i MANUAL OF ANATOMY SYSTEMATIC AND PRACTICAL, INCLUDING EMBRYOLOGY MANUAL OF ANATOMY SYSTEMATIC AND PRACTICAL. INCLUDING EMBRYOLOGY BY A. M. BUCHANAN, M.A., M.D., CM., F.R.F.P.S. Glas. PKOFhlSSOR OF ANATOMY IX THE ANDERSON COLLEGE OF MEDICINE, GLASGOW ; EXAMINER IX ANATOMY FOR THE TRIPLE QUALIFICATION OF THE SCOTTISH LICENSING BODIES ; EXAMINER IN ANATOMY FOR THE DENTAL DIPLOMA, AND EXA5IINER IN ANATOMY (HUMAN AND COMPARATn-E) FOR THE FELLOWSHIP, OF THE ROYAL FACULTY OF PHYSICIAN'S AND SURGEON'S OF GLASGOW ; EX-KXAMINER IX ANATOMY TO THE UNIVERSITY OF GLASGOW; FORMERLY SENIOR DEMONSTRATOR OF ANATOMY IN XH£ UNIVERSITY OF GLASGOW WITH 6j5 ILLUSTRATIONS, MOSTLY ORIGINAL AND IN COLOURS th:rd edition TORONTO THE MACMILLAN COMPANY OF CANADA, LTD. 1916 Printed in England QM t-fu\ DEDICATED BY PERMISSION . . . TO THE RIGHT HONOURABLE LORD LISTER, O.M., LL.D., D.C.L.. F.R.S., Etc.. IN GRATEFUL ACKNOWLEDGMENT OF THE POWERFUL INFLUENCE WHICH HE EXERCISED OVER THE INTELLECTUAL CULTURE OF HIS GLASGOW STUDENTS, OF WHOM THE AUTHOR WAS ONE. PREFACE TO THIRD EDITION E\-ERY section of this manual has been carefully and completely revised. Some have been partially, and many, such cis the Ner\'ous System and its Development, have been entirely rewritten. It has still been considered advisable to retain the old anatomical nomen- clature until such time as a standard nomenclature has been fixed and generally accepted. The Appendix, however, containing a large number of the terms of the Basle nomenclature, has been re- tained for those who A^ash to refer to them. The subject of Embry- ology is still partially dealt with by appending to the description of each organ a concise accoimt of its development. Over and above this an entirely new and complete chapter, dealing with General Embryology, has been added, with the \4ew of elucidating many points in the various concise developments. This chapter has been specially and skilfully illustrated. The author has to acknowledge with deep gratitude the valuable assistance which he has so willingly received from his demonstrator. Dr. Peter Thomson, M.A., B.Sc, in preparing this edition for the press. He has also to thank the pubhshers for the great labour which they have kindly imdertaken in various directions, and for the great care which they have bestowed upon the pubUcation of this edition. Many new figures have been added, all of which have been executed bv the well-known anatomical artist, Mr. James T. Murray, Edin- burgh, who has done his work with rare excellence, and whom the author desires to thank most cordially. He also begs to thank all those authors who have kindly and generously granted permission to use their figures. The Anderson College of Medicine. Glasgow, January, 1916. / PREFACE TO SECOND IMPRESSION The First Edition of this Manual has been so favourably received, and was published such a short time ago, that it has seemed un- necessary to make any very important alterations, or to effect a thorough and complete revisal in the meantime, in view of the early call for a Second Edition, In reprinting this Second Impression it has been considered advisable not to allow the Manual to remain out of print (as a revised edition throughout would necessitate), it being the only text-book of its kind which adheres to the old anatomical nomenclature. The feeling among many teachers of anatomy seems to be setting against the adoption of the Basle nomenclature in its entirety. Moreover, among students there is a great deal of dissatisfaction at its use on account of its being so cumbrous, and occasionally not quite accurate. It has therefore been considered advisable to retain the old nomenclature, which is so simple and so correct for all practical purposes, until such time as a standard nomenclature has been fixed and generally accepted. The Appendix containing a large number of the terms of the Basle nomenclature has, however, been retained for the use of those who may desire to refer to it. The errata and omissions, noted in the First Edition, have been put right, and certain critical remarks have received willing attention. The subject of the ossification of bones, now so much modified, has been made more in conformity with the views of recent investigators, and in certain cases will be doubtless more acceptable to students than previous accounts. The Anderson College of Medicine, Glasgow, May, 1914. CONTENTS OSTEOLOGY ARTHROLOGY UPPER LIMB GUIDE TO - - LOWER LIMB GUIDE TO - ABDOMEN GUIDE TO - THORAX - - - GUIDE TO - HEAD AND NECK GUIDE TO - NOSE - - - GUIDE TO - NERVOUS SYSTEM SPINAL CORD, GUIDE TO BRAIN, GUIDE TO EYE - - - GUIDE TO - EAR - - - GUIDE TO - GENTERAL EMBRYOLOGY - BASLE NOMENCLATURE - GLOSSARY INDEX 1679 A MANUAL OF ANATOMY OSTEOLOGY The skeleton is the hard ' dry ' osseous and cartilaginous frame- work of the body. It consists in the adult of 200 bones, exclusive of the small bones of the ear and sesamoid bones, most of which are held together by Ugaments. The functions of the bones are as follows : (i) they impart shape to the body ; (2) they support the soft parts ; (3) they protect important organs ; and (4) thfy afford attachment to the muscles. In the performance of t^r^ latter function the bones are to be regarded as passive organs 01 locomotion, the activ^e organs being the muscles — that is to say, the bones act as levers to the muscles. There are two varieties of skeleton, namely, endoskeleton and exoskeleton. * In the former, as in man, the bones are covered by soft parts. In the latter, as in Crustacea, the bones are so disposed as to he upon the surface, where they form a case which contains the soft parts of the animal. The human skeleton is arranged in two divisions, axial and appen- dicular. The axial skeleton comprises the head and trunk, and the appendicular represents the limbs. The head is composed of 23 bones, including the hyoid bone. The trunk is made up of the vertebral column, containing 26 separate bones in adult life ; the sternum ; and the ribs, with their costal cartilages, 24 in number, thus making 51 bones in all in the trunk. The appendicular skeleton comprises the two upper or pectoral hmbs, each containing 32 bones, exclusiv'e of sesamoid bones, and the two lower or pelvic limbs, each containing 31 bones, also exclusive of sesamoid bones. Descriptive Terms. Ankylosis : bony union between two bones which are normally separate. Apophysis {' grow from ') : this is any process or swelling on a bone. Capitellutn : a small head. Caudal : towards the tail. 1 2 A MANUAL OF ANATOMY Cephalic : towards the head. Clinoid : hke the knob of a bedpost. Condyle (' knuckle ') : a small round eminence covered by cartilage — in reality a capitellum. Cotyloid : cup-like. Diaphysis {' grow between ') : this term is applicable to long bones. It is the shaft of the bone, or the part which grows between the epiphyses. Dorsal : pertaining to the back aspect. In man ventral and dorsal are synonymous with anterior and posterior in the erect posture. Epiphysis (' grow upon ') : this is a process of bone which has a secondary centre of ossification, and which is attached for a time to the principal part of the bone by cartilage, but subse- quently becomes consolidated. Facet (Fr. facette, ' a little face ') : a small plane articular surface. Fissure : a cleft or slit. Foramen : an opening in the sense of a hole. Fossa : a shallow depression. Glenoid : like a shallow socket. Groove : a furrow or gutter. V Head : a rounded eminence, covered by cartilage, at the extremity rl a bone. Hiatus : an opening in the sense of a gap. Malleolus : a small hammer. Meatus (pi. meatus): a passage or canal. Medullary : pertaining to the medulla or marrow. Neck : a constricted portion supporting a head. Neural : pertaining to the nervous system. Sinus or antrum : a cavity in the interior of a bone. spine : this is a sharp-pointed process, and in certain bones is erroneously applied. Styloid : pen-like. Trochanter ('running round' or 'rolled'): a prominence which has a rolled or wheel-like arrangement, and which runs round a portion of a bone. Trochlea : a pulley. Tubercle ('swelling '): a small rounded prominence on a bone. Tuberosity : an exaggerated tubercle. Ventral : pertaining to the belly aspect of the body. Mesial plane : this is the imaginary longitudinal plane which divides the body into two very nearly symmetrical halves, right and left. It extends from the mesial line on the ventral aspect to the mesial line on the dorsal aspect. Sagittal : this means pertaining to the antero-posterior mesial plane with which it is parallel, and it practically means dorso- ventral or antero-posterior. Coronal : this means intersecting the antero-posterior mesial plane at right angles in a vertical direction, and it is practically synonymous with transverse. OSTEOLOGY 3 Internal or mesial : near to the mesial plane ; and external or lateral : farther away from the mesial plane. Preaxial and postaxial : these terms were originally used in connection with the embryo. Preaxial, proximal, or cephalic means towards the head (superior), and postaxial, distal, or caudal means towards the tail (inferior). Morphology. — This is the science which investigates the form and structure of parts and organs in reference to the series of changes through which they pass during their development. In a morphological sense parts of man's body may be compared with one another, or parts of the body of one animal may be compared with apparently similar parts in the body of another animal, and in this way their actual identity may be established. Homology. — Parts or organs which are represented in different animals are said to be homologous (homogenetic) when they are constructed on the same t^-pe and have the same embryonic origin, although they may differ in function. For example, the upper . limb of man and the fore-limb of a quadruped are homologous (homo- genetic). Parts in the body of man are said to hejerially homologous (homodynamic) when they are repeated. For example, the humerus is serially homologous with the femur. Analogy. — This is identity in function, but not necessarily in structure. The gills of a fish are analogous with the lungs of man, though differing in structure. Segmental Type. — This consists in the repetition longitudinally of a series of segments similar to each other — e.g., vertebrae, and ribs. Chemical Composition of Bone. — Osseous tissue belongs to the connective tissues, and it consists of an organic matrix or ground substance, impregnated with mineral matter. The mineral matter is composed chiefly of calcium salts, and so it petrifies the ground substance. The organic matrix is usually spoken of as the animal matter, and it forms about 33 per cent, of the entire bone. The mineral matter is spoken of as the earthy matter, and it forms about 67 per cent, of the bone. The animal matter imparts flexibility and elasticity to the bone, and is composed of very delicate fibres, which are collected into bundles, held together by cement substance. The fibres consist of collagen, which is converted into gelatin by boiling. The animal matter can be separated from the earthy matter by steeping a bone for some time in dilute hydrochloric acid, the effect of the acid being to dissolve out the earthy matter. When bone is so treated it is said to be decalcified. There is left a tough, flexible, elastic substance, which can be bent and twisted in various direc- tions, and even tied into a knot, but no amount of force applied to it, or pressure laid upon it, would cause it to break. A bone when so treated retains its original shape, but it loses weight to the extent of about two-thirds, and it also loses its property of hardness, so that it is incapable of beaiing weight. 4 A MANUAL OF ANATOMY The earthy matter imparts hardness and rigidity to the bone, and is composed principally of calcium salts, of which the most abundant is calcium phosphate, there being about 57 per cent, of this salt present. Besides this there are calcium carbonate in the proportion of about 7 per cent., and calcium fluoride in the proportion of about i per cent. In addition to the calcium salts there are about i per cent, of magnesium phosphate, and about ^ per cent, of sodium chloride. The earthy matter may be separated from the animal matter by burning a bone. The first effect of the heat is to char the animal matter, which is Fig. I. — Longitudinal Section through the Upper End of the Femur, SHOWING Compact and Cancellated Osseous Tissues. subsequently coisumed. When so treated a bone is said to be calcined, and the process is spoken of as combustion or calcination. There is left a white, chalk-like, very brittle substance, which, if of small size and carefully handled, retains its original shape. The slightest rough handling, however, will cause it to break, or crumble into a coarse powder. Calcined bone undergoes no change in shape, but it loses weight to the extent of about one-third. It also loses its flexibility and elasticity. The only property it now possesses is hardness. As stated, it is also very brittle, and, by reason of this, it cannot be bent nor twisted in OSTEOLOGY 5 the slightest degree. The ailimal and earthy matter, as they form bone, are intimately combined. The proportion of about one-third of animal matter to about two-thirds of earthy matter apphes to the healthy adult. In young children the relative amount of animal matter is much greater, so that in them the bones are ver\' tough and elastic, but not very hard, and therefore not capable of bearing much weight. In old age there is a relatively large amount of earthy matter present. The bones of old persons, therefore, are very hard and brittle, but not ver^ tough and elastic ; hence the f requeue}^ of fractures in old persons from slight causes. Structure of Bone.— There are two varieties of osseous tissue, namely, compact, and spongy or cancellated. Compact osseous tissue is so named because its constituents are so closely packed together that the bone appears to the naked eye {macroscopic) r:G. -Structure of Compact B. A, Longitudinal section, sho\v-ing Haversian canals ; B, Transverse section, showng Haversian systems. to be dense and close like ivory. Spongy or cancellated osseous tissue, on the other hand, presents an open porous appearance like a sponge. It is called cancellated because it resembles lattice- work. These two varieties of osseous tissue merge very gradually into one another. When compact bone is viewed under the microscope in thin transverse section it presents a number of small round or oval openings, and when viewed in thin vertical section it presents short longitudinal tuhes, called Haversian canals. These pervade every part of compact bone, and the innermost open into the marrow canal of long bones, whilst the outermost open by minute orifices on the external surface. They range in diameter irom ywoxj to 2^ inch, the average being 5^ inch. The smallest lie nearest the external surface, and the largest are nearest the marrow canal. They are very short and longitudinal in direction, and they com- A MANUAL OF ANATOMY municate freely with one another by connecting canals, some of which are oblique and others transverse. These connecting canals are very small, having a diameter of only irjiso inch. The Haversian canals "thus form a freely intercomrnunicating system of tubes throughout compact bone. The largest canals contain each an arteriole, a radicle vein, one or two lymphatics, and a small amount of marrow tissue. The smallest canals contain only one bloodvessel, which is of the nature of a capillary. Those nearest the external surface also contain very delicate thread-like processes of the periosteum. Nerve fibrils have been demonstrated in bone by Kolhker, Remy, and Variot. The bone around the Haversian canals is arranged in the form of concentric plates, called Haversian or concentric hone lamella. In transverse section these appear as concentric rings, and in longi- Lacuna, with Bone Cell and Canaliculi Marrow Tissue Large Haversian Canal ; Venous Radicle • Lymphatic Vessel Arteriole Nerve Fibrils Fig. 3. — Diagram of a Haversian System, minus the Concentric Bone Lamell.^. tudinal section as parallel lines. In the interspaces between the systems of Haversian or concentric lamellae there are intermediate, interstitial, or ground lamellce, and near the external surface there are circumferential or peripheral lamellce, which are parallel with the surface. Some of the canals which pierce the circumferential lamellae are devoid of concentric lamellae, and are known as Volikmann's canals. In the interspaces between the Haversian or concentric lamellae there are small fusiform cavities, known as the hone lacuncB. These are about vr^Vir inch in length, and, like the lamellae, they are arranged concentrically round the Haversian canals. Radiating from these lacunae there are minute channels, called bone canaliculi, which pass through perforations in the lamellae, and so serve to connect the various lacunae with one another. Some of those radiating from the innermost ring of lacunae communicate OSTEOLOGY 7 directly with the Haversian canal. The canaliculi thus constitute a system of intercommunicating channels ■ which maintain a con- nection directly and indirectly between a given Haversian canal and the lacunae arranged concentrically around it, and traverse the lamellse in their course. Each lacuna contains a protoplasmic nucleated cell, called the hofie cell, which almost completely fills it, and sends off processes into the canaliculi communicating with it. The canaliculi contain nutritive fluid derived from the arteriole. A given Haversian canal, with its concentric bone lamella, concentric bone lacunae, and canalicuh, constitutes a Haversian system, and compact bone is simply an aggregation of such systems, with, in addition, the intermediate and circumfer- ential lamellae. Certain lamellae are perforated perpendicularly by fibres which thus bind them together. These fibres are known as the perforating fibres of Sharpey. Some of them are composed of white fibrous tissue, and others of elastic tissue, and those nearest the periphery are connected with the periosteum from which they are derived. Others, however, more deeply placed, have no apparent direct connection with the periosteum. The perforating fibres are absent from the lamellae of the Haversian systems. Cancellated bone is composed of very slender trabeculae, which are arranged in a reticular manner so as to enclose spaces, known as the medullary spaces. These spaces, in the recent state, are filled with marrow. The trabeculae consist of superimposed lamellae of compact bone. The strongest lamellae are disposed in the direction in which the greatest pressure has to be borne, and these are known as -pressure lamella. Other lamellae which intersect these, are spoken of as tension lamellce. The use of cancellated bone is to impart sufficient strength without adding unduly to weight. Classification of Bones. — Bones are arranged in four classes, as follows: Long; short; tabular; and irregular. A long bone consists of a shaft and two articular extremities. The shaft is more or less cylindrical, and contains a marrow canal, which is surrounded principally by compact bone. The articular extremities are composed of cancellated tissue, except at the sur- face where there is a thin shell of compact bone. Long bones are found in the appendicular skeleton. A short bone consists mainly of cancellated tissue, except at the surface where there is a thin covering of compact bone. Short bones are more or less oblong in shape, and are found in the carpus and tarsus. A tabular bone is composed of two plates or tables of compact bone, which enclose between them cancellated tissue. The scapula, ilium, and tegmental bones of the skull belong to this class. In the case of the latter the cancellated tissue is called diplo'e. An irregular bone is one which is so irregular in form and in the relative distribution of the compact and cancellated tissues as to be 8 A MANUAL OF ANATOMY excluded from any of the preceding classes. The vertebrae belong to this class. Ossiflcation. — All bones are originally membranous. vSome of them— for example, the tegmental bones of the cranium and most of the bones of the face — ossify in membrane, but the majority pass through a cartilaginous stage before becoming ossified. There are, therefore, two modes of ossification, namely intramembranous and intracartilaginous, and bones are consequently spoken of as membrane- and cartilage-hones. Centres of Ossification. — These are primary and secondary. The primary centre, which as a rule appears early in intra-uterine life, Fig. 4. — Ossification in Membrane. IS that from which the ossification of the principal part of the bone proceeds. This, in the case of a long bone, is the shaft or diaphysis. 'ihe secondary centres, which for the most part do not appear until after birth, are those from which the ossification of outgrowths of a bone proceeds, these forming what are known as the epiphyses. Ossiflcation in Membrane. — In this mode of ossification the bone is preceded by fibrous tissue. The fibres of this tissue are known as osteogenetic fibres, and they are arranged in small bundles. The tissue is very vascular, and contains many nucleated cells, called osteoblasts. At the centre of ossification the osteogenetic fibres, which have a covering of osteoblasts, become calcified, and bony spicnla are thus formed, which radiate towards the circuniference of the bone. These radiating spicula are connected at frequent intervals, and OSTEOLOGY so build up a bony reticulum. As the osteogenetic fibres grow and shoot out, they carry with them coatings of osteoblasts, and the process of cal- careous incrustation goes on, so that the bony spicula increase in length, and gradually approach the periphery. During this process of spicular bony formation many of the osteoblasts are left behind, and become imprisoned in the lacunar spaces of the forming bone, where they represent the future bone cells. The ossification of a membrane bone is thus effected by means of osteogenetic fibres plus osteoblasts, the fibres acting as outrunners and becoming calcified. Ossifieation in Cartilage. — The cartilage is covered by a membrane, called the perichondrium, which corresponds to the periosteum, and the process of ossification takes place in three stages. First Stage. — In this stage the ossification is 'partly endochondral, and partly ectocliotuiral or on the surface beneath the perichondrium. In the endo- chondral lormthe cartilage cells at the centre become enlarged, and the intervening matrix becomes cal- cified. Above and below the centre the cartilage cells are arranged in long columns, directed towards each extremity. The matrix between these columns becomes calcified by an extension of the calcareous matter at the centre, which now surrounds the cell- columns. The spaces in the calcified matrix, which contain these columns, are known as the primary areolcB. At the same time, ectochondral cr sabperi- ehondral ossification is proceeding in a manner similar to what takes place in membranous ossifica- tion, that is to say, by osteogenetic fibres, osteo- blasts, and calcareous impregnation. In this way several layers cf bone are laid down at the surface beneath the perichondrium, and these constitute the circumferential lamellae. During this process some of the osteoblasts are detained in lacunar spaces, and form the bone cells. Second Stage. — This is known as the stage of irrup- tion. The inner or osteogenetic layer of the peri- chondrium bursts in through openings in the cir- cumferential lamellae, in the form of osteogenetic fibres, osteoblasts, and osteoclasts or bone destroyers. These incursions reach the calcified matrix, and the osteoclasts now commence their destructive work. The cartilage cells of the primary areolae, as well as the walls of these areolae, are absorbed, and larger spaces, called secondary areolx or medullary spaces, are formed in the original calcified matri,x. These spaces contain osteogenetic fibres and osteoblasts, and the latter now build up lamellae of bone. Third Stage. — ^This is a repetition of the preceding two stages. The cartilage cells arrange them- selves in rows ; the intervening matrix becomes calcified, and invests them; the enclosed cartilage cells atrophy and give rise to primary areolae; the osteoclasts produce partial absorption of the calcified cartilage, giving rise to medullary spaces; and the osteogenetic fibres and osteoblasts build up lamellae of bone. Simultaneously with these processes, subperiosteal ossification is going on. The medullary canal is due to absorption by the osteoclasts of the osseous tissue in the centre of the shaft. The ossification of the epiphyses of a bone is endochondral. Periosteum. — ^The periosteum is a fibrous, vascular membrane, v.hich closely invests bones, except where there is articular cartilage. Fig. 5. — Ossification IN Cartilage. lo A MANUAL OF ANATOMY at the margin of which it Ceases. It consists of two layers — outer and inner. The fibres of the outer layer are arranged closely, and it is therefore dense. The inner layer consists chiefly of ramifying elastic fibres. Between the inner layer and the surface of the shaft of a long bone there is, especially during the development and growth of the bone, a layer of subperiosteal areolar tissue. Within its meshes cells, called osteoblasts, accumulate during the period of growth. These cells emerge from the outermost Haversian canals along the course of the entering arteries, and they represent the hotie cells of the bone-lacunae of compact bone which have migrated outwards. The osteoblasts take an important part in the formation of bone during its growth. The periosteum is richly supplied with arteries which, after ramify- ing, enter the outermost Haversian canals, along with fine processes of the inner periosteal layer. The periosteum serves (i) as a bed in which the arteries subdivide before entering the bone, and (2) to give a firm hold to tendons and ligaments. It also takes part in ossification and regeneration of bone. When the periosteum is stripped from a bone the uncovered portion is liable to necrosis and exfoliation. Marrow or Medulla. — The marrow fills the marrow canals of long bones and the medullary spaces of cancellated bone, and it also sends processes into the innermost Haversian canals. It is composed of a reticular fibrous matrix, which is pervaded by many blood- vessels and cells, the latter being called myelocytes (marrow cells). There are two kinds of marrow, yellow and red, which differ as to the character of the cells. In yellow marrow most of the cells have become transformed into fat ceUs, so that the marrow resembles adipose tissue. Red marrow contains very few fat cells. Many of its cells are colourless, protoplasmic, nucleated cells, which resemble the leucocytes of the blood, though of larger size, and like them are capable of amoeboid movement. Other reddish cells, called ery- throblasts, are present, which are the sources from which large numbers of red blood corpuscles are formed. In addition to these two sets of cells, there are large multinucleated, protoplasmic cells, called the myeloplaxes of Robin, which play an important part in the absorption of bone. Yellow marrow is found in the marrow canals of long bones, whilst red marrow occurs in (i) articular ends of long bones ; (2) medullary spaces of cancellated bone ; (3) bodies of the vertebrae; (4) sternum; (5) ribs; and (6) the diploe of the cranial bones. Marrow serves the following uses: (i) it (red marrow) is an important blood-forming organ (red corpuscles); (2) it contributes to the nourishment of bone; and (3) it serves as a light packing material for all hollow spaces within bones, with the exception of the air-sinuses in the bones of the head. The wall of the marrow canal of all long bones and that of the medullary spaces of all cancellated bone are lined with a very delicate layer of areolar tissue, which is richly provided THE BONES OF THE TRUNK ii with bloodvessels. This is knov^Ti as the endosteum or medullary membrane. Osseous tissue is richly suppUed with bloodvessels, which are derived from the periosteum and marrow. I. THE BONES OF THE TRUNK. A. The Vertebral Column. The vertebral column is composed of thirty-three vertebrae in the young subject, and these in the adult are divided into two classes, namely, true or movable, and false, immovable, or fixed. The true vertebrae are those which, though connected by hgaments, are quite distinct from each other, so that a hmited amount of movement is allowed between them. The false vertebrae are those Pedicle Superior Articular Process Fig. 6. — The Sixth Thoracic Vertebra (Superior View). which, though distinct up to a certain period of hfe, subsequently become ankylosed. The true vertebrae are subdivided into three groups — cervical, thoracic, and lumbar. The false vertebrae are subdivided into two groups — sacral, and coccygeal. Component Parts of a Complete Vertebra, — A complete vertebra is composed of a body or centrum ; a neural arch, consisting of two pedicles and two laminae {neur apophyses) ; a spinous pro- cess, or neural spine ; two transverse processes ; four articular processes {zygapophyses), two superior and two inferior ; and a spinal or neural foramen. The body forms the anterior or ventral part of the bone, and is somewhat disc-shaped. The neural arch consists of two halves, the anterior portion of each being the pedicle^ and the posterior portion the lamina. The pedicles 12 • A MANUAL OF ANATOMY present, above and below, the superior and inferior vertebral notches. The spinous process is formed by the fusion of the two laminae in the median line posteriorly. The transverse processes project out- wards, one at either side, from the neural arch at the junction of the pedicle and lamina. The articular processes, two superior and two inferior, project upwards and downwards from the junction of the pedicle and lamina at either side, and they are covered by cartilage. The spinal or neural foramen is enclosed by the body and neural arch. It is bounded in front by the posterior surface of the body, on either side by a pedicle and lamina, and behind by the fusion of the laminae to form the spinous process. Structure of a Vertebra. — The body is composed of cancellated tissue, covered by a thin layer of compact bone. The chief lamellae are disposed in almost vertical curves, the convexities of which are directed towards the periphery. Crossing these there are horizontal lamellae, which are nearly parallel with the superior and inferior surfaces. The cancellated tissue is permeated by venous channels which converge to the two large foramina on the posterior surface of the body. The neural arch and its processes are chiefly com- posed of compact bone, the amount of cancellated tissue being for the most part small. The Cervical Vertebrae. The cervical vertebrae are seven in number, and they occupy the region of the cervix or neck. The distinctive character of all cervical vertebrae is the presence of an aperture at either side of the body, called the costo-transverse foramen. The first or atlas, the second or axis, and the seventh or vertebra prominens have such pronounced characters that they require a special description. A Typical Cervical Vertebra.— The body is small and elongated from side to side. The superior surface presents at either side an antero-posterior. lip, the inner surface of which is sloped towards the superior surface, and embraces the corresponding bevelled lateral border of the inferior surface of the body above. The whole surface is thus concave from side to side, and the posterior lip is on a slightly higher level than the anterior. The inferior surface is bevelled laterally, and its anterior lip is on a lower level than the posterior. The inferior surface is convex from side to side, and concave from before backwards. The superior and inferior surfaces give attachment to the intervertebral discs. The anterior surface is convex from side to side, and concave from above down- wards. It is covered by the anterior common ligament, and it presents a number of nutrient foramina. The posterior surface is , flat, and presents several nutrient foramina, two of which, one at [ either side of the middle line, are large, for the escape of the venae ' basis vertebrae. The posterior surface is related to the posterior common ligament. Each lateral surface forms the inner boundary of. the costo-transverse foramen. The pedicles spring at either side from the posterior part of the THE BONES OF THE TRUNK 13 lateral surface of the body, where each encroaches rather nearer the upper than the lower surface. They are smooth and almost cylindrical, and their direction is outwards and backwards. Above and below' each pedicle there is a well-marked vertebral notch, the superior being narrower and slightly shallower than the inferior. The superior notch lodges a spinal nerve. When two vertebrae are in position the contiguous vertebral notches, at either side, form an intervertebral foramen. The laminsB spring each from a pedicle. They are compressed Costo-transverse Foramen Anterior Tubercle Costo-transverse Lamella ^ Body Back of Inferior ' Articular Process Costal Process Transverse Process _ Pedicle Superior Articular Lamina Process Inferior Notch B Inferior Articular Process Fig. 7. — The Fifth Cervical Vertebra. A, Superior view ; B, Lateral view. from before backwards, and their direction is backwards and inwards to the middle line, where they fuse, and so give rise ta the spinous process. The upper border and adjacent portion of the posterior surface of each lamina give attachment to the liga- mentum subflavum connecting it to the lamina above, whilst the lower part of the anterior surface near the lower border gives attachment to the ligamentum subflavum connecting it to the lamina below. The spinous process is formed by the fusion of the two laminae. 14 A MANUAL OF ANATOMY It is triangular, and its direction is backwards and slightly down- wards. Superiorly it presents an antero-posterior ridge for an interspinous ligament, and inferiorly a grooved surface, also for an interspinous ligament. It terminates behind in a bifid extremity, which, in the case of the third, fourth, and fifth vertebrae, pre- sents a distinct triangular notch. The bifurcated extremity gives attachment to the deep fibres of the ligamentum nuchae. The cervical spinous processes are very short, except those of the sixth and seventh, especially the latter, and in this way backward flexion or over- extension of the neck is not interfered with. The articular processes spring from the junction of the pedicle and lamina at either side. Each is nearly circular, the plane being oblique, and the surface almost flat. The superior pair look backwards and upwards, and the inferior pair forwards and downwards. The transverse processes {diapophyses) spring at either side from the junction between the pedicle and lamina, and are serially homologous with the transverse processes of a thoracic vertebra. Each terminates in a projection, known as the posterior tubercle. The costal processes {pleurapophyses) project outwards from either side of the body anteriorly, and are serially homologous with the vertebral part of a rib. Each terminates in a projection, known as the anterior tubercle, which, with the posterior tubercle of the corresponding transverse process, gives attachment to the inter- transversales muscles. The transverse and costal processes are connected, at a short distance from the body, by a plate of bone, called the costo-trans- verse lamella, which is deeply grooved superiorly for a spinal nerve, this groove being continuous with the superior vertebral notch. There is thus formed, at either side, an aperture, called the costo- transverse foramen. This foramen is circular, vertical in direc- tion (except in the case of the axis), and it transmits the following structures : the vertebral artery ; the vertebral plexus of veins ; and the vertebral sympathetic plexus of nerves. Though the foramen is present in each transverse process, it does not give passage to the foregoing structures in the case of the seventh. The vertebral vein, however, may pass through it. In many cases an additional foramen of small size is present on one or both sides, lying behind the main foramen, and when this is so, it transmits a small vein. The costo- transverse foramina of either side, when in position, build up a canal, which is open in each intertransverse space. The neural foramen is situate;! behind the body, and is triangular, with the angles rounded off. It is of larger size than in the thoracic or lumbar vertebrae, its direction is vertical, and it lodges the sj^inal cord with its membranes. The Atlas. — ^The atlas is the first cervical vertebra, and is so named because it supports the head. Its distinctive characters are the absence of a body and spinous process. It has the form of a ring, narrow in front and wide behind, and its component parts THE BONES OF THE TRUNK 1 5 are as follows : an antador arch : a posterior arch ; two lateral masses ; and a ring. The anterior arch is a curved plate of bone which connects the antero-intemal parts of the lateral masses. It is compressed from before backwards, convex in front, and concave behind. The anUricr surface presents at its centre a conical prominence, called the anterior tubercle. This gives attachment at either side to a portion of the longus colh muscle, and its central port receives the accessory ligament. The posterior sitrface presents at its centre a circular concave facet, called the odontoid facet, for articu- lation with the anterior surface of the odontoid process of the axis. The upper border gives attachment to the anterioar occipito- Tiaisvcrse Process Vertebrarteral ' Gfoove PostericH- Tafaode Fig. 8- — ^The Atlas (Scpekiob View). (The Verteixartetial Groove cm this bone was ccmveited into a Foramen on botli ades.) atlantal l^ami^it, and the lower to the anterior atlanto-axial liga- ment. The posterior areh is smaUy homoIogoQs with the laminae of other vertebrae. It springs at either side from the back part of a lateral mass, from which it sweeps backwards and inwards. The part close to the lateral mass at either side is flattened from above downwards. It presents on its upper surface a shallow depression, called the vertebrarterial groove, which lodges the vertebral artery and suboccipital nerve. This groove is sometimes converted into a foramen on one or both sides by a spiculum of bone extending from the back part of the superior articular process to the posterior arch behind the groove. The vertebrarterial groove is serially homologous with the superior vertebral notch of other vertebrae, but, unlike them, it hes behind the superior articular process. The inferior surface of the posterior arch, behind each lateral mass. 16 A MANUAL OF ANATOMY presents a shallow vertebral notch, which lies behind the inferior articular process. The centre of the posterior arch presents the posterior tubercle, which is the only representative of a spinous process. At either side of this tubercle the rectus capitis posticus minor arises. The upper aspect of the posterior arch gives attach- ment to the posterior occipito-atlantal hgament, and the lower aspect to the posterior atlanto axial ligamen*^. The lateral masses support the superior and inferior articular pro- cesses, and laterally the transverse and costal processes spring from them. The anterior surface of each gives partial origin to the rectus capitis anticus minor. The in ternal surface of each presents anteriorly a tubercle for the transverse ligament. The superior articular pro- cesses are oval and deeply concave, to articulate with the con- dyles of the occipital bone. Their long axes are directed backwards Anterior Arch Inferior Articular Process \ \ Inferior Vertebral Notch Posterior Arch Fig. 9. — The Atlas (Inferior View). and outwards, so that they converge in front and diverge behind. Anteriorly they reach as far as the anterior arch, and posteriorly they overhang the vertebrarterial grooves on the posterior arch to a slight extent, but they do not extend farther back than about the centre of the ring. The plane of each is sloped down- wards and inwards, and the direction of the surface is upwards and inwards. The movement between them and the occipital condyles is one of flexion and extension, or nodding. Some- times one or both of them may be divided by a groove into two circular facets. The inferior articular processes are circular and slightly concave. The plane of each is sloped upwards and in- wards, and the direction of the surface is downwards and inwards. They articulate with the superior articular })rocesses of the axis, and the movement allowed i? rotation. The articular processes of the atlas, being placed in front of the points of exit of the spinal THE BONES OF THE TRUNK 17 nerv'es, do not correspond in position with the articular processes of succeeding vertebrae (with the exception of the superior pair of the axis). They occupy a position corresponding with the pedicular portions of the bodies of vertebrae, and in this way the superincumbent weight is transmitted to the vertebral bodies. The transverse and costal processes spring from the side of each lateral mass, and, external to the cos to- transverse foramen, the costo- transverse lamella and the anterior and posterior tubercles are more or less fused into one long irregular mass, though the posterior tubercle usually remains conspicuous. The upper surface of this mass at its front part gives origin to the rectus capitis lateralis, and at its back part to the obliquus capitis superior, whilst the lower surface at its back part gives insertion to the obliquus capitis inferior. The costo - transverse foramen is of large size in order to guard against the vertebral artery being compressed during the rotatory movements of the bone upon the axis. The ring of the atlas, in the recent state, is divided into two com- partments by the transverse ligament. The anterior small division is called the odontoid compartment, and it lodges the odontoid pro- cess of the axis. The posterior large division represents the neural foramen of other vertebrae, and it lodges the spinal cord with its membranes. Varieties. — (i) The posterior arch may be incomplete at the centre, the deficiency being bridged over by fibrous tissue. (2) The costal process may be incomplete, the deficiency in the costo-transverse foramen being filled b\' fibrous tissue. (3) There is sometimes an additional small foramen on either side, a httle behind the costo-transverse foramen, for the peissage of the sub- occipital radicles of the vertebral plexus of veins. The Axis. — The axis is the second cer\'ical vertebra, and is so named because its odontoid process, which is the distinctive character of the bone, forms a pivot on which the atlas, support- ing the head, rotates. From the presence of this process the axis is sometimes called the vertebra dentata. The odontoid process {processus dentatus) springs from the superior surface of the body, and represents the body of the atlas. It is constricted and somewhat circiilar close to the body, this part being called the 7teck. Above this it expands into a head, which tapers off at either side by two sloping surfaces, forming by their convergence an antero-posterior ridge, known as the summit. The anterior surface presents a circular convex facet, called the atlantal facet, for articulation with the odontoid facet on the posterior surface of the anterior arch of the atlas. The posterior surface presents a shallow transverse groove for the play of the transverse Ugament of the atlas. The lateral sloping surfaces on either side of the summit give attachment to the lateral odontoid ligaments, whilst the summit itself gives attachment to the middle odontoid ligament. 2 18 A MANUAL OF ANATOMY The superior surface of the body is occupied by the odontoid process and portions of the superior articular processes. The inferior surface differs from that of other cervical vertebrae only in the greater downward projection of its anterior lip. The anterior surface presents a median vertical ridge which bifurcates inferiorly into diverging lips, enclosing a small triangular surface. On either side of the median ridge the surface is depressed, and gives attachment to a portion of the longus colli muscle. The other surfaces of the body present noting peculiar. The pedicles are concealed above by the superior articular pro- cesses. Each, on its inferior aspect, presents a wide and deep inferior vertebral notch, which is placed in front of an inferior articular process. The superior vertebral notches, which are very shallow, are situated on the upper borders of the laminae, and, like Atlanta! Facet Odontoid Process Groove for Transverse Ligament Superior Articular Process perior _ , , Inferioi Body 1 Notch Costo-transverse Foramen Spine Lamina Inferior Articular Process Fig. io. — The Axis (Lateral View). those of the atlas, are placed behind the superior articular pro- cesses. The laminae are massive, and give attachment by their upper borders to the posterior atlanto-axial ligaments, whilst their anterior surfaces, near the lower borders, give attachment to ligamenta subflava, as in other vertebrae. The spinous process is massive. Its direction is backwards, and it terminates in two strong tubercles, separated inferiorly by a triangular cleft. Each of these tubercles gives attachment to some of the deep fibres of the ligamentum nuchae, and to the following muscles from above downwards: the rectus capitis posticus major; the obliquus capitis inferior; and the highest portion of the semi- spinalis colli. The superior articular processes are situated on the upper surface of the pedicle at either side, the upper surface of the costal pro- cess, and a portion of the superior surface of the body, upon which THE BONES OF THE TRUNK 19 latter it encroaches very near to the odontoid process. The plane of each is sloped outwards and downwards. The surface is slightly convex from before back- wards and circular, its direc- tion being upwards and out- wards. They articulate with the inferior articular pro- cesses of the atlas, and the movement allowed is rota tion. The inferior articular processes differ from those of most vertebrae only in being situated principally upon the lower borders of the laminae. The superior pair, like all four articular processes of the atlas, being placed in front of the points of exit of the spinal nerves, do not corre- spond in position with the superior articular processes of succeeding vertebrae, but Fig. II. — ^The Axis (Superior View). occupy a position corresponding with the pedicular portions of the bodies of vertebrae. The transverse processes are very short, and are directed out- wards and downwards. Each terminates in a single tubercle. The costal processes also terminate in tubercles, and the costo- transverse lamellae are not grooved superiorly. The costo-transverse foramen is directed upwards and outwards, the reason of this obliquity being as follows : when the atlas and axis are in position each costo-transverse foramen in the atlas lies farther out than that in the axis. In order, therefore, to obviate any sudden and urdue bend in the vertebral artery, the foramen in the axis is directed obliquely upwards and outwards so as to guide the vertebral artery gradually to the foramen in the atlas. There is nothing peculiar about the neural foramen. Varieties. — (i) The summit of the odontoid process may present a facet, indicating an articulation with the anterior margin of the foramen magnum of the occipital bone, which in such cases presents a prominence known as the middle occipital condyle. (2) The odontoid process may, in ver>' rare cases, remain separate from the body, thus forming the os dentatum. (3) An odontoid process in two halves has been recorded. The seventh cervical vertebra. — ^The distinctive character of this vertebra is the great length of its spinous process, which is the only cervical s^ine that can readily be felt beneath the integiunent of the neck. On account of this outstanding prominence the seventh cervical is known as the vertebra prominens. The spinous process 20 A MANUAL OF ANATOMY is directed straight backwards, and terminates in a single large tubercular eminence. The other characters of this vertebra to be noted are as follows : the antero-posterior measurement of the body exceeds that of other cervical vertebrae ; the trans- verse process is massive and comparatively long ; the posterior tubercle is very distinct, but the anterior is rudimentary, or wanting ; the costo- transverse foramen is of small size, and does not transmit the vertebral vessels and vertebral sympathetic plexus. The vertebral vein, however, may pass through it. Varieties. — (i) The costal process may remain separate from the transverse process, thus giving rise to a cervical rib. (2) The costal process may be wanting on one or both sides, in which cases there is no costo-transverse foramen. Fig. 12 — The Seventh Cervical Vertebra (Superior View). (The Costal Process of the Left Side was undeveloped in this vertebra.) It is to be noted that the sixth cervical vertebra is peculiar in the following respects : the spinous process, like that of the vertebra prommens, terminates in a single large tubercular eminence; and the tubercle of each costal process, known as the anterior tubercle, is of large size, and is called the carotid tubercle of jChas- saignac. The cervical vertebrae receive their blood-supply from branches of the vertebral arteries. The Thoracic Vertebrae. The thoracic vertebrae are twelve in number, and their distinctive character is the presence of one or more facets on either side of the bodies for articulation with the heads of ribs. The first. THE BONES OF THE TRUNK 21 tenth, eleventh, and twelfth (sometimes also the ninth) are peculiar, and require separate descriptions. A Typical Thoracic Vertebra. — The body is larger than that of a cervical vertebra, but smaller than that of a lumbar. When viewed from above or below it is cordate or heart-shaped, being broad ar.d hollowed out behind, and narrow ard rounded off in front. The posterior depth of the body exceeds the anterior, in adaptation to the backward curve of the vertebral column in the thoracic region. The superior and inferior surfaces present a raised rim round the circumference, due to the original epiphysial plate, and this renders the whole of each surface slightly con- cave from the periphery towards the centre. The anterior and Superior Articular Procos ^ Superior Notch Superior Demi-facet '. Co^to-tiibercular Facet Inferior .\rticular Proce-is ' Fig. 13. — The Sixth Thoracic Vertebra (Lateral View). lateral surfaces merge gradually into each other, and are con- cave from above downwards, the entire antero-lateral surface being convex from side to side and pierced by numerous nutrient foramina. Each lateral surface, close to the neural arch, presents two articular demi-facets, superior and inferior, of which the superior is the larger, and is situated upon the pedicular portion of the body, the nferior smaller one being just in front of the lower part of the inferior vertebral notch. These demi-facets are for articulation with the heads of the ribs, and are called the costo- capitular facets. When two vertebrae are in position the superior demi-facet of the lower vertebra and the inferior demi-facet of the upper form an articular cavity for the head of a rib. The posterior surface of the body is concave from side to side, and presents 22 A MANUAL OF ANATOMY nutrient foramina, as in the cervical vertebrae. The superior and inferio - surfaces are related to the intervertebral discs, and the anterior and posterior surfaces are related to the anterior and posterior common ligaments. The pedicles spring from either lateral extremity of the posterior surface of the body, and their upper borders are very nearly on a level with its superior surface. Each pedicle is laterally compressed, and is directed backwards and slightly outwards. "The superior vertebral notches are shallow, and each is usually bounded in front by a transverse neuro-central lip. The inferior vertebral notches are deep and wide. The laminae are short, deep, and compressed from before back- wards, their planes being sloped downwards and backwards. The _ Body Superior Articular Process Fig. 14.— The Sixth Thoracic Vertebra (Superior View). markings for the ligamenta subflava are the same as in cervical vertebrae. The spinous process is triangular or bayonet-shaped. Its direc- tion is downwards and slightly backwards, and it terminates in a sloping border ending below in a sharp point. The spinous processes of the central thoracic vertebrae are imbricated or over- lapping. The articular processes are nearly circular, their surfaces are flat, and their planes are almost vertical. The superior pair pro- ject upwards from the junction between the pedicles and laminae, and they look backwards and slightly upwards and outwards. The inferior pair are placed on the anterior surfaces of the laminae, and they look forwards and slightly downwards and inwards. TH£ BONES OF THE TRUNK 23 The transverse processes spring from the junction of the pedicles and laminae, and each is directed outwards and backwards. They are long and club-shaped, being somewhat constricted at their bases, but expanding into knob-like enlargements at their ex- tremities. The anterior surface of the extremity of each presents a circular concave facet, called the costo-tuhercular facet, for articula- tion with the tubercle of a rib. The posterior surface of the extremity gives attachment to the posterior costo - transverse ligament. The anterior svu^face of the transverse process faces the posterior surface of the neck of a rib, and gives attachment to the middle costo- transverse or interosseous ligament. This region corresponds with the costo- transverse foramen in a cervical vertebra. The lower border of the transverse process gives attachment to the superior costo- transverse ligament, which connects it with the crest, or upper border of the neck, of the rib below. The transverse process is serially homologous with a cervical transverse process. The neural foramen is almost circular, and is of smaller size than in the cervical or lumbar vertebrae. Peculiar Thoracic Vertebrae. — ^These are the first, tenth, eleventh, and twelfth (sometimes also the ninth). The Fiftt Thoracic Vertebra. — ^This vertebra closely resembles the seventh cervical, as, indeed, do one or two below it. Its distinctive character is the presence on each side of the body of one entire facet close to the upper part, and situated on the pedicular portion, for the head of the lirst rib, and one demi -facet close to the lower part for a portion of the head of the second rib. With the exception of the inferior articular and transverse processes, this vertebra in other respects closely corresponds with the seventh cervical, with this difference, that the antero-posterior lips of the superior surface of the body of the seventh cervical are replaced by transverse lips lying in front of the superior vertebral notches. The inferior articular and transverse processes are similar to those of a t\-pical thoracic vertebra, each transverse process haWng the usual costo - tubercular facet on the anterior surface of its extremity. The Tenth Thoracic Vertebra. — ^This vertebra has usually bne entire facet on either side, mainly on the pedicle, for the head of the tenth rib. This facet, however, may only be a three-quarter tacet, if the ninth thoracic vertebra is normal. It has, usually, a costo- tubercular facet on the anterior aspect of the extremitj' of each transverse process for the tubercle of the tenth rib, but this facet may be wanting. The body and spinous process of this vertebra show indications of the lumbar type, its other characters being thoracic. The Eleventh Thoracic Vertebra. — ^This vertebra has an entire facet on the outer surface of each pedicle for the head of the eleventh rib, but there is no facet on the transverse process, which has become short and stunted, the tendency to the club shape being, however. 24 A MANUAL OF ANATOMY still perceptible. The lumbar type of the bone is more pronounced than in the case of the tenth. The Twelfth Thoracic Vertebra. — This, like the eleventh, has an entire facet on the outer surface of each pedicle for the head of the Superior Tubercle -External do. - - Inferior do. -- Mammillary Process __ , _ Accessory Process Transverse Process Fig. :5. — The Peculiar Thoracic VERTEBRiii and the First Lumbar Vertebra. twelfth rib, and no facet on the transverse process; The transverse processes are very stunted, and each presents three tubercles — external, superior, and inferior — a condition which also manifests itself, though not so conspicuously, in the transverse processes of the eleventh, and even the tenth. The external tubercle, along THE BONES OF THE TRUNK . iS with the twelfth rib, is serially homologous with a lumbar trans- verse process, the superior with a lumbar mammillary process, and the inferior with a lumbar accessory process. The superior articular processes are thoracic in type, whilst the inferior are like those of a lumbar vertebra, being convex and directed outwards and for%vards, or away from each other. Sometimes the superior articular processes are also lumbar in type, being concave and looking inwards and backwards, or towards each other. When this is so, the inferior articular processes of the eleventh thoracic vertebra are also lumbar in type. The twelfth thoracic vertebra very closely resembles a lumbar vertebra, from which, how- ever, it differs in having a facet on the outer surface of each pedicle. The thoracic vertebrae receive their blood-supply from the inter- costal arteries. The Lumbar Vertebrae. The lumbar vertebrae are five in number, and are so named because they occupy the region of the loins. They are the largest of the true vertebrae, and their negative characters are — the absence of a costo- transverse foramen in the transverse process ; and the absence of any kind of costal facet on the side of the body. They increase in size from above downwards, the fifth being the largest, but, as this vertebra has certain distinctive characters, it will be separately described. A Typical Lumbar Vertebra. — The body, when viewed from above or below, is reniform, being flattened from above downwards, convex transversely over its antero-lateral surface, and slightly concave transversely on its posterior surface. It is wider from side to side than from before backwards. The anterior depth is slightly greater than the posterior, in adaptation to the forward curve of the vertebral column in the lumbar region. There is no facet on either side of the bod3^ The pedicles are short, strong, and directed backwards. The superior vertebral notches are shallow, the inferior being deep and wide. The laminae are short, thick, and deep, and their planes are almost vertical. The spinous process is axe-shaped, its direction being straight backwards, and it terminates in a round elonga':ed border. The articular processes are strong. The superior pair project upwards from the junction of the pedicles and laminae, and the inferior pair project downwards from the lower borders of the laminae. The superior pair are concave, their planes being vertical, and their direction being inwards and backwards, so that thev almost face each other. They stand wide apart, so as to embrace the inferior articular processes of the vertebra above. On the posterior border of each there is a nipple-shaped projection directed back- wards and slightly upwards, called the nuivimillary process {nie'.a- 26 A MANUAL OF ANATOMY pophysis), which corresponds with the superior tubercle of the lower thoracic transverse processes. The inferior articular pro- cesses are convex, their planes being vertical, and their direction being outwards and forwards, so that they look away from each other. They are nearer to each other than the superior pair, and are received between the superior pair of the vertebra below. The transverse processes are comparatively slender, except in the case of the fifth; they are directed outwards and slightly backwards, and they increase in length from the first to the fourth. Each is spatula - shaped, being compressed from before Body Transverse Process ; I Accessory Process I Mammillary Process / Back of Inferioi Articular Process Superior Articular Proces Fig. i6. — The Third Lumbar Vertebra (Superior View). backwards, and terminates in a short round border. It repre- sents the vertebral portion of a rib, and therefore constitutes the costal element of the vertebra. Situated on the posterior aspect of the base of the transverse process, just external to and below the lower border of the superior articiilar process, there is a small sharp projection directed downwards, called the accessory process {anapophysis) , which is the rudiment of the true transverse process, and is serially homologous with the inferior tubercles of the lower thoracic vertebras and the other thoracic transverse processes. In the case of the fourth and fifth lumbar vertebras the transverse process becomes shifted on to the pedicle, and even slightly on to the body. Between the base of the transverse process and the accessory process posteriorly there are a few nutrient THE BONES OF THE TRUNK 27 foramina which correspond with the costo- transverse foramen in cervical vertebrae. The lumbar transverse processes (costal elements) of man are serially- homologous with the ribs, and also, in the case of the lower thoracic vertebrae, with the external tubercles of the transverse processes. In the lumbar region each transverse process (costal element) has fused with the accessory process (true transverse process), and so the costo- transverse foramen in the transverse process of a cervical vertebra is represented only by a few nutrient foramina. The neural foramen is larger than in the thoracic vertebrae, but not so large as in the cervical, its shape being triangular with rounded angles. The Fifth Lumbar Vertebra. — ^The distinctive characters of this Fig. 17. — The Fifth Lumbar Vertebra (Superior View), vertebra are as follows : (i) it is the most massive of all the lumbar . vertebrae ; (2) the greater d^pth of the body in front is more con- spicuous than in the others ; (3) the transverse processes are thick and conical ; and (4) the inferior articular processes are wide apart. The lumbar vertebrae receive their blood-supply from the lumbar arteries. Ossification of the True Vertebrae. Each true vertebra ossifies in cartilage from three primary, and five secondary, centres. One primary centre is for the principal part of the body, and two are for the neural arch and its processes, including also a small portion of the body at either side adjacent to the pedicle. The centres for the neural arch appear 28 A MANUAL OF ANATOMY about the seventh week of intra-uterine life at the junction of the pedicles and laminae, and from these ossification invades the neural arch, with its processes, and the adjacent portions of the body. The centre for the principal part of the body appears about the eighth week in the portion of cartilage dorsal to B Appears about the 8th Week Appears about the 7th Week of intra-uterine Hfe Neural Arch Neural Arch Fig. 18. — Ossification of the True VERTEBRi^. A, Cervical Vertebra at the Third Month ; B, Cervical Vertebra at Birth ; C, Thoracic Vertebra at Birth. the notochord. It is usually single at first, but it soon assumes a bilobed form, and so it comes to surround the notochord, which becomes constricted, and ultimately disappears. This nucleus may be double, and, if this character persists, the body ossifies in two separate parts, or, if one nucleus should be A tr^ ;• ■ ■'iif 1 '* 1 /"'*• =3: \ . 