' .J-^! QM/3/ N-S5' I College of :|pt)^siicians anu g)urgeons( aaetetence ^.ibrarp Digitized by tine Internet Arciiive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/anatomyofjointsoOOmorr FRONTIS PI EICE THE ANATOMY OF THE JOIFTS OF MA^ N BY HENRY MORRIS, M.A., M.B. Lond., F.R.C.S. SENIOB ASSISTANT STTRG^Olf TO, AND LECTUEKE ON ANATOMY AND DEMONSTBATOK OF OPBBATIVE SUBGERT AT, THE MIDDLESEX HOSPITAL. LONDON J. & A. CHURCHILL, NEW BUELINGTON STEEET 1879 TO THE PAST AND PRESENT STUDENTS OP THE MIDDLESEX HOSPITAL, IN RECOGNITION OF THE GOOD FEELING AND UNVARYING COURTESY THEY HAVE AT ALL TIMES SHOWN HIM, AND AS A TESTIMONY OF HIS SINCERE INTEREST IN THEIR PERSONAL WELFARE AND PROFESSIONAL SUCCESS, Cfeis Moxh XB g^trkatib- BY THE AUTHOE. h 348416 PREFACE. To those who are or have been engaged in anatomical teaching, the appearance of a new work on the " Anatomy of the Joints" will not be surprising. For some years past it has seemed to me that such a book was needed ; and I have reason for thinking that many others have, like myself, felt the deficiency to the surgeon, as well as to the anatomical student and teacher, of a comprehensive description of the joints. It has hitherto been customary to describe, in the various text-books of anatomy, under the head of "The Joints," the ligaments and synovial membranes only, without giving any account of the bursas and muscles in relation with them, or of the articular ends of the bones ; and without any reference whatever, except in the case of the larger joints, to the arteries and nerves which supply, or to the movements which are per- mitted at, the articulations. The consequence of this has been that the student has had to look under one section for the ligaments, under another for the bones, under a third for the blood supply, and so on ; but by the arrangement adopted in this treatise, all the various structures of a joint are brought under notice together, and thereby much loss of time and inconvenience will, it is hoped, be spared the reader. It has further been my endeavour to connect the study of the anatomical structures with that of their physiological actions and uses, the correct knowledge of the one being necessary for a proper understanding of the other. In composing this book, the plan I have followed has been to write independent descriptions from my own observations and dissections, and afterwards to enlarge upon and improve them by reference to the works of some of the best anatomical authors, more especiaUy those of Bourgery, Weitbrecht, Goodsir, Wood, Humphry, and the various English text-books. &2 VIU PKEFACE. It lias been stated sometime that only two things justify the puhHcation of a book, viz., the author must either commu- nicate something new, or he must have a new method of stating what is already known. Wliile conscious of the many shortcomings of this work, I am, I think, justified in introducing it to the profession on the second ground ; but I shall be more than compensated for somewhat prolonged labour if it be considered by capable judges that I have also added to the accuracy and fulness of previous descriptions of some of the joints. To my friend, Mr. Davies-Colley, Lecturer on Anatomy at Guy's Hospital, my best thanks are due, both for the care with which he has shared with me the labour of correcting for the press, and also for many valuable criticisms and suggestions. The illustrations have been made chiefly from my own dissections ; those of the bursse., however, are copies from Monro's work. Two of the woodcuts are after figures in Ward's Osteology, and one is copied from the Encyclopsedia of Anatomy. Not possessing the power of using the pencil and brush, like my predecessor Sir C. Bell, I have been fortunate in obtaining the assistance of my colleague Mr. Hensman, and Mr. Steele, each of whom has bestowed great patience and pains upon the drawings. The plates have been prepared by Messrs. West and Co., and I cannot omit thanking Mr. Knight of that firm for the general fidehty with which they have been executed. HENEY MOEPJS. 2, Mansfield Street, Cavendish Square, January, 1879. CONTENTS. PART I. CHAPTER I. 1. General Remarks. The dependence of Life upon Movement. 2. The various structures which enter into the construction of a joint — Bones, Cartilage, Ligaments, Synovial Membrane, Bursse, Muscles, Arteries, Nerves. pp. 1—15 CHAPTER II. 1. The varieties of Joints. (a) Synarthrosis, or Immovable Joint. (6) Amphiarthrosis. (c) Diarthrosis. 2. The varieties of Diarthrosis, or Diarthrodial Joints. (a) The Gliding Joint, or Arthrodia. (^) The Hinge Joint, or Ginglymus. (c) The Lateral Hinge Joint, or Trochoides, (d) The Ball-and- Socket Joint, or Enarthrosis, pp. 16—22. CHAPTER III. The Articulations of the Skull : — The Temporo-maxillary Articulation pp. 23 — 37 CHAPTER IV. The Ligaments and Joints connecting the Head with the Spinal Column : — 1. The Articulations between the Atlas and Occipital Bone. 2. The Articulations between the Atlas and Axis. (a) The Lateral Atlanto-axoidean Joints. (6) The Central Athmto-axoidean Joints. 3. The Ligaments uniting the Occiput and Axis. pp. 37—64 CONTENTS. PAET II.— THE TEUNK. CHAPTER V. The Ligaments and Joints of the Spinal Column, or the connexion of the Vertebrae with one another : — 1. The Articulations of the Bodies of the Vertebrse. 2. The Joints and Ligaments of the posterior part of the Spine. (a) The Ligaments connecting the Larainse ; and the Joints of the Articular Processes. (b) The Ligaments connecting the Non-articular Processes. pp. 65—99 CHAPTER VI. The Connexion of the Vertebral Column with the Pelvis, or the Lumbo-pelvic Union pp. 100 — 110 CHAPTER VH. The Pelvis :— 1. General Features of the Pelvis. 2. The Mechanism of the Pelvis. 3. The Bony "Wall of the Pelvis imperfect. 4. The Fasciae connected with the Pelvis. 5. Movements of the Pelvis upon the Thighs. 6. The Sacro-iliac Synchondrosis and Sacro-sciatic Ligaments. 7. The Sacro-coccygeal Articulation. 8. The Inter-coccygeal Joints. 9. The Symphysis Pubis. pp. 111—153 CHAPTER VIII. The Thorax:^ 1. The Cavity of the Thorax. 2. The Apertures of the Thorax. 3. The Shape. 4. The Enumeration of the Joints of the Thorax. 5. The Ligaments and Joints which connect the Vertebral Column with the Ribs. (a) The Costo-central Articulation. (b) The Costo-transverse Articulation. 6. The Costo-chondral Joints, or the Union of the Ribs with their Costal Cartilages. 7. The Union of the Segments of the Sternum with one another. 8. The Chondro-sternal Articnlations, or the Ligaments and Joints which connect the Costal Cartilages with the Sternum. 9. The Inter-chondral Articulations, or the Union of the Costal Cartilages with one another. 10. The Muscles of the Thorax. 11. The Movements of the Costal Arches and the Sternum as a whole pp. 154 — 185 CONTENTS. XI PAET III.— UPPEE EXTEEMITY. CHAPTER IX. The Sterno-clavicular Joint and the Costo-clavicular Ligament. pp. 186—194 CHAPTER X. The Scaptilo-clavicular Union : — 1. The Acromio-clavicular Joint. 2. The Coraco-clavicular Ligaments. 3. The Scapular Ligaments. pp. 195—209 CHAPTER XI, The Shoulder-joint pp. 210—226 CHAPTER XH. 1. The Elbow-joint. 2. Movements of the Upper Limb as an aid to the expression of Passions and Feelings. pp. 227—248 CHAPTER Xm. The Union of the Radius with the Ulna, or the Radio-ulnar Articula- tions. 1. The Superior Radio-ulnar Articulation. 2. The Union between the Shalts of the Radius and Ulna. 3. The Inferior Radio-ulnar Joint. pp. 249—269 CHAPTER XIV. The Ligaments and Joints of the "Wrist, or the Radio-carpal Articu- lation pp. 270—282 CHAPTER XV. The Ligaments and Joints of the Hand : — 1. Of the First Row of the Carpus. 2. Of the Second Row of the Ca-^nus. 3. The Medio-carpal Joint, or the Articulation of the Upper with the Jvower Row of the Carpus. 4. The Carpo-metacarpal Joints, or the Articulations of the Carpal with the Metacarpal Bones. 5. The Carpo-metacarpal Joint of the Thumb. 6. The Union of the Bases of the Metacarpal Bones with one another. 7. The Connexion of the Heads of the Metacarpal Bones. 8. The Metacarpo-phalangeal Joints of the Fingers. 9. The Metacarpo-phalangeal Joint of the Thumb. 10. The Inter -phalangeal Articulations, pp. 283—316 xil CONTENTS. PAET IV.— THE LOWER EXTREMITY. CHAPTER XVI. The Hip-joint . . pp. 317— 341 CHAPTER XYII. The Knee-joint pp. 342—377 CHAPTER XVIII. The Tibio-fibular or Peroneo-tibial Joints : — 1. The Superior Tibio-fibular Articulation. 2. The Tibio-fibular Interosseous Membrane. 3. The Inferior Tibio-fibular Articulation. pp. 378—386 CHAPTER XIX. The Ankle-joint pp. 387—397 CHAPTER XX. The Joints and Ligaments of the Foot : — 1. General remarks upon the Foot. 2. The Joints and Ligaments of the posterior part of the Tarsus. («) The Posterior Calcaneo-astragaloid Joint. (b) The Anterior Calcaneo-astragaloid Joint. 3. The Joints and Ligaments of the Anterior part of the Tarsus. (a) The Scapho-cuboid Articulation. (b) The Inter-cuneiform ; and (c) the Cubo-cuneiform Articulations. 4. The Medio-tarsal or Transverse Tarsal Joints. (a) The Astragalo-scaphoid and (b) the Calcaneo- cuboid Articulations. 5. The Tarso-metatarsal Joints. (a) The Inner Tarso-metatarsal. {d) The Middle Tarso-metatarsal. (c) The Cubo-metatarsal Articulations. 6. The Connexion between the Metatarsal Bones. 7. The Metatarso-phalangeal Joints of the four Outer Toes. 8. The Metatarso-phalangeal Joint of the Great Toe. 9. The Inter-phalangeal Joints. pp. 398—450 EXPLANATORY LIST OF PLATES. Feontispiece. — Front Yiew of Skeleton, showing Ligaments connecting the several bones. Plate I. Figs. 1 and 2. — Temporo-maxillary Joint, showing Internal and External Lateral Ligaments 28 Plate II, Antero-posterior Vertical Section through Temporo- maxillary Joint, showing the Synovial Cavity above and below the Inter-articular Fibro-cartilage 80 Plate III. Fig. 1. — Ligaments of the upper end of the Spinal Column seen from the front. Fig. 2. — Temporo-maxillary Joint seen from the inner side, showing the Short Internal Lateral Ligament .... 44 Plate IV. Fig. 1. — Vertical Section through the Atlo-odontoid or Central Atlo-axoidean Joints, showing the Atlo- odontoid and the Transver so-odontoid Synovial Sacs. Fig. 2. — Horizontal Section through the Central Atlo- axoidean Joints, showing the Fibro-areolar Tissue separating the Synovial Cavities from one another, and the Ligaments behind the Transverso-odontoid Sac . . 54 Plate V. Fig. 1. — Transverse Vertical Section through Occiput and Upper Four Cervical Vertebrse in the line of the Occipito-atlantal Joints, showing Dura Mater covering over the Posterior Common Vertebral Ligament. Fig. 2. — Ditto, showing Posterior Common Vertebral Liga- ment seen after removing the Dura Mater 58 Plate VI. Transverse Vertical Section through Occiput and Upper Vertebrae, showing the Ligaments connecting the Head with the Spinal Column. Fig. 1. — Crucial and Check Ligaments, with the Occipito- cervical Ligament cut and thrown down. Fig. 2. — Occipito-cervical Ligament seen after removing the Dura Mater and the Posterior Common Vertebral Ligament 59 Plate VII. Fig. 1. — Front View of the Ligaments connected with the Dorsal Vertebras, viz., the Anterior Common Vertebral Ligament, the Short Intervertebral, the Stellate, and the Superior Costo-transverse Ligaments. Fig. 2. — Capsular Ligaments of some of the Cervical Vertebrae, and of the first Costo-transverse Articulation . 72 XIV EXPLANATORY LIST OF PLATES. PAGE Plate VIII. Posterior Common Vertebral Ligaments. Fig. 1. — In tlie Lower Dorsal Region. Fig. 2. — ^In the Lumbar Eegion .73 Plate IX. Fig. 1 . — Horizontal Section tbroxigli one pair of Eibs and an Intervertebral Substance. Fig. 2. — Portion of the Ischium and Pubis, to show (1) the Cotyloid Notch with part of the Ligamentum Teres at- tached to the Ischium outside the Acetabulum ; (2) the Decussation of the Fibres of the Transverse Ligament of the Cotyloid Notch. Fig. 3. — Ligamentum Subflavum in the Lumbar Region and its relation to the Articular Process 82 Plate X. Fig. 1. — Ligaments connecting the Sacrum and the Coccyx posteriorly. The Supra-spinous Ligament is cut and turned up so as to lay open the Spinal Canal and expose the lower end of the Posterior Common Vertebral Ligaments connecting the Cornua of the Sacrum with those of the Coccyx, and the fibrous tissue between the Transverse Processes of these Bones are also seen. Fig. 2. — Supra- and Inter-spin ous Ligaments in the Lumbar Region 86 Plate XI. Ligaments of the Pelvis. Fig. 1. — The Ilio-lumbar and the Sacro-lumbar Ligaments, and the foramina in the latter for the passage of Blood- vessels to the Sacro-iliac Joint. Fig. 2. — Vertical Section throagh the Sacrum and Sym- phvsis Pubis ; the Sacro-sciatic Ligaments seen from within, the Pelvis 106 Plate Xn. Posterior View of Sacro-sciatic Ligaments, showing the direct continuity of the Tendons of the Hamstring Muscles into the Great Sacro-sciatic Ligament . . . .134 Plate XIII. Fig. 1. — Transverse Vertical Section through the Symphysis Pubis, showing a Fissure in the upper and back part of the connecting Cartilage ; and the Liga- men turn Arena turn. Fig. 2. — Antero-posterior Vertical Section through the Dorsal Vertebrse and their intervertebral Substances . . 148 Plate XIV. — Ligaments of the Symphysis Pubis. Fig. 1. — Posterior View of the Symphysis. Fig. 2. — Anterior View of the Symphysis (Female), showing the Decussation of the Fibres of the Ligament. Fig. 3. — Ditto ditto (Male) 149 Plate XV. — Vertical Section through the Chondro-sternal and Inter-chondral Joints. The Rhomboid or Costo-clavicular Ligament, the Sterno-clavicular Joints, and the Costo- xiphoid Ligament, are also well seen 174 EXPLANATORY LIST OF PLATES. xv PAGE Plate XYI. Fig. 1. — Section through Sterno -clavicular Joint, showing Inter- articular Fibro-cartilage. Fig. 2. — Front Yiew of the Inter-clavicular Ligament. Fig. 3. — Posterior Yiew of the Inter-clavicular Ligament . 190 Plate XYII. Fig. 1. — Ligaments connecting the Shoulder Bones, viz., the Cla\T.cle and Scapula ; together with the Capsule of the Shoulder-joint and the relation of the Biceps and Subscapularis Muscles to it. Fig. 2. — Intercarpal Joint laid open from the Dorsum, show- ing also the Inferior Eadio-ulnar, and the "Wrist-joints ; the Glenoid or Dorsal Transverse Ligament between the Scaphoid and Cuneiform Bones ; and the Carpo-metacarpal Articulation 200 Plate XYIII. Fig. 1. — Outer Yiew of the Capsular Ligament of the Shoulder -joint ; and the Coraco-clavicular Ligaments. Fig. 2. — Ligaments of the Wrist; and the Anterior Annular Ligament of the Carpus, with the Tendon of the Flexor- carpi EadiaKs passing through its Outer Pillar .... 201 Plate XIX. Fig. 1. — Head of Humerus, with the Capsnle of the Shoulder-joint attached, some of the Fibres of which are reflected upon the lower and outer sides of the Neck of the Bone ; the Gleno-humeral Ligament, and a Sesamoid Bone in the Subscapularis Tendon, are also seen. Fig. 2. — The upper extremity of the Ulna, showing the Osteo-hgamentous Collar for the Head and Neck of the Eadius, viz., the Lesser Sigmoid Cavity, the Annular Ligament, and the Ligamentous Fibres between the latter and the Neck of the Eadius. Fig. 3. — Portion of Scapula, showing Glenoid Fossa, its Marginal Ligament, and the Bifurcation of the Long Tendon of the Biceps to join the Ligament .... 212 Plate XX. — Yertical Section through the Shoulder-joint, showing Ligaments and Tendons, as seen on the inner side from the interior of the Joint 216 Plate XXI. — Bursas in connexion with the Shoulder-joint . . 220 Plate XXII. Fig. 1. — Elbow-joint seen from the outer side. Fig. 2. — Ditto seen from the inner side 234 Plate XXIII. Fig. 1. — The upper extremity of the Ulna, show- ing the Annular Ligament divided and drawn open ; the Attachment of the Capsule of the Superior Eadio-ulnar Joint to the Neck of the Eadius, is seen. Fig. 2. — Elbow-joint laid open from in front to show the Attachment of the Capsule to the Humerus, Ulna, and Annular Ligament 2.50 Plate XXIY. — Section showing the Synovial Cavities of the "Wrist and Hand, and the Triangular Fibro-cartilage shutting off the Inferior Eadio-ulnar from the Eadio-carpal Joint . 298 XVI EXPLANATORY LIST OF PLATES. PAGE Plate XXV. — Metacarpo-plialangeal and luter-phalangeal Joints seen from the Palm. The Anterior Annular Ligament of the Carpus, the Transverse Ligament of the Metacarpus, and the Sesamoid Plates or Fibro-cartilages of the Fingers and Thumb, are shown 310 Plate XXYI. Fig. 1. — Vertical Section through the Hip-joint, showing the relative thickness of the upper and under parts of the Capsule, and the Attachments of the Pound Ligament Fig. 2. — Head of the Tibia (Left) with the Semilunar Carti- lages and Transverse and Crucial Ligaments 322 Plate XXVIl. Fig. 1. — Front View of the Capsule of the Hip- joint, shoAving the Ilio-femoral portion of it; and the ten- dinous band between the External Vastus and the Pectus Muscles strengthening it. Fig. 2. — Posterior View of the Capsule of the Hip-joints, showing the zonular condition of its fibres during ex- tension ; and the Ischio-femoral Ligament 324 Plate XXVHL Fig. 1. — Hip-joint after dividing its Capsule and disarticulating the Head of the Femur. The Pound Liga- ment, and the reflection of the Synovial Membrane from off the floor of the Acetabulum on to it, are shown, Fio". 2. — Back of the Knee-joint, showing the Ligamentum Winslomi 330 Plate XXIX. — Ligamentum Teres of the Hip-joint, shown by- trephining the floor of the Acetabulum. Fig. 1. — The Ligament slacJc in flexion. Fio-. 2. — The Ligament not tight in complete extension, fio-. 3. — The Ligament tight in flexion, adduction, and rotation outwards 331 Plate XXX. — Burs« in connexion with the front of the Hip- joint 334 Plate XXXI. — Burs^ in connexion with the back of the Hip- joint 335 Plate XXXII. — Vertical Antero-posterior Section through the Knee-joint ; showing the extent of the Synovial Cavity ; the Bursse over "the PateUa and behind the Ligamentum PateU^ ; the Ligamentum Mucosum ; Crucial Ligaments ; and the Fatty Tissue of the Joint 350 Plate XXXIH. Fig. 1 — The Front of the Knee, showing the Anterior Crucial Ligament. The Knee-joint is in the position of extension. Ficr. 2. — The Transverse Section through the Condylar End of the Femur, and a horizontal section through the Tubero- sities of the Tibia to show the Posterior Crucial Ligament. The Joint is in the position of Flexion 358 EXPLANATORY LIST OF PLATES. XVu PAGE Plate XXXIV. — A View of tlie Front of the Knee-joint after cutting through and raising the Capsular Ligament, and removing the Ligamentum Mucosum. A communication between the Synovial Cavity and the Bursa beneath the Quadriceps Extensor Tendon ; the FiLro-cartilages and Coronary Ligament ; the Transverse and Anterior Crucial Ligaments are also in view. Joint flexed 362 Plate XXXV. — Front View of the Knee-joint after cutting through and throwing down the Quadriceps Extensor Tendon and the Capsular Ligament. The Alar Ligaments, Ligamentum Mucosum, the Patella, and the attachment of the Posterior Crucial Ligament are shown. Knee in flexed position 366 Plate XXXVL — Bursae in connexion with the front of the Knee- joint 370 Plate XXXVII. — Burs« at the back of the Knee-joint . . . 371 Plate XXXVIII. Fig. 1. — Front of the Knee-joint, showing the crossing of the Crucial Ligaments ; the Semilunar Fibro- Cartilages, and their Transverse Ligament are also seen. Fig. 2. — Back of the Ankle-joint, showing the Posterior Ligament of the Ankle-joint, the Posterior and Middle Fasciculi of the External Lateral, the posterior part of the Internal Lateral Ligaments of the Ankle, and the Transverse Ligament of the Inferior Tibio-fibular Joint . 392 Plate XXXIX. — Bursse between the front of the Ankle-joint and the lower end of the Tibia and the Tendons passing over the joint 394 Plate XL. — Bursas at the back of the Heel and outer and inner sides of the Ankle-joint 395 Plate XLI. — Longitudinal Vertical Section of the Ankle and the Foot through the line of the Great Toe ; showing the Calcaneo-astragaloid Interosseous Ligament and the Joints along the inner border of the Foot 405 Plate XLII Fig, 1. — Ligaments of the Sole of the Foot, showing the separation between the long and short Plantar Liga- ments. The Tendon of the Peroneus longus passing into the groove of the Cuboid ; and the Inferior Calcaneo- scaphoid Ligament are also seen. Fig. 2. — The Ligaments of the Ankle and of the Dorsum of the Foot as seen with the outer border of the Foot towards the spectator 421 Plate XLIII. — An oblique section of Foot, showing the Synovial Cavities of the Tarsus and Metatarsus,, with the Ligaments separating the one from the other 432 LIST OF WOODCUTS. PASB Diagram I. — Curves of the Spinal Column from the Atlas to the Fifth Lumbar Vertebra. (a) Without Intervertebral Substances. (b) With Intervertebral Substances ' . 71 Diagram II. — Section of the Pelvis through Cotylo-sacral Arch , 139 Diagram III. — Head of the Humerus, showing the relative extent of the Articular Facet above and below the Horizontal Axis 212 Diagram IV. — To illustrate the Axis of Rotation of the Radius upon the Ulna 254 Diagram V. — Head of the Femur, showing the relative extent of the Articular Surface above and below the Horizontal Axis 319 Diagram VI. — To illustrate the Bearing Surfaces of the Femur and Acetabulum 339 Diagram VII. — Anterior View of the Head of the Left Tibia, showing the Line of the Epiphysis 346 Diagram VHI. — Posterior View of the Head of the Left Tibia, showing the Line of the Epiphysis 346 Diagrams IX. and X. — To show the Direction and Points of Attachment of the External and Internal Lateral Liga- ments of the Knee-joint; and the separation of these points in extension, whereby the Ligaments are tightened 375 Diagram XI, — Showing the relative positions of the Tibia and Femur, and the state of the External Lateral Ligament of the Knee in Semiflexion 376 Diagram XII. — Showing the relative positions of the Tibia and Femur, and the state of the External Lateral Ligament ol the Knee-joint in complete Flexion 376 Diagram XIII. — The Tibio-fibular Interosseous Membrane ; and the Anterior Inferior Tibio-fibular Ligament .... 382 ANATOMY OF THE JOINTS. PART I. CHAPTER I. PARTS ENTEEING INTO THE CONSTEUCTION OF JOINTS. It may with truth be said that every kind of structure in, and every organ of, the body is to a certain extent subservient to the perfection and uses of the joints. AH animals, indeed all living things, live by movement of some kind ; and in animals which possess joints, movement by means of joints is necessary to the continuance of life. Plants and animals alike require, in order to live, the move- ment within their tissues of air, of water conta inin g air, of food particles, of blood or of some equivalent fluid ; but in animals which respire by lungs, which move from place to place, which seize their prey and masticate their food, the anatomical and physiological integrity of joints is an absolute requirement of existence. Man must walk, must lie down and rise up, must turn from side to side ; scarcely one of the ordinary conditions of his life could be fulfilled were he deprived of the use of his hands and forearms ; did he not move his ribs, respnation would soon cease, and if he were not to masticate or chew he must quickly die. By the beating of his heart and the circulation of his blood, the joints are nourished and repaired. He takes food because he must eat to live, but to eat he must move, and so even in this respect he moves to live. His senses and intel- lect, the ear, eye, taste, touch, and brain, are from the first employed to guide his movements, and in return they gather information and obtain experience for him by the action of his joints. 4 PARTS ENTERING INTO firmly as to seem like a continuous structure : its other surface is directed towards tlie cavity of the joint, and in the fcetus is coated by a thin film of epithelium continuous with the epithe- lium of the synovial membrane of the articulation ; but when the joint is brought much into use and as age advances, this film of epithelium is gTadually worn away by friction up to the margin of the cartilage. The cartilage terminates abruptly, and extends upon the bones no further than friction requires it. (2.) Another form of " hyaline cartilage of joints" is foimd in the costal cartilages of the thorax and the xi2yhoid cartilage of the sternum. It is the form of hyaline cartilage which is substi- tuted for bone where flexibility is required. The cartilages of the ribs form the medium of union between flat bones — viz., the ribs and the sternum. It resembles articular cartilage in this respect, that at one end it is continuous with bone — i.e., with the anterior extremity of the rib, while at the other it is in relation with a synovial cavity — i.e., the chondro-sternal joint. The ends of the costal cartilages correspond to the surfaces, and the parts between the ends to the margins of the articular car- tilage ; but there is this difference, that the prolonged margins are covered over by perichondrium, which does not exist upon the margins of the articular variety. The use of these cartilages is to unite the ribs and sternum, and thus to complete the wall of the chest, part of the framework of which it forms ; while at the same time that it protects the contents of the thoracic cavity it allows of movements, and is capable of yielding, instead of breaking, under pressure. B. Wliite Fibrous Cartilage of Joints. — White fibrous cartilage resembles in structure and texture both fibrous tissue, such as ligament, and hyaline cartilage, and therefore partakes of the phy- sical properties of each. It has to a certain extent the strength and flexibility of the one and the elasticity of the other, and may be considered as a link between the two. It occurs in joints in different forms : (1) inter-articular fibro- cartilage, such as is found in the temporo-maxillary, sterno- clavicular, inferior radio-ulnar, the knee, and sometimes the acromio-clavicular articulations. They are confined to diarthro- dial joints. They are nearly free, being connected only at their edges with the ligamentous and synovial tissues of the joint; their sm-faces are unattached and are interposed between the articular surfaces of bone, so as in some cases to divide the joint into two THE CONSTRUCTION OF JOINTS. 5 distinct cavities. This is usually the case in the teniporo- maxillary and sterno-clavicular joints. In the knee there are two imperfect fibro-cartilages, which, instead of completely sepa- rating the bones, merely project into the articulation and allow the synovial membrane to be continued as a thin epithelial film over their surfaces. If, however, we consider these two im- perfect cartilages as one, having a perforation at its centre, we find a strong analogy between them and the occasional con- dition of the most perfect inter-articular cartilages — viz., an opening sometimes exists at the thin central part allowing of a communication between the two portions of the joint cavity which the cartilage separates ; or, in other words, owing to this perforation of the fibro-cartilage, what would otherwise be two shut sacs becomes one. They occur in joints at which there is frequent and violent motion, and serve the pm^pose, owing to their elasticity, of breaking the shock of concussions ; they act as adjusters to adapt dissimilar bony surfaces to one another ; increase the extent and variety of motion by allowing it to take place at one time between the cartilage and the bone on one side, and at another between the cartilage and the bone on the other side; and lastly, they add to the strength and security of the joint. (2.) " Circumferential or marginal" fibro-cartilage occurs on the edges of the acetabulum and glenoid fossa, and serves to deepen the sockets for the reception of the heads of the femur and humerus respectively. In this form they are found only in that variety of diarthrodial joints known as " ball and socket." Another form of what may be called marginal, though not cir- cumferential, fibro-cartilage is to be seen in the joints of the fingers. Here small plates of white fibro-cartilage, closely con- nected with the base of one phalanx, serve to deepen the socket for the reception of the head of the bone above it, and to add to the stability of the articulation. (3.) A third form of white fibro-cartilage is the " connect- ing." It is found interposed between, but binding together in a solid manner, two bones, as in the case of the intervertebral substances and bodies of the vertebrse. These connecting fibro- cartilages occur only in amphiarthrodial joints, and the amount of motion which is possible between the bones so bound to- gether is only as much as the elasticity and flexibility of the ;"inituig fibro-cartilage will allow. Although limited, yet the 6 PARTS ENTERING INTO degree of motion at these joints is often far from being insignifi- cant, whilst they possess, through this fihro-cartilaginous nnion, a gTeat degTee of strength and a capacity for resisting violent concussions, together with a tendency to assume their natural position after having been disturbed therefrom by muscular action or other forces. The easy flexibility and the gTeat strength of the spinal column sufficiently attest the utility of this structure. Besides the bodies of the vertebrae, there are other examples in the skeleton of bone being united with bone by means of " connecting cartilages." Such are found in the pelvis at the symphysis pubis and sacro-iliac synchondrosis. In structure these latter are essentially fibro-cartilages, for they have fibres in their matrix, but the projDortion of cells to matrix is much greater in them than in the fibro-cartilaginous portions of the intervertebral substances. But this is only a matter of more or less, and at the other extreme are the circumferential fibro- cartilages, which are composed almost entirely of fibres, with sometimes hardly a trace of cells. There is, however, this difference in the joints formed by the more fibrous and the more cellular connecting cartilages, that the former allow a manifest degree of motion and compression, while the other usually permit ordy a minimum amount of yielding ; but at periods, as during pregnancy, the pelvic symphysial cartilages sweU. up and enlarge considerably, and are then capable of a considerably increased amount of yielding. A preparation which I obtained from a woman in the seventh month of pregnancy, and placed in the Middlesex Hospital Museum, shows the gTeat thickness which these substances sometimes attain. Ligaments. — Ligaments are strong fibrous bands passing from one bone to another, and in doing so they blend with the margins of fibro-cartilages which separate the bones, and give support and protection to the synovial lining of joints when such exist. They give stability to the skeleton at the points of junction of bone with bone, or bone with cartilage, and serve to limit and control the motions of the articulations ; they sometimes extend between different parts of the same bone, as in the case of the transverse ligament of the aceta- bulum, the supra-spinous, and the coraco-acroniial ligaments of the scapula. Like hyaliiie and wliite fibro-cartilage, ligamentous tissue is THE CONSTKUCTION OF JOINTS. 7 to be found in other parts of the body besides at the joints, and serving other purposes besides joining bone with bone or cartilage. For instance, it occiu's in the form of the so-called annular ligaments, which serve the pm-pose (sometimes exclu- sivelj) of tying down tendons as they pass to their insertions ; and in the form of tendon itself, ligamentous tissue intervenes between muscular fibres and bone, and serves to fix the former to the latter. Here we have only to do with articular ligamentous tissue, or ligaments commonly so called. They are composed of fasciculi of inelastic parallel and crossing fibres of a white, silvery colour, and covered over with a fine envelope of cellular tissue. They vary in tliickness, length, strength, and shape, according to the form and motions of the joint. They differ in number in the several joints, sometimes being numerous, at others few. They are intimately connected at their attached extremities with the periosteum of the bones, and are indeed sometimes regarded as dhect and thickened continuations of that mem- brane from one bone to another. Though of the same struc- ture they differ in their deep relations, for while periosteum is always intimately adherent to bone, the ligaments are either lined by synovial membrane or attached to intermediate fibro-cartilage. The dh-ection of the fibres of ligaments varies at different parts of the same joint, and depends upon the direction of the motions that each has to control. Between the fibres of the Hgaments the minute bloodvessels of the joint penetrate so as to reach the external aspect of the synovial membrane, upon wliich, as well as between it and the bones at the margins of articular cartilage, they ramify. Articular ligaments may conveniently be divided into four classes— viz. : 1. Those which connect the bones of diarthrodial joints together, and in doing so form fibrous envelopes for the articulation. Of these we have good examples in the capsular ligaments of the ball and socket joints — ^viz., the hip and shoul- der, and also in those less imperfect capsules surrounding such joints as the elbow, knee, and ankle. It is often the custom, and is always convenient, to speak of these less perfect capsules as consisting of anterior and posterior and lateral ligamentous bands, but these bands are always loosely connected with each other by intervening fibres. Even the most perfect capsules are thickened m places by superadded bancl=i of fibres like the 8 PARTS ENTERING INTO coraco-liumeral ligament of the slioulder and the ilio-femoral of the hip. Some of the ligaments of this class wind round the end of a bone like a ring, as the coronary ligament does round the head of the radius, and the transverse ligament round the odontoid process. 2. Those which connect the slightly movable or amphiartlirodial joints at which the union between the bones is established by a connecting cartilage. They con- sist of short fibres passing in different ways across from bone to bone, sometimes transversely, sometimes obliquely, but always in a manner that will give strength and limit move- ment. Instances of this sort exist at the symphysis of the pelvis and along the front and back of the bodies of the vertebrae. 3. Certain ligaments exist within the ligamentous capsules of a joint, though not within the cavity of the synovial sac. They serve to connect together the bones between wMch they pass, and to limit motion. They are called inter-articular ligaments, and are found in the knee-joint as crucial ligaments, and in the hip as the round ligament- — the ligamentum teres. The latter in the human skeleton is insignificant in importance, whether we regard it as a means of uniting the bones or as a check to movement. 4. Some ligaments which are tightly extended between bones become still more tightly stretched as the bones are separated a little more widely from each other. They need therefore be elastic as well as fiexible, a property not possessed by ordinary ligament. They are formed of yellow elastic instead of white fibres. By their elastic property they do away with the necessity of muscles as a means of restoring the parts to which they are attached to the state of rest after disturbance therefrom. They perhaps can hardly be said to be articular ligaments, yet they are important structures in connecting bony parts ; they only exist between the laminee or bony arches of the vertebrae. Synovial membrane enters into the composition of all diar- throdial joints, and secretes a fluid which lubricates the surfaces and facilitates their movements. Except where the articular cartilage occm's the inner surfaces of joints are lined by syno- vial membrane. Usually they form closed sacs without any external openings, but as age advances and use becomes more frequent they sometimes communicate with one or other of the bursse which are situated in the neighbourhood of some of the joints of the extremities. While the internal surface of the THE CONSTRUCTION OF JOINTS. » synovial membrane presents a smootli, glistening appearance, its external surface is rough and adherent to the ligamentous and osseous structures of the joint. In the natural state it is very thin, but frequently forms delicate folds which lie fiat upon the edges of the cartilage, and thus project into the cavity of the joint. Enveloped between the layers of these folds are looped vessels and little masses of fat ; they are usually covered with little processes like villi, which sometimes in diseased joints form polypous bodies hanging from the lining membrane, or overhanging the cartilages. Appended to the synovial mem- brane are masses of soft fat, which serve the purpose of filling up during movements the spaces left between the several tis- sues of the joints. These have been described by some of the older anatomists as glands whose pm-pose is the secretion of the synovial fluid, but they are now known not to be so. They pro- ject into the articulation between the bones, carrying the syno- vial membrane with them, or they lie in the hollows or depres- sions and notches of the bones of the joints, and form soft cushions for the contigTious bone. They are to be seen in the diagTams and in the dissection of such joints as the knee, ankle, metacarpo-phalangeal, and several others. The synovial membranes are very vascular, particularly near the margins of the articular cartilage, and in their fringes and folds ; so also are the fatty masses above referred to, as witness those about the elbow, knee, and at the bottom of the acetabulum. They are also supphed with nerves and absorbents. In their minute structure they resemble other serous tissues, such as the pleura and pericardium. The synovial cavities are mapped out very early in the process of development ; indeed as soon as the limbs are sufficiently advanced for any movement to occur between the segments of them. They have been seen quite distinct in the hip and shoulder joints before the third month of intra-uterine life. Bursce. — Where a tendon rubs over a bone, or beneath the integTiments, or where a bone works so as to cause friction, a cavity or sac is formed iu the cellular tissue between the two structures, and this sac contains fluid of the same kind as the synovia of joints. As age advances these sacs or bursse often com m unicate with the cavity of a joint. They are met with as a rule only in the extremities. There are about 140 altogether in the body, 33 of which are in each upper extremity and 37 in 10 PARTS ENTERING INTO each lower limb. They occur (1) between tendons and bones ; (2) between tendons or superficial bony points and external parts ; (3) between tendons and ligaments ; (4) between con- tiguous tendons ; (5) where processes of bones play on liga- ments ; (6) where one bone plays on another. Sometimes a bursa is common to two tendons, and then it divides where the tendons separate. Bursse of contiguous tendons sometimes com- municate. In their structure they resemble the synovial mem- branes, in that they have a wall of condensed cellular tissue lined by a thin, smooth secreting membrane. At the sides of bursse, as well as of joints where no pressure or friction is exer- cised, adipose tissue abuts upon and is cormected with the cellular wall ; while from these fatty masses are suspended into the buTsae, as into the joints, fringes or folds containing within them bloodvessels, serving for the secretion of the lubricating fluid. By the pressure which the motions of the joints or tendons make upon these fimbrise and fatty masses it is pro- bable that the synovia is thrown out in greater or less quantity according to the requirements of the part ; just as is the case with the salivary glands, more saliva being secreted by the motion of mastication or talking. Further, small cartilaginous bodies are often formed in the cavities of bursse as well as of joints — of burste mucosae and of bursse synoviales ; and such bodies, wherever situated, may be either movable or fixed. Some of these sacs or bursse have received the name of bursse mucosse, others of bursse synoviales. In structure and uses they are identical ; the former are large simple sacs, which may or may not be in connexion with tendons. They are to be found about the shoulder, hip, elbow, and knee joints, sometimes between tendons and the joint, sometimes between bony prominences and the integuments. The latter are hga- mentary sheaths, along which tendons are conducted over such hinge joints as the ankle, Avrist, toes, and fingers. These synovial bm^sse are lined by a thin, smooth membrane, which is likewise reflected over the tendon, and secretes a synovia- like fluid, for the piu'pose of lubricating the surfaces during the play of the tendons within their sheaths. There is a resemblance between the synovial sacs of joints and bursse on the one hand, and the pleurfe, pericardium, and peritoneum on the other. In intimate structure, in the de- position of fatty tissue upon their exterior, and the presence THE CONSTRUCTION OF JOINTS. 11 of fat in tiie reduplications of these membranes, there are strong resemblances to the fat at the apex of the heart, in the omenta and the appendices epiploicse of the colon. There are no fimbrise or fidnges projecting from these visceral mem- branes, and proportionately fewer bloodvessels ramify between them and the fat outside them. Small cartilaginous bodies are sometimes found in the cavity of at least one of them — viz., the human vaginalis testis. The foregoing are the several parts, some or all of which are necessary for the construction of a joint. There stdl remain to be briefly considered the muscles which move it, the bloodvessels which nourish it, and the nerves which vivify it. Tlie Muscles are the agents of motion, and their use is to move one part of a joint upon another. Their relation to joints is very various. Some muscles pass over and move only one joint ; others pass over and move several simultaneously or in quick succession. Much force is lost by the muscle passing over several joints ; but it is a law that the more joints a muscle passes over the gxeater is the number of offices it has to perform, and the gTeater the number of joints it moves. Some muscles are inserted into bone near to an articulation, and this is attended with a loss of power, though with a rapidity of effect. Others are inserted at a distance from an articulation, and then there is less loss of power but less rapidity of motion. Such insertions are called short and long levers. The true levers of the body are very few in number, but they are those that most favour muscular power. The mastoid process, coro- noid process of jaw, and the occiput are levers for the head ; the spinous and transverse processes for the back ; the tro- chanters, a tuberosity of the ischium, the crest of the ilium, the patella, the os calcis, and the arch of the foot, are levers for the lower limb ; the acromion, olecranon, coronoid process of ulna, and pisiform bone of the hand, are levers for the upper limb. Speaking generally, there is nearly always some loss of muscular power owing either to the form of bone the muscle is intended to move, to the position of the insertion of the muscle, or to the obliquity of its direction, with respect to the motion to be effected. Nature often sacrifices power to fitness and to form, that the joints may be small and the limbs well proportioned ; but she has supplied to muscles a quantity of 12 PARTS ENTERING INTO vital contractile power, which more than compensates for the loss of mechanical advantage. In the words of that great sm-geon, John Bell : — " Nature is not seeking to compensate for want of power by the advantages of pulleys and levers and mechanical helps ; nor is it in the forms of the parts that the Infinite "Wisdom is to be found ; for among other gifts such a portion of this spirit is given to man, that he has used the pulleys and lever, accelerations of motions, and all the mechanical powers that result from it ; he has invented valves of infinite variety ; he has anticipated all that he has found in the mechanism of the human body ; but the living power which compensates for the want of levers, which allows everywhere power to be sacrificed to the beauty of form, which has strength in convidsive and violent actions to break the very bones ; this is the act of Infinite Wisdom, on which our admiration should chiefly dweU." Another and by no means an insignificant purpose served by muscles is to give strength and security to the union of bones at certain joints. Thus the hip is strengthened by the small rotator muscles (notably by the strong tendon of the obturator internus), and by the rectus and vastus tendons ; the shoulder by the small muscles inserted into the tuberosities, and by the long tendon of the biceps. So in the case of the biceps and semimembranosus at the knee, the triceps at the elbow, the flexors and extensors at the wrist, and the crossing of the peroneus longus and tibialis posticus in the foot. The muscles which surround an articulation afford almost as strong, in some cases even a stronger, power for restraining undue motion than the ligaments. About many of the joints we find one set of muscles acting as antaoonisers to the others, so that when the first has acted upon a joint in one direction, the other set comes into play to check them by acting upon it in the opposite. Occasionally, however, tliis antagonising power is lost or overcome, and then the joint is dislocated by action of the muscles which move it. The contraction of the surrounding muscles assists the liga- ments of a joint, and the influence of atmospheric pressure, in preventing dislocations ; and at the same time diminishes the strain upon the ligaments. Sprains occur when forces act upon the joints while the muscles are off their guard ; for THE CONSTRUCTION OF JOINTS. 13 in the ordinary normal state the contraction of muscles pro- bahly prevents the ligaments from even being put upon the stretch. A purpose served by muscles, and in some few instances (as in the subcrureus and subanconeus) the only purpose, is to act upon the capsule of the joint in certain positions, so as to pre- vent its being nipped between the edges of the bones. A wise economy is seen in the mode of attachment of muscles to bones near a joint. Tluy are, so disposed as never to strain the ligaments of a joint hy tending to pull one hone from the other with which it a7iicidates ; bid, on the con- trary, add strength to the Joint sometitnes hy decnsscding loith the fibres of muscles of the opposite side, sometimes by the same muscle pulling tighter together the two bones of an articulcdion. This statement, which I believe to have such a general appli- cation to the joints of the trunk as to be worthy of the name of a law, could be numerously illustrated. Take, for example, the decussation of the fibres of the muscles of the abdominal wall over the front of the symphysis pubis ; the origin of the gluteus maximus, the latissimus dorsi, and the erector spinse from both bones of the sacro-iliac synchondrosLS ; of the trape- zius, deltoid, pectoralis major, and sterno-mastoid from each of the bones of the joints in connexion with which they are situated. Were it not for this, and had, for instance, the external oblique muscle of the abdomen not decussated over to the opposite side, or had not the deltoid arisen from both clavicle and acro- mion, a necessary result of their contraction would have been to strain the ligaments of the joints formed between those bones respectively. Many other examples illustrative of the same law might be adduced. As a further instance of the same design in sparing strain upon ligaments, the rotator muscles of the skull may be quoted. Here again we find a provision against such an immense strain, as would be caused by the dragging of the cranium, upon the ligaments of the occipito- atlantal joints during rotation of the head, if the muscles which turn the head and atlas round the odontoid process acted only on the atlas. Besides the muscles which are attached to the atlas, certain others are inserted at the skull, which, besides having a tendency to pull the head backwards or forwards, and to one side, are able to act in association with the muscles inserted into the transverse process of the atlas, and thus both 14 PARTS ENTERING INTO skull and atlas are pulled upon at the same time, and tlie occipito-atlantal ligaments are saved the strain. These points will be further brought out in the description of the sjjecial joints, but they are of sufficient importance in the construction of the body to be mentioned here. The Arteries. — Blood is supplied to all the structures of a joint, although some of the structures, such as articular carti- lage, are what is called ?io5*-vascular — i.e., have not blood- vessels penetrating their substance, but receive their nourish- ment from the vessels which are brought up to their surfaces. The synovial membrane is the most vascular structure of joints, and, to reach it, numerous minute arteries penetrate between the fibres of the ligaments to ramify in the fatty tissue about the joint, in the cellular tissue connecting the synovial with the ligamentous capsule, in the synovial membrane itself, as well as between its layers, where it forms fringes, fimbriae, or mucous ligaments within a joint. The bloodvessels of a joint generally run quite up to the edges of the articular cartilages, and often form fine zones or circles around the articular margins of the bones ; occasionally they may be seen passing over the edges and on to the surface of the cartilages and fibro-cartilages, as shown in the diagTam of the semilunar cartilages of the knee-joint. It is a point of interest too in general and surgical anatomy, that it is in the neighbourhood of the articulations that the anastomoses between branches of different trunk vessels occur. The Nerves. — It is very difficult, indeed often quite impos- sible, to trace with any certainty, even in weU prepared and recent subjects, nerve filaments to the different tissues of a joint. But that some of the structures of joints are higlily supplied with nerves is amply proved by the pain and startings caused by diseased joints. Often, however, and especially into the larger and more important joints, it is easy enough to follow nerve branches through the ligamentous fibres of the articula- tions. By way of generalisation, and on account of the_ gTeat practical unportance of a knowledge of the nerve sympathies of joints, it is well for the student and the practitioner to remember the great law, fu'st pointed out by my friend and master, John Hilton, and subsequently, though perhaps quite independently, by Schroeder Van der Kolk — viz. : " The same trunks of nerves whose branches supply the THE CONSTEUCTION OF JOINTS. 15 groups of nmscles moving a joint, furnish also a distribution of nerves to the skin over the insertions of the same muscles, and the interior of the joint receives its nerves from the same source. This implies an accurate and consentaneous physiological har- mony in these various co-operating structures." Instances of this law will immediately occur to the advanced student, in the circumflex, subscapular, and supra-scapular nerves of the shoulder-joint, the suboccipital of the occipito-atlantal, the anterior crural of the hip, and many others. 16 CHAPTER II. THE VAEIETIES OF JOINTS. The name joint or articulation is given to the union of two or more bones ; or of a bone with a cartilage, or of two or more cartilages. In most cases this union is effected by some inter- vening medium differing in structure from both bone and cartilage, but in some instances the bones are in the closest apposition, with no other connecting medium but their own proper covering — the periosteum. In the previous chapter it has been stated that the structures which are immediately concerned in the union of the several bones of the skeleton with one another, are cartilage, fibro- cartilage, synovial membrane, and ligaments. Of these struc- tures the only one that is found in all joints of the skeleton is bone itself, with perhaps a little iaterveniag connective tissue. Even bone is not found iu all the joints of the body — though it is in every joint of the skeleton — for the articulations of the larynx are formed between cartilages, not bone. As the offices of joints are more complex and numerous, or what comes to the same thing, as the joint is more perfect, the o-reater is the number of the above structures which enter into its formation. Thus, where (1) no movement at all is allowed, as in the cranial bones, the connexion is by simple close contact, or by overlapping of their edges, or by the invagination of one bone by another, or by direct apposition of their edges with a thin membranous layer of connective tissue — a sutural ligament — extending from the border of one to that of the other. Even this tissue — the sutural ligament — as age advances becomes entirely removed. (2.) Where only a slight amount of move- ment of one bone upon another is required, but great strength with some elasticity of union is also needed, the apposed sur- faces of bone are connected by an intervening layer of fibro- cartHage of variable thickness. (3.) Where a greater amount THE VAEIETIES OF JOINTS. 17 of movement is necessary, the articular surfaces of the bones are coated with cartilage, and layers or bundles of fibrous tissue — I.e., ligaments — pass from one bone to the other so as to surround the articular surfaces, while the joint is further provided with a synovial membrane. In the most complete and perfect of the joints we find also inter-articular fibro- cartilage, either inserted between the cartilage-covered surfaces of the bones or deepening the surface of one of them for the reception of that of the other. Thus then we find in the most perfect and movable joints hone, giving firmness ; cartilage, affording elasticity ; synovial membrane, supplying a viscid fluid to obviate friction ; Jlbro-cartilage, in some cases to lessen friction, in others for the better adaptation of bony surfaces, and occasionally, as in the sterno-clavicular joint, in addition to securing both these ends, the fibro-cartilage affords also a very powerful bond of uuion between the bones ; finally, ligaments, to bind the whole together and prevent dislo- cation. In the human body there are instances of every possible gradation between the most freely movable and the absolutely immovable articulations ; but by the distinctions which have been now pointed out, we are able to classify all joints under three heads — ^viz., the movable, the yielding, and the im- moTfable, Every movable articulation, or diarthrosis, includes in its construction all the tissues above enumerated, except fibro- cartilage, wliich occm's only in some of them. The yielding, or amphiarthrosis, has no proper synovial capsule or lining, but always a fibro-cartilage and ligaments ; and the immovable, or synarthrosis, possesses nothing beyond bone, except in some instances a sutural ligament. We must now consider each of these three species of joints separately. Synarthrosis or Immovable Joint. — This kind of joining is made use of to unite different bony portions into one solid shaft or case. By this combination increase in size by growth is provided for ; the chances and results of injury are diminished ; while more complete protection is afforded to the parts which the bones surround. It includes all those articulations in which the bones are in direct, or almost direct, contact, where there is no intervening fibro-cartilage or synovial cavity, where c 18 THE VARIETIES OF JOINTS. periosteum alone passes from one bone to the otlier, and where movement is also absolutely impossible. In those bones which are developed in cartilage, cartilage for a time — i.e., until the process of ossification is completed — intervenes and binds together the osseous parts. This is the case in the base of the skull, where the basilar part of the occipital bone joins the body of the sphenoid, and is also the way in which the epiphyses are connected with the shafts of bones. But it is not usual to regard the occipito-sphenoid union, or the connexion of the epiphyses with the shafts of long bones, as joints, seeing that there is only a temporary difference of structure at these joinings, and that they have no relation whatever to movement, but only to growth and development. The immovable or synarthrodial joints are like the union of the epiphyses and diaphysis of bones in this respect, and therefore, though interesting from the point of Adew of the construction of a skeleton, yet as having no relation whatever to movement do not fall witliin the scope of this work. Amphiarthrosis. — In this form of articulation, where slight movement is required to be combined with gTeat strength and with the means of breaking shocks, the contiguous osseous surfaces are connected together by broad flattened discs of fibro-cartilage bound over by ligamentous fibres. In this manner the bodies of the vertebrje are connected together. In their modes of union these joints somewhat resemble synar- throsis, from which, however, they are distinguished by the invariable presence of fibro-cartilage and by the motion or yielding which occm's at them. It is true that as life advances the connecting structure gradually loses its elasticity, but the joint has but slight tendency to become obliterated by ossifi- cation. Sometimes, as in the pubic and sacro-iliac articulations, the connecting fibro-cartilage is split through a greater or less extent, and a synovial-like membrane lines the interspace. In this respect — i.e., from the slight synovial interval in the carti- laginous substance, and from the mobility which is permitted — these joints resemble the diarthrodial. The amount of mobility in the joiats of the pelvis is often much increased during preg- nancy by the swelling of the symphysial cartilages. Occa- sionally these joints become obliterated in old age. After some fractm-es, such as those of the patella, neck of THE VARIETIES OF JOINTS. 19 the femur, and olecranon, the bones become reunited by an intervening substance which, allows of movement taking place between the fractured parts : thus a supernumerary or abnormal amphiarthrodial joint may be formed. Diarthrosis. — This is the most movable class of articulation. It includes the greater number of the joints in the body. It is the kind of connexion which exists between the bones of the extremities, as well as between the extremities and the trunk. It allows of constant motion, as witness the costo-vertebral articulations in their movements of respiration. It is lined by synovial membrane and strengthened more or less by liga- ments. In some joints of this class fibro-cartilage occurs in the form of inter-articular discs, but these discs serve no purpose in holding the bones together. Union is effected by bands and layers of ligamentous tissue, by the tendons of muscles, and by atmospheric pressure. Neither the shape of the osseous sur- faces, which is the mode of union in the synarthrosis ; nor the intervening soft elastic tissue wliich unites the osseous edges in amphiarthrosis, has any effect in holding the bones of diarthrosis together. There is, in fact, no single instance of a diarthrodial joint in which the separation or falling asunder of the bones is prevented by either of these means, nor is there an instance of such a joint in which the movements are checked by the shape of the osseous surface or by the fibro- cartilages ; for either the tension of ligaments, or the appo- sition of soft parts checks movement before the edges of the osseous surfaces have any influence upon it. The shape of the articular osseous surfaces varies much in different joints, and as a result of this variation the motions of the joints differ, and according to this difference in their movements a classifica- tion of joints of this kind is made under four headings : — 1. The gliding joint : Artlirodia. 2. The hinge joint : Ginglymus. 3. The lateral hinge joint : Trochoides. 4. The ball and socket joint : Enarthrosis. Arthrodia is formed by the apposition of two plane or nearly plane cartilage-covered articulatory sm'faces. It is the least movable of all the diarthrodial joints, and the movements consist only of a slight gliding of one bone upon the other. A number of small bones are generally united in this manner, and while they allow of a considerable amount of pliability and yielding and even of combined movement, they also pro- c 2 20 THE VARIETIES OF JOINTS. vide a security against injury. Such is the case in the tarsus and carpus. Ginglymus. — In the hinge joints, instead of two nearly plane surfaces there is a convexity presented by one bone and a corresponding concavity by the other. Both articular siu-faces are lengthened laterally, and owing either to the processes of bone or to strong lateral bands of ligament motion is allowed only in two directions — viz., forward and backward — i.e., flexion and extension. The most perfect examples of the hinge joint are the elbow and the ankle. Trochoides is the name given to such joints as that between the odontoid process of the axis and the ring formed by the transverse ligament and the anterior arch of the atlas, and that between the -upper extremity of the radius and ulna. The osseous surfaces are one convex and the other concave, the convex being held to the concave by a strong ligament em- bracing it as at the superior radio-ulnar articulation, or by a fibro-cartilaginous plate as at the inferior radio-ulnar joint. The movement permitted at these joints is of a rotatory character ; in one case the rotation is of the convex bone round its own axis and within an osseo-ligamentous ring — e.g., the head of the radius ; or the osseo-ligamentous ring rotates round the convex bone as at the atlo-odontoid, and occa- sionally at the superior radio-ulnar joints. In the inferior radio-ulnar joint either of the bones may rotate round the other ; the one being held in constant apposition with the other by means of the triangular fibro-cartilage which corre- sponds to the radius of the circle of rotation. Enarthrosis is a joint in which the smooth rounded head of one bone plays within a deep, or upon a shallow, socket in the other. The two are kept in apposition by muscles or atmo- spheric pressure, assisted by a capsular ligament. They differ from one another according as the socket is shallow or deep. The shoulder and the hip are the best instances of the two kinds respectively. Movement is permitted in the ball and socket joint in all directions ; thus we have forward and back- ward movement — i.e., flexion and extension ; movement towards or away from the median plane of the body — i.e., adduction or abduction ; a succession of these four angular movements, as when we swing the arm round and round so as to describe a THE VARIETIES OF JOINTS. 21 cone, the base of which is formed by the hand and the apex at the shoulder-joint : this is called circumduction. Further, there is permitted at the ball and socket joints a rotation of the long bone around its own long axis ; this is true rotation as distinct from circumduction. Finally, there is a considerable amount of gliding going on during the several angular movements. Thus then all the kinds of movements which are possible at any other joint take place at the ball and socket articulations, and they are therefore by far the most freely movable species of diarthrosis, and consequently of all joints in the body. The degTee of motion permitted is regulated, not by the depth of the socket, but by the muscles and the contact of the soft parts of the limb with the trunk, as at the hip and shoulder ; or by ligament, as in the case of the ilio-femoral ligament in the erect position. As there is a gradual transition from the immovable to the movable through the amphiarthrodial or mixed articulations, so there is a gTadual transition from or merging of the characters of one species of diarthrosis with those of another. It is sometimes difhcult to draw the line between a true hinge joint and an arthrodial ; there is gTeat similarity between the true arthrodial and the enarthrodial with a shallow socket, and the characters of the hinge are sometimes combined with those of the ball and socket. Thus in some of the joints with an inter-articular cartilage, such as the temporo-maxillary and the sterno-clavicular, gliding" is combined with a hinge motion so intimately as to make it impossible to say that these joints belong strictly to either arthrodia or gingiymus. In the inter- carpal joint the two rows of carpal bones are so adjusted to one another as to resemble a double ball and socket joint with very shallow sockets. The joint between the metacarpal bone of the thumb and the carpus is intermediate between the hinge and ball and socket varieties. In some situations where a variety of movement is re- quired to be associated with great strength and security, the object is gained by the juxtaposition of two or more joints, each of which allows of a different class of motions. This is the case in the connexion of the head with the spine ; at the junction of the hand with the bones of the forearm, where the radio-carpal and inferior radio-ulnar work in unison to pro- 22 THE VARIETIES OF JOINTS. duce a combined result ; and of the foot with the leg, for while flexion and extension take place at the ankle, lateral movement and slight rotation occur between the astragalus and OS calcis. Occasionally two or more joints combine to increase or add security to the same kind of movement. This associated effect is seen between the radio-carpal, the intercarpal, and the carpo-metacarpal joints ; and between the atlas and axis, where the two lateral arthrodial articulations support and steady the atlas while it is revolving round the odontoid process at the lateral hinge joints — viz., the central atlo-axoidean. This multiplication of joints serves to combine freedom of movement with strength ; a necessary provision in certain places, for as a rule the strength of any single joint, and its power of resisting injury, is inversely proportioned to the freedom of mobility. Take, for example, the shoulder and elbow ; or the hip-joint and the ankle ; or the temporo-maxillary and the joints of the spinal column ; in each of these mobility is in inverse proportion to strength and security. Although similar structures are employed in the construc- tion of all diarthrodial joints, yet the joints vary much in their solidity and extent and direction of movement. These dif- ferences depend upon the shape of the articular surfaces of the bones, and upon the direction and length of the fibres of the ligaments connecting them. Indeed the course of the fibres, and the direction in which they pass to then insertion into the bones of the joint, illustrate with tolerable certainty in what manner they regulate and limit the movements of the articulation. Supernumerary diarthrodial joints are occasionally formed by the non-union of fractures, the fractured ends becoming smooth and rounded off by friction, and surrounded by a ligamentous capsule, the inner sm-face of which yields a synovial-like fluid. Supplemental diarthrodial joints sometimes result from un- reduced dislocations. They are most frequent about the hip and shoulder. 23 CHAPTER III. THE AKTICULATIONS OF THE SKULL. Theee are only two pairs of movable joints connected with the skull — viz., the temforo-maxillary and the occipito-atlantal. At the former the condyles of the inferior maxilla move like hinges in the glenoid fossse of the temporal bones ; at the latter the skull, as a whole, moves by means of its occipital condyles in the boat-shaped sockets of the lateral masses of the atlas. These articulations of the skvill resemble one another in that each consists of two complete, symmetrical joints, placed one on either side of the median line of the base of the skull. Further, the articular surfaces of each separate joint are oblique with regard to both the vertical and the horizontal plane ; thus the condyles of the lower maxilla have their long axis obliquely transverse, being dii-ected backwards and inwards, while the inner ends of the condyles are on a slightly higher plane than the outer ; those of the occiput have their long axis oblique in the antero-posterior direction, but with an in- clination outwards and backwards, while then- inner borders are prolonged to a lower plane than their outer. The sockets in the squamous bone and the atlas are correspondingly oblique both vertically and in their long axis in adaptation to the condyles which they respectively receive. This bilateral arrangement, or arrangement in pairs of joints, gives great width to the basis of support at the top of the spine upon wliich the head rests, and upon which its movements take place ; it also provides a combination of strength and security with great freedom of movement, which could not possibly have been afforded by a single joint, even of much larger dimensions. These several joints share both the hinge and arthrodial characters. In each the chief, but not the only movements, are hinge-like, as is shown by the nodding movement of the head and the opening and the closing of the mouth. There 24 THE ARTICULATIONS OF THE SKULL. is also permitted a certain amount of gliding (more especially at the temporo-maxillary joint), and some oblique rotatory movement of both pairs of condyles within their sockets. There are, however, the following differences between the temporo-maxillary and the occipito-atlantal articulations, which will be more fully brought out in the subsequent descrip- tions of these joints : (1) At the former the convex articular surfaces belong to the lower jaw, and the concave sockets to the base of the skull ; at the latter the convex articular surface belongs to the base of the skull, and the concave facets to the atlas. (2) At the former the hinge-like movements occur round a transverse axis, which nearly corresponds in direction with the long axis of the condyles of the jaw : at the latter the hinge-like movements take place round a transverse axis, which cuts the long axis of the occipital condyles obliquely. (3) At the former pair of joints there is an inter- articular fibro-cartilage on each side ; at the latter there is no such structm'e. The Temporo-maxillary Articulation. Class, Diarthrosis. Subdivision, Ginglymo-arthrodia. The lower jaw is the only bone of the skull which is capa- ble of sejDarate movement — -i.e., of movement independent of the rest of the cranium. In man, as in all mammalia, this articu- lation is formed between the inferior maxilla and the squamous portion of the temporal bone. Perhaps the temporo-maxillary joint, more than any other fragment of the vertebrate skeleton, gives the fullest information respecting the animal to which it belonged. In all mammalia, the convexity of the lower jaw is received into the concavity of the squamous portion of the tem- poral bone ; whereas, in the three other divisions of the verte- brate kingdom, the inferior maxilla presents a concavity to the convexity of the cranial bone with wMch it articulates — viz., with the homologue of the human tympanic ring (the os quad- ratum) . in birds, reptiles, and osseous fishes, and with the homologue of the human internal pterygoid plate in cartila- ginous fishes. Thus therefore, if we see a temporo-maxillary joint, or even the articular process of the lower jaw, we can tell whether the animal to whom it belonged suckled its young, or had a diaphragm or an epiglottis, or an epidermic exoskeleton THE TEMPORO-M AXILLARY ARTICULATION. 25 in the form of hairs, for if so, the lower jaw has a convex arti- cular surface ; or whether it laid eggs and had been without hair, a diaphragm, or an epiglottis, in which case the lower jaw has a concave articular surface. No physiological reason that I am aware of can be given for this difference of construction ; it seems to have no relation to external conditions, or to the circumstances of the animal's existence, but to be due only to the position of the animal in the vertebrate series. For the purposes of life and utility, it appears a matter of indifference whether the articular surface of the lower jaw is convex or concave, for " the bat that flies, but not the swallow ; the whale that swims, but not the codfish ; the camel that walks the desert, but not the ostrich ; the carnivorous lion, seal, and weasel, but not the eagle, penguin, crocodile, and shark, have convex articrdations to their lower jaw, and present to them their squamosal bones." In some of the mammalia the joint is a true hinge ; tliis is the case in the carnivora, and reaches its acme in the badger, in the dry skull of wMch the lower jaw remains locked in the deep socket of the cranium, without any artificial contrivance, and can be removed only by slipping each half out sideways when the symphysis has been divided. In others of the mammalia — the Euminants — the articular facets approach more nearly to plane sm^faces, and the movements are of the arthrodial nature ; hence the extensive lateral movements of the jaw while chewing the cud, and the limited power these animals possess of gaping, which is a movement of the hinge character. But in man, who is an omnivorous animal, there is a combiaation of these two extreme forms, and thus the human temporo-maxillary joint cannot be classed with either the true ginglymoid or arthrodial joints, but partaking of the movements of each, ought to be called " Gingiymo-arthrodia." The OSSEOUS paets of this joint are the squamous portion of the temporal bone including the glenoid fossa, and the glenoid ridge (i.e., the anterior root of the zygoma, and called also the eminentia articularis), which stands just in front of the fossa ; and the condyle of the lower jaw. - They are all coated with articular cartilage, which stretches even over the front of the glenoid ridge, for the easy play of the inter-articular fibro- cartilage. TJie Squamous portion of the Tem'pond Bone is situated at 26 THE TEMPORO-MAXILLARY ARTICULATION. the lower lateral region, and extends a little inwards on to tlie base of tlie skull. Where the basal joins with the lateral por- tion of the cranium, there arises from its external surface a flattened branch of bone — the zygoma — which runs first hori- zontally outwards, and then, twisting upon its own axis, curves horizontally forwards. The zygoma arises by two roots, an anterior and a posterior. The anterior is also inferior, and takes a transverse course along the basal part of the temporal bone : it forms the front boundary of a large fossa, also situated on that part of the squamous bone which extends inwards to form part of the base of the skull : it is covered in the recent state by articular cartilage, and sometimes receives the name of " emiuentia articularis." The posterior, also the superior, root arises by two branches ; one of these is short, tliick, and obHque, commencing in front of the outer end of the Glaserian fissure, and of a plate of bone which separates the glenoid fossa from the auditory canal — viz., the tympanic plate of the tem- poral bone ; the other has a horizontal course above the external auditory meatus, and is continuous behind with the curved ridge, separating the squamous from the mastoid bone. Where the anterior and posterior roots join there is on the outer and lower side a rough tubercle, to which the external lateral liga- ment of the jaw is attached. The glenoid fossa is an oval-shaped, deep depression, whose long axis is directed inwards and backwards and a little up- wards, and measures rather over one inch ; from anterior to posterior edge across the fossa is usually rather less than half an inch. It is divided by a narrow fissure, named the Glaserian fissure, into two nearly equal parts — viz., an anterior and external, which is articular and covered by cartilage ; and a posterior and internal portion, which is non- articular, and lodges the deep part of the parotid gland. Although the glenoid fossa is wider transversely than from behind forwards, yet the articular surface for the fibro-cartilage of the joint measures more in an antero-posterior than in the transverse direction, owing to the extent to which the articular surface is continued over the glenoid ridge, and to the fact that all the parts of the glenoid fossa behind the Glaserian fissure are non-articular. This is to allow of the considerable forward and backward gliding movement which goes on in the temporo- maxillary joint. THE TEMPORO-MAXILLARY ARTICULATION. 27 Situated iminediately behind the fossa from without in- wards, are the external auditory meatus, the styloid process with its vaginal sheath, and the posterior lacerated foramen. To its inner side from before backwards, are the opening of the carotid canal, the processus coclileariformis, and opening for the Eustacliian tube, and the spine of the great wing of the sphenoid ; in front is the anterior root of the zygoma, and externally and above the posterior root. The Inferior Maxillary Bone. — Each of the condyles of the lower jaw is supported upon a narrow neck surmounting the posterior border of the ascending ramus. The neck is flattened from before backwards ; smooth and convex behind ; concave in front where it gives insertion to the external pterygoid muscle. It is strengthened by ridges which descend from the sides of the condyle ; that from the outer end of the condyle is continued on so as to form the upper border of the ramus at the sigmoid notch, that from the inner end of the condyle descends on to the inner surface of the ramus above the infe- rior dental foramen. The neck is somewhat curved so as to make the condyle look a Kttle forwards. The condyle is elon- gated in the transverse - direction, is convex both from side to side, and from before backwards, and is obhquely inchned, so that the long axes of the two condyles if prolonged would meet at the front margin of the foramen magnum and form an angle of from 155° to 160°. This obliquity facilitates the so-called rotatory movement of the jaw. The condyles are covered with cartilage, which is thickest over the front aspect, and is con- tinued lower down behind than in front. Anterior to the neck is the sigmoid notch, and in front of the notch and prolonged upwards from the anterior border of the ramus is a flattened triangular process — the coronoid — which gives insertion to the temporal muscle. The Ligaments. — Uniting the bones of this articulation is a capsular ligament. Within the capsule and between the osseous articular surfaces is a disc or plate of fibro-cartilage. Also in connexion with this joint the stylo-maxillary ligament must be described. The Capsular Ligament. — Everywhere passing between the temporal and inferior maxillary bones near the margins of their articular surfaces are numerous scattered Kgamentous fibres which serve to strengthen the synovial sacs, and to form a 28 THE TEMPORO-MAXILLARY ARTICULATION. nearly complete capsule for the articulation. In some places tliese filtres are much tliicker than at others, and hence it is usual to describe the capsule as composed of four parts or ligaments. It must be understood, however, that these four parts are continuous with one another around the arti- culation. 1. The Anterior Ligament. — The anterior portion of the cap- sule is so thin and its fibres so scattered, as scarcely to deserve a special notice. It consists of a few stray fibres, connected with the anterior margin of the fibro-cartilage, which are at- tached above to the forepart of the anterior root of the zygoma (eminentia articularis), and below to the anterior edge of the condyle. Some of the fibres of the external pterygoid mus- cles pass between these ligamentous fibres to be inserted into the anterior margin of the fibro-cartilage. This part of the capsule retains the fibro-cartilage towards the forepart of the glenoid fossa, so that even when the mouth is closed the thin central part of the cartilage is on the eminentia articularis, and the thick posterior edge is at the bottom of the fossa. 3. The Posterior Ligament. — The posterior portion of the capsule is attached above to the hinder edge of the articular part of the glenoid fossa — i.e., just in front of the Glaserian fissure, and is inserted into the back of the jaw just below its neck. It checks forward movement of the jaw. 3. The External Lateral Ligament. — The external portion of the capsule is the strongest of all, and connects the posterior portion with the stray fibres of the anterior part. It is broader above than below, being attached to the lower edge of the zygoma in nearly its whole length, as well as to the tubercle at the point where the two roots of the zygoma meet. It is inclined downwards and backwards to be inserted into the ridge on the outer side of the neck of the condyle. Its fibres diminish both in obliquity and strength from before backwards, those arising from the tubercle of the zygoma being very short and nearly straight. By the greater number of its fibres this ligament prevents the condyle of the jaw being carried backwards, so as to press against the tympanic plate of the petrous bone. By its short posterior fibres it checks the forward gliding of the condyle in opening the mouth. It braces the jaw firmly up to the base of the skull, by fixing the neck of the condyle ; yet it also allows , . , r r r I -V V THE TEMPORO-MAXILLARY ARTICULATION. 29 of the condyle advancing and receding under cover of it, as in opening and closing the mouth. TTie Short Internal Lateral Ligaments. — There are two struc- tures named internal lateral ligaments, the long and the short. One of them, the long, is distinct and independent of the cap- sule, and will be further on described. They have by some been considered as a single ligament, which divides immediately beyond its origin into two parts. The internal portion of the capsule, or the short internal lateral ligament, has above a broad attachment to the outer part of the spine of the sphenoid bone and to the internal edge of the glenoid fossa, and below has a narrow insertion into the ridge on the inner side of the neck of the condyle. Behind it is continuous with the pos- terior portion, and in front are the scattered fibres of the ante- rior portion of the capsule, and the insertion of the external pterygoid muscle. It is separated from the long internal lateral ligament which is on its inner side by fatty and cellular tissue. It consists of well-defined ligamentous fibres which assist the external lateral ligament in checking both the forward and backward gliding movements during the opening and shutting of the mouth. Like the external ligament it fixes the neck of the jaw, into which both are inserted on nearly the same level, during the gliding movements of the condyle ; and the condyle plays forwards and backwards between the two ligaments which prevent its lateral displacement, and limit the extent of ante- rior and posterior ghding. The Inter-articular Fibro-cartilage is constantly met with in the mammalian, but not in either of the other vertebrate classes. Its shape is adapted both to the condyle of the jaw, and to the articular portion of the squamous bone. It is thinner at its centre than at its circumference, and is thicker behind, •where it covers the thin bone at the bottom of the glenoid cavity which separates it from the dura mater, than in front where it projects on to the articular eminence. Its inferior surface is concave in adaptation to the convexity of the con- dyle, and its superior surface is concavo-convex from before backwards, and is in contact with the articular surface of the temporal bone, which is convexo-concave from before backwards. As seen from above it is oval in shape. Occasionally it is perforated at its centre, otherwise it completely divides the joint into two distinct cavities, an upper 30 THE TEMPORO-MAXILLARY ARTICULATION. t and a lower, eacli having its own special synovial membrane. It is connected at its circumference by loose fibro-cellular tissue with the lateral and posterior portions of the capsular ligament ; in front the slender scattered capsular fibres are immediately attached to the margin of the cartilage, and some of the fibres of the external pterygoid are inserted into it as well as into the anterior fibres of the capsule. This inter-articular cartilage acts as an elastic buffer between the bones, and intercepts the pressure and breaks the jars which necessarily occur during the movements of mastication ; by making good any want of adaptation of the articular sur- faces to one another it tends to prevent luxation ; and thirdly, like the inter-articular cartilage at the sterno-clavicular joint, it takes an important part in the movements of the articulation, accompanying the condyle in the forward and backward gliding- movements, and affording a concave sm^face for the condyle to turn upon in the hinge-like movements. TJie Synovial Memhranes. — The articular surface of the temporal bone is larger than the condyle of the jaw, and as a consequence the upper cavity of the joint is larger than the lower. In accordance with this difference the superior synovial sac is larger than the lower. It is also necessarily looser, owing to the backward and forward movements of the fibro- cartilage with the condyle. The sacs are strengthened by the anterior fibres of the capsule, by the lateral and posterior portions of the capsule, and by the fibro-cellular tissue which connects these portions with the fibro-cartilage. The Long Internal Lateral Ligainent is a thin, loose, and elongated slip situated at some distance from the joint. It extends from the spinous process of the sphenoid and the contiguous part of the temporal bones downwards, outwards, and a little forwards, to be inserted into the forepart of the. tip of the inferior dental foramen. It covers the hinder — i.e., the upper part of the mylo-hyoid groove as it passes forwards and downwards to its insertion. Its origin is a little internal to and behind, but close to the superior attachment of the short internal lateral ligament, and is concealed by the origin of the external pterygoid muscle. It has no immediate con- nexion whatever with the articulation, being separated from it by a considerable interval along which pass the external pterygoid muscle to its insertion, the inferior dental nerve. ANTERO - POBTERIOR VERTICAL SECTION THROUGH JAW. Inf-^rarbLojiLar izhro cartiloicfe.. VarticnL Sectwi thro ' ronajf l^e Posterior Ixgajyverd- of jaw. Long intemoL Ucfowrient cut. ounaL -ttirowrc dci/n. Style maxillary U^ounteyvt vhere aHxtcked^ tp ike yyiax.iHou . A.Hen^m/wi 6A tuL >tat Ylist 'He.wnuufv & C^ dlrtnu. UA- THE TEMPORO-MAXILLARY ARTICULATION. 31 and the internal maxillary artery and vein with their middle meningeal and inferior dental branches. The middle meningeal is conducted upwards to the foramen spinosum, and the in- ferior dental downwards to the dental canal along the side of the ligament. The influence of this ligament on the movements of the joints must be very slight, and can only act in assisting to limit the opening of the mouth. The Stylo-viaxillary Ligament. — The stylo-maxillary or suspensory ligament is in truth a process of the deep cervical fascia, but is generally enimierated as one of the ligaments of the temporo-maxillary joint. It extends from the styloid pro- cess of the temporal bone to the angle of the jaw, where it is attached along a somewhat extended surface of bone between the masseter and internal pterygoid muscles. It separates the parotid from the submaxillary glands, and gives origin to some of the fibres of the stylo-giossus muscle ; indeed, it is of more importance as a sm-face of attachment for this muscle than as a means of connexion between the temporal bone and the lower jaw. Aetekies. — Sometimes articidar arterial twigs are given off from (1) the branches to the parotid gland from the posterior auricular artery; (2) from the tympanic branch of internal maxillary, as it passes up between the articulation to enter the Glaserian fissure ; and (3) from the inferior or ascending palatine branch of facial, by the twigs wMch run along the Eustachian tube. The temporal artery gives branches off directly to the articu- lation. The middle meningeal, which is conducted along internal lateral ligament. Ascending pharyngeal, by branches to Eustachian tube. JSTeeves. — The masseteric branch of the inferior maxillary division of the fifth gives a filament or two to the joint. Auriculo-temporal trunk of inferior maxillary nerve olves articular branches directly from itself, or twigs from its parotid or auricular branches, or from the branches to the meatus audi- torius. The Muscles. — Of the muscles connected with the temporal and inferior maxiUary bones some have no action whatever upon the movements of the temporo-maxillary articulation. Such is the case with the chief part of the genio-hyo-glossus attached to 32 THE TEMPOKO-MAXILLARY AKTICULATION. the superior genial tubercle of the symphysis ; the superior con- strictor of the pharynx, which arises in part from the hack of the mylo-hyoid ridge ; the small mylo-giossus (of Wood), which usually springs from near the angle of the jaw ; the buccinator, which arises partly from the back part of the alveolar process of the lower jaw ; the depressor anguli oris, the depressor labii inferioris, and the levator menti, all of which are attached to the outer surface of the horizontal ramus ; the levator palati, which springs in part from the petrous bone in front of the orifice of the carotid canal ; the tensor palati, part of whose origin is from the edge of the tympanic plate of the temporal ; the stylo-hyoid, stylo-glossus, and stylo-pharyngeus. None of these muscles produce any effect whatever upon the movements of tliis joint. Of the rest — those which move the jaw on the head — may be grouped as protractors, retractors, elevators, and depressors of the lower jaw ; whilst those which move the head on the jaw, when the chin is kept fixed, are the same muscles which extend and flex the head at the occipito-atlantal articulation. The Elevators of the Lower Jaw are — the temporal, which acts upon the coronoid process ; the masseter, which is inserted into the outer side of the ascending ramus and of the angle ; and the internal pterygoid, which is attached to the angle on the deep aspect of the bone. These muscles usually act together, and by bringing the lower teeth forcibly into contact with the upper are the great powers of mastication — i.e., for grinding the food. As they have to resist the force and over- come the hardness of the substances which require to be triturated before being swallowed, they are necessarily muscles of large size and of great strength. The Depressors of the Lower Jaw are much smaller in size and of less strength than the elevators. The jaw almost faUs by its own weight, and these muscles have therefore to over- come little or no force in moving it downwards. They are the digastricus, which pulls upon the symphysis of the jaw at the digastric fossa ; the mylo-hyoid, attached to the ridge of the same name ; the platysma, inserted into the outer side of the lower jaw from symphysis to masseter ; the inferior fibres of the genio-hyo-giossus ; and the genio-hyoid, inserted into the lower tubercle on the deep sm-face of the symphysis. Each of these muscles serves other purposes besides that of depressing THE TEMPORO-MAXILLARY AETICULATION. 33 the lower jaw ; the genio-hyoid, mylo-liyoid, and the anterior belly of the digastricus (when acting apart from the posterior belly) all draw the hyoid bone upwards and forwards ; the posterior beUy of the digastriens (acting without the anterior belly) draws the hyoid upwards and backwards ; and when both bellies act together and the lower jaw is fixed, their combined effect is- to elevate the hyoid bone. Probably their action on the hyoid bone should be regarded as the chief use of these muscles, but whether or no their connexion with that bone shows, that in order to depress the lower jaw, then action must be associated with that of the muscles which hold down the hyoid itself — i.e., of the sterno-hyoid, omo-hyoid, and the sterno-thyroid with its continuation the thyro-hyoid. The Protractors of the Lower Jaw. — The external pterygoid is the chief protractor. It is inserted into the forepart of the neck of the condyle of the lower jaw, and into the margin of the inter- articular fibro-cartilage. All the fibres of the internal and external pterygoids, and many of the fibres of the masseter, arise in front of their insertion, and thus have to pass back- wards to their attachment (the pterygoids also incline outwards, and the masseter slightly inwards) to the inferior maxilla. The external pterygoid has the great bulk of its fibres so hori- zontal that they have no effect in elevating the jaw ; the internal pterygoid and the masseter being more obliquely directed can elevate as well as protract. In most people, when the jaws are closed, the lower incisor teeth are behind the upper ; but when the pterygoids on both sides of the head act simultaneously, they so far protract the lower jaw as to allow of the lower incisors being advanced beyond the upper. In simply opening the mouth the external pterygoids are associated with the depressor muscles, and come into play to draw the condyles slightly forwards. Usually the muscles of one side only act at once, and alternate with those of the opposite side ; in this way the teeth are moved away from the side on which the muscles are acting, and thus is produced the grinding and chewing movements of the molar teeth. In these movements the external pterygoid is associated with the internal pterygoid (which assists protraction), as well as with the other elevators of the jaw. The Retractor of the Lower Jaw. — Only the temporal muscle can retract the jaw, for it is the only muscle of mastication D 34 THE TEMPOKO-MAXILLAKY ARTICULATION. which has any fibres directed forwards to their insertion. All the fibres of the temporal muscle converge and terminate in a strong tendon, which is inserted into the coronoid process. This process serves as a lever for the more forcible action of this powerful muscle. Certain muscles can be made to move the head upon the condyles of the lower jaw when the jaw is kept fixed. They are the same which produce the corresponding movements at the occipito-cervical articulation. The posterior recti, the tra- pezius, the splenius capitis, the trachelo-mastoid and complexus, all assist in extending the head on the neck, and therefore to open the mouth by tilting back the head — i.e., by rotating it upon the maxillary condyles, as well as on the facets of the atlas. In the same way the short anterior recti muscles and the sterno- mastoid bring the head forward and thereby close the mouth. The action of these muscles on the occipito-cervical union will be discussed more fully in the next section ; here it is suffi- cient to enumerate them as tlie miisdes other than those of mas- tication, which can open and close the mouth when the lower jaw is kept fixed. The Movements. — As man is omnivorous, his temporo- maxillary joint is not only intermediate in construction between the carnivorous badger and the cud-chewing ruminants, but is capable of movement in more various directions than either of them, because the substances taken as food by him require different actions for their complete trituration and mastication. When the jaw is depressed, whether for eating, or speaking, or yawning, &c., the condyles rotate on a transverse axis, the fibro-cartilages ^nth the condyles glide forward, the angles of the jaw are thrown backwards, and the coronoid processes are depressed and tilted forwards ; the external lateral ligament, especially, is rendered tense, and the stylo-maxillary ligament is relaxed. When the mouth is closed, precisely the reverse conditions to these hold good. Thus (1) the cliief movement of the temporo-maxillary joint is of a ginglymoid or hinge character, accompanied by slight gliding ; (2) there is also permitted a horizontal gliding in an antero-posterior direction, whereby the lower incisors are thrust forwards and drawn backwards, as when we bite with the front teeth. In these two sets of movements the joints on the two sides are similarly and simultaneously engaged. THE TEMPORO-M AXILLARY ARTICULATION. 35 (3) There is further a grinding or chewing movement, whereby the jaw is pulled obliquely from side to side : this combination of lateral shifting with rotation is produced chiefly by the external pterygoids acting alternately on the two sides ; it consists of a gliding of the articular surfaces on one another ; but the two joints do not act similarly at the same instant, for while one condyle and its fibro-cartilage is gliding forwards and inwards, and rotating but slightly, the other is revolving to a greater extent round the vertical axis drawn through the outer part of its neck, and gliding but slightly backwards and inwards. As far as concerns the horizontal gliding movements, this articulation belongs to the class Arthrodia. Had there been no more ghding permitted than that which accompanies the opening and closing of the mouth, it would have been as strictly a hinge joint as the knee, at which a considerable amount of gliding accompanies flexion and extension. But inas- much as some of the gliding movements occur independently of any hinge-like motions, the joint is a complex one, and com- pounded of the two varieties, ginglymus and arthrodia. The movements which occur in the two divisions of the joint are of different kinds. In the upper the fibro-cartilage, moving on the glenoid fossa and eminentia articularis, glides forwards and backwards as in protraction and retraction; or obliquely from side to side as in grinding and chewing. In the lower division the condyle moves against the under surface of the fibro-cartilage, rotates on its transverse axis as in opening or shutting the mouth, or turns on the vertical axis of its neck as in grinding and chewing. Movements in the two divisions of the joint sometimes occur simultaneously in both joints. Thus, in opening the mouth the condyle turns like a hinge in the lower compartment, and at the same time the fibro-cartilage, together with the condyle, moves forwards so as to rise upon the eminentia articularis. In this movement the fibro-cartilage extends as far as the anterior edge of the glenoid ridge, which is coated with articular cartUage to receive it ; at the same time the fibro-cartilage presents a concave surface for the condyle of the jaw ; but the condyle itself never reaches quite so far as the summit of the glenoid ridge, being checked by the fibres of the lateral and posterior ligaments. In shutting the mouth, the condyle revolves back again, and the fibro-cartilage glides back again, taking the condyle with it. By this combination D 2 86 THE TEMPORO-MAXILLARY ARTICULATION. of Hnge and gliding action, a greater range of movement of the lower teeth is secured by the same expenditure of mus- cular power, while a tearing as well as a cutting action is given to the incisor teeth by their being drawn backwards at the same time that they are closed upon the upper jaw. Again, in the chewing and grinding — i.e., the oblique rotatory — movement whilst the condyle rotates round the vertical axis of its neck, and moves agaiust the fibro-cartilage, the fibro-cartilage itself glides obliquely forwards and inwards on one side, and obhquely backwards and inwards on the other. If the sym- physis be simply moved towards one side and back again (and not from side to side as in gi^indnig), the condyle of that side moves round the perpendicular axis of its neck, and the oppo- site condyle glides forwards and inwards upon the glenoid ridge. But in the ordinary grinding movement one condyle advances and the other recedes, and then recedes whilst the other advances, and so on ; slight rotation taking place in each joint meanwhile. The jaw is drawn inwards by the pterygoids of one side, and outwards or straight again by the pterygoids of the opposite side. The deformity which follows fracture of the jaw, when the fragments are made to overlap by approaching the middle line illustrates the action of pterygoids on the frag- ment of their own side. The movements of protrusion and retraction — i.e., of forward and backward ghding — are confined almost entirely to the upper compartment. This is owing to the more limited size of the inferior synovial cavity, to the closer connexion of the fibro-cartilage to the condyle than to the glenoid fossa, and to the insertion of some of the fibres of the external pterygoid into the margin of the cartilage, whilst the rest are attached to the front of the neck of the condyle. Thus the same muscle which protrudes the jaw drags forwards at the same instant the fibro-cartilage which is closely connected with it. It has been stated above that the head can be made to move on the condyles of the inferior maxilla if the chin be held steady. Anatomists are quite silent with regard to, if indeed they have not quite overlooked, this movement, and though it is not of any great importance in the animal eco- nomy, it is a feature of interest and worthy of being pointed out ; besides, it is occasionally employed, as when the head is THE TEMPORO-MAXILLARY ARTICULATION. 37 suddenly bobbed forwards to give greater force to the masti- catory muscles, as in cracking a nut for instance. It may be illustrated by simply fixing the cbin in the hand, and then throwing the head back as in looking up to the ceiling ; or after opening wide the mouth, closing it, by dropping the head forwards and downwards towards the lower jaw instead of raising the lower jaw towards the upper. In these move- ments the ix-outh is opened and closed, but the jaw does not move, and the chin is fixed and supported by the palm of the hand. Under these circumstances the head is resting upon two columns instead of one — -viz., {a) the spine, and (b) the lower jaw supported by the forearm ; and it moves on two pairs of ginglymo-arthrodial joints at the same time — viz., the occipito-atlantal and the temporo-maxillary. Two sets of effects are thus produced, for whilst the head is extended or flexed on the spinal column, the mouth, by the same muscles and movements, is respectively opened and closed. 38 LIGAMENTS AND JOINTS CONNECTING THE CHAPTEE IV. THE LIGAMENTS AND JOINTS CONNECTING. THE HEAD WITH THE SPINAL COLUMN. In considering the mode in which the head is united to the spine, it is impossible to avoid taking into account the union of the axis with the atlas, not only because the atlas with the head rotates upon the axis, but also because the ligament whereby these rotatory movements are rendered secure is a part of the apparatus between the axis and atlas ; and further and especially, because the ligaments which check rotation, as well as other very strong ligaments, pass between the axis and occiput, and so provide for the security of the union in a manner in which the ligaments extending from the atlas to the occiput alone could not do. Moreover, the characters of the atlas, which are all modified to allow of the requisite movements of the head upon it, and of it together mth the head upon the axis, exclude it from the general description of the ligaments and joints connecting the several other vertebrae together. In the following description, the articulations between the occiput and atlas with their ligaments will be first described ; then those between the atlas and axis ; and finally, the ligaments which extend between the axis and occiput. The articulations between occiput and atlas are imperfect hinge joints, and those between the lateral masses of the atlas and axis are arthrodial joints ; but in addition there is between the anterior portion of the atlas and the odontoid process a lateral ginglymoid joint, which is completed by the transverse portion of the crucial ligament. The ligaments passing between the atlas and axis, and those connecting the atlas and occiput, are mediate and immediate. The capsular ligaments are immediate — i.e., they hold together parts of the bone wliich are in contact with one another ; the anterior and posterior ligaments are mediate — i.e., they pass HEAD WITH THE SPINAL COLUMN. 39 between bony parts which are not in contact. Further, the ligaments which connect the atlas and occiput, and those which connect the atlas and axis, are for the most part ex- ternal to the spinal canal ; certainly, with the exception of the transverse ligament, they can be examined without dividing the bones or opening the canal, although it must be admitted that the capsular ligaments of each set of joints, to be com- pletely viewed, must also be seen from within. On the other hand, the ligaments which most strongly con- nect the head to the spine, and which serve to retain it in position during the rotatory and nodding movements, pass from the axis and other cervical vertebrse to the occiput, are all contained within the spinal canal, and can only be examined or dissected after laying open the canal. To do this the arch of the axis, the posterior arch of the atlas, and the portion of the occipital bone which bounds the foramen magnum poste- riorly, as well as the tube of dm^a mater and the medulla, and upper part of the spinal cord, must all be taken away. Tlie Art'ictdations hetiveen the Atlas and Occipital Bone. Class, Diartlirosis. Subdivision, Ginglymo-arfcbrodia. The Occipital Boxe. — It is through this bone, which is situated at the lower and back part of the cranium, which is fused with the sphenoid into one mass, and is locked together by means of deep serrations or rough edges with the parietal and temporal bones, that the whole weight of the skull is borne and transmitted to the spine. The general form of the occiput is rhomboidal or lozenge- shaped, with a large oval hole in its anterior part, which forms the communication between the cranium and spinal canal, and is called the foramen magnum. It is with the ring of bone which surrounds the foramen magnum that we are now concerned; but it is more especially with the lateral segments of the riag — i.e., the condylar portions of the occiput, on which the articulating facets or condyles are situated, that we have most to do. The tabular portion of the bone wliich is behind the foramen, and the basilar portion which is in front of it, also afford attachment to occipito-atlantal liga- ments, and the basilar portion to occipito-axoidean ligaments as well. 40 LIGAMENTS AND JOINTS CONNECTING THE The condyles or articulating processes are elliptical in shape, varying from a little less to sometliing more than an inch in length, and half an inch in breadth, and are three-fourths of an inch apart at their anterior extremities. Situated, one on each side, on the external siu-face of the occiput, close to the margin of the foramen magnum at its antero-lateral portion, they have their long axes directed from beliind forwards and inwards ; and they converge in front to the extent of half an inch, the posterior extremities being one and a quarter inch apart. They are convex from side to side, as well as from before backwards, and are often marked about their middle in the dry bone by an obliquely transverse groove. A line drawn between these grooves corresponds pretty nearly with the axis round which the hinge-like, nodding movements occur ; is as nearly as possible the mid-line between vertical planes through the occipital protuberance and the incisor teeth ; and through it the Line of gravity in the erect position falls. Besides their doubly convex contour and their obliquely antero-posterior axes, the condyles are far from being parts of a horizontal j)lane, as they are considerably everted, so as to look outwards as well as downwards. Thus while their outer margins pass gTadually into the bone beyond, their inner edges are prolonged some distance downwards, and in tliis manner serve to deepen to a very marked degxee the lateral portions of the ring of the foramen magnum. Here the ring ]Dresents a rough and uneven surface on each side instead of a mere bony edge, to which the strong odontoid or cheek ligaments are attached, and on which the inner opening of the anterior condyloid foramen is seen. The articular surfaces of the two condyles, owing to then- shape, inclination, and direction, may be regarded as parts of one and the same sphere, with an interval between them, which play in corresponding distant parts of a socket formed by the atlas. If the bone surrounding the condyles be carefully observed, it win be noticed that there is a deep fossa and a foramen — the posterior condyloid fossa and foramen — ^behind. This, by making room for the cups of the atlas during extension of the head on the spine, allows of freer movement in this direction than could othervdse have been possible. The bone over a large area in this situation, where not actually perforated, is very thin and papery. Again in front, and somewhat to the outer OCCIPUT WITH THE ATLAS. 41 side of the condyle, there is another large foramen, the anterior condyloid ; while the mass of bone vertically and immediately ahove the condyle is always perforated obliquely by the anterior, and frequently by an extension forwards and upwards of the posterior condyloid foramen. To counteract the weaken- ing effects of such deficiencies of bone in a situation through w. ich so much weight as that of the skull and its contents (to say nothing of the extraordinary burdens which are often placed upon the head) has to be transmitted, and at which very fre- quent movements occur, we find on the outer surface of the occipital bone, between the weakened points, three strong bony ridges passing in different directions from each condyle. One is directed forwards along the side of the foramen magnum, and meets its fellow of the opposite side in the middle line at the pharyngeal ridge or spine on the basilar process ; another curves backwards along the foramen, and joins the fellow of the opposite side at the lower end of the occipital crest ; whilst the third is the strong jugular or transverse process which extends outwards to unite with the mastoid and petrous portions of the temporal bone on either side. Each condyle may therefore be said to have three strong ribs of bone converging to it from different sides, along which the weight which has to be borne by the condyles is conducted to it. These ribs are so situated as to be in the lines of the chief pressure ; thus the anterior rib runs backwards from the basilar process, and b'ears the strain of the front portion of the skull ; the lateral rib bears that of the side of the skull, transmitted through the temporal bone ; and the posterior receives the pressure of the back and vault of the head, transmitted in part along the crest of the occiput. In connexion with this last rib it is worth noticing that the tabular portion of the occipital bone is everywhere thin enough to transmit light, excepting (1) along the median line between the upper border of the bone and the foramen magnum ; (2) along a trans- verse but somewhat curved line, which crosses the former at the occipital protuberance, and extends between the lateral angles of the bone ; (3) along the margin of the bone, and more especially the portion of it above and between the lateral angles. Now it is along these dense parts of the occiput that the pressm-e of the parietal bones, the weight of the posterior lobes of the cerebrum, and the drag of the tentorium cerebelli 42 LIGAMENTS AND JOINTS CONNECTING THE tell ; and these forces are transmitted from them partly along the occipital crest, to be divided at the foramen magnum between the posterior ribs of the two condyles ; and partly along the inferior curved lines and the lower third of the lateral borders of the occiput to the jugular process — i.e., to the lateral rib of the condyle on each side. Further, the mechanism of the articulation of the skull with the spine cannot be thoroughly understood nor fully appre- ciated until the entire skull is looked at with reference to it. It is then seen that, in the erect position with the orbits directed ever so little upwards, the condyles are on a slightly but clearly lower level than the hard palate ; and that the base of the skull proper — i.e., of the cranium — formed by the basilar portion of the occipital, the body and wings of the sphenoid, and the ethmoid — ascends rapidly and considerably from the foramen magnum forwards. The weight of the ante- rior and middle lobes of the brain is therefore borne upon a sloping plane whose dhection is downwards and backwards to the condyles. Thus the construction of the anterior portion of the base of the cranium, as well as the position of the con- dyles themselves, dispose the head to balance on the condyles. Immediately in front of the jugular process and a little to the outer side of the condyle is the jugular foramen, through which the jugular sinus passes into the internal jugular vein, and the eighth cranial nerve escapes. These structures are therefore very close to the occipito-atlantal joint. Looked at from the inner surface, the foramen magnum appears larger than when seen from outside, owing to the bevelling off of its margin behind. Over the situation of the condyles there is a considerable heaping up of bone into a ridge or large tubercle. This bony mass is seen tunnelled by the condyloid foramina, and is continued behind into the margin of the foramen magnum ; outwards into the base of the jugular process ; and in front it is prolonged onwards on each side of the basilar gTOOve on which the medulla rests. It looks like a bridge of bone over the canal for the hypoglossal nerve, the piers of which spring from the tlu-ee several strong ribs of bone which diverge from the condyle. It serves the purpose of strengthening the condyles, acting indeed like a " flying arch." To the ridges thus prolonged forwards, as well as to the intervening basilar groove, the posterior common OCCIPUT WITH THE ATLAS. 48 vertebral ligaments, the cervico-basilar, and the occipito- axoidean ligaments are attached. The Atlas consists of a ring of bone having a transverse diameter of rather less and an antero-posterior diameter of somewhat more' than an inch. Situated at the antero-lateral portion of the ring on either side, on what is called the lateral mass of the atlas, is an elongated elliptical concave articulating fossa, which looks upwards and inwards, and receives the con- dyles of the occiput. Like the condyles, the long axis of each fossa is directed obliquely forwards and towards the middle line, so that their anterior extremities are about three-quarters of an inch, and their posterior extremities one inch and a quarter apart. Like the condyles, too, they are often marked by an obliquely transverse gTOove across the middle of their sur- face, or their lateral margins are notched so as to give the facets a somewhat hourglass-like outline. Eecei^dng as they do the condyles, the long axes of the facets necessarily corre- spond to those of the condyles ; but their inclination fi^om the horizontal is the reverse of that of the condyles ; and thus, while the inner borders of the latter are prolonged downwards, the outer lip of the articular facets of the atlas ascend so as to reach a considerably higher plane than any other part of the bone. Separating the lateral masses in front is the anterior arch of the atlas. It is a thick and dense rib of bone, slightly curved from side to side, and forming an arc of about one-fifth of the ring of the atlas. In the median Hne on its anterior surface is a smaU tubercle — the anterior tubercle of the atlas — and on each side of the tubercle is a depression or fossa for muscles. On its posterior aspect is a small circular and slightly concave facet for the odontoid process of the axis. This facet extends the whole depth of the arch, and is three-eighths of an inch in diameter. Behind the lateral masses is the posterior arch, which forms about two-fifths of the ring of the atlas, and is on the whole slighter and shallower than the anterior. Immediately behind the lateral masses on the upper surface of this arch there is a deep groove, often a complete bony canal, which conducts the vertebral artery from the foramen in the transverse process to the spinal canal. It is this groove, and a somewhat similar one on the under surface of the arch, which makes this portion of the ring so slender and shallow. In the 44 LIGAMENTS AND JOINTS CONNECTING THE middle line behind the bone is considerably deeper, and pro- jects backwards slightly into a sharp tubercle — called the posterior tubercle of the atlas — which is the only representative of a spinous process in this vertebra. Standing outwards on either side is a long transverse pro- cess, which arises, like the corresponding processes of all the other cervical vertebrae, by two roots, and like them is perfo- rated by the foramen for the vertebral artery ; one of the roots springs from the front part of the lateral mass, much nearer the upper 'surface than the lower ; the other springs from the point of junction of the lateral mass and the posterior arch, into the borders of which it is indeed continued. Unlike most of the cervical vertebrae, the tip of this process is tuberculated, not bifurcated. The foramen for the vertebral artery is inclined upwards and backwards, and passes by a very gradual and well- rounded border into the gToove on the upper surface of the posterior arch. The Ligaments. — The ligaments connecting these bones are an anterior and posterior occipito-atlantal and two capsular. The anterior occipito-atlantal, when looked at from in front, appears as a broad strong membrane extending from the base of the transverse process on one side to that on the opposite, and considerably thickened in the middle line so as to form what is by some described as a separate ligament, the " central or superficial anterior occipito-atlantal." But in truth much of this broad ligamentous membrane belongs to the capsular ligament of either side, and all that can properly be called anterior occipito-atlantal is the median portion which covers in the triangular space between the front of the foramen magnum and that part of the anterior arch of the atlas between and in front of the superior articular facets. It is about one inch wide, and is composed of densely woven fibres, most of which radiate slightly outwards as they ascend from the front surface and upper margin of the atlas to the basilar border of the foramen magnum ; it is continuous laterally with the capsular ligaments, and its fibres are overlapped by others taking an opposite direction, inwards and upwards, wliich form the anterior part of the capsule of the occipito-atlantal joint. Others, the central fibres, take quite a vertical course as they ascend from the anterior tubercle of the atlas to the pharyn- geal tubercle of the basilar bone ; they are thicker than the LIGAMENTS OF THE UPPER END OF THE SPINAL COLUMN SEEN FROM THE FRONT '"*' -^ ^ ^^iinr^ 3^ 1^^ ^ -t?^ '''»««;, -"^l Ke cerUbrcti occijpito iborvbcid^ Tiij cicyt%enJt seen- cijoiJbo oOJjoattexjL f%^1'^' ,, ^^^ ^tZo-o^coicf/ea**- joint h ,i~" ^ jLnterior ccmJ-nan, /otttooched/ to f>cnjterzai tuhercle- oP otilccs F . Steele- oiel.oiA. .Tvoot. TEMPORO MAXILLARY JOINT SEEN FROM INNER SIDE S Jvo ft ihJbeKruxL 'iccber'ndb OCCIPUT WITH THE ATLAS. 45 more lateral fibres, and are continuous below with the anterior atlo-axoidean ligament, and through it with the anterior common ligament of the vertebral column. This ligament is of considerable strength, and besides serving to unite the two bones together, acts also to limit extension of the head upon the spine. The posterior occipito-atlantal ligament is much broader than, but not so strong a ligament as, the anterior. It extends from the posterior sirrface and upper border of the atlas to the posterior margin of the occiput from condyle to condyle. It is somewhat thickened in the middle line by fibres which are attached to the posterior tubercle of the atlas and the lower end of the occipital crest. It is incomplete on each side, to allow of the passage of the vertebral artery into, and of the sub-occipital nerve out of, the canal. It is on its inner surface pretty closely connected with the dm-a mater. It is not tightly stretched between its bony attachments, and adds little to the security of the connexion between the skull and the spinal column. I^or does it limit in any way the movements of the skull, as it is not even put upon the stretch by the forward or nodding movements of the head. It corresponds in situation with the ligamenta subflava of the other vertebrae, but it has no elastic tissue, Kke those Kgaments, in its composition. It serves chiefly the purpose of covering in the spinal canal at a spot where the interval between the bones is as con- siderable as at the other extremity of the column — viz., where the spine joins the pelvis, i.e., between the fifth lumbar vertebra and the sacrum. At this interval, between occiput and atlas, the knife is introduced in the performance of what is called "pithing" animals. The Capsular Ligaments are very distinct and strong on the outer side as well as in front and behind; but on the inner side the capsule is thin and formed only of short membranous or areolar fibres. The inner margin of the socket of the atlas is very shallow, and the transverse ligament is attached just below it, whilst the check hgaments are inserted into the rough surface above the condyles of the occiput. These structures serve the purpose of strengthening the capsule and of giving support to the synovial membrane of the joint ; but the thin capsular fibres cannot add strength to the union of the atlas and 46 LIGAMENTS AND JOINTS CONNECTING THE occiput, nor are they required to do so, other strong ligaments being sufficient for this purpose. In front, the capsule descends upon the atlas for some distance below the margin of the arti- cular socket, and is attached to the front surface of the lateral mass and to the base of its transverse process ; the fibres take an oblique com-se upwards and inwards, many of them overlying the anterior occipito-atlantal ligament. At the side, the capsule is connected to the atlas just internal to the foramen for the vertebral artery, while further back it is attached to the prominent tubercle at the extremity of the socket which overhangs the groove on the posterior arch for the sub- occipital nerve and vertebral artery. These fibres also take a somewhat oblique course upwards and forwards, and are all attached to the rough outer border of the condyle just above the articular surface. The capsule is strengthened on the outer side in front by an oblique thick band of fibres, sometimes quite separate and distinct from the rest, which passes upwards and inwards from the upper surface of the transverse process beyond the foramen for the vertebral artery to the inner edge of the foramen lacerum posticum (jugular foramen). This accessory band is described in some works on anatomy as the lateral occipito- atlantal, but has been more properly styled by Professor Humphry the anterior oblique ligament. The capsule is also further strengthened on the posterior aspect by another and stronger band of oblique fibres which extends from the overhanging tubercle of the atlantal socket upwards and inwards and backwards to the tabular margin of the foramen magnum. These oblique bands serve to prevent rotation of the head on the atlas, and to draw the head with the atlas round the odontoid process. The anterior band also helps to limit extension, the posterior to check flexion of the head on the spine. Arteeies. — These are supplied from the vertebral ; occasion- ally tiny twigs are furnished to this joint, on one or the other side of the body, from the meningeal branches of the ascending pharyngeal wliich pass through the jugular and anterior condyloid foramina. Nerves. — The sub-occipital nerve supplies the joint and affords a good illustration of Hilton's law, referred to in OCCIPUT WITH THE ATLAS. 47 Chapter I. ; for besides supplying the posterior recti, the oblique and the complexus muscles, and sometimes also, the skin over the lower part of the occiput, the sub-occipital nerve by its anterior division supplies also the lateral and anterior recti, so that indeed all the muscles which act most directly upon the occipito-atlantal joints are supplied by the same trunk nerve that supplies the joints and the skin over the insertion of the muscles. Muscles. — The muscles related to the occipito-atlantal joints are, for the most part, the same as those related to the atlo- axoidean. They will be examined after the atlo-axoidean joints have been described. Movements. — The occipito-atlantal articulations form one of the pairs of movable joints in connexion with the cranium, and at them the cranium moves upon the spitie. Like the temporo-maxillary articulations, they consist of two symme- trical joints placed one on each side of the median line, and have also, like those joints, a doubly oblique direction ; but they converge towards the middle line in front, where they are not more than three-quarters of an inch apart, whereas the temporo-maxillary converge towards the middle line beliind, and are from two and a quarter to two and a half inches from each other. By the symmetrical and bilateral arrangement of these joints, security and strength is gained at the expense of a very small extent of actual articular siu?face ; the basis of support and the area of action are equal to the width between the most distant borders of the joints, wliile the interspace is rendered available in the present case for the medulla and its membranes, for the anterior recti muscles which move, and various ligaments which strengthen, the joints ; and in the case of the temporo-maxillary joints for the carotid vessels, the third part of the fifth nerves, the Eustachian tubes, the muscles of the palate and- the upper part of the pharynx, besides many other important structures. Almost the only movement which is permitted at these occipito-atlantal joints is flexion and extension upon a trans- verse axis ; this axis corresponds with a transverse line drawn from the slightly constricted part of one condyle to the corre- sponding point of the other. In flexion, the forehead and chin drop, and what .is called the nodding movement is made ; in extension, the chin is thrown up and the forehead recedes. 