a loose tooth) indicates a pathological state affecting the supporting tissues of the tooth. However, microscopic movements here give us information (via the sense of proprioception) about how hard we are biting or clenching our teeth and whether we have a particle stuck between our teeth. The articulating structures of cartilaginous joints are united by hyaline cartilage or fibrocartilage. In primary cartilaginous joints, or synchondroses, the bones are united by hyaline cartilage, which permits slight bending during early life. Primary cartilaginous joints are usually temporary unions, such as those present during the development of a long bone (Figs. I.14 and I.16C), where the bony epiphysis and the shaft are joined by an epiphysial plate. Primary cartilaginous joints permit growth in the length of a bone. When full growth is achieved, the epiphysial plate converts to bone and the epiphyses fuse with the diaphysis. Secondary cartilaginous joints, or symphyses, are strong, slightly movable joints united by fibrocartilage. The fibrocartilaginous intervertebral discs (Fig. I.16C) between the vertebrae consist of binding connective tissue that joins the vertebrae together. Cumulatively, these joints provide strength and shock absorption as well as considerable flexibility to the vertebral column (spine).

Synovial joints, the most common type of joint, provide free movement between the bones they join; they are joints of locomotion, typical of nearly all limb joints. Synovial joints are usually reinforced by accessory ligaments that are either separate (extrinsic) or are a thickening of a portion of the joint capsule (intrinsic). Some synovial joints have other distinguishing features, such as fibrocartilaginous articular discs or menisci, which are present when the articulating surfaces of the bones are incongruous. The six major types of synovial joints are classified according to the shape of the articulating surfaces and/or the type of movement they permit (Fig. I.17): 

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Plane joints permit gliding or sliding movements in the plane of the articular surfaces. The opposed surfaces of the bones are flat or almost flat, with movement limited by their tight joint capsules. Plane joints are numerous and are nearly always small. An example is the acromioclavicular joint between the acromion of the scapula and the clavicle. Hinge joints permit flexion and extension only, movements that occur in one plane (sagittal) around a single axis that runs transversely; thus hinge joints are uniaxial joints.

The joint capsule of these joints is thin and lax anteriorly and posteriorly where movement occurs; however, the bones are joined by strong, laterally placed collateral ligaments. An example is the elbow joint.


Figure I.16. Three classes of joints. Examples of each class are shown, as well as a model demonstrating the basic features of a synovial joint.


Figure I.17. Types of synovial joints. Synovial joints are classified according to the shape of their articulating surfaces and/or the type of movement they permit. 

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Saddle joints permit abduction and adduction as well as flexion and extension, movements occurring around two axes at right angles to each other; thus saddle joints are biaxial joints that allow movement in two planes, sagittal and frontal. The performance of these movements in a circular sequence (circumduction) is also possible. The opposing articular surfaces are shaped like a saddle (i.e., they are reciprocally concave and convex). The carpometacarpal joint at the base of the 1st digit (thumb) is a saddle joint. Condyloid joints permit flexion and extension as well as abduction and adduction; thus condyloid joints are also biaxial. However, movement in one plane (sagittal) is usually greater (freer) than in the other. Circumduction, more restricted than that of saddle joints, is also possible. The metacarpophalangeal joints (knuckle joints) are examples.

Clinically Oriented Anatomy, 5th Edition By Keith Moore 

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Ball and socket joints allow movement in multiple axes and planes: flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction; thus ball and socket joints are multi‐axial joints. In these highly mobile joints, the spheroidal surface of one bone moves within the socket of another. An example is the hip joint, in which the spherical head of the femur rotates within the socket formed by the acetabulum of the hip bone. Pivot joints permit rotation around a central axis; thus they are uniaxial. In these joints, a rounded process of bone rotates within a sleeve or ring. An example is the central atlantoaxial joint, in which the atlas (C1 vertebra) rotates around a finger‐like process, the dens (odontoid process) of the axis (C2 vertebra) during rotation of the head.

Joint Vasculature and Innervation Joints receive blood from articular arteries that arise from the vessels around the joint. The arteries often anastomose (communicate) to form networks (periarticular arterial anastomoses) to ensure a blood supply to and across the joint in the various positions assumed by the joint. Articular veins are communicating veins that accompany arteries (L. venae comitantes) and, like the arteries, are located in the joint capsule, mostly in the synovial membrane. Joints have a rich nerve supply; the nerve endings are in the joint capsule. In the distal parts of the limbs (hands and feet), the articular nerves are branches of the cutaneous nerves supplying the overlying skin. However, most articular nerves are branches of nerves that supply the muscles that cross and therefore move the joint. Hilton's Law states that the nerves supplying a joint also supply the muscles moving the joint or the skin covering their distal attachments. Joints transmit a sensation called proprioception, which provides an awareness of movement and position of the parts of the body. The synovial membrane is relatively insensitive. Pain fibers are numerous in the fibrous layer and associated ligaments, causing considerable pain when the joint is injured. The sensory nerve endings respond to the twisting and stretching that occurs during sports activities such as basketball. People with arthritis will confirm that joints are well supplied with pain endings. Joints of the Newborn Cranium The bones of the calvaria (skullcap) of a newborn infant do not make full contact with each other (Fig. BI.5). At these sites, the sutures form wide areas of fibrous tissue called fontanelles. The anterior fontanelle is the most prominent; laypeople call it the baby's “soft spot.” The fontanelles in a newborn are often felt as ridges because of the overlapping of the cranial bones by molding of the calvaria as it passes through the birth canal. Normally, the anterior fontanelle is flat. A bulging fontanelle may indicate increased intracranial pressure; however, the fontanelle normally bulges during crying. Pulsations of the fontanelle reflect the pulse. A depressed fontanelle may be observed when the baby is dehydrated (Swartz, 2001).


Figure BI.5. Degenerative Joint Disease Synovial joints are well designed to withstand wear, but heavy use over several years can cause degenerative changes. Some destruction is inevitable during such activities as jogging, which wears away the articular cartilages and sometimes erodes the underlying articulating surfaces of the bones. The normal aging of articular cartilage begins early in adult life and progresses slowly thereafter, occurring on the ends of the articulating bones, particularly those of the hip, knee, vertebral column, and hands (Salter, 1998). These irreversible degenerative changes in joints result in the articular cartilage becoming less effective as a shock absorber and a lubricated surface. As a result, the articulation becomes increasingly vulnerable to the repeated friction that occurs during joint movements. In some people, these changes do not produce significant symptoms; in others, they cause considerable pain. Degenerative joint disease, osteoarthritis, is often accompanied by stiffness, discomfort, and pain. Osteoarthritis is common in older people and usually affects joints that support the weight of their bodies (e.g., the hips and knees). Most substances in the bloodstream, normal or pathological, easily enter the joint cavity. Similarly, traumatic infection of a joint may be followed by arthritis, inflammation of a joint, and septicemia, blood poisoning. Arthroscopy The cavity of a synovial joint can be examined by inserting a cannula and an arthroscope (a small telescope) into it. This surgical procedure—arthroscopy— enables an orthopedic surgeon to examine joints for abnormalities, such as torn articular discs. Some surgical procedures can also be performed during arthroscopy (e.g., by inserting instruments through small puncture incisions). Because the opening in the joint capsule for inserting the arthroscope is small, healing is more rapid after this procedure than after traditional joint surgery.


The Bottom Line A joint is a union between two or more bones or rigid parts of the skeleton. Three general types of joints are recognized: fibrous, cartilaginous, and synovial. Synovial joints are the most common type and can be classified into plane, hinge, saddle, condyloid, ball and socket, and pivot. Joints receive their blood supply from articular arteries that often form networks. Articular veins are usually located in the synovial membrane. Joints are richly innervated and transmit the sensation of proprioception, an awareness of movement and position of parts of the body. Muscle Tissue and the Muscular System The muscular system consists of all the muscles of the body. Although the muscles of the muscular system are all composed of one specific type of muscle tissue, other types of muscle tissue form important components of the organs of other systems, including the cardiovascular, digestive, genitourinary, and integumentary systems. Types of Muscle (Muscle Tissue) Muscle cells, often called muscle fibers because they are long and narrow when relaxed, are specialized contractile cells. They are organized into tissues that move body parts or temporarily alter the shape (reduce the circumference of all or part) of internal organs. Associated connective tissue conveys nerve fibers and capillaries to the muscle cells as it binds them into bundles or fascicles. Three types of muscle are described based on distinct characteristics relating to:   

Whether it is normally willfully controlled (voluntary vs. involuntary). Whether it appears striped or unstriped when viewed under a microscope (striated vs. smooth or unstriated). Whether it is located in the body wall and limbs or makes up the hollow organs (viscera) of the body cavities or blood vessels (somatic vs. visceral).

As explained in “Nervous System” (later in this chapter), somatic muscle and visceral muscle are also distinct in regard to their innervation. The three muscle types are (Table I.1) as follows: 

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Skeletal striated muscle is voluntary somatic muscle that makes up the gross skeletal muscles that compose the muscular system, moving or stabilizing bones and other structures (e.g., the eyeballs). Cardiac striated muscle is involuntary visceral muscle that forms most of the walls of the heart and adjacent parts of the great vessels, such as the aorta, and pumps blood. Smooth muscle (unstriated or unstriped muscle) is involuntary visceral muscle that forms part of the walls of most vessels and hollow organs (viscera), moving substances through them by coordinated sequential contractions (pulsations or peristaltic contractions).

Skeletal Muscles Form, Features, and the Naming of Muscles All skeletal muscles, commonly referred to simply as “muscles,” have fleshy, reddish, contractile portions (one or more heads or bellies) composed of skeletal striated muscle. Some muscles are fleshy throughout, but most also have white non‐


contractile portions (tendons), composed mainly of organized collagen bundles, that provide a means of attachment (Fig. I.18A). When referring to the length of a muscle, both the belly and the tendons are included. In other words, a muscle's length is the distance between its attachments. Most skeletal muscles are attached directly or indirectly to bones, cartilages, ligaments, or fascias or to some combination of these structures. Some muscles are attached to organs (the eyeball, for example), skin (such as facial muscles), and mucous membranes (intrinsic tongue muscles). Muscles are organs of locomotion (movement), but they also provide static support, give form to the body, and provide heat. Figure I.19 identifies the skeletal muscles that lie most superficially. The deep muscles are identified when each region is studied. The architecture and shape of muscles vary (Fig. I.18B). The tendons of some muscles form flat sheets, or aponeuroses, that anchor the muscle to the skeleton (usually a ridge or a series of spinous processes) and/or to deep fascia (such as the latissimus dorsi muscle), or to the aponeurosis of another muscle (such as the oblique muscles of the anterolateral abdominal wall) (Fig. I.19). Most muscles are named on the basis of their function or the bones to which they are attached. The abductor digiti minimi muscle, for example, abducts the little finger. The sternocleidomastoid muscle (G., kleidos, bolt or bar, clavicle) attaches inferiorly to the sternum and clavicle and superiorly to the mastoid process of the temporal bone of the cranium. Other muscles are named on the basis of their position (medial, lateral, anterior, posterior) or length (brevis, short; longus, long). Muscles may be described or classified according to their shape, for which a muscle may also be named (Figs. I.18 and I.19):

Clinically Oriented Anatomy, 5th Edition By Keith Moore T a b l e I . 1 . T y p e s o f M u s c l e Muscle Type

Location C o m p o s e s g r o s s , named muscles (e.g., biceps of arm) attached to skeleton and f a s c i a o f li m b s , body wall, and head/neck

Appearance of Cells L a r g e , v e r y l o n g , unbranched, cylindrical fibers with transverse s t r i a t i o n s ( s t r i p e s ) a r r a n g e d i n p a r a l l e l b u n d le s ; m u l t i p l e , peripherally located nuclei

T y p e o f A c t i v i t y Strong, quick intermittent (phasic) contraction above a b a s e l i n e to n u s ; a c t s p r i m a r il y t o produce m o v e m e n t or resist gravity

Stimulation Voluntary (or r e f l e x i v e ) by somatic nervous s y s te m

M u s c l e o f h e a r t (myocardium) and a d j a ce n t p o rt i o n s of great vessels (aorta, vena cava)

Branching and a n a s t o m o s in g shorter fibers with transverse s t r i a t i o n s ( s t r i p e s ) r u n n i n g p a ra l l e l a n d connected end to end by complex junctions (intercalated discs); single, central nucleus Single or a g g l o m e r a te d s m a l l , s p i n d le ‐ s h a p e d fibers without striations; single, c e n t r a l n u c le u s

Strong, quick, continuous rhythmic contraction; acts to pump blood f r o m h e a r t

Involuntary; intrinsically (myogenically) stimulated and propagated; rate and strength of contraction modified by autonomic n e r v o u s s y s te m

Walls of hollow viscera and blood vessels, iris, and ciliary body of eye; attached to hair follicles of skin ( a r r e c t o r m u s c l e o f h a ir )

Weak, slow, Involuntary by rhythmic, or autonomic s u s ta i n e d t o n i c n e r v o u s s y s te m contraction; acts mainly to propel s u b s t a n ce s (peristalsis) and to restrict flow (vasoconstriction and sphincteric activity)

Figure I.18. Skeletal muscles. A. The belly is the fleshy contractile part of a muscle. This muscle has a belly with two heads; tendons provide attachment to bone at both ends. B. The architecture and shape of a skeletal muscle depend on the arrangement of its fibers.

Introduction to Clinically Oriented Anatomy  

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Flat muscles have parallel fibers often with an aponeurosis—for example, external oblique. Pennate muscles are feather‐like (L. pennatus, feather) in the arrangement of their fascicles, and may be unipennate, bipennate, or multi‐pennate—for example, extensor digitorum longus (unipennate), bellies of the gastrocnemius (bipennate), and deltoid (multi‐pennate). Fusiform muscles are spindle shaped with a round, thick belly (or bellies) and tapered ends—for example, biceps brachii. Quadrate muscles have four equal sides (L. quadratus, square)—for example, pronator quadratus. Circular or sphincteral muscles surround a body opening or orifice, constricting it when contracted—for example, orbicularis oris (closes the mouth). Multi‐headed or multi‐bellied muscles have more than one head of attachment or more than one contractile belly, respectively—for examples, biceps muscles (biceps brachii) have two heads of attachment, triceps muscles have three heads (triceps brachii), and the digastric and gastrocnemius muscles have two bellies (those of the former are tandem; those of the latter, parallel).

Contraction of Muscles Skeletal muscles function by contracting; they pull and never push. However, certain phenomena—such as “popping of the ears” to equalize air pressure and the musculovenous pump (p. 43)—take advantage of the expansion of muscle bellies during contraction. When a muscle contracts and shortens, one of its attachments usually remains fixed while the other (more mobile) attachment is pulled toward it, often resulting in movement. Attachments of muscles are commonly described as the origin and insertion; the origin is usually the proximal end of the muscle, which remains fixed during muscular contraction, and the insertion is usually the distal end of the muscle, which is movable. However, this is not always the case. Some muscles can act in both directions under different circumstances. For example, when doing push‐ups, the distal end of the upper limb (the hand) is fixed (on the floor) and the proximal end of the limb and the trunk are being moved. Therefore, this book usually uses the terms proximal and distal or medial and lateral when describing most muscle attachments. Note that if the attachments of a muscle are known, the action of the muscle can usually be deduced (rather than memorized). When studying muscle attachments, act out the action; you are more likely to learn things you have experienced.


Figure I.19. Superficial skeletal muscles. Most of these muscles move the skeleton, but some muscles move other parts (e.g., the eyeballs and scalp). The sheath of the left rectus abdominis has been opened to reveal the muscle. The orbicularis oris encircles the mouth and plays important roles in controlling entrance and exit, chewing, speech, and facial expression.

Reflexive Contraction Although skeletal muscles are also referred to as voluntary muscles, certain aspects of their activity are automatic (reflexive) and therefore not voluntarily controlled. Examples are the respiratory movements of the diaphragm, controlled most of the time by reflexes stimulated by the levels of oxygen and carbon dioxide in the blood (although we can willfully control it within limits), and the myotatic reflex, which results in movement after a muscle stretch produced by tapping a tendon with a reflex hammer. Tonic Contraction Even when “relaxed” the muscles of a conscious individual are almost always slightly contracted. This slight contraction, called muscle tone (tonus), does not produce movement or active resistance (as phasic contraction does) but gives the muscle a certain firmness, assisting the stability of joints and the maintenance of posture, while keeping the muscle ready to respond to appropriate stimuli. Muscle tone is


usually absent only when unconscious (as during deep sleep or under general anesthesia) or after a nerve lesion resulting in paralysis. Phasic Contraction There are two main types of phasic (active) muscle contractions: isotonic contractions, in which the muscle changes length in relationship to the production of movement, and isometric contractions, in which muscle length remains the same—no movement occurs, but the force (muscle tension) is increased above tonic levels (Fig. I.20). The latter type of contraction is important in maintaining upright posture and when muscles act as fixators or shunt muscles. There are two types of isotonic contractions. The type we most commonly think of is concentric contraction, in which movement occurs as a result of the muscle shortening—for example, when lifting a cup, pushing a door, or striking a blow. The ability to apply exceptional force by means of concentric contraction often is what distinguishes an athlete from an amateur. The other type is eccentric contraction, in which a contracting muscle lengthens—that is, it undergoes a controlled and gradual relaxation while continually exerting a (diminishing) force, like playing out a rope. While not as familiar, eccentric contractions are as important as concentric contractions for coordinated, functional movements such as walking, running, and setting objects (or one's self) down. Often, when the main muscle of a particular movement (the prime mover) is undergoing a concentric contraction, its antagonist is undergoing a coordinated eccentric contraction. In walking, we contract concentrically to pull our center of gravity forward and then, as it passes ahead of the limb, we contract eccentrically to prevent a lurching during the transfer of weight to the other limb. Eccentric contractions require less metabolic energy at the same load but, with a maximal contraction, are capable of generating much higher tension levels than concentric contractions—as much as 50% higher (Marieb, 2004).

Figure I.20. Isometric and isotonic contractions. Isometric contraction sustains the position of a joint without producing movement. Concentric and eccentric contractions are isotonic contractions in which the muscle changes length: concentric contractions by shortening, and eccentric contractions by actively controlled lengthening (relaxation).


Figure I.21. Motor unit. A motor unit consists of a single motor neuron and the muscle fibers innervated by it.

Whereas the structural unit of a muscle is a skeletal striated muscle fiber, the functional unit of a muscle is a motor unit, consisting of a motor neuron and the muscle fibers it controls (Fig. I.21). When a motor neuron in the spinal cord is stimulated, it initiates an impulse that causes all the muscle fibers supplied by that motor unit to contract simultaneously. The number of muscle fibers in a motor unit varies from one to several hundred. The number of fibers varies according to the size and function of the muscle. Large motor units, in which one neuron supplies several hundred muscle fibers, are in the large trunk and thigh muscles. In the small eye and hand muscles, where precision movements are required, the motor units include only a few muscle fibers. Movement (phasic contraction) results from the activation of an increasing number of motor units, above the level required to maintain tonus. Functions of Muscles Muscles serve specific functions in moving and positioning the body. 

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A prime mover or agonist is the main muscle responsible for producing a specific movement of the body. It contracts concentrically to produce the desired movement, doing most of the work (expending most of the energy) required. In most movements, there is a single prime mover, but some movements involve two prime movers working in equal measure. Fixators steady proximal parts of a limb through isometric contraction while movements are occurring in distal parts. A synergist complements the action of a prime mover. It may directly assist a prime mover, providing a weaker or less mechanically advantaged component of the same movement, or it may assist indirectly, by serving as a fixator of an intervening joint when a prime mover passes over more than one joint, for example. It is not unusual to have several synergists assisting a prime mover in a particular movement. An antagonist is a muscle that opposes the action of another muscle. A primary antagonist directly opposes the prime mover, but synergists may also be opposed by secondary antagonists. As the active movers concentrically


contract to produce a movement, antagonists eccentrically contract, relaxing progressively in coordination to produce a smooth movement. The same muscle may act as a prime mover, antagonist, synergist, or fixator under different conditions. Note also that the actual prime mover in a given position may be gravity. In such cases, a paradoxical situation may exist in which the prime mover usually described as being responsible for the movement is inactive (passive), while the controlled relaxation (eccentric contraction) of the antigravity antagonist(s) is the active (energy requiring) component in the movement. An example is lowering (adducting) the upper limbs from the abducted position (stretched out laterally at 90° to the trunk) when standing erect. The prime mover (adductor) is gravity; the muscles described as the prime movers for this movement (pectoralis major and latissimus dorsi) are inactive or passive; and the muscle being actively innervated (contracting eccentrically) is the deltoid (an abductor, typically described as the antagonist for this movement). A muscle whose pull is exerted along a line that parallels the axis of the bones to which it is attached (e.g., the brachioradialis) is at a disadvantage for producing movement. Instead it acts to maintain contact between the articular surfaces of the joint it crosses (i.e., it resists dislocating forces); this type of muscle is a shunt muscle. The more oblique a muscle's line of pull is oriented to the bone it moves (i.e., the less parallel the line of pull is to the long axis of the bone, e.g., the biceps brachii during flexion of the elbow), the more capable it is of rapid and effective movement; this type of muscle is a spurt muscle. Nerves and Arteries to Muscles Variation in the nerve supply of muscles is rare; it is a nearly constant relationship. In the limb, muscles of similar actions are generally contained within a common fascial compartment and share innervation by the same nerves; therefore, you should learn the innervation of limb muscles in terms of the functional groups, making it necessary to memorize only the exceptions. Nerves supplying skeletal muscles (motor nerves) usually enter the fleshy portion of the muscle (vs. the tendon), almost always from the deep aspect (so it is protected by the muscle it supplies). The few exceptions will be pointed out in the text. When a nerve pierces a muscle, by passing through its fleshy portion or between two heads of attachment, it usually supplies that muscle. Exceptions are the cutaneous branches of posterior (dorsal) rami and the superficial muscles of the back. The blood supply of muscles is not as constant as the nerve supply and is usually multiple. Arteries generally supply the structures they contact. Thus you should learn the course of the arteries and deduce that a muscle is supplied by all the arteries in its vicinity. Muscle Dysfunction and Paralysis From the clinical perspective, it is important not only to think in terms of the action normally produced by a given muscle but also to consider what loss of function would occur if the muscle failed to function (paralysis). How would the dysfunction of a given muscle or muscle group be manifest (i.e., what are the visible signs)?


Absence of Muscle Tone Although a gentle force, muscle tone can have important effects; the tonus of muscles in the lips helps keep the teeth aligned, for instance. When this gentle but constant pressure is absent (owing to paralysis or a short lip that leaves the teeth exposed), teeth migrate, becoming everted (“buck teeth” ). The absence of muscle tone in an unconscious patient (e.g., under a general anesthetic) may allow joints to be dislocated as he or she is being lifted or positioned. When a muscle is denervated (loses its nerve supply) it becomes paralyzed (flaccid, lacking both its tonus and its ability to contract phasically on demand or reflexively). In the absence of a muscle's normal tonus, that of opposing (antagonist) muscle(s) may cause a limb to assume an abnormal resting position. In addition, the denervated muscle will become fibrotic and lose its elasticity, also contributing to the abnormal position at rest. Muscle Soreness and “Pulled” Muscles Because eccentric contractions are capable of generating higher tension levels, eccentric contractions that are either excessive or associated with a novel task are often the cause of delayed‐onset muscle soreness. Thus walking down many flights of stairs would actually result in more soreness, owing to the eccentric contractions, than walking up the same flights of stairs. The muscle stretching that occurs during the lengthening type of eccentric contraction appears to be more likely to produce microtears in the muscles and/or periosteal irritation than that associated with a shortening (concentric) contraction. Skeletal muscles are limited in their ability to lengthen. Usually muscles cannot elongate beyond one third of their resting length without sustaining damage. This is reflected in their attachments to the skeleton, which usually do not permit excessive lengthening. An exception is the hamstring muscles of the posterior thigh. When the knee is extended, the hamstrings typically reach their maximum length before the hip is fully flexed (i.e., flexion at the hip is limited by the hamstring's ability to elongate). Undoubtedly this, as well as forces related to their eccentric contraction, explains why hamstrings muscles are “pulled” (sustain tears) more commonly than other muscles (Fig. BI.6).


Figure BI.6. Growth and Regeneration of Skeletal Muscle Skeletal striated muscle fibers cannot divide, but they can be replaced individually by new muscle fibers derived from satellite cells of skeletal muscle. Located inside the basement membranes of the muscle fibers, these satellite cells represent a potential source of myoblasts, precursors of muscle cells, which are capable of fusing with each other to form new skeletal muscle fibers if required (Cormack, 2001). The number of new fibers that can be produced is insufficient to compensate for major muscle degeneration or trauma. Instead of becoming regenerated effectively, the new skeletal muscle is composed of a disorganized mixture of muscle fibers and fibrous scar tissue. Skeletal muscles are able to grow larger in response to frequent strenuous exercise, such as body building. This growth results from hypertrophy of existing fibers, not from the addition of new muscle fibers. Hypertrophy lengthens and increases the myofibrils within the muscle fibers (Fig. I.21), thereby increasing the amount of work the muscle can perform. Muscle Testing Muscle testing helps an examiner diagnose nerve injuries. There are two common testing methods: 

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The person performs movements that resist those of the examiner. For example, the person keeps the forearm flexed while the examiner attempts to extend it. This technique enables the examiner to gauge the power of the person's movements. The examiner performs movements that resist those of the person. When testing flexion of the forearm, the examiner asks the person to flex his or her


forearm while the examiner resists the efforts. Usually muscles are tested in bilateral pairs for comparison. Electromyography (EMG), the electrical stimulation of muscles, is another method for testing muscle action. The examiner places surface electrodes over a muscle, asks the person to perform certain movements, and then amplifies and records the differences in electrical action potentials of the muscles. A normal resting muscle shows only a baseline activity (tonus), which disappears only during deep sleep, paralysis, and when under anesthesia. Contracting muscles demonstrate variable peaks of phasic activity. EMG makes it possible to analyze the activity of an individual muscle during different movements. EMG may also be part of the treatment program for restoring the action of muscles. The Bottom Line Muscles are categorized as skeletal striated, cardiac striated, or smooth. Skeletal muscles are further classified according to their shape as flat, pennate, fusiform, quadrate, circular or sphincteral, and multi‐headed or multi‐bellied. Skeletal muscle functions by contracting, enabling automatic (reflexive) movements, maintaining muscle tone (tonic contraction), and providing for phasic (active) contraction with (isotonic) or without (isometric) change in muscle length. Isotonic movements are either concentric (producing movement by shortening) or eccentric (allowing movement by controlled relaxation). Prime movers or agonists are the muscles primarily responsible for particular movements. Fixators “fix” a part of a limb while another part of the limb is moving. Synergists augment the action of prime movers. Antagonists oppose the actions of another muscle. Cardiac Striated Muscle Cardiac striated muscle forms the muscular wall of the heart, the myocardium. Some cardiac muscle is also present in the walls of the aorta, pulmonary vein, and superior vena cava (SVC). Cardiac striated muscle contractions are not under voluntary control. Heart rate is regulated intrinsically by a pacemaker, an impulse‐conducting system composed of specialized cardiac muscle fibers; they in turn are influenced by the autonomic nervous system (ANS) (discussed later in this chapter). Cardiac striated muscle has a distinctly striped appearance under microscopy (Table I.1). Both types of striated muscle—skeletal and cardiac—are further characterized by the immediacy, rapidity, and strength of their contractions. Note: Even though the trait applies to both skeletal and cardiac striated muscle, in common use the terms striated and striped are used to designate voluntary skeletal striated muscle. Cardiac muscle is distinct from skeletal muscle in both behavior and appearance. Unlike striated skeletal muscle fibers, cardiac muscle fibers:   

Contract spontaneously (without extrinsic stimuli) and rhythmically. Bifurcate (split or branch). Are traversed at intervals by intercalated discs (disks)—unique, specialized end‐to‐end junctions—where they are linked into a chain or mesh with other bifurcating cardiac muscle fibers.


To support its continuous level of high activity, the blood supply to cardiac muscle is twice as rich as that to skeletal muscle. Smooth Muscle Smooth muscle, named for the absence of striations in the appearance of the muscle fibers under microscopy, forms a large part of the middle coat or layer (tunica media) of the walls of blood vessels (above the capillary level) (Fig. I.23 and Table I.1). Consequently, it occurs in all vascularized tissue. It also makes up the muscular part of the walls of the digestive tract and ducts. Smooth muscle is found in skin, composing the arrector muscle of hair associated with hair follicles (Fig. I.6), and in the eyeball, where it controls lens thickness and pupil size. Like cardiac striated muscle, smooth muscle is involuntary muscle; however, it is directly innervated by the ANS. Its contraction can also be initiated by hormonal stimulation or by local stimuli, such as stretching. Smooth muscle responds more slowly than striated muscle and with a delayed and more leisurely contraction. It can undergo partial contraction for long periods and has a much greater ability than striated muscle to elongate without suffering paralyzing injury. Both of these factors are important in regulating the size of sphincters and the caliber of the lumina (interior spaces) of tubular structures. In the walls of the digestive tract, uterine tubes, and ureters, smooth muscle cells are responsible for peristalsis, rhythmic contractions that propel the contents along these tubular structures. Hypertrophy of the Myocardium and Myocardial Infarction In compensatory hypertrophy, the myocardium responds to increased demands by increasing the size of its fibers. When cardiac striated muscle fibers are damaged by loss of their blood supply during a heart attack, the tissue becomes necrotic (dies) and the fibrous scar tissue that develops forms a myocardial infarct (MI), an area of myocardial necrosis (pathological death of cardiac tissue). Muscle cells that degenerate are not replaced, because cardiac muscle cells do not divide. Furthermore, there is no equivalent to the satellite cells of skeletal muscle that can produce new cardiac muscle fibers. Hypertrophy and Hyperplasia of Smooth Muscle Smooth muscle cells undergo compensatory hypertrophy in response to increased demands. Smooth muscle cells in the uterine wall during pregnancy increase not only in size but also in number (hyperplasia) because these cells retain the capacity for cell division. In addition, new smooth muscle cells can develop from incompletely differentiated cells (pericytes) that are located along small blood vessels (Cormack, 2001; Gartner and Hiatt, 2001). The Bottom Line Cardiac muscle is a striated muscle type found in the walls of the heart, or myocardium, as well as in some major blood vessels. Contraction of cardiac muscle is not under voluntary control but is instead activated by specialized cardiac muscle fibers forming the pacemaker, the activity of which is regulated by the autonomic nervous system. Smooth muscle does not have striations. It occurs in all vascular tissues and in the walls of the digestive tract and other organs. Smooth muscle is


directly innervated by the autonomic nervous system and thus is not under voluntary control. Cardiovascular System The circulatory system transports fluids throughout the body; it consists of the cardiovascular and lymphatic systems. The heart and blood vessels make up the blood transportation network, the cardiovascular system (Fig. I.22). Through this system, the heart pumps blood through the body's vast system of blood vessels. The blood carries nutrients, oxygen, and waste products to and from the cells. There are three types of blood vessels: arteries, veins, and capillaries. Blood under high pressure leaves the heart and is distributed to the body by a branching system of thick‐walled arteries. The final distributing vessels, arterioles, deliver oxygenated blood to capillaries. Capillaries form a capillary bed, where the interchange of oxygen, nutrients, waste products, and other substances with the extracellular fluid occurs. Blood from the capillary bed passes into thin‐walled venules, which resemble wide capillaries. Venules drain into small veins that open into larger veins. The largest veins, the superior and inferior venae cavae, return poorly oxygenated blood to the heart. Most vessels of the circulatory system have three coats, or tunics (Fig. I.23): 

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Tunica intima, an inner lining consisting of a single layer of extremely flattened epithelial cells, the endothelium, supported by delicate connective tissue. Capillaries consist only of this tunic, with blood capillaries also having a supporting basement membrane. Tunica media, a middle layer consisting primarily of smooth muscle. Tunica adventitia, an outer connective tissue layer or sheath.

The tunica media is the most variable. Arteries, veins, and lymphatic ducts are distinguished by the thickness of this layer relative to the size of the lumen, its organization, and, in the case of arteries, the presence of variable amounts of elastic fibers. Arteries Arteries carry blood from the heart and distribute it to the body. The blood passes through arteries of decreasing caliber. The different types of arteries are distinguished from each other on the basis of overall size, relative amounts of elastic tissue or muscle in the tunica media, the thickness of the wall relative to the lumen, and function. Artery size and type is a continuum—that is, there is a gradual change in morphological characteristics from one type to another. There are three types of arteries: 

Large elastic arteries (conducting arteries) have many elastic layers (sheets of elastic fibers) in their walls. These large arteries initially receive the cardiac output. Their elasticity enables them to expand when the heart contracts (when they receive the cardiac output), minimizing the pressure change, and return to normal size between cardiac contractions, pushing the blood into the medium arteries downstream. This maintains the blood pressure in the arterial system between cardiac contractions (at a time when ventricular pressure falls to zero). Overall, this minimizes the ebb in blood pressure as the heart


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contracts and relaxes. Examples of large elastic arteries are the aorta, the arteries that originate from the arch of the aorta (brachiocephalic, subclavian, and carotids arteries), and the pulmonary trunk and arteries. Medium muscular arteries (distributing arteries) have walls that consist chiefly of circularly disposed smooth muscle fibers. Their ability to decrease their diameter (vasoconstrict) regulates the flow of blood to different parts of the body as required by circumstance (e.g., activity, thermoregulation). Pulsatile contractions of their muscular walls (regardless of current diameter) temporarily and rhythmically constrict their lumina in progressive sequence, propelling and distributing blood to various parts of the body. Most of the named arteries, including those observed in the body wall and limbs during dissection such as the brachial or femoral arteries, are medium muscular arteries.


Figure I.22. Cardiovascular system. Most arteries carry oxygenated blood away from the heart and most veins carry deoxygenated blood to the heart; however, the pulmonary arteries arising from the pulmonary trunk carry deoxygenated blood to the lungs, and the pulmonary veins carry oxygenated blood from the lungs to the heart. Although commonly depicted as a single vessel, as shown here, the deep veins of the limbs usually occur as a pair of accompanying veins (L. venae comitantes).


Figure I.23. Blood vessel structure. The walls of most blood vessels have three concentric layers of tissue, called tunics (L. tunicae, coats). With less muscle, veins are thinner walled than their companion arteries and have wide lumens (L. luminae) that usually appear flattened in tissue sections. Most medium veins that return blood to the heart against gravity (e.g., leg veins) have valves that break up the columns of blood and, if healthy, allow blood to flow only toward the heart. 

Small arteries and arterioles have relatively narrow lumina and thick muscular walls. The degree of filling of the capillary beds and level of arterial pressure within the vascular system are regulated mainly by the degree of tonus (firmness) in the smooth muscle of the arteriolar walls. If the tonus is above normal, hypertension (high blood pressure) results. The small arteries are usually not named or specifically identified during dissection, and arterioles can be observed only under magnification.

Anastomoses (communications) between the multiple branches of an artery provide numerous potential detours for blood flow in case the usual pathway is obstructed by compression, the position of a joint, pathology, or surgical ligation. If a main channel is occluded, the smaller alternate channels can usually increase in size in a relatively short time, providing a collateral circulation that ensures the blood supply to structures distal to the blockage. However, collateral pathways require time to open adequately; they are usually insufficient to compensate for sudden occlusion or ligation. There are areas, however, where collateral circulation does not exist, or is inadequate to replace the main channel. Arteries that do not anastomose with adjacent arteries are anatomical or true terminal or end arteries. Occlusion of an end artery interrupts the blood supply to the structure or segment of an organ it supplies. True terminal arteries supply the retina, for example, where occlusion will result in blindness. While not true terminal arteries, functional terminal arteries (arteries with ineffectual anastomoses) supply segments of the brain, liver, kidneys, spleen, and intestines; they may also exist in the heart.


Arteriosclerosis: Ischemia and Infarction The most common acquired disease of arteries—and a common finding in cadaver dissection—in developed countries is arteriosclerosis (hardening of the arteries), a group of diseases characterized by thickening and loss of elasticity of the arterial walls. A common form, atherosclerosis, is associated with the buildup of fat (mainly cholesterol) in the arterial walls. A calcium deposit forms an atheromatous plaque (atheroma)—well‐demarcated, hardened yellow areas or swellings on the intimal surfaces of arteries (Fig. BI.7A). The consequent arterial narrowing and surface irregularity may result in thrombosis (local intravascular clotting), which may occlude the artery or be flushed into the bloodstream (forming a thrombus) and block smaller vessels distally (Fig. BI.7B). The consequences of atherosclerosis include ischemia (reduction of the blood supply to an organ or region) and infarction (local death, or necrosis, of an area of tissue or an organ resulting from the reduced blood supply). These consequences are particularly significant in regard to the heart (ischemic heart disease and myocardial infarction or heart attack), brain (stroke), and distal parts of limbs (gangrene).

Figure BI.7.

Veins Veins generally return deoxygenated (venous) blood from the capillary beds to the heart, which gives the veins a dark blue appearance. The large pulmonary veins are atypical in that they carry well‐oxygenated blood (commonly called “arterial blood” ) from the lungs to the heart. Because of the lower blood pressure in the venous system, the walls (specifically, the tunica media) of veins are thinner than those of their companion arteries (Fig. I.23). Normally, veins do not pulsate and do not squirt or spurt blood when severed. There are three sizes of veins: 



Venules are the smallest veins. Venules drain capillary beds and join similar vessels to form small veins. Magnification is required to observe venules. Small veins are the tributaries of larger veins that unite to form venous plexuses, such as the posterior venous arch of the foot (Fig. I.22). Small veins are unnamed. Medium veins drain venous plexuses and accompany medium arteries. In the limbs, and in some other locations where the flow of blood is opposed by the




pull of gravity, the medium veins have flap valves that permit blood to flow toward the heart but not in the reverse direction. Examples of medium veins include the named superficial veins (cephalic and basilic veins of the upper limb and great and small saphenous veins of the lower limb) and the accompanying veins that are named according to the artery they accompany. Large veins are characterized by wide bundles of longitudinal smooth muscle and a well‐developed tunica adventitia. An example is the superior vena cava.

Veins are more abundant than arteries. Although their walls are thinner, their diameters are usually larger than those of the corresponding artery. The thin walls allow veins to have a large capacity for expansion, and do so when blood return to the heart is impeded by compression or internal pressures (e.g., after taking a large breath and holding it; this is the Valsalva maneuver). Since the arteries and veins make up a circuit, it might be expected that half the blood volume would be in the arteries and half in the veins, but because of veins' larger diameter and ability to expand, typically only 20% of the blood occupies arteries, whereas 80% is in the veins. Although often depicted as single vessels in illustrations for simplicity, veins tend to be double or multiple. Those that accompany deep arteries—accompanying veins (L. venae comitantes)—surround them in an irregular branching network (Fig. I.24). This arrangement serves as a countercurrent heat exchanger, the warm arterial blood warming the cooler venous blood as it returns to the heart from a cold extremity. The accompanying veins occupy a relatively unyielding fascial vascular sheath with the artery they accompany. As a result, they are stretched and flattened as the artery expands during contraction of the heart, which aids in driving venous blood toward the heart—an arteriovenous pump. Systemic veins are more variable than arteries, and venous anastomoses—natural communications, direct or indirect, between two veins—occur more often between them. The outward expansion of the bellies of contracting skeletal muscles in the limbs, limited by the deep fascia, compresses the veins, “milking” the blood superiorly toward the heart; another (musculovenous) type of venous pump (Fig. I.25). The valves of the veins break up the columns of blood, thus relieving the more dependent parts of excessive pressure, allowing venous blood to flow only toward the heart. The venous congestion that hot and tired feet experience at the end of a busy day is relieved by resting the feet on a footstool that is higher than the trunk. This position of the feet also helps the veins return blood to the heart. Figure I.24. Accompanying veins (venae comitantes). Although most veins of the trunk occur as large single vessels, the veins in the limbs occur as two or more smaller vessels that accompany an artery in a common vascular sheath.


Figure I.25. Musculovenous pump. Muscular contractions in the limbs function with the venous valves to move blood toward the heart. The outward expansion of the bellies of contracting muscles is limited by deep fascia and becomes a compressive force, propelling the blood against gravity. Black arrows indicate the direction of blood flow.

Varicose Veins When the walls of veins lose their elasticity, they become weak. A weakened vein dilates under the pressure of supporting a column of blood against gravity. This results in varicose veins—abnormally swollen, twisted veins—most often seen in the legs (Fig. BI.8). Varicose veins have a caliber greater than normal, and their valve cusps do not meet or have been destroyed by inflammation. These veins have incompetent valves; thus the column of blood ascending toward the heart is unbroken, placing increased pressure on the weakened walls, further exacerbating the varicosity problem. Varicose veins also occur in the presence of degenerated deep fascia. Such incompetent fascia is incapable of containing the expansion of contracting muscles; thus the (musculofascial) musculovenous pump is ineffective.


Figure BI.8. Blood Capillaries In order for the oxygen and nutrients carried by the arteries to benefit the cells that make up the tissues of the body, they must leave the transporting vessels and enter the extravascular space between the cells, the extracellular (intercellular) space in which the cells live. Capillaries are simple endothelial tubes connecting the arterial and venous sides of the circulation that allow the exchange of materials with the interstitial or extracellular fluid (ECF). Capillaries are generally arranged in capillary beds, networks that connect the arterioles and venules (Fig. I.23). The blood enters the capillary beds through arterioles that control the flow and is drained from them by venules. As the hydrostatic pressure in the arterioles forces blood into and through the capillary bed, it also forces fluid containing oxygen, nutrients, and other cellular materials out of the blood at the arterial end of the capillary bed (upstream) into the extracellular spaces, allowing exchange with cells of the surrounding tissue. Capillary walls are relatively impermeable, however, to plasma proteins. Downstream, at the venous end of the bed, most of this ECF—now containing waste products and carbon dioxide—is then reabsorbed into the blood as a result of the osmotic pressure from the higher concentrations of proteins within the capillary. (Although firmly established, this principle is referred to as the Starling hypothesis.) In some regions, such as in the fingers, there are direct connections between the small arterioles and venules proximal to the capillary beds they supply and drain. The sites of such communications—arteriolovenular anastomoses (AV shunts)—permit blood to pass directly from the arterial to the venous side of the circulation without passing through capillaries. AV shunts are numerous in the skin, where they have an important role in conserving body heat. In some situations, blood passes through two capillary beds before returning to the heart; a venous system linking two capillary beds constitutes a portal venous system. The venous system by which nutrient‐rich blood passes from the capillary beds of the alimentary tract to the capillary beds or sinusoids of the liver—the hepatic portal system—is the major example (Chapter 2).


The Bottom Line The cardiovascular system consists of the heart and blood vessels—the arteries, veins, and capillaries. Most of these vessels have three coats, or tunics—tunica intima, tunica media, and tunica adventitia. Arteries have both elastic and muscle fibers in their walls, which allow them to propel blood throughout the cardiovascular system. Veins have thinner walls than arteries and are distinguished by valves, which prevent backflow of blood. Capillaries are the smallest blood vessels and provide the linkage between the smallest arteries (arterioles) and veins (venules). Lymphatic System Although widely distributed throughout most of the body, most of the lymphatic (lymphoid) system is not apparent in the cadaver, yet it is essential to survival. Knowledge of the anatomy of the lymphatic system is important for clinicians. The Starling hypothesis (mentioned earlier) explains how most of the fluid and electrolytes entering the extracellular spaces from the blood capillaries is also reabsorbed by them. However, as much as 3 L each day fails to be reabsorbed by the blood capillaries. Furthermore, some plasma protein does leak into the extracellular spaces, and material originating from the tissue cells themselves that cannot pass through the walls of blood capillaries, such as cytoplasm from disintegrating cells, continually enters the space in which the cells live. If this material were to accumulate in the extracellular spaces, a reverse osmosis would occur, bringing even more fluid and resulting in edema (an excess of interstitial fluid, manifest as swelling). However, the amount of interstitial fluid remains fairly constant under normal conditions, and proteins and cellular debris normally do not accumulate in the extracellular spaces because of the lymphatic system. The lymphatic system thus constitutes a sort of “overflow” system that provides for the drainage of surplus tissue fluid and leaked plasma proteins to the bloodstream, as well for the removal of debris from cellular decomposition and infection. The important components of the lymphatic system are (Fig. I.26): 







Lymphatic plexuses, networks of lymphatic capillaries that originate blindly in the extracellular (intercellular) spaces of most tissues. Because they are formed of a highly attenuated endothelium lacking a basement membrane, along with surplus tissue fluid, plasma proteins, bacteria, cellular debris, and even whole cells (especially lymphocytes) can readily enter them. Lymphatic vessels (lymphatics), a nearly bodywide network of thin‐walled vessels with abundant lymphatic valves. In living individuals, the vessels bulge where each of the closely spaced valves occur, giving lymphatics a beaded appearance. Lymphatic capillaries and vessels occur almost everywhere blood capillaries are found, except, for example, teeth, bone, bone marrow, and the entire central nervous system (excess tissue fluid here drains into the cerebrospinal fluid). Lymph (L. lympha, clear water), the tissue fluid that enters lymph capillaries and is conveyed by lymphatic vessels. Usually clear, watery, and slightly yellow, lymph is similar in composition to blood plasma. Lymph nodes, small masses of lymphatic tissue located along the course of lymphatic vessels through which lymph is filtered on its way to the venous system.

Introduction to Clinically Oriented Anatomy  

Lymphocytes, circulating cells of the immune system that react against foreign materials. Lymphoid tissue, sites that produce lymphocytes, such as that aggregated in the walls of the digestive tract (alimentary canal); in the spleen, thymus, and lymph nodes; and as myeloid tissue in red bone marrow.

Superficial lymphatic vessels, more numerous than veins in the subcutaneous tissue and anastomosing freely, converge toward and follow the venous drainage. These vessels eventually drain into deep lymphatic vessels that accompany the arteries and also receive the drainage of internal organs. It is likely that the deep lymphatic vessels are also compressed by the arteries they accompany, milking the lymph along these valved vessels in the same manner described earlier for accompanying veins. Both superficial and deep lymphatic vessels traverse lymph nodes (usually several sets) as they course proximally, becoming larger as they merge with vessels draining adjacent regions. The larger lymphatic vessels enter large collecting vessels, called lymphatic trunks, which unite to form either the right lymphatic duct or the thoracic duct (Fig. I.26): 



The right lymphatic duct drains lymph from the body's right upper quadrant (right side of the head, neck, and thorax plus the right upper limb). At the root of the neck, it enters the junction of the right internal jugular and right subclavian veins, called the right venous angle. The thoracic duct drains lymph from the remainder of the body. The lymphatic trunks draining the lower half of the body merge in the abdomen, sometimes forming a dilated collecting sac, the chyle cistern (L. cisterna chyli). From this sac (if present), or from the merger of the trunks, the thoracic duct ascends into and then through the thorax to enter the left venous angle (junction of left internal jugular and left subclavian veins).

Although this is the typical drainage pattern of most lymph, lymphatic vessels communicate with veins freely in many parts of the body. Consequently, ligation of a lymphatic trunk or even the thoracic duct itself may have only a transient effect as a new pattern of drainage is established through more peripheral lymphaticovenous— and later interlymphatic—anastomoses. Additional functions of the lymphatic system include: 



Absorption and transport of dietary fat. Special lymphatic capillaries, called lacteals (L. lacteus, milk), receive all lipid and lipid‐soluble vitamins absorbed by the intestine. Visceral lymphatics then convey the milky fluid, chyle (G. chylos, juice), to the thoracic duct and into the venous system. Formation of a defense mechanism for the body. When foreign protein drains from an infected area, antibodies specific to the protein are produced by immunologically competent cells and/or lymphocytes and dispatched to the infected area.


Figure I.26. Lymphatic system. The lymphatic system includes lymphatic vessels, lymphatic ducts, lymphatic trunks, lymph nodes, lymphoid tissue, and lymph organs, such as the spleen. Black arrows indicate the flow (leaking) of interstitial fluid out of blood vessels and (absorption) into the lymphatic capillaries.


The Spread of Cancer Cancer invades the body by contiguity (growing into adjacent tissue) or by metastasis (the dissemination of tumor cells to sites distant from the original or primary tumor). Metastasis occurs by one of three ways:  Direct seeding of the serous membranes of body cavities.  Lymphogenous spread (via lymphatic vessels).  Hematogenous spread (via blood vessels). It is surprising that often even a thin fascial sheet or serous membrane deflects tumor invasion. However, once a malignancy penetrates into a potential space, the direct seeding of cavities—that is, of its serous membranes—is likely. Lymphogenous spread is the most common route for the initial dissemination of carcinomas (epithelial tumors), the most common type of cancer. Cells loosened from the primary tumor enter and travel via lymphatics. The lymph‐borne cells are filtered through and trapped by the lymph nodes, which thus become secondary (metastatic) cancer sites. The pattern of lymph node involvement follows the natural routes of lymph drainage. Thus when removing a potentially metastatic tumor, surgeons stage the metastasis (determine the degree to which cancer has spread) by removing and examining lymph nodes that receive drainage from the organ or region in the order the lymph normally passes through them. Therefore, it is important for the physician to know the lymphatic drainage backward and forward—that is, to know what nodes are likely to be affected when a tumor is identified in a certain site or organ (and the order in which they receive lymph) and to be able to determine likely sites of tumors (sources of metastasis) when an enlarged node is detected. Cancerous nodes become enlarged as the tumor(s) within them grows; however, unlike swollen infected nodes, they are not usually painful when compressed. Hematogenous spread is the most common route for the metastasis of the less common (but more malignant) sarcomas (connective tissue cancers). Because veins are more abundant and have thinner walls that offer less resistance, metastasis occurs more often by venous than arterial routes. Since the blood‐borne cells follow venous flow, the liver and lungs are the most common sites of secondary sarcomas. Typically, the treatment or removal of a primary tumor is not difficult, but the treatment or removal of all the affected lymph nodes or other secondary (metastatic) tumors may be impossible (Cotran et al., 1999) Lymphangitis, Lymphadenitis, and Lymphedema Lymphangitis and lymphadenitis are the secondary inflammation of lymphatic vessels and lymph nodes, respectively. These conditions may occur when the lymphatic system is involved in chemical or bacterial transport after severe injury or infection. The lymphatic vessels, not normally evident, may become apparent as red streaks in the skin, and the nodes become painfully enlarged. This is potentially dangerous because the uncontained infection may lead to septicemia (blood poisoning). Lymphedema (or edema), the localized accumulation of interstitial fluid, occurs when lymph does not drain from an area of the body. For instance, if cancerous lymph nodes are surgically removed from the axilla (armpit), lymphedema of the limb may occur. Solid cell growths may permeate lymphatic vessels and form minute cellular emboli (plugs), which may break free and pass to regional lymph nodes. In this way, further lymphogenous spread to other tissues and organs may occur.


The Bottom Line The lymphatic system drains surplus fluid from the extracellular spaces to the bloodstream. It also functions as the body's defense system. Important components of the lymphatic system are networks of lymphatic capillaries, the lymphatic plexuses; lymphatic vessels; lymph; lymph nodes; lymphocytes; and lymphoid tissue. The lymphatic system provides a (relatively) predictable route for the spread of certain types of cancerous cells throughout the body. Inflammation of the lymphatic vessels and lymph nodes is an important harbinger of injury or inflammation. Nervous System The nervous system enables the body to react to continuous changes in its internal and external environments. It also controls and integrates the various activities of the body, such as circulation and respiration. For descriptive purposes, the nervous system is divided:  

Structurally into the central nervous system (CNS) and peripheral nervous system (PNS). Functionally into the somatic nervous system (SNS) and autonomic nervous system (ANS).

Nervous tissue consists of two main cell types: neurons (nerve cells) and neuroglia (glial cells), which support the neurons. 



Neurons are the structural and functional units of the nervous system specialized for rapid communication (Fig. I.27). A neuron is composed of a cell body with processes (extensions) called dendrites and an axon, which carry impulses to and away from the cell body, respectively. Myelin, layers of lipid, and protein substances form a myelin sheath around some axons, greatly increasing the velocity of impulse conduction. Neurons communicate with each other at synapses, points of contact between neurons. The communication occurs by means of neurotransmitters, chemical agents released or secreted by one neuron, which may excite or inhibit another neuron, continuing or terminating the relay of impulses or the response to them. Neuroglia (glial cells or glia), approximately five times as abundant as neurons, are non‐neuronal, non‐excitable cells that form a major component (scaffolding) of nervous tissue, supporting, insulating, and nourishing the neurons. In the CNS, neuroglia include oligodendroglia, astrocytes, ependymal cells, and microglia (small glial cells). In the PNS, neuroglia include satellite cells around the neurons in the spinal (posterior root) and autonomic ganglia and neurolemma (Schwann) cells.

Central Nervous System The central nervous system consists of the brain and spinal cord (Fig. I.28). The principal roles of the CNS are to integrate and coordinate incoming and outgoing neural signals and to carry out higher mental functions, such as thinking and learning. A collection of nerve cell bodies in the CNS is called a nucleus. A bundle of nerve fibers (axons) connecting neighboring or distant nuclei of the CNS is a tract. The brain and spinal cord are composed of gray matter and white matter. The nerve cell


bodies lie within and constitute the gray matter; the interconnecting fiber tract systems form the white matter (Fig. I.29). In transverse sections of the spinal cord, the gray matter appears roughly as an H‐shaped area embedded in a matrix of white matter. The struts (supports) of the H are horns; hence there are right and left posterior (dorsal) and anterior (ventral) gray horns. Three membranous layers—pia mater, arachnoid mater, and dura mater—collectively constitute the meninges. The meninges and the cerebrospinal fluid (CSF) surround and protect the CNS. The brain and spinal cord are intimately covered on their outer surface by the innermost meningeal layer, a delicate, transparent covering, the pia mater. The CSF is located between the pia mater and the arachnoid mater. External to the pia mater and arachnoid mater is the thick, tough dura mater. The dura mater of the brain is intimately related to the internal aspect of the bone of the surrounding neurocranium (braincase); that of the spinal cord is separated from the surrounding bone of the vertebral column by a fat‐filled epidural space. Damage to the CNS When the brain or spinal cord is damaged, the injured axons do not recover in most circumstances. Their proximal stumps begin to regenerate, sending sprouts into the area of the lesion; however, this growth is blocked by astrocyte proliferation at the injury site, and the axonal sprouts are soon retracted. As a result, permanent disability follows destruction of a tract in the CNS. For discussions of axonal degeneration and regeneration in the CNS, see Hutchins et al. (2002). Figure I.27. Multipolar motor neuron exhibiting several processes. Impulses pass to the cell body through the many dendrites, and the axon carries impulses away from the cell body. A neuron influences other neurons at synapses. Inset: Detailed structure of an axodendritic synapse. Neurotransmitters diffuse across the synaptic cleft between the two cells and become bound to receptors.


Peripheral Nervous System The peripheral nervous system consists of nerve fibers and cell bodies outside the CNS that conduct impulses to or away from the CNS (Fig. I.28). The PNS is organized into nerves that connect the CNS with peripheral structures. It is important to distinguish between nerve fibers and nerves, which are sometimes depicted diagrammatically as being one and the same. A peripheral nerve fiber consists of an axon, its neurolemma (G. neuron, nerve + G. lemma, husk), and surrounding endoneurial connective tissue (Figs. I.30). The neurolemma (also spelled neurilemma) consists of the neurolemma (Schwann) cells that immediately surround the axon, separating it from other axons. In the PNS, the neurolemma may take two forms, creating two classes of nerve fibers: 



The neurolemma of myelinated nerve fibers consists of neurolemma cells specific to an individual axon, organized into a continuous series of enwrapping cells that form myelin. The neurolemma of unmyelinated nerve fibers is composed of cells that do not make up such an apparent series; multiple axons are separately embedded within the cytoplasm of each cell. These neurolemma cells do not produce myelin. Most fibers in cutaneous nerves are unmyelinated.


F i g u re I . 2 8 . B a s i c o r g a n i z a t i o n o f t h e n e r v o u s s y s t e m . T h e p e r i p h e r a l n e r v o u s s y s t e m c o n s i s ts o f n e r v e f i b e r s a n d g a n g l i a . P e r i p h e r a l n e r v e s a re e i t h e r c r a n i a l n e r v e s o r s p i n a l n e rv e s . E x c e p t i n t h e c e r v i c a l r e g io n , e a c h s p in a l n e r v e b e a r s t h e s a m e l e t t e r — n u m e r a l d e s i g n a t i o n a s t h e v e r t e b ra forming the superior boundary of its exit from the vertebral column. In the cervical region, each s p i n a l n e r v e b e a r s th e s a m e l e t t e r— n u m e r a l d e s i g n a t i o n a s t h e v e r t e b r a f o r m i n g it s i n f e r i o r b o u n d a r y . S p i n a l n e r v e C 8 e x i t s b e t w e e n v e r te b r a e C 7 a n d T 1 . T h e c e r v i c a l a n d l u m b a r e n l a r g e m e n ts o f th e s p in a l c o r d o c c u r i n r e l a t i o n s h i p t o t h e i n n e r v a t i o n o f th e l i m b s .


Figure I.29. Spinal cord and spinal meninges. The dura mater and arachnoid mater are incised and reflected to show the posterior and anterior roots and the denticulate ligament (a bilateral, longitudinal, toothed thickening of the pia that anchors the cord in the center of the vertebral canal). The spinal cord is sectioned to show its horns of gray matter. These membranes or coverings extend along the nerve roots to the point where the posterior and anterior roots join, forming the dural root sleeves that enclose the sensory (posterior root) ganglia.

A peripheral nerve consists of (1) a bundle of peripheral nerve fibers (or a “bundle of bundled fibers,” or fascicles, in the case of a larger nerve), (2) the connective tissue coverings that surround and bind the nerve fibers and fascicles together, and (3) the blood vessels (vasa nervorum) that nourish the nerve fibers and their coverings (Fig. I.31). Peripheral nerves are fairly strong and resilient because the nerve fibers are supported and protected by three connective tissue coverings:  



Endoneurium, delicate connective tissue immediately surrounding the neurolemma cells and axons. Perineurium, a layer of dense connective tissue that encloses a fascicle of peripheral nerve fibers, providing an effective barrier against penetration of the nerve fibers by foreign substances. Epineurium, a thick connective tissue sheath that surrounds and encloses a bundle of fascicles, forming the outermost covering of the nerve; it includes fatty tissue, blood vessels, and lymphatics.


Figure I.30. Myelinated and unmyelinated peripheral nerve fibers. Myelinated nerve fibers have a sheath composed of a continuous series of neurolemma (Schwann) cells that surround the axon and form a series of myelin segments. Multiple unmyelinated nerve fibers are individually engulfed within a single neurolemma cell that does not produce myelin.

A peripheral nerve is organized much like a telephone cable: the axons are like individual wires insulated by the neurolemma and endoneurium; the insulated wires are bundled by the perineurium, and the bundles are surrounded by the epineurium forming the cable's outer wrapping. A collection of nerve cell bodies outside the CNS is a ganglion. There are both motor (autonomic) and sensory ganglia. Types of Peripheral Nerves The PNS is anatomically and operationally continuous with the CNS (Fig. I.28). Its afferent (sensory) fibers convey neural impulses to the CNS from the sense organs (e.g., the eyes) and from sensory receptors in various parts of the body (e.g., in the skin). Its efferent (“motor” ) fibers convey neural impulses from the CNS to effector organs (muscles and glands).


Figure I.31. Arrangement and ensheathment of peripheral, myelinated nerve fibers. All but the smallest peripheral nerves are arranged in bundles called fascicles. The peripheral nerve consists of the bundles of nerve fibers, the layers of connective tissue binding them together, and the blood vessels (vasa nervorum) that serve them.

Peripheral nerves are either cranial nerves or spinal nerves. 

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Cranial nerves exit the cranial cavity through foramina (openings) in the cranium (G. kranion, skull) and are identified by a descriptive name (e.g., trochlear) or a Roman numeral (e.g., CN IV). Only 11 of the 12 pairs of cranial nerves arise from the brain; the other pair (CN XI) arises from the superior part of the spinal cord. Spinal nerves exit the vertebral column (spine) through intervertebral foramina. All 31 pairs arise from the spinal cord and are identified by a letter and number (e.g., T4) designating the order of their origin from the 31 consecutive spinal cord segments (C, cervical; T, thoracic; L, lumbar; S, sacral; Co, coccygeal).

Spinal Nerves Spinal nerves initially arise from the spinal cord as rootlets (commonly omitted from diagrams for the sake of simplicity), which converge to form two nerve roots (Fig. I.32): 



An anterior (ventral) root, consisting of motor (efferent) fibers passing from nerve cell bodies in the anterior horn of spinal cord gray matter to effector organs located peripherally. A posterior (dorsal) root, consisting of sensory (afferent) fibers from cell bodies in the spinal sensory or posterior (dorsal) root ganglion (commonly abbreviated DRG) that extend peripherally to sensory endings and centrally to the posterior horn of spinal cord gray matter.


The posterior and anterior nerve roots unite, within or just proximal to the intervertebral foramen, to form a mixed spinal nerve, which immediately divides into two primary rami (L. branches): a posterior (dorsal) ramus and an anterior (ventral) ramus. As branches of the mixed spinal nerve, the posterior and anterior rami carry both motor and sensory fibers, as do all their subsequent branches. The terms motor nerve and sensory nerve are almost always relative terms, referring to the majority of fiber types conveyed by that nerve. Nerves supplying muscles of the trunk or limbs (motor nerves) also contain about 40% sensory fibers, which convey pain and proprioceptive information. Conversely, cutaneous (sensory) nerves contain motor fibers, which serve sweat glands and the smooth muscle of blood vessels and hair follicles. The unilateral area of skin innervated by the fibers of a single spinal nerve is called a dermatome; the unilateral muscle mass receiving innervation from the fibers conveyed by a single spinal nerve is a myotome (Fig. I.33A). From clinical studies of lesions of the posterior roots or spinal nerves, dermatome maps have been devised to indicate the typical pattern of innervation of the skin by specific spinal nerves (Fig. I.33B). However, a lesion of a single posterior root or spinal nerve would rarely result in numbness over the area demarcated for that nerve in these maps because the fibers conveyed by adjacent spinal nerves overlap almost completely as they are distributed to the skin, providing a type of double coverage. The lines indicating dermatomes on dermatome maps would thus be better represented by smudges or gradations of color. Generally, at least two adjacent spinal nerves (or posterior roots) must be interrupted to produce a discernible area of numbness. Figure I.32. Spinal cord gray matter, spinal roots, and spinal nerves. The meninges are incised and reflected to show the H‐shaped gray matter in the spinal cord and the posterior and anterior rootlets and roots of two spinal nerves. The posterior and anterior rootlets enter and leave the posterior and anterior gray horns, respectively. The posterior and anterior nerve roots unite distal to the spinal ganglion to form a mixed spinal nerve, which immediately divides into posterior and anterior rami.

The posterior rami remain separate from each other, supplying nerve fibers to the synovial joints of the vertebral column, deep muscles of the back, and the overlying skin in a segmental pattern. The anterior rami supply nerve fibers to the much larger remaining area, consisting of the anterior and lateral regions of the trunk and the upper and lower limbs.


The anterior rami distributed exclusively to the trunk remain separate from each other, also innervating muscles and skin in a segmental pattern (Figs. I.33C and I.34). However, primarily in relationship to the innervation of the limbs, the majority of anterior rami merge with all or portions of one or more adjacent anterior rami, forming nerve plexuses (networks) in which their fibers intermingle and from which a new set of multisegmental peripheral nerves emerges (Figs. I.34 and I.35A & B). The anterior rami of segmental nerves participating in plexus formation contribute fibers to multiple peripheral nerves arising from the plexus (Fig. I.35A); therefore, peripheral nerves arising from the plexus contain fibers from multiple spinal nerves (Fig. I.35B). Although the spinal nerves lose their identity as they split and merge in the plexus, the fibers arising from a specific spinal cord segment and conveyed from it by a single spinal nerve are ultimately distributed to one segmental dermatome, although they may reach it by means of a multisegmental peripheral nerve arising from the plexus that also conveys fibers to all or parts of other adjacent dermatomes (Fig. I.35C). It thus becomes important to distinguish between the distribution of the fibers carried by spinal nerves (spinal nerve innervation or segmental distribution—i.e., dermatomes and myotomes labeled with a letter and a number, such as T4) and of the fibers carried by branches of a plexus (peripheral nerve innervation or distribution, labeled with the names of peripheral nerves, such as the median nerve) (Fig. I.33B & C). Mapping segmental innervation (dermatomes, determined by clinical experience) and mapping the distribution of peripheral nerves (determined by dissecting the branches of a named nerve distally) produce entirely different maps, except for most of the trunk where, in the absence of plexus formation, segmental and peripheral distributions are the same. (Overlapping also occurs in the cutaneous distribution of peripheral nerves derived from plexuses.) Cranial Nerves Some cranial nerves convey only sensory fibers, some only motor fibers (initially, at least), and some carry a mixture of both types of fibers. Communication occurs between cranial nerves, and between cranial nerves and upper cervical (spinal) nerves; thus a nerve that initially conveys only motor fibers may receive sensory fibers distally in its course, and vice versa. Except for the first two (those involved in the senses of smell and sight), cranial nerves that convey sensory fibers into the brain bear sensory ganglia (similar to spinal sensory or posterior root ganglia), where the cell bodies of those fibers are located. Although, by definition, the term dermatome applies only to spinal nerves, similar areas of skin supplied by single cranial nerves can be identified and mapped. Unlike dermatomes, however, there is little overlap in the innervation of zones of skin supplied by cranial nerves.


Figure I.33. Dermatomes, myotomes, and cutaneous distribution of multi‐segmental peripheral nerves. A. A single dermatome (the unilateral area of skin) and myotome (portion of skeletal muscle of one side) innervated by a single spinal nerve are shown. B. Dermatome maps of the body are based on an accumulation of clinical findings following spinal nerve injuries; this map is based on the studies of Keegan and Garrett (1948). Spinal nerve C1 lacks a significant afferent component and does not supply the skin; therefore, no C1 dermatome is depicted. C. Maps of the cutaneous distribution of peripheral nerves are based on dissection and supported by clinical findings.


Figure I.34. Anterior rami and their participation in p l e x u s f o rm a t i o n . Although the posterior rami ( n o t s h o wn ) r e m a i n s e p a ra t e f r o m e a c h o th e r and follow a distinctly segmental pattern of distribution, most anterior rami (20 of 31 pairs) participate i n t h e f o r m a ti o n of plexuses, which are primarily i n v o l v e d i n th e innervation of the limbs. The anterior rami distributed only t o t h e t ru n k d o , however, remain separate and follow a segmental distribution similar to that of t h e p o s t e r i o r rami.


Figure I.35. Plexus formation. Adjacent anterior rami merge to form plexuses in which their fibers are exchanged and redistributed, forming a new set of multisegmental peripheral (named) nerves. A. The fibers of a single spinal nerve entering the plexus are distributed to multiple branches of the plexus. B. The peripheral nerves derived from the plexus contain fibers from multiple spinal nerves. C. Although segmental nerves merge and lose their identity in the plexus formation that results in multisegmental peripheral nerves, the segmental (dermatomal) pattern of nerve fiber distribution remains.


Somatic and Visceral Fibers The types of fibers conveyed by cranial or spinal peripheral nerves are as follows (Fig. I.36): 



Somatic fibers o General sensory fibers (general somatic afferent [GSA] fibers) transmit sensations from the body to the CNS; they may be exteroceptive sensations from the skin (pain, temperature, touch, and pressure) or pain and proprioceptive sensations from muscles, tendons, and joints. Proprioceptive sensations are usually subconscious, providing information regarding joint position and the tension of tendon and muscles that is combined with input from the vestibular apparatus of the internal ear, resulting in awareness of the orientation of the body and limbs in space, independent of visual input. o Somatic motor fibers (general somatic efferent [GSE] fibers) transmit impulses to skeletal (voluntary) muscles. Visceral fibers o Visceral sensory fibers (general visceral afferent [GVA] fibers) transmit pain or subconscious visceral reflex sensations (information concerning distension, blood gas, and blood pressure levels, for example) from hollow organs and blood vessels to the CNS. o Visceral motor fibers (general visceral efferent [GVE] fibers) transmit impulses to smooth (involuntary) muscle and glandular tissues. Two varieties of fibers, presynaptic and postsynaptic, work together to conduct impulses from the CNS to smooth muscle or glands (explained later in this chapter). o


Figure I.36. Somatic and visceral innervation via spinal, splanchnic, and cranial nerves. The somatic motor system permits voluntary and reflexive movement caused by contraction of skeletal muscles, such as occurs when one touches a hot iron.

Both types of sensory fibers—visceral sensory and general sensory—are processes of pseudo‐unipolar neurons with cell bodies located outside of the CNS in spinal or cranial sensory ganglia (Figs. I.36 and I.37). The motor fibers of peripheral nerves are axons of multi‐polar neurons. The cell bodies of somatic motor and presynaptic visceral motor neurons are located in the gray matter of the spinal cord. Cell bodies of postsynaptic motor neurons are located outside the CNS in autonomic ganglia. In addition to the fiber types listed above, some cranial nerves also convey special sensory fibers for the special senses (smell, sight, hearing, balance, and taste). (On the basis of the embryologic/phylogenetic derivation of certain muscles of the head and neck, some motor fibers conveyed by cranial nerves to striated muscle have


traditionally been classified as “special visceral” ; however, the designation is confusing and not applied clinically, and its practicality is questionable. That term will not be used here. When it is appropriate to do so, these fibers will be designated as branchial motor, referring to muscle tissue derived from the pharyngeal arches in the embryo.)

Figure I.37. Neurons of the PNS. Note the types of neurons involved in the somatic and visceral nervous systems, the general location of their cell bodies in relation to the CNS, and their receptors or effector organs.

Rhizotomy The posterior and anterior roots are the only sites where the motor and sensory fibers of a spinal nerve are segregated. Therefore, only at these locations can the surgeon selectively section either functional element for the relief of intractable pain or spastic paralysis (rhizotomy). Peripheral Nerve Degeneration and Ischemia of Nerves Neurons do not proliferate in the adult nervous system, except those related to the sense of smell in the olfactory epithelium. Therefore, neurons destroyed through disease or trauma are not replaced (Hutchins et al., 2002). When peripheral nerves are stretched, crushed, or severed, their axons degenerate mainly distal to the lesion because they depend on their cell bodies for survival. If the axons are damaged but the cell bodies are intact, regeneration and return of function may occur in certain circumstances. The chance of survival is best when a peripheral nerve is compressed. Pressure on a nerve commonly causes paresthesia, the pins‐and‐needles sensation that occurs when you sit too long with your legs crossed, for example. A crushing nerve injury damages or kills the axons distal to the injury site; however, the neuronal cell bodies usually survive, and the nerve's connective tissue coverings remain intact. No surgical repair is needed for this type of nerve injury because the


intact connective tissue coverings guide the growing axons to their destinations. Regeneration is less likely to occur in a severed peripheral nerve. Sprouting occurs at the proximal ends of the axons, but the growing axons may not reach their distal targets. A cutting nerve injury requires surgical intervention because regeneration of the axon requires apposition of the cut ends by sutures through the epineurium. The individual nerve bundles are realigned as accurately as possible. Anterograde (wallerian) degeneration is the degeneration of axons detached from their cell bodies (Hutchins et al., 2002). The degenerative process involves the axon and its myelin sheath, even though this sheath is not part of the injured neuron. Compromising a nerve's blood supply for a long period by compression of the vasa nervorum (Fig. I.31) can also cause nerve degeneration. Prolonged ischemia (inadequate blood supply) of a nerve may result in damage no less severe than that produced by crushing or even cutting the nerve. The Saturday night syndrome, named after an intoxicated individual who “passes out” with a limb dangling across the arm of a chair or the edge of a bed, is an example of a more serious, often permanent, paresthesia. This condition can also result from the sustained use of a tourniquet during a surgical procedure. If the ischemia is not too prolonged, temporary numbness or paresthesia results. Transient paresthesias are familiar to anyone who has had an injection of anesthetic for dental repairs. The Bottom Line The nervous system can be functionally divided into the central nervous system, which consists of the brain and spinal cord, and the peripheral nervous system, which consists of the nerve fibers and their cell bodies that reside outside the central nervous system. Neurons are the functional units of the nervous system. They are composed of a cell body, dendrites, and axons. The neuronal axons (nerve fibers) transmit impulses to other neurons or to a target organ or muscle or, in the case of sensory nerves, transmit impulses to the CNS from peripheral sensory organs. Neuroglia are the non‐neuronal, supporting cells of the nervous system. Within the CNS, a collection of nerve cell bodies is called a nucleus; within the PNS, it is called a ganglion. In the CNS, a bundle of nerve fibers that connect the nuclei is called a tract; in the PNS, a bundle of nerve fibers, the connective tissue holding it together, and the blood vessels serving it (vasa nervorum) constitute a nerve. Nerves exiting the cranium are cranial nerves; those exiting the vertebral column (formerly, the spine), are spinal nerves. Although some cranial nerves convey a single type of fiber, most nerves convey a variety of visceral or somatic and sensory or motor fibers. Somatic Nervous System The somatic nervous system, composed of somatic parts of the CNS and PNS, provides sensory and motor innervation to all parts of the body (G. soma), except the viscera in the body cavities, smooth muscle, and glands (Figs. I.36 and I.37). The somatic sensory system transmits sensations of touch, pain, temperature, and position from sensory receptors. Most of these sensations reach conscious levels (i.e., we are aware of them). The somatic motor system innervates only skeletal muscle, stimulating voluntary and reflexive movement by causing the muscle to contract, as occurs in response to touching a hot iron.


Autonomic Nervous System The autonomic nervous system, classically described as the visceral nervous system or visceral motor system (Figs. I.33 and I.37), consists of motor fibers that stimulate smooth (involuntary) muscle, modified cardiac muscle (the intrinsic stimulating and conducting tissue of heart), and glandular (secretory) cells. However, the visceral efferent fibers of the ANS are accompanied by visceral afferent fibers. As the afferent component of autonomic reflexes and in conducting visceral pain impulses, these fibers also play a role in the regulation of visceral function. Thus some authors consider the visceral afferent fibers to be part of the ANS. In any case, these fibers should be considered along with this system. The efferent nerve fibers and ganglia of the ANS are organized into two systems or divisions: the sympathetic (thoracolumbar) division and the parasympathetic (craniosacral) division. Unlike sensory and somatic motor innervation, in which the passage of impulses between the CNS and the sensory ending or effector involves a single neuron, in both divisions of the ANS, conduction of impulses from the CNS to the effector organ involves a series of two multi‐polar neurons (Fig. I.37). The cell body of the first presynaptic (preganglionic) neuron is located in the gray matter of the CNS. Its fiber (axon) synapses only on the cell body of a postsynaptic (postganglionic) neuron, the second neuron in the series. The cell bodies of these second neurons are located outside the CNS in autonomic ganglia, with fibers terminating on the effector organ (smooth muscle, modified cardiac muscle, or glands). The anatomical distinction between the two divisions of the ANS is based primarily on (1) the location of the presynaptic cell bodies and (2) which nerves conduct the presynaptic fibers from the CNS. A functional distinction of pharmacological importance for medical practice is that the postsynaptic neurons of the two divisions generally liberate different neurotransmitter substances: norepinephrine by the sympathetic division (except in the case of sweat glands) and acetylcholine by the parasympathetic division. Sympathetic (Thoracolumbar) Division of the ANS The cell bodies of the presynaptic neurons of the sympathetic division of the ANS are found in only one location: the intermediolateral cell columns (IMLs) or nuclei of the spinal cord (Fig. I.38). The paired (right and left) IMLs are a part of the gray matter of the thoracic (T1—12) and the upper lumbar (T1—L2 or 3) segments of the spinal cord (hence the alternate name for the division). In transverse sections of this part of the spinal cord, the IMLs appear as small lateral horns of the H‐shaped gray matter, looking somewhat like an extension of the cross‐bar of the H between the posterior and the anterior horns. The IMLs are organized somatotopically (i.e., arranged like the body, the cell bodies involved with innervation of the head located superiorly, and those involved with innervation of the pelvic viscera and lower limbs located inferiorly). Thus it is possible to deduce the location of the presynaptic sympathetic cell bodies involved in innervation of a specific part of the body.


Figure I.38. Intermediolateral cell columns. Each IML or nucleus constitutes the lateral horn of gray matter of spinal cord segments T1—L2 or 3 and consists of the cell bodies of the presynaptic neurons of the sympathetic nervous system, which are somatotopically arranged.


Figure I.39. Ganglia of the sympathetic nervous system. Paravertebral ganglia are linked to form right and left sympathetic trunks on each side of the vertebral column. Paravertebral ganglia are associated with all spinal nerves, although at the cervical levels, eight spinal nerves share three ganglia—superior, middle, and inferior. Prevertebral (preaortic) ganglia occur in the plexuses that surround the origins of the main branches of the abdominal aorta, such as the celiac artery, and are specifically involved in the innervation of abdominopelvic viscera.

The cell bodies of postsynaptic neurons of the sympathetic nervous system occur in two locations, the paravertebral and prevertebral ganglia (Fig. I.39): 

Paravertebral ganglia are linked to form right and left sympathetic trunks (chains) on each side of the vertebral column and extend essentially the length of this column. The superior paravertebral ganglion (the superior cervical ganglion of each sympathetic trunk) lies at the base of the cranium. The ganglion impar forms inferiorly where the two trunks unite at the level of the coccyx.

Introduction to Clinically Oriented Anatomy 

Prevertebral ganglia are in the plexuses that surround the origins of the main branches of the abdominal aorta (for which they are named), such as the two large celiac ganglia that surround the origin of the celiac trunk (a major artery arising from the aorta).

Because they are motor fibers, the axons of presynaptic neurons leave the spinal cord through anterior roots and enter the anterior rami of spinal nerves T1—L2 or 3 (Fig. I.40). Almost immediately after entering, all the presynaptic sympathetic fibers leave the anterior rami of these spinal nerves and pass to the sympathetic trunks through white rami communicantes. Within the sympathetic trunks, presynaptic fibers follow one of four possible courses:    

Ascend in the sympathetic trunk to synapse with a postsynaptic neuron of a higher paravertebral ganglion. Descend in the sympathetic trunk to synapse with a postsynaptic neuron of a lower paravertebral ganglion. Enter and synapse immediately with a postsynaptic neuron of the paravertebral ganglion at that level. Pass through the sympathetic trunk without synapsing, continuing through an abdominopelvic splanchnic nerve (a branch of the trunk involved in innervating abdominopelvic viscera) to reach the prevertebral ganglia.


Figure I.40. Courses taken by sympathetic motor fibers. Presynaptic fibers all follow the same course until they reach the sympathetic trunks. In the sympathetic trunks, they follow one of four possible courses. Fibers involved in providing sympathetic innervation to the body wall and limbs or viscera above the level of the diaphragm follow paths 1—3. They synapse in the paravertebral ganglia of the sympathetic trunks. Fibers involved in innervating abdominopelvic viscera follow path 4 to prevertebral ganglion via abdominopelvic splanchnic nerves.

Presynaptic sympathetic fibers that provide autonomic innervation within the head, neck, body wall, limbs, and thoracic cavity follow one of the first three courses, synapsing within the paravertebral ganglia. Presynaptic sympathetic fibers innervating viscera within the abdominopelvic cavity follow the fourth course.


Postsynaptic sympathetic fibers greatly outnumber the presynaptic fibers; each presynaptic sympathetic fiber synapses with 30 or more postsynaptic fibers. Those postsynaptic sympathetic fibers, destined for distribution within the neck, body wall, and limbs, pass from the paravertebral ganglia of the sympathetic trunks to adjacent anterior rami of spinal nerves through gray rami communicantes (Fig. I.41). By this means, they enter all branches of all 31 pairs of spinal nerves, including the posterior rami, to stimulate contraction of the blood vessels (vasomotion) and arrector muscles associated with hairs (pilomotion, resulting in “goose bumps” ), and to cause sweating (sudomotion). Postsynaptic sympathetic fibers that perform these functions in the head (plus innervation of the dilator muscle of the iris) all have their cell bodies in the superior cervical ganglion at the superior end of the sympathetic trunk. They pass from the ganglion by means of a cephalic arterial branch to form periarterial plexuses of nerves, which follow the branches of the carotid arteries, or they may pass directly to nearby cranial nerves, to reach their destination in the head (Maklad et al., 2001). Splanchnic nerves convey visceral efferent (autonomic) and afferent fibers to and from the viscera of the body cavities. Postsynaptic sympathetic fibers destined for the viscera of the thoracic cavity (e.g., the heart, lungs, and esophagus) pass through cardiopulmonary splanchnic nerves to enter the cardiac, pulmonary, and esophageal plexuses (Fig. I.40). The presynaptic sympathetic fibers involved in the innervation of viscera of the abdominopelvic cavity (e.g., the stomach and intestines) pass to the prevertebral ganglia through abdominopelvic splanchnic nerves (making up the greater, lesser, least, and lumbar splanchnic nerves) (Figs. I.40, I.41, and I.42). All presynaptic sympathetic fibers of the abdominopelvic splanchnic nerves, except those involved in innervating the suprarenal (adrenal) glands, synapse here. The postsynaptic fibers from the prevertebral ganglia form periarterial plexuses, which follow branches of the abdominal aorta to reach their destination. Some presynaptic sympathetic fibers pass through the prevertebral (celiac) ganglia without synapsing, continuing to terminate directly on cells of the medulla of the suprarenal gland (Fig. I.42). The suprarenal medullary cells function as a special type of postsynaptic neuron that, instead of releasing their neurotransmitter substance onto the cells of a specific effector organ, release it into the bloodstream to circulate throughout the body, producing a widespread sympathetic response. Thus the sympathetic innervation of this gland is exceptional. As described earlier, postsynaptic sympathetic fibers are components of virtually all branches of all spinal nerves. By this means and via periarterial plexuses, they extend to and innervate all the body's blood vessels (the sympathetic system's primary function) as well as sweat glands, arrector muscles of hairs, and visceral structures. Thus the sympathetic nervous system reaches virtually all parts of the body, with the rare exception of such avascular tissues as cartilage and nails. Because the two sets of sympathetic ganglia are centrally placed in the body and are close to the midline (hence relatively close to the spinal cord), in this division the presynaptic fibers are relatively short, whereas the postsynaptic fibers are relatively long, having to extend to all parts of the body.


Parasympathetic (Craniosacral) Division of the ANS Presynaptic parasympathetic neuron cell bodies are located in two sites within the CNS, their fibers exiting by two routes. This arrangement accounts for the alternate name of the parasympathetic (craniosacral) division of the ANS (Fig. I.43): 



In the gray matter of the brainstem, the fibers exit the CNS within cranial nerves (CN) III, VII, IX, and X; these fibers constitute the cranial parasympathetic outflow. In the gray matter of the sacral segments of the spinal cord (S2—4), the fibers exit the CNS through the anterior roots of sacral spinal nerves S2—4 and the pelvic splanchnic nerves that arise from their anterior rami; these fibers constitute the sacral parasympathetic outflow.

Not surprisingly, the cranial outflow provides parasympathetic innervation of the head, and the sacral outflow provides the parasympathetic innervation of the pelvic viscera. However, in terms of the innervation of thoracic and abdominal viscera, the cranial outflow through the vagus nerve (CN X) is dominant. It provides innervation to all the thoracic viscera and most of the gastrointestinal (GI) tract from the esophagus through most of the large intestine (to its left colic flexure). The sacral outflow to the GI tract supplies only the descending and sigmoid colon and rectum. Regardless of the extensive influence of its cranial outflow, the parasympathetic system is much more restricted than the sympathetic system in its distribution. The parasympathetic system distributes only to the head, visceral cavities of the trunk, and erectile tissues of the external genitalia. With the exception of the latter, it does not reach the body wall or limbs; and except for the initial parts of the anterior rami of spinal nerves S2—4, its fibers are not components of spinal nerves or their branches.


Figure I.41. The sympathetic (thoracolumbar) division of the A N S . P o s ts y n a p t i c s y m p a t h e t i c fibers exit from the sympathetic trunks by different means, d e p e n d i n g o n t h e i r d e s ti n a t i o n : T h o s e d e s ti n e d f o r p a r i e t a l distribution within the neck, body wall, and limbs pass from the sympathetic trunks to a d j a ce n t a n t e r i o r r a m i o f a l l s p i n a l n e rv e s t h r o u g h g r a y r a m i c o m m u n i c a n te s ; t h o s e d e s t i n e d for the head pass from cervical g a n g l i a b y m e a n s o f ce p h a l i c a r t e r i a l r a m i t o f o r m a c a r o t i d p e r i a r t e r i a l p l e x u s ; a n d t h o s e destined for viscera of the thoracic cavity (e.g., the heart) p a s s t h r o u g h c a r d i o p u l m o n a ry splanchnic nerves. Presynaptic s y m p a t h e t i c f i b e rs i n v o l v e d in t h e i n n e r v a t io n o f v i s ce r a o f t h e a b d o m in o p e l v i c c a v i t y ( e . g . , t h e stomach) pass through the sympathetic trunks to the p r e v e r t e b ra l g a n g l i a b y m e a n s o f a b d o m in o p e l v i c splanchnic n e r v e s . P o s ts y n a p t i c f i b e r s f r o m t h e p re v e r te b r a l g a n g l i a f o r m p e r i a r t e r i a l p l e x u s e s , which f o l l o w b r a n c h e s o f t h e a b d o m i n a l aorta to reach their destination.


Figure I.42. Sympathetic supply to medulla of suprarenal gland. The sympathetic supply to the suprarenal gland is exceptional. The secretory cells of the medulla are postsynaptic sympathetic neurons that lack axons or dendrites. Consequently, the suprarenal medulla is supplied directly by presynaptic sympathetic neurons. The neurotransmitters produced by medullary cells are released into the bloodstream to produce a widespread sympathetic response.

Four discrete pairs of parasympathetic ganglia occur in the head (see Chapters 7 and 9). Elsewhere, presynaptic parasympathetic fibers synapse with postsynaptic cell bodies, which occur singly in or on the wall of the target organ (intrinsic or enteric ganglia). Consequently, in this division, most presynpatic fibers are very long, extending from the CNS to the effector organ, whereas the postsynaptic fibers are very short, running from a ganglion located near or embedded in the effector organ. Functions of the Divisions of the ANS Although both sympathetic and parasympathetic systems innervate involuntary (and often affect the same) structures, they have different, usually contrasting yet coordinated, effects (Figs. I.41 and I.43). In general, the sympathetic system is a catabolic (energy‐expending) system that enables the body to deal with stresses, such as when preparing the body for the fight‐or‐flight response. The parasympathetic system is primarily a homeostatic or anabolic (energy‐conserving) system, promoting the quiet and orderly processes of the body, such as those that allow the body to feed and assimilate. Table I.2 summarizes the specific functions of the ANS and its divisions. The primary function of the sympathetic system is to regulate blood vessels. This is accomplished by several means having different effects. Blood vessels throughout the body are tonically innervated by sympathetic nerves, maintaining a resting state of moderate vasoconstriction. In most vascular beds, an increase in sympathetic signals causes increased vasoconstriction, and a decrease in the rate of sympathetic signals allows vasodilation. However, in certain regions of the body, sympathetic signals are vasodilatory (i.e., sympathetic transmitter substances inhibit active vasoconstriction,


allowing the blood vessels to be passively dilated by the blood pressure). In the coronary vessels, the vessels of skeletal muscles, and the external genitals, sympathetic stimulation results in vasodilation (Wilson‐Pauwels et al., 1997). Visceral Sensation Visceral afferent fibers have important relationships to the ANS, both anatomically and functionally. We are usually unaware of the sensory input of these fibers, which provides information about the condition of the body's internal environment. This information is integrated in the CNS, often triggering visceral or somatic reflexes or both. Visceral reflexes regulate blood pressure and chemistry by altering such functions as heart and respiratory rates and vascular resistance.


Figure I.43. Parasympathetic (craniosacral) division of the ANS. Presynaptic parasympathetic nerve cell bodies are located in opposite ends of the CNS and their fibers exit by two different routes: (1) in the gray matter of the brainstem, with fibers exiting the CNS within cranial nerves II, VII, IX, and X (these fibers constitute the cranial parasympathetic outflow), and (2) in the gray matter of the sacral (S2—4) segments of the spinal cord, with fibers exiting the CNS via the anterior roots of spinal nerves S2—4 and the pelvic splanchnic nerves that arise from their anterior rami (these fibers constitute the sacral parasympathetic outflow). The cranial outflow provides parasympathetic innervation of the head, neck, and most of the trunk; the sacral outflow provides the parasympathetic innervation of the pelvic viscera.

Introduction to Clinically Oriented Anatomy Table I.2. Functions of the Autonomic Nervous System (ANS) Organ, Tract, or Effect of Sympathetic Stimulation a Effect of Parasympathetic System Stimulation b Eyeballs Pupil Dilates pupil (admits more light for Constricts pupil (protects pupil from increased acuity at a distance) excessively bright light) Ciliary body Contracts ciliary muscle, allowing lens to thicken for near vision (accommodation) Skin Arrector Causes hairs to stand on end No effect (does not reach) c muscle of (gooseflesh or goose bumps) hair Peripheral Vasoconstricts (blanching of skin, lips, No effect (does not reach) c blood and turning fingertips blue) vessels Sweat Promotes sweating d No effect (does not reach) c glands Other Lacrimal Slightly decreases secretion e Promotes secretion glands glands Salivary Secretion decreases, becomes thicker, Promotes abundant, watery secretion glands more viscous e Heart Increases rate and strength of Decreases the rate and strength of (conserving energy); contraction; inhibits effect of contraction parasympathetic system on coronary constricts coronary vessels in relation to reduced demand vessels, allowing them to dilate e Lungs Inhibits effect of parasympathetic Constricts bronchi (conserving energy) system, resulting in bronchodilation and promotes bronchial secretion and reduced secretion, allowing for maximum air exchange Digestive tract Inhibits peristalsis and constricts Stimulates peristalsis and secretion of blood vessels to digestive tract so that digestive juices; contracts rectum; blood is available to skeletal muscle; inhibits internal anal sphincter to contracts internal anal sphincter to cause defecation aid fecal continence Liver and gallbladder Promotes breakdown of glycogen to Promotes building/conservationof glucose (for increased energy) glycogen; increases secretion of bile Urinary tract Vasoconstriction of renal vessels slows Inhibits contraction of internal urine formation; internal sphincter of sphincter of bladder; contracts bladder contracted to maintain urinary detrusor muscle of bladder wall continence causing urination Genital system Causes ejaculation and Produces engorgement (erection) of vasoconstriction resulting in remission erectile tissues of external genitals of erection Suprarenal medulla Release of adrenaline into blood No effect (does not innervate) a In general, the effects of sympathetic stimulation are catabolic, preparing body for the fight‐or‐flight response. b In general, the effects of parasympathetic stimulation are anabolic, promoting normal function and conserving energy. c The parasympathetic system is restricted in its distribution to the head, neck, and body cavities (except for erectile tissues of genitalia); otherwise, parasympathetic fibers are never found in the body wall and limbs. Sympathetic fibers, by comparison, are distributed to all vascularized portions of the body. d With the exception of the sweat glands, glandular secretion is parasympathetically stimulated. e With the exception of the coronary arteries, vasoconstriction is sympathetically stimulated; the effects of sympathetic stimulation on glands (other than sweat glands) are the indirect effects of vasoconstriction.


Visceral sensation that reaches a conscious level is generally perceived as pain that is either poorly localized or felt as cramps or that may convey a feeling of hunger, fullness, or nausea. Surgeons operating on patients who are under local anesthesia may handle, cut, clamp, or even burn (cauterize) visceral organs without evoking conscious sensation. However, adequate stimulation, such as the following, may elicit true pain:     

Sudden distension. Spasms or strong contractions. Chemical irritants. Mechanical stimulation, especially when the organ is active. Pathological conditions (especially ischemia) that lower the normal thresholds of stimulation.

Normal activity usually produces no sensation but may do so when the blood supply is inadequate (ischemia). Most visceral reflex (unconscious) sensation and some pain travel in visceral afferent fibers that accompany the parasympathetic fibers retrograde. Most visceral pain impulses (from the heart and most organs of the peritoneal cavity) travel centrally along visceral afferent fibers accompanying sympathetic fibers. The Bottom Line The autonomic nervous system is a sub‐division of the motor nervous system that controls functions of the body not under conscious control. Two neurons, a presynaptic and a postsynaptic fiber, connect the CNS with an end organ, consisting of smooth muscle, gland, or modified cardiac muscle. Based on the location of the cell body of the presynaptic fibers, the ANS can be subdivided into two divisions: the sympathetic and parasympathetic. Presynaptic cell bodies of the sympathetic division are found only in the intermediolateral cell columns of gray matter in the thoracolumbar spinal cord, which are organized somatotopically. The presynaptic sympathetic nerve fibers terminate in sympathetic ganglia formed of the cell bodies of postsynaptic sympathetic neurons. Sympathetic ganglia occur in the sympathetic trunks (paravertebral ganglia) or around the roots of the major branches of the abdominal aorta (prevertebral ganglia). Cell bodies of the presynaptic neurons of the parasympathetic division are located in the gray matter of the brainstem and sacral segments of the spinal cord. Cell bodies of postsynaptic parasympathetic neurons of the trunk are located in or on the structure being innervated, whereas those in the head are organized into discrete ganglia. The sympathetic and parasympathetic divisions usually have opposite but coordinated effects. The sympathetic system facilitates emergency (flight‐or‐fight) responses. The parasympathetic system— distributed only to the viscera of the head, neck, and cavities of the trunk and the erectile tissues of the genitalia—is primarily concerned with body conservation, often reversing the effects of sympathetic stimulation. Some nerves distributing autonomic fibers ANS to the body cavities also convey visceral sensory fibers carrying impulses for pain or reflexes.


Medical Imaging Techniques Radiological anatomy is the study of the structure and function of the body using medical imaging techniques. It has become an important part of anatomy and is the anatomical basis of radiology, the branch of medical science dealing with the use of radiant energy in the diagnosis and treatment of disease. Being able to identify normal structures on radiographs (X‐rays) makes it easier to recognize the changes caused by disease and injury. Familiarity with medical imaging techniques commonly used in clinical settings enables one to recognize congenital anomalies, tumors, and fractures. The most commonly used medical imaging techniques are     

Conventional radiography (ordinary X‐ray images). Computerized tomography (CT). Ultrasonography (US). Magnetic resonance imaging (MRI). Nuclear medicine imaging.

Although the techniques differ, each is based on the receipt of attenuated beams of energy that have been passed through, reflected off of, or generated by the body's tissues. Learn to interpret medical images. Along with surface anatomy, they are the only views of a person's anatomy that are commonly available after completion of the gross anatomy course. Medical imaging techniques permit the observation of anatomical structures in living people and the study of their movements in normal and abnormal activities (e.g., the heart and stomach). Conventional Radiography Wilhelm Roentgen, a German physicist and Nobel laureate, discovered X‐rays in 1895. His discovery enabled observation of the living structure of the human skeletal system, readily visualized on radiographs (roentgenograms). A conventional radiograph, in which special techniques such as contrast media have not been used, is referred to clinically as a plain film (Fig. I.44). In a radiological examination, a highly penetrating beam of X‐rays transilluminates the patient, showing tissues of differing densities of mass within the body as images of differing intensities (areas of relative light and dark) on the film or monitor (Fig. I.45). A tissue or organ that is relatively dense in mass (e.g., compact bone) absorbs or reflects more X‐rays than does a less dense tissue (e.g., spongy bone). Consequently, a dense tissue or organ produces a somewhat transparent area on the X‐ray film because fewer X‐rays reach the film or detector. Therefore, relatively fewer grains of silver are developed at this area when the film is processed. A dense substance is radiopaque, whereas a substance of less density is radiolucent. Many of the same principles that apply to making a shadow apply to conventional radiography. When making a shadow of your hand on a wall, the closer your hand is to the wall, the sharper the shadow produced. The farther your hand is from the wall (and therefore the closer to light source), the more the shadow is magnified. Radiographs are made with the part of the patient's body being studied close to the X‐ray film or detector to maximize the clarity of the image and minimize magnification artifacts. In basic radiological nomenclature, posteroanterior (PA) projection refers to a radiograph in which the X‐rays traversed the patient from posterior (P) to anterior (A); the X‐ray tube was posterior to the patient and the X‐


ray film was anterior (Fig. I.46A). A radiograph using anteroposterior (AP) projection radiography is the opposite. Both PA and AP projection radiographs are viewed as if you and the patient were facing each other (the patient's right side is opposite your left); this is referred to as an anteroposterior (AP) view. (Thus the standard chest X‐ ray, taken to examine the heart and lungs, is an AP view of a PA projection.) For lateral radiographs, radiopaque letters (R or L) are used to indicate the side placed closest to the film or detector, and the image is viewed from the same direction that the beam was projected (Fig. I.46B). Figure I.44. Radiograph of thorax (chest). AP view of a PA projection radiograph demonstrates the arch of the aorta, parts of the heart, and domes of the diaphragm. Note that the dome of the diaphragm is higher on the right side. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)

The introduction of contrast media (radiopaque fluids such as iodine compounds or barium) allows the study of various luminal or vascular organs and potential or actual spaces—such as the digestive tract, blood vessels, kidneys, synovial cavities, and the subarachnoid space—that are not visible in plain films (Fig. I.47). Most radiological examinations are performed in at least two projections at right angles to each other. Because each radiograph presents a two‐dimensional representation of a three‐ dimensional structure, structures sequentially penetrated by the X‐ray beam overlap each other. Thus more than one view is usually necessary to detect and localize an abnormality accurately. Computerized Tomography In computerized tomography, the scans show radiographic images of the body that resemble transverse anatomical sections (Fig. I.48). In this technique, a beam of X‐ rays passes through the body as the X‐ray tube and detector rotate around the axis of the body. Multiple overlapping radial energy absorptions are measured, recorded, and compared by a computer to determine the radiodensity of each volume element (voxel) of the chosen body plane. The radiodensity of (amount of radiation absorbed


by) each voxel is determined by factors that include the amount of air, water, fat, or bone in that element. The computer maps the voxels into a planar image (slice) that is displayed on a monitor or printout. CT images relate well to conventional radiographs, in that areas of great absorption (e.g., bone) are relatively transparent (white) and those with little absorption are black (Fig. I.48). CT scans are always displayed as if the viewer were standing at a supine patient's feet. Figure I.45. Principles of X‐ray image formation. Portions of the beam of X‐rays traversing the body become attenuated to varying degrees based on tissue thickness and density. The beam is diminished by structures that absorb or reflect it, causing less reaction on the film or by the detector, compared with areas that allow the beam to pass relatively uninterrupted.

Figure I.46. Orientation of patient's thorax during radiography. A. When taking a PA projection, the X‐rays from the X‐ray tube pass through the thorax from the back to reach the X‐ray film or detector anterior to the person. B. When taking a lateral projection, the X‐rays pass through the thorax from the side to reach the X‐ray film adjacent to the person's other side.


Ultrasonography Ultrasonography or sonography is a technique that visualizes superficial or deep structures in the body by recording pulses of ultrasonic waves reflecting off the tissues (Fig. I.49). Ultrasonography has the advantage of a lower cost than CT and MRI, and the machine is portable. The technique can be performed virtually anywhere, including the clinic examination room, bedside, or on the operating table. A transducer in contact with the skin generates high‐frequency soundwaves that pass through the body and reflect off tissue interfaces between tissues of differing characteristics, such as soft tissue and bone. Echoes from the body reflect into the transducer and convert to electrical energy. The electrical signals are recorded and displayed on a monitor as a cross‐sectional image, which can be viewed in real time and recorded as a single image or on videotape. A major advantage of ultrasonography is its ability to produce real‐time images, demonstrating motion of structures and flow within blood vessels. In Doppler ultrasonography, the shifts in frequency between emitted ultrasonic waves and their echoes are used to measure the velocities of moving objects. This technique is based on the principle of the Doppler effect. Blood flow through vessels is displayed in color, superimposed on the two‐dimensional cross‐sectional image. Scanning of the pelvic viscera from the surface of the abdomen requires a fully distended bladder. The urine serves as an “acoustical window,” transmitting soundwaves to and from the posteriorly placed pelvic viscera with minimal attenuation. The distended bladder also displaces gas‐filled intestinal loops out of the pelvis. Transvaginal sonography permits the positioning of the transducer closer to the organ of interest (e.g., the ovary) and avoids fat and gas, which absorb or reflect soundwaves. Bone reflects nearly all ultrasound waves, whereas air conducts them poorly. Consequently, the CNS and lungs of adults cannot be examined by ultrasonography. Figure I.47. Radiograph of stomach, small intestine, and gallbladder. Observe the gastric folds, or rugae (longitudinal folds of the mucous membrane). Also note the peristaltic wave that is moving the gastric contents toward the duodenum, which is closely related to the gallbladder. (Courtesy of Dr. J. Heslin, Toronto, ON, Canada.)


The appeal of ultrasonography in obstetrics is that it is a non‐invasive procedure that does not use radiation; it can yield useful information about the pregnancy, such as determining whether it is intrauterine or extrauterine (ectopic) and whether the embryo is living. It has also become a standard method of evaluating the growth and development of the embryo and fetus. Magnetic Resonance Imaging Magnetic resonance imaging provides images of the body similar to those of CT scans, but MRI is better for tissue differentiation. MRI studies closely resemble anatomical sections, especially in the brain (Fig. I.50). The person is placed in a scanner with a strong magnetic field, and the body is pulsed with radiowaves. Signals subsequently emitted from the patient's tissues are stored in a computer and reconstructed into various images of the body. The appearance of tissues on the generated images can be varied by controlling how radiofrequency pulses are sent and received. Free protons in the tissues that become aligned by the surrounding magnetic field are excited (flipped) with a radiowave pulse. As the protons flip back, minute but measurable energy signals are emitted. Tissues that are high in proton density, such as fat and water, emit more signals than tissues that are low in proton density. The tissue signal is based primarily on three properties of protons in a particular region of the body. These are referred to as T1 relaxation, T2 relaxation, and proton density. Although liquids have a high density of free protons, the excited free protons in moving fluids such as blood tend to move out of the field before they flip and give off their signal and are replaced by unexcited protons. Consequently, moving fluids appear black. Computers associated with MRI scanners have the capacity to reconstruct tissues in any plane from the data acquired: transverse, median, sagittal, frontal, and even arbitrary oblique planes. The data may also be used to generate three‐dimensional reconstructions. MRI scanners produce good images of soft tissues without the use of ionizing radiation. Motion made by the patient during long scanning sessions created problems for early‐generation scanners, but fast scanners now in use can be gated or paced to visualize moving structures, such as the heart and blood flow, in real time.


Figure I.48. Technique for producing an abdominal CT scan. The X‐ray tube rotates around the person in the CT scanner and sends a fan‐shaped beam of X‐rays through the upper abdomen from a variety of angles. X‐ray detectors on the opposite side of the body measure the amount of radiation that passes through a horizontal section. A computer reconstructs the images from several scans, and an abdominal CT scan is produced. The scan is oriented so it appears the way an examiner would view it when standing at the foot of the bed and looking toward a supine person's head.

Figure I.49. Technique for producing an abdominal ultrasound image of the upper abdomen. The image results from the echo of ultrasound waves from abdominal structures of different densities. The ultrasound image of the right kidney is displayed on a monitor.


Figure I.50. Median MRI of the head. Many details of the CNS and structures in the nasal and oral cavities and upper neck are seen in this study. The black low signal areas superior to the anterior and posterior aspects of the nasal cavity are the air‐filled frontal and sphenoidal sinuses.

Nuclear Medicine Imaging Nuclear medicine imaging techniques provide information about the distribution or concentration of trace amounts of radioactive substances introduced into the body. Nuclear medicine scans show images of specific organs after intravenous (I.V.) injection of a small dose of radioactive material. The radionuclide is tagged to a compound that is selectively taken up by an organ, such as technetium‐99m methylene diphosphonate ( 9 9 m Tc‐MDP) for bone scanning (Fig. I.51). Positron emission tomography (PET) scanning uses cyclotron‐produced isotopes of extremely short half‐life that emit positrons. PET scanning is used to evaluate the physiological function of organs, such as the brain, on a dynamic basis. Areas of increased brain activity will show selective uptake of the injected isotope. Images can be viewed as the whole organ or in cross sections, which are referred to as single‐ photon emission computerized tomography (SPECT) scans.


Figure I.51. Bone scans of the head and neck, thorax, and pelvis. These nuclear medicine images can be viewed as a whole or in cross section.

The Bottom Line Medical imaging techniques enable the visualization of normal anatomy in the living. This allows us to view structures with their normal tonus, fluid volumes, internal pressures, etc., which are not present in the cadaver. The primary goal of medical imaging is, of course, to detect pathology. However, a sound knowledge of radiological anatomy is required to distinguish pathologies and abnormalities from normal anatomy.


References and Suggested Readings Amadio PC: Reaffirming the importance of dissection. Clin Anat 9:136, 1996. Behrman RE, Kliegman RM, Jenson HB (eds): Nelson Textbook of Pediatrics, 17th ed. Philadelphia, Saunders, 2004. Bergman RA, Thompson SA, Afifi AK, Saadeh FA: Compendium of Human Anatomic Variation: Text, Atlas, and World Literature. Baltimore, Urban & Schwarzenberg, 1988. This useful source has been updated and is available from the Virtual Hospital's Web site Illustrated Encyclopedia of Human Anatomic Variation at http://www.vh.org/Providers/Textbooks/AnatomicVariants/AnatomyHP.html (accessed May 2004). P.73 Cahill DR, Leonard RJ: The role of computers and dissection in teaching anatomy: A comment. Clin Anat 10:140, 1997. Cormack DH: Essential Histology, 2nd ed. Baltimore, Lippincott Williams & Wilkins, 2001. Cotran RS, Kumar V, Collins T: Robbin's Pathologic Basis of Disease, 6th ed. Philadelphia, Saunders, 1999. Federative Committee on Anatomical Terminology: Terminologia Anatomica: International Anatomical Nomenclature. Stuttgart, Thieme, 1998. Gartner LP, Hiatt JL: Color Textbook of Histology, 2nd ed. Philadelphia, Saunders, 2001. Haines DE (ed): Fundamental Neuroscience, 2nd ed. New York, Churchill Livingstone, 2002. Hutchins JB, Naftel JP, Ard MD: The cell biology of neurons and glia. In Haines DE (ed): Fundamental Neuroscience, 2nd ed. New York, Churchill Livingstone, 2002. Keegan JJ, Garrett FD: The segmental distribution of the cutaneous nerves in the limbs of man. Anat Rec 102:409, 1948. Maklad A, Quinn T, Fritsch B: Intracranial distribution of the sympathetic system in mice: DiI tracing and immunocytochemical labeling. Anat Rec 263:99, 2001. Marieb, E: Human Anatomy and Physiology, 6th ed. Menlo Park, CA, Benjamin/Cummings, 2004. Mehta LA, Natrajan M, Kothari ML: Understanding anatomical terms. Clin Anat 9:330, 1996.


Moore KL, Persaud TVN: The Developing Human: Clinically Oriented Embryology, 7th ed. Philadelphia, Saunders, 2003. Mutyala S, Cahill DR: Catching up. Clin Anat 9:53, 1996. O'Rahilly R: Making planes plain. Clin Anat 10:129, 1997. Persaud TVN: Early History of Human Anatomy from Antiquity to the Beginning of the Modern Era. Springfield, IL, Thomas, 1984. Persaud TVN: A History of Anatomy. The Post‐Vesalian Era. Springfield, IL, Thomas, 1997. Ross MH, Kaye G, Pawlina W: Histology. A Text and Atlas, 4th ed. Baltimore, Lippincott Williams & Wilkins, 2003. Salter RB: Textbook of Disorders and Injuries of the Musculoskeletal System, 3rd ed. Baltimore, Lippincott Williams & Wilkins, 1998. Stedman's Medical Dictionary, 28th ed. Baltimore, Lippincott Williams & Wilkins, 2005. Swartz MH: Textbook of Physical Diagnosis, History and Examination, 4th ed. Philadelphia, Saunders, 2001. Willis MC: Medical Terminology: The Language of Health Care. Baltimore, Lippincott Williams & Wilkins, 1995. Wilson‐Pauwels L, Stewart PA, Akesson E: Autonomic Nerves: Basic Science, Clinical Aspects, Case Studies. Hamilton, ON, Decker, 1997.


Chapter 1: Thorax The thorax is the superior part of the trunk between the neck and abdomen. Commonly the term chest is used as a synonym for thorax, but our concept of the chest (upper part of the torso) is much more extensive than the thoracic wall and cavity contained within it. The chest is generally conceived as being broadest superiorly owing to the presence of the pectoral, or shoulder, girdle (clavicles and scapulae), with much of its girth accounted for by the associated pectoral and scapular (upper limb) musculature. Our concept of the well‐formed chest is one that narrows inferiorly to the waist and, in adult females, gains further dimension from the breasts.

Chapter 1: Thorax

Figure 1.1. Thoracic skeleton. A and B. The osteocartilaginous thoracic cage includes the sternum, 12 pairs of ribs and costal cartilages, and 12 thoracic vertebrae and intervertebral discs. The clavicles and scapulae form the pectoral (shoulder) girdle. The dotted line indicates the position of the diaphragm, which separates the thoracic and abdominal cavities. The thoracic cavity is much smaller than the surrounding thoracic cage.

The thoracic cavity and the wall specific to it are actually the opposite of this. They have the shape of a truncated cone, being narrowest superiorly, with the circumference increasing inferiorly, and reaching its maximum at the junction with the abdominal portion of the trunk. The wall of the thoracic cavity is relatively thin, essentially as thick as its skeleton. The thoracic skeleton takes the form of a domed birdcage, the thoracic cage (rib cage), with the horizontal bars formed by ribs and costal cartilages supported by the vertical sternum (breastbone) and thoracic vertebrae (Fig. 1.1). Furthermore, the floor of the thoracic cavity (the diaphragm) is deeply invaginated inferiorly (i.e., is pushed upward) by viscera of the abdominal cavity. Consequently, nearly the lower half of the thoracic wall surrounds and protects abdominal rather than thoracic viscera. Thus the true thorax and especially


the thoracic cavity are much smaller than one might expect based on external appearances of the chest. The thorax includes the primary organs of the respiratory and cardiovascular systems. The thoracic cavity is divided into three major spaces: The central compartment, or mediastinum, houses the conducting structures that make up the thoracic viscera, except for the lungs. The lungs occupy the lateral compartments or pulmonary cavities that lie on each side of the mediastinum. Thus the majority of the thoracic cavity is occupied by the lungs, which provide for the exchange of oxygen and carbon dioxide between air and blood, whereas most of the remainder of the thoracic cavity is occupied with structures involved in conducting the air and blood to and from the lungs. Nutrients (food) traverse the thoracic cavity via the esophagus, passing from the intake organ (mouth) to the site of digestion and absorption (abdomen). Although in terms of function and development the mammary glands are most related to the reproductive system, the breasts are located on the thoracic wall and thus are included in this chapter.

Chest Pain Although chest pain can result from pulmonary disease, it is probably the most important symptom of cardiac disease (Swartz, 2002). However, chest pain may also occur in intestinal, gallbladder, and musculoskeletal disorders. When evaluating a patient with chest pain, the examination is largely concerned with discriminating between serious conditions and the many minor causes of pain. People who have had a heart attack usually describe the associated pain as a “crushing” sub‐sternal pain (deep to the sternum) that does not disappear with rest.

The Bottom Line The thorax, consisting of the thoracic cavity, its contents, and the wall that surrounds it, is the part of the trunk between neck and abdomen. The shape and size of the thoracic cavity and the wall specific to it are much different from (especially smaller than) that of the chest (upper torso), because the latter includes some upper limb bones and muscles and, in adult females, the breasts.

Thoracic Wall The true thoracic wall includes the thoracic cage and the muscles that extend between its elements as well as the skin, subcutaneous tissue, muscles, and fascia covering its anterolateral aspect; the same structures covering its posterior aspect are considered to belong to the back. The mammary glands of the breasts lie within the subcutaneous tissue of the thoracic wall. Although the shoulders are clearly part of the upper limb, the anterolateral thoracoappendicular muscles (see Chapter 6) that overlie the thoracic cage and form the bed of the breast (pectoralis major and serratus anterior—distinctly upper limb muscles based on function and innervation) are encountered in the thoracic wall and may be considered part of it (but will be mentioned only briefly here). Similar thoracoappendicular muscles placed posteriorly (trapezius and latissimus dorsi) have commonly been considered to be superficial muscles of the back, although in terms of function they are clearly upper limb muscles (and are also covered in Chapter 6).

Chapter 1: Thorax

The domed shape of the thoracic cage provides remarkable rigidity, given the light weight of its components, enabling it to:    

Protect vital thoracic and abdominal internal organs (most air or fluid filled) from external forces. Resist the negative (sub‐atmospheric) internal pressures generated by the elastic recoil of the lungs and inspiratory movements. Provide attachment for and support the weight of the upper limbs. Provide the anchoring attachment (origin) of many of the muscles that move and maintain the position of the upper limbs relative to the trunk as well as provide the attachments for muscles of the abdomen, neck, back, and respiration.

Although the shape of the thoracic cage provides rigidity, its joints and the thinness and flexibility of the ribs allow remarkable flexibility, permitting it to absorb many external blows and compressions without fracture and to change its shape repetitively and sufficiently as required for respiration. Because the most important structures within the thorax (heart, great vessels, lungs, and trachea) as well as its floor and walls are constantly in motion, the thorax is one of the most dynamic regions of the body. With each breath, the muscles of the thoracic wall—working in concert with the diaphragm and muscles of the abdominal wall—vary the volume of the thoracic cavity, first by expanding the capacity of the cavity, thereby causing the lungs to expand and draw air in and then (mostly owing to lung elasticity and muscle relaxation) decreasing the volume of the cavity, compressing the lungs, and causing them to expel air.

Skeleton of the Thoracic Wall The thoracic skeleton forms the osteocartilaginous thoracic cage (Fig. 1.1), which protects the thoracic viscera and some abdominal organs. The thoracic skeleton includes 12 pairs of ribs and associated costal cartilages, 12 thoracic vertebrae and the intervertebral (IV) discs interposed between them, and the sternum. The ribs and costal cartilages form the largest part of the thoracic cage.

Ribs, Costal Cartilages, and Intercostal Spaces Ribs (L. costae) are curved, flat bones that form most of the thoracic cage (Figs. 1.1 and 1.2). They are remarkably light in weight yet highly resilient. Each rib has a spongy interior containing bone marrow (hematopoietic tissue), which forms blood cells. There are three types of rib:  



True (vertebrocostal) ribs (1st—7th ribs): They attach directly to the sternum through their own costal cartilages. False (vertebrochondral) ribs (8th, 9th, and usually 10th ribs): Their cartilages are connected to the cartilage of the rib above them; thus their connection with the sternum is indirect. Floating (vertebral, free) ribs (11th, 12th, and sometimes 10th ribs): The rudimentary cartilages of these ribs do not connect even indirectly with the sternum; instead they end in the posterior abdominal musculature.


Typical ribs (3rd—9th) have the following components: 

 



Head: wedge‐shaped and has two facets, separated by the crest of the head (Figs. 1.2 and 1.3); one facet for articulation with the numerically corresponding vertebra and one facet for the vertebra superior to it. Neck: connects the head with the body at the level of the tubercle. Tubercle: at the junction of the neck and body and has a smooth articular part, for articulating with the corresponding transverse process of the vertebra, and a rough non‐articular part, for attachment of the costotransverse ligament. Body (shaft): thin, flat, and curved, most markedly at the costal angle where the rib turns anterolaterally (also the point of the lateral limit of attachment of the erector spinae muscles to the ribs; see Chapter 4); the concave internal surface of the body has a costal groove paralleling the inferior border of the rib, which provides some protection for the intercostal nerve and vessels.

Atypical ribs (1st, 2nd, and 10th—12th) are dissimilar (Fig. 1.3): 



 

The 1st rib is the broadest (i.e., its body is widest and nearly horizontal), shortest, and most sharply curved of the seven true ribs. It has a single facet on its head for articulation with the T1 vertebra only and two transversely directed grooves crossing its superior surface for the subclavian vessels; the grooves are separated by a scalene tubercle and ridge, to which the anterior scalene muscle is attached. The 2nd rib is more typical; its body is thinner, less curved, and substantially longer than the 1st rib, and its head has two facets for articulation with the bodies of the T1 and T2 vertebrae; its main atypical feature is a rough area on its upper surface, the tuberosity for serratus anterior, from which part of that muscle originates. The 10th—12th ribs, like the 1st rib, have only one facet on their heads and articulate with a single vertebra. The 11th and 12th ribs are short and have no neck or tubercle.

Costal cartilages prolong the ribs anteriorly and contribute to the elasticity of the thoracic wall, providing a flexible attachment for their anterior or distal ends (tips). The cartilages increase in length through the first 7 and then gradually decrease. The first 7 cartilages (and sometimes the 8th; Fig. 1.16) attach directly and independently to the sternum; the 8th, 9th, and 10th articulate with the costal cartilages just superior to them, forming a continuous, articulated, cartilaginous costal margin (Fig. 1.1A). The 11th and 12th cartilages form caps on the anterior ends of these ribs and do not reach or attach to any other bone or cartilage. The costal cartilages of ribs 1—10 clearly anchor the anterior end (tips) of the rib to the sternum, limiting its overall movement as the posterior end rotates around the transverse axis of the rib (Fig. 1.5).

Chapter 1: Thorax

Figure 1.2. Typical ribs. A. The 3rd—9th ribs have common characteristics. Each rib has a head, neck, tubercle, and body (shaft). B. Cross section of a rib at midbody. Figure 1.3. Atypical ribs. The atypical 1st, 2nd, 11th, and 12th ribs differ from typical ribs (e.g., the 8th rib, shown in center). The 1st rib is short and flattened and the tubercle merges with the angle. The body of the 2nd rib bears a tuberosity for attachment of the serratus anterior. The 11th and 12th ribs lack a neck and tubercle, and the 12th rib is shorter than most ribs.


Intercostal spaces separate the ribs and their costal cartilages from one another (Fig. 1.1A). The spaces are named according to the rib forming the superior border of the space—for example, the 4th intercostal space lies between rib 4 and rib 5. There are 11 intercostal spaces and 11 intercostal nerves. Intercostal spaces are occupied by intercostal muscles and membranes, and two sets (main and collateral) of intercostal blood vessels and nerves, identified by the same number assigned to the space. The space below the 12th rib does not lie between ribs and thus is referred to as the subcostal space, and the anterior ramus of spinal nerve T12 is the subcostal nerve. The intercostal spaces are widest anterolaterally, and they widen with inspiration. They can be further widened by extension and/or lateral flexion of the thoracic vertebral column to the contralateral side.

Rib Fractures The short, broad 1st rib, posteroinferior to the clavicle, is rarely fractured because of its protected position (it cannot be palpated). When it is broken, however, injury to the brachial plexus of nerves and subclavian vessels may occur. The middle ribs are most commonly fractured. Rib fractures usually result from blows or from crushing injuries. The weakest part of a rib is just anterior to its angle; however, direct violence may fracture a rib anywhere, and its broken end may injure internal organs such as a lung and/or the spleen. Lower rib fractures may tear the diaphragm and result in a diaphragmatic hernia (see Chapter 2). Rib fractures are painful because the broken parts move during respiration, coughing, laughing, and sneezing.

Flail Chest Multiple rib fractures may allow a sizable segment of the anterior and/or lateral thoracic wall to move freely. The loose segment of the wall moves paradoxically (inward on inspiration and outward on expiration). Flail chest (stove‐in chest) is an extremely painful injury and impairs ventilation, thereby affecting oxygenation of the blood. During treatment, the loose segment is often fixed by hooks and/or wires so that it cannot move.

Thoracotomy, Intercostal Space Incisions, Rib Excision, and Bone Grafting The surgical creation of an opening through the thoracic wall to enter a pleural cavity is a thoracotomy (Fig. B1.1). An anterior thoracotomy may involve making H‐shaped cuts through the perichondrium of one or more costal cartilages and then shelling out segments of costal cartilage to gain entrance to the thoracic cavity (Fig 1.16). The posterolateral aspects of the 5th—7th intercostal spaces are important sites for posterior thoracotomy incisions. In general, a lateral approach is most satisfactory for entry into the thoracic cage. With the patient lying on the contralateral side, the upper limb is fully abducted, placing the forearm behind the patient's head. This elevates and laterally rotates the inferior angle of scapula, allowing access as high as the 4th intercostal space. Surgeons use an H‐shaped incision to incise the superficial aspect of the periosteum that ensheaths the rib, strip the periosteum from the rib, and then

Chapter 1: Thorax

Figure B1.1 remove a wide segment of the rib to gain better access, as might be required to enter the thoracic cavity and remove a lung (pneumonectomy), for example. In the rib's absence, entry into the thoracic cavity can be made through the deep aspect of the periosteal sheath, sparing the adjacent intercostal muscles. After the operation, the missing pieces of ribs regenerate from the intact periosteum, although imperfectly. Sometimes surgeons use a piece of rib so removed for autogenous bone grafting in procedures such as reconstruction of the mandible (lower jaw) after tumor excision.

Supernumerary Ribs People usually have 12 ribs on each side, but the number is increased by the presence of cervical and/or lumbar ribs, or decreased by failure of the 12th pair to form (see Chapter 4 for details). Cervical ribs are relatively common (0.5—2%), but lumbar ribs are less common. Cervical ribs may interfere with neurovascular structures exiting the superior thoracic aperture (See “Thoracic Outlet Syndromes,” in Chapter 6.) Supernumerary (extra) ribs also have clinical significance in that they may confuse the identification of vertebral levels in radiographs and other diagnostic images.

Protective Function and Aging of Costal Cartilages Costal cartilages provide resilience to the thoracic cage, preventing many blows from fracturing the sternum and/or ribs. Because of the remarkable elasticity of the ribs and costal cartilages in children, chest compression may produce injury within the thorax even in the absence of a rib fracture. In elderly people, the costal cartilages lose some of their elasticity and become brittle; they may undergo calcification, making them radiopaque (e.g., in radiographs).


Thoracic Vertebrae Thoracic vertebrae are typical vertebrae in that they are independent, have bodies, vertebral arches, and seven processes for muscular and articular connections (Figs. 1.4 and 1.5). Characteristic features of thoracic vertebrae include   

Bilateral costal facets (demifacets) on their bodies, usually occurring in inferior and superior pairs, for articulation with the heads of ribs. Costal facets on their transverse processes for articulation with the tubercles of ribs, except for the inferior two or three thoracic vertebrae. Long, inferiorly slanting spinous processes.

Superior and inferior costal facets, most of which actually occur in the form of demifacets, make up only a portion of a compound articular surface. They occur as bilaterally paired, planar surfaces on the superior and inferior posterolateral margins of typical (T2—T9) thoracic vertebrae. Functionally, the facets are arranged in pairs on adjacent vertebrae, flanking an interposed IV disc: an inferior (demi)facet of the superior vertebra and a superior (demi)facet of the inferior vertebra. Typically, two demifacets paired in this manner and the posterolateral margin of the IV disc between them form a single socket to receive the head of the rib that is assigned the same number as the inferior vertebra. Atypical thoracic vertebrae bear whole costal facets in place of demifacets: 

 

The superior costal facets of vertebra T1 are not demifacets because there are no demifacets on the C7 vertebra above, and rib 1 articulates only with vertebra T1. T1 has a typical inferior costal (demi)facet. T10 has only one bilateral pair of (whole) costal facets, located partly on its body and partly on its pedicle. T11 and T12 also have only a single pair of (whole) costal facets, located on their pedicles.

The spinous processes projecting from the vertebral arches of typical thoracic vertebrae are long and slope inferiorly, usually overlapping the vertebra below (Fig. 1.4D). They cover the intervals between the laminae of adjacent vertebrae, thereby preventing sharp objects such as a knife from entering the vertebral canal and injuring the spinal cord. The superior articular facets of the superior articular processes face mainly posteriorly and slightly laterally, whereas the inferior articular facets of the inferior articular processes face mainly anteriorly and slightly medially. The bilateral joint planes between the respective articular facets of the adjacent vertebrae describe an arc, centering on an axis of rotation within the vertebral body (Fig. 1.4A—C). Thus small rotatory movements are permitted between adjacent vertebra, but they are limited by the attached rib cage.

Chapter 1: Thorax

Figure 1.4. Thoracic vertebrae. A. T1 has a vertebral foramen and body similar to a cervical vertebra. B. T5—T9 vertebrae have typical characteristics of thoracic vertebrae. C. T12 has bony processes and a body size similar to a lumbar vertebra. The planes of the articular facets of thoracic vertebrae define an arc (red arrows) that centers on an axis traversing the vertebral bodies vertically. D. Superior and inferior costal facets (demifacets) on the vertebral body, costal facets on the transverse processes, and long sloping spinous processes are characteristic of thoracic vertebrae.

Figure 1.5. Costovertebral articulations of a typical rib. The costovertebral joints include the joint of head of rib, in which the head articulates with two adjacent vertebral bodies and the intervertebral disc between them, and the costotransverse joint, in which the tubercle of the rib articulates with the transverse process of a vertebra. The rib moves (elevates and depresses) around an axis that traverses the head and neck of the rib (arrows).

The Sternum The sternum (G. sternon, chest) is the flat, elongated bone that forms the middle of the anterior part of the thoracic cage (Fig. 1.6). The sternum consists of three parts: manubrium, body, and xiphoid process.


The manubrium (L. handle, as in the handle of a sword, the sternal body forming the blade) is a roughly trapezoidal bone. The manubrium is the widest and thickest of the three parts of the sternum. The easily palpated concave center of the superior border of the manubrium is the jugular notch (suprasternal notch). The notch is deepened in an articulated skeleton (and in life) by the medial (sternal) ends of the clavicles, which are much larger than the relatively small clavicular notches in the manubrium that receive them, forming the sternoclavicular (SC) joints. Inferolateral to the clavicular notch, the costal cartilage of the 1st rib is tightly attached to the lateral border of the manubrium—the synchondrosis of the first rib (Fig. 1.1A). The manubrium and body of the sternum lie in slightly different planes superior and inferior to their junction, the manubriosternal joint (Fig. 1.6A & B); hence, their junction forms a projecting sternal angle (of Louis). The body of the sternum, which is longer, narrower, and thinner than the manubrium, is located at the level of the T5—T9 vertebrae (Fig. 1.6A—C). Its width varies because of the scalloping of its lateral borders by the costal notches. In young people, four sternebrae (primordial segments of the sternum) are obvious. The sternebrae articulate with each other at primary cartilaginous joints (sternal synchondroses). These joints begin to fuse from the inferior end between puberty (sexual maturity) and age 25. The nearly flat anterior surface of the body of the sternum is marked in adults by three variable transverse ridges (Fig. 1.6A), which represent the lines of fusion (synostosis) of its four originally separate sternebrae. The xiphoid process, the smallest and most variable part of the sternum, is thin and elongated. It lies at the level of T10 vertebra. Although often pointed, the process may be blunt, bifid, curved, or deflected to one side or anteriorly. It is cartilaginous in young people but more or less ossified in adults older than age 40. In elderly people, the xiphoid process may fuse with the sternal body. The xiphoid process is an important landmark in the median plane because 



Its junction with the sternal body at the xiphisternal joint indicates the inferior limit of the central part of the thoracic cavity projected onto the anterior body wall; this joint is also the site of the infrasternal angle (subcostal angle) of the inferior thoracic aperture (Fig. 1.1). It is a midline marker for the superior limit of the liver, the central tendon of the diaphragm, and the inferior border of the heart.

Chapter 1: Thorax

Figure 1.6. Sternum. A. The felt‐like covering of the sternum—formed as the thin, broad membranous bands of the radiate sternocostal ligaments pass from the costal cartilages to the anterior and posterior surfaces of the sternum—is shown on the upper right side. B. Observe the thickness of the superior third of the manubrium between the clavicular notches. C. The relationship of the sternum to the vertebral column is shown.

Ossified Xiphoid Processes Many people in their early 40s suddenly become aware of their partly ossified xiphoid process and consult their physician about the hard lump in the “pit of their stomach” (epigastric fossa). Never having been aware of their xiphoid process before, they fear they have developed a tumor, such as “stomach cancer.”

Sternal Fractures Despite the subcutaneous location of the sternum, sternal fractures are not common. Crush injuries can occur after traumatic compression of the thoracic wall in automobile accidents when the driver's chest is forced into the steering column, for example. The installation and use of air bags in vehicles has reduced the number of sternal fractures. A fracture of the sternal body is usually a comminuted fracture (the sternum is broken into several pieces). Displacement of the bone fragments is uncommon because the sternum is invested by deep fascia (fibrous continuities of radiate sternocostal ligaments; Fig. 1.6A) and the sternal attachment of the pectoralis major muscles. The most common site of sternal fracture is at the sternal angle, after the manubriosternal joint has fused in elderly people, resulting in dislocation of the (re‐established) manubriosternal joint. In sternal injuries, the concern is not primarily for the fracture itself but for the likelihood of heart injury (myocardial contusion, cardiac rupture, tamponade) or pulmonary injury. The mortality (death rate) associated with sternal fractures is reported as 25—45%, largely owing to these underlying injuries. All patients with sternal contusion should be evaluated for underlying visceral injury (Rosen, 1998).


Median Sternotomy To gain access to the thoracic cavity for surgical operations in the mediastinum—for example, for coronary artery bypass grafting—the sternum is divided (split) in the median plane and retracted. The flexibility of ribs and costal cartilages enables spreading of the halves of the sternum. Sternal splitting also gives good exposure for removal of tumors in the superior lobes of the lungs. After surgery, the halves of the sternum are joined (e.g., with wire sutures).

Sternal Biopsy The sternal body is often used for bone marrow needle biopsy because of its breadth and subcutaneous position. The needle pierces the thin cortical bone and enters the vascular trabecular (cancellous) bone. Sternal biopsy is commonly used to obtain specimens of marrow for transplantation and for detection of metastatic cancer and blood dyscrasias (abnormalities).

Sternal Anomalies The cartilaginous halves of the sternum of the fetus (sternal plates) may not fuse because of defective ossification. Complete sternal cleft is uncommon. Sternal clefts involving the manubrium and superior half of the body are V‐ or U‐shaped and can be repaired during infancy by direct apposition and fixation of the cartilaginous sternal halves. Sometimes there is a perforation (sternal foramen) in the sternal body because of incomplete fusion of the fetal sternal plates. It is not clinically significant; however, one should be aware of its possible presence so that it will not be misinterpreted on a medical image of the thorax as a bullet wound. Although the xiphoid process is commonly perforated in elderly persons because of age‐related changes, this perforation is not clinically significant. Similarly, a protruding xiphoid process in infants is not unusual; when it occurs, it usually does not require correction.

The Bottom Line The functions of the thoracic wall are to protect the contents of the thoracic cavity; to provide the mechanics for breathing; and to provide for attachment of neck, back, upper limb and abdominal musculature. Its domed shape endows the thoracic cage with the necessary strength, and its light, relatively flexible osteocartilaginous elements and joints enable the flexibility necessary especially for respiration. Posteriorly, the thoracic cage consists of a column of 12 thoracic vertebrae and interposed IV discs. Laterally and anteriorly, it consists of 12 ribs, most continuous with a costal cartilage anteriorly that articulates directly or indirectly with the sternum. The ribs, the intercostal spaces between them, and vertical lines extrapolated from visible or palpable structures provide a grid for precisely locating related structures or pathologies.

Thoracic Apertures While the thoracic cage provides a complete wall peripherally, it is open superiorly and inferiorly. The much smaller superior opening is a passageway that allows communication with the neck and upper limb. The larger inferior opening provides

Chapter 1: Thorax

the ring‐like origin of the diaphragm, which completely occludes the opening, and the excursions of which primarily control the volume/internal pressure of the thoracic cavity, providing the basis for tidal respiration.

Superior Thoracic Aperture The superior thoracic aperture, the anatomical thoracic inlet, is bounded as follows (Fig. 1.7):   

Posteriorly, by vertebra T1 (protruding or convex posterior boundary/landmark). Laterally, by the 1st pair of ribs and their costal cartilages. Anteriorly, by the superior border of the manubrium (anterior landmark).

Structures that pass between the thoracic cavity and the neck through the oblique, kidney‐shaped superior thoracic aperture include the trachea, esophagus, nerves, and vessels that supply and drain the head, neck, and upper limbs. The adult superior thoracic aperture measures approximately 6.5 cm anteroposteriorly and 11 cm transversely. To visualize the size of this opening, note that it is slightly larger than necessary to allow the passage of a 2Ã—4 piece of lumber. Because of the obliquity of the 1st pair of ribs, the aperture slopes anteroinferiorly.

Inferior Thoracic Aperture The inferior thoracic aperture, the anatomical thoracic outlet, is bounded as follows:  

Posteriorly, by the 12th thoracic vertebra (posterior landmark). Posterolaterally, by the 11th and 12th pairs of ribs. Figure 1.7. Thoracic apertures. The superior thoracic aperture is the “doorway” between the thoracic cavity and the neck and upper limb. The inferior thoracic aperture (thoracic outlet) provides attachment for the diaphragm, which protrudes upward so that upper abdominal viscera receive protection from the thoracic cage. The continuous cartilaginous bar formed by the articulated cartilages of the 7th—10th (false) ribs makes up the costal margin.

 

Anterolaterally, by the joined costal cartilages of ribs 7—10, forming the costal margins. Anteriorly, by the xiphisternal joint (anterior landmark).


The inferior thoracic aperture is much more spacious than the superior thoracic aperture and is irregular in outline. It is also oblique because the posterior thoracic wall is much longer than the anterior wall. In closing the inferior thoracic aperture, the diaphragm separates the thoracic and abdominal cavities almost completely. Structures passing from or to the thorax from the abdomen pass through openings that traverse the diaphragm (e.g., esophagus and inferior vena cava), or pass posterior to it (e.g., aorta). Just as the size of the thoracic cavity (or its contents) is often overestimated, its inferior extent (corresponding to the boundary between thoracic and abdominal cavities) is often incorrectly estimated because of the discrepancy between the inferior thoracic aperture and the location of the diaphragm (the floor of the thoracic cavity) in living persons. Although the diaphragm takes origin from the structures that make up the inferior thoracic aperture, the domes of the diaphragm rise to the level of the 4th intercostal space, and abdominal visceral, including the large liver, spleen, and stomach, lie superior to the plane of the inferior thoracic aperture, within the thoracic wall (Fig. 1.1A & B).

Thoracic Outlet Syndrome Anatomists refer to the superior thoracic aperture as the thoracic inlet because non‐ circulating substances (air and food) may enter the thorax only through this aperture. When clinicians refer to the superior thoracic aperture as the thoracic outlet, they are emphasizing the arteries and T1 spinal nerves that emerge from the thorax through this aperture to enter the lower neck and upper limbs. Hence, various types of thoracic outlet syndrome (TOS) exist in which emerging structures are affected by obstructions of the superior thoracic aperture (Rowland, 2000). Although TOS implies a thoracic location, the obstruction actually occurs outside the aperture in the root of the neck (see Chapter 8), and the manifestations of the syndromes involve the upper limb (see Chapter 6).

The Bottom Line Although the thoracic wall is complete peripherally, the thoracic cage is open superiorly and inferiorly. The superior thoracic aperture is a relatively small passageway for the transmittal of structures to and from the neck and upper limbs, and the inferior thoracic aperture provides a rim to which the diaphragm is attached.

Joints of the Thoracic Wall Although movements of the joints of the thoracic wall are frequent—for example, in association with normal respiration—the range of movement at the individual joints is relatively small; nonetheless, any disturbance that reduces the mobility of these joints interferes with respiration. During deep breathing, the excursions of the thoracic cage (anteriorly, superiorly, or laterally) are considerable. Extending the vertebral column farther increases the anteroposterior (AP) diameter of the thorax. Joints of the thoracic wall (Table 1.1) occur between the  

Vertebrae (intervertebral joints). Ribs and vertebrae (costovertebral joints: joints of heads of ribs and costotransverse joints).

Chapter 1: Thorax     

Ribs and costal cartilages (costochondral joints). Costal cartilages (interchondral joints). Sternum and costal cartilages (sternocostal joints). Sternum and clavicle (sternoclavicular joints). Parts of the sternum (manubriosternal and xiphisternal joints) in young people—the manubriosternal (and sometimes the xiphisternal) joint usually fuses in the elderly.

The intervertebral joints between the bodies of adjacent vertebrae are joined together by longitudinal ligaments and intervertebral discs. These joints are discussed with the back in Chapter 4; the sternoclavicular joints are discussed in Chapter 6. The manubriosternal and xiphisternal joints were discussed earlier in this chapter, with the sternum.

Costovertebral Joints A typical rib articulates with the vertebral column at two joints: the joints of heads of ribs and the costotransverse joints (Fig. 1.8).

Joints of Heads of Ribs The head of each typical rib articulates with demifacets or costal facets of two adjacent thoracic vertebrae (Fig. 1.4) and the IV disc between them. The head articulates with the superior part of the corresponding (same‐numbered) vertebra, the inferior part of the vertebra superior to it, and the adjacent IV disc uniting the two vertebrae. For example, the head of the 6th rib articulates with the superior part of the body of the T6 vertebra, the inferior part of T5, and the IV disc between these vertebrae (Fig. 1.8). The crest of the head of the rib attaches to the IV disc by an intra‐articular ligament within the joint, dividing the enclosed space into two synovial cavities. Exceptions to this general arrangement of articulation occur with the heads of the 1st, sometimes the 10th, and usually the 11th and 12th ribs; they articulate only with their own vertebral bodies (bodies of the same number as the rib). In these cases no intra‐articular ligaments exist, and the joint cavities are not divided. A joint capsule surrounds each joint and connects the head of the rib with the circumference of the joint cavity. The fibrous layer of the capsule is strongest anteriorly, where it forms a radiate sternocostal ligament that fans out from the anterior margin of the head of the rib to the sides of the bodies of two vertebrae and the IV disc between them. The heads of the ribs connect so closely to the vertebral bodies that only slight gliding movements occur at the (demi)facets (pivoting around the intra‐articular ligament) of the joints of the heads of ribs; however, even slight movement here may produce a relatively large excursion of the distal (sternal or anterior) end of a rib.


Costotransverse Joints The tubercle of a typical rib articulates with the transverse costal facet on the anterior surface of the end of the transverse process of its own vertebra (vertebra of the same number). These small synovial joints are surrounded by thin joint capsules that attach to the edges of the articular facets. A costotransverse ligament passing from the neck of the rib to the transverse process and a lateral costotransverse ligament passing from the tubercle of the rib to the tip of the transverse process strengthen the anterior and posterior aspects of the joint, respectively. A superior costotransverse ligament is a broad band that joins the crest of the neck of the rib to the transverse process superior to it. The aperture between this ligament and the vertebra permits passage of the spinal nerve and the posterior branch of the intercostal artery. The superior costotransverse ligament may be divided into a strong anterior costotransverse ligament and a weak posterior costotransverse ligament. The strong costotransverse ligaments binding these joints limit their movements to slight gliding. However, the articular surfaces on the tubercles of the superior 6 ribs are convex and fit into concavities on the transverse processes (Fig. 1.8C). As a result, rotation occurs around a mostly transverse axis that traverses the intra‐articular ligament and the head and neck of the rib (Fig. 1.8A & B). This results in elevation and depression movements of the distal (sternal) ends of the ribs (and the sternum to which they attach) in the sagittal plane (pump‐handle movement) (Fig. 1.9A & C). Flat articular surfaces of tubercles and transverse processes of the 7th— 10th ribs allow gliding here (Fig. 1.8C), resulting in elevation and depression of the lateral‐most portions of these ribs in the transverse plane (bucket‐handle movement) (Fig. 1.9B & C). The floating 11th and 12th ribs do not articulate with transverse processes and have even freer movements as a result.

Costochondral Joints The costochondral articulations are hyaline cartilaginous joints. Each rib has a cup‐ shaped depression in its sternal end into which the costal cartilage fits (Table 1.1). The rib and its cartilage are firmly bound together by the continuity of the periosteum of the rib with the perichondrium of the cartilage. No movement normally occurs at these joints.

Interchondral Joints The interchondral joints—articulations between the adjacent borders of the 6th and 7th, 7th and 8th, and 8th and 9th costal cartilages—are plane synovial joints (Table 1.1). Each of these joints usually has a synovial cavity that is enclosed by a joint capsule. The joints are strengthened by interchondral ligaments. The articulation between the 9th and the 10th costal cartilages is a fibrous joint.

Chapter 1: Thorax

Table 1.1. Joints of Thoracic Wall

Joint Intervertebral

Type Symphysis (second‐ary cartilaginous) Costovertebral Synovial plane Joints of head of joint rib

Costotransverse

Costochondral

Interchondral

Sternocostal

Articulation Adjacent vertebral bodies bound together by IV disc Head of each rib with superior demifacet or costal facet of corresponding vertebral body and inferior demifacet or costal facet of vertebral body superior to it Articulation of tubercle of rib with transverse process of corresponding vertebra

Ligaments Anterior and posterior longitudinal Radiate and intra‐ articular ligaments of head of rib

Comments

Heads of 1st, 11th, and 12th ribs (sometimes 10th) artculate only with corresponding vertebral body

Lateral and 11th and 12th ribs superior do not articulate costotransverse with transverse process of corresponding vertebrae Primary Articulation of lateral Cartilage and bone No movement cartilaginous end of costal bound together by normally occurs at joint cartilage with sternal periosteum this joint end of rib Synovial plane Articulation between Interchondral Articulation joint costal cartilages of ligaments between costal 6th and 7th, 7th and cartilages of 9th 8th, and 8th and 9th and 10th ribs is ribs fibrous 1st: primary Articulation of 1st cartilaginous costal cartilages with


Sternoclavicular

Manubriosternal

Xiphisternal

joint (synchondrosis) 2nd—7th: synovial plane joint

manubrium of sternum Articulation of the 2nd—7th pairs of costal cartilages with sternum Saddle type of Sternal end of synovial joint clavicle with manubrium of sternum and 1st costal cartilage Secondary cartilaginous joint (symphysis) Primary cartilaginous joint (synchondrosis)

Articulation between manubrium and body of sternum Articulation between xiphoid process and body of sternum

Anterior and posterior radiate sternocostal Anterior and posterior sternoclavicular ligaments; costoclavicular ligament

This joint is divided into two compartments by an articular disc

This joint often fuses and becomes a synostosis in older individuals

Figure 1.8 Costovertebral joints. A and B. The ligaments of the costovertebral articulations with transverse axes of rib rotation (asterisks, dotted lines). C. Conformation of articular surfaces, revealed in sagittal sections of the costotransverse joints, demonstrates how the 1st—7th ribs rotate about an axis that runs longitudinally through the neck of the rib to change thoracic volume for respiration (left), whereas the 8th—10th ribs glide (right).

Sternocostal Joints

Chapter 1: Thorax

The 1st—7th ribs articulate through their costal cartilages with the lateral borders of the sternum; in mature adults, the articulations are (Fig. 1.1; Table 1.1):    

The 1st pair of cartilages with the manubrium only. The 2nd pair of cartilages with the manubrium and body of the sternum (i.e., with components of manubriosternal joint). The 3rd—6th pairs of cartilages with the body of the sternum. The 7th pair of cartilages with the body of the sternum and the xiphoid process (i.e., with the components of the xiphisternal joint).

The 1st pair of costal cartilages articulates with the manubrium by means of a thin dense layer of tightly adherent fibrocartilage interposed between cartilage and the manubrium, the synchondrosis of the 1st rib (Williams et al., 1995). The 2nd—7th pairs of costal cartilages articulate with the sternum at synovial joints with fibrocartilaginous articular surfaces on both the chondral and sternal aspects, allowing movement during respiration. The weak joint capsules of these joints are reinforced (thickened) anteriorly and posteriorly to form radiate sternocostal ligaments. These continue as thin, broad membranous bands passing from the costal cartilages to the anterior and posterior surfaces of the sternum, forming a felt‐like covering for this bone (Fig. 1.6A; Table 1.1).


F i g u re 1 . 9 . M o v e m e n t s o f t h o r a c i c w a l l . A . W h e n t h e u p p e r r i b s a r e e l e v a t e d , t h e A P d i m e n s i o n o f t h e th o r a x i s i n c r e a s e d ( p u m p ‐ h a n d l e m o v e m e n t ) , w i t h a g re a te r e x cu r s i o n ( i n c r e a s e ) o cc u r r i n g i n f e r i o r l y , a t t h e e n d o f t h e p u m p h a n d le . B . T h e m i d d le p a r t s o f t h e l o w e r r i b s m o v e l a t e r a l l y w h e n t h e y a r e e l e v a t e d , i n c r e a s i n g t h e t r a n s v e rs e d i m e n s i o n (b u c k e t ‐ h a n d l e m o v e m e n t) . C . T h e c o m b i n a t i o n o f r i b m o v e m e n t s ( a r r o w s ) t h a t o c c u r d u r i n g f o r c e d i n s p i r a t i o n in c r e a s e t h e A P a n d t r a n s v e rs e d i m e n s i o n s o f t h e t h o r a c i c c a g e . D . T h e t h o r a x w i d e n s d u r i n g f o r c e d i n s p i r a t i o n a s t h e r i b s a re e le v a te d ( a r r o w s ) . E . T h e th o r a x n a r r o w s d u r i n g e x p i r a t i o n a s t h e r i b s a r e d e p re s s e d ( a r r o w s ) . F . T h e p r i m a r y m o v e m e n t o f i n s p i r a t i o n ( r e s t i n g o r f o r c e d ) i s c o n t ra c t i o n o f th e d i a p h ra g m , w h i c h i n c r e a s e s the vertical dimension of the thoracic cavity (arrows). When the diaphragm relaxes, decompression of the abdominal v i s c e r a p u s h e s th e d i a p h r a g m u p w a rd , r e d u c i n g t h e v e r t i c a l d i m e n s i o n f o r e x p i r a t i o n .

Chapter 1: Thorax

Dislocation of Ribs A rib dislocation (slipping rib syndrome) is the displacement of a costal cartilage from the sternum—dislocation of a sternocostal joint or the displacement of the interchondral joints. Rib dislocations are common in body‐contact sports; complications may result from pressure on or damage to nearby nerves, vessels, and muscles. Displacement of interchondral joints usually occurs unilaterally and involves ribs 8, 9, and 10. Trauma sufficient to displace these joints often injures underlying structures such as the diaphragm and/or liver, causing severe pain, particularly during deep inspiratory movements. The injury produces a lump‐like deformity at the displacement site.

Separation of Ribs Rib separation refers to dislocation of a costochondral junction between the rib and its costal cartilage. In separations of the 3rd—10th ribs, tearing of the perichondrium and periosteum usually occurs. As a result, the rib may move superiorly, overriding the rib above and causing pain.

Movements of the Thoracic Wall Movements of the thoracic wall and diaphragm during inspiration produce increases in the intrathoracic volume and diameters of the thorax (Fig. 1.9D & F). Consequent pressure changes result in air being alternately drawn into the lungs (inspiration) through the nose, mouth, larynx, and trachea and expelled from the lungs (expiration) through the same passages. During passive expiration, the diaphragm, intercostal muscles, and other muscles relax, decreasing intrathoracic volume and increasing the intrathoracic pressure (Fig. 1.9E & C). Concurrently, intra‐abdominal pressure decreases and abdominal viscera are decompressed. This allows the stretched elastic tissue of the lungs to recoil, expelling most of the air. The vertical dimension (height) of the central part of the thoracic cavity increases during inspiration as contraction of the diaphragm causes it to descend, compressing the abdominal viscera (Fig. 1.9F). During expiration, the vertical dimension returns to the neutral position as the elastic recoil of the lungs produces sub‐atmospheric pressure in the pleural cavities, between the lungs and the thoracic wall. As a result of this and the absence of resistance to the previously compressed viscera, the domes of the diaphragm ascend, diminishing the vertical dimension. The AP dimension of the thorax increases considerably when the intercostal muscles contract: Movement of the ribs (primarily 2nd—6th) at the costovertebral joints around an axis passing through the necks of the ribs causes the anterior ends of the ribs to rise—the pump‐handle movement (Fig. 1.9A & C). Because the ribs slope inferiorly, their elevation also results in anterior—posterior movement of the sternum, especially its inferior end, with slight movement occurring at the manubriosternal joint in young people, in whom it has not yet synostosed. The transverse dimension of the thorax also increases slightly when the intercostal muscles contract, raising the middle (lateral‐most parts) of the ribs (especially the lower ones)—the bucket‐handle movement (Fig. 1.9B & C). The combination of all these movements moves the thoracic cage anteriorly, superiorly, and laterally (Fig. 1.9C & F).


Paralysis of the Diaphragm Paralysis of half of the diaphragm (one dome or hemidiaphragm) because of injury to its motor supply from the phrenic nerve does not affect the other half because each dome has a separate nerve supply. One can detect paralysis of the diaphragm radiographically by noting its paradoxical movement. Instead of descending as it normally would during inspiration owing to diaphragmatic contraction (Fig. B1.2A), the paralyzed dome ascends as it is pushed superiorly by the abdominal viscera that are being compressed by the active contralateral dome (Fig. B1.2B). Instead of ascending during expiration, the paralyzed dome descends in response to the positive pressure in the lungs.

Figure B1.2

The Bottom Line The movements of most ribs occur around a generally transverse axis that passes through the head, neck, and tubercle. This axis, plus the slope and curvature of the ribs, results in bucket‐handle‐type movements that alter the transverse diameter of the thorax and pump‐handle‐type movements that alter its AP diameter. Most important, however, is contraction and relaxation of the superiorly convex diaphragm that alters its vertical dimensions. Increasing dimensions result in inhalation, and decreasing dimensions produce exhalation.

Surface Anatomy of the Thoracic Wall Skeleton The clavicles (collar bones) lie subcutaneously, forming bony ridges at the junction of the thorax and neck (Fig. SA1.1). They can be palpated easily throughout their length, especially where their medial ends articulate with the manubrium of the sternum. The clavicles demarcate the superior divide between zones of lymphatic drainage: above the clavicles, lymph flows ultimately to inferior jugular lymph nodes; below them, parietal lymph (that from the body wall and upper limb) flows to the axillary lymph nodes. The sternum lies subcutaneously in the anterior median line and is palpable throughout its length. Between the prominences of the medial ends of the clavicles at the sternoclavicular joints, the jugular notch in the manubrium can be palpated between the prominent medial ends of the clavicles. The notch lies at the level of the

Chapter 1: Thorax

inferior border of the body of T2 vertebra and the space between the 1st and 2nd thoracic spinous processes. The manubrium, approximately 4 cm long, lies at the level of the bodies of T3 and T4 vertebrae (Fig. SA1.2). The sternal angle is palpable and often visible in young people because of the slight movement that occurs at the manubriosternal joint during forced respiration. The sternal angle lies at the level of the T4—T5 IV disc and the space between the 3rd and 4th thoracic spinous processes. The sternal angle marks the level of the 2nd pair of costal cartilages. The left side of the manubrium is anterior to the arch of the aorta, and its right side directly overlies the merging of the brachiocephalic veins to form the superior vena cava (SVC). Because it is common clinical practice to insert catheters into the SVC for feeding extremely ill patients and other purposes (Ger et al., 1996), it is essential to know the surface anatomy of this large vein. The SVC passes inferiorly deep to the manubrium and manubriosternal junction but projects as much as a fingerbreadth to the right of the margin of the bony structures. The SVC enters the right atrium of the heart opposite the right 3rd costal cartilage. The body of the sternum, approximately 10 cm long, lies anterior to the right border of the heart and vertebrae T5—T9. The intermammary cleft (midline depression or cleavage between the mature female breasts) overlies the sternal body. The xiphoid process lies in a slight depression, the epigastric fossa, where the converging costal margins form the infrasternal angle. This angle is used in cardiopulmonary resuscitation (CPR) for locating the proper hand position on the inferior part of the sternal body. You can feel the xiphisternal joint, often seen as a ridge, at the level of the inferior border of T9 vertebra. The costal margins, formed by the joined costal cartilages of the 7th—10th costal cartilages, are easily palpable because they extend inferolaterally from the xiphisternal joint. The costal margins form the sides of the infrasternal angle. The ribs and intercostal spaces provide a basis for locating or describing the position of structures or sites of trauma or pathology on or deep to the thoracic wall, much like lines of latitude are used in navigation. For example, “the beat of the mitral valve of the heart may be heard by placing the stethoscope in the intercostal space between the 5th and 6th ribs inferior to the left nipple.” Because the 1st rib is not palpable, rib counting in physical examinations starts with the 2nd rib adjacent to the subcutaneous and easily palpated sternal angle.

Figure SA1.1


Figure SA1.2 To count the ribs and intercostal spaces anteriorly, slide the fingers laterally from the sternal angle onto the 2nd costal cartilage and begin counting the ribs and spaces by moving the digits from here. The 1st intercostal space is that superior to the 2nd costal cartilage—that is, intercostal spaces are numbered according to the rib forming their superior boundary. Generally, it is more reliable to count intercostal spaces, since the fingertip tends to rest in (slip into) the gaps between ribs. One finger should remain in place while another is used to locate the next space. Using all the fingers, it is possible to locate four spaces at a time. The spaces are widest anterolaterally (approximately in the midclavicular line). If the fingers are removed from the thoracic wall while counting spaces, the finger may easily be returned to the same space, mistaking it for the one below. Posteriorly, the medial end of the spine of the scapula overlies the 4th rib. While the ribs and/or intercostal spaces provide the “latitude” for navigation and localization on the thoracic wall, several imaginary lines facilitate anatomical and clinical descriptions by providing “longitude.” The following lines are extrapolated over the thoracic wall based on visible or palpable superficial features:   



The anterior median (midsternal) line (AML) indicates the intersection of the median plane with the anterior thoracic wall (Fig. SA1.3A). The midclavicular line (MCL) passes through the midpoint of the clavicle, parallel to the AML. The anterior axillary line (AAL) runs vertically along the anterior axillary fold that is formed by the inferolateral border of the pectoralis major as it spans from the thoracic cage to the humerus in the arm (Fig. SA1.3B). The midaxillary line (MAL) runs from the apex (deepest part) of the axillary fossa, parallel to the AAL.

Chapter 1: Thorax 

 

The posterior axillary line (PAL), also parallel to the AAL, is drawn vertically along the posterior axillary fold formed by the latissimus dorsi and teres major muscles as they span from the back to the humerus. The posterior median (midvertebral) line (PML) is a vertical line along the tips of the spinous processes of the vertebrae (Fig. SA1.3C). The scapular line (SL) is parallel to the posterior median line and intersects the inferior angles of the scapula.

Additional lines (not illustrated) are extrapolated along the borders of palpable bony formations such as the sternum and vertebral column, such as the parasternal and paravertebral lines (G. para, alongside of, adjacent to).

Figure SA1.3

Muscles of the Thoracic Wall Several upper limb (thoracoappendicular) muscles attach to the thoracic cage— including the pectoralis major, pectoralis minor, subclavius, and serratus anterior muscles anteriorly and latissimus dorsi muscles posteriorly—as do the anterolateral abdominal muscles and some back and neck muscles (Fig. 1.10). The thoracoappendicular muscles usually act on the upper limbs (see Chapter 6). But several, including the pectoralis major and pectoralis minor and the inferior part of the serratus anterior may also function as accessory muscles of respiration, helping elevate the ribs to expand the thoracic cavity when inspiration is deep and forceful (e.g., after a 100‐m dash). The scalene muscles of the neck, which descend to the 1st and 2nd ribs, also serve as accessory respiratory muscles by fixing these ribs and enabling the muscles connecting the ribs below to be more effective in elevating the lower ribs during forced inspiration. The serratus posterior, levatores costarum, intercostal, subcostal, and transverse thoracic are muscles of the thoracic wall (Table 1.2). The serratus posterior muscles, extending from the vertebrae to the ribs, have traditionally been described as inspiratory muscles, but this function is not supported by electromyography or other evidence. The serratus posterior superior lies at the junction of the neck and back. It arises from the inferior part of the nuchal ligament (L. ligamentum nuchae) in the neck and the spinous processes of the C6 or C7 through T2 or T3 vertebrae. This muscle runs inferolaterally and attaches by a series


of digitations to the superior borders of the 2nd—5th ribs, immediately lateral to their angles. On the basis of its attachments and disposition, the serratus posterior superior was said to elevate the superior four ribs, thus increasing the AP diameter of the thorax and raising the sternum. The serratus posterior inferior lies at the junction of the thoracic and lumbar regions (see Chapter 4). It arises from the spinous processes of the last two thoracic spinous processes, the first two lumbar spinous processes, and the thoracolumbar fascia. It runs superolaterally and attaches to the inferior borders of the inferior three or four ribs, also just lateral to their angles. On the basis of its attachments and disposition, the serratus posterior inferior was said to depress the inferior ribs, preventing them from being pulled superiorly by the diaphragm. However, recent studies (Vilensky et al., 2001) suggest that these muscles, which span the superior and inferior thoracic apertures as well as the transitions from the relatively inflexible thoracic vertebral column to the much more flexible cervical and lumbar segments of the column, may not be primarily motor in function. Rather, they may have a proprioceptive function. These muscles, particularly the superior one, have been implicated as a source of chronic pain in myofascial pain syndromes.

Figure 1.10. Thoracoappendicular and anterolateral abdominal muscles overlying thoracic wall. The pectoralis major has been removed on the left side to expose the pectoralis minor, subclavius, and external intercostal muscles. When the upper limb muscles are removed, the domed shape of the thoracic cage is revealed.

Chapter 1: Thorax

Table 1.2. Muscles of Thoracic Wall The levatores costarum muscles are attached to the transverse processes of the C7 and T1—T11 vertebrae (Fig. 1.14) and pass inferolaterally to attach to the ribs, close to their tubercles. As their name indicates, these 12 fan‐shaped muscles elevate the ribs; but their role, if any, in normal inspiration is uncertain. They may play a role in vertebral movement and/or proprioception. The intercostal muscles occupy the intercostal spaces (Figs. 1.10, 1.11, and 1.12; Table 1.2). The superficial layer is formed by the external intercostals, the inner layer by the internal intercostals. The deepest fibers of the latter, lying internal to the intercostal vessels are somewhat artificially designated as a separate muscle, the innermost intercostals. 