4i;\^ Appears about the i6th, and joins about the 25th, Year Transverse Epiphysis (i6th and 25th Ye.nr) Mammillary Epiphysis (i6th and 25th Year) Spinous Epiphysis - • ■ ;th -• • (i6th and 25th Year) Fig. 19. — Lumbar Vertebra, showing the Epiphyses. A, The Body ; B. The Neural Arch. arrested, only one-half of the body ossifies (Turner). At birth a vertebra is composed of three osseous parts, connected by cartilage, namely, the principal part of the body, and the two halves of the neural arch, each bearing a small portion of the body. The lamina; unite behind in the first year, except in the THE BONES OF THE TRUNK 29 axis, where the union is delayed until the fourth year, and the neural arch joins the body in the third year. The cartilaginous union between the neural arch and the body at either side is called the neuro-central synchondrosis. In the thoracic vertebrae the superior demi-facets lie behind this, and so they are shown to be placed on the pedicular portion of the body. All vestiges of this svnchondrosis have disappeared prior to the sixth year. The secondary centres, five in number, appear about the sixteenth year, and they are consolidated about the twenty-fifth year. One appears at the extremity of the spinous process, one at the extremity of each transverse process, and the other two take the form of epiphysial plates, one on the upper surface and the other on the under surface of the body. In the case of the seventh cervical vertebra, and sometimes one or two above it, the costal process has a special centre which apj)ears before birth, and it may be developed into a cer\'ical rib. The transverse process (costal element) of the first lumbar has occasionally a special centre, and in these cases it may be developed into a lumbar rib. The lumbar mammillary processes are ossified from special secondary centres. The fifth lambar has sometimes four centres for the neural arch, two at either side, one of which is for the pedicle, transverse process, and superior articular process, and the other for the lamina, inferior articular process, and one-half of the spinous process. These parts may fail to unite, in which cases the neural arch presents a synchondrosis on either side, situated between the superior and inferior articular processe.- (Turner). Sometimes the laminae of the fifth lumbar fail to unite, and so a space is left, bridged over by fibrous tissue. The Atlas. — The atlas has three centres of ossification, two for the lateral masses and posterior arch, appearing in the seventh week of intra -uterine Ufe. and one (sometimes two) for the anterior arch, which does not appear until the A p;. ears in 7th Week (intra-uterine) Fig. 20. — Ossification of the Atlas. first year. The two halves of the neural arch usually join towards the end of the third year, there being sometimes a special osseous deposit at the place of junction. The two halves, however, may remain separate throughout life, the interval being bridged over by fibrous tissue. The anterior arch joins the lateral masses in the sixth year. The anterior arch represents the hypochordal brace of the first vertebral bow. The Axis. — Excluding the odontoid process, the axis has three primary centres, like an ordinary vertebra, two for the neural arch appearing about the seventh week, and one (sometimes tvvo) appearing in the lower part of the common cartilage of the body and odontoid process in the fourth month. In the upper part of this common cartilage two centres, laterally disposed, appear in the fifth month for the odontoid process, and these unite into one centre about the sixth month. At birth the axis is composed of four osseous parts connected by cartilage, namely, a body, an odontoid process surmounted by cartilage, and two halves of the neural arch. The odontoid process joins the body about the fourth year. The two halves of the neural arch join each other, and the arch joins the body, in the fourth year. The apical part of the odontoid process has a special centre appearing in the fourth year, and it joins the rest of the process in the tweljth year. The body of the axis has the usual epiphysial plate on the under surface of the body, but there is no such plate 30 A MANUAL OF ANATOMY on the upper surface. The union between the odontoid process and the body is indicated by a small cartilaginous disc in the centre, which persists until advanced life. The odontoid process is to be regarded as the original body of the atlas for the following reasons: (i) in the embryo the notochord passes through its cartilage; (2) the notochord presents a swelling between . Appears in the 4th Year, and joins in the 1 2th Ytar Appear in the 5th Month and coalesce in the 6th Month Appears in the 4th Month of intra-uterine life Body Odontoid Process (joins Body about the 4th Year) Fig. 21. — Ossification of the Axis. A, At the Fifth Month; B, at the Fourth Year. the cartilage of the odontoid process and that of the body of the axis, as it does in the case of other vertebrae; (3) there is a cartilaginous disc concealed within the odontoid process, which is persistent until advanced Ufe; (4) the odontoid process has two primary centres of ossification ; (5) in chelonians it forms a separate ossicle; (6) a permanently separate odontoid process in man has been recorded. The False Vertobrse. The false vertebrae are usually nine in number, the upper five of which form the sacrum, and the lower four the coccyx. The Sacrum. The sacrum lies below the fifth lumbar vertebra, and is wedged in between the ossa innominata, where it forms the greater part of the posterior wall of the pelvis, its direction being downwards and backwards. The sacral vertebrae diminish in size from above downwards, which renders the bone triangular, the base being upwards. The ventral or pelvic surface, which is directed downwards and forwards, is concave from above downwards, and from side to side. It presents along the centre a solid mass, representing the ankylosed bodies and ossified intervertebral discs, which is marked by four transverse ridges situated at the places of junction. Superiorly it presents a projecting lip, called the promontory. On either side there is a row of anterior sacral foramina, four in number, which diminish in size from above downwards, and are directed outwards and for- wards from the intervertebral foramina, by means of which they communicate with the sacral canal. They transmit the anterior primary divisions of the first four sacral nerves. The lateral masses are situated external to the anterior sacral THE BOXES OF THE TRUNK 31 foramina at either side, and each is marked anteriorly by four transverse grooves, which prolong outwards the foramina and lodge the transmitted nerves. The pyriformis muscle arises from the front of each lateral mass by three shps, which are inter- posed between, and lie external "^to, the foramina. The lateral masses are formed by the fusion of the pedicles, transverse pro- cesses, and costal elements of the sacral vertebrse. Superior Ardcnlar Process . .Iliacns ^ ^-Pyrifonnis Inferior Lateral Angle — Coccygf us 4th Anterior Sacral Foramen Fig. 22. — The Sacrum (Anterior View.) The dorsal surface, which is directed upwards and backwards, is irregularly convex and narrower than the ventral. In the middle line it presents four eminences, which may be distinct, or fused to form a ridge, representing the spinous processes of the upper four sacral vertebrae. The spinous process of the fifth vertebra is absent, the development of its laminae having been arrested, and there is thus left a triangular opening, which is the outlet of the sacral canal, to be presently described. On either side of the median 32 A MANUAL OF ANATOMY row of spines there is a solid mass formed by the ankylosed lamina}, which forms the sacral groove for the origin of a portion of the multifidus spinas. External to this groove there is a row of for- amina, four in number at either side, called the posterior sacral foramina, which are smaller than the anterior, and, like them, diminish in size from above downwards. These foramina open outwards and backwards from the intervertebral foramina (by which they communicate with the sacral canal), and transmit the Rudimentary Articular Processes (fused) Superior Articular ProccGs Ligamentous Surface Auricular Surface Multifidus SpinEE Transverse Process (rudimentary) Gluteus Maximus Outlet of Sacral Canal , — Notch for 5th Sacral Nerve 2nd Posterior Sacral Foramen '*■ Inferior Lateral Angle Sacral Cornu Fig. 23. — The Sacrum (Posterior View). posterior primary divisions of the first four sacral nerves. It is to be noted that they lie directly behind the anterior foramina. Internrd to the posterior foramina, and encroaching upon them, there is a row of small projections which represent the articular processes of the sacral vertebrae. The lower pair, which belong to the fifth sacral vertebra, are prolonged downwards as two plates which end in enlargements. These are called the sacral cornua, and they are connected with the cornua of the first coccygeal vertebra, usually by ligaments, but sometimes by osseous union. The THE BONES OF THE TRUNK 33 interval thus bridged over at either side represents a fifth inter- vertebral foramen, through which the fifth sacral nerve passes. The solid portion external to the posterior foramina at either side is the lateral mass, and it presents a row of four tubercles, each of which is situated external to a posterior foramen. These represent the transverse processes of the lower four sacral vertebrae. The boundaries of the triangular outlet of the sacral canal are the spine of the fourth sacral vertebra above, and the imperfect laminae of the fifth sacral and the sacral cornua at either side. It Promontory- .'Auricular Surface ist Spine Ligamentous Surface _ Sacral Coma Tip of Coco-x. ^^ ;^^^ - Coccygeal Comn Fig. 24. — The Sacrum (Left Lateral View). transmits the fifth pair of sacral nerves and the two coccygeal nerves. The lateral surface is broad above and narrow below. The upper part is divided into two portions — articular and non-articular. The articular division, anterior in position, is covered by cartilage, and is shaped like an ear, on which account it is called the auricular surface. It articulates with the iliac portion of the os innominatum, and extends over at least the first two sacral vertebrae. The non- articular division, posterior in position, is rough and irregular for 3 34 A MANUAL OF ANATOMY the attachment of the posterior sacro-iliac Ugament, and it is known as the ligamentous surface. The lower part of the lateral surface corresponds with at least the lower two sacral vertebrae, and may include more or less of the third. It gives attachment to fibres of the great and small sacro-sciatic ligaments and a portion of the coccygeus muscle, whilst the adjacent portion of the posterior aspect gives origin to fibres of the gluteus maximus, Inferiorly the lower part is thinned away to a mere margin, and presents a process, called the inferior lateral angle. Below this is the trans- verse process of the first coccygeal vertebra when that is in position, a notch being thus formed on the side of the fifth sacral vertebra. The inferior lateral angle inclines towards the coccygeal transverse process, with which it is usually connected by a hgament, though in some cases the two processes become ankylosed. There is thus constructed a fifth anterior sacral foramen at either side for the Body Articular Process, i with Mammillary Process Sacral Canal Spine Fig. 25. — The Base of the Sacrum. passage of the anterior primary division of the fifth sacral nerve. The base presents a central and two lateral divisions. The central division corresponds in its characters with the superior surface of a lumbar vertebra. Each superior vertebral notch lodges a fifth lumbar spinal nerve, and the superior articular pro- cesses stand wide apart. The lateral divisions of the base are called the alee. Each ala is triangular with the apex directed backwards. The alar surface is depressed, concave from side .to side, and convex from behind forwards. It gives attachment to fibres of the iliacus, the lateral lumbo-sacral and anterior sacro- iliac ligaments, and it supports the lumbo-sacral nervous cord and the internal iliac vessels. The ala is formed by the fusion of the pedicle, transverse process, and costal element of the first sacral vertebra. The apex is transversely oval, and articulates with the first THE BONES OF THE TRUNK 35 ^ Appeal in the yd month ' of intra-uterine life ^i Appeal about the 6th Month ^ Appear after the 5th Month Netual Arch coccygeal vertebra, \Wth the intervention of an intervertebral disc until advanced life, when ankylosis takes place. The sacral canal is situated behind the bodies of the first four sacral vertebrse, as a rule. It is triangular in the upper part, but somewhat crescentic below^. It is closed in front by the ankylosed bodies, and behind by the ankylosed laminae. Along each side it presents four intervertebral foramina for the passage of nerves. These are bounded externally by the lateral mass, but each opens on the ventral and dorsal siurfaces by the anterior and posterior sacral foramina, which represent the limbs of a capital V, the apex of which corresponds \\ath an intervertebral foramen. The '"PPjSL'Kt'^e^l^ yS "^ superior aperture or inlet is i large, triangular, and wide transversely. It represents the spinal or neural foramen of the first sacral vertebra. The inferior aperture or out- let is compara- ( tively small and i^J^i,^^]J somewhat trian- ^d join about] , , . the 25th Yeai. I gular, and is usu- V ally situated on the back of the body of the fifth sacral vertebra. It is bounded above by the tubercle which represents the spinous pro- cess of the fourth sacral vertebra, and on either side by (i) the imperfectly de- veloped lamina of the fifth sacral vertebra, and (2) the sacral comu. The outlet transmits the fifth pair of sacral nerves and the two coccygeal nerves. The con- tents of the canal are the sacral and coccygeal nerves, and the filum terminale of the spinal cord. The sacrum derives its blood-supply from the lateral sacral and middle sacral arteries. Articulations.— SM/>mor/y with the fifth lumbar vertebra, in- ferior ly with the cocc5rx, and at either side with the os innominatum. Varieties. — (i) The number of sacral segments may be six, or more rarely four. Increase in the number is usually due to the incorporation of the first coccygeal vertebra, or sometimes the fifth lumbar. The decrease may be due to the fifth sacral vertebra forming a part of the coccyx, or to the first sacral forming a sixth lumbar. (2) The bodies of the first and second sacral vertebrae may remain permanently separate, though ankylosis has taken place in all their other parts. (3) The first sacral vertebra may be normal on one side. Transverse Process Costal Process Body Fig. 26. — Ossification of the Sacrum. A, Anterior View; B, First Sacfal Vertebra in early life (Superior View). 36 A MANUAL OF ANATOMY but on the other side it may remain separate from the second, and present the characters of a fifth lumbar. (4) The number of sacral spines may be reduced from four to three, two, or one, or they may be entirely absent. As a con- sequence of this, the sacral canal, which usually opens on the back of the fifth sacral vertebra, may do so on the back of the fourth, third, second, or first, so that in some cases it may be entirely open posteriorly. (5) The sacrum is liable to much variety as regards the extent of its vertical curve. Characters of the Female Sacrum. — In the female the sacrum is smoother, shorter, broader, less curved, and is set more backwards than in the male. Ossification. — The sacrum ossifies in cartilage from thirty-five centres. Each segment has three primary centres, one for the body and two for the neural arch. The centre for the body appears in the third month of intra- uterine life in the case of the first three, and after the fifth month in the last two. The centres for the neural arches appear about the sixth month. The neural arches join the bodies, in order from below upwards, from the second to the sixth year. The unidn of the laminae takes place from the eighth to the twelfth year. It, however, fails in the lowest, and sometimes in those higher up. The anterior parts of the lateral masses of the first three vertebrae, which represent the costal elements, have separate centres, which appear about the sixth month. These join the neural arches before uniting with the bodies, the latter union taking place rather later than the union between the neural arches and the bodies. Each vertebra has two annular circumferential epiphysial plates, superior and inferior, which begin to ossify about the sixteenth year. On each side of the sacrum there are two epiphyses, an upper for the auricular surface, and a lower for the sharp edge below, which appear about the eighteenth year. Consolidation begins about the eighteenth year, and pro- ceeds from below upwards, union taking place earlier between the segments of the lateral masses than between the bodies. In the latter case the ossifica- tion invades the intervertebral discs, but in the former it is direct union. The union is complete about the twenty -fifth year, at which period also the lateral epiphyses join the bone. The Coccyx. . The coccyx is composed as a rule of four rudimentary vertebrae, and it lies below the apex of the sacrum, which constitutes its only articulation. The direction of the bone is downwards and for- wards, and its elements diminish in size from above downwards. It is triangular. The first coccygeal vertebra is compressed from before backwards, broad above, narrow below, concave in front, and convex behind. The superior and inferior surfaces are transversely oval, and the lateral borders are sloped downwards and inwards. Two processes project upwards from the dorsal surface at either side, called the cornua, which articulate with the sacral cornua, usually by ligaments, but sometimes directly. Each lateral border presents, superiorly, a projection, called the transverse process, which inclines towards the inferior lateral angle of the sacrum, and is usually connected to it by a ligament, which is sometimes ossified. The second coccygeal vertebra presents traces of transverse processes and cornua, whilst the third and fourth are reduced to mere nodules. THE BOXES OF THE TRUNK 37 The muscular attachments of the coccyx are as follows: the gluteus maximus to the back of the upper three segments close to the lateral border; the sphincter ani extemus to the tip; the posterior fibres of the levator ani and a portion of the coccygeus to the lateral border. The great and small sacro-sciatic ligaments Coccygeus Levator Ani dateas Maximus Comu Transverse Process (mdimentar)-) _, Transverse Process (rudimentary) Comu (rudimentary Sphincter Ani Extemus Fig. 27. — ^The Coccyx. A, Anterior View; B, Posterior View. are partially attached to the lateral border of the first coccygeal vertebra. The coccyx derives its blood-supply from the lower lateral sacral and middle sacral arteries. Varieties. — The number of coccygeal segments may be increased to five, due either to the addition of an extra nodule, or to incorporation of the fifth sacral segment. The number may be reduced to three, due either to incorpora- tion of the first coccygeal segment with the sacrum, or to suppression of one of the nodules. Ossification. — The coccygeal vertebrae are cartilaginous at birth. Each vertebra has one primary centre and two secondary centres, the first vertebra having an additional pair of secondary centres. Primary Centres. — The primary- centre for the first vertebra appears from the second to the fifth year; that for the second vertebra from the sixth to the tenth year, and those for the third and fourth vertebrae about puberty. 38 A MANUAL OF ANATOMY Secondary Centres. — Each vertebra has two secondary centres for the epiphysial plates — one on the upper surface, and the other on the under surface of the rudimentary vertebra (centrum or body). In addition, the lirst coccygeal vertebra has two special secondary centres, one for each comu. Union of the four coccygeal vertebrae takes place from below upwards, as in the sacrum. It commences shortly after the eighteenth year, and is not completed until the thirtieth year or later, the last two coccygeal vertebrae to join being the first and second. In advanced life it is not uncommon to find the coccyx snkylosed to the sacrum, thus forming one sacro-coccygeal bone. The Vertebral Column as a Whole. The vertebral column supports the other parts of the skeleton, directly or indirectly. Its average length is about 28 inches in the male, and rather less in the female. When viewed from the front, it presents four pyramids. The first extends from the axis to the seventh cervical vertebra, its base being dovi^nwards. The second extends from the first to the fourth thoracic vertebra, its base being upwards. The third extends from the fifth thoracic to the fifth lumbar, its base being downwards. The fourth extends from the base of the sacrum to the tip of the coccyx. These pyramids are due to the differences in breadth of the bodies in different parts. The column presents certain curves, which are arranged in two groups, antero-posterior and lateral. The antero-posterior group comprises four curves, named cervical, thoracic, lumbar, and pelvic. The cervical and lumbar curves have their convexities directed forwards, and the thoracic and pelvic curves have their convexities directed backwards. The lumbar and pelvic curves meet rather abruptly and form a projection, called the sacro- vertehral angle, which is estimated at 117 degrees in the male and 130 degrees in the female. The curves impart springiness or elasticity to the column, and so guard it against shock. The thoracic and pelvic curves are associated with the thoracic and pelvic cavities, the capacity of which they serve to increase. They appear in early foetal life, and are known as primary curves. The cervical and lumbar curves do not appear until after birth, and are known as secondary or compensatory curves. The primary curves are brought about by the greater depth posteriorly of the thoracic and sacral bodies, whilst the compensatory curves are largely due to the intervertebral discs, though in the lumbar region the greater depth of the bodies anteriorly, especially in the fifth lumbar, must also be taken into account. The lateral group comprises two curves. One is situated in the upfper thoracic region, with its convexity directed towards the right side in right-handed persons, and it is to be regarded as due to the greater use made of the right arm. To compensate for this curve there is another slight curve in the upper lumbar region, with the convexity to the left. When viewed anteriorly, the column presents the bodies, which form the pyramids already described. When viewed laterally, it presents the sides of the bodies, pedicles, intervertebral foramina, and articular and transverse processes. The intervertebral foramina THE BONES OF THE TRUNK 39 ~! ist Thorac*; ist Lumbar I Sacrum j Ciiccyx Fig. 2Sa.-The Vertebral Column (Lateral View). (The Blue Markings represent the Facets on the Bodies and Trans- verse Processes.) . ist C. .ist T. ■ V* ist L. .ist Co. Fig. 28b. -The Vertebral Column (Posterior View). 40 A MANUAL OF ANATOMY are formed by the apposition of the superior and inferior vertebral notches of contiguous pedicles. They lead outwards from the spinal canal, and each transmits a spinal nerve. They increase in size from above downwards until the sacrum is reached, in which, though hidden at either side of the central mass, they diminish in size from above downwards. In this region each intervertebral foramen opens on the front and back of the sacrum by means of an anterior and posterior sacral foramen, the arrangement thu? formed resem' ling a capital V, the apex being at an intervertebral foramen. On the lateral aspect of the thoracic portion of the column are seen the costo-capitular facets, which are twelve in number. The first is situated on the upper part of the side of the first thoracic body. The second to the tenth inclusive are situated on the contiguous margins of the bodies of the vertebrae, each being formed by the small inferior demi-facet of the upper body and the large superior demi-facet of the lower. The eleventh and twelfth are situated on the sides of the corresponding pedicles. The tenth facet may belong entirely to the tenth thoracic vertebra. The thoracic transverse processes, except the eleventh and twelfth (and sometimes the tenth), are faceted in front at their extremities for the tubercles of the ribs. When the column is viewed from behind the following parts are seen : the spinous processes ; the laminae ; the articular pro- cesses ; the backs of the transverse processes ; and the dorsum of the sacrum and coccyx. The cervical spines, except the sixth and seventh, are short, so as not to interfere with backward flexion or over-extension of the neck. The middle thoracic spines are imbricated, and the lumbar spines stand out horizontally. On either side of the spines there is the vertebral groove, which is occupied by the deep muscles of the back, the deepest being the multifidus spinae. This groove is bounded internally by the spines, and externally by the transverse processes in the cervical and thoracic regions, and by the mammillary tubercles in the lumbar region. The floor is formed by the laminae, and its continuation over the back of the sacrum is known as the sacral groove. The spinal canal is situated behind the bodies of the vertebrae, and is formed by the neural foramina of all the vertebrae except the fifth sacral and four coccygeal. It commences at the level of the atlas, and it terminates as a rule upon the back of the body of the fifth sacral vertebra. It adapts itself to the various curves of the column, and is large and triangular in the cervical and lumbar regions, small and circular in the thoracic, and triangular in the upper part, but crescentic in the lower part, of the sacral region. It contains the spinal cord and its membranes as low as about the level of the disc between the first and second lumbar bodies, and a copious plexus of vessels. Below the level just mentioned it con- tains the filum terminale of the spinal cord and the leash of nerves known as the cauda equina, with their coverings. The dura- matral covering or theca ceases by taking attachment to the back THE BONES OF THE TRUNK 41 of the second sacral body, and the filum terminale passes on to be attached to the back of the fifth sacral or first coccygeal vertebra. B. The Ribs. The ribs (costae) are twelve in number at either side, and are arranged in two groups, true or sternal, and false or asternal. The true ribs are those which articulate directly with the sternum by their costal cartilages, and they represent as a rule the first seven at either side. The false ribs are those which have no direct articulation by their costal cartilages with the sternum, and they represent, as a rule, the last five at either side. The last two false ribs, eleventh and twelfth, are called the free or floating ribs, because their costal cartilages stand quite clear of each other and of the tenth. The ribs are elastic, and increase in length from the first to the seventh, whence they decrease to the twelfth. The first is the broadest, and the twelfth the narrowest. Their direction is at first down- wards, outwards, and slightly backwards, then downwards and forwards, and finally inwards. The upper ribs are not so oblique as those lower down, the most oblique being the ninth. With the exception of the first rib, the surfaces of the others are vertically disposed posteriorly, but in front they are sloped downwards and forwards, and this circimistance renders most of them twisted. A Typical Rib. — A typical rib presents for consideration a head, neck, tubercle, shaft, and sternal extremity. The head (capitulum) forms the posterior or vertebral extremity, and is slightly expanded. It presents an irregularly flat smface and an anterior margin. The surface is marked by two oblique facets, upper and lower, which are separated by a horizontal ridge. The lou-er or primary facet is the larger of the two, and articulates with the large upper or primary demi-facet of the lower of the two thoracic bodies with which the head is connected. The upper facet articulates with the small lower demi-facet on the side of the upper thoracic body, and the intervening ridge gives attachment to the interarticular ligament. The anterior margin gives attach- ment to the anterior costo-central hgament. The neck is about i inch long, and is compressed from before backwards. Its anterior surface is smooth and covered by the costal pleura. Its posterior surface, which is rough, faces the anterior surface of the lower thoracic transverse process, or that with which its tubercle articulates, and it gives attachment to the middle costo- transverse or interosseous ligament. Its superior border forms a sharp lip, called the crest, which gives attachment to the superior costo-transverse ligament. Its inferior border may show traces of the subcostal groove. The tubercle is situated on the external surface of the rib at the outer extremity of the neck, and presents two divisions, articular and non-articular. The articular division, inferior and slightly 42 A MANUAL OF ANATOMY internal in position, presents a somewhat oval facet for articulation with that on the front of the extremity of the lower thoracic trans- verse process. The non-articular division, superior and slightly Neck Subcostal Groove "^^ Articular Part of Tubercle Ligamentous Part of Ttibercle External Intercostal Internal Intercostal Fig. 29 — The Sixth Left Rib (Internal View). external in position, gives attachment to the posterior costo-trans- verse ligament. The shaft is curved and twisted. It presents- two surfaces and THE BONES OF THE TRUNK 43 two borders. The external surface is convex, and its plane is vertical behind, but oblique in front, being here sloped downwards and fonsards. Opposite the greatest bend of the rib it presents an oblique ridge, directed do%vnwards and outwards, called the angle, for a tendinous shp of the erector spinje. The surface between the tubercle and the angle gives attachment to the longissimus dorsi. Near to the anterior extremity (about 2 inches from it) the external surface presents another obhque ridge directed downwards and outwards, knoNXTi as the anterior angle, where the rib describes a slight curve. The internal surface, which is concave, is covered by the costal pleura. At its lower part it presents the subcostal groove, to be presently described. The superior border is thick and round behind, but thin and sharp in front. Its outer hp gives attachment to an external intercostal muscle, and its inner Up to an internal intercostal, a collateral intercostal artery Ijdng between the two muscles. The inferior border is for the most part sharp and wiry. Immediately within and above it there is the subcostal groove, which conmiences behind at the tubercle and disappears over the anterior fifth. Posteriorly the groove belongs to the inferior border. Its upper hp is rovmded and gives attachment to an internal intercostal muscle, whilst the lower hp gives attach- ment to an external intercostal. The nutrient foramen is situated in the subcostal groove a httle anterior to the centre of the bone, and the canal to which it leads is directed towards the head. It gives passage to a branch of the intercostal artery which lies in the groove. The contents of the groove from above downwards are an intercostal vein, artery, and nerve. The interior or sternal extremity presents an oval pit, which is almost vertical in direction, for the costal cartilage. The Peculiar Ribs. — ^These are the first, second, tenth, eleventh and twelfth. The First Rib. — ^This is the shortest, broadest, and flattest of all the ribs, and its curs'e is very distinct, but there is no twist. The head is small, and presents a nearly circular facet for articula- tion with the entire facet on the body of the first thoracic vertebra. The neck is narrow, and compressed from above downwards. The tubercle, which is large, is situated on the external border at the junction of the neck with the shaft. Being placed opposite the greatest bend of the bone, it takes the place of the angle, and pre- sents the usual articular and non-articular portions, the former being for the first thoracic transverse process. The shaft is broad and compressed from above downwards, its surfaces being superior and inferior, whilst the borders are internal and external. The superior surface close to the anterior extremity gives attachment to the tendon of the subclavius and the costo-coracoid ligament. Farther back there are two oblique grooves, separated to a limited extent by a tubercle or spine for the scalenus anticus. The anterior groove is shallow, and lodges the subclavian vein, whilst the posterior deeper groove 44 A MANUAL OF ANATOMY is occupied by the third part of the subclavian artery and the trunks of the brachial plexus of nerves. Behind the posterior groove, and extending as far back as the tubercle, there is a rough impression for the insertion of the scalenus medius. The inferior surface is flat and covered by the costal pleura. Near the external border it gives attachment to the internal intercostal muscle of the first space. The internal border, which is thin and concave, gives attachment to Sibson's fascia. Fully i inch from _ Scalenus Posticus Groove for Subclavian Artery Scalenus Anticus Serratus Magnus Groove for Subclavian Vein Sternal Extremity Subclavius Fig. 30. — The First and Second Ribs of the Left Side (Superior View). the anterior extremity this border presents a projection, called the scalene tubercle or spine {tuhercU of Lisfranc), for the insertion of the scalenus anticus. It encroaches slightly on the adjacent part of the superior surface, and is inclined backwards. The external border is convex. It gives attachment to the external inter- costal muscle of the first space, and a portion of the first serration of the serratus magnus at a point opposite the groove for the sub- clavian artery, where the external border is often prominent. The THE BONES OF THE TRUNK 45 anterior extremity presents the usual oval pit for the first costal cartilage, its direction being horizontal from before backwards The first rib has no subcostal groove. The Second Rib. — The surfaces of the shaft of this rib occupy a transitional plane between that of the first and those of the suc- ceeding ribs. It is practically destitute of a twist. The neck is compressed from above downwar .' s, and from before backwards. The distinctive character of the bone is the presence on its supero-extemal surface, near the centre, of a rough oval eminence for a portion of the first and the second slips of the serratus magniis. Behind this im- pression the surface gives insertion to the scalenus posticus. The Tenth Rib. — This bone may or may not be peculiar. If the body of the ninth thoracic vertebra has a lower demi-facet, there is nothing peculiar about the head of the tenth rib. If, however, the lower demi-facet is wanting on the ninth thoracic body, the head of the tenth rib has only one facet for that on the body and pedicle of the tenth thoracic vertebra. The tubercle has usually an articular facet for the tenth thoracic trans- verse process, but this may be awanting. The angle and subcostal groove are well marked. The EUeventh Rib.— The head of this rib has one facet for that on the pedicle of the eleventh thoracic vertebra. There is a sUght tubercle, destitute of an articular facet, a faint angle, and an equally faint subcostal groove. The anterior ex- tremity is pointed, and only tipped with a costal cartilage, which is free. The Twelfth Rib.— This is a very short bone. Its head has one facet for that on the pedicle of the twelfth thoracic vertebra. The tubercle, angle, and subcostal groove are awanting. The shaft is very narrow, and terminates anteriorly in a pointed extremity, which is merely tipped with a free costal cartilage. The lower border of the shaft has a rough, sharp outUne, and gives attachment to a portion of the quadratus lumborum muscle, whilst the upper border, especially towards the back part, is smooth and round. Fig. 31. — The Eleventh Twelfth Ribs of the Side (Inferior View). AND Left 46 A MANUAL OF ANATOMY Ihe ribs are supplied with blood by branches of the intercostal arteries. Structure. — A rib is composed of loose cancellated tissue sur- rounded by compact bone. Varieties. — (i) The number may be increased to thirteen on one or both sides, and the supernumerary rib may be cervical or lumbar. If cervical, it is d e veloped in connection with the costal process of the seventh cervical vertebra. It may join the shaft of th3 first thoracic rib, or it may reach the sternum. If lumbar, it is developed in connection with the costal element of the first lumbar vertebra, is usually very short, and does not articulate with the body of that . , . . . ^ . ,r vertebra. (2) In rare cases the Appears about Appear about the i6th Year, , il j j t_ the 8th Week .^,-., and join about the number may be decreased by one, (intra-uterine)^ r/^ip, \ 25th Year at the expense of the twehth rib. (3) The ribs are subject to variety in form as follows : (a) the verte- bral end of the first thoracic rib may be joined by a cervical rib, or by the vertebral end of the second rib, in which cases the variety known as bicipital rib occurs; {b) the anterior extremity of a rib may be bifurcated; (c) adjacent ribs may be connected by small plates of bone. Ossification. — ^An ordinary rib has one primary centre and three secondary centres. The primary centre for the shaft appears about the sixth week near the angle. Ossification proceeds so rapidly along the shaft that by the fourth month the shaft is completely ossified. The second- ary centres appear about the six- teenth year. One gives rise to the head, and of the other two one is for the rough part of the tubercle and the other for its articular part. The head and two parts of the tubercle join the shaft about the twenty-fifth year. The two secondary tubercular centres are absent in the eleventh and twelfth ribs. The Costal Cartilages. The costal cartilages, which are composed of hyaline cartilage, are twelve in number on either side. The outer extremity of each is received into the oval pit on the anterior extremity of a rib, and is there maintained in position by the continuity which takes place between the periosteum of the rib and the perichondrium of the cartilage. The inner extremities of the true ribs articulate with the side of the sternum by means of synovial joints, except in the case of the first, which is directly united to the presternum without the intervention of a synovial membrane. The eighth as a rule, ninth, and tenth do not reach the sternum, and they articulate with each other by synovial joints, each cartilage being widened at the place of articulation, where it sends downwards a • process to the upper border of the cartilage below. In this way interchondral joints are formed between these cartilages, as well Fig. 32. — Ossification of a Rib. THE BONES OF THE TRUNK 47 as between the eighth, seventh, sixth, and sometimes the fifth. The eleventh and twelfth cartilages are mere nodules tipping the corresponding ribs, and they have no articulation with each other, nor has the eleventh with the tenth. The cartilages increase in length from the first to the seventh, beyond which they gradually diminish to the twelfth. They diminish in breadth from above downwards. The direction of the first cartilage is inwards and downwards, and that of the second horizontally inwards, whilst the succeeding ones, except the eleventh and twelfth, incline more and more upwards as they pass inwards. Prior to middle Hfe the first costal cartilage undergoes superficial ossification underneath the perichondrium, and so a thin shell of bone is formed around it. In advanced hfe this condition may be met with in the other costal cartilages to a certain extent. C. The Sternum. The sternum or breast-bone is situated in the middle line of the anterior wall of the thorax, where it articulates on either side with the first seven costal cartilages, and superiorly with the clavicle. It occupies an oblique plane, which is directed downwards and forwards, forming an angle with the vertical of about 20 degrees. It is compressed from before backwards, of unequal width at different parts, and more or less curved from above downwards, the convexity being directed forwards, and being very pronounced in the condition known as ' pigeon-breast.' The bone is originally composed of six segments, called sternebrae. The first sternebra forms the manubrium (' handle ') or presternum. The succeeding four sternebrae form the body, gladiolus, or raeso-sternum, and the sixth sternebra forms the ensiform or xiphoid process [xiphi- sternum), otherwise known as the metasternum. The presternum is irregularly four-sided, and broader above than below. It presents two surfaces and four borders. The anterior surface is convex from side to side, and concave from above downwards. It gives origin at either side to a portion of the pectorahs major, and at its upper and outer part to the sternal head of the sterno-cleido mastoid. Between the latter point and the clavicular depression on the upper border it gives attachment to the anterior sterno-clavicular ligament. The posterior surface is concave. At its \ipper and outer part it gives origin to portions of the sterno-hyoid and sterno-thyroid, the former being the higher of the two, and close to the clavicular depression it gives attach- ment to the posterior sterno-clavicular Ugament. The superior border over its middle portion presents the interclavicular or semi- lunar notch, which gives attachment to fibres of the interclavicular ligament. At either side of this there is a large, oval, concavo- convex articular surface for the clavicle, which is directed upwards, outwards, and slightly backwards, an interarticular fibro-cartilage intervening between the bones. Close to the inner end of each. 48 A MANUAL OF ANATOMY clavicular depression there may be found, on the anterior aspect, an ossicle, known as the episternal bone. The inferior border, which is short and straight, articulates with the mesosternum, a disc of fibro-cartilage intervening. In this situation there is a transverse Interclavicular Notch Sterno-cleido-mastoid Pectoralis Major Rectus Abdominis Clavicular Surface Fcr ist Costal Cartilage Fig. 33. — The Sternum (Anterior Surface). elevation, called the sternal angle, which serves as a guide to the second rib at either side. Each lateral border slopes downwards and inwards. The upper part presents a triangular depression for the first costal cartilage, and close to the lower part a demi-facet for a portion of the second costal cartilage. THE BONES OF THE TRUf^R 49 The mesosternum presents two surfaces and four borders. The interior surface is marked by three transverse hnes, which indicate the places of junction of the original four sternebrae. At either side it gives origin to a large portion of the pectorahs major. The posterior surface presents traces of the highest transverse hne, but the lower two have usually become effaced. Adjacent to each lateral border it gives origin to a portion of the triangularis sterni, as high as the level of the third costal facet. Each lateral border presents a series of costal facets, disposed as follows : close to the upper extremity there is a demi-facet for a portion of the second costal cartilage ; opposite each of the three transverse lines there is an entire facet for the third, fourth, and fifth costal carti- lages ; and on the side of the fourth segment of the body there are usually one entire facet and one demi-facet lying close together, the former being for the sixth costal cartilage, and the latter for a portion of the seventh. Altogether there are usually four entire facets and two demi- facets on each lateral border, the demi - facets being situated one at either extremity. Sometimes, however, the inferior demi - facet is replaced by an entire facet for the whole of the seventh costal cartilage. Each of the upper three entire facets is made up of the contiguous demi -facets of two adjacent sternebrae, as in the bodies of most of the thoracic vertebrae. The superior border of the meso- sternum articulates, as stated, with the presternum. The inferior border, which is very narrow, articulates with the metasternum, an intersternebral disc inter- vening until about the fortieth year, when osseous union usually takes place. The metasternum is subject to much variety as regards condition, Fig. 34. — The Sternum (Lateral View). so A MANUAL OF ANATOMV direction, and form. It may be entirely osseous, or osseous above and cartilaginous below. Its typical direction is downwards between the seventh pair of costal cartilages, but it may have an inclination forwards, backwards, or even to one side. It is narrow from side to side, and compressed from before backwards. It may terminate in a thin transverse border, in a sharp point, or in a bifurcated extremity. The anterior surface lies at the bottom of the infrasternal depression. The posterior surface gives origin at either side to a portion of the triangularis sterni, and inferiorly it gives origin to a portion of the diaphragm, usually in the form of two fleshy slips. The superior border articulates with the meso- sternum, and the inferior border gives attachment to the linea alba. Each lateral border usually presents superiorly a demi-facet for a portion of the seventh costal cartilage, but this may be transferred to the fourth segment of the mesosternum. In rare cases there may be an entire facet for the eighth costal cartilage, this being constant in early life. The lateral border gives insertion at either side to some of the fibres of the internal oblique aponeurosis, and occasion- ally, at its upper part, to a portion of the rectus abdominis. The sternum derives its blood-supply from branches of the internal mammary artery. Articulations. — With the clavicle and first seven costal cartilages, at either side. Structure. — The sternum is composed of cancellated tissue covered by a thin layer of compact bone. Varieties. — (i) The sternum is sometimes characterized by its shortness, breadth, and great depression in its lower part. This condition is Uable to be met with in cobblers. (2) A sternal foramen may be present in the mesosternum, usually in the third or fourth segment. (3) A sternal foramen may be present in the metasternum. (4) In very rare cases the sternum may be intersected from end to end by a sternal fissure, in which cases the heart and pericardium are left uncovered (ectopia cordis). (5) The costal cartilages may articulate with the sternum asymmetrically. The Sternum of the Female. — The bone is usually shorter than in the male, the shortness affecting the mesosternum. Ossification. — The sternum ossifies in cartilage from a variable number of centres. There is usually one centre for the presternum, which appears in the sixth month of intra-uterine life. Sometimes there are two, placed one above the other, and there may be as many as six, placed thus • • • The first segment of the mesosternum usually ossifies from one centre, appearing in the seventh month, though there may be two, disposed laterally. The second, third, and fourth segments of the mesosternum usually ossify from two centres each, which are disposed laterally and remain separate for some time, but subsequently unite as a rule. There may, however, be only one mesial centre for each of these segments. In the second segment they appear in the eighth month, in the third just before birth, and in the fourth during the first year. The metasternum ossifies from one centre, which appears in its upper part from the third to the sixth year, though it may be delayed to a later period. The lower three segments of the mesosternum unite in order from below upwards, the union commencing about puberty and being com- pleted shortly afterwards. The first segment of the mesosternum joins the remainder about twenty-five. The metasternum unites with the mesosternum THE BONES OF THE TRUNK 5t about forty, but the presternum usually remains permanently separate unless in advanced life, when it may become ankylosed to the mesosternum. The sternal cartilage from which the bone is developed consists origin- ally of two elongated strips, each of which bears the cartilages of nine ribs. The strips are separated for some time by a median fissure, but fusion sub- sequently takes place, and so a single sternal cartilage is formed. The eighth costal cartilage usually loses its connection with the sternum, though it may articulate permanently with the metastemum. The ninth costal cartilage at either side is regarded as dividing into two parts, one of which .Epistemal Bone ..Appears in the 6th Month (intra-uterine) ^^ I ._— 7th Month ,8th Month 9th Month ist Year /_ 3'd to 6th Year Fig. 35A.- -ossification of the Sternum. Fig. 35B. — Development of . THE Sternum (Modified from Ruge). remains connected with the sternal cartilage and forms with its fellow the metastemum, whilst the other acquires a connection with the eighth costal cartilage. If the parts of the ninth costal cartilages, which remain connected with the sternal cartilage, do not unite with each other over their whole extent, a bifurcated metastemum is the result. They usually, however, unite wholly, or sometimes in such a manner as to leave a foramen at the centre. A sternal fissure is due to the permanent separation of the two original car- tilaginous strips, which, as a rule, unite to form the sternal cartilage. A sternal foramen in the second, third, or fourth segment of the mesosternum is due to ossification from two collateral centres failing to meet at the median line. Sometimes two ossicles, called the epistemal bones, are met with at either side of the interclavicular notch of the sternum. These are developed in connection with the suprasternal ligaments, which extend between the inner end of each clavicle and the upper end of the sternum. The Thorax as a Whole. The thorax constitutes an osseous and cartilaginous cage which lodges the heart and lungs, along with important bloodvessels and nerves, as well as the trachea and oesophagus. It is bounded anteriorly by the sternum, with the costal cartilages and anterior extremities of the first eight or nine ribs ; posteriorly by the bodies of the thoracic vertebrae and the vertebral extremities of the ribs 52 A MANUAL OF ANATOMY from the heads to the angles ; and laterally by the ribs beyond their angles. It is conical, the truncated apex being directed upwards, and it is somewhat flattened from before backwards. The superior aperture is bounded in front by the upper border of the presternum and the first costal cartilages, on either side by Fig. 36. — The Thorax (Anterior View). the first rib, and behind by the body of the first thoracic vertebra. Its transverse measurement exceeds the antero-posterior, and it is reniform, due to the forward projection of the first thoracic body. Its plane is oblique, being sloped downwards and forwards, so that the upper border of the presternum is on a level with the disc between the second and third thoracic bodies. The superior THE BONES Of THE TRUNK 55 aperture transmits the following structures : the apical parts o! the lungs and pleura;, the trachea and oesophagus, the pneumo- gastric, sympathetic, and phr^iic nerves, the terminal part of the innominate artery, the left common carotid and left subclavian arteries, and the right and left innominate veins. In early life it also transmits the thymus gland. The inferior aperture is of large size, and is boimded posteriorly by the twelfth thoracic body, laterally by the twelfth rib at either side, and anteriorly by a line, at either side, connecting the costal cartilages from the twelfth to the seventh inclusive. These two lines constitute the subcostal angle, within which the metastemum is situated. The inferior aperture is occupied by the diaphragm, which presents certain openings for the passage of important structures. The cavity, on either side of the thoracic bodies, presents an elongated groove, called the pulmonary groove, which lodges the thick posterior border of a lung. The cavity has the following diameters, namely, vertical, transverse, and antero-posterior. The vertical diameter extends from the superior aperture to the inferior. The transverse diameter extends from the centre of a given inter- costal space to the centre of the corresponding space of the opposite side. The antero-posterior diameter extends from the anterior to the posterior wall, and is necessarily of less extent in the median line than at either side, on accovmt of the projection formed by the thoracic bodies, its increase at each side being due to the presence of the pulmonary groove. The cavity is increased in all these diameters during inspiration, and diminished during expiration. The intercostal spaces are eleven in number at either side. They increase in length from the first to the fifth, and are occupied for the greater part of their extent by the external and internal inter- costal muscles. The thorax of the female is rather shorter than that of the male, and is not so much flattened from before backwards. In early life the thorax is flattened from side to side, and its height is relatively less than in the adult. The Notoehord and the Development of the Vertebral Column, Ribs, and Sternum. Notoehord. The notoehord forms the primitive basis of the axial skeleton, and around it the bodies of the vertebrae are developed. It is a soUd cylindrical rod of cells, derived from the cephalic end of the primitive streak, and it occupies the median line, corresponding to the centres of the bodies of the future vertebrae. It Ues along the ventral aspect of the neural tube, which con- stitutes the primitive tubular nervous sj-stem, and along the dorsal aspect of the archenteron, or primitive intestinal cax-ity-. The cephalic end of the notoehord is situated on the ventral aspect of the mid-brain, and corresponds to the posterior part of the pituitary region of the base of the future cranium. From this region it extends to the caudal end of the future axial skeleton, 54 A MANUAL OF ANATOMY where it is continuous with the wall of the neurenteric canal. On either side of it there are the mesodermic somites. The notochord is of temporary duration, and a considerable part of it is replaced by the bodies of the vertebrae. Certain vestiges of it, however, persist throughout life, these being represented by the central pulp of the inter- vertebral discs. Development. — The notochord is developed from the entoderm. Its development may be considered under three stages — namely, (i) the formation of the notochord al plate, (2) the conversion of this plate into the notochordal tube, and (3) the solidifi- cation of this tube to form the notochord. First Stage. — The cells of the entoderm along the dorsal or upper wall of the archenteron (beneath the neural tube) become thickened, and so form the notochordal plate. Second Stage. — (i) The notochordal plate be- comes curved; (2) its lateral margins incline ventrally or downwards; and (3) they turn inwards and meet at the median line on the ventral aspect of the notochordal plate. In this manner the notochordal tube is formed. Third Stage. — -The notochordal tube is at first hollow. The cells of its walls, however, are pro- liferous, and by an increase in their number the lumen of the tube becomes occluded, and the fully-developed notochord is formed as a solid cylindrical rod. '■■ m Odontoid Process Notochord passing through Primitive Body Swelling between two Primitive Bodies Fig. 37. — The Noto- chord (Cervical Region). Development of the Vertebral Column. The notochord forms the axis round which the vertebral column is developed, and the formation of the notochord may be regarded as constituting the first or notochordal stage. The notochord and the neural tube, which lies along its dorsal aspect, become surrounded by mesenchyme (mesoderm), and this undergoes chondrification and subsequently ossification. As the process of ossification proceeds, a great part of the notochord becomes con- stricted at regular intervals, where the bodies of the vertebrae are undergoing ossification, and these portions of it ultimately disappear. The parts of it, however, round which the intervertebral discs are formed persist and con- stitute the central pulp of each disc, as stated. In addition to the notochordal stage of development, there are three other stages — namely, membranous, cartilaginous, and osseous. Membranous Stage. — The notochord and neural tube become surrounded, as stated, by a mesenchyme, which forms a membranous sheath, spoken of as the skeletogenous sheath. This sheath constitutes the primitive membranous vertebral column. It is derived from the sclerotomes of the mesodermic somites which lie along either side of the notochord. Each sclerotome is the innermost segment of a somite, and the successive sclerotomes he serially on either side of the notochord and close to it. They are formed of mesenchyme, and their cells multiply very rapidly. As they do so, they extend ventralwards, dorsalwards, cephalicwards, caudalwards, and mesially, between the notochord and the neural tube. In this manner the notochord becomes surrounded by a sheath. On either side this sheath furnishes two prolongations, which pass dorsalwards, one on either side of the neural tube, and meet over its dorsal aspect. There are thus formed continuous sheaths for the notochord and neural tube, and so the chordal or skeletogenous sheath is formed. The cells of the sclerotomes also extend in an outward direction, and these lateral extensions he between, and separate, contiguous muscle-segments, each of these being a segment of a mesodermic somite, in which it lies external to the sclerotome. These lateral extensions are called the intersegmental septa, or li^amenta intermuscularia. THE BONES OF THE TRUNK 55 The skeletogenous sheath soon acquires great density at regular inte^^'als— namely, opposite the intersegmental areas, which Ue between the muscle- segments. Each of these dense parts is curved, somewhat hke a horse- shoe, and is knovin as the Tertebral bow, or seleromere. The central part of the bow lies on the ventral aspect of, or below, the notochord and is caUed the hypoehordal bar. The lateral extremities of the bow divide each mto wo Umbs dorsal and ventral. The dorsal iimbs. called the neural pre cesses, right and left, extend dorsalwards. one on either side of the neural tube, on Nennl Tube Neural Proces' Costal Process ' ' ^^Sj^^S^f- -^ Vertebral Bow Chordal Sheath ■' ] Notochoid Hypocbordal Bar Fig. 38. — ^Thb Vertebral Bow (Schematic). the dorsal aspect of which they meet. They form the primitive neural arehes of the vertebrae. The vetilral limbs, called the eost&l processes, extend ven- tralwards on either side. In the thoracic region they form the primitive ribs; in the cervical region, the primitive costal processes of the cer%ical vertebrae; in the lumbar region, the primitive transverse processes (costal elements) of the lumbar vertebrae ; and in the sacral region tiiey form the primitive costal elements of the upper three sacral vertebrae. The vertebral bows £ire ztrranged in regular series, opposite the interseg- mental areas, each ha\-ing on either side a neural process passing dorsal- wards, and a costal process extending ventralwards. The neural processes, right and left, of a vertebral bow, as just stated, meet on the dorsal asjject of the neural tube, and they form the primitive neural arch of a vertebra The costal processes, as just stated, give rise to the following parts : Thoracic Region : Lumbar Region : The Bibs. Transverse Processes (Costal Elements). Cervical Region : Sacral Region : The Costal Processes. Costal Elements of Upper Three Sacral Vertebrae. The hypoehordal brace or bar (central part of the vertebral bow) dis- appears, except in the atlas, of which it forms the anterior arch. Cartilaginous Stage.