48 LIGAMENTS AND JOINTS CONNECTING THE Thus these joints are ginglymoid or hinge-like in their action. There is, however, also a slight amount of gliding movement permitted, and this occurs in two directions. In the one it is ohliquely lateral, and takes place in the antero-posterior axis of each condyle, so that the anterior extremity of one approaches to a trifling degree towards the median line, and projects beyond the anterior edge of the socket of the atlas, whilst that of the other recedes to a corresponding extent within the edge of the atlas, and away from the middle line ; in the other it is directly lateral, the outer edge of one condyle sinking a little within the outer edge of the socket of the atlas, and that of the opposite condyle projecting to a corresponding degree. In this latter movement there must be a tilting of the head to one side, and it is even possible that the weight of the skull may be borne almost entirely upon one joint, the articular surfaces of the opposite joint being thrown out of actual contact ; this also occurs at the atlo-axoidean joints. The relative con- dition of the joints on the opposite sides may then not in- aptly be compared to the relative state of the hip-joints in the stand-at-ease position. By these gliding movements one side of the head is lowered and the other raised slightly ; when the movement is obliquely lateral or diagonal the lower side of the head will be a trifle in front of the elevated side. When either the hinge or the gliding movements are carried beyond a cer- tain point, the atlo-axoidean joints and the rest of the cervical vertebree assist in their production ; the hinge and either of the gliding movements may also be combined — i.e., they may take place together ; when this is the case, something very like rotation occurs. There is, however, no true rotation round a vertical axis possible between the occiput and atlas. These various movements are checked partly by the Kga- ments between the atlas and occiput, and partly by the occi- pito-axoidean ligaments. Thus flexion is limited almost entirely by these latter, the only occipito-atlantal ligament which assists being the posterior oblique-accessory band of the capsule. Extension, on the other hand, is limited entirely by the anterior occipito-atlantal, and the anterior oblique-accessory band of the capsule ; the anterior atlo-axoidean, by fixing the atlas upon the axis, indirectly assists those ligaments by steadying the bone from which they arise and act. The gliding movements are checked nearly equally by the ATLAS WITH THE AXIS. 49 cteck ligaments on the interior, and by the outer part of the capsules on the exterior of the articulations. The Articulations letiueen the Atlas and Axis. The Lateral Atlo-axoidean Joints. Class, Diarthrosis. Subdivision, Arthrodia. The Central Atlo-axoidean Joints. Class, Diartlirosis. Subdivision, Trochoides. The atlas articulates with the axis in the same general manner as the rest of the vertebrte articulate with one another. Thus there are central and lateral joints, each of which is dis- tinct and complete in itself. The lateral joints, however, are situated more towards the front, instead of at the sides of the arch of the bone as is the case in the other vertebrae ; the central joint, instead of being single and ampliiarthrodial in Mnd, and therefore wanting in a synovial membrane, is double, and has two. synovial sacs, but no intervertebral substance ; and lastly, as the body of the atlas is detached from that bone and is consolidated with the body of the axis to form the odontoid process, the central articulations (the atlo-odontoid) occupy a vertical, not a horizontal, plane, so as to permit of a wide range of rotatory movement round a vertical line. We must look again at the atlas, and then examine the axis, to ascertain how they are adapted to each other in the formation of these articulations. The Atlas presents on each side, upon the under aspect of the lateral mass, a rounded, sKghtly cupped, articular facet. These facets are not so large as the sockets for the occipital condyles, and as they are placed vertically beneath the middle of these sockets, their posterior borders do not extend quite so far backwards. Like the sockets, they are oblique in direction from side to side, sloping downwards and outwards. As the sockets slope upwards and outwards, it follows that the outer sm'face of the lateral mass — from which the transverse process springs — is much deeper than the inner sm^face, and measures nearly three-quarters of an inch, while the inner surface is not much more than one-eighth of an inch in depth. Immediately above the inner surface of each lateral mass is a rough excavated depression the size of a split pea, which lodges a little mass of fat, covered by synovial membrane, and useful in the E 50 LIGAMENTS AND JOINTS CONNECTING THE movements of the occipito-atlantal joints. This depression encroaches considerably upon the central part of the socket for the occipital condyle, and, with a slight indentation of the outer border, gives the socket quite an hour-glass outline. In front of the rough depression is a prominent tubercle for the trans- verse ligament, and in front of this again a slight recess, which allows of ample room for the play of the bone around the odontoid process, and gives attachment to some strong fibres connecting the odontoid process to the atlas. Behind the arti- cular facets for the axis there is a grooved depression on the posterior arch for the passage of the second spinal nerve ; this is situated immediately below the one on the upper border for the vertebral artery and sub-occipital nerve. These gTOOves make this the weakest part of the ring of the atlas, but strength is not here required, as no weight has to be transmitted, and no muscles and no ligaments of importance are attached. The posterior tubercle, from which muscles do arise, is thick and tuber- culated. The space between the anterior borders of the facets for the axis is from one-eighth to two-eighths of an inch less than that between the sockets for the condyles, and the lower edge of the ring running upwards from them gTadually rises in a curved manner to the anterior tubercle. On the posterior aspect of this tubercle is a circular and concave facet, for the odontoid process of the axis, which usually extends the whole depth of the bone, and is about three-eighths of an inch in diameter. The Axis has a body and four articular processes like the rest of the vertebrae ; what distinguishes it from all the others is the odontoid process, round which the atlas with the head rotates ; the breadth and strength of its spinous process, which gives attachment to muscles which move the skull and atlas upon it ; the shortness of its transverse processes, which are merely rudimentary and are interposed between the superior articular processes above and in front, and the inferior which are behind and below it ; and the prolongation down- wards of the forepart of the body, together with the deep depression on either side of the middle line in front, for the attachment of muscles. The odontoid process, which is about three-quarters of an inch in height, projects upwards from the body of the axis so as to occupy the anterior and smaller portion of the ring of the atlas. ATLAS WITH THE AXIS. 51 It is rather in front of the line through the centre of the condyles of the occiput, and would bisect, if extended upwards, a line drawn between the anterior border of the jugular pro- cesses of the occiput. It tapers somewhat towards the summit where the check and central occipito-odontoid ligaments are attached. Its base is strengthened by a strong vertical ridge which extends downwards upon the front of the body, and by two lateral ridges which curve outwards on each side to the superior articular facets. In front and behind, the process is marked by two convex articular surfaces ; that in front, being for the facet on the back of the anterior tubercle of the atlas ; and that behind, which is somewhat lower down than the anterior, for the transverse ligament of the atlas. Below these articular facets the odontoid is constricted slightly into what is called the neck. The superior articular facets are situated partly upon the body and partly upon the arch of the axis, and from their under aspect strong buttresses slope downwards and inwards towards the lower part of the body. The facets are somewhat oblique, being inclined a little outwards and upwards, so that the weight which they sustain is conveyed chiefly downwards and inwards along the buttresses to the lower surface of the body, and is thence transmitted to the body of the third ver- tebra ; but it is partly conveyed downwards and backwards through the strong short pedicles to the inferior articular pro- cesses, and through them to the articular processes of the vertebrae below. Like the inferior articular facets of the atlas they are rounded in outline, but their long axis is directed obliquely forwards an(^ inwards, and measures about three- quarters of an inch, whi^ e the transverse diameter is not more than half an inch. Ihey are considerably undermined be- neath their external borders by the canal for the vertebral artery, which forms a sort of archway between the buttress projecting downwards in front, and the pedicle which curves downwards behind. Beliind the lateral articular facets the pedicles are gTOOved for the second spinal nerve, which like the sub-occipital passes out of the canal behind the articular pro- cesses, instead of in front of them, as is the case with all the succeeding. The inferior articular processes descend from the junction of the pedicle and lamina, and have in front of them a groove E 2 52 LIGAMENTS AND JOINTS CONNECTING THE wliicli, with the groove in the pedicle of the third vertebra, forms the intervertebral foramen for the passage of the third spinal nerve. The transverse process springs by two roots, one continuous with the anterior border of the superior articular facet, and the other springing from the pedicle midway between the upper and the lower articular facets. It is stunted and slender, and the foramen which pierces it obliquely is bounded partly by the edge of the superior articular facet. The ring formed by the axis is about one inch in antero-posterior, and half an inch in transverse diameter. The whole bone is very strong, but the most striking feature about it is the advantageous way in which the superior lateral articular facets are inclined so as to receive the weight of the skull from above, and distribute it, in part, to the articular processes, but chiefly, to the bodies of the vertebrse below. The Ligaments. — There are four distinct articulations between the atlas and axis — ^viz., the two central and the two lateral atlanto-axoidean. The ligaments which hold the bones in close contact — i.e., at these articulations — are the transverse, which retains the odontoid process against the front of the atlas ; and the capsular ligaments, which surround the lateral joints. The ligaments which connect the atlas and axis where they are not in contact are the anterior and posterior atlanto-axoidean. These ligaments, except the transverse, can be dissected and examined to a gTeat extent without opening the spinal canal. The Anterior Atlanto-axoidean Ligament is a narrow but strong membrane extending from the lower border and front surface of the atlas, where it is blended with the periosteum, to the front of the axis, and fills up the narrow interval between the lateral atlanto-axoidean joints. The fibres of which it is composed are vertical, and those in the median line are more numerous than those at either side, so as to form a dense central band, which is continued into the occipito- atlantal ligament above, and continues upwards the anterior common vertebral ligament from below. This central portion of the ligament is tense in all positions of the joints, while the lateral portions assist in limiting the rotation of the atlas upon the axis. The Posterior Atlanto-axoidean Ligament is a deeper but ATLAS WITH THE AXIS. 53 thinner and looser membrane than the anterior. It extends from the jDOsterior root of the transverse process of one side to that of the other, and therefore projects outwards beyond the posterior part of the capsules which are connected with it. It is perforated on each side by the second spinal nerve. It is attached above to the posterior surface and lower edge of the ring of the atlas, and below to the superior edge of the arch of the axis at its dorsal aspect. Between the posterior tubercle of the atlas and the spinous process of the axis the ligament is denser and much stronger than on either side. This ligament has upon its deep or anterior surface a layer of dense yellow fibres, resembling those composing the liga- menta subflava. The Lateral Atlanto-axoidean Joints. The Capsular Ligaments are very loose sacs completely surrounding the lateral articular facets. Outside the canal the fibres are attached to the bones at some distance from the edges of the articular surfaces. They extend along the anterior and posterior roots of the transverse process nearly to the tip, but between the roots are inserted into the edge of bone above the foramen for the vertebral artery. Behind, each capsule is thickened by the posterior, and in front by the anterior atlanto-axoidean ligaments. On the inner side the capsule is thinner ; the fibres are attached nearer to the edges of the articular surfaces, and are blended at their attachments with some of the other intra-spinal ligaments, and especially with the edge of the occipito-cervical, and the transverse, and lower half of the vertical portions of the crucial ligaments. There is a strong band of slightly oblique fibres thickening the capsule behind, and passing upwards and outwards, along the border of the occipito-cervical ligament, from the lower part of the body of the axis to the atlas just posterior to the attachment of the transverse ligament ; some of these fibres pass further upwards, thicken and blend with the capsule of the occipito-atlantal joint, and get insertion at the margin of the foramen magnum. These obKque fibres help to check rotation of the head, and like the anterior atlanto- axoidean ligament, by being attached to the atlas itself, they serve to prevent the atlas from rotating further, after the skull has been stopped by the pull of the check ligaments on the occiput.- 54 THE MOVEMENTS WHICH OCCUR Synovial Membrane. — A synovial membrane lines the fibroiis capsule of each of these joints. The Central Atlanto-axoidcan Joints. The articulations between the odontoid process, atlas, and transverse ligament are generally described as one joint of the lateral hinge kind. In reality there are two joints quite separate from one anotlier, though the synovial sac of the posterior is not quite distinct, as it communicates with the joints between the occiput and atlas. The movements which occur are like those between the head of the radius and the idna ; but instead oi the pivot quite filling the ring and rotating in contact with it all around, it is in apposition only at two spots, and elsewhere ligamentous fibres pass between the pivot and the ring. The movements rather than the anatomy of the joint require it to be classed as Trochoides. The Transverse Ligament is one of the most important structures in the body, for upon its integiity the life of each one of us depends. When it becomes destroyed by disease or broken by accident the odontoid process, no longer held forwards against the front part of the ring of the atlas, is free on the slightest movement to tilt backwards and press upon the medulla oblongata. It is a thick and very strong band, wliich crosses the ring of the atlas in a curved way so as to have its concavity forwards. At its ends it is attached to the tubercle on the inner surface of each lateral mass, so that, with the front arch and the anterior half of each lateral mass of the atlas, it forms a ring which encloses the odontoid process. Its structure is as dense and closely woven as fibro-cartilage ; it is about a quarter of an inch in depth at each side, and somewhat more in the middle line, and its anterior sm-face is smooth and covered with a synovial lining to allow it to glide smoothly upon the posterior facet of the odontoid. The synovial cavity communicates with the anterior portion of the occipito-atlantal joints, and is closed in above and below by some loose fibro-cellular tissue between the upper and lower border of the transverse ligament, and the margins of the articular facet upon the posterior aspect of the neck of the odontoid. It is separated fi-om the synovial cavity of the atlanto-odontoid joint by some very strong, short VERTICAL SECTION THROUGH ATLO-ODONT Ol D OR CENTRAL ATLANTO - AXOI D T AN JOINTS- \-nt: occijoito-eUlmitM tLo-odori-toid- sryno-i-'iril- Sect/io-n. of cK^tLcts .^ tt.-atli'vnto-citxo-id^a^v Zi^ A.sce*uAjJng -portion of crouxccL Ixcjcanent Ch cok.li.ij tfyialit sic^e. - Ocapiio ctilccntfj' joint Xrcavsyers o - oclo-y\JxruL syyvoviah scjj; - Section (Jwori-cih. ti'-a.yxsversf Decenf^xn^Oj -joor'tborc oP HORIZONTAL StCTIOM THROUGH CENTRAL ALTO-/\XOIDt.AN JOirsJTS 2. synxiYtyOjL solc^ liio cefyurcct h^ /^* '^ \^^M Antei'vor' or octia - ooloixtaici iyyvoyi,CfX. sac ^ost- Gomtvton- \'c v t&hr cub li. " odorucid, synovtaX Sa J) TXfct- -mctte;r -pcLr tx-ocLly cieJxA^ie* and TouXLeA lootcl^ rJensrvu^.ii. del.ouv.riccc BETWEEN THE ATLAS AND AXIS. 55 ligamentous fibres, which pass from the margins of the articular facet on the front of the odontoid, to the grooves in front of the tubercles for the transveree ligament. These fibres help to form a complete capsule for the joint between the atlas and odontoid process. The transverse ligament where attached to the atlas is well roimded off and very smooth, so as to provide a gTadual and easy floor of commimication between the transverso-odontoid synovial sac and those of the occipito- atlantal joints. Passing upwards and downwards from the transverse ligament in the middle line is a strong band of vertical fibres, which, together with the transverse, forms what is called the crucial ligament — the third in order of depth of the ligaments connecting the occiput and axis. The Atlo-odontoid CapsiiJar Ligament. — The apposed articular siu'faces of the atlas and axis are completely smrounded by a tough, loose membrane of strong fibres which forms a perfectly separate synovial cavity for this joint. These fibres at the odontoid process are united above with the front of the check and the central occipito-odontoid ligaments, and arise all along the sides of the articular facet as far as the neck of the process, where they are very thick and blend with the capsule of the lateral atlo-axoidean joint. At the atlas the fibres are attached from upper to lower border to the wide groove in front of the tubercles for the transverse ligament, while above and below the borders of the bone they blend with the back of the anterior occipito-atlantal and atlo-axoidean ligaments, and with the inner part of the capsular ligaments between the occiput and atlas, and atlas and axis. This ligament holds the axis to the front part of the ring of the atlas after the crucial, check, and capsular ligaments of the lateral joints have all been divided. Synovial Membeane. — There are two synovial sacs in con- nexion with the central atlo-axoidean or atlo-odontoid articula- tions — viz., one for the joint between the transverse Kgament and the back of the odontoid which communicates with the occipito-atlantal synovial sacs ; and one for the joint between the central facet of the atlas and the facet on the front surface of the odontoid. Aeteries. — Blood is supplied to the atlanto-axoidean joints from branches of the vertebral artery. 56 LIGAMENTS CONNECTING THE Nerves. — Twigs are derived from the second cervical or tlie loop between it and the sub-occipital. Muscles. — The description of the muscles will follow that of the ligaments between the occiput and axis. The Movements between the Atlas and Axis. — The chief as well as the characteristic movements between these bones is rotation, in a nearly horizontal plane, of the collar formed by the anterior part of the atlas and the transverse ligament, round the pivot formed by the odontoid process. In this movement the head is carried with the atlas, partly on account of the ligaments uniting the atlas with the occiput, and partly on account of the shape of the articular sm-faces of these bones, which renders it impossible for the atlas to rotate by itself between the head above and the axis below. Moreover, some of the muscles which assist in producing the rotatory move- ments are inserted into the occiput, and so make traction upon the head, at the same time that the inferior oblique muscle prdls upon the atlas. The degree of this rotation may be estimated by remembering that man can take a complete survey around him by simply moving the head from side to s:de without twist- ing or tmrdng the trunk. This rotation is checked partly by ligaments passing from axis to occiput, and partly by the atlanto-axoidean ligaments ; it is clear that just as the liga- ments uniting atlas to occiput will tend to drag occiput with atlas round the axis, so those uniting atlas and axis will tend to check rotation of atlas beyond a certain point. The sha^DC of the articular surfaces upon which this rotation occurs, is such, that the movement is not in an accurately hori- zontal plane, but in a slightly curvilinear direction. In the dry bones, and still more in the recent state when coated with articular cartilage, the facets of the atlas, though of nearly the same size and outline, are so ill adapted to those of the axis upon which they move, that their surfaces are never in com- plete contact. This is owing to the fact that both sets of facets are convex from before backwards, and have thicker articular cartilage in their centres than at their edges. Consequently when the head is erect the most convex portions are in contact, and there is a considerable gap between their circumferential surfaces ; but duiing rotation these lateral facets of the atlas glide obliquely upon those of the axis, so as to project beyond them — in front on one side and behind on the other — and in OCCIPUT WITH THE AXIS. 57 (ioing so tlie convex central part of the facets of the atlas leave the convex central part of those of the axis, and descend, the one forwards and the other backwards. In this way the space between the bones is diminished to an extent corresponding to the degree of rotation, so that the ligaments are slackened, as it were, in their vertical direction to provide for their length- ening in an obliquely transverse one. Were this not the case rotation would be very limited or impossible ; or would be pos- sible only at the expense of the security of union of the head with the spine, for the length of ligament which would be requi- site for the rotation of accurately apposed surfaces upon one another in a truly horizontal plane, would necessitate then- being slack when the erect and non-rotated position was assumed. It must not be supposed, however, as seems sometimes to be done, that the ligaments which pass over the odontoid pro- cess to the occiput are always quite tight when the head is straight. "Were this the case no forward flexion would be possible ; but this movement is we know permitted to a great extent at the occipito-atlantal, and to a less extent at the lateral atlanto-axoidean joints. The fact is that muscular action, not ligamentous tension, is employed for steadying the head in the erect position, and that the vertical intra-spinal ligaments between the skull and column are not rendered quite tight until the head droops forward, nor the check and other oblique ligaments until rotation is completed. Besides rotation, forward and backward movements and some lateral flexion, are permitted between the altas and axis as well as between the other vertebrse. Indeed, even to a greater extent than in most of the other vertebral joints. The pivot of the axis is not so tightly embraced by its collar as to limit these movements to the same degree that the interverte- bral substances do the movements of the other vertebrse ; while the want of coaptation of the lateral articular facets, together with their forward position on the bones, their obliquely horizontal direction, and loose capsular ligaments, favour motion round an antero-posterior as well as a transverse axis. The Ligaments smiting the Occiput and Axis. These connect bones not in contact. They are all to be seen from withia the spiaal canal after removing the posterior arch 58 LIGAMENTS CONNECTING THE of the axis, and the back part of the rings of the atlas and of the foramen magnum. They are arranged in four strata beneath the dura mater and the contiimation upwards to the occiput of the posterior common vertebral ligament; (1) the occipito- cervical ligament ; (2) the ascending part of the crucial liga- ment — the occipito-axoidean ; (3) the central occipito-odontoid ligament. The fibres of all these take a vertical or nearly vertical course, but there are in addition to them (4) two liga- ments — \dz., the check ligaments, which are almost transverse in direction, one on each side, and which are in a position between the second and third strata. The posterior common vertebral ligament passes over the odontoid and reaches as far upwards and forwards as the posterior clinoid processes and the petrous portion of the tem- poral bone. Between the body of the tliird cervical vertebra, to which it is attached, and the points of the skull just named, it lies upon the following strata of ligaments— viz. : The Occipito-cervical, or Cervico-hasilar Ligament. This is a very strong band of fibres connected below to the upper part of the body of the third vertebra, and the lower part of the body of the axis, on their posterior aspect, and above to the basilar gTOOve of the occiput. It is narrow below, but widens out as it passes upwards, and along its lateral borders it is connected with some strong scattered fibres which are auxiliary to the capsules of the atlanto-axoidean joints. The Crucial Ligament is exposed after reflecting the foregoing. Its stronger portion is the transverse ligament, which extends from side to side of the atlas and forms the back part of the encirchng collar which plays round the odontoid pivot : it has been described with the ligaments of the atlo-axoidean articulation. The vertical part or occijnto-axoidean ligament consists of parallel bundles of strong fibres posterior to, but closely connected with, the transverse ligament, from which indeed some of its fibres are derived ; it extends from the upper half of the body of the axis to the basilar border of the foramen magnum on the cranial surface. It thus assists the two previous strata of ligaments in holding the odontoid process in its place with respect to the skull ; while its transverse part holds the same process in its place with reference to the atlas. These three ligaments check the flexion or nodding movements of the head upon the spine. TRANSVERSE SECTION THROUGH OCC I PUT & U PPER FOUR CERVICAL VERTEBRAE / . SJrowina cLvvtol yyvOLtef trv sUtL cifoito ciilpthVtcU, orweoc ccrtlcvOiDW '. ococts s " ^ 'Povrt oP occtfoi ^5%, ubLountoCL ccqosx ^1 •?*2^ ~yjiy'.]CLm.(;*tJb U Groove on, oU for -trertAbycu C^qosvd^ o F odtXx) - the. cbucrcL. motter r >^^-^it^'1. > ^,^m " ~" -Axi-s jLtLoos 3^^ Cervicod -Treytejyyoc hir/ PLATE VI. LIGAMENTS CONNECTING THE HEAD WITH THE SPINAL COLUMN CrvLciaJi XLcfcunvetvt S' ^&^ r- Q%^ mM/ ^ Occipibo oer-vxcaJL Upfcurtervt V Post: comtrvon, Izcftxment AS. i. cat k. iltro^yn cioYrn s. ccifotto cUJjKntaX joxtvb -_ ^ ,^ ILactirijent fr^.^ OcdpttX) cervicccL Transverse, -process of a,0. ht— - SecUyOn- oP eucJyS ■^ Se-ctioH. oP 3 - tre-rtebret- OCCIPUT WITH THE AXIS. 59 The Occipito-odontoid Ligaments, on a deeper or more anterior stratum than the crucial ligament, are the two check ligaments and the central odontoid. The central occipito-odontoid liga- ment, sometimes called the suspensory Kgament, consists of a slender band of fibres which passes from the summit of the odontoid process to the under surface of the basilar bone close to the foramen magnum. It is best seen from in front after removing the anterior occipito-atlantal ligament, but can be seen from within by drawing aside the upper part of the crucial ligament. It is relaxed not tightened by flexion or nodding, and serves to check the extension of the skull on the spine. The Check Ligaments extend from the sides of the truncated summit of the odontoid transversely outwards to the inner edge of the anterior portion of the occipital condyles. They are to be seen irmnediately above the upper border of the transverse ligament, which they cross obliquely, owing to the forward curve of the transverse ligament as it approaches the tubercles of the lateral masses of the atlas. At the odontoid process they are connected with the tough loose fibres which connect that process with the anterior arch of the atlas and enclose the synovial cavity of the central atlanto-axoidean joint, and at the condyles they strengthen the inner part of the occipito-atlantal capsules. They limit the rotatory movements of the head and atlas upon the axis, and what is more, by binding the occiput to the pivot round which the rotation occurs, they steady the head, and prevent its undue lateral inclination upon the spine. By experiments it has been proved that the head, when placed so that the orbits look a little upwards, balances upon the occipital condyles in a transverse line drawn a little in front of their middle. To obtain this balance the amount of elevation varies slightly in different cases, but the balance is always to be obtained in the human body, to which it is peculiar. This balancing of the head is sufficient for maintain- ing the erect posture without undue strain upon muscles ; or the development of any such powerful structure as the ligamentum nuchse, and the prominence of the dorsal spinous process, such as is seen in the lower animals. But when the head is so placed that the orbits are directed forwards, or a little downwards, the balance being disturbed, the head would fall forwards were it not for the muscles of the back of the neck. Hence when the 60 MUSCLES MOVING THE muscles cease to . act from any cause, such as sleep, injury, or disease, the head droops, the chin falls, and pain is experienced from the tension made upon the ligaments which check tlie nodding or anterior flexion movements. It is, however, perfectly familiar to every one that the head will sometimes drop backwards on the cessation of muscular action, as during sleep when the face is turned considerahly upwards. This shows that the line of gravity of the head can he thrown backwards beyond the balance plane through the condyles. From the condyles the weight is transmitted through the lateral masses of the atlas, the lower facets of which look downwards and inwards ; and thence to the superior articidar facets of the axis which look upwards and outwards. These last are placed partly over the body of the axis and partly over the pedicles, so as to form a kind of bridge above the inter- vertebral foramen for the third cervical nerve. From these facets the weight is directed chiefly downwards and inwards to the lower j)art of the body of the axis, but also to a less extent downwards, outwards, and backwards to the inferior articidar facets of the axis, and thence onwards through the bodies and articular processes of the rest of the vertebrae. Although, as has been said, the head would but for muscular action fall forwards, until checked by the ligaments which ascend to the occiput, when the line of gxavity is in front of the condyles ; it must be admitted that, in spite .of muscular action, the atlas would have a tendency to fall away from the odontoid process were it not for the transverse portion of the crucial ligament, and the atlo-odontoid capsular ligament. Still, even when these are divided, there yet remain the liga- ments ascending over the odontoid to the occiput to resist the backward displacement of the odontoid process, while the action of the inferior oblique muscles, when acting together, is to hold back the atlas against the odontoid. In order therefore that the odontoid process should fall back and impale, as it were, the medulla oblongata (as has not unfrequently happened in cases of sudden death from disease of the upper end of the spine), it is necessary that all the four strata of ligaments which connect the skull to the axis should be destroyed, as weU as the atlanto-odontoid capsule and the transverse portion of the crucial ligament. Eegarding all these several joints and ligaments as HEAD UPON THE SPINAL COLUMN. 61 entering into the union of the head with the cohunn — as indeed they trxily do — it may be stated that the stall is connected with the spine hy two pahs of joints, placed one above the other, and arranged symmetrically on each side of the median line, and that through the median line there passes a pivot, which is also provided with a pair of joints, but placed one in front of the other. At these joints the movements are so various and so rapidly executed, that they would not have been possible at any single joint, excepting of the universal or ball and socket kind. Now, although a ball and socket joint can be made compatible with gTeat strength, as we see in the hip-joints, yet such joints are very prone to dislocations from even moderate twisting forces, and therefore their security is not sufficient for parts such as those under consideration, where the life of the individual depends upon the perfection of the articulations. As it is, through the combination of six several joints the head enjoys freedom of movement, remarkable strength, almost absolute security from violence, and a fairly broad basis of support. This basis consists of articular masses which are placed symmetrically on each side of the line of gravity, and converge as they descend to the body of the axis. It will be well again to observe that such are the connexions between the occiput, atlas, and axis, that anything which tends to check rotation through its attachment to the occiput will also act indirectly upon the atlas ; while at the same time parts of the atlanto-axoidean ligaments tend directly to check the rotation of the atlas. Conversely, whatever acts upon the atlas to produce rotation, indirectly acts upon the head with the same result ; while at the same time there are muscles attached to the head which produce rotation by theh indirect action, through the occipito-atlantal ligaments, upon the atlas. Muscles connecting the Head with the Spine, or moving the Head upon the Spine, These may be conveniently and simply classed into two sets — those in front of, and those behind, the column : while each of these may be subdivided into the short cranio-vertebral and long muscles. 1. The muscles in front of the column consist of the prse- vertebral muscles strictly so called — viz., the anterior recti and 62 MUSCLES MOVING THE the longus colli, the lateral recti and the sterno-cleido-mastoid. Of these, the lateral recti and the rectus capitis anticus major and minor are the anterior crcmio-vertebral set. a. These latter all arise from the transverse processes of the cervical vertebrae, and are inserted into the occipital bone ; the recti antici into the basilar process, the rectus laterahs into the jugular eminence. The rectus anticus minor and the rectus laterahs arise from the atlas, and can therefore act only on the occipito-atlantal joints. The rectus anticus major arises from the anterior tubercles of the third, fourth, fifth, and sixth cer- vical vertebrae, and approaches its fellow of the opposite side in the mesial line : it can act indirectly on the atlanto-axial joints after its full influence has been exerted on the occipito-atlantal. They all act as flexors of the head upon the spine. The anterior muscles when acting together are du^ect flexors for- wards ; when those of one side only act, they bend the head obliquely forwards and to their own side. The rectus lateralis, when acting singly, inclines the head directly to its own side. The rectus anticus major of one side acting alone produces slight rotation towards its own side at the atlanto-axial joint. The rectus anticus minor and the rectus lateralis co-operate with the rotator muscles in holding the head tightly down upon the atlas during the rotation of that bone upon the axis. h. The long muscles are the longus colli and the sterno- mastoid. The longus colli does not extend to the occiput, but is attached by a narrow tendinous process to the anterior tubercle of the atlas, as well as to the body of the axis. It is a forward flexor of the neck, and in this action it tilts the atlas forward on the axis; by its upper oblique portion it rotates the atlas on the axis when the muscle of one side only is acting. The sterno-cleido-mastoid is inserted into the outer part of the superior curved line of the occipital bone by a thin aponeurosis, as well as into the mastoid portion of the temporal. Wlien the muscles of the two sides act together they bend forward the head and neck towards the sternum ; their action is well seen in raising the head from a pillow while the body is in the recumbent posture. Wlien the muscle of one side only acts, it bends the head sideways towards its own side, while at the same time it rotates the head towards the opposite in such a manner that the chin is turned towards the point of the opposite shoidder. HEAD UPON THE SPINAL COLUMN. 63 They thus act upon the occipito-atlantal joints alone to cause forward flexion ; or on these together with the atlanto-axial joints at the same time, to produce oblique flexion forwards and to one side — i.e., flexion with rotation. After the head Tias been pulled backwards by other muscles, so that the Kne of gravity is behind the condyles, the sterno- mastoids together act to extend the head on the spine, and to throw upwards and forwards the chin. 2. The muscles behind the column consist of the short posterior cranio -vertebral muscles, and the following : the trapezius, the splenius colli and capitis, the traclielo-mastoid, the complexus, and the inter-transversalis and inter-spinalis between the atlas and axis. The transversalis colli, semi-sj)inalis colli, multifidus spinse, and the spinalis cervicis reach the axis, but have no action directly on the joints of the head and spine. a. The posterior cranio-vertebral muscles are four in number, three of which are inserted into the occiput below the inferior curved line of that bone ; and one, the inferior oblique, the largest and strongest of all, extends from the spinous process of the axis to the extremity of the transverse process of the atlas. The rectus capitis posticus minor and superior oblique are attached to the atlas below, and therefore can only act on the occipito-atlantal joints. Their office is to extend and pull backwards the head, and they co-operate with the small anterior and with the lateral recti in fixing the head on the atlas during the rotation of the atlas on the axis. The rectus posticus major, which passes obliquely upwards and outwards from the spinous process of the axis to the outer part of the inferior curved line, and the part of the bone imme- diately below it, rotates the atlas and head on the axis, its pull being exerted upon the head ; the inferior oblique assists the action of the rectus posticus major, its pull being exerted in the most advantageous manner upon the extremity of the trans- verse process of the atlas. It is obvious that these muscles can only produce motion when those of one side act alone ; on the other hand, the rectus minor and superior oblique are most effective when those of both sides act simultaneously. These four muscles are brought into association with each other through their nerve supply from the sub-occipital trunk. b. The Long Muscles. — The trapezius, which is attached by 64 MUSCLES MOVING THE HEAD UPON SPINAL COLUMN. a thin aponeiu'osis to the protuberance, and the inner third of the superior curved line, of the occipital Lone, acts on the head when the upper extremity is in a fixed condition. If the upper parts of both trapezii act together they extend the head by pulling it backwards on the atlas. Thfey thus assist the sterno-mastoid in depressing the occiput, and throwing forwards and upward the chin. When one trapezius acts alone it assists the sterno-mastoid of its own side to draw the head downwards and forwards in such a manner that while the occipital protuberance approaches the shoulder of its own side the chin is raised and turned towards the shoulder of the opposite. This movement involves both sets of joints ; rota- tion occurs at the atlanto-axial, and flexion at the occipito- atlantal as well as at the atlanto-axial. It will be remem- bered that these muscles are brought into very intimate asso- ciation by their nerve supply, the spinal accessory being distributed between them. The splenius capitis and the trachelo-mastoid, which pass upwards and outwards to the mastoid process of the temporal bone and the outer part of the superior curved line of the occipital, rotate the head and atlas on the axis, so as to tm-n the face towards their own side ; they also incline the head back- wards and to theb own side. Their pull being exerted on the head, they act indirectly upon the atlanto-axial, directly on the occipito-atlantal joints. Wlien the muscles of both sides act together they extend the head — i.e., draw it backwards. They are assisted in this action by the splenius colli, which acts upon the upper cervical vertebra. The splenii and trachelo-mastoid are the antagonists of the sterno-mastoid ; when they act with the sterno-mastoid they draw the ear to the shoulder. The complexus, which extends from the transverse and articular processes, as well as from the capsular ligaments of the vertebrae to the large impression between the two curved lines of the occiput near the occipital crest, is also an extensor of the head, and acts as such in conjunction with the muscle of the opposite side, and the rest of the muscles of the back wliich extend to the head. When the complexus of one side only acts it serves to draw the head backwards obliquely to its own side, instead of directly backwards as when both muscles act together. PART 11. CHAPTER V. THE TRUNK. The Ligaments and Joints of the Spinal Column, or the connexion of the Vertehrce with one another. TwENTY-FOUE vertebree, articulated together, assist in form i no- the spinal column; seven are in the neck, twelve have ribs connected with them and contribute to form the thorax, and five are in the loins. Each vertebra articulates with those adjacent to it by means of its body and articular processes ; in the case of the first vertebra, the body of which is represented by the odontoid process of the axis, a special articulation is provided between the ring of the atlas and the odontoid, as has been described under "The Ligaments and Joints connecting the Head with the Spinal Column." Between the bodies of all the other vertebrae, as well as between the last lumbar and the base of the sacrum, a tough and elastic substance consisting of fibrous tissue and fibro-cartilage, and called an intervertebral substance, is interposed. Thus, in addition to the twenty-four vertebrae, there are twenty-three intervertebral substances i^ the spinal column. The column may conveniently be divided into two parts — an anterior, consisting of the bodies of the vertebrae and the intervertebral substances ; and a posterior, consisting of the arches of the vertebrae with their outstanding processes. These two parts which together complete the canal for the protection of the spinal cord, may be separated from one another so as to leave the ligaments and intervertebral substances intact, by dividing the pedicles of the vertebrae, which are devoid of all ligamentous attachments. F 66 THE AETICULATIONS The todies of the vertebrse support and transmit tlie weight of the head and trunk, while each is capable through the agency of the intervertebral substances of some slight move- ments upon the others. The Articular Processes have for their chief purpose to preserve the proper relation of the arches of the vertebrse to one another during the movements of the bodies ; while at the same time they provide smooth, ghdiug surfaces whereby each arch may yield with the bending or tilting of the cor- resjDonding body upon the intervertebral substance. The Lamince, by closing the spinal canal upon its more superficial and exposed aspect, afford protection to the spinal cord, and are in their turn protected by the spinous processes which stand backwards from them, as well as by the mass of spinal muscles resting upon them. To these laminse are attached a series of short elastic springs, whereby the column is restored to its natural form after any movement of the vertebrse upon one another. The Spinous and Transverse Processes serve for the origin and insertion of the muscles of the back and some of those of the trunk; their connexion with ligaments is insignificant and altogether secondary. In addition to affording attachment and leverage for muscles, the transverse processes in the dorsal region give support to the necks and tubercles of the ribs. The Pedicles serve to carry the processes and laminse away from the bodies, and to form the buttresses of the arches which cover in the spinal canal. The ligaments of the spine are connected with all the several parts of the vertebrse except the pedicles ; but those passing between the transverse and spinous processes, excepting perhaps the supra-spinous Kgament, are of but little consequence and use — if indeed they have any such as belongs to Kgaments proper. The ligaments which bind together (1) the bodies and inter- vertebral substances and (2) the articular processes, are the immediate ligaments of the spine, because they connect parts which are in contact ; those, on the other hand, which pass between (1) the laminse and (2) the non-articular processes, are the mediate ligaments of the spine, because they connect parts which are not in contact. It must be remarked, however, that the ligamenta subflava OF THE VERTEBRAL COLUMN. 67 are both mediate and immediate ligaments, ; mediate in so far as they pass from one lamina to the next, but immediate in so far as they form parts of the capsules of the articulating processes. Between the pedicles of one vertebra and those of the next no ligament extends, so that spaces are left between them, called the intervertebral foramina, through which the spinal nerves emerge from the canal. Having made these general remarks upon the several parts of which the spine consists, and of the connexion of these parts with one another, we now proceed to the detailed consideration of the two portions of the vertebral column as above defined — viz., the anterior and posterior. Articulations of Bodies of Vertebrm, Class, Amphiarthi'osis. The Anterior Portion of the Column consists of the (1) bodies of the vertebrse, (2) the intervertebral substances, and (3) the ligaments which bind them together. The Bodies of the Veetebe^ are more or less rounded flattened discs, the width of wliich is nearly twice that of their depth. They are composed of porous, spongy bone, surrounded by a thin layer of compact tissue which becomes thicker towards the upper and lower surfaces of the vertebrae, and is there seen, on the dry bones, to form a narrow white border which is most strongly marked towards the front, more espe- cially in the dorsal region. To this white border or circumference of the upper and lower surfaces of the body, some of the lamellae of which the intervertebral substances are partly formed are immediately attached. Within this border, the spongy, porous character of the bone extends to the surface of the bodies, but this is covered in the recent state by a thin plate of articular cartilage which separates the less perfect lamellae and the central pulpy portions of the intervertebral substances from immediate contact with the bone. While they are convex from side to side, and concave from above downwards in front of the arches, they are concave from side to side, and flat from above down- wards lehind {i.e., between the pedicles) in the dorsal and lumbar regions, and flat from side to side as well as from above . F 3 68 THE ARTICULATIONS downwards in the cervical region. On the upper and lower surfaces the border of compact bone rises somewhat above the rest of the surface, which is thus made slightly concave. In the cervical region the border of the upper surface projects upwards at the back, and still more so at the sides, but is bevelled off in front ; on the under surface the border is bevelled off on the sides, but projects downwards both in front and behind. It is thus impossible to place the bodies of two cervical vertebrae in apposition with one another, as may be done with the dorsal and lumbar vertebrae, an interval of considerable size filled up of course in the recent state by intervertebral substance always existing between them in the dry state, The bodies of the vertebrae increase in size and weight from above downwards, although those of some of the lower cervical and the three upper dorsal appear larger when looked at from in front than do the bodies of some of the vertebrae immediately below them. This is partly owing to the dif- ference of shape in the bodies themselves, and partly to the forward position of the transverse processes in the cervical region. In the cervical and lumbar regions the transverse is greater than the antero-posterior measurement of the bodies ; in the dorsal vertebrae these two measurements are equal, or nearly so. As seen from the upper and lower surfaces of the bodies of the dorsal vertebrae, the cortical layer of compact bone is much thicker at the forepart than at the sides ; this is on account of the concavity forwards of the dorsal curve of the column and the consequent strain along the front of the bodies made by the superincumbent weight of the head and trunk. It is usually stated that the cervical and lumbar vertebrae are deeper in front than behind, but this is hardly correct. There is no uniformity whatever in the relative depths of the anterior and posterior surfaces of the cervical vertebrae ; some are equal in front and behind, others a little deeper behind than in front ; but when all the cervical vertebrae are placed firmly together without their intervertebral substances there is a very slight concavity in front. In a good representative set of vertebrae taken without selection, the measurement along the posterior surface of the bodies of the lower five cervical vertebrae when closely applied to each other was 2^ inches, while along the OF THE BODIES OF THE VERTEBRiE. 69 front it was 2^ inches ; and when all the cervical vertebrse were placed firmly together, the measurement along the back of the bodies was 4-| inches, and along the front 4^ inches. In the lumbar region when the dry bones are examined alone — i.e., without intervertebral substance — there is usually though not invariably a slight convexity in front owing to the projection forwards of the third and fourth bones. From the upper edge of the eleventh dorsal to the lower edge of the fourth lumbar vertebra, there is .a gradual sloping forwards from above ; the fifth recedes slightly. The five lumbar ver- tebrse when closely apphed to one another, measured 5^ inches along the front, and 5-|- inches along the back of their bodies. This one-eighth excess in front was exactly equivalent to the greater anterior depth of the fifth vertebra. The third bone was nearly uniform throughout, but while the first and second were somewhat deeper beliind (in this, resembling the dorsal vertebrae) than in front, the difference was counterbalanced by the fourth, which was deeper in front than behind. The bodies of the dorsal vertebrse are deeper behind than in front, some of them showing more difference in this respect than others. Along the back of the twelve dorsal vertebrse closely applied together the measurement was 11 inches, while along the front it was 9|- inches. The Intervertebeal Substances are tough but elastic and compressible discs of composite structure, which serve as the chief bond of union between the vertebrse. They are twenty- three in number, and are interposed between the bodies of all the vertebrse from the axis downwards. Similar substances occur Ukewise between the segments of the sacrum, and of the coccyx, but they undergo ossification at their surfaces and often throughout their extent. Between the sacrum and coccyx there is a very perfect little disc of the same general characters and structm-e as those between the vertebrse. The description of the sacrum and coccyx, however, is not included in the description of the spinal column, but falls more naturally under the section " Pelvis." The intervertebral substances differ from every other structure in the body ; though not truly ligamentous nor truly car- tilaginous, they are of an intermediate nature. Each disc is composed of a circumferential laminar and a central soft pulpy portion ; the former tightly surrounds and braces in the latter, 70 THE ARTICULATIONS and forms somewhat more than half the disc. The laminar portion consists of alternate layers of fibrous tissue and fibro- cartilage. The component fibres of these lamellae are firmly connected with two vertebrae and pass obliquely between their (ijoposing surfaces in such a way that those of one lamella descend from left to right, while those of the next pass from right to, left. A few of the superficial lamellae project slightly beyond the edges of the bodies, and their fibres are connected with the edge of the anterior and lateral surfaces of the vertebrae ; some of ibese lamellae do not completely surround the rest, but terminau^ at the intervertebral notches, so that a horizontal section showe the circumferential portion as being thinner at the posterior part than elsewhere. The more central lamellae, are incomplete, and less firm and distinct than the rest ; while those nearest the pulp become more fibro-cartilaginous'and less fibrous in structure, have carti- lage cells and fluid amongst them, and gTadually assume more and more the character of the pulpy material. The pulpy portion is somewhat behind the centre of the disc, and is so soft and elastic that when the confining pressure of the laminar portion is removed, by making either a vertical or a horizontal section, it bulges freely or rises up considerably into a smooth and rounded eminence. It is yellowish in colour, and is composed of loose cartilaginous substance, with a large quantity of fluid and many cartilage cells in the interspaces of its matrix. It is the persistent part of the chorda dorsalis. It is not in immediate contact with the bodies of the ver- tebrae, but together with some of the most central and imperfect lamellae it is separated from the bone by a thin layer of articular cartilage. It forms a ball of tightly compressed and elastic material, which has a constant tendency to spring out from its confinement in the dh'ection of least resistance ; hence it constitutes a pivot round which the bodies of the vertebrae in contact with it tilt, or on which they twist or incline in one direction or another. The intervertebral substances vary in shape with the bodies of the vertebrae which they unite. They have therefore a wider area the lower they are situated in the column. Their thickness is also greatest in the lumbar region. Together they form nearly one-quarter of the whole length of the column, so that iu a column of twenty-eight inches the intervertebral OF THE BODIES OF THE VERTEBRA. 71 substances together measure about seven incbes. Tbe total length along their front aspect is greater than that along their posterior surface ; and this difference is chiefly due to the cer- vical and lumbar substances. Thus they are the cause of the convexity forwards ia the cervical region, and increase that in the lumbar. It will be seen on referring to figure how great is the difference ia the curves of the spine (b) in the recent state, and {a) in the dry after the intervertebral substances have been removed and the vertebrae are placed in close contact with each other, both with respect to their bodies and articular processes. In the dry state the convexity of the cervical and lumbar regions almost disappears, and the vertebrae present one gTeat DiAGBAM I. Curves of Spinal Column between Atlas and Fifth Lumbar Vertebra. Without intervertebral substances. With intervertebral substances. curve, the concavity of which looks forwards, and is most marked a little below the middle of the dorsal region. Such is the curve of old age, owing to the shrinking and drying up of the intervertebral substances, which in their perfect state not only straighten out the column, but give to it the forward 72 THE ARTICULATIONS projections in the cervical and lumbar regions, and produce those gentle curves in the line of the column which have led to its being called " the line of beauty" in all ages. The concavity forwards of the dorsal region is almost entirely due to the shape of the bodies of the vertebrae, but is somewhat increased by the intervertebral substances. The Ligaments. — The intervertebral substances are closely bound by the ligaments which pass over them and the bodies of the vertebrae ; and in the dorsal region, the inter-articular ligaments of the heads of the ribs are also firmly attached to the intervertebral substances. By means of the intervertebral substances alone the ver- tebrae are ujiited together very firmly, in much the same way as the several parts of the pelvis are by their symphysial car- tilages ; but the column so constructed is too supple and flexible, so that the union of the several segments requires to be further bound together by long, and short immediate liga- ments. These ligaments are the anterior and posterior common vertebral, and the short intervertebral Hgaments. Further, the stellate ligaments of the costo-vertebral joints, though not ligaments properly speaking of the spinal column, yet give strength to it by binding two vertebrae and the inter- vening substance to the same rib or lateral buttress. Tlie Anterior Common Vertebral Ligament extends, as a very distinct longitudinal band, from the second cervical vertebra to the sacrum. At the middle of the sacrum it becomes gra- dually lost in the periosteum of that bone, but is again dis- tinguishable as a ligament in fi-ont of the sacro-coccygeal articulation. At its upper extremity it is continuous with the narrow central portion of the anterior atlo-axoidean ligament, which, like it, is firmly connected with the front of the body of the axis. At first narrow and pointed, it gTadually widens as it descends, until it measures from one and three-quarters to two inches at the fifth lumbar vertebra. It is thickest in the dorsal region, and thicker in the lumbar than in the cervical region. Its structure is bright pearly white and glistening, with straight and well-defined borders. These borders are parti- cularly well marked in the dorsal region, where, over the bodies of the vertebrae, the finger-nail can be inserted beneath them. The ligament can be detached from end to end as a ribbon-like POSTERIOR COMMON LIGAMENTS PLATE VIII, IN THE LOWER H/^LF OF DORSAL REGION IN THE LUMBAR REGION. ' Jjia: tumtid- Ufa showvvtcj Xcurcje FoTrdtnA^Ji' for hlood -vessels lyv _A Ktktsnwcn clet.ouii.-noU. . West TTcMrryian & Co H/th- OF THE BODIES OF THE VERTEBRiE. 73 "band. It is firmly connected with the bodies of the vertebrae. Its superficial fibres extend over several, its deeper over only- two or three bones. It is strengthened in the cervical region by the tendinous fibres of the prsevertebral muscles, and in the limibar region by the crura of the diaphragm. The anterior common hgaments prevent undue backward movement of the vertebrae — i.e., over-extension of the spine. The Posterior Common Vertebral Ligament extends from the occipital bone to the coccyx. It is wider above than below, and at its commencement has a broad attachment to the cranial surface of the basilar portion of the occipital bone. As it passes over the back of the bodies and intervertebral substances, it varies somewhat in the different regions of the column. Throughout the cervical portion it is of nearly uniform width, although on the level of the intervertebral sub- tances it retains the same thickness somewhat further outwards on each side than over the bodies of the bones, and it is con- tinuous with the short intervertebral ligaments at the interver- tebral foramina. In the dorsal and lumbar regions it has distinctly dentated borders, being broader over the intervertebral substances and the edges of the bones than over the middle of the bodies of the vertebrae. In the latter situations, where its close attach- ment to the bone is not req^uisite for strength, and where numerous bloodvessels pass into and out of the osseous sub- stance, the ligament is a narrow band along the median line. These narrow portions consist of longitudinal fibres, some of which are superficial and pass over several vertebrae, and others are deeper and extend only fi'om one vertebra to the next but one below. The broader portions or expansions of the ligament are formed by oblique fibres, which, springing from the lateral surface of the bodies near the intervertebral foramina, take a curved course downwards and backwards over an intervertebral substance, and reach the narrow portion of the ligament on the centre of the vertebra next below. They again diverge outwards to pass over the next succeeding intervertebral substance, and end on the lateral aspect of the body of the vertebra beyond. The same fibres therefore are in connexion with the bodies of three vertebrae and two intervertebral substances — i.e., two amphiarthrodial joints ; they enter into two expansions and decussate in each of them with other fibres similarly disposed ; 74 THE ARTICULATIONS they also blend near the intervertebral foramina with the short ligaments upon the sides of the column. Deeper still are other fibres thickening these expansions of the common ligament, and extending only from one bone to the next. The last well-marked expansion is' situated behind the inter- vertebral substance between the first two segments of the sacrum ; below this spot the ligament becomes a slender, deli- cate, central cord, with only rudimentary expansions, but when it reaches the sacro-coccygeal joint it again becomes more pro- nounced, and helps to strengthen that joint as it does the several amphiarthrodial joints between the vertebrse. On the back of the coccyx it blends with other stronger ligamentous tissues. In the cervical region the ligament rests flat upon and ex- tends quite across the bodies of the vertebrae ; in the dorsal and limibar regions it is stretched over without resting upon the backs of the bodies of the vertebrse, from which it is sepa- rated by bloodvessels and some loose cellular tissue, which serves as a delicate periosteum for the bones where the liga- ment is not connected with them. At the foramen magnum and on the occipital bone it is closely united with the dura mater, which, however, can be dissected up from off it. Along the sacrum and at the coccyx the filum terminale becomes blended with it. Elsewhere a loose cellular membrane attaches the dura mater to the ligament. The posterior common ligament checks undue flexion, and prevents displacement forwards of the vertebrae. By its great strength and breadth in the neck and its ascent to the cranium it helps to hold up the head upon the spinal column. In this it is assisted by the dura mater and the supra-spinous ligament. Its expansions over the joints of the bodies serve the same purpose within the spinal canal as the intervertebral ligaments serve on the exterior — viz., to strengthen the union of the intervertebral substances with the contiguous bodies of the vertebrae. Thelntervertehral or Short Vertehral Ligaments. — Along each side of the column, between the anterior and posterior common ligament, are numerous short fibres passing from the body of one vertebra to that of the next, and on tliis account they may be called intervertebral ligaments. The more superficial fibres of these short ligaments are more or OP THE BODIES OF THE VEKTEBE^.. 75 less vertical ; tiiose near the anterior common ligament being more so than those nearer the pedicles. The deepest and shortest fibres pass from the lower edge of the vertical surface of one vertebra to near the upper edge of the vertical surface of the next. As they pass over the intervertebral substances many of these fibres decussate with one another, so that they may be called crucial from their arrangement. They are closely united to the intervertebral substances, and it is no doubt owing to this, and to the fact that these short ligaments are connected with the deep surface and more central portion of the anterior common ligament, that the latter is usually described as being more, firmly fixed to the edges of the bodies and to the intervertebral substances than to the central concave part of the vertical sur- face of the bodies. In the cervical region the fibres of these short ligaments are more scattered and less weU marked ; they are covered by the longus colli muscle, the tendinous slips of which can hardly be separated from them. In the dorsal region they overlie the fibres of the stellate ligament, and in the lumbar they even radiate towards the transverse processes (as the stellate Kgament does towards the rib), from the vertebra and substance above, as well as from the vertebra to which the transverse process belongs. In the case of the fom'th and fifth lumbar vertebrae, the fibres thus passing to the transverse process are very strongly marked, and some of them are continued into the lumbo-iliac ligament. Much the same arrangement is to be seen on the front of the sacrum, where the strong fibres of the periosteum radiate to- wards the ribs of bone between the anterior sacral foramina. At the intervertebral foramina in each region of the column these short ligaments blend with the expanded areas of the posterior common ligament, while in front, as stated above, they are connected with the anterior common ligament. Thus is formed a complete casing of ligamentous tissue around each amphiarthrodial joint between the bodies of the vertebrae. The intervertebral or short vertebral ligaments limit move- ment in every direction, and assist the intervertebral substances in binding the bodies firmly together. The great strength given to the spinal column by these liga- ments, and the extent to which they limit the yielding of the intervertebral substances and the movements of the vertebrae, 76 THE LIGAMENTS AND JOINTS can be appreciated by noticing the increased pliability of a por- tion of the column after these ligaments have been removed by dissection. Ligaments and Joints connecting the Posterior part of the Spine. The jposterior portion of the spinal column consists of the arches with their outstanding processes, and of the ligaments connecting them. We shall consider first the laminse of the arches ; secondly, the articular processes ; thirdly, the non- articular processes ; and fourthly, the ligaments of these several parts in the same order. The Osseous Steuctuees. — The Lamince vary in shape and dimensions in the different regions. Those of the last dorsal and the upper three lumbar vertebrte are the shortest of all from side to side, and very deep from above downwards. Those of the fourth lumbar vertebra are longer from side to side, and somewhat deeper than those of the bones immediately above, this difference being due to the more lateral position of the inferior articulating processes of the fourth lumbar, which are as widely apart from each other as the superior of the same bone. The laminse of the fifth lumbar are still longer from side to side — indeed they are the longest in the colimm ; they are also much shallower than either those in the dorsal or in the rest of the lumbar region. They are longer at the lower (sacral) border than above, owing to the greater width between the inferior than between the superior articular processes. Excepting along the middle line, immediately beneath the roots of the spinous processes, there is no interval between the lamina! of any of the lumbar vertebrse (except the fourth and fifth) appreciable from the outside — i.e., behind. This inter- laminar interval along the middle line is the result partly of the horizontal direction of the spinous processes, and partly of the considerable downward and upward prolongation of the outer end of the laminge into the inferior and superior arti- culating processes respectively. In the dorsal region the laminse are nearly square, flattened plates, with their sm-faces forwards and backwards, and borders above and below. Owing to the different direction of the articulating processes, and to the downward inclination of the spinous processes one over the other, there is no appreciable space between the laminse even along the median line. In OF THE POSTERIOR PART OF THE COLUMN. 77 tliis way therefore the spinal canal is entirely shielded by bone in the region where its contents are most exposed to injury owing to the backward curve of the column. In the cervical region the laminae are not so deep as in the lumbar and dorsal regions ; and their surfaces, especially about the middle of the region, are somewhat curved, so that while their surfaces face forwards and backwards near the arti- cular processes, they incline upwards and backwards, and down- wards and forwards, near the roots of the spinous processes. A distinct interlaminar space, resulting from the obhquity of the articular processes, and the horizontal direction of the spinous processes, is especially marked about the middle of the region. In aU parts of the spinal column the inclination of the laminae foUows pretty nearly that of the articular processes, which are merely prolongations from the outer ends of the laminge. Thus in the cervical region the processes look ob- Hquely upwards and backwards, and downwards and forwards ; so do the laminse in part of their extent. In the dorsal region both articular processes and laminse face almost directly back- wards and forwards ; while in the lumbar region there is a slight twist, together with a groove on the posterior surface of the laminge, whereby the superior articular processes are made to look inwards and backwards, and the inferior outwards and forwards. It is to be noticed that where there exists an interlaminar space the curve of the spine is forwards, and the movements are the freest ; but where there is no interlaminar space beneath the roots of the spinous processes, the curve of the spine is backwards, and the movements are not free. There is, however, no direct relation between the interlaminar space and the thickness and strength of the interlaminar ligament — i.e., the ligamentum subflavum. In all the regions of the column the laminse of each vertebra are marked by the attachment of two ligamenta subflava. Along the upper edge, and extending a little way along the posterior surface near the middle line, is a rough ridge (often very uneven) to which the lower border of the ligament above is attached. This is best marked in the middle and lower parts of the dorsal region, where there is often a distinct horseshoe-shaped roughness, the concavity of which is upwards on the posterior surface of the laminee, between the articular facets. 78 THE LIGAMENTS AND JOINTS Sliarp and strong spicula of "bone are sometimes seen projecting upwards from it. On the deep or anterior surface there is a rough ridge, with a depression below it extending upwards and outwards from the root of the spinous process along the inner side of, and then above, the inferior articular process as far as the junction of the pedicle with the lamina. This is for the attachment of the upper border of the lower of the two ligamenta subflava connected with that vertebra. This ridge and depression are also best marked in the dorsal region where those of the two sides form quite a Y shaped impression ; the upright of the Y extends along the under surface of the spinous process, while the arms spread upwards, one on each side, beyond the median border of the articular facets to the pedicles. The Aeticular Processes are two superior and two inferior for each vertebra. They project upwards and downwards respectively, two on each side at the junction of the pedicles with the laminse. Although they are always called processes, they are not such ' in the same sense as the transverse and spinous processes are. They are not separate elements of a vertebra but merely facet-like prolongations of the laminse. They have no separate centres of development as have the spinous and transverse processes. The outer extremity of each lamina becomes deeper and thicker just before it merges into the pedicle of the arch, and in the posterior and anterior surfaces of this wide part of the lamina the articular facets are placed. In the cer^dcal and dorsal region this relation of parts is obvious enough, but in the lumbar it is less evident at first sight, owing to the strong inward and outward curves of upper and lower facets respectively. In all the regions of the column the posterior non-articular surface of the inferior arti- cular processes forms part of the vertebral groove for the erector spinal muscles, or their prolongations, to the head and neck. In the dorsal and lumbar regions, the transverse process projects laterally from the arch between the upper articular process which is above its root and the lower articular process which is below it. In all regions the superior facets look more or less backwards, and the inferior (which are on a slightly more posterior plane than the anterior) more or less forwards. " In the lumbar the superior are concave, more or less OF THE POSTERIOR PART OF THE COLUMN. 79 rounded, and (except in the case of the fourth and fifth bones) further apart than the inferior. While they are directed some- what backwards they look considerably inwards, and embrace between them the inferior processes of the vertebrae above. The inferior facets are convex, and look more outwards than forwards. Those of the fourth are in the same vertical plane with the superior — i.e., they are equally wide apart owing to the greater width of the fifth vertebra. Those of the fifth are even wider apart than the superior facets of the same bone, owing to the greater distance between the articular processes of the first segment of the sacrum. Nowhere in the lumbar vertebrae do we find the inferior processes of one bone tightly embraced by the superior of the next. In no case can the facets on the two sides be placed in immediate apposition at the same time, and hence rotatory movements become possible in the lumbar region, which, but for this space between the articular facets, could not have taken place. In the dorsal region the articular facets are not more than half the size of the lumbar. The superior are flat, and directed vertically backwards with a slight inclination outwards. The inferior are slightly concave, and are in a plane a very little behind the superior : they are directed forwards, with a faint inclination inwards. In the cervical region they are somewhat concave, larger than the dorsal, but smaller than the lumbar facets. The superior, which are directed backwards, look considerably upwards, and have a slight inward inclination. The inferior, which are directed forwards, look considerably downwards, and have a slight outward inclination. The relative position of these processes to the bodies of the vertebrae varies in different parts of the column. In the cervical region, when looked at from in front, the whole of the articular processes can be seen on the sides of, though somewhat posterior to, the body. In the upper part of the dorsal region, although the processes are stUl seen, they are getting more and more behind the body as they descend, so that those of the sixth dorsal vertebra are nearly hidden by the body of that bone. In the lower dorsal, and in the lumbar region as low as the third vertebra, they are entirely hidden behind the bodies ; but in the fourth and fifth lumbar vertebrae, especially the 80 THE LIGAMENTS AND JOINTS fifth, the processes again stand somewhat out from behind the bodies, and are seen from in front of the cohimn. Thus, while all the facets at which movements occur between the occiput and atlas, and atlas and axis, are in the same transverse vertical plane, or nearly so ; the articular processes of the dorsal and lumbar vertebrae, with the exception of the fourth and fifth lumbar, are in vertical planes more and more behind the posterior border of the bodies of the same bones according as they are situated lower in the column. To this difference in the relative position of the articular processes is also due the apparently greater width of the cervical bodies as compared Avith the upper dorsal ; the greater size of the spinal or vertebral canal in the cervical region ; and the greater width of the vertebral groove. This is easily under- stood, for where the articular processes project most beyond the lateral lines of the bodies of the vertebrse there the laminae are necessarily widest, and the space on each side of the spinous pro- cess between it and the articular processes is the greatest. Move- ment also is most free at those parts of the column where the bodies and articular facets are most nearly in the same trans- verse plane. The Non-aeticulak Peocesses. — The spinous processes vary in the several regions. In the cervical, they are nearly horizontal, and (excluding the atlas and the seventh vertebra) are bifid. Those of the third and fourth are short; that of the axis is merely rudimentary ; that of the seventh is long, broad, and tuberculated. In the dorsal region, as low as the ninth dorsal vertebra, they are long, prismatic, incKned downwards over one another Kke the tiles on a roof, and tuberculated at their extremity. Their downward inclination prevents any undue projection in that part of the column which has its convexity back- wards. The spinous processes of the tenth, eleventh, and twelfth dorsal, and those of the lumbar vertebrae, are broad, thick, long, and horizontal in direction. The largest of all the spinous processes are those belonging to the first three lumbar vertebrae. That of the fifth lumbar is altogether smaller than the rest in this region. Thus we notice that where movement is free the spinous processes are nearly horizontal. OF THE POSTERIOR PART OF THE COLUMN. 81 The Transverse Processes. — In the cervical region there are two roots to each process — one, which springs from the side of the body, and the lateral hp of the upper articular disc of the body; and the other from the neural arch between the superior and inferior articular processes. The anterior root is the larger except in the case of the seventh cervical. The two roots are united at their outer ends, and, together with the pedicle between them, enclose the foramen for the vertebral artery. It is hardly correct therefore to describe, as is com- mordy done, the cervical transverse processes as being pierced at their base by the vertebral foramen. Between the foramen and the tip of the process the upper sm*face of the transverse process is deeply channelled for the passage of the cervical spinal nerves. Each process is somewhat curved downwards, and projects slightly forwards as well as outwards. They thus slightly overhang in front the capsular ligaments and the arti- cular processes. In the dorsal region, with the exception of the eleventh and twelfth, the processes are large and long. They project back- wards as well as outwards, are tuberculated at their extremities, and are marked by facets for the tubercles of the ribs. They arise by only one root, which is connected with the neural arch between the superior and inferior articular processes. The cap- sular ligaments of two joints are partly attached to each pro- cess — that of the upper one to the upper and back part, that of the lower to the anterior and lower surface of the base of the process. The eleventh and twelfth dorsal vertebrse have stunted rudimentary processes, which indeed are generally only represented by three partially amalgamated tubercles. These tubercles become differentiated in the lumbar region, and are known as the accessory transverse and mamillary processes. In the lumbar region the transverse processes vary with each ver- tebra : those of the upper four are horizontal, and spring, like the dorsal, simply from the neural arch between the upper and lower articular processes, from which, however, they are separated by a considerable interval. This origin of the lumbar transverse processes is strongly opposed to the opinion held by some anatomists, that they are homologous with ribs. If the anterior roots of the cervical processes are rightly considered to be the homologues of ribs, it is difficult to see how the processes of the four upper lumbar G 82 THE LIGAMENTS AND JOINTS vertebrae, whicli are equivalent to the posterior roots of the cervical transverse processes, have any snch homology. That of the fifth Imnbar is very broad and massive, and is inchned backwards, ontwards, and sMghtly upwards. It springs, like the cervical transverse processes, fi-om the side of the body as well as from the neural arch, only, unlike the cervical processes, it has no large foramen between its roots, but only a Httle hole or two for small vessels : hence the process seems to be massed together both with the pedicle and with the side of the body of the bone. Great strength is given to this vertebra by the consohdation of these parts, while at the same time we see in it the commencement of an arrangement which attains its fulness in the construction of the sacrum. In length the transverse processes of the five lumbar ver- tebrae usually stand to one another thus : the thii'd is the longest, the second next, and then the first, fom-th, and fifth, in succession. They are each slighter, and the third is often longer than the corresponding dorsal processes. Ligaments connecting the LAMiNiE and Aeticulae Peo- CESSES. — The ligamenhtm suhjlavuin is a shallow plate of closely woven yellow elastic tissue, interposed between the arches of two adjacent vertebrse. The first plate connects the axis with the thii'd cervical vertebra, and the last connects the fifth lumbar with the first segment of the sacrum. Each ligament extends from the inner and posterior edge of the intervertebral foramen on one side to the corresponding point on the opposite ; and thus besides closing the interlaminar spaces and acting as a bond of union for the vertebral arches, they each form part of two capsular ligaments. They are convex from above downwards in front, but concave from side to side, making a more decided transverse curve than the arches of the vertebrse between which they are placed. This concavity is more marked in the dorsal and still more in the lumbar region than in the cervical, as they extend in the former regions a short distance between the roots of the spinous processes where they blend with the interspinous ligaments. There is therefore in the dorsal and lumbar regions no actual separation of the ligament into two lateral halves, although in the latter there appears at first sight to be such, owing to the decided folding of the ligament upon itself, in the middle line, whereby the inner surface is in apposition with itself, for a short distance as the ligament projects back- OF THE POSTEEIOE PAET OF THE COLUMN. 83 •wards a little way between the roots of the spinous processes. This folding and backward extension give the appearance of a median sulcus when seen from the front. In the dorsal region there is only a median depression, not amounting to a sulcus. In the cervical region, where the spinous processes are bifid, there is a median fissure in the yellow hgament, which is filled up by fibro-areolar tissue, but there is no actual interval between the two halves, only an interruption in the nature of its structure. To the higher of the two arches between which it extends each ligamentum subflavum is attached on the inner or anterior surface of the lamina, and close to the inner edge of the inferior articulating processes, along wliich it ascends on each side of the middle line, from the root of the spinous process. Owing to the more antero-lateral situation of the articular processes of the cervical vertebrae, the yellow ligament does not enter quite so freely into the formation of the ca]3sular liga- ments of this region, as of those of the dorsal and lumbar. To the lower of the two arches the hgament is attached on the upper edge of the lamina, descending in the middle line, especially in the dorsal region, over the outer or posterior surface ; laterally it is attached to the inner or anterior surface of the arch close to the inner border of the superior articulating processes. The ligaments are thickest and strongest in the lumbar region ; narrow, but strong, in the dorsal ; and broader, thinner, and more membranous in the cervical region. There are, as stated above, well marked rough ridges on the arches of the dried vertebrae, showing the attaclmients of these ligaments ; those of the superior attachments are stronger than those of the inferior. The dorsal vertebrse show the strongest markings ; the lumbar are also strongly impressed by the Hga- ments, but the cervical are much less so. Uses of the Ligamenta Suhfiava. — It is invariably stated that the ligamenta subflava are stretched during flexion forwards of the spine, and that by virtue of their elasticity they assist the muscles in bringing the column back again to, and in retaining it in, the erect posture. A careful examination of the hgament in different parts of the column convinces one (1) that it is stretched throughout on bending the spine forwards ; (3) that the right half of the hgaments is stretched on lending the g2 84 THE LIGAMENTS AND JOINTS column to the left, and the left half on hcnding the column to the right side ; and (3) that the right portions of the Hgaments are stretched on twisting the left side of the body forwards, and the left portions on twisting the right side forward. A good idea may be obtained of the elasticity of these Hga- ments, after separating the arches from the bodies of the cleanly dissected spine, by putting them on stretch between the two hands like a piece of elastic. In tliis way I have increased the length of the lumbar portion of the column (consisting of the arches of five vertebrae and four hgamenta subfiava) half an inch, which is equivalent to one-eighth of an inch for each ligamentum subflavum. This fact I had ascertained long be- fore seeing Dr. Sayre's demonstrations of his excellent method of treating spinal diseases by the application of plaster ban- dages after extending the spine by compound pulleys ; and if we bear in mind that there are twenty-three yellow Hgaments in the column, and that the intervertebral substances are Hke springs compressed, we can understand how tliree-quarters of an inch, or even an inch and three-quarters, in stature might be added to the height of the patient, by means of extension, without any of the important adhesions around the diseased parts being destroyed. It must be borne in mind, however, that in the living sub- ject the intervertebral substances are tightly covered over by inelastic white fibrous Hgaments — viz., the anterior and pos- terior common vertebral and intervertebral Hgaments — and that the Hgamenta subfiava cannot be stretched so much before as after the removal of these encasing Hgaments. I cannot there- fore concur in the view that the yellow Hgaments assist the muscles in restoring and preserving the upright position. The degTee to wMcli the Hgaments are stretched by ordinary for- ward flexion of the human body must be very sHght, so that the resiHency of then- structure is brought insufficiently into play for the purpose named. Moreover, the central portions of the intervertebral substances (elastic springs much nearer to, indeed in the very axis of, movement) would by their elasticity restore the bones after they have been disturbed from their position of rest. Nor is it Hkely that these Hgaments offer any material resistance to the continual forward pull of the viscera and other soft parts of the body which are placed in front of the column. Such a continual drag upon elastic structures would or THE POSTEEIOR PART OF THE COLUMN. 85 soon wear out their elasticity and render them inert. Besides, we know that when the muscles of the back become enfeebled, as in illness, or the intervertebral substances ossify, as in old age, the column curves forwards in spite of these ligaments, so as to assume, in extreme cases, the form illustrated in Diagram I. a, page 71. This figure represents the dry bones of the human spinal column, with their bodies and articular facets in appo- sition, but without their intervertebral substances. In the Hunterian Museiun there is a column thus curved, owing to ossification of the intervertebral substances and ankylosis of the bodies of the vertebrae by means of bridges of bone thrown out from their edges. Nor have the ligamenta subflava any power to preserve the upright position in advancing age when the intervertebral substances are shrinking, and as a conse- quence the stature is diminishing and the arch of the back progressing. To counteract the effects of the forward disposition of the viscera on the spine there are several provisions. In those parts of the trunk in which the largest viscera are placed, the column itself curves backwards ; the ribs also curve consider- ably back before they arch forwards, and thereby allow of some portions of the viscera being placed at the sides of, and even on a posterior plane to, the column. The position of the scapula upon the posterior surfaces of the most backward projecting ribs throws back the weight of the shoulders, while powerful and extensive muscles pass to the upper extremity from the whole series of spinous processes between the occiput and coccyx. If then the ligamenta subflava are not requii'ed, and cannot act to restore and preserve the erect posture, what are the uses of these wonderful little structures ? 1. They complete the roofing in of the vertebral canal in the interlaminar spaces, and yet at the same time they permit constant variations in the width of the interspa/ es — varia- tions required by the shifting of the articulating processes upon one another, and therefore of the laminae in relation to one another. 2. They restore the articulating surfaces to their normal position with respect to each other after they have been dis- turbed therefrom by muscular action, either in antero-posterior, lateral, or rotatory movements. 86 THE LIGAMENTS AND JOINTS This normal position of the articular surfaces in the cervical and dorsal vertebree is one of almost complete appo- sition ; hut in the lumbar region, the superior processes are so much wider apart than the inferior of the vertebrae next above with which they articulate, that complete apposition is not possible on both sides at the same time. 3. By forming the inner portion of the capsule of the articulating processes they prevent it from being nipped between the moving surfaces. Elsewhere in the body we find muscles connected with capsular ligaments for tliis purpose, and even here, on the posterior and outer sides of these little joints, tliere are small muscles connected with the inelastic part of the capsule. In the vertebral canal, however, muscles and muscular action would be incompatible with the nerve structures against which they would be placed. Here we find the capsules completed by elastic tissue, which can protect itself through its own elasticity, from being plicated and caught between the facets of the moving bones. In the cervical region, where these facets are thrown considerably beyond the sides of the bodies of the vertebree, and where the capsular hgaments are connected with muscles in front as well as on the outer side and behind, the ligamenta subflava do not extend so far in front of the joints as in the other regions of the spine. The Capsular Ligaments are composed partly of elastic yellow tissue — the ligamenta subflava — and partly of white fibrous tissue. They bind together the articular processes of the vertebrae, and are lined by a distinct synovial- membrane. In the cervical region, only the inner side of the capsule is formed by the yellow elastic ligament, whereas in the dorsal and lumbar regions, not only its inner side, but the anterior portion up as far as the margin of the intervertebral foramen, is formed by it. The portions composed of the inelastic wliite fibrous tissue — ordihary ligamentous tissue — consist of short, well- marked fibres, which in the cervical vertebrge extend obhquely downwards and forwards over the joints between the articular and posterior transverse processes of two contiguous vertebrae ; in the dorsal region the fibres are shorter and vertical in direction, and are attached to the bases of the transverse processes in the manner referred to in the description of tliose parts of the vertebrae ; in the lumbar region they are obliquely ^i^l 1 OF THE POSTERIOR PART OF THE COLUMN. 87 transverse in direction, and pass over tlie joints from one articular process to the otlier. In the cervical and lumbar regions a very considerable portion of each capsule can be seen after removing the tissues in the intervertebral foramina and the muscles of the neck or loin ; but in the dorsal region very little of them can be seen from outside, owing to the ribs masking them on the outer side and, as a result of the overlapping of the articular processes behind, to the consequent shortness of the fibres of the capsules. After removing the arches from the bodies of the vertebrte, the joints can be laid open in front by cutting away the ligamenta subflava as shown in the plate of these ligaments. The capsular ligaments in the cervical region are the most loose, those in the lumbar the next so, and those in the dorsal the least. This is in accordance with the different degrees of movement permitted to the vertebrae in the three regions. Synovial Meivibeaxe. — The capsidar ligament of each pair of articular processes has a distinct synovial lining. The Ligaments connecting the Non-aeticulae (the Spinous and Teansvekse) Peocesses. — These processes give origin and insertion to the muscles of the spine, but do not directly add to the strength or security of the column. The ligaments wliich connect these processes are chiefly inter- muscular septa or aponem^otic structures, and are insignificant as Hgamentous structures proper — that is, as checks to move- ments or as media of union between bones. The ligaments of the spinous processes are stronger and better marked than those of the transverse processes. The Stcjjra-spinous Ligament extends along the tips of the spines of the lumbar and dorsal vertebrse as a well-marked band of longitudinal fibres, which are continuous at the sides with the aponeurotic structm-es of the back. It is thicker in the lumbar region than in the dorsal. Its more superficial fibres are much longer than the deeper. Above it is continuous with the ligamentum nuchce which reaches to the occiiDut ; a thin tendinous expansion passes between the tips of the cervical spines and the deep aspect of the ligamentum nuchse. Below the supra-spinous ligament passes over the sacrum to the coccyx, and ends on the back of the latter. It adds very materially to the security of the sacro-coccygeal joint, and 88 THE ARTERIES OF THE SPINAL COLUMN. covers in the spinal canal, where for the want of the laminae of the sacrum and coccyx it would otherwise be exposed. The intersjmioiis ligaments are membranous structures, which extend between the spines of adjacent vertebrae from their roots to their tips. They are connected at the roots of the spine with the ligamenta subflava, and near the tips with the supra-spinous hgament. They are best marked in the lumbar region, and are ill defined in the neck. Their fibres do not extend directly from spine to spine, but run obUquely from the root of one towards the tip of the other. They form septa along the middle line between the muscles of the two sides of the back. Ligaments of the Transverse Process are barely worthy of the name. In the cervical region they can hardly be said to exist at all, and are never anytliing more than a few fibres between the apices of the processes. In the dorsal region they form small round bundles, wliich extend somewhat obhquely downwards and outwards near the tips of the processes. They are best seen from behind. In the lumbar region they are thin membranous bands, quite incapable of acting as bands of union. Akteeies of the Spinal Column. — jSTumerous small arteries are given off to the front, side and back of the bodies of the ver- tebrae from the vertebral artery ; and the ascending cervical branch of the inferior thyroid artery in the neck ; from the intercostal arteries in the dorsal region ; and from the last dorsal and lumbar arteries in the loins. On the front of the column some of these little vessels pass beneath the sharp edge of the anterior common vertebral ligament to reach the vertical surface of the bodies of the vertebree, which they penetrate ; on the sides other small twigs enter the bones by passing between the fibres of the short intervertebral ligaments ; and at the back branches are given off from the anastomosing arches within the spinal canal to enter the bodies of the vertebrae beneath the posterior common Hgament. Blood is conveyed by these vessels over the surfaces of the intervertebral sub- stances ; and to the articular discs of the vertebrae by the ves- sels which ascend and descend through the cancellous tissue of the bodies. To the capsules of the articular processes branches are given off, in the cervical region from the deep cervical of the THE MOVEMENTS OF THE SPINAI, COLUMN. 89 superior intercostal, and deep cervical branch of the occipital arteries ; in the back from the dorsal branches of the inter- costal, and in the loins from the dorsal branches of the lumbar arteries. They supply the muscles in the vertebral groove, and send one or more minute twigs to ramify over the back of the capsular hgaments, which they penetrate to reach the synovial hning of the joints. A further blood supply is derived from the " spinal hranches" of the vertebral and ascending cervical arteries in the neck, and from the spinal subdi\dsion of the dorsal branches of the intercostal and lumbar arteries. After passing into the spinal canal through the intervertebral foramina, these spinal hranches break up in the soft fat which surrounds the sheath of the nerve-roots into three divisions ; one runs along the nerve-root to the cord and its membranes, another goes forward to the backs of the bodies of the vertebrse, and the third backwards to the lamina of the vertebra. This last vessel passes over the joint of the articular processes, and gives one or two minute twigs to the capsule, which they penetrate to reach the syno- vial membrane. I have never seen anything like an arterial zone around the margin of the articular cartilages of these joints, as is formed by the arteries of the larger articulations. Nerves. — Filaments are supplied to the articulations by the spinal nerves in each region. Movements of the Spinal Columx. — The spinal column is so formed of a number of bones and intervertebral substances arranged in curves, and bound together by elastic and inelastic ligaments, as to serve many purposes. It is the axis of the skeleton, upon it the brain-case is supported, and with _^ it the walls of the cavities of the trunk, and also the limbs, are connected. As a fixed column it is capable of bearing great weight, and through the elastic intervertebral substances, of resisting, and breaking the transmission of, shocks. Moreover it is flexible, and therefore capable of movement. I^ow the range of movements of the spinal column as a whole is very con- siderable, but the movements between any two of the vertebree are slight, so that motions of the spine take place without any change in the shape of the column, and without any marked dis- turbance in the relative position of the vertebras. It is to the intervertebral substances that these movements are owing ; and 90 THE MOVEMENTS OF THE SPINAL COLUMN. it is about the central semi-fluid and tightly compressed part of these substances, which forms an elastic pivot or ball upon which the middle of the bodies of the vertebrae rest, that these movements occur. Hence this semi-fluid central cushion is most marked in those regions of the spine where movement is most free. The amount of movement is everywhere lionitedhj the common vertebral ligaments ; but it depends in part also upon the "oddth of the vertebral bodies, as well as upon their contiguity — i.e., upon the thickness of the intervertebral sub- stances ; for it is evident that, given the same dimensions of the elastic semi-fluid pivot, the movements will be most free where the area of the vertebral bodies is smallest. In the loins where, owing to the great superincumbent weight, the vertebral bodies are necessarily large and wide, the inter- vertebral substances are very deep, and thus prevent that restriction of the range of movements which the gTcat size of the bones would otherwise produce. On the other hand, in the neck, where the intervertebral substances are much shallower, the area of the bodies of . the vertebrae is small, so that the movements are on the whole as free as in the loins. In the back the vertebral bodies increase in area from above downwards, and are everywhere much larger than the bodies of the cervical vertebrae ; while the intervertebral substances are less deep than those in the neck, with the exception of that between the axis and the third vertebra, which is shallower than any other in the column. The soft pulpy portion of the intervertebral substance is then the centre of the movement of each vertebra — " the ball upon which the socket, formed by the contiguous surfaces of the vertebrae, revolves ;" and it must be obvious that the movements of a column formed in this manner, of sockets and balls, must be of a rolling character, and may take place in any direction. While therefore, as has been stated, the amount of movement depends upon the depth of the intervertebral substances and the area of vertebral bodies, the direction of the movements must be regulated by some other means. It is one of the uses of the articular processes to limit the direction of motion, and their office further is to give steadiness to the column, and to assist the vertebral bodies in bearing the superincumbent weight. Were it not for these processes the column, instead of being a stationary one, endowed with THE MOVEMENTS OF THE SPINAL COLUMN. 91 tlie capacity of movement tkrougli the agency of voluntary muscles, would be a tottering one, which it would require the agency of the muscles to steady. As then the vertebral bodies are free to deflect or incline in any direction upon their intervertebral substances witliin the limits permitted by the uniting hgaments, by their own shape and size, and by the shape and size of the intervertebral substances ; the influence of the articular processes in limiting the direction of inchnation will appear from a study of the various movements in the tln-ee regions of the spine. In the, neck, forward and backward movements are free, much more so than in the back, though less so than in the loins ; but while the capacity of motion backwards from the upright position is greater than that of motion forwards in the neck, the reverse is the case in the loins. Flexion to either side is more free in the neck than in any other region. Eotatory movements are also free in the neck, especially in the lower part of the region. There is but slight movement of any sort between the axis and third vertebra, owing chiefly to the shallowness of the intervertebral substance, and the great prolongation of the anterior hp of the lower surface of the axis, which checks forward flexion considerably. The obhquity of the articulating surfaces of the cervical vertebrae permits of all these movements, but is especially favourable for extension or backward flexion. This increases the extension movement of the occipito-atloidean joints, and makes it still more easy to man — " erectos ad sidera toUere vultus" — to cast upward looks to heaven. ' In the hack, especially near its middle, antero-posterior flexion and extension are very slight. As the concavity of the curve of the column here is forwards, the flat and nearly vertical surfaces of the articular processes prevent anytliing like shding in a curvihnear manner of the one set of processes over the sharp upper edges of the other, which would be necessary for forward flexion. These processes do not prevent a fair amount of lateral flexion, which, however, is less than it otherwise would be owing to the impediment offered by the ribs ; whilst the outward inclination of the superior processes and the corresj)onding inward turn of the inferior, enable the latter to revolve slightly upon the former so as to permit a rotation of the bodies of the dorsal vertebrse around their own 92 THE MUSCLES IN CONNEXION vertical axis. Indeed, in the upi^er part of the back rotation is very free. In the loins the antero-posterior movements are very free, especially between the tliird and fourth, and fourth and fifth vertebrae, where the lumbar curve is sharpest ; lateral inclina- tion is also very free between these same vertebrae ; and rota- tion also is permitted to a considerable extent and is often greatly increased after disease of the hip-joint, and in the rotatory- lateral curvature of the spine. It is stated on the authority of some excellent anatomists that the shape and position of the articular processes of the lumbar and lower two or three dorsal vertebrae are such as to prevent any rotation in these regions. This argument is supported by the statement that the horizontal motion of the arches and articulating processes necessary for any rotation of the bodies of the vertebrae around their own axis cannot take place owing to the manner in which the superior processes of one bone embrace the inferior processes of the next above. This objection would hold good if the one set of processes tightly embraced the other ; in which case antero-posterior movement only would be possible in the loins, as lateral inclination equally with rotation would be impossible. But the fact is, as has been pointed out above, that the two sets of articular processes are not in contact with each other on both sides of the bodies at the same time, and that there is therefore always some space in which horizontal motion of the arches and processes can occur round an axis drawn through the central jpart of the bodies and the semi-fiuid nuclei of the intervertebral substarvces. It will be observed u]oon a careful study of the spinal column, that where the movements are most free the curves of the spine have their convexity forwards ; also that their curves are due to the increased tliickness in front of the intervertebral substances and not of the bodies ; that there are no resisting bony walls surrounding cavities or viscera ; that the viscera attached to the vertebras are tubular and movable, not solid and fixed organs ; further, that the muscular masses lodged in the vertebral groove are tliicker and bulkier than elsewhere ; that the spinal canal is larger, and the spinal cord, with its membranes and the spinal nerves, is less closely connected with the backs of the vertebral bodies ; and finally, that the pedicles and the articular processes are more nearly on the same transverse level with WITH THE SPINAL COLUMN. 93 the backs of tlie bodies of the vertebrse. These points are strikingly seen by comparing the cervical with the dorsal regions. • The Muscles in connexion with the Spinal Column. — As the spinal colrnnn is the centre of the skeleton, the basis of support for the head, trunk, and upper hmbs, and the axis about which most of the movements take place, so is it the point of attachment of numerous muscles which extend to and act upon all these various parts of the skeleton, as well as of those which in their functions as well as connexions are con- fined to the vertebrae. It will be convenient, therefore, in an enumeration of these muscles, to divide them into two principal groups — viz., the extrinsic, or those which pass from the colimm to some other part of the skeleton; and the intrinsic, which exclusively belong to the spine. Extrinsic Muscles of the Spinal Column. — 1. Those passing to and moving the head are the trapezius, the splenius capitis, the trachelo-mastoid, the complexus, and the short cranio- vertebral muscles — ^including the lateral and anterior recti. 2. Those passing to and moving the upper extremity are the trapezius, the latissimus dorsi, the levator anguli scapulae, and the rhomboidei. Through the two former the upper limb is brought into connexion with the whole length of the vertebral column from the occiput to the pelvis. 3. Those passing to and acting on the thorax are the scaleni above ; the diapln^agm below ; and the serratus superior and inferior, the levatores costarum, and the quadratus lum- borum, behind. The transversalis abdominis attached to the lumbar vertebrae through its posterior aponeurosis is connected with the front of the thorax. 4. Those passing to and acting on the pelvis are the quad- ratus lumborum, the transversalis abdominis, and, when present, the psoas parvus. 5. There is one muscle extending from the lumbo-dorsal region to the lower extremity, and acting on the thigh — ^viz., the psoas magnus. It is no doubt partly owing to the action of this muscle in young life that the spinal column, which is nearly straight in the first year or two after birth, obtains its strong lumbar convex curve. If now we exclude the short cranio-vertebral muscles as 94 THE MUSCLES IN CONNEXION being concerned more with tlie union of the head with the vertebral column than with the union of the vertebrse with each other, we observe that all these extrinsic muscles, with the exception of tliree, arise from the dorsal aspect of the column. Thus the trapezius, splenius capitis, rhomboids, and serratus superior, arise from the spinous processes of the cervical or dorsal vertebrae, or both ; and the latissimus dorsi and serratus inferior from the lumbar and dorsal spines. The complexus, levator anguli scapulae, and scaleni posticus and medius, arise from the transverse (posterior) processes of the cervical ver- tebrae : the complexus being HkeT^dse connected with the dorsal transverse processes and the cervical articular processes. The levatores costarum arise from the transverse processes of the last cervical and all the dorsal vertebrae down to the eleventh ; the quadratus lumbonun and transversalis abdominis spring fi'om the transverse processes of the lumbar vertebrae. The tliree praevertebral muscles are the scalenus anticus, which arises from the anterior transverse processes in the neck, and the diaphragm and psoas magnus (with the psoas minor when it exists), which spring from the bodies of the lumbar vertebrae. Few only of these extrinsic muscles have any decided action on the spinal column. The scalenus anticus and also the posterior and middle scalene muscles act as lateral flexors of the neck when the ribs are fixed ; if the anterior muscles of the two sides act together, they assist in bending the neck forwards. The psoas serves to bend the body on the thigh, as well as the thigh on the body, at the hip-joint. When the lower limb is fixed, its action is to bend the trunk ; when the trunk is fixed, to bend the thigh. For the rest, the trapezius, latissimus dorsi, and rhomboids act upon the spine when the upper extremities, includuig the shoulders, are fixed. In such movements, for instance, as those required for climbing, and for many exercises in the gymnasium, these muscles draw the trunk upwards and forwards, so as to make it approach the fixed and outstretched arms, wliich for the time are sustaining the weight of the body. Intrinsic Muscles of the Simial Column. — There is only one intrinsic muscle situated in front of the spine, and tliis is the longus colli, which is attached to the transverse processes and the bodies of the vertebrae from the third dorsal to the atlas. It is a flexor of the cervical portion of the column. The rest WITH THE SPINAL COLUMN. 95 of these muscles occupy the vertebral groove on each side — i.e., the space from the spinous processes outwards to the trans- verse processes of the cer\ical vertebrae, the most projecting parts of the ribs, and the crest of the ilium. These are the muscles concerned in keeping the body erect. They extend from the skull to the sacrum, passing between the pelvis and thorax below, and the thorax and cranium above ; as well as between the transverse processes, the transverse and spinous processes, and the spinous processes, respectively ; and in the different regions they thus brace up the column strongly on each side of the middle line. They may be grouped into three classes : — 1. The splenius coUi and long erectors of the spine ; the fibres of which for the most part pass outwards from the median line as they ascend. 2. The transverso-spinales, including the semi-spinaKs colli and semi-spinahs dorsi, the multifidus spinse and the rotatores spinse; the fibres of all which for the most part incHne inwards towards the median line as they ascend. 3. The inter-spinales and inter-transversales ; the fibres of which take a nearly vertical direction. The erector spinse, which takes origin as a common mass, partly fleshy and partly tendinous, from the crest and back of the ilium, the back of the sacrum, and the sacral and lumbar spines, may either be regarded as one large composite muscle, or as composed of seven distinct parts. In either view it consists of three longitudinal columns. The innermost column is very slender, and is connected only with the spinous processes of the two upper lumbar and the dorsal vertebrae. The middle column is subdivided from below upwards into longissimus dorsi, trans- versalis cervicis, and trachelo-mastoid ; the first is attached to the transverse processes of the limibar and dorsal vertebrae ; the second to the transverse processes of the dorsal and cervical vertebrae ; whilst the latter — trachelo-mastoid — though arising from the two upper dorsal transverse processes and the cervical articular processes, is inserted into the mastoid part of the temporal bone and acts more upon the latter than the former bones. The outer column is also subdi-vdded into three parts named from below upwards, the ilio-costalis, the musculus accessorius ad iho-costalem, and the cervicalis ascendens. Only the latter subdivision of this column has any dhect connexion with the vertebrae ; the lower two divisions 96 THE MUSCLES IN CONNEXION are attached to the ribs, but the cervicalis ascendens, though arising from the four or five higher ribs, is inserted into the posterior transverse processes of the fourth, fifth, and sixth cervical vertebrjB. Of the seven portions of the erector spinte, therefore, two are altogether unconnected with the vertebrae — viz., (a) the sacro-lumbalis, which arises muscular from the posterior fifth of the crest of the ilium and is inserted into the lower six or seven ribs near their angles ; and (&) the musculus accessorius, which both arises and is inserted by tendons attached near the angles of all the ribs ; while a third — viz., the trachelo-mastoid, though it arises from the vertebrae, might both from its insertion and action be more fitly included under the extrinsic muscles of the spine. In classing these three parts of the great longitudinal dorsal muscle amongst the intrinsic muscles of the column, the convenience of following the common nomenclature of muscles, and not strict accui-acy in the descrip- tion of their attachments and uses, has been considered. The name " erector spinse" applied to this gTcat muscular and tendinous mass, expresses only part of its action ; it should be called " erector trunci et capitis ;" for, besides extend- ing the spine, it extends also the whole trunk through its extensive connexion with the ribs, and the head through its trachelo-mastoid prolongation. The splenius colli turns the neck obliquely to one side ; when both act together they pull the neck backwards — i.e., extend it. The action of these posterior or post-vertebral intrinsic muscles varies according as those of only one side, or of the two sides, are in action at the same time. When those of the two sides act together they all tend to bend backwards the vertebral column and trunk ; their power is enormous, and more or less of it is brought into play in the respiratory movements, as well as in almost all the gTeat muscular efforts of the body and limbs. When those of one side act alone the extension is accompanied by lateral inclination or flexion, together with rotation. In the more decided rotatory movements certain of the muscles of one side will co-operate with others of the opposite. Thus in rotation of the upper part of the trunk to the left, not only will the splenius and the prolongations of the erector spinse of the left side be brought into action, but the muscles of the opposite side, THE SPINAL COLUMN. 97 whose fibres take an upward and inward direction — ^viz., the semi-spinalis, the multifidus, and rotatores spinse, will assist the former in their work. Indeed, stated in general terms, it may be said that those muscles on one side of the median plane of the column which pass from transverse processes to spines, rotate the vertebrae towards the opposite side, and are assisted in this action by the muscles on the opposite side which pass from spines to transverse processes. The inter-spinales approximate the spinous processes between which they pass, and thus extend the part of the spinal column to which the muscles in action are attached. The inter-transversales, when the muscles of the two sides act together, must assist in extending the column, for the transverse processes are behind the bodies of the vertebrse, and the muscles which pass between them must therefore tilt back- wards the arches and extend the spine. When those of one side act alone the tendency must be for them to cause postero- lateral flexion, or inclination of the column towards their own side, as well as slightly backward. The connexion of the quadratus lumborum with the tips of the transverse processes of the lumbar vertebrae resembles the attachments of the scalenus posticus muscle in the neck. It is of interest too, as furnishing a compensating means of support and strength to that part of the column which is devoid of lateral buttresses, such as the ribs, yet has to bear greater weight than the dorsal vertebrae. At the same time that it affords support it also provides an additional power for movement, and serves with the muscle of the opposite side to keep the Irunbar portion of the column erect, and to extend it ; while if one muscle acts alone it turns the lumbar vertebrae upon their axis, and inclines them to its own side, just as the scalenus posticus acts upon the cervical vertebrae. The quadratus lumborum, like the sacro-lumbalis, acts also on the ribs, pulling them downwards, and thus assisting the lower serratus muscle to fix, as it were, the lower part of the thorax for the more advantageous action of the diaphragm. It seems at first thought strange that, whereas the head is steadied and moved upon the spinal column, and the trunk is steadied, balanced, and moved upon the heads of the femora by muscles situated on all sides of the joints, the muscles which steady and move the several vertebrae are placed upon the II 98 THE MUSCLES IN CONNEXION posterior aspect only of the spinal column. But it must be observed that the weight of the viscera, of the head as well as of the trunk, tends to pull the body forwards — i.e., to bend the spine ; and that therefore the muscular power of the column in most positions is requisite, not for forward movements, but to prevent them ; whilst for lateral and rotatory movements, more especially as the articular processes are behind the bodies of the vertebrae, the muscles are more advantageously situated as they are than they would be were they in front of the axis of the column. There are some positions, however, in which the muscular force is required to be in front of the column, in order to effect the necessary movements ; but in these cases other muscles, which have no connexion mth the spine, come into action upon it through the trunk and upper limbs. For instance, in rising from the horizontal position, as after lying on one's back, or even in rising from a low-backed easy-chair, we first draw our head and neck forwards by such muscles as the sterno-cleido-mastoid, the longus coUi, anterior recti, and scalenus anticus, and then we bend forwards the rest of our spinal column through the agency, not only of the psoas magnus, which is directly attached to the column, but also of the abdominal muscles which act on the sternum and ribs, and through them on the spine, and of the muscles of the upper limbs, which by fixing the shoulders enable the latissimus, trapezius, and rhomboids to act as it were from in front of the column. Moreover, in forcible and violent respiratory move- ments, the serratus magnus is capable of moving the bodies of the upper eight dorsal vertebrae upon one another in the following manner : — The scapula, being itself attached to the spinal column by the rhomboids and the trapezius, has attached to its base the serratus magnus, and these two sets of muscles may be practically regarded, so far as certain movements of the spinal column are concerned, as one set with the scapula inter- posed in their substance. Now when the scapula is fixed and drawn back by the trapezius and rhomboids, the serratus magnus acts with greater effect upon the ribs to which it is attached ; but the ribs, may be regarded as levers, the long arms of which are curved towards the sternum, while the short arms are passing to and resting against the transverse processes and bodies of the vertebrae, so that when the long arms are acted upon by the muscle WITH THE SPINAL COLUMN. 99 the short arms by their pressure upon the vertebrae cause them to rotate. Unequal action of this kind on the two sides of the body is doubtless one of the causes of lateral curvature of the spine, a deformity which is due to irregular muscular contrac- tion, and not to organic changes in the vertebral bodies or intervertebral substances. In connexion with the attachment of muscles to the spine, mention must not be omitted of the so-called dorsal or lumtar fascia or aponeurosis, which in the lumbar region is attached to the vertebrse in three planes. The anterior, opposite the outer border of the erector spinse muscle, is continuous with the posterior aponeurosis of the transversalis abdominis muscle, and passes in front of the quadratus lumborum muscle to the roots of the lumbar transverse processes ; at its upper part it is connected with the last rib, and forms the hgamentum arcuatum externum of the diaphragm. The middle layer passes between the quadratus and erector spinse to be attached to the tips of the lumbar transverse processes. The posterior layer, which is sometimes distinguished by the name vertebral aponeurosis, is attached to the spines of the dorsal, lumbar, and sacral vertebrse ; above it separates the muscles which belong to the shoulder and arm from those belonging to the head and spine, and extends upwards beyond the superior serratus muscle to the neck; below it covers in the vertebral groove of the sacrum, and is blended with the superior expansion of the great sciatic ligament. Through the connexion of the vertebral aponeurosis with this ligament, and of this ligament mth the tendons of the hamstring muscles, the traction exerted by the hamstring muscles is extended to the spines of the lumbar and dorsal vertebrse. And as this aponeurosis is penetrated by branches of the same nerves which supply the erector muscles of the spine, and as traction on the aponeurosis must necessarily in-itate these nerves, we see how the erector spinse is brought into associated action with the hamstring muscles, so that they at once set about to elevate the head and upper end of the bent trunk as soon as the ham- strings commence to extend the pelvis on the thigh bones. H 2 100 THE LIGAMENTS AND JOINTS WHICH CONNECT CHAPTEE VI. THE LIGAMENTS AND JOINTS WHICH CONNECT THE VERTEBEAL COLUMN WITH THE PELVIS ; Or the SacTO-lumhar, Sacro-vertebral, or Lumho-Pelvic Union. The vertebral column is united with the pelvis at what is called the sacro-lumbar or Inmbo-pelvic union. Like the connection of the several segments of the column with one another, it consists of an amphiarthrodial joint between the bodies, and of a pair of arthrodial joints between the articular processes of the bones. Entering into this union, besides the sacro-lumbar joints and their own intimate ligaments, there are also the accessory or lumbo-pelvic hgaments which connect the processes of the fifth lumbar vertebra with the sacrum and ilium. The bones which enter into the sacro-lumbar articulations are the fifth lumbar vertebra by the under surface of its body and its inferior articulating processes, and the sacrum by its base and superior articulating processes. The Fifth Lumbar Vertebra. — The centrum or hody, though somewhat wider in every direction than the bodies of the ver- tebrse above it, is not so deep as they are, and especially not as the body of the fom-th. The under surface which is connected through the intervertebral substance with the facet on the base of the sacrum measures two and a quarter inches wide, by nearly one and a quarter inches from before backwards ; it is deeper in front than behind by about a quarter of an inch. When looked at from in front it appears much ^ider in the upper three- quarters of its depth than do the bones above. This is on account of the strong transverse processes which arise from the sides of the body, whereas the transverse processes of the rest of the lumbar vertebrae spring from the points of meeting of the pedicle and lamina. THE VERTEBRAL COLUMN WITH THE PELVIS. 