The external intercostal muscles (11 pairs) occupy the intercostal spaces from the tubercles of the ribs posteriorly to the costochondral junctions anteriorly (Figs. 1.10, 1.11, and 1.13). Anteriorly, the muscle fibers are replaced by the external intercostal membranes (Fig. 1.13A). These muscles run inferoanteriorly from the rib above to the rib below. Each muscle attaches superiorly to the inferior border of the rib above and inferiorly to the superior border of the rib below (Fig. 1.13C). These muscles are continuous inferiorly with the external oblique muscles in the anterolateral abdominal wall. The external intercostals are most active during inspiration; they maintain or increase the tonus of the intercostal space. They elevate the ribs during forced inspiration. The internal intercostal muscles (11 pairs) run deep to and at right angles to the external intercostals (Figs. 1.12 and 1.13C). Their fibers run inferoposteriorly from the floors of the costal grooves to the superior borders of the ribs inferior to them. The internal intercostals attach to the bodies of the ribs and their costal cartilages as far anteriorly as the sternum and as far posteriorly as the angles of the ribs. Between the ribs posteriorly, medial to the angles, the internal intercostals are replaced by the internal intercostal membranes (Fig. 1.13A). The inferior internal intercostals are continuous with the internal oblique muscles in the anterolateral abdominal wall. The internal intercostals—weaker than the external intercostal muscles—are most active


during expiration; they maintain or increase the tonus of the intercostal space. Their interosseous (vs. interchondral) portions may depress ribs during forced respiration (Fig. 1.13C). The interchondral portion of the internal intercostals appears to act with the external intercostals during active inspiration (discussed later in this chapter).

Figure 1.11. Dissection of anterior aspect of anterior thoracic wall. The external intercostal muscles are replaced by membranes between costal cartilages. The H‐shaped cuts through the perichondrium of the 3rd and 4th costal cartilages are used to shell out pieces of cartilage, as was done with the 4th costal cartilage, illustrating how one type of thoracotomy is performed. It is not uncommon for the 8th rib to attach to the sternum, as in this specimen. The internal thoracic vessels and the parasternal lymph nodes (green) lie inside the thoracic cage lateral to the sternum.

Chapter 1: Thorax

Figure 1.12. Posterior aspect of anterior thoracic wall. The internal thoracic arteries arise from the subclavian arteries and have paired accompanying veins (L. venae comitantes) inferiorly. Superior to the 2nd costal cartilage, there is only a single internal thoracic vein on each side, which drains into the brachiocephalic vein. The continuity of the transverse thoracic with the transverse abdominal becomes apparent when the diaphragm is removed, as has been done here on the right side. 

The innermost intercostal muscles are similar to the internal intercostals and are essentially their deeper parts. The innermost intercostals are separated from the internal intercostals by the intercostal nerves and vessels (Fig. 1.13). These muscles pass between the internal surfaces of adjacent ribs and occupy the lateralmost parts of the intercostal spaces. It is likely (but undetermined) that their actions are the same as those of the internal intercostal muscles.

The subcostal muscles are variable in size and shape, usually being well developed only in the lower thoracic wall. These thin muscular slips extend from the internal surface of the angle of one rib to the internal surface of the second or third rib inferior to it. Crossing one or two intercostal spaces, the subcostals run in the same direction as the internal intercostals and blend with them (Fig. 1.13B). Thus it is assumed that the subcostals act with the internal intercostals, and that they may depress ribs. The transverse thoracic (L. transversus thoracis) muscles, consist of four or five slips that attach posteriorly to the xiphoid process, the inferior part of the body of the sternum, and the adjacent costal cartilages (Figs. 1.11 and 1.12). They pass superolaterally and attach to the 2nd—6th costal cartilages. The transverse thoracic muscles are continuous inferiorly with the transverse abdominal muscles in the anterolateral body wall. These muscles appear to have a weak expiratory function,


drawing downward on the costal cartilages to which they attach. They may provide proprioceptive information. Although the external and internal intercostals are active during inspiration and expiration, respectively, most activity is isometric; the role of these muscles in producing movement of the ribs appears to be related mainly to forced respiration. The diaphragm is the primary muscle of inspiration. Expiration is passive unless one is exhaling against resistance (e.g., inflating a balloon) or trying to expel air more rapidly than usual (e.g., coughing, sneezing, blowing one's nose, or shouting), the elastic recoil of the lungs and decompression of abdominal viscera expel previously inhaled air. The primary role of the intercostal muscles in respiration is to support (increase the tonus or rigidity of) the intercostal space, resisting paradoxical movement especially during inspiration when internal thoracic pressures are lowest (most negative). This is most apparent following a high spinal cord injury, when there is an initial flaccid paralysis of the entire trunk but the diaphragm remains active. In these circumstances, the vital capacity is markedly compromised by the paradoxical incursion of the thoracic wall during inspiration. Several weeks later, the paralysis becomes spastic; the thoracic wall stiffens and vital capacity rises (Williams et al., 1995). The mechanical action of the intercostal muscles in rib movement, especially during forced respiration, can be appreciated by means of a simple model (Fig. 1.13C). A pair of curved levers, representing the ribs bordering an intercostal space, are hinged posteriorly to a fixed, vertical (vertebral) column; their anterior ends (costal cartilages) are hinged to a moveable, vertical column (the sternum). The ribs (and intervening intercostal space) descend as they run anteriorly, reaching their low point approximately at the costochondral junction, and then ascend to the sternum. The concentric contraction of the muscle fibers that most closely approximate the slope of the ribs at their attachments (fibers A and C in Fig. 1.13C) rotate the ribs superiorly at their posterior axes, elevating the ribs and sternum. The concentric contraction of muscle fibers that are approximately perpendicular to the slope of the ribs at their attachment (fibers B in the figure) rotate the ribs inferiorly at their posterior axes, depressing the ribs and sternum. Fibers A represent the external intercostal muscles, and fibers B represent the interosseous portion of the internal intercostal muscles. Fibers A run nearly perpendicular to fibers B. Thus the external intercostal muscles elevate and the interosseous internal intercostal muscles depress the ribs. Note that even though the fibers of the interchondral portion of the internal interosseous muscles (fibers C) run parallel to the fibers of the interosseous portion (fibers B), they approximate the slope of the ribs (instead of being perpendicular to the slope). Therefore, the interchondral portion of the internal intercostal muscles (fibers C) act with the external intercostal muscles (fibers A) to elevate the ribs (Slaby et al., 1994).

Chapter 1: Thorax

Figure 1.13. Contents of an intercostal space. A. This transverse section shows nerves (right side) and arteries (left side) in relation to the intercostal muscles. B. The posterior part of an intercostal space is shown. The joint capsule (radiate ligament) of one costovertebral joint has been removed. Innermost intercostal muscles bridge one intercostal space; subcostal muscles bridge two. The mnemonic for the order of the neurovascular structures in the intercostal space from superior to inferior is VAN—vein, artery, and nerve. Communicating branches (L. rami communicantes) extend between the intercostal nerves and the sympathetic trunk. C. A simple model of the action of the intercostal muscles is shown. Contraction of the muscle fibers that most closely parallel the slope of the ribs at a given point (fibers A and C) will elevate the ribs and sternum; contraction of muscle fibers that are approximately perpendicular to the slope of the ribs (fibers B) will depress the ribs.


The diaphragm is a shared wall (actually floor/ceiling) separating the thorax and abdomen. Although it has functions related to both compartments of the trunk, its most important (vital) function is serving as the primary muscle of inspiration. The detailed description of the thoracic diaphragm appears in Chapter 2 because the attachments of its crura occur at abdominal levels (i.e., to lumbar vertebrae) and all of its attachments are best observed from its inferior (abdominal) aspect; they are essentially inaccessible from the thoracic side if the abdominal viscera are still in place. Consequently, the diaphragm is usually most fully studied when, during dissections, the abdominal viscera and kidneys have been removed. However, you may wish to read about the diaphragm at this time.

Dyspnea: Difficult Breathing When people with respiratory problems (e.g., asthma) or with heart failure struggle to breathe, they use their accessory respiratory muscles to assist the expansion of their thoracic cavity. They lean on their knees or on the arms of a chair to fix their pectoral girdle so these muscles are able to act on their rib attachments and expand the thorax.

The Bottom Line The thorax is overlapped by the thoracoappendicular muscles of the upper limb. These muscles account for many of the anatomical features of its surface, along with the breasts. Most of these muscles can effect deep respiration when the pectoral girdle is fixed. The muscles that are truly thoracic, however, provide few if any surface features. The serratus posterior muscles are thin with small bellies that may be proprioceptive organs. The costal muscles can move the ribs and do so during forced respiration, but most of the time they function to support (provide tonus for) the intercostal spaces, resisting negative and positive intrathoracic pressures. The diaphragm is the primary muscle of respiration.

Fascia of the Thoracic Wall Each part of the deep fascia is named for the muscle it invests or the structure(s) to which it is attached. Consequently, a large portion of the deep fascia overlying the anterior thoracic wall, forming a major part of the bed of the breast (area or structures immediately deep to the breast, i.e., on which the breast lies), is called pectoral or pectoralis fascia for its association with the pectoralis major muscles (Fig. 1.15). Deep to the pectoralis major and its fascia is another layer of deep fascia suspended from the clavicle and investing the pectoralis minor muscle, the clavipectoral fascia. (The pectoral and clavipectoral fascias are explained and illustrated in Chapter 6 in relation to the axillary fossa or armpit.) The thoracic cage is lined internally with endothoracic fascia. This thin fibroareolar layer attaches the adjacent portion of the lining of the lung cavities (the costal parietal pleura) to the thoracic wall. It becomes more fibrous over the apices of the lungs as the suprapleural membrane (see clinical correlation [blue] box “Extrapleural Intrathoracic Surgical Access.”

Chapter 1: Thorax

Extrapleural Intrathoracic Surgical Access Fixation makes it difficult to appreciate in the embalmed cadaver, but in surgery the relatively loose nature of the thin endothoracic fascia provides a natural cleavage plane, allowing the surgeon to separate the costal parietal pleura lining the lung cavity from the thoracic wall. This allows intrathoracic access to extrapleural structures (e.g., lymph nodes) and instrument placement without opening and perhaps contaminating the potential space (pleural cavity) that surrounds the lungs.

The Bottom Line Deep fascia overlies and invests the muscles of the thoracic wall, as it does elsewhere. Where the fleshy portions of the intercostal muscles are absent, their fascia is continued as intercostal membranes, so that the wall is complete. The endothoracic fascia is a thin, fibroareolar layer between the internal aspect of the thoracic cage and the lining of the pulmonary cavities, which can be opened surgically to gain access to intrathoracic structures.

Nerves of the Thoracic Wall The 12 pairs of thoracic spinal nerves supply the thoracic wall. As soon as they leave the IV foramina in which they are formed, the mixed thoracic spinal nerves divide into anterior and posterior primary rami (Fig. 1.13A). The anterior rami of nerves T1—T11 form the intercostal nerves that run along the extent of the intercostal spaces. The anterior ramus of nerve T12, coursing inferior to the 12th rib, is the subcostal nerve (see Chapter 2). The posterior rami of thoracic spinal nerves pass posteriorly, immediately lateral to the articular processes of the vertebrae (Fig. 1.14), to supply the joints, muscles, and skin of the back in the thoracic region (see Chapter 4).

Typical Intercostal Nerves The 3rd—6th intercostal nerves enter the medial‐most parts of the posterior intercostal spaces, running initially within the endothoracic fascia between the parietal pleura (serous lining of the pulmonary cavity) and the internal intercostal membrane nearly in the middle of the intercostal spaces (Figs. 1.13 and 1.14). Near the angles of the ribs, the nerves pass between the internal intercostal and the innermost intercostal muscles. At this point, the intercostal nerves pass to and then continue to course within the costal grooves, running inferior to the intercostal arteries (which, in turn, run inferior to the intercostal veins) (Fig. 1.13B). The neurovascular bundles are thus sheltered by the inferior margins of the overlying ribs. Collateral branches of these nerves arise near the angles of the ribs and run along the superior border of the rib below. The nerves continue anteriorly between the internal and the innermost intercostal muscles, giving branches to these and other muscles and giving rise to lateral cutaneous branches in approximately the MAL. Anteriorly, the nerves appear on the internal surface of the internal intercostal muscle. Near the sternum, the intercostal nerves turn anteriorly, passing between the costal cartilages to become anterior cutaneous branches.


Figure 1.14. Dissection of posterior aspect of thoracic wall. The iliocostalis and longissimus muscles (two of the three components of the erector spinae muscles of the back) have been removed to expose the levatores costarum muscles. In the 8th and 10th intercostal spaces, varying parts of the external intercostal muscle have been removed to expose the underlying internal intercostal membrane, which is continuous with the internal intercostal muscle. In the 9th intercostal space, the levator costae has been removed to expose the intercostal vessels and nerve.

Through its posterior ramus and the lateral and anterior cutaneous branches of its anterior ramus, each spinal nerve supplies a strip‐like dermatome extending from the posterior median line to the anterior median line (Fig. 1.16). The group of muscles supplied by the posterior ramus and anterior ramus (intercostal nerve) of each pair of thoracic spinal nerves constitutes a myotome. Constituting the myotome supplied by the muscular branches of a typical intercostal nerve is the intercostal, subcostal, transverse thoracic, levatores costarum, and serratus posterior muscles associated with the intercostal space that includes the nerve. The branches of a typical intercostal nerve are: 

Rami communicantes, or communicating branches, that connect each intercostal nerve to the ipsilateral sympathetic trunk (Fig. 1.13A & B). Presynaptic fibers leave the initial portions of the anterior ramus of each thoracic (and upper lumbar) spinal nerve by means of a white communicating ramus and pass to the sympathetic trunk. Postsynaptic fibers distributed to the body wall and limbs pass from the ganglia of the sympathetic trunk via gray rami to join the anterior ramus of the nearest spinal nerve, including all intercostal nerves. Sympathetic nerve fibers are distributed through all

Chapter 1: Thorax





branches of all spinal nerves (anterior and posterior rami) to reach the blood vessels, sweat glands, and smooth muscle of the body wall and limbs. Collateral branches that arise near the angles of the ribs and descend to course along the superior margin of the lower rib, helping supply intercostal muscles and parietal pleura (Fig. 1.13B). Lateral cutaneous branches that arise near the MAL and pierce the internal and external intercostal muscles approximately halfway around the thorax (Figs. 1.13A & B, 1.15, and 1.16). The lateral cutaneous branches divide in turn into anterior and posterior branches that supply the skin of the lateral thoracic and abdominal walls. Figure 1.15. Superficial dissection of male pectoral region. The platysma is cut short on the right side and is reflected on the left side, together with the underlying supraclavicular nerves. Observe the filmy, deep fascia covering the right pectoralis major. The fascia has been removed on the left side. The cutaneous branches of the intercostal nerves that supply the breast are shown.

Figure 1.16. Segmental innervation (dermatomes) of thoracic wall. Spinal nerve C5 supplies skin at the level of the clavicles and immediately below. Anteriorly, the dermatome immediately inferior to the C5 dermatome is that of spinal nerve T1. Dermatomes C6—C7 are located mostly in the upper limbs and are represented on the posterior, but not the anterior, body wall. Since the anterior rami of spinal nerves T2—T12 are not involved in plexus formation, there is no difference between the dermatomes and the zones of peripheral nerve distribution here. Dermatome T4 includes the nipple; dermatome T10 includes the umbilicus.


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Anterior cutaneous branches that supply the skin on the anterior aspect of the thorax and abdomen. After penetrating the muscles and membranes of the intercostal space in the parasternal line, the anterior cutaneous branches divide into medial and lateral branches. Muscular branches that supply the intercostal, subcostal, transverse thoracic, levatores costarum, and serratus posterior muscles (Fig. 1.13A).

Atypical Intercostal Nerves Although the anterior ramus of most thoracic spinal nerves is simply the intercostal nerve for that level, the anterior ramus of the 1st thoracic (T1) spinal nerve first divides into a large superior and a small inferior part. The superior part joins the brachial plexus, the nerve plexus supplying the upper limb (see Chapter 6), and the inferior part becomes the 1st intercostal nerve. Other atypical features of specific intercostal nerves include the following:  

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The 1st and 2nd intercostal nerves course on the internal surface of the 1st and 2nd ribs, instead of along the inferior margin in costal grooves (Fig. 1.12). The 1st intercostal nerve has no anterior cutaneous branch and often no lateral cutaneous branch. When there is a lateral cutaneous branch, it supplies the skin of the axilla and may communicate with either the intercostobrachial nerve or the medial cutaneous nerve of the arm. The 2nd (and sometimes 3rd) intercostal nerve gives rise to a large lateral cutaneous branch, the intercostobrachial nerve; it emerges from the 2nd intercostal space at the MAL, penetrates the serratus anterior, and enters the axilla and arm. The intercostobrachial nerve usually supplies the floor—skin and subcutaneous tissue—of the axilla and then communicates with the medial brachial cutaneous nerve to supply the medial and posterior surfaces of the arm. The lateral cutaneous branch of the 3rd intercostal nerve frequently gives rise to a second intercostobrachial nerve. The 7th—11th intercostal nerves, after giving rise to lateral cutaneous branches, cross the costal margin posteriorly and continue on to supply abdominal skin and muscles. No longer being between ribs (intercostal), they now become the thoracoabdominal nerves of the anterior abdominal wall (see Chapter 2). Their anterior cutaneous branches pierce the rectus sheath, becoming cutaneous close to the median plane.

Herpes Zoster Infection of the Spinal Ganglia A herpes zoster infection causes a classic, dermatomally distributed skin lesion— shingles—an agonizingly painful condition (Fig. B1.3). Herpes zoster is primarily a viral disease of spinal ganglia, usually a reactivation of the varicella‐zoster virus (VZV), or chickenpox virus. After invading a ganglion, the virus produces a sharp burning pain in the dermatome supplied by the involved nerve (Fig. 1.16). The affected skin area becomes red, and vesicular eruptions appear. The pain may precede or follow the skin eruptions. Although primarily a sensory neuropathy (pathological change in the nerve) weakness from motor involvement occurs in 0.5— 5.0% of people, commonly in elderly cancer patients (Rowland, 2000). Muscular weakness usually occurs in the same myotomal distribution, as do the dermatomal pain and vesicular eruptions.

Chapter 1: Thorax

Figure B1.3

Intercostal Nerve Block Local anesthesia of an intercostal space is produced by injecting a local anesthetic agent around the intercostal nerves between the paravertebral line and the area of required anesthesia. This procedure, an intercostal nerve block, involves infiltration of the anesthetic around the intercostal nerve trunk and its collateral branches (Fig. B1.4). The word block indicates that the nerve endings in the skin and the transmission of impulses through the sensory nerves carrying information about pain are interrupted (blocked) before the impulses reach the spinal cord and brain. Because any particular area of skin usually receives innervation from two adjacent nerves, considerable overlapping of contiguous dermatomes occurs. Therefore, complete loss of sensation usually does not occur unless two or more intercostal nerves are anesthetized.

Figure B1.4


Vasculature of the Thoracic Wall In general, the pattern of vascular distribution in the thoracic wall reflects the structure of the thoracic cage—that is, it runs in the intercostal spaces, parallel to the ribs.

Arteries of the Thoracic Wall The arterial supply to the thoracic wall (Fig. 1.17; Table 1.3) derives from the:   

Thoracic aorta, through the posterior intercostal and subcostal arteries. Subclavian artery, through the internal thoracic and supreme intercostal arteries. Axillary artery, through the superior and lateral thoracic arteries.

The intercostal arteries course through the thoracic wall between the ribs. With the exception of the 10th and 11th intercostal spaces, each intercostal space is supplied by three arteries: a large posterior intercostal artery (and its collateral branch) and a small pair of anterior intercostal arteries. The posterior intercostal arteries:  

Of the 1st and 2nd intercostal spaces arise from the supreme (superior) intercostal artery, a branch of the costocervical trunk of the subclavian artery. Of the 3rd—11th intercostal spaces (and the subcostal arteries of the subcostal space) arise posteriorly from the thoracic aorta (Fig. 1.17). Because the aorta is slightly to the left of the vertebral column, the right 3rd—11th intercostal arteries have a longer course than those on the left side. The right arteries cross the vertebrae and pass posterior to the esophagus, thoracic duct, azygos vein (Fig. 1.27), and the right lung and pleura.

Table 1.3. Arterial Supply of Thoracic Wall Artery Origin Posterior Superior intercostal artery intercostals (intercostal spaces 1 and 2) and thoracic aorta (remaining intercostal spaces) Anterior Internal thoracic (intercostal intercostals spaces 1—6) and musculophrenic arteries (intercostal spaces 7—9) Internal Subclavian artery thoracic

Subcostal

Thoracic aorta

Course Distribution Pass between internal and Intercostal muscles, innermost intercostal muscles overlying skin, and parietal pleura

Passes inferiorly and lateral to sternum between costal cartilages and transverse thoracic muscle to divide into superior epigastric and musculophrenic arteries Courses along inferior border of 12th rib

By way of anterior intercostal arteries to intercostal spaces 1—6

Muscles anterolateral abdominal wall

of

Chapter 1: Thorax

Figure 1.17. Arteries of thoracic wall. The arterial supply to the thoracic wall derives from the thoracic aorta through the posterior intercostal and subcostal arteries (A, B, and D), from the axillary artery (B), and from the subclavian artery through the internal thoracic (C) and supreme (superior) intercostal arteries (B). Connections (anastomoses) between the arteries permit collateral circulation pathways to develop (D).


 



All give off a posterior branch that accompanies the posterior ramus of the spinal nerve to supply the spinal cord, vertebral column, back muscles, and skin. Give rise to a small collateral branch that crosses the intercostal space and runs along the superior border of the rib. Accompany the intercostal nerves through the intercostal spaces. Close to the angle of the rib, the arteries enter the costal grooves, where they lie between the intercostal vein and nerve. At first the arteries run in the endothoracic fascia between the parietal pleura and the internal intercostal membrane (Fig. 1.14); then they run between the innermost intercostal and internal intercostal muscles. Have terminal and collateral branches that anastomose anteriorly with anterior intercostal arteries (Fig. 1.17A).

The internal thoracic arteries (historically, the internal mammary arteries):    

 

Arise in the root of the neck from the inferior surfaces of the first parts of the subclavian arteries. Descend into the thorax posterior to the clavicle and 1st costal cartilage (Figs. 1.11, 1.12, and 1.17). Are crossed near their origins by the ipsilateral phrenic nerve. Descend on the internal surface of the thorax slightly lateral to the sternum and posterior to the upper six costal cartilages and intervening internal intercostal muscles. After descending past the 2nd costal cartilage, the internal thoracic artery runs anterior to the transverse thoracic muscle (Figs. 1.13A and 1.17C). Between slips of the transverse thoracic muscle, the artery contacts parietal pleura posteriorly. Terminate in the 6th intercostal space by dividing into the superior epigastric and the musculophrenic arteries. Directly give rise to the anterior intercostal arteries supplying the superior six intercostal spaces.

Ipsilateral pairs of anterior intercostal arteries:       

Supply the anterior parts of the upper 9 intercostal spaces. Pass laterally in the intercostal space, one near the inferior margin of the superior rib and the other near the superior margin of the inferior rib. Of the first 2 intercostal spaces lie initially in the endothoracic fascia between the parietal pleura and the internal intercostal muscles. Supplying the 3rd—6th intercostal spaces are separated from the pleura by slips of the transverse thoracic muscle. Of the 7th—9th intercostal spaces derive from the musculophrenic arteries, also branches of the internal thoracic arteries. Supply the intercostal muscles and send branches through them to supply the pectoral muscles, breasts, and skin. Are absent from the inferior two intercostal spaces; these spaces are supplied only by the posterior intercostal arteries and their collateral branches.

Chapter 1: Thorax

Veins of the Thoracic Wall The intercostal veins accompany the intercostal arteries and nerves and lie most superior in the costal grooves (Figs. 1.13 and 1.18). There are 11 posterior intercostal veins and one subcostal vein on each side. The posterior intercostal veins anastomose with the anterior intercostal veins (tributaries of internal thoracic veins). As they approach the vertebral column, the posterior intercostal veins receive a posterior branch, which accompanies the posterior ramus of the spinal nerve of that level, and an intervertebral vein draining the vertebral venous plexuses. Most posterior intercostal veins (4—11) end in the azygos/hemiazygos venous system, which conveys venous blood to the SVC (see “Vessels and Lymph Nodes of the Posterior Mediastinum” in this chapter). The posterior intercostal veins of the 1st intercostal space usually enter directly into the corresponding and nearby brachiocephalic veins. The posterior intercostal veins of the 2nd and 3rd (and occasionally 4th) intercostal spaces unite to form a trunk, the superior intercostal vein (Fig. 1.60A & B). The right superior intercostal vein is typically the final tributary of the azygos vein, before it enters the SVC. The left superior intercostal vein, however, usually empties into the left brachiocephalic vein. This requires the vein to pass anteriorly along the left side of the superior mediastinum, specifically across the arch of the aorta or the root of the great vessels arising from it and between the vagus and phrenic nerves (Fig. 1.60B). It usually receives the left bronchial veins and may receive the left pericardiacophrenic vein as well. Typically, it communicates inferiorly with the accessory hemiazygos vein. The internal thoracic veins are the companion veins (L. venae comitantes) of the internal thoracic arteries. Figure 1.18. Veins of thoracic wall. Although depicted here as continuous channels, the anterior and posterior intercostal veins are separate vessels, normally draining in opposite directions, the tributaries of which communicate (anastomose) in approximately the anterior axillary line. Because these veins lack valves, however, flow can be reversed.


The Bottom Line The pattern of distribution of neurovascular structures to the thoracic wall reflects the construction of the thoracic cage. These structures course in the intercostal spaces, parallel to the ribs, and serve the intercostal muscles as well as the integument and parietal pleura on their superficial and deep aspects. Because plexus formation does not occur in relationship to the thoracic wall, the pattern of peripheral and segmental (dermatomal) innervation is identical in this region. The intercostal nerves run a posterior to anterior course along the length of each intercostal space, and the anterior and posterior intercostal arteries and veins converge toward and anastomose in approximately the anterior axillary line. The posterior vessels arise from the thoracic aorta and drain to the azygos venous system, and the anterior vessels arise from the internal thoracic artery, branches, and tributaries and drain to the internal thoracic vein, branches, and tributaries.

Breasts Both men and women have breasts (L. mammae); normally they are well developed only in women (Fig. 1.19). The mammary glands in the breasts are accessory to reproduction in women but are rudimentary and functionless in men, consisting of only a few small ducts or epithelial cords. Usually, the fat present in the male breast is not different from that of subcutaneous tissue elsewhere, and the glandular system does not normally develop. The breasts are the most prominent superficial structures in the anterior thoracic wall, especially in women. The mammary glands are in the subcutaneous tissue overlying the pectoralis major and minor muscles. The amount of fat surrounding the glandular tissue determines the size of non‐lactating breasts. At the greatest prominence of the breast is the nipple, surrounded by a circular pigmented area of skin, the areola (L. small area).

Female Breasts The roughly circular body of the female breast rests on a bed that extends transversely from the lateral border of the sternum to the midaxillary line and vertically from the 2nd through 6th ribs. Two thirds of the bed of the breast are formed by the pectoral fascia overlying the pectoralis major; the other third, by the fascia covering the serratus anterior (Figs. 1.19 and 1.20). Between the breast and the pectoral fascia is a loose connective tissue plane or potential space—the retromammary space (bursa). This plane, containing a small amount of fat, allows the breast some degree of movement on the pectoral fascia. A small part of the mammary gland may extend along the inferolateral edge of the pectoralis major toward the axillary fossa (armpit), forming an axillary process or tail (of Spence). Some women discover this (especially when it may enlarge during a menstrual cycle) and become concerned that it may be a lump (tumor) or enlarged lymph nodes. The mammary gland is firmly attached to the dermis of the overlying skin, especially by substantial skin ligaments (L. retinacula cutis), the suspensory ligaments (of Cooper). These condensations of fibrous connective tissue, particularly well developed in the superior part of the gland, help support the mammary gland lobules. During puberty (ages 8—15 years), the breasts normally enlarge, owing in part to glandular development but primarily from increased fat deposition. The areolae and nipples also enlarge. Breast size and shape are determined by genetic, ethnic, and

Chapter 1: Thorax

dietary factors. The lactiferous ducts give rise to buds that form 15—20 lobules of glandular tissue, which constitute the parenchyma of the mammary gland. Each lobule is drained by a lactiferous duct, which usually opens independently on the nipple. The ducts converge toward the nipple like the spokes of a bicycle wheel. Deep to the areola, each duct has a dilated portion, the lactiferous sinus, in which a small droplet of milk accumulates or remains in the nursing mother. As the infant begins to suckle, compression of the areola (and the lactiferous sinus beneath it) expresses the accumulated droplets and encourages the infant to continue nursing as the hormonally mediated let‐down reflex ensues and the mother's milk is secreted into— not sucked from the gland by—the baby's mouth. Figure 1.19. Superficial dissection of female pectoral region. The pectoral fascia has been removed, except where it lies deep to the breast. The bed of the breast extends from the 2nd through the 6th ribs. The axillary tail of the breast extends toward or into the axillary fossa. The non‐lactating breast consists primarily of fat.

Figure 1.20. Sagittal section of female breast and anterior thoracic wall. The breast consists of glandular tissue and fibrous and adipose tissue between the lobes and lobules of glandular tissue, together with blood vessels, lymphatic vessels, and nerves. The superior two thirds of the figure demonstrates the suspensory ligaments and alveoli of the breast with resting mammary gland lobules; the inferior part shows lactating mammary gland lobules.


The areolae contain numerous sebaceous glands, which enlarge during pregnancy and secrete an oily substance that provides a protective lubricant for the areola and nipple, which are particularly subject to chaffing and irritation as mother and baby begin the nursing experience. The nipples are conical or cylindrical prominences in the centers of the areolae. The nipples have no fat, hair, or sweat glands. The tips of the nipples are fissured with the lactiferous ducts opening into them. The nipples are composed mostly of circularly arranged smooth muscle fibers that compress the lactiferous ducts during lactation and erect the nipples in response to stimulation, as when a baby begins to suckle. The mammary glands are modified sweat glands; therefore, they have no special capsule or sheath. The rounded contour and most of the volume of the breasts are produced by subcutaneous fat, except during pregnancy when the mammary glands enlarge and new glandular tissue forms. The milk‐secreting alveoli (L. small hollow spaces) are arranged in grape‐like clusters. In most women, the breasts enlarge slightly during the menstrual period from increased release of the gonadotropic hormones—follicle‐stimulating hormone (FSH) and luteinizing hormone (LH)—on the glandular tissue.

Changes in the Breasts Changes, such as branching of the lactiferous ducts, occur in the breast tissues during menstrual periods and pregnancy (Ferguson et al., 1992). Although mammary glands are prepared for secretion by midpregnancy, they do not produce milk until shortly after the baby is born. Colostrum, a creamy white to yellowish premilk fluid, may secrete from the nipples during the last trimester of pregnancy and during initial episodes of nursing. Colostrum is believed to be especially rich in protein, immune agents, and a growth factor affecting the infant's intestines. In multiparous women, the breasts often become large and pendulous. The breasts in elderly women are usually small because of the decrease in fat and the atrophy of glandular tissue.

Breast Quadrants For the anatomical location and description of tumors and cysts, the surface of the breast is divided into four quadrants (Fig. B1.5). For example, a physician's record might state: “A hard irregular mass was felt in the superior medial quadrant of the breast at the 2 o'clock position, approximately 2.5 cm from the margin of the areola.”

Figure B1.5

Chapter 1: Thorax

Vasculature of the Breast The arterial supply of the breast (Fig. 1.21A & B) derives from the:   

Medial mammary branches of perforating branches and anterior intercostal branches of the internal thoracic artery, originating from the subclavian artery. Lateral thoracic and thoracoacromial arteries, branches of the axillary artery. Posterior intercostal arteries, branches of the thoracic aorta in the 2nd, 3rd, and 4th intercostal spaces.

The venous drainage of the breast is mainly to the axillary vein, but there is some drainage to the internal thoracic vein (Fig. 1.21C). The lymphatic drainage of the breast is important because of its role in the metastasis of cancer cells. Lymph passes from the nipple, areola, and lobules of the gland to the subareolar lymphatic plexus (Fig. 1.22A & B). From this plexus: 

Most lymph (> 75%), especially from the lateral breast quadrants, drains to the axillary lymph nodes, initially to the anterior or pectoral nodes for the most part. However, some lymph may drain directly to other axillary nodes or even to interpectoral, deltopectoral, supraclavicular, or inferior deep cervical nodes. (The axillary lymph nodes are covered in detail in Chapter 6.)


Figure 1.21. Vasculature of breast. A. The mammary gland is supplied from its medial aspect mainly by perforating branches of the internal thoracic artery and by several branches of the axillary artery (principally the lateral thoracic artery) superiorly and laterally. B. The breast is supplied deeply by branches arising from the intercostal arteries. C. Venous drainage is to the axillary (mainly) and internal thoracic veins.

Chapter 1: Thorax

Figure 1.22. Lymphatic drainage of breast. A. The lymph nodes in the region are shown. B. The red arrows indicate lymph flow from the right breast. Most lymph, especially that from the superior lateral quadrant and center of the breast, drains to the axillary lymph nodes, which, in turn, are drained by the subclavian lymphatic trunk and then into the venous system via the right lymphatic duct. C. Most lymph from the left breast returns to the venous system via the thoracic duct, which enters the left venous angle.


Most of the remaining lymph, particularly from the medial breast quadrants, drains to the parasternal lymph nodes or to the opposite breast, whereas lymph from the inferior quadrants may pass deeply to abdominal lymph nodes (subdiaphragmatic inferior phrenic lymph nodes).

Lymph from the skin of the breast, except the nipple and areola, drains into the ipsilateral axillary, inferior deep cervical, and infraclavicular lymph nodes and also into the parasternal lymph nodes of both sides. Lymph from the axillary nodes drains into clavicular (infraclavicular and supraclavicular) lymph nodes and from them into the subclavian lymphatic trunk, which also drains lymph from the upper limb. Lymph from the parasternal nodes enters the bronchomediastinal lymphatic trunk, which also drains lymph from the thoracic viscera. The termination of these lymphatic trunks varies; traditionally, these trunks are described as merging with each other and with the jugular lymphatic trunk, draining the head and neck to form a short right lymphatic duct on the right side or entering the termination at the thoracic duct on the left side. However, in many (perhaps most) cases, the trunks open independently into the junction of the internal jugular and subclavian vein, the venous angle, to form the brachiocephalic veins (Fig. 1.22C). In some cases, they open into both of these veins.

Nerves of the Breast The nerves of the breast derive from anterior and lateral cutaneous branches of the 4th—6th intercostal nerves (Fig. 1.13). The anterior primary rami of T1—T11 are called intercostal nerves because they run within the intercostal spaces. Rami communicantes connect each anterior ramus to a sympathetic trunk. The branches of the intercostal nerves pass through the deep fascia covering the pectoralis major to reach the skin, including the breast in the subcutaneous tissue overlying this muscle. The branches of the intercostal nerves thus convey sensory fibers to the skin of the breast and sympathetic fibers to the blood vessels in the breasts and smooth muscle in the overlying skin and nipple.

Carcinoma of the Breast Understanding the lymphatic drainage of the breasts is of practical importance in predicting the metastasis of carcinoma of the breast (breast cancer). Carcinomas of the breast are malignant tumors, usually adenocarcinomas arising from the epithelial cells of the lactiferous ducts in the mammary gland lobules (Fig. B1.6A). Metastatic cancer cells that enter a lymphatic vessel usually pass through two or three groups of lymph nodes before entering the venous system. Interference with the lymphatic drainage by cancer may cause lymphedema (edema, excess fluid in the subcutaneous tissue), which in turn may result in deviation of the nipple and a thickened, leather‐like appearance of the skin. Prominent or “puffy” skin between dimpled pores give it an orange‐peel appearance (peau d'orange sign). Larger dimples (fingertip size or bigger) result from cancerous invasion of the glandular tissue and fibrosis (fibrous degeneration), which causes shortening or places traction on the suspensory ligaments. Subareolar breast cancer may cause inversion of the nipple by a similar mechanism involving the lactiferous ducts.

Chapter 1: Thorax

Breast cancer typically spreads by means of lymphatic vessels (lymphogenic metastasis), which carry cancer cells from the breast to the lymph nodes, chiefly those in the axilla. The cells lodge in the nodes, producing nests of tumor cells (metastases). Abundant communications among lymphatic pathways and among axillary, cervical, and parasternal nodes may also cause metastases from the breast to develop in the supraclavicular lymph nodes, the opposite breast, or the abdomen. Because most of lymphatic drainage of the breast is to the axillary lymph nodes, they are the most common site of metastasis from a breast cancer. Enlargement of these palpable nodes suggests the possibility of breast cancer and may be key to early detection. However, the absence of enlarged axillary lymph nodes is no guarantee that metastasis from a breast cancer has not occurred because the malignant cells may have passed to other nodes, such as the infraclavicular and supraclavicular lymph nodes. The posterior intercostal veins drain into the azygos/hemiazygos system of veins alongside the bodies of the vertebrae (Fig. 1.31B) and communicate with the internal vertebral venous plexus surrounding the spinal cord. Cancer cells can also spread from the breast by these venous routes to the vertebrae and from there to the cranium and brain. Cancer also spreads by contiguity (invasion of adjacent tissue). When breast cancer cells invade the retromammary space (Fig. 1.20), attach to or invade the deep pectoral fascia overlying the pectoralis major, or metastasize to the interpectoral nodes, the breast elevates when the muscle contracts. This movement is a clinical sign of advanced cancer of the breast. To observe this upward movement, the physician has the patient place her hands on her hips and press while pulling her elbows forward to tense her pectoral muscles.

Mammography Radiographic examination of the breasts, or mammography, is one of the techniques used to detect breast masses (Fig. B1.6B). A carcinoma appears as a large, jagged density in the mammogram (upper two arrows in Fig. B1.6C). The skin is thickened over the tumor. The lower arrow points to the depressed nipple. Surgeons use mammography as a guide when removing breast tumors, cysts, and abscesses.


Figure B1.6

Surgical Incisions of the Breast Incisions are placed in the inferior breast quadrants when possible because these quadrants are less vascular than the superior ones. The transition between the thoracic wall and breast is most abrupt inferiorly, producing a line, crease, or deep skin fold—the inferior cutaneous crease. Incisions made along this crease will be least evident and may actually be hidden by overlap of the breast. Incisions that must be made near the areola or on the breast itself are usually directed radially to either side of the nipple (Langer tension lines run transversely here; see the Introduction) or circumferentially. Mastectomy (breast excision) is not as common as it once was as a treatment for breast cancer. In simple mastectomy, the breast is removed down to the retromammary space. Radical mastectomy, a more extensive surgical procedure, involves removal of the breast, pectoral muscles, fat, fascia, and as many lymph nodes as possible in the axilla and pectoral region. In current practice, often only the tumor and surrounding tissues are removed—a lumpectomy or quadrantectomy (known as breast‐conserving surgery, a wide local excision)—followed by radiation therapy (Goroll, 2000).

Chapter 1: Thorax

Polymastia, Polythelia, and Amastia Polymastia (supernumerary breasts) or polythelia (accessory nipples) may occur superior or inferior to the normal pair, occasionally developing in the axillary fossa or anterior abdominal wall (Figs. B1.7 and SA1.5). Supernumerary breasts usually consist of only a rudimentary nipple and areola, which may be mistaken for a mole (nevus) until they change pigmentation with the normal nipples during pregnancy. However, glandular tissue may also be present and further develop with lactation. Extra breasts may appear anywhere along a line extending from the axilla to the groin—the location of the embryonic mammary ridge (the milk line) from which the breasts develop (Moore and Persaud, 2003), and along which breasts develop in animals with multiple breasts. In either sex, there may be no breast development (amastia), or there may be a nipple and/or areola, but no glandular tissue.

Figure B1.7

Breast Cancer in Men Approximately 1.5% of breast cancers occur in men. As in women, the cancer usually metastasizes to lymph nodes but also to bone, pleura, lung, liver, and skin. Carcinoma of the breast affects approximately 1000 men per year in the United States (Swartz, 2002). A visible and/or palpable subareolar mass or secretion from a nipple may indicate a malignant tumor. Breast cancer in males tends to infiltrate the pectoral fascia, pectoralis major, and apical lymph nodes in the axilla. Although breast cancer is uncommon in men, the consequences are serious because they are frequently not detected until extensive metastases have occurred—for example, in bone.

Gynecomastia Slight temporary enlargement of the breasts is a normal occurrence (frequency = 70%) in males at puberty (age 10—12 years). Breast hypertrophy in males after puberty (gynecomastia) is relatively rare (40 years of age) Less common (one third to one quarter of inguinal hernias)

Exit from abdominal cavity Peritoneum plus transversalis fascia (lies (Fig. B2.3A & B) outside inner one or two fascial coverings of cord) Course (Fig. B2.3C)

Exit from abdominal wall

Passes through or around inguinal canal, usually traversing only medial third of canal, external and parallel to vestige of processus vaginalis anterior Via superficial ring, lateral to cord; rarely enters scrotum

Indirect (Congenital) Patency of processus vaginalis (complete or at least superior part) in younger persons, the great majority of which are males More common (two thirds to three quarters) of inguinal hernias Peritoneum of persistent processus vaginalis plus all three fascial coverings of cord/round ligament Traverses inguinal canal (entire canal if it is of sufficient size) within processus vaginalis Via superficial ring inside cord, commonly passing into scrotum/labium majus

Figure B2.3.

Chapter 2: Abdomen

Cremasteric Reflex Contraction of the cremaster muscle is elicited by lightly stroking the skin on the medial aspect of the superior part of the thigh with an applicator stick or tongue depressor. The ilioinguinal nerve supplies this area of skin. The rapid elevation of the testis on the same side is the cremasteric reflex. This reflex is extremely active in children; consequently, hyperactive cremasteric reflexes may simulate undescended testes. A hyperactive reflex can be abolished by having the child sit in a cross‐legged, squatting position; if the testes are descended, they can then be palpated in the scrotum.

Cysts and Hernias of the Canal of Nuck Indirect inguinal hernias can occur in women; however, they are approximately 20 times more common in men. If the processes vaginalis persists in females, it forms a small peritoneal pouch, known as the canal of Nuck, in the inguinal canal that may extend to the labium majus. In female infants, such remnants can enlarge and form cysts in the inguinal canal. The cysts may produce a bulge in the anterior part of the labium majus and have the potential to develop into an indirect inguinal hernia.

Hydrocele A hydrocele is the presence of excess fluid in a persistent processus vaginalis. This congenital anomaly may be associated with an indirect inguinal hernia. The fluid accumulation results from secretion of an abnormal amount of serous fluid from the visceral layer of the tunica vaginalis. The size of the hydrocele depends on how much of the processus vaginalis persists. A hydrocele of the testis is confined to the scrotum and distends the tunica vaginalis (Fig. B2.4A). A hydrocele of the cord is confined to the spermatic cord and distends the persistent part of the stalk of the processus vaginalis (Fig. B2.4B). A congenital hydrocele of the cord and testis may communicate with the peritoneal cavity.

Figure B2.4.


Detection of a hydrocele requires transillumination, a procedure during which a bright light is applied to the side of the scrotal enlargement in a darkened room. The transmission of light as a red glow indicates excess serous fluid in the scrotum. Newborn male infants often have residual peritoneal fluid in their tunica vaginalis; however, this fluid is usually absorbed during the 1st year of life. Certain pathological conditions, such as injury and/or inflammation of the epididymis, may also produce a hydrocele in adults—a collection of serous fluid in the tunica vaginalis of the testis.

Hematocele A hematocele of the testis is a collection of blood in the tunica vaginalis that results, for example, from rupture of branches of the testicular artery by trauma to the testis (Fig. B2.4C). Trauma may produce a scrotal and/or testicular hematoma (accumulation of blood, usually clotted, in any extravascular location). Blood does not transilluminate; therefore, transillumination can differentiate a hematocele or hematoma from a hydrocele. A hematocele of the testis may be associated with a scrotal hematocele, resulting from effusion of blood into the scrotal tissues.

Torsion of the Spermatic Cord Torsion (twisting) of the spermatic cord is a surgical emergency because the testicle may die. The torsion obstructs the venous drainage, with resultant edema and hemorrhage, and subsequent arterial obstruction. If not untwisted promptly, necrosis of the entire testicle is likely. Testicular torsion may occur at any age, but it is most common during adolescence. The twisting usually occurs just above the superior pole of the testis (Fig. B2.5). A high scrotal incision is made to approach the cord, and the testis and/or cord is rotated as necessary to reduce the torsion. To prevent recurrence or occurrence on the contralateral side, which is likely, both testes are surgically fixed to the scrotal septum.

Figure B2.5.

Chapter 2: Abdomen

The Bottom Line In their passage through the inguinal canal, the processus vaginalis, testis, ductus deferens, and neurovascular structures of the testis (or processus vaginalis and lower ovarian gubernaculum of the female) become engulfed by fascial extensions derived from most (three of four) of the layers traversed. This results in a trilaminar covering. The transversalis fascia, internal oblique, and external oblique layers contribute the internal spermatic fascia, cremasteric muscle and fascia, and external spermatic fascia, respectively, to the spermatic cord. Although the portion of the processus vaginalis within the spermatic cord occludes, that adjacent to the testis remains patent as the tunica vaginalis testis. The contents of the spermatic cord are the duct and neurovascular structures, which trailed the testis as it descended from the posterior abdominal wall during development.

Scrotum The scrotum is a cutaneous sac consisting of two layers: heavily pigmented skin and the closely related dartos fascia, a fat‐free fascial layer including smooth muscle fibers (dartos muscle) responsible for the rugose (wrinkled) appearance of the scrotum (Fig. 2.8B; Table 2.6). Because the dartos muscle attaches to the skin, its contraction causes the scrotum to wrinkle when cold, thickening the integumentary layer while reducing scrotal surface area and assisting the cremaster muscles in holding the testes (testicles) closer to the body, all of which reduces heat loss. The scrotum is divided internally by a continuation of the dartos fascia, the septum of the scrotum, into right and left compartments. The septum is demarcated externally by the scrotal raphe (see Chapter 3), a cutaneous ridge marking the line of fusion of the embryonic labioscrotal swellings (Moore and Persaud, 2003). The superficial dartos fascia of the scrotum is devoid of fat and is continuous anteriorly with the membranous layer of subcutaneous tissue of the abdomen (Scarpa fascia) and posteriorly with the membranous layer of subcutaneous tissue of the perineum (Colles fascia) (Fig. 2.8B). The development of the scrotum is closely related to the formation of the inguinal canals. The scrotum develops from the labioscrotal swellings, two cutaneous outpouchings of the anterior abdominal wall that fuse to form a pendulous cutaneous pouch. Later in the fetal period, the testes and spermatic cords enter the scrotum. The arterial supply of the scrotum (Fig. 2.15) is from the:   

Posterior scrotal branches of the perineal artery: a branch of the internal pudendal artery. Anterior scrotal branches of the deep external pudendal artery: a branch of the femoral artery. Cremasteric artery: a branch of the inferior epigastric artery.

Scrotal veins accompany the arteries. The lymphatic vessels of the scrotum drain into the superficial inguinal lymph nodes. The nerves of the scrotum (Fig. 2.15) include branches of the lumbar plexus to the anterior surface: 

Genital branch of the genitofemoral nerve (L1, L2): supplying the anterolateral surface.


Anterior scrotal nerves: branches of the ilioinguinal nerve (L1) supplying the anterior surface.

The nerves also include branches of the sacral plexus to the posterior and inferior surfaces:  

Posterior scrotal nerves: branches of the perineal branch of the pudendal nerve (S2—S4) supplying the posterior surface. Perineal branches of the posterior femoral cutaneous nerve (S2, S3): supplying the inferior surface.

Anesthetizing the Scrotum The anterior third of the scrotum is supplied by the L1 segment of the spinal cord through the ilioinguinal nerve, and the posterior two thirds of the scrotum are supplied mainly by the S3 spinal segment through the perineal and posterior femoral cutaneous nerves. Therefore, when a spinal anesthetic agent is administered, it must be injected more superiorly to anesthetize the anterior surface of the scrotum than is necessary to anesthetize the posterior surface.

The Bottom Line The scrotum is the integumentary bag formed from the labioscrotal swellings of the male to house the testes after their descent. The fatty layer of subcutaneous tissue of the abdominal wall is replaced in the scrotum by the smooth dartos muscle, whereas the membranous layer is continued as the dartos fascia and scrotal septum. The scrotum receives anterior scrotal arteries from the thigh (via the external pudendal artery), posterior scrotal arteries from the perineum (internal pudendal artery), and internally cremasteric arteries from the abdomen (inferior epigastric artery). Anterior scrotal nerves are derived from the lumbar plexus (via the genitofemoral and ilioinguinal nerves) and posterior scrotal nerves from the sacral plexus (via the pudendal nerve).

Testis The testes (G. orchis) are the male gonads—paired ovoid male reproductive glands that produce the male germ cells (sperms, or spermatozoa) and male hormones, primarily testosterone (Fig. 2.16). The testes are suspended in the scrotum by the spermatic cord, with the left testis (testicle) usually suspended (hanging) more inferiorly than the right testis. The testes have a tough fibrous outer surface, the tunica albuginea, that thickens into a ridge on its internal, posterior aspect as the mediastinum of the testis (Fig. 2.16B). From this internal ridge, fibrous septa extend inward between lobules of minute but long and highly coiled seminiferous tubules in which the sperms are produced. The seminiferous tubules are joined by straight tubules to the rete testis (L. rete, a net), a network of canals in the mediastinum of the testis. The surface of each testis is covered by the visceral layer of the tunica vaginalis, except where the testis attaches to the epididymis and spermatic cord (Fig. 2.16A). The tunica vaginalis is a closed peritoneal sac partially surrounding the testis, which represents the closed‐off distal part of the embryonic processus vaginalis. The visceral layer of the tunica vaginalis is closely applied to the testis, epididymis, and

Chapter 2: Abdomen

inferior part of the ductus deferens. The slit‐like recess of the tunica vaginalis, the sinus of the epididymis, is between the body of the epididymis and the posterolateral surface of the testis. The parietal layer of the tunica vaginalis, adjacent to the internal spermatic fascia, is more extensive than the visceral layer and extends superiorly for a short distance into the distal part of the spermatic cord. The small amount of fluid in the cavity of the tunica vaginalis separates the visceral and parietal layers, allowing the testis to move freely in the scrotum. The long and slender testicular arteries arise from the anterolateral aspect of the abdominal aorta just inferior to the renal arteries (Figs. 2.15 and 2.16B). They pass retroperitoneally (posterior to the peritoneum) in an oblique direction, crossing over the ureters and the inferior parts of the external iliac arteries to reach the deep inguinal rings. They enter the inguinal canals through the deep rings, pass through the canals, exit them through the superficial inguinal rings, and enter the spermatic cords to supply the testes. The testicular artery or one of its branches anastomoses with the artery of the ductus deferens. The veins emerging from the testis and epididymis form the pampiniform venous plexus, a network of 8—12 veins lying anterior to the ductus deferens and surrounding the testicular artery in the spermatic cord. The pampiniform plexus is part of the thermoregulatory system of the testis (along with the cremasteric and dartos muscles) helping keep this gland at a constant temperature. The veins of each pampiniform plexus converge superiorly, forming a right testicular vein, which enters the inferior vena cava (IVC), and a left testicular vein, which enters the left renal vein. The lymphatic drainage of the testis follows the testicular artery and vein to the right and left lumbar (caval/aortic) and preaortic lymph nodes (Fig. 2.15). The autonomic nerves of the testis arise as the testicular plexus of nerves on the testicular artery, which contains vagal parasympathetic and visceral afferent fibers and sympathetic fibers from the T7 segment of the spinal cord.

Epididymis The epididymis is an elongated structure on the posterior surface of the testis (Fig. 2.16). Efferent ductules of the testis transport newly developed sperms to the epididymis from the rete testis. The epididymis is formed by minute convolutions of the duct of the epididymis, so tightly compacted that they appear solid (Fig. 2.16B). The duct becomes progressively smaller as it passes from the head of the epididymis on the superior part of the testis to its tail. At the tail of the epididymis, the ductus deferens begins as the continuation of the epididymal duct. In the lengthy course of this convoluted duct, the sperms are stored and continue to mature. The epididymis consists of the:   

Head of the epididymis: the superior expanded part that is composed of lobules formed by the coiled ends of 12—14 efferent ductules. Body of the epididymis: consists of the convoluted duct of the epididymis. Tail of the epididymis: continuous with the ductus deferens, the duct that transports the sperm from the epididymis to the ejaculatory duct for expulsion via the urethra during ejaculation (see Chapter 3).


Spermatocele and Epididymal Cyst A spermatocele is a retention cyst (collection of fluid) in the epididymis (Fig. B2.6A), usually near its head. Spermatoceles contain a milky fluid and are generally asymptomatic. An epididymal cyst is a collection of fluid anywhere in the epididymis (Fig. B2.6B).

Vestigial Remnants of Embryonic Genital Ducts When the tunica vaginalis is opened, rudimentary structures may be observed at the superior extremities of the testes and epididymis (Fig. B2.7). These structures are small remnants of genital ducts in the embryo (Moore and Persaud, 2003). They are rarely observed unless pathological changes occur. The appendix of the testis is a vesicular remnant of the cranial end of the paramesonephric duct, the embryonic genital duct that in the female forms half of the uterus. It is attached to the superior pole of the testis. The appendices of the epididymis are remnants of the cranial end of the mesonephric duct, the embryonic genital duct that in the male forms part of the ductus deferens, which are attached to the head of the epididymis. This part of the duct, together with the mesonephric tubules associated with it, normally forms the efferent ductules and epididymis.

Varicocele The vine‐like pampiniform plexus of veins may become dilated (varicose) and tortuous, producing a varicocele, which is usually visible only when the man is standing or straining (the enlargement usually disappears when the person lies down, particularly if the scrotum is elevated while supine, allowing gravity to empty the veins). Palpating a varicocele can be likened to feeling a bag of worms. Varicoceles may result from defective valves in the testicular vein, but kidney or renal vein problems can also result in distension of the pampiniform veins. Consequently, it is necessary to rule out kidney or other abdominal causes of varicocele.

Figure B2.6. A. Spermatocele. B. Epididymal cyst.

Chapter 2: Abdomen

Varicocele occurs predominantly (99%) on the left side, probably because the acute angle at which the right vein enters the IVC is more favorable to flow than the nearly right angle at which the left testicular vein enters the left renal vein, making it more susceptible to obstruction or reversal of flow. Patients with the sudden onset of a varicocele, a right‐sided varicocele, or a varicocele that does not reduce in size in the supine position should be suspected of having a retroperitoneal neoplasm in the region of termination of the testicular vein.

Cancer of the Testis and Scrotum Lymphogenous metastasis is common to all testicular tumors, so a knowledge of lymphatic drainage is helpful in treatment (Cotran et al., 1999). Because the testes descend from the posterior abdominal wall to the scrotum during fetal development, their lymphatic drainage differs from that of the scrotum, which is an outpouching of anterolateral abdominal skin (Fig. 2.15). Consequently: 



Cancer of the testis: metastasizes initially to the retroperitoneal lumbar lymph nodes, which lie just inferior to the renal veins; subsequent spread may be to mediastinal and supraclavicular nodes. Cancer of the scrotum: metastasizes to the superficial inguinal lymph nodes, which lie in the subcutaneous tissue inferior to the inguinal ligament and along the terminal part of the great saphenous vein.

However, metastasis of testicular cancer may also occur by hematogenous spread to the lungs, liver, brain, and bone.

Figure B2.7.


The Bottom Line The mature testis is the male gonad, shaped and sized like a large olive or small plum, that produces sperms and male hormones. It is engulfed, except posteriorly and superiorly, by a double‐layered serous sac, derived developmentally from the peritoneum, the tunica vaginalis. The outer surface is covered with the fibrous tunica albuginea, which is thickened internally and posteriorly as the mediastinum of the testis from which septa radiate. Between the septa are the loops of fine seminiferous tubules in which the sperms develop. The tubules converge and empty into the rete testis in the mediastinum, which is connected in turn to the epididymis by the efferent ductules. The innervation, blood vasculature, and lymphatic drainage all reflect the posterior abdominal origin of the testis and are, for the main part, independent of the surrounding scrotal sac. The epididymis is formed of the highly convoluted and compacted epididymal duct leading from the efferent ductules to the ductus deferens. It is the site of sperm storage and maturation. The epididymis clings to the more protected superior and posterior aspects of the testis.

Surface Anatomy of the Anterolateral Abdominal Wall The umbilicus is an obvious feature of the anterolateral abdominal wall and is the reference point for the trans‐umbilical plane (Fig. SA2.1). This puckered indentation of skin in the center of the anterior abdominal wall is typically at the level of the IV disc between the L3 and L4 vertebrae; however, its position varies with the amount of subcutaneous fat present. It indicates the level of the T10 dermatome. The epigastric fossa (pit of the stomach) is a slight depression in the epigastric region, just inferior to the xiphoid process. This fossa is particularly noticeable when a person is in the supine position because the abdominal organs spread out, drawing the anterolateral abdominal wall posteriorly in this region. The pain caused by pyrosis (“heartburn,” resulting from reflux of gastric acid into the esophagus) is often felt at this site. The 7th—10th costal cartilages unite on each side of the epigastric fossa, their medial borders forming the costal margin. Although the abdominal cavity extends higher, the costal margin is the demarcation between the thoracic and abdominal portions of the body wall. When a person is in the supine position, observe the rise and fall of the abdominal wall with respiration: superiorly with inspiration and inferiorly with expiration. The rectus abdominis muscles can be palpated and observed when a supine person is asked to raise the head and shoulders against resistance. The location of the linea alba is visible because of the vertical skin groove superficial to this raphe. The groove is usually obvious because the linea alba is approximately 1 cm wide between the two parts of the rectus abdominis superior to the umbilicus. Inferior to the umbilicus, the linea alba is not indicated by a groove. Some pregnant women, especially those with dark hair and a dark complexion, have a heavily pigmented line, the linea nigra, in the midline skin external to the linea alba. After pregnancy, the color of this line fades.

Chapter 2: Abdomen

Figure SA2.1. The upper margins of the pubic bones (pubic crest) and the cartilaginous joint that unite them (pubic symphysis) can be felt at the inferior end of the linea alba. The inguinal folds are shallow oblique grooves overlying the inguinal ligaments as they extend between the anterior superior iliac spines (ASIS) and the pubic tubercles. The bony iliac crest at the level of L4 vertebra can be easily palpated as it extends posteriorly from the ASIS. The pubic crest, inguinal folds, and iliac crests demarcate the inferior limit of the anterior abdominal wall, distinguishing it from the perineum centrally and the lower limbs (thigh) laterally. The semilunar lines (L. lineae semilunares) are slightly curved, linear impressions in the skin that extend from the inferior costal margin near the 9th costal cartilages to the pubic tubercles. These semilunar skin grooves (5—8 cm from the midline) are clinically important because they are parallel with the lateral edges of the rectus sheath. Skin grooves also overlie the tendinous intersections of the rectus abdominis, which are clearly visible in persons with well‐developed rectus muscles. The interdigitating bellies of the serratus anterior and external oblique muscles are also visible. The site of the inguinal ligament is indicated by the inguinal groove, a skin crease that is parallel and just inferior to the inguinal ligament, which is readily visualized by having the person drop one leg to the floor while lying supine on an examining table. The inguinal groove marks the division between the anterolateral abdominal wall and the thigh.


Peritoneum and Peritoneal Cavity The peritoneum is a continuous, glistening and slippery transparent serous membrane. It lines the abdominopelvic cavity and invests the viscera (Fig. 2.17). The peritoneum consists of two continuous layers: the parietal peritoneum, which lines the internal surface of the abdominopelvic wall, and the visceral peritoneum, which invests viscera such as the stomach and intestines. Both layers of peritoneum consist of mesothelium, a layer of simple squamous epithelial cells. The parietal peritoneum is served by the same blood and lymphatic vasculature and the same somatic nerve supply as is the region of the wall it lines. Like the overlying skin, the peritoneum lining the interior of the body wall is sensitive to pressure, pain, heat and cold, and laceration. Pain from the parietal peritoneum is generally well localized, except for that on the inferior surface of the central part of the diaphragm, where innervation is provided by the phrenic nerve (discussed later in this chapter); irritation here is often referred to the C3—C5 dermatomes over the shoulder. The visceral peritoneum and the organs it covers are served by the same blood and lymphatic vasculature and visceral nerve supply. The visceral peritoneum is insensitive to touch, heat and cold, and laceration; it is stimulated primarily by stretching and chemical irritation. The pain produced is poorly localized, being referred to the dermatomes of the spinal ganglia providing the sensory fibers, particularly to midline portions of these dermatomes. Consequently, pain from foregut derivatives is usually experienced in the epigastric region, that from midgut derivatives in the umbilical region, and that from hindgut derivatives in the pubic region. The peritoneum and viscera are in the abdominopelvic cavity. The relationship of the viscera to the peritoneum is as follows: 



Intraperitoneal organs are almost completely covered with visceral peritoneum (e.g., the stomach and spleen). Intraperitoneal in this case does not mean inside the peritoneal cavity (although the term is used clinically for substances injected into this cavity). Intraperitoneal organs have conceptually, if not literally, invaginated into the closed sac, like pressing your fist into an inflated balloon (see the discussion of potential spaces in the Introduction). Extraperitoneal, retroperitoneal, and subperitoneal organs are also outside the peritoneal cavity—external, posterior, or inferior to the parietal peritoneum— and are only partially covered with peritoneum (usually on just one surface). Organs such as the kidneys are between the parietal peritoneum and the posterior abdominal wall and have parietal peritoneum only on their anterior surfaces (unless fat intervenes). Similarly, the urinary bladder has parietal peritoneum only on its superior surface.

The peritoneal cavity is within the abdominal cavity and continues inferiorly into the pelvic cavity. The peritoneal cavity is a potential space of capillary thinness between the parietal and visceral layers of peritoneum. It contains no organs but contains a thin film of peritoneal fluid, which is composed of water, electrolytes, and other substances derived from interstitial fluid in adjacent tissues. Peritoneal fluid lubricates the peritoneal surfaces, enabling the viscera to move over each other without friction and allowing the movements of digestion. In addition to lubricating

Chapter 2: Abdomen

the surfaces of the viscera, the peritoneal fluid contains leukocytes and antibodies that resist infection. Lymphatic vessels, particularly on the inferior surface of the unceasingly active diaphragm, absorb the peritoneal fluid. The peritoneal cavity is completely closed in males; however, there is a communication pathway in females to the exterior of the body through the uterine tubes, uterine cavity, and vagina. This communication constitutes a potential pathway of infection from the exterior. Figure 2.17. Transverse section of abdomen at level of omental bursa. The orientation figure indicates the level of the section superficially. The dark arrow passes from the greater sac of the peritoneal cavity through the omental (epiploic) foramen and across the full extent of the omental bursa (lesser sac).

Patency and Blockage of the Uterine Tubes While theoretically it is possible for organisms to enter the female peritoneal cavity directly via the uterine tubes, such primary peritonitis is rare, bearing testimony to the effectiveness of the protective mechanisms of the female reproductive tract. A primary mechanism in preventing such infection is a mucous plug that effectively (but not literally) blocks the external opening of the uterus. However, for fertilization to occur, the pathway from the peritoneal cavity to the vaginal orifice must be patent. The patency of the uterine tubes can be tested clinically by means of a technique in which air or radiopaque dye is injected into the uterine cavity, from which it normally flows through the uterine tubes and into the peritoneal cavity (hysterosalpingography; see Chapter 3).

The Peritoneum and Surgical Procedures Because the peritoneum is well innervated, patients undergoing abdominal surgery experience more pain with large, invasive, open incisions of the peritoneum (laparotomy) than they do with small, laparoscopic incisions or vaginal operations. It is the covering of peritoneum (often referred to clinically as the serosa) that makes watertight end‐to‐end anastomoses of intraperitoneal organs, such as the small


intestine, relatively easy to achieve. It is more difficult to achieve watertight anastomoses of extraperitoneal structures that have an outer adventitial layer, such as the thoracic esophagus. Because of the high incidence of complications such as peritonitis and adhesions (see clinical correlation [blue] box “Peritoneal Adhesions and Adhesiotomy,” on this page) after operations in which the peritoneal cavity is opened, efforts are made to remain outside the peritoneal cavity whenever possible (e.g., translumbar or extraperitoneal anterior approach to the kidneys). When opening the peritoneal cavity is necessary, great effort is made to avoid contamination of the cavity.

Peritonitis and Ascites When bacterial contamination occurs during laparotomy or when the gut is traumatically penetrated or ruptured as the result of infection and inflammation (as in appendicitis), allowing gas, fecal matter, and bacteria to enter the peritoneal cavity, the result is infection and inflammation of the peritoneum, called peritonitis. Exudation of serum, fibrin, cells, and pus into the peritoneal cavity occurs, accompanied by pain in the overlying skin and an increase in the tone of the anterolateral abdominal muscles. Given the extent of the peritoneal surfaces and the rapid absorption of material, including bacterial toxins, from the peritoneal cavity, when a peritonitis becomes generalized (widespread in the peritoneal cavity), the condition is dangerous and perhaps lethal. In addition to the severe abdominal pain, tenderness, nausea and/or vomiting, fever, and constipation are present. General peritonitis occurs not only as a result of infection but also when an ulcer perforates the wall of the stomach or duodenum, spilling acid content into the peritoneal cavity. Excess fluid in the peritoneal cavity is called ascitic fluid. The clinical condition in which one has ascitic fluid is referred to as ascites. Ascites may also occur as a result of mechanical injury (which may also produce internal bleeding) or other pathological conditions, such as portal hypertension (venous congestion), widespread metastasis of cancer cells to the abdominal viscera, and starvation (when plasma proteins fail to be produced, altering concentration gradients and producing a paradoxically protuberant abdomen). In all these cases, the peritoneal cavity may be distended with several liters of abnormal fluid, interfering with movements of the viscera. Rhythmic movements of the anterolateral abdominal wall normally accompany respirations. If the abdomen is drawn in as the chest expands (paradoxical abdominothoracic rhythm) and muscle rigidity is present, either peritonitis or pneumonitis (inflammation of the lungs) may be present. Because the intense pain worsens with movement, people with peritonitis commonly lie with their knees flexed to relax their anterolateral abdominal muscles and breath shallowly (and hence more rapidly) reducing the intra‐abdominal pressure and pain.

Peritoneal Adhesions and Adhesiotomy If the peritoneum is damaged, by a stab wound for example, or infected, the peritoneal surfaces become inflamed, making them sticky with fibrin. As healing occurs, the fibrin may be replaced with fibrous tissue, forming abnormal attachments between the visceral peritoneum of adjacent viscera or between the visceral

Chapter 2: Abdomen

peritoneum of a viscus and the parietal peritoneum of the adjacent abdominal wall. Adhesions (scar tissue) may also form after an abdominal operation (e.g., owing to a ruptured appendix) and limit the normal movements of the viscera. This tethering may cause chronic pain or emergency complications such as intestinal obstruction when the gut becomes twisted around an adhesion (volvulus). Adhesiotomy refers to the surgical separation of adhesions. Adhesions are often found during dissection of cadavers (see the adhesion binding the spleen to the diaphragm in Fig. 2.31B, for example).

Abdominal Paracentesis Treatment of generalized peritonitis includes removal of the ascitic fluid and, in the presence of infection, administration of large doses of antibiotics. Occasionally, more localized accumulations of fluid may have to be removed for analysis. Surgical puncture of the peritoneal cavity for the aspiration or drainage of fluid is called paracentesis. After injection of a local anesthetic agent, a needle or trocar and a cannula are inserted through the anterolateral abdominal wall into the peritoneal cavity through the linea alba, for example. The needle is inserted superior to the empty urinary bladder and in a location that avoids the inferior epigastric artery.

Intraperitoneal Injection and Peritoneal Dialysis The peritoneum is a semipermeable membrane with an extensive surface area, much of which (the subdiaphragmatic portions in particular) overlies blood and lymphatic capillary beds; therefore, fluid injected into the peritoneal cavity is absorbed rapidly. For this reason, certain anesthetic agents, such as solutions of barbiturate compounds, may be injected into the peritoneal cavity by intraperitoneal (I.P.) injection. In renal failure, waste products such as urea accumulate in the blood and tissues and ultimately reach fatal levels. Peritoneal dialysis may be performed in which soluble substances and excess water are removed from the system by transfer across the peritoneum, using a dilute sterile solution that is introduced into the peritoneal cavity on one side and then drained from the other side. Diffusible solutes and water are transferred between the blood and the peritoneal cavity as a result of concentration gradients between the two fluid compartments. Peritoneal dialysis is usually employed only temporarily, however, because changes in the mesothelial cells of the peritoneum and in the underlying connective tissue cause it to become progressively ineffective. For the long term it is preferable to use direct blood flow through a renal dialysis machine.

Embryology of the Peritoneal Cavity When it is initially formed, the gut is the same length as the developing body. It undergoes exuberant growth, however, to provide the large absorptive surface required by nutrition, and by the end of the 10th week of development, it is much longer than the body that contains it. For this increase in length to occur, the gut must gain freedom of movement relative to the body wall at an early stage, while still maintaining the connection with it necessary for innervation and blood supply. This growth (and later, the activity of the gut) is accommodated by the development of a


serous cavity within the trunk that houses the increasingly lengthy and convoluted gut in a relatively compact space. The rate of growth of the gut initially outpaces the development of adequate space within the trunk, and for a time the rapidly lengthening gut extends outside the developing body wall (see “Brief Review of the Embryological Rotation of the Midgut,” in this chapter). Early in its development, the embryonic body cavity (intraembryonic coelom) is lined with mesoderm, the primordium of the peritoneum (Moore and Persaud, 2003). At a slightly later stage, the primordial abdominal cavity is lined with parietal peritoneum derived from mesoderm, which forms a closed sac. The lumen of the peritoneal sac is the peritoneal cavity. As the organs develop, they invaginate (protrude) to varying degrees into the peritoneal sac, acquiring a peritoneal covering, the visceral peritoneum. A viscus such as the kidney protrudes only partially into the peritoneal cavity; hence, it is primarily retroperitoneal, always remaining external to the peritoneal cavity and posterior to the peritoneum lining the abdominal cavity. Other viscera, such as the stomach and spleen, protrude completely into the peritoneal sac and are almost completely invested by visceral peritoneum—that is, they are intraperitoneal. These viscera are connected to the abdominal wall by a mesentery of variable length, which is composed of two layers of peritoneum with a thin layer of loose connective tissue between them. Generally, viscera that vary relatively little in size and shape, such as the kidneys, are retroperitoneal, whereas viscera that undergo marked changes in shape owing to filling, emptying and peristalsis, such as the stomach, are invested with visceral pleura. Intraperitoneal viscera with a mesentery, such as most of the small intestine, are mobile, the degree of which varies with the length of the mesentery. Although the liver and spleen do not change shape as a result of intrinsic activity (although they may slowly change in size when engorged with blood), their need for a covering of visceral peritoneum is dictated by the need to accommodate passive changes in position imposed by the adjacent, highly active diaphragm. As organs protrude into the peritoneal sac, their vessels, nerves, and lymphatics remain connected to their extraperitoneal (usually retroperitoneal) sources or destinations so that these connecting structures lie between the layers of the peritoneum forming their mesenteries. Initially, the entire primordial gut is suspended in the center of the peritoneal cavity by a posterior mesentery attached to the midline of the posterior body wall. As the organs grow, they gradually reduce the size of the peritoneal cavity until it is only a potential space between the parietal and the visceral layers of peritoneum. As a consequence, several parts of the gut come to lie against the posterior abdominal wall, and their posterior mesenteries become gradually reduced because of pressure from overlying organs (Fig. 2.18). For example, during development, the growing coiled mass of small intestine pushes the part of the gut that will become the descending colon to the left side and presses its mesentery against the posterior abdominal wall. The mesentery is held there until the layer of peritoneum that formed the left side of the mesentery, and the part of the visceral peritoneum of the colon lying against the body wall, fuse with the parietal peritoneum of the body wall. As a result, the colon becomes fixed to the posterior abdominal wall on the left side with peritoneum covering only its anterior aspect. The descending colon (as well as the ascending colon on the right side) has thus become secondarily retroperitoneal, having once been intraperitoneal.

Chapter 2: Abdomen

The layers of peritoneum that fused now form a fusion fascia, a connective tissue plane in which the nerves and vessels of the descending colon continue to lie. Thus the descending colon of the adult can be freed from the posterior body wall (surgically mobilized) by incising the peritoneum along the lateral border of the descending colon and then bluntly dissecting along the plane of the fusion fascia, elevating the neurovascular structures from the posterior body wall until the midline is reached. The ascending colon can be similarly mobilized on the right side. Several parts of the digestive tract and associated organs become secondarily retroperitoneal (e.g., most of the duodenum and pancreas as well as the ascending and descending parts of the colon). They are covered with peritoneum only on their anterior surface. Other parts of the viscera (e.g., the sigmoid colon and spleen) retain a short mesentery. However, the roots of the short mesenteries do not remain attached to the midline but shift to the left or right by a fusion process like that described for the descending colon.

The Bottom Line The peritoneum is a continuous, serous membrane that lines the abdominopelvic cavity (the parietal peritoneum) and the contained viscera (the visceral peritoneum). The collapsed peritoneal cavity between these layers normally contains only enough peritoneal fluid (about 50 mL) to lubricate the inner surface of the membrane. This arrangement allows the gut the freedom of movement required for alimentation. Adhesions formed as a result of infection or injury interfere with these movements. The parietal pleura is a sensitive, semipermeable membrane, with blood and lymphatic capillary beds especially abundant deep to its subdiaphragmatic surface. Figure 2.18. Migration and fusion of d e s ce n d in g mesocolon. Starting from t h e p r i m o rd i a l p o s i t i o n , suspended from the m i d l i n e o f t h e p o s t e r io r a b d o m in a l w a l l ( A ) , t h e mesocolon shifts to the left (B) and gradually fuses w i t h t h e l e f t p o s t e r io r p a r i e t a l p e r it o n e u m ( C ) . D . The descending colon has become secondarily r e t r o p e r i t o n e a l . T h e a r ro w i n d i c a t e s t h e l e f t p a r a c o l ic g u t t e r , t h e s i t e w h e re a n i n c i s i o n i s m a d e d u r i n g m o b i l i z a t i o n o f t h e c o l o n d u r i n g s u rg e r y . S o m e t i m e s t h e d e s c e n d in g c o l o n r e t a i n s a s h o r t m e s e n te r y , s i m i l a r to t h e s t a g e s h o w n i n p a r t C , e s p e c i a l l y w h e r e t h e c o l o n i s i n th e il i a c f o s s a .


Peritoneal Formations The peritoneal cavity has a complex shape. Some of the facts relating to this include the following:  



The peritoneal cavity houses a great length of gut, most of which is covered with peritoneum. Extensive continuities are required between the parietal and visceral peritoneum to convey the necessary neurovascular structures from the body wall to the viscera. Although the volume of the abdominal cavity is a fraction of the body's volume, the parietal and visceral peritoneum lining the peritoneal cavity within it have a much greater surface area than the body's outer surface (skin); therefore, the peritoneum must be highly convoluted.

Various terms are used to describe the parts of the peritoneum that connect organs with other organs or to the abdominal wall, and the compartments and recesses that are formed as a consequence. A mesentery is a double layer of peritoneum that occurs as a result of the invagination of the peritoneum by an organ and constitutes a continuity of the visceral and parietal peritoneum. It provides a means for neurovascular communication between the organ and the body wall (Fig. 2.19A & E). A mesentery connects an intraperitoneal organ to the body wall—usually the posterior abdominal wall (e.g., the mesentery of the small intestine). The small intestine mesentery is usually referred to simply as “the mesentery” ; however, mesenteries related to other specific parts of the alimentary tract are named accordingly—for example, the transverse and sigmoid mesocolons (Fig. 2.19B), mesoesophagus, mesogastrium, and mesoappendix. Mesenteries have a core of connective tissue containing blood and lymphatic vessels, nerves, lymph nodes, and fat (Table 2.9, fig. A). An omentum is a double‐layered extension or fold of peritoneum that passes from the stomach and proximal part of the duodenum to adjacent organs in the abdominal cavity (Fig. 2.19). 



The greater omentum is a prominent peritoneal fold that hangs down like an apron from the greater curvature of the stomach and the proximal part of the duodenum (Fig. 2.19A, C, & E). After descending, it folds back and attaches to the anterior surface of the transverse colon and its mesentery. The lesser omentum connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver (Fig. 2.19B & D); it also connects the stomach to a triad of structures that run between the duodenum and liver in the free edge of the lesser omentum (Fig. 2.17).

A peritoneal ligament consists of a double layer of peritoneum that connects an organ with another organ or to the abdominal wall.

Chapter 2: Abdomen

F i g u re 2 . 1 9 . P r i n c i p a l fo rm a t i o n s o f p e r i t o n e u m . A . I n t h i s a n t e r i o r v i e w o f t h e o p e n e d p e r i t o n e a l ca v i t y , p a r t s o f t h e g r e a te r o m e n t u m , t r a n s v e rs e c o l o n , a n d t h e s m a l l i n te s t i n e a n d i ts m e s e n te r y h a v e b e e n c u t a w a y t o r e v e a l d e e p s t r u c t u r e s a n d t h e l a y e rs o f t h e m e s e n t e r i c s t r u c t u r e s . T h e m e s e n t e ry o f t h e j e j u n u m a n d i l e u m ( s m a l l i n t e s t i n e ) a n d s i g m o i d m e s o c o l o n h a v e b e e n c u t c l o s e t o th e i r p a r i e t a l a t t a c h m e n t s . B . T h e m e d i a n s e c t i o n o f t h e a b d o m i n o p e lv i c c a v i t y o f a m a l e s h o w s t h e r e l a t i o n s h ip s o f th e p e r i t o n e a l a t t a c h m e n ts . C . T h e g r e a te r o m e n tu m i s s h o w n i n i t s “ n o r m a l ” p o s i t i o n , c o v e r i n g m o s t o f t h e a b d o m i n a l v i s c e r a . D . T h e l e s s e r o m e n t u m , a t t a c h i n g t h e l i v e r t o t h e l e s s e r c u rv a t u r e o f t h e s t o m a ch , i s s h o wn b y r e f l e c t i n g t h e l i v e r a n d g a l l b l a d d e r s u p e r i o r l y . T h e g r e a t e r om e n tu m h a s b e e n r e m o v e d f r o m t h e g r e a t e r c u r v a tu r e o f t h e s to m a c h a n d t r a n s v e rs e c o l o n t o r e v e a l t h e in t e s t i n e s . E. T h e g r e a te r o m e n t u m h a s b e e n r e f l e c t e d s u p e r i o r l y a n d t h e s m a l l in t e s t i n e h a s b e e n re t r a c t e d t o t h e r ig h t s i d e t o r e v e a l t h e m e s e n te r y o f t h e s m a l l i n t e s t i n e a n d t h e m e s e n t e r y o f t h e t r a n s v e r s e c o l o n ( t r a n s v e rs e m e s o c o l o n ) .


The liver is connected to the:   

Anterior abdominal wall by the falciform ligament (Fig. 2.20). Stomach by the hepatogastric ligament, the membranous portion of the lesser omentum. Duodenum by the hepatoduodenal ligament, the thickened free edge of the lesser omentum, which conducts the portal triad: portal vein, hepatic artery, and bile duct (Fig. 2.17).

The hepatogastric and hepatoduodenal ligaments are continuous parts of the lesser omentum and are separated only for descriptive convenience (Fig. 2.20). Figure 2.20. Parts of greater and lesser omenta. The blue arrows indicate that the liver and gallbladder have been reflected superiorly. The central part of the greater omentum has been cut out to show its relation to the transverse colon and mesocolon. The term greater omentum is often used as a synonym for the gastrocolic ligament, but it actually also includes the gastrosplenic and gastrophrenic ligaments, all of which have a continuous attachment to the greater curvature of the stomach. The hepatoduodenal ligament (free edge of the lesser omentum) conveys the portal triad: hepatic artery, bile duct, and portal vein.

The stomach is connected to the:   

Inferior surface of the diaphragm by the gastrophrenic ligament. Spleen by the gastrosplenic ligament (gastrolienal ligament), which reflects to the hilum of the spleen. Transverse colon by the gastrocolic ligament, the apron‐like part of the greater omentum, which descends from the greater curvature, turns under, and then ascends to the transverse colon.

Chapter 2: Abdomen

These structures have a continuous attachment along the greater curvature, and are all part of the greater omentum, separated only for descriptive purposes. Although intraperitoneal organs may be almost entirely covered with visceral peritoneum, every organ must have an area that is not covered to allow the entrance or exit of neurovascular structures. Such areas are called bare areas, formed in relation to the attachments of the peritoneal formations to the organs, including mesenteries, omenta, and ligaments that convey the neurovascular structures. A peritoneal fold is a reflection of peritoneum that is raised from the body wall by underlying blood vessels, ducts, and obliterated fetal vessels (e.g., the medial and lateral umbilical folds on the internal surface of the anterolateral abdominal wall). Some peritoneal folds contain blood vessels and bleed if cut, such as the lateral umbilical folds, which contain the inferior epigastric arteries (see “Vessels of the Anterolateral Abdominal Wall,” in this chapter). A peritoneal recess, or fossa, is a pouch of peritoneum that is formed by a peritoneal fold (e.g., the inferior recess of the omental bursa between the layers of the greater omentum and the supravesical and umbilical fossae between the umbilical folds).

Functions of the Greater Omentum The greater omentum, large and fat laden, prevents the visceral peritoneum from adhering to the parietal peritoneum. It has considerable mobility and moves around the peritoneal cavity with peristaltic movements of the viscera. It often forms adhesions adjacent to an inflamed organ such as the appendix, sometimes walling it off and thereby protecting other viscera from it. Thus it is common when entering the abdominal cavity, in either dissection or surgery, to find the omentum markedly displaced from the “normal” position in which it is almost always depicted in anatomical illustrations. The greater omentum also cushions the abdominal organs against injury and forms insulation against loss of body heat.

Abscess Formation Perforation of a duodenal ulcer, rupture of the gallbladder, or perforation of the appendix may lead to the formation of a circumscribed collection of purulent exudate in the subphrenic recess. The abscess may be walled inferiorly by adhesions (see clinical correlation [blue] box “Subphrenic Abscesses,” in this chapter).

Spread of Pathological Fluids Peritoneal recesses are of clinical importance in connection with the spread of pathological fluids such as pus, a product of inflammation. The recesses determine the extent and direction of the spread of fluids that may enter the peritoneal cavity when an organ is diseased or injured (see also other clinical correlation [blue] boxes in this chapter).

Subdivisions of the Peritoneal Cavity After the rotation and development of the greater curvature of the stomach during development (see clinical correlation [blue] box “Brief Review of the Embryological Rotation of the Midgut,” in this chapter), the peritoneal cavity is divided into the


greater and lesser peritoneal sacs (Fig. 2.21A). The greater sac is the main and larger part of the peritoneal cavity. A surgical incision through the anterolateral abdominal wall enters the greater sac. The omental bursa (lesser sac) lies posterior to the stomach and lesser omentum. The transverse mesocolon (mesentery of the transverse colon) divides the abdominal cavity into a supracolic compartment, containing the stomach, liver, and spleen, and an infracolic compartment, containing the small intestine and ascending and descending colon. The infracolic compartment lies posterior to the greater omentum and is divided into right and left infracolic spaces by the mesentery of the small intestine (Fig. 2.21B). Free communication occurs between the supracolic and the infracolic compartments through the paracolic gutters, the grooves between the lateral aspect of the ascending or descending colon and the posterolateral abdominal wall.

Flow of Ascitic Fluid and Pus The paracolic gutters are of considerable clinical importance because they provide pathways for the flow of ascitic fluid and the spread of intraperitoneal infections (Fig. 2.21B). Purulent material (consisting of or containing pus) in the abdomen can be transported along the paracolic gutters into the pelvis, especially when the person is upright. Thus, to facilitate the flow of exudate into the pelvic cavity where absorption of toxins is slow, patients with peritonitis are often placed in the sitting position (at least a 45° angle). Conversely, infections in the pelvis may extend superiorly to a subphrenic recess situated under the diaphragm (see clinical correlation [blue] box “Subphrenic Abscesses,” in this chapter), especially when the person is supine. Similarly, the paracolic gutters provide pathways for the spread of tumor cells that have sloughed from the ulcerated surface of a tumor and entered the peritoneal cavity. Figure 2.21. Subdivisions of peritoneal cavity. A. This median section of the abdominopelvic cavity shows the subdivisions of the peritoneal cavity. B. The supracolic and infracolic compartments of the greater sac are shown after removal of the greater omentum. The infracolic spaces and paracolic gutters determine the flow of ascitic fluid (arrows) when inclined or upright.

Chapter 2: Abdomen

The omental bursa is an extensive sac‐like cavity that lies posterior to the stomach, lesser omentum, and adjacent structures (Figs. 2.21A, 2.22B, and 2.23). The omental bursa has a superior recess, limited superiorly by the diaphragm and the posterior layers of the coronary ligament of the liver, and an inferior recess between the superior parts of the layers of the greater omentum (Fig. 2.23A). The omental bursa permits free movement of the stomach on the structures posterior and inferior to it because the anterior and posterior walls of the omental bursa slide smoothly over each other. Most of the inferior recess of the bursa becomes sealed off from the main part posterior to the stomach after adhesion of the anterior and posterior layers of the greater omentum (Fig. 2.23B). The omental bursa communicates with the greater peritoneal sac through the omental foramen (epiploic foramen), an opening situated posterior to the free edge of the lesser omentum (hepatoduodenal ligament). The omental foramen can be located by running a finger along the gallbladder to the free edge of the lesser omentum (Fig. 2.22A). The omental foramen usually admits two fingers. The boundaries of the omental foramen are  Anteriorly: the hepatoduodenal ligament (free edge of the lesser omentum), containing the portal vein, hepatic artery, and bile duct (Fig. 2.22B).  Posteriorly: the IVC and right crus of the diaphragm, covered anteriorly with parietal peritoneum (they are retroperitoneal).  Superiorly: the liver, covered with visceral peritoneum (Fig. 2.23).  Inferiorly: the superior or first part of the duodenum.

Fluid in the Omental Bursa Perforation of the posterior wall of the stomach results in the passage of its fluid contents into the omental bursa. An inflamed or injured pancreas can also result in the passage of pancreatic fluid into the bursa, forming a pancreatic pseudo‐cyst.

Intestine in the Omental Bursa Although uncommon, a loop of small intestine may pass through the omental foramen into the omental bursa and be strangulated by the edges of the foramen. As none of the boundaries of the foramen can be incised because each contains blood vessels, the swollen intestine must be decompressed using a needle so it can be returned to the greater peritoneal sac through the omental foramen.

Severance of the Cystic Artery The cystic artery must be ligated or clamped and then severed during cholecystectomy, removal of the gallbladder. Sometimes, however, it is accidentally severed before it has been adequately ligated. The surgeon can control the hemorrhage by compressing the hepatic artery as it traverses the hepatoduodenal ligament. The index finger is placed in the omental foramen and the thumb on its anterior wall (Fig. 2.22). Alternate compression and release of pressure on the hepatic artery allows the surgeon to identify the bleeding artery and clamp it.


Figure 2.22. Omental (epiploic) foramen and omental bursa. A. The index finger is passing from the greater sac through the omental foramen into the omental bursa (lesser sac). B. The hepatic artery is being compressed between the index finger (passing through the omental foramen into the omental bursa) and the thumb (on the anterior wall of the foramen).

Chapter 2: Abdomen

Figure 2.23. W alls and recesses of omental bursa. A. This section of the abdomen of an infant shows that the omental bursa (lesser sac) is an isolated part of the peritoneal cavity, lying dorsal to the stomach and extending superiorly to the liver and diaphragm (superior recess of the omental bursa) and inferiorly between the layers of the greater omentum (inferior recess of the omental bursa). B. This section shows the abdomen of an adult after fusion of the layers of the greater omentum. The inferior recess of the omental bursa now extends inferiorly only as far as the transverse colon because of the fused layers of the greater omentum. The red arrows pass from the greater sac through the omental (epiploic) foramen into the omental bursa.

The Bottom Line Continuities and connections between the visceral and the parietal peritoneum occur where the gut enters and exits the abdominopelvic cavity. They also occur as double folds (mesenteries and omenta, and subdivisions called ligaments) that convey neurovascular structures and the ducts of accessory organs to and from the viscera. Peritoneal ligaments are named for the particular structures connected by them. As a result of the rotation and exuberant growth of the gut during development, the disposition of the peritoneal cavity becomes complex. The main part of the peritoneal cavity (the greater sac) is divided by the transverse mesocolon into supracolic and infracolic compartments. A smaller part of the cavity, the omental bursa (lesser sac) lies posterior to the stomach, separating it from retroperitoneal viscera on the posterior wall. It communicates with the greater sac via the omental foramen. The complex disposition of the peritoneal cavity determines the flow and pooling of excess (ascitic) fluid occupying the peritoneal cavity during pathological conditions.

Abdominal Viscera The principal viscera of the abdomen are the terminal part of the esophagus and the stomach, intestines, spleen, pancreas, liver, gallbladder, kidneys, and suprarenal (adrenal) glands (Figs. 2.24 and 2.25). When the abdominal cavity is opened to study these organs, it becomes evident that the liver, stomach, and spleen almost fill the domes of the diaphragm. By thus indenting the thoracic cavity, they receive protection from the lower thoracic cage. It is also seen that the falciform ligament normally attaches along a continuous line to the anterior abdominal wall as far


inferiorly as the umbilicus and divides the liver superficially into right and left lobes. The fat‐laden greater omentum, when in its typical position, conceals almost all of the intestine. The gallbladder projects inferior to the sharp border of the liver (Fig. 2.25A). Figure 2.24. Overview of thoracic and abdominal viscera. A and B. Some abdominal organs extend superiorly into the thoracic cage (rib cage) and are protected by it. A large part of the small intestine is in the pelvis, and the right kidney is lower than the left kidney, owing to the mass of the liver on the right side. The appendix projects posteriorly and inferomedially toward the pelvic brim; consequently, it is visible only in the posterior view.

Chapter 2: Abdomen

Figure 2.25. Abdominal contents in situ and in relation to alimentary system. A. The undisturbed abdominal contents are shown. The anterior abdominal and thoracic walls are cut away. The fundus of the gallbladder projects inferior to the sharp, inferior border of the liver. The falciform ligament (Falc. lig.) is severed at its attachment to the anterior abdominal wall. B. An overview of the alimentary system (gastrointestinal tract and accessory glands, the liver, and the pancreas) is presented.

Food passes from the mouth and pharynx through the esophagus to the stomach, where it mixes with gastric secretions (Fig. 2.25B). Digestion mostly occurs in the stomach and duodenum. Peristalsis, a series of ring‐like contraction waves that begin around the middle of the stomach and move slowly toward the pylorus, is responsible for mixing the masticated (chewed) food mass with gastric juices and for emptying the contents of the stomach into the duodenum. Absorption of chemical compounds occurs principally in the small intestine, a coiled 5‐ to 6‐m‐long tube (shorter in life, when tonus is present, than in the cadaver) consisting of the duodenum, jejunum, and ileum. Peristalsis also occurs in the jejunum and ileum; however, it is not forceful unless an obstruction is present. The stomach is continuous with the duodenum, which receives the openings of the ducts from the pancreas and liver (major glands of the digestive tract). The large intestine consists of the cecum (which receives the terminal part of the ileum), appendix, colon (ascending, transverse, descending, and sigmoid), rectum, and anal canal (which ends at the anus). Most reabsorption of water occurs in the ascending colon. Feces form in the descending and sigmoid colon and accumulate in the rectum before defecation. The esophagus, stomach, and intestine constitute the alimentary (digestive) tract and are derived from the primordial foregut, midgut, and hindgut. The arterial supply to the alimentary tract is from the abdominal aorta. The three major branches of the aorta supplying the gut are the celiac trunk and the superior and inferior mesenteric arteries (Fig. 2.26A).


The portal vein (Fig. 2.26B), formed by the union of the superior mesenteric and splenic veins, is the main channel of the portal venous system, which collects blood from the abdominal part of the alimentary tract, pancreas, spleen, and most of the gallbladder and carries it to the liver.

Esophagus The esophagus is a muscular tube (approximately 25 cm [10 in.] long) with an average diameter of 2 cm that conveys food from the pharynx to the stomach (Fig. 2.27A). As seen under fluoroscopy after a barium swallow, the esophagus normally has three constrictions where adjacent structures produce impressions (see “Medical Imaging of the Abdomen,” in this chapter): 





Cervical constriction: at its beginning at the pharyngoesophageal junction, approximately 15 cm from the incisor teeth; caused by the cricopharyngeus muscle (see Chapter 8); referred to clinically as the upper esophageal sphincter. Thoracic (broncho‐aortic) constriction: a compound constriction where it is first crossed by the arch of the aorta, 22.5 cm from the incisor teeth, and then where it is crossed by the left main bronchus, 27.5 cm from the incisor teeth; the former is seen in anteroposterior views, the latter in lateral views. Diaphragmatic constriction: where it passes through the esophageal hiatus of the diaphragm, approximately 40 cm from the incisor teeth.

Awareness of these constrictions is important when passing instruments through the esophagus into the stomach (Williams et al., 1995) and when viewing radiographs of patients who are experiencing dysphagia (difficulty in swallowing). The esophagus:  







Follows the curve of the vertebral column as it descends through the neck and mediastinum—the median partition of the thoracic cavity (Fig. 2.27A). Has internal circular and external longitudinal layers of muscle (Fig. 2.27B). In its superior third, the external layer consists of voluntary striated muscle; the inferior third is composed of smooth muscle, and the middle third is made up of both types of muscle. Passes through the elliptical esophageal hiatus in the muscular right crus of the diaphragm, just to the left of the median plane at the level of the T10 vertebra. Terminates by entering the stomach at the cardial orifice of the stomach (Fig. 2.27C) to the left of the midline at the level of the 7th left costal cartilage and T11 vertebra. Is encircled by the esophageal nerve plexus distally (Fig. 2.28).

Food passes through the esophagus rapidly because of the peristaltic action of its musculature, aided by but not dependent on gravity (one can still swallow if inverted). The esophagus is attached to the margins of the esophageal hiatus in the diaphragm by the phrenicoesophageal ligament (Fig. 2.27C), an extension of inferior

Chapter 2: Abdomen

diaphragmatic fascia. This ligament permits independent movement of the diaphragm and esophagus during respiration and swallowing. The trumpet‐shaped abdominal part of the esophagus, only 1.25 cm long, passes from the esophageal hiatus in the right crus of the diaphragm to the cardial (cardiac) orifice of the stomach, widening as it approaches, passing anteriorly and to the left as it descends inferiorly. Its anterior surface is covered with peritoneum of the greater sac, continuous with that covering the anterior surface of the stomach. It fits into a groove on the posterior (visceral) surface of the liver. The posterior surface of the esophagus is covered with peritoneum of the omental bursa, continuous with that covering the posterior surface of the stomach. The right border of the esophagus is continuous with the lesser curvature of the stomach; however, its left border is separated from the fundus of the stomach by the cardial notch. The esophagogastric junction lies to the left of the T11 vertebra on the horizontal plane that passes through the tip of the xiphoid process. Surgeons and endoscopists designate the Z‐line, a jagged line where the mucosa abruptly changes from esophageal to gastric mucosa, as the junction. Immediately superior to this junction, the diaphragmatic musculature forming the esophageal hiatus functions as a physiological inferior esophageal sphincter that contracts and relaxes. Radiological studies show that food stops here momentarily and that the sphincter mechanism is normally efficient in preventing reflux of gastric contents into the esophagus. When one is not eating, the lumen of the esophagus is normally collapsed superior to this level to prevent food or stomach juices from regurgitating into the esophagus. Details concerning the neurovasculature of the cervical and thoracic portions of the esophagus are provided in Chapters 1 and 8. The arterial supply of the abdominal part of the esophagus is from the left gastric artery, a branch of the celiac trunk, and the left inferior phrenic artery (Fig. 2.26A). The venous drainage from the submucosal veins of this part of the esophagus is both to the portal venous system through the left gastric vein (Fig. 2.26B) and into the systemic venous system through esophageal veins entering the azygos vein. The lymphatic drainage of the abdominal part of the esophagus is into the left gastric lymph nodes (Fig. 2.28); efferent lymphatic vessels from these nodes drain mainly to celiac lymph nodes. The esophagus is innervated by the esophageal nerve plexus, formed by the vagal trunks (becoming anterior and posterior gastric branches) and the thoracic sympathetic trunks via the greater (abdominopelvic) splanchnic nerves and periarterial plexuses around the left gastric and inferior phrenic arteries. (For an overview of the innervation of the abdominal organs, see “Summary of the Innervation of the Abdominal Viscera,” in this chapter.)


Figure 2.26. Arterial supply and venous drainage of GI tract. A. The arterial supply is demonstrated. B. The venous drainage is shown. The portal vein drains poorly oxygenated, nutrient‐rich blood from the gastrointestinal tract, spleen, pancreas, and gallbladder to the liver. The black arrow indicates the communication of the esophageal vein with the azygos (systemic) venous system.

Chapter 2: Abdomen

F i g u re 2 . 2 7 . T h e e s o p h a g u s a n d i t s r e l a t i o n s h i p s . A . T h e l a te r a l v ie w s h o w s t h e e s o p h a g u s a n d r e l a t e d s t r u c t u r e s ( t r a ch e a , v e r te b ra l c o l u m n , d e s ce n d in g a o r t a , a n d s t o m a c h ) . T h e e s o p h a g u s b e g in s a t t h e l e v e l o f th e p a l p a b le c r i c o i d c a r t i l a g e a n d d e s c e n d s p o s t e r i o r to t h e t ra c h e a . I t le av e s t h e t h o r a x th r o u g h t h e e s o p h a g e a l h i a t u s o f t h e d i a p h ra g m . B . T h e t r a n s v e r s e s e c t i o n o f t h e e s o p h a g u s s h o w s t h e m u s c u l a r a n d m u c o s a l l a y e rs o f i t s w a l l . C . A c o r o n a l s e c t i o n o f th e i n f e r i o r e s o p h a g u s , d i a p h r a g m , a n d s u p e r i o r s to m a c h i s s h o w n . T h e p h r e n i c o e s o p h a g e a l l i g a m e n t c o n n e c t s t h e e s o p h a g u s f l e x i b l y to t h e d i a p h r a g m ; i t l i m i t s u p w a r d m o v e m e n t o f t h e e s o p h a g u s w h i l e p e r m i t t i n g s o m e m o v e m e n t d u r i n g s w a ll o w i n g a n d re s p i r a t i o n .

Clinically Oriented Anatomy, 5th Edition By Keith Moore Figure 2.28. Nerves and lymphatics of abdominal esophagus and s t o m a c h . T h e r i g h t a n d le f t v a g u s nerves (CN X) divide into branches that form the esophageal plexus around the inferior esophagus. A n t e r i o r a n d p o s t e r i o r g a s t r i c b r a n c h e s o f t h e p le x u s a c c o m p a n y the esophagus through th e e s o p h a g e a l h i a t u s f o r d is t r i b u t i o n t o t h e a n te r i o r a n d p o s t e r i o r aspects of the stomach. The anterior branches also extend to t h e p y l o r u s a n d l i v e r . P o s t s y n a p t i c sympathetic nerve fibers from the c e l i a c p l e x u s a r e d is t r i b u t e d t o these organs through periarterial plexuses. The lymphatic vessels of t h e s t o m a ch f o l l o w a p a t t e r n s i m i l a r t o t h a t o f th e a r t e r i e s , although the flow is in the o p p o s i te d i re c t i o n . T h u s , l y m p h f r o m t h e s to m a c h a n d a b d o m in a l p a r t o f t h e e s o p h a g u s d ra i n s t o t h e gastric and then celiac lymph nodes.

Esophageal Varices Because the submucosal veins of the inferior esophagus drain to both the portal and the systemic venous systems, they constitute a portosystemic anastomosis. In portal hypertension (an abnormally increased blood pressure in the portal venous system), blood is unable to pass through the liver via the portal vein, causing a reversal of flow in the esophageal tributary. The large volume of blood causes the submucosal veins to enlarge markedly, forming esophageal varices (Fig. B2.8). These distended collateral channels may rupture and cause severe hemorrhage that is life‐threatening and difficult to control surgically. Esophageal varices commonly develop in alcoholics who have developed cirrhosis (fibrous scarring) of the liver (see clinical correlation [blue] box “Cirrhosis of the Liver,” in this chapter).

Figure B2.8.

Chapter 2: Abdomen

Pyrosis Pyrosis, or heartburn, is the most common type of esophageal discomfort or substernal pain. This burning sensation in the abdominal part of the esophagus is usually the result of regurgitation of small amounts of food or gastric fluid into the lower esophagus (gastroesophageal reflux disorder; GERD). Pyrosis (G. burning) may also be associated with hiatal (hiatus) hernia (see clinical correlation [blue] box “Hiatal Hernia,” in this chapter). As indicated by its common name, heartburn, pyrosis is commonly perceived as a “chest” (vs. abdominal) sensation. As mentioned in Chapter 1, determining the nature and source of chest pains can be one of the more challenging aspects of physical diagnosis.

The Bottom Line The esophagus is a tubular conveyer of food, delivering it from the pharynx to the stomach. It penetrates the diaphragm at the T10 vertebral level, passing through its right crus, which decussates around it to form the physiological inferior esophageal sphincter. The trumpet‐shaped abdominal part, composed entirely of smooth muscle innervated by the esophageal nerve plexus, enters the cardial part of the stomach. It receives blood from esophageal branches of the left gastric artery (from the celiac trunk). Its submucosal veins drain to both the systemic and the portal venous systems and thus constitute portocaval anastomoses that may become varicose in the presence of portal hypertension. Internally, in the living, the esophagus is demarcated from the stomach by an abrupt mucosal transition, the Z‐line.

Stomach The stomach is the expanded part of the alimentary tract between the esophagus and the small intestine (Fig. 2.25B). It is specialized for the accumulation of ingested food, which it chemically and mechanically prepares for digestion and passage into the duodenum. In most people, the shape of the stomach resembles the letter J; however, the shape and position of the stomach can vary markedly in persons of different body types (bodily habitus) and even in the same individual as a result of diaphragmatic movements during respiration, the stomach's contents, and the position of the person (i.e., whether lying down or standing) (Fig. 2.29). The stomach acts as a food blender and reservoir; its chief function is enzymatic digestion. The gastric juice gradually converts a mass of food into a semiliquid mixture, chyme (G. juice), which passes fairly quickly into the duodenum. An empty stomach is only of slightly larger caliber than the large intestine; however, it is capable of considerable expansion and can hold 2—3 L of food. A newborn infant's stomach, approximately the size of a lemon, can expand to hold up to 30 mL of milk.


Figure 2.29. Effect of body type (bodily habitus) on disposition and shape of stomach. A. A heavily built hyper‐sthenic individual with short thorax and long abdomen is likely to have a stomach that is placed high and more transversely disposed. B. In those with a slender asthenic physique, the stomach is low and vertical.

Parts of the Stomach The stomach has four parts (Fig. 2.30A):  



Cardia: the part surrounding the cardial orifice. Fundus: the dilated superior part that is related to the left dome of the diaphragm and is limited inferiorly by the horizontal plane of the cardial orifice. The superior part of the fundus usually reaches the level of the left 5th intercostal space. The cardial notch is between the esophagus and the fundus. The fundus may be dilated by gas, fluid, food, or any combination of these. Body: the major part of the stomach between the fundus and the pyloric antrum.

Chapter 2: Abdomen

Figure 2.30. Abdominal part of esophagus and stomach. A. The stomach and the greater and lesser omenta are shown. The left part of the liver is cut away so that the lesser omentum and the omental foramen (entrance to omental bursa) can be seen. The extent of the intact liver is indicated by a dotted line. The stomach is inflated with air. B. The internal surface (mucous membrane) is demonstrated. The longitudinal gastric folds, or rugae, disappear on distension. Along the lesser curvature, several longitudinal mucosal folds extend from the esophagus to the pylorus, making up the gastric canal along which ingested liquids pass. C. The pylorus is the significantly constricted terminal part of the stomach. The pyloric orifice is the distal opening of the pyloric canal into the duodenum.

P.250


Pyloric part: the funnel‐shaped outflow region of the stomach; its wide part, the pyloric antrum, leads into the pyloric canal, its narrow part (Fig. 2.30A & B). The pylorus (G. gatekeeper), the distal, sphincteric region of the pyloric part, is a marked thickening of the circular layer of smooth muscle (Fig. 2.30B & C), which controls discharge of the stomach contents through the pyloric orifice into the duodenum.

The stomach also has two curvatures: 



Lesser curvature: forms the shorter concave border of the stomach; the angular incisure (notch) is the sharp indentation approximately two thirds the distance along the lesser curvature that indicates the junction of the body and the pyloric part of the stomach (Fig. 2.30A). Greater curvature: forms the longer convex border of the stomach.

Intermittent emptying of the stomach occurs when intragastric pressure overcomes the resistance of the pylorus (Fig. 2.30C). It is normally tonically contracted so that the pyloric orifice is reduced, except when emitting chyme. At irregular intervals, gastric peristalsis passes the chyme through the pyloric canal and orifice into the small intestine for further mixing, digestion, and absorption.

Interior of the Stomach The smooth surface of the gastric mucosa is reddish brown during life, except in the pyloric part, where it is pink. In life, it is covered by a continuous mucous layer that protects its surface from the gastric acid the stomach's glands secrete. When contracted, the gastric mucosa is thrown into longitudinal ridges called gastric folds, or gastric rugae (Fig. 2.30B); they are most marked toward the pyloric part and along the greater curvature. A gastric canal (furrow) forms temporarily during swallowing between the longitudinal gastric folds of the mucosa along the lesser curvature. It can be observed radiographically and endoscopically. The gastric canal forms because of the firm attachment of the gastric mucosa to the muscular layer, which does not have an oblique layer at this site. Saliva and small quantities of masticated food and other fluids pass through the gastric canal to the pyloric canal when the stomach is mostly empty. The gastric folds diminish and obliterate as the stomach is distended (fills).

Relations of the Stomach The stomach is covered by peritoneum, except where blood vessels run along its curvatures and in a small area posterior to the cardial orifice. The two layers of the lesser omentum extend around the stomach and leave its greater curvature as the greater omentum (Figs. 2.23, 2.25, and 2.30A). Anteriorly, the stomach is related to the diaphragm, the left lobe of liver, and the anterior abdominal wall. Posteriorly, the stomach is related to the omental bursa and the pancreas; the posterior surface of the stomach forms most of the anterior wall of the omental bursa (Fig. 2.31A). The bed of the stomach, on which the stomach rests in the supine position, is formed by the structures forming the posterior wall of the omental bursa. From superior to

Chapter 2: Abdomen

inferior, the stomach bed is formed by the left dome of the diaphragm, spleen, left kidney and suprarenal gland, splenic artery, pancreas, and transverse mesocolon and colon (Fig. 2.31B).

Displacement of the Stomach Pancreatic pseudo‐cysts and abscesses in the omental bursa may push the stomach anteriorly. This displacement is usually visible in lateral radiographs of the stomach and other diagnostic images, such as CT studies. Following pancreatitis (inflammation of the pancreas), the posterior wall of the stomach may adhere to the part of the posterior wall of the omental bursa that covers the pancreas. This adhesion occurs because of the close relationship of the posterior wall of the stomach to the pancreas.

Hiatal Hernia A hiatal, or hiatus, hernia is a protrusion of a part of the stomach into the mediastinum through the esophageal hiatus of the diaphragm. The hernias occur most often in people after middle age, possibly because of weakening of the muscular part of the diaphragm and widening of the esophageal hiatus. The hernias are often distressful and cause pain. Although clinically there are several types of hiatal hernias (Skandalakis et al., 1996), the two main types are paraesophageal hiatal hernia and sliding hiatal hernia. In the less common paraesophageal hiatal hernia, the cardia remains in its normal position (Fig. B2.9A). However, a pouch of peritoneum, often containing part of the fundus, extends through the esophageal hiatus anterior to the esophagus. In these cases, usually no regurgitation of gastric contents occurs because the cardial orifice is in its normal position. In sliding hiatal hernia, the abdominal part of the esophagus, the cardia, and parts of the fundus of the stomach slide superiorly through the esophageal hiatus into the thorax, especially when the person lies down or bends over (Fig. B2.9B). Some regurgitation of stomach contents into the esophagus is possible because the clamping action of the right crus of the diaphragm on the inferior end of the esophagus is weak.


Figure B2.9.

Congenital Diaphragmatic Hernia In congenital diaphragmatic hernia (CDH), part of the stomach and intestine herniate through a large posterolateral defect (foramen of Bochdalek) in the diaphragm. This type of hernia is found in approximately 1 of every 2200 newborn infants. CDH results from the complex development of the diaphragm (Moore and Persaud, 2003). With abdominal viscera in the limited space of the prenatal pulmonary cavity, the lungs (especially the left lung) does not have room to develop. Because of the consequent pulmonary hypoplasia, the mortality rate in these infants is high (approximately 76%).

Chapter 2: Abdomen

Figure 2.31. Omental bursa and stomach bed. A. In this anterior approach to the omental bursa, the greater omentum and gastrosplenic ligament have been cut along the greater curvature of the stomach, and the stomach has been reflected superiorly to open the bursa anteriorly. At the right end of the bursa, two of the boundaries of the omental foramen can be seen: the inferior root of the hepatoduodenal ligament (containing the portal triad) and the caudate lobe of the liver. B. The stomach and most of the lesser omentum have been excised, and the peritoneum of the posterior wall of the omental bursa covering the stomach bed is largely removed to reveal the organs in the bed. Although adhesions, such as those binding the spleen to the diaphragm here, are common postmortem findings, they are not normal anatomy.

Vessels and Nerves of the Stomach The stomach has a rich arterial supply arising from the celiac trunk and its branches. The origin, course, and distribution of the arteries of the stomach are described in Table 2.7. Most blood is supplied by anastomoses formed along the lesser curvature by the right and left gastric arteries, and along the greater curvature by the right and left gastro‐omental arteries. The fundus and upper body receive blood from the short and posterior gastric arteries.

Clinically Oriented Anatomy, 5th Edition By Keith Moore T a b l e 2 . 7 . A r t e r i a l S u p p l y t o A b d o m i n a l F o re gu t D e r i v a t i v e s : Es o p h a gu s , S t o m a c h , L i v e r, G al l b l ad d e r, P an c re a s , a n d Spleen

Artery C e l i a c t r u n k

Left gastric

Origin Initial abdominal aorta (within aortic h i a t u s )

Course After short anteroinferior course, bifurcates into splenic and common m e s e n te r i c a r t e r i e s

C e l i a c t r u n k

Ascends retroperitoneally t o esophageal hiatus, giving rise to an esophageal branch; then descending a l o n g l e s s e r c u r v a t u r e t o a n a t o m os e with right gastric artery R u n s r e t r o p e r i t o n e a l l y a lo n g s u p e r i o r border of p a n c r e a s ; traverses spenorenal ligament to hilum of spleen

S p l e n i c

Posterior gastric

S p l e n i c artery Ascends re t r o p e r i t o n e a l l y along posterior to stomach p o s t e r i o r wa l l o f l e s s e r o m e n t a l bursa t o e n te r g a s t r op h r e n ic ligament L e f t g a s t r o ‐ o m e n ta l ( l e f t S p l e n i c a rt e r y in Passes between l a y e rs of g a s t r o e p i p l o ic ) h i l u m o f s p le e n g a s t r os p l e n i c l i g a m e n t to s t o m a c h , t h e n a l o n g g r e a te r cu r v a t u re i n g r e a te r o m e n t u m t o a n a s t o m o s e w i th r i g h t g a s t r o ‐ o m e n ta l a r t e r y S h o r t g a s t r i c ( n = 4 — 5 ) Passes between l a y e rs of g a s t r os p l e n i c l i g a m e n t t o f u n d u s of stomach Hepatica C e l i a c t r u n k P a s s e s re t ro p e r i t o n e a l l y t o r e a c h h e p a t o d u od e n a l l i g a m e n t ; p a s s i n g b e t w e e n la ye r s t o p o r ta h e p a t i s ; b i f u r c a t e s i n t o r i g h t a n d l e f t h e p a t i c a r t e r i e s Cystic

R i g h t h e p a t i c a r t e r y

D i s t ri b u t i o n E s o p h a g u s , s t o m a c h , p r o x i m a l d u o d e n u m , liver/biliary a p p a ra t u s , p a n c r e a s Distal (mostly a b d o m in a l ) p a r t o f esophagus and lesser curvature of stomach B o d y o f p a n c r e a s , s p l e e n , a n d g r e a t e r curvature and posterior stomach body Posterior wall and f u n d u s o f s t om a c h

Left p o r t io n of g r e a te r c u r v a t u r e o f stomach

F u n d u s o f s to m a c h

Liver, g a l l b l a d d e r and biliary ducts, s t o m a c h , d u o d e n u m , pancreas and r e s p e c t i v e lo b e s o f liver Arises w it h i n h e p a t i d u o d e n a l G a l l b l a d d e r and l i g a m e n t i n tr i a n g l e of C a l o t c y s t i c d u c t

Chapter 2: Abdomen Right gastric

H e p a t i c a r t e ry

Runs along lesser curvature of Right portion of s t o m a c h t o a n a s t o m o s e w i t h l e f t l e s s e r c u r v a t u r e o f g a s t r i c a r te r y stomach Gastroduodenal D e s c e n d s r e tr o p e r i t o n e a l l y , p o s t e r i o r S t o m a c h , p a n c r e a s , to gastroduodenal junction first p a rt of d u o d e n u m , and distal part of bile duct R i g h t g a s t r o ‐ o m e n ta l ( r i g h t G a s t r o d u o d e n a l P a s s e s b e t we e n l a y e rs o f g r e a t e r R i g h t p o r t i o n o f g a s t r o e p i p l o ic ) artery o m e n tu m a lo n g g re a t e r c u r v a t u r e o f g r e a te r c u r v a t u r e o f s t o m a c h t o a n a s t o m o s e w i t h l e f t s t o m a c h g a s t r o ‐ o m e n ta l a r t e r y Superior Gastroduodenal D i v i d e s i n t o a n t e r i o r a n d p o s t e r i o r P r o x i m a l p o r t i o n o f pancreaticoduodenal artery a r t e r i e s t h a t d e s c e n d o n e a c h s i d e o f d u o d e n u m and pancreatic head, anastomosing with superior part of similar branches of inferior head of pancreas p a n c r e a t i c o d u o d e n a l a r te r y Inferior S u p e r i o r m e s e n t e r i c D i v i d e s i n t o a n t e r i o r a n d p o s t e r i o r D i s t a l p o r t i o n o f pancreaticoduodenal artery a r t e r i e s t h a t a s c e n d o n e a c h s i d e o f d u o d e n u m a n d h e a d pancreatic head, anastomosing with of pancreas similar branches of s u p e r i o r p a n c r e a t i c o d u o d e n a l a r te r y a F o r d e s c r i p t i v e p u r p o s e s , t h e h e p a t i c a r t e r y i s o f te n d i v i d e d i n to t h e c o m m o n h e p a t i c a r te r y , f r o m i t s o r i g i n t o t h e o r i g i n o f th e g a s t r o d u o d e n a l a r t e r y , a n d h e p a t i c a r t e r y p r o p e r , m a d e u p o f t h e re m a i n d e r o f t h e v e s s e l .

Figure 2.32. Veins of stomach, duodenum, and spleen. Venous drainage from the stomach and duodenum is into the portal vein, either directly or indirectly via the splenic or superior mesenteric vein (SMV). The splenic vein usually receives the inferior mesenteric vein and then unites with the SMV to form the portal vein, as shown here.


The gastric veins parallel the arteries in position and course (Fig. 2.32). The right and left gastric veins drain into the portal vein; the short gastric veins and left gastro‐ omental veins drain into the splenic vein, which joins the superior mesenteric vein (SMV) to form the portal vein. The right gastro‐omental vein empties in the SMV. A prepyloric vein ascends over the pylorus to the right gastric vein. Because this vein is obvious in living persons, surgeons use it for identifying the pylorus. The gastric lymphatic vessels (Fig. 2.33A) accompany the arteries along the greater and lesser curvatures of the stomach. They drain lymph from its anterior and posterior surfaces toward its curvatures, where the gastric and gastro‐omental lymph nodes are located. The efferent vessels from these nodes accompany the large arteries to the celiac lymph nodes. The following is a summary of the lymphatic drainage of the stomach: 

 

Lymph from the superior two thirds of the stomach drains along the right and left gastric vessels to the gastric lymph nodes; lymph from the fundus and superior part of the body of the stomach also drains along the short gastric arteries and left gastro‐omental vessels to the pancreatico‐splenic lymph nodes. Lymph from the right two thirds of the inferior third of the stomach drains along the right gastro‐omental vessels to the pyloric lymph nodes. Lymph from the left one third of the greater curvature drains along the short gastric and splenic vessels to the pancreaticoduodenal lymph nodes.

The parasympathetic nerve supply of the stomach (Fig. 2.33B) is from the anterior and posterior vagal trunks and their branches, which enter the abdomen through the esophageal hiatus. The anterior vagal trunk, derived mainly from the left vagus nerve (CN X), usually enters the abdomen as a single branch that lies on the anterior surface of the esophagus. It runs toward the lesser curvature of the stomach, where it gives off hepatic and duodenal branches, which leave the stomach in the hepatoduodenal ligament. The rest of the anterior vagal trunk continues along the lesser curvature, giving rise to anterior gastric branches. The larger posterior vagal trunk, derived mainly from the right vagus nerve, enters the abdomen on the posterior surface of the esophagus and passes toward the lesser curvature of the stomach. The posterior vagal trunk supplies branches to the anterior and posterior surfaces of the stomach. It gives off a celiac branch, which runs to the celiac plexus, and then continues along the lesser curvature, giving rise to posterior gastric branches.

Chapter 2: Abdomen

Figure 2.33. Lymphatic drainage and innervation of stomach and small intestine. A. The lymphatic drainage is demonstrated. The arrows indicate the direction of lymph flow to the lymph nodes. B. Innervation of the stomach is both parasympathetic, from the vagus nerves (CN X) via the esophageal plexus, and sympathetic, via the greater (abdominopelvic) splanchnic, the celiac plexus, and periarterial plexuses.


The sympathetic nerve supply of the stomach from the T6 through T9 segments of the spinal cord passes to the celiac plexus through the greater splanchnic nerve and is distributed through the plexuses around the gastric and gastro‐omental arteries (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter.)

Pylorospasm Spasmodic contraction of the pylorus sometimes occurs in infants, usually between 2 and 12 weeks of age. Pylorospasm is characterized by failure of the smooth muscle fibers encircling the pyloric canal to relax normally. As a result, food does not pass easily from the stomach into the duodenum and the stomach becomes overly full, usually resulting in vomiting.

Congenital Hypertrophic Pyloric Stenosis Congenital hypertrophic pyloric stenosis is a marked thickening of the smooth muscle in the pylorus that affects approximately 1 of every 150 male infants and 1 of every 750 female infants (Moore and Persaud, 2003). Normally, gastric peristalsis pushes chyme through the pyloric canal and orifice into the small intestine at irregular intervals (Fig. B2.10A). In these babies, however, the elongated overgrown pylorus is hard, and severe stenosis (narrowing) of the pyloric canal is present (Fig. B2.10B), resisting gastric emptying. The proximal part of the stomach becomes secondarily dilated because of the pyloric obstruction. Although the cause of congenital hypertrophic pyloric stenosis is unknown, genetic factors appear to be involved because of this condition's high incidence in infants of monozygotic twins.

Carcinoma of the Stomach When the body or pyloric part of the stomach contains a malignant tumor, the mass may be palpable. Using gastroscopy, physicians can inspect the mucosa of the air‐ inflated stomach, enabling them to observe gastric lesions and take biopsies. The extensive lymphatic drainage of the stomach and the impossibility of removing all the lymph nodes create a surgical problem. The nodes along the splenic vessels can be excised by removing the spleen, gastrosplenic and splenorenal ligaments, and the body and tail of the pancreas. Involved nodes along the gastro‐omental vessels can be removed by resecting the greater omentum; however, removal of the aortic and celiac nodes and those around the head of the pancreas is difficult.

Chapter 2: Abdomen

Figure B2.10. Congenital hypertrophic pyloric stenosis. A. Normal passage through the pyloric sphincter is shown. B. Stoppage of flow owing to stenosis is demonstrated.

Gastrectomy Total gastrectomy (removal of the entire stomach) is uncommon. Partial gastrectomy (removal of part of the stomach) may be performed to remove a region of the stomach involved by a carcinoma, for example. Because the anastomoses of the arteries supplying the stomach provide good collateral circulation, one or more arteries may be ligated during this procedure without seriously affecting the blood supply to the part of the stomach remaining in place. When removing the pyloric antrum, for example, the greater omentum is incised parallel and inferior to the right gastro‐omental artery, requiring ligation of all the omental branches of this artery. The omentum does not degenerate, however, because of anastomoses with other arteries, such as the omental branches of the left gastro‐omental artery, which are still intact. Partial gastrectomy to remove a carcinoma usually also requires removal of all involved regional lymph nodes. Because cancer frequently occurs in the pyloric region, removal of the pyloric lymph nodes as well as the right gastro‐omental lymph nodes also receiving lymph drainage from this region is especially important. As stomach cancer becomes more advanced, the lymphogenous dissemination of malignant cells involves the celiac lymph nodes, to which all gastric nodes drain.

Gastric Ulcers, Helicobacter pylori, and Vagotomy An ulcer is an open sore. Gastric ulcers are open lesions of the mucosa of the stomach, whereas the term peptic ulcers is applied to lesions of the mucosa of the pyloric canal or, more often, the duodenum. Most ulcers (9 of 10) of the stomach and duodenum are associated with an infection of a specific bacterium, Helicobacter pylori (H. pylori). People experiencing severe chronic anxiety are most prone to the development of peptic ulcers. They often have gastric acid secretion rates that are as


much as 15 times higher than normal between meals. It is thought that the high acid in the stomach and duodenum overwhelms the bicarbonate normally produced by the duodenum and reduces the effectiveness of the mucous lining, leaving it vulnerable to H. pylori. The bacteria erode the protective mucous lining of the stomach, inflaming the mucosa and making it vulnerable to the effects of the gastric acid and digestive enzymes (pepsin) produced by the stomach. If the ulcer erodes into the gastric arteries, it can cause life‐threatening bleeding. Most ulcers are eradicated, with low rates of recurrence, after antibiotic therapy combined with use of antacids. Because the secretion of acid by parietal cells of the stomach is largely controlled by the vagus nerves, vagotomy (surgical section of the vagus nerves) is performed in some people with chronic or recurring ulcers to reduce the production of acid. Vagotomy may also be performed in conjunction with resection of the ulcerated area (antrectomy, or resection of the pyloric antrum) to reduce acid secretion. A truncal vagotomy (surgical section of the vagal trunks) is rarely performed because the innervation of other abdominal structures is also sacrificed (Fig. B2.11A). In selective gastric vagotomy, the stomach is denervated but the vagal branches to the pylorus, liver and biliary ducts, intestines, and celiac plexus are preserved (Fig. B2.11B). A selective proximal vagotomy attempts to denervate even more specifically the area in which the parietal cells are located, hoping to affect the acid‐producing cells while sparing other gastric function (motility) stimulated by the vagus nerve (Fig. B2.11C). A posterior gastric ulcer may erode through the stomach wall into the pancreas, resulting in referred pain to the back. In such cases, erosion of the splenic artery results in severe hemorrhage into the peritoneal cavity. Pain impulses from the stomach are carried by visceral afferent fibers that accompany sympathetic nerves. This fact is evident because the pain of a recurrent peptic ulcer may persist after complete vagotomy, whereas patients who have had a bilateral sympathectomy may have a perforated peptic ulcer and experience no pain. Figure B2.11. Vagotomy. Truncal (A), selective gastric (B), and selective proximal (C) vagotomy are shown.

Chapter 2: Abdomen

Visceral Referred Pain Pain is an unpleasant sensation associated with actual or potential tissue damage and mediated by specific nerve fibers to the brain, where its conscious appreciation may be modified. Organic pain arising from an organ such as the stomach varies from dull to severe; however, the pain is poorly localized. It radiates to the dermatome level, which receives visceral afferent fibers from the organ concerned. Visceral referred pain from a gastric ulcer, for example, is referred to the epigastric region because the stomach is supplied by pain afferents that reach the T7 and T8 spinal sensory ganglia and spinal cord segments through the greater splanchnic nerve (Fig. B2.12). The brain interprets the pain as though the irritation occurred in the skin of the epigastric region, which is also supplied by the same sensory ganglia and spinal cord segments. Pain arising from the parietal peritoneum is of the somatic type and is usually severe. The site of its origin can be localized. The anatomical basis for this localization of pain is that the parietal peritoneum is supplied by somatic sensory fibers through thoracic nerves, whereas a viscus such as the appendix is supplied by visceral afferent fibers in the lesser splanchnic nerve. Inflamed parietal peritoneum is extremely sensitive to stretching. When digital pressure is applied to the anterolateral abdominal wall over the site of inflammation, the parietal peritoneum is stretched. When the fingers are suddenly removed, extreme localized pain is usually felt, known as rebound tenderness.

Figure B2.12.

Surface Anatomy of the Stomach The surface markings of the stomach vary because its size and position change under various circumstances (e.g., after a heavy meal). In the supine position, the stomach commonly lies in the right and left upper quadrants, or epigastric, umbilical, and left hypochondriac and lumbar regions (Fig. SA2.2). In the erect position, the stomach moves inferiorly. In asthenic (thin, weak) individuals, the body of the stomach may extend into the pelvis (Fig. 2.29). The stomach is usually partially overlain by the transverse colon near the left colic flexure. The surface markings of the stomach in the supine position include (Fig. SA2.2) the:


Figure SA2.2.    





Cardial orifice: which usually lies posterior to the 6th left costal cartilage, 2—4 cm from the median plane at the level of the T11 vertebra. Fundus: which usually lies posterior to the left 6th rib in the plane of the MCL. Greater curvature: which passes inferiorly to the left as far as the 10th left cartilage before turning medially to reach the pyloric antrum. Lesser curvature: which passes from the right side of the cardia to the pyloric antrum; the most inferior part of the curvature is marked by the angular incisure, which lies just to the left of the midline. Pyloric part of the stomach in the supine position: which usually lies at the level of the 9th costal cartilages at the level of L1 vertebra; the pyloric orifice is approximately 1.25 cm left of the midline. Pylorus in the erect position: which usually lies on the right side; its location varies from the L2 through L4 vertebra.

The Bottom Line The stomach is the dilated portion of the alimentary tract between the esophagus and the duodenum, specialized to accumulate ingested food and prepare it chemically and mechanically for digestion. The stomach lies asymmetrically in the abdominal cavity, to the left of the midline and usually in the upper left quadrant. The abdominal portion of the esophagus enters its cardial portion, and its pyloric part leads to the exit to the duodenum. Gastric emptying is controlled by the pylorus. In life, its internal surface is covered with a protective layer of mucus, overlying gastritic folds that disappear with distension. The stomach is intraperitoneal, with the lesser omentum (enclosing the anastomoses between right and left gastric vessels) attached to its lesser curvature, and the greater omentum (enclosing the

Chapter 2: Abdomen

anastomoses between right and left gastro‐omental vessels) attached to its greater curvature. The vessels of its curvatures serve the body and pyloric antrum of the stomach. The upper body and fundus are served by short and posterior gastric vessels. The trilaminar smooth muscle of the stomach and gastric glands receive parasympathetic innervation from the vagus; sympathetic innervation to the stomach is vasoconstrictive and antiperistaltic.

Small Intestine The small intestine, consisting of the duodenum, jejunum, and ileum (Fig. 2.34), is the primary site for absorption of nutrients from ingested materials, and extends from the pylorus to the ileocecal junction where the ileum joins the cecum (the first part of the large intestine). The pyloric part of the stomach empties into the duodenum, duodenal admission being regulated by the pylorus.

Duodenum The duodenum (L. the breadth of 12 fingers), the first and shortest (25 cm) part of the small intestine, is also the widest and most fixed part. The duodenum pursues a C‐shaped course around the head of the pancreas (Fig. 2.35C). The duodenum begins at the pylorus on the right side and ends at the duodenojejunal junction on the left side (Fig. 2.35B & C). This junction occurs approximately at the level of the L2 vertebra, 2—3 cm to the left of the midline. The junction usually takes the form of an acute angle, the duodenojejunal flexure. Most of the duodenum is fixed by peritoneum to structures on the posterior abdominal wall and is considered partially retroperitoneal. The duodenum is divisible into four parts (Fig. 2.35C; Table 2.8):    

Superior (first) part: short (approximately 5 cm) and lies anterolateral to the body of the L1 vertebra. Descending (second) part: longer (7—10 cm) and descends along the right sides of the L1—L3 vertebrae. Horizontal (third) part: 6—8 cm long and crosses the L3 vertebra. Ascending (fourth) part: short (5 cm) and begins at the left of the L3 vertebra and rises superiorly as far as the superior border of the L2 vertebra.

The first 2 cm of the superior part of the duodenum, immediately distal to the pylorus, has a mesentery and is mobile. This free part, called the ampulla (duodenal cap), has an appearance distinct from the remainder of the duodenum when observed radiographically using contrast medium. The distal 3 cm of the superior part and the other three parts of the duodenum have no mesentery and are immobile because they are retroperitoneal. The principal relationships of the duodenum are outlined in Table 2.8 and illustrated in Figure 2.35. The superior part of the duodenum ascends from the pylorus and is overlapped by the liver and gallbladder. Peritoneum covers its anterior aspect, but it is bare of peritoneum posteriorly, except for the ampulla. The proximal part has the hepatoduodenal ligament (part of the lesser omentum) attached superiorly and the greater omentum attached inferiorly (see Fig. 2.20). The descending part of the duodenum runs inferiorly, curving around the head of the pancreas (Fig. 2.35; Table 2.8). Initially, it lies to the right of and parallel to the IVC.


The bile and main pancreatic ducts enter its posteromedial wall. These ducts usually unite to form the hepatopancreatic ampulla, which opens on the summit of an eminence, called the major duodenal papilla, located posteromedially in the descending duodenum. The descending part of the duodenum is entirely retroperitoneal. The anterior surface of its proximal and distal thirds is covered with peritoneum; however, the peritoneum reflects from its middle third to form the double‐layered mesentery of the transverse colon, the transverse mesocolon.

Figure 2.34. Small and large intestines. A. Note the convolutions of small intestine in situ, encircled on three sides by the large intestine and revealed by elevating greater omentum. B. The convolutions of small intestine have been retracted superiorly to demonstrate the mesentery. C. This orientation drawing of the alimentary system indicates the general position and relationships of the intestines. D. The blood supply of the ileocecal region is shown.

Chapter 2: Abdomen

The inferior or horizontal part of the duodenum runs transversely to the left, passing over the IVC, aorta, and L3 vertebra. It is crossed by the superior mesenteric artery and vein and the root of the mesentery of the jejunum and ileum. Superior to it is the head of the pancreas and its uncinate process. The anterior surface of the horizontal part is covered with peritoneum, except where it is crossed by the superior mesenteric vessels and the root of the mesentery. Posteriorly it is separated from the vertebral column by the right psoas major, IVC, aorta, and the right testicular or ovarian vessels. Figure 2.35. D u o d e n u m , p a n c r e a s , a n d s p l e e n . A. T h e d u o d e n u m , p a n c r e a s and spleen and their blood supply are r e v e a l e d by r e m o v a l of the stomach, t r a n s v e r s e colon , a n d p e r i t o n e u m . B . T h e a n t e r i o r a s pe c t o f t h e d u o d e n u m , p a n c r e a s , and r e l a t e d vasculature is shown. The duodenum is molded around the h e a d o f t h e p a n c r e a s. C. The posterior aspect of the duodenum and p a n c r e a s is s h o w n . The abdominal aorta and inferior vena c a v a ( I V C ) oc c u p y t he v e r t i c a l concavity posterior to the head o f t h e p a n c r e a s a n d third part of the duodenum. The u n c i n a t e p ro c e s s i s t h e e xt e n s io n o f t h e h e a d o f t he p a n c r e a s t h a t p a ss e s p o s t e r i o r to the superior m e s e n t e r i c v e s s e l s . T h e b i l e d u c t i s d e s c e n d i n g in a f i s s u r e ( o pe n e d u p ) in the posterior part of the head of the p a n c r e a s. SMV, s u p e r i o r m e s e n te r i c vein.


Table 2.8. Relationships of the Duodenum The ascending part of the duodenum runs superiorly and along the left side of the aorta to reach the inferior border of the body of the pancreas. Here it curves anteriorly to join the jejunum at the duodenojejunal junction, supported by the attachment of a suspensory muscle of the duodenum (ligament of Treitz). This muscle is composed of a slip of skeletal muscle from the diaphragm and a fibromuscular band of smooth muscle from the third and fourth parts of the duodenum. Contraction of this muscle widens the angle of the duodenojejunal flexure, facilitating movement of the intestinal contents. The suspensory muscle passes posterior to the pancreas and splenic vein and anterior to the left renal vein. The arteries of the duodenum arise from the celiac trunk and the superior mesenteric artery (Fig. 2.35). The celiac trunk, via the gastroduodenal artery and its branch, the superior pancreaticoduodenal artery, supplies the duodenum proximal to the entry of the bile duct into the descending part of the duodenum. The superior mesenteric artery, through its branch, the inferior pancreaticoduodenal artery, supplies the duodenum distal to the entry of the bile duct. The pancreaticoduodenal arteries lie in the curve between the duodenum and the head of the pancreas and supply both structures. The anastomosis of the superior and inferior pancreaticoduodenal arteries, which occurs approximately at the level of entry of the bile duct (or, according to some authors, at the junction of the descending and horizontal parts of the duodenum) is formed between the celiac and the superior mesenteric arteries. An important transition in the blood supply of the digestive tract occurs here: proximally, extending orad (toward the mouth) to and including the abdominal part of the esophagus, the blood is supplied to the alimentary tract by the celiac trunk;

Chapter 2: Abdomen

distally, extending aborad (away from the mouth) to the left colic flexure, the blood is supplied by the SMA. The basis of this transition in blood supply is embryological; this is the junction of the foregut and midgut (Moore and Persaud, 2003). The veins of the duodenum follow the arteries and drain into the portal vein, some directly and others indirectly, through the superior mesenteric and splenic veins (Fig. 2.32). The lymphatic vessels of the duodenum follow the arteries. The anterior lymphatic vessels of the duodenum drain into the pancreaticoduodenal lymph nodes, located along the superior and inferior pancreaticoduodenal arteries, and into the pyloric lymph nodes, which lie along the gastroduodenal artery (Fig. 2.36). The posterior lymphatic vessels pass posterior to the head of the pancreas and drain into the superior mesenteric lymph nodes. Efferent lymphatic vessels from the duodenal lymph nodes drain into the celiac lymph nodes. Figure 2.36. Lymphatic drainage and innervation of duodenum, pancreas, and spleen. The close positional relationship of these organs results in sharing of blood vessels, lymphatic vessels, and nerve pathways, in whole or in part.

The nerves of the duodenum derive from the vagus and greater and lesser (abdominopelvic) splanchnic nerves by way of the celiac and superior mesenteric plexuses, from which they are conveyed to the duodenum via periarterial plexuses extending to the pancreaticoduodenal arteries (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter).


Duodenal Ulcers Duodenal (peptic) ulcers are inflammatory erosions of the duodenal mucosa. Most (65%) duodenal ulcers occur in the posterior wall of the superior part of the duodenum within 3 cm of the pylorus. Occasionally, an ulcer perforates the duodenal wall, permitting the contents to enter the peritoneal cavity and causing peritonitis. Because the superior part of the duodenum closely relates to the liver, gallbladder, and pancreas, any of these structures may become adherent to the inflamed duodenum and also become ulcerated as the lesion continues to the tissue that surrounds it. Although bleeding from gastric or duodenal ulcers commonly occurs, erosion of the gastroduodenal artery (a posterior relation of the superior part of the duodenum) by a duodenal ulcer results in severe hemorrhage into the peritoneal cavity and subsequent peritonitis.

Developmental Changes in the Mesoduodenum During the early fetal period, the entire duodenum has a mesentery; however, most of it fuses with the posterior abdominal wall because of pressure from the overlying transverse colon. Because the attachment of the mesoduodenum to the wall is secondary (has occurred through formation of a fusion fascia; discussed under “Embryology of the Peritoneal Cavity,” in this chapter), the duodenum and the closely associated pancreas can be separated (surgically mobilized) from the underlying retroperitoneal viscera during surgical operations involving the duodenum without endangering the blood supply to the kidney or the ureter.

Paraduodenal Hernias There are two or three inconstant folds and fossae (recesses) around the duodenojejunal junction (Fig. B2.13). The paraduodenal fold and fossa are large and lie to the left of the ascending part of the duodenum. If a loop of intestine enters this fossa, it may strangulate. During repair of a paraduodenal hernia, care must be taken not to injure the branches of the inferior mesenteric artery and vein or the ascending branches of the left colic artery, which are related to the paraduodenal fold and fossa.

Figure B2.13.

Chapter 2: Abdomen

The Bottom Line The duodenum is the first part of the small intestine, receiving chyme mixed with gastric acid and pepsin directly from the stomach via the pylorus. It follows a mostly secondarily retroperitoneal, C‐shaped course around the head of the pancreas. Its descending part receives both the bile and the pancreatic ducts. At or just distal to this level, a transition occurs in the blood supply of the abdominal part of the alimentary tract. Proximal to this point it is supplied by branches of the celiac trunk; distal to this point, it is supplied by branches of the superior mesenteric artery.

Jejunum and Ileum The second part of the small intestine, the jejunum, begins at the duodenojejunal flexure where the alimentary tract resumes an intraperitoneal course. The third part of the small intestine, the ileum, ends at the ileocecal junction, the union of the terminal ileum and the cecum (Figs. 2.34D and 2.37). Together, the jejunum and ileum are 6—7 m long, the jejunum constituting approximately two fifths and the ileum approximately three fifths of the intraperitoneal section of the small intestine. Most of the jejunum lies in the left upper quadrant of the infracolic compartment, whereas most of the ileum lies in the right lower quadrant. The terminal ileum usually lies in the pelvis from which it ascends, ending in the medial aspect of the cecum. Although no clear line of demarcation between the jejunum and ileum exists, they have distinctive characteristics that are surgically important (Table 2.9). Figure 2.37. Jejunum and ileum. The jejunum begins at the duodenojejunal flexure and the ileum ends at the cecum. The combined term jejunoileum is sometimes used as an expression of the fact that there is no clear external line of demarcation between the jejunum and the ileum. LUQ, left upper quadrant; RLQ, right lower quadrant.


The mesentery is a fan‐shaped fold of peritoneum that attaches the jejunum and ileum to the posterior abdominal wall (Fig. 2.34B; Table 2.9A). The root (origin) of the mesentery (approximately 15 cm long) is directed obliquely, inferiorly, and to the right (Fig. 2.38A). It extends from the duodenojejunal junction on the left side of vertebra L2 to the ileocolic junction and the right sacroiliac joint. The average breadth of the mesentery from its root to the intestinal border is 20 cm. The root of the mesentery crosses (successively) the ascending and horizontal parts of the duodenum, abdominal aorta, IVC, right ureter, right psoas major, and right testicular or ovarian vessels. Between the two layers of the mesentery are the superior mesenteric vessels, lymph nodes, a variable amount of fat, and autonomic nerves. The superior mesenteric artery supplies the jejunum and ileum (Fig. 2.38). The SMA usually arises from the abdominal aorta at the level of the L1 vertebra, approximately 1 cm inferior to the celiac trunk, and runs between the layers of the mesentery, sending 15—18 branches to the jejunum and ileum. The arteries unite to form loops or arches, called arterial arcades, which give rise to straight arteries, called vasa recta (Fig. 2.38B; Table 2.9C). The superior mesenteric vein drains the jejunum and ileum (Fig. 2.38B). It lies anterior and to the right of the SMA in the root of the mesentery (Fig. 2.38A). The SMV ends posterior to the neck of the pancreas, where it unites with the splenic vein to form the portal vein (Fig. 2.35). Specialized lymphatic vessels in the intestinal villi (tiny projections of the mucous membrane) that absorb fat are called lacteals. They empty their milk‐like fluid into the lymphatic plexuses in the walls of the jejunum and ileum. The lacteals drain in turn into lymphatic vessels between the layers of the mesentery. Within the mesentery, the lymph passes sequentially through three groups of lymph nodes (Fig. 2.39):   

Juxta‐intestinal lymph nodes: located close to the intestinal wall. Mesenteric lymph nodes: scattered among the arterial arcades. Superior central nodes: located along the proximal part of the SMA.

Efferent lymphatic vessels from the mesenteric lymph nodes drain to the superior mesenteric lymph nodes. Lymphatic vessels from the terminal ileum follow the ileal branch of the ileocolic artery to the ileocolic lymph nodes. The SMA and its branches are surrounded by a perivascular nerve plexus through which the nerves are conducted to the parts of the intestine supplied by this artery (Fig. 2.40). The sympathetic fibers in the nerves to the jejunum and ileum originate in the T8—T10 segments of the spinal cord and reach the superior mesenteric nerve plexus through the sympathetic trunks and thoracic abdominopelvic (greater, lesser, and least) splanchnic nerves. The presynaptic sympathetic fibers synapse on cell bodies of postsynaptic sympathetic neurons in the celiac and superior mesenteric (prevertebral) ganglia. The parasympathetic fibers in the nerves to the jejunum and ileum derive from the posterior vagal trunks. The presynaptic parasympathetic fibers synapse with postsynaptic parasympathetic neurons in the myenteric and submucosal plexuses in the intestinal wall (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter).

Chapter 2: Abdomen

Table 2.9. Distinguishing Characteristics of the Jejunum and Ileum in the Living Body

Clinically Oriented Anatomy, 5th Edition By Keith Moore Figure 2.38. Arterial supply and mesenteries of intestines. A. The arteries supplying the large intestine are shown. The transverse and sigmoid mesocolons and the mesentery of the jejunum and ileum have been cut at their roots. The ileocolic and right colic arteries on the right side and the left colic and sigmoid arteries on the left side originally coursed within mesenteries (ascending and descending mesocolons) that became fused to the posterior wall; they can be re‐established surgically. B. Arterial supply and venous drainage of the small intestine. The superior mesenteric artery supplies the jejunoileum, the ascending, and most of the transverse colon (not shown). The superior mesenteric vein drains blood from the intestine into the portal vein.

Chapter 2: Abdomen

Figure 2.39. Mesenteric lymph nodes. The superior mesenteric lymph nodes form a system in which the central nodes, at the root of the superior mesenteric artery, receive lymph from the mesenteric, ileocolic, right colic, and middle colic lymph nodes. The nodes are more numerous adjacent to the intestine (juxta‐intestinal lymph nodes) and less numerous along the arteries. The efferent vessels of the celiac and superior mesenteric lymph nodes form the intestinal lymphatic trunk, which usually ends in the left lumbar trunk but ends in the chyle cistern in 25% of people.

In general, sympathetic stimulation reduces motility of the intestine and secretion and acts as a vasoconstrictor, reducing or stopping digestion and making blood (and energy) available for “fleeing or fighting.” Parasympathetic stimulation increases motility of the intestine and secretion, restoring digestive activity following a sympathetic reaction. The small intestine also has sensory (visceral afferent) fibers. The intestine is insensitive to most pain stimuli, including cutting and burning; however, it is sensitive to distension that is perceived as colic (spasmodic abdominal pains).

Brief Review of the Embryological Rotation of the Midgut An understanding of the rotation of the midgut clarifies the adult arrangement of the intestines. The primordial gut comprises the foregut, midgut, and hindgut (Moore and Persaud, 2003). Pain arising from foregut derivatives—esophagus, stomach, pancreas, duodenum, liver, and biliary ducts—localizes in the epigastric region. Pain arising from midgut derivatives—the small intestine distal to bile duct, cecum, appendix, ascending colon, and most of the transverse colon—localizes in the periumbilical region. Pain arising from hindgut derivatives—the distal part of the transverse colon, descending colon, sigmoid colon, and rectum—localizes in the hypogastric region. For 4 weeks, the rapidly growing midgut, supplied by the SMA, is physiologically herniated into the proximal part of the umbilical cord (Fig. B2.14A). It is attached to the yolk sac by the yolk stalk. As it returns to the abdominal cavity, the midgut rotates 270° around the axis of the SMA (Fig. B2.14B—C). As the relative size of the liver and kidneys decreases, the midgut returns to the abdominal cavity as increased space becomes available. As the parts of the intestine reach their definitive positions, their mesenteric attachments undergo modification (Fig. B2.14D—E). Some


mesenteries shorten and others disappear (e.g., most of duodenal mesentery). Malrotation of the midgut results in several congenital anomalies such as volvulus (twisting) of the intestine.

Navigating the Small Intestine When portions of the small intestine have been delivered through a surgical wound, the proximal (orad) and distal (aborad) ends of a loop of bowel are not apparent. If you are trying to follow the intestine in a particular direction (e.g., attempting to follow the ileum to the ileocecal junction), it is important to know which end is which. Normal peristalsis may not be present to provide a clue. Place your hands on each side of the intestine and its mesentery, and then follow the mesentery with your fingers to its root (its attachment to the posterior abdominal wall), untwisting the loop of intestine as necessary. Once the mesentery and intestine are straightened to match the direction of the root, the cranial end must be the orad end, and the caudal end the aborad end.

Ischemia of the Intestine Occlusion of the vasa recta by emboli results in ischemia of the part of the intestine concerned. If the ischemia is severe, necrosis of the involved segment results and ileus (obstruction of the intestine) of the paralytic type occurs. Ileus is accompanied by a severe colicky pain, along with abdominal distension, vomiting, and often fever and dehydration. If the condition is diagnosed early (e.g., using a superior mesenteric arteriogram), the obstructed part of the vessel may be cleared surgically.

Ileal Diverticulum An ileal diverticulum (of Meckel) is a congenital anomaly that occurs in 1—2% of the population. A remnant of the proximal part of the embryonic yolk stalk, the diverticulum usually appears as a finger‐like pouch (Fig. B2.15A). It is always at the site of attachment of the yolk stalk on the antimesenteric border (border opposite the mesenteric attachment) of the ileum. The diverticulum is usually located 30—60 cm from the ileocecal junction in infants and 50 cm in adults. It may be free (74%) or attached to the umbilicus (26%) (Fig. B2.15B). Although its mucosa is mostly ileal in type, it may also include areas of acid‐producing gastric tissue, pancreatic tissue, or jejunal or colonic mucosa. An ileal diverticulum may become inflamed and produce pain mimicking that produced by appendicitis. If gastric tissue is included, a peptic ulcer may occur here. For discussion and illustrations of the various types of ileal diverticula, see Moore et al. (2000) and Moore and Persaud (2003).

Chapter 2: Abdomen

Figure B2.14


Figure B2.15

Figure 2.40. Innervation of small intestine. Presynaptic sympathetic nerve fibers originate in T8 or T9 through T10 or T11 segments of the spinal cord and reach the celiac plexus through the sympathetic trunks and greater and lesser (abdominopelvic) splanchnic nerves. After synapsing in the celiac and superior mesenteric ganglia, postsynaptic nerve fibers accompany the arteries to the intestine. Afferent fibers are concerned with reflexes and pain. Presynaptic parasympathetic (vagus) nerves originate in the medulla (oblongata) and pass to the intestine via the posterior vagal trunk. They synapse with intrinsic postsynaptic neurons located in the intestinal wall. SMA, superior mesenteric artery.

Chapter 2: Abdomen

The Bottom Line The jejunum and ileum make up the convolutions of the small intestine occupying most of the infracolic division of the greater sac of the peritoneal cavity. The jejunum is mostly to the upper right, and the ileum to the lower left. Together they are 3—4 m in length (in the cadaver; less in living people owing to the structures' tonicity). The orad two fifths is jejunum and the aborad three fifths is ileum, although there is no clear line of transition. The diameter of the small intestine becomes increasingly smaller as the semifluid chyme progresses through it. Its blood vessels also become smaller, but the number of tiers of arcades increases while the length of the vasa recta decreases. However, the fat in which the vessels are embedded within the mesentery increases, making these features more difficult to see. The ileum is characterized by an abundance of lymphoid tissue, aggregated into nodules (Peyer patches). As the intraperitoneal portion of the small intestine, the jejunum and ileum are suspended by the mesentery, the root of which extends from the duodenojejunal junction to the left of the midline at the L2 level, to the ileocecal junction in the right iliac fossa. An ileal diverticulum is a congenital anomaly present in 1—2% of the population, is 3—6 cm in length, and is typically located 50 cm from the ileocecal junction.

Large Intestine The large intestine is the site where water is absorbed from the indigestible residues of the liquid chyme, converting it into semisolid stool or feces that is stored temporarily and allowed to accumulate until defecation occurs. The large intestine consists of the cecum; the appendix; the ascending, transverse, descending, and sigmoid colon; the rectum; and the anal canal (Fig. 2.41). The large intestine can be distinguished from the small intestine by:  

 

Omental appendices: small, fatty, omentum‐like projections. Three teniae coli: (1) mesocolic, to which the transverse and sigmoid mesocolons attach; (2) omental, to which the omental appendices attach; and (3) free (L. libera), to which neither mesocolons nor omental appendices are attached. Haustra: sacculations of the wall of the colon between the teniae A much greater caliber (internal diameter).

The teniae coli (thickened bands of smooth muscle representing most of the longitudinal coat) begin at the base of the appendix as the thick longitudinal layer of the appendix splits to form three bands. The teniae run the length of the large intestine, merging again at the rectosigmoid junction into a continuous longitudinal layer around the rectum. Because the teniae are shorter than the intestine, the colon becomes sacculated between the teniae, forming the haustra.

Cecum and Appendix The cecum is the first part of the large intestine that is continuous with the ascending colon. It is a blind intestinal pouch, approximately 7.5 cm in both length and breadth, located in the right lower quadrant, where it lies in the iliac fossa inferior to the junction of the terminal ileum and cecum (Figs. 2.41 and 2.42). If


distended with feces or gas, the cecum may be palpable through the anterolateral abdominal wall. The cecum usually lies within 2.5 cm of the inguinal ligament, is almost entirely enveloped by peritoneum, and can be lifted freely. However, the cecum has no mesentery. Because of its relative freedom, it may be displaced from the iliac fossa, but it is commonly bound to the lateral abdominal wall by one or more cecal folds of peritoneum (Fig. 2.42B). The terminal ileum enters the cecum obliquely and partly invaginates into it. Figure 2.41. Terminal ileum and large intestine (including appendix). The mucosa, musculature (teniae), haustra, and omental (fatty) appendices of the colon are demonstrated. There are no teniae coli (thickened bands of longitudinal muscle) or omental appendices associated with the rectum.

Traditionally, based on cadaveric studies, this manner of entrance produces ileocolic lips (superior and inferior) at the ileal orifice, which form the ileal papilla (Fig. 2.42A). The folds meet laterally to form ridges, called the frenula of the valve. When the cecum is distended or when it contracts, the frenula tighten, closing the valve to prevent reflux from the cecum into the ileum. However, direct observation by endoscopy in living persons does not support this description. The circular muscle is poorly developed around the orifice; therefore, the valve is unlikely to have any sphincteric action that controls passage of the intestinal contents from the ileum into the cecum. The orifice is usually closed by tonic contraction, however, making it appear as the ileal papilla on the cecal side (Fig. 2.42B). The valve probably does prevent reflux from the cecum into the ileum as contractions occur to propel contents up the ascending colon and into the transverse colon (Magee and Dalley, 1986).

Chapter 2: Abdomen Figure 2.42. Terminal ileum, cecum, and appendix. A. The cecum was filled with air until dry, and then opened. Observe the ileocecal valve and ileal orifice. The frenulum is a fold (more evident in cadavers) that runs from the ileocecal valve along the wall at the junction of the cecum and ascending colon. B. The interior of the cecum showing the endoscopic (living) appearance of the ileocecal valve. C. The approximate incidences of various locations of the appendix, based on an analysis of 10,000 cases, are shown.

The appendix (traditionally, vermiform appendix; L. vermis, worm‐like) is a blind intestinal diverticulum (6—10 cm in length) that contains masses of lymphoid tissue. It arises from the posteromedial aspect of the cecum inferior to the ileocecal junction. The appendix has a short triangular mesentery, the mesoappendix, which derives from the posterior side of the mesentery of the terminal ileum (Fig. 2.41). The mesoappendix attaches to the cecum and the proximal part of the appendix. The position of the appendix is variable, but it is usually retrocecal (Fig. 2.42C). The cecum is supplied by the ileocolic artery, the terminal branch of the SMA (Table 2.10). The appendicular artery, a branch of the ileocolic artery, supplies the appendix. A tributary of the SMV, the ileocolic vein, drains blood from the cecum and appendix (Fig. 2.43A). The lymphatic vessels from the cecum and appendix pass to lymph nodes in the mesoappendix and to the ileocolic lymph nodes that lie along the ileocolic artery (Fig. 2.43B). Efferent lymphatic vessels pass to the superior mesenteric lymph nodes.

Clinically Oriented Anatomy, 5th Edition By Keith Moore Table 2.10. Arterial Supply to the Intestines

Artery Superior mesenteric

Origin Abdominal aorta

Intestinal (jejunal and Superior mesenteric ileal) (n = 15—18) artery Middle colic Superior mesenteric artery Right colic

Course Distribution Runs in root of mesentery to Part of gastrointestinal ileocecal junction tract derived from midgut Passes between two layers of Jejunum and ileum mesentery Ascends retroperitoneally Transverse colon and passes between layers of transverse mesocolon Passes retroperitoneally to Ascending colon reach ascending colon Runs along root of mesentery Ileum, cecum, and and divides into ileal and ascending colon colic branches Passes between layers of Appendix mesoappendix Descends retroperitoneally to Supplies part of left of abdominal aorta gastrointestinal tract derived from hindgut Passes retroperitoneally Descending colon toward left to descending colon Passes retroperitoneally Descending and sigmoid toward left to descending colon colon Descends retroperitoneally to Proximal part of rectum rectum

Appendicular

Superior mesenteric artery Terminal branch of superior mesenteric artery Ileocolic artery

Inferior mesenteric

Abdominal aorta

Left colic

Inferior mesenteric artery

Sigmoid (n = 3—4)

Inferior mesenteric artery

Superior rectal

Terminal branch of inferior mesenteric artery Internal iliac artery Passes retroperitoneally to Midpart of rectum rectum Internal pudendal Crosses ischioanal fossa to Distal part of rectum artery reach rectum and anal canal

Ileocolic

Middle rectal Inferior rectal

Chapter 2: Abdomen

The nerve supply to the cecum and appendix derives from the sympathetic and parasympathetic nerves from the superior mesenteric plexus (Fig. 2.43C). The sympathetic nerve fibers originate in the lower thoracic part of the spinal cord, and the parasympathetic nerve fibers derive from the vagus nerves. Afferent nerve fibers from the appendix accompany the sympathetic nerves to the T10 segment of the spinal cord (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter).

Position of the Appendix A retrocecal appendix extends superiorly toward the right colic flexure and is usually free (Fig. 2.42C). It occasionally lies beneath the peritoneal covering of the cecum, where it is often fused to the cecum or the posterior abdominal wall. The appendix may project inferiorly toward or across the pelvic brim. The anatomical position of the appendix determines the symptoms and the site of muscular spasm and tenderness when the appendix is inflamed. The base of the appendix lies deep to a point that is one third of the way along the oblique line joining the right ASIS to the umbilicus (the McBuney point on the spinoumbilical line).

Appendicitis Acute inflammation of the appendix is a common cause of an acute abdomen (severe abdominal pain arising suddenly). Usually, digital pressure over the McBurney point registers maximum abdominal tenderness. Appendicitis in young people is usually caused by hyperplasia of lymphatic follicles in the appendix that occludes the lumen. In older people, the obstruction usually results from a fecalith (coprolith), a concretion that forms around a center of fecal matter. When secretions from the appendix cannot escape, the appendix swells, stretching the visceral peritoneum. The pain of appendicitis usually commences as a vague pain in the periumbilical region because afferent pain fibers enter the spinal cord at the T10 level. Later, severe pain in the right lower quadrant results from irritation of the parietal peritoneum lining the posterior abdominal wall. Extending the thigh at the hip joint elicits pain. Acute infection of the appendix may result in thrombosis (clotting of blood) in the appendicular artery, which often results in ischemia, gangrene (death of tissue), and perforation of an acutely inflamed appendix. Rupture of the appendix results in infection of the peritoneum (peritonitis), increased abdominal pain, nausea and/or vomiting, and abdominal rigidity (stiffness of the abdominal muscles). Flexion of the right thigh ameliorates the pain because it causes relaxation of the right psoas muscle, a flexor of the thigh.