— The skeletogenous sheath undergoes chondrification at regular intervals opposite the intersegmental areas and the portions of the muscle-segments which limit these areas, or, it may be. entirely opposite the muscle-segments. In each part two nodules of cartilage appear, one on each side of the notochord. These rapidly surround the chord, and so form the cartilaginous body of a vertebra. The neural processes of the lateral extremi- ties of a vertebral bow, which lie on either side of the neural tube and coalesce along its dorsal aspect, also undergo chondrification jmd form the cartilaginous neural arch of a vertebra, as well as the processes connected with that arch. In this manner a cartilaginous sheath is constructed for the neural tube, which tube to a large extent becomes converted into the spinal cord. 56 A MANUAL OF ANATOMY The skeletogenous (mesencliymatous) tissue between the cartilaginous bodies of successive vertebrae forms the intervertebral discs, and the skeletog- enous tissue between the successive cartilaginous neural arches forms the ligamenta subflava. Osseous Stage. — For the stage of ossification see Ossification Of the Verte- brae. Development of the Ribs. The ribs are developed from the mesenchyme of the costal processes of the lateral extremities of the vertebral bows in the thoracic region, which pro- cesses invade the intersegmental septa or ligamenta intermuscularia between contiguous muscle-segments. They are at first curved membranous rods, which subsequently undergo chondrification and form the cartilaginous ribs, these in turn undergoing ossification, and giving rise to the osseous ribs. They are intersegmental in position, and are confined to the thoracic region of the trunk. In the other regions their development is arrested, but rudi- ments of them persist. Thus, as stated, in the cervical region they are repre- sented by the costal processes of cervical vertebraj; in the lumbar region, by the transverse processes (costal elements) of lumbar vertebrae; and in the sacral region, by the costal elements of the upper three sacral vertebrae. Development of the Sternum. The ventral extremities of the upper nine cartilaginous ribs, on either side, become expanded, and these portions unite. In this manner an elongated strip of cartilage is formed on either side, each of which bears nine cartila- ginous ribs. These strips are known as the hemisternal cartilages, and by their union a single sternal cartilage is formed. This cartilaginous sternum undergoes ossification in the manner described in connection with the sternum as a bone. " The eighth and ninth cartilaginous ribs, on either side, lose their connec- tion with the hemisternal cartilages, and the portions of these hemisternal cartilages, which are contributed by the expanded ventral or anterior ends of the eighth and ninth cartilaginous ribs, give rise, by their union, to the cartilaginous metasternum (ensiform process). In exceptional cases ossification may take place in each hemisternal cartilage independently, and under these circumstances the hemisterna may remain permanently separate, thus giving rise to the extremely rare con- dition of sternal fissure. The two halves of the cartilaginous metasternum usually unite along their entire extent. Their distal ends, however, may remain permanently separate, and so give rise to a bifurcated metasternum. Again, the two halves may unite in such a manner as to leave a permanent metasternal foramen. The presence of a sternal foramen is explained under Varieties of the Sternum. n— THE BONES OF THE HEAD. The head or skull is supported on the upper end of the vertebral column, and is divisible into the cranium and face. The cranium or brain-case is composed of eight bones, namely, the occipital, two parietals, frontal, two temporals, sphenoid, and ethmoid. The face, which protects organs of special sense, such as the eyes, the olfactory mucous membrane, and the tongue, is composed of the following fourteen bones, the majority of which are arranged in pairs : the two superior maxillae, two malars, two nasals, two lachrymals, two inferior turbinates, two palate bones, the vomer, and the inferior maxilla. All the bones of the skull, except the inferior maxilla, are immovably united by sutures. THE BONES OF THE HEAD 57 The Occipital Bone. The occipital bone is so named because it is situated against the posterior and inferior parts of the cranium. It is quadrilateral and curved, its long axis extending from above downwards and forwards. At its lower and anterior part there is a large opening, called the foramen magnum, by which the cranial cavity communicates with the spinal canal. The bone is divisible into four parts, which meet around this opening. The part behind is called the tabular portion, that in front ihe basilar process, and the part at either side the condylar portion. The tabular portion presents two surfaces, three angles, and four borders. The posterior or external surface is convex and projected at its centre into the external occipital protuberance, from which a median ridge, called the external occipital crest, passes dowTiwards and forwards to the foramen magnum. The protuberance and crest give attachment to the ligamentum nuchae. Arching outwards on either side from the protuberance to the lateral angle there is the superior curved line, the convexity of which is directed upwards. The two lines with the protuberance divide this surface into an upper or interparietal and a lower or supra-occipital part. A little above each superior curved line there is the highest curved line, which has a bold cur\'e with the convexity upwards, and gradually subsides in the superior curved line externally. Between these two lines there is a semilunar area, over which the bone is smooth and dense. The highest curs-ed line gives attachment to the epicranial apo- neurosis internally, and to fibres of the occipitalis externally. The superior curved line gives origin over about its inner third to the trapezius, and externally to fibres of the occipitalis, whilst over its outer half, or more, it gives insertion to the stemo-cleido-mastoid, immediately below which the splenius capitis is inserted over about the outer third. The portion of this surface above the highest curved lines is smooth, convex, and covered by the epicranial apo- neurosis. The portion below the superior curved lines, which is rough and irregular, is divided into two equal lateral parts by the crest, and each of these is subdivided into an upper and lower portion by the inferior curved line, which extends from the centre of the crest to the extremity of the jugular process. The space between the superior and inferior curved lines gives insertion internally to the complexus, and externally, from above down- wards, to the splenius capitis and obliquus capitis superior. The inferior curved line gives insertion over its outer part to the rectus capitis posticus major. The inner third of this line and the surface between that extent of it and the foramen magnum give insertion to the rectus capitis posticus minor. The anterior or internal surface is irregularly concave and divided into four fossae by two ridges— a longitudinal, extending from the superior angle to the foramen magnum, and a transverse, extending from one lateral angle to the other. At the point where these two 58 A MANUAL OF ANATOMY ridges intersect there is the internal occipital protuberance. The upper half of the longitudinal ridge gives attachment to a portion of the falx cerebri, and is marked by a groove for the superior longi- tudinal venous sinus, this groove being confined to one side of it, usually the right. The lower half is sharp and wiry, and is called the internal occipital crest. It gives attachment to the falx cerebelli, Upper or Interparietal part of Tabular Portion External Occipital Crest Highest Curved Line ,^ Complexus Rectus Capitis Posticus Minor^s Obliquus Capitis Superior Rectus Capitis Posticus Major Rectus Capitis Lateralis Posterior Condylar Fossa and Foramen (latter inconstant) ' Anterior Condylar P'oramen Rectus Capitis Anticus Minor ■' Rectus Capitis Anticus Major External Occipital Protuberance ' Trapezius • Superior Curved Line /\ii\ U^> Inferior Curved Line ^7v\™Bi11 . /^/Occipitalis Stemo-cleido-mastoic Splenius Capiti Lateial AngL Inferior Lateral Border of Tabular Portion Jugular Process Jugular Notch Condyle Pharyneeal Tubercle on Basilar Process Fig. 39. — The Occipital Bone (External View). and is occasionally grooved for the occipital venous sinus. Near the foramen magnum it divides into two parts, which diverge as they pass to that opening, and enclose between them the vermiform fossa, which receives a part of the vermiform process of the cere- bellum. The transverse ridge gives attachment to the tentorium cerebelli, and is deeply grooved along each half for the lateral venous sinus. On one side of the internal occipital protuberance, usually THE BONES OF THE HEAD 59 the right, there is a wide depression, at which point the longitudinal groove is continued into the corresponding lateral groove. This depression lodges the torcular HerophUi, which is a dilatation formed where the superior longitudinal sinus bends sharply to become continuous with the right lateral sinus. The four fossae are arranged in a superior pair, called superior occipital or cerebral, and an inferior pair, called inferior occipital or cerebellar. Each cerebral fossa presents a number of digitate impressions for the convolutions of the occipital lobe of the cerebrum, which is lodged in it. The cerebellar fossae, which are separated by the internal occipital crest, are smooth, but may show transverse striations. They are much thinner than the cerebral, and lodge the hemispheres of the cerebellum. The angles are superior and two lateral. The superior angle forms the highest part of the bone, and fits in between the postero- superior angles of the parietals. The lateral angles are situated at either end of the transverse ridge on the internal surface. The borders are two superior and two inferior. Each superior border extends from the superior angle to the lateral angle, and is serrated for the posterior border of the corresponding parietal. Each inferior border extends from the lateral angle to the jugular process, and is faintlv serrated for the mastoid portion of the temporal. The basilar process (basi-occipital) is a compressed quadrilateral mass, which projects forwards and upwards in front of the foramen magmmi. Its superior surface presents a broad median depression, called the basilar groove, which is sloped dovs-nwards and back- wards to the foramen magnum, and lodges the medulla oblongata. At either side of this groove there is a narrow groove for the inferior petrosal venous sinus The inferior surface presents at its centre the pharyngeal tubercle for the fibrous raphe of the phar^Tix. On either side of this tubercle there is a rough, oblique impression for the insertion of the rectus capitis anticus major, and between the outer part of this impression and the foramen magmun the surface gives insertion to the rectus capitis anticus minor. The anterior border is thick, rough, and truncated, and up to the twentieth year it articulates with the body of the sphenoid by synchon- drosis, but thereafter ankylosis takes place. The posterior border, which is thin, smooth, and concave, bounds anteriorly the foramen magnum, and sometimes presents a third occipital condyle of small size for articulation with the tip of the odontoid process of the axis. This border gives attachment to the middle odontoid or suspensory ligament. Each lateral border is thick and rough for the petrous portion of the temporal. The condylar portions (exoccipitals) are placed on either side of the foramen magniun, where they extend as far back as its posterior margin, and very nearly as far forwards as its anterior margin. Each bears on its under surface a condyle. The condyles are oval, convex, and covered by cartilage, and they articulate with the superior articular processes of the atlas. Their long axes are 6o A MANUAL OF ANATOMY directed forwards and inwards, and the direction of each surface is downwards and slightly outwards. They do not extend farther back on the lateral margins of the foramen magnum than the level of the centre, and the front part of each belongs to the basilar portion. The circumference of a condyle gives attachment to the capsular ligament of the corresponding occipito-atlantal joint, and on the inner aspect of each there is a tubercle for the lateral odontoid or check ligament. External to the front of each condyle is the Superior Angle Depression for Torcular Herophili Superior Lateral Bortler Groove for Superior Longitudinal Sinus Cerebral Fossa ^.Internal '' Occipital Protuberance Lateral Angle Inferior Lateral Border Posterior Condylar >- Foramen Cerebellar Fossa -Vermiform Fossa .,Groove for Lateral Sinus •'Jugular Process Jugular Notch Basilar Groove Basilar Process Fig. 40. — The Occipital Bone (Internal View). anterior condylar foramen, which opens forwards and outwards from the cranial cavity. It transmits the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery. Behind each condyle is the posterior condylar fossa, which may be pierced by a posterior condylar foramen, on one or both sides, for an emissary vein passing between the intracranial lateral sinus and the extracranial suboccipital venous plexus. The part external to the condyle is called the jugular process, which lies above the TH£ 60A?£^ OF THE HEAD 6l transverse process of the atlas, and is homologous with it. Pos- teriorly it is continuous with the tabulcir portion, and anteriorly it presents the jugular notch, which, with the jugular fossa of the petrous portion of the temporal, forms the jugular foramen. Superiorly it presents a short, but deep and \\-ide, groove for a portion of the lateral venous sinus just before it leaves by the jugular fora- men. This groove may be pierced by a posterior condylar fora- men. Interiorly it gives attachment to the rectus capitis lateralis, and ma}' send downwards a projection towards the transverse process of the atlas, which represents the paramastoid process of com- parative anatomy. Externally the jugular process articulates with the jugular facet on the petrous portion of the temporal by synchon- drosis up to the twenty-fifth year, after which ankylosis takes place. The foramen magnum is situated at the lower and anterior part of the bone, and is oval, its long axis extending from before back- wards. The inferior margin, in front of the condyles, gives attach- ment to the anterior occipito-atlantal ligament, and, behind them, to the posterior occipito-atlantal ligament. The foramen transmits the medulla oblongata and its membranes, the spinal accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and parts of the cerebellar amygdalae. The chief blood-supply of the bone is derived from the occipital and posterior auricular arteries. Articulations. — Superiorly with the parietals, laterally with the temporals (mastoid and petrous portions), anteriorly with the sphenoid, and inferiorly with the atlas, and in rare cases with the odontoid process of the axis. Structure. — The occipital, being a tabular bone, is composed of two tables of compact bone, with cancellated tissue, called diploe, between them. Varieties. — (i) There may be a minute foramen piercing the external occipital protuberance for an emissary vein, which passes between the intra- cranial torcular HeropMli and one of the tributaries of the extracranial occipital vein. (2) The upper di\-ision of the tabular portion mav be separate, representing the interparietal bone of comparative anatomy, and it may be in one piece, or in two or more. (3) The semilunar area between the highest and superior curved hnes may be prominent, constituting the torus occipitalis transversus. (4) The anterior condylar foramen may be double on its cranial aspect. (5) There may be a third occipital condyle on the anterior margin of the foramen magnum. (6) There may be a paramastoid process on the under aspect of the jugular process. (7) The condyle may be di\'ided into two parts, anterior and posterior. (8) There may be an intrajugular process on the front of the jugular notch, which mav extend as far as the petrous portion of the temporal. Ossification. — The bone is developed in four parts. The tabular portion usually ossifies from four centres, which appear around the internal occipital protuberance about the eighth week of intra-uterine life. Two are deposited in cartilage, one for each cerebellar fossa, which soon fuse and give rise to the lower or supra-occipital division. The other two are deposited in membrane, one in each cerebral fossa, which also soon fuse and give rise to the upper or interparietal division. Indeed, as a general rule, all four ultimately blend. There may, however, be two other centres for the interparietal portion, placed 62 A MANUAL OF ANATOMY on either side of the middle hne not far from the future superior angle, which occasionally remain as separate ossicles, or they may fuse and give rise to the pre-interparietals. The interparietal portion may remain separate from the supra-occipital, with which it may be connected by a suture, or they may be separated by a partial fissure. Fissures, which persist for some time after birth, intersect the tabular part at the superior and lateral angles, and a membranous interval extends from the protuberance to the foramen magnum in early life, which remains for some weeks, after which it is replaced by bone. It is in this latter situ- ation where an ence- phalocele may occur. The basilar and con- dylar parts have each one centre appearing in cartilage about the ninth week, the an- terior part of each condylar portion de- riving its ossification from the basilar cen- tre. At birth the bone is in four parts, con- nected by cartilage. Union between the tabular and condylar portions is completed by the fourth year, and the condylar and basilar portions unite about the sixth year. After the twentieth year _ , Tabular Part. 4 Centres, which appear about the 8th Week (intra-uterine) — Obstetrical Hinge-joint of Budin ^ Condylar Part, i Centre, which appears about the 9th Week (intra-uterine) Basilar Part, i Centre, which appears about the gth Week (intra-uterine) Fig. 41. — Ossification of the Occipital Bone. (The figure shows the condition of the bone at birth.) the basilar portion joins the sphenoid, and at the twenty-fifth year the jugular process becomes ankylosed to the petrous portion of the temporal. Obstetrical Hinge-Joint of Budin. — At birth the tabular or squamous portion of the occipital bone is connected with the two condylar portions by a band of cartilage. This region is known as the obstetrical hinge- joint of Budin. The connection is such as to allow of Hmited swinging or see-saw movements in front of, and behind, the cartilaginous band, by which movements the dia- meters and form of the child's head are liable to be modified during labour. The Parietal Bones. The parietal bones are so named because they form a large part of the cranial wall. They lie between the frontal and occipital, and superiorly they articulate with each other by the sagittal or interparietal suture. Each bone is quadrilateral and curved, and presents two surfaces, four borders, and four angles. The external surface is convex, and near its centre is more elevated than elsewhere, this part, from which ossification originally proceeds, being called the parietal eminence. A little below this the surface is crossed from before backwards by two curved lines, called the superior and inferior temporal ridges, the narrow space between which is smoother and more glistening than the rest of the surface. The part above the superior ridge is covered by the iepicranial aponeurosis, and the ridge itself gives attachment to the temporal fascia. The inferior temporal ridge limits the origin of the THE BONES OF THE HEAD 63 temporal muscle, and the portion between it and the inferior border, which is vertically striated and called the planum iemporale, forms a part of the temporal fossa, and gives origin to fibres of the temporal muscle. Near the superior border, about an inch in front of the postero-superior angle, is the parietal foramen, for an emissary vein which passes between the intracranial superior longitudingil sinus and one of the tributaries of the extracranial occipital vein. The internal surface is concave, its deepest part, opposite the parietal eminence, being known as the parietal fossa. This siu-face presents a number of digitate impressions for the convolutions of Superior Border Parietal Foramen Anterior Border Posterior Border Superior Temporal Ridge Inferior Border Inferior Temporal Ridge Fig. 42. — The Right Parietal Bone (External View). the parietal and part of the frontal lobes of the cerebrum, and a system of branching meningeal grooves for the divisions of the middle meningeal artery. These commence as two grooves, each of which soon becomes arborescent. The anterior, the larger of the two, commences on the inner surface of the antero-inferior angle, where it may be bridged over into a short canal, and the posterior starts from the centre of the inferior border. Superiorly, close to the superior border, there is a half groove which, ^^dth that of the opposite bone, lodges the superior longitudinal venous sinus. Along the course of this groove, but external to it, are several depressions, best marked in old persons, which lodge the 64 A MANUAL OF AN ATOM V Pacchionian bodies. Close to the postero-inferior angle there is a short groove for part of the lateral venous sinus. Borders. — The posterior, anterior, and superior borders are serrated. The posterior border articulates with the occipital ; the superior, with its fellow ; and the anterior with the frontal. The anterior border is bevelled below at the expense of the inner plate, where it overlaps the frontal, and it is slightly bevelled above at the expense of the outer plate, where it is overlapped by the frontal. The inferior border, which is the shortest, is for the most part concave and markedly bevelled at the expense of the outer plate, Superior Border and Groove for Superior Longitudinal Sinus Pacchionian Depressions Parietal Foramen Anterior... Border Antero-inferior Angle Anterior Meningeal Groove Posterior Meningeal Groove at Inferior Border Postero-inferior Angle Groove for Lateral Sinus Fig. 43. — The Right Parietal Bone (Internal View). where it is overlapped by the squamous portion of the temporal. Posteriorly, however, it is serrated for the superior border of the mastoid portion of the temporal. Angles. — The antero-superior angle, with its fellow, lies in the situation of the original anterior fontanelle. The postero-superior angle, with its fellow, occupies the region of the original posterior fontanelle. The postero-inferior angle is truncated, and articulates with the mastoid portion of the temporal, being also recognised by the short groove for the lateral venous sinus on its inner aspect. The antero-inferior angle is prolonged and pointed, and articulates with the great wing of the sphenoid, bein^ also THE BONES OF THE HEAD 65 recognised by the large anterior meningeal groove on its inner surface. The bone receives its chief blood-supply from the middle meningeal artery internall}^ and the occipital externally. Articulations. — Posteriorly with the occipital, superiorly with its fellow, anteriorly with the frontal, antero-inferiorly with the sphenoid, and inferiorly with the temporal. Structure.— It is a characteristic tabular bone. Varieties. — (i) The bone may persist in two parts, upper and lower, con- nected by an antero-posterior suture. (2) The parietal foramen may be absent on one or both sides. Ossification. — The parietal ossifies in membrane from two centres, which apgear about the seventh week in the region of the future parietal eminence, one above and the other below it, and soon coalesce. The ossification radiates - . Appear about the ^ 7th Week Jj (intra-uterine) Fig. 44. — Ossification of the Parietal Bone. from this point in such a manner as to leave a notch on the upper border a little in front of the postero-superior angle, which forms one-half of the sagittal fontanelle of the earlier half of foetal life. The Frontal Bone. The frontal bone forms the forehead and greater part of the roof of each orbit, and it lies in front of the parietals. It is divisible into a frontal portion and two orbital plates, the latter being situated inferiorly, where they are separated by the ethmoidal notch. The frontal portion presents two surfaces, external and internal. The external surface, which is smooth and convex, presents a little below its centre, on either side, an elevation, called the frontal eminence. Below this, and separated from it by a shallow groove, there is the curved superciliary ridge which supports the eyebrow. This ridge is prominent internally, but it subsides externally. It supports the upper half of the orbicularis palpebrarum, and internally it gives origin to the comigator supercilii, whilst the surface above each ridge supports the frontalis and part of the epicranial aponeurosis. Between the two superciliary ridges is an elevation, called the nasal eminence or glabella. Below each ridge is the curved supra-orbital arch, which is most prominent over its 66 A MANUAL OF ANATOMY outer two-thirds. At the junction of the inner third and outer two- thirds is the supra-orbital notch, sometimes a foramen, for the passage of the supra-orbital nerve and artery. Occasionally there is a frontal notch, inside the normal notch, for a branch of the supra-orbital nerve. The extremities of the supra-orbital arch form the external and internal angular processes. The external process is stout and serrated for articulation with the malar. The internal process is faintly marked, and lies by the side of the nasal Parietal Border I Superior Temporal Ridge Inferior Temporal Ridge Frontal Eminence Temporal Surface for Temporal Muscle Lachrymal Fossa Glabella Nasal Process ^External \ Angular Process Superciliary Ridge Supra-orbital Notch Internal Angular Process Nasal Spine Fig. 45. — The Frontal Bone (Anterior View). notch, where it articulates with the lachrymal, and gives origin to "some fibres of the orbicularis palpebrarum. On the lateral aspect of the external surface there are two curved lines, called the superior and inferior temporal ridges, the superior being faint and the inferior bold. They spring from the external angular process, and arch upwards and backwards to become con- tinuous with the corresponding ridges on the parietal. The superior gives attachment to the temporal fascia, and the inferior limits the temporal muscle, which arises from it and the surface below, this latter forming a paf t of the temporal fossa. Below the glabella THE BONES OF THE HEAD 67 on the under aspect there is a rough, semilunar, serrated surface for articulation with the nasal bones and nasal processes of the superior maxillae, and behind this is the nasal notch, bounded at either side by the internal angular process. Within the notch is the nasal process, which supports the nasal bones, and projecting downwards from it is the sharp nasal spine, which articulates in front with the upper part of the crest of the nasal bones, and behind w th the vertical plate of the ethmoid. This spine enters into the nasal septmn. On either side of the spine is the ala, which is grooved to take part in the roof of the corresponding nasal fossa. The internal or cerebral surface of the frontal portion is concave, and in the middle line presents a groove, called the frontal sulcus, which lodges a part of the superior longitudinal venous sinus. On either side of the upper pait of this groove there are a few depressions for the Pacchionian bodies. In'eriorly the groove is replaced by the frontal crest, which terminates at the foramen caecum. This foramen is sometimes partly formed by the crista galli of the ethmoid, and it may be closed below, or it may transmit an emissary vein, which passes between the intracranizd superior longitudinal sinus and the veins of the roof of the nose. The internal surface presents numerous digitate impressions for the convolutions of the frontal lobes of the cerebrum, and laterally there are a few meningeal grooves, transversely disposed, for branches of the middle meningeal arteries. The supero-laiera! or parietal border of the frontal portion is serrated for the parietal bones. Superiorly it is slightly bevelled near the middle line at the expense of the inner plate, where it over- laps the parietal, and at either lower extremity it is distinctly bevelled at the expense of the outer plate, where it is overlapped by the parietal. Internal to its lower termination at either side there is a rough triangular surface, which is serrated for the great wing of the sphenoid. The orbit^ plates, thin and brittle, project backwards in a curved manner from the supra - orbital arches, and are widely separated by the ethmoia^ 1 notch, which is occupied by the cribri- form plate of the ethmoid. Each is triangular, with the truncated apex directed backwards and inwards, and presents two surfaces and three borders. The superior or cerebral surface is irregularly convex, and marked by digitate impressions for the convolutions of the orbital surface of the frontal lobe, which rests upon it. The inferior or orbital surface, smooth and concave, forms the principal part of the roof of the orbit. Within the external angular process is the lachrymal fossa, which lodges the lachrj-mal gland, and near to the internal angular process is the small trochlear fossa, which gives attachment to the trochlea of the superior oblique muscle of the eyeball. The borders are anterior, external, and internal. The anterior border represents the supra-orbital arch, and is free. The external border is sharp and irregular, and its diiection is backwards and 68 A MANUAL OF ANATOMY inwards. It forms a right angle with its fellow of the opposite side, and abuts against the great wing of the sphenoid. The internal border is directed from before backwards, is parallel with its fellow of the opposite side, and forms the lateral boundary of the ethmoidal notch. It is bevelled at the expense of the lower plate, and the bevelled surface presents several excavations, which close in the ethmoidal cells on the upper border of the lateral mass of the ethmoid. This surface is crossed by two transverse grooves, anterior and posterior, which, with similar grooves on the contiguous part of the ethmoid, form the anterior and posterior ethmoidal (internal orMtal) canals. These open on the inner wall Nasal Spine Ala For Nasal Process of Superior Maxilla ^ Frontal Sinus Trochlear Fossa Frontal Crest and Ethmoidal Notch Nasal Notch Groove for Ant. Ethmoidal Canal Supra-orbital Notch Orbital Plate / ' Lachrymal Fossa Ext. Angular Process Surf, for Great Wing of Sphenoid For Small Wing of Sphenoid Groove for Posterior Ethmoidal Canal Parietal Border Fig. 46. — The Frontal Bone (Inferior View). of the orbit, and the anterior gives passage to the nasal nerve and anterior ethmoidal vessels, whilst the posterior transmits the posterior ethmoidal vessels and spheno- ethmoidal nerve. The truncated apex of the orbital plate articulates with the small wing of the sphenoid. In front of the anterior ethmoidal groove on either side is the opening of the frontal air sinus. Each leads into a cavity within the bone, which extends outwards from near the middle line for a variable distance behind the superciliary ridge. The sinuses are separated by a median septum, and may be unilocular or multi- locular. In the latter case the subdivisions may extend back- THE BONES OF THE HEAD 69 wards for a variable distance within the roof of the orbit. Each sinus is lined by mucous membrane continuous with that of the corresponding nasal fossa, wdth which it communicates by a passage called the infuadibulum. The bone derives its blood-supply from the middle meningeal, meningeal branches of the internal carotid, and anterior and posterior ethmoidal arteries internally, and the supra-orbital and frontal arteries externally. Articulations.— These are twelve in number, as follows : pos- teriorly with the two parietals above, and the sphenoid (great and small wings) below ; by the external angular processes with the two malars ; between the orbits with the two nasals, two superior maxillae, and two lachr^nnals ; and in the middle line vdth the lateral masses and vertical plate of the ethmoid. Structure. — It is a tabular bone. The orbital plates, being destitute of diploe, are thin and translucent, except in those cases where extensions of the frontal air sinuses invade them. Varieties. — (i) There may be a persistent frontal suture, called the metopic suture, this condition being known as metopism. (2) Wormian bones are sometimes met vdth at the centre of the supero-lateral border in the region of the anterior fontanelle, and, if these remain permanent, they give rise bj- their union to a breg matic bone. Ossification. — The frontal ossifies in membrane from two centres, one for each half, which appear about the seventh week of intra-u ferine Ufe in the situation of the future frontal eminences. At birth the bone con- sists of two halves united by mem- brane, and in the course of the first year they become united by a vertical frontal or metopic suture. This suture gradually becomes ob- literated from below upwards, and usually disappears about the sixth year, though shght traces may persist above and below, especially in the latter situation. Three pairs of secondary centres are described, two mesiaUy placed for the nasal spine, one at either side in the region of the future trochlear fossa, and one for each external angular process. The frontal air sinuses begin to appear about the seienth year, but ihey do not attain any size till after puberty. They axe rather larger in the male than in the female. Fig. Appears about the 7th Week (iDtia-uterine) 47. — Ossification of the Frontal Bone. The Temporal Bones. The temporal bones (ossa temporis) are so named because the hair over the temple is the first to become gray, thus indicating advance in life Each bone is situated on the lateral aspect of the head below the parietal. For convenience of description each is divided into three parts, namely : the squamous portion, which bears the ;o A MANUAL OP ANATOMY zygoma ; the mastoid portion ; and the petrous portion^ which bears inferiorly the styloid process. The squamous portion (squamo-zygomatic) hes almost vertically, and presents two surfaces, outer and inner, and a superior border. The outer surface is convex towards its centre, and forms a large part of the temporal fossa. It gives origin to fibres of the temporal muscle, and is marked by a groove for the middle temporal artery, which extends upwards and slightly forwards from a point just above the external auditory meatus to the superior border. The inner surface, which is concave, is related to the temporo-sphenoidal lobe of the cerebrum, and presents a few digitate impressions and meningeal grooves. The superior border is much arched, and describes about two- thirds of a circle. Except over the lower part of its anterior portion, it is markedly bevelled at the expense of the inner plate for the parietal, which it overlaps. Anteriorly over its lower part it is thick and serrated for the external border of the great wing of the sphenoid. The place of junction of the squamous and petrous portions is indicated at the lower part of the inner surface of the former by the narrow petro-squamous groove or suture. The zygoma (jugal process) springs from the lower part of the outer surface of the squamous portion. Its base is compressed from above downwards, and directed outwards. It then under- goes a twist, and is directed forwards in a curved manner, being laterally compressed. This part of it presents two borders, two surfaces, and an extremity. The superior border, sharp and convex, extends farther forwards than the inferior, and gives attachment to the temporal fascia in two divisions. The inferior border gives origin to fibres of the masseter. The outer surface is convex and subcutaneous, whilst the inner, which is concave and looks towards the upper part of the zygomatic fossa, gives origin to fibres of the deep part of the masseter. The extremity is bevelled at the expense of the lower border, and serrated for the malar. The base of the zygoma presents two roots, anterior and posterior. The anterior root, which is continuous with the inferior border of the process, is directed inwards in front of the glenoid fossa. It is at first narrow, but subsequently thick and convex, where it is covered by cartilage. This portion is called the eitiinentia articularis, and in front of it there is a small triangular area which looks into the zygomatic fossa. The posterior root, which is continuous with the superior border of the process, passes backwards above the external auditory meatus, then between the squamous and mastoid portions, where it is known as the supramastoid crest, and finally it turns upwards, where it forms part of the posterior boundary of the temporal fossa. In front of the external auditory meatus it sends downwards a short offshoot, which lies between the external audi- tory meatus and the anterior part of the glenoid fossa. This is called the postglenoid process, and is sometimes referred to as the middle root of the zygoma. THE BONES OF THE HEAD 71 On the outer surface of the zygoma, above the place where the anterior root becomes continuous with its lower border, there is a projection, called the preglenoid tubercle, which gives attach- ment to the external lateral ligament of the temporo-maxillary articulation. Behind the anterior root is the glenoid fossa, which extends on to the tympanic plate. It is elongated from before backwards and inwards, and is divided mto t\vo parts by the fissure of Glaser. The anterior part, which belongs to the squamo-z>'gomatic portion ^ Sqoamoas Portion Groove for Mid. Temp. Artery ^ Suprameatal Spine^ and Triangle Supramastoid Crest ^ ?arietal Notch ^ Mastoid Mastoid Portion Mastoid Process' "External Auditory Meatus' Ext. .Aud. Process Zygqna I*reglenoid Tuberck ^ Ant. Root of Zygoma (Eminent, .\rtic.} Ant. Part of Glenoid Fos.«a Fissure of Glaser Post. Part of Glenoid Fossa (Tympanic Plate) Vaginal Process ■ ' Styloid Process Fig. 48. — The Right Temporal Bone (External View). of the bone, is covered by cartilage, and is triangular, with the apex at the preglenoid tubercle and the base at the Glaserian fissure. It is deeply concave, and is boimded anteriorly by the eminentia articularis, externally by the commencement of the posterior root of the zygoma, and posteriorly from without inwards by the post- glenoid process and Glaserian fissure. 1 1 articulates \^ith the condyle of the inferior maxilla when the mouth is closed, an interarticular fibro-cartilage inter\'ening ; but, when the mouth is open, the condyle with the fibro-cartilage moves forwards on to the eminentia articu- laris. The posterior part of the glenoid fossa is situated behind the 72 . A MANUAL OF ANATOMY Glaserian fissure, and is formed by the tympanic plate, which separates it from the external auditory meatus. It is shallow, non-articular, and quadrilateral, and it lodges the deep part of the parotid gland. The fissure of Glaser, which is the remains of the petro-tympanic fissure, is closed in its outer part, and is divided into two internally by means of a thin plate which descends from the tegmen tym- pani, and forms the chief part of the outer wall of the canals for the osseous part of the Eustachian tube and tensor tympani muscle. Between this plate and the tympanic plate the processus gracilis of the malleus is located internally, and there is a small opening leading to the tympanic cavity for the passage of the tympanic branch of the internal maxillary artery and the anterior ligament of the malleus (so-called laxa'.or tympani muscle) or band of Meckel. At the inner end of the Glaserian fissure is another minute opening leading from the tympanic cavity, called the canal of Huguier, or iter chordae anterius, which transmits the chorda tympani nerve. The mastoid portion is so named from the mastoid process which it bears. It is limited above by the supramastoid crest and its own superior border, in front by the external auditory meatus and auricular or tympano-mastoid fissure, and behind by its posterior border. It presents two surfaces and two borders. The external surface, rough and convex, is prolonged downwards behind the external auditory meatus into the mastoid process, which presents on its inner surface two grooves. The outer, called the digastric groove, is deep, and gives origin to the posterior belly of the digastric ; and the inner, called the occipital groove, is narrow, and lodges the occipital artery. The upper part of the outer surface of the mastoid process gives origin over its posterior half to the retrahens auriculam and part of the occipitalis, in this order from before backwards ; and lower down, it gives insertion to the sterno- cleido-mastoid, splenius capitis, and trachelo-mastoid, in this order from above downwards. At the upper and back part of the mastoid portion, a little below the supramastoid crest, there may be the remains of the squamo-mastoid suture directed downwards and forwards, indicating the line of junction of the squamo-zygo- matic and basal part of the petrous portions. Directly in front of the root of the mastoid process there is an important depressed area, called the suprameatal triangle (Macewen), which is bounded as follows : above by part of the posterior root of the zygoma, below by the postero-superior part of the external auditory meatus, and behind by a vertical line connecting the upper and lower boundaries, which line is continuous with the posterior part of the external auditory meatus. In the lower part of the suprameatal triangle is the suprameatal spine, a sharp, antero-posterior scale of bone, which gives attachment to a portion of the cartilage of the external ear. The outer surface of the mastoid portion presents several small nutrient foramina, and often there is a large opening, called THE BONES OF THE HEAD 73 the mastoid foramen, usually placed near the posterior border, for a large emissary vein, which passes between the lateral sinus internally and the outermost tributary of the occipital vein, or the posterior auricular vein externally. In addition to these, there is the minute arterial fissure on the outer surface of the mastoid process below its centre for the mastoid branch of the occipital artery. The inner surface presents the deep sinuous sigmoid groove, which lodges a part of the lateral venous sinus, and from which the mastoid foramen opens. The genu or bend of this groove and its descend- ing limb lie behind the mastoid antrum. The superior border, thick and serrated, articulates with the back part of the inferior border of the parietal. Near its anterior part it presents the parietal notch, which receives a portion of the parietal bone. The posterior border, also thick and serrated, articulates with the inferior border of the tabular portion of the occipital. The interior of the mastoid portion contains a number of cavities lined with mucous membrane, called the mastoid air cells. These open into an irregular chamber, known as the mastoid antrum, which is situated at the upper part of the posterior wall of the tympanum, and is lined by mucous membrane continuous with that of the tympanum and mastoid cells. The upper part of the antrum com- municates with the upper part or attic of the tympanum by an opening which faces that of the Eustachian tube, but the lower part is shut off from the tympanic cavity, and its floor is on a lower level than the floor of that cavity, which explains the difficulty in the drainage of fluid. The roof of the antrum, called tegmen antri, is continuous with the tegmen tympani, and both enter into the forma- tion of the middle fossa of the base of the skull. The outer wall is formed by the squamo-mastoid junction in the region of the supra- meatal triangle ; the floor and inner wall are constructed by the petro-mastoid portion ; and the posterior wall represents that part of the mastoid portion which bears the genu or bend and descending limb of the sigmoid groove. The mastoid cells extend from the antrum into the mastoid portion in a backward and downward direc- tion, and are subject to variety as regards number and size. They are aiTanged in two groups — horizontal or superior, and vertical or inferior. The former are purely pneumatic or air cells, but the latter are of two kinds, the upper ones being pneumatic, and the lower ones, which extend to the tip of the mastoid process, being diploetic and of large size. Superiorly the cells extend forwards over the roof of the external auditory meatus, upwards as high as the supramastoid crest, and inwards for a certain distance into the petrous portion. They may also extend into the jugular process of the occipital in old persons. At birth the mastoid cells are not developed, but the antrum is present. The petrous portion is so named from its rocky consistence, and its direction is inwards and forwards into the base of the skull. It 74 A MANUAL OF ANATOMY has the shape of a four-sided pyramid, and presents four surfaces (one of which is concealed by the tympanic plate), four borders, an apex, and a base. The surfaces are superior, posterior, inferior, and axxterior. The superior surface, which has an inclination forwards, looks into the middle fossa of the base of the skull, and towards its outer part presents a few digitate impressions for convolutions of the temporo- sphenoidal lobe of the cerebrum. Near the apex is the Gasserian depression for the Gasserian ganglion, and below this is the outlet of Superior Border of Squamous Portion Petro-squamous Groove or Suture- Zygoma ^ Eminentia Arcuata Sigmoid Groove for Lateral Sinus Meningeal Groove Petro-squamous Angle Outlet of Carotid Canal Mastoid Foramen / 1 Internal .-Vuditory Meatus ' ' I Aqueductus Cochlex Styloid Process Fig. 49. — The Right Temporal Bone (Internal View). the carotid canal for the internal carotid artery. Proceeding back- wards and outwards, there is a small groove leading to a foramen very nearly in line with the petro-squamous angle, called the hiatus Fallopii, within the thin margin of which there may be two openings. The inner and larger of these openings leads to the commencement of the aqueduct oJ[ Fallopius, and thence to the internal auditory meatus, and it transmits the great superficial petrosal nerve, along with the petrosal branch of the middle meningeal artery. The outer opening, of small size, also leads to the aqueduct of Fallopius, THE BONES OF THE HEAD 75 and transmits the external superficial petrosal nerve. This latter, however, with the nene, is inconstant. Another small groove marks the upper wall of the canal for the tensor tympani muscle at the petro-squamous angle, and leads backwards and outwards, parallel with the preceding groove, to a minute foramen, situated a little external to the hiatus FaUopii, called the accessory hiatus, which transmits the small superficial petrosal ner\e. Behind and external to the hiatus Fallopii is an elevation, called the eminentia arcuata, which coincides wath the |X)sition of the superior semi- circular canal of the internal ear. Between this eminence and the hiatus Fallopii internally and the petro-squamous fissure externally there is a plate of bone, called the tegmen tympani, which forms the roof of the tympanic cavity and of the canal for the tensor tympani muscle. The posterior surface, which looks backwards and inwards, forms part of the posterior cranial fossa. It presents about its centre a large opening, which leads into a short canal, called the internal auditory meatus, for the passage of the facial and auditory nerves, the pars intermedia of Wrisberg, and the auditory artery. At the deep end of this meatus there is a perforated plate of bone, known as the lamina cribrosa, which is divided into an upper and a lower fossa by a transverse ridge, called the faleiform erest. The upper fossa presents at its anterior part a special foramen which leads into the aqueduct of Fallopius, and by this foramen the facial nerve leaves the meatiis. The remainder of the upper fossa is known as the superior vestibular area, and it is pierced by the nerves and arteries destined for the utricle and the ampullae of the superior and external semicircular canals. The lower fossa contains the cochlear area, which is pierced by the cochlear ner\-es and arteries, the inferior vestibular area for the ner\-es and arteries to the saccule, and the foramen singulare for the ner\-es and arteries to the arapuUa of the posterior semicircular canal. The aqueduct of Fallopius, for the facial nerve, extends from the deep end of the internal auditory meatus to the stylo-mastoid foramen, between which points it takes a very circuitous course. It passes at first horizontally outwards between the cochlea and vestibule to the inner wall of the tympanum, then it bends sharply backwards, lying above the fenestra ovalis, and finally, making another abrupt bend, it descends in the angle between the inner and posterior walls of the tympanum to the st\lo-mastoid foramen. The hiatus Fallopii leads from the commencement of the aqueduct to the superior surface of the petrous portion, and, as stated, transmits the great superficial petrosal nerve. The aqueduct, as it descends behind the tjTiipanum communicates with the canal of the pyramid by an opening through which the nerve to the stapedius reaches that muscle, and below the pjTamid it presents another opening, called the iter chordae posterius, by which the chorda tympani nerve passes into the t5anpanum. About \ inch external to the opening of the internal auditory 76 A MANUAL OF ANATOMY meatus there is a narrow fissure, overhung by a thin scale of bone, called the aqueductus vestibuli, which contains a small artery and vein, and the ductus endolymphaticus. Close to the superior border, about midway between the opening of the internal auditory meatus and the aqueductus vestibuli, there is a depression containing a small opening, known as the fossa subarcuata, which represents the floccular fossa of early life. The inferior surface appears on the exterior of the base of the skull. Near the apex there is a large rough surface which gives origin to fibres of the levator palati, and behind this a circular opening, called the carotid foramen, which is the inlet to the carotid Mastoid Antrum Pyramid, with Opening for Stapedius Fenestra Ovale Aqueduct of Fallopius at Hiatus Fallopii Gasserian Depression , > Mastoid Cells Outlet of Carotid Canal Promontory ' ^ \ Fenestra Rotunda r Sinus Tympani Outlet of Aqueduct of Fallopius at Stylo-mastoid Foramen Fig. 50. — Section through the Petrous and Mastoid Portions of the Temporal Bone, showing the Tympanum and M.\stoid Cells. canal. This canal, which transmits the internal carotid artery and the carotid sympathetic plexus, passes at first vertically upwards, and then, bending at a right angle, it passes horizontally forwards and inwards, to open at the apex, below the Gasserian depression, into the foramen lacerum medium. On the posterior wall of the vertical portion of the canal is a minute foramen for the tympanic branch of the carotid sympathetic plexus and tympanic branch of the internal carotid artery. Behind the carotid foramen is the jugular fossa, which, with the jugular notch of the occipital, forms the jugular foramen. On the outer wall of this fossa, near the root of the styloid process, there is the opening of the auricular canaliculus for the auricular branch (Arnold's nerve) of the pneumo- gastric. On the carotid ridge, between the carotid foramen and THE BONES OF THE HEAD 77 the jugular fossa, is the opening of the tympanic canaliculus for the tympanic branch (Jacobson's nerve) of the glosso-phar>'ngeal and the tympanic branch of the ascending pharyngeal artery. Behind the jugular fossa, internal to the stylo-mastoid foramen, is the rough jugular facet for articulation with the extremity of the jugular process of the occipital, by synchondrosis up to the twenty-fifth year, after which ankylosis takes place. External to the jugular facet is the styloid process, unmediately behmd Squamous Portion Zygoma — Surf, for Zygom. Fossa — Eminentia Ardcularis ; - Ant. Part of Glen. Fossa Fissure of Glaser Post. Part of Glen. Fossa' Ext. \ud. Process Stylo-mastoid Foramen Mastoid Process , Digastric Groove Occipital Groove Orifice of Eustachian Canal Surface for Levator Palati I Outlet of Carotid Canal I [ Apex of Petrous Portion '^>'' " Groove for Inf Petr. Sinus Carotid Foramen Aqueductus Cochlea >r. for Ty jmpanic ( \ ^^ JuguUr Fossa N^ ^^ ^For. for Tymp. Sympath. Nerve ■^ '^-Tvmpanic Canaliculus Auricular Canaliculus Jugular Facet Styloid Process I Tympanic Plate Fig. 51. — The Right Temporal Bone (Inferior View). the root of which is the stylo-mastoid foramen. This foramen is the outlet of the aqueduct of Fallopius, and by it the facial nerve makes its exit, whilst the stylo-mastoid branch of the posterior auricular artery passes in. A little behind the stylo- mastoid foramen, between the mastoid process and tympanic plate, is the auricular or tympano-mastoid fissure for the exit of Arnold's nerve. The anterior or tympanic surface which is concealed by the tympanic plate, looks into the tympanic cavity, of which it 78 A MANUAL OF ANATOMY forms the posterior and inner walls, and it presents the mastoid antrum. The borders are anterior, superior, posterior, and inferior. The anterior border separates the superior from the anterior or tympanic surface. It is very short, and forms an acute angle with the squamous portion within which the posterior pointed extremity of the great wing of the sphenoid is received. This angle presents an opening, called the Eustachian orifice, and the canal to which it leads is divided into two compartments by a thin transverse shelf of bone, scooped out on its under surface, called the processus cochleariformis. The upper small compartment lodges the tensor tympani muscle, and the lower large one forms the osseous part of the Eustachian tube. Both of these canals lead upwards and backwards to the anterior part of the tympanic cavity. The superior border, which is the longest, separates the superior from the posterior surface. It gives attachment to the tentorium cerebelli, and is grooved for the superior petrosal venous sinus. The inner part of this border frequently presents a process, which projects over the upper end of the groove for the inferior petrosal venous sinus, and gives attachment to the petro-sphenoidal ligament. This ligament connects it with the lateral border of the dorsum sellae of the sphenoid (which may present a superior petrosal process), and, if it ossifies, it bridges over a foramen through which the inferior petrosal sinus and sixth cranial nerve pass. The posterior border separates the posterior from the inferior surface. Its outer part, opposite the jugular fossa, enters into the formation of the jugular foramen, and its inner part presents a groove for the inferior petrosal sinus, and articulates with the side of the basilar portion of the occipital. In line with the opening of the internal auditory meatus it presents a triangular depression, which encroaches on the inferior surface and leads to a small canal, called the aqueductus cochleae. This aqueduct transmits a small vein from the cochlea to the inferior petrosal sinus, and also a com- munication between the perilymph of the scala tympani and the subarachnoid space, sometimes called the ductus perilymphaticus. The inferior border separates the inferior from the anterior surface, and coincides with the line of contact of the tympanic plate with the petrous portion. The apex of the petrous portion presents on its anterior aspect the Gasserian depression superiorly, and the outlet of the carotid canal inferiorly. The base is the part of the petrous portion which appears on the external surface, and it presents a large opening leading into the external auditory meatus. This opening is oval, its long axis lying vertically, and it is bounded above by the posterior root of the zygoma, whilst the remainder of its circumference is formed mainly by the external auditory process of the tympanic plate. The external auditory meatus is formed chiefly by the tympanic and squamous portions, but also slightly by the mastoid portion. Its direction THE BONES OF THE HEAD 79 is inwards, slightly fonvards, and finally downwards, its length being rather more than | inch (14 millimetres). It leads to the t}Tnpanum.. and its deep end, which is nearly circular, is closed by the membrana tympani. This membrane is placed obliquely, and forms an acute angle with the lower wall and an obtuse angle with the upper, so that the floor of the meatus is longer than the roof, the anterior wall being also longer than the posterior. Its floor presents a slight elevation at the centre, where the passage is narrower than elsewhere, this portion being called the isthmus. The tympanic plate is situated behind the fissure of Glaser, and is quadrilateral. It presents two surfaces and four borders. The external surface forms the posterior part of the glenoid fossa, and lodges the deep portion of the parotid gland. The internal surface forms the anterior, inferior, and part of the posterior, walls of the external auditory meatus, and the anterior and inferior walls of the t\Tnpanum, and at its inner or deep end it presents a groove, deficient above, for the membrana tvTiipani, caUed the sulcus tym- panicus. The outer border forms the external auditory process, and is curved and rough for the cartilage of the pinna. The inne,- border is situated immediately outside the bony part of the Eustachian tube, and is short and irregular. The upper border bounds the fissure of Glaser posteriorly, and the lower b&rder forms at its back part the vaginal process, which ensheathes the base of the styloid process externally. The tympanic plate sometimes presents a small opening at its centre, called the foramen of Buschke. The styloid process, which is cylindrical and tapering, starts ■from a point immediately in front of the stylo-mastoid foramen, and is directed downwards and inwards. The muscular and ligamentous relations of the process are as follows: The stylo- phar^mgeus muscle arises from the iimer aspect of the base; the stylo-hyoid muscle from the posterior and outer aspect of the process near its base; the stylo-glossus muscle from the front of the process near its tip; the stylo-mandibular ligament is attached to it just below the stylo-glossus; and the stylo-hyoid ligament is attached exactly to the tip. The blood - supply of the bone is chiefly derived from the following sources: The squamous portion receives externally branches from the anterior and posterior deep temporal arteries of the internal maxillary, and internally branches of the middle meningeal. Other arterial twigs enter the bone at definite points, as follows : internal auditory from the basilar, through the internal auditory meatus ; petrosal from the middle meningeal, through the hiatus Fallopii ; stylo-mastoid from the posterior auricular, through the stylo-mastoid foramen ; t\-mpanic from the internal maxillary, through the Glaserian fissure; tj-mpanic from the ascending pharyngeal, through the t>'mpanic canaliculus; t}Tnpanic from the internal carotid, through the foramen on the posterior wall of the vertical portion of the carotid canal; the mastoid from the occipital, through the arterial fissure on the outer surface of the 8o A MANUAL OF ANATOMY mastoid process ; and twigs from the mastoid division of the posterior auricular, through the foramina on the outer surface of the mastoid portion. Articulations. — These are usually five in number, as follows : posteriorly and internally with the occipital, superiorly with the parietal, anteriorly with the sphenoid and malar, and externally with the condyle of the inferior maxilla, the latter being a movable articulation. Sometimes the temporal articulates with the frontal, giving rise to a fronto-squamosal suture. Structure. — The squamous portion is thin, and is practically composed of two plates of compact bone. The mastoid portion is thick, and, as stated, contains the mastoid antrum and mastoid cells. The petrous portion is remarkable for its hardness, and it contains all the divisions of the organ of hearing, except the carti- laginous pinna on the outer side of the head. Thus it contains (i) the osseous external auditory meatus; (2) the tympanum or middle ear, with its three ossicles, malleus, incus, and stapes, etc. ; and (3) the osseous labyrinth or internal ear, which contains the membranous labyrinth, consisting of the utricle, saccule, semicircular canals, and membranous cochlea. It also contains, for a certain distance, extensions of the mastoid cells. Varieties. — (i) Foramen of Huschke in the centre of the tympanic plate, due to imperfect ossification. (2) Absence of petro-squamous suture. (3) Absence of the foramen within the hiatus Fallopii for the external superficial petrosal nerve. Ossification. — The temporal bone is developed in three parts, namely; squamosal, tympanic, and petrosal. The squamosal and tympanic elements are formed in membrane, and the petrosal in cartilage. The squamosal gives rise to the squamo-zygomatic portion, and the upper and front part of the mastoid portion ; the tympanic forms the tympanic annulus ; and from the petrosal are developed the petrous portion and the greater part of the mastoid portion. It is to be noted that the mastoid portion is not an independent part developmentally, but belongs chiefly to the petrous and partly to the squamosal portions. The centre for the squamosal appears towards the end of the second month of intra-uterine life in the region of the root of the zygoma, and from this ossification extends upwards into the squamosal, forwards into the zygoma, and inwards into the glenoid fossa in front of the Glaserian iiSsure. From the posterior part of the squamosal a downward growth of bone takes place below the supramastoid crest, called the postauditory process, which forms the outer wall of the mastoid antrum, and gives rise to the upper and front part of the mastoid portion. The centre for the tympanic element appears towards the end of the third month of intra-uterine life in the lower part of the external membranous wall of the tympanum, and from this is developed the tympanic annulus. This ring forms about five-sixths of a circle, the deficiency being above, where it is closed by the squamosal, and within the circumference of the ring there is a groove for the membrana tympani. Previous to birth the extremities of the ring become ankylosed to the squamosal, and the tympanic plate is formed by an outward growth from it, so that it is ultimately located at the deep end of the external auditory meatus. The petrosal element or periotic cartilaginous capsule is developed from four centres, which appear towards the end of the fifth month, and from which ossification proceeds rapidly, union between the four centres being effected by the end of the sixth month of intra-uterine life. These centres are called opisthotic, pro-otic, pterotic, and epiotic, in the order of their appear- THE BONES OF THE HEAD 8i ance. The opisthotic centre appears on the promontory on the inner wall of the tympanum, from which point ossification extends downwards around the fenestra rotunda, and forms (i) the floor of the vestibule, (2) the lower part of the fenestra ovahs, (3) the floor 01 the internal auditory meatus, (4) the greater part of the bony investment of the cochlea, (5) the carotid canal, and (6) the floor of the tympanum. The pro-Otic centre appears near the inner hmb of the superior semicircular canal in the region of the eminentia arcuata, and from it are formed (i) the bony investment of the superior semicircular Squaln.