101 The inferior articulating processes are nearly one incli and a half apart, and are irregularly circular in outKne ; they are larger, much less convex, and are directed more forwards and much less outwards than the corresponding processes of the other lumbar vertebrse. On this account somewhat more rotation round a vertical axis is permitted between them and the sacrum than is possible between the lumbar vertebrae themselves. The transverse processes are shorter, but thicker and stronger, than the transverse processes of any of the other lumbar verte- brae. They are curved somewhat upwards as they extend out- wards, so that their upper border is concave and the lower convex; then- anterior surface looks upwards and is smooth, while their posterior is inclined downwards and is rough and uneven. Their strength is for the purpose of giving strong attachment to the lumbo-pelvic hgaments. They are on a lower level than the middle of the crest of the ilium, and the iho- lumbar Hgaments extend outwards and upwards from them to the ilium, bounding the false pelvis posteriorly between these bony points. In the transverse processes of this vertebra we have a return to the cervical form where each process arises by two roots, one from the side of the body, and the other from the junction of the pedicle and lamina. In the case of the fifth lumbar, however, the vertebral foramen is represented only by a shght fossa, pierced by small holes for bloodvessels, and the extremity is tubercular and massive, not bifid. At the same time we see here the cormnencement, in a small way, of that increase of bony matter in the transverse processes which leads to the formation of the lateral masses of the sacrum. The spinous process is shorter and shallower than those above ; the lamince are much more expanded — i.e., wider from the middle line outwards — but much shallower than the lamina of the rest of the lumbar vertebrae. The Saceum. — The base of the sacrum measures from four to four and three-quarter inches from side to side, and is wider in the female than in the male ; the variations in the width of different bones do not correspond with those of other dimen- sions, so that bones which in other respects are unequal may be of the same width. In the centre of the base is an oval- shaped flat facet, which is united by means of the intervertebral fibro-cartilage mth the fifth lumbar vertebra. Immediately on 102 THE LIGAMENTS AND JOINTS WHICH CONNECT either side of this facet the base is constricted from before backwards, but it bulges again near the lateral border where the measm-ement from front to back varies from two to two and a half inches. Thus on each side of the central facet there is a large non-articular, slightly concave and fan-shaped surface. The articular facet of the base would be oval in shape, if its posterior border were not nearly straight. It measures about two inches from side to side, and one inch from before backwards. It is very sHghtly cupped in the centre, where the osseous structm-e looks spongy and porous ; but at the cbcumference there is a margin of from one-eighth to one-quarter of an inch wide, composed of dense and compact bone. The margin of the facet is lipped and projecting, so as to increase the surface to wliich the intervertebral substance is attached, and consequently the area of support for the super- imposed column. In the separated sacrum the base appears to be horizontal, but in the articulated skeleton, owing to the oblique position of the sacrum and the inclination of the pelvis, the base is directed forwards as well as upwards, and assists in forming the sacro- lumbar or sacro-vertebral angle. Eunning outwards and backwards from the margin of the oval facet to the rounded prominence at the posterior and outer angle of the base is an oblique ridge. Also extending outwards from the postero-lateral margin of the facet to the articulating process is another shorter and less marked ridge. Between these ridges and the lateral margin of the facet is a small triangular fossa or depression. From the apex or outer ex- tremity of this depression a sulcus or groove passes, and thus separates the articular process from the rounded prominence. Numerous foramina for bloodvessels perforate the floor of this fossa, and overhanging it is the root of the transverse process of the fifth lumbar vertebra ; along the groove passes the posterior primary branch of the fifth lumbar nerve. These ridges and the groove are the representatives of the anterior root of the transverse processes of the pedicle, and of the intervertebral groove, which is seen on the upper sm-face of each process in the cervical vertebrae. In fi^ont of the anterior ridge the bone is depressed, being concave from side to side, and bevelled downwards in front. Limiting the fan-shaped portion of the base externally is the rounded superior border of the lateral THE VERTEBRAL COLUMN WITH THE PELVIS. 103 mass of the sacrum, the posterior angle of which forms the tliick and projecting nodule before referred to. This osseous nodule or prominence, as weU as a portion of the superior border immediately in front of it, overhangs the hollow non-arti- cular surface which lodges the interosseous sacro-ihac ligament. The anterior extremity of the superior border is tliin and sharp, and passes by a weU-rounded curve into the anterior border of the latter mass of the sacrum. The superior articulating processes of the sacrum are situated behind the fan-shaped portions of the base, one on each side of the middle line. Each is separated from the facet for the inter- vertebral substance by a deeply gTOOved and narrow mass of bone which represents the pedicle of the first sacral vertebra. They are situated wide apart, are almost vertical in position, with their articular facets directed backwards and a little inwards, and they project above the level of the base of the sacrum. The facets are concave from side to side, irregularly circular in outline, with a diameter of from half to three- quarters of an inch, and receive the inferior articular processes of the fifth lumbar vertebra. On their non-articular surface is sometimes to be seen a bony prominence corresponding to the mammillary process of the lumbar and lower dorsal vertebrae. The amalgamated contiguous articulating processes of the succeeding sacral vertebrae are represented by tubercles situated just to the inner side of the posterior sacral foramina. By looking into the sacral portion of the spinal canal these tubercles are seen to be supported by strong pedicles which completely separate the anterior and posterior sacral foramina for one pair of nerves from those for the pair above. It will be also seen that both the anterior and posterior primary branches of these nerves must pass above the pedicle in front of the superior articulating process of the succeeding vertebra before they can escape through their respective foramina. In tliis respect they exactly resemble alL the other spinal nerves. Hie Superior Laminae and the Spinous Process. — Sloping downwards very considerably from the lower border of the articulating process and from the thick pedicle is the broad, flat lamina which generally though not invariably meets its fellow of the opposite side to form a rudimentary spinous process. These laminse are so much sloped downwards and backwards that a large space leading into the spinal canal is 104 THE LIGAMENTS AND JOINTS WHICH CONNECT left between the last lumbar vertebra and tlfe first sacral. The spinous process is often fused with the corresponding processes of the second and third segments of the sacrum so as to form the sacral crest. In the lower segments of the sacrum the laminae and spines are deficient, and the spinal canal is completed behind by ligaments only. The lateral mass of the sacrutn is formed by the amalga- mation of the transverse processes of the sacral vertebrae, those of the upper three bones being much exaggerated in size. On the front aspect of the bone are seen five horizontal ridges homologous with the anterior roots of the transverse processes of the cer\dcal vertebrae. These ridges extend outwards from the bodies of the sacral segments and are merged into the lateral mass on each side, and like the anterior roots of the cervical transverse processes they are on nearly the same plane as the front surface of the bodies from which they spring. In the first sacral vertebra this anterior portion of the transverse process is a broad, rounded, thick mass, the upper surface of wliich forms an important part of the base of the sacrum, and over it passes the anterior primary branch of the fifth lumbar nerve and below it the anterior primary branch of the first sacral nerve. In each succeeding vertebra the anterior portion of the process assists in forming the boundary of two anterior sacral foramina, and over each passes the anterior primary branch of a sacral nerve. That of the fifth vertebra is thin and short, and passes obliquely outwards and upwards to terminate at what is caUed the angle of the lateral border of the sacrum. This process forms with the transverse process of the coccyx a deep notch traversed by the anterior primary branch of the fifth sacral nerve. On the posterior aspect of the sacrum are seen the amalga- mated posterior roots of the transverse processes. That of the first segment projects in front of and frnther from the middle line than the superior articulating process. It is separated from the latter, as previously stated, by a deep sulcus, along which courses the posterior primary branch of the fifth lumbar nerve. Those of the other segments are represented by a row of tubercles situated vertically one above the other on the outer side of the posterior sacral foramina. By comparing the sacrum with the vertebrae in other parts of the spinal column, the formation of the lateral masses and THE VERTEBsJAL COLUMN WITH THE PELVIS. 105 of the foramina, as well as the course of the anterior and posterior sacral nerves, becomes apparent. If on looking to the cervical region in the articulated skeleton one imagines a mass of bone interposed between the tips of the transverse processes of any two contiguous vertebrae, one sees that two foramina would be formed by each mass. One of these would be seen from the front at the side of the body of each vertebra through which the anterior primary branch of the cervical nerve would pass ; and the other would be seen from behind between the superior articulating process and the posterior tip of the transverse process, or rather the portion of the lateral mass formed thereby. Through the latter the posterior primary branch of the same nerve would pass. Each of the primary branches of the cervical nerves would then have reached its foramen by passing over the pedicle of the vertebra below it, as is the case in each region of the spine, while a lateral mass on the outer side of the foramina would be formed which would exactly correspond to the condition of parts in the sacrum. The double root of the transverse processes, together with a large deposit of bone in place of the vertebral foramen (sug- gestive of the condition which aids in the formation of the sacral lateral mass), is seen in the case of the transverse pro- cess of the fifth lumbar vertebra. The Ligaments of this union are of two kinds, viz., (1) those connected with the sacro-lumbar articulations, and which may be called therefore the articular or intimate ligaments ; and (2) those extending between non-articular portions of the bones, and which therefore may be called additional or accessory ligaments. 1. The articular ligaments which unite the sacrum, and through it the pelvis, to the fifth lumbar vertebra, are of exactly the same character as those which connect the vertebrse with each other. First, there is the amphiarthrodial joint, formed by the intervertebral substance and the bodies of the fifth lumbar vertebra and first segment of the sacrum, together with the anterior and posterior common and short intervertebral liga- ments of the column. Secondly, there are the two arthrodial joints, formed by the contiguous articular processes and the capsular ligaments surrounding them. These joints do not require separate description ; it is only necessary to remark that the intervertebral substance between the fifth lumbar 106 THE SACRO-LUMBAR LIGAMENT. vertebra and the sacrum is niucli thicker than any other, and is much thicker in front than behind. 2. The accessory ligaments also correspond to others wliich are present in the various regions of the vertebral colimin ; only two of them require special notice. They are — First, the hgamenta subflava between the laminae of the vertebra and the sacrum. Secondly, the interspinous and supra-spiuous ligaments between and upon the spine of the vertebra and crest of the sacrum. Thirdly, the sacro-kmibar ligament, a representative of the inter- transverse, extends between the transverse process of the ver- tebra and the non-articular portion of the base of the sacrum. Lastly, the ilio-lumbar hgament extends between the fourth and fifth lumbar vertebrae and the crest of the ilium. It is a representative of the stellate ligament of the dorsal region, for the ossa innominata, homologically considered, constitute the visceral arches of the pelvis as the ribs do of the thorax and abdomen. TJie sacro-lumhar ligament is strong, and assists very mate- rially in binding together the pelvis and the spinal column. It attaches the transverse process of the fifth lumbar ver- tebra to the sacrum and ilium. It is triangular in shape, with its apex internal and above, and its base external and below, at the iliac fossa. At the spine, the ligament is attached to the lower border, from base to tip, of the transverse process, as well as to the pedicle and body of the fifth lumbar vertebra : it is intimately blended with the ilio-lumbar liga- ments at their origin. Below it has a wide fan-shaped attach- ment extending from the edge of the ilio-lumbar ligament forwards to the brim of the true pelvis ; behind it reaches a Httle further back than the posterior edge of insertion of the ilio-lumbar hgament to the iliac crest ; elsewhere it is blended with the periosteum of the base of the sacrum, with the superior sacro-ihac ligament and with the periosteum of the ilium, into which it gTadually fades away along the iliac fossa. This ligament limits externally the sacro-limibar interverte- bral foramen {i.e., the intervertebral foramen for the last lum- bar nerve) by means of a sharp thin border which, descending gradually and in a gentle curve to the base of the sacrum, passes along the brim of the true pelvis and blends with the periosteum, wliich is there very thick. It is pierced by two large foramina, which transmit arteries into the sacro-ihac joint; PLATE XI. THE ILIO-LUMBAR LIGAMENT. 107 one of these is a little in front of tlie ilio-lumbar ligament, the other penetrates the middle of the upper border of the sacro- iliac synchondrosis. The ilio-lumbar is a strong dense ligament of a triangular shape, having its apex at the spinal column when looked at from behind, and at the ilium when seen from the front. At the ilium, one of its surfaces looks backwards and upwards, the other forwards and downwards towards the iliac fossa ; near the spine the surfaces are almost directly forward and backward. Thus the ligament gets somewhat twisted on its own axis as it passes outwards, so as to form more and more a transverse instead of a vertical plane as it approaches its insertion into the crest of the ilium. At the spine it is connected with the front surface of the transverse process of the fifth lumbar vertebra as far inwards as the body of that bone, and by a strong fasciculus with the posterior surface near the tip of the same process ; also with the lower edge and front surface of the transverse process and the pedicle of the fourth lumbar vertebra as far inwards as the body; sometimes, too, a strong slip springs from the inferior articular process of the fourth vertebra. At the pelvis the hgament is attached to the inner lip of the crest of the ilium for two inches, extending as far forwards as a spot four inches in front of the posterior superior spine of the ilium. The highest fibres at the vertebral column form the anterior edge of the hgament at the pelvis, while those which spring from the back of the transverse process of the fifth lumbar vertebra incline a Httle backwards as they pass outwards to form the posterior edge of the ligamient at the pelvis. Many of the fibres wliich arise from the front of the transverse process of the fifth lumbar pass almost horizontally outwards to their insertion into the iliac fossa. When looked at from in front, the ligament appears to have three borders, owing to the twisting of the fibres on the axis of the ligament itself. The lower one is adjacent to the upper edge of the sacro-lumbar ligament and is horizontal in direc- tion ; the upper border is oblique and from it the quadratus lumborimi arises, and to it the anterior layer of the lumbar fascia is attached ; the inner border is crescentic, with its concavity looking inwards towards the median Hne; it forms the outer boundary of the foramen through which passes the 108 THE ARTERIES, NERVES, AND MUSCLES anterior primary branch of the fourth lumbar nerve. The anterior surface of the ligament forms part of the posterior boundary of the cavity of the false pelvis above ; and below closely overlies the upper part of the posterior sacro-iliac ligament; the posterior surface looks towards the sacral por- tion of the spinal groove, the floor of which it helps to form, and it gives origin to the multifidus spinas muscle. At the transverse process of the fifth lumbar vertebra the Ilio and sacro-lumbar ligaments are interwoven with one another ; some of the fibres of the former decussate with some of those of the latter, and spread downwards upon the side of the body of that vertebra ; other fibres of the ilio-lumb^r radiate upwards beyond the body of the fifth vertebra, upon the fourth intervertebral substance. The portion of the ilio-lumbar wliich arises from the fourth transverse process is inseparably connected with the inter- transverse ligament, between the fourth and fifth lumbar vertebrae. Arteries. — There is a very free blood supply on all sides to the structures forming the sacro-vertebral union. To the amphiarthrodial joint, the lateral sacral, ilio-lumbar, and last lumbar give off twigs which pass between the fibres of the ligaments to enter directly into the bodies of the bones and reach the intervertebral substance ; on the posterior aspect, branches pass beneath the posterior common ligament from the arteries of the spinal canal. The arthrodial joints formed by the articulating processes are supplied by vessels entering the spinal canal through the intervertebral foramina, and by the bloodvessels of the muscles wliich arise from the articular processes and laminae. Nerves. — The nervous supply to these joints is derived from the sympathetic, and from twigs of the fourth and fifth lumbar nerves. Muscles. — The muscles which arise from, or which are in relation with, the structures belonging to the lumbo-pelvic union, are the following : — Psoas. — This muscle arises from the lumbar vertebrae, in- cluding the fifth, and the intervertebral substance between it and the sacrum, as well as from the ilio-lumbar ligament. Transversalis, — The anterior layer of the posterior aponeu- rosis of this muscle, which separates the quadratus from the OF THE SACRO-VERTEBRAL UNION. 109 psoas, is connected with the transverse process of the fifth lumbar vertebra and with the ilio-himbar ligament. Quadratus luinborum, which arises from the ilio-liimbar ligament, and from the transverse process of each of the lowest three lumbar vertebrae. Multifidus spince, which arises from sacrum, ilium, sacro-iliac, and ilio-lumbar ligaments, as well as from the mammillary pro- cess of the fifth lumbar vertebra. Erector spince, especially the longissimus dorsi portion of it. This latter arises by tendons from the accessory processes, and by fleshy slips from the whole length of the transverse pro- cesses of the lumbar vertebrae, as well as from the sacrum and lumbar aponeurosis. Latissimus dorsi, which through the medium of the pos- terior layer of the lumbar aponeurosis is attached to the spines of both sacrum and fifth lumbar vertebra. Movements. — The angle formed by the sacrum with the spinal column is called the saero-vertehral angle. The pelvic inclination does not, as has been supposed by some, depend entirely on this angle, but in great part upon the obliquity of the innominate bones to the sacrum, so that in males, in whom the average pelvic obliquity is a little greater, the average sacro-vertebral angle is considerably less than in females. The sacro-vertebral angle averages 117° in the male, 130° in the female, while the pelvi-vertebral angle — i.e., pelvic incli- nation — averages 155° in the male, 150° in the female. The smaller sacro-vertebral angle in the male shows that there is a gTeater and more sudden change of direction in the sacro-vertebral union than in the female. A part of this change of direction is attributable to the greater thickness in the forepart of the intervertebral substance between the last lumbar vertebra and the sacrum. In both females and males this substance is thicker than any of the others, and thus a greater amount of movement is permitted between those bones than between any two of the lumbar or dorsal vertebrae. The central soft portion of the intervertebral substance is the centre of movements ; it is, in fact, the ball upon which those bones revolve, and upon the thickness and amount of this substance the extent though not the direction of those movements depends. So far as this centre of movement is concerned, the motion may take place in any direction. The movements 110 THE MOVEMENTS AT THE SACRO- VERTEBRAL UNION. resemble, but are somewhat less limited than, tbose which occur between any two of the lumbar vertebra. As the diameter of the contiguous bones is less in an antero-posterior than in a transverse direction, the backward and forward movements are freer than the lateral. These backward and forward move- ments take place each time the sitting is exchanged for the standing position, and vice, versd. In rising from the sitting position the back is extended upon the pelvis at the sacro- lumbar union, and the pelvic inclination is also no doubt some- what increased at the sacro-iliac joints by the action of the erector spinse muscles. In sitting down the reverse move- ment takes place — i.e., there is a forward movement at the sacro-lumbar joint. The lateral movement — i.e., flexion from side to side — is also more free between the sacrum and fifth lumbar vertebra than between the lumbar or dorsal vertebrae. The articular processes provide for the gliding up and down of these contiguous surfaces of the two bones in the extension, flexion, and lateral movements which are permitted upon the intervertebral substance. Further, they allow also of some amount of horizontal movement necessary to the rotation of the pelvis on the spinal column, or of the spinal column on the pelvis. If the inferior articulating processes of the last lumbar vertebra be examined critically, they will be seen to differ considerably from the inferior processes of the rest of the lumbar vertebrae, and to resemble somewhat in direction the corresponding' processes of the cervical vertebree ; while the superior articulating processes of the sacrum differ to a similar degree from the superior processes of the lumbar vertebrge. This difference provides for the freer rotation which is possible at the lumbo-pelvic than at the interlimibar joints. Ill CHAPTEE VII. LIGAMENTS AND JOINTS OF THE PELYIS. By the term "pelvis" is meant the portion of the skeleton formed by the sacrum, coccyx, and ossa innominata. The space enclosed by these bones is called the " cavity of the pelvis." The relations of the pelvis to the vertebral column and to the lower Lmabs should be carefully studied, because it is through the pelvis that the weight of the trunk is transmitted to the extremities, and because it is at the femoro-pelvic joints, i.e., the hip-joints, that the chief movements of the trunk occur. The sacnmi, which is situated at the back of the cavity, and which very largely enters into the formation of the pelvis, is sometimes described as a part of the vertebral column. Like the coccyx, it is an imperfect continuation of the spine, at the lower extremity of which it is placed. It may indeed be regarded as the base of the spinal column of which the head is the capital. Along the bone there runs a canal, complete above, though imperfect below, for the lodgment and protection of the cauda equina. The anterior and pos- terior sacral foramina are in communication with this canal, and out of them pass the anterior and posterior primary branches respectively of the sacral spinal nerves. Also through the first three segments of the sacrum, as through the vertebra of the lumbar and other regions of the column, the superin- cumbent weight of the body is transmitted. Thus in function, as well as in homology of parts and structm^e, the sacrum is fairly considered a part of the column. Again, the occipital bone, in so far as it is traversed by the meduUa oblongata and transmits the weight of the parts above to those below it, may be looked upon as a modified vertebra, just as the sacrum is regarded as an amalgamation of several modified vertebrae. On the other hand, as the tliree upper segments of the sacrum transmit the weight of the body, not. 112 LIGAMENTS AND JOINTS OF THE PELVIS. as do the vertebrae above them, to the segments below, but to the ossa innominata at their sides ; and as they have a very- firm connexion with the innominate bones, the whole sacrum may be considered as entering as completely into the formation of the pelvis as the occipital bone does into that of the cranium. For the above reasons the sacrum is here described as belonging to the pelvis, and the union between the spinal column and the pelvis as being between the last lumbar vertebra and the sacrum. This union is called the sacro-lumbar, and an account of it has been given in the preceding section under the "ligaments and joints which connect the vertebral column with the pelvis." The sacro-iliac joint is described further on in this chapter. With reference to the union of the pelvis with the lower extremities, it must be noticed that the hip-joints are the chief means of connexion between the trunk and the thighs. In this respect there is a remarkable difference between the upper and lower limbs. The former being required for a wide range of swift and free, and sometimes forcible movements, are con- nected with the trunk principally by means of muscles. These muscles are of great size and area, pass from both the anterior and posterior surfaces of the body to the arms and shoulders, and extend over the whole length of the back and neck, be- tween the occipital and temporal bones above and the sacrum and ilium below. The only articular or osseous connexion which the upper limbs have with the trunk is at the sterno- clavicular joint. The lower limbs, on the contrary, are united with the trunk principally by means of the strong capsular Kgaments of the hip-joints, especially their upper and outer portion, and by the deep articular cups into which the heads of the thigh bones are fitted ; while, with the exception of the psoas, all the muscles which pass from the trunk to the legs arise from one or more of the pelvic bones. Moreover, the ossa innominata or haunch bones, which are the homologues of the clavicles and scapulae, enter so largely into the construction of the pelvis, are so firmly fixed to the sacrum and to one another, and so immovable with respect to the lower limbs, that they are generally regarded as part of the trunk, and not as belonging to the extremities. On the other hand, the clavicle and scapulte form no portion of the trunk, while they move SOME GENERAL FEATURES OF THE PELVIS. 113 freely with the rest of the upper limbs, and are therefore always considered as segments of them. This difference between the arms and legs with respect to their connexion with the trunk pertains throughout the whole class of mammalia. In connexion with the pelvis there are no less than nine joints. As originally the sacrum was formed of five segments and the coccyx of four, there were of course foiu^ articulations special to the former and three to the latter ; as a matter of fact, the seg- ments of the coccyx often remain separate until very late in life ; but for a description of the joints of the pelvis it suffices to consider the sacrimi and coccyx as two complete and sepa- rate bones. First, we have the articulation of the pelvis proper with the vertebral column, consisting of three distinct " sacro-lumbar" joints. Secondly, the os innominatum articulates with the side of the sacrum at the sacro-iliac symphysis. Thirdly, the sacrum forms with the coccyx the sacro-coccygeal joint. Fourthly, the ossa innominata are joined together at the pubic symphysis. Lastly, the -pelvis is supported upon the thighs at the hip-joints. Excluding, however, the sacro-limibar union and the hip-joints four articulations remain which belong to the pelvis proper. These are the two sacro-iliac, the pubic, and the sacro-coccygeal articulations ; they all belong to the class of mixed or fibro-cartilaginous joints called " amphiar- throsis." The sacro-iliac synchondrosis and pubic symphysis are frequently described as presenting two separate plates of incrusting cartilage, with a small synovial space between them. This condition I have not myself found to exist as a rule ; but where it does, the joint ought to be considered as " arthrodial" instead of " amphiarthrodial." Besides their connexion at the joints, the sacrum and coccyx are bound to each other and also to each innominate bone, by means of the sacro-sciatic ligaments. As, however, these liga- ments are more extensively attached to the sacrum and os innominatum than to the coccyx, the description of them is given with the sacro-iliac synchondrosis. Before describing the joints of the pelvis proper, in detail, attention will be first directed to some general features of the pelvis as a whole. By means of its four joints and additional ligaments, the four bones of the pelvis are bound together with sufficient firmness and strength as to be able to support great I 114 SOME GENERAL FEATURES OF THE PELVIS. weight with steadiness and security ; the bones so united form an arch along which the weight is transmitted to the lower limbs ; the joints in vu-tue of their elasticity and the move- ments they permit, act as springs or buffers to prevent shocks ; the pelvis affords a fixed point for the attachment of numerous and powerful muscles, and strong and extensive fascise ; and provides the sockets whereat the trunk moves with fi-ee and varied movements upon the buttresses which support , the pelvic arch. Further, its admirable arcliitectural arrangements are designed to adapt our frames for the erect posture ; consequently the mechanism of the human pelvis differs considerably from that of other animals, none of which, not even the apes, can with ease or for any length of time maintain the erect position, but support themselves on their fore-legs even when they rest upon their haunches. But this is not all ; the cavity enclosed by the pelvis serves to protect, and in some way to support movable and distensible viscera, and forms a short canal through which the fcetus passes in parturition. There is necessarily a marked difference in character between the inner and the outer surfaces of the pelvis. Internally it is very smooth : the bodies of the sacral vertebrse recede from instead of standing forward in the middle line of the cavity, which they assist in bounding, as do the bodies of the dorsal and lumbar vertebrse ; there are no rough inequalities or irregularities of the bony wall like the ridge of the petrous bone and the lesser wings of the sphenoid on the inner surface of the cranium ; and the ligaments are much thinner than those on the outer surface, and though they assist in holding the several bones together, are little more than greatly thickened periosteum, extending from one to the other. These ligaments form a smooth covering for the margins of the articular surfaces of the bones, without encroaching at all upon the capa- city of the canal. Externally the bones of the pelvis are rough and uneven, and the ligaments thick, fasciculated, and irregular. Everything seems to be subsidiary to strength and to the ad- vantageous attachment of muscles of the spine, of the abdomen, and of the lower limbs. For this latter purpose the arch or ring of the jDelvis is expanded into outstanding processes ; two of these, viz., the ilia, ascend, and by their outer surfaces and borders give rise to the abdominal and gluteal muscles ; two project downwards, viz., the ischial tuberosities, and from THE MECHANISM OF THE PELVIS. 115 tliem muscles arise whicli act upon the lower limbs ; and one curves downwards and forwards, viz., the coccyx, and gives attachment to part of the sacro-sciatic ligaments. Behind the ossa innominata overhang the posterior and rugged surface of the sacrum, and help to form a deep gToove on either side of the middle line. In the recent state this is filled up by strong muscles of the back, so that the upper portion of the sacrum is deeply placed below the surface ; the last two segments only are superficial, and the fourth is the most posteriorly projecting portion of the pelvis. The descending processes surround what is called the inferior strait or outlet of the pelvis ; the ascending bound the cavity of the false pelvis. The Mechanism of the Pelvis. — The essential feature of the mechanism of the pehds is the arches which are formed for the transmission of the weight of the body to the points upon which we stand and sit. In each case the sacrum, which supports the lumbar vertebrae, forms the key-stone of the arch ; and the innominate bones as far as the acetabula, the pendentives, or voussoirs : in the erect attitude, the piers of the arch are the thigh bones, whilst in the sitting position they are the tuberosities and bodies of the ischia. When we stand upright, the pendentives, i.e., the innominate bones, join the piers, i.e., the heads of the thigh bones, at the strongest and deepest part of the waU of the acetabulum, viz., its upper portion. When we sit, the pendentives join the piers, i.e., the ischia, nearly at the same spot, but a little below the deepest part of the socket. The position of the tuberosity of the ischiiun is such, that its narrow anterior and lower extremity is in nearly the same vertical line as the posterior edge of the cotyloid notch of the acetabulum, and its thick and broad posterior and upper extre- mity is vertically below the thick outer wall of the acetabulum. Thus, while the pendentives of both the standing and the sitting arches extend between the acetabuliun and the sacro-iliac joint, and are almost identical, the piers of the sitting arch are on a slightly posterior plane to the piers of the standing arch. The latter may be called the femoro-sacral and the former the ischio-sacral arch. These arches are wider, and consequently weaker, in the female than in the male ; the greater interval be- tween the piers in women explains their somewhat waddling gait. I 3 116 THE MECHANISM OF THE PELVIS. Wlien very considerable strength is requisite in an arcli it is continued into a ring, so as to form a counter-arcli, or what is called a tie is made to connect together the ends of the arch, and thus to prevent them from starting outwards. By these means a portion of the superincumbent weight is conveyed to the centre of the counter- arch, and borne in what is called the sine of the arch. The body and horizontal rami of the pubis form the tie or counter-arch of the femoro-sacral, and the united rami of the pubis and ischium the tie of the ischio-sacral arch. Thus the ties of both arches are united in front at the symphysis pubis, which like the sacrum or key-stone is common to both arches. Through the tie, thus formed, of the ischio-femoral arch, the force which tends to push the extremities of that arch up- wards and forwards while we sit is conveyed to the symphysis pubis, and thence b&,ck along the horizontal rami of the pubis, so that the weight of the trunk is distributed throughout the whole ring of the pelvis. The tie of the femoro-sacral arch not only strengthens that arch itself but resists, at the symphysis pubis, the upward and inward pressure of the heads of the thigh bones at the acetabula. The symphysis pubis is, in fact, the centre of the counter-arch which the anterior portion of the pelvis forms to both the femoro- and the ischio-sacral arches. This explains how it is that so much strain is made upon the sym- physis when any increased weight has to be supported by the pelvis, as in pregnancy; why there is such powerlessness, with inability to stand or sit, in cases in wliich this joint is weakened or diseased ; and why the anterior portion of the pelvis yields under the weight of the body, and becomes deformed in rickets and moUities ossium. In connexion with the femoro-sacral arch, it should be noticed that though the middle portion of the wing of the ilium is thin enough to transmit light, the anterior portion is very thick, and forms quite a strong rib of bone, ascending from the aceta- bulum to the crest of the ilium. Along this rib of bone part of the direct vertical pressure of the head of the femiu* is con'- veyed to the iliac crest, and thus indirectly to the sacro-iliac ligaments and the sacrum, as well as to Poupart's ligament and the pubic sjnnphysis. The ring formed by the sacrum, the ilia, and the pubes is called the brim of the pelvis, and the area it encloses is called the inlet or the superior outlet of the. pelvis. The THE MECHANISM OF THE PELVIS. 117 portion of the brim which is formed by the iHum and pubis on each side is called the linea ilio-pectinea. This bony ring is not circular but somewhat heart-shaped, with its inden- tation at the sacrum, the base of which encroaches upon the cavity of the pelvis behind, and constitutes what is called the promontory of the sacrum. The apex of the emblematical heart-shaped outline is at the symphysis pubis. The ring is a well-rounded edge or border which divides the expanded cavity of the false from the more contracted cavity of the true pelvis. As was stated previously, the pelvis is formed by four bones, and these all assist in bounding the cavity of the true pelvis. Into the wall of the false pelvis the coccyx does not enter at all, nor does the sacrum except the lateral masses of its base which are du-ected forwards and upwards. In the middle line in the articulated skeleton appears the body of the fifth lumbar vertebra, which with the lumbo-pelvic ligaments fills up the space otherwise left between the crests of the iMa. It should be also noticed that there is a striking difference in the thickness and strength of different parts of the inno- minate bones, and that while some portions — such, for instance, as the wings of the ilia and the floor of each acetabulum — are so thin as to transmit light, yet all portions along which weight is borne are very thick and strong. The sacrum rapidly diminishes in thickness from above downwards, and chiefly at the expense of its anterior sm-face, though its posterior surface suffers as well, especially in the deficiency of spinous processes and prominent laminee. The weakest points in the pelvis are at or near the junction of the key-stone with the pendentives, at the centre of the counter-arch, and on each side of the latter. Such, however, is the strength of the uniting ligaments, and so firmly is the sacrum, by its doubly wedged shape, locked in between the ossa innominata, that it is a very rare thiag for dislocation to occur, although the bones are sometimes fractm^ed by accidents. The pelvic arches, besides being rigid curves for supporting weight, are also elastic springs to break shocks, and so to preserve the viscera and nerve centres from concussions. The buffer-like cartilages in the sacro-iliac and pubic articulations ; the lateral as well as the antero-posterior curve of the sacrum ; the forward direction of the base of the sacral wedge ; and the 118 THE MECHANISM OF THE PELVIS. obliquity of the pelvis to tlie vertical and horizontal planes of the J)ody, are all conducive to the elasticity of the pelvis. The sacrum, owing to its shape and oblique position, has a tendency to turn round an axis, passing transversely tlu'ough the sacro-iliac joints in such a manner that forces acting on the sacro-vertebral union would, but for the ligaments of the pelvis, throw the promontory of the sacrum downwards and forwards, and tilt the apex of the sacrum and the coccyx up- wards and backwards. This tendency could not have existed had the base of the sacrum not been narrower behind than in front. To counteract this tendency there are two very strong and elastic springs, one acting on the sacro-lumbar, and the other on the sacro-coccygeal curves formed by the ilio-lumbar and posterior sacro-iliac ligaments and by the sacro-sciatic ligaments respectively. The ilio-lumbar ligament, which passes backwards and outwards to the crest of the ilium, holds up the last lumbar vertebra, and with it the base of the sacrum, which is thus prevented from rota- ting forwards ; the sacro-sciatic ligaments passing downwards, forwards, and outwards prevent the apex of the sacrum fi-om tilting backwards and upwards ; but though by these provisions any undue amount of movement is checked, a con- siderable amount of elasticity is provided. The obHquity of the pelvis is another means for increasing the power of breaking shocks by enabling forces applied from below to become distributed throughout the pelvic ring instead of being conveyed at once to the vertebral column, as they must have been had the pelvis occupied a more vertical position. This obliquity is considerable. A line drawn from the promontory of the sacrum to the upper border of the symphysis pubis forms with a line drawn through the chords of the curves of the spinal column an angle of 150° to 155 , and the same antero-posterior line forms with the horizon an angle of from 55° to 60°. These which are sometimes spoken of as the angles of inclina- tion of the pelvic brim, are greater in man than in woman, and about the same in the infant of both sexes as in man. There is in the vertebrate kingdom a great variety in the degree of obliquity of the pelvis to the spinal column ; and it may be stated as a pretty general rule, that those animals which have the greatest strength have their pelvis placed THE BONY WALL OF THE PELVIS IMPERFECT. 119 nearly vertically, i.e., the openings of the cavity of the pelvis are nearly horizontal, and their thigh bones make nearly a right angle with the pelvis ; and that those possessed of great speed have their pelvis almost horizontal, i.e., the apertures of the cavity of the pelvis are nearly perpendicular, and their thigh bones make a much more acute angle with the pelvis. In the apes the thigh bones form an obtuse angle with the pelvis. In man, whose pelvis is stronger in proportion to his size than that of any quadruped, the angle of inclination is such that the transverse vertical plane through the bodies of the axis and last lumbar vertebra passes through the acetabula, and the thigh bones in the erect posture deviate but little from the axis of the vertebral column. The centre of gravity of the whole body is in tliis vertical plane at a spot just above the sacro-lumbar angle, and is exactly over the mid-point of a line between the heads of the femora, i.e., the piers of the femoro- sacral arch. In the erect posture the piers of the ischio-sacral arch, i.e., the ischial tuberosities, are somewhat behind the transverse vertical plane ; but in sitting upright, owing to the slight flexion of the pehds on the spine at the sacro-lumbar union, they are brought within the plane through which the line of gravity falls. If it be remembered that the coccyx is so situated that its tip is a little higher than the lower border of the symphysis pubis, it will be seen at once that the trunk does not (except when thrown far back) rest on a tripod formed by the ischial tuberosities and the coccyx when we are sitting down, as it was erroneously stated to do by some of the older writers. So far forwards does the sacro-lmnbar union project, and so great is the curve of the sacrum, that a line let fall from the front surface of the third lumbar vertebra strikes the upper surface of the symphysis pubis. The inclination of the pubis is such that it helps by its inner surface, which looks upwards as well as backwards, to support some of the abdominal viscera, and during the latter months of pregnancy the en- larged uterus rests upon it in part. Bony Wall of Pelvis imperfect. — In connexion with the parturient state, it is a fact of gTcat importance that no portion of the cavity of the true pelvis has a bony wall completely surrounding it. Opposite nearly the whole length of the sacrum and on the same horizontal plane with it, is the front 120 THE MUSCLES CONNECTED WITH THE PELVIS. wall of the hypogastric region of the abdomen. Opposite to, and on the same horizontal level as the smooth and sloping but extensive plane of bone forming the floor of the acetabulum, are the sacro-sciatic foramina and ligaments, and the obturator foramina. The latter as well as the lower part of the great sacro-sciatic foramina are also on the same horizontal plane as the bodies of the pubes and the pubic symphysis. Moreover, it is a significant fact that the upper border of the symphysis pubis is in the same horizontal plane as the upper segment of the coccyx, while the lower border is a few lines below the lower extremity of the coccyx. Thus the only portion of the anterior wall of the true pelvic cavity, which is formed by bone, has opposite to it the only really movable bone which enters into the formation of the pelvis, viz., the coccyx, the movement of the different segments of which on one another, and of the first segment upon the sacrum, generally remain free until a late period of life. By this movement, which is a backward one upon a transverse axis, at least an extra inch is gained in the antero-posterior diameter of the outlet ; when the head of the fcetus has passed into the sub-pubic arch, it is below the level of the coccyx, and the posterior boundary on the horizontal level of the rami of the pubis and ischium is formed by the soft structures of the perineum. In no horizontal plane therefore does the pelvis form a complete bony and unyielding ring, but everywhere the resisting bony portion has opposite to it one and often two or three soft and yielding arcs in the boundary of the cavity. These points have hardly received the attention they merit in the study of the mechanism of parturition. The Muscles in eo7inexion with the Pelvis. — It has been already stated that one of the leading functions of the pelvis is to afford a fixed point for the attachment of muscles. The nmnber to which it gives origin is very large and their im- portance is very great. They may be divided, according to their action upon different parts of the body, into two classes — viz., the muscles of the trunk, and the muscles of the lower limb. 1. The muscles of the trunk may again be divided into those of the spine, those of the abdomen, and those of the perineum. A. The spinal group consists of the multifidus spinas, the inter-spinalis attached to the upper part of the sacral crest ; according to some anatomists, the extensor coccygis to the THE FASCIA. CONNECTED WITH THE PELVIS. 121 lower part 'of the sacnim and to the coccyx ; the erector spinse ; and the latissimus dorsi, which, besides having a considerable attachment to the iliac and sacral crests and the vertebral spines, extends beyond the trunk to the bicipital groove of the humerus. B. The abdominal group includes the external and internal oblique and the transversalis, the quadratus lumborum, the rectus and pyramidalis, and the psoas parvus when present. C. The perineal group may be subdivided into two, the genito-urinary and the anal. (a.) The genito-urinary. set includes in the male the trans- versus perinsei, the ischio-cavernosus or erector penis, the deep transversus perinsei, and the constrictor urethrse. In the female the muscles of this gToup arising from the pelvis are the same as those in the male, except that there is no constrictor urethrae, and the erector clitoridis is a diminutive representative of the erector penis. (6.) The anal group consists of the levator ani, the coccygeus, and the external sphincter ani. 2. The muscles of the lower extremity are enumerated further on, and are classed under five heads — viz., the flexors, extensors, adductors, abductors, and rotators of the thigh. In addition to the muscles several important fascice get their firm attachment at the pelvis. They are (1) the lumbar fascia, consisting of three layers, the posterior of which is called the vertebral aponeurosis, and is attached to the sacral spines, to the lower part of the posterior surface of the sacrum, and to the posterior half of the iliac crest ; the middle layer is the external or more superficial stratum into which the posterior tendon of the transversalis muscle splits ; it separates the erector spinas from the quadratus lumborum, joins with the posterior layer at the outer border of the former, and with the deep or anterior layer at the exterior edge of the latter muscle, and is fixed to_ the tips of the transverse processes of the lumbar vertebrae and to the inner lip of the iliac crest between the transversalis and iliacus mascles. The anterior or deepest stratum of the fascia lumborum is the anterior layer of the transversalis tendon ; it separates the quadratus from the psoas muscle, and is attached to the iliac crest, to the ilio-lumbar ligament, and to the roots of the transverse processes of the lumbar vertebrae. 122 MOVEMENTS OF THE PELVIS AS A WHOLE. (2) The abdominal fascise — viz., the fascia transversalis which is connected with the inner lip of the crest of the ilium, with the pectineal line, and with the spine and crest of the pubis ; and the fascia iliaca which is attached to the brim of the pelvis, the base of the sacrum, the crest of the ilium, and the ilio -lumbar ligament. 3. The fascia lata of the thigh, which is attached nearly all around the margin of the innominate bone on its outer surface, and separates the muscles going to the leg from those belonging to the trunk. 4. The pelvic fascia is connected. with the promontory and anterior surface of the sacrum and with the brim of the true pelvis. It blends with the periosteum, the anterior sacro-iliac ligament, and the iliac fascia. Along the origin of the levator ani it separates into the recto-vesical and obturator fasciae. 5. The perineal fascise are deep and superficial. The super- ficial covers in the anterior perineal region, and is united behind with the deep fascia ; but in front it passes into the superficial fascia of the abdomen. The deep perineal fascia, or triangular ligament, is composed of the anterior and posterior layers, be- tween which pass several important structures, including the membranous portion of the urethra. The lumbar, iliac, and pelvic fasciae exercise some influence in holding the sacrum and iimominate bones together, and add to the security and strength of the pelvis. The Movements of the Pelvis. — The pelvis moves upon the spinal column at the sacro-lumbar articulations, i.e., sacro- vertebral union ; and upon the thighs at the hip-joints. The movements which occur at the sacro-lumbar joints have been described at the end of the last chapter. It was there stated that they consist of slight forward and backward as well as of lateral inclination ; and also of some amount of rotation upon a vertical axis. The lateral movements of the spinal column upon the sacrum can be appreciated by firmly sitting upon a hard seat and bending the body from side to side ; the tuberosities of the ischia thus remaining in the same place, the pelvis as a whole is kept immovable, while the lowest part of the column moves upon the sacrum, and the lower lumbar vertebras upon one another. The forward and backward, or flexion and extension move- ments upon a transverse axis, takes place each time the body MOVEMENTS OF THE PELVIS UPON THE THIGHS. 123 passes from a standing into a sitting, or from a sitting into a standing position. The pelvic inclination is increased — i.e., a backward or extension movement of the pelvis on the spine occurs — each time the sitting is converted into the standing posture, and a flexion movement each time the standing is exchanged for a sitting attitude. These movements are similar to, though con- siderably less free than, the flexion and extension of the head on the spine in looking up or down. 2. The pelvis moves upon both thigh bones at the same time, or upon one at once. The movements upon the heads of both bones at the same moment consist of flexion and extension only. This flexion takes place in a forward direction upon a transverse axis through the heads of the femora. Extension beyond the erect position is prevented by the strong anterior portion of the capsular ligament, by the " vasto-rectal" tendinous band of the capsule, and by the mechanical (not the contractile or vital) influence of the ilio-psoas muscle, all of which are quite tight when the trunk is fully extended. It is an important feature in the construction of the human figure, mth regard to its adaptation for the erect position, that when the body is upright further rolling of the trunk backwards is thus checked without the expenditure of muscular force, and in a similar manner forward rotation at the knee-joint — i.e., of the tibia upon the condyles— is prevented, and the erect posture main- tained, not by muscular action, but by the restraining influence of the posterior ligament (ligamentum Winslowii), and the crucial ligaments of the knee. The only direction in which the trunk can be moved from the upright position at the hip-joints when both feet are on the ground, is forwards ; and the only direction in which the thighs can be moved upon the tibisB when both feet are on the ground, is backwards. Hence the tendency to fall forwards in epilepsy, or fainting, or intoxi- cation, owing to the failure of the muscles which act to keep the trunk iipright upon the thighs ; and hence too the tendency to drop backwards on to the buttocks when the control over the muscles about the knee is destroyed. The movements of the pelvis upon one thigh can take place in almost any direction, as the hip-joint is of the ball and socket kind ; these movements are limited by the means which will be described under the head of the Mip-Joint. To effect the several movements, as well as for the purpose of securely ] 24 MOVEMENTS OF THE PELVIS UPON THE THIGHS. balancing the trunk in any position upon one femur, muscles surround the hip-joint, and extend from the several bones of the pelvis to some point of the thigh or leg bones. They may be classed in five groups according to their functions, and according to their situation at the pelvis with reference to a vertical line dra^m through the acetabulum. The Jiexors of the trunk are situated in front, and include the rectus, iliacus, and sartorius. The psoas, also a flexor, though not attached to the pelvis, passes along the brim of the pelvis. The extensors are placed behind, and include the hamstrings and the gluteus maximus. The work required of these muscles is to bring the trunk from the stooping into the erect posture ; owing to the great weight of the head and trunk and the length of the column of the back, this is the most severe effort which any of the muscles have to make. Hence we find that the gluteus maximus is not only the most biQky muscle, and the muscle of the strongest fibre in the body, but that it has a very extensive origin. It arises from the sacrum, coccyx, and ilium and great sacro-sciatic, and other ligaments which hold the pelvic bones together, but it is connected also with the lumbar fascia. So too the hamstring muscles arise not only from the tuberosity of the ischium, but are continued, structure with structure, into the great sacro-sciatic ligament. As this ligament by its upper extremity is attached to the posterior part of the ilium, to the sacrum, to the sacro- coccygeal ligaments, and the coccyx, and is blended with part of the posterior sacro-iliac ligament as well as with the Imnbar aponeurosis, the hamstring muscles exert traction upon all these parts, and thus not only get a greater leverage for performing the difiicult movement they have to accomplish, but (like that of the gluteus maximus) their force is not con- fined to any one bone of the pelvis, nor even to the pelvis as a whole, but extends to the spinal column beyond, through the lumbar aponeurosis ; and further in their pull upon the pelvis their tendency is to hold together and not to separate the several bones which enter into its formation. The abductor group is placed to the outer side of the hip, and includes the gluteus medius and gluteus minimus, and the tensor vaginae femoris. The adductor group is situated upon the inner side, and MOVEMENTS OF THE PELVIS UPON THE THIGHS. 125 inckides the several muscles named adductors, together with the gracilis and pectineus. Tliey extend from the anterior ex- tremity of the ischial tuberosity to the superior ramus and to the body of the pubis. The muscles forming the external rotator group are variously situated at the pelvis with regard to a vertical line through the acetabulum, but they all pass to the femur over the lower and posterior part of the hip-joint. Tliis gToup consists of the pyriformis, the obturator externus and internus, the gemelli, and quadratus femoris ; a set of muscles which, collectively, arise from the inner as well as the outer surface of the pelvis, and from the sacrum as well as from each of the three portions of the innominate bone. It ought further to be observed that the four groups which affect the angular movements of the pelvis arise from processes of the pelvis which project, on their respective sides, beyond the hip-joint, and in this manner increase the leverage of the muscles ; thus the anterior spines of the ilium which give origin to the flexor muscles (sartorius and rectus) overhang the acetabulum in front ; the tuberosity of the ischium and the sacrum, coccyx, and back of ilium, which give rise to the extensor muscles, project or overhang behind ; the anterior portion of the dorsimi ilii from which the great abductor, the gluteus medius, arises, overhangs on the outer side ; while all parts of the pelvis from which the adductors proceed project far from the joint on its inner side. As the leverage afforded by these processes is greater according as they are farther from the axis of motion, it follows that when the balance of the trunk is varied and the dilhculty of maintaining a position is thrown more especially upon any one group of muscles, this difficulty is partly met by the in- crease in the distance between the bony processes from which these muscles arise and the axis of movement, which is in a plane carried vertically through the head of the thigh bone. Thus during flexion the bony parts from which these exten- sors arise are carried away from this plane ; during adduc- tion the bony points from which the abductors, and during abduction those fi'om which the adductors arise, are re- moved from this axis, and the muscles derive a corresponding advantage in increased leverage. During extension, as has been stated, the flexor muscles are not required to balance the 126 MOVEMENTS OF THE PELVIS UPON THE THIGHS. ' tmiik and to prevent it from falling backwards, as tlie liga- ments of the liip-joint serve this purpose ; therefore it is that the bony points from which these muscles arise are less strong and less distant from this plane than are the points of origin of the muscles of the other groups. But the most important and frequent movements of the trunk are not those which take place upon one femur alone, or upon both femora at the same time, but those which occur alternately upon the thigh bones. Such are the movements of walking and running. In walking, when the right thigh is flexed and carried forward, the body is bent slightly and carried forwards, and the right side of the pelvis is advanced ; the trunk by its own weight falls a little upon the right side and is supported by, while it rotates upon, the head of the left thigh bone. Next, the right limb having swung forwards penduluTn-like as far as the in- clination of the body at the time will permit, swings back again a little — ^like the reverse stroke of the pendulum — so that the right foot may be firmly planted on the gTOund while the trunk at the same time assumes a nearly vertical position. Then the left thigh is flexed, elevated, and carried forwards, and the trunk is again bent forwards, while the pelvis in turn is supported by and rotates upon the head of the right thigh bone, whereby its left side is advanced. The movements in running are much the same as those in walking, but while in walking there is always one foot on the ground, in running both feet are for a time off the ground together. The pendulum-like movement of the legs in man during running and walking is a gTcat economy of muscular energy. The movements are chiefly mechanical; the muscles have only to flex the joints of the lower limbs, but are not required to carry them forwards, nor to straighten them out again previous to planting first one and then the other foot upon the ground. SACRO-ILIAC SYNCHONDROSIS. 127 SACEO-ILIAC SYNCHONDROSIS AND SACEO-SCIATIC LIGAMENTS. Sacro-iliac Synchondrosis. Class, Amphiartlirosis, This, Kke the symphysis pubis, is an amphiarthrodial articula- tion, but it. differs from the pubic joint in that, besides having an interosseous or symphysial cartilage, and being surrounded by ligaments, the bones are further also held together by a strong interosseous ligament. The bones entering into the joint are the sacrum and iKum. The Sacrum, — By its broad irregular lateral border the sacrum articulates, with the uneven inner surface of the posterior portion of the expanded wing of the ilium. It is only the portion of this border which corresponds with the amalgamated transverse processes of the three upper sacral vertebrae that is in apposi- tion with the ilium ; the rest of the lateral border is free, and gives attachment behind to the great sacro-sciatic ligament, in front to the oblique fibres of the inferior sacro-iliac ligament, and along its free edge to the small sacro-sciatic ligament. The articulating portion of the lateral horder diminishes in antero-posterior measurement as it descends, being at the base of the sacrum nearly two inches, and at its lower part but little more than one inch from before backwards. Vertically it measures, in front, between two and two and a half inches, and corresponds pretty accurately with the vertical measure- ment of the ear-shaped facet of the ilium. Above it is sepa- rated from the smooth concave surface of the base by a sharp prominent edge, which extends from the posterior angle of the first transverse process forwards to the front surface of the sacrum. In front, a prominent, still sharper, and somewhat sinuous edge separates it from the grooves on the front surface or "hollow" of the sacrum, which run outwards from the three upper anterior sacral foramina, as well as from the ridges be- tween the grooves. Posteriorly it is limited by the projecting tubercles of the fused transverse processes, and is separated from the three superior posterior sacral foramina by a ridge, connecting the tubercles with one another. Inferiorly, a rough curved ridge passes from the tubercle of junction of the third and fourth transverse processes to the front edge of the bone, and separates the articulating from the non-articulating portion of the lateral surface. 128 SACRO-ILIAC SYNCHONDROSIS AND The articulating portion is fuither divided hy a vertical "/"- shaped promiiient ridge into two unequal parts ; the front part forms an ear-shaped facet for the connecting cartilage, and the hinder part gives attachment to the interosseous ligament. The facet projects laterally beyond the rest of the bone, and occupies the anterior and greater portion of the surface, being one inch and a half wide above, and rather more than half an inch wide below. It is not so nearly " ear-shaped" as the corresponding facet on the ilium, being longer with the angle formed by the front and superior borders, less rounded, and more rectangular. This angle projects further forward than any other part of the bone. The facet is concave from above downwards, as well as from side to side ; its posterior edge, which is raised and sharply cut, is concave, with the concavity looking backwards and upwards ; the anterior edge is convex and sharp, and sepa- rates the lateral surface from the " hollow" of the sacrum. The rough uneven surface, behind the facet, for the interosseous ligament, is of the form of an italic /, curving backwards above and forwards below. It is like a rough excavation in the side of the bone, with a broad ridge crossing it (like the cross line of the "/") about the middle ; this ridge which is formed by the united transverse processes of the first and second vertebrae, gives strong attachment to the interosseous ligament, and separates a deep recess in the lateral mass of the first from another in the lateral mass of the second, and sometimes of the thu-d sacral vertebrae. Into the upper of these two recesses or depressions is received a rough process of the ilium, whereby the two bones are locked into one another, while ligamentous fibres further unite these parts of them together ; the lower recess does not receive any corresponding process of ilium, but gives attachment to some very strong fibres of the interosseous ligament, between which a quantity of fat and some of the articular vessels and a nerve are lodged. When united with the ilium, the ridge is on the same level as the posterior superior spine of the ilium ; some- times the lower recess is subdivided into two by a second ridge, formed by the united transverse processes of the second and third vertebrae. The iLroM. — On the posterior part of the inner surface of the wing of the ilium is a very irregular rough surface, the anterior four-fifths of which articulate with the sacrum, while the posterior superior fifth projects backwards and inwards over the posterior SACRO-SCIATIC LIGAMENTS. 129 surface of the upper part of the sacrum, and assists very consider- ably in deepening the sacral groove for the erector spinse muscles. This rough plane is u-regularly quadrilateral ; its posterior horder is formed by about three inches of the crest of the ilium ; its anterior, by a prominent raised lip two inches long, and situated at a distance varying from three-fourths to one-fourth of an inch above and behind the border of the great sacro-sciatic notch ; its superior border is also a raised lip, about three inches long, extending forwards from the crest of the ilium in a line with the ilio-pectineal ridge, it separates the articular facet from the iliac fossa; inferiority, the border is not more than an inch and ahalf, and corresponds with the posterior superior and posterior inferior spines of the ilium, and the notch between them. Extending the whole length of the anterior and along nearly the front half of the superior borders, is an uneven ear- shaped facet, half an inch wide at its narrowest part, and some- what wider above, where the anterior and superior borders of the articular surface form a well-rounded angle with the con- vexity forwards. This facet, like the corresponding one on the sacrum, gives attachment to the connecting cartilage. Behind it the bone is undulating enough for the attachment of the strong interosseous ligament, and about half-way between the upper and lower borders there is generally a large rough pro- minence, which fits into the rough superior depression or recess of the sacrum, above the transverse process of the united first and second sacral vertebrEe. Immediately behind the lower end of the ear-shaped facet, and curving upwards from the notch between the posterior spines of the ilium, is a well-marked groove, sometimes overhung by a bony plate, for the lodgment and protection of the articular branch of the superior gluteal nerve and gluteal artery. Along the inner side of the crest of the ilium the bone is less uneven, and here affords attachment to the posterior sacro-iHac and the ilio-lumbar hgaments, and gives origin to the erector spiase and quadratus lumborum muscles. The articular rough portion forms with the smooth iliac fossa of the iHum an angle of 140°, for while the part of the bone forming the fossa for the iliacus muscle curves in- wards behind, the rest of the bone inclines backwards and curves downwards in order to overhang the sacrum. By this means the sacrum is received upon a surface of the ilium much wider than the lateral border of the sacrum itself ; and whi' > K 130 SACRO-ILIAC SYNCHONDROSIS AND it is overhung by the ilium behind, it is somewhat underhung by it below. Moreover, the weight of the trunk transmitted through the base of the sacrum, and especially along the ridges which extend from the articulating centrum for the fifth lumbar vertebra to the rounded angle of the ear-shaped facet, is thus communicated directly to the strongest part of the ilium — viz., along the brim of the true pelvis. This brim forms an arch of which the sacriim is the key-stone, and which, descend- ing from the lumbar portion of the spine at an angle of 150°, transmits the whole weight of the trunk to the heads of the femora in the standing posture, and along the ischial arches, to the tuberosities of the ischium in the sitting attitude. The outer surface or reverse side of the articular portion of the ilium forms a portion of the gluteal fossa or dorsum ilii, from wMch the gluteus medius arises. It is also marked by an oblique rough ridge running downwards and backwards to the back of the great sacro-sciatic notch, and giving origin, like the bone behind it, to the gluteus maximus muscle. The Ligaments. — Ligaments surround the articulation on every side, and cover in the symphysial cartilage. In addition, numerous scattered but strong bands pass between the apposed surfaces of the bones, so as to form a strong interosseous ligament. The anterior ligament consists of well-marked glistening fibres, thickening the periosteum and forming part of a con- tinuous covering over the joint. It passes uninterruptedly into the superior ligament above, and into the inferior ligament below. It blends with the periosteum of the sacrum and ilium, and becomes thinner as it stretches away from the united edges of the bones. It extends from the first three bones of the sacrum to the ilium above the great sacro-iliac foramen. The superior ligament extends across the upper margins of the joint between the base of the sacrum and the iliac fossa. It is far stronger behind, especially beneath the transverse pro- cess of the' fifth lumbar vertebra, than elsewhere ; but it is also well marked along the brim of the pelvis, where it is thickened by some closely packed fibres which pass forwards into the periosteum covering the ilio-pectineal Kne, and back- wards along the oblique ridge of the sacrum to the anterior sacral ligament. This ligament is connected with the strong sacro-lumbar ligament, which spreads outwards and forwards SACRO-SCIATIC LIGAMENTS. 131 over the joint to reach the iliac fossa and the ilio-pectineal line. The posterior ligament is of very great strength, and consists of a strong expansion of fibres between the back of the sacrum and the posterior two inches of the iliac crest, including the pos- terior superior spine of the ilium. In addition to, and strength- ening the back of this fibrous expansion, at its upper part, there are two or three strong rounded bundles of ligamentous fibres, which extend more or less transversely from the inner surface of the iliac crest (1) to the articular process of the first sacral vertebra, and (2) to the bone between it and the first posterior sacral foramen. Another strong band passes from the ilium to the articular tubercle of the second sacral vertebra, and forms a ridge over the second sacral foramen, under which the second posterior sacral nerve passes. An oblique band often connects this last fasciculus with the articular process of the first sacral vertebra. Over the lower part of the back of the joint fibres run obliquely downwards and inwards from the inner surface of the hindermost inch of the iliac crest (where they are attached under cover of some of the transverse fibres) to the side of the sacrum, external to the second and third posterior sacral foramina. To the edge of this ligament is attached the lumbar fascia covering the erector spinas muscle. The inferior ligament is covered behind by the upper end of the great sacro-sciatic ligament. It consists of some strong fibres which extend upwards from the lateral border of the sacrum below the articular facet, to the posterior iliac spines, while some are attached on the deep surface of the ilium above the inter-spinous notch and join the inter-articular ligament. Some of the anterior fibres of this Kgament are very distinct, and take a very oblique course upwards and outwards beneath the lower fibres of the anterior ligament. The inter-articular or interosseous ligament is the strongest of all, except perhaps the posterior sacro-iliac. It consists of fibres of different lengths passing in various directions between the rough surfaces of the two bones. These fibres are attached alike to the depressions and to the intervening ridge of the sacrum on the one side, and to the corresponding portions of the ilium on the other. Immediately above the inter- spinous notch of the ilium the fibres of this ligament are very K 2 132 SACRO-ILIAC SYNCHONDROSIS AND strong, and form an open network. The intersjiaces of tliis network are occupied by a quantity of fat, in which a large articular artery and some veins ramify. The ear-shcqxd cartilaginous i^late which unites the bones firmly is accm^ately applied to the ear-shaped facets of the sacrum and ilium. It is about one-twelfth of an inch in thickness in its centre, but is somewhat thinner near its free margins. Though closely adherent to the bony surfaces, it tears away entirely from one, or partly from both on the application of violence. Sometimes the cartilage will break in an irregular manner, so that the greater portion remains connected with one bone, leaving the corresponding part of the other rough and bare. In conformity with the positions of the bones between which it is placed, the fiat surfaces of the cartilage do not look directly outwards and inwards ; the sm^face connected with the sacrum looks forwards slightly as well as inwards, while that united to the ilium faces sHghtly backwards as well as outwards. Along the anterior and lower borders of the joint the edges of the cartilage come to the surface, and are bound over by the ligaments on these aspects. The thickness of the cartilage at the edges is not, however, much greater than that of a sheet of writing-paper. The posterior edge is directed towards the rough interosseous space, and is connected with the interosseous ligament. I agree with those writers who have described this cartilage as being composed of one mass, and not of two plates (one connected with each bone) with a synovial space between them. Such may be the case some- times, but it is not the constant arrangement — certainly not in the male, though more frequent in the female. Where two plates exist the joint is of the arthrocUal character. Besides the structures entering into the sacro-iliac synchon- drosis two other strong ligaments assist in binding together the sacrum and the os innominatum on each side. They are the great and small, or the posterior and anterior sacro-sciatic ligaments. The great or posterior sacro-sciatic ligament is attached above to the posterior extremity of the crest of the ilium, as well as to the posterior spines on their external aspect. From this attach- ment most of the fibres pass downwards and backM^ards (the posterior partly overlapping and blending with the oblique fibres of the posterior sacro-iliac ligament), to be fixed to the outer SACRO-SCIATIC LIGAMENTS. 133 "border and posterior surface of tlie tliird, fourth, and fifth sacral vertebrae, and one or two of the u]3per pieces of the coccyx ; while others, after passing for a certain distance backwards with the rest, curve forwards and outwards to the ischium, and form the anterior free margin of the ligament, where it limits posteriorly the sciatic foramina. At the ischium it is fixed to the inner border of the tuberosity, and sends a sharp thin process, called the " falciform ligament," upwards along the inner edge of the ramus of the ischium. This " falciform" process is a prolon- gation of the posterior — i.e., inferior border of the ligament, and forms with the ischial ramus an elongated recess for the lodg- ment of the pudic artery and nerve as they pass along the outer boundary of the ischio-rectal fossa. With the thin edge of this process the obturator fascia is connected. The fibres of the great sacro-sciatic ligament are twisted on the axis of the Kgament at its narrowest part — i.e., a Kttle below where the small sciatic crosses it ; so that some of the superior fibres pass to the lower border, and vice versa. It is thin and broad at its attached extremities, and narrow and somewhat thicker between. It looks Kke two triangular expansions continuous by a thick flat band, the larger triangle being connected with the iliac spines and sacrum, and the smaller with the ischium. At the ilium it has an important connexion with the thick fascia over the gluteus medius muscle, and with the vertebral aponeurosis, with both of which it is continuous beneath the gluteus maximus ; through it traction is exerted upon those structures, as well as upon the crista ilii and spinous processes of the vertebral column, by the contraction of the hamstring muscles. It gives origin in part to the gluteus maximus muscle, and assists to close in the pelvis below ; it unites the ilium with the sacrum, and is directly continuous with the tendons of origin of the hamstring muscles. By a very little dissection the fibres of these tendons are seen to pass onwards into the ligament, and by pulling upon either one of the muscles the whole liga- ment is tightened. More tension is made by pulling on the biceps than on the semi-tendinosus and semi-membranosus, but each gives a marked effect, and by traction on the biceps the coccyx can be made to move on the sacrum. In fact, the liga- ment may be not unfaMy described as a tendinous expansion of these muscles, whereby their action is in part exerted on the crest 1 34 SACRO-SCIATIC LIGAMENTS. of the ilium, on the spinous processes of the vertebrae, and on the sacrum, as well as upon the tuber ischii. The amount of leverage which these processes afford is greater than that of the tuberosities of the ischiimi, in proportion as they are farther away from the axis of rotation of the pelvis — \'iz., a line drawn through the head of the femur and acetabulum on each side. Thus these muscles get a much more advantageous purchase on the pelvis, and their -power in extending the trunk on the thighs is considerably greater than if they had been limited in their attachment, as they are stated to be, to the tuberosity of the iscliium. This fact, which seems hitherto to have been overlooked, gives great importance to the ligament, and affords a much more satisfactory explana- tion of its size and wide connexions than that usually given — viz., that it assists in closing the pelvis. It is not requisite for the latter purpose, as the muscles of the outlet are sufficient for this, while the viscera of the pelvis are supported by their own immediate connexions ; and, as a matter of common experience, when these become relaxed, the rectum and uterus descend and become prolapsed, in spite of the ligaments ; whilst the whole tendency of the bladder during distension is to rise out of, and not to descend in, the pelvic cavity. The Small Sacro-sciatic Ligament. — The small or anterior ligament is triangular and thin, with its base at the sacrum and coccyx, and its apex at the spine of the ischium. Its fibres decussate in the same manner as those of the large ligament, so that the anterior and lower fibres pass upwards to the highest point of the ischial spine. It is situated in front of the central part of the great ligament as it passes transversely outwards and forwards, and is closely connected with it near the sacral attachment. It springs from the lateral border of the sacrum and coccyx, from the front of the sacrum both above and below the level of the fom-th sacral foramen, and from the coccyx nearly as low down as its apex. At the ischium it is attached to the front surface, and the upper and lower borders of the ischial spine as far outwards as its base. In front it gives support to the coccygeus muscle, which covers it on the pelvic aspect. Behind it is so hidden by the gTeat ligament that only about the outer inch, and a part of its attachment to the coccyx, can be seen from the gluteal aspect. Besides separating the great from the small sciatic foramen, and PLATE XH. rill PCSTERIOR VIEW OF THE SACRO - SCI ATIC LIGAMENTS SHaWliHGl THE DIRECT CONTINUITY OF THE HAM — STRING TENDONS f NTO * ' THE GREAT LIGAMENT. Posteri4jr or larje liqoun-w Falciform edx^e- of yreai hgarmyit Ayvterior or jl ' smad hjjOLm.e.nt . BoaJc of capsvle of hip joini,. Tendon of ,^ dhtiorator exteryuLS. THE ARTERIES OF THE SACRO-ILIAC JOINT. 135 giving attachment to the coccygeus muscle, it strengthens the thin expansion of the great ligament where this latter is giving origin, to the gluteus maxim us muscle, and yet is unsupported by bone. These two ligaments give great additional security to the union of the sacrum with the ilium, and serve to hold the sacrum and coccyx together along their edges. The iha are connected and held together, and to the spines of the sacrum, by means of the strong lumbar fascia, which being attached to these bony points assists in retaining the ilia upon the sides of the sacrum. The Aeteeies. — ^All the arteries of the joint are derived from the branches of the internal iliac trunk. 1. The gluteal artery, after giving off its nutrient branch to the ilium and as it is passing through the great sacro-sciatic foramen above the pyriformis muscle, sends a vessel of some size to the lower part of the sacro-ibac synchondrosis, which it enters on the pelvic aspect of the joint. ISTumerous small branches perforate the iliac attachment of the great sacro- sciatic ligament and reach the margin of the joint. 2. The ilio-lumbar artery, after dividing into iliac and lumbar branches, supplies the upper part of the joint. The lumbar division sends downwards through the lumbo-sacral and superior sacro-sciatic ligaments a large branch. After laying open the joint this articular vessel can be traced a long way down behind the connecting cartilage and amongst the fibres of the interosseous ligament. As it descends it ramifies freely in several dnections, supplying the surrounding structures. Small twigs from the iliac portion of the artery often penetrate the anterior ligament and enter the cartilage. 3. Two or three of the sacral spinal arteries, after they have emerged from the posterior sacral foramina, give off small twigs to the articulation. These penetrate between the bundles of ■ the posterior ligament. A very distinct branch passes from the second posterior sacral artery, runs downwards beneath the oblique portion of the posterior sacro-sciatic ligament, and passes into the joint at the notch between the posterior spines of the ilium. This artery runs amongst the fatty, tissue of the joint, and often grooves the ilium behind the lower end of the ear-shaped facet. Other smaU branches from the lateral sacral (or the lower of 136 NERVES AND MUSCLES OF THE ARTICULATION. the two when more than one is present) supply the front and lower part of the joint. The Neeves. — The nerv^es are derived from the posterior sacral spinal nerves, fi-om the lumbo-sacral cord, and probably from the lumbar as well as the sacral plexus. 1. The superior gluteal, a branch of the lumbo-sacral cord, as it passes through the great sacro-sciatic notch above the pyri- formis with the gluteal artery sends a small nerve with the articular branch of that artery into the lower part of the joint. 2. The part of the sacral plexus formed by the lumbo- sacral cord and first sacral nerve is in close proximity to the joint, and gives off one or two small filaments to the front part of it. 3. The external branches of the first and second posterior sacral nerves, as they pass beneath the multifidus spinse and under part of the posterior ligament of the joint, send some small twigs to the back part of it. 4. The obturator branch of the lumbar plexus lies over the front of the sacro-iliac synchondrosis, though not quite so near to it as the lumbo-sacral cord. I cannot state from my own knowledge that it supplies the joint, but Mr. Hilton is disposed to think it does, and remarks in his work on Best and Pain, that the nerve " would be likely to suffer from its proximity to it when diseased." BuES^. — There are no bursse in connexion with the sacro- iliac synchondrosis, as there is no pressm-e fi'om without exerted upon it, and no tendons play about it. The Muscles. — There are several large and important muscles in relation with and taking origin near this joint, but none of them produce any movement between the two bones. It will be noticed that each of the muscles arises from both bones, so that during their action they are not exercising any strain upon the ligaments of the articulation by pulling the bones apart, as might be the case if each muscle had been connected with only one bone. 1. Through the medium of the lumbar aponeurosis, the latissimus dorsi is attached to the sacral spines and posterior part of the iliac crest. 2. The erector spinse arises by muscular fibres from the posterior fifth of the iliac crest, and by tendinous fibres from the hinder part of the ilium and from the lower part of the sacrum ^'HE JOINT AN IMMOVABLE ONE. 137 and sacral spines. It is inseparably united with the lumbar aponeurosis. 3. The multifidus spinse arises from the groove at the back of the sacrum as low as the fourth sacral vertebra, from the inner side of the posterior extremity of the iliac crest, and from the posterior sacro-iliac ligament. 4. The ihacus arises from the base of the sacrum and the iliac fossa of the innominate, as well as from the ligaments over the upper part of the sacro-iliac synchondrosis. The psoas magnus passes over the front and inner side of the joint, but is not attached to either the sacrum or ilium. 5. The pyriformis passes over the front of the articulation, and by its origin is connected with both bones, as well as with the great sacro-sciatic ligament. 6. The gluteus maximus arises from the vertebral aponeu- rosis which is attached to the sacrum and ilium ; from the posterior angle of the ilium, from the back and lower part of the sacrum, and from the great sciatic ligament. It is thus in relation with the inferior posterior aspect of the joint. The Movements. — It is quite clear, from the nature of the osseous surfaces, from the wedge-shape of the sacrum, and the manner in which it is locked in between the ossa innominata, as well as from the amphiarthrodial character of the articulation, that there can be no actual movement of one bone upon the other. Wliile the joint serves a useful purpose in breaking shocks, and in preventing concussions of the spinal cord and brain, the interosseous cartilage is too thin and too firmly fixed to the bones to allow even of any appreciable yielding, such as occurs upon the intervertebral discs. It is certain, however, that in disease of this joint sufficient loosening of the ligaments and swelling of the cartilage take place to permit of slight movement, and that thus is to be explained some of the pain experienced in such cases during sitting and standing; positions whereby the sacrum under these cncumstances would tend to force apart the ossa inno- minata, and rotate to a slight degree upon its own transverse axis. It was for centuries a received opinion that during parturition and pregnancy this joint, as well as the pubic symphysis, becomes loosened, so as to allow of an increase in the diameter of the pelvic cavity, by a partial separation of the bones, or by their movement upon one another. When, as 188 THE SECURITY OF THE ARTICULATION. occasionally happens, this is the case, the movement at the sacro-iHac joint must be caused by the abdominal muscles acting either directly by raising the pubis, and thereby rotating the innominate bones on the sacrum ; or indirectly, and by the contractile efforts of the uterus, in propelling the head of the foetus, whereby the ligaments are stretched and the capacity in- creased by a force thus applied from within the pelvic cavity. The shape of the sacrum, and the mode in which it articu- lates with the ossa iimominata, render its position a secure and ordinarily an immovable one. Being doubly wedge-shaped, with its broader surfaces at the base and on the front, disloca- tion by forces acting from above downwards, as well as from before backwards, is amply provided against. Nor are there wanting provisions against the forward displace- ment of the sacrum. If sections are made of the sacriun at different levels from above downwards, it will be found that although the majority show the anterior surface of the bone to be wider than the posterior, yet that at a level about opposite to the middle of the auricular facet the posterior surface is generally somewhat broader than the anterior. Again, the sinuous cha- racter of the opposed surfaces of the sacrum and ilium is such that eminences of the one are received into fossae on the other. The posterior extremity of the crest of the ilium on each side projects backwards considerably over the upper part of the sacrum, and by doing so diminishes the effect of any violence before it reaches the back of the sacrum. The direction of the fibres of the posterior sacro-iliac ligament is forwards and inwards from the ilium to the sacrum ; the fibres of the sacro- • lumbar ligament radiate upon the iliac fossa, and blend with the superior sacro-iliac ligament, while the ilio-lumbar ligament passes outwards to a firm attachment along the iliac crest. All these conditions obviate the forward displacement of the sacrum, by preventing the base of the bone from being carried for- wards ; while the attachment of the sacro-sciatic ligaments to the ischium on the one side, and to the edges and posterior surface of the sacrum on the other, prevents the tilting back- wards and upwards of the lower end of the bone. In this manner rotation forwards is as entirely checked as rotation backwards is by the shape and position of the sacrum. The downward displacement of the sacrum is impossible, because of the expanded width of the base ; whilst the weight MEANS POR PREVENTING DISPLACEMENTS. 139 of tlie spine and the connexions of the ligaments, including the ilio- and sacro-lumbar and the great sacro-sciatic, prevent its displacement upwards by any forces which compress the haunches, and which may be powerful enough to break the bones of the pehic wall, without disturbing the synchondroses. The anterior and downward displacements of the sacrum are likewise prevented by the interosseous and posterior sacro-sciatic ligaments. Passing as they do between the ilia and the sacrum, they act in the same manner as the chains of a suspension bridge to support the sacrum, the spines of the ilia being the buttresses of the suspension bridge. These ligaments, too, while they resist forces directed downwards and forwards upon the sacrum, at the same time draw the bones more tightly together : DiAGEAM II. Diagram of Section of Pelvis through Cotylo-sacral Arch. a. Posterior spine of ilium. 6 c. Base of sacrum, d. Posterior sacro-iliac ligament, e. Interosseous ligament. /. Ear-shaped connecting cartilaae. 140 SACRO-COCCYGEAL JOINT. the more tightly the greater the disturbing force. This will be understood by referring to the diagram of the section of the pelvis through the cotylo-sacral arch. It will be noticed that the direction of the ligaments is such as to hold upwards and backwards the sacrum between the ilia ; and that their sec- tion is triangular owing to the ligaments becoming narrower where they fit into the angle between the bones. The sus- pension bridge construction of the sacro-iliac synchondrosis is admirably adapted to give strength and elasticity to the pelvis. While the " arch" construction (aided by muscular contrac- tion which assists to hold the bones firmly together, and thus to increase the strength of the arch) affords a strong support for the trunk, the various hgaments of tliis articulation, together with the ilio-lumbar ligament, break the force of sudden shocks through the resiliency of theu^ "suspension chain" like arrangement. The wedge-shape of the base of the sacrum, and the wavy section of the joint, are well seen in the above diagram. The Sacro-coccygeal Articulation. Class, Amphiarthrosis. This is by no means the unimportant joint which its small size and the meagre descriptions given of it would lead one to suppose. As regards its perfection as an amphiarthrodial joint ; the extent and importance of the sacro-sciatic ligaments which assist in binding the bones together ; the importance of the muscles which act upon it, and the large size of some of them ; and lastly the free nerve and arterial supply to the parts about it, the articulation is well worthy the consideration of the anatomist. From the part it plays during j)arturition in modifying the shape and diameter of the outlet of the pelvis, it attracts the notice of the accoucheur ; while from its being occasionally the seat of real disease and frequently of hysterical pains, the attention of the surgeon has often to be given to it. It especially interests the surgeon to know the nerves and muscles connected with the joint, so that he may by putting the muscles at rest be able to release it from the nerve irritation excited by muscular contractions. The Saceum articulates with the coccyx by means of an oval-shaped and nearly flat surface at its apex, which forms the inferior disc of the body of the last sacral vertebra. The THE BONES OF THE SACRO-COCCYGEAL JOINT. 14 L long axis of this surface is transverse and about three-quarters of an inch from side to side. It is bevelled sKghtly down- wards in front. From the sides of this facet the lateral border of the sacrum curves upwards and outwards to the angle of the sacrum, forming a notch or concavity looking downwards and outwards, to which the sacro-sciatic ligaments are attached. In a line with the amalgamated articular processes of the upper sacral vertebrae are the sacral cornua, which project downwards somewhat towards the ascending cornua of the coccyx, from which they are separated, however, by an interval varying from one-fourth to half an inch. Between the sacral cornua is the opening of the spinal canal, which is exposed to a variable extent in different bones according as the laminae of the fourth and third sacral vertebree do or do not meet in the middle line. The backs of the exposed sacral bodies are covered in the recent state by the posterior common ligament of t]ie spinal column and give sup- port to the filum terminale, lowest spinal nerves and their ganglia, and the fatty tissue of the canal. The Coccyx articulates with the apex of the sacrum by means of a slightly concave facet on the upper aspect of the body of the first coccygeal vertebra. In shape and size this articular facet resembles the corresponding one of the sacrum. It is somewhat bevelled downwards in front, and is rather broader before than behind. It is perhaps altogether a little longer than the surface on the sacrum, which is received upon it. On each side of the body of the first coccygeal ver- tebra is an outstanding transverse process, the upper border of which is on the same level as the articular facet. They in- crease the transverse measurement of the base of the coccyx by about one-half, so that if the upper facet measures three- quarters of an inch, the bone from tip to tip of its transverse processes measures an inch and a half. Laterally, the transverse processes do not project outwards quite so far as the angles of the sacrum, with which they form the " sacro-coccygeal notch." With the edges of the notch the sacro-sciatic ligaments are connected, and the last sacral nerve escapes from the spinal canal behind them. Ascending, behind, from the point of junction of the transverse processes and the facet, are the cornua of the coccyx. They are in the same vertical lines as the cornua of the sacrum, and are from one-sixth to one-fourth of an inch 142 THE BONES OF THE SACRO-COCCTGEAL JOINT. in length. Extending between the cornua along the posterior border of the articular facet is a ridge, which by deepening the margin of the articular surface increases its forward and down- ward inclination. The upper half of the posterior surface of the first coccygeal vertebra is smooth and flat (or even shghtly concave), and forms the lower extremity of the spinal canal. It also gives attachment to the posterior common ligament of the spinal cohimn, and upon it rests a quantity of the fatty tissue of the spinal canal and the filum terminale, which becomes fixed to the coccyx lower down. Lower down upon the back of the coccyx the continuation of the supra-spinous ligament blends with the posterior common ligament, and together with it is fixed to several segments of the coccyx. The sloping forwards of the facets of the sacrum and coccyx provides for the forward cmwe of the terminal part of the spinal column ; for although the shape of the sacrum itself secures this in part, the curve of the column at the sacro- coccygeal joint is still more marked in most cases. The movements of the coccyx on the sacrum are of a hinge- like character, and are provided for by the absence of all bony union behind the centrum of each bone. The cornua of the coccyx on the front aspect of their bases are smooth, and con- tinuous with the articular facet of the coccyx, and are the hinges or pivots upon which the rotation occurs ; while the apices of the cornua being free, except for ligamentous con- nexions, approach in the backward movement of the coccyx the posterior surface of the sacrum. In advanced life, and after the bodies of the sacrum and coccyx are immovably united, the ligamentous union of the cornua of the two bones is sometimes replaced by osseous tissue, so that the cornua of the sacrum appear to have been originally continuous with those of the coccyx ; but it is quite clear that if such had been the case, no movement whatever could at any time have occurred at the sacro-coccygeal joint, and this would be a very serious defect in this articulation in the female. As a rule, the union of the cornua of the sacrum with the coccyx is only ligamentous, even after the bodies of the bones are ossified together. Sometimes the segments of the coccyx, especially the first two, move on one another long after the sacro-coccygeal joint LIGAMENTS OF THE SACKO-COCCYGEAL JOINT. 143 has been ancliylosed ; on the other hand, the sacro-coccygeal joint will be sometimes found free after the several segments are immovably united. Ligaments. — There is an amphiarthrodial joint between the oval-shaped facets of the sacrum and coccyx, as there is be- tween the bodies of the several vertebrse in other parts of the column ; but the sacro-coccygeal is by far the most movable of them all. Besides the ligaments connecting together the bodies of the sacrum and coccyx, others unite them behind, and pass between their cornua as well as over the middle line. In this way the lower end of the spinal canal is covered in, where the laminae of the sacral and first coccygeal vertebrae being defi- cient it is left destitute of a bony wall. Strong ligamentous tissue binds the transverse processes of the coccyx to the lateral border of the sacrum. Intervertebral Substance. — A small intervertebral disc occupies the space between the facets of the sacrum and coccyx. On a transverse section through the joint, it is seen to be about three- fourths of an inch wide from side to side, but somewhat less from before backwards, and to be closely connected with the ligaments which surround the bodies of the two bones. In structure it resembles the rest of the intervertebral substances, but is softer and more jelly-like than they, although the laminae of the circumferential fibrous portion are well and strongly marked. The anterior sacro-coccygeal ligament is a prolongation of the pearly-white glistening fibrous structure on the front of the sacrum, which is continuous above with the anterior common ligament of the column. It is in fact the lower extremity of the anterior common ligament, which is thicker over this joint than over the central part of either of the bones. Supra-cornual Ligament. — ^At the back of the sacrum the vertebral groove of the column becomes very shallow where the bone bends forwards, and ceases to exist about on a level with the lamina of the third vertebra. At this spot the strong aponeurosis of the erector spinse, which elsewhere blends with the supra-spinous ligament of the column, becomes inseparably woven with it, and is thus prolonged downwards upon the back of the coccyx passing over the lower end of the sacral portion of the spinal canal, which it covers in where the 144 LIGAMENTS OF THE SACRO-COCCYGEAL JOINT. lamiiiEe fail to meet to form a rudimentary spinous process. Some of the fibres of this strong membrane run straiglit onwards or even curve outwards to their attachment ; others, well marked and of a pearly-white appearance, decussate in bundles across the middle line from the stunted lamina of one vertebra to that of the next below, and likewise from the cornu of the sacrum to the cornu of the coccyx on the opposite side. The median non-decussating fibres run over the back of the coccyx to its tip and blend with the posterior common ligament and filiim terminale, after roofing in the lower ex- tremity of the spinal canal. The supra-cornual ligament is composed of a. superficial and deep set of fibres, which may be separated without difficulty and without laying open the spinal canal. Some of the deeper-set extend between the cornu of the sacrum and the cornu of the coccyx on the same side, and bridge over the aperture through which the fifth sacral nerve emerges. Arising from the posterior surface of this ligament or its lateral extension is part of the gluteus maximus. The fascia covering this muscle passes freely over the ligament from side to side. On the deep surface the ligament looks towards the spinal canal, and lower down is attached to the back of the coccyx. Posterior sacro-eoccygeal ligament is a direct continuation of the posterior common ligament of the column. It consists of a well-marked narrow band of closely packed fibres, which passes over the back of the coccyx, and at the lower border of the first segment, or on the back of the second, becomes blended with the supra-spinous ligament and the filum terminale. Resting upon it are the fibrous cord continuous with the spinal marrow and its membranes, the last sacral and coccygeal nerves, the termination of the spinal arterial chain, and the fatty tissue of the spinal canal. Intertransverse Ligament. — Between the transverse process of the coccyx and the lateral border of the sacrum below its angle, the bones are firmly held together by a quantity of dense fibrous tissue connected with the sacro-sciatic ligaments at their attachment. It scarcely deserves a special name, and would be indistinguishable from the sciatic ligaments except that the great sacro-sciatic is contmuous with the supra-cornual liga- ment, in front of which the fifth sacral nerve escapes while it ARTERIES AND NERVES OF SACRO-COCCYGEAL JOINT. 145 passes behind the inter-transverse fibres. It is perforated by small branches of the lateral sacral artery, as well as by the coccygeal nerve, on their way to the back of the coccyx. The Aeteries are derived from the lateral sacral, median sacral, and the anterior arterial column of the spinal canal. Lateral Sacral. — A branch of some size passes back through the ligament above the transverse process of the coccyx, and enters the spinal canal beneath the inter-cornual Kgament along- side of the last sacral nerve. It sends a loop upwards on the back of the sacrum to anastomose with the artery which emerges from the last posterior sacral foramen, and one downwards over the transverse process of the coccyx to join with another branch of the lateral sacral trunk. It supplies the structures of the joint. Four or five other branches pierce the coccygeus muscle and the sciatic ligaments to reach the back of the coccyx ; one constant branch takes a course along the coccygeal nerve, and enters the lowest extremity of the spinal canal, where it anastomoses like the other spinal arteries and supplies the sacro-coccygeal joint. The sacralis-media sends tiny twigs to the front of the joint, and others from the spinal arterial plexus pierce the joint on its posterior aspect. The Nerves. — The anterior as weU as the posterior primary branches of both the fifth sacral and coccygeal nerves pass close to, and supply the fibrous structures surrounding this joint. The posterior branches of the fourth and fifth sacral nerves are partly distributed on the back of the coccyx, and that of the fifth joins in a loop with the posterior primary branch of the coccygeal nerve. The anterior primary branches of the fifth sacral and of the coccygeal nerve supply the coccygeus muscle, and turn back- wards through tl^at muscle and the sciatic ligaments to end in the soft structures on the side and back of the coccyx. Further, the posterior branches of the second and third sacral nerves descend over the back of the sacrum, forming loops upon the great sciatic ligaments and supplying the gluteus maximus muscle. These same nerves, which are distributed in the ligaments around the joint, supply the various muscles which act upon the bones. L 146 MOVEMENTS OF THE SACRO-COCCYGEAL JOINT. The Muscles. — The muscles in connexion with the sacro- coccygeal articulation are — The gluteus maximus which, besides its other origins, arises from the side of the coccyx, and last piece of the sacrum on their dorsal aspect, and from the back of the great sacro- sciatic ligament. The levator ani converges to its insertion at the middle line ; posterior fibres of this muscle are inserted into the side of the lower end of the coccyx towards the pelvic aspect. The coccygeus diverges to its insertion into the side of the coccyx, and the lower part of the sacrum on their pelvic aspect. It is supported in its whole length by the small sacro-sciatic ligament. The external sphincter ani arises by a small tendon from the tip, and back of the coccyx. The hamstring muscles are attached to the coccyx through the medium of the gTcat sacro-sciatic ligament, with the fibres of which they are directly continuous. Lastly, a few muscular fibres have been described as some- times passing from the lower end of the sacrum to the coccyx, both on the front, and posterior aspects. Those in front have been dignified by the name of " cm-vator coccygis," and those behind by that of " extensor coccygis." BuES^. — There is no bursa usually in connexion with the bones of this joint, or with the muscles at their attachment to them. The Movements. — The movements of the coccyx on the sacrum, as well as of the pieces of the coccyx on one another, are of a simple backward and forward, hinge-like, character. In the act of defecation the bone is pushed backwards by the escaping faecal mass, and in parturition by the foetus : but this backward movement is regulated and controlled by the up- ward and forward pull of the levator ani and coccygeus. The action of the external sphincter ani tends to pull forwards the coccyx, so as to allow of the tighter contraction of its fibres about the anal orifice. The muscles which tend to pull the bone backwards are the gluteus maximus, and the hamstring, in such movements as rising from the bent, or sitting postm-es, and in rapid progres- sion, or in walking with long strides. THE SYMPHYSIS PUBIS. 147 Inter-coccygeal Joints. The several segments of the coccyx are held together by prolongations of the anterior, and posterior common ligaments, which completely cover these bony nodules on their front and posterior aspects. Laterally the sacro-sciatic ligament, being attached to the whole length of the coccyx, serves to connect together its various pieces. Between the first and second pieces of the coccyx there is a very perfect amphiarthrodial joint, with a well-marked iatervertebral substance; and in addition, a few ligamentous fibres pass downwards from the cornu of the coccyx on each side, to the posterior surface of the second segment of that bone. The bloodvessels and nerves of these joints are included under the sacro-coccygeal joint. The same muscles which move the coccyx on the sacrum, move also the pieces of the coccyx on each other. The Symphysis Pubis. Class, Amphiarthrosis. The bones entering into this articulation are the ossa inno- minata by theu^ pubic portions, where they meet in the middle line of the body. The joint is shorter and broader in the female than in the male, and like the other pelvic articulations is of much importance in obstetrics. Pubic Bone. — The hody of the pubis is fiat, of a somewhat triangular shape, and is continuous with the ascending ramus above and the descending ramus below. It extends from the obtu- rator foramen to the articular surface ; measures on an average from one and three-quarters to one and a half inches vertically, one and a half inches from side to side, at its upper part, and three-quarters of an inch at its lower end ; while at its articular surface it is five-eighths of an inch from before backwards. It is placed obliquely iu the body, so that its posterior surface looks somewhat upwards, and its anterior slightly downwards ; the joint in consequence is not vertical. It has two surfaces, namely, anterior and posterior; and three borders, namely, superior, internal, and external. The superior border forms part of the brim of the true pelvis, gives attachment to the rectus abdominis muscle, and is designated in different parts from the middle line outwards L 2 148 THE LIGAMENTS OF THE SYMPHYSIS PUBIS. the angle, the crest, and the spine of the pubis. The external border is a sharp edge forming the tipper end of the injier boundary of the obturator foramen. Its Internal or Articular Border. — It is with the inner border that we are especially concerned. It is in the dried bone rough, slightly serrated, and of a nearly oval outline, but narrower at the lower end than above ; extending the whole height of the pubic body ; and, owing to the eversion of its margins, it is of somewhat greater area than the thickness of the body of the bone elsewhere. It is convex from before backwards ; and sometimes convex from above downwards, though occasionally the angle of the pubis overhangs it above. Continuous with it is the inner edge of the descending ramus, which is free and everted so as to form with the corresponding part of the opposite bone the pubic arch. This arch widens as it descends to the iscliial tuberosities, and the centre or summit of it is the lower end of the pubic articu- lation, i.e., the symphysis. The Ligaments. — The ligaments completely surround the edges of the articular surfaces of the bones, together with their intervening and connecting cartilage. They are called from their situations — the superior, anterior, inferior, and posterior ; and the uniting cartilage is named interosseous. Interosseous Fihro-cartilage. — The cartilage of the symphysis varies in thickness in different subjects, and is thicker in the female than in the male. It is thicker in front than behind, and projects beyond the edges of the bones, especially the posterior. The several ligaments, especially the lower and posterior, are intimately blended with it at its margins. It varies likewise in its construction — sometimes being uninterruptedly woven throughout, at others having a fissure running through more or less of the antero-posterior as well as of the vertical depth. This fissure is always elongated and narrow ; it partially divides the cartilage into two plates, with a minute viscid pulp or a little fluid in the interspace, and usually extends about half the length of the cartilage. It is situated nearer to the posterior than the anterior, and to the upper than the lower border, but does not quite reach to either, and is found in males as well as in females, but not constantly in either sex. I have seen it want- ing in females who have died of cancer of the pelvic organs, and whose pelvic bones were soft enough to be transfixed and cut through with a knife. When the fissure is not present, and PLATE Xlll. I \ I 1 1 J SYMPHYSIS PUBIS /. Posterior vU^ of jauhvc sy-rnphysui P' ATF XIV. A^. Anterior view of yiuhU sytrvphysi^ (Female) STiowina oLectcssoU-voft, of nhi^eN of lufn^viettt- ■ S.ArtUrior \-ie.w of pubu' .symphysis f Ma/e) JLJr/^n~yyin^ deZ.cvd, >uxfc . Tfei'*J\/^e>v^»w»*t * < THE LIGAMENTS OF THE SYMPHYSIS PUBIS. 149 in the parts beyond it when it is present, coarse white granular- looking fibres pass from side to side through the substance of the cartilage, and firmly weld it together. On forcibly stretching the two bones apart, the cartilage does not always or throughout split into two plates, but is torn from the bone on one or other, or both sides. This symphysial cartilage is immediately adherent to the osseous surfaces, which are without an independent coating of ordinary articular cartilage. Superior Ligament. — The superior, or supra-pubic, ligament is a well-marked stratum of yellowish-looking fibres, which extend outwards along the the crest of the pubis on each side, and at the middle line are intimately blended with the inter- osseous cartilage. It gives origin to the rectus abdominis tendon; in front, it is continuous with the deep transverse fibres of the anterior ligament, and is covered by the tendons of the obKque muscles of the abdomen ; beliind, it is blended with the strong upper part of the posterior ligament, and with the fibres extending along the ilio-pectineal line. Posterior Ligament. — The posterior ligament is much slighter than the anterior, and, excepting above and below, consists of little else than thickened periosteum. Near the upper part is a band of strong pearly glistening fibres, which reaches the whole width of the pubic bodies, and is continuous with the fibres which thicken the periosteum along the ilio-pectineal line. Some of these superior fibres decussate obliq[uely across the middle line, forming gentle arches with their concavity downwards. Below, many of the upper and superficial fibres of the infra-pubic ligament ascend over the back of the joint, interlacing across the middle line with fibres from the opposite side, as high as the middle of the symphysis. Slender fibres faintly decussate between the upper and lower portions of this ligament. Anterior Ligament. — The anterior ligament is thick and strong, and is closely connected with the fascial covering of the muscles arising from, the body of the pubis. In front, it is covered by the interlacing fibres of the pillars of the ex- ternal abdominal ring, and by tTie conjoined tendon, and pyra- midahs muscle. It consists of several strata of thick decussat- ing fibres of different degrees of obliquity, the superficial being the most oblique and extending the lowest over the joint. 150 THE LIGAMENTS OF THE SYMPHYSIS PUBIS. The most superficial descending fibres extend from the upper border of the pubis, cross others from the corresponding part of the opposite bone above the middle of the symphysis, and are attached to the ramus of the opposite pubis. The most superficial ascending fibres, being inseparably connected with the infra-pubic ligament, arch upwards, decussate with other fibres across the middle line, and are lost on the opposite side beneath the descending set. In a deeper stratum the descending fibres arise below the angles, interlace with others from the other side, but do not descend so far as the superficial sets ; the deeper ascending fibres decussate, and reach higher than the more superficial ascending sets ; but, like them, are inseparable from the inferior ligament. Some few fibres pass transversely from side to side, more especially above and below the point of decussation of the descending deep set. Inferior Ligament. — The inferior, or infra-pubic, ligament, called also the ligamentum arcuatum, is an arch-like and thick band of closely packed glistening fibres, which fill up the angle between the pubic rami, limit the symphysis below, and form a smooth rounded summit to the pubic arch, which is one of the cardinal obstetric points of the pelvis. On transverse sec- tion it is of a yeliow colour, like the supra-pubic ligament; it is inseparably connected with the interosseous cartilage, and mea- sures about three-eighths of an inch, vertically, in the middle line. The lower component fibres pass from one side of the pubic arch to the other, below the symphysis, while the other fibres are shorter and end nearer and nearer to the middle line on the opposite side as they lie deeper and deeper. It has been stated above, that the lower decussating fibres on both front and posterior aspects of the joint are prolonged upwards from the sub-pubic ligament ; in fact, this ligament may be said to split superiorly into two thin layers, one of which passes some distance upwards over the front, and the other over the back of the articulation. Nothing can more firmly brace the pubic bones together than this interlacement of fibres in the anterior and inferior ligaments. Whatever tendency there is for the joint to be dislocated, either by the violent action of the abdominal muscles, or from blows, or compressing forces applied to the pelvis as a whole, or by weights borne or carried upon the ARTERIES OF THE SYMPHYSIS PUBIS. 151 crest of the ilium, is successfully resisted by the interosseous cartilage aided by these strata of decussating fibres. Passing as they do over the front and lower part of the symphysis in every direction, they can withstand considerable force, no matter how applied, and as a practical consequence we hear of fractures of the pelvis and ischium, but never of dislocation at the symphysis. The necessity of a stronger anterior than posterior ligament arises from the downward and forward drag of the adductor muscles of the thighs, and of the abdominal walls in stout persons ; and from the tendency of compressiag forces when applied to the sides of the pelvis to burst forwards the bones at this joint, just as in fractures of the ribs from indirect violence, the fractured ends start outwards away from the cavity of the pleura. The Arteries. — Numerous small vessels ramify upon the posterior surface of this joint. Blood is supplied to the symphysis pubis from the internal and external iliac as well as from the femoral tnmks by means of small arterial twigs which pierce the interosseous cartilage on the anterior and posterior aspects of the joint. From the internal iliac trunk. — (1) The internal pubic artery just before it passes below the sub-pubic ligament gives a branch which pierces the symphysial cartilage low down on the posterior surface. (2) One or more twigs are sent from the pubic branches of the obturator artery to pierce the posterior ligament, and enter the joint about the middle or a little higher. From the external iliac trunk. — (3) The pubic branch of the deep epigastric artery sends a small vessel to the upper part of the articulation. Mounting over the- crest of the pubis it descends through the tendon of origin of the rectus muscle, and penetrates the front of the cartilage. From the deep femoral. — (4) The ascending branch of the internal circumflex sends small twigs through the origin of the gracilis to the front of the joint. From the common femoral. — (5) The superficial external pudic sends small twigs to the upper and front part of the symphysis. They perforate the anterior ligament, but do not always penetrate the cartilage. BuRS^. — There are no bursse in connexion with this joint. 152 MUSCLES AND MOVEMENTS The Muscles. — There are muscles on both the upper and anterior aspects. (1) Along the upper border of the articulation is the rectus abdominis, which arises from the crest and superior ligament of the pubis. Also attached to this border of the symphysis in the middle line is the linea alba, which separates the rectus of one side from that of the other. Attached to the front of the pubis are the aponeurosis of the external oblique, and the conjoined tendon of the internal oblique and transversalis abdominis muscles. (2) That portion of the aponeurosis of the external oblique which forms the pillars of the abdominal ring passes over the front of the joint in the folio whig way : the inner fibres of the external pillar are continued over the crest of the bone, and beneath the spermatic cord in the male ; form what is called the " triangular ligament ;" and decussate with the fibres of the opposite side. The inner pillar is attached to the angle of the pubis and to the front of the symphysis, where its fibres interlace with those of the opposite side. (3) Behind the external oblique is the conjoined tendon of the internal oblique and transversalis, which is attached in part to the front of the symphysis. (4) Behind and above this again, and arising from the anterior and superior ligaments, is the small pyramidalis. Im- mediately on each side of the symphysis, in front, are the adductor longus and gracilis. Below and behind no muscles are in connexion with the articulation ; but the levator ani, which arises in part from the middle of the posterior surface of the body of the pubis, is very near to the symphysis behind. The Movements. — Being an amphiarthrodial joint there is but little movement, amounting only to a slight yielding of the cartilage. ISTeither muscular action nor extrinsic forces produce any appreciable movement in the ordinary condition. Occa- sionally, however, as the result of child-bearing, the joint becomes unnaturally loose, and walking and standing are rendered painful and unsteady, if not actually impossible. In the case of a lady after the bu-th of her second child, this con- dition ensued and has persisted several years, in spite of treat- ment by rest and bandages ; and in her it produces such a degree of insecurity, that she requu-es to use a tight belt around OF THE SYMPHYSIS PUBIS. 153 the pelvis to give firmness to the trunk during the action of the muscles of the thigh. It is known that during pregnancy •and parturition, the symphysial cartilage becomes softer and more vascular, so as to permit of the temporary enlargement of the pelvis ; doubtless for this purpose the joint is very freely supplied with blood. This being the case, it might be supposed that the abdominal muscles, attached as they are to the top and front of the joint, would help to increase the outlet of the pelvis by elevating and somewhat rotating forwards, during their expulsive action, the lower ends of the ossa pubis ; that in fact they would produce a slight movement resembling the movement of the ribs during inspu^ation, which increases the diameter of the chest by theii' elevation and the rotation out- wards of their lower borders. But it must also be remembered, although the recti may elevate, and the oblique muscles may rotate the pubic bones, that many of the fibres of the latter decussate, and that therefore, when in action, the tendency of these muscles must partly be to draw the bones together. Thus at the very moment they increase the strain on the joint, by forcing down the head of the child, they give it gi-eater strength to bear the strain. In cases in which the antero-posterior diameter of the pelvis is much contracted, and natural labour impossible, M. Sigault proposed, in 1768, that di\'ision of the symphysis pubis should be performed instead of Csesarian section for the purpose of saving the child and delivering the mother. Experiments, however, prove that in order to gain half an inch in the antero-posterior diameter, the pubic bones must be separated to the extent of two inches. On simple division of the joint, although the bones gape a Httle, much force is required to widen the gap, and when the separation extends an inch and a half, it has been found that the sacro-iliac ligaments are lacerated, and much damage -done to the bladder and its attachments. For these reasons, although M. Sigault received a medal, pension, and extravagant applause for his invention, the " Sigaultean operation" has been entirely abolished from obstetric practice, at any rate in Great Britain. CHAPTEE VIII. THE THOEAX. The Thorax is the name given to the parietes of the upper por- tion of the trunk. These are composed partly of osseous and cartilaginous, and partly of muscular structures. The bones and cartilages consist of the dorsal vertebrse and their inter- vertebral substances behind, the ribs on either side, and the costal cartilages and the sternum in front. They are so joined with one another as to permit of free mobility in various direc- tions, whereby the cubic capacity of the thoracic cavity can be increased or diminished ; while at the same time they are so securely locked together as to afford protection to the organs which they help to surround. The cavity of the thorax is the whole of the space enclosed by the five upper costal arches, and the circumferential portion of the space enclosed by the seven lower arches. But more than the " cavity of the thorax" is walled in by the osseous, cartilaginous, and muscular structures which form " the thorax." The diaphragm forms the floor of the cavity of the thorax ; but the muscular fibres of the diaphragm, though they arise from the lower six ribs, and from the xiphoid cartilage, arch upwards to ' the central tendon of the muscle, which is placed as high as the level of the fifth intercostal space. Thus a con- siderable part of the viscera of the abdomen is contained within the boundary of the thoracic fi'amework. Indeed, in the mam- malian class the space bounded by the thorax may be de- scribed as being divided into two parts by the diaphragm. Of these, the upper is the " cavity of the thorax" proper, and contains the heart and lungs, and several important structures on their way to the abdomen — viz., the descending aorta, the oesophagus, and pneumo-gastric nerves ; the phrenic nerves on their way to the diaphragm ; the ganglionated cord of the sympathetic ; the thoracic duct also passes through the thoracic THE THORAX. 