Appendectomy Surgical removal of the appendix (appendectomy) is usually performed through a transverse or gridiron (muscle‐splitting) incision centered at the McBurney point in the right lower quadrant (see clinical correlation [blue] box “Abdominal Surgical Incisions,” in this chapter). Traditionally, a gridiron incision is made perpendicular to the spinoumbilical line, but a transverse incision is also commonly used. The choice of incision site and type is at the surgeon's discretion. While typically the


inflamed appendix is deep to the McBurney point, the site of maximal pain and tenderness indicates the actual location. The following description outlines the clinical anatomy of an appendectomy—not the technique. Following incision of the skin and subcutaneous tissue, the external oblique aponeurosis is incised along the lines of its fibers. An opening is then made in the same way in the internal oblique and transverse abdominal muscles, thus avoiding their nerve supply. The iliohypogastric nerve is identified between the fleshy muscle layers and retracted. The transversalis fascia and peritoneum are incised, and the cecum is delivered into the surgical wound. The appendix arises from the convergence of the three teniae coli. Thus, if the appendix is not obvious, one of the teniae coli is traced to its base. The mesoappendix containing the appendicular vessels is firmly ligated and divided. The base of the appendix is tied, the appendix is excised, and its stump is usually cauterized and invaginated into the cecum. The incision is then closed in layers. Because each muscle layer runs in a different direction, the incision is well protected when the retracted layers are returned to their normal position. In unusual cases of malrotation of the intestine, or failure of descent of the cecum, the appendix is not in the lower right quadrant (Moore and Persaud, 2003). When the cecum is high (subhepatic cecum), the appendix is in the right hypochondriac region and the pain localizes there, not in the lower right quadrant.

Laparoscopy When the diagnosis is unclear, examination of the abdominal contents with a laparoscope passed through a small incision in the anterolateral abdominal wall is useful in differentiating acute appendicitis from other causes of abdominal pain, including inflammatory pelvic disease. Laparoscopy has been used for many years by gynecologists in evaluating women with lower abdominal pain (Soper, 2000). In addition, laparoscopy is used for removing the gallbladder and appendix and for treating abdominal obstruction.

Chapter 2: Abdomen

Figure 2.43. Veins, lymphatics, and innervation of large intestine and appendix. A. The venous drainage by the superior and inferior mesenteric veins corresponds to the pattern of the arteries they accompany. The IMV is most commonly a tributary of the splenic vein (as shown here), which then merges with the SMV to form the portal vein. B. From any part of the large intestine, the lymph flows sequentially to (1) epicolic nodes directly on the gut; (2) paracolic nodes along the


mesenteric border; (3) intermediate (meso‐) colic nodes, along the colic arteries (ileo‐, right, middle, and left); and then (4) to the superior or inferior mesenteric nodes, which usually drain by intestinal trunks to the chyle cistern. C. Presynaptic sympathetic fibers from T10 through L2 spinal cord levels pass through thoracic and lumbar splanchnic nerves to postsynaptic neurons in the superior and inferior (prevertebral) ganglia. Postsynaptic sympathetic fibers travel along the colic arteries to reach the large intestine. Presynaptic parasympathetic fibers from the vagus (CN X) nerves also pass along the colic arteries to the cecum, ascending colon, and most of the transverse colon. D. Presynaptic parasympathetic fibers from S2 through S4 spinal cord levels pass through pelvic splanchnic nerves to the inferior hypogastric (pelvic) plexuses and continue by way of nerves ascending from both right and left plexuses (left plexus not shown) to reach the sigmoid colon, descending colon, and most of the distal transverse colon. Pain fibers from most of the large intestine follow the sympathetic fibers retrograde to sensory ganglia of spinal nerves T10—L2; pain fibers from the distal sigmoid colon and rectum follow the parasympathetic fibers retrograde to sensory ganglia of spinal nerves S2—S4.

The Bottom Line The large intestine consists of the cecum; appendix; ascending, transverse, descending, and sigmoid colon; rectum; and anal canal. The large intestine is characterized by teniae coli, haustra, omental appendices, and a large caliber. The large intestine begins at the ileocecal valve; but its first part, the cecum, is a pocket that hangs inferior to the valve. The pouch‐like cecum, the widest part of the large intestine, is completely intraperitoneal and lacking a mesentery, so that it is mobile within the right iliac fossa. The ileocecal valve is a combination valve and weak sphincter, actively opening periodically to allow entry of ileal contents and forming a largely passive one‐way valve between the ileum and the cecum, preventing reflux. The appendix is an intestinal diverticulum, rich in lymphoid tissue, that enters the medial aspect of the cecum, usually deep to the junction of the lateral third and medial two thirds of the spinoumbilical line. Most commonly, the appendix is retrocecal in position, but 32% of the time it descends into the lesser pelvis. The cecum and appendix are supplied by branches of the ileocecal vessels.

Colon The colon is described as having four parts—ascending, transverse, descending, and sigmoid—that succeed one another in an arch (Fig. 2.41). The colon lies first to the right of the small intestine, then successively superior and anterior to it, to the left of it, and eventually inferior to it. The ascending colon is the second part of the large intestine. It passes superiorly on the right side of the abdominal cavity from the cecum to the right lobe of the liver, where it turns to the left at the right colic flexure (hepatic flexure). The ascending colon is narrower than the cecum and is secondarily retroperitoneal along the right side of the posterior abdominal wall. The ascending colon is covered by peritoneum anteriorly and on its sides; however, in approximately 25% of people it has a short mesentery. The ascending colon is separated from the anterolateral abdominal wall by the greater omentum. A deep vertical groove lined with parietal peritoneum, the right paracolic gutter, lies between the lateral aspect of the ascending colon and the adjacent abdominal wall (Fig. 2.38A).

Chapter 2: Abdomen

The arterial supply to the ascending colon and right colic flexure is from branches of the SMA, the ileocolic and right colic arteries (Table 2.10). These arteries anastomose with each other and with the right branch of the middle colic artery, the first of a series of anastomotic arcades that is continued by the left colic and sigmoid arteries to form a continuous arterial channel, the marginal artery (juxtacolic artery), that parallels and extends the length of the colon close to its mesenteric border. Tributaries of the SMV, the ileocolic and right colic veins, drain blood from the ascending colon (Fig. 2.43A). The lymphatic vessels pass first to the epicolic and paracolic lymph nodes, next to the ileocolic and intermediate right colic lymph nodes, and from them to the superior mesenteric lymph nodes (Fig. 2.43B). The nerves to the ascending colon derive from the superior mesenteric nerve plexus (Fig. 2.43C).

Mobile Ascending Colon When the inferior part of the ascending colon has a mesentery, the cecum and proximal part of the colon are abnormally mobile. This condition, present in approximately 11% of individuals, may cause volvulus of the colon (L. volvo, to roll), an obstruction of intestine resulting from twisting. Cecopexy may avoid volvulus and possible obstruction of the colon. In this anchoring procedure, a tenia coli of the cecum and proximal ascending colon is sutured to the abdominal wall. The transverse colon (approximately 45 cm long) is the third, longest, and most mobile part of the large intestine (Fig. 2.41). It crosses the abdomen from the right colic flexure to the left colic flexure, where it bends inferiorly to become the descending colon. The left colic flexure (splenic flexure) is usually more superior, more acute, and less mobile than the right colic flexure. It lies anterior to the inferior part of the left kidney and attaches to the diaphragm through the phrenicocolic ligament (Fig. 2.20). The mesentery of the transverse colon, the transverse mesocolon, loops down, often inferior to the level of the iliac crests, and is adherent to or fused with the posterior wall of the omental bursa. The root of the transverse mesocolon (Fig. 2.38A) lies along the inferior border of the pancreas and is continuous with the parietal peritoneum posteriorly. Being freely movable, the transverse colon is variable in position, usually hanging to the level of the umbilicus (L3 vertebral level) (Fig. 2.44A). However, in tall thin people, the transverse colon may extend into the pelvis (Fig. 2.44B).


Figure 2.44. Effect of body type (bodily habitus) on disposition of transverse colon. A. A heavily built hypersthenic individual with a short thorax and long abdomen is likely to have a transverse colon that is placed high. B. Individuals with a slender asthenic physique are likely to have a transverse colon that dips down toward or into the pelvis.

The arterial supply of the transverse colon is mainly from the middle colic artery (Table 2.10), a branch of the SMA. However, the transverse colon may also receive arterial blood from the right and left colic arteries via anastomoses, part of the series of anastomotic arcades that collectively form the marginal artery (juxtacolic artery). Venous drainage of the transverse colon is through the SMV (Fig. 2.43A). The lymphatic drainage of the transverse colon is to the middle colic lymph nodes, which in turn drain to the superior mesenteric lymph nodes (Fig. 2.43B). The nerves of the transverse colon pass from the superior mesenteric nerve plexus via the periarterial plexuses of the right and middle colic arteries (Fig. 2.43C). These nerves transmit sympathetic, parasympathetic (vagal), and visceral afferent nerve fibers (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter). The descending colon occupies a secondarily retroperitoneal position between the left colic flexure and the left iliac fossa, where it is continuous with the sigmoid colon (Fig. 2.41). Thus peritoneum covers the colon anteriorly and laterally and binds it to the posterior abdominal wall. Although retroperitoneal, the descending colon, especially in the iliac fossa, has a short mesentery in approximately 33% of people; however, it is usually not long enough to cause volvulus of the colon. As it descends, the colon passes anterior to the lateral border of the left kidney. As with the ascending colon, the descending colon has a paracolic gutter (the left) on its lateral aspect (Fig. 2.38A). The sigmoid colon, characterized by its S‐shaped loop of variable length (usually approximately 40 cm), links the descending colon and the rectum (Fig. 2.41). The sigmoid colon extends from the iliac fossa to the S3 segment, where it joins the rectum. The termination of the teniae coli, approximately 15 cm from the anus, indicates the rectosigmoid junction. The sigmoid colon usually has a long mesentery and, therefore, has considerable freedom of movement, especially its middle part. The root of the sigmoid mesocolon has an inverted V‐shaped attachment, extending first medially and superiorly along the external iliac vessels and then medially and inferiorly from the bifurcation of the common iliac vessels to the anterior aspect of

Chapter 2: Abdomen

the sacrum. The left ureter and the division of the left common iliac artery lie retroperitoneally, posterior to the apex of the root of the sigmoid mesocolon. The omental appendices of the sigmoid colon are long; they disappear when the sigmoid mesentery terminates. The teniae coli also disappear as the longitudinal muscle in the wall of the colon broadens to form a complete layer in the rectum. The arterial supply of the descending and sigmoid colon is from the left colic and sigmoid arteries, branches of the inferior mesenteric artery (Table 2.10). Thus, at approximately the left colic flexure, a second transition occurs in the blood supply of the abdominal part of the alimentary tract: the superior mesenteric artery supplying blood to that part orad to the flexure (the embryonic midgut), and the inferior mesenteric artery supplying blood to that part aborad to the flexure (the embryonic hindgut). The sigmoid arteries descend obliquely to the left, where they divide into ascending and descending branches. The superior branch of the most superior sigmoid artery anastomoses with the descending branch of the left colic artery, thereby forming a part of the marginal artery. The inferior mesenteric vein returns blood from the descending colon and sigmoid colon, flowing usually into the splenic vein and then the portal vein on its way to the liver (Figs. 2.43A and 2.88). The lymphatic vessels from the descending colon and sigmoid colon pass to the epicolic and paracolic nodes and then through the intermediate colic lymph nodes along the left colic artery (Fig. 2.43B). Lymph from these nodes passes to the inferior mesenteric lymph nodes that lie around the inferior mesenteric artery. However, lymph from the left colic flexure may also drain to the superior mesenteric lymph nodes. Orad to the left colic flexure, sympathetic and parasympathetic fibers travel together from the abdominal aortic plexus via periarterial plexuses to reach the abdominal part of the alimentary tract (Fig. 2.43C); however, aborad to the flexure, they follow separate routes. The sympathetic nerve supply of the descending and sigmoid colon is from the lumbar part of the sympathetic trunk via lumbar (abdominopelvic) splanchnic nerves, the superior mesenteric plexus, and the periarterial plexuses following the inferior mesenteric artery and its branches. The parasympathetic nerve supply is from the pelvic splanchnic nerves via the inferior hypogastric (pelvic) plexus and nerves, which ascend retroperitoneally from the plexus, independent of the arterial supply to this part of the alimentary tract (Fig. 2.43D). Orad to the middle of the sigmoid colon, visceral afferents conveying pain sensation pass retrogradely with sympathetic fibers to thoracolumbar spinal sensory ganglia, whereas those carrying reflex information travel with the parasympathetic fibers to vagal sensory ganglia. Aborad to the middle of the sigmoid colon, all visceral afferents follow the parasympathetic fibers retrogradely to the sensory ganglia of spinal nerves S2—S4 (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter).

Rectum and Anal Canal The rectum is the fixed (primarily retroperitoneal and subperitoneal) terminal part of the large intestine. It is continuous with the sigmoid colon at the level of S3 vertebra. The junction is at the inferior end of the mesentery of the sigmoid colon (Fig. 2.41). The rectum is continuous inferiorly with the anal canal. These parts of the large intestine are described with the pelvis in Chapter 3.


Colitis, Colectomy, Ileostomy, and Colostomy Chronic inflammation of the colon (ulcerative colitis, Crohn disease) is characterized by severe inflammation and ulceration of the colon and rectum. In some cases a colectomy is performed, during which the terminal ileum and colon, as well as the rectum and anal canal, are removed. An ileostomy is then constructed to establish an opening between the ileum and the skin of the anterolateral abdominal wall (Fig. B2.16A). Sometimes a colostomy is performed to create an artificial cutaneous opening into the colon (Fig. B2.16B). A sigmoidostomy establishes an artificial anus by creating a cutaneous opening into the sigmoid colon.

Figure B2.16. A. Ileostomy. B. Colostomy.

Colonoscopy The interior of the colon can be observed and photographed in a procedure called colonoscopy or coloscopy (Fig. B2.17A), using an elongated endoscope, usually a fiberoptic colonoscope (Fig. B2.17B). The endoscope is a flexible tube that inserts into the colon through the anus and rectum (Fig. B2.17A). Small instruments can be passed through the colonoscope and used to facilitate minor operative procedures, such as biopsies or removal of polyps. Most tumors of the large intestine occur in the rectum; approximately 12% of them appear near the rectosigmoid junction. The interior of the sigmoid colon is observed with a sigmoidoscope (sigmoscope), a shorter endoscope, in a procedure called sigmoidoscopy.

Chapter 2: Abdomen

Figure B2.17. Examination of large intestine. A. The colonoscopic procedure is shown. B. The parts of a colonoscope are shown. C. Diverticulosis of the colon can be photographed through a colonoscope. D. Diverticula in the sigmoid colon are shown.

Diverticulosis Diverticulosis is a disorder in which multiple false diverticula (external evaginations or out‐pocketings of the mucosa of the colon) develop along the intestine. It primarily affects middle‐aged and elderly people. Diverticulosis is commonly (60%) found in the sigmoid colon (Fig. B2.17C & D). Colonic diverticula are not true diverticula because they are formed from protrusions of mucous membrane only, evaginated through weak points (separations) developed between muscle fibers rather than involving the whole wall of the colon. They occur most commonly on the mesenteric side of the two nonmesenteric teniae coli, where nutrient arteries perforate the muscle coat to reach the submucosa. Diverticula are subject to infection and rupture, leading to diverticulitis, and they can distort and erode the nutrient arteries, leading to hemorrhage. Diverticulosis is less likely to develop in individuals adhering to a diet high in fiber.

The Bottom Line The colon is described as having four parts: ascending, transverse, descending, and sigmoid. The ascending colon is a superior, secondarily retroperitoneal continuation of the cecum, extending between the level of the ileocecal valve and the right colic flexure. The transverse colon, suspended by the transverse mesocolon between the right and the left flexures, is the longest and most mobile part of the large intestine. The level to which it descends depends largely on body type (habitus). The descending colon occupies a secondarily retroperitoneal position between the left


colic flexure and the left iliac fossa, where it is continuous with the sigmoid colon. The typically S‐shaped sigmoid colon, suspended by the sigmoid mesocolon, is highly variable in length and disposition, ending at the rectosigmoid junction. The teniae, haustra, and omental appendices cease at the junction, located anterior to the third sacral segment. Proximal (orad) to the left colic flexure, the large intestine (cecum, appendix, and ascending and transverse colons) is supplied by branches of the superior mesenteric vessels; distal (aborad) to the flexure, the colon (descending and sigmoid colons and superior rectum) is supplied by the inferior mesenteric vessels. The left colic flexure also marks the divide between cranial (vagal) and sacral (pelvic splanchnic) parasympathetic innervation of the alimentary tract. Sympathetic fibers are conveyed to the large intestine via abdominopelvic (lesser and lumbar) splanchnic nerves via the prevertebral (superior and inferior mesenteric) ganglia and periarterial plexuses. The middle of the sigmoid colon marks a divide in the sensory innervation of the abdominal alimentary tract. Orad, visceral afferents for pain travel retrogradely with sympathetic fibers to spinal sensory ganglia, whereas those conveying reflex information travel with parasympathetic fibers to vagal sensory ganglia. Aborad, both types of visceral afferent fibers travel with parasympathetic fibers to spinal sensory ganglia.

Spleen The spleen is an ovoid, usually purplish, pulpy mass about the size and shape of one's fist. It is relatively delicate and considered the most vulnerable abdominal organ. The spleen is located in the left upper abdominal quadrant or hypochondrium, where it receives the protection of the lower thoracic cage (Figs. 2.45A and 2.46). As the largest of the lymphatic organs, it participates in the body's defense system as a site of lymphocyte (white blood cell) proliferation and of immune surveillance and response. Prenatally, it is a hematopoietic (blood‐forming) organ, but after birth is involved primarily in identifying, removing, and destroying expended red blood cells (RBCs) and broken‐down platelets, and in recycling iron and globin. It serves as a blood reservoir, storing RBCs and platelets, and, to a limited degree, can provide a sort of “self‐transfusion” as a response to the stress imposed by hemorrhage. In spite of its size and the many useful and important functions it provides, it is not a vital organ (not necessary to sustain life). To accommodate these functions, the spleen is a soft, vascular (sinusoidal) mass with a relatively delicate fibroelastic capsule, entirely surrounded by peritoneum except at the splenic hilum, where the splenic branches of the splenic artery and vein enter and leave (Fig. 2.45B). Consequently, it is capable of marked expansion and some relatively rapid contraction. It is a mobile organ although it normally does not descend inferior to the costal (rib) region; it rests on the left colic flexure. It is associated posteriorly with the left 9th—11th ribs and separated from them by the diaphragm and the costodiaphragmatic recess—the cleft‐like extension of the pleural cavity between the diaphragm and the lower part of the thoracic cage (see Chapter 1). The relations of the spleen are  

Anteriorly, the stomach. Posteriorly, the left part of the diaphragm, which separates it from the pleura, lung, and ribs 9—11.

Chapter 2: Abdomen  

Inferiorly, the left colic flexure. Medially, the left kidney.

The spleen varies considerably in size, weight, and shape; however, it is usually approximately 12 cm long and 7 cm wide. (A nonmetric memory device exploits odd numbers: the spleen is 1 inch thick, 3 inches wide, 5 inches long, and weighs 7 ounces.) The diaphragmatic surface of the spleen is convexly curved to fit the concavity of the diaphragm. The anterior and superior borders of the spleen are sharp and often notched, whereas its posterior (medial) end and inferior border are rounded. The spleen normally contains a large quantity of blood that is expelled periodically into the circulation by the action of the smooth muscle in its capsule and trabeculae. The large size of the splenic artery (or vein) indicates the volume of blood that passes through the spleen's capillaries and sinuses. The thin fibrous capsule of the spleen is composed of dense, irregular, fibroelastic connective tissue (Fig. 2.45C). The fibrous capsule is thickened at the splenic hilum. Internally the trabeculae, arising from the deep aspect of the capsule, carry blood vessels to and from the parenchyma or splenic pulp, the substance of the spleen (Fig. 2.45C).

F i g u re 2 .4 5 . T h e s p l e e n . A . T h e s u r f a ce a n a t o m y o f th e s p l e e n a n d a s s o c i a t e d o r g a n s a re s h o w n . B . Th e v i s c e r a l s u r f a c e of the spleen is exposed. Notches are c h a r a c t e r i s t ic o f t h e s u p e r i o r b o r d e r . C o n c a v i t i e s on t h e v i s ce r a l s u r f a ce a re i m p r e s s i o n s f o r m e d b y th e s t r u c t u r e s i n c o n t a c t w i t h t h e s p l e e n . P a n c . , s i t e of c o n t a c t w i t h t a i l o f p a n c r e a s . C . Th e i n t e r n a l s t r u c t u r e o f th e s p l e e n is s e e n , including capsule, trabeculae, and pulp.


Figure 2.46. Pancreas, duodenum, biliary ducts, and spleen. A. The pancreas, extrahepatic bile passages, pancreatic ducts, and duodenum are shown. B. The entry of the bile duct and pancreatic duct into the duodenum through the hepatopancreatic ampulla—the dilation within the major duodenal papilla that normally receives the bile duct and the main pancreatic duct—is shown. Smooth muscle sphincters encircle the bile and pancreatic ducts and the hepatopancreatic ampulla. C. The interior of the descending part of the duodenum reveals the major and minor duodenal papillae. There is a hood over the larger papilla onto which the hepatopancreatic ampulla is opening. The bile duct and main pancreatic duct open separately on the papilla in approximately 5% of people. The accessory pancreatic duct opens on the minor duodenal papilla. D. The structure of the acinar (enzyme‐producing) tissue is demonstrated. The photomicrograph of the pancreas displays secretory acini and a pancreatic islet.

Chapter 2: Abdomen

The spleen contacts the posterior wall of the stomach and is connected to its greater curvature by the gastrosplenic ligament and to the left kidney by the splenorenal ligament (Fig. 2.22). These ligaments, containing splenic vessels, are attached to the hilum of the spleen on its medial aspect (Fig. 2.45B). The splenic hilum is often in contact with the tail of the pancreas and constitutes the left boundary of the omental bursa. The splenic artery is the largest branch of the celiac trunk and follows a tortuous course posterior to the omental bursa, anterior to the left kidney, and along the superior border of the pancreas (Figs. 2.47A and 2.48A). Between the layers of the splenorenal ligament, the splenic artery divides into five or more branches that enter the hilum. The lack of anastomosis of the arterial vessels in the spleen results in the formation of vascular segments of the spleen: two in 84% of spleens and three in the others, with relatively avascular planes between them, enabling subtotal splenectomy (see clinical correlation [blue] box, “Splenectomy and Splenomegaly,” in this chapter). The splenic vein is formed by several tributaries that emerge from the hilum (Figs. 2.46A and 2.47B). It is joined by the IMV and runs posterior to the body and tail of the pancreas throughout most of its course. The splenic vein unites with the SMV posterior to the neck of the pancreas to form the portal vein.

Figure 2.47. Arterial supply and venous drainage of pancreas. Because of the close relationship of the pancreas and duodenum, their blood vessels are the same in whole or in part.

The splenic lymphatic vessels leave the lymph nodes in the splenic hilum and pass along the splenic vessels to the pancreaticosplenic lymph nodes (Fig. 2.48A). These nodes relate to the posterior surface and superior border of the pancreas. The nerves of the spleen, derived from the celiac nerve plexus (Fig. 2.48B), are distributed mainly along branches of the splenic artery, and are vasomotor in function.


Rupture of the Spleen Although well protected by the 9th—12th ribs, the spleen is the most frequently injured organ in the abdomen. Severe blows on the left side may fracture one or more of these ribs, resulting in sharp bone fragments that can lacerate the spleen. In addition, blunt trauma to other regions of the abdomen that cause a sudden, marked increase in intra‐abdominal pressure (e.g., by impalement on the steering wheel of a car or the handlebars of a motor cycle) can cause the thin capsule and overlying peritoneum of the spleen to burst, disrupting its soft parenchyma or pulp (ruptured spleen). If ruptured, there is profuse bleeding (intraperitoneal hemorrhage) and shock.

Splenectomy and Splenomegaly Repair of a ruptured spleen is difficult; consequently, splenectomy (removal of the spleen) is often performed to prevent the person from bleeding to death. Sub‐total (partial) splenectomy, when possible, is followed by rapid regeneration. Even total splenectomy usually does not produce serious effects, especially in adults, because most of its functions are assumed by other reticuloendothelial organs (e.g., the liver and bone marrow), but there is a greater susceptibility to certain bacterial infections. When the spleen is diseased, resulting from, for example, granulocytic leukemia (high leukocyte and white blood cell count), it may enlarge to 10 or more times its normal size and average a weight of 100—250 g (splenomegaly). Spleen engorgement sometimes accompanies hypertension (high blood pressure). The spleen is not usually palpable in the adult; generally, if its lower edge can be detected when palpating below the left costal margin at the end of inspiration (Fig. B2.18A), it is enlarged about three times its “normal” size. Splenomegaly also occurs in some forms of hemolytic or granulocytic anemias, in which RBCs or white blood cells (WBCs), respectively, are destroyed at abnormally high rates (Fig. B2.18B). In such cases, a splenectomy may be life‐saving. Figure B2.18. Examination of spleen. A. Palpation of the spleen is demonstrated. B. This 4200 g spleen was seen at autopsy.

Chapter 2: Abdomen

Accessory Spleen(s) One or more small accessory spleens may form near the splenic hilum; they may be embedded partly or wholly in the tail of the pancreas, between the layers of the gastrosplenic ligament, in the infracolic compartment in the mesentery, or in close proximity to the ovary or testis (Fig. B2.19). In most affected individuals, only one accessory spleen is present. Accessory spleens are common (10%), are usually small (approximately 1 cm in diameter, but range from 0.2 to 10 cm), and often resemble a lymph node. Awareness of the possible presence of an accessory spleen is important because if not removed during splenectomy, the symptoms that indicated removal of the spleen (e.g., splenic anemia) may persist.

Figure B2.19. Potential sites of accessory spleens. The dots indicate where small accessory spleens may be located.

Splenic Needle Biopsy and Splenoportography The relationship of the costodiaphragmatic recess of the pleural cavity to the spleen is clinically important (see Fig. 2.31B). This potential space descends to the level of the 10th rib in the midaxillary line. Its existence must be kept in mind when doing a splenic needle biopsy, or when injecting radiopaque material into the spleen for visualization of the portal vein (splenoportography). If care is not exercised, this material may enter the pleural cavity, causing pleuritis (inflammation of the pleura).


Figure 2.48. Lymphatic drainage and innervation of pancreas and spleen. A. The arrows indicate lymph flow to the lymph nodes. B. The nerves of the pancreas are autonomic nerves from the celiac and superior mesenteric plexuses. A dense network of nerve fibers passes from the celiac plexus along the splenic artery to the spleen. Most are postsynaptic sympathetic fibers to smooth muscle of the splenic capsule, trabeculae, and intrasplenic vessels.

Chapter 2: Abdomen

The Bottom Line The spleen is highly vascular (sinusoidal), pulpy mass surrounded by a delicate fibroelastic capsule. It is completely covered by peritoneum, except at the splenic hilum, where the splenorenal ligament (conveying splenic vessels to the spleen) and gastrosplenic ligament (conveying the short gastric and left gastro‐omental vessels to the stomach) attach. Its average size is about that of one's fist, within a considerable range of normal variation. It is the largest of the lymphoid organs, but is not vital. As a blood reservoir, it is normally capable of considerable temporary expansion and contraction, but may undergo much more marked, chronic enlargement in disease. Although it receives protection from the overlying left 9th—11th ribs, the relatively delicate spleen is the abdominal organ most vulnerable to indirect trauma. Strong blows to the abdomen can cause a sudden increase in intra‐abdominal pressure that may rupture the organ, resulting in profuse intraperitoneal hemorrhage.

Pancreas The pancreas is an elongated, accessory digestive gland that lies retroperitoneally and transversely across the posterior abdominal wall, posterior to the stomach between the duodenum on the right and the spleen on the left (Fig. 2.46A). The transverse mesocolon attaches to its anterior margin. The pancreas produces  

An exocrine secretion (pancreatic juice from the acinar cells) that enters the duodenum through the main and accessory pancreatic ducts. Endocrine secretions (glucagon and insulin from the pancreatic islets [of Langerhans]) that enter the blood (Fig. 2.46D).

For descriptive purposes the pancreas is divided into four parts: head, neck, body, and tail. The head of the pancreas is the expanded part of the gland that is embraced by the C‐shaped curve of the duodenum to the right of the superior mesenteric vessels. It firmly attaches to the medial aspect of the descending and horizontal parts of the duodenum. The uncinate process, a projection from the inferior part of the pancreatic head, extends medially to the left, posterior to the SMA (Fig. 2.47A). The head of the pancreas rests posteriorly on the IVC, right renal artery and vein, and the left renal vein. On its way to opening into the descending part of the duodenum, the bile duct lies in a groove on the posterosuperior surface of the head or is embedded in its substance (Fig. 2.46A & B). The neck of the pancreas is short (1.5—2 cm) and overlies the superior mesenteric vessels (Fig. 2.46A), which form a groove in its posterior aspect (Fig. 2.35B & C). The anterior surface of the neck, covered with peritoneum, is adjacent to the pylorus of the stomach. The SMV joins the splenic vein posterior to the neck to form the portal vein. The body of the pancreas continues from the neck and lies to the left of the superior mesenteric vessels, passing over the aorta and L2 vertebra, posterior to the omental bursa. The anterior surface of the body of the pancreas is covered with peritoneum and lies in the floor of the omental bursa and forms part of the stomach bed. The posterior surface of the pancreatic body is devoid of peritoneum and is in contact with the aorta, SMA, left suprarenal gland, and left kidney and renal vessels (Fig. 2.46A).


The tail of the pancreas lies anterior to the left kidney, where it is closely related to the splenic hilum and the left colic flexure. The tail is relatively mobile and passes between the layers of the splenorenal ligament with the splenic vessels (Figs. 2.46A and 2.47A). The tip of the tail is usually blunted and turned superiorly. The main pancreatic duct begins in the tail of the pancreas and runs through the parenchyma of the gland to the pancreatic head: here it turns inferiorly and is closely related to the bile duct (Fig. 2.46A & B). Most of the time, the main pancreatic duct and the bile duct unite to form the short, dilated hepatopancreatic ampulla (of Vater), which opens into the descending part of the duodenum at the summit of the major duodenal papilla (Fig. 2.46B & C). At least 25% of the time, the ducts open into the duodenum separately. The sphincter of the pancreatic duct (around the terminal part of the pancreatic duct), the sphincter of the bile duct (around the termination of the bile duct), and the hepatopancreatic sphincter (of Oddi)—around the hepatopancreatic ampulla—are smooth muscle sphincters that control the flow of bile and pancreatic juice into the duodenum. An accessory pancreatic duct (Fig. 2.46A) opens into the duodenum at the summit of the minor duodenal papilla (Fig. 2.46C). Usually (60%), the accessory duct communicates with the main pancreatic duct. In some cases, the main pancreatic duct is smaller than the accessory pancreatic duct and the two are not connected. In such people, the accessory duct carries most of the pancreatic juice. These variations of the pancreatic ducts are explainable from their fusion or lack of fusion during pancreatic development (Moore and Persaud, 2003). The pancreatic arteries derive mainly from the branches of the markedly tortuous splenic artery, which form several arcades with pancreatic branches of the gastroduodenal and superior mesenteric arteries (Fig. 2.47A). Up to 10 branches of the splenic artery supply the body and tail of the pancreas. The anterior and posterior superior pancreaticoduodenal arteries, branches of the gastroduodenal artery, and the anterior and posterior inferior pancreaticoduodenal arteries, branches of the SMA, supply the head. The corresponding pancreatic veins are tributaries of the splenic and superior mesenteric parts of the portal vein; however, most of them empty into the splenic vein (Fig. 2.47B). The pancreatic lymphatic vessels follow the blood vessels (Fig. 2.48A). Most vessels end in the pancreaticosplenic lymph nodes, that lie along the splenic artery. Some vessels end in the pyloric lymph nodes. Efferent vessels from these nodes drain to the superior mesenteric lymph nodes or to the celiac lymph nodes via the hepatic lymph nodes. The nerves of the pancreas are derived from the vagus and abdominopelvic splanchnic nerves passing through the diaphragm (Fig. 2.48B). The parasympathetic and sympathetic fibers reach the pancreas by passing along the arteries from the celiac plexus and superior mesenteric plexus (see also “Summary of the Innervation of the Abdominal Viscera,” in this chapter). In addition to sympathetic fibers that pass to blood vessels, sympathetic and parasympathetic fibers are distributed to pancreatic acinar cells and islets. The parasympathetic fibers are secretomotor, but pancreatic secretion is primarily mediated by secretin and cholecystokinin, hormones formed by the epithelial cells of the duodenum and upper intestinal mucosa under the stimulus of acid contents from the stomach.

Chapter 2: Abdomen

Blockage of the Hepatopancreatic Ampulla and Pancreatitis Because the main pancreatic duct joins the bile duct to form the hepatopancreatic ampulla and pierces the duodenal wall, a gallstone passing along the extrahepatic bile passages may lodge in the constricted distal end of the ampulla, where it opens at the summit of the major duodenal papilla (Fig. 2.46A & B). In this case, both the biliary and pancreatic duct systems are blocked and neither bile nor pancreatic juice can enter the duodenum. However, bile may back up and enter the pancreatic duct, usually resulting in pancreatitis (inflammation of the pancreas). A similar reflux of bile sometimes results from spasms of the hepatopancreatic sphincter. Normally, the sphincter of the pancreatic duct prevents reflux of bile into the pancreatic duct; however, if the hepatopancreatic ampulla is obstructed, the weak pancreatic duct sphincter may be unable to withstand the excessive pressure of the bile in the hepatopancreatic ampulla. If the accessory pancreatic duct connects with the main pancreatic duct and opens into the duodenum, it may compensate for an obstructed main pancreatic duct or spasm of the hepatopancreatic sphincter.

Accessory Pancreatic Tissue It is not unusual for accessory pancreatic tissue to develop in the stomach, duodenum, ileum, or an ileal diverticulum; however, the stomach and duodenum are the most common sites. The accessory pancreatic tissue may contain pancreatic islet cells that produce glucagon and insulin.

Pancreatectomies In the treatment of some people with chronic pancreatitis, most of the pancreas is removed, a procedure called pancreatectomy. The anatomical relationships and the blood supply of the head of the pancreas, bile duct, and duodenum make it impossible to remove the entire head of the pancreas (Skandalakis et al., 1995). Usually a rim of the pancreas is retained along the medial border of the duodenum to preserve the duodenal blood supply.

Rupture of the Pancreas The pancreas is centrally located within the body and thus is well protected from all but the most severe penetrating trauma. The duodenum, into which its duct opens, is normally sterile. The pancreas, like the liver, has a considerable functional reserve. For all these reasons, the pancreas, as an exocrine organ, is not commonly a primary cause of clinical problems (discounting diabetes, an endocrine disorder of the islet cells); most exocrine pancreatic problems are secondary to biliary problems. Pancreatic injury can result, however, from sudden, severe, forceful compression of the abdomen, such as the force of impalement on a steering wheel in an automobile accident. Because the pancreas lies transversely, the vertebral column acts as an anvil, and the traumatic force may rupture the friable pancreas. Rupture of the pancreas frequently tears its duct system, allowing pancreatic juice to enter the parenchyma of the gland and to invade adjacent tissues. Digestion of pancreatic and other tissues by pancreatic juice is quite painful.


Pancreatic Cancer Cancer involving the pancreatic head accounts for most cases of extrahepatic obstruction of the biliary ducts. Because of the posterior relationships of the pancreas, cancer of the head often compresses and obstructs the bile duct and/or the hepatopancreatic ampulla. This condition causes obstruction, resulting in the retention of bile pigments, enlargement of the gallbladder, and jaundice (obstructive jaundice). Jaundice (Fr. jaune, yellow) is the yellow staining of most body tissues, skin, mucous membranes, and conjunctiva by circulating bile pigments. Approximately 90% of people with pancreatic cancer have ductular adenocarcinoma. Severe pain in the back is frequently present. Cancer of the neck and body of the pancreas may cause portal or inferior vena caval obstruction because the pancreas overlies these large veins (Fig. 2.46B). The pancreas's extensive drainage to relatively inaccessible lymph nodes and the fact that pancreatic cancer typically metastasizes to the liver early, via the portal vein, make surgical resection of the cancerous pancreas nearly futile (median survival time, regardless of therapy, is 2—3 months after diagnosis; Cotran et al., 1999).

The Bottom Line The pancreas is both an exocrine gland, producing pancreatic juice that is secreted into the duodenum for digestion, and an endocrine gland, producing insulin and glucagon that are released as hormones into the blood. The secondarily retroperitoneal pancreas consists of a head and uncinate process, neck, body, and tail. The head, to the right of the SMA, is embraced by the C‐shaped duodenum and penetrated by the termination of the bile duct, whereas its extension, the uncinate process, passes posterior to the SMA. The neck passes anterior to the SMA and SMV, the latter merging there with the splenic vein to form the portal vein. The body lies to the left of the SMA, running transversely across the posterior wall of the omental bursa and crossing anteriorly over the L2 vertebral body and abdominal aorta. The tail enters the splenorenal ligament as it approaches the splenic hilum. The splenic vein runs parallel and posterior to the tail and body as it runs from the spleen to the portal vein. The main pancreatic duct runs a similar course within the pancreas, continuing transversely through the head to merge with the bile duct to form the hepatopancreatic ampulla, which enters the descending part of the duodenum. As an endocrine gland, the pancreas receives an abundant blood supply from the pancreaticoduodenal and splenic arteries. Although it receives vasomotor sympathetic and secretomotor parasympathetic nerve fibers, regulation of pancreatic secretion is primarily hormonal. The pancreas is well protected by its central location in the abdomen. The exocrine pancreas is seldom the cause of clinical problems; although diabetes, involving the endocrine pancreas, has become increasingly common.

Surface Anatomy of the Spleen and Pancreas The spleen lies superficially in the left hypochondrium between the 9th and 11th ribs; its costal surface is convex to fit the inferior surface of the diaphragm and the curved bodies of these adjacent bones (Fig. SA2.3A). In the supine position, the long axis of the spleen is roughly parallel to the long axis of the 10th rib (Fig. SA2.3B). The close relationship of the spleen to the ribs that normally protect it can be a

Chapter 2: Abdomen

detrimental one in the presence of rib fractures. Normally, the spleen does not extend inferior to the left costal margin; thus it is seldom palpable through the anterolateral abdominal wall unless it is enlarged. When it is hardened and enlarged to approximately three times its normal size, it moves inferior to the left costal margin, and its notched superior border lies inferomedially. The notched border is helpful when palpating an enlarged spleen because when the person takes a deep breath, the notches can often be palpated.

Figure SA2.3. The neck of the pancreas overlies the L1 and L2 vertebrae in the transpyloric plane (Fig. SA2.3A). Its head is to the right and inferior to this plane, and its body and tail are to the left and superior to this level. Because the pancreas is deep in the abdominal cavity, posterior to the stomach and omental bursa, it is usually not palpable.

Liver The liver is the largest gland in the body and, after the skin, the largest single organ. It weighs approximately 1500 g and accounts for approximately 2.5% of adult body weight. In the late fetus—in which it also serves as a hematopoietic organ—it is proportionately twice as large (5% of body weight). From early childhood onward, it occupies almost all of the right hypochondrium and epigastrium. It extends into the left hypochondrium, inferior to the diaphragm, which separates it from the pleura, lungs, pericardium, and heart (Fig. 2.49A). Except for fat, all nutrients absorbed from the gastrointestinal tract are initially conveyed first to the liver by the portal venous system. In addition to its many metabolic activities, the liver stores glycogen and secretes bile. Bile passes from the liver via the biliary ducts—right and left hepatic


ducts that join to form the common hepatic duct, which unites with the cystic duct to form the bile duct. The liver produces bile continuously; however, between meals it accumulates and is stored in the gallbladder, which also concentrates the bile by absorbing water and salts. When food arrives in the duodenum, the gallbladder sends concentrated biliary through the bile ducts to the duodenum.

Surfaces, Peritoneal Reflections, and Relationships of the Liver The liver has a convex diaphragmatic surface (anterior, superior, and some posterior) and a relatively flat or even concave visceral surface (posteroinferior), which are separated anteriorly by its sharp inferior border (Fig. 2.49A). The diaphragmatic surface of the liver is smooth and dome shaped, where it is related to the concavity of the inferior surface of the diaphragm (Fig. 2.49A & C). Subphrenic recesses—superior extensions of the peritoneal cavity (greater sac)— exist between diaphragm and the anterior and superior aspects of the diaphragmatic surface of the liver. The subphrenic recesses are separated into right and left recesses by the falciform ligament, which extends between the liver and the anterior abdominal wall. The portion of the supracolic compartment of the peritoneal cavity immediately inferior to the liver is the subhepatic space (Figs. 2.49A and 2.21A). The hepatorenal recess (hepatorenal pouch; Morison pouch) is the posterosuperior extension of the subhepatic space, lying between the right part of the visceral surface of the liver and the right kidney and suprarenal gland (Fig. 2.49A & B). The hepatorenal recess is a gravity‐dependent part of the peritoneal cavity in the supine position; fluid draining from the omental bursa flows into this recess (Figs. 2.49E and 2.17). The hepatorenal recess communicates anteriorly with the right subphrenic recess (Fig. 2.49A). Recall that normally all recesses of the peritoneal cavity are potential spaces only, containing only enough peritoneal fluid to lubricate the adjacent peritoneal membranes.

Chapter 2: Abdomen

Figure 2.49. Surfaces and peritoneal relationships of liver. A. This sagittal section through the diaphragm, liver, and right kidney demonstrates the two surfaces of the liver and related peritoneal recesses. B. The peritoneal reflections (ligaments) and cavity related to the liver are shown. The attachments of the liver are cut through and the liver is turned to the right and posteriorly, as when turning the page of a book. C. The anterior part of the domed diaphragmatic surface of the liver conforms to the inferior surface of the diaphragm. This extensive surface of the liver is divided into superior, anterior (shown here), right, and posterior parts. D. In the anatomical position, the visceral surface of the liver is directed inferiorly, posteriorly, and to the left. In embalmed specimens, impressions remain where this surface is contacted by adjacent structures. E. In the supine position, the hepatorenal recess is gravity dependent, receiving drainage from the omental bursa and upper abdominal (supracolic) portions of the greater sac.


The diaphragmatic surface of the liver is covered with visceral peritoneum, except posteriorly in the bare area of the liver (Fig. 2.49A, B, & D), where it lies in direct contact with the diaphragm. The bare area is demarcated by the reflection of peritoneum from the diaphragm to it as the anterior (upper) and posterior (lower) layers of the coronary ligament. These layers meet on the right to form the right triangular ligament and diverge toward the left to enclose the triangular bare area. The anterior layer of the coronary ligament is continuous on the left with the right layer of the falciform ligament, and the posterior layer is continuous with the right layer of the lesser omentum. Near the apex (the left extremity) of the wedge‐shaped liver, the anterior and posterior layers of the left part of the coronary ligament meet to form the left triangular ligament (Fig. 2.49C & D). The inferior vena cava traverses a deep groove for the vena cava within the bare area of the liver. The visceral surface of the liver is covered with peritoneum (Fig. 2.49D), except at the fossa for the gallbladder and the porta hepatis—a transverse fissure where the vessels (portal vein, hepatic artery, and lymphatic vessels), the hepatic nerve plexus, and hepatic ducts that supply and drain the liver enter and leave it. In contrast to the smooth diaphragmatic surface, the visceral surface bears multiple fissures and impressions from contact with other organs. Two sagittal fissures, linked centrally by the transverse porta hepatis, form the letter H on the visceral surface (Fig. 2.50A). The right sagittal fissure is the continuous groove formed anteriorly by the fossa for the gallbladder and posteriorly by the groove for the vena cava; the left sagittal fissure is the continuous groove formed anteriorly by the fissure for the ligamentum teres or round ligament, and posteriorly by the fissure for the ligamentum venosum. The round ligament of the liver is the fibrous remnant of the umbilical vein, which carried well‐oxygenated and nutrient‐rich blood from the placenta to the fetus; the round ligament and small paraumbilical veins course in the free edge of the falciform ligament. The ligamentum venosum is the fibrous remnant of the fetal ductus venosus, which shunted blood from the umbilical vein to the IVC, short‐circuiting the liver (Moore and Persaud, 2003). The lesser omentum, enclosing the portal triad (bile duct, hepatic artery, and portal vein) passes from the liver to the lesser curvature of the stomach and the first 2 cm of the superior part of the duodenum (Fig. 2.51). The thick, free edge of the lesser omentum extends between the porta hepatis and the duodenum (the hepatoduodenal ligament) and encloses the structures that pass through the porta hepatis. The sheet‐ like remainder of the lesser omentum, the hepatogastric ligament, extends between the groove for the ligamentum venosum of the liver and the lesser curvature of the stomach.

Chapter 2: Abdomen

Figure 2.50. Visceral surface of the liver. A. The four anatomical lobes of the liver are defined by external features (peritoneal reflections and fissures). The left sagittal fissure (and the falciform ligament on the diaphragmatic surface) demarcate right and left lobes. The right and left sagittal fissures and the porta hepatis connecting them form an H on the visceral surface, demarcating the quadrate and caudate lobes.B. Structures forming the fissures of the visceral surface are shown. The round ligament of the liver is the occluded remains of the fetal umbilical vein. The ligamentum venosum is the fibrous remnant of the ductus venosum that shunted blood from the umbilical vein to the IVC.

F i g u re 2 . 5 1 . L e s s e r o m e n t u m a n d p o rt a l t r i a d . T h e a n te r i o r s a g i t t a l c u t i s m a d e i n t h e p l a n e o f t h e f o s s a f o r t h e g a l l b l a d d e r , a n d t h e p o s t e r i o r s a g it t a l c u t i s i n t h e p l a n e o f t h e f is s u re f o r t h e l i g a m e n t u m v e n o s u m . T h e s e c u t s h a v e b e e n j o i n e d b y a n a r r o w c o r o n a l c u t i n t h e p l a n e o f t h e p o r ta h e p a t i s . T h e p o r t a l t r i a d p a s s e s b e t w e e n t h e l a y e r s o f t h e h e p a t o d u o d e n a l l i g a m e n t t o e n t e r t h e l i v e r a t t h e p o r t a h e p a t i s . T h e c o m m o n h e p a t i c a r t e r y p a s s e s b e t we e n t h e l a y e rs o f th e h e p a t o g a s t r ic l i g a m e n t .


In addition to the fissures, impressions on (areas of) the visceral surface reflect the liver's relationship to the:      

Right side of the anterior aspect of the stomach (the gastric and pyloric areas). Superior part of the duodenum (the duodenal area). Lesser omentum (extends into the fissure for the ligamentum venosum). Gallbladder (fossa for gallbladder). Right colic flexure and right transverse colon (the colic area). Right kidney and suprarenal gland (the renal and suprarenal areas).

Subphrenic Abscesses Peritonitis may result in the formation of localized abscesses in various parts of the peritoneal cavity. A common site for pus to collect is in a subphrenic recess or space. These subphrenic abscesses are more common on the right side because of the frequency of ruptured appendices and perforated duodenal ulcers. Because the right and left subphrenic recesses are continuous with the hepatorenal recess (the lowest [most gravity dependent] parts of the peritoneal cavity when supine), pus from a subphrenic abscess may drain into one of the hepatorenal recesses, especially when patients are bedridden. A subphrenic abscess is often drained by an incision inferior to, or through, the bed of the 12th rib (Ellis, 1992), obviating the formation of an opening in the pleura or peritoneum. An anterior subphrenic abscess is often drained through a subcostal incision located inferior and parallel to the right costal margin.

Anatomical Lobes of the Liver Externally, the liver is divided into two topographical (anatomical) lobes and two accessory lobes by the reflections of peritoneum from its surface, the fissures formed in relation to those reflections, and the vessels serving the liver and gallbladder. These superficial “lobes” are not true lobes as the term is generally used in relation to glands and are only secondarily related to the liver's internal architecture. The essentially midline plane defined by the attachment of the falciform ligament and the left sagittal fissure separates a large right lobe from a much smaller left lobe (Figs. 2.49C & D and 2.50). On the slanted visceral surface, the right and left sagittal fissures surround and the transverse porta hepatis demarcates two accessory lobes (parts of the anatomic right lobe): the quadrate lobe anteriorly and inferiorly and the caudate lobe posteriorly and superiorly. The caudate lobe is so‐named not because it is caudal in position (it is not) but because it often gives rise to a “tail” in the form of an elongated papillary process (Fig. 2.49D). A caudate process extends to the right, between the IVC and the portal hepatis, connecting the caudate and right lobes (Fig. 2.50B).

Functional Subdivision of the Liver Although not distinctly demarcated internally, where the parenchyma appears continuous, the liver has functionally independent right and left livers (parts or portal lobes) that are much more equal in size than the anatomical lobes; however, the right liver is still somewhat larger (Fig. 2.52; Table 2.11). Each part receives its own primary branch of the hepatic artery and portal vein and is drained by its own

Chapter 2: Abdomen

hepatic duct. The caudate lobe may in fact be considered a third liver; its vascularization is independent of the bifurcation of the portal triad (it receives vessels from both bundles) and is drained by one or two small hepatic veins, which enter directly into the IVC distal to the main hepatic veins. The liver can be further subdivided into four divisions and then into eight surgically resectable hepatic segments, each served independently by a secondary or tertiary branch of the portal triad (Fig. 2.52; see legend for details).

Blood Vessels of the Liver The liver, like the lungs, has a dual blood supply (afferent vessels): a dominant venous source and a lesser arterial one (Fig. 2.51). The portal vein brings 75—80% of the blood to the liver. Portal blood, containing about 40% more oxygen than blood returning to the heart from the systemic circuit, sustains the liver parenchyma (liver cells or hepatocytes). The portal vein carries virtually all of the nutrients absorbed by the alimentary tract (except lipids, which bypass the liver in the lymphatic system) to the sinusoids of the liver (Fig. 2.53). Arterial blood from the hepatic artery, accounting for only 20—25% of blood received by the liver, is distributed initially to non‐parenchymal structures, particularly the intrahepatic bile ducts. The portal vein, a short, wide vein, is formed by the superior mesenteric and splenic veins posterior to the neck of the pancreas and ascends anterior to the IVC as part of the portal triad in the hepatoduodenal ligament (Fig. 2.51). The hepatic artery, a branch of the celiac trunk, may be divided into the common hepatic artery, from the celiac trunk to the origin of the gastroduodenal artery, and the hepatic artery proper, from the origin of the gastroduodenal artery to the bifurcation of the hepatic artery. At or close to the porta hepatis, the hepatic artery and portal vein terminate by dividing into right and left branches; these primary branches supply the right and left livers, respectively. Within each part, the simultaneous secondary branchings of the portal vein and hepatic artery (portal pedicles) are consistent enough to supply the medial and lateral divisions of the right and left liver, with three of the four secondary branches undergoing further (tertiary) branchings to supply independently seven of the eight hepatic segments (Fig. 2.52). Between the divisions are the right, intermediate (middle), and left hepatic veins, which are intersegmental in their distribution and function, draining parts of adjacent segments. The hepatic veins, formed by the union of collecting veins that in turn drain the central veins of the hepatic parenchyma (Fig. 2.53), open into the IVC just inferior to the diaphragm. The attachment of these veins to the IVC helps hold the liver in position.

Hepatic Lobectomies and Segmentectomy When it was discovered that the right and left hepatic arteries and ducts, as well as branches of the right and left portal veins, do not communicate, it became possible to perform hepatic lobectomies, removal of the right or left (part of the) liver, without excessive bleeding. Most injuries to the liver involve the right liver. More recently, especially since the advent of the cauterizing scalpel and laser surgery, it has become possible to perform hepatic segmentectomies. This procedure makes it possible to remove (resect) only those segments that have sustained a severe injury or are affected by a tumor. The intersegmental hepatic veins serve as guides to the


planes between the hepatic divisions; however, they also provide a major source of bleeding with which the surgeon must contend. While the pattern of branching described here is the most common pattern, the segments vary considerably in size and shape as a result of individual variation in the branching of the hepatic and portal vessels, so that each hepatic resection is empirical, requiring ultrasonography, injection of dye, or balloon catheter occlusion to establish the patient's segmental pattern. (Cheng et al., 1997) A more extensive injury that is likely to leave large areas of the liver devascularized may still require lobectomy.

Figure 2.52. Hepatic segmentation. Except for the caudate lobe (segment I), the liver is divided into right and left livers based on the primary (1°) division of the portal triad into right and left branches, the plane between the right and the left livers being the main portal fissure (1) in which the middle hepatic vein lies. On the visceral surface, this plane is demarcated by the right sagittal fissure. The plane is demarcated on the diaphragmatic surface by an imaginary line—the Cantlie line (Cantlie, 1898)—running from the notch for the fundus of the gallbladder to the IVC (Table 2.11). The right and left livers are subdivided vertically into medial and lateral divisions by the right portal (2) and left portal (umbilical) (3) fissures, in which the right and left hepatic veins lie. The left portal fissure is demarcated externally by the falciform ligament and the left sagittal fissure. The right portal fissure has no external demarcation. Each division receives a secondary (2°) branch of the portal triad (a portal pedicle). (Note: the medial division of the left liver is part of the right anatomical lobe; the lateral division of the left liver is the same as the left anatomical lobe.) A transverse plane at the level of the horizontal parts of the right and left branches of the portal triad (4) subdivides three of the four divisions (all but the left medial division), creating six hepatic segments receiving tertiary branches. The left medial division is also counted as a hepatic segment, so that the main part of the liver has seven segments (segments II—VIII, numbered clockwise). The caudate lobe (segment I, bringing the total number of segments to eight) is supplied by branches of both divisions and is drained by its own minor hepatic veins. Each segment thus has its own blood supply and biliary drainage. The hepatic veins are intersegmental, draining the portions of the multiple segments adjacent to them.

Chapter 2: Abdomen

Rupture of the Liver The liver is easily injured because it is large, fixed in position, and friable (easily crumbled). Often a fractured rib that perforates the diaphragm tears the liver. Because of the liver's great vascularity and friability, liver lacerations often cause considerable hemorrhage and right upper quadrant pain. In such cases, the surgeon must decide whether to remove foreign material and the contaminated or devitalized tissue by dissection or to perform a segmentectomy. Table 2.11. Terminology for subdivisions of the Liver

Anatomical Term Functional/Surgical Term**

Right Lobe Right (part of) Liver [Right portal lobe*] Right lateral Right medial division division

Left Lobe Left (part of) Liver [Left portal lobe+] Left medial Left lateral division division

Posterior lateral segment Segment VII [Posterior superior area]

[Medial superior area] Left medial segment Segment IV [Medial inferior area = quadrate lobe]

Right anterior lateral segment Segment VI [Posterior inferior area]

Posterior medial segment Segment VIII [Anterior superior area] Anterior medial segment Segment V [Anterior inferior area]

Lateral segment Segment II [Lateral superior area]

Caudate Lobe Posterior (part of) Liver Right caudate lobe*] Posterior Segment I

[Left caudate lobe+] segment

Left lateral anterior segment Segment III [Lateral inferior area]

**The labels in the table and figure above reflect the new Terminologia Anatomica: International Anatomical Terminology. Previous terminology is in brackets. *+ Under the schema of the previous terminology, the caudate lobe was divided into right and left halves, and * the right half of the caudate lobe was considered a subdivision of the right portal lobe; + the left half of the caudate lobe was considered a subdivision of the left portal lobe. ++ Cantlie line and the right sagittal fissure are surface markings defining the main portal fissure.


Figure 2.53. Flow of blood and bile in the liver. A. This view of a small part of a liver lobule illustrates the components of the interlobular portal triad and the positioning of the sinusoids and bile canaliculi. The enlarged view of the surface of a block of parenchyma removed from the liver in part B shows the hexagonal pattern of lobes and the place of part A within that pattern.B. Extrahepatic bile passages, gallbladder, and pancreatic ducts are demonstrated. C. The bile duct and pancreatic duct enter into the hepatopancreatic ampulla, which opens into the descending part of the duodenum.

Chapter 2: Abdomen

Aberrant Hepatic Arteries A more common variety of right or left hepatic artery that arises as a terminal branch of the hepatic artery proper may be replaced in part or entirely by an aberrant (accessory or replaced) artery arising from another source. The most common source of an aberrant right hepatic artery is the SMA (Fig. B2.20A). The most common source of an aberrant left hepatic artery is the left gastric artery (Fig. B2.20B).

Variations in the Relationships of the Hepatic Arteries In most people, the right hepatic artery crosses anterior to the portal vein (Fig. B2.20C); however, in some people, the artery crosses posterior to the portal vein (Fig. B2.20D). In most people, the right hepatic artery runs posterior to the common hepatic duct (Fig. B2.20F). In some individuals the right hepatic artery crosses anterior to the common hepatic duct (Fig. B2.20E), or the right hepatic artery arises from the IVC and so does not cross the common hepatic duct at all (Fig. B2.20G).

Figure B2.20.


Unusual Formation of the Portal Vein Usually, the portal vein forms posterior to the neck of the pancreas by the union of the superior mesenteric and splenic veins and ascends anterior to the IVC. In approximately one third of individuals, the IMV joins the confluence of the superior mesenteric and splenic veins; hence, all three veins form the portal vein. In most people, the IMV enters the splenic vein (60%) or the SMV (40%).

Lymphatic Drainage and Innervation of the Liver The liver is a major lymph‐producing organ. Between one quarter and one half of the lymph received by the thoracic duct comes from the liver. The lymphatic vessels of the liver occur as superficial lymphatics in the subperitoneal fibrous capsule of the liver (Glisson capsule), which forms its outer surface (Fig. 2.51), and as deep lymphatics in the connective tissue, which accompany the ramifications of the portal triad and hepatic veins (Fig. 2.53A). Most of the lymph is formed in the perisinusoidal spaces (of Disse) and drains to the deep lymphatics in the surrounding intralobular portal triads. Superficial lymphatics from the anterior aspects of the diaphragmatic and visceral surfaces and the deep lymphatic vessels accompanying the portal triads converge toward the porta hepatis. They drain to the hepatic lymph nodes scattered along the hepatic vessels and ducts in the lesser omentum (Fig. 2.54A). Efferent lymphatic vessels from the hepatic nodes drain into celiac lymph nodes, which in turn drain into the chyle cistern, a dilated sac at the inferior end of the thoracic duct. Superficial lymphatics from the posterior aspects of the diaphragmatic and visceral surfaces of the liver drain toward the bare area of the liver. Here they drain into phrenic lymph nodes, or join deep lymphatics that have accompanied the hepatic veins converging on the IVC, and pass with this large vein through the diaphragm to drain into the posterior mediastinal lymph nodes. Efferent vessels from these nodes join the right lymphatic and thoracic ducts. A few lymphatic vessels follow different routes:   

From the posterior surface of the left lobe toward the esophageal hiatus of the diaphragm to end in the left gastric lymph nodes (Fig. 2.54A). From the anterior central diaphragmatic surface along the falciform ligament to the parasternal lymph nodes. Along the round ligament of the liver to the umbilicus and lymphatics of the anterior abdominal wall.

The nerves of the liver are derived from the hepatic plexus (Fig. 2.54B), the largest derivative of the celiac plexus. The hepatic plexus accompanies the branches of the hepatic artery and portal vein to the liver. It consists of sympathetic fibers from the celiac plexus and parasympathetic fibers from the anterior and posterior vagal trunks. Nerve fibers accompany the vessels and biliary ducts of the portal triad. Other than vasoconstriction, their function is unclear.

Hepatomegaly The liver is a soft and highly vascular organ that receives a large amount of blood immediately before it enters the heart. Both the inferior vena cava and hepatic veins lack valves. Any rise in central venous pressure is directly transmitted to the liver,

Chapter 2: Abdomen

which enlarges as it becomes engorged with blood. Marked temporary engorgement stretches the fibrous capsule of the liver, producing pain around the lower ribs, particularly in the right hypochondrium. This engorgement, particularly in conjunction with increased or sustained diaphragmatic activity, has been proposed as an underlying cause of “runner's stitch,” perhaps explaining why it is a right‐sided phenomenon. In addition to diseases that produce hepatic engorgement such as congestive heart failure, bacterial and viral diseases such as hepatitis cause liver enlargement, or hepatomegaly. When the liver is massively enlarged, its inferior edge may be readily palpated below the right costal margin and may even reach the pelvic brim in the right lower quadrant of the abdomen. Tumors also enlarge the liver. The liver is a common site of metastatic carcinoma (secondary cancers spreading from organs drained by the portal system of veins). Cancer cells may also pass to the liver from the thorax, especially from the right breast, because of the communications between thoracic lymph nodes and the lymphatic vessels draining the bare area of the liver. Metastatic tumors form hard, rounded nodules within the hepatic parenchyma. In view of the great functional reserve of the liver, signs of liver failure may be absent in a liver loaded with metastatic tumors.

Cirrhosis of the Liver The liver is the primary site for detoxification of substances absorbed by the digestive system, and so it is vulnerable to cellular damage and consequent scarring, accompanied by regenerative nodules. There is progressive destruction of hepatocytes (parenchymal liver cells) in hepatic cirrhosis and replacement of them by fat and fibrous tissue. Although many industrial solvents, such as carbon tetrachloride, produce cirrhosis, the condition develops most frequently in persons suffering from chronic alcoholism. Alcoholic cirrhosis, the most common of many causes of portal hypertension, is characterized by enlargement of the liver resulting from fatty changes and fibrosis. The liver has great functional reserve, and so the metabolic evidence of liver failure is late to appear. Fibrous tissue surrounds the intrahepatic blood vessels and biliary ducts, making the liver firm, and impeding the circulation of blood through it (portal hypertension). The treatment of advanced cirrhosis may include the surgical creation of a portosystemic or portocaval shunt, anastomosing the portal and systemic venous systems (see clinical correlation [blue] box “Portosystemic Shunts,” in this chapter).

Clinically Oriented Anatomy, 5th Edition By Keith Moore Figure 2.54. Lymphatic drainage and innervation of liver. A. Lymph from the posterior aspect of the liver (superficial and deep) flows toward the bare area to enter the phrenic lymph nodes, or pass with the IVC through the caval foramen in the diaphragm to enter mediastinal lymph nodes. Lymph from the anterior and inferior aspects (superficial and deep) flows toward the porta hepatis to enter hepatic lymph nodes in the lesser omentum. B. The nerves of the liver derive from the hepatic plexus, the largest derivative of the celiac plexus. The hepatic plexus accompanies the branches of the hepatic artery and portal vein to the liver. It consists of sympathetic fibers from the celiac plexus and parasympathetic fibers from the anterior and posterior vagal trunks.

P.300

Surface Anatomy of the Liver The liver lies mainly in the right upper quadrant of the abdomen where it is hidden and protected by the thoracic cage and diaphragm. The normal liver lies deep to ribs 7—11 on the right side and crosses the midline toward the left nipple. Consequently, the liver occupies most of the right hypochondrium, the upper epigastrium, and extends into the left hypochondrium. The liver is located more inferiorly when one is erect because of gravity. Its sharp inferior border follows the right costal margin. When a person in the supine position is asked to inspire deeply, the liver may be palpated because of the inferior movement of the diaphragm and liver (Fig. SA2.4A). One method of palpating the liver is to place the left hand posteriorly behind the

Chapter 2: Abdomen

lower rib cage. Then, put the right hand on the person's right upper quadrant, lateral to the rectus abdominis and inferior to the costal margin (Fig. SA2.4B). The person is asked to take a deep breath as the examiner presses posterosuperiorly with the right hand and pulls anteriorly with the left hand (Bickley and Szilagyi, 2003).

Figure SA2.4.

Liver Biopsy Hepatic tissue may be obtained for diagnostic purposes by liver biopsy. Because the liver is located in the right hypochondriac region where it receives protection from the overlying thoracic cage, the needle is commonly directed through the right 10th intercostal space in the midaxillary line. Before the physician takes the biopsy, the person is asked to hold his or her breath in full expiration to reduce the costodiaphragmatic recess and to lessen the possibility of damaging the lung and contaminating the pleural cavity.

The Bottom Line The liver has multiple functions. It is our greatest metabolic organ, initially receiving all absorbed foodstuffs, except fats. It is also our largest gland, functioning as an extrinsic intestinal gland in producing bile. The liver occupies essentially all of the right dome of the diaphragm and extends to the apex of the left dome. Consequently, it enjoys protection from the lower thoracic cage, and moves with respiratory excursions. It is divided superficially by the falciform ligament and groove for the ligamentum venosum into a large anatomical right lobe and a much smaller left one; formations on its visceral surface demarcate caudate and quadrate lobes. It is covered with peritoneum except for a sizable bare area, demarcated by peritoneal reflections comprising the coronary ligaments. Based on interdigitated branchings of the portal triad (portal vein, hepatic artery and intrahepatic bile ducts) and hepatic veins, its continuous parenchyma can be divided into right and left livers (plus the caudate lobe). It can be further subdivided into four divisions and then eight surgically resectable hepatic segments. The liver, like the lungs, receives a dual blood supply, with 75—80% of the blood arriving via the portal vein, meeting the nutritional needs of the hepatic parenchyma; 20—25% arrives via the hepatic artery,


delivered primarily to the non‐parenchymal elements. These vessels enter the liver via the porta hepatis, where the hepatic ducts exit. Three large hepatic veins drain directly to the IVC as it is embedded in the liver's bare area. The liver is also the body's largest lymph‐producing organ. Its visceral aspect drains via an abdominal route and its diaphragmatic aspect drains via a thoracic route.

Biliary Ducts and Gallbladder The biliary ducts convey bile from the liver to the duodenum. Bile is produced continuously by the liver and stored and concentrated in the gallbladder, which releases it intermittently when fat enters the duodenum. Bile emulsifies the fat, so that it can be absorbed in the distal intestine. Normal hepatic tissue, when sectioned, is traditionally described as demonstrating a pattern of hexagonal‐shaped liver lobules (Fig. 2.53A) when viewed under low magnification. Each lobule has a central vein running through its center from which sinusoids (large capillaries) and plates of hepatocytes (liver cells) radiate toward an imaginary perimeter extrapolated from surrounding interlobular portal triads (terminal branches of the portal vein and hepatic artery, and initial branches of the biliary ducts). Although commonly said to be the anatomical units of the liver, hepatic “lobules” are not structural entities; instead, the lobular pattern is a physiological consequence of pressure gradients and is altered by disease. Because the bile duct is not central, the hepatic lobule does not represent a functional unit like acini of other glands. However, the hepatic lobule is a firmly established concept and is useful for descriptive purposes. The hepatocytes secrete bile into the bile canaliculi formed between them. The canaliculi drain into the small interlobular biliary ducts and then into large collecting bile ducts of the intrahepatic portal triad, which merges to form the right and left hepatic ducts (Fig. 2.53B). The right and left hepatic ducts drain the right and left (parts of the) liver, respectively. Shortly after leaving the porta hepatis, the right and left hepatic ducts unite to form the common hepatic duct, which is joined on the right side by the cystic duct to form the bile duct (part of the extrahepatic portal triad of the lesser omentum), which conveys the bile to the duodenum.

Bile Duct The bile duct (formerly, common bile duct) forms in the free edge of the lesser omentum by the union of the cystic duct and the common hepatic duct (Figs. 2.51 and 2.53B). The length of the bile duct varies from 5 to 15 cm, depending on where the cystic duct joins the common hepatic duct. The bile duct descends posterior to the superior part of the duodenum and lies in a groove on the posterior surface of the head of the pancreas. On the left side of the descending part of the duodenum, the bile duct comes into contact with the main pancreatic duct. These ducts run obliquely through the wall of this part of the duodenum, where they unite to form the hepatopancreatic ampulla, the dilation within the major duodenal papilla. The distal end of the ampulla opens into the duodenum through the major duodenal papilla (Fig. 2.47). The circular muscle around the distal end of the bile duct is thickened to form the sphincter of the bile duct. When this sphincter contracts, bile cannot enter the ampulla and the duodenum; hence bile backs up and passes along the cystic duct to the gallbladder for concentration and storage.

Chapter 2: Abdomen

The arteries supplying the bile duct include (Fig. 2.55) the:   

Cystic artery: supplying the proximal part of the duct. Right hepatic artery: supplying the middle part of the duct. Posterior superior pancreaticoduodenal artery and gastroduodenal artery: supplying the retroduodenal part of the duct. Figure 2.55. Lymphatic drainage of gallbladder and bile duct. Lymph passes from the cystic and hepatic lymph nodes and the node of the omental foramen to the celiac lymph nodes surrounding the celiac trunk. The lymphatic vessels of the gallbladder and biliary passages anastomose superiorly with those of the liver and inferiorly with those of the pancreas.

Figure 2.56. Nerves and veins of liver and biliary system. Nerves are prominent along the hepatic artery, portal vein, and bile duct. The sympathetic nerve supply is vasomotor in the liver and biliary system. The veins of the gallbladder neck communicate with veins along the cystic and biliary ducts. Small cystic veins pass from the gallbladder into the liver.


The veins from the proximal part of the bile duct and the hepatic ducts usually enter the liver directly. The posterior superior pancreaticoduodenal vein drains the distal part of the bile duct and empties into the portal vein or one of its tributaries. The lymphatic vessels from the bile duct pass to the cystic lymph nodes near the neck of the gallbladder, the node of the omental foramen, and the hepatic lymph nodes. Efferent lymphatic vessels from the bile duct pass to the celiac lymph nodes.

Gallbladder The gallbladder (7—10 cm long) lies in the fossa for the gallbladder on the visceral surface of the liver (Figs. 2.49D and 2.56). This shallow fossa lies at the junction of the right and left (parts of the) liver. The relationship of the gallbladder to the duodenum is so intimate that the superior part of the duodenum is usually stained with bile in the cadaver (Fig. 2.57). Because the liver and gallbladder must be retracted superiorly to expose the gallbladder during an anterior approach (and atlases often depict it in this position), it is easy to forget that in its natural position the body of the gallbladder lies anterior to the duodenum, and its neck and the cystic duct are immediately superior to the duodenum. The pear‐shaped gallbladder can hold up to 50 mL of bile. Peritoneum completely surrounds the fundus of the gallbladder and binds its body and neck to the liver. The hepatic surface of the gallbladder attaches to the liver by connective tissue of the fibrous capsule of the liver. The gallbladder has three parts (Figs. 2.53B and 2.56) the: 

Fundus: the wide end of the organ, projects from the inferior border of the liver and is usually located at the tip of the right 9th costal cartilage in the MCL (Fig. 2.24A).

Figure 2.57. Normal relationship of gallbladder to superior part of the duodenum.

Chapter 2: Abdomen

Figure 2.58. Variation in origin and course of cystic artery. A. The cystic artery usually arises from the right hepatic artery in the cystohepatic triangle (of Calot), bounded by the cystic duct, common hepatic duct, and visceral surface of the right liver. B and C. Variations in the origin and course of the cystic artery occur in 24.5% of people (Daseler et al., 1947), which is of clinical significance during cholecystectomy (surgical removal of the gallbladder).

 

Body: contacts the visceral surface of the liver, the transverse colon, and the superior part of the duodenum. Neck: narrow and tapered; directed toward the porta hepatis; it makes an S‐ shaped bend and joins the cystic duct.

The cystic duct (3—4 cm long) connects the neck of the gallbladder to the common hepatic duct (Figs. 2.53B and 2.56). The mucosa of the neck spirals into the spiral fold (spiral valve) (Fig. 2.53B). The spiral fold helps keep the cystic duct open; thus bile can easily be diverted into the gallbladder when the distal end of the bile duct is closed by the sphincter of the bile duct and/or hepatopancreatic sphincter, or bile can pass to the duodenum as the gallbladder contracts. The spiral fold also offers additional resistance to sudden dumping of bile when the sphincters are closed, and intra‐abdominal pressure is suddenly increased, as during a sneeze or cough. The cystic duct passes between the layers of the lesser omentum, usually parallel to the common hepatic duct, which it joins to form the bile duct. The cystic artery, supplying the gallbladder and cystic duct (Figs. 2.56 and 2.58A), commonly arises from the right hepatic artery in the angle between the common hepatic duct and the cystic duct (cystohepatic triangle). Variations occur in the origin and course of the cystic artery (Fig. 2.58B & C). The cystic veins, draining the neck of the gallbladder and cystic duct, enter the liver directly or drain through the portal vein to the liver, after joining the veins draining the hepatic ducts and upper bile duct (Fig. 2.56). The veins from the fundus and body of the gallbladder pass directly into the visceral surface of the liver and drain into the hepatic sinusoids. Because this is drainage from one capillary (sinusoidal) bed to another, it constitutes an addition (parallel) portal system. The lymphatic drainage of the gallbladder is to the hepatic lymph nodes (Fig. 2.55), often through cystic lymph nodes located near the neck of the gallbladder. Efferent lymphatic vessels from these nodes pass to the celiac lymph nodes.


The nerves to the gallbladder and cystic duct (Fig. 2.56) pass along the cystic artery from the celiac nerve plexus (sympathetic and visceral afferent [pain] fibers), the vagus nerve (parasympathetic), and the right phrenic nerve (actually somatic afferent fibers). Parasympathetic stimulation causes contractions of the gallbladder and relaxation of the sphincters at the hepatopancreatic ampulla. However, these responses are generally stimulated by the hormone cholecystokinin (CCK), produced by the duodenal walls (in response to the arrival of a fatty meal) and circulated through the bloodstream.

Infundibulum of the Gallbladder In diseased states of the gallbladder, a dilation or pouch appears at the junction of the neck of the gallbladder and the cystic duct. This pouch is called the infundibulum of the gallbladder (Hartmann pouch). When this pouch is large, the cystic duct arises from its upper left aspect, not from what appears to be the apex of the gallbladder. Gallstones commonly collect in the infundibulum. If a peptic duodenal ulcer ruptures, a false passage may form between the infundibulum and the superior part of the duodenum, allowing gallstones to enter the duodenum (see the clinical correlation [blue] box “Gallstones in the Duodenum,” in this chapter).

Mobile Gallbladder The gallbladder has a short mesentery in approximately 4% of people. Such gallbladders are subject to vascular torsion and infarction (sudden insufficiency of arterial or venous blood supply).

Variations in the Cystic and Hepatic Ducts Occasionally, the cystic duct runs alongside the common hepatic duct and adheres closely to it. The cystic duct may be short or even absent. In some people, there is low union of the cystic and common hepatic ducts (Fig. B2.21A).

Figure B2.21. Union of cystic and common hepatic ducts. A. Low union. B. High union. C. Swerving course.

Chapter 2: Abdomen

As a result, the bile duct is short and lies posterior to the superior part of the duodenum, or even inferior to it. When there is low union, the two ducts may be joined by fibrous tissue, making clamping the cystic duct difficult without injuring the common hepatic duct. Occasionally, there is high union of the cystic and common hepatic ducts near the porta hepatis (Fig. B2.21B). In other cases, the cystic duct spirals anteriorly over the common hepatic duct before joining it on the left side (Fig. B2.21C). Understanding the variations in arteries and bile duct formation is important for surgeons when they ligate the cystic duct during cholecystectomy, the surgical removal of the gallbladder.

Accessory Hepatic Ducts Accessory (aberrant) hepatic ducts are common and are in positions of danger during cholecystectomy. An accessory duct is a normal segmental duct that joins the biliary system outside the liver instead of within it (Fig. B2.22). Because it drains a normal segment of the liver, it leaks bile if inadvertently cut during surgery (Skandalakis et al., 1995). Of 95 gallbladders and biliary ducts studied, 7 had accessory ducts, 4 joined the common hepatic duct near the cystic ducts, 2 joined the cystic duct, and 1 was an anastomosing duct connecting the cystic duct with the common hepatic duct (Agur and Dalley, 2005).

Figure B2.22.

Gallstones A gallstone is a concretion in the gallbladder, cystic duct, or bile duct composed chiefly of cholesterol crystals. Gallstones are much more common in females, and incidence increases with age. However, in approximately 50% of persons, gallstones are “silent” (asymptomatic). Over a 20‐year period, two thirds of asymptomatic people with gallstones remain symptom free. The longer stones remain quiescent, the less likely symptoms are to develop. For gallstones to cause clinical symptoms, they must obtain a size sufficient to produce mechanical injury to the gallbladder or obstruction of the biliary tract (Townsend, 2001).


The distal end of the hepatopancreatic ampulla is the narrowest part of the biliary passages and is the common site for impaction of gallstones. The infundibulum of the gallbladder is another common site for impaction. Gallstones may also lodge in the hepatic and cystic ducts. A stone lodged in the cystic duct causes biliary colic (intense, spasmodic pain). When the gallbladder relaxes, the stone may pass back into the gallbladder. If the stone blocks the cystic duct, cholecystitis (inflammation of the gallbladder) occurs because of bile accumulation, causing enlargement of the gallbladder. Pain develops in the epigastric region and later shifts to the right hypochondriac region at the junction of the 9th costal cartilage and the lateral border of the rectus sheath, indicated by the linea semilunaris. Inflammation of the gallbladder may cause pain in the posterior thoracic wall or right shoulder owing to irritation of the diaphragm. If bile cannot leave the gallbladder, it enters the blood and causes jaundice (see clinical correlation [blue] box “Pancreatic Cancer,” in this chapter). Ultrasound and CT scans are common non‐invasive techniques for locating stones.

Gallstones in the Duodenum Normal anatomy may be distorted by disease processes. A gallbladder that is dilated and inflamed owing to an impacted gallstone in its duct may develop adhesions with adjacent viscera. Continued inflammation may break down (ulcerate) the tissue boundaries between the gallbladder and a part of the alimentary tract adherent to it, resulting in a cholecystenteric fistula. Because of their proximity to the gallbladder, the superior part of the duodenum and the transverse colon are most likely to develop a fistula of this type (Fig. 2.24A). The fistula would enable a large gallstone, incapable of passing though the cystic duct, to enter the alimentary tract (Fig. B2.23). A large gallstone entering the small intestine in this way may become trapped at the ileocecal valve, producing a bowel obstruction (gallstone ileus). A cholecystenteric fistula also permits gas from the alimentary tract to enter the gallbladder, providing a diagnostic radiographic sign.

Figure B2.23.

Chapter 2: Abdomen

Cholecystectomy People with severe biliary colic usually have their gallbladders removed. Laparoscopic cholecystectomy often replaces the open surgical method (for details of this technique, see Skandalakis et al., 1995). The cystic artery most commonly arises from the right hepatic artery in the cystohepatic triangle (Calot triangle) (Fig. 2.56). In current clinical use, the cystohepatic triangle is defined inferiorly by the cystic duct, medially by the common hepatic duct, and superiorly by the inferior surface of the liver (Calot originally described the cystic artery itself as the superior boundary) (Fig. 2.58A). Careful dissection of the cystohepatic triangle early during cholecystectomy safeguards these important structures should there be anatomical variations. Errors during gallbladder surgery commonly result from failure to appreciate the common variations in the anatomy of the biliary system, especially its blood supply. Before dividing any structure and removing the gallbladder, surgeons identify all three biliary ducts, as well as the cystic and hepatic arteries. It is usually the right hepatic artery that is in danger during surgery and must be located before ligating the cystic artery. Bile duct injury is a serious complication of cholecystectomy, which is estimated to occur in 1 per 600 cases, and the risk appears to be modestly higher for laparoscopic cholecystectomy (Sabiston and Lyerly, 1994).

The Bottom Line Right and left hepatic ducts drain the bile produced by the right and left livers into the common hepatic duct, which thus carries all bile from the liver. The common hepatic duct merges with the cystic duct to form the bile duct, which conveys the bile to the duodenum. When the sphincter of the bile duct is closed, bile backs up in the bile and cystic ducts, filling the gallbladder, where bile is stored and concentrated between meals. Although parasympathetic innervation can open the sphincter of the bile duct (and the weaker sphincter of the hepatopancreatic ampulla) and contract the gallbladder, typically these are hormonally regulated responses to fat entering the duodenum, emptying the accumulated bile into the duodenum. The pear‐shaped gallbladder is attached to the visceral surface of the liver, with its fundus projecting from the liver's inferior border against the anterior abdominal wall at the intersection of the transpyloric plane and the right MCL. The gallbladder, cystic duct, and uppermost bile duct are supplied by the cystic artery, a branch arising from the right hepatic artery within the cystohepatic triangle. In addition to drainage via cystic veins that accompany the cystic artery and enter the portal vein, veins from the fundus and body make up a mini‐portal system that drains directly into the hepatic sinusoids deep to the visceral surface of the liver.

Portal Vein and Portal—Systemic Anastomoses The portal vein is the main channel of the portal venous system (Figs. 2.51 and 2.59). It is formed anterior to the IVC and posterior to the neck of the pancreas (close to the level of the L1 vertebra and the transpyloric plane) by the union of the superior mesenteric and splenic veins. Although it is a large vessel, it runs a short course (7—8 cm), most of which is contained within the hepatoduodenal ligament. As it approaches the porta hepatis, the portal vein divides into right and left branches. The portal vein collects blood of reduced oxygenation but rich in nutrients from the abdominal part of the alimentary tract, including the gallbladder, pancreas, and spleen, and carries it to the liver. Streaming of the blood flow is said to occur in


which blood from the splenic vein, carrying the products of RBC breakdown from the spleen, passes mostly to the left liver. Blood from the SMV, rich in absorbed nutrients from the intestines, passes mostly to the right liver. Within the liver, its branches are distributed in a segmental pattern (see “Blood Vessels of the Liver,” in this chapter) and end in expanded capillaries, the venous sinusoids of the liver (Fig. 2.53A). Figure 2.59. Portal—systemic anastomoses. Anastomoses provide a collateral circulation in cases of obstruction in the liver or portal vein. Here, the portal tributaries are darker blue and systemic tributaries are lighter blue. A—D indicate sites of anastomoses. A is between the submucosal esophageal veins draining into either the azygos vein (systemic) or the left gastric vein (portal); when dilated these are esophageal varices. B is between the inferior and middle rectal veins draining into the inferior vena cava (systemic) and the superior rectal vein, continuing as the inferior mesenteric vein (portal). The submucosal veins involved are normally dilated (varicose in appearance), even in newborns. When the mucosa containing them prolapses, they form hemorrhoids. (The varicose appearance of the veins and the occurrence of hemorrhoids are not typically related to portal hypertension, as is commonly stated.) C shows paraumbilical veins (portal) anastomosing with small epigastric veins of the anterior abdominal wall (systemic); this may produce the “caput medusae” (Fig. B2.24). D is on the posterior aspects (bare areas) of secondarily retroperitoneal viscera, or the liver, where twigs of visceral veins—for example, the colic vein, splenic veins, or the portal vein itself (portal system)—anastomose with retroperitoneal veins of the posterior abdominal wall or diaphragm (systemic system).

Portal—systemic anastomoses, in which the portal venous system communicates with the systemic venous system, are formed in the submucosa of the inferior esophagus, in the submucosa of the anal canal, in the paraumbilical region, and on the posterior aspects (bare areas) of secondarily retroperitoneal viscera, or the liver (Fig. 2.59; see legend for details). When portal circulation through the liver is diminished or obstructed because of liver disease or physical pressure from a tumor, for example, blood from the alimentary tract can still reach the right side of the heart through the IVC by way of these collateral routes. These alternate routes are available because the portal vein and its tributaries have no valves; hence blood can flow in a reverse direction to the IVC.

Chapter 2: Abdomen

Figure B2.24.

Portosystemic Shunts A common method for reducing portal hypertension is to divert blood from the portal venous system to the systemic venous system by creating a communication between the portal vein and the IVC. This portacaval anastomosis or portosystemic shunt may be done where these vessels lie close to each other posterior to the liver (Fig. B2.24A—C). Another way of reducing portal pressure is to join the splenic vein to the left renal vein, after splenectomy (splenorenal anastomosis or shunt) (Fig. B2.24D) (Skandalakis et al., 1995).

Portal Hypertension When scarring and fibrosis from cirrhosis obstruct the portal vein in the liver, pressure rises in the portal vein and its tributaries, producing portal hypertension. The large volume of blood flowing from the portal system to the systemic system at the sites of portal—systemic anastomoses produces varicose veins, especially in the lower esophagus. The veins may become so dilated that their walls rupture, resulting in hemorrhage (see Fig. B2.8). Bleeding from esophageal varices (abnormally dilated veins) at the distal end of the esophagus is often severe and may be fatal. In severe cases of portal obstruction, the veins of the anterior abdominal wall (normally caval tributaries) that anastomose with the paraumbilical veins (normally portal tributaries) may become varicose and look somewhat like small snakes radiating under the skin around the umbilicus. This condition is referred to as caput medusae because of its resemblance to the serpents on the head of Medusa, a character in Greek mythology. Figure B2.25 shows the more typical variation seen in relation to portal hypertension; a more unusual variation, occurring as a result of caval obstruction, is shown in Figure B2.2.


Figure B2.25.

The Bottom Line The large but short portal vein, formed posterior to the neck of the pancreas by the merger of the SMV and splenic vein, conveys all venous blood and bloodborne nutrients from the GI tract to the liver. The portal vein terminates at the porta hepatis, bifurcating into the right and left portal vein, distributed in a segmental pattern to the right and left livers. The portal vein traverses the hepatoduodenal ligament (free edge of the lesser omentum and anterior boundary of the omental foramen) as part of an extrahepatic portal triad (portal vein, hepatic artery, bile duct). Portal—systemic anastomoses provide a potential collateral pathway by which blood can return to the heart when there is an obstruction of the portal vein or disease of the liver. However, when the collateral pathways must convey large volumes, potentially lethal esophageal varices may develop.

Kidneys, Ureters, and Suprarenal Glands The superior urinary organs (kidneys and ureters) and their vessels are primary retroperitoneal structures on the posterior abdominal wall (Fig. 2.60)—that is, they were originally formed as and remain retroperitoneal viscera. The kidneys produce urine that is conveyed by the ureters to the urinary bladder in the pelvis. The superomedial aspect of each kidney normally contacts a suprarenal gland enclosed in a fibrous capsule and a cushion of pararenal fat (Fig. 2.61). A weak fascial septum separates the glands from the kidneys so that they are not actually attached to each other. The suprarenal glands function as part of the endocrine system, completely separate in function from the kidneys. Perinephric fat (the perirenal fat capsule) surrounds the kidneys and their vessels as it extends into their hollow centers, the renal sinuses (Fig. 2.61B). The kidneys,

Chapter 2: Abdomen

suprarenal glands, and the fat surrounding them are enclosed (except inferiorly) by a condensed, membranous layer of renal fascia, which continues medially to ensheath the renal vessels, blending with the vascular sheaths of the latter. Inferomedially, a delicate extension of the renal fascia is prolonged along the ureter as the periureteric fascia. External to the renal fascia is paranephric fat (or the pararenal fat body), the extraperitoneal fat of the lumbar region that is most obvious posterior to the kidney. The renal fascia sends collagen bundles through the paranephric fat. The collagen bundles, renal fascia, and perinephric and paranephric fat, along with the tethering provided by the renal vessels and ureter, hold the kidneys in a relatively fixed position. However, movement of the kidneys occurs during respiration and when changing from the supine to the erect position, and vice versa. Normal renal mobility is approximately 3 cm, approximately the height of one vertebral body. Superiorly, the renal fascia is continuous with the fascia on the inferior surface of the diaphragm (diaphragmatic fascia); thus the primary attachment of the suprarenal glands is to the diaphragm. Inferiorly, the anterior and posterior layers of renal fascia are only loosely united, if attached at all.

Perinephric Abscess The attachments of the renal fascia determine the path of extension of a perinephric abscess. For example, fascia at the renal hilum attaches to the renal vessels and ureter, usually preventing the spread of pus to the contralateral side. However, pus from an abscess (or blood from an injured kidney) may force its way into the pelvis between the loosely attached anterior and posterior layers of the pelvic fascia.

Nephroptosis Because the layers of renal fascia do not fuse firmly inferiorly to offer resistance, abnormally mobile kidneys may descend more than the normal 3 cm when the body is erect. When kidneys descend, the suprarenal glands remain in place because they lie in a separate fascial compartment and are firmly attached to the diaphragm. Nephroptosis (dropped kidney) is distinguished from an ectopic kidney (congenital misplaced kidney) by a ureter of normal length that has loose coiling or kinks because the distance to the bladder has been reduced. The kinks do not seem to be of significance. Symptoms of intermittent pain in the renal region, relieved by lying down, appear to result from traction on the renal vessels. The lack of inferior support for the kidneys in the lumbar region is one of the reasons transplanted kidneys are placed in the iliac fossa of the greater pelvis. Other reasons for this placement are the availability of major blood vessels and convenient access to the nearby bladder.


Figure 2.60. Posterior abdominal wall showing great vessels, kidneys, and suprarenal glands. Most of the fascia has been removed in this view. The ureter crosses the external iliac artery just beyond the common iliac bifurcation. In males, the testicular vessels cross anterior to the ureter and join the ductus deferens to enter the inguinal canal. The renal arteries are not seen because they lie posterior to the renal veins. The left renal vein is compressed between the aorta posteriorly and the superior mesenteric artery anteriorly, the latter being pulled inferiorly by the weight of the intestine.

Chapter 2: Abdomen

Figure 2.61. Lumbar approach to kidney and relationships of kidney to muscles and fascia. A. The external aspect of the right posterior abdominal wall is shown. On dividing the posterior aponeurosis of the transverse abdominal muscle between the subcostal and the iliohypogastric nerves, and lateral to the oblique lateral border of the quadratus lumborum, the retroperitoneal fat surrounding the kidney is exposed. The renal fascia is within this fat. The fat inside the renal fascia is termed th e perirenal fat capsule (perinephric fat); the fat outside the capsule is the pararenal fat body (paranephric fat). See Figure. 2.76A for an earlier stage of this dissection. B. This transverse section of the kidney shows the relationships of the muscles and fascia. Because the renal fascia surrounds the kidney as a separate sheath, it must be incised in any surgical operation on the kidney, whethe r from an anterior or a posterior approach.


Kidneys The ovoid kidneys remove excess water, salts, and wastes of protein metabolism from the blood while returning nutrients and chemicals to the blood. They lie retroperitoneally on the posterior abdominal wall, one on each side of the vertebral column at the level of the T12—L3 vertebrae (Figs. 2.60 and 2.62). The right kidney usually lies slightly inferior to the left kidney, probably owing to its relationship to the liver. During life, the kidneys are reddish brown and measure approximately 10 cm in length, 5 cm in width, and 2.5 cm in thickness. Superiorly, the kidneys are associated with the diaphragm, which separates them from the pleural cavities and the 12th pair of ribs. More inferiorly, the posterior surfaces of the kidney are related to the quadratus lumborum muscle (Figs. 2.60 and 2.61). The subcostal nerve and vessels and the iliohypogastric and ilioinguinal nerves descend diagonally across the posterior surfaces of the kidneys. The liver, duodenum, and ascending colon are anterior to the right kidney (Fig. 2.63). The right kidney is separated from the liver by the hepatorenal recess. The left kidney is related to the stomach, spleen, pancreas, jejunum, and descending colon. Figure 2.62. Arterial supply of kidneys and ureters. The abdominal aorta lies anterior to the L1—L4 vertebral bodies, usually immediately to the left of the midline. An accessory left renal artery is present. Multiple renal arteries are common and usually enter the hilum of the kidney, as shown here. Extrahilar renal arteries from the renal artery or aorta may enter the external surface of the kidney, commonly at their poles. Their presence presents a hazard during operations on the kidney.

At the concave medial margin of each kidney is a vertical cleft, the renal hilum, where the renal artery enters and the renal vein and renal pelvis leave the renal sinus (Fig. 2.64A). At the hilum, the renal vein is anterior to the renal artery, which is anterior to the renal pelvis. The renal hilum is the entrance to a space within the kidney, the renal sinus (Fig. 2.64B), which is occupied by the renal pelvis, calices, vessels, and nerves and a variable amount of fat (Fig. 2.64C & D). Each kidney has anterior and posterior surfaces, medial and lateral margins, and superior and inferior poles. However, because of the protrusion of the lumbar vertebral column into the abdominal cavity, the kidneys are obliquely placed, lying at an angle to each other

Chapter 2: Abdomen

(Fig. 2.61B). Consequently, the transverse diameter of the kidneys is foreshortened in anteroposterior (AP) radiographs. The lateral margin of each kidney is convex, and the medial margin is concave where the renal sinus and renal pelvis are located. The indented medial margin gives the kidney a somewhat bean‐shaped appearance. The renal pelvis is the flattened, funnel‐shaped expansion of the superior end of the ureter (Fig. 2.64B—D). The apex of the renal pelvis is continuous with the ureter. The renal pelvis receives two or three major calices (calyces), each of which divides into two or three minor calices. Each minor calyx is indented by the renal papilla, the apex of the renal pyramid, from which the urine is excreted. In living persons, the renal pelvis and its calices are usually collapsed (empty). The pyramids and their associated cortex form the lobes of the kidney. The lobes are visible on the external surfaces of the kidneys in fetuses, and evidence of the lobes may persist for some time after birth (Moore and Persaud, 2003).

Renal Transplantation Renal transplantation is now an established operation for the treatment of selected cases of chronic renal failure. The kidney can be removed from the donor without damaging the suprarenal gland because of the weak septum of renal fascia that separates the kidney from this gland. The site for transplanting a kidney is in the iliac fossa of the greater pelvis. This site supports the transplanted kidney, so that traction is not placed on the surgically anastomosed vessels. The renal artery and vein are joined to the external iliac artery and vein, respectively, and the ureter is sutured into the urinary bladder.

Renal Cysts Cysts in the kidney, multiple or solitary, are common findings during ultrasound examinations and dissection of cadavers. Adult polycystic disease of the kidneys is an important cause of renal failure; it is inherited as an autosomal dominant trait. The kidneys are markedly enlarged and distorted by cysts as large as 5 cm.

Pain in the Pararenal Region The close relationship of the kidneys to the psoas major muscles explains why extension of the hip joints may increase pain resulting from inflammation in the pararenal areas. These muscles flex the thighs at the hip joints.


Figure 2.63. Relationships of kidneys, suprarenal glands, pancreas, and duodenum. The right suprarenal gland is at the level of the omental foramen, indicated by the black arrow.

The Bottom Line The abdominal urinary organs and the suprarenal glands are primary retroperitoneal structures, embedded within perinephric fat (perirenal fat capsule) that is separated from the surrounding extraperitoneal paranephric fat by a membranous condensation, the renal fascia. The kidneys are bean‐shaped structures located between the T12 and the L3 vertebral levels, deep (anterior) to the 12th ribs. Closely related to the diaphragm, the kidneys move with its excursions. The suprarenal glands are located superomedially to the kidneys but are not attached to them. The kidneys are hollow. The central renal sinus is occupied by the renal calices and renal pelvis, segmental arteries and renal veins that are embedded in perinephric fat. The papillae of the renal pyramids, from which urine is excreted, evaginate into and are surrounded by minor calices. The minor calices merge to form major calices that in turn merge to form the renal pelvis. The vascular structures and renal pelvis exit the renal sinus at the medially directed hilum.

Chapter 2: Abdomen

Figure 2.64. External and internal appearance of kidneys. A. The right kidney is shown. B. Renal sinus, as seen through the renal hilum, is demonstrated. As shown here and in part A, the renal sinus contains the renal pelvis and renal vessels. C. The anterior lip of the renal hilum has been cut away to expose the renal pelvis and calices within the renal sinus. D. This coronal section of the kidney shows the organ's internal structure. The renal pyramids contain the collecting tubules and form the medulla of the kidney. The renal cortex contains the renal corpuscles. The renal papillae (the blunted apices of the pyramids) project into the minor calices, into which they discharge urine, which then passes into the major calices and renal pelvis.

Ureters The ureters are muscular ducts (25—30 cm long) with narrow lumina that carry urine from the kidneys to the urinary bladder (Figs. 2.60 and 2.64). They run inferiorly from the apex of the renal pelves at the hila of the kidneys, passing over the pelvic brim at the bifurcation of the common iliac arteries. They then run along the lateral wall of the pelvis and enter the urinary bladder. The abdominal parts of the ureters adhere closely to the parietal peritoneum and are retroperitoneal throughout their course. As demonstrated radiographically using contrast medium (Fig. 2.89), the ureters are normally constricted to a variable degree in three places: (1) at the junction of the ureters and renal pelves, (2) where the ureters cross the brim of the pelvic inlet, and (3) during their passage through the wall of the urinary bladder (Fig. 2.65). These constricted areas are potential sites of obstruction by ureteric (kidney) stones. Arterial branches to the abdominal portion of the ureter arise consistently from the renal arteries, with less constant branches arising from the testicular or ovarian


arteries, the abdominal aorta, and the common iliac arteries (Fig. 2.62). The branches approach the ureters medially and divide into ascending and descending branches, forming a longitudinal anastomosis on the ureteric wall. However, ureteric branches are small and relatively delicate, and disruption may lead to ischemia in spite of the continuous anastomotic channel formed. In operations in the posterior abdominal region, surgeons pay special attention to the location of ureters and are careful not to retract them laterally or unnecessarily. The arteries supplying the pelvic portion of the ureter are discussed in Chapter 3. Veins draining the abdominal part of the ureters drain into the renal and gonadal (testicular or ovarian) veins (Fig. 2.66). The lymphatic vessels of the ureters join the renal collecting vessels or pass directly to right or left lumbar (caval or aortic) lymph nodes and the common iliac lymph nodes (Fig. 2.65). Lymph drainage from the pelvic parts of the ureters is into the common, external, and internal iliac lymph nodes. Figure 2.65. Lymphatics of kidneys and suprarenal glands. The lymphatic vessels of the kidneys form three plexuses: one in the substance of the kidney, one under the fibrous capsule, and one in the perirenal fat. Four or five lymphatic trunks leave the renal hilum and are joined by vessels from the capsule (arrows). The lymphatic vessels follow the renal vein to the lumbar (caval and aortic) lymph nodes. Lymph from the suprarenal glands also drains to the lumbar nodes. Lymphatic drainage of the ureters is also illustrated. The lumbar lymph nodes drain through the lumbar lymphatic trunks to the chyle cistern. Also demonstrated are the three sites at which the ureter is normally relatively constricted: 1 the junction of pelvis and ureter, as it crosses the 2 external iliac vessels and pelvic brim, and 3 as it penetrates the wall of the urinary bladder.

Accessory Renal Vessels During their “ascent” to their final site, the embryonic kidneys receive their blood supply and venous drainage from successively more superior vessels (Moore and Persaud, 2003). Usually the inferior vessels degenerate as superior ones take over the blood supply and venous drainage. Failure of these vessels to degenerate results in accessory renal arteries (Fig. 2.62) and veins (known as “polar arteries and veins” when they enter/exit the poles of the kidneys). Variations in the number and position of these vessels occur in approximately 25% of people.

Chapter 2: Abdomen

Congenital Anomalies of the Kidneys and Ureters Bifid renal pelvis and ureter are fairly common (Fig. B2.26A & B). These anomalies result from division of the metanephric diverticulum (ureteric bud), the primordium of the renal pelvis and ureter (Moore and Persaud, 2003). The extent of ureteral duplication depends on the completeness of embryonic division of the metanephric diverticulum. The bifid renal pelvis and/or ureter may be unilateral or bilateral; however, separate openings into the bladder are uncommon. Incomplete division of the metanephric diverticulum results in a bifid ureter; complete division results in a supernumerary kidney. Figure B2.26.

An uncommon anomaly is a retrocaval ureter (Fig. B2.26C), which leaves the kidney and passes posterior to the IVC. The embryonic kidneys are close together in the pelvis. In approximately 1 in 600 fetuses, the inferior poles (rarely, the superior poles) of the kidneys fuse to form a horseshoe kidney (Fig. B2.26D). This U‐shaped kidney usually lies at the level of L3— L5 vertebrae because the root of the inferior mesenteric artery prevented normal ascent of the abnormal kidney. Horseshoe kidney usually produces no symptoms; however, associated abnormalities of the kidney and renal pelvis may be present, obstructing the ureter. Sometimes the embryonic kidney on one or both sides fails to ascend to the abdomen and lies anterior to the sacrum. Although uncommon, awareness of the possibility of an ectopic pelvic kidney (Fig. B2.26E) should prevent it from being mistaken for a pelvic tumor and removed. A pelvic kidney in a woman also can be injured by or


cause obstruction during childbirth. Pelvic kidneys usually receive their blood supply from the common iliac arteries. Figure 2.66. Blood vessels of suprarenal glands, kidneys, and superior part of ureters. The celiac plexus of nerves and ganglia that surrounds the celiac trunk has been removed. The IVC has been transected, and its superior part has been elevated from its normal position to reveal the arteries that pass posterior to it. The renal veins have been cut so that the kidneys could be moved laterally. For the normal relationships of the kidneys and suprarenal glands with the great vessels, see Figure 2.60. Observe the gross structure of the suprarenal glands and their rich arterial supply. The cross section of the suprarenal gland (inset) shows that it is composed of two distinct parts: the cortex and medulla, which are two separate endocrine glands that became closely related during embryonic development. Multiple suprarenal arteries arise from the inferior phrenic artery; one or more inferior suprarenal arteries often arise from the renal artery, and a middle suprarenal artery arises from the abdominal artery. The number and patterns of arrangement of the suprarenal arteries are very variable. The endocrine function of the suprarenal glands make their abundant blood supply necessary.

Surface Anatomy of the Kidneys and Ureters The hilum of the left kidney lies near the transpyloric plane, approximately 5 cm from the median plane (Fig. SA2.5). The transpyloric plane passes through the superior pole of the right kidney, which is approximately 2.5 cm lower than the left pole. Posteriorly, the superior parts of the kidneys lie deep to the 11th and 12th ribs. The levels of the kidneys change during respiration and with changes in posture. Each kidney moves 2—3 cm in a vertical direction during the movement of the diaphragm that occurs with deep breathing. Because the usual surgical approach to the kidneys is through the posterior abdominal wall, it is helpful to know that the inferior pole of the right kidney is approximately a finger's breadth superior to the iliac crest. The kidneys may be impalpable. In lean adults, the inferior pole of the right kidney is palpable by bimanual examination as a firm, smooth, somewhat rounded mass that descends during inspiration. Palpation of the right kidney is possible because it is 1—

Chapter 2: Abdomen

2 cm inferior to the left one. To palpate the kidneys, press the flank (the side of the trunk between the 11th and 12th ribs and the iliac crest) anteriorly with one hand while palpating deeply at the costal margin with the other. The left kidney is usually not palpable unless it is enlarged or a retroperitoneal mass has displaced it inferiorly. From the back, the surface marking of the ureter is a line joining a point 5 cm lateral to the L1 spinous process and the posterior superior iliac spine. The ureters occupy a sagittal plane that intersects the tips of the transverse processes of the lumbar vertebrae.

Figure SA2.5.

The Bottom Line The abdominal portions of the ureters descend on the anterior surface of the psoas muscles from the apex of the renal pelvis to the pelvic brim. The ureters normally have three sites of relative constriction, where kidney stones may lodge: the uteropelvic junction, the pelvic brim, and the bladder wall. The abdominal portions of the ureters receive multiple, relatively delicate ureteric branches from the renal, testicular or ovarian, and common iliac arteries and from the abdominal aorta, which approach the ureters medially. A vertical line 5 cm lateral to the lumbar spinous processes, intersecting the posterior superior iliac spine, approximates the position of the ureter.


Suprarenal Glands The suprarenal (adrenal) glands, yellowish in living persons, are located between the superomedial aspects of the kidneys and the diaphragm (Fig. 2.66), where they are surrounded by connective tissue containing considerable perinephric fat. The glands are enclosed by renal fascia by which they are attached to the crura of the diaphragm. Despite their name, this is the primary relationship of the suprarenal glands. They are separated from the kidneys by a thin septum (part of the renal fascia). The shape and relations of the suprarenal glands differ on the two sides. The pyramidal right gland is more apical (situated over the superior pole) relative to the right kidney, lies anterolateral to the right crus of the diaphragm, and makes contact with the IVC anteromedially (Fig. 2.63) and the liver anterolaterally. The crescent‐ shaped left gland is medial to the superior half of the left kidney and is related to the spleen, stomach, pancreas, and the left crus of the diaphragm. Each gland has a hilum, where the veins and lymphatic vessels exit the gland; whereas arteries and nerves enter the glands at multiple sites. The medial borders of the suprarenal glands are 4—5 cm apart. In this area, from right to left, are the IVC, right crus of the diaphragm, celiac ganglion, celiac trunk, SMA, and the left crus of the diaphragm. Each suprarenal gland has two parts: the suprarenal cortex and suprarenal medulla Fig. 2.66, inset); these parts have different embryological origins and different functions (Moore and Persaud, 2003). The suprarenal cortex derives from mesoderm and secretes corticosteroids and androgens. These hormones cause the kidneys to retain sodium and water in response to stress, increasing the blood volume and blood pressure. They also affect muscles and organs such as the heart and lungs. The suprarenal medulla is a mass of nervous tissue permeated with capillaries and sinusoids that derives from neural crest cells associated with the sympathetic nervous system. The chromaffin cells of the medulla are related to sympathetic ganglion (postsynaptic) neurons in both derivation (neural crest cells) and function. These cells secrete catecholamines (mostly epinephrine) into the bloodstream in response to signals from presynaptic neurons (Naftel and Hardy, 2002). The powerful medullary hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) activate the body to a flight‐or‐fight status in response to traumatic stress. They also increase heart rate and blood pressure, dilate the bronchioles, and change blood flow patterns, preparing for physical exertion.

The Bottom Line The suprarenal glands are located superomedially to the kidneys but are attached primarily to the diaphragmatic crura by the surrounding renal fascia. Each suprarenal gland is actually two endocrine glands of different origin and function: suprarenal cortex and suprarenal medulla (the latter surrounded by the former). The adrenal cortex derives from mesoderm and secretes corticosteroids and androgens; the adrenal medulla derives from neural crest cells and secretes catecholamines (mostly epinephrine). The right suprarenal gland is more pyramidal in shape and apical in position relative to the right kidney, whereas the left gland is more crescentic and lies more medial to the superior half of the kidney.

Chapter 2: Abdomen

Vessels and Nerves of the Kidneys and Suprarenal Glands The Renal Arteries and Veins The renal arteries arise at the level of the IV disc between the L1 and the L2 vertebrae (Figs. 2.62 and 2.66). The longer right renal artery passes posterior to the IVC. Typically, each artery divides close to the hilum into five segmental arteries that are end arteries (i.e., they do not anastomose significantly with other segmental arteries, so that the area supplied by each segmental artery is an independent, surgically resectable unit or renal segment). Segmental arteries are distributed to the renal segments as follows (Fig. 2.67): 



The superior (apical) segment is supplied by the superior (apical) segmental artery; the anterosuperior and anteroinferior segments are supplied by the anterosuperior segmental and anteroinferior segmental arteries; and the inferior segment is supplied by the inferior segmental artery. These arteries originate from the anterior branch of the renal artery. The posterior segmental artery, which originates from a continuation of the posterior branch of the renal artery, supplies the posterior segment of the kidney.

Several renal veins drain each kidney and unite in a variable fashion to form the right and left renal veins. The right and left renal veins lie anterior to the right and left renal arteries. The longer left renal vein receives the left suprarenal vein, the left gonadal (testicular or ovarian) vein, and a communication with the ascending lumbar vein, then passes anterior to the aorta. Each renal vein drains into the IVC.

The Suprarenal Arteries and Veins The endocrine function of the suprarenal glands makes their abundant blood supply necessary. The suprarenal arteries branch freely before entering each gland so that 50—60 arteries penetrate the capsule covering the entire surface of the glands (Fig. 2.66). Suprarenal arteries arise from three sources:   

Superior suprarenal arteries (6—8) from the inferior phrenic arteries. Middle suprarenal arteries (â‰¤ 1) from the abdominal aorta near the level of origin of the SMA. Inferior suprarenal arteries (â‰¤ 1) from the renal arteries.

The venous drainage of the suprarenal gland is into a large suprarenal vein (Fig. 2.66). The short right suprarenal vein drains into the IVC, whereas the longer left suprarenal vein, often joined by the inferior phrenic vein, empties into the left renal vein.

Lymphatics of the Kidneys, Ureters, and Suprarenal Glands The renal lymphatic vessels follow the renal veins and drain into the right and left lumbar (caval and aortic) lymph nodes (Fig. 2.65). Lymphatic vessels from the superior part of the ureter may join those from the kidney or pass directly to the lumbar nodes. Lymphatic vessels from the middle part of the ureter usually drain into


the common iliac lymph nodes, whereas vessels from its inferior part drain into the common, external, or internal iliac lymph nodes. The suprarenal lymphatic vessels arise from a plexus deep to the capsule of the gland and from one in its medulla. The lymph passes to the lumbar lymph nodes. Many lymphatic vessels leave the suprarenal glands.

Figure 2.67. Renal segments and segmental arteries A. According to its arterial supply, the kidney has five segments: superior (apical), anterosuperior, anteroinferior, inferior, and posterior. B. Only the superior and inferior arteries supply the whole thickness of the kidney. The posterior artery crosses superior to the renal pelvis to reach its segment. C. Typically, the renal artery divides into five branches, each supplying a segment of the kidney, as seen in this renal arteriogram. Although the veins of the kidney anastomose freely, segmental arteries are end arteries. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)

Nerves of the Kidneys, Ureters, and Suprarenal Glands Nerves to the kidneys arise from the renal nerve plexus and consist of sympathetic and parasympathetic fibers (Fig. 2.68B). The renal nerve plexus is supplied by fibers from the abdominopelvic (especially the least) splanchnic nerves. The nerves of the abdominal part of the ureters derive from the renal, abdominal aortic, and superior hypogastric plexuses (Fig. 2.68A). Visceral afferent fibers conveying pain sensation (e.g., resulting from obstruction and consequent distension) follow the sympathetic fibers retrograde to spinal ganglia and cord segments T11—L2. Ureteric pain is usually referred to the ipsilateral lower quadrant of the anterior abdominal wall and especially to the groin (see the adjacent clinical correlation [blue] box “Renal and Ureteric Calculi” ). The suprarenal glands have a rich nerve supply from the celiac plexus and abdominopelvic (greater, lesser and least) splanchnic nerves. Myelinated presynaptic sympathetic fibers—mainly derived from the intermediolateral cell column (IML), or lateral horn, of gray matter of the spinal cord segments T10—L1—traverse both the paravertebral and the prevertebral ganglia, without synapse, to be distributed to the chromaffin cells in the suprarenal medulla (Fig. 2.68B).

Chapter 2: Abdomen

Renal and Ureteric Calculi Calculi (L. pebbles) are composed of salts of inorganic or organic acids or of other materials. They may form and become located in the calices of the kidneys, ureters, or urinary bladder. A renal calculus (kidney stone) may pass from the kidney into the renal pelvis and then into the ureter. If the stone is sharp, or it is larger than the normal lumen of the ureter (approximately 3 mm) causing excessive distension of this muscular tube, the ureteric calculus will cause severe intermittent pain (ureteric colic) as it is gradually forced down the ureter by waves of contraction. The calculus may cause complete or intermittent obstruction of urinary flow. Depending on the level of obstruction, which changes, the pain may be referred to the lumbar or inguinal regions, or the external genitalia and/or testis. The pain is referred to the cutaneous areas innervated by spinal cord segments and sensory ganglia, which also receive visceral afferents from the ureter, mainly T11— L2. The pain passes inferoanteriorly “from the loin to the groin” as the stone progresses through the ureter. (The loin is the lumbar region, and the groin is the inguinal region.) The pain may extend into the proximal anterior aspect of the thigh by projection through the genitofemoral nerve (L1, L2), the scrotum in males and the labia majora in females. The extreme pain may be accompanied by marked alimentary upset (nausea, vomiting, cramping, and diarrhea) and a generalized sympathetic response that may to various degrees mask the more specific symptoms. Ureteric calculi can be observed and removed with a nephroscope, an instrument that is inserted through a small incision. Another technique, lithotripsy, focuses a shockwave through the body that breaks the stone into small fragments that pass with the urine.


Figure 2.68. Nerves of the kidneys and suprarenal glands. A. The nerves of the kidneys and suprarenal glands are derived from the celiac plexus, abdominopelvic (lesser and least) splanchnic nerves, and the aorticorenal ganglion. Most of the fibers conveyed by the abdominopelvic splanchnic nerves to the prevertebral ganglia are presynaptic sympathetic fibers that passed through the paravertebral ganglia without synapsing. The main efferent innervation of the kidney is vasomotor, autonomic nerves supplying the afferent and efferent arterioles. B. Exclusively in the case of the suprarenal medulla, the presynaptic sympathetic fibers pass through both the paravertebral and prevertebral ganglia without synapsing to end directly on the secretory cells of the suprarenal medulla.

The Bottom Line The renal arteries arise from the abdominal aorta at the level of the L1—L2 IV disc. They lie anterior to the renal veins, with the right renal artery being longer than the left, and the left renal vein being longer than the right. Both renal veins receive renal and superior ureteric veins and drain into the IVC, but the long left vein also receives the left suprarenal vein, the left gonadal vein, and a communication with the left ascending lumbar vein. Near the hilum, the renal arteries divide into anterior and posterior branches, the anterior branches giving rise to four segmental renal arteries, whereas the posterior branch makes up a fifth. The segmental renal arteries are end arteries, so that each supplies an independent, surgically resectable segment of the kidney (renal segment). Suprarenal arteries arise from three sources: superior suprarenal arteries from the inferior phrenic arteries, middle suprarenal arteries from the abdominal aorta, and inferior suprarenal arteries from the renal arteries. The suprarenal glands drain via

Chapter 2: Abdomen

one large suprarenal vein, the right entering the IVC and the left entering the left renal vein. Lymphatics from the suprarenal glands, kidneys, and upper ureters follow the venous drainage to the right or left lumbar (caval or aortic) lymph nodes. Visceral afferent fibers (accompanying the sympathetic fibers) conduct pain sensation from the ureters to spinal cord segments T11—L2, with sensation referred to the corresponding dermatomes overlying the loin and groin. The suprarenal glands receive a rich nerve supply via presynpatic sympathetic fibers originating in the IML of the T10—L1 spinal cord segments. These fibers traverse both the paravertebral (sympathetic trunks) and prevertebral (celiac) ganglia without synapsing. They terminate directly on the chromaffin cells of the suprarenal medulla.

Summary of the Innervation of the Abdominal Viscera For autonomic innervation of the abdominal viscera, several different splanchnic nerves and one cranial nerve (the vagus, CN X) deliver presynaptic sympathetic and parasympathetic fibers, respectively, to the abdominal aortic plexus and its associated sympathetic ganglia (Fig. 2.69; Table 2.12). The periarterial extensions of these plexuses deliver postsynaptic sympathetic and the continuations of the parasympathetic fibers to the abdominal viscera, where intrinsic parasympathetic ganglia occur.

Sympathetic Innervation The sympathetic part of the autonomic innervation of the abdominal viscera consists of the:   

Abdominopelvic splanchnic nerves from the thoracic and abdominal sympathetic trunks. Prevertebral sympathetic ganglia. Abdominal aortic plexus and its extensions, the periarterial plexuses.

The plexuses are mixed, shared with the parasympathetic nervous system and visceral afferent fibers. The abdominopelvic splanchnic nerves (Fig. 2.69B; Table 2.12) convey presynaptic sympathetic fibers to the abdominopelvic cavity. The fibers arise from cell bodies in the IML (or lateral horn) of the gray matter of spinal cord segments T5—L2 or L3. The fibers pass successively through the anterior roots, anterior rami, and white communicating branches of thoracic and upper lumbar spinal nerves to reach the sympathetic trunks. They pass through the paravertebral ganglia of the trunks without synapsing to enter the abdominopelvic splanchnic nerves, which convey them to the prevertebral ganglia of the abdominal cavity. The abdominopelvic splanchnic nerves include the:  

Lower thoracic splanchnic nerves (greater, lesser, and least): from the thoracic part of the sympathetic trunks. Lumbar splanchnic nerves: from the lumbar part of the sympathetic trunks.


The lower thoracic splanchnic nerves are the main source of presynaptic sympathetic fibers serving abdominal viscera. The greater (from the sympathetic trunk at T5 through T9 or T10 vertebral levels), lesser (from T10 and T11 levels), and least (from the T12 level) splanchnic nerves are the specific abdominopelvic splanchnic nerves that arise from the thoracic part of the sympathetic trunks and pierce the corresponding crus of the diaphragm to convey the presynaptic sympathetic fibers to the celiac, superior mesenteric, and aorticorenal (prevertebral) sympathetic ganglia, respectively. The lumbar splanchnic nerves arise from the abdominal part of the sympathetic trunks. Medially, the lumbar sympathetic trunks give off three to four lumbar splanchnic nerves, which pass to the intermesenteric, inferior mesenteric, and superior hypogastric plexuses, conveying presynaptic sympathetic fibers to the associated prevertebral ganglia of those plexuses. The cell bodies of postsynaptic sympathetic neurons constitute the major prevertebral ganglia that cluster around the roots of the major branches of the abdominal aorta: the celiac, aorticorenal, superior mesenteric, and inferior mesenteric ganglia. Minor, unnamed prevertebral ganglia occur within the intermesenteric and superior hypogastric plexuses. With the exception of the innervation of the suprarenal medulla (discussed earlier in this chapter), the synapse between presynaptic and postsynaptic sympathetic neurons occurs in the prevertebral ganglia. Postsynaptic sympathetic nerve fibers pass from the prevertebral ganglia to the abdominal viscera by means of the periarterial plexuses associated with the branches of the abdominal aorta. Sympathetic innervation in the abdomen, as elsewhere, is primarily involved in producing vasoconstriction. With regard to the alimentary tract, it acts to inhibit (slow down or stop) peristalsis. Visceral afferent fibers conveying pain sensations accompany the sympathetic (visceral motor) fibers; the pain impulses pass retrogradely to those of the motor fibers along the splanchnic nerves to the sympathetic trunk, through white communicating branches to the anterior rami of the spinal nerves. Then they pass into the posterior root to the spinal sensory ganglia and spinal cord. Progressively lower spinal sensory ganglia and spinal cord segments are involved in innervating the abdominal viscera as the tract proceeds caudally. The stomach (foregut) receives innervation from the T6 to T9 levels, small intestine through transverse colon (midgut) from the T8 to 12 levels, and descending colon (hindgut) from the T12 to L2 levels (Fig. 2.70). Starting from the midpoint of the sigmoid colon, visceral pain fibers run with parasympathetic fibers, the sensory impulses being conducted to S2—S4 sensory ganglia and spinal cord levels. These are the same spinal cord segments involved in the sympathetic innervation of those portions of alimentary tract.

Chapter 2: Abdomen

Figure 2.69. Autonomic nerves of posterior abdominal wall. A. Origin and distribution of presynapatic and postsynapatic sympathetic and parasympathetic fibers, and the ganglia involved in supplying abdominal viscera are shown. B. The fibers supplying the intrinsic plexuses of abdominal viscera are demonstrated.


T a b l e 2 . 1 2. A u t o n o m i c I n n e r v a t i o n o f t h e A b d o m i n al V i s c e r a ( S p l a n c h n i c N e r v e s )

S p l an c h n i c N e r v e s

Autonomic F i b e r T yp e a A . C a rd i o p u l m o n a ry P o s t s y n a p t i c ( C e r v i c a l a n d u p p e r thoracic) B . A b d o mi n o p e l v i c

S y s t e m

Origin

Destination

C e r v i c a l a n d u p p e r thoracic s y m p a t h e t i c t r u n k Lower thoracic and a b d o m in o ‐ p e l v i c s y m p a t h e t i c t r u n k :

Thoracic cavity (viscera s u p e r i o r t o le v e l o f d i a p h r a g m )

1 . L o w e r t h o r a c i c

S y m p a t h e t i c

a. b. c.

G r e a te r L e s s e r L e a s t

2 . L u m b a r

3 . S a c r a l

Presynaptic

A b d om i n o p e l v i c cavity ( p r e v e r te b r a l g a n g l i a s e r v i n g v i s c e r a a n d s u p r a re n a l g l a n d s i n f e r i o r t o l e v e l o f d i a p h ra g m ) 1. Thoracic 1. A b d om i n a l p r e v e rt e b r a l s y m p a t h e t i c t r u n k : ganglia: a. T5—T9 o r a. Celia ganglia T 1 0 l e v e l b. Aorticorenal ganglia b. T10—T11 c . & 2 . O t h e r a b d o m i n a l l e v e l p r e v e r t e b ra l ganglia c . T 1 2 l e v e l (superior and inferior m e s e n te r i c , and of i n t e r m e s e n t e r i c / h y p o g a 2. A b d o m i n a l stric plexuses s y m p a t h e t i c t r u n k

3 . P e l v i c ( s a c r a l ) 3 . P e l v i c p re v e r t e b r a l g a n g l i a s y m p a t h e t i c t r u n k C. Pelvic Presynaptic Parasympathetic Anterior rami of Intrinsic ganglia of descending S 2 — S 4 s p i n a l n e r v e s a n d s ig m o i d c o l o n , r e c t u m , a n d p e l v i c v i s ce ra a S p l a n c h n i c n e r v e s a ls o c o n v e y v is c e r a l a f f e r e n t f i b e r s , w h i c h a re n o t p a r t o f th e a u t o n om i c n e r v ou s s y s t e m .

Chapter 2: Abdomen

Figure 2.70. Approximate spinal cord segments and spinal sensory ganglia involved in sympathetic and visceral afferent (pain) innervation of abdominal viscera.

Parasympathetic Innervation The parasympathetic part of the autonomic innervation of the abdominal viscera (Fig. 2.69; Table 2.12, figure) consists of the following:    

Anterior and posterior vagal trunks. Pelvic splanchnic nerves. Abdominal (para‐aortic) autonomic plexuses and their extensions, the periarterial plexuses. Intrinsic (enteric) parasympathetic ganglia.

The nerve plexuses are mixed, shared with the sympathetic nervous system and visceral afferent fibers. The anterior and posterior vagal trunks are the continuation of the left and right vagus nerves that emerge from the esophageal plexus and pass through the esophageal hiatus on the anterior and posterior aspects of the esophagus and stomach (Figs. 2.28 and 2.69A; Table 2.12). The vagus nerves convey presynaptic parasympathetic and visceral afferent fibers (mainly for unconscious sensations associated with reflexes) to the abdominal aortic plexuses and the periarterial plexuses, which extend along the branches of the aorta. The pelvic splanchnic nerves are distinct from other splanchnic nerves (Table 2.12) in that they:

Clinically Oriented Anatomy, 5th Edition By Keith Moore   

Have nothing to do with the sympathetic trunks. Derive directly from anterior rami of spinal nerves S2—S4. Convey presynaptic parasympathetic fibers to the inferior hypogastric (pelvic) plexus.

Presynaptic fibers terminate on the isolated and widely scattered cell bodies of postsynaptic neurons lying on or within the abdominal viscera, constituting intrinsic ganglia (Fig. 2.69B). The presynaptic parasympathetic and visceral afferent reflex fibers conveyed by the vagus nerves extend to intrinsic ganglia of the lower esophagus, stomach, small intestine, including the duodenum, ascending colon, and most of the transverse colon (Fig. 2.69A). Those conveyed by the pelvic splanchnic nerves supply the descending and sigmoid parts of the colon, rectum, and pelvic organs. Thus, in terms of the alimentary tract, the vagus nerves provide parasympathetic innervation of the smooth muscle and glands of the gut as far as the left colic flexure; the pelvic splanchnic nerves provide the remainder. The abdominal autonomic plexuses are nerve networks consisting of both sympathetic and parasympathetic fibers, which surround the abdominal aorta and its major branches (Table 2.12). The celiac, superior mesenteric, and inferior mesenteric plexuses are interconnected. The prevertebral sympathetic ganglia are scattered among the celiac and mesenteric plexuses. The intrinsic parasympathetic ganglia, such as the myenteric plexus (Auerbach plexus) in the muscular coat of the stomach and intestine, are in the walls of the viscera (Fig. 2.69B; Table 2.9A). The celiac plexus, surrounding the root of the celiac (arterial) trunk, contains irregular right and left celiac ganglia (approximately 2 cm long) that unite superior and inferior to the celiac trunk (Fig. 2.69A; Table 2.12). The parasympathetic root of the celiac plexus is a branch of the posterior vagal trunk, which contains fibers from the right and left vagus nerves. The sympathetic roots of the plexus are the greater and lesser splanchnic nerves. The superior mesenteric plexus and ganglion or ganglia surround the origin of the SMA. The plexus has one median and two lateral roots. The median root is a branch of the celiac plexus, and the lateral roots arise from the lesser and least splanchnic nerves, sometimes with a contribution from the first lumbar ganglion of the sympathetic trunk. The inferior mesenteric plexus surrounds the inferior mesenteric artery and gives offshoots to its branches. It receives a medial root from the intermesenteric plexus and lateral roots from the lumbar ganglia of the sympathetic trunks. An inferior mesenteric ganglion may also appear just inferior to the root of the inferior mesenteric artery. The intermesenteric plexus is part of the aortic plexus of nerves between the superior and the inferior mesenteric arteries. It gives rise to renal, testicular or ovarian, and ureteric plexuses. The superior hypogastric plexus is continuous with the intermesenteric plexus and the inferior mesenteric plexus and lies anterior to the inferior part of the abdominal aorta at its bifurcation (Table 2.12). Right and left hypogastric nerves join the superior hypogastric plexus to the inferior hypogastric plexus. The superior hypogastric plexus supplies ureteric and testicular plexuses and a plexus on each common iliac artery.

Chapter 2: Abdomen

The inferior hypogastric plexus is formed on each side by a hypogastric nerve from the superior hypogastric plexus. The right and left plexuses are situated on the sides of the rectum, uterine cervix, and urinary bladder. The plexuses receive small branches from the superior sacral sympathetic ganglia and the sacral parasympathetic outflow from S2 through S4 sacral spinal nerves (pelvic [parasympathetic] splanchnic nerves). Extensions of the inferior hypogastric plexus send autonomic fibers along the blood vessels, which form visceral plexuses on the walls of the pelvic viscera (e.g., the rectal and vesical plexuses).

The Bottom Line Presynaptic sympathetic nerve fibers involved in innervating abdominal viscera arise from cell bodies in the lower two thirds of the IML, (T5—T6 to L2—L3 spinal cord levels) and travel via spinal nerves, anterior rami, and white communicating branches to the sympathetic trunks. The fibers traverse the paravertebral ganglia of the trunks without synapsing, continuing as components of abdominopelvic splanchnic nerves. These nerves convey them to the abdominal aortic plexus, where they are joined by presynaptic parasympathetic fibers delivered by the vagus nerve. The sympathetic fibers pass to prevertebral ganglia, most of which are clustered around the major branches of the abdominal aorta. After synapsing within the ganglia, the postsynaptic sympathetic fibers join the presynaptic parasympathetic fibers, traveling via periarterial plexuses around the branches of the abdominal aorta to reach the viscera. A continuation of the abdominal aortic plexus inferior to the aortic bifurcation (the superior and inferior hypogastric plexuses) convey sympathetic innervation to most of the pelvic viscera. The sympathetic fibers mainly innervate the blood vessels of abdominal viscera and are inhibitory to the parasympathetic stimulation. The parasympathetic fibers synapse on or in the walls of the viscera with intrinsic postsynaptic parasympathetic neurons, which terminate on the smooth muscle or glands of the viscera. The vagus nerve supplies parasympathetic fibers to the alimentary tract from the esophagus through the transverse colon. Pelvic splanchnic nerves supply the descending and sigmoid colon and rectum. Parasympathetic stimulation promotes peristalsis and secretion (although much of the latter is usually hormonally regulated). Visceral afferent fibers follow the autonomic fibers retrograde to sensory ganglia. Afferent fibers conveying pain sensation from abdominal viscera orad to the middle of the sigmoid colon run with the sympathetic fibers to thoracolumbar spinal sensory ganglia; all other visceral afferent fibers run with the parasympathetic fibers. Thus visceral afferent fibers conveying reflex information from the gut orad to the middle of the sigmoid colon pass to vagal sensory ganglia; fibers conveying both pain and reflex information from the gut aborad to the middle of the sigmoid colon pass to spinal sensory ganglia S2—S4.

Diaphragm The diaphragm is a double‐domed, musculotendinous partition separating the thoracic and abdominal cavities. Its mainly convex superior surface faces the thoracic cavity, and its concave inferior surface faces the abdominal cavity (Fig. 2.71). The diaphragm is the chief muscle of inspiration (actually, of respiration altogether, because expiration is largely passive). It descends during inspiration; however, only


its central part moves because its periphery, as the fixed origin of the muscle, attaches to the inferior margin of the thoracic cage and the superior lumbar vertebrae. The pericardium, containing the heart, lies on the central part of the diaphragm, depressing it slightly (Fig. 2.72A). The diaphragm curves superiorly into right and left domes; normally the right dome is higher than the left owing to the presence of the liver. During expiration, the right dome reaches as high as the 5th rib and the left dome ascends to the 5th intercostal space. The level of the domes of the diaphragm varies according to the:   

Phase of respiration (inspiration or expiration). Posture (e.g., supine or standing). Size and degree of distension of the abdominal viscera.

Figure 2.71. Abdominal surface of diaphragm and its attachments. The fleshy sternal, costal, and lumbar origins of the diaphragm attach centrally to the trefoil‐shaped central tendon, the aponeurotic insertion of the diaphragmatic muscle fibers.

The muscular part of the diaphragm is situated peripherally with fibers that converge radially on the trifoliate central aponeurotic part, the central tendon (Fig. 2.71). The central tendon has no bony attachments and is incompletely divided into three leaves, resembling a wide cloverleaf. Although it lies near the center of the diaphragm, the central tendon is closer to the anterior part of the thorax. The caval opening (vena caval foramen), through which the terminal part of the IVC passes to enter the heart, perforates the central tendon. The surrounding muscular part of the diaphragm forms a continuous sheet; however, for descriptive purposes it is divided into three parts, based on the peripheral attachments:

Chapter 2: Abdomen  



Sternal part: consisting of two muscular slips that attach to the posterior aspect of the xiphoid process; this part is not always present. Costal part: consisting of wide muscular slips that attach to the internal surfaces of the inferior six costal cartilages and their adjoining ribs on each side; the costal parts form the right and left domes. Lumbar part: arising from two aponeurotic arches, the medial and lateral arcuate ligaments, and the three superior lumbar vertebrae; the lumbar part forms right and left muscular crura that ascend to the central tendon.

The crura of the diaphragm are musculotendinous bundles that arise from the anterior surfaces of the bodies of the superior three lumbar vertebrae, the anterior longitudinal ligament, and the IV discs. The right crus, larger and longer than the left crus, arises from the first three or four lumbar vertebrae. The left crus arises from the first two or three. Because it lies to the left of the midline, it is surprising to find that the esophageal hiatus is a formation in the right crus; however, if the muscular fibers bounding each side of the hiatus are traced inferiorly, it will be seen that they pass to the right of the aortic hiatus. The right and left crura and the fibrous median arcuate ligament, which unites them as it arches over the anterior aspect of the aorta, form the aortic hiatus. The diaphragm is also attached on each side to the medial and lateral arcuate ligaments. These are thickenings of the fascia covering the psoas major (and spanning between lumbar vertebral bodies and the tip of the transverse process of L1) and the quadratus lumborum muscles (continuing from the L12 transverse process to the tip of the 12th rib), respectively. The superior aspect of the central tendon of the diaphragm (the thin, strong aponeurotic tendon of all the muscular fibers of the diaphragm) is fused with the inferior surface of the fibrous pericardium, the strong, external part of the fibroserous pericardial sac that encloses the heart.

Vessels and Nerves of the Diaphragm The arteries of the diaphragm form a branch‐like pattern on both its superior and inferior surfaces. The arteries supplying the superior surface of the diaphragm (Fig. 2.72; Table 2.13) are the pericardiacophrenic and musculophrenic arteries, branches of the internal thoracic artery, and the superior phrenic arteries, arising from the thoracic aorta. The arteries supplying the inferior surface of the diaphragm are the inferior phrenic arteries, which typically are the first branches of the abdominal aorta; however, they may arise from the celiac trunk.


Figure 2.72. Blood vessels of diaphragm. A. The arteries and veins of the superior surface of the diaphragm are derived from the pericardiacophrenic and musculophrenic arteries and veins (branches of the internal thoracic artery and vein) and from the superior phrenic arteries. B. The inferior phrenic arteries and veins supply and drain blood from the inferior surface of the diaphragm. The inferior phrenic arteries are usually the first branches of the abdominal aorta, but they may arise as branches of the celiac trunk. The right inferior phrenic vein drains to the IVC; the left inferior phrenic vein is often double, with one (anterior) branch ending in the IVC and the other (posterior) branch ending in the left renal or suprarenal vein. The two veins may anastomose with each other, as shown here.

The veins draining the superior surface of the diaphragm are the pericardiacophrenic and musculophrenic veins, which empty into the internal thoracic veins and, on the right side, a superior phrenic vein, which drains into the IVC. Some veins from the posterior curvature of the diaphragm drain into the azygos and hemiazygos veins (see Chapter 1). The inferior phrenic veins drain blood from the inferior surface of the diaphragm. The right inferior phrenic vein usually opens into the IVC, whereas the left inferior phrenic vein is usually double, with one branch passing anterior to the esophageal hiatus to end in the IVC and the other, more posterior branch usually joining the left suprarenal vein. The lymphatic plexuses on the thoracic and abdominal surfaces of the diaphragm communicate freely (Fig. 2.73A). The anterior and posterior diaphragmatic lymph nodes are on the thoracic surface of the diaphragm. Lymph from these nodes drains into the parasternal, posterior mediastinal, and phrenic lymph nodes. Lymphatic vessels from the abdominal surface of the diaphragm drain into the anterior diaphragmatic, phrenic, and superior lumbar (caval/aortic) lymph nodes. Lymphatic capillaries are dense on the inferior surface of the diaphragm, constituting the primary means for absorption of peritoneal fluid and substances introduced by I.P. injection.

Chapter 2: Abdomen

The entire motor supply to the diaphragm is from the right and left phrenic nerves, each of which arises from the anterior rami of C3—C5 segments of the spinal cord and is distributed to ipsilateral half of the diaphragm from its inferior surface (Fig. 2.73B). The phrenic nerves also supply sensory fibers (pain and proprioception) to most of the diaphragm. Peripheral parts of the diaphragm receive their sensory nerve supply from the intercostal nerves (lower six or seven) and the subcostal nerves. Table 2.13. Neurovascular Structures of the Diaphragm Vessels and Superior Surface of Diaphragm Nerves Arterial Superior phrenic arteries from thoracic aorta supply Musculophrenic and pericardiophrenic arteries from internal thoracic arteries Venous Musculophrenic and pericardiacophrenic veins drainage drain into internal thoracic veins; superior phrenic vein (right side) drains into IVC Lymphatic drainage Innervation

Inferior Surface of Diaphragm Inferior phrenic abdominal aorta

arteries

Inferior phrenic veins; right vein drains into IVC; left vein is doubled and drains into IVC and suprarenal vein Diaphragmatic lymph nodes to phrenic nodes, Superior lumbar lymph nodes; then to parasternal and posterior mediastinal lymphatic plexuses on superior and nodes inferior surfaces communicate freely Motor supply: phrenic nerves (C3—C5) Sensory supply: centrally by phrenic nerves (C3—C5), peripherally by intercostal nerves (T5—T11), and subcostal nerves (T12)

Hiccups Hiccups (hiccoughs) are involuntary, spasmodic contractions of the diaphragm, causing sudden inhalations that are rapidly interrupted by spasmodic closure of the glottis (aperture of the larynx) which checks the inflow of air and produces a characteristic sound. Hiccups result from irritation of afferent or efferent nerve endings or of medullary centers in the brainstem that control the muscles of respiration, particularly the diaphragm. Hiccups have many causes, such as indigestion, diaphragm irritation, alcoholism, cerebral lesions, and thoracic and abdominal lesions, all which disturb the phrenic nerves.

Diaphragmatic Apertures The diaphragmatic apertures (openings, hiatuses) permit structures (vessels, nerves, and lymphatics) to pass between the thorax and the abdomen (Figs. 2.71, 2.72, and 2.74). There are three large apertures for the IVC, esophagus, and aorta and a number of small ones.

from


Caval Opening The caval opening (vena caval aperture) is an opening in the central tendon primarily for the IVC. Also passing through the caval opening are terminal branches of the right phrenic nerve and a few lymphatic vessels on their way from the liver to the middle phrenic and mediastinal lymph nodes. The caval opening is located to the right of the median plane at the junction of the tendon's right and middle leaves. The most superior of the three large diaphragmatic apertures, the caval opening lies at the level of the IV disc between the T8 and T9 vertebrae. The IVC is adherent to the margin of the opening; consequently, when the diaphragm contracts during inspiration, it widens the opening and dilates the IVC. These changes facilitate blood flow through this large vein to the heart.

Esophageal Hiatus The esophageal hiatus (aperture) is an oval opening for the esophagus in the muscle of the right crus of the diaphragm at the level of the T10 vertebra. The esophageal hiatus also transmits the anterior and posterior vagal trunks, esophageal branches of the left gastric vessels, and a few lymphatic vessels. The fibers of the right crus of the diaphragm decussate (cross one another) inferior to the hiatus, forming a muscular sphincter for the esophagus that constricts it when the diaphragm contracts. The esophageal hiatus is superior to and to the left of the aortic hiatus. In most individuals (70%), both margins of the hiatus are formed by muscular bundles of the right crus. In others (30%), a superficial muscular bundle from the left crus contributes to the formation of the right margin of the hiatus.

Aortic Hiatus The aortic hiatus (aperture) is the opening posterior to the diaphragm for the aorta. Because the aorta does not pierce the diaphragm, movements of the diaphragm do not affect blood flow through it during respiration. The aorta passes between the crura of the diaphragm posterior to the median arcuate ligament, which is at the level of the inferior border of the T12 vertebra. The aortic hiatus also transmits the thoracic duct and sometimes the azygos and hemiazygos veins.

Small Apertures in the Diaphragm In addition to the three main apertures, there is a small opening, the sternocostal triangle (foramen), between the sternal and the costal attachments of the diaphragm. This triangle transmits lymphatic vessels from the diaphragmatic surface of the liver and the superior epigastric vessels. The sympathetic trunks pass deep to the medial arcuate ligament, accompanied by the least splanchnic nerves. There are two small apertures in each crus of the diaphragm; one transmits the greater splanchnic nerve and the other the lesser splanchnic nerve.

Chapter 2: Abdomen

Figure 2.73. Lymphatics and nerves of diaphragm. A. Lymphatics are formed in two plexuses, one on the thoracic surface of the diaphragm and the other on its abdominal surface; they communicate freely. Lymph from the thoracic surface of the diaphragm passes to the anterior and posterior diaphragmatic nodes; the anterior drainage continues to the parasternal lymph nodes, and posterior drainage passes to phrenic and posterior mediastinal nodes. Lymph drainage from the abdominal surface of the diaphragm drains into anterior diaphragmatic, phrenic, and superior lumbar (caval/aortic) nodes. B. Each phrenic nerve (from spinal nerves C3—C5) is the sole motor nerve to the ipsilateral half of the diaphragm; it also carries sensory fibers to the central part of that half, including the pleura superiorly and the peritoneum inferiorly. The lower six or seven intercostal and subcostal nerves carry sensory fibers from the peripheral part of the diaphragm.

Figure 2.74. Apertures of diaphragm. There are three large apertures in the diaphragm for major structures to pass to and from the thorax into the abdomen. The caval opening for the IVC, most anterior, is at the T8 level and to the right of the midline; the esophageal hiatus, intermediate, is at T10 and to the left of the midline; the aortic hiatus for the aorta passes posterior to the vertebral attachment of the diaphragm in the midline at T12 (see also Fig. 2.71).


Actions of the Diaphragm When the diaphragm contracts, its domes are pulled inferiorly so that the convexity of the diaphragm is somewhat flattened. Although this movement is often described as the “descent of the diaphragm,” only the domes of the diaphragm descend. Its periphery remains attached to the ribs and cartilages of the inferior six ribs. As the diaphragm descends, it pushes the abdominal viscera inferiorly. This increases the volume of the thoracic cavity and decreases the intrathoracic pressure, resulting in air being taken into the lungs. In addition, the volume of the abdominal cavity decreases slightly and intra‐abdominal pressure increases somewhat. Movements of the diaphragm are also important in circulation because the increased intra‐ abdominal pressure and decreased intrathoracic pressure help return venous blood to the heart. When the diaphragm contracts, compressing the abdominal viscera, blood in the IVC is forced superiorly into the heart. The diaphragm is at its most superior level when a person is supine (with the upper body lowered, the Trendelenburg position). In this position, the abdominal viscera push the diaphragm superiorly in the thoracic cavity. When a person lies on one side, the hemidiaphragm rises to a more superior level because of the greater push of the viscera on that side. Conversely, the diaphragm assumes an inferior level when a person is sitting or standing. For this reason, people with dyspnea (difficult breathing) prefer to sit up, not lie down; non‐ tidal (reserve) lung volume is increased, and the diaphragm is working with gravity rather than opposing it).

Section of a Phrenic Nerve Section of a phrenic nerve in the neck results in complete paralysis and eventual atrophy of the muscular part of the corresponding half of the diaphragm, except in persons who have an accessory phrenic nerve (see Chapter 8). Paralysis of a hemidiaphragm can be recognized radiographically by its permanent elevation and paradoxical movement (Fig. B2.27). Instead of descending on inspiration, it is forced superiorly by the increased intra‐abdominal pressure secondary to descent of the opposite unparalyzed hemidiaphragm.

Referred Pain from the Diaphragm Pain from the diaphragm radiates to two different areas because of the difference in the sensory nerve supply of the diaphragm (Table 2.12). Pain resulting from irritation of the diaphragmatic pleura or the diaphragmatic peritoneum is referred to the shoulder region, the area of skin supplied by the C3—C5 segments of the spinal cord (see clinical correlation [blue] box “Visceral Referred Pain,” in this chapter). These segments also contribute anterior rami to the phrenic nerves. Irritation of peripheral regions of the diaphragm, innervated by the inferior intercostal nerves, is more localized, being referred to the skin over the costal margins of the anterolateral abdominal wall.

Chapter 2: Abdomen

Rupture of the Diaphragm and Herniation of Viscera Rupture of the diaphragm and herniation of viscera can result from a sudden large increase in either the intrathoracic or intra‐abdominal pressure. The common cause of this injury is severe trauma to the thorax or abdomen during a motor vehicle accident. Most diaphragmatic ruptures are on the left side (95%) because the right side of the diaphragm receives reinforcement from its close association with the liver. A non‐muscular area of variable size called the lumbocostal triangle usually occurs between the costal and the lumbar parts of the diaphragm (Figs. 2.71 and 2.75B). This part of the diaphragm is normally formed only by fusion of the superior and inferior fascias of the diaphragm. When a traumatic diaphragmatic hernia occurs, the stomach, small intestine and mesentery, transverse colon, and spleen may herniate through this area into the thorax. Hiatal or hiatus hernia, a protrusion of part of the stomach into the thorax through the esophageal hiatus, was discussed earlier in this chapter. The structures that pass through the esophageal hiatus (vagal trunks, left inferior phrenic vessels, esophageal branches of the left gastric vessels) may be injured in surgical procedures on the esophageal hiatus (e.g., repair of a hiatus hernia).

Congenital Diaphragmatic Hernia Posterolateral defect of the diaphragm is the only relatively common congenital anomaly of the diaphragm (Moore and Persaud, 2003). Herniation almost always occurs on the left owing to the presence of the liver on the right. This defect occurs approximately once in 2200 newborn infants and is associated with congenital diaphragmatic hernia (prenatal herniation of abdominal contents into the thoracic cavity). Life‐threatening breathing difficulties may be associated with this anomaly because of the compromised space available for the development and inflation of lungs.

Figure B2.27.


The Bottom Line The diaphragm is the double‐domed, musculotendinous partition separating the thoracic and abdominal cavities and is the chief muscle of inspiration. Its muscular portion arises from the ring‐like inferior thoracic aperture from which the diaphragm rises steeply, invaginating the thoracic cage and forming a common central tendon. The right dome (higher because of the underlying liver) rises nearly to the level of the nipple, whereas the left dome is slightly lower. The central portion is slightly depressed by the heart within the pericardium and is fused to the mediastinal surface of the central tendon. In the neutral respiratory position, the central tendon lies at the level of the T8—T9 IV disc and the xiphisternal joint. When stimulated by the phrenic nerves, the domes are pulled downward (descend), compressing the abdominal viscera. When stimulation ceases and the diaphragm relaxes, the diaphragm is pushed upward (ascends) by the combined decompression of the viscera and tonus of the muscles of the anterolateral abdominal wall. The diaphragm is perforated by the IVC and phrenic nerves at the T8 vertebral level. The fibers of the right crus form a sphincteric hiatus for the esophagus at the T10 vertebral level. The descending aorta and thoracic duct pass posterior to the diaphragm at the T12 vertebral level, in the midline between the crura, overlapped by the median arcuate ligament connecting them. Superior and inferior phrenic arteries and veins supply most of the diaphragm, with additional drainage occurring via the musculophrenic and azygos/hemiazygos veins. In addition to exclusive motor innervation, the phrenic nerves supply most of the pleura and peritoneum covering the diaphragm. Peripheral parts of the diaphragm receive sensory innervation from the lower intercostal and subcostal nerves. The left lumbocostal triangle and the esophageal hiatus are potential sites of acquired hernias through the diaphragm. Developmental defects in the left lumbocostal region account for most congenital diaphragmatic hernias.

Posterior Abdominal Wall The posterior abdominal wall (Figs. 2.75 and 2.76) is mainly composed of the:      

Five lumbar vertebrae and associated IV discs (centrally). Posterior abdominal wall muscles, including the psoas, quadratus lumborum, iliacus, transverse abdominal, and oblique muscles (laterally). Diaphragm, which contributes to the superior part of the posterior wall. Fascia, including the thoracolumbar fascia. Lumbar plexus, composed of the anterior rami of lumbar spinal nerves. Fat, nerves, vessels (e.g., aorta and IVC), and lymph nodes.

If observing the anatomy of the posterior abdominal wall in only two‐dimensional diagrams, such as Figure 2.76B, it would be easy to suppose that it is flat. In observing a dissected cadaver, or a transverse cross section such as that in Figures 2.61B and 2.75, it is apparent that the lumbar vertebral column is a marked central prominence in the posterior wall, creating two paravertebral “gutters” on each side. The deepest (most posterior) part of these gutters is occupied by the kidneys and their surrounding fat. The abdominal aorta lies on the anterior aspect of the anteriorly protruding vertebral column. It is usually surprising to find how close the lower abdominal aorta lies to the anterior abdominal wall in lean individuals (see Fig.

Chapter 2: Abdomen

B2.28C). Of course, many structures lie anterior to the aorta (SMA, parts of the duodenum, pancreas and left renal vein, etc.) and so these “posterior abdominal structures” may approach the anterior abdominal wall closer than might be expected in thin persons, especially when they are in the supine position.

Fascia of the Posterior Abdominal Wall The posterior abdominal wall is covered with a continuous layer of endoabdominal fascia that lies between the parietal peritoneum and the muscles (Figs. 2.61B and 2.75). The fascia lining the posterior abdominal wall is continuous with the transversalis fascia that lines the transverse abdominal muscle. It is customary to name the fascia according to the structure it covers. The psoas fascia covering the psoas major (psoas sheath) is attached medially to the lumbar vertebrae and pelvic brim (Fig. 2.75). The psoas fascia (sheath) is thickened superiorly to form the medial arcuate ligament (Fig. 2.71). The psoas fascia fuses laterally with the quadratus lumborum and thoracolumbar fascias. Inferior to the iliac crest, the psoas fascia is continuous with the part of the iliac fascia covering the iliacus. The psoas fascia also blends with the fascia covering the quadratus lumborum. The thoracolumbar fascia is an extensive fascial complex attached to the vertebral column medially that, in the lumbar region, has posterior, middle and anterior layers with muscles enclosed between them (Figs. 2.61B and 2.75). It is thin and transparent where it covers the thoracic parts of the deep muscles but is thick and strong in the lumbar region (Fig. 2.75C). The enclosure of the vertical deep back muscles (erector spinae) by the posterior and middle layers of the thoracolumbar fascia on the posterior aspect of the trunk is comparable to the enclosure of the rectus abdominis by the rectus sheath on the anterior aspect (Fig. 2.75A). This posterior sheath is even more formidable than the rectus sheath, however, because of the thickness of its posterior layer and the central attachment to the lumbar vertebrae, as opposed to the rectus sheaths, which lack bony support where they fuse to each other at the linea alba. The lumbar part of this posterior sheath, extending between the 12th rib and the iliac crest, attaches laterally to the internal oblique and transverse abdominal muscles, as does the rectus sheath. However, in contrast to the rectus sheath, the thoracolumbar fascia is not attached to the external oblique; it is attached to the latissimus dorsi (Figs. 2.61B and 2.75C)


Figure 2.75. Fascia and aponeuroses of the abdominal wall at the level of the renal hilum. A. The relationships of the muscles, aponeurotic muscle sheaths, and fascia of the abdominal wall are demonstrated in transverse section. The three flat abdominal muscles forming the lateral walls span between complex anterior and posterior aponeurotic formations that ensheath vertically disposed muscles. The thin anterolateral walls (appearing disproportionately thick here) are distensible. Although flexible, the posterior abdominal wall is weight bearing and so is reinforced by the vertebral column and muscles that act on it; thus it is not distensible. B. Details of the disposition of the aponeurotic and fascial layers of the posterior abdominal wall. For details concerning those of the anterior abdominal wall, see Figure 2.5B. C. Dimensional view of the region demonstrated in section in B. Note the free posterior border of the external oblique muscle.

Chapter 2: Abdomen

The anterior layer of the thoracolumbar fascia (quadratus lumborum fascia), covering the quadratus lumborum, a thinner, more transparent layer than the other two layers, attaches to the anterior surfaces of the transverse processes of the lumbar vertebrae, the iliac crest, and the 12th rib. The anterior layer is continuous laterally with the aponeurotic origin of the transverse abdominal muscle (Fig. 2.61A). It thickens superiorly to form the lateral arcuate ligament and is adherent inferiorly to the iliolumbar ligaments (Fig. 2.76).

Muscles of the Posterior Abdominal Wall The main paired muscles in the posterior abdominal wall (Table 2.14) are the:   

Psoas major: passing inferolaterally. Iliacus: lying along the lateral sides of the inferior part of the psoas major. Quadratus lumborum: lying adjacent to the transverse processes of the lumbar vertebrae and lateral to superior parts of the psoas major.

The attachments, nerve supply, and main actions of these muscles are summarized in Table 2.14.

Psoas Abscess Although the prevalence of tuberculosis (TB) has been greatly reduced, there is currently a resurgence of TB, especially in Africa and Asia, sometimes in pandemic proportions, owing to AIDS and drug resistance. TB of the vertebral column is quite common. An infection may spread through the blood to the vertebrae (hematogenous spread), particularly during childhood. An abscess resulting from tuberculosis in the lumbar region tends to spread from the vertebrae into the psoas sheath, where it produces a psoas abscess. As a consequence, the psoas fascia thickens to form a strong stocking‐like tube. Pus from the psoas abscess passes inferiorly along the psoas muscle within this fascial tube over the pelvic brim and deep to the inguinal ligament. The pus usually surfaces in the superior part of the thigh. Pus can also reach the psoas sheath by passing from the posterior mediastinum when the thoracic vertebrae are diseased. The inferior part of the iliac fascia is often tense and raises a fold that passes to the internal aspect of the iliac crest. The superior part of this fascia is loose and may form a pocket, the iliacosubfascial fossa, posterior to the above‐mentioned fold. Part of the large intestine, such as the cecum and/or appendix on the right side and the sigmoid colon on the left side, may become trapped in this fossa, causing considerable pain.

Clinically Oriented Anatomy, 5th Edition By Keith Moore Table 2.14. Muscles of Posterior Abdominal Wall

Muscle P s o a s m a j o r

Iliacus

Q u a d r a tu s lumborum

Superior A t t a c h me n t Transverse p r o c e s s e s of lumbar vertebrae; sides of b od i e s of T12—L5 vertebrae and intervening i n t e r v e r te b r a l discs Superior two thirds of iliac fossa, ala of s a c r u m , and anterior sacroiliac ligaments M e d i a l h a lf o f inferior border of 12th ribs and tips of l u m b a r transverse p r o c e s s e s

Inferior A t t a c h me n t By a strong t e n d on t o l e s s e r t r o c h a n t e r of f e m u r

I n n e r v at i o n

M a i n A c ti o n

Lumbar plexus via a n t e ri o r branches of L2—L4 nerves

A c t i n g i n f e r io r l y w i t h i l i a c u s , i t f l e x e s t h i g h ; a c t in g s u p e r i o r l y i t f l e x e s v e r t e b r a l c o l u m n l a t e ra l l y ; i t i s u s e d t o b a l a n c e t h e t r u n k ; w h e n s i t t i n g i t a c t s i n f e r i o r l y w i th i l i a c u s t o f l e x t r u n k

L e s s e r t r o c h a n t e r F e m o r a l n e rv e F l e x e s t h i g h a n d s t a b i l iz e s h ip j o i n t ; a c t s w i t h p s o a s m a j o r of femur and (L2—L4) shaft inferior to it, and to psoas m a j o r te n d on

Iliolumbar ligament and internal lip of iliac crest

Anterior E x t e n d s a n d l a t e r a l l y f l e x e s v e r te b ra l branches o f c o l u m n ; f i x e s 1 2 t h r i b d u r in g i n s p i r a t i o n T 1 2 a n d L 1— L 4 nerves

Psoas Major The long, thick, fusiform psoas major lies lateral to the lumbar vertebrae (Fig. 2.76). Psoas is a Greek word meaning “muscle of the loin.” (Butchers refer to the psoas of animals as the tenderloin.) The psoas passes inferolaterally, deep to the inguinal ligament to reach the lesser trochanter of the femur (see Chapter 4). The lumbar plexus of nerves is embedded in the posterior part of the psoas, anterior to the lumbar transverse processes.

Chapter 2: Abdomen

Iliacus The iliacus is a large triangular muscle that lies along the lateral side of the inferior part of the psoas major. This muscle extends across the sacroiliac joint and attaches to the superior two thirds of the iliac fossa. Most of its fibers join the tendon of the psoas major. Together the psoas and iliacus form the iliopsoas, the chief flexor of the thigh. It is also a stabilizer of the hip joint and helps maintain the erect posture at this joint. The psoas and iliacus share in hip flexion; however, only the psoas can produce movement (flexion or lateral bending) of the lumbar spine.

Quadratus Lumborum The quadrilateral quadratus lumborum forms a thick muscular sheet in the posterior abdominal wall (Figs. 2.75 and 2.76). It lies adjacent to the lumbar transverse processes and is broader inferiorly. Close to the 12th rib, the lateral arcuate ligament crosses the quadratus lumborum. The subcostal nerve passes posterior to this ligament and runs inferolaterally on the quadratus lumborum. Branches of the lumbar nerve plexus run inferiorly on the anterior surface of this muscle.

Posterior Abdominal Pain The iliopsoas has extensive and clinically important relations to the kidneys, ureters, cecum, appendix, sigmoid colon, pancreas, lumbar lymph nodes, and nerves of the posterior abdominal wall. When any of these structures is diseased, movement of the iliopsoas usually causes pain. When intra‐abdominal inflammation is suspected, the iliopsoas test is performed. The person is asked to lie on the unaffected side and to extend the thigh on the affected side against the resistance of the examiner's hand (Bickley and Szilagyi, 2003). The elicitation of pain with this maneuver is a positive psoas sign. An acutely inflamed appendix, for example, will produce a positive right psoas sign. Because the psoas lies along the vertebral column and the iliacus crosses the sacroiliac joint, disease of the intervertebral and sacroiliac joints may cause spasm of the iliopsoas, a protective reflex. Adenocarcinoma of the pancreas in advanced stages invades the muscles and nerves of the posterior abdominal wall, producing excruciating pain because of the close relationship of the pancreas to the posterior abdominal wall.

The Bottom Line Large, complex aponeurotic formations cover the central parts of the trunk both anteriorly and posteriorly, forming dense sheaths centrally that house vertical muscles and attach laterally to the flat muscles of the anterolateral abdominal wall. The thoracolumbar fascia is the posterior aponeurotic formation. In addition to ensheathing the erector spinae between its posterior and middle layers, it encloses the quadratus lumborum between its middle and anterior layers. The anterior layer, part of the endoabdominal fascia, is continuous medially with the psoas fascia (enclosing the psoas) and laterally with the transversalis fascia (lining the transverse abdominal). The tube‐like psoas fascia provides a potential pathway for the spread of infections between the vertebral column and hip joint. The endoabdominal fascia covering the anterior aspects of both the quadratus lumborum and psoas is thickened over the superiormost aspects of the muscles, forming the lateral and medial arcuate


ligaments, respectively. A highly variable layer of extraperitoneal fat intervenes between the endoabdominal fascia and the peritoneum. It is especially thick in the paravertebral gutters of the lumbar region, comprising the paranephric fat (pararenal fat body).