-Zyg. Portion Internal Auditory Meatus Fenestra Ovalis -Tympanic Annulus _,Floccular Fossa ^ Aqueductus Vestibuli - '- Aqueductus Cochleae Squam.-Zyg. Portion Petrosal Portion (Petro-Mastoid) Pyramid, with opening for _. _ . Stapedius ~~ Sinus Tympani Fenestra Rotunda Tympanic Annulus Promontory Fig. 52. — The Temporal Bone in Early Life. A. Squamo-ZA'gomatic Portion and Tympanic Annulus; B, Petrosal Portion; C, The Bone at Birth. canal, (2) the roof of the vestibule, (3) the roof of the cochlea, (4) the roof of the internal auditory meatus, (5) the upper part of the fenestra ovalis, and (6) the upper and inner part of the mastoid portion. The pterotic centre (Bland- Sutton) appears over the outer limb of the external semicircular canal, and from it are formed (i) the covering of the external semicircular canal, and (2) the tegmen tympani. The eplotic centre, sometimes double, appears in the region of the back part of the posterior semicircular canal, and from it the lower part of the mastoid is formed, as well as the investment of the posterior semicircular canal. At the period of birth (the tympanic having previously joined the squamosal) the temporal bone is composed of two parts — (i ) a united 6 82 A MANUAL OF ANATOMY squamo-zygomatic and tympanic, and (2) a petrosal, a plate of cartilage inter- vening, and these unite in the course of the first year. At birth the bone is of loose consistence, the mastoid portion is flat, the external auditory meatus is un- developed, the tympanic annulus and membrana tympani are on a level with the exterior of the bone, the glenoid and jugular fossae are shallow, the floccular fossa is conspicuous, and the hiatus Fallopii is an open groove./~The tympanic plate now becomes formed in fibrous tissue, by the extension of osseous matter outwards from two tubercles on the anterior and posterior parts of the outer aspect of the tympanic annulus superiorly. As these tubercles grow, they meet and enclose an opening in the floor of the external auditory meatus, which usually becomes closed before the period of puberty, but it may persist throughout life as the foramen of Huschke. The mastoid antrum is present at birth, and is of large proportionate size, its outer wall being very thin. The mastoid process becomes developed in the course of the second year, and the antrum becomes relatively smaller, its outer wall at the same time becoming thicker. The mastoid cells do not appear until the approach of the period of puberty. Styloid Process. — This process is developed separately from the upper end of the cartilage of the second visceral arch. It has two centres of ossification, one for the tympano-hyal or basal part appearing before birth, which soon joins the rest of the bone, and the other for the stylo-hyal appearing in the second year. The latter portion does not attain marked development until after puberty, and its union with the tympano-hyal usually takes place in adult life, but it sometimes persists in an independent condition. The Sphenoid Bone. The sphenoid bone is so named from the wedge-like position which it occupies in the base of the skull, where it lies with its long axis placed transversely. It enters into the formation of the anterior, middle, and posterior, fossae of the base, the temporal and nasal fossae, and the orbits. It consists of a central portion or body, two great wings, two small wings, and two pterygoid processes. The body presents six surfaces — superior, inferior, anterior, posterior, and two lateral, one at either side. Within the body are two large cavities, called the sphenoidal air sinuses, each of which opens on the anterior surface by a small circular aperture. The superior surface presents at its centre a depression, called the sella turcica or pituitary fossa, for the pituitary body 01 hypo- physis cerebri, and in the foetus .t is pierced by the superior opening of the cranio-pharyngeal canal. In front of the sella turcica is the olivary eminence, which indicates the place of junction of the presphenoid and postsphenoid portions, and anterior to this is a transverse furrow, called the optic groove, both of which support the optic commissure or chiasma. The groove leads at either side to the optic foramen, by which the optic nerve leaves the cranial cavity, and anteriorly it is limited by a transverse ridge, called the limbus sphenoidalis. In front of the limbus (border) is a smooth elevated platform, called the jugum sphenoidale, which is con- tinuous laterally with the superior surface of the small wing, and presents at either side the olfactory groove for the olfactory bulb. The anterior border of the jugum is projected in the middle line into the ethmoidal spine, which articulates with the posterior THE BONES OF THE HEAD 83 margin of the cribriform plate of the ethmoid. The sella turcica is bounded posteriorly by a prominent quadrilateral plate of bone, called the dorsum sellae or dorsum ephippii (back of the saddle), which is directed forwards and upwards. The antero-inferior surface of this plate overhangs the sella turcica, and the postero- superior surface, called the elivus (slope), is inchned downwards and backwards to become continuous with the basilar groove of the occipital. The elivus lodges the upper part of the pons Varolii and the basilar artery. The antero-superior border of the dorsum sellae presents at either side the posterior clinoid process for a portion Limbus Sphenoidalis Mid. Clinoid Process Oplic Foramen \ .\nt. Clinoid Process \ Sphenoidal Fissure \ '• \ Ethmoidal T o u -J 1 Spine Optic Groove Jugum Sphenoidale "^ \ \ < Olfactory Groove ', i ! ' 01i\'ary Eminence \ . I 1 , '■ ; .' _/ f Carotid Notch \ ', ; ; / / / Small Wing \ i • ; / .•■ / .' Sylvian Border of Small Wing \ \ : .' ; ." / ;■ .• Great Wing Foram. Rotundum T^~ — ~ Foramen Vesalii "b'-^^^S^ Foramen Ovale Foram. Spinosnm Canaliculus Innominatus j : | Lingula | .' • Cavernous Groove ! ! Post. Clinoid Process I Clivns \ V Spinous Process Notch for 6th Cranial Nerve Posterior Petrosal Process Dorsum Sellz Sella Turcica Fig. 53. — The Sphenoid Bone (Superior View). of the tentorium cerebeUi and the interclinoid ligament, which latter connects it with the anterior clinoid process, and is some- times ossified. On each lateral border of the dorsum seUae, a little below the posterior clinoid process, is a notch, which transmits the sixth cranial nerve. At the lower end of each lateral border there is a projection, called the posterior petrosal process, which articulates with the apex of the petrous portion of the temporal, and bounds internally the foramen lacerum medium. The inferior surface of the body is limited it either side by the internal pterygoid plate of the pterygoid process. In the middle line it presents a vertical, antero-posterior ridge, called 84 A MANUAL OF ANATOMY the rostrum, which is continuous with the sphenoidal crest on the anterior surface, and is received into the cleft between the alae of the vomer. At either side of the rostrum there is a thin scale of bone projecting inwards for a short distance from the root of the internal pterygoid plate, called the vaginal process, which articulates with the ala on the upper border of the vomer, and with it covers the greater part of the inferior surface of the body at either side of the middle line. On the inferior surface of this process there is a groove, which is converted by the sphenoidal process of the palate bone into a canal, called the pterygo-palatine canal, for the passage of the pharyngeal nerve and pterygo-palatine artery. The anterior surface presents in the middle line a vertical ridge, continuous above with the ethmoidal spine and below with the rostrum, called the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid and forms part of the nasal septum. On either side of this crest the surface is divided into two parts, outer and inner. The outer part is rough, and articulates with the back part of the lateral mass of the ethmoid and the orbital process of the palate bone. The inner part presents the opening of the sphenoidal air sinus of its own side, with the margins of which the sphenoidal turbinate or spongy bone articulates. When this bone is in position the opening of the sinus is small and circular, and is placed superiorly, but when the bone has been removed the opening is of large size and irregular outline. It communi- cates anteriorly with the spheno-ethmoidal recess of the nasal fossa above and behind the superior meatus. The part of the anterior surface which presents the opening of the sphenoidal air sinus enters into the formation of the roof of the corresponding nasal fossa. The posterior surface is rough and truncated. It articulates with the basilar process of the occipital by synchondrosis up to the twentieth year, after which ankylosis takes place. The lateral surface gives attachment to the great wing and a portion of the small wing. Anteriorly, beneath the small wing, it forms the inner boundary of the sphenoidal fissure and the back part of the inner wall of the orbit. Above the attachment of the great wing it presents a winding groove, called the cavernous or carotid groove, which contains the cavernous venous sinus and the internal carotid artery. The direction of this groove is from behind forwards, and its deepest part is placed posteriorly, where it is bounded internally by the posterior petrosal process, and externally by the lingula sphenoidalis or anterior petrosal process. This latter process is a sharp scale of bone which projects back- wards in the angle between the great wing and body. The small or orbital wings (orbito-sphenoids) extend almost horizontally outwards on a level with the anterior part of the upper surface of the body. Each arises by two roots — an upper, which is expanded and compressed from above downward.s, THE BONES OF THE HEAD 85 and is on a level with the anterior part of the upper surface of the body ; and a lower, slender and compressed from before backwards, which arises from the anterior part of the side of the body. The wing is triangular and flattened from above downwards. The superior surface, smooth and somewhat concave, forms the back part of the anterior cranial fossa. The inferior surface overhangs the sphenoidal fissure, and forms the back part of the roof of the orbit. Externally the wing ends in a slender, pointed extremity, which lies very near the great wing, but does not as a rule touch Opening of Sphenoidal Sinus Sphenoidal Fissure Ethmoidal Spine Optic Foramen Temp. Div. of Ext. Surf, of Great Wing Vidian C«nal — Zygom. Div. of Ext. Surf of Great Wing spinous Process External Pterygoid Plate Hamular Process Internal Pterygoid Plate Sphenoidal Spongy Bone' Vaginal Process' ^- Foramen Rotnndum NSphen.-maxilL Surf, of Great Wing '^•Sphenoidal Crest ^ Pterygoid Notch Pterygo-palatine Groove r^ostnim Fig. 54. — The Sphenoid Bone (Anterior View). it, though it may do so. The anterior border is thin and serrated for the orbital plate of the frontal. The posterior border, smooth, thick, and round, corresponds with the Sylvian fissure of the cerebrum, from which circumstance it is known as the Sylvian horde-. It forms at either side the line of demarcation between the anterior and middle cranial fossae, and terminates internally in the anterior clinoid process for a portion of the tentorium cerebeUi and the interclinoid ligament. Between the anterior clinoid process and the side of the olivary eminence is the semicircular carotid notch, which is the anterior 86 A MANUAL OF ANATOMY termination of the carotid groove, and lodges the internal carotid artery. On either side of the body, close to the inner side of the anterior extremity of the carotid groove and posterior to the carotid notch, opposite the anterior clinoid process, there is usually a small tubercle, called the middle clinoid process. It is connected with the anterior clinoid process by the carotico-clinoid ligament, which bridges over the carotid notch. When this ligament undergoes ossification a carotico-clinoid foramen is formed, through which the internal carotid artery ascends after leaving the carotid groove. In front of the carotid notch, between the upper and lower roots of the small wing, there is a circular aperture, called the optic foramen, which leads forwards and outwards into the orbit, and transmits the optic nerve and the ophthalmic artery. The great or temporal wings (alisphenoids) extend outwards, upwards, and forwards from the sides of the body. The posterior part of each projects backwards, and ends in a pointed extremity, which is received within the petro-squamous angle of the temporal bone. From this extremity a sharp projection extends downwards for a short distance, called the spinous process or alar spine, which presents a groove on its inner aspect for the chorda tympani nerve. Anterior to this groove and encroaching on the posterior border of the great wing, is another groove for the cartilaginous part of the Eustachian tube. The spinous process gives attachment to (i) the spheno-mandibular ligament, (2) some fibres of the tensor palati, and (3) the anterior ligament of the malleus, or band of Meckel. Each great wing presents three surfaces — superior, antero- internal, and external : and four borders — posterior, external, anterior, and internal. The superior or cerebral surface, which at its front part rises almost vertically upwards, is concave, and enters into the formation of the lateral division of the middle cranial fossa. It supports the temporo-sphenoidal lobe of the cerebrum, and presents a few digitate impressions, whilst externally it is grooved for a branch of the middle meningeal artery. This surface presents several important foramina. At the anterior part of its attachment to the side of the body, just below the inner end of the sphenoidal fissure, is the foramen rotundum, which is directed from behind forwards and transmits the superior maxillary division of the fifth cranial nerve. A little behind and external to this foramen is the foramen ovale, of large size and opening vertically dovn wards, for the passage of the inferior maxillary division and the motor root of the fifth cranial nerve, the small meningeal artery, an emissary vein from the cavernous sinus, and sometimes the small superficial petrosal nerve. Internal and anterior to the foramen ovale, between it and the lingula sphenoidalis, there is sometimes a small opening, called the toramen Vesalii, which leads to the scaphoid fossa on the outer side of the root of THE BONES OF THE HEAD 87 the internal pterygoid plate, or to the pterygoid fossa external to the scaphoid fossa. It transmits a small emissary vein from the cavernous sinus. Behind and external to the foramen ovale is the small circular foramen spinosum, close to the spinous process, which opens vertically downwards. It transmits the middle meningeal artery and a recurrent branch of the inferior maxillary nerve, and is sometimes incomplete posteriorly. Internal to this foramen, between it and the foramen ovale, there is sometimes a small opening, called the canaliculus innominatus, for the small superficial petrosal nerve. The antero -internal surface is divisible into a large orbital portion and a small spheno-maxillary portion. The orbital division is quadrilateral, smooth, and slightly concave, and it forms the greater part of the outer wall of the orbit. The spheno-maxillarv division is situated at the lower and inner part above the root of the pterygoid process. It is pierced by the foramen rotundmn, and lies in the posterior wall of the spheno-majcillary fossa. The external or iemporo-zygomatic surface is elongated from above downwards, and is continuous with the outer surface of the external pterygoid plate of the pterygoid process. Towards its lower part it is crossed by the infratemporal crest, which divides it into a large upper and a small lower portion. The upper or temporal division, which is directed outwards, forms part of the temporal fossa, and gives origin to fibres of the temporal muscle. The lower or zygomatic division looks dowTiwards into the zygomatic fossa, and gives origin to the upper head of the external pterygoid muscle. At its lower and back part it presents the openings of the foramen ovale and foramsn spinosum. The posterior border extends from the spinous process to the body, passing in its course behind the foramen ovale. Over its inner two-thirds it bounds the foramen lacerum medium anteriorly, and over its outer third, where it becomes serrated, it articulates with the petrous portion of the temporal, the two forming a groove for the cartilaginous part of the Eustachian tube. The external border separates the superior or cerebral from the external or temporo- zygomatic surface. It is serrated behind, where it is bevelled at the expense of the upper or inner plate, but in front it is squamous and bevelled at the expense of the outer plate. The entire border articulates with the squamous portion of the temporal. The anterior border or malar crest separates the orbital and temporal surfaces. Its direction is downwards and inwards, and it is sharp and irregular for the malar. The internal border is situated between the orbital and cerebral surfaces. Its direction is backwards and inwards, and it forms the lower boundary of the sphenoidal fissure. About its centre it presents a small spine, which gives origin to fibres of the lower head of the external rectus muscle of the eye- ball. The great wing antero-superiorly becomes thick and expanded, and it here presents a rough, triangular, serrated surface for the frontal. At the outer end of this surface there is another small 88 A MANUAL OF ANATOMY triangular, errated impression, for the anteroinferior angle of the parietal. The sphenoidal fissure, also called the foramen lacerum anterius or orbitale, is situated between the great and small wings. It is triangular, and its direction is inwards and downwards. It is bounded above by the small wing, below by the internal border of the great wing, and internally by the anterior part of the side of the body, whilst externally it is closed by the frontal, or, it may be, the meeting between the two wings. It leads from the middle cranial fossa to the orbit, and transmits the following structures : the third cranial nerve, the fourth, the three branches of the ophthal- mic division of the fifth (namely, frontal, lachrymal, and nasal), and the sixth cranial nerves, the sympathetic root of the ciliary ganglion, Posterior Clinoid Process Anterior Clinoid Process Post, or Sylvian Border of Small Wing Dorsum Sellae I Back Part of Carotid Groove I I ! 1 Sphenoidal Fissure Ext. Bord. of Great Wing, for Squam. Port, of Temporal Sup. Surf, of Great Wing Spinous Process-' Lingula/ Vidian Canal y / Scaphoid Fossa Ext. Pterygoid Plate Groove for Chorda Tjmpani Nerve ^ ■ Pterygoid Tubercle ^ Vaginal Process ^ Rostrum ^ Pterygoid Fossa Int. Pterygoid Plate ' Fig. S5- — The Sphenoid Bone (Posterior View) Pterygoid Notch Hamular Process the superior and inferior ophthalmic veins, the orbital branch of the middle meningeal artery, and a portion of the dura mater to form the orbital periosteum. The pterygoid processes project downwards from the junction of the body and great wings. Each is composed of two plates, external and internal, united in front to form a thick round border, except inferiorly, where they are separated by the pterygoid notch, which receives the pyramidal process or tuber- osity of the palate bone. At the upper end of the anterior border a triangular surface opens out, which lies in the posterior wall of the spheno-maxillary fossa, and presents the anterior orifice Of the Vidian or pterygoid canal. Posteriorly the two plates diverge, and enclose between them the pterygoid fossa, which contains the internal pterygoid and tensor or circumflexus palati muscles. THE BONES OF THE HEAD 89 The external pterygoid plate is broader and shorter than the internal, and is directed backwards and shghtly outwards. Its . outer surface looks into the zygomatic fossa, and gives origin to the lower head of the external pterygoid muscle. Its inner surface looks into the pterygoid fossa, and gives origin to the internal pterygoid muscle. The posterior border usually presents towards its upper part a sharp spine, from which the pterygo-spinous ligament extends backwards and outwards to the spinous process. This ligament sometimes becomes ossified, and a foramen is then formed, called the pterygo-spinous foramen, for the passage of muscular branches of the inferior maxillary nerve. 'Sometimes there is another spine towards the lower end of this border for another pterygo-spinous ligament. The internal pterygoid plate, narrower and longer than the external, is prolonged inferiorly into the hamular process, which is inclined outward , its outer and inferior aspects being smooth and grooved for the play of the tendon of the tensor or circum- flexus palati. Superiorly this plate is inflected as the vaginal process, which articulates with the ala of the vomer, and presents on its under surface a groove forming part of the pterygo-palatine canal already referred to. The outer surface of the internal pterygoid plate looks into the pterygoid fossa, and is related to the tensor or circumflexus palati. The inner surface forms the back part of the outer wall of the nasal fossa. The posterior border at its upper end presents the pterygoid tubercle, which has the posterior end of the Vidian canal above and external to it. Between this tubercle and the Vidian canal on the one hand, and the pterygoid fossa on the other, is the scaphoid fossa, which gives origin to the tensor or circumflexus palati. On the posterior border of the internal pterygoid plate, below the lower pointed end of the scaphoid fossa, is the Eustachian spine or processus tubarius, which supports the cartilage of the Eustachian tube. The lower third of the posterior border aad the hamular process give origin to fibres of the superior constrictor muscle of the pharynx, and the hamular process also gives attachment to the pterygo-mandibular ligament. The anterior border articulates with the posterior border of the perpendicular plate of the palate bone. The Vidian or pterygoid canal pierces the bone from before back- wards at the junction of the internal pterygoid plate and body on either side. Its anterior orifice appears on the posterior wall of the spheno-maxillary fossa, below and internal to the anterior orifice of the foramen rotundum, and posteriorly it opens on the anterior wall of the foramen lacerum medium, above and external to the pterygoid tubercle. It gives passage to the Vidian nerve and artery. Summary of Openings in the Sphenoid Bone. — (i) Sphenoidal fissure, between small and great wings ; (2) optic foramen, between the two roots of the small wing ; and, in the great wing, (3) foramen rotundum ; (4) foramen ovale ; (5) foramen Vesalii (inconstant) ; (6) foramen spinosum ; (7) canaliculus innominatus (inconstant) ; go A MANUAL OF ANATOMY and (8) Vidian or pterygoid canal, the last-named being between the internal pterygoid plate and the body. All these openings are common to each side. The sphenoidal air sinuses are situated within the body, and are two in number, right and left. They are separated from each other by a septum, which is usually slightly bent to the left side. The sinuses are — at least, after adult life — usually multilocular, and they may extend backwards so as to invade the basilar process of the occipital, especially in old age. Each sinus may even extend slightly into the attached portion of the great wing. They are lined with mucous membrane, which is continuous with that of the nasal fossae, and each opens anteriorly by a small circular aperture into the spheno-ethmoidal recess above and behind the corresponding superior meatus. The sphenoidal turbinate or spongy bones (sphenoidal turbinals or bones of Bertin) are situated on the anterior and inferior surfaces of the body of the sphenoid, of which they form a large part. In the adult they are blended with the sphenoid and adjacent parts of the ethmoid and palate bones, but in early life they are quite distinct. Each has the form of a three-sided, hollow pyramid, the apex of which is directed backwards and down- wards to the front part of the vaginal process, whilst the base is in contact with the back part of the lateral mass of the ethmoid. The inferior surface looks into the posterior part of the roof of the nasal fossa, and it converts the spheno-palatine notch on the upper border of the perpendicular plate of the palate bone into a foramen. The external surface appears on the inner wall of the spheno-maxillary fossa, and a portion of it is sometimes seen on the inner wall of the orbit, behind the os planum of the ethmoid. The superior surface is in contact with the anterior and inferior surfaces of the front part of the body of the sphenoid. It is at the upper part of this surface, on either side of the middle line, where the openings of the sphenoidal air sinuses ultimately appear as small circular apertures. When the sphenoidal spongy bones are broken away these openings are of large size and irregular outline. The blood-supply of the bone is derived from branches of the deep temporal arteries externally, the middle and small meningeal internally, and the Vidian, pterygo-palatine, and spheno-palatine branches of the internal maxillary, as these traverse their respective passages. Articulations^— The sphenoid articulates with fourteen bones, as follows : occipifal, two temjffbrals, two par?eta^s, frontal, ethrftoid, two sphenoidal turbinates, two malars, two palates, and vomer. It sometimes also articulates with the superior maxillae. Structure. — The body of the bone is excavated into two air sinuses. Varieties. — (i) Middle clinoid process. (2) Carotico-clinoid foramen. (3) Ossification of interclinoid ligament between anterior and posterior clinoid processes. (4) The lateral margin of the dorsum sellae may present a superior THE BONES OF THE HEAD 91 petrosal process for the attachment of the petro-sphenoidal ligament, which connects it with a projection sometimes present on the inner part of the superior border of the petrous portion of the temporal. This Ugament, which is some- times ossified, bridges over a foramen through which the inferior petrosal venous sinus and sixth cranial nerve pass. (5) Pterygo-spinous foramen. (6) Foramen ovale and foramen spinosum are sometimes incomplete. (7) Foramen Vesalii. (8) Canahculus innominatus. (9) The cranio-pharyn- geal canal may remain persistent, opening into the pituitary fossa. Ossification. — The sphenoid is developed in cartilage, with the exception of the internal pterygoid plates, which are developed in fibrous tissue.* The bone is originaUy di\'ided into two parts — presphenoid, representing the part of the body in front of the ohvary eminence, and the small wings ; and post- sphenoid, including the part of the body behind the oUvar^- eminence, the great wings, and the pter^^goid processes. The postsphenoid division is developed from four pairs of centres. One pair appear in the eighth week of intra-uterine life, one at either side in the great wing between the foramen SmaU Wing Presphenrnd Portion of Body I Great Wing Dorsum Sellz TL Internal Pterygoid Plate Fig. 56. — The Sphenoid Bone in Early Life. I, Presphenoid Division ; II, Postsphenoid Portion of Body ; III, Great Wing and Pterygoid Process; IV, Elements of Pter^'goid Process. rotundum and foramen ovale, and from this ossification extends outwards into the great wing and dovs-nwards into the external pter^'goid plate. Another pair appear about the same time in the sella turcica on either side of the cranio-pharj-ngeal canal, from which ossification extends around the canal. graduaUy constricting it, and finally leading to its closure. At this time another pair (sphenotics of Bland-Sutton) appear, one at either side, for the Ungula. In the fourth month (ninth or tenth week, Fawcett) another pair of centres appear in fibrous tissue, one at either side, for the internal pterygoid plate, which unites ^^-ith the external pterygoid plate before the sixth month. The presphenoid division is developed from two pairs of centres. Two appear in the ninth week, one at either side, external to the optic foramen, for the smaU wing. Another pair appear in the eleventh week internal to the optic foramina for the presphenoid portion of the body. The latter pair soon unite with each other, and also with those for the small \vings. The presphenoid division, bearing the small wings, joins the post- sphenoid dix-ision shortly before birth in the region of the oUvary eminence. At birth the place of junction is indicated by a wide depression on the under * According to recent observations made by Fawcett the external pterygoid plates are also developed in fibrous tissue. 92 A MANUAL OF ANATOMY aspect of that eminence, which may even extend through it and give rise to a small foramen on its upper surface. At birth the bone is composed of three parts — a central, representing the presphenoid and postsphenoid portions of the body, the former bearing the small wings ; and two lateral, each of which represents a great wing bearing a pterygoid process. In the first year the lingula joins the great wing, and the wing and body unite. About the same time the small wings come together and blend over the anterior part of the upper surface of the presphenoid portion of the .body, where they give rise to a smooth, elevated, flat platform, called the jugum sphenoidale. In foetal hfe a canal, called the cranio-pharyngeal canal, leads downwards from the sella turcica into the body, and contains a process of the dura mater. This canal is the remains of a cleft originally present in the base of the skull, through which a diverticulum of the buccal epiblast, known as the pouch ol Rathke, originally passed upwards to form the anterior lobe of the pituitary body. The sphenoidal air sinuses do not appear until after the seventh year. In some animals the presphenoid and postsphenoid portions remain permanently separate, and the internal pterygoid plates form the pterygoid bones. The sphenoidal turbinate bones commence to ossify in the fifth month of intra-uterine life. At birth each partially envelops a small extension of the nasal mucous membrane, and by the third year it has surrounded it in the form of a bony capsule, except anteriorly, where an opening, called the sphe- noidal foramen, is left. Subsequently a portion of this capsule becomes absorbed, and its place is taken by the presphenoid, which latter, after the seventh year, is gradually invaded by the original extension of the nasal mucous membrane. The sphenoidal spongy bones become ankylosed to the ethmoid about the fourth year, and are sometimes regarded as belonging to that bone. By the twelfth year they have become united to the sphenoid, and also to the palate bones. The Ethmoid Bone. The ethmoid bone is situated at the anterior part of the base of the skull, where it lies in the middle line in front of the sphenoid. A portion of it occupies the ethmoidal notch between the orbital plates of the frontal, whence the greater part of the bone projects downwards to take part in the formation of the orbits and nasal fossae. The only portions of the bone visible in the interior of the base are the cribriform plate and crista galli. It is irregularly cubical, its long axis being directed from before backwards, and it is remarkable for its lightness, which is due to the great number of enclosed air cells, these being surrounded by very thin plates of bone. It is composed of four parts, namely, a cribriform plate, a perpendicular plate, and two lateral masses. The cribriform plate connects the upper borders of the lateral masses, and enters into the formation of the middle division of the anterior cranial fossa, where it occupies the ethmoidal notch of the frontal bone. In the middle line anteriorly it presents an upward extension of the perpendicular plate, called the crista galli. This is a stout, triangular, laterally-compressed process, which presents a smooth, sloping posterior border, for the falx cerebri. The anterior border, short and vertical, is somewhat narrow above, but soon expands into two alar processes, for the frontal bone, THE BONES OF THE HEAD 93 and it here sometimes completes the foramen caecum. The posterior border is prolonged backwards as a median ridge, and on either side of this ridge and the crista galli is the olfactory groove, which lodges the olfactory tract and bulb. Each half of the cribriform plate, which lies in the roof of the corresponding nasal fossa, is pierced by foramina for the filaments of the olfactory bulb. The foramina in each half are arranged in three sets, as follows — a middle set, which are simple perforations, and an internal and external set, which lead into small canals. These canals descend on the perpendicular plate and inner surface of the lateral mass respectively, branching and opening out as they descend. All the foramina lead to the upper part of the corresponding nasal fossa. At the anterior and inner part of each half of the cribriform plate, close to the side of the crista galli, near its anterior border, Crista Gall Nasal Groove., Groove for Anterior Ethmoidal Canal , Vertical Plate -Right Max Process Ant. Ethmoidal Cells Infundibulum Orbital Plate i Olfactory Groove on Cribriform Plate Groove for Post. Ethmoidal Canal Fig. 57. — The Ethmoid Bone (Superior View). there is an antero-posterior fissure, called the nasal slit, whicK transmits the nasal branch of the ophthalmic nerve and nasal branch of the anterior ethmoidal artery to the nasal fossa. Leading backwards and outwards from this slit to the anterior, ethmoidal groove on the upper border of the lateral mass is the nasal groove, also foi the nasal nerve. The posterior border of the cribriform plate articulate^ ..Icii the ethmoidal spine of the sphenoid. The perpendicular plate (meseLamoid) extends downwards from the cribriform plate in the middle line. It lies between the lateral masses, where it forms about the upper third of the nasal septum, and it is usually inclined more to one side than the other. It is very thin and irregularly quadrilateral. The superior border projects above the cribriform plate and forms the crista galli. The inferior border articulates, in front, with the septal cartilage of the nose, and behind, with the alae of the vomer in the intervening cleft. 92 A MANUAL OF ANATOMY aspect of that eminence, which may even extend through it and give rise to a small foramen on its upper surface. At birth the bone is composed of three parts — a central, representing the presphenoid and postsphenoid portions of the body, the former bearing the small wings ; and two lateral, each of which represents a great wing bearing a pterygoid process. In the first year the lingula joins the great wing, and the wing and body unite. About the same time the small wings come together and blend over the anterior part of the upper surface of the presphenoid portion of the .body, where they give rise to a smooth, elevated, flat platform, called the jugum sphenoidale. In foetal life a canal, called the cranio-pharyngeal canal, leads downwards from the sella turcica into the body, and contains a process of the dura mater. This canal is the remains of a cleft originally present in the base of the skull, through which a diverticulum of the buccal epiblast, known as the poucb of Rathke, originally passed upwards to form the anterior lobe of the pituitary body. The sphenoidal air sinuses do not appear until after the seventh year. In some animals the presphenoid and postsphenoid portions remain permanently separate, and the internal pterygoid plates form the pterygoid bones. The sphenoidal turbinate bones commence to ossify in the fifth month of intra-uterine life. At birth each partially envelops a small extension of the nasal mucous membrane, and by the third year it has surrounded it in the form of a bony capsule, except anteriorly, where an opening, called the sphe- noidal foramen, is left. Subsequently a portion of this capsule becomes absorbed, and its place is taken by the presphenoid, which latter, after the seventh year, is gradually invaded by the original extension of the nasal mucous membrane. The sphenoidal spongy bones become ankylosed to the ethmoid about the fourth year, and are sometimes regarded as belonging to that bone. By the twelfth year they have become united to the sphenoid, and also to the palate bones. The Ethmoid Bone. The ethmoid bone is situated at the anterior part of the base of the skull, where it lies in the middle line in front of the sphenoid. A portion of it occupies the ethmoidal notch between the orbital plates of the frontal, whence the greater part of the bone projects downwards to take part in the formation of the prbits and nasal fossae. The only portions of the bone visible in It r interior of the base are the cribriform plate and crista galli. of the^rregularly cubical, its long axis being directed from before inner mals, and it is remarkable for its lightness, which is due to behind thnumber of enclosed air cells, these being surrounded by the postero-htes of bone. It is composed of four parts, na"^^'-'^' it may be, wiolate, a perpendicular plate, and two 1-^^ • -lu. At the lower part of Tm plate connects , +^'=' .-w'the os planum, there is a deep channel, <^nyf=o'r.'>:a*trom before backwards, which forms the middle meatus of the nose, and is limited below by the inferior rolled border of the inferior turbinate process. This groove turns upwards in front, under cover of the anterior part of the inferior turbinate process, and is continued into the infundibulum which communicates with the frontal sinus of the same side. The anterior ethmoidal cells open into the ascending part of the middle meatus, whilst the middle ethmoidal cells and the antrum of Highmore THE BONES OF THE HEAD 93 and it here sometimes completes the foramen caecmn. The posterior border is prolonged backwards as a median ridge, and on either side of this ridge and the crista galli is the olfactory groove, which lodges the olfactory tract and bulb. Each half of the cribriform plate, which lies in the roof of the corresponding nasal fossa, is pierced by foramina for the filaments of the olfactory bulb. The foramina in each half are arranged in three sets, as follows — a middle set, which are simple perforations, and an internal and external set, which lead into small canals. These canals descend on the perpendicular plate and inner surface of the lateral mass respectively, branching and opening out as they descend. All the foramina lead to the upper part of the corresponding nasal fossa. At the anterior and inner part of each half of the cribriform plate, close to the side of the crista galli, near its anterior border, Crista Galli Nasal Groove. ' Groove for Anterior Ethmoidal Canal , Vertical Plate -Right Alar Process nt. Ethmoidal Cells Infiindibulum Orbital Plate i Olfactory Groove on Cribriform Plate Groove for Post. Ethmoidal Canal Fig. 57. — The Ethmoid Bone (Superior View). there is an antero-posterior fissure, called the nasal slit, whuj transmits the nasal branch of the ophthalmic nerve and nasal li^tUS. of the anterior ethmoidal artery to the nasal fossa, ^{a, and backwards and outwards from this slit to the anterior, ~,s^oove on the upper border of the lateral mass is the Tj- margin of the 01-L.l.the nasal nerve. The posterior border of t depressions upon it, and coji.iciuj tifel ethmoidal spine of the si these depres- sions this border presents two trknsvelsc' ^^'"nds doibout half an inch apart, which, with corresponding grooves' on the orbital plate of the frontal, form the anterior and posterior ethmoidal or internal orbital canals. These open upon the inner wall of the orbit, and the antctior transmits the anterior ethmoidal vessels and the nasal nerve, whilst the posiertor gives passage to the posterior ethmoidal vessels and the spheno'-ethmoidal nerve. The inferior border, which is free on the outer wall of the nasal 96 A MANUAL OF ANATOMY fossa, is formed by the lower border of the inferior turbinate process. Anteriorly it articulates with the superior turbinate crest of the superior maxilla, and posteriorly with the ethmoidal or superior turbinate cre^t of the palate bone. The anterior border, like the superior, presents depressions, which form air cells when the lachrymal and nasal process of the superior maxilla are in position. This border projects slightly in advance of the front of the OS planum, and from the lower part of this projecting portion there springs the uncinate process. This is a long, thin, curved plate which extends downwards, backwards, and slightly outwards into the anterior part of the middle meatus. In its course it crosses the opening of the antrum of Highmore in the superior maxilla, and thus forms part of the inner wall of that air sinus. The lower border of the process presents two spur-like projections, between which the border is markedly concave. The posterior terminal spur articulates with the ethmoidal process of the inferior turbinate bone. The posterior border of the, lateral mass presents a few depressions, closed by the sphenoidal spongy bone and orbital process of the palate bone, which latter process becomes ankylosed with it about the fourth year. The ethmoidal cells are contained within each lateral mass, and are lined with mucous membrane, which is continuous with that of the nose. They are arranged in three sets — anterior, middle, and })osterior. The anterior ethmoidal cells, along with the frontal sinus of the same side, open by a common passage, already described as the infundibulum, into the ascending front part of the middle meatus ; the middle ethmoidal cells open into the horizontal part of the middle meatus ; and the posterior ethmoidal cells open into the superior meatus. The bone receives its blood - supply from the anterior and posterior ethmoidal branches of the ophthalmic, and the spheno- palatine branch of the internal maxillary. Articulations. — The ethmoid articulates with fifteen bones, as follows : (i) frontal (nasal spine and orbital plates) ; (2) sphenoid (ethmoidal spine and sphenoidal crest) ; (3) two sphenoidal spongy bones ; (4) two nasal bones (nasal crest) ; (5) vomer (cleft between alse) ; (6) two palate bones (ethmoidal or superior turbinate crests and orbital processes) ; (7) two lachrymals (upper part of internal surface) ; (8) two superior maxillae (nasal processes, orbital plates, and opening of each antrum) ; and (9) two inferior turbinates (ethmoidal processes). Structure. — The lateral masses are excavated into many thin- walled air cells, and the crista galli contains a small amount of cancellated tissue. Ossification. — The ethmoid is developed in cartilage from three centres. Two of these appear in the fifth month of intra uterine life, one in each os planum, from which ossification extends into the superior and inferior turbinate processes. At birth the lateral masses are ossiiied, but the perpendicular plate and crista galli are cartilaginous. In the first year a centre appears at the base of the crista galli, and from this ossification extends upwards into THE BONES OF THE HEAD 97 that process, downwards into the perpendicular plate, and outwards into the cribriform plate, into which latter osseous matter also extends inwards from each lateral mass. The three original parts unite about the fifth year. The osseous ethmoidal cells usually make their appearance about the third year. The Superior Maxillary Bones. The superior maxillary bone forms, with its fellow, a large part of the face, and, besides supporting the upper teeth of its own side, it enters into the formation of the orbit, nasal fossa, and hard palate. It is composed of a central portion or body, and four processes — nasal, malar, ah^eolar, and palatal. The body is excavated into a large cavity, called the antrum of Highmore or maxillary air sinus, and it presents four surfaces — antero-external, postero-extemal, superior, and internal. The 'antero-external or facial surface is limited above by the infra-orbital border, below by the alveolar border, mternally by the mesial border, presenting the nasal notch, and externally by the malar process and a ridge of bone extending downwards from it to the first molar alveolus. It presents inferiorly five ridges, coinciding with the roots of the incisor, canine, and bicuspid teeth, of which that of the canine is conspicuous, and is called the canine ridge. Internal to this ridge is the incisor or myrtilorm fossa (like a myrtle-berry), which gives origin internally to the depressor alae nasi, and externally to a deep slip of the orbicularis oris, whilst above, and external to, the latter the compressor naris arises. External to the canine ridge is the canine fossa, which, at its upper part, gives origin to the levator anguli oris, the bone being here thin and translucent in front of the antrum. Above the canine fossa, near the infra-orbital border, is the infra-orbital foramen, which is the outlet of the infra-orbital canal, and trans- mits the infra-orbital nerve and vessels. Immediately above this foramen the levatc ; labii superioris arises. The mesial border of the facial surface presents the deep nasal notch, at the lower and inner part of which is a sharp projection, forming, with its fellow, the anterior nasal spine, below which the border is vertical. The postero-external or zygomatic surface is situated behind the malar process and the ridge connecting that process with the first molar alveolus. Superiorly it is hmited by the posterior border of the orbital surface, inferiorly by the molar portion of the alveolar border, and posteriorly by the posterior border of the bone. It looks into the zygomatic and spheno-maxillary fossae, and its outhne is convex. Towards the centre it presents the openings of two or three posterior dental canals, which lead to the molar alveoli, and transmit branches of the posterior superior dental nerve and artery. At the lower and back part this surface gives rise to the tuberosity, which lies above and behind the last molar tooth. This tuberosity articulates with the pyramidal process of the palate bone, and gives origin to some fibres of the internal pterygoid muscle. 7 98 A MANUAL OF ANATOMY The superior or orbital surface is triangular, smooth, and slightly concave, and it forms the greater part of the floor of the orbit. This portion of the bone is known as the orbital plate. It presents the infra-orbital groove, which, commencing at the posterior border in a notch, ultimately becomes converted into the infra-orbital canal. This canal transmits the infra-orbital nerve and vessels. From its posterior part the middle dental canal, for the middle superior dental nerve and artery, passes downwards and forwards Nasal Process For Lachrymal Bone Lachrymal Tubercle ^^ Lachrymal Notch \ \ For Nasal Bone Orbital Surface 1 Infra-orbital Groove I 1 Openings of ^' Post Dental Canals - Nasal Notch -Anterior Nasal Spine Tuberosity Zygomatic Surface Malar Process ' Palatal Process Incisor Fossa Canine Fossa Infra-orbital Foramen Fig. 6o. — The Right Superior Maxillary Bone (External View). to the bicuspid alveoli, lying at first in the postero-external wall of the antrum, and subsequently in the antero-external wall. This canal is often for the most part a groove. The anterior dental canal, for the anterior superior dental nerve and artery, descends in a branching manner from the anterior part of the infra-orbital canal to the incisor and canine alveoli, lying in the antero-external wall of the antrum. At the anterior and inner part of the orbital plate, external to the lachrymal groove, there is a slight depression which gives origin to the inferior oblique muscle of the eyeball. THE BONES OF THE HEAD 99 The borders of the orbital surface are anterior, posterior, and internal. The anterior border coincides with the infra-orbital border. The posterior border, which has an inclination outwards, forms the anterior boimdary of the spheno-maxillary fissure, and presents a notch representing the commencement of the infra- orbital groov^e. The internal border, antero-posterior in direction, presents, behind the nasal process, the lachrymal notch for the lachr\Tnal bone, and behind this it articulates, from before back- wards, with the lower border of the os planum of the ethmoid and the orbital process of the palate bone. This border presents a few depressions which close in ethmoidal cells. The internal or nasal surface forms part of the outer waU of the nasal fossa. It is limited in front by the mesial border of the bone, behind by the posterior border, above by the internal border of the orbital surface, and below for the most part by the palatal process. It presents the opening of the antrum of riighmore, in front of which is the deep lachrymal groove, directed downwards, outwards, and backwards, and, after a course of about ^ inch, opening into the front part of the inferior meatus of the nose. This groove is converted posteriorly and internally into the lachrymal canal by the lacluymal and inferior turbinate bones, and it transmits the nasal duct. In front of the lachrymal groove is a shghtly obhque ridge, called the inferior turbinate crest, for articulation with the inferior turbinate bone, and below this is a smooth concave siuface which forms the anterior part of the inferior meatus-. Above the crest is the commencement of another smooth surface, which extends upwards on to the inner aspect of the nasal process, and forms the outer wall of the atritun of the middle meatiis. Behind the opening of the antrum the internal surface articulates with the perpendicular plate of the palate bone, and it presents, from the centre downwards, a grocrs'^e, directed downwards and fon^-ards, which, with the palate bone, forms the posterior palatine canal for the great or anterior palatine nerve, and the superior or descending palatine artery. Above the opening of the antrmn are a few depressions on the internal border of the orbital surface, forming ethmoidal cells. The nasal or frontal process ascends vertically from the mesial part of the facial surface above the nasal notch. It is somewhat triangular, and presents two surfaces and three borders. The external surface is continuous with the facial surface of the body, and gives attachment to the orbicularis palpebrarum, tendo ocuU, and levator labii superioris alaeque nasi. The internal surface forms part of the outer wall of the nasal fossa, and, at its back part superiorly, it presents one or two depressions, completing cells on the anterior border of the lateral mass of the ethmoid. The surface is crossed obliquely backwards and upwards by a ridge, called the agger nasi (mound) or superior turbinate crest, which represents the naso-turbinal of most mammals (Schwalbe). This crest boimds superiorly the atriima of the middle meatus, and A MANUAL OF ANATOMY articulates posteriorly with the anterior extremity of the inferior turbinate process of the ethmoid. Above the agger nasi there is a groove, called the sulcus olfadorius. The superior border is short, thick, and serrated for the frontal. The anterior border is sharp and articulates with the nasal. The posterior border is thick, and in. its lower part presents a continuation of the lachrymal groove which here lodges the lachrymal sac. The lips of this part of the groove are sharp, the inner articulating with the lachrymal, and the outer, which is crescentic, being continuous Sulcus Olfactorius ,Sup. Turbinate Crest (Agger Nasi) Atrium of Middle Meatus _ Inf. Turbinate Crest Int. Bord. of Orbital Surface Antrum Post Palatine Groove Anterior Nasal Spine | Incisor Crest Incisor or Naso-Palatine Groove Inferior Meatus Palatal Process Nasal Crest Lachrymal Groove Fig. 6i. — The Right Superior Maxillary Bone (Internal View). with the infra-orbital margin, at which point there is a projection, called the lachrymal tubercle. The malar process is stout and triangular. Its anterior surface is continuous with the facial surface of the body, and its posterior with the zygomatic surface, whilst the superior surface is rough and slightly serrated for the malar. The alveolar process forms the dependent part of the bone, and is thick and curved, being convex externally and concave internally. The outer plate is known as the labial plate; and the inner as the lingual. The two plates are widely separated, and; THE BONES OF THE HEAD lOi the intervening space is partitioned off into alveoli or sockets by septa which pass between the two plates. The number of alveoli in the adult bone is as a rule eight, and they gradually narrow towards their upper or deep ends, where they are perforated by foramina for the ner\'es and arteries of the teeth. They lodge the roots of the teeth, which, in order from the middle line outwards and backwards, are as follows : central incisor, lateral incisor, canine, first bicuspid, second bicuspid, and first, second, and third molars. The alveoli correspond in shape with the roots of the teeth, the canine being the deepest. The outer surface of the alveolar border, over the extent of the three molar sockets, gives origin to fibres of the buccinator. C The palatal process is situated on the internal surface of the body, from which it projects horizontally inwards, and, with its fellow, it forms three-fourths of the hard palate, i It is quadrilateral, and presents two surfaces and four borders.''^he superior surface forms three-fourths of the floor of the nasal fossa, and is smooth, concave, and covered in the recent state by the nasal mucous membrane. The inferior surface forms a part of the hard palate, and is rough, arched, and covered in the recent state by the buccal mucous membrane. It presents several depressions for the palatal mucous glands, and is perforated by several nutrient foramina. Laterally it is marked by a groove, directed from behind forwards, for the nerv^e and artery which reach the hard palate through the posterior palatine canal. The posterior border stops short of the back part of the alveolar border, and is short and serrated for the horizontal plate of the palate bone. The anterior border, superiorly, forms the lower part of the nasal notch. The external border is attached to the body. The internal or mesial border is faintly serrated, and articulates with its fellow. At the place of meeting it is elevated into a ridge, forming, with that of its feUow, the nasal crest, which is grooved to receive the lower border of the vomer. This mesial ridge becomes prominent in front, where it forms the incisor crest, which is projected to constitute, with its fellow, the anterior nasal spine. It supports the septal nasal cartilage, and the anterior extremity of the vomer lies behind it. Close to the outer side of the incisor crest the palatal process is pierced by an opening leading into a canal, which is bounded internally by a thin plate of bone, and descends to the front part of the hard palate, being ultimately converted into a groove, due to its inner thin wall becoming deficient. This passage is variously known as the incisor or naso-palatine canal, or canal of Stensen (Steno), and the two canals, right and left, in the articulated condition form interiorly a large orifice, called the anterior palatine fossa. This fossa, which is somewhat diamond- shaped, is situated in the middle line of the hard palate, behind the central incisor teeth. On looking into it from below four foramina are seen, two of which are placed in the middle line, I02 A MANUAL OF ANATOMY where they he in the intermaxillary suture. These are known as the foramina of Scarpa, and they transmit the naso-palatine nerves, the left nerve passing through the anterior, which usually communicates with the left nasal fossa, and the right through the posterior, which usually communicates with the right nasal fossa. The other two foramina are situated one at either side, and are known as the foramina of Stensen, and the canal into which each leads opens superiorly on the floor of the corresponding nasal fossa, close to the outer side of the incisor crest. Each of Stensen's canals transmits a branch of the superior or descending palatine artery from the anterior palatine fossa to the nasal fossa. The inner wall of Stensen's canal, on each side, represents the mesial palatal process of the premaxilla or intermaxillary bone, and also a portion developed from the prepalatine centre. The canals of Stensen correspond to the incisor foramina of many animals — e.g., the ruminantia, in which they are of large size, and each opens independently on the front part of the hard palate as a large aper- ture, there being no anterior palatine fossa. In such animals each incisor foramen leads up to the orifice of Jacobson's organ, which is a supplementary organ of smell. In man the canals of Stensen are the remains of a communication which existed in early foetal life between the nasal and buccal cavities. Passing transversely outwards from the anterior palatine fossa at its back part to the interval between the lateral incisor and canine teeth a suture is always present in early life, and may persist in the adult, which indicates the line of junction of the maxillary portion proper and the premaxilla or intermaxillary bone, the latter representing the part which bears the central and lateral incisor teeth. This intermaxillary portion forms an independent bone in many animals. The antrum of Highmore or maxillary air sinus is situated within the body of the bone, and is of large size, its capacity in health being equal to about 2 drachms. It has the shape of a four-sided pyramid, and is lined with mucous membrane continuous with that of the nasal fossa. The apex corresponds to the malar process, and the base represents the internal or nasal aspect. The superior wall or roof is formed by the orbital plate. The inferior wall or floor is formed by that portion of the alveolar border which contains the molar and second bicuspid alveoli, and, in some cases, the first bicuspid alveolus also. It is often very irregular, due tc projections of the upper ends of the alveoli, and in some cases the root of the first molar, and, it may be, that of the second, projects into the antral cavity. The ant ero- external wall is formed by the facial surface, and is thin and translucent over the region of the canine fossa. It contains the anterior, and the lower part of the middle, dental canals. The postero- external wall is formed by the zygomatic surface, and it contains the upper part of the middle dental canal. The opening of the antrum, which is large and irregular, is situated on the base or nasal aspect. In the articu- THE BONES OF THE HEAD 103 lated skull its size is considerably diminished by the perpendicular plate of the palate bone behind, the maxillary process of the in- ferior turbinate below, and above this by the uncinate process of the ethmoid. The opening is further curtailed by the adjacent mucous membrane. Under these circumstances it is reduced to a small aperture, situated near the upper part, which opens into the middle meatus of the nasal fossa. The antrum is usually uni- locular, but it may be partially divided into compartments. The bone derives its blood - supply from many sources, such as posterior dental, infra-orbital, middle and anterior dental, facial, frontal, superior or descending palatine, and naso-palatine arteries. Articulations. — ^The superior maxilla articulates with nine bones, as follows: malar, nasal, frontal, lachrymal, ethmoid, inferior turbinate, palate, vomer, and its fellow of the opposite side. In addition to these it may articulate with the pterygoid process and great wing of the sphenoid. Fig. 62. — The Fcetal Superior Maxillary Bone. A, External View, showing the Infra-orbital Groove and Foramen, with Fissure ; B, Inferior View, showing the Incisor Fissure and Alveoli ; C, Internal View, showing the Antrum and Incisor Fissure. Structure. — The bone contains the maxillary air sinus. For the most part cancellated tissue is absent, except in the alveolar process around the alveoli. Ossification. — ^The superior maxillary bone is ossified in membrane. Accord- ing to ^lalland Fawcett it has two centres — maxillary proper and premaxillary, which appear about the sixth week, and join about the third month. The centre referred to as maxillary proper appears in the region of the future canine alveolus, and from it ossification proceeds backwards into the malar process, upwards into the posterior half of the nasal process, inwards into the posterior three-quarters of the palatal process, and downwards into the alveolar border, excluding the incisor portion. The premaxillary centre gives rise to the premaxilla, which Ues on the mesial side of the maxilla proper and bears the upper incisor teeth. It also gives rise to (i) the anterior fourth of the palatal plate, and (2), according to Fawcett, the anterior half of the nasal process. It is to be noted that, whilst the anterior half of the nasal process is ossified from the premaxillary centre, the posterior halfoi that process (bearingthelachyrmal groove) is ossified from the maxillary proper centre. Besides the premaxillary centre there is an infravomerine centre, according to Rambaud and Renault. This centre Ues beneath the anterior part of the vomer, and it gives rise to the infravomerine part of the bone, which forms the mesial wall of Stensen's canal. The Une of union between the premaxilla I04 A MANUAL OF ANATOMY and maxilla proper is indicated by the premaxillary suture on the palatal surface of young bones, which may, though somewhat rarely, persist in adult life. This suture extends outwards and forwards from a point directly behind the lower end of Stensen's canal to the alveolar border between the lateral incisor and canine alveoli. The premaxilla of each side forms an independent bone in many animals. It may be developed in two parts from separate centres of ossification — an inner for the portion bearing the central incisor alveolus, and an outer for the portion containing the lateral incisor alveolus, and these two portions may remain separate. The inner portion is known as the endognathion, and the outer portion as the mesognathion, whilst the remainder and greater part of the bone is referred to as the maxilla proper. The varieties of alveolar cleft palate are explained by a reference to these conditions of the bone. In mesial clelt palate the two premaxillae (right and left) are separated by a mesial cleft. Lateral cleft palate may occur in two forms — the maxilla proper or excgnathion and the entire premaxilla may fail to unite, and the cleft is situated between them, and invades the alveolar border between the lateral incisor and canine alveoli; or the premaxilla may exist in two parts, inner or endognathion, and outer or mesognathion, and the cleft may be between these two, in which case it invades the alveolar border between the central and lateral incisor alveoli. These conditions may occur on one or both sides. In the earlier stages of intra uterine life there is no trace of the antrum, and the alveolar border lies close to the infra-orbital border. In the course of the fourth month, however, the antrum makes its appearance as a shallow depres- sion on the inner aspect of the bone, and, as this increases, it gradually separates the orbital, alveolar, and palatal portions. In the process of development the alveolar border first presents an elongated furrow, called the dental groove, on either side of which a plate grows downwards, forming the labial and lingual plates. The groove is thus converted into a trench with these ramparts on either side. Subsequently these plates are connected by a number of septa, which intersect the trench and break it up into alveoli. At this stage these are only five in number for each bone, and the canine alveolus is the first to be partitioned off. In early life the bone contains the temporary teeth, which are five in number on either side, but in the adult, as stated, it contains eight alveoli for the eight permanent teeth. The Malar Bones. The malar or cheek-bone is situated between the external angular process of the frontal and zygoma of the temporal on the one hand, and the malar process of the superior maxilla on the other, where it separates the orbit from the temporal fossa. It is quadrilateral, and presents two surfaces, four processes, and four borders. The external surface is convex, and near its centre there is the malar tuberosity. Above this is the malar foramen for the passage of the malar branch of the temporo-malar or orbital nerve, and a branch of the lachrymal artery. The portion of this surface close to the zygomatic process gives origin to the zygo- maticus major, and the lower and anterior part to the zygomaticus minor. The internal surface, which is concave, looks into the temporal fossa above and zygomatic fossa below, and it is overhung superiorly by a curved plate of bone, called the orbital process. Anteriorly it presents a rough, slightly serrated, triangular area for the malar process of the superior maxilla. The orbital process projects backwards and inwards, in a curved manner, from the THE BONES OF THE HEAD 105 upper part of the internal surface on a level with the orbital border. It is triangular, and its superior or orbital surface presents a sweep- ing concavity, which enables it to form the front part of the outer wall of the orbit, and a portion of the floor. This surface is pierced by one or, it may be, two openings. If there is one, it ultimately leads to two canals — malar, which opens on the external surface, and temporal, which opens on the temporal di\4sion of the internal surface, as a rule near the frontal process. These canals transmit the malar and temporal branches of the temporo-malar or orbital nerve. If there are two, each leads to its own canal. The inferior surface of the orbital process, which is convex, forms the anterior part of the temporal fossa. The rough margin of the process articulates by its superior part wdth the anterior border or malar crest of the Frontal Process (Sup. Ang.) Malar Foramen 1 1 Marginal Process Tenqioral Border Orbital Border Zygomatic Process (Post. Ang.) Masseteric Border Malar Tuberosity Malar Tuberck (Inf. Ang.) Maxillary Border Infra-orbital Process (Ant. Ang.) Fig. 63. — The Right M.