155 cavity on its way to the root of the neck ; and the vena azygos as it ascends to the superior vena cava. The lower division forms a large portion of the cavity of the abdomen, and contains the stomach, liver, spleen, snpra-renal capsules, kidneys, part of the intestines, descending aorta and inferior cava. The bony part of the thorax in the human subject stops short of the pelvis, for the purpose of allowing a moderate range of flexion and rotation of the trunk. To facilitate these movements the lowest two ribs are small, short, and attached only at their vertebral extremity ; while the costal arches immediately above slant upwards towards the median line in front, and each is attached to the costal cartilage of the arch next above it. The Apertures of the Thorax. — The superior is wider from side to side than from before backwards. It is about sixteen inches in circumference, and being the smaller end is called the apex. It is bounded in fi-ont by the upper end of the sternum and the inter- clavicular ligament, laterally by the first costal arch of the two sides, and posteriorly by the first dorsal vertebra. The inferior aperture is about thirty-one inches in circum- ference, and forms the base of the chest. It is bounded in front by the xiphoid cartilage and the cartilages of the three superior false ribs ; laterally by the bodies of those ribs, and the eleventh and twelfth costal arches ; posteriorly by the last dorsal vertebra. In the living subject the thorax looks conical with its base above ; this is owing to the breadth of the shoulders, but as soon as the upper extremities are removed the base of the cone is seen to be below and the apex above. Hence the idea that broad shoulders and a broad back iadicate great breadth of thorax and great breathing capacity, is a mistake. The diameter of the neck is a better index to the diameter of the true thoracic cavity. The shape of the thorax, both externally and internally, varies with age, and is affected by disease and occupation. In the foetal thorax the sternum projects forwards, and the antero- posterior diameter exceeds the transverse ; and as the ribs are less curved at their angles, those deep grooves seen from the interior on each side of the spine in adult life are almost 156 THE THORAX. wanting. In the decline of life the thorax has a tendency to contract and droop forward. Lateral and angular curvature of the spine ; lung diseases, such as emphysema and phthisis ; and the pressure of tight-lacing, or of awkward nursing, all cause alterations in the conformity of the thorax. Again, the tailor and the clerk have a different shaped thorax to that of the mountaineer or the sailor. Externally the thorax varies also with the sex, for in women there is less breadth of shoulders and greater fulness in front, owing to the largeness of the mammse. Tha internal form of the thorax is the same in males and females, except that in the latter it is absolutely smaller. Throughout the vertebrate kingdom the thorax is constructed upon an uniform plan, although the whole of the bony and cartilaginous structures above enumerated are not invariably present in all the lower orders of this kingdom. Frogs have a sternum, but no ribs ; serpents have ribs, but no sternum ; tortoises have ribs, vertebrse, and sternum fused together into one rigid and inflexible mass ; the crocodile and lizard have perfect ribs, but their sternum is almost entirely cartilaginous. The great characteristic of the thorax of man is the excess of the transverse over the antero-posterior measurement. In all the lower mammalia the vertical, which corresponds to the antero- posterior in man, exceeds the transverse ; and though in the quadrumana the transverse equals, and in some cases exceeds the antero-posterior, it never has such a great proportionate breadth as in man. Another characteristic of man's thorax is the sharp back- ward curve of the ribs from their heads to their angles, whereby the latter points are brought into nearly the same transverse plane as the spinous processes of the vertebrse. This is a provision for the proper balancing of the body in the erect position, and is a necessity of that position and of the biped mode of progression. It also gives breadth and flatness to the middle portion of the back, and adds to the strength and perfection of the figure. Man is thus too enabled to be at rest upon his back, a position which but for tliis backward curve of the ribs would be uncomfortable, if not actually impossible, on account of the prominence of the spines of the vertebree. This backward curve of the ribs, together with the projection forward of the bodies of the dorsal vertebrse, renders the antero- THE THOKAX. 157 posterior diameter much less in the middle line than at an inch on either side of the median line. The average forward pro- jection of the spine is about two and a half inches, and the average antero-posterior diameter between the bodies of the vertebrae and the sternum is but little more than four inches ; even this is much reduced in phthisis, when the vertebral column has the appearance of being wedged forwards towards the sternum. The curvature of the several ribs varies much ; it undergoes a gradual diminution from the first to the last, in wliich the angle can scarcely be said to exist at all. In addition to the general curvature in the horizontal direction, the ribs are also curved vertically. This vertical curve too varies in different ribs, but is such as to make it. impossible for the rib to lie with both its ends at the same time on a flat surface. All the ribs incline obliquely downwards from the spine ; the upper border of the sternum is on the level of the second dorsal vertebra, being usually not more than two inches from the spine. The intercostal spaces are wider beyond the angle and towards the anterior extremity of the ribs than near the spinal column, but towards the median line in front the spaces become very narrow, owing to the way in which the costal cartilages converge to the sternum or to one another. The several spaces are not of ^^niform width; the first, second, and third being, as a rule, broader than the succeeding; the tenth and eleventh are generally the widest. There is no uniformity in the corresponding spaces of the two sides of the body. The joints of the thorax are numerous, and consist of — 24 between the heads of ribs and the bodies of vertebree. These are called the costo-central. 20 between the tubercles of the ribs and the transverse processes of vertebrae — the costo-transverse. 14 between costal cartilages and sternum — the chondro-sternal. 6 between cartilages — the " inter-chondral." %4i between ribs and their own costal cartilages — the costo- chondral. Besides the above, and the union of the various segments of the sternum with one another, more especially of the manu- brium and xiphoid, with the body of that bone, there are the joints between the bodies of the vertebrae. 1,58 the costo-central articulation. The Costo-vertebral Articulations; or, the Ligaments AND Joints which connect the Vertebral Column WITH THE RIBS. The costo-vertebral joints and ligaments consist of two sets — viz., (a) those which connect the head of the rib with the bodies of the vertebrse and the intervertebral substance to form the costo-central articulation ; and (h) those which connect the neck and tubercle of the rib with the transverse process of the vertebra to form the costo-transverse articulation. The Costo-central Articulation. Class, Diarthrosis. Subdivision, Ginglymus. This is a ginglymoid or hinge-joint, having an up-and- down movement upon an obliquely transverse axis, combined with some slight backward and forward motion. It is a very perfect joint, with an inter- articular, an anterior or stellate, and a capsular ligament. In the case of the first, tenth, eleventh, and twelfth ribs, exception must be made to the general description which follows, on the ground that each of those ribs articulates with only one vertebra, and with no intervertebral substance at aU, consequently they have no inter-articular ligament, and there is not the same perfect steUate outline to their anterior costo-central ligament. We must first notice the markings on the bodies of the vertebrae and on the head of the ribs, and then consider the lisaments which bind the bones together. The Vertebra. — There are two half-facets on each side of the dorsal vertebrse, from the second to the eighth inclu- sive. These are placed one at the upper, the other at the lower border of the body, far back upon its side. Indeed, the upper half-facet, in most instances, is situated as much upon the outer surface of the pedicle, near its upper border, as upon the side and upper border of the body, whilst the lower facet is directed downwards and outwards, and slightly backwards upon a prominent overhanging tubercle of bone, which is con- tinued above into the curved lower edge of the pedicle. The prominence of these overhanging tubercles, upon which the lower half-facets are situated, is most marked in the upper six vertebrse. The lower facets are more uniform in shape and size than the upper, somewhat circular in outline, and never THE COSTO-CENTRAL ARTICULATION. 159 larger than a split pea. The upper facets are sometimes cir- cular like the lower, but are more frequently crescentic in shape, and elongated from before backwards, with their con- carntj upwards ; they are generally rather larger than the lower, and give the idea of having been more worn by friction. This no doubt is actually the case, for as the upper facet on each side of each vertebra forms the loioer half of the articulation for its own rib, it bears most of the direct inward pressure of the rib ; whereas the lower facet of the vertebra above resists the upward tendency which is given to the head of the rib by the action of the elevator muscles, and for this purpose it looks downwards and overhangs the rest of the articulation. In the first dorsal vertebra there is an entire facet near the upper border on each side of the body close to where the pedicle springs. This part of the first dorsal is prolonged upwards on each side as are the cervical vertebrae, so as to give the well-marked transverse concavity to the upper disc of the body. In this way room is provided for the whole of the head of the first rib without encroaching unduly on the side of the body, or approximating the first too nearly to the second rib. As the first rib is almost horizontal and im- movable, there is no necessity for any overhanging tubercle at its upper border. The demi-f acet at the lower border resembles those of the vertebrae below. In the ninth vertebra there is only half a facet on each side at the upper border which forms part of the socket for the ninth rib. This demi-facet is situated a good way back, and extends partly upon the upper and outer border of the pedicle. At the lower border of this bone there is, as in the vertebra above, an overhanging pro- minent tubercle i but usually there is no half -facet upon it for the tenth rib. On the tenth vertebra there is a circular entire facet at the upper border, and an overhanging non-articular tubercle at the lower. On the eleventh vertebra the single articular facet is a little lower down on the side of the body, extends often upon the outer surface of the pedicle, and has a small overhanging tubercle at its upper border. There is a slightly marked tubercle at the lower border of the body of this vertebra, which can have, however, no effect in resisting the upward tendency of the twelfth rib, but like a 160 THE COSTO-dllNTRAL ARTICULATION. similar one on the lower border of the twelfth vertebra, is only the representative of a part which in the bones above has a definite function. On the twelfth dorsal vertebra the entire facet for the twelfth rib is still lower down on the side of the body, and is surmounted by a well-marked tubercle between its margin and the upper border of the vertebra. The Eibs. — The rib articulates with the vertebrae by its head. The head of the rib consists of a facet on the some- what enlarged extremity of the bone, the external surface of which is bevelled off to form it. This facet cannot therefore be seen from before, as it nowhere extends upon the inner surface. The vertical diameter of the articular surface equals the depth of the rib ; the horizontal diameter is from one- fourth to three-eighths of an inch. The surface is very oblique in direction, being sloped from behind forwards and inwards to the extremity of the inner surface. In all the ribs from the second to the ninth inclusive, the facet is divided into two parts by a nearly transverse ridge ; the lower segment is larger than the upper, and though nearly vertical looks slightly down- wards : the upper segment looks considerably upwards, and is prolonged a little along the upper edge of the bone. The anterior edge of the facet is V"Sliaped ; the point of the V corresponds to the anterior extremity of the ridge between the two segments of the articular surface which gives attachment to the inter-articular ligament. The posterior, upper, and lower borders of the facet are rough, prominent, and well defined. It is upon the transverse ridge and its ligamentous connexion with the intervertebral substance that the rotation of the rib takes place ; and it is to resist the upward pull of the muscles which produce the rotation, that the upper part of the facets is inclined upwards so as to be locked against the overhanging and downward-looking facet on the lower border of the upper of the two vertebrse with which it articulates. The first rib presents an undivided concavo-convex facet which, though situated more fully on the extremity than in the other ribs, still bevels off the posterior, i.e., external surface, to a slight degi-ee. The articular surface is not larger than the upper segment of the facet of most of the succeeding ribs, and has a prominent and well-defined border separating it from the constricted neck. THE THORAX. 161 The tenth rib has frequently only a single sKghtly concave facet, which extends nearly the whole vertical depth of the rib ; like the rest it is bevelled at the expense of the external surface, and cannot be seen from in front ; it is overhung above and below by a rounded prominent margin. The eleventh is very similar to the tenth ; but the tenth occasionally shows a very unequal division of its facets for two vertebrae, the upper one being very small. The facet of the eleventh is always single. The twelth has a small articular facet which occupies only half the depth of the bone, and extends upwards from the lower border of the rib. It is overhung by a prominent and tuberculous little mass of bone which very effectively prevents its too great elevation. It is formed at the expense of the external surface of the rib. It will be seen on looking to one of the middle articula- tions in the recently dissected subject, that the vertebrae and intervening intervertebral substance form for the head of the rib a well-marked concave surface, with a trochlea or pulley-like groove opposite the fibro-cartilage ; that, conversely, the head of the rib presents a suitable convexity from above down- wards, and that the summit of the convexity, which is the ridge dividing the facet, plays in the deepest part of the trochlea. The same kind of arrangement is seen on the bony surfaces of most of the other ginglymoid joints of the body ; it exists in all the central costo-vertebral joints, from the second to the ninth inclusive. The Ligaments. — There are three sets of ligaments in this joint — 1. The capsular ; 2, the inter-articular ; 3, the stellate, or anterior costo-central. The capsular ligament consists of short, strong, woolly fibres, which are attached to each of the bones and to the inter- vertebral substance a . little beyond their articular margins. It completely surrounds the joint, and at its upper part reaches a little way around the intervertebral foramen towards the backs of the bodies of the vertebrae, and so into the spinal canal. Here the capsule is covered and strengthened by fibres which at intervals connect the posterior with the anterior common ligament, by curving upwards over the root of the pedicle of the lower of the two vertebrae which bounds the intervertebral foramen through which they pass. In this way M 162 THE THORAX. the upward strain of the head of the rib during elevation of the thorax is in part resisted. Below, the capsule consists of somewhat longer fibres than elsewhere, which extend down- wards to the tubercle upon which is situated the demi-facet for the rib next below. Behind, the capsule is slightly continuous with the middle costo-transverse ligament, and in front it is thickened and overlaid by the stellate. The inter-articular ligament consists of short strong fibres, which are closely interwoven with the outermost ring of the intervertebral substance, and at the head of the rib are attached to the transverse ridge between the segments of the articular facet. This ligament completely divides the articulation into two parts, each of which is provided with a perfect synovial sac. It does not brace the rib tightly to the spine, but is loose enough to permit a moderate amount of rotation upon its own axis. There is no inter-articular ligament in the costo -vertebral joints of the first, tenth, eleventh, and twelfth ribs. The stellate ligament is the most striking of all, and is seen without any special dissection after cleaning the front of the column. It consists of bright white pearly fibres, which are attached to the upper and lower edges, and the whole of the intervening anterior or inner surface, of the neck of the rib a little way beyond the border of the articular facet of its head. From this they radiate upwards, forwards, and down- wards, so as to form one continuous layer of distinct and sharply defined fibres ; the upper ascend to the lower half of the lateral sm^face of the upper of the two vertebrae ; the middle fibres run straight forwards to the intervertebral substance, and the lower descend to be attached to the upper half of the lateral surface of the body of the vertebra to which the rib belongs — i.e., to whose number fi'om above downwards it corresponds. This ligament is overlapped at its attachment to the spine by the lateral portion of the anterior common ligament, and at its upper border by the communicating fibres between the anterior and posterior common vertebral ligaments. Like the capsular, the stellate ligament checks the hinge-like movements of the head of the rib upon the bodies of the vertebrae. The inter-articular ligament, upon which the move- ments take place, allows more freedom than if the head tm-ned directly upon its transverse ridge ; while at the same time it THE COSTO-CENTRAL JOINT. 163 retains tlie ridge in due relation to the intervertebral substance, and the synovial sacs above and below it. It should be observed that the synovial sacs are confined to the vertebrae and do not extend to the intervertebral substance, which acts as a buffer to break shocks ; whilst the friction of movement occurs at the synovial cavities. All three of these ligaments assist the costo-transverse in retaining the rib in its place ; but in this respect the stellate ligament serves a special function. Owing to the obliquely forward and inward slope of the articular surfaces, especially of those of the rib, as well as to the gradual narrowing of the bodies of the dorsal vertebrae from behind forward, there is a constant tendency, more especially in inspiration, for the head of the rib to glide forwards. The stellate ligament prevents this forward displacement, sometimes by its whole width, but sometimes by its upper fibres cMefly, and at others by its lower. The lower fibres form the broadest and largest portion of the ligaments, and prevent the undue elevation of the rib in inspiration ; the upper fibres are rendered tense when the lower fibres are relaxed by the depression of the rib. In resisting the descent of the ribs in forcible expu-ation, the upper part of the stellate is aided by the superior costo- transverse Hgament. Another purpose served by the stellate ligament is to act as a bond of union between the contiguous vertebrae and the intervening substance. The ribs are like lateral wings or buttresses to the spine, and the fibres of these stellate liga- ments pass off from them to three distinct pieces of the column, and thus add materially to the security of the whole. The Synovial Membrane forms two closed sacs, which do not communicate with each other ; one for the part of the costo-vertebral articulation above, and another for the part below, the inter-articular ligament. In the first, tenth, eleventh, and twelfth articulations there is but one sac, as these joints are undivided. Aeteeies. — Branches spring from the intercostal arteries before they give off their posterior branches, some of which ascend to the joint above, others descend to the joint below, and after piercing the stellate and capsular ligaments reach the synovial membrane of the articulation. Nerves. — Twigs are derived from the anterior primary M 2 164 THE THORAX, branches of the spinal nerves in the immediate neighbourhood of the joints. Movements. — The costo-central articulations are gingiymoid in character, and the movements are limited to a slight degree of elevation and depression around an obliquely horizontal axis, corresponding with the inter-articular hgament ; and to a slight amount of forward and backward gliding. The cavity of each hinge (with certain exceptions before alluded to) is formed by the adjacent bodies of two vertebrae and the intervening inter- vertebral substance, and in this cavity the head of the rib moves in the manner described, with occasionally a slight degree of rotation, or screwing movement. There is considerable difference in the degree of mobility of different ribs, for while the first rib is almost immovable, except in very deep inspiration, and the second rib is but slightly movable, the mobihty of the others increases from the second to the last : the two floating ribs are the most movable of all. The head of the rib is the most fixed point of the costal arch, and upon it the whole arch rotates ; the inter-articular ligament is so short that it allows only a very limited amount either of flexion and extension {i.e., elevation and depression), ■or of gliding, and the gliding is further checked by the strong stellate or anterior costo-central hgament. In inspiration, the rib is elevated and ghdes forwards in the cavity of the vertebrse ; too great elevation is checked, not only by ligaments, but by the overhanging upper edge of the cavity itself. In expiration, the rib is depressed and ghdes back again in its cavity. Although the range of movement at these and the other points of the thorax is very hmited, the movements themselves are very regular and incessant. Sleeping or waking, in health and in disease, while respiration goes on, these joints are in use; yet they are seldom the seat of disease, and are but Httle exposed to injury from violence of any sort. The Costo-transverse Articulation. Class, Diarthrosis. Subdivision, Arthrodia. The costo-transverse articulation, or the connexion between the neck and tubercle of the rib and the transverse processes of two vertebrse, consists of a synovial cavity sm-rounded by a capsular hgament, and of two other ligaments (the middle and THE COSTO-TRANSVERSE JOINT. 165 posterior costo-transverse) between each rib and the vertebra to which it belongs ; and of one Kgament, the superior costo- transverse ligament, between the rib and the vertebra above it. Thus, e.g., the second rib is connected with the transverse pro- cess of the second dorsal vertebra by means of a capsular ligament, a middle and a posterior costo-transverse ligament ; and with the transverse process of the first rib by a superior costo-transverse Kgament. So with the other ribs to the tenth inclusive. The first rib has no superior costo-transverse ligament, i.e., no bond of union with the seventh cervical ; but its connexion with its own vertebra is the same as that of the others. The eleventh and twelfth ribs having no tubercle, and the eleventh and twelfth dorsal vertebrae having only rudimentary transverse processes, there is no synovial articulation, and no capsular or posterior costo-transverse ligament. There is a rudimentary middle costo-transverse ligament between the back of the neck of these ribs, and the rudimentary transverse process of the eleventh and twelfth dorsal vertebrae ; and a well-marked superior costo-transverse ligament connects the eleventh and twelfth ribs with the transverse process of the tenth and eleventh vertebrae respectively. The Vertebra. — The transverse processes of the dorsal ver- tebrae vary in height with reference to the pedicles of their respec- tive bones ; those of the upper vertebrae are on the same hori- zontal level, those of the lower are somewhat below the level of the corresponding pedicles. This agrees with and explains the descent of the lower ribs as they pass outwards and for- wards from the spine. It also accounts for the articular facets of the lower transverse processes being seated upon their upper borders, and of the articular facet on the tubercle of the lower ribs being situated on their lower sides, and looking obliquely downwards. The processes of the upper ten dorsal vertebrae are long, trun- cated at their extremities, and slope considerably backwards as they pass in nearly horizontal planes outwards. They are each marked by a more or less circular facet, concave from side to side and from above downwards, and measuring usually from_ two-eighths to three-eighths of an inch in diameter ; the facets of the middle vertebrae (fourth to eighth) are the largest and best marked. Above and behind the facet is a tubercle, and 166 THE THORAX. below and behind it is another, each of which adds to the bulbous outline of the extremity of the process. The Eibs. — The tubercle of the rib is promment in the upper and middle ribs, but from the eighth downwards it is less so ; and in the eleventh and twelfth it does not exist at all. In some of the ribs there appear to be two tubercles, but when this is the case it is the lower and inner one which has the facet upon it, while the other is but the rough projection for the posterior costo-transverse ligament, detached from the tubercle which it usually surmounts. The facets are usually elongated horizontally, and are convex to fit into the concave facets of the transverse processes of the vertebrse. The facets in all the ribs are nearer to the lower than the upper margins of the tubercles, and become more and more so in the lower ribs. The short portion of the rib between the head and tubercle is the neck. It varies in different ribs ; but averages from an inch to an inch and a half. It is longer in the upper ribs than in those below, and is absent in the eleventh and twelfth ribs. Though shorter in the middle than in the upper ribs, it is broader, and measures usually from half to five-eighths of an inch. The Ligaments. — The capsular ligament is a loose fibrous envelope to the synovial membrane. Its fibres are attached to the bones beyond the margins of their articular facets, and are connected on the inner side with the middle, on the outer side with the posterior, and above with the superior costo- transverse ligaments. The capsular fibres are thickest below, where they are not strengthened by any other structure. It does not exist in the eleventh and twelfth ribs. The middle costo-transverse ligament consists of very short fibres between the back of the neck of the rib and the front of the transverse process of the vertebra with which the tubercle articulates. It extends from the capsule of the costo-vertebral to the capsule of the costo-transverse joint, and limits all the movements of both joints. In order to expose this hgament, a horizontal section of the bones must be made or the rib must be forcibly detached from the transverse process. The posterior costo-transverse ligament extends outwards and upwards from the extremity of the transverse process to the rough projection overhanging the facet on the tubercle of the ribs. Its fibres are short, but thick, strong, and broad. It THE COSTO-TRANSVERSE JOINT. 167 limits movements both of inspiration and expiration, but it checks the ascent {i.e., inspiratory movement) more effectually than it does the descent of the ribs. The superior costo-transverse ligament has nothing to do with the vertebra with which the tubercle of the rib articulates, but passes to the transverse process of the vertebra above. The first rib has no such hgament. It presents a large anterior and a small posterior part. The anterior part forms by far the greater portion of the hgament, and consists of fibres which extend from the prominent ridge on the upper border of the neck of the rib, upwards and outwards to the lower border of the transverse process. The posterior portion is very small, being composed of a few scattered fibres which ascend inwards to the lower border of the transverse process ; it limits the descent of the ribs in expiration. The anterior portion checks the downward movement of expiration, but it also prevents, like the middle costo-transverse, the separation of the neck of the rib from the transverse process of the vertebra below. They do not check the elevation of the ribs in inspiration, but they tend to prevent the rotation which accompanies and facihtates that elevation. The anterior surface of this ligament is easily cleaned ; the posterior surface and the posterior costo-transverse hga- ments are dissected with difficulty, owing to the close adhesion thereto of muscular fibres. Aeteries. — The arterial twigs supplying the structures which unite the ribs and transverse processes are derived from the intercostal arteries, and from the branches of the posterior spinal vessels which supply the muscles of the back. Neeves, — Twigs are derived from the posterior primary branches of the dorsal nerves. Movements. — The costo-transverse are arthrodicd joints, and the movements which occur at them are limited to a ghding of the tubercle of the rib upon the facet of the transverse process. It has been stated that the exact position of the facet on the transverse process varies slightly from above downwards, being placed higher on the processes of the lower vertebrae. The plane of the opposed facets in most of the costo-transverse joints is, however, inclined upwards and backwards, so that the tubercles of the ribs ghde backwards and upwards in inspira- tion, and downwards and forwards in expiration. The point 168 THE THORAX. round which these movements occur is the head of the rib ; the tubercle of the rib ghdes upon the transverse process of the vertebra in the circumference of a circle, the centre of which is at the costo-central jomt. The Costo-chondral Joints, or the Union of the Ribs with their Costal Cartilages. Class, Synarthrosis. These joints are of the synarthrodial kind. The extremity of the cartilage is received upon the end of the rib, which is somewhat larger than the end of the cartilage. The two are joined together by a mere continuity of theu^ investing mem- brane ; the periosteum of one being continued into the peri- chondrium of the other, much in the same way as the epiphyses of bones are joined to their shafts. It is probable, however, that the costal cartilages are not merely unossified portions of ribs, but that they are distinct parts of the skeleton separated, both from the sternum and from the ribs in foetal life, by a formative material, which becomes converted into synovial membrane between certain cartilages and the sternum, but elsewhere usually disappears. The Union of the Segments of the Sternum with one another. The sternum is situated at the forepart of the thorax in the median plane of the body. It is connected with the costal arches by the first seven cartilages, and in addition gives support to the upper extremities at the sterno-clavicular joints. It is composed of five bony segments and an osseo- cartilaginous appendage, called the xiphoid cartilage, wliich together form a fiat and symmetrical column. This column, like the vertebral column behind, gives support to the costal arches, completes the chest wall, and forms a sort of buckler to the thoracic viscera. It is usual to speak of the sternum as consisting of the manubrium, body, and xiphoid or ensiform process ; or in other words, of the praesternum, mesosternum, and metasternum, respectively. The manubrium is the largest segment of the sternal column, at the summit of which it is placed. It is flat and somewhat triangular in shape, with its narrower end down- wards. It is never, or rarely if ever, even in extreme old age, THE COSTO-CHONDRAL JOINTS. 169 united with the body of the sternum by bone ; but the two are connected together by intervening cartilage, and by a strong investing periosteum which is tliickened by longitudinal liga- mentous fibres, both behind and in front, as well as by the radiating and decussating fibres of the chondro-sternal ligaments. If this union be regarded as a joint it must be classed with the amphiarthrodial. There is usually a well-marked curve with its convexity forwards in the sternal column opposite the union of the manubrium and body, and frequently there is a larger interval between these two segments behind than in front, so that the bones are there joined together by strong short bundles of fibrous tissue instead of by cartilage. Sometimes this fibrous tissue stretches forwards to the front of the column so as to give the appearance of two plates of cartilage, one for the manubrium and one for the body, united by means of short fibrous bundles. The mesosternum, or body of the bone, consists of four segments which at the age of twenty-five years have usually united into one soKd plate. Up to the time of their union by ossification a thin plate of cartilage intervened between the adjacent edges of the segments, and these were strengthened by the investing membrane and the longitudinal and radiating and decussating ligamentous fibres, like those referred to in the union of the manubrium and body. The metasternum or onplioid process is joined to the lower end of the body of the sternum by a thick investing membrane, by anterior and posterior longitudinal fibres, and by ~ the radiating chondro-sternal ligaments of the sixth and seventh articulations. It is also connected with the fore surface of the sixth and seventh cartilages by the cliondro- xiphoid ligament ; and with the hinder surface of the seventh cartilage, for one-half or three-quarters of an inch, near the sternum, by means of some fine fibro-areolar tissue. The junction of the xiphoid with the lower end of the body of the sternum is on a level somewhat posterior to the junction of the seventh costal cartilage with the sternum. This union is synarthrodial. Movements. — The permanency of the soft union between the manubrium and body of the sternum is for the purpose of providing elasticity in the column, and so enabling it to 170 THE THOEAX. resist external pressure rather than to permit of movements taking place between them. At the junction of the xiphoid and sternum, a backward and forward movement of this appendage is constantly going on in respiration ; and this is aided by the flexibility of the xiphoid itself. Dming the contraction of the diaphi^agm the ensiform or xiphoid process would be pulled backwards to a great extent were it not for the elevation of the sternum and costal arches, and the resistance offered by the descending viscera and by the chondro-xiphoid ligament. During expiration, on the other hand, the diaphragm ceases to pull the process backwards, and it returns into its normal line with the sternum. The Chondro-stemal Articulations, or the Ligaments and Joints which connect the Costal Cartilages with the Sternum. Class, Diarthrosis. Subdivision, Ginglymus. (Joint of first cartilage excepted, which belongs to class Synarthrosis.) There is no uniformity in the manner in which the cartilages articulate with the borders of the sternum. It varies in different individuals, and in different joints of the same individual, and also in the corresponding joints on the two sides of the body. In the first joint, which is an example of synarthrosis, there is little or no movement. The first costal arch is needed to support the manubrium sterni, and through it the clavicle and the upper limb. It is the point cVappui from which the movements of the lower true ribs take then' start. In each of the other six joints there is a synovial cavity which in some instances is divided into two by an inter-articular ligament. The Sternum. — We are concerned only with the lateral borders of tliis bone. The average length in the adult is about six inches and a half (inclusive of the xiphoid cartilage, which is about an inch long). Its width varies in different parts, being gTeatest between the cartilages of the first rib, where it measures from two to two and a half inches ; and, if the xiphoid cartilage be excluded, its narrowest part is be- tween the second costal cartilaoes or in the interval between the second and third, where it measures about three-quarters THE CHONDRO-STERNAL JOINTS. 171 of an inch. The bone presents along each lateral border seven facets for as many costal cartilages, and in the recent state each facet is coated with a layer and sometimes a very thick layer of articular cartilage. The superior facet is the largest and longest of aU; it is oval in shape, but much narrower from before backwards at its lower part than above. It is overhung in front and above by a prominent lip or margin, which separates it from the oval articular surface on the upper border for the clavicle. This lip serves to prevent the upward and forward displacement of the first costal arch during the action of the muscles which play upon it ; it also prevents the backward displacement of the sternum by violence. Below tliis facet the border of the sternum slopes rapidly from above downwards and inwards to the narrowest part of the bone, and then succeed at irregular intervals six shallow cavities for the cartilages of the second, third, fourth, fifth, sixth, and seventh ribs. The upper three of these cavities or facets are about an inch from one another, and that for the second cartilage is about the same distance from the facet for the first. The upper edge of each of these facets is more prominent than the lower, and the front is more prominent than the posterior, for the same purpose as in the case of the first. The lower three facets are much nearer to each other ; thus the fifth is about half an inch from the fom^th, the sixth about a quarter of an inch from the fifth, and the seventh less than one-eighth of an inch from the sixth. The fifth facet is sHghtly overhung above and in front by its margiti, but to a less extent than those higher than it. The sixth and seventh, especially the seventh, are situated more at the lower angle of the body of the sternum than on the lateral border. The lower end of the body widens out a httle, and in the centre of its inferior border the xiphoid cartilage unites with it ; wliile on each side of the union with the xiphoid cartilage the costal cartilages of the seventh and sixth ribs are close together. Thus these cartilages also are overhung by bone above, at their union with the sternum, but by the sternal body, and not by an out- standing margin of the articular facet. The third, fourth, and fifth cartilages articulate with the body of the sternum, in the line of union of two of its primi- tive segments ; the second, at the line of union of the manubrium 172 THE THORAX. with the body ; the seventh, at the line of union of the body with the xiphoid cartilage. The sixth is not related to two segments, but articulates at the angle between the lateral and the in- ferior borders of the body of the bone. The intervals between the facets are somewhat concave, and correspond to the inter- costal spaces. There is, it will be observed, considerable analogy between the mode in which the costal arches are connected with the sternal and vertebral columns. Thus each cartilage, except the first and sixth, is united with two segments of the sternal column as the head of each rib is with two vertebrse, wliile the articular facets of both sternal and vertebral column are overhung, above, so as to prevent the upward displacement of the arches by the pull of the muscles of inspiration, and for the same reason a strong stellate or radiating ligament passes over the front of both vertebral and sternal joints. The analogy, moreover, is carried out in the case of the first costal arch, which is connected with only one vertebra behind, just as it is with only one segment (the manubrium) of the sternum in front. The Costal Cartilages have, by some anatomists, been regarded as the anterior epiphyses of the ribs. Like the ribs, they differ from one another, thus they increase in length to the seventh, and decrease from the eighth to the twelfth. They decrease in thickness from the first to the twelfth. The first descends to the sternum, in continuation of the direction of the first rib. Its inner extremity is dhectly united with the osseous tissue of the sternum, so as to afford strong support to the clavicle, and by giving attachment to the costo- clavicular ligament the cartilage adds to the security of the sterno-clavicular articulation. The second cartilage joins the sternum at a right angle, and is of nearly the same width throughout. It forms an obtuse angle with its own rib. The sternal extremity is very convex from above downwards, and its articular facet is divided by a horizontal ridge into two parts, one of which looks upwards to articulate with the lower angle of the manubrium, and the other downwards to articulate with the superior angle of the body of the sternum. The other cartilages, as low as the tenth, make, each one in succession, a more acute angle with the rib than its predecessor ; THE CHONDO-STERNAL JOINTS. 173 for as the ribs are incliiied downwards and forwards from their vertebral joints, with an obhquity increasing from the first to the last, so the costal cartilages have to ascend with a corresponding degTee of obhquity from their junction with theu' ribs to thek sternal joints or anterior free extremities. Each is shallower at its anterior end than elsewhere, as they diminish in width from their costal extremity forwards. The articular facets at the anterior extremity of the third, foiu'th, fifth, sixth, and seventh are sHghtly convex from above down- wards, and play in the corresponding cavities on the lateral border of the sternum. The Ligaments. — Except at the synarthrodial joint between the first cartilage and the sternum, each of the chondro-sternal articulations has an anterior and a posterior, a superior and inferior chondro-sternal ligament, wliich together form a com- plete capsule. A synovial cavity lines the joint, and is com- monly in the second, and occasionally in one or more of the third, fourth, fifth, and sixth joints, divided into two parts by an inter-articular ligament. The anterior chondro-sternal ligament is a triangular layer of strong fibres which covers the inner half inch of the front of the cartilage, and radiates upwards and downwards upon the front of the sternum. Some of the fibres decussate across the middle Hne with the fibres of the corresponding ligament of the opposite joint ; while along the upper and lower borders of the Hgament they are in contact with the superior and inferior chondro-sternal ligaments respectively. By the lower part of this Hgament, traction is made upon the sternum during the act of inspiration ; the downward and inward obliquity of the fibres allows them to pull upon and raise the sternum during the elevation of the ribs. It is obvious, however, that apart from this obliquity the mere connexion of the cartilages with the sternum by means of facets with overhanging upper edges would insure the elevation of the sternum, together with the costal arches. The jposterior chondro-sternal ligament consists of little more than a thickening of the fibrous covering of the bone and cartilage ; indeed, it may be fairly said that these joints are completed behind by a continuity of the perichondrium into the periosteum. The superior a.nd inferior chondro-sternal ligaments are 174 THE THORAX. strong and well-marked bands of fibres extending over the borders of the joints from the front to the posterior surface. In the case of the second, third, fourth, and fifth they are re- flected some distance along the curved lateral border of the sternum at the intercostal intervals. The sixth and seventh joints are so close together that the articular cartilage on the sternal facets is continuous, and the inferior hgament of the sixth and the superior of the seventh are blended together, so as to form a kind of inter-articular ligament between the two separate joints. Deeper than the fibres of these several ligaments are some shorter ones connecting the margins of the articidar cartilage on the sternal facets with the edges of the facets of the costal cartilages. Tliey are generally most distinct at the front and lower part of the joint, and in some cases are so numerous, and encroach so considerably upon the synovial cavity, that they reduce it to a very small size, or almost obliterate it. The sixth and seventh, but especially the seventh, are the joints most frequently modified in this manner. The inter-articular ligament is by no means a constant con- stituent of the chondro-sternal joints. It is usually present in the second joint on one, if not on both sides of the same svibject. It consists of a strong transverse bundle of short fibres between the ridge on the facet of the cartilage and the symphysial substance between the manubrium and the body of the sternum. Sometimes the part of the synovial cavity above this hgament is almost replaced by fine hgamentous fibres, in the same way that the synovial cavity of one or other of the joints below is sometimes nearly or quite obliterated. The chondro-xiphoid ligament is a strong flat band of fibres passing obliquely upwards and outwards from a considerable part of the front surface of the xiphoid cartilage to the anterior surface of the sternal end of the seventh costal cartilage, and most frequently to that of the sixth also. It has an important action besides helping to unite the seventh costal cartilage to the sternal column ; for it fix:es the xiphoid cartilage during the elevation of the sternum and costal arches in inspiration, and thus prevents it from being drawn backwards to any great extent during this movement by the contraction of the diaphragm, which occurs at the same moment as the elevation of the chest wall. 'ERTICAL SECTfON OF CHO N DRO - STERNA l_ & I NTERC HONORAU JOINTS rivn 1'^ Th Ayiis stern/w- clctvicaXccr Hoj- .i:ttrru>-cZa*'icliUKr joxnt d.f-0-stje.r-n.-il jtrvnt: ocfte-r" cc fvtmt of Fiby-oi^s Ussa^ on. front oF steryvMnt- Costo-xifalxoi^ ZiactA^n^nt htterelto wdTC^ Ijuoj t*«-M' - da'C,cL*L^y^^^ - Westlfewmem &. 'Ji'Utiv. THE INTER-CHONDRAL JOINTS. 175 Arteeies. — The anterior or perforating branches from the internal mammary artery ramify over the front of the joints, and supply them. Nerves. — Twigs are supplied from the anterior extremity of the upper intercostal trunks. Movements. — Most of the chondro-sternal are gingiymoid joints. The movement permitted at them is very limited, but consists of a hinge-like action in two directions : first, there is a smaU amount of elevation and depression, which takes place round a transverse axis ; and secondly, there is some forward and backward movement round an obliquely vertical axis. The depressions on the lateral borders of the stermmi are the sockets or cavities of the hinge-joint, and into these the ends of the cartilages are received. In inspiration the cartilage is elevated, and the lowest part of its articular facet is pressed into the socket of the sternum, and the sternum is thrust forwards, so that the upper and front edges of the opposed articular surfaces separate a little. In expiration the cartHage is depressed, and the sternum returns to its former position, so that the articular surfaces regain their former state of apposition. Thus the two ex- tremities of the costal arches move in their respective sockets in opposite directions ; for whereas in inspiration the hinge - like action at the head is such that the upper part of the articular facet rolls into the socket, the lower part of the articular end of the cartilage sinks a Kttle deeper into its cavity on the sternum. This difference results necessarily from the fact that the costal arch moves upon the vertebral column, and having been elevated, it in its turn elevates the sternum by pushing it upwards and forwards. Were this not the case the sternum would be depressed by the elevation of the costal arches. The Inter-chondral Articulations, or the Union of the Costal Cartilages with one another. Class, Diarthrosis. Subdivision, Arthrodia. The anterior extremities of the lower five ribs are unconnected with the sternal column ; and whilst the upper three of these are closely connected with one another and the seventh, each with the lower border of the preceding, by means of short 176 THE THORAX. fibro-areolar and muscular fibres, the two lowest are at some distance from the tenth, and from one another. A little in front of the point where the costal cartilages bend upwards towards the median line the sixth is united with the seventh, the seventh with the eighth, the eighth with the ninth, and the ninth with the tenth. At this point each of the cartilages, from the sixth to the ninth inclusive, is deeper than elsewhere, owmg to the projection downwards from its lower edge of a broad blunt process, which comes into contact with the upper edge of the cartilage next below. Each of the apposed surfaces is flattened and smooth, and connected together at their margins by Kgamentous tissue, which forms a complete capsule for the articulation, and is lined by a synovial membrane. The largest of these synovial cavities is between the seventh and eighth cartilages, and is five-eighths of an inch in width. Those between the eighth and ninth, ancj the ninth and tenth, are generally much smaller, as the flattened sm^faces, instead of being free to play upon each other in the whole of their extent, are in part held together by the ligamentous tissue which extends betw^een these surfaces at their anterior margins. Sometimes indeed fibrous tissue alone forms the bond of union between these lower cartilages, as it does occa- sionally between one or other of the costal cartilages and the sternum ; in w^hich case, of course, there is no synovial articulation. In the interspaces between the cartilages, both in front of and behind the inter-chondral joints, are the muscular and fibrous tissues of the chest wall. Sometimes the fifth and sixth cartilages are united together, like those below them. The eleventh and twelfth cartilages are not in contact with the tenth and with one another, and therefore have no inter- chondral joint, but are connected only by the intercostal and abdominal muscles and areolar tissue. Aetekies. — The musculo-phrenic artery from the internal mammary supplies the structm-es of these small joints by means of the branches it sends outwards along the intercostal spaces. Nerves. — Twigs are supplied from the intercostal nerves of the corresponding spaces. THE MUSCLES OF THE THORAX. 177 Movements. — By means of the costal cartilages and of this series of inter-chondral joints, strength with elasticity is given to the wall of the trunk at a part where the cartilages are the only firm structure in its composition, while at the same time a slight gliding movement is permitted between the costal cartilages themselves. Tliis movement takes place round an axis which corresponds to the long axis of the cartilages ; by it the outward projection of the lower part of the thoracic .wall is increased in deep inspiration, and thereby more room is provided for the viscera of the abdomen. These viscera are compressed between the descending diaphragm and the upper part of the abdominal wall, which sinks in considerably towards the end of a long inspiration. The Muscles of the Thorax. — In all animals whose respii-atory organs are contained within a true thoracic cavity, the framework of the thorax serves other purposes than those subservient to respu^ation, i.e., the drawing in and the expul- sion of air. In all it gives attachment to large muscles of the upper limb, whether they are used for prehension or locomotion; to muscles of the back for the extension of the trunk, and to muscles of the abdomen which act upon the trunk and pelvis. Thus it is evident that the muscles connected xoitli the thorax are by no means synonymous with the muscles of resjmrition. As the thorax is part of the boundary of the trunk, it affords advantageous attachment for muscles which move the trunk as a whole, quite irre- spective of the movements necessary for respiration. The muscles of respnation are destined especially to act upon the thorax so as to expand or contract its cavity ; but there are a number of other muscles attached to the thorax destined especially for other ends than those of inspiration and respira- tion, which also do occasionally act to enlarge or diminish the cavity of the chest, and thus to increase the power of inspir- ing or expiring. These latter are sometimes spoken of as the indirect ■ tmtscles of respiration ; but in difficult inspiration patients are sometimes seen employing nearly their whole mus- cular apparatus, so that " scarcely any particle remains in the body which is not more or less concerned in the business of respiration." In this sense the group of indirect respiratory muscles would N 178 THE MUSCLES OF THE THORAX. nclude nearly every muscle m tlie body not included in the group of direct muscles of rcsjnration. In the followino; enumeration the muscles of the thorax are divided into the direct — or those whose sole or chief purpose is to act upon the costal arches ; and the indirect — whose pri- mary use is to move some distant part of the skeleton whilst acting from the thorax as theu' fixed point. Most of the direct muscles of the thoracic wall are also intrinsic muscles of respiration, but not all. The sacro-lumbalis, longissimus dorsi, and musculus accessorius, for instance, are direct muscles of the ribs — i.e., their chief purpose is to act upon the costal arches, but with the object of extending the trunk, not primarily with the view of aiding in respiration. These muscles afford another good illustration of what I have described as a general law — viz., that muscles wliich by their action upon bones near their articular surfaces would have the effect of straining the hgaments, or weakening the joints, unless they were attached to both bones of the articulation, do as a matter of fact give secmity to the joints by being inserted into both bones. Part of the longissimus and the spinalis dorsi, the middle and inner columns of the erector spinse, are inserted into the processes of the dorsal vertebrae, and in their action to extend the back are resisted by the weight of the thoracic and abdo- minal viscera, wliich by dragging upon the ribs and sternum tend to pull away the head and neck of the ribs from the spinal column. These conflicting forces would unduly strain the costo- vertebral ligaments were it not for the outer column of the erector spinse (sacro-lumbalis) and part of the longissimus dorsi, which by acting in conjunction with the rest of the erector and by being inserted into the ribs from the tubercles to the angles, assist in holding the ribs to the spinal column, at the same time that they act to extend the back. But although the muscles of the back are not direct muscles of respiration, they — even those which have no attach- ment whatever to the ribs — assist inspiration. For inspiration to be full and complete, there must be extension of the spine. When the column is bent forwards the ribs fall together, and though ordinary and quiet inspiration goes on well for a time in this position, the column must be erect before the ribs can THE MUSCLES OF THE THORAX. 179 he separated to tlteir fullest extent and a full inspiration made. The long-continued effects of a curved spinal column upon inspiration is seen in the laboured and short breathing and in the deficient aeration of the blood in sufferers from spinal deformities ; and explains the great relief experienced by patients from extension of the back in a fixed apparatus such as has of late been introduced into surgical practice by Dr. Sayre, of ISTew York, Again, those portions of the muscles of the back which are inserted into the ribs depress the costal arches when the peMs and spine are fixed, and thus occasionally assist in, and therefore are indirect muscles of, expiration. The direct muscles of the thorax — i.e., those whose chief purpose is to act upon the costal arches, whether for the purposes of respiration or otherwise — may be divided into two groups ; (A) those which arise beyond the thorax, and are only inserted into it ; and (B) those which are not connected with any other part of the skeleton except the thorax, A. Those which arise beyond the thorax, are — 1, The serratus posticus superior, 3. The serratus posticus inferior. 3, The scalenus anticus, scalenus medius and scalenus pos- ticus, 4, The sacro-lumbalis and longissimus dorsi. 5, The quadratus Imnborum. Of these only the serrati postici are purely muscles of respiration, the rest serve other purposes as well ; while the scaleni and the quadratus lumborum act occasionally upon the neck and pelvis respectively. The scalene muscles are elevators of the first two costal arches, and aid constantly in the movements of inspiration, not only by their own dii-ect action upon the ribs, but by fixing the arches to which they are connected, and thus making them the "point d'appui" from which the intercostal muscles act. The sacro-lunibalis, longissimus dorsi, and quadratus lum- horum serve mainly to extend the trunk, but together with the serratus posticus inferior they depress the lower ribs and thereby aid indirectly in inspiration. During the action of the diaphragm its circumferential muscular portion tends to pull N 3 180 THE MUSCLES OP THE THORAX. upwards and inwards the lower six ribs from which it arises towards its own central inelastic tendon, but this tendency is counteracted by these several muscles (as well as by the descending viscera), wMch give firmness to the costal arches by depressing them ; just as the scalene muscles and the serratus posticus superior give firmness to the superior arches by elevating them. These same muscles of the back also aid in forcible expira- tion, by depressing the ribs to wliich they are attached. This they do by continuing their action after the diaphragm has ceased to contract. B. Those which both arise from and are inserted into the thorax. 1. The subcostales and the triangularis sterni, the former near the angles of the ribs, and the latter at the costal cartilages from the sixth to the second inclusive, depress the costal arches and thereby aid directly in forcible expiration. 2. The diaphragm, the chief muscle of respiration. 3. The intercostales, muscles of inspu-ation. 4. The levatores costarum, muscles of inspiration. 5. The musculus accessorius ad sacro-lumbalem. All the muscles in this group, excepting the last, are simply and purely muscles of respiration. The diaphragm is concerned in a large number of physio- logical processes, and aided more or less by the other respi- ratory muscles, contributes to such acts as coughing, sighing, singing, sneezing, sucking, whistling, yawning, vomiting, talking, as well as defecation and mictmition. The musculus accessorius, it is true, assists in expiration by approximating the upper and lower ribs towards one another, but its chief purpose is to co-operate with the other muscles of the back in extending the trunk. It also acts, however, with those muscles to produce forcible expiration. The fullest inspu-ation that is possible is made in the erect posture, but hyperextension of the back diminishes the capacity for inhaling, and is attended with some involuntary expiration if made immediately after a full breath has been taken in the erect attitude. This is doubtless due to the depression of the ribs by the extreme contraction of the sacro- lumbalis and longissimus dorsi, and to the approximation of the ribs by the musculus accessorius which acts at the same time. THE MUSCLES OF THE THORAX. 181 The indirect muscles of the thorax have one of their attach- ments at the thorax and the other at some remote part of the skeleton, and their chief action is not to move any part of the thorax, but to act from it as thcK fixed point. They may be grouped according to the division of the body which they act upon. {a) Those to the upper limb — 1. The pectoralis major; 2. Pectoralis minor; 3. Sub- clavius ; 4. Serratus magnus ; 5. Latissimus dorsi. The last-named has but a shght connexion with the thorax, being attached only to the three lowest ribs. All these muscles act secondarily upon the thorax, and serve to draw upwards or forwards the trimk when the outstretched arms are made the fixed point, as in chmbing or pulling. The pectoralis major and minor, and the subclavius, occasionally act as assistant muscles of inspiration. The pectoralis major affords another good illustration of the law above referred to respecting the attacliment of muscles to both bones of an articulation. The serratus magnus, at first sight, might seem to contradict this law ; but not so, for not only is it attached to the ribs at some distance from either extremity, but it pulls upon a very movable part of the skeleton, viz., the scapula, and in an oblique direction, so that it in reality exerts no influence to disturb the joints of the costal arches. Again, the law is illustrated by the abdominal muscles. The opposite direction of the fibres of the external and internal oblique, and the position of the transversalis upon the inner surface while the external oblique arises from the outer surface of the costal arches, neutralise one another. The rectus abdominis is attached to the sternum, cartilages, and ribs, and therefore acts simultaneously upon all. (&) To the spine — The cervicaHs ascendens, wMch takes origin from four- or five of the upper ribs, acts in conjunction with the rest of the erector spinse muscles and extends the neck. It has little if any independent action on the thorax. (c) To the head anteriorly, and to the larynx — 1. The sterno-cleido-mastoid. 2. The sterno-thyroid, and generally the sterno-hyoid. All these muscles act from the sternum upon the parts into which they are inserted. They may assist in fixing or raising the sternum, for the purposes of respnation, but this only rarely. 182 THE MOVEMENTS OF THE THORAX. It is interesting to remark that wliile the sterno-mastoid muscle is attached both to the sternum and clavicle in illustra- tion of the law above stated, yet that the sterno-hyoid and sterno-thyroid, being small feeble muscles and acting upon a very movable part like the laiynx and hyoid bone, are not invariably attached to the bone on each side of the joints near which they arise, for the reason no doubt that their pull upon the sternum is not sufficient to exert any deleterious effect upon the articulations. (d) To abdominal wall — 1. The obliquus externus ; 3. The obliquus internus ; 3. The transversalis ; and 4. The rectus abdominis. These muscles form the greater part of the wall of the abdomen, and compress the viscera of that cavity as well as the viscera of the pelvis. When the vertebral column is fixed, they are able to draw down the ribs and to assist in forcible expiration by contracting the lower portion of the thorax, and forcing up the viscera against the diaphragm. When the column is not fixed, they pidl upon the thorax, and thereby bend the trunk forwards and downwards or laterally and downwards. Movements of the Costal Aeches and the Steenum as A WHOLE. — Before describing the movements of the thorax as a whole, it must be premised that there are some few modifica- tions in the movements of certain ribs which result from the pecuHarities in the shape of those ribs. Thus the first rib (and to a less extent the second also), which is flat on its upper and under surfaces and is placed at the iipper end of the thorax, re- volves on a transverse axis which passes through the costo-trans- verse and costo-vertebral joints, and coincides pretty nearly with the axis of movement of the corresponding rib of the opposite side. During inspiration and expiration these costal arches with the sternum between them play up and down in such a manner, that while the transversely elongated tubercles of the ribs move upon the depressed sockets on the transverse processes in a hinge-like manner, the rounded heads of the ribs are moving similarly, but with a slight screwing or rotatidn in their sockets, and the anterior extremity of these costal arches are simply raised and depressed. The other ribs, more particularly those in the mid-region of THE MOVEMENTS OF THE THORAX. 183 tlie thorax, move in a somewhat more complex manner. Besides the elevation of their anterior extremities, the bodies and angles of the ribs rise nearly as much in inspiration as these extremities themselves, and the whole costal arch revolves upon an axis drawn from before backwards from the costo- central to the chondro-sternal articulations. This axis cor- responds in the former joints to the oblique ridge on the head of each rib. It is incorrect to say that the rotation takes place upon a line connecting the two extremities of the rib itself. Without this difference the movements of the ribs of the mid-region of the thorax would not have increased the trans- verse diameter of the chest to so great an extent, and consequently would not have rendered the same assistance in inspiration. In conformity with this difference the movement of the tubercles of the ribs upon the transverse processes is one of gliding upwards and backwards in inspiration, and downwards and forwards in expiration ; and for tliis purpose the apposed articular surfaces at these costo-transverse joints are flat and a little elongated from above downwards. During inspiration the movements of the thorax enlarge in every direction the space surrounded by it. The antero- posterior diameter is increased by the forward movement of the sternum, and by the elevation of the costal cartilages and of the forepart of the ribs, whereby they are brought to nearly the same level as the heads of the ribs. The transverse diameter is increased both anteriorly and posteriorly. When at rest the middle part of the ribs themselves dips considerably, owing to a downward curve in their body in front of the angle, and is thus on a lower level than either the costo-vertebral or the chondro-sternal articulation. Owing to this obliquity, when the rib is raised the transverse diameter of the chest is increased, and the increase is proportionate to the degree of obliquity which is greatest in the ribs in the mid-region of the thorax. Fm^ther forward the anterior extremity of the rib is not only elevated and advanced, it is also carried a Kttle outwards from the median line. Thus the transverse diameter is increased behind by the elevation of the middle part of the ribs, and in front by the abduction of their anterior extremity ; and it is 184 THE MOVEMENTS OF THE THORAX. throughout further increased by the outward roll of the lower border of the costal arch iu its rotation upon a line drawn between the vertebral and sternal joints. The increase in a vertical diameter is due to the elevation. of the ribs, especially of the upper ones, and to the consequent widening of the intercostal spaces. The descent of the diaphragm, however, chiefly increases the " cavity of the thorax" in the vertical dh-ection. It will be seen that the dorsal vertebrae take no share in this general increase in the size of the thorax ; they act like a fixed rod or column, which only occasionally, during forced inspi- ration, becomes extended to a slight degree. After the ver- tebrae, the sternum is the next least movable part of the thorax, and the part of the thoracic area intervening between them does not need to undergo such great variations in size, owing to the natm^e of the contents of the mediastinum, which instead of being lung, are the heart and great vessels, the oesophagus, areolar tissue and glands. The greatest increase, both in a transverse and antero- posterior direction, takes place at those parts of the thorax which are themselves of the greatest extent — i.e., where the ribs are longest, most oblique, and most curved at their angle ; and where the bulkiest portion of the lung is enclosed. This is on a level with the sixth, seventh, and eighth ribs. More- over, the hinder portion of the costal arches — i.e., about the angle of the ribs — by their movements cause the gTeatest increase in the thoracic measurement, and in this part the tliickest and most active and important part of the lungs are contained. At the lower part of the thorax, where the ribs have no relation to the lungs, and do not affect respiration dii-ectly by their movements, it is important that the costal arches should be well thrown outwards in order that thereby they may counteract the disadvantageous effect upon the contraction of the diaphragm, which would be otherwise sustained by their elevation. By widening the lower part of the thorax diu-ing inspu'ation the origin of the muscular fibres of the diaphragm is widened, and their power is thus increased. The muscles by which the various movements of inspiration are effected have been enumerated above. For the diversity of views respecting the action of the intercostal muscles, standard THE MOVEMENTS OF THE THORAX. 185 works on anatomy of the thorax may be referred to. Here it is sufficient to state, that both external and internal muscles are regarded by the author as muscles of inspiration. Ordinary expiration is not produced by muscular action, but is a return of parts to their state of rest after they have been disturbed therefrom by the muscles of inspiration. PART III. THE LIGAMENTS AND JOINTS OF THE UPPER EXTREJiHTY. CHAPTEE IX. THE STEENO-CLAVICULAK JOINT AND COSTO-CLAVICULAR LIGAMENT, Class, Diarthrosis. Subdivision, Arthrodia. At this joint the inner and larger end of the clavicle is united to the superior angle of the manubrium sterni. The first costal cartilage, moreover, assists the sternum in giving support to the clavicle. Looking at the hones, one would say that they were in no way adapted to articulate with one another, and yet they assist in constructing a joint of great strength, security, and im- portance. It is true that the bones themselves are nowhere in actual contact, being separated completely by the inter-articular hgament. The sterno-clavicular is the only articulation be- tween the upper limb and the trunk, and takes part both in the upward and downward, and in the forward and backward movements of the arm, as well as in the movements of cir- cumduction of the upper extremity. It is an arthrodial joint. The interval between the joints of the two sides varies in different subjects from an inch to an inch and a half. The STEENUM presents at the superior angle of the manubrium a large concave articular facet looking upwards, outwards, and a little backwards. Its longest diameter is, in the transverse direction, from mthin outwards, and measures rather over three-quarters of an inch. Its antero-posterior diameter is less than half an inch, and is wider near the notch of the sternum than near the first chondro-sternal joint. It is markedly, but irregularly, concave from above downwards and outwards, and is often concave from before backwards also. Occasionally, o\^^ng to the bevelKng off of the articular surface near to its anterior and posterior margins, the socket looks to THE STERNO-CLAVICULAE JOINT. 187 be very slightly convex from before backwards, but even tben tlie centre of the socket is always the deepest part of it. The margin of the facet is sharply defined all around, but is ap- parently more projecting in front, owdng to the backward inchnation of the facet. Looking at the bone from in front none of the articular surface can be seen, whereas looking from behind the entire facet is in view. This obHquity has importance in relation to the movements of the thorax in respiration, rather than to those of the upper extremity ; by tliis backward slope of the facet the sternum is able to advance a little upon the end of the clavicle diu-ing its elevation in inspiration ; had the slope of the facet been for- ward, the upper end of the manubrium must have tilted back- wards upon the end of the clavicle, at the same time that the body of the sternum was raised and advanced by the inspira- tory muscles. The interval between the facet on the two sides ' varies much more in different subjects than does the size of the facet itself. In some subjects this space, which corresponds with what is called the sternal notch, is not wider than three- quarters of an inch, in others it exceeds an inch. The depth of this notch is considerably increased by the inner end of the clavicle, so that it is much greater in the living subject and the articulated skeleton than would be supposed from an examination of the manubrium alone. This notch is also called the inter-clavicular notch. Immediately below the facet for the clavicle is the junction of the cartilage of the first rib with the manubrium. This is a synarthrodial joint, the two structures being directly united with one another. The cartilage on its way from the rib to the manubrium slopes downwards as weU as forwards ; and as it is so inclined that its upper surface looks forwards and its under sui^face backwards, the posterior border is the highest part of it. It is this border wliich increases considerably the concavity of the sterno-clavicular socket, the lower and outer part of whicli it completes. Indeed the two form together the arc of a circle, the diameter of which is about an inch, and may be roughly stated to be the horizontal line drawn between the upper border of the sternum and the first costo -chondral joint. It is upon the inner three-fourths of this arc that the clavicle moves. The Clavicle. — The inner two-thirds of the shaft of the clavicle is strongly curved in a horizontal plane, with the con- 188 THE STERNO-CLAVICULAR JOINT. vexity of the curve forwards, and presents a marked difference' fi'om the outer one-tliird, in that it is cylindrical in outline instead of being flattened on its superior and inferior aspects. At the inner end the bone suddenly enlarges, like the ex- tremities of the shaft of many of the long bones, into an articular surface ; this is for the sternum, or, more properly speaking, for the inter-articular ligament of the sterno- cla\dcular joint, and it faces almost directly towards the middle line of the body. The ligament corresponds in shape, direc- tion, and size . to the extremity or base of the clavicle, wliich is not the case with the socket upon the sternum. Unless the arm is raised above the shoulder only the lower portion of the inner or sternal end of the clavicle rests on the sterno-clavicular socket, and this only upon that part of the socket which is immediately above and internal to the union of the first costal cartilage with the sternum. Between the rest of the articular surfaces at the sterno-clavicular joint there is a V-shaped interval, which is occupied by the inter-articular fibro-cartilage and the synovial sacs, and is tightly bound over by the inter- clavicular ligament. The articular sm^face at the inner end of the bone is triangular in outline, and of its three borders or margins one, the anterior, is nearly vertical ; another, the inferior, is nearly horizontal, and extends from before backwards and inwards ; wliile the third, the posterior, slopes downwards and backwards to meet the inferior border at the rounded apex behind. The angles of this triangular surface are well roimded, its base is above and in front, and its apex behind and below. The surface is convex from above down- wards in its posterior portion, and sometimes throughout its extent ; but usually there is a depression near its centre which makes it somewhat cup-shaped in the dry state. When de- prived of its articular cartilage it is generally very rough and uneven, excepting below, where it rests upon the sternum. Here it is faceted and smooth ; and frequently this faceted surface extends not only from the apex behind to the anterior vertical border of the extremity in front, but reaches also along the under surface of the shaft as far as the clavicle rests upon the upper border of the first costal cartilage. The circumference of the inner end of the clavicle varies from two and a half to three and a half inches ; its longest diameter is from above downwards, backwards, and a little LIGAMENTS OF STERNO-CLAVICULAE JOINT. 189 inwards, and varies from three-quarters of an inch to one and one-third of an inch ; its shortest diameter is from before back- wards at its lowest part, where the bone tapers to a rounded apex. Where the shaft begins to enlarge into the extremity the bone is rough and raised, more especially at the back and lower aspects, for the purpose of gi^ong secure attachment to the strong ligaments which surround the articulation; and where the posterior passes into the inferior surface of the shaft, a little external to the apex of the articular extremity, there is a rough tubercle often prolonged into a ridge — the rhomboid tubercle or ridge — for the attachment of the costo-clavicular or rhomboid ligament. The Ligaments. — The ligaments of this joint have been always described as fom^ in number, in addition to the inter- articular fibro-cartilage — ^viz., the anterior and posterior sterno- clavicular, the inter-clavicular, and the rhomboid or costo- clavicular. This description is, however, somewhat forced, for there is no distinction of what may most correctly be called the capsular ligament of the joint into anterior and posterior portions. The Gapsidar Ligament. — Ligamentous fibres, taking varying directions, and of various strength and thickness, completely sur- round the articulation, so as to form a capsule ; and as they pass between the margins of the articular surfaces are firmly con- nected with the edges of the inter-articular cartilage. The fibres at the back of the joint — the posterior sterno-clavicular ligament — are stronger than those in front or below; the more superficial set passes from the manubrium sterni on the median side of and below the sternal facet, outwards and upwards to the clavicle, many of them being attached to the projecting posterior edge of the inner extremity of the clavicle, while a few are prolonged onwards upon the posterior surface of the bone, where they blend with the periosteum. The deeper fibres, more especially those at the posterior inferior angle of the joint, which are very thick and numerous at their clavicular attachment, connect the inter-articular cartilage with the clavicle and with the sternum without passing between the sternum and the clavicle. This portion of the capsule checks the forward movements of the clavicle on the sterniun. The fibres in front of the joint — the anterior sterno-clavicular ligament — are well marked, but more lax and less tough than 190 LIGAMENTS OF STERNO-CLAVICULAR JOINT. tlie posterior, and are overlaid by the tendinous sternal origin of the sterno-mastoid muscle, the fibres of which are parallel to those of the ligament. They extend obliquely upwards and outwards from the prominent margin of the sternal facet, to be attached to the anterior surface of the clavicle at some little distance from the edge of the articular cartilage on the extremity of the bone. They limit the backward rolling of the clavicle on the sternal socket. The fibres which cover in the joint below are short, woolly, and consist more of fibro-areolar than true fibrous tissue. They extend between the upper border of the first costal cartilage and the lower border of the clavicle just external to the articular surface of the extremity, and fill up the gap between this surface and the inner border of the costo- coracoid ligament. The superior portion of the capsule consists chiefly of short tough fibres passing from the sternum to the inter-articular cartilage, and of others welding this cartilage to the upper border of the extremity of the clavicle, while only a few pass over the joint from the upper edge of the sternum to the upper surface of the clavicle. The Inter-clavicular Ligament. — The most prominent and conspicuous of the ligaments of the sterno-clavicular joint is one common to the joints of the opposite sides, which thickens and strengthens materially the superior portion of the capsular licrament of each joint — the inter-clavicular ligament. Its fibres form a strong concave band along the posterior aspect of the upper border of the manubrium, nearly a quarter of an inch deep, with its concavity upwards, and its upper border taper- ing to a narrow, almost sharp edge. It is connected with the posterior superior angle of the inner extremity of each clavicle, and with the fibres which weld together the inter-articular fibro-cartilage and the clavicle, and it then passes across from clavicle to clavicle above the sternum, to which it is attached on its anterior aspect, only by means of a thin membranous layer wliich covers it and the periosteum of the front of the sternum. Posteriorly the lowest fibres are slightly attached to the sternum, and are continuous with the posterior sterno- clavicular fibres of the capsule of each joint. It prevents the upward displacement of the clavicle during forcible depression of the arm or shoulder. The rJwmhoid or costo-clavicular ligament is a dense strong SECTION THROUGH STEIRNO CLAVICULAR JOINT 1 Interoo'ttcvCLa*' NJn-o ^ SyrvoyuiCL coL*-ijby op J<7ion-vbou^ liyQjOv '^T1> /''*'*~*^'' " ' ' ""^ INTER CLAVICULAR LIGAMENT BACK VIEW x . cJ^ THE INTER-ARTICULAR CARTILAGE. 191 ligament, composed of fine fibres massed together into a mem- branif orm structure. It extends from the anterior edge of the upper border of the first costal cartilage upwards, backwards, and distinctly outwards to the posterior lip of the under sur- face of the inner end of the clavicle, to which it is attached external to the lower part of the capsule. Frequently some of the fibres at the outer border of the ligament pass upwards and inwards to the clavicle behind the rest, and in tliis way the ligament has the appearance of being formed of fibres wMch decussate as they reach from cartilage to clavicle. It is from a half to three-quarters of an inch broad. It prevents the upward displacement of the inner end of the clavicle in such move- ments as the elevation of the arm above the head. It prevents the tendency (if any such exists) to upward displacement by the pull of the sterno-mastoid muscle. It also resists displacement of the inner end of the clavicle backwards. Lastly, it tends to lift the first costal arch during the elevation of the clavicle, and by so doing gives a more advantageous point d'a'ppui for the action of the inspiratory muscles ; in this manner the advantage of elevating the shoulders in forcible inspiration is partly explained, and is not wholly due to the extrinsic mus- cular action permitted by the fixation of the arms. The inter-articular fibro-cartilage is a flattened disc of nearly the same size and outline as the inner articular end of the clavicle which it pretty accurately fits. It is attached above to the upper extremity of the posterior edge of the clavicle, and below to the cartilage of the first rib at its union with the sternum, where it assists in forming the socket for the clavicle. At its circimiference it is connected with the cap- sular ligament, and this connexion is very strong behind and above, and more especially above, where it is also blended with the fibres of the inter-cla^dcular ligament which spring from the clavicle near the point of attachment of the fibro- cartilage. It is usually thinnest below, where it is connected with the costal cartilage. It varies in thickness in different parts, sometimes being thinner in the centre than at the edges, sometimes the reverse ; it also varies in different joints, and is occasionally perforated in the centre. The cartilage divides the joint into two compartments, and by being attached to the lower part of the sternal socket, but to the upper edge of the clavicular facet, it serves mate- 192 MOVEMENTS OF STERNO-CLAVICULAR JOINT. rially to bind the bones together, and to prevent more especially the inward and upward displacements of the clavicle from the sternum and costal cartilage. It also forms an elastic buffer or cusliion between the bones, which tends much to break shocks ; while at the same time, by its similarity in outline to the end of the clavicle and its adaptability to the socket of the sternum, it adds very much to the general security of the joint. Synovial Membranes. — There are two membranes in this articulation; for, owing to the peculiar attachment of the inter- articular ligament to the socket below and the clavicle above, as well as to the capsular ligament at its margins, there is formed a complete space or cavity between the fibro-cartilage and the sternum and costal cartilage on the inner side ; and between the clavicle and the fibro-cartilage on the outer side. Thus one membrane is reflected over the outer side of the fibro-cartilage from the clavicle and capsule, and another over the inner side from the sternum, costal cartilage, and capsule. The former is more loose and sac-like than the latter. Occasionally a commu- nication takes place between the two cavities. Collectively the ligaments of this joint are very strong, and make up for the want of adaptation of the two bones. The joint indeed is stronger than the collar-bone, which is often fractured ; whereas dislocation of the inner end of the clavicle is a very rare occurrence. The Movements. — The movements permitted at this joint are various though limited, owing to the capsular ligament being moderately tense in every position of the clavicle. The joint is the centre at which many of the movements of the shoulder occur — such as the elevation of the arm over the head, and the forward and backward play of the arms, as in walking, running, swimming, rowing, and such like exercises. Motion therefore occurs at the sterno-clavicular joint in nearly every direction — upwards, downwards, backwards, forwards, and in a circumductory direction. The upward and downward movements of the clavicle take place between that bone and the inter-articular fibro-cartilage. During elevation, the upper edge of the clavicle with its attached fibro-cartilage is pressed inwards into the sternal socket, and the lower edge of the clavicle is raised from the fibro-cartilage ; during depression of the clavicle, the lower MUSCLES OF THE STEENO-CLAVICULAR JOINT. 193 edge of the clavicle presses downwards and inwards upon the fibro-cartilage, and the rest of the articular surface inclines outwards, bringing with it to a slight degree the upper edge of the iibro-cartilage. These movements occur upon an axis drawn from before backwards through the outer compartment of the joint. The forward and backward movements occur between the fibro-cartilage and the sternal socket, the clavicle together with the inter-articular cartilage rolling backwards and forwards respectively upon the sternum ; and the move- ments occur round an axis dra^vn nearly vertically through the sternal socket. In circumduction, the movements are of course a compound of a quick succession of these four angular movements, and therefore take place partly between clavicle and fibro-cartilage, and partly between fibro-cartilage and sternum. The Muscles. — The muscles in immediate connexion with this joint are few in number, being only those which arise from the manubrium sterni, the inner end of the clavicle, and the costal cartilage of the first rib. These are the sterno-mastoid and the pectoraHs major in front, the sterno-hyoid and sterno- thyroid behind, and the subclavius which is in front and to the outer side of the rhomboid ligament. The sternal origin of the sterno-mastoid, which is tendinous, passes obliquely upwards and outwards (in the same direction as the anterior portion of the capsular ligament), over the front of the articulation, and strengthens very considerably the anterior sterno-clavicular portion of the capsule. This muscle affords a good illustration of the general law respectiag the attachment of muscles to both bones of an articulation when they arise or are inserted in the near neighbourhood of a joint. The sterno-hyoid muscle usually arises from the posterior ligamentous fibres of the joint, as well as from the clavicle, or the sternum. It gives security to the back of the joint. The subclavius muscle may be considered as one of the uniting structures of the articulation, and like the costo- clavicular ligament it heljjs to prevent the too forcible or extreme elevation of the clavicle. It also assists the other ligaments in keeping the inner end of the clavicle in its place upon the sternum and costal cartilage — i.e., in preventing avulsion of the clavicle from the sternum. In addition to the above-named muscles, it must be remem- 194 MUSCLES OF THE STEKNO-CLAVICULAR JOINT. bered that the clavicle moves upon the sternal socket in every forward, backward, upward, and downward movement of the shoulder. So that all the muscles which move the shoulder act indii'ectly upon the sterno-clavicular joint ; thus the tra- pezius and latissimus dorsi, the serratus magnus and pectoralis minor, the rhomboids and levator anguli scapulae, will each and all influence tliis joint in accordance with their own actions, and in conformity with what is stated respecting the move- ments which occur at the sterno-clavicular articulation. Indeed it is these muscles only which produce any of the ordinary movements at the sterno-clavicular joint ; for none of the muscles in immediate relation with it act usually upon the clavicle, but have their Jixed point at or near this articula- tion. Thus the sterno-hyoid, sterno -thyroid, and sterno-mastoid muscles, as well as the pectoralis major, act from, not upon, it ; and, by the very nature of their connexion with it, do not tend to move one bone upon the other. The subclavius, however, by depressing the outer end of the clavicle causes the inner end to glide upwards and inwards upon the sternal socket, revolv- ing round an antero-posterior axis, and thereby tightening the superior portion of the capsular ligament and the inter- clavicular ligament. CHAPTEE X. THE LIGAMENTS AND JOINT CONNECTING THE SCAPULA WITH THE CLAVICLE; OE, THE SCAPULO-CLAVICULAK UNION. The scapula is connected with the clavicle by a synovial joint, which may be either divided or single, between the acromion process and the outer end of the clavicle ; as well as by liga- ments passing from the coracoid process to the under surface of the outer end of the clavicle. We have therefore to consider — 1st. The acromio-clavicular articulation ; and 2nd. The coraco- clavicular ligaments. It will also be most convenient and apposite to describe in this section the ligaments which pass from one part of the scapula to another — viz., the coraco- acromial, and the supra-scapular ligaments. The Acromio-clavicular Joint. Class, Diarthrosis, Subdivision, Arthrodia. This joint is formed between the outer extremity of the clavicle and the inner edge of the acromion. Ligaments pass from one bone to the other on all their aspects, and there is frequently an inter-articular fibro-cartilage which sometimes is imperfect, and only partially separates the articular surfaces of the bones, but occasionally is complete, and divides the synovial cavity into two distinct parts. The Clavicle. — ^The outer end of the clavicle ascends towards the acromion in the male, so as to give height and squareness to the shoulders. It is flattened upon its superior and inferior surfaces, and has a narrow, convex posterior, and a narrow, con- cave anterior border. By its outer border, which is somewhat thicker than the anterior, but shallower than the posterior, it articulates with the anterior part of the internal edge of the acromion, and is marked by an oval-shaped, nearly flat facet for that purpose. The facet varies much ia different bones, being sometimes large and irregular, and either slightly convex 2 196 THE ACROMIO-CLAVICULAR JOINT. or concave ; its long axis is in the antero-posterior direction, but the surface is somewhat oblique as it is sloped off inwards behind, and bevelled off slightly along its lower edge. This obliquity serves to explain the greater frequency of displace- ment of the outer end of the clavicle upwards upon, than downwards beneath, the acromion. The upper and under surfaces, as well as the anterior and posterior borders of the clavicle near the extremity, are rough, sometimes very rough and uneven, for the attachment of ligaments ; and upon the upper surface there is often an oblique ridge running back- wards and inwards to a little tubercle, or heaping-up of bone, at the posterior border, about midway between the conoid tubercle and the facet for the acromion. Its superior surface gives attachment to the trapezius beliind, and the deltoid in front, for nearly equal distances. Its inferior surface is marked by a tubercle and ridge for the attachment of the coraco- clavicular ligaments. The Scapula. — It is by means of the acromion process alone that the scapula is brought into articular connexion with the clavicle. This process is a large and somewhat triangular prolongation of the spine of the scapula, about two inches in its longest, and rather over one inch in its broadest diameter. It has a general inclination upwards, so that in the undissected subject its extremity forms the highest part of the bone, and overhangs the glenoid fossa on its outer side. The elevation of the tip of the acromion above the rest of the scapula ex- plains how it is that the clavicle in man has to ascend a little as it passes outwards from the top of the sternum, notwith- standing that the blade of the scapula does not reach higher than the second rib. It is directed at first outwards, and then forwards, twisting a little inwards, and has beneath it, and between it and the outer surface of the neck of the scapula, a large space leading from the supra- to the infra- spinous fossa, and called the great scapular notch. Its upper surface is rough and du^ectly continuous with the outer or posterior border of the sjDine of the scapula ; it looks chiefly upwards, but also outwards and backwards, and gives attachment along its outer edge to the deltoid, and along its inner edge to the trapezius. It is immediately beneath the skin, and forms the summit of the shoulder. The under surface is smooth and slightly concave, and is THE ACROMIO-CLAVICULAR JOINT. 197 directly continuous witli the anterior or short border of the spine of the scapula ; it looks chiefly downwards, but also slightly forwards and inwards, over the outer and upper part of the glenoid fossa. Its outer harder is convex and rough, and continuous with the lower lip of the outer border of the spine, and to it the deltoid is attached. Its inner harder is concave, thinner and much shorter than the outer ; it is continuous with the upper lip of the outer border of the scapular spine, and has the trapezius attached along its posterior two-thirds. At the anterior part of the inner border there is a nearly flat or slightly convex facet for the clavicle, wMcli measures from a half to three-quarters of an inch in the antero- posterior, and a quarter of an inch in the vertical direction ; it is sloped slightly outwards beliind, and bevelled off along the upper edge, its obliquity being the reverse of that of the facet on the clavicle, which slopes inwards behind and is bevelled off below. The apex of the acromion is the thin and somewhat pointed anterior edge between the facet for the clavicle and the outer border of the process. It projects an inch further forwards than the glenoid fossa, and overhangs the middle of the head of the humerus, when the arm is hanging loosely by the side. The acromion process and clavicle together form an arch over the front and outer part of the thorax. This arch has one fixed pier, viz., the sternum ; and one movable pier, viz., the spine and body o£ the scapula. The arch is connected with the fixed pier by an articulation at which all the movements of the Mdiole arch take place ; but is structm-ally continuous with the movable pier, which therefore moves together with the arch. The vault of the arch itself is jointed, so that the outer and shorter limb can move upon the inner and longer, viz., at the acromio-clavicular joint. Beneath the arch thus formed important structm^es pass. The coracoid process projects upwards and forwards, so as to divide the subway into two portions, the larger being on the inner or thoracic side of the process. In the thoracic portion, that is, under the cla^dcular part of the arch, lies the subclavius muscle, and the axillary vessels, respiratory nerve of Bell, and cords of the brachial plexus descend through it into the upper arm. 198 THE ACROMIO-CLAVICULAR JOINT. In the acromial portion of the subway there are the supra- scapular nerve and artery, passing to the great scapular notch ; the supra-spinatus, passing forwards to the great tuberosity of the humerus ; the sub-acromion bursa, which protects the cap- sule from the deltoid, and the shoulder-joint itself, which is overhung by the acromion process. LiGAiiENTS. — There is one ligament, and occasionally an inter-articular fibro-cartilage, concerned in the construction of the acromio-cla^icular joint. The cajysular ligament completely sm^rounds the articular margins, and is composed of coarse strong fibres, having an uniform and definite direction, which are attached to the anterior and posterior borders, as well as to the upper and under surfaces of the acromion and clavicle. The ligament is somewhat lax in nearly every position of the joint, so that the clavicle is by no means tightly braced to the acromion, but is retained somewhat loosely in apposition with it. The fibres reach a variable distance upon the different aspects of the bones ; thus posteriorly, they extend inwards for three-quarters of an inch or more upon the clavicle, as far as a little tubercle external to the one for the conoid hgament ; superiorly, they are attached to the oblique line which runs outwards and forwards upon the upper surface of the clavicle, and thus they extend a shorter distance upon the bone as they reach nearer and nearer the anterior border. At the anterior border they do not extend more than a quarter of an inch along the cla- vicle ; and inferiorly, they reach outwards to the ridge for the trapezoid ligament, with the fibres of which they blend. At the acromion the fibres of the ligament reach about half-way outwards upon both the upper and lower surface, while along the borders of the process they are very short, being attached immediately in front of, and behind the articular facet. The anterior, and a few of the antero-inferior fibres are blended at their insertion into the apex of the acromion ^^dth the coraco- acromial ligament. The capsule is of pretty uniform thickness, but is strength- ened above by the aponeuroses of the trajDezius and deltoid muscles ; it is about as thick as a sliilling, and its fibres are arranged in coarse and parallel fasciculi. These fibres all run inwards and backwards from the acromion to the cla^dcle, and the posterior fibres extend much fiuther inwards upon the THE CORACO-CLAVICULAR UNION. 199 convex border and upon the posterior part of the upper and lower surfaces of the clavicle than elsewhere. TMs definite direction and varied length of the fibres serve the purpose of dragging the clavicle forwards when the acromion is advanced ; while the anterior part of the capsule, and the projection of the apex of the acromion in front of the extremity of the clavicle, secure the backward movement of the latter when the scapula is pulled towards the dorsal spines. Were it not for the bevelling of the facets, abeady referred to, the laxity of the ligament would permit of a slight di^opping of the clavicle from the acromion ; as it is, the clavicle some- what overlaps so as to rest upon the acromion. This over- lapping of the clavicle, which in some instances is so marked as to cause quite an elevation, tends also to prevent any upward displacement of the acromion by the pressure of the head of the humerus, during such muscular efforts as pushing or bearing the weight of the trunk upon the palms of the hands. The Inter-articular Fihro-cartilage. — A fibro-cartilage is occasionally present ; when it is so it is usually imperfect, and extends only half-way through the joint from above downwards. Sometimes it reaches the whole depth and is perforated in the centre. It is usually thicker at the circumference than towards the interior, and some of the fibres of the capsular ligament are blended with its edges. The Synovial Membkane. — A synovial membrane lines the joint, and when the inter-articular cartilage is present the cavity it forms is either partly or completely divided according to the state of the cartilage upon which the membrane is reflected. The Coraco-clavimdar Union. CoEACOiD Process. — The coracoid or hook-like process over- hanging the upper border of the glenoid fossa on its inner side, to the very margin of which it often extends, is situated beneath the acromio-clavicular arch, the subway of which it divides into two unequal parts. It springs by a broad thick base an inch wide, from the upper costa of the scapula between the supra-scapular notch, one margin of which it forms, and the edge of the glenoid fossa. It may indeed be said to contribute to the formation of the fossa, and with it is situated in advance of the surgical neck of the scapula. It 200 THE CORACO-CLAVICULAR UNION. affords powerful leverage to the coraco-bracliialis and biceps muscles which are attached to the outer edge near the apex ; and it is marked on its inner border near the apex by a smooth facet into which the pectorahs minor is inserted. Its surfaces look upwards and outwards, and downwards and inwards, and serve to separate the great scapular notch from the sub-scapular fossa. Having ascended, with a considerable leaning over the sub-scapular fossa, for about half an inch, the process suddenly becomes contracted to a quarter of an inch in width. It is twisted on itself so that its surfaces now look upwards and inwards, and downwards and outwards over the glenoid fossa ; and its direction is changed so that it projects forwards for three-quarters of an inch beyond the edge of the glenoid fossa. Its apex, its narrowest point, is bent very slightly downwards. It thus, as its name implies, somewhat resembles the beak of a raven. It is situated an inch and a half to the thoracic «ide of, and half an inch below, the level of the acromion, and is on a level with the upjDcr surface of the head of the humerus. The centre point of the outer curve of the clavicle is situated in a vertical line immediately above the angle of the coracoid at a distance of about half an inch. Extending forwards from the angle where the ascending suddenly changes into the horizontal part, the bone is raised into a rough and oblique ridge, which separates the outer surface of the vertical from the upper surface of the horizontal portion of the process, and is prolonged upon the outer edge to the apex. This ridge gives attaclnnent to the coraco-acromial ligament. The inner edge is marked by a rough ridge which extends forwards for an inch or more, and gives attachment to the trapezoid portion of the coraco-clavicular ligament. On the inner side of the angle of the coracoid is a smooth and sometimes facetted surface, against which plays the conoid ligament in the back- ward and forward movement of the scapula. The coraco-clavicular ligament consists of two parts — the conoid and the trapezoid. The conoid ligament is the most internal as well as the posterior portion. It is a very strong and coarsely fasciculated band of triangular shape, extending upwards and outwards from the inner side of the root of the coracoid, to the tubercle on the under surface, and posterior edge of the outer curve of the clavicle. Its apex is at the inner and posterior edge of the ^C^^ovd. \ ^<""^'^''y coraco. clowt cu^a^- . ln( /owl-- Aon oF sTch- Ho-yi oF hi I eft Dorsxi traruvei ^t Ugoumen/ hebneen mt civnciform i sc t/i l id \ FcLcet on 4-- metauc hone for os rfuxg T&ridorv of extensor carpi vCLnans hone. ^-:.atUng oFF geiLerat syyi^-ial cu*-vty 'rorn, thM, y/<'sr- JVfn..!i.>i kC'cio'lixn. Ui a. < I- < U. Ill o r ii .,i*gs*- THE CORACO-CLAVICULAK UNION. 201 root of the coracoid process and immediately in front of the supra-scapular notch ; some of its fibres are connected with the scapula even below the supra-scapular notch, and reach into the venter for some short distance. Others pass back- wards over the supra-scapular notch and form part of the transverse ligament. Its base is at the clavicle, where it widens out laterally so as to be attached to the posterior edge of the lower surface of the clavicle, on the outer side of, as well as into the tubercle above mentioned. The ligament is somewhat twisted on its own axis as it ascends, so that the anterior fibres at the coracoid become internal at the clavicle, and are inserted into that bone at and near to the tubercle, while the fibres which are posterior at the coracoid, pass outwards upon the clavicle and are prolonged from the inner and upper edge of the supra-scapular ligament to the posterior edge of the trajDezoid ligament. Without being absolutely distinct it is easily separated from the trapezoid ligament, both at the coracoid and the clavicle. It works backwards and forwards on the facet on the inner aspect of the angle of the coracoid, between wliich and the ligament there is often a distinct ■ bursa. The conoid ligament chiefly checks the backward movements of the scapula as the trapezoid does the forward movements of that bone. It therefore protects the scapula against back- ward displacement, either from the action of the posterior muscles, such as the rhomboids and part of the trapezius, or by blows on the front of the shoulder. The coraco-clavicular ligament as a whole limits the movements of the acromio- clavicular joint, just as the costo-clavicular does those of the sterno-clavicular joint. The trapezoid ligament is the anterior and outer portion of the coraco-clavicular. It is a strong flat plane of closely woven fibres, the surfaces of which look respectively upwards and inwards towards the clavicle, and downwards and outwards over the upper surface of the coracoid process, and the gle- noid fossa. It is more oblique in direction than the conoid, which is nearly vertical. It is quadrilateral in shape, with its anterior edge longer than the posterior, and its upper surface sloped off obliquely behind. At the coracoid it is attached for about an inch to the rough ridge which runs forwards from the angle along the inner edge of the process, as well as to the 202 THE MOVEMENTS BETWEEN angle itself immediately above tlie facet for the play of the conoid ligament ; some of its fibres are placed under cover of the conoid ligament. At the clavicle it has rather a more lengthy attachment to the obHque ridge which runs out- wards and forwards from the tubercle for the conoid on the under sm-face of the bone. Its posterior edge is in juxta- position to the outer and hinder portion of the conoid liga- ment, while its anterior border is free in the dissected state, and overlies the base of the coraco-acromial ligament. At the extremity of the clavicle it blends with the inferior part of the acromio-clavicular capsule. The trapezoid ligament chiefly limits the forward movements of the scapula, as the conoid does the backward movements of that bone. Like the conoid, it strengthens very materially the acromio-clavicular joint, preventing the scapula from being displaced inwards beneath the clavicle either by violence or muscular action — a tendency to which the obliquely cut sur- faces of the clavicle and acromion dispose the joint. The Movements between the Scapula and Clavicle. — Owing to the want of security afforded by the shape of the articular surfaces of the acromion, and outer end of the clavicle, the entire strength of the acromio-clavicular joint must be derived from ligaments. These ligaments, while knitting the bones together wdth sufficient firmness to enable them to resist all ordinary displacing forces, do not permit of more than very limited movements taking place between them. To under- stand what these movements are, we must bear in mind that it is the scapula which moves upon the outer end of the cla- vicle, although the clavicle in its tm^n, carried by the ligaments which unite it with the scapula, moves upon the sternum. But the scapula, in moving upon the end of the clavicle, moves- likewise upon the thorax in a forward and backward, as well as in an upward and downward direction, and also in a rotatory manner around a line, drawn at right angles to the flattened blade, below the spine of the scapula. Throughout these move- ments the lower angle and the base of the scapula are kept in contact with the ribs by the latissimus dorsi, which straps down the former, and by the serratus magnus and rhomboids attached to the latter. This being the case, had there been no acromio- clavicular joint, as the scapula ghded forwards and backwards on the thorax, the glenoid socket could not have preserved its THE SCAPULA AND CLAVICLE. 203 obliquely forward direction ; on the contrary, tlie socket would have shifted round a vertical axis, and the shoulder would have pointed inwards when the scapula was advanced, and outwards when it was drawn backwards towards the spine, to a degree greater than would be desirable or convenient. This dis- advantage would have been especially felt in striking forwards from the shoulder ; for at the same time that the arm was outstretched, the scapula rolling forwards round the thorax, and having its centre of motion at the sterno-clavicular joint, would, if immovably fixed to the outer end of the clavicle, have had the direction of the glenoid fossa so diverted inwards that it would no longer have afforded a surface fairly opposed to the head of the humerus, but would have presented an inclined surface, off which the head of the humerus would have had a tendency to glide, and thus to force its way through the inner and forepart of the capsule of the shoulder -joint. By means of the acromio-clavicular joint the scapula can be forcibly advanced upon the thorax and yet keep its glenoid socket facing fairly forwards, the scapula so moving upon the clavicle as to make the posterior angle between the clavicle and acromion process more acute. In this way the force of the muscles of the shoulder, arm, and forearm can be com- bined in giving a direct blow ; v/hile at the same time the shock received by the fist, and passing through the length of the humerus, is transmitted directly from the head of that bone to the glenoid cavity, and is thence distributed to the anterior costa and the superior costa through the base of the coracoid process, and indirectly transmitted through the acromion and along the spine of the scapula to the posterior costa of the scapula, and forwards to the clavicle, and along it to the sterno-clavicular joint. It is well known that the most forcible blow that can be delivered is when the side of the body is inclined towards the object to be struck, and the arm is thrown outwards and forwards from that side. This is the movement of boxing, and the attitude and movement of fencing. With the scapula well drawn back towards the spine, the posterior angle formed by the acromion and clavicle at its most obtuse degree, and the shoulder and elbow joints bent, the muscles wlhch draw the scapula away from the spine are ready to act simultaneously with those which straighten the shoulder and elbow ; during then- action the glenoid socket is 204 THE MOVEMENTS BETWEEN kept fully against the head of the humerus, and the clavicle and acromion are brought to their most acute angle at the acromio-clavicular joint. It must be borne in mind that whilst the base of the scapula is held against the thorax and revolves upon it, yet that the entire scaj)ula moves in the arc of a circle, whose centre is the sterno-clavicular joint, and whose radius is the clavicle ; and not in the arc of the circle formed by any one of the five costal arches upon winch it is placed, each one of which, moreover, differs from the rest. Now as tliis radius is elastic ; as part of the venter of the scapula has to be retained in contact with the thoracic wall ; and as owing to the pull of the various muscles which act on the scapula there is a con- siderable tendency to drag the scapula inwards in such a manner that it would, if possible, get nearer the centre of the circle the further towards the front it came ; the radius, instead of remaining straight, would gradually become curved back- wards near its junction with the arc, while a counter, forward, curve would be formed at the opposite end. This, too, would occur notwithstanding the movements of the acromio-clavicular joint. Thus it seems to me that the curves of the clavicle are to be explained by the shape of the thorax, against which the scapula is held by muscles, and by the direction of the pull of those muscles as they drag forwards the scapula upon the outer extremity of the radius formed by the clavicle. Hence, too, we see more considerably curved clavicles in males than in females, and in muscular men than in the weakly or inactive. Again, were it not for the acromio-clavicular joint, the lower angle of the scapula could not have been retained in contact with the chest wall during the rising and falling of the shoulder, owing to the increase in the diameter of the chest from the second to the seventh ribs ; while the glenoid fossa would have shifted round a transverse axis, so that its upper end would be tilted downwards when the body of the scapula was raised, and thrown upwards when the scapula was depressed. When moving forwards and backwards the scapula turns round a vertical axis drawn through the acromio-clavicular joint, in a hinge-like manner upon the end of the clavicle, carrying with it at the same time the outer end of the clavicle itself, so that both advance and retire together ; and the inner THE SCAPULA AND CLAVICLE. 205 end of the clavicle moves upon the fibro-cartilage of the sterno-clavicular joint. When the scapula ascends and de- scends, it turns in a hinge-like manner round a transverse axis drawn through the joint, upon the extremity of the clavicle, while at the same time the clavicle together with the fihro- cartilage of the sterno-clavicular joint moves upon the costo- sternal socket. In the rotation of the scapula, round an axis through its own centre, and at right angles to its flat surfaces, the acromion moves in a complex manner upon the clavicle round both the vertical and transverse axes. Such rotation occurs when we raise, and at the same time advance, the shoulder, as when we reach anything above our head, or take off our hat ; and when we depress and at the same time draw back the shoulder. There are no movements in which the clavicle moves upon the acromion while the scapula is fixed, nor in which the scapula moves on the fixed clavicle. They mutually affect each other, so that the muscles which act upon the one move both bones. The Muscles moving the Scapula and the Clavicle. From what has been said above, it will be understood that the scapula and clavicle together move in the arc of a circle, the radius of which is the clavicle, and the centre the sterno- clavicular joint ; that while the posterior costa and inferior angle of the scapula are retained by muscles against the chest wall, the rest of the scapula is thrown off from the side and front of the thorax, as it advances or rises, by its connexion with the clavicle, i.e., with the radius of the circle in which it moves ; but that this connexion is a movable and not a fixed one, in order that while moving together the bones may also move on one another, for the purpose of giving uniformity to the direction of the glenoid socket, joints, and the shoulder. The acromio-clavicular joint being a hinge joint, in which neither part of the hinge is fixed, any muscle which tends to move one portion in any direction vnll similarly affect the other, and will at the same time move the two bones upon the sterno-clavicular joint. The muscles may be grouped into those which act directly/, and those which act only occasionally and indirectly upon the joint. 1. Most of the muscles which act directly upon it are 206 THE MUSCLES WHICH MOVE THE inserted into the scapnla alone. Tliey are the levator anguli scapulae, inserted into the upper angle of the posterior costa ; and the rliomhoids, attached to the posterior costa, all of which pull the bone back towards the spine, and help to keep the base of the scapula against the chest wall. The levator also elevates the scapula and rotates it so as to depress the glenoid fossa. The serratus magnus, inserted into the whole length of the base as well as the upper and lower angles on the ventral surface, draws the scapula forwards and keeps the base and upper and lower angles against the chest wall ; the pedoralis minor inserted into the inner side of the tip of the coracoid process pulls the anterior angle of the scapula downwards and forwards, and thus tends to throw the inferior angle backwards. 2. One important muscle, acting directly upon the joint, is inserted into both clavicle and scapula — ^viz., the trapezius. The superior fibres of the trapezius elevate the outer half of the clavicle, the middle fibres elevate the acromion, and the inferior fibres draw the spine of the scapula downwards and towards the spinal column. Wlien all the fibres of the muscles act together the scapula is rotated, so that the acromion is raised and drawn inwards towards the coliunn, the superior angle is depressed and drawn inwards, and the inferior angle is thrown away from the spinal column and elevated. 3. One muscle, acting on the joint, is inserted into the clavicle alone — viz., the subclavius. Attached to the groove on the under sm-face of the bone, as far outwards as the recess between the conoid and trapezoid ligaments, it depresses the outer end of the clavicle. All the muscles, excepting the sub- clavius and the superior fibres of the trapezius, act first on the scapula, which then carries with it the clavicle, whereas these two muscles act first on the clavicle, which then carries with it the scapula. It should be noticed that the subclavius extends obliquely the whole way between the costo-clavicular "and coraco- clavicular ligaments, and by assisting these ligaments to keep the clavicle in its proper position it must give support and security to both the sterno- and the acromio-clavicular joints ; to the former by holding the inner end of the clavicle inwards against the chondro-sternal facet ; and to the acromio-clavicular by preventing the upward and outward displacement of the outer end of the clavicle upon the acromion. SCAPULA AND CLAVICLE. 207 If tlie actions of the several muscles be considered collec- tively, the trapezius, levator anguli scapulae, and the rhomboids elevate the scapula and outer part of the clavicle ; the lower part of the trapezius, the pectoraHs minor, and the subclavius depress them. The serratus magnus carries them forwards, and the trapezius and rhomboids draw them backwards. By the associated action of these muscles rotation is produced. The muscles which act indirectly upon the bones of the shoulder act from the humerus and forearm when these parts are fixed. They are (I) the latissimus dorsi, which arises by a few fibres from the inferior angle of the scapula, and by passing over it Kke a strap assists the lower part of the serratus magnus in keeping it against the thorax, and limits its out- ward projection when the arm is raised. The latissimus dorsi and pectoralis major act powerfully upon the shoulder when they have brought the arm into contact with the side, or when the deltoid has fixed the shoulder-joint ; thus the pectorahs major draws forwards and downwards the shoulder when we cringe with cold or fear ; and the latissimus dorsi, with arms against the sides, throws the shoulders downwards and backwards at the order " attention." (2) The deltoid, biceps, coraco-brachialis, and triceps depress the shoulder when the arm is fixed in a downward position. (3) The supra- and infra-spinatus, the teres major and minor, and sub-scapularis draw it forwards. But all these muscles are concerned primarily in moving the humerus at the shoulder-joint, and only under exceptional con- ditions move the shoulder bones upon the sterno-clavicular joint, or on one another at the acromio-clavicular articulation. BuES^. — There are usually three bursse in association with this joint and its ligaments. 1. In the recess between the conoid and trapezoid ligaments. 2. Between the base of the cora- coid process on its inner side, and the apex of the conoid liga- ment. 3. Below the coraco-acromial hgament, between it and the acromion above, and the capsule of the shoulder- joint below. This last is usually of considerable size, the other two are but very small sacs. Arteeies. — The sujjra-sca^ular artery gives off behind the clavicle a branch which supplies the subclavius muscle, and extends along it as far as the conoid and trapezoid ligaments. These ligaments are pierced by twigs from this branch, wliich afterwards get into the joint on the inferior aspect. 208 SCAPULAR LIGAMENTS. Another brancli is given ojff from the supra-scapular artery, which curves round the lower edge of the supra-spinatus, reaches the under aspect of the acromion and acromio-clavicular joint, and supphes it. There is quite a free anastomosis of small arteries on the under surface of this joint, and the coraco- clavicular ligaments are also supplied from the same source. The acromial branch of the acromio-thoracic axis, the anterior circumflex, the siqora-scapular, 'and sometimes a branch from the transversalis colli, anastomose upon and supply the joint by piercing it on the upper surface. Nerves. — Branches are sent to tliis joint from the supra- scapular and the circumflex. Scapular Ligaments. There are tv/o ligaments proper to the scapula — that is, passing from one point to another of the bone, and not con- nected with any other bone. These are the coraco-acromial, and the transverse or supra-scapular ligaments. •The coraco-acromial ligament is a broad, triangular, flat membrane, wide at the coracoid and contracted to a blunt apex at the acromion process. It is composed of strong fibres, which are attached all along the outer edge of the horizontal portion of the coracoid, and after passing with varying degrees of obliquity outwards and a little upwards, they are inserted into the apex of the acromion, as well as into the process immediately below the facet for the clavicle, close to the inferior fibres of the acromio-clavicular capsule. The fibres which arise most posteriorly from the coracoid are the tlhckest, and run forwards shghtly, as well as oiitwards and upwards, to their insertion. Some few of them overlap the rest, and get inserted into the apex of the acromion. The fibres wliich arise most anteriorly from the coracoid are also strong, and most of them are inserted into the apex of the acromion, but a few pass beneath the rest to be attached below the facet for the clavicle. The intermediate fibres are thinner and more membranous, and are inserted at the acromion beneath the anterior and pos- terior fibres. The surfaces of this ligament look — the one, upwards and slightly forwards, the other, downwards with a slight inclination backwards. It overhangs the shoulder-joint. SCAPULAR LIGAMENTS. 209 from the capsule of wMch it is separated by a bursa, and the tendon of the sub-scapularis muscle. The posterior edge is in the same vertical plane as the anterior border of the outer end of the cla\dcle. The anterior edge projects over the centre of the head of the humerus. The ligament measures more than an inch and a quarter from before backwards at the coracoid, but less than half an inch at the acromion. It is barely one-third of an inch above the capsule of the shoulder-joint, and in the undissected subject, especially near the glenoid cavity, there is not a quarter of an inch interval. It serves to bind the coracoid and acromion processes toge- ther, and to strengthen each by their union, enabling the acro- mion to resist forces wliich tend to drive it outwards, and the coracoid forces which would displace it inwards. It likewise holds off the deltoid muscle from the capsule of the shoulder, and protects the joint fr^om violence directed downwards and backwards upon it. In some animals, such as the sloths, the two processes are still further strengthened by a bony arch. The transverse, coracoid, or supra-scapular ligament is a small triangular band of fibrous tissue, having its surfaces looking inwards and outwards, and its edges, wMch are thin and sharp, turned upwards and downwards. It forms a continuation of the superior costa, which it con- nects with the angle of the coracoid process, while it bridges over the supra-scapular notch. Its base is behind, where it springs fr^om the upper border, especially on its external aspect, of the scapula, for a distance of one-third of an inch behind the notch. Its apex is at the outer lip of the angle of the coracoid process, where its fibres are inserted under the edge of the trapezoid ligament ; but some of its internal and upper fibres are continued directly onwards into the outer edge of the conoid ligament, with the fibres of which they are inserted into the clavicle. The posterior edge of the trapezoid ligament is thus embraced by or interdigitated between fibres of the supra-scapular ligament. It serves to bridge over the supra-scapular notch, and to make the superior costa of the scapula directly continuous with the coracoid process. CHAPTEE XI. THE SHOULDEK-JOINT. Class, Diarthi-osis. Subdivision, Enarthrodia. The shoulder is one of the most perfect and beautiful, and at the same time the most movable of joiats. Like the hip, it is an enarthrodial, or ball and socket joint, and consists of a large ball — viz., the head of the humerus, play- ing in a shallow cup — viz., the glenoid fossa of the scapula. It is retained in position much less by hgaments than by muscles and the effect of atmospheric pressure ; and from the looseness of its capsule, as weU as from all the other conditions of its construction and position, it is exceedingly liable to be dis- placed. As against its exposed position it has this defence, that it is sheltered beneath large projecting processes — the acromion and coracoid. The Scapula. — The portion of the scapula which enters into the formation of this joint is the most important segment of the bone, and to its functions the general shape and dispo- sition of the rest are adapted. It is usually described under the name of external or articular angle of the scapula, but may more appropriately be styled the glenoid process. This pro- cess presents an articular depression — the glenoid cavity ; by its body it supports the coracoid process, while it is marked off from the expanded ala of the scapula by a constriction immediately behind the root of the coracoid process, named the surgical neck of the scapula. It forms the anterior or external angle of the scapula. The glenoid cavity is a very shallow articular depression, situated on the free surface of the glenoid process. It is of an oval shape, with its long diameter vertical, or nearly so, and measures usually about an inch and a half ; it is wider below than above, being usually an inch fi^om side to side at its widest part, and gradually narrowing towards the upper end, it BONES OF THE SHOULDER- JOINT. 