Nerves of the Posterior Abdominal Wall Components of both the somatic and the autonomic (visceral) nervous systems are associated with the posterior abdominal wall. The subcostal nerves (anterior rami of T12) arise in the thorax, pass posterior to the lateral arcuate ligaments into the abdomen, and run inferolaterally on the anterior surface of the quadratus lumborum (Fig. 2.76). They pass through the transverse abdominal and internal oblique muscles to supply the external oblique and skin of the anterolateral abdominal wall. The lumbar spinal nerves (L1—L5) pass from the spinal cord through the IV foramina inferior to the corresponding vertebrae, where they divide into posterior and anterior rami. Each ramus contains sensory and motor fibers. The posterior rami pass posteriorly to supply the muscles of the back and overlying skin, whereas the anterior rami pass laterally and inferiorly, to supply the skin and muscles of the inferiormost trunk and lower limb. The initial portions of the anterior rami of the L1, L2, and occasionally L3 spinal nerves give rise to white communicating branches (L. rami communicantes), which convey presynaptic sympathetic fibers to the lumbar sympathetic trunks. The abdominal part of the sympathetic trunks (lumbar sympathetic trunks), consisting of four lumbar paravertebral sympathetic ganglia and the interganglionic branches that connect them, are continuous with the thoracic part of the trunks deep to the medial arcuate ligaments of the diaphragm. The lumbar trunks descend on the anterolateral aspects of the bodies of the lumbar vertebrae in a groove formed by the adjacent psoas major. Inferiorly, they cross the sacral promontory and continue inferiorly into the pelvis as the sacral part of the trunks. For the innervation of the abdominal wall and lower limbs, synapses between the presynaptic and postsynaptic fibers occur in the sympathetic trunks. Postsynaptic sympathetic fibers travel from the lateral aspect of the trunks via gray communicating branches to the anterior rami. They become the thoracoabdominal and subcostal nerves, and the lumbar plexus (somatic nerves) that stimulate vasomotion, sudomotion and pilomotion in the lowermost trunk and lower limb. Lumbar splanchnic nerves arising from the medial aspect of the lumbar sympathetic trunks convey presynaptic sympathetic fibers for the innervation of pelvic viscera. The lumbar plexus of nerves is formed anterior to the lumbar transverse processes, within the proximal attachment of the psoas major. This nerve network is composed of the anterior rami of L1 through L4 nerves. The following nerves are branches of the lumbar plexus; the three largest are listed first: 



The femoral nerve (L2—L4) emerges from the lateral border of the psoas major and innervates the iliacus and passes deep to the inguinal ligament/iliopubic tract to the anterior thigh, supplying the flexors of the hip and extensors of the knee. The obturator nerve (L2—L4) emerges from the medial border of the psoas major and passes into the lesser pelvis, passing inferior to the superior pubic

Chapter 2: Abdomen











ramus (through the obturator foramen) to the medial thigh, supplying the adductor muscles. The lumbosacral trunk (L4, L5) passes over the ala (wing) of the sacrum and descends into the pelvis to participate in the formation of the sacral plexus with the anterior rami of S1—S4 nerves. The ilioinguinal and iliohypogastric nerves (L1) arise from the anterior ramus of L1, entering the abdomen posterior to the medial arcuate ligament and passing inferolaterally, anterior to the quadratus lumborum. They run superior and parallel to the iliac crest, piercing the transverse abdominal near the ASIS. They then pass through the internal and external obliques to supply the abdominal muscles and skin of the inguinal and pubic regions. The division of the L1 anterior ramus may occur as far distally as the ASIS, so that often only one nerve (L1) crosses the posterior abdominal wall instead of two. The genitofemoral nerve (L1, L2) pierces the psoas major and runs inferiorly on its anterior surface, deep to the psoas fascia; it divides lateral to the common and external iliac arteries into femoral and genital branches. The lateral cutaneous nerve of the thigh, or lateral femoral cutaneous nerve (L2, L3) runs inferolaterally on the iliacus and enters the thigh deep to the inguinal ligament/iliopubic tract, just medial to the ASIS; it supplies skin on the anterolateral surface of the thigh. An accessory obturator nerve (L3, L4) is present almost 10% of the time. It parallels the medial border of the psoas, anterior to the obturator nerve, crossing superior to the superior pubic ramus in close proximity to the femoral vein.

Although the larger branches (femoral, obturator, and lumbosacral trunk) are consistent in their placement, variation should be anticipated in the disposition of the smaller branches of the lumbar plexus.


Figure 2.76. Muscles and nerves of posterior abdominal wall. Most of the right psoas major has been removed to show that the lumbar plexus of nerves is formed by the anterior rami of the first four lumbar spinal nerves, and that it lies in the substance of the psoas major.

Partial Lumbar Sympathectomy The treatment of some patients with arterial disease in the lower limbs may include a partial lumbar sympathectomy, the surgical removal of two or more lumbar sympathetic ganglia by division of their rami communicantes. Surgical access to the sympathetic trunks is commonly through a lateral extraperitoneal approach because the sympathetic trunks lie retroperitoneally in the extraperitoneal fatty tissue (Fig. 2.76B). The surgeon splits the muscles of the anterior abdominal wall and moves the peritoneum medially and anteriorly to expose the medial edge of the psoas major, along which the sympathetic trunk lies. The left trunk is often overlapped slightly by the aorta. The right sympathetic trunk is covered by the IVC. The intimate relationship of the sympathetic trunks to the aorta and IVC also makes these large vessels vulnerable to injury during lumbar sympathectomy. Consequently, the surgeon carefully retracts them to expose the sympathetic trunks that usually lie in the groove between the psoas major laterally and the lumbar vertebral bodies medially. These trunks are often obscured by fat and lymphatic tissue. Knowing that identification of the sympathetic trunks is not easy, great care is taken not to remove inadvertently part of the genitofemoral nerve, lumbar lymphatics, or ureter.

The Bottom Line The lumbar sympathetic trunks deliver postsynaptic sympathetic fibers to the lumbar plexus for distribution with somatic nerves, and presynaptic parasympathetic fibers to the abdominal aortic plexus, the latter ultimately innervating pelvic viscera. With

Chapter 2: Abdomen

the exception of the subcostal nerve (T12) and lumbosacral trunk (L4—L5), the somatic nerves of the posterior abdominal wall are products of the lumbar plexus, formed by the anterior rami of L1—L4 deep to the psoas. Only the subcostal nerve and the derivatives of the anterior ramus of L1 (iliohypogastric and ilioinguinal nerves) have an abdominal distribution—to the muscles and skin of the inguinal and pubic regions. All other nerves pass to the muscles and skin of the lower limb.

Vessels of the Posterior Abdominal Wall The major neurovascular bundle of the inferior trunk, including the abdominal aorta, the inferior vena cava, and the aortic periarterial nerve plexus, courses in the midline of the posterior abdominal wall, anterior to the bodies of the lumbar vertebrae (Figs. 2.60 and 2.75).

Abdominal Aorta Most arteries supplying the posterior abdominal wall arise from the abdominal aorta (Table 2.15A). The subcostal arteries arise from the thoracic aorta and distribute inferior to the 12th rib. The abdominal aorta is approximately 13 cm in length. It begins at the aortic hiatus in the diaphragm at the level of the T12 vertebra and ends at the level of the L4 vertebra by dividing into the right and left common iliac arteries. The level of the aortic bifurcation is 2—3 cm inferior and to the left of the umbilicus at the level of the iliac crests. The common iliac arteries diverge and run inferolaterally, following the medial border of the psoas muscles to the pelvic brim. Here each common iliac artery divides into the internal and external iliac arteries. The internal iliac artery enters the pelvis (its course and branches are described in Chapter 3). The external iliac artery follows the iliopsoas muscle. Just before leaving the abdomen, the external iliac artery gives rise to the inferior epigastric and deep circumflex iliac arteries, which supply the anterolateral abdominal wall.

Relations of the Abdominal Aorta From superior to inferior, the important anterior relations of the abdominal aorta are the:     

Celiac plexus and ganglion (Figs. 2.54 and 2.60). Body of the pancreas and splenic vein (Fig. 2.55). Left renal vein (Figs. 2.66 and 2.72B). Horizontal part of the duodenum. Coils of the small intestine.

The abdominal aorta descends anterior to the bodies of the T12—L4 vertebrae. The left lumbar veins pass posterior to the aorta to reach the IVC (Fig. 2.77). On the right, the aorta is related to the azygos vein, chyle cistern, thoracic duct, right crus of the diaphragm, and right celiac ganglion. On the left, the aorta is related to the left crus of the diaphragm and the left celiac ganglion.


Branches of the Abdominal Aorta The branches of the descending (thoracic and abdominal) aorta may be described as arising and coursing in three “vascular planes,” and can be classified as being visceral or parietal and paired or unpaired (Table 2.15). Paired parietal branches of the aorta serve the diaphragm and posterior abdominal wall. The median sacral artery, an unpaired parietal branch, may be said to occupy a fourth (posterior) plane because it arises from the posterior aspect of the aorta just proximal to its bifurcation. Although markedly smaller, it could also be considered a midline “continuation” of the aorta, in which case its lateral branches, the small lumbar arteries (L. arteriae lumbales imae) and lateral sacral branches, would also be included as part of the paired parietal branches.

Pulsations of the Aorta and Abdominal Aortic Aneurysm Because the aorta lies posterior to the pancreas and stomach, a tumor of these organs may transmit pulsations of the aorta that could be mistaken for an abdominal aortic aneurysm, a localized enlargement of the aorta (Fig. B2.28A & B). Deep palpation of the midabdomen can detect an aneurysm, which usually results from a congenital or acquired weakness of the arterial wall (Fig. B2.28C & D). Pulsations of a large aneurysm can be detected to the left of the midline; the pulsatile mass can be moved easily from side to side. Medical imaging can confirm the diagnosis in doubtful cases. Acute rupture of an abdominal aortic aneurysm is associated with severe pain in the abdomen or back. If unrecognized, such an aneurysm has a mortality rate of nearly 90% because of heavy blood loss (Swartz, 2001). Surgeons can repair an aneurysm by opening it, inserting a prosthetic graft (such as one made of Dacron), and sewing the wall of the aneurysmal aorta over the graft to protect it. Many vascular problems formerly treated with open repair, including aneurysm repair, are now being treated by means of endovascular catheterization procedures When the anterior abdominal wall is relaxed, particularly in children and thin adults, the inferior part of the abdominal aorta may be compressed against the body of the L4 vertebra by firm pressure on the anterior abdominal wall, over the umbilicus (Fig. B2.28C & D). This pressure may be applied to control bleeding in the pelvis or lower limbs.

Chapter 2: Abdomen

Figure B2.28.

Clinically Oriented Anatomy, 5th Edition By Keith Moore Table 2.15. Branches of the Abdominal Aorta

Vascular Plane

1

Anterior midline

2

Lateral

3

Posterolateral

Class

Distribution

Abdominal Branches (Arteries) Unpaired visceral Alimentary tract Celiac Superior mesenteric Inferior mesenteric Paired visceral Urogenital and Suprarenal endocrine organs Renal Gonadal (testicular or ovarian) Paired parietal Diaphragm; body Subcostal (segmental) wall Inferior phrenic Lumbar

Vertebral Level T12 L1 L3 L1 L1 L2

L2 T12 L1—L4

The Bottom Line Except for the subcostal arteries, the arteries supplying the posterior abdominal wall arise from the abdominal aorta. The abdominal aorta descends from the aortic hiatus, coursing on the anterior aspects of the T12—L4 vertebra, immediately left of the midline, and bifurcates into the common iliac arteries at the level of the supracristal plane. Branches of the aorta arise and course in three vascular planes:

Chapter 2: Abdomen

anterior (unpaired visceral branches), lateral (paired visceral branches), and posterolateral (paired parietal). The median sacral may be considered a diminutive continuation of the aorta, which continues to give rise to paired parietal branches.

Veins of the Posterior Abdominal Wall The veins of the posterior abdominal wall are tributaries of the IVC, except for the left testicular or ovarian vein, which enters the left renal vein instead of entering the IVC (Fig. 2.77). The IVC, the largest vein in the body, has no valves except for a variable, non‐functional one at its orifice in the right atrium of the heart. The IVC returns poorly oxygenated blood from the lower limbs, most of the back, the abdominal walls, and the abdominopelvic viscera. Blood from the abdominal viscera passes through the portal venous system and the liver before entering the IVC through the hepatic veins.

Surface Anatomy of the Abdominal Aorta The abdominal aorta may be represented on the anterior abdominal wall by a band (approximately 2 cm wide) extending from a median point, approximately 2.5 cm superior to the transpyloric plane to a point slightly inferior to and to the left of the umbilicus (Fig. SA2.6). This point indicates the level of bifurcation of the aorta into the common iliac arteries. The site of the aortic bifurcation is also indicated just to the left of the midpoint of a line joining the highest points of the iliac crests. This line is helpful when examining obese persons in whom the umbilicus is not a reliable surface landmark.

Figure SA2.6. The IVC begins anterior to the L5 vertebra by the union of the common iliac veins. This union occurs approximately 2.5 cm to the right of the median plane, inferior to the bifurcation of the aorta and posterior to the proximal part of the right common iliac artery (Fig. 2.60). The IVC ascends on the right sides of the bodies of the L3—L5


vertebrae and on the right psoas major to the right of the aorta. The IVC leaves the abdomen by passing through the caval opening in the diaphragm to enter the thorax at the T8 vertebral level. Because it is formed one vertebral level inferior to the bifurcation of the aorta, and traverses the diaphragm four vertebral levels superior to the aortic hiatus, the overall length of the IVC is 7 cm greater than that of the abdominal aorta, although most of the additional length is intrahepatic. The IVC collects poorly oxygenated blood from the lower limbs and non‐portal blood from the abdomen and pelvis. Almost all the blood from the digestive tract is collected by the portal system and passes through the hepatic veins to the IVC. The tributaries of the IVC correspond to the paired visceral and parietal branches of the abdominal aorta. The veins that correspond to the unpaired visceral branches of the aorta are instead tributaries of the portal vein. The blood they carry does ultimately enter the IVC via the hepatic veins, after traversing the liver. The branches corresponding to the paired viscera branches of the abdominal aorta include the right suprarenal vein, the right and left renal veins, and the right gonadal (testicular or ovarian) vein. The left suprarenal and gonadal veins drain indirectly into the IVC because they are tributaries of the left renal vein. Paired parietal branches of the IVC include the inferior phrenic veins, the 3rd (L3) and 4th (L4) lumbar veins, and the common iliac veins, formed by union of the external and internal iliac veins. The ascending lumbar and azygos veins connect the IVC and superior vena cava, either directly or indirectly (see Chapter 1). Figure 2.77. Inferior vena cava and its tributaries. The asymmetry in the renal and common iliac veins reflects the placement of the IVC to the right of the midline.

Chapter 2: Abdomen

Collateral Routes for Abdominopelvic Venous Blood Three collateral routes, formed by valveless veins of the trunk, are available for venous blood to return to the heart when the IVC is obstructed or ligated. Two of these routes (one involving the superior and inferior epigastric veins, and another involving the thoracoepigastric vein) were discussed earlier in this chapter with the anterior abdominal wall. The third collateral route involves the epidural venous plexus inside the vertebral column (illustrated and discussed in Chapter 3), which communicates with the lumbar veins of the inferior caval system, and the tributaries of the azygos system of veins, which is part of the superior caval system. The inferior part of the IVC has a complicated developmental history because it forms from parts of three sets of embryonic veins (Moore and Persaud, 2003). Therefore, IVC anomalies are relatively common and most of them, such as a persisting left IVC, occur inferior to the renal veins (Fig. B2.29). These anomalies result from the persistence of embryonic veins on the left side, which normally disappear. If a left IVC is present, it may cross to the right side at the level of the kidneys.

Figure B2.29.

The Bottom Line The veins of the posterior abdominal wall are mostly direct tributaries of the IVC, although some enter indirectly via the left renal vein. The IVC is the largest vein and lacks valves. The IVC is formed at the L5 vertebral level by the union of the common iliac veins. It ascends to the T8 vertebral level, passing through the diaphragm and entering the heart almost simultaneously. It drains poorly oxygenated blood from the body inferior to the diaphragm. The IVC receives the drainage of the abdominal viscera indirectly via the portal vein, liver, and hepatic veins. Except for the hepatic veins, the tributaries of the IVC mostly correspond to the lateral paired visceral and posterolateral paired parietal branches of the abdominal aorta. Three collateral routes (two involving the anterior abdominal wall, and one involving the vertebral canal) are available to return blood to the heart when the IVC is obstructed.


Lymphatics of the Posterior Abdominal Wall Lymphatic vessels and lymph nodes lie along the aorta, IVC, and iliac vessels (Fig. 2.78A). The common iliac lymph nodes receive lymph from the external and internal iliac lymph nodes. Lymph from the common iliac lymph nodes passes to the right and left lumbar lymph nodes. Lymph from the alimentary tract, liver, spleen, and pancreas passes along the celiac and superior and inferior mesenteric arteries to the preaortic lymph nodes (celiac and superior and inferior mesenteric nodes) scattered around the origins of these arteries from the aorta. Efferent vessels from these nodes form the intestinal lymphatic trunks, which may be single or multiple, and participate in the confluence of lymphatic trunks that gives rise to the thoracic duct (Fig. 2.78B).

Figure 2.78. Lymphatic drainage of posterior abdominal wall and lymphatic trunks of abdomen. A. The parietal lymph nodes are shown. The external iliac, common iliac, and lumbar (aortic) lymph nodes lie in a continuous chain along the abdominal aorta and its terminal branches, receiving lymph from the posterior abdominal wall as well as the efferent drainage of lymph nodes of the abdominal viscera and lower limbs. B. The abdominal lymphatic trunks are shown. The thoracic duct begins posterior to the aorta at the aortic hiatus as a convergence of lymphatic trunks that may or may not take the form of a chyle cistern. The converging lymphatic trunks include the paired lumbar lymph trunks, the intestinal lymphatic trunk(s), and a pair of descending thoracic lymphatic trunks. All lymphatic drainage from the lower half of the body converges in the abdomen to enter the beginning of the thoracic duct. The thoracic duct conducts it to the convergence of the left internal jugular and subclavian veins (left venous angle) where the lymph enters the venous system.

Chapter 2: Abdomen

The right and left lumbar (caval and aortic) lymph nodes lie on both sides of the IVC and aorta. These nodes receive lymph directly from the posterior abdominal wall, kidneys, ureters, testes or ovaries, uterus, and uterine tubes. They also receive lymph from the descending colon, pelvis, and lower limbs through the inferior mesenteric and common iliac lymph nodes. Efferent lymphatic vessels from the large lumbar lymph nodes form the right and left lumbar lymphatic trunks. The inferior end of the thoracic duct lies anterior to the bodies of the L1 and L2 vertebrae between the right crus of the diaphragm and the aorta. The thoracic duct begins with the convergence of the main lymphatic ducts of the abdomen, which in only a small proportion of individuals takes the form of the commonly depicted, thin‐ walled sac or dilation, the chyle cistern (L. cisterna chyli) (Fig. 2.78). Chyle cisterns vary greatly in size and shape. More often there is merely a simple or plexiform convergence at this level of the right and left lumbar lymphatic trunks, the intestinal lymph trunk(s), and a pair of descending thoracic lymphatic trunks, which carry lymph from the lower six intercostal spaces on each side. Consequently, essentially all the lymphatic drainage from the lower half of the body (deep lymphatic drainage inferior to the level of the diaphragm, and all superficial drainage inferior to the level of the umbilicus) converges in the abdomen to enter the beginning of the thoracic duct. The thoracic duct ascends through the aortic hiatus in the diaphragm into the posterior mediastinum, where it collects more parietal and visceral drainage, particularly from the left upper quadrant of the body. The duct ultimately ends by entering the venous system at the junction of the left subclavian and internal jugular veins (the left venous angle).

The Bottom Line Lymphatic drainage from the abdominal viscera courses retrograde along the ramifications of the three unpaired visceral branches of the abdominal aorta. Lymphatic drainage from the abdominal wall merges with that from the lower limbs, both pathways following the arterial supply retrograde from those parts. Ultimately, all lymphatic drainage from structures inferior to the diaphragm, plus that draining from the lower six intercostal spaces via the descending thoracic lymphatic trunks, enters the beginning of the thoracic duct at the T12 level, posterior to the aorta. The origin of the thoracic duct may take the form of a saccular chyle cistern.

Medical Imaging of the Abdomen Radiographs of the abdomen demonstrate abnormal anatomical relationships of organs such as those resulting from tumors. Radiographs also demonstrate gas and calcifications in the intestine. Abnormal intestinal gas patterns indicate a dilated large intestine and intestinal perforation. The anatomy of the esophagus and alimentary tract can be demonstrated radiographically after the swallowing of barium meal, a contrast medium composed of a mixture of barium sulfate and water. Examinations of the alimentary tract are performed with fluoroscopic guidance, supplemented by cineradiography or videotape and radiographs. These procedures enable the radiologist to detect abnormalities of the esophagus, stomach, and intestines as well as lesions in adjacent structures that displace these organs. Most early knowledge concerning the shape, position, and movements of the esophagus, stomach, and intestines came from barium studies.


Peristaltic waves in the esophagus appear as ring‐like contractions that propel the barium toward the stomach (Fig. 2.79). Once the stomach is distended, circular peristaltic waves begin in the body of the stomach and sweep toward the pyloric canal, where they stop. Gas in the fundus of the stomach is clearly visible superior to the barium shadow (Fig. 2.80A). When the pyloric sphincter opens and closes, the proximal part of the duodenum expands to form the ampulla (duodenal cap). The outline of the barium in the superior part of the duodenum is smooth; in other parts, the outline has a feathery appearance because of the circular folds in the duodenum (Fig. 2.80B & C). To examine the colon, a barium enema is given after the bowel is cleared of fecal material by a cleansing enema. Radiographs show the typical haustra (Fig. 2.81). The single‐contrast examinations of the colon show its various parts; the dilated rectum is well illustrated. In chronic stages of colitis (inflammation of the colon), the mucosa atrophies and the typical pattern of the haustra disappears. The outline of the haustra is accentuated by the double‐contrast method: the patient evacuates the barium and air is injected through the anal canal to distend the colon that is still lined with a thin layer of barium (Fig. 2.81B). MRI can also be used to study the intestines. This imaging procedure is particularly effective after double‐contrast radiographic studies when the structures are still distended with air (Fig. 2.81C). A wide variety of radiographic methods are available for studying the structure and function of the bile passages and gallbladder clinically, each with its own criteria, advantages, and disadvantages. Radiographic examination of the biliary ducts at the time of surgery (preoperative cholangiography) is an important procedure for all patients undergoing cholecystectomy to determine the presence and location of stones in the biliary tract, that all calculi have been removed, and that no other obstructions are present (Fig. 2.82A). A tube is implanted directly into the biliary duct system to inject radiopaque dye. Endoscopic retrograde cholangiopancreatography (ERCP) has become a standard procedure for the diagnosis of both pancreatic and biliary disease (Fig. 2.82B). First, a fiberoptic endoscope is passed through the mouth, esophagus, and stomach. Then the duodenum is entered and a cannula is inserted into the major duodenal papilla and advanced under fluoroscopic control into the duct of choice (bile duct or pancreatic duct) for injection of radiographic contrast medium. One radiographic method of studying the anatomy and function of the gallbladder has been used for more than 8 decades (Fig. 2.82C). This procedure, oral or intravenous cholecystography, is a test of gallbladder function and also demonstrates its location and shape. This procedure has largely been replaced by ultrasonography and cholescintigraphy. The latter is a dynamic function test, in many ways similar to cholecystography; however, radioactive tracer and marker compounds are used.

Chapter 2: Abdomen

Figure 2.79. Radiograph of esophagus after swallowing barium meal. In this left posterior oblique (LPO) view, note the normal “constrictions” (impressions) caused by the arch of the aorta and left main bronchus. The phrenic ampulla, which is seen only radiographically, is the distensible part of the esophagus, lying just superior to the diaphragm. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)


Figure 2.80. Radiographs of stomach, small intestine, and gallbladder. A. Observe the peristaltic wave in the stomach and the longitudinal gastric folds (rugae) of mucous membrane. (A, Courtesy of Dr. J. Helsin, Toronto, ON, Canada.) B. The stomach and small intestine were imaged after a barium meal. Observe the peristaltic wave (arrowheads), pylorus, ampulla (duodenal cap), and the feathery appearance of the barium in the small intestine. Also observe the relationship of the gallbladder to the ampulla in the superior part of the duodenum. C. This radiograph demonstrates the pyloric region of the stomach and the superior part of the duodenum. (B and C, Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)

Chapter 2: Abdomen

Figure 2.81. Barium enema examination of colon and MRI study of intestine. A. In this single‐ contrast study, barium can be seen coating the walls of the colon distended with air, giving a vivid view of the mucosa and haustra. A, ascending colon; C, cecum; D, descending colon; G, sigmoid colon; H, hepatic or right colic flexure; R, rectum; S, splenic or left colic flexure; T, transverse colon; U, haustra. (Courtesy of Dr. C. S. Ho, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.) B. In this double‐contrast study, barium has filled the colon. Observe the level of the right colic flexure. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.) C. A coronal MRI of the lower thoracic cage and abdomen is shown. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, ON, Canada.)


Figure 2.82. Radiographs of bile passages and gallbladder. A. After an open‐incision cholecystectomy, contrast medium was injected through a T tube inserted into the bile passages. (Courtesy of Dr. J. Helsin, Toronto, ON, Canada.) B and C. Endoscopic retrograde cholangiography studies of the gallbladder and bile passages are shown. The cystic duct usually lies on the right side of the common hepatic duct and joins it just superior to the superior part of the duodenum. (Courtesy of Dr. G. B. Haber, Assistant Professor of Medicine, University of Toronto, Toronto, ON, Canada.)

Chapter 2: Abdomen

Figure 2.83. Intravenous urogram (pyelogram). The contrast medium was injected intravenously and was concentrated and excreted by the kidneys. This AP projection shows the calices, renal pelves, and ureters outlined by the contrast medium filling their lumina. Note the difference in shape and level of the renal pelves and the constrictions and dilations in the ureter resulting from peristaltic contractions of their smooth muscle walls. The arrows indicate narrowing of the lumen resulting from peristaltic contractions. (Courtesy of Dr. John Campbell, Department of Medical Imaging, Sunnybrook Medical Centre, University of Toronto, Toronto, ON, Canada.)

The radiological anatomy of the kidneys and ureters can be examined by intravenous urography, or pyelography (Fig. 2.83). The kidneys excrete an intravenously injected contrast medium. In retrograde pyelography, the contrast medium is injected into the ureters and ascends to fill the pelves and calices of the kidneys. Ultrasound, CT scans, and MRIs are also used to examine the abdominal viscera (Figs. 2.84, 2.85, 2.86, 2.87, and 2.88). Because MRIs provide better differentiation between soft tissues, its images are more revealing. An image in virtually any plane can be reconstructed after scanning is completed. Abdominal arteriography, radiography after the injection of radiopaque material directly into the bloodstream, detects abnormalities of the abdominal arteries, such as blood clots (Fig. 2.89A). Angiographic studies may also now be performed using MRA (magnetic resonance angiography) (Fig. 2.89B & C). Nuclear scanning is useful for detection of lower GI hemorrhage. A positive nuclear scan may be followed by arteriography.

Clinically Oriented Anatomy, 5th Edition By Keith Moore Figure 2.84. Ultrasound scan of abdomen. A. The orientation drawings demonstrate the placement of the transducer on the anterior abdominal wall. The transverse anatomical section (B) and ultrasound scan (C) of the liver demonstrate the hepatic veins. (Courtesy of Dr. A. M. Arenson, Assistant Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)

Chapter 2: Abdomen

Figure 2.85. Ultrasound scans of abdomen. A. A transverse scan through the celiac trunk is shown. B. A transverse scan through the pancreas is shown. C. A sagittal scan through the aorta is shown. (Courtesy of Dr. A.M. Arenson, Assistant Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.)


Figure 2.86. Transverse MRIs of abdomen. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, ON, Canada.)

Chapter 2: Abdomen

Figure 2.87. MRI studies of abdomen and pelvis. Both coronal (A) sagittal (B) scans are shown. Note that the location of the plane of section B is shown in part A, and vice versa. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, ON, Canada.)


Figure 2.88. CT scans of abdomen at progressively lower levels showing viscera and blood vessels. (Courtesy of Dr. Tom White, Department of Radiology, The Health Sciences Center, University of Tennessee, Memphis, TN.)

Chapter 2: Abdomen

Figure 2.89. Arteriogram and angiograms. A. For this conventional (radiographic) superior mesenteric arteriogram, radiopaque dye was injected into the artery by means of the catheter introduced into the femoral artery and advanced through the iliac arteries and aorta to the opening of the SMA. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, ON, Canada.) B and C. These coronal MR angiograms demonstrate abdominal venous anatomy. Both show the formation of the portal vein from the superior mesenteric vein (SMV) and splenic vein. In part B, the inferior mesenteric vein (IMV) is a tributary of the splenic vein, close to the spleen. In part C, the inferior mesenteric vein enters the junction of the superior mesenteric and splenic veins.


References and Suggested Readings Agur AMR, Dalley AF: Grant's Atlas of Anatomy, 11th ed. Baltimore, Lippincott Williams & Wilkins, 2005. Behrman RE, Kliegman RM, Jenson HB (eds): Nelson Textbook of Pediatrics, 16th ed. Philadelphia, Saunders, 2000. Bickley LS, Szilagyi PG: Bates' Guide to Physical Examination and History Taking, 8th ed. Baltimore, Lippincott Williams & Wilkins, 2003. Cantlie J: On a new arrangement of the right and left lobes of the liver. J Anat Physiol [Lond] 32:iv, 1898. Cheng YF, Huang TL, Chen CL, Chen TY, Huang CC, Ko SF, Yand BY, Lee TY: Variations of the middle and inferior right hepatic vein: Application in hepatectomy. J Clin Ultrasound 25:175, 1997. Cotran RS, Kumar V, Collins T: Robbins Pathological Basis of Disease, 6th ed. Philadelphia, Saunders, 1999. Daseler EH, Anson BJ, Hambley WC, Reimann AF: The cystic artery and constituents of the hepatic pedicle. Surg Gynecol Obstet 85:47, 1947. Ellis H: Clinical Anatomy: A Revision and Applied Anatomy for Clinical Students. 8th ed. Oxford, Blackwell Scientific, 1992. Fruchaud H: Anatomie chirurgicales des hernies de l'aine. Paris, Doin, 1956. [Cited in Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE: Modern Hernia Repair: The Embryological and Anatomical Basis of Surgery. New York, Parthenon, 1996.] Magee DF, Dalley AF: Digestion and the Structure and Function of the Gut [Karger Continuing Education Series, Vol. 8]. Basel, Karger, 1986. Moore KL, Persaud TVN: The Developing Human. Clinically Oriented Embryology, 7th ed. Philadelphia, WB Saunders, 2003. Moore KL, Persaud TVN, Shiota K: Color Atlas of Clinical Embryology, 2nd ed. Philadelphia, Saunders, 2000. Naftel JP, Hardy SGP: Visceral motor pathways. In Haines DE (ed): Fundamental Neuroscience, 2nd ed. New York, Churchill Livingstone, 2002. Rosse C, Gaddum‐Rosse P: Hollinshead's Textbook of Anatomy, 5th ed. Philadelphia, Lippincott‐Raven, 1997. Sabiston DC Jr, Lyerly H (eds): Sabiston Essentials of Surgery, 2nd ed. Philadelphia, Saunders, 1994.

Chapter 2: Abdomen

Skandalakis JE, Skandalakis PN, Skandalakis JL: Surgical Anatomy and Technique. A Pocket Manual. New York, Springer‐Verlag, 1995. Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE: Modern Hernia Repair. The embryology of anatomical basis of surgery. New York, Parthenon, 1996. Soper DF: Upper genital tract infections. In Copeland LJ (ed): Textbook of Gynecology, 2nd ed. Philadelphia, Saunders, 2000. Swartz MH: Textbook of Physical Diagnosis, History and Examination, 4th ed. Philadelphia, Saunders, 2001. Townsend CM, Beauchamp RD, Evers BM, Mattox KL: Sabiston Textbook of Surgery, 16th ed. Philadelphia, Saunders, 2001. Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ (eds): Gray's Anatomy, The Anatomical Basis of Medicine and Surgery, 38th British ed. New York, Churchill Livingstone, 1995.


Chapter 3:Pelvis and Perineum Introduction to the Pelvis and Perineum The term pelvis (L. basin) is used to denote a variety of structures: a region, the pelvic girdle, and the pelvic cavity. In common usage, the pelvis is the part of the trunk inferoposterior to the abdomen and is the area of transition between the trunk and the lower limbs. Anatomically, the pelvis is the space or compartment surrounded by the pelvic girdle (bony pelvis), part of the appendicular skeleton of the lower limb (Fig. 3.1). The pelvis is subdivided into greater and lesser pelves. The greater pelvis affords protection to inferior abdominal viscera similar to the way the inferior thoracic cage protects superior abdominal viscera. The lesser pelvis provides the skeletal framework for both the pelvic cavity and the perineum—compartments of the trunk separated by the musculofascial pelvic diaphragm. Externally, the pelvis is covered or overlapped by the inferior anterolateral abdominal wall anteriorly, the gluteal region of the lower limb posterolaterally, and the perineum inferiorly. The perineum 1 refers both to the area of the surface of the trunk between the thighs and the buttocks, extending from the coccyx to the pubis, and to the shallow compartment lying deep (superior) to this area and inferior to the pelvic diaphragm. The perineum includes the anus and external genitalia: the penis and scrotum of the male and the vulva of the female. Anatomically, “regions” are defined by an area of the surface of the body, so there is no external “pelvic region” per se; although commonly used, it is not a term recognized by Terminologia Anatomica (FICAT, 1998).

The Bottom Line The pelvis is the space enclosed by the pelvic girdle, which is subdivided into the greater pelvis (the inferior part of the abdominal cavity, which receives the protection of the alae of the ilia) and the lesser pelvis (the space inside the bony ring of pelvis inferior to the pelvic brim). The lesser pelvis provides the skeletal framework for both the pelvic cavity and the perineum, which are separated by the musculofascial pelvic diaphragm. The term perineum refers to both the region that includes the anus and external genitalia and to a shallow compartment deep to that area. The inferior anterolateral abdominal wall, gluteal region, and perineum overlap the pelvis.

Pelvic Girdle The pelvic girdle is a basin‐shaped ring of bones that connects the vertebral column to the two femurs. The primary functions of the pelvic girdle are to:  

Bear the weight of the upper body when sitting and standing. Transfer that weight from the axial to the lower appendicular skeleton for standing and walking.

Chapter 3: Pelvis and Perineum

Figure 3.1. Pelvis and perineum. A and B. The pelvis (green) is the space (compartment) within the pelvic girdle, overlapped externally by the abdominal and gluteal (lower limb) regions and the perineum. Thus the pelvis has no external surface area. The greater pelvis (light green) is pelvic by virtue of its bony boundaries, but abdominal in terms of its contents. The lesser pelvis (dark green) provides the bony framework for the pelvic cavity and deep perineum.



Provide attachment for the powerful muscles of locomotion and posture, as well as those of the abdominal wall, withstanding the forces generated by their actions.

Consequently, the pelvic girdle is quite strong and rigid, especially compared to the pectoral (shoulder) girdle. These aspects of the pelvic girdle will be discussed more thoroughly elsewhere (Chapter 2, in relation to the abdominal wall; Chapter 4, in relation to the vertebral column; and Chapter 6, in relation to the lower limb). The secondary functions of the pelvic girdle, discussed here, are to: 

  

Contain and protect the pelvic viscera (inferior parts of the urinary tracts and the internal reproductive organs) especially but also the inferior abdominal viscera (intestines), while permitting passage of their terminal parts (and, in females, a full‐term fetus) via the perineum. Provide support for the abdominopelvic viscera and gravid (pregnant) uterus. Provide attachment for the erectile bodies of the external genitalia. Provide attachment for the muscles and membranes that assist in these functions by forming the pelvic floor and filling gaps that exist in or around it.

Bones and Features of the Pelvic Girdle In the mature individual, the pelvic girdle is formed by three bones (Fig. 3.2A): 



Right and left hip bones (coxal bones; pelvic bones): large, irregularly shaped bones, each of which develops from the fusion of three bones, the ilium, ischium, and pubis. Sacrum: formed by the fusion of five, originally separate, sacral vertebrae.


The internal (medial or pelvic) aspects of the hip bones bound the pelvis, forming its lateral walls; these aspects of the bones are emphasized here. Their external aspects, primarily involved in providing attachment for the lower limb muscles, are discussed in Chapter 5. As they are part of the vertebral column, the sacrum and coccyx are discussed in detail in Chapter 4. In infants and children, the hip bones consist of three separate bones that are united by a triradiate (i.e., radiating in three directions) cartilage at the acetabulum (Fig. 3.2B), the cup‐like depression in the lateral surface of the hip bone, which articulates with the head of the femur. After puberty, the ilium, ischium, and pubis fuse to form the hip bone. The two hip bones are joined anteriorly at the pubic symphysis (L. symphysis pubis) and articulate posteriorly with the sacrum at the sacroiliac joints to form the pelvic girdle. The ilium is the superior, fan‐shaped part of the hip bone (Fig. 3.2B & C). The ala, or wing of the ilium, represents the spread of the fan; and the body of the ilium, the handle of the fan. On its external aspect, the body participates in formation of the acetabulum. The iliac crest, the rim of the fan, has a curve that follows the contour of the ala between the anterior and the posterior superior iliac spines. The anteromedial concave surface of the ala forms the iliac fossa. Posteriorly, the sacropelvic surface of the ilium features an auricular surface and an iliac tuberosity, for synovial and syndesmotic articulation with the sacrum, respectively. The ischium has a body and ramus (L. branch). The body of the ischium helps form the acetabulum and the ramus of the ischium forms part of the obturator foramen. The large posteroinferior protuberance of the ischium is the ischial tuberosity; the small pointed posteromedial projection near the junction of the ramus and body is the ischial spine. The concavity between the ischial spine and the ischial tuberosity is the lesser sciatic notch. The larger concavity, the greater sciatic notch, is superior to the ischial spine and is formed in part by the ilium. The pubis is an angulated bone with a superior pubic ramus, which helps form the acetabulum, and an inferior pubic ramus, which helps form the obturator foramen. A thickening on the anterior part of the body of the pubis is the pubic crest, which ends laterally as a prominent knob or swelling, the pubic tubercle. The lateral part of the superior pubic ramus has an oblique ridge, the pecten pubis (pectineal line of pubis). The pelvis is divided into greater (false) and lesser (true) pelves by the oblique plane of the pelvic inlet (superior pelvic aperture) (Figs. 3.1 and 3.2A). The bony edge (rim) surrounding and defining the pelvic inlet is the pelvic brim, formed by the:  



Promontory and ala of the sacrum (superior surface of its lateral part, adjacent to the body). A right and left linea terminalis (terminal line) together form a continuous oblique ridge consisting of the: o Arcuate line on the inner surface of the ilium. o Pecten pubis (pectineal line) and pubic crest, forming the superior border of the superior pubic ramus and body.


Figure 3.2. Pelvic girdle. A. The pelvic girdle is formed by the two hip bones anteriorly and laterally and the sacrum posteriorly. The sacrum is also part of the vertebral column, in continuity with the lumbar vertebrae superiorly and the coccyx inferiorly. B. When a child's hip bone is in the anatomical position, the anterior superior iliac spine (ASIS) and the anterior aspect of the pubis lie in the same vertical plane. The hip bone at this stage is composed of three bones—ilium, ischium, and pubis—that meet in the cup‐shaped acetabulum. The bones are not fused at this age but are united by a triradiate cartilage along a Y‐shaped line (blue). C. An adult's right hip bone in the anatomical position shows the bones when fused.


The pubic arch is formed by the ischiopubic rami (conjoined inferior rami of the pubis and ischium) of the two sides (Fig. 3.2A & C). These rami meet at the pubic symphysis, their inferior borders defining the subpubic angle. The width of the subpubic angle is determined by the distance between the right and the left ischial tuberosities, which can be measured with the fingers in the vagina during a pelvic examination. The pelvic outlet (inferior pelvic aperture) is bounded by the (Fig. 3.3C):    

Pubic arch anteriorly. Ischial tuberosities laterally. Inferior margin of the sacrotuberous ligament (running between the coccyx and the ischial tuberosity) posterolaterally. Tip of the coccyx posteriorly.

Figure 3.3. Joints and ligaments of pelvis. A. The joints of the adult pelvic girdle include the sacroiliac joints and the pubic symphysis. The lumbosacral and sacrococcygeal are joints of the axial skeleton directly related to the pelvic girdle. B and C. The ligaments of the pelvis are shown.


The boundaries of the pelvic outlet are also the deep boundaries of the perineum. The greater pelvis (false pelvis, pelvis major) is the part of the pelvis (Fig. 3.2A):   

Superior to the pelvic inlet. Bounded by the iliac alae posterolaterally and the anterosuperior aspect of the S1 vertebra posteriorly. Occupied by abdominal viscera (e.g., the ileum and sigmoid colon).

The lesser pelvis (true pelvis, pelvis minor) is the part of the pelvis:    

Between the pelvic inlet and the pelvic outlet. Bounded by the pelvic surfaces of the hip bones, sacrum, and coccyx. That includes the true pelvic cavity and the deep parts of the perineum (perineal compartment), specifically the ischioanal fossae. Of major obstetrical and gynecological significance.

The concave superior surface of the musculofascial pelvic diaphragm forms the floor of the true pelvic cavity, which is thus deepest centrally. The convex inferior surface of the pelvic diaphragm forms the roof of the perineum, which is therefore shallow centrally and deep peripherally. Its lateral parts (ischioanal fossae) extending well up into the lesser pelvis. The terms pelvis, lesser pelvis, and pelvic cavity are commonly used incorrectly, as if they were synonymous terms.

Orientation of the Pelvic Girdle When a person is in the anatomical position, the right and left ASISs and the anterior aspect of the pubic symphysis lie in the same vertical plane (Fig. 3.2B). When a pelvic girdle in this position is viewed anteriorly (Fig. 3.2A; Table 3.1A & B), the tip of the coccyx appears close to the center of the pelvic inlet, and the pubic bones and pubic symphysis constitute more of a weight‐bearing floor than an anterior wall. In the median view (Fig. 3.1A), the sacral promontory is located directly superior to the center of the pelvic outlet (site of the perineal body). Consequently, the curved axis of the pelvis intersects the axis of the abdominal cavity at an oblique angle.


Table 3.1. Comparison of Male and Female Bony Pelves

Bony Pelvis General structure Greater pelvis (pelvis major) Lesser pelvis (pelvis minor) Pelvic inlet (superior pelvic aperture) Pelvic outlet (inferior pelvic aperture) Pubic arch and subpubic angle Obturator foramen Acetabulum Greater sciatic notch

Male (â™‚) Thick and heavy Deep Narrow and deep, tapering Heartshaped, narrow

Female (â™€) Thin and light Shallow Wide and shallow, cylindrical Oval and rounded; wide

Comparatively small

Comparatively large

Narrow ( 80°) Oval Small Almost 90°

The pelvic girdles of males and females differ in several respects (Table 3.1). These sexual differences are related mainly to the heavier build and larger muscles of most men and to the adaptation of the pelvis (particularly the lesser pelvis) in women for parturition (childbearing). The male pelvic girdle is heavier and thicker than the


female girdle and usually has more prominent bone markings. The female pelvic girdle is wider, shallower, and has a larger pelvic inlet and outlet. The subpubic angle is nearly a right angle in females; it is considerably less in males (approximately 60°).

Variations in the Male and Female Pelves Although anatomical differences between male and female pelves are usually clear cut, the pelvis of any person may have some features of the opposite sex. The pelvic types shown in Figure B3.1A and C are most common in males, B and A in white females, B and C in black females, whereas D is uncommon in both sexes. The gynecoid pelvis is the normal female type (Fig. B3.1B); its pelvic inlet typically has a rounded oval shape and a wide transverse diameter. An android (masculine or funnel‐shaped) pelvis in a woman may present hazards to successful vaginal delivery of a fetus (Fig. B3.1A). In forensic medicine (the application of medical and anatomical knowledge for the purposes of law), identification of human skeletal remains usually involves the diagnosis of sex. A prime focus of attention is the pelvic girdle because sexual differences usually are clearly visible. Even fragments of the pelvic girdle are useful in determining sex.

Pelvic Diameters (Conjugates) The size of the lesser pelvis is particularly important in obstetrics because it is the bony canal through which the fetus passes during a vaginal birth. To determine the capacity of the female pelvis for childbearing, the diameters of the lesser pelvis are noted radiographically or manually during a pelvic examination. The minimum anteroposterior (AP) diameter of the lesser pelvis, the true (obstetrical) conjugate from the middle of the sacral promontory to the posterosuperior margin (closest point) of the pubic symphysis (Fig. B3.2A & B), is the narrowest fixed distance through which the baby's head must pass in a vaginal delivery. This distance, however, cannot be measured directly during a pelvic examination because of the presence of the bladder. Consequently, the diagonal conjugate (Fig. B3.2B) is measured by palpating the sacral promontory with the tip of the middle finger, using the other hand to mark the level of the inferior margin of the pubic symphysis on the examining hand (Fig. B3.2C). After the examining hand is withdrawn, the distance between the tip of the index finger (1.5 cm shorter than the middle finger) and the marked level of the pubic symphysis is measured to estimate the true conjugate, which should be 11.0 cm or greater. In all pelvic girdles, the ischial spines extend toward each other, and the interspinous distance between them is normally the narrowest part of the pelvic canal (the passageway through the pelvic inlet, lesser pelvis and pelvic outlet, through which a baby's head must pass at birth; Fig. B3.2B), but it is not a fixed distance (see clinical correlation [blue] box “Relaxation of Pelvic Ligaments and Increased Joint mobility during Pregnancy,” in this chapter). During a pelvic examination, if the ischial tuberosities are far enough apart to permit three fingers to enter the vagina side by side, the subpubic angle is considered sufficiently wide to permit passage of an average fetal head at full term.


Figure B3.1

Figure B3.2


Pelvic Fractures Anteroposterior compression of the pelvis occurs during crush accidents (e.g., when a heavy object falls on the pelvis) (Fig. B3.3A). This type of trauma commonly produces fractures of the pubic rami. When the pelvis is compressed laterally, the acetabula and ilia are squeezed toward each other and may be broken. Fractures of the bony pelvic ring are almost always multiple fractures or a fracture combined with a joint dislocation. To illustrate this, try breaking a pretzel ring at just one point. Some pelvic fractures result from the tearing away of bone by the strong ligaments associated with the sacroiliac joints (these ligaments are shown in Figs 3.3 and 3.4A). Pelvic fractures can result from direct trauma to the pelvic bones, such as occurs during an automobile accident (Fig. B3.3A), or be caused by forces transmitted to these bones from the lower limbs during falls on the feet (Fig. B3.3B). Weak areas of the pelvis, where fractures often occur, are the pubic rami, the acetabula (or the area immediately surrounding them), the region of the sacroiliac joints, and the alae of the ilium. Pelvic fractures may cause injury to pelvic soft tissues, blood vessels, nerves, and organs. Fractures in the pubo‐obturator area are relatively common and are often complicated because of their relationship to the urinary bladder and urethra, which may be ruptured or torn. Falls on the feet or buttocks from a high ladder may drive the head of the femur through the acetabulum into the pelvic cavity, injuring pelvic viscera, nerves, and vessels. In individuals 50% of vaginal deliveries in the United States (Gabbe et al., 2002). It is generally agreed that episiotomy is indicated when descent of the fetus is arrested or protracted, when instrumentation is necessary (e.g., use of obstetrical forceps), or to expedite delivery when there are signs of fetal distress. However, routine prophylactic episiotomy is widely debated. The perineal body is the major structure incised during a median episiotomy (Fig. B3.24A). The rationale of the median incision is that the scar produced as the wound heals will not be greatly different from the fibrous tissue surrounding it. Also, because the incision extends only partially into this fibrous tissue, some physicians believe that the incision is more likely to be self‐limiting, resisting further tearing. However, when further tearing does occur, it is directed toward the anus, and sphincter damage or anovaginal fistulae are potential sequelae. Recent studies indicate median episiotomies are associated with an increased incidence of severe lacerations, associated in turn with an increased incidence of long‐term incontinence and pelvic prolapse.


Figure B3.24 Mediolateral episiotomies are also performed (Fig. B3.24A). These episiotomies do not appear to increase the incidence of severe laceration and are less likely to be associated with damage to the anal sphincters and canal. (Note: the clinical use of the term mediolateral is technically inappropriate here; it actually refers to an incision that is initially a median incision that then turns laterally as it proceeds posteriorly, circumventing the perineal body and directing further tearing away from the anus.)


Figure 3.39. Male and female layers of perineum. The layers of the perineum are shown as being built up from deep (A) to superficial (E) layers. A. The pelvic outlet is almost closed by the pelvic diaphragm (levator ani and coccygeus muscles), forming the floor of the pelvic cavity and, as viewed here, the roof of the perineum. The urethra (and vagina in females) and rectum pass through the urogenital hiatus of the pelvic diaphragm. B and C. The external urethral sphincter and deep transverse perineal muscle span the region of the urogenital hiatus, which is closed inferiorly by the perineal membrane extending between the ischiopubic rami. D and E. Inferior to perineal membrane, the superficial perineal pouch or space contains the erectile bodies and the muscles associated with them.


The Bottom Line The perineum is the diamond‐shaped compartment bounded peripherally by the osseofibrous pelvic outlet and deeply (superiorly) by the pelvic diaphragm. The term is also applied to the surface area overlying this compartment. The urogenital triangle (anteriorly) and anal triangle (posteriorly) that together compose this diamond‐shaped area lie at angles to each other. Their intersecting planes define the transverse line (extending between ischial tuberosities) that is the base of each triangle. Centrally, the UG triangle is perforated by the urethra and, in females, by the vagina; the anal triangle is perforated by the anal canal. The perineal body is a musculofibrous mass between the UG and the anal perforating structures at the center point of the perineum.

Fasciae and Pouches of the Urogenital Triangle Perineal Fasciae 2

The perineal fascia consists of superficial and deep layers. The subcutaneous tissue of the perineum, or superficial perineal fascia, like that of the inferior anterior abdominal wall (see Chapter 2) consists of a superficial fatty layer and a deep membranous layer (Colles fascia) (Fig. 3.40A & B). In females, the fatty layer makes up the substance of the labia majora and mons pubis and is continuous anteriorly and superiorly with the fatty layer of subcutaneous tissue of the abdomen (Camper fascia) (Fig. 3.40A & C). In males, the fatty layer is greatly diminished in the urogenital triangle, being replaced altogether in the penis and scrotum with smooth (dartos) muscle. It is continuous between the penis or scrotum and thighs with the fatty layer of subcutaneous tissue of the abdomen (Fig. 3.40B & E). In both sexes, the fatty layer of subcutaneous tissue of the perineum is continuous posteriorly with the ischioanal fat pad in the anal region (Fig. 3.40D). The membranous layer of subcutaneous tissue of the perineum does not extend into the anal triangle, being attached posteriorly to the posterior margin of the perineal membrane and the perineal body (Fig. 3.40A & B). Laterally it is attached to the fascia lata (deep fascia) of the superiormost medial aspect of the thigh (Fig. 3.40C & E). Anteriorly in the male, the membranous layer of subcutaneous tissue is continuous with the dartos fascia of the penis and scrotum; however, on each side of and anterior to the scrotum, the membranous layer becomes continuous with the membranous layer of subcutaneous tissue of the abdomen (Scarpa fascia) (Fig. 3.40B). In females, the membranous layer passes superior to the fatty layer forming the labia majora and becomes continuous with the membranous layer of subcutaneous tissue of the abdomen (Fig. 3.40A & C). The (deep) perineal fascia (investing or Gallaudet fascia) intimately invests the ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles (Fig. 3.40A & E). It is also attached laterally to the ischiopubic rami. Anteriorly it is fused to the suspensory ligament of the penis (Fig. 3.50) and is continuous with the deep fascia covering the external oblique muscle of the abdomen and the rectus sheath. In females, the perineal fascia is fused with the suspensory ligament of the clitoris and, as in males, with the deep fascia of the abdomen.


The Bottom Line The subcutaneous tissue of the perineum includes a superficial fatty layer and a deeper membranous layer (Colles fascia), which are continuous with corresponding layers of the inferior anterior abdominal wall. In females, the fatty layer is thick within the mons pubis and labia majora, but in males, it is replaced by smooth dartos muscle in the penis and scrotum. The membranous layer is limited to the UG triangle, fusing with the deep fascia at the posterior border (base) of the triangle. In males, this layer extends into the penis and scrotum, where it is closely associated with the loose, mobile skin of those structures.

Superficial Perineal Pouch The superficial perineal pouch (compartment) is a potential space between the membranous layer of subcutaneous tissue and the perineal membrane, bounded laterally by the ischiopubic rami (Figs. 3.39D & E and 3.40). In males, the superficial perineal pouch contains the:    

Root (bulb and crura) of the penis and associated muscles (ischiocavernosus and bulbospongiosus). Proximal (bulbous) part of the spongy urethra. Superficial transverse perineal muscles. Deep perineal branches of the internal pudendal vessels and pudendal nerves.

In females, the superficial perineal pouch contains the:     

Clitoris and associated muscles (ischiocavernosus). Bulbs of the vestibule and surrounding muscle (bulbospongiosus). Greater vestibular glands. Superficial transverse perineal muscles. Related vessels and nerves (deep perineal branches of the internal pudendal vessels and pudendal nerves).

The structures of the superficial perineal pouch will be discussed in greater detail, specific to each sex, under “Male Perineum” and “Female Perineum,” later in this chapter.

Deep Perineal Pouch The deep perineal pouch (space) is bounded inferiorly by the perineal membrane, superiorly by the inferior fascia of the pelvic diaphragm, and laterally by the inferior portion of the obturator fascia (covering the obturator internus muscle) (Fig. 3.40C & E). It includes the fat‐filled anterior recesses of the ischioanal fossa. The superior boundary in the region of the urogenital hiatus is indistinct. In both sexes, the deep perineal pouch contains   

Part of the urethra, centrally. The inferior part of the external urethral sphincter muscle, above the center of the perineal membrane, surrounding the urethra. Anterior extensions of the ischioanal fat pads.


In males, the deep perineal pouch contains the:  

 

Intermediate part of the urethra, the narrowest part of the male urethra. Deep transverse perineal muscles, immediately superior to the perineal membrane (on its superior surface), running transversely along its posterior aspect. Bulbourethral glands, embedded within the deep perineal musculature. Dorsal neurovascular structures of the penis.

In females, the deep perineal pouch contains the: 

Proximal part of the urethra.


Figure 3.40. Fasciae of perineum. A and B. These median sections, viewed from left, demonstrate the fasciae in the female and male. The planes of the sections shown in parts C—E are indicated. C. This coronal section of the female UG triangle is in the plane of the vagina. D. This coronal section of the anal triangle is in the plane of the lower rectal and anal canals. E. This coronal section of the male UG triangle is in the plane of the prostatic urethra.

Chapter 3: Pelvis and Perineum 

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A mass of smooth muscle in the place of deep transverse perineal muscles on the posterior edge of the perineal membrane, associated with the perineal body. Dorsal neurovasculature of the clitoris.

Past and Current Concepts of Deep Perineal Pouch and External Urethral Sphincter Traditionally, a trilaminar, triangular UG diaphragm has been described as making up the deep perineal pouch. Although the classical descriptions appear justified when viewing only the superficial aspect of the structures occupying the deep pouch (Fig. 3.41A), the long‐held concept of a flat, essentially two‐dimensional diaphragm is erroneous. According to this concept, the UG diaphragm consisted of the perineal membrane (inferior fascia of the UG diaphragm) inferiorly and a superior fascia of the UG diaphragm superiorly. The deep pouch was the space between the two fascial membranes, occupied by a flat muscular sheet consisting of a disc‐like sphincter urethra anterior to or within an equally two‐dimensional, transversely oriented deep transverse perineal muscle. In males, the bulbourethral glands were also considered occupants of the pouch. Only the descriptions of the perineal membrane and deep transverse perineal muscles of the male (with embedded glands) appear to be supported by evidence, which includes medical imaging of live subjects (Myers et al., 1998a, 1998b). In the female, the posterior edge of the perineal membrane is typically occupied by a mass of smooth muscle in the place of the deep transverse perineal muscles (Wendell‐Smith, 1995). Immediately superior to the posterior half of the perineal membrane, the flat, sheet‐like, deep transverse perineal muscle, when developed (typically only males), offers dynamic support for the pelvic viscera. As described by Oelrich (1980), however, the urethral sphincter muscle is not a flat, planar structure, and the only “superior fascia” is the intrinsic fascia of the external urethral sphincter muscle. Contemporary views consider the inferior fascia of the pelvic diaphragm to be the superior boundary of the deep pouch (Fig. 3.40C—E). In both views, the strong perineal membrane is the inferior boundary (floor) of the deep pouch, separating it from the superficial pouch. The perineal membrane is indeed, with the perineal body, the final passive support of the pelvic viscera. The external urethral sphincter is more like a tube or trough than like a disc. In the male only the inferior part of the muscle forms a circular investment (a true sphincter) for the intermediate part of the urethra inferior to the prostate (Fig. 3.41B). Its larger, trough‐like part extends vertically to the neck of the bladder as part of the isthmus of the prostate, displacing glandular tissue and investing the prostatic urethra anteriorly and anterolaterally only. Apparently, the muscular primordium is established around the whole length of the urethra before development of the prostate. As the prostate develops from urethral glands, the posterior and posterolateral muscle atrophies or is displaced by the prostate. Whether this part of the muscle compresses or dilates the prostatic urethra is a matter of some controversy. In the female, the external urethral sphincter is more properly a “urogenital sphincter,” according to Oelrich (1983). Here, too, he describes a part forming a true anular sphincter around the urethra (Fig. 3.41C), with several additional parts


extending from it: a superior part, extending to the neck of the bladder; a subdivision described as extending inferolaterally to the ischial ramus on each side (the compressor urethrae muscle); and yet another band‐like part, which encircles both the vagina and the urethra (urethrovaginal sphincter). In both the male and female, the musculature described is oriented perpendicular to the perineal membrane, rather than lying in a plane parallel to it. Other authors substantiate most of Oelrich's description but dispute the encircling of the urethra in the female, claiming that the muscle is not capable of sphincteric action. Furthermore, they assert that sectioning the perineal nerve supplying the “sphincter” does not result in incontinence, but this may be a consequence of innervation from multiple sources.

Rupture of the Urethra in Males and Extravasation of Urine Fractures of the pelvic girdle, especially those resulting from separation of the pubic symphysis and puboprostatic ligaments, often cause a rupture of the intermediate part of the urethra. Rupture of this part of the urethra results in the extravasation of urine and blood into the deep perineal pouch (Fig. B3.25A); the fluid may pass superiorly through the urogenital hiatus and distribute extraperitoneally around the prostate and bladder. The common site of rupture of the spongy urethra and extravasation (escape) of urine is in the bulb of the penis (Fig. B3.25B). This injury usually results from a forceful blow to the perineum (straddle injury), such as falling on a metal beam or, less commonly, from the incorrect passage (false passage) of a transurethral catheter or device that fails to negotiate the angle of the urethra in the bulb of the penis. Rupture of the corpus spongiosum and spongy urethra results in urine passing from it (extravasating) into the superficial perineal space. The attachments of the perineal fascia determine the direction of flow of the extravasated urine. Urine may pass into the loose connective tissue in the scrotum, around the penis, and superiorly, deep to the membranous layer of subcutaneous connective tissue of the inferior anterior abdominal wall. The urine cannot pass far into the thighs because the membranous layer of superficial perineal fascia blends with the fascia lata, enveloping the thigh muscles, just distal to the inguinal ligament. In addition, urine cannot pass posteriorly into the anal triangle because the superficial and deep layers of perineal fascia are continuous with each other around the superficial perineal muscles and with the posterior edge of the perineal membrane between them. Rupture of a blood vessel into the superficial perineal pouch resulting from trauma would result in a similar containment of blood in the superficial perineal pouch.


Figure B3.25

The Bottom Line The planar perineal membrane divides the urogenital triangle of the perineum into superficial and deep perineal pouches. The superficial perineal pouch is between the membranous layer of subcutaneous tissue of the perineum and the perineal membrane and is bounded laterally by the ischiopubic rami. The deep perineal pouch is between the perineal membrane and the inferior fascia of the pelvic diaphragm and is bounded laterally by the obturator fascia. The superficial pouch contains the erectile bodies of the external genitalia and associated muscles, the superficial transverse perineal muscle, deep perineal nerves and vessels, and in females the greater vestibular glands. The deep pouch includes the fat‐filled anterior recesses of the ischioanal fossae (laterally), the deep perineal muscle and inferiormost part of the external urethral sphincter, the part of the urethra traversing the perineal membrane and inferiormost external urethral sphincter (the intermediate urethra of males), the dorsal nerves of the penis/clitoris, and in males the bulbourethral glands.

Features of the Anal Triangle Ischioanal Fossae The ischioanal fossae (formerly called ischiorectal fossae) on each side of the anal canal are large fascia‐lined, wedge‐shaped spaces between the skin of the anal region and the pelvic diaphragm (Figs. 3.40D, 3.42A, and 3.43). The apex of each fossa lies superiorly where the levator ani muscle arises from the obturator fascia. The ischioanal fossae, wide inferiorly and narrow superiorly, are filled with fat and loose connective tissue. The two ischioanal fossae communicate by means of the deep postanal space over the anococcygeal ligament (body), a fibrous mass located between the anal canal and the tip of the coccyx (Figs. 3.40A & B and 3.42B). Each ischioanal fossa is bounded

Clinically Oriented Anatomy, 5th Edition By Keith Moore  

 

Laterally by the ischium and overlapping inferior part of the obturator internus, covered with obturator fascia. Medially by the external anal sphincter, with a sloping superior medial wall or roof formed by the levator ani as it descends to blend with the sphincter; both structures surround the anal canal. Posteriorly by the sacrotuberous ligament and gluteus maximus. Anteriorly by the bodies of the pubic bones, inferior to the origin of the puborectalis. These parts of the fossae, extending into the UG triangle superior to the perineal membrane (and musculature on its superior surface), are known as the anterior recesses of the ischioanal fossae.


Figure 3.41. Deep perineal pouch and male and female external urethral sphincters. A. The deep perineal pouch is seen through (left side) and after removal of the perineal membrane (right side). B. The trough‐like fibers of the male external urethral sphincter ascend to neck of bladder as part of isthmus of prostate. C. The female urethral sphincter is shown.


Figure 3.42. Pelvic diaphragm and ischioanal fossae. A. Coronal section of the pelvis in the plane of the rectum, anal canal, and ischioanal fossae. B. Inferior view of pelvic diaphragm in situ. Left sacrospinous ligament has been removed.

Each ischioanal fossa is filled with a fat body of the ischioanal fossa. These fat bodies support the anal canal but they are readily displaced to permit descent and expansion of the anal canal during the passage of feces. The fat bodies are traversed by tough, fibrous bands, as well as by several neurovascular structures, including the inferior anal/rectal vessels and nerves and two other cutaneous nerves, the perforating branch of S2 and S3 and the perineal branch of S4 nerve.

Pudendal Canal and Its Neurovascular Bundle The pudendal canal (Alcock canal) is an essentially horizontal passageway within the obturator fascia that covers the medial aspect of the obturator internus and lines the lateral wall of the ischioanal fossa (Figs. 3.42A and 3.43). The internal pudendal artery and vein, the pudendal nerve, and the nerve to the obturator internus enter this canal at the lesser sciatic notch, inferior to the ischial spine. The internal pudendal vessels and the pudendal nerve supply and drain blood from and innervate, respectively, most of the perineum. As the artery and nerve enter the canal, they give rise to the inferior rectal artery and nerve, which pass medially to supply the external anal sphincter and the perianal skin (Figs. 3.43 and 3.44; Table 3.8). Toward the distal (anterior) end of the pudendal canal, the artery and nerve both bifurcate, giving rise to the perineal nerve and artery, which are distributed mostly to the superficial pouch (inferior to the perineal membrane), and to the dorsal artery and nerve of the penis or clitoris, which run in the deep pouch (superior to the membrane). When the latter structures reach the dorsum of the penis or clitoris, the nerves run distally on the lateral side of the continuation of the internal pudendal artery as they both proceed to the glans.


The perineal nerve has two branches: the superficial perineal nerves give rise to posterior scrotal or labial (cutaneous) branches, and the deep perineal nerve supplies the muscles of the deep and superficial perineal pouches, the skin of the vestibule, and the mucosa of the inferiormost part of the vagina. The inferior rectal nerve communicates with the posterior scrotal or labial and perineal nerves. The dorsal nerve of the penis or clitoris is the primary sensory nerve serving the male or female organ, especially the sensitive glans at the distal end. Figure 3.43. Rectum and anal canal, levator ani, and ischioanal fossa. The left posterolateral third of the rectum and anal canal have been removed to demonstrate the luminal features. The pudendal canal, the space within the obturator fascia covering the medial surface of the obturator internus and lining the lateral wall of the ischioanal fossa, transmits the pudendal vessels and nerves.

Starvation and Rectal Prolapse The fat bodies of the ischioanal fossae, along with the buccal fat pads (see Chapter 7), are among the last reserves of fatty tissue to disappear with starvation. In the absence of the support provided by the ischioanal fat, rectal prolapse is relatively common.

The Bottom Line The ischioanal fossae are fascia‐lined, wedge‐shaped spaces occupied by ischioanal fat bodies. The fat bodies provide supportive packing that can be compressed or pushed aside to permit the temporary descent and expansion of the anal canal or vagina for passage of feces or a fetus. The fat bodies are traversed by inferior anal/rectal neurovasculature. The pudendal canal is an important passageway in the lateral wall of the fossa, between layers of the obturator fascia, for neurovasculature passing to and from the UG triangle.


Figure 3.44. Distribution of pudendal nerve. The five regions traversed by the nerve are shown. The pudendal nerve supplies the skin, organs, and muscles of the perineum; therefore, it is concerned with micturition, defecation, erection, ejaculation, and, in the female, parturition. Although the pudendal nerve is shown here in the male, its distribution is similar in the female because the parts of the female perineum are homologs of those in the male.

Anal Canal The anal canal is the terminal part of the large intestine, and of the entire alimentary canal. It extends from the superior aspect of the pelvic diaphragm to the anus (Figs. 3.42B and 3.43). The canal (2.5—3.5 cm long) begins where the rectal ampulla narrows at the level of the U‐shaped sling formed by the puborectalis muscle (Fig. 3.7). The canal ends at the anus, the external outlet of the alimentary tract. The anal canal, surrounded by internal and external anal sphincters, descends posteroinferiorly between the anococcygeal ligament and the perineal body. The canal is collapsed, except during passage of feces. Both sphincters must relax before defecation can occur. The internal anal sphincter (Figs. 3.42A and 3.43) is an involuntary sphincter surrounding the superior two thirds of the anal canal. It is a thickening of the circular muscle layer. Its contraction (tonus) is stimulated and maintained by sympathetic fibers from the superior rectal (periarterial) and hypogastric plexuses; its contraction is inhibited by parasympathetic fiber stimulation, both intrinsically in relation to peristalsis and extrinsically by fibers passing through the pelvic splanchnic nerves. This sphincter is tonically contracted most of the time to prevent leakage of fluid or flatus; however, it relaxes (is inhibited) temporarily in response to distension of the rectal ampulla by feces or gas, requiring voluntary contraction of the puborectalis and external anal sphincter if defecation or flatulence is not to occur. The ampulla relaxes after initial distension (when peristalsis subsides) and tonus returns until the next peristalsis or until a threshold level of distension occurs, at which point inhibition of the sphincter is continuous until distension is relieved.


The external anal sphincter is a large voluntary sphincter that forms a broad band on each side of the inferior two thirds of the anal canal (Figs. 3.39E, 3.42, and 3.43). This sphincter is attached anteriorly to the perineal body and posteriorly to the coccyx via the anococcygeal ligament (body); it blends superiorly with the puborectalis muscle. For descriptive purposes, it is described as having subcutaneous, superficial, and deep parts; these are zones rather than muscle bellies and are often indistinct. The external anal sphincter is supplied mainly by S4 through the inferior rectal nerve (Fig. 3.44), although its deep part also receives fibers from the nerve to the levator ani, in common with the puborectalis, with which it contracts in unison to maintain continence when the internal sphincter is relaxed (except during defecation). Table 3.8. Arteries of the Perineum

Artery Internal pudendal

Origin Course Anterior Leaves pelvis through greater division of sciatic foramen; hooks around internal iliac ischial spine to enter perineum artery via lesser sciatic foramen; immediately enters pudendal canal Inferior rectal Internal Arises at entrance to pudendal pudendal canal; traverses ischioanal fossa artery to anal canal Perineal Terminal Arises within pudendal canal; branch of passes to superficial pouch perineal (space) on exit artery Posterior scrotal Terminal Runs in superficial fascia of or labial branch of posterior scrotum or labia majora perineal artery Artery of bulb of Terminal Pierces perineal membrane to penis or branch reach bulb of penis or vestibule vestibule

Distribution in Perineum Primary artery of perineum and external genital organs

Anal canal inferior to pectinate line; anal sphincters; perianal skin Supplies superficial perineal muscles and scrotum of male/vestibule of female Skin of scrotum or labia majora and minora

Supplies bulb of penis (including bulbar urethra) and bulbourethral gland (male) or bulb of vestibule and greater vestibular gland (female)

Clinically Oriented Anatomy, 5th Edition By Keith Moore Deep artery of Terminal penis or clitoris branch

Dorsal artery of penis or clitoris

External Femoral pudendal, artery superficial, and deep branches

Pierces perineal membrane to enter crura of corpora cavernosa of penis or clitoris; branches run proximally and distally Passes to deep pouch; pierces perineal membrane and traverses suspensory ligament of penis or clitoris to run along dorsum of penis or clitoris to glans Pass medially from thigh to reach anterior aspect of the urogenital triangle of perineum

Supplies most erectile tissue of corpora cavernosa of penis or clitoris via helicine arteries Deep perineal pouch; skin of penis; fascia of penis or clitoris; distal corpus spongiosum of penis, including spongy urethra; glans of penis or clitoris Anterior aspect of scrotum and skin at root of penis of male; mons pubis and anterior aspect of labia of female

Internally, the superior half of the mucous membrane of the anal canal is characterized by a series of longitudinal ridges called anal columns (Fig. 3.43). These columns contain the terminal branches of the superior rectal artery and vein. The anorectal junction, indicated by the superior ends of the anal columns, is where the rectum joins the anal canal. At this point, the wide rectal ampulla abruptly narrows as it traverses the pelvic diaphragm. The inferior ends of the anal columns are joined by anal valves. Superior to the valves are small recesses called anal sinuses. When compressed by feces, the anal sinuses exude mucus, which aids in evacuation of feces from the anal canal. The inferior comb‐shaped limit of the anal valves forms an irregular line (the pectinate line), which indicates the junction of the superior part of the anal canal (visceral; derived from the embryonic hindgut) and the inferior part (somatic; derived from the embryonic proctodeum). The anal canal superior to the pectinate line differs from the part inferior to the pectinate line in its arterial supply, innervation, and venous and lymphatic drainage (Fig. 3.45). These differences result from the different embryological origins of the superior and inferior parts of the anal canal (Moore and Persaud, 2003). Arterial Supply of the Anal Canal The superior rectal artery supplies the anal canal superior to the pectinate line (Figs. 3.34A and 3.45). The two inferior rectal arteries supply the inferior part of the anal canal as well as the surrounding muscles and perianal skin. The middle rectal arteries assist with the blood supply to the anal canal by forming anastomoses with the superior and inferior rectal arteries. Venous and Lymphatic Drainage of the Anal Canal The internal rectal venous plexus drains in both directions from the level of the pectinate line. Superior to the pectinate line, the internal rectal plexus drains chiefly into the superior rectal vein (a tributary of the inferior mesenteric vein) and the portal system (Figs. 3.34B and 3.45). Inferior to the pectinate line, the internal rectal plexus drains into the inferior rectal veins (tributaries of the caval venous system) around the margin of the external anal sphincter. The middle rectal veins (tributaries of the internal iliac veins) mainly drain the muscularis externa of the ampulla and form anastomoses with the superior and inferior rectal veins. In addition to the abundant venous anastomoses, the rectal plexuses receive multiple arteriovenous anastomoses (AVAs) from the superior and middle rectal arteries.


The normal submucosa of the anorectal junction is markedly thickened and in section has the appearance of cavernous (erectile) tissue owing to the presence of the sacculated veins of the internal rectal venous plexus. The vascular submucosa is especially thickened in the left lateral, right anterolateral, and right posterolateral positions, forming “anal cushions” (also referred to as threshold pads, corpora cavernosa recti, and anorectal cavernous bodies) at the point of closure of the anal canal. Because these cushions contain plexuses of saccular veins capable of directly receiving arterial blood via multiple AVAs, they are variably pliable and turgid and form a sort of flutter valve that contributes to the normally water‐ and gas‐tight closure of the anal canal. Superior to the pectinate line, the lymphatic vessels drain deeply into the internal iliac lymph nodes and through them into the common iliac and lumbar lymph nodes (Figs. 3.35 and 3.47). Inferior to the pectinate line, the lymphatic vessels drain superficially into the superficial inguinal lymph nodes, as does most of the perineum (Table 3.6).

Figure 3.45. Changes occurring at pectinate line. Vessels and nerves superior to the pectinate line are visceral; those inferior to the pectinate line are parietal or somatic. This orientation reflects the embryological development of the anorectum.


Figure 3.46 Male urethra and associated structures. The urethra has four parts: the vesicular part (in the bladder neck), the prostatic urethra, the intermediate part (membranous urethra), and the spongy (cavernous) urethra. The ducts of the bulbourethral glands open into the proximal part of the spongy urethra. The urethra is not uniform in its caliber: the external urethral orifice and intermediate part are narrowest. Attempting to approach this “straight‐line” position as much as possible facilitates passage of a catheter or other transurethral device.

Innervation of the Anal Canal The nerve supply to the anal canal superior to the pectinate line is visceral innervation from the inferior hypogastric plexus, involving sympathetic, parasympathetic, and visceral afferent fibers (Figs. 3.36 and 3.45). Sympathetic fibers maintain the tonus of the internal anal sphincter. Parasympathetic fibers inhibit the tonus of the internal sphincter and evoke peristaltic contraction for defecation. The superior part of the anal canal, like the rectum superior to it, is inferior to the pelvic pain line; all visceral afferents travel with the parasympathetic fibers to spinal sensory ganglia S2—S4. Superior to the pectinate line, the anal canal is sensitive only to stretching, which evokes sensations at both the conscious and the unconscious (reflex) levels. For example, distension of the rectal ampulla inhibits (relaxes) the tonus of the internal sphincter. The nerve supply of the anal canal inferior to the pectinate line is somatic innervation derived from the inferior anal (rectal) nerves, branches of the pudendal nerve. Therefore, this part of the anal canal is sensitive to pain, touch, and temperature. Somatic efferent fibers stimulate contraction of the voluntary external anal sphincter. The Pectinate Line—A Clinically Important Landmark The pectinate line (also called the dentate or mucocutaneous line by some clinicians) is a particularly important landmark because it is visible and approximates the level of important anatomical changes related to the transition from visceral to parietal (Fig. 3.45), affecting such things as the types of tumors that occur, and the direction in which they metastasize.


Anal Fissures and Perianal Abscesses The ischioanal fossae are occasionally the sites of infection, which may result in the formation of ischioanal abscesses (Fig. B3.26A). These collections of pus are quite painful. Infections may reach the ischioanal fossae in several ways:    

After cryptitis (inflammation of the anal sinuses). Extension from a pelvirectal abscess. After a tear in the anal mucous membrane. From a penetrating wound in the anal region.

Diagnostic signs of an ischioanal abscess are fullness and tenderness between the anus and the ischial tuberosity. A perianal abscess may rupture spontaneously, opening into the anal canal, rectum, or perianal skin. Because the ischioanal fossae communicate posteriorly through the deep postnatal space, an abscess in one fossa may spread to the other one and form a semicircular “horseshoe‐shaped” abscess around the posterior aspect of the anal canal. In chronically constipated persons, the anal valves and mucosa may be torn by hard feces. An anal fissure (slit‐like lesion) is usually located in the posterior midline, inferior to the anal valves. It is painful because this region is supplied by sensory fibers of the inferior rectal nerves. Perianal abscesses may follow infection of anal fissures, and the infection may spread to the ischioanal fossae and form ischioanal abscesses or spread into the pelvis and form pelvirectal abscesses. An anal fistula may result from the spread of an anal infection and cryptitis. One end of this abnormal canal (fistula) opens into the anal canal and the other end opens into an abscess in the ischioanal fossa or into the perianal skin.

Hemorrhoids Internal hemorrhoids (piles) are prolapses of rectal mucosa (more specifically, of the so‐called rectal cushions) containing the normally dilated veins of the internal rectal venous plexus (Fig. B3.26B). Internal hemorrhoids are thought to result from a breakdown of the muscularis mucosae, a smooth muscle layer deep to the mucosa. They occur quite predictably in the left lateral, right anterolateral, and right posterolateral positions (positions of anal cushions). Internal hemorrhoids that prolapse through the anal canal are often compressed by the contracted sphincters, impeding blood flow. As a result, they tend to strangulate and ulcerate. Because of the presence of abundant arteriovenous anastomoses, bleeding from internal hemorrhoids is characteristically bright red. Although all forms of internal hemorrhoids (including normal anal cushions misinterpreted as abnormalities) were once treated aggressively, current practice is to treat only prolapsed, ulcerated internal hemorrhoids. External hemorrhoids are thromboses (blood clots) in the veins of the external rectal venous plexus and are covered by skin. Predisposing factors for hemorrhoids include pregnancy, chronic constipation and prolonged toilet sitting and straining, and any disorder that impedes venous return, including increased intra‐abdominal pressure. The anastomoses between the superior, middle, and inferior rectal veins form clinically important communications between the portal and systemic venous systems (see Fig. 2.59). The superior rectal vein drains into the inferior mesenteric vein, whereas the middle and inferior rectal veins drain through the systemic system into


the inferior vena cava. Any abnormal increase in pressure in the valveless portal system or veins of the trunk may cause enlargement of the superior rectal veins, resulting in an increase in blood flow or stasis in the internal rectal venous plexus. In the portal hypertension that occurs in relation to hepatic cirrhosis, the portocaval anastomosis between the superior and the middle and inferior rectal veins, along with portocaval anastomoses elsewhere, may become varicose. Those in the esophagus are especially prone to rupture. It is important to note that the veins of the rectal plexuses normally appear varicose (dilated and tortuous), even in newborns, and that internal hemorrhoids occur most commonly in the absence of portal hypertension. Figure B3.26

Regarding pain from and the treatment of hemorrhoids, it is important to note that the anal canal superior to the pectinate line is visceral; thus it is innervated by visceral afferent pain fibers, so that an incision or needle insertion in this region is painless. Internal hemorrhoids are not painful and can be treated without anesthesia. However, inferior to the pectinate line, the anal canal is somatic, supplied by the inferior anal (rectal) nerves containing somatic sensory fibers. Therefore, it is sensitive to painful stimuli (e.g., to the prick of a hypodermic needle). External hemorrhoids can be painful but often resolve in a few days. Anorectal Incontinence Stretching of the pudendal nerve(s) during a traumatic childbirth can result in pudendal nerve damage and anorectal incontinence.


The Bottom Line The anal canal is the terminal part of both the large intestine and the alimentary tract, the anus being the external outlet. Closure (and thus fecal continence) is maintained by the coordinated action of the involuntary internal and voluntary external anal sphincters. The sympathetically stimulated tonus of the internal sphincter maintains closure, except during filling of the rectal ampulla and when inhibited during a parasympathetically stimulated peristaltic contraction of the rectum. During these moments, closure is maintained (unless defecation is permitted) by voluntary contraction of the puborectalis and external anal sphincter. Internally, the pectinate line demarcates the transition from visceral to somatic neurovascular supply and drainage. The canal is surrounded by superficial and deep venous plexuses, the veins of which normally have a varicose appearance. Thromboses in the superficial plexus, and mucosal prolapse, including portions of the deep plexus, constitute painful external and insensitive internal hemorrhoids, respectively.

Male Perineum The male perineum includes the external genitalia, perineal muscles, and anal canal. The male external genitalia include the urethra, scrotum, and penis. Distal Male Urethra The male urethra is subdivided into four parts: intramural (preprostatic), prostatic, intermediate, and spongy. The intramural and prostatic parts are described with the pelvis (earlier in this chapter). Details concerning all four parts of the male urethra are provided and compared in Table 3.7. The intermediate (membranous) part of the urethra begins at the apex of the prostate and traverses the deep perineal pouch, surrounded by the external urethral sphincter. It then penetrates the perineal membrane, ending as the urethra enters the bulb of the penis (Fig. 3.46). Posterolateral to this part of the urethra are the small bulbourethral glands and their slender ducts, which open into the proximal part of the spongy urethra. The spongy urethra begins at the distal end of the intermediate part of the urethra and ends at the external urethral orifice, which is slightly narrower than any of the parts of the urethra. The lumen of the spongy urethra is approximately 5 mm in diameter; however, it is expanded in the bulb of the penis to form the intrabulbar fossa and in the glans of the penis to form the navicular fossa. On each side, the slender ducts of the bulbourethral glands open into the proximal part of the spongy urethra; the orifices of these ducts are extremely small. There are also many minute openings of the ducts of mucus‐secreting urethral glands (LittrÃ© glands) into the spongy urethra. Arterial Supply of the Distal Male Urethra The arterial supply of the intermediate and spongy parts of the urethra is from branches of the dorsal artery of the penis (Fig. 3.39C; Table 3.8). Venous and Lymphatic Drainage of the Distal Male Urethra Veins accompany the arteries and have similar names. Lymphatic vessels from the intermediate part of the urethra drain mainly into the internal iliac lymph nodes (Fig.


3.47; Table 3.6); whereas most vessels from the spongy urethra pass to the deep inguinal lymph nodes, but some lymph passes to the external iliac nodes. Innervation of the Distal Male Urethra The innervation of the intermediate part of the urethra is the same as that of the prostatic part: autonomic (efferent) innervation via the prostatic nerve plexus, arising from the inferior hypogastric plexus. The sympathetic innervation is from the lumbar spinal cord levels via the lumbar splanchnic nerves, and the parasympathetic innervation is from the sacral levels via the pelvic splanchnic nerves. The visceral afferent fibers follow the parasympathetic fibers retrogradely to sacral spinal sensory ganglia. The dorsal nerve of the penis, a branch of the pudendal nerve, provides somatic innervation of the spongy part of the urethra (Fig. 3.44). Figure 3.47. Lymphatic drainage of penis, spongy urethra, and scrotum. The arrows indicate the direction of lymph flow to the lymph nodes.

Urethral Catheterization Urethral catheterization is done to remove urine from a person who is unable to micturate. It is also performed to irrigate the bladder and to obtain an uncontaminated sample of urine. When inserting catheters and urethral sounds (slightly conical instruments for exploring and dilating a constricted urethra) the curves of the male urethra must be considered. Just distal to the perineal membrane, the spongy urethra is well covered inferiorly and posteriorly by erectile tissue of the bulb of the penis; however, a short segment of the intermediate part of the urethra is unprotected (Fig. B3.27). Because the urethral wall is thin and because of the angle that must be negotiated to enter the intermediate part of the spongy urethra, it is vulnerable to rupture during the insertion of urethral catheters and sounds. The intermediate part, the least distensible part, runs inferoanteriorly as it passes through the external urethral sphincter. Proximally, the prostatic part takes a slight curve that is concave anteriorly as it traverses the prostate.


Figure B3.27 Urethral stricture may result from external trauma of the penis or infection of the urethra. Urethral sounds are used to dilate the constricted urethra in such cases. The spongy urethra will expand enough to permit passage of an instrument approximately 8 mm in diameter. The external urethral orifice is the narrowest and least distensible part of the urethra; hence, an instrument that passes through this opening normally passes through all other parts of the urethra. The Bottom Line The intermediate urethra is the shortest and narrowest part of the male urethra, the limit of its distension normally being the same as that of the external urethral orifice. It is encircled by voluntary muscle of the inferior part of the external urethral sphincter before perforating the perineal membrane. Immediately inferior to the membrane, the urethra enters the corpus spongiosum and becomes the spongy urethra, the longest part of the male urethra. The spongy urethra has expansions at each end, the intrabulbar and navicular fossae. The intermediate and spongy parts are supplied and drained by the same dorsal (blood) vessels of the penis but differ in terms of innervation and lymphatic drainage, that for the intermediate part following visceral paths and that for the spongy part follows somatic paths.

Scrotum The scrotum is a cutaneous fibromuscular sac for the testes and associated structures. It is situated posteroinferior to the penis and inferior to the pubic symphysis. The bilateral embryonic formation of the scrotum is indicated by the midline scrotal raphe (Fig. 3.48), which is continuous on the ventral surface of the penis with the penile raphe and posteriorly along the median line of the perineum with the perineal raphe. Internally, deep to the scrotal raphe, the scrotum is divided into two compartments, one for each testis, by a prolongation of the dartos fascia,


the septum of the scrotum. The testes and epididymides and their coverings are described with the abdomen (see Chapter 2). Arterial Supply of the Scrotum Anterior scrotal arteries, terminal branches of the external pudendal arteries (from the femoral artery), supply the anterior aspect of the scrotum; posterior scrotal arteries, terminal branches of the superficial perineal branches of the internal pudendal arteries, supply the posterior aspect (Table 3.8). The scrotum also receives branches from the cremasteric arteries (branches of the inferior epigastric arteries). Venous and Lymphatic Drainage of the Scrotum The scrotal veins accompany the arteries, sharing the same names but draining primarily to the external pudendal veins. Lymphatic vessels from the scrotum carry lymph to the superficial inguinal lymph nodes (Fig. 3.47; Table 3.6). Innervation of the Scrotum The anterior aspect of the scrotum is supplied by derivatives of the lumbar plexus: anterior scrotal nerves, derived from the ilioinguinal nerve, and the genital branch of the genitofemoral nerve. The posterior aspect of the scrotum is supplied by derivatives of the sacral plexus: posterior scrotal nerves, branches of the superficial perineal branches of the pudendal nerve, and the perineal branch of the posterior femoral cutaneous nerve (Figs. 3.44 and 3.49A). Sympathetic fibers conveyed by these nerves assist in the thermoregulation of the testes (see Chapter 2), stimulating contraction of the smooth dartos muscle in response to cold or stimulating the scrotal sweat glands while inhibiting contraction of the dartos muscle in response to excessive warmth. Distension of the Scrotum The scrotum is easily distended. In persons with large indirect inguinal hernias, for example (see Chapter 2), the intestine may enter the scrotum, making it as large as a soccer ball. Similarly, inflammation of the testes (orchitis), associated with mumps, bleeding in the subcutaneous tissue, or chronic lymphatic obstruction (as occurs in the parasitic disease elephantiasis), may produce an enlarged scrotum. Palpation of the Testes The soft, pliable skin of the scrotum makes it easy to palpate the testes and the structures related to them (e.g., the epididymis and ductus deferens). The left testis commonly lies at a more inferior level than does the right one. The Bottom Line The scrotum is a dynamic, fibromuscular cutaneous sac for the testes and epididymides. Its internal subdivision by a septum of dartos fascia is demarcated externally by a median scrotal raphe. The anterior aspect of the scrotum is served by anterior scrotal blood vessels and nerves, continuations of external pudendal blood vessels and branches of the lumbar nerve plexus; the posterior aspect of the scrotum is served by posterior scrotal blood vessels and nerves, continuations of internal pudendal blood vessels and branches of the sacral nerve plexus. Sympathetic innervation of smooth dartos muscle and sweat glands assists thermoregulation of the testes.


Penis The penis is the male copulatory organ and, by conveying the urethra, provides the common outlet for urine and semen (Figs. 3.46, 3.48, and 3.49). The penis consists of a root, body, and glans. It is composed of three cylindrical bodies of erectile cavernous tissue: the paired corpora cavernosa dorsally and single corpus spongiosum ventrally. (Note that in the anatomical position, the penis is erect; when the penis is flaccid, its dorsum is directed anteriorly.) Each cavernous body has an outer fibrous covering or capsule, the tunica albuginea (Fig. 3.48C). Superficial to the outer covering is the deep fascia of the penis (Buck fascia), the continuation of the deep perineal fascia that forms a strong membranous covering for the corpora cavernosa and corpus spongiosum, binding them together (Fig. 3.48C & D). The corpus spongiosum contains the spongy urethra. The corpora cavernosa are fused with each other in the median plane, except posteriorly where they separate to form the crura of the penis (Figs. 3.47 and 3.50). Internally, the cavernous tissue of the corpora is separated (usually incompletely) by the septum penis (Fig. 3.48C). Figure 3.48. Penis and s c r o t u m . A . T h e u r e t h ra l s u r f a ce o f t h e c i r c u m c i s e d p e n is i s s h o wn . T h e s p o n g y urethra is deep to the cutaneous penile raphe. T h e s c r o t u m i s d i v i d e d i n to right and left halves by the cutaneous scrotal raphe, which is continuous with t h e p e n i l e a n d p e r i n e a l raphes. B. The dorsum of the circumcised penis and t h e a n t e r i o r s u r f a ce o f t h e scrotum are shown. The p e n is c o m p r i s e s a r o o t , body, and glans. C. The p e n is contains t h re e erectile masses: tw o corpora cavernosa and a corpus spongiosum (containing the spongy urethra). D. The skin of t h e p e n i s e x t e n d s d i s t a l ly as the p r e p u ce , overlapping the neck and corona of the glans. E. An uncircumcised penis.

The root of the penis (L. radix penis), the attached part, consists of the crura, bulb, and ischiocavernosus and bulbospongiosus muscles (Fig. 3.46). The root is located in the superficial perineal pouch, between the perineal membrane superiorly and the deep perineal fascia inferiorly. The crura and bulb of the penis contain masses of erectile tissue. Each crus is attached to the inferior part of the internal surface of the corresponding ischial ramus (Fig. 3.39D), anterior to the ischial tuberosity. The


enlarged posterior part of the bulb of the penis is penetrated superiorly by the urethra, continuing from its intermediate part (Fig. 3.49B).

Figure 3.49. Male perineum and structure of penis. A. The anal canal is surrounded by the external anal sphincter, with an ischioanal fossa on each side. The inferior anal (rectal) nerve branches from the pudendal nerve at the entrance to the pudendal canal and, with the perineal branch of S4, supplies the external anal sphincter. B. The corpus spongiosum has been separated from the corpora cavernosa. The natural flexures of the penis are preserved. The glans penis fits like a cap over the blunt ends of the corpora cavernosa.

The body of the penis is the free pendulous part that is suspended from the pubic symphysis (Figs. 3.46 and 3.48B). Except for a few fibers of the bulbospongiosus near the root of the penis and the ischiocavernosus that embrace the crura, the body of the penis has no muscles. The penis consists of thin skin, connective tissue, blood


and lymphatic vessels, fascia, the corpora cavernosa, and the corpus spongiosum containing the spongy urethra (Fig. 3.48C). Distally, the corpus spongiosum expands to form the conical glans of the penis, or head of the penis (Figs. 3.48A, B, & D and 3.49B). The margin of the glans projects beyond the ends of the corpora cavernosa to form the corona of the glans. The corona overhangs an obliquely grooved constriction, the neck of the glans, which separates the glans from the body of the penis. The slit‐like opening of the spongy urethra, the external urethral orifice (meatus), is near the tip of the glans. Figure 3.50. Vessels and nerves on dorsum of penis and contents of spermatic cord. This dissection of the penis and spermatic cord shows their vessels and nerves. The skin, including the scrotum, has been removed. The superficial (dartos) fascia covering the penis has also been removed to expose the midline deep dorsal vein and the bilateral dorsal arteries and nerves of the penis. The triangular suspensory ligament of the penis attaches to the pubic symphysis and blends with the deep fascia of the penis.

The skin of the penis is thin, darkly pigmented relative to adjacent skin, and connected to the tunica albuginea by loose connective tissue. At the neck of the glans, the skin and fascia of the penis are prolonged as a double layer of skin, the prepuce (foreskin), which in uncircumcised males covers the glans to a variable extent (Fig 3.48E). The frenulum of the prepuce is a median fold that passes from the deep layer of the prepuce to the urethral surface of the glans (Fig. 3.48A & D). The suspensory ligament of the penis is a condensation of deep fascia that arises from the anterior surface of the pubic symphysis (Fig. 3.50). The ligament passes inferiorly and splits to form a sling that is attached to the deep fascia of the penis at the junction of its root and body. The fibers of the suspensory ligament are short and taut, anchoring the erectile bodies of the penis to the pubic symphysis. The fundiform ligament of the penis is an irregular mass or condensation of collagen and elastic fibers of the subcutaneous tissue that descends in the midline from the linea alba superior to the pubic symphysis. The ligament splits to surround the penis and then unites and blends inferiorly with the dartos fascia forming the scrotal septum. The fibers of the fundiform ligament are relatively long and loose and lie superficial (anterior) to the suspensory ligament.


Arterial Supply of the Penis The penis is supplied mainly by branches of the internal pudendal arteries (Figs. 3.48C & D and 3.50; Table 3.8). 





Dorsal arteries of the penis: run on each side of the deep dorsal vein in the dorsal groove between the corpora cavernosa, supplying the fibrous tissue around the corpora cavernosa, the corpus spongiosum and spongy urethra, and the penile skin. Deep arteries of the penis: pierce the crura proximally and run distally near the center of the corpora cavernosa, supplying the erectile tissue in these structures. Arteries of the bulb of the penis: supply the posterior (bulbous) part of the corpus spongiosum and the urethra within it as well as the bulbourethral gland.

In addition, superficial and deep branches of the external pudendal arteries supply the penile skin, anastomosing with branches of the internal pudendal arteries. The deep arteries of the penis are the main vessels supplying the cavernous spaces in the erectile tissue of the corpora cavernosa and are, therefore, involved in the erection of the penis. They give off numerous branches that open directly into the cavernous spaces. When the penis is flaccid, these arteries are coiled, restricting blood flow; they are called hel‐icine arteries of the penis (G. helix, a coil). Venous and Lymphatic Drainage of the Penis Blood from the cavernous spaces is drained by a venous plexus that joins the deep dorsal vein of the penis in the deep fascia (Figs. 3.48C and 3.50). This vein passes between the laminae of the suspensory ligament of the penis, inferior to the arcuate pubic ligament and anterior to the perineal membrane, to enter the pelvis, where it drains into the prostatic venous plexus. Blood from the superficial coverings of the penis drain into the superficial dorsal vein(s), which drain(s) into the superficial external pudendal vein. Some blood also passes to the internal pudendal vein. Lymph from the skin of the penis drains initially to the superficial inguinal lymph nodes, that from the glans and distal spongy urethra drain to the deep inguinal and external iliac nodes, and that from the cavernous bodies and proximal spongy urethra drain to the internal iliac nodes (Fig. 3.47; Table 3.6). Innervation of the Penis The nerves derive from the S2—S4 spinal cord segments and spinal ganglia, passing through the pelvic splanchnic and pudendal nerves, respectively (Fig. 3.51). Sensory and sympathetic innervation is provided primarily by the dorsal nerve of the penis, a terminal branch of the pudendal nerve, which arises in the pudendal canal and passes anteriorly into the deep perineal pouch. It then runs to the dorsum of the penis, where it runs lateral to the dorsal artery (Figs. 3.48C and 3.50). It supplies both the skin and glans of the penis. The penis is richly provided with a variety of sensory nerve endings, especially the glans penis. Branches of the ilioinguinal nerve supply the skin at the root of the penis. Cavernous nerves, conveying parasympathetic fibers independently from the prostatic nerve plexus, innervate the helicine arteries of the


erectile tissue. The sexual functions of the penis are explained under “Erection, Emission, and Ejaculation,” later in this chapter. Figure 3.51. Nerves of perineum. The pudendal nerve conveys the majority of sensory, sympathetic, and somatic motor fibers to the perineum. Although originating from the same spinal cord segments from which the pudendal nerve is derived, the parasympathetic fibers of the cavernous nerves course independently of the pudendal nerve. W ith the exception of the cavernous nerves, parasympathetic fibers do not occur outside of the head, neck, or cavities of the trunk. The cavernous nerves arise from the prostatic plexus of males and from the vesical plexus of females. They terminate on the arteriovenous anastomoses and helicine arteries of the erectile bodies, which, when stimulated, produce erection of the penis or engorgement of the clitoris and vestibular bulb in females.

Hypospadias Hypospadias is a common congenital anomaly of the penis, occurring in 1 in 300 newborns. In the simplest and most common form, glanular hypospadias, the external urethral orifice is on the ventral aspect of the glans. In other infants, the defect is in the body of the penis (penile hypospadias) (Fig. B3.28), or in the perineum (penoscrotal or scrotal hypospadias). Hence, the external urethral orifice is on the urethral surface of the penis. The embryological basis of glanular and penile hypospadias is failure of the urogenital folds to fuse on the ventral surface of the developing penis and form the spongy urethra. The embryological basis of scrotal hypospadias is failure of the labioscrotal folds to fuse and form the scrotum. The cause of hypospadias is not clearly understood, but it appears to have a multifactorial origin (i.e., genetic and environmental factors are involved). Close relatives of patients with hypospadias are more likely than the general population to have the anomaly. It is generally believed that hypospadias is associated with an inadequate production of androgens by the fetal testes. Differences in the timing and degree of hormonal insufficiency probably account for the different types of hypospadias (Moore and Persaud, 2003). The less common but more severe forms of hypospadias, in which the external urethral orifice is located on the penile body or in the perineum, may interfere with normal urination in the usual male standing position. (Walsh, 1998)


Phimosis, Paraphimosis, and Circumcision The prepuce of the penis is usually sufficiently elastic for it to be retracted over the glans penis. In some males, it fits tightly over the glans and cannot be retracted easily (phimosis) if at all. As there are modified sebaceous glands in the prepuce, the oily secretions of cheesy consistency (smegma) from them accumulate in the preputial sac, located between the glans and prepuce, causing irritation. In some males, retraction of the prepuce over the glans constricts the neck of the glans so much that there is interference with the drainage of blood and tissue fluid. In patients with this condition (paraphimosis) the glans may enlarge so much that the prepuce cannot be drawn over it. Circumcision is commonly performed in such cases. Circumcision, surgical excision of the prepuce, is the most commonly performed minor surgical operation on male infants. Although it is a religious practice in Islam and Judaism, it is often done routinely for non‐religious reasons (a preference usually explained in terms of tradition or hygiene) in North America. In adults, circumcision is usually performed when phimosis or paraphimosis is present.

Figure B3.28

The Bottom Line The penis is the male copulatory organ and common final conveyor of urine and semen. It is formed mainly of thin, mobile skin overlying three cylindrical bodies of erectile cavernous tissue, the paired corpora cavernosa, and a single corpus spongiosum containing the spongy urethra. The erectile bodies are bound together by deep fascia of the penis, except posteriorly (at the root) where they separate into the crura and bulb of the penis. The crura attach to the ischiopubic rami, but all parts of the root are attached to the perineal membrane. At the junction of root and body, the penis is attached to the pubic syphysis by the suspensory ligament of the penis.


The ischiocavernosus muscles ensheath the crura, and the bulbospongiosus ensheaths the bulb, its most anterior fibers encircling the most proximal part of the body (which otherwise has no muscles) and deep dorsal vessels. The glans of the penis is a distal expansion of the corpus spongiosum, which has the external urethral orifice at its tip and a projecting corona that overhangs the neck of the glans. Unless removed by circumcision, the neck is covered by the prepuce or foreskin. Except for skin near its root, the penis is supplied mainly by branches of the internal pudendal arteries. The dorsal arteries supply most of the body and glans, whereas the deep arteries supply the cavernous tissue, their terminal helicine arteries opening to engorge the sinuses with blood at arterial pressure, causing erection. Superficial structures drain via the superficial dorsal vein to external pudendal veins, whereas the erectile bodies drain via the deep dorsal vein to the prostatic venous plexus. Sensory and sympathetic innervation is provided mainly by the dorsal nerve of the penis, but the helicine arteries that directly produce erection are innervated by cavernous nerves, extensions of the prostatic nerve plexus.

Perineal Muscles of the Male The superficial perineal muscles, located in the superficial perineal pouch, include the superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles (Fig. 3.49A). Details about the attachments, innervation, and actions of these muscles are provided in Table 3.9. The superficial transverse perineal muscles and bulbospongiosus muscles join the external anal sphincter in attaching centrally to the perineal body, crossing the pelvic outlet like intersecting beams, supporting the perineal body to aid the pelvic diaphragm in supporting the pelvic viscera. Simultaneous contraction of the superficial perineal muscles (plus the deep transverse perineal muscle) during penile erection provides a firmer base for the penis. The bulbospongiosus muscles form a constrictor that compresses the bulb of the penis and the corpus spongiosum, thereby aiding in emptying the spongy urethra of residual urine and/or semen. The anterior fibers of the bulbospongiosus, encircling the most proximal part of the body of the penis, also assist erection by increasing the pressure on the erectile tissue in the root of the penis. At the same time, they also compress the deep dorsal vein of the penis, impeding venous drainage of the cavernous spaces and helping promote enlargement and turgidity of the penis. The ischiocavernosus muscles surround the crura in the root of the penis. They force blood from the cavernous spaces in the crura into the distal parts of the corpora cavernosa, which increases the turgidity (firm distension) of the penis during erection. Contraction of the ischiocavernosus muscles also compresses the tributaries of deep dorsal vein of the penis leaving the crus of the penis, thereby restricting venous outflow from the penis and helping maintain the erection. Because of their function during erection and the activity of the bulbospongiosus subsequent to urination and ejaculation to expel the last drops of urine and semen, the perineal muscles are generally more developed in males than in females.


The Bottom Line In addition to their bony origins, the voluntary superficial and deep muscles of the perineum are also attached to the perineal membrane (by which they are separated) and the perineal body. In addition to the sphincteric functions of the external anal and urethral sphincters for maintaining fecal and urinary continence, the male perineal muscles function as a group to provide a base for the penis and support for the perineal body (which in turn supports the pelvic diaphragm). The ischiocavernosus and bulbospongiosus muscles both constrict venous outflow from the erectile bodies to assist erection, simultaneously pushing blood from the penile root into the body. In addition, the bulbospongiosus muscle constricts around the bulb of the penis to express the final drops of urine or semen. Because of these multiple functions, the perineal muscles are generally relatively well developed in males. The perineal muscles are innervated by muscular branches of the pudendal nerve.

Erection, Emission, and Ejaculation When a male is stimulated erotically, arteriovenous anastomoses, by which blood is normally able to bypass the “empty” potential spaces or sinuses of the corpora cavernosa, are closed. The smooth muscle in the fibrous trabeculae and coiled helicine arteries relaxes (is inhibited) as a result of parasympathetic stimulation (S2—S4 through the cavernous nerves from the prostatic nerve plexus). Consequently, the helicine arteries straighten, enlarging their lumina and allowing blood to flow into and dilate the cavernous spaces in the corpora of the penis. The bulbospongiosus and ischiocavernosus muscles compress veins egressing from the corpora cavernosa, impeding the return of venous blood. As a result, the corpora cavernosa and corpus spongiosum become engorged with blood at venous pressure, causing the erectile bodies to become turgid (enlarged and rigid), and an erection occurs. During emission, semen (sperms and secretions) is delivered to the prostatic urethra through the ejaculatory ducts after peristalsis of the ductus deferentes and seminal glands. Prostatic fluid is added to the seminal fluid as the smooth muscle in the prostate contracts. Emission is a sympathetic response (L1—L2 nerves). During ejaculation, semen is expelled from the urethra through the external urethral orifice. Ejaculation results from:   

Closure of the internal urethral sphincter at the neck of the urinary bladder, a sympathetic response (L1—L2 nerves). Contraction of the urethral muscle, a parasympathetic response (S2—S4 nerves). Contraction of the bulbospongiosus muscles, from the pudendal nerves (S2— S4).

After ejaculation, the penis gradually returns to a flaccid state (remission), resulting from sympathetic stimulation, which causes constriction of the smooth muscle in the coiled arteries. The bulbospongiosus and ischiocavernosus muscles relax, allowing more blood to be drained from the cavernous spaces in the penile corpora into the deep dorsal vein.


When a lesion of the prostatic plexus or cavernous nerves results in an inability to achieve an erection (impotence), a surgically implanted, semirigid or inflatable penile prosthesis may assume the role of the erectile bodies, providing the rigidity necessary to insert and move the penis within the vagina during intercourse. Table 3.9. Muscles of the Perineum

Muscle External sphincter

Origin and Skin and fascia surrounding anus; coccyx via anococcygeal ligament Bulbospongiosus Male: median raphe on ventral surface of bulb of penis; perineal body

Female: perineal body

Course and distribution Passes around lateral aspects of anal canal, insertion into perineal body

Innervation Inferior anal (rectal) nerve, a branch of pudendal nerve (S2—S4)

Male: surrounds lateral aspects of bulb of penis and most proximal part of of body of penis, inserting into perineal membrane, dorsal aspect of corpora spongiosum and cavernosa, and fascia of bulb of penis Female: passes on each side of lower vagina, enclosing bulb and greater vestibular gland; inserts into pubic arch and fascia of corpora cavernosa of clitoris

Muscular (deep) branch perineal of nerve, a branch of pudendal nerve (S2—S4)

Main Action Constricts anal canal during peristalsis, resisting defecation; supports and fixes perineal body and pelvic floor Male: supports and fixes perineal body/pelvic floor; compresses bulb of penis to expel last drops of urine/semen; assists erection by compressing outflow via deep perineal vein and by pushing blood from bulb into body of penis Female: supports and fixes perineal body/pelvic floor; “sphincter” of vagina; assists in erection of clitoris (and perhaps bulb of vestibule); compresses greater vestibular gland

Clinically Oriented Anatomy, 5th Edition By Keith Moore Ischiocavernosus

Internal surface of ischiopubic ramus and ischial tuberosity

Embraces crus of penis or clitoris, inserting onto the inferior and medial aspects of crus and to perineal membrane medial to crus Superficial Internal Passes along inferior transverse surface of aspect of posterior perineal ischiopubic border of perineal ramus and membrane to perineal ischial body Deep transverse tuberosity Passes along superior perineal aspect of posterior border of perineal (Compressor membrane to perineal urethra portion body and external anal only) sphincter External urethra Surrounds urethra sphincter superior to perineal membrane; in males, it also ascends anterior aspect of prostate; in females, some fibers also enclose vagina (urethrovaginal sphincter)

Muscular (deep) branch of perineal nerve, a branch of pudendal nerve (S2—S4)

Dorsal nerve of penis or clitoris, the terminal branch of the pudendal nerve (S2—S4)

Maintains erection of penis or clitoris by compressing outflow veins and pushing blood from the root of penis or clitoris into the body of penis or clitoris Supports and fixes perineal body/pelvic floor to support abdominopelvic viscera and resist increased intra‐abdominal pressure

Compresses urethra to maintain urinary continence; in females, urethrovaginal sphincter portion also compresses vagina

Female Perineum The female perineum includes the female external genitalia, perineal muscles, and anal canal. Female External Genitalia The female external genitalia (Figs. 3.52, 3.53, 3.54, 3.55) include the mons pubis and labia majora (enclosing the pudendal cleft), labia minora (enclosing the vestibule), clitoris, bulbs of the vestibule, and greater and lesser vestibular glands. The synonymous terms vulva and pudendum include all these parts; the term pudendum is commonly used clinically. The vulva serves:   

As sensory and erectile tissue for sexual arousal and intercourse. To direct the flow of urine. To prevent entry of foreign material into the urogenital tract.

Mons Pubis The mons pubis is the rounded, fatty eminence anterior to the pubic symphysis, pubic tubercles, and superior pubic rami (Fig. 3.52). The eminence is formed by a mass of fatty subcutaneous tissue (Fig. 3.53A). The amount of fat increases at puberty and decreases after menopause. The surface of the mons is continuous with the anterior abdominal wall. After puberty, the mons pubis is covered with coarse pubic hairs.


Figure 3.52. Female external genitalia. The labia majora and minora are separated to show the vestibule, into which the external urethral orifice and the vaginal orifice open.

Figure 3.53. Female perineum. A. A superficial dissection of the superficial pouch is shown. Encapsulated digital processes of fat pass deep to the thick superficial fatty tissue of the mons pubis, largely filling the labia majora. The prepuce of the clitoris forms a hood over the clitoris. Notice the ischioanal fossae lateral to the anal canal. B. This deeper dissection of the superficial pouch reveals the bulbs of the vestibule and the greater vestibular glands and ducts. The internal pudendal vessels and pudendal nerve are shown emerging from the pudendal canal.


Figure 3.54. Female perineum. This subcutaneous dissection demonstrates the posterior labial vessels and nerves (S2—S3), joined by the perineal branch of the posterior cutaneous nerve of the thigh (S1— S3) running anteriorly almost to the mons pubis. The vessels anastomose here with the external pudendal vessels and the terminal branches of the nerves overlapping with those of the ilioinguinal nerve (L1). On the right side, the round ligament of the uterus terminates in the fat of the labium majus.

Labia Majora The labia majora are prominent folds of skin that indirectly provide protection for the urethral and vaginal orifices. Each labium majus—largely filled with a finger‐like “digital process” of loose subcutaneous tissue containing smooth muscle and the termination of the round ligament of the uterus (Figs. 3.53B and 3.54)—passes infero‐posteriorly from the mons pubis toward the anus. The labia majora lie on the sides of a central depression (a narrow slit when the thighs are adducted), the pudendal cleft, within which are the labia minora and vestibule (Fig. 3.52). The external aspects of the labia majora in the adult are covered with pigmented skin containing many sebaceous glands and are covered with crisp pubic hair. The internal aspects of the labia are smooth, pink, and hairless. The labia are thicker anteriorly where they join to form the anterior commissure. Posteriorly, in nulliparous women (never having borne children) they merge to form a ridge, the posterior commissure, which overlies the perineal body and is the posterior limit of the vulva. This commissure usually disappears after the first vaginal birth. Figure 3.55. Clitoris. The surrounding soft tissues have been removed to reveal the parts of the clitoris. In many details, the clitoris resembles the structure of the penis, of which it is a homolog, although it is of reduced scale and has no association with the urethra.


Labia Minora The labia minora are rounded folds of fat‐free, hairless skin. They are enclosed in the pudendal cleft and immediately surround the vestibule into which both the external urethral and the vaginal orifices open. They have a core of spongy connective tissue containing erectile tissue at their base and many small blood vessels. Anteriorly, the labia minora form two laminae. The medial laminae of each side unite as the frenulum of the clitoris. The lateral laminae unite anterior to (or often anterior and inferior to, thus overlapping and obscuring) the glans of the clitoris, forming the prepuce (foreskin) of the clitoris. In young women, especially virgins, the labia minora are connected posteriorly by a small transverse fold, the frenulum of the labia minora (fourchette). Although the internal surface of each labium minus consists of thin moist skin, it has the pink color typical of mucous membrane and contains many sebaceous glands and sensory nerve endings.

Clitoris The clitoris is an erectile organ located where the labia minora meet anteriorly. The clitoris consists of a root and a body, which are composed of two crura; two corpora cavernosa; and the glans of the clitoris, which is covered by a prepuce (Figs. 3.53 and 3.55). Together, the body and glans of the clitoris are approximately 2 cm in length and 90°, the movement being ultimately limited by the TCL. The chiasm (point of crossing) of the cruciate ligaments serves as the pivot for rotatory movements at the knee. Because of their oblique orientation, in every position one cruciate ligament, or parts of one or both ligaments, is tense. It is the cruciate ligaments that maintain contact with the femoral and tibial articular surfaces during flexion of the knee.

Chapter 5: Lower Limb

The anterior cruciate ligament (ACL), the weaker of the two cruciate ligaments, arises from the anterior intercondylar area of the tibia, just posterior to the attachment of the medial meniscus (Fig. 5.60A). The ACL has a relatively poor blood supply. It extends superiorly, posteriorly, and laterally to attach to the posterior part of the medial side of the lateral condyle of the femur (Fig. 5.60C). It limits posterior rolling (turning and traveling) of the femoral condyles on the tibial plateau during flexion, converting it to spin (turning in place). It also prevents posterior displacement of the femur on the tibia and hyperextension of the knee joint. When the joint is flexed at a right angle, the tibia cannot be pulled anteriorly (like pulling out a drawer) because it is held by the ACL. The posterior cruciate ligament (PCL), the stronger of the two cruciate ligaments, arises from the posterior intercondylar area of the tibia (Fig. 5.60A & D). The PCL passes superiorly and anteriorly on the medial side of the ACL to attach to the anterior part of the lateral surface of the medial condyle of the femur (Fig. 5.60B & C). The PCL limits anterior rolling of the femur on the tibial plateau during extension, converting it to spin. It also prevents anterior displacement of the femur on the tibia or posterior displacement of the tibia on the femur and helps prevent hyperflexion of the knee joint. In the weight‐bearing flexed knee, the PCL is the main stabilizing factor for the femur (e.g., when walking downhill). The menisci of the knee joint are crescentic plates (“wafers” ) of fibrocartilage on the articular surface of the tibia that deepen the surface and play a role in shock absorption (Fig. 5.61). The menisci (G. meniskos, crescent) are thicker at their external margins and taper to thin, unattached edges in the interior of the joint. Wedge shaped in transverse section, the menisci are firmly attached at their ends to the intercondylar area of the tibia (Fig. 5.60A). Their external margins attach to the joint capsule of the knee. The coronary ligaments are portions of the joint capsule extending between the margins of the menisci and most of the periphery of the tibial condyles (Fig. 5.60B). A slender fibrous band, the transverse ligament of the knee joins the anterior edges of the menisci (Fig. 5.61A), tethering them to each other during knee movements. The medial meniscus is C shaped, broader posteriorly than anteriorly. Its anterior end (horn) is attached to the anterior intercondylar area of the tibia, anterior to the attachment of the ACL (Fig. 5.60A). Its posterior end is attached to the posterior intercondylar area, anterior to the attachment of the PCL. The medial meniscus firmly adheres to the deep surface of the TCL (Figs. 5.59C and 5.61). Because of its widespread attachments laterally to the tibial intercondylar area and medially to the TCL, the medial meniscus is less mobile on the tibial plateau than is the lateral meniscus. The lateral meniscus is nearly circular, smaller, and more freely movable than the medial meniscus. The tendon of the popliteus has two parts proximally. One part attaches to the lateral epicondyle of the femur and passes between the lateral meniscus and inferior part of the lateral epicondylar surface of the femur (on the tendon's medial aspect) and the FCL that overlies its lateral aspect (Figs. 5.59A and 5.60B & D). The other, more medial part of the popliteal tendon attaches to the posterior limb of the lateral meniscus. A strong tendinous slip, the posterior meniscofemoral ligament, joins the lateral meniscus to the PCL and the medial femoral condyle (Figs. 5.60D and 5.61B).


F i g u re 5 . 6 0 . C r u c i a t e l i g a m e n t s o f k n e e j o i n t . A . S u p e r i o r a s p e c t o f th e s u p e r i o r a r t i cu l a r s u r f a c e o f t h e t i b i a ( t i b i a l p l a t e a u ) s h o w i n g t h e m e d i a l a n d l a te r a l c o n d y l e s ( a r t i c u l a r s u r f a ce s ) a n d t h e i n t e r co n d y l a r e m i n e n c e b e t w e e n t h e m . T h e s i t e s o f a t t a c h m e n t o f t h e c r u c i a t e l i g a m e n ts a r e c o l o r e d g r e e n ; t h o s e o f t h e m e d i a l m e n is c u s , p u r p l e ; a n d t h o s e o f t h e l a t e r a l m e n i s c u s , o r a n g e . B . T h e q u a d r i c e p s t e n d o n h a s b e e n s e v e r e d a n d t h e p a t e l l a ( w i t h i n t h e t e n d o n a n d i t s c o n t i n u a t i o n , t h e p a te l l a r l i g a m e n t ) h a s b e e n r e f l e c t e d i n f e r i o r l y . T h e k n e e i s f l e x e d t o d e m o n s t r a t e t h e c ru c i a t e l i g a m e n t s . C . I n t h e s e l a te r a l a n d m e d i a l v i e w s , t h e f e m u r h a s b e e n s e c t i o n e d l o n g i t u d i n a l l y a n d th e n e a r h a l f h a s b e e n r e m o v e d w i t h t h e p r o x i m a l p a r t o f t h e c o r r e s p o n d i n g c r u c i a t e l i g a m e n t . T h e l a t e r a l v i e w d e m o n s t r a t e s h o w t h e p o s te r i o r c r u c i a t e l i g a m e n t re s i s ts a n t e r i o r d is p l a c e m e n t o f t h e f e m u r o n t h e t i b i a l p l a t e a u . T h e m e d i a l v i e w d e m o n s t ra te s h o w t h e a n t e r i o r c r u c i a t e l i g a m e n t r e s i s ts p o s t e r i o r d is p l a c e m e n t o f t h e f e m u r o n t h e t i b i a l p l a t e a u . D . B o t h h e a d s o f t h e g a s t r o c n e m i u s a r e r e f l e c t e d s u p e r i o r l y , a n d t h e b i c e p s f e m o r is i s r e f l e c t e d i n f e r i o r l y . T h e a r t i c u l a r c a v i t y h a s b e e n i n f la t e d w i t h p u r p l e l a t e x t o d e m o n s t r a te i t s c o n t i n u i t y w i t h t h e v a r i o u s b u r s a e a n d t h e r e f l e ct i o n s a n d a t t a c h m e n t s o f th e co m p l e x s y n o v i a l m e m b r a n e .


Figure 5.61. Menisci of knee joint. A. The quadriceps tendon is cut, and the patella and patellar ligament are reflected inferiorly and anteriorly. The menisci, their attachments to the intercondylar area of the tibia, and the tibial attachments of the cruciate ligaments are shown. B. The band‐like tibial collateral ligament is attached to the medial meniscus. The cord‐like fibular collatera l ligament is separated from the lateral meniscus. The posterior meniscofemoral ligament attaches the lateral meniscus to the medial femoral condyle. C and D. The numbers on the MRI study refer to the structures labeled in the corresponding anatomical coronal section. (Part C courtesy of Dr. W. Kucharczyk, Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Magnetic Resonance Centre, Toronto, Ontario, Canada.)


Movements of the Knee Joint Flexion and extension are the main knee movements; some rotation occurs when the knee is flexed. When the knee is fully extended with the foot on the ground, the knee passively “locks” because of medial rotation of the femoral condyles on the tibial plateau. This position makes the lower limb a solid column and more adapted for weight bearing. When the knee is “locked,” the thigh and leg muscles can relax briefly without making the knee joint too unstable. To unlock the knee, the popliteus contracts, rotating the femur laterally about 5° on the tibial plateau so that flexion of the knee can occur. The main movements of the knee joint, the muscles producing them, and relevant details are provided in Table 5.16. Table 5.16. Movements of the Knee Joint and the Muscles Producing Them

Movement Degrees Possible

Muscles Producing Movement Primary Secondary

Comments

Extension

Quadriceps femoris

Ability of quadriceps to produce extension is most effective when hip joint is extended; flexion diminishes its efficiency

Factors Limiting (Checking) Movement Weakly: tensor Anterior edge of of fascia lata lateral meniscus contacts shallow groove between tibial and patellar surfaces of femoral condyles; anterior cruicate ligament contacts groove in intercondylar fossa


Flexion

120° (hip extended); 140° (hip flexed); 160° passively

Hamstrings (semitendinosus, semimembranosus, long head of biceps); short head of biceps

Gracilis, sartorius, gastrocnemius, popliteus

Medial rotation

10° with knee flexed; 5° with knee extended

Semitendinosus and Gracilis, semimembranosus sartorius when knee is flexed; popliteus when non‐ bearing knee is extended

Lateral rotation

30°

Biceps femoris when knee is flexed

Calf of leg contacts thigh; length of hamstrings is also a factor— more knee flexion is possible when hip joint is flexed; cannot fully flex knee when hip is extended Collateral ligaments, loose during flexion without rotation, become taut at limits of rotation

Collateral ligaments become taut; anterior cruciate ligament becomes wound around posterior cruciate ligament

Normally, role of gastroc‐ nemius is minimal, but in presence of a supracondylar fracture, it rotates (flexes) distal fragment of femur

When extended knee is bearing weight, action of popliteus laterally rotates femur; when not bearing weight, popliteus medially rotates patella At end of rotation, with no opposition, tensor of fascia lata can assist in maintaining position

Movements of the Menisci Although the rolling movement of the femoral condyles during flexion and extension is limited (converted to spin) by the cruciate ligaments, some rolling does occur, and the point of contact between the femur and the tibia moves posteriorly with flexion and returns anteriorly with extension. Furthermore, during rotation of the knee, one femoral condyle moves anteriorly on the corresponding tibial condyle while the other femoral condyle moves posteriorly, rotating about the chiasm of the cruciate ligaments. The menisci must be able to migrate on the tibial plateau as the points of contact between femur and tibia change.

Blood Supply of the Knee Joint The arteries supplying the knee joint are the 10 vessels that form the periarticular genicular anastomoses around the knee: the genicular branches of the femoral, popliteal, and anterior and posterior recurrent branches of the anterior tibial recurrent and circumflex fibular arteries (Figs. 5.62 and 5.63B). The middle genicular branches of the popliteal artery penetrate the fibrous layer of the joint capsule and supply the cruciate ligaments, synovial membrane, and peripheral margins of the menisci.


Innervation of the Knee Joint Reflecting Hilton's law, the nerves supplying the muscles crossing (acting on) the knee joint also supply the joint (Fig. 5.63D); thus articular branches from the femoral (the branches to the vasti), tibial, and common fibular nerves supply its anterior, posterior, and lateral aspects, respectively. In addition, however, the obturator and saphenous (cutaneous) nerves supply articular branches to its medial aspect.

Bursae around the Knee Joint There are at least 12 bursae around the knee joint because most tendons run parallel to the bones and pull lengthwise across the joint during knee movements. The subcutaneous prepatellar and infrapatellar bursae are located at the convex surface of the joint, allowing the skin to be able to move freely during movements of the knee (Figs. 5.58B and 5.59A). The main bursae of the knee are illustrated and described in Table 5.17. Figure 5.62. Arterial anastomoses around knee. In addition to providing collateral circulation, the genicular arteries of the genicular anastomosis supply blood to the structures surrounding the joint as well as to the joint itself (e.g., its joint or articular capsule). Compare these views with the anterior view in Figure 5.63B.

Four bursae communicate with the synovial cavity of the knee joint: suprapatellar bursa, popliteus bursa (deep to the distal quadriceps), anserine bursa (deep to the tendinous distal attachments of the sartorius, gracilis, and semitendinosus), and gastrocnemius bursa (Figs. 5.59A and 5.60D). The large suprapatellar bursa (Figs. 5.57A and 5.59A) is especially important because an infection in it may spread to the knee joint cavity. Although it develops separately from the knee joint, the bursa becomes continuous with it.

Knee Joint Injuries Knee joint injuries are common because the knee is a low‐placed, mobile, weight‐ bearing joint, serving as a fulcrum between two long levers (thigh and leg). Its stability depends almost entirely on its associated ligaments and surrounding muscles. The knee joint is essential for everyday activities such as standing, walking,


and climbing stairs. It is also a main joint for sports that involve running, jumping, kicking, and changing directions. To perform these activities, the knee joint must be mobile; however, this mobility makes it susceptible to injuries. The most common knee injuries in contact sports are ligament sprains, which occur when the foot is fixed in the ground (Fig. B5.26A). If a force is applied against the knee when the foot cannot move, ligament injuries are likely to occur. The tibial and fibular collateral ligaments (TCL and FCL) are tightly stretched when the leg is extended, normally preventing disruption of the sides of the knee joint.


Figure 5.63. Joints and neurovascular structures of leg and foot. A. The tibiofibular articulation s include the synovial tibiofibular joint and the tibiofibular syndesmosis; the latter is made up of the interosseous membrane of the leg and the anterior and posterior tibiofibular ligaments. The oblique direction of the fibers of the interosseous membrane, primarily extending inferolaterally from the tibia, allows slight upward movement of the fibula but resists downward pull on it. B. The arterial supply of the joints of the leg and foot is demonstrated. Periarticular anastomoses surround the knee and ankle. C. Of the nine muscles attached to the fibula, all except one exert a downward pull on the fibula. D. The nerve supply of the leg and foot is demonstrated. Starting with the knee and progressing distally in the limb, cutaneous nerves become increasingly involved in providing innervation to joints, taking over completely in the distal foot and toes.

Table 5.17. Bursae about the Knee Joint

Bursae Suprapatellar

Popliteus Anserine

Gastrocnemius

Semimembranosus

Subcutaneous prepatellar Subcutaneous infrapatellar Deep infrapatellar

Locations Between femur and quadriceps femoris

Comments of Held in position by articularis genu muscles; communicates freely with (superior extension of) synovial cavity of knee joint Between tendon of popliteus and Opens into synovial cavity of knee lateral condyle of tibia joint inferior to lateral meniscus Separates tendons of sartorius, Area where tendons of these gracilis, and semitendinosus from muscles attach to tibia; resembles a tibia and tibial collateral ligament goose's foot (L. pes anserinus) Deep to proximal attachment of An extension of synovial cavity of tendon of medial head of knee joint gastrocnemius Between medial head of Related to distal attachment of gastrocnemius and semimembranosus semimembranosus tendon Between skin and anterior surface of Allows free movement of skin over patella patella during movements of leg Between skin and tibial tuberosity Helps knee withstand pressure when kneeling Between patellar ligament and Separated from knee joint by anterior surface of tibia infrapatellar fat pad tendon


The firm attachment of the TCL to the medial meniscus is of considerable clinical significance because tearing of this ligament frequently results in concomitant tearing of the medial meniscus. The injury is frequently caused by a blow to the lateral side of the extended knee or excessive lateral twisting of the flexed knee that disrupts the TCL and concomitantly tears and/or detaches the medial meniscus from the joint capsule (Fig. B5.26A). This injury is common in athletes who twist their flexed knees while running (e.g., in basketball, the various forms of football, and volleyball). The ACL, which serves as a pivot for rotatory movements of the knee and is taut during flexion, may also tear subsequent to the rupture of the TCL, creating an “unhappy triad” of knee injuries. Hyperextension and severe force directed anteriorly against the femur with the knee semiflexed (e.g., a cross‐body block in football) may tear the ACL. ACL ruptures are also common knee injuries in skiing accidents. This injury causes the free tibia to slide anteriorly under the fixed femur, known as the anterior drawer sign (Fig. B5.26B). The ACL may tear away from the femur or tibia; however, tears commonly occur in the midportion of the ligament.


Figure B5.26 Although strong, PCL ruptures may occur when a player lands on the tibial tuberosity with the knee flexed (e.g., when knocked to the floor in basketball). PCL ruptures usually occur in conjunction with tibial or fibular ligament tears. These injuries can also occur in head‐on collisions when seat belts are not worn and the proximal end of the tibia strikes the dashboard. PCL ruptures allow the free tibia to slide posteriorly under the fixed femur, known as the posterior drawer sign (Fig. B5.26C). Meniscal tears usually involve the medial meniscus. The lateral meniscus does not usually tear because of its mobility. Pain on lateral rotation of the tibia on the femur indicates injury of the lateral meniscus (Fig. B5.27A), whereas pain on medial


rotation of the tibia on the femur indicates injury of the medial meniscus (Fig. B5.27B). Most meniscal tears occur in conjunction with TCL or ACL tears. Peripheral meniscal tears can often be repaired or may heal on their own because of the generous blood supply to this area. Meniscal tears that do not heal or cannot be repaired are usually removed (e.g., by arthroscopic surgery). Knee joints from which the menisci have been removed suffer no loss of mobility; however, the knee may be less stable and the tibial plateaus often undergo inflammatory reactions.

Figure B5.27

Arthroscopy of the Knee Joint Arthroscopy is an endoscopic examination that allows visualization of the interior of the knee joint cavity with minimal disruption of tissue (Fig. B5.28). The arthroscope and one (or more) additional canula(e) are inserted through tiny incisions, known as portals. The second canula is for passage of specialized tools (e.g., manipulative probes or forceps) or equipment for trimming, shaping, or removing damaged tissue. This technique allows removal of torn menisci, loose bodies in the joint (such as bone chips), and debridement (the excision of devitalized articular cartilaginous material) in advanced cases of arthritis. Ligament repair or replacement may also be performed using an arthroscope. Although general anesthesia is usually preferable, knee arthroscopy can be performed using local or regional anesthesia. During arthroscopy, the articular cavity of the knee must be treated essentially as two separate (medial and lateral) femorotibial articulations owing to the imposition of the synovial fold around the cruciate ligaments. For further information see Soames (1995).

Aspiration of the Knee Joint Fractures of the distal end of the femur or lacerations of the anterior thigh may involve the suprapatellar bursa and result in infection of the knee joint. When the knee joint is infected and inflamed, the amount of synovial fluid may increase. Joint


effusions, the escape of fluid from blood or lymphatic vessels, results in increased amounts of fluid in the joint cavity. Because the suprapatellar bursa communicates freely with the synovial cavity of the knee joint, fullness of the thigh in the region of the suprapatellar bursa may indicate increased synovial fluid. This bursa can be aspirated to remove the fluid for examination. Direct aspiration of the knee joint is usually performed with the patient sitting on a table with the knee flexed. The joint is approached laterally, using three bony points as landmarks for needle insertion: the anterolateral tibial (Gerdy) tubercle, the lateral epicondyle of the femur, and the apex of the patella. In addition to being the route for aspiration of serous and sanguineous (bloody) fluid, this triangular area also lends itself to drug injection for treating pathology of the knee joint.

Figure B5.28

Bursitis in the Knee Region Prepatellar bursitis is caused by friction between the skin and the patella; however, the bursa may also be injured by compressive forces resulting from a direct blow or from falling on the flexed knee (Anderson et al., 2000). If the inflammation is chronic, the bursa becomes distended with fluid and forms a swelling anterior to the knee. This condition has been called “housemaid's knee” (Fig. B5.29); however, other people who work on their knees without knee pads, such as hardwood floor and rug installers, may also develop prepatellar bursitis. Subcutaneous infrapatellar bursitis is caused by excessive friction between the skin and the tibial tuberosity; the edema occurs over the proximal end of the tibia. This condition was formerly called “clergyman's knee” because of frequent genuflecting (L. genu, knee); however, it occurs more commonly in roofers and floor tilers if they do not wear knee pads. Deep infrapatellar bursitis results in edema between the patellar ligament and the tibia, superior to the tibial tuberosity. The inflammation is


usually caused by overuse and subsequent friction between the patellar tendon and the structures posterior to it, the infrapatellar fat‐pad and tibia (Anderson et al., 2000). Enlargement of the deep infrapatellar bursa obliterates the dimples normally occurring on each side of the patellar ligament when the leg is extended.

Figure B5.29

Figure B5.30 Abrasions or penetrating wounds may result in suprapatellar bursitis, an infection caused by bacteria entering the bursa from the torn skin. The infection may spread to the cavity of the knee joint, causing localized redness and enlarged popliteal and inguinal lymph nodes.


Popliteal Cysts Popliteal cysts (Baker cysts) are abnormal fluid‐filled sacs of synovial membrane in the region of the popliteal fossa. A popliteal cyst is almost always a complication of chronic knee joint effusion (Slaby et al., 1994). The cyst may be a herniation of the gastrocnemius or semimembranosus bursa through the fibrous layer of the joint capsule into the popliteal fossa, communicating with the synovial cavity of the knee joint by a narrow stalk (Fig. B5.30). Synovial fluid may also escape from the knee joint (synovial effusion) or a bursa around the knee and collect in the popliteal fossa. Here it forms a new synovial‐lined sac, or popliteal cyst. Popliteal cysts are common in children but seldom cause symptoms. In adults, popliteal cysts can be large, extending as far as the midcalf, and may interfere with knee movements.

Knee Replacement If a person's knee is diseased, resulting from osteoarthritis, for example, an artificial knee joint may be inserted (total knee replacement arthroplasty) (Fig. B5.31). The artificial knee joint consists of plastic and metal components that are cemented to the femoral and tibial bone ends after removal of the defective areas. The combination of metal and plastic mimics the smoothness of cartilage on cartilage and produces good results in “low‐demand” people who have a relatively sedentary life. In “high‐demand” people who are active in sports, the bone—cement junctions may break down, and the artificial knee components may loosen; however, improvements in bioengineering and surgical technique have provided better results. For more information see Soames (1995).

Figure B5.31 P.700

The Bottom Line The knee is a hinge joint with a wide range of motion (primarily flexion and extension, with rotation increasingly possible with flexion). It is our most vulnerable joint owing to its incongruous articular surfaces and the mechanical disadvantage resulting from bearing the body's weight plus momentum while serving as a fulcrum between two long levers. Compensation is attempted by several features, including (1) strong intrinsic, extracapsular, and intracapsular ligaments; (2) splinting by many


surrounding tendons (including the iliotibial tract); and (3) menisci that fill the spatial void, providing mobile articular surfaces. Of particular clinical importance are (1) collateral ligaments that are taut during (and limit) extension and are relaxed during flexion, allowing rotation for which they serve as check ligaments; (2) cruciate ligaments that maintain the joint during flexion, providing the pivot for rotation; and (3) the medial meniscus that is attached to the tibial collateral ligament and is frequently injured because of this attachment.

Tibiofibular Joints The tibia and fibula are connected by two joints: the superior tibiofibular joint and the tibiofibular syndesmosis (inferior tibiofibular) joint. In addition, an interosseous membrane joins the shafts of the two bones (Fig. 5.63A). The fibers of the interosseous membrane and all ligaments of both tibiofibular articulations run inferiorly from the tibia to the fibula. Thus the membrane and ligaments strongly resist the downward pull placed on the fibula by eight of the nine muscles attached to it (Fig. 5.63C). However, they allow slight upward movement of the fibula that occurs when the wide (posterior) end of the trochlea of the talus is wedged between the malleoli during dorsiflexion at the ankle. Movement at the superior tibiofibular joint is impossible without movement at the inferior tibiofibular syndesmosis. The anterior tibial vessels pass through a hiatus at the superior end of the interosseous membrane (Fig. 5.63A & B). At the inferior end of the membrane is a smaller hiatus through which the perforating branch of the fibular artery passes.

Superior Tibiofibular Joint The superior tibiofibular joint is a plane type of synovial joint between the flat facet on the fibular head and a similar articular facet located posterolaterally on the lateral tibial condyle (Figs. 5.61B & D and 5.63A). A tense joint capsule surrounds the joint and attaches to the margins of the articular surfaces of the fibula and tibia. The joint capsule is strengthened by anterior and posterior tibiofibular ligaments, which pass superomedially from the fibular head to the lateral tibial condyle (Fig. 5.61B). The joint is crossed posteriorly by the tendon of the popliteus. A pouch of synovial membrane from the knee joint, the popliteus bursa (Table 5.17), passes between the tendon of the popliteus and the lateral condyle of the tibia. About 20% of the time, the bursa also communicates with the synovial cavity of the tibiofibular joint, enabling transmigration of inflammatory processes between the two joints.

Movement Slight movement of the joint occurs during dorsiflexion of the foot as a result of wedging of the trochlea of the talus between the malleoli (see “Articular Surfaces of the Ankle Joint,” later in this chapter).

Blood Supply The arteries of the superior tibiofibular joint are from the inferior lateral genicular and anterior tibial recurrent arteries (Figs. 5.62A and 5.63B).


Nerve Supply The nerves of the tibiofibular joint are from the common fibular nerve and the nerve to the popliteus (Fig. 5.63D).

Tibiofibular Syndesmosis The tibiofibular syndesmosis is a compound fibrous joint. It is the fibrous union of the tibia and fibula by means of the interosseous membrane (uniting the shafts) and the anterior, interosseous and posterior tibiofibular ligaments (the latter making up the inferior tibiofibular joint, uniting the distal ends of the bones). The integrity of the inferior tibiofibular joint is essential for the stability of the ankle joint because it keeps the lateral malleolus firmly against the lateral surface of the talus.

Articular Surfaces and Ligaments The rough, triangular articular area on the medial surface of the inferior end of the fibula articulates with a facet on the inferior end of the tibia (Fig. 5.63A). The strong deep interosseous tibiofibular ligament, continuous superiorly with the interosseous membrane, forms the principal connection between the tibia and the fibula. The joint is also strengthened anteriorly and posteriorly by the strong external anterior and posterior inferior tibiofibular ligaments. The distal deep continuation of the posterior inferior tibiofibular ligament, the inferior transverse (tibiofibular) ligament, forms a strong connection between the distal ends of the tibia (medial malleolus) and the fibula (lateral malleolus). It contacts the talus and forms the posterior “wall” of a square socket (with three deep walls and a shallow or open anterior wall), the malleolar mortise, for the trochlea of the talus. The lateral and medial walls of the mortise are formed by the respective malleoli (Fig. 5.64).

Movement Slight movement of the joint occurs to accommodate wedging of the wide portion of the trochlea of the talus between the malleoli during dorsiflexion of the foot.

Blood Supply The arteries are from the perforating branch of the fibular artery and from medial malleolar branches of the anterior and posterior tibial arteries (Fig. 5.63B).

Nerve Supply The nerves to the syndesmosis are from the deep fibular, tibial, and saphenous nerves (Fig. 5.63D).

The Bottom Line The tibiofibular joints include a superior synovial joint and the tibiofibular syndesmosis, consisting of an interosseous membrane and an inferior tibiofibular joint with anterior, interosseous, and posterior tibiofibular ligaments. Together they make up a compensatory system that allows a slight upward movement of the fibula owing to forced transverse expansion of the malleolar mortise (deep square socket) during maximal dorsiflexion of the ankle. All fibrous tibiofibular connections run downward from tibia to fibula, allowing this slight upward movement while strongly resisting the downward pull applied to the fibula by the contraction of eight of the nine muscles attached to it.


Figure 5.64. Radiograph of ankle joint of a 14‐year‐old boy. The trochlea of the body of the talus fits into the mortise formed by the medial and lateral malleoli. Epiphysial (growth) plates are evident at this age.

Ankle Joint The ankle joint (talocrural articulation) is a hinge‐type synovial joint. It is located between the distal ends of the tibia and the fibula and the superior part of the talus. The ankle joint can be felt between the tendons on the anterior surface of the ankle as a slight depression, approximately 1 cm proximal to the tip of the medial malleolus.

Articular Surfaces of the Ankle Joint The distal ends of the tibia and fibula (along with the inferior transverse part of the posterior tibiofibular ligament) (Figs. 5.63A and 5.65B) form a malleolar mortise into which the pulley‐shaped trochlea of the talus fits (Fig. 5.64). The trochlea (L. pulley) is the rounded superior articular surface of the talus (Table 5.18A). The medial surface of the lateral malleolus articulates with the lateral surface of the talus. The tibia articulates with the talus in two places:  

Its inferior surface forms the roof of the malleolar mortise, transferring the body's weight to the talus. Its medial malleolus articulates with the medial surface of the talus.

The malleoli grip the talus tightly as it rocks in the mortise during movements of the joint. The grip of the malleoli on the trochlea is strongest during dorsiflexion of the foot (as when “digging in one's heels” when descending a steep slope or during tug‐ of‐war) because this movement forces the wider, anterior part of the trochlea posteriorly between the malleoli, spreading the tibia and fibula slightly apart. This spreading is limited especially by the strong interosseous tibiofibular ligament as well as the anterior and posterior tibiofibular ligaments that unite the tibia and


fibula (Figs. 5.63A and 5.65). The interosseous ligament is deeply placed between the nearly congruent surfaces of the tibia and fibula; although demonstrated in the inset for Figure 5.63A, the ligament can actually be observed only by rupturing it or in a cross section. The ankle joint is relatively unstable during plantarflexion because the trochlea is narrower posteriorly and, therefore, lies relatively loosely within the mortise. It is during plantarflexion that most injuries of the ankle occur (usually as a result of sudden, unexpected—and therefore inadequately resisted—inversion of the foot).

Joint Capsule of the Ankle Joint The joint capsule is thin anteriorly and posteriorly but is supported on each side by strong collateral ligaments (Figs. 5.65 and 5.66; thin areas of the capsule have been removed in Figure. 5.65, leaving only the reinforced parts—the ligaments—and a synovial fold). Its fibrous layer is attached superiorly to the borders of the articular surfaces of the tibia and the malleoli and inferiorly to the talus. The synovial membrane is loose and lines the fibrous layer of the capsule. The synovial cavity often extends superiorly between the tibia and the fibula as far as the interosseous tibiofibular ligament.


Figure 5.65. Dissection of ankle joint and joints of inversion and eversion. A and B. The foot has been inverted (note wedge under foot) to demonstrate the articular areas and the lateral ligaments that become taut during inversion of the foot.

Ligaments of the Ankle Joint The ankle joint is reinforced laterally by the lateral ligament of the ankle, a compound structure consisting of three completely separate ligaments (Fig. 5.65A & B):  



Anterior talofibular ligament, a flat, weak band that extends anteromedially from the lateral malleolus to the neck of the talus, Posterior talofibular ligament, a thick, fairly strong band that runs horizontally medially and slightly posteriorly from the malleolar fossa to the lateral tubercle of the talus. Calcaneofibular ligament, a round cord that passes posteroinferiorly from the tip of the lateral malleolus to the lateral surface of the calcaneus.


The joint capsule is reinforced medially by the large, strong medial ligament of the ankle (deltoid ligament) that attaches proximally to the medial malleolus (Fig. 5.66). The medial ligament fans out from the malleolus, attaching distally to the talus, calcaneus, and navicular via four adjacent and continuous parts: the tibionavicular part, the tibiocalcaneal part, and the anterior and posterior tibiotalar parts. The medial ligament stabilizes the ankle joint during eversion and prevents subluxation (partial dislocation) of the joint. Table 5.18. Joints of Foot

Joint

Type

Subtalar (talocalcaneal, anatomical subtalar joint)

Plane synovial joint

Talocalcaneonavicular

Synovial joint; talonavicular part is ball and socket type

Calcaneocuboid

Plane synovial joint(s)

Articulating Surfaces Inferior surface of body of talus (posterior calcaneal articular facet) articulates with superior surface (posterior talar articular surface) of calcaneus Head of talus articulates with calcaneus and navicular bones Anterior end of calcaneus articulates

Joint Capsule Fibrous layer of joint capsule is attached to margins of articular surfaces

Ligaments

Movements

Medial, lateral, and posterior talocalcaneal ligaments support capsule; interosseous talocalcaneal ligament binds bones together

Inversion and posterior of foot

Joint capsule incompletely encloses joint

Plantar calcaneonavicular (spring) ligament supports head of talus

Gliding and rotatory movements possible

Fibrous capsule encloses joint

Dorsal calcaneocuboid ligament, plantar calcaneocuboid,

Inversion and eversion of foot; circumduction

Blood Supply Posterior tibial and fibular arteries

Anterior tibial artery via lateral tarsal artery, a branch of dorsal artery of foot

Nerve Supply Plantar aspect: medial or lateral plantar nerve; Dorsal aspect: deep fibular nerve


with posterior surface of cuboid Anterior navicular articulates with bases of metatarsal bones Anterior tarsal bones articulate with bases of metatarsal bones

Cuneonavicular joint

Tarsometatarsal

Intermetatarsal

Plane synovial joint

Metatarsophalangeal

Condyloid synovial joint

Interphalangeal

Hinge synovial joint

Bases of metatarsal bones articulate with each other Heads of metatarsal bones articulate with bases of proximal phalanges Head of one phalanx articulates with base of one distal to it

Common capsule encloses joints

and long plantar ligaments support joint capsule Dorsal and plantar cuneonavicular ligaments

Separate joint capsules enclose each joint

Dorsal, plantar, and interosseous tarsometatarsal ligaments bind bones together

Gliding sliding

Separate joint capsules enclose each joint

Dorsal, plantar, and interosseous tarsometatarsal ligaments bind bones together

Little individual movement occurs

Collateral ligaments support capsule on each side; plantar ligament supports plantar part of capsule Collateral and plantar ligaments support joints

Flexion, extension, and some abduction, adduction and circumduction Flexion and extension

Little movement occurs

or

Lateral metatarsal artery (a branch of dorsal artery of foot)

Digital branches of plantar arch

Deep fibular; medial and lateral plantar nerves; sural nerve Digital nerves


Figure 5.66. Ankle and tarsal joints. A. The flexor tendons, which descend the posterolateral aspect of the ankle region and enter the foot, are shown as is their relationship to the medial malleolus and talar shelf. Except for the part tethering the flexor hallucis longus tendon, the flexor retinaculum has been removed. B. This dissection of the ankle and tarsal joints demonstrates the four parts of the medial (deltoid) ligament of the ankle.

Movements of the Ankle Joint The main movements of the ankle joint are dorsiflexion and plantarflexion of the foot, which occur around a transverse axis passing through the talus (Table 5.18A). Because the narrow end of the trochlea of the talus lies loosely between the malleoli when the foot is plantarflexed, some “wobble” (small amounts of abduction, adduction, inversion, and eversion) is possible in this unstable position. 

Dorsiflexion of the ankle is produced by the muscles in the anterior compartment of the leg (Table 5.10). Dorsiflexion is usually limited by the passive resistance of the triceps surae to stretching and by tension in the medial and lateral ligaments.

Chapter 5: Lower Limb 

Plantarflexion of the ankle is produced by the muscles in the posterior compartment of the leg (Table 5.13). In toe dancing by ballet dancers, for example, the dorsum of the foot is in line with the anterior surface of the leg.

Blood Supply of the Ankle Joint The arteries are derived from malleolar branches of the fibular and anterior and posterior tibial arteries (Fig. 5.63B).

Nerve Supply of the Ankle Joint The nerves are derived from the tibial nerve and the deep fibular nerve, a division of the common fibular nerve (Fig. 5.63D).

Ankle Injuries The ankle is the most frequently injured major joint in the body. Ankle sprains (torn fibers of ligaments) are most common. A sprained ankle is nearly always an inversion injury, involving twisting of the weight‐bearing plantarflexed foot. The person steps on an uneven surface and the foot is forcibly inverted. Lateral ligament sprains occur in sports in which running and jumping are common, particularly basketball (70—80% of players have had at least one sprained ankle). The lateral ligament is injured because it is much weaker than the medial ligament and is the ligament that resists inversion at the talocrural joint. The anterior talofibular ligament—part of the lateral ligament—is most vulnerable and most commonly torn during ankle sprains, either partially or completely, resulting in instability of the ankle joint (Fig. B5.32). The calcaneofibular ligament may also be torn. In severe sprains, the lateral malleolus of the fibula may be fractured. Shearing injuries fracture the lateral malleolus at or superior to the ankle joint. Avulsion fractures break the malleolus inferior to the ankle joint; a fragment of bone is pulled off by the attached ligament(s). A Pott fracture—dislocation of the ankle occurs when the foot is forcibly everted (Fig. B5.33). This action pulls on the extremely strong medial ligament, often tearing off the medial malleolus. The talus then moves laterally, shearing off the lateral malleolus or, more commonly, breaking the fibula superior to the tibiofibular syndesmosis. If the tibia is carried anteriorly, the posterior margin of the distal end of the tibia is also sheared off by the talus, producing a “trimalleolar fracture.” In applying this term to this injury, the entire distal end of the tibia is erroneously considered to be a “malleolus.”

Tibial Nerve Entrapment The tibial nerve leaves the posterior compartment of the leg by passing deep to the flexor retinaculum in the interval between the medial malleolus and the calcaneus (Fig. 5.46B). Entrapment and compression of the tibial nerve (tarsal tunnel syndrome) occurs when there is edema and tightness in the ankle involving the synovial sheaths of the tendons of muscles in the posterior compartment of the leg. The area involved is from the medial malleolus to the calcaneus, and the heel pain results from compression of the tibial nerve by the flexor retinaculum.


Figure B5.32


Figure B5.33

The Bottom Line The ankle (talocrural) joint is composed of a superior mortise, formed by the weight‐ bearing inferior surface of the tibia and the two malleoli, which receive the trochlea of the talus. The joint is maintained medially by a strong, medial (deltoid) ligament, and a much weaker lateral ligament. The lateral ligament (specifically its anterior talofibular ligament component) is the most frequently injured ligament of the body. Injury occurs primarily by inadvertent inversion of the plantarflexed, weight‐bearing foot). About 70° of dorsiflexion and plantarflexion is possible at the joint, in addition to which small amounts of wobble occur in the less stable plantarflexed position.

Foot Joints The many joints of the foot involve the tarsals, metatarsals, and phalanges (Table 5.18). The important intertarsal joints are the subtalar (talocalcaneal) joint and the transverse tarsal joint (calcaneocuboid and talonavicular joints). Inversion and eversion of the foot are the main movements involving these joints. The other intertarsal joints (e.g., intercuneiform joints) and the tarsometatarsal and intermetatarsal joints are relatively small and are so tightly joined by ligaments that only slight movement occurs between them. In the foot, flexion and extension occurs in the forefoot at the metatarsophalangeal and interphalangeal joints (Table 5.19) Inversion is augmented by flexion of the toes (especially the great and 2nd toes), and eversion by their extension (especially of the lateral toes). All bones of the foot proximal to the metatarsophalangeal joints are united by dorsal and plantar ligaments. The bones of the metatarsophalangeal and interphalangeal joints are united by lateral and medial collateral ligaments. The subtalar joint occurs where the talus rests on and articulates with the calcaneus. The anatomical subtalar joint is a single synovial joint between the slightly concave


posterior calcaneal articular surface of the talus and the convex posterior articular facet of the calcaneus (Table 5.18). The joint capsule is weak but is supported by medial, lateral, posterior, and interosseous talocalcaneal ligaments (Fig. 5.65). The interosseous talocalcaneal ligament lies within the tarsal sinus, which separates the subtalar and talocalcaneonavicular joints and is especially strong. Orthopaedic surgeons use the term subtalar joint for the compound functional joint consisting of the anatomical subtalar joint plus the talocalcaneal part of the talocalcaneonavicular joint. The two separate elements of the clinical subtalar joint straddle the talocalcaneal interosseous ligament. Structurally, the anatomical definition is logical because the anatomical subtalar joint is a discrete joint, having its own joint capsule and articular cavity. Functionally, however, the clinical definition is logical because the two parts of the compound joint function as a unit; it is impossible for them to function independently. The subtalar joint (by either definition) is where the majority of inversion and eversion occurs, around an axis that is oblique. The transverse tarsal joint is a compound joint formed by two separate joints aligned transversely: the talonavicular part of the talocalcaneonavicular joint and the calcaneocuboid joint. At this joint, the midfoot and forefoot rotate as a unit on the hindfoot around a longitudinal (AP) axis, augmenting the inversion and eversion movements occurring at the clinical subtalar joint. Transection across the transverse tarsal joint is a standard method for surgical amputation of the foot. Table 5.19. Movements of the Joints of the Forefoot and the Muscles Producing Them

Movement Metatarsophalangeal joints Flexion (A)

Muscles a Flexor digitorum brevis Lumbricals Interossei Flexor hallucis brevis Flexor hallucis longus Flexor digit minimi brevis Flexor digitorum longus


Extension (B)

Extensor hallucis longus Extensor digitorum longus Extensor digitorum brevis Abduction (C) Abductor hallucis Abductor digiti minimi Dorsal interossei Adduction (D) Adductor hallucis Plantar interossei Interphalangeal joints Flexion (fig. A) Flexor hallucis longus Flexor digitorum longus Flexor digitorum brevis Quadratus plantae Extension (fig. B) Extensor hallucis longus Extensor digitorum longus Extensor digitorum brevis a Muscles in boldface are chiefly responsible for the movement; the other muscles assist them.


Figure 5.67. Plantar ligaments. A and B. Deep dissection of the sole of the right foot showing the attachments of the ligaments and the long tendons of the long evertor and invertor muscles. The main ligaments from this view are the plantar calcaneonavicular and the long and short plantar ligaments.

Major Ligaments of the Foot The major ligaments of the plantar aspect of the foot (Fig. 5.67) are the: 

Plantar calcaneonavicular ligament (spring ligament), which extends across and fills a wedge‐shaped gap between the talar shelf and the inferior margin of the posterior articular surface of the navicular (Fig. 5.67A & B). The spring ligament supports the head of the talus and plays important roles in the transfer of weight from the talus and in maintaining the longitudinal arch of the foot, of which it is the keystone (superiormost element).

Chapter 5: Lower Limb 



Long plantar ligament, which passes from the plantar surface of the calcaneus to the groove on the cuboid. Some of its fibers extend to the bases of the metatarsals, thereby forming a tunnel for the tendon of the fibularis longus (Fig. 5.67A). The long plantar ligament is important in maintaining the longitudinal arch of the foot. Plantar calcaneocuboid ligament (short plantar ligament), which is located on a plane between the plantar calcaneonavicular and the long plantar ligaments (Fig. 5.67B). It extends from the anterior aspect of the inferior surface of the calcaneus to the inferior surface of the cuboid. It is also involved in maintaining the longitudinal arch of the foot.

Arches of the Foot If the feet were more rigid structures, each impact with the ground would generate extremely large forces of short duration (shocks) that would be propagated through the skeletal system. Because the foot is composed of numerous bones connected by ligaments, it has considerable flexibility that allows it to deform with each ground contact, thereby absorbing much of the shock. Furthermore, the tarsal and metatarsal bones are arranged in longitudinal and transverse arches passively supported and actively restrained by flexible tendons that add to the weight‐bearing capabilities and resiliency of the foot. Thus much smaller forces of longer duration are transmitted through the skeletal system. The arches distribute weight over the pedal platform (foot), acting not only as shock absorbers but also as springboards for propelling it during walking, running, and jumping. The resilient arches add to the foot's ability to adapt to changes in surface contour. The weight of the body is transmitted to the talus from the tibia. Then it is transmitted posteriorly to the calcaneus and anteriorly to the “ball of the foot” (the sesamoids of the 1st metatarsal and the head of the 2nd metatarsal), and that weight/pressure is shared laterally with the heads of the 3rd—5th metatarsals as necessary for balance and comfort (Fig. 5.68). Between these weight‐bearing points are the relatively elastic arches of the foot, which become slightly flattened by body weight during standing. They normally resume their curvature (recoil) when body weight is removed. The longitudinal arch of the foot is composed of medial and lateral parts (Fig. 5.69). Functionally, both parts act as a unit with the transverse arch of the foot, spreading the weight in all directions. The medial longitudinal arch is higher and more important than the lateral longitudinal arch (Fig. 5.69A & D). The medial longitudinal arch is composed of the calcaneus, talus, navicular, three cuneiforms, and three metatarsals. The talar head is the keystone of the medial longitudinal arch. The tibialis anterior, attaching to the 1st metatarsal and medial cuneiform, helps strengthen the medial longitudinal arch. The fibularis longus tendon, passing from lateral to medial, also helps support this arch (Fig. 5.69A). The lateral longitudinal arch is much flatter than the medial part of the arch and rests on the ground during standing (Fig. 5.69B & D). It is made up of the calcaneus, cuboid, and lateral two metatarsals.


Figure 5.68. Weight‐bearing areas of foot. Body weight is divided approximately equally between the hindfoot (calcaneus) and the forefoot (heads of the metatarsals). The forefoot has five points of contact with the ground: a large medial one that includes the two sesamoid bones associated with the head of the 1st metatarsal and the heads of the lateral four metatarsals. The 1st metatarsal supports the major share of the load, with the lateral forefoot providing balance.

The transverse arch of the foot runs from side to side (Fig. 5.69C). It is formed by the cuboid, cuneiforms, and bases of the metatarsals. The medial and lateral parts of the longitudinal arch serve as pillars for the transverse arch. The tendons of the fibularis longus and tibialis posterior, crossing under the sole of the foot like a stirrup (Fig. 5.69C), help maintain the curvature of the transverse arch. The integrity of the bony arches of the foot is maintained by both passive factors and dynamic supports (Fig. 5.69E). Passive factors involved in forming and maintaining the arches of the foot include  

The shape of the united bones (both arches, but especially the transverse arch). Four successive layers of fibrous tissue that bowstring the longitudinal arch (superficial to deep): o Plantar aponeurosis. o Long plantar ligament. o Plantar calcaneocuboid (short plantar) ligament. o Plantar calcaneonavicular (spring) ligament.


Figure 5.69. Arches of foot. A and B. The medial longitudinal arch is higher than the lateral longitudinal arch, which may contact the ground when standing erect. C. The transverse arch is demonstrated at the level of the cuneiforms, receiving stirrup‐like support from a major invertor (tibialis posterior) and evertor (fibularis longus). D. The components of the medial (dark gray) and lateral (light gray) longitudinal arches are indicated. The calcaneus (medium gray) is common to both. The medial arch is primarily weight bearing, whereas the lateral arch provides balance. E. The active (red lines) and passive (gray) supports of the longitudinal arches are represented. There are four layers of passive support (1—4).

Dynamic supports involved in maintaining the arches of the foot include  

Active (reflexive) bracing action of intrinsic muscles of foot (longitudinal arch). Active and tonic contraction of muscles with long tendons extending into foot: o Flexors hallucis and digitorum longus for the longitudinal arch. o Fibularis longus and tibialis posterior for the transverse arch.

Of these factors, the plantar ligaments and the plantar aponeurosis bear the greatest stress and are most important in maintaining the arches of the foot.


The Bottom Line Functionally, there are three compound joints in the foot: (1) the clinical subtalar joint between the talus and the calcaneus, where inversion and eversion occur about an oblique axis; (2) the transverse tarsal joint, where the midfoot and forefoot rotate as a unit on the hindfoot around a longitudinal axis, augmenting inversion and eversion; and (3) the remaining joints of the foot, which allow the pedal platform (foot) to form dynamic longitudinal and transverse arches. The arches provide the resilience necessary for walking, running, and jumping, and are maintained by four layers of passive, fibrous support plus the dynamic support provided by the intrinsic muscles of the foot and the long fibular, tibial, and flexor tendons.

Hallux Valgus Hallux valgus is a foot deformity caused by pressure from footwear and degenerative joint disease; it is characterized by lateral deviation of the great toe (Fig. B5.34). The L in valgus indicates l ateral deviation. In some people, the painful deviation is so large that the great toe overlaps the 2nd toe (Fig. B5.34A), and there is a decrease in the medial longitudinal arch. Such deviation occurs especially in females, and its frequency increases with age. These individuals cannot move their 1st digit away from their 2nd digit because the sesamoids under the head of the 1st metatarsal are usually displaced and lie in the space between the heads of the 1st and 2nd metatarsals (Fig. B5.34B). The 1st metatarsal shifts medially and the sesamoids shift laterally. Often the surrounding tissues swell and the resultant pressure and friction against the shoe cause a subcutaneous bursa to form; when tender and inflamed, the bursa is called a bunion (Fig. B5.34A). Often hard corns (inflamed areas of thick skin) also form over the proximal interphalangeal joints, especially the little toe.

Hammer Toe Hammer toe is a foot deformity in which the proximal phalanx is permanently and markedly dorsiflexed (hyperextended) at the metatarsophalangeal joint and the middle phalanx strongly plantarflexed at the proximal interphalangeal joint. The distal phalanx of the digit is often also hyperextended. This gives the digit (usually the 2nd) a hammer‐like appearance (Fig. B5.35A). This deformity of one or more toes may result from weakness of the lumbrical and interosseous muscles, which flex the metatarsophalangeal joints and extend the interphalangeal joints. A callosity or callus, hard thickening of the keratin layer of the skin, often develops where the dorsal surface of the toe repeatedly rubs on the shoe.