\lar Bone (External View). great wing of the sphenoid, and below with a part of the orbital plate of the superior maxUla. The part of this border between the sphenoidal and maxillary portions sometimes closes the cmterior and outer extremity of the spheno-maxillary fissure, and thus intervenes between the great wing of the sphenoid and the superior maxilla. The processes are four in number — superior, posterior, inferior, and anterior. The superior or frontal process is stout and promi- nent. Its direction is vertically upwards, and it terminates in a thick serrated extremity for the external angular process of the frontal. The posterior or zygomatic process is short and usually blunt. Its direction is backwards, and it terminates in a serrated extremity for the zygoma of the temporal. The inferior or maxillary process is blunt and truncated. Its direction is downwards, and io6 A MANUAL OF ANATOMY it articulates with part of the malar process of the superior maxilla. The anterior or infra-orbital process is slender and pointed. Its direction is forwards, and it articulates with the superior maxilla near the infra-orbital foramen. The borders are four in number — temporal, masseteric, maxillary, and orbital. The temporal border extends from the frontal process to the zygomatic, and is directed backwards. It is sinuous, and continuous with the upper border of the zygoma, and it gives attachment to the temporal fascia. Near the frontal process it usually presents a slight prominence, called the marginal process, to which a stout slip of the temporal fascia is attached. The masseteric border extends from the zygomatic process to the maxillary process, and looks downwards. It is thick, rough, and continuous with the lower border of the zygoma, and it gives origin Frontal Process I Orbital Surface of Orbital Process Opening of Temporal Canal Opening of Malar Canal Zygomatic Process Temporo-Zygoniatic Surface Malar Tubercle Infra-orbital Process For Sup. Maxilla Fig. 64. — The Right Malar Bone (Internal View). to the anterior fibres of the superficial part of the masseter. The maxillary border extends from the maxillary process to the infra- orbital process, and it looks forwards and slightly downwards. It is rough and slightly concave, and, together with the rough, shghtly serrated, triangular area on the internal surface adjacent to it, articulates with the malar process of the superior maxilla. The orbital border extends from the infra-orbital process to the frontal, and is smooth, round, and concave. Its direction is outwards and upwards, and it forms a large part of the circumference of the orbit. The bone derives its blood-supply froni the lachrymal, anterior deep temporal, and transverse facial arteries. Articulations.— The malar articulates with four bones, as follows: superiorly with the frontal and sphenoid, posteriorly with the tem- poral, and anteriorly with the superior maxilla. Structure. — The bone is mainly composed of compact tissue, the amount of cancellated tissue being small. THE BONES OF THE HEAD 107 Varieties. — ^The bone may persist in two parts connected by a suture, which ma)' be horizontal or vertical. It sometimes persists in three parts. Ossification. — ^The malar is developed in membrane from three centres. which appear in the eighth week of intra-uterine life, and they unite at the end of the fourth month. These centres are called premalar, postmalar, and hypomalar. If all three centres should fail to unite, then a tripartite malar is the result. If the premalar and postmalar unite, and the h5rpomalar remains separate, a bipartite malar persists with a horizontal suture. If the postmalar and hjrpomalar unite, and the premalar remains separate, the suture is vertical. A bipartite malar occurs with great frequentcy amongst the Japanese, and from this cuncumstance the bone is known as the os Japooieam. The Nasal Bones. The nasal bone, which articulates with its fellow by its mesial border, forms with it the bridge of the nose. It Hes in front of the nasal process of the superior maxilla, where it enters into the formation of the face and nasal fossa. The bone is elongated from above downwards, and presents two sur- faces and four borders. The anterior or facial surface is smooth, concavo-convex from above do\Miwards, and convex from side to side. Near its centre it usually presents a minute foramen for the passage of a small vein from the nose to the com- mencement of the facial vein. This surface supports the common aponeurosis of the pyramidalis nasi and compressor naris muscles. The posterior or nasal surface is rough superiorly, where it articulates with the nasal process of the frontal. Elsewhere it is smooth and concave from side to side, and in the recent state is covered by the nasal mucous membrane. It is traversed longitudinally near the centre by the nasal groove for the nasal ner\-e. The superior border is short, thick, and serrated for the nasal notch of the frontal: The inferior border is thin and ex- panded for the upper lateral nasal cartilage. It usually presents the nasal notch, which is situated near its inner end. The mesial border articulates with its fellow. It is usually rather shorter and thicker than the external, and projecting backwards from it is a ledge of bone, which, wdth its fellow, forms the nasal crest for articulation with the nasal spine of the frontal and the anterior border of the perpendicular plate of the ethmoid. The external border, long and thin, is finely serrated for the nasal process of the superior maxilla. ,, Superior Border — Mesial Botder — Nasal Notch Inferior Botdet Nasal Crest 1 — Nasal Groove Fig. 65.— The Right Nasal Bone. A, Anterior View; B. Pos- terior View. io8 A MANUAL OF ANATOMY The bone receives its blood-supply from the angular branch of the facial, and the nasal and anterior ethmoidal branches of the ophthalmic, arteries. Articulations. — ^The nasal articulates with four bones, as follows : superiorly with the frontal, externally with the superior maxilla, internally with its fellow, and posteriorly with the ethmoid and again with the frontal. Structure. — The bone is composed of compact tissue, and is there- fore dense. Ossification. — The nasal is developed in membrane from one centre, which appears about the eighth week of intra-uterine life. The Lachrymal Bones. The lachrymal or tear-bone is situated at the anterior part of the inner wall of the orbit, where it lies behind the nasal process of the superior maxilla, and in front of the os planum of the ethmoid. It is very thin and scale-like. From its resemblance in this sense to a finger-nail, it is known as the os unguis. It is quadrilateral and presents two surfaces and four borders, the inferior border being recognised by its presenting a hamular and a descending pro- cess. The external or orbital surface is traversed by the lachrymal crest, which is nearer the anterior than the posterior border, and divides the surface into two unequal Superior Border parts. The anterior division, represent- I ing one- third, presents the lachrymal groove, which lodges the lachrymal sac L... Anterior Border and the Commencement of the nasal Lachrymal Groove duct. The loWCr CUd of this divisiOU is Orbital Surface prolonged into the descending process, ,-- Hamular Process which takcs part in the wall of the lach- Descending Process j-ymal canal, and articulates with the Fig. 66.-THE Right Lack- |?^^7"'^lr^P'°i^'' °^ ^^f- ^"^'"°' *^^- RYMAL Bone (External bmate. Ihe posterior division, repre- ViEw). senting two-thirds, is smooth and forms part of the inner wall of the orbit. The lachrymal crest gives origin to the tensor tarsi muscle, and inferiorly terminates in a hook-like projection, called the hamular process. This process is curved in a forward direction, and is received into the lachrymal notch at the front part of the internal border of the orbital plate of the superior maxilla, where it bounds externally the superior orifice of the lachrymal canal. It articulates with the lachrymal tubercle of the superior maxilla. The internal surface presents a vertical furrow corresponding with the position of the lachrymal crest on the external surface. Superiorly it articulates with the front part of the lateral mass of the ethmoid, where it helps to close ethmoidal cells, and forms part of the infundibulum. Inferiorly it forms part of the outer wall of the nasal fossa, and looks into the middle meatus. THE BONES OF THE HEAD 109 The superior border is short, and articulates with the internal angular process of the frontal. The inferior harder, behind the lachrymal crest, articulates with the internal border of the orbital surface of the superior maxilla, whilst in front of the crest it forms, as stated, the descending process, and articulates with the lachrymal process of the inferior turbinate. The anterior harder articulates with the inner lip of the lachrymal groove on the posterior border of the nasal process of the superior maxilla. The posterior harder articulates with the anterior border of the os planum of the ethmoid. The bone derives its blood-supply from the nasaJ and anterior ethmoidal branches of the ophthalmic artery. Articulations. — The lachrymal articulates with four bones, as follows : superiorly with the frontal, anteriorly with the superior maxilla, inferiorly with the inferior turbinate, and again with the superior maxilla, and posteriorly with the ethmoid. Structure. — ^The bone consists of a thin translucent plate. Ossification. — The lachrymal is developed in membrane usually from one centre, which appears during the third month of intra-u ferine life. The Inferior Turbinate Bones. The inferior turbinate or spongy bone (maxillo-turbinal) some- times called the inferior concha, is situated on the outer wall of the Lachrymal Process 1. A Ethmoidal Process Front Part of Superior- Border , "-^ ^^^^^"^""--rtS^^^^ Back Part of Superior Bord<;r )erior -^^ - " -' • ibR^ i Anterior ExUemity - -^^ ■' f¥*'x - ' ^ *^ ~*'J!P)'^/^ ^'^~~^^ir^^^T~Tf'J.!^i-^'^ Inferior Border L Lachrymal Process Ethmoidal Process 1 Maxillary Process ^ Anterior Extremity Inferior Border Fig. 67. — The Right Inferior Turbinate Bone. A, Internal View ; B, External View. nasal fossa, where it overhangs the inferior meatus, and is in series with the inferior turbinate process (middle spongy bone) of the ethmoid. It is elongated from before backwards, and presents no A MANUAL OP ANATOMY two surfaces, two borders, and two extremities. The external - surface is concave, and is overhung above, over about its middle third, by the maxUlary process. It looks towards the outer wall of the nasal fossa. The internal surface is irregularly convex, pitted, and marked by a few antero-posterior grooves. It bulges into the nasal fossa, and limits interiorly the middle meatus. The superior border, which is attached, slopes downwards and forwards in front, where it articulates with the inferior turbinate crest of the superior maxilla. Behind this it presents a slight concavity, limited in front by the lachrymal process, which articu- lates with the descending process of the lachrymal, and forms part of the lachrymal canal. Behind the concavity is the ethmoidal process for the uncinate process of the ethmoid. The portion of the superior border between these two processes is folded down- wards and outwards into a thin plate, called the maxillary process, which forms part of the inner wall of the antrum of Highmore below the opening of that cavity. Behind the ethmoidal process the superior border slopes downwards and backwards, and articu- lates with the inferior turbinate crest of the palate bone. The inferior border is convex, thick, pitted, and free. The anterior extremity is short and stunted, whilst the posterior is long, slender, and pointed. The bone receives its blood-supply from the spheno-palatine branch of the internal maxillary, and anterior ethmoidal branch of the ophthalmic, arteries. Articulations. — The inferior turbinate articulates with the follow- ing four bones : superior maxilla, lachrymal, ethmoid, and palate. Structure. — ^The bone is light and porous. Ossification. — The inferior turbinate is developed in cartilage from one centre, which appears in the fifth month of intra-u ferine Ufe. The Palate Bones. The palate bone enters into the formation of the hard palate, the outer wall of the nasal fossa, and the floor of the orbit. It consists of a horizontal and perpendicular plate, which meet at a right angle, and of three processes, namely, pyramidal process or tuberosity, situated at the meeting of the two plates posteriorly, and orbital and sphenoidal processes, situated at the upper ex- tremity of the perpendicular plate, where they are separated by the spheno-palatine notch. The horizontal or palatal plate is quadrate, and presents two surfaces and four borders. The superior or nasal surface is smooth and concave from side to side. It forms the posterior fourth of the floor of the nasal fossa, and is covered in the recent state by the nasal mucous membrane. The inferior or palatal surface forms the pos- terior fourth of one-half of the hard palate, and near its posterior border it presents a short transverse ridge, which gives insertion to a portion of the tendon of the tensor palati. The anterior border THE BONES OF THE HEAD ill is serrated for the posterior border of the palatal process of the superior maxilla. The posterior border is concave and sharp. It gives attachment to one-half of the soft palate, and at its inner extremity it forms a backward projection, which, with its fellow, constitutes the palatal or posterior nasal spine, for the attachment of the azygos uvulae muscle. The external border is attached, and meets the perpendicular plate at a right angle. On its outer aspect posteriorly it is excavated by the lower part of the posterior palatine canal. The internal border is thick and serrated, and articulates with its fellow, forming an upward elevation, called the nasal crest. This crest is continuous with that of the palatal processes of the superior maxillse, and, like it, is grooved superiorly for a portion of the inferior border of the vomer. The perpendicular plate rises upwards from the outer border of the horizontal plate. It is long and thin, and presents two Internal or Ethmoidal Surf. ^ ^^^^ Sup. or Orbit. Surf, of Orbital Process Anterior or Maxillary Surt-^ -^jWt Posterior or Sphenoidal Surface SjAeno-palatine Notch ^_ ifs^jjwl ^V^Sphenoiaal Process Superior Turbinate or j||||B^^^%^^^ Ethmoidal Crest /•yj^^llJfc^^i^'''- Superior Meatus J. ^ Middle Meatus / '^^y^-fi-'i^^f^ Inferior Turbinate Crest Maxillary Process . jL -^^i i \ . ^^Wl~ Inferior Meatus X. , ' _,^v?t\ ^^^k , ^°'' P'^ygoid Fossa of Sphenoid \^,/l' l^^Js'^^\.'- ^"^ ^•'"' P^'^O'goid Plate J^''M~j.^y^^^^fel^py of Sphenoid Nasal Crest { | Tuberosity Posterior Nasal Spine For InL Pterygoid Plate of Sphenoid Fig. 68. — The Right Palate Bone (Internal View). surfaces and four borders. The internal zurface forms part of the outer wall of the nasal fossa, and is crossed from before backwards by two ridges. The lower ridge is called the inferior turbinate crest, and articulates with the posterior sloping part of the superior border of the inferior turbinate bone. The upper ridge, which crosses the roots of the orbital and sphenoidal processes, is called the ethmoidal or superior turbinate crest, and it articulates with the inferior turbinate process of the ethmoid. Below the inferior turbinate crest is a smooth groove, which forms part of the inferior meatus of the nose ; between the inferior and superior turbinate crests is another groove, which forms part of the middle meatus ; and above the superior turbinate crest there is a third groove, which forms part of the superior meatus. The external or maxillary surface, towards its upper and posterior part, forms the inner boundary of the pterygo-maxillary fissure, and leading dowTiwards from this part is a groove, which, with Lhe superior maxilla, forms A MANUAL OF ANATOMY the posterior palatine or palato-maxillary canal for the great or anterior descending palatine nerve and the superior or descending palatine artery. In front of this groove the external surface articulates with the inner surface of the superior maxilla behind the opening of the an rum. Behind the groove the external surface articulates interiorly with the posterior border of the superior maxilla, and superiorly with the internal pterygoid plate of the sphenoid. The anterior border of the perpendicular plate presents, just below the inferior turbinate crest, a leaf-like projection, called the maxillary process, which closes the lower and back part of the opening of the antrum of Highmore. Superiorly it articulates with the ethmoid, and interiorly with the superior maxilla. The pos- terior border articulates superiorly with the anterior border of the internal pterygoid plate of the sphenoid, and interiorly it Spheno-maxillary Surfaces^.,,^ Sphenoidal Process.^ Inner Boundary of Pterj'go-maxillary Fissure Orbital Process % ^ Spheijo-palatine Notch '*^ For Superior Maxilla .Maxillary Process for Maxillary Sinus Tuberosity j Groove for Post. Palatine Canal ! i For Zygomatic Fossa For Post. Border of Sup. Maxilla Fig. 69. — The Right Palate Bone (External View). is prolonged into the tuberosity. The inferior border is attached, and m:'ets the horizontal plate. The superior border presents the orbital and sphenoidal processes and the spheno-palatine notch, to be presently described. The pyramidal process or tuberosity projects backwards, down- wards, and outwards from the meeting of the horizontal and per- pendicular plates, and is received into the pterygoid notch of the sphenoid. Posteriorly it presents three grooves. The central groove forms part of the pterygoid fossa, and gives origin to fibres of the internal pterygoid. The grooves on either side are rough, and articulate with the anterior borders of the correspond- ing pterygoid plates. The tuberosity on its inferior aspect, close to the horizontal plate, presents two small openings, which are the orifices of the posterior and external accessory palatine canals, the latter being the smaller of the two, and inconstant. These canals transmit the posterior and external descending palatine THE BONES OF THE HEAD 113 nerves and arteries. Internally the tuberosity gives origin to a few fibres of the superior constrictor muscle of the pharynx. Externally there is a small free surface, which looks into the zygomatic fossa, between the pterygoid process of the sphenoid and the tuberosit}' of the superior maxilla. The orbital process surmoimts the anterior border of the per- pendicular plate. It is of large size, and presents six surfaces, three of which are articular. The superior or orbital surface forms a small part of the floor of the orbit posteriorly. The external or spheno-maxillary surface looks into the spheno-maxUlary fossa. The anterior or maxillary surface is continuous with the external surface of the perpendicular plate, and articulates with the back part of the internal border of the orbital surface of the superior maxilla. The internal or ethmoidal surface, which is excavated, articulates with the lower border of the os planum of the Post, or Sphenoidal Surf, of Orbital Proces Superior or Sphenoidal Surface . ^ of Sphenoidal Process Groove for Pterygo-palatine Canal — -' Inferior Turbinate Crest Nasal Crest Posterior Nasal Spine / Horizontal Plate' For Int. Pterygoid Plate of Sphenoid ' Superior or Orbital Surface . _.Ext. or Spheno-maxillary Surface >Spheno-palatine Notch .Groove for Post. Palatine Canal (on Ext. Surf.) , For Pterj-goid Fossa of Sphenoid For Ext. Pterygoid Plate of Sphenoid Tuberosity Fig. 70. — The Right Palate Bone (Posterior View). ethmoid at its back part, close to the postero-inferior angle. The posterior or sphenoidal surface small and excavated, articulates ; with the front of the body of the sphenoid, and, as a rule, com- municates with the sphenoidal air sinus. The inferior or nasal surface is continuous with the internal surface of the perpendicular plate, and forms part of the outer wall of the nasal fossa at its upper and back part, where it overhangs the groove for the superior meatus. The sphenoidal process surmounts the posterior border of the perpendicular plate, and is shghtly incurved. It presents three surfaces, and three borders. The superior or sphenoidal surface, wluch is grooved, articulates with the inferior surface of the body, and the vaginal process, of the sphenoid. The groove on this surface, with that on the under surface of the vaginal process, forms the pterygo-palatine canal for the pharyngeal nerve and pterygo- palatine artery. The internal or nasal surface is scooped out, and 114 A MANUAL OF ANATOMY has an inclination downwards as well as inwards. It forms part of the outer wall and roof of the nasal fossa. The external or spheno-maxillary surface forms part of the inner wall of the spheno- maxillary fossa. The anterior border bounds the spheno-palatine notch posteriorly, and may be projected over it to join the orbital process. The posterior border articulates with the internal ptery- goid plate of the sphenoid. The internal border articulates with the ala of the vomer. The spheno-palatine notch is situated between the orbital and sphenoidal processes, and is converted into a foramen usually by the inferior surface of the body of the sphenoid, representing the part formed by a sphenoidal spongy bone. It leads from the spheno-maxillary fossa into the superior meatus of the nose, and transmits the internal branches of the spheno-palatine or Meckel's ganglion, and spheno-palatine artery. The bone derives its blood-supply from the spheno-palatine, descending palatine, and pterygo-palatine branches of the internal maxillary artery. Articulations. — The palate bone articulates with six bones, as follows: the superior maxilla, inferior turbinate, ethmoid, vomer, sphenoid, and its fellow. Structure. — The bone is very thin, especially over the upper part of the perpendicular plate. Varieties. — (i) The groove for the posterior palatine canal may be bridged over. (2) The external accessory palatine canal may be absent. (3) The spheno-palatine notch may be converted into a foramen by a forward extension of the sphenoidal process. Ossiflcation. — The palate bone is ossified in membrane from one primary centre. The primary centre appears about the seventh week, at the angle of junction between the horizontal and vertical plates, or in the vertical plate (Fawcett). There may be a secondary centre for the orbital process. The Vomer. The vomer is situated in the median plane, and forms part of the septum of the nose. It presents two surfaces, four borders, and an anterior extremity. The surfaces are disposed laterally, and each looks into the corresponding nasal fossa. Traversing each there is a groove, directed forwards and downwards, for the naso-palatine nerve. The superior border is characterized by two thick, everted alae, separated by a groove, which receives the rostrum of the sphenoid, Each ala by its upper aspect fits against the inferior surface of the body of the sphenoid, and the lateral margin of each meets the vaginal process of that bone, and also articulates with the internal border of the sphenoidal process of the palate bone. The inferior border is irregular, and is received into the groove which marks the nasal crests of the palatal plates of the superior maxillae and palate bones. The anterior border is sloped downwards and THE BONES OF THE HEAD "5 Anterior Border Groove for Naso-palatine Nerve Inferior Border forwards, and it may present two alae, but these are very thin, and lie near each other, being separated by a narrow cleft. These characters are always more pronounced in earlier life. The cleft in its lower part receives the septal nasal cartilage, and superiorly the perpendicular plate of the ethmoid fits into it, being usually ankylosed with one or both alae. In many cases, however, the anterior border is simply grooved. The posterior border is sharp, and almost vertical, and lies between the posterior nares. The anterior extremity forms a short irregular lip, which touches the back parts of the incisor crests of the superior maxillae. The bone receives its blood-supply from the spheno-palatine branch of the in- ternal maxillary Superio^r Border artery. Articulations. — The vomer ar- ticulates with six bones, as follows : the sphenoid, two palate bones, eth- Posterior Border moid, and superior maxiUae. In addi- tion to these, it articulates with the septal nasal carti- lage. Structure. — ^The vomer is composed of two thin pkites of compact bone, which are blended into one, except superiorly, and, it may be, to a certain extent anteriorly. Varieties. — The bone is often much deflected to one or other side, more frequently the left, and so it may curtail the cavity of the nasal fossa to which it is deflected. Ossifieation. — The vomer is developed in membrane from two centres, which appear about the eighth week of intra-uterine hfe. The centres unite below in the third month, and form a groove in which the septal nasal cartilage lies. The laminae forming the lips of the groove continue to grow upwards and forwards, and subsequently fuse, the enclosed cartilage becoming absorbed. Ultimately there are left the alae on the superior border, and, it may be, on the anterior border, which are permanent indications of the original bilaminar condition of the bone. The Inferior Maxillary Bone. The inferior maxillary bone or mandible supports the lower teeth, and articulates at either side with the anterior part of the glenoid fossa of the temporal in a freely movable manner. It has the shape of a horse-shoe, and consists of a central horizontal portion, called the body, and two upright portions, called the rami. The body is arched, being convex in front and concave behind, and it presents two surfaces and two borders. The external surface presents a slight median vertical ridge over its upper two-thirds, which marks the symphysis or place of union of the two halves Fig. 71. — The Vomer (Lateral View). Ii6 A MANUAL OF ANATOMY of which the bone is originally composed. This ridge bifurcates at the lower third, and its two divisions, diverging, pass to the lower border, where each terminates in the mental tubercle. Between these diverging divisions there is a triangular elevated surface, called the mental protuberance or chin. On either side of the sym- physis is the incisor fossa, which gives origin to the levator menti and a deep slip of the orbicularis oris. A little external to this fossa is the mental foramen, which opens outwards from the inferior dental canal, and transmits the mental nerve and vessels. This Sigmoid Notch Left Coronoid Process Temporal Muscle j External Pterygoi Left Condyle Impression for Temporal Muscle Incisor Fossa Levator Menti Depressor Labii Inferioris Mental Protuberance Mental Tubercle Posterior — Border of Rami -Masseter Mental Foramen Base Platysma Myoides External Oblique Line and Depressor Anguli Oris Fig. 72. — The Inferior Maxillary Bone (External View). foramen is in line with the septum between the two bicuspid alveoli, and in the adult it is midway between the superior and inferior borders. Below it is the external oblique line, which extends from the mental tubercle to the lower extremity of the anterior border of the ramus. This line gives origin to the depressor anguli oris. The lower part of the external surface, from near the symphysis to about the level of the mental foramen, gives origin to the depressor labii inferioris. The internal surface presents a slight median groove over about its upper two-thirds, which coincides with the symphysis. Lower down there are four small projections, called collectively the genial , spines, which are arranged in pairs on either side of the middle line. The upper spine gives origin, at either side, to the genio-hyo- glossus, and the lower to the genio-hyoid. Close to the lower border, at either side of the symphysis, is the oval digastric impression, THE BONES OF THE HEAD 117 which gives origin to the anterior belly of the digastric. Coin- ciding with the position of the external oblique line there is the internal oblique line or mylo-hyoid ridge. This commences near the symphysis below the lower genial spine, and, passing obliquely backwards and upwards, it terminates a little behind the last molar alveolus. It gives origin to the mylo-hyoid muscle over its whole length, whilst at its upper and back part it gives attachment to some fibres of the superior constrictor muscle of the phar\-nx and the pterygo-mandibular ligament. Below the posterior part of this Coronoid Process Temporal Musde Lingnla Inferior Dental Furamen Buccinator Fossa for Submaxillary Gland Internal Oblique Line Fossa for Sublingual Gland Interna! - - - Pterygoid Upper Genial - - ' ' Spine and Genio-hyo-glossus Lower Genial Spine and Genio-hyoid Mylo-hyoid Groove Digastric Impression and Anterior Belly of Digastric Fig. 73. — The Left Half of the Inferior Maxillary Bone (Internal View). ridge is the submaxillary fossa for the submaxillary gland, and above fk& anterior part is the sublingual fossa for the sublingual gland. t The superior or alveolar border is excavated into sixteen alveoli or sockets, eight in each half of the bone, which correspond with those in each superior maxilla. The outer surface of the alveolar border, over the extent of the three molar alveoli at either side, gives origin to some fibres of the buccinator. The inferior border or base terminates, at either side, on a level with the anterior border of the ramus. It projects more than the superior border, and gives insertion on its outer aspect to a portion of the platysma myoides. Near its termination it is marked by a short vertical groove for the facial artery. ii8 A MANUAL OF ANATOMY The ramus rises, at either side, from the extremity of the body. It is compressed from without inwards and presents two surfaces and four borders. The external surface gives insertion to the masseter, and, in the vicinity of the angle, it presents a few oblique ridges for the tendinous bands of that muscle. The internal surface presents, a little below its centre, the inferior dental foramen, which is on a level with the summit of the crown of the third molar tooth. This foramen leads to the dental canal, which traverses the bone to near the symphysis, and from which, near its anterior part, the mental foramen opens on the external surface. This canal lodges the inferior dental nerve and vessels, and communicates with the foramina which open on the extremities of the fangs of the teeth. The inferior dental foramen presents anteriorly and internally a thin, sharp plate of bone, called the lingula. Behind the lower end of the latter is a short crescentic margin on the inner aspect of the foramen, and proceeding downwards and forwards from this is the mylo-hyoid groove, which terminates a little below the posterior extremity of the mylo-hyoid ridge, and transmits the mylo-hyoid nerve and artery. The spheno -mandibular liga- ment is attached to the lingula and to the crescentic margin behind it. Between the inferior dental foramen and the angle there is a rough impression, often strongly ridged, which gives insertion to the internal pterygoid. The anterior border is continuous with the external oblique line opposite the third molar alveolus, and is shorter than the posterior. The posterior border meets the inferior border, thus forming the angle, which, in muscular subjects, is strongly marked and slightly everted. Externally and internally it presents rough impressions for portions of the masseter and internal pterygoid respectively, and between these muscles it gives attachment to the stylo-man- dibular ligament. The angle is obtuse, and in the adult amounts on an average to 120 degrees. In early infancy it is as much as 150 degrees, and in old age it amounts to about 140 degrees. The inferior border is continuous with the inferior border or base of the body. The superior border presents the sigmoid notch, the coronoid process, and the condyle. The sigmoid notch communicates with the zygomatic fossa, and transmits the masseteric nerve and artery to the deep surface of the masseter. The coronoid process surmounts the anterior border of the ramus, and is triangular and compressed from without inwards. Its external surface gives insertion to fibres of the masseter, and its internal surface, as well as the superior and anterior borders, to part of the temporal muscle. The internal surface is marked by a ridge which extends downwards on the internal surface of the ramus, not far from the anterior border, to a point on the inner side of the last molar alveolus, where it becomes continuous with the mylo-hyoid ridge. The temporal muscle continues to take inser- tion into this ridge, as well as into the elongated triangular depres- sion between it and the anterior border of the ramus. THE BONES OF THE HEAD 119 The condyle surmounts the posterior border of the ramus. It is oval and convex, and it articulates with the anterior part of the glenoid fossa of the temporal, an interarticular fibro - cartilage inter\-ening. Its long axis is oblique, so that the axes of the two condvles, if sufficiently prolonged inwards and slightly backwards, would meet near the anterior margin of the foramen magnum. Extemallv the condyle presents a projection, called the condylar tubercle, for the external lateral ligament of the temporo-mandi- bular articulation. Below the condyle is the neck, which presents anteriorly a depression for the inser- tion of the greater part of the external pter\'goid muscle. The bone receives its chief blood- supply from the inferior dental branch of the internal maxillary artery. Other sources are the facial, and the sublingual branch of the lingual. Articulations. — With the glenoid fossae of the temporal bones. Structure. — ^The inferior maxilla is composed of two dense plates of compact bone, which are particu- larly strong in the region of the base, but become thinner superiorly at the alveolar border. Between these plates there is cancellated tissue with wide meshes. Ossification. — The mandible is a mixed bone, being chiefly a membrane bone, but in part also a cartilage bone. It is ossified in connection with Meckel's cartilage and its fibrous investment. Each half of the bone has one centre (Low and Fawcett), which appears about the sixth week of intra- Coronoid Process Fig. 74A, — The Inferior Maxill.\ry Bone at Birth. Mai leas Alveolar Groove Hamulus ^3 _Tym panic .'\nnulus and Membrane Mecke^^ Cartilage Manubrium of Malleus Long Process of Incus Fig. 74B. — Meckel's Cartil.\ge. {From Keibel .\nd Mall. After KotLM.\NN). uterine hfe, being only preceded by the primary centres for the cla\icle. It is deposited in the membrane which covers the outer surface of Meckel's cartilage in the region of the future mental foramen. From this centre one- half of the bone is ossified, chiefly in membrane, but also in cartilage, namely, the mesial end of Meckel's cartilage, and certain other accessory cartilages. The original centre gives membranous origin to (i) the walls of the alveoli and A MANUAL OF ANATOMY dental canal, (2) the basilar border and angle, and (3) the ramus as high as the interior dental foramen. The mesial part of Meckel's cartilage is invaded by osseous extension from the primordial membrane-bone formed from the single centre, the mesial part of Meckel's cartilage becoming incorporated with the bone so formed, and constituting the incisor portion of the mandible. AT BIRTH Fig. 75. — The Inferior Maxillary Bone at Different Periods of Life. The accessory cartilages, which are distinct from Meckel's cartilage, are as follows: (i) Condylar, (2) coronoid, and (3) symphysial. All these accessory cartilages become surrounded and invaded by osseous extension from the primordial membrane-bone formed from the single centre, and they become incorporated with the parts of the mandible so formed. The condylar cartilage gives rise to (i) the condyle, and (2) the posterior THE BONES OF THE HEAD I2I part of the ramus as low as the inferior dental foramen. The eoronoid cartilage gives rise to (i) the eoronoid process, and (2) the anterior part ot the ramus as low as the inferior dental foramen. The symphysial cartilage gives rise to the hmited symphysial part of the mandible. At birth the mandible consists of two halves, connected at the symphysis by fibrous tissue. In the course of theirs/ year osseous union takes place, which is completed towards the end of the first year or beginniog of the second year. Meckel's cartilage extends on either side downwards and forwards from the periotic cartilaginous capsule to the median Une, where it meets its fellow. It is surrounded by a fibrous investment. The proximal end of the cartilage gives rise to the malleus and incus, two of the three ossicles of the tympanum. The part of the cartilage between the periotic cartilaginous capsule and the inferior dental foramen disappears, and the membranous investment of this part persists as the spheno-mandibular ligament. The part of the cartilage between the inferior dental foramen and the mental foramen also disappears, and its membranous investment undergoes ossification from a single centre. and gives rise to (i) the greater part of one-half of the body of the mandible (incisor and symphj'sial parts excepted), and (2) the lower half of the ramus as high as the inferior dental foramen. The mesial part of Meckel's cartilage, when ossified, becomes the incisor part of the mandible. At birth the inferior border is but little developed, and the body is consequently shallow. The rami are very short, so that each condyle is nearly on a level with the upper border of the symphysis, and the eoronoid process is rather longer than the condyle. The mental foramen is nearer the inferior than the superior border, and the angle amounts to 1 50 degrees or more. Subsequently the body increases in depth, the rami lengthen, the angledecreases, and the mental foramen gradually assumes a position midway between the superior and inferior borders. In old age, after the bone becomes edentulous, the alveolar border undergoes absorption, the body consequently becomes shallower, the mental foramen lies near the superior border, the rami droop backwards, and each angle becomes increased to about 140 degrees. For the development of the alveolar border, and its relation to the milk-teeth, see the superior maxilla. The Hyoid Bone. The hyoid bone is situated in the median line of the neck, between the chin and the thyroid cartilage of the larynx, with which latter it is connected by means of the thyro-hyoid membrane and thyro-hyoid liga- ments. It is closelj' connected with the base of the tongue, and is hence known as the os linguce. In its development it is associated with the skull, and it is sus- pended from the lower ends of the styloid processes of the tem- poral bones by two fibrous bands. Great Comn' called the stylo-hyoid ligaments Smaiicomii (epi-hyals). It consists of a central " | v portion or body and two pairs of Body and Hyoid Tubercle Superior Border cornua, great and small. tt,^ ,a t„„ tt t, Ti,„ v^j„ • 1 i J . '^^^- 76. — The Hyoid Bone The body is elongated trans- (Anterior View). versely, compressed from before backwards, and quadrilateral. Its surfaces, which are anterior and posterior, occupy an obUque plane, being sloped downwards and for- A MANUAL OF ANATOMY wards. The anterior surface is convex, and is crossed transversely by a ridge, which divides it into an upper and a lower part. At the middle line this is intersected at right angles by a vertical ridge, which, however, is often incomplete, being sometimes con- fined to the upper half, and sometimes to the lower. At the place of intersection of the two ridges there is a slight projection, called the hyoid tubercle. Each half of the anterior surface is thus mapped out into an upper and a lower irregular muscular division. The upper division, provided the uppsr border is not very thick, gives attachment to the genio-hyoid and genio-hyo-glossus, and the lower division to the digastric, stylo-hyoid, and mylo-hyoid. The posterior surface is concave, and is covered by the thyro-hyoid membrane as it ascends to be attached to the superior border, a synovial bursa intervening. This surface is related to the epiglottis. Great Cornu ■- Small Cornu Body _ —"-Middle Constrictor — -"ilyo-glossus " ■ Chondro-glossiLs -- Genio-hyo-glossus - Digastric Stylo-hyoid Omo-hyoid (Ant. Belly) Thyro-hyoid . Mylo-hyoid I Sterno-hyoid Genio-hyoid Fig. yy. — The Hyoid Bone, showing its Muscui,ar Attachments. The superior border is somewhat thick, and occasionally is really a surface, in which cases it gives attachment to the genio-hyo- glossus, whilst its posterior lip gives attachment to the thyro-hyoid membrane. The inferior border is sharp, and gives insertion to the sterno-hyoid, anterior belly of the omo-hyoid, and thyro-hyoid muscles. Each lateral border is connected with a great cornu. The great cornua project upwards and backwards from the lateral borders of the body. Each is compressed from above downwards, and gradually diminishes in size to its termination, where it ends in a small tubercle for the attachment of the thyro-hyoid ligament. It gives attachment to fibres of the thyro-hyoid, hyo-glossus, middle constrictor muscle of the pharynx, and the thyro-hyoid membrane. Each great cornu is connected with the body by synchondrosis up to middle life, after which ankylosis usually takes place. THE BONES OF THE HEAD 123 The small cornua are short conical nodules, each of which projects upwards and backwards from the junction between the body and great comu. Its tip gives attachment to the stylo- hyoid ligament, which is sometimes ossified, a possible condition to be borne in mind during digital examination of the upper part of the pharynx. Elsewhere it gives attachment to the middle constrictor muscle of the pharynx, and sometimes to the chondro- glossus. The small cornua may be wholly or partially cartilaginous, and they articulate with the body by a synovial joint, imles in advanced hfe, when ankylosis usually takes place. Ossifieation. — The hyoid bone is developed in connection with the second and third visceral arches. The cartilaginous bar of the second visceral arch is known as the hyoid bar, and is continuous with its fellow at the median line. The cartilaginous bar of the third visceral arch is known as the thyro-hyoid bar, and at the median Une it blends with the junction of the hyoid bars. With the foregoing proviso, the hyoid bone is developed from five, or. it may be, six centres. One, or, it may be, two are deposited during the last month of intra-uterine life at the place of fusion of the two hyoid bars. If there are two centres they soon join, and give rise to the greater part of the body of the hyoid bone or basi-hyaL About the same time a centre appears at either side in the thjTO-hyoid bar of the third \-isceral arch, and from these centres are developed the great cornua or thyro-hyals, and the adjacent portions of the body. In the course of the first year the two remaining centres appear, one at either side, in the lower or mesiad part of each hyoid bar, and these centres give rise to the small cornua or eerato-hyals. The great cornua join the body in middle life, but the small cornua do not join until advanced life. The stylo-hyoid ligaments may become ossified more or less completely, and 50 represent the epi-hyal bones of many animals. The Skull as a Whole. Sutures. The only bone of the skull which has movable articulations is the mandible. Each condyle of that bone articulates with the anterior part of the glenoid fossa of the corresponding temporal bone, with the inter\'ention of an interarticular fibro-cartUage, the articulation so formed being called the temporo-mandibular joint. The other bones of the skuU, for the most part, are in close con- tact with each other, a small amount of fibrous tissue being inter- posed, which is continuous with the periosteum. These articula- tions are called sutures. Certain cranial bones, however, are separ- ated at first by a plate of hyaline cartilage, the articulation being called synchondrosis. This, however, is a temporary joint, inas- much as ankylosis takes place after a certain period of Hfe. It appHes to (i) the articulation between the basilar process of the occipital and the body of the sphenoid, and (2) the articulation between the jugvdar process of the occipital bone and the jugular impression on the inferior surface of the petrous portion of the temporal bone. The occipito-parietal or lambdoid suture connects the superior lateral borders of the tabular part of the occipital bone with the 124 ^ MANUAL OF ANATOMY posterior borders of the two parietal bones. The two limbs of the suture, right and left, become continuous with each other at the superior angle of the tabular part of the occipital bone, from which point each Hmb passes outwards and downwards. The margins of the bones are strongly serrated, and along the course of the suture supernumerary ossicles, called Wormian bones, are frequently present. The occipito-mastoid suture, on either side, connects the inferior lateral border of the tabular part of the occipital bone with the posterior border of the mastoid part of the temporal bone. It is one of the bifurcations of the lower end of the corresponding limb of the occipito-parietal suture, the other bifurcation being the parieto-mastoid suture. Its direction is downwards and forwards. The interparietal or sagittal suture connects the superior borders of the two parietal bones. It is serrated, and occupies the median Coronal Suture " Bregma (Anterior Fontanelle) J ■ Sagittal Suture , , , \ SeSK/^r' /Parietal Foramen Lambda \ i / (Posterior Fontanelle) -V- 7i''*ife'Vj_ / \ _j5^ — ^'^i ■ X^-^mbdoid Suture Fig. 78. — Sutures of Superior Surface of Skull. line, its direction being from behind forwards. Posteriorly it meets the lambdoid suture, the place of meeting constituting the lambda, which indicates the situation of the posterior fontanelle of early life. From the lambda three sutures radiate — namely, the interparietal suture and the two limbs of the occipito-parietal suture. Anteriorly the interparietal suture meets the coronal- suture, the place of meeting constituting the bregma, which indicates the situation of the anterior fontanelle of early life. The part of the sagittal suture in the region of the two parietal foramina is usually less serrated than elsewhere, and is the first part to show signs of obliteration. It constitutes the obelion, which indicates the situation of the sagittal fontanelle of early intra-uterine life. The fronto-parietal or coronal suture connects the supero-lateral or parietal border of the frontal portion of the frontal bone with the anterior borders of the two parietal bones. It crosses the THE BONES OF THE HEAD 125 superior surface of the skull in an arched manner, extending on either side as low as the superior border of the great wing of the sphenoid. As it crosses the median hne it is joined by the anterior end of the interparietal suture. The place of junction is, as stated, called the bregma, which indicates the position of the anterior fontanelle of early Ufe. From the bregma three sutures radiate — namel3^ the interparietal suture and the two hmbs, right and left, of the fronto-parietal suture. Each hmb of the fronto-parietal suture is serrated, but more so over the central part than the upper and lower parts, and more so over the upper part near the median line than over the lower part, in which two latter situations over- lapping takes place. Superiorly the frontal bone shghtly overlaps the parietal bone, and inferiorly the parietal bone distinctly over- laps the frontal bone, the opposed bevelled surfaces in the latter region being ridged. This latter portion of the coronal suture is spoken of as a limbous suture. The metopic or frontal suture, which connects the two halves of the frontal bone during the first year of hfe, may persist throughout life. Under these circumstances, it extends in the median hne from the bregma to the centre of the nasal notch of the frontal bone. Superiorly it is continuous with the interparietal suture, and inferiorly Nvith the internasal suture. Even though the suture may not persist entirely, traces of it may be present inferiorly and superiorly, especially inferiorly. As a rule, however, the suture is entirely obhterated by the end of the sixth year of hfe. The parieto-mastoid suture connects the posterior part of the inferior border of the parietal bone with the superior border of the mastoid part of the temporal bone. Its direction is from behind forwards, and, as stated, it is one of the bifurcations of the lower end of the corresponding hmb of the occipito-parietal suture. It is serrated, and anteriorly is continuous with the posterior end of the squamo-parietal suture. It is on a level with the upper border of the zygoma. The point, situated at its posterior extremity, coincides with the asterlon, which indicates the situation of the postero-lateral or mastoid fontanelle of early hfe. From this point three sutures radiate — namely, the corresponding limb of the occipito-parietal suture, the parieto-mastoid suture, and the occipito- mastoid suture. Near the anterior part of the parieto-mastoid suture there is the parietal notch on the superior border of the pars mast&idea, which coincides with the entomion. The parieto-squamosal suture connects the greater part of the inferior border of the parietal bone with the superior border of the squamous part of the temporal bone. It is arched, the convexity being directed upwards, and after haWng descended posteriorly, it becomes continuous with the parieto-mastoid suture. Anteriorly it is continuous with the spheno-parietal suture. The parieto-squamosal suture presents a marked contrast to the foregoing serrated sutures, inasmuch as it is a squamous suture, the squamous part of the temporal overlapping the lower border of the parietal bone. 126 A MANUAL OF ANATOMY The spheno-parietal suture connects the posterior part of the superior border of the great wing of the sphenoid with the antero- inferior angle and anterior part of the inferior border of the parietal bone. Its direction is from behind forwards. Posteriorly it is continuous with the parieto-squamosal suture, and anteriorly with the spheno-frontal suture. The spheno-parietal suture, like the parieto-squamosal, is a squamous suture. The region of the spheno- parietal suture coincides with the pterion. The spheno-parietal suture may be very short, or entirely absent, in which latter case the lower and posterior part of the frontal bone articulates directly with the squamous part of the temporal bone, thus excluding the antero-inferior part of the parietal bone from any articulation with the great wing of the sphenoid. In such cases the pterion is situated at the posterior end of the spheno-fronal suture. In all cases the guide to it is the lower end of the posterior border of the Abnormal. Normal. Fig. 79. — Sutures of Right Lateral Surface of Skull. S.P., Spheno-parietal; S.F., Spheno-frontal; P.S., Parieto-squamosal; X, Pterion; C, Coronal; S.S., Spheno-squamosal. external angular process of the frontal bone, the pterion being situated about i| inches behind it, and about 2 inches above the zygomatic arch. The pterion indicates the situation of the antero- lateral or sphenoidal fontanelle of early hfe. In this region a Wormian bone, called the epipteric bone, is sometimes met with. The fronto-squamosal suture is not constant. When present, it connects the lower and posterior part of the frontal bone with the upper and anterior portion of the squamous part of the temporal bone. Its direction is vertical, and it is usually continuous with the terminal part of the coronal suture. It excludes the antero- inferior part of the parietal bone from any articulation with the great wing of the sphenoid. The spheno-frontal suture, which is a squamous suture, connects the superior border of the great wing of the sphenoid bone with the lower part of the lateral aspect of the frontal bone. Posteriorly it is continuous with the spheno-parietal suture, and in cases where. THE BONES OF THE HEAD 127 that suture is absent, with the parieto-squamosal suture. Anteriorly it is continuous with the fronto-malar suture. There are tvvo other spheno-frontal sutures. One connects the rough triangular surface on the antero-superior part of the great -wing of the sphenoid bone with the rough triangular surface on the frontzd bone behind the external angular process. This is a harmonic suture. The other spheno-frontal suture (orbito-spheno-frontal suture) will be described under the orbital suturts. It also appears, however, in the anterior fossa of the internal sur- face of the base of the skull. The spheno-squamosal suture connects the external border of the great wing of the sphenoid bone with the antero-inferior border of the squamous part of the temporal bone, its direction being down- wards and backwards as far as the inner end of the fissure of Glaser. Its upper part forms a squamous suture, but its lower part is serrated. The zygomatico-malar suture connects the extremity of the zygo- matic process of the temporal bone with the posterior or zygomatic process of the malar bone. It Ues obHquely, being directed down- wards and backwards, and it is finely serrated. The fronto-malar suture will be described imder the orbital sutures. The fronto-maxillary suture, which is serrated, connects the lateral part of the nasal notch of the frontal bone with the superior border of the nasal process of the superior maxilla. It lies almost transversely. The fronto-nasal suture connects the mesial part of the nasal notch of the frontal bone with the superior border of the nasal bone. It lies transversely, and is serrated. Across the median Hne it is continuous with its fellow of the opposite side, and lateredly it is continuous with the fronto-maxillary suture. The point corre- sponding to the meeting of the two fronto-nasal sutures coincides with the nasal point or nasion. The internasal suture connects the mesial borders of the nasal bones. Its direction is vertical, and it is a harmonic suture. The lower end of the suture coincides with the rhinlon. The naso-maxillary suture connects the external border of the nasal bone \vith the anterior border of the nasal process of the superior maxilla. Its direction is almost vertical, and it is finely serrated. The malo-maxillary suture connects the rough triangular area at the anterior part of the internal surface of the malar bone with the rough superior surface of the malar process of the superior maxilla. The opposed surfaces are rough, and a false suture is formed of the harmonic variety. The orbito-malo-maxillary suture will be described under the orbital sutures. The intermaxillary suture is only partially seen on the facial surface of the skull. This part extends from the centre of the anterior nasal spine to the point of meeting of the alveolar margins of the superior maxillae. The palatal part of the suture connects the mesial borders of the palatal plates of the superior maxillae. Its direction is antero-posterior, and it is a harmonic suture. 