211 is there less tlian three-eighths' of an inch. The curve of the outer margin is uniform, but that of the inner is slightly notched " or indented near the apex, so that the general outline of the cavity presents the appearance of a section through a some- what irregularly shaped pear. Its general direction is outwards, forwards, and a little downwards. It is coated in the recent state by articular cartilage, which is thinnest at the centre, and gradually thickens towards the circumference. To the margins is attached the glenoid Kgament — a fibro-cartdaginous structure, by which the cavity is deepened ; and to the rough surface beyond the margin — the neck of the glenoid 'process, or as it is sometimes described, the anatomical neck of the scapula — the capsular ligament of the shoulder is connected. The margin of the cavity is a Httle more prominent on the inner side than on the outer, and in this direction a greater liability to displacement lies ; but the thickest and strongest part of the margin, as well as the broadest part of the cavity, is below. It is this lower part which sustains the chief pressure of the head of the humerus both from muscular action and violence, and on this account it is strengthened by the thick curved an- terior costa of the scapula, as weU. as by a thick ridge running downwards from the margin of the cavity along the costa. The base of the coracoid process forms the upper edge of the glenoid cavity, and, together with the glenoid process, is situated beyond the neck of the scapula — usually described as the surgical neck of the scapula. The great scapular notch, which leads from the supra- to the infra-sj)inous fossa, is on the outer part of the neck of the scapula, or, in other words, of the glenoid process, between the spine and glenoid cavity. The Humerus. — The superior extremity of the humerus consists of a globular head and two non-articular eminences — called the greater and lesser tuberosities. The head forms part of a true sphere, and in the recent state is covered with articular cartilage which is thickest over the middle. The smooth articular surface of the head is Kmited by a sinuous irregular margin forming by no means a true circle, and is received into the glenoid cavity of the scapula. It looks upwards, inwards, and a little backwards, being set off obliquely from the inner and back aspect of the extremity of the shaft. Below the sinuous margin is a slight and narrow constriction, best marked in the upper half of its circumference p 3 212 THE SHOULDER-JOINT. Diagram III. and gradually merging off into' the sliaft below ; it separates the head from the shaft and tuberosities, and is styled the anatomical neck of the huvicrus. It forms a contrast to the elongated neck of the femur wMch carries off the head of that bone to some distance from the shaft. This neck is perforated in its lower half by several large foramina for bloodvessels, and gives attachment all around to the capsular ligament of the shoulder. The greatest measurement of the articular facet is in a horizontal direction on a line with the base of the greater tuberosity and the mid- dle of the lesser ; this measurement is usually about two and a half inches ; the next greatest is in a vertical direction from the ridge on the greater tuberosity separating the facet for the supra- from that for the infra-spinatus muscle, to the under side of the anatomical neck ; this is usually about one-eighth of an inch less than the foregoing. It will be seen on looking at the accompanying diagTam how much more of the articular sm^face is above than below the hori- zontal axis of the head. The greater tuberosity surmounts the outer side of the shaft of the bone, and extends obliquely around to the posterior aspect. It is separated from the globular articular surface of the head by the narrow constriction forming the anatomical neck, and from the lesser tuberosity by the deep groove for the biceps tendon. Its upper surface is marked by three flattened smooth facets separated by two narrow slight ridges which mark the insertion of the supra- and infra-spi- natus and teres minor muscles. Its outer surface is rough and continuous with the shaft of the humerus. The lesser titberosity surmounts the anterior aspect of the shaft, and is more prominent, though smaller, than the gxeater. It slopes obliquely downwards and inwards from the inner margin of the bicipital groove, and like the greater tuberosity is most prominent where it forms part of the boundary of that groove. It is separated from the articular surface of the head by the anatomical neck, and on its summit is a facet for the insertion of the tendon of the sub-scapularis. The bicipital groove is deep and narrow above, where it is 214 THE CAPSULAR LIGAMENT. downwards and outwards its sheath is attached to the under side of the capsule. At the humerus the upper half is fixed to the ana- tomical neck of the bone — i.e., to the gi'oove between the tuberosities and the margin of the articular head ; between the tuberosities it sends down over the bicipital groove and biceps tendon a thick prolongation, which gradually attenuates as it descends. The lower half of the capsule descends upon the humerus further from the margin of the articular facet, but some of the deeper fibres are reflected upwards so as to be attached close to the articular margin, and they thus form, but to a much slighter degree, a kind of fibrous invest- ment for this part of the neck of the humerus, as fibres similarly reflected in the capsule of the hip, do for the cervix femoris. The tendons of the shoulder muscles which pass outwards over the capsule from the dorsal and ventral surfaces of the scapula to be inserted into the tuberosities of the humerus, strengthen the capsule very considerably, more espe- cially near their insertions, and are cliiefly instrumental in holding the head of the humerus against the cavity of the scapula. With care, however, the tendons of the three muscles inserted into the gTeat tuberosity can be separated from the capsule right onwards to their bony attachment ; generally also this can be done with the tendon of the sub-scapularis. Some- times, when the bursa between this tendon and the neck of the scapula communicates with the synovial sac of the joint, the capsule beneath the tendon is very thin and can only with difiiculty, if at all, be separated from it. Where the sub-scapularis is inserted into the lesser tuberosity there is sometimes a well-formed sesamoid bone, the size of a flattened marble, with a polished surface next the tuberosity. More often than not, however, the capsule is as thick on its inner aspect as on its outer, and I have sometimes seen the inner portion below the border of the sub-scapularis the thickest part of the whole capsule, while the outer has been very thin. At any rate there is no one area of tliis capsule which is constantly so different from the rest in density and strength, as is the case with the hip-joint capside, and the reason is clear. In the hip-joint the greater thickness of certain portions of the LIGAMENTS OF THE SHOULDEE-JOINT. 215 capsular ligament is requisite for steadiness and support, and to economise muscular action, but in the slioidder-joint nothing like the same degree of steadiness or strength is wanted, as the upper limb of man serves not the purpose of bearing weight, but is almost solely designed for rapidity and extensive range of movement. The, Coraco-humeral Ligament. — One portion of the capsule is strengthened by a superadded band, which deserves the honour of a special name. This passes from the coracoid process to the greater tuberosity, and is hence called the coraco- humeral band or ligament. To see it satisfactorily, all the other soft parts must be removed from the joint, and the hgamen- tous tissue alone left. Though not completely separated from the rest of the capsule, it is quite a distinct process of hgament. It is attached above to the outer edge of the root and horizontal arm of the coracoid process, nearly up to its tip, and from the dorsal aspect of the scapula looks like an uninterrupted con- tinuation of the back of the capsule. When seen from the ventral surface, it looks like a fan-like prolongation above the rest of the ligament. Having passed over the capsule along the line of the biceps tendon, it is inserted into the outer tube- rosity of the humerus, and assists the capsule, with which it becomes incorporated, to bridge over the bicipital groove. The Gleno-humeral Process of the Cafpsule- — Besides the coraco- humeral hgament above described, the capsular ligament is some- times said to be strengthened by three accessory bands or supple- mental sets of fibres, passing from the scapula to the humerus. One of these extends from the inner edge of the glenoid cavity, along the lower edge of the sub-scapularis tendon, to the lower part of the small tuberosity ; another passes from the under edge of the cavity to the imder part of the neck of the humerus, thickening the lower surface of the capsule, and is the part put on stretch when the arm is fully raised ; and a third, seen only from within the capsule, extends along the imier edge of the biceps tendon. Although there is nearly always to be seen along the two first-mentioned lines some thickening of the capsule, yet this is usually but slight, and the extra fibres pro- ducing it do not deserve a separate name. But the thin narrow riband-like slip which runs along beside the biceps tendon, and which, has been styled the gleno-humeral ligament, deserves a brief notice. After laying open the capsule freely on 216 THE GLENOID LIGAMENT. the ventral side, it is found to he attached above to the edge of the glenoid fossa at the root of the coracoid, and below to the lesser tuberosity of the humerus. It presents two sides free, and covered by synovial membrane ; one edge, tliin and sharp, projecting outwards a little way under the tendon of the biceps, and another attached to the deep surface of the capsular ligament." It thus lielps to form a groove or sulcus for the biceps tendon, keeping it in its proper line as it traverses the capsule, and checking any tendency to its inward displacement. It is supposed to correspond to the ligamentum teres of the hip-joint of man, and to the ligamentum teres of the shoulder- joint of the fi'og. As the ligamentum teres is, however, quite a superfluous and unnecessary structure in the hip, it is still more difficult to understand what pm-pose, as its homologue, this gieno-hmneral slip can serve in the shoulder ; and it seems to me that its only use is, as I have pointed out above, to form a sulcus in the interior of the capsule for the play of the biceps tendon. It is sometimes described as a part of the coraco-humeral ligament, but as that ligament is superadded to the capsule on its exterior, and the gleno-humeral is a process from its interior, this view is incorrect unless the whole thickness of that particular area of the capsule be considered coraco-humeral ligament, which in the above description is not the case. Besides the support which the capsule receives from the ten- dons of muscles, extra strength is given to it by a strong fascia, which passes over it from the under surface of the acromion and coracoid processes, as well as by a fascia from the anterior part of the coraco-acromial ligament immediately beneath the deltoid muscle. The glenoid ligament is a narrow rim of dense fibro- cartilage, which is attached to and deepens the circumferential portion of the glenoid socket.- Its structure is almost entirely fibrous, with but few cartilage cells intermixed, and the fibrous bundles are chcularly disposed, and more or less interlacing. It is about one-fourth of an inch wide above and below, and usually not much more than half that width along the outer and inner borders of the socket. Its outer edge is one- eighth to one-fom-th of an inch deep, and is inseparably welded, near its attachment to the bone, with the fibres of the VERT/CAL. SECTION THROUGH SHOULDER JOINT Suf)TPi*MS-irvvi^scL& V GUno Tattyt£rct3^ Ti/^ct*rv&n.t r^viljm. oF ? ■toioL lioj oufie.yvt t.e- I Cccjo i^ liUii' Ir^tu-M^nt- Ali^^'U'trtcot . Yf&St, ifcwyvLKn, &. C OU.!v- LIGAMENTS OF THE SHOULDER- JOINT. 217 capsular ligament. The inner edge is fchin, and in contact with the articular cartilage ; in some places, especially above and along the inner side, it often overlaps the cartilage, and forms quite a long loose irregular fringe ; at others it is separated by a very narrow interval covered with fibro-cartilage of a more loosely woven character, so that the line of demar- cation between articular cartilage and fibro-cartilage is usually quite evident to the naked eye. At the upper part of the fossa the biceps tendon is pro- longed into the glenoid ligament, and forms an integral and important part of it. Sometimes the fibres of the tendon curve along the outer, sometimes along the inner, and sometimes again along both outer and inner sides for a considerable distance. Indeed, the tendon sends into the ligament fibres wMch wmd round nearly the entire circumference of the socket. The articular cartilage covering the glenoid socket is thicker at the ch'cumference than in the centre. In the former situa- tion it is about three lines in depth, in the latter less than two lines. It thus assists the glenoid ligament to deepen the fossa for the head of the humerus. It is generally thickest of all at the lowest part of the fossa, for it is here that the head of the humerus revolves when the arm is raised by the deltoid muscle ; and against this part of the socket the head of the bone is pressed by the action of the sub- scapularis, infra-spinatus, coraco-brachialis, and the biceps ten- dons. Over the head of the humerus the articular cartilage is thickest at the centre and a little below the centre, for it is this part of the head of the bone which is in contact with the socket whilst the the arm is raised, and the shoulder muscles are therefore in action, to press the surfaces closely together. The Biceps Tendon. — This tendon forms a peculiar feature in the shoulder-joint, as it traverses it from the glenoid fossa to reach the upper end of the bicipital groove in the humerus. While it is covered by the fibrous capsule it Lies first in a sulcus of the capsule formed, as described above, by the pro- jecting gleno-humeral band, and then in the groove between the tuberosities of the humerus. It passes over the head of the humerus a Httle on the inner side of its summit ; and, until it reaches the bicipital groove in that bone, where it changes to a rounded form, it is flat, with one surface looking to the 218 THE BICErS TENDON. capsule, the other towards the head of the humerus. Its inner edge is sheltered by the gleno-humeral hgament when this structure is weU developed and its outer edge is free. At its upper extremity, some of the fibres composing it arise from the glenoid process between the attachment of the fibres of the capside and the articular margin, and external to the root of the coracoid process ; but the greater number spread out widely and merge into the glenoid ligament, some- times both to the right and left, sometimes only to the right or left. Though loose within, and detached from, the cap- sular ligament, it is shut out from the synovial cavity by a reflection of the sjoiovial membrane which completely ensheathes it. This sheath is continuous with the synovial lining of the capsule, both at the attached extremity of the tendon and at the bicipital groove ; elsewhere it formed a theca for the tendon, wliich, like the tendon itself, is unattached to the capsular ligament. Eunning upwards from the bicipital groove of the humerus on the surface, or in the substance, of the tendon, is a branch of artery (sometimes two branches), which often reaches as high as the origin of the tendon above the fossa. The biceps tendon strengthens the upper part of the articu- lation along the same course as the coraco-humeral ligament, and tends to prevent the head of the humerus being pulled too closely upwards against the under surface of the acromion. It also serves the purpose of a ligament by steadying the head of the humerus in the various movements of the arm and forearm ; and to this end it is let into the sulcus or groove at the upper end of the bone, from which it cannot escape on account of the prominence of the abutting tuberosities, and the strong- fibrous wall which covers it in. Further, it acts like the four shoulder muscles which pass over the capsule, to keep the head of the humerus against the glenoid socket ; and more especially, it resists the tendency of the pectoralis major and latissimus muscles in certain actions, when the arm is away from the side of the body, to pull the head of the humerus below the lower edge of the cavity. The SYNOVIAL MEMBRANE lines the fibro-cartilaginous rim — i.e., the glenoid ligament — and is then reflected over the inner sm-face of the capsule to its attachment at the humerus, from which it is continued upwards as far as to the edge of the articular cartilage. The tendon of the biceps receives a long •ARTERIES OF THE SHOULDER-JOINT. 219 tubular slieath, as above described. The synovial cavity some- times communicates with the subscapular bursa, and sometimes, though less frequently, with a bursa beneath the tendon of the infra-spinatus muscle on the outer side of the joint. It also sends a pouch-like prolongation beneath the coracoid process when the fibrous capsule is attached at this part wide of the margin of the glenoid fossa. A few fringes or pro- cesses of the synovial membrane are often found near the edge of the glenoid cavity, especially at the upper and inner side ; occasionally similar smaller processes spring off near the humeral head. Arteeies. — The arteries of the shoulder-joint are derived from the subclavian through the supra-scapular ; and from the axillary through the anterior and posterior circumflex, the sub- scapular, dorsaKs scapulae, and sometimes also through a branch direct to the joint. The anastomosis upon the capsular liga- ment is very free, and besides the several vessels which run more or less directly to the joint, many twigs from the arteries to the muscles which pass off to it near the insertion of their tendons, are connected with the capsule. From the ramifications on the outer surface of the capsule little vessels penetrate its substance, and can be seen, in a well-injected body, from the inner surface, ramifying beneath the synovial membrane. Arterial twigs enter the substance of both bones near to the attachment of the capsule. The suprascapular artery, immediately after passing over the transverse ligament, gives a branch which runs forwards beneath the outer end of the clavicle, external to the coraco-clavicular liga- ments, and, after supplying these, ends in the top of the capsule. While the trunk is beneath the supra-spinatus muscle, another branch arises which winds over the surface of the muscle to the upper and outer aspect of the joint ; this gives off branches to the acromio-clavicular joint. Another branch reaches the capsule by running to it between the contiguous borders of the supra- and infra-spinatus ; and another, after passing over the infra-spinatus, reaches the capsule between this muscle and the teres minor. Besides the above-named, there is a free supply of blood to the shoulder-joint through muscular branches ; as well as through vessels which, running off from, the trunk in the scapular notch {i.e., beneath the acromion at the anterior border of the spine of the scapula), pass directly to 220 ARTERIES OF THE SHOULDER- JOINT. the joint beneath the muscles, and some of them send branches into the bone on the dorsal aspect near the margin of the glenoid fossa. Tlie anterior circmnjiex supplies the inner, front, and lower parts of the capsule, while a branch passes upwards from it to the joint along the bicipital groove. A branch which passes beneath the lower border of the sub-scapularis, near its inser- tion, supplies the subjacent part of the capsule. Sometimes there are two anterior circumflex arteries, one of which is dis- tributed entu^ely to the joint which it reaches along the lower border of the sub-scapularis, while the other passes outwards upon the latissimus dorsi tendon to get beneath the coraco- brachialis, where it sends branches upwards and downwards along the biceps tendon. A branch of the anterior circumflex pierces the humerus at its anatomical neck on the inner side of the bicipital groove. The "posterior circurnfiex gives off a branch which runs forward beneath the deltoid towards the great tuberosity of the humerus, and then courses upwards, ramifying over the outer and front parts of the capsule, and anastomosing with the anterior cir- cumflex and supra-scapular vessels. A branch from the pos- terior circumflex to the teres minor runs on to the capsule, and another passes beneath that muscle to supply the humerus, and the capsule near its attachment to the humerus. The dorsalis scapulce artery, whilst in the substance of the teres minor, sends up branches to the lower and outer part of the joint. The subscapular artery supplies the inner side of the capsule near the glenoid fossa. One long branch usually runs upon the anterior surface of the long head of the triceps, and under cover of the sub-scapularis, to supply the capsule and the bone near the attachment of the capsule, and then ramifies on the venter of the scapula. A small twig from this branch usually pierces the scapula near the glenoid fossa. A considerable branch from the second part of the axillary artery runs over the anterior surface of the sub-scapularis muscle to its upper border, and then reaches the capside beneath the origin of the coraco-brachialis and biceps, and the coracoid process. The Nerves. — The supra-scapular nerve gives off a branch BURS/E IN CONNECTION WITH SHOULDER JOINT GU/ tendorvof &tiscap vHaris MuseliB'— ntral, Surf'an of ScccpuJin. j^ J^ of Acramioa ibacfomuH' liur.va ( rcasijyrtpl (>ijLtsa. hetweeix biceps &CcT'chCo brcuJuxxlxs ajui Y t'oq.>Hnh3- ci -jaird:. between tip cf Corneal & Capsule cfShxmJbde^ Vl ^ -v ., ' T \ B "C"""-? Leres -major -' Eursci. lyenjsxjuK teres moJor tx TS a-nzm Jjjy-s i LoJx&sutnxijS Aorsx. & capsuCLe^ whlchy cfteru commuriL- cci/tes. with, (uwity of Oije, joint-. Manerryaxv SUH'. ofterManro y>kst,Nafrma^n. &. ^9Ziih. NERVES OF THE SHOULDER-JOINT. 221 or two, to the shoiilder, whilst in the supra-spinous fossa ; the nerve then passes through the great scapular notch into the lower fossa, oiving off other twigs to enter the joint, and some which penetrate the scapula. The circumflex nerve, after springing from the posterior cord of the brachial plexus, winds round the joint beneath the deltoid muscle ; as it does so, it supphes twigs to the capsule. Other branches from it enter the capsule at the lower border of the sub-scapularis muscle. The subscapular nerves also give branches to the interior of the joint; the upper one penetrates the upper part of the subscapular muscle to reach the capsule, and the middle gives off a twig at the lower edge of the muscle. The nerve supply of the shoulder-joint is thus derived from the same source as the supply to the shoulder muscles. The supra- and infra-spinatus are supplied by the supra- scapular ; the sub-scapularis by the subscapular ; and the deltoid and teres minor, together with the skin over the shoulder muscles, by the circumflex. The BuESiE. — There are several bursce in connexion with this joint. (1) The largest, and the one most frequently brought under the notice of the surgeon, is situated between the acromion and coraco-acromial ligament above, and the capsular liga- ment of the shoulder below. In elderly people, this bursa some- times communicates through a large irregular opening with the synovial cavity of the joint. (2) A large bursa exists beneath the sub-scapularis, between it on the one hand, and the neck of the scapula and iuner side of the capsular ligament on the other. It very frequently communicates with the cavity of the joint, but not so con- stantly as it is sometimes stated to do. (3) Occasionally there is another and a much smaller bursa placed further out upon the capsule, between it and the sub- scapular tendon. This, when it is present, generally commu- nicates with the joint. (4) A smaU bursa, sometimes wanting, is interposed between the under surface of the tip of the coracoid process and the capsule. (5) Another elongated bursa, similar in shape to, but a little 222 MUSCLES OF THE SHOULDER-JOINT. larger than the last, and like it sometimes wanting, is often situated between the united coraco-brachialis and biceps tendons, and the capsular ligament of the shoulder. In addition to the above, three other bursse, though not directly placed over the capsule, are yet in near relation to it. These are (6) a bursa between the tendon of the teres major and the humerus on the one side, and the upper part of the latissimus on the other. (7) One between the tendon of the latissimus dorsi and the humerus ; (8) and one between the tendon of the biceps and the humerus. The Muscles. — It must here be observed, that in no other joint in the body do the muscles add so gTeatly to the strength of the articulation, or take so large a share in controlling move- ments, in keeping the bones in normal apposition, and in preventing theu^ displacement, as at the shoulder. Four muscles may be said to be inserted into the capsule ; whilst another passes beneath it, and acts like a strap to prevent upward as well as lateral displacement, and yet at the same time acts as a sling to hold the bone upwards against the humerus. There is a close similarity between the shoulder-joint and the hip, in the way in which the muscles are disposed about the capsule. Thus, on the outer or extensor side of the shoulder we have the supra- and infra-spinatus and the teres minor ; at the corresponding aspect of the hip, there are the pyriformis, gemelli and obturator internus. On the flexor or anterior side, the sub-scapularis covers the shoulder ; the ilio-psoas the hip : while the long head of the rectus femoris bears somewhat the same relation to the capsule of the hip as the long tendon of the biceps does to the shoulder ; and the deltoid covers over the whole of the upper and outer side of the shoulder, as the glutsei do the hip. As in the hip, so in the shoulder, the portion of the cap- sule least supported by muscles is the lower or inner side. Here, too, the shoulder capsule is often very thin, and there is no projecting bony prominence like the acromion and coracoid, to counteract the deficiency of the muscular support in bearing the pressure of the head of the humerus in states of abduction. Hence abduction in the case of the shoulder, as well as of the hip, is the position of least safety, and the one in which dis- location nearly always occurs. THE SHOULDER- JOINT. 223 The muscles wMch effect the various movements of the shoulder may "be grouped according to their action into flexors, extensors, ahductors, adductors, and rotators, although it must be premised that some of the muscles can produce different, though not of course contrary actions, according to the action of other muscles wherewith for the time they are associated, and some combine movement in two dkections. Flexors. — The carrying forward of the humerus constitutes flexion ; it is a much freer movement than its opposite, exten- sion, and is produced by the pectoralis major, the anterior fibres of the deltoid when acting alone, the coraco-brachialis, and long and short tendons of the biceps ; and when the arm is raised from the side, i.e., abducted, by the sub-scapularis also. Extensors. — Extension, or the movement of the arm back- wards, is effected by the latissimus dorsi, the posterior fibres of the deltoid when acting alone, and, when the arm is raised, by the infra-spinatus. The movements of flexion and extension, or the swinging to and fro, of the humerus, are made more free than they otherwise would be by the forward and backward, and rotatory move- ments of the scapula. This is more particularly the case with flexion, the scapula following the head of the humerus so that the muscles which have been enumerated as moving the scapula forwards come into associated action with the flexors ; and the muscles which withdraw the scapula after it has been advanced with the extensors. Abductors. — Abduction, or the movement of the humerus away from the side of the body, is accomplished by those muscles which elevate the arm, of which the chief is the deltoid. The supra-spinatus is a simple elevator or abductor. The deltoid and supra-spinatus can raise the humerus to a right angle with the trimk ; any further elevation is produced by the action of the trapezius upon the scapula, and is not a movement of the shoulder-joint. Adductors. — Adduction, or drawing the arm to the side and therefore depressing the raised arm, may be accompanied either with flexion or extension. The adductors which draw forwards are the pectoralis major and the coraco-brachialis and biceps. The adductors that draw the humerus backwards are the 224 MOVEMENTS OF THE SHOULDER- JOINT. latissimns clorsi and the teres major and minor. The long head of the triceps adducts the arm after it has been abducted. Botators. — Eotation inwards is effected by the sub-scapularis, and to a less extent by the latissunus dorsi and teres major, when the arm hangs by the side. Eotation outwards by the teres minor and infra-spinatus, when the arm is hanging by the side. Circumduction is effected by the quick succession of the four angailar movements. The Movements. — In the shoulder- joint there are the common angular movements in four directions : viz., flexion, extension, abduction, and adduction; the combination of these in quick succession, which is called circumduction ; and rotation. Flexion is the swinging forwards, extension the swinging back- wards of the humerus ; abduction is the raising of the humerus from, adduction the depression of it to, the side of the body. In flexion and extension the head of the humerus moves on the centre of the glenoid fossa round an oblique line corre- sponding to the axis of the head and neck of the bone. Flexion is more free than extension, and in extreme flexion the scapula foUows the head of the humerus so as to keep the articular surfaces together. In extension the scapula moves much less, if at aU. In abduction and adduction the scapula is fixed, and the humerus rolls upwards and downwards upon its fossa; during abduction the head descends until it projects beyond the lower edge of the glenoid socket against the capsule, and the great tuberosity impinges against the arch of the acromion; during adduction the head of the humerus ascends upon the socket, the arm at last reaches the side of the trunk, and the capsule is completely relaxed. In circumduction the humerus by passing quickly through the several angular movements describes a cone, whose apex is at the shoulder-joint and whose base is at the condylar extre- mity ; or if we consider the movements at the shoulder-joint as of the whole upper limb, the base is at the terminal phalanges of the fingers. Eotation is movement round a vertical axis through the extremities of the humerus from the point of the head to the inner condyle. In rotation forwards, i.e., inwards, the head of the bone rolls backwards on the socket, as the great tube- MOVEMENTS OF THE SHOULDER-JOINT. 225 rosity and the shaft are tm-necl forwards. In rotation back- wards, i.e., outwards, the head of the bone glides forwards on the glenoid cavity, and the tuberosity, shaft, and lower end of the hnmerus are turned backwards, i.e., outwards. Great freedom of movement is permitted at the shoulder, and greater freedom is added by the free-play mobility of the scapula. Restraint is scarcely at all exercised upon the move- ments of the shoulder proper by the ligaments, but chiefly by the muscles of the joint. In abduction the lower part of the capsule is somewhat, and in extreme abduction considerably, tightened ; in rotation inwards and outwards, the up2:)er part of the capsule is made tense. The movements of abduction and extension have the most decided and definite resistance offered to them othermse than by muscles and the shoulder- joint ligaments, for the great tuberosity of the humerus by striking against the acromion process, and the coraco-acromial ligament, stops short any further advance of the bone in these directions, and thus abduction ceases altogether as soon as the arm is raised to a right angle with the trunk; and extension shortly after the humerus passes the line of the trunk. The further elevation of the arm is effected by the rotation of the scapula round its own axis by the action of the trapezius muscle upon the sterno-clavicular and acromio-clavicular joints. The insertion of the trapezius muscle, as is well known, is along a bony line parallel with that from which the deltoid arises ; the fibres of the muscles are in the same continuous lines, and the spine of the scapula, the acromion, and clavicle may be looked upon simply as a bony interruption of the fibres of these two muscles. The trapezius therefore is ^A-ell adapted to continue the direction of the motion of the deltoid after the action of the latter is completed. The acromion and coracoid processes together with the liga- ment which extends between them form an arch, sejoarated by a bursa from the capsule of the shoulder. Beneath this arch the movements of the joint have to take place, and against it the head and tuberosities are pressed when the weight of the trunk rests upon the arms ; and the great tuberosity and upper part of the shaft impinge upon it when abduction and extension are carried to their fullest extent. The movements of the shoulder, Kke those of the other joints of the upper limb, are used as aids to words and looks 226 MOVEMENTS OF THE SHOULDER- JOINT. in giving expression to the feelings and emotions of the human mind. We see force and emphasis added to the speech of the orator, and to the representation of passions by the actor or actress by these movements. It is not easy to specialise in any decided manner, hut it may he stated, with some approach to truth, that the portrayal of feelings of a widely impressed kind, whether it he of despair, resignation, admiration, entreaty, or love, is assisted hy movements which occur at the shoulder, often in combination with those effected at the wrist. So again in the more concentrated and decisive states of mind, as when we give a command, a dismissal, or definite instructions with dignity or firmness, the shoulder movements are employed, with others of the wrist and index-finger, the elbow all the time remainmg rigid, or moving but slightly. CHAPTEE XII. THE E L B W-J I N T. Class, Diarthrosis. Subdivision, Ginglymus. The elbow is a complete hinge joint, and, unlike the knee, depends for its security and strength upon the configuration of the bones rather than on the number, strength, or arrangement of the ligaments. The bones composing it are the lower end of the humerus above, and the upper ends of the radius and ulna below ; the articular surfaces of the former being received partly within the great sigmoid cavity of the ulna, and partly upon the cup- like surface of the head of the radius. The Humerus presents at its lower extremity two condyles, with a remarkable double articular surface intervening between them. The shaft, which is cylindrical in its upper two-thirds, becomes flattened antero-posteriorly at the lower end, where it measures from point to point of the condyles from two and a half to three inches across ; from before backwards it varies in thickness at different spots, being in places quite translucent, and nowhere more than one inch through. It curves forwards a little from the shaft, and presents, when looked at from in front, two sharp, strong lateral ridges, separating the anterior from the posterior surface ; and a median ridge running down the centre of the anterior surface of the shaft, which bifurcates just above the articular surface so as to enclose the coronoid fossa. "When seen from behind, the bone is flat above the olecranon fossa, but articular below it ; rough and bevelled forwards over the outer condyle ; flattened and grooved over the inner condyle. The external ridge, called usually the external condyloid ridge, is by far the most prominent ; it terminates at the external condyle, and may be traced up to the back of the great tube- rosity. The internal condyloid ridge terminates at the inner condyle, and may be traced up to the root of the lesser tube- Q 3 228 , THE ELBOW- JOINT. rosity. The anterior or supra-trochlear ridge ascends to the anterior border of the great tuberosity, and the ridges into which it bifurcates below terminate, the one at the outer, the other at the inner border of the troclilear facet for the ulna. All these ridges assist in conducting forces from the elbow to the shoulder-joint; but the condyloid ridges, with the flattened bone between them, serve also to divide off sharply the muscles behind which extend, from those in front which flex the elbow. The two projections in which the lateral ridges end are the condyles ; these are very different from the condyles of the femur, which afford large articular surfaces for the tibia. The condyles of the humerus are merely bony tubercles for the advantageous origin of muscles, and do not enter at all into the immediate formation of the elbow. They do not descend quite to the lowest extremity of the bone, so that the articular surface reaches beyond them. The inner condyle is much the most prominent, and gives rise to the flexors and pronators — the strongest sets of muscles of the forearm. It also descends somewhat lower than the ex- ternal, and projects horizontally inwards for three-quarters of an inch or more, beyond the inner margin of the trochlea. Between it and the trochlea in front is a rough, narrow depres- sion, and below and behind it is a deep and narrow gi"oove, along which the ulnar nerve passes over the elbow-joint. The outer condyle gives rise to the extensor muscles — a much less powerful set than the flexors. It projects less than a quarter of an inch beyond the outer edge of the capitulum, in front ; and about three-quarters of an inch beyond the outer margin of the trochlea, behind. The articular surface at the lower end of the humerus is situated between the condyles, extends round the extremity upon both aspects of the bone, and owing to the obliquity of the bone descends lower on the inner than on the outer side. It is divided in front and below by a shallow groove, which separates a small external and globular portion about the size of a large cherry — the capitulum or capitellum — from a wide pulley-like and oblique surface, called the trochlea. The cajntulum, or lesser head, does not extend at all upon the posterior surface of the humerus, but is seen only on the anterior surface, and at the end. It articulates with the cup- .like facet at the top of the radius, and the groove between it THE ELBOW-JOINT THE HUMERUS. 229 and the trochlea receives the inner margin of the rim of the radial facet. In complete extension of the joint, when pressure is not directed upon the lower end of the bone, the radius is not in contact with the capitulum at all, and the posterior margin of the rim projects beyond it. During flexion the bones come more and more into apposition, and in complete flexion the anterior portion of the rim of the radial cavity sinks into the curved shallow fossa above the capitulum. The trochlea extends equally over front and back surfaces, as well as upon the extremity. It is convex from before back- wards, concave from side to side, and wider by about an eighth of an inch in front than beliind. It is bounded by two mar- gins, the outer of which is but sMghtly prominent in front and below, but becomes sharp and pronotmced behind. Immediately to its outer side is the gTOOve separating the capitulum from it. The inner margin is thick, strong, prominent, and descends lower than the outer. The groove between these margins extends from the coronoid fossa in front to the olecranon fossa behind, and in doing so is inclined obliquely outwards. Owing to the obliquity of the humerus, and the greater prominence of the inner margin of the trochlea below as well as in front, the shaft of the bone, when held with its lower end resting upon a flat surface, slants very considerably outwards. From within outwards we find the articular surface of the lower extremity presents, first, the trochlea with its prominent inner border, its deep groove, and less well-marked outer border ; next, the groove between the trochlea and capitulum, which receives the inner margin of the cup-like cavity of the radius ; and lastly, the capitulum, which receives the cup-like cavity itself. Above the articular surface, behind, is the large olecranon fossa, which receives the olecranon process of the ulna in exten- sion of the forearm. It is a deep, oval-shaped, transversely elongated fossa, to which the posterior ligament is attached, and in wMch is lodged a quantity of articular fatty tissue. Above the articular surface in front are two fossae. One, the larger — fossa anterior major — is placed immediately above the groove of the trochlea, and between the bifurcated lower ends of the supra-trochlear ridge ; it is large enough to admit the tip of the finger, receives the coronoid process in flexion, and lodges articular fat. The other fossa — fossa anterior minor — 230 THE ELBOW-JOINT. is a narrow, shallow, and crescentic depression aLove the capi- tulum, which receives the anterior margin of the cup-like cavity of the radius in extreme flexion. The thin lamina of bone separating the olecranon from the coronoid fossa is often perforated by a hole of some size. The Ulna is of large size at its upper extremity, where it forms a very important part of the elbow-joint, as well as of the superior radio-iilnar articulation. It presents two articular facets, the large and the small sigmoid cavities, and two vip- standing processes, each of which assists in forming the large sigmoid cavity ; whilst by their non-articular surface, the larger of these gives attachment to the extensor, and the smaller to the chief flexor muscle of the forearm. The great sigmoid cavity is a large semilunar excavation formed by the anterior surface of the olecranon, the superior surface of the coronoid process, and the end of the shaft of the ulna, which intervenes between them. It is concave from above downwards, and measures from one and a half to two inches along the middle of its surface ; convex from side to side, and measures about one inch and an eighth across, near the top of the olecranon, about one inch across at the base of the coronoid process, and about seven-eighths of an inch, though oftentimes very much less, where the olecranon joins the shaft. Dividing the cavity into two vertical portions is a prominent smooth ridge, which extends from the tip of the olecranon to the tip of the coronoid. The surface on the inner side of the ridge is larger than that on Lhe outer side. Dividing the cavity into two transverse portions is a notch or constriction in each lateral border opposite the junction of the olecranon with the shaft ; and between the notches a depression, in which there is often no articular cartilage. The portion of the fossa above this depression is formed entirely by the olecranon, and is more extensive both ver- tically and transversely than the part in front. The portion of the fossa in front of this depression is formed by the end of the shaft, and the upper surface of the coronoid process, of the ulna. The notch and outer end of this depression separate widely the lesser sigmoid cavity from the facetted surface of the olecranon. Sharp and projecting margins limit the great sigmoid fossa everywhere, except on the outer side of the portion formed by the shaft. Here the articular cartilage THE ELBOW- JOINT THE ULNA. 231 extends over a well-defined, but not projecting, edge into the lesser sigmoid cavity for the radius. The lesser sigmoid cavity will be described under the superior radio-ulnar articulation. The oUcranon is a large square-shaped process connected by one of its surfaces with the summit of the ulna. It forms the strong, posterior bony part of the elbow. It bends for- ward at the top, so that the edge which separates the superior from the anterior surface somewhat overhangs the great sig- moid cavity, and terminates in a central tip, which during extension of the forearm rests against the floor of the olecranon fossa of the humerus. The superior surface is irregularly quadrilateral, and gives attachment to the posterior ligament of the joint, and behind that to the extensor triceps muscle ; a bursa intervening between them. The posterior surface has marked upon it two ridges, which meet upon the top of the shaft, and to which are fix:ed pro- cesses of the triceps tendon. The triangular surface enclosed between them is sub- cutaneous, but gives attachment to strong longitudinal fibres connected with the triceps tendon, and over it a bursa is placed ; in front of the outer ridge, the anconeus is inserted ; from the depressed surface of bone in front of the inner edge, the flexor profundus digitorum arises. The coroiioid is a much smaller process than the olecranon, and ascends from the front of the shaft with a slight inclination forwards. It is triangular in shape, with its upper or posterior surface forming part of the gTeat sigmoid cavity ; and its anterior surface rough, for the attachment of the anterior liga- ment of the elbow and the brachialis anticus muscle. Its* superior edges, which meet at the tip of the coronoid process, slope gradually into the edges of the free end of the shaft ; the outer one changes its direction, after bounding the sigmoid fossa in front for a little way, and then passes vertically downwards, limiting the lesser sigmoid cavity. Wliere the edges of the coronoid process meet with the edges of the portion of the fossa formed by the shaft, two ridges start, and descending downwards a little way, meet each other on the front surface of the shaft ; thus the front surface of the coronoid being limited by these edges and ridges, presents an irregularly diamond shape, into the lower two-thirds of which 232 THE ELBOW-JOINT — THE RADIUS. tlie bracliialis anticiis is inserted, as well as into the upper end of tlie shaft of the ulna. At the top of the shaft, to the inner side of the coronoid process, and widening the inner portion of the great sigmoid fossa, there is a projection which overhangs the deep depres- sion on the inner surface of the shaft, from w^hich the flexor profundus digitorum arises. The Eadius. — The upper extremity of the radius presents a circular head supported upon a smooth and constricted neck. The head is hollowed out a little at its free end into a shallow cup-like dej)ression, which receives the capitulum of the humerus in certain positions of the joint. The margins of the cup are raised and rounded off, and pass over on to a smooth cartilage-covered vertical border, which is surrounded in the recent state by the annular ligament. This border at some parts is not more than one-fifth of an inch deep, but on the inner side, where the radius articulates with the lesser sigmoid cavity of the ulna, it descends in some cases fuUy half an inch. Below the cartilage-covered vertical border the radius suddenly contracts into a smooth constricted neck. The neck is about an inch long and inclines a little inwards, so as to form with the shaft a curve having the convexity dhected inwards. On this convexity is a rough tubercle, which at its posterior part gives insertion to the bicej)s tendon, whilst over the anterior portion a bursa is interposed between the tendon and the bone. The Ligamejtts of the Elbow-joint. — The ligaments of the elbow-joint are so arranged as to form one large and capacious capsule, which encloses the articular surfaces, and something •more, of the adjoining ends of the humerus, ulna, and radius. It may indeed be said to embrace not only the elbow but also the superior radio-ulnar articulation, and to unite them into one joint ; and this is due to its being fixed round the neck of the radius after being intimately blended with the coronary ligament. This capsule is, however, strengthened very considerably at the sides by some strong superadded fibres, or fasciculi of fibres, which arise from the condyles of the humerus and spread out upon the capsule, so as to be quite inseparable from it, as they descend to the bones of the forearm. On this account, no doubt, it is that the elbow is usually described as having an THE LIGAMENTS OF THE ELBOW-JOINT. 233 anterior, a posterior, and two lateral ligaments ; a mode of description which is objectionable, as it leads to the supposition that there are four distinct Kgaments, whereas they are but areas or portions of one continuous structure. Though in the following account, for the sake of convenience, the attachments of the capsule on the different aspects will be spoken of separately, the four segments will be described as parts of the capsule, and not as separate and distinct ligaments. The anterior segment of the capsular ligament is attached to the front of the humerus above its articular surface, and the coronoid fossa, in an inverted V'Sl^^P^d naanner. Tliere are generally to be traced at the lower end of the dry bone (and it will become apparent at once when the dissected joint is examined at the same time as the dry bone) two faintly marked ridges, of which the lower ends reach to the point of the external and internal condyles respectively, and the upper meet at a variable distance, from half an inch to an inch, above the coronoid fossa. To these ridges the front of the capsule is attached above. Below, to the ulna, it is fixed to a faintly marked and nearly transverse ridge on the front of the coronoid process, which is on a level with, or somewhat below the smooth outer border of the great sigTaoid cavity ; and on the radius, it reaches to the neck of the bone a little way below the vertical margin of the head. It is very intimately connected with the orbicular or annular ligament. It is of varying thickness and strength, sometimes being so weak and thin as barely to cover the synovial membrane and fatty tissue near the coronoid fossa. At other times it is thick and strong, and consists of coarse decussating fibres, the chief of which pass from above and within, downwards and outwards to the radius ; whilst other fibres descend vertically from above the coronoid fossa to the ulna, and others again pass downwards and inwards to the ulna. This portion of the capsule is tightened in extension, and as extension proceeds it becomes very much stretched over the prominent inner border of the trochlea ; dm^ing flexion it becomes transversely ^Tinkled, but is prevented from being squeezed between the apposed surfaces of the bones by falling over the front of the radius and ulna near the line of attach- ment of the capsule to the humerus. The posterior portion of the capsular ligament is thin and 234 THE ELBOW-JOINT. membrauous, and is attached superiorly to the humerus in much the same inverted V-shaped manner as the anterior. It reaches upwards from the back of the internal condyle along the inner edge, nearly to the top, of the olecranon fossa ; then it is fixed to a line passing transversely across the upper portion of the fossa till it reaches the outer edge, along which it is also attached ; next it is attached in a continuous line to the back of the external condyle as far down as the rough surface a little external to the angle between the trochlea and hinder border of the capitulum ; and finally it curves forwards . along the posterior edge of the capitulum. Inferiorly, it is attached to the superior and external surfaces of the olecranon, at a considerable distance from the articular margin of the ulna ; to the rough surface of the ulna behind the lesser sigmoid notch ; and to the upper end of the ridge which separates the anconeus from the supinator brevis muscles, and runs downwards upon the shaft from the hinder margin of the notch ; and lastly, it is connected with the back part of the neck of the radius and with the coronary ligament, with which it blends as it passes over it. This portion of the ligament is composed partly of decussating fibres, most of which pass vertically from then- upper to their lower attachment, many obliquely downwards and inwards from the external condyle to the back of the lesser sigmoid cavity of the ulna and the neck of the radius ; whilst others, again, take a transverse coui'se superficial to, and decussating with the rest, from one border of the olecranon fossa to the other. This j)art of the capsule is usually weaker than the anterior, and often is especially thin near the top of the olecranon fossa. It is made tight during flexion, and is thrown into numerous transverse folds, which are pushed upwards by the point of the olecranon during extension. The internal jJortion of the caijsular ligament, like the ex- ternal, is much thicker, denser, and stronger than either the anterior or posterior. It is triangular in form, with its apex above, and its base, which is curved, below. It is attached to the humerus on the anterior and under aspect of the internal condyle, and to the condyloid edge of the groove betv*^een the trochlea and condyle ; and the fibres radiate as they pass to their insertion into the inner side of tlie shaft of the ulna and of the olecranon. HAtM Mhl !'l ELBOW JOINT FROM OUTER SIDE Tjxjternii.1 cand-yTe f ¥/ 2 E.I- Ei O VV JOl NT FROM INNER S IDI JrUero-rstMi*^ mfml'ftj-yi^ y*^ lyuter-ytd- laJ'e>-a.L THE LIGAMENTS OF THE ELBOW- JOINT. 235 The anterior set of fibres pass forwards as they descend to the rough overhanging and projecting edge of the sigmoid cavity at the inner side of the coronoid process. The middle set descend less obliquely, and some of them quite vertically from the under edge of the internal condyle to a ridge on the ulna, which curves upwards between the coronoid and "olecranon processes ; and the posterior set pass obliquely backwards to be attached to the inner surface of the olecranon, at a short distance from the articular margin. The anterior set are much the thickest, strongest, and most pronounced, and like the anterior portion of the capsule, they become tight during exten- sion. The posterior set are associated in action with the posterior portion of the capsule, and become tense only on flexion ; whereas the middle fibres, owing to their points of attachment being in or near the axis of motion of the joint, are, like most lateral ligaments, tight in every position. The external portion of the capsule is attached above to the lower portion of the external condyle, and to the bone in front between it and the capitulum, for a little way. Its fibres radiate to their attachment into the outer side of the neck of the radius, and the coronary ligament. The anterior fibres advance farther in front of the joint, than the posterior ones recede upon the back of it. This part of the capsule is strong and well-marked, though less so than the internal lateral portion. Many of the fibres, for the same reason as applies to the central set of the inner segment of the capsule, are tight in every position of the forearm ; whereas the rest, being for the most part attached in front of the condyle, and the condyle being a Kttle in front of the axis of motion, are rendered tense during extension. The Fatty Cushions or Pads, ivithin the Joint. — Outside the synovial membrane, there is in several places a c[uantity of soft fine fatty tissue, which forms often large pads or cushions at certain spots. The most constant of these are one at the notch in the gTeat sigmoid caiaty at the base of the olecranon, and the other along the outer side of the olecranon, projecting into the cavity between the ulna and radius. (They are well shown in the coloured plates of the elbow-joint.) The latter, together with a fold of synovial membrane, which generally exists opposite the front part of the outer lip of the trochlea of the humerus, suggests a division of the synovial cavity of 236 THE ARTERIES OF THE ELBOW-JOINT. the joint into two parts — viz., 1, that between the ulna and troclilea ; and 2, that between radius and capitulum, such as is seen to be produced in the knee-joint by the ligamentum mucosum. Other situations in which fatty tissue exists are at the top of the olecranon, and in the bottom of the olecranon and coronoid fossae. The SYNOVIAL MEMBKANE being limited only by the attach- ment of the capsule, extends into the superior radio-ulnar joint, and lines the coronary or orbicular ligament. Arteries. — A very free anastomosis takes place about this joint, between branches given off" from the brachial above, and the anterior and posterior ulnar recurrent, the radial recurrent, and posterior interosseous recurrent below. The brachial artery gives off the superior profunda to the posterior and outer sides, and a special branch from the lower third of its course to the forepart and outer side of the joint ; while on the inner side, both in front and behind, there are branches from the anastomotica magna ; and behind from the inferior profunda. The Superior profunda, just as it is turning round the inner side of the humerus, sends a branch over the back of the triceps to the inner and back of part of the joint, where it anastomoses with the anastomotica magna and the posterior ulnar recurrent. While between the brachialis anticus and the triceps it gives off a large branch to the outer and back part of the joint, which anastomoses with the posterior interosseous recurrent. The artery forms an arch near the humeral attachment of the capsule with the anastomotica magna, and near the olecranon attacliment of the capsule with the posterior ulnar recurrent. Some large twigs enter the capsule along the outer edge of the trochlea of the humerus ; whilst in the groove of the humerus it gives off a branch which has been called " the posterior articular," which descends to the joint between the triceps muscle and the bone, and anastomoses with the other branches both on the inner and outer side of the olecranon fossa. Branch direct from the Muscular Offsets of the Brachial. — From the outer side of the lower end of the brachial two vessels pass into the brachialis anticus, supplying it. The lower of these takes a deep course in a downward direction and gives off a long branch which descends in the middle line as far as the fatty tissue about the coronoid fossa and the capsule beyond ; THE ARTERIES OF THE ELBOW-JOINT. 287 it sends off numerous twigs as it descends, and anastomoses in front of the joint, on the inner side with tlie anterior branch of the anastomotica, on the outer side with the recurrent radial, and below, with the anterior ulnar recurrent. The inferior profunda sometimes reaches the capsule on the inner side of the olecranon fossa, and ramifies upon it, between the inner condyloid process and the olecranon. It anastomoses with the posterior ulnar recurrent and the posterior branch of the anastomotica magna. The Anastomotica magna, besides giving off non-articular branches to the pronator teres, brachiahs anticus, and bicej)s, sends others to the capsule, and to the humerus within the capsule, which pass between the internal condyle and the pro- jecting condyloid process. Another branch comes from that portion of the vessel which runs backwards through the inter- muscular septum, and breaks up into twigs, which ramify over the condyloid process, enter the joint posteriorly, between the olecranon and inner condyle, and anastomose with the posterior ulnar recurrent. There is a perfect arterial crescent along the inner edge of the articidar cartilage of the trochlea, formed between the anterior and posterior branches of this vessel ; this sends filaments off from either side to ramify beneath the synovial membrane. Another branch passes beneath the brachialis anticus to the fatty tissue of the coronoid fossa, and anastomoses upon the front of the capsule with the deep articular branch from the lower end of the brachial. Branches which ascend to the Joint from Vessels heloiv it. — The Anterior ulnar recurrent reaches the capsule by sending branches both over and beneath the brachialis anticus. The branch which ascends upon the insertion of the brachialis runs under cover of the pronator teres, and ramifies on the inner side of the capsule and the humerus, between the condyloid process and the trochlea ; it here anastomoses with the anasto- motica magna. The deep branch passes beneath the border of the brachiahs anticus to the coronoid process, which it supplies ; it also ramifies over the annular ligament to the neck of the radius and the lower and outer part of the front of the capsule, where it anastomoses with the radial recurrent and the branch direct from the brachial. The Posterior ulnar recurrent after giving off branches to the muscles under which it passes, and ascending beneath the 238 THE ARTERIES OF THE ELBOW-JOINT. flexor carpi iilnaris, and between its two heads of origin, sends several small twigs to ramify upon, and penetrate the capsule between the inner condyle and the olecranon ; others extend over the back of the capsule beneath the tendon of the triceps, as far outwards as the external border of the great sigmoid fossa, where it anastomoses with the superior profunda and interosseous recurrent. The Posterior interosseous recurrent passes upwards beneath and in the substance of the anconeus muscle to the interval be- tween the olecranon and outer condyle ; it helps to supply the corresponding part of the capsule and bones of the joint, as well as the back of the radio-ulnar articulation ; and anastomoses with the superior profunda and posterior ulnar recurrent arteries. The Radial recurrent sends branches to muscles, both upwards and downwards. Some of these ascend in and beneath the supinator brevis to the lower and outer part of the capsule ; to the front and outer part of the annular ligament, and the bulging synovial membrane along its lower border ; and like- wise to the neck of the radius. It anastomoses with the ter- minal branches of the superior profunda, as well as with twigs of the posterior interosseous recurrent. An arterial zone of considerable fineness surrounds the arti- cular surfaces of the bones, close to the edge of the articular cartilage, either immediately beneath the synovial membrane, where it passes off from the capsule, in which case the vessels can be seen from the inner siu-face of the joint, or between the fibres of the capsule. On the humerus the anastomotica magna and superior profunda help to form the zone behind ; and the anastomotica magna, reciUTent radial, and direct branch of the brachial in front. On the ulna and radius, the anterior and posterior ulnar recurrent join the zone on the front and inner side of the elbow, as well as along the top of the olecranon; and the anterior ulnar recurrent also extends outwards to the radio-ulnar joint ; the interosseous recurrent joins it on the outer side of the great sigmoid fossa, and upon the back of the neck of the radius ; while the radial recurrent occupies the part of the neck of the radius between the interosseous recurrent behind and the anterior ulnar recurrent in front. At the hour-glass contraction of the olecranon on each side, small twigs penetrate the bone, fi'om the posterior ulnar THE NERVES OF THE ELBOW-JOINT. 239 recurrent on the inner, and from the posterior interosseous recurrent on the outer side. Nerves. — The musculo-cutaneous supplies the cliief of the branches to the elbow-joint. Small iilaments are given off from it to the humerus and the elbow-joint in the arm. Like the circumflex nerve of the shoulder, the sub-occipital nerve, and many others, the musculo-cutaneous affords a good illustration of the associate distribution of the muscular, cutaneous, and articular branches of a single trunk ; and furnishes an illustra- tion of the truth of that law first pointed out and enforced by Mr. Hilton in his work on Eest and Pain, viz., that " the same trunks of nerves, the branches of which supply the gToups of muscles mo\dng any joint, furnish also a distribution of nerves to the skin over the same muscles and their insertions, and the interior of the joint moved by those muscles receives its nerves from the same source." The ulnar nerve gives an articular branch as it lies in the space between the condyle of the humerus and the olecranon of the ulna. The median nerve, either above the level of the elbow-joint or whilst beneath the pronator radii teres, generally gives a few filaments to the joint, They usually arise above the branches for the superficial muscles, except when the branch to the pronator teres arises above the joint. The mitsculo-spiral nerve gives filaments to the back of the joint from an internal branch which supplies the short inferior fibres of the triceps ; and others from the long slender branch to the anconeus, which takes the same course through the triceps muscle as the posterior articular branch from the superior profunda artery. BuRS^. — There are but three bursse in immediate connexion with the parts of this joint ; there is also a bursa between the tendon of the biceps and the tubercle of the radius. 1. On the outer aspect of the elbow, but more towards the front than the back of the limb, there is a small bursa between the tendon common to the extensor carpi radialis brevior and extensor communis digitorum on the one hand, and the capsule covering the rounded head of the radius on the other. 2. On the back of the capsule there is a bursa of varying size between the tendon of the triceps and that part of the 240 THE MUSCLES OF THE ELBOW-JOINT. upper surface of the olecranon wliicli is behind the attachment of the capsule of the elbow. 3. There is a large bursa mucosa in the subcutaneous areolar tissue over the olecranon, similar to that between the integument and the front of the patella and ligamentum patella at the knee. 4. The bursa between the forepart of the tubercle of the radius and the deep surface of the tendon of the biceps, just in front of its insertion, can scarcely be said to be in connexion with this joint. The Muscles. — The muscles in connexion with the elbow, like those in connexion with the knee, may be arranged into three sets : first, those which pass over and move tlie joint above the elbow as well as the elbow itself ; secondly, those which pass over and move it alone, without reaching to the joint either above or below it ; and thirdly, those which pass over and move the joints below the elbow as well as the elbow itself. There are, however, two important differences between the actions of the muscles of the upper and lower limbs ; {a) in the forearm the movements between the radius and ulna are very free, and in consequence two of the muscles which flex the elbow also act upon the radio-ulnar joints ; and (h) some of the muscles which act on the elbow and upon the wrist act also upon the digits. In the case of the lower limb there is no appreciable movement between the tibia and fibula, so that none of the muscles which move the knee can be said to have any distinct, still less any inde- pendent, action upon the joints between the two bones of the leg ; and further, none of the flexors of the knee which pass over the ankle and extend that joint reach far enough to move any of the anterior tarsal joints, still less the joints of the digits. The 'muscles which act on the shoulder and the elhoio-joint are : — 1. The biceps in front; and 2, the long head of the triceps behind. The biceps is a flexor of the forearm, but besides acting on the shoulder and elbow-joint it acts also upon the radio-ulnar articulation, for if it be called into action when the hand is pronated its first effect is to produce supination of the forearm. The triceps, by its long head, adducts the arm at the THE MUSCLES OF THE ELBOW-JOINT. 241 shoulder-joint in addition to its action on the elbow which it extends. The muscles tohich act on the elbow, hut do not extend to either the shoulder or wrist, are : — 1. The brachialis anticus ; 2, the pronator radii teres ; and 3, the supinator longus, in front. 4, The anconeus ; 5, the two short heads of the triceps ; and 6, the sub-anconeus, behind. The brachialis anticus is a simple flexor of the elbow. The pronator teres also acts on the radio-ulnar joints, but it flexes the elbow when pronation has been completed, or when it is prevented by opposing muscles. The anconeus and the external and internal heads of the triceps are simple extensors. The sub-anconeus being inserted into the capsule of the elbow, acts only to raise that structure during extension of the forearm. The supinator longus extends along the outer and anterior part of the forearm, from the external condyloid ridge, to be inserted into the external border of the radius near the base of the styloid process. It acts principally as a flexor of the forearm, but this action on the elbow only takes place after flexion has been commenced by some other, i.e., the more imme- diate flexor muscles. The action of this muscle upon the radio-ulnar joints is but slight, supination being principally effected by the biceps and supinator brevis ; stni, however, supi- nation is partially accomplished by its contraction, especially when the forearm has been previously fully pronated. The muscles which act upon the elbow and the wrist may be grouped into tioo sets : — {a) Those which reach to their insertion into the palmar fascia, or into the carpus or the metacarpus only, but not to the phalanges ; and which therefore, while they move the hand on the forearm, do not move the fingers. 1. The flexor carpi radiahs ; 2, the palmaris longus; and 3, the flexor carpi ulnaris, in front of the limb. 4, The ex- tensor carpi radialis longior ; 5, the extensor carpi radialis brevior ; and 6, the extensor carpi ulnaris, behind. The first three act chiefly as flexors of the wrist, but when this movement is either concluded or prevented they flex the elbow. They correspond with the gastrocnemius and plantaris in their action, which is exerted first on the foot and then to bend the knee. R 242 THE MUSCLES OF THE ELBOW-JOINT. The last three act primarily upon the wrist to extend it, but that action accomplished or prevented, they assist, the fore- arm being supinated, to extend the forearm at the elbow ; the forearm being pronated, the radial extensors assist in bending the forearm. (b) Those which reach to their insertion into the phalanges, and which therefore act not only on the elbow and wrist, but on the fingers. In the lower limb there are no muscles which, arising above the knee, are inserted so far down upon the extremity as to be able to move the toes. The muscles which move the toes arise either from the leg bones, and pass over the ankle, or from the foot. The muscles which move the fingers arise either from the hand ; or from the forearm, and thus move the wrist as well ; or from the condyles of the humerus, and thu>s move both fingers, wrist, and forearm. One effect of this variety of origin is that the movements of the fingers can be brought into immediate muscular association with those of the wrist and elbow ; a necessity, owing to the fre- quency with which these several joints are required to be moved at the same moment. In the case of the foot, the toes take but little share in the uses of the lower limb, and, except to give a last impulse to the spring in jumping, in standing on tiptoe, and in some of the movements of the opera dancer, they are seldom of any special use ; and even in these uses, though the flexors of the toes are associated with flexion (properly described), of the ankle, the knees are fixed with the legs extended. These muscles are : — 1. The flexor sublimis digitorum, in front. 2, The ex- tensor communis digitorum ; and 3, the extensor minimi digiti, behind. The flexor sublimis acts chiefly to bend the second phalanges, and when this action is either completed or opposed, to bend the wrist ; when again this action is completed or opposed, it assists in bending the elbow, as when the open hand is pressed against a box or heavy weight which is being drawn towards the body by flexing the elbow. This action would be of course also assisted by the flexors of the wrist. Conversely, the extensor muscles act first upon the phalanges to extend the fingers, then upon the wrist, and lastly they may assist in extending the elbow, as when we give a back- handed blow with the closed fist, the wrist being tightly set. MOVEMENTS OF THE ELBOW-JOINT. 243 In this action they would be assisted of course by the ex- tensors of the wrist. Thus if we group the muscles which are in connexion with the elbow into flexors and extensors, we see at once that the following muscles can all take part in the most powerful efforts at flexion : — The brachialis anticus and biceps, the one inserted into the base of the coronoid process and the top of the shaft of the ulna, and the other into the tubercle of the radius, so that both bones are acted upon by these the most immediate flexors ; the pronator teres, the supinator longus, the flexors of the wrist, the palmaris longus, and the flexor sublimis digitorum. The radial extensors flex the pronated forearm. The following muscles can all assist in the most complete efforts at extension : — The anconeus and the triceps, both inserted into the ulna ; the two radial extensors (the forearm being supinated) and the ulnar extensor of the wrist ; the com- mon extensor of the digits, and the extensor of the little finger. The Movements of the Mhoia. — The elbow is a true hinge joint, and, as such, flexion and extension are the only move- ments which can take place at it. These movements are oblique, so that the forearm is inclined inwards in flexion, and outwards in extension. They are limited by the contact respectively of the coronoid and olecranon processes of the ulna, with their corresponding fossae in the humerus. The extent of these hinge-like movements is determined by the relative proportion between the length of the processes of the ulna and the depth of the fossae which receive them. The ligaments in front of and behind the joint, with certain portions of the lateral ligaments, are put on stretch during extension and flexion ; but though they assist in checking the velocity and force of the movements before the limits of those move- ments is attained, and therefore in preventing any undue violence of contact of the bony processes with the lamina separating the fossa on the front from that on the back of the humerus, they do not control or determine the extent of flexion and extension. The limit of extension is not reached until the ulna is nearly in a straight bine with the humerus, and the limit of flexion not untH the forearm makes with the humerus an angle varying between something less than 30° and something over 40°. This variation does not depend upon the bulk of the soft parts covering the joint, but, as just said, K 2 244 MOVEMENTS OF THE ELBOW-JOINT. upon the proportion which the length of the olecranon and coronoid processes bear to the depth of the olecranon and coro- noid fosScC. This can be proved by measuring with the same goniometer the angle of flexion at the elbow in the living subject, and in the dead in various stages of dissection. Thus I have found, while some living elbows cannot be flexed to a more acute angle than 35° or 40° ; others, dissected cleanly to the capsular ligament, could only attain to 42° or 43°; while another asain, with the skin and fascise removed, and the muscles dissected cleanly, but not removed, could be brought to an angle of a Kttle less than 30°. While the articulation between the radius and humerus allows of the radius rotating upon the humerus in supination and pronation, and accompanying the ulna in its motions of flexion and extension, it gives no security to the elbow-joint, and adds nothing to the hinge-like arrangement of the humero- ulnar portion of it, at which the movements take place. The plane in wliich the movements occur is a nearly vertical one, with a slight obliquity inwards of about 10° from the axis of the shaft of the humerus ; and the transverse axis round which the ulna revolves corresponds to a line through the lower and forepart of the outer condyle, and through a ridge which runs upwards and backwards from the inner side of the trochlea to the lower part of the internal condyle. The obliquity of the plane of movement is occasioned by the greater prominence of the inner lip of the trochlea below, and by the eversion or outward inchnation of the upper and back part of the trochlea, A consequence of this obliquity is that the ulna and radius have a slightly outward inclination from the axis of the humerus, which is most marked in extension of the elbow, though it is observable in slightly flexed positions of the joint. In spite of this, however, and even as a result of the obliquity of the plane of motion, the hand in flexion is carried towards tht middle third of the clavicle, instead of being directed vertically to the acromion overhanging the shoulder-joint ; but any greater inclination of the forearm towards the median line oi the body, as in buttoning a waistcoat or bringing the hand t( the face, is caused by rotation of the humerus at the shoulder^ and not by anything in the construction of the elbow. The inward direction of the shaft of the humerus, the back- ward inclination of the head of that bone, together with the MOVEMENTS OF THE ELBOW-JOINT. 245 inward obliquity of the forepart of tlie elbow-joint, and the great freedom and facility of pronation, all assist in bringing the band, when in use, towards the middle line, so that, as it were, they might be under the immediate observation of their owner ; or, in other words, that the eyes may see what the fingers are about. This is just the reverse of what we find in the lower extremity, when the direction of the head and neck and the inclination of the shaft of the femur, the rotation of the knee and the construc- tion of the ankle, are all subservient to the outward turning of the foot, whereby in walking or running any awkwardness of movement or injury to the opposite foot is prevented. In flexion and extension, the cup-like depression of the head of the radius moves upon the capitulum of the humerus, and the inner margin of that depression upon the groove between the capitulum and the trochlea. In full extension and supination, the head of the radius is barely in contact with the inferior surface of the capitulum, but projects so much backwards that its posterior margin can be felt as a prominence at the back of the elbow, and the tip of a knife-blade can be introduced, flat, between the articular surfaces of the two bones. In full flexion the anterior margin of the head of the radius is received into and checked against the depression above the capitulum. In mid-flexion the cup-like depression fairly receives upon it the capitulum, and the radius being more completely steadied by the humerus in this position than in any other, pronation and supination take place most perfectly. Though in the extended position of the limb the hand by pronation can make a more complete sweep round than in any other, yet this movement is not all true pronation, but is in large part due to the rotation of the humerus at the shoulder. There is nothing in the shape of the radius or humerus which prevents the radius completely revolving round its axis, as is shown by dividing all the structures which attach the radius to the ulna, except the orbicular ligament, and then just loosening the capsule of the elbow from the neck of the radius. This done, the radius can be turned round and round on the capitulum, like a spindle in its bush. In the undissected state, this rotation is checked by the middle and inferior radio-ulnar connexions. 246 MOVEMENTS OF THE ELBOW-JOINT. It has been stated above, tbat tlie elbow is a true and typical hinge joint, but anatomists have been divided in opinion as to the possibility of any lateral movement at the elbow. Monro and Bichat assert that this movement is possible in the semiflexed state of the elbow, when the lateral ligaments are least tense, and they consider that it consists in a slight degree of rolling of the middle prominent part of the greater sigmoid ea^dty of ■ the ulna in the trochlea of the humerus. Probably this movement is produced by the lowest, and therefore nearly horizontal fibres of the triceps, on each side of the olecranon, and by the anconeus muscle. As a means of expressing passions and feelings, the move- ments of the elbow are frequently employed in elocution to assist the voice and the facial muscles. In this relation it will be found, I think, as a general rule, that flexion and extension at the elbow generally indicate feelings of a quick, passionate, and decided character, and are not employed, like the various movements of the shoulder, to suggest or em- phasise any transcendent, deep, or tender feelings. The move- ments of the elbow for the purposes of expression are often associated with the flexion or closure of the fingers ; whereas those of the shoulder are most frequently employed with wrist movements, and, sometimes together with those of the wrist, "v\dth others of the index-finger also. Thus, in resolutely striking with the closed fist upon the table ; in hastily brushing away a tear which is unacceptably stealing upon the cheek ; in tearing at the hair in rage ; in attitudes of mental agony, such as that assumed by the actor, when as Othello he says, with linked fingers and uplifted hands — " Not a jot, not a jot ! Blood, lago, blood ! But oh, the pity of it, lago ! — the pity of it ;" and in such like moods, the elbow and the fingers work together. In the attitude of the suppKant ; in giving expression to feelings of com- placent triumph, such as are implied in the opening speech of " Eichard III.," — "Now is the winter of our discontent Made glorious summer by this sun of York ;" when, with the upraised and extended arm, a graceful curl of the wrist, the actor with a rich, deep, thrilling note upon "buried," indicates how the clouds which lowered round his MOVEMENTS OF THE ELBOW- JOINT. 247 head, were " in the deep bosom of the ocean bnry'd :" so in the rhapsody of boundless passion, as when, in " Eomeo and Juliet,". Juliet, in solemn attestation of her love for Eomeo, says (with arms upraised and hands drooping at the wrist), " When he shall die, Take him and cut him out in little stars. And he will make the face of heaven so fine That all the world will be in love with night, And pay no worship to the garish sun." In these and such-like mental states the shoulder combines with the wrist for the purpose of appropriately suiting the action to the word. Sometimes, too, in giving a command, the shoulder and wrist with the extended index-finger, produce a marked effect, such as accompanies the word " Begone !" but in such cases the elbow takes the initiative, as the hand, with most of the fingers nearly closed, is first brought across the chest to the opposite shoulder, to give point and decision ; while the fully extended Kmb is afterwards thrown forwards by a movement at the shoulder, to give dignity or impressiveness to the injunction. The movements of the elbow and fingers are employed in anger or defiance when the fist is shaken and the elbow bent. In the calmness of bestowing benediction, the arm is raised at the shoulder and the fingers outstretched, so that the open palm can be placed upon the recipient's head. In the bitter- ness of shame the face is covered by the hands, while we bend the elbows, and involuntarily attempt to close the fingers upon the palms as they lie pressed against the forehead. In the agony of gTief we bend the elbows and wring the locked fingers ; while, on the contrary, in the abandonment of despair we throw our open hands and arms above our heads. The movement of supination is one indicative of disgnist, impotence, and annoyance, as when the palms are turned quickly forwards or upwards, as if to say we " will have none of it ;" or " I wash my hands of the whole affair." That of pronation is suggestive both of power and determina- tion, as well as of repose and resignation, as when striking the table with the open palm, and in letting the forearm drop helpless by one's side. Complete pronation is a position of the greatest elegance and 248 MOVEMENTS OF THE ELBOW-JOINT.^ grace, and is the one most agreeable to the eye as well as to the feelings. Tennyson knew this when he described Vivien (trying to arouse the impassioned Merlin) thus : — " Curved an anu about his neck, Clung like a snake ; and letting her left hand Droop from his mighty shoulder, as a leaf, Made with her right a comb of pearl to part The lists of such a beard as youth gone out Had left in ashes." Were this the proper place, and space permitted, instances might be multiphed to show how frequently the movements of the upper limbs are employed as a means of expressing feelings and emotions ; and much might be said in support of the opinion, that a considerable amount of constancy exists in the association of movements of the shoulder with those of the wrist ; and of the elbow with those of the fingers. In movements fro7n the body expressive of command or repulsion ; in expanding gestures suitable to feelings of liberahty, acquiescence, candour, and distribution ; in rising motions which express suspension, climax, or appeal, as well as in falling motions which suggest completion, declaration, or resignation ; and in broad and sweeping gestures which illus- trate a general statement, or imply boldness, freedom, and power, the shoulder and the wrist-joints move together, or the wrist a little later than the shoulder, the fingers meanwhile, in most cases, being kept extended. In movements towards the body, which indicate self-esteem or egotism ; in the contracting gestures which imply frugality or reserve, obeisance, and mock humility, or which express doubt, meditation, or listening; in the sudden movement of decision or discovery, harshness or temerity, the elbow and fingers move simultaneously, the fingers sometimes being tightly clenched into a fist, at others slowly contracting downwards upon the palm, or slowly or forcibly extended from it. CHAPTEE XIII. THE UNION OF THE EADIUS WITH THE ITLNA. THE EADIO-ULNAR ARTICULATIONS. The radius is firmly bound to the ulna by two articulations, one at each extremity ; and by two intermediate ligaments between their shafts. In the superior radio-ulnar joint the ulna receives the head of the radius upon a small cavity on the outer side of its upper end, and the articular surfaces are so related to one another that the ulna somewhat underhangs the radius ; in the inferior radio-ulnar joint, on the contrary, the radius receives the rounded inferior extremity, or head of the ulna, upon a lateral cavity on its inner side, which underhangs the end of the ulna. Thus the ulna, which is more widely connected with the humerus than the radius, supports that bone against forces which drag the forearm from the arm ; and at the same time receives from the radius part of the forces transmitted from the wrist. In the superior radio-ulnar joint the round head of the radius rotates round its own axis in the lesser sigmoid socket of the ulna ; in the inferior radio-ulnar joint, the radius re- volves upon the rounded end of the ulna (and its facet is concave in adaptation to this movement) around an axis which corresponds to a line drawn through the head of the radius, the lower end of the ulna, and the metacarpal bone of the ring-finger. The Sxi-perioT Radio-ulnar Articulation. Class, Disrthrosis. Subdivision, Trochoides. The bones entering into this joint are the lesser sigmoid notch of the ulna, and the smooth vertical surface of the head of the radius. Ulna. — The lesser sigmoid cavity of the ulna is situated at the top of the outer side of the shaft of the ulna, and is therefore 250 THE RADIO-ULNAR ARTICULATIONS. at right angles to, and continuous over a sharp articular edge with, the great sigmoid cavity. It faces directly outwards, is crescentic in outline, measures one inch from before backwards, and three-eighths of an inch from above downwards. It forms about one-fourth of a circle, which is completed by the orbicular Hgament. The anterior edge is prominent, projects outwards, and is formed by the outer border of the coronoid process. The posterior edge is also prominent, and separates the fossa from the excavated posterior surface of the shaft for the anconeus muscle. The lower border is also prominent and well-defined, and separates the sigmoid cavity from the depres- sion for the supinator brevis muscle. As the cavity is inclined a little obliquely outwards at its lower end, especially towards the front, it somewhat underhangs the head of the radius ; but this only to a slight extent. Eadius. — The articular portion of the head of the radius which enters into this joint is the smooth rim or vertical border which extends completely all around the bone. It is about three inches in circumference. At some parts it is not more than one-fifth of an inch deep ; but on the inner side, where it is in contact with the ulnar cavity, it is usually about three-eighths and sometimes one-half of an inch in depth. Below this surface the bone is constricted into a slender neck, which is usually less than two inches in circumference. The Ligaments. — There is but one ligament proper to this articulation — viz., the coronary or annular ; but the anterior, posterior, and external portions of the capsule of the elbow are connected with, tighten, and strengthen this one Kgament, and help to enclose the joint, which it must be understood is continuous with the elbow-joint itself. Moreover, some thin fibrous bundles pass from the lower edge of the coronary ligament, and the ulna below the lesser sigmoid cavity, to the neck of the radius and cover in the joint below. The coronary ligament consists of bands of strong fibres, somewhat thicker than the capsule of the elbow-joint, which pass circularly around the head of the radius, retaining it against the side of the ulna. The bulk of these fibres forms about three-fourths of a ch'cle, and together with the lesser sigmoid cavity completes a collar for the head of the radius -to rotate within ; but some of the lowermost fibres are continued round below the sigmoid cavity so as to form a PLATE xxm. LIGAMENTS OF THE RADIO-ULNAR ARTICULATIONS. 251 complete circle of ligamentous fibres. Thus the ligament encircles the whole of the articular edge of the head of the radius, except that part of it which occupies the lesser sigmoid cavity of the ulna. The ligament is inseparably connected along its upper edge and external, i.e., non-articular surface, with the external, anterior, and posterior segments of the capsule. Some few of these fibres, especially of the external segment, pass downwards to be attached to the neck of the radius ; but the lower part of the articulation is covered in by a thin, independent layer of felt-like membranous fibres which pass down from the lower edge of the coronary ligament to the neck of the radius, where they are connected loosely enough to allow of the head and neck of the bone rotating around its own axis. These fibres are the only portion of the ligaments at the elbow and superior radio-ulnar joints, which serve to check the rotation of the radius in pronation and supination. The fibres of the orbicular ligament (aU but the lowest, which pass quite around below the sigmoid fossa) are fixed to the anterior and posterior margins of the lesser sigmoid cavity of the ulna, and to the ridges ef bone extending downwards from them ; behind, by means of a strong fibrous expansion to the rough ridge which separates the surface on the shaft for the anconeus, from that for the supinator breads ; and in front, to the oblique ridge which descends along the inner side of the coronoid process. The SYNOVIAL MEMBRANE of tliis joint is one with that of the elbow, and a prolongation forwards of the fatty tissue at the back of the elbow-joint projects into the angle between the head of the radius and the back of the lesser sigmoid cavity ; often too there are little fringes of synovial membrane contain- ing fat attached along the edge of the coronary ligament. The membrane, after lining the inner surface of the coronary ligament, passes upon the fibrous tissue between its lower edge and the neck of the radius, and is thence refiected upwards on the neck of the bone to the articular cartdage with which it is continuous, and with which it can be peeled off. Thus, like the necks of the femur and of the humerus, the non-articular neck of the radius is invested by synovial membrane, and a few fibres are reflected upon it from the ligamentous tissue which surrounds it. 252 ARTERIES, NERVES, AND MUSCLES OF The Arteries. — Being part of the elbow-joint, this articula- tion gets its blood supply from the vessels which ramify upon the outer side of the elbow in front and behind. They are the superior profunda, interosseous recurrent, radial recurrent, and anterior ulnar recurrent. 1. The superior profunda artery gives off branches which descend to anastomose with the posterior interosseous recurrent, and to penetrate the joint close to the back of the lesser sigmoid cavity. 2. The interosseous recurrent reaches the joint by passing upwards in the substance of the anconeus muscle to the interval between the olecranon and outer condyle, where it sends twigs into the bones and others through the capsule into the joint. It suppHes the back of the radio-uLiar articulation and anastomoses with the superior profunda branches. 3. The radial recurrent sends branches which ascend in and beneath the supinator brevis to the front and outer part of the annular ligament and the loose baggy synovial membrane along its lower border, as well as to the neck of the radius. 4. The anterior ulnar recurrent sends a deep branch beneath the border of the brachialis anticus to the neck of the radius, the front of the annular ligament, and the lower and outer part of the capsular fibres, amongst which it anastomoses with the radial recurrent. The Nerves. — This joint, from being so entirely a part of the elbow, must share with it the influence of the nerves which supply it. The interosseous division of the musculo-spiral, whilst in the substance of the supinator brevis muscle, gives small filaments to the lower part of the superior radio-ulnar articulation. The Muscles. — The muscles which pass over this joint are the following : — The supinator longus, extensor carpi radialis longior and brevior, on the outer side ; the anconeus, immediately in contact with it behind ; and below and external to the anconeus, the extensor carpi ulnaris and extensor communis digitorum, each of which is separated from the joint by the supinator brevis. The supinator brevis closely surrounds the annular ligament, and the capsular fibres below that ligament, and is indeed attached to both. The biceps tendon passes over the fore and inner part, and THE KADIO-ULNAR ARTICULATIONS. 253 the brachialis anticus spreads out laterally over the inner and front part. The pronator radii teres crosses obliquely at the lower and front part of the joint. Of these muscles, which from their situation are in con- nexion with the joint, those which act upon it most directly, are the supinator longus, the supinator brevis, the pronator radii teres, and the biceps. There are two other muscles at least which effect movements at this joint, though they are situated at a distance from it — viz., the pronator quadratus and the flexor carpi radialis ; the latter muscle contributes slightly to pronate the forearm. There can be little doubt that the extensors of the fingers, which arise from the outer condyle of the humerus, and pass obliquely to the back of the lower end of the radius, where they are retained in their direct course by the posterior annular ligament, assist the action of pronation when the fingers are kept rigidly extended, as in the last movement of the hands in swimming. Certainly the extensor carpi radialis longior and brevior, when the hand is tm-ned back to the greatest degree, pronate it. The chief pronators are the radii teres and the quadratus, one of which is a pronator pure and simple, and acts upon the radius at its lower extremity — viz., the pronator quadratus; while the other, acting upon the radius at its centre, though a powerful muscle in pronating the forearm, acts also to assist in bending the elbow when pronation is either completed or prevented. The biceps, when acting upon the pronated forearm, first acts to supinate the radius, and this is indeed one of its chief uses. How strongly it acts in this way may be tested by feeling the degree of firmness of the belly of the biceps, first when the elbow is flexed with the forearm pro- nated, and next when it is flexed with the forearm supinated. The muscle is much harder in the latter case, because its fibres are then more tightly contracted. Of the other supinators, one acts immediately upon the radius, as a supinator pure and simple ; it is the supinator brevis, and by it supination is prmcipally effected. The other, the supinator longus, is principally of use in flexing the elbow, and only secondarily supinates the radius by acting upon it at its lower end. The extensor ossis metacarpi pollicis, and extensor secundi 254 MOVEMENTS OF THE RADIO-ULNAR ARTICULATIONS. internodii pollicis, from tlieir oblique direction over the wrist, must assist in supination. The Movements. — The radius rotates around the axis through its own head and neck, within the collar formed by the lesser sigmoid cavity of the ulna and the coronary ligament. This rotation is called pronation when the radius from a position parallel, or nearly so, to the ulna turns inwards so that it crosses the ulna obliquely; and supination when it turns back again from within ovitwards, so as to uncross as it were the ulna and become again nearly parallel to it. In pronation and supination, the radius carries with it the hand, and communicates to it the movements popularly attributed to the wrist. Thus, in pronation, the hand is carried over so as to face backwards, as in holding the hand to receive anything from behind ; or downwards, as in the act of ^Titing or playing the piano ; whereas, in supi- nation, the hand is facing forwards, as in throwing an under- hand ball at a wicket ; or upwards, as in tossing a coin in the open hand. In these movements of the radius, the hand is made to rotate around an axis drawn through it a little to the inner side of its middle line. It has occurred to Mr. Ward to enunciate the following general formula to express the relation of the two extremities of the radius in pronation and supi- nation : — " The head of the radius is so disposed in relation to the sigmoid cavity of the lower extremity, that the axis of the former, if prolonged downwards, falls upon the centre of the circle, of which the latter is a segment." Thus the real axis round which pronation and supination occur is one corre- sponding to the axis of the head and neck of the radius, but which leaves the radius just below the bicipital tuberosity, crosses the interosseous mem- brane or interval between the bones, and passes through the inferior extremity of the ulna, and on- wards to the tip of the ring-finger. The real axis of rotation is the hue, a h, in. the accompanying diagram : e f represent the apex, and c d the base of a blunt-topped cone. The centre of the apex corresponds with the centre of the head of the radius, and the centre of the base with the centre of the circle, of which the sigmoid cavity of the radius is a segment — i.e., with the centre of the head of the ulna. Tlie axis of the cone corre- MOVEMENTS OF THE SHAFTS OF RADIUS AND ULNA. 255 sponds with the axis of the head of the radius. It is around the lower part of this axis that the hand rotates when moving with the radius, and if the radius rotated around any other axis than the one described, some slight hinge-joint movement would take place at the superior radio-ulnar articulation, which is not the case. Associated with this rotation, however, in the ordinary way, there is some rotation of the humero-ulnar shaft, which causes a lateral shifting of the forearm and hand from side to side ; thus with pronation there is some abduction, and with supination some adduction combined, so that the hand may be able to keep on the same superficies in both pronation and supination. Pronation and supination can scarcely be said to be in any way checked by any of the structures concerned in the superior radio-ulnar articulation. Only one portion of the ligaments about the elbow could possibly have any effect whatever in controlling the rotation of the radius ; this is the membranous felt-like ligamentous tissue which passes from the lower edge of the annular ligament on to the neck of the radius, and the few fibres of the capsule of the elbow-joint which are inserted into the radius. But these structures can usually be detached from the bone by a few forcible rotations ; and this done, the radius, if free of all muscles and all ligaments below the elbow, can be turned round and round within its osteo- ligamentous collar like a spindle in its bush. In sujpination the oblique ligament and the lowest portion of the interosseous membrane are put on stretch, and with the internal lateral ligament of the wrist, are the chief obstacles to over-supination. The upper and middle portions of the interosseous ligament are relaxed by supination. In jyronation, the lower and middle portions of the interosseous ligament are on stretch, and the oblique ligaments slackened. As will be mentioned in the description of the inferior radio- ulnar joint, the posterior ligament of that articulation tends to check pronation, the anterior ligament supination. The internal lateral ligament of the wrist helps to limit each movement, but especially supination. Further, the muscles, more especially the pronators, offer some check to over-supination, and the supinator brevis to over-pronation. The convex capitulum of the humerus when the radius is in contact with it — ie., in the semi- and completely flexed 256 UNION OF THE SHAFTS OF THE RADIUS AND ULNA. positions — steadies the head of the radius in its movements, and tends to define more precisely the axis of rotation of the upper end of the bone. Both in the structure and the resulting movements there are many analogies and similarities between the articulation of the odontoid process of the axis and the anterior part of the rinff of the atlas on the one hand, and the head of the radius and osteo-hgamentous ring of the ulna on the other. Free supination is only found in those animals who use their fore-limbs for prehensile purposes ; and in proportion as the fore-limb is more needed for support; the bones of the forearm are less adapted for rotation. In the carnivorous, ruminant, pachydermatous and many other animals, the radius extends a long way across the articular facet of the humerus, so that it is always in a state of pronation ; but in the quadrumanous and some other animals, e.g., sloth and seal, as well as in man, the head of the radius is confined to the outer condyle of the humerus, and supination becomes possible. In no animal is the movement so free as in man. The power of supination in man is greater than that of pronation, owing to immense leverage and great power obtained by the attachment of the biceps to the tubercle and inward curve of the radius. For this reason, the tools of workmen are so made that screw- driving, gimlet-turning, and other mechanical work of this kind, is done by supination of the right hand. It should be pointed out, however, that the pronator teres obtains all the advantage it can by its insertion into the most convex point on the outer side of the lower curve of the radius, just as the biceps does from its insertion into the most prominent point of the convexity of the upper curve. The Union hetween the Shafts of the Badius and Ulna. The Eadio-ulnar Interosseous Ligaments. — Two ligaments extend between the bones of the forearm ; one, a short narrow fibrous band, passes obliquely downwards and outwards from the ulna to the radius, and is called the oblique ligament ; the other occupies the greater part of the interval as far down as the inferior radio-ulnar articulation, and its fibres chiefly pass downwards and inwards to the ulna. 1. The oUique ligament is a narrow but usually a strong THE RADIO-ULNAE INTEROSSEOUS MEMBRANE. 257 "band, but uot unfrequently removed in dissecting. It is con- nected above to the lower part of the rough outer ridge of the coronoid process, and to the upper end of the line descending from that process to the outer edge of the shaft ; and below, to the lower end of the posterior edge of the tubercle of the radius, and to the irregular vertical ridge descending from it to the inner edge of the bone. Unless care be used it is easy to detach this ligament from the ulna with the tendon of the brachialis anticus, or with the flexor profundus digitorum, or from the radius with the tendon of the biceps ; indeed the fibres of the ligament run into, and blend with those of the biceps tendon. Behind, especially at the ulna, the supinator brevis is in close relationship with this Kgament ; and below, a thin membra- niform tissue passes off from it to the upper edge of the interosseous ligament, and through the space thus occupied the posterior interosseous vein and artery pass backwards. 2. The interosseous ligament or membrane is attached to the ulna at the lowest part of the ridge in front of the depression for the supinator brevis, which passes downwards from the base of the coronoid process to the outer edge of the shaft ; then along the whole length of this sharp edge as far as the pronator quadratus ; thence along the rounded border, which gradually approaches nearer to the fore than back sui-face of the bone, as far as the inferior radio-ulnar articulation. To the radius it is attached along the inner edge of the bone from an inch below the tubercle to the sigmoid notch for the ulna. It is strongest in the centre, where its fibres are very dense and closely packed ; it is also well-marked beneath the pronator quadratus muscle ; and quite at the lower end it thickens considerably, forming a strong bond of union between the upper margin of the sigmoid cavity and the rounded head of the ulna, and some of its fibres are prolonged over the head of the ulna to be attached beyond the margin of its articular surface both on the front and back aspects, though more especially over the front. The direction of the fibres of tMs ligament is chiefly inwards and downwards from radius to ulna ; but some fibres pass in the opposite direction, and others are transverse, especially at the lower end. Still it is quite true that the ligament is com- posed chiefly of fibres whose direction is from radius to ulna, and this is most declared where the ligament is strongest — viz., in the centre. On the posterior surface of the membrane one s 258 ITS ARTEKIES, NERVES, AND MUSCLES. or two linear bands of fibres, well marked, are often found to pass obliquely downwards and outwards from ulna to radius ; and very frequently there is a very strong bundle as large as the obhque ligament, and wliich may be called the inferior oblique ligainent, on the posterior surface of the membrane, which extends from the ulna an inch and a half above its rounded extremity to the prominent ridge above and behind the sio-moid notch of the radius. The upper edge of the inter- osseous membrane is concave, and connected with the oblique Ho-ament above by a thin membraniform structure, pierced by the posterior interosseous artery. At its attachment to the radius and ulna the ligament is blended with the periosteum. Arteeies. — Throughout it is very vascular, being well sup- plied with blood by the anterior interosseous artery. This artery gives numerous branches to it, some of which penetrate it and supply the deep extensors ; others ramify in the substance of the ligament. Below, the artery pierces the ligament about an inch and a quarter from its lower end, sometimes running in between its layers, and after giving off the communicating branch to the posterior interosseous artery, returns to descend to the inferior radio-ulnar joint upon the front surface of the membrane. Neeves. — The interosseous branch of the median nerve accompanies the anterior interosseous artery, and descends with it upon the front surface of the interosseous membrane, and supplies filaments to it. The Muscles. — The muscles in connexion with the inter- osseous membrane of the forearm are the following : — In Front. — The flexor profundus digitorum, from the ulna half, for three-fourths the length of the membrane. The flexor longus pollicis, from the part adjacent to the radius between the oblique line above and the edge of the pronator quadratus below. The pronator quadratus, at the lower two inches of its extent. Behind. — The supinator radii teres, in the upper third. This muscle separates the anconeus and some of the extensors of the wrist and fingers from the membrane. The extensor ossis metacarpi pollicis, from the whole width of the membrane a little above the middle of the forearm. The extensor primi internodii pollicis, from the interosseous membrane near the middle of the forearm. INFLUENCE OF LIGAMENTS ON MOVEMENTS. 259 The extensor secundi internodii poUicis, from about an inch of the membrane at its lower end. The extensor indicis passes obliquely over it at quite its lower end, but is not usually attached to it. Influence on Movements. — The use of these ligaments is to bind the shafts of the bones together, and thus to increase the security of the radio-ulnar joints. The oblique ligament acts as a stay or support to the radius at a point rendered weak by the meeting of two curves in that bone — viz., one with convexity inwards at the tubercle for the biceps insertion ; and the other with convexity outwards for the pronator radii teres insertion. These curves give great leverage and advantage to their •espective muscles, each of which is inserted into the most 3onvex part of the curve ; and the oblique ligament gives strength to what is otherwise a weak point in the shaft. This oblique ligament and the inferior oblique Kgament, above described, when present, assist in checking supination. They are put on stretch during this movement, the superior one by the eversion of the tubercle of the radius from the coronoid process, and the inferior by its winding round the lower end of the ulna. But the chief influence in checking supination is not to be found in ligament at all, but in the contact of the posterior edge of the sigmoid cavity of the radius with the tendon of the extensor carpi ulnaris, as it lies in the groove between the styloid process and the round head of the ulna. From their direction, too, the oblique and the inferior oblique ligaments are able to resist any forces which tend to pull the radius with the hand from the humerus. The ulna is much more firmly bound to the humerus than the radius, whilst it is but slightly connected with the hand, and any forces acting on the hand tending to drag the forearm from the arm would strain unduly the annular ligament were it not for these ligaments, and for the transverse fibres of the interosseous membrane. The interosseous membrane exerts but very little influence in checking movements ; none at all over supination, except by its lowest oblique fibres. Its lower fibres, and to a less degree its middle fibres also, have some effect in checking pronation. Pronation is also checked partly by the posterior inferior radio- ulnar ligament, but perhaps chiefly by the contact of the soft parts as the radius rolls forwards and inwards, so as to cross obliquely over the front of the ulna. s 2 260 THE INFERIOR RADIO-ULNAR ARTICULATION. I have always been in the habit of teaching that one of the chief uses of this membrane, and of the veiy definite inward and downward direction of the bnlk of its fibres, is for the purpose of transmitting the weight of the body from the ulna to the radius in the extended position of the elbow ; as, for instance, in pushing forwards with outstretched arms, or in crawling on " all fours," or in stooping from the erect posture, and bearing down upon a table. In these positions the ulna is little or not at all in contact with the carpus, but forms the chief connexion at the elbow; and the radius is but slightly in contact with the large articular surface of the humerus, but forms the chief connexion of the forearm at the wrist. When then weight or other forces pass from the humerus to the head of the ulna, this bone is pressed downwards towards the wrist; but at the same time, for the same reason and to a proportionate degree, the ulna drags on the interosseous mem- brane, which, owing to the direction of the fibres, becomes tighter and tighter as the force increases ; not looser and looser, as would be the case if the fibres passed in the oppo- site direction, as do those of the oblique ligaments. Thus the membrane tends to pull the radius more firmly against the carpus ; and thus the weight passes on into the hand, and so to the supporting surface. Or, conversely, the pressure com- municated from the hand to the radius forces up the radius against the capitellum, but at the same time slings the ulna, and drags it up more forcibly against the trochlea of the humerus. By this arrangement the violence of a fall upon the hand is broken, for were it not for these fibres of the interosseous mem- brane the whole of the impulse would be communicated directly through the head of the radius to the capiteUum. Another and an important use of the interosseous membrane is to give origui to the various muscles in connexion with it on the front and back of the forearm. The Inferior Radio-tdnar Joint. Class, Diartlirosis. Subdivision, Lateral Ginglymus. The inferior radio-uluar articulation is in one respect the reverse of the superior, for the radius, instead of presenting a circular head to rotate upon a concave facet of the ulna, has a concave facet which rolls upon the rounded lower end of the u^pa. In several respects it differs widely from the superior joint. 1. THE INFEUIOR RADIO-ULNAR ARTICULATION. 261 In the superior, the head of the radius rotates round its own axis ; in the inferior, the radius turns in the arc of a circle, whose centre is the fossa between the styloid process and the articular surface of the ulna — i.e., the poiut at which the fibro- cartilage is attached. 2. In the superior, the most important structure is the annular ligament within which the head of the radius rotates ; in the iuferior, the most important structure is a fibro-cartnage, which acts as a flexible or movable spoke to hold the radius against the ulna as it rotates in. the arc of a circle. 3. The superior joint is in communication with the elbow^ ; the inferior has usually no connexion with the wrist-joint, and when it has, it is only by means of an imperfection in the fibro-cartilage. 4. The radius forms but an insignificant part of the construction of the elbow-joint, the ulna but an insig- nificant part of the wrist ; but whilst the terminal facet of the head of the radius articulates with the capitellum of the humerus, the terminal facet on the head of the ulna articulates with the fibro-cartilage wliich shuts it off from any direct con- tact with the carpus. The constituent parts of the joint are — the lower ends of the radius and ulna, the fibro-cartilage, and the ligaments which assist in forming an imperfect capsule, together with a synovial membrane. The articulation may be said to consist of two parts at right angles to one another — viz., one between the sigmoid fossa of the radius and the lateral facet on the head of the ulna ; which is limited above by the inferior portion of the interosseous membrane, and in front and behind by the anterior and posterior radio-ulnar ligaments : and the other between the facet at the extremity of the ulna and the upper surface of the fibro-cartilage ; which is limited on the tuner side by the fixation of the fibro-cartilage to the pit in the ulna, and by the iuternal lateral ligament of the wrist which unites with the fibro-cartilage, and in front and behind by those fibres of the radio-ulnar ligament which are attached to the margins of the fibro-cartilage. The lower end or head of the ulna is of smaller size than the head of the radius, which rotates iu the annular liga- ment of the superior joint. It is two inches or thereabouts in circumference, exceeding the circumference of the shaft immediately above it by half an inch or more. At its base this rounded end of the idna presents (1) a smooth, nearly circular surface, convex from side to side and from before back- 262 THE INFERIOR RADIO-ULNAU ARTICULATION. wards, measuring about three-eiglitlis of an inch across ; (2) internal to this is a deep fossa, which gives a fixed attachment to the apex of the triangular fibro-cartilage ; this fossa extends right across the base, and merges into two other grooves, one on the anterior, and the other on the posterior surface of the lower end of the bone ; (3) to the inner side of the fossa, and pro- jecting downwards at the inner and posterior aspect of the bone, is a small pyramidal process about a quarter of an inch in length — the styloid process of the ulna. On the outer margin of the base, a smooth crescentic ridge separates the surface for the fibro-cartilage from the lateral articular surface for the sigmoid fossa of the radius. This lateral articular sur- face is convex from before backwards, and bevelled off below as it descends from the overhanging or projecting upper margin wliich separates it from the constricted shaft above. In the horizontal direction it is a little longer than the sigmoid cavity of the radius, and forms about a quarter of a circle. The lowek end of the radius presents two large surfaces — viz., an anterior, which is rough for ligament ; and a posterior, which is rough for ligament and grooved for tendons ; a narrow outer surface, grooved by the tendons of the thumb muscles and prolonged into the outer styloid process of the wrist ; a large smooth concave lower surface, which enters into the formation of the wrist-joint ; and an inner surface, which presents a smooth concave cartilage-covered facet, which forms about one- fifth of a circle, to articulate with the head of the ulna. This facet, the sigmoid cavity of the radius, looks slightly upwards and articulates with the bevelled lateral facet on the head of the ulna; it is about half an inch from before back- wards, and one-fourth of an inch from above downwards, and is much smaller than the head of the ulna, upon which it rolls or turns. The upper lip of this facet slopes upwards, and is ill-defined, so that the facet fades off into the rough depressed bone above it ; the lower lip is smooth, gives attachment to the fibro- cartilage, and is a little concave in adaptation to the curve of the carpus against which it rests ; as the upper and lower lips diverge behind, the posterior vertical border is nearly twice as deep as the anterior, it is also somewhat more prominent than the anterior — though both are pronounced — and very com- monly gives attachment to some strong oblique fibres of the interosseous membrane which descend to it from the ulna. LIGAMENTS OF THE LOWER RADIO-ULNAR JOINT. 263 The Ligaments. — The triangular fibro-cartilage is seen either "by laying open the wrist-joint, or by dividing the lower end of the ulna and the interosseous and anterior and posterior radio- ulnar Kgaments, so that the lower part of the ulna can be drawn away from the sigmoid ca\'ity of the radius, and hang only by the internal lateral ligament of the wrist, and its attachment to the apex of the cartilage. It is triangular in shape, about three-eighths of an inch wide at its base, and the same in length from base to apex. It is thicker at its circumference than in the centre ; is concave on its upper surface so as to be adapted to the terminal facet on the head of the ulna ; below, it is slightly concave from before backwards, and is in contact with the upper surface of the cuneiform bone. It assists the radius in forming the arch under which is received the first row of carpal bones. Its upper surface is continuous with the synovial membrane of the inferior radio-ulnar joint, and its inferior surface with that of the wrist. Its anterior and posterior borders are united with the anterior and posterior radio-carpal and radio-ulnar ligaments. Its apex is fixed to the fossa, at the base of the styloid process, from the anterior to the posterior surface ; and its base is attached to the margin of the radius wliich separates the sig- moid cavity of that bone from its large articular surface for the radio-carpal articulation. It gradually and uniformly dimi- nishes in width as it extends inwards ; but towards its apex it becomes rounded or cord-like where it joins the ulna and is joined by the internal lateral ligament of the wrist. Like most of the fibro-cartilages, its tissue varies in character in different parts ; thus while at its centre there is a pre- ponderance of cells, at its circumference it is entirely fibrous, like the glenoid ligament and other similar structures. This fibro-cartilage differs from every other fibro-cartilage in the body, in that it forms part of two distinct articulations. It assists in forming the loose capsule of the inferior radio- ulnar joint, and enters in an important manner into the construction of the wrist. It is the most important structure in the inferior radio-ulnar articulation, as it is not only the chief, but the only real and firm bond of union between the lower ends of the radius and ulna ; and besides tying the bones together, it serves to limit their movements upon one another in a much greater degree 264 THE INFERIOR RADIO-ULNAR ARTICULATION. ^ than any other structure in either the upper or lower radio- ulnar joint. The ligaments which close in the joint in front, behind, and above, and which with the fibro-cartilage form a boundary or capsule for it, are the lower end of the interosseous membrane and the anterior and posterior inferior radio-ulnar ligaments. The interosseous mcTribrane at quite its lower end passes between ulna and radius just above their points of contact. Sometimes a strong oblique band passes from the radius to the back of the head of the ulna ; sometimes a strong oblique band — the inferior oblique ligament — passes from the ulna to the posterior margin of the sigmoid cavity of the radius, and always there are transverse or slightly oblique fibres between the two bones. "WTiere these latter fibres are attached to the radius they form a sort of arch along the upper margin of the articular facet, so as to be continuous with the anterior and posterior radio-ulnar ligaments, and thus to cover in the synovial sac above. The anterior radio-ulnar ligament is attached by one end to the anterior edge of the sigmoid cavity of the radius, and by the other to the rough bone above the articular surface of the ulna as far inwards as the notch on the anterior aspect of the head, as well as into the margin of the triangular fibro-cartilage from base to apex. The ijosterior radio-ulnar ligament is similarly attached to the posterior margin of the sigmoid cavity at one end, and at the other to the rough bone above the articular surface of the head of the ulna as far inwards as the groove for the extensor carpi ulnaris tendon, and also into the posterior margin of the fibro-cartilage from base to apex. The sheath of tlie extensor carpi ulnaris tendon is closely connected with this ligament. These ligaments consist of thin, sometimes almost scattered fibres, but they serve to complete a capsule for the support and protection of the synovial membrane. They also put some restraint, though probably not much, on supination and prona- tion, for when, in the dissected state of the forearm, forcible pronation is made, the posterior ligament bursts so as to allow of the lateral articular surface of the idna being seen. The synovial membeane, sometimes called the membrana sacciformis, is large in proportion to the size of the joint, and loose. It is not only interposed between the radial and ulnar ITS AETERIES, NERVES, x\ND MUSCLES. 265 articular surfaces, but it is continued uninterruptedly inwards to the terminal articular surface of the ulna and the upper surface of the triangular fibro-cartilage. The Akteries which supply this articulation are derived from the anterior and posterior interosseous and from the carpal arch. 1. The anterior interosseous sends a terminal branch along the fore surface of the interosseous membrane as far as the articulation, which it then supplies. 2. The posterior interosseous artery sends two or three twigs along the course and within the sheaths of the extensor tendon. From those running with the common extensor of the fingers and the extensor of the little finger, small twigs pass forwards into the joint. 