Figure B5.34

Figure B5.35

Claw Toes Claw toes are characterized by hyperextension of the metatarsophalangeal joints and flexion of the distal interphalangeal joints (Fig. B5.35B). Usually, the lateral four toes are involved. Callosities develop on the dorsal surfaces of the toes because of pressure of the shoe. They may also form on the plantar surfaces of the metatarsal heads and the toe tips because they bear extra weight when claw toes are present.


Pes Planus (Flatfeet) The flat appearance of the foot before age 3 is normal and results from the thick subcutaneous fat‐pad in the sole. As children get older, the fat is lost, and a normal medial longitudinal arch becomes visible (Fig. B5.35C). Flatfeet can either be flexible (flat, lacking a medial arch, when weight bearing but normal in appearance when not bearing weight [Fig. B5.35D]) or rigid (flat even when not bearing weight). The more common flexible flatfeet result from loose or degenerated intrinsic ligaments (inadequate passive arch support). Flexible flatfoot is common in childhood but usually resolves with age as the ligaments grow and mature. The condition occasionally persists into adulthood and may or may not be symptomatic. Rigid flatfeet with a history that goes back to childhood are likely to result from a bone deformity (such as a fusion of adjacent tarsal bones). Acquired flatfeet (“fallen arches” ) are likely to be secondary to dysfunction of the tibialis posterior (dynamic arch support) owing to trauma, degeneration with age, or denervation. In the absence of normal passive or dynamic support, the plantar calcaneonavicular ligament fails to support the head of the talus. Consequently, the talar head displaces inferomedially and becomes prominent (Fig. B5.35D, red arrow). As a result, some flattening of the medial part of the longitudinal arch occurs, along with lateral deviation of the forefoot. Flatfeet are common in older people, particularly if they undertake much unaccustomed standing or gain weight rapidly, adding stress on the muscles and increasing the strain on the ligaments supporting the arches.

Clubfoot (Talipes) Clubfoot refers to a foot that is twisted out of position. Of the several types, all are congenital (present at birth). Talipes equinovarus, the common type (2 per 1000 live births), involves the subtalar joint; boys are affected twice as often as girls. The foot is inverted, the ankle is plantarflexed, and the forefoot is adducted (turned toward the midline in an abnormal manner) (Fig. B5.36). The foot assumes the position of a horse's hoof, hence the prefix “equino” (L. equinus, horse). In half of those affected, both feet are malformed. A person with an uncorrected clubfoot cannot put the heel and sole flat and must bear the weight on the lateral surface of the forefoot. Consequently, walking is painful. The main abnormality is shortness and tightness of the muscles, tendons, ligaments, and joint capsules on the medial side and posterior aspect of the foot and ankle.


Figure B5.36

Surface Anatomy of the Ankle and Foot The surface anatomy of the bones of the foot was presented earlier in this chapter (see “Surface Anatomy of the Bones of the Foot” ). If the foot is actively inverted, the tendon of the tibialis posterior may be palpated as it passes posterior and distal to the medial malleolus, then superior to the talar shelf, to reach its attachment to the tuberosity of the navicular. Hence the tibialis posterior tendon is the guide to the navicular. The tendon of the tibialis posterior also indicates the site for palpating the posterior tibial pulse (halfway between the medial malleolus and the calcaneal tendon). The talar shelf (L. sustentaculum tali), approximately 2 cm distal to the tip of the medial malleolus, is best felt by palpating it from below where it is somewhat obscured by the tendon of the flexor digitorum longus, which crosses it (Fig. SA5.4B). On the lateral side, when the foot is inverted, the lateral margin of the anterior surface of the calcaneus is uncovered and palpable. This indicates the site of the calcaneocuboid joint. When the foot is plantarflexed, the head of the talus is exposed. Palpate it dorsal to where the anterior surface of the calcaneus is felt. The calcaneal tendon at the posterior aspect of the ankle is easily palpated and traced to its attachment to the calcaneal tuberosity. In the depression on each side of the tendon, the ankle joint is superficial. When the joint is overfilled with fluid, these depressions may be obliterated. The tendons in the ankle region can be identified satisfactorily only when their muscles are acting. The tendons of the fibularis longus and brevis may be followed distally, posterior and inferior to the lateral malleolus, and then anteriorly along the lateral aspect of the foot (Fig. SA5.4C). The fibularis longus tendon can be palpated as far as the cuboid, and then it disappears as it turns into the sole. The fibularis brevis tendon can easily be traced to its attachment to the dorsal surface of the tuberosity on the base of the 5th metatarsal. This tuberosity is located at the middle of the lateral border of the foot. With toes actively extended, the small fleshy belly of the extensor digitorum brevis may be seen and palpated anterior to the lateral malleolus. Its position should be observed and palpated so that it may not be mistaken subsequently for an abnormal edema. The metatarsophalangeal joint of the great toe lies distal to the knuckle formed by the head of the 1st metatarsal (Fig. SA5.4A). Gout, a metabolic disorder, commonly causes edema and tenderness of this joint, as does osteoarthritis (degenerative joint


disease). Severe pain in the 1st metatarsophalangeal joint is called podagra (from G. pous + G. agra, a seizure). Often the 1st metatarsophalangeal joint is the first one affected by arthritis. The tendons on the anterior aspect of the ankle (from medial to lateral side) are easily palpated when the foot is dorsiflexed. 



 

The large tendon of the tibialis anterior leaves the cover of the superior extensor tendon (Fig. SA5.4A), from which level the tendon is invested by a continuous synovial sheath; the tendon may be traced to its attachment to the 1st cuneiform and the base of the 1st metatarsal. The tendon of the extensor hallucis longus, obvious when the great toe is dorsiflexed against resistance, may be followed to its attachment to the base of the distal phalanx of the great toe. The tendons of the extensor digitorum longus may be followed easily to their attachments to the lateral four toes (Fig. SA5.4C). The tendon of the fibularis tertius may also be traced to its attachment to the base of the 5th metatarsal. This muscle is of minor importance and may be absent.

The transverse tarsal joint is indicated by a line from the posterior aspect of the tuberosity of the navicular to a point halfway between the lateral malleolus and the tuberosity of the 5th metatarsal (Table 5.18).


Figure SA5.4


Medical Imaging of the Lower Limb Radiography Pelvic Girdle and Hip Joint Radiographs of the pelvis and hip show bone and joint abnormalities or malalignment. In the AP projection of the hip joint shown in Figure 5.70A, the patient is in the supine position on the radiographic table. The central X‐ray beam is centered over the hip joint (see orientation figures). Superimposed on the femoral head is the posterior rim of the acetabulum (PR). At the junction of the femoral neck and shaft, the greater and lesser trochanters may be seen. Between the trochanters is an oblique line cast by the superimposed intertrochanteric line and crest (IC). When viewing a full‐size radiograph of the hip joint (i.e., on film or a monitor), observe the architecture of the trabecular bone of the head, neck, and proximal shaft of the femur. The strength of the angled bone depends on this structure. In a healthy femur without osteoporosis, the trabeculae correspond to tension and pressure lines reflecting the weight‐bearing function of this bone. The dense compact bone appears transparent (white), whereas the less dense spongy bone appears dark. Extrapolated lines and curves superimposed on the radiographic image (e.g., the Kohler, Shenton, and iliofemoral lines in Figure 5.70A) in specific views are used to assess normal alignment of bony features. Interrupted lines, irregular curve or lack of symmetry between left and right sides indicates dislocations, fractures, or slipped epiphyses. To ensure detection of a fracture of the femoral neck, several views must be obtained (Fig. 5.70B).

Knee Joint Multiple radiographic projections (AP, lateral, and oblique) are necessary to evaluate the knee properly. In an AP projection of the knee joint (Fig. 5.71B), the person is in the supine position with the knee extended. The central X‐ray beam is directed through the joint cavity. Outlines of the femoral and tibial condyles and the shadows of the patella are superimposed over the distal end of the femur. The joint cavity appears large because the menisci are not visible. The menisci can be visualized if air or opaque fluid is injected into the joint cavity. The adductor tubercle is evident just superior to the medial epicondyle of the femur. The lateral femoral epicondyle appears more prominent than the medial one. The intercondylar fossa is opposite the medial and lateral tubercles of the intercondylar eminence of the proximal tibia. The articular surfaces of the condyles of the tibia are concave in an AP view.


Figure 5.70. Radiographs of normal hip joint. A. On the femur, observe the head, neck, greater trochanter, intertrochanteric crest (IC), and shaft. On the hip bone, observe the lunate surface of the acetabulum, the posterior rim of the acetabulum (PR), the anterior superior iliac spine (ASIS), the ischial spine, and the sacroiliac joint. Several different lines and curvatures are used in the detection of hip abnormalities (dislocations, fractures or slipped epiphyses). The Kohler line (A) is normally tangential to the pelvic inlet and the obturator foramen. The acetabular fossa should lie lateral to this line. A fossa that crosses the line suggests an acetabular fracture with inward displacement. The Shenton line (B) and the iliofemoral line (C) should appear in a normal AP radiograph as smooth, continuous lines that are bilaterally symmetrical. The Shenton line is a radiographic indication of the angle of inclination. B. In this view the left thigh was abducted. Observe the acetabular fossa, anterior inferior iliac spine (AIIS), head of the femur (H), neck of the femur (N), greater trochanter (G), lesser trochanter (L), intertrochanteric crest (IC), and shaft of femur (S).

Figure 5.71. Knee joint. A and B. The orientation drawing depicts the structures visible in the AP radiograph of the right knee joint.


In the lateral projection of an arthrogram of the knee joint shown in Figure 5.72, the knee is slightly flexed. A contrast medium was injected through the joint capsule to show the joint cavity and the extent of the synovial membrane. The articular cartilage on the femoral condyle is radiolucent and the fibrous layer of the joint capsule, lined with synovial membrane, is distinct. The large suprapatellar bursa is continuous with the joint cavity. Although MRI has largely replaced arthrography, it is sometimes useful for detecting loose articular bodies if the MRI is inconclusive.

Ankle Joint and Foot The most common radiographic views of the ankle joint and foot are lateral and AP. A lateral radiograph is taken with the lateral malleolus placed against the X‐ray detector (Fig. 5.73A). In Figure 5.73, the articulation of the convex surface of the trochlea of the talus (T) with the malleoli of the tibia and fibula is apparent, and shadows of the malleoli are visible. The neck (N) and head (H) of the talus, the disc‐ shaped navicular (Na), and the talonavicular joint can be seen. The calcaneus (Ca) and cuboid (C) articulate at the calcaneocuboid joint. The tarsal sinus (TS), the space between the calcaneus and talus, contains the interosseous talocalcaneal ligament. Figure 5.72. Arthrogram of knee joint. Contrast medium was injected into the synovial cavity. The knee is slightly flexed. The large suprapatellar bursa communicates with the knee joint cavity.


Figure 5.73. Radiographs of lower leg, ankle, and foot. A. The left foot is shown in a neutral position. B. The left foot, in slight plantarflexion, is shown. C. The left ankle is shown. C, cuboid; Ca, calcaneus; H, head of talus; L, lateral malleolus; M, medial malleolus; N, neck of talus; Na, navicular; T, talus; TS, tarsal sinus (tunnel). (Part C Courtesy of Dr. P. Bobechko and Dr. E. Becker, Department of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.)

In the dorsoplantar projection, the patient is supine with the knee flexed, and the plantar surface of the foot is placed on the X‐ray detector (Fig. 5.73B). The central X‐ ray beam is centered on the base of the 3rd metatarsal. This view demonstrates the phalanges and interphalangeal joints. However, because the toes are in slight flexion, the interphalangeal joints of the 2nd—5th toes are not clear. The sesamoids on the plantar surface of the head of the 1st metatarsal are evident, as is the articulation of the base of the 1st metatarsal with the medial cuneiform and the base of the 2nd metatarsal. The bases of the 2nd—5th metatarsals overlap, so the intermetatarsal joints are easy to see. The tarsal bones overlap somewhat because of the normal curvature of the foot. Consequently, all the tarsal joints do not show clearly. Only anterior parts of the talus and calcaneus are visible because of the overlap of the malleoli.


An AP radiograph is taken with the person in the supine position with the foot dorsiflexed to a right angle and the great toe pointed slightly medially (Fig. 5.73C). To visualize all the bones and joints of the ankle and foot, other projections are required.

Arteriography Visualization of arteries by X‐ray imaging after injection of a radiopaque contrast medium is a helpful way of studying selected arteries to determine the existence of abnormalities such as popliteal aneurysm (circumscribed dilation of the popliteal artery). In a popliteal arteriogram (Fig. 5.74), the radiopaque material is injected into the femoral artery and spreads through the popliteal artery and its branches, the tibial and fibular arteries.

Computed Tomography CT uses X‐rays that pass through the limb at various angles; however, the images are created by computer reconstructions of the data. CT scans can be set to display soft tissues or bone. Hypodense areas on CT scans suggest strains (swelling), and hyperdense areas suggest hematomas. CT of the knee (arthrotomography) provides a reliable assessment of the cruciate ligaments, menisci, patellar cartilage, and localizes of osteochondral defects and loose bodies.

Magnetic Resonance Imaging MRI produces images of exquisite resolution of limbs without the use of radiation. MRI scanning requires the individual to keep the limbs motionless for 5—10 min. MRIs show much more detail in the soft tissues than do radiographs or CTs (Figs. 5.75, 5.76, 5.77 and 5.78).

Hip Joint In Figure 5.75, observe that the joint capsule of the joint is thick near the iliofemoral ligament and thin posterior to the psoas bursa and tendon. In sections at this level, the femoral sheath, which encloses the femoral artery, vein, lymph node, lymphatic vessels, and fat, protrudes into the subcutaneous tissue. The loose connective tissue nearly surrounds it except posteriorly where, between the iliopsoas and the pectineus, it is attached to the capsule of the hip joint. The femoral artery is separated from the hip joint by the iliopsoas muscle and/or tendon. In the interval between the iliopsoas, the pectineus, and the femoral nerve, the femoral vein lies between the iliopsoas and its fascia.

Knee MRIs are extremely helpful for determining if there are injuries to the menisci, collateral ligaments, and cruciate ligaments (Fig. 5.76). It is the procedure of choice for assessing internal derangements of the knee.


Figure 5.74. Popliteal arteriogram. The popliteal artery begins at the site of the adductor hiatus (where it may be compressed) and then lies successively on the distal end of the femur, joint capsule of the knee joint, and popliteus muscle (not visible) before dividing into the anterior and posterior tibial arteries at the inferior angle of the popliteus fossa. Here it is subject to entrapment as it passes beneath the tendinous arch of the soleus muscle. (Courtesy of Dr. K. Sniderman, Associate Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada)


Figure 5.75. Sectional and radiographic anatomy of gluteal region and proximal anterior thigh at level of hip joint. A and B. A descriptive drawing and transverse (axial MRI) study of an anatomical section of the thigh are shown. C. The orientation drawing shows the level of the section.

Figure 5.76. Sectional anatomy of knee joint. A and B. The orientation drawing depicts the structures visible in the coronal MRI of the knee joint. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Magnetic Resonance Centre, Toronto, Ontario, Canada.)


Figure 5.77. Transverse MRIs of lower limb, from below. A. Sections at the mid‐thigh level (A) and mid‐ leg level (B) are shown.

Figure 5.78. Sectional anatomy of ankle region. A and B. The orientation drawing depicts the structures visible in the MRI of the ankle. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Magnetic Resonance Centre, Toronto, Ontario, Canada.)

Thigh, Leg, and Ankle MRIs are helpful for identifying the soft tissue (such as muscle) and osseous and neurovascular anatomy of the thigh and leg (Fig. 5.77). In the coronal MRI shown in Figure 5.78, the tibia rests on the talus and the talus rests on the calcaneus. Between the calcaneus and the skin, several encapsulated cushions of fat are evident. It is also


clearly seen that the lateral malleolus descends much farther inferiorly than the medial malleolus. In the anatomical coronal section, the interosseous band between the talus and calcaneus separates the subtalar joint from the talocalcaneonavicular joint. Both the anatomical section and the MRI demonstrate the talar shelf acting as a pulley for the flexor hallucis longus and giving attachment to the calcaneotibial band of the medial ligament.

Footnote 1

Because of its anterior position, the tensor of the fascia lata is often studied with the anterior thigh muscles for convenience (i.e., when the cadaver is supine); however, it is actually part of the gluteal group, and will be included with that group in this book.


References and Suggested Readings Anderson MK, Hall SJ, Martin M: Sports Injury Management, 2nd ed. Baltimore, Lippincott Williams & Wilkins, 2000. Birrer RB (ed): Sports Medicine for the Primary Care Physician, 2nd ed. Boca Raton, FL, CRC Press, 1994. Clay JH, Pounds DM: Basic Clinical Message Therapy: Integrating Anatomy and Treatment. Baltimore, Lippincott Williams & Wilkins, 2003. Foerster O: The dermatomes in man. Brain 56:1, 1933. Frick H, Leonhardt H, Starck D: Human Anatomy 1: General Anatomy, Special Anatomy: Limbs, Trunk Wall, Head and Neck. Stuttgart, Thieme, 1991. Ger R, Sedlin E: The accessory soleus muscle. Clin Orthop 116: 200, 1976. Gross A: Orthopedic surgery adult. In Gross A, Gross P, Langer B (eds): Surgery: A Complete Guide for Patients and Their Families. Toronto, Harper & Collins, 1989. Hamill J, Knutzen KM: Biomechanical Basis of Human Movement. Baltimore, Lippincott Williams & Wilkins, 1995. Jenkins DB: Hollinshead's Functional Anatomy of the Limbs and Back, 8th ed. Philadelphia, Saunders, 2002. Kapandji IA: The Physiology of the Joints, Vol. 2. Lower Limb, 5th ed. Edinburgh, UK, Churchill Livingstone, 1987. Keegan JJ, Garrett FD: The segmental distribution of the cutaneous nerves in the limbs of man. Anat Rec 102:409, 1948. Lawson, JP: Clinically significant radiologic anatomic variants of the skeleton. Am J Radiol 163:249, 1994. Levandowski R, Difiori JP: Thigh injuries. In Birrer RB (ed): Sports Medicine for the Primary Care Physician, 2nd ed. Boca Raton, FL, CRC Press, 1994. Markhede G, Stener G: Function after removal of various hip and thigh muscles for extirpation of tumors. Acta Orthop Scand 52:373, 1981. Middleton JA, Kolodon EL. Plantar fasciitis: Heel pain in athletes. J Ath Train 27:70, 1992. Moore KL, Persaud TVN: The Developing Human. Clinically Oriented Embryology, 7th ed., Philadelphia, Saunders, 2003. Palastanga N, Field D, Soames R: Anatomy and Human Movement, 4th ed., Oxford, UK, Butterworth‐Heinemann, 2002.


Rose J, Gamble JG: Human Walking, 2nd ed., Baltimore, Lippincott Williams & Wilkins, 1994. Salter RB: Orthopedic surgery pediatric. In Gross A, Gross P, Langer B (eds): Surgery: A Complete Guide for Patients and Their Families. Toronto, Harper & Collins, 1989. Salter RB: Textbook of Disorders and Injuries of the Musculoskeletal System, 3rd ed. Baltimore, Lippincott Williams & Wilkins, 1999. Slaby FJ, McCune SK, Summers RW: Gross Anatomy in the Practice of Medicine. Baltimore, Lea & Febiger, 1994. Soames RW: Arthroscopy of the knee. In Williams PH, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ (eds): Gray's Anatomy, 38th ed. New York, Churchill Livingstone, 1995. Soderberg GL: Kinesiology: Application to Pathological Motion. Baltimore: Williams & Wilkins, 1986. Swartz MH: Textbook of Physical Diagnosis, 4th ed. Philadelphia, Saunders, 2002. Williams PH, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ: Gray's Anatomy, 38th ed. New York, Churchill Livingstone, 1995.


Chapter 6: Upper Limb

Overview The upper limb is characterized by its mobility and ability to grasp, strike, and conduct fine motor skills (manipulation). These characteristics are especially marked in the hand when performing manual activities such as buttoning a shirt. Synchronized interplay occurs between the joints of the upper limb to coordinate the intervening segments to perform smooth, efficient motion at the most workable distance or position required for a specific task. Efficiency of hand function results in large part from the ability to place it in the proper position by movements at the scapulothoracic, glenohumeral, elbow, radioulnar, and wrist joints. The upper limb consists of four segments (Fig. 6.1): 







Shoulder: proximal segment of the limb that overlaps parts of the trunk (thorax and back) and lower lateral neck. It includes the pectoral, scapular, and lateral supra‐clavicular regions and is built on half of the pectoral girdle. The pectoral (shoulder) girdle is a bony ring, incomplete posteriorly, formed by the scapulae and clavicles and completed anteriorly by the manubrium of the sternum (part of the axial skeleton). Arm (L. brachium): first segment of the free upper limb (more mobile part of the upper limb independent of the trunk) and the longest segment of the limb. It extends between and connects the shoulder and the elbow and is centered around the humerus. Forearm (L. antebrachium): second longest segment of the limb. It extends between and connects the elbow and the wrist and contains the ulna and radius. Hand (L. manus): part of the upper limb distal to the forearm that is formed around the carpus, metacarpus, and phalanges. It is composed of the wrist, palm, dorsum of hand, and fingers (including an opposable thumb) and is richly supplied with sensory endings for touch, pain, and temperature.

Upper Limb Injuries Because the disabling effects of an injury to the upper limb, particularly the hand, are far out of proportion to the extent of the injury, a sound understanding of the structure and function of the upper limb is of the highest importance. Knowledge of its structure without an understanding of its functions is almost useless clinically because the aim of treating an injured limb is to preserve or restore its functions.

Comparison of the Upper and Lower Limbs Developing in a similar fashion (see Chapter 5), the upper and lower limbs share many common features. However, they are sufficiently distinct in structure to enable markedly different functions and abilities. Because the upper limb is not usually involved in weight bearing or motility, its stability has been sacrificed to gain


mobility. The upper limb still possesses remarkable strength. And because of the hand's ability to conform to a paddle or assume a gripping or platform configuration, it may assume a role in motility in certain circumstances. Both the upper and the lower limbs are connected to the axial skeleton (cranium, vertebral column, and associated thoracic cage) via the bony pectoral and pelvic girdles, respectively. The pelvic girdle consists of the two hip bones connected to the sacrum (see Chapter 5). The pectoral girdle consists of the scapulae and clavicles, connected to the manubrium of the sternum. Both girdles possess a large flat bone located posteriorly, which provides for attachment of proximal muscles and connects with its contralateral partner anteriorly via small bony braces, the pubic rami and clavicles. However, the flat iliac bones of the pelvic girdle are also connected posteriorly through their primary attachment to the sacrum via the essentially rigid, weight‐ transferring sacroiliac joints. This posterior connection to the axial skeleton places the lower limbs inferior to the trunk, enabling them to be supportive as they function primarily in relation to the line of gravity. Furthermore, because the two sides are connected both anteriorly and posteriorly, the pelvic girdle forms a complete rigid ring that limits mobility, making the movements of one limb markedly affect the movements of the other. The pectoral girdle, however, is connected to the trunk only anteriorly via the sternum by flexible joints with 3° of freedom and is an incomplete ring because the scapulae are not connected with each other posteriorly. Thus the motion of one upper limb is independent of the other, and the limbs are able to operate effectively anterior to the body, at a distance and level that enables precise eye—hand coordination. Figure 6.1. Regions and bones of upper limb. The joints divide the superior appendicular skeleton, and thus the limb itself, into four main regions: shoulder, arm, forearm, and hand.


In both the upper and the lower limbs, the long bone of the most proximal segment is the largest and is unpaired. The long bones increase progressively in number but decrease in size in the more distal segments of the limb. The second most proximal segment of both limbs (i.e., the leg and forearm) has two parallel bones, although only in the forearm do both articulate with the bone of the proximal segment and only in the leg do both articulate directly with the distal segment. While the paired bones of both the leg and forearm flex and extend as a unit, only those of the upper limb are able to move (supinate and pronate) relative to each other, the bones of the leg being fixed in the pronated position. The wrist and ankle have a similar number of short bones (eight and seven, respectively). Both groups of short bones interrupt a series of long bones that resumes distally with several sets of long bones of similar lengths, with a similar number of joints of essentially the same type. The digits of the upper limb (fingers including the thumb) are the most mobile parts of either limb, but all the other parts of the upper limb are more mobile than the comparable parts of the lower limb.

The Bottom Line Although the upper and lower limbs have much in common regarding their development and structure, the upper limb has evolved into a mobile organ of manipulation that, along with the brain, allows humans not only to respond to their environments but to manipulate and control them to a large degree. The upper limb is composed of four increasingly mobile segments, the proximal three (shoulder, arm, and forearm) serving primarily to position the fourth (hand), which is for grasping, manipulation and touch. Four distinctions from the lower limbs enable the independent operation of the upper limbs, allowing the hands to be precisely positioned anterior to the body at a distance and height that enables accurate eye— hand coordination: (1) the upper limbs are not involved in weight bearing or ambulation, (2) the pectoral girdle is attached to the axial skeleton only anteriorly via a very mobile joint, (3) paired bones of the forearm are able to be moved relative to each other, and (4) the hands have long, mobile fingers and an opposable thumb.

Bones of the Upper Limb The pectoral girdle and bones of the free part of the upper limb form the superior appendicular skeleton (Fig. 6.2); the pelvic girdle and bones of the free part of the lower limb form the inferior appendicular skeleton. The superior appendicular skeleton articulates with the axial skeleton only at the sternoclavicular joint, allowing great mobility. The clavicles and scapulae of the pectoral girdle are supported, stabilized, and moved by axioappendicular muscles that attach to the relatively fixed ribs, sternum, and vertebrae of the axial skeleton.


Figure 6.2. Bones of upper limb. A. The right superior appendicular skeleton includes the right half of the pectoral (shoulder) girdle, composed of the right clavicle and scapula, and the skeleton of the free right upper limb, formed by the remaining bones distal to the scapula. B. The superior appendicular and thoracic parts of the axial skeleton demonstrate that the scapula overlaps parts of the 2nd—7th ribs. Only the thin clavicle links the axial and superior appendicular skeletons. Although not a “true” anatomical joint, the scapula rests and moves on (articulates with) the posterosuperior thoracic wall via the physiological “scapulothoracic joint.”

Figure 6.3. Right clavicle. Prominent features of the superior and inferior surfaces of the clavicle are shown. The bone acts as a mobile strut (supporting brace), connecting the trunk to the upper limb.


Clavicle The clavicle (collar bone) connects the upper limb to the trunk (Fig. 6.3). The shaft of the clavicle has a double curve in a horizontal plane. Its medial half is convex anteriorly, and its sternal end is enlarged and triangular where it articulates with the manubrium of the sternum at the sternoclavicular (SC) joint. Its lateral half is concave anteriorly, and its acromial end is flat where it articulates with the acromion of the scapula at the acromioclavicular (AC) joint (Figs. 6.2B and 6.3). The medial two thirds of the shaft of the clavicle are convex anteriorly, whereas the lateral third is flattened and concave anteriorly. These curvatures increase the resilience of the clavicle and give it the appearance of an elongated capital S. The clavicle: 





Serves as a moveable, crane‐like strut (rigid support) from which the scapula and free limb are suspended, keeping them away from the trunk so that the limb has maximum freedom of motion. The strut is movable and allows the scapula to move on the thoracic wall at the “scapulothoracic joint,” 1 increasing the range of motion of the limb. Fixing the strut in position, especially after its elevation, enables elevation of the ribs for deep inspiration. Forms one of the bony boundaries of the cervicoaxillary canal (passageway between the neck and the arm), affording protection to the neurovascular bundle supplying the upper limb. Transmits shocks (traumatic impacts) from the upper limb to the axial skeleton.

Although designated as a long bone, the clavicle has no medullary (marrow) cavity. It consists of spongy (trabecular) bone with a shell of compact bone. The superior surface of the clavicle, lying just deep to the skin and platysma (G. flat plate) muscle in the subcutaneous tissue, is smooth. The inferior surface of the clavicle is rough because strong ligaments bind it to the 1st rib near its sternal end and suspend the scapula from its acromial end. The conoid tubercle, near the acromial end of the clavicle (Fig. 6.3), gives attachment to the conoid ligament, the medial part of the coracoclavicular ligament by which the remainder of the upper limb is passively suspended from the clavicle. Also, near the acromial end of the clavicle is the trapezoid line, to which the trapezoid ligament attaches; it is the lateral part of the coracoclavicular ligament. The subclavian groove (groove for the subclavius) in the medial third of the shaft of the clavicle is the site of attachment of the subclavius muscle. More medially is the impression for the costoclavicular ligament, a rough, often depressed, oval area that gives attachment to the ligament binding the 1st rib (L. costa) to the clavicle, limiting elevation of the shoulder.

Variations of the Clavicle The clavicle varies more in shape than most other long bones. Occasionally, the clavicle is pierced by a branch of the supraclavicular nerve. The clavicle is thicker and more curved in manual workers, and the sites of muscular attachments are more marked. The right clavicle is usually stronger and shorter than the left clavicle.


Fracture of the Clavicle The clavicle is one of the most frequently fractured bones. Clavicular fractures are especially common in children and are often caused by an indirect force transmitted from an outstretched hand through the bones of the forearm and arm to the shoulder during a fall. A fracture may also result from a fall directly on the shoulder. The weakest part of the clavicle is the junction of its middle and lateral thirds. After fracture of the clavicle, the sternocleidomastoid muscle elevates the medial fragment of bone (Fig. B6.1). Because of the subcutaneous position of the clavicles, the end of the superiorly directed fragment is prominent—readily palpable and/or apparent. The trapezius muscle is unable to hold the lateral fragment up owing to the weight of the upper limb, and thus the shoulder drops. The strong coracoclavicular ligament usually prevents dislocation of the AC joint. People with fractured clavicles support the sagging limb with the other limb. In addition to being depressed, the lateral fragment of the clavicle may be pulled medially by the adductor muscles of the arm, such as the pectoralis major. Overriding of the bone fragments shortens the clavicle.

Figure B6.1

The slender clavicles of newborn infants may be fractured during delivery if the neonates are broad shouldered; however, the bones usually heal quickly. A fracture of the clavicle is often incomplete in younger children—that is, it is a greenstick fracture, in which one side of a bone is broken and the other is bent. This fracture was so named because the parts of the bone do not separate; the bone resembles a tree branch (greenstick) that has been sharply bent but not disconnected.


Ossification of the Clavicle The clavicle is the first long bone to ossify (via intramembranous ossification), beginning during the 5th and 6th embryonic weeks from medial and lateral primary centers that are close together in the shaft of the clavicle. The ends of the clavicle later pass through a cartilaginous phase (endochondral ossification); the cartilages form growth zones similar to those of other long bones. A secondary ossification center appears at the sternal end and forms a scale‐like epiphysis that begins to fuse with the shaft (diaphysis) between 18 and 25 years of age and is completely fused to it between 25 and 31 years of age. This is the last of the epiphyses of long bones to fuse. An even smaller scale‐like epiphysis may be present at the acromial end of the clavicle; it must not be mistaken for a fracture. Sometimes fusion of the two ossification centers of the clavicle fails to occur; as a result, a bony defect forms between the lateral and the medial thirds of the clavicle. Awareness of this possible congenital defect should prevent diagnosis of a fracture in an otherwise normal clavicle. When doubt exists, both clavicles are radiographed because this defect is usually bilateral (Ger et al., 1996).

The Bottom Line The subcutaneous clavicle connects the upper limb (superior appendicular skeleton) to the trunk (axial skeleton). It serves as a movable crane‐like strut from which the scapula and free limb are suspended at a distance from the trunk that enables freedom of motion. Shocks received by the upper limb (especially the shoulder) are transmitted through the clavicle, resulting in a fracture that most commonly occurs between its middle and lateral thirds. The clavicle is the first long bone to ossify and the last to be fully formed.

Scapula The scapula (shoulder blade) is a triangular flat bone that lies on the posterolateral aspect of the thorax, overlying the 2nd—7th ribs (Fig. 6.2B). The convex posterior surface of the scapula is unevenly divided by a thick projecting ridge of bone, the spine of the scapula, into a small supraspinous fossa and a much larger infraspinous fossa (Fig. 6.4A). The concave costal surface of most of the scapula forms a large subscapular fossa. The broad bony surfaces of the three fossae provide attachments for fleshy muscles. The triangular body of the scapula is thin and translucent superior and inferior to the scapular spine; although its borders, especially the lateral one, are somewhat thicker. The spine continues laterally as the flat expanded acromion (G. akros, point), which forms the subcutaneous point of the shoulder and articulates with the acromial end of the clavicle. The deltoid tubercle of the scapular spine is the prominence indicating the medial point of attachment of the deltoid. The spine and acromion serve as levers for the attached muscles, particularly the trapezius.


Figure 6.4. Right scapula. A. The bony features of the costal and posterior surfaces of the scapula are demonstrated. B. The scapula is suspended from the clavicle by the coracoclavicular ligament, at which a balance is achieved among the weight of the scapula, its attached muscles, and the muscular activity medially and the weight of the free limb laterally. C. The borders and angles of the scapula are demonstrated.

Because the acromion is a lateral extension of the scapula, the AC joint is placed lateral to the mass of the scapula and its attached muscles (Fig. 6.4B). The glenohumeral (shoulder) joint on which these muscles operate is almost directly inferior to the AC joint; thus the scapular mass is balanced with that of the free limb, and the suspending structure (coracoclavicular ligament) lies between the two masses. Superolaterally, the lateral surface of the scapula has a glenoid cavity (G. socket), which receives and articulates with the head of the humerus at the glenohumeral joint (Fig. 6.4A & B). The glenoid cavity is a shallow, concave, oval fossa (L. fossa ovalis), directed anterolaterally and slightly superiorly, that is considerably smaller than the ball (head of the humerus) for which it serves as socket. The beak‐like coracoid process (G. korakoÃ©dÃ©s, like a crow's beak) is superior to the glenoid cavity and projects anterolaterally. This process also resembles in size, shape, and direction a bent finger pointing to the shoulder, the knuckle of which provides the inferior attachment for the passively supporting coracoclavicular ligament. The scapula has medial, lateral, and superior borders and superior, lateral, and inferior angles (Fig. 6.4C). When the scapular body is in the anatomical position, the thin medial border of the scapula runs parallel to and approximately 5 cm lateral to the spinous processes of the thoracic vertebrae (Fig. 6.2B); hence it is often called the vertebral border (Fig. 6.4C). From the inferior angle, the lateral border of the scapula runs superolaterally toward the apex of the axilla; hence it is often called the axillary border. The lateral border is made up of a thick bar of bone that prevents


buckling of this stress‐bearing region of the scapula. The lateral border terminates in the truncated lateral angle of the scapula, the thickest part of the bone that bears the broadened head of the scapula. The glenoid cavity is the primary feature of the head. The shallow constriction between the head and the body defines the neck of the scapula. The superior border of the scapula is marked near the junction of its medial two thirds and lateral third by the suprascapular notch, which is located where the superior border joins the base of the coracoid process. The superior border is the thinnest and shortest of the three borders. The scapula is capable of considerable movement on the thoracic wall at the physiological scapulothoracic joint, providing the base from which the upper limb operates. These movements, enabling the arm to move freely, are discussed later in this chapter with the muscles that move the scapula.

Fracture of the Scapula Fracture of the scapula is usually the result of severe trauma, as occurs in pedestrian—vehicle accidents. Usually there are also fractured ribs. Most fractures require little treatment because the scapula is covered on both sides by muscles. Most fractures involve the protruding subcutaneous acromion.

The Bottom Line The scapula forms the mobile base from which the free upper limb acts. This triangular flat bone is curved to conform to the thoracic wall and provides large surface areas and edges for attachment of muscles. These muscles (1) move the scapula on the thoracic wall at the physiological scapulothoracic joint and (2) extend to the proximal humerus maintaining the integrity of—and producing motion at—the glenohumeral joint. Its spine and acromion serve as levers; the acromion enables the scapula and attached muscles to be located medially against the trunk with the AC and glenohumeral joints, thereby allowing movement lateral to the trunk. Its coracoid process is the site of attachment for the coracoclavicular ligament that passively supports the upper limb and a site for muscular (tendon) attachment.

Humerus The humerus (arm bone), the largest bone in the upper limb, articulates with the scapula at the glenohumeral joint and the radius and ulna at the elbow joint (Figs. 6.1 and 6.2). The proximal end of the humerus has a head, surgical and anatomical necks, and greater and lesser tubercles. The spherical head of the humerus articulates with the glenoid cavity of the scapula. The anatomical neck of the humerus is formed by the groove circumscribing the head and separating it from the greater and lesser tubercles. It indicates the line of attachment of the glenohumeral joint capsule. The surgical neck of the humerus, a common site of fracture, is the narrow part distal to the head and tubercles. The junction of the head and neck with the shaft of the humerus is indicated by the greater and lesser tubercles, which provide attachment and leverage to some scapulohumeral muscles. The greater tubercle is at the lateral margin of the humerus, whereas the lesser tubercle projects anteriorly from the bone. The intertubercular (bicipital) groove separates the tubercles and provides protected passage for the slender tendon of the long head of the biceps muscle.


The shaft (body) of the humerus has two prominent features: the deltoid tuberosity laterally, for attachment of the deltoid muscle, and the oblique radial groove (groove for radial nerve, spiral groove) posteriorly, in which the radial nerve and deep artery of the arm lie as they pass anterior to the long and between the medial and lateral heads of the triceps brachii muscle. The inferior end of the humeral shaft widens as the sharp medial and lateral supraepicondylar (supracondylar) ridges form and then end distally in the especially prominent medial epicondyle and the lateral epicondyle, providing for muscle attachment. The distal end of the humerus, including the trochlea; the capitulum; and the olecranon, coronoid, and radial fossae, makes up the condyle of the humerus (Fig. 6.5). The condyle has two articular surfaces: a lateral capitulum (L. little head) for articulation with the head of the radius and a medial, spool‐shaped or pulley‐like trochlea (L. pulley) for articulation with the proximal end (trochlear notch) of the ulna. Two hollows or fossae occur back to back superior to the trochlea, making the condyle quite thin between the epicondyles. Anteriorly, the coronoid fossa receives the coronoid process of the ulna during full flexion of the elbow. Posteriorly, the olecranon fossa accommodates the olecranon of the ulna during full extension of the elbow. Superior to the capitulum anteriorly, a shallower radial fossa accommodates the edge of the head of the radius when the forearm is fully flexed.

Figure 6.5. Distal end of right humerus. A and B. Anterior and posterior views illustrate the lateral and medial epicondyles, supraepicondylar ridges, and condyle of the humerus. The condyle (the boundaries of which are indicated by the dashed line) consists of the capitulum; the trochlea; and the radial, coronoid, and olecranon fossae.

Fractures of the Humerus Most injuries of the proximal end of the humerus are fractures of the surgical neck. These injuries are especially common in elderly people with osteoporosis, whose demineralized bones are brittle. Humeral fractures are often result in one fragment being driven into the spongy bone of the other fragment (impacted fracture). The injuries usually result from a minor fall on the hand, with the force being transmitted up the forearm bones of the extended limb. Because of impaction of the fragments, the fracture site is sometimes stable and the person is able to move the arm passively with little pain.


An avulsion fracture of the greater tubercle of the humerus (pulling the tubercle away from the humeral head) is seen most commonly in middle‐aged and elderly people (Fig. B6.2A). The fracture usually results from a fall on the acromion, the point of the shoulder. In younger people, an avulsion fracture of the greater tubercle usually results from a fall on the hand when the arm is abducted. Muscles (especially the subscapularis) that remain attached to the humerus pull the limb into medial rotation.

Figure B6.2. Humeral fractures. A. An avulsion fracture of the greater tubercle of the humerus is shown. B. A transverse fracture of humeral body is demonstrated.

A transverse fracture of the shaft of the humerus frequently results from a direct blow to the arm. The pull of the deltoid muscle carries the proximal fragment laterally (Fig. B6.2B). Indirect injury resulting from a fall on the outstretched hand may produce a spiral fracture of the humeral shaft. Overriding of the oblique ends of the fractured bone may result in foreshortening. Because the humerus is surrounded by muscles and has a well‐developed periosteum, the bone fragments usually unite well. An intercondylar fracture of the humerus results from a severe fall on the flexed elbow. The olecranon of the ulna is driven like a wedge between the medial and lateral parts of the condyle, separating one or both parts from the humeral shaft. The following parts of the humerus are in direct contact with the indicated nerves:    

Surgical neck: axillary nerve. Radial groove: radial nerve. Distal end of humerus: median nerve. Medial epicondyle: ulnar nerve.


These nerves may be injured when the associated part of the humerus is fractured. These injuries are discussed later in this chapter.

The Bottom Line The long, strong humerus is a mobile strut—the first in a series of two—used to position the hand at a height (level) and distance from the trunk to maximize its efficiency. Its spherical head enables a great range of motion on the mobile scapular base, and the trochlea and capitulum at its distal end facilitate the hinge movements of the elbow and, at the same time, the pivoting of the radius. The long shaft of the humerus enables reach and makes it an effective lever for power in lifting as well as providing surface area for attachment of muscles that act primarily at the elbow. Added surface area for attachment of flexors and extensors of the wrist is provided by the epicondyles, the medial and lateral extensions of the shaft.

Bones of the Forearm The two forearm bones serve together to form the second unit of an articulated mobile strut (the first unit being the humerus), with a mobile base formed by the shoulder, that positions the hand. However, because this unit is formed by two parallel bones, one of which (the radius) can pivot about the other (the ulna), supination and pronation are possible. This makes it possible to rotate the hand when the elbow is flexed.

Ulna The ulna is the stabilizing bone of the forearm and is the medial and longer of the two forearm bones (Figs. 6.6 and 6.7). Its more massive proximal end is specialized for articulation with the humerus proximally and the head of the radius laterally. For articulation with the humerus, it has two prominent projections: (1) the olecranon, which projects proximally from its posterior aspect (forming the point of the elbow) and serves as a short lever for extension of the elbow, and (2) the coronoid process, which projects anteriorly. The olecranon and coronoid processes form the walls of the trochlear notch, which in profile resembles the jaws of a crescent wrench as it “grips” (articulates with) the trochlea of the humerus (Fig. 6.6B & C). The articulation between the ulna and the humerus primarily allows only flexion and extension of the elbow joint, although a small amount of abduction—adduction occurs during pronation and supination of the forearm. Inferior to the coronoid process is the tuberosity of the ulna for attachment of the tendon of the brachialis muscle (Fig. 6.6A).


Figure 6.6. Bones of right elbow region. A. The proximal part of the ulna is shown. B. The bones of the elbow region are shown, demonstrating the relationship of the distal humerus and proximal ulna and radius during extension of the elbow joint. C. The relationship of the humerus and forearm bones during flexion of the elbow joint is demonstrated.

Figure 6.7. Right radius and ulna. A and B. The radius and ulna are shown in the articulated position, connected by the interosseous membrane. C and D. The features of the distal ends of the forearm bones include grooves for tendons; a dorsal tubercle of the radius (used as a pulley); and articular surfaces for articulation with (1) each other (ulnar notch of radius, articular circumference of head of ulna; see part A), (2) an articular disc (ulna), and (3) the proximal carpal bones (radius). E. In cross section, the shafts of the radius and ulna appear almost as mirror images of one another for much of the middle and distal thirds of their lengths.


On the lateral side of the coronoid process is a smooth, rounded concavity, the radial notch, which receives the broad periphery of the head of the radius. Inferior to the radial notch on the lateral surface of the ulnar shaft is a prominent ridge, the supinator crest. Between it and the distal part of the coronoid process is a concavity, the supinator fossa. The deep part of the supinator muscle attaches to the supinator crest and fossa. The shaft (body) of the ulna is thick and cylindrical proximally; but it tapers, diminishing in diameter, as it continues distally (Fig. 6.7A). At the narrow distal end of the ulna is a small but abrupt enlargement, the disc‐like head of the ulna with a small, conical ulnar styloid process. The ulna does not reach—and therefore does not participate in—the wrist (radiocarpal) joint.

Radius The radius is the lateral and shorter of the two forearm bones. Its proximal end includes a short head, neck, and medially directed tuberosity (Fig. 6.7A). Proximally, the smooth superior aspect of the discoid head of the radius is concave for articulation with the capitulum of the humerus during flexion and extension of the elbow joint. The head also articulates peripherally with the radial notch of the ulna; thus the head is covered with articular cartilage. The neck of the radius is a constriction distal to the head. The oval radial tuberosity is distal to the medial part of the neck and demarcates the proximal end (head and neck) of the radius from the shaft. The shaft (body) of the radius, in contrast to that of the ulna, gradually enlarges as it passes distally. The distal end of the radius is essentially four sided when sectioned transversely. Its medial aspect forms a concavity, the ulnar notch (Fig. 6.7C & D), which accommodates the head of the ulna. Its lateral aspect becomes increasingly ridge‐like, terminating distally in the radial styloid process. Projecting dorsally, the dorsal tubercle of the radius lies between otherwise shallow grooves for the passage of the tendons of forearm muscles. The radial styloid process is larger than the ulnar styloid process and extends farther distally. This relationship is of clinical importance when the ulna and/or the radius is fractured. Most of the length of the shafts of the radius and ulna are essentially triangular in cross section, with a rounded, superficially directed base and an acute, deeply directed apex (Fig. 6.7E). The apex is formed by a section of the sharp interosseous border of the radius or ulna that connects to the thin, fibrous interosseous membrane of the forearm (Fig. 6.7A, B, & E). The majority of the fibers of the interosseous membrane run an oblique course, passing inferiorly from the radius as they extend medially to the ulna (Fig. 6.7A & B). Thus they are positioned to transmit forces received by the radius (via the hands) to the ulna for transmission to the humerus.

Fractures of the Radius and Ulna Fractures of both the radius and the ulna are usually the result of severe injury. A direct injury usually produces transverse fractures at the same level, usually in the middle third of the bones. Isolated fractures of the radius or ulna also occur. Because


the shafts of these bones are firmly bound together by the interosseous membrane, a fracture of one bone is likely to be associated with dislocation of the nearest joint. Fracture of the distal end of the radius is a common fracture in adults > 50 years of age and occurs more frequently in women because their bones are more commonly weakened by osteoporosis. A complete transverse fracture of the distal 2 cm of the radius, called a Colles fracture, is the most common fracture of the forearm (Fig. B6.3). The distal fragment is displaced dorsally and is often comminuted (broken into pieces). The fracture results from forced dorsiflexion of the hand, usually as the result of trying to ease a fall by outstretching the upper limb. Often the ulnar styloid process is avulsed (broken off). Normally the radial styloid process projects farther distally than the ulnar styloid (Fig. B6.3A); consequently, when a Colles fracture occurs, this relationship is reversed because of shortening of the radius (Fig. B6.3B). This clinical condition is often referred to as a dinner fork (silver fork) deformity because a posterior angulation occurs in the forearm just proximal to the wrist and the normal anterior curvature of the relaxed hand. The posterior bending is produced by the posterior displacement and tilt of the distal fragment of the radius. The typical history of a person with a Colles fracture includes slipping or tripping and, in an attempt to break the fall, landing on the outstretched limb with the forearm and hand pronated. Because of the rich blood supply to the distal end of the radius, bony union is usually good. When the distal end of the radius fractures in children, the fracture line may extend through the distal epiphysial plate. Epiphysial plate injuries are common in older children because of their frequent falls in which the forces are transmitted from the hand to the radius and ulna. The healing process may result in malalignment of the epiphysial plate and disturbance of radial growth.

Figure B6.3. Right wrist. A. A normal wrist is shown. B. A Colles fracture with a dinner fork deformity is demonstrated.

The Bottom Line The ulna and radius together make up the second unit of a two‐unit articulated strut (the first unit being the humerus), projecting from a mobile base (shoulder) that


serves to position the hand. Because the forearm unit is formed by two parallel bones, and the radius is able to pivot about the ulna, supination and pronation of the hand are possible during elbow flexion. Proximally, the larger medial ulna forms the primary articulation with the humerus, whereas distally, the shorter lateral radius forms the primary articulation with the hand via the wrist. Because the ulna does not reach the wrist, forces received by the hand are transmitted from the radius to the ulna via the interosseous membrane.

Bones of the Hand The wrist, or carpus, is composed of eight carpal bones (carpals) arranged in proximal and distal rows of four (Fig. 6.8). These small bones give flexibility to the wrist. The carpus is markedly convex from side to side posteriorly and concave anteriorly. Augmenting movement at the wrist joint, the two rows of carpals glide on each other; in addition, each bone glides on those adjacent to it. From lateral to medial, the four bones in the proximal row of carpals (purple in Fig. 6.8) are the: 







Scaphoid (G. skaphÃ©, skiff, boat): a boat‐shaped bone that articulates proximally with the radius and has a prominent scaphoid tubercle; it is the largest bone in the proximal row of carpals. Lunate (L. luna, moon): a moon‐shaped bone between the scaphoid and the triquetral bones; it articulates proximally with the radius and is broader anteriorly than posteriorly. Triquetrum (L. triquetrus, three‐cornered): a pyramidal bone on the medial side of the carpus; it articulates proximally with the articular disc of the distal radioulnar joint. Pisiform (L. pisum, pea), a small, pea‐shaped bone that lies on the palmar surface of the triquetrum.

From lateral to medial, the four bones in the distal row of carpals (green in Fig. 6.8) are the: 

 



Trapezium (G. trapeze, table): a four‐sided bone on the lateral side of the carpus; it articulates with the 1st and 2nd metacarpals, scaphoid, and trapezoid bones. Trapezoid: a wedge‐shaped bone that resembles the trapezium; it articulates with the 2nd metacarpal, trapezium, capitate, and scaphoid bones. Capitate (L. caput, head): a head‐shaped bone with a rounded extremity and the largest bone in the carpus; it articulates primarily with the 3rd metacarpal distally, and with the trapezoid, scaphoid, lunate, and hamate. Hamate (L. hamulus, a little hook): a wedge‐shaped bone on the medial side of the hand; it articulates with the 4th and 5th metacarpal, capitate, and triquetral bones; it has a distinctive hooked process, the hook of the hamate, that extends anteriorly.

The proximal surfaces of the distal row of carpals articulate with the proximal row of carpals, and their distal surfaces articulate with the metacarpals.


The metacarpus forms the skeleton of the palm of the hand between the carpus and the phalanges. It is composed of five metacarpal bones (metacarpals). Each metacarpal consists of a base, shaft, and head. The proximal bases of the metacarpals articulate with the carpal bones, and the distal heads of the metacarpals articulate with the proximal phalanges and form the knuckles. The 1st metacarpal (of the thumb) is the thickest and shortest of these bones. The 3rd metacarpal is distinguished by a styloid process on the lateral side of its base. Figure 6.8. Bones of right hand. A and B. The skeleton of the hand consists of three segments: carpals of the wrist, metacarpals of the palm, and phalanges of the fingers or digits.

Each digit has three phalanges except for the first (the thumb), which has only two; however, the phalanges of the first digit are stouter than those in the other fingers. Each phalanx has a base proximally, a shaft (body), and a head distally (Fig. 6.8). The proximal phalanges are the largest, the middle ones are intermediate in size, and the distal ones are the smallest. The shafts of the phalanges taper distally. The terminal phalanges are flattened and expanded at their distal ends, which underlie the nail beds.

Fracture of the Scaphoid The scaphoid is the most frequently fractured carpal bone. It often results from a fall on the palm when the hand is abducted, the fracture occurring across the narrow part (“waist” ) of the scaphoid (Fig. B6.4). Pain occurs primarily on the lateral side of the wrist, especially during dorsiflexion and abduction of the hand. Initial radiographs of the wrist may not reveal a fracture; often this injury is (mis‐ )diagnosed as a severely sprained wrist. Radiographs taken 10—14 days later reveal a fracture because bone resorption has occurred there. Owing to the poor blood supply to the proximal part of the scaphoid, union of the fractured parts may take at least 3 months. Avascular necrosis of the proximal fragment of the scaphoid (pathological death of bone resulting from inadequate blood supply) may occur and produce degenerative joint disease of the wrist. In some cases, it is necessary to fuse the carpals surgically (arthrodesis).


Figure B6.4

Fracture of the Hamate Fracture of the hamate may result in non‐union of the fractured bony parts because of the traction produced by the attached muscles. Because the ulnar nerve is close to the hook of the hamate, the nerve may be injured by this fracture, causing decreased grip strength of the hand. The ulnar artery may also be damaged when the hamate is fractured.

Fracture of the Metacarpals The metacarpals (except the 1st) are closely bound together; hence isolated fractures tend to be stable. Furthermore, these bones have a good blood supply, and fractures usually heal rapidly. Severe crushing injuries of the hand may produce multiple metacarpal fractures, resulting in instability of the hand. Fracture of the 5th metacarpal, often referred to as a boxer's fracture, occurs when an unskilled person punches someone with a closed fist. The head of the bone rotates over the distal end of the shaft, producing a flexion deformity.

Fracture of the Phalanges Crushing injuries of the distal phalanges are common (e.g., when a finger is caught in a car door). Because of the highly developed sensation in the fingers, these injuries are extremely painful. A fracture of a distal phalanx is usually comminuted, and a painful hematoma (local collection of blood) soon develops. Fractures of the proximal and middle phalanges are usually the result of crushing or hyperextension injuries. Because of the close relationship of phalangeal fractures to the flexor tendons, the bone fragments must be carefully realigned to restore normal function of the fingers.

The Bottom Line Each segment of the upper limb increases the functionality of the end unit, the hand. Located on the free end of a two‐unit articulated strut (arm and forearm) projecting from a mobile base (shoulder), the hand can be positioned over a wide range relative to the trunk. Its connection to the flexible strut via the multiple small bones of the wrist, combined with the pivoting of the forearm, greatly increases its ability to be


placed in a particular position with the fingers able to flex (push or grip) in the necessary direction. The carpal bones are organized into two rows of four bones each, and as a group articulate with the radius proximally and the metacarpals distally. The highly flexible, elongated fingers—extending from a semirigid base (the palm)—enable the ability to grip, manipulate, or perform complex tasks involving multiple and simultaneous individual motions (e.g., when typing or playing a piano).

Surface Anatomy of the Upper Limb Bones Most bones of the upper limb offer a palpable segment or surface (notable exceptions being the lunate and trapezoid), enabling the skilled examiner to discern abnormalities owing to trauma (fracture or dislocation) or malformation (Fig. SA6.1). The clavicle is subcutaneous and can be easily palpated throughout its length. Its sternal end projects superior to the manubrium (Fig. SA6.1A). Between the elevated sternal ends of the clavicles is the jugular notch (suprasternal notch). The acromial end of the clavicle often rises higher than the acromion, forming a palpable elevation at the acromioclavicular (AC) joint. The acromial end can be palpated 2—3 cm medial to the lateral border of the acromion, particularly when the arm is alternately flexed and extended. Either or both ends of the clavicle may be prominent; when present, this condition is usually bilateral. Note the elasticity of the skin over the clavicle and how easily it can be pinched into a mobile fold. This property of the skin is useful when ligating the third part of the subclavian artery: the skin lying superior to the clavicle is pulled down onto the clavicle and then incised; after the incision is made, the skin is allowed to return to its position superior to the clavicle, where it overlies the artery (thus not endangering it during the incision). The acromion of the scapula is easily felt and often visible. The superior surface of the acromion is subcutaneous and may be traced medially to the AC joint. The lateral and posterior borders of the acromion meet to form the acromial angle (Fig. SA6.1B). Inferior to the acromion, the deltoid muscle forms the rounded curve of the shoulder. The crest of the scapular spine is subcutaneous throughout and easily palpated. When the upper limb is in the anatomical position, the:   

Superior angle of the scapula lies at the level of the T2 vertebra. Medial end of the root of the scapular spine is opposite the spinous process of the T3 vertebra. Inferior angle of the scapula lies at the level of the T7 vertebra, near the inferior border of the 7th rib and 7th intercostal space.

The medial border of the scapula is palpable inferior to the root of the spine of the scapula as it crosses the 3rd—7th ribs; the lateral border of the scapula is not easily palpated because it is covered by the teres major and minor muscles. When the upper limb is abducted and the hand is placed on the back of the head, the scapula is rotated, elevating the glenoid cavity such that the medial border of the scapula parallels the 6th rib and thus can be used to estimate its position and, deep to the rib, the oblique fissure of the lung. The inferior angle of the scapula is easily felt and is often visible. It is grasped when testing movements of the glenohumeral joint to


immobilize the scapula. The coracoid process of the scapula can be felt by palpating deeply at the lateral side of the clavipectoral triangle (Fig. SA6.2).

Figure SA6.1. The head of the humerus is surrounded by muscles, except inferiorly; consequently, it can be palpated only by pushing the fingers well up into the axillary fossa (armpit). The arm should not be fully abducted, otherwise the fascia in the axilla will be tense and impede palpation of the humeral head. When the arm is moved and the scapula is fixed (held in place), the head of the humerus can be palpated. The greater tubercle of the humerus may be felt with the person's arm by the side on deep palpation through the deltoid, inferior to the lateral border of the acromion. In this position, the greater tubercle is the most lateral bony point of the shoulder and, along with the deltoid, gives the shoulder its rounded contour. When the arm is abducted, the greater tubercle is pulled beneath the acromion and is no longer


palpable. The lesser tubercle of the humerus may be felt with difficulty by deep palpation through the deltoid on the anterior aspect of the arm, approximately 1 cm lateral and slightly inferior to the tip of the coracoid process. Rotation of the arm facilitates palpation of this tubercle. The location of the intertubercular groove, between the greater and the lesser tubercles, is identifiable during flexion and extension of the elbow joint by palpating in an upward direction along the tendon of the long head of the biceps brachii as it moves through the intertubercular groove. The shaft of the humerus may be felt with varying distinctness through the muscles surrounding it. No part of the proximal part of the humeral shaft is subcutaneous. The medial and lateral epicondyles of the humerus are subcutaneous and easily palpated on the medial and lateral aspects of the elbow region. The knob‐like medial epicondyle, projecting posteromedially, is more prominent than the lateral epicondyle. When the elbow joint is partially flexed, the lateral epicondyle is visible. When the elbow joint is fully extended, the lateral epicondyle can be palpated but not seen deep to a depression on the posterolateral aspect of the elbow.

Figure SA6.2 The olecranon of the ulna can be easily palpated (Fig. SA6.3). When the elbow joint is extended, observe that the tip of the olecranon and the humeral epicondyles lie in a straight line (Fig. SA6.3A & B). When the elbow is flexed, the olecranon descends until its tip forms the apex of an approximately equilateral triangle, of which the epicondyles form the angles at its base (Fig. SA6.3C). These normal relationships are important in the diagnosis of certain elbow injuries (e.g., dislocation of the elbow joint). The posterior border of the ulna, palpable throughout the length of the forearm, demarcates the posteromedial boundary between the flexor—pronator and the extensor—supinator compartments of the forearm. The head of the ulna forms a


large, rounded subcutaneous prominence that can be easily seen and palpated on the medial side of the dorsal aspect of the wrist, especially when the hand is pronated. The pointed subcutaneous ulnar styloid process may be felt slightly distal to the rounded ulnar head when the hand is supinated. The head of the radius can be palpated and felt to rotate in the depression on the posterolateral aspect of the extended elbow joint, just distal to the lateral epicondyle of the humerus. The radial head can also be palpated as it rotates during pronation and supination of the forearm. The ulnar nerve feels like a thick cord where it passes posterior to the medial epicondyle of the humerus; pressing the nerve here evokes an unpleasant “crazy bone” sensation. The radial styloid process can be easily palpated in the anatomical snuff box on the lateral side of the wrist; it is larger and approximately 1 cm more distal than the ulnar styloid process. The radial styloid process is easiest to palpate when the thumb is abducted. It is overlaid by the tendons of the thumb muscles. Because the radial styloid process extends more distally than the ulnar styloid process, more ulnar deviation than radial deviation of the wrist is possible. The relationship of the radial and ulnar processes is important in the diagnosis of certain wrist injuries (e.g., Colles fracture). Proximal to the radial styloid process, the anterior, lateral, and posterior surfaces of the radius are palpable for several centimeters. The dorsal radial tubercle is easily felt around the middle of the dorsal aspect of the distal end of the radius. The dorsal tubercle acts as a pulley for the long extensor tendon of the thumb, which passes medial to it.

Figure SA6.3


The pisiform can be felt on the anterior aspect of the medial border of the wrist and can be moved from side to side when the hand is relaxed. The hook of the hamate can be palpated on deep pressure over the medial side of the palm, approximately 2 cm distal and lateral to the pisiform. The tubercles of the scaphoid and trapezium can be palpated at the base and medial aspect of the thenar eminence (ball of thumb) when the hand is extended. The metacarpals, although overlain by the long extensor tendons of the digits, can be palpated on the dorsum of the hand. The heads of these bones form the knuckles of the fist; the 3rd metacarpal head is most prominent. The styloid process of the 3rd metacarpal can be palpated approximately 3.5 cm from the dorsal radial tubercle. The dorsal aspects of the phalanges can also be easily palpated. The knuckles of the fingers are formed by the heads of the proximal and middle phalanges. When measuring the upper limb, or segments of it, for comparison with the contralateral limb or with standards for normal limb growth or size, the acromial angle, lateral epicondyle of the humerus, styloid process of the radius, and tip of the third finger are most commonly used as measuring points, with the limb relaxed (dangling) but with palms directed anteriorly.

The Bottom Line The upper limb presents multiple palpable bony features that are useful (1) when diagnosing fractures, dislocations, or malformations; (2) for approximating the position of deeper structures; and (3) for precisely describing the location of incisions and sites for therapeutic puncture or of pathology or injury.

Superficial Structures of the Upper Limb Deep to the skin is subcutaneous tissue (superficial fascia) containing fat and deep fascia surrounding the muscles. If no structure (no muscle, tendon, or bursa, for example) intervenes between the skin and the bone, the deep fascia is usually attached to bone.

Fascia of the Upper Limb The fascia of the pectoral region is attached to the clavicle and sternum. The pectoral fascia invests the pectoralis major and is continuous inferiorly with the fascia of the anterior abdominal wall (Fig. 6.9). The pectoral fascia leaves the lateral border of the pectoralis major and becomes the axillary fascia, which forms the floor of the axilla. Deep to the pectoral fascia and the pectoralis major, another fascial layer, the clavipectoral fascia, descends from the clavicle, enclosing the subclavius and then the pectoralis minor, becoming continuous inferiorly with the axillary fascia. The part of the clavipectoral fascia between the pectoralis minor and the subclavius, the costocoracoid membrane, is pierced by the lateral pectoral nerve, which primarily supplies the pectoralis major. The part of the clavipectoral fascia inferior to the pectoralis minor, the suspensory ligament of the axilla, supports the axillary fascia and pulls it and the skin inferior to it upward during abduction of the arm, forming the axillary fossa. The scapulohumeral muscles that cover the scapula and form the bulk of the shoulder are also ensheathed by deep fascia. The deltoid fascia descends over the superficial surface of the deltoid from the clavicle, acromion, and scapular spine. From the deep surface of the deltoid fascia, numerous septa penetrate between the fascicles (bundles) of the muscle. Inferiorly, the deltoid fascia is continuous with the pectoral


fascia anteriorly and the dense infraspinous fascia posteriorly. The muscles that cover the anterior and posterior surfaces of the scapula are covered superficially with deep fascia, which is attached to the margins of the scapula and posteriorly to the spine of the scapula. This arrangement creates osseofibrous subscapular, supraspinous, and infraspinous compartments; the muscles in each compartment attach to (originate from) the deep surface of the overlying fascia in part, allowing the muscles to have greater bulk (mass) than would be the case if only bony attachments occurred. The supraspinous and infraspinous fascia overlying the supraspinatus and infraspinatus muscles, respectively, on the posterior aspect of the scapula are so dense and opaque that they must be removed during dissection to view the muscles. The brachial fascia, a sheath of deep fascia, encloses the arm like a snug sleeve deep to the skin and subcutaneous tissue (Fig. 6.10A & B); it is continuous superiorly with the deltoid, pectoral, axillary, and infraspinous fasciae. The brachial fascia is attached inferiorly to the epicondyles of the humerus and the olecranon of the ulna and is continuous with the antebrachial fascia, the deep fascia of the forearm. Two intermuscular septa, the medial and lateral intermuscular septa, extend from the deep surface of the brachial fascia to the central shaft and medial and lateral supraepicondylar ridges of the humerus (Fig. 6.10B). These septa divide the arm into anterior (flexor) and posterior (extensor) fascial compartments, each of which contains muscles serving similar functions and sharing common innervation. As discussed in relation to the fascial compartments of the lower limb (see Chapter 5), the fascial compartments of the upper limb are important clinically because they also contain and direct the spread of infection or hemorrhage in the limb. Figure 6.9. Anterior wall and floor of axilla. A. Axillary fascia forms the floor of the axilla and is continuous with the pectoral fascia. B. The pectoral fascia surrounds the pectoralis major, forming the anterior layer of the anterior axillary wall. The clavipectoral fascia extends between the coracoid process of the scapula, the clavicle, and the axillary fascia, enveloping the subclavius and pectoralis minor muscles and forming the posterior layer of the anterior axillary wall. The suspensory ligament of the axilla is the part of the clavipectoral, which attaches to the axillary fascia; when the arm is abducted, traction by the suspensory ligament pulls the axillary fascia superiorly, producing the hollow of the axillary fossa.


Figure 6.10. Fascia and compartments of upper limb. A. Brachial and antebrachial fascia surround the structures of the free upper limb. B. The intermuscular septa and humerus divide the space inside the brachial fascia into anterior and posterior compartments, each of which contains muscles serving similar functions and the nerves and vessels supplying them. C. The interosseous membrane and the radius and ulna similarly separate the space inside the antebrachial fascia into anterior and posterior compartments. D. Continuing distal to the radius and ulna onto the carpal bones, the deep fascia of the forearm thickens to form the extensor retinaculum posteriorly and a corresponding thickening anteriorly (palmar carpal ligament). At a deeper level to the latter, a ligamentous formation, the flexor retinaculum (transverse carpal ligament) extends between the anterior prominences of the outer carpal bones, converting the anterior concavity of the carpus into an osseofibrous carpal tunnel.

In the forearm, similar fascial compartments are surrounded by the antebrachial fascia and separated by the interosseous membrane connecting the radius and ulna (Fig. 6.10C). The antebrachial fascia thickens posteriorly over the distal ends of the


radius and ulna to form a transverse band, the extensor retinaculum, which retains the extensor tendons in position. The antebrachial fascia also forms an anterior thickening, which is continuous with the extensor retinaculum but is officially unnamed; some authors identify it as the palmar carpal ligament (Fig. 6.10D). Immediately distal and at a deeper level to the latter, the antebrachial fascia is also continued as the flexor retinaculum (transverse carpal ligament). 2 This fibrous band extends between the anterior prominences of the outer carpal bones and converts the anterior concavity of the carpus into a carpal tunnel, through which the flexor tendons and median nerve pass. The deep fascia of the upper limb continues beyond the extensor and flexor retinacula as the palmar fascia. The central part of the palmar fascia, the palmar aponeurosis, is thick, tendinous, and triangular and it overlies the central compartment of the palm. Its apex, located proximally, is continuous with the tendon of the palmaris longus (when it is present) (Fig. 6.10A). The aponeurosis forms four distinct thickenings that radiate to the bases of the fingers and become continuous with the fibrous tendon sheaths of the digits. The bands are traversed distally by the superficial transverse metacarpal ligament, which forms the base of the palmar aponeurosis. Innumerable minute, strong skin ligaments (L. retinacula cutis) extend from the palmar aponeurosis to the skin (see the Introduction). These ligaments hold the palmar skin close to the aponeurosis, allowing little sliding movement of the skin.

The Bottom Line The firm deep fascia of the upper limb surrounds and contains the structures of the upper limb as an expansion‐limiting membrane deep to the skin and subcutaneous tissue. Its deep surface, which occasionally serves to extend the surface area available for muscular origin, is attached directly or via intermuscular septa to the enclosed bones. The deep fascia thus forms fascial compartments containing individual muscles or muscle groups of similar function and innervation. The compartments also contain or direct the spread of infection or hemorrhage.

Cutaneous Nerves of the Upper Limb The cutaneous nerves of the upper limb follow a general pattern that is easy to understand if it is noted that developmentally the limbs grow as lateral protrusions of the trunk, with the 1st digit (thumb or great toe) located on the cranial side (thumb is directed superiorly). Thus the lateral surface of the upper limb is more cranial than the medial surface. There are two dermatome maps in common use. One has gained popular acceptance because of its more intuitive aesthetic qualities, corresponding to concepts of limb development (Keegan and Garrett, 1948); the other is based on clinical findings and is generally preferred by neurologists (Foerster, 1933). Both maps are approximations, delineating dermatomes as distinct zones when actually there is much overlap between adjacent dermatomes and much variation (even from side to side in the same individual). In both maps, observe the progression of the segmental innervation of the various cutaneous areas around the limb when it is placed in its “initial embryonic position” (abducted with thumb directed superiorly) (Fig. 6.11A— D):

Clinically Oriented Anatomy, 5th Edition By Keith Moore       

C3 and C4 nerves supply the region at the base of the neck extending laterally over the shoulder. C5 nerve supplies the arm laterally (i.e., on the superior aspect of the abducted limb). C6 nerve supplies the forearm laterally and the thumb. C7 nerve supplies the middle and ring fingers (or middle three fingers) and the middle of the posterior surface of the limb. C8 nerve supplies the little finger, the medial side of the hand, and the forearm (i.e., the inferior aspect of the outstretched limb). T1 nerve supplies the middle of the forearm to the axilla. T2 nerve supplies a small part of the arm and the skin of the axilla. (This is not indicated on the Keegan and Garrett map; however, pain experienced during a heart attack, considered to be mediated by T1 and T2, is commonly described as “radiating down the medial side of the left arm” ).

Most cutaneous nerves of the upper limb are derived from the brachial plexus, a major nerve network formed by the anterior rami of the C5—T1 spinal nerves (see “Brachial Plexus,” later in this chapter). The nerves to the shoulder, however, are derived from the cervical plexus, a nerve network consisting of a series of nerve loops formed between adjacent anterior rami of the first four cervical nerves. The cervical plexus lies deep to the sternocleidomastoid muscle on the anterolateral aspect of the neck. The cutaneous nerves of the arm and forearm 3 are as follows (Fig. 6.11E & F): 

The supraclavicular nerves (C3, C4) pass anterior to the clavicle, immediately deep to the platysma, and supply the skin over the clavicle and the superolateral aspect of the pectoralis major.


Figure 6.11. Segmental (dermatomal) and peripheral (cutaneous nerve) innervation of upper limb. A and B. The pattern of segmental (dermatomal) innervation of the upper limb proposed by Foerster (1933) depicts innervation of the medial aspect of the limb by upper thoracic (T1—T3) spinal cord segments, consistent with the experience of heart pain (angina pectoris) referred to that area. C and D. The pattern of segmental innervation proposed by Keegan and Garrett (1948) has gained popular acceptance, perhaps because of the regular progression of its stripes and correlation with developmental concepts. In both patterns, the dermatomes progress sequentially around the periphery of the outstretched limb (with the thumb directed superiorly), providing a way to approximate the segmental innervation. E and F. The distribution of the peripheral (named) cutaneous nerves in the upper limb is demonstrated. Most of the nerves are branches of nerve plexuses and therefore contain fibers from more than one spinal nerve or spinal cord segment.


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The posterior cutaneous nerve of the arm (C5—C8), a branch of the radial nerve, supplies the skin on the posterior surface of the arm. The posterior cutaneous nerve of the forearm (C5—C8), also a branch of the radial nerve, supplies the skin on the posterior surface of the forearm. The superior lateral cutaneous nerve of the arm (C5, C6), the terminal branch of the axillary nerve, emerges from beneath the posterior margin of the deltoid and supplies skin over the lower part of this muscle and on the lateral side of the midarm inferior to its distal attachment to the lateral side of the arm a little above its middle. The inferior lateral cutaneous nerve of the arm (C5, C6), a branch of the radial nerve, supplies the skin over the inferolateral aspect of the arm; it is frequently a branch of the posterior cutaneous nerve of the forearm. The lateral cutaneous nerve of the forearm (C6, C7), the terminal cutaneous branch of the musculocutaneous nerve, supplies the skin on the lateral side of the forearm. The medial cutaneous nerve of the arm (C8—T2) arises from the medial cord of the brachial plexus, often unites in the axilla with the lateral cutaneous branch of the 2nd intercostal nerve, and supplies the skin on the medial side of the arm. The intercostobrachial nerve (T2), a lateral cutaneous branch of the 2nd intercostal nerve, also contributes to the innervation of the skin on the medial surface of the arm. The medial cutaneous nerve of the forearm (C8, T1) arises from the medial cord of the brachial plexus and supplies the skin of the anterior and medial surfaces of the forearm.

Note that there are lateral, medial, and posterior (but no anterior) cutaneous nerves of the arm and forearm; as discussed later in this chapter, this pattern corresponds to that of the cords of the brachial plexus.

The Bottom Line As a consequence of plexus formation, two patterns of cutaneous innervation occur in the upper limb: (1) segmental innervation (dermatomes) by spinal nerves and (2) innervation by multisegmental peripheral (named) nerves. The former pattern is easiest to visualize if the limb is placed in its initial embryonic position (abducted with the thumb directed superiorly). The segments then progress in descending order around the limb (starting with C4 dermatome at the root of the neck, proceeding laterally or distally along the superior surface and then medially or proximally along the inferior surface, as the T2 dermatome continues onto the thoracic wall). Like the brachial plexus, which forms posterior, lateral, and medial (but no anterior) cords, the arm and forearm have posterior, lateral, and medial (but no anterior) cutaneous nerves.

Superficial Veins of the Upper Limb The main superficial veins of the upper limb, the cephalic and basilic veins, originate in the subcutaneous tissue on the dorsum of the hand from the dorsal venous network (Fig. 6.12). Perforating veins form communications between the superficial


and deep veins. Like the dermatomal pattern, the logic for naming the main superficial veins of the upper limb cephalic (toward the head) and basilic (toward the base) becomes apparent when the limb is placed in its initial embryonic position.

Figure 6.12. Superficial veins and lymph nodes of upper limb. A. The digital veins drain into the dorsal venous network on the dorsum of the hand, which leads to two prominent superficial vessels: the cephalic and basilic veins. B. The basilic and cephalic veins ultimately drain into the origin and termination of the axillary vein, respectively. The median cubital vein is th e communication between the basilic and the cephalic veins in the cubital fossa. Perforating veins connect the superficial veins to the deep veins. Arrows indicate the flow of lymph within lymphatic vessels that converge toward the vein and drain into the cubital and axillary lymph nodes.

The cephalic vein (G. kephalÃ©, head) ascends in the subcutaneous tissue from the lateral aspect of the dorsal venous network, proceeding along the lateral border of the wrist and the anterolateral surface of the proximal forearm and arm; it is often visible through the skin. Anterior to the elbow, the cephalic vein communicates with the median cubital vein, which passes obliquely across the anterior aspect of the elbow in the cubital fossa (a depression in front of the elbow) and joins the basilic vein. The cephalic vein courses superiorly between the deltoid and the pectoralis major muscles along the deltopectoral groove and enters the clavipectoral triangle


(Fig. 6.12B). It then pierces the costocoracoid membrane, part of the clavipectoral fascia, and joins the terminal part of the axillary vein. The basilic vein ascends in the subcutaneous tissue from the medial end of the dorsal venous network along the medial side of the forearm and the inferior part of the arm; it is often visible through the skin. It then passes deeply near the junction of the middle and inferior thirds of the arm, piercing the brachial fascia and running superiorly parallel to the brachial artery and the medial cutaneous nerve of the forearm to the axilla, where it merges with the accompanying veins (L. venae comitantes) of the axillary artery to form the axillary vein. The highly variable median antebrachial vein (median vein of the forearm) begins at the base of the dorsum of the thumb, curves around the lateral side of the wrist, and ascends in the middle of the anterior aspect of the forearm between the cephalic and the basilic veins. The median antebrachial vein sometimes divides into a median basilic vein, which joins the basilic vein, and a median cephalic vein, which joins the cephalic vein.

Lymphatic Drainage of the Upper Limb Superficial lymphatic vessels arise from lymphatic plexuses in the skin of the fingers, palm, and dorsum of the hand and ascend mostly with the superficial veins, such as the cephalic and basilic veins (Fig. 6.13). Some vessels accompanying the basilic vein enter the cubital (lymph) nodes, located proximal to the medial epicondyle and medial to the basilic vein. Efferent vessels from these lymph nodes ascend in the arm and terminate in the humeral (lateral) axillary lymph nodes (see Chapter 1). Most superficial lymphatic vessels accompanying the cephalic vein cross the proximal part of the arm and the anterior aspect of the shoulder to enter the apical axillary lymph nodes; however, some vessels previously enter the more superficial deltopectoral lymph nodes. Deep lymphatic vessels, less numerous than superficial vessels, accompany the major deep veins in the upper limb and terminate in the humeral axillary lymph nodes. They drain lymph from the joint capsules, periosteum, tendons, nerves, and muscles and ascend with the deep veins; a few deep lymph nodes may occur along their course. The axillary lymph nodes are drained by the subclavian lymphatic trunk; both are discussed in greater detail with the axilla, later in this chapter.


Figure 6.13. Lymphatic drainage of upper limb. Superficial lymphatic vessels originate from the digital lymphatic vessels of the digits and lymphatic plexus of the palm; most drainage from the palm passes to the dorsum of the hand (arrows). The vessels ascend through the forearm and arm, converging toward the cephalic and especially the basilic veins. Some lymph following this superficial route passes through the cubital lymph nodes in the elbow region or deltopectoral nodes in the shoulder region. The superficial and deep lymphatics of the upper limb drain initially to the humeral (lateral) and apical axillary lymph nodes; axillary nodes are drained in turn by the subclavian lymphatic trunk.

The Bottom Line Like the dermatomes, the pattern of the superficial veins is easy to visualize when the limb is placed in its embryonic position (abducted to 90° with the thumb directed superiorly). The cephalic vein courses along the cranial (cephalic) margin of the limb, while the basilic vein courses along the caudal (basic) margin of the limb. Both veins come from the dorsal venous network on the dorsum of the hand and drain into the beginning (basilic vein) and end (cephalic vein) of the axillary vein. The superficial lymphatic vessels generally converge on and follow the superficial veins, whereas the deep lymphatics follow the deep veins. The lymph collected from the upper limb by both superficial and deep lymphatics drains into the axillary lymph nodes.


Anterior Axioappendicular Muscles of the Upper Limb Four anterior axioappendicular (thoracoappendicular or pectoral) muscles move the pectoral girdle: pectoralis major, pectoralis minor, subclavius, and serratus anterior. The attachments, nerve supply, and main actions of these muscles are illustrated in Figure 6.14 and summarized in Table 6.1. The pectoralis major is a large, fan‐shaped muscle that covers the superior part of the thorax. It has clavicular and sternocostal heads. The latter head is much larger and its lateral border forms the muscular mass that makes up most of the anterior wall of the axilla. Its inferior border forms the anterior axillary fold (see “Axilla,” later in this chapter). The pectoralis major and adjacent deltoid form the narrow deltopectoral groove, in which the cephalic vein runs (Fig. 6.12B); however, the muscles diverge slightly from each other superiorly and, along with the clavicle, form the clavipectoral (deltopectoral) triangle (Fig. 6.12). Producing powerful adduction and medial rotation of the arm when acting together, the two parts of the pectoralis major can also act independently: the clavicular head flexing the humerus, and the sternocostal head extending it back from the flexed position. To test the clavicular head of pectoralis major, the arm is abducted 90°; the individual then moves the arm anteriorly against resistance. If acting normally, the clavicular head can be seen and palpated. To test the sternocostal head of the pectoralis major, the arm is abducted 60° and then adducted against resistance. If acting normally, the sternocostal head can be seen and palpated. The pectoralis minor lies in the anterior wall of the axilla where it is almost completely covered by the much larger pectoralis major (Fig. 6.14). The pectoralis minor is triangular in shape: Its base (proximal attachment) is formed by fleshy slips attached to the anterior ends of the 3rd—5th ribs near their costal cartilages; its apex (distal attachment) is on the coracoid process of the scapula. Variations in the costal attachments of the muscle are common. The pectoralis minor stabilizes the scapula and is used when stretching the upper limb forward to touch an object that is just out of reach. The pectoralis minor also assists in elevating the ribs for deep inspiration when the pectoral girdle is fixed or elevated. The pectoralis minor is a useful anatomical and surgical landmark for structures in the axilla (e.g., the axillary artery). With the coracoid process, the pectoralis minor forms a “bridge” under which vessels and nerves must pass to the arm. The subclavius lies almost horizontally when the arm is in the anatomical position. This small, round muscle is located inferior to the clavicle and affords some protection to the subclavian vessels and the superior trunk of the brachial plexus if the clavicle fractures. The subclavius anchors and depresses the clavicle, stabilizing it during movements of the upper limb. It also helps resist the tendency for the clavicle to dislocate at the SC joint, for example, when pulling hard during a tug‐of‐war game. The serratus anterior overlies the lateral part of the thorax and forms the medial wall of the axilla. This broad sheet of thick muscle was named because of the sawtoothed appearance of its fleshy slips or digitations (L. serratus, a saw). The muscular slips pass posteriorly and then medially to attach to the whole length of the anterior surface of the medial border of the scapula, including its inferior angle. The serratus anterior is one of the most powerful muscles of the pectoral girdle. It is a strong protractor of the scapula that is used when punching or reaching anteriorly


(sometimes called the “boxer's muscle” ). Its strong inferior part rotates the scapula, elevating its glenoid cavity so the arm can be raised above the shoulder. It also anchors the scapula, keeping it closely applied to the thoracic wall, enabling other muscles to use it as a fixed bone for movements of the humerus. The serratus anterior holds the scapula against the thoracic wall when doing push‐ups or when pushing against resistance (e.g., pushing a car). To test the serratus anterior (or the function of the long thoracic nerve that supplies it), the hand of the outstretched limb is pushed against a wall. If the muscle is acting normally, several digitations of the muscle can be seen and palpated.

Absence of the Pectoral Muscles Absence of part of the pectoralis major, usually its sternocostal part, is uncommon, but when it occurs, no disability usually results. However, the anterior axillary fold, formed by the skin and fascia overlying the inferior border of the pectoralis major, is absent on the affected side, and the nipple is more inferior than usual. In Poland syndrome, both the pectoralis major and minor are absent; breast hypoplasia and absence of two to four rib segments are also seen. Figure 6.14. Muscular walls of the axilla. Most of the anterior wall of the axilla and the axillary fat have been removed, revealing the axilla's medial and posterior walls and neurovascular contents. Of the structures forming the anterior wall, only portions of the pectoralis major (attaching ends, a central part overlying the pectoralis minor, and a cube of muscle reflected superior to the clavicle), the pectoralis minor, and subclavius remain. All the clavipectoral fascia and axillary fat have been removed, as has the axillary sheath surrounding the neurovascular bundle. This enables observation of the medial wall of the axilla, formed by the serratus anterior overlying the lateral thoracic wall, and of the muscles forming the posterior wall.


Paralysis of the Serratus Anterior When the serratus anterior is paralyzed owing to injury to the long thoracic nerve (Fig. 6.14), the medial border of the scapula moves laterally and posteriorly away from the thoracic wall, giving the scapula the appearance of a wing, especially when the person leans on a hand or presses the upper limb against a wall. When the arm is raised, the medial border and inferior angle of the scapula pull markedly away from the posterior thoracic wall, a deformation known as a winged scapula (Fig. B6.5). In addition, the upper limb cannot be abducted above the horizontal position because the serratus anterior is unable to rotate the glenoid cavity superiorly to allow complete abduction of the limb. Although protected when the limbs are at one's sides, the long thoracic nerve is exceptional in that it courses on the superficial aspect of the serratus anterior, which it supplies. Thus when the limbs are elevated, as in a knife fight, the nerve is especially vulnerable. Weapons, including bullets directed toward the thorax, are a common source ofinjury. Table 6.1. Anterior Axioappendicular Muscles


Muscle Pectoralis major

Proximal Attachment Clavicular head: anterior surface of medial half of clavicle Sternocostal head: anterior surface of sternum, superior six costal cartilages, aponeurosis of external oblique muscle

Innervation a Lateral and medial pectoral nerves; clavicular head (C5, C6), sternocostal head (C7, C8, T1)

Main Action Adducts and medially rotates humerus; draws scapula anteriorly and inferiorly Acting alone, clavicular head flexes humerus and sternocostal head extends it from the flexed position Pectoralis 3rd—5th ribs near their Medial border and Medial pectoral Stabilizes minor costal cartilages superior surface of nerve (C8, T1) scapula by coracoid process of drawing it scapula inferiorly and anteriorly against thoracic wall Subclavius Junction of 1st rib and Inferior surface of Nerve to sub‐ Anchors and its costal cartilage middle third of clavius (C5, C6) depresses clavicle clavicle Serratus External surfaces of Anterior surface of Long thoracic Protracts scapula anterior lateral parts of 1st—8th medial border of nerve (C5, C6, C7) and holds it ribs scapula against thoracic wall; rotates scapula a The spinal cord segmental innervation is indicated (e.g., “C5, C6” means that the nerves supplying the subclavius are derived from the fifth and sixth cervical segments of the spinal cord). Numbers in boldface (C5) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

Figure B6.5 P.751

Distal Attachment Lateral lip of intertubercular groove of humerus


Posterior Axioappendicular and Scapulohumeral Muscles The posterior axioappendicular muscles (superficial and intermediate groups of extrinsic back muscles) attach the superior appendicular skeleton (of the upper limb) to the axial skeleton (in the trunk). The intrinsic back muscles, which maintain posture and control movements of the vertebral column, are described in Chapter 4. The posterior shoulder muscles are divided into three groups (Table 6.2):   

Superficial posterior axioappendicular (extrinsic shoulder) muscles: trapezius and latissimus dorsi. Deep posterior axioappendicular (extrinsic shoulder) muscles: levator scapulae and rhomboids. Scapulohumeral (intrinsic shoulder) muscles: deltoid, teres major, and the four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis).

Superficial Posterior Axioappendicular (Extrinsic Shoulder) Muscles The superficial axioappendicular muscles are the trapezius and latissimus dorsi. The attachments, nerve supply, and main actions of these muscles are given in Table 6.2.

Trapezius The trapezius provides a direct attachment of the pectoral girdle to the trunk. This large, triangular muscle covers the posterior aspect of the neck and the superior half of the trunk (Fig. 6.15). It was given its name because the muscles of the two sides form a trapezium (G. irregular four‐sided figure). The trapezius attaches the pectoral girdle to the cranium and vertebral column and assists in suspending the upper limb. The fibers of the trapezius are divided into three parts, which have different actions at the physiological scapulothoracic joint between the scapula and the thoracic wall (Table 6.3): (1) superior fibers elevate the scapula (e.g., when squaring the shoulders), (2) middle fibers retract the scapula (i.e., pull it posteriorly), and (3) inferior fibers depress the scapula and lower the shoulder. Superior and inferior trapezius fibers act together in rotating the scapula on the thoracic wall in different directions, twisting it like a wing nut. The trapezius also braces the shoulders by pulling the scapulae posteriorly and superiorly, fixing them in position on the thoracic wall with tonic contraction; consequently, weakness of this muscle causes drooping of the shoulders. To test the trapezius (or the function of the accessory nerve [CN XI] that supplies it), the shoulder is shrugged against resistance (the person attempts to raise the shoulders as the examiner presses down on them). If the muscle is acting normally, the superior border of the muscle can be easily seen and palpated.


Figure 6.15. Trapezius. This large, superficial, triangular muscle is responsible for the lateral slope between the neck and the shoulder. It assists in suspending the pectoral girdle and elevates, retracts, and rotates the scapula.

Table 6.2. Posterior Axioappendicular and Scapulohumeral Muscles


Muscle Proximal Attachment Distal Attachment Innervation a Superficial posterior axioappendicular (extrinsic shoulder) muscles Trapezius Medial third of Lateral third of Accessory nerve superior nuchal line; clavicle; acromion (CN XI) (motor external occipital and spine of fibers) and C3, C4 protuberance; nuchal scapula spinal nerves (pain ligament; spinous and proprioceptive processes of C7—C12 fibers) vertebrae

Latissimus dorsi

Spinous processes of Floor of inferior 6 thoracic intertubercular vertebrae, groove of humerus thoracolumbar fascia, iliac crest, and inferior 3 or 4 ribs Deep posterior axioappendicular (extrinsic shoulder) muscles Levator scapulae Posterior tubercles Medial border of of transverse scapula superior processes of C1—C4 to root of spine vertebrae

Thoracodorsal nerve (C6, C7, C8)

Main Action Descending part elevates; ascending part depresses; and middle part (or all parts together) retracts scapula; descending and ascending parts act together to rotate glenoid cavity superiorly Extends, adducts, and medially rotates humerus; raises body toward arms during climbing

Dorsal scapular Elevates scapula (C5) and cervical and tilts its (C3, C4) nerves glenoid cavity inferiorly by rotating scapula


Rhomboid minor Minor: nuchal Minor: smooth and major ligament; spinous triangular area at processes of C7 and medial end of T1 vertebrae scapular spine Major: spinous processes of T2—T5 Major: medial vertebrae border of scapula from level of spine to inferior angle Scapulohumeral (intrinsic shoulder) muscles Deltoid Lateral third of Deltoid tuberosity clavicle; acromion of humerus and spine of scapula

Supraspinatus b

Supraspinous of scapula

Infraspinatus b

Infraspinous fossa of Middle facet of scapula greater tubercle of humerus Middle part of lateral Inferior facet of border of scapula greater tubercle of humerus Posterior surface of Medial lip of inferior angle of intertubercular scapula groove of humerus Subscapular fossa Lesser tubercle of (most of anterior humerus surface of scapula)

Teres minor b

Teres major

Subscapularis b

a

fossa Superior facet of greater tubercle of humerus

Dorsal scapular Retract scapula nerve (C4, C5) and rotate it to depress glenoid cavity; fix scapula to thoracic wall

Axillary nerve (C5, Anterior part: C6) flexes and medially rotates arm Middle part: abducts arm Posterior part: extends and laterally rotates arm Suprascapular Initiates and nerve (C4, C5, C6) assists deltoid in abduction of arm and acts with rotator cuff muscles b Suprascapular Laterally rotate nerve (C5, C6) arm; help hold humeral head in Axillary nerve (C5, glenoid cavity of scapula C6) Lower subscapular Adducts and nerve (C5, C6) medially rotates arm Upper and lower Medially rotates subscapular nerves and adduct arm; (C5, C6, C7) helps hold humeral head in glenoid cavity

T h e s p i n a l c o r d s e g m e n t a l i n n e r v a t i o n i s i n d i c a t e d ( e . g . , “ C 5 , C 6 ” m e a n s th a t t h e n e rv e s s u p p l y i n g t h e d e l t o i d are derived from the fifth and sixth cervical segments of the spinal cord). Numbers in boldface (C5) indicate the m a i n s e g m e n t a l i n n e rv a t io n . D a m a g e t o o n e o r m o r e o f t h e l i s t e d s p in a l co r d s e g m e n t s o r t o th e m o t o r n e rv e roots arising f r om t h e m results in paralysis of the muscles concerned. b C o l l e c t i v e l y , t h e s u p r a s p i n a t u s , i n f ra s p i n a tu s , t e re s m i n o r , a n d s u b s c a p u l a r i s m u s c l e s a r e r e f e r r e d t o a s t h e r o t a t o r c u f f , o r S I T S , m u s c l e s . Th e i r p ri m a r y f u n c t i o n d u r i n g a l l m o v e m e n t s of t h e g le n o h u m e r a l (s h o u l d e r ) j o in t i s t o h o l d t h e h u m e r a l h e a d i n t h e g l e n o i d c a v i t y of t h e s c a p u l a .


Table 6.3. Movements of the Scapula

Latissimus Dorsi The name latissimus dorsi (L. widest of the back) was well chosen because the muscle covers a wide area of the back (Fig. 6.16; Table 6.2E). This large, fan‐shaped muscle passes from the trunk to the humerus and acts directly on the glenohumeral joint and indirectly on the pectoral girdle (scapulothoracic joint). The latissimus dorsi extends, retracts, and rotates the humerus medially (e.g., when folding the arms


behind the back or scratching the skin over the opposite scapula). In combination with the pectoralis major, the latissimus dorsi is a powerful adductor of the humerus, and plays a major role in downward rotation of the scapula in association with this movement (Table 6.3). It is also useful in restoring the upper limb from abduction superior to the shoulder; hence the latissimus dorsi is important in climbing. In conjunction with the pectoralis major, the latissimus dorsi raises the trunk to the arm, which occurs when performing chin‐ups (hoisting oneself so the chin touches an overhead bar) or climbing a tree, for example. These movements are also used when chopping wood, paddling a canoe, and swimming (particularly during the crawl stroke). To test the latissimus dorsi (or the function of the thoracodorsal nerve that supplies it), the arm is abducted 90° and then adducted against resistance provided by the examiner. If the muscle is normal, the anterior border of the muscle can be seen and easily palpated in the posterior axillary fold (see “Axilla,” later in this chapter). Figure 6.16. Latissimus dorsi. This broad, triangular, mostly superficial muscle extends, adducts, and medially rotates the humerus. It is a powerful adductor and extensor of the arm and raises the body toward the arm during climbing.

Triangle of Auscultation Near the inferior angle of the scapula is a small triangular gap in the musculature. The superior horizontal border of the latissimus dorsi, the medial border of the scapula, and the inferolateral border of the trapezius form a triangle of auscultation (Table 6.2E). This gap in the thick back musculature is a good place to examine posterior segments of the lungs with a stethoscope. When the scapulae are drawn anteriorly by folding the arms across the chest and the trunk is flexed, the auscultatory triangle enlarges and parts of the 6th and 7th ribs and 6th intercostal space are subcutaneous.


Injury of the Accessory Nerve (CN XI) The primary clinical manifestation of accessory nerve palsy is a marked ipsilateral weakness when the shoulders are elevated (shrugged) against resistance. Injury of the accessory nerve is discussed in greater detail in Chapters 8 and 9.

Injury of the Thoracodorsal Nerve Surgery in the inferior part of the axilla puts the thoracodorsal nerve (C6—C8) supplying the latissimus dorsi at risk of injury. This nerve passes inferiorly along the posterior wall of the axilla and enters the medial surface of the latissimus dorsi close to where it becomes tendinous (Fig. B6.6). The nerve is also vulnerable to injury during surgery on scapular lymph nodes because its terminal part lies anterior to them and the subscapular artery (Fig. B6.7). The latissimus dorsi and the inferior part of the pectoralis major form an anteroposterior muscular sling between the trunk and the arm; however, the latissimus dorsi forms the more powerful part of the sling. With paralysis of the latissimus dorsi, the person is unable to raise the trunk with the upper limbs, as occurs during climbing. Furthermore, the person cannot use an axillary crutch because the shoulder is pushed superiorly by it. These are the primary activities for which active depression of the scapula is required; the passive depression provided by gravity is adequate for most activities.

Figure B6.6


Figure B6.7

Deep Posterior Axioappendicular (Extrinsic Shoulder) Muscles The deep posterior thoracoappendicular muscles are the levator scapulae and rhomboids. These muscles provide direct attachment of the appendicular skeleton to the axial skeleton. The attachments, nerve supply, and main actions are given in Table 6.2.

Levator Scapulae The superior third of the strap‐like levator scapulae lies deep to the sternocleidomastoid; the inferior third is deep to the trapezius. From the transverse processes of the upper cervical vertebrae, the fibers of the levator of the scapula pass inferiorly to the superomedial border of the scapula (Fig. 6.17). True to its name, the levator scapulae acts with the descending part of the trapezius to elevate the scapula, or fix it (resists forces that would depress it, as when carrying a load). With the rhomboids and pectoralis minor, it rotates the scapula, depressing the glenoid cavity (tilting it inferiorly by rotating the scapula) (Table 6.3). Acting bilaterally (also with the trapezius), the levators extend the neck; acting unilaterally, the muscle may contribute to lateral flexion of the neck (toward the side of the active muscle).


Figure 6.17. Levator scapulae. This thick, strap‐like muscle descends from the first four cervical vertebrae and attaches to the medial border of the superior angle of the scapula. It elevates and rotates the scapula, tilting the glenoid cavity inferiorly.

Rhomboids The rhomboid major and rhomboid minor, which are not always clearly separated from each other, have a rhomboid appearance—that is, they form an oblique equilateral parallelogram (Fig. 6.18). The rhomboids lie deep to the trapezius and form broad parallel bands that pass inferolaterally from the vertebrae to the medial border of the scapula. The thin, flat rhomboid major is approximately two times wider than the thicker rhomboid minor lying superior to it. The rhomboids retract and rotate the scapula, depressing its glenoid cavity (Table 6.3). They also assist the serratus anterior in holding the scapula against the thoracic wall and fixing the scapula during movements of the upper limb. The rhomboids are used when forcibly lowering the raised upper limbs (e.g., when driving a stake with a sledge hammer). To test the rhomboids (or the function of the dorsal scapular nerve that supplies them), the individual places the hands posteriorly on the hips and pushes the elbows posteriorly against resistance provided by the examiner. If the rhomboids are acting normally, they can be palpated along the medial borders of the scapulae; because they lie deep to the trapezius, they are unlikely to be visible during testing.

Injury to the Dorsal Scapular Nerve Injury to the dorsal scapular nerve, the nerve to the rhomboids, affects the actions of these muscles. If the rhomboids on one side are paralyzed, the scapula on the affected side is located farther from the midline than that on the normal side.


The Bottom Line In terms of their attachments, the muscles of the proximal upper limb are axioappendicular or scapulothoracic muscles. The former consist of anterior, superficial posterior, and deep posterior groups. As a group, the axioappendicular muscles serve to position the base from which the upper limb will be extended and function relative to the trunk. The muscles work in antagonistic groups to elevate— depress and protract—retract the entire scapula or rotate it to elevate or depress the glenoid cavity and the glenohumeral joint (Table. 6.3). These movements extend the functional range of movements that occur at the glenohumeral joint. All of these movements involve both the clavicle and the scapula; the limits to all movements of the latter are imposed by the former, which provides the only attachment to the axial skeleton. Most of these movements involve the cooperation of a number of muscles with different innervations. Therefore, single nerve injuries typically weaken but do not eliminate most movements. Notable exceptions are upward rotation of the lateral angle of the scapula (superior trapezius/accessory nerve only) and lateral rotation of the inferior angle of the scapula (inferior serratus anterior/long thoracic nerve only). Figure 6.18. Rhomboids. The rhomboid muscles (major and minor) retract the scapula and rotate it to depress the glenoid cavity. They also fix the scapula to the thoracic wall.

Scapulohumeral (Intrinsic Shoulder) Muscles The six scapulohumeral muscles (the deltoid, teres major, supraspinatus, infraspinatus, subscapularis, and teres minor) are relatively short muscles that pass from the scapula to the humerus and act on the glenohumeral joint. The attachments, nerve supply, and main actions of these intrinsic shoulder muscles are summarized in Table 6.2.


Deltoid The deltoid is a thick, powerful, coarse‐textured muscle covering the shoulder and forming its rounded contour (Fig. 6.19; Table 6.2E). As its name indicates, the deltoid is shaped like the inverted Greek letter delta (Î”). The muscle is divided into unipennate anterior and posterior parts and a multipennate middle part; the parts of the deltoid can act separately or as a whole. When all three parts contract simultaneously, the arm is abducted. The anterior and posterior parts act like guy ropes to steady the arm as it is abducted. To initiate movement during the first 15° of abduction, the deltoid is assisted by the supraspinatus (Table 6.2B). When the arm is fully adducted, the line of pull of the deltoid coincides with the axis of the humerus; thus it pulls directly upward on the bone and cannot initiate or produce abduction. It is, however, able to act as a shunt muscle, resisting inferior displacement of the head of the humerus from the glenoid cavity, as when lifting and carrying suitcases. From the fully adducted position, abduction must be initiated by the supraspinatus, or by leaning to the side, allowing gravity to initiate the movement. The deltoid becomes fully effective as an abductor following the initial 15° of abduction. Figure 6.19. Deltoid. This thick, coarse‐textured, triangular muscle covers the glenohumeral joint and forms the rounded contour of the shoulder. The middle, multipennate part of the deltoid is the principal abductor of the arm, the anterior part flexes and medially rotates the arm, and the posterior part extends and laterally rotates the arm.


Figure 6.20. Testing deltoid muscle. The examiner resists the patient's abduction of the limb by the deltoid. If the deltoid is acting normally, contraction of the middle part of the muscle can be palpated.

The anterior and posterior parts of the deltoids are used to swing the limbs during walking. The anterior part assists the pectoralis major in flexing the arm, and the posterior part assists the latissimus dorsi in extending the arm. The deltoid also helps stabilize the glenohumeral joint and hold the head of the humerus in the glenoid cavity during movements of the upper limb. To test the deltoid (or the function of the axillary nerve that supplies it), the arm is abducted, starting from approximately 15°, against resistance (Fig. 6.20). If acting normally, the deltoid can easily be seen and palpated. The influence of gravity is avoided when the person is supine.

Injury to the Axillary Nerve The deltoid atrophies when the axillary nerve (C5 and C6) is severely damaged. Because it passes inferior to the humeral head and winds around the surgical neck of the humerus, the axillary nerve is usually injured during fracture of this part of the humerus. It may also be damaged during dislocation of the glenohumeral joint and by compression from the incorrect use of crutches. As the deltoid atrophies, the rounded contour of the shoulder disappears. This gives the shoulder a flattened appearance and produces a slight hollow inferior to the acromion. In addition to atrophy of the deltoid, a loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm (red in Fig. B6.8). The deltoid is a common site for the intramuscular injection of drugs. The axillary nerve runs transversely under cover of the deltoid at the level of the surgical neck of the humerus. Awareness of its location avoids injury to it during surgical approaches to the shoulder.


Figure B6.8. Area of anesthesia (red).

Teres Major The teres major (L. teres, round) is a thick, rounded muscle that forms a raised oval area on the inferolateral third of the scapula when the arm is adducted against resistance (Fig. 6.21A; Table 6.2B & E). The inferior border of the teres major forms the inferior border of the lateral part of the posterior wall of the axilla. The teres major adducts and medially rotates the arm (Fig. 6.21B). It can also help extend it from the flexed position and is an important stabilizer of the humeral head in the glenoid cavity—that is, it steadies the head in its socket. To test the teres major (or the lower subscapular nerve that supplies it), the abducted arm is adducted against resistance. If acting normally, the muscle can be easily seen and palpated in the posterior axillary fold.

Rotator Cuff Muscles Four of the scapulohumeral muscles (intrinsic shoulder muscles)—supraspinatus, infraspinatus, teres minor, and subscapularis (referred to as the SITS muscles)—are called rotator cuff muscles because they form a musculotendinous rotator cuff around the glenohumeral joint (Fig. 6.22). All except the supraspinatus are rotators of the humerus; the supraspinatus, besides being part of the rotator cuff, initiates and assists the deltoid in the first 15° of abduction of the arm. The tendons of the SITS muscles blend with and reinforce the fibrous layer of the joint capsule of the glenohumeral joint, thus forming the rotator cuff that protects the joint and gives it stability. The tonic contraction of the contributing muscles holds the relatively large head of the humerus in the small, shallow glenoid cavity of the scapula during arm movements. The attachments, nerve supply, and main actions of the rotator cuff muscles are given in Table 6.2. The supraspinatus occupies the supraspinous fossa of the scapula. A bursa separates it from the lateral quarter of the fossa. (See “Deltoid,” earlier in this chapter for discussion of this muscle's cooperative action in abducting the upper limb.) To test the supraspinatus, abduction of the arm is attempted from the fully adducted position against resistance, while the muscle is palpated superior to the spine of the scapula.


Figure 6.21. Scapulohumeral muscles. A. These muscles pass from the scapula to the humerus and act on the glenohumeral joint. The surface anatomy of the scapular muscles and the latissimus dorsi are shown. B. The position of the scapula and humerus when the limb is abducted 90° is shown. The teres major is a thick, rounded muscle that adducts and medially rotates the arm. The latissimus dorsi and teres major form the posterior axillary fold. When the arm is adducted against resistance, this fold is accentuated. Figure 6.22. Disposition of rotator cuff muscles. The primary combined function of the four scapulohumeral (SITS) muscles is to “grasp” and pull the relatively large head of the humerus medially, holding it against the smaller, shallow glenoid cavity of the scapula. The tendons of the muscles (represented by three fingers and the thumb) blend with the fibrous layer of the capsule of the glenohumeral joint to form a musculotendinous rotator cuff, which reinforces the capsule on three sides (anteriorly, superiorly, and posteriorly) as it provides active support for the glenohumeral joint.

The infraspinatus occupies the medial three quarters of the infraspinous fossa and is partly covered by the deltoid and trapezius. In addition to helping stabilize the glenohumeral joint, the infraspinatus is a powerful lateral rotator of the humerus. To test the infraspinatus, the person flexes the elbow and adducts the arm. The arm is then laterally rotated against resistance. If acting normally, the muscle can be palpated inferior to the scapular spine. To test the function of the supra‐scapular nerve, which supplies the supraspinatus and infraspinatus, both muscles must be tested as described.


The teres minor is a narrow, elongate muscle that is completely hidden by the deltoid and is often not clearly delineated from the infraspinatus (Table 6.2B). The teres minor works with the infraspinatus to rotate the arm laterally and assist in its adduction. The teres minor is most clearly distinguished from the infraspinatus by its nerve supply. The teres minor is supplied by the axillary nerve, whereas the infraspinatus is supplied by the suprascapular nerve. The subscapularis is a thick, triangular muscle that lies on the costal surface of the scapula and forms part of the posterior wall of the axilla. It crosses the anterior aspect of the scapulohumeral joint on its way to the humerus. The subscapularis is the primary medial rotator of the arm and also adducts it. It joins the other rotator cuff muscles in holding the head of the humerus in the glenoid cavity during all movements of the glenohumeral joint (i.e., it helps stabilize this joint during movements of the elbow, wrist, and hand).

Fracture—Dislocation of the Proximal Humeral Epiphysis A direct blow or indirect injury of the shoulder of a child or adolescent may produce a fracture—dislocation of the proximal humeral epiphysis because the joint capsule of the glenohumeral joint, reinforced by the rotator cuff (tendons of the SITS muscles), is stronger than the epiphysial plate. In severe fractures, the shaft of the humerus is markedly displaced, but the humeral head retains its normal relationship with the glenoid cavity of the scapula (Fig. B6.9).

Figure B6.9

Rotator Cuff Injuries and the Supraspinatus Injury or disease may damage the musculotendinous rotator cuff, producing instability of the glenohumeral joint. Trauma may tear or rupture one or more of the tendons of the SITS muscles; that of the supraspinatus is most commonly involved


(Fig. B6.10). Degenerative tendonitis of the rotator cuff is common, especially in older people. These syndromes are discussed in detail (later in this chapter) in relationship to the glenohumeral joint.

Figure B6.10

The Bottom Line The scapulohumeral muscles (deltoid, teres major, and SITS muscles), along with certain axioappendicular muscles, act in opposing groups to position the proximal strut (humerus) of the upper limb, producing abduction—adduction, flexion— extension, medial—lateral rotation, and circumduction of the arm. This establishes the height, distance from the trunk, and direction from which the forearm and hand will operate. Essentially all movements produced by the scapulohumeral muscles at the glenohumeral joint are accompanied by movements produced by axioappendicular muscles at the sternoclavicular and scapulothoracic joints, especially beyond the initial stages of the movement. A skilled examiner, knowledgeable in anatomy, can manually fix or position the limb to isolate and test distinctive portions of specific upper limb movements. The SITS muscles contribute to the formation of the rotator cuff, which both rotates the humeral head and holds it firmly against the shallow socket of the glenoid cavity, increasing the integrity of the glenohumeral joint capsule.

Axilla The axilla is the pyramidal space inferior to the glenohumeral joint and superior to the axillary fascia at the junction of the arm and thorax (Fig. 6.23). The axilla provides a passageway or “distribution center,” usually protected by the adducted upper limb, for the neurovascular structures that serve the upper limb. From this distribution center, neurovascular structures pass (1) superiorly via the cervicoaxillary canal to (or from) the root of the neck, (2) anteriorly via the


clavipectoral triangle to the pectoral region, (3) inferiorly and laterally into the limb itself, (4) posteriorly via the quadrangular space to the scapular region, and (5) inferiorly and medially along the thoracic wall to the inferiorly placed axioappendicular muscles (serratus anterior and latissimus dorsi). The shape and size of the axilla varies, depending on the position of the arm; it almost disappears when the arm is fully abducted—a position in which its contents are vulnerable. A “tickle” reflex causes most people to rapidly resume the protected position when invasion threatens. The axilla has an apex, a base, and four walls, three of which are muscular: 







The apex of axilla is the cervicoaxillary canal, the passageway between the neck and the axilla, bounded by the 1st rib, clavicle, and superior edge of the scapula. The arteries, veins, lymphatics, and nerves traverse this superior opening of the axilla to pass to or from the arm (Fig. 6.23A). The base of axilla is formed by the concave skin, subcutaneous tissue, and axillary (deep) fascia extending from the arm to the thoracic wall (approximately the 4th rib level), forming the axillary fossa (armpit). The base of the axilla or axillary fossa is bounded by the anterior and posterior axillary folds, the thoracic wall, and the medial aspect of the arm (Fig. 6.23C). The anterior wall of axilla has two layers, formed by the pectoralis major and pectoralis minor and the pectoral and clavicopectoral fascia associated with them (Figs. 6.9B and 6.23B & C). The anterior axillary fold is the inferiormost part of the anterior wall that may be grasped between the fingers; it is formed by the pectoralis major, as it bridges from thoracic wall to humerus, and the overlying integument (Fig. 6.23C & D). The posterior wall of axilla is formed chiefly by the scapula and subscapularis on its anterior surface and inferiorly by the teres major and latissimus dorsi (Fig. 6.23B & C). The posterior axillary fold is the inferiormost part of the posterior wall that may be grasped. It extends farther inferiorly than the anterior wall and is formed by latissimus dorsi, teres major, and overlying integument.


F i g u re 6 . 2 3 . L o c a t i o n , b o u n d a r i e s , a n d c o n t e n t s o f a x i l l a . A . T h e a x i l l a i s a p y r a m i d a l s p a c e i n f e r i o r to the glenohumeral joint and superior to the skin of the axillary fossa at the junction of the arm and t h o r a x . O b s e r v e i t s a p e x , b a s e , a n d w a l l s . B . T h i s t r a n s v e rs e s e c t i o n o f t h e a x i l l a i l l u s t r a t e s i t s t h r e e m u s c u l a r w a l l s . T h e s m a l l , l a t e r a l b o n y w a l l o f t h e a x i l l a is t h e i n te r tu b e r c u l a r g ro o v e o f t h e h u m e r u s . C . A s a g i t t a l s e c t i o n o f t h e s h o u l d e r s h o w s t h e c o n te n t s o f t h e a x i l l a a n d t h e s c a p u l a r a n d


p e c t o r a l m u s c l e s f o r m i n g i t s p o s te r i o r a n d a n t e r i o r w a l l s , r e s p e c t i v e l y . T h e a x i l l a i s p r i m a r i l y f i l l e d w i t h a x i l l a r y f a t ( y e l l o w ) , f o r m i n g a m a t r i x i n w h i c h t h e n e u r o v a s c u l a r s t r u ct u r e s a n d l y m p h n od e s are embedded. Inferiorly, the inferior border of the pectoralis major forms the anterior axillary fold, a n d th e l a t is s i m u s d o r s i a n d te r e s m a j o r f o r m t h e p os t e r i or a x i l l a r y f o ld . D . I n t h i s s u p e r f i c i a l d i s s e c t i o n o f t h e p e c t o r a l r e g i o n , t h e s u b c u ta n e o u s p l a t y s m a m u s c l e , w h i c h d e s ce n d s f r om t h e n e c k t o t h e 2 n d o r 3 r d r i b , i s c u t s h o r t o n th e r i g h t s i d e . T h e s e v e r e d m u s c l e i s re f le c t e d s u p e r i o r l y o n t h e l e f t s i d e , t o g e t h e r w i t h t h e s u p r a c l a v i c u l a r n e rv e s , s o t h a t t h e c l a v i c u l a r a t t a c h m e n t s o f t h e p e c t o r a l i s m a j o r a n d a n t e r i o r d e l t o i d ca n b e o b s e r v e d . Figure 6.24. C o n t e n ts of axilla. A. This cross section of the axilla d e m on s t r a te s t h e c o n t e n ts o f the axilla, including the axillary sheath enclosing the axillary artery and vein and the three cords of the brachial plexus. The innervation of the muscular walls of the a x i l l a i s a l s o shown. B. In this d i s s e c t i o n , m o s t of the pectoralis major has been r e m o v e d a n d t h e c l a v i p e c t o r a l f a s c i a , a x i l l a r y f a t , a n d a x i l l a r y s h e a t h h a v e b e e n c o m p le t e l y r e m ov e d . T h e b r a c h i a l p l e x u s of n e r v e s s u r r o u n d s t h e a x i l l a r y a r t e r y o n i t s l a te r a l a n d m e d i a l a s p e c t s ( a p p e a r i n g h e re t o b e i t s s u p e r i o r a n d i n f e r i o r a s p e c t s b e c a u s e th e l i m b i s a b d u c t e d ) a n d o n i ts p o s t e r i o r a s p e c t ( n o t v i s i b l e f r o m t h i s v ie w ) .

 

The medial wall of axilla is formed by the thoracic wall (1st—4th ribs and intercostal muscles) and the overlying serratus anterior (Fig. 6.23A & B). The lateral wall of axilla is a narrow bony wall formed by the intertubercular groove in the humerus.

The axilla contains axillary blood vessels (axillary artery and its branches, axillary vein and its tributaries), lymphatic vessels, and several groups of axillary lymph nodes, all embedded in a matrix of axillary fat (Fig. 6.23C). The axilla also contains large nerves that make up the cords and branches of the brachial plexus, a network of interjoining nerves that pass from the neck to the upper limb. Proximally, these neurovascular structures are ensheathed in a sleeve‐like extension of the cervical fascia, the axillary sheath (Fig. 6.24A).

The Bottom Line The axilla is a pyramidal, fat‐filled fascial compartment (distribution center) giving passage to or housing the major “utilities” serving (supplying, draining, and communicating with) the upper limb. Although normally protected by the arm, axillary structures are vulnerable when the arm is abducted. The “tickle” reflex


causes us to recover the protected position rapidly when a threat is perceived. The structures are ensheathed in a protective wrapping (axillary sheath), embedded in a cushioning matrix (axillary fat) that allows flexibility, and are surrounded by musculoskeletal walls. From the axilla, neurovascular structures pass to and from the entire upper limb, including the pectoral, scapular, and subscapular regions as well as the free upper limb.

Axillary Artery The axillary artery begins at the lateral border of the 1st rib as the continuation of the subclavian artery and ends at the inferior border of the teres major (Table 6.4). It passes posterior to the pectoralis minor into the arm and becomes the brachial artery when it passes the inferior border of the teres major, at which point it usually has reached the humerus. For descriptive purposes, the axillary artery is divided into three parts by the pectoralis minor (the part number also indicates the number of its branches): 





The first part of the axillary artery is located between the lateral border of the 1st rib and the medial border of the pectoralis minor; it is enclosed in the axillary sheath and has one branch—the superior thoracic artery (Fig. 6.24B; Table 6.4). The second part of the axillary artery lies posterior to pectoralis minor and has two branches—the thoracoacromial and lateral thoracic arteries—which pass medial and lateral to the muscle, respectively. The third part of the axillary artery extends from the lateral border of pectoralis minor to the inferior border of teres major and has three branches. The subscapular artery is the largest branch of the axillary artery. Opposite the origin of this artery, the anterior circumflex humeral and posterior circumflex humeral arteries arise, sometimes by means of a common trunk.

The branches of the axillary artery are illustrated and their origin and course described in Table 6.4. The superior thoracic artery is a small, highly variable vessel that arises just inferior to the subclavius. It commonly runs inferomedially posterior to the axillary vein and supplies the subclavius, muscles in the 1st and 2nd intercostal spaces, superior slips of the serratus anterior, and overlying pectoral muscles. It anastomoses with the intercostal and/or internal thoracic arteries. The thoracoacromial artery, a short wide trunk, pierces the costocoracoid membrane and divides into four branches (acromial, deltoid, pectoral, and clavicular), deep to the clavicular head of the pectoralis major (Fig. 6.25). The lateral thoracic artery has a variable origin. It usually arises as the second branch of the second part of the axillary artery and descends along the lateral border of the pectoralis minor, following it onto the thoracic wall (Fig. 6.24B); however, it may arise instead from the thoracoacromial, suprascapular, or subscapular arteries. The lateral thoracic artery supplies the pectoral, serratus anterior, and intercostal muscles, the axillary lymph nodes, and the lateral aspect of the breast. The subscapular artery, the branch of the axillary artery with the greatest diameter but shortest length descends along the lateral border of the subscapularis on the


posterior axillary wall. It soon terminates by dividing into the circumflex scapular and thoracodorsal arteries. The circumflex scapular artery, often the larger terminal branch of the subscapular artery, curves posteriorly around the lateral border of the scapula, passing posteriorly between the subscapularis and the teres major to supply muscles on the dorsum of the scapula. It participates in the anastomoses around the scapula. The thoracodorsal artery continues the general course of the subscapular artery to the inferior angle of the scapula and supplies adjacent muscles, principally the latissimus dorsi. It also participates in the arterial anastomoses around the scapula. The circumflex humeral arteries encircle the surgical neck of the humerus, anastomosing with each other. The smaller anterior circumflex humeral artery passes laterally, deep to the coracobrachialis and biceps brachii. It gives off an ascending branch that supplies the shoulder. The larger posterior circumflex humeral artery passes medially through the posterior wall of the axilla via the quadrangular space with the axillary nerve to supply the glenohumeral joint and surrounding muscles (e.g deltoid, teres major and minor, and long head of the triceps) (Table 6.4).

Compression of the Axillary Artery The axillary artery can be palpated in the inferior part of the lateral wall of the axilla. Compression of the third part of this artery against the humerus may be necessary when profuse bleeding occurs (e.g., resulting from a stab or bullet wound in the axilla). If compression is required at a more proximal site, the axillary artery can be compressed at its origin (as the subclavian artery crosses the 1st rib) by exerting downward pressure in the angle between the clavicle and the inferior attachment of the sternocleidomastoid.

Arterial Anastomoses around the Scapula Many arterial anastomoses (communications between arteries) occur around the scapula. Several vessels join to form networks on the anterior and posterior surfaces of the scapula: the dorsal scapular, suprascapular, and (via the circumflex scapular) subscapular arteries (Fig. B6.11). The importance of the collateral circulation made possible by these anastomoses becomes apparent when ligation of a lacerated subclavian or axillary artery is necessary. For example, the axillary artery may have to be ligated between the 1st rib and subscapular artery; in other cases, vascular stenosis (narrowing) of the axillary artery may result from an atherosclerotic lesion that causes reduced blood flow. In either case, the direction of blood flow in the subscapular artery is reversed, enabling blood to reach the third part of the axillary artery. Note that the subscapular artery receives blood through several anastomoses with the suprascapular artery, transverse cervical artery, and intercostal arteries. Slow occlusion of the axillary artery (e.g., resulting from disease or trauma) often enables sufficient collateral circulation to develop, preventing ischemia. Sudden occlusion usually does not allow sufficient time for adequate collateral circulation to develop; as a result, there is an inadequate supply of blood to the arm, forearm, and hand. While potential collateral pathways (periarticular anastomoses) exist around the shoulder joint proximally and the elbow joint distally, surgical ligation of the axillary artery between the origins of the subscapular artery and the deep artery of the arm will cut off the blood supply to the arm because the collateral circulation is inadequate.


Aneurysm of the Axillary Artery The first part of the axillary artery may enlarge (aneurysm of the axillary artery) and compress the trunks of the brachial plexus, causing pain and anesthesia (loss of sensation) in the areas of the skin supplied by the affected nerves. Aneurysm of the axillary artery may occur in baseball pitchers because of their rapid and forceful arm movements.

Figure B6.11


Table 6.4. Arteries of the Proximal Upper Limb (Shoulder Region and Arm)


Figure 6.25. Anterior wall of axilla. The clavicular head of the pectoralis major is excised except for its clavicular and humeral attaching ends and two cubes, which remain to identify its nerves. The anterior wall of the axilla is formed by the pectoralis major and minor (and the pectoral and clavipectoral fascia that envelops them). The pectoralis major covers the whole of this wall and forms the anterior axillary fold. Extending between the superior border of the pectoralis minor and the clavicle is the costocoracoid membrane (part of the clavipectoral fascia), which is perforated by the thoracoacromial artery and pectoral nerves (both exiting the axilla) and the cephalic vein (entering the axilla).

Axillary Vein The axillary vein lies initially (distally) on the anteromedial side of the axillary artery, with its terminal part anteroinferior to the artery (Fig. 6.26). This large vein is formed by the union of the brachial vein (the accompanying veins of the brachial artery) and the basilic vein at the inferior border of the teres major. The axillary vein is described as having three parts that correspond to the three parts of the axillary artery. Thus the initial, distal end is the third part, whereas the terminal, proximal end is the first part. The axillary vein (first part) ends at the lateral border of the 1st rib, where it becomes the subclavian vein. The veins of the axilla are more abundant than the arteries, are highly variable, and frequently anastomose. The axillary vein receives tributaries that generally correspond to branches of the axillary artery with a few major exceptions: 



The veins corresponding to the branches of the thoracoacromial artery do not merge to enter by a common tributary; some enter independently into the axillary vein, but others empty into the cephalic vein, which then enters the axillary vein superior to the pectoralis minor, close to its transition into the subclavian vein. The axillary vein receives, directly or indirectly, the thoracoepigastric vein(s), which is(are) formed by the anastomoses of superficial veins from the inguinal region with tributaries of the axillary vein (usually the lateral thoracic vein). These veins constitute a collateral route that enables venous return in the presence of obstruction of the inferior vena cava (see clinical correlation [blue] box “Collateral Routes for Abdominopelvic Venous Blood,” in Chapter 2).


Injuries to the Axillary Vein Wounds in the axilla often involve the axillary vein because of its large size and exposed position. When the arm is fully abducted, the axillary vein overlaps the axillary artery anteriorly. A wound in the proximal part of the axillary vein is particularly dangerous, not only because of profuse bleeding but also because of the risk of air entering it and producing air emboli (air bubbles) in the blood.

The Role of the Axillary Vein in Subclavian Vein Puncture Subclavian vein puncture, in which a catheter is placed into the subclavian vein, has become a common clinical procedure (see clinical correlation [blue] box “Subclavian Vein Puncture,” in Chapter 8). The axillary vein becomes the subclavian vein as the first rib is crossed. Because the needle is advanced medially to enter the vein as it crosses the rib, the vein actually punctured (the point of entry) in a “subclavian vein puncture” is the terminal part of the axillary vein. However, the needle tip proceeds into the lumen of the subclavian vein almost immediately. Thus it is clinically significant that the axillary vein lies anterior and inferior (i.e., superficial) to the axillary artery and the parts of the brachial plexus that begin to surround the artery at this point.

Axillary Lymph Nodes The fibrofatty connective tissue of the axilla (axillary fat) contains many lymph nodes. The axillary lymph nodes are arranged in five principal groups: pectoral, subscapular, humeral, central, and apical. The groups are arranged in a manner that reflects the pyramidal shape of the axilla (Fig. 6.23A). Three groups of axillary nodes are related to the triangular base, one group at each corner of the pyramid (Fig. 6.27A & B): The pectoral (anterior) nodes consist of three to five nodes that lie along the medial wall of the axilla, around the lateral thoracic vein and the inferior border of the pectoralis minor. The pectoral nodes receive lymph mainly from the anterior thoracic wall, including most of the breast (especially the superolateral [upper outer] quadrant and subareolar plexus; see Chapter 1). The subscapular (posterior) nodes consist of six or seven nodes that lie along the posterior axillary fold and subscapular blood vessels. These nodes receive lymph from the posterior aspect of the thoracic wall and scapular region.


Figure 6.26. Veins of axilla. Observe that the basilic vein parallels the brachial artery to the axilla, where it merges with the accompanying veins (L. venae comitantes) of the axillary artery to form the axillary vein. Note the large number of highly variable veins in the axilla, which are also tributaries of the axillary vein.


Figure 6.27. Axillary lymph nodes and lymphatic drainage of right upper limb and breast. A. Of the five groups of axillary lymph nodes, most lymphatic vessels from the upper limb terminate in the humeral (lateral) and central lymph nodes, but those accompanying the upper part of the cephalic vein terminate in the apical lymph nodes. The lymphatics of the breast are discussed in Chapter 1. B. Lymph passing through the axillary nodes enters efferent lymphatic vessels that form the subclavian lymphatic trunk, which usually empties into the junctions of the internal jugular and subclavian veins (the venous angles). Occasionally, on the right side, this trunk merges with the jugular lymphatic and/or bronchomediastinal trunks to form a short right lymphatic duct; usually on the left side, it enters the termination of the thoracic duct. C. The positions of the five groups of axillary nodes, relative to each other and the pyramidal axilla. The typical pattern of drainage is shown.


The humeral (lateral) nodes consist of four to six nodes that lie along the lateral wall of the axilla, medial and posterior to the axillary vein. These nodes receive nearly all the lymph from the upper limb, except that carried by the lymphatic vessels accompanying the cephalic vein, which primarily drain directly to the apical axillary and infraclavicular nodes. Efferent lymphatic vessels from these three groups pass to the central nodes (Fig. 6.27C). The central nodes are three or four large nodes situated deep to the pectoralis minor near the base of the axilla, in association with the second part of the axillary artery. Efferent vessels from the central nodes pass to the apical nodes. The apical nodes are located at the apex of the axilla along the medial side of the axillary vein and the first part of the axillary artery. The apical nodes receive lymph from all other groups of axillary lymph nodes as well as from lymphatics accompanying the proximal cephalic vein. Efferent vessels from the apical group of nodes traverse the cervicoaxillary canal. These efferent vessels ultimately unite to form the subclavian lymphatic trunk, although some vessels may drain en route through the clavicular (infraclavicular and supraclavicular) nodes. Once formed, the subclavian trunk may be joined by the jugular and bronchomediastinal trunks on the right side to form the right lymphatic duct, or it may enter the right venous angle independently. On the left side, the subclavian trunk most commonly joins the thoracic duct (Fig. 6.27A & B).

Enlargement of the Axillary Lymph Nodes An infection in the upper limb can cause the axillary nodes to enlarge and become tender and inflamed, a condition called lymphangitis (inflammation of lymphatic vessels). The humeral group of nodes is usually the first to be involved. Lymphangitis is characterized by the development of warm, red, tender streaks in the skin of the limb. Infections in the pectoral region and breast, including the superior part of the abdomen, can also produce enlargement of axillary nodes. In metastatic cancer of the apical group, the nodes often adhere to the axillary vein, which may necessitate excision of part of this vessel. Enlargement of the apical nodes may obstruct the cephalic vein superior to the pectoralis minor.

Dissection of the Axillary Lymph Nodes Excision and pathologic analysis of axillary lymph nodes are often necessary for staging and determining the appropriate treatment of a cancer such as breast cancer (see Chapter 1). Because the axillary lymph nodes are arranged and receive lymph (and therefore metastatic breast cancer cells) in a specific order, removing and examining the lymph nodes in that order is important in determining the degree to which the cancer has developed and is likely to have metastasized. Lymphatic drainage of the upper limb may be impeded after the removal of the axillary nodes, resulting in lymphedema, swelling as a result of accumulated lymph, especially in the subcutaneous tissue. During axillary node dissection, two nerves are at risk of injury. During surgery, the long thoracic nerve to the serratus anterior is identified and maintained against the thoracic wall. As discussed earlier in this chapter, cutting the long thoracic nerve results in a winged scapula. If the thoracodorsal nerve to the latissimus dorsi is cut,


medial rotation and adduction of the arm are weakened, but deformity does not result. If the nodes around this nerve are obviously malignant, sometimes the nerve has to be sacrificed as the nodes are resected to increase the likelihood of complete removal of all malignant cells.

The Bottom Line The axilla gives passage to important vascular structures passing between the neck and the upper limb. The axillary vein lies anterior and slightly inferior to the axillary artery, both being surrounded by the fascial axillary sheath. For descriptive purposes, the axillary artery and vein are assigned three parts located medial, posterior, and lateral to the pectoralis minor. Coincidentally, the first part of the artery has one branch; the second part, two branches; and the third part, three branches. The axillary lymph nodes are embedded in the axillary fat external to the axillary sheath. The axillary lymph nodes occur in groups that are arranged and receive lymph in a specific order, which is important in staging and determining appropriate treatment for breast cancer. In addition to transporting blood and lymph to and from the upper limb, the vascular structures of the axilla also serve the scapular and pectoral regions and lateral thoracic wall. The axillary lymph nodes receive lymph from the upper limb as well as the entire upper quadrant of the superficial body wall, from the level of the clavicles to the umbilicus including most from the breast.

Brachial Plexus Most nerves in the upper limb arise from the brachial plexus, a major nerve network supplying the upper limb; it begins in the neck and extends into the axilla. Almost all branches of the brachial plexus arise in the axilla (after the plexus has crossed the 1st rib). The brachial plexus is formed by the union of the anterior rami of the last four cervical (C5—C8) and the first thoracic (T1) nerves that constitute the roots of the brachial plexus (Fig. 6.28; Table 6.5). The roots usually pass through the gap between the anterior and the middle scalene (L. scalenus anterior and medius) muscles with the subclavian artery (Figs. 6.29 and 6.30). The sympathetic fibers carried by each root of the plexus are received from the gray rami of the middle and inferior cervical ganglia as the roots pass between the scalene muscles. In the inferior part of the neck, the roots of the brachial plexus unite to form three trunks (Fig. 6.28):   

A superior trunk, from the union of the C5 and C6 roots. A middle trunk, which is a continuation of the C7 root. An inferior trunk, from the union of the C8 and T1 roots.

Each trunk of the brachial plexus divides into anterior and posterior divisions as the plexus passes through the cervicoaxillary canal posterior to the clavicle. Anterior divisions of the trunks supply anterior (flexor) compartments of the upper limb, and posterior divisions of the trunks supply posterior (extensor) compartments. The divisions of the trunks form three cords of the brachial plexus:   

Anterior divisions of the superior and middle trunks unite to form the lateral cord. Anterior division of the inferior trunk continues as the medial cord. Posterior divisions of all three trunks unite to form the posterior cord.


The cords bear the relationship to the second part of the axillary artery that is indicated by their names. For example, the lateral cord is lateral to the axillary artery, although it may appear to lie superior to the artery because it is most easily seen when the limb is abducted. Figure 6.28. Formation of brachial plexus. This large nerve network is shown extending from the neck to the upper limb via the cervicoaxillary canal (bound by the clavicle, 1st rib, and superior scapula) to provide innervation to the upper limb and shoulder region. The brachial plexus is typically formed by the anterior rami of the C5—C8 nerves and the greater part of the anterior ramus of the T1 nerve (the roots of the brachial plexus). Observe the merging and continuation of certain roots of the plexus to three trunks, the separation of each trunk into anterior and posterior divisions, the union of the divisions to form three cords, and the derivation of the main terminal branches (peripheral nerves) from the cords as the products of plexus formation.

Figure 6.29. Dissection of right lateral cervical region (posterior triangle). The brachial plexus and subclavian vessels have been dissected. The anterior rami of spinal nerves C5—C8 (plus T1, concealed here by the third part of the subclavian artery) constitute the roots of the brachial plexus (numbered). Merging and subsequent splitting of the nerve fibers conveyed by the roots form the trunks and divisions at the level shown. The subclavian artery emerges between the middle and anterior scalene muscles with the roots of the plexus. As the neurovascular structures pass posterior to the clavicle, they are traversing the cervicoaxillary canal connecting the neck and axilla. The subclavius, although not of major importance as a muscle, affords some protection to the underlying neurovascular structures when the clavicle is (commonly) fractured in its middle third.


The products of plexus formation are multisegmental, peripheral (named) nerves. The brachial plexus is divided into supraclavicular and infraclavicular parts by the clavicle (Fig. 6.28; Table 6.5). Four branches of the supraclavicular part of the plexus arise from the roots (anterior rami) and trunks of the brachial plexus (dorsal scapular nerve, long thoracic nerve, nerve to subclavius, and suprascapular nerve) and are approachable through the neck. In addition, officially unnamed muscular branches arise from all five roots of the plexus (anterior rami C5—T1), which supply the scaleni and longus colli muscles. The C5 root of the phrenic nerve (considered a branch of the cervical plexus) arises from the C5 plexus root, joining the C3—C4 components of the nerve on the anterior surface of the anterior scalene muscle (Fig 6.29). Branches of the infraclavicular part of the plexus arise from the cords of the brachial plexus and are approachable through the axilla. Counting side and terminal branches, three branches arise from the lateral cord, whereas the medial and posterior cords each give rise to five branches (counting the roots of the median nerve as individual branches). The branches of the supra‐clavicular and infraclavicular parts of the brachial plexus are listed in Table 6.5, along with the origin, course and distribution of each branch.

Variations of the Brachial Plexus Variations in the formation of the brachial plexus are common (Bergman et al., 1988). In addition to the five anterior rami (C5—C8 and T1) that form the roots of the brachial plexus, small contributions may be made by the anterior rami of C4 or T2. When the superiormost root (anterior ramus) of the plexus is C4 and the inferiormost root is C8, it is a prefixed brachial plexus. Alternately, when the superior root is C6 and the inferior root is T2, it is a postfixed brachial plexus. In the latter type, the inferior trunk of the plexus may be compressed by the 1st rib, producing neurovascular symptoms in the upper limb. Variations may also occur in the formation of trunks, divisions, and cords; in the origin and/or combination of branches; and in the relationship to the axillary artery and scalene muscles. For example, the lateral or medial cords may receive fibers from anterior rami inferior or superior to the usual levels, respectively. In some individuals, trunk divisions or cord formations may be absent in one or other parts of the plexus; however, the makeup of the terminal branches is unchanged. Because each peripheral nerve is a collection of nerve fibers bound together by connective tissue, it is understandable that the median nerve, for instance, may have two medial roots instead of one (i.e., the nerve fibers are simply grouped differently). This results from the fibers of the medial cord of the brachial plexus dividing into three branches, two forming the median nerve and the third forming the ulnar nerve. Sometimes it may be more confusing when the two medial roots are completely separate; however, understand that although the median nerve may have two medial roots, the components of the nerve are the same (i.e., the impulses arise from the same place and reach the same destination whether they go through one or two roots).


Table 6.5. Brachial Plexus and Nerves of the Upper Limb

Nerve Origin a Supraclavicular branches Dorsal scapular Posterior aspect of anterior ramus of C5 with a frequent contribution from C4 Long thoracic Posterior aspect of anterior rami of C5, C6, C7

Suprascapular

Superior trunk, receiving fibers from C5, C6 and often C4

Subclavian Superior trunk, nerve (nerve to receiving fibers subclavius) from C5, C6 and often C4 (Fig. 6.29)

Course

Structures Innervated

Pierces middle scalene; descends Rhomboids; occasionally deep to levator scapulae and supplies levator scapulae rhomboids

Passes through cervicoaxillary canal (Fig. 6.14), descending posterior to C8 and T1 roots of plexus (anterior rami); runs inferiorly on superficial surface of serratus anterior Passes laterally across lateral cervical region (posterior triangle of neck), superior to brachial plexus; then through scapular notch inferior to superior transverse cervical ligament Descends posterior to clavicle and anterior to brachial plexus and subclavian artery (Fig. 6.29); often giving an accessory root to phrenic nerve

Serratus anterior

Supraspinatus and infraspinatus muscles; glenohumeral (shoulder) joint

Subclavius and sternoclavicular joint (accessory phrenic root innervates diaphragm)


Infraclavicular branches Lateral pectoral Side branch of lateral cord, receiving fibers from C5, C6, C7

Musculo‐ cutaneous

Terminal branch of lateral cord, receiving fibers from C5—C7

Median

Lateral root of median nerve is a terminal branch of lateral cord (C6, C7); medial root of median nerve is a terminal branch of medial cord (C8, T1)

Medial pectoral

Side branches of medial cord, receiving fibers from C8, T1

Medial cutaneous nerve of arm

Median cutaneous nerve of forearm

Ulnar

Larger terminal branch of medial cord, receiving fibers from C8, T1 and often C7

Upper subscapular

Side branch of posterior cord, receiving fibers from C5

Pierces costocoracoid membrane to reach deep surface of pectoral muscles; a communicating branch to the medial pectoral nerve passes anterior to axillary artery and vein Exits axilla by piercing coracobrachialis (Fig. 6.28); descends between biceps brachii and brachialis (Fig. 6.31), supplying both; continues as lateral cutaneous nerve of forearm Lateral and medial roots merge to form median nerve lateral to axillary artery; descends through arm adjacent to brachial artery, with nerve gradually crossing anterior to artery to lie medial to artery in cubital fossa (Fig. 6.32A)

Primarily pectoralis major; but some lateral pectoral nerve fibers pass to pectoralis minor via branch to medial pectoral nerve (Fig. 6.30A) Muscles of anterior compartment of arm (coracobrachialis, biceps brachii and brachialis) (Fig. 6.30B); skin of lateral aspect of forearm

Muscles of anterior forearm compartment (except for flexor carpi ulnaris and ulnar half of flexor digito‐rum profundus), five intrinsic muscles in thenar half of palm and palmar skin (Fig. 6.30B) Passes between axillary artery Pectoralis minor and and vein; then pierces pectoralis sternocostal part of minor and enters deep surface of pectoralis major pectoralis major; although it is called medial for its origin from medial cord, it lies lateral to lateral pectoral nerve Smallest nerve of plexus; runs Skin of medial side of along medial side of axillary and arm, as far distal as brachial veins; communicates medial epicondyle of with intercostobrachial nerve humerus and olecranon of ulna Initially runs with ulnar nerve Skin of medial side of (with which it may be confused) forearm, as far distal as but pierces deep fascia with wrist basilic vein and enters subcutaneous tissue, dividing into anterior and posterior branches Descends medial arm; passes Flexor carpi ulnaris and posterior to medial epicondyle of ulnar half of flexor humerus; then descends ulnar digitorum profundus aspect of forearm to hand (Figs. (forearm); most intrinsic 6.30C and 6.32A) muscles of hand; skin of hand medial to axial line of digit 4 Passes posteriorly, entering Superior portion of subscapularis directly subscapularis


Lower subscapular

Side branch of posterior cord, receiving fibers from C6 Side branch of posterior cord, receiving fibers from C6, C7, C8

Passes inferolaterally, deep to Inferior portion of subscapular artery and vein subscapularis and teres major

Axillary

Terminal branch of posterior cord, receiving fibers from C5, C6

Glenohumeral (shoulder) joint; teres minor and deltoid muscles (Fig. 6.30D); skin of superolateral arm (over inferior part of deltoid)

Radial

Larger terminal branch of posterior cord (largest branch of plexus), receiving fibers from C5—T1

Thoracodorsal

a

Arises between upper and lower subscapular nerves and runs inferolaterally along posterior axillary wall to apical part of latissimus dorsi Exits axillary fossa posteriorly, passing through quadrangular space b with posterior circumflex humeral artery (Fig. 6.31); gives rise to superior lateral brachial cutaneous nerve; then winds around surgical neck of humerus deep to deltoid (Fig. 6.30D) Exits axillary fossa posterior to axillary artery; passes posterior to humerus in radial groove with deep brachial artery, between lateral and medial heads of triceps; perforates lateral intermuscular septum; enters cubital fossa, dividing into superficial (cutaneous) and deep (motor) radial nerves (Fig. 6.30D)

Latissimus dorsi

All muscles of posterior compartments of arm and forearm (Fig. 6.30D); skin of posterior and inferolateral arm, posterior forearm, and dorsum of hand lateral to axial line of digit 4

B o l d f a ce (C5) indicates primary c o m p o n e n t of the nerve. B ou n d e d s u p e r i o r l y b y th e s u b s c a p u la r i s , h e a d of h u m e r u s , a n d t e re s m in o r ; i n f e r i o rl y b y t h e t e r e s m a j o r ; m e d i a l l y b y th e l o n g h e a d o f t h e t r i c e p s ; a n d l a t e ra l l y b y t h e c o r a c o b r a c h i a l i s a n d s u rg i c a l n e c k o f t h e h u m e r u s ( F i g . 6 . 31 ) . b

Brachial Plexus Injuries Injuries to the brachial plexus affect movements and cutaneous sensations in the upper limb. Disease, stretching, and wounds in the lateral cervical region (posterior triangle) of the neck (see Chapter 8) or in the axilla may produce brachial plexus injuries. Signs and symptoms depend on the part of the plexus involved. Injuries to the brachial plexus result in paralysis and anesthesia. Testing the person's ability to perform movements assesses the degree of paralysis. In complete paralysis, no movement is detectable. In incomplete paralysis, not all muscles are paralyzed; therefore, the person can move, but the movements are weak compared with those on the normal side. Determining the ability of the person to feel pain (e.g., from a pinprick of the skin) tests the degree of anesthesia.

Clinically Oriented Anatomy, 5th Edition By Keith Moore Figure 6.30. Summary of innervation of upper limb muscles. A. The medial and lateral pectoral nerves arise from the medial and lateral cords of the brachial plexus, respectively (or from the anterior divisions of the trunks that form them, as shown here for the lateral pectoral nerve). B. The courses of the median and musculocutaneous nerves and the typical pattern of branching of their motor branches are shown. C. The course of the ulnar nerve and the typical pattern of branching of its motor branches are shown. D. The courses of the axillary and radial nerves and the typical pattern of branching of their motor branches are shown. The posterior interosseous nerve is the continuation of the deep branch of the radial nerve, shown here bifurcating into two branches to supply all the muscles with fleshy bellies located entirely in the posterior compartment of the forearm. The dorsum of the hand has no fleshy muscle fibers; therefore, no motor nerves are distributed there.


Injuries to superior parts of the brachial plexus (C5 and C6) usually result from an excessive increase in the angle between the neck and the shoulder. These injuries can occur in a person who is thrown from a motorcycle or a horse and lands on the shoulder in a way that widely separates the neck and shoulder (Fig. B6.12A). When thrown, the person's shoulder often hits something (e.g., a tree or the ground) and stops, but the head and trunk continue to move. This stretches or ruptures superior parts of the brachial plexus or avulses (tears) the roots of the plexus from the spinal cord. Injury to the superior trunk of the plexus is apparent by the characteristic position of the limb (“waiter's tip position” ), in which the limb hangs by the side in medial rotation (Fig. B6.12B). Upper brachial plexus injuries can also occur in a newborn when excessive stretching of the neck occurs during delivery (Fig. B6.12C). As a result of injuries to the superior parts of the brachial plexus (Erb‐Duchenne palsy), paralysis of the muscles of the shoulder and arm supplied by the C5 and C6 spinal nerves occurs: deltoid, biceps, brachialis, and brachioradialis. The usual clinical appearance is an upper limb with an adducted shoulder, medially rotated arm, and extended elbow. The lateral aspect of the upper limb also experiences loss of sensation. Chronic microtrauma to the superior trunk of the brachial plexus from carrying a heavy backpack can produce motor and sensory deficits in the distribution of the musculocutaneous and radial nerves. A superior brachial plexus injury may produce muscle spasms and a severe disability in hikers (backpacker's palsy) who carry heavy backpacks for long periods. Acute brachial plexus neuritis (brachial plexus neuropathy) is a neurologic disorder of unknown cause that is characterized by the sudden onset of severe pain, usually around the shoulder (Rowland, 2000). Typically, the pain begins at night and is followed by muscle weakness and sometimes muscular atrophy (neurologic amyotrophy). Inflammation of the brachial plexus (brachial neuritis) is often preceded by some event (e.g., upper respiratory infection, vaccination, or non‐ specific trauma). The nerve fibers involved are usually derived from the superior trunk of the brachial plexus. Figure B6.12. Injuries to brachial plexus. A. Note the excessive increase in the angle between the head and the left shoulder. B. The waiter's tip position (left upper limb) is demonstrated. C. Observe the excessive increase in the angle between the head and the left shoulder during this delivery. D and E. Excessive increases in the angle between the trunk and the right upper limb are demonstrated. F. A claw hand is shown (person is attempting to assume lightly shaded “fist” position).


Compression of cords of the brachial plexus may result from prolonged hyperabduction of the arm during performance of manual tasks over the head, such as painting a ceiling. The cords are impinged or compressed between the coracoid process of the scapula and the pectoralis minor tendon. Common neurologic symptoms are pain radiating down the arm, numbness, paresthesia (tingling), erythema (redness of the skin caused by capillary dilation), and weakness of the hands. Compression of the axillary artery and vein causes ischemia of the upper limb and distension of the superficial veins. These signs and symptoms of hyperabduction syndrome result from compression of the axillary vessels and nerves. Injuries to inferior parts of the brachial plexus (Klumpke paralysis) are much less common. Inferior brachial plexus injuries may occur when the upper limb is suddenly pulled superiorly—for example, when a person grasps something to break a fall (Fig. B6.12D) or a baby's upper limb is pulled excessively during delivery (Fig. B6.12E). These events injure the inferior trunk of the brachial plexus (C8 and T1) and may avulse the roots of the spinal nerves from the spinal cord. The short muscles of the hand are affected, and a claw hand results (Fig. B6.12F).

Brachial Plexus Block Injection of an anesthetic solution into or immediately surrounding the axillary sheath interrupts nerve impulses and produces anesthesia of the structures supplied by the branches of the cords of the plexus (Fig. 6.24A). Sensation is blocked in all deep structures of the upper limb and the skin distal to the middle of the arm. Combined with an occlusive tourniquet technique to retain the anesthetic agent, this procedure enables surgeons to operate on the upper limb without using a general anesthetic. The brachial plexus can be anesthetized using a number of approaches, including an interscalene, supraclavicular, and axillary approach or block (Leonard, et al., 1999).

The Bottom Line The brachial plexus is an organized intermingling of the nerve fibers of the five adjacent anterior rami (C5—T1, the roots of the plexus) innervating the upper limb. Although their segmental identity is lost in forming the plexus, the original segmental distribution to skin (dermatomes) and muscles (myotomes) remains, exhibiting a cranial to caudal distribution for the skin (see “Cutaneous Nerves of the Upper Limb,” earlier in this chapter) and a proximal to distal distribution for the muscles. For example, C5 and C6 fibers primarily innervate muscles that act at the shoulder or flex the elbow; C7 and C8 fibers innervate muscles that extend the elbow or are part of the forearm; and T1 fibers innervate the intrinsic muscles of the hand. Formation of the brachial plexus initially involves merging of the superior and inferior pairs of roots, resulting in three trunks that each divide into anterior and posterior divisions. The fibers traversing anterior divisions innervate flexors and pronators of the anterior compartments of the limb, whereas the fibers traversing posterior divisions innervate extensors and supinators of the posterior compartments of the limb. The six divisions merge to form three cords that surround the axillary artery. Two of the three cords give rise in turn to 5 nerves, and the third (lateral cord) gives rise to 3 nerves. In addition to the nerves arising from the cords, 10 more


nerves arise from the various parts of the plexus. Most nerves arising from the plexus contain fibers from two or more adjacent anterior rami.

Surface Anatomy of the Pectoral and Scapular Regions The clavicle is the boundary demarcating the root of the neck from the thorax. It also indicates the “divide” between the deep cervical and the axillary “lymph sheds” (like a mountain range dividing watershed areas): lymph from structures superior to the clavicles drain via the deep cervical nodes; and lymph from structures inferior to the clavicles, as far inferiorly as the umbilicus, drain via the axillary lymph nodes. As the clavicle passes laterally, its medial part can be felt to be convex anteriorly (Fig. SA6.4). The large vessels and nerves to the upper limb pass posterior to this convexity. The flattened acromial end of the clavicle does not reach the point of the shoulder, formed by the lateral tip of the acromion of the scapula. The acromion is palpable and may be obvious when the deltoid contracts against resistance. The infraclavicular fossa is the depressed area just inferior to the lateral part of the clavicle. This depression overlies the clavipectoral (deltopectoral) triangle, bounded by the clavicle superiorly, the pectoralis major medially, and the deltoid laterally, which may be evident in the fossa in lean individuals. The cephalic vein ascending from the upper limb enters the clavipectoral triangle and pierces the clavipectoral fascia to enter the axillary vein. The coracoid process of the scapula is not subcutaneous; it is covered by the anterior border of the deltoid; however, the tip of the process can be felt on deep palpation on the lateral aspect of the clavipectoral triangle. The coracoid process is used as a bony landmark when performing a brachial plexus block, and its position is of importance in diagnosing shoulder dislocations. While lifting a weight, palpate the anterior sloping border of the trapezius and where its superior fibers attach to the lateral third of the clavicle. When the arm is abducted and then adducted against resistance, the sternocostal part of the pectoralis major can be seen and palpated. If the anterior axillary fold bounding the axilla is grasped between the fingers and thumb, the inferior border of the sternocostal head of the pectoralis major can be felt. Several digitations of the serratus anterior are visible inferior to the anterior axillary fold. The posterior axillary fold is composed of skin and muscular tissue (latissimus dorsi and teres major) bounding the axilla posteriorly.

Figure SA6.4


The lateral border of the acromion may be followed posteriorly with the fingers until it ends at the acromial angle (Fig. SA6.5). Clinically, the length of the arm is measured from the acromial angle to the lateral condyle of the humerus. The spine of the scapula is subcutaneous throughout and is easily palpated as it extends medially and slightly inferiorly from the acromion. The root of the scapular spine (medial end) is located opposite the tip of the T3 spinous process when the arm is adducted. The medial border of the scapula may be palpated inferior to the root of the spine as it crosses ribs 3—7 (Fig. SA6.6). It may be visible in some people, especially thin people. The inferior angle of the scapula is easily palpated and is usually visible. Grasp the inferior scapular angle with the thumb and fingers and move the scapula up and down. When the arm is adducted, the inferior scapular angle is opposite the tip of the T7 spinous process and lies over the 7th rib or intercostal space. The deltoid covering the proximal part of the humerus forms the rounded muscular contour of the shoulder. The greater tubercle of the humerus is the most lateral bony point in the shoulder when the arm is adducted and may be felt on deep palpation through the deltoid inferior to the lateral border of the acromion. When the arm is abducted, observe that the greater tubercle disappears beneath the acromion and is no longer palpable. The borders and parts of the deltoid are usually visible when the arm is abducted against resistance. Loss of the rounded muscular appearance of the shoulder and the appearance of a surface depression distal to the acromion are characteristic of a dislocated shoulder, or dislocation of the glenohumeral joint. The depression results from displacement of the humeral head. The teres major is prominent when the abducted arm is adducted and medially rotated against resistance (as when an acrobat stabilizes or fixes the shoulder joint during an iron cross maneuver on the ring. [Fig. SA6.7]). When the upper limbs are abducted, the scapulae move laterally on the thoracic wall, enabling the rhomboids to be palpated. Because they are deep to the trapezius, the rhomboids are not always visible. If the rhomboids of one side are paralyzed, the scapula on the affected side remains farther from the midline than on the normal side because the paralyzed muscles are unable to retract it.

Figure SA6.5


Figure SA6.6

Figure SA6.7

Arm The arm extends from the shoulder to the elbow. Two types of movement occur between the arm and the forearm at the elbow joint: flexion—extension and pronation—supination. The muscles performing these movements are clearly divided into anterior and posterior groups. The chief action of both groups is at the elbow joint, but some muscles also act at the glenohumeral joint. The superior part of the humerus provides attachments for tendons of the shoulder muscles.


Muscles of the Arm Of the four major arm muscles, three flexors (biceps brachii, brachialis, and coracobrachialis) are in the anterior (flexor) compartment, supplied by the musculocutaneous nerve (Figs. 6.31 and 6.32), and one extensor (triceps brachii) is in the posterior compartment, supplied by the radial nerve. A distally placed assistant to the triceps, the anconeus, also lies within the posterior compartment. The flexor muscles of the anterior compartment are almost twice as strong as the extensors in all positions; consequently, we are better pullers than pushers. It should be noted, however, that the extensors of the elbow are particularly important for raising oneself out of a chair and for wheelchair activity. Therefore, conditioning of the triceps is of particular importance in elderly or disabled persons. The arm muscles are illustrated and their attachments, innervation, and actions are described in Table 6.6.

Biceps Brachii As the term biceps brachii indicates, the proximal attachment of this fusiform muscle usually has two heads (bi, two + L. caput, head). However, approximately 10% of people have a third head to the biceps. The usual two heads of the biceps arise proximally by tendinous attachments to processes of the scapula, their fleshy bellies uniting just distal to the middle of the arm (Fig. 6.31). When present, the third head extends from the superomedial part of the brachialis (with which it is blended), usually lying posterior to the brachial artery. In either case, a single biceps tendon forms distally and attaches primarily to the radius. F i g u r e 6. 3 1 . P o s t e r i o r w a l l o f a x i l l a , m u s cu l o c u t a n e ou s n e r v e , a n d p o s te r io r c o r d o f b r a c h i a l p l e x u s . Th e p e c t o r a l i s m a j o r a n d m i n o r m u s c l e s a re r e f l e c t e d s u p e r o l a t e r a ll y , a n d t h e l a t e r a l a n d m e d i a l co r d s o f t h e b r a c h i a l plexus are reflected s u p e r o m e d i a l l y . A l l m a j o r v e s s e l s a n d t h e ne rv e s a r i s i n g f r o m t h e m e d i a l a n d l a t e r a l c o r d s o f the b r a c h i a l p l e x u s (e x c e p t f o r the m u s c u l o c u t a n e o u s n e r v e f r o m the l a t e r a l c o r d ) a r e r e m ov e d . T h e posterior cord, formed by the m e r g i n g o f t h e p o s te r i o r d i v i s i o n s o f a l l t h r e e tr u n k s of t h e b r a c h i a l p l e x u s , g i v e s r i s e t o f i v e n e r v e s : radial, axillary, upper and lower s u b s c a p u l a r , a n d t h o ra c o d o r s a l . N o t e t h a t t h e m u s c u l o c u t a n e ou s nerve p i e rc e s th e c o r a c o b r a c h i a l i s m u s c l e a n d t h a t t h e l o w e r s u b s c a p u l a r n e r v e s u p p l i e s t h e te r e s m a j o r a s we l l a s t h e s u b s c a p u l a r i s .


Although the biceps is located in the anterior compartment of the arm (Fig. 6.32), it has no attachment to the humerus. The biceps is a “three‐joint muscle,” crossing and capable of effecting movement at the glenohumeral, elbow, and radioulnar joints, although it primarily acts at the latter two. Its action and effectiveness is markedly affected by the position of the elbow and forearm. When the elbow is extended, the biceps is a simple flexor of the forearm; however, as elbow flexion approaches 90° and more power is needed against resistance, the biceps is capable of two powerful movements, depending on the position of the forearm. When the elbow is flexed close to 90° and the forearm is supinated, the biceps is most efficient in producing flexion. Alternately, when the forearm is pronated, the biceps is the primary (most powerful) supinator of the forearm. For example, it is used when right‐ handed people drive a screw into hard wood and when inserting a corkscrew and pulling the cork from a wine bottle. The biceps barely operates as a flexor when the forearm is pronated, even against resistance. In the semiprone position, it is active only against resistance (Hamill and Knutzen, 2003). Arising from the supraglenoid tubercle of the scapula and crossing the head of the humerus within the cavity of the glenohumeral joint, the rounded tendon of the long head of the biceps continues to be surrounded by synovial membrane as it descends in the intertubercular groove of the humerus. A broad band, the transverse humeral ligament, passes from the lesser to the greater tubercle of the humerus and converts the intertubercular groove into a canal (Table 6.6). The ligament holds the tendon of the long head of the biceps in the groove.


Figure

6.32. Muscles, neurovascular structures, and compartments of arm. A. In this dissection of the right arm, the veins have been removed, except for the proximal part of the axillary vein. The courses of the musculocutaneous , median, and ulnar nerves and the brachial artery along the medial (protected) aspect of the arm are demonstrated. Their courses generally parallel the medial intermuscular septum that separates the anterior and posterior compartments in the distal two thirds of the arm. B. In this transverse section of the right arm, the three heads of the triceps and the radial nerve and its companion vessels (in contact with the humerus) lie in the posterior compartment. C. This transverse MRI demonstrates the features shown in part B. The numbered structures are identified in part B. (Courtesy of Dr. W. Kucharczyk, Chair of Medical Imaging and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, Ontario, Canada.)


Distally, the major attachment of the biceps is to the radial tuberosity via the biceps tendon. However, a triangular membranous band, called the bicipital aponeurosis, runs from the biceps tendon across the cubital fossa and merges with the antebrachial (deep) fascia covering the flexor muscles in the medial side of the forearm. It attaches indirectly by means of the fascia to the subcutaneous border of the ulna. The proximal part of the bicipital aponeurosis can be easily felt where it passes obliquely over the brachial artery and median nerve (Fig. 6.33A). The bicipital aponeurosis affords protection for these and other structures in the cubital fossa. It also helps lessen the pressure of the biceps tendon on the radial tuberosity during pronation and supination of the forearm. To test the biceps brachii, the elbow joint is flexed against resistance when the forearm is supinated. If acting normally, the muscle forms a prominent bulge on the anterior aspect of the arm that is easily palpated.

Bicipital Myotatic Reflex The biceps reflex is one of several deep‐tendon reflexes that are routinely tested during physical examination. The relaxed limb is passively pronated and partially extended at the elbow. The examiner's thumb is firmly placed on the biceps tendon, and the reflex hammer is briskly tapped at the base of the nail bed of the examiner's thumb (Fig. B6.13). A normal (positive) response is an involuntary contraction of the biceps, felt as a momentarily tensed tendon, usually with a brief jerk‐like flexion of the elbow. A positive response confirms the integrity of the musculocutaneous nerve and the C5 and C6 spinal cord segments. Excessive, diminished, or prolonged (hung) responses may indicate central or peripheral nervous system disease or metabolic disorders (e.g., thyroid disease).