128 A MANUAL OF ANATOMY The interpalatal suture connects the mesial borders of the hori- zontal plates of the palate bones. It is continuous with the inter maxillary suture, and is a harmonic suture. The transverse palato-maxillary suture connects the anterior border of the horizontal plate of the palate bone with the posterior border of the palatal plate of the superior maxilla. Its direction is transverse, it is continuous with its fellow of the opposite side, and it is a finely serrated suture. The vertical palato-maxillary suture connects the lower part of the anterior border of the perpendicular plate of the palate bone with the interna] surface of the superior maxilla behind the opening of the antrum of Highmore. It is a harmonic suture. The orbito- palato-maxillary suture will be described under the orbital sutures. The incisor or premaxillary suture is usually of temporary dura- tion. It connects the incisor or premaxillary part of the superior maxilla with the superior maxilla proper. It extends from a point immediately behind the lower end of Stensen's canal to the alveolar border at a point between the lateral incisor and canine alveoli, its direction being outwards and forwards. It is always present in early life, and traces of it may be present in adult life on the inferior surface of the palatal plate of the superior maxilla. The pterygo-maxillary suture connects the lower part of the anterior border of the pterygoid process of the sphenoid with the lower part of the posterior border of the superior maxilla. Its direction is vertical, and it is a harmonic suture. The pterygo- maxillary fissure lies above it. The petro-squamosal suture connects the petrous and squamous parts of the temporal bone, and is situated on the internal or cere- bral surface of the bone. Its direction is antero-posterior, and it extends from the petro-squamosal angle anteriorly to the parietal notch (entomion) on the superior border of the pars mastoidea pos- teriorly, where it meets the squamo-mastoid suture. It is a har- monic suture, and ankylosis usually takes place in the course of the first year of hfe. The suture, however, may persist until puberty, or later. Even though ankylosis takes place at the normal period of time, it may occur in such an imperfect manner that the suture is drilled by several channels. Under the foregoing circumstances pyogenic infection may extend from the tympanic cavity to the cerebral meninges and brain. The petro-squamosal venous sinus of foetal life extends along the petro-squamosal suture. The squamo-mastoid suture connects the mastoid and squamous parts of the temporal bone, and is situated on the external surface of the bone. Its direction is almost vertical, and it extends from the parietal notch (entomion) on the superior border of the pars mastoidea anteriorly to a point behind the posterior limb of the tympanic annulus. The lower part of the suture intervenes between the contiguous part of the pars mastoidea and the post-meatal plate of the pars squamosa, which latter forms the supra-meatal triangle and outer wall of the antrum. Superiorly it meets the petro- THE BONES OF THE HEAD 129 squamosal suture. The squamo-mastoid suture is a harmonic suture, and ankylosis usually takes place in the course of the first year of hfe. The suture, however, may persist until puberty, or even throughout life. Even though ankylosis takes place at the normal period of life, it may occiu" in such an imperfect manner that the suture is drilled by several channels. Under these circum- stances, pus may find an exit from the t^-mpanic cavity to the exterior. The petro-sphenoidal suture connects a portion of the anterior border of the petrous part of the temporal bone with the outer portion of the posterior border of the great wing of the sphenoid. It lies obliquely, its direction being inwards and forwards. The petro-basilar suture connects the inner half of the posterior border of the petrous portion of the temporal bone with the lateral border of the basilar portion of the occipital bone. Its direction is forvvards and sHghtly inwards, and it is a harmonic suture. Su- periorly it is grooved for the inferior petrosal venous sinus. Orbital Sutures. — The orbito-spheno-frontal suture connects the anterior border of the small wing of the sphenoid with the posterior border of the orbital plate of the frontal. It Ues transversely at the back part of the roof of the orbit, and is finely serrated. The orbito-malo-maxUlary suture connects the lower part of the posterior border of the orbital plate of the malar with the postero- internal boundary of the rough superior surface of the malar process of the superior maxilla. It is situated on the outer part of the floor of the orbit, and extends forwards and inwards from the anterior end of the spheno-maxillarj' fissure to the infra-orbital margin at a point above, and slightly internal to, the infra-orbital foramen. It is a hmbous suture, the orbital plate of the malar slightly overlapping the contiguous part of the superior maxilla. The orbito-palato-maxillary suture connects the orbital process of the palate bone with the back part of the internal border of the orbital plate of the superior maxilla. It is situated on the pos- terior part of the floor of the orbit. Its direction is antero-posterior, and it is a harmonic suture. The orbito-palato-ethmoidal suture connects the orbital process of the palate bone with the back part of the inferior border of the OS planum, or orbital plate, of the ethmoid. It hes on the back part of the inner wall of the orbit, where that wall meets the floor. Its direction is antero-posterior, and it is a harmonic suture. The spheno-malar suture connects the anterior border or malar crest of the great wing of the sphenoid with the upper part of the posterior border of the orbital plate of the malar. It is situated towards the front part of the outer wall of the orbit. Its direction is vertical, and it is a limbous suture, the orbital plate of the malar sUghtly overlapping the malar crest of the sphenoid. The fronto-malar suture connects the external angular process of the frontal bone and the short serrated border directly behind that process with the superior or frontal process of the malar and the 9 I30 A MANUAL OF ANATOMY superior border of its orbital plate. A portion of this suture lies on the facial surface of the skull, and the other part lies on the anterior and upper part of the outer wall of the orbit. Its direc- tion is antero-posterior, and it is a serrated suture. It is in line with the spheno-frontal suture. The lachrymo-maxillary suture connects the anterior border of the lachrymal bone with the inner lip of the lachrymal groove on the posterior border of the nasal process of the superior maxilla. It lies on the anterior part of the inner wall of the orbit. Its direc- tion is vertical, and it is a harmonic suture. The place of meeting between the vertical lachrymo-maxillary and almost horizontal fronto-maxillary sutures coincides with the dacryon. The lachrymo-ethmoidal suture connects the posterior border of the lachrymal bone with the anterior border of the os planum, or orbital plate, of the ethmoid. It lies on the inner wall of the orbit. Its direction is vertical, and it is a harmonic suture. The orbito-spheno-ethmoidal suture connects the posterior border of the OS planum, or orbital plate, of the ethmoid with the sphenoidal spongy bone, or with the anterior margin of the lateral surface of the body of the sphenoid bone. It lies vertically on the back part of the inner wall of the orbit, and it is a harmonic suture. There are two other spheno-ethmoidal sutures, which, however, are not orbital. One of these connects the ethmoidal spine of the sphenoid bone and the contiguous portions of the anterior border of the superior surface of the body with the posterior border of the cribriform plate of the ethmoid. It lies in the anterior fossa of the internal surface of the base of the skull, and is irregularly continuous, on either side, with the orbito-spheno-frontal suture, which connects the small wing of the sphenoid with the orbital plate of the frontal. It is a limbous suture, and it may be called the basal spheno- ethmoidal suture. The remaining spheno-ethmoidal suture connects the sphenoidal crest of the sphenoid with the posterior border of the perpendi- cular plate of the ethmoid bone. It is situated at the back part of the osseous nasal septum, its direction being vertical, and it is a harmonic suture. It may be called the septal spheno-ethmoidal suture. The fronto - lachrymal suture connects the internal angular process of the frontal bone and the contiguous part of the outer lip of the bevelled and excavated inner border of its orbital plate, which lies close behind the internal angular process, with the superior border of the lachrymal bone. It is situated on the anterior part of the inner wall of the orbit, where that wall meets the roof; its direction is antero-posterior, and it is a harmonic suture. The fronto-ethmoidal suture connects the inner bevelled and excavated border of the orbital plate of the frontal bone with the superior excavated border of the lateral mass of the ethmoid. It is situated on the inner wall of the orbit, where that wall meets the roof. Its direction is antero-posterior, and it is continuous with the fronto-lachrjmial suture. It may be regarded as a much- modified harmonic suture. The anterior and posterior ethmoidal, or internal orbital, canals lie transversely along its course. The ethmo-maxillary suture connects the inferior border of the OS planum, or orbital plate, of the ethmoid with the inner border iS,VIV (if'li ^^bUi ur ,.; :-v THE BONES OF THE HEAD 13I of the orbital plate of the superior maxilla. It is situated on the inner wall of the orbit, where that wall meets the floor, and its direction is antero-posterior. It is parallel to the fronto-ethmoidal suture, and is a harmonic suture. Schindylesis. — There are only a few examples of this variety of synarthrosis, or immovable joint, in the skull. These are as follows : (i) The articulation between the inferior border of the vomer and the cleft which Hes along the nasal crests of the palatcd plates of the superior maxillary and palate bones; (2) the articulation between the rostrum of the sphenoid and the cleft on the superior border of the vomer between the two thick, everted alae ; and (3) the. articulation between the inferior border of the perpendicular plate of the ethmoid with the narrow cleft on the anterior border of the vomer. Gomphosis. — ^This variety of synarthrosis is illustrated in the impaction of the fangs of the teeth within the alveoh of the superior and inferior maxiUae. Synehondroses. The following are examples of this temporary form of synar- throsis : Synchondrosis Spheno-Occipitalis. — This is situated between the posterior surface of the body of the sphenoid and the anterior surface of the basilar part of the occipitcd bone. Synchondrosis Petro-Occipitalis. — This is situated between the jugular impression on the inferior surface of the petrous part of the temporal bone and the extremity of the jugular process of the occipital. Synchondrosis Spheno-Petrosa. — This is situated between the posterior border of the great wing of the sphenoid and the anterior part of the petrous portion of the temporal bone. There are also intra-occipital and intra-sphenoidal synchondroses until the ossification of these bones is completed. I. The Posterior Region of the Skull. The posterior region (norma occipitalis) is formed by the posterior parts of the parietal bones and the upper or interparietal division of the tabular part of the occipital. It is limited above by a line connecting the parietal eminences, and below by the superior curved lines of the occipital, whilst laterally it is limited by a line connecting the parietal eminence w'ith the lateral angle of the tabular part of the occipital. A little above the centre it presents the lambda, which is the place where the sagittal meets the lambdoid suture in the situation of the posterior fontaneUe of early hfe. Radiating from the lambda there are three sutures. One passes upwards and forms the posterior part of the sagittal or interparietal suture. The other two, diverging, pass out%vards and downwards, and form together the lambdoid or occipito-parietal suture. About I inch above the lambda, at either side of the sagittal suture, is the n 132 A MANUAL OF ANATOMY parietal foramen, and the point where the horizontal line connecting the parietal foramina intersects the sagittal suture i-, known as the obelion, which coincides with the situation of the sagittal fontanelle of early foetal life. This part of the sagittal suture is less serrated than elsewhere, and is the first to show signs of obliteration. At the lower part of the posterior region in the middle line is the external occipital protuberance, which is known as the inion. A little above this is the occipital point, which is the part in the median plane at the greatest distance from the glabella of the frontal. The tabular part of the occipital may present an occipital suture, if the interparietal division persists as a separate bone. 2. The Superior Region. The superior region (norma verticalis) varies in shape. It may be oval with its long axis antero-posterior, and broader behind than in front. Such skulls are called dolicocephalic, and in them the zygomatic arches are usually visible at either side from above, a condition known as phenozygous. In other cases the superior region assumes a circular shape, due to the broadening of its anterior part. Such skulls are called brachycephalic, and in them the zygoma ic arches are usually concealed from above, a condition known as cryptozygous. Some skulls are intermediate between the dolicocephalic and brachycephalic, and ar known as mesaticephalic. Ihe bones which enter into the superior region are the upper part of the frontal and the anterior parts of the parietals. It is limited in front by a line connecting the frontal eminences, behind by a line connecting the parietal eminences, and on either side by the superior temporal ridges of the parietal and frontal bones. The highest point is situated in the course of the sagittal suture, and is called the vertex. The sutures in this region are usually two in number, coronal and sagittal, but there is sometimes a third, namely, the metopic or frontal. The coronal or fronto-parietal suture lies between the frontal and parietal bones. The anterior part of the sagittal or interparietal suture meets the coronal suture from behind, and the place of junction is known as the bregma, which coincides with the anterior fontanelle of early life. If there is a metopic or frontal suture present it connects the two halves of the frontal bone, and is a continuation of the sagittal suture as far as the fronto-nasal suture. The superior region, as viewed from above, reveals certain parts of the posterior region, namely, the posterior portions of the parietals, with the parietal foramina and obelion, the lambda, the interparietal portion of the occipital, and the lambdoid suture, 3. The Anterior Region. The anterior region (norma frontalis et facialis) is limited above by a line connecting the frontal eminences, and bejow by the lower THE BONES OF THE HEAD 133 border of the inferior maxilla. It is formed by a portion of the frontal, the nasals, superior maxillae, malars, and inferior maxUla. It is subdivided into two portions, frontal and facial. The frontal division is limited laterally by the superior temporal ridge, below by the supra-orbital border at either side of the median line, and by the fronto-nasal and fronto-maxillary sutures close to the median line. It presents the frontal eminences, superciliary ridges, external and internal angular processes, supra- orbital notches, or it may be foramina, aU on either side of the median line, and the nasal eminence or glabella at the median line, between the two superciliary ridges. The most prominent point of the glabella is known as the antinion. The meeting of the two fronto-nasal sutures is known as the nasion or nasal point. The centre of a line drawn from one temporal ridge to the other across the narrowest part of the frontal region is known as the ophryon. The upper part of the facial division presents the openings of the orbits. . These cavities are separated at the median line by the bridge of the nose, which is formed by the nasal bones and the nasal processes of the superior maxillae, whilst externally each orbit is limited by the malar bone and the external angular process of the frontal. The point at the inner angle of the orbit where the horizontal fronto-maxillary suture meets the vertical lachrymo- maxiUary suture is known as the dacryon, and the lower part of the intemasal suture is known as the rhinion. Below the nasal bones is the anterior nasal aperture. It is bounded on either side by the nasal notch on the mesial border of the superior maxiUa, and above by the inferior borders of the nasal bones, whilst inferiorly in the median line is the anterior nasal spine in two halves. The central point of the base of this spine is known as the subnasal point. The anterior nascd aperture is the common external opening of the two nasal fossae, which are separated by a septum compiosed of bones and cartilage. An inspection of each nasal fossa will reveal two bulging prominences on its outer wall, the lower of which is formed by the inferior turbinate bone, and the upper by the inferior turbinate process of the ethmoid. Below the former is the inferior meatus, whilst between the two is the middle meatus. The outer wall, from its irregularity, thus presents a marked contrast to the floor, which is smooth and imbroken. The osseous septum is, as a rule, deflected to one side, most commonly the left, thus diminishing the capacity of the left fossa. Below the anterior nasal aperture are the alveolar borders of the superior maxillae, which lodge the upper teeth. The point where the anterior margins of these two borders meet in the median line is known as the alveolar point. Below these borders is the entrance to the buccal cavity, and below this is the alveolar border of the inferior maxilla, which lodges the lower teeth. The middle point of the anterior lip of the lower border of the inferior maxilla is known as the mental point or gnathion. The superior maxillae having a wider range than the inferior 134 A MANUAL OF ANATOMY maxilla, the upper teeth slightly overlap the lower. According to the degree of projection of the maxillary bones, skulls are spoken of as orthognathous, prognathous, or mesognathous. The chief small foramina of the anterior region are as follows, from above downwards at either side : supra-orbital, at the junction of the outer two-thirds and inner third of the supra-orbital arch of the frontal (which in most cases is a notch) ; infra- orbital, in the superior maxilla near the infra-orbital margin ; mental, in the inferior maxilla in line with the septum between the bicuspid alveoli ; and malar, situated above the malar tuberosity. The supra-orbital, infra-orbital, and mental foramina are in the same perpendicular line, and transmit the following important sensory nerves, in order from above downwards : supra-orbital, infra- orbital, and mental, which are branches of the ophthalmic, superior maxillary, and inferior maxillary divisions of the Gasserian ganglion on the sensory root of the fifth cranial nerve. The malar foramen transmits the malar branch of the temporo-malar or orbital nerve, from the superior maxillary division of the fifth. The sutures in the anterior region are as follows : fronto-malar, fronto-maxillary, lachrymo-maxillary, fronto-nasal, internasal, naso- maxillary, malo-maxillary, and intermaxillary. The Orbits. — The orbits have the shape of four-sided pyramids, their bases being directed forwards and outwards, and their apices backwards and inwards. The inner walls are nearly parallel, and occupy an antero-posterior plane, but the outer walls diverge, the plane of each being directed forwards and outwards, so that they almost fo:m a right angle with each other. Each orbit is lined with periosteum, which is continuous with the dura mater through the sphenoidal fissure, and it contains the eyeball, with the ocular muscles, nerves, and bloodvessels, the lachrymal gland, and a large amount of fat. It presents an apex, a base, and four sides or walls. The apex, which is directed backwards and inwards, is formed by the inner end of the sphenoidal fissure, and just above and internal to this is the optic foramen. The base is free, and is directed forwards and outwards. Its circumference presents the fronto-malar suture externally, the malo-maxillary inferiorly, and the fronto-maxillary internally. The walls are superior, inferior, external, and internal. The superior wall or roof, which is thin and brittle, is formed mainly by the orbital plate of the frontal, and behind this by the small wing of the sphenoid. It is smooth and concave. Within the external angular process it p esents the lachrymal fossa lor the lachrymal gland, and near the internal angular process the trochlear fossa, which gives attachment to the cartilaginous pulley of the superior oblique muscle of the eyeball. The inferior wall or floor is fo med by three bones, namely, the orbital surface (orbital plate) of the superior maxilla, external to which is a part of the orbital process of the malar, whilst posteriorly is the orbital process of the palate bone. The floor is thin, and sepa- THE BONES OF THE HEAD 135 Anterior Ethmoidal Canal Posterior Ethmoidal Canal Supra-orbital Notch Optic Foramen [^enoidal Fissure Sphen. Fissure Optic Foramen Subnasal Point Mental Foramen' Symphys Mental Protuberance Fig. 80.- Gnathlon -The Anterior Region of the Skull (Norma Frontalis et Facialis). I, Nasal. II, Nas. Proc. of Sup. Maxilla. Ill, LachrvinaL IV, Ethmoid (Os Planum). V, Orbital Proc. of Malar. VI, Orb. Surf, of Great Wing of Sphenoid. VII, Orb. Plate of Frontal. VIII, Orb. Surf, of Sup. Maxilla. IX Frontal. I X', Temp. Div. of Frontal. X, Parietal. XI, Great Wing of Sphenoid. XII, Squam. Port, of Temporal. XIII, Malar. XIV, Inf. Maxilla. XV, Temporal Fossa. 136 A MANUAL OF ANATOMY rates the orbit from the subjacent antrum of Highmore. It is traversed from behind forwards by the infra-orbital canal, which posteriorly is a groove. At its anterior and inner part is the upper orifice of the lachrymal canal, and external to this is a small depression which gives origin to the inferior oblique muscle of the eyeball. The outer wall looks forwards and inwards, and is formed mainly by the orbital surface of the great wing of the sphenoid, and in front of this by a part of the orbital process of the malar. Between the outer wall and the floor is the spheno-maxillary fissure, the front part of which communicates with the zygomatic fossa, and the back part with the spheno-maxillary fossa. Between the outer wall and the roof, towards the posterior part, is the outer portion of the sphenoidal fissure. The part of the orbital process of the malar which forms the front part of this wall presents two foramina (sometimes one) leading to the malar and temporal canals. The inner wall is almost vertical, and looks directly outwards. It is formed by four (sometimes five) bones, in the following order from before backwards : (i) the nasal process of the superior maxilla ; (2) the lachrymal ; (3) the os planum or orbital plate of the ethmoid ; and (4) the anterior part of the lateral surface of the body of the sphenoid. If there are five bones, the fifth is a portion of the sphenoidal spongy bone, which would lie behind the os planum of the ethmoid. Between the inner wall and roof, in the ethmo-frontal suture, are the openings of the anterior and posterior ethmoidal or internal orbital canals. At the anterior part of this wall is the lachrymal groove, which lodges the lachrymal sac, and behind this is the lachrymal crest, which gives origin to the tensor tarsi muscle. The orbital sutures are as follows : superiorly, the orbito- sphenoidal ; inferiorly, the malo-maxillary and palato-maxillary ; externally, the spheno-malar ; and internally, from before backwards, the lachrymo-maxillary, ethmo-lachrymal, and ethmo-sphenoidal, all of which three are disposed vertically, and ethmo-frontal, which is antero-posterior. The orbit has ten (sometimes nine) openings communicating with it. (i) The sphenoidal fissure or foramen lacerum anterius or orbitale, the wide inner end of which forms the apex of the cavity, whilst the narrow outer part lies between the roof and the outer wall. This fissure transmits {a) the third nerve, the sympa- thetic filament to the lenticular ganglion, the fourth, the three branches (frontal, lachrymal, and nasal) of the ophthalmic division of the fifth, and the sixth, cranial nerves ; (b) the superior and in- ferior ophthalmic veins ; (c) the orbital branch of the middle meningeal artery ; and (d) a portion of the dura mater. (2) The optic foramen, situated above and internal to the apex, for the optic nerve and the ophthalmic artery, along with a plexus of sympa- thetic nerve fibres. (3) The supra-orbital notch (or it may be foramen), on the supra-orbital border, for the supra-orbital nerve THE BONES OF THE HEAD 137 and vessels. (4) The opening of the infra-orbital canal, on the floor, transmitting the infra-orbital nerve and vessels. (5) The opening of the temporal canal, and (6) the opening of the malar canal, both on the outer wall, for the branches of the temporo-malar or orbital nerve from the superior maxillary division of the fifth cranial nerve. (The temporal and malar openings may be combined into one.) (7) The spheno-maxillary fissure, at the junction of the outer wall and floor, which transmits the superior maxillary nerve to become the infra- orbital, and the infra- orbital vessels. (8) The lachrymal canal, at the anterior part of the inner wall, for the nasal duct. (9) The anterior ethmoidal canal, and (10) the posterior ethmoidal canal, both situated on the inner wall, the former transmitting the nasal nerve and anterior ethmoidal vessels, and the latter the posterior ethmoidal vessels and the spheno-ethmoidal nerve. Eight muscles take their origin within each orbit. The four recti arise from a fibrous ring surrounding the optic foramen. The levator palpebrae superioris arises above and in front of the optic foramen, and the superior oblique arises internal to the last named. The inferior oblique arises from the depression at the anterior and inner part of the floor, external to the orifice of the lachrymal canal, and the tensor tarsi arises from the lachrymal crest behind the lachrymal groove. The Nasal Fossae. — The nasal fossae are two in number, right and left, and they lie on either side of the median plane. They extend horizontally from before backwards, opening on the face as the anterior nares by means of the anterior nasal aperture, and com- .municating posteriorly with the naso-pharynx by the posterior nares. The vertical and antero-posterior dimensions of each fossa greatly exceed the transverse. The two fossae are separated from each other by a partition, called the septum nasi, which is partly osseous and (in the recent state) partly cartilaginous. Each fossa presents a roof, floor, and two walls, inner and outer. The roof over its central part is horizontal but in front and behind it is inclined downwards. Six bones enter into its formation. The central portion is formed by one-half of the cribriform plate of the ethmoid. The sloping anterior part is formed by the grooved ala of the frontal bone by the side of the nasal spine, and the posterior surface of the nasal bone. The sloping posterior part is formed by portions of the anterior and inferior surfaces of the body of the sphenoid, the ala of the vomer, and a part of the sphenoidal pro- cess of the palate bone. The central part of the roof is perforated by the foramina of one-half of the cribriform plate, including the nasal slit, and, at its back part, the aperture of the sphenoidal air sinus opens into the spheno-ethmoidal recess. The floor is smooth and concave from side to side. Over its anterior three-fourths it is formed by the palatal process of the superior maxilla, and over its posterior fourth by the horizontal plate of the palate bone. Near its anterior extremity, close to 138 A MANUAL OF ANATOMY the incisor crest of the superior maxilla, is the upper opening of Stensen's canal. The inner wall is known as the septum nasi. The osseous septum is formed by ten bones, in the following order, as nearly as possible, from below upwards : the nasal crests of the palatal processes of the superior maxillae and palate bones ; the vomer ; the perpendicular plate of the ethmoid ; the rostrum of the Frontal Sinus Crista Galli Half of Cribriform Plate. Perpend Plate of Ethmoid (showing Olfact. Grooves) \ Sphenoidal Sinus Sella Turcica Dorsum Sellse i Clivus Atrium of Middle Meatus Ant. Nasal / Spine Ext. Pteryg. Platen Hamular Process of ^ Int. Pterygoid Plate Vomer Upper Opening of Stensen s Canal Foramen of Stensen Fig. Si. —Sagittal Section of the Anterior Part of the Skull TO THE Right of the Nasal Septum. sphenoid ; the nasal crest of the nasal bones ; and the nasal spine of the frontal. The anterior border of the osseous septum presents a triangular deficiency, which is occupied in the recent state by the septal cartilage. The posterior border is formed by the posterior border of the vomer, which lies between the posterior nares. As previously stated, the septum is usually deflected to one side, most commonly the left. THE BONES OF THE HEAD 139 The outer wall is characterized by great irregularity, and is formed by seven bones, in the following order, as nearly as possible, from before backwards : (i) the nasal ; (2) the nasal process of the superior maxilla ; (3) the lachrymal ; (4) the internal surface of the lateral mass of the ethmoid, presenting the superior and inferior turbinate processes (superior and middle spongy bones) ; (5) the inferior turbinate or spongy bone which lies below the last named ; (6) the perpendicular plate of the palate bone, together with parts of its orbital and sphenoidal processes ; and (7) the internal pterygoid plate of the pterygoid process of the sphenoid. The bulging projections on this wall are produced by the superior and inferior turbinate processes of the ethmoid and the inferior turbinate bone, in this order from above downwards, and the deep channels thereby formed are known as the tneatH. These are three in number — superior, middle, and inferior. The superior meatus is situated towards the back part of the outer wal', where it lies between the superior and inferior turbinate processes of the ethmoid. It is comparatively short, and is directed obliquely forwards and upwards. The posterior ethmoidal cells open into it anteriorly, and the spheno-palatine foramen posteriorly. The middle meatus, which is longer than the superior, lies between the inferior turbinate process of the ethmoid and the inferior turbinate bone. At its anterior part it turns upwards, and is continued into the passage known as the infundibulum, which communicates with the frontal air sinus of its own side. The ascending part also communicates with the anterior ethmoidal cells. The middle portion communicates with the middle ethmoidal cells, and pre- sents the opening of the antrum of Highmore. The inferior meatus, which is the longest of the three, lies between the inferior turbinate bone and the floor of the nasal fossa. Near its anterior part is the lower orifice of the lachrymal canal, which lodges the nasal duct. The Air Sinuses. — These are hollow cavities lined with mucous membrane, which are contained within the following bones : the frontal, sphenoid, ethmoid, superior maxillae, and mastoid portions of the temporals. They commimicate directly with the nasal fossae, except the mastoid cells, which at either side are in communica- tion with the tympanum, that in turn being connected by means of the Eustachian tube with the naso-pharynx, at a point external to the posterior naris. The maxillary air sinus or antrum of Highmore appears about the fourth month of intra-uterine life, but the other air sinuses do not appear until chUdhood, and they, do not show much development until the period of puberty (see the individual bones). In old age they all tend to become enlarged. The frontal sinus (through means of the infundibulum) and the anterior ethmoidal cells open into the ascending front part of the middle meatus. The middle ethmoidal cells and the maxillary sinus open into the central portion of the middle meatus. The 140 A MANUAL OF ANATOMY posterior ethmoidal cells open into the superior meatus, and the sphenoidal sinus opens into the spheno-ethmoidal recess. The foramina which perforate the cribriform plate of the ethmoid transmit the filaments of the olfactory bulb, and are arranged in three sets, as follows : a middle set, which are simple perforations, and an external and internal set, which lead into small canals. These canals descend on the inner surface of the lateral mass and corresponding part of the perpendicular plate respectively, branching and opening out as they descend. The nasal slit transmits the nasal nerve and anterior ethmoidal artery. The spheno-palatine foramen leads from the spheno- maxillary fossa, and transmits the internal nerves of Meckel's ganglion and the spheno-palatine artery. The anterior nares are the orifices by which the nasal fossae open on the face through means of the anterior nasal aperture. Each naris is semipyriform, and is bounded above by the lower border of the nasal, externally by the nasal notch of the superior maxilla, and interiorly by the premaxillary portion of that bone. The posterior nares or choanae are situated at the posterior extremities of the nasal fossae, between the pterygoid processes of the sphenoid, and they communicate in the recent state with the naso-pharynx. They are oblong from above down- wards, and their plane is oblique, being directed downwards and slightly forwards. Each naris is bounded externally by the internal pterygoid plate of the sphenoid, internally by the posterior border of the vomer, which separates the two nares, inferiorly by the posterior border of the horizontal plate of the palate bone, and superiorly by the vaginal process of the sphenoid, ala of the vomer, and sphenoidal process of the palate bone. 4. The Lateral Region. The lateral region (norma lateralis) is formed by portions of the frontal, parietal, sphenoid, temporal, malar, superior maxilla, and inferior maxilla. It is somewhat triangular, with the base directed upwards. The base represents, for the most part, the superior tem- poral ridge, and corresponds with a curved line connecting the external angular process of the frontal with the lateral angle of the tabular part of the occipital. In front and behind it is limited by lines connecting the extremities of the base with the ramus of the inferior maxilla in the vicinity of the angle. This region presents the zygomatic arch, and, from behind forwards, are seen the mastoid process, opening of the external auditory meatus and suprameatal triangle, condyle of the inferior maxilla, lying in the anterior part of the glenoid fossa, eminentia articularis, and the sigmoid notch and coronoid process of the inferior maxilla, the latter lying within the front part of the zygomatic arch. The central point of the orifice of the external auditory meatus is known as the auricular point, and the outer side of the angle of the inferior maxilla is; THE BOXES OF THE HEAD 141 Fig. 82, — The Lateral Region of the Skull (Norma Lateralis). I, I, Frontal ; II, II, Parietal ; III, Occipital ; IV, Great Wing of Sphenoid ; V, Squamous Portion of Temporal ; VI, Mastoid Portion of Temporal ; VII, Zygoma ; VIII, Malar ; IX, Nasal ; X, Superior Maxilla (Nasal Process) ; XI, Lachrymal ; XII, Ethmoid (Os Planum) ; XIII, Inferior Maxilla. I, Bregma ; 2, Superior Temporal Ridge ; 3, Inferior Temporal Ridge ; 4, Obelion ; 5, Occipital Point ; 6, Inion ; 7, Asterion ; 8, Entomion ; 9, Auricular Point; 10, Gonion ; 11, Mental Foramen; 12, Alveolar Point; 13, Subnasal Point; 14, Jugal Point; 15, Lachrymal Groove; 16, Dacryon ; 17, Nasion ; 18, Glabella ; 19, Ophryon ; 20, Pterion ; 21, Stephanion, 142 A MANUAL OF ANATOMY known as the gonion. The point, situated at the angle which the posterior border of the frontal process of the malar makes with the superior border of its zygomatic process, is known as the jugal point. The sutures in this region are the fronto-malar, spheno-malar, fronto-sphenoidal, spheno-parietal, squamo-sphenoidal, coronal, squamous or squamo-parietal, temporo-malar (zygomatic), parieto- mastoid, and a portion of the occipito-mastoid. The point where the superior temporal ridge crosses the coronal suture is known as the stephanion, and the point where the parieto-mastoid, occipito-mastoid, and lambdoid sutures meet is known as the asterion. The latter coincides with the position of the postero-lateral fontanelle in early life. The point near the anterior part of the parieto-mastoid suture, where a process of the parietal is received into the parietal notch of the mastoid, is known as the entomion. The lateral region is divided by the zygomatic arch into the temporal and zygomatic fossae, the former being above the arch, and the latter within and below it. The temporal fossa is bounded above by the superior temporal ridges of the frontal and parietal, and below by the upper border of the zygomatic arch externally, and the infratemporal crest of the great wing of the sphenoid internally. It is formed by five bones, as follows : in front by the orbital process of the malar, above by the lower portions of the frontal and parietal, and below by the temporal division of the outer surface of the great wing of the sphenoid and the squamous portion of the temporal. The place where the parietal, frontal, great wing of the sphenoid, and squamous portion of the temporal are related to one another, and more particularly the region of the spheno-parietal suture, is known as the pterion, which coincides with the position of the antero-lateral fontanelle of early life. In this situation a Wor- mian bone is sometimes present, called the epipteric bone. The temporal fossa gives origin to the temporal muscle as high as the inferior temporal ridge, and the temporal fascia, which covers that muscle, is attached to the superior temporal ridge. The zygomatic fossa is situated below the level of the infra- temporal crest of the sphenoid. It is bounded externally by the ramus of the inferior maxilla and the inner surface of the zygomatic arch, and, between the two, it communicates with the exterior by means of the sigmoid notch. Internally it is bounded by the external pterygoid plate of the sphenoid. Superiorly it is limited by the zygomatic surface of the great wing of the sphenoid below the infratemporal crest, where it presents the foramen ovale and foramen spinosum, and by a small part of the squamous portion of the temporal. Anteriorly its wall is formed by the lower portion of the internal surface of the malar and the zygomatic surface of the superior maxilla, which latter presents the openings of the posterior dental canals. Its superior limit is THE BONES OF THE HEAD 143 the infratemporal crest of the sphenoid, the inferior limit being the molar portion of the alveolar border of the superior maxilla and the lower border of the external pterygoid plate. The contents of the fossa are as follows : the coronoid process of the inferior maxilla with the insertion of the temporal muscle ; the external and internal pterygoid muscles ; the first and second parts of the internal maxillary artery, and the pterygoid plexus of veins ; the inferior maxillary division of the fifth cranial nerve and Fronto-Malar Suture Orbital Plate of Frontal Glabella Fronto-nasal Suture ^ Fronto-maxill. Suture _ Nasal Bone Nas. P. of Sup. Max -^ Lachrymal Groove Orbital Surf. o{-^-- Lachrymal Bone Great Wing of Sphenoid I , Spheno-maxillary Fissure I / /Back Part of Infra-orb. Groove /Spheno-maxillary Fossa Infratemporal Crest *Spheno-palat. Foramen \\V''\ VA /I / /' /' ,Zygom. Surf, of Great ffe:;-\\/,VV/^/ / Wing of Sphenoid w>\:;. \>, >\r >A; / Pteiygo-maxiUary / / }'> 'XVV y Fissure /^\y^ /Zygoma y Preglenoid Tubercle ■* Foramen Ovale Foram. Spinosum -■^■^__ Spine of Sphenoid Openings of Posterior Dental Canals External Pterygoid Plate of Sphenoid I Hamular Process Tuberosity of Palate Bone Tuberosity of Superior Maxilla Fig. 83. — The Zygom.\tic and Spheno-Maxillary Foss;e. Incisor Fossa Canine Fossa its branches, together with the otic (Arnold's) ganglion ; the chorda tympani ner\'e ; and the spheno-mandibular ligament. The foramina which communicate with the fossa are as follows : the foramen ovale ; the foramen spinosum ; the openings of the posterior dental canals ; and the inferior dental foramen. The fossa presents two fissures — spheno-maxillary and pterygo- maxillary. The spheno-maxillary fissure lies horizontally between the great wing of the sphenoid and the superior maxilla. Externally it is 144 A MANUAL OF ANATOMY closed, as a rule, by the malar, but sometimes by the great wing of the sphenoid, which may here articulate with the superior maxilla. Internally it is bounded by the zygomatic surface of the orbital process of the palate bone. The fissure leads into the orbit, and transmits the superior maxillary nerve to become the infra- orbital, the infra - orbital vessels, the temporo - malar or orbital branch of the superior maxillary nerve, the orbital branches of Meckel's ganglion, and a communicating vein which passes between the inferior ophthalmic vein and the pterygoid plexus. The pterygo-maxillary fissure lies vertically between the anterior border of the pterygoid process of the sphenoid and the posterior border of the superior maxilla, at their upper ends. Inferiorly the fissure is closed by the approximation of the bones forming its lips, a part of the tuberosity of the palate bone usually intervening between them, though direct articulation sometimes takes place between the pterygoid process and the superior maxilla. Internally the fissure is bounded by the perpendicular plate of the palate bone. It transmits the internal maxillary artery to the spheno-maxiUary fossa. The pterygo-maxillary fissure meets the spheno-maxillary fissure at a right angle, and situated deeply within this angle is the spheno-maxillary fossa. The boundaries of the spheno-maxillary fossa are as follows : anteriorly, the zygomatic surface of the superior maxilla at its inner and back part superiorly ; posteriorly, the base of the pterygoid process of the sphenoid, and the lower and inner part of the anterior surface of its great wing; internally, the perpen- dicular plate of the palate bone, with its orbital and sphenoidal processes ; and superiorly, the under surface of the body of the sphenoid. The contents of the fossa are the third part of the internal maxillary artery, the superior maxillary nerve, and the spheno-palatine or Meckel's ganglion, along with their branches. Two fissures communicate with this fossa, namely, the spheno- maxillary, leading into the orbit, and the pterygo-maxillary, opening into the zygomatic fossa. It also communicates with the, superior meatus of the nose by means of the spheno-palatine foramen on its inner wall. The foramina which open into the spheno-maxillary fossa are as follows : three on the posterior wall, in the following order from above downwards, and from without inwards : the foramen rotundum for the superior maxillary nerve, the Vidian or pterygoid canal for the Vidian nerve and vessels, and the pterygo-palatine canal for the pharyngeal nerve and pterygo-palatine vessels. On the internal wall is the splieno-palatine foramen for the internal branches of Meckel's ganglion and the spheno-palatine artery. Inferiorly is the opening of the posterior palatine canal for the great* or anterior descending palatine nerve and the descending palatine artery. In this situation there may also be the openings of the posterior and external accessory palatine canals for the posterior and external descending palatine nerves, but these openings usually branch off THE BONES OF THE HEAD 145 from the main canal. Anteriorly is the spheno-maxillary fissure. Externally the fossa communicates with the zygomatic fossa through the pterygo- maxillary fissure. 5. The Inferior Region. The inferior region or external base (norma basilaris), from which the inferior maxilla is excluded, is limited in front by the central portions of the alveolar borders of the superior maxillae, and behind by the superior curved hues of the occipital. At either side it is limited by the lateral portion of the alveolar border of the superior maxilla, and by a line connecting the tuberosity of that bone with the lateral angle of the tabular part of the occipital. It is very irregular, and presents three divisions — anterior, middle, and posterior. The anterior division forms the hard palate, and resembles a horseshoe. It is bounded in front and laterally by the alveolar borders of the superior maxillae, and behind by the posterior borders of the horizontal plates of the palate bones. The posterior border presents in the middle line the posterior nasal spine in two halves, from which the azygos uvTilae muscle arises. At either side of this it is sharp and concave for the attachment of the soft palate. The bones forming the hard palate are the palatal pro- cesses of the superior maxillae over the anterior three- fourths, and the horizontal plates of the palate bones over the posterior fourth. The surface is vaulted, and is intersected by two sutmres, middle palatal and transverse palatal. The middle palatal suture extends from the alveolar point to the posterior nasal spine, and indicates the meeting of the palatal plates of the superior maxillae and palate bones of opposite sides. The transverse palatal suture crosses the middle one at right angles about h inch in front of the posterior border, and externedly it turns backwards to end at the posterior palatine foramen. It indicates the meeting of the palatal process of the superior maxilla and the horizontal plate of liie palate bone of either side. In young skulls two additional sutures are present, called maxiUo-premaxillary, each of which extends from the posterior part of the anterior palatine fossa to the inter^^al between the lateral incisor and canine teeth. Each of these sutures corre- sponds with the place of junction of the maxilla proper and the premaxilla. The hard psdate presents several openings. At the anterior extremity of the middle palatal suture is the diamond-shaped anterior palatine fossa. Within this are four openings, two being placed laterally, one at either side, called the foramina of Stensen (incisor foramina), and two in the median line in the intermaxillary suture, called the foramina of Scarpa, anterior and posterior respec- tively. Each of the former transmits a branch of the descending 10 Fig. 84. 1. Ant. Palatine Fossa 2. Post. Nasal Spine 3. Post. Border of Vomer 4. Facial Surf, of Sup. Maxilla 5. Hamular Process of Int. Pterygoid Plate of Sphenoid 6. Pterygoid Fossa 7. Ext. Pterygoid Plate 8. Zygomatic Process of Malar 9. Zygoma of Temporal 10. Pharyngeal Tubercle (pointer crosses Foram. Lacerum Med.) 11. Kustachian Groove 12. Groove for Chorda Tympani Nerve 13. Petrous Portion of Temporal (Ori- gin of Levator Palati) 14. Carotid Foramen 15. V.xt. Auditory Meatus 16. ICxt. Auditory Process J7. Basion '9 28 27 26 -The External Base of the Skull. Mastoid Process Jugular Foramen Ant. Condylar Foramen Digastric Groove Occipital Groove Post. Condylar Foramen Sup Curved Line of Occipital Inf. Curved Line Ext. Occipital Crest Ext. Occipital Protuberance Opisthion Foramen Magnum Right Occipital Condyle Foram. Lacerum Medium at + Vaginal Proc. of Tymp. Plate Mastoid Foramen Stylo-Mastoid Foramen Styloid Process Tympanic Plate (Post, part of Glenoid Fossa) Spinous Proc. of Sphenoid Ant. part of Glenoid Fossa Foramen Spinosum Foramen Ovale Foramen Vesalii Preglenoid Tubercle Eminentia Anicularis Zygomatic F'ossa Infratemporal Crest Temporal Division of Gre Wing of Sphenoid Spheno-Maxillary Fissure Tuberosity of .Sup. Maxilla Ext. Access. Palat. Foran>< Post. Access. Palat. Foram Post. Palatine Foramen Right Post. Naris (pointer ridge for Tensor Palati) Groove for Descend. Palat. Horiz. Plate of Palate Bon Palat. Proc. of Sup. Maxit THE BONES OF THE HEAD 147 palatine artery from the palate to the nasal fossa, whilst each of the latter transmits the naso-palatine nerve from the nasal fossa to the hard palate, the anterior, which usually opens from the left nasal fossa, containing the left nerve, and the posterior, which usually opens from the right nasal fossa, containing the right nerve." Internal to the last molar alveolus at either side is the posterior palatine foramen, which is the outlet of the posterior palatine or palato-maxillary canal, and through which the great or anterior descending palatine nerve and the descending palatine vessels pass. Leading forwards from this foramen there is a groove for the transmitted structures. A little behind the posterior palatine foramen is the posterior accessory palatine foramen for the posterior de cending palatine nerve, and outside this is the external accessory palatine foramen for the external descending palatine nerve, but the last-named foramen is inconstant. Besides the foregoing openings, there are a number of nutrient foramina. Over its anterior three-fourths the hard palate presents several depressions for the palatal mucous glands, and extending inwards from the back part of the posterior palatine foramen at either side is a transverse ridge which gives partial insertion to the tensor palati muscle. The middle division extends from the posterior border of the hard palate to a transverse line on a level with the anterior margin of the foramen magnum. Laterally it is limited by a line extending from the tuberosity of the superior maxilla to the styloid process of the temporal. It is on a higher level than the anterior division, and its central or basilar part is known as the guttural fossa. The bones forming it at either side are the tuberosity of the palate bone, the pterygoid process, and a small part of the great wing, of the sphenoid, and the inferior surface of the petrous portion of the temporal. The central part is formed by the basilar process of the occipital, the body and vaginal processes of the sphenoid, the superior border and alae of the vomer, and the sphenoidal processes of the palate bones. Anteriorly it presents the posterior nares, already described, and at either side of these openings is the pterygoid fossa, which is bounded internally by the internal, and externally by the external, pterygoid plate of the sphenoid, the fossa being completed in- feriorly by the tuberosity of the palate bone. In a line extending backwards and outwards from the extemcd pterygoid plate to the styloid process the following parts are seen, in order from before backwards : foramen ovale ; foramen spinosum ; spinous process of the sphenoid ; internal border of the tympanic plate of the temporal, forming posteriorly the vaginal process ; and styloid process. Inside the foregoing line anteriorly is the Eustachian groove, which lies obliquely between the great wing of the sphenoid and the apical part of the petrous portion of the temporal. This groove lodges the cartilaginous part 148 A MANUAL OF ANATOMY of the Eustachian tube, and, when followed outwards and backwards, it leads to the Eustachian canal in the angle between the squamous and petrous portions of the temporal. On either side of the basilar process of the occipital is the foramen lacerum medium. It lies between the basilar process, the apex of the petrous portion of the temporal, and the great wing of the sphe- noid near the root of the pterygoid process. In the recent state it is closed below by fibrous tissue, which is pierced by a meningeal branch of the ascending pharyngeal artery, and one or more emissary veins from the cavernous sinus. In a line extending backwards and outwards from the foramen lacerum medium are the following markings on the inferior surface of the petrous portion of the temporal : the rough surface from which the levator palati arises ; the carotid foramen, which transmits the internal carotid artery and the ascending branch of the superior cervical ganglion of the sympathetic ; a minute foramen, on the posterior wall of the vertical portion of the carotid canal, for the tympanic branch of the carotid sympathetic plexus and tympanic branch of the internal carotid artery; the jugular fossa, which forms part of the jugular foramen ; the tympanic canaliculus, on the ridge between the carotid foramen and jugular fossa, for the tympanic branch (Jacobson's nerve) of the glosso- pharyngeal and the tympanic branch of the ascending pharyngeal artery ; and the auricular canaliculus, on the outer wall of the jugular fossa, for the auricular branch (Arnold's nerve) of the pneumogastric. Between the petrous portion of the temporal and the jugular process of the occipital is the foramen lacerum posterius or jugular foramen, which lodges the commencement of the internal jugular vein, and transmits the following structu es : the glosso-pharyngeal, pneumogastric, and spinal accessory nerves ; the inferior petrosal sinus ; and meningeal branches of the ascending pliaryngeal and occipital arteries. External to the front of the occipital condyle is the anterior] condylar foramen for the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery. The under surface of the basilar process of the occipital presents the pharyngeal tubercle The posterior division is limited in front by a transverse line on a level with the anterior margin of the foramen magnum, and behind by the external occipital protuberance ana thf superior curved line at either side. It is formed by the supra j occipital and condylar portions of the occipital, and the mastoicj portions of the temporal bones. In the middle line is the foramen magnum, which transmits tlui medulla oblongata and its membranes, the spinal accessory nerves the vertebral arteries, the anterior and posterior spinal arteries, anc parts of the cerebellar amygdalae. The centre of the anterio margin of the foramen magnum is known as the basion, and th centre of the posterior margin as the opisthion. Proceeding outward i^l THE BONES OF THE HEAD 149 from this foramen are the occipital condyle, jugular process, occipital groove for the occipital artery, digastric groove for the posterior belly of the digastric, and the mastoid process. Behind the occipital condyle is the posterior condylar fossa, in which there may be a posterior condylar foramen for the passage of an emissary vein from the lateral sinus. Behind the foramen magnum is the supra-occipital portion of the occipital, which presents the external occipital crest in the median line, and the inferior curved line extending outwards on either side from its centre. The Interior of the Cranium. A sagittal or antero-posterior section of the skull a little to one side of the median plane shows the septum nasi alreadj'^ described. Along, and at either side of, the vault of the cranium is the groove for the superior longitudinal venous sinus, which extends from before backwards, and on either side of its parietal portion are the Pacchionian depressions. The internal openings of the parietal foramina may be seen, as well as the branching system of menin- geal grooves, and digitate impressions. The basi-cranial, basi- facial, and basi-bregmatic axes are to be studied from this section. The basi-cranial axis represents a line drawn upwards and forwards from the basion to the spheno-ethmoidal suture. The basi-facial axis corresponds ^vith a line dra\vn from the spheno-ethmoidal suture to the subnasal point. The angle formed by these tvvo axes is known as the cranio-facial angle. The basi-bregmatic axis represents a line drawn vertically from the basion to the bregma. The most instructive coronal or transverse section is one made in the plane of the basi-bregmatic axis. Such a section gives important views of the parts within the petrous portion of the temporal, such as the external auditory meatus, tympanum, and vestibule. When a horizontal section has been made on a level with the occi- pital point and the most prominent part of the glabella, the vaulted roof of the cranium is removed. This is called the calvaria, or skull-cap, and it is formed by portions of the frontal, parietals, squamous portions of the temporals, and occipital. The outer plate is strong, except over the temporal region, but the inner is brittle and readily cracked, from which circumstance it is known as the vitreous (glassy) plate. Between the two plates there is cancellated tissue, here called diploe. The interior of the calvaria presents branching meningeal grooves, digitate impressions, and along the middle line the groove for the superior longitudinal venous ~ nus, with depressions at either side for the Pacchionian bodies. The openings of the parietal foramina may be noted. I50 A MANUAL OF ANATOMY Fig. 85. — Sagittal Section of the Skull to the Right of the Median Plane. F, Frontal ; P, Parietal ; O, Occipital ; T, Temporal. 22. Anterior Nasal Spine 23. Inferior Turbinate Bone 24. Middle Meatus 25. Inferior Turbinate Process of Ethmoid 26. Infundibulum 27. Nasal Bone 28. Right Sphenoidal Sinus 29. Right Frontal Sinus 30. Crista Galli 31. Optic Foramen 32. Pterion I. Coronal Suture II. Anterior Condylar Foramen 2. Anterior and Posterior Me- 12. Internal Auditory Meatus ningeal Grooves 13- Styloid Process 3- Lambdoid Suture 14. Dorsum Sellae 4- Hiatus Subarcuatus IS- Sella Turcica 5- Sigmoid Groove 16. External Pterygoid Plate 6. Inion (External Occipital '7- Hamular Process Protuberance) 18. Superior Turbinate Process 7- Asterion of Ethmoid, 8. Sigmoid Groove 19. Superior Meatus 9- Aqueductus Vestibuli 20. Inferior Meatus 0. Jugular Foramen 21. Right Superior Maxilla The Internal Base of the Skull. The internal base forms the floor of the cranial cavity, and is of very irregular outline and thickness. The thickest and densest parts are the petrous portions of the temporals. The mastoid portion of the temporal and the basilar part of the occipital are also thick. The thinnest parts are the cribriform plate of the ethmoid and the orbital plates of the frontal, but the central portions of the cerebellar fossae of the occipital are also thin, sometimes remarkably so. The interior of the base is divided into three fossae — anterior, middle, and posterior. Anterior Fossa. — The floor of this fossa is formed by the orbital THE BONES OF THE HEAD 151 plates of the frontal, the cribriform plate of the ethmoid, and the small wings, jugum sphenoidale, and ethmoidal spine of the sphenoid. It is limited posteriorly by the posterior or Sylvian border of the small wing of the sphenoid at either side, and by the limbus sphen- oidalis in the centre. It is subdivided into a central and two lateral parts. The central portion, which is depressed, is formed by the cribri- form plate of the ethmoid and the ethmoidal spine and jugum of the sphenoid. In the middle line it presents the crista galli, which gives attachment to the falx cerebri. In front of this is the foramen caecum, which, when pervious, transmits an emissary- vein passing between the intracranial superior longitudinal sinus and the veins of the roof of the nose. At each side of the crista gaUi are the nasal slit for the nasal nerve and anterior ethmoidal artery ; the cribriform foramina for the filaments of the olfactory bulb ; the cranial opening of the anterior ethmoidal canal for the anterior ethmoidal artery and nasal nerve ; and the cranial opening of the posterior ethmoidal canal for the posterior ethmoidal artery and spheno-ethmoidal branch of the nasal nerve. The last two open- ings are situated at the outer side of the cribriform plate, external to the olfactory groove which marks it. Directly beneath each half of the cribriform plate is the corresponding nasal fossa. Each lateral portion of the anterior fossa is irregularly convex, and forms the roof of the orbit. It is formed by the orbital plate of the frontal and the small wing of the sphenoid. It is very thin, and, except over the small wing of the sphenoid, it presents digitate impressions for the convolutions of the orbital surface of the frontal lobe of the cerebrum, which it supports. The sutures in the anterior fossa cire the fronto-ethmoidal, fr on to- sphenoidal, and spheno- ethmoidal. Middle Fossa. — This fossa is on a lower level thm the anterior. It is bounded in front by the posterior or Sylvian border of the small wing of the sphenoid at either side, and by the limbus sphenoidalis in the centre. Behind, it is limited by the superior border of the petrous portion of the temporal at either side, and by the dorsum sellae of the sphenoid in the centre. It presents a central and two lateral divisions. The central division is formed by the superior sur- face of the body of the sphenoid, posterior to the limbus sphenoidalis. Each lateral division, which is much depressed, is formed anteriorly by the superior surface of the great wing of the sphenoid, externally by part of the squamous portion of the temporal, and posteriorly by the superior surface of the petrous portion of that bone. It lodges the temporo-sphenoidal lobe of the cerebrum, and it presents the following sutiu-es : the spheno-parietal ; squamous or squamo- parietal ; squamo-sphenoidal ; and petro-sphenoidal. The central division presents the following parts: the optic groove and olivary eminence for the optic commissure ; the optic foramen of each side for the optic nerve and ophthalmic artery; the anterior clinoid process of each side ; the sella turcica or 152 A MANUAL OF ANATOMY pituitary fossa for the pituitary body; the cavernous or carotid groove, at either side of the sella turcica, for the cavernous venous sinus and internal carotid artery, the latter being accom- panied by the cavernous sympathetic plexus of nerves, and having the sixth cranial nerve on its outer side ; the middle clinoid process of each side (sometimes connected with the anterior, which it faces) ; the dorsum sellae ; the posterior clinoid process of each side, at either lateral angle of the dorsum sellae ; and the notch for the sixth cranial nerve, on each side of the dorsum sellae a little below the posterior clinoid process. The central division corresponds with the interpeduncular region at the base of the cerebrum. Each lateral division i? marked by menirgeal grooves and digitate impressior;s, and presents the following openings : the sphenoidal fissure, or foramen lacerum anterius or orbitale, for the third cranial nerve, the fourth, the three branches of the ophthalmic division of the fifth (namely, frontal, lachrymal, and nasal), and the sixth cranial nerves, the sympathetic root of the ciliary ganglion, the superior and inferior ophthalmic veins, the orbital branch of the middle meningeal artery, and a portion of the dura mater to form the orbital periosteum ; the foramen rotundum, leading to the spheno-maxillary fossa, and transmitting the superior maxillary division of the fifth cranial nerve ; the foramen ovale, leading to the zygomatic fossa, and transmitting the inferior maxillary division and the motor root of the fifth cranial nerve, the small meningeal artery, an emissary vein from the cavernous sinus, and occasionally the small superficial petrosal nerve ; the foramen Vesalii (inconstant), leading to the scaphoid fossa at the root of the internal pterygoid plate, or to the pterygoid fossa external to the scaphoid fossa, and transmitting an emissary vein from the cavernous sinus; the foramen spinosum, leading to the zygomatic fossa, and trans- mitting the middle meningeal artery and a recurrent branch of the inferior maxillary nerve; and the foramen lacerum medium situated between the basilar process of the occipital, the apex of the petrous portion of the temporal, and the great wing of the sphenoid near the root of the pterygoid process. The posterior opening of the Vidian canal, which leads to the spheno-maxillary fossa and transmits the Vidian nerve and artery, is to be fourd on its anterior wall, while the carotid canal for the internal carotid artery, with a plexus of sympathetic nerve fibres, opens on its j external wall. 1 The superior surface of the petrous portion of the temporal presents the following markings : the Gasserian depression, near the apex, for the Gasserian ganglion ; the hiatus Fallopii, to which a groove conducts for the great superficial petrosal nerve and the petrosal branch of the middle meningeal artery ; (within this opening there may be a small one for the external superficial petrosal nerve) ; the accessory hiatus, to which a groove conducts, for the small superficial petrosal nerve ; the eminentia arcuata. THE BONES OF THE HEAD 153 27 26 Fig. 86. — The Internal Base of the Skull. The Superior Surface of the Petrous Portion of the Right Temporal Bene has been removed to expose the Internal Auditory Meatus and Semicircular Canals.) Foramen Caecum Crista Galli Ethmoidal Spine of Sphenoid Jugum Sphenoidale Anterior Fossa Limbus Sphenoidalis Optic Groove Olivary Eminence Sylvian Border of Small Wing of Sphenoid Anterior Clinoid Process Middle Clinoid Process Sella Turcica Posterior Clinoid Process Dorsum Sellse Basilar Groove Groove for Inf. Petrosal Sinus Superior Semicircular Canal External Semicircular Canal Posterior Semicircular Canal Internal Auditory Meatus (laid ojjen) Opening of Internal Audi- tory Meatus Anterior Condylar Foramen Basion Groove for Lateral Sinus Vermiform Fossa Torcular Herophili Int. Occipital Protuberance Internal Occipital Crest Opisthion Cerebral Fossa Cerebellar Fossa . Jugular Foramen Sigmoid Groove Internal Auditory Meatus Gasserian Depression Emioentia Arcuata 37. Hiatus Fallopii 38. Accessory Hiatus 39. Foramen Lacerum Medium 40. Foramen Spinosum 41. Foramen Ovale 42. Middle Fossa 43. Foramen Vesalii 44. Ljn^la of Sphenoid 45. Parietal Bone 46. Coronal Suture 47. Cavemotis Groove 48. Pterion 49. Foramen Rotundum 50. Orbital Plate of Frontal 51. Sf^enoidal Fissiue 52. Carotid Notch 53. Optic Foramen 54. Posterior Ethmoidal Canal 55. Anterior Ethmoidal Canal 56. Left Frontal Sinus 154 . ^ MANUAL OF ANATOMY which coincides with the position of the superior semicircular canal of the internal ear ; and the tegmen tympani. Posterior Fossa. — This fossa is on a lower level than the middle. It is limited in front by the dorsum sellae of the sphenoid in the centre, and the superior border of the petrous portion of the temporal at either side. Behind, it is limited by the internal occipital protuber- ance and the groove at either side for the lateral venous sinus, which groove also marks its lateral extent. It lodges the pons Varolii, medulla oblongata, and cerebellum. The bones which form it are as follows : the dorsum sellae of the sphenoid ; the basilar, condylar, and supra-occipital portions of the occipital ; the petrous and mastoid portions of the temporal ; and the postero- inferior angle of the parietal. It presents the following sutures : the occipito-mastoid ; parieto-mastoid ; and petro-basilar. The following parts are to be noted : the basilar groove, the upper part of which lodges the pons Varolii and basilar artery, whilst the lower part contains the medulla oblongata ; the foramen magnum, which transmits the medulla oblongata and its mem- branes, the spinal accessory nerves, and the vertebral, anterior spinal, and posterior spinal, arteries; the anterior condylar foramen, on either side of the foramen magnum, for the hypo- , glossal nerve and a meningeal branch of the ascending pharyngeal artery; the internal occipital crest, which gives attachment to the falx cerebelli, and is occasionally grooved for the occipital process of thf^'r^r^K^r/^^^ ^^^ foramen magnum this crest presents hemisnhprpc^f +J,"!]' ^^^'^'e. receives a part of the vermiform meatus on fl! ^f ^bellum ; the opemT^abellar fossa, which lodge the t~al,' for VtdT T'^^I- ^^ the Veir:^ of th^ internal auditory Wrisber^ ^n/ J. ^^ ^"^ auditory nerves fe ^^^-ous portion of the i inch external f -^ .1 ""^ ^""^^^^ ' ^^^ aqueductus Vfe 5^'^^^ intermedia of the ductus en Inl *^^ .P^^^^ding, for a small artery anZ'^^'-tibuli, about thefioccular W^Lrlvl"/' '^l' ''''"^ subarcuata, ?epr"* ^^---' -^ of the petrous Dor^inn I !' '^*^^*"^ ^^^^^ to the s^perfo^P "^^^enting internafauTtor^^^'Ss ,,'d' "^'^^J'^ ^^^ween the oPZ^ "PJ^T^f* foramen or foSm^„^«^Lf aqueductus vestibuli ; and the im^ "f "^^ ^^^ externa? coVrtment'" J°SV"'', ^fd^ The por.eCts t become the internal jugular tdn and » '"' ^f""^ ^""^ ' ' ascendmg pharyngea artery he mfddl."'"