3. The carpal arch, formed by the anterior ulnar and anterior radial carpal arteries, passes over the front of the radio-ulnar articulation, and gives branches to it as well as to the wrist- joint. The Nerves. — 1. The median nerve through the terminal twigs of its interosseous branch supplies this joint ; as does also, 2, the posterior interosseous nerve, which before it terminates on the back of the carpus in a ganghform enlargement gives off filaments to this as well as to other neighbouring joints and their ligaments. Thus both the nerves which supply the muscles moving the bones at tliis joint, supply also the joint. The pronator radii teres and the flexor carpi radialis are supplied by the trunk of the median, the pronator quadratus, and the joint by the anterior interosseous branch of the median. The supinator longus is supplied by the musculo-spiral, the supinator brevis, the extensors, and the joint by the posterior interosseous branch of the musculo-spiral. The biceps muscle is a very powerful supinator, but acts chiefly upon the upper end of the radius at the superior radio- ulnar articulation ; ' it is supplied by a nerve which also supplies the superior joint — ^viz., the musculo-cutaneous. The Muscles. — The muscles in relation with this joint are the supinator longus and tho pronator quadratus, together with all the extensors and flexors which pass over the wrist to the hand. Those most directly in relation with the articulation are, in front, the superficial and deep flexors of the fingers and 266 MOVEMENTS OF RADIUS UPON THE ULNA. the flexor carpi ulnaris ; and behind, the extensor communis digitorum, the extensor minimi digiti, and the extensor carpi ulnaris. All the muscles which have been described under the superior radio-ulnar joint as moving it, must necessarily move the inferior articulation also. The Movements. — The movements of the lower end of the radius may be as easily deduced from the ligaments and fibro- cartilage of the inferior radio-ulnar joint as are the movements of the head of the radius from the anatomy of the superior. The shape of the articular surfaces and the attachment of the triangular cartilage alike point to the turning or rotation of the lower end of the radius upon the head of the ulna, since there is almost a complete identity between the point of attachment of the fibro-cartilage to the ulna and the centre of the circle of which the sigmoid fossa of the radius is the arc. But the movements of the radius as a whole are not so readily understood from a consideration of the anatomical peculiarities of these joints. By many good anatomists they have been described as consisting in a rotation of the radius on its own axis ; it is to Mr. Ward, however, that we are indebted for the correction of this error and for giving us a precise account of the combined movements of the radius. It was he who pointed out that the axes of the head and neck of the radius {i.e., the axis of rotation of the upper end of the bone), and of the lower extremity or head of the ulna {i.e., the axis of rotation of the radius below), form different portions of one and the same axis line, and that this line is the axis of the movements of the bone as a whole. This, he goes on further to explain, is why the partial rotation of the bone is unassociated with any hinge-like or antero-posterior motion of its head ; and why pronation or supination, and the simultaneous advance and inward movement, or retrogression and outward movement respectively of its lower extremity, occur " without disturbance to the parallelism of its superior joint." It will be readily conceived from the shape of the greater sigmoid fossa of the ulna and the truly hinge-like manner in which it is locked upon the trochlea of the humerus, that no rotation whatever can occur of this bone independent of that of the humerus itself at the shoulder-joint. And also that owing to the necessity of strong flexion and extension move- MOVEMENTS OF RADIUS UPON THE ULNA. 267 ment at the wrist as well as at the elbow, and to the fact that these movements are best provided for by a ginglymoid joint, the form of the wrist-joint is not suited to the rotatory move- ments of pronation and supination. Yet such rotation is rec[uisite to allow of the alteration of aspect of the hand, i.e., to allow of our at one time turning the palm upwards and at another downwards. This requirement is met by the articulations between the two bones of the forearm, and is indeed the immediate cause or necessity of the existence of two bones in the forearm. At the same time it is necessary that one of these two bones (the radius) whilst having the hand attached to it so as to move with it, must be associated with the humerus only in the flexion and extension movements of the elbow, but must be independent of it, as regards rotation ; whilst the other bone of the forearm must supply the " terminal fixatures" of the rotating shaft, AH this is accomplished by giving the radius a very limited share in the construction of the elbow, and the ulna but very little participation in that of the wrist-joint. The extremes of the rotation of the lower end of the radius constitute the states of pronation and supination ; in neither of these positions are the bones parallel to one another, or the whole of the interosseous membrane evenly extended between them. In supination there is a greater approach to parallelism than in pronation ; in pronation the bones are quite athwart one another. The only position in which they are parallel, and in which the interosseous membrane is uncoiled throughout, is the mid-state between pronation and supination, when the thumb is directed upwards. For this reason this position is the one selected for the application of splints in the treatment of fractures of the upper limb. In the dissected subject, with the posterior inferior radio- ulnar ligament ruptured, these extremes of rotation amount to complete opposition of direction, i.e., to 180°, and even to a distance beyond this, amounting sometimes to nearly another 90°, when it is checked by the contact of the root of the styloid process of the ulna against the anterior margin of the sigmoid cavity of the radius, the twist of the internal lateral ligament of the wrist, and by some of the innermost fibres of the posterior ligament of the wrist ; only the lowest and a few of the middle fibres of the interosseous membrane where the 2G8 THK RADIO-ULNAR ARTICULATIONS. bones arcli away from one another are on stretch, the rest with the oblique bgament are relaxed. But in the undissected state the extremes of rotation, i.e., of pronation and supination, amount only to a quadrant and a half, i.e., 135°, so that neither the palm of the hand nor the fore sxu-face of the lower end of the radius can be turned quite into completely opposite directions. This may be proved by fixing the elbow on a flat surface and carrying the bent forearm and hand from extreme supination into extreme pronation. Yet in the living body pronation and supination may be carried far beyond this limit of radial rotation, by the aid of the rotation of the humerus inwards and outwards respectively, for then the hand, when the elbow is extended, may be carried through even a greater number of degrees of a circle than in the dissected state above referred to. This may be proved by holding the slightly bent forearm downwards and carrying the lower end of the humerus (and olecranon with it, of course) outwards and upwards at the same time that the hand is pronated. By these movements not only is the radius rolled inwards and the palm carried backwards with it, but the lower end of the ulna is also carried outwards and upwards. In this way the structures which were checking pronation, when the humero-ulnar shaft was fixed at the shoulder-joint, become relaxed, and allow of still further rotation of the lower end of the radius on the head of the ulna, i.e., of more complete pronation. The structures which check pronation in the living subject are the posterior inferior radio-ulnar ligament, strengthened by the connexion of the sheaths of the extensor tendons with it ; by the lowermost fibres of the interosseous membrane, and a few of its middle and strongest ones ; by the back part of the internal and the internal fibres of the posterior ligaments of the wrist-joint, and by the meeting of the soft parts on the fore surface of the forearm. Both in the dissected and the living subject supination is checked chiefly by the internal lateral ligament of the wrist- joint, but also by the oblique radio-ulnar ligament as well as by the anterior inferior radio-ulnar, and the lowermost fibres of the interosseous ligaments. It has not been sufficiently represented by writers on anatomy that the rotation of what I will here call the humero- ulnar shaft at the shoulder-joint, increases the range of pro- MOVEMENTS OF EADIUS UPON THE ULNA. 269 nation of the hand; and certainly it seems to have been quite overlooked that the rotation of the radius around the axis line above described, is not the only movement of which the radio- ulnar articulations permit. Although in a general way, and especially in all movements to which the terms pronation and supination are usually confined, the ulna furnishes the terminal fixatures upon which the radius rotates, yet sometimes the radius supplies the terminal fixatures for the rotation of the ulna in exactly a converse manner, i.e., the lesser sigmoid fossa of the ulna turns upon the head of the radius in the arc of a circle, whose centre is the centre of the radial head ; whilst at the lower end, the head of the ulna rotates within the sigmoid cavity of the radius around the axis drawn through the attached apex of the triangular fibro-cartilage. In other words, the axis of movement is exactly the same as in ordinary pronation and supination, only the ulna, and not the radius, is the moving bone. The range of this rotation of the ulna is, it is true, limited in the living, though very extensive in the dissected limb, and is effected by rotation of the "humero- ulnar" shaft when the hand is fixed, as for example in vaulting, or in fixing firmly one hand on the back of a chair and walking round the seat ; the movement of the styloid process of the ulna may then be plainly felt or seen. That this movement is by no means one of slight im- portance, becomes evident enough when it is remembered that without it there could be no rotation of the humerus at the shoulder-joint as long as the hand and the lower end of the radius remained fixed. The reason it has been overlooked is probably because of the absence of any muscles in the forearm which at first sight could move the ulna on the radius ; but if the humero-ulnar shaft be regarded as a rigid rod, it becomes obvious that the muscles which rotate the humerus also rotate the ulna upon the fixed radius : and further, some of the muscles which pronate and supinate the radius will, when the hand is fixed, have the reverse action on the ulna. It has been previously stated that pronation and supination as ordinarily employed are associated respectively with abduc- tion and adduction of the forearm and hand, due to rotation at the shoulder. Were this not the case the hand could not be turned over and back again, round an axis drawn through the middle of the hand, but would rotate upon the inner border of the hand. CHAPTEE XIV. THE LIGAMENTS AND JOINT OF THE WEIST, OE, THE EADIO-CAEPAL AETICULATION, Class, Diarthrosis. Subdivision, Ginglymus (with double-hinge action). The wrist is a double-hinge joint allowing of movement round a transverse axis, i.e., flexion and extension ; and around an antero-posterior axis, ttirough the lower end of tlie radius, i.e., of abduction and adduction. It also, as a matter of course, permits of a combination of these various movements, i.e., of cir- cumduction, so that it possesses most of the movements of a ball- and-socket joint, without having the weakness and the liability to displacement which is peculiar to the circular and free-moving enarthrodial joints. It lacks, however, that important adjunct of the ball-and-socket joints, rotation round a vertical axis ; no rotation whatever is permitted at it. But this deficiency of the wrist-joint is made good to the hand, through the radio- ulnar articulations, at which, as has been already fully ex- plained, rotation of the forearm and hand takes place round an axis through the head of the radius, the head of the ulna, and the finger of the hand. Thus do we see at the wrist and in the mode of union of the radius and ulna, a very similar, but, as the special requirements of the parts demand, somewhat different method for producing the same results as are found in the junction of the head with the spine. There also do we find two sets of articulations — (1) those between the occiput and atlas, at which flexion and extension, abduction and adduction {i.e., lateral flexion to either side and back again), as well as circumduction take place ; and (2) those between the axis and atlas, at which rotation round a vertical axis occurs. The wrist-joint, by possessing the possibility of abduction and adduction, is by so much a more complicated hinge than either the elbow or the ankle, at which flexion and extension are really the only possible appreciable movements. The lateral THE RADIO-CARPAL ARTICULATION. 271 movements wliich are permitted to the foot occur not at the ankle, but between the os calcis and astragalus, and at the medio-tarsal articulation ; so that what is done freely by the hand at one joint, viz., radio-carpal, is less perfectly and freely performed by the foot at, at least, three sets of articulations. The strength of this joint is not dependent upon any deep socket as at the hip ; is not guarded by any overhanging pro- cesses as is the shoulder ; has no strong and long lateral but- tresses like the ankle, but only short and diminutive styloid processes ; is not shut in behind an eminence as is the jaw, and is not locked securely by hook-like processes as is the elbow. Neither does its strength lie, like that of the knee, in uhe number, size, or arrangement of the ligaments which unite the bones ; but rather in the number of tendons which pass over the joint, and in the close connexion which exists between the fibrous tissue of the sheaths of these tendons and the cap- sule of the wrist. And another additional source of strength to the wrist is its proximity to two other rows of joints — viz., the middle carpal, and the carpo-metacarpal ; and the fact that each row has its own separate parts united by other arthro- dial joints. Thus not only the movements, but shocks and jars, and all violence are shared between and distributed amongst all the several articulations. At no one of them, however, except the wrist, are the movements at all free, and yet the aggregate motion is considerable. Another source of security lies in the fact that a long lever does not exist on the distal side of the joint. The wrist is the junction of the hand with the forearm, and is formed by the union of the radius and the triangular fibro- cartilage above, with the scaphoid, semilunar, and cuneiform bones of the carpus below. The ulna is excluded from the wrist-joint by the intervention of the fibro-cartilage. The radius and triangidar fibro-cartilage together present a smooth sm-face, slightly concave both from before backwards, and from side to side ; whilst the three bones of the carpus present a corresponding smooth convex surface, made uniformly even and uninterrupted by the interosseous ligaments between the scaphoid and lunar, and the lunar and the cuneiform. The bones which, so far as they enter into the formation of the wrist-joint, now require description, are — the radius, the scaphoid, the semilunar, and the cuneiform. The Eadius. — The lower end of the radius is much larger 272 THE RADIO-CARPAL ARTICULATION. than the upper, and presents a somewhat quadrilateral outline, and is so curved as to present a slight concavity in front, and a sHght convexity behind. It usually measures over an inch from side to side, and three-quarters of an inch from before backwards at its centre. Its extremity is marked by a large triangular articular facet, which is somewhat prolonged down- wards upon the styloid process of the bone. The apex of this facet is placed at the styloid process, and the base is formed by the sharp edge which separates the inferior articular surface from the sigmoid cavity of the radius, and gives attachment to the broad extremity of the triangular fibro-cartilage. The anterior and posterior margins of this surface are somewhat pro- jecting, the anterior being slightly more so than the posterior, and give the articular surface its slightly concave character ; and to the rough surface of bone, just above them, the anterior and posterior portions of the capsular hgament are attached. Owing to the shght curve forwards in the lower end of the radius, this facet looks slightly forwards as well as down- wards ; it has also a very shght inchnation inwards. The facet is divided into two parts by an antero-posterior ridge extending across the surface, and by a slight indentation, or hour-glass contraction of its margins. An inner quadrilateral portion, nearly half an inch wide by three-quarters of an inch from before backwards, articulates with the semilunar bone ; and an outer and triangular-shaped portion, about five-eighths of an inch wide, varying in measurement from before back- wards at different points, and becoming smaller towards the apex of the triangular area, articulates with the scaphoid. At the inner side of the extremity, and placed at right angles to the facet for the scaphoid, is the sigmoid fossa for the ulna, which has been described under the inferior radio-ulnar articu- lation. At the outer side a conical process, the styloid -process, is prolonged downwards from a very narrow surface ; it is about a quarter of an inch long, and is thus the lowermost point of the radius. To the base of this process is attached the supinator longus, and to the tip the external lateral hga- ment of the wrist. The anterior surface immediately above the articular edge is rough and uneven, and is marked by a ridge which extends outwards from the margin of the sigmoid cavity to the ridge THE RADIO-CARPAL ARTICULATION. 273 in front of the tendon of the extensor ossis metacarpi pollicis, and then curves downwards on the front of the styloid process to its tip. Below the ridge is an uneven depression which gives attachment to some very strong oblique anterior fibres of the capsular ligament of the wrist. Where this ridge curves down- wards, it is joined by another, which descends almost vertically from the outer side of the shaft, and forms the front limit of the groove for the extensor ossis metacarpi and extensor primi internodii pollicis ; this gTOOve is a little in front of the plane of the apex of the styloid process. The posterior surface is convex and irregular, being marked by grooves and ridges for the passage of the tendons of the extensor muscles. Thus a prominent rough ridge descends upon the outer surface of the styloid process to its tip, where it meets with the ridge which descends on the anterior surface of the process ; it separates the gTOOve for the extensor ossis metacarpi and extensor primi internodii pollicis from the broad groove for the radial extensors of the wrist. This groove is again divided by a faint ridge between the long and short radial extensors, and to its inner side and nearly in the middle of this surface of the bone is a prominent rough ridge, which is continued up- wards on the back of the shaft and bifurcates, the outer portion ascending to the rough surface of insertion of the pronator radii teres, while the other joins the interosseous border of the bone in its lower third. Under cover of this ridge and to its inner side is a groove for the extensor secundi internodii pol- Kcis, and to the inner side of tliis again is a broad groove for the extensor communis digitorum and extensor indicis. These tendons increase considerably the security of the wrist-joint. The radius, like the ulna, undergoes a great change of form from end to end ; thus instead of being cylindrical, as above, it becomes much expanded and assumes the quadilateral outline. This expansion is at the expense of its solidity, for a section of the bone shows its compact wall to be very thia. The First Eow of the Carpal Bones. — The scaphoid, semilunar, and cuneiform bones present superiorly a surface which is smooth, covered with articular cartilage, except over the interosseous ligaments, pretty uniformly convex, and directed upwards and slightly backwards. The articular 274 THE TRIANGULAR FIBRO-CARTILAGE. facetted surface of these bones extends furtlier on tlie dorsal than the palmar aspect ; that of the scaphoid is triangular in form, and articulates with the outer facet on the lower end of the radius, and through its mediimi the metacarpal bones of the thumb and forefinger are indirectly supported on the radius. The semilunar presents a quadrilateral-shaped facet in correspondence with the inner portion of the lower end of the radius ; through the os magnimi it bears the middle or longest and most prominent finger, and therefore the one most liable to be injured, upon the strongest part of the radius. The cuneiform presents a triangular-shaped facet for the fibro-cartilage, which is interposed between it and the ulna ; it supports the unciform bone, and transmits pressure from the little and ring fingers to the end of the ulna. The cuneiform and scaphoid bones rest upon the fibro- cartilage and the outer part of the radius respectively in a slanting manner. TMs is necessarily so on account of the arch into which they are received, but a result of it is that a portion of the forces received by them is transmitted to the semi- lunar bone which rests more perpendicularly upon the radius, and that too upon the largest and strongest part of the radius. The TrianCtUlar Fibro-cartilage. — The ulna is excluded from the wrist-joint by the triangular fibro-cartilage, which besides presenting a concave under surface for the cuneiform of the carpus, presents also a concave upper surface for the head of the ulna. To its margins the loose fibrous capsule of the inferior radio-ulnar, as well as the capsular ligament of the wrist joint, is attached ; and as the cartilage stretches trans- versely below the ulna, from the inner border of the radius to the fossa at the root of the styloid process of the ulna, it assists in forming the boundary of each articulation. It is about three-quarters of an inch from base to apex, and half an inch from before backwards at the base. Its edges are very ill-defined, owing to the quantity of ligamentous fibres connected with it, and near its apex it is blended intimately with the internal lateral ligament of the wrist. By its base it is connected with the projecting anterior and posterior ridges of the sigmoid cavity of the radius, as well as with the angular line which separates the facet for the ulna from that for the semilimar bone of the carpus. The inferior surface of the cartilage is almost on the same plane with the terminal articular surface of the radius, but THE CAPSULAR LIGAMENT OF THE WRIST. 275 slopes downwards considerably towards its apex, so as to form with the radius the arched superior surface of the wrist-joint. This arched surface is somewhat oval or diamond-shaped, being considerably narrower at the inner and outer ends, viz., at the styloid processes, than at the inner part of the radial surface ; the anterior and posterior borders of the radial sittface gra- dually approximate as they pass towards the styloid process. The outer lateral buttress of the arch, i.e., the styloid process of the radius, has the articular surface prolonged down upon it. The Capsule, or Capsular Ligament, of the Wrist. — The capsule of the wrist-joint has been usually described as four separate ligaments, and it will be convenient for the sake of a complete description to follow this method ; but it must at the outset be understood that these four portions form one continuous and uninterrupted structure, extending from styloid process to styloid process on both aspects of the joint. Considered as a whole, the capsule arises from the margins of the lower end of the radius ; from the margins of the tri- angular fibro- cartilage, where it blends with the anterior and posterior inferior radio-ulnar Kgaments ; and from the edges and surfaces of the styloid process of the ulna. It is attached below to the bones of both rows of the carpus, and thus adds strength to the union of the several carpal bones with one another. More especially is this the case on the palmar aspect, where it forms the floor of the sheath upon which the flexor tendons glide just before they pass beneath the annular ligament of the carpus. Tliis ligamentous envelope is strengthened by superadded fibres, both in front and behind {i.e., on palmar and dorsal aspects), which pass on to the carpal bones from the little irregular rough points at the lower ends of the radius and ulna ; and some very strong additional fasciculi of fibres strengthen the sides of the capsule and radiate from the styloid processes upon the bones of the carpus so as to form lateral ligaments suitable for and necessary to the hinge-like character of the articulation. The anterior radio-carpal ligament, i.e., the anterior portion of the capsule of the wrist, is attached superiorly to the radius immediately above the margin of the terminal articular facet, to the curved ridge at the root of the styloid process of the radius, and to the anterior margin of the triangular fibro-cartilage, where it is blended with some of the fibres of the capsule of t 2 276 THE CAPSULAR LIGAMENT OF tlie inferior radio-iilnar joint. Tlience they pass downwards, and for the most part inwards, to be connected with both rows, but specially with the second row of the carpus and with the fibrous tissue connecting the two rows with one another, i.e., the anterior intercarpal ligament. The strongest and most oblique fibres arise from the curved ridge at the root of the styloid process of the radius, and from the large uneven depression between it and the margin of the facet for the scaphoid ; only a few of these fibres have any connexion with the scaphoid itself, the rest pass obliquely over it, and are inserted into the semilunar, the os magnum, and the cuneiform bones. Another strong but less oblique set passes from the radius, above the margin of the facet for the semilunar bone, to be attached to the adjacent parts of the os magnum, unciform, and cuneiform bones. Between the two sets of fibres, small vessels pass through the capsule into the joint. The obliquely inward direction of the fibres of this portion of the capsule gives to it the power of dragging over the hand with the radius in the powerful movements of supination, and in this they are assisted by the anterior portion of the external lateral ligament, whose fibres have the same direction, whilst the fibres of the anterior portion of the internal lateral liga- ment have an opposite direction, and therefore tend to check supination. The anterior radio-carpal ligament also checks or limits extension of the wrist. The posterior radio-carpal ligament, i.e., the posterior part of the capsule of the wrist, is attached superiorly to the dorsal edge of the carpal end of the radius and to the back of the styloid process of the radius, as well as to the posterior margin of the triangular fibro-cartilage. It passes downwards and inwards to be connected with the first row of carpal bones, and to the ligament connecting the first with the second row, but chiefly to the semilunar and the cuneiform. If the joint be laid open, and the ligament held up to the light, some parts of it will appear opaque and others transparent. On dissection, the thick opaque parts are found to have the follow- ing connexions : — (1) Some strong fibres pass from the back of the fibro- cartilage, where they are blended at their origin with the posterior inferior radio-ulnar ligament, and from the edge of the radius just behind the sigmoid fossa, to be attached to the cuneiform bone. (2) From the prominent ridge and the groove for the extensor THE EADIO-CAEPAL ARTICULATION. 277 secundi internodii poUicis to the back of the semilimar and cuneiform bones. And (3) from the groove for the radial extensors (which includes the posterior surface of the styloid process), to the back of the scaphoid and the semilunar. This posterior ligament is not so strong as the anterior ; it is m relation with the sheaths of the extensor tendons which pass over it. It limits flexion of the hand, and from the obliquely dowif?fard and inward direction of its fibres, it carries the hand with the radius iu pronation. The internal lateral ligament, i.e., the inner side of the capsule of the wrist-joint, is fan-shaped, with its apex above at the styloid process of the ulna. It is attached to the styloid process of the ulna on all sides, and blends with the apex of the fibro-cartilage. Some of the fibres, as they descend to the carpus, pass obliquely forwards and outwards to the base of the pisiform bone, and to the inner part of the upper border of the anterior annular ligament of the carpus, where that ligament springs from the pisiform bone ; these fibres form a round, thick, and prominent fasciculus on the front aspect of the wrist, and whilst they assist the anterior ligament and the anterior por- tion of the external lateral ligament in limiting extension, they counteract them by limiting instead of facilitating supina- tion. Other fibres pass down vertically to the inner side of the cuneiform bone, and others again outwards and downwards to the dorsal surface of the cimeiform. These latter fibres assist in limiting pronation. The tendon of the extensor carpi ulnaris is posterior to, and passes over, part of the fibres of this ligament. Besides its influence in limiting pronation and supination, and the assistance given by the long anterior fasciculus to the anterior ligament in limiting extension, the whole ligament acts to limit abduction of the wrist, which is the least exten- sive movement of the joint, not only on account of the strength of this ligament, but also because the styloid process impinges against the scaphoid bone in the extreme of this movement. The external lateral ligament, i.e., the outer part of the capsule of the wrist, consist of fibres which radiate from the extremity and forepart of the styloid process of the radius. Of these some pass downwards and inwards in front to the scaphoid and the adjacent edge of the os magnum ; others downwards, and a little forwards and inwards, to the tubercle of the scaphoid and the ridge of the trapezium ; and others 278 THE POSTERIOR ANNULAR LIGAMENT. afrain downwards, aud a little outwards, on to the rougli dorsal sm-face of the scaphoid. The fibres of this ligament do not radiate so much, nor are they so long or strong, as those of the internal lateral Hgament. The radial artery passes over tliis ligament, and so do the extensor ossis metacarpi, and extensor primi internodii, pollicis. The artery separates these tendons from the ligament. This ligament limits adduction. By its anterior fibres it assists the anterior ligament and the anterior portion of the internal lateral ligament to limit extension. By its anterior fibres, which like the anterior ligament itself pass obliquely downwards and inwards, it drags or carries over the hand in the powerful movements of sujDination. Supination being a more powerful movement than pronation, the hand has there- fore the additional advantage and security of these fibres of the external ligament, although the anterior lio-ament is itself stronger than the posterior, which carries the hand with the radius in the movement of pronation. At the same time there is provided in the anterior portion of the internal lateral liga- ment a very powerful check over supination. The posterior annular ligament of the wrist assists the pos- terior portion of the capsule of the wrist-joint in binding the hand to the forearm, and in carrying the hand with the radius in pronation. It is a strong fibrous band, extending somewhat obliquely across the back of the joint, with an inclination downwards and inwards. It is attached externally to the posterior margin and the ridges on the hinder surface of the radius, and internally to the cuneiform, pisiform and base of the fifth metacarpal bone. The superior fibres bind down the extensor carpi ulnaris tendon, and on their way to the carpus pass below the end of the ulna. As it passes across the wrist some of its fibres are attached to the ridge on the back of the radius. Above, it is continuous with the fascia of the forearm. The subway between its deep surface and the wrist is divided into six compartments for the passage of the extensor tendons. Thus this hgament serves three distinct purposes — (1) it binds down the extensor tendons, keeping them in their places as they pass over the convex dorsal surface of the carpus, and giving to them their proper direction, which, from their obKquity in the forearm, they would not otherwise get; (2) it strengthens the connexion between the forearm and the hand ; and (3) it assists the ARTERIES OF THE RADIO-CARPAL ARTICULATION. 279 posterior radio-carpal ligament in dragging the hand over with the radius in the movement of pronation. The Synovial Membrane. — The synovial membrane of the wrist-joint is very extensive, but has the same relation to the other structures as in simple joints, i.e., where there are only two bones in their construction. It does not commu- nicate usually with the inferior radio-ulnar articulation, being shut off from it by the triangular fibro-cartilage ; nor with the joints between the bones of the first row of the carpus, being shut out from them by the interosseous hgaments wMch make even and uniform the convexity of the carpal portion of the joint. The styloid process of the radius (but not of the ulna) is cartilage-coated, and comes within the limits of the synovial sac. Outside the synovial membrane along the pos- terior border of the radius a few fatty processes project, fringe- like, into the articulation. The Aeteries. — (1) The arch formed by the two anterior carpal branches from the radial and ulnar trunks is in front of the articulation. It lies beneath the median nerve and the sjmovial apparatus of the flexor tendons as they pass the wiist, and in immediate contact with the anterior portion of the capsule of the joint. This arch receives tributaries from the descending branches of the anterior interosseous, and a recurrent or ascending branch from the deep palmar arch. Twigs from these sources ramify deeply in the substance of the ligament, and form a more or less complete zone beneath the synovial membrane. This zone is close to the edge of the articular surface of the bones, and from that part of it upon the carpal bones little vessels are sent along upon the two interosseous carpal ligaments. (2) On the back of the articulation there are {a) recurrent branches from the posterior carpal arch, and (h) from the first dorsal interosseous artery ; and (c) branches from the posterior interosseous. The posterior interosseous, or posterior termi- nation of the anterior interosseous, forms a free anastomosis with branches from the radial and ulnar, which curve round the respective bones, and from the chain thus formed twigs run along in the synovial sheath of each of the tendons, supplying the sheath and giving filaments to the tendons. From these branches to the sheath and tendons vessels enter the back of the wrist and carpal joints. (3) Piercing the external lateral ligament, and thus entering 280 MUSCLES OF THE RADIO-CARPAL ARTICULATION. immediately into tlie \vidst-joint, are twigs derived from tlie radial as that vessel passes over the external lateral ligament. (4) Similarly others enter the wrist from the ulnar on the inner side, while others penetrate the internal lateral ligament to reach the inter-articular cartilage and the inferior radio-ulnar joint. The Nerves. — In front, the ulnar and the median ; and behind, the posterior interosseous. Each gives filaments to this joint. The Muscles. — The muscles in connexion with, or which move the wrist-joint, are all those which pass over it to be inserted into some parts of the bones of the hand. Thus, iu front there are the superficial and deep flexors of the fingers, the flexor longus pollicis, the flexor carpi ulnaris and flexor carpi radiahs, and the palmaris longus. Behind, there are from without inwards the radial extensors major and minor, the extensor secundi internodii pollicis, the extensor communis digitorum and extensor indicis, the extensor minimi digiti and the extensor carpi ulnaris. And on the outer side, the extensor ossis metacarpi pollicis, and extensor primi internodii pollicis. The action of the muscles on the wrist-joint can be easily surmised from their relation to it, and from their names. Flexors. — Flexion of the wrist is effected primarily by the two flexors of the carpus — viz., the flexor carpi ulnaris and flexor carpi radialis ; but when flexion of the fingers is either prevented or completed, then aR the flexors of the digits act to flex the wrist ; so with the palmaris longus, which, when its action in tightening the palmar fascia is completed or pre- vented, also assists to bend the wrist. Extensors. — Extension of the wrist is produced primarily by the three extensors of the carpus — viz., the extensor carpi ulnaris, extensor radialis major, and extensor radialis minor ; but all the long extensors of the fingers assist in extending the wrist when their action on the fingers is prevented or completed. Abductors. — The extensor carpi radiahs longior and brevior, the flexor carpi radialis, and the extensor ossis metacarpi and primi internodii pollicis, acting unopposed singly or together, abduct the hand. Adductors. The flexor carpi ulnaris and extensor carpi ulnaris, acting unopposed singly or together, bend the ulnar edge of the hand downwards or towards the styloid process of the ulna, i.e., adduct it. BUES^. OF THE RADIO-CARPAL ARTICULATION. 281 In other words, if the extensors of the carpus act together, the hand is bent backwards, i.e., extended ; when the flexors of the carpus act together, the hand is bent forwards, i.e., flexed ; and when the flexor and extensors of the carpus on the radial side act together (those of the ulnar side not acting), the hand is bent towards the radius, i.e., abducted ; but when the flexor and extensors on the ulnar side act together (those of the radial side not acting), the hand is bent towards the ulna, i.e., adducted. The Bues^. — There are several bursse in relation with the wrist, but hke those about the ankle, and unlike those about the hip and shoulder, knee and elbow, they are nearly all of the form of synovial sheaths for tendons. Those on the front of the joint are (1) a large long bursa for the tendon of the flexor longus pollicis ; this extends from above the line of the wrist, all along the palm to the thumb, near the insertion of the tendon. (2) Four short bursse on the forepart of the tendons of the flexor sublimis. (3) A large bursa behind the tendon of the flexor longus pollicis, which intervenes between it and the front of the radius and capsule of the wrist. (4) A large bursa between the flexor profundus digitorum tendons, and the front of the lower end of the radius and the capsule of the wrist. Sometimes this communicates with the last. (5) A short oblong bursa surrounding the flexor carpi radialis, ex- tending from above the wrist to the groove in the trapezium, and passing between the outer attachments of the annular ligament of the carpus, as shown in the plate illustrating the palm of the hand. (6) A small round bursa connected with the flexor carpi ulnaris, between it and the internal lateral ligament at its insertion into the pisiform bone. On the outer side of the wrist there is a bursa separating the extensors of the thumb from the radius and capsule of the joint. On the back of the wrist^a bursa is found in connexion with each tendon, or set of tendons, as they pass along the grooves in the bones at the back of the joint. The largest, and those in closest connexion with the joint, are — (1) one separating the radial extensors from the radius and capsule ; (2) one separating the index and common extensors from the capsule ; and (3) one separating the extensor carpi ulnaris from the capsule and ulna. The extensor minimi digiti, and extensor secundi internodii pollicis, are each provided with a bursa, or bursal sheath. 282 MOVEMENTS OF THE EADIO-CARPAL ARTICULATION. The Movements. — The movements of the wrist-joint are the four angular movements — flexion, extension, abduction, and adduction ; and the movements of these combined, or made to follow each other in quick succession, i.e., circumduction. In flexion and extension, tlie carpus rolls backwards or forwards respectively, beneath the arch formed by the radius and fibro- cartilage, moving round a transverse axis through the styloid processes. Flexion is limited by the posterior ligament, and posterior portions of the lateral ligaments ; extension, by the anterior ligament, and the anterior portion of the lateral ligaments. In abduction and adduction, the carpal bones glide from without inwards and from within outwards respectively, be- neath the arch formed by the radius and fibro-cartilage, around an antero-posterior axis through the lower end of the radius. Abduction is more limited than adduction, and is checked by the long and strong internal lateral ligament of the wrist, and by the contact of the styloid process of the radius with the trapezium. Adduction is checked by the external lateral liga- ment alone. One reason for adduction being more free than abduction is because the ulna does not reach so low down as the radius, and the yielding fibro-cartilage allows of greater movement upwards of the inner extremity of the carpus. In circumduction, the hand moves so as to describe a cone, the apex of which is at the wrist. This last movement, like each of its components, is made more easy and more free and exten- sive by the slight gliding movement of the carpal bones on one another, and by the comparatively free movement permitted at the medio-carpal joint. It has been already fully pointed out that pronation and supination are not permitted in the least degree at the wrist, but take place at the radio-ulnar joints. The obhque direction of the fibres of the lateral ligaments prevents any rotation at the .radio-carpal joint, while it per- mits much freedom of abduction and adduction. In these latter movements both ligaments become somewhat relaxed by the approach of the carpus to the forearm on the side towards which the movement occurs, and the lateral shifting of the carpus towards the styloid process of the opposite side. CHAPTER XV. THE JOINTS AND LIGAMENTS OF THE HAND. The hand, which is the inferior segment of the upper limb, is characteristic of man and the quadrumana. It might even be said to belong exclusively to man ; for the anterior extremity of the monkey is as much a foot as a hand, indeed, as much as its posterior extremity is a hand ; whereas in man the hand corresponds in its sensibility and varied movements to the superiority of his mental endowments over all other animals ; and the two together — mind and hand — make him the ruler over the rest of nature. All the other parts of the superior extremity, from the shoulder downwards, are subservient to the uses and functions of the hand : the strength and freedom of motion of the ball-and-socket joint of the shoulder, the security of the Mnge of the elbow, the pronation and supina- tion between the bones of the forearm, the strength and gliding angular movements of the wrist, are all provisions for the easy, rapid, varied and powerful actions of the hand. The skeleton of the hand consists of twenty-seven distinct bones, and these are united together by means of hgaments — dorsal, inter- osseous, and palmar — and their movements upon one another facilitated by synovial membrane. In the hand are sub- divisions analogous to those in the foot ; thus the carpus cor- responds to the tarsus, the Tnetacarpus corresponds to the meta- tarsus, and the phalanges of the fingers are in every way analogous to those of the toes. But whilst in the foot all the toes are nearly parallel to the middle line of the foot, in the hand only the four inner digits are parallel to the middle line of the hand, and the thumb forms an angle with this line of rather more than 45°. This makes the carpo-metacarpal joint of the thumb a much more important articulation than any of the tarso-metatarsal joints ; and is the cause of its requiring a special description. 284 JOINTS OF THE FIRST ROW OF THE CARPUS. We will take the several parts in the order named, begin- ning with the joints and ligaments of the carpus. First, let us examine how the bones in each of the two rows of the carpus are joined together, and then how the two rows themselves are united. Joints and Ligaments of the First Roiv of the Carpus. Class, Diarthrosis. Subdivision, Arthrodia. The Bones. — In the first or upper row of the carpus the scaphoid, semilunar, and cuneiform bones form by their com- bined superior articular surfaces a convex surface adapted to the radius, and contributing to the formation of the wrist. The pisiform has a separate and independent articulation with the cuneiform. The scaphoid, like each of the other carpal bones, has six surfaces. In most of these bones, four of the surfaces are arti- cular, and two, the anterior and posterior, are rough for the attachment of ligaments. By its internal surface the scaphoid articulates with both the semilunar and the os magnum, and its smooth cartilaginous facets are separated by a horizontal cres- centic ridge ; the superior is directed inwards and forwards, and is narrow, semilunar, and flat, to articulate with the correspond- ingly shaped outer surface of the semilunar bone. The inferior and larger portion presents an oval-shaped and deeply concave facet, which looks inwards, forwards, and downwards, and assists in the formation of the socket for the head of the OS magnum. By its outer surface, which is narrow and rough, and directed upwards and outwards, the scaphoid gives attach- ment to the external lateral ligament of the wrist. The semilunar hone, by the whole of its external surface, articulates with the superior facet of the internal surface of the scaphoid. This surface is directed outwards and slightly towards the dorsum ; it is narrow, semilunar, flat, and smooth, with a cartilaginous coating. Its internal surface is inclined in the opposite direction- — viz., inwards and forwards, as well as slightly downwards : it is smooth, quadrilateral, and plane, or slightly convex for articulation with the cuneiform bone. The cuneiforrti lone by its outer surface presents a smooth, flat, or slightly concave surface for the semilunar. This sm-face is quadrilateral in shape, with its superior angles LIGAMENTS OF THE FIRST ROW OF THE CARPUS. 285 somewliat rounded off, and it looks outwards, upwards, and backwards. The anterior surface is rough, externally for liga- ments of the wrist and carpus, and internally and below presents a smooth and nearly flat surface for the pisiform bone. The internal surface is small and non-articular ; it is the lowest point of the bone, and is roughened for the attachment of the anterior annular ligament, and a fasciculus of the internal lateral ligament of the wrist. The pisiform lone is placed on the front {i.e., on the palmar) aspect of the cuneiform, with which it articulates by a smooth and nearly flat facet, upon its posterior, or dorsal, aspect. It is the smallest of all the carpal bones ; presents no other articular surface, but is everywhere else rough for the attachment of muscles and ligaments, viz., the anterior annular ligament of the carpus ; the internal lateral ligament of the wrist ; the capsular ligament, which unites it with the cuneiform bone ; the tendon of insertion of the flexor carpi ulnaris, and the fibres of origin of the abductor minimi digiti. Lastly, there are two distinct, strong fibrous bands uniting the pisiform to the process of the unciform and the base of the fifth meta- carpal bone, but these are in truth only the prolongation downwards of the tendon of the flexor carpi ulnaris. The Ligaments. — The bones of the first row, the pisiform excepted, are united by two sets of ligaments, and two inter- osseous fibro-cartilages. Two dorsal ligaments extend transversely between the bones and connect the scaphoid with the semilunar, and the semi- lunar with the cuneiform. Their posterior surface is in contact with the posterior ligament of the wrist-joint. Two palmar ligaments extend nearly transversely between the bones, and connect the scaphoid with the semilunar, and the semilunar with the cuneiform. They are stronger than the dorsal ligaments, and are placed beneath the anterior ligament of the wrist-joint. The two Interosseous Fihro-cartilages. — Between the scaphoid and the lunar, as well as between the lunar and the cuneiform bone, there is interposed in the whole antero-posterior length of the articulation, i.e., from dorsal to palmar surfaces, a narrow fibro-cartilage, which, however, extends between only a small portion of the osseous surfaces. These interosseous laminae are best seen by laying open the radio-carpal joint, the 286 JOINTS OF THE SECOND ROW OF THE CARPUS. convex carpal surface of which they help to form. They are attached to the pahnar and dorsal ligaments by the anterior and posterior extremities. When dissected out they are seen to be somewhat wedge-shaped, with their thick edge towards the wrist-joint, and their tliin edge between the adjacent articular surfaces of the bones. These laminse are usually described as ligaments, but their real structure is fibro-cartilaginous. The SYNOVIAL MEMBRANE of thcse Small articulations, like that between the bones of the second row of the carpus, is merely a prolongation from the large synovial membrane between the two rows themselves. Ligaments connecting Pisiform Bone with the Carpus. — The pisiform bone articulates with the cuneiform, so as to form a separate joint, and takes no part in the construction of the wrist. A small loose fibrous capsule is attached to both the pisiform and cuneiform, just beyond the margin of their articular surface for one another, and this is lined by a separate and_ distinct synovial membrane. Two strong rounded or flattened bands pass downwards from the pisiform, one to the process of the unciform, and the other to the base of the fifth metacarpal bone. These, however, are to be regarded as prolongations of the tendon of the flexor carpi ulnaris muscle, and the pisiform itself may be looked upon as a sesamoid bone developed in that tendon, as the patella is in that of the quadriceps extensor femoris. Joints and Ligaments of the Lower Row of the Carpus. The Bones, — In this row the trapezium, the trapezoid, the OS magnimi, and the unciform follow one another in order from the radial to the ulnar side. By their united superior articular surfaces they are adapted to the united inferior articular surfaces of the upper row (the pisiform bone ex- cepted), and thus contribute to form the " medio-carpal arti- culation," whereas by the inferior articular surfaces they enter into the construction of the carpo-metacarpal joints. The trapezium by its internal surface articulates with the second bone of this row, viz., the trapezoid. This surface is divided by a horizontal ridge into two parts ; one, the upper and larger portion, is concave and looks inwards and backwards to articulate with the trapezoid ; the other is directed down- LIGAMENTS OF THE SECOND ROW OF THE CARPUS. 287 wards and inwards, and articulates with the side of the base of the second metacarpal bone. The external surface is rough and gives attachment to the external lateral hgament of the wrist. The trapezoid is interposed between the trapezium and os magnum, articulating with the former by its external and with the latter by its internal surface. The external surface is convex, and directed outwards and forwards. The internal surface is concave and smooth over nearly its whole extent to articulate with the OS magnum, but near the dorsum it is rough for the attachment of an interosseous ligament. The OS magnum — the central, the chief, and the largest bone in the carpus — presents a small facet on its outer surface for the trapezoid, and a large one on its internal surface for the unciform. The external surface, in addition to the small semi- circular facet for the trapezoid, which is situated at its lower and anterior part, has above and behind tliis smooth surface a rough depression for the attachment of an interosseous ligament ; above this again, a rough constriction, forming part of the neck of the bone ; and above this again, the outer side of the smooth facetted head, which articulates with the scaphoid. Thus a considerable part of this surface projects upwards beyond the line of the trapezium and trapezoid, and so fits into the hollow formed by the scaphoid and the lunar. On the internal surface, besides the large concave articular surface for the unciform, which extends over the side of the head as well as the neck and body of the bone, there is ante- riorly a rough depression for the attachment of an interos- seous hgament ; this rough space does not quite reach to the dorsal, but extends right down to the palmar surface of the bone in correspondence with the rough portion of the apposed surface of the unciform. The unciform hone presents on its outer side an irregularly shaped articular facet for the os magnum. It occupies nearly the whole of this aspect of the bone, excepting a smaU square, rough, and non-articular portion at the anterior inferior corner, where an interosseous ligament is attached. The Ligaments. — The four bones of this row are united to one another by three dorsal, three palmar, and two interosseous ligaments. The three dorsal ligaments extend transversely and connect the trapezium with the trapezoid, the trapezoid with the os magnum, and the os magnum with the unciform. 288 THE MEDIO-CARPAL JOINT. The three palmar ligaments are stronger than the dorsal, and are deeply placed beneath the mass of flexor tendons and the anterior annular ligament of the carpus. They have the same relation and connexion with the several bones on their anterior as the dorsal ligaments have on their posterior aspect. The two interosseous ligaments are situated one on each side of the OS magnum, which they connect with the trapezoid on the outer and with the unciform on the inner side. That between the os magnum and trapezoid is attached to the apposed surfaces near their dorsal, i.e., posterior aspect. That between the unciform and os magnum is attached to the apposed surfaces at their lower and anterior, i.e., palmar aspect. Like all articular bony surfaces the facets on these carpal bones which play upon one another are coated with a layer of articular cartilage. The SYNOVIAL MEMBKANE, Hke that between the bones of the first row of the carpus, is a prolongation of the membrane belonging to the medio-carpal joint. The Medio-carpal Joint, or Tlie Articulation of the Upper with the Lower Bow of the Carpus. The inferior articular surfaces of the upper row, i.e., of the scaphoid, semilunar, and cuneiform bones, are adapted to the superior articular surfaces of the bones of the second row. The line of tliis articulation is concavo-convex from side to side ; thus the first row presents a wavy surface for the reception of the second. The outer or radial part of the first row, consisting of the scaphoid alone, is convex, and bears the trapezium and trapezoid. Then follows a large transversely elongated socket, formed by the deep concavity of the inner part of the scaphoid and the lower part of the semilunar and cuneiform, into which are received (1) the head of the os magnum, wliich articulates with both scaphoid and semilunar; (2) the upper and outer angle of the unciform, which articulates with the semilunar ; and (3) the upper convex portion of the internal surface of the unciform, which articulates with the external and concave portion of the inferior surface of the cuneiform. Thirdly, the innermost part of the inferior surface of the cuneiform bone is convex and turned a little backwards to fit into the lower LIGAMENTS OF THE MEDIO-CARPAL JOINT. 289 portion of the internal surface of the unciform (which it quite overlaps on the inner border of the carpus) and which is concave and turned a little forwards to receive it. The line of this articulation is sometimes described as having the course of the Eoman S placed horizontally thus C/), a resemblance which is by no means strained, as can be seen by carrying the eye along the inferior surfaces of the upper row of bones. That part of the articulation where the first row forms a concavity or socket for the os magnum and unciform, viz., the large central portion, has somewhat the character of a compound complex ball-and-socket joint ; the other portions, that, viz., where the scaphoid supports the trapezium and trapezoid, and that of the innermost part between cuneiform and unciform, are typically arthrodial, and consist of but slightly curved or nearly plane surfaces. The Ligaments. — The articular surfaces are covered by a thin layer of cartilage, and are held in apposition by the following ligaments : — The anterior, or palmar 7nedio-carpal ligament, which is of considerable strength, consists of fibres most of which radiate from the os magnum to the scaphoid, lunar, and cuneiform ; some few others, however, connect the trapezoid and the trapezium with the scaphoid, and others again pass between the unciform and cuneiform. It is covered over and tliickened by a quantity of fibrous tissue derived from the sheaths of the flexor tendons, and the fibres of origin of the small muscles of the thumb and little finger. The posterior, or dorsal medio-caripal ligament, consists of fibres extending obhquely from the bones of the upper to those of the lower row. It is stronger on the ulnar than on the radial side, but not so strong as the palmar ligament. Transverse Dorsal Ligament. — ^An additional ligamentous band, well-marked and often of considerable strength, which may be called the " transverse dorsal ligament" of the carpus, passes across the head of the os magnum from the back of the scaphoid to the back of the cuneiform bone. Besides binding down the head of the os magnum, it serves to fix also the upper and outer angle of the unciform in the socket formed by the upper row of bones. This is one of the liga- ments which Cruveilhier called glenoid ligaments, but in front there is nothing worthy a special name. u 290 MEDIO-CARPAL JOINT THE ANNULAR LIGAMENT. The dorsal ligaments, Like the palmar, are strengthened by the quantity of fibrous tissue belonging to the sheaths of the tendons which pass over the carpus, as well as by an extension of some of the fibres of the ligaments {i.e., the capsule) of the wrist. Most authors speak of lateral ligaments to this inter- or medio-carpal joint, but these so-called " medio-carpal lateral ligaments" are but prolongations of the lateral ligaments of the wrist. The SYNOVIAL MEMBEANE of the carpus is common to all the joints of the carpus, and extends to the bases of the four inner metacarpal bones. It is therefore very extensive, and besides lining the intercarpal articulation and extending for some distance on the palmar and dorsal surfaces of the os magnimi, it sends two processes upwards between the contiguous surfaces of the three bones of the first row, and three downwards between the contiguous siu'faces of the trapezium and trapezoid, trapezoid and os magnum, and os magnum and unciform. From these latter, further prolongations of the membrane are con- tinued to the four inner carpo-metacarpal joints, as well as to the contiguous surfaces of the bases of the four inner meta- carpal bones. The Anterior Annular Ligament. — The carpal bones are held together, and the ligaments of the several carpal joints are strengthened, by the annular ligament which passes like a strong fibrous bridge from radial to ulnar borders on the palmar aspect, converting the groove formed by the concave anterior surface of the carpus into a canal. It bridges over the super- ficial and deep tendons of the fingers and the long fiexor of the thumb ; the palmaris longns is inserted into it, the flexor carpi ulnaris passes over, and is blended with, it. The flexor carpi radialis tunnels through its outer attaclnnent ; the small mus- cles of the thumb and little finger arise from its surface and lower border ; and the ulnar vessels and nerve, and the cuta- neous branches of the median and ulnar nerves for the palm, pass over it. Above it is continuous with the fascia of the fore- arm, and below with the palmar fascia. Internally it is attached to the inner side of the process of the unciform, and to the base and outer side of the pisiform. The anterior fasciculus of the internal lateral ligament of the wrist runs into it near the pisiform bone. Externally it is inserted (1) into the tip of the ridge of the trapezium and the outer side of the tubercle of the scaphoid ; ARTERIES OF THE MEDIO-CARPAL JOINT. 291 and (2) into the palmax surface of the tubercle and the ridge on the pahnar surface of the scaphoid, as well as into the superior and inner angle of the trapezium and the pahnar surface of the trapezoid. Between these two sets of outer attachments the tendon of the flexor carpi radialis passes, being covered over by the fibres which reach to the outer points of the bones, and being separated by the inner set from the canal or subway common to the flexor tendons of the fingers, the median nerve, and long flexor of the thrmib. From an examination of these attachments, it will be seen that the various bones of the carpus are not only braced together transversely, but also that the extremities of the wavy line of the inUrcar'pal articulation are held together firmly by this anterior annular ligament. Thus the unciform is bound to the base of the pisiform, and, through the anterior fasciculus of the internal lateral ligament, to the styloid process of the ulna ; whilst on the radial side, not only are the trapezium and the trapezoid held in union, but these two bones of the second row are braced by strong and numerous fibres to the scaphoid. This compoiisates for the weakness of parts of the anterior carpal Kgament, which consists, as has been described above, for the most part of fibres which bind the os magnum to the three bones of the first row of the carpus, leaving in great degree the trapezium, trapezoid, and unciform to be securely connected with the bones above by means of this anterior- annular ligament. The Akteeies. — It would be aKke tedious and useless to take each of the carpal articulations separately, and describe in detail the arterial and nerve supplies to them ; nor is it possible to enumerate the muscles in connexion with or moving each separate joint, as their action affects several, if not all, the joints simultaneously. It will be sufficient therefore to refer to the arterial, nerve, and muscular supply of these joints collectively. Blood is conveyed to them through — 1. The anterior and posterior carpal branches of the radial artery. 2. The anterior and posterior branches of the ulnar artery. 3. The carpal branch of the anterior interosseous on their palmar aspect. 4. The recurrent carpal branch of the deep palmar arch. 5. The terminal twigs of both the anterior and posterior inter- u2 292 NERVES AND MUSCLES OF MEDIO-CARPAL JOINT. osseous on the dorsal aspect of the carpus, which usually inoscu- late with the posterior carpal branches of the radial and ulnar. The Nerves. — The nerve supply is derived from — (1) The posterior interosseous nerve; a branch of the great musculo-spii-al trunk, through which, directly or indirectly, all the extensors and supinators of the forearm and hand, as well as the skin over the back of the carpus, metacarpus, and pha- langes are supplied. The posterior interosseous terminates on the back of the carpus in a ganghon, from which filaments pass off to the adjoining ligaments and articulations. (2) The median nerve supplies a few filaments to the radial side of the joint. (3) The ulnar by its deep branch supphes those on the ulnar side of the third interosseous space. The Muscles. — Besides the muscles which pass over the front and back of the carpus to reach the phalanges or the bases of the metacarpal bones, there are in connexion with the carpal bones and their ligaments the small muscles of the thumb and little finger. Thus, taking the several bones in order, the following muscles are attachad to them :- — The scaphoid, semilunar, and cuneiform usually have no muscle connected with them. The PisiFOEM gives insertion to the flexor carpi ulnaris, and origin to the abductor minimi digiti. The trapezium, by its oblique ridge on the palmar aspect, gives origin to the opponens, abductor, and flexor hrevis pollicis. The opponens {i.e., the flexor ossis metacarpi) pollicis and the abductor pollicis are attached, the former to the trapezimn, and the latter to the trapezium and sometimes to the scaphoid on the outer side of the attachment of the annular hgament, as well as to the superficial aspect of that ligament itself. The flexor bre\ds pollicis, by its outer, i.e., its superficial head, is attached to the trapezium on the inner side of the tendon of the flexor carpi radialis and to the anterior edge, as well as the palmar surface of the annular ligament. The trapezoid gives origin to the deep or inner part of the flexor hrevis pollicis. The OS MAGNUM gives origin to the deep or inner part of the flexor hrevis pollicis. The UNCIFORM, by the lower border of its process, gives origin to the opponens and flexor hrevis minimi digiti. MOVEMENTS OF THE MEDIO-CARPAL JOINT. 293 The actions of these several muscles are sufficiently indi- cated by their names. Though arising from the carpal bones and their palmar ligaments, they can in no appreciable sense act upon the carpal or medio-carpal articulations. The Movements. — Movements of the carpal articulations between bones of the same row are very limited indeed, and consist only of slight gliding one upon the other. Yet these gliding movements, slight as they are, give sufficient elas- ticity to the carpus to break the jars and shocks which result from blows or falls upon the hand. The movements of one row of bones upon the other, at the medio-carpal articulation, are much more extensive, especially in the direction of flexion and extension, so that the hand enjoys a greater range of these movements than is permitted at the wrist-joint alone. In the wrist-joint extension is more free than flexion, owing to the greater extent of the articular surface upon the dorsal than upon the palmar aspect of the scaphoid, lunar, and cunei- form bones. But this limitation of flexion is compensated for by the greater freedom of flexion than of extension at the medio-carpal joint, and by the flexion permitted at the carpo- metacarpal joint, so that on the whole the degree of flexion of the hand is greater than that of extension. Flexion and extension are not the only movements which are permitted at this joint. A slight amount of lateral motion, i.e., abduction and adduction, accompanied with a limited degree of rotation, takes place. This rotation of the hand consists in a rotation of the head of the os magnum, and of the superior and outer angle of the unciform in the socket formed by the three bones of the upper row, and in a gliding forwards and backwards of the trapezium and trapezoid upon the scaphoid. In addition to the hgaments, the wavy outline of the arti- cular surfaces, and the extent and variety of shape of the apposed facets, render this joint very secure. Thus dislocation of the second row forwards is prevented by the trapezium and trapezoid resting on the posterior, i.e., dorsal aspect of the scaphoid, and by the cuneiform winding forwards towards the anterior side of the inner surface of the unciform ; and dis- location of this same row backwards is resisted by the forward and downwards inclination of the socket of the scaphoid, lunar, and cuneiform, wMch receives the os magnum and unciform. The movements at the medio-carpal joint are produced in 294 MOVEMENTS OF THE MEDIO-CARPAL JOINT. the same way, and by the same muscles, as the corresponding movements of the. wrist. Thus flexion results from the con- traction of the flexor carpi ulnaris and flexor carpi radialis ; and by the pahnaris longus, which being inserted into the anterior annular ligament, acts directly in bending forwards the hand, as well as in tightening the palmar fascia. It may be mentioned here, however, that probably one of the chief uses of the palmaris longus is to hold off the annular ligament from the flexor tendons of the fingers whilst they are them- selves in action. When these flexors are resisted in, or have completed, their action upon the fingers, they have the effect of flexing the medio-carpal as well as the wrist-joint. Exten- sion is produced by the radial and ulnar extensors of the carpus ; as well as by the extensors of the digits, as soon as their action on the fingers is completed or resisted. As in the case of the wrist-joint, so of the medio-carpal, if the flexor and extensor of the radial side act together (those of the ulnar side not acting), the joint yields a little towards the radial side, and abduction is increased. When the flexor and extensor of the ulnar side act together (those of the radial side not acting), the joint yields a little towards the ulnar side, and adduction is increased. Bearing in mind the mobility of this medio-carpal articula- tion, and that of the carpo-metacarpal joint, we see at once the reason for the radial and idnar flexors and extensors of the carpus being prolonged downwards to their insertion into the base of the metacarpus ; for thus they produce the combined effect of motion in the same direction at each of three trans- verse articulations — (1) the wrist; (2) the medio-carpal; (3) the carpo-metacarpal. The elasticity conferred upon the carpus by the several joints above described, the sUght ghding movements which take place between the several bones, the increased range of motion enjoyed by the hand through the medio-carpal articulation, and at the same time the great strength of the carpus as a whole, owing to its numerous and strong ligaments, are not the only features of interest and importance in connexion with the carpus. The variously moulded, obhquely inchned articular surfaces of the several bones, and the way in which any one is united to three or more others, serves the very important pur- pose of breaking shocks and dispersing the force of them in . CARPO-METACARPAL JOINTS. 295 different directions amongst tlie carpal bones themselves, and thus to all parts of the lower end of the radius. If it were not for this provision, there would be a constant and great liability to injury of the wrist and lower end of the forearm. This subject will be again referred to after the other joints of the hand have been considered. Carpo-metacarpal Joints, or the Articulations of the Carpal with the Metacarpal Bones. Class, Diarthrosis. Subdivision, Arthrodia. As three of the bones constituting the first row of the carpus are so connected that they present one continuous surface for articulation with the radius and triangular fibro- cartilage, and another for the united superior surfaces of the second row; so the inferior articular surfaces of three of the bones of this second row present a combined sur- face for the four inner metacarpal bones. The trapezium presents a distinct and separate saddle-shaped surface for the base of the metacarpal bone of the thumb. We will first examine the articulation between the trapezium, trapezoid, os magnum and unciform above, and the four inner metacarpal bones below ; and then the carpo-metacarpal joint of the thumb. The Bones. — The trapezium presents upon its internal surface two articular facets, divided by a projecting ridge. The upper of these is the larger, ajid articulates with the trapezoid ; the lower is small and flat, looking inwards for articulation with a small facet on the outer side of the ter- minal carpal surface of the second metacarpal bone. The trapezoid articulates by its inferior surface with the second metacarpal bone. The surface is concave from the palmar to the dorsal surface, and convex from side to side. It sometimes articulates also with the extremity of the third metacarpal bone by a narrow facet at its internal part near the dorsum. The OS magnum articulates by its inferior surface with three metacarpal bones, and is divided accordingly by two ridges into three facets. The largest of these is the central one, wliich extends the whole depth from dorsal to palmar surface, and is limited on the inner side by the border of the bone in the greatest part of its extent, and on the outer side by the ridge 296 CARPO-METACARPAL JOINTS. separating it from the outer facet. It is convex for a short space posteriorly, concave in chief part and . anteriorly ; it articulates with the third metacarpal bone. The outer facet is also of large size ; it is concave, and inclined a little outwards, and articulates with the second metacarpal bone. The inner facet is not larger than a melon seed, is situated at the dorsal corner of the sm-face, is incHned a little inwards, and articidates with the fourth metacarpal bone. The unciform, by its inferior surface, articulates with two, viz., the fourth and fifth, metacarpal bones, and for this reason is divided by an antero-posterior ridge into two facets of nearly equal size, each of which is concave fi'om before backwards. The outer looks directly downwards, and receives the fourth metacarpal bone ; the inner, often a little larger than the outer, and convex from side to side, inclines a little inwards to articulate with the fifth metacarpal bone. The Metacarpal Bones. — The superior or carpal extremity, i.e., the base of each of these bones, has five surfaces, and is expanded. Somewhat cuneiform, it is wider at the dorsum than in front. By its superior sui'face it articulates with the carpus ; its anterior and posterior surfaces are rough and uneven, for the attachment of ligaments ; its internal and external surfaces are either free, or facetted to articulate with one another. The second inetacaripal hone is at its carpal end prolonged upwards internally, and its terminal or superior surface is divided into three facets. for as many carpal bones. The outer is a flat square-shaped surface, situated near the dorsum, and inclined outwards and forwards for the trapezium ; the inner is narrow, and inclined inwards for the os magnum ; whilst the middle one, the largest, articulates with the trapezoid. The third r)ietacarpal hone is prolonged upwards externally, and sometimes reaches far enough to articulate with the posterior and internal angle of the trapezoid, notwithstanding the second articulates with the os magnum at the palmar aspect and for some distance backwards, towards the dorsum. By its terminal' carpal sui'face it articulates with the middle facet on the inferior surface of the os magnum. The fourth metacarpal hone presents on its terminal carpal surface two very unequal facets ; one, situated externally and close to the dorsum, articulates with the minute internal facet LIGAMENTS OF THE CARPO-METACARPAL JOINTS. 297 on the inferior surface of the os magnum ; the other is large, and articulates with the unciform. The fifth metacarpal hone has a nearly square-shaped articular surface, convex from dorsum to palm, and concave from side to side, and directed a little outwards for articulation with the innermost facet on the inferior smiace of the unciform. The line of the carpo-metacarpal joint of the fingers is nearly plane, but has a slight convexity downwai'ds or towards the metacarpus. The base of the second bone, i.e., of the metacarpal of the index-finger, is firmly locked in its position owing to the projection downwards of the inner inferior angle of the trapezium, and upwards of the outer angle of the base of the third metacarpal bone. In this respect it resembles the second metatarsal bone of the foot. The fifth metacarpal bone is set off at a slight angle from the other three, and like the bone of the thumb (the first) its base is concavo-convex, so that it enjoys the same kind of movements, but more limited in degree. The base of the third bone is also very securely fixed by the upward pro- jection of the outer side of its base into an angle formed by the trapezoid and os magnum. The Ligaments. — Dorsal, palmar, and interosseous ligaments connect the bones of the carpus with the metacarpus. The Dorsal Ligaments. — Three dorsal Kgaments pass to the second bone ; one from each of the carpal bones, with which it articulates — viz., trapezium, trapezoid, and os magnum. Two dorsal bands pass from the os magniun to the third meta- carpal bone. Two dorsal ligaments extend from the fourth metacarpal bone to the carpus — ^viz., one to the os magnum, and the other to the unciform. Sometimes only a single dorsal ligament attaches this bone to the carpus, and that passes from the unciform. The fifth has a single ligament, and that connects it with the unciform. The Palmar Ligaments. — A strong ligamentous band connects the second metacarpal bone with the trapezium, internal to the ridge for the annular ligament. It is covered by the sheath of the flexor carpi radialis. Three ligamentous bands connect the third bone of the metacarpus with the carpus ; one extends obliquely outwards to the trapezium, a middle one passes vertically upwards to the 298 iMUSCLES OF THE CABPO-METACARPAL JOINTS, OS magnum, and an internal band passes over the carpal end of the fourth metacarpal bone and its ligament, and is inserted into the unciform and the fifth metacarpal bone. One ligament connects the fourth metacarpal bone with the unciform. One ligament, and that a feeble one, connects the fifth bone with the unciform ; fibres extend all around the inner aspect of this articulation from dorsal to palmar surface. It is further strengthened on the palmar aspect by the ligamentous or rather tendinous fibres (flexor carpi ulnaris) prolonged from the pisiform bone to it, and by the strong inner slip of the ligament of the third metacarpal bone ; and on the dorsal aspect, by the tendon of the extensor carpi ulnaris. TJie Interosseous Ligament.— -Tins, is limited to one part of the articulation, and intervenes between the two inner meta- carpal bones and the third metacarpal. It consists of short strong fibres, connecting together the contiguous angles of the unciform and os magnum, and the fourth and tlnrd metacarpal bones towards their palmar aspect. Besides the above ligaments, there is a short but thick and strong ligament connecting the edge of the trapezium with the outer border of the base of the second metacarpal bone. It is especially thick immediately below the facet on the trapezium for the second bone. It helps to separate the carpo-metacarpal joint of the thumb from the common carpo-metacarpal articu- lation, and serves to close in the radial side of the common carpo-metacarpal joint itself. The SYNOVIAL MEMBEANE is a Continuation of that of the medio-carpal and small carpal articulations. Occasionally there is a separate membrane for that part of the carpo-meta- carpal joint formed by the unciform and the two inner meta- carpal bones. The joint between the fourth metacarpal bone and the os magnum is hned by the general synovial membrane. This is important surgically, as it shows the danger to the whole carpal synovial sac of interfering with the base of the fourth bone. The Muscles.— The muscles in connexion with this articu- lation, besides the flexors of the fingers which pass over them to their insertion into the phalanges, are the flexors and extensors of the carpus, and the following small muscles of the thumb and little finger : — 1. The deep portion of the flexor brevis pollicis arises partly SECTION SHOWING THE SYNOVIAL CAVITIES OF THE WRIST & HAND wrist [if^H/fjn XKr ->yuiL ct^cfily of Iihro cny-tilc int UnJ>: lioj:oi /vftst intt-fosse.ovs b MUSCLES OF THE CARPO-METACARPAL JOINTS. 299 from the base of the tliird metacarpal bone, as well as from the palmar sm^face of the os magnum and the trapezoid. 2. The adductor pollicis arises from the carpal extremity, as well as from the whole length of the shaft of the third meta- carpal bone, on its palmar aspect. 3. The opponens minimi digiti is inserted into the whole length of the palmar aspect of the fifth metacarpal bone. Both the other small muscles of the little finger, the abductor and flexor brevis minimi digiti, pass over the joint, and in- directly act upon it, though they are not attached to a meta- carpal bone. The latter arises from one of the bones of the carpo-metacarpal articulation, viz., the unciform. The abductor arises from the pisiform. The interossei muscles are also connected with the meta- carpus, but have no relation to this articulation. Of the muscles which have a direct action on the articu- lation : — {a) The flexor carpi radialis is inserted into the base of the second and third, i.e., metacarpal bones of the index and middle finger, (b) The flexor carpi ulnaris, into the base of the metacarpal bone of the Httle finger, as well as into the pisiform bone, (c) The extensor carpi radialis longior is inserted into the dorsal aspect of the base of the second metacarpal bone on its radial side, {d) The extensor carpi radialis brevior into the dorsal aspect of the carpal end of the third metacarpal bone on its radial side, {e) The extensor carpi ulnaris into the base of the meta- carpal bone of the fifth, or little finger, on its dorsal aspect. Thus it will be observed that the bone of the ring-finger only is without either flexor or extensor tendon ; that the middle finger bone has the short radial extensor, but no flexor ; and that the index and httle fingers are each provided with both a flexor and extensor muscle. The muscles, though acting most freely upon those parts at which they are attached, yet act upon the whole carpo-metacarpal joint, owing to the intimate union of the bases of the four metacarpal bones with one another. After producing their effect on this joint, they continue in action to move, first the medio-carpal, and second the radio-carpal, articulations. The opponens minimi digiti acts directly on the carpo-metacarpal joint of the little finger, making this 300 MOVEMENTS OF THE CARPO-METACARPAL JOINTS. finger antagonistic to tlie rest, just as the opponens pollicis makes tlie thumb. Owing to the close connexion of the bases of the metacarpal bones, it also, by bending the little finger, affects the whole carpo-metacarpal articulation. It increases the hollow of the carpus, and assists in forming what is called " Diogenes' drinking-cup." The Movements of the Caepo-metacaepal Joints. — The portion of the carpo-metacarpal joint, formed by the fifth metacarpal and unciform bones, approaches in shape and mobility somewhat to the first or thumb carpo-metacarpal joint. It has a greater range of forward and backward move- ment than the tlu-ee others, but its lateral motion is nearly as limited as theKS. This part of the joint is protected above in front by the process of the unciform bone, which limits its flexion. The lateral motion towards the ulnar side is checked by the strong palmar ligamentous band which unites it to the base of the third metacarpal bone ; and by the strong trans- verse ligament at the heads of the bones, to be presently described. The motion of the second and third and fourth metacarpal bones is very limited indeed, especially that of the middle and ring fingers, to which no long fiexor muscle is attached. It consists almost entirely of slight forward and backward gliding movements of the metacarpal on the carpal bones, i.e., of flexion and extension. These movements are produced by the same muscles, and in the same way, as the flexion and extension at the medio- and radio-car23al joints, i.e., directly by the muscles inserted into the bases of the metacarpal bones, and indirectly through the muscles inserted into the phalanges. Owing to the close connexion of the bases of the metacarpal bones, the ■contraction of the flexor and extensor carpi muscles affects the whole carpo-metacarpal articulation by their actions upon the particular bones into which they are inserted. Abduction and adduction of the four metacarpal bones toge- ther may be spoken of in the same way as abduction and adduction of the vn.ist, i.e., abduction as lateral movement towards the radial side, adduction as lateral movement towards the ulnar side. This is not what is meant by abduction and adduction of the fingers, which is from and to the middle line of the hand through the middle finger. Abduction is prevented by the locking or impaction of the CARPO-METACARPAL JOINT OF THE THUMB. 301 second bone against tlie inner surface of the trapezium, and the flexor and extensor carpi radialis restore the metacarpus after it has been moved towards the uMa, i.e., adducted by the flexor and extensor carpi uhiaris. Adduction is permitted to a moderate degree^ and is favoured by the inward and upward slope given to the unciform and fifth metacarpal bones. Besides these angular movements, a slight amount of sliifting or gliding of the fourth and fifth metacarpal bones takes place at this joint, when the concavity wliich they present towards the palm is increased, as in deepening the hollow of the hand to form the " cup of Diogenes." This effect is produced by the simultaneous action of the flexor carpi ulnaris and opponens mirn'mi digiti, acting on the fifth bone, whilst the flexor carpi radialis pulls forwards and steadies the radial side of the metacarpus. The movements necessary for the formation of " Diogenes' cup" are complex, and involve many muscles ; for whilst the metacarpus and the first phalanges have to be slightly bent, and the thumb and little and ring fingers arched towards the centre of the hand, the phalanges must be kept extended upon each other in order to make the " cup" complete ; the depth of which varies inversely with the flexion of those bones. The interossei and lumbricales, therefore, must be in action. The degree of flexion or extension at the wrist is indifferent to its formation. The Carpo-metacarpal Joint of the Thumh. Class, Diarthi'osis. Subdivision, Arthrodia. The divergence of the first metacarpal bone from the line of direction of the other four contrasts very strongly with what is found to be the case in the foot, and is the gxeat peculiarity which characterises the hand. Wlien the hand is fully ex- tended, the angle which the thumb forms with the vertical line through the middle finger is between 50° and 55°. To this divergence of the thumb is due the facility of opposing it to each and all the fingers, and the great power of the hand as an organ of prehension and of varied usefulness. The length of the thumb in man distinguishes his hand from that of the quadrumanous animal, in which the short weak 302 CAEPO-METACARPAL JOINT OF THE THUMB. thumb barely reaches to the level of the head of the meta- carpal bone of the forefinger. The chief feature which distinguishes this joint from the other carpo-metacarpal articulations, from which it is quite detached, is its great moljility. In many respects it resembles the sterno-clavicular joint ; but there is this difference — that the articular surfaces of the two bones are more equal in size, and more evenly adjusted to one another, and there is no fibro- cartilage separating them. The bones are the trapezium and the first metacarpal. The trapezium, which is situated to the radial side, and pro- jects a little in advance of the other bones in the second row of the carpus, presents on its external and inferior aspect a large articular surface for the metacarpal bone of the thumb. This facet is oval in shape, with its long axis obliquely trans- verse, in which direction it is concave ; from before backwards it is conve:^. The first metacarpal hone is the shortest and tliickest of all, is placed on a plane anterior to the other four, and is so inclined that its palmar surface looks somewhat inwards to- wards the median line of the hand. Owing to its divergence from the other four bones, the space between it and the second metacarpal bone is larger and more distinctly triangular. Its carpal extremity has not the wedge shape of the succeeding three bones, and is rather wider on the palmar than the dorsal aspect. Its articular facet for the trapezium occupies the whole of its superior terminal surface, and is concave from behind forwards, and convex from side to side, just the con- verse of the facet on the trapezium to which it is adapted, and on which it moves freely. It has no lateral articular facets, being separated by a distinct interval from the base of the second metacarpal bone ; but on its outer side it presents a rough tubercle nearer the palmar than the dorsal aspect for the insertion of the extensor ossis metacarpi pollicis. The Ligaments. — The ligamentous apparatus of this joint consists of a capsule, the fibres of which are thicker and more numerous in the situations at which there is the greatest strain. The bundles or bands of fibres of which this capsule is formed pass from the trapezium around the margin of the saddle-shaped articular facet for the thumb to the sides, dorsum, and palmar surface of the carpal end of the first meta- ITS CAPSULAE LIGAMENT AND MUSCLES.. 303 carpal bone. They are stronger upon the dorsal than on the palmar surface, for here the joint is less protected by muscles than elsewhere. They are not tense enough to hold the bones in close contact, so that whilst they restrict they do not pre- vent motion in any direction. Some anatomists have described this capsule as made up of four separate ligaments — viz., dorsal, palmar, and external and internal lateral — but this is quite unnecessary. It is sufficient to observe that the dorsal band is stronger than the palmar, and limits flexion (in this con- clusion I agree with Weitbrecht, and dissent from Cruveilhier) whilst the palmar limits extension ; that the internal lateral is stronger than the external to limit abduction, whilst the external lateral Kgament limits adduction of the thumb. The SYNOVIAL MEMBRANE of tliis joint is lax, like the capsule, and is quite distinct from the general synovial membrane of the carpal and carpo-metacarpal articulations. The Muscles. — There are several muscles to be considered as acting on this joint, and yet only three are attached to the first metacarpal bone ; these are the (1) extensor ossis metacarpi pollicis, inserted into the outer or radial side of its base. (2) The opponens (or flexor ossis metacarpi) pollicis, inserted into the whole length of the metacarpal bone on its radial side ; and (3) the abductor indicis, which arises from the upper half of the ulnar border of the first metacarpal bone, and from the os trapezium. The trapezium gives origin to the abductor and opponens and flexor brevis pollicis, as well as to the abductor indicis. All the muscles, however, which are attached to the phalanges of the thumb move also the metacarpal bone ; for it is a rule, that in proportion to the number of joints that a muscle passes over, its offices must be more numerous ; thus, e.g., the flexor profundus digitorum not only moves the third phalanx on the second, the second on the first, and these again on the metacarpal bone, but it likewise flexes the carpo-metacarpal, medio-carpal, and radio-carpal articulations ; whilst the flexor subKmis, which bends the second joint of the finger on the first, and the first on the metacarpal bone, flexes all the other transverse carpal joints, including the wrist, and even bends the forearm on the arm at the elbow. Bearing this law in mind then, and remembering that a muscle acts primarily upon the joint formed by the bone into 304 CARPO-METACAKPAL JOINT OF THE THUMB. wMcli it is inserted, and secondarily upon the joints above it, i.e., nearer to its origin, we may gronp the muscles which act ^^pon the carpo-metacarpal joint of the thumb as flexors, extensors, abductors, and adductors. Flexors. — The opponens (flexor ossis metacarpi) pollicis acts directly upon the metacarpal bone, drawing it forwards at the same time that it abducts. The flexor brevis pollicis acts directly on the first phalanx, to draw it towards the palm. The flexor longus pollicis acts primarily upon the terminal phalanx. The abductor pollicis acts primarily upon the first phalanx. The adductor pollicis acts primarily upon the first phalanx, and adducts while it flexes. Extensors. — The extensor ossis metacarpi pollicis acts di- rectly upon the metacarpal bone, and abducts chiefly, though it extends, i.e., draws backwards, the bone at the same time. The extensor primi internodii pollicis acts, as its name indicates, primarily on the first phalanx, and abducts at the same time it draws backwards the thumb. The extensor secundi internodii pollicis acts primarily on the terminal phalanx, and is an adductor as well as an extensor. Abductors. — The extensor ossis metacarpi pollicis, the ex- tensor primi internodii pollicis, abduct and draw backwards at the same time. The abductor and opponens pollicis abduct and draw forwards at the same time. Adductors. — The adductor and inner portion of the flexor brevis pollicis adduct and draw forwards at the same time. The abductor indicis, when its action on the index -finger is pre- vented, adducts the thumb by pulling on the metacarpal bone. The extensor secundi internodii pollicis is also an adductor. The Movements. — The motion of this joint is regulated by the shape of the articular surfaces of the trapezium and first metacarpal bone more than by its ligaments. It consists of flexion, extension, abduction, and adduction, i.e., of forward, back- ward, outward, and inward movements respectively, and of circumduction, but no rotation. In flexion and extension the metacarpal bone slides to and fro upon the trapezium ; in abduction and adduction it glides from side to side, or, more correctly, revolves upon the antero-posterior axis of the joint. UNION OF METACARPAL BONES WITH ONE ANOTHER. 305 The thumb can be drawn away from the fingers both when they are flexed upon the palm and when they are extended widely open. It can be brought into contact with the tip of each one singly, or with the tips of all collectively. ' It can be made to touch any part of the palmar or radial surfaces of any of the fingers separately, and can be brought down firmly upon the dorsal aspect of the first, second, or third when flexed, as in the formation of the fist. The power of opposing the thumb to any of the fingers is due to the forward and inward obliquity of its movement of flexion, which is by far the most extensive movement of the thumb. The motion of adduction is limited on account of the proximity of the second metacarpal bone ; that of abduction is very free. The movement of the trapezium upon the rest of the carpus somewhat increases the range of all the movements of the thumb. The Union of the Metacarpal Bones with one another. Class, Diarthrosis. Subdivision, Arthrodia. The metacarpal bone of the thumb is not connected with any other metacarpal bone. Those of the index, middle, ring, and little fingers are in actual contact at their bases, and the joints between them are furnished with small prolongations of the common or general synovial membrane of the carpus. They are held closely and firmly together by dorsal, palmar, and interosseous Kgaments, which pass transversely from one bone to the other, so as to form them into one continuous surface which articulates with the carpus at the carpo-metacarpal joint. A transverse ligament binds together their inferior extremities, or heads. The Bones. — The second metacarpal lone has upon the inner sm-face of its carpal end two flat facets, placed one before the other to articulate with corresponding surfaces on the third metacarpal bone. The third hone has upon each of the lateral surfaces of its carpal end two little facets — one near the dorsum, the other near the palmar aspect, and separated by a deep groove (that on the inner side being the deeper) to articulate with similar facets on the adjacent bones. Sometimes these two small facets on one or both lateral surfaces are run together, so as to form but a single facet for the adjacent bone. X 30(j UNION OF METACARPAL BONES WITH ONE ANOTHER. The fourth hone presents on its outer surface two oval facets, separated by a deep narrow groove ; and on its inner aspect a semicircular and slightly concave articular facet for the fifth metacarpal *bone. The Jifth hone has on its outer lateral surface a narrow semicircular convex articular facet for the fourth bone ; and on its inner lateral surface a tubercle for the attachment of the extensor carpi ulnaris. The Ligaments. — The dorsal ligaments are layers of variable thickness of strong short fibres, which pass transversely from bone to bone. They fill up the irregularities on the dorsal surface of the carpal ends of these bones, and the fibres are therefore more numerous opposite the depressions and little hollows on the bones. The ipalmar ligaments are transverse layers of ligamentous tissue passing from bone to bone. They cannot be well defined from the other ligaments and fibrous tissue covering the palmar surface of the bones. The interosseous ligaments pass between the apposed surfaces of adjacent bones, and are attached on the distal side of the lateral articular facets of each bone, so as to close in the synovial cavities on this aspect. Where there are two articular facets on one side, the fibres of this ligament extend upwards in the interval between them, so as to connect the bones nearly as far as their carpal terminal surfaces. The interosseous ligament between the fomth and fifth bones is weaker than the rest, and is nothing more than a fibrous covering to the synovial membrane on its lower aspect. Connexion of the Heads of the Metacarpal Bones. The digital extremities of the metacarpal bones are con- nected together on their palmar aspect by what is called the transverse ligament. Tliis consists of three short narrow bands of fibrous tissue, one uniting the ulnar side of the second bone with the radial side of the third, another uniting the ulnar side of the third with the radial side of the fourth, and the third passing between the ulnar side of the fom-th and the radial side of the fifth. They are each rather more than a quarter of an inch in depth, and rather less in width from side to side. They limit the distance to which the metacarpal bones can be separated in such actions as grasping, or in the spreading out METAGARPO-PHALANGEAL JOINTS OF THE FINGERS. 307 of the liand, as when the weight of the trunk is borne upon it. They do not limit the range of separation of the fingers, which depends on the degree of lateral movement permitted at the metacarpo-phalangeal joints. The bands are continuous above with the fascia covering over the interosseous muscles, ■and are connected below with the areolar tissue beneath the skin of the web of the hand. They are on a level with the front surfaces of the bones, and are blended with the other structures at the sides of the metacarpo-phalangeal joints, viz., with the edge of the fibro-cartilage in front and the lateral ligament at the sides of the joint, and with the sheath of the tendons where it springs from the line of union of the fibro- cartilage with the lateral ligament. Over the front of each band a lumbrical muscle passes to its insertion, and the digital nerves and arteries travel on to their destination. Behind each band the interosseous muscles of the corresponding space pass to their insertion. The bands are not in direct relation with the flexor tendons of the fingers ; for as the tendons pass over the front of the joints while these transverse bands of ligament are blended along the line of union of the fibro- cartilage and lateral ligament, they are consequently in the interspaces between the tendons. There is no transverse band connected with the thumb. The adductor and flexor brevis pollicis and the ligaments of the carpo-metacarpal joint set the limits to the range of abduction enjoyed by the thumb. The Metacarpo-jpludangeal Joints of the Fingers. Class, Diarthrosis. Subdivision, Ginglymus. The metacarpo-phalangeal joint of the thumb differs sKghtly from that of the fingers, and will therefore be separately described. Those of the fingers resemble one another. The first phalanx is articulated with the head of a meta- carpal bone, and united to it by means of three ligaments. The Bones. — ITie Metacarpal Bone. — The head or inferior extremity of each of the metacarpal bones is convex from side to side and from before backwards ; smooth, and in the recent state covered with cartilage, for articulation with the base of the first phalanx. This articular surface extends much further on the flexor, i.e., palmar aspect, than on the dorsal. On each lateral surface is a deep depression bounded towards the x2 308 METACAUPO-PHALANGEAL JOINTS OF THE FINGERS. dorsum by a small tulDercle. To both tubercle and depression the lateral ligament is attached. The dorsal surface is smooth and flat. The anterior surface presents two little tubercles, between which the head is slightly excavated, and along this concavity the flexor tendons pass. The antero-posterior diameter of the head is larger than the transverse. The Phalanx of the First Row. — Each of these bones pre- sents at its base, i.e., upper end, a shallow articular concavity with which the rounded head of the metacarpal bone articulates. This concavity is not nearly deep enough for the head of the metacarpal to be received into it, but it is made deeper in the recent state by a glenoid ligament which is very firmly attached to the anterior border of this oval-shaped facet. Its transverse diameter is greater than the antero-posterior — the reverse being the case "v^dth the metacarpal bone, and hence the great extent of lateral motion allowed by the joints. The Ligaments. — These bones are connected by two strong lateral ligaments and by an anterior fibro- cartilage ; whilst posteriorly the joint is covered in by the expansion of the extensor tendon, and by some loose areolar tissue passing from the under surface of the tendon to the bone. Each joint has its own synovial membrane. The Glenoid Ligament. — The anterior fibro- cartilaginous plate was called by Cruveilhier the glenoid ligament, as it seems more intended to increase the depth of the phalangeal articular facet than to unite the two bones together. It is much more firmly attached to the margin of the phalanx than to the metacarpal bone. Indeed, it is only very loosely connected to the palmar surface of the latter by some lax areolar tissue which covers over the synovial sac, which here is prolonged some little distance upon the shaft of the bone. Laterally, it is intimately blended with the lateral Kgaments as well as with the transverse bands connecting the heads of the metacarpal bones with one another. Like the sesamoid bones at the corresponding joint of the thumb, whose place it takes in the fingers, it serves to prevent backward dislocation ; but when dislocation does occur, it increases the difficulty of reduc- tion, for owing to its much firmer connexion with the phalanx it follows it backwards behind the head of the metacarpal bone. A sesamoid bone occasionally exists at the inner border of the joint of the little finger. The Lateral Ligaments. — These are very strong, and firmly METACARPO-PHALANGEAL JOINTS OF THE FINGERS. 309 bind together the ends of the bones. Each is attached above to the lateral tubercle near the dorsum, and to the depression in front of the tubercle of the metacarpal bone. From this the fibres pass forwards as they descend, and spread out widely on the side of the base of the phalanx. Their anterior fibres are connected with the fibro-cartilaginous plate, and their posterior fibres blend with the tendinous expansion at the back of the joint. The SYNOVIAL MEMBRANE lines the joint, and forms a loose capacious sac, more especially over the head of the metacarpal bone in front, and the base of the phalanx beliind. It is pro- tected on the sides by the lateral hgaments ; in front, by the cartilaginous plate, and by some loose cellular tissue attaching the plate to the palmar surface of the metacarpal bone ; and behind, by the expansion of the extensor tendon, and by very loose tissue holding the tendon down to the bone above and below the joint. Aeteeies. — Little branches of arteries penetrate the tissues around the joint, and reach the synovial membrane. They come from the superficial digital branches, as well as from the anterior interosseous vessel^ which lie upon the front of the interosseous muscles. Arterial arches are sometimes formed on the ends of the bones by the anastomoses of the minute vessels of the two sides. ISTeeves. — These are derived from the cutaneous digital branches, or from the small branches for the interosseous muscles. Muscles. — The muscles in connexion with the metacarpo- phalangeal joints are, (1) the superficial and deep tendons which pass over the concave anterior surface of the fibro- cartilaginous plates in front of the joint. The sheaths of these tendons are attached laterally to the margins of the plates, and to the lateral and transverse ligaments where they meet toge- ther. (3) The interosseous muscles pass behind the transverse ligament, partly to be inserted into the side of the base of the first phalanx, and partly into the expansion of the extensor tendon. (3) The lumbrical muscles pass over the front of the transverse bands to their insertion into the radial side of the expansion of the extensor tendon at the base of the metacarpal phalanx. (4) The tendon of the long extensor muscles. The four lumbricales and the seven interossei muscles have each a double action, for while they bend the first phalanx on 310 METACARPO-PHALANGEAL JOINTS OF THE FINGERS. the metacarpal bone, they at the same time extend the second and third phalanges on the first and second. The lumbricales do this by passing over the front of the transverse ligament to their insertion into the tendinous expansion ; and the interossei by ha\dng some fibres inserted directly into the side of the base of the first phalanx, which therefore act directly upon it, while others blend with the tendinous expansion. Bearing in mind then the statement made above, that if a muscle passes over a joint part of its ofl&ce is to act upon that joint, we may group the muscles of the metacarpo-phalangeal joints into : — Mexors : The long flexors (deep and superficial) i.e., flexor sublimis and profundus digitorum ; the lumbricales ; and the interossei and flexor brevis minimi digiti. Extensors : The extensor communis digitorum, extensor indicis, and extensor TniuiTni digiti. Ahchictors. — The four dorsal interossei abduct the index, middle, and ring fingers : the abductor minimi digiti acts on the little finger. Adductors. — The three palmar interossei are adductors of the index, fourth, and Httle fingers. The Movements. — Flexion, extension, abduction, and adduc- tion, and the combination of these — viz., circumduction — are all permitted at these joints. Flexion is the freest movement, and may be continued until the phalanx is at a right angle with the metacarpal bone. It is on this account that the articular surface of the head of the metacarpal bone is prolonged so much further on the palmar aspect, and that the synovial sac is here so ample and loose. Extension is the most limited of the movements, and can only be carried to a little beyond the straight Hne. Abduction and adduction are pretty free, but not so free as flexion. As a rule, although these movements can be executed separately, flexion is associated with adduction, and extension with abduction. This may be proved by simply opening the hand, when the fingers involuntarily separate a little from one an- other as they become extended ; so they as naturally close together in bending the fingers on the palm. Circumduction being composed of the four angular move- ments, its degree of freedom depends upon the range of these several movements individually. Doubtless the abduction and adduction and circumduction enjoyed by these joints is due to the loner axis of the articular facets of the two bones of the JOINTS OF THE FINGERS ^ THUMB SEEN FROM THE f-ALMAR. SURFACE. Nuimerous bloodvessels are- s&en, supplying joints and, liafcuntent . i '''M' ^^ marijvn- of fiiirous sheath tbf -Flexor tefUJLans ~'- Jt'ihro caraLoiges ove?- /:■>'-, ir (tF metaxxcrpo ■phaloMygeaL cu-.d phoiZajvaeaZ lov'Vts. Se-sa.nu.>idy bones ai> tmtoiccuyo phcdcuiaeal joint SaSft^^- AJitenor Uqai'i'terii cwb loncjvtiUboUnaMy Suhway ibr passcLge of fl^exxjr ti riilons . A^ilensma^L AcL (td- not . ffest^^ METACARPAL-PHALANGEAL JOINT OF THE THUMB. 311 joint being at right angles to one another, so that from the shape of the bone the joint assumes almost an enarthrodial character. The anterior fibro-cartilage, it is true, increases the cup-like articular facet of the phalanx which plays upon the rounded head of the metacarpal bone ; and for this reason it was called glenoid ; but the very firm connexion of the cartilage with the phalanx and its loose attachment to the metacarpal bone, increase the hinge-hke nature of the articulation, and suggest to our mind the olecranon process of the ulna in the security it affords against dislocation, and the purpose it serves in keeping the moving surfaces of the bones in due relation to one another. If there were permitted at these joints any appreciable amount of rotation round the long axis of the digits, they would be properly described as the ball-and-socket joints, notwithstanding that the bone which forms the "socket" moves upon the bone which presents the " ball." Some anato- mists indeed have spoken of the metacarpo-phalangeal joints as enarthroses. The Metacarpo-phalangeal Joint of the Thumb. Class, Diarthrosis. Subdivision, Ginglymus. The Metacaepal Bone. — The inferior extremity of the meta- carpal bone of the thumb differs very materially from the corresponding ends of the metacarpal bones of the fingers. Its terminal and articular surface is less convex, especially in the transverse direction ; its widest measurement is from side to side instead of from before backwards ; the edge of the arti- cular sm-face is raised, and irregular on the palmar aspect, and there is on each side of this aspect of the facet a little smooth surface for the sesamoid bones, which take the place of the fibro- cartilage found on the front of the articulations of the fingers. The depressions on the lateral surfaces are well-marked, but not so deep as those on the corresponding bones of the fingers, and they do not encroach so much upon the articular facet. The First Phalanx of the Thumb. — The base of this bone resembles more the base of the second than that of the first phalanx of the fingers, so that the anterior edge of its articular surface is prolonged a little in the centre, so as to form a little process which intervenes between the sesamoid bones, and pre- vents any lateral motion, more especially during flexion. The Ligaments. — In place of a plate of fibro-cartilage there 312 METACARPAL-PEALAKGEAL JOINT OF THE THUMB. are in tliis joint two small sesamoid bones, enveloped in liga- mentous filjres on all sides, excepting that wMch faces towards the interior of the joint. The lateral ligaments resemble the corresponding Hgaments in the joints of the fingers, and pos- teriorly the capsule is completed by some ligamentous fibres passing between them. Tlie Sesamoid Bones. — These are situated one on each side of the middle line of the palmar surface of the thumb. On their sides which do not face one another they are connected with the anterior fibres of the lateral hgament, some of which are inserted into them. On the sides facing one another, they are connected together by some very strong thick fibres having a transverse direction, and over the front aspect of which the flexor tendon plays. Above, they, as well as their transverse connecting fibres, are connected with the front of the metacarpal bone ; and below some very strong but short fibres pass off from these to the front of the base of the phalanx. Anteriorly they give attachment to the tendons of the short muscles of the thumb, and over their surface the various ligamentous fibres blend. Posteriorly they are smooth and facetted to play upon the little articular tubercles which are prolonged upwards on the palmar surface of the head of the metacarpal bone. They provide a shifting leverage for the tendons of the flexor brevis poUicis muscle by increasing their angle of insertion into the sides of the base of the first phalanx. The Lateral Ligaments. — A short strong band of fibres radiates from the depression on each side of the head of the meta- carpal bone to the same side of the base of the phalanx, and to the sesamoid bone. As they descend, the fibres pass a Kttle forwards, so that the greater number of them are inserted in front of the centre of motion. They keep the joint firm and steady, and together with the shape of the articidar surfaces of bone prevent lateral motion. Tlie Posterior Ligament. — Passing from the lateral ligament on one side to that on the other, across the back of the joint, are some scattered fibres which serve to protect the synovial sac, and to complete the capsule of the articulation. Arteries. — The joint is supplied by fine capillaries and arteries, which penetrate the ligamentous tissue, and reach the synovial sheath. They are derived from the branches of the radial artery which supply the soft structures of the thumb. Nerves. — Filaments are given to the joint from the branches THE INTER-PHALANGE AL ARTICULATIONS. 313 of tlie median and radial nerves which supply the skin of the thumb, and from the branches of the ulnar which supply the adductor and inner part of the flexor brevis pollicis. The Muscles. — The flexor longus pollicis, the flexor brevis pollicis, the abductor and adductor pollicis, and the extensor primi and secundi internodii pollicis, all act upon this articu- lation of the thumb. The action of these muscles is sufficiently explained by their names, and it is therefore unnecessary to group or describe them further. The ]\Iovements. — This is more strictly a hinge-joint than the corresponding articulations of the fingers. Flexion and extension are the two chief movements. Very little lateral movement, or abduction and adduction, is permitted, and that little only when the joint is slightly bent. The abductor and adductor pollicis, pulling upon the base of the first phalanx of the thumb, effect movement at the carpo-metacarpal articulation, and act scarcely at all upon the metacarpo-phalangeal. It is in consequence of the free play of the metacarpal bone of the thumb at the carpus that there is so little lateral movement requisite here, so that we see what the thumb gains at the carpal end of its metacarpal bone it loses at its phalangeal extremity ; and vice versd, what the fingers lack at the carpus is made up to them at the metacarpo-phalangeal joints, but not sufficiently to give them the same free and extensive move- ments possessed by the thumb. The similarity between the motions of the thumb upon the carpus, and of the phalanges of the fingers upon their own metacarpal bones, has been assigned as one of the reasons for considering the thumb to be composed of three phalanges, which are immediately connected with the carpus, i.e., without the interposition of a meta- carpal bone. The Inter-phalangeal Articulations. Class, Diarthrosis. Subdivision, Ginglymus. The Bones. — The pJialanges of the first and second rows present at their inferior extremities a smooth trochlear surface, consisting of two lateral convexities separated by a shallow concave articular interspace. The articular surface is prolonged further on the palmar than on the dorsal aspect ; and whereas it is broad and extends across the whole width of the front, it is much narrower on the back of the bone. On the sides 314 THE INTER-PHALANGE AL ARTICULATIONS. of this extremity there are well-marked rough depressions for the attachment of the lateral ligaments. The phalanges of the second and third rows present at their su'perior extremities an articular surface, which is broader from side to side than from before backwards, and which is divided into two lateral concave smooth facets by an articular ridge, which extends from the posterior to the anterior border of the articular surface. Thus these terminal facets at the superior extremities of the bones of the second and third row are adapted to fit on to the trochlear surface at the inferior extremities of the bones of the first and second row. The lateral surface of the superior end of the second and third phalanges is not excavated, but instead presents a prominent rough border which gives attachment to the lateral ligaments. The Ligaments. — The phalanges of each finger and of the thumb are bound together respectively end to end by means of an anterior flattened plate of fibro-cartilage, by two lateral ligaments and by the expansion of the extensor tendon. Other ligamentous fibres pass between the phalanges and the skin. The Fibro-cartilage, or Glenoid Ligament. — This is sometimes spoken of as the " sesamoid body," from its taking the place of and serving the same purposes (viz., giving leverage to tendons, and preventing posterior dislocation of the phalanx to which it is united) as, the sesamoid bones at the metacarpal phalangeal joint of the thumb. It resembles in position, connexion, and uses the fibro-cartilage of the metacarpo-phalangeal joints of the fingers. Like it, it is but slightly connected (by means of fibro-areolar tissue) with the bone on the proximal side of the joint, which it helps to construct, but very firmly with the bone on the distal side. It blends with the lateral ligaments of the joint. Over it passes the flexor tendons, and to its edges are connected the lateral boundaries of the sheaths of the tendons. Occasionally a sesamoid bone is developed in the cartilage of the inter-phalangeal joint of the thumb, but seldom, if ever, ia those of the joints of the fingers. The lateral ligaments are strong bands which are attached above to the rough depressions on the sides of the upper phalanx and to the projecting lateral margins of the lower phalanx of each joint, as well as into the edges of the fibro-cartilaginous plate. They are tense in every position of the joint, and entirely prevent any lateral motion. Posteriorly, they are connected with the lateral expansion of THE INTER-PHALANGEAL ARTICULATIONS. 315 the extensor tendon, wMcli covers in the joint behind. Pass- ing between the deep surface of the extensor tendon and the bone above and below the joint, is a little white fibro-areolar tissue which thickens the synovial sac posteriorly, and completes the capsule where the tendon, by passing onwards, would other- wise leave it imperfect. Cutaneo-phalangeal Ligaments. — Strong ligamentous fibres, first described I believe by Professor Cleland, extend from the sides of the phalanges near their articulations and are inserted into the skin about the joints, more especially into the thicker and wrinkled skin of their dorsal aspect. These ligaments retain in its place the integument at the back and sides of the joints during fiexion. They are present about the joints of the thumb as well as of the fingers. Though seen at the distal joints, they are best developed at the first inter-phalangeal articulations of the fingers. The fibres are attached to the lateral ridges of both the phalanges of a joint and decussate — some passing upwards and others downwards — as they proceed, behind the digital artery and nerve, before spreading out into the skin on both palmar and dorsal aspects. The SYNOVIAL MEMBEANE of each of these joints is ample and loose, and extends upwards a Kttle way along the shaft of the proximal bone. It is very thinly covered above the upper margin of the fibro-cartilaginous plate. The Arteries. — Blood is freely supplied to these joints by little vessels, which after coming off from the digital arteries run along in the sheaths of the tendons, one on each side. These little vessels anastomose beneath the tendons at both ends of each phalanx, and send branches through the fibrous tissue to the synovial lining of the joint. These vessels are very constant and uniform in their arrangement and distribution. The Nerves are supplied from the digital branches of the corresponding fingers. The Muscles. — Over the joints between the first and second rows of phalanges there pass the tendons of the muscles which are inserted into the terminal phalanges, as well as those which are inserted into the second phalanges. Their actions are sufiiciently explained by their names, and by what has gone before. It will be sufficient here to enumerate them according to their mode of insertion. Thus, into the rough lateral borders of the second phalanx of the fingers near its base is inserted the divided tendon of the flexor sublimis 316 THE INTER-PHALANGE AL ARTICULATIONS. digitormn — flexor perforatus ; and into the posterior surface of the base of the same bone the central slip of the extensor communis digitorum. The thumb is usually spoken of as being deficient in the second phalanx. Again, into the anterior surface of the terminal phalanx of the thimib the flexor longus pollicis is fixed ; into the posterior surface the extensor secundi internodii pollicis is inserted. Into the anterior surface of the corresponding phalanx of each of the fingers the flexor digitorum profundus, the flexor per- forans, is inserted ; and into the dorsal surface the conjoined lateral slips of the extensor communis digitorum tendon. Nearer the carpus this tendon divides into three parts, the central of which gets attached to the base of the second phalanx, whilst the other two pass on, reunite, and are fixed to the base of the last phalanx. The lumbricales and interossei muscles blend with the extensor tendon and extend the second and third phalanges. The Movements. — Flexion and extension are the only movements possible at these joints. Flexion is much more free than extension, and can be continued till the one bone is at right angles to the other. The second phalanx can be flexed through from 110° to 115° upon the first, when the first is not flexed upon the metacarpal bone. Extension is checked when the finger is straight, i.e., it cannot go beyond a right line. The great freedom of flexion is due to the forward slope and the greater anterior extent of the articular facet of the inferior ends of the bones, and to the direction of the fibres of the lateral ligaments which pass a little forwards to their inser- tion into the distal bone. It is interesting to remark that at the metacarpo-phalangeal articulation, and at each of the inter-phalangeal, the extreme of flexion is reached when the distal bone has been brought to a right angle with the one next immediately above it ; and as we have four bones and tlu'ee joints for each finger, when the hand is closed, the several bones of each finger form a four-sided figure, whose opposite sides are parallel, and at right angles with the other two ; thus the metacarpal bone and the second phalanx are parallel with each other, and at right angles to both the first and third phalanges : similarly the first and third phalanges are parallel with one another. PART IV. THE LOWER LIMB. CHAPTEE XVL THE HIP-JOINT. Class, Diarthrosis. Subdivision, Enarthrodia. The bones which enter into the formation of this joint are the innominate and the femur ; the former at its acetabular part, the latter by its head and neck. Acetabulum is a deep hemispherical recess on the outer surface of the os innominatum, at the spot where the three component parts of that bone unite. The ilium forms a little less than two-fifths, the ischium a little more than two-fifths, while the pubis completes the remaining one-fifth of the cup- shaped cavity. In the dry bone it forms between 170 and 175 degrees of a circle ; but in the recent state it is deepened, and its orifice is contracted by the fibro- cartilaginous rim, called the cotyloid ligament. Its diameter varies in different cases, but in the adult bone is usually between two and two and a haK inches. Its direction is downwards, outwards, and forwards, so that it receives the head of the femur obliquely. At its deepest part the bone is so thin that it transmits light ; but the upper and posterior wall is formed by the thickest and strongest part of the os innominatum, and is capable of bearing great weight and resisting immense force. The margin of the cavity reaches from the obturator foramen in front and below, to the constricted part of the ilium above and behind ; and from the pectineal eminence 318 THE ACETABULUM. above and in front, to the groove above the tuber ischii below and behind. Adjacent to the obturator foramen there is a notch, nearly an inch wide, in the rim of the cavity, converted into a foramen by the transverse ligament ; this notch is nearly at the lowest part of the margin, so that the bone is seen very nearly as in the natural position in the body, when held with it downwards. Between the pectineal eminence and the anterior inferior spine of the ilium, there is an indentation in the rim which marks the place of union of the iliac and pubic portions, and over it passes the ilio-psoas muscle. Between the middle of the sciatic notch and the rim of the acetabulum is a shghtly marked transverse ridge, showing the line of union of the ischium and ihum, which at the anterior extremity forms often a slight tliickening and elevation of the acetabular rim. The outer surface of the margin slopes towards the free edge, where it is rounded off. It is rough and uneven, and gives attachment to the capsular ligament, and above to the long tendon of the rectus. The inner edge of the margin where it meets the external is sharply defined. The acetabulum is partly articular, partly non-articular. The articular portion is of horseshoe shape, and extends inwards from the margin, more or less. It is altogether deficient at the cotyloid notch, which corresponds with the gap of the horse- shoe. It is the widest at the iKac part, where it is over one inch from without inwards ; then it very gradually gets narrower along the ischium, but widens out again at the ischial end of the cotyloid notch ; forwards from the pubo-iliac suture it narrows more rapidly, and does not extend quite up to the pubic end of the cotyloid notch. At its narrowest point in an adult bone it measures half an inch in width. When coated with cartilage, and fringed round with the cotyloid ligament, it fits very closely upon the head of the femur, so as entirely to exclude .air from between the apposed surfaces of the bones ; and thus the joint derives support from without to the full extent of the pressure of the atmosphere. The non-articular part extends from the cotyloid notch as a rough recess in the floor of the acetabulum, and corresponds to the area enclosed by the horseshoe. It varies in form and size, but is generally quadrilateral, with its longer axis directed THE FEMUR AT THE HIP- JO INT. 319 upwards and somewhat backwards from the cotyloid notch ; following the curve of the bone it measures two inches in this direction, and about an inch and three-quarters transversely. The anterior superior angle of the recess is the highest point, and is situated above and in front of the mid-spot of the cotyloid notch ; the posterior superior angle is near the line of union of the Hium and ischium, or a little below it. The recess widens as it passes upwards ; it gives lodgment to a quantity of fatty tissue, with which, however, it is but sKghtly connected, and is the area over which the ligamentum teres plays, although in some cases it is certainly too extensive to allow the ligament to reach its upper limits. The inner or pelvic surface of the innominate bone, where it corresponds to the floor of the acetabulum, presents a trian- gular smooth plane, from which, as well as from the obturator membrane, the internal obtm^ator muscle arises. Thus the floor of the acetabulum forms also part of the wall of the true pelvis by a surface which looks upwards and inwards, and in its posterior extent forwards. It is occasionally perforated in disease of the hip-joint. In some few cases it has no doubt given rise to the idea of stone in the bladder — an error which is to be accounted for by the pelvis being small, or laterally contracted, and the sound in consequence striking upon it here, Femue, — The head of this bone forms two-thirds of a sphere, the circumference of wliich at its base, i.e., where it joins the neck, varies in different specimens from something less than six inches to six inches and a half. It is very smooth, being covered by articular cartilage, but the articular sur- face is unevenly distributed, being much greater above the horizontal plane through its centre than below it. If a vertical line be drawn so as to skirt the prominent inner side of the head, the articular surface above the point of contact extends outwards from this line about an inch and two-thirds, but below it only about three-eighths of an inch. The head bulges a little at a spot below the dimple for the round ligament, otherwise it forms part of a true sphere ; the part above the dimple recedes outwards. Diagram V. 320 THE FEMUR AT THE HIP- JOINT. the part below projects inwards a little. This construction of the head, together with the du-ection of the neck of the bone, and the dii-ection of the acetabulum, as well as the notch in the margin of the acetabulum, are features which facilitate dislocation of the thigh in positions of ad- duction. The articular sm^face, where the head is passing into the neck of the bone, is limited by a sinuous, not an even outline. This sinuous outhne only imperfectly corresponds to the limits of the movements of the head of the bone ; for when these are carried to an extreme degree it passes within the margin of the acetabulum. A little below the level of the anterior and upper angle of the gTcat trochanter, the articular cartilage is pro- longed further outwards than elsewhere. The position of the fossa for the ligamentum teres is just below and behind the middle point of the articular sm^face. If two lines be drawn at right angles to one another, the one vertically and the other horizontally, across the middle point, the pit is seen near this point in the lower and posterior quarter. The form of the fossa in the recent state is somewhat triangular, the base of the triangle being in front and nearly vertical, while the apex is behind ; the long axis is directed nearly horizontally back- wards, but with an inclination downwards as well as back- wards. The fossa is usually larger, and is always deeper before the articular cartilage has been removed than in the dried bone. It is also deeper in front than behind, so as to resemble a little pit, with a groove running off from it. The round hgament is attached only to the anterior part of the fossa, i.e., the pit, and lies in the posterior part of it, i.e., the groove, only when the ligament is in action, viz., in flexion, with outward rotation. In the bottom of the dimple are two or three foramina for bloodvessels. The neck of the fernm^ is inclined to the shaft at an angle of 125°. It is cyhndrical near the head, and becomes flattened as it proceeds outwards. It is deeper vertically than hori- zontally in its outer half ; it is convex in front, concave behind ; is marked on the middle of its anterior surface by a shght depression for the ilio-psoas muscle, and outside this, near the root of the trochanter, there is a heaping-up of bone sometimes called the tubercle of the femur, which gives origin to the tendon of the vastus externus muscle. THE FEMUR AT THE HIP- JOINT. 