Figure B6.13. Method of eliciting biceps reflex.

Biceps Tendinitis The tendon of the long head of the biceps is enclosed by a synovial sheath and moves back and forth in the inter‐tubercular groove of the humerus. Wear and tear of this mechanism can cause shoulder pain. Inflammation of the tendon (biceps tendinitis), usually the result of repetitive microtrauma, is common in sports involving throwing


(e.g., baseball and cricket) and use of a racquet (e.g., tennis). A tight, narrow, and/or rough intertubercular groove may irritate and inflame the tendon, producing tenderness and crepitus (a crackling sound).

Dislocation of the Tendon of the Long Head of the Biceps The tendon of the long head of the biceps can be partially or completely dislocated from the intertubercular groove in the humerus. This painful condition may occur in young persons during traumatic separation of the proximal epiphysis of the humerus. The injury also occurs in older persons with a history of biceps tendinitis. Usually a sensation of popping or catching is felt during arm rotation.

Rupture of the Tendon of the Long Head of the Biceps Rupture of the tendon usually results from wear and tear of an inflamed tendon as it moves back and forth in the intertubercular groove of the humerus. This injury usually occurs in individuals > 35 years of age. Typically, the tendon is torn from its attachment to the supraglenoid tubercle of the scapula. The rupture is commonly dramatic and is associated with a snap or pop. The detached muscle belly forms a ball near the center of the distal part of the anterior aspect of the arm (Popeye deformity) (Fig. B6.14). Rupture of the biceps tendon may result from forceful flexion of the arm against excessive resistance, as occurs in weight lifters (Anderson et al., 2000). However, the tendon ruptures more often as the result of prolonged tendinitis that weakens it. The rupture results from repetitive overhead motions, such as occurs in swimmers and baseball pitchers, which tear the weakened tendon where it passes through the intertubercular groove.

Figure B6.14


Table 6.6. Muscles of the Arm

Muscle Biceps brachii

Brachialis

Coraco‐ brachialis

Proximal Attachment Short head: tip of coracoid process of scapula Long head: supraglenoid tubercle of scapula

Distal Attachment Innervation a Tuberosity of Musculocutaneous radius and fascia of nerve b (C5, C6) forearm via bicipital aponeurosis

Distal half of anterior Coronoid process surface of humerus and tuberosity of ulna Tip of coracoid process Middle third of Musculocutaneous of scapula medial surface of nerve (C5, C6, C7) humerus

Main Action Supinates forearm and, when it is supine, flexes forearm; short head resists dislocation of shoulder Flexes forearm in all positions Helps flex and adduct arm; resists dislocation of shoulder


Triceps brachii

Anconeus

Long head: infra‐ glenoid tubercle of scapula Lateral head: posterior surface of humerus, superior to radial groove Medial head: posterior surface of humerus, inferior to radial groove Lateral epicondyle of humerus

Proximal end of Radial nerve (C6, Chief extensor of olecranon of ulna C7, C8) forearm; long head and fascia of resists dislocation of forearm humerus; especially important during abduction

Lateral surface of Radial nerve (C7, Assists triceps in olecranon and C8, T1) extending forearm; superior part of stabilizes elbow joint; posterior surface may abduct ulna of ulna during pronation a The spinal cord segmental innervation is indicated (e.g., “C5, C6” means that the nerves supplying the biceps brachii are derived from the fifth and sixth cervical segments of the spinal cord). Numbers in boldface (C6) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned. b Some of the lateral part of the brachialis is innervated by a branch of the radial nerve.

Figure 6.33. Dissections of cubital fossa. A. In this superficial dissection, the distal end of the brachial artery lies medial to the biceps tendon. During the measurement of blood pressure, a stethoscope is placed


here to listen to pulsations of the brachial artery. At this level, the median nerve lies on the medial aspec t of the brachial artery, and both are deep to the bicipital aponeurosis (Fig. 6.38A). B. In this deep dissection, part of the biceps is excised and the cubital fossa is opened widely by retracting the forearm extensor muscles laterally and the flexor muscles medially. The radial nerve, which has just left the posterior compartment of the arm by piercing the lateral intermuscular septum, emerges between th e brachialis and the brachioradialis and divides into a superficial (sensory) and a deep (motor) branch (Fig. 6.39A). The superficial branch remains under the protection of the brachioradialis, but the deep branch pierces the supinator to return to the posterior aspect of the limb. The brachial artery is dividing into its terminal branches: the ulnar artery, which runs deeply, and the radial artery, which remains superficial; thus its pulsations are palpable throughout the forearm.

Brachialis The brachialis is a flattened fusiform muscle that lies posterior (deep) to the biceps. Its distal attachment covers the anterior part of the elbow joint (Figs. 6.31, 6.32, 6.33 and 6.39A). The brachialis is the main flexor of the forearm. It is the only pure flexor, producing the greatest amount of flexion force. It flexes the forearm in all positions, not being affected by pronation and supination; during both slow and quick movements; and in the presence or absence of resistance. When the forearm is extended slowly, the brachialis steadies the movement by slowly relaxing—that is, eccentric contraction (you use it to pick up and put down a teacup carefully, for example). The brachialis always contracts when the elbow is flexed and is primarily responsible for sustaining the flexed position. Because of its important and almost constant role, it is regarded as the workhorse of the elbow flexors.

Coracobrachialis The coracobrachialis is an elongated muscle in the superomedial part of the arm. It is a useful landmark for locating other structures in the arm (Figs. 6.31 and 6.32; Table 6.6). For example, the musculocutaneous nerve pierces it, and the distal part of its attachment indicates the location of the nutrient foramen of the humerus. The coracobrachialis helps flex and adduct the arm and stabilize the glenohumeral joint. With the deltoid and long head of the triceps, it serves as a shunt muscle, resisting downward dislocation of the head of the humerus, as when carrying a heavy suitcase. The median nerve and/or the brachial artery may run deep to the coracobrachialis and be compressed by it.

Triceps Brachii The triceps brachii is a large fusiform muscle in the posterior compartment of the arm (Figs. 6.32 and 6.34; Table 6.6). As indicated by its name, the triceps has three heads: long, lateral, and medial. The triceps is the main extensor of the forearm. Because its long head crosses the glenohumeral joint, the triceps helps stabilize the adducted glenohumeral joint by serving as a shunt muscle, resisting inferior displacement of the head of the humerus. The long head also aids in extension and adduction of the arm, but it is actually the least active head. The medial head is the workhorse of forearm extension, active at all speeds and in the presence or absence


of resistance. The lateral head is strongest but is recruited into activity primarily against resistance. (Hamill and Knutzen, 2003). Pronation and supination of the forearm do not affect triceps operation. Just proximal to the distal attachment of the triceps is a friction‐reducing subtendinous olecranon bursa, between the triceps tendon and the olecranon. To test the triceps (or to determine the level of a radial nerve lesion), the arm is abducted 90° and then the flexed forearm is extended against resistance provided by the examiner. If acting normally, the triceps can be seen and palpated. Its strength should be comparable with the contralateral muscle, given consideration for lateral dominance (right or left handedness).

Anconeus The anconeus is a small, relatively unimportant triangular muscle on the posterolateral aspect of the elbow; it is usually partially blended with the triceps (Table 6.6). The anconeus helps the triceps extend the forearm and tenses of the capsule of the elbow joint, preventing its being pinched during extension. It is also said to abduct the ulna during pronation of the forearm.

Brachial Artery The brachial artery provides the main arterial supply to the arm and is the continuation of the axillary artery (Fig. 6.35). It begins at the inferior border of the teres major (Figs. 6.32A and 6.35) and ends in the cubital fossa opposite the neck of the radius where, under cover of the bicipital aponeurosis, it divides into the radial and ulnar arteries (Figs. 6.33B and 6.35). The brachial artery, relatively superficial and palpable throughout its course, lies anterior to the triceps and brachialis. At first it lies medial to the humerus where its pulsations are palpable in the medial bicipital groove (Fig. 6.32B). It then passes anterior to the medial supraepicondylar ridge and trochlea of the humerus (Figs. 6.35 and 6.36). As it passes inferolaterally, the brachial artery accompanies the median nerve, which crosses anterior to the artery (Figs. 6.32A and 6.36). During its course through the arm, the brachial artery gives rise to many unnamed muscular branches and the humeral nutrient artery (Fig. 6.35), which arise from its lateral aspect. The unnamed muscular branches are often omitted from illustrations, but they are evident during dissection.


Figure 6.34. Muscles of scapular region and posterior region of arm. The lateral head of the triceps brachii is divided and displaced to show the radial nerve and the deep artery of the arm. The exposed bone of the radial groove, which is devoid of muscular attachment, separates the humeral attachments of the lateral and medial heads of the triceps (bony attachments are illustrated in Table 6.6). The structures traversing the quadrangular space and the ulnar nerve passing posterior to the medial epicondyle of the humerus (where the nerve is most commonly injured) are also demonstrated.

Figure 6.35. Arterial supply of arm and proximal forearm. Functionally and clinically important periarticular arterial anastomoses surround the elbow. The resulting collateral circulation allows blood to reach the forearm when flexion of the elbow compromises flow through the terminal part of the brachial artery.


The main named branches of the brachial artery arising from its medial aspect are the deep artery of the arm and the superior and inferior ulnar collateral arteries. The collateral arteries help form the periarticular arterial anastomoses of the elbow region. Other arteries involved are recurrent branches, sometimes double, from the radial, ulnar, and interosseous arteries, which run superiorly anterior and posterior to the elbow joint. These arteries anastomose with descending articular branches of the deep artery of the arm and the ulnar collateral arteries.

Deep Artery of the Arm The deep artery of the arm (L. arteria profunda brachii) is the largest branch of the brachial artery and has the most superior origin. The deep artery accompanies the radial nerve along the radial groove as it passes posteriorly around the shaft of the humerus (Figs. 6.34 and 6.36). The deep artery terminates by dividing into middle and radial collateral arteries that participate in the periarticular arterial anastomoses around the elbow.

Humeral Nutrient Artery The main humeral nutrient artery arises from the brachial artery around the middle of the arm (Fig. 6.35) and enters the nutrient canal on the anteromedial surface of the humerus. The artery runs distally in the canal toward the elbow. Other smaller humeral nutrient arteries also occur. Figure 6.36. Relationship of the arteries and nerves of the arm to the humerus. The cords of the brachial plexus surround the axillary artery. The radial nerve and accompanying deep artery of the arm wind posteriorly around, and directly on the surface of, the humerus in the radial groove. The radial nerve and radial collateral artery then pierce the lateral intermuscular septum to enter the anterior compartment. The ulnar nerve pierces the medial intermuscular septum to enter the posterior compartment and then lies in the groove for the ulnar nerve on the posterior aspect of the medial epicondyle of the humerus. The median nerve descends in the arm to the medial side of the cubital fossa, where it is well protected and rarely injured (Figs. 6.33 and 6.39).


Superior Ulnar Collateral Artery The superior ulnar collateral artery arises from the medial aspect of the brachial artery near the middle of the arm and accompanies the ulnar nerve posterior to the medial epicondyle of the humerus (Figs. 6.32A and 6.35). Here it anastomoses with the posterior ulnar recurrent artery and the inferior ulnar collateral artery, participating in the periarticular arterial anastomoses of the elbow.

Inferior Ulnar Collateral Artery The inferior ulnar collateral artery arises from the brachial artery approximately 5 cm proximal to the elbow crease (Figs. 6.32A, 6.33, and 6.35). It then passes inferomedially anterior to the medial epicondyle of the humerus and joins the anastomoses of the elbow region by anastomosing with the anterior ulnar recurrent artery.

Interruption of Blood Flow in the Brachial Artery Stopping bleeding through manual or surgical control of blood flow is hemostasis. The best place to compress the brachial artery to control hemorrhage is medial to the humerus near the middle of the arm (Fig. B6.15). Because the arterial anastomoses around the elbow provide a functionally and surgically important collateral circulation, the brachial artery may be clamped distal to the origin of the deep artery of the arm without producing tissue damage. The anatomical basis for this procedure is that the ulnar and radial arteries will still receive sufficient blood through the anastomoses around the elbow. Although collateral pathways confer some protection against gradual temporary and partial occlusion, sudden complete occlusion or laceration of the brachial artery creates a surgical emergency because paralysis of muscles results from ischemia of the elbow and forearm within a few hours. Muscles and nerves can tolerate up to 6 hours of ischemia (Salter, 1999); after this, fibrous scar tissue replaces necrotic tissue and causes the involved muscles to shorten permanently, producing a flexion deformity, the ischemic compartment syndrome (Volkmann or ischemic contracture). Contraction of the fingers and sometimes the wrist results in loss of hand power as a result of irreversible necrosis of the forearm flexor muscles.

Figure B6.15. Compression of brachial artery.


Fracture of the Humeral Shaft A midhumeral fracture may injure the radial nerve in the radial groove in the humeral shaft. When this nerve is damaged, the fracture is not likely to paralyze the triceps because of the high origin of the nerves to two of its three heads. A fracture of the distal part of the humerus, near the supraepicondylar ridges, is called a supraepicondylar fracture (Fig. B6.16). The distal bone fragment may be displaced anteriorly or posteriorly. The actions of the brachialis and triceps tend to pull the distal fragment over the proximal fragment, shortening the limb. Any of the nerves or branches of the brachial vessels related to the humerus may be injured by a displaced bone fragment.

Figure B6.16. Supraepicondylar fracture.

Veins of the Arm Two sets of veins of the arm, superficial and deep, anastomose freely with each other. The superficial veins are in the subcutaneous tissue, and the deep veins accompany the arteries. Both sets of veins have valves, but they are more numerous in the deep veins than in the superficial veins.

Superficial Veins The two main superficial veins of the arm, the cephalic and basilic veins (Figs. 6.32B & C and 6.33), are described in “Superficial Structures of the Upper Limb,” earlier in this chapter.

Deep Veins Paired deep veins, collectively constituting the brachial vein, accompany the brachial artery (Fig. 6.33A). Their frequent connections encompass the artery, forming an anastomotic network within a common vascular sheath. The pulsations of the brachial artery help move the blood through this venous network. The brachial vein begins at the elbow by union of the accompanying veins of the ulnar and radial arteries and end by merging with the basilic vein to form the axillary vein. Not uncommonly, the deep veins join to form one brachial vein during part of their course.


Nerves of the Arm Four main nerves pass through the arm: median, ulnar, musculocutaneous, and radial (Fig. 6.36). Their origins from the brachial plexus, courses in the upper limb, and the structures innervated by them are summarized in Table 6.5. The median and ulnar nerves supply no branches to the arm.

Musculocutaneous Nerve The musculocutaneous nerve begins opposite the inferior border of the pectoralis minor, pierces the coracobrachialis, and continues distally between the biceps and brachialis (Fig. 6.33B). After supplying all three muscles of the anterior compartment of the arm, the nerve emerges lateral to the biceps as the lateral cutaneous nerve of the forearm. It becomes truly subcutaneous when it pierces the deep fascia proximal to the cubital fossa to course initially with the cephalic vein in the subcutaneous tissue. After crossing the anterior aspect of the elbow, it continues to supply the skin of the lateral aspect of the forearm.

Radial Nerve in the Arm The radial nerve supplies all the muscles in the posterior compartment of the arm (and forearm). The radial nerve enters the arm posterior to the brachial artery, medial to the humerus, and anterior to the long head of the triceps, where it gives branches to the long and medial heads of the triceps (Fig. 6.31). The radial nerve then descends inferolaterally with the deep brachial artery and passes around the humeral shaft in the radial groove (Figs. 6.32B, 6.34, and 6.36). The branch to the lateral head of the triceps arises within the radial groove. When it reaches the lateral border of the humerus, the radial nerve pierces the lateral intermuscular septum and continues inferiorly in the anterior compartment of the arm between the brachialis and the brachioradialis to the level of the lateral epicondyle of the humerus (Fig. 6.33B). The radial nerve then divides into deep and superficial branches.  

The deep branch of the radial nerve is entirely muscular and articular in its distribution. The superficial branch of the radial nerve is entirely cutaneous in its distribution, supplying sensation to the dorsum of the hand and fingers.

Median Nerve in the Arm The median nerve runs distally in the arm on the lateral side of the brachial artery until it reaches the middle of the arm, where it crosses to the medial side and contacts the brachialis (Fig. 6.36). The median nerve then descends into the cubital fossa, where it lies deep to the bicipital aponeurosis and median cubital vein (Fig. 6.33). The median nerve has no branches in the axilla or the arm, but it does supply articular branches to the elbow joint.

Ulnar Nerve in the Arm The ulnar nerve passes distally from the axilla anterior to the insertion of the teres major and to the long head of the triceps, on the medial side of the brachial artery (Fig. 6.32). Around the middle of the arm it pierces the medial intermuscular septum with the superior ulnar collateral artery and descends between the septum and the


medial head of the triceps (Fig. 6.36). The ulnar nerve passes posterior to the medial epicondyle and medial to the olecranon to enter the forearm (Fig. 6.30C). Posterior to the medial epicondyle, where the ulnar nerve is referred to in lay terms as the “crazy bone,” it is superficial, easily palpable, and vulnerable to injury. Like the median nerve, the ulnar nerve has no branches in the arm, but it also supplies articular branches to the elbow joint.

Injury to the Musculocutaneous Nerve Injury to the musculocutaneous nerve in the axilla (uncommon in this protected position) is typically inflicted by a weapon such as a knife. A musculocutaneous nerve injury results in paralysis of the coracobrachialis, biceps, and brachialis. Consequently, flexion of the elbow joint and supination of the forearm are greatly weakened but not lost. Weak flexion and supination are still possible, produced by the brachioradialis and supinator, respectively, both of which are supplied by the radial nerve. Loss of sensation may occur on the lateral surface of the forearm supplied by the lateral antebrachial cutaneous nerve, the continuation of the musculocutaneous nerve.

Injury to the Radial Nerve in the Arm Injury to the radial nerve superior to the origin of its branches to the triceps brachii results in paralysis of the triceps, brachioradialis, supinator, and extensor muscles of the wrist and fingers. Loss of sensation in areas of skin supplied by this nerve also occurs. When the nerve is injured in the radial groove, the triceps is usually not completely paralyzed but only weakened because only the medial head is affected; however, the muscles in the posterior compartment of the forearm that are supplied by more distal branches of the nerve are paralyzed. The characteristic clinical sign of radial nerve injury is wrist‐drop (inability to extend the wrist and the fingers at the metacarpophalangeal joints (Fig. B6.17A). Instead, the relaxed wrist assumes a partly flexed position owing to unopposed tonus of flexor muscles and gravity (Fig. B6.17B).

Figure B6.17. Wrist‐drop.


The Bottom Line The arm forms a column with the humerus at its center. The humerus, along with intermuscular septa in its distal two thirds, divides the arm lengthwise (or more specifically, the space inside the brachial fascia) into anterior or flexor and posterior or extensor compartments. The anterior compartment contains three flexor muscles supplied by the musculocutaneous nerve. The coracobrachialis acts (weakly) at the shoulder, and the biceps and brachialis act at the elbow. The biceps is also the primary supinator of the forearm (when the elbow is flexed). The brachialis is the primary flexor of the forearm. The posterior compartment contains a three‐headed extensor muscle, the triceps, which is supplied by the radial nerve. One of the heads (the long head) acts at the shoulder, but mostly the heads work together to extend the elbow. Both compartments are supplied by the brachial artery, the posterior compartment primarily via its major branch, the deep artery of the arm. The primary neurovascular bundle is located on the medial side of the limb; thus it is usually protected by the limb it serves.

Cubital Fossa The cubital fossa is seen superficially as a depression on the anterior aspect of the elbow. Deeply, it is a space filled with a variable amount of fat anterior to the most distal part of the humerus and the elbow joint. The three boundaries of the triangular cubital fossa are as follows (Figs. 6.33 and 6.37C):  



Superiorly, an imaginary line connecting the medial and lateral epicondyles. Medially, the mass of flexor muscles of the forearm arising from the common flexor attachment on the medial epicondyle; most specifically, the pronator teres. Laterally, the mass of extensor muscles of the forearm arising from the lateral epicondyle and supraepicondylar ridge; most specifically, the brachioradialis.

The floor of the cubital fossa is formed by the brachialis and supinator muscles of the arm and forearm, respectively. The roof of the cubital fossa is formed by the continuity of brachial and antebrachial (deep) fascia reinforced by the bicipital aponeurosis (Figs. 6.38 and 6.39), subcutaneous tissue, and skin. The contents of the cubital fossa are the (Figs. 6.33 and 6.38A): 

   

Terminal part of the brachial artery and the commencement of its terminal branches, the radial and ulnar arteries. The brachial artery lies between the biceps tendon and the median nerve. (Deep) accompanying veins of the arteries. Biceps brachii tendon. Median nerve. Radial nerve, deep between the muscles forming lateral boundary of the fossa (the brachioradialis, in particular) and the brachialis, dividing into its superficial and deep branches. The muscles must be retracted to expose the nerve.


Superficially, in the subcutaneous tissue overlying the fossa are the median cubital vein, lying anterior to the brachial artery, and the medial and lateral antebrachial cutaneous nerves, related to the basilic and cephalic veins.

Figure 6.37. Bones, muscles, and compartments of forearm. A. An anteroposterior (AP) radiograph of the forearm in pronation is shown. (Courtesy of Dr. J. Heslin, Toronto, Ontario, Canada.) B. The bones of the forearm and the radioulnar ligaments are demonstrated. C. In this dissection the superficial muscles of the forearm and the palmar aponeurosis are revealed. D. This stepped transverse section demonstrates the compartments of the forearm. E. The flexor digitorum superficialis (FDS) and related structures are shown. Observe the ulnar artery descending obliquely posterior to the FDS to meet and accompany the ulnar nerve.


F i g u re 6 . 3 8 . C r o s s s e c t i o n s d e m o n s t ra t i n g r e l a t i o n s h i p s a t l e v e l o f c u b i t a l f o s s a , p r o x i m a l f o r e a r m , a n d w r i s t . A . A t t h e l e v e l o f t h e c u b i t a l f o s s a , t h e f l e x o r s a n d e x t e n s o r o f t h e e l b o w o c c u p y t h e a n te r i o r a n d p o s t e r i o r a s p e c ts o f t h e h u m e r u s . L a te r a l a n d m e d i a l e x t e n s i o n s ( e p i c o n d y le s a n d s u p r a e p i c o n d y l a r r i d g e s ) o f t h e h u m e r u s p r o v i d e p r o x i m a l a t t a c h m e n t (o r i g i n ) f o r t h e f o re a r m f l e x o r s a n d e x t e n s o r s . B . C o n s e q u e n t l y , in t h e p r o x i m a l f o r e a rm , t h e “ a n te r i o r ” f l e x o r — p r o n a t o r c o m p a r tm e n t a c t u a l ly l i e s a n te r o m e d i a l l y , a n d t h e “ p o s te r i o r ” e x t e n s o r — s u p i n a t o r c o m p a r t m e n t l i e s p o s t e r o la t e r a l l y . T h e r a d i a l a r t e ry ( l a t e r a l l y ) a n d t h e s h a r p , s u b c u ta n e o u s p o s t e r i o r b o r d e r o f t h e u l n a ( m e d i a l ly ) a r e p a l p a b l e f e a tu r e s s e p a r a t i n g t h e a n te r i o r a n d p o s te r i o r c o m p a r t m e n ts . N o m o t o r n e r v e s c r o s s e i t h e r d e m a r c a t i o n , m a k i n g t h e m u s e f u l f o r s u r g i c a l a p p ro a c h e s . E x t . d i g i t . , e x t e n s o r d i g i t o r u m ; E C U , e x t e n s o r c a r p i u l n a r i s . C . A t t h e l e v e l o f t h e w r is t , n i n e t e n d o n s f r o m t h re e m u s c l e s (a n d o n e n e rv e ) o f t h e a n t e r i o r c o m p a r t m e n t o f th e f o r e a r m t r a v e r s e t h e c a r p a l t u n n e l ; e ig h t o f th e t e n d o n s s h a r e a c o m m o n s y n o v i a l f l e x o r s h e a t h .


Figure 6.39. Antebrachial fascia and superficial muscles of forearm. The brachioradialis, representing the lateral group of muscles, slightly overlaps the radial artery. The four superficial muscles of the anterior (flexor—pronator) compartment of the forearm (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris) radiate from the medial epicondyle of the humerus (Fig. 6.38C). Over the distal ends of the radius and ulna, the antebrachial fascia thickens to form the extensor retinaculum posteriorly and a corresponding thickening, the palmar carpal ligament, anteriorly. Immediately distal and at a deeper level to the latter thickening, the flexor retinaculum (also continuous with the distal part of the antebrachial fascia), retains the tendons of the flexor muscles of the hand and fingers in the carpal tunnel.

Venipuncture in the Cubital Fossa The cubital fossa is the common site for sampling and transfusion of blood and intravenous injections because of the prominence and accessibility of veins. Usually, the median cubital vein or basilic vein is selected. The median cubital vein lies directly on the deep fascia, crossing the bicipital aponeurosis, which separates it from the underlying brachial artery and median nerve and provides some protection to the latter. Historically, during the days of bloodletting, the bicipital aponeurosis was known as the grace Deux (Fr. grace of God) tendon, by the grace of which arterial hemorrhage was usually avoided. A tourniquet is placed around the midarm to distend the veins in the cubital fossa. Once the vein is punctured, the tourniquet is removed so that when the needle is removed the vein will not bleed extensively. The cubital veins are also a site for the introduction of cardiac catheters to secure blood samples from the great vessels and chambers of the heart. These veins may also used for cardioangiography (see Chapter 1).

Variation of Veins in the Cubital Fossa The pattern of veins in the cubital fossa varies greatly. In approximately 20% of people, the median antebrachial vein (median vein of the forearm) divides into a median basilic vein, which joins the basilic vein. and a median cephalic vein, which joins the cephalic vein (Fig. B6.18). In these cases, a clear M formation is produced


by the cubital veins. It is important to observe and remember that either the median cubital vein or the median basilic vein, whichever pattern is present, crosses superficial to the brachial artery, from which it is separated by the bicipital aponeurosis. These veins are good sites for drawing blood but are not ideal for injecting an irritating drug because of the danger of injecting it into the brachial artery. In obese people, a considerable amount of fatty tissue may overlie the vein.

Figure B6.18

Surface Anatomy of the Arm and Cubital Fossa The borders of the deltoid are visible when the arm is abducted against resistance. The distal attachment of the deltoid can be palpated on the lateral surface of the humerus (Fig. SA6.8). The long, lateral, and medial heads of the triceps brachii form a bulge on the posterior aspect of the arm and are identifiable when the forearm is extended from the flexed position against resistance. The olecranon, to which the triceps tendon attaches distally, is easily palpated. It is separated from the skin only by the olecranon bursa, which accounts for the mobility of the overlying skin. The triceps tendon is easily felt as it descends along the posterior aspect of the arm to the olecranon. The fingers can be pressed inwards on each side of the tendon, where the elbow joint is superficial. An abnormal collection of fluid in the elbow joint or in the triceps bursa or subtendinous olecranon bursa is palpable at these sites; the bursa lies deep to the triceps tendon. The biceps brachii forms a bulge on the anterior aspect of the arm; its belly becomes more prominent when the elbow is flexed and supinated against resistance (Fig. SA6.9). The biceps brachii tendon can be palpated in the cubital fossa, immediately lateral to the midline, especially when the elbow is flexed against resistance. The proximal part of the bicipital aponeurosis can be palpated where it passes obliquely over the brachial artery and median nerve. Medial and lateral bicipital grooves


separate the bulges formed by the biceps and triceps and indicate the location of the medial and lateral intermuscular septa (Fig. SA6.10). The cephalic vein runs superiorly in the lateral bicipital groove, and the basilic vein ascends in the medial bicipital groove. Deep to the latter is the main neurovascular bundle of the limb. No part of the shaft of the humerus is subcutaneous; however, it can be palpated with varying distinctness through the muscles surrounding it, especially in many elderly people. The head of the humerus is surrounded by muscles on all sides, except inferiorly; thus it can be palpated by pushing the fingers well up into the axilla. The arm should be close to the side so the axillary fascia is loose. The humeral head can be identified by its movements when the arm is moved and the inferior angle of the scapula is held so the scapula does not move. The brachial artery may be felt pulsating deep to the medial border of the biceps. The medial and lateral epicondyles of the humerus are subcutaneous and can be easily palpated at the medial and lateral aspects of the elbow. The medial epicondyle is more prominent.

Figure SA6.8 In the cubital fossa, the cephalic and basilic veins in the subcutaneous tissue are clearly visible when a tourniquet is applied to the arm, as is the median cubital vein. This vein crosses the bicipital aponeurosis as it runs superomedially connecting the cephalic to the basilic vein (Figs. SA6.11 and 6.38A). If the thumb is pressed into the cubital fossa, the muscular masses of the long flexors of the forearm will be felt forming the medial border, the pronator teres most directly. The lateral group of forearm extensors (a soft mass that can be grasped separately), the brachioradialis (most medial) and the long and short extensors of the wrist, can be grasped between the fossa and the lateral epicondyle.


Figure SA6.9

Figure SA6.10


Figure SA6.11 P.800

Forearm The forearm is the distal unit of the articulated strut of the upper limb. It extends from the elbow to the wrist and contains two bones, the radius and ulna (Fig. 6.37A, B, & D), which are joined by an interosseous membrane. Although thin, this fibrous membrane is strong. In addition to firmly tying the forearm bones together while permitting pronation and supination, the interosseous membrane provides the proximal attachment for some deep forearm muscles. The head of the ulna is at the distal end of the forearm, whereas the head of the radius is at its proximal end. The role of forearm movement, occurring at the elbow and radioulnar joints, is to assist the shoulder in the application of force and in controlling the placement of the hand in space.

Compartments of the Forearm As in the arm, the muscles of similar purpose and innervation are grouped within the same fascial compartments in the forearm. Although the proximal boundary of the forearm per se is defined by the joint plane of the elbow, functionally the forearm includes the distal humerus. For the distal forearm, wrist, and hand to have minimal bulk to maximize their functionality, they are operated by “remote control” by extrinsic muscles having their bulky, fleshy, contractile parts located proximally in the forearm, distant from the site of action. Their long, slender tendons extend distally to the operative site, like long ropes reaching to distant pulleys. Furthermore, because the structures on which the muscles and tendons act (wrist and fingers) have an extensive range of motion, a long range of contraction is needed, requiring that the muscles have long contractile parts as well as a long tendon(s).


The forearm proper is not, in fact, long enough to provide the required length and sufficient area for attachment proximally, so the proximal attachments (origins) of the muscles must occur proximal to the elbow—in the arm—and be provided by the humerus. Generally, flexors lie anteriorly and extensors posteriorly; however, the anterior and posterior aspects of the distal humerus are occupied by the chief flexors and extensors of the elbow (Fig. 6.38A). To provide the required attachment sites for the flexors and extensors of the wrist and fingers, medial and lateral extensions (epicondyles and supraepicondylar ridges) have developed from the distal humerus. The medial epicondyle and supraepicondylar ridge provide attachment for the forearm flexors, and the lateral formations provide attachment for the forearm extensors. Thus rather than lying strictly anteriorly and posteriorly, the proximal parts of the “anterior” (flexor—pronator) compartment of the forearm lie anteromedially, and the “posterior” (extensor—supinator) compartment lies posterolaterally (Figs. 6.37D, 6.38B, and 6.40C). Spiraling gradually over the length of the forearm, the compartments become truly anterior and posterior in position in the distal forearm and wrist. These fascial compartments, containing the muscles in functional groups, are demarcated by the subcutaneous border of the ulna posteriorly (in the proximal forearm) and then medially (distal forearm) and by the radial artery anteriorly and then laterally. These structures are palpable (the artery by its pulsations) throughout the forearm. Because neither boundary is crossed by motor nerves, they also provide sites for surgical incision.


F i g u re 6 . 40 . E x t e n s o r m u s c l e s o f r i gh t f o r e a r m . A . T h e s u p e r f ic i a l l a y e r o f e x t e n s o r m u s c l e s i s s h ow n . T h e d is t a l e x t e n s o r t e n d o n s h a v e b e e n r e m ov e d f r o m t h e d o rs u m o f t h e h a n d w i t h o u t d i s t u r b i n g t h e a r t e r i e s b e c a u s e t h e y l i e o n t h e s k e le t a l p l a n e . T h e f a s c i a on t h e p o s te r i o r a s p e c t o f t h e f o r e a r m i s th i c k e n e d t o f o r m t h e e x t e n s o r r e t i n a c u l u m , w h i c h i s a n ch o r e d on i t s d e e p a s p e c t t o t h e r a d i u s a n d u ln a . B . T h e d e e p l a y e r o f e x t e n s o r m u s c l e s i s s h o w n . T h re e o u t c r o p p i n g m u s c l e s of t h e t h u m b * e m e r g e f r o m b e t w e e n th e e x t e n s o r c a r p i r a d i a l i s b r e v i s a n d th e e x t e n s o r d i g it o r u m : a b d u c t o r p o l l i c i s l o n g u s , e x t e n s o r p o l l i c i s b r e v i s , a n d e x t e n s o r p o l l ic i s l o n g u s . Th e f u r r o w f ro m w h i c h t h e th r e e m u s c le s e m e r g e h a s b e e n o p e n e d p r o x i m a l l y t o t h e l a te r a l e p i c o n d y l e , e x p os i n g t h e s u p i n a t o r m u s c l e . C . T h i s t r a n s v e r s e s e c t i o n o f t h e f o r e a rm s h o w s t h e s u p e r f i c i a l a n d d e e p l a y e rs o f m u s c l e s in t h e p os t e r io r c o m p a r t m e n t ( p i n k ) , s u p p l i e d b y th e ra d i a l n e r v e , a n d t h e a n t e r i o r c o m p a r t m e n t ( g o l d ) , s u p p l i e d b y t h e u l n a r a n d m e d i a n n e r v e s . F i g u r e 6 . 3 8 B a ls o d e m o n s t r a te s t h e s e c o n ce p ts .


The flexors and pronators of the forearm are in the anterior compartment and are served mainly by the median nerve; the one and a half exceptions are innervated by the ulnar nerve. The extensors and supinators of the forearm are in the posterior compartment and are all served by the radial nerve (directly or by its deep branch). The fascial compartments of the limbs generally end at the joints; therefore, fluids and infections in compartments are usually contained and cannot readily spread to other compartments. The anterior compartment is exceptional in this regard because it communicates with the central compartment of the palm through the carpal tunnel (Fig. 6.38C).

Muscles of the Forearm There are 17 muscles crossing the elbow joint, some of which act on the elbow joint exclusively, whereas others act at the wrist and fingers. In the proximal part of the forearm, the muscles form fleshy masses extending inferiorly from the medial and lateral epicondyles of the humerus (Figs. 6.37C and 6.38A). The tendons of these muscles pass through the distal part of the forearm and continue into the wrist, hand, and fingers (Figs. 6.37C & E and 6.38C). The flexor muscles of the anterior compartment have approximately twice the bulk and strength of the extensor muscles of the posterior compartment.

Flexor—Pronator Muscles of the Forearm The flexor muscles of the forearm are in the anterior (flexor—pronator) compartment of the forearm and are separated from the extensor muscles of the forearm by the radius and ulna (Fig. 6.38B) and, in the distal two thirds of the forearm, by the interosseous membrane that connects them (Fig. 6.37B & D). The tendons of most flexor muscles are located on the anterior surface of the wrist and are held in place by the palmar carpal ligament and the flexor retinaculum (transverse carpal ligament), thickenings of the antebrachial fascia (Figs. 6.37C and 6.39). The flexor muscles are arranged in three layers or groups (Table 6.7): 

 

A superficial layer or group of four muscles (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris). These muscles are all attached proximally by a common flexor tendon to the medial epicondyle of the humerus, the common flexor attachment. An intermediate layer, consisting of one muscle (flexor digitorum superficialis). A deep layer or group of three muscles (flexor digitorum profundus, flexor pollicis longus, and pronator quadratus).

The five superficial and intermediate muscles cross the elbow joint; the three deep muscles do not. With the exception of the pronator quadratus, the more distally placed a muscle's distal attachment lies, the more distally and deeply placed is its proximal attachment. All muscles in the anterior compartment of the forearm are supplied by the median and/or ulnar nerves (most by the median; only one and a half exceptions are supplied by the ulnar). Functionally, the brachioradialis is a flexor of the forearm, but it is located in the posterior (posterolateral) or extensor compartment and is thus supplied by the radial nerve. Therefore, the brachioradialis is a major exception to


the rule that (1) the radial nerve supplies only extensor muscles and (2) that all flexors lie in the anterior (flexor) compartment. The long flexors of the digits (flexor digitorum superficialis and flexor digitorum profundus) also flex the metacarpophalangeal and wrist joints. The flexor digitorum profundus flexes the fingers in slow action; this action is reinforced by the flexor digitorum superficialis when speed and flexion against resistance are required. When the wrist is flexed at the same time that the metacarpophalangeal and interphalangeal joints are flexed, the long flexor muscles of the fingers are operating over a shortened distance between attachments, and the action resulting from their contraction is consequently weaker. Extending the wrist increases their operating distance, and thus their contraction is more efficient in producing a strong grip (Fig. 6.48). Tendons of the long flexors of the digits pass through the distal part of the forearm, wrist, and palm and continue to the medial four fingers. The flexor digitorum superficialis flexes the middle phalanges, and the flexor digitorum profundus flexes the distal phalanges. The attachments, innervation, and main actions of the muscles of the anterior compartment of the forearm are listed by layers, in Table 6.7. The following discussion provides additional details, beginning with the muscles of the superficial and intermediate layers.

Pronator Teres The pronator teres, a fusiform muscle, is the most lateral of the superficial forearm flexors. Its lateral border forms the medial boundary of the cubital fossa. To test the pronator teres, the person's forearm is flexed at the elbow and pronated from the supine position against resistance provided by the examiner. If acting normally, the muscle is prominent and can be palpated at the medial margin of the cubital fossa.

Flexor Carpi Radialis The flexor carpi radialis (FCR) is a long fusiform muscle located medial to the pronator teres. In the middle of the forearm, its fleshy belly is replaced by a long, flattened tendon that becomes cord‐like as it approaches the wrist. The FCR produces flexion (when acting with the flexor carpi ulnaris) and abduction of the wrist (when acting with the extensors carpi radialis longus and brevis). When acting alone, the FCR produces a combination of flexion and abduction simultaneously at the wrist so that the hand moves anterolaterally. To reach its distal attachment, the FCR tendon passes through a canal in the lateral part of the flexor retinaculum and through a vertical groove in the trapezium in its own synovial tendinous sheath of the flexor carpi radialis (Fig. 6.38C). The FCR tendon is a good guide to the radial artery, which lies just lateral to it (Fig. 6.37C). To test the flexor carpi radialis, the person is asked to flex the wrist against resistance. If acting normally, its tendon can be easily seen and palpated.


Table 6.7. Muscles of the Anterior Compartment of the Forearm

Muscle

Proximal Attachment Superficial (first) layer Pronator teres Ulnar head Coronoid process

Humeral head Flexor carpi radialis (FCR) Palmaris longus Flexor carpi ulnaris (FCU)

Medial epicondyle of humerus (common flexor origin)

Humeral head Ulnar head Olecranon and posterior border (via aponeurosis)

Distal Attachment Middle of convexity of lateral surface of radius Base of 2nd metacarpal Distal half of flexor retinaculum and apex of palmar aponeurosis Pisiform, hook of hamate, 5th metacarpal

Innervation a

Main Action

Median nerve Pronates and flexes forearm (C6, C7) (at elbow)

Flexes and abducts hand (at wrist) Median nerve Flexes hand (at wrist) and (C7, C8) tenses palmar aponeurosis Flexes and adducts hand (at wrist)

Ulnar nerve (C7, C8)


Intermediate (second) layer Flexor digitorum superficialis (FDS) Humeroulnar Medial epicondyle head (common flexor origin and coronoid process) Radial head Superior half of anterior border Deep (third) layer Flexor Proximal three digitorum quarters of medial profundus and anterior (FDP) surfaces of ulna and interosseous Medial part membrane Lateral part

Flexes middle phalanges at proximal interphalangeal joints of middle four fingers; acting more strongly, it also Shafts (bodies) Median nerve flexes proximal phalanges at metacarpophalangeal joints of middle (C7, C8, T1) phalanges of medial four fingers

Bases of distal Ulnar phalanges of (C8, T1) 4th and 5th fingers

nerve Flexes distal phalanges 4 and 5 at distal interpha‐langeal joints

Anterior Flexes distal phalanges 2 and interosseous 3 at distal interpha‐langeal nerve, from joints Flexor pollicis Anterior surface Base of distal median nerve Flexes phalanges of 1st digit longus (FPL) of radius and phalanx of (C8, T1) (thumb) adjacent thumb interosseous membrane Pronator Distal quarter of Distal quarter Pronates forearm; deep fibers quadratus anterior surface of anterior bind radius and ulna together of ulna surface of radius a The spinal cord segmental innervation is indicated (e.g., “C6, C7” means that the nerves supplying the pronator teres are derived from the sixth and seventh cervi‐cal segments of the spinal cord). Numbers in boldface (C7) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

Palmaris Longus The palmaris longus, a small fusiform muscle, is absent on one or both sides (usually the left) in approximately 14% of people, but its actions are not missed. It has a short belly and a long, cord‐like tendon that passes superficial to the flexor retinaculum and attaches to it and the apex of the palmar aponeurosis (Figs. 6.37C and 6.39). The palmaris longus tendon is a useful guide to the median nerve at the wrist. The tendon lies deep and slightly medial to this nerve before it passes deep to the flexor retinaculum. To test the palmaris longus, the wrist is flexed and the pads of the little finger and thumb are tightly pinched together. If present and acting normally, the tendon can be easily seen and palpated.


Flexor Carpi Ulnaris The flexor carpi ulnaris (FCU) is the most medial of the superficial flexor muscles. The FCU simultaneously flexes and adducts the hand at the wrist if acting alone. It flexes the wrist when it acts with the FCR and adducts it when acting with the extensor carpi ulnaris. The ulnar nerve enters the forearm by passing between the humeral and the ulnar heads of its proximal attachment (Fig. 6.37C). This muscle is exceptional among muscles of the anterior compartment, being fully innervated by the ulnar nerve. The tendon of the FCU is a guide to the ulnar nerve and artery, which are on its lateral side at the wrist (Fig. 6.37C & E). To test the flexor carpi ulnaris, the person puts the posterior aspect of the forearm and hand on a flat table and is then asked to flex the wrist against resistance while the examiner palpates the muscle and its tendon.

Flexor Digitorum Superficialis The flexor digitorum superficialis (FDS) is often included with the superficial muscles of the forearm, which attach to the common flexor origin and therefore cross the elbow (Table 6.7). When considered this way, it is the largest superficial muscle in the forearm. However, the FDS actually forms an intermediate layer between the superficial and the deep groups of forearm muscles (Fig. 6.37C & E). The median nerve and ulnar artery enter the forearm by passing between its humeroulnar and radial heads (Table 6.7A & C). Near the wrist, the FDS gives rise to four tendons, which pass deep to the flexor retinaculum through the carpal tunnel to the fingers. The four tendons are enclosed (along with the four tendons of the flexor digitorum profundus) in a synovial common flexor sheath (Fig. 6.38C). The FDS flexes the middle phalanges of the medial four fingers at the proximal interphalangeal joints. In continued action, the FDS also flexes the proximal phalanges at the metacarpophalangeal joints and the wrist joint. The FDS is capable of flexing each finger it serves independently. To test the flexor digitorum superficialis, one finger is flexed at the proximal interphalangeal joint against resistance and the other three fingers are held in an extended position to inactivate the flexor digitorum profundus. The fascial plane between the intermediate and the deep layers of muscles makes up the primary neurovascular plane of the anterior (flexor—pronator) compartment; the main neurovascular bundles exclusive to this compartment course within it. The following three muscles form the deep layer of forearm flexor muscles.

Flexor Digitorum Profundus The flexor digitorum profundus (FDP) is the only muscle that can flex the distal interphalangeal joints of the fingers (Fig. 6.37E). This thick muscle “clothes” the anterior aspect of the ulna. The FDP flexes the distal phalanges of the medial four fingers after the FDS has flexed their middle phalanges (i.e., it curls the fingers and assists with flexion of the hand, making a fist). Each tendon is capable of flexing two interphalangeal joints, the metacarpophalangeal joint and the wrist joint. The FDP divides into four parts, which end in four tendons that pass posterior to the FDS tendons and the flexor retinaculum within the common flexor sheath (Fig. 6.38C). The part of the muscle going to the index finger usually separates from the rest of the


muscle relatively early in the distal part of the forearm and is capable of independent contraction. Each tendon enters the fibrous sheath of its digit, posterior to the FDS tendons. Unlike the FDS, the FDP can flex only the index finger independently; thus the fingers can be independently flexed at the proximal but not the distal interphalangeal joints. To test the flexor digitorum profundus, the proximal interphalangeal joint is held in the extended position while the person attempts to flex the distal interphalangeal joint. The integrity of the median nerve in the proximal forearm can be tested by performing this test using the index finger, and that of the ulnar nerve can be assessed by using the little finger.

Flexor Pollicis Longus The flexor pollicis longus (FPL), the long flexor of the thumb (L. pollex, thumb), lies lateral to the FDP, where it clothes the anterior aspect of the radius distal to the attachment of the supinator (Fig. 6.37C & E; Table 6.7A & D). The flat FPL tendon passes deep to the flexor retinaculum, enveloped in its own synovial tendinous sheath of the flexor pollicis longus on the lateral side of the common flexor sheath (Fig. 6.38C). The FPL primarily flexes the distal phalanx of the thumb at the interphalangeal joint and, secondarily, the proximal phalanx and 1st metacarpal at the metacarpophalangeal and carpometacarpal joints, respectively. The FPL is the only muscle that flexes the interphalangeal joint of the thumb. It also may assist in flexion of the wrist joint. To test the flexor pollicis longus, the proximal phalanx of the thumb is held and the distal phalanx is flexed against resistance.

Pronator Quadratus The pronator quadratus, as its name indicates, is quadrangular and pronates the forearm (Figs. 6.37E and 6.39). It cannot be palpated or observed, except in dissections, because it is the deepest muscle in the anterior aspect of the forearm. Sometimes it is considered to constitute a fourth muscle layer. The pronator quadratus clothes the distal fourth of the radius and ulna and the interosseous membrane between them (Table 6.7A & E). The pronator quadratus is the only muscle that attaches only to the ulna at one end and only to the radius at the other end. The pronator quadratus is the prime mover for pronation. The muscle initiates pronation; it is assisted by the pronator teres when more speed and power are needed. The pronator quadratus also helps the interosseous membrane hold the radius and ulna together, particularly when upward thrusts are transmitted through the wrist (e.g., during a fall on the hand).

The Bottom Line The superficial and intermediate muscles of the anterior (flexor—pronator) compartment of the forearm are located anteromedially because they arise mainly from the common flexor attachment (medial epicondyle and supraepicondylar ridge) of the humerus. Muscles in superficial layer “bend” the wrist to position the hand (i.e., flex the wrist when acting exclusively and abduct or adduct the wrist when working with their extensor counterparts) and assist pronation. The only muscle of the intermediate layer (FDS) primarily flexes the proximal joints of 2nd—5th fingers.


Muscles of the deep layer attach to the anterior aspects of the radius and ulna, flex all (but especially the distal) joints of all five digits, and pronate the forearm. The muscles of the anterior compartment are innervated mostly by the median nerve, but one and a half muscles (the FCU and ulnar half of the FDP) are innervated by the ulnar nerve. The nerves and the ulnar artery traverse the compartment in the fascial plane between the intermediate and the deep layers of muscles. Flexion of the wrist and hand is used for grasping, gripping, and drawing things toward one self. Pronation is used for positioning the hand to manipulate or pick things up. Both movements are basic protective (defensive) movements.

Extensor Muscles of the Forearm The extensor muscles are in the posterior (extensor—supinator) compartment of the forearm, and all are innervated by branches of the radial nerve (Figs. 6.40 and 6.41; Table 6.8). These muscles can be organized physiologically into three functional groups:   

Muscles that extend and abduct or adduct the hand at the wrist joint (extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris). Muscles that extend the medial four fingers (extensor digitorum, extensor indicis, and extensor digiti minimi). Muscles that extend or abduct the thumb (abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus).

The extensor tendons are held in place in the wrist region by the extensor retinaculum, which prevents bowstringing of the tendons when the hand is extended at the wrist joint. As the tendons pass over the dorsum of the wrist, they are provided with synovial tendon sheaths that reduce friction for the extensor tendons as they traverse the osseofibrous tunnels formed by the attachment of the extensor retinaculum to the distal radius and ulna (Fig. 6.41). The extensor muscles of the forearm are organized anatomically into superficial and deep layers. Four of the superficial extensors (extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris) are attached proximally by a common extensor tendon to the lateral epicondyle (Fig. 6.40; Table 6.8). The proximal attachment of the other two muscles in the superficial group (brachioradialis and extensor carpi radialis longus) is to the lateral supraepicondylar ridge of the humerus and adjacent lateral intermuscular septum. The four flat tendons of the extensor digitorum pass deep to the extensor retinaculum to the medial four fingers. The common tendons of the index and little fingers are joined on their medial sides near the knuckles by the respective tendons of the extensor indicis and extensor digiti minimi (extensors of the index and little fingers, respectively).


Figure 6.41. Synovial sheaths and tendons on distal forearm and dorsum of hand. A. Observe that the six synovial tendon sheaths (blue) occupy six osseofibrous tunnels formed by attachments of the extensor retinaculum to the ulna and especially the radius, which give passage to 12 tendons of nine extensor muscles. Numbers refer to the labeled osseofibrous tunnels. B. This slightly oblique transverse section of the distal end of the forearm shows the extensor tendons traversing the six osseofibrous tunnels deep to the extensor retinaculum.

The attachments, innervation, and main actions of the muscles of the posterior compartment of the forearm are provided, by layer, in Table 6.8. The following discussion provides additional details.

Brachioradialis The brachioradialis, a fusiform muscle, lies superficially on the anterolateral surface of the forearm (Figs. 6.39 and 6.40). It forms the lateral border of the cubital fossa (Fig. 6.38C). As mentioned previously, the brachioradialis is exceptional among muscles of the posterior (extensor) compartment in that it has rotated to the anterior aspect of the humerus and thus flexes the forearm at the elbow. It is especially active during quick movements or in the presence of resistance during flexion of the forearm (e.g., when a weight is lifted), acting as a shunt muscle resisting subluxation of the head of the radius. The brachioradialis and the supinator are the only muscles of the compartment that do not cross and therefore are incapable of acting at the wrist. As it descends, the brachioradialis overlies the radial nerve and artery where they lie together on the supinator, pronator teres tendon, FDS, and FPL. The distal part of the tendon is covered by the abductors pollicis longus and brevis as they pass to the thumb (Fig. 6.40). To test the brachioradialis, the elbow joint is flexed against resistance with the forearm in the midprone position. If the brachioradialis is acting normally, the muscle can be seen and palpated.


Extensor Carpi Radialis Longus The extensor carpi radialis longus (ECRL), a fusiform muscle, is partly overlapped by the brachioradialis, with which it often blends (Figs. 6.40 and 6.41). As it passes distally, posterior to the brachioradialis, its tendon is crossed by the abductor pollicis brevis and extensor pollicis brevis. The ECRL is indispensable when clenching the fist. Table 6.8. Muscles of the Posterior Compartment of the Forearm

Muscle

Proximal Attachment

Innervation a

Distal Attachment

Superficial layer Brachioradialis Proximal two thirds Lateral of supraepicondylar surface of ridge of humerus distal end of radius proximal to styloid process Extensor carpi Lateral Dorsal aspect radialis longus supraepicondylar of base of 2nd (ECRL) ridge of humerus metacarpal Extensor carpi Lateral epicondyle of Doral aspect radialis brevis humerus (common of base of 3rd (ECRB) extensor origin) metacarpal Extensor Extensor digitorum expansions of medial four fingers Extensor digiti minimi (EDM)

Extensor expansion 5th finger

of

Main Action

Radial nerve Relatively week flexion of (C5, C6, C7) forearm, maximal when forearm is in midpronated position

Radial (C6, C7)

nerve Extend and abduct hand at the wrist joint; ECRL active during fist Deep branch of clenching radial nerve (C7, C8) Posterior Extends medial four interosseous fingers primarily at nerve (C7, C8), metacarpophalangeal continuation of joints, secondarily at deep branch of interphalangeal joints E x t e n d s 5 t h f i n g e r p r i m a ri l y radial nerve at metacarpophalangeal joint, secondarily at i n t e r p h a la n g e a l j o i n t


Extensor carpi Lateral epicondyle of ulnaris (ECU) humerus; posterior border of ulna via a shared aponeurosis Deep layer Supinator Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna Extensor indicis

Dorsal aspect of base of 5th metacarpal

Extends and adducts hand at wrist joint (also active during fist clenching)

Lateral posterior, and anterior surfaces of proximal third of radius Posterior surface of Extensor distal third of ulna expansion of and interosseous 2nd finger membrane

Deep branch of Supinates forearm; radial nerve rotates radius to turn (C7, C8) palm anteriorlyor superiorly (if elbow is flexed)

Outcropping muscles of deep layer Abductor Posterior surface of pollicis longus proximal halves of (APL) ulna, radius, and interosseous membrane Extensor pollicis Posterior surface of longus (EPL) middle third of ulna and interosseous membrane

Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve

Extends 2nd finger (enabling its independent extension); helps extend hand at wrist

Base of 1st Posterior metacarpal interosseous nerve (C7, C8), continuation of deep branch of Dorsal aspect radial nerve of base of distal phalanx of thumb

Abducts thumb and extends it at carpometacarpal joint

Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints Extensor pollicis Posterior surface of Dorsal aspect Extends proximal phalanx brevis (EPB) distal third of radius of base of of thumb at and interosseous proximal metacarpophalangeal membrane phalanx of joint; extends thumb carpometacarpal joint a The spinal cord segmental innervation is indicated (e.g., “C7, C8” means that the nerves supplying the extensor carpi radialis brevis are derived from the seventh and eighth cervical segments of the spinal cord). Numbers in boldface (C7) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

To test the extensor carpi radialis longus, the wrist is extended and abducted with the forearm pronated. If acting normally, the muscle can be palpated inferoposterior to the lateral side of the elbow. Its tendon can be palpated proximal to the wrist.

Extensor Carpi Radialis Brevis The extensor carpi radialis brevis (ECRB), as its name indicates, is a shorter muscle than the ECRL because it arises distally in the limb, yet it attaches adjacent to the ECRL in the hand (but to the base of the 3rd metacarpal rather than the 2nd). As it passes distally, it is covered by the ECRL. The ECRB and ECRL pass under the extensor retinaculum together within the tendinous sheath of the extensor carpi radiales (Fig. 6.41). The two muscles act together to various degrees, usually as synergists to other


muscles. When the two muscles act by themselves, they abduct the hand as they extend it. Acting with the extensor carpi ulnaris, they extend the hand (the brevis is more involved in this action); acting with the FCR they produce pure abduction. Their synergistic action with the extensor carpi ulnaris is important in steadying the wrist during tight flexion of the medial four fingers (clenching a fist), a function in which the longus is more active.

Extensor Digitorum The extensor digitorum, the principal extensor of the medial four fingers, occupies much of the posterior surface of the forearm (Figs. 6.40, 6.41, 6.42). Proximally its four tendons join the tendon of the extensor indicis to pass deep to the extensor retinaculum through the tendinous sheath of the extensor digitorum and extensor indicis (common extensor synovial sheath) (Fig. 6.41A & B). On the dorsum of the hand, the tendons spread out as they run toward the fingers. Adjacent tendons are linked proximal to the knuckles (metacarpophalangeal joints) by three oblique intertendinous connections that restrict independent extension of the fingers (especially the ring finger). Consequently, normally no finger can remain fully flexed as the other ones are fully extended. Commonly, the fourth tendon is fused initially with the tendon to the ring finger and reaches the little finger by a tendinous band. On the distal ends of the metacarpals and along the phalanges, the four tendons flatten to form extensor expansions (Fig. 6.42). Each extensor digital expansion (dorsal expansion or hood) is a triangular, tendinous aponeurosis that wraps around the dorsum and sides of a head of the metacarpal and proximal phalanx. The visor‐ like “hood” formed by the extensor expansion over the head of the metacarpal, holding the extensor tendon in the middle of the digit, is anchored on each side to the palmar ligament (a reinforced portion of the fibrous layer of the joint capsule of the metacarpophalangeal joints) (Fig. 6.42B & D). In forming the extensor expansion, each flexor digitorum tendon divides into a median band, which passes to the base of the middle phalanx, and two lateral bands, which pass to the base of the distal phalanx (Fig. 6.42D & E). The tendons of the interosseous and lumbrical muscles of the hand join the lateral bands of the extensor expansion (Fig. 6.42). The retinacular ligament is a delicate fibrous band that runs from the proximal phalanx and fibrous digital sheath obliquely across the middle phalanx and two interphalangeal joints (Fig. 6.42C). It joins the extensor expansion to the distal phalanx. During flexion of the distal interphalangeal joint, the retinacular ligament becomes taut and pulls the proximal joint into flexion. Similarly, on extending the proximal joint, the distal joint is pulled by the retinacular ligament into nearly complete extension.


Figure 6.42. Dorsal digital (extensor) apparatus of 3rd digit. The metacarpal bone and all three phalanges are shown in parts A, B, D, and E; only the phalanges are shown in part C. A. This posterior view shows the extensor digitorum tendon trifurcating (expanding) into three bands: two lateral bands that unite over the middle phalanx to insert into the base of the distal phalanx, and one median band that inserts into the base of the middle phalanx. B. Part of the tendon of the interosseous muscles attaches to the base of the proximal phalanx; the other part contributes to the extensor expansion, attaching primarily to the lateral bands, but also fans out into an aponeurosis. Some of the aponeurotic fibers fuse with the median band, and other fibers arch over it to blend with the aponeurosis arising from the other side. On the radial side of each digit, a lumbrical muscle attaches to the radial lateral band. The dorsal hood consists of a broad band of transversely oriented fibers attached anteriorly to the palmar ligaments of the metacarpophalangeal (MP) joints that encircle the metacarpal head and MP joint, blending with the extensor expansion to keep the apparatus centered over the dorsal aspect of the digit. C. Distally, retinacular ligaments extending from the fibrous digital sheath to the lateral bands also help keep the apparatus centered and coordinate movements at the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. D. Contraction of the extensor digitorum alone results in extension at all joints (including the MP joint in the absence of action by the interossei and lumbricals). E. Because of the relationship of the tendons and the lateral bands to the rotational centers of the joints (red dots in parts D and E), simultaneous contraction of the interossei and lumbricals produces flexion at the MP joint but extension at the PIP and DIP joints (the so‐called Z‐ movement).


The extensor digitorum acts primarily to extend proximal phalanges and, through its collateral reinforcements, it secondarily extends the middle and distal phalanges as well. After exerting its traction on the digits, or in the presence of resistance to digital extension, it helps extend the hand at the wrist joint. To test the extensor digitorum, the forearm is pronated and the fingers are extended. The person attempts to keep the fingers extended at the metacarpophalangeal joints as the examiner exerts pressure on the proximal phalanges by attempting to flex them. If acting normally, the extensor digitorum can be palpated in the forearm, and its tendons can be seen and palpated on the dorsum of the hand.

Extensor Digiti Minimi The extensor digiti minimi (EDM), a fusiform slip of muscle, is a partially detached part of the extensor digitorum (Figs. 6.40 and 6.41). The tendon of this extensor of the little finger runs through a separate compartment of the extensor retinaculum, posterior to the distal radioulnar joint, within the tendinous sheath of the extensor digiti minimi. The tendon then divides into two slips; the lateral one is joined to the tendon of the extensor digitorum, with all three tendons attaching to the dorsal digital expansion of the little finger. After exerting its traction primarily on the 5th finger, it contributes to extension of the hand.

Extensor Carpi Ulnaris The extensor carpi ulnaris (ECU), a long fusiform muscle located on the medial border of the forearm, has two heads: a humeral head from the common extensor tendon and an ulnar head that arises by a common aponeurosis attached to the posterior border of the ulna and shared by the FCU, FDP, and deep fascia of the forearm. Distally, its tendon runs in a groove between the ulnar head and its styloid process, through a separate compartment of the extensor retinaculum within the tendinous sheath of the extensor carpi ulnaris. Acting with the ECRL and ECRB, it extends the hand; acting with the FCU, it adducts the hand. Like the ECRL, it is indispensable when clenching the fist. To test the extensor carpi ulnaris, the forearm is pronated and the fingers are extended. The extended wrist is then adducted against resistance. If acting normally, the muscle can be seen and palpated in the proximal part of the forearm and its tendon can be felt proximal to the head of the ulna.


Figure 6.43. Relationship of radial nerve to brachialis and supinator muscles. In the cubital fossa, lateral to the brachialis, the radial nerve divides into deep (motor) and superficial (sensory) branches. The deep branch penetrates the supinator muscle and emerges in the posterior compartment of the forearm as the posterior interosseous nerve. It joins the artery of the same name to run in the plane between the superficial and the deep extensors of the forearm.

Supinator The supinator lies deep in the cubital fossa and, along with the brachialis, forms its floor (Figs. 6.40 and 6.43). Spiraling medially and distally from its continuous, osseofibrous origin, this sheet‐like muscle envelops the neck and proximal part of the shaft of the radius. The deep branch of the radial nerve passes between its muscle fibers, separating them into superficial and deep parts, as it passes from the cubital fossa to the posterior part of the arm. As it exits the muscle and joins the posterior interosseous artery, it may be referred to as the posterior interosseous nerve. The supinator is the prime mover for slow, unopposed supination, especially when the forearm is extended. The biceps brachii also supinates the forearm and is the prime mover during rapid and forceful supination against resistance when the forearm is flexed (e.g., when a right‐handed person drives a screw). The deep extensors of the forearm act on the thumb (abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis) and the index finger (extensor indicis) (Figs. 6.40 and 6.41; Table 6.8). The three muscles acting on the thumb are deep to the superficial extensors and “crop out” (emerge) from the furrow in the lateral part of the forearm that divides the extensors. Because of this characteristic, they are referred to as outcropping muscles (Fig. 6.40A).

Abductor Pollicis Longus The abductor pollicis longus (APL) has a long, fusiform belly that lies just distal to the supinator and is closely related to the extensor pollicis brevis. Its tendon, and sometimes its belly, is commonly split into two parts, one of which may attach to the trapezium instead of the usual site at the base of the 1st metacarpal. The APL acts with the abductor pollicis brevis during abduction of the thumb and with the extensor pollicis muscles during extension of this digit. Although deeply situated, the APL emerges at the wrist as one of the outcropping muscles. Its tendon passes deep


to the extensor retinaculum with the tendon of the extensor pollicis brevis in the common synovial tendinous sheath of the abductor pollicis longus and extensor pollicis brevis. To test the abductor pollicis longus, the thumb is abducted against resistance at the metacarpophalangeal joint. If acting normally, the tendon of the muscle can be seen and palpated at the lateral side of the anatomical snuff box and on the lateral side of the adjacent extensor pollicis brevis tendon.

Extensor Pollicis Brevis The belly of the extensor pollicis brevis (EPB), the fusiform short extensor of the thumb, lies distal to the APL and is partly covered by it. Its tendon lies parallel and immediately medial to that of the APL but extends farther, reaching the base of the proximal phalanx (Fig. 6.41). In continued action after acting to flex the proximal phalanx of the thumb, or acting when that joint is fixed by its antagonists, it helps extend the 1st metacarpal and extend and abduct the hand. When the thumb is fully extended, a hollow called the anatomical snuff box, can be seen on the radial aspect of the wrist (Fig. 6.44). To test the extensor pollicis brevis, the thumb is extended against resistance at the metacarpophalangeal joint. If the EPB is acting normally, the tendon of the muscle can be seen and palpated at the lateral side of the anatomical snuff box and on the medial side of the adjacent APL tendon (Figs. 6.40 and 6.41).

Extensor Pollicis Longus The extensor pollicis longus (EPL) is larger and its tendon is longer than that of the EPB (Figs. 6.40 and 6.41). The tendon passes under the extensor retinaculum in its own tunnel, within the tendinous sheath of the extensor pollicis longus, medial to the dorsal tubercle of the radius. It uses the tubercle as a trochlea (pulley) to change its line of pull as it proceeds to the base of the distal phalanx of the thumb. The gap thus created between the long extensor tendons of the thumb is the anatomical snuff box. In addition to its main actions (Table 6.8), the EPL also adducts the extended thumb and rotates it laterally. To test the extensor pollicis longus, the thumb is extended against resistance at the interphalangeal joint. If the EPL is acting normally, the tendon of the muscle can be seen and palpated on the medial side of the anatomical snuff box. The tendons of the APL and EPB bound the anatomical snuff box anteriorly, and the tendon of the EPL bounds it posteriorly (Figs. 6.40, 6.41, and 6.44). The snuff box is visible when the thumb is fully extended; this draws the tendons up and produces a triangular hollow between them. Observe that the:  

Radial artery lies in the floor of the snuff box. Radial styloid process can be palpated proximally and the base of the 1st metacarpal can be palpated distally in the snuff box.


Figure 6.44. Anatomical snuff box. A. When the thumb is extended, a triangular hollow appears between the tendon of the extensor pollicis longus (EPL) medially and the tendons of the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) laterally. B. The floor of the snuff box, formed by the scaphoid and trapezium bones, is crossed by the radial artery as it passes diagonally from the anterior surface of the radius to the dorsal surface of the hand.



Scaphoid and trapezium can be felt in the floor of the snuff box between the radial styloid process and the 1st metacarpal (see clinical correlation [blue] box “Fracture of the Scaphoid,” earlier in this chapter).

Elbow Tendinitis or Lateral Epicondylitis Elbow tendinitis (tennis elbow) is a painful musculoskeletal condition that may follow repetitive use of the superficial extensor muscles of the forearm. Pain is felt over the lateral epicondyle and radiates down the posterior surface of the forearm. People with elbow tendinitis often feel pain when they open a door or lift a glass. Repeated forceful flexion and extension of the wrist strain the attachment of the common extensor tendon, producing inflammation of the periosteum of the lateral epicondyle (lateral epicondylitis).

Mallet or Baseball Finger Sudden severe tension on a long extensor tendon may avulse part of its attachment to the phalanx. The most common result of the injury is a mallet or baseball finger (Fig. B6.19A). This deformity results from the distal interphalangeal joint suddenly being forced into extreme flexion (hyperflexion when, for example, a baseball is miscaught or a finger is jammed into the base pad (Fig. B6.19B). These actions avulse the attachment of the tendon to the base of the distal phalanx. As a result, the person cannot extend the distal interphalangeal joint. The resultant deformity bears some resemblance to a mallet.


Figure B6.19. Mallet finger. The clinical appearance (A) and mechanism of injury (B) are shown.

Fracture of the Olecranon Fracture of the olecranon, called a “fractured elbow” by laypersons, is common because the olecranon is subcutaneous and protrusive. The typical mechanism of injury is a fall on the elbow combined with sudden powerful contraction of the triceps. The fractured olecranon is pulled away by the active and tonic contraction of the triceps (Fig. B6.20), and the injury is often considered to be an avulsion fracture (Salter, 1999). This is a serious fracture requiring the services of an orthopedic surgeon. Because of the traction produced by the tonus of the triceps on the olecranon fragment, pinning is usually required. Healing occurs slowly, and often a cast must be worn for nearly a year.

Synovial Cyst of the Wrist Sometimes a non‐tender cystic swelling appears on the hand, most commonly on the dorsum of the wrist (Fig. B6.21). Usually the cyst is the size of a small grape, but it varies and may be as large as a plum. The thin‐walled cyst contains clear mucinous fluid. The cause of the cyst is unknown, but it may result from mucoid degeneration (Salter, 1999). Flexion of the wrist makes the cyst enlarge, and it may be painful. Clinically, this type of swelling is called a “ganglion” (G. swelling or knot). Anatomically, a ganglion refers to a collection of nerve cells (e.g., a spinal ganglion). These synovial cysts are close to and often communicate with the synovial sheaths on the dorsum of the wrist. The distal attachment of the ECRB tendon to the base of the 3rd metacarpal is another common site for such a cyst. A cystic swelling of the common flexor synovial sheath on the anterior aspect of the wrist can enlarge enough to produce compression of the median nerve by narrowing the carpal tunnel (carpal tunnel syndrome). This syndrome produces pain and paresthesia in the sensory distribution of the median nerve and clumsiness of finger movements (see clinical correlation [blue] box “Carpal Tunnel Syndrome,” earlier in this chapter.


Figure B6.20

Figure B6.21

Extensor Indicis The extensor indicis has a narrow, elongated belly that lies medial to and alongside that of the EPL (Figs. 6.40 and 6.41). This muscle confers independence to the index finger in that the extensor indicis may act alone or together with the extensor digitorum to extend the index finger at the proximal interphalangeal joint, as in pointing. It also helps extend the hand.

The Bottom Line Proximally, the extensor—supinator muscles are located posterolaterally. Generally, the more distal their distal attachment (insertion) the more distal and more deeply placed is their proximal attachment (origin). Thus the most proximal muscle (brachioradialis) does not cross and thus cannot act at the wrist (true also of the supinator). The next most proximal muscles act to “bend” the wrist (extend or act with their flexor counterparts to abduct and adduct). The most distal muscles, which make up the deep layer, act at the thumb and index finger. The extensors of the wrist and hand enable reach (extension), opening of the hand in preparation for grasping, and pushing; supination enables the holding of objects and feeding. Extension is an aggressive movement (hitting, striking, pushing). Extension of the wrist, however, is also an important component of tight grip (clenching).

Arteries of the Forearm The main arteries of the forearm are the ulnar and radial arteries, which usually arise opposite the neck of the radius in the inferior part of the cubital fossa as terminal branches of the brachial artery (Fig. 6.45). The origins and courses of the named arteries of the forearm are described in Table 6.9. The following discussion provides additional details.


Ulnar Artery Pulsations of the ulnar artery can be palpated on the lateral side of the FCU tendon, where it lies anterior to the ulnar head. The ulnar nerve is on the medial side of the ulnar artery. Branches of the ulnar artery arising in the forearm participate in the periarticular anastomosis of the elbow and supply muscles of the medial and central forearm, the common flexor sheath, and the ulnar and median nerves. 

The anterior and posterior ulnar recurrent arteries anastomose with the inferior and superior ulnar collateral arteries, respectively, thereby participating in the periarticular arterial anastomoses of the elbow. The anterior and posterior arteries may be present as anterior and posterior branches of a (common) ulnar recurrent artery. Figure 6.45. Flexor digitorum superficialis and related vasculature. Three muscles of the superficial layer (pronator teres, flexor carpi radialis, and palmaris longus) have been removed, leaving only their attaching ends; the fourth muscle of the layer (the flexor carpi ulnaris) has been retracted medially. The tendinous humeral attachment of the FDS to the medial epicondyle is thick; and the linear attachment to the radius, immediately distal to the radial attachments of the supinator and pronator teres, is thin (Table 6.7). The ulnar artery and median nerve pass between the humeral and the radial heads of the FDS. The artery descends obliquely deep to the FDS to join the ulnar nerve, which descends vertically near the medial border of the FDS (exposed here by splitting a fusion of the FDS and the FCU). A (proximal) probe is elevating the FDS tendons (and median nerve and persisting median artery). A second (distal) probe is elevating all the remaining structures that cross the wrist (radiocarpal) joint anteriorly.


Table 6.9. Arteries of the Forearm and Wrist

Artery Ulnar

Origin As larger terminal branch of brachial artery in cubital fossa

Anterior ulnar Ulnar artery just distal recurrent artery to elbow joint

Posterior ulnar Ulnar artery distal to recurrent artery anterior ulnar recurrent artery Common interosseous

Anterior interosseous

Posterior interosseous

Ulnar artery in cubital fossa, distal to bifurcation of brachial artery As terminal branches of common interosseous artery, between radius and ulna

Course in Forearm Descends inferomedially and then directly inferiorly, deep to superficial (pronator teres and palmaris longus) and intermediate (flexor digitorum superficialis) layers of flexor muscles to reach medial side of forearm; passes superficial to flexor retinaculum at wrist in ulnar (Guyon) canal to enter hand Passes superiorly between brachialis and pronator teres, supplying both; then anastomoses with inferior ulnar collateral artery anterior to medial epicondyle Passes superiorly, posterior to medial epicondyle and deep to tendon of flexor carpi ulnaris; then anastomoses with superior ulnar collateral artery Passes laterally and deeply, terminating quickly by dividing into anterior and posterior interosseous arteries Passes distally on anterior aspect of interosseous membrane to proximal border of pronator quadratus; pierces membrane and continues distally to join dorsal carpal arch on posterior aspect of interosseous membrane Passes to posterior aspect of interosseous membrane, giving rise to recurrent interosseous artery; runs distally between superficial and deep extensor muscles, supplying both; replaced distally by anterior interosseous artery


Recurrent interosseous Palmar branch

Posterior interosseous artery, between radius and ulna carpal Ulnar artery in distal forearm

Dorsal branch

carpal Ulnar artery, proximal to pisiform

Radial

As smaller terminal branch of brachial artery in cubital fossa

Radial recurrent

Palmar branch

Dorsal branch







Lateral side of radial artery, just distal to brachial artery bifurcation carpal Distal radial artery near distal border of pronator quadratus

carpal Distal radial artery in proximal part of snuff box

P a s s e s s u p e ri o r l y , p o s t e r io r t o p r o x i m a l r a d i o u l n a r j o i n t a n d ca p i t u l u m , t o a n a s t o m os e w i t h m i d d le collateral artery (from deep brachial artery)

Runs across anterior aspect of wrist, deep to tendons of flexor digitorum profundus, to anastomose with the palmar carpal branch of the radial artery, forming palmar carpal arch Passes across dorsal surface of wrist, deep to extensor tendons, to anastomose with dorsal carpal branch of radial artery, forming dorsal carpal arch Runs inferolaterally under cover of brachioradialis; lies lateral to flexor carpi radialis tendon in distal forearm; winds around lateral aspect of radius and crosses floor of anatomical snuff box to pierce first dorsal interosseous muscle Ascends between brachioradialis and brachialis, supplying both (and elbow joint); then anastomoses with radial collateral artery (from deep brachial artery) Runs across anterior wrist deep to flexor tendons to anastomose with the palmar carpal branch of ulnar artery to form palmar carpal arch Runs medially across wrist deep to pollicis and extensor radialis tendons, anastomoses with ulnar dorsal carpal branch forming dorsal carpal arch

The common interosseous artery, a short branch of the ulnar artery, arises in the distal part of the cubital fossa and divides almost immediately into anterior and posterior interosseous arteries. The anterior interosseous artery passes distally, running directly on the anterior aspect of the interosseous membrane with the anterior interosseous nerve, whereas the posterior interosseous artery courses between the superficial and the deep layers of the extensor muscles in the company of the posterior interosseous nerve. The relatively small posterior interosseous artery is the principal artery serving the structures of the middle third of the posterior compartment. Thus it is mostly exhausted in the distal forearm and is replaced by the anterior interosseous artery, which pierces the interosseous membrane near the proximal border of the pronator quadratus. Unnamed muscular branches of the ulnar artery supply muscles on the medial side of the forearm, mainly those in the flexor—pronator group.

Radial Artery The pulsations of the radial artery can be felt throughout the forearm, making it useful as an anterolateral demarcation of the flexor and extensor compartments of the forearm. When the brachioradialis is pulled laterally, the entire length of the artery is visible (Fig. 6.45; Table 6.9). The radial artery lies on muscle until it reaches


the distal part of the forearm. Here it lies on the anterior surface of the radius and is covered by only skin and fascia, making this an ideal location for checking the radial pulse. The course of the radial artery in the forearm is represented by a line joining the midpoint of the cubital fossa to a point just medial to the radial styloid process. The radial artery leaves the forearm by winding around the lateral aspect of the wrist and crosses the floor of the anatomical snuff box (Figs. 6.44 and 6.45). 





The radial recurrent artery participates in the periarticular arterial anastomoses around the elbow by anastomosing with the radial collateral artery, a branch of the deep artery of the arm. The palmar and dorsal carpal branches of the radial artery participate in the periarticular arterial anastomosis around the wrist by anastomosing with the corresponding branches of the ulnar artery and terminal branches of the anterior and posterior interosseous arteries, forming the palmar and dorsal carpal arches. The unnamed muscular branches of the radial artery supply muscles in the adjacent (anterolateral) aspects of both the flexor and the extensor compartments because the radial artery runs along (and demarcates) the anterolateral boundary between the compartments.

High Division of the Brachial Artery Sometimes the brachial artery divides at a more proximal level than usual. In this case, the ulnar and radial arteries begin in the superior or middle part of the arm, and the median nerve passes between them (Fig. B6.22). The musculocutaneous and median nerves commonly communicate as shown in this illustration.

Superficial Ulnar Artery In approximately 3% of people, the ulnar artery descends superficial to the flexor muscles (Fig. B6.23). Pulsations of a superficial ulnar artery can be felt and may be visible. This variation must be kept in mind when performing venesections for withdrawing blood or making intravenous injections. If an aberrant ulnar artery is mistaken for a vein, it may be damaged and produce bleeding. If certain drugs are injected into the aberrant artery, the result could be fatal.


Figure B6.22

Measuring the Pulse Rate The common place for measuring the pulse rate is where the radial artery lies on the anterior surface of the distal end of the radius, lateral to the tendon of the FCR. Here the artery is covered by only fascia and skin. The artery can be compressed against the distal end of the radius, where it lies between the tendons of the FCR and APL. When measuring the radial pulse rate, the pulp of the thumb should not be used because it has its own pulse, which could obscure the patient's pulse. If a pulse cannot be felt, try the other wrist because an aberrant radial artery on one side may make the pulse difficult to palpate. A radial pulse may also be felt by pressing lightly in the anatomical snuff box.

Variations in the Origin of the Radial Artery The origin of the radial artery may be more proximal than usual; it may be a branch of the axillary artery or the brachial artery. Sometimes the radial artery is superficial to the deep fascia instead of deep to it. When a superficial vessel is pulsating near the wrist, it is probably a superficial radial artery. The aberrant vessel is vulnerable to laceration.


Figure B6.23

Veins of the Forearm In the forearm, as in the arm, there are superficial and deep veins. The superficial veins ascend in the subcutaneous tissue. The deep veins accompany the deep arteries of the forearm.

Superficial Veins The pattern, common variations, and clinical significance of the superficial veins of the upper limb were discussed earlier in this chapter.

Deep Veins Deep veins accompanying arteries are plentiful in the forearm (Fig. 6.46). These accompanying veins (L. venae comitantes) arise from the anastomosing deep venous palmar arch in the hand. From the lateral side of the arch, paired radial veins arise and accompany the radial artery; from the medial side, paired ulnar veins arise and accompany the ulnar artery. The veins accompanying each artery anastomose freely with each other. The radial and ulnar veins drain the forearm but carry relatively little blood from the hand. The deep veins ascend in the forearm along the sides of the corresponding arteries, receiving tributaries from veins leaving the muscles with which they are related. Deep veins communicate with the superficial veins. The deep interosseous veins, which accompany the interosseous arteries, unite with the accompanying veins of the radial and ulnar arteries. In the cubital fossa the deep veins are connected to the median cubital vein, a superficial vein. These deep cubital veins also unite with the accompanying veins of the brachial artery.


Figure 6.46. Deep venous drainage of upper limb. The deep accompanying veins surround the arteries as their companions, with which they share names. They are relatively small, usually paired, and interconnected at intervals by transverse branches.

Nerves of the Forearm The nerves of the forearm are the median, ulnar, and radial. The median nerve is the principal nerve of the anterior (flexor—pronator) compartment of the forearm (Figs. 6.38B and 6.48). Although the radial nerve appears in the cubital region, it soon enters the posterior (extensor—supinator) compartment of the forearm. Besides the cutaneous branches, there are only two nerves of the anterior aspect of the forearm: the median and ulnar nerves. The named nerves of the forearm are illustrated and their origins and courses are described in Table 6.10. The following discussion provides additional details and discusses unnamed branches.

Median Nerve in the Forearm The median nerve is the principal nerve of the anterior compartment of the forearm (Fig. 6.47). It supplies muscular branches directly to the muscles of the superficial and intermediate layers of forearm flexors (except the FCU), and deep muscles (except for the medial [ulnar] half of the FDP) via its branch, the anterior interosseous nerve. The median nerve has no branches in the arm other than small twigs to the brachial artery. Its major named nerve in the forearm is the anterior interosseous nerve (Table 6.10). In addition, the following unnamed branches of the median nerve arise in the forearm: 

Articular branches. These branches pass to the elbow joint as the median nerve passes it.






Muscular branches. The nerve to the pronator teres usually arises at the elbow and enters the lateral border of the muscle. A broad bundle of nerves pierces the superficial flexor group of muscles and innervates the FCR, the palmaris longus, and the FDS. Anterior interosseous nerve. This branch runs distally on the interosseous membrane with the anterior interosseous branch of the ulnar artery. After supplying the deep forearm flexors (except the ulnar part of the FDP, which sends tendons to 4th and 5th fingers), it passes deep to and supplies the pronator quadratus, then ends by sending articular branches to the wrist joint. Palmar cutaneous branch of the median nerve. This branch arises in the forearm, just proximal to the flexor retinaculum, but is distributed to skin of the central part of the palm.

Median Nerve Injury When the median nerve is severed in the elbow region, flexion of the proximal interphalangeal joints of the 1st—3rd fingers is lost and flexion of the 4th and 5th fingers is weakened. Flexion of the distal interphalangeal joints of the 2nd and 3rd fingers is also lost. Flexion of the distal interphalangeal joints of the 4th and 5th fingers is not affected because the medial part of the FDP, which produces these movements, is supplied by the ulnar nerve. The ability to flex the metacarpophalangeal joints of the 2nd and 3rd fingers is affected because the digital branches of the median nerve supply the 1st and 2nd lumbricals. Thus, when the person attempts to make a fist, the 2nd and 3rd fingers remain partially extended (“hand of benediction” ) (Fig. B6.24). Thenar muscle function (function of the muscles at the base of the thumb) is also lost, as in carpal tunnel syndrome (see clinical correlation [blue] box “Carpal Tunnel Syndrome,” later in this chapter). Figure B6.24. Pronator syndrome. A. Testing the flexion of the distal interphalangeal joint of the index finger is shown. B. The hand of benediction is demonstrated.

Pronator Syndrome Pronator syndrome, a nerve entrapment syndrome, is caused by compression of the median nerve near the elbow. The nerve may be compressed between the heads of the pronator teres as a result of trauma, muscular hypertrophy, or fibrous bands.


Individuals with this syndrome are first seen clinically with pain and tenderness in the proximal aspect of the anterior forearm. Symptoms often follow activities that involve repeated elbow movements. Table 6.10. Nerves of the Forearm

Nerve Median

Origin B y u n i o n of l a t e r a l root of m e d i a n n e r v e ( C 6 a n d C 7 , from l a t e r a l c o r d of b r a c h i a l p l e x u s ) w i t h m e d i a l root ( C 8 a n d T 1 ) fr om m e d i a l c o r d )

Course in Forearm

E n t e r s c u b i ta l f o s s a m e d i a l t o b r a c h i a l a r t e r y ; e xi t s b y p a s s i n g b e t w e e n he a d s of p r o n a t o r t e r e s ; d e s c e n d s in f a s c i a l plane b e tw e e n f l e xo r s digitorum s u p e r f i c i a l i s a n d p r o f u n d u s ; r u n s d e e p t o p a l m a r i s l o n g u s t e n d o n a s it a p p r o a c h e s f lexor r e t i n a c u l u m t o t r a v e r s e c a rp a l t u n n e l A n t e r i o r i n t e r o s s e o u s M e d i a n n e r v e in d i s t a l p a r t of D e s c e n d s on a n t e r i o r a s p e c t of c u b i t a l f o s s a i n t e r o s s e o u s m e m b r a n e w i t h a r t e r y of s a m e n a m e , b e t w e e n FDP a n d F P L, t o p a s s de e p t o p r o n a t o r q u a d r a t u s P a l m a r c u t an e o u s b r a n c h M e d i a n n e r v e of m i d d l e t o d i s t a l P a s se s s u p e r f i c i a l t o flexor r e t i c u l u m t o of m e d i a n n e r v e f o r e a r m , p r o x i m a l t o f lexor r e a c h s k i n of c e n t r a l p a lm retinaculum Ulnar L a r g e r t e r m i n a l b r a n c h of m e d i a l E n t e r s f o r e a r m b y pa s s i n g b e tw e e n c o r d of b r a ch i a l p l e x u s (C8 a n d T 1 , h e a d s of fle xor c a r p i u l n a r i s , a f t e r o f t e n r e c e i ve s f i b e r s from C 7 ) p a s s i n g p o s t e r i o r t o m e d i a l e p i c o n d y l e of h u m e r u s ; d e s c e n d s for e a r m b e t w e e n F C U a n d FDP ; b e c o m e s s u p e r f i c i a l in d i s t a l f o r e a rm


P a l m a r c u t an e o u s b r a n c h U l n a r n e r v e n e a r m i d d l e of f o r e a r m of u l n a r n e rve

D o r s a l c u t an e o u s b r a nc h U l n a r n e r v e in d i s t a l h a l f of f o r e a r m of u l n a r n e rve

R a d i a l

L a r g e r t e r m i n a l b r a n c h of p o s t e r i o r c o r d of b r a ch i a l p l e x u s (C5 — T 1 )

P o s t e r i o r c ut a n e o u s ne rve R a d i a l nerve, a s it t r a v e r s e s r a d i a l of f o r e a r m groove of p o s t e r i o r h u m e r u s S u p e r f i c i a l branch r a d i a l n e r v e

of S e n s o r y te r min a l b r a n c h of r a d i a l n e r v e , in c ub i t a l f o s s a

D e e p br a n c h radial/posterior i n t e r o s s e o u s n e r v e

of M o t o r t e r m i n a l b r a n c h of r a d i a l n e r v e , in c ub i t a l f o s s a

L a t e r a l c u ta n e o u s n e rve C o n t i n u a t i o n of m u s c u l o c u t a n e o u s of f o r e a r m n e r v e d i s t a l t o m u s c u l a r b r a n c h e s

M e d i a l c u t an e o u s n e r v e of M e d i a l c o r d of b r a c h i a l p l e x u s , f o r e a r m r e c e i v i n g C8 a n d T 1 f i b e rs

D e s c e n d s an t e r ior t o u l n a r a r t e r y ; p e r f o r a t e s de e p f a s c i a in d i s t a l f o r e a r m ; r u n s in s u bc u t a n e o u s tis s u e t o p a lma r s k i n m e d i a l to a x i s of 4 t h f i n g e r P a s se s p o s te r o i n f e r i o r l y b e t w e e n u l n a a n d f lexor c a r p i u l n a r i s ; e n t e r s s u b c u t a n e o us t i s s u e t o s u p p l y s k in of d o r s u m m e d i a l t o a x i s of 4 t h f i n g e r Enters cubital fossa b e t we e n brachioradialis and brachialis; anterior t o l a t e r a l e p i c o n d y l e d i v i d e s i n t o t e r m i n a l s u p e r f i c i a l a n d d e e p b r a nc he s P e r f o r a t e s l a t e r a l he ad of t r i c e p s ; d e s c e n d s a lo n g l a t e r a l s i d e of a r m a n d p o s t e r i o r a sp e c t of f o r e a r m t o w r i s t D e s c e n d s be t w e e n p r on a t o r t e r e s a n d b r a c h i o r a d i a l i s , e m e r g i n g from l a t t e r t o a r b o r i z e o v e r a n a t o m i c al s n u f f b o x a n d s u p p l y s k i n of d o r s u m l a t e r a l t o a x i s of 4 t h f i n g e r D e e p b r a n c h e xi t s c u b i t a l f o s s a w i n d i n g a r o u n d n e c k of r a d i u s , p e n e t r a t i n g a n d supplying supinator; e m e r g es in p o s t e r i o r c o m p a r t m e n t of f o r e a r m a s p o s t e r i o r i n t e r o s s e o u s ; d e s c e n d s on m e m b r a n e wit h a r t e ry of s a m e n a m e E m e r g e s l a t e r a l t o b i c e p s b r a c h i i on b r a c h i a l i s , ru n n i n g i n i t i a l l y w i t h cephalic v e i n ; d e s c e n d s a l o n g l a t e r a l b o r de r of f o r e a r m t o w r i s t P e r f o r a t e s d e e p f a s c ia of a r m w i t h b a s i l i c v e i n p r o x i m a l t o c u b i t a l f o s s a ; d e s c e n d s me d ia l a s p e ct of f o r e a r m in s u b c u t a n e o us t i s s u e t o wr is t


Figure 6.47. Neurovascular structures in anterior aspect of forearm and wrist. A. At the elbow, the brachial artery lies between the biceps tendon and the median nerve. It bifurcates into the radial and ulnar arteries. In the forearm, the radial artery courses between the extensor and the flexor muscle groups. B . This deep dissection of the distal part of the forearm and proximal part of the hand shows the course of the arteries and nerves.

Ulnar Nerve in the Forearm Like the median nerve, the ulnar nerve does not give rise to branches during its passage through the arm. In the forearm it supplies only one and a half muscles, the FCU (as it enters the forearm by passing between its two heads of proximal attachment) and the ulnar part of the FDP, which sends tendons to the 4th and 5th fingers. The ulnar nerve and artery emerge from beneath the FCU tendon and become superficial just proximal to the wrist. They pass superficial to the flexor retinaculum and enter the hand by passing through a groove between the pisiform and the hook of the hamate. A band of fibrous tissue from the flexor retinaculum bridges the groove to form the small ulnar canal (Guyon canal) (Fig. 6.47B). The branches of the ulnar nerve arising in the forearm include unnamed muscular and articular branches, and cutaneous branches that pass to the hand:


Articular branches pass to the elbow joint while the nerve is between the olecranon and medial epicondyle. Muscular branches supply the FCU and the medial half of the FDP. The palmar and dorsal cutaneous branches arise from the ulnar nerve in the forearm, but their sensory fibers are distributed to the skin of the hand.

Communications between the Median and the Ulnar Nerves Occasionally, communications occur between the median and the ulnar nerves in the forearm. These branches are usually represented by slender nerves, but the communications are important clinically because even with a complete lesion of the median nerve, some muscles may not be paralyzed. This may lead to an erroneous conclusion that the median nerve has not been damaged.

Ulnar Nerve Injury More than 27% of nerve lesions of the upper limb affect the ulnar nerve (Rowland, 2000). Ulnar nerve injuries usually occur in four places: (1) posterior to the medial epicondyle of the humerus, (2) in the cubital tunnel formed by the tendinous arch connecting the humeral and ulnar heads of the FCU, (3) at the wrist, and (4) in the hand. Ulnar nerve injury occurs most commonly where the nerve passes posterior to the medial epicondyle of the humerus (Fig. B6.25). The injury results when the medial part of the elbow hits a hard surface, fracturing the medial epicondyle (“funny bone” ). Compression of the ulnar nerve at the elbow (cubital tunnel syndrome) is also common (see clinical correlation [blue] box “Cubital Tunnel Syndrome,” later in this chapter). Ulnar nerve injury usually produces numbness and tingling (paresthesia) of the medial part of the palm and the medial one and a half fingers (Fig. B6.26). Pluck your ulnar nerve at the posterior aspect of your elbow with your index finger and you may feel tingling in these fingers. Severe compression may also produce elbow pain that radiates distally. Uncommonly, the ulnar nerve is compressed as it passes through the ulnar canal (see clinical correlation [blue] box “Ulnar Canal Syndrome (Guyon Tunnel Syndrome),” later in this chapter). Ulnar nerve injury can result in extensive motor and sensory loss to the hand. An injury to the nerve in the distal part of the forearm denervates most intrinsic hand muscles. Power of wrist adduction is impaired, and when an attempt is made to flex the wrist joint, the hand is drawn to the lateral side by the FCR (supplied by the median nerve) in the absence of the “balance” provided by the FCU. After ulnar nerve injury, the person has difficulty making a fist because, in the absence of opposition, the metacarpophalangeal joints become hyperextended, and he or she cannot flex the 4th and 5th fingers at the distal interphalangeal joints when trying to make a fist. Furthermore, the person cannot extend the interphalangeal joints when trying to straighten the fingers. This characteristic appearance of the hand, resulting from a distal lesion of the ulnar nerve, is known as claw hand (main en griffe). The deformity results from atrophy of the interosseous muscles of the hand supplied by the ulnar nerve. The claw is produced by the unopposed action of the extensors and FDP.


Figure B6.25. Vulnerable position of ulnar nerve.

Cubital Tunnel Syndrome The ulnar nerve may be compressed (ulnar nerve entrapment) in the cubital tunnel formed by the tendinous arch joining the humeral and ulnar heads of attachment of the FCU (Table 6.7). The signs and symptoms of cubital tunnel syndrome are the same as an ulnar nerve lesion in the ulnar groove on the posterior aspect of the medial epicondyle of the humerus.

Figure B6.26. Claw hand and sensory distribution of ulnar nerve.


Radial Nerve in the Forearm Unlike the medial and ulnar nerves, the radial nerve serves motor and sensory functions in both the arm and the forearm (but only sensory functions in the hand). However, its sensory and motor fibers are distributed in the forearm by two separate branches, the superficial (sensory or cutaneous) and deep radial/posterior interosseous nerve (motor). It divides into these terminal branches as it appears in the cubital fossa, anterior to the lateral epicondyle of the humerus, between the brachialis and the brachioradialis (Fig. 6.43). The two branches immediately part company, the deep branch winding laterally around the radius, piercing the supinator enroute to the posterior compartment. The posterior cutaneous nerve of the forearm arises from the radial nerve in the posterior compartment of the arm, as it runs along the radial groove of the humerus. Thus it reaches the forearm independent of the radial nerve, descending in the subcutaneous tissue of the posterior aspect of the forearm to the wrist, supplying the skin. The superficial branch of the radial nerve is also a cutaneous nerve, but it gives rise to articular branches as well. It is distributed to skin on the dorsum of the hand and to a number of joints in the hand, branching soon after it emerges from the overlying brachioradialis and crosses the roof of the anatomical snuff box (Fig. 6.44). After it pierces the supinator, the deep branch of the radial nerve runs in the fascial plane between superficial and deep extensor muscles in close proximity to the posterior interosseous artery; it is usually referred to as the posterior interosseous nerve (Fig. 6.43). It supplies motor innervation to all the muscles with fleshy bellies located entirely in the posterior compartment of the forearm (distal to the lateral epicondyle of the humerus).

Radial Nerve Injury in the Forearm The radial nerve is usually injured in the arm by a fracture of the humeral shaft. This injury is proximal to the branches to the extensors of the wrist, and so wrist‐drop is the primary clinical manifestation of an injury at this level (see clinical correlation [blue] box “Injury to the Radial Nerve in the Arm,” earlier in this chapter). Injury to the deep branch of the radial nerve may occur when wounds of the forearm are deep (penetrating). Severance of the deep branch of the radial nerve results in an inability to extend the thumb and the metacarpophalangeal (MP) joints of the other digits. Thus the integrity of the deep radial nerve may be tested by asking the person to extend the MP joints while the examiner provides resistance (Fig. B6.27). If the nerve is intact, the long extensor tendons should appear prominently on the dorsum of the hand, confirming that the extension is occurring at the MP joints rather than at the interphalangeal joints (movements under the control of other nerves). Loss of sensation does not occur because the deep branch of the radial nerve is entirely muscular and articular in distribution. See Table 6.8 to determine the muscles that are paralyzed (e.g., extensor digitorum) when this nerve is severed. When the superficial branch of the radial nerve, a cutaneous nerve, is severed, sensory loss is usually minimal. Commonly, a coin‐shaped area of anesthesia occurs distal to the bases of the 1st and 2nd metacarpals. The reason the area of sensory loss is less than expected, given the areas highlighted in Table 6.10, is the result of the considerable overlap from cutaneous branches of the median and ulnar nerves.


Figure B6.27. Testing the radial nerve.

Lateral and Medial Cutaneous Nerves of Forearm The lateral cutaneous nerve of the forearm (lateral antebrachial cutaneous nerve) is the continuation of the musculocutaneous nerve after its motor branches have all been given off to the muscles of the anterior compartment of the arm. The medial cutaneous nerve of the forearm (medial antebrachial cutaneous nerve) is an independent branch of the medial cord of the brachial plexus. With the posterior cutaneous nerve of the forearm from the radial nerve, each supplying the area of skin indicated by its name, these three nerves provide all the cutaneous innervation of the forearm. There is no “anterior cutaneous nerve of the forearm.” (Memory device: This is similar to the brachial plexus, which has lateral, medial and posterior cords, but no anterior cord.) Although the arteries, veins, and nerves of the forearm have been considered separately, it is important to place them into their anatomical context. Except for the superficial veins, which often course independently in the subcutaneous tissue, these neurovascular structures usually exist as components of neurovascular bundles. These bundles are composed of arteries, veins (in the limbs, usually in the form of accompanying veins), and nerves as well as lymphatic vessels, which are usually surrounded by a neurovascular sheath of varying density.

The Bottom Line Well‐developed subcutaneous veins course in the subcutaneous tissue of the forearm. These veins are subject to great variation. Once they have penetrated the deep fascia, cutaneous nerves run independently of the veins in the subcutaneous tissue where they remain constant in location and size, with lateral, medial, and posterior cutaneous nerves of the forearm supplying the aspects of the forearm described by their names. Three major (radial, median or middle, and ulnar) and two minor (anterior and posterior interosseous) neurovascular bundles occur deep to the antebrachial fascia.


The radial bundle—containing the radial artery, accompanying veins, and superficial radial nerve—course along and define the border between the anterior and the posterior forearm compartments (the vascular structures serving both) deep to the brachioradialis. The middle (median nerve and variable median artery and veins) and ulnar (ulnar nerve, artery, and accompanying veins) bundles course in a fascial plane between the intermediate and the deep flexor muscles. The median nerve supplies most muscles in the anterior compartment, many via its anterior interosseous branch, which courses on the interosseous membrane. The ulnar nerve supplies the one and a half exceptions (FCU and ulnar half of the FDP). The deep radial nerve penetrates the supinator to join the posterior interosseous artery in the plane between the superficial and the deep extensors. This nerve supplies all the muscles arising in the posterior compartment. The flexor muscles of the anterior compartment have approximately twice the bulk and strength of the extensor muscles of the posterior compartment. This, and the fact that the flexor aspect of the limb is the more protected aspect, accounts for the major neurovascular structures being located in the anterior compartment, with only the relatively small posterior interosseous vessels and nerve in the posterior compartment.

Surface Anatomy of the Forearm Three bony landmarks are easily palpated at the elbow: the medial and lateral epicondyles of the humerus and the olecranon of the ulna (Fig. SA6.12). In the hollow located posterolaterally when the forearm is extended, the head of the radius can be palpated distal to the lateral epicondyle. Supinate and pronate your forearm and feel the movement of the radial head. The posterior border of the ulna is subcutaneous and can be palpated distally from the olecranon along the entire length of the bone. This landmark demarcates the posteromedial boundary separating the flexor—pronator (anterior) and extensor—supinator (posterior) compartments of the forearm. The cubital fossa, the triangular hollow area on the anterior surface of the elbow, is bounded medially by the prominence formed by the flexor—pronator group of muscles that are attached to the medial epicondyle. To estimate the position of these muscles, put your thumb posterior to your medial epicondyle and then place your fingers on your forearm as shown in Figure SA6.13. The black dot on the dorsum of the hand indicates the position of the medial epicondyle. The cubital fossa is bounded laterally by the prominence of the extensor—supinator group of muscles attached to the lateral epicondyle (Fig. SA6.14). The pulsations of the radial artery can be palpated throughout the forearm as it runs its superficial course from the cubital fossa to the wrist (anterior to the radial styloid process), demarcating the anterolateral boundary separating the flexor—pronator and extensor—supinator compartments of the forearm. The head of the ulna is at its distal end and is easily seen and palpated. It appears as a rounded prominence at the wrist when the hand is pronated. The ulnar styloid process can be palpated just distal to the ulnar head. The larger radial styloid process can be easily palpated on the lateral side of the wrist when the hand is supinated, particularly when the tendons covering it are relaxed. The radial styloid process is located approximately 1 cm more distal than the ulnar styloid process. This relationship of the styloid processes is important in the diagnosis of certain injuries


in the wrist region (e.g., fracture of the distal end of the radius). Proximal to the radial styloid process, the surfaces of the radius are palpable for a few centimeters. The lateral surface of the distal half of the radius is easy to palpate.

Figure SA6.12

Figure SA6.13


Figure SA6.14

Hand The wrist is located at the junction of the forearm and hand, and the hand is the manual part of the upper limb distal to the forearm. Once positioned at the desired height and location relative to the body by movements at the shoulder and elbow, and the direction of action is established by pronation and supination of the forearm, the working position or attitude (tilt) of the hand is adjusted by movement at the wrist joint. The skeleton of the hand consists of carpals in the wrist, metacarpals in the hand proper, and phalanges in the digits. The digits are numbered from one to five, beginning with the thumb and ending with the little finger. The palmar aspect of the hand features a central concavity that, with the crease proximal to it (over the wrist bones) separates two eminences: a lateral, larger and more prominent thenar eminence at the base of the thumb, and a medial, smaller hypothenar eminence proximal to the base of the 5th finger (Fig SA6.13). Because of the importance of manual dexterity in occupational and recreational activities, a good understanding of the structure and function of the hand is essential for all persons involved in maintaining or restoring its activities: free motion, power grasping, precision handling, and pinching.


Figure 6.48. Functional positions of hand. A. In the power grip, when grasping an object, the metacarpophalangeal (MP) and interphalangeal (IP) joints are flexed, but the radiocarpal and midcarpal joints are extended. “Cocking” (extension of) the wrist increases the distance over which the flexor tendons act, increasing tension of the long flexor tendons beyond that produced by maximal contraction of the muscles alone. B. The hook grip (flexion of the IP joints of the 2nd—4th digits) resists gravitational (downward) pull with only digital flexion. C. The precision grip is used when writing. D and E. One uses the precision grip to hold a coin to enable manipulation (D) and when pinching an object (E). F. Casts for fractures are applied with the hand and wrist in the resting position. Note the mild extension of the wrist. G and H. When gripping an unattached rod loosely (G) or firmly (H), the 2nd and 3rd carpometacarpal joints are rigid and stable, but the 4th and 5th are saddle joints permitting flexion and extension. The increased flexion changes the angle of the rod during the firm grip.


The power grip (palm grasp) refers to forcible motions of the digits acting against the palm; the fingers are wrapped around an object with counterpressure from the thumb—for example, when grasping a cylindrical structure (Fig. 6.48A). The power grip involves the long flexor muscles to the fingers (acting at the interphalangeal joints), the intrinsic muscles in the palm (acting at the metacarpophalangeal joints), and the extensors of the wrist (acting at the radiocarpal and midcarpal joints). The “cocking” of the wrist by the extensors increases the distance over which the flexors of the fingers act, producing the same result as a more complete muscular contraction. Conversely, as flexion increases at the wrist, the grip becomes weaker and more insecure. A hook grip is the posture of the hand that is used when carrying a briefcase (Fig. 6.48B). This grip consumes less energy, involving mainly the long flexors of the fingers, which are flexed to a varying degree, depending on the size of the object that is grasped. The precision handling grip involves a change in the position of a handled object that requires fine control of the movements of the fingers and thumb—for example, holding a pencil, manipulating a coin, threading a needle, or buttoning a shirt (Fig. 6.48C & D). In a precision grip, the wrist and fingers are held firmly by the long flexor and extensor muscles, and the intrinsic hand muscles perform fine movements of the digits. Pinching refers to compression of something between the thumb and the index finger—for example, handling a teacup or holding a coin on edge (Fig. 6.48E)—or between the thumb and the adjacent two fingers—for example, snapping the fingers. The position of rest is assumed by an inactive hand—for example, when the forearm and hand are laid on a table (Fig. 6.48F). This position is often used when it is necessary to immobilize the wrist and hand in a cast to stabilize a fracture.

Fascia of the Palm The fascia of the palm is continuous with the antebrachial fascia and the fascia of the dorsum of the hand (Fig. 6.39). The palmar fascia is thin over the thenar and hypothenar eminences, but it is thick centrally where it forms the fibrous palmar aponeurosis and in the fingers where it forms the digital sheaths (Figs. 6.39 and 6.49). The palmar aponeurosis, a strong, well‐defined part of the deep fascia of the palm, covers the soft tissues and overlies the long flexor tendons. The proximal end or apex of the triangular palmar aponeurosis is continuous with the flexor retinaculum and the palmaris longus tendon. When the palmaris longus is present, the palmar aponeurosis is the expanded tendon of the palmaris longus. Distal to the apex, the palmar aponeurosis forms four longitudinal digital bands or rays that radiate from the apex and attach distally to the bases of the proximal phalanges and become continuous with the fibrous digital sheaths.


Figure 6.49. Palmar fascia and fibrous digital sheaths. A. The palmar fascia is continuous with the antebrachial fascia. The thin thenar and hypothenar fascia covers the intrinsic muscles of the thenar and hypothenar eminences, respectively. Between the thenar and the hypothenar muscle masses, the central compartment of the palm is roofed by the thick palmar aponeurosis. When present (approximately 80% of the time), the distal end of the palmaris longus tendon blends with the aponeurosis superficial to the flexor retinaculum. Fibrous digital sheaths (shown here for the middle and index fingers), continuous with the longitudinal fiber bundles of the palmar aponeurosis, form the coverings of the digital portions of the tendons of the FDS and FDP. B. A transverse section of the 4th finger (proximal phalanx level) is shown. Within the fibrous digital sheath and proximal to its attachment to the base of the middle phalanx, the FDS tendon has split into two parts to allow continued central passage of the FDP tendon to the distal phalanx. The palmar digital nerve, artery, and vein are adjacent to the sheath, not to the phalanx (Bone). The dorsal digital neurovascular structures become exhausted near the midpoint of the middle phalanges; thus the palmar nerves, arteries, and veins serve all (palmar and dorsal aspects) of the digits distally.

The fibrous digital sheaths are ligamentous tubes that enclose the synovial sheaths, the superficial and deep flexor tendons, and the tendon of the FPL in their passage along the palmar aspect of their respective fingers (Figs. 6.39, 6.42C, and 6.49). The flexor digital sheaths are composed of five anular and four cruciform (cross‐shaped) parts or “pulleys.” A medial fibrous septum extends deeply from the medial border of the palmar aponeurosis to the 5th metacarpal (Fig. 6.50A). Medial to this septum is the medial or hypothenar compartment containing the hypothenar muscles. Similarly, a lateral fibrous septum extends deeply from the lateral border of the palmar aponeurosis to the 3rd metacarpal. Lateral to this septum is the lateral or thenar compartment containing the thenar muscles. Between the hypothenar and the thenar compartments is the central compartment containing the flexor tendons and their sheaths, the lumbricals, the superficial palmar arterial arch, and the digital vessels and nerves. The deepest muscular plane of the palm is the adductor compartment containing the adductor pollicis. Between the flexor tendons and the fascia covering the deep palmar muscles are two potential spaces, the thenar space and the midpalmar space (Fig. 6.50). The spaces are bounded by fibrous septa passing from the edges of the palmar aponeurosis to the metacarpals. Between the two spaces is the especially strong lateral fibrous


septum, which is attached to the 3rd metacarpal. Although most fascial compartments end at the joints, the midpalmar space is continuous with the anterior compartment of the forearm via the carpal tunnel.

F i g u re 6 . 5 0 . C o m p a r t me n t s , s p a c e s , an d f a s c i a o f p a l m . A . T h is t r a n s v e rs e s e c t i o n t h r ou g h t h e m i d d l e o f t h e p a l m i l l u s t r a t e s the f a s c i a l c o m p a r t m e n ts o f t h e h a n d . T h e h y p o t h e n a r f a s c i a , a t t a c h e d t o t h e l a t e ra l s i d e o f t h e 5t h m e t a c a r p a l , b o u n d s t h e h y p o t h e n a r c om p a r t m e n t . S i m i l a r l y , t h e t h e n a r f a s ci a , a t t a c h e d t o t h e p a l m a r a s p e c t o f the 1 s t m e t a c a rp a l , b o u n d s ( w i t h t h e m e t a c a r p a l ) t h e t h e n a r c o m p a r t m e n t . T h e c e n t r a l c o m p a r t m e n t of t h e p a l m is c o v e r e d b y t h e p a l m a r a p o n e u r o s i s a n d s e p a r a t e d f r o m t h e t h e n a r a n d h y p o t h e n a r c o m p a r t m e n ts b y m e d i a l a n d l a t e r a l f i b r ou s s e p t a a t ta c h i n g t o t h e 5 t h a n d 3 r d m e t a c a r p a l s , r e s p e c t i v e l y . T h e s e p t u m a t t a c h e d t o t h e 3 r d m e t a c a r p a l a l s o s e p a r a t e s t h e m i d p a l m a r a n d th e n a r s p a c e s T h e a d d u ct o r c o m p a r tm e n t c o n ta i n s t h e a d d u c t o r p o l l i c i s m u s c l e . B . T h e m id p a l m a r s p a ce u n d e r l i e s th e c e n t r a l c o m p a r t m e n t of t h e p a lm a n d i s r e l a t e d d i s t a l l y t o t h e s y n ov i a l t e n d o n s h e a t h s o f t h e 3 r d — 5 t h d i g i t s a n d p r o x i m a l l y t o t h e c o m m o n f l e x o r s h e a t h a s i t e m e r g e s f r o m t h e c a r p a l t u n n e l . T h e t h e n a r s p a c e u n d e r l i e s t h e t h e n a r c o m p a r t m e n t a n d i s r e l a t e d d i s ta l l y t o t h e s y n o v i a l t e n d o n s h e a t h of t h e i n d e x f i n g e r a n d p r o x i m a ll y t o t h e c o m m o n f le x o r s h e a t h d i s ta l to t h e c a rp a l t u n n e l .

Dupuytren Contracture of Palmar Fascia Dupuytren contracture is a disease of the palmar fascia resulting in progressive shortening, thickening, and fibrosis of the palmar fascia and aponeurosis. The fibrous degeneration of the longitudinal bands of the palmar aponeurosis on the medial side of the hand pulls the 4th and 5th fingers into partial flexion at the metacarpophalangeal and proximal interphalangeal joints (Fig. B6.28A). The contracture is frequently bilateral and is seen in some men >50 years of age. Its cause is unknown, but evidence points to a hereditary predisposition. The disease first manifests as painless nodular thickenings of the palmar aponeurosis that adhere to the skin. Gradually, progressive contracture of the longitudinal bands produces raised ridges in the palmar skin that extend from the proximal part of the hand to the base of the 4th and 5th fingers (Fig. B6.28B). Treatment of Dupuytren contracture usually involves surgical excision of all fibrotic parts of the palmar fascia to free the fingers (Salter, 1999).


Hand Infections Because the palmar fascia is thick and strong, swellings resulting from hand infections usually appear on the dorsum of the hand, where the fascia is thinner. The potential fascial spaces of the palm are important because they may become infected. The fascial spaces determine the extent and direction of the spread of pus formed by these infections. Depending on the site of infection, pus will accumulate in the thenar, hypothenar, or adductor compartments. Antibiotic therapy has made infections that spread beyond one of these fascial compartments rare; however, an untreated infection can spread proximally through the carpal tunnel into the forearm, anterior to the pronator quadratus and its fascia.

Figure B6.28. Dupuytren contracture.

Muscles of the Hand The intrinsic muscles of the hand are located in five compartments (Fig. 6.50):     

Thenar muscles in the thenar compartment: abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. Adductor pollicis in the adductor compartment. Hypothenar muscles in the hypothenar compartment: abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. Short muscles of the hand, the lumbricals, are in the central compartment with the long flexor tendons. The interossei lie in separate interosseous compartments between the metacarpals.


Thenar Muscles The thenar muscles form the thenar eminence on the lateral surface of the palm and are chiefly responsible for opposition of the thumb. Normal movement of the thumb is important for the precise activities of the hand. The high degree of freedom of movements of the thumb results from the 1st metacarpal being independent, with mobile joints at both ends. Thus several muscles are required to control its freedom of movement:     

Extension: extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus. Flexion: flexor pollicis longus and flexor pollicis brevis. Abduction: abductor pollicis longus and abductor pollicis brevis. Adduction: adductor pollicis and 1st dorsal interosseous. Opposition: opponens pollicis. This movement occurs at the carpometacarpal joint and results in a “cupping” of the palm. Bringing the tip of the thumb into contact with the 5th finger or any of the other fingers involves considerably more movement than can be produced by the opponens pollicis alone. This complex movement begins with the thumb in the extended position and initially involves abduction and medial rotation of the 1st metacarpal (cupping the palm) produced by the action of the opponens pollicis at the carpometacarpal joint and then flexion at the metacarpophalangeal joint (Fig. 6.51). The reinforcing action of the adductor pollicis and FPL increases the pressure that the opposed thumb can exert on the fingertips. In pulp‐to‐pulp opposition, movements of the finger opposing the thumb are also involved.

The first four movements occur at the carpometacarpal and metacarpophalangeal joints. The thenar muscles are illustrated in Figure 6.52; their attachments, innervations, and main actions are summarized in Table 6.11.

Abductor Pollicis Brevis The abductor pollicis brevis (APB), the short abductor of the thumb, forms the anterolateral part of the thenar eminence. In addition to abducting the thumb, the APB assists the opponens pollicis during the early stages of opposition by rotating its proximal phalanx slightly medially. To test the abductor pollicis brevis, abduct the thumb against resistance. If acting normally, the muscle can be seen and palpated.

Flexor Pollicis Brevis The flexor pollicis brevis (FPB), the short flexor of the thumb, is located medial to the APB (Fig. 6.52A). Its two bellies, located on opposite sides of the tendon of the FPL, share (with each other and often with the APB) a common, sesamoid‐containing tendon at their distal attachment. The bellies usually differ in their innervation: The larger superficial head of the FPB is innervated by the recurrent branch of the median nerve, whereas the smaller deep head is usually innervated by the deep palmar branch of the ulnar nerve. The FPB flexes the thumb at the carpometacarpal and metacarpophalangeal joints and aids in opposition of the thumb.


Figure 6.51. Movements of thumb. The thumb is rotated 90° to the other digits. (This can be confirmed by noting the direction the nail of the thumb faces compared with the nails of the other fingers.) Thus abduction and adduction occur in a sagittal plane and flexion and extension occur in a coronal plane. Opposition, the action bringing the tip of the thumb in contact with the pads of the other fingers (e.g., with the little finger), is the most complex movement. The components of opposition are abduction and medial rotation at the carpometacarpal joint and flexion of the metacarpophalangeal joint.

Table 6.11. Intrinsic Muscles of the Hand


Muscle

Proximal Attachment Thenar muscles Opponens Flexor pollicis retinaculum and tubercles of scaphoid and Abductor trapezium pollicis brevis Flexor pollicis brevis Superficial head Deep head Adductor Bases of 2nd and pollicis 3rd metacarpals, capitate, Oblique adjacent carpals head Transverse Anterior surface head of shaft of 3rd metacarpal Hypothenar muscles Abductor Pisiform digiti minimi Flexor digiti Hook of hamate minimi and flexor brevis retinaculum Opponens digiti minimi

Short muscles Lumbricals Lateral two 1st and 2nd tendons of flexor digitorum profundus (as unipennate muscles) 3rd and 4th Medial three tendons of flexor digitorum profundus (as bipennate muscles) Dorsal Adjacent sides of interossei, two metacarpals 1st—4th (as bipennate muscles)

Distal Attachment

Innervation a

Lateral side of Recurrent 1st metacarpal branch of medial nerve Lateral side of (C8, T1) base of proximal phalanx of thumb

Main Action

To oppose thumb, it draws 1st metacarpal medially to center of palm and rotates it medially Abducts thumb; helps oppose it

Flexes thumb

Adducts thumb toward lateral border of palm Deep branch Medial side of of ulnar nerve base of proximal (C8, T1) phalanx of thumb

Medial side of Deep branch base of proximal of ulnar nerve phalanx of 5th (C8, T1) finger

Abducts 5th finger; assists in flexion of its proximal phalanx Flexes proximal phalanx of 5th finger

Medial border of 5th metacarpal

Draws 5th metacarpal anterior and rotates it, bringing 5th finger into opposition with thumb

Lateral sides of Median nerve Flex metacarpophalangeal joints; extensor (C8, T1) extend interphalangeal joints of expansions of 2nd—5th fingers 2nd—5th fingers

Deep branch of ulnar nerve (C8, T1)

Bases of proximal phalanges; extensor expansions of 2nd—4th fingers

Abduct 2nd—4th fingers from axial line; act with lumbricals in flexing metacarpophalangeal joints and extending interphalangeal joints


Palmar interossei, 1st—3rd

Palmar surfaces of 2nd, 4th, and 5th metacarpals (as unipennate muscles)

Bases of Adduct 2nd, 4th, and 5th fingers proximal toward axial line; assist phalanges; lumbricals in flexing metacar‐ extensor pophalangeal joints and expansions of extending interphalangeal joints; 2nd, 4th, and extensor expansions of 2nd—4th 5th fingers fingers a The spinal cord segmental innervation is indicated (e.g., “C8, T1” means that the nerves supplying the opponens pollicis are derived from the eighth cervical segment and first thoracic segment of the spinal cord). Numbers in boldface (C8) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

To test the flexor pollicis brevis, flex the thumb against resistance. If acting normally, the muscle can be seen and palpated; however, keep in mind that the FPL also flexes the thumb.

Opponens Pollicis The opponens pollicis is a quadrangular muscle that lies deep to the APB and lateral to the FPB (Fig. 6.52B). The opponens pollicis opposes the thumb, the most important thumb movement. It flexes and rotates the 1st metacarpal medially at the carpometacarpal joint during opposition; this movement occurs when picking up an object. During opposition, the tip of the thumb is brought into contact with the pad of the little finger, as shown in Figure 6.51.

Adductor Pollicis The adductor pollicis is the deeply placed, fan‐shaped adductor of the thumb. It is located in the adductor compartment of the hand (Figs. 6.50A and 6.53). The adductor pollicis has two heads of origin, which are separated by the radial artery as it enters the palm to form the deep palmar arch. Its tendon usually contains a sesamoid bone. The adductor pollicis adducts the thumb, moving the thumb to the palm of the hand (Fig. 6.51), thereby giving power to the grip (Fig. 6.48G & H).

Hypothenar Muscles The hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi) produce the hypothenar eminence on the medial side of the palm and move the little finger. These muscles are in the hypothenar compartment with the 5th metacarpal (Figs. 6.50A and 6.52). The attachments, innervations, and main actions of the hypothenar muscles are summarized in Table 6.11.

Abductor Digiti Minimi The abductor digiti minimi is the most superficial of the three muscles forming the hypothenar eminence. The abductor digiti minimi abducts the 5th finger and helps flex its proximal phalanx.


Figure 6.52. Superficial dissections of right palm. The skin and subcutaneous tissue have been removed, as have most of the palmar aponeurosis and the thenar and hypothenar fasciae. A. The superficial palmar arch is located immediately deep to the palmar aponeurosis, superficial to the long flexor tendons. This arterial arch gives rise to the common palmar digital arteries. In the digits, a digital artery (e.g., radialis indicis) and nerve lie on the medial and lateral sides of the fibrous digital sheath. The pisiform bone protects the ulnar nerve and artery as they pass into the palm. B. Three thenar and three hypothenar muscles attach to the flexor retinaculum and to the four marginal carpal bones united by the retinaculum.


Figure 6.53. Muscles and arteries of distal forearm and deep palm. This deep dissection of the palm reveals the anastomosis of the palmar carpal branch of the radial artery with the palmar carpal branch of the ulnar artery to form the palmar carpal arch, and the deep palmar arch. The deep palmar arch lies at the level of the bases of the metacarpal bones, 1.5—2 cm proximal to the superficial palmar arch.

Flexor Digiti Minimi Brevis The flexor digiti minimi brevis is variable in size; it lies lateral to the abductor digiti minimi. The flexor digiti minimi brevis flexes the proximal phalanx of the 5th finger at the metacarpophalangeal joint.

Opponens Digiti Minimi The opponens digiti minimi is a quadrangular muscle that lies deep to the abductor and flexor muscles of the 5th finger. The opponens digiti minimi draws the 5th metacarpal anteriorly and rotates it laterally, thereby deepening the hollow of the palm and bringing the 5th finger into opposition with the thumb (Fig. 6.51). Like the opponens pollicis, the opponens digiti minimi acts exclusively at the carpometacarpal joint.

Palmaris Brevis The palmaris brevis is a small, thin muscle in the subcutaneous tissue of the hypothenar eminence (Fig. 6.52A); it is not in the hypothenar compartment. The palmaris brevis wrinkles the skin of the hypothenar eminence and deepens the hollow of the palm, thereby aiding the palmar grip. The palmaris brevis covers and protects the ulnar nerve and artery. It is attached proximally to the medial border of the palmar aponeurosis and to the skin on the medial border of the hand.


Short Muscles of the Hand The short muscles of the hand are the lumbricals and interossei (Table 6.11).

Lumbricals The four slender lumbrical muscles were named because of their worm‐like form (L. lumbricus, earthworm) (Fig. 6.52A & B). The lumbricals flex the fingers at the metacarpophalangeal joints and extend the interphalangeal joints.

Interossei The four dorsal interosseous muscles (dorsal interossei) are located between the metacarpals; the three palmar interosseous muscles (palmar interossei) are on the palmar surfaces of the metacarpals in the interosseous compartment of the hand (Fig. 6.50A). The 1st dorsal interosseous muscle is easy to palpate; oppose the thumb firmly against the index finger and it can be easily felt. (Some authors describe four palmar interossei; in so doing, they are including the deep head of the FPB because of its similar innervation and placement on the thumb; Table 6.11). The four dorsal interossei abduct the fingers, and the three palmar interossei adduct them. A mnemonic device is to make acronyms of Dorsal ABduct (DAB) and Palmar ADuct (PAD). Acting together, the dorsal and palmar interossei and the lumbricals produce flexion at the metacarpophalangeal joints and extension of the interphalangeal joints (the so‐called Z‐movement). This occurs because of their attachment to the lateral bands of the extensor expansions (Fig. 6.42B). Understanding the Z‐movement is useful because it is the opposite of claw hand, which occurs in ulnar paralysis when the interossei and the 3rd and 4th lumbricals are incapable of acting together to produce the Z‐movement (see clinical correlation [blue] box “Ulnar Nerve Injury,” earlier in this chapter).

Long Flexor Tendons and Tendon Sheaths in the Hand The tendons of the FDS and FDP enter the common flexor sheath (ulnar bursa) deep to the flexor retinaculum (Fig. 6.54A). The tendons enter the central compartment of the hand and fan out to enter their respective digital synovial sheaths. The flexor and digital sheaths enable the tendons to slide freely over each other during movements of the fingers. Near the base of the proximal phalanx, the tendon of FDS splits and surrounds the tendon of FDP (Figs. 6.49B and 6.54B). The halves of the FDS tendon are attached to the margins of the anterior aspect of the base of the middle phalanx (Fig. 6.42D). The tendon of FDP, after passing through the split in the FDS tendon, the tendinous chiasm, passes distally to attach to the anterior aspect of the base of the distal phalanx. The fibrous digital sheaths are the strong ligamentous tunnels containing the flexor tendons and their synovial sheaths (Figs. 6.49 and 6.54C). The sheaths extend from the heads of the metacarpals to the bases of the distal phalanges. These sheaths prevent the tendons from pulling away from the digits (bowstringing). The fibrous digital sheaths combine with the bones to form osseofibrous tunnels through which the tendons pass to reach the digits. The anular and cruciform parts (often referred to clinically as “pulleys” ) are thickened reinforcements of the fibrous digital sheaths (Fig. 6.54B). The long flexor tendons are supplied by small blood vessels that pass within synovial folds (vincula) from the periosteum of the phalanges (Fig. 6.42B). The tendon of the


FPL passes deep to the flexor retinaculum to the thumb within its own synovial sheath. At the head of the metacarpal, the tendon runs between two sesamoid bones, one in the combined tendon of the FPB and APB and the other in the tendon of the adductor pollicis.

The Bottom Line The larger (wider range) and stronger movements of the hand and fingers (grasping, pinching, pointing, etc.) are produced by extrinsic muscles with fleshy bellies located distant from the hand (near the elbow) and long tendons passing into the hand and fingers. The shorter, more delicate and weaker movements (typing, playing musical instruments, and writing) and positioning of the fingers for the more powerful movements are accomplished largely by the intrinsic muscles. The muscles and tendons of the hand are organized into five fascial compartments: two radial compartments (thenar and adductor) that serve the thumb; an ulnar (hypothenar) compartment that serves the little finger; and two more central compartments that serve the medial four fingers (a palmar one for the long flexor tendons and lumbricals, and a deep one between the metacarpals for the interossei). The greatest mass of intrinsic muscles is dedicated to the highly mobile thumb. Indeed, when extrinsic muscles are also considered, the thumb has eight muscles producing and controlling the wide array of movements that distinguish the human hand. The interossei produce multiple movements: the dorsal interossei (and abductors pollicis and digiti minimi) abduct the fingers, whereas the palmar interossei (and adductor pollicis) adduct them. Both movements occur at the metacarpophalangeal joints. Acting together with the lumbricals, the interossei flex the metacarpophalangeal and extend the interphalangeal joints of the medial four fingers (the Z‐movement).

Tenosynovitis Injuries such as a puncture of a finger by a rusty nail can cause infection of the digital synovial sheaths. When inflammation of the tendon and synovial sheath occurs (tenosynovitis), the digit swells and movement becomes painful. Because the tendons of the 2nd, 3rd, and 4th fingers nearly always have separate synovial sheaths, the infection is usually confined to the infected finger. If the infection is untreated, however, the proximal ends of these sheaths may rupture, allowing the infection to spread to the midpalmar space (Fig. 6.51B). Because the synovial sheath of the little finger is usually continuous with the common flexor sheath (Fig. 6.54B), tenosynovitis in this finger may spread to the common sheath and thus through the palm and carpal tunnel to the anterior forearm, draining into the space between the pronator quadratus and the overlying flexor tendons (Parona space). Likewise, tenosynovitis in the thumb may spread via the continuous synovial sheath of the FPL (radial bursa). How far an infection spreads from the fingers depends on variations in their connections with the common flexor sheath. The tendons of the APL and EPB are in the same tendinous sheath on the dorsum of the wrist. Excessive friction of these tendons on their common sheath results in fibrous thickening of the sheath and stenosis of the osseofibrous tunnel. The excessive friction is caused by repetitive forceful use of the hands during gripping and wringing (e.g., squeezing water out of clothes). This condition, called Quervain tenovaginitis stenosans, causes pain in the wrist that radiates proximally to the


forearm and distally toward the thumb. Local tenderness is felt over the common fibrous sheath on the lateral side of the wrist. Thickening of a fibrous digital sheath on the palmar aspect of the digit produces stenosis of the osseofibrous tunnel, the result of repetitive forceful use of the fingers. If the tendons of the FDS and FDP enlarge proximal to the tunnel, the person is unable to extend the finger. When the finger is extended passively, a snap is audible. Flexion produces another snap as the thickened tendon moves. This condition is called digital tenovaginitis stenosans (trigger finger or snapping finger). Figure 6.54. Flexor tendons, common flexor sheath, fibrous digital sheaths, and synovial sheaths of digits. A. This dissection of the anterior aspect of the distal forearm and hand shows the synovial sheaths of the long flexor tendons to the digits. Observe the two sets: (1) proximal or carpal, posterior to the flexor retinaculum, and (2) distal or digital, within the fibrous sheaths of the digital flexors. B. This dissection of the palm illustrates the tendons and fibrous digital sheaths. The fibrous sheaths of the digits attach along the borders of the proximal and middle phalanges to capsules (palmar ligaments) of the interphalangeal joints and to the surface of the distal phalanx. C. The structure of an osseo‐ fibrous tunnel of a finger, containing a tendon, is shown. Within the fibrous sheath, the synovial sheath consists of the (parietal) synovial lining of the tunnel and the (visceral) synovial covering of the tendon. These layers of the synovial sheath are actually separated by only a capillary layer of synovial fluid, which lubricates the synovial surfaces to facilitate gliding of the tendon (see Introduction).


Arteries of the Hand Because its function requires it to be placed and held in many different positions, often while grasping or applying pressure, the hand is supplied with an abundance of highly branched and anastomosing arteries so that oxygenated blood is generally available to all parts in all positions. Furthermore, the arteries or their derivatives are relatively superficial, underlying skin capable of sweating, so that excess heat can be released. To prevent undesirable heat loss in a cold environment, the arterioles of the hands are capable of reducing blood flow to the surface and to the ends of the fingers. The ulnar and radial arteries and their branches provide all the blood to the hand. The arteries of the hand are illustrated and their origins and courses are described in Table 6.12.

Ulnar Artery The ulnar artery enters the hand anterior to the flexor retinaculum between the pisiform and the hook of the hamate via the ulnar canal (Guyon canal) (Fig. 6.47B). The ulnar artery lies lateral to the ulnar nerve (Fig. 6.52A). The artery divides into two terminal branches, the superficial palmar arch and the deep palmar branch. The superficial palmar arch, the main termination of the ulnar artery, gives rise to three common palmar digital arteries that anastomose with the palmar metacarpal arteries from the deep palmar arch. Each common palmar digital artery divides into a pair of proper palmar digital arteries that run along the adjacent sides of the 2nd— 4th fingers.

Radial Artery The radial artery curves dorsally around the scaphoid and trapezium and crosses the floor of the anatomical snuff box (Fig. 6.44C). It enters the palm by passing between the heads of the 1st dorsal interosseous muscle and then turns medially, passing between the heads of the adductor pollicis. The radial artery ends by anastomosing with the deep branch of the ulnar artery to form the deep palmar arch, which is formed mainly by the radial artery. This arch lies across the metacarpals just distal to their bases (Fig. 6.53). The deep palmar arch gives rise to three palmar metacarpal arteries and the princeps pollicis artery. The radialis indicis artery passes along the lateral side of the index finger. It usually arises from the radial artery, but it may originate from the princeps pollicis.

Laceration of the Palmar Arches Bleeding is usually profuse when the palmar (arterial) arches are lacerated. It may not be sufficient to ligate only one forearm artery when the arches are lacerated, because these vessels usually have numerous communications in the forearm and hand and thus bleed from both ends. To obtain a bloodless surgical operating field for treating complicated hand injuries, it may be necessary to compress the brachial artery and its branches proximal to the elbow (e.g., using a pneumatic tourniquet). This procedure prevents blood from reaching the ulnar and radial arteries through the anastomoses around the elbow.


Ischemia of the Fingers Intermittent bilateral attacks of ischemia of the fingers, marked by cyanosis and often accompanied by paresthesia and pain, is characteristically brought on by cold and emotional stimuli. The condition may result from an anatomical abnormality or an underlying disease. When the cause of the condition is idiopathic (unknown) or primary, it is called Raynaud syndrome (disease). The arteries of the upper limb are innervated by sympathetic nerves. Postsynaptic fibers from the sympathetic ganglia enter nerves that form the brachial plexus and are distributed to the digital arteries through branches arising from the plexus. When treating ischemia resulting from Raynaud syndrome, it may be necessary to perform a cervicodorsal presynaptic sympathectomy (excision of a segment of a sympathetic nerve) to dilate the digital arteries.

Veins of the Hand Superficial and deep venous palmar arches, associated with the superficial and deep palmar (arterial) arches, drain into the deep veins of the forearm (Fig. 6.46). The dorsal digital veins drain into three dorsal metacarpal veins, which unite to form a dorsal venous network (Fig. 6.12A). Superficial to the metacarpus, this network is prolonged proximally on the lateral side as the cephalic vein. The basilic vein arises from the medial side of the dorsal venous network.

Nerves of the Hand The median, ulnar, and radial nerves supply the hand (Figs. 6.47, 6.52, and 6.55). These nerves and their branches in the hand are illustrated and their origins, courses, and distributions are provided in Table 6.13. In addition, branches or communications from the lateral and posterior cutaneous nerves may contribute some fibers that supply the skin of the dorsum of the hand.


Table 6.12. Arteries of the Hand

Artery Superficial arch

Origin palmar Direct continuation of ulnar artery; arch is completed on lateral side by superficial branch of radial artery or another of its branches

Course Curves laterally deep to palmar aponeurosis and superficial to long flexor tendons; curve of arch lies across palm at level of distal border of extended thumb Deep palmar arch Direct continuation of radial artery; arch Curves medially, deep to long flexor is completed on medial side by deep tendons; is in contact with bases of branch of ulnar artery metacarpals Common palmar Superficial palmar arch Pass distally on lumbricals to digitals webbing of fingers Proper palmar Common palmar digital arteries Run along sides of 2nd—5th fingers digitals Princeps pollicis Radial artery as it turns into palm Descends on palmar aspect of 1st metacarpal; divides at base of proximal phalanx into two branches that run along sides of thumb Radialis indicis Radial artery but may arise from princeps Passes along lateral side of index pollicis artery finger to its distal end Dorsal carpal arch Radial and ulnar arteries Arches within fascia on dorsum of hand

The Median Nerve in the Hand The median nerve enters the hand through the carpal tunnel, deep to the flexor retinaculum, along with the nine tendons of the FDS, FDP, and FPL (Fig. 6.55). The carpal tunnel is the passageway deep to the flexor retinaculum between the tubercles of the scaphoid and trapezoid bones on the lateral side and the pisiform and hook of the hamate on the medial side. Distal to the carpal tunnel, the median nerve supplies two and a half thenar muscles and the 1st and 2nd lumbricals (Table 6.13). It also sends sensory fibers to the skin on the entire palmar surface, the sides of the first three digits, the lateral half of the 4th digit, and the dorsum of the distal


halves of these digits. Note, however, that the palmar cutaneous branch of the median nerve, which supplies the central palm, arises proximal to the flexor retinaculum and passes superficial to it (i.e., it does not pass through the carpal tunnel).

Lesions of the Median Nerve Lesions of the median nerve usually occur in two places: the forearm and the wrist. The most common site is where the nerve passes through the carpal tunnel.

Carpal Tunnel Syndrome Carpal tunnel syndrome results from any lesion that significantly reduces the size of the carpal tunnel (Fig. B6.29A—D) or, more commonly, increases the size of some of the nine structures (or their coverings) that pass through it (e.g., inflammation of synovial sheaths). Fluid retention, infection, and excessive exercise of the fingers may cause swelling of the tendons or their synovial sheaths. The median nerve is the most sensitive structure in the carpal tunnel (Fig. B6.29B—D) and therefore is the most affected. This nerve has two terminal sensory branches that supply the skin of the hand; hence, paresthesia (tingling), hypoesthesia (diminished sensation), or anesthesia (absence of sensation) may occur in the lateral three and a half digits. Recall, however, that the palmar cutaneous branch of the median nerve arises proximal to and does not pass through the carpal tunnel; thus sensation in the central palm remains unaffected. The nerve also has one terminal motor branch, the recurrent branch, which serves the three thenar muscles (Table 6.11). Progressive loss of coordination and strength in the thumb (owing to weakness of the APB and opponens pollicis) may occur if the cause of compression is not alleviated. Individuals with carpal tunnel syndrome are unable to oppose the thumb (Fig. B6.29E) and have difficulty buttoning a shirt or blouse as well as gripping things such as a comb. As the condition progresses, sensory changes radiate into the forearm and axilla. Symptoms of compression can be reproduced by compression of the median nerve with your finger at the wrist for approximately 30 s. To relieve both the compression and the resulting symptoms, partial or complete surgical division of the flexor retinaculum, a procedure called carpal tunnel release, may be necessary. The incision for carpal tunnel release is made toward the medial side of the wrist and flexor retinaculum to avoid possible injury to the recurrent branch of the median nerve.


Figure B6.29


Figure 6.55. Structures in distal forearm (wrist region). A. A distal skin incision was made along the transverse wrist crease, crossing the pisiform bone. The skin and fasciae are removed proximally, revealing the tendons and neurovascular structures. A circular incision and removal of the skin and thenar fascia reveals the recurrent branch of the median nerve to the thenar muscles, vulnerable to injury when this area is lacerated because of its subcutaneous location. B. This transverse section of the distal forearm demonstrates the long flexor and extensor tendons and neurovascular structures en route from forearm to hand. The ulnar nerve and artery are under cover of the flexor carpi ulnaris; therefore, the pulse of the artery cannot be easily detected here. C. Orientation drawing indicating the plane of the section shown in part B.


Table 6.13. Nerves of the Hand

Nerve Median nerve

Recurrent (thenar) branch of median nerve Lateral branch of median nerve Medial branch of median nerve Palmar cutaneous branch of median nerve

Origin a Arises by two roots, one from lateral cord of brachial plexus (C6, C7 fibers) and one from medial cord (C8, T1 fibers)

Course Becomes superficial proximal to wrist; passes deep to flexor retinaculum (transverse carpal ligament) as it passes through carpal tunnel to hand

Distribution Thenar muscles (except adductor pollicis and deep head of flexor pollicis brevis) and lateral lumbricals (for digits 2 and 3); provides sensation to skin of palmar and distal dorsal aspects of lateral (radial) 3Â½ digits and adjacent palm Arises from median Loops around distal border Abductor pollicis brevis; nerve as soon as it of flexor retinaculum; opponens pollicis; superficial has passed distal to enters thenar muscles head of flexor pollicis brevis flexor retinaculum Arises as lateral Runs laterally to palmar 1st lumbrical; skin of palmar division of median thumb and radial side of and distal dorsal aspects of nerve as it enters 2nd finger thumb and radial half of 2nd palm of hand finger Arises as medial Runs medially to adjacent 2nd lumbrical; skin of palmar division of median sides of 2nd—4th fingers and distal dorsal aspects of nerve as it enters adjacent sides of 2nd—4th palm of hand fingers Arisies from median P a s s e s b e t we e n t e n d o n s of Skin of central palm nerve just proximal p a l m a r i s l o n g u s a n d f l e x o r to flexor retinaculum c a r p i r a d i a l i s ; r u n s s u p e r f i c i a l t o f l e x o r re t i n a c u l u m


Ulnar nerve

Terminal branch of medial cord of brachial plexus (C8 and T1 fibers; often also receives C7 fibers)

Palmar cutaneous branch of ulnar nerve Dorsal branch of ulnar nerve

Arises from ulnar nerve near middle of forearm Arises from ulnar nerve about 5 cm proximal to flexor retinaculum

Superficial Arises from ulnar branch of nerve at wrist as ulnar nerve they pass between pisiform and hamate bones Deep branch of ulnar nerve

Radial nerve Arises from radial Superficial nerve in cubital fossa branch

Becomes superficial in distal forearm, passing superficial to flexor retinaculum (transverse carpal ligament) to enter hand

The majority of intrinsic muscles of hand (hypothenar, interosseous, adductor pollicis, and deep head of flexor pollicis brevis, plus the medial lumbricals [for digits 4and 5]); provides sensation to skin of palmar and distal dorsal aspects of medial (ulnar) 1Â½ digits and adjacent palm Descends on ulnar artery Skin at base of medial palm, and perforates deep fascia overlying the medial carpals in the distal third of forearm Passes distally deep to Skin of medial aspect of dorsum flexor carpi ulnaris, then of hand and proximal portions dorsally to perforate deep of little and medial half of ring fascia and course along finger (occasionally also medial side of dorsum of adjacent sides of proximal hand, dividing into 2 to 3 portions of ring and middle dorsal digital nerves fingers) Passes palmaris brevis and Palmaris brevis and sensation to divides into two common skin of the palmar and distal palmar digital nerves dorsal aspects of digit 5 and of the medial (ulnar) side of digit 4 and proximal portion of palm Passes between muscles of Hypothenar muscles (abductor, hypothenar eminence to flexor, and opponens digiti pass deeply across palm minimi), lumbricals of digits 4 with deep palmar (arterial) and 5, all interossei, adductor arch pollicis, and deep head of flexor pollicis brevis Courses deep to Skin of the lateral (radial half of brachioradialis, emerging dorsal aspect of the hand and from beneath it to pierce thumb, the proximal portions of the deep fascia lateral to the dorsal aspects of digits 2 distal radius and 3, and of the lateral (radial) half of digit 4

Trauma to the Median Nerve Laceration of the wrist often causes median nerve injury because this nerve is relatively close to the surface. In attempted suicides by wrist slashing, the median nerve is commonly injured just proximal to the flexor retinaculum. This results in paralysis of the thenar muscles and the first two lumbricals. Hence, opposition of the thumb is not possible and fine control movements of the 2nd and 3rd digits are impaired. Sensation is also lost over the thumb and adjacent two and a half fingers. Most nerve injuries in the upper limb affect opposition of the thumb. Undoubtedly, injuries to the nerves supplying the intrinsic muscles of the hand, especially the median nerve, have the most severe effects on this complex movement. If the median nerve is severed in the forearm or at the wrist, the thumb cannot be opposed;


however, the APL and adductor pollicis (supplied by the posterior interosseous and ulnar nerves, respectively) may imitate opposition. Median nerve injury resulting from a perforating wound in the elbow region results in loss of flexion of the proximal and distal interphalangeal joints of the 2nd and 3rd digits. The ability to flex the metacarpophalangeal joints of these fingers is also affected because digital branches of the median nerve supply the 1st and 2nd lumbricals. Ape hand (Fig. B6.29F) refers to a deformity in which thumb movements are limited to flexion and extension of the thumb in the plane of the palm. This condition is caused by the inability to oppose and by limited abduction of the thumb. The recurrent branch of the median nerve to the thenar muscles (Fig. 6.55A) lies subcutaneously and may be severed by relatively minor lacerations of the thenar eminence. Severance of this nerve paralyzes the thenar muscles and the thumb loses much of its usefulness.

The Ulnar Nerve in the Hand The ulnar nerve leaves the forearm by emerging from deep to the tendon of the FCU (Figs. 6.52 and 6.55). It continues distally to the wrist via the ulnar canal (Fig. 6.48). Here the ulnar nerve is bound by fascia to the anterior surface of the flexor retinaculum as it passes between the pisiform (medially) and the ulnar artery (laterally). Just proximal to the wrist, the ulnar nerve gives off a palmar cutaneous branch that passes superficial to the flexor retinaculum and palmar aponeurosis and supplies skin on the medial side of the palm (Table 6.13). The dorsal cutaneous branch of the ulnar nerve supplies the medial half of the dorsum of the hand, the 5th finger, and the medial half of the 4th finger (Fig. 6.55B). The ulnar nerve ends at the distal border of the flexor retinaculum by dividing into superficial and deep branches (Fig. 6.52B). The superficial branch of the ulnar nerve supplies cutaneous branches to the anterior surfaces of the medial one and a half fingers. The deep branch of the ulnar nerve supplies the hypothenar muscles, the medial two lumbricals, the adductor pollicis, the deep head of the FPB, and all the interossei. The deep branch also supplies several joints (wrist, intercarpal, carpometacarpal, and intermetacarpal). The ulnar nerve is often referred to as the nerve of fine movements because it innervates most of the intrinsic muscles that are concerned with intricate hand movements (Table 6.13).

Ulnar Canal Syndrome (Guyon Tunnel Syndrome) Compression of the ulnar nerve may occur at the wrist where it passes between the pisiform and the hook of the hamate. The depression between these bones is converted by the pisohamate ligament into an osseofibrous tunnel, the ulnar canal (Guyon tunnel; Fig. 6.47B). Ulnar canal syndrome is manifest by hypoesthesia in the medial one and a half fingers and weakness of the intrinsic muscles of the hand. “Clawing” of the 4th and 5th fingers (hyperextension at the metacarpophalangeal joint with flexion at the proximal interphalangeal joint) may occur, but—in contradistinction to proximal ulnar nerve injury—their ability to flex is unaffected and there is no radial deviation of the hand.

Handlebar Neuropathy People who ride long distances on bicycles with their hands in an extended position against the hand grips put pressure on the hooks of their hamates, which compresses


their ulnar nerves. This type of nerve compression, which has been called handlebar neuropathy, results in sensory loss on the medial side of the hand and weakness of the intrinsic hand muscles.

Radial Nerve in the Hand The radial nerve supplies no hand muscles (Table 6.13). The superficial branch of the radial nerve is entirely sensory (Fig. 6.55A). It pierces the deep fascia near the dorsum of the wrist to supply the skin and fascia over the lateral two thirds of the dorsum of the hand, the dorsum of the thumb, and proximal parts of the lateral one and a half digits (Table 6.10).

Radial Nerve Injury and the Hand Although the radial nerve supplies no muscles in the hand, radial nerve injury in the arm can produce serious hand disability. The characteristic handicap is inability to extend the wrist resulting from paralysis of extensor muscles of the forearm, all of which are innervated by the radial nerve (Fig. 6.40B; Table 6.8). The hand is flexed at the wrist and lies flaccid, a condition known as wrist‐drop (see clinical correlation [blue] box “Injury to the Radial Nerve in the Arm,” earlier in this chapter). The fingers of the relaxed hand also remain in the flexed position at the metacarpophalangeal joints. The interphalangeal joints can be extended weakly through the action of the intact lumbricals and interossei, which are supplied by the median and ulnar nerves (Table 6.11). The radial nerve has only a small area of exclusive cutaneous supply onthe hand. Thus the extent of anesthesia is minimal, even in serious radial nerve injuries, and is usually confined to a small area on the lateral part of the dorsum of the hand.

The Bottom Line The vasculature of the hand is characterized by multiple anastomoses between both radial and ulnar vessels and palmar and dorsal vessels. The arteries of the hand collectively constitute a periarticular arterial anastomosis around the collective joints of the wrist and hand. Thus blood is generally available to all parts of the hand in all positions as well as while performing functions (gripping or pressing) that might otherwise compromise especially the palmar structures. The arteries to the digits are also characterized by their ability to vasoconstrict during exposure to cold to conserve heat and to dilate (while the hand becomes sweaty) to radiate excess heat. Unlike the dermatomes of the trunk and proximal limbs, the zones of cutaneous innervation and the roles of motor innervation are well defined, as are functional deficits. In terms of intrinsic structure, the radial nerve is only sensory via its superficial branch to the dorsum of the hand. The median nerve is most important to the function of the thumb and sensation from the lateral three and half digits and adjacent palm, whereas the ulnar nerve supplies the remainder. The intrinsic muscles of the hand constitute the T1 myotome. The palmar nerves and vessels are dominant, supplying not only the more sensitive and functional palmar aspect but also the dorsal aspect of the distal part of the digits (nail beds). The superficial dorsal venous network is commonly used for administering intravenous fluids.


Surface Anatomy of the Hand The radial artery pulse, like other palpable pulses, is a peripheral reflection of cardiac action. The radial pulse rate is measured where the radial artery lies on the anterior surface of the distal end of the radius, lateral to the FCR tendon, which serves as a guide to the artery (Fig. SA6.15). Here the artery can be felt pulsating between the tendons of the FCR and the APL and where it can be compressed against the radius. The tendons of FCR and palmaris longus can be palpated anterior to the wrist, a little lateral to its middle, and are usually observed by flexing the closed fist against resistance. The palmaris longus tendon is smaller than the FCR tendon and is not always present. The palmaris longus tendon serves as a guide to the median nerve, which lies deep to it (Fig. 6.55B). The FCU tendon can be palpated as it crosses the anterior aspect of the wrist near the medial side and inserts into the pisiform. The FCU tendon serves as a guide to the ulnar nerve and artery. The tendons of the FDS can be palpated as the fingers are alternately flexed and extended. The ulnar pulse is often difficult to palpate. The tendons of the APL and EPB indicate the anterior boundary of the anatomical snuff box (Fig. SA6.16). The tendon of the EPL indicates the posterior boundary of the box. The radial artery crosses the floor of the snuff box, where its pulsations may be felt. The scaphoid and, less distinctly, the trapezium are palpable in the floor of the snuff box. The skin covering the dorsum of the hand is thin and loose when the hand is relaxed. Prove this by pinching and pulling folds of your skin here. The looseness of the skin results from the mobility of the subcutaneous tissue and from the relatively few fibrous skin ligaments that are present. Hair is present in this region and on the proximal parts of the digits, especially in men. If the dorsum of the hand is examined with the wrist extended against resistance and the digits abducted, the tendons of the extensor digitorum to the fingers stand out, particularly in thin individuals. These tendons are not visible far beyond the knuckles because they flatten here to form the extensor expansions of the fingers (Fig. 6.42B). The knuckles that become visible when a fist is made are produced by the heads of the metacarpals. Under the loose subcutaneous tissue and extensor tendons on the dorsum of the hand, the metacarpals can be palpated. A prominent feature of the dorsum of the hand is the dorsal venous network (Fig. 6.12A).

Figure SA6.15


Figure SA6.16

The skin on the palm is thick because it must withstand the wear and tear of work and play (Fig. SA6.17). It is richly supplied with sweat glands but contains no hair or sebaceous glands. The superficial palmar arch lies across the center of the palm, level with the distal border of the fully extended thumb. The main part of the arch ends at the thenar eminence. The deep palmar arch lies approximately 1 cm proximal to the superficial palmar arch. The palmar skin presents several more or less constant flexion creases, where the skin is firmly bound to the deep fascia, that help locate palmar wounds and underlying structures:  



Wrist creases, proximal, middle, distal: The distal wrist crease indicates the proximal border of the flexor retinaculum. Palmar creases, transverse, longitudinal: The longitudinal creases deepen when the thumb is opposed; the transverse creases deepen when the metacarpophalangeal joints are flexed. o Radial longitudinal crease (the “life line” of palmistry): partially encircles the thenar eminence, formed by the short muscles of the thumb. o Proximal (transverse) palmar crease: commences on the lateral border of the palm, superficial to the head of the 2nd metacarpal; extends medially and slightly proximally across the palm, superficial to the bodies of the 3rd—5th metacarpals. Distal (transverse) palmar crease: begins at or near the cleft between the index and the middle fingers; crosses the palm with a slight convexity, superficial to the head of the 3rd metacarpal and then proximal to the heads of the 4th and 5th metacarpals.


Each of the medial four fingers usually has three transverse digital flexion creases:   

Proximal digital crease: located at the root of the finger, approximately 2 cm distal to the metacarpophalangeal joint. Middle digital crease: lies over the proximal interphalangeal joint. Distal digital crease: lies over or just proximal to the distal interphalangeal joint.

The thumb, having two phalanges, has only two flexion creases. The proximal digital crease of the thumb crosses obliquely, at or proximal to the 1st metacarpophalangeal joint. The skin ridges on the pads of the digits, forming the fingerprints, are used for identification because of their unique patterns. The physiological function of the skin ridges is to reduce slippage when grasping objects.

Figure SA6.17

Dermatoglyphics The science of studying ridge patterns of the palm, called dermatoglyphics, is a valuable extension of the conventional physical examination of people with certain congenital anomalies and genetic diseases (Nussbaum et al., 2004). For example, people with trisomy 21 (Down syndrome) have dermatoglyphics that are highly characteristic. In addition, they often have a single transverse palmar crease (simian crease); however, approximately 1% of the general population has this crease with no other clinical features of the syndrome.

Palmar Wounds and Surgical Incisions The location of superficial and deep palmar arches should be kept in mind when examining wounds of the palm and when making palmar incisions. Furthermore, it is important to know that the superficial palmar arch is at the same level as the distal


extremity of the common flexor sheath (Figs. 6.52 and 6.54). As mentioned previously, incisions or wounds along the medial surface of the thenar eminence may injure the recurrent branch of the median nerve to the thenar muscles (see clinical correlation [blue] box “Trauma to the Median Nerve,” earlier in this chapter).

Joints of the Upper Limb Movement of the pectoral girdle involves the sternoclavicular, acromioclavicular, and glenohumeral joints (Fig. 6.56), usually all moving simultaneously. Functional defects in any of the joints impair movements of the pectoral girdle. Mobility of the scapula is essential for free movement of the upper limb. The clavicle forms a strut that holds the scapula, and hence the glenohumeral joint, away from the thorax so it can move freely. The clavicle establishes the radius at which the shoulder (half of the pectoral girdle and glenohumeral joint) rotates at the SC joint. The 15—20° of movement at the AC joint permits positioning of the glenoid cavity that is necessary for arm movements. When testing the range of motion of the pectoral girdle, both scapulothoracic (movement of the scapula on the thoracic wall) and glenohumeral movements must be considered. Although the initial 30° of abduction may occur without scapular motion, in the overall movement of fully elevating the arm, the movement occurs in a 2:1 ratio: For every 3° of elevation, approximately 2° occurs at the glenohumeral joint and 1° at the physiological scapulothoracic joint. In other words, when the upper limb has been elevated so that the arm is vertical at the side of the head (180° of arm abduction or flexion), 120° occurred at the glenohumeral joint and 60° occurred at the scapulothoracic joint. This is known as scapulohumeral rhythm. The important movements of the pectoral girdle are scapular movements (Table 6.3): elevation and depression, protraction (lateral or forward movement of the scapula) and retraction (medial or backward movement of the scapula), and rotation of the scapula.

Sternoclavicular Joint The sternoclavicular joint is a saddle type of synovial joint but functions as a ball‐ and‐socket joint. The SC joint is divided into two compartments by an articular disc. The disc is firmly attached to the anterior and posterior sternoclavicular ligaments, thickenings of the fibrous layer of the joint capsule, as well as the interclavicular ligament. The great strength of the SC joint is a consequence of these attachments. Thus, although the articular disc serves as a shock absorber of forces transmitted along the clavicle from the upper limb, dislocation of the clavicle is rare, whereas fracture of the clavicle is common. The SC joint is the only articulation between the upper limb and the axial skeleton, and it can be readily palpated because the sternal end of the clavicle lies superior to the manubrium of the sternum.

Articulation of the Sternoclavicular Joint The sternal end of the clavicle articulates with the manubrium and the 1st costal cartilage. The articular surfaces are covered with fibrocartilage.


Joint Capsule of the Sternoclavicular Joint The joint capsule surrounds the SC joint, including the epiphysis at the sternal end of the clavicle. It is attached to the margins of the articular surfaces, including the periphery of the articular disc. A synovial membrane lines the internal surface of the fibrous layer of the joint capsule, extending to the edges of the articular surfaces.

Ligaments of the Sternoclavicular Joint The strength of the SC joint depends on ligaments and its articular disc. Anterior and posterior sternoclavicular ligaments reinforce the joint capsule anteriorly and posteriorly. The interclavicular ligament strengthens the capsule superiorly. It extends from the sternal end of one clavicle to the sternal end of the other clavicle. In between, it is also attached to the superior border of the manubrium. The costoclavicular ligament anchors the inferior surface of the sternal end of the clavicle to the 1st rib and its costal cartilage, limiting elevation of the pectoral girdle.

Movements of the Sternoclavicular Joint Although the SC joint is extremely strong, it is significantly mobile to allow movements of the pectoral girdle and upper limb (Figs. 6.57 and 6.58C). During full elevation of the limb, the clavicle is raised to approximately a 60° angle.

Figure 6.56. Pectoral girdle and associated tendons and ligaments. The pectoral (shoulder) girdle is a partial bony ring (incomplete posteriorly) formed by the manubrium of the sternum, the clavicle, and the scapulae. Joints associated with these bones are the sternoclavicular, acromioclavicular, and glenohumeral (shoulder). The girdle provides for attachment of the superior appendicular skeleton to the axial skeleton and provides the mobile base from which the upper limb operates.


Figure 6.57. Movements of upper limb at joints of pectoral girdle. A. Range of motion of lateral end of clavicle permitted by movements at the sternoclavicular joint. Aâ†”C = protraction/retraction; Aâ†”D = elevation/depression. B—E. Circumduction of upper limb requires coordinated movements of the pectoral girdle and glenohumeral joint. B. Beginning with extended limb, retracted girdle; C. Neutral position. D. Flexed limb, protracted girdle; E. Elevated limb and girdle.

P.850


Figure 6.58. Acromioclavicular and sternoclavicular joints. A. This view of the right AC joint shows the joint capsule and partial disc (inset). B. The function of the coracoclavicular ligament is demonstrated. As long as this ligament is intact with the clavicle tethered to the coronoid process, the acromion cannot be driven inferior to the clavicle. The ligament, however, does permit protraction and retraction of the acromion. C. Clavicular movements at the SC and AC joints permit protraction and retraction of the scapula on the thoracic wall (red and green lines) and winging of the scapula (blue line). Movements of a similar scale occur during elevation, depression, and rotation of the scapula. The latter movements are shown in Table 6.3, which also indicate the muscles specifically responsible for these movements.

When elevation is achieved via flexion, it is accompanied by rotation of the clavicle around its longitudinal axis. The SC joint can also be moved anteriorly or posteriorly over a range of up to 25—30°. Although not a typical movement, except perhaps during calisthenics, it is capable of performing these movements sequentially, moving the acromial end along a circular path—a form of circumduction.


Blood Supply of the Sternoclavicular Joint The SC joint is supplied by internal thoracic and suprascapular arteries (Table 6.4).

Nerve Supply of the Sternoclavicular Joint Branches of the medial supraclavicular nerve and the nerve to the subclavius supply the SC joint (Table 6.5).