^"'^ '"■*°<='' °f "■-poral the glosso-pharyn|eal, pneumogastrfc f ^H "™P"'">»' transmits^^ea petrosal \"*r-W-rnaf con^aftoe" t &a°st»^?^'y "V'' ^'h lets, ata, THE BONES OF THE HEAD ISS The posterior fossa is grooved by the following venous sinuses : the lateral sinus, which extends from the internal occipital pro- tubercince to the jugular foFcimen, grooving in its sinuous course the tabular part of the occipital, the postero-inferior angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, (opening from which there is usually the mastoid foramen, and occasionally the posterior condylar foramen) ; the superior petrosal sinus, which grooves the superior border of the petrous bone ; the inferior petrosal sinus, along the course of the petro-basilar suture ; and the occipital sinus, which sometimes grooves the internal occipital crest. Wormian Bones. The Wormian bones (so named after Wormius) are supernumerary bones which are frequently met with in the course of the cranial sutures, and occasionally in the face, as in the region of the laclu-5anal bones, and at the outer extremity of each spheno- maxillary fissure. From their position in the course of sutures they are known as ossa suturarum. They are for the most part of small size and triangular outhne, and are hence sometimes spoken of as ossa triqueira. They are usually due to the appearance of special ossific centres. Their most common situation is along the course of the lambdoid suture, where they may form a regular chain. The superior angle of the occipital sometimes persists as a Wormian bone, called pre-interparietal, which may be double. One is often found between the an tero- inferior angle of the parietal and great wong of the sphenoid in the region of the pterion, and it is known as the epipteric bone. If the me topic or frontal suture is persistent one or more Wormian bones may be present along its course, and, if at the upper part, they may give rise by their persistence and union to a bregmatic bone. In the condition known as chronic hydrocephalus Wormian bones of large size are present in great numbers along the cranial sutures. The SkuU at Birth. The skull at birth is remarkable for its large size, and for the great development of the cranimn as compared with the face. The face is equal to one-eighth of the cranium, whereas in the adult it is equal to one-half. The occipital, parietal, and frontal regions are well developed, the parietal and frontal eminences are very conspicuous, and the mastoid processes are absent. The bones are not united by sutures, but are connected by fibrous tissue, continuous with the periosteum externally and diua mater inter- nally. Membranous intervals exist between the angles of certain bones, these being called fontanelles from the pulsation, or welling- ip sensation, which can be felt there. They are six in number, iwo being placed in the median line, anterior and posterior, and two at either side, antero-lateral and postero-lateral. The anterior fontanelle is situated between the antero-superior angles of the 156 A MANUAL OF ANATOMY Anterior parietals and the superior angles of the two halves of the frontal. It is large and diamond-shaped, and it is not completely closed, as a rule, until towards the end of the second year. The posterior fontanelle is situated between the postero-superior angles of the parietals and the superior angle of the occipital. /It is small and triangular, and is usually closed at, or shortly after, birth, but the surrounding bones are still movable. The antero-lateral and postero-lateral fontanelles correspond with these angles of the parietal. The antero-lateral is situated between the parietal, sphenoid, frontal, and squamous portion of the temporal, whilst the postero-lateral is situated between the parietal, occi- pital, and mastoid portion of the temporal. For the sagittal fontanelle of the earlier part of foetal life, see p. 63. The skull increases rapidly in sire during the first six years, and a further marked increase commences on the ap- proach of puberty, wh:ch is associated with the development of the air sinuses. The latter in- crease affects chiefly the frontal and facial regions. In old age the cranial bones become thinne r, the air sinuses under- go enlargement, and the sutures show indications of obliteration. Characters of the Female Skull. — The bones are smaller and smoother than in the male. The mastoid processes, superciliary ridges, and glabella are less prominent. The frontal and occipital regions are not so well developed relatively to the parietal. The cranial capacity is rather less. The face as a rule is narrower, and bears a smaller proportion to the cranium. Posterior Fig. 87. — The Skull at Birth, showing the Anterior and Posterior Fontanelles, AND the Parietal Eminences. Racial Peculiarities of the Skull. In comparing the skulls of different races attention has to be directed to the following points : the capacity of the cranium, its circumference, its relative length, breadth, and height, the degree of forward elongation of the jaws, and the shape of the anterior nasal and orbital apertures. The cranial capacity may be ascertained by filling the skull with shot, or various kinds of seeds, an \ THE BONES OF THE HEAD 157 then measuring the contents in a graduated vessel. The capacity ranges from about 60 to no cubic inches, and, according to their capacity, skulls are divided into three groups, namely, mesoeephalic, ^\'ith a capacity of about 85 cubic inches, as in Chinese ; megacephalic, wth a capacity exceeding that, as in Europeans ; and microcephalic, with a capacity under it, as in Australians. . In regard to craniometry the following craniometncal terms may here be summarized : • r u 1 1 Alveolar point = the point of meeting of the an tenor margins ot the alveolar borders of the superior maxillae. Antinion = the most prominent point of the glabella. Asterion = the point where the parieto-mastoid, occipito-mastoid. and lamb doid sutures meet. Auricular point = the centre of the opening of the external auditory meatus. Basion = the centre of the anterior margin of the foramen magnum. Bregma = the point of junction of the sagittal and coronal sutures. Dacryon = the point where the horizontal fronto-maxillary suture meets the vertical lachr>'mo-maxillary suture. Fig. 83.- -The Skull at Birth, showing the Antero-laterai. AND Postero-lateral Fontanelles. Entomion = the point near the anterior part of the parieto-mastoid sntiire v.-here a process of the parietal is received into the parietal.notch of the mastoid. Glabella = a point midway between the supercihary ridges of the frontal. Gnathion, or mental point = the middle point of the anterior Up of the lower border of the inferior maxilla. Gonion = the outer side of the angle of the inferior maxilla. Inion = the external occipital protuberance. Jugal point = a point situated at the angle which the posterior border of the frontal process of the malar forms with the superior border of its zygomatic process. Lambda = the meeting of the sagittal and lambdoid sutares. Nasion, or nasal point = the meeting of the two fronto-nasal sutures. Obelion = the point where the horizontal line connecting the parietal fora- mina intersects the sagittal suture. Occipital point = the part of the occipital in the median plane at the greatest distance from the glabella. Opliryon=the centre of a line drawn from one temporal ridge to the other across the narrowest part of the frontal region. Opisthion = the centre of the posterior margin of the foramen magnura. 1S8 A MANUAL OF ANATOMY Pterion = the region of the spheno-parietal suture. Rhinion-the lower part of the internasal suture. Stephanion = the point where the superior temporal ridge crosses the coronal suture. Subnasal point=the centre of the base of the anterior nasal spine. The horizontal circumference of the cranium represents the measurement at the level of a plane passing through the most prominent part of the glabella in front, the pterion laterally, and the occipital point behind. The greatest length represents the measurement from the most prominent part of the glabella to the occipital point. The greatest breadth represents the transverse measurenient at the level of the most prominent parts of the temporal fossae above the supramastoid crests. The proportion of greatest breadth to greatest length is the index of breadth, or cephalic index. In civilized races about 7 inches represents an average length, and about 5 5 inches an average breadth. According to their cephalic index, skulls are arranged in three classes, namely, brachycephalic (broad and short), with a cephalic index over 80, as in Malays, etc. ; mesaticephalic (intermediate), with an index of 75 to 80, as in Europeans and Chinese ; and dolicocephalic (long and narrow), with a cephalic index below 75, as in Kaffirs and Fijians. The height of the skull represents the measurement from the basion to the bregma, and its proportion to the length is the index of height, or vertical index. Its average in civilized races corresponds with the breadth. The longitudinal arc of the skull represents the measurement from the nasion to the opisthion carried over the roof, and the basi-nasal length repre- sents the measurement from the basion to the nasion. These two measure ments, plus the distance between the basion and the opisthion, represent the vertical circumference of the cranium in the median plane. The degree of projection of the jaws is ascertained from the gnathic or alveolar index. This index represents the proportion of the basi-alveolar length to the basi- nasal. According to the gnathic index, skulls are arranged in three classes, namely, orthognathous (straight and upright jaw), with a gnathic index below 98, as in Europeans ; mesognathous (intermediate jaw), with an index of from 98 to 103, as in Chinese and Japanese ; and prognathous (forward jaw), with an index over 103, as in Australians. The form of the anterior nasal aperture is ascertained from the nasal index. This represents the proportion of the greatest transverse measurement of the aperture to the height, which latter is the measurement from the nasion to the subnasal point. According to their nasal index, skulls are arranged in three classes, namely, leptorhine (narrow nose), with a nasal index below 48, as in Europeans ; mesorhine (intermediate nose), with an index of from 48 to 53, as in Chinese and Japanese ; and platyrhine (broad nose), with an index above 53, as in Australians and Kaffirs. The form of the orbital aperture is ascertained from the orbital index, which re])resents the proportion of the height to the width of the orbital aperture. There are three varieties of orbital index, namely, megaseme (great index), when it exceeds 89, as in the Chinese ; mesoseme (intermediate index), when it is between 89 and 84, as in Europeans ; and microseme (small index), when it is below 84, as in Australians. Deformities of the Skull. The most common cause of cranial deformities is premature synostosis or osseous union of bones which are normally separate, the result being closure or obliteration of certain sutures. When the sagittal suture becomes prema- turely obliterated transverse growth is arrested, and, to compensate for this, in- creased growth takes place at the coronal and lambdoid sutures. The antero- posterior diameter of the cranium is greatly increased, and the vault assumes a boat-like shape. This variety is known as scaphocephalus. When the coronal suture becomes prematurely obliterated, increased growth takes place upwards, and the vertical diameter is greatly increased. Tliis variety is known as acrocephalus (pointed head). When one-half of the coronal or lambdoid suture becomes prematurely obliterated, obUque deformity takes place, this THE BONES OF THE HEAD 159 form being known as plagioeephalas (oblique or awry head). \\Tien the metopic or frontal suture becomes prematurely obUterated, growth is arrested in the frontal region, and the skull assumes a triangular shape. This variety is known as trigonocephalas. When premature obliteration of the sutures at the base of the skull takes place, the deformity known as cretin skull results. This is characterized by enlargement of the cranium (except in the occipital region), which becomes very hea\y, and assumes an irregular, somewhat conical shape, with the apex at the sagittal suture. It is associated with mental dulness, idiocy, and stunted growth, and the general condition is known as cretinism. Development of the Skull. The skuU is composed of two divisions, which are genetically distinct from each other. One division represents the cranium, which is developed from the mesenchyme (mesoderm) . around the cephalic part of the notochord. The other division, which includes the faca and the hyoid bone, represents the Tlsceral- FiG. 89. — Diagrams of the Primitive Cartilaginous Cranium (Wiedersheim). A. First Stage. — N, Notochord; PchC, Parachordal Cartilage; Tr, Prechordal Cartilage; PPS, -Primitive Pituitary Space; Olf, Opt, Aud, positions of Organs of Smell, Sight, and Hearing. B. Second Stage. — N, Notochord ; PchR, Parachordal Region (Basilar Plate) ; TrR, Fusion of Prechordal Cartilages; PPS, Primitive Pituitary Space; TrR, Prechordal Region; Olf, Opt, Aud, as in A. arch skeleton, and is developed, for the most part, from the first, second, and third visceral arches. The stages in the development of the skull £ire, as in the vertebral column, membranous, chondral or cartilaginous, and osseous. The Cranium. The cranium, as jiist stated, is developed from the mesenchjTne which sur- rounds the cephalic part of the notochord. This chord, after passing through the future odontoid process of the axis, extends forwards to the posterior part of the pituitary region of the base of the cranium, where the dorsum sellae of the sphenoid bone is subsequently developed. In this situation it Ues on the ventral aspect of the mid-brain, and within the sharp ventral bend described by the fore-brain. The cephalic part of the notochord carries along with it the skeletogenous sheath of mesen- chyme. t6o A MANUAL OF ANATOMY Membranous Stage. — The crajiium is at first entirely membranous, and is formed by the mesenchyme which surrounds the cephaHc part of the noto- chord. This mesenchyme expands forwards laterally, and then backwards, so as to form a membranous capsule for the cerebral vesicles. This capsule forms the primitive membranous cranium, which presents a base and a vault, or tegmental part. Cliondral or Cartilaginous Stage. — The base of the primitive membranous cranium undergoes chondrification, but the vault or tegmental portion is not involved in this process. Having, therefore, regard to the development of the bones which construct the osseous cranium, the membranous cranium is to be considered under two aspects — chondral and membranous. Chondrocranium. — The chondrocranium involves the basal part of the primitive membranous cranium, which has become converted into cartilage. Chondrification gives rise to a single plate of cartilage, extending from the basi-occipital to the ethmoidal region'. This basal cartilage may be regarded as consisting of two segments — chordal and prechordal. The chordal segment . embraces the cephalic part of the notochord, and the prechordal segment is in front of the notochord. Septum Nasi Optic Foramen Presphenoid Basi-occipii -sphenoid .Presphenoid Periotic Capsule — CranioPharyngea Canal ii||_ Ex -occipital Foramen Magnum Fig. 90. — The Chondrocranium (after Huxley). The chordal segment represents the parachordal cartilages of certain animals. The prechordal segment represents the prechordal cartilages, or trabeculae cranii of Rathke, present in certain animals. In man, however, it is a con- tinuous cartilage, which is interrupted at the centre by a membranous interval, representing the primitive pituitary space. In this region the cranial cavity communicates with the primitive mouth, or stomodasum, from which latter the pouch of Rathke ascends to form the anterior lobe of the pituitary body. The chordal segment, as stated, embraces the cephalic end of the notochord, but the chord soon disappears, and the cartilage of the chordal segment extends backwards, so as to embrace the foramen magnum and involve the supra-occipital region. The prechordal segment is continuous posteriorly with the chordal seg- ment. Anteriorly, in front of the primitive pituitary space, the basal plate of cartilage (prechordal segment) here spreads out laterally. Subsequently the pituitary space becomes closed by the encroachment upon it, from either side, of the prechordal cartilage. On each side of the chordal segment of the basal cartilage is the periotic cartilaginous capsule. THE BONES OF THE HEAD i6t The basal Cartilage is conveniently di\-idcd, for purposes of development, into three regional parts, which, in order from behind forwcirds, are as follows: (i) bcisi-occipital, (2) basisphenoid, and (3) ethmoidal. In addition to these three parts there are the two periotic cartilaginous capsules, right and left. The basi-occipital cartilage gives rise to the following parts of the occipital bone— namely, (i) the basi-occipital, or basilar process; (2) the exoccipitals, or condylar portions; and (3) the supra-occipital, or lower division of the tabular portion. The basisphenoid cartilage gives rise to the following parts of the sphenoid bone — namely: (i) the basisphenoid, or posterior part of the body, inclusive of the sella turcica; (2) the aJisphenoids, or great wings; and (3) the external pter^'goid plates. The ethmoidal cartilage gives rise to osseous parts as follows: the posterior portion gives rise to (i) the presphenoid, or anterior part of the body of the sphenoid, and (2) the orbito-sphenoids, or small wings of the sphenoid. B m npr m n pr npr Fig. 91. — Head of an Embryo (His). A, View from above. — B. View showng roof of mouth after removal of the Mandible. /«/»', Fronto-Nasal Process; mnpr. Mesial Nasal Process, terminating in Globular Process ; Inpr. Lateral Nasal Process | mx. Maxillary Process; mn. Mandibular Arch; hy, Hyoid Arch. The X in B indicates the Nasal Lamina. The anterior portion gives rise mesiaUy to the mesethmoid, or crista galli, and perpendicular plate of the ethmoid, as well as to the septal cartilage of of the nose. It is also prolonged anteriorly at its centre into the fronto- nasal process, of which it forms the core. Each lateral part of the anterior portion of the ethmoidal cartilage gives rise to the foUow-ing parts— nam ety, (i) the ethmo-turbinal, or lateral mass of the ethmoid, inclusive of the superior and middle conchae of the ethmoid ; (2) the inferior concha ; and (3) the sphenoidal turbinate bone of one side. Each periotic cartilagiooos capsule gives rise to the greater part of the petro-mastoid portion of the temporal bone. The ethmoidal division of the basal cartilage undergoes considerable modi- fication. It spreads out laterally, so, that it forms a broad plate. On either side in the region of each olfactory pit it assumes a deeply-curved crescentic outline, and forms the cartilaginous nasal capsule, this being the part which gives rise on either side to the ethmo-turbinal. inferior concha, and sphenoidal II i62 A MANUAL OF ANATOMY turbinate bone. Though known as the ethmoidal division or region, it gives rise not only to the ethmoid, etc., but also to the presphenoid and alisphenoids posteriorly, whilst anteriorly and mesially it dips down to form the septal nasal cartilage, and is prolonged as the core of the fronto-nasal process. Those bones of the cranium which are ossified from centres appearing in the basal sheet of cartilage, or chondrocranium, are called endochondral or cartilage bones, and the following is a summary of them : 1. Occipital, except the interparietal part, or upper division of the tabular portion. 2. Sphenoid, except the two internal pterygoid plates, but including the two sphenoidal turbinate bones. 3. Ethmoid. 4. Petro-Mastoid portion {greater part) of the temporal bone. Membranous Cranium, or Tegmental. — As previously stated, the primitive membranous cranium undergoes chondrification along its basal part. The tegmental part is not involved in this process, but forms a connective-tissue membrane, which subsequently gives rise to certain cranial bones. From the fact that these bones are ossified from centres which appear in this mem- brane they are called membrane-bones, and, inasmuch as they constitute the covering of the cranial vault, they are known as tegmental bones. The following is a summary of these bones: 1 . The Interparietal, or upper division of the tabular portion of the Occipital. 2. The two Parietal bones. 3. The Frontal bone (originally in two halves). 4. The Squamo-Zygomatic portion of each Temporal bone, as well as the pars tympanic a. The Visceral Arch Skeleton of the Skull. The visceral arch skeleton comprises the face and the hyoid bone. The Face. — The structures concerned in the development of the bones <5f the face are — (i) The fronto-nasal process, and the ethmoidal division of the basal .sheet of cartilage which constitutes the chondro-cranium ; and (2) the first visceral, or mandibular, arch, right and left, along with the maxillary process of each of these arches. Fronto-Nasal Process. — This process occupies a median position, and con- sists of a central part or core, and an external covering. The core is carti- laginous, and is a downward and forward extension of the anterior part of the ethmoidal division of the basal sheet of cartilage which forms the chon- drocranium. The external covering of the process is derived from the primi- tive cerebral capsule on the ventral aspect of the fore-brain, and is therefore membranous, being formed by mesenchyme. The process grows downwards and forwards, and from either side of its base a bud grows in a downward and forward direction, this bud having the same structure as the parent process. The fronto-nasal process then becomes somewhat complicated. The central portion of it is called the mesial nasal process, and this terminates below in two well-marked protuberances, one on either side of the median line, called the globular processes. The lateral bud on either side becomes the lateral nasal process. The fronto-nasal process, then, consists of (i) an undivided upper portion, (2) a mesial nasal process, terminating in two globular pro- cesses, and (3) two lateral nasal processes, right and left. As seen super- ficially on the embryonic face, the mesial nasal process and its two globular processes lie between the widely-separated ventral or mesial extremities of the two maxillar processes, and form the cephalic, or superior, boundary of the primitive mouth, or stomodaeum. The globular processes at first stand distinctly apart from each other, and each globular process is separated from the corresponding maxillary process by a groove which leads to the nasal pit of that side. The lateral nasaL process is separated from the globular process by the nasal pit, and externa' to the lateral nasal process is the optic or ocular de- THE BONES OF THE HEAD 163 pression. The position of parts, then, is as follows: The globular process forms the inner boundary of the nasal pit, and the lateral nasal process forms its outer boundary, the optic or ocular depression lying on the outer side of the lateral nasal process. In other words, the lateral nasal process hes between the nasal pit internally and the optic or ocular depression externally. The two nasal pits communicate widely with the primitive mouth or stomo- daeum. Inferiorly the lateral nasal process is contiguous to the ventral part of the maxillary process, from which it is at first separated by a groove, called the oculonasal, naso-optic, or lachrymal sulcus, which extends from the ocular depression to the nasal pit. This sulcus subsequently disappears, but it indicates the position of the future lachrymal sac and nasal duct. The lateral nasal process joins the maxillarj' process, and the two fuse with the globular process. Fronto-Nasal Process. Parts developed from it. (i) Globular Process. — Each globular process, as stated, consists of a core of cartilage, covered by a connective-tissue investment. The cartilaginous core disappears, and from the connective-tissue investment of each process the following parts are developed: [a) The incisor or premaxillary portion of the superior maxilla; (b) the anterior part of the palatal plate of the superior maxilla — that is to say, the part in front of the incisor or premaxillary suture through means of the nasal lamina : and (c) the portion of the upper lip, which corresponds to the premaxilla. The portion of the mesial nasal process which lies between the two globular processes gives rise superiorly to the dorsum of the nose, and inferiorly to the lower and anterior part of the nasal septum, which part is called the columella nasi. A prolongation of each globular process takes place in a backward direction in the form of a plate. These two plates are called the nasal lamincs. At first they are some distance apart, but they gradually come together, and each forms the anterior part of the palatal plate of the corresponding superior maxilla — that is to say, the part in front of the incisor or premaxillary suture, and belonging to the premaxilla. (2) Lateral Nasal Processes. — Each of these, as stated, consists of a core of cartilage, covered by a connective-tissue investment. The cartilaginous core gives rise to the upper and lower lateral nasal cartilages. The connective- tissue investment gives rise to the ala nasi, and the nasal and lachrymal bones. First Visceral, or Mandibular Arches, and their Maxillary Processes. — Simultaneously with the foregoing developmental changes, the mesoderm of each mandibular arch is undergoing differentiation. From the dorsal or proximal part of each mandibular arch a budding of its mesoderm takes place. This outgrowth gives rise to the well-marked maxillary process, which is for the most part membranous. Maxillary Processes. — ^The two maxillary processes grow in a ventral and mesial direction, below the ocular depressions, and, as seen superficially, on the primitive face, they Ue transversely, one on either side of the primi- tive mouth. Their ventral or mesial extremities are widely separated from each other, cind the mesial nasal process, with its two globular processes, lies between them, forming the cephalic or superior boundary of the primitive mouth. The lateral nasal process is contiguous superiorly to the ventral part of the maxUlary process, the two being separated by the oculo-nasal, naso-optic, or lachr\'mal groove, all as previously stated. Inferior to the maxUlarj- process is the corresponding mandibular arch. The upper border of the maxillary process is joined by the lateral nasal process, the oculo-motor or naso-optic groove becoming obliterated, and being replaced deeply by the lachry-mal sac and nasal duct. The ventral extremity of the maxillary process abuts against, and fuses with, the globular process. As the result of this fusion between the maxillarj' process and globular process, the external orifice (anterior nares) of the nasal pit of the corresponding side (now developing into the nasal fossa) is cut off from direct communication with the primitive mouth, but the nasal pit itself still remains in free communication with that cavity. i64 A MANUAL Oh ANATOMY The mesodennic maxillary process gives rise to — (i) The chief part of the superior maxilla, and the chief part of its palatal plate, the premaxilla and anterior part of the palatal plate being developed from the mesodermic investment of the globular process and its nasal lamina : (2) the corresponding part of the upper lip; (3) the malar bone; (4) the palate bone ; and (5) the internal pterygoid plate of the sphenoid. As has been stated, the lateral nasal process gives rise to the ala nasi, and the nasal and lachrymal bones. From the inner surface of each maxillary process there grows, in a mesial direction, a shelf-like plate of mesoderm. The two plates, right and left, are known as the palatal shelves, and they meet along the median line. Each gives rise to (i) the horizontal plate of the palate bone, and (2) the palatal plate of the superior maxilla, except its anterior or premaxillary part, which is developed from the nasal lamina of the globular process. In this manner the hard palate is formed, and the primitive mouth, or stomodseum, is uow divided into two chambers, upper and lower. The upper chamber represents the two nasal fossae, which open anteriorly through the anterior nares, and communicate posteriorly with the naso-pharynx through the posterior nares. 'J" he lower chamber constitutes the permanent mouth. The wide communica- tion between the original nasal pits and the primitive mouth now becomes considerably curtailed, and is only represented in adult life by the canals of Stensen in the region of the anterior palatine fossa. Each maxillary process at its dorsal or proximal end — that is to say, where it springs from the mandibular arch — contains for a short distance an off- shoot from the cartilaginous bar of the mandibular arch, this prolongation being known as the pterygo-palatine bar. The bar soon disappears, but its mesodermic investment gives rise to (i) the internal pterygoid plate of the sphenoid, and (2) the perpendicular plate of the palate bone. Mandibular Arches. — The two mandibular arches having parted with their maxillary processes, meet each other at the median line, and form the caudal or posterior boundary of the primitive mouth. The cartilaginous bar of each arch is called Meckel's cartilage. The mesial portion of this cartilage gives rise to the incisor part of the inferior maxilla or mandible. The chief part of the body of the mandible, however, and the lower part of its ramus, as high as the inferior dental foramen, are developed from the mesodermic invest- ment of that portion of Meckel's cartilage which intervenes between the incisor part and the level at which the cartilage gives off the pterygo-palatine bar. This mesodermic investment also gives rise to one-half of the lower lip. From the foregoing description it will be evident that the first visceral or mandibular arches build up the chief part of the facial portion of the visceral-arch skeleton of the skull, as shown by the following summary: The maxillary process of each mandibular arch gives rise to (i) the chief part of the superior maxilla, including the chief part of its palatal plate; (2) the malar bone; and (3) the palate bone, including its horizontal plate. The mandibular arch itself gives rise to the greater part of the mandible. The premaxillary portion of the superior maxilla, and the premaxillary part of its palatal plate, are developed from the globular process of the mesial nasal process and the nasal lamina of the globular process. The nasal bone and the lachrymal bone are developed from the lateral nasal process of the fronto-nasal process. Each inferior turbinate bone, as already stated, like the lateral mass of the ethmoid (ethmo-turbinal), is developed in the lateral portion of the ethmoidal division of the basal sheet of cartilage, or chondrocranium, from which it becomes differentiated. The ethmoid bone, though tabulated as a cranial bone, is chiefly facial in its disposition, inasmuch as it forms (i) a large part of the inner wall of the orbit, (2) a large part of the outer wall of the nasal fossa, and (3) a large part of the nasal septum. The only parts of the bone which belong to the base of the granium are the cribriform plate and the crista galli. All parts of the bone are developed from the ethmoidal division of the chondrocranium , as already stated. Tliere now only remain for consideration the vomer and the styloid process of the temporal bone. THE BONES OF THE HEAD 165 Vomer. — This bone is developed in the mesoderm, which nvests the ■posterior and inferior parts of the septal cartilage of the nose, that cartilage being derived from the ethmoidal division of the basal sheet of cartilage or chondrocranium . Styloid Process of Temporal Bone. — Both parts of this process — namely, the tympano-hyal and st^^lo-hj-al — are developed from the proximal or dorsal end of the hyoid bar (Reichert's cartilage) of the second visceral or hyoid arch. Summary. — The first visceral or mandibular arches contribute the following bones to the facial portion of the visceral-arch skeleton: (i) The greater part of each superior maxilla; (2) the greater part of the inferior maxilla or man- dible; (3) the two malar bones; and the two palate bones. The fronto-nasal process and the ethmoidal division of the basal cartilage, or chondrocranium, contribute the following bones : (i) Pre maxillary portion of each superior maxilla; (2) the two nasal bones; (3) the two lachrymal bones; and (4) the two inferior turbinate bones. The vomer, as just stated, belongs to the mesodermic investment of the posterior and inferior part of the septcd cartilage of the nose, which cartilage is derived from the ethmoidal division of the chondrocranium. The greater part of the hard palate is derived from the palatal shelves of the two maxillary processes of the mandibular arches, but the premaxillary part is formed by the nasal laminae of the globular processes of the mesial nasal process of the fronto-nasal process. The Hyoid Bone. The hyoid bone forms a part of the visceral-arch skeleton of the skull, and the structures concerned in its development are the second and third visceral arches of each side. Second Visceral or Hyoid Arch. — ^The cartilage of this arch is known as the hyoid bar, or cartilage of Reichert, and its distal or ventral segment gives rise to the small cornu or cerato-hyal. Third Visceral or Thyro-hyoid Arch. — ^The distal or ventral end of the cartilage of this arch is connected with that of its fellow of the opposite side by a median piece of cartilage, which acts as a bond of union between them, and is from that circumstance called the copula. The copula also connects the right and left hyoid bars. The body of the hyoid bone, or the basi-hyal, is developed from the copula; and each great cornu^ or thyro-hyal, is developed from the cartilaginous bar of the corresponding third visceral arch. The bones of the visceral-arch skeleton of the skull, genetically considered, are (i) membranous, (2) complex or mixed — that is to say, partly membranous and partly cartilaginous — and (3) cartilaginous. Membrane Bones : Complex or Mixed Bone : Superior Maxillae. Inferior Maxilla. Malars. Cartilage Bones : Nasals. Inferior Turbinates. Lachrymals. Hyoid Bone. Palate Bones. Vomer. Osseous Stage. — The osseous stage in the development of the skull is treated under each individual bone. THE TEETH. The teeth are divided into two sets, namely, the temporary, milk, or deciduous, which belong to early infancy, and the permanent, which replace the temporary. The temporary teeth are twenty in number — ten upper, five in each superior maxilla, and ten lower, five in each half of the inferior maxilla. The number of permanent teeth is thirty-two — sixteen upper, and sixteen lower. 1 66 A MANUAL OF ANATOMY Upper Lower Incisors Upper Canines I^owet Upper Lower BiCUSJ'iDS Upper Lower Pig g2. — The Permanent Teeth OF THE Left Side. The Permanent Teeth. — Pro-, ceeding from the median line in a direction outwards and backwards, the permanent teeth are as fol- lows: mesial incisor, lateral in- cisor, canine, first bicuspid, second bicuspid, and first, second, and third molars. The third molar is known as the dens sapientics or wisdom tooth. Each tooth is composed of the following parts: the crown, which is the part above the gum; the root, which is the part embedded in the alveolus; and the neck, which lies between the crown and root. The surface of a tooth which looks towards the lip is called labial, and that look- ing towards the tongue lingual, whilst of the opposed surfaces one is called mesial or proximal, and the other lateral or distal. The Incisors. — There are eight incisor teeth — two in each upper jaw, and two in each half of the lower jaw. In each case the two incisors are known as mesial and lateral respectively, and they are called ' incisor ' because their crowns are so formed as to be adapted for the division of food. The cutting edges of the crowns of the upper incisors are bevelled behind, and those of the lower incisors in front. The upper mesial incisor is larger than the lateral, and it gradually tapers from the cutting edge of the crown to the root. The length of the crown exceeds its breadth. The labial surface is slightly con- vex, whilst the lingual surface is concave. The Ungual surface Molars prcscuts near the gum a ridge, called the basal ridge, or cingulum. The mesial angle of the cutting edge of the crown is longer or more projecting than the lateral angle. The root is long, tapering, conical, and slightly flattened on either side. THE TEETH 167 The upper lateral incisor is smaller than the mesial, which it for the most part resembles. The lateral angle of the cutting edge of the crown is rounded off, and the cingulum is more prominent than in the upper central incisor. The lower mesial incisor is smaller than the lateral, and narrower than the upper mesial incisor. The cingulum, if present, is not well marked. The root is much compressed laterally. The lower lateral incisor is larger than the mesial, which it for the most part resembles. The presence of a cingulum is rare. The root is longer than that of the central incisor, and on each flat- tened lateral surface there may be an indication of a longitudinal groove. The Canines. — There are four canine teeth — one in each upper jaw, and one in each half of the lower jaw. The crown of a canine tooth is larger than that of an incisor. It is somewhat conical, and terminates in a cusp, from which cir- cumstance the canine teeth are known as the cuspidate teeih. The labial surface of the crown is convex. In the upper canines the lingual surface of the crown usually presents a shght median ridge, which extends from the cusp to a ridge which represents the cingulum. The root is long, thick, and almost round. The lower canines have no median ridge on the lingual surface, which may be sUghtly concave. The citigulum is absent. The root is shorter than in the upper canines. The Bicuspids, or Premolars. — There are eight bicuspid teeth — two in each upper jaw, and two in each half of the lower jaw. Upper Bicuspids. — The crown is quadrilateral, and its labial border is longer than the lingual. It has two cusps — ^labial and lingual — both of which are prominent. The labial cusp is the larger and broader of the two, and the cusps are separated by a deep transverse fissure. The labial and lingual surfaces of the crown are convex, and there is no cingulum. The root is single, much compressed laterally, and usually marked on either side by a longitudinal groove. The first upper bicuspid has frequently two slender fangs. This occurs so often that it may be regarded as the normal condition in that tooth. The second upper bicuspid differs from the first in the following respects: (i) Its crown is larger, and approaches more nearly the molar type; and (2) its lingual cusp is larger and broader than that of the first upper bicuspid, so that its labial and lingual cusps are of nearly equal size. Lower Bicuspids. — ^These teeth are smaller than the upper bicuspids. The labial cusp has an inclination inwards towards the mouth, and the lingual cusp is depressed. The cusps are connected by a lou-lying ridge. The root is single, round, and tapering. The second lower bicuspid differs from the first in the following respects: (i) Its crown is larger, and approaches more nearly the 108 A MANUAL OF ANATOMY molar type; and (2) its lingual cusp is stout, and not so much de- pressed as that of the first lower bicuspid. The second lower bicuspid has occasionally two fangs. The Molars {MuUicuspidate Teeth). — There are ti&elve molar, or grinding teeth — three in each upper jaw, and three in each half of the lower jaw. First and Second Upper Molars. — The crown is somewhat square, the angles being rounded off. The grinding surface is furnished with four cusps, situated at each angle of the square, two of them being labial and two lingual. The anterior lingual cusp is the largest, and it is connected with the posterior labial cusp by a stout oblique ridge. The labial cusps are longer or more projecting than the lingual cusps, which applies to all the upper molars. The fissure between the two labial cusps and that between the two lingual cusps appear for a short distance on the labial and lingual surfaces of the crown respectively. The posterior lingual cusp is occasionally suppressed. The root has three fangs — two labial and one lingual. The lingual fang is the largest and most divergent, its direction being obliquely inwards towards the tongue. Third Upper Molar. — This tooth is subject to much variety. Its crown is usually of smaller size than that of the first and second. The two lingual cusps of the crown are frequently confluent. The three fangs are blended together to form a tapering cone. Lower Molars. — The first lower molar is the largest. The crown is somewhat square, and its grinding surface is provided with five cusps. Four of these are placed at the angles of the square, and are separated from each other by a crucial fissure. The posterior limb of this fissure bifurcates, and the fifth cusp lies in the angle of bifurcation. This cusp may be in the median Hne, but it usually lies towards the labial aspect, from which aspect it can readily be seen. The lingual cusps are longer or more projecting than the labial cusps, which applies to all the lower molars. The fissure which separates the two labial cusps usually passes for a short distance on to the labial surface of the crown, but the fissure be- tween the two lingual cusps only occasionally passes on to the lingual surface of the crown. The root has two fangs — anterior and posterior. Each fang is much compressed from before backwards, and in most cases each presents a slight backward curve. The second lower molar bears a general resemblance to the first. The fifth cusp is often absent, and, when present, it is of small size. The two fangs of the root are frequently blended together. The third lower molar is of larger size than the third upper molar. Its crown is large, and is usually provided with five cusps. Its root may have two separate fangs, or these may be confluent. In the latter case a groove indicates the double condition of the root. Dental Arches. — The alveolar borders of the superior and inferior maxillary bones, and the upper and lower teeth, are so disposed as to form two, almost similar, curves. When the mouth is closed, THE TEETH 169 the summits of the crowns of the upper and lower teeth are brought together, the line of contact being known as the dental articulation. A hne drawn through this articulation forms the best means of determining the breadth of the crown of each tooth. The crowns of the upper eight anterior teeth — namely, the four incisors, two canines, and the two first bicuspids — are broader than the crowns of the corresponding lower eight anterior teeth, measured according to the foregoing Hne. The crowns of the lower eight posterior teeth — namely, the six molars and the two second bicuspids — similarly measured, are broader than the crowns of the corresponding upper eight posterior teeth. The difference in breadth between the crowns of the upper and lower eight anterior teeth is equal to the difference in breadth between the crowns of the lower and upper eight posterior teeth. Fig. 93. — The Superior and Inferior Maxillary Bones at the Seventh Year, showing Most of the Temporary Teeth, and the Permanent Teeth about to replace them. The First Permanent Molars and the Permanent Lower Central Incisors are in position. The result is that, if the dental arches could be straightened out, the crowns of the upper and lower sets of teeth would have the same measurement as regards breadth. The crowns of the upper six anterior teeth — namely, the four incisors and the two canines — overlap the crowns of the corre- sponding lower six anterior teeth. The Temporary Teeth.—Proceeding from the median hne, these are as follows on either side: two incisors, central and lateral, one canine, and two molars, first and second. Their necks are more constricted than in the permanent set. The incisors and canines resemble, for the most part, those of the permanent set, but they are smaller. The molars, which are replaced by the permanent bicuspids, exceed them in size, the second molars being particularly large. The first upper molar has three cusps — two labial and one I/O A MANUAL OF ANATOMY lingual, the second upper and first lower molars have each four, and the second lower molar has five. Eruption of the Teeth. — ^The eruption of particular teeth of the lower jaw precedes that of the corresponding teeth of the upper jaw, and the periods are as follows: Temporary Teeth. Incisors First molars Canines Second molars 6th to 1 2th month, rath to 14th ,, 14th to 2oth „ 20th to 24th „ Dentine ., Pulp Cavity . Prolongation of Pulp Cavity into Fangs y Enamel on Crown — Dentine -Neck ..Pulp Cavity -" Dentine Crusta Petrosa Fig. Opening on Apex of Fang 94. — Sections of Teeth. A, Lower Molar; B, Lower Incisor. Permanent Teeth. First molars Central incisors. . Lateral incisors . . First bicuspids . . Second bicuspids Canines . . Second molars . . Third molars Gth year. 7th 8th gth loth nth 1 2th „ 1 7th to 25th year. About the sixth year is the period at which most teeth are present in the jaws, there being the twenty temporary teeth, and all the permanent, except the four wisdom teeth, (namely, twenty-eight), making in all forty-eight. THE TEETH 171 Structure of a Tooth. — ^The crown of a tooth contains a central cavit}', called the pulp cavity, which is occupied by the dental pulp. The shape of the pulp cavity corresponds with that of the crown, and it extends into the root, and as man}^ fangs as compose it, terminating in a small opening on the apex of the fang. The cavity also extends for a little into the cusps of the bicuspids and molars, and in the incisors it is continued into each angle of the crown. The wall of the cavity presents a number of openings, which lead into the dentinal tubules. The dental pulp is composed of a matrix of connective tissue, containing bloodvessels, nerves. Fig. 95. — Section of the Fang of A Tooth. I, Cement; 2, Granular Layer of Purkinje; 3. Dentinal Tubule». Fig. 96. — Enamel Prisms. A. Four prisms (Longitudinal View) ; B, Surface of the Enamel. cells, and fibres, which latter seem to be processes of the cells. It is destitute of lymphatics. The cells are scattered throughout the matrix, and at the surface of the pulp they form a continuous layer, being there known as the odontoblasts. This layer is some- times spoken of as the memhrana eboris. The pulp is very vascular and sensitive, its vessels and nerves reaching it through the minute openings at the apices of the fangs. The substance of the tooth is formed of three tissues, namely, ivory or dentine, enamel, and cement or crusta petrosa. The 172 A MANUAL OF ANATOMY dentine forms the principal part of the tooth, surrounding the pulp cavity and its prolongations; the enamel covers the exposed part or crown; and the cement covers the root. Dentine. — ^This bears a resemblance to bone, but contains rather less animal, and more earthy, matter, the proportion in lOO parts being about 28 of animal matter to 72 of earthy. The dentine has a striated appearance, due to the fact that it is traversed by a number of minute branched channels, called the dentinal tubules, which radiate in a curved manner outwards from the pulp cavity to the deep aspect of the enamel and cement. These tubules contain processes of the odontoblasts which form the membrana eboris, and are known as Tomes' fibres. The part of the dentine adjacent to the enamel and cement is known as the granular layer of Purkinje. It presents a number of irregular spaces, known as the interglobular spaces, which are surrounded by minute globules of calcareous matter. Enamel. — ^This caps and protects the dentine of the crown. It is exceedingly hard, which is due to the fact that it contains no animal matter — at least, to any appreciable extent. It consists of solid hexagonal prisms, which are marked by transverse stria- tions. These are received by their deep extremities into depres- sions on the dentine, and are placed vertically on the summit of the crown, but horizontally on its sides. At the period of eruption of a tooth, and for some little time thereafter, the enamel of the crown is covered by a thin membrane, called the enamel cuticle, or Nasmyth's membrane. Cement, or Crusta Petrosa. — ^This covers the dentine which forms the root of the tooth. It is true bone, and contains lacunae and canaliculi, but it is destitute of Haversian canals. The root of a tooth is maintained in its alveolus by the peri- dental membrane or dental periosteum, which covers the cement, and lines the wall of the alveolus, being continuous with the gum at the neck of the tooth. The articulation is called gomphosis. Development of the Teeth. The teeth are calcified papillae of the gingival mesoderm, their crowns being covered by calcified ectodermic cells. Three structures are involved in the development of a tooth — namely, (i) the enamel organ, which furnishes the enamel : (2) the dental papilla, which gives rise to the dentine and dental pulp : and (3) the dental sac, from the inner layer of which the cement is formed. The enamel organ is developed from the ectoderm, whilst the dental papilla and the dental sac are of mesodermic origin. The development of the temporary teeth commences as ingrowths o.f the epithelium along the margins of the embryonic jaws into the mesodermic tissue of the jaws. Each of these ingrowths, which consists of epithelial cells, soon gives rise to two vertical layers — an outer or labial, and an inner or lingual. The outer layer is called the labio-dcnial lamina, and the inner layer is the true dental lamina. The labio-dental or labio-gingival lamina is concerned with the lip and gum, and it presents superficially a furrow, called the labio-dental or labio-gingival groove, which divides it into two parallel ridges — labial for the lip, and gingival for the gum. The labio- gingival groove itself deepens, and separates the lip from the gum. THE TEETH 173 The true dental lamina is concerned witli the enamel. Along its attach- ment to the oral epithehum a furrow is formed, called the dental groove, and its deep margin is received into the mesoderm of the embryonic jaw. The true dental laminae, which are of ectodermic origin, are at first un- broken, but they soon become broken up into separate masses, called enamel organs, there being twenty of these for the temporary teeth, ten upper and ten lower. Each enamel organ appears as a thickening or protuberance of ectodermic cells on the deep margin of the true dental lamina, which pro- tuberance soon becomes flask-shaped, the neck being directed superficially. 1 his neck soon disappears, and the connection between the enamel organ and the ectodermic cells of the free surface of the gum is thereby severed. More- o%'er, the enamel organs become isolated from one another. The dental papilla appears as an elevation of the mesoderm of the floor of the dental groove, subjacent to each enamel organ. The number of papillae, therefore, corresponds to the number of enamel organs. As the dental papilla grows, it becomes capped by the enamel organ, which also invests it laterally. The enamel organ thus becomes moulded over the dental papilla in the form of a cap. Dental Ridge Superficial Layer of Epitheliuoi Deep Layer of Epithelium Dental Ridge [ Enamel Germ • ; Superficial Layer of Epithelium Deep Layer Neck of Enamel Germ Tooth-sac (Inner Layer) Outer Layer of Growing Tooth-sac — Dental Germ Enamel Organ : Dental Germ Tooth-sac (Outer Layer) Bone Enamel Org Tooth-papilla Fig. 97. — Development of Tooth (Frey, after Thiersch) Vertical Transverse Section of Upper Jaw. Enamel Organ. — As stated, the enamel organ is of ectodermic origin being denved from the true dental lamina, which, in turn, is derived from the ectodermic cells covering the surface of the gum. The chief cells of the enamel organ are situated deeply, and lie close to the surface of the dental papilla. They are long columnar cells, which are called enamel cells, ada- mantoblasts, or ameloblasts, and they give rise to the enamel prisms Formation of Enamel Prisms.— Each enamel cell gives rise to one enamel prism, ihe deep part of each cell undergoes calcification. The superficial ends of the enamel cells do not become calcitied, but form a delicate mem- brane, called the enamel cuticle, or Nasmyth's membrane, which covers the crown of the tooth for a short time after its eruption. Dental Papilla.— As stated, the dental papilla is of mesodermic origin and It gives rise to the dentine and dental pulp. Essentially, the papilla is a 174 A MANUAL OF ANATOMY collection of mesodermic cells, which become transformed into connective tissue, this being permeated by bloodvessels and nerves. The cells at the surface of the papilla become enlarged, and are called odontoblasts. These cells are identical with the osteoblasts of developing bone, and they form a continuous layer, known as the membrana eborls. From these cells the dentine is laid down. The central portion of the dental papilla, consisting of connective tissue, bloodvessels, and nerves, constitutes the dental pulp. Formation of Dentine. — The dentine is laid down in successive layers. Each layer consists at first of a fibrous dentinal matrix, called prodentine, the fibres of which are continuous with those of the dental pulp. Subsequently the matrix undergoes calcification by the deposits of calcareous matter. D uring the formation of these layers the odontoblasts become shifted inwards toT.