321 The neck is overhung ahove and behind by the posterior and upper half of the great trochanter, and in the angle between them is the deep digital fossa. Into this fossa the tendon of the external obturator is inserted after it has passed upwards over the smooth outer third of the back of the neck, from which it is separated by a bursa. On the upper surface of the neck are numerous large foramina for the passage of nutrient vessels. At the root of the neck in front is the anterior inter- trochanteric, which is continued into the spiral, line ; behind is the posterior inter-trochanteric line. The under surface of the neck forms with the inner side of the shaft a well-marked curve or arch, which increases the strength of the bone, while it gives grace to the outline of the lower limb. By placing the finger on the neck of the femur immediately below the fossa for the ligamentum teres, the bone balances so that the articular surfaces of the condyles are on the same level, and can together rest evenly on a flat surface. The length of the .neck varies ; behind, it is about two inches- and three-quarters ; below, about three inches ; while in front and above it is much less. As has been remarked, the articular surface of the head extends furthest on the upper and anterior aspects, and this helps to give the under and posterior sides of the neck greater length. It is owing to the obliquity of the neck and the inclination of the acetabulum that there is but little loss of supporting power during flexion, as the head of the femur in this move- ment rotates within, instead of being displaced from the acetabulum, as would necessarily be the case if the axis of the head and neck had been in a line with that of the shaft, and the head had then supported the acetabulum on its summit. It is owing to the obliquity, together with the length of the neck, that room is made between the thigh bones for the adductor muscles ; and to the length — the trochanters thereby being removed from the joint — that greater leverage is given to the muscles inserted into those prominences, and that a wide range of movement is possible. Ligaments. — There are three ligaments and a circiun- ferential or marginal fibro-cartilage in the hip-joint ; these are named the capsular and the transverse ligaments, and the Y 822 LIGAMENTS OF THE HIP-JOINT. ligamentum teres or round ligament ; the cotyloid fibro-cartilage is also generally, though improperly, sjDoken of as a ligament. The capsular ligavient is at once the strongest, and yet one of the weakest, ligaments in the body. Besides completely covering the articular portions of the bones, it also encloses the ligamentum teres and the cotyloid cartilage, while it partially springs from the outer surface of the ti-ansverse ligament. It is large and somewhat loose, so that in every position of the limb some portion of it is relaxed. At the pelvis, it is attached near to, but at a slightly varying dis- tance from, the edge of the acetabulum. Thus superiorly it reaches as high as the base of the anterior inferior iliac spine, thence it curves backwards and becomes blended with the deep surface of the long tendon of the rectus femoris muscle. Posteriorly it is only a few lines from the acetabular rim, and is firmly fixed to the bodies of the ilium and ischium. Inferiorly it is attached to the upper lip of the groove between the acetabulum and tuberosity of the ischium, in which the posterior or lower edge of the belly of the obturator externus muscle is compressed during extension of the limb. Thus it reaches the transverse ligament, to the outer surface of which it is firmly blended, and frequently several long stout fibres are prolonged over the notch to the obturator fascia to which they are firmly attached. Anteriorly it is attached to the pubis near the notch, to the pectineal eminence, and from this backwards along the pubis to the base of the inferior iliac spiae. From the superficial asjDect of the capsule on the posterior part, a thin but strong stratum extends beneath the gluteus minimus and small rotators, to be attached above to the dorsum of the iliiun higher than the long tendon of the rectus, and behind to the ilium and ischium, nearly as far back as the sciatic notch. As this expansion passes over the long tendon of the rectus, part of the origin of the muscle may correctly be described as being within the substance or between the layers of the capsule. At the femur, the capsule is fixed to the anterior portion of the upper border of the great trochanter, and to the tubercle of the femur close to the insertion of the gluteus minimus and the origin of the vastus externus, with slijDS from each of. which it is blended. Thence it runs along the upj)er and flats: xxvr, 1 f VERTICAL SECTION THROUGH HIP JOINT Cctjosvilar' U^ci.Tne*ut TvlC svi^ttibeje- oF e^tyZcv^ l^otsmei^^ •.teA. fiihfes oP iT^ci*M«>-tttU"i ter-\ _A,~tIefisf*v:vi^ ^^.oc^rrveot. HEAD OF TIBIA WITH SEMILUNAR CARTILAGES & CRUCIAL LIGAMENTS iXfactn&ions of ejcfcen^or" TeruLo-n. of 'hie^s -^ '^^ JEx-ten-uxL semUxvncn/r c^artiiMCjt: Int •■ SetraJxci^j/Vf Fo&t- cr'Vi.djotL 'vux^ifvetrtt CAPSULAU LIGAMENT. 323 outer part of the anterior inter-troclianteric line, but it soon gets below it, and at the inner border of the femur is on the level of the lower surface of the small trochanter. It is then inclined upwards and backwards along an oblique line two- thirds of an inch in front of the small trochanter, to reach the back of the neck ; here it is attached above the posterior inter- trochanteric line at a distance varying from half an inch, at the lower and upper ends, to over two-thirds of an inch oppo- site the middle of that line. Several strong fibres containing fatty tissue between them are fixed at the inner side of the digital fossa, beneath the small external rotator tendons ; they are continuous in front with the fibres attached to the anterior superior angle of the trochanter. After laying open the capsule it is seen that some of the deeper fibres of this ligament are reflected upwards along the neck, so as to be attached to the femur much nearer its head. These reflected fibres occur at three places, one corresponding in position to the middle of the ilio-femoral ligament, another to the pectineo-femoral, and the thii-d on the upper and back part of the neck. A thin fold of synovial membrane stretches between the reflected and the um^eflected fibres of the capsule. There are also to be seen encircling more or less of the capsule, but more especially the anterior and upper parts, many obliquely transverse fibres. These are placed superficial to the fibres passing from ilium to femur ; several of them blend with the inner portion of the ilio-femoral ligament near the femur, and above are lost beneath the expansion from the gluteus and vastus externus to the capsule. In thickness and strength the capsule varies extremely in different parts ; thus, if two lines be drawn, one from the anterior inferior iliac spine to the inner border of the femur near the lesser trochanter, the other from the anterior part of the groove for the external obturator (i.e., the upper part of the tuberosity of the ischium) to the digital fossa, all the ligament outside and above those Hues is very thick and strong ; whereas all to the inner side and below, except along the narrow pectineo-femoral band, is very thin and weak, so that the head of the bone can be seen through it. It is thickest in the course of the ilio-femoral ligament, at the outer part of which it is y2 324 ACCESSOKY BANDS TO THE CAPSULE. over a quarter of an inch in tliickness ; it becomes thinner towards the lower border of the ischio-femoral band, although here it is seldom less than one-eiglith of an inch thick near the acetabulum, where the fibres are extremely well- marked. There are three sets of auxiliary fibres, which have been already alluded to under separate names — viz., ilio-femoral, ischio-femoral, and pectineo-femoral. The ilio-femoral band is the longest and widest, as well as the thickest of the three. Above it is connected in a curved line (mth the convexity upwards), two-tMrds of an inch in length, to the ilium immediately below and behind the anterior inferior spine ; thence it extends obliquely downwards and outwards to the front of the trochanter major, and the anterior trochanteric and spiral lines as far as the inner border of the shaft. Its fibres have not all the same degxee of obliquity, for those which are highest on the ilium have also the highest femoral attachment, and vice versd ; so that the uppermost fibres are shorter and more nearly transverse than the rest ; the central fibres take a straight course, and are fix;ed to the femur, where the sphal joins with the inter-trochanteric hne. This varying obliquity of the fibres, together with some accu- mulation of the fibres both along the inner and outer borders of the band near the femur, possibly explains how it has come to be described as the Y'^l^aped ligament. It has been said to resemble an inverted \, one arm of which is supposed to be attached near the trochanter major, and the other to the spiral line near the inner border of the femur, with but little, if any, ligamentous tissue between them. This, however, is not correct, for although the appearance may be produced by dissection (and especially if the strong dense fibres between the capsule and gluteus minimus, and between the long tendon of the rectus and the tendon of origin of the vastus externus, be not removed), it does not naturally exist. About the centre of the band, near its attachment to the trochanteric line, is an aperture leading into the joint. It is very constant, and transmits the transverse branch of the external circumflex artery through the ilio-femoral ligament into the joint. This portion of the capsule limits extension, and by pre- FRONT VIEW OF CAPSULAR LIGAMENT OF HIP vJOIN" !^1 nCo PerrvoraZ Ixyj octrvent or stfonjj joocrt oP C(xfasvi2/>ct- lujcOTvent- Thin, -par-t oF aoips-ULocf li^conewi BecbCrvec- Pe*rvo-raL Jicu- TiOnrjdccr Ftbr&s of hdck oF cctjosule., The-Ischxo -femoraL oMo^ch^ci to IjticcJs: of BACK VIEW OF CAPSULE OF H»P JOINT THE HIP-JOINT. 325 venting tlie natural tendency of the trunk to roll back- wards on the thigh bones in the erect posture, it does away with the necessity of muscular power for this piu^pose. It is made tense in every position of extension except when abduc- tion is combined with extension, and then the outer fibres are relaxed. Abduction might be described as flexion out- wards, so that the points of attachment of the outer fibres are approximated. When adduction is combined with complete ex- tension the points of attachment separate, and the whole ligament (but especially the inner portion of it) is put upon the stretch. The outer fibres are tightened in outward rotation even during flexion. In extension with outward rotation the whole ilio- femoral band is tight, but as flexion is increased the outer fibres become more and more tense as the inner ones are relaxed. In rotation inwards the inner fibres of the ligament receive most of the strain. The ischio-femoral band is formed by very strong fibres attached all along the upper border of the groove for the external obturator, and to the ischial margin of the acetabulum above the groove. The hiohest of these incline a little upwards as they pass outwards to be fixed to the trochanter in front of the insertion of the pyriformis tendon ; the other fibres, as they pass outwards, curve more and more upwards, and are fixed to the upper and back part of the neck internal to the digital fossa, where they are blended with the tendons of insertion of the external rotators. Wlien the femur is flexed these fibres pass in almost straight lines to their femoral attachment, and are spread out uniformly over the head of the bone ; but in extension of the thigh they wind upwards over the back of the head and neck of the femur in a zonular manner, and form quite a folded band along the lower border of the ligament. This band does not limit simple flexion, nor is it made tight until adduction or rotation inwards is combined with flexion. In flexion with rotation outwards, or with abduction, it is quite relaxed, as it is also in extension. Between the ilio- and the ischio-femoral bands the capsule is stout and strong, and with it here, near the acetabulum, is incor- porated the long tendon of the rectus ; while at the femoral end the longitudinal fibres composing it are concentrated to a narrow insertion into the ridge on the front border of the 326 ACCESSORY BANDS TO THE CAPSULE. trochanter close to the gluteus minimus. • It is this portion . of the capsule which is greatly strengthened hy a strong fasci- culus of fibres passing fi-om the under surface of the gluteus minimus to the capsule half-way between the iliac and femoral attachments ; while further forwards, and near to the outer edge of the ilio-femoral ligament, a tendinous band, closely blended with the surface of the capsule, stretches between the upper extremity of the tendon of origin of the A^astus externus and the long tendon of the rectus. By this band traction on either of these tendons moves the other in the dissected joint, so that it is possible there is some direct association in their action. This part of the capsule assists the ilio-femoral hgament in limiting extension, but it is made tighter in adduction, especially m adduction combined with slight flexion, e.g., the stand-at-ease position of the limb upon "which the weight of the body is not resting. The pectineo-femoral band is a distinct but narrow set of fibres, individually less marked than those of either the ilio- femoral or ischio-femoral ligaments. They are fixed above to the anterior border of the pectineal eminence reaching down as far as the pubic end of the cotyloid notch ; to the neck of the femur they are attached above and behind the ilio-femoral ligament, with the lowermost fibres of which they blend. It is put upon the stretch in abduction, whether combined with flexion or extension ; it is very tight in abduction com- bined with rotation outwards and flexion, and abduction with slight simple flexion. In both these latter positions the head of the bone is in great part out of the acetabulum, and sup- ported by the fibres of this band ; whilst both the ischio- and ilio-femoral bands are relaxed. The fibres of all these auxiliary bands are superficial to, but inseparably blended with, the rest of the capsular Hgament ; in fact, although called by distinct names, they are in no way distinct ligaments, but merely very greatly thickened portions of the capsule."'" The ilio-femoral fibres and the ischio-femoral. * In one instance, described in the eighth volume of "Journal of Anatomy and Physiology" (p. 134), an abnormal ligament was observed stretching from the ischium to the trochanter, and quite distinct from the capsule in its posterior half. THE HIP-JOINT. 327 near the iscMum, are very distinguishable by their greater coarseness. The ilio-femoral and pectineo-femoral bands, and the pubic rim of the acetabulum, enclose a triangular space where the capsule is thinnest. This part is never tightly stretched in any position of the joint ; over it the ilio-psoas muscle passes, only separated from it by a bursa, which sometimes communi- cates with the synovial sac. The capsule, opposite the lower and back part of the neck of the femur, especially near its attachment to the back of the femoral neck, and again opposite the cotyloid notch, is very thin. It is, however, thickened near the transverse liga- ment by some curved and decussating fibres, which arise from each extremity of the Kgament ; the liinder ones pass forwards and blend with the pectineo-fempral band in the middle of its course, those which arise in front are lost on the under and back part of the capsule. Some extra fibres from the border of the external obturator groove help to strengthen the under part of the capsule, and are lost upon it. In nearly every position of the joint it is relaxed, but there is one, viz., extreme flexion combined with abduction, in which it has to resist the head of the bone when all the rest of the capsule, except the pectineo-femoral ligament, is quite relaxed. Such a position is assumed when the thigh is thrown side- ways over the arm of an easy-chair, or when sitting in a hip- bath with the thighs apart, and the knee bent over the edge, or in stooping low with the legs wide apart. The capsular ligament is supported externally by muscles and tendons on every side, and by several of them great addi- tional strength is given to the joint. Some of them, from being closely connected with the ligament, serve to raise it during the movement of the joint, and thus prevent it from being pinched agaiust the edge of the acetabulum. In front is the ilio-psoas muscle, the sheath of which is adherent to the capsule, while the iliacus in part arises from it. Above are the rectus femoris, the slip from the vastus externus to the long head of the rectus, and the gluteus minimus with its strong fibrous connexion with the capsule. Above and behind are the pyriformis (a shp from which joins the tendon of the smaU gluteal), and behind the internal obturator and gemeUi. The obturator internus is by far the strongest of all 328 THE LIGAMEXTUM- TERES. the small rotators, and acts much like a ligament, owing to the extension backwards of many of the ultimate fibres of its several tendons well-nigh to the bony origin of the muscle ; the four or five closely formed tendons which pass over the ischial gTOOve result from the blending of eight or nine strong bands, which are seen on raising the muscle from its origin ; these bands radiate along the borders and the body of the muscle, and extend from within a short distance of its extreme Kmits, while they again are composed of individual slender fibres, which pass from origin to insertion of the muscle. Its power of resistance too is increased by the play of the tendons over the trochlear groove of the ischium, whereby strain on the muscles is diminished. Below, and behind, the external obturator muscle passes over the capsule ; some few of its upper fibres are inserted into the under part of the ligament, and a dense band of fibro-cellular tissue, extending from the groove to the digital fossa, connects its sheath with the capsule along the posterior border of the muscle. As the tendon of the muscle approaches the digital fossa, it turns on its own axis and rests on the neck of the femur along the Ihie of attachment of, and beyond the capsule. The ligamentuTn teres, or round ligament, is an inter-articular flat band, which extends from the acetabular notch to the dimple in the head of the femur. At the acetabulum it has two bony attachments, one on each side of the notch, while intermediate fibres spring from the under surface of the trans- verse ligament ; indeed, some lowermost fibres of the trans- verse ligament consist of these intermediate fibres of the round ligament. It is usually about one and a half to one inch and three-quarters long. To the acetabulum-, on the pubic side of the notch, it is fixed to the acetabular surface, imme- diately below the articular cartilage. On the ischial side it is also fixed close to the notch, immediately below the articular facet, but several of the fibres arise outside the cavity, below and in connexion with the origin of the transverse ligament, where it is also continuous with the capsular ligament and periosteum of the ischium. The posterior or ischial portion is much stronger than the anterior or pubic, but it is not strictly correct to say that the origin is bifid, as between the posterior and anterior USES OF THE LIGAMENTUM TERES, 329 bands there are the fibres connected with the under edge of the transverse ligament. To the femur the ligament is attached at the anterior part {i.e., the pit) of the dimple in the head, as well as to the cartilage which forms the margin of this part of the dimple. Its axis of insertion corresponds to the base of the triangular- shaped dimple ; the ischial fibres pass chiefly into the upper angle, the pubic fasciculus into the anterior and lower angle. In connexion with the ligamentum teres the fatty tissue at the bottom of the rough recess in the acetabulum requires a word of notice. It forms quite a thick quadi-angular pad or cushion, which occupies all the non-articrdar portion of the cavity, and projects outwards, beneath the transverse ligament, through the acetabular notch. Into it pass the articular nerves and arteries, which, as they enter the cavity to run along the round liga- ment to the head of the femur, lie between the bony origins of the ligamentum teres, and beneath its connexion with the transverse ligament. The synovial membrane which covers the fatty cushion is of unusual thickness ; from the cushion, as well as from the lower edge of the transverse ligament, the synovial membrane is reflected along the round ligament to the head of the femur. The part of the membrane reflected from the cushion does not cleave closely to the round liga- ment, but forms a triangular fold, the apex of which is at the dimple in the head of the femur ; one side is continuous with the round ligament, and the other, free, looks towards the back of the acetabulum ; while the flat surfaces (in the erect pos- ture) face towards and from the lower part of the femoral head. The ligamentum teres presents the appearance of two trian- gular planes at right angles to each other, one formed by the broad fibrous ligament, and the other by the reflected synovial membrane as described above. The ligamentum teres is shut out from the synovial cavity of the joint by the reflected membrane, as the lungs are by the pleura, and the abdominal viscera by the peritoneum. The use of the ligamentum teres is to check rotation outwards during flexion, and adduction during flexion. As a ligament can only be in use when it is tight, and as there have been various and very difi'erent opinions published as to the posi- tions which the joint is in when the round ligament is tight, I shaU give the results of different modes of examination. 330 THE HIP-JOINT. When examined after division of the entire circumference of the capsule, the round ligament is on stretch during extension, and adduction in the nearly extended position. During simple extension, the ischial band is alone tense ; during extension with adduction, the rest becomes tense also. After trephining the acetabulum, removing the fat and synovial membrane corresponding to the excised bone, and dividing the fibres of the ilio-femoral ligament through part of its thickness, then adduction in the nearly extended position brings the ligament tight, though perhaps not so tight as rotation outwards with flexion. But if the ilio-femoral liga- ment be left untouched, so that it offers its full resistance in extension and adduction, there is no tension on the ligamentum teres in the extended or nearly extended positions ; but the ligament is stUl very tight during flexion combined with out- ward rotation. In this position the ligament is quite flat, and rests in the posterior portion of the dimple (i.e., the groove) of the head of the femur. In flexion with adduction it is also tight ; the fibres are almost flat, but twisted a little on them- selves near the dimple of the femur. During adduction, as the limb passes from flexion into extension, the round ligament gets less and less tight until it becomes quite lax. After flexion with adduction, it is as tight in flexion with rotation inwards as in any other position. It is at its loosest in abduction with flexion, in which position the two ends of the ligament are close together, and opposite to one another. It is very loose in abduction with extension. It is also loose in abduction combined with flexion and outward rotation. The tension of the- ligament was tested by threading a piece of whipcord round it and pulling on the cord in the various positions. In this mode of exainination, the results are very unmistakable — viz., the ligament is tightest in flexion com- bined with adduction and rotation outwards, and almost as tight in flexion with external rotation alone ; and in adduction combined with flexion. Its most lax state is in abduction. As this method of examination requires the removal from the floor of the cavity of a piece of the synovial membrane near where it is reflected along the round hgament, and as this reflected synovial membrane, together with the fibrous ligament itself, forms a broad triangular structure, it was deemed well HIP -JOINT AFTER DIVIDING CAPSULAR LIGAMENT AND DISARTICULATING THE FEMUR. i CcLpsuLar Ii-ciai'nenL If- ^ Cotyloid, 'i '-"' f (iJ^ jr circwytih r vt ^l LiVQunLeyttu-m, 1.J ^terasy/kerr attotd IsS, to tiie -i<, jhidi Li^ounentutn teres where iUta£}u/i to Iliad, of fetniu- V -ciy I in^ynvrcLTi-e: '^>ai:>. S 3 c ^v^ ^H H IP JOINT, PLATE XXIX, 2. JjZgccrrijeixtuJrv t&res in- oornplete eocteinsioyv. 3 J .(^(tyrcentuyn' ter-e^ cLrcvwn. tight ul F/jaxiott JlTlen^rrux^L ciet.ouci'^xai:. West, N^ewman., TRANSVERSE AND COTYLOID LIGAMENTS. 331 to test the results thus obtained by opening the joint at a spot where the division of the synovial membrane could not possibly have any effect upon the round ligament. The capsule was accordingly opened by removing the thin portion over which the ilio-psoas plays and the corresponding portion of the rim of the acetabulum was gouged away ; but the results obtained were in no way different from those seen through the trephine- hole in the floor of the acetabulum. The transverse ligament supports the cotyloid fibro-cartilage, and is intimately connected with the ligamentum teres. It is composed of decussating fibres, those which arise from the pubis being more superficial than those arising from the ischium. Attached to the pubis, at some distance above the acetabular notch, some of the superficial fibres soon reach the upper border of the ligament, and then pass over the notch to their ischial insertion on the deep aspect of the ligament ; others arise from the pubis nearer the notch, and then pass obliquely across below the former to blend with the iscMal portion of the ligament on its outer surface. Some of the deep fibres arise near the margin of the acetabulum at the ischial side of the notch, and pass obliquely across to form the upper border of the ligament near the pubis ; while others, attached lower down and farther from the notch, form the lower and deep portion of the pubic side of the ligament. This ligament converts the notch in the acetabulum into a foramen through which nerves, arteries, and fat enter the ace- tabulum, and out through which the fatty tissue is compressed in certain positions of the joint. The use of the ligament is to complete the rim of the acetabulum and to furnish a basis of support to the cotyloid cartilage. The cotyloid fibro-cartilage is a yellowish white structure, which deepens the acetabulum by surmounting its margin. It varies in depth and thickness, and is altogether stronger at its iliac and ischial portions than over the pubis and trans- verse ligament. Nowhere, however, is it more than a quarter of an inch from its attached to its free edge. It is broader at its attachment than elsewhere, and becomes very thin along its free border. It is somewhat lunated on section, having its outer surface convex and its articular face concave, and very smooth in adaptation to the head of the bone which it tightly 332 THE ARTICULAR CARTILAGES OF THE JOINT. embraces a little beyond its greatest circumference. It some- what contracts the aperture of the acetabulum, and retains the head of the femur within its grasp after the capsule and all muscles have been completely divided. It is firmly fixed to the bony rim, as well as to the articular cartilage on the inner, and the periosteum on the outer side of it, while at the notch it is inseparably blended with the transverse hgament, if indeed it can be said to exist at all as a distinct structure. It is covered on both aspects by the synovial membrane, which is reflected over its free edge from the capsule to the articular cartilage of the acetabulum. The aHicular cartilage lines a large part of the acetabulum, and covers the smooth portion of the head of the femur. In the acetabulum the width and thickness of the cartilage are great in those parts which have to bear most pressure, and greatest on the ilium behind a vertical hne from the anterior inferior spinous process. To the head of the femur the cartilage gives much the appearance of a white billiard-ball ; to the dimple for the round ligament it gives the raised margin and triangular shape seen in the recent state, for as soon as the cartilage is removed the appearance of the dimple is much altered. Into it at the dimple (especially at the upper margin) the round ligament is inserted, and a large scale is often torn away with the ligament from off the femur in dislocation of the thigh. It is much thicker over the upper than the lower part, and is thicker near the dimple than towards the circumference. At its thickest part, just above the dimple, it is about one-twelfth of an inch deep, while at the under part of the head it is so thin that the bone can be seen through it. The extent of the cartilage corresponds with the smooth part of the head of the dried bone, and its limit with the sinuous outline of the head. The SYNOVIAL MEMBEANE Knes the capsule, and passes over the border of the acetabulum to reach the fatty cushion and the round Hgament. By the latter it is conducted, in the manner already described, to the head and neck of the femur, and thus to the femoral attachment of the capsule. Aeteries. — Blood is supplied to the hip-joint from the deep femoral and the internal ihac arteries. (1) From the deep femoral, the transverse branch of the internal circumflex as it winds above the small trochanter AETERIES AND NERVES OF THE HIP-JOINT. 333 gives off, wlien opposite the joint, an articular Lranch which enters at the cotyloid notch, supplies the fatty tissue, synovial membrane, and round ligament, and, like the following, some- times reaches the head of the femur. (3) The transverse branch of the external circumflex, as it passes outwards beneath the vastus externus, gives a branch of considerable size to the joint. It enters through a well-marked and constant aperture in the ilio-femoral band a little above the middle of its femoral attachment. A second branch, from the same source, sometimes enters the joint through the ligament lower down. (8) From the, internal iliac, blood is derived through the obturator, gluteal, and sciatic branches. The external, lower, and posterior branch of the obturator gives an articular twig, which enters beneath the transverse ligament, ramifies in the fatty cushion of the acetabulum, and runs along the round ligament to the head of the femur, (4) The inferior division of the deep portion of the gluteal sends small branches to the hip, which pierce the gluteus minimus and penetrate the capsule. (5) The sciatic artery gives off directly some branches to the back of the capsule of the joint ; and the branch from it to the quadratus femoris, after passing beneath the gemelli and internal obturator, sends twigs to the hip-joint before it terminates in the muscle. N'eeves are derived from the lumbar and sacral plexuses. From the lumbar plexus (1) the anterior crural furnishes one or more branches to the front part of the capsule, as the nerve is passing over the joint, and just after it has escaped from be- neath Poupart's ligament, (2) The anterior portion of the obturator sends articular branches to the hip-joint when near the thyroid membrane, one of which enters at the acetabular notch, and reaches the ligamentum teres, another suppKes the anterior, while a third goes to the lower part of the capsule. (3) The a^ccessory obturator, when present, gives off, behind the pectineus muscle, an articular branch, which sometimes enters the hip-joint with the branch of the obturator artery, and at others perforates the capsule. From the sacral plexus (1) the nerve to the quadratus femoris furnishes a small branch to the back of the joint, while it is lying between the external rotators and the capsule, (2) Several 334 BURS^ OF THE HIP-JOINT. branches, derived either from the upper part of the great sciatic nerve, or from the lower part of the sacral plexus itself, or from both sources, enter the joint by perforating the back of the capsule. BuESiE are found on the front, outer side, and back of the joint. On the front and outer side there are five, viz. — 1. A large bursa beneath the psoas and iliacus, between them and the thin portion of the capsular ligament. It often communicates with the synovial cavity of the joinc. 2. A small bursa between the gluteus medius and the upper and front part of the trochanter major. It extends some way between the tendon of this muscle and that of the pyriformis, which is covered by the gluteus. Sometimes there are two bursse instead of one ; one between the tendon and the bone, another between the tendon and the pyriformis. 3. Between the tendon of gluteus minimus and the front of the trochanter. This bursa sometimes extends between the insertion of the small gluteus and the origin of the vastus externus tendon. 4. A large bursa is situated in front of the gluteus maxim us, and between it and the vastus externus ; over it rides the strong fascia of the buttock as it passes downwards to the thigh towards the insertion of the gluteus maximus. It is below the following : 5. A large multilocular bursa extends across the external surface of the base of the great trochanter, and some way upon the shaft below, over which the tendon of the gluteus maximus and the dense fascia play. On the back of the joint there are four bursse, viz. — 6. The external obturator muscle plays over a bursa which is situated between it and the back of the neck of the femur. 7. A large bursa exists between the quadratus femoris and the posterior surface of the small trochanter. 8. An elongated bursa often exists between the back of the capsule and the gemeUi and internal obturator muscles. It is often in communication with the bursa which lies between the latter muscle and the trochlear groove of the ischium. 9. Bursal interspaces, containing a light currant-jelly-coloured fluid, occur between the quadratus femoris and the obturator externus and back part of the capsule. Muscles, — Numerous muscles act upon the hip-joint. Some aURS>€ IN CONNECTION W fTH THE FRONT OF THE HIP JOINT. UjUlCXkS tU) ; psoas & cxxpsiJ^vf "\^&-, vifi •' often. car>iiru.vnxact±iyict '^ -yvvitujoirvt- . AAdtuctcrr Ifeyis Glxnt&us rranhrruLs -minijnus * trv<^utrLtef OluteiiS rrveJius. nialh feurwo/ Tietwee-rugLutetAjS \ h ( tM' ; q7n te us Chi O-ics Tiwuexnyuui Vastus ex-t^rrvLLS. A Hejzs^;jxn. oUL.a£terM.OTvro. West, NiMTTrux^ 4 C.XiA, PLATE XXXI. BURS/E ON THE BACK OK THE HIP / '^lfH(fJi'/f,:f, GLutPAis Tnxnuruts Pyr-i/ortrvus J5itrs~uoy Tx.q oon'i£iV\jt the. hyijeje-^icckLn-ci -utXo jx.Ar'hcJJ- of ':y }tcvl/tl anents Pibfes ofanuy'i.c7 A.TeoZo Fa/ty ist-.crvuc uxX 1a/^ A.HsnsyHccn oUl-u^nicu:,. liVest TTeyvyruia^ & ARTICULAR EXPANSION OF EXTENSOR TENDON. 351 mediately above the head of the fibula beneath the posterior ligament. On the outer side the tendon of the biceps is closely connected with the external lateral Kgament, Let us first understand the connexions of the several portions of this cap- sular investment. The Fibrmts Expansion of the Extensor Tendon. — The qua- driceps extensor tendon, which extends for several inches along the front of the thigh, is a densely thick and strong structure, about one and a half inches broad. As it approaches the patella, it receives along each of its borders fresh tendinous fibres from the vasti and criu-eus, so that just above the patella we find the conjoined tendon consisting of a very thick and strong central portion, with a thinner but still strong lateral portion continuous with it on each side. This aponeurotic expansion of the tendon, together with the fascia lata of the thigh, covers the whole of the front aspect of the condylar portion of the femur. The central portion of the tendon is inserted into the anterior two-thiixls of the upper border of the patella, while many of its superficial fibres pass over the subcutaneous sur- face of that bone, and are continuous below it with the liga- mentum patellse. The lateral portions are similarly inserted into the upper border of the patella on each side of the thick central mass, as well as into the lateral borders of the bone (nearer the anterior than the posterior surface), as low down on each side as the attachment of the ligamentum patellae. Still further outwards its fibres are attached to the oblique lines which extend upwards from the tubercle of the tibia to the inner and outer tuberosities, and thus reach as far as the internal and external lateral ligaments. On the inner side the fibres are prolonged below the oblique line, and, like the internal lateral ligament, become blended with the perios- teum of the shaft. On the outer side, numerous well-marked fibres belonsino; to the fascia lata on the outer side of the thigh are prolonged downwards and inwards to reach the external oblique ridge of the tibia, and in their course blend with the expanded quadriceps tendon. These fibres are con- tinuous with that portion of the fascia lata into which the tensor vaginae femoris is inserted. We have thus, in the conjoined tendon, a large hood spread over the whole of the front of the joint, surrounding 352 LIGAMENTS OF THE KNEE-JOINT. the patella along the anterior margin of its border, and cover- ing its anterior surface, but leavmg its posterior surface and the posterior margin of the border of the patella free ; while on the sides of the patella it reaches to the lateral ligaments of the knee. It is continued into the ligamentum^ patellae in the middle line, and on each side is attached to the front surface of the tibia, as far out as the insertion of the lateral ligaments. On the deep surface of the tendon, and between it and the lower end of the shaft of the thigh-bone, we have a large bursa, whilst the large and loose synovial membrane of the knee-joint extends upwards for some distance over the front of the con- dyloid extremity of the femur. This hood of fibrous tissue is, however, everywhere separated from the synovial membrane, which it protects by a layer of fat. This fatty tissue is of considerable thickness both above and below the patella, more especially in the middle line below it, where there is a large cushion or pad between the ligamentum patellse and the syno- vial sac. The ligamentum patellm is simply the continuation of the central portion of the conjoined tendon. It is attached above to the lower border of the patella, and, as already mentioned, is continued over the front surface into the central portion of the quadriceps extensor tendon ; below it is inserted into the lower part of the tubercle, as well as into the upper end of the crest of the tibia. Its insertion into the tibia is very oblique, being prolonged much further down on the outer side, so that whereas along the inner border it measures about two and a half inches in length, it is fully one inch longer on the outer border. This mode of insertion, together with a corresponding obliquity in the surface of the tibia at this spot, causes the leg to be slightly rotated outwards in complete extension by the extensor muscles. IsTo effect is produced by this ligament in hmiting flexion or other movements of the knee. The internal lateral ligament is a strong flat band, which extends from the depression on the tubercle at the inner side of the internal condyle of the femur, to the inner border and inner surface of the shaft of the tibia, for an inch and a half below the head. It is three and a half inches in length, weU-defined along its anterior edge, where it blends with the aponeurotic expansion of the conjoined tendon ; not weU-defined posteriorly, THE LIGAMENTS OF THE KNEE-JOINT. 353 where it merges into the posterior ligament. The semi- membranosus mviscle passes beneath it. It is firmly connected with the edge of the inner semilunar cartilage and with the coronary ligament, which binds that cartilage to the tibia. At its lower extremity some of its fibres are deflected into the descending portion of the semi-membranosus tendon. A twig of the inferior internal articular artery passes between the tendon and the ligament. When the tibia, as in flexion, is brought into contact with the hindermost part of the condyles of the femur, the distance between the points of attachment of the lateral hgaments is reduced to its minimum, and the ligaments are relaxed ; whereas, when the tibia is brought into contact with the fore part of the condyles, as in extension, the distance between the points increases until extension is complete, and the lateral ligaments are tightened. (Vide Diagrams on pages 375 and 376.) The lateral ligaments are therefore quite relaxed during flexion of the knee, and do not interfere with any of the movements ; but, as extension is made, they are gxadually tightened, and in complete extension they hold the articular surfaces firmly together. They resist over-extension by not permitting the tibia to slide further forwards upon the condyles, nor any increase in the space between the hinder part of the articular facets of the tibia and the femur. During extension they resist rotation outwards of the tibia upon a vertical axis, by the oblique direction which the ligaments assume during extension, viz., the outer one slants backwards to the fibula, and the inner one forwards to the tibia. TJie external lateral ligament consists of two distinct parts ; the anterior is the best-marked and the longer of the two ; it is attached above to the tubercle on the outer side of the external condyle, having the origin of the popliteus below and in front of it, and the origin of the outer head of the gastrocnemius above and behind. AH three of these structures are close together, but the popliteal tendon is .^hidden from view until the capsule of the joint has been removed. Below, the ligament is fixed to the middle of the outer sm^face of the head of the fibula, half an inch or more anterior to the styloid process. On the superficial aspect is the tendon of the biceps, which splits to embrace the ligament near its lower end ; beneath it is the popliteal tendon contained in its sheath, and the inferior A A 354 THE LIGAMENTS OF THE KNEE-JOINT. external articular artery. It is about two inches in length, and is not connected with the semilunar cartilage, nor with the tibia. The posterior portion of the external ligament is one-third of an inch behind the anterior. Although broader, it is shorter and less defined. Below, it is fixed to the styloid process of the fibula ; and incluiing somewhat backwards as it passes upwards it ties down the pophteus against that part of the outer tuberosity which is immediately above and behind the facet for the head of the fibula. It blends with the posterior ligament beneath the outer head of the gastrocnemius muscle. The external lateral ligament, like the internal, is tight in extension and relaxed in flexion. It checks over-extension of the knee in the same manner as does the internal ligament, and by the backward direction of its fibres during extension it limits rotation outwards of the tibia round a vertical axis. It has no influence over pronation and supination of the leg, as those movements only occur while the knee is bent, and consecjuently while the ligament is relaxed, and they are not more restricted before than after division of the ligament. The external and internal lateral ligaments of the knee differ from the lateral ligaments of the true hinge-joints in being tense only in one position, instead of in every position of the joint. The external lateral ligament differs from the internal in being rope-like instead of flat ; it is freer from the joint, and not united to tlie semilunar cartilage or coronary ligament ; and while it is attached to the femur on a little lower level than the internal, its connexion vrith the fibula is higher than that of the internal with the tibia, so that it is an inch, or more, shorter than the internal lateral ligament. Both ligaments have a special and peculiar relation to the tendons of muscles, the internal to the semi-membranosus, and the external to the popliteus and biceps. Tlie p)Osterior ligament, or ligamentum Winslowii, is a broad, and for the most part a dense structure of interlacing fibres, with large orifices between them for the passage of blood- vessels. Its thinnest point is below the oblique fibres of the semi-membranosus tendon just opposite the popliteal notch in the border of the tibia. The tendon of the semi-membranosus muscle is so incorporated with it, that it is impossible to describe THE POSTERIOR LIGAMENT OF KNEE-JOINT. 355 the ligament fully without also describing the tendon. Below the Kgamentj is the popliteus muscle, with the sheath of the tendon of which it is blended ; above it are the origins of the gastrocnemius muscle. It is attached to the femur close beyond the articular surface of the condyles, and between the condyles it stretches along the posterior and upper margin of the inter-condyloid notch. It reaches from the external to the internal lateral ligament. The outer head of the gastrocnemius and the plan- taris are incorporated with it. Inferiorly it is fixed to the border of the outer tuberosity of the tibia, to the bone below the popliteal notch, and to the shaft below the inner tuberosity of the tibia, where it is blended with the descending or vertical slip of the semi-membranosua tendon, and the internal lateral Ligament. On the superficial aspect of the ligament another slip of the semi-membranosus tendon is reflected upwards and outwards as far as the outer head of the gastrocnemius, forming a strong oblique band of union with the gastrocnemius ; where it joins the gastrocnemius over the outer condyle there is sometimes a sesamoid bone developed. This slip vastly strengthens the pos- terior ligament, of which indeed^ if not the chief constituent, it at least is an important part. On its deep surface the ligament is closely connected with the back of the semilunar cartilages (but especially with the inner), as well as with the coronary Kgaments ; while in the interval between the cartilages it is inseparable from the dense mass of fibro-fatty tissue which fills up the part of the ]3opliteal notch not occupied by the posterior crucial ligament ; similar tissue fixes it to the inter-condyloid notch of the femur. In fact, although the ligament passes freely from femur to tibia over the condyles, it is firmly connected in the interspace with the posterior crucial ligament and fibro-fatty tissue within the joint ; and it is the contraction of this tissue and of the posterior ligament which offers the chief resistance to exten- sion in cases of fibrous ankylosis of the knee. The dis- section of such an ankylosed knee in the dead-house proved that extension was resisted after division of all the other tissues around the joint except the posterior ligament, and the struc- tures connected with, and extending forwards from its deep surface in the median plane of the joint. A A 2 356 THE ANTERIOR LIGAMENT OF THE KNEE-JOINT. The tendon of the semi-memhranosus, which is such an im- portant part of the ligamentum Winslowii, spreads out in three directions behind the inner tuberosity, but cannot be said to divide into three parts. Each portion blends with the posterior ligament. The oblique part has been specially referred to above, the anterior passes horizontally forwards beneath the internal lateral ligament, while the descending portion is blended with the lower and inner j)art of the posterior ligament, and then is attached to the tibia along the internal lateral ligament, with which also it is closely united. The posterior ligament with the semi-membranosus tendon gives great steadiness and strength to the back of the knee- joint, and like the anterior portion of the capsule of the hip saves the necessity of muscular action in keeping the body erect. As the line of graAdty falls through the knee a little in front of the bearing point of the femur on the tibia, the tendency of the weight of the body is to over- extend the knee. This tendency is resisted by all the liga- ments of the joint, for all are made tense by extension, but especially by the ligamentum Winslowii. The practical result of this is that the knee is kept straight without the aid of muscles in such attitudes as the " stand-at-ease" position, when the weight is borne entirely by the bones and ligaments of the knee upon which one rests. The Anterior Ligament. — It will have been understood from what has been said, that the aponeurotic expansion of the quadriceps extensor tendon, strengthened by the fascia lata of the thigh, together with the patella and ligamentum patellae, form a strong continuous investment for the front of the knee- joint ; and also that these structures, together with the lateral and posterior ligaments, close the knee-joint below, on the sides, and posteriorly. It remains to be seen, however, how the joint is closed in anteriorly above the patella ; how in fact the joint is shut off from the under surface of the extensor muscles of the thigh and the lower end of the shaft of the femur. After dissecting down the conjoined tendon and the fatty tissue beneath it, a thin but strong and very distinct mem- brane is exposed, which looks like a loose sac or bag between the patella and the front of the femur. This membrane stretches from the outer side of the external to the inner side of the internal condyle. Above, it is attached to the femur at a THE LIGAMENTS WITHIN THE KNEE-JOINT. 357 varying distance from its articular surface, for whilst it is often only a few lines above the inner margin of the inner condyle and the inner half of the patellar facet on the femur, it is fixed fully half an inch above the outer portion of this facet, and still further from the outer border of the external condyle. Below, it is connected with the upper and lateral borders of the patella near to its articular facets, and with the front border of the head of the tibia. On the outer side it spreads beneath the anterior portion of the external lateral ligament, and blends with the sheath of the popliteus tendon. On the inner side of the joint it joins the internal lateral ligament. The synovial membrane lines its deep surface and holds it against the borders of the semilunar cartilage, and it is also attached to the coronary ligaments. On its superficial aspect it is strengthened, between the femur and patella, by the thin expansion from the subcrureus muscle, and over this a quantity of fatty tissue is interposed between it and the expansion of the quadriceps extensor tendon. Adipose tissue and a bursa separate it from the ligamentum patellae. We have now seen how the articular surfaces of the bones and the synovial membrane of the knee are covered in by the following external ligmiients : — 1. The ligamentum patellse ; 2. The ligamentum Winslowii ; 3. The internal lateral ; 4. The long and short external lateral ; 5. The anterior. We have next to examine the internal ligaments, some of which are fibrous, others composed merely of synovial membranes, and the fibro-cartilages, all of which are enclosed by the above. The ligaments within the joint are the following : — 1. The anterior or external crucial; 2. The posterior or internal crucial ; 3. The transverse ; 4. The coronary ; 5, The liga- mentum mucosum ; and 6. The alar. Lastly, there are the internal and external semilunar fibro-cartilages. The two crucial, like the lateral ligaments, are attached one to each of the condyles, and being tense, or nearly so, in every position of the knee, may be compared with the lateral ligaments of true hinge-joints. The anterior crucial ligament is attached to the inner half of the fossa in front of the spine of the tibia, behind the line of the transverse ligament ; and to the outer border of the articular facet for the inner condyle, as far back as the inner 358 THE CRUCIAL LIGAMENTS OF THE KNEE-JOINT. tubercle of the spine of the tibia ; near this tubercle it some- times sends off a distinct slip into the posterior crucial ligament. It passes upwards, backwards, and outwards to the posterior part of the outer margin of the inter-condyloid notch ; or, in other words, it is attached to the back part of the internal surface of the external condyle of the femur. Its connexion with the tibia is between the anterior horn of the internal semilunar fibro-cartilage which is in front of it, and the anterior horn of tlie outer semilunar cartilage, which for the most part is behind and to the outer side of it, but some few fibres of this cartilage spKt off from the rest and are attached in front of its outer edge. The component fibres of the anterior crucial ligament are not parallel nor of equal length ; those wliich are in front at the tibia are the longest, are attached the highest on the femiu', and are also the strongest. The posterior fibres are shorter and more oblique, and spring from the spine of the tibia. The anterior crucial ligament resists forward displacement of the tibia, and limits extension. In full extension all its fibres are on the stretch. As the knee passes from the ex- tended into the bent position the ligament becomes gradually relaxed, i.e., first the short posterior and then the long anterior fibres yield a little ; but the degxee of relaxation is never great, being indeed only just sufficient to allow of a sliglit inward rotation of the tibia upon the condyles round a vertical axis, i.e., of pronation. During extension this move- ment is impossible, as the anterior crucial together with the lateral ligaments combine to prevent it. It has no influence in limiting flexion of the knee. Its action is best shown in a negative manner, i.e., by cutting it across whilst the posterior crucial ligament is left entire ; it will be then seen that the head of the tibia can be brought in front of the lower end of the femm^ in the half-bent position of the joint, but it cannot be put further back than before the ligament was divided. The ijosterior crucial ligament is attached to the gTcater part of the fossa behind the spine of the tibia, but especially to its outer and posterior portion; it then passes upwards and inwards along the posterior spinous notch (which slopes in corre- spondence with this obliqiiity of the ligament), and after being joined by many scattered fibres which arise from the depres- 360 THE CRUCIAL LIGAMENTS OF THE KNEE-JOINT. From behind, even tliis cliink cannot be seen until after the removal of the areolar or fibro-fatty tissue which mats the liga- mentum Winslowii with the posterior crucial ligament and the posterior border of the semilunar cartilage, and fills up the inter-condyloid notch. The posterior crucial ligament resists backward displacements of the tibia, and tends to limit fiexion. In extreme flexion the tibia slides backwards beneath the condyles, and the ligament in consequence becomes tight. It has no effect in checking rotation, either outwards or inwards. Inward rotation is cliecked by the anterior crucial, but outward rotation, owing to the direction of the decussation of the ligaments, is not checked by either. When the other ligaments of the joint are divided, but the crucial left intact, outward rotation can be continued till these ligaments uncross, and the tibia is turned hind-foremost. The posterior crucial is stronger and less oblique in direction than the anterior ligament ; and it needs to be so, because the flexor tendons which it resists have a more direct and powerful influence on the tibia than the extensor muscles, whose tendon is attached firstly and largely into the patella. The action of the flexors upon the tibia is greatest when the knee is bent, and all the fibres of this ligament are rendered tense by flexion ; but it is only in the dissected joint that the ligament can be said to actually limit flexion, for in the living, the soft parts of the popliteal region in- terfere to check the movement before the ligament is tight enough to do so. In the slightest degrees of flexion the ligament is a little relaxed, but in extension all its fibres are tense ; they would not permit of full extension if it were not for the sliding for- wards of the tibia upon the femur in the extension movement. Thus the simultaneous movements of the joint exert counter- acting influences upon the ligament ; for while the forward sliding of the tibia in extension somewhat relaxes the fibres of the Kgament, so in the same proportion does the turning of the hinder edge of the tibia away from the femur tighten them. Conversely, flexion by depressing the anterior edge of the tibia, and turning it away from the femur, would tighten the anterior ligament, so that flexion could not take place with- out being accompanied by sliding of the tibia backwards ; nor THE SEMILUNAR CARTILAGES OF THE KNEE-JOINT. 361 could this sliding of the tibia backwards in flexion take place, unless at the same time the posterior edge of the tibia was turned upwards towards the femur ; nor, again, would the sliding forwards of the tibia in extension, which is required by the conditions of the posterior crucial ligament, be permitted by the anterior, unless at the same time the tibia rotated on the transverse axis through its superior articular surface, so as to bring its anterior edge towards the femur. Thus the crucial ligaments are so adapted to the articular surfaces, that while they possess all the advantages of lateral ligaments to hinge-joints, by maintaining a nearly imiform tension in all positions of the joint, tliey do not restrict the movements of the knee to simple flexion and extension. TJie inter-articular, or semilunar, fihro-cartilages are two crescentic plates resting upon the circumferential portion of the articular facets of the tibia, and moving with the tibia upon the femm-. They somewhat deepen the tibial articular surfaces, and are dense and compact in their struc- ture, except near their extremities, where they become looser and more fibrous. They are firmly fixed in front and behind the spine of the tibia, and somewhat loosely attached all around by the reflection from off their surfaces of the synovial membrane, as well as by the coronary ligaments which fix them to the borders of the tuberosities of the tibia. They leave uncovered more than one-third of each of the articular facets of the tibia. In width (as measured on their upper surfaces) each fibro-cartilage tapers somewhat towards its cornua; the outer somewhat more than the inner. At their widest part they are from one-half to five-eighths of an inch across ; the widest part of the outer is in front of the external lateral ligament, the widest part of the inner is behind the internal lateral ligament. Owing to a slight bevelling off of their margins the upper surfaces are rather narrower than their lower. The circumferential border of each is convex, and from one-eighth to one-fourth of an inch deep ; the inner border is concave and free, and not thicker than good thick note-paper ; the thickness diminishes gradually from the outer to the inner border ; they are thicker, i.e., deeper, behind than in front. Their lower surfaces are flat, their upper slightly concave, owing to the sudden increase in the depth of the cartilages close to their outer margin. In outline each is 362 THE SEMILUNAR CARTILAGES OF KNEE-JOINT. adapted to the shape of tlie tuberosity upon which it reste, so that the outer is somewhat more circular than the inner, and forms ahnost a complete circle. TJie outer semilunar cartilage is somewhat less fixed than the inner, and consequently can slide more freely backwards and forwards upon the articular facet of the tibia ; its anterior cornu is attached to the deep and narrow depression in the anterior fossa along the outer articular facet, and just in front of the external tubercle of the tibial spine. Its attachment is close to, and on the outer side of, the tibial origin of the anterior crucial ligament, and the loose fibrous tissue of the cornu generally splits, so as to send forwards a slip to be connected witli the tibia in front of the crucial ligament. The posterior cornu is attached firmly to the tibia behind the external tubercle, and blends very intimately with the fibrous tissue in the posterior fossa of the tibia, and through tliis with the posterior crucial ligament. It also sends forwards a narrow but well- marked slip into the back and lower part of the anterior crucial ligament. The cornua of this cartilage are separated only by the outer tubercle of the spine of the tibia. The outer margin is grooved towards its posterior part by the tendon of the popliteus muscle, which is held to it by fibrous tissue and synovial membrane, and separates it from the external lateral ligament. Attached to the anterior border of the fibro- cartilage is the transverse ligament. The inner semilunar cartilage, owing to the shape of the inner tuberosity and to the wider points of attachment of its cornua, is a segment of a larger circle than the outer, or, more properly speaking, lias an outline more oval than circular. Its anterior cornu, which is wide and seen completely only after cut- ting through the cartilage and turning it forward, has a broad and oblique attaclmient to the anterior margin of the head of the tibia. It reaches backwards and outwards from the margin of the tuberosity towards the middle of the fossa in front of the tibial spine. It is altogether in front of the anterior crucial ligament, the attachment of which to the tibia is between it and the anterior cornu of the outer cartilage. Its posterior cornu is also firmly fixed to the tibia by a broad insertion, which extends in an antero-posterior line along the inner side of the posterior fossa, from the internal tubercle of the spine to the posterior margin of the head of PLATE XXXW. VIEW OF FRONT OF KNEE JOIHX AFTER RAISING CAPSULAR: UGAMZ.NT &. CUTTING AWAY THE LIGAMEMTUM MUCOSUM 'f ccttvcc'hyn.fi^it ofi a u vCLe of hnee to renuvw ipi. of f cutty- tis^vL-e crvu^l fttet^ih'r'cO-u:- tfaivLHa^f CMftiiaqe- OTOt-Lcur^y 1iaa>yi-e>vt to fair^TA-y. Ant cfVUrietL lu)i Pa-cet of Uhici- THE USES OF THE SEMILUxVAR CARTILAGES. 3G3 the tibia. It is firmly connected with the posterior crucial ligament, and with the fibrous tissue in the fossa of the tibia. The posterior crucial ligament is attached to the tibia on its outer side, and ' behind it reaches down somewhat lower into the popliteal notch. Its convex border is connected with the internal lateral ligament and the tendon of the semi- membranosus muscle. ISTeither cartilage can be satisfactorily examined except by raising it from the tibia after dividing the coronary ligament. The purposes served by the semilunar cartilages are, first, to interrupt shocks or jarring vibrations, which but for them would be transmitted from the leg to the thigh, not only in jumping or stamping, and such like actions, but even in walking and running ; secondly, they serve to fill the angular intervals between the articular surfaces of the femur and tibia, which sometimes, as during extension, are but slight, but at others, as during flexion, are considerable ; thirdly, they deepen the facets of the tibia for the condyles ; and to serve this latter purpose they are less fixed at their forepart than behind, so as to be able to close in upon the spherical portions of the condyles in flexion, and to slide forwards and be squeezed out into large circles by the anterior nearly flat portions of the condyles in extension. This adjustment of the fibro-cartilages to the condyles of the femur in the varying positions of the joint is due partly to theu^ own tendency to shift, partly to their connexions, and partly to the pressure and pull of sur- rounding parts. In flexion and extension the cartilages move with the tibia upon the femur. In supination and pronation the tibia moves upon them while they remain unaltered in their position to the femur ; the outer cartilage is steadied chiefly by the pres- sure of the popliteus (which is the muscle chiefly concerned in rotating the tibia inwards, i.e., in pronating the leg) against the outer margin of the cartilage, whilst it is acting upon the tibia. The transverse ligament is a rounded slender short cord, which extends between the front of the convex border of the external semilunar cartilage and the concave border or anterior cornu of the inner cartilage, near which it sometimes dips downwards to be attached to the fossa in front of the spine of the tibia. It is situated immediately beneath the synovial 364 THE CORONAKY LIGAMENTS OF THE KNEE-JOINT. membrane, and is best seen after laying open the front of the joint by detaching the ligamentuin mucosum from the femur as far as its base on the infra-patellar fat. It is a mere acces- sory band of the external cartilage. The purpose of this ligament is to keep the semilunar cartilages in their due relative positions to one another, and it is especially of use in preventing the anterior portion of the external cartilage, which slides so much more freely upon the tibia than does the inner, from being displaced outwardly. The coronary ligaments. — This name is given to the structure which attaches the semilunar cartilages to the head of the tibia. Were it not for these so-called ligaments there would be nothing to prevent the cartilages from being moved freely away from the borders of the tuberosities. In reality they are nothing more than the connexion between the margin of the inter-articular cartilages and the fibrous envelope of the joint, such as is found in each of the joints of the body which possesses an inter-articular fibro-cartilage. As in other joints, so in the knee, there is a synovial space on each surface of the cartilage, but those of the knee differ apparently from othei- inter-articular fibro-cartilages by being fixied at their cornua into the articular extremity of the tibia. This difference, however, is not real, for the fossae and spine of the head of the tibia form a non-articular space between the two articular facets, and are indeed one of the limits of each of those facets, and therefore the attachment of the cornua of the fibro- cartilages to them is in no way different from the attachment of the cartilage of the sterno-clavicular joint to the clavicle above and the costal cartilage below ; or of that of the radio- carpal joint to the styloid process of the ulna and the edge of the articular surface of the radius. These coronary ligaments are not in reality separate structures, but consist of the several ligaments which are connected with the rim of the cartilages as they pass over them to be attached to the head of the tibia. Thus in front on each side of the median line the anterior ligament ; on the inner side, the internal lateral ligament ; on the outer side, the sheath of the popliteus muscle ; and behind, on either side of the popliteal notch, the ligamentum Winslowii enter into their construction. The external coronary ligament is much more lax than the internal, so that the external cartilage can be raised higher from ALAR LIGAMENTS AND THE LIGAMENTUM MUCOSUM. 365 off the tibia — as liigli as three-eighths of an inch. In doing so the fossa, both in front of and beliind the spine of the tibia, is exposed. On raising the inner cartilage the inner border of the anterior fossa is scarcely uncovered, though part of the posterior fossa is exposed. This loose attachment of the outer semilunar cartilage permits of it changing its position more freely than the inner, in the flexion and extension movements of the joint. The synovial membrane of the joint dips downwards between the under surface of the external semilunar cartilage and the outer tuberosity of the tibia as low as the superior tibio-fibular ligament, and in doing so stretches nearly as far towards the middle line as the popliteal notch ; in this way it forms a bursa in connexion with the joint, over which the popliteus plays at the back of the tibia. The Alar Ligaments. — After laying open the synovial sac in front, and drawing down the patella and capside, and then flexing the tibia acutely upon the femur, there is seen passino- backwards from the capsule, near the sides of the patella, a prominent crescentic fold or wing on each side, formed by a doubling upon itself of the synovial membrane. These are the alar ligaments. Their free margin is concave and thin, and curves downwards and backwards upon the mass of fat below \the patella, until it is lost in the hgamentum mucosum. Each mas a pouch or fossa above and below it, the one above being bounded along the middle line by the synovial membrane as it passes backwards from the apex of the patella, to form the upper margin of the Hgamentum mucosum. The Ligamentum Mucosum. — This so-called ligament is the central portion of the large process of synovial membrane, of which thi alar ligaments form the lateral free margins. It extends from the infra-patellar fat backwards and upwards to the inter-condyloid notch of the femur, where it is attached in front of the anterior crucial, and to the outer side' of the posterior crucial Ligament. Near the femur it is thin and transparent, consisting only of a double thickness of the synovial membrane, but near the patella, i.e., at its base, the layers of synovial membrane contain between them some of the fatty tissue of this part of the joint. It is deeper from before backwards near the femur than elsewhere, and measures three-quarters of an inch in this direction. It is attached alou'^ 366 THE KNEE-JOINT. nearly the whole antero-posterior distance of the inter-condyloid notch, and is separated from the posterior crucial ligament on the inner side, and from the inner surface of the external con- dyle on its outer side, by a small fossa or recess. Near the patella the ligament is wider from side to side than elsewhere, but not so deep from before backwards as it is above by a quarter of an inch. Its anterior or upper edge is free, and fully one inch long ; its posterior edge is attached above by the reflection of its layers on to the crucial ligaments at the inter- condyloid notch, but is free below. It is not more than half the length of the anterior edge. From off the sides of the ligament, both above and below the alar ligaments, there are often little processes or fringes of synovial membrane, which sometimes attain to a large size, and in a diseased state develop into melon-seed-like solid bodies. The synovial membrane of the knee forms the largest synovial sac in the body. It bulges upwards, following the capsule of the joint, into a large cul-de-sac beneath the ex- tensor tendon on the front of the femur, which reaches some distance beyond the articular surface of the bone, and commu- nicates most frequently with a large bursa, interposed between the tendon and the femur above the line of attachment of the anterior ligament. After investing the cu'cumference of the lower end of the femur, it is reflected upon the fibrous envelope of the joint formed by the anterior, posterior, and lateral ligaments. It passes also over the greater portion of the crucial hgaments ; but the posterior surface of the posterior ligament, which is connected by means of fibro-areolar tissue to the front of the ligamentum posticum, and the lower portions of both crucial ligaments, where they are united together, of course cannot receive a complete covering from the membrane. The crucial ligaments, though partially enveloped by it, are of course shut out from the synovial cavity, like the tendon of the biceps from the shoulder-joint, the testicle from the tunica vaginalis, and the intestines from the peritoneum. Along the above structures the synovial membrane is conducted to the semilunar cartilages, over both surfaces of which it passes, and thence along the inner surface of the coronary ligaments to the head of the tibia, around the PLATE XXXV. fxONT VIEW OF KNEE JOINT AFTER DETACHING CAPSULAR LIGAMENT BY CUTTING ACROSS THE QUADRICEPS EXTENSOR OFThiE LEG ■:invtx^ FaX Alcr Uficcm-erU iojr H^ct^U'vOtC '.«iar'i:r>riMS-— -^s^^"-^ CrrcLCiiLe.. SemxjterulxrLosii^ of the^ TiecwL of Omy Ubr^^y TOnxiy- ^^ Qiuixlrireps extensor , fr-nrnj hiaVicL'ir joirvb. / PCCUU-CL^ Li/jcurteTLtjovtcTUj pa tedrtyto tibia/ eut oixr- luj axrcerUxunypcubellcc '?■ tnp pftibtay. — fljljula^ A..HerhSTfijotTi^ th-e-re^ve ou commxau-ccLi u viXc Taiee^ jouvt. Inner ti^xxd/ of turned-' ztpwaJ-ris . Extertuxh condvu of feraixr Inte^rnaL con-dyley of ferruir. Si-oef>s turn&d dowravourds K -Bursdu hetween/ gas (rocTvemjJbcs oorvcL 5 ernim-emJbrcmxisue. .J Sur^cu herteiO-Oipcpliteiv Jdni ^ ( ---- -, ri/> Ptu"t- ofpopUteiui ftuLSClf^ y^ , "S&rrd-mejmhmincstJUi tUTTw/L dcwmvcaxis. ^itrso/behveert. umerSLcUi of sefntnhejTvbraTLostis & t>a>; LoLt-:i of TtTteji^jointsorruetime-S coirunu, nicMJttno ^vii^uth.e-kr^JieJO^nt . AJIens 3/eh. cufier llcvr-o West,ITe^i~Trt-lus internal to the peroneal groove, to the hinder part of the lower end of the tibia, external to the groove for the tibialis posticus tendon, and to the posterior tibio-fibular ligament ; below it is attached to the posterior surface of the astragalus from the internal to the external lateral ligaments. It is separated from the tendon of the flexor longus pollicis, which is superficial to it, by some fatty tissue, and it must be observed that the course of this tendon over the back of the joint serves the purpose of a much stronger posterior ligament. The internal lateral or deltoid ligament is attached superiorly to the internal malleolus along the lower border, and to its anterior surface superficial to the anterior ligament, very strong fibres being fixed to the notch in the lower border of the malleolus. Erom this connexion it radiates, the posterior fibres are short, and incline a little backwards to be fixed to the rough inner surface of the astragalus, close to the superior articular facet, and into the tubercle to the inner side of the flexor longus jDollicis groove. The fibres next in front are numerous and form a thick and strong mass, filling up the rough depression on the inner surface of the astragalus, whilst some pass over the calcaneo-astragaloid joint to the upper and inner border of the sustentaculum tali. The portion which is con- nected above with the anterior surface of the malleolus passes PLATE XXXVISI. f -% .,^^"-'^' - THE EXTERNAL LATERAL LIGAMENT. 393 downwards and somewhat forwards to be attached to the calcaheo-scaphoid ligament. The external lateral ligament consists of three distinct slips. The anterior portion is ribbon-like, and is connected with the anterior border of the external malleolus just below the point of attachment of the anterior ligament of the ankle. Below, it is fixed to the astragalus in front of the facet for the fibula, i.e., on the rough surface overhanging the sinus pedis. The middle portion is a strong roundish bundle, which extends obliquely downwards and somewhat backwards from the anterior border close to the attachment of the anterior portion of the ligament, and from the outer sm-face of the malleolus just in front of the apex, to a tubercle on the outer surface of the OS calcis. The posterior portion is almost horizontal ; it is a strong tliick band, attached at one end to the border of the malleolus, which separates the peroneal groove from the fossa on the inner surface, and slightly to the lower part of the fossa itself ; and at the other end to the rough outer surface of the astragalus below and behind the articular facet for the fibula, as well as into the tubercle to the outer side of the groove for the flexor longus pollicis tendon on the posterior surface of the astragalus. Often a slip curves upwards from this ligament, and becomes blended with the posterior ligament. The SYNOVIAL MEMBRANE of the ankle is extensive ; besides lining all the ligaments just described, it sends upwards a short cul-de-sac for the inferior joint between the tibia and fibula. Tliis little sac is limited above by the strong interosseous liga- ment uniting the bones. Upon the anterior and posterior part of the ankle the synovial membrane is very loose, and extends beyond the limits of the articular facets as it lines the thin and delicate anterior and posterior ligaments of the joint. It is said to contain a greater quantity of synovia than any other joint in the body. Arteeies. — From the anterior tibial artery two or three fair-sized vessels arise between the external malleolar and tarsal branches of the same trunk, and enter the joint after ramifying on and in the anterior ligament. The anterior peroneal, as it passes down in front of the outer malleolus to join the external malleolar artery, sometimes supplies it, or the external malleolar itself sends little twigs to the joint ; sometimes a supply is derived from both sources. The internal malleolar 394 NERVES AND BURSiE OF THE ANKLE-JOINT. branch of the anterior tibial sends in small twigs through the anterior and internal lateral ligament. The posterior tibial sup- plies a well-marked branch as it curves round the inner ankle, which pierces the ligament beneath the posterior tibial tendon ; and another branch comes off liigher up, and enters the joint close below the edge of the tibia, near the base of the malleolus. The posterior peroneal contributes a branch which pierces the posterior ligament close to the fibular attachment of the external lateral ligament. ZSTerves. — -The ankle-joint is supplied with nerve-twigs from (1) the internal saphenous, a branch from which given off in the leg descends along the margin of the tibia, and sends filaments into the ankle-joint in front of the inner malleolus ; (2) the external division of the anterior tibial nerve. By the first som-ce the ankle-joint is brought into association through the anterior crural with the lumbar plexus, and by the second through the sciatic trunk with the sacral plexus. BuESJ];. — The bursse about the ankle, like those about the wrist, and in fact about ginglymoid joints in general, are of the vaginal, not of the vesicular form, i.e., they are sheaths formed by the reflection of the synovial-Hke membrane from the fibrous sheath of the tendon on to the tendon itself, and not simple globular sacs placed between bone and tendon, without enveloping the tendon. Usually the only vesicular bursa about the ankle is one between the os calcis and tendo Achillis ; occasionally others are connected with the flexor longus poUicis. The lov\^er part of the anterior annular ligament, which binds down the four tendons in front of the ankle, is divided into three compartments, within each of which tendons play over the joints in loose synovial sheaths. Thus there is one for the tibialis anticus, another for the extensor longus pollicis, and a third common to the extensor longus digitorum and peroneus tertius. Behind the ankle there is a bursa common to both the peroneus longus and brevis tendons, between them and the lower end of the fibula, as low down as the apex of the malleolus. This continues inwards upon the peroneus longus as far as the sole of the foot, but in front of the malleolus and between the tendon and the os calcis there is a bursa proper to the peroneus brevis. There is a loose synovial sheath or bursa, like those in which the muscles in front of the ankle and the peroneal muscles play, for the flexor longus pollicis ; this extends over ri_/^ ( IT- /»./»> /v 1/^ . BURS/E BETWEEN THE FRONT OF ANKLE J O I NT sl LOVyER END OF TIBIA, AND THE TENDONS PASSING OVER THE JOINT. TervBTTUtn^ del' '. after ^ihrvra . WesT.Iit^-.-.-n.i^n. Sr.Cc.liCh.. SURS/E AT THE BACK OF THE HEEL & OUTER 8e INJNER SIDES OF ANKLE. dOJNT, j cxsnXxxJJTLed^'iVtthjxL/ ' ay 'briAx^ou ojjrarujn/ ^^ to 'both. '^--., Teruaioru of tibixHi , -ubSctihxjOu &: ..... ,^^ Fleaior dbLq-vUjriJL '^ i ,lhLCL& -*5^, IOcTUjc Bursa- hetwe, LendoAchil 'i &OS colds JBuT-Scu proper tojjerorvezcs hrevis, JSicrscujoroper to peroneus Zonqus . ■I Jltin^nuxrt d-eL-'\fter MoTvro. We^b, ;Ve1 .ACfi.Lia-i.. MUSCLES OF THE ANKLE-JOINT. 395 •the tendon from some distance above the lower end of the tibia to beyond the groove in the sustentaculum taK. Similarly there is a bursa to ease the play of the flexor communis digitonmi over the lower end of the tibia, the in- ternal lateral hgament, and os calcis ; and of the tibialis posticus tendon over the tibia, internal lateral ligament, and head of ths astragalus, as far as the tubercle of the scaphoid. Although not in dhect connexion with the ankle-joiut, this seems the best place to mention the synovial sac, or bursa, between the tendo Achillis and the upper and back part of the os calcis. Part of the wall of this bm^sa is often much thickened with fat, into which the tendon of the plantaris is partly in- serted. It has been said of this little muscle, that one of its uses is to compress this fatty tissue of the bm-sa. Muscles. — All the muscles which arise from the tibia and fibida pass over the ankle, some to be inserted into the tarsus and metatarsus, and others into the digital phalanges. Only two muscles which arise above the knee pass beyond the ankle ; these are the gastrocnemius and plantaris, which, arising from the condyles of the femur, are inserted wdth the soleus into the OS calcis by means of the tendo Achillis. In all, twelve muscles are in relation to the ankle — ^dz., in front, the tibialis anticus, the extensor longus pollicis, extensor communis digitorum, and peroneus tertius ; behind the outer ankle, the peroneus longus and brevis, which rest on the posterior and middle por- tions of the external lateral ligament, the brevis lying nearest to the joint ; beliind the inner ankle, from the malleolus to the heel, the tibiahs posticus, the flexor longus digitorum, and the flexor longus poUicis ; and lastly, the three muscles which go to the OS calcis. The tibiahs anticus and posticus, and the peroneus longus, brevis and tertius, are inserted into the tarsus and metatarsus. The two former acting; together raise the inner border of the foot and adduct it ; the tliree latter acting together raise the outer border of the foot and abduct it. The tibialis anticus and peroneus tertius acting together flex the foot on the leg, i.e., draw up the dorsum of the foot to- wards the front of the leg; whereas the peronei longus and brevis and tibialis posticus extend the foot. The tibialis posticus, owing to its wide insertion into the bones and liga- ments of the tarsus, and the peroneus longus by crossing 396 MOVEMENTS OF THE ANKLE-JOINT. obliquely from the outer border of the tarsus to the inner border of the metatarsus, assist materially in supporting the transverse as well as the longitudinal arches of the foot; the former assists also several ligaments in holding the various bones of the tarsus together. The flexor longus digitorum, flexor longus pollicis, extensor communis digitorum, and extensor longus pollicis are inserted into the phalanges. The two former flex their respective toes ; and when this action is either completed or prevented, they assist the tibiahs posticus and peronei longus and brevis to extend the ankle. The oblique direction in which the flexor longus digitorum enters the foot is corrected by the musculus acces- sorius, which, besides altering the line of action of the muscle, increases its power upon the toes, and gives a fixed point to the long tendon when acting on the ankle-joint. The ex- tensors of the toes also assist the tibialis anticus and peroneus tertius to flex the ankle-joint when their action on the pha- langes is either prevented or completed. The muscles of the calf are the powerful extensors of the foot, by means of which chiefly the heel is raised and the weight of the body is thrown on to the ball of the foot, as in walking, leaping, and running. The gastrocnemius, besides acting with the soleus as an extensor of the ankle, is a flexor of the knee, when the ankle is flxed by the muscles passing over the front of that joint. Movements. — Although it has been stated that certain muscles turn the inner border of the foot upwards and move it inwards, and that others tm^n the outer border upwards and move the foot outwards, these movements do not occur at the ankle-joint. This is a true hinge- joint, and flexion and exten- sion are the only movements of wliich it is capable. No lateral movement whatever is permitted, except the very slightest, when the foot is in a state of extreme extension, and thereby the narrowest part of the astragalus is tin-own forwards into the widest part of the tibio-fibular arch. The ligaments which limit flexion are — (1) nearly the whole of the internal lateral ligament, none but the most anterior fibres of it being relaxed ; (2) the posterior and middle portions of the external lateral Ligament, but especially the posterior portion; (3) the posterior ligament of the joint. HOW MOVEMENTS ARE LIMITED. 397 Flexion is also limited by the neck of the astragalus pressing against the edge of the tibia. Extension is limited (1) by the anterior fibres of the internal lateral hgament ; (2) the anterior and middle portions of the external lateral ligament ; and (3) the inner fibres of the anterior ligament. Extension is also checked by the posterior part of the astragalus meeting with the back of the tibia. The middle portion of the external lateral ligament is always on the stretch owing to its obliquely backward direction, whereby it limits flexion ; and its attachment to the fibula in front of the apex of the malleolus, whereby undue extension is prevented as soon as the toes begin to twist inwards. This twisting inwards of the toes in extreme extension is partially due to the greater posterior length of the inner border of the superior articular sur- face of the astragalus and to the lesser proportionate height poste- riorly of the outer border of that surface, the hindermost part of which is, in extension, brought into the tibio-fibular arch ; but partly also to the lateral movement ia the calcaneo-astra- galoid joints. Flexion and extension take place round a transverse line drawn through the body of the astragalus. The movements are not in a direct antero-posterior plane, but along a plane inclined outwards and drawn through the foot from the middle of the astragalus to the apposed surfaces of the bases of the second and third metatarsal bones. This oblique plane corre- sponds to the outward incKnation of the toes, to the slight twisting of the shaft of the tibia, and to the posterior position of the external malleolus. CHAPTEE XX. THE JOINTS AND LIGAMENTS OF THE FOOT. The foot forms the inferior segment of the lower limb, and is placed at a right angle to the leg at the ankle-joint. It is thus horizontal in direction when the body is erect, indeed this relation of the foot to the leg, like the similar relation of the head to the spine, is an adaptation of the erect attitude of man. In scarcely any animal, except man, is there a similar disposition of the foot to the leg. Moreover, the human foot is distinguished from that of the quadrumana and other animals (1) by the small size of its phalanges, (2) by the relatively larger size of the tarsus ; (3) by the great strength of the poUex, which is able to bear a considerable part of the weight of the body ; (4) by the position of the pollex in front of the tarsus, and its parallelism with the other toes, instead of being set off at an angle like the thumb ; and (5) by the secure manner in which the bones of the tarsus are bound together, and to the metatarsus by strong ligaments,, whereby they form a double arch upon which the body can be supported with steadiness, or move with elasticity and ease. The size of the foot varies in different individuals. It always exceeds the hand in length and thickness, but should fall short of it in width. The shape of the foot is ovoidal, with its long axis from before backwards. It consists of three segments of different constructions, and named in order from behind forwards, the tarsus, metatarsus, and phalanges or toes. The toes are much smaller and weaker than the fingers. They enlarge the area of the foot, confer upon it some amount of clinging or grasping power, and add to the elastic spring of the foot through the agency of their joints and tendons. Their small size is a characteristic feature of the human skeleton. Practically they are almost useless amongst civilised races. JOINTS AND LIGAMENTS OF THE FOOT. 399 owing to their confinement within the close limits of boots ; but, in primitive states, and in those in which shoes are not employed, they are of service in climbing, and, by their capacity for clinging to inequalities of surface, they prevent slipping during the act of walking upon uneven ground. Occasionally they have been turned to great and varied uses by persons deficient of hands ; but these cases are altogether exceptional, and in the ordinary way the phalanges in man are quite unnecessary to the well- being of the individual. The tarsus and metatarsus are much more solid, and vastly stronger than the phalanges, but they do not equal them in their degree of mobility. Although the phalanges of the foot are so much smaller, and so much less mobile, than the corre- sponding parts in the hand, the tarsus and metatarsus are larger, stronger, and of more significance in every way than their corresponding parts in the hand. In other words, the degxee of importance of different parts of the hand is inverse to that of the homologous parts of the foot ; the anterior por- tion of the former, and the posterior of the latter, possessing the most striking characters and the chief value. The foot is indeed like the hand in certain respects, but is modified so as to serve as a basis of support, whereas the hand is adapted, not for the purpose of bearing weight (though this it is able to do to a considerable degree), but of accomplishing rapid, varied, and delicate movements. Both hand and foot possess great elasticity, but one of the most striking modifica- tions of the foot is the great size and strength of the metatarsal bone of the great toe, and its mode of articulating with the tarsus, whereby only a very limited degree of movement is permitted. In animals which use the distal segment of both anterior and posterior extremities for prehension, e.g., the quadru- mana, these segments in all four extremities are developed like thumbs ; the foot cannot bear weight without the assistance of the hand, and the several parts of the foot are less closely adapted to one another, and form much less perfect arches. The arches of the human foot are formed entirely by the tarsus and metatarsus combined, the phalanges taking no share in them; they are two in number — an antero-posterior,and a transverse. The antero-posterior arch has its summit at the top of the 400 JOINTS AND LIGAMENTS OF THE FOOT. astragalus, wliere tliat bone articulates with the tibia to form the ankle-joint. Its hinder limb, or pier, is formed by the back of the astragalus, and somewhat more than the posterior half of the OS calcis ; while the anterior limb, or pier, is formed by the anterior parts of the astragalus and os calcis, by the other tarsal bones, and by the metatarsus. Thus, when the foot is planted firmly on the ground it rests upon the point of the os calcis behind, and upon the anterior extremities of all the metatarsal bones in front, as well as upon the outer border of the foot. These two piers differ from one another strikingly in width, length, solidity, inclination from the summit of the arch, in the number of articulations formed by them, and, as a consequence of the latter difference, in their degTee of elasticity. The hinder pier measures about one inch and a half in width, and from two and a half to three inches in length, being just about half the width and length of the anterior pier. The inclination of the liinder pier to the vertical line drawn through the centre of the astragalus makes an angle of about 40°, whilst the angle made by the anterior pier with this line is between 70° and 75°. The hinder pier is nearly solid, being broken by the line of one articulation only, viz., the calcaneo-astragaloid ; by this construction the muscles of the calf which raise the foot act at once upon the ankle-joint, without being weakened by any moving surfaces between their insertion and point of action. The anterior pier is composed of many articulations, viz., tarsal, tarso-metatarsal, and metatarsal ; and by means of these several joints and their ligaments, an elasticity and spring are given to the foot, which are of great use in leaping, running, and walk- ing ; whilst concussions are broken or prevented by them. The anterior pillar widens out as it extends forwards, and thus the jarring effects of shocks are diminished by their distribution over a wider area. The difference in the capacity of these two piers to prevent shocks to the foot, or rest of the body, is expe- rienced in jumping from a height ; if we alight upon the hinder pier, an unpleasant shaking occurs, which is but rarely felt, and then to a less extent if we descend upon the balls of the toes. The anterior pier of the arch may be regarded as com- posed of two divisions, an inner and an outer ; the inner is formed by the astragalus, scaphoid, the three cuneiform, and the three inner metatarsal bones ; and the outer by the os JOINTS AND LIGAMENTS OF THE FOOT. 401 calcis, cuboid, and fourth aud fifth metatarsal bones. The tarsal part of the inner division is less solid than that of the outer ; but it is more elastic, and to it the chief part of the weight of the body is transmitted directly from the astragalus, and is conveyed forwards to the balls of the three inner toes. The metatarsal portion of the inner division, owing to the great size of the first metatarsal bone, is much more solid than the corre- sponding part of the outer division of this pier. The second metatarsal bone is the longest of all, whilst the two sesamoid bones of the metatarso-phalangeal joint of the great toe com- pensate for the diminished length of the first metatarsal bone. Possibly the second metatarsal bone touches the ground before the balls of any of the other toes, except the fifth ; if so, it would explain the wearing away of the soles of the boots beneath this part of the foot. Practically, it must be understood, when the foot is firmly resting on the ground, the weight of the body is borne upon the extremities of all the metatarsal bones, and not simply upon those of the first and fifth, as has been some- times stated. The inner division is much more highly arched than the outer, especially in its tarsal portion. The outer division bears less weight, and this is transmitted to it indirectly from the astragalus through the os calcis. It forms a lateral support or stay to the inner division. The inner border of the foot taken as a whole is concave, the outer border is convex ; and from heel to balls of toes there is an inclination of the whole foot out- wards — an arrangement well adapted for receiving weight from the leg which is directed inwards. The transverse arch, which is most marked across the cunei- form bones, like the antero-posterior, gives elasticity to the foot, and provides for the safe lodgment of the vessels and nerves of the sole ; the arches result from the shape of the articular surfaces of the bones, and their integrity is maintained by the fascia3 of the sole of the foot, the strong ligaments of the tarsus and metatarsus, the decussation of the tendons of the tibialis posticus and peroneus longus, by the small muscles of the sole, and by the tibialis anticus. The foot is composed of twenty-eight bones, arranged ia three divisions, named from behind forwards, the tarsus, meta- tarsus, and phalanges. In the tarsus there are seven bones, ten articulations, and four synovial sacs ; in the metatarsus D D 402 THE CALCANEO-ASTRAGALOID JOINTS. there are five bones, three articulations, but no separate synovial sac. Between the tarsus and metatarsus there are five articula- tions, with one separate synovial sac, and two synovial sacs in com- mon with those between the several tarsal and metatarsal bones. There are fourteen phalanges, forming nine inter-phalangeal articulations, each joint having its own synovial sac ; and finally, there are five metatarso-phalangeal joints, each with its own synovial sac. The bones of the tarsus articulate with one another, and four of them with the metatarsus ; the four outer metatarsal bones articulate laterally with one another ; the phalanges of the second row articulate at their bases with the heads of the phalanges of the first row, and at their heads with the bases of the phalanges of the third row ; whilst the pha- langes of the first row articulate by their bases with the meta- tarsal bones of their own toes, and those of the third row taper off at their distal ends into flattened, rough, non-articular surfaces. The inter-tarsal articulations, with only one exception, are of the arthrodial character ; they may be di\'ided into (1) those which unite the posterior bones of the tarsus, viz., the poste- rior and anterior, calcaneo-astragaloid ; (2) those which unite the anterior bones of the tarsus with one another, viz., the three scapho-cuneiform, the two inter-cuneiform, the cubo- cuneiform, and cubo-scaphoid ; and (3) into those which unite the two bones of the posterior portion of the tarsus with two of the bones of the anterior portion of the tarsus, viz., the astragalo-scaj)hoid and the calcaneo-cuboid ; these two together form what is commonly called the medio-tarsal articulation. The Joints and Ligaments of the Posterior Part of the Tarsus, or the Calcaneo-astragaloid Articulations. Class, Diarthrosis. Subdivision, Arthrodia. The OS calcis articulates with the astragalus by a double joint, the anterior and posterior ; the anterior communicates with the medio-tarsal articulation ; the posterior is separate and complete in itself. The Posterior Calcaneo-astragaloid Joint. The Os Calcis presents on its superior surface two articular facets of unequal size, of different aspects, and separated from one another by a deep groove. Besides the two articular facets THE POSTERIOR CALCANEO-ASTRAGALOID JOINT. 403 and tlie groove between tliem the upper surface of the bone is characterised by a {a) large non-articular portion behind ; (5) by an inwardly projecting process, partly articular and partly non-articular, called the sustentaculum tali, in front of the inner extremity of the groove ; and (c) by a sudden alteration in the level of the surface, so that the anterior tliird is one inch lower than the posterior two-thirds, owing to the dif- ference in the vertical thickness of the bone. The posterior and larger facet is convex, situated somewhat in front of the middle of the upper surface, and articulates with the large - concave posterior articular facet on the under surface of the astragalus. It occupies in part the elevated portion of this surface, but cliiefly the precipitous surface formed by the sudden alteration in the levels of the anterior and posterior portions of tliis bone ; the facet is oblong in form, with its long diameter directed obhquely outwards and forwards; it stretches across the whole mdth of the calcis, and looks upwards with a very considerable inclination forwards. Indeed, when the bone is examined separately, and placed with its under surface on a flat table, the anterior and outer two-tlurds of the facet look almost directly forwards, while the posterior and inner one-third looks upwards and inwards. Tliis inclination of the facet is somewhat altered in the articulated foot, owing to the long axis of the os calcis being directed upwards and outwards from the heel, on account of the bone entering into the formation of the antero-posterior arch of the foot. The posterior part of this facet slopes downwards and forwards on the inner side of the bone, so as to approach the sustentaculimi taK. From the inwardly projecting posterior edge of this process the facet is only separated by the very narrow inner end of the interosseous groove. Between the facet and this end of the sustentaculum tali there is a cup-like concavity, into which the projecting posterior, inferior, and internal angle of the astragalus is re- ceived in certain positions of the foot, as when the heel is raised in walking ; whilst the angle of the astragalus becomes wedged against the sustentaculum tali. Again, in front of the outer end of the interosseous groove the upper surface is some- what raised, so that a cup-like depression is formed between the lower and outer end of the large facet and the non-articular front part of the upper surface of the calcis ; into this de- pression the anterior, inferior, and external angle of the astra- D D 3 404 CALCANEO-ASTHAGALOID LIGAMENTS. galus is received in certain positions of the foot, as when the heel is raised in walking. Thus these parts of the calcis act as strong stops or checks, against which the astragalus is pressed when the heel is raised, and the weight of the body is directed from the vertical into the obliquely forward direction. The interosseous groove is narrow at the inner end, and widens as it proceeds outwards ; it extends obhquely forwards and outwards from the inner to the outer edge of the os calcis. This OTOOve, with a similar one on the under surface of the astragalus, forms the sinus pedis, and gives attachment to the strong interosseous ligament which connects the two bones together. The AsTKAGALUS presents on its inferior surface two articular facets separated by a deep rough groove : the posterior fca^et articulates with the posterior facet on the body of the os calcis ; it is much the larger of the two, and extends obliquely across the whole width of the bone, being about one inch and a half in length, and nearly three-quarters of an inch in width. It looks downwards and backwards, has its long axis obliquely forwards and outwards, va. which direction it is concave, while it is flat, or nearly so, from side to side. Its hinder part is broader than its anterior extremity ; its posterior edge forms one of the boundaries of the groove for the flexor longus pollicis tendon, its external edge is separated by a narrow groove from the articular surfaces for the tibia and external malleolus, and its anterior edge limits the interosseous groove. Overhanging this passage on the inner side of the bone, and forming a prominent edge to the groove for the flexor longus pollicis, is a projecting angle of bone, which in certain positions is pressed forwards against and resisted by the posterior edge of the sustentaculum tali. Again, another angle projects beyond the anterior and external extremity of the facet, and is resisted by the elevation on the upper surface of the body of the os calcis. In this way the forward and inward displacement of the astragalus by the weight of the body when the heel is raised is prevented ; and in the same •way the weight is distributed to the cuboid and two outer metatarsal bones through the calcaneum from the astragalus. The Ligaments. — The ligaments in connexion with the posterior calcaneo-astragaloid joint form a complete capsule. They consist of the interosseous ligament, wliich is the cMef {"^X JL V~!c« CALCANEO-ASTRAGALOID LIGAMENTS. 405 bond of union between the bones, forming the anterior portion of the capsule, and of the external, internal, and posterior calcaneo-astragaloid ligaments. The interosseous calcaneo-astragaloid ligament is the strong band connecting the opposed surfaces of the os calcis and the astragalus along their oblique grooves. It is composed of several vertical laminse of fibres, sometimes ten or more may be distinctly seen, amongst which is a quantity of fatty tissue. This ligament is much deeper and broader, and better marked towards the outer end than elsewhere. Strong laminse of fibres reach between the rough superior surface of the anterior extremity of the os calcis, and the rough external and inferior surface of the neck of the astragalus. They have sometimes been described as the anterior interosseous ligament, and they form the posterior boundary of the anterior calcaneo-astragaloid joint. The most posterior lamiase occupy the hinder part of the sinus pedis, and extend downwards and backwards from its roof to the os calcis immediately in front of the large facet for the astragalus. They thus form the anterior part of the capsule of this joint. The external calcaneo-astragaloid ligament extends between the bones on their outer side. It is attached to the groove on the side of the astragalus near its lower margin, and to the os calcis at some little distance below the edge of the articular surface. The middle portion of the external lateral ligament of the ankle-joint passes over and strengthens it. The interval between the anterior and middle portions of the external lateral ligament of the ankle is occupied by the fibres of this calcaneo-astragaloid hgament ; and a considerable fascicrdus of its fibres passes from the astragalus to blend with the middle portion of the ankle-joint ligament along its anterior border. The posterior calcaneo-astragaloid ligament passes from the process of bone behind the groove for the flexor longus pollicis, and from the lower edge of that groove downwards and back- wards to the rough superior surface of the os calcis at a variable distance behind the margin of the large articular facet. The space between the posterior calcaneo-astragaloid ligament and the tendo Achillis is occupied by a quantity of fatty tissue. The internal calcaneo-astragaloid ligament, a narrow strip of very short but well-marked fibres, passes obliquely downwards 406 ANTEKIOR CALCANEO-ASTRAGALOID JOINT. and backwards from a depression upon the astragalus imme- diately behind the inner extremity of the sinus pedis to the os calcis, behind the sustentaculum tali. This ligament therefore completes the floor of the groove for the flexor longus poUicis tendon. It must be remembered that owing to the obliquity of the articular surfaces and the sinus pedis, the inner border of this posterior calcaneo-astragaloid joint is necessarily very small. The SYNOVIAL MEMBEANE is distinct from any other synovial sac. The Arteeies. — 1. A branch passes into the interosseous canal on the inner side, from the posterior tibial artery, and supplies the structures of this joint. 2. Other twigs are derived from a branch of the tarsal artery which enters the interosseous canal on the outer side. 3. The external malleolar of the anterior tibial ; and (4) the terminal branches of the peroneal artery supj)ly articular branches to it on the outer side. The Nerves. — The posterior tibial, or one of the plantar branches into which it divides. BuES^. — The bursse of the tendons which pass over the back of the ankle-joint extend also over the line of this articulation. Tlie Anterior Calcaneo-astragaloid Joint. This joint is bounded behind and on each side by ligaments, but is incomplete in front v^here it communicates with the astragalo-scaphoid articulation. It is formed between the anterior articular facet on the upper surface of the os calcis and the facets on the lower surface of the neck and head of the astragalus. Os Calcis. — The anterior facet on the superior surface of this bone is separated from the posterior by the interosseous groove and by the rough anterior portion of its upper surface. It is internal to and narrower than the posterior facet, and is longitudinally concave, instead of being convex, Hke the posterior. It is oblong in shape, has its long diameter inclined forwards and outwards, and its surface looking upwards and forwards. It occupies chiefly the superior aspect of the sustentaculum tali, but in part also the anterior internal edge of the upper surface of the body of the os calcis. The portion upon the sustentaculum tali articulates with the facet on the under surface of the neck of the astragalus, the portion upon the body of the bone articu- THE LIGAMENTS OF THE ANTERIOR JOINT. 407 lates Mdth the small facet on the lower and outer part of the head of the astragalus ; these two portions are sometimes separated by a narrow rough depression, which corresponds to a slight ridge on the apposed surface of the astragalus, separating the facet on the neck from that on the lower and outer side of the head of that bone. Astragalus. — The anterior articulating facet on the inferior surface of this bone for the os calcis occupies, as has been said above, partly the neck and partly the lower aspect of the head. Its long axis is obliquely forwards and outwards ; its surface is directed backwards and downwards, and it is convex to suit the corresponding concavity of the apposed facet of the os calcis. It is divided into two parts by a short ridge which runs obHquely forwards and inwards, and together with a constriction in the hinder border of the facet corresponds to the groove on the apposed surface of the os calcis. The portion on the outer side of the ridge rests in part on the body of the OS calcis, and in part on the calcaneo-scaphoid ligament, whilst in 'the movements of the bones it slides backwards and forwards on both. The inner and larger part of this facet is often separated by a small non-articular interval from the facet on the rounded head for the scaphoid. The Ligaments. — The ligaments are situated on the pos- terior, internal, and external aspects of the joint. Anteriorly there is no ligament, for here it is continued into the astragalo- scaphoid articulation. The interosseous calcaneo-astragaloid ligament by its anterior laminae limits this articulation posteriorly. It has been de- scribed under the posterior calcaneo-astragaloid joint. The internal calcaneo-astragaloid ligatnent consists of short fibres attached above to the rough depression on the internal surface of the neck of the astragalus, and below to the inner free border of the sustentaculum tali close to its upper margin. These fibres are blended posteriorly with the inner extremity of the interosseous ligament, and anteriorly with the upper border of the calcaneo-scaphoid ligament on its deep aspect. They are strengthened by the internal lateral ligament of the ankle-joint, part of the fibres of which are attached to the calcaneo-scaphoid ligament on its superficial aspect. The external calcaneo-scaphoid ligament limits this as well as the astragalo-scaphoid joint on the outer side. It consists of a 4t)8 MUSCLES CONNECTING CALCANEO-ASTRAGALOID JOINT. strong well-marked but short band, which extends from the rough superior surface of the anterior part of the os calcis, and from the ridge separating the facet for the cuboid from the anterior facet for the astragalus, in a dii-ection obliquely forwards and inwards to the rough and narrow outer surface of the scaphoid bone. It is blended above with the astragalo- scaphoid Hgament, and below with the inferior calcaneo- scaphoid ligament. The internal and external lateral ligaments of the ankle- joint pass over the astragalus to the os calcis and add to the security of the joints, as well as limit the movements between these bones. The SYNOVIAL MEMBEANE of tliis joint is a continuation of that of the astragalo-scaphoid. The Aeteries. — 1. The branch to the interosseous canal from the tarsal artery. 2. The internal plantar sends a deep branch on the inner side of the long plantar ligament which supplies the medio-tarsal joint as well as this. The Nerves. — The anterior tibial nerve by, most commonly, its external branch which turns outwards over the tarsus. The Muscles connected with the Calcaneo-asteagaloid Joints. — Twelve muscles of the leg pass over the ankle to be inserted into the foot, and of these all but three are attached in front of the medio-tarsal joint, and therefore move that joint as well as the ankle and calcaneo-astragaloid articulations. Attached to the os calcis are the three muscles of the leg which are inserted behind the medio-tarsal joint. They are all inserted into the heel bone by means of the tendo AchilKs, and move the ankle and calcaneo-astragaloid joints only ; these are the gastrocnemius, soleus, and plantaris. The tibialis posticus likewise sends a slip from its tendon of insertion at the scaphoid to the under part of the sustentaculum tali. In addition to the muscles of the leg, four of the muscles of the sole act on the calcaneo-astragaloid joints by pulling on the os calcis, as well as on the toes and plantar fascia, to keep up the longitudinal arch of the foot. The muscles attached to the os calcis, besides those which form the tendo Achillis, are the extensor brevis digitorum, abductor minimi digiti, abductor poUicis, flexor brevis digitorum, and flexor accessorius, all of which arise from it. The muscles of the leg which pass over and groove the os calcis on its outer side, are the peronei longus and brevis. Those MUSCLES MOVING ASTRAGALUS ON OS CALCIS. 409 wMcli pass over it on the inner side, are the flexor longiis poUicis, the flexor communis digitorum, and the tibiahs posticus. The muscles of the leg which pass over the front of the ankle and move the foot upon the astragalus, are the tibialis anticus, the extensor proprius pollicis, the extensor longus digitorum, and the peroneus tertius. The astragalus is grooved by the flexor longus pollicis, but no muscle is attached to it. Of these several muscles, those which pass from heel to toes cannot produce any definite movement except by depressing the heel and causing the OS calcis to glide forward and inward beneath the astragalus, whereby the arch of the foot is increased. Elevators of the Heel. — The muscles which raise the heel and extend the ankle, are the tendo Achillis, tibialis posticus, the flexor longus pollicis, the flexor communis digitorum, and peroneus longus. When the heel is raised by these muscles, the astragalus, by the weight of the body, is made to slide for- wards on the OS calcis. Dejpressors of the Heel. — In addition to the muscles of the sole above referred to, others besides depress the heel. The muscles which pass over the front of the ankle raise the toes and flex the ankle-joint, and when the heel is kept in contact with the ground, the astragalus in this position of the foot is made to slide backwards on the os calcis by the superincumbent weight of the body. Adductors and Inward Rotators of the Foot heneath the Astra- galus. — The tibiahs posticus, the flexor longus pollicis, and flexor longus digitorum, which pass behind the inner malleolus ; and the tibialis anticus, and extensor longus pollicis, which pass in front of it, produce adduction or inversion, i.e., turn the inner side of the foot upwards, and rotate the toes inwards and the heel outwards. Abductors and Outward Rotators. — The peroneus longus and brevis which pass behind the external malleolus, and the peroneus tertius and the outer tendon of the extensor longus digitorum which pass in front of it, help to turn the outer border of the foot upwards, i.e., abduct or evert it, and rotate the toes outwards and the heel inwards. The Movements between the Asteagalus and Os Calcis. — The movements which occur between the astragalus and OS calcis are so intimately associated with those which 410 MOVEMENTS AT CALCANEO-ASTRAGALOID JOniITS> take place at the medio-tarsal joint, i.e., between the astragalus and OS calcis behind, and scaphoid and cuboid in front, that they might fitly be described together. It will, however, be more convenient to consider them separately. The joints between the os calcis and astragalus permit of adduction and abduction, with some rotation of the foot beneath the astra- galus, and thereby increase the variety and range of the movements of the foot upon the leg, which at the ankle-joint are limited almost entirely to flexion and extension. These movements between the astragalus and os calcis take place around an axis drawn in an antero-posterior direction, through the under surface of the astragalus, at right angles to the axis of motion at the ankle-joint. Adduction and abduction of the foot upon the astragalus are combined with some rotation, which occurs in a nearly horizontal plane ; adduc- tion or inclination of the sole inwards being associated with a tm-ning of the toes inwards, and of the heel outwards, while abduction or inclination of the sole outwards is asso- ciated with a turning of the heel inwards and of the toes outwards. In these movements the cuboid moves with the OS calcis, and the scaphoid, carrying with it the bones in front of it, revolves upon the rounded head of the astragalus. As abduction and adduction cannot occur without some rota- tion, so rotation cannot occur without some adduction or abduction. The shape of the articular facets of the two bones allows of neither true lateral nor true rotatory movements. In walking, when the foot is placed upon the ground, the heel is the first part to make contact, and the foot is slightly adducted beneath the astragalus. As the body is swung forwards to the vertical position, first the outer toes and then the inner touch the sur- face, whilst the head of the astragalus presses forwards against the scaphoid and sinks downwards upon the calcaneo-scaphoid ligament, the foot meanwhile becomes slightly abducted beneath the astragalus. When the foot is firmly placed upon the ground it has to bear the weight of the body, which is trans- mitted to it in an oblique direction from above downwards and inwards ; this being so, if the ligaments between the astragalus and OS calcis and the internal lateral ligament of the ankle- joint did not check abduction, inward displacement of the astragalus from beneath the arch of the leg bones would only MOVEMENTS AT CALCANEO-ASTRAGALOID JOINTS. 411 be prevented by tlie tendons passing round the inner ankle. So far, however, from the astragalus and inner ankle being entirely dependent for support ujDon these tendons, they also enjoy the extra security afforded by the ligaments ; but when these ligaments are too weak to limit abduction, the weight of the body increases it, and forces the inner malleolus and the astragalus downwards and inwards, and gives rise to the con- dition known as flat foot ; and if in addition, as sometimes is the case, the peronei muscles are contracted so as to draw the OS calcis and rest of the foot outwards and upwards, or if the tibialis anticus is wasted and paralysed so as no longer to assist in keeping up the arch of the foot on the inner side, taKpes valgus complicates the flatness of the foot. The advantages of the obhquity and peculiar arrangement of the articular surfaces of the posterior calcaneo-astragaloid joint become apparent from a consideration of the movements which occur in the act of walking. "When the foot is advanced in front of the body the heel is first planted on the ground, and the whole weight is thrown upon the back of the foot, i.e., upon the heel bone, as it is received upon the posterior facet of the OS calcis. When the body has been carried forwards, and the toes touch the ground, the large articular facet of the OS calcis pushes against the astragalus as the heel is being raised, so as to transfer the weight of the body on to the ball of the toes, whilst the hinder edge of the sustentaculum tali, and the anterior and outer part of the upper surface of the OS calcis, prevent the astragalus from being displaced too far forwards by the superincumbent burden ; thirdly, whilst the heel is kept raised by muscular action and the other foot is swung forwards, and before the toes leave the ground, the OS calcis serves to suspend the weight of the body by the pres- sure of the astragalus against the hinder edge of the sustenta- culiun tah and the upper and anterior part of the body of the OS calcis. In this way the weight is distributed through the OS calcis to the cuboid and outer division of the metatarsus, as well as through the head of the astragalus to the scaphoid, and through the latter to the cuneiform bones and the inner division of the metatarsus. 412 JOINTS AND LIGAMENTS OF THE FOOT. TJie Joints and Ligaments of the anterior part of the Tarsus ; or, Tlie Ciibo-scaphoid, Scapho-cuneiform, Inter-cuneiform, and Cubo-cuneiform Articulations. Class, Diarthrosis. Subdivision, Arthrodia. The bones in front of the astragalus and os calcis are arranged in two transverse rows, into each of which the cuboid enters. These rows are placed one in front of the other ; thus we find the scaphoid and cuboid united to each other, forming the whole width of the tarsus and entering into the medio- tarsal joint by their posterior surfaces, while in front of the scaphoid are placed the three cuneiform bones, which, together with the cuboid, also occupy the whole width of the tarsus, and enter into the formation of the tarso-metatarsal joints by their anterior surfaces. These several bones are united by ligaments with one another, so as to form one firmly and closely united but yielding structure, in which are found no less than seven articulations. The Union hetween the Scaphoid and the Cnhoid. The Scaphoid. — The narrow outer end of the scaphoid is united with the posterior part of the internal surface of the cuboid by ligaments passing between the dorsal, plantar, and apposed surfaces of the bones. Tliis surface of the scaphoid is rough and convex, but has occasionally a minute facet for the cuboid towards its anterior part which is continuous over a sharp edge with the surface on the same bone for the external cuneiform bone. The Cuboid. — The inner surface of the cuboid looks inwards, upwards, and a little forwards ; and presents upon its posterior third a deep rough depression for the attachment of an inter- osseous Kgament — viz., the cubo-scaphoid ; surrounding this depression is a rough ridge which is very prominent above and in front, and separates it from the facet for the outer cuneiform bone. Sometimes a second small cartilage-covered siirface is present immediately behind this larger facet ; this is for the scaphoid. When the scaphoid and cuboid are in contact, the CUBO-SCAPHOID UNION. 