Dislocation of the Sternoclavicular Joint The rarity of dislocation of the SC joint attests to its strength, which depends on its ligaments, its disc, and the way forces are generally transmitted along the clavicle. When a blow is received to the acromion of the scapula, or when a force is transmitted to the pectoral girdle during a fall on the outstretched hand, the force of the blow is usually transmitted along the length of the clavicle, i.e., along its long axis. The clavicle may fracture near the junction of its middle and lateral thirds, but it is rare for the SC joint to dislocate. Most dislocations of the SC joint in persons 50 years of age, is discussed in the clinical correlation (blue) box “Fractures of the Radius and Ulna,” earlier in this chapter. Fracture of the scaphoid, relatively common in young adults, is discussed in the clinical correlation (blue) box “Fracture of the Scaphoid,” earlier in this chapter. Anterior dislocation of the lunate is an uncommon but serious injury that usually results from a fall on the dorsiflexed wrist (Fig. B6.37A). The lunate is pushed out of its place in the floor of the carpal tunnel toward the palmar surface of the wrist. The displaced lunate may compress the median nerve and lead to carpal tunnel syndrome


(discussed earlier in this chapter). Because of its poor blood supply, avascular necrosis of the lunate may occur. In some cases, excision of the lunate may be required. In degenerative joint disease of the wrist, surgical fusion of carpals (arthrodesis) may be necessary to relieve the severe pain. Figure B6.37. Wrist fractures. A. Dislocation of lunate is shown. B. This radiograph of a young person shows a normal epiphyseal plate (arrow). E, distal radial epiphysis (R); U, ulna. C. A fracture‐separation of the distal radial epiphysis is shown.

Fracture—separation of the distal radial epiphysis is common in children because of frequent falls in which forces are transmitted from the hand to the radius (Fig. B6.37B & C). In a lateral radiograph of a child's wrist, dorsal displacement of the distal radial epiphysis is obvious (Fig. B6.37C). A small fracture of the shaft of the radius is also visible (not obvious). When the epiphysis is placed in its normal position during reduction, the prognosis for normal bone growth is good.

Intercarpal Joints The intercarpal (IC) joints, interconnecting the carpal bones, are plane synovial joints (Fig. 6.71), which may be summarized as:    

Joints between the carpal bones of the proximal row. Joints between the carpal bones of the distal row. The midcarpal joint, a complex joint between the proximal and distal rows of carpal bones. The pisotriquetral joint, formed from the articulation of the pisiform with the palmar surface of the triquetrum.


Joint Capsule of the Intercarpal Joints A continuous, common articular cavity is formed by the IC and carpometacarpal joints, with the exception of the carpometacarpal joint of the thumb, which is independent. The wrist joint is also independent. The continuity of the articular cavities, or the lack of it, is significant in relation to the spread of infection and to arthroscopy, in which a flexible fiberoptic scope is inserted into the articular cavity to view its internal surfaces and features. The fibrous layer of the joint capsule surrounds these joints, which helps unite the carpals. The synovial membrane lines the fibrous layer and is attached to the margins of the articular surfaces of the carpals.

Ligaments of the Intercarpal Joints The carpals are united by anterior, posterior, and interosseous ligaments (Figs. 6.72 and 6.74A).

Movements at the Intercarpal Joints The gliding movements possible between the carpals occur concomitantly with movements at the wrist (radiocarpal) joint, augmenting them and increasing the overall range of movement. Flexion and extension of the hand are actually initiated at the midcarpal joint, between the proximal and the distal rows of carpals (Figs. 6.71B and 6.73). Investigators disagree regarding the amount of movement occurring at the wrist vs. the midcarpal joints. Most state that flexion and adduction occur mainly at the wrist joint whereas extension and abduction occur primarily at the midcarpal joint. Movements at the other IC joints are small, with the proximal row being more mobile than the distal row.

Blood Supply of the Intercarpal Joints The arteries supplying the IC joints are derived from the dorsal and palmar carpal arches.

Innervation of the Intercarpal Joints The IC joints are supplied by the anterior interosseous branch of the median nerve and the dorsal and deep branches of the ulnar nerve.


Figure 6.74. Joints of hand. A. This dissection of the hand shows the palmar ligaments of the radioulnar, radiocarpal, intercarpal, carpometacarpal, and interphalangeal joints. B. A dissection showing the metacarpophalangeal and interphalangeal joints. The palmar ligaments (plates) are modifications of the anterior aspect of the MP and IP joint capsules. C. The flexed index finger demonstrates its phalanges and the position of the MP and IP joints. The knuckles are formed by the heads of the bones, with the joint plane lying distally.

Carpometacarpal and Intermetacarpal Joints The carpometacarpal (CMC) and intermetacarpal (IM) joints are the plane type of synovial joint, except for the CMC joint of the thumb, which is a saddle joint (Fig. 6.71).

Articulations of the Carpometacarpal and Intermetacarpal Joints The distal surfaces of the carpals of the distal row articulate with the carpal surfaces of the bases of the metacarpals at the CMC joints. The important CMC joint of the thumb is between the trapezium and the base of the 1st metacarpal and has a separate articular cavity. Like the carpals, adjacent metacarpals articulate with each other; IM joints occur between the radial and the ulnar aspects of the bases of the metacarpals.


Joint Capsule of the Carpometacarpal and Intermetacarpal Joints The medial four CMC joints and three IM joints are enclosed by a common joint capsule on the palmar and dorsal surfaces. A common synovial membrane lines the internal surface of the fibrous layer of the joint capsule, surrounding a common articular cavity. The fibrous layer of the CMC joint of the thumb surrounds the joint and is attached to the margins of the articular surfaces. The synovial membrane lines the internal surface of the fibrous layer. The looseness of the capsule facilitates free movement of the joint.

Ligaments of the Carpometacarpal and Intermetacarpal Joints The bones are united in the region of the joints by palmar and dorsal CMC and IM ligaments (Fig. 6.74A) and by interosseous IM ligaments (Fig. 6.71B). In addition, the superficial and deep transverse metacarpal ligaments (the former part of the palmar aponeurosis), associated with the distal ends of the metacarpals, play a role in limiting movement at the CMC and IM joints as they limit separation of the metacarpal heads.

Movements at the Carpometacarpal and Intermetacarpal Joints The CMC joint of the thumb permits angular movements in any plane (flexion— extension, abduction—adduction, or circumduction) and a restricted amount of axial rotation. Most important, the movement essential to opposition of the thumb occurs here. Although the opponens pollicis is the prime mover, all of the hypothenar muscles contribute to opposition. Almost no movement occurs at the CMC joints of the 2nd and 3rd fingers, that of the 4th finger is slightly mobile, and that of the 5th finger is moderately mobile, flexing and rotating slightly during a tight grasp (Fig. 6.48G & H). When the palm of the hand is “cupped,” (as during pad‐to‐pad opposition of thumb and little finger), two thirds of the movement occur at the CMC joint of the thumb, and one third occurs at the CMC and IC joints of the 4th and 5th fingers.

Blood Supply of the Carpometacarpal and Intermetacarpal Joints The CMC and IM joints are supplied by periarticular arterial anastomoses of the wrist and hand (dorsal and palmar carpal arches, deep palmar arch, and metacarpal arteries) (Fig. 6.79).

Innervation of the Carpometacarpal and Intermetacarpal Joints The CMC and IM joints are supplied by the anterior interosseous branch of the median nerve, posterior interosseous branch of the radial nerve, and dorsal and deep branches of the ulnar nerve.

Metacarpophalangeal and Interphalangeal Joints The metacarpophalangeal joints are the condyloid type of synovial joint that permit movement in two planes: flexion—extension and adduction—abduction. The interphalangeal joints are the hinge type of synovial joint and permit flexion— extension only (Fig. 6.74B).


Articulations of the Metacarpophalangeal and Interphalangeal Joints The heads of the metacarpals articulate with the bases of the proximal phalanges in the MP joints, and the heads of the phalanges articulate with the bases of more distally located phalanges in the IP joints.

Joint Capsule of the Metacarpophalangeal and Interphalangeal Joints A joint capsule encloses each MC and IP joint with a synovial membrane lining a fibrous layer that is attached to the margins of each joint.

Ligaments of the Metacarpophalangeal and Interphalangeal Joints The fibrous layer of each MC and IP joint capsule is strengthened by two (medial and lateral) collateral ligaments. These ligaments have two parts: (1) denser cord‐like parts that pass distally from the heads of the metacarpals and phalanges to the bases of the phalanges (Fig. 6.74A & B), and (2) thinner fan‐like parts that pass anteriorly to attach to thick, densely fibrous or fibrocartilaginous plates, the palmar ligaments (plates), which form the palmar aspect of the joint capsule. The fan‐like parts of the collateral ligaments cause the palmar ligaments to move like a visor over the underlying metacarpal or phalangeal heads. The strong cord‐like parts of the collateral ligaments of the MP joint, being eccentrically attached to the metacarpal heads are slack during extension and taut during flexion. As a result, the fingers cannot usually be spread (abducted) when the MP joints are fully flexed. The interphalangeal joints have corresponding ligaments but the distal ends of the proximal and middle phalanges, being flattened anteroposteriorly and having two small condyles, permit neither adduction or abduction. The palmar ligaments blend with the fibrous digital sheaths and provide a smooth, longitudinal groove that allows the long flexor ligaments to glide and remain centrally placed as they cross the convexities of the joints. The palmar ligaments of the 2nd—5th MP joints are united by deep transverse metacarpal ligaments that hold the heads of the metacarpals together. In addition, the dorsal hood of each extensor apparatus attaches anteriorly to the sides of the palmar plates of the MP joints.

Movements of the Metacarpophalangeal and Interphalangeal Joints Flexion—extension, abduction—adduction, and circumduction of the 2nd—5th digits occur at the 2nd—5th MP joints. Movement at the MP joint of the thumb is limited to flexion—extension. Only flexion and extension occur at the IP joints.

Blood Supply of the Metacarpal and Interphalangeal Joints Deep digital arteries that arise from the superficial palmar arches supply the MC and IP joints (Fig. 6.79).

Innervation of the Metacarpal and Interphalangeal Joints Digital nerves arising from the ulnar and median nerves supply the MC and IP joints.

The Bottom Line Motion at the wrist moves the entire hand, making a dynamic contribution to a skill or movement, or allowing it to be stabilized in a particular position to maximize the effectiveness of the hand and fingers in manipulating and holding objects. Complexity


as well as flexibility of the wrist results from the number of bones involved. Extension—flexion, abduction—adduction, and circumduction occur. Overall, most wrist movement occurs at the wrist (radiocarpal) joint between the radius and articular disc of the distal radioulnar joint and the proximal row of carpal bones (primarily the scaphoid and lunate). However, concomitant movement at the IC joints (especially the midcarpal IC joint) augments these movements. The CMC joints of the four medial fingers, which share a common articular cavity, have limited motion (especially those of the 2nd and 3rd digits), contributing to the stability of the palm as a base from and against which the fingers operate. Motion occurs at the CMC joints for the 3rd and 4th digits, mostly in association with a tight grip or cupping of the palm, as during opposition. However, the great mobility of the CMC joint of the thumb, a saddle joint, provides the digit with the major portion of its range of motion and specifically enables opposition. Therefore it is key to the effectiveness of the human hand. In contrast to the CMC joints, the MP joints of the medial four fingers offer considerable freedom of movement (flexion—extension and abduction— adduction), whereas that of the thumb is limited to flexion—extension, as are all IP joints.

Bull Rider's Thumb Bull rider's thumb refers to a sprain of the radial collateral ligament and an avulsion fracture of the lateral part of the proximal phalanx of the thumb. This injury is common in individuals who ride mechanical bulls.

Skier's Thumb Skier's thumb (historically, game‐keeper's thumb) refers to the rupture or chronic laxity of the collateral ligament of the 1st MP joint (Fig. B6.38). The injury results from hyperabduction of the MP joint of the thumb, which occurs when the thumb is held by the ski pole while the rest of the hand hits the ground or enters the snow. In severe injuries, the head of the metacarpal has an avulsion fracture.

Figure B6.38


Medical Imaging of the Upper Limb Radiography Radiographs are often taken when an injury produces bone tenderness, angulation, rotation, or instability. Anteroposterior (AP), lateral, axial, and oblique views are usually sufficient to detect bony and other injuries. Radiological examinations of the upper limb focus mainly on bony structures, because muscles, tendons, and nerves are not well visualized. When examining radiographs of the upper limb, it is essential to know the median times of appearance of postnatal ossification centers and when fusion of epiphyses is radiographically complete in males and females. Without such knowledge, an epiphysial line could be mistaken for a fracture.

Pectoral Girdle and Joints The usual radiograph is an AP view with the humerus laterally rotated so that its epicondyles are parallel with the X‐ray film cassette (Figs. 6.77A and 6.76A). Because some obliquity of the glenoid cavity occurs normally, it appears oval in shape. In this view, the lateral two thirds of the clavicle is visible. The articulation of the acromial end of the clavicle with the acromion of the scapula at the AC joint is apparent. This is a frequent site of subluxation of the joint. The surgical neck of the humerus, approximately 2.5 cm distal to the greater and lesser tubercles, is a common site of fracture. The axillary nerve is in contact with the surgical neck and vulnerable to injury. Examination of the humerus reveals dense cortical bone along the shaft, which thins out proximally and becomes extremely thin over the head of the bone. The radial nerve runs inferolaterally in the radial groove on the posterior surface of the humerus and is vulnerable to injury in a midhumeral fracture. An axial projection of the shoulder provides an essential additional view of the AC and glenohumeral joints. To obtain an axial projection, the person is asked to abduct the arm and extend the shoulder over the X‐ray film cassette. In Figure 6.75B, the acromion, glenoid cavity, humeral head, coracoid process, and suprascapular notch are visible.

Elbow Joint In an AP projection, the extended elbow is placed on the X‐ray film cassette with the forearm supinated. The X‐ray beam is directed perpendicular to the cassette and at the elbow joint. Figure 6.76A shows the distal end of the humerus as it flares out and ends as the prominent medial epicondyle and the more flattened lateral epicondyle. The ulnar nerve is in contact with the medial epicondyle and may be injured when it is fractured or its epiphysis is dislocated. Distal to the epicondyles are the convex capitulum and pulley‐shaped trochlea. Between the epicondyles is a radiolucent area representing the superimposed olecranon and coronoid fossae. The disc‐shaped radial head and its concave articular surface, distal to the capitulum, is apparent. Fractures of the radial head are relatively common in young adults after a fall on the hand. The radial notch in the ulna is overlapped by the medial aspect of the radial head where they are in contact, forming the proximal radioulnar joint. The olecranon of the ulna is superimposed on the distal end of the humerus where it lies in the olecranon fossa. Just distal to the trochlea of the humerus is the coronoid process of the ulna.


In a lateral projection of the elbow (Fig. 6.76B), the elbow is flexed 90°, and the arm and forearm are placed on the X‐ray film cassette with the thumb extended. In this projection, the epicondyles, capitulum, and trochlea are superimposed. The superimposed supraepicondylar ridges form a dense radiopaque shadow. The coronoid process of the ulna is partly obscured by the radial head.

Forearm To obtain the AP view shown in Figure 6.77A, the forearm is positioned so that it is supinated and the elbow joint is fully extended. Note that both the elbow and wrist joints are shown. Observe the translucent area between the capitulum and the radial head and between the trochlea and the coronoid process. This area is where the articular cartilages of the articulating bones are located. The radius and ulna bow (are outwardly convex) as they extend distally from the elbow. The bones become increasingly separated from each other in their distal two thirds, coming into contact more abruptly distally. The interosseous membrane is radiolucent (invisible to radiographic study). To detect fractures and verify their correct reduction (restoration to the normal position), keep in mind that the radial styloid process normally ends 1 cm distal to the ulnar styloid process. In Figure 6.77B, the way in which the radius crosses the ulna during forearm pronation is demonstrated.

Wrist and Hand Radiographs of the wrist and hand are commonly used to assess skeletal age. For clinical studies, the radiographs are compared with a series of standards in a radiographic atlas of skeletal development to determine the age of the child. Epiphysial fractures are more common in young children than in adolescents because tight fusion of the epiphyses with the bodies of the bones has not occurred. Fusion of the distal radial and ulnar epiphyses is complete radiographically at age 16 in females and at age 18 in males. The carpal bones are superimposed on each other; however, when compared with a skeleton of the wrist and hand, the bones can be identified. A lateral projection of the wrist and hand is of great importance because certain fractures may be revealed only in this projection (Fig. 6.78A). A fall on the outstretched hand may result in fracture of the scaphoid, generally across its narrow part. A radiologist looks for a scaphoid fracture if the physician reported tenderness over the scaphoid in the anatomical snuff box; however, it may not be detectable even in several oblique views until approximately 2 weeks after the injury (see clinical correlation [blue] box “Fracture of the Scaphoid.” earlier in this chapter). Each carpal usually ossifies from one center postnatally. The centers for the capitate and hamate appear first. Ossification centers are usually obvious during the 1st year; however, they may appear before birth. Accessory ossicles (small bones) are sometimes observed between the usual carpals; their possible occurrence should be kept in mind when examining radiographs of the carpus. Carpal fusions (e.g., between the lunate and the triquetrum) may occur and should be regarded as variations.


Figure 6.75. Radiographs of glenohumeral joint. A. The head of the humerus and the glenoid cavity overlap, obscuring the joint plane because the scapula does not lie in the coronal plane (therefore the glenoid cavity is oblique, not in a sagittal plane, which is especially evident in part B). (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada) B. The orientation drawing shows how the axial projection radiograph was taken.


Figure 6.76. Radiographs of elbow joint. A. The joint planes (occupied by radiolucent articular cartilage) are especially evident in the extended joint. B. The elbow is flexed to a 90° angle. The spherical nature of the capitulum, around which the superior surface of the radius glides, is especially evident. The head of the radius and the radial notch of the ulna overlap at the proximal radioulnar joint. (Courtesy of Dr. E. Becker, Associate Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.)


Figure 6.77. Radiographs of radioulnar joints. A. In the supinated position, the radius and ulna are parallel. B. During pronation, the inferior end of the radius moves anteriorly and medially around the inferior end of the ulna, carrying the hand with it; thus in the pronated position, the radius crosses the ulna anteriorly. 1—5, the metacarpals. (Courtesy of Dr. J. Heslin, Toronto, Ontario, Canada.)


Figure 6.78. Radiographs of right wrist and hand. A. This lateral view shows the adult hand. (Courtesy of Dr. E. L. Lansdown, Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.) B. The distal end of the forearm and the hand of a 2.5‐year‐old child are shown. Ossification centers of only four carpal bones are visible. Observe the distal radial epiphysis (R). C, capitate; H, hamate; L, lunate; Tq, triquetrum. C. The inferior end of the forearm and hand of an 11‐ year‐old child are shown. Ossification centers of all carpal bones are visible. The arrow indicates the pisiform lying on the anterior surface of the triquetrum. The distal epiphysis of the ulna (U) has ossified but all epiphyseal plates (lines) “remain open” (i.e., they are still unossified). S, scaphoid; Td, trapezoid; Tz, trapezium. (Courtesy of Dr. D. Armstrong, Associate Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.)

Except for the thumb, the metacarpals and phalanges of the fingers are superimposed, and little information can be obtained by examining them in this view (Fig. 6.78A). If a particular finger is injured and suspected of having a fracture, it is viewed laterally with the other fingers flexed. The shaft of each metacarpal begins to ossify during fetal life, and ossification centers appear postnatally in the heads of the four medial metacarpals and in the base of the 1st metacarpal (Fig. 6.78B). By age 11, ossification centers of all carpal bones are visible (Fig. 6.78C). Pseudoepiphyses (accessory centers) are occasionally seen in the head of the 1st metacarpal and in the base of the 2nd metacarpal.

Ultrasonography Ultrasonography is highly accurate for rotator cuff tears (Halpern, 2004). Doppler ultrasound is used to visualize blood flowing through the vessels of the limbs and to measure its velocity. Color Doppler ultrasound technology allows red and blue colors to be superimposed on the standard gray‐scale images.

Arteriography Arteriography (visualization of arteries) is used to detect vascular injuries, ischemia, and variations of arteries. Arteriograms are produced by injecting a dye into an artery as a radiograph is taken (Fig. 6.79). When interest is in a specific artery, the dye is injected directly into it, usually through a catheter. Arteriography may be used to determine the patency of arteries before and after surgical procedures in the upper limb to repair injuries resulting from trauma.

Computed Tomography CT scans of the upper limb are produced by X‐rays, but the anatomical images are created by computer reconstructions of the electronic data. The reconstructed images look like cross sections of the limb, and they can be reconstructed in the coronal and sagittal planes. Because the person must be in the CT scanner for only brief periods, fast (2‐s) scans can be produced; consequently, involuntary movement produces minimal distortion of the images. For example, arthrotomography enhanced by CT is able to demonstrate subtle fractures (e.g., of the rim of the glenoid cavity) and reactive bone changes around a recurrently dislocating glenohumeral joint (Halpern, 2004).


Figure 6.79. Angiogram of hand. The superficial palmar arch, formed primarily by the ulnar artery, is usually completed by the superficial palmar branch of the radial artery. In this teenage hand, the carpal bones are fully ossified, but the epiphyseal lines of the long bones (e.g., radius and ulna) are still open. Closure occurs when growth is complete, usually at the end of the teenage years. (Courtesy of Dr. D. Armstrong, University of Toronto, Toronto, Ontario, Canada)

Magnetic Resonance Imaging MRI produces images with good resolution of the various soft tissues of the limbs because adults can keep their limbs motionless for the 5—10 min required for scanning. This technique produces cross‐sectional, coronal, and sagittal images and has the advantage that it does not involve the use of X‐rays. Because MRI requires the person to remain still for several minutes, this technique is difficult to use with children. In Figure 6.80, observe the good resolution of the muscles, bones, and joints. MRI is helpful in the diagnosis of subluxation, dislocation, impingement of nerves, cartilage tears, and rotator cuff tears of the glenohumeral joint (Halpern, 2004). Coronal MRIs are helpful in demonstrating ruptured tendons in the shoulder, elbow, hand, and wrist regions.


Figure 6.80. MRI studies of upper limb. A. The glenohumeral and acromioclavicular joints are shown. The “white” (signal‐intense) parts of the identified bones are the fatty matrix of cancellous bone; the thin black outlines (absence of signal) of the bones are the compact bone that forms their outer surfaces. A, acromion; C, clavicle; G, glenoid cavity; Gr, greater tubercle of humerus; H, head of humerus; N, surgical neck of humerus. B. The elbow region is shown. C. The proximal part of the forearm is shown. The orientation drawing shows the plane of the MRI. The subcutaneous border of the ulna (U) and the radial artery demarcate the anteromedial flexor and posterolateral extensor compartments. R, radius. D. In this image of the wrist and hand, the bones, joints, and interosseous muscles can be observed. (Courtesy of Dr. W. Kucharczyk, Professor and Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Magnetic Resonance Centre, Toronto, Ontario, Canada.)


Footnotes 1

The scapulothoracic joint is a physiological “joint,” in which movement occurs between musculoskeletal structures (between the scapula and associated muscles and the thoracic wall), rather than an anatomical joint, in which movement occurs between directly articulating skeletal elements. The scapulothoracic joint is where the scapular movements of elevation—depression, protraction—retraction, and rotation occur. 2 It is awkward that the structure officially identified as the flexor retinaculum does not correspond in position and structure to the extensor retinaculum when there is another structure (the palmar carpal ligament, currently unrecognized by Terminologia Anatomica) that does. The clinical community has proposed and widely adopted the use of the more structurally based term transverse carpal ligament to replace the term flexor retinaculum. The authors urge FICAT to adopt this terminology in future editions of Terminologia Anatomica. 3 The preferred English‐equivalent terms listed by Terminologia Anatomica are used here. Official alternate TA terms replace of the arm with brachial, and of the forearm with antebrachial.


References and Suggested Readings Anderson MK, Hall SJ, Martin, M: Sports Injury Management, 2nd ed. Baltimore, Lippincott Williams & Wilkins, 2000. Bergman RA, Thompson SA, Afifi AK, Saadeh FA: Compendium of Human Anatomic Variation: Text, Atlas and World Literature. Baltimore, Urban & Schwarzenberg, 1988. Foerster O: The dermatomes in man. Brain 56:1, 1933. Ger R, Abrahams P, Olson T: Essentials of Clinical Anatomy, 3rd ed. New York, Parthenon, 1996. Halpern BC: Shoulder injuries. In Birrer RB, O'Connor FG (eds): Sports Medicine for the Primary Care Physician, 3rd ed. Boca Raton, FL, CRC Press, 2004. Hamill J, Knutzen KM: Biomechanical Basis of Human Movement, 2nd ed. Baltimore, Lippincott Williams & Wilkins, 2003. Keegan JJ, Garrett FD: The segmental distribution of the cutaneous nerves in the limbs of man. Anat Rec 102:409, 1948. Leonard LJ (Chair), Educational Affairs Committee, American Association of Clinical Anatomists: The clinical anatomy of several invasive procedures. Clin Anat 12:43, 1999. Moore KL, Persaud TVN: The Developing Human: Clinically Oriented Embryology, 7th ed. Philadelphia, Saunders, 2003. Nussbaum RL, McInnes RR, Willard HF: Thompson & Thompson Genetics in Medicine, 6th ed., Philadelphia, Saunders, 2004. Rowland LP (ed): Merritt's Textbook of Neurology, 10th ed. Baltimore: Lippincott Williams & Wilkins, 2000. Sabiston DC Jr, Lyerly HK: Sabiston Essentials of Surgery, 2nd ed. Philadelphia, Saunders, 1994. Salter RB: Textbook of Disorders and Injuries of the Musculoskeletal System, 3rd ed. Baltimore, Lippincott Williams & Wilkins, 1999. Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Fergusson MWJ (eds): Gray's Anatomy, 38th ed. Edinburgh, UK, Churchill Livingstone, 1995.


Chapter 7: Head Overview The head is the superior part of the body that is attached to the trunk by the neck. It is the control and communications center as well as the “loading dock” for the body. It houses the brain and therefore is the site of our consciousness: ideas, creativity, imagination, responses, decision making, and memory. It includes special sensory receivers (eyes, ears, mouth, and nose), broadcast devices for voice and expression, and portals for the intake of fuel (food), water, and oxygen and the exhaust of carbon dioxide. The head consists of the brain and its protective coverings, the ears, and the face. The face includes openings and passageways, with lubricating glands and valves (seals) to close some of them, the masticatory (chewing) devices, and the orbits that house the visual apparatus. The face also provides our identity as individuals. Disease, malformation, or trauma of structures in the head form the bases of many specialties, including dentistry, maxillofacial surgery, neurology, neuroradiology, neurosurgery, ophthalmology, oral surgery, otology, rhinology, and psychiatry.

Head Injuries Head injuries are a major cause of death and disability. The complications of head injuries include hemorrhage, infection, and injury to the brain and cranial nerves. Disturbance in the level of consciousness (LOC) is the most common symptom of head injury. Almost 10% of all deaths in the United States are caused by head injuries, and approximately half of traumatic deaths involve the brain (Rowland, 2000). Head injuries occur mostly in young persons between the ages of 15 and 24 years. The major cause of brain injury varies but motor vehicle and motorcycle accidents are prominent. Men are affected three to four times as often as women.

Headaches and Facial Pain Few complaints are more common than headaches and facial pain. Although usually benign and frequently associated with tension, fatigue, or mild fever, headaches may indicate a serious intracranial problem such as a brain tumor, subarachnoid hemorrhage, or meningitis. Neuralgias (G. algos, pain) are characterized by severe throbbing or stabbing pain in the course of a nerve caused by a demyelinating lesion. They are a common cause of facial pain. Terms such as facial neuralgia describe diffuse painful sensations. Localized aches have specific names, such as earache (otalgia) and toothache (odontalgia). A sound knowledge of the anatomy of the head helps in understanding the causes of headaches and facial pain.

Cranium The cranium (skull) is the skeleton of the head (Fig. 7.1A). A series of bones form its two parts, the neurocranium and viscerocranium (Fig. 7.1B). The neurocranium (cranial vault) is the bony covering (case) of the brain and its membranous coverings, the cranial meninges. It also contains proximal parts of the cranial nerves and the

Chapter 7: Head

vasculature of the brain. The neurocranium has a dome‐like roof, the calvaria (skullcap), and a floor or cranial base (basicranium). The neurocranium in adults is formed by a series of eight bones: four singular bones centered on the midline (frontal, ethmoidal, sphenoidal, and occipital) and two sets of bones occurring as bilateral pairs (temporal and parietal) (Fig. 7.1A & D). The bones forming the calvaria are primarily flat bones (frontal, temporal, and parietal) formed by intramembranous ossification of head mesenchyme from the neural crest. The bones contributing to the cranial base are primarily irregular bones with substantial flat portions (sphenoidal and temporal) formed by endochondral ossification of cartilage (chondrocranium) or from more than one type of ossification. The ethmoid bone is an irregular bone that makes a relatively minor midline contribution to the neurocranium but is primarily part of the viscerocranium. The “flat” bones and “flat” portions of the bones forming the neurocranium are actually curved, with convex external and concave internal surfaces.

Figure 7.1


Figure 7.1. Adult cranium. A. The cranium is in the anatomical position when the inferior margin of the orbit and the superior margin of the external acoustic meatus lie in the same horizontal orbitomeatal or Frankfort horizontal plane, a standard craniometric reference. The temporal fossa is the region of the lateral aspect of the cranium superior to the zygomatic arch and inferior to the temporal lines. B. The neurocranium and viscerocranium are the two primary functional parts of the cranium. C. The irregularly shaped palatine bone contributes to the formation of the nasal cavity, the hard palate, and a small part of the orbit. The spinal cord is continuous with the brain through the foramen magnum, the large opening in the basal part of the occipital bone. D. The supraorbital notch, the infraorbital foramen, and the mental foramen are approximately in a vertical line.

Most calvarial bones are united by fibrous interlocking sutures; however, during childhood, some bones (sphenoid and occipital) are united by hyaline cartilage (synchondroses). The spinal cord is continuous with the brain through the foramen magnum, a large opening in the cranial base (Fig. 7.1C). The viscerocranium (facial skeleton) comprises the facial bones that mainly develop in the mesenchyme of the embryonic pharyngeal arches (Moore and Persaud, 2003). The viscerocranium forms the anterior part of the cranium and consists of the bones surrounding the mouth (upper and lower jaws), nose/nasal cavity, and most of the orbits (eye sockets or orbital cavities). It consists of 15 irregular bones: three singular bones centered on or lying in the midline (mandible, ethmoid, and vomer) and 6 bones occurring as bilateral pairs (maxillae; inferior nasal conchae; and zygomatic, palatine, nasal, and lacrimal bones) (Fig. 7.1A, C, & D). The maxillae and mandible house the teeth—that is, they provide the sockets and supporting bone for the maxillary and mandibular teeth. The maxillae contribute the greatest part of the upper facial skeleton, forming the skeleton of the upper jaw, which is fixed to the cranial base. The mandible forms the skeleton of the lower jaw, which is movable because it articulates with the cranial base at the temporomandibular joints (TMJs). Several bones of the cranium (frontal, temporal, sphenoid, and ethmoid bones) are pneumatized bones, which contain air spaces (air cells or larger sinuses), presumably to decrease their weight. The total volume of the air spaces in these bones increases with age. In the anatomical position, the cranium is oriented so that the inferior margin of the orbit and the superior margin of the external acoustic opening of the external acoustic meatus of both sides lie in the same horizontal plane (Fig. 7.1A). This standard craniometric reference is the orbitomeatal plane (Frankfort horizontal plane).

Chapter 7: Head

Facial Aspect of the Cranium Features of the anterior or facial (frontal) aspect of the cranium (L. norma facialis or frontalis) are the frontal and zygomatic bones, orbits, nasal region, maxillae, and mandible (Fig. 7.1D). The frontal bone, specifically its squamous (flat) part, forms the skeleton of the forehead, articulating inferiorly with the nasal and zygomatic bones. In some adults a remnant of the frontal suture, the metopic suture, is visible in the midline of the glabella, the smooth, slightly depressed area between the superciliary arches. The frontal suture divides the frontal bones of the fetal cranium (see clinical correlation [blue] box “Development of the Cranium,” later in this chapter). The intersection of the frontal and nasal bones is the nasion (L. nasus, nose), which in most people is related to a distinctly depressed area (bridge of the nose). The frontal bone also articulates with the lacrimal, ethmoid, and sphenoids, and a horizontal portion of bone (the orbital part) forms both the roof of the orbit and part of the floor of the anterior part of the cranial cavity. The supraorbital margin of the frontal bone, the angular boundary between the squamous and the orbital parts, has a supraorbital foramen or notch in some crania for passage of the supraorbital nerve and vessels. Just superior to the supraorbital margin is a ridge, the superciliary arch, that extends laterally on each side from the glabella. The prominence of this ridge, deep to the eyebrows, is generally greater in males. Within the orbits are the superior and inferior orbital fissures and optic canals. The zygomatic bones (cheek bones, malar bones), forming the prominences of the cheeks, lie on the inferolateral sides of the orbits and rest on the maxillae. The anterolateral rims, walls, floor, and much of the infraorbital margins of the orbits are formed by these quadrilateral bones. A small zygomaticofacial foramen pierces the lateral aspect of each bone (Fig. 7.2A & B). The zygomatic bones articulate with the frontal, sphenoid, and temporal bones and the maxillae. Inferior to the nasal bones is the pear‐shaped piriform aperture, the anterior nasal opening in the cranium (Fig. 7.1A & D). The bony nasal septum can be observed through this aperture, dividing the nasal cavity into right and left parts. On the lateral wall of each nasal cavity are curved bony plates, the nasal conchae (Figs. 7.1D and 7.2A).


Figure 7.2. Bones of adult cranium. A. The forehead, the orbits, the bony part of the external nose, and the upper (maxilla) and lower (mandible) jaws are shown. B. Within the temporal fossa, the pterion is a craniometric point at the junction of the greater wing of the sphenoid, the squamous temporal bone, the frontal, and the parietal bones. C and D. Sutural bones occurring along the temporoparietal (C) and lambdoid (D) sutures are shown.

Chapter 7: Head

The maxillae form the upper jaw; their alveolar processes include the tooth sockets (alveoli) and constitute the supporting bone for the maxillary teeth. The maxillae surround most of the piriform aperture and form the infraorbital margins medially. They have a broad connection with the zygomatic bones laterally and an infraorbital foramen inferior to each orbit for passage of the infraorbital nerve and vessels (Fig. 7.2A). The two maxillae are united at the intermaxillary suture in the median plane (Fig. 7.2A). The mandible is a U‐shaped bone with an alveolar process that supports the mandibular teeth. It consists of a horizontal part, the body, and a vertical part, the ramus (Fig. 7.2B). Inferior to the second premolar teeth are the mental foramina for the mental nerves and vessels (Fig. 7.2A). The mental protuberance, forming the prominence of the chin, is a triangular bony elevation inferior to the mandibular symphysis (L. symphysis menti), the osseous union where the halves of the infantile mandible fuse (Fig. 7.1D).

Injury to the Superciliary Arches The superciliary arches are relatively sharp bony ridges; consequently, a blow to them (e.g., during boxing) may lacerate the skin and cause bleeding. Bruising of the skin surrounding the orbit causes tissue fluid and blood to accumulate in the surrounding connective tissue, which gravitates into the superior (upper) eyelid and around the eye (“black eye” ).

Malar Flush The zygomatic bone was once called the malar bone; consequently, you will hear the clinical term malar flush. This redness of the skin covering the zygomatic prominence (malar eminence) is associated with a rise in temperature in various fevers occurring with certain diseases, such as tuberculosis and systemic lupus erythematosus disease (SLE).

Fractures of the Maxillae and Associated Bones Dr. Léon‐Clement Le Fort (Paris surgeon and gynecologist, 1829—1893) classified three common variants of fractures of the maxillae (Fig. B7.1): 





Le Fort I fracture: wide variety of horizontal fractures of the maxillae, passing superior to the maxillary alveolar process (i.e., to the roots of the teeth), crossing the bony nasal septum and possibly the pterygoid plates of the sphenoid. Le Fort II fracture: passes from the posterolateral parts of the maxillary sinuses (cavities in the maxillae) superomedially through the infraorbital foramina, lacrimals, or ethmoids to the bridge of the nose. As a result, the entire central part of the face, including the hard palate and alveolar processes, is separated from the rest of the cranium. Le Fort III fracture: horizontal fracture that passes through the superior orbital fissures and the ethmoid and nasal bones and extends laterally through the greater wings of the sphenoid and the frontozygomatic sutures. Concurrent fracturing of the zygomatic arches causes the maxillae and zygomatic bones to separate from the rest of the cranium.


Figure B7.1

Fractures of the Mandible A fracture of the mandible usually involves two fractures, which frequently occur on opposite sides of the mandible; thus if one fracture is observed, a search should be made for another. For example, a hard blow to the jaw often fractures the neck of the mandible and its body in the region of the opposite canine tooth. Fractures of the coronoid process are uncommon and usually single (Fig. B7.2, line A). Fractures of the neck of the mandible are often transverse and may be associated with dislocation of the TMJ on the same side (Fig. B7.2, line B). Fractures of the angle of the mandible are usually oblique and may involve the bony socket or alveolus of the 3rd molar tooth (Fig. B7.2, line C). Fractures of the body of the mandible frequently pass through the socket of a canine tooth (Fig. B7.2, line D).

Chapter 7: Head

Figure B7.2. Fractures of mandible. A, Fracture of the coronoid process; B, fracture of the neck of the mandible;C, fracture of the angle of the mandible; D, fracture of the body of the mandible.

Resorption of Alveolar Bone Extraction of teeth causes the alveolar bone to resorb in the affected region(s) (Fig. B7.3). Following complete loss or extraction of maxillary teeth, the sockets begin to fill in with bone and the alveolar process begins to resorb. Similarly, extraction of mandibular teeth causes the bone to resorb. Gradually, the mental foramen lies near the superior border of the body of the mandible. In some cases, the mental foramina disappear, exposing the mental nerves to injury. Pressure from a dental prosthesis (e.g., a denture resting on an exposed mental nerve) may produce pain during eating. Loss of all the teeth results in a decrease in the vertical facial dimension and mandibular prognathism (overclosure). Deep creases in the facial skin also appear that pass posteriorly from the corners of the mouth.

Figure B7.3. Resorption of edentulous alveolar bone.

Lateral Aspect of the Cranium The lateral aspect of the cranium (L. norma lateralis) is formed by both the neurocranium and the viscerocranium (Figs. 7.1B and 7.2B). The main features of the neurocranial part include the temporal fossa, the external acoustic opening, and the


mastoid process of the temporal bone. The main features of the viscerocranial part include the infratemporal fossa, zygomatic arch, and lateral aspects of the maxilla and mandible. The temporal fossa (Fig. 7.1D) is bounded superiorly and posteriorly by the superior and inferior temporal lines, anteriorly by the frontal and zygomatic bones, and inferiorly by the zygomatic arch (Fig. 7.2A & B). The superior border of this arch corresponds to the inferior limit of the cerebral hemisphere of the brain. The zygomatic arch is formed by the union of the temporal process of the zygomatic bone and the zygomatic process of the temporal bone. Table 7.1. Craniometric Points of the Cranium

Landmark Pterion (G. wing)

Shape and Location Junction of the greater wing of the sphenoid, squamous temporal, frontal, and parietal bones; overlies course of anterior division of middle meningeal artery the Point on calvaria at junction of lambdoid and sagittal sutures

Lambda (G. letter L) Bregma (G. forepart of head) Vertex (L. whirl, whorl) Asterion (G. asterios, starry) Glabella (L. smooth, hairless) Inion (G. back of head) Nasion (L. nose)

Point on calvaria at junction of coronal and sagittal sutures Superior point of neurocranium, in the middle with the cranium oriented in anatomical (orbitomeatal or Frankfort) plane Star shaped; located at junction of three sutures: parietomastoid, occipitomastoid, and lambdoid Smooth prominence; most marked in males; on the frontal bones superior to root of nose; most anterior projecting part of forehead Most prominent point of external occipital protuberance Point on cranium where frontonasal and internasal sutures meet

Chapter 7: Head

In the anterior part of the temporal fossa, 3—4 cm superior to the midpoint of the zygomatic arch, is a clinically important area of bone junctions: the pterion (G. pteron, wing) (Fig. 7.2B; Table 7.1). It is usually indicated by an H‐shaped formation of sutures that unite the frontal, parietal, sphenoid (greater wing), and temporal bones. Less commonly, the frontal and temporal bones articulate; sometimes all four bones meet at a point. The external acoustic opening is the entrance to the external acoustic meatus (canal), which leads to the tympanic membrane (eardrum). The mastoid process of the temporal bone is posteroinferior to the external acoustic pore. Anteromedial to the mastoid process is the styloid process of the temporal bone, a slender needle‐ like, pointed projection. The infratemporal fossa is an irregular space inferior and deep to the zygomatic arch and the mandible and posterior to the maxilla.

Fractures of the Calvaria The convexity of the calvaria distributes and thereby usually minimizes the effects of a blow to the head. However, hard blows in thin areas of the calvaria are likely to produce depressed fractures, in which a bone fragment is depressed inward, compressing and/or injuring the brain (Fig. B7.4). Linear calvarial fractures, the most frequent type, usually occur at the point of impact; but fracture lines often radiate away from it in two or more directions. In comminuted fractures, the bone is broken into several pieces. If the area of the calvaria is thick at the site of impact, the bone may bend inward without fracturing; however, a fracture may occur some distance from the site of direct trauma where the calvaria is thinner. In a contrecoup (counterblow) fracture, no fracture occurs at the point of impact, but one occurs on the opposite side of the cranium.

Fracture of the Pterion Fracture of the pterion can be life‐threatening because it overlies the anterior branches of the middle meningeal vessels, which lie in grooves on the internal aspect of the lateral wall of the calvaria (Fig. 7.2B). The pterion is two fingers' breadth superior to the zygomatic arch and a thumb's breadth posterior to the frontal process of the zygomatic bone (Fig. B7.5A). A hard blow to the side of the head may fracture the thin bones forming the pterion (Fig. 7.2A), producing a rupture of the anterior branch of the middle meningeal artery crossing the pterion (Fig. B7.5B). The resulting hematoma exerts pressure on the underlying cerebral cortex. An untreated middle meningeal artery hemorrhage may cause death in a few hours.


Figure B7.4. Fractures of calvaria

Figure B7.5

Occipital Aspect of the Cranium The posterior or occipital aspect of the cranium (L. norma occipitalis) is composed of the occiput (L. back of head, the convex posterior protuberance of the occipital bone), parts of the parietal bones, and mastoid parts of the temporal bones (Fig. 7.3A). The external occipital protuberance (Table 7.1), is usually easily palpable in the median plane; however, occasionally (especially in females) it may be inconspicuous. A craniometric point (a point used in making cranial measurements and comparisons) defined by the tip of the external protuberance is the inion (G. nape of neck).

Chapter 7: Head

The external occipital crest descends from the protuberance toward the foramen magnum, the large opening in the basal part of the occipital bone (Figs. 7.1C and 7.3B). The superior nuchal line, marking the superior limit of the neck, extends laterally from each side of the protuberance; the inferior nuchal line is less distinct. In the center of the occiput, the lambda indicates the junction of the sagittal and lambdoid sutures (Fig. 7.3A; Table 7.1). The lambda can sometimes be felt as a depression. One or more sutural bones (accessory bones) may be located at the lambda or near the mastoid process (Fig. 7.2B—D).

Figure 7.3. Occiput of adult cranium. A. The posterior aspect of the cranium, or occiput, is composed of parts of the parietal bones, the occipital bone, and the mastoid parts of the temporal bones. The sagittal and lambdoid sutures meet at lambda, which can often be felt as a depression in living persons. B. The squamous part of the occipital bone has been removed to expose the anterior part of the anterior cranial fossa.

Superior Aspect of the Cranium The superior (vertical) aspect of the cranium (L. norma superioris or verticalis), usually somewhat oval in form, broadens posterolaterally at the parietal eminences (Figs. 7.2B and 7.3B). In some people, frontal eminences are also visible, giving the calvaria an almost square appearance. The coronal suture separates the frontal and parietal bones (Figs. 7.4A & B), the sagittal suture separates the parietal bones, and the lambdoid suture separates the parietal and temporal bones from the occipital bone (Figs. 7.3A and 7.4C). The bregma is the landmark formed by the intersection of the sagittal and coronal sutures (Fig. 7.4A; Table 7.1). The vertex, the most superior point of the calvaria, is near the midpoint of the sagittal suture. The parietal foramen is a small, inconstant aperture located posteriorly in the parietal bone near the sagittal suture (Fig. 7.4C); paired parietal foramina may be present. Most irregular, highly variable foramina that occur in the neurocranium are emissary foramina that transmit emissary veins, veins connecting scalp veins to the venous sinuses of the dura mater (see “Structure of the Scalp,” later in this chapter) (Fig 7.4B).


External Surface of the Cranial Base The cranial base (basicranium) is the inferior portion of the neurocranium (floor of the cranial cavity) and viscerocranium minus the mandible (Fig. 7.5A—C). The external surface of the cranial base (L. basis cranii externa) features the alveolar arch of the maxillae (the free border of the alveolar processes surrounding and supporting the maxillary teeth); the palatine processes of the maxillae; and the palatine, sphenoid, vomer, temporal, and occipital bones (Fig. 7.5A & B). The hard palate (bony palate) is formed by the palatine processes of the maxillae anteriorly and the horizontal plates of the palatine bones posteriorly. The free posterior border of the hard palate projects posteriorly in the median plane as the posterior nasal spine. Posterior to the central incisor teeth is the incisive fossa, a depression in the midline of the bony palate into which the incisive canals open. The right and left nasopalatine nerves pass from the nose through a variable number of incisive canals and foramina (they may be bilateral or merged into a single formation). Posterolaterally are the greater and lesser palatine foramina. Superior to the posterior edge of the palate are two large openings: the choanae (posterior nasal apertures), which are separated from each other by the vomer (L. plowshare), a flat unpaired bone of trapezoidal shape that forms a major part of the bony nasal septum. Wedged between the frontal, temporal, and occipital bones is the sphenoid, an irregular unpaired bone that consists of a body and three pairs of processes: greater wings, lesser wings, and pterygoid processes. The greater and lesser wings of the sphenoid spread laterally from the lateral aspects of the body of the bone (Fig. 7.5C). The pterygoid processes, consisting of lateral and medial pterygoid plates, extend inferiorly on each side of the sphenoid from the junction of the body and greater wings. The groove for the cartilaginous part of the pharyngotympanic (auditory) tube lies medial to the spine of the sphenoid, inferior to the junction of the greater wing of the sphenoid and the petrous (L. rock‐like) part of the temporal bone. Depressions in the squamous (L. flat) part of the temporal bone, called the mandibular fossae (Fig. 7.5B), accommodate the mandibular condyles when the mouth is closed. The cranial base is formed posteriorly by the occipital bone, which articulates with the sphenoid anteriorly.

Chapter 7: Head

Figure 7.4. Anterior part of adult calvaria. A. The external aspect demonstrates the bregma, where the coronal and sagittal sutures meet, and the vertex, the superiormost point of the cranium. B. The internal aspect of the calvaria reveals the pits (granular foveolae; dotted lines) in the frontal and parietal bones, which are produced by enlarged arachnoid granulations or clusters of smaller ones (Fig. 7.7). Multiple small emissary veins pass between the superior sagittal sinus and veins in the diploä (D) and scalp through the emissary foramina (arrows) located on each side of the sagittal suture. The spongy diploä of cancellous bone contains red marrow in life. The sinuous vascular groove (M) on the lateral wall is formed by the frontal branch of the middle meningeal artery. The cerebral falx, a short process of dura mater (the outermost covering of the brain), attaches to the frontal crest (FC). C. This external view demonstrates a prominent, unilateral parietal foramen. Although emissary foramina often occur in this general location, there is much variation. They may be bilateral but are more commonly absent.


Chapter 7: Head Figure 7.5. Cranial base. A. The external aspect demonstrates the contributing bones. The inferior surface is formed posteriorly by the occipital bone, which becomes continuous anteriorly with the sphenoid bone following synostosis. B. Features of external cranial base are shown. The foramen magnum is located midway between and on a level with the mastoid processes. The hard palate forms both a part of the roof of the mouth and the floor of the nasal cavity. The large choanae on each side of the vomer are the posterior entrance to the nasal cavities. C. The internal aspect demonstrates the contributing bones and features. D. The floor of the cranial cavity is divisible into three levels (steps): the anterior, middle, and posterior cranial fossae.

The four parts of the occipital bone are arranged around the foramen magnum, the most conspicuous feature of the cranial base. The major structures passing through this large foramen are the spinal cord (where it becomes continuous with the medulla oblongata of the brain), the meninges (coverings) of the brain and spinal cord, the vertebral arteries, the anterior and posterior spinal arteries, and the accessory nerve (CN XI). On the lateral parts of the occipital bone are two large protuberances, the occipital condyles, by which the cranium articulates with the vertebral column (Fig. 7.5B). The large opening between the occipital bone and the petrous part of the temporal bone is the jugular foramen, from which the internal jugular vein (IJV) and several cranial nerves (CN IX—CN XI) emerge from the cranium (Fig. 7.5C). Superolateral to the jugular foramen is the internal acoustic meatus, a passage for CN VII and CN VIII. The entrance to the carotid canal for the internal carotid artery is just anterior to the jugular foramen (Fig. 7.5B). The mastoid processes provide for muscle attachments. The stylomastoid foramen, transmitting the facial nerve (CN VII) and stylomastoid artery, lies posterior to the base of the styloid process.


Internal Surface of the Cranial Base The internal surface of the cranial base (L. basis cranii interna) has three large depressions that lie at different levels: the anterior, middle, and posterior cranial fossae (Fig. 7.5D), which form the bowl‐shaped floor of the cranial cavity. The anterior cranial fossa is at the highest level, and the posterior cranial fossa is at the lowest level.

Anterior Cranial Fossa The inferior and anterior parts of the frontal lobes of the brain occupy the anterior cranial fossa, the shallowest of the three cranial fossae (Fig. 7.5D). The fossa is formed by the frontal bone anteriorly, the ethmoid bone in the middle, and the body and lesser wings of the sphenoid posteriorly (Fig. 7.5C; Table 7.2). The greater part of the fossa is formed by the orbital parts of the frontal bone, which support the frontal lobes of the brain and form the roofs of the orbits. This surface shows sinuous impressions (brain markings) of the orbital gyri (ridges) of the frontal lobes (Table 7.2). The frontal crest is a median bony extension of the frontal bone. At its base is the foramen cecum of the frontal bone, which gives passage to vessels during fetal development but is insignificant postnatally. The crista galli (L. cock's comb) is a thick, median ridge of bone posterior to the foramen cecum, which projects superiorly from the ethmoid. On each side of this ridge is the sieve‐like cribriform plate of the ethmoid (Fig. 7.5C). Its numerous tiny foramina transmit the olfactory nerves (CN I) from the olfactory areas of the nasal cavities to the olfactory bulbs of the brain, which lie on this plate (see Chapter 9).

Middle Cranial Fossa The butterfly‐shaped middle cranial fossa has a central part composed of the sella turcica on the body of the sphenoid and large, depressed lateral parts on each side. The middle cranial fossa is posteroinferior to the anterior cranial fossa, separated from it by the sharp sphenoidal crests laterally and the sphenoidal limbus centrally. The sphenoidal crests are formed mostly by the sharp posterior borders of the lesser wings of the sphenoid bones, which overhang the lateral parts of the fossae anteriorly. The sphenoidal crests end medially in two sharp bony projections, the anterior clinoid processes. A variably prominent ridge, the sphenoid limbus forms the anterior boundary of the transversely oriented prechiasmatic sulcus extending between the right and the left optic canals. The bones forming the lateral parts of the fossa are the greater wings of the sphenoid and squamous parts of the temporal bones laterally and the petrous parts of the temporal bones posteriorly (Fig. 7.5C; Table 7.2). The lateral parts of the middle cranial fossa support the temporal lobes of the brain. The boundary between the middle and the posterior cranial fossae is the superior border of the petrous part of the temporal bone laterally and a flat plate of bone, the dorsum sellae of the sphenoid, medially. The sella turcica (L. Turkish saddle) is the saddle‐like bony formation on the upper surface of the body of the sphenoid, which is surrounded by the anterior and posterior clinoid processes (Fig. 7.5C). Clinoid means “bedpost,” and the four processes (two anterior and two posterior) surround the hypophysial fossa, the “bed” of the pituitary gland, like the posts of a four‐poster bed. The sella turcica is composed of three parts:

Chapter 7: Head 





The tuberculum sellae (horn of the saddle): a variable slight to prominent median elevation forming the posterior boundary of the prechiasmatic sulcus and the anterior boundary of the hypophysial fossa. The hypophysial fossa (pituitary fossa): a median depression (seat of the saddle) in the body of the sphenoid that accommodates the pituitary gland (L. hypophysis). The dorsum sellae (back of the saddle): a square plate of bone projecting superiorly from the body of the sphenoid. It forms the posterior boundary of the sella turcica, and its prominent superolateral angles make up the posterior clinoid processes.

On each side of the body of the sphenoid a crescent of four foramina perforate the roots of the greater wings of the sphenoids (Fig. 7.5C; Table 7.2): 





Superior orbital fissure: Located between the greater and lesser wings, it communicates with the orbit and transmits the ophthalmic veins and nerves (CN III, CN IV, CN V 1 , CN VI, and sympathetic fibers) entering the orbit. Foramen rotundum (round foramen): Located posterior to the medial end of the superior orbital fissure, it transmits the maxillary nerve (CN V 2 ) that supplies the skin, teeth, and mucosa related to the maxilla (i.e., lining the upper jaw and maxillary sinus). Foramen ovale (oval foramen): A large foramen posterolateral to the foramen rotundum, it opens inferiorly into the infratemporal fossa and transmits the mandibular nerve (CN V 3 ) and a small accessory meningeal artery.

Table 7.2. Foramina and Other Apertures of the Cranial Fossae and Contents


Foramina/Apertures Anterior cranial fossa Foramen cecum Cribriform foramina in cribriform plate Anterior and posterior ethmoidal foramina Middle cranial fossa Optic canals Superior orbital fissure

Contents Nasal emissary vein (1% of population) Axons of olfactory cells in olfactory epithelium that form olfactory nerves Vessels and nerves with same names

Optic nerves (CN II) and ophthalmic arteries Ophthalmic veins; ophthalmic nerve (CN V1); CN III, IV, and VI; and sympathetic fibers Foramen rotundum Maxillary nerve (CN V 2 ) Foramen ovale Mandibular nerve (CN V 3 ) and accessory meningeal artery Foramen spinosum Middle meningeal artery and vein and meningeal branch of CN V 3 Foramen lacerum a Internal carotid artery and its accompanying sympathetic and venous plexuses a Groove or hiatus of greater Greater petrosal nerve and petrosal branch of middle meningeal artery petrosal nerve Posterior cranial fossa Foramen magnum Medulla and meninges, vertebral arteries, CN XI, dural veins, anterior and posterior spinal arteries Jugular foramen CN IX, X, and XI; superior bulb of internal jugular vein; inferior petrosal and sigmoid sinuses; and meningeal branches of ascending pharyngeal and occipital arteries Hypoglossal canal Hypoglossal nerve (CN XII) Condylar canal Emissary vein that passes from sigmoid sinus to vertebral veins in neck Mastoid foramen Mastoid emissary vein from sigmoid sinus and meningeal branch of occipital artery

P.900 

Foramen spinosum (spinous foramen): Located posterolateral to the foramen ovale, it transmits the middle meningeal vessels and the meningeal branch of the mandibular nerve.

The foramen lacerum (lacerated or torn foramen) is not part of the crescent of foramina. This ragged foramen lies posterolateral to the hypophysial fossa and is an artifact of a dried cranium. In life, it is closed by a cartilage plate. Only some meningeal arterial branches and small veins are transmitted vertically through the cartilage, completely traversing this foramen. The internal carotid artery and its accompanying sympathetic and venous plexuses pass across the superior aspect of the cartilage (i.e., pass over the foramen), and some nerves traverse it horizontally, passing to a foramen in its anterior boundary. Extending posteriorly and laterally from the foramen lacerum is a narrow groove for the greater petrosal nerve on the anterosuperior surface of the petrous part of the temporal bone. There is also a small groove for the lesser petrosal nerve.

Chapter 7: Head

Posterior Cranial Fossa The posterior cranial fossa, the largest and deepest of the three cranial fossae, lodges the cerebellum, pons, and medulla oblongata (Fig. 7.5C & D). The posterior cranial fossa is formed mostly by the occipital bone, but the dorsum sellae of the sphenoid marks its anterior boundary centrally and the petrous and mastoid parts of the temporal bones contribute its anterolateral “walls” (Fig. 7.5C; Table 7.2). From the dorsum sellae there is a marked incline, the clivus, in the center of the anterior part of the fossa leading to the foramen magnum. Posterior to this large opening, the posterior cranial fossa is partly divided by the internal occipital crest into bilateral large concave impressions, the cerebellar fossae. The internal occipital crest ends in the internal occipital protuberance formed in relationship to the confluence of the sinuses, a merging of dural venous sinuses (discussed later in this chapter). Broad grooves show the horizontal course of the transverse sinus and the S‐shaped sigmoid sinus. At the base of the petrous ridge of the temporal bone is the jugular foramen, which transmits several cranial nerves in addition to the sigmoid sinus that exits the cranium as the IJV. Anterosuperior to the jugular foramen is the internal acoustic meatus for the facial and vestibulocochlear nerves (CN VIII) and the labyrinthine artery. The hypoglossal canal for the hypoglossal nerve (CN XII) is superior to the anterolateral margin of the foramen magnum.

Walls of the Cranial Cavity The walls of the cranial cavity vary in thickness in different regions. They are usually thinner in females than in males and are thinner in children and elderly people. The bones tend to be thinnest in areas that are well covered with muscles, such as the squamous part of the temporal bone (Fig. 7.2B). Thin areas of bone can be seen by holding a dried cranium up to a bright light. Most bones of the calvaria consist of internal and external tables of compact bone, separated by diploä (Fig. 7.5C). The diploä is cancellous bone containing red bone marrow during life, through which run canals formed by diploic veins. The diploä in a dried calvaria is not red because the protein was removed during preparation of the cranium. The internal table of bone is thinner than the external table and in some areas there is only a thin plate of compact bone with no diploä. The bony substance of the cranium is unequally distributed. Relatively thin (but mostly curved) flat bones provide the necessary strength to maintain cavities and protect their contents. However, in addition to housing the brain, the bones of the neurocranium (and processes from them) provide proximal attachment for the strong muscles of mastication that attach distally to the mandible; consequently, high traction forces occur across the nasal cavity and orbits that are sandwiched between. Thus thickened portions of the cranial bones form stronger pillars or buttresses that transmit forces, bypassing the orbits and nasal cavity. The main buttresses are the frontonasal buttress, extending from the region of the canine teeth between the nasal and the orbital cavities to the central frontal bone, and the zygomatic arch— lateral orbital margin buttress from the region of the molars to the lateral frontal and temporal bones (Fig. 7.6). Similar buttresses transmit forces received lateral to the foramen magnum from the vertebral column. Perhaps to compensate for the denser bone required for these buttresses, some areas of the cranium not as mechanically stressed become pneumatized (“air‐filled” ).


Figure 7.6. Buttresses of cranium. The strong muscles of mastication extending between the neurocranium and mandible produce high traction forces across the nasal cavity and orbits. Thickened portions of the bones of the cranium form stronger pillars or buttresses that transmit forces, bypassing the orbits and nasal cavity. Occipital buttresses transmit forces received lateral to the foramen magnum from the vertebral column.

Development of the Cranium The bones of the calvaria and some parts of the cranial base develop by intramembranous ossification; most parts of the cranial base develop by endochondral ossification. At birth, the bones of the calvaria are smooth and unilaminar; no diploä is present. The frontal and parietal eminences are especially prominent (Fig. B7.6). The cranium of a newborn infant is disproportionately large compared to other parts of the skeleton; however, the facial aspect is small compared to the calvaria, which forms approximately one eighth of the cranium. In the adult, the facial skeleton forms one third of the cranium. The large size of the calvaria in infants results from precocious growth and development of the brain and eyes. The rudimentary development of the face makes the orbits appear relatively large (Fig. B7.6A). The smallness of the face results from the rudimentary development of the maxillae, mandible, and paranasal sinuses (air‐filled bone cavities), the absence of erupted teeth, and the small size of the nasal cavities. The halves of the frontal bone in the newborn are separated by the frontal suture, the frontal and parietal bones are separated by the coronal suture, and the maxillae and mandibles are separated by the intermaxillary suture and mandibular symphysis (secondary cartilaginous joint), respectively. There are no mastoid and styloid processes (Fig. B7.6B). Because there are no mastoid processes at birth, the facial nerves are close to the surface when they emerge from the stylomastoid foramina. As a result, the facial nerves may be injured by forceps during a difficult delivery or later by an incision posterior to the auricle of the external ear (as for the surgical treatment of mastoiditis or middle ear problems). The mastoid processes form gradually during the 1st year as the sternocleidomastoid muscles complete their development and pull on the petromastoid parts of the temporal bones.

Chapter 7: Head

(C)

Figure B7.6. Cranial development. A and B. Anterior and lateral aspects of an infant's cranium are shown. C. This anterosuperior view shows a persistent frontal suture.

The bones of the calvaria of a newborn infant are separated by membranous intervals; the largest occur between the angles (corners) of the flat bones (Fig. B7.6A & B). They include the anterior and posterior fontanelles and the paired sphenoidal and mastoid fontanelles. Palpation of the fontanelles during infancy, especially the anterior and posterior ones, enables physicians to determine the:   

Progress of growth of the frontal and parietal bones. Degree of hydration of an infant (a depressed fontanelle indicates dehydration). Level of intracranial pressure (a bulging fontanelle indicates increased pressure on the brain).

The anterior fontanelle, the largest one, is diamond or star shaped; it is bounded by the halves of the frontal bone anteriorly and the parietal bones posteriorly. Thus it is located at the junction of the sagittal, coronal, and frontal sutures, the future site of the bregma (Table 7.1). By 18 months of age, the surrounding bones have fused and the anterior fontanelle is no longer clinically palpable. Union of the halves of the frontal bone begins in the 2nd year. In most cases, the frontal suture is obliterated by the 8th year. However, in approximately 8% of people, a remnant of it, the metopic suture, persists (Fig. 7.1D); and much less frequently, the entire suture remains (Fig. B7.6C). A persistent suture must not be interpreted as a fracture in a radiograph or other medical image.


The posterior fontanelle is triangular and bounded by the parietal bones anteriorly and the occipital bone posteriorly. It is located at the junction of the lambdoid and sagittal sutures, the future site of lambda (Fig. 7.3A and 7.4C). The posterior fontanelle begins to close during the first few months after birth; and by the end of the 1st year, it is small and no longer clinically palpable. The sphenoidal and mastoid fontanelles, overlain by the temporal (L. temporalis) muscle, fuse during infancy and are less important clinically than the midline fontanelles. The halves of the mandible fuse early in the 2nd year. The two maxillae and nasal bones usually do not fuse. The softness of the cranial bones in infants and their loose connections at the sutures and fontanelles enable the shape of the calvaria to change (mold) during birth (Fig. B7.7). During passage of the fetus through the birth canal, the halves of the frontal bone become flat, the occipital bone is drawn out, and one parietal bone slightly overrides the other. Within a few days after birth, the shape of the calvaria returns to normal. The resilience of the cranial bones of infants allows them to resist forces that would produce fractures in adults. The fibrous sutures of the calvaria also permit the cranium to enlarge during infancy and childhood. The increase in the size of the calvaria is greatest during the first 2 years, the period of most rapid brain development. The calvaria normally increases in capacity for 15—16 years. After this, the calvaria usually increases slightly in size for 3—4 years as a result of bone thickening.

Figure B7.7. Molding of calvaria.

Age Changes in the Face The mandible is the most dynamic of our bones; its size and shape and the number of teeth it normally bears undergo considerable change with age. In the newborn, the mandible consists of two halves united in the median plane by a cartilaginous joint, the mandibular symphysis. Union between the halves of the mandible is effected by means of fibrocartilage; this union begins during the 1st year and the halves are fused by the end of the 2nd year. The body of the mandible in newborn infants is a mere shell lacking an alveolar process, each half enclosing five deciduous (primary) teeth. These teeth usually begin

Chapter 7: Head

to erupt in infants at approximately 6 months of age. The body of the mandible elongates, particularly posterior to the mental foramen, to accommodate this development and later eight permanent (secondary) teeth, which begin to erupt during the 6th year of life (Fig. B7.8). Eruption of the permanent teeth is not complete until early adulthood. Rapid growth of the face during infancy and early childhood coincides with the eruption of deciduous teeth. Vertical growth of the upper face results mainly from dentoalveolar development. These changes are more marked after the permanent teeth erupt. Figure B7.8. Left lateral view of dentition. Arrows, unerupted secondary teeth.

Concurrent enlargement of the frontal and facial regions is associated with the increase in the size of the paranasal sinuses, the air‐filled extensions of the nasal cavities in certain cranial bones (Fig. B7.9). Most paranasal sinuses are rudimentary or absent at birth. Growth of the paranasal sinuses is important in altering the shape of the face and in adding resonance to the voice.

Obliteration of the Cranial Sutures The obliteration of sutures between the bones of the calvaria usually begins between the ages of 30 and 40 years on the internal surface and approximately 10 years later on the external surface (Fig. B7.10; compare with Fig. 7.4A). Obliteration of sutures usually begins at the bregma and continues sequentially in the sagittal, coronal, and lambdoid sutures.

Age Changes in the Cranium As people age, the cranial bones normally become progressively thinner and lighter, and the diploä gradually become filled with a gray gelatinous material. In these individuals, the bone marrow has lost its blood cells and fat, giving it a gelatinous appearance.


Craniosynostosis and Cranial Malformations Premature closure of the cranial sutures (primary craniosynostosis) results in several cranial malformations (Fig. B7.11). The incidence of primary craniosynostosis is approximately 1 per 2000 births (Behrman et al., 2004). The cause of craniosynostosis is unknown, but genetic factors appear to be important. The prevailing hypothesis is that abnormal development of the cranial base creates exaggerated forces on the dura mater (outer covering membrane of the brain) that disrupt normal cranial sutural development. These malformations are more common in males than in females and are often associated with other skeletal anomalies. The type of malformed cranium that forms depends on which sutures close prematurely.

Figure B7.9

Figure B7.10. Obliteration (synostosis) of cranial sutures.

Chapter 7: Head

Premature closure of the sagittal suture, in which the anterior fontanelle is small or absent, results in a long, narrow, wedge‐shaped cranium, a condition called scaphocephaly (Fig. B7.11A). When premature closure of the coronal or the lambdoid suture occurs on one side only, the cranium is twisted and asymmetrical, a condition known as plagiocephaly (Fig. B7.11B). Premature closure of the coronal suture results in a high, tower‐like cranium, called oxycephaly or turricephaly (Fig. B7.11C). The latter type of cranial malformation is more common in females. Premature closure of sutures usually does not affect brain development.

Figure B7.11. Scaphocephaly (A), plagiocephaly (B), and oxycephaly (C).

The Bottom Line The cranium is the skeleton of the head, an amalgamation of functional components united to form a single skeletal formation. The basic functional components include the neurocranium, the container of the brain and internal ears, and viscerocranium, providing paired orbits, nasal cavities and teeth‐bearing plates (alveolar processes) of the oral cavity. Although some mobility between cranial bones is advantageous during birth, they become fixed together by essentially immovable joints (sutures), allowing independent movement of only the mandible. Abundant fissures and foramina facilitate communication and passage of neurovascular structures between functional components. The bony substance of the cranium is unequally distributed. Relatively thin (but mostly curved) flat bones provide the necessary strength to maintain cavities and protect contents. However, the bones and processes of the neurocranium also provide proximal attachment for the strong muscles of mastication that attach distally to the mandible. The high traction forces generated across the nasal cavity and orbits sandwiched between the muscle attachments are resisted by thickened portions of the bones forming stronger pillars or buttresses. The mostly superficial surface of the cranium provides both visible and palpable landmarks. Internal features of the cranial base reflect the major formations of the brain that rest on it. Bony ridges radiating from the centrally located sella turcica or hypophysial fossa divide it into three cranial fossae. The frontal lobes of the brain lie in the anterior cranial fossa. The temporal lobes lie in the middle cranial fossa. The hindbrain, consisting of the pons, cerebellum, and medulla, occupies the posterior


cranial fossa, with the medulla continuing through the foramen magnum where it is continuous with the spinal cord. The complex construction of the cranium can be observed radiographically, facilitating the diagnosis of pathology and trauma involving the head.

Structure of the Scalp The scalp consists of skin (normally hair bearing) and subcutaneous tissue, which cover the neurocranium, from the superior nuchal lines on the occipital bone to the supraorbital margins of the frontal bone. Laterally, the scalp extends over the temporal fascia to the zygomatic arches. The discussion of the scalp has been divided into two parts. Because the scalp must be reflected or removed to enter the cranial cavity and because the layered pattern evident in the scalp continues deeply with the laminae of the cranium and the meninges, the structure of the scalp is presented before that of the cranial meninges and brain. The neurovascular structures of the scalp will be discussed with those of the face, to which they are most directly related. The scalp is composed of five layers, the first three of which are connected intimately and move as a unit (e.g., when wrinkling the forehead and moving the scalp). Each letter in the word scalp serves as a memory key for one of its five layers (Fig. 7.7A): 

 





Skin: thin, except in the occipital region, containing many sweat and sebaceous glands and hair follicles. It has an abundant arterial supply and good venous and lymphatic drainage. Connective tissue: forms the thick, dense, richly vascularized subcutaneous layer that is well supplied with cutaneous nerves. Aponeurosis (epicranial aponeurosis): the broad, strong, tendinous sheet that covers the calvaria and serves as the attachment for muscle bellies converging from the forehead and occiput (the occipitofrontalis muscle) (Fig. 7.7B) and from the temporal bones on each side (the temporoparietalis and superior auricular muscles). Collectively, these structures constitute the musculoaponeurotic epicranius. The frontal belly of the occipitofrontalis pulls the scalp anteriorly, wrinkles the forehead, and elevates the eyebrows; the occipital belly of the occipitofrontalis pulls the scalp posteriorly, smoothing the skin of the forehead. The superior auricular muscle (actually a specialized posterior part of the temporoparietalis) elevates the auricle of the external ear. All parts of the epicranius are innervated by the facial nerve. Loose areolar tissue: a sponge‐like layer including potential spaces that may distend with fluid as a result of injury or infection. This layer allows free movement of the scalp proper (the first three layers—skin, connective tissue, and epicranial aponeurosis) over the underlying calvaria. Pericranium: a dense layer of connective tissue that forms the external periosteum of the neurocranium. It is firmly attached but can be stripped fairly easily from the crania of living persons, except where the pericranium is continuous with the fibrous tissue in the cranial sutures.

Chapter 7: Head

Scalp Wounds The epicranial aponeurosis is clinically important. Because of the strength of this aponeurosis, superficial scalp wounds do not gape and the margins of the wound are held together. Furthermore, deep sutures are not necessary when suturing superficial wounds because the epicranial aponeurosis does not allow wide separation of the skin. Deep scalp wounds gape widely when the epicranial aponeurosis is lacerated in the coronal plane because of the pull of the frontal and occipital bellies of the occipitofrontalis muscle in opposite directions (anteriorly and posteriorly).

Scalp Infections The loose connective tissue layer (layer four) of the scalp is the danger area of the scalp because pus or blood spreads easily in it. Infection in this layer can also pass into the cranial cavity through emissary veins, which pass through parietal foramina in the calvaria, and reach intracranial structures such as the meninges (Fig. 7.4C). An infection cannot pass into the neck because the occipital bellies of the occipitofrontalis muscle attach to the occipital bone and mastoid parts of the temporal bones. Neither can a scalp infection spread laterally beyond the zygomatic arches because the epicranial aponeurosis is continuous with the temporal fascia that attaches to these arches. An infection or fluid (e.g., pus or blood) can enter the eyelids and the root of the nose because the frontalis inserts into the skin and subcutaneous tissue and does not attach to the bone. Consequently, “black eyes” can result from an injury to the scalp and/or the forehead (Fig. B7.12). Ecchymosis, or purple patches, develop as a result of extravasation of blood into the subcutaneous tissue and skin of the eyelids and surrounding regions.

Sebaceous Cysts The ducts of sebaceous glands associated with hair follicles in the scalp may become obstructed, resulting in the retention of secretions and the formation of sebaceous cysts (wens). Because they are in the skin, sebaceous cysts move with the scalp.

Cephalhematoma Sometimes after a difficult birth, bleeding occurs between the baby's pericranium and calvaria, usually over one parietal bone. Blood becomes trapped in this area, causing a cephalhematoma. This benign condition frequently results from birth trauma that ruptures multiple, minute periosteal arteries that nourish the bones of the calvaria.

Figure B7.12. Ecchymosis.


Bone Flaps Because the adult pericranium has poor osteogenic (bone‐forming) properties, little regeneration occurs after bone loss (e.g., when pieces of bone are removed during repair of a comminuted cranial fracture). Surgically produced bone flaps are put back into place and wired to other parts of the calvaria.

Figure 7.7. Layers of scalp, cranium, and meninges. A. The skin is bound tightly to the epicranial aponeurosis, which moves freely over the pericranium and cranium because of the intervening loose connective tissue. The aponeurosis is the flat intermediate tendon of the occipitofrontalis muscle. The cranial meninges and the subarachnoid (leptomeningeal) space are shown. CSF, cerebrospinal fluid. B. The occipitofrontalis muscle, including its occipital and frontal bellies, and the epicranial aponeurosis. Innervation of the two bellies by the posterior auricular and temporal branches of the facial nerve is also demonstrated.

Chapter 7: Head

The Bottom Line The scalp is the somewhat mobile soft tissue mantle covering the calvaria. The primary subcutaneous component of the scalp is the musculoaponeurotic epicranius to which the overlying skin is firmly attached but is separated from the outer periosteum (pericranium) of the cranium by loose areolar tissue. The areolar layer enables the mobility of the scalp over the calvaria and permits traumatic separation of the scalp from the cranium. Attachment of the skin to the epicranial aponeurosis keeps the edges of superficial wounds together, but a wound that also penetrates the epicranial aponeurosis gaps widely. Blood may collect in the areolar space deep to the aponeurosis after a head injury.

Cranial Meninges The cranial meninges are coverings of the brain that lie immediately internal to the cranium (Figs. 7.7A and 7.8). The cranial meninges:   

Protect the brain. Form the supporting framework for arteries, veins, and venous sinuses. Enclose a fluid‐filled cavity, the subarachnoid space, which is vital to the normal function of the brain.

The meninges are composed of three membranous connective tissue layers:   

Dura mater (dura): tough, thick external fibrous layer. Arachnoid mater (arachnoid): thin intermediate layer. Pia mater (pia): delicate internal vasculated layer.

The intermediate and internal layers (arachnoid and pia) are continuous membranes that collectively make up the leptomeninx (G. slender membrane). The arachnoid is separated from the pia by the subarachnoid (leptomeningeal) space, which contains cerebrospinal fluid (CSF). This fluid‐filled space helps maintain the balance of extracellular fluid in the brain. CSF is a clear liquid similar to blood in constitution; it provides nutrients but has less protein and a different ion concentration. CSF is formed by the choroid plexuses of the four ventricles of the brain (Fig. 7.8). This fluid leaves the ventricular system and enters the subarachnoid space between the arachnoid and the pia mater, where it cushions and nourishes the brain.

Dura Mater The dura mater, a bilaminar membrane, is also called the pachymeninx (G. pachy, thick + G. menix, membrane) (Figs. 7.8 and 7.9). It is adherent to the internal table of the calvaria. The two layers of the cranial dura mater are an external periosteal layer, formed by the periosteum covering the internal surface of the calvaria, and an internal meningeal layer, a strong fibrous membrane that is continuous at the foramen magnum with the spinal dura mater covering the spinal cord. The external periosteal layer of the dura mater adheres to the internal surface of the cranium; its attachment is tenacious along the suture lines and in the cranial base (Haines, 2002). The external periosteal layer is continuous at the cranial foramina with the periosteum on the external surface of the calvaria (Fig. 7.8C). This outer


layer is not continuous with the dura mater of the spinal cord, which consists of only a meningeal layer. Except where the dural sinuses and infoldings occur (Fig. 7.8B), the internal meningeal layer is intimately fused with the periosteal layer and cannot be separated from it (Fig. 7.8B & C). The fused external and internal layers of dura over the calvaria can be easily stripped from the cranial bones (e.g., when the calvaria is removed at autopsy). In the cranial base, the two dural layers are firmly attached and difficult to separate from the bones. In life, such separation at the dural—cranial interface occurs only pathologically, creating an actual (blood‐ or fluid‐filled) epidural space.

Figure 7.8. Meninges and their relationship to calvaria, brain, and spinal cord. A. The dura mater and subarachnoid space (purple) surround the brain and are continuous with that around the spinal cord. B. The two layers of dura separate to form dural venous sinuses, such as the superior sagittal sinus. Arachnoid granulations protrude through the meningeal layer of the dura into the dural venous sinuses and effect transfer of cerebrospinal fluid to the venous system. C. The normal fat‐ and vein‐filled spinal epidural (extradural) space is not continuous with the potential or pathological cranial epidural space. Cranial dura mater has two layers, whereas spinal dura mater consists of a single layer.

Chapter 7: Head

Dural Infoldings or Reflections The internal meningeal layer of dura mater is a sustentacular (supporting) layer that reflects away from the external periosteal layer of dura to form dural infoldings (reflections) (Figs. 7.8B and 7.10). The dural infoldings divide the cranial cavity into compartments, forming partial partitions (dural septa) between certain parts of the brain and providing support for other parts. The dural infoldings include the:    

Cerebral falx (L. falx cerebri). Cerebellar tentorium (L. tentorium cerebelli). Cerebellar falx (L. falx cerebelli). Sellar diaphragm (L. diaphragma sellae). Figure 7.9. External surface of dura mater and arachnoid granulations. The calvaria is removed. In the median plane, a part of the thick roof of the superior sagittal sinus has been incised and retracted; laterally, parts of the thin roof of two lateral lacunae are reflected to demonstrate the abundant arachnoid granulations, which are responsible for absorption of CSF. On the right, an angular flap of dura is turned anteriorly; the convolutions of the cerebral cortex are visible through the arachnoid mater.


Figure 7.10. Dural infoldings and dural venous sinuses. The left side of the bisected head is shown. A. The two sickle‐shaped dural folds (septae), the cerebral falx and cerebellar falx, are vertically oriented in the median plane. The two roof‐like folds, the cerebellar tentorium and the small sellar diaphragm, lie horizontally. The left members of the paired arteries that supply the brain, the internal carotid and vertebral arteries, are shown. B. Venous sinuses of the dura mater and their communications are demonstrated. Cavernous sinuses lie on each side of the body of the sphenoid . These sinuses communicate anteriorly with the facial vein through the superior and inferior ophthalmic veins. The cavernous sinus also communicate inferiorly with the pterygoid venous plexus and posteriorly with the basilar plexus, which in turn communicates with the internal vertebral venous plexus.

Chapter 7: Head

The cerebral falx (L. falx, a sickle‐shaped structure), the largest dural infolding, lies in the longitudinal cerebral fissure that separates the right and left cerebral hemispheres. The cerebral falx attaches in the median plane to the internal surface of the calvaria, from the frontal crest of the frontal bone and crista galli of the ethmoid bone anteriorly to the internal occipital protuberance posteriorly (Figs. 7.10A and 7.11). It ends by becoming continuous with the cerebellar tentorium. The cerebellar tentorium, the second largest dural infolding, is a wide crescentic septum that separates the occipital lobes of the cerebral hemispheres from the cerebellum. The cerebellar tentorium attaches rostrally to the clinoid processes of the sphenoid, rostrolaterally to the petrous part of the temporal bone, and posterolaterally to the internal surface of the occipital bone and part of the parietal bone. The cerebral falx attaches to the cerebellar tentorium and holds it up, giving it a tent‐like appearance (L. tentorium, tent). The cerebellar tentorium divides the cranial cavity into supratentorial and infratentorial compartments. The supratentorial compartment is divided into right and left halves by the cerebral falx. The concave anteromedial border of the cerebellar tentorium is free, producing a gap called the tentorial notch through which the brainstem (midbrain, pons, and medulla oblongata) extends from the posterior into the middle cranial fossa (Fig. 7.12A & B). The cerebellar falx is a vertical dural infolding that lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa (Figs. 7.10A & B and 7.11). It is attached to the internal occipital crest and partially separates the cerebellar hemispheres. The sellar diaphragm, the smallest dural infolding, is a circular sheet of dura that is suspended between the clinoid processes forming a partial roof over the hypophysial fossa in the sphenoid (Fig. 7.10A). The sellar diaphragm covers the pituitary gland in this fossa and has an aperture for passage of the infundibulum and hypophysial veins.

Blunt Trauma to the Head A blow to the head can detach the periosteal layer of dura mater from the calvaria without fracturing the cranial bones. In the cranial base the two dural layers are firmly attached and difficult to separate from the bones. Consequently, a fracture of the cranial base usually tears the dura and results in leakage of CSF. The innermost part of the dura, the dural border cell layer, is composed of flattened fibroblasts that are separated by large extracellular spaces. This layer constitutes a plane of structural weakness at the dura—arachnoid junction (Haines, 2002).

Tentorial Herniation The tentorial notch is the opening in the cerebellar tentorium for the brainstem, which is slightly larger than is necessary to accommodate the midbrain. Hence space‐ occupying lesions, such as tumors in the supratentorial compartment, produce increased intracranial pressure and may cause part of the adjacent temporal lobe of the brain to herniate through the tentorial notch. During tentorial herniation, the temporal lobe may be lacerated by the tough cerebellar tentorium and the oculomotor nerve (CN III) may be stretched, compressed, or both. Oculomotor lesions may produce paralysis of the extrinsic eye muscles supplied by CN III.


Bulging of the Sellar Diaphragm Pituitary tumors may extend superiorly through the aperture in the sellar diaphragm or cause it to bulge. These tumors often expand the sellar diaphragm, producing disturbances in endocrine function early or late (i.e., before or after enlargement of the sellar diaphragm). Superior extension of a tumor may cause visual symptoms owing to pressure on the optic chiasm (L. chiasma opticum), the place where the optic nerve fibers cross.

Figure 7.11. Interior of base of cranium. The internal occipital protuberance is formed in relationship to the confluence of sinuses (Fig. 7.12A), and grooves are formed in the cranial base by the dural venous sinuses (e.g., the sigmoid sinus). The cerebellar tentorium is attached along the lengths of the transverse and superior petrosal sinuses.

Chapter 7: Head

Figure 7.12. Venous sinuses of dura mater. Blood from the brain drains into the sinuses within the dura. A. The brain and part of the calvaria are removed to demonstrate the sinuses related to the cerebral falx and cerebellar tentorium. B. This view of the interior of the base of the cranium demonstrates the most communications of the cavernous sinuses (the inferior communication with the pterygoid venous plexus is a notable exception) and drainage of the confluence of sinuses. The ophthalmic veins drain into the cavernous sinus. C. The orientation and placement of this section of the right cavernous sinus and the body of the sphenoid are indicated in parts A and B. The cavernous sinus is situated bilaterally at the lateral aspect of the hollow body of the sphenoid and the hypophysial fossa. The internal carotid artery, having made an acute bend, is cut twice. Inferiorly, the cavernous part of the artery is sectioned as it passes anteriorly along the carotid groove toward the acute bend of the artery (radiologists refer to the bend as the “carotid siphon” ); superiorly, the cerebral part of the artery is sectioned as it passes posteriorly from the bend to join the cerebral arterial circle. The ophthalmic artery has just arisen from the latter.


Dural Venous Sinuses The dural venous sinuses are endothelium‐lined spaces between the periosteal and the meningeal layers of the dura. They form where the dural septa attach along the free edge of the falx cerebri and in relation to formations of the cranial floor (Figs. 7.10, 7.12, and 7.13). Large veins from the surface of the brain empty into these sinuses and most of the blood from the brain ultimately drains through them into the IJVs (Fig. 7.13). The superior sagittal sinus lies in the convex attached border of the cerebral falx (Fig. 7.10). It begins at the crista galli and ends near the internal occipital protuberance (Fig. 7.11) at the confluence of sinuses, a meeting place of the superior sagittal, straight, occipital, and transverse sinuses (Fig. 7.13). The superior sagittal sinus receives the superior cerebral veins and communicates on each side through slit‐like openings with the lateral venous lacunae, lateral expansions of the superior sagittal sinus (Fig. 7.9). Arachnoid granulations (collections of arachnoid villi) are tufted prolongations of the arachnoid that protrude through the meningeal layer of the dura mater into the dural venous sinuses, especially the lateral lacunae, and effect transfer of CSF to the venous system. Enlarged arachnoid granulations (often called pacchionian bodies) may erode bone, forming pits called granular foveolae in the calvaria (Fig. 7.4B). They are usually observed in the vicinity of the superior sagittal, transverse, and some other dural venous sinuses. Arachnoid granulations are structurally adapted for the transport of CSF from the subarachnoid space to the venous system (see “Subarachnoid Cisterns,” later in this chapter). Figure 7.13. Venograms of dural sinuses. A and B. Radiopaque dye injected into the arterial system has circulated through the capillaries of the brain and collected in the dural venous sinuses, as shown in these radiographic studies. C, confluence of sinuses; I, internal jugular vein; S, sigmoid sinus; T, transverse sinus. In the AP view (A), notice the left‐sided dominance in the drainage of the confluence of sinuses. (Courtesy of Dr. D. Armstrong, Associate Professor of Medical Imaging, University of Toronto, Toronto, Ontario, Canada.)

The inferior sagittal sinus is much smaller than the superior sagittal sinus (Fig. 7.10). It runs in the inferior concave free border of the cerebral falx and ends in the straight sinus. The straight sinus (L. sinus rectus) is formed by the union of the inferior sagittal sinus with the great cerebral vein. It runs inferoposteriorly along the line of

Chapter 7: Head

attachment of the cerebral falx to the cerebellar tentorium, where it joins the confluence of sinuses. The transverse sinuses pass laterally from the confluence of sinuses, forming a groove in the occipital bones and the posteroinferior angles of the parietal bones (Figs. 7.11, 7.12, 7.13). The transverse sinuses course along the posterolateral attached margins of the cerebellar tentorium and then become the sigmoid sinuses as they approach the posterior aspect of the petrous temporal bones. Blood received by the confluence of sinuses is drained by the transverse sinuses, but rarely equally. Usually the left sinus is dominant (larger). The sigmoid sinuses follow S‐shaped courses in the posterior cranial fossa, forming deep grooves in the temporal and occipital bones. Each sigmoid sinus turns anteriorly and then continues inferiorly as the IJV after traversing the jugular foramen. The occipital sinus lies in the attached border of the cerebellar falx and ends superiorly in the confluence of sinuses (Fig. 7.10B). The occipital sinus communicates inferiorly with the internal vertebral venous plexus. The cavernous sinus is located on each side of the sella turcica on the upper surface of the body of the sphenoid, which contains the sphenoid (air) sinus (Figs. 7.10B and 7.12). The cavernous sinus consists of a venous plexus of extremely thin‐walled veins that extends from the superior orbital fissure anteriorly to the apex of the petrous part of the temporal bone posteriorly. It receives blood from the superior and inferior ophthalmic veins, superficial middle cerebral vein, and sphenoparietal sinus. The venous channels in these sinuses communicate with each other through venous channels anterior and posterior to the stalk of the pituitary gland—the intercavernous sinuses (Fig. 7.12A & B)—and sometimes through veins inferior to the pituitary gland. The cavernous sinuses drain posteroinferiorly through the superior and inferior petrosal sinuses and emissary veins to the pterygoid plexuses (Figs. 7.10B and 7.13B). Inside each cavernous sinus is the internal carotid artery with its small branches, surrounded by the carotid plexus of sympathetic nerve(s), and the abducent nerve (CN VI) (Fig. 7.13C). The oculomotor (CN III) and trochlear (CN IV) nerves, plus two of the three divisions of the trigeminal nerve (CN V) are embedded in the lateral wall of the sinus. The artery, carrying warm blood from the body's core, traverses the sinus filled with cooler blood returning from the capillaries of the body's periphery, allowing for heat exchange to conserve energy or cool the arterial blood. This does not appear to be as important in humans as it is in running animals (e.g., horses and cheetahs) in which the carotid artery runs a longer, more tortuous course through the cavernous sinuses, allowing cooling of blood before it enters the brain. Pulsations of the artery within the cavernous sinus are said to promote propulsion of venous blood from the sinus, as does gravity (Williams et al., 1995). The superior petrosal sinuses run from the posterior ends of the veins making up the cavernous sinus to the transverse sinuses at the site where these sinuses curve inferiorly to form the sigmoid sinuses (Fig. 7.13B). Each superior petrosal sinus lies in the anterolateral attached margin of the cerebellar tentorium, which attaches to the superior border (crest) of the petrous part of the temporal bone (Fig. 7.11). The inferior petrosal sinuses also commence at the posterior end of the cavernous sinus inferiorly (Fig. 7.13B). Each inferior petrosal sinus runs in a groove between the petrous part of the temporal bone and the basilar part of the occipital bone (Fig.


7.12). The inferior petrosal sinuses drain the veins of the lateral cavernous sinus directly into the origin of the IJVs. The basilar plexus connects the inferior petrosal sinuses and communicates inferiorly with the internal vertebral venous plexus (Fig. 7.10B). Emissary veins connect the dural venous sinuses with veins outside the cranium. Although they are valveless and blood may flow in both directions, flow in the emissary veins is usually away from the brain. The size and number of emissary veins vary; many small ones are unnamed. A frontal emissary vein is present in children and some adults. It passes through the foramen cecum of the cranium, connecting the superior sagittal sinus with veins of the frontal sinus and nasal cavities. A parietal emissary vein, which may be paired bilaterally, passes through the parietal foramen in the calvaria, connecting the superior sagittal sinus with the veins external to it, particularly those in the scalp (Fig. 7.4C). A mastoid emissary vein passes through the mastoid foramen and connects each sigmoid sinus with the occipital or posterior auricular vein (Fig. 7.14). A posterior condylar emissary vein may also be present, passing through the condylar canal, connecting the sigmoid sinus with the suboccipital plexus of veins.

Occlusion of Cerebral Veins and Dural Venous Sinuses Occlusion of cerebral veins and dural venous sinuses may result from thrombi (clots), thrombophlebitis (venous inflammation), or tumors (e.g., meningiomas). The dural sinuses most frequently thrombosed are the transverse, cavernous, and superior sagittal sinuses (Fishman, 2000a). The facial veins make clinically important connections with the cavernous sinus through the superior ophthalmic veins (Fig. 7.10B). Cavernous sinus thrombosis usually results from infections in the orbit, nasal sinuses, and superior part of the face (the danger triangle). In persons with thrombophlebitis of the facial vein, pieces of an infected thrombus may extend into the cavernous sinus, producing thrombophlebitis of the cavernous sinus. The infection usually involves only one sinus initially but may spread to the opposite side through the intercavernous sinuses. Thrombophlebitis of the cavernous sinus may affect the abducent nerve as it traverses the sinus (see Chapter 9) and may also effect the nerves embedded within the lateral wall of the sinus (Fig. 7.12C). Septic thrombosis of the cavernous sinus often results in the development of acute meningitis.

Metastasis of Tumor Cells to the Dural Sinuses The basilar and occipital sinuses communicate through the foramen magnum with the internal vertebral venous plexuses (Fig. 7.10B). Because these venous channels are valveless, compression of the thorax, abdomen, or pelvis, as occurs during heavy coughing and straining, may force venous blood from these regions into the internal vertebral venous system and from it into the dural venous sinuses. As a result, pus in abscesses and tumor cells in these regions may spread to the vertebrae and brain.

Fractures of the Cranial Base In fractures of the cranial base, the internal carotid artery may be torn, producing an arteriovenous fistula within the sinus. Arterial blood rushes into the cavernous sinus, enlarging it and forcing retrograde blood flow into its venous tributaries, especially the ophthalmic veins. As a result, the eyeball protrudes (exophthalmos) and the

Chapter 7: Head

conjunctiva becomes engorged (chemosis). The protruding eyeball pulsates in synchrony with the radial pulse, a phenomenon known as pulsating exophthalmos. Because CN III, CN IV, CN V 1 , CN V 2 , and CN VI lie in or close to the lateral wall of the cavernous sinus, these nerves may also be affected when the sinus is injured (Fig. 7.12C). Figure 7.14. Deep dissection of suboccipital region. The external vertebral venous system has numerous intercommunications and connections, some of which are shown here. Superiorly, the system communicates with the veins of the scalp and the intracranial venous sinuses via the foramen magnum, the mastoid foramina, and the condylar canals. Anteromedially, it passes between the laminae and through the intervertebral foramina to communicate with the internal vertebral venous plexus and veins around the vertebral artery. Inferiorly, it drains via the deep cervical vein.

Vasculature of the Dura Mater The arteries of the dura supply more blood to the calvaria than to the dura. The largest of these vessels, the middle meningeal artery, is a branch of the maxillary artery (Fig. 7.9). It enters the floor of the middle cranial fossa through the foramen spinosum, runs laterally in the fossa, and turns superoanteriorly on the greater wing of the sphenoid, where it divides into anterior and posterior branches. The anterior branch of the middle meningeal artery runs superiorly to the pterion and then curves posteriorly to ascend toward the vertex of the cranium. The posterior branch of the middle meningeal artery runs posterosuperiorly and ramifies (breaks up into distributing branches) over the posterior aspect of the cranium. Small areas of dura are supplied by other arteries: meningeal branches of the ophthalmic arteries, branches of the occipital arteries, and small branches of the vertebral arteries. The veins of the dura accompany the meningeal arteries, often in pairs (Fig. 7.9). The middle meningeal veins accompany the middle meningeal artery, leave the cranial cavity through the foramen spinosum or foramen ovale, and drain into the pterygoid plexus (Fig. 7.10B).


Nerve Supply of the Dura Mater The dura of the floors of the anterior and middle cranial fossa and the roof of the posterior cranial fossa is innervated by meningeal branches arising directly or indirectly from the trigeminal nerve (CN V) (Fig. 7.15). There are three divisions of CN V (CN V 1 , CN V 2 , and CN V 3 ), each of which contributes a meningeal branch or branches. The anterior meningeal branches of the ethmoidal nerves (CN V 1 ) and the meningeal branches of the maxillary (CN V 2 ) and mandibular (CN V 3 ) nerves supply the dura of the anterior cranial fossa. The latter two nerves also supply the dura of the middle cranial fossa (Fig. 7.15B). The meningeal branches of CN V 2 and CN V 3 are distributed as periarterial plexuses accompanying the branches of the middle meningeal artery (Fig. 7.15A, inset). The dura forming the roof of the posterior cranial fossa (tentorium cerebelli) and posterior part of the cerebral falx is supplied by the tentorial nerve (a branch of the ophthalmic nerve), whereas the anterior cerebral falx is innervated by ascending branches of the anterior meningeal branches (Fig. 7.15A). The dura of the floor of the posterior cranial fossa receives sensory fibers from the spinal ganglia of C2 and C3 carried by those spinal nerves or by fibers transferred to and traveling centrally with the vagus (CN X) and hypoglossal (CN XII) nerves. Sensory endings are more numerous in the dura along each side of the superior sagittal sinus and in the cerebellar tentorium than they are in the floor of the cranium. Pain fibers are most numerous where arteries and veins course in the dura. Pain arising from the dura is generally referred, perceived as a headache arising in cutaneous or mucosal regions supplied by the involved cervical nerve or division of the trigeminal nerve.

Dural Origin of Headaches The dura is sensitive to pain, especially where it is related to the dural venous sinuses and meningeal arteries. Consequently, pulling on arteries at the cranial base or veins near the vertex where they pierce the dura causes pain. Distension of the scalp or meningeal vessels (or both) is believed to be one cause of headache (Raskin, 2000). Many headaches appear to be dural in origin, such as the headache occurring after a lumbar spinal puncture for removal of CSF (see Chapter 4). These headaches are thought to result from stimulation of sensory nerve endings in the dura. When CSF is removed, the brain sags slightly, pulling on the dura; this may also cause a headache. For this reason, patients are asked to keep their heads down after a lumbar puncture to minimize the pull on the dura, reducing the chances of getting a headache.

Leptomeninx (Arachnoid Mater and Pia Mater) The arachnoid mater and pia mater (arachnoid—pia) develop from a single layer of mesenchyme surrounding the embryonic brain, becoming the parietal part (arachnoid mater) and visceral part (pia mater) of the leptomeninx. CSF‐filled spaces form within this layer and coalesce to form the subarachnoid or leptomeningeal space (Fig. 7.16). The derivation of the arachnoid—pia from a single embryonic layer is indicated in the adult by the numerous web‐like arachnoid trabeculae passing between the arachnoid and the pia, which give the arachnoid its name (G. arachnÄ“, spider, cobweb + G. eidos, resemblance). The trabeculae are composed of flattened, irregularly shaped fibroblasts that bridge the subarachnoid space (Haines, 2002). The arachnoid and pia

Chapter 7: Head

are in continuity immediately proximal to the exit of each cranial nerve from the dura mater. The arachnoid mater contains fibroblasts, collagen fibers, and some elastic fibers. Although thin, the arachnoid is thick enough to be manipulated with forceps. The avascular arachnoid, although closely applied to the meningeal layer of the dura, is not attached to the dura; it is held against the inner surface of the dura by the pressure of the CSF. The pia mater is an even thinner membrane that is highly vascularized by a network of fine blood vessels. The pia is difficult to see, but it gives the surface of the brain a shiny appearance. The pia adheres to the surface of the brain and follows all its contours. When the cerebral arteries penetrate the cerebral cortex, the pia follows them for a short distance, forming a pial coat and a periarterial space (Fig. 7.16).

Meningeal Spaces Of the three meningeal “spaces” commonly mentioned in relation to the cranial meninges, only one exists as a space in the absence of pathology: 

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The dura—cranial interface (extradural or epidural “space” ) is not a natural space between the cranium and the external periosteal layer of the dura because the dura is attached to the bones. It becomes a space only pathologically, for example, when blood from torn meningeal vessels pushes the periosteum away from the cranium (Fig. 7.8C). The potential or pathological cranial epidural space is not continuous with the spinal epidural space (a natural space occupied by epidural fat and a venous plexus) because the former is external to the periosteum lining the cranium and the latter is internal to the periosteum covering the vertebrae. The dura—arachnoid junction or interface (“subdural space” ) is likewise not a natural space between the dura and the arachnoid. A space may develop in the dural border cell layer as the result of trauma, such as after a blow to the head (Haines, 2002). The subarachnoid space, between the arachnoid and the pia, is a real space that contains CSF, trabecular cells, arteries, and veins.

Although it is commonly stated that the brain “floats” in CSF, the brain is suspended in the CSF‐filled subarachnoid space by the arachnoid trabeculae.


Figure 7.15. Innervation of dura mater. The dura of the floor of the anterior and middle cranial fossa and the roof of the posterior cranial fossa is innervated by meningeal branches arising directly or indirectly from the trigeminal nerve (CN V). A. The right side of the calvaria and brain is removed and CN V is dissected. The cerebral falx is innervated by the ophthalmic nerve (CN V 1 ), through anterior meningeal branches of the ethmoid nerves and the tentorial nerve. The meningeal branches of the maxillary (CN V 2 ) and mandibular (CN V 3 ) nerves are distributed to the dura of the lateral part of the anterior and the middle cranial fossae as periarterial plexuses that accompany the branches of the middle meningeal artery along with vasomotor sympathetic nerve fibers from the superior cervical ganglion (inset). The dura of the cranial base is most sensitive in the region of the arterial branches and the superior sagittal sinus. B. The internal aspect of the cranial base shows innervation of the dura by branches of the trigeminal and sensory fibers of cervical spinal nerves (C2, C3) passing directly from those nerves or via meningeal branches of the vagus (CN X) and hypoglossal (CN XII) nerves.

Chapter 7: Head

Leptomeningitis Leptomeningitis is an inflammation of the leptomeninges resulting from pathogenic microorganisms. The infection and inflammation are usually confined to the subarachnoid space and the arachnoid—pia (Miller and Jubelt, 2000). The bacteria may enter the subarachnoid space through the blood (septicemia, or “blood poisoning” ) or spread from an infection of the heart, lungs, or other viscera. Microorganisms may also enter the subarachnoid space from a compound cranial fracture or a fracture of the nasal sinuses. Acute purulent meningitis can result from infection with almost any pathogenic bacteria (e.g., meningococcal meningitis).

Head Injuries and Intracranial Hemorrhage Extradural or epidural hemorrhage is arterial in origin. Blood from torn branches of a middle meningeal artery collects between the external periosteal layer of the dura and the calvaria, usually following a hard blow to the head, and forms an extradural or epidural hematoma (Fig. B7.13A). Typically, a brief concussion (loss of consciousness) occurs, followed by a lucid interval of some hours. Later, drowsiness and coma (profound unconsciousness) occur. Compression of the brain occurs as the blood mass increases, necessitating evacuation of the blood and occlusion of the bleeding vessels. A dural border hematoma is classically called a subdural hematoma (Fig. B7.13B); however, this term is a misnomer because there is no naturally occurring space at the dura—arachnoid junction. Hematomas at this junction are usually caused by extravasated blood that splits open the dural border cell layer. The blood does not collect within a pre‐existing space, but rather creates a space at the dura—arachnoid junction (Haines, 2002). Dural border hemorrhage usually follows a blow to the head that jerks the brain inside the cranium and injures it. The precipitating trauma may be trivial or forgotten. Dural border hemorrhage is typically venous in origin and commonly results from tearing a superior cerebral vein as it enters the superior sagittal sinus (Fig. 7.10B) (Haines et al., 1993).


Figure B7.13. Intercranial hemorrhages. A. An extradural (epidural) hemorrhage is shown. B. A dural border (subdural) hematoma is shown. C. A subarachnoid hemorrhage is shown.

Subarachnoid hemorrhage is an extravasation (escape) of blood, usually arterial, into the subarachnoid space (Fig. B7.13C). Most subarachnoid hemorrhages result from rupture of a saccular aneurysm (sac‐like dilation on the side of an artery), such as an aneurysm of the internal carotid artery (see clinical correlation [blue] box “Strokes,” later in this chapter). Some subarachnoid hemorrhages are associated with head trauma involving cranial fractures and cerebral lacerations. Bleeding into the subarachnoid space results in meningeal irritation, a severe headache, stiff neck, and often loss of consciousness.

Chapter 7: Head

Figure 7.16. Section of scalp, calvaria, and cranial meninges. The coronal section (left) indicates the site of the tissue block (right). The subarachnoid space separates the arachnoid mater and pia mater. The main site of absorption of CSF into the venous system is through the arachnoid granulations projecting into the dural venous sinuses, especially the superior sagittal sinus and adjacent venous lacunae (Fig. 7.9).

The Bottom Line The meninges consist of three intracranial layers: a substantial, fibrous bilaminar outer layer—the dura mater—and two continuous, delicate, membranous inner layers—the arachnoid mater and pia mater. The outer (periosteal) lamina of the dura mater is continuous with the external periosteum of the cranium and is intimately applied to the internal surface of the cranial cavity. The inner (meningeal) lamina is a sustentacular (supporting) layer that more closely reflects the contours of the brain. It leaves the outer layer in certain locations to form dural folds or reflections that penetrate the large fissures between parts of the brain, partially subdividing the cranial cavity into smaller compartments that prevent inertial brain movement. In separating from the periosteal lamina, intralaminar spaces are created that accommodate the dural venous sinuses, which receive the venous drainage of the brain and mainly drain, in turn, to the IJV. The arachnoid and pia are the continuous parietal and visceral layers, respectively, of the leptomeninx that surround the CSF‐filled subarachnoid space. They are connected by fine trabeculae that traverse the space. The subarachnoid space of the cranial cavity is continuous with that of the vertebral canal. The arachnoid is normally applied to the internal surface of the dura by CSF pressure. The pia intimately invests the neural tissue and its surface vasculature, coursing deeply along the vessels as they enter or exit the central nervous system. The cranial meninges receive blood primarily from the middle meningeal branches of the maxillary arteries. The dura receives sensory innervation from meningeal branches of all three divisions of the trigeminal nerve and fibers from the C2 spinal ganglion.


Brain Because the brain is usually studied in detail in a separate neuroanatomy course, the brain is covered by only a superficial survey of the gross structure in the typical anatomy course, with attention primarily concerned with the relationship between the brain and its environment—that is, its meningeal coverings, the CSF‐filled subarachnoid space, and internal features of its bony encasement (the neurocranium). Because of their role in the production of CSF, the ventricles of the brain and the CSF‐producing choroid plexuses found there are also covered. Furthermore, 11 of 12 cranial nerves arise from the brain (see Chapter 9).

Parts of the Brain The brain is composed of the cerebrum, cerebellum, and brainstem (Fig. 7.17). When the calvaria and dura are removed, gyri (folds), sulci (grooves), and fissures (clefts) of the cerebral cortex are visible through the delicate arachnoid—pia layer. Whereas the gyri and sulci demonstrate much variation, the other features of the brain, including overall brain size, are remarkably consistent from individual to individual. 

 

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The cerebrum (L. brain) includes the cerebral hemispheres and basal ganglia. The cerebral hemispheres, separated by the cerebral falx within the longitudinal cerebral fissure, are the dominant features of the brain (Fig. 7.17A & B). Each cerebral hemisphere is divided for descriptive purposes into four lobes, each of which is related to, but the boundaries of which do not correspond to, the overlying bones of the same name. From a superior view, the cerebrum is essentially divided into quarters by the median longitudinal cerebral fissure and the coronal central sulcus. The central sulcus separates frontal lobes (anteriorly) from parietal lobes (posteriorly). In a lateral view, these lobes lie superior to the transverse lateral sulcus and the temporal lobe inferior to it. The posteriorly placed occipital lobes are separated from the parietal and temporal lobes by the plane of the parieto‐occipital sulcus, visible on the medial surface of the cerebrum in a hemisected brain (Fig. 7.17C). The anteriormost points of the anteriorly projecting frontal and temporal lobes are the frontal and temporal poles. The posteriormost point of the posteriorly projecting occipital lobe is the occipital pole. The hemispheres occupy the entire supratentorial cranial cavity. The frontal lobes occupy the anterior cranial fossae, the temporal lobes occupy the lateral parts of the middle cranial fossae, and the occipital lobes extend posteriorly over the cerebellar tentorium. The diencephalon is composed of the epithalamus, dorsal thalamus, and hypothalamus and forms the central core of the brain. The midbrain, the rostral part of the brainstem, lies at the junction of the middle and posterior cranial fossae. CN III and IV are associated with the midbrain. The pons is the part of the brainstem between the midbrain rostrally and the medulla oblongata caudally; it lies in the anterior part of the posterior cranial fossa. CN V is associated with the pons (Fig. 7.17A & C).

Chapter 7: Head 

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The medulla oblongata (medulla) is the most caudal subdivision of the brainstem that is continuous with the spinal cord; it lies in the posterior cranial fossa. CN IX, X, and XII are associated with the medulla, whereas CN VI—VIII are associated with the junction of pons and medulla. The cerebellum is the large brain mass lying posterior to the pons and medulla and inferior to the posterior part of the cerebrum. It lies beneath the cerebellar tentorium in the posterior cranial fossa. It consists of two lateral hemispheres that are united by a narrow middle part, the vermis.

Cerebral Injuries Cerebral concussion is an abrupt, brief loss of consciousness immediately after a head injury. Consciousness may be lost for only 8—10 sec, as occurs in a knockdown during boxing. With a more severe injury, such as that resulting from an automobile accident, consciousness may be lost for hours and even days. If a person recovers consciousness within 6 hr, the long‐term outcome is excellent (Rowland, 2000). If the coma lasts longer than 6 hr, brain tissue injury usually occurs. Professional boxers are especially at risk for chronic traumatic encephalopathy, or punchdrunk syndrome, a brain injury characterized by weakness in the lower limbs, unsteady gait, slowness of muscular movements, tremors of the hands, hesitancy of speech, and slow cerebration (use of one's brain). The injuries result from acceleration and deceleration of the head that shears or stretches axons (diffuse axonal injury). The sudden stopping of the moving head results in the brain hitting the suddenly stationary cranium. Cerebral contusion results from brain trauma in which the pia is stripped from the injured surface of the brain and may be torn, allowing blood to enter the subarachnoid space. The bruising results either from the sudden impact of the still‐ moving brain against the suddenly stationary cranium or from the suddenly moving cranium against the still‐stationary brain. Cerebral contusion may result in an extended loss of consciousness, but if there is no diffuse axonal injury, brain swelling, or secondary hemorrhage, recovery from a contusion may be excellent (Rowland, 2000). Cerebral lacerations are often associated with depressed cranial fractures or gunshot wounds. Lacerations result in rupture of blood vessels and bleeding into the brain and subarachnoid space, causing increased intracranial pressure and cerebral compression. Cerebral compression may be produced by:    

Intracranial collections of blood. Obstruction of CSF circulation or absorption. Intracranial tumors or abscesses. Brain swelling caused by brain edema, an increase in brain volume resulting from an increase in water and sodium content (Fishman, 2000b).


Figure 7.17. Structure of brain. A. Whereas distinct central and lateral sulci demarcate the frontal lobe and anterior boundaries of the parietal and temporal lobes of the cerebrum, the demarcation of the posterior boundaries of the latter and the occipital lobe is less distinct externally. The cerebral surface has gyri (folds) and sulci (grooves). B. The lobes of the cerebrum are color coded. C. The medial surface of the cerebrum and deeper parts of the brain (diencephalon and brainstem) are shown after bisection of the brain. The parieto‐occipital sulcus demarcating the parietal and occipital lobes can be seen on the medial aspect of the cerebrum.

Ventricular System of the Brain The ventricular system of the brain consists of two lateral ventricles and the midline 3rd and 4th ventricles connected by the cerebral aqueduct (Fig. 7.18). CSF, largely secreted by the choroid plexuses of the ventricles, fills these brain cavities and the subarachnoid space of the brain and spinal cord.

Chapter 7: Head

Ventricles of the Brain The lateral ventricles, the 1st and 2nd ventricles, are the largest cavities of the ventricular system and occupy large areas of the cerebral hemispheres. Each lateral ventricle opens through an interventricular foramen into the 3rd ventricle. The 3rd ventricle, a slit‐like cavity between the right and the left halves of the diencephalon, is continuous posteroinferiorly with the cerebral aqueduct, a narrow channel in the midbrain connecting the 3rd and 4th ventricles (Fig. 7.18B). The pyramid‐shaped 4th ventricle in the posterior part of the pons and medulla extends inferoposteriorly. Inferiorly, it tapers to a narrow channel that continues into the cervical region of the spinal cord as the central canal (Fig. 7.18A). CSF drains into the subarachnoid space from the 4th ventricle through a single median aperture and paired lateral apertures. These apertures are the only means by which CSF enters the subarachnoid space. If they are blocked, CSF accumulates and the ventricles distend, producing compression of the substance of the cerebral hemispheres.

Subarachnoid Cisterns Although it is not accurate to say that the brain “floats” in the CSF, the brain actually has minimal attachment to the neurocranium. At certain areas on the base of the brain, the arachnoid and pia are widely separated by subarachnoid cisterns (Fig. 7.18B), which contain CSF, and soft tissue structures that “anchor” the brain, such as the arachnoid trabeculae, vasculature, and in some cases, cranial nerve roots. The cisterns are usually named according to the structures related to them. Major intracranial subarachnoid cisterns include the: 

   

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Cerebellomedullary cistern: The largest of the subarachnoid cisterns, located between the cerebellum and the medulla, and receives CSF from the apertures of the 4th ventricle. It is divided into the posterior cerebellomedullary cistern (L. cisterna magna) and the lateral cerebellomedullary cistern. Pontocerebellar cistern (pontine cistern): An extensive space ventral to the pons, continuous inferiorly with the spinal subarachnoid space. Interpeduncular cistern (basal cistern): Located in the interpeduncular fossa between the cerebral peduncles of the midbrain. Chiasmatic cistern: Inferior and anterior to optic chiasm, the point of crossing or decussation of optic nerve fibers. Quadrigeminal cistern (cistern of the great cerebral vein): Located between the posterior part of the corpus callosum and the superior surface of the cerebellum. It contains parts of the great cerebral vein. Ambient cistern (L. cisterna ambiens): Located on the lateral aspect of the midbrain and continuous posteriorly with the quadrigeminal cistern.

Secretion of Cerebrospinal Fluid CSF is secreted (at the rate of 400—500 mL daily) by choroidal epithelial cells (modified ependymal cells) of the choroid plexuses in the lateral, 3rd, and 4th ventricles (Figs. 7.17C and 7.18). The choroid plexuses consist of vascular fringes of pia mater (tela choroidea) covered by cuboidal epithelial cells. They are invaginated into the roofs of the 3rd and 4th ventricles and on the floors of the bodies and inferior horns of the lateral ventricles.


Circulation of Cerebrospinal Fluid CSF leaves the lateral ventricles through the interventricular foramina and enters the 3rd ventricle (Fig. 7.18A). From here, CSF passes through the cerebral aqueduct into the 4th ventricle. Some CSF leaves this ventricle through its median and lateral apertures and enters the subarachnoid space, which is continuous around the spinal cord and posterosuperiorly over the cerebellum. However, most CSF flows into the interpeduncular and quadrigeminal cisterns. CSF from the various subarachnoid cisterns flows superiorly through the sulci and fissures on the medial and superolateral surfaces of the cerebral hemispheres. CSF also passes into the extensions of the subarachnoid space around the cranial nerves, the most important of which are those surrounding the optic nerves. Figure 7.18. Ventricles, subarachnoid spaces, and cisterns. A. The ventricular system and circulation of the CSF are shown. The production of CSF is mainly by the choroid plexuses of the lateral, 3rd, and 4th ventricles. The plexuses of the lateral ventricles are the largest and most important. CSF is absorbed into the venous system through the arachnoid granulations that project into the superior sagittal sinus and its lateral lacunae. B. The subarachnoid cisterns, expanded regions of the subarachnoid space, contain more substantial amounts of CSF.

Chapter 7: Head

Absorption of Cerebrospinal Fluid The main site of CSF absorption into the venous system is through the arachnoid granulations (Figs. 7.16 and 7.18A), especially those that protrude into the superior sagittal sinus and its lateral lacunae (Fig. 7.9). The subarachnoid space containing CSF extends into the cores of the arachnoid granulations. CSF enters the venous system through two routes: (1) most CSF enters the venous system by transport through the cells of the arachnoid granulations into the dural venous sinuses; (2) some CSF moves between the cells making up the arachnoid granulations (Corbett et al., 2002).

Functions of Cerebrospinal Fluid Along with the meninges and calvaria, CSF protects the brain by providing a cushion against blows to the head. The CSF in the subarachnoid space provides the buoyancy that prevents the weight of the brain from compressing the cranial nerve roots and blood vessels against the internal surface of the cranium. Because the brain is slightly heavier than the CSF, the gyri on the basal surface of the brain are in contact with the cranial fossae in the floor of the cranial cavity when a person is standing erect. In many places at the base of the brain, only the cranial meninges intervene between the brain and the cranial bones. In the erect position, the CSF is in the subarachnoid cisterns and sulci on the superior and lateral parts of the brain; therefore, CSF and dura normally separate the superior part of the brain from the calvaria. Small, rapidly recurring changes take place in intracranial pressure owing to the beating heart; slow recurring changes result from unknown causes. Momentarily large changes in pressure occur during coughing and straining and during changes in position (erect vs. supine). Any change in the volume of the intracranial contents (e.g., a brain tumor, an accumulation of ventricular fluid caused by blockage of the cerebral aqueduct, or blood from a ruptured aneurysm) will be reflected by a change in intracranial pressure. This rule is called the Monro‐Kellie doctrine, which states that the cranial cavity is a closed rigid box and that a change in the quantity of intracranial blood can occur only through the displacement or replacement of CSF.

Cisternal Puncture CSF may be obtained from the posterior cerebellomedullary cistern through a cisternal puncture for diagnostic or therapeutic purposes. The needle is carefully inserted through the posterior atlanto‐occipital membrane into the cistern. The subarachnoid space or the ventricular system may also be entered for measuring or monitoring CSF pressure, injecting antibiotics, or administering contrast media for medical imaging. The cerebellomedullary cistern is the site of choice in infants and young children; the lumbar cistern is used most frequently in adults (see Chapter 4).

Hydrocephalus Overproduction of CSF, obstruction of CSF flow, or interference with CSF absorption results in excess fluid in the cerebral ventricles and enlargement of the head, a condition called obstructive hydrocephalus (Fig. B7.14A). The excess CSF dilates the ventricles, thins the cerebral cortex, and separates the bones of the calvaria in


infants. Although an obstruction can occur any place, the blockage usually occurs in the cerebral aqueduct (Fig. B7.14B) or an interventricular foramen. Aqueductal stenosis (narrow aqueduct) may be caused by a nearby tumor in the midbrain or by cellular debris following intraventricular hemorrhage or bacterial and fungal infections of the central nervous system (Corbett et al., 2002). Blockage of CSF circulation results in dilation of the ventricles superior to the point of obstruction and in pressure on the cerebral hemispheres. This condition squeezes the brain between the ventricular fluid and the calvarial bones. In infants, the internal pressure results in expansion of the brain and calvaria because the sutures and fontanelles are still open. It is possible to produce an artificial drainage system to bypass the blockage and allow CSF to escape, thereby lessening damage to the brain. In communicating hydrocephalus, the flow of CSF through the ventricles and into the subarachnoid space is not impaired; however, movement of CSF from this space into the venous system is partly or completely blocked. The blockage may be caused by the congenital absence of arachnoid granulations, or the granulations may be blocked by red blood cells as the result of a subarachnoid hemorrhage (Corbett et al., 2002).

Leakage of Cerebrospinal Fluid Fractures in the floor of the middle cranial fossa may result in CSF leakage from the external acoustic meatus (CSF otorrhea) if the meninges superior to the middle ear are torn and the tympanic membrane is ruptured. Fractures in the floor of the anterior cranial fossa may involve the cribriform plate of the ethmoid, resulting in CSF leakage through the nose (CSF rhinorrhea). CSF can be distinguished from mucus by testing its glucose level; the glucose level of the CSF reflects that of the blood. CSF otorrhea and rhinorrhea may be the primary indications of a cranial base fracture and increase the risk of meningitis because an infection could spread to the meninges from the ear or nose (Rowland, 2000).

Figure B7.14. Hydrocephalus (A) and aqueductal stenosis (B).

Chapter 7: Head

The Bottom Line The two hemispheres of the cerebral cortex, separated by the cerebral falx, are the dominant features of the human brain. Although the pattern of gyri and sulci are highly variable, other features of the brain, including overall brain size, are remarkably consistent from individual to individual. Each cerebral hemisphere is divided for descriptive purposes into four lobes that are related to, but the boundaries of which do not correspond to, the overlying bones of the same name. The diencephalon forms the central core of the brain, with the midbrain, pons, and medulla oblongata making the brainstem; the medulla is continuous with the spinal cord. The cerebellum is the subtentorial brain mass occupying the posterior cranial fossa. Each cerebral hemisphere includes a lateral ventricle in its core; otherwise, the ventricular system of the brain is an unpaired, median formation that communicates with the subarachnoid space that surrounds brain and spinal cord. Choroid plexuses secrete CSF into the ventricles, which flows out of them into the subarachnoid space. CSF is absorbed into the venous system, normally at the same rate at which it is produced, by the arachnoid granulations related to the superior sagittal sinus.

Arterial Blood Supply of the Brain Although it accounts for only about 2.5% of body weight, the brain receives about one sixth of the cardiac output and one fifth of the oxygen consumed by the body at rest. The blood supply to the brain is derived from the internal carotid and vertebral arteries (Figs. 7.19, 7.20, 7.21; Table 7.3), which lie in the subarachnoid space. Venous drainage occurs via cerebral and cerebellar veins that drain to the adjacent dural venous sinuses.

Internal Carotid Arteries The internal carotid arteries arise in the neck from the common carotid arteries. The cervical part of the artery ascends vertically through the neck, without branching, to the cranial base. Each internal carotid artery enters the cranial cavity through the carotid canals in the petrous part of the temporal bones. The intracranial course of the internal carotid artery is illustrated and described in Figure 7.19 and demonstrated radiographically in Figure 7.20. In addition to the carotid arteries, the carotid canals contain venous plexuses and carotid plexuses of sympathetic nerves. The internal carotid arteries course anteriorly through the cavernous sinuses, with the abducent nerves (CN VI) and in close proximity to the oculomotor (CN III) and trochlear (CN IV) nerves, running in the carotid groove on the side of the body of the sphenoid (Fig. 7.12). The terminal branches of the internal carotids are the anterior and middle cerebral arteries (Figs. 7.20 and 7.21; Table 7.3).


Figure 7.19. Course of internal carotid artery. The orientation drawing (left) indicates the plane of the coronal section that intersects the carotid canal (right). The cervical part of the internal carotid artery ascends vertically in the neck to the entrance of the carotid canal in the petrous temporal bone. The petrous part of the artery turns horizontally and medially in the carotid canal, toward the apex of the petrous temporal bone. It emerges from the canal superior to the foramen lacerum, closed in life by a cartilage plate, and enters the cranial cavity. The artery runs anteriorly across the cartilaginous plate; then the cavernous part of the artery runs along the carotid grooves on the lateral side of the body of the sphenoid, traversing the cavernous sinus. Inferior to the anterior clinoid process, the artery makes a 180° turn, its cerebral part heading posteriorly to join the cerebral arterial circle (Fig. 7.21).

Figure 7.20. Carotid arteriogram. Radiopaque dye was injected into the carotid arterial system before the radiograph was taken. The four parts of the internal carotid artery (I), from inferior to superior, are the cervical part (in the neck), the petrous part (in the carotid canal of the petrous temporal bone), the cavernous part (in the cavernous sinus), and the cerebral part (in the cranial subarachnoid space). A, anterior cerebral artery and its branches; M, middle cerebral artery and its branches; O, ophthalmic artery. See also Figure 7.83. (Courtesy of Dr. D. Armstrong, Associate Professor of Medical Imaging, University of Toronto, Ontario, Canada.)

Chapter 7: Head

Figure 7.21. Base of brain with cerebral arterial circle. The three arteries that converge and anastomose to supply the brain are the right and left internal carotid arteries and the basilar artery; the latter is formed by the union of the two vertebral arteries. The three arteries form the arterial circle (of Willis) through the linkages provided by the anterior communicating artery and the two posterior communicating arteries. The cerebellum is mainly supplied by branches from the vertebral and basilar arteries. The left temporal pole is removed to show the middle cerebral artery in the lateral sulcus of the brain. The frontal lobes are separated to expose the anterior cerebral arteries.

Table 7.3 Arterial Supply of the Cerebral Hemispheres


Artery Internal carotid

Anterior cerebral Anterior communicating Middle cerebral

Vertebral Basilar Posterior cerebral Posterior communicating

Origin Common carotid artery at superior border of thyroid cartilage Internal carotid artery Anterior cerebral artery Continuation of internal carotid artery distal to anterior cerebral artery Subclavian artery Formed by union of vertebral arteries Terminal branch of basilar artery Posterior cerebral artery

Distribution Gives branches to walls of cavernous sinus, pituitary gland, and trigeminal ganglion; provides primary supply to brain Cerebral hemispheres, except for occipital lobes Cerebral arterial circle (of Willis) Most of lateral surface of cerebral hemispheres

Cranial meninges and cerebellum Brainstem, cerebellum, and cerebrum Inferior aspect of cerebral hemisphere and occipital lobe Optic tract, cerebral peduncle, internal capsule, and thalamus

Clinically, the internal carotids and their branches are often referred to as the anterior circulation of the brain. The anterior cerebral arteries are connected by the anterior communicating artery. Near their termination, the internal carotid arteries are joined to the posterior cerebral arteries by the posterior communicating arteries, completing the cerebral arterial circle around the interpeduncular fossa, the deep depression on the inferior surface of the midbrain between the cerebral peduncles.

Vertebral Arteries The vertebral arteries begin in the root of the neck (the prevertebral parts of the vertebral arteries) as the first branches of the first part of the subclavian arteries. The two vertebral arteries are usually unequal in size, the left being larger than the right. The cervical parts of the vertebral arteries ascend through the transverse foramina of the first six cervical vertebrae. The atlantic parts of the vertebral arteries (parts related to the atlas, vertebra C1) perforate the dura and arachnoid and pass through the foramen magnum (Fig. 7.10A). The intracranial parts of the vertebral arteries unite at the caudal border of the pons to form the basilar artery (Fig. 7.20; Table 7.3). The vertebrobasilar arterial system and its branches are often referred to clinically as the posterior circulation of the brain. The basilar artery, so‐named because of its close relationship to the cranial base, ascends the clivus, the sloping surface from the dorsum sellae to the foramen magnum, through the pontocerebellar cistern to the superior border of the pons. It ends by dividing into the two posterior cerebral arteries.

Chapter 7: Head

Cerebral Arteries In addition to supplying branches to deeper parts of the brain, the cortical branches of each cerebral artery supply a surface and a pole of the cerebrum (Table 7.3). The cortical branches of the:   

Anterior cerebral artery supply most of the medial and superior surfaces of the brain and the frontal pole. Middle cerebral artery supply the lateral surface of the brain and the temporal pole. Posterior cerebral artery supply the inferior surface of the brain and the occipital pole.

Anastomoses of Cerebral Arteries and Cerebral Embolism Branches of the three cerebral arteries anastomose with each other on the surface of the brain; however, if a cerebral artery is obstructed by a cerebral embolism (e.g., a blood clot), these microscopic anastomoses are not capable of providing enough blood for the area of cerebral cortex concerned. Consequently, cerebral ischemia and infarction occur and an area of necrosis results. Large cerebral emboli occluding major cerebral vessels may cause severe neurologic problems and death (Haines, 2002; Rowland, 2000).

Cerebral Arterial Circle The cerebral arterial circle (of Willis) is a roughly pentagon‐shaped circle of vessels on the ventral surface of the brain. It is an important anastomosis at the base of the brain between the four arteries (two vertebral and two internal carotid arteries) that supply the brain (Fig. 7.20; Table 7.3). The arterial circle is formed sequentially in an anterior to posterior direction by the:     

Anterior communicating artery. Anterior cerebral arteries. Internal carotid arteries. Posterior communicating arteries. Posterior cerebral arteries.

The various components of the cerebral arterial circle give numerous small branches to the brain.

Variations of the Cerebral Arterial Circle Variations in the size of the vessels forming the cerebral arterial circle are common. The posterior communicating arteries are absent in some individuals; in others there may be two anterior communicating arteries. In approximately 1 in 3 persons, one posterior cerebral artery is a major branch of the internal carotid artery. One of the anterior cerebral arteries is often small in the proximal part of its course; the anterior communicating artery is larger than usual in these individuals.


Strokes An ischemic stroke denotes the sudden development of focal neurological deficits that are usually related to impaired cerebral blood flow. An ischemic stroke is generally caused by an embolism in a major cerebral artery. Strokes are the most common neurologic disorders affecting adults in the United States (Sacco, 2000); they are more often disabling than fatal. The cardinal feature of a stroke is the sudden onset of neurological symptoms. The cerebral arterial circle is an important means of collateral circulation in the event of gradual obstruction of one of the major arteries forming the circle. Sudden occlusion, even if only partial, results in neurological deficits. In elderly persons, the anastomoses of the arterial circle are often inadequate when a large artery (e.g., the internal carotid) is occluded, even if the occlusion is gradual (in which case function is impaired at least to some degree). The most common causes of strokes are spontaneous cerebrovascular accidents, such as cerebral thrombosis, cerebral hemorrhage, cerebral embolism, and subarachnoid hemorrhage (Rowland, 2000). Hemorrhagic stroke follows the rupture of an artery or a saccular aneurysm, a sac‐ like dilation on a weak part of the arterial wall (Fig. B7.15A). The most common type of saccular aneurysm is a berry aneurysm, occurring in the vessels of or near the cerebral arterial circle and the medium arteries at the base of the brain (Fig. B7.15B). Aneurysms also occur at the bifurcation of the basilar artery into the posterior cerebral arteries. In time, especially in individuals with hypertension (high blood pressure), the weak part of the wall of the aneurysm expands and may rupture (Fig. B7.15C), allowing blood to enter the subarachnoid space. Sudden rupture of an aneurysm usually produces a severe, almost unbearable headache and a stiff neck. These symptoms result from gross bleeding into the subarachnoid space.

Brain Infarction An atherosclerotic plaque at a bend of an artery (e.g., at the bifurcation of a common carotid artery) results in progressive narrowing (stenosis) of the artery, producing increasingly severe neurologic deficits (Fig. B7.16). An embolus separates from the plaque and is carried in the blood until it lodges in an artery, usually an intracranial branch that is too small to allow its passage. This event usually results in acute cortical infarction, a sudden insufficiency of arterial blood to the brain (e.g., of the left parietal lobes). An interruption of blood supply for 30 sec alters a person's brain metabolism. After 1—2 min, neural function may be lost; after 5 min, lack of oxygen (anoxia) can result in cerebral infarction. Quickly restoring oxygen to the blood supply may reverse the brain damage (Sacco, 2000).

Transient Ischemic Attacks Transient ischemic attacks (TIAs) refer to neurologic symptoms resulting from ischemia. Most TIAs last only a few minutes, but some persist for up to an hour. With major carotid or vertebrobasilar stenosis, the TIA tends to last longer and causes distal closure of intracranial vessels. The symptoms of TIA may be ambiguous: staggering, dizziness, light‐headedness, fainting, and paresthesias. Persons with TIAs are at increased risk for myocardial infarction and ischemic stroke (Brust, 2000).

Chapter 7: Head

Figure B7.15

Figure B7.16


Venous Drainage of the Brain The thin‐walled, valveless veins draining the brain pierce the arachnoid and meningeal layer of dura to end in the nearest dural venous sinuses (Figs. 7.9, 7.10, 7.11), which ultimately drain for the most part into the IJVs. The superior cerebral veins on the superolateral surface of the brain drain into the superior sagittal sinus; inferior and superficial middle cerebral veins from the inferior, posteroinferior, and deep aspects of the cerebral hemispheres drain into the straight, transverse, and superior petrosal sinuses. The great cerebral vein (of Galen) is a single, midline vein formed inside the brain by the union of two internal cerebral veins; it ends by merging with the inferior sagittal sinus to form the straight sinus (Figs. 7.10 and 7.13A & B). The cerebellum is drained by superior and inferior cerebellar veins, draining the respective aspect of the cerebellum into the transverse and sigmoid sinuses.

The Bottom Line A continuous supply of oxygen and nutrients is essential for brain function. The brain receives a dual blood supply from the cerebral branches of the bilaterally paired internal carotid and vertebral arteries. Anastomoses between these arteries form the cerebral arterial circle. Anastomoses also occur between the branches of the three cerebral arteries on the surface of the brain. In adults, if one of the four arteries delivering blood to the brain is blocked, the remaining three are not usually capable of providing adequate collateral circulation; consequently, impaired cerebral blood flow (ischemia) and an ischemic stroke result. Venous drainage from the brain occurs via the dural venous sinuses and internal jugular veins.

Face The face is the anterior aspect of the head from the forehead to the chin and from one ear to the other. The face provides our identity as an individual human. Thus defects (malformations, scarring, or other alterations resulting from pathology or trauma) have marked consequences beyond their physical effects. The basic shape of the face is determined by the underlying bones. The individuality of the face results primarily from anatomical variation: variations in the shape and relative prominence of the features of the underlying cranium; in the deposition of fatty tissue; in the color and effects of aging on the overlying skin; and in the abundance, nature, and placement of hair on the face and scalp. The relatively large size of the buccal fat‐pads in infants prevents collapse of the cheeks during sucking and produces their chubby‐cheeked appearance. Growth of the facial bones takes longer than those of the calvaria. The ethmoid bone, orbital cavities, and superior parts of the nasal cavities have nearly completed their growth by the 7th year. Expansion of the orbits and growth of the nasal septum carry the maxillae inferoanteriorly. Considerable facial growth occurs during childhood as the paranasal sinuses develop and the permanent teeth erupt. The face plays an important role in communication. Our interactions with others take place largely via the face (including the ears); hence the term “interface” for a site of interactions. Whereas the shape and features of the face provide our identity, much of our effect on others and their perceptions about us result from the way we use facial muscles to make the slight alterations in those features that constitute facial expression.

Chapter 7: Head

Muscles of the Face and Scalp The facial muscles (muscles of facial expression) are in the subcutaneous tissue of the anterior and posterior scalp, face, and neck. They move the skin and change facial expressions to convey mood. Most muscles attach to bone or fascia and produce their effects by pulling the skin. The muscles of the scalp and face are illustrated and their attachments and actions are provided in Table 7.4. Certain muscles and/or muscle groups will be discussed in further detail. All muscles of facial expression develop from mesoderm in the second pharyngeal arches. A subcutaneous muscular sheet forms during embryonic development that spreads over the neck and face, carrying branches of the nerve of the arch (the facial nerve, CN VII) with it to supply all the muscles formed from the arch (Moore and Persaud, 2003). The muscular sheet differentiates into muscles that surround the facial orifices (mouth, eyes, and nose), serving as sphincter and dilator mechanisms that also produce facial expressions (Fig. 7.22). Because of their common embryological origin, the platysma and facial muscles are often fused, and their fibers are frequently intermingled.

Facial Lacerations and Incisions Because the face has no distinct deep fascia and the subcutaneous tissue between the cutaneous attachments of the facial muscles is loose, facial lacerations tend to gape (part widely). Consequently, the skin must be carefully sutured to prevent scarring. The looseness of the subcutaneous tissue also enables fluid and blood to accumulate in the loose connective tissue following bruising of the face. Similarly, facial inflammation causes considerable swelling (e.g., a bee sting on the bridge of the nose may close both eyes). As a person ages, the skin loses its resiliency (elasticity). As a result, ridges and wrinkles occur in the skin perpendicular to the direction of the facial muscle fibers. Skin incisions along these cleavage or wrinkle lines (Langer lines) heal with minimal scarring (see clinical correlation [blue] box “Skin Incisions and Scarring,” in the Introduction).

Muscles of the Scalp, Forehead, and Eyebrows The occipitofrontalis is a flat digastric muscle, with occipital and frontal bellies that share a common tendon, the epicranial aponeurosis (Fig. 7.22; Table 7.4A & B). Because the aponeurosis is a layer of the scalp, independent contraction of the occipital belly retracts the scalp and contraction of the frontal belly protracts it. Acting simultaneously, the occipital belly, with bony attachments, works as a synergist with the frontal belly, which has no bony attachments, to elevate the eyebrows and produce transverse wrinkles across the forehead. This gives the face a surprised look.

Muscles of the Mouth, Lips, and Cheeks The lips and the shape and degree of opening of the mouth are important for clear speech. In addition, we add emphasis to our vocal communication with our facial expressions. Several muscles alter the shape of the mouth and lips during speaking as well as during such activities as singing, whistling, and mimicry. The shape of the mouth and lips is controlled by a complex three‐dimensional group of muscular slips, which include the following:

Clinically Oriented Anatomy, 5th Edition By Keith Moore    

Elevators, retractors, and evertors of the upper lip. Depressors, retractors, and evertors of the lower lip. The orbicularis oris, the sphincter around the mouth. The buccinator in the cheek.

At rest, the lips are in gentle contact and the teeth are close together. Table 7.4. Muscles of the Scalp and Face

Muscle a Occipitofrontalis Frontal belly 1

Occipital belly a

Origin Epicranial aponeurosis

Insertion

Main Action(s)

Skin and Elevates eyebrows and subcutaneous tissue wrinkles skin of forehead; of eyebrows and protracts scalp (indicating forehead surprise or curiosity) Lateral two thirds of Epicranial Retracts scalp; increasing superior nuchal line aponeurosis effectiveness of frontal belly

Chapter 7: Head

O r b i c u l a r i s o c u l i M e d i a l o r b i t a l m a r g i n ; ( o r b i t a l s p h i n c t e r ) 1 , 2 m e d i a l p a l p e b r a l l i g a m e n t ; l a c r i m a l b o n e Corrugator supercilii1 M e d i a l e n d of s u p e r c i l i a r y a r c h

P r o c e r u s t r a n s v e r s e nasalis3

part

plus Fascia a p o n e u r o s i s S k i n of of c o v e r i n g n a s a l b o n e and f o r e h e a d , l a t e r a l na s a l c a r t i l a g e e y e b r o w s

A l a r p a r t of n a s a l i s plus l ev a t o r labii superioris a l a e q ue nasii3 O r b i c u l a r i s oris ( o r a l sphincter)3

Zygomaticus major3 L e v a t o r a n g u l i oris 3

M e d i a l ma x i l l a a n d M u c o u s m e m b r a n e of m a n d i b l e ; d e e p s u r f a ce of l i p s p e r i o r a l s ki n ; a n g l e of mouth (modiolus)

P a r o t i d f a s c i a a n d b u c ca l s k i n ( h i g h l y v a r i a b l e )

D e p r e s s o r anguli oris 4

A n t e r o l a t e r a l mandible

Platysma5

a

S k i n of u p p e r lip

Angle of mouth (modiolus); orbicularis oris

L a t e r a l aspect of Angle of z y g o m a ti c b o n e (modiolus) I n f r a o r b i t a l maxilla (canine fossa)

Risorius3

Mentalis4

inferior be tween

F r o n t a l p r o c e s s of maxilla M a j o r a l a r c a r t i l a g e ( i n f e r o m e d i a l m a r g i n of orbit)

Levator l a b i i I n f r a o r b i t a l margin superioris3 (maxilla) Z y g o m a t i c u s mi no r 3 A n t e r i o r a s p e c t , z y g omat ic bone Buccinator ( c h e e k M a n d i b l e , a l v e o l a r muscle)3 p r o c e s s e s of ma x illa a n d m a n d i b l e , p t e r y g o m a n d i b u l a r r a p he

D e p r e s s o r inferioris4

S k i n a r o u n d m a r g i n of o r b i t ; s u p e r i o r a n d i n f e r i o r t a r sa l p l a t e s Skin superior t o m i d d l e of s u p r a o r b i t a l margin a n d s u p e r c i l i a r y a r c h

l a b i i P l a t y s m a a n t e r o l a t e r a l mandible

base

body

mouth

of

a n d S k i n of lower lip of

Body of mandible ( a n t e r i o r to r o o t s of inferior incisors) S u b c u t a n e o us t i s s u e of infraclavicular and supraclavicular regions

Skin of chin ( m e n t o l a b i a l s u l c u s ) B a s e of m a n d i b l e ; s k i n of c h e e k a n d l o w e r l i p ; angle of mouth (modiolus); orbicularis oris

C l o s e s e ye l i d s : p a l p e b ra l p a r t d o e s s o ge n t ly ; o r b i t a l p a r t t i g h t l y ( w i n kin g ) D r a w s e y e br o w m e d i a l l y a n d i n f e r i o r l y , c r e a t i n g v e r t i c a l wrinkles a b o v e n o s e ( d e m o n s t r a tin g c o n c e r n or worry) D e p r e s s es m e d i a l e n d of e y e b r o w ; wr in k le s s k i n o v e r d o r s u m of n o s e ( c o n v e y i n g d i s d a i n or d i s l i k e ) D e p r e s s es ala l a t e r a l l y , d i l a t i n g a n t er i o r n a s a l a pe r t u r e ( i . e . , “ f l a r i n g n o s t r i l s , ” a s d u r i n g a n g e r or e xe r t i o n ) T o n u s c l o s es r ima o r i s ; p h a s i c c o n t r a c t i o n c o m p r e s se s a n d p r o t r u d e s l i p s ( k i s s i ng) or resists d is t e n s i o n ( w h e n b lowin g) P a r t of d il a t o r s of m o u t h ; r e t r a c t ( e l e v a t e ) a n d / or e v e r t u p p e r l i p ; d e e p e n na sola b ia l s u l c u s ( s h o win g s a d n e s s ) P r e s se s c h ee k a g a i n s t m o l a r t e e t h ; w o r ks w i t h t o n g u e t o k e e p food b e t w e e n o c c l u s a l s u r f a c e s and o u t o f o r a l v e s t i b u l e ; r e s i s t s d i s te n s i o n ( w h e n b lowin g) P a r t of d il a t o r s of m o u t h ; e l e v a t e l a b i a l c o m m i s s u r e — bilaterally t o s m i l e ( h a p p i n e s s ) ; u n i l a t e r a lly t o s n e e r ( d i s d a i n ) P a r t of d il a t o r s of m o u t h ; w i d e n s r i m a o r i s , a s w h e n g r i n n i n g or g r i m a c i n g P a r t of d il a t o r s of m o u t h ; d e p r e s s e s la b ia l c o m m i s s u r e b i l a t e r a l l y to f r o w n ( s a dn e s s ) P a r t of d il a t o r s of m o u t h ; r e t r a c t s ( de p r e s se s ) a n d / o r e v e r t s l o w e r lip ( p o u t i n g , s a d n e s s) E l e v a t e s a nd p r o t r u d e s l o w e r l i p ; e l e v a t e s s k i n of c h i n (showing doubt) D e p r e s s es m a n d i b l e ( a g a i n s t r e s i s t a n ce ) ; t e n s e s sk in of inferior face a n d n e c k ( c o n v e y i n g te n s ion a n d st r e s s )

A l l f a c i a l m u s c l e s a r e i n n e r v a t e d b y t h e f a c i a l n e r v e ( C N V I I ) v i a i t s p o s te r i o r a u r i c u l a r ( p a ) b r a n c h o r v i a t h e t e m p o r a l ( 1 ) , z y g o m a t i c ( 2 ) , b u c c a l ( 3 ) , m a r g i n a l m a n d i b u l a r ( 4 ) , o r c e r v i c a l ( 5 ) b r a n c h e s of t h e p a r o t i d p l e x u s .


The orbicularis oris, the first of the series of sphincters associated with the alimentary system (digestive tract), encircles the mouth within the lips, controlling entry and exit through the oral fissure (L. rima oris, the opening between the lips). The orbicularis oris is important during articulation (speech). The buccinator (L. trumpeter) is a thin, flat, rectangular muscle that attaches laterally to the alveolar processes of the maxillae and mandible, opposite the molar teeth, and to the pterygomandibular raphe, a tendinous thickening of the buccopharyngeal fascia separating and giving origin to the superior pharyngeal constrictor posteriorly (Table 7.4C). It occupies a deeper, more medially placed plane than the other facial muscles, passing deep to the mandible so that it is more closely related to the buccal mucosa than the skin of the face. The buccinator, active in smiling, also keeps the cheek taut, thereby preventing it from folding and being injured during chewing. Anteriorly, the fibers of the buccinator mingle medially with those of the orbicularis oris, and the tonus of the two muscles compresses the cheeks and lips against the teeth and gums. The tonic contraction of the buccinator and especially of the orbicularis oris, provides a gentle but continual resistance to the tendency of the teeth to tilt in an outward direction. In the presence of a short upper lip, or retractors that remove this force, crooked or protrusive (“buck” ) teeth develop. The orbicularis oris (from the labial aspect) and buccinator (from the buccal aspect) work with the tongue (from the lingual aspect) to keep food between the occlusal surfaces of the teeth during mastication (chewing) and to prevent food from accumulating in the oral vestibule. The buccinator also helps the cheeks resist the forces generated by whistling and sucking. The buccinator was given its name because it compresses the cheeks during blowing (e.g., when a musician plays a wind instrument). Some trumpeters (notably the late Dizzy Gillespie) stretch their buccinators and other cheek muscles so much that their cheeks balloon out when they blow forcibly on their instruments. Several dilator muscles radiate from the lips and angles of the mouth, somewhat like the spokes of a wheel, retracting the various borders of the oral fissure collectively, in groups, or individually. Lateral to the angles of the mouth or labial commissures (the junctions of the upper and lower lips) fibers of as many as nine facial muscles interlace or merge in a highly variable and multiplanar formation called the modiolus, which is largely responsible for the occurrence of dimples in many individuals. The platysma (G. flat plate) is a broad, thin sheet of muscle in the subcutaneous tissue of the neck. The anterior borders of the two muscles decussate over the chin and blend with the facial muscles. Acting from its superior attachment, the platysma tenses the skin, producing vertical skin ridges, conveying great stress, and releasing pressure on the superficial veins. Acting from its inferior attachment, the platysma helps depress the mandible and draw the corners of the mouth inferiorly, as in a grimace.

Chapter 7: Head

Figure 7.22. Muscles of facial expression in action. These muscles are superficial sphincters and dilators of the orifices of the head. The facial muscles, supplied by the facial nerve (CN VII), are attached to and move the skin of the face, producing many facial expressions.

Muscles of the Orbital Opening The function of the eyelids (L. palpebrae) is to protect the eyeballs from injury and excessive light. The eyelids also keep the cornea moist by spreading the tears. The orbicularis oculi closes the eyelids and wrinkles the forehead vertically (Fig. 7.23; Table 7.4A & B). Its fibers sweep in concentric circles around the orbital margin and eyelids. Contraction of these fibers narrows the palpebral fissure (aperture between the eyelids) and assists the flow of lacrimal fluid (tears) by bringing the lids together laterally first, closing the palpebral fissure in a lateral to medial direction. The orbicularis oculi consists of three parts: 



Palpebral part: arising from the medial palpebral ligament and mostly located within the eyelids, gently closes the eyelids (as in blinking or sleep) to keep the cornea from drying. Lacrimal part: passing posterior to the lacrimal sac, draws the eyelids medially, aiding drainage of tears.


Figure 7.23. Disposition and actions of orbicularis oculi muscle. A. The orbital (O) and palpebral (P) parts of the orbicularis oculi are demonstrated. B. The palpebral part gently closes the eyelids. C. The orbital part tightly closes the eyelids.



Orbital part: overlying the orbital rim and attached to the frontal bone and maxilla medially, tightly closes the eyelids (as in winking or squinting) to protect the eyeballs against glare and dust.

When all three parts of the orbicularis oculi contract, the eyes are firmly closed (Figs. 7.22 and 7.23C).

Muscles of the Nose and Ears As demonstrated in the clinical correlation (blue) box “Flaring of the Nostrils” (below), the muscles of the nose may provide evidence of breathing behaviors. Otherwise, although these muscles are functionally important in certain mammals (elephants, tapirs, rabbits, and some diving mammals). They are relatively unimportant in humans except in terms of facial expression and in the specialized field of aesthetic plastic surgery. The muscles of the ears, important in animals capable of cocking or directing the ears toward the sources of sounds, are even less critical in humans.

Flaring of the Nostrils The actions of the nasalis muscles have generally been held as insignificant; however, observant clinicians study their action because of their diagnostic value. For example, true nasal breathers can flare their nostrils distinctly. Habitual mouth breathing, caused by chronic nasal obstruction, for example, diminishes and sometimes eliminates the ability to flare the nostrils. Children who are chronic mouth breathers often develop dental malocclusion (improper bite) because the alignment of the teeth is maintained to a large degree by normal periods of occlusion and labial closure. Antisnoring devices have been developed that attach to the nose to flare the nostrils and maintain a more patent air passageway.

Paralysis of Facial Muscles Injury to the facial nerve (CN VII) or its branches produces paralysis of some or all facial muscles on the affected side (Bell palsy). The affected area sags and facial expression is distorted, making it appear passive or sad. The loss of tonus of the orbicularis oculi causes the inferior eyelid to evert (fall away from the surface of the eyeball). As a result, lacrimal fluid is not spread over the cornea, preventing

Chapter 7: Head

adequate lubrication, hydration, and flushing of the surface of the cornea. This makes it vulnerable to ulceration. A resulting corneal scar can impair vision. If the injury weakens or paralyzes the buccinator and orbicularis oris, food will accumulate in the oral vestibule during chewing, usually requiring continual removal with a finger. When the sphincters or dilators of the mouth are affected, displacement of the mouth (drooping of its corner) is produced by contraction of unopposed contralateral facial muscles and gravity, resulting in food and saliva dribbling out of the side of the mouth, a sad look when the face is relaxed (Fig. B7.17), and a markedly contorted smile. Weakened lip muscles affect speech as a result of an impaired ability to produce labial (B, M, P, or W) sounds. Affected persons cannot whistle or blow a wind instrument. They frequently dab their eyes and mouth with a handkerchief to wipe the fluid (tears and saliva), which runs from the drooping lid and mouth; the fluid and constant wiping may result in localized skin irritation.

Figure B7.17

The Bottom Line The face provides our identity as an individual human. Thus congenital or acquired defects have consequences beyond their physical effects. The individuality of the face results primarily from anatomical variation. The way in which the facial muscles alter the basic features is critical to communication. Lips and the shape and degree of opening of the mouth are important components of speech, but emphasis and subtleties of meaning are provided by our facial expressions. The facial muscles play important roles as the dilators and sphincters of the portals of the digestive, respiratory, and visual systems (oral and palpebral fissures and nostrils), controlling what enters and some of what exits from our bodies. Other facial muscles assist the muscles of mastication by keeping food between the teeth during chewing. Fleshy portions of the face (eyelids, cheeks) form dynamic containing walls for the orbits and oral cavity. Facial muscles are all derived from the second pharyngeal arch and


are therefore supplied by the nerve of this arch, the facial nerve (CN VII). Facial muscles are subcutaneous, most having a skeletal origin and a cutaneous insertion. The face lacks the deep fascia present elsewhere in the body.

Nerves of the Face Cutaneous (sensory) innervation of the face is provided primarily by the trigeminal nerve (CN V), whereas motor innervation to the facial muscles is provided by the facial nerve (CN VII).

Cutaneous Nerves of the Face The cutaneous nerves of the neck overlap those of the face. Cutaneous branches of cervical nerves from the cervical plexus extend over the posterior aspect of the neck and scalp. The great auricular nerve in particular innervates the inferior aspect of the auricle and much of the parotid region of the face (the area overlying the angle of the jaw). The trigeminal nerve (CN V) originates from the lateral surface of the pons of the midbrain by two roots: motor and sensory. These roots are comparable to the motor (anterior) and sensory (posterior) roots of spinal nerves. The sensory root consists of the central processes of pseudounipolar neurons located in a sensory ganglion (the trigeminal ganglion) at the distal end of the root, which is bypassed by the multipolar neuronal axons making up the motor root. CN V is the sensory nerve for the face and the motor nerve for the muscles of mastication and several small muscles (Fig. 7.24). The peripheral processes of the neurons of the trigeminal ganglion constitute three divisions of the nerve: the ophthalmic nerve (CN V 1 ), the maxillary nerve (CN V 2 ), and the sensory component of the mandibular nerve (CN V 3 ). These nerves are named according to their main areas of termination: the eye, maxilla, and mandible, respectively. The first two divisions (ophthalmic and maxillary nerves) are wholly sensory. The mandibular nerve is largely sensory but it also receives the motor fibers (axons) from the motor root of CN V that mainly supply the muscles of mastication. The cutaneous nerves derived from each division of CN V are illustrated and the origin, course and distribution of each nerve are listed and mapped in Table 7.5.

Ophthalmic Nerve The ophthalmic nerve (CN V 1 ), the superior division of the trigeminal nerve, is the smallest of the three divisions of CN V. It arises from the trigeminal ganglion as a wholly sensory nerve and supplies the area of skin derived from the embryonic frontonasal prominence (Moore and Persaud, 2003). As CN V 1 enters the orbit through the superior orbital fissure, it trifurcates into the frontal, nasociliary, and lacrimal nerves (Fig. 7.24). Except for the external nasal nerve, the cutaneous branches of CN V 1 reach the skin of the face via the orbital opening (Fig. 7.25). The frontal nerve, the largest branch produced by the trifurcation of CN V 1 , runs along the roof of the orbit toward the orbital opening, bifurcating approximately midway into the cutaneous supraorbital and supratrochlear nerves, distributed to the forehead and scalp (Fig. 7.26). The nasociliary nerve, the intermediate branch of the CN V 1 trifurcation, supplies branches to the eyeball and divides within the orbit into the posterior ethmoidal, anterior ethmoidal, and infratrochlear nerves. The posterior and anterior ethmoidal

Chapter 7: Head

nerves leave the orbit, the latter running a circuitous course passing through the cranial and nasal cavities. Its terminal branch, the external nasal nerve, is a cutaneous nerve supplying the external nose. The infratrochlear nerve is a terminal branch of the nasociliary nerve and its main cutaneous branch. The lacrimal nerve, the smallest branch from the trifurcation of CN V 1 , is primarily a cutaneous branch, but it also conveys some secretomotor fibers, sent via a communicating branch, from a ganglion associated with the maxillary nerve for innervation of the lacrimal gland.

Maxillary Nerve The maxillary nerve (CN V 2 ), the intermediate division of the trigeminal nerve, also arises as a wholly sensory nerve (Fig. 7.24). CN V 2 passes anteriorly from the trigeminal ganglion and leaves the cranium through the foramen rotundum in the base of the greater wing of the sphenoid (Fig. 7.5C). It enters the pterygopalatine fossa, where it gives off branches to the pterygopalatine ganglion and continues anteriorly, entering the orbit through the inferior orbital fissure (Fig. 7.24). It gives off the zygomatic nerve and passes anteriorly into the infraorbital groove as the infraorbital nerve. Table 7.5. Cutaneous Nerves of the Face and Scalp

Nerve Origin Course Cutaneous nerves derived from ophthalmic nerve (CN V 1 ) Supraorbital Largest branch from Continues anteriorly along bifurcation of frontal roof of orbit, emerging via nerve, approximately supraorbital notch or in middle of orbital foramen; ascends forehead, roof breaking into branches

Distribution Mucosa of frontal sinus; skin and conjunctiva of middle of superior eyelid; skin and pericranium of anterolateral forehead and scalp to vertex (interauricular line)


Supratrochlear

Smaller branch from bifurcation of frontal nerve, approximately in middle of orbital roof

Continues anteromedially along roof of orbit, passing lateral to trochlea and ascending forehead

Lacrimal

Smallest branch from trifurcation of CN V 1 proximal to superior orbital fissure

Runs superolaterally through orbit, receiving secretomotor fibers via a communicating branch from the zygomaticotemporal nerve

Infratrochlear

Terminal branch (with Follows medial wall of orbit, anterior ethmoidal passing inferior to trochlea nerve) of nasociliary nerve

External nasal

Terminal anterior nerve

branch of Emerges from nasal cavity by ethmoidal passing between nasal bone and lateral nasal cartilage

Skin and conjunctive of medial aspect of superior eyelid; skin and pericranium of anteromedial forehead Lacrimal gland (secretomotor fibers); small area of skin and conjunctiva of lateral part of superior eyelid Skin lateral to root of nose; skin and conjunctiva of eyelids adjacent to medial canthus, lacrimal sac, and lacrimal caruncle Skin of nasal ala, vestibule, and dorsum of nose, including apex

Cutaneous nerves derived from maxillary nerve (CN V 2 ) Infraorbital Continuation of CN V 2 Traverses infraorbital groove distal to its entrance and canal in orbital floor, into the orbit via the giving rise to superior inferior orbital fissure alveolar branches; then emerges via infraorbital foramen, immediately dividing into inferior palpebral, internal and external nasal, and superior labial branches

Mucosa of maxillary sinus; premolar, canine, and incisor maxillary teeth; skin and conjunctiva of inferior eyelid; skin of cheek, lateral nose, and anteroinferior nasal septum; skin and oral mucosa of superior lip Zygomaticofacial Smaller terminal Traverses zygomaticofacial Skin on prominence branch (with canal in zygomatic bone at of cheek zygomaticotemporal inferolateral angle of orbit nerve) of zygomatic nerve Zygomaticotemporal Larger terminal branch Sends communicating branch Hairless skin anterior (with zygomaticofacial to lacrimal nerve in orbit; part of temporal nerve) of zygomatic then passes to temporal fossa fossa nerve via zygomaticotemporal canal in zygomatic bone Cutaneous nerves derived from mandibular nerve (CN V 3 ) Auriculotemporal In infratemporal fossa Passes posteriorly deep to S k i n a n t e r i o r t o a u r i c l e via two roots from ramus of mandible and a n d p o s te r i o r t w o posterior trunk of CN superior deep part of parotid t h i r d s o f t e m p o r a l V 3 that encircle middle gland, emerging posterior to r e g i o n ; s k i n o f t r a g u s a n d ad j a ce nt h e l i x o f meningeal artery temporomandibular joint a u r i c l e ; s k i n o f r o o f of e x t e r n a l acoustic meatus; and skin of superior tympanic membrane

Chapter 7: Head

Buccal

In infratemporal fossa Passes between two parts of as sensory branch of lateral pterygoid muscle, anterior trunk of CN V 3 emerging anteriorly from cover of ramus of mandible and masseter, uniting with buccal branches of facial nerve

Skin and oral mucosa of cheek (overlying and deep to anterior part of buccinator); buccal gingivae (gums) adjacent to second and third molars Mental Terminal branch of Emerges from mandibular Skin of chin and skin; inferior alveolar nerve canal via mental foramen in oral mucosa of (CN V 3 ) anterolateral aspect of body inferior lip of mandible Cutaneous nerves derived from anterior rami of cervical spinal nerves Greater auricular Spinal nerves C2 and Ascends vertically across Skin overlying angle C3 via cervical plexus sternocleidomastoid, of mandible and posterior to external jugular inferior lobe of vein auricle; parotid sheath Lesser occipital Follows posterior border of Scalp posterior to sternocleidomastoid; then auricle ascends posterior to auricle Cutaneous nerves derived from posterior rami of cervical spinal nerves Greater occipital As medial branch of Emerges between axis and Scalp of occipital nerve posterior ramus of obliquus capitis inferior; then region spinal nerve C2 pierces trapezius Third occipital nerve As lateral branch of Pierces trapezius Scalp of lower posterior ramus of occipital and spinal nerve C3 suboccipital regions

The zygomatic nerve runs to the lateral wall of the orbit, giving rise to two of the three cutaneous branches of CN V 2 , the zygomaticofacial and zygomaticotemporal nerves. The latter sends a communicating branch conveying secretomotor fibers to the lacrimal nerve. En route to the face, the infraorbital nerve gives off palatine branches, branches to the mucosa of the maxillary sinus, and branches to the posterior teeth. It reaches the skin of the face by traversing the infraorbital foramen on the infraorbital surface of the maxilla. The three cutaneous branches of the maxillary nerve supply the area of skin derived from the embryonic maxillary prominences.

Mandibular Nerve The mandibular nerve (CN V 3 ), the inferior and largest division of the trigeminal nerve, is formed by the union of sensory fibers from the sensory ganglion and the motor root of CN V in the foramen ovale in the greater wing of the sphenoid through which CN V 3 emerges from the cranium (Fig. 7.24). CN V 3 has three sensory branches that supply the area of skin derived from the embryonic mandibular prominence. It also supplies motor fibers to the muscles of mastication (Fig. 7.24C). CN V 3 is the only division of CN V that carries motor fibers. The major cutaneous branches of CN V 3 are the auricotemporal, buccal, and mental nerves. En route to the skin, the


auriculotemporal nerve passes deep to the parotid gland, conveying secretomotor fibers to it from a ganglion associated with this division of CN V.

Figure 7.24. Distribution of trigeminal nerve (CN V). A. The three divisions of CN V arise from the trigeminal ganglion. The maxillary nerve (CN V 2 ) gives off two nerves (roots) to the pterygopalatine ganglion. B. Branches of the mandibular nerve (CN V 3 ) pass to the muscles of mastication. C. This “opened book” view of the lateral wall and septum of the right nasal cavity demonstrates the distribution of CN I, CN V 1 , and CN V 2 .

Chapter 7: Head

Figure 7.25. Innervation of eyelids. The cutaneous nerves serving the orbital region are shown in relation to the skeleton of the eyelids. This skeleton is formed by the superior and inferior tarsi and their attachments, the medial and lateral palpebral ligaments, and the orbital septum. The fan‐shaped aponeurosis of the levator palpebrae superioris is attached to the superior tarsus. The skin of the superior eyelid is supplied by branches of the ophthalmic nerve (CN V1), whereas the inferior eyelid is supplied mainly by branches of the maxillary nerve (CN V2).

Figure 7.26. Nerves of scalp. The nerves appear in sequence: CN V1, CN V2, CN V3, anterior rami of C2 and C3, and posterior rami of C2 and C3.

Nerves of the Scalp Innervation of the scalp anterior to the auricles is through branches of all three divisions of CN V, the trigeminal nerve (Fig. 7.26). Posterior to the auricles, the nerve supply is from spinal cutaneous nerves (C2 and C3).


Infraorbital Nerve Block For treating wounds of the upper lip and cheek or, more commonly, for repairing the maxillary incisor teeth, local anesthesia of the inferior part of the face is achieved by infiltration of the infraorbital nerve with an anesthetic agent. The injection is made in the region of the infraorbital foramen, by elevating the upper lip and passing the needle through the junction of the oral mucosa and gingiva at the superior aspect of the oral vestibule. To determine where the infraorbital nerve emerges, pressure is exerted on the maxilla in the region of the infraorbital foramen. Too much pressure on the nerve causes considerable pain. Because companion infraorbital vessels leave the infraorbital foramen with the nerve, aspiration of the syringe during injection prevents inadvertent injection of anesthetic fluid into a blood vessel. Because the orbit is located just superior to the injection site, a careless injection could result in passage of anesthetic fluid into the orbit, causing temporary paralysis of the extraocular muscles.

Mental and Incisive Nerve Blocks Occasionally, it is desirable to anesthetize one side of the skin and mucous membrane of the lower lip and the skin of the chin (e.g., to suture a severe laceration of the lip). Injection of an anesthetic agent into the mental foramen blocks the mental nerve that supplies the skin and mucous membrane of the lower lip from the mental foramen to the midline, including the skin of the chin.

Buccal Nerve Block To anesthetize the skin and mucous membrane of the cheek (e.g., to suture a knife wound), an anesthetic injection can be made into the mucosa covering the retromolar fossa, located posterior to the 3rd mandibular molar between the anterior border of the ramus and the temporal crest.

Trigeminal Neuralgia Trigeminal neuralgia (tic douloureux) is a sensory disorder of the sensory root of CN V that occurs most often in middle‐aged and elderly persons. It is characterized by sudden attacks of excruciating, lightening‐like jabs of facial pain. A paroxysm (sudden sharp pain) can last for 15 min or more. The pain may be so intense that the person winces; hence the common term tic (twitch). In some cases, the pain may be so severe that psychological changes occur, leading to depression and even suicide attempts. CN V 2 is most frequently involved, then CN V 3 , and least frequently, CN V 1 . The paroxysms of sudden stabbing pain are often set off by touching the face, brushing the teeth, shaving, drinking, or chewing. The pain is often initiated by touching an especially sensitive trigger zone, frequently located around the tip of the nose or the cheek (Haines, 2002). The cause of trigeminal neuralgia is unknown; however, some investigators believe that most affected persons have an anomalous blood vessel that compresses the nerve (Lange et al., 2000). Often, when the aberrant artery is moved away from the sensory root of CN V, the symptoms disappear. Other scientists believe the condition is caused by a pathological process affecting neurons in the trigeminal ganglion; still others believe that neurons in the nucleus of the spinal tract may be involved (see Chapter 9).

Chapter 7: Head

Medical or surgical treatment or both are used to alleviate the pain. In cases involving the CN V 2 , attempts have been made to block the infraorbital nerve at the infraorbital foramen by using alcohol. This treatment usually relieves pain temporarily. The simplest surgical procedure is avulsion or cutting of the branches of the nerve at the infraorbital foramen. Other treatments have used radiofrequency selective ablation of parts of the trigeminal ganglion by a needle electrode passing through the cheek and the foramen ovale. In some cases, it is necessary to section the sensory root for relief of the pain. To prevent regeneration of nerve fibers, the sensory root of the trigeminal nerve may be partially cut between the ganglion and the brainstem (rhizotomy). Although the axons may regenerate, they do not do so within the brainstem. Surgeons attempt to differentiate and cut only the sensory fibers to the division of CN V involved. The same result may be achieved by sectioning the spinal tract of CN V (tractotomy). After this operation, the sensation of pain, temperature, and simple (light) touch is lost over the area of skin and mucous membrane supplied by the affected component of the CN V. This loss of sensation may annoy the patient, who may not recognize the presence of food on the lip and cheek or feel it within the mouth on the side of the nerve section, but these disabilities are usually preferable to excruciating pain

Lesions of the Trigeminal Nerve Lesions of the entire trigeminal nerve cause widespread anesthesia involving the:   

Corresponding anterior half of the scalp. Face, except for an area around the angle of the mandible, the cornea, and conjunctiva. Mucous membranes of the nose, mouth, and anterior part of the tongue.

Paralysis of the muscles of mastication also occurs.

Herpes Zoster Infection of the Trigeminal Ganglion A herpes zoster virus infection may produce a lesion in the cranial ganglia. Involvement of the trigeminal ganglion occurs in approximately 20% of cases (Bernardini, 2000). The infection is characterized by an eruption of groups of vesicles following the course of the affected nerve (e.g., ophthalmic herpes zoster). Any division of CN V may be involved, but the ophthalmic division is most commonly affected. Usually, the cornea is involved, often resulting in painful corneal ulceration and subsequent scarring of the cornea.

Testing the Sensory Function of CN V The sensory function of the trigeminal nerve is tested by asking the person to close his or her eyes and respond when types of touch are felt. For example, a piece of dry gauze is gently stroked across the skin of one side of the face and then to the corresponding position on the other side. The test is then repeated until the skin of the forehead (CN V 1 ), cheek (CN V 2 ), and lower jaw (CN V 3 ) have been tested. The person is asked if one side feels the same as or different from the other side. The testing may then be repeated using warm or cold instruments and the gentle touch of a sharp pin, again alternating sides (Fig. B7.18).


Figure B7.18

Motor Nerves of the Face The motor nerves of the face are the facial nerve to the muscles of facial expression and the motor root of the trigeminal nerve/mandibular nerve to the muscles of mastication (masseter, temporal, medial, and lateral pterygoids). These nerves also supply some more deeply placed muscles (described later in this chapter in relation to the mouth, middle ear, and neck) (Fig. 7.24A).

Facial Nerve CN VII, the facial nerve, has both a motor root and a sensory/parasympathetic root (the latter being the intermediate nerve). The motor root of CN VII supplies the muscles of facial expression, including the superficial muscle of the neck (platysma), auricular muscles, scalp muscles, and certain other muscles derived from mesoderm in the embryonic second pharyngeal arch (Fig. 7.27). Following a circuitous route through the temporal bone, CN VII emerges from the cranium through the stylomastoid foramen located between the mastoid and the styloid processes (Fig. 7.5A). It immediately gives off the posterior auricular nerve, which passes posterosuperior to the auricle of the ear to supply the auricularis posterior and occipital belly of the occipitofrontalis muscle (Fig. 7.27). The main trunk of CN VII runs anteriorly and is engulfed by the parotid gland, in which it forms the parotid plexus, which gives rise to the five terminal branches of the facial nerve: temporal, zygomatic, buccal, marginal mandibular, and cervical. The names of the branches refer to the regions they supply. Specific muscles supplied by each branch are identified in Table 7.4. The temporal branch of CN VII emerges from the superior border of the parotid gland and crosses the zygomatic arch to supply the auricularis superior and auricularis anterior; the frontal belly of the occipitofrontalis; and, most important, the superior part of the orbicularis oculi (Fig. 7.27A; Table 7.4). The zygomatic branch of CN VII passes via two or three branches superior and mainly inferior to the eye to supply the inferior part of the orbicularis oculi and other facial muscles inferior to the orbit.

Chapter 7: Head

The buccal branch of CN VII passes external to the buccinator to supply this muscle and muscles of the upper lip (upper parts of orbicularis oris and inferior fibers of levator labii superioris). The marginal mandibular branch of CN VII supplies the risorius and muscles of the lower lip and chin. It emerges from the inferior border of the parotid gland and crosses the inferior border of the mandible deep to the platysma to reach the face. In approximately 20% of people, this branch passes inferior to the angle of the mandible. The cervical branch of CN VII passes inferiorly from the inferior border of the parotid gland and runs posterior to the mandible to supply the platysma (Fig. 7.27B).

Injuries to the Facial Nerve Injury to branches of the facial nerve causes paralysis of the facial muscles (Bell palsy), with or without loss of taste on the anterior two thirds of the tongue or altered secretion of the lacrimal and salivary glands (see clinical correlation [blue] box “Paralysis of Facial Muscles,” earlier in this chapter). Lesions near the origin of CN VII from the pons of the brain or proximal to the origin of the greater petrosal nerve (in the region of the geniculate ganglion), result in loss of motor, gustatory (taste), and autonomic functions. Lesions distal to the geniculate ganglion, but proximal to the origin of the chorda tympani nerve, produce the same dysfunction, except that lacrimal secretion is not affected. Lesions near the stylomastoid foramen result in loss of motor function only (i.e., facial paralysis). Facial nerve palsy has many causes. The most common non‐traumatic cause of facial paralysis is inflammation of the facial nerve near the stylomastoid foramen, probably as a result of a viral infection. This produces edema (swelling) and compression of the nerve in the facial canal. Injury of the facial nerve often results from fracture of the temporal bone; facial paralysis is evident soon after the injury. If the nerve is completely sectioned, the chances of complete or even partial recovery are remote. Muscular movement usually improves when the nerve damage is associated with blunt head trauma; however, recovery may not be complete (Rowland, 2000). Facial nerve palsy may be idiopathic, occurring without a known cause (e.g., Bell palsy); but it often follows exposure to cold, as occurs when riding in a car or sleeping with a window open. Facial paralysis may be a complication of surgery; consequently, identification of the facial nerve is essential during surgery (e.g., parotidectomy, removal of a parotid gland). The facial nerve is most distinct as it emerges from the stylomastoid foramen; if necessary, electrical stimulation may be used for confirmation. Facial nerve palsy may also be associated with dental manipulation, vaccination, pregnancy, HIV infection, Lyme disease (inflammatory disorder causing headache and stiff neck), and infections of the middle ear (otitis media). Because the branches of the facial nerve are superficial, they are subject to injury by stab and gunshot wounds, cuts, and injury at birth:  

A lesion of the zygomatic branch of CN VII causes paralysis, including loss of tonus of the orbicularis oculi in the inferior eyelid. Paralysis of the buccal branch of CN VII causes paralysis of the buccinator and superior portion of the orbicularis oris and upper lip muscles.


Paralysis of the marginal mandibular branch of CN VII may occur when an incision is made along the inferior border of the mandible. Injury to this branch (e.g., during a surgical approach to the submandibular gland) causes paralysis of the inferior portion of the orbicularis oris and lower lip muscles.

The consequences of such paralyses are discussed in clinical correlation (blue) box “Paralysis of Facial Muscles.”

Figure 7.27. Branches of facial nerve (CN VII). A. The terminal branches of CN VII arise from the parotid plexus within the parotid gland. They emerge from the gland under cover of its lateral surface and radiate in a generally anterior direction across the face. Although intimately related to the parotid gland (and often contacting the submandibular gland via one or more of its lower branches), CN VII does not send nerve fibers to the salivary glands. Two muscles representing the extremes of the distribution of CN VII, the occipitofrontalis and platysma, are also shown. B. A simple method for demonstrating and remembering the general course of the five terminal branches of CN VII to the face and neck. C. Dissection of the right side of the head showing the great auricular nerve (C2 and C3), which supplies the parotid sheath and skin over the angle of the mandible, and terminal branches of the facial nerve, which supply the muscles of facial expression. B, buccal; C, cervical; M, marginal mandibular; T, temporal; Z, zygomatic.

Chapter 7: Head

The Bottom Line The face is highly sensitive. It receives sensory innervation from the three divisions of the trigeminal nerve (CN V). The major terminal branches of each division reach the subcutaneous tissue of each side of the face via three foramina that are aligned vertically. Each division supplies a distinct sensory zone, similar to a dermatome but without the overlapping of adjacent nerves; therefore, injuries result in distinct and defined areas of paresthesia. The divisions of CN V supply sensation not only to the superficial skin of the face but also to deep mucosal surfaces of the conjunctival sacs, cornea, nasal cavity and paranasal sinuses, and the oral cavity and vestibule. The skin covering the angle of the mandible is innervated by the great auricular nerve, a branch of the cervical plexus. The facial nerve (CN VII) is the motor nerve of the face, supplying all the muscles of facial expression, including the platysma, occipital belly of the occipitofrontalis, and auricular muscles that are not part of the face per se. The muscles receive innervation from CN VII primarily via five branches of the parotid (nerve) plexus. Eight nerves supply sensation to the scalp via branches arising from all three divisions of CN V anterior to the auricle of the ear and branches of cervical spinal nerves posterior to the auricle.

Superficial Vasculature of the Face and Scalp The face is richly supplied by with superficial arteries and external veins, as is evident in blushing and blanching. The terminal branches of both arteries and veins anastomose freely, including anastomoses across the midline with contralateral partners. Most arteries of the face are branches or derivatives of branches of the external carotid artery; the origin, course, and distribution of these arteries are presented in Table 7.6. Most external facial veins are drained by veins that accompany the arteries of the face. As with most superficial veins, they are subject to many variations; a common pattern is shown in Table 7.7. The venous return from the face is normally superficial, but anastomoses with deep veins, a dural sinus, and venous plexus can provide deep drainage for the valveless veins.

Superficial Arteries of the Face The superficial arteries of the face are illustrated and their origins, courses, and distributions are listed in Table 7.6. The facial artery provides the major arterial supply to the face. It arises from the external carotid artery and winds its way to the inferior border of the mandible, just anterior to the masseter (Fig. 7.27C). The artery lies superficially here, immediately deep to the platysma. The facial artery crosses the mandible, buccinator, and maxilla as it courses over the face to the medial angle (canthus) of the eye, where the superior and inferior eyelids meet. The facial artery lies deep to the zygomaticus major and levator labii superioris muscles. Near the termination of its sinuous course through the face, the facial artery passes approximately a finger's breadth lateral to the angle of the mouth. It sends branches to the upper and lower lips (the superior and inferior labial arteries), ascends along the side of the nose, and anastomoses with the dorsal nasal branch of the ophthalmic artery. Distal to the lateral nasal artery at the side of the nose, the terminal part of the facial artery is called the angular artery.


Table 7.6. Superficial Arteries of the Face and Scalp

Artery

Origin

F a c i a l

E x t e r n a l c a rot i d a r t e r y

Inferior labial S u p e r i o r l a b ia l

L a t e r a l n a s a l Angular

O c c i p i t a l

A s c e n d s d e e p t o s u b m a n d i b u l a r g l a n d ; w i n d s a r o u n d i n f e r i o r b o r d e r of m a n d i b l e a n d e n t e r s f a c e F a c i a l a r te r y n e a r a n g l e of R u n s m e d i a l ly in l o w e r lip mouth R u n s m e d i a l ly in u p p e r lip

F a c i a l a r t e ry a s it a sc e n ds a l o n g s i d e n o s e T e r m i n a l b r a n c h of f a c ia l a r t e r y E x t e r n a l c a rot i d a r t e r y

P o s t e r i o r a ur i c u l a r

S u p e r f i c i a l te mp or a l S m a l l e r t e rmi n a l b r a n c h of e xt e r n a l ca rot id a r t e ry T r a n s v e r s e f a c i a l

M e n t a l Supraorbitala S u p r a t r o c h l ea r a a

Course

S u p e r f i c i a l t e m p o r a l a r t e r y w i th i n p a r o t i d gland T e r m i n a l b r a n c h of i n f e r i o r a l v e o l a r a r t e r y T e r m i n a l b r a n c h of ophthalmic a r t e ry , a b r a n c h of i n t e r n a l ca rot id a r t e r y

S o u r c e i s i n te r n a l c a r o t i d a r t e r y .

Distribution M u s c l e s of f a c i a l e xp r e s s i o n and f a c e

L o w e r lip U p p e r lip a n d a l a ( s i d e ) a n d s e p t u m of nose P a s se s t o a la of n o s e S k i n on a l a a n d d o r s u m of n o s e P a s se s t o me d ia l a n g l e (c a n t h u s ) S u p e r i o r part of of e y e c h e e k a n d i n f e r i o r e y e l i d P a s se s m e d ia l t o p o s t e ri o r b e l l y S c a l p of b a c k of of d i g a s t r i c a n d m a s t o i d p r o c e s s ; h e a d , a s f a r a s v e r t e x a c c o m p a n i e s o c c i p i t a l n e r v e in occipital region P a s se s p o s t e r i o r l y , d e e p t o S c a l p p o s te r i o r t o p a r o t i d g l a n d , a l o n g s t y l o i d a u r i c l e a n d a u r i c l e process b e t w e e n mastoid p r o c e s s a n d e a r A s c e n d s an t e r ior t o e a r t o F a c i a l m u s c l e s a n d t e m p o r a l r e g i o n a n d e n d s in s k i n of f r o n t a l a n d s c a l p t e m p o r a l regions C r o s s e s f a c e s u p e r f i c i a l t o P a r o t i d g l a n d a n d m a s s e t e r and i n f e r io r t o d u c t , m u s c l e s a n d z y gomat ic a r c h s k i n of f a c e E m e r g e s from m e n t a l f o r a m e n F a c i a l m u s c l e s a n d a n d p a s s e s to c h i n s k i n of c h i n P a s se s superiorly from M u s c l e s a nd s k i n of s u p r a o r b i t a l f o r a m e n f o r e h e a d a nd s c a l p P a s se s superiorly from M u s c l e s a nd s k i n of s u p r a t r o c h l ea r n o t c h s c a l p

Chapter 7: Head

Table 7.7. Veins of the Face and Scalp

Vein Supratrochlear

Supraorbital

Angular

Origin Begins from venous plexus on forehead and scalp, through which it communicates with frontal branch of superficial temporal vein, its contralateral partner, and supraorbital vein Begins in the forehead by anastomosing with frontal tributary of superficial temporal vein

Course Termination Area Drained Descends near midline Angular vein at Anterior part of of forehead to root of root of nose scalp and nose, where it joins forehead supraorbital vein

Passes medially superior to orbit; joins supratrochlear vein; a branch passes through supraorbital notch and joins with superior ophthalmic vein Begins at root of Descends obliquely Becomes facial Anterior part of nose by union of along root and side of vein at inferior scalp and supratrochlear and nose to inferior orbital margin of orbit forehead; supraorbital veins margin superior and inferior eyelids and conjunctiva; may receive drainage from cavernous sinus


Facial

Continuation of angular vein past inferior margin of orbit

Deep facial

Pterygoid plexus

Superficial temporal

Begins from widespread plexus of veins on side of scalp and along zygomatic arch

venous

Retromandibular Formed anterior to ear by union of superficial temporal and maxillary veins

Descends along lateral border of nose, receiving external nasal and inferior palpebral veins; then passes obliquely across face to cross inferior border of mandible; receives communication from retromandibular vein (after which, it is sometimes called common facial vein) Runs anteriorly on maxilla superior to buccinator and deep to masseter, emerging medial to anterior border of masseter onto face Frontal and parietal tributaries unite anterior to the auricle; crosses temporal root of zygomatic arch to pass from temporal region and enter substance of the parotid gland Runs posterior and deep to ramus of mandible through substance of parotid gland; communicates at inferior end with facial vein

Internal jugular vein opposite or inferior to level of hyoid bone

Anterior scalp and fore‐head; eyelids; external nose; anterior cheek; lips; chin; and submandibular gland

Enters posterior Infratemporal aspect of facial fossa (most areas vein supplied by maxillary artery)

Joins maxillary vein posterior to neck of mandible to form retromandibular vein

Side of scalp; superficial aspect of temporal muscle; and external ear

Unites with Parotid gland and posterior masseter muscle auricular vein to form external jugular vein

The superficial temporal artery is the smaller terminal branch of the external carotid artery; the other branch is the maxillary artery. The superficial temporal artery emerges on the face between the TMJ and the auricle, enters the temporal fossa, and ends in the scalp by dividing into frontal and parietal branches. These arterial branches accompany or run in close proximity to the corresponding branches of the auriculotemporal nerve. The transverse facial artery arises from the superficial temporal artery within the parotid gland and crosses the face superficial to the masseter (Fig. 7.27C), approximately a finger's breadth inferior to the zygomatic arch. It divides into numerous branches that supply the parotid gland and duct, the masseter, and the skin of the face. It anastomoses with branches of the facial artery. In addition to the superficial temporal arteries, several other arteries accompany cutaneous nerves in the face. Supraorbital and supratrochlear arteries, branches of

Chapter 7: Head

the ophthalmic artery, accompany nerves of the same name across the eyebrows and forehead. The supraorbital artery continues and supplies the anterior scalp to the vertex. The mental artery, the only superficial branch derived from the maxillary artery, accompanies the nerve of the same name in the chin.

Arteries of the Scalp The scalp has a rich blood supply (Table 7.6). The arteries course within layer two of the scalp, the subcutaneous connective tissue layer between the skin and the epicranial aponeurosis. They anastomose freely with one another. The arterial walls are firmly attached to the dense connective tissue in which they are embedded, limiting their ability to constrict when cut. Consequently, bleeding from scalp wounds is profuse. The arterial supply is from the external carotid arteries through the occipital, posterior auricular, and superficial temporal arteries and from the internal carotid arteries through the supratrochlear and supraorbital arteries. The arteries of the scalp supply little blood to the neurocranium, which is supplied primarily by the middle meningeal artery.

Compression of the Facial Artery The facial artery can be occluded by pressure against the mandible where the vessel crosses it. Because of the numerous anastomoses between the branches of the facial artery and other arteries of the face, compression of the facial artery on one side does not stop all bleeding from a lacerated facial artery or one of its branches. In lacerations of the lip, pressure must be applied on both sides of the cut to stop the bleeding. In general, facial wounds bleed freely and heal quickly.

Pulses of the Arteries of the Face The pulses of the superficial temporal and facial arteries can be used for taking the pulse. For example, anesthesiologists at the head of the operating table often take the temporal pulse anterior to the auricle where the superficial temporal artery crosses the zygomatic process just anterior to the auricle. Clench your teeth and feel the facial pulse as the facial artery crosses the inferior border of the mandible immediately anterior to the masseter muscle.

Stenosis of the Internal Carotid Artery At the medial angle of the eye, an anastomosis occurs between the facial artery, a branch of the external carotid artery, and the cutaneous branches of the internal carotid artery. With advancing age, the internal carotid artery may become narrow (stenotic) owing to atherosclerotic thickening of the intima of the arteries. Because of the arterial anastomosis, intracranial structures such as the brain can receive blood from the connection of the facial artery to the dorsal nasal branch of the ophthalmic artery.

Scalp Lacerations Scalp lacerations are the most common type of head injury requiring surgical care. These wounds bleed profusely because the arteries entering the periphery of the scalp bleed from both ends owing to abundant anastomoses. The arteries do not retract when lacerated because they are held open by the dense connective tissue in layer two of the scalp. Spasms of the occipitofrontalis can increase gaping of scalp


wounds. Bleeding from scalp lacerations can be fatal if not controlled (e.g., by sutures).

Scalp Injuries Because the scalp arteries arising at the sides of the head are well protected by dense connective tissue and anastomose freely, a partially detached scalp may be replaced with a reasonable chance of healing as long as one of the vessels supplying the scalp remains intact. During an attached craniotomy (surgical removal of a segment of the calvaria with a soft tissue scalp flap to expose the cranial cavity) the incisions are usually made convex upward, and the superficial temporal artery is included in the tissue flap. The scalp proper, the first three layers of the scalp, is often regarded clinically as a single layer because they remain together when a scalp flap is made during a craniotomy and when part of the scalp is torn off (e.g., during industrial accidents). Nerves and vessels of the scalp enter inferiorly and ascend through layer two to the skin. Consequently, surgical pedicle scalp flaps are made so that they remain attached inferiorly to preserve the nerves and vessels, thereby promoting good healing. The arteries of the scalp supply little blood to the calvaria, which is supplied by the middle meningeal arteries. Therefore, loss of the scalp does not produce necrosis of the calvarial bones.

External Veins of the Face The major external veins of the head and face are illustrated and their origins, courses, terminations, and the areas drained by each are provided in Table 7.7. Like veins elsewhere, they are highly variable and have abundant anastomoses that allow drainage to occur by alternate routes during periods of temporary compression. The alternate routes include both superficial pathways (via the facial and retromandibular/external jugular veins) and deep drainage (via the anastomoses with the cavernous sinus, pterygoid venous plexus, and the internal jugular vein). The facial veins, coursing with or parallel to the facial arteries, are valveless veins that provide the primary superficial drainage of the face. Tributaries of the facial vein include the deep facial vein, which drains the pterygoid venous plexus of the infratemporal fossa. Inferior to the margin of the mandible, the facial vein is joined by the anterior (communicating) branch of the retromandibular vein. The facial vein drains directly or indirectly into the IJV. At the medial angle of the eye, the facial vein communicates with the superior ophthalmic vein, which drains into the cavernous sinus. The retromandibular vein, formed by the union of the superficial temporal and maxillary veins, is a deep vein of the face formed by the union of the superficial temporal vein and the maxillary vein, the latter draining the pterygoid plexus. The retromandibular vein runs posterior to the ramus of the mandible within the substance of the parotid gland, superficial to the external carotid artery and deep to the facial nerve. As it emerges from the inferior pole of the gland, the retromandibular vein divides into an anterior branch that unites with the facial vein and a posterior branch that joins the posterior auricular vein inferior to the parotid gland to form the external jugular vein. This vein passes inferiorly and superficially in the neck to empty into the subclavian vein.

Chapter 7: Head

Veins of the Scalp The venous drainage of superficial parts of the scalp is through the accompanying veins of the scalp arteries, the supraorbital and supratrochlear veins (Table 7.7). The superficial temporal veins and posterior auricular veins drain the scalp anterior and posterior to the auricles, respectively. The posterior auricular vein often receives a mastoid emissary vein from the sigmoid sinus, a dural venous sinus. The occipital veins drain the occipital region of the scalp. Venous drainage of deep parts of the scalp in the temporal region is through deep temporal veins, which are tributaries of the pterygoid venous plexus.

Thrombophlebitis of the Facial Vein The facial vein makes clinically important connections with the cavernous sinus, a venous sinus of the dura mater, through the superior ophthalmic vein, and the pterygoid plexus, a network of small veins within the infratemporal fossa, through the inferior ophthalmic and deep facial veins (Fig. 7.12; Table 7.7). Because of these connections, an infection of the face may spread to the cavernous sinus and pterygoid venous plexus. Blood from the medial angle of the eye, nose, and lips usually drains inferiorly through the facial vein, especially when a person is erect. Because the facial vein has no valves, blood may pass through it in the opposite direction; consequently, venous blood from the face may enter the cavernous sinus. In individuals with thrombophlebitis of the facial vein, inflammation of the facial vein with secondary thrombus (clot) formation, pieces of an infected clot may extend into the intracranial venous system and produce thrombophlebitis of the cavernous sinus. Infection of the facial veins spreading to the dural venous sinuses may result from lacerations of the nose or be initiated by squeezing pustules (pimples) on the side of the nose and upper lip. Consequently, the triangular area from the upper lip to the bridge of the nose is considered the danger triangle of the face (Fig. B7.19).

Figure B7.19


Lymphatic Drainage of the Face and Scalp There are no lymph nodes in the scalp and except for the parotid/buccal region, there are no lymph nodes in the face. Lymph from the scalp, face, and neck drains into the superficial ring (pericervical collar) of lymph nodes—submental, submandibular, parotid, mastoid, and occipital—located at the junction of the head and neck (Fig. 7.28A). The lymphatic vessels of the face accompany other facial vessels. Superficial lymphatic vessels accompany veins, and deep lymphatics accompany arteries. All lymphatic vessels from the head and neck drain directly or indirectly into the deep cervical lymph nodes (Fig. 7.28B), a chain of nodes mainly located along the IJV in the neck. Lymph from these deep nodes passes to the jugular lymphatic trunk, which joins the thoracic duct on the left side and the IJV or brachiocephalic vein on the right side. A summary of the lymphatic drainage of the face follows.    

Lymph from the lateral part of the face and scalp, including the eyelids, drains to the superficial parotid lymph nodes. Lymph from the deep parotid nodes drains to the deep cervical lymph nodes. Lymph from the upper lip and lateral parts of the lower lip drains to the submandibular lymph nodes. Lymph from the chin and central part of the lower lip drains to the submental lymph nodes.

Squamous Cell Carcinoma of the Lip Squamous cell carcinoma (cancer) of the lip usually involves the lower lip (Fig. B7.20). Overexposure to sunshine over many years, is a common factor in these cases. Chronic irritation from pipe smoking is also a contributing cause. Cancer cells from the central part of the lower lip, the floor of the mouth, and the apex of the tongue spread to the submental lymph nodes, whereas cancer cells from lateral parts of the lower lip drain to the submandibular lymph nodes.

Figure B7.20

Chapter 7: Head

The Bottom Line The face and scalp are highly vascular. The terminal branches of the arteries of the face anastomose freely (including anastomoses across the midline with their contralateral partners); thus bleeding from facial lacerations may be diffuse, with the lacerated vessel bleeding from both ends. Most arteries of the face are branches or derivatives of branches of the external carotid artery; the arteries arising from the internal carotid that supply the forehead are exceptions. The main artery to the face is the facial artery. The arteries of the scalp are firmly embedded in the dense connective tissue overlying the epicranial aponeurosis. Thus, when lacerated, the arteries bleed from both ends, like those of the face, but are less able to constrict or retract than other superficial vessels; therefore, profuse bleeding results. The veins of the face and scalp generally accompany arteries, providing a primarily superficial venous drainage. However, they also anastomose with the pterygoid venous plexus and with dural venous sinuses via emissary veins, which provides a potentially dangerous route for the spread of infection. Most nerves and vessels of the scalp run vertically toward the vertex; thus a horizontal laceration may produce more neurovascular damage than a vertical one. The lymphatic drainage of most of the face follows the venous drainage to lymph nodes around the base of the anterior part of the head (submandibular, parotid, and superficial cervical nodes). An exception to this pattern is the lymph drainage of the central part of the lip and chin, which initially drains to the submental lymph nodes. All these nodes drain in turn to the deep cervical lymph nodes. Figure 7.28. Lymphatic drainage of face and scalp. A. The superficial drainage is shown. A pericervical collar of superficial lymph nodes is formed at the junction of the head and neck by the submental, submandibular, parotid, mastoid, and occipital nodes. These nodes initially receive most of the lymph drainage from the face and scalp. B. The deep drainage is shown. All lymphatic vessels from the head and neck ultimately drain into the deep cervical lymph nodes, either directly from the tissues or indirectly after passing through an outlying group of nodes.


Parotid Gland The parotid gland is the largest of three paired salivary glands. From a functional viewpoint, it would seem logical to discuss all three glands simultaneously in association with the anatomy of the mouth. However, from an anatomical viewpoint, particularly in dissection courses, the parotid gland is usually examined with or immediately subsequent to the dissection of the face to expose the facial nerve. Dissection of the parotid region must be completed before dissection of the infratemporal region and muscles of mastication or the carotid triangle of the neck. The submandibular gland is encountered primarily during dissection of the submandibular triangle of the neck, and the sublingual glands when dissecting the floor of the mouth. The parotid gland is enclosed within a tough fascial capsule, the parotid sheath, derived from the investing layer of deep cervical fascia (Fig. 7.29). The parotid gland has an irregular shape because the area occupied by the gland, the parotid bed, is anteroinferior to the external acoustic meatus, where it is wedged between the ramus of the mandible and the mastoid process (Fig. 7.27A). Fatty tissue between the lobes of the gland confers the flexibility the gland must have to accommodate the motion of the mandible. The apex of the parotid gland is posterior to the angle of the mandible, and its base is related to the zygomatic arch. The subcutaneous lateral surface of the parotid gland is almost flat. The parotid duct passes horizontally from the anterior edge of the gland (Fig. 7.29). At the anterior border of the masseter, the duct turns medially, pierces the buccinator, and enters the oral cavity through a small orifice opposite the 2nd maxillary molar tooth. Embedded within the substance of the parotid gland, from superficial to deep, are the parotid plexus of the facial nerve (CN VII) and its branches (Figs. 7.27A & C and 7.29), the retromandibular vein, and the external carotid artery. On the parotid sheath and within the gland are parotid lymph nodes (Figs. 7.28A and 7.29).

Innervation of Parotid Gland and Related Structures Although the parotid plexus of CN VII is embedded within it, the CN VII does not provide innervation to the gland. The auriculotemporal nerve, a branch of CN V 3 , is closely related to the parotid gland and passes superior to it with the superficial temporal vessels. The great auricular nerve, a branch of the cervical plexus composed of fibers from C2 and C3 spinal nerves, innervates the parotid sheath (Fig. 7.29) as well as the overlying skin. The parasympathetic component of the glossopharyngeal nerve (CN IX) supplies presynpatic secretory fibers to the otic ganglion. The postsynaptic parasympathetic fibers are conveyed from the ganglion to the gland by the auriculotemporal nerve (Fig. 7.24A). Stimulation of the parasympathetic fibers produces a thin, watery saliva. Sympathetic fibers are derived from the cervical ganglia through the external carotid nerve plexus on the external carotid artery (Fig. 7.29). The vasomotor activity of these fibers may reduce secretion from the gland. Sensory nerve fibers pass to the gland through the great auricular and auriculotemporal nerves.

Chapter 7: Head

Figure 7.29. Relationships of parotid gland. A transverse slice through the bed of the parotid gland demonstrates the relationship of the gland to surrounding structures. The gland passes deeply between the ramus of the mandible, flanked by the muscles of mastication anteriorly and the mastoid process and sternocleidomastoid muscle posteriorly. The dimensions of the parotid bed change with movements of the mandible. The external carotid artery and periarterial plexus, retromandibular vein, and parotid plexus of the facial nerve (CN VII) are embedded within the gland itself. The parotid duct turns medially at the anterior border of the masseter muscle and pierces the buccinator.

Parotidectomy About 80% of salivary gland tumors occur in the parotid glands. Most tumors of the parotid glands are benign, but most salivary gland cancer begins in the parotid. Surgical excision of the parotid gland (parotidectomy) is often performed as part of the treatment. Because the parotid plexus of CN VII is embedded in the parotid gland, the plexus and its branches are in jeopardy during surgery. An important step in parotidectomy is the identification, dissection, isolation, and preservation of the facial nerve. A superficial portion of the gland (often erroneously referred to as a “lobe” ) is removed, after which the parotid plexus, which occupies a distinct plane within the gland, can be retracted to enable dissection of the deep portion of the gland. The parotid gland makes a substantial contribution to the posterolateral contour of the face, the extent of its contribution being especially evident after it has been surgically removed. See clinical correlation (blue) box “Paralysis of Facial Muscles,” earlier in this chapter, for a discussion of the functional consequences of injury to the facial nerve.

Infection of the Parotid Gland The parotid gland may become infected by infectious agents that pass through the bloodstream, as occurs in mumps, an acute communicable viral disease. Infection of the gland causes inflammation (parotiditis) and swelling of the gland. Severe pain occurs because the parotid sheath limits swelling. Often the pain is worse during chewing because the enlarged gland is wrapped around the posterior border of the ramus of the mandible and is compressed against the mastoid process of the


temporal bone when the mouth is opened. The mumps virus may also cause inflammation of the parotid duct, producing redness of the parotid papilla, the small projection at the opening of the duct into the superior oral vestibule. Because the pain produced by mumps may be confused with a toothache, redness of the papilla is often an early sign that the disease involves the gland and not a tooth. Parotid gland disease often causes pain in the auricle, external acoustic meatus, temporal region, and TMJ because the auriculotemporal nerve, from which the parotid gland and sheath receive sensory fibers, also supplies sensory fibers to the skin over the temporal fossa and auricle.

Abscess in the Parotid Gland A bacterial infection localized in the parotid gland usually produces an abscess. The infection could result from extremely poor dental hygiene and spread to the gland through the parotid ducts. Physicians and dentists must determine whether a swelling of the cheek results from infection of the parotid gland or from an abscess of dental origin.

Sialography of the Parotid Duct A radiopaque fluid can be injected into the duct system of the parotid gland through a cannula inserted through the orifice of the parotid duct in the mucous membrane of the cheek. This technique (sialography) is followed by radiography of the gland. Parotid sialograms (G. sialon, saliva + G. grapho, to write) demonstrate parts of the parotid duct system that may be displaced or dilated by disease.

Blockage of the Parotid Duct The parotid duct may be blocked by a calcified deposit, called a sialolith or calculus (L. pebble). The resulting pain in the parotid gland is made worse by eating. Sucking a lemon slice is painful because of the buildup of saliva in the proximal part of the blocked duct.

Accessory Parotid Gland Sometimes an accessory parotid gland lies on the masseter muscle between the parotid duct and the zygomatic arch. Several ducts open from this accessory gland into the parotid duct.

The Bottom Line The largest of the salivary glands, the parotid gland makes a substantial contribution to the contour of the face. Occupying a complex space anterior to the auricle, the gland straddles most of the posterior aspect of the ramus of the mandible. Fatty tissue in the gland gives it flexibility to accommodate the motion of the mandible. The parotid duct passes anteriorly across the masseter, parallel and about a finger's breadth inferior to the zygomatic arch, and then turns medially to enter the superior oral vestibule opposite the 2nd maxillary molar. Parotid fascia, continuous with the investing layer of deep cervical fascia, invests the gland as the parotid sheath. The sheath is innervated by the great auricular nerve, but the gland receives parasympathetic secretomotor innervation from the glossopharyngeal nerve via a complex route involving the otic ganglion.

Chapter 7: Head

Surface Anatomy of the Head Regions of the Head To allow clear communications regarding the location of structures, injuries, or pathologies, the head is divided into regions (Fig. SA7.1). The large number of regions into which the relatively small area of the face is divided (eight) is a reflection of both its functional complexity and personal importance, as are annual expenditures for elective aesthetic surgery. With the exception of the auricular region, which includes the external ear, the names of the regions of the neurocranial portion of the head correspond to the underlying bones or bony features: frontal, parietal, occipital, temporal, and mastoid regions. The viscerocranial portion includes the facial region, which is divided into five bilateral and three median regions related to superficial features (oral and buccal regions), to deeper soft tissue formations (parotid region), and to skeletal features (orbital, infraorbital, nasal, zygomatic, and mental regions). The remainder of this chapter discusses several of these regions in detail as well as some deep regions not represented on the surface (for example, the infratemporal region and the pterygopalatine fossa). The surface anatomy of these regions will be discussed with the description of each region.

Surface Anatomy of the Face Despite the apparently infinite variations that enable people to be identified as individuals, the features that the human face bears are constant (Fig. SA7.2). The eyebrows (L. supercilia) are linear growths of hair overlying the superior orbital margin. The hairless region between the eyebrows overlies the glabella, and the prominent ridges that extend laterally on each side above the eyebrows are the superciliary arches. The eyelids (L. palpebrae) are mobile, musculofibrous folds that overlie the eyeball. They are joined at each end of the palpebral fissure between them at the medial and lateral angles (canthi) of the eye. The epicanthal fold (epicanthus) is a fold of skin that covers the medial angle of the eye in some people, chiefly Asians. The depressions superior and inferior to the lids are the suprapalpebral and infrapalpebral sulci. The external nose presents a prominent apex (tip), and is continuous with the forehead at the root of the nose (bridge). The rounded anterior border between the root and apex is the dorsum of the nose. Inferior to the apex, the nasal cavity of each side opens anteriorly by a naris (pleural = nares), bounded medially by the nasal septum and laterally by an ala (wing) of the nose. The lips surround the opening of the mouth, the oral fissure. The vermillion border of the lip marks the beginning of the transitional zone (commonly referred to as the lip) between the skin and the mucous membrane of the lip. The skin of the transitional zone is hairless and thin, increasing its sensitivity and causing its color to be different (because of underlying capillary beds) from that of the adjacent skin of the face. The lateral junction of the lips is the labial commissure; the angle between the lips, medial to the commissure, that increases as the mouth opens and decreases as it closes is the angle of the mouth. The median part of the upper lip features a tubercle, superior to which is a shallow groove, the philtrum (G. love charm), extending to the nasal septum.


Figure SA7.1 The musculofibrous folds of the lips continue laterally as the cheek, which also contains the buccinator and buccal fat‐pad. The cheek is separated from the lips by the nasolabial sulcus, which runs obliquely between the ala of the nose and the angle of the mouth. These grooves are easiest to observe during smiling. The lower lip is separated from the mental protuberance (chin) by the mentolabial sulcus. The lips, cheeks, and chin of the mature male grow hair as part of the secondary sex characteristics, the beard.

Figure SA7.2

Chapter 7: Head

Orbit, Orbital Region, and Eyeball The orbits are bony cavities in the facial skeleton that resemble hollow quadrangular pyramids with their bases directed anterolaterally and their apices, posteromedially (Fig. 7.30A). The medial walls of the two orbits, separated by the ethmoidal sinuses and the upper parts of the nasal cavity, are parallel, whereas their lateral walls are nearly at a right (90°) angle. Consequently, the axes of the orbits diverge at approximately 45°. The optical axes (axes of gaze, the direction or line of sight) for the two eyeballs, are parallel, however. The orbits contain and protect the eyeballs (globes of eyes) and accessory visual structures, which include the:     

Eyelids, which bound the orbits anteriorly, controlling exposure of the anterior eyeball. Extraocular muscles, which position the eyeballs and raise the superior eyelids. Nerves and vessels in transit to the eyeballs and muscles. Orbital fascia surrounding the eyeballs and muscles. Mucous membrane (conjunctiva) lining the eyelids and anterior aspect of the eyeballs and most of the lacrimal apparatus, which lubricates it.

All space within the orbits not occupied by the above structures is filled with orbital fat; thus it forms a matrix in which the structures of the orbit are embedded. The pyramidal orbit has a base, four walls, and an apex (Fig. 7.30B): 









The base of the orbit is outlined by the orbital margin that surrounds the orbital opening. The bone forming the orbital margin is reinforced to afford protection to the orbital contents and provides attachment for the orbital septum, an interrupted fibrous sheet that extends into the eyelids. The superior wall (roof) is approximately horizontal and is formed mainly by the orbital part of the frontal bone, which separates the orbital cavity from the anterior cranial fossa. Near the apex of the orbit, the superior wall is formed by the lesser wing of the sphenoid. Anterolaterally, a shallow depression in the orbital part of the frontal bone, called the fossa for the lacrimal gland (lacrimal fossa), accommodates the lacrimal gland. The medial walls of the contralateral orbits are essentially parallel and are formed primarily by the ethmoid bone, along with contributions from the frontal, lacrimal, and sphenoids. Anteriorly, the medial wall is indented by the lacrimal groove and fossa for the lacrimal sac. Much of the bone forming the medial wall is paper thin; the ethmoid bone is highly pneumatized with ethmoidal cells, often visible through the bone of a dried cranium. The inferior wall (floor) is formed mainly by the maxilla and partly by the zygomatic and palatine bones. The thin inferior wall is shared by the orbit and maxillary sinus. It slants inferiorly from the apex to the inferior orbital margin. The inferior wall is demarcated from the lateral wall of the orbit by the inferior orbital fissure. The lateral wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid. This is the strongest and thickest wall, which is important because it is most exposed and vulnerable to direct trauma. Its posterior part separates the orbit from the temporal and middle cranial fossae.




The lateral walls of the contralateral orbits are nearly perpendicular to each other. The apex of the orbit is at the optic canal in the lesser wing of the sphenoid just medial to the superior orbital fissure.

The widest part of the orbit corresponds to the equator of the eyeball, an imaginary line encircling the eyeball equidistant from its anterior and posterior poles. The bones forming the orbit are lined with periorbita (periosteum of orbit). The periorbita is continuous at the optic canal and superior orbital fissure with the periosteal layer of the dura mater. The periorbita is also continuous over the orbital margins and through the inferior orbital fissure with the periosteum covering the external surface of the cranium (pericranium), and with the orbital septa at the orbital margins, with the fascial sheaths of the extraocular muscles, and with orbital fascia that forms the fascial sheath of the eyeball (Fig. 7.31A).

Periorbital Ecchymosis The skin of the eyelid is the thinnest of the body and is delicate and sensitive. Because of the loose nature of the subcutaneous tissue within the eyelids, even a relatively slight injury or inflammation may result in an accumulation of fluid, causing the eyelids to swell. Blows to the periorbital region usually produce soft tissue damage because the tissues are crushed against the strong and relatively sharp margin. Significant swelling and hemorrhage into the eyelids and extravasation of blood into the periorbital skin (ecchymosis) occur. This type of injury is common in boxers.

Fractures of the Orbit The orbital margin is strong to protect the orbital content. However, when the blows are powerful enough and the impact is directly on the bony rim, the resulting fractures usually occur at the sutures between the bones forming the orbital margin. Because of the thinness of the medial and inferior walls of the orbit, a blow to the eye may fracture the orbital walls while the margin remains intact. Indirect traumatic injury that displaces the orbital walls is called a “blowout” fracture. Fractures of the medial wall may involve the ethmoidal and sphenoidal sinuses, whereas fractures of the inferior wall may involve the maxillary sinus. Although the superior wall is stronger than the medial and inferior walls, it is thin enough to be translucent and may be readily penetrated. Thus a sharp object may pass through it and enter the frontal lobe of the brain. Orbital fractures often result in intraorbital bleeding, which exerts pressure on the eyeball, causing exophthalmos (protrusion of the eyeball). Any trauma to the eye may affect adjacent structures—for example bleeding into the maxillary sinus, displacement of maxillary teeth, and fracture of nasal bones resulting in hemorrhage, airway obstruction, and infection that could spread to the cavernous sinus through the ophthalmic vein.

Orbital Tumors Because of the closeness of the optic nerve to the sphenoidal and posterior ethmoidal sinuses, a malignant tumor in these sinuses may erode the thin bony walls of the orbit and compress the optic nerve and orbital contents. Tumors in the orbit

Chapter 7: Head

produce exophthalmos. The easiest entrance to the orbital cavity for a tumor in the middle cranial fossa is through the superior orbital fissure; tumors in the temporal or infratemporal fossa gain access to this cavity through the inferior orbital fissure. Although the lateral wall of the orbit is nearly as long as the medial wall because it extends laterally and anteriorly, it does not reach as far anteriorly as the medial wall does, which occupies essentially a sagittal plane (Fig. 7.30A). Thus nearly 2.5 cm of the eyeball is exposed when the pupil is turned medially as far as possible. This is why the lateral side affords a good approach for operations on the eyeball. Figure 7.30. Orbits. A. The diagram and MRI study demonstrate the orbits' disposition relative to each other, and to the optical axes (line of gaze). The orbits are separated by ethmoidal cells and the upper nasal cavity and septum. B. The bony walls of the orbit are shown. The word ethmoid is printed directly on the thin orbital plate of the ethmoid bone that separates the orbit from the ethmoidal sinuses. The optic canal is situated at the apex (deepest part) of the pyramidal orbital cavity, where it passes between the body of and the two roots of the lesser wing of the sphenoid. A straight probe must pass along the lateral wall of the cavity if it is to traverse the canal.


Figure 7.31. Orbit, eyeball, and eyelids. A. The contents of the orbit are shown. The subarachnoid space around the optic nerve is continuous with the space between the arachnoid and the pia covering the brain. The numbers refer to structures labeled in part C. B. This MRI study shows a sagittal section through the optic nerve (CN II) and eyeball. M, maxillary sinus; S, superior ophthalmic vein; arc, optic canal. C. This detail shows the superior eyelid. The tarsus forms the skeleton of the eyelid and contains tarsal glands. (Part B courtesy of Dr. W. Kucharczyk, Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, Ontario, Canada.)

The Bottom Line The orbits are pyramidal cavities, with bases directed anteriorly and apices posteriorly, that house the eyeballs and accessory visual structures. The medial walls of the contralateral orbits are parallel, and the lateral walls are perpendicular to each other. The margins and lateral walls of the orbits, being most vulnerable to direct trauma, are strong. The superior wall (roof) and inferior wall (floor) are shared with the anterior cranial fossa and the maxillary sinus, respectively, and much of the paper‐thin medial wall is common to the ethmoidal cells. The medial wall and floor are thus vulnerable to the spread of disease processes from the paranasal sinuses and to blowout fractures when blunt force is applied to the orbital contents, suddenly increasing intraorbital pressure. The optic canal and superior orbital fissure at the apex of the orbit are the primary paths by which structures enter and exit the orbits.

Chapter 7: Head

Eyelids and Lacrimal Apparatus The eyelids and lacrimal fluid, secreted by the lacrimal glands, protect the cornea and eyeball from injury and irritation (e.g., by dust and small particles).

Eyelids When closed, the eyelids cover the eyeball anteriorly, thereby protecting it from injury and excessive light. They also keep the cornea moist by spreading the lacrimal fluid. The eyelids are movable folds that are covered externally by thin skin and internally by transparent mucous membrane, the palpebral conjunctiva (Fig. 7.31A & C). This part of the conjunctiva is reflected onto the eyeball, where it is continuous with the bulbar conjunctiva. This part of the conjunctiva is thin and transparent and attaches loosely to the anterior surface of the eyeball. The bulbar conjunctiva, loose and wrinkled over the sclera (where it contains small, visible blood vessels), is adherent to the periphery of the cornea (Fig. 7.32A). The lines of reflection of the palpebral conjunctiva onto the eyeball form deep recesses, the superior and inferior conjunctival fornices (Fig. 7.31A). The conjunctival sac is the space bound by the palpebral and bulbar conjunctivae; it is a closed space when the eyelids are closed, but opens via an anterior aperture, the palpebral fissure (L. rima palpebrae, the gap between the eyelids), when the eye is “open” (eyelids are parted). The conjunctival sac is a specialized form of mucosal “bursa” that enables the eyelids to move freely over the surface of the eyeball as they open and close. The superior (upper) and inferior (lower) eyelids are strengthened by dense bands of connective tissue, the superior and inferior tarsi (sing. tarsus) which form the “skeleton” of the eyelids (Figs. 7.31C and 7.33A). Fibers of the palpebral portion of the orbicularis oculi (the sphincter of the palpebral fissure) are in the connective tissue superficial to these tarsi and deep to the skin of the eyelids. Embedded in the tarsi are tarsal glands, the lipid secretion of which lubricates the edges of the eyelids and prevents them from sticking together when they close. The lipid secretion also forms a barrier that lacrimal fluid does not cross when produced in normal amounts. When production is excessive, it spills over the barrier onto the cheeks as tears. The eyelashes (L. cilia) are in the margins of the lids. The large sebaceous glands associated with the eyelashes are ciliary glands. The junctions of the superior and inferior eyelids make up the medial and lateral palpebral commissures, defining the angles of the eye (G. kanthos, corner of eye). Thus each eye has medial and lateral angles, or canthi (Fig. 7.33B). Between the nose and the medial angle of the eye is the medial palpebral ligament, which connects the tarsi to the medial margin of the orbit (Fig. 7.33A). The orbicularis oculi originates and inserts onto this ligament. A similar lateral palpebral ligament attaches the tarsi to the lateral margin of the orbit but does not provide for direct muscle attachment. The orbital septum is a weak membrane that spans from the tarsi to the margins of the orbit, where it becomes continuous with the periosteum. It keeps the orbital fat contained and can limit the spread of infection to and from the orbit.


Lacrimal Apparatus The lacrimal apparatus (Fig. 7.33B) consists of the: 



Lacrimal glands: secrete lacrimal fluid, a watery physiological saline containing the bacteriocidal enzyme lysozyme. The fluid moistens and lubricates the surfaces of the conjunctiva and cornea and provides some nutrients and dissolved oxygen to the cornea; when produced in excess, it constitutes tears. Lacrimal ducts: convey lacrimal fluid from the lacrimal glands to the conjunctival sac.

Figure 7.32. Orbit and eyeball. A. In this anterior approach dissection of the orbit, the eyelids, orbital septum, levator palpebrae superioris, and some fat have been removed. Part of the lacrimal gland is seen between the bony orbital wall laterally and the eyeball and lateral rectus muscle medially. B. The surface features of the eye are shown. The fibrous outer coat of the eyeball includes the tough white sclera and the central transparent cornea, through which the pigmented iris with its aperture, the pupil, can be seen. The inferior eyelid has been everted to show the reflection of conjunctiva from the anterior surface of the eyeball to the inner surface of the eyelid. Arrow, the inferior lacrimal punctum (opening) of the lacrimal canaliculi. The semilunar fold is a vertical fold of conjunctiva near the medial angle, at the lacrimal caruncle.

Chapter 7: Head

Figure 7.33. Skeleton of eyelids and lacrimal apparatus. A. The superior and inferior tarsi and their attachments are shown. Their ciliary margins are free but they are attached peripherally to the orbital septum (palpebral fascia in the eyelid). The angles are anchored by medial and lateral palpebral ligaments . The fan‐shaped aponeurosis of the levator palpebrae superioris is attached to the anterior surface and superior edge of the superior tarsus. B. The components of the lacrimal apparatus, by which tears flow from the superolateral aspect of the conjunctival sac to the nasal cavity, are demonstrated.

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Lacrimal canaliculi (L. small canals): commence at a lacrimal punctum (opening) on the lacrimal papilla near the medial angle of the eye and drain lacrimal fluid from the lacrimal lake (L. lacus lacrimalis; a triangular space at the medial angle of the eye where the tears collect) to the lacrimal sac (the dilated superior part of the nasolacrimal duct). Nasolacrimal duct: conveys the lacrimal fluid to the inferior nasal meatus.

The lacrimal gland, almond shaped and approximately 2 cm long, lies in the fossa for the lacrimal gland in the superolateral part of each orbit (Figs. 7.30B, 7.32A, and 7.33A). The gland is divided into superior (orbital) and inferior (palpebral) parts by the lateral expansion of the tendon of the levator palpebrae superioris (Fig. 7.33A). Accessory lacrimal glands are also present; they are more numerous in the superior eyelid than in the inferior eyelid. Production of lacrimal fluid is stimulated by parasympathetic impulses from CN VII. It is secreted through 8—12 excretory ducts that open into the lateral part of the superior conjunctival fornix of the conjunctival sac. The fluid flows inferiorly within the sac under the influence of gravity. When the cornea becomes dry, the eye blinks. The eyelids come together in a lateral to medial sequence pushing a film of fluid medially over the cornea, somewhat like windshield wipers when washing the car windshield. In this way, lacrimal fluid containing foreign material such as dust is pushed toward the medial angle of the eye, accumulating in the lacrimal lake from which they drain by capillary action through the lacrimal puncta and lacrimal canaliculi to the lacrimal sac. From this sac, the tears pass to the inferior nasal meatus of the nasal cavity through the nasolacrimal duct. They drain posteriorly across the floor of the nasal cavity to the nasopharynx and are eventually swallowed.


In addition to cleansing particles and irritants from the conjunctival sac, lacrimal fluid provides the cornea with nutrients and oxygen. The nerve supply of the lacrimal gland is both sympathetic and parasympathetic. The presynaptic parasympathetic secretomotor fibers are conveyed from the facial nerve by the greater petrosal nerve and then by the nerve of the pterygoid canal to the pterygopalatine ganglion, where they synapse with the cell body of the postsynaptic fiber. Vasoconstrictive, postsynaptic sympathetic fibers, brought from the superior cervical ganglion by the internal carotid plexus and deep petrosal nerve, join the parasympathetic fibers to form the nerve of the pterygoid canal and traverse the pterygopalatine ganglion. The zygomatic nerve (from the maxillary nerve) brings both types of fibers to the lacrimal branch of the ophthalmic nerve, by which they enter the gland.

Injury to the Nerves Supplying the Eyelids Because it supplies the levator palpebrae superioris, a lesion of the oculomotor nerve causes paralysis of the muscle, and the superior eyelid droops (ptosis). Damage to the facial nerve involves paralysis of the orbicularis oculi, preventing the eyelids from closing fully. Normal rapid protective blinking of the eye is also lost. The loss of tonus of the muscle in the inferior eyelid causes the lid to fall away (evert) from the surface of the eyeball, leading to drying of the cornea. This leaves the eyeball unprotected from dust and small particles. Thus irritation of the unprotected eyeball results in excessive but inefficient lacrimation (tear formation). Excessive lacrimal fluid also forms when the lacrimal drainage apparatus is obstructed, thereby preventing the fluid from reaching the inferior part of the eyeball. People often dab their eyes constantly to wipe the tears, resulting in further irritation.

Inflammation of the Palpebral Glands Any of the glands in the eyelid may become inflamed and swollen from infection or obstruction of their ducts. If the ducts of the ciliary glands are obstructed, a painful red suppurative (pus‐producing) swelling, a sty (hordeolum), develops on the eyelid. Cysts of the sebaceous glands of the eyelid, called chalazia, may also form. Obstruction of a tarsal gland produces inflammation, a tarsal chalazion, that protrudes toward the eyeball and rubs against it as the eyelids blink. Chalazia are usually more painful than sties.

Hyperemia of the Conjunctiva The conjunctiva is colorless, except when its vessels are dilated and congested (“bloodshot eyes” ). Hyperemia of the conjunctiva is caused by local irritation (e.g., from dust, chlorine, or smoke). An inflamed conjunctiva, conjunctivitis (“pinkeye” ), is a common contagious infection of the eye.

Subconjunctival Hemorrhages Subconjunctival hemorrhages are common and are manifested by bright or dark red patches deep to and within the bulbar conjunctiva. The hemorrhages may result from injury or inflammation. A blow to the eye, excessively hard blowing of the nose, and paroxysms of coughing or violent sneezing can cause hemorrhages resulting from rupture of small subconjunctival capillaries.

Chapter 7: Head

The Bottom Line The eyelids and lacrimal apparatus are protective devices for the eyeball. The conjunctival sac is a special form of mucosal bursa, which enables the eyelids to move over the surface of the eyeball as they open and close, spreading the moistening and lubricating film of lacrimal fluid within the sac. The fluid is secreted into the lateral superior fornix of the sac and is spread by gravity and blinking across the anterior eyeball, cleansing and providing the cornea with nutrients and oxygen as it is pushed toward the medial angle of the eye. The fluid and contained irritants accumulate in the lacrimal lake. They are drained from here by capillary action through superior and inferior lacrimal puncta into lacrimal canaliculi that pass to the lacrimal sac. The sac drains via the nasolacrimal duct into the nasal cavity, where the fluid flows posteriorly and is eventually swallowed. Although the conjunctival sac opens anteriorly via the palpebral fissure, the watery lacrimal fluid will not cross the lipid barrier secreted by the tarsal glands onto the margins of the fissure unless it is produced in excess, as in crying.

The Eyeball The eyeball contains the optical apparatus of the visual system and occupies most of the anterior portion of the orbit. All anatomical structures within the eyeball have a circular or spherical arrangement. The eyeball proper has three layers; however, there is an additional loose connective tissue layer that surrounds the eyeball, allowing its movement within the orbit. The loose connective tissue layer is composed posteriorly of bulbar fascia, which forms the true socket for the eyeball, and anteriorly of bulbar conjunctiva. The three layers of the eyeball are the (Fig. 7.34):   

Fibrous layer (outer coat), consisting of the sclera and cornea. Vascular layer (middle coat), consisting of the choroid, ciliary body, and iris. Inner layer (inner coat), consisting of the retina that has both optic and non‐ visual parts.

Fibrous Layer of the Eyeball The sclera is the tough opaque part of the fibrous layer (coat) of the eyeball covering the posterior five sixths of the eyeball. It is the fibrous skeleton of the eyeball, providing shape and resistance as well as attachment for both the extrinsic (extraocular) and the intrinsic muscles of the eye. The anterior part of the sclera is visible through the transparent bulbar conjunctiva as “the white of the eye.” The cornea is the transparent part of the fibrous coat covering the anterior one sixth of the eyeball. The two parts differ primarily in terms of the regularity of the arrangement of the collagen fibers of which they are composed and the degree of hydration of each.

Vascular Layer of the Eyeball The vascular layer of the eyeball (also called the uvea or uveal tract) consists of the choroid, ciliary body, and iris. The choroid, a dark reddish brown layer between the sclera and the retina, forms the largest part of the vascular layer of the eyeball and lines most of the sclera. Within this pigmented and dense vascular bed, larger vessels of the vascular lamina are located externally (near the sclera). The finest vessels (the


capillary lamina of the choroid or choriocapillaris, an extensive capillary bed) are innermost, adjacent to the avascular light‐sensitive layer of the retina, which it supplies with oxygen and nutrients. Engorged with blood in life, this layer is responsible for the “red eye” reflection that occurs in flash photography. The choroid is continuous anteriorly with the ciliary body. The choroid attaches firmly to the pigment layer of the retina, but it can easily be stripped from the sclera. The ciliary body, which is muscular as well as vascular, connects the choroid with the circumference of the iris. The ciliary body provides attachment for the lens; contraction and relaxation of the smooth muscle of the ciliary body controls thickness (and therefore the focus) of the lens. Folds on the internal surface of the ciliary body, the ciliary processes, secrete aqueous humor, which fills the anterior and posterior chambers of the eye (Fig. 7.34B). The anterior chamber of the eye is the space between the cornea anteriorly and the iris/pupil posteriorly. The posterior chamber of the eye is between the iris/pupil anteriorly and the lens and ciliary body posteriorly. The iris, which literally lies on the anterior surface of the lens, is a thin contractile diaphragm with a central aperture, the pupil, for transmitting light. When a person is awake, the size of the pupil varies continually to regulate the amount of light entering the eye. Two involuntary muscles control the size of the pupil: the parasympathetically stimulated sphincter pupillae closes the pupil, and the sympathetically stimulated dilator pupillae opens it. The nature of the pupillary responses is paradoxical: sympathetic responses usually occur immediately, yet it may take up to 20 min for the pupil to dilate in response to low lighting, as in a darkened theater. Parasympathetic responses are typically slower than sympathetic responses, yet parasympathetically stimulated papillary constriction is normally instantaneous.

Pupillary Light Reflex The pupillary light reflex is tested using a penlight during a neurological examination. This reflex, involving CN II (afferent limb) and CN III (efferent limb), is the rapid constriction of the pupil in response to light. When light enters one eye, both pupils constrict because each retina sends fibers into the optic tracts of both sides. The sphincter pupillae muscle is innervated by parasympathetic fibers; consequently, interruption of these fibers causes dilation of the pupil because of the unopposed action of the sympathetically innervated dilator pupillae muscle. The first sign of compression of the oculomotor nerve is ipsilateral slowness of the pupillary response to light.

Uveitis Uveitis, inflammation of the vascular layer of the eyeball (uvea), may progress to severe visual impairment and blindness.

Chapter 7: Head

Figure 7.34. Eyeball with quarter section removed. A. The inner aspect of the optic part of the retina is supplied by the central artery of the retina, whereas the outer, light sensitive aspect is nourished by the capillary lamina of the choroid (Fig. 7.38). The central artery courses through the optic nerve and divides at the optic disc into superior and inferior branches. The branches of the central artery are end arteries that do not anastomose with each other or any other vessel. B. The structural details of the ciliary region are shown. The ciliary body is both muscular and vascular, as is the iris, the latter including two muscles: the sphincter pupillae and dilator pupillae muscles. Venous blood from this region, as well as the aqueous humor in the anterior chamber, drain into the scleral venous sinus.

Inner Layer of the Eyeball The inner layer of the eyeball is the retina. Grossly, the retina consists of two functional parts with distinct locations: an optic part and a non‐visual retina. The optic part of the retina is sensitive to visual light rays and has two layers: a neural layer and pigment cell layer. The neural layer is light receptive. The pigment cell layer consists of a single layer of cells that reinforces the light‐absorbing property of the choroid in reducing the scattering of light in the eyeball. The non‐visual retina is an anterior continuation of the pigment cell layer and a layer of supporting cells over the ciliary body (ciliary part of the retina) and the posterior surface of the iris (iridial part of the retina), respectively.


The fundus is the posterior part of the eyeball. It has a circular depressed area called the optic disc (optic papilla) where the sensory fibers and vessels conveyed by the optic nerve enter the eyeball (Fig. 7.34A). Because it contains no photoreceptors, the optic disc is insensitive to light. Consequently, this part of the retina is commonly called the blind spot. Just lateral to the optic disc is the macula lutea (L. yellow spot). The yellow color of the macula is apparent only when the retina is examined with red‐free light. The macula lutea is a small oval area of the retina with special photoreceptor cones that is specialized for acuity of vision. It is not normally observed with an ophthalmoscope (a device for viewing the interior of the eyeball through the pupil). At the center of the macula lutea is a depression, the fovea centralis (L. central pit), the area of most acute vision. The fovea is approximately 1.5 mm in diameter; its center, the foveola, does not have the capillary network visible elsewhere deep to the retina. The functional optic part of the retina terminates anteriorly along the ora serrata (L. serrated edge), an irregular border slightly posterior to the ciliary body. The ora serrata marks the anterior termination of the light‐receptive part of the retina. Except for the cones and rods of the neural layer, the retina is supplied by the central artery of the retina, a branch of the ophthalmic artery. The cones and rods of the outer neural layer receive nutrients from the capillary lamina of the choroid, or choriocapillaris (discussed in “Vasculature of the Orbit,” later in this chapter). It has the finest vessels of the inner surface of the choroid, against which the retina is pressed. A corresponding system of retinal veins unites to form the central vein of the retina.

Development of the Retina The retina and optic nerve develop from the optic cup, an outgrowth of the embryonic forebrain, the optic vesicle. As it evaginates from the brain, the optic vesicle carries the developing meninges with it (Moore and Persaud, 2003). Hence the optic nerve is invested with cranial meninges and an extension of the subarachnoid space. The central artery and vein of the retina cross the subarachnoid space and run within the distal part of the optic nerve. The pigment cell layer of the retina develops from the outer layer of the optic cup, and the neural layer develops from the inner layer of the cup.

Ophthalmoscopy Physicians use an ophthalmoscope (funduscope) to view the fundus (posterior part) of the eye (Fig. B7.21A). The retinal arteries and veins radiate over the fundus from the optic disc. The pale, oval disc appears on the medial side with the retinal vessels radiating from its center in the ophthalmoscopic view of the retina shown in Figure B7.21A. Pulsation of the retinal arteries is usually visible. Centrally, at the posterior pole of the eyeball, the macula appears darker than the reddish hue of surrounding areas of the retina because the black melanin pigment in the choroid and pigment cell layer is not screened by capillary blood.

Retinal Detachment The layers of the developing retina are separated in the embryo by an intraretinal space. During the early fetal period, the embryonic layers fuse, obliterating this space. Although the pigment cell layer becomes firmly fixed to the choroid, its

Chapter 7: Head

attachment to the neural layer is not firm. Consequently, detachment of the retina may follow a blow to the eye (Fig. B7.21B). A detached retina usually results from seepage of fluid between the neural and pigment cell layers of the retina, perhaps days or even weeks after trauma to the eye. Persons with a retinal detachment may complain of flashes of light or specks floating in front of the eye (Anderson et al., 2000).

Figure B7.21. Ophthalmoscopic photograph of normal fundus (A) and retinal detachment (B).

Papilledema An increase in CSF pressure slows venous return from the retina, causing edema of the retina (fluid accumulation). The edema is viewed during ophthalmoscopy as swelling of the optic disc, a condition called papilledema. Normally, the disc is flat and does not form a papilla. Papilledema results from increased intracranial pressure and increased CSF pressure in the extension of the subarachnoid space around the optic nerve (Fig. 7.34A). A sudden reduction of pressure in the spinal subarachnoid space, as might occur with lumbar puncture, could result in a potentially fatal herniation of brain tissue into the vertebral canal if performed when intracranial pressure is elevated.

Refractive Media of the Eyeball On their way to the retina, lightwaves pass through the refractive media of the eyeball: cornea, aqueous humor, lens, and vitreous humor (Fig. 7.34). The cornea is the circular area of the anterior part of the outer fibrous layer of the eyeball; it is largely responsible for refraction of the light that enters the eye. It is transparent, owing to the extremely regular arrangement of its collagen fibers and its dehydrated state. The cornea is sensitive to touch; its innervation is provided by the ophthalmic nerve (CN V 1 ). It is avascular. Its nourishment is derived from the capillary beds at its periphery, the aqueous humor, and lacrimal fluid. The latter also provides oxygen absorbed from the air.


The aqueous humor in the anterior and posterior chambers of the eye is produced in the posterior chamber by the ciliary processes of the ciliary body. This clear watery solution provides nutrients for the avascular cornea and lens. After passing through the pupil into the anterior chamber, the aqueous humor drains into the scleral venous sinus (L. sinus venosus sclerae, canal of Schlemm) at the iridocorneal angle. The humor is removed by the limbal plexus, a network of scleral veins close to the limbus, which drain in turn into both tributaries of the vorticose and the anterior ciliary veins (Fig. 7.34B). The lens is posterior to the iris and anterior to the vitreous humor of the vitreous body. It is a transparent, biconvex structure enclosed in a capsule. The highly elastic capsule of the lens is anchored by the zonular fibers (suspensory ligament of the lens) to the ciliary body and encircled by the ciliary processes. Although most refraction is produced by the cornea, the convexity of the lens, particularly its anterior surface, constantly varies to fine‐tune the focus of near or distant objects on the retina. The ciliary muscle in the ciliary body changes the shape of the lens; in this way the isolated unattached lens assumes a nearly spherical shape. Stretched within the circle of the relaxed ciliary body, the attachments around its periphery pull the lens relatively flat so that its refraction enables far vision. When parasympathetic stimulation causes the smooth muscle of the circular ciliary body to contract, the circle, like a sphincter, becomes smaller in size and the tension on the lens is reduced, allowing the lens to round up. The increased convexity makes its refraction suitable for near vision. In the absence of parasympathetic stimulation, the ciliary muscles relax again and the lens is pulled into its flatter, far‐vision shape. The vitreous humor is a watery fluid enclosed in the meshes of the vitreous body, a transparent jelly‐like substance in the posterior four fifths of the eyeball posterior to the lens (postremal or vitreous chamber, or posterior segment). In addition to transmitting light, the vitreous humor holds the retina in place and supports the lens.

Corneal Abrasions and Lacerations Foreign objects such as sand or metal filings (particles) produce corneal abrasions that cause sudden, stabbing pain in the eyeball and tears. Opening and closing the eyelids is also painful. Corneal lacerations are caused by sharp objects such as fingernails or the corner of a page of a book.

Presbyopia and Cataracts As people age, their lenses become harder and more flattened. These changes gradually reduce the focusing power of the lenses, a condition known as presbyopia (G. presbyos, old). Some people also experience a loss of transparency (cloudiness) of the lens from areas of opaqueness (cataracts). Cataract extraction is a common operation.

Hemorrhage into the Anterior Chamber Hemorrhage within the anterior chamber of the eyeball (hyphema or hyphemia) usually results from blunt trauma to the eyeball, such as from a squash or racquet ball or a hockey stick (Fig. B7.22). Initially, the anterior chamber is tinged red but blood soon accumulates in this chamber. The initial hemorrhage usually stops in a few days and recovery is usually good.

Chapter 7: Head

Figure B7.22. Hyphema.

The Bottom Line The eyeball contains the optical apparatus of the visual system. It has a trilaminar construction, with (1) a supporting outer fibrous layer, consisting of the opaque sclera and transparent anterior cornea; (2) a middle vascular layer, consisting of the choroid (largely concerned with providing nourishment to the cones and rods of the retina), the ciliary body (producer of the aqueous humor and adjuster of the lens), and the iris (protector of the retina); and (3) an inner layer, consisting of optic and non‐visual parts of the retina. The cornea is the major refractive component of the eyeball, with focusing adjustments made by the lens. Parasympathetic stimulation of the ciliary body reduces tension on the lens, allowing it to thicken for near vision. Relaxation of the ciliary body in the absence of stimulation stretches the lens, making it thinner for far vision. Parasympathetic stimulation also constricts the sphincter of the iris, which closes the pupil in response to bright light. Sympathetic stimulation of the dilator of the iris opens the pupil to admit more light. The anterior segment of the eyeball is filled with aqueous humor, produced by the ciliary processes in the posterior chamber. The humor passes through the pupil into the anterior chamber and is absorbed into the venous circulation at the scleral venous sinus. The postremal or vitreous chamber is filled with vitreous humor, which maintains the shape of the eye, transmits light, and holds the retina in place against the choroid.

Extraocular Muscles of the Orbit The extraocular muscles of the orbit are the levator palpebrae superioris, four recti (superior, inferior, medial, and lateral), and two obliques (superior and inferior). These muscles work together to move the superior eyelids and eyeballs. They are illustrated in Figures 7.35, 7.36, 7.37 and Table 7.8. The attachments, nerve supply, and main actions of the orbital muscles, beginning from the primary position, are described in Table 7.8. Additional details concerning some of the extraocular muscles are provided in the following text. Although actions of the muscles are described separately, in fact extraocular muscles rarely act independently; synergistic and antagonistic activity occurs between muscles most of the time. Muscles that are synergistic for one action may be antagonistic for another.


Levator Palpebrae Superioris The levator palpebrae superioris broadens into a wide bilaminar aponeurosis as it approaches its distal attachments. The superficial lamina attaches to the skin of the superior eyelid and the deep lamina to the superior tarsus (Fig. 7.33A). This muscle is opposed most of the time by gravity and is the antagonist of the superior half of the orbicularis oculi, the sphincter of the palpebral fissure. The deep lamina includes smooth muscle fibers, the superior tarsal muscle, that produce additional widening of the palpebral fissure during a sympathetic response (e.g., fright). Figure 7.35. Dissections of orbit. A. The lateral approach is shown. The ciliary ganglion receives sensory fibers from the nasociliary branches of CN V1, sympathetic fibers from the internal carotid plexus traveling around the ophthalmic artery, and parasympathetic fibers (which synapse in the ganglion) from the inferior branch of the oculomotor nerve (CN III). Between 8 and 10 short ciliary nerves pass from the ganglion to the eyeball. B. In this superior approach, the orbital part of the frontal bone has been removed. Observe the three nerves applied to the roof of the orbital cavity: trochlear, frontal, and lacrimal.

Chapter 7: Head

Figure 7.36. Nerves of orbit. A. After enucleation (excision) of the eyeball, structures near the apex of the orbit can be seen, including the common tendinous ring and the motor nerves of the orbit. The four rectus muscles arise from the common tendinous ring. This ring encircles the dural sheath of the optic nerve (CN II), the abducent nerve (CN VI), and the superior and inferior divisions of the oculomotor nerve (CN III). B. Structures in the apex of the orbit are shown. Nerves entering the orbit through the superior orbital fissure supply the muscles of the eyeball: oculomotor (CN III), trochlear (CN IV), and abducent (CN VI).

Recti and Oblique Muscles The four recti muscles (L. rectus, straight) arise from a fibrous cuff, the common tendinous ring, that surrounds the optic canal and part of the superior orbital fissure (Fig. 7.36B). Structures that enter the orbit through this canal and the adjacent part of the fissure lie at first in the cone of recti (Fig. 7.35A). The lateral and medial recti lie in the same horizontal plane, and the superior and inferior recti lie in the same vertical plane (Fig. 7.36A). Neither the superior rectus nor the inferior rectus pulls directly parallel to the long axis of the eyeball (neutral axis of gaze) (Table 7.8). As a result, from the primary position both recti tend to move the pupil medially (adduction). This medial pull of the superior and inferior recti is normally balanced by a similar tendency of the oblique muscles to move the pupil laterally (abduction). From the primary position, the inferior oblique directs the pupil laterally and superiorly; therefore, when the superior rectus and inferior oblique work synergistically, pure elevation of the eyeball occurs. Similarly, the superior oblique directs the pupil inferiorly and laterally; therefore, when the superior oblique works synergistically with the inferior rectus, pure depression results. When the pupil is already in the adducted position (as in the convergence involved in close reading), the oblique muscles are responsible for elevation (inferior oblique) and depression (superior oblique), moving the gaze up or down the page. Elevation and depression in the adducted position is the primary function of the oblique muscles.


Figure 7.37. Innervation of muscles of eyeball. The oculomotor (CN III), trochlear (CN IV), and abducent (CN VI) nerves are distributed to the muscles of the eyeball. The nerves enter the orbit through the superior orbital fissure. CN IV supplies the superior oblique, CN VI supplies the lateral rectus, and CN III supplies the remaining five muscles.

Chapter 7: Head

Table 7.8. Extraocular Muscles of the Orbit Muscle Levator palpebrae superioris

Inferior oblique

Insertion Innervation Superior tarsus and skin of Oculomotor nerve; superior eyelid deep layer (superior tarsal muscle) is supplied by sympathetic fibers Its tendon passes through a Trochlear nerve (CN fibrous ring or trochlea, IV) changes its direction, and inserts into sclera deep to superior rectus muscle Anterior part of Sclera deep to lateral rectus Oculomotor nerve floor of orbit muscle (CN III)

Superior rectus

Common tendinous ring

Superior oblique

Inferior rectus

Medial rectus Lateral rectus a

Origin Lesser wing of sphenoid bone, superior and anterior to optic canal Body of sphenoid bone

Main Action a Elevates superior eyelid

Abducts, depresses, and medially rotates eyeball

Abducts, elevates, and laterally rotates eyeball Sclera just posterior to Elevates, corneoscleral junction adducts, and rotates eyeball medially Depresses, adducts, and rotates eyeball medially Adducts eyeball Abducent nerve (CN Abducts VI) eyeball

I t i s e s s e n ti a l t o a p p re c i a t e t h a t a l l m u s c l e s a r e c o n t i n u ou s l y i n v o l v e d i n e y e b a l l m o v e m e n t s ; t h u s t h e i n d i v i d u a l a c t i o n s a r e n ot u s u a l l y t e s t e d c l i n i c a l l y . S R , s u p e r i or r e c t u s ( C N I I I ) ; L R , l a te r a l r e c t u s ( C N V I ) ; I R , i n f e r i o r r e c tu s ( C N I I I ) ; I O , i n f e r i o r ob l i q u e ( C N I I I ) ; M R , m e d i a l r e c t u s ( C N I I I ) ; S O , s u p e r io r o b l i q u e ( C N I V ) .

In addition to these four movements around the horizontal and vertical axes, the superior and inferior recti and obliques cause rotation of the eyeball around an anteroposterior axis. Medial movement of the superior pole of the eyeball is intorsion; lateral movement of the superior pole is extorsion. These movements accommodate changes in the tilt of the head. Absence of these movements resulting from nerve lesions contributes to double vision. To direct the gaze, coordination of both eyes must be accomplished by the paired action of contralateral yoke muscles. For example, in directing the gaze to the right, the right lateral rectus and left medial rectus act as yoke muscles.

Fascial Sheath of the Eyeball The fascial sheath of the eyeball (L. fascia bulbi, Tenon capsule) envelops the eyeball from the optic nerve nearly to the corneoscleral junction, forming the actual socket for the eyeball (Fig. 7.31A). The fascial sheath is pierced by the tendons of the extraocular muscles and is reflected onto each of them as a tubular muscle sheath. The muscle sheaths of the levator and superior rectus muscles are fused; thus, when


the gaze is directed superiorly, the superior eyelid is further elevated out of the line of vision. Triangular expansions from the sheaths of the medial and lateral rectus muscles, called the medial and lateral check ligaments, are attached to the lacrimal and zygomatic bones, respectively. These ligaments limit abduction and adduction. A blending of the check ligaments with the fascia of the inferior rectus and inferior oblique muscles forms a hammock‐like sling, the suspensory ligament of the eyeball. A potential episcleral space between the eyeball and the fascial sheath allows the eyeball to move inside the cup‐like sheath. A similar check ligament from the fascial sheath of the inferior rectus retracts the inferior eyelid when the gaze is directed downward.

Artificial Eye The fascial sheath of the eyeball forms a socket for an artificial eye when the eyeball has to be removed (enucleated). After this operation, the eye muscles cannot retract too far because their fascial sheaths remain attached to the fascial sheath of the eyeball. Thus some coordinated movement of a properly fitted artificial eyeball is possible. Because the suspensory ligament supports the eyeball, it is preserved when surgical removal of the bony floor of the orbit is performed (e.g., during the removal of a tumor).

Nerves of the Orbit In addition to the optic nerve (CN II), the nerves of the orbit include those that enter through the superior orbital fissure and supply the ocular muscles: oculomotor (CN III); trochlear (CN IV); and abducent (CN VI) nerves (Figs. 7.35 and 7.36; Table 7.8). A memory device for the innervation of the extraocular muscles moving the eyeball is similar to a chemical formula: LR 6 SO 4 AO 3 (lateral rectus, CN VI; superior oblique, CN IV; all others, CN III). The three terminal branches of the ophthalmic nerve, CN V 1 (the frontal, nasociliary, and lacrimal nerves), pass through the superior orbital fissure and supply structures related to the anterior orbit (e.g., lacrimal gland and eyelids), face, and scalp. The cutaneous branches of CN V 1 (lacrimal, frontal and infratrochlear nerves) were described under “Cutaneous Nerves of the Face,” earlier in this chapter, and in Table 7.5. The ciliary ganglion is a small group of postsynaptic parasympathetic nerve cell bodies associated with CN V 1 . It is located between the optic nerve and the lateral rectus toward the posterior limit of the orbit (Fig. 7.35B). The ganglion receives nerve fibers from three sources:   

Sensory fibers from CN V 1 via the communicating branch of the nasociliary nerve (the sensory or nasociliary root of the ciliary ganglion). Presynaptic parasympathetic fibers from CN III via the parasympathetic or oculomotor root of the ciliary ganglion. Postsynaptic sympathetic fibers from the internal carotid plexus via the sympathetic root of the ciliary ganglion.

The short ciliary nerves arise from the ciliary ganglion and are considered to be branches of CN V 1 . They carry parasympathetic and sympathetic fibers to the ciliary

Chapter 7: Head

body and iris. The short ciliary nerves consist of postsynaptic parasympathetic fibers originating in the ciliary ganglion, afferent fibers from the nasociliary nerve that pass through the ganglion, and postsynaptic sympathetic fibers that also pass through it. Long ciliary nerves, branches of the nasociliary nerve (CN V 1 ) that pass to the eyeball, bypassing the ciliary ganglion, convey postsynaptic sympathetic fibers to the dilator pupillae and afferent fibers from the iris and cornea. The posterior and anterior ethmoidal nerves, branches of the nasociliary nerve arising in the orbit, exit via openings in the lateral wall of the orbit to supply the mucous membrane of the sphenoidal and ethmoidal sinuses and the nasal cavities as well as the dura of the anterior cranial fossa.

Corneal Reflex During a neurological examination, the examiner touches the cornea with a wisp of cotton. A normal (positive) response is a blink. Absence of a blink response suggests a lesion of CN V 1 ; a lesion of CN VII (the motor nerve to the orbicularis oculi) may also impair this reflex. The examiner must be certain to touch the cornea (not just the sclera) to evoke the reflex. The presence of a contact lens may hamper or abolish the ability to evoke this reflex.

Corneal Ulcers and Transplants Damage to the sensory innervation of the cornea from CN V 1 leaves the cornea vulnerable to injury by foreign particles. People with scarred or opaque corneas may receive corneal transplants from donors. Corneal implants of non‐reactive plastic material are also used.

Oculomotor Nerve Palsy Complete oculomotor nerve palsy affects most of the ocular muscles, the levator palpebrae superioris, and the sphincter pupillae. The superior eyelid droops and cannot be raised voluntarily because of the unopposed activity of the orbicularis oculi (supplied by the facial nerve). The pupil is also fully dilated and non‐reactive because of the unopposed dilator pupillae. The pupil is fully abducted and depressed (“down and out” ) because of the unopposed activity of the lateral rectus and superior oblique, respectively.

Horner Syndrome Horner syndrome results from interruption of a cervical sympathetic trunk and is manifest by the absence of sympathetically stimulated functions on the ipsilateral side of the head. The syndrome includes the following signs: constriction of the pupil (miosis), drooping of the superior eyelid (ptosis), redness and increased temperature of the skin (vasodilation), and absence of sweating (anhydrosis). Constriction of the pupil occurs because the parasympathetically stimulated sphincter of the pupil is unopposed. The ptosis is a consequence of the paralysis of the smooth muscle fibers interdigitated with the aponeurosis of the levator palpebrae superioris that collectively constitute the superior tarsal muscle, supplied by sympathetic fibers.

Paralysis of the Extraocular Muscles One or more extraocular muscles may be paralyzed by disease in the brainstem or by a head injury, resulting in diplopia (double vision). Paralysis of a muscle is apparent


by the limitation of movement of the eyeball in the field of action of the muscle and by the production of two images when one attempts to use the muscle. When the abducent nerve (CN VI) supplying only the lateral rectus is paralyzed, the individual cannot abduct the pupil on the affected side. The pupil is fully adducted by the unopposed pull of the medial rectus.

The Bottom Line There are seven extraocular muscles: four recti, two obliques, and a levator of the superior eyelid. Six originate from the apex of the orbit, and the four rectus muscles arise from a common tendinous ring. Only the inferior oblique arises anteriorly in the orbit. The levator palpebrae superioris elevates the superior eyelid. Associated smooth muscle (superior tarsal muscle) widens the palpebral fissure even more during sympathetic responses; ptosis results from the absence of sympathetic innervation to the head (Horner syndrome). When the eyes are adducted (converged) as for close reading, the superior and inferior obliques produce depression and elevation, respectively, directing the gaze down or up the page. Coordination of the contralateral extraocular muscles as yoke muscles is necessary to direct the gaze in a particular direction. All muscles of the orbit are supplied by CN III, except for the superior oblique and lateral rectus, which are supplied by CN IV and VI, respectively. (Memory device: LR 6 SO 4 AO 3 ; lateral rectus, CN VI; superior oblique, CN IV; all others, CN III.)

Vasculature of the Orbit Arteries of the Orbit The blood supply of the orbit is mainly from the ophthalmic artery, a branch of the internal carotid artery; the infraorbital artery, from the external carotid artery, also contributes blood to structures related to the orbital floor (Figs. 7.35 and 7.36; Table 7.9 and 7.10). The central artery of the retina, a branch of the ophthalmic artery arising inferior to the optic nerve, runs within the dural sheath of the optic nerve until it approaches the eyeball (Fig. 7.38). The central artery pierces the optic nerve and runs within it, emerging at the optic disc. Its branches spread over the internal surface of the retina. The terminal branches are end arteries, which provide the only blood supply to the internal aspect of the retina. The external aspect of the retina is also supplied by the capillary lamina of the choroid (choriocapillaris). Of the eight or so posterior ciliary arteries (also branches of the ophthalmic artery), six short posterior ciliary arteries directly supply the choroid, which nourishes the outer non‐vascular layer of the retina. Two long posterior ciliary arteries, one on each side of the eyeball, pass between the sclera and the choroid to anastomose with the anterior ciliary arteries (continuations of the muscular branches of the ophthalmic artery to the rectus muscles) to supply the ciliary plexus.

Chapter 7: Head Table 7.9. Arteries of the Orbit

Artery Ophthalmic

Origin Internal carotid artery

Course and Distribution Traverses optic foramen to reach orbital cavity Central artery of retina Ophthalmic artery Runs in dural sheath of optic nerve and pierces nerve near eyeball; appears at center of optic disc; supplies optic retina (except cones and rods) Supraorbital Passes superiorly and posteriorly from supraorbital foramen to supply forehead and scalp Supratrochlear Passes from supraorbital margin to forehead and scalp Lacrimal Passes along superior border of lateral rectus muscle to supply lacrimal gland, conjunctiva, and eyelids Dorsal nasal Courses along dorsal aspect of nose and supplies its surface Short posterior ciliaries Pierce sclera at periphery of optic nerve to supply choroid, which in turn supplies cones and rods of optic retina Long posterior ciliaries Pierce sclera to supply ciliary body and iris Posterior ethmoidal Passes through posterior ethmoidal foramen to posterior ethmoidal cells Anterior ethmoidal Passes through anterior ethmoidal foramen to anterior cranial fossa; supplies anterior and middle ethmoidal cells, frontal sinus, nasal cavity, and skin on dorsum of nose Anterior ciliary Muscular (rectus) branches Pierces sclera at attachments of rectus of ophthalmic artery muscles and forms network in iris and ciliary body Infraorbital Third part of maxillary Passes along infraorbital groove and foramen artery to face

Veins of the Orbit Venous drainage of the orbit is through the superior and inferior ophthalmic veins, which pass through the superior orbital fissure and enter the cavernous sinus (Fig. 7.39). The central vein of the retina (Fig. 7.38) usually enters the cavernous sinus


directly, but it may join one of the ophthalmic veins. The vortex or vorticose veins from the vascular layer of the eyeball drain into the inferior ophthalmic vein. The scleral venous sinus is a vascular structure encircling the anterior chamber of the eyeball through which the aqueous humor is returned to the blood circulation. Figure 7.38. Partial horizontal section of right eyeball. The artery supplying the inner part the retina (central retinal artery) and the choroid, which in turn nourishes the outer non‐vascular layer of the retina, are shown. The choroid is arranged so that the supplying vessels and larger choroidal vessels are externally placed and the smallest vessels (the capillary lamina) are most internal, adjacent to the non‐vascular layer of the retina. The vorticose vein (one of four to five) drains venous blood from the choroid into the posterior ciliary and ophthalmic veins. The scleral venous sinus returns the aqueous humor, secreted into the anterior chamber by the ciliary processes, to the venous circulation.

Figure 7.39. Ophthalmic veins. The superior ophthalmic vein empties into the cavernous sinus, and the inferior ophthalmic vein empties into the pterygoid venous plexus. They communicate with the facial and supraorbital veins anteriorly and each other posteriorly. The superior ophthalmic vein accompanies the ophthalmic artery and its branches.

Chapter 7: Head

Glaucoma When drainage of aqueous humor through the scleral venous sinus into the blood circulation decreases significantly, pressure builds up in the anterior and posterior chambers of the eye, a condition called glaucoma. Blindness can result from compression of the inner layer of the eyeball (retina) and the retinal arteries if aqueous humor production is not reduced to maintain normal intraocular pressure.

Blockage of the Central Artery of the Retina Because terminal branches of the central artery of the retina are end arteries, obstruction of them by an embolus results in instant and total blindness. Blockage of the artery is usually unilateral and occurs in older people.

Blockage of the Central Vein of the Retina Because the central vein of the retina enters the cavernous sinus, thrombophlebitis of this sinus may result in the passage of a thrombus to the central retinal vein and produce a blockage in one of the small retinal veins. Occlusion of a branch of the central vein of the retina usually results in slow, painless loss of vision.

The Bottom Line Extraocular circulation is provided mainly by the ophthalmic (internal carotid) and infraorbital (external carotid) arteries, the latter supplying structures near the orbital floor. Superior and inferior ophthalmic veins drain anteriorly to the facial vein, posteriorly to the cavernous sinus, and inferiorly to the pterygoid venous plexus. Intraocular circulation is exclusively from the ophthalmic artery, with the central retinal artery supplying all of the retina except the layer of cones and rods, which is nourished by the capillary lamina of the choroid. The ciliary‐iridial structures receive blood from anterior ciliary arteries (from the rectus muscle branches of the ophthalmic artery) and two long posterior ciliary arteries. Multiple short posterior ciliary arteries supply the choroid. Superior and inferior vorticose veins drain the eyeballs to the respective ophthalmic veins.

Temporal Region The temporal region includes the temporal and infratemporal fossae, superior and inferior to the zygomatic arch, respectively (Fig. 7.40).

Temporal Fossa The temporal fossa, in which the temporal muscle (L. temporalis) is located, is bounded (Fig. 7.40A):    

Posteriorly and superiorly by the temporal lines. Anteriorly by the frontal and zygomatic bones. Laterally by the zygomatic arch. Inferiorly by the infratemporal crest (Fig. 7.40B).


Surface Anatomy of the Eyeball and Lacrimal Apparatus For a description of the surface anatomy of the eyelids, see “Surface Anatomy of the Face,” earlier in this chapter. The anterior part of the sclera (the “white” of the eye) is covered by the transparent bulbar conjunctiva, which contains minute but apparent conjunctival blood vessels (Fig. SA7.3A & B). When irritated, the vessels may enlarge noticeably, and the bulbar conjunctiva may take on a distinctly pink appearance when inflamed (“red” eyes). The normal tough, opaque sclera often appears slightly blue in infants and children and commonly has a yellow hue in many older people. The anterior transparent part of the eye is the cornea, which is continuous with the sclera at its margins. In a lateral view (Fig. SA7.3A), most of the visible part of the eyeball protrudes slightly through the palpebral fissure. It is apparent that the cornea has a greater curvature (convexity) than that of the rest of the eyeball (the part covered by sclera); thus a shallow angle occurs at the sclerocorneal junction, or corneal limbus (Fig. SA7.3B). The prominence of the cornea also makes movements of the eyeball apparent when the eyelids are closed. The dark circular opening through which light enters the eyeball, the pupil, is surrounded by the iris (plural = irides), a circular pigmented diaphragm. The relative sizes of the pupil and iris varies with the brightness of the entering light; however, the size of the contralateral pupils and irides should be uniform. Normally, when the eyes are open and the gaze is directed anteriorly, the superior part of the cornea and iris are covered by the edge of the superior eyelid, and the inferior part of the cornea and iris are fully exposed above the inferior eyelid, usually exposing a narrow rim of sclera. Even slight variations in the position of the eyeballs are noticeable, causing a change in facial expression to a surprised look when the superior eyelid is elevated (as occurs in exophthalmos, or protrusion of the eyeballs, caused by hyperthyroidism), or a sleepy appearance (as occurs when the superior eyelid droops, ptosis, owing to an absence of sympathetic innervation in Horner syndrome). The bulbar conjunctiva is reflected from the sclera onto the deep surface of the eyelid. The palpebral conjunctiva is normally red and vascular and, with experience, can provide some assessment of hemoglobin levels. It is commonly examined in cases of suspected anemia, a blood condition commonly manifested by pallor (paleness) of the mucous membranes. When the superior eyelid is everted, the size and extent of the enclosed superior tarsus can be appreciated, and commonly the tarsal glands can be distinguished through the palpebral conjunctiva as slightly yellow vertical stripes. Under close examination, the openings of these glands (approximately 20 per eyelid) can be seen on the margins of the eyelids, posterior to the two to three rows of emerging cilia or eyelashes. As the bulbar conjunctiva is continuous with the anterior epithelium of the cornea and the palpebral conjunctiva, it forms the conjunctival sac. The palpebral fissure is the “mouth,” or anterior aperture, of the conjunctival sac.

Chapter 7: Head

Figure SA7.3 In the medial angle of the eye, a reddish shallow reservoir of tears, the lacrimal lake, can be observed. Within the lake is the lacrimal caruncle, a small mound of moist modified skin. Lateral to the caruncle is a semilunar conjunctival fold, which slightly overlaps the eyeball. The semilunar fold is a rudiment of the nictitating membrane of birds and reptiles. When the edges of the eyelids are everted, a small pit, the lacrimal punctum, is visible at its medial end on the summit of a small elevation, the lacrimal papilla. The floor of the temporal fossa is formed by parts of the four bones that form the pterion: frontal, parietal, temporal, and greater wing of the sphenoid. The fan‐shaped temporal muscle arises from the bony floor and the overlying temporal fascia (Fig. 7.41), which forms the roof of the temporal fossa. This tough fascia covers the temporal muscle, attaching superiorly to the superior temporal line. Inferiorly, the fascia splits into two layers, which attach to the lateral and medial surfaces of the zygomatic arch. The temporal fascia also tethers the zygomatic arch superiorly. When the powerful masseter muscle, which is attached to the inferior border of the arch, contracts and exerts a strong downward pull on the arch, the temporal fascia provides resistance.


Infratemporal Fossa The infratemporal fossa is an irregularly shaped space deep and inferior to the zygomatic arch, deep to the ramus of the mandible and posterior to the maxilla (Fig. 7.40B). It communicates with the temporal fossa through the interval between (deep to) the zygomatic arch and (superficial to) the cranial bones.

Boundaries of the Infratemporal Fossa The boundaries of the infratemporal fossa are as follows (Fig. 7.40A & B):      

Laterally: the ramus of the mandible. Medially: the lateral pterygoid plate. Anteriorly: the posterior aspect of the maxilla. Posteriorly: the tympanic plate and the mastoid and styloid processes of the temporal bone. Superiorly: the inferior (infratemporal) surface of the greater wing of the sphenoid. Inferiorly: where the medial pterygoid muscle attaches to the mandible near its angle.

Contents of the Infratemporal Fossa The infratemporal fossa contains the (Fig. 7.41):     

Inferior part of the temporal muscle. Lateral and medial pterygoid muscles. Maxillary artery. Pterygoid venous plexus. Mandibular, inferior alveolar, lingual, buccal, and chorda tympani nerves and the otic ganglion.

The temporal and pterygoid muscles are described with the muscles of mastication. The maxillary artery is the larger of the two terminal branches of the external carotid artery (Table 7.10). It arises posterior to the neck of the mandible and is divided into three parts based on its relation to the lateral pterygoid muscle (Figs. 7.41B & C and 7.42). The courses of the three parts of the maxillary artery are illustrated and described and their branches and distributions are listed in Table 7.10. The pterygoid venous plexus is located partly between the temporal and the pterygoid muscles (Table 7.7). It is the venous equivalent of most of the maxillary artery—that is, most of the veins that accompany the branches of the maxillary artery drain into this plexus. The plexus anastomoses anteriorly with the facial vein via the deep facial vein and superiorly with the cavernous sinus via emissary veins. The extensive nature and volume of this plexus is difficult to appreciate in the cadaver, in which it is usually drained of blood. The mandibular nerve descends through the foramen ovale into the infratemporal fossa and divides into sensory and motor branches (Fig. 7.42). The branches of CN V 3 are the auriculotemporal, inferior alveolar, lingual, and buccal nerves. Branches of

Chapter 7: Head

the CN V 3 also supply the four muscles of mastication but not the buccinator, which is supplied by the facial nerve. The otic ganglion (parasympathetic) is located in the infratemporal fossa, just inferior to the foramen ovale, medial to CN V 3 and posterior to the medial pterygoid muscle. Presynaptic parasympathetic fibers, derived mainly from the glossopharyngeal nerve, synapse in the otic ganglion. Postsynaptic parasympathetic fibers, which are secretory to the parotid gland, pass from the otic ganglion to this gland through the auriculotemporal nerve. The auriculotemporal nerve encircles the middle meningeal artery and divides into numerous branches, the largest of which passes posteriorly, medial to the neck of the mandible, and supplies sensory fibers to the auricle and temporal region. The auricotemporal nerve also sends articular fibers to the TMJ and parasympathetic secretomotor fibers to the parotid gland. The inferior alveolar nerve enters the mandibular foramen and passes through the mandibular canal, forming the inferior dental plexus, which sends branches to all mandibular teeth on its side. Another branch of the plexus, the mental nerve, passes through the mental foramen and supplies the skin and mucous membrane of the lower lip, the skin of the chin, and the vestibular gingiva of the mandibular incisor teeth. The lingual nerve lies anterior to the inferior alveolar nerve (Figs. 7.41B & C and 7.42). It is sensory to the anterior two thirds of the tongue, the floor of the mouth, and the lingual gingivae. It enters the mouth between the medial pterygoid muscle and the ramus of the mandible and passes anteriorly under cover of the oral mucosa, just inferior to the 3rd molar tooth. The chorda tympani nerve, a branch of CN VII carrying taste fibers from the anterior two thirds of the tongue, joins the lingual nerve in the infratemporal fossa (Fig. 7.41C). The chorda tympani also carries secretomotor fibers for the submandibular and sublingual salivary glands.


Figure 7.40. Bony boundaries of temporal and infratemporal fossae. A. The lateral wall of the infratemporal fossa is formed by the ramus of the mandible. The space is deep to the zygomatic arch and is traversed by the temporal muscle and the deep temporal nerves and vessels. Through this interval, the temporal fossa communicates inferiorly with the infratemporal fossa. B. The roof and three walls of the infratemporal fossa are shown. The fossa is an irregularly shaped space posterior to the maxilla (anterior wall). The roof of the fossa is formed by the infratemporal surface of the greater wing of the sphenoid. The medial wall is formed by the lateral pterygoid plate; and the posterior wall is formed by the tympanic plate, styloid process, and mastoid process of the temporal bone. The infratemporal fossa communicates with the pterygopalatine fossa through the pterygomaxillary fissure.

Chapter 7: Head

Figure 7.41. Dissections of temporal and infratemporal regions. A. In this superficial dissection of the great muscles on the side of the cranium, the parotid gland and most of the temporal fascia have been removed. The temporal and masseter muscles are both supplied by the trigeminal nerve (CN V) and both close the jaw. The facial artery passes deep to the submandibular gland, whereas the facial vein passes superficial to it. B. In this superficial dissection of the infratemporal region, most of the zygomatic arch and attached masseter, the coronoid process and adjacent parts of the ramus of the mandible, and the inferior half of the temporal muscle have been removed. The first part of the maxillary artery, the larger of the two end branches of the external carotid, run anteriorly, deep to the neck of the mandible and then pass deeply between the lateral and the medial pterygoid muscles. C. In this deep dissection of the infratemporal region, more of the ramus of the mandible, the lateral pterygoid muscle, and most branches of the maxillary artery have been removed. Branches of the mandibular nerve (CN V3), including the auriculotemporal nerve, and the second part of the maxillary artery pass between the sphenomandibular ligament and the neck of the mandible.


Mandibular Nerve Block To produce a mandibular nerve block, an anesthetic agent is injected near the mandibular nerve where it enters the infratemporal fossa. In the extraoral approach, the needle passes through the mandibular notch of the ramus of the mandible into the infratemporal fossa. The injection usually anesthetizes the auriculotemporal, inferior alveolar, lingual, and buccal branches of CN V 3 .

Inferior Alveolar Nerve Block An inferior alveolar nerve block anesthetizes the inferior alveolar nerve, a branch of CN V 3 . The site of the anesthetic injection is around the mandibular foramen, the opening into the mandibular canal on the medial aspect of the ramus of the mandible. This canal gives passage to the inferior alveolar nerve, artery, and vein. When this nerve block is successful, all mandibular teeth are anesthetized to the median plane. The skin and mucous membrane of the lower lip, the labial alveolar mucosa and gingivae, and the skin of the chin are also anesthetized because they are supplied by the mental nerve, a branch of the inferior alveolar nerve.

Temporomandibular Joint The TMJ is a modified hinge type of synovial joint (Fig. 7.43). The articular surfaces involved are the condyle of the mandible, the articular tubercle of the temporal bone, and the mandibular fossa. The joint capsule of the TMJ is loose. The fibrous layer of the capsule attaches to the margins of the articular area on the temporal bone and around the neck of the mandible (Fig. 7.43A & C). The joint has two synovial membranes: the superior synovial membrane lines the fibrous layer of the capsule superior to the articular disc, and the inferior synovial membrane lines the fibrous layer of the capsule inferior to the articular disc (Fig. 7.43A & E—G). The articular disc divides the TMJ into two separate compartments. The gliding movements of protrusion and retrusion (translation) occur in the superior compartment; the hinge movements of depression and elevation occur in the inferior compartment. The thick part of the joint capsule forms the intrinsic lateral ligament (temporomandibular ligament), which strengthens the TMJ laterally and, with the postglenoid tubercle, acts to prevent posterior dislocation of the joint. Two extrinsic ligaments and the lateral ligament connect the mandible to the cranium. The stylomandibular ligament, which is actually a thickening of the fibrous capsule of the parotid gland, runs from the styloid process to the angle of the mandible (Fig. 7.43C & D). It does not contribute significantly to the strength of the joint. The sphenomandibular ligament runs from the spine of the sphenoid to the lingula of the mandible (Fig. 7.43A & D). It is the primary passive support of the mandible, although the tonus of the muscles of mastication usually bears the mandible's weight. However, the ligament does serve as a “swinging hinge” for the mandible, serving both as a fulcrum and as a check ligament for the movements of the mandible at the TMJs.

Chapter 7: Head

Table 7.10. Parts and Branches of the Maxillary Artery

Part Course First (mandibular) Proximal (posterior) to part lateral pterygoid muscle; runs horizontally, deep (medial) to neck of condylar process of mandible and lateral to stylomandibular ligament

Branches Distribution Deep auricular Supplies external acoustic meatus, artery external tympanic membrane, and temporomandibular joint Anterior Supplies internal aspect of tympanic artery tympanic membrane Middle Enters cranial cavity via foramen meningeal artery spinosum to supply periosteum, bone, red bone marrow, dura mater of lateral wall and calvaria of neurocranium, trigeminal ganglion, facial nerve and geniculate ganglion, tympanic cavity, and tensor tympani muscle Accessory Enters cranial cavity via foramen meningeal artery ovale; its distribution is mainly extracranial to muscles of infratemporal fossa, sphenoid bone, mandibular nerve, and otic ganglion Inferior alveolar Descends to enter mandibular artery canal of mandible via mandibular foramen; supplies mandible, mandibular teeth, chin, mylohyoid


Second (pterygoid) part

Adjacent (superficial or deep) to lateral pterygoid muscle; ascends obliquely anterosuperiorly, medial to temporal muscle

Third (pterygopalatine) part

Distal (anteromedial) to lateral pterygoid muscle; passes between heads of lateral pterygoid and through pterygomaxillary fissure into pterygopalatine fossa

Masseteric artery

Traverses mandibular notch, supplying temporomandibular joint and masseter Deep temporal Anterior and posterior arteries arteries ascend between temporal muscle and bone of temporal fossa, supplying mainly muscle Pterygoid Irregular in number and origin; branches supply pterygoid muscle Buccal artery Runs anteroinferiorly with buccal nerve to supply buccal fat‐pad, buccinator, and buccal oral mucosa Posterior Descends on maxilla's superior infratemporal surface with alveolar artery branches traversing alveolar canals to supply maxillary molar and premolar teeth, adjacent gingiva, and mucous membrane of maxillary sinus Infraorbital Traverses inferior orbital fissure, artery infraorbital groove, canal, and foramen; supplies inferior oblique and rectus muscles, lacrimal sac, maxillary canines and incisors teeth, mucous membrane of the maxillary sinus, and skin of infraorbital region of face Artery of Passes posteriorly through pterygoid canal pterygoid canal; supplies mucosa of upper pharynx, pharyngotympanic tube, and tympanic cavity Pharyngeal Passes through palatovaginal branch canal to supply mucosa of nasal roof, nasopharynx, sphenoidal air sinus, and pharyngotympanic tube Descending Descends through palatine canal, palatine artery dividing into greater and lesser palatine arteries to mucosa and glands of hard and soft palate Sphenopalatine Terminal branch of maxillary artery artery, traverses sphenopalatine foramen to supply walls and septum of nasal cavity; frontal, ethmoidal, sphenoid, and maxillary sinuses; and anteriormost palate

Chapter 7: Head

Figure 7.42. Innervation of teeth. The upper teeth are innervated by the superior alveolar nerves from the maxillary nerve (CN V2). These nerves form a superior dental plexus within the upper jaw, which sends dental branches to the roots of each maxillary tooth. The posterior and middle alveolar nerves arising from the maxillary nerve and the anterior alveolar nerve from the infraorbital nerve supply the maxillary molar teeth. The lower teeth are innervated by the inferior alveolar branch of the mandibular nerve (CN V3), the nerve entering the mandibular foramen on the medial surface of the ramus of the mandible. As in the upper jaw, an inferior dental plexus is formed, which sends dental branches to the roots of each mandibular tooth.


Figure 7.43. Temporomandibular joint. A. This coronal section of the right TMJ demonstrates that the articular disc divides the joint cavity into superior and inferior compartments. B. This orientation drawing shows the plane of the coronal section in part A. C and D. The TMJ and the extrinsic stylomandibular and sphenomandibular ligaments are shown. The sphenomandibular ligament passively bears the weight of the lower jaw and is the “swinging hinge” of the mandible, permitting protrusion and retrusion as well as elevation and depression. E. The right TMJ and related structures are shown. The tendon from the upper belly of the lateral pterygoid muscle is attached to the anterior aspect of the articular disc and fibrous layer of the joint capsule (not shown); the lower belly attaches to a depression, the pterygoid fovea of the neck of the mandible. F and G. The position of the TMJ with the mouth open is demonstrated. Note the position of the articular disc (D) and the head of the mandible (H) in relation to the mandibular fossa (F) and the articular tubercle of the temporal bone. (Part G courtesy of Dr. W. Kucharczyk, Chair of Medical Imaging, University of Toronto, and Clinical Director of Tri‐Hospital Resonance Centre, Toronto, Ontario, Canada.)

Chapter 7: Head

The movements of the mandible at the TMJs and the muscles (or forces) producing them are summarized in Table 7.11. To enable more than a small amount of depression of the mandible—that is, to open the mouth wider than just to separate the upper and lower teeth—the head of the mandible and articular disc must move anteriorly on the articular surface until the head lies inferior to the articular tubercle (a movement referred to as “translation” by dentists) (Fig. 7.43E & F). If this anterior gliding occurs unilaterally, the head of the contralateral mandible rotates (pivots) on the inferior surface of the articular disc, permitting simple side‐to‐side chewing or grinding movements over a small range. During protrusion and retrusion of the mandible, the head and articular disc slide anteriorly and posteriorly on the articular surface of the temporal bone, with both sides moving together. Table 7.11. Movements of the Temporamandibular Joint

Movements Elevation (close mouth) Depression (open mouth) Protrusion (protrude chin) Retrusion (retrude chin)

Muscle(s) Temporal, masseter, and medial pterygoid Lateral pterygoid and suprahyoid and infrahyoid muscles a Lateral pterygoid, masseter, and medial pterygoid b Temporal (posterior oblique and near horizontal fibers) and masseter Lateral movements (grinding and Temporal of same side, pterygoids of opposite side, and chewing) masseter a The prime mover is normally gravity; these muscles are mainly active against resistance. b The lateral pterygoid is the prime mover here, with minor secondary roles played by the masseter and medial pterygoid.


TMJ movements are produced chiefly by the muscles of mastication. These four muscles (temporal, masseter, and medial and lateral pterygoid muscles) develop from the mesoderm of the embryonic first pharyngeal (mandibular) arch; consequently, they are all innervated by the nerve of that arch, the (motor root) of the mandibular nerve (CN V 3 ). The muscles of mastication are illustrated and their attachments, details concerning their innervation, and their main actions are described in Table 7.12. In addition to the movements listed, studies indicate that the upper head of the lateral pterygoid muscle is active during the retraction movement produced by the posterior fibers of the temporal muscle. Traction is applied to the articular disc so that it is not pushed posteriorly ahead of the retracting mandible. Generally, depression of the mandible is produced by gravity. The suprahyoid and infrahyoid muscles are strap‐like muscles on each side of the neck that are primarily used to raise and depress the hyoid bone and larynx, respectively—for example, during swallowing (see Chapter 8). Indirectly they can also help depress the mandible, especially when opening the mouth suddenly or against resistance. The platysma can be similarly used.

Dislocation of the TMJ Sometimes during yawning or taking a large bite, excessive contraction of the lateral pterygoids may cause the heads of the mandible to dislocate anteriorly (pass anterior to the articular tubercles) (Fig. B7.23). In this position, the mandible remains wide open and the person is unable to close it. Most commonly, a sideways blow to the chin when the mouth is open dislocates the TMJ on the side that received the blow. Dislocation of the TMJ may also accompany fractures of the mandible. Posterior dislocation is uncommon, being resisted by the presence of the postglenoid tubercle and the strong intrinsic lateral ligament. Usually in falls on or direct blows to the chin, the neck of the mandible fractures before dislocation occurs. Because of the close relationship of the facial and auriculotemporal nerves to the TMJ, care must be taken during surgical procedures to preserve both the branches of the facial nerve overlying it and the articular branches of the auriculotemporal nerve that enter the posterior part of the joint. Injury to articular branches of the auriculotemporal nerve supplying the TMJ, associated with traumatic dislocation and rupture of the articular capsule and lateral ligament, leads to laxity and instability of the TMJ.

Chapter 7: Head

Figure B7.23. Dislocation of temporomandibular joint.

Arthritis of the TMJ The TMJ may become inflamed from degenerative arthritis, for example. Abnormal function of the TMJ may result in structural problems such as dental occlusion and joint clicking (crepitus). The clicking is thought to result from delayed anterior disc movements during mandibular depression and elevation.

The Bottom Line The temporal fossa and its inferior continuation deep to the zygomatic arch and ramus of the mandible, the infratemporal fossa, are largely occupied by derivatives of the embryonic first pharyngeal arch: three of the four muscles of mastication (the temporal muscle and two pterygoid muscles) and the nerve that conveys motor fibers to them, the mandibular nerve (CN V 3 ). Although not part of the fossae per se, it is convenient to consider the TMJ and the fourth muscle of mastication (the masseter) at the same time. Also contained in the infratemporal fossa is the second part of the maxillary artery and its venous equivalent, the pterygoid venous plexus. Adjacent cranial compartments communicate with the fossae, and neurovascular structures pass to and from the fossae via bony passages, including the oval foramen (through which the mandibular nerve enters from the middle cranial fossa), the foramen spinosum (through which the middle meningeal artery enters and the meningeal branch of CN V 3 returns to the middle cranial fossa), the pterygomaxillary fissure (through which the maxillary artery passes into the pterygopalatine fossa for further distribution), the inferior orbital fissure (through which the inferior ophthalmic veins drain to the pterygoid venous plexus), and the mandibular foramen (through which the inferior alveolar nerve passes to mandibular canal for distribution to lower jaw and teeth).


Oral Region The oral region includes the oral cavity, teeth, gingivae, tongue, palate, and the region of the palatine tonsils. The oral cavity is where food is ingested and prepared for digestion in the stomach and small intestine. Food is chewed by the teeth, and saliva from the salivary glands facilitates the formation of a manageable food bolus (L. lump). Deglutition (swallowing) is voluntarily initiated in the oral cavity. The voluntary phase of the process pushes the bolus from the oral cavity into the pharynx, the expanded part of the alimentary (digestive) system, where the automatic phase of swallowing occurs.

Oral Cavity The oral cavity consists of two parts: the oral vestibule and the oral cavity proper (Fig. 7.44). It is in the oral cavity that food and drinks are tasted and savored and where mastication and lingual manipulation of food occur. The oral vestibule is the slit‐like space between the teeth and buccal gingiva and the lips and cheeks. The vestibule communicates with the exterior through the mouth. The size of the oral fissure (the oral opening; L. rima oris) is controlled by the circumoral muscles, such as the orbicularis oris (the sphincter of the oral fissure), the buccinator, risorius, and depressors and elevators of the lips (dilators of the fissure). The oral cavity proper is the space between the upper and the lower dental arches or arcades (maxillary and mandibular alveolar arches and the teeth they bear). It is limited laterally and anteriorly by the maxillary and mandibular alveolar arches housing the teeth. The roof of the oral cavity is formed by the palate. Posteriorly, the oral cavity communicates with the oropharynx (oral part of the pharynx). When the mouth is closed and at rest, the oral cavity is fully occupied by the tongue.

Chapter 7: Head

Table 7.12. Muscles Acting on the Mandible/Temporomandibular Joint (TMJ)

Muscle(s)

Proximal Attachment Muscles of mastication Temporal Triangular muscle with broad attachment to floor of temporal fossa and deep surface of temporal fascia

Masseter

Quadrate muscle attaching to inferior border and medial surface of maxillary process of zygomatic bone and the zygomatic arch

Lateral pterygoid

T r i a n g u l a r two‐ headed m u s c le from (1) infratemporal s u r f a ce a n d c r e s t o f g re a t e r w i n g o f s p h e n o i d a n d ( 2 ) l a t e r a l s u rf a c e o f lateral p t e r y g o id plate

Distal Attachment

Innervation

Action Mandible

Narrow attachment to tip and medial surface of coronoid process and anterior border of ramus of mandible Angle and lateral surface of ramus of mandible

Anterior Via deep trunk of temporal mandibular branches nerve (CN V 3 )

Elevates mandible, closing jaws; posterior, more horizontal fibers are 1° retractors of mandible

Upper head attaches primarily to joint capsule and articular disc of TMJ; inferior head attaches primarily to pterygoid fovea on anteromedial aspect of neck of condyloid process of mandible

Via masseteric nerve

on

Elevates mandible, closing jaws; superficial fibers make limited contribution to protrusion of mandible

b i la t e r a l l y , Via lateral A c t i n g p r o t r a c t s m a n d ib l e pterygoid a n d d e p re s s es chin; nerves a c t i n g u n i la t e r a l l y , swings jaw toward c o n t r a l a t e r a l s i d e ; a l t e r n a te u n i l a t e r a l contraction produces l a r g e r lateral chewing movements


Medial pterygoid

Quadrangular two‐headed muscle from (1) medial surface of lateral pterygoid plate and pyramidal process of palatine bone and (2) tuberosity of maxilla

Medial surface of ramus of mandible, inferior to mandibular foramen; in essence, a “mirror image” of the ipsilateral masseter, the two muscles flanking the ramus

Suprahyoid muscles Digastric Base of cranium

Stylohyoid Mylohyoid Geniohyoid

Hyoid bone

Facial and Depresses mandibular nerves mandible against resistance when infrahyoid muscles fix or depress hyoid bone Facial nerve Mandibular nerve Nerve to geniohyoid (C1—2)

Hyoid bone

Ansa cervicalis Fixes or depresses from cervical hyoid bone plexus (C1—3)

Styloid process Medial body of mandible Anterior body of mandible

Infrahyoid muscles Omohyoid Scapula

Via medial Acts synergistically pterygoid with masseter to nerve elevate mandible; contributes to protrusion; alternate unilateral activity produces smaller grinding movements

Sternohyoid Manubrium of sternum Sternothyroid Manubrium of sternum and and thyroid cartilage thyrohyoid Muscle of facial expression Platysma Subcutaneous tissue of Base of Cervical branch of Depresses infraclavicular and mandible, skin facial nerve (CN mandible against supraclavicular regions of cheek and VII) resistance lower lip, angle of mouth (modiolus), and orbicularis oris

Chapter 7: Head

Figure 7.44. Coronal section of mouth region. The orientation drawing shows the plane of the section. During chewing, the tongue (centrally), the buccinator (laterally), and the orbicularis oris (anteriorly) work together to retain the bolus of food between the occlusive surfaces of the molar teeth.

Lips, Cheeks, and Gingivae Lips and Cheeks The lips are mobile, musculofibrous folds surrounding the mouth, extending from the nasolabial sulci and nares laterally and superiorly to the mentolabial sulcus inferiorly (Fig. 7.45). They contain the orbicularis oris and superior and inferior labial muscles, vessels, and nerves. The lips are covered externally by skin and internally by mucous membrane. The lips function as the valves of the oral fissure, containing the sphincter (orbicularis oris) that controls entry and exit from the mouth and upper alimentary and respiratory tracts. The lips are used for grasping food, sucking liquids, keeping food out of the oral vestibule, forming speech, and osculation (kissing). The transitional zone of the lips (commonly considered by itself to be the lip), ranging from brown to red, continues into the oral cavity where it is continuous with the mucous membrane. This membrane covers the intraoral, vestibular part of the lips (Fig. 7.46). The labial frenula (Mod. L. bridle) are free‐edged folds of mucous membrane in the midline, extending from the vestibular gingiva to the mucosa of the upper and lower lips; the one extending to the lower lip is smaller. Other smaller frenula sometimes appear laterally in the premolar vestibular regions. The superior and inferior labial arteries, branches of the facial arteries, anastomose with each other in the lips to form an arterial ring (Table 7.6). The pulse of these arteries may be palpated by grasping the upper or lower lip lightly between the first two digits. The upper lip is supplied by superior labial branches of the facial and infraorbital arteries. The lower lip is supplied by inferior labial branches of the facial and mental arteries. The upper lip is supplied by the superior labial branches of the


infraorbital nerves (of CN V 2 ), and the lower lip is supplied by the inferior labial branches of the mental nerves (of CN V 3 ). Lymph from the upper lip and lateral parts of the lower lip passes primarily to the submandibular lymph nodes (Fig. 7.45), whereas lymph from the medial part of the lower lip passes initially to the submental lymph nodes. Figure 7.45. Lymphatic drainage of lips. Lymph from the upper lip and lateral parts of the lower lip drains to the submandibular nodes. Lymph from the middle part of the lower lip drains to the submental nodes.

Cleft Lip Cleft lip (harelip) is a congenital anomaly (usually of the upper lip) that occurs in 1 of 1000 births (Moore and Persaud, 2003); 60—80% of affected infants are males. The clefts vary from a small notch in the transitional zone and vermilion border to a notch that extends through the lip into the nose (Fig. B7.24). In severe cases, the cleft extends deeper and is continuous with a cleft in the palate. Cleft lip may be unilateral or bilateral.

Cyanosis of the Lips The lips, like the fingers, have an abundant, relatively superficial blood flow. Because of this, they can lose a disproportionate amount of body heat when exposed to a cold environment. Both are provided with sympathetically innervated arteriovenous anastomoses, capable of redirecting a considerable portion of the blood back to the body core, reducing heat loss while producing cyanosis of the lips and fingers. Cyanosis, a dark bluish or purplish coloration of the lips and mucous membranes, results from deficient oxygenation of capillary blood and is a sign of many pathologic conditions. The common blue discoloration of the lips owing to cold exposure does not indicate pathology; instead, it results from the decreased blood flow in the capillary beds supplied by the superior and inferior labial arteries and the increased extraction of oxygen. Simple warming restores the normal coloring of the lips.

Chapter 7: Head

Figure B7.24. Unilateral cleft lip.

Large Labial Frenula Excessively large superior labial frenula in children may cause a space between the central incisor teeth. Resection of the frenulum and the underlying connective tissue (frenulectomy) between the incisors allows approximation of the teeth, which may require an orthodontic appliance (“brace” ). Large lower labial frenula in adults may pull on the labial gingiva and contribute to gingival recession, which results in abnormal exposure of the roots of the teeth. Figure 7.46. Oral vestibule and gingivae. A. The vestibule and gingivae of the maxilla are shown. B. The vestibule and gingivae of the mandible are shown. As the alveolar mucosa approaches the necks of the teeth, it changes in texture and color to become the gingiva proper. (Courtesy of Dr. B. Liebgott, Professor, Division of Anatomy, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.)


The cheeks (L. buccae) have essentially the same structure as the lips with which they are continuous. The cheeks form the movable walls of the oral cavity. Anatomically, the external aspect of the cheeks constitutes the buccal region, bounded anteriorly by the oral and mental regions (lips and chin), superiorly by the zygomatic region, posteriorly by the parotid region, and inferiorly by the inferior border of the mandible (Fig. SA7.1). The prominence of the cheek occurs at the junction of the zygomatic and buccal regions. The zygomatic bone underlying the prominence and the zygomatic arch that continues posteriorly are commonly referred to as the “cheek bone.” Lay persons consider the zygomatic and parotid regions also to be part of the cheek. The principal muscles of the cheeks are the buccinators (Fig. 7.44). Numerous small buccal glands lie between the mucous membrane and the buccinators. Superficial to the buccinators are encapsulated collections of fat; these buccal fat‐ pads are proportionately much larger in infants, presumably to reinforce the cheeks and keep them from collapsing during sucking. The cheeks are supplied by buccal branches of the maxillary artery and innervated by buccal branches of the mandibular nerve.

The Bottom Line The mouth is the primary portal of the alimentary system and a secondary portal for the respiratory system, especially important for speech in the latter case. The oral cavity extends from the oral fissure to the oropharyngeal isthmus. It is divided by the upper and lower jaws and their dental arcades into a superficial oral vestibule (between the lips and cheeks and the gingival and teeth) and a deeper oral cavity proper (internal to the jaws and dental arcades). The oral cavity (and specifically the oral vestibule) is bounded by the lips and cheeks, which are flexible dynamic musculofibrous folds containing muscles, neurovasculature, and mucosal glands, covered superficially with skin and deeply with oral mucosa. The cheeks also include buccal fat‐pads.

Gingivae The gingivae (gums) are composed of fibrous tissue covered with mucous membrane. The gingiva proper (attached gingiva) is firmly attached to the alveolar processes of the jaws and the necks of the teeth (Figs. 7.44 and 7.46). The gingiva proper is normally pink, stippled, and keratinizing. The alveolar mucosa (unattached gingiva) is normally shiny red and non‐keratinizing. The nerves and vessels supplying the gingiva, underlying alveolar bone, and periodontium (which surrounds the root[s] of a tooth, anchoring it to the tooth socket), are presented in Table 7.13.

Gingivitis Improper oral hygiene results in food and bacterial deposits in tooth and gingival crevices that may cause inflammation of the gingivae (gingivitis). The gingivae swell and redden as a result. If untreated, the disease spreads to other supporting structures, including alveolar bone, producing periodontitis (inflammation and destruction of the bone and the periodontium). Dentoalveolar abscesses (collections of pus resulting from death of inflamed tissues) may drain to the oral cavity and lips.

Chapter 7: Head

Teeth The chief functions of the teeth are to:   

Incise, reduce, and mix food material with saliva during mastication (chewing). Help sustain themselves in the tooth sockets by assisting the development and protection of the tissues that support them. Participate in articulation (distinct connected speech).

Table 7.13. Nerves and Vessels of Gingiva and Teeth The teeth are set in the tooth sockets and are used in mastication and in assisting in articulation. A tooth is identified and described on the basis of whether it is deciduous (primary) or permanent (secondary), the type of tooth, and its proximity to the midline or front of the mouth (e.g., medial and lateral incisors; the 1st molar is anterior to the 2nd). Children have 20 deciduous teeth; adults normally have 32 permanent teeth (Fig. 7.47A & C). The usual ages of the eruption (“cutting” ) of these teeth are given in Table 7.14. Before eruption, the developing teeth reside in the alveolar arches as tooth buds (Fig. 7.47B). The types of teeth are identified by their characteristics: incisors, thin cutting edges; canines, single prominent cones; premolars (bicuspids), two cusps; and molars, three or more cusps. The vestibular surface (labial or buccal) of each tooth is directed outwardly, and the lingual surface is directed inwardly. As used in clinical (dental) practice, the mesial (proximal) surface of a tooth is directed toward the median plane of the facial part of the cranium. The distal surface is directed away from this plane; both mesial and distal surfaces are contact surfaces—that is, surfaces that contact adjacent teeth. The masticatory surface is the occlusal surface.


Figure 7.47. Secondary dentition. A. The teeth are shown in occlusion. There is a supernumerary midline tooth (mesodont) in this specimen (*). B. Maxillary and mandibular jaws of a child acquiring secondary dentition are shown. The alveolar processes are carved to reveal the roots of the teeth and tooth buds. C. A pantomographic radiograph of an adult mandible and maxilla is shown. The left lower 3rd molar is not present. I, incisor; C, canine; PM, premolar; M1, M2, and M3, 1st, 2nd, and 3rd molars. (Part C courtesy of M. J. Pharoah, Associate Professor of Dental Radiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.)

Parts and Structure of the Teeth A tooth has a crown, neck, and root (Fig. 7.48). The crown projects from the gingiva. The neck is between the crown and the root. The root is fixed in the tooth socket by the periodontium; the number of roots varies. Most of the tooth is composed of dentin (L. dentinium), which is covered by enamel over the crown and cement (L. cementum) over the root. The pulp cavity contains connective tissue, blood vessels, and nerves. The root canal (pulp canal) transmits the nerves and vessels to and from the pulp cavity through the apical foramen.

Chapter 7: Head Table 7.14. Primary (Deciduous) and Secondary Teeth

Deciduous Central Incisor Lateral Incisor Canine 1st Molar 2nd Teeth Molar Eruption 6—8 8—10 16—20 12—16 20—24 (months) a Shedding 6—7 7—8 10—12 9—11 10—12 (years) a In some normal infants, the first teeth (medial incisors) may not erupt until 12—13 months of age. Permanent Central Lateral Canine 1st 2nd 1st 2nd 3rd Teeth Incisor Incisor Premolar Premolar Molar Molar Molar Eruption 7—8 8—9 10—12 10—11 11—12 6—7 12 13—25 (years)


The tooth sockets are in the alveolar processes of the maxillae and mandible and are the skeletal features that display the greatest change during a lifetime (Fig. 7.47B). Adjacent sockets are separated by interalveolar septa; within the socket, the roots of teeth with more than one root are separated by interradicular septa. The bone of the socket has a thin cortex separated from the adjacent labial and lingual cortices by a variable amount of trabeculated bone. The labial wall of the socket is particularly thin over the incisor teeth; the reverse is true for the molars, where the lingual wall is thinner. Thus the labial surface commonly is broken to extract incisors and the lingual surface is broken to extract molars. Figure 7.48. Sections of teeth. A. An incisor tooth is shown. B. A molar tooth is shown. In living people, the pulp cavity is a hollow space within the crown and neck of the tooth containing connective tissue, blood vessels, and nerves. The cavity narrows down to the root canal in a single‐rooted tooth or to one canal per root of a multirooted tooth. The vessels and nerves enter or leave through the apical foramen.

The roots of the teeth are connected to the bone of the alveolus by a springy suspension forming a special type of fibrous joint called a dento‐alveolar syndesmosis or gomphosis. The periodontium (periodontal membrane) is composed of collagenous fibers that extend between the cement of the root and the periosteum of the alveolus. It is abundantly supplied with tactile, pressoreceptive nerve endings, lymph capillaries, and glomerular blood vessels that act as hydraulic cushioning to curb axial masticatory pressure. Pressoreceptive nerve endings are capable of receiving changes in pressure as stimuli.

Vasculature of the Teeth The superior and inferior alveolar arteries, branches of the maxillary artery, supply the maxillary and mandibular teeth, respectively (Fig. 7.41B; Table 7.10). Alveolar veins with the same names and distribution accompany the arteries. Lymphatic vessels from the teeth and gingivae pass mainly to the submandibular lymph nodes (Fig. 7.45).

Chapter 7: Head

Innervation of the Teeth The nerves supplying the teeth are illustrated in Figure 7.42 and listed in Table 7.13. The named branches of the superior (CN V 2 ) and inferior (CN V 3 ) alveolar nerves give rise to dental plexuses that supply the maxillary and mandibular teeth. The lingual nerve is closely related to the medial aspect of the 3rd molars; therefore, caution is taken to avoid injuring this nerve during their extraction.

Dental Caries, Pulpitis, and Tooth Abscesses Decay of the hard tissues of a tooth results in the formation of dental caries (cavities). Treatment involves removal of the decayed tissue and restoration of the anatomy of the tooth with a dental material. Neglected dental caries eventually invade and inflame tissues in the pulp cavity. Invasion of the pulp by a deep carious lesion results in infection and irritation of the tissues (pulpitis). Because the pulp cavity is a rigid space, the swollen tissues cause considerable pain (toothache). If untreated, the small vessels in the root canal may die from the pressure of the swollen tissue, and the infected material may pass through the apical canal and foramen into the periodontal tissues. An infective process develops and spreads through the root canal to the alveolar bone, producing an abscess. Pus from an abscess of a maxillary molar tooth may extend into the nasal cavity or the maxillary sinus. The roots of the maxillary molar teeth are closely related to the floor of this sinus. As a consequence, infection of the pulp cavity may also cause sinusitis or sinusitis may stimulate nerves entering the teeth and simulate a toothache.

Extraction of the Teeth Sometimes it is not practical to restore a tooth because of extreme tooth destruction. The only alternative is tooth extraction. A tooth may lose its blood supply as a result of trauma. The blow to the tooth disrupts the blood vessels entering and leaving the apical foramen. It is not always possible to save the tooth. Unerupted 3rd molars are common dental problems; these teeth are the last to erupt, usually when people are in their late teens or early 20s. Often there is not enough room for these molars to erupt, and they become lodged (impacted) under or against the 2nd molars (Fig. B7.25, insets). If impacted 3rd molars become painful, they are usually removed. When doing so, the surgeon takes care not to injure the alveolar nerves.


Figure B7.25. Superior view of normal adult mandible with full dentition. Insets: impacted 3rd molars.

The Bottom Line The strong alveolar parts of the maxilla and mandible bear, in sequence, two sets of teeth (20 deciduous and 32 permanent teeth). The crowns of the teeth project from the gingiva, and the roots are anchored in tooth sockets by periodontium. The upper jaw, its teeth, gingivae, and adjacent vestibule are supplied by branches of the maxillary nerve (CN V 2 ), an artery and accompanying veins. The same features of the lower jaw are supplied by the mandibular nerve (CN V 3 ) and inferior alveolar vessels.

Palate The palate forms the arched roof of the mouth and the floor of the nasal cavities (Figs. 7.49, 7.50, 7.51). It separates the oral cavity from the nasal cavities and the nasopharynx, the part of the pharynx superior to the soft palate. The superior (nasal) surface of the palate is covered with respiratory mucosa, and the inferior (oral) surface is covered with oral mucosa, densely packed with glands (Fig. 7.51B). The palate consists of two regions: the hard palate anteriorly and the soft palate posteriorly.

Hard Palate The hard palate is vaulted (concave); this space is mostly filled by the tongue when it is at rest (Fig. 7.49). The anterior two thirds of the palate has a bony skeleton formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones (Fig. 7.50A). The incisive fossa is a depression in the midline of the bony palate posterior to the central incisor teeth into which the incisive canals open. The nasopalatine nerves pass from the nose through a variable number of incisive canals and foramina that open into the incisive fossa (Fig. 7.50B). Medial to the 3rd molar tooth, the greater palatine foramen pierces the lateral border of the bony palate (Fig. 7.50A). The greater palatine vessels and nerve emerge from this foramen and

Chapter 7: Head

run anteriorly on the palate. The lesser palatine foramina posterior to the greater palatine foramen pierce the pyramidal process of the palatine bone. These foramina transmit the lesser palatine nerves and vessels to the soft palate and adjacent structures (Fig. 7.52A & B). Figure 7.49. Median section of head and neck. The airway and food passageways cross in the pharynx. The soft palate acts as a valve, elevating to seal the pharyngeal isthmus connecting the nasal cavity and nasopharynx with the oral cavity and oropharynx.

Soft Palate The soft palate is the movable posterior third of the palate and is suspended from the posterior border of the hard palate. The soft palate has no bony skeleton; however, it has an anterior aponeurotic part, the palatine aponeurosis, which attaches to the posterior edge of the hard palate, and a posterior muscular part (Fig. 7.50B). The soft palate extends posteroinferiorly as a curved free margin from which hangs a conical process, the uvula (Figs. 7.50B and 7.51B). The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle (Fig. 7.50B). The aponeurosis is thick anteriorly and thin posteriorly. When a person swallows, the soft palate initially is tensed to allow the tongue to press against it, squeezing the bolus of food to the back of the mouth. The soft palate is then elevated posteriorly and superiorly against the wall of the pharynx, thereby preventing passage of food into the nasal cavity. Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal arches, respectively (Figs. 7.49 and 7.51B). A few taste buds are located in the epithelium covering the oral surface of the soft palate, the posterior wall of the oropharynx, and the epiglottis. The fauces (L. the throat) is the space between the cavity of the mouth and the pharynx. The fauces is bounded superiorly by the soft palate, inferiorly by the root of the tongue, and laterally by the pillars of the fauces, the palatoglossal and palatopharyngeal arches (Fig. 7.49). The isthmus of the fauces is the short constricted space that establishes the connection between the oral cavity proper and


the oropharynx. The isthmus is bounded anteriorly by the palatoglossal folds and posteriorly by the palatopharyngeal folds. The palatine tonsils, often referred to as “the tonsils,” are masses of lymphoid tissue, one on each side of the oropharynx. Each tonsil is in a tonsillar sinus (fossa), bounded by the palatoglossal and palatopharyngeal arches and the tongue.

Superficial Features of the Palate The mucosa of the hard palate is tightly bound to the underlying bone (Fig. 7.51); consequently, submucous injections here are extremely painful. The lingual gingiva, the part of the gingiva covering the lingual surface of the teeth and the alveolar process, is continuous with the mucosa of the palate; therefore, injection of an anesthetic agent into the gingiva of a tooth anesthetizes the adjacent palatal mucosa. Deep to the mucosa are mucus‐secreting palatine glands (Fig. 7.51B). The orifices of the ducts of these glands give the palatine mucosa a pitted (orange‐peel) appearance. In the midline, posterior to the maxillary incisor teeth, is the incisive papilla. This elevation of the mucosa lies directly anterior to the underlying incisive fossa. The incisive foramina are the openings of the incisive canals that transmit the nasopalatine nerves and vessels (Fig. 7.50A). Figure 7.50. Palate. A and B. The bones of the hard palate and nerves and vessels of the edentulous palate are shown. The palate has bony, aponeurotic, and muscular parts. The mucosa has been removed on each side of the palatine raphe, demonstrating a branch of the greater palatine nerve on each side and the artery on the lateral side. There are four palatine arteries, two on the hard palate (greater palatine and the terminal branch of posterior nasal septal/sphenopalatine artery) and two on the soft palate (lesser palatine and ascending palatine).

Chapter 7: Head

Figure 7.51. Maxillary teeth and palate. A. The maxillary teeth and the mucosa covering the hard palate in a living person are shown. (Courtesy of Dr. B. Liebgott, Professor, Division of Anatomy, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.) B. The mucous membrane and glands of the palate are demonstrated. The orifices of the ducts of the palatine glands give the mucous membrane an orange‐skin appearance. The palatine glands form a thick layer in the soft palate, a thin one in the hard palate, and are absent in the region of the incisive fossa and the anterior part of the palatine raphe.

Figure 7.52. Nerves and vessels of palate. In this dissection of the posterior part of the lateral wall of the nasal cavity and the palate, the mucous membrane of the palate, containing a layer of mucous glands, has been separated from the hard and soft regions of the palate by blunt dissection. The posterior ends of the middle and inferior nasal conchae are cut through; these and the mucoperiosteum are pulled off the side wall of the nose as far as the posterior border of the medial pterygoid plate. The perpendicular plate of the palatine bone is broken through to expose the palatine nerves and arteries descending from the pterygopalatine fossa in the palatine canal.

Radiating laterally from the incisive papilla are several parallel transverse palatine folds or rugae (Fig. 7.51A & B). These folds assist with manipulation of food during mastication. Passing posteriorly in the midline of the palate from the incisive papilla is a narrow whitish streak, the palatine raphe. It may present as a ridge anteriorly and a groove posteriorly. The palatine raphe marks the site of fusion of the embryonic palatine processes (palatal shelves) (Moore and Persaud, 2003). You can feel the transverse palatine folds and the palatine raphe with your tongue.


Muscles of the Soft Palate The five muscles of the soft palate arise from the base of the cranium and descend to the palate. The soft palate may be elevated so that it is in contact with the posterior wall of the pharynx. This closes the pharyngeal isthmus, requiring that one breathes through the mouth. The soft palate may also be drawn inferiorly so that it is in contact with the posterior part of the tongue. This closes the isthmus of the fauces, so that expired air passes through the nose (even when the mouth is open) and prevents substances in the oral cavity from passing to the pharynx. Tensing the soft palate pulls it tight at an intermediate level so that the tongue may push against it, compressing masticated food and propelling it into the pharynx for swallowing. The muscles of the soft palate are illustrated and their attachments, nerve supply, and actions are described in Table 7.15. Note that the direction of pull of the belly of the tensor veli palatini is redirected approximately 90° because its tendon uses the pterygoid hamulus as a pulley or trochlea, allowing it to pull horizontally on the aponeurosis.

Vasculature and Innervation of the Palate The palate has a rich blood supply, chiefly from the greater palatine artery on each side, a branch of the descending palatine artery (Figs. 7.50B and 7.52). The greater palatine artery passes through the greater palatine foramen and runs anteromedially. The lesser palatine artery, a smaller branch of the descending palatine artery, enters the palate through the lesser palatine foramen and anastomoses with the ascending palatine artery, a branch of the facial artery (Fig. 7.50B). The veins of the palate are tributaries of the pterygoid venous plexus. The sensory nerves of the palate are branches of the maxillary nerve (CNV 2 ) that branch from the pterygopalatine ganglion (Fig. 7.52). The greater palatine nerve supplies the gingivae, mucous membrane, and glands of most of the hard palate. The nasopalatine nerve supplies the mucous membrane of the anterior part of the hard palate. The lesser palatine nerves supply the soft palate. The palatine nerves accompany the arteries through the greater and lesser palatine foramina, respectively. Except for the tensor veli palatini supplied by CN V 2 , all muscles of the soft palate are supplied through the pharyngeal plexus of nerves (see Chapter 8).

Nasopalatine Block The nasopalatine nerves can be anesthetized by injecting anesthetic into the incisive fossa in the hard palate. The needle is inserted immediately posterior to the incisive papilla. Both nerves are anesthetized by the same injection where they emerge through the incisive fossa (Fig. 7.50). The affected tissues are the palatal mucosa, the lingual gingivae and alveolar bone of the six anterior maxillary teeth, and the hard palate.

Greater Palatine Block The greater palatine nerve can be anesthetized by injecting anesthetic into the greater palatine foramen. The nerve emerges between the 2nd and the 3rd molar teeth. This nerve block anesthetizes all the palatal mucosa and lingual gingivae posterior to the maxillary canine teeth and the underlying bone of the palate. Branches of the greater palatine arteries should be avoided. The anesthetic should be injected slowly to prevent stripping of the mucosa from the hard palate.

Chapter 7: Head

Cleft Palate Cleft palate, with or without cleft lip, occurs in approximately 1 of 2500 births and is more common in females than in males (Moore and Persaud, 2003). The cleft may involve only the uvula, giving it a fishtail appearance, or it may extend through the soft and hard regions of the palate (Fig B7.26). In severe cases associated with cleft lip, the cleft palate extends through the alveolar processes of the maxillae and the lips on both sides. The embryological basis of cleft palate is failure of mesenchymal masses in the lateral palatine processes to meet and fuse with each other, with the nasal septum, and/or with the posterior margin of the median palatine process.

Figure B7.26. Intra‐oral view of bilateral cleft palate. Table 7.15. Muscles of the Soft Palate


Muscle Tensor palatini

Superior Attachment

Inferior Attachment veli Scaphoid fossa of Palatine medial pterygoid plate, aponeurosis spine of sphenoid bone, and cartilage of pharyngotympanic tube

Levator palatini

veli Cartilage of pharyngotympanic tube and petrous part of temporal bone Palatoglossus Palatine aponeurosis Side tongue

Medial pterygoid nerve (a branch of mandibular nerve, CN V 3 ) via otic ganglion Pharyngeal branch of vagus nerve (CN X) via pharyngeal of plexus

Palatopharyngeus Hard palate and Lateral wall palatine aponeurosis of pharynx

Musculus uvulae

Posterior nasal spine Mucosa and palatine uvula aponeurosis

Innervation

of

Main Action Tenses soft palate and opens mouth of pharyngotympanic tube during swallowing and yawning

Elevates soft palate during swallowing and yawning Elevates posterior part of tongue and draws soft palate onto tongue Tenses soft palate and pulls walls of pharynx superiorly, anteriorly, and medially during swallowing Shortens uvula and pulls it superiorly

P.1002

The Bottom Line The roof of the oral cavity proper is formed by the hard (anterior two thirds) and soft (posterior one third) palates, the latter being a controlled flap that allows or limits communication with the nasal cavity. The mucosa of the hard palate includes abundant palatine glands. Branches of the maxillary (greater and lesser palatine arteries) and facial (ascending palatine artery) arteries supply the palate, its venous blood draining to the pterygoid plexus. The palate receives sensory innervation from the maxillary nerve (CN V 2 ); the muscles of the soft palate receive motor innervation from the pharyngeal plexus (CN X) plus a branch from the mandibular nerve (CN V 3 ) for the tensor veli palatini.

Tongue The tongue (L. lingua; G. glossa) is a mobile muscular organ that can assume a variety of shapes and positions. It is partly in the oral cavity and partly in the oropharynx. The tongue is involved with mastication, taste, deglutition (swallowing), articulation, and oral cleansing; however, its main functions are forming words during speaking and squeezing food into the oropharynx when swallowing.

Parts and Surfaces of the Tongue The tongue has a root, a body, an apex, a curved dorsum, and an inferior surface (Fig. 7.53). The root of the tongue is the part of the tongue that rests on the floor of the mouth. It is usually defined as the posterior third of the tongue. The body of the tongue is the anterior two thirds of the tongue. The apex (tip) of the tongue is the

Chapter 7: Head

anterior end of the body, which rests against the incisor teeth. The body and apex of the tongue are extremely mobile. The dorsum (dorsal surface) of the tongue is the posterosuperior surface, which is located partly in the oral cavity and partly in the oropharynx. It is characterized by a V‐shaped groove, the terminal sulcus or groove (L. sulcus terminalis), the angle of which points posteriorly to the foramen cecum. This small pit, frequently absent, is the non‐functional remnant of the proximal part of the embryonic thyroglossal duct from which the thyroid gland developed (Moore and Persaud, 2003). The terminal sulcus divides the dorsum of the tongue into the anterior (oral) part in the oral cavity proper and the posterior (pharyngeal) part in the oropharynx. The margin of the tongue is related on each side to the lingual gingivae and lateral teeth. The mucous membrane on the anterior part of the tongue is rough because of the presence of numerous small lingual papillae: 

 



Vallate papillae: Large and flat topped, they lie directly anterior to the terminal sulcus and are arranged in a V‐shaped row. They are surrounded by deep moat‐like trenches, the walls of which are studded with taste buds. The ducts of the serous glands of the tongue open into the trenches. Foliate papillae: Small lateral folds of the lingual mucosa. They are poorly developed in humans. Filiform papillae: Long and numerous, they contain afferent nerve endings that are sensitive to touch. These scaly, conical projections are pinkish gray and are arranged in V‐shaped rows that are parallel to the terminal sulcus, except at the apex, where they tend to be arranged transversely. Fungiform papillae: Mushroom shaped pink or red spots, they are scattered among the filiform papillae but are most numerous at the apex and margins of the tongue.

The vallate, foliate, and most of the fungiform papillae contain taste receptors in the taste buds. Figure 7.53. Features of dorsum of tongue. The parts of the tongue (body and root) are separated by the terminal sulcus (groove) and foramen cecum. The arms of the V‐ shaped terminal sulcus diverge from the foramen, demarcating the posterior third of the tongue from the anterior two thirds. Brackets indicate the parts of the tongue and do not embrace specific labels.


Figure 7.54. Floor of mouth and oral vestibule. The tongue is elevated and retracted superiorly. (Courtesy of Dr. B. Liebgott, Professor, Division of Anatomy, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.)

The mucous membrane over the anterior part of the dorsum of the tongue is thin and closely attached to the underlying muscle. A shallow midline groove of the tongue divides the tongue into right and left halves. The groove also indicates the site of fusion of the embryonic distal tongue buds (Moore and Persaud, 2003). The mucous membrane of the posterior part of the tongue is thick and freely movable. It has no lingual papillae, but the underlying lymphoid nodules give this part of the tongue an irregular, cobblestone appearance. The lymphoid nodules are known collectively as the lingual tonsil. The pharyngeal part of the tongue constitutes the anterior wall of the oropharynx and can be inspected only with a mirror or downward pressure on the tongue with a tongue depressor. The inferior surface of the tongue is covered with a thin, transparent mucous membrane through which one can see the underlying veins. This surface is connected to the floor of the mouth by a midline fold called the frenulum of the tongue (Fig. 7.54). The frenulum allows the anterior part of the tongue to move freely. On each side of the frenulum, a deep lingual vein is visible through the thin mucous membrane. A sublingual caruncle (papilla) is present on each side of the base of the lingual frenulum that includes the opening of the submandibular duct from the submandibular salivary gland.

Muscles of the Tongue The tongue is essentially a mass of muscles that is mostly covered by mucous membrane (Fig. 7.53; Table 7.16). Although it is traditional to do so, providing descriptions of the actions of tongue muscles ascribing (1) a single action to a specific muscle, or (2) implying that a particular movement is the consequence of a single muscle acting, greatly oversimplifies the actions of the tongue and is misleading. The muscles of the tongue do not act in isolation and some muscles perform multiple actions; parts of a single muscle are capable of acting independently, producing different, even antagonistic actions. In general, however,

Chapter 7: Head

extrinsic muscles alter the position of the tongue while intrinsic muscles alter its shape. The four intrinsic and four extrinsic muscles in each half of the tongue are separated by a median fibrous lingual septum, which merges posteriorly with the lingual aponeurosis.

Extrinsic Muscles of the Tongue The extrinsic muscles (genioglossus, hyoglossus, styloglossus, and palatoglossus) originate outside the tongue and attach to it. They mainly move the tongue but they can alter its shape as well. They are illustrated and their shape, position, attachments, and main actions are described in Table 7.16.

Intrinsic Muscles of the Tongue The superior and inferior longitudinal, transverse, and vertical muscles are confined to the tongue. They have their attachments entirely within the tongue and are not attached to bone. They are illustrated and their shape, position, attachments, and main actions are described in Table 7.16. The superior and inferior longitudinal muscles act together to make the tongue short and thick and to retract the protruded tongue. The transverse and vertical muscles act simultaneously to make the tongue long and narrow, which may push the tongue against the incisor teeth or protrude the tongue from the open mouth (especially when acting with the posterior inferior part of the genioglossus).

Innervation of the Tongue All muscles of the tongue, except the palatoglossus (actually a palatine muscle supplied by the pharyngeal plexus), receive motor innervation from CN XII, the hypoglossal nerve (Fig. 7.55). For general sensation (touch and temperature), the mucosa of the anterior two thirds of the tongue is supplied by the lingual nerve, a branch of CN V 3 (Fig. 7.42). For special sensation (taste), this part of the tongue, except for the vallate papillae, is supplied through the chorda tympani nerve, a branch of CN VII (Fig. 7.41C). The chorda tympani joins the lingual nerve and runs anteriorly in its sheath. The mucous membrane of the posterior third of the tongue and the vallate papillae are supplied by the lingual branch of the glossopharyngeal nerve (CN IX) for both general and special sensation. Twigs of the internal laryngeal nerve, a branch of the vagus nerve (CN X), supply mostly general but some special sensation to a small area of the tongue just anterior to the epiglottis. These mostly sensory nerves also carry parasympathetic secretomotor fibers to serous glands in the tongue. Parasympathetic fibers from the chorda tympani nerve travel with the lingual nerve to the submandibular and sublingual salivary glands. These nerve fibers synapse in the submandibular ganglion, which hangs from the lingual nerve (Fig. 7.59A).


Table 7.16. Muscles of the Tongue

Muscle

Shape and Position Extrinsic muscles of the tongue Genioglossus Fan‐shaped muscle; constitutes bulk of tongue

Proximal Attachment

Distal Attachment

Main Action(s)

Via a short tendon from superior part of mental spine of mandible

Entire dorsum of tongue; inferior most and posterior most fibers attach to body of hyoid bone

Hyoglossus

Thin, quadrilateral muscle

Body and Inferior aspects of greater horn of lateral part of hyoid bone tongue

Styloglossus

Small, short Anterior border triangular muscle of distal styloid process; stylohyoid ligament Narrow crescent‐ Palatine shaped palatine aponeurosis of muscle; forms soft palate posterior column of isthmus of fauces

Bilateral activity depresses tongue, especially central part, creating a longitudinal furrow; posterior part pulls tongue anteriorly for protrusion; a most anterior part retracts apex of protruded tongue; unilateral contraction deviates (“wags” ) tongue to contralateral side Depresses tongue, especially pulling its sides inferiorly; helps shorten (retrude) tongue Retrudes tongue and curls (elevates) its sides, working with genioglossus to form a central trough during swallowing Capable of elevating posterior tongue or depressing soft palate; most commonly acts to constrict isthmus of fauces

Palatoglossus

Sides of tongue posteriorly, interdigitating with hyoglossus Enters p o s t e r o l a te ra l t o n g u e t r a n s v e r s e l y , blending with i n t r i n s i c t r a n s v e rs e muscles

Chapter 7: Head

Intrinsic muscles of tongue Superior Thin layer deep longitudinal to mucous membrane of dorsum Inferior Narrow band longitudinal close to inferior surface

Submucous fibrous layer and median fibrous septum Root of tongue and body of hyoid bone

Margins of tongue Curls tongue longitudinally and mucous upward, elevating apex membrane and sides of tongue; shortens (retrudes) tongue Apex of tongue Curls tongue longitudinally downward, depressing apex; shortens (retrudes) tongue Transverse Deep to superior Median fibrous Fibrous tissue at Narrows and elongates longitudinal septum lateral lingual (protrudes) tongue a muscle margins Vertical Fibers intersect Submucous Inferior surface of Flattens and broadens transverse fibrous layer of borders of tongue tongue a muscle dorsum of tongue a Act simultaneously to protrude tongue.

Figure 7.55. Nerve supply of tongue. The anterior two thirds of the tongue are supplied by the lingual nerve (CN V3) for general sensation and by the chorda tympani, a branch of the facial nerve (CN VII) transferring nerve fibers to the lingual nerve, for taste. The posterior third of the tongue and the vallate papillae are supplied by the lingual branch of the glossopharyngeal nerve (CN IX) for both general sensation and taste. Another contribution is made by the internal laryngeal branch of the vagus (CN X) for general sensation and taste. Hence CN VII, CN IX, and CN X provide nerve fibers for taste; those from CN VII are ultimately conveyed by CN V3.

There are four basic taste sensations: sweet, salty, sour, and bitter. Sweetness is detected at the apex, saltiness at the lateral margins, and sourness and bitterness at the posterior part of the tongue. All other “tastes” expressed by gourmets are olfactory (smell and aroma).

Vasculature of the Tongue The arteries of the tongue are derived from the lingual artery, which arises from the external carotid artery (Fig. 7.56). On entering the tongue, the lingual artery passes deep to the hyoglossus muscle. The dorsal lingual arteries supply the posterior part (root); the deep lingual arteries supply the anterior part. The deep lingual arteries communicate with each other near the apex of the tongue. The dorsal lingual arteries are prevented from communicating by the lingual septum (Table 7.16C).


Figure 7.56. Blood supply of tongue. The main artery to the tongue is the lingual, a branch of the external carotid artery. The dorsal lingual arteries provide the blood supply to the root of the tongue and a branch to the palatine tonsil. The deep lingual arteries supply the body of the tongue. The sublingual arteries provide the blood supply to the floor of the mouth, including the sublingual glands.

Figure 7.57. Venous drainage of tongue. The deep lingual vein runs posteriorly and visibly deep to the mucous membrane of the underside of the tongue at the side of the lingual frenulum. It unites with the sublingual vein from the floor of the mouth and the sublingual salivary gland and then receives the dorsal lingual veins. All these veins drain directly or indirectly into the internal jugular vein.

The veins of the tongue are the dorsal lingual veins, which accompany the lingual artery; the deep lingual veins, which begin at the apex of the tongue, run posteriorly beside the lingual frenulum to join the sublingual vein (Fig. 7.57). The sublingual veins in elderly people are often varicose (enlarged and tortuous). All these lingual veins terminate, directly or indirectly, in the IJV. The lymphatic drainage of the tongue is exceptional. Most of the lymphatic drainage converges toward and follows the venous drainage; however, lymph from the tip of the tongue, frenulum, and central lower lip runs an independent course. Lymph from the tongue takes four routes (Fig. 7.58):  

Lymph from the posterior third drains into the superior deep cervical lymph nodes. Lymph from the medial part of the anterior two thirds drains directly to the inferior deep cervical lymph nodes.

Chapter 7: Head  

Lymph from the lateral parts of the anterior two thirds drains to the submandibular lymph nodes. The apex and frenulum drain to the submental lymph nodes.

The posterior third and the medial part of the anterior two thirds drain bilaterally. Figure 7.58. Lymphatic drainage of tongue. A. The dorsum of the tongue is shown. B. Lymph drains to the submental, submandibular, and superior and inferior deep cervical lymph nodes, including the jugulodigastric and jugulo‐omohyoid nodes. Extensive communications occur across the midline of the tongue

Gag Reflex It is possible to touch the anterior part of the tongue without feeling discomfort; however, when the posterior part is touched, the individual gags. CN IX and CN X are responsible for the muscular contraction of each side of the pharynx. Glossopharyngeal branches provide the afferent limb of the gag reflex.

Paralysis of the Genioglossus When the genioglossus muscle is paralyzed, the tongue has a tendency to fall posteriorly, obstructing the airway and presenting the risk of suffocation. Total relaxation of the genioglossus muscles occurs during general anesthesia; therefore, an airway is inserted in an anesthetized person to prevent the tongue from relapsing.

Injury to the Hypoglossal Nerve Trauma, such as a fractured mandible, may injure the hypoglossal nerve (CN XII), resulting in paralysis and eventual atrophy of one side of the tongue. The tongue deviates to the paralyzed side during protrusion because of the action of the unaffected genioglossus muscle on the other side.

Sublingual Absorption of Drugs For quick absorption of a drug, for instance, when nitroglycerin is used as a vasodilator in angina pectoris, the pill or spray is put under the tongue where it dissolves and enters the deep lingual veins in

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