413 cubo-scaphoid interosseous ligament is behind the articular facets, whilst the facets themselves are continuous with other facets on the respective bones for the external cuneiform. The posterior inferior and internal angle of the cuboid forms a large rounded tubercle which projects backwards beneath the OS calcis, and inwards beneath the outer end of the scaphoid. The latter is supported by the tubercle, with only the interven- tion of their uniting ligaments. The scaphoid and cuboid together form a well-marked transverse arch, the highest point of which is at the junction of the outer and middle thirds of the dorsum of the scaphoid. The outer pier of this arch, which is the tubercle or outer end of the ridge of the cuboid, descends much lower than the inner pier which is formed' by the tubercle of the scaphoid. Ligaments connecting the two Bones of the second Eow OF THE Tarsus together. — The dorsal cuho-scaphoid ligament runs forwards and outwards from the outer end of the dorsal surface of the scaphoid to the middle third of the inner border of the cuboid on its dorsal aspect. It passes over the posterior external angle of the outer cuneiform bone, and is wider towards its outer than at its scaphoid attachment. The plantar cubo-scaphoid ligament is a well-marked and strong band taking the same oblique course forwards and out- wards to the cuboid as does the dorsal ligament. It is attached to the plantar surface of the scaphoid some distance external to the tubercle, and to the depression on the inner side of the cuboid, and slightly into the plantar surface of the cuboid immediately below this depression. The Interosseous Cubo-scaphoid Ligament. — A strong ligament passes between the apposed surfaces of these bones from the dorsal to the plantar ligaments. Some of its posterior fibres reach the plantar surface of the foot behind the cubo-scaphoid plantar ligament, radiate outwards and backwards over the inner border of the cuboid to blend with the anterior extremity of the short calcaneo-cuboid ligament. ITie Articulation between the Scaphoid and the three Cuneiform Bones. The Scaphoid. — The anterior surface of the scaphoid, which is slightly convex from side to side, has curved superior and inferior margins, the convexity of which is upwards and in- 414 THE SCAPHO-CUNEIFOKM JOINT. wards ; a narrow inner extremity, and a somewhat wider outer end. It articulates with the posterior surfaces of the three cuneiform bones ; the portions occupied by the inner and outer bones are marked off from that upon which the middle cunei- form rests by two slight ridges, which converge somewhat as they descend from che dorsal to the plantar aspect. The facet for the internal cuneiform is the largest of the three ; it is convex in every direction, triangular in shape, with its base below, its apex above, and its longest border curved with its convexity looking inwards. The middle facet is also triangular, with its base at the dorsal, and its blunt apex at the plantar border ; its longest diameter is fi'om above downwards, in which direction it measures more than either of the other facets. The outer facet is somewhat square-shaped, with its outer angles rounded off. The internal facet looks forwards and slightly inwards, the middle facet directly forwards, and the outer facet forwards and somewhat outwards. The Cukeifoem Boxes. — The three cuneiform bones have facets on their posterior surfaces adapted to those portions of the anterior sm^face of the scaphoid with which they articulate ; thus, that of the inner bone is concave in every dnection, triangular in shape with its base downwards, and its longest border, the internal, curved ; that of the middle bone is tri- angular, concave, and has its base above and apex below; that on the external bone is oblong and broader on the dorsal than the plantar aspect. The facet of the inner bone looks back- wards and somewhat outwards, that of the middle bone directly backwards, and that of the external bone backwards and inwards. If the antero-posterior line through the centre of the tlnee portions of the scapho-cuneiform articulation be prolonged backwards they will meet in the middle of the head of the astragalus ; thus the scaphoid is admirably adapted by its situation with respect to the astragalus, and by the mode of its articulation with the cuneiform bones, to distribute weight to the three inner metatarsal bones. Ligaments connecting the second with the thied eow OF THE Taesal Bones. — -The dorsal scapho-cuneiform ligament is very strong, and extends from the dorsal surface of the scaphoid to the dorsal surface of the three cuneiform bones. It stretches as a continuous structure between the tubercle of the scaphoid on the inner side, and the attachment of the dorsal THE SCAPHO-CUNEIFORM JOINT, 41.5 cubo-scaphoid ligament on the outer side, and passes forwards with an oblique inclination outwards. The InUrnal Scapho-cuneiform Ligament. — A very strong thick band connects the tubercle of the scaphoid with the inner jsurface of the large cuneiform bone. It is continuous with the dorsal ligament above and with the plantar ligament below. The plantar scapho-cuneiforTn ligament forms, like the corresponding dorsal ligament, a continuous structure extending between the plantar surfaces of the bones. Its fibres are inclined forwards and outwards. To see this ligament and the lower border of the internal scapho-cuneiform ligament, it is necessary to remove the tendon of the tibialis posticus, which lies on their under siu-face. The tendon of the tibialis posticus sends onwards from the tubercle of the scaphoid to which it has a considerable attachment (1) a strong and compact band to be attached to the base of the internal cuneiform, and especially to the tubercle near the proximal end of the base ; (2) a strong fan-shaped expansion, inclined forwards and outwards to be attached to the inner extremity of the oblique ridge of the cuboid, and to the bone in front of the ridge, as well as to the plantar surfaces of the middle and external cuneiform and the bases of their corresponding metatarsal bones ; (3) a distinct and almost transverse band passing outwards beneath the peroneus longus tendon across the groove of the cuboid, to be attached chiefly to the inner side of the base of the fifth metatarsal, and slightly to the base of the fourth meta- tarsal bone, under cover of the long plantar Kgament. Over the last-mentioned part of the tendon the long plantar ligament passes on its way to the metatarsal bones ; while the tendon of the peroneus longus crosses it nearly at a right angle. It must be noticed that these expansions of the tibialis posticus tendon, and the Kgaments which connect the scaphoid with the cuboid and the cuneiform bones, are inclined forwards and outwards, while the tendon of the peroneus longus and all the ligaments which connect the first with the second row of tarsal bones on their plantar and dorsal surfaces (except the inner half of the dorsal astragalo-scaphoid ligament), are inclined forwards and inwards. The inward inclination of the "peroneal tendon, of the short plantar, of the anterior portion of 416 JOINTS AND LIGAMENTS OF THE FOOT. the long plantar, and of the calcaneo-scaphoid ligaments, is very marked ; so is the outward inclination of the external part of the tendon of the tibialis posticus^ and of the ligaments between the second and tliird rows of bones. This arrange- ment is admkably adapted to preserve the arches, and especially the transverse arch of the tarsus. Had these tendons and ligaments run directly forwards, all the strain made by the weight of the body on the transverse arch in standing, walking, and jumping, would have fallen on the interosseous ligaments, whereas by the arrangement referred to the structures passing from within outwards brace up the outer side, and those passing from without inwards brace up the inner side of the arch. Union of the three Cuneiform Bones loith one another, and of the outer Cuneiform with the Cuhoid. The Bones. — The inner cuneiform presents on its outer surface a narrow riband-like articular facet along its upper border, and another at right angles to it along its hinder border. That along the upper border is marked by a vertical ridge at the junction of its middle and anterior thirds ; the portion in front of the ridge articulates with the inner side of the base of the second metatarsal bone, that behind, like the whole of the facet along the hinder border, articulates with the inner surface of the middle cuneiform. The rest of the outer surface of this bone is rough for interosseous ligaments. The middle cuneiform lone is marked upon its inner surface by a riband-like facet, which extends the whole length of both upper and hinder borders. The rest of the inner sm-face is rough for the attachment of an interosseous ligament. Its outer surface is divided by an oblique line, which extends downwards and backwards from the junction of the anterior and middle tliirds of the upper border to the junction of the hinder and middle thirds of the lower border. All the surface behind this oblique line is articular for the external cuneiform, all in front is rough and excavated for the interosseous ligament, except that occasionally there is at the anterior and inferior angle a minute articular facet for the external cuneiform. The external cuneiform presents on its inner surface an irregular articular facet along its posterior third ; this is rather JOINTS OF THE ANTERIOR PART OF THE TARSUS. 417 broader above than below, is somewhat constricted about half- way down at its anterior border, and does not usually reach quite to the plantar surface. At the anterior border of the inner surface of this bone there is another articular facet indented at its posterior edge, and marked upon its lower part by a short vertical ridge. All this anterior facet, except the small part behind the small ridge, articulates with the outer side of the base of the second metatarsal bone ; the portion behind the ridge is for the facet at the anterior inferior angle of the outer surface of the middle cuneiform. The rest of the inner surface of the external cuneiform is rough and de- pressed for the interosseous ligament. The outer surface of this bone is partly articular and partly non-articular ; the articular part is smaller than and posterior to the other, and extends the whole depth of the surface ; it is broader above than below, where it occupies little more than the posterior inferior angle of this surface, whereas above it extends over fully one-half of it. It is the upper part of this facet which is chiefly in contact with the cuboid ; the lower part slides upwards so as to make contact with the facet on the cuboid only when the transverse arch of the foot is contracted. The cuboid presents at the upper part of its inner surface an irregularly triangular-shaped facet, somewhat less than half an inch in diameter, both along its base and from base to apex. It looks inwards and slightly upwards and forwards. The base is at the dorsal aspect, and the apex vertically placed at the junction of the middle and plantar thirds. Between the apex and inferior border is a very deep depression for the cubo-cuneiform interosseous ligament. Behind the facet the bone is rough and depressed, wliere it gives attachment to the cubo-scaphoid, and in front of the facet it is also rough for the, cubo-cuneiform interosseous ligament. These four bones are arranged so as to form an arch from side to side, the convexity of which looks upwards and out- wards. The outer pier of this arch which is formed by the cuboid, descends much lower than the inner which is formed by the internal cuneiform bone. The security of the cuboid is increased by its wedge shape, its base being directed inwards and its narrow end outwards ; and by the tubercle of the fifth metatarsal bone projecting backwards over its outer surface. E E 418 ligaments of anterior part of the tarsus. Ligaments connecting the Bones of the thied eow of THE Tarsus with one another. — Dorsal Ligaments. — ^Two ligaments connect together the three cuneiform bones on their dorsal aspects, and a third connects the fourth cuneiform with the cuboid. These pass between the contiguous margins of the several bones, and are blended behind with the dorsal ligaments connecting the scaphoid with the cuboid and cunei- form bones. Plantar Ligaments. — A very strong ligament passes obliquely outwards and forwards from the outer side of the base of the internal cuneiform to the apex of the wedge of the second cunei- form, winding somewhat round to its outer side. No distinct ligament connects the middle and outer bones on this aspect, but the lower part of the interosseous ligament between them reaches low down on both bones. Another ligament connects the apex of the external cuneiform with the anterior half of the inner surface of the cuboid along its plantar surface. At its posterior point of attachment to the cuboid, this ligament is blended with the plantar scapho-cuboid ligament. Both these ligaments are under cover of the expanded tendon of the tibialis posticus, and cannot be seen until it is dissected up and thrown forwards. Interosseous Ligaments. — Strong and deep masses of ligaments connect the middle with the external and internal cuneiform, and the external with the cuboid bone. These occupy all the non-articular portions of the opposed surfaces of these bones. These between the middle and external cuneiform bones, and the external cuneiform and the cuboid, extend the whole vertical depth of the bones, and blend with other ligaments on the dorsal and plantar surfaces, and are situated in front of the articular facets of the bones ; they thus shut off completely in this situation their synovial cavity from the corresponding tarso-metatarsal articula- tions. That between the internal and middle cuneiform bones occupies the inferior and anterior two-thirds of the opposed surfaces, and does not generally extend high enough to separate the synovial cavity of the joint from the articulation between the second metatarsal and the cuneiform bones. If it does extend upwards to the dorsal margin, it then divides the facets on these opposed smiaces of the inner and middle cuneiform -bones into a vertical posterior and a horizontal upper portion. In this case there will be the portions of two synovial cavities MUSCLES OF ANTERIOR PART OF THE TARSUS. 419 between tliem; that between tlie posterior facets belonging to the common synovial cavity of the anterior part of the tarsus, that between the upper and anterior belonging to the tarso- metatarsal joints of the second and third bones. Synovial Cavity of the anterior paet of the Tarsus. — There is one synovial membrane between the scaphoid and the three cuneiform bones ; this sends prolongations forwards between the cuneiform bones and also between the external cuneiform and cuboid, wliilst this again sends backwards a short prolongation between the scaphoid and cuboid when these two bones articulate by cartilage-coated surfaces. Usually this synovial membrane extends the whole way between the inner and middle cuneiform bones, and is prolonged into the articulations between them and the second metatarsal bone, as well as into the articulations between the third metatarsal bone and the outer cuneiform, and between the base of the third metatarsal bone and the bases of the second and fourth metatarsal bones. Arteries. — The articulations of the anterior part of the tarsus are supplied by twigs from the metatarsal artery on the dorsum and from the plantar arteries in the sole. Nerves. — The anterior tibial and the external and internal plantar nerves supply these joints. Muscles connected with the anterior part of the' Tarsus. — To the Scaphoid one muscle is attached, viz., the' tibialis posticus, which is inserted into its tuberosity. To the Internal Cuneiform, two muscles, viz., the tibiaKs posticus and tibialis anticus, which are inserted into its tuberosity. To the Middle and External Cuneiform Bones ^ two muscles,' viz., a slip from the tibialis posticus is sent to each of these bones, and some of the fibres of the flexor brevis pollicis arise from this tendinous slip as it covers them. With the Cuboid three muscles are connected ; the tibialifj posticus is inserted into it, and the flexor brevis pollicis arises from the inner end of the ridge behind the groove on the plantar surface of the cuboid. The peroneus longus runs along the groove on the external and inferior surfaces of the bone, but is not attached to any part of it. The Movements of the Joints of the anterior part of the Tarsus. — These joints are susceptible of only very E E 2 420 MOVEMENTS OF ANTERIOR JOINTS OF TARSUS. limited movements, and exist only for the purpose of adding to the general pliability and elasticity of the tarsus without allowing of any sensible alteration in the position of different parts of the foot, like the medio-tarsal and calcaneo-astra- galoid joints. The motion between them all is simply that of gliding, and has the effect merely of deepening or widening the transverse arch of the foot. The external cimeiform bone which corresponds in position with the os magnum in the hand is wedged in between the others, is less movable than they, and is the centre or pivot upon which the cuboid on the outer side, the inner and middle cuneiform bones on the inner side, and the scaphoid on the inner side and behind, move. It should be observed too that this movement is produced more by the action of the weight of the body than by direct muscular action upon the individual bones. It will have been noticed in the enumeration of the muscles attached to this part of the tarsus, that of the four muscles two of them, viz., the tibialis posticus and flexor brevis poUicis, are attached to several bones ; the tibialis to every one of them as well as to the os calcis behind, and the bases of four metatarsal bones in front ; wliile both the others are inserted into the internal cuneiform, the tibialis anticus after passing obliquely over the front of the ankle and dorsum of the foot, and the peroneus longus after crossing obliquely forwards from the outer to the inner border of the sole. Consequently the action of all but the tibialis anticus is to pull the bones together and deepen the arch ; while that of the tibialis anticus is to pull the inner cuneiform upwards on the inner border, and thus to drag it away from the others, and thereby to widen and flatten out the transverse arch. THE MEDIO-TARSAL ARTICULATION. 421 The Medio-tarsal or Transverse Tarsal Joint ; or, The Articulations hetween the Astragalus and Scaphoid on the inner side, and the Os Calcis and Cuboid on the outer side of the Foot. What is often spoken of as the articulation of the anterior and posterior portions of the tarsus with one another, under the name of the medio-tarsal or transverse tarsal joint, is in reality two articulations, each of which is separate and distract from the other. These two joints are, however, in the same trans- verse line, and the movements of the anterior portion of the foot upon the posterior take place at both of them simul- taneously. The two anterior bones, viz., the scaphoid and cuboid, are united together by means of dorsal, plantar, and interosseous ligaments ; and, as has been stated above, sometimes each bone is marked by a small articular facet when the outer extremity of the former is in contact with the inner surface of the cuboid. The two posterior bones are united in the manner which has been fully described above, and form between them two important articulations, the anterior of which is in communica- tion with the astragalo-scaphoid portion of the transverse tarsal joint, and the movements of both are in intimate relationship with those of the transverse tarsal joint. It will be most convenient to consider the two parts of this joint separately so far as regards their bones and ligaments, under the heads of the astragalo-scaphoid and the calcaneo-cuboid articulations, and afterwards to enumerate the muscles and describe the movements which are common to them both. The Astragalo-scaphoid Articulation. Class, Diarthrosis. Subdivision, Enarthrodia. This is the only ball-and-socket joint in the tarsus. It is not complete in itself, being in communication with the anterior calcaneo-astragaloid joint, and two of the ligaments which assist in closing it in are not attached to the astragalus at all, but pass from the os calcis to the scaphoid. The Asteagalus. — The articular surface of the head of the astragalus is situated one inch in front of the anterior edge of the facet on the upper surface of the bone for the tibia, being 422 THE ASTRAGALO-SCAPHOID JOINT. separated from it by a rougli depressed and somewhat con- stricted sm^face — %dz., the upper aspect of the neck. Below, the surface for the scaphoid is separated by only a narrow rough and non-articular interval (which extends obliquely backwards and inwards) from the facet on the under surface of the neck for the sustentaculum tali ; but it is continuous with that which articulates with the anterior internal angle of the upper surface of the body and with the upper surface of the calcaneo-scaphoid ligament. The articular surface of the head which fits into the socket of the scaphoid is convex from side to side and from above downwards ; it is two inches from side to side, and is prolonged further back on the inner asj)ect than on the outer, so that when the foot is in a position of rest the scaphoid does not cover the whole of the articular surface by half an inch or more on its inner side, though it extends quite to the limit of the facet on the outer side. From above downwards the surface measures at its middle one inch, but towards the outer and inner extremity it is not quite so deep ; and at the inner end, which is shallower than the outer, the vertical measure- ment is barely half an inch. On the inner surface of the astragalus, behind the inner end of the articular facet for the scaphoid, there is a rough depression for the attachment of some of the fibres of the internal lateral ligament of the ankle- joint. The Scaphoid. — The posterior surface of the scaphoid presents a large doubly concave articular surface, measuring a little over an inch from side to side, and being deeper on the outer side, where it measures three-quarters of an inch from above downwards, than on the inner side, where it does not measure more than a quarter of an inch. The whole of this surface of the scaphoid, except a narrow vertical triangular portion at the inner end which corresponds to the back of the tubercle of the scaphoid, is articular. The Ligaments. — Three ligaments assist in keeping the posterior concave siu'face of the scaphoid in contact with the head of the astragalus. Of these one has been already described, viz., the external calcaneo-scaphoid, under the ligaments of the anterior calcaneo-astragaloid joint. The other two are the inferior calcaneo-scaphoid on the plantar surface, and the astragalo-scaphoid ligament on the dorsal surface. LIGAMENTS OF THE ASTEAGALO-SCAPHOID JOINT. 423 The inferior calcaneo-sca'plioid is an exceedingly dense and tMck plate of fibrous tissue. It extends from the sustentaculum tali and from the ujider surface of the os calcis in front of a ridge curving outwards from that process to the anterior tubercle, to the whole width of the under surface of the scaphoid near its posterior border, and to the inner surface of the scaphoid behind the tubercle. Internally, the ligament is blended with the anterior portion of the internal lateral ligament of "the ankle-joint, and externally with the lower border of the external calcaneo-scaphoid ligament. The thickest portion of the ligament is that along the inner border of the sole, which passes to the scaphoid behind the tubercle. At this part the ligament loses the well-marked fibrous appearance which it has in the sole of the foot, and becomes smooth and facetted ; and over it here the tendon of the tibialis posticus passes into the sole of the foot, giving considerable support to the head of the astragalus, and assisting the power and spring of the ligament. Moreover, by coming into action when the heel is raised, it helps the ligament to support the head of the astra- galus, and to maintain the arch of the foot when the weight of the body is thrown forward upon the instep. Besides support- ing the head of the astragalus, and providing a smooth surface upon which the under part of the head of the astragalus moves, this hgament also limits the movements of the scaphoid on the astragalus. The direction of the fibres of the ligament being inwards as well as forwards, they are kept tight in flexion as well as in extension of the sole of the foot ; for the rotation inwards which accompanies flexion prevents the approximation of the under surface of the scaphoid to the os calcis which would otherwise result from flexion; and the approximation of the under surfaces of these bones which would otherwise arise during the rotation outwards which accompanies extension, is obviated by the separation caused by the extension movement itself. Flat foot is a consequence of the weakening of this ligament, for then the head of the astragalus is pressed forwards and inwards, and over-extension and rotation outwards of the fore- part of the foot results. The asfragalo-scaphoid ligament is a broad, thin, but well- . marked layer of fibres, attached to the dorsal and external surfaces of the neck of the astragalus, and all along the dorsal 424 THE CALCANEO-CUBOID JOINT. surface of the scaplioid. Many of the fibres converge to their insertion on the scaphoid. The fibres low down on the outer side blend a little way from their origin from the neck of the astragalus with the ujjper part of the external calcaneo-scaphoid ligament, and then pass forwards and inwards to the scaphoid ; those next above pass obliquely, and with a distinct twist in their course, over the outer and upper side of the head of the astragalus to the centre of the dorsum of the scaphoid. These latter overlap some fibres which incline outwards from the inner side of the astragalus, as well as others which are pro- longed onwards from the anterior ligament of the ankle-joint. The Synovial Membrane. — The same synovial membrane which lines the anterior calcaneo-astragaloid articulation lines also the astragalo-scaphoid joint, Calcaneo-cuhoid Articulation. Class, Diarthrosis. Subdivision, Arthrodia. This joint forms the outer portion of the medio-tarsal arti- culation, and from its construction is susceptible of less move- ment than the inner portion, viz., the astragalo-scaphoid. The Os Calcis. — The anterior surface of the os calcis presents a concavo-convex facet for the posterior surface of the cuboid bone, the concavity being from above downwards and inwards. This facet measures about three-quarters of an inch from above downwards, and about one inch from side to side. Its inferior border is nearly straight but shghtly arched upward, whilst its lateral and superior borders form almost the half of a circle. It is depressed from above downwards, near its inner end, to receive the convexity of the cuboid, and the articular surface is prolonged onwards somewhat upon the plantar surface of the bone, to articulate with the posterior internal and inferior angle of the cuboid, which looks upwards and projects backwards beneath it, whilst the superior internal angle of the os calcis projects for- wards so as to overhang the inferior internal angle of the cuboid. A small but elongated part of tins anterior surface of the OS calcis, towards its upper and inner side, is non-articular, for the attachment of the external calcaneo-scaphoid and the internal calcaneo-cuboid hgaments. The anterior facet of the OS calcis for the astragalus is situated upon the upper surface of this overhanging corner of the bone, and the anterior edge of LIGAMENTS OF THE CALCANEO-CUBOID JOINT. 425 this facet is separated from the facet for the cuboid by only a very narrow strip of bone, to which the internal calcaneo-cuboid ligament is attached. The Cuboid. — The posterior surface of the cuboid, which faces a little outwards, is occupied by an irregularly shaped facet for articulation with the os calcis. It measures about an inch from side to side, three-quarters of an inch from above downwards at the ioner end, and about three-eighths of an inch at the outer end. Its upper and lower margins are arched from side to side with their convexity upwards, and its inferior and internal angle is prolonged backwards beneath the overhanging upper and inner angle of the os calcis. It is obliquely convex from above downwards and inwards, in adaptation to the concavity of the anterior surface of the os calcis. Ligaments. — The ligaments connecting these bones are the long and short plantar or inferior calcaneo-cuboid ligaments, together with the internal and the dorsal calcaneo-cuboid liga- ments. The internal or interosseous calcaneo-cuboid ligament is at- tached to the inner and slightly also to the under part of the anterior surface of the os calcis, close to the margin of the arti- cular facet of the cuboid, and it passes forwards to be attached to the rough internal posterior and inferior angle, and also to the depression of the internal surface of the cuboid. It is closely connected at the os calcis with the external calcaneo- scaphoid ligament. Towards the sole it is connected with the deep or short inferior calcaneo-cuboid ligament, and superiorly with the dorsal calcaneo-cuboid ligament. The dorsal calcaneo-cuboid ligament is attached to the dorsal surfaces of the two bones and extends low down upon their sides towards the sole, so as to blend with the short inferior calcaneo-cuboid ligament. Over the inner half or more the ligament stretches some distance beyond the margins of the articular surfaces, and reaches well forwards upon the cuboid so as to be attached about midway between its anterior and posterior borders ; but towards the outer side the ligament is much shorter, and is attached to the cuboid behind its tubercle. The inferior calcaneo-cuboid ligaments, or the long and the short plantar ligaments, are two very strong bands which pass 426 THE PLANTAR LIGAMENTS. between the under surface of the os calcis and cuboid. They are separated by a slight interval occupied by fatty and areolar tissue, where the long overlaps the small ligament. The long ligament is attached behind to the whole of the under surface of the calcaneum between the posterior tubercles and the anterior tubercle. Most of its fibres pass directly forwards, and are fixed to the outer two-thirds or more of the oblique ridge, behind the peroneal groove on the cuboid bone ; while some of the fibres pass still further forwards and inwards, expand into a broad layer, and are inserted into the bases of the second, third, and fourth, and inner half of the base of the fifth metatarsal bones. This anterior expanded portion completes the canal for the peroneus longus tendon, and from its under or plantar aspect there arise the adductor pollicis and the flexor brevis minimi digiti muscles. The sliort plantar ligament is attached posteriorly to the anterior tubercle of the calcaneum and to the bone immediately in front of this ; it then takes an oblique course forwards and inwards, and is attached to the whole of the depressed tri- angular inferior surface of the cuboid behind the oblique ridge, except its outer angle. Erom the plantar aspect of this ligament the flexor brevis pollicis in part arises. This liga- ment connects the contiguous edges of the os calcis and the cuboid, and therefore its upper surface is to some extent lined by the synovial membrane of the calcaneo-cuboid joint. It is strongest near the outer edge of the foot. The long and short plantar ligaments limit extension at the medio-tarsal joint, i.e., of the second row of the tarsal bones upon the fii-st ; they are also the chief support of the outer part of the antero-posterior arch of the foot, and indeed the long ligament seems intended to strengthen the rest of the arch also. They are sometimes unnaturally contracted and give rise to a deformed arching of the foot, commonly called by surgical writers talipes plantaris, which is an abnormal and permanent flexion of the foot at the medio-tarsal joint. It should be noticed that all the ligaments which connect the posterior with the anterior segments of the tarsus are attached behind to the os calcis, with the exception of one, viz., the superior astragalo-scaphoid. Thus besides the internal, dorsal, and inferior calcaneo-cuboid ligaments, there MUSCLES OF THE MEDIO-TAESAL JOINT. 427 are also tlie inferior and external calcaneo-scaphoid ligaments ; so that the os calcis which forms with the cuboid a far less movable articulation than the astragalus forms with the scaphoid, is yet held to and united with the scaphoid, though it is not in contact with it ; and in this way the two portions of the medio-tarsal joints are held together and are made to move as if they formed but one articulation. The Synovial Membrane. — The calcaneo-cuboid articulation has a synovial linin g distinct from that of any other joint in the tarsus. It is less capacious than that which belongs to the astragalo-scaphoid articulation. The Aeteries of the Medio-tarsal Joint. — 1. The anterior tibial sends a branch over the inner border of the foot, which furnishes twigs to the astragalo-scaphoid joint. 2. The tarsal artery sends forwards branches which anastomose with recurrent branches of the (3) metatarsal artery. 4. The plantar arteries, but most frequently the internal plantar, supply the articulations on the under aspect. The ISTerves of the Medio-tarsal Joint. — Branches are suppHed to the astragalo-scaphoid and calcaneo-cuboid joints from the external branch of the anterior tibial, and occasionally from the musculo-cutaneous or the external plantar. The Muscles in relation with the Medio-tarsal Joint. — The muscles which act upon the medio-tarsal joint either arise from the bones of the leg and move the foot at the ankle, and the OS calcis with the foot upon the astragalus, as well as the transverse joint; or, they arise from the os calcis and are inserted into the phalanges of the toes. Of the nine muscles which arise in the leg and pass over the medio-tarsal joint to their insertion, three, viz., the peroneus longus, the peroneus brevis, and the peroneus tertius, are attached to the bases of the meta- tarsal bones ; one, viz., the tibialis anticus, is inserted into the internal cuneiform and the base of first metatarsal bone ; and one, the tibialis posticus, spreads out so as to be attached to all the bones of the anterior part of the tarsus, as well as to the bases of the second, third, fourth, and part of the fifth metatarsal bones ; whilst in addition a slip passes backwards also to the sustentaculum taK. Most of these muscles produce upon this joint an increased degree of the same action as that which they excite upon the 428 MUSCLES OF THE MEDIO-TARSAL JOINT. calcaneo-astragaloid joint, but an opposite effect to that which they have upon the ankle-joint. Of the muscles which arise from the os calcis, viz., the abductor pollicis, the flexor brevis digitorum, and the abductor minimi digiti, and also the extensor brevis digitorum, all pass over the joint to be inserted into the phalanges, whilst the musculus accessorius is attached to the tendon of the flexor longus digitorum. The extensors are the tibialis anticus, the extensor proprius pollicis, the extensor longus digitorum, and the peroneus tertius. These muscles also extend the toes, and flex the ankle. The extensor brevis digitorum extends the foot at the trans- verse joint, and the toes at the phalangeal, but has no effect upon the ankle. The flexors are the tibialis posticus, the peroneus longus, the peroneus brevis, the flexor longus pollicis, and the flexor longus digitorum, all of which also extend the foot at the ankle. The abductor pollicis, abductor minimi digiti, and the flexor brevis digitorum, as well as (indirectly) the musculus acces- sorius, flex the transverse joint, but cannot act on the ankle. The Adductors. — The tibialis anticus and posticus draw the toes inwards, and turn the inner border of the sole upwards. The Abductors. — The peronei draw the toes outwards and turn the outer border of the foot upwards. In the case of the joints of the foot as of those of the hand, and in fact elsewhere generally, the muscles which pass over several joints act first upon the joint immediately behind its point of insertion, and then in succession upon those which are further and further behind. The Movements. — The great difference between the move- ments of the medio-tarsal and tarso-metatarsal joints on the one hand, and of the medio-carpal and carpo-metacarpal joints on the other, is that in the latter the movements are not of a different kind from, though of less extent than those at the wrist, and flexion or extension occurs at all at the same time; whereas in the former movements are more various than at the ankle, and the lateral and rotatory movements are superadded to those of extension and flexion, and flexion at the transverse MOVEMENTS OF THE MEDIO-TARSAL JOINT. 429 joint of the foot is simultaneous with extension at the ankle- joint, and vice versd. Flexion and extension at the medio-tarsal joints are not movements consisting merely of turning upon a transverse axis. The direction of movement is regulated by the articular surface of the head of the astragalus, and the axis of move- ment is oblique from within outwards, and somewhat back- wards and downwards through the astragalus and os calcis. Combined with flexion and extension are also some rotatory movements round an antero-posterior axis, and a fair amount of lateral movement, whereby the anterior part of the foot can be inclined inwards or outwards. Thus flexion is associated with inward rotation of the sole, together with inclination inwards of the toes ; and extension with rotation outwards of the sole, together with outward inclination of the toes. These movements of the transverse joint occur, as has been stated, in conjunction with movements of the calcaneo- astragaloid and ankle-joint. Eotation at the calcaneo- astragaloid joints differs in direction and in effect from rota- tion at the medio-tarsal joint. At the former it occurs in a nearly horizontal plane round a vertical axis ; at the latter, round an antero-posterior axis, in a nearly vertical plane. As regards the results of rotation at the two joints, rotation at the calcaneo-astragaloid turns the toes inwards or outwards, whilst at the transverse joint it turns the inner or the outer edge of the foot upwards. Again, the gliding movements of the calcaneo-astragaloid joints have the effect of elevating or depressing the edge, of the foot, whilst those of the transverse tarsal joint cause the toes to turn towards or away from the middle line of the body without altering the position of the OS calcis with respect to the astragalus. Flexion at the medio-tarsal joint is associated with adduction and inward rotation of the foot, which occurs simultaneously with extension of the ankle ; and extension at this joint, which is associated with abduction and rotation outwards, occurs simul- taneously with flexion of the ankle. Thus we find in the foot that the movements of the ankle and tarsus are intimately associated, as are those of the hand at the wrist and carpus ; but whilst those in the hand are simple, and those about the wrist are made complex by the rolling of the radius upon the ulna ; the movements of the foot are 430 MOVEMENTS OF THE MEDIO-TARSAL JOINT. made complex by the calcaneo-astragaloid aud transverse joints, whilst those at the ankle are simple and limited to flexion and extension. riexion and adduction are more free at the transverse joint than extension and abduction, which latter are arrested by the ligaments of the sole as soon as the foot is brought into the position in which it rests on the ground. Although the astragalo-scaphoid is a ball-and-socket joint, and therefore might allow of movement in any direction, yet the movement at the medio-tarsal joint, owing to the union of the cuboid with the scaphoid, is arrested by the shape of the calcaneo-cuboid joint. The articular surfaces of the latter being concavo-convex from above downwards, prevent rotation round a vertical axis, and also any side-to-side movement except in an oblique direction, downwards and inwards, and upwards and outwards. This is also the direction of the freest movement at the astragalo-scaphoid joint, for the articular facet on the head of the astragalus is most prolonged downwards and inwards, i.e., on the under and inner side. The ligamentous connexion of the os calcis with the scaphoid also helps to limit the movements of the transverse joint. The lateral movements of the foot, which have often been supposed to take place at the ankle, really occur at the calcaneo- astragaloid and the medio-tarsal joints. Turning the toes out or in, in so far as these movements are not of the tarsal joints, is effected by rotation of the limb at the hip-joint chiefly ; but shghtly also, when the leg is flexed on the thigh, by rotation of the tibia and fibula at the knee-joint. The twisting movements of the foot, such as turning the sole up on the inner or outer side, and in increasing or diminishing the arch, take place at the tarsal joints, especially at the medio-tarsal and calcaneo-astragaloid joints. It is also at the medio-tarsal joint that those changes occur, owing to paralysis of some muscles or contraction of others, which result in talipes equinus, varus, or valgus ; in the former there is a dropping of the anterior part of the tarsus, and in the other forms a twisting upwards of the inner or outer border of the foot respectively. THE INNEE TARSO-META TARSAL JOINT. 431 Hie Tarso-metatarsal Articulations. Class, Diarthrosis. Subdivision, Arthrodia, There may be said to be tbree separate joints between the tarsus and metatarsus ; 1st, the articulation between the in- ternal cuneiform and the first metatarsal bone ; 2nd, the arti- culation between the three cuneiform and the second and third metatarsal bones ; and 3rd, the cubo-metatarsal, or the joint between the cuboid and the fourth and fifth metatarsal bones. Looked at as a whole, the union of the tarsus with the meta- tarsus is very uneven, owing to the backward projection of the second, fourth, and fifth bones behind the line of the third ; and of the forward position of the first, which articulates with the inner cuneiform nearly half an inch in advance of the second, and about a quarter of an inch in fi-ont of the third metatarsal bone, where they articulate with the middle and outer cunei- form bones respectively. The second metatarsal bone is supported by the middle cuneiform, and is let back into a space bounded on the outer and inner sides by the external and internal cuneiform bones. The outer three metatarsal bones are placed pretty evenly, in a line having a gentle curve with its convexity towards the phalanges. We will consider first the internal, next the middle, and lastly the outer or cubo-metatarsal joints. The Inner Tarso-metatarsal Joint. The Bones. — The anterior surface of the internal cuneiform hone is entirely occupied by a large, nearly flat, kidney-shaped articular surface, which is inclined a little inwards. It is placed with its long axis vertically, its convex border inwards, and its concave border outwards. It measures an inch from above downwards, and half an inch from side to side. The tarsal surface of the base of the first metatarsal bone is slightly concave from side to side. It is of the same general shape as the anterior surface of the inner cuneiform, which it accurately fits. At its outer side, where the border of the facet is concave, this surface presents an elongated, rough, shallow groove for the attachment of a ligament, and in front of it, but situated upon the outer surface of the base, is the facet for the second metatarsal bone when present. 432 THE MIDDLE TARSO-METATARSAL JOINT. Ligaments. — The first metatarsal bone is connected with the internal cuneiform by a complete capsular ligament, the fibres of which are very thick on the under and inner aspects. Those on the outer side pass fi-om behind forwards in the interval between the interosseous ligaments which connect these two bones with the second metatarsal bone. The plantar ligament is by far the strongest, and at the cuneiform bone it is blended with the inferior scapho-cuneiform ligament. Synovial Membeane. — This articulation is completely sepa- rated from, and on a line anterior to, all the other tarso- metatarsal joints. The Middle Tarso-metatarsal Articidation. Into this part of the union of the tarsus with the meta- tarsus there enter the three cuneiform, and the second and third metatarsal bones. The outer surface of the internal cuneiform hone presents at the anterior part of its upper border a small elongated facet for the inner surface of the base of the second metatarsal bone, which is continuous with, but marked off by a slight vertical ridge from the facet for the middle cuneiform bone. The rest of the outer surface of this bone, where it faces the second metatarsal, is rough for the attachment of ligaments. The anterior surfax^e of the middle cuneiform hone receives upon it the terminal facet at the base of the second metatarsal bone. It is flat, somewhat triangular in shape, with its base at the dorsum and its rounded apex at the plantar aspect. It is about three-quarters of an inch in vertical measurement, and about half an inch across at the dorsum, but much narrower below. The outer cuneiform hone enters into this articulation (1) by its anterior surface, which is of the same size and character as that of the middle bone, and articulates with the terminal facet on the base of the third metatarsal bone ; and (2) by the anterior edge of its inner surface, which presents two small facets, separated by a rough interval, which look a little forwards as well as inwards to articulate with the posterior two facets on the outer side of the base of the second metatarsal bone. Sometimes these facets are continuous with each other, like those on the second metatarsal bone. I I Co ^^*f ^Wi' #- .# M tl ^ t 3 s LIGAMENTS OF THE TAESO-METATARSAL JOINT. 433 The second and third metatarsal hones present at their tarsal extremities facets which correspond in shape and size with the facets on the anterior surfaces of the middle and outer cuneiform bones. The second bone also presents on its outer surface two small facets, which look outwards and back- wards, for the inner surface of the outer cuneiform. These are . continuous over a small margin with the facet for the middle cuneiform bone, and over slight vertical ridges with the facets for the inner side of the third metatarsal bone. The Ligaments. — ^Dorsal, plantar, and interosseous liga- ments connect the cuneiform bones with the metatarsus, and serve to enclose this middle part of the tarso-metatarsal joint. The Dorsal Ligaments. — Some fibres pass between the inner cuneiform bone and the second metatarsal bone. These short fibres cross obKquely from the outer edge of the cunei- form to the inner border of the base of the metatarsal bone ; they take the place of a dorsal metatarsal ligament which is wanting between the first and second, metatarsal bones. Between the middle cuneiform bone and the base of the second metatarsal bone some fibres run directly forwards. Between the external cuneiform and (1) the outer corner of the second metatarsal bone a narrow band is directed obhquely inwards ; (2) another short band passes obliquely out- wards from the outer cuneiform to the inner edge of the base of the fourth metatarsal bone ; and (3) between these two sets of oblique fibres others run directly forwards from the cuneiform to the third metatarsal bone. The Plantar Ligaments. — A strong ligament passes be- tween the inner cuneiform and the bases of the second and third metatarsal bones. The tibialis posticus is inserted into these bones close to it. Other slender ligaments connect the middle cuneiform with the second, and the outer cuneiform with the third metatarsal bones. Lnterosseous Ligaments. — The middle portion of the tarso- metatarsal joint is shut off from the inner portion by a very strong and broad interosseous ligament, which extends between the outer surface of the first cuneiform and the inner surface of the base of the second metatarsal bone ; to both bones it is attached below and in front of the articular facets. The second band is attached behind to a fossa on the anterior and external edge of the external cuneiform, and to F F 434 CUBO-METATARSAL JOINT. the interosseous ligament between this bone and the cuboid : it then passes horizontally forwards to be attached to the whole depth of the fourth metatarsal bone behind its internal lateral facet, and to the opposed surfaces of the third and fourth meta- tarsal bones below their lateral articular facets. This ligament limits the ndddle tarso-metatarsal joint on the outer side, and shuts it and the inter-metatarsal articulation between the third and fourth bones off from the external or cubo-metatarsal joint. It is more firmly connected with the third bone than the fourth. A third very slender ligament, composed of only a few fibres, often passes from a small tubercle on the inner and anterior edge of the external cuneiform to the middle of the outer edge of the second metatarsal bone, where it is attached to the horizontal groove between the two lateral facets for the external cuneiform. Synovial Cavity. — The synovial membrane of this part of the joint is an extension forwards from the synovial membrane of the scapho-cuneiform and the inter-cuneiform articulations. Tlie Cuho-metatarsal Articulation. Into this part of the tarso-metatarsal joint the anterior surface of the cuboid bone and the terminal facets on the bases of the fourth and fifth metatarsal bones enter. The Bones. — The anterior surface of the cuboid hone looks for- wards with a considerable inclination outwards. It is facetted over its whole area, and the facet is divided into two unequal parts by a vertical ridge. The internal portion is oblong, with its long axis from above downwards ; its outer part is triangular, with its long axis from side to side, in which direction it is slightly convex, whilst from above downwards it is somewhat concave. The fourth metatarsal lone presents at the tarsal aspect of its base an oblong facet for the cuboid, the long axis of which is from above downwards. The fifth metatarsal lone presents on the tarsal aspect of its base a triangular facet which looks inwards as well as back- wards, being oblique with its outer part prolonged backwards ; it is slightly concave to suit the convexity of the cuboid facet. The outer part of the base of this bone is prolonged back- wards into a prominent rounded rough tubercle, which gives attachment to several muscles and helps to keej) the cuboid LIGAMENTS OF THE CUBO-METATARSAL JOINT. 435 securely fixed in its proper place between the os calcis and metatarsus. The Ligaments. — Ligaments connect the cuboid with the fourth and fifth bones on all sides. The plantar cubo-Tiietatarsal ligament is a broad, but well- marked ligament, which extends from the cuboid behind to the bases of the metatarsal bones in front. It is by no means a thick ligament, and to see it the long plantar Kgament, the peroneus longus, and the external slip of the tibiahs posticus must be removed. The attachment of these structures to the fourth and fifth metatarsal bones assists their union with the tarsus very considerably. This ligament is continuous along the groove at the base of the fifth metatarsal bone with the dorsal ligament ; as it passes round the outer border of the foot it is somewhat thickened, and may be described as the external cuho-metatarsal ligament. On the inner side it joins the interosseous ligament connecting the cuboid and external cuneiform behind, with the third and fourth metatarsal bones in front, and thus completes on the under side a well-formed capsular ligament for tlie cubo-metatarsal joint, as the inter- osseous ligament itself completes it on the inner side. TJie Dorsal Cubo-metatarsal Ligament. — On the dorsal aspect, ligamentous fibres pass obliquely forwards and outwards froni the cuboid to the bases of the fourth and fifth metatarsal bones, and cover in the synovial membrane above ; those which are attached to the latter reach outwards to the tuberosity and are very oblique ; they are continuous on the outer side with what has just been referred to as the external cubo-metatarsal ligament. The interosseous ligament shuts off this joint from the middle tarso-metatarsal joint. It is attached to the external cuneiform behind, and to the whole depth of the posterior and inner angle of the base of the fourth metatarsal bone, and to the apposed sides of the fourth and third metatarsal bones towards the plantar surface. Synovial Membeane. — The synovial membrane of this joint is shut off from the rest of the tarsal and tarso-metatarsal joints, but sends a prolongation forwards to the inter-metatarsal articulation between the fourth and fifth metatarsal bones. The septum between the cubo-metatarsal and the middle tarso- metatarsal joints is very seldom absent. F F 2 436 MUSCLES OF THE TARSO-METATARSAL JOINTS. Arteeies of the Tarso-metatarsal Articulations. — To the joint of the great toe on the dorsal aspect, one or two "branches are given off from the inner side of the dorsalis pedis before it divides in the first interosseous space. On the plantar aspect of this joint twigs are supplied from the internal plantar artery. The metatarsal artery which usually crosses the proximal end of the shafts of the four outer metatarsal bones supplies the corresponding joints by twigs given off from the under side of the recurrent branches which anastomose with the tarsal artery. On the plantar surface branches are given to these joints from the deep plantar arch. Nerves. — Branches are supplied from the anterior tibial and the plantar nerves. The Muscles connected with the Tarso-metatarsal Articulations. — Of the muscles in relation with these joints, some arise in the leg and pass over the foot to be inserted into the metatarsal bones, and others into the phalanges ; and some arise from the tarsus, and are inserted into the phalanges. Other muscles arise from the metatarsal bones themselves, and are inserted into the phalanges ; but they do not act on this joint, and will be best considered under the head of the meta- tarso-phalangeal joints. The muscles which arise in the leg and are inserted into the metatarsus are : (1) the three peroneal muscles ; (2) the tibialis anticus and posticus, both of wliich are in part inserted into the tarsus and in part into the metatarsus ; and (3) the ex- tensor ossis metatarsi pollicis, which occasionally is present either as a distinct muscle or as a slip from one of the long extensors. The muscles which arise in the leg and are inserted into the phalanges, are the extensor proprius pollicis, and when present the extensor primi internodii pollicis, which is generally an offshoot of the extensor proprius pollicis ; the flexor longus pollicis, and the flexor longus digitorum. All of these are inserted into the terminal phalanges of their respective toes. The extensor longTis digitorum, which (after blending with the extensor brevis digitorum) is inserted into the second and third phalanges. The muscles which arise in the tarsus and are inserted into the ^phalanges, are the extensor brevis digitorum, which arises from the outer surface of the os calcis and from the lower band of the anterior annular ligament, to be inserted by four slips. MUSCLES OF THE TARSO-METATARSAL JOINTS. 437 one into the dorsal surface of the first phalanx of the great toe, and the other three with slips of the extensor longiis digi- torum into the bases of the second and third phalanges of the second, tliird, and fourth toes. The flexor accessorius, which arises by two heads from the os calcis and long plantar liga- ment, and is inserted into the external border and upper and lower surfaces of the flexor longus digitorum ; it thus acts primarily with that muscle on the terminal phalanges of the four outer toes. The abductor pollicis, which is inserted with the inner head of the flexor brevis pollicis into the inner side of the base of the first phalanx of the great toe. The abductor mirdmi digiti, which is inserted into the external surface of the base of the first phalanx of the fifth toe. The flexor brevis digitorum, which is inserted into the second phalanx of each of the four outer toes by slender tendons, which divide so as to allow of the tendon of the flexor longus digitorum passing between them on its way to the terminal phalanges of the same toes. All these arise from the under sur- face of the OS calcis. The flexor brevis pollicis arises from the OS cuboides and from the tendon of the tibiaHs posticus, where it is attached to the cuneiform bones ; it divides into two muscular bellies, each of which ends in a tendon, one to be inserted into the inner and the other into the outer side of the base of the first phalanx of the great toe, as well as into the sesamoid bones on its own side of the metatarso-phalangeal joint. The adductor poUicis arises from the sheath of the peroneus longus, as well as from the bases of the third and fourth metatarsal bones, and is inserted with the outer head of the flexor brevis pollicis into the outer side of the base of the first phalanx of the great toe. The flexor brevis minimi digiti arises from the sheath of the peroneus longus, as well as from the base of the fifth metatarsal bone, and its tendon is inserted into the base and outer border of the first phalanx of the fifth toe. One muscle occasionally exists, which arises from the ex- ternal tubercle of the os calcis, and is inserted into the tubercle of the base of the fifth metatarsal bone beneath the plantar fascia, viz., the abductor ossis metatarsi mim'Tui digiti. The muscles which are inserted into the phalanges act first upon the phalangeal and metatarso-phalangeal articulations, and secondarily, when their action on the two former has been completed or prevented, upon the tareo-metatarsal joints, as 43S MOVEMENTS AT THE TARSO-METATAKSAL JOINTS. flexors and extensors, abductors and adductors respectively. The muscles wliicli act primarily and directly on the tarso- metatarsal articulation are the tibialis anticus, which is attached to the inner bone of the metatarsus ; the peroneal muscles, which are attached, one to the inner and two to the outer bone of the metatarsus only ; and the tibialis posticus, which is attached to the four outer bones. These muscles move the metatarsus upon the tarsus as well as the metatarsal bones on one another ; the peroneus longus and tibialis posticus act to draw the bones together, and thus to increase the depth of the transverse arch of the foot ; and the tibialis anticus, besides its action on the inner cunei- form, abducts the metatarsal bone of the gTeat toe, while the peroneus brevis, peroneus tertius, and abductor ossis metatarsi minimi digiti when present, abduct the metatarsal bone of the little toe, and through the intimate union of the bases of the three outer toes, they act also in the same way upon the fourth and third bones. The second metatarsal bone, owing to its position between the cuneiform bones, is not disturbed by the action of these muscles. The Movements at the TAES0-^rETATAESAL Aeticulations are flexion and extension of the metatarsus upon the tarsus. In the outer and inner divisions of this union, abduction and adduction are also allowed. In the outer or cubo- metatarsal joint this lateral movement is much more free than at the inner, and is more free betvv'een the fifth bone and the cuboid than between the fourth and the cuboid. At the inner joint, flexion is associated with some abduction, and extension with adduction. The movements in the middle joint are very limited indeed. Besides tlie above, there is some gliding movement at all parts of the joints, whereby the transverse arch of the foot is increased or diminished in depth ; this consists in a sliding downwards of the innermost and the two outer bones, and a sliding up to a less extent of the second and third bones when the arch is increased ; and in the contrary movements when the arch is spread out. BASES OF THE METATARSAL BOXES. 439 The Inter-metatarsal Articulations. Class, Diarthrosis. Subdivision, Artkrodia. The Bones. — The base of each of the metatarsal bones is wedge-shaped, except that of the fourth, which is cuboidal, and each presents a terminal facet for articulation with the tarsus, and one or more lateral facets for articulation with one another ; but in this respect they differ somewhat from one another. The base of the first metatarsal hone, as a rule, presents no lateral articular facet ; but I have seen occasionally a small facetted surface at the centre of the concave border of the base of this bone to articulate with the inner surface of the base of the second bone. The inferior and external angle of the base projects slightly outwards, and is marked by a rough circular depression, to wliich the peroneus longus is attached. • The hase of the second metatarsal hone has upon its inner side near the dorsum a small, nearly square facet, continuous with the facet at the tarsal extremity of the bone, for the outer surface of the inner cuneiform bone. Occasionally there exists below and in front of this anotlier, but smaller and much less marked, facet for the outer surface of the base of the first metatarsal bone. Whilst the lateral facet on the first metatarsal bone, when present, is close to the terminal facet for the inner cuneiform, that on the inner surface of the second bone is on the side of the shaft immediately in front of the base, and rather nearer the plantar than the dorsal aspect. Upon its outer surface are two facets, separated by a deep narrow antero-posterior groove, to which an interosseous liga- ment is attached, and each of these facets is divided into two unequal parts by a vertical ridge ; the parts behind the ridges look outwards and backwards, are smaller than those in front, and articulate with the inner surface of the external cuneiform bone ; and the parts in front of the ridges look outwards and forwards, and articulate with the inner surface of the third metatarsal bone. The hase of the third metatarsal hone presents on its inner aspect two articular facets, separated by an antero-posterior depression ; the upper one is smaller than the lower ; both are continuous with the terminal facet. On its outer side is a large circular facet, occupying half the vertical depth of the surface, the margin of wliich extends up to the dorsal and back 440 LIGAMENTS OF THE METATARSAL BONES. to the terminal surfaces of tlie bone. Below the facet is a rough and irregular depression for the interosseous ligament. The base of the fourth metatarsal bone presents along the dorsal half of the inner surface an elongated facet five-eighths of an inch in the antero-posterior direction, i.e., from the tarsal surface towards the shaft, which is divided by a vertical ridge into two parts of nearly equal size, that behind, which is somewhat the smaller, being for the outer surface of the outer cuneiform bone, and that in front being for the outer surface of the base of the third metatarsal bone. The ridge which divides this facet into two parts, like the corresponding ridges on the outer side of the base of the second bone, is coated by articular car- tilage ; and thus we see that the synovial cavity between these bones and the tarsus is continuous, and indeed is one with the synovial cavity between the bones and the third metatarsal bone. On the outer side of the base of this bone is a tri- angular slightly concave articular facet for the fifth bone ; its base is at the dorsal aspect, its apex near the plantar surface at the tarsal edge, and its anterior margin, which is convex in front, is separated from the bone in front by a deep sulcus which runs downwards and backwards for the interosseous ligament. This facet is rather overhimg by the dorsal surface of the base. The base of the fifth metatarsal bone presents on its inner aspect a large irregularly triangular facet, the base of which is the smooth facetted but angular border wliich separates tliis lateral surface for the fourth bone from the terminal facet for the cuboid. The outer surface of this bone is prolonged back- wards into a rough tubercle, to which is attached the peroneus brevis muscle. The Ligaments, — The bases of the metatarsal bones are connected together firmly by three sets of ligaments, which hold their facetted surfaces in apposition. At their proximal ends these bones are loosely united by transverse ligaments. Be- tween the bases of the first and second bones there are a few interosseous bands chiefly situated towards the plantar aspect. The place of a dorsal ligament between these two bones is occupied by the ligament which extends from the inner cunei- form bone to the second metatarsal. When these two bones are in articular contact the facets are surrounded by some short fibrous tissue. MUSCLES OF INTEE-METATARSAL JOINTS. 441 Dorsal Ligaments. — Broad membranous ligaments pass between the contiguous bones of the four outer toes on their dorsal aspect. Plantar Ligaments. — Strong, thick, well-marked ligaments similarly connect them on the plantar aspect. Lnterosseous Ligaments. — Three very strong interosseous ligaments connect the same bones, and fill up the (often deep) sulci on their sides. They are situated at the point of union of the shafts and bases of the bones, so as to limit the synovial cavities in front of the lateral facets. Synovial Membrane. — The common synovial membrane of the tarsus extends between the bases of the second and third and thhd and fourth bones. The synovial membrane of the cubo- metatarsal joint extends between the fourth and fifth bones. Arteries of the Inter-metatarsal Joint. — On the dorsal aspect the metatarsal artery, and on the plantar smiace, the deep plantar arch supply these joints. Nerves. — The anterior tibial and the plantar nerves supply twigs to these as well as to the tarso-metatarsal joints. The Muscles connected with the Metatarsal Bones, are either inserted into them or arise from the sides of their shafts, and pass to be inserted into the phalanges. The peroneus longus, which is inserted into the outer side of the base of the first bone on its plantar aspect ; and the tibialis ^posticus, which is inserted into the plantar surface of the base of the second, third, fourth, and fifth bones, require to be especially mentioned, because by their action they tend to keep up the transverse arch formed by the metatarsal bones. The jperoneus tertius and peroneus hrevis, and the occasional muscle, viz., the abdtcctor ossis metatarsi minimi digiti, are attached to the tuberosity of the fifth bone, and tend to draw it away from the side of the fourth bone whilst they abduct it upon the cuboid. The peronei have this tendency, and at the same time they raise the outer side of the foot. The tibialis anticus is attached to the inner and lower part of the base of the first metatarsal bone, and in its action of raising the inner border of the foot it tends to draw the first bone from the second. The abductor minimi digiti slides along a smooth impression on the plantar surface of the base of the fifth bone, but is not attached to it. The other muscles which are connected with the metatarsal 442 TRANSVERSE METATARSAL LIGAMENT. bones act on tlie metatarso-phalangeal and phalangeal joints, and will be enumerated under the former. The Movements at the inter-metatarsal joints consist only of a gliding of the one upon the other, for the purpose of increasing the depth of their transverse arch, or of diminishing the depth so as to allow of the widening of the foot by the spreading out of the bones. When the arch is increased the outer and inner bones slide downwards upon the fourth and second, and the third rises upwards between the last two, whilst they are all drawn nearer together on their plantar aspect. When the anterior part of the foot is flattened out the third bone descends, whilst the outer and inner rise a little upon the fourth and second. Considerable flexibility and elasticity is given to the anterior part of the foot by these joints, enabhng it to become moulded to the irregularities of the ground on wliich it rests. Tlie Connexion of the, Heads of the Metatarsal Bones. The heads of the metatarsal bones are connected together on their plantar aspect by what is called the transverse ligament. This consists of four bands of fibres which pass in a transverse direction from bone to bone, like those at the head of the meta- carpal bones, with this exception, that a band extends to the head of the metatarsal bone of the great toe, wliilst the ligament in the hand does not extend to the metacarpal bone of the thimib. They limit the distance to which the metatarsal bones can be separated in bearing the weight of the body. They are blended with the lateral borders of the fibro- cartilaginous plates of the metatarso-phalangeal joints, and with the sheaths of the flexor tendons where they are connected with the fibro-cartilages. The metatarsal bones form a considerable part of the foot. The metatarsus is square in shape, of about two inches and a half in diameter, with four interosseous spaces between the bones. It presents a convexity upon the dorsal aspect, both longitudinally and transversely. It is rather wider in front than behind. Its inner border is thick and straight, and is formed by the first metatarsal bone ; its external border formed by the fifth metatarsal bone is thinner and concave; its anterior limit is the line of the metatarso-phalangeal joints, METATARSO-PHALANGEAL JOINTS. 443 and is convex ; tlie posterior is rendered uneven by the line of the tarso-metatarsal joints. The Metatarso-phcdanjecd Articulations of tlu four Outer Toes. Class, Diarthrosis. Subdivision, Ginglymus. These joints resemble the metacarpo-phalangeal. The con- cave articular surface of the posterior extremity of each proximal phalanx is adapted to the head of the metatarsal bone. A separate synovial membrane belongs to each joint. The Bones. — The anterior or digital extremity of each meta- tarsal hone presents a rounded articular head, which is more Xjronounced and projecting on the plantar surface, upon which aspect the facet is prolonged furtliest to allow of the greater freedom of flexion than of extension ; it is flattened upon the sides. On each side of the head, behind the articular surface, is a depression or groove, and behind the groove a ridge or tubercle, to which the lateral ligament of the joint is attached. The jjroximal extremity of the metatarsal yhcdanx of each toe forms a concave facet for the rounded head of the metatarsal bone. This facet is very shallow, but is deepened in the recent state by the fibro-cartilaginous plate connected with its plantar margin. Its transverse diameter is greater than the dorso- plantar, the reverse of the shape of the head of the meta- carpal bone, which is extensive from before backwards, but compressed from side to side. The Ligaments. — The chief of these are the lateral liga- m.ents, but the synovial sac is everywhere covered in by ligamentous, and tendinous, or cartilaginous structures. TJu Lateral Ligaments. — Two lateral ligaments, one on each side, maintain the bones in apposition. Each passes from the ridge on the side of the head of the metatarsal bone to the side of the proximal end of the first phalanx, and to the side of the sesamoid body. On the plantar side they are connected toge- ther by the sesamoid or fibro-cartilaginous plate ; on the dorsal aspect, by short ligamentous fibres, which extend across the ends of the bones and are connected with the under surface of the extensor tendons. Plantar Fibro-cartilaginotcs Plcde. — This, like the corre- sponding structure, sometimes called the glenoid ligament, in the fingers, helps to deepen the shallow facet of the phalanx for 444 MUSCLES OF METATARSO-PHALANGEAL JOINTS the head of the metatarsal bone. It is more firmly connected with the phalanx than with the metatarsal bone, to which latter it is held by some loose areolar tissue. Laterally, it is connected with the lateral ligaments and with the bands of the intertransverse ligament, which unites the heads of the metatarsal bones. Like the sesamoid bones of the great toe, and the fibrous tissue which connects them, the cartilaginous plates of the other toes serve to prevent dorsal dislocation of the phalanx. This plate is grooved inferiorly, where it forms a part of the sheath of the flexor tendons. ■ Tlie Dorsal or Superior Ligament. — On the dorsal aspect the joint is covered in by the expansion of the extensor tendons, and by some loose fine fibres of areolo-fibrous tissue, which extend across the bones to which they are connected, so as to form mth the lateral ligaments and the plantar cartilage a capsular investment. These dorsal hgaments assist in hold- ing the extensor tendons down to the bones. The Synovial Membeane forms a loose capacious sac, which is protected on the sides by the lateral ligaments ; beneath, by the fibro-cartilaginous plate, and by some loose cellular tissue attaching the plate to the plantar surface of the metatarsal bone ; and above, by the dorsal or superior ligament. . Akteries. — Little branches of the digital and interosseous arteries penetrate the ligaments, and supply the synovial membrane. The joint of the second toe derives twigs from the dorsal artery of the great toe, and from the plantar branch of the dorsal artery of the foot to the first interosseous space. Nerves. — Twigs are derived from the cutaneous digital branches, or from the small branches for the interosseous muscles. Muscles. — The muscles in connexion with the metatarso- phalangeal joint, are (1) the superficial and deep flexors, which pass over the smooth surface of the fibro-cartilaginous plate on the plantar surface of the joint, and the sheath of which is attached to the margins of the plate, and to the lateral and trans- verse ligaments where they meet together. (2) The plantar and dorsal interosseous muscles which arise from the metatarsal bones pass above the transverse ligament, and are inserted partly into the side of the base of the first jjhalanx, and partly into the expansion of the extensor tendon. (3) The lumbrical muscles, which pass below the transverse ligament, and are OF THE FOUR OUTER TOES. 445 inserted into the inner side of tlie extensor tendon over the base of the metatarsal phalanx. (4) The tendons of the ex- tensor muscles. (5) The transversus pedis arises from the inner side of the joints of the four outer toes. Flexion is performed by the flexor longus digitorum, flexor brevis digitorum, flexor accessorius, the interossei, and the lumbricales ; and in the case of the little toe by the flexor brevis minimi digiti. Extension by the extensor longus digitorum, and, except in the case of the little toe, by the extensor brevis digitorum. Abduction, which has reference to the middle line of the second toe, is performed by the dorsal interossei, two of which abduct the second toe, one the fourth toe, and one the third toe. The abductor minimi digiti acts on the little toe. Adduction is eflected by the three plantar interossei which act on the middle, fourth, and fifth toes ; and by the transversus pedis which act on these same toes through their connexion with the internal lateral ligaments of the joints, as well as on the great toe through its insertion into the base of the first phalanx. The four lumbricales and the seven interossei muscles have each a double action, for while they bend the first phalanx on the metatarsal bone they extend the second and third pha- langes on the first and second. The lumbricales do this by passing over the plantar surface of the transverse ligament to their insertion into the extensor tendon ; and the interossei, by having some fibres of their tendons inserted directly into the sides of the base of the phalanx itself, which therefore act directly upon it ; whilst others blend with the extensor tendon, and thus act on the second and third phalanges indirectly through their connexion with it. The muscles which act on these joints give a powerful support to the antero-posterior arch of the foot ; and the muscles which arise from the hinder part of the os calcis, by arising also in part from the plantar fascia, make that structure tense, by preserving its curve (which corresponds to the curve of the plantar arch, the concavity of which is downwards) in the various positions of the foot, and thus render it also capable of supporting the arch during their action. This action of the muscles on the plantar fascia, and on the anterior pillar of the arch of the foot, as well as the action of the fascia upon the arch, are well observed in the foot of the opera dancer. Not 446 METATARSO-PHALANGEAL JOINT OF GREAT TOE. only are these muscles numerous and powerful, but they are so placed as to act almost all of them from the same centre, and therefore with greater advantage, for strengthening the arch. Movements. — These are described under the following sections. The Metatarso-phalangeal Joint of the Great Toe. Class, Diarthrosis. Subdivision, Ginglymus. The metatarso-phalangeal articulation of the gTeat toe differs in some respects from the corresponding joints of the other toes. The bones are on a larger scale ; their articular surfaces are more extensive, and on the plantar aspect of the head of the metatarsal bone there is a smooth depression on each side of the middle line, which receives a sesamoid bone. The liga- ments of the articulation are like those of the corresponding joint of the other toes ; but in place of a plate of fibro- cartilage, the sesamoid bones are substituted. The Sesamoid Bones are two small hemispherical bodies developed in the tendons of the flexor brevis pollicis muscle, and which are situated, one on each side, in the depression on the plantar aspect of the head of the metatarsal bone. Their convex sides are directed downwards, and their flattened arti- cular surfaces, which are free to play upon the metatarsal bone, look towards the cavity of the joint. They are united to one another by strong ligamentous bands, the fibres of which take a transverse direction, and the under surface of the band is smooth, and forms part of the channel along which the long flexor tendon plays. Anteriorly, the sesamoid bones and their uniting ligament are connected by short strong hgamentous fibres to the base of the phalanx ; and posteriorly, by some- what looser fibres, to the head of the metatarsal bone beyond the articular surface. On their sides which look away from one another, the sesamoid bones are connected mth the lateral ligament, and with the sheath of the flexor tendon, in the same way that the sesamoid plates or flbro-cartilages of the other joints are. Thus these bones of the great toe, Hke those of the thumb, are surrounded by ligamentous fibres on all sides, ex- cept towards the joint, and by means of the fibres they are held to the phalanx and metatarsus, and help to enclose the cavity of the articulation. These bones provide a shifting leverage for the tendons of the flexor brevis pollicis, and increase the angle of their inser- MOVEMENTS OF THE METATARSO-PHALANGEAL JOINTS. 447 tion into the sides of the base of the first phalanx. They also give leverage to the tendon of the flexor longus pollicis. The Arteries of the Metatarso-phala]S"geal Joint of THE Great Toe, — The dorsal artery of the great toe ; and, on the plantar aspect, the plantar digital branches of the dorsalis pedis. Nerves. — The anterior tibial on the dorsal aspect ; and the internal plantar nerve in the sole. Occasionally the long saphenous nerve gives a branch to the inner side of this joint. The Muscles. — On the plantar aspect the following muscles are in relation to this joint : 1. The flexor longus pollicis passes over it to the base of the second phalanx. 2. The flexor brevis pollicis is inserted by two tendons into the sides of the base of the first phalanx. 3. The abductor pollicis is inserted with the inner tendon of the flexor brevis pollicis into the inner sesa- moid bone and the inner side of the base of the first phalanx:. 4. The adductor pollicis, with the outer tendon of the flexor brevis pollicis, into the outer sesamoid bone and outer side of the base of the first phalanx. 5. The transversalis pedis arises from the inner lateral metatarso-phalangeal ligaments of each of the four outer toes, and is inserted into the outer side of the plantar surface of the base of the first phalanx with the adductor pollicis. On the dorsal aspect of the joint there are (1) the extensor proprius pollicis, and (2) the inner tendon of the extensor brevis digitorum, which is inserted into the dorsal surface of the first phalanx near its base. The action of these muscles is sufficiently explained by their names. The transversus pedis acts on all the toes ; by drawino- the heads of the four outer metatarsal bones together, and the great toe towards the others, it strengthens the antero-posterior arch by holding the parts of its anterior pier together, and deepens the transverse arch in the same way. The long flexor •and long extensor are the only two muscles which pass beyond the first phalanx, and they, by going to the base of the second phalanx, act first upon the inter-phalangeal joint, and afterwards upon the metatarso-phalangeal. The Movements of the Metatarso-phalangeal Joints consist of flexion and extension with some lateral motion, viz., abduction and adduction; and the combination of these four movements, viz., circumduction. Flexion is more free than 448 THE INTER-PHALANGEAL JOINTS. extension, and is limited by the extensor tendon and dorsal ligament, and by tbe dorsal fibres of the lateral ligament : extension is limited by the plantar articular structures, and by the plantar fibres of the lateral ligament, and by the flexor tendons. Abduction and adduction are possible, owing to the shape of the articular surfaces of the bones, but are limited by the lateral ligaments and sesamoid plates. They are freest in the joint of the great toe. The Inter-phalangeal Joints. Class, Diarthrosis. Subdivision, Ginglymus. The articulations between the first and second and the second and third phalanges of the toes are exactly similar to those of the fingers, with this important difierence, that the bones are smaller, and the joints, especially between the second and third phalanges, are often ankylosed. The Bones. — The phalanges of the first and second row present at their distal extremities a smooth trochlear surface, consisting of a median depression with a slight convexity on each side of it. The articular surface is prolonged further on the plantar than dorsal surface, and is broader from side to side than from above downwards. The phalanges of the second and third row present at their proximal ends a smooth articular facet, consisting of a slight concavity on each side of a dorso-plantar ridge. The ridge plays in the trochlea on the head of the bone behind it, and the little fossse on each side of the ridge receive the condylar portions of the head of the same phalanx. The Ligaments. — Two well-marked lateral ligaments pass one on each side of the joint, from a little rough depression on the head of the proximal to the rough border on the side of the base of the distal phalanx of the joint. Glenoid Ligament. — On the plantar surface a fibro-carti- laginous plate, called sometimes the glenoid ligament, covers in the joint, and is connected along its proximal and distal borders with the phalanges by short ligamentous fibres, and along its lateral edges with the lateral ligaments. The plantar surface of these plates is smooth, and grooved for the flexor tendons. Dorsal Ligament. — On the dorsal aspect a thin membranous ligament extends across the joint from one lateral ligament to THE CUTANEO-PHALANGEAL LIGAMENTS. 449 the other beneath the extensor tendons, with the deep surface of which it is connected. At the inter-phalangeal joint of the great toe there is frequently a small sesamoid bone which plays upon the plantar surface of the fii-st phalanx, just as the sesamoid bones of the metatarso-phalangeal joint play upon the plantar surface of the head of the first metatarsal bone. The, Cutaneo-phalangeal Ligaments. — These, like the corre- sponding ligaments of the fingers, are well-marked bands of ligamentous fibres, which pass from the ridges on the lateral borders of the phalanges to the skin over the plantar and dorsal aspects of the inter-phalangeal joints. Those of the great toe are especially well developed; and those connected with the first joint more so than those inserted into the skin over the distal joints. The fibres over the first inter-phalangeal joint arise from the first phalanx, back as far as the sides of the metatarso-phalangeal joint, those of one side having passed on the dorsal side of the digital artery and nerve, decussate with fibres from the opposite side of the same phalanx before they are inserted into the skiii over the first inter-phalangeal joint, on both the plantar and dorsal surfaces, but more particularly on the dorsal aspect. The Synovial Membeane is complete for each joint, and that belongiag to the articulation between the first and second phalanges is ample, and even loose. Often those of the distal joints are completely or partially destroyed, as the joints them- selves become more or less ankylosed. The Arteries. — Blood is supplied to these joints by little vessels which spring from the digital arteries, and run along in the sheaths of the tendons, one on each side, and then end in twigs, which penetrate the fibrous tissue and reach the synovial membrane. Others are given from the inter- osseous branches of the metatarsal artery ; and in the case of the second and great toes from the dorsal artery of the great toe, and from the plantar digital branches of the dorsaKs pedis. Nerves are derived from the digital branches of the cor- responding toes. BurStE. — A bm-sa mucosa of the flexor tendons begins just above the first joint of each toe, and ends at the base of the last phalanx close to the insertion of the tendon. G G 450 THE INTER-PHALANGEAL JOINTS. Muscles. — Over the joints between the first and second plialanges there pass the tendons of the flexor and extensor muscles of the phalanges, some of which also pass over the joint between the second and thii^d phalanges, to be inserted into the terminal phalanges ; those which do not extend beyond the second phalanges are inserted into the bases of those bones. Into the base of the terminal phalanx of each of the four outer toes there is inserted the tendon of the flexor longus digitorum on the plantar surface, and into that of the great toe on the same surface is the flexor longus pollicis. Into the base of the second phalanx on the plantar aspect of the four outer toes is inserted a tendon of the flexor brevis digi- torum. Into the base of the second phalanx of each of the four outer toes, on its dorsal aspect, is inserted the central portion of the expansion of the extensor tendon, consisting of the extensor longus digitorum tendon and the lumbricales and interossei ; and in the case of the second, third, and fourth toes, of a slip from the extensor brevis digitorum also. Into the base of the second phalanx of the great toe, on its dorsal aspect, the tendon of the extensor proprius pollicis is inserted. MovEiVrEXTS. — Flexion and extension are the only move- ments permitted at these joints ; the extent of these move- ments, so far as they are not limited by the stiffness which results from confinement within tight boots, and such-hke abnormal restricting influences, is checked by the lateral Kgaments and by the antagonism of the flexor and extensor muscles. INDEX. A CCESSORY ligament, oecipito-atlan- -^ tal, 46 ligaments between pelvis and spinal column, i 05 Acetabulum in connexion with hip-joint, 317 Acromio-clavicular joint, 195 arteries of, 207 bursse of, 207 ligaments of, 198 movements of, 202 muscles of, 205 nerves of, 208 synovial membrane of, 199 Adductor longus, 152 Alar ligaments of the knee, 365 Amphiarthrosis, occasional obliteration of, from old age, 18 Angle, sacro -vertebral, 109 Ankle-joint, 387 arteries of, 393 bones of, 388 bursas of, 394 ligaments of, 391 movement of, 396 muscles of, 395 nerves of, 394 synovial membrane of, 393 Annular ligament, posterior of the wrist, 278 anterior of carpus, 290 of superior radio-ulnar joint, 250 Anterior crucial ligament, 357 annular ligament of carpus, 290 circumflex artery of the shoulder- joint, 220 Aponeurosis of external abdominal oblique muscle, 152 lumbar, 99 vertebral, 99 Arch, ischio-sacral, 115 femoro^sacral, 115 Arches of the foot, 399 antero-posterior, 399 piers of, 400 transverse arch of, 401 Arteries, anastomoses of, about joints, 14 of atlo-axoidean joints, 56 of the anterior calcaneo-astragaloid joint, 408 of anterior part of tarsus, 419 of the ankle-joint, 393 of the acromio-clavicular joint, 207 Arteries of central atlanto-axoidean joint, 55 of the carpal joints, 291 of the chondro sternal joints, 175 of costo-transverse joints, 167 of costo-central joint, 163 distribution of, to joints, 14 of the elbow-joint, 236 gluteal, 135 of hip-joint, 332 iliolumbar, 135 of the inter-phalangeal joints of fingers, 315 of the inter-chondral joints, 176 of the inferior peroneo- tibial joint, 386 of inferior radio-ulnar joint, 265 intercostal joint, 163, 167 of inter-metatarsal joint, 441 of inter-phalangeal joints of toes, 449 of the knee-joint, 367 lateral sacral, 145 of the lumbo-pelvic, sacro-lumbar, or sacro-vertebral union, 108 of metatarso-phalangeal joints of four outer toes, 444 of metatarso-phalangeal joint of great toe, 447 of metacarpo-phalangeal joints of thumb, 312 of medio-tarsal joints, 427 metacarpo-phalangeal joints of fingers, 309 of medio-tarsal joint, 427 of occipito-atlan tal joint, 46 of posterior calcaneo-astragaloid joint, 406 of the radio-ulnar interosseous membrane, 258 of the sacro- coccygeal joint, 145 of the saero-iliac joint, 135 sacralis -media, 145 sacro-spinal, 135 of shoulder- joint, 219 of the spinal column, 88 of the superior radio-ulnar joint, 252 of superior tibio-fibular joint, 381 of the symphysis pubis, 151 of tarso-metatarsal joints, 436 of temporo-maxillary joint, 31 of the ■wrist-joint, 279 Arthrodia, 19 Articular cartilage, 3 G G 2 452 INDEX. Articular cartilage, a form of hyaline cartilage, 3 cartilage over humerus and glenoid socket, 217 cartilage of hip-joint, 332 ligaments, 7 ,, between sacrum and pelvis, 105 processes of spine, capsular liga- ment of, 86 processes of vertebrae limit the direction of motion and give steadiness to column, 90 Articulation, vide Joint Astragalus in connexion witb astragalo- scaphoid joint, 421 in connexion with the anterior calcaneoastragaloid joint, 407 in connexion with the posterior calcaneo-astragaloid joint, 404 in connexion with the ankle-joint, 390 Astragalo-scaphoid joint, 421 bones of, 421 ligaments of, 422 synovial membrane of, 424 Atlas, transverse ligament of, 54 connexion with occiput, 39 connexion with axis, 49 description of, 43 Atlanto-axoidean joint, central arteries of, 55 muscles of, 56 nerves of, 56 Atlo-axoidean joints, 52, 53, 54 arteries of, 56 transverse ligament of, 54 movements of, 55 muscles of, 56 nerves of, 56 Atlo-axoidean capsular ligament, 55 synovial membrane of, 55 Aud tory meatus, 27 Axis, connexion v;ith atlas, 47 odontoid process of, 58 BICEPS tendon of the knee, 380 connexion of the biceps tendon with the great sacro-sciatic ligament, 133 of the shoulder, 217 Bicipital groove of humerus, 21 3 Bones, the basis of most joints, 2 Bursse of the ankle-joint, 394 of the acromio-clavicular joint, and between the coraco-clavicular liga- ments, 207 of the calcaneo-astragaloid joint, 406 of the elbow-joint, 239 of the hip-joint, 334 of the inter-phalangeal joints of the toes, 449 of the knee-joint, 369 of the inferior peroneo-tibial joint, 386 Bursffi of the superior peroneo-tibial joint, 381 of the shoulder-joint, 221 of the wrist-joint, 281 mucosse, 10 number of, 9 resemblance between and serous sacs, 10 situations of, 10 structure of, 10 synoviales, 10 nALCANEO-ASTRAGALOID joint, an- ^ terior, 406 arteries of, 408 bones of, 406 ligaments of, 407 nerves of, 408 synovial membrane of, 408 Calcaneo-astragaloid joint, the posterior, 402 arteries of, 406 bones of, 402 bursse of, 406 ligaments of, 404 nerves of, 406 synovial membrane of, 406 Calcaneo-astragaloid joints, movements of, 409 muscles of, 408 Calcaneo- cuboid joint, 424 arteries of, 427 bones of, 424 ligaments of, 425 nerves of, 427 synovial membrane of, 427 ■ Capsular ligaments, 7 acromio-clavicular, 198 atlo-axoidean, 52 atlo- odontoid, 55 of articular processes of spine, 86 of costo-transverse joint, 166 of C'isto-central articulation, 161 of the hip joint, 322 connexion of capsule of hip-joint at the pelvis, 322 co/.nexion of capsule of liip-joint at the femur, 322 lateral atlanto axoidean, 53 occipito-atlantal, 44, 45 of shoulder-join >■•, 213 of the sterno-clavicular joint, 189 of the superior tibid-fibular joint, 880 of temporo-maxillary joint, 27 of the wrist, 275 Carpal bones, first row of, in connexion with wrist-joint, 273 Carpus, anterior annular ligament of, 290 arteries of, 291 bones of first row, 284 bones of second row, 286 ligaments of first row, 285 INDEX. 453 Carpus, ligaments of second row, 287 ligaments connecting pisiform bone with, 286 muscles of, 292 nerves of, 292 synovial membrane, 285, 286 transverse dorsal ligament of, 289 Cartilage, articular, 3 costal, 4, 172 hyaline, 3 white fibrous of joints, 4 xiphoid, 4, 169 Carpo-metacarpal joint of thumb, 301 ligaments of, 302 movements of, 304 muscles of, 303 synovial membrane of, 303 joints of fingers, 295 ligaments of, 297 movements of, 300 muscles of, 298 synovial membrane of, 298 Circumflex nerve, 221 Check ligaments, 59 Chondro-sternal joint, 170 arteries of, 175 ligaments of, 173 movements of, 175 nerves of, 175 Chondro-xiphoid ligament, 174 Clavicle in connexion with acromio- clavicular joint, 195 in cojinexion with the sterno- clavicular joint, 187 union of, with scapula, 195 Coccygeus, 146 Coccyx, relation of to symphyis pubis, 119, 120 Coccyx, in connexion with sacro coccy- geal joint, 140 Column, differences in various parts of spinal coluojn, 79 Connexion of heads of metacarpal bones with one another, 306 Conoid ligament, 200 Conjoined tendon of internal oblique and transversalis, 152 Coraco, acromial ligament, 208 clavicular ligament, 200 humeral ligament, 215 Coracoid ligament, 209 process, 199 Coronary ligaments of the knee-joint, 364 of the superior radioulnar joint, 250 Costal cartilage, a form of hyaline carti- lage of joints, 4 cartilages in connexion with the chondro-sternal joints, 172 Costo-clavicular ligament, ] 90 Costo-central articulation, 158 arteries of, 163 ligaments of, 161 Costo-central articulation, movements of, 164 nerves of, 163 synovial membrane of, 163 Costo-chondra] joints, 168 Costo-transverse joint, 164 arteries of, 166 ligaments of, 166 movements of, 167 nerves of, 167 Costo-vertebral articulations, 158 Cotyloid ligament, 331 Crucial ligaments, 357 ligament, occipito atlo-axoidean, 58 Cubo-cuneiform joint, bones of, 417 ligaments of, 418 Cuboid in connexion with calcaneo- cuboid joint, 425 in connexion with cubo-cuneiform joint, 417 in connexion with scapho-cuboid joint, 412 Cuneiform bones, 274, 284 joints between, 416 „ with scaphoid, 413 ,, between external and cuboid, 417 ligaments of, 418 in connexion with the scapho- cuneiform joint, 414 bones in connexion with tarso- metatarsal joints, 431, 432 Curvator cuccygis, 146 Cutaneo-phalangeal ligaments of fingers, 315 of toes, 449 "TjELTOID ligaments of ankle-joint, ■L' 392 or costo-clavicular ligament, 190 Dorsalis scapulae artery, 220 L'^AR- SHAPED cartilage of sacro-iliac ^^ synchondrosis, 132 Elbow-joint, 227 arteries of, 236 bursas of, 239 fatty cushions or pads of, 235 ligaments of, 232 movements of, 243 muscles of, 240 nerves of, 239 synovial membrane of, 236 Enarthrosis, 20 Expression, movements of joints as a mode of, 246 X^ATTY cushions or pads of the elbow- -■- joint, 235 Femoro-sacral arch, 115 Femur, in connexion with the hip-joint, 319 in connexion with knee-joint, 343 454 INDEX. Fibro-cartilage, circumferential or mar- ginal, 5 cotyloid of hip-joint, 331 connecting^, 5 •white of joints, 4 of the inferior ladio-ulnar joint, 263 inter-articular, 4 inter-phalangeal joints of fingers, 314 inter-phalangeal joints of toes, 448 of the knee, 361 of inetatarso-phalangeal joint of the outer toes, 443 of temporo-maxillary joint, 29 of carpus, 285 Fibula in connexion with ankle joint, 388 inferior peroneo-tibial joint, 384 superior peroneo-tibial joint, 379 Fibrous expansion of extensor tendon over knee, 351 Fifth lumbar vertebra in connexion with sacro-vertebral joint, 100 Foot, human, as distinguished from quadrumanous, 3S8 arches of, 399 modified hand, 399 number of bones in, 401 size of, 398 Forearm, interosseous membrane of, 258 pronators of, 253 supinators of, 253 niNGLYMUS, 20 ^ Glasserian fissure, 26 Glenoid cavity of scapula, 210 fossa of temporal bone, 26 ligaments of the inter-phalangeal joints of hand, 314 of foot, 448 of metacarpo-phalangeal joints of hand, 3C8 of fout, 443 Gleno-humeral ligament, 215 process of the capsule of the shoulder, 215 Gluteal artery, 135 Gluteus maximus, 146 Gracilis, 152 Great sacro-sciatic ligament, 132 TJAMSTRING muscles, 146 -*"^ their connexion with the great sacro- sciatic ligament, 133 Hand, 283 Heel, muscles of, 409 Hilton, lav/ respecting nerves, 14 examples of law respecting nerve supply to joints, 15 Hip-joint, 317 arteries of, 332 buisse of, 334 ligaments of, 321 Hip-joint, movements of, 338 muscles of, 334 nerves of, 333 synovial membrane of, 332 Hip-joint, fibro-cartilage of, 331 Hip-joint, the chief means of connexion between the trunk and the thighs, 112 Humerus connected with the elbow- joint, 227 in connexion with shoulder-joint, 211 .Hyaline cartilage, as found in joints, 3 "j LIO-FEMORAL ligament, 324 *■ llio-lumbar artery, 135 ligament, 107 Ilium in connexion with sacro- iliac syn- chondrosis, 128 Inferior radio-ulnar joint, 260 arteries of, 265 ligaments of, 263 movements of, 266 muscles of, 265 nerves of, 265 synovial membrane of, 264 Inter-articular fibro-cartilage, 4 of the acromio-clavicular joint, 199 of the knee, 361 of sterno clavicular joint, 191 of temporo-iiiaxillary joint, 29 ligaments, 8 or interosseous ligament of the sacro- iliac synchondrosis, 131 ligament of costo central articulation, 162 ligament of chondro-sternal joints, 174 Inter-chondral articulations, 175 Interchondral joint, arteries of, 176 movements of, 177 neives of, 176 Inter-clavicular ligament, 190 Intercostal arteries, 163, 167 Inter- coccygeal joints, 147 Inter- metatarsal joints, 439 arteries of, 441 bones of, 439 ligaments of, 439 movements of, 442 muscles of, 441 nerves of, 441 synovial membrane of, 441 Internal mammary artery in connexion with chondro-sternal joints, 175 Interosseous fibro- cartilages of carpal bones, 285 of symphysis pubis, 148 calcaneoastragaloid ligament, 405, 407 cubo-scaphoid ligament, 413 calcaneo-cuboid, 425 of the carpo metacarpal joints, 298 INDEX. 45S Interosseous fibre- cartilage of metatarsal bones, 441 between metatarsal bones, 441 Inteiosseous ligament of inferior peroneo- tibial joint, 385 between radius and ulna, 256 influence of, on movements of the bones, 259 of the sacro-iliac synchondrosis, 131 of the superior tibio-fibular joint, 380 of the tarso- metatarsal joints, 433, 435 of third row of tarsus, 418 between metacarpal bones, 306 Interosseous membrane of the leg, 382 muscles in relation with, 383 membrane of forearm, 264 Inter-phalangeal articulations of the hand, 313 arteries of, 315 ligaments of, 314 movements of, 316 muscles of, 153 nerves of, 315 synovial membrane of, 315 Inter-phalangeal joints of the foot, arteries of, 449 bones of, 448 bursse of, 449 fibro-cartilage of, 448 glenoid cartilage, 448 ligaments of, 448 movements of, 450 muscles of, 450 nerves of, 449 synovial membrane of, 449 Intersjiinous ligaments, 88 Intertransverse ligament of the sacro- coccygeal joint, 144 ligaments, 88 Intervertebral ligaments, 74 substance, sacro-coccygeal, 143 substances, 69 Ischio-femoral ligament, 325 Ischio-sacral arch, 115 JOINT, ankle, 387 '■^ atlo-axuidean, 52, 53, 54 astragalo-scaphoid, 421 bilateral arrangement of, in the skull, 23 bones the basis of most, 2 ealcaneo-astragaloid, the posterior, 402 ealcaneo-astragaloid, the anterior,406 calcaneo-cuboid, 424 carpal, 284, 286 carpo-metacarpal of the thumb, 301 carpometacarpal, 295 cartilages of, 3 chondro-sternal, 170 combination of two or more for variety of movement, 22 Joint, costo-chondral, 168 costo-transverse, 164 costo- vertebral, 158 cubo-cuneiforin, 417 definition of, 16 distribution of arteries to, 14 elbow, 227 hip, 317 inter-chondral, 175 inter-coccygeal, 147 inter-metacarpal, 305 inter-metatarsal, 439 inter-phalangeal of hand, 314 of foot, 448 knee, 342 medio caipal, 288 medio-tarsal, 421 metacarpo-phalangeal of thumb, 311 of finger, 307 metatarso phalangeal of great toe, 446 metatarso phalangeal, of four outer toes, 443 the most movable, the most com- plex in structure, 16 nerve supply to, 14 occipito-atlantal, 39 of the pelvis, 111 peroneo-tibial, 378, 384 radio-carpal or wrist, 270 radio-ulnar, 249, 260 sacro-coccygeal, 140 scapho-cuboid, 412 scapho- cuneiform, 413 shoulder, 210 of posterior part of spinal column, 76 sterno-clavicular, 186 structures entering into construction of, 2 tarso-metatarsal, 431 of the anterior part of the tarsus, 412 tibio-fibular, 378, 384 transverse tarsal, 421 which connect the vertebral column with the pelvis, 100 TZNEE-JOINT, 342 -^ arteries of, 367 bones of, 343 bursee of, 369 differences between it and hinge joints, 374 fibro-cartilages of, 361 ligaments of, 350 movements of, 373 muscles of, 371 nerves of, 368 synovial membrane of, 366 J ATERAL sacral arteries, 145 '-' Laminffl of vertebrte, 76 Levator ani, 146, 152 456 INDEX. Ligaments of tbe acromio-clavicular joint, 198 in connexion with the ankle-juint, 391 anterior annular of carpus, 29 1) annular of radio- ulnar joint, 250 articular, 7 of astragalo- scaphoid joint, 422 of the anterior calcaneoastragaloid joint, 407 calcaneo-astragaloid interosseous, 405, 407 of calcaueo-cuboid joint, 425 capsular, 7 of the carpo-metacarpal joints, 297 carpo-metacarpal interosseous, 298 of the carpo metacarpal joint of thumb, 302 of the first row of the carpus, 285 of second row of carpus, 287 check of skull, 59 chnndro- xiphoid, 174 of the chondro-sternal joints, 173 chondro-sternal interarticular, 174 connecting, 8 connecting the cuboid and scaphoid, 413 connecting metacarpal bones, 306 connecting pisiform bone with carpus, 286 coracoid, 209 coronary, 250 coraco-acromial, 208 coraco-clavicular, 200 coraco-humeral, 215 coronoid, 200 of costo-central articulation, 161 costo-clavicular, 190 of costo- transverse joint, 166 cotyloid, 331 crucial of knee-joint, 357 crucial, connecting skull and spine, 58 of cubo- cuneiform joint, 418 cubo-scaphoid interosseous, 413 cutaneo-phalangeal, of fingers, 315 cutaneo-phalangeal, of toes, 449 deltoid or costo-clavicular, 190 direction of fibres of, as a means of regulating movement, 22 elastic, 8 of the elbow-joint, 232 gleno-humeral, 215 of the hip-joint, 321 ilio-femoral, 324 ischio-femoral, 325 ilio-lumbar, 107 inter-clavicular, 190 inter-articular, 8 inter- metatarsal joint, 439 interosseous of forearm, 256 interosseous of third row of tarsus, 418 Ligaments of the inter-iihalanijea! joints, 314, 448 interosseous between uietacarpal bone, 306 interspinous, 88 intertransverse, 88 intertransverse of hand, 306 of the knee, 350 of raedio-carpal joint, 289 of metacarpo-phalangeal joint of thumb, 3i2 of metatarsal bones, 440, 442 of metacarpo-phalangeal joints of fingers, 308 of thumb, 312 of the outer toes, 443 non -articular, 7 accessory occipito-atlantal, 46 occipito-axoidean,57, 58 occipito cervical, 58 of occipito-atlantal, 44 occipito-odontoid, 59 oblique radio-ulnar, 256 occipito-basilar, 58 pectineo-femoral, 326 of the pelvis. 111 of the inferior peroneo-tibial, 384 of the posterior calcaneo-astragaloid joint, 404 of the radio carpal joint, 275 of the superiur radio-ulnar joint, 250 of the inferior radioulnar joint, 263 round of hip, 328 of the sacio-coccygeal joint, 143 sacro-lumbar, 106 sacro-sciatic, 127 of the sacro-iliac synchondrosis, 130 of scapho-cuneiform joints, 414 of shoulder-joint, 213 of anterior part of spinal column, 72 of posterior part of spinal column, 82 of the sterno-clavicular joint, 189 structure of, 7 supra-scapular, 209 supra-spinous, 87 articular, between sacrum and pelvis, 105 of the symphysis pubis, 148 of tarso-metatarsal joint, 432, 433, 435 of the anterior part of the tarsus, 412 of temporo-maxillary joint, 27 teres of hip, 328 of the superior tibio-fibular joint, 380 of the inferior tibio-fibular interos- seous, 385 transverse, of atlas, 54 transverse, of hip, 331 transverse, of scapula, 209 transverse, of inferior tibio fibular joint, 385 transverse, of metatarsal bones, 442 INDEX. 457 Ligaments, trapezoid, 201 uses of, 6 ■which connect the vertebral column with the pelvis, 100 connecting vertebral column with the pelvis, 105 posterior annular of the wrist, 278 Ligamenrum arcuatum, 150 mucosum, 365 nuchse, 87 patella, 352 subflavum, 82 uses of ligamentum subflavum, 82 teres, 328 „ uses of the, 329 ,, mode of ascertaining tbe use of, 330 Winslowii, 354 Lumbar fascia, 99 Lumbo-pelvic union, 100 lyrESO-STERNUM, 169 -"-^ Manubrium sterui, 1 8 Maxilla, inferior, 27 Meatus, external auditory, 27 Medio-carpa] joint, 288 ligaments ..f, 289 movements of, 293 synovial membrane of, 290 Medio -tarsal joint, 421 arteries of, 427 muscles of, 427 movements of, 428 nerves of, 427 Membrane, interosseous, of forearm, 258 arteries of, 258 muscles of, 258 nerves of, 25S interosseous, of leg, 382 Metasternum, 169 Metacarpal bones, 296, 302 ligaments connecting, 306 joints between, 3c- 5 Metacarpo-phalangeal joints of the fingers, 307 arteries of, 309 ligaments of, 308 movements of, 310 muscles of, 309 nerves of, 309 synovial membrane of, 309 Metacarpo-pbalangeal joint of thumb, 311 arteries of, 312 ligament of, 312 muscles of, 313 movement of, 313 nerves of, 312 sesamoid bones of, 312 Metatarsal bones ; in connexion with the tarso- metatarsal joints, 431, 433, 434 in connexion with inter-metarsal joints, 439 Metatarsal bones with raetatarso phalan- geal joints, 443 with inter-metatarsal joints, 443 interosseous ligaments of, 441 ligaments of, 440, 442 movements of, 442 muscles of, 441 Metatarso-phalangeal joint of great toe, 446 arteries of, 447 movements of, 447 muscles of, 447 nerves of, 447 sesamoid bones of, 446 toes, 443 arteries of, 444 Mttatarso-phalangeal joiut of four outer toes, 443 arteries of, 444 bones of, 443 fibro-cartilaginous, plate of, 443 ligaments of, 443 movements of, 446 muscles of, 444 nerves of, 444 synovial membrane of, 444 Metatarsus, muscles inserted into, 436 Movement, necessity of, for life, 1 muscles necessary for, 1 1 freedom of, dependent on complexity of structure, 16 variety of, produced by two or more joints, 22 Movements of the ankle-joint, 396 at atlo-axoidean joints, 56 between astragalus and os calcis, 409 of the carpo- metacarpal joint of the thumb, 304 of the carpo-metacarpal joints of the fingers, 300 of costo-central joint, 164 of costo-transverse joints, 167 of the chondro-sternal joint-!, 175 of the elbow, 243 a mode of expression, 246 regulated by direction of fibres of ligaments, 22 of the hip-joint, 338 of theinter-phalangealjoints,31 6, 450 of inter-m eta tarsal joints, 442 of the inter-chondral joints, 177 of the knee joint, 373 of metatarsal bones, 442 of metatarso-phalangeal j oint of great toe, 447 of the medio -carpal joints, 293 of metacarpal-phalangeal joints of thumb, 313 of "metacarpo-phalangeal joints of fingers, 310 of metatarso phalangeal joints of four outer toes, 446 of medio-tarsal joint, 428 45S INDEX. Movements of occipito-atlantal joint, 47 of the pelvis, 122 at the sacro-vertebral union, 122 upou the thighs, 123 muscles effecting movements of pelvis on thii;hs, 124 pendulum-like of lower limbs, 126 of inferior peroneo-tibial joint, 386 of the superior radio-ulnar articula- tion, 254 of inferior radio-ulnar joint, 266 of the symphysis piubis, 152 of the sacro iliac synchondrosis, 137 of the spinal column, 89 the amount of in spinal column limited, by common vertebral ligaments, and varies with thick- ness of intervertebral substances, 90 articular processes in regard to, 90 of the skull, 23 between the scapula and clavicle, 202 between the sternum and the xiphoid, 169 of the shoulder-joint, 224 of the sterno-clavicular joint, 192 of the sacro-coccygeal joint, 146 of tarso- metatarsal, 4B8 of the thoracic wall, 182 of the superior tibio-fibular joint, 382 of temporo-maxillary joint, 34 of the anterior part of the tarsus, 419 of the sacro-lumbar joints, 109 of the wrist-joint, 282 Muscles of the ankle-j"int, 395 of atlo-axoidean joints, 56 of central atlanto-axoidean joint, 56 connected with the calcaneo-astra- galoid joints, 408 of the car po- metacarpal joint of the thumb, 303 of the carpo-metacarpal joint of fingers, 298 of the carpal joints, 292 of thf. elbow-joint, 240 between head and spinal column, 61 of the hip-joi!.t, 339 of the heel, 409 of inter-phalangeal joints of fingers, 315 of inter- metatarsal joints, 441 in relation with the interosseous membrane of the leg, 383 of the inter-phalangeal joints of toes, 450 necessary for movement of j'jints, 11 functions of, in relation to joints, 11 in relation with the knee-joint, 371 law regarding the attachment to the bones of a joint, 13 connected with metatarsal bones, 441 Muscles of metatarso-phalangeal joint of great toe, 447 metatarso-phalangeal joint of four outer toes, 444 of metacarpo phalangeal joints of fingers, 309 of metacarpo-phalangeal joint of thumb, 313 inserted into metatarsus, 436 in relation vrith medio-tarsal joint, 427 of occipito-atlantal joint, 47 in connexion with the pelvis, 120 movements of the pelvis on thighs eff-cted by, 1 24 inserted into phalanges, of the toes, 436 of inferior peroneo-tibial joint, 386 of the radio-ulnar interosseous mem- brane, 258 of inferior radio-ulnar, 265 of the superior radio-ulnar joint, 252 in connexion with the spinal column, 93 extrinsic of spinal column, 93 intrinsic of s|iinal column, 94 chiefly placed behind the column, 98 of the sacro-coccygeal joint, 146 moving the scapula and the clavicle, 205 of the sacro-lumbar union, 108 of the sterno-clavicular joint, 193 connected with the shoulder- joint, 222 of the symphysis pubis, 152 of sacro-iliac joint, 136 of the thorax, 177 direct muscles of the thorax, 179 indirect muscles of the thorax, 181 of the superior tibio-fibular joint, 381 of temporo-maxillary joint, 31 connected with the anterior part of the tarsus, 419 connected with tarso-metatarsal joint, 436 of the wrist-joint, 280 "M'ECK of glenoid process of scapula, 211 -'-" neck of scapula, 211 Nerves of the ankle-joint, 394 of atlo-axoidean joint, 56 of cential atlanto axoidean joint, 56 of acromio-clavicular joint, 208 of the chondro-sternal joint, 175 of the anterior ca'.caneo-astragaloid joiut, 40S of the carpal joints, 292 of the costo-central joint, 163 of the costo-transverse joint, 167 of posterior calcaneo-astragaloid joint, 406 of the elbow-joint, 239 INDEX. 459 Nerves of the hip-joint, 333 Hilton, law respecting, li of inter-phalangeal joints of foot, 449 of inter-phalangeal joints of hand, 315 of inter-metatarsal joints, 451 of the inter-chondral joints, 176 of the knee-joint, 368 of the metacarpo-phalaugeal joint of the thumb, 312 of metatarso-phalangeal joint of great toe, 447 of uietarso-phalangeal joints of four outer toes, 444 of medio-tarsal joint, 427 of metacarpo-phalangeal joints of fingers, 309 difficulty in tracing nerves into small joints, 14 of occipito-atlantal joint, 46 of the inferior peroneo-tibial joint, S86 of the radioulnar interosseous mem- brane, 258 of inferior radio-ulnar, 265 of the superior radio ulnar joint, 252 of the sacro-iliac joint, 136 of the shoulder-joint, 220 of the sacro-lumbar union, 108 of the sacro-coccygeal joint, 145 of the spinal column, 89 of the anterior part of the tarsus, 419 of tempore- maxillary joint, 31 of the superior tibio-fibular joint, 381 of tarso- metatarsal, 436 of the wrist-joint, 280 ABLIQUE ligament between radius and ^ ulna, 256 Occipito-atlantal joints, 39 arteries of, 46 capsular ligament, 44 differences between, and the temporo- maxillary, 24 ligaments, 44 muscles of, 47 movements of, 47 nerves of, 46 Occipito-atlo-axoidean crucial ligament, 58 Oceipito-axoidean ligament, 58 Oecipito-basilar ligament, 58 Occipito-cervical ligament, 58 Occipito-odontoid ligaments, 59 Occiput, connexion with atlas, 39 Odontoid process of axis, 50 Os calcis in connexion with calcaneo- cuboid joint, 424 in connexion with the posterior calcaneo-astragaloid joint, 402 Os magnum, 287, 292, 295 T)ATELLA in connexion with knee- -*- joint, 347 Pectineo-fendoral ligament, 326 Pelvis, arches of, 115 cavity of, 114 general features of, as a whole, 113 imperfection of the bony wall of, 119 joints of, 111 ligaments connecting it with spinal column, lUo ligaments of, 111 movements at the sacro- vertebral union, 122 movements of the, upon the thighs, 123 muscles affecting the movements of the, ou thighs 124 muscles in connexion with, 120 obliquity of, 118 reasons for describing sacrum as part of ihe. 111 Peroneo-tibial joints, superior, 378 inferior, 384 Pendulum-like movements of the lower limbs, 126 Phalanges of the first row, 308, 313 of the second row, 313, 314 of the third row, 314 in connexion with metatarso-phalan- geal joints, 443 muscles inserted into, 436 Phalanx, first of thumb, 311 Pisiform bone, 285, 292 Plantar ligaments, long and short, 426 Posterior circumflex artery, 220 Posterior crucial ligament, 358 Processus cochleartformis, 27 Pronator of the furearm, 253 Pronation, 255 Pubic bone in relation to symphysis pubis, 147 Pubis, symphysis of, 147 Pyramidalis, 152 "DADIO-CARPAL joint, 270 -^^ arteries of, 279 bursse of, 281 ligaments, 275 movemeEts of, 282 muscles of, 280 nerves of, 280 synovial membrane of, 279 Radio-ulnar articulations, 249 ligaments, superior, 250 inferior, 264 Radius in connexion with the elbow- joint, 232 in connexion with superior radio- ulnar articulation, 250 in connexion with inferior radio- ulnar joint, 262 in connexion with wrist-joint, 271 460 INDEX. Rectus abdominis, 152 Ribs in connexion with costo-central articulation, 160 in connexion with costo-transverse joint, 166 Round ligament of the hip, 328 (^ACRAL SPINAL arteries, 135 ^ Sacralis media artery, 145 Sacro-coccygeal articulation, 140 ankylosis of, 142 arteries of, 145 coccyx in connexion with, 140 hinge-like movements of, 142 intervertebral substance of, 143 ligaments, J 43 movements of, 146 muscles of, 146 nerves of, 145 sacrum in connexion with, 140 Sacro-lumbar joint, 100 arteries of, 108 ligament, 106 movements of, 109 muscles of, 108 nerves of, 108 Sacro-iliac synchondrosis, 127 arteries of, 135 ear-shaped cartilage of, 132 interosseous ligament of, 131 ligaments of, 1^30 movements of, 137 muscles of, 136 nerves of, 136 Sacro-vertebral joint, 100 angle in male and in female, 109 Sacro-sciatic ligaments, 132 Sacrum, means of preventing displace- • ments of, 138 reasons for describing it as a part of the pelvis. 111 in connexion with sacro-iliac syn- chondrosis, 127 in connexion with sacro-vertebral joint, 101 in connexion with sacro-coccygeal articulation, 140 Scapula in connexion with acromio-cla- vicular joint, 1 96 Scaphoid in connexion with astragalo- scaphoid joint, 422 Scaphoid bone, 274, 284 Scapulo-clavicular union, 195 Scapula, union of, with clavicle, 195 Scapular ligaments, 203 Scapho-cuboid joint, 412 bones of, 412 ligaments of, 413 Scapho-cuneiform joints, 413 bones of, 41 3 ligaments of, 414 Scaphoid iu connexion v^ith the scapho- cuneiform joint, 413 Scaphoid in connexion with scapho-cnbuid joint, 412 Scapula in connexion with the shoulder- joint, 210 Semilunar bone, 274, 284 fibro-cartilages of the knee, 361 Semi-membranosus tendon in connexion with the knee-joint, 356 Sesamoid bones of metacarpo-phalangeal joint of thumb, 312 Sesamoidal bones of metatarso- phalangeal joints of great toe, 446 Shoulder-joint, 210 arteries of, 219 bursse of, 221 ligaments of, 213 movements of, 224 muscles of, 222 nerves of, 220 synovial membrane, 218 Sigaultean operation, 153 Skull, articulations of, 23 bilatei'al arrangement of joints of, 23 balance of, upon occipital condyles, 59 connexion of, with spinal column, 38 differences between articulations of, 24 movements of, 23 suspensory ligament of, 59 use of several joints between the, and spinal column, 81 Small sacro-sciatic ligament, 134 Sphincter ani, 146 Spinal column, anterior and posterior parts of, 65 arteries of, 88 curves of, 71 ligaments connecting it with pelvis 105 movements of, 89 muscles in connexion with, 93 muscles chiefly placed behind the column, 98 nerves of, 89 Spine, capsular ligament of articular processes of, 86 Stellate ligament of costo-central articu- lation, 162 Sterno-clavicular joint, 186 ligaments of, 189 movements of, 192 muscles of, 193 synovial membrane of, 192 Sternum in connexion with the chondro- sternal joints, 170 Sternum in connexion with the sterno-' clavicular joint, 186 Sternum, union of the segments of with one another, 168 Styloid process of temporal bone, 27 Subscapular artery, 220 nerves, 221 INDEX. 461 Superior radio-ulnar articulation, 249 arteries of, 252 ligaments of, 250 movements of, 254 muscles of, 252 nerves of, 252 synovial membrane of, 251 Superior tibio-fibular joint, 378 Supination, 255 Supra- cornual ligament of the sacro- coccygeal joint, 143 Supra-scapular artery, 219 ligament, 209 nerve, 221 Supra-spinous ligament, 87 Suspensory ligament of skull, 59 Supinators of the forearm, 253 Symphysis pubis, 147, 148 arteries of, 151 ligaments of, 148 movements of, 152 muscles of, 152 relation of, to coccyx, 119, 120 Synarthrosis, 17 similarity between, and the union of epiphyses with diaphysis of bones, 18 Synchondrosis, sacro-iliac, 127 Synovial membrane, communication of with bursse, 8 Synovial membrane — of acromio-clavicular joint, 199 of the ankle-joint, 393 of astragalo-scaphoid joint, 424 of articular processes of spine, 87 of atlo-axoidean joints, 54 of atlo-odontoid joint, 55 of the carpo-metacarpal joint, 298 of the carpo-metacarpal thumb, 303 of carpal joints, 286, 288 of posterior calcaneo-astragaloid joint, 406 of the anterior calcaneo-astragaloid joint, 408 of calcaneo-cii.boid joint, 427 of costo-cential jiiint, 163 of the elbow-joint, 236 of hip-joint, 332 of inter- metatarsal joints, 441 of the inter-phalangeal joints, 315, 449 of the knee-joint, 366 of medio-carpal joint, 290 of metatarso-phalangeal joint of outer toes, 444 of metacarpo-phalangeal joints of fingers, 309 of inferior radio-ulnar joint, 264 of superior radio-ulnar joint, 251 of shoulder joint, 218 of sterno-clavicular joint, 192 of the anterior part of the tarsus, 419 Synovial membrane of tempore- maxillary joint, 30 of tarso-metatarsal joints, 432, 434, 435 of the inferior tibio-fibular joint, 385 of superior tibio-fibular joint, 381 of transverso-odontoid joint, 55 of the wrist, 279 uses of, 8 n^AESAL, transverse or middle joint, -■- 421 Tarso-metatarsal joint, arteries of, 436 bones of, 431, 432, 433, 434 ligaments of, 432, 433, 435 movements of, 438 muscles of, 436 nerves of, 436 synovial membrane of,432, 434, 435 inner portion of joint, 431 middle portion, 432 outer portion, 434 Tarsus, anterior part of — arteries, 419 movements, 419 muscles, 419 nerves, 419 synovial membrane, 419 interosseous ligament of third row of, 418 enumeration of joints of, 402 joints, anterior part of, 412 Temporal bone, processus cochleariformis, 27 external auditory meatus, 27 glenoid fossa of, 26 Glasserian fissure of, 26 squamous part of, 25 styloid process of, 27 zygoma, 26 Temporo-niaxillary joint — arteries of, 31 bones of, 25 ligaments of, 27 information afforded by study of, 24 long interna] lateral ligament of, 30 movements of, 34 muscles of, 31 nerves of, 31 difierences between, and occipito- atlantal joints, 24 short internal lateral ligament of, 29 synovial membranes of, 30 Tendon of biceps of the arm, 217 of tibialis posticus, 395, 415 of the peroneus longus, 395 Thorax, 154 apertures of, 155 cavity of the, 154 joints of, 157 shape of, 155 movements of, 182 muscles of, 177 462 INDEX. Thorax, direct muscles of, 179 indirect muscles of, 181 Thumb, carpo-metacarpal joint of, 301 Tibia, in connexion with the ankle-joint, 389 in connexion with the knee-joint, 345 in connexion with inferior tibio- fibular joint, 384 in connexion with the superior tibio-fibular joint, 378 Tibio-fibular interosseous membrane, 382 Tibio-fibular joint, inferior, 384 arteries of, 386 bones of, 384 bursee of, 386 ligaments of, 384 muscles of, 386 movements of, 386 nerves of, 386 synovial membrane of, 385 Tibio-fibular joint, superior arteries of, 381 bones of, 378 bursas of, 381 ligaments of, 380 movements of, 382 muscles of, 381 nerves of, 381 synovial membrane of, 381 Tibialis posticus tendon, 395, 415 Toes, cutaneo-phalangeal ligaments of, 449 Transverse ligament, of atlas, 54 „ dorsal, ligament of carpus, 289 „ ligament of hip-joint, 331 ,, of knee-joint, 363 ,, of metatarsal bones, 442 ,, of inferior peroneo-tibial joint, 385 „ of scapula, 209 Transverso-odontoid synovial membrane, 55 Transverse tarsal joint, 421 Trapezoid bone, 287, 292, 295 ,, ligament, 201 Trapezium, 286, 292, 295, 302 Triangular fibro- cartilage of inferior radio-ulnar joint, 263 of the wrist, 263, 274 Trochoides, 20 Trunk connexion of lower limbs with, differs from that of upper limbs, with, 112 Tubeiosities of humerus, 212 ULNA, in connexion with the elbow- joint, 230 in connexion with the superior radio-ulnar articulation, 249 in connexion with inferior radio- ulnar joint, 261 Unciform bone, 287, 292, 295 "\7ERTEBR^, articular processes of, ^ 78 in connexion with costo-central articulation, 158 in connexion with costo-transverse joint, 165 connexion of, with one another, 65 differences of, in different parts of the column, 79 lamiuas of, 76 purposes served by the several parts of, 66 non-articular processes of, 80 spiuous processes of, 80 transverse processes of, 81 aponeurosis of, 99 Vertebral ligaments, anterior common, 72 posterior common, 73 short, 74 WRIST-JOINT, 270 VIPHOID cartilage, 4, 169 -^^ movements of, upon sternum, 169 r^YGOMA, 26 THE END. 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H.) on Skin Diseases of Children, 10 Fox (Wilson), AtlasofPathologicalAnatomyofLungs, 6 Treatise on Diseases of the Lungs, 6 Frankland and Japp's Inorganic Chemistry, 13 Eraser's Operations on the Brain, 8 Fresenius Qualitative Analysis, 13 Quantitative Analj'sis, 13 Galabin's Diseases of Women. 3 Manual of Midwiferj', 3 Gardner's Brewing, Distilling, and Wine Manuf., 14 Glassington's Dental Materia Medica, 10 Godlee's Atlas of Human Anatomy, 1 Goodhart's Diseases of Children, 4 Gorgas' Dental Medicine, 10 Gowers' Diagnosis of Diseases of the Brain, 7 Manual of Diseases of Nervous System, 7 Clinical Lectures, 7 Epilepsy, 7 Medical Ophthalmoscopy, 7 Syphilis and the Nervous System, 7 Granville on Gout, 7 Gray's Treatise on Physics, 14 Green's Manual of Botany, 5 Vegetable Physiology, 5 Greenish's Materia Medica, 4 Groves' and Thorp's Chemical Technology, 14 Guy's Hospital Reports, 7 Habershon's Diseases of the Abdomen, 7 Haig's Uric Acid, 6 Diet and Food, 2 Harley on Diseases of the Liver, 7 Harris's (V. D.) Diseases of Chest, 6 Harrison's Urinarj^ Organs, 11 Hartridge's Refraction of the Eye, g Ophthalmoscope, g Hawthorne's Galenical Preparations of B. P., 5 Heath's Injuries and Diseases of the Jaws, 8 Minor Surgery and Bandaging, 8 Operative Surgery, 8 Practical Anatomy, i Surgical Diagnosis, 8 Hedley's Therapeutic Electricity, 5 Hellier's Notes on Gynaecological Nursing, 4 Hewlett's Bacteriology, 3 Hill on Cerebral Circulation, 2 Holden's Human Osteology, i Landmarks, i Holthouse on Strabismus, 9 Hooper's Physicians' Vade-Mecum, 5 Horrock's Bacteriological Examination of Water 3 Horton- Smith on Typhoid, 7 Hovell's Diseases of the Ear, 10 Hughes and Keith's Practical Anatomy, i Human Nature and Physiognomy, i^ Hyslop's Mental Physiology, 3 Impey on Leprosy, 10 Ireland on Mental Affections of Children, 3 Jacobson's Male Organs of Generation, 12 Operations of Surgerj', 8 Jellelt's Practice of Midwifery, 3 Gj'nsecology, 3 Jessop's Ophthalmic Surgery and Medicine, 9 Johnson's (Sir G.) Asphj'xia, 6 Medical Lectures and Essays, 6 (A. E.) Analyst's Companion, 13 Journal of Mental Science, 3 Kelynack's Pathologist's Handbook, i Keyes' Genito-Urinary Organs and Syphilis, 12 Kohlrausch's Physical Measurements, 14 Lancereaux's Atlas of Pathological Anatomy, 2 Lane's Rheumatic Diseases, 7 Langdon-Down's Mental Affections of Childhood, 3 Lawrie on Chloroform. 4 Lazarus-Barlow's General Pathologj', i Lee's Microtomist's Vade Mecum, 14 Lewis (Bevan) on the Human Brain, 2 Liebreich (O.) on Borax and Boracic Acid, 2 [Continued on the tiext page. Index to J. & A. Churchill's List — continued Liebreich's (R). Atlas of Ophthalmoscopy, lo Lucas's Practical Pharmacy, 4 MacMunn's Clinical Chemistry of Urine, 11 Macnamara's Diseases and Refraction of the Eye, 9 Macnamara's Diseases of Bones and Joints, 8 McNeill's Epidemics and Isolation Hospitals, 2 Malcolm's Phj'siology of Death, 9 Martin's Ambulance Lectures, 8 Maxwell's Terminologia Medica Polyglotta, 12 Maylard's Surgerj' of Alimentary Canal, 9 Mayne's Medical Vocabulary, 12 Microscopical Journal, 14 Mills and Rowan's Fuel and its Applications, 14 Moore's (N.) Pathological Anatomy of Diseases, i Moore's (Sir W. J.) Family Medicine for India, 5 Manual of the Diseases of India, 5 MorrLs's Human Anatomy, i Anatomy of Joints, i Moullin's (Mansell) Surgery, 8 Nettleship's Diseases of the Eye, 9 Notter's Hygiene, 2 Ogle on Tympanites, 8 Oliver's Abdominal Tumours, 3 Diseases of Women, 3 Ophthalmic (Royal London) Hospital Reports, 9 Ophthalmological Society's Transactions, 9 Ormerod's Diseases of the Nervous System, 7 Parkes' (E.A.) Practical Hygiene, 2 Parkes' (L.C.) Elements of Health, 2 Pavy's Carbohydrates, 6 Pereira"s Selecta e Prescriptis. 3 Phillips' Materia Medica and Therapeutics, 4 Pitt-Lewis's Insane and the Law, 3 Pollock's Histology of the Eye and Eyelids, 9 Proctor's Practical Pharmacy, 4 Pj'e-Smith's Diseases of the Skin, 10 Ramsay's Elementary Sj'stematic Chemistry, 13 Inorganic Chemistry, 13 Richardson's Mechanical Dentistry, 10 Richmond's Antiseptic Principles for Nurses, 4 Roberts' (C. H.) Gynaecological Pathology, 3 Roberts' (D. Lloyd) Practice of Midwifery, 3 Robinson's (Tom) Eczema, 11 Illustrations of Skin Diseases, 11 Syphilis, II Ross's Diseases of the Nervous S3'stem, 7 St. Thomas's HospitaJ Reports, 7 Sansom's Valvular Disease of the Heart, 7 Scott's Atlas of Urinary Deposits, ii Shaw's Diseases of the Ej'e, g.--^' Shaw-Mackenzie on Maternal Sj'phllis, 12 Short Dictionary of Medical Terms, 12 Silk's Manual of Nitrous Oxide, 10 Smith's (Ernest A.) Dental Metallurgy, 10 Smith's (Eustace) Clinical Studies, 4 Disease in Children, 4 WastingDiseasesoflnfants and Children, 4 Smith's (F. J.) Medical Jurisprudence, 2 ismith's (J. Greig) Abdominal Surgery, 8 Smith's (Priestley) Glaucoma, 10 Snow's Cancer and the Cancer Process, 11 Palliative Treatment of Cancer, 11 Reappearance of Cancer, 11 Solly's Medical Climatology, 8 Southall's Materia Medica, 5 Squire's (P.) Companion to the Pharmacopoeia, 4 London Hospitals Pharmacopoeias, 4 Methods and Formulae, 14 Starling's Elements of Human Physiology, 2 Sternberg's Bacteriologj', 5 Stevenson and Murphy's Hygiene, 2 Sutton's (J. B.J, General Pathology, i Sutton's(F.) Volumetric Analysis, 13 Swain's Surgical Emergencies, 8 Swayne's Obstetric Aphorisms, 3 Taylor's (A. S.) Medica! Jurisprudence, 2 Taylor's (F.) Practice of Medicine, 6 Thin's Cancerous Affections of the Skin, 10 Pathology and Treatment of Ringworm, 10 • on Psilosis or " Sprue," 5 Thompson's (Sir H.) Calculous Disease, 11 Diseases of theUrinaryOrgans, 13 Lithotomy and Lithotrity, 11 Stricture of the Urethra, 11 Suprapubic Operation, 11 Tumours of the Bladder, 11 Thome's Diseases of the Heart, 7 Thresh's Water Anal3'sis, 2 Tilden's Manual of Chemistry, 12 Tirard's Medical Treatment, 6 Tobm's Surgery, 8 Tomes' (C. S.) Dental Anatomy, 10 Tomes' (J. and C. S.) Dental Surgery, 10 Tooth's Spinal Cord, 7 Treves and Lang's German-English Dictionary, 12 Tuke's Dictionary of Psychological Medicine, 3 Tuson's Veterinary Pharmacopoeia, 14 Valentin and Hodgkinson's Practical Chemistry, 13 Vintras on the Mineral Waters, &c., of France, 8 Wagner's Chemical Technology, 14 Wallace on Dental Caries, 10 Walsham's Surgery : its Theory and Practice, Waring's Indian Bazaar Medicines, 5 Practical Therapeutics, 5 Watts' Organic Chemistry, 12 West's (S.) How to Examine the Chest, 6 White's (Hale) Materia Medica, Pharmacy, &c., 4 Wilks' Diseases of the Nervous System, 7 Wilson's (Sir E.) Anatomists' Vade-Mecura, i Wilson's (G.) Handbook of Hygiene, 2 Wolfe's Diseases and Injuries of the Eye, g Wynter and Wethered's Practical Pathology, i Year-Book of Pharmacy, 5 Yeo's (G. F.) Manual of Physiology, 2 N.B.^J. 4' A. Chur chill's larger Catalogue of about 600 works on Anatomy, Physiology^ Hygiene^ Midwifery, Materia Medica^ Medicine^ Surgery, Chemistry, Botany, ^~c. ^-c, with a complete Index to their Subjects, for easy reference, will be forwarded post free on application. America. — -/. 4' ^- Churchill being in constant communication with various publishing houses in America are able to conduct negotiations favourable to English Authors. P LONDON: 7, GREAT MARLBOROUGH STREET. Date Due -APR 2 4 AUG Ann 455 8 19. 1 S 19* m AP P 'Q a 1QS.E" i&^^ftil. -ot ft (^; fitsr /^J ^ v^J T0^\ V