-ards the centre, and they leave behind them fine processes, which become invested by the calcified fibrous matrix of the dentine. In this manner the dentinal tubules are formed, with processes of the odontoblasts within them, which represent the fibres of Tomes. The dentine so formed constructs a case for each dental papilla. The central part of the papilla, consisting of connective tissue, bloodvessels, and nerves, forms, as stated, the dental pulp. The peripheral part of the dentine has several small uncalcified areas, which lie between globular masses of calcareous matter. These areas represent the interglobular spaces of the adult tooth. Dental Sac. — This sac, like the dental papilla, is of mesodermic origin. As the dental papilla is undergoing differentiation into dentine and dental pulp, the mesodermic connective tissue around the papilla becomes condensed into a follicle, called the dental sac, which encloses both the dental papilla and the corresponding enamel organ. The developing tooth (enamel organ and dental papilla) thus becomes isolated, the enamel organ having previously lost its connection with the ectoderm of the gum by rupture of its neck. The part of the dental sac which is related to the crown of the tooth is connected with the surface of the gum by a band of connective tissue, called the gubcr- naculum dentis. This part of the sac, along with the gubemaculum, dis- appears. The part of it which is related to the root of the tooth undergoes important developments. It consists of two layers — inner and outer. The inner layer gives rise to the cement, or crusta petrosa, whilst the outer layer, remaining fibrous, forms the alveolo-dental periosteum, or peridental membrane. Permanent Teeth. — The process of development of the permanent teeth is similar to that of the temporary teeth. The enamel organs of those perma- nent teeth [teeth of succession) which are to replace the temporary teeth — namely, the permanent incisors, canines, and bicuspids — are developed as thickenings or protuberances of the true dental laminae, as in the case of the temporary teeth, and they grow inwards on the lingual aspects of the tem- porary enamel organs. The enamel organs of the three permanent molar teeth spring from a back- ward prolongation of the true dental lamina. Teeth Present at Birth. — At the period of birth the gums contain forty-four teeth. These consist of — (i) the twenty temporary teeth; (2) the twenty permanent teeth, which are to replace the temporary teeth; and (3) the four first permanent molar teeth. At birth the second and third permanent molar teeth, eight in all, are not yet developed. Eruption of the Temporary Teeth. — As the permanent teeth grow, they exercise pressure upon the fangs of those temporary teeth which they are about to replace. This continued pressure leads to partial absorption of the fangs of the temporary teeth. These teeth, therefore, become loosened in their alveoli, and as the permanent teeth continue to advance, the loosened temporary teeth are pushed out by the advancing permanent teeth. Osteo- clasts also take part in the absorption of the fangs. THE BONES OF THE UPPER LIMB m. THE BONES OF THE UPPER LIMB. The upper limb is arranged in four divisions, namely, the pectoral or shoulder-girdle, brachiuni or arm proper, antibrachium or fore- arm, and manus or hand. The shoulder-girdle consists of the clavicle and scapula, the brachium comprises the humerus, the antibrachium is composed of the radius and ulna, and the hand is subdivided into a carpus, comprising eight bones, a metacarpus, consisting of five bones, and phalanges, which number fourteen. The Clavicle. The clavicle or collar-bone is situated at the lower part of the neck anteriorly, where it lies above the first rib, and it extends outwards and backwards from the upper border of the presternum to the acromion process of the scapula. The bone presents two curves, an inner or sternal, occup)dng two-thirds, with its con- Pectoralis Major Deltoid Acromial Facet Trapezius Fig. 98. — The Right Clavicle (Superior View). vexity directed forwards, and an outer or acromial, extending over the outer third, with its convexity directed backwards. These curves impart elasticity to the bone. The clavicle is divided into a shaft and two articular extremities. The shaft is somewhat quadrilateral over its inner two- thirds, and compressed from above downwards over its outer third. The superior surface is for the most part narrow, but externally it becomes broad. At its inner end, near the postero-superior border, it pre- sents a rough ridge, about i| inches long, for the origin of the clavicular head of the stemo-cleido-mastoid. At its outer ex- panded part it is encroached upon by the tendinous fibres of the trapezius and deltoid. Elsewhere it is covered by the skin, fascia, and platysma myoides. The anterior surface is convex over its inner two-thirds, and concave over its outer third, where it is reduced to a mere rough border. Over the inner haJf it is rough for the origin of the clavicular portion of the pectoralis major, and over its outer marginal third it gives origin to the claviciilar portion of the deltoid. At the inner end of the deltoid impression there is sometimes a pointed projection, knowTi as the deltoid spine. The 176 A MANUAL OF ANATOMY posterior surface is concave over its inner two-thirds, and convex over its outer third, where it is narrowed into a rough border. The inner two- thirds overhang the subclavian vessels and trunks of the brachial plexus, whilst the outer marginal third gives insertion to the upper fibres of the trapezius. At the inner end of the im- pression for these fibres, opposite the deltoid spine, there is a conical projection which extends on to the inferior surface for a little, called the conoid tubercle, for the conoid ligament. About the centre of the posterior surface there is the medullary foramen for the medullary artery, which is a branch of the suprascapular. The canal to which the foramen leads is directed outwards. The foramen may be situated on the inferior surface in, or close to, the subclavian groove, or there may be two foramina, one on the posterior and one on the inferior surface, about an inch apart. Rhomboid Impression -Acromial Medullary Pectoralis Facet Deltoid 1 Sub- clavius Foramen i A Major 1 1 Trapezoid Ridge Sternal Articular Surface Fig. 99. — The Right Clavicle. A. Inferior View ; B. Sternal Extremity. Close to the sternal end the posterior surface gives partial origin to the sterno-hyoid. The inferior surface presents near its sternal end the rhomboid impression, about an inch long, for the costo- clavicular or rhomboid ligament. External to this there is the subclavian groove, which extends from the rhomboid impression to near the conoid tubercle, and gives insertion to the subclavius. The groove is bounded by two lips, anterior and posterior, to which the costo-coracoid membrane is attached in two laminae. At the outer extremity of the inferior surface there is a rough oblique line, called the trapezoid ridge, which extends forwards and outwards from the conoid tubercle, and gives attachment to the trapezoid ligament. The conoid tubercle is more fully seen here than on the posterior border, and is situated at the postero-internal extremity of the trapezoid ridge. The borders of the clavicle over its outer third are anterior and posterior. The anterio/ border bifurcates, over the inner two-thirds, THE BONES OF THE UPPER LIMB 177 into an antero-snperior and aniero-infefiot border, which enclose between them the anterior surface. The posterior border bifurcates, over the inner two-thirds, into a postero-superior and posfero- inferior border, the latter forming the posterior lip of the sub- clavian groove. The antero-superior and postero-superior borders limit the superior surface, the postero-superior and postero-inferior limit the posterior surface, the postero-inferior and antero- inferior limit the inferior surface, and, as stated, the antero-inferior and antero-superior limit the anterior surface. The sternal extremity is enlarged and covered by cartilage. As viewed on end, it is somewhat triangular, and presents a prominent posterior angle which is directed downwards, inwards, and back- wards. The surface is concave from before backwards, and convex from above downwards, and it articulates \nth the clavicular impression on the upper border of the presternum, an inarticular fibro-cartilage interv^ening. The circimiference of the sternal end is rough for the stemo-clavicular and interclavicular ligaments, except inferiorly, where there is a narrow strip for the first costal cartilage. The acromial extremity presents an oval facet for the acromion process of the scapula. The clavicle receives its blood-supply from the suprascapular artery- and the thoracic axis. Articulations. — Internally with the presternum cind first costal cartilage, and externally v^ith the acromion process of the scapula. Structnre. — The exterior is composed of compact bone which is thickest towards the centre, and the interior of coarse cancellated tissue, the principal lamellae being disposed longitudinally. The clavicle has no medullary canal, but, towards the centre of the shaft, the medullary spaces of the cancellated tissue are of large size. Varieties. — (i) There may be a deltoid spine. (2) The superior surface may present a small sUt-Uke aperture, N^ariously situated, for one of the descending branches of the cervical plexus of nerves. The Clavicle of the Female. — The bone is smoother, more slender, straighter, and more cylindrical over its inner two-thirds, than that of the male. Ossification. — The clavicle, which is the earliest bone to ossify, has two primary centres and one secondary centre. It is preceded by a rod of con- Appears in the 18U1 year, and joins about 25 I L I Appears in the 6th week (intra-uterine) FiG.loa— OssiFic.vrioN of the Cl.wicle. nective tissue. Within the two halves of this rod collections of ' precartila- ginous tissue ' are formed, and within these at their contiguous ends the primary centres appear about the 6th week. Subsequently the precartilag- 12 178 A MANUAL OF ANATOMY inous collections fuse, and thereafter the primary centres coalesce Ossifi- cation from these two centres proceeds at first in the precartilaginous tissue, but subsequently in the cartilage to which this tissue gives place. The primary centres may fail to join, w^ith the result that the clavicle may persist in two halves. The secondary centre appears in the cartilage of the sternal end about the zoth year, and this epiphysis joins the shaft about the 25/A year (Mall and Fawcett) . The law of ossification applicable to bones having a shaft and one epiphysis is as follows: the medullary foramen and the canal to which it leads are directed towards that extremity which has no epi- physis. This law is illustrated in the clavicle and the metacarpal, metatarsal, and phalangeal bones. The Scapula. The scapula or shoulder-blade is situated on the posterior aspect of the thorax, where it extends from the second to the seventh rib, being separated by muscles from the thoracic wall. It consists of a body and three processes, namely, a spine, an acromion and a coracoid process. The body is a thin triangular plate, and it presents two surfaces, three borders, and three angles. The anterior surface, venter, or subscapular fossa is concave, and the bone forming it is for the most part thin, except near the external or axillary border, where there is a thick, round, elongated ridge. It gives origin to the subscapularis, except (i) along the anterior aspect of the base from the superior to the inferior angle, where the serratus magnus is inserted, and (2) over the front of the neck. The venter is crossed by three or four oblique ridges, which extend upwards and outwards from the base, and give attachment to tendinous septa intersect- ing the subscapularis muscle. The posterior surface or dorsum is irregularly convex, and is divided into two unequal parts by the spine. The upper division, along with the superior surface of the spine, forms the supraspinous fossa. It represents about one-fourth of the dorsum, and gives origin over its inner two-thirds to the supraspinatus. In the region of the neck it presents a nutrient foramen for a branch of the suprascapular artery. The lower division, along with the inferior surface of the spine, forms the infraspinous fossa, and it represents about three- fourths of the dorsum. Towards the external or axillary border it presents an elongated concavity, external to which is an oblique line extending from its upper end downwards and inwards to the base near the inferior angle. The infraspinous fossa, as far out as this oblique line, gives origin to the infraspinatus, except at the upper and outer part, and it presents a nutrient foramen superiorly, close to the spine near the centre, for a branch of the dorsalis scapulae artery. The oblique line marks off impressions for the teres muscles and dorsalis scapulae artery, as follows: the teres minor arises from about the upper two-thirds, near the centre of which there is a groove for the dorsalis scapulae artery, and the THE BONES OF THE UPPER LIMB 179 teres major arises from about the lower third. The impression for the latter muscle is oval ; it extends on to the back of the inferior angle, and it is separated from the impresssion for the teres minor by a short rough line. This line gives attachment to an inter- muscular septum which separates the teres muscles, and the oblique line to a septum which separates these muscles from the infra- spinatus. The supra- and infraspinous fossae communicate with each other by means of the great scapular notch, which lies outside Coracoid Process Clavicular j Acromion Process Facet 1 Deltoid ' ' Pectoralis Minor -- Suprascapular Notch Superior Angle Upper part of Serratus Magnus Short Head of Biceps - ' and Coraco-brachialis Glenoid Cavity - ■ Neck'- Infraglenoid Ridge and Long Head of Triceps ' Middle part of Serratus Magnus --Subscapular Fossa and Subscapularis — Vertebral Border (Base) Axillary Border Inferior Angle Fig. tot. — The Right Scapula (Anterior View ). the short external border of the spine, and transmits the supra- scapular artery and nerve. The borders are superior, internal or vertebral, and external or axillary. The superior border, which is the shortest and thinnest, extends from the superior angle to the coracoid process. Close to that process it presents the suprascapular notch. This is converted into a foramen by the suprascapular or transverse ligament, which sometimes undergoes ossification. The supra- l8o A MANUAL OF ANATOMY scapular nerve passes backwards beneath the ligament, and the suprascapular artery over it, whilst the posterior belly of the omo-hyoid arises from its inner part and from the adjacent portion of the superior border. The internal or vertebral border is known as the base. It is the longest, intermediate in thickness, and extends from the superior to the inferior angle. It is convex, and is divisible into three parts. One part represents the base of the small triangular surface by which the spine arises from the vertebral border, and it gives insertion to the rhomboideus minor ; another extends from this to the superior angle, and gives insertion to the levator anguli scapulae ; and the third extends downwards to the inferior angle, and gives insertion to the rhomboideus major. On the ventral aspect close to this border there is a long narrow linear impression, which widens towards the superior and inferior angles, and gives insertion to the serratus magnus. The external or axillary border, which is the thickest and intermediate in length, extends from the inferior angle to the lower margin of the glenoid cavity. Below that cavity it presents a rough impression, an inch long, called the infra- glenoid ridge, which gives origin to the long head of the triceps, and a little below this a groove for the dorsalis scapulae artery, which also marks the dorsal aspect. The ventral aspect of the bone close to this border presents a" groove over the upper two- thirds, which gives origin to many fibres of the subscapularis. The angles are superior, inferior, and external. The superior angle, which is thin, is situated at the meeting of the superior and vertebral borders, and it forms the highest part of the body, being on a level with the second rib. Its ventral aspect gives insertion to a part of the serratus magnus, and its edge to a portion of the levator anguli scapulae. The inferior angle, somewhat thick and round, is situated at the meeting of the vertebral and axillary borders, and it forms the lowest part of the bone, being on a level with the seventh rib. Its ventral aspect gives insertion to a part of the serratus magnus, and its dorsal aspect gives- origin to a portion of the teres major. Below the impression for the latter muscle there is sometimes a rough semilunar marking for a slip of origin of the latissimus dorsi. The external angle, which is massive, is situated at the upper end of the axillary border. It forms the head of the bone, and supports the glenoid cavity, which articulates with the head of the humerus. The glenoid cavity, so named from its shallowness, is pyriform, with the narrow end upwards, and its direction is outwards and forwards. Its margin is slightly elevated and rough for the glenoid ligament, and immediately outside the margin the capsular ligament of the shoulder- joint is attached. Superiorly it presents a small rough elevation, called the supraglenoid tubercle, which gives origin to the long head of the biceps. The neck is the constricted portion which extends from the suprascapular notch to a point immediately above the infraglenoid ridge, and it is most evident posteriorly, THE BONES OF THE UPPER LIMB i8i where it forms, with the external border of the spine, the great scapular notch. In this latter situation there are numerous fora- mina for branches of the suprascapular artery. The spine is situated on the dorsum of the bone, which it crosses in a direction outwards and slightly upwards. It commences at the \ertebrcd border in a flat triangiilar surface, over which the tendon receiving the lower fibres of the trapezius glides, with the interven- tion of a bursa. It soon becomes very prominent, and at its outer Suprascapular Coracoid Posterior Belly of Omo-hyoid Notch Process Trapezius Supraspiuons Fossa and Supraspinatus \ i Superior Angle I ', J Levator Anguli Scapulas Spine For Tendon of Trapezius Rhomboideus Minor Rbomboideus Major. Infraspinous Fosia and Infraspinatus Groove for Dorsalis Scapube Artery .Acromion Process Deltoid Great Scapular Notch Glenoid Cavity Infraglenoid Ridge and Long Head of Triceps --« Axillary Bofder > Teres Minor », Ttres Major ""•*•. Inferior Angle Latissimus Dorsi Fig. I02. — The Right Scapula (Posterior View). extremity it undergoes a slight twist and forms the acromion process. It is triangular, and compressed from above downwards. The superior surface forms part of the supraspinous fossa, and gives origin to fibres of the supraspinatus, whilst the inferior surface forms part of the infraspinous fossa, and gives origin to fibres of the infraspinatus. The external border, which is short, boimds internally the great scapular notch. The anterior border is continuous \y\ih the body of the bone. The posterior border or crest presents an upper lip, which gives insertion to part of the trapezius, a lower lip, giving partial 1 82 A MANUAL OF ANATOMY origin to the deltoid, and an intervening rough surface which is encroached upon by the tendinous fibres of these two muscles. The upper lip is often very projecting at its inner end, where the tendon receiving the lower fibres of the trapezius is inserted. The acromion process is situated at the outer extremity of the spine, and its direction is outwards, upwards, and forwards, so as to overhang the glenoid cavity. It is somewhat triangular, and is compressed from above and behind downwards and forwards. The postero-superior surface, which is rough, gives origin at its lower and inner part to some fibres of the deltoid, and elsewhere is subcutaneous. The antero -inferior surface, which is smooth and concave, overhangs the glenoid cavity, and is related to the subacromial bursa. The outer border is continuous with the lower lip of the posterior border of the spine, where there is a pro- jection called the acromial angle, and this outer border gives origin to a portion of the deltoid. The inner border is continuous with the upper lip of the posterior border of the spine, near which it gives insertion to a part of the trapezius, whilst near the tip of the acro- mion it presents an oval facet for the outer extremity of the clavicle. The upper and lower margins of this facet are rough for the acromio- clavicular ligaments. The tip or apex of the process is situated at the meeting of the outer and inner borders. The acromion pro- cess is pierced by many arterial twigs derived from the acromial rete. The coracoid process, which is strong and curved, springs from the upper aspect of the head, immediately external to the suprascapular notch. It is directed at first upwards and forwards for about ^ inch, and then, bending sharply, it is directed forwards and outwards to terminate in a blunt tip. The ascending portion is compressed from before backwards. Its anterior surface is related to the subscapularis, and the posterior to the supraspinatus. Its outer border gives attachment to a portion of the coraco - humeral ligament, and the inner border, which bounds the suprascapular notch externally, gives attachment at its upper part to the suprascapular or transverse ligament. The horizontal portion of the process is compressed from above downwards. Its antero -internal border, which is long and convex, and the adjacent portion of the superior surface, give insertion anteriorly to the pectoralis minor, whilst posteriorly they give attachment to the costo-coracoid membrane and ligament. The postero-external border, which is short, receives the fibres of the coraco-acromial ligament, and gives attachment to a portion of the coraco-humeral ligament. At the back part of the antero-internal border there is the conoid impression for the conoid ligament. On the back part of the superior surface there is the trapezoid ridge for the trapezoid ligament, which ridge extends forwards and out- wards from the conoid impression. The inferior surface of the horizontal portion is smooth and concave. The tip or apex, which is blunt, gives origin to the conjoined short head of the biceps and coraco-brachialis. THE BONES OF THE UPPER LIMB 183 The coracoid process of man represents the coracoid bone of monotremata and lower vertebrates. The scapula derives its blood-supply from the dorsalis scapulae, suprascapular, and posterior scapular, arteries. Articulations. — By its acromion process with the outer extremity of the clavicle, and by the glenoid cavity with the head of tfee humerus. Structure. — ^The scapula is a flat or tabular bone, and is composed Subcoracoid Epiphysis, Appears at loth Year, and joins at 16 Apical Epiphysb. Appears about i8th Year, and joins about 25. Accessory Coracoid. Appears about puberty, and soon joins. Appears about the i6th Year, and joins about 25 Coracoid Element. Appears ic ist Year, and joins at 15 \ Appear about the i6th Year, ' and join Spine about 25 ~- . Line of junction of Coracoid Element Appears about the i6th Year, and joins about 25 Fig. 103. — Ossification of the Scapula. of two tables of compact bone. In the head, axillary border, inferior angle, and processes there is cancellated tissue between the two tables, but in the central portions of the supra- and infra- spinous fossae there is none, and the two tables coalesce, so that the bone is very thin and transparent. Varieties. — (i) Suprascapular foramen. (2) Fenestrated scapula, pre- senting one or more perforations in the subscapular fossa. (3) Separation of i84 A MANUAL OF ANATOMY the acromion process, which may be connected with the spine by a plate of cartilage, or by fibrous tissue. {4) Imperfect ankylosis of the coracoid process, which, however, is extremely rare. Ossification. — ^The scapula has one primary centre and eleven secondary centres. The primary centre appears in the body near the neck about the 8th week. The coracoid process, cartilaginous at birth, has four secondary centres — coracoid, accessory coracoid, supracoracoid, and apical. The coracoid centre appears in the end of the 15^ year, and gives rise to the chief part of the process, which joins about the i sth year. The accessory coracoid centre appears about puberty, and soon joins the main coracoid. It forms the triangular part of the process which enters slightly into the extreme upper and inner part of the glenoid cavity. The supracoracoid centre appears about the iSth year, and forms a thin laminar epiphysis on the upper surface of the process. It gives about the 25^/1 year. The apical centre appears about the i^tth year, and forms an epiphysis which caps the tip of the process, and joins about the 2$th year. Acromion Process. — The inner or basal portion is ossified from the spine, which in turn is ossified from the primary centre for the body. The greater portion constitutes an epiphysis, which has two secondary centres. These appear about the i6th year and soon join. The acromial epiphysis usually joins the rest of the process about the 25^^ year or earlier. Union, however, may not take place, and then the acromial epiphysis forms a separate acromial bone, connected with the rest of the process by cartilage or by fibrous tissue, and this condition may simulate a fracture. Glenoid Cavity. — The fundus or bed of this cavity is ossified from tlie primary centre for the body, and its extreme upper and inner part is formed from the accessory coracoid centre. Besides these the cavity has two special secondary centres — supsrior and inferior. The superior glenoid or sub- coracoid centre appears about the loth year, and it joins the fundus or bed of the fossa about the i6th year. The inferior glenoid centre appears about the i6th year, and forms' the glenoid epiphysial plate. It joins about the 20th year, and gives rise to the slight concavity of the fossa. The other secondary centres are allocated as follows: (i) Posterior border of spine; (2) inferior angle; (3) base. These centres appear about the \bth year, and join about the 25th year. The Humerus. The humerus extends from the shoulder to the elbow, its direction being downwards and slightly inwards. It is a long bone, and is divisible into a shaft and two extremities, upper and lower. The upper extremity includes the head, anatomical neck, great and small tuberosities, commencement of the bicipital groove, and surgical neck. The head, which is almost hemispherical, is smooth, convex, and covered by cartilage. Its direction is upwards, inwards, and backwards, and it articulates with the glenoid cavity of the scapula. The anatomical neck is the constriction immedi- ately beyond the cartilage of the head. It is best marked above, especially between the head and great tuberosity, and it gives attachment to the capsular ligament of the shoulder -joint. It is THE BONES OF THE UPPER LIMB Head 185 Anatomical Neck A Large Nutrient Foramen Great Tuberosity am Supraspinatus Infraspinatus ' Surgical Neck Pcctoralis Major "* ' ^mall Tuberosity and Subscapularis ' — , Bicipital Groove — Ladssimus Doisi Teres Major Dtliuid- Brachio-radialis - Brachialis Anticus Exteroal Supracondylar Ridge _. >— Coraco-bracfaialis — „ Medullary Foramen Internal Supracondylar Ridge Extensor Carpi Radialis Longior Radial Fossa External Epicondyle ' ; Common Origin of / ; Kxtensor Carpi Radialis Brevior • Extensor Communis Digitorum Extensor Minimi Digiti Extensor Carpi Ulnaris, and Supmator Radii Brevis i^'^r^^ Capitelium Trochlea ,Coronoid Fossa Superficial Head of Pronator Radii Teres Internal Epicondyle \_ Common Origin of Flexor Carpi Radialis Palmaris L/>ngus Flexor Sublimis Digitorum, and Small Head of Flexor Caipi Ulnaris Fig. 104.— The Right Humerus (Anterior View). 1 86 A MANUAL OF ANATOMY pierced by numerous nutrient foramina. The great tuberosity is situated obliquely on the outer surface, immediately beyond the anatomical neck. It presents three fiat muscular impressions — an upper for the insertion of the supraspinatus, a middle for the infra- spinatus, and a lower for the teres minor, which latter muscle con- tinues to take insertion into a rough marking on the shaft for at least i inch below the lower impression. The small tuberosity is an oval prominence situated on the anterior aspect, immediately beyond the anatomical neck. It gives insertion to the subscapu- lari§, which continues to take insertion into the adjacent part of the shaft for about \ inch. The commencement of the bicipital groove, which lodges the long tendon of the biceps, lies between the two tuberosities, where it is bridged over by the transverse humeral ligament. It presents a large nutrient foramen close to the great tuberosity for an offset of the ascending branch of the anterior circumflex artery. The surgical neck is the constriction below the tuberosities. The upper extremity of the humerus receives its principal blood- supply from the anterior and posterior circumflex arteries. The shaft is almost cylindrical in its upper half, but it is laterally expanded and triangular in its lower half. The anterior aspect presents superiorly the bicipital groove, which commences between the tuberosities, where it is deep, and passes downwards and slightly inwards, terminating about the junction of the upper and middle thirds. It is bounded by two rough ridges, outer and inner. The outer bicipital ridge^ which is the more prominent, gives insertion over about its lower three-fourths to the pectoralis major, this portion being called the pectoral ridge. It is in line with the anterior border of the lower half of the shaft. The inner bicipital ridge gives inser- tion over about its lower two-thirds to the teres major, this portion being known as the teres ridge. It is in line with the internal border of the lower half of the shaft. The floor of the groove over about its middle third gives insertion to the latissimus dorsi. The groove is occupied by the long tendon of the biceps, invested by a tubular prolongation of the synovial membrane of the shoulder- joint ; and the ascending branch of the anterior circumflex artery. The outer aspect of the shaft presents a rough V-shaped mark, called the deltoid impression, for the insertion of the deltoid. The point of the V, which is embraced by two slips of the brachialis anticus, is at the centre of the shaft, whence it extends upwards for about 2 inches. Its anterior margin is in line with the pectoral ridge, and its posterior margin bounds superiorly the lower part of the spiral groove. On the inner aspect of the shaft, about the centre, there is a rough line about lA inches long, placed in the course of the internal border, for the insertion of the coraco-brachialis. Immediately below this line is the principal medullary foramen for the nutrient or medullary branch of the brachial artery, the canal to which it leads being directed downwards. The posterior and external aspects of the upper part of the shaft present a winding groove, called the THE BONES OF THE UPPER LIMB Head lofiraspinatus 187 AnaKHnkal Neck Teres Minor ':^'» Surgical Neck External Head of Triceps A Nutrient Foramen ^Deltoid Impression and Deltoid Spiral Groove Internal Head of Triceps Brachialis Anticus -W- Olecranon Fossa.^ External EiHcondyle Anconeus Groove for Ulnar Nerve Trochlea Fig. 105. — The Right Humerus (Posterior View). Internal Epicondyle and Small Head of Flexor Carpi Ulnaris 1 88 A MANUAL OF ANATOMY spiral groove, for the musculo-spiral nerve and superior profunda vessels. It commences in the upper third posteriorly, and is directed downwards and forwards on to the external surface, where it ter- minates a little below and behind the apex of the deltoid impression. The lower part of this groove is occupied by a pointed slip of the brachialis anticus. In the upper part of the groove there is usually a nutrient foramen for a branch of the superior profunda artery. On the posterior aspect of the shaft, over about its upper third, external to the spiral groove, there is a rough marking which gives origin to the external head of the triceps, extending as high as the lower part of the insertion of the teres minor. The internal head of the triceps commences to arise in a pointed manner from the back of the shaft internal to the spiral groove, where it reaches a little above and behind the lower border of the tendon of the teres major. The lower half of the shaft, being triangular, presents three surfaces and three borders. The posterior surface, which is flat, terminates at the olecranon fossa, and it gives origin to most of the fibres of the internal head of the triceps. The external and internal surfaces, as well as the anterior border which separates them, give origin to the brachialis anticus. The anterior border, which is round, separates the lateral surfaces, and is in line with the anterior margin of the deltoid impression, and, above this, with the outer bicipitcJ ridge. The external border is called the external supra- condylar ridge. It is sharp and prominent, and extends from the external epicondyle to the spiral groove. It gives attachment to the external intermuscular septum. Anteriorly its upper two-thirds give origin to the brachio-radialis (supinator radii longus), and the lower third to the extensor carpi radialis longior. Posteriorly it gives origin to the inner head of the triceps. The internal border forms the internal supracondylar ridge, and is not so prominent as the external. It commences at the internal epicondyle, and it can be followed up through the line for the insertion of the coraco- brachialis into the inner bicipital ridge. It gives attachment to the internal intermuscular septum. Anteriorly it gives origin to the brachialis anticus, posteriorly to the inner head of the triceps, and "in its lower part to some fibres of the superficial head of the pronator radii teres. The internal surface of the shaft, in front of the internal supracondylar ridge and about 2| inches above the internal epicon- dyle, sometimes presents a sharp spur-like projection directed down- wards, called the supracondylar process. When present it gives attachment to a fibrous band which passes to the internal epicon- dyle, and gives origin to a third head of the pronator radii teres. In such cases the band forms an arch through which the median nerve passes, and frequently the brachial artery. The supra- condylar process represents a portion of bone which forms a supra- condylar foramen in many carnivora — e.g., the felidce. The lower extremity presents at either side the internal and ex- ternal epicondyles, and interiorly a transversely elongated articular THE BONES OF THE UPPER LIMB l8g surface covered by cartilage, and divided by a vertical curved ridge into an external part, called the capitellura, and an internal, called the trochlea. Above the capitellum in front there is a rough transverse depression, called the radial fossa. Above the trochlea in front is the coronoid fossa, and above it posteriorly is the olecranon fossa. The internal epicondyle {epitrochlea) is very prominent, and is directed inwards and slightly backwards. Its lower part and the adjacent portions of its anterior and posterior aspects give attach- ment to the internal lateral ligament of the elbow- joint. Its anterior aspect gives origin to the cormnon tendon of the superficial head of the pronator radii teres, flexor carpi radialis, palmaris longus, part of the flexor sublimis digitorum, and one head' of the flexor carpi ulnaris. Behind the internal epicondyle, close to the trochlea, is the ulnar groove, through which the ulnar ner\^e passes. The external epicondyle is much less prominent than the internal. Anteriorly it gives origin to the common tendon of the extensor carpi radialis brevior, extensor communis digitorum, extensor minimi digiti, extensor carpi ulnaris, and supinator radii brevis. Posteriorly it presents an impression for the anconeus, and inferiorly a depres- sion near the capiteUmn for the external lateral ligament of the elbow-joint. The capitellum mainly takes the form of a rounded eminence. It is limited to the anterior and inferior aspects of the bone, and articulates with the cup-shaped depression on the head of the radius. Internal to the rounded portion there is a groove for the play of the inner convex part on the head of the radius. The radial fossa receives the anterior margin of the head of the radius in complete flexion of the elbow-joint. The trochlea is puUey-shaped, and turns completely round from the front to the back of the bone, becoming rather broader pos- teriorly. It is concave from side to side, and convex from before backwards. The internal border is more prominent and thicker than the external, and extends lower down. As viewed from before, the borders are inclined do\vnwards and slightly inwards, but posteriorly they incline upwards and slightly outwards, and so the trochlea is here brought into the centre of the bone. The trochlea articulates with the great sigmoid cavity of the ulna. The coronoid fossa receives the coronoid process of the ulna in flexion of the elbow- joint, and the anterior ligament is attached just above it. The olecranon fossa, much larger than the coronoid, receives the olecranon process of the ulna in extension of the joint, and its margins give attachment to the posterior ligament. The portion of bone which separates the two fossae is thin, and is sometimes perforated by a foramen, called the supratrochlear foramen. In the vicinity of the lower extremity there are numerous nutrient foramina for branches of the superior and inferior profunda and anastomotica magna of the brachial, radial and ulnar recurrent, and interosseous recurrent, arteries. I go A MANUAL OF ANATOMY Articulations. — Superiorly with the scapula, and inferiorly with the radius externally, and ulna internally. Structure. — ^The shaft is composed of compact bone, which is thicker at the centre than at the extremities. It contains a medul- lary canal lined with a thin coating of cancellated tissue. The articular extremities are filled with cancellated tissue, except at the surface, where there is a thin layer of compact bone. Varieties. — These are (i) a supracondylar process, and (2) a supratrochlear foramen. Ossification. — The humerus ossifies in cartilage from one primary, and seven secondary, centres. The primary centre appears at the middle of the shaft in the eighth week of intra-uterine life. At birth the shaft is ossified, but the Appears in the ist Year (^--•A.. Appears in the 3rd Year Appears in the 5th Year All three coalesce at the 6th Year, and join at 20 i^- . Appears at the 8th Week (intra-uterine) Appears in the 14th Year —Appears in the 5th Year, and joins at 18 Appears in the 3rd Year Appears in the 12th Yeai The External Epicondyle, Capitellum, and Trochlea, having previously coalesced, join at 17 Fig. 106. — Ossification of the Humerus. extremities are cartilaginous. The superior extremity is ossified from three secondary centres. The centre for the head appears in the first year (some- times just before birth), that for the great tuberosity in the third year, and that for the small tuberosity in the fifth year. The upper epiphyses join to form one compound epiphysis in the sixth year, and this unites with the shaft in the twentieth year. The lower extremity is ossified from four secondary centres, as follows: one for the capitellum and outer half of the trochlea appearing in the third year ; one for the internal epicondyle in the fifth year ; one for the inner half of the trochlea in the twelfth year ; and one for the external epicondyle in the fourteenth year. The trochlea, capitellum, and external epicondyle join to form one compound epiphysis, and this unites with the shaft in the seventeenth year. The internal epicondyle unites with the shaft, as an independent epiphysis, in the eighteenth year. The law of ossification applicable to long bones with an epiphysis or epiphyses at either end is as follows : the epiphysis or epiphyses, THE BONES OF THE UPPER LIMB 191 at the eni towards which the medullary foramen and the canal to which it leads are directed, are the last to show signs of ossification, hut they are the first to join the shaft. The only exception to this rule occurs in the fibula. The Radius. The radius is the external bone of the forearm (which is assumed to be in a position of supination). It is parallel with, and shorter than, the ulna, and extends from the elbow to the wrist. It is a long bone, and is divisible into a shaft and two extremities. The upper extremity, which is small, presents a head and neck. The head is disc-shaped, and covered by cartilage, both on its upper surface and circumference. The upper surface, at its centre, presents a depression which articulates with the rounded portion of the capitellum of the humerus in flexion of the elbow-joint. Around this depression the surface is convex, especially on the inner side, and this portion glides on the inner grooved part of the capitellum. The circumferential cartilage is deeper on the inner aspect than elsewhere, and this portion articulates with the small sigmoid cavity of the ulna, whilst the remainder plays within the orbicular ligament. The constricted portion below the head is called the neck. It is cylindrical, and its upper part is embraced by the orbicular ligament, whilst beyond this on the outer aspect it gives insertion to a few fibres of the supinator radii brevis. The upper extremity presents several nutrient foramina for branches of the radial recmrent and interosseous recurrent arteries. The shaft increases in size from above downwards, and is curved, the convexity being directed outwards and slightly backwards. This curve imparts elasticity to the bone, and guards it against the shocks to which it is so much exposed from the fact that it supports the hand. The shaft is triangular, and presents superiorly, on its antero-intemal aspect just below the neck, an oval eminence, called the bicipital tuberosity. This is divided vertically into two parts, a rough posterior portion which gives insertion to the tendon of the biceps, and a smooth anterior part which is sepsirated from that tendon by a bursa. Below the bicipital tuberosity the shaft presents three borders and three surfaces. The anterior border extends from the lower cind anterior part of the bicipital tuberosity * to the anterior border of the styloid process. In its upper third it crosses the shaft obliquely downwards and outwards, this portion of it being called the anterior oblique line. This line limits ex- ternally the insertion of the supinator radii brevis, and internally the origin of the flexor longus poUicis, whilst its prominent edge gives origin to the thin radial portion of the flexor sublimis digitorum. The internal or interosseous border commences at the lower and back part of the bicipital tuberosity, and near the lower extremity of the shaft it divides into two ridges, which pass to 192 A MANUAL OF ANATOMY Olecranon Process ^ Great Sigmoid Cavity Head of Radius « 1 Neck™ — Posterior part of Bicipital Tuberosity and Tendon of Biceps Supinator Radii Brevis Anterior Oblique Line Flexor Sublimis Digitorum Medullary Foramen — - Flexor Longus PoUicis .- Pronator Radii Teres — Anterior Border — r Coronoid Process . Flexor Sublimis Digitorum ' Deep Head of Pronator Radii Teres Brachialis Anticus .Supinator Radii Brevis ...Medullary Foramen .Anterior Border .Flexor Profundus Digitorum Pronator Quadratus 1. : Pronator Quadratus Brachio-radialis ._ Head Styloid Process of Ulna Styloid Process of Radius Fig. 107.— The Right Radius and Ulna (Anterior View). THE BONES OF THE UPPER LIMB I93 the anterior and posterior margins of the sigmoid cavity. At its commencement it is round and indistinct, and immediately below the bicipital tuberosity it gives attachment to the oblique ligament. Over the rest of its extent it is sharp and wiry for the attachment of the interosseous membrane, which is also connected with the posterior of the two lower di\asions. The posterior border extends from the back of the bicipital tuberosity to the prominent radial tubercle about the centre of the posterior border of the lower extremity. In its upper third it crosses the shaft obliquely down- wards and outwards, this portion of it, which is prominent, being called the posterior oblique line. This line limits the insertion of the supinator radii brevis above, and the origin of the extensor ossis metacarpi poUicis below. The anterior surface is situated between the anterior and internal or interosseous borders. In the upper two-thirds it is concave, and gives origin to the flexor longus pollicis. In the lower third it is flat and expanded, and this portion gives insertion to the pronator quadratus, except close to the anterior border of the lower extremity, where it gives attachment to the anterior ligament of the wrist- joint. The anterior surface presents the medullary foramen about the junction of the upper and middle thirds. The direction of the canal to which it leads is upwards, and it gives passage to the medullary branch of the anterior inter- osseous artery. The portion of bone between the anterior oblique line, the lower part of the front of the neck, and the bicipital tuber- osity gives insertion to a portion of the supinator radii brevis The external surface is situated between the anterior and posterioi borders. It is convex from above do%vnwards, and from side to side. In its upper third it gives insertion to the supinator radii brevis ; at its centre there is a rough impression, fully an inch long, for the insertion of the pronator radii teres ; and below this it supports the tendons of the extensores carpi radialis longioi et brevior, and is crossed obliquely by the tendons of the extensor ossis metacarpi pollicis and extensor brevis pollicis (primi int^modii pollicis). The external surface also supports the brachio-radialis, which is inserted into its lower extremity close to the base of the styloid process. The posterior surface is situated between the posterior and internal or interosseous borders. Above the posterior oblique line it is covered by the supinator radii brevis, which takes insertion into its outer half. Below the posterior oblique line it is concave over about the middle third, where it gives origin from above downwards to the extensor ossis metacarpi pollicis and extensor brevis pollicis. The lower third is broad and convex, and it supports the tendons of the extensor longus pollicis, extensor communis digitorum, and extensor indicis. The lower extremity is large and pentagonal, as viewed from below. Externally it presents the styloid process, internally the sigmoid cavity, and inferiorly the carpal articular surface, the latter two being covered by cartUage. The styloid process projects down-- 13 194 A MANUAL OF ANATOMY Head »*'! i. Neck Bicipital Tuberosity Supinator Radii Brevis x\- Posterior Oblique Line . _ Extensor Ossis Metacarpi Pollicis — Internal or Interosseus Border Pronator Radii Teres Extensor Brevis Pollicis Posterior Border //, V/ I u .. Brachio-radialis _ _ Tip of Styloid Process Extensor Communis Digitorum and Extensor Indicis i | Extensor I^ngus Pollicis i i Radial Tubercle | | Extensor Carpi Radialis Brevior | Extensor Carpi Radialis Longior Fig. io8. — The Right Radius (Posterior Surface). THE BONES OF THE UPPER LIMB 195 wards as a stout conical process, terminating in a round tip which gives attachment to the external lateral ligament of the wrist-joint. The inner surface is covered by the cartilage of the carpal articular surface. The outer surface presents a groove directed downwards and slightly forwards, and subdivided into two compartments, the outer of which transmits the tendon of the extensor ossis metacarpi poUicis, and the inner that of the extensor bre\as polUcis. This groove is separated from the pronator surface in front by a promi- nent ridge which gives attachment to the posterior annular ligament. The anterior surface supports a portion of the radial artery. The sigmoid cavity is concave from before backwards, and articu- lates vdth the outer convex surface of the head of the ulna. The carpal articular surface is of large size, and its plane is oblique, being sloped outwards and a little downwards. It is concave from before backwards, and from side to side, and is divided into two parts by an ant€ro- posterior elevation. The outer division is triangular, its cartilage being prolonged on to the inner surface of the styloid process, and it articulates with the scaphoid bone. The inner division is quadrilateral, and articulates with the semilunar bone. It is separated from the sigmoid cavity by a sharp concave margin, which gives attach- ment to the base of the triangular interarticular fibro-cartilage. Immediately above the anterior border there is a rough sur- face for the attachment of the anterior ligament of the wrist - joint. The posterior border is on a slightly lower level than the anterior, and is irregularly convex. It presents about its centre a prominent elevation, called the radial tubercle, and is divided into three grooves — outer, middle, and inner. The outer groove, which is broad, is bounded externally by a ridge which separates it from the groove on the outer surface of the styloid process, and internally by the radial tubercle. It is usually subdivided by a faint line into two compartments, the outer of which transmits the tendon of the extensor carpi radialis longior, and the inner that of the extensor carpi radialis brevior. The middle groove, narrow and deep, is directed from above downwards and outwards, and is boimded externally by the radial tubercle, which slightly overhangs it, and internally by an oblique ridge separating it from the inner groove. It transmits the tendon of the extensor longus pollicis (secimdi intemodii poUicis). The inner groove is single, and transmits the tendons of the extensor communis digitorum and extensor indicis. It is separated from the sigmoid cavity by a sharp ridge which, with the ulna in position, bounds a groove for the tendon of the extensor minimi digiti. The ridges separating the grooves give attachment to deep expansions of the posterior annular ligament, which, with the ligament, convert the grooves into fibro-osseous canals. The lower extremity presents several nutrient foramina for branches of the anterior and posterior interosseous cirteries, and anterior and posterior carpal arches. 196 A MANUAL OF ANATOMY Articulations. — Superiorly with the capitellum of the humerus and small sigmoid cavity of the ulna, and inferiorly with the head of the ulna, scaphoid, and semilunar. For Posterior Ligament Groove for Ext. Longus Pollicis Radial Tubercle 1 Groove for Ext. Carpi Rad. Brev, Groove for Ext. Carpi Radial is Longior j Groove for Ext. Oss Metacarp. Poll, and^^ Ext. Brev. Pollicis Groove for Ext. Com. Dig. and Ext. Indicis I Groove for Ext. Minimi Digiti ! I Groove for Ext. Carpi Ulnaris Ulnar Styloid Process For Scaphoid | For Anterior Ligament For Apex of Triangular Fibro-Cartilage For Upper Surface of Triangular For Semilunar Fibro-Cartilage Fig. 109. — The Lower Ends of the Left Radius and Ulna AS seen from below in Pronation. (The Dorsal Aspect is upwards. ) Structure. — ^This is similar to that of long bones. At the lower extremity the cancellated tissue extends upwards for about i| inches above the styloid process, this level being the site of Colles' fracture. Ossification. — The radius ossifies in cartilage from one primary, and two secondary, centres. The primary centre appears at the middle of the shaft in the eighth week of intra-uterine life. At birth the shaft is ossified, but the extremities are cartilaginous. The secondary centre for the lower extremity appears in the second year, and that for the head in the fifth year. The rZS> - - Appears in the 5th Year, I 7 and joins about i3 Appears in the 8th Week (intra-uterine) I Appears in the 2nd Year, ' and joins about 20 Fig. 110. — Ossification of the Radius. upper epiphysis joins the shaft about the eighteenth year, and the lower epiphysis about the twentieth year. Sometimes the rough part of the bicipital tuberosity forms an epiphysis, in which cases there is a special secondary centre for it, appearing about the fourteenth year, and joining the rest of the shaft very soon thereafter. THE BONES OF THE UPPER LIMB 197 The Ulna. The ulna is the internal bone of the forearm (which is assumed to be in a position of supination). It is parallel with, and longer than, the radius, and extends from the elbow to the WTist, being separated from the latter joint by the triangular interarticular fibro-cartilage. It is a long bone, and is divisible into a shaft and two extremities, the upper of which is of large size. The upper extremity presents the olecranon and coronoid processes, and the great and smaU sigmoid cavities. The olecranon process forms the highest part of the bone, and is curved forwards at its upper part. It is largely subcutaneous. Superiorly it presents a broad, flat, quadrilateral surface, at the back part of which is a rough elevation for the insertion of the triceps. In front of this there is a smooth area where a bursa intervenes between that muscle and the bone. At its anterior part, near the anterior margin, there is a narrow transverse impression f(3r part of the posterior hgament of the elbow-joint. The superior surface is limited anteriorly by a sharp convex border, projected at its centre into a process, called the beak, which overhangs the upper part of the great sigmoid cavity, and is received into the olecranon fossa of the humerus in extension of the joint. The anterior surface is directed down- wards and forwards, and forms the upper part of the great sigmoid cavity. The posterior surface, smooth, flat, and triangular, is subcutaneous, and covered by a bursa. The inner surface pre- sents a tubercle for the ulnar head of the flexor carpi ulnaris, and the inner border gives attachment to the posterior part of the internal lateral ligament of the elbow- joint. The outer surface gives insertion to a portion of the anconeus, and the outer border gives attacb_ment to fibres of the posterior hgament of the joint. The coronoid process is triangular, and projects forwards. The superior surface forms the lower and anterior part of the great sigmoid cavity. The inferior surface is rough and concave, and the roughness is prolonged upon the anterior surface of the shaft for I about an inch, giving rise to a triangular impression, the inner half ol [which gives insertion to the brachialis anticus. The upper part I of this surface, close to the anterior border of the process, affords attachment to the anterior ligament of the elbow-joint. The {lower pointed portion presents externally a rough prominence, I called the tuberosity, \\\nch. gives insertion to fibres of the brachialis I anticus, and attachment to the oblique ligament. The anterior I margin is sharp, convex, and curved slightly upwards, and it is I projected at its outer part into a process, called the beak, which is ^received into the coronoid fossa of the humerus in flexion of the elbow- joint. The inner border gives attachment to the anterior (portion of the internal lateral ligament, and at its upper part it presents a tubercle for the ulnar head of the flexor sublimis digi- torum. Leading downwards from this there is a short ridge for origin of the deep head of the pronator radii teres, below which 198 A MANUAL OF ANATOMY a slip of the flexor longus poUicis sometimes arises. Behind the flexor subHmis tubercle there is a depressed surface which gives origin to the highest fibres of the flexor profundus digitorum. The outer surface presents the small sigmoid cavity. The great sigmoid cavity, which articulates with the trochlea of the humerus, when viewed from the side, forms half a circle. The upper half of the cavity is formed by the anterior surface of the olecranon process, and the lower half by the upper surface of the coronoid process. It is constricted at the centre by a notch at either side, which marks the meeting of the olecranon and coronoid processes, the inner notch being bridged over by a fibrous band with which the middle part of the internal lateral ligament blends. The cartilage of the cavity is sometimes broken up at this part by a narrow, rough, transverse interval. Extending from the beak of the olecranon to the beak of the coronoid there is a longitudinal elevation, which divides the cavity into two lateral halves, the inner being concave from side to side, and the outer convex. The small sigmoid cavity, which is situated on the outer surface of the coronoid process, is concave from before backwards, and ar ticulates with the inner aspect of the head of the radius. Its anterior and posterior margins give attachment to the cornua of the orbicular ligament. The upper extremity presents several nutrient foramina for branches of the anterior and posterior ulnar recurrent and interosseous recurrent arteries. Triceps ._ Beak of Olecranon Process -Great Sigmoid Cavity -For Olecranon. Bursa ,Beak of Coronoid Process --Small Sigmoid Cavity — Anconeus ■ Supinator Radii Brevis Oblique I-ine Extensor Ossis Metacarpi PoUicis Posterior Border Extensor Longus PoUicis .,... External or Interosseous Border Extensor ludicis ^For Sigmoid Cavity of Radiil* • > - "^Head . - \ Groove for Extensor Carpi Ulnaris ! " Styloid Process Fig. III.— The Right Ulna (Posterior Surface). THE BONES OF THE UPPER LIMB 199 The shaft diminishes in size from above downwards, and is triangular in its upper three-fourths, where it is slightly curved with the convexity directed backwards. In the lower fourth it is slender and subcylindrical, being flattened in front. It presents three borders and three surfaces. The anterior border extends from the flexor sublimis tubercle on the inner margin of the coronoid process to the front of the styloid process. Over its upper three-fourths it is round, and gives origin to fibres of the flexor profimdus digitorum. Over its lower fourth it is sharp, and gives origin to the pronator quadratus. The posterior border, which is subcutaneous, extends from the apex of the triangular subcutaneous surface on the back of the olecranon to the back of the styloid process. Over its upper two- thirds it gives attachment to a strong aponeurosis, which gives common origin to the flexor, and extensor, carpi ulnaris, and flexor profundus digitonmi. The external or interosseous border extends from the apex of the bicipital hollow, about two inches below the small sigmoid cavity, to the outer aspect of the head. Over the middle three-fifths of the shaft it is sharp and prominent, but over the lower fifth it is very faint. It gives attachment to the interosseous membrane. The anterior surface is situated between the anterior and inter- osseous borders. It is concave over its upper three- fourths, and gives origin to part of the flexor profundus digitorum. The lower fourth is flat, and gives origin to the pronator quadratus. This surface presents the medullary foramen a little above the centre, the direction of the canal to which it leads being upwards. It gives passage to the medullary branch of the anterior inter- osseous artery. The internal surface is situated between the anterior and posterior borders. Over its upper two-thirds it gives origin to part of the flexor profundus digitorum, the lower portion being subcutaneous. The posterior surface is situated between the posterior and interosseous borders, and is directed backwards and outwards. It presents superiorly the oblique line, which extends from the supinator ridge on the posterior margin of the bicipital hollow to the posterior border at the junction of the upper and middle thirds. The triangular portion above this line is called the anconeal surface, which extends over the outer surface of the olecranon. It gives insertion to the anconeus. The posterior surface, below the oblique line, is divided into two lateral parts by a vertical ridge. The inner portion supports the extensor carpi ulnaris, and the outer gives origin, from above downwards, to the extensor ossis metacarpi pollicis, extensor longus pollicis, and extensor indicis. On the outer aspect of the shaft superiorly there is a triangular depression, which commences immediately below the small sigmoid cavity, and extends downwards for about 2 inches. It is bounded in front and behind by prominent lips, the anterior of which passes above into the outer margin of the coronoid process, and the posterior into the posterior margin of the small sigmoid cavity. The upper part of the posterior lip, which is prominent. A MANUAL OF ANATOMY is called the supinator ridge, and it gives origin to a part of the supinator radii brevis. The two lips form by their meeting the commencement of the external or interosseous border. The anterior part of this surface superiorly receives the bicipital tuberosity of the radius, with the tendon of insertion of the biceps, in pronation, whilst the posterior part gives origin to fibres of the supinator radii brevis. The lower extremity is small, and presents a head and styloid process. These are separated behind by a groove for the tendon of the extensor carpi ulnaris, and below by a rough pit which gives attachment to the apex of the triangular interarticular fibro-cartUage. The outer aspect of the head is convex, and covered by cartilage for articulation with the sigmoid cavity of the radius, a portion of the synovial membrane, called membrana sacciformis, intervening. The inferior surface, also covered by cartilage, is flat, and is related to the upper surface of the triangular interarticular fibro- cartilage, with the intervention of another portion of the mem- brana sacciformis. The styloid process, of small size and subcutaneous, projects downwards from the posterior and inner part of the head (mainly from the back part), and it terminates in a round tip which gives attachment to the internal lateral ligament of the wrist- joint. The lower extremity presents several nutrient foramina for branches of the anterior and posterior interosseous arteries. Articulations. — Superiorly with the trochlea of the humerus, and the inner aspect of the head of the radius ; inferiorly with the sigmoid cavity of the radius, and the triangular interarticular fibro-cartilage, the latter structure separating it from the cuneiform or pyramidal bone. Structure. — This is similar to that of long bones. Ossification. — The ulna ossifies in cartilage from one primary, and two secondary, centres. The primary centre appears at the middle of the shaft in the eighth week, and from it the shaft, coronoid process, and greater part of the olecra- non process are ossified. At birth the shaft and ■ coronoid process are ossified, but the greater part of the olecranon and the lower extremity are cartilaginous. The secondary centre for the lower extremity appears in the fourth year, and from it the head and styloid process are ossified. The secondary centre for the upper extremity appears in the tenth year, and may involve only a thin scale on the summit of the olecranon process, or it may afford ossification to a third, or even a half, of that process. The upper epiphysis joins about the sixteenth year, and the lower about the twentieth year. Appears in the loth Year, and joins about i6 Appears in the 8th Week (intra-uterine) Appears in the 4th Year, and joins about 20 Fig. 112. — Ossification OF THE Ulna. THE BONES OF THE UPPER LIMB 201 The Carpus. The carpus or wrist is composed of eight short bones, which are arranged in two rows, there being four bones in each row. The rows are called first or proximal, and second or distal. The bones of the first row, from without inwards, are called scaphoid, semilunar, cuneiform, and pisiform, whilst those of the second row, in a similar order, are named trapezium, trapezoid, os magnum, and unciform. The Scaphoid Bone. The scaphoid bone, which is characterized by its boat-like shape, lies with its long axis oblique, the broad end being directed upwards and inwards, and the narrow end or prow downwards, outwards and forvs'ards. Superiorly it presents a convex articular surface for the radius, which encroaches on the dorsal aspect. Injeriorly it also presents a convex articular surface directed downwards, out- Superior Surface for Radius Posterior Surface For Semilunar For Os Magnam Inferior Surface for Trapezium and Trapezoid Fig. 1 13 . — The Right Scaphoid Bone. A, Posterior View ; B, Internal View. wards, and backwards, which likewise encroaches on the dorsal aspect, and is divisible into two parts — an outer for the trapezium, and an inner for the trapezoid. The internal surface presents two articular facets — a superior, crescentic, narrow from above down- wards, and looking inwards, for the semilunar, and an inferior, large, concave, and directed downwards as well as inwards, for the outer side of the head of the os magnum. The external aspect takes the form of a rough border, extending from the radial surface to the tuberosity, and giving attachment to the external lateral ligament of the wrist-joint. At its lower end there is a prominent tuherosity, directed forwards, which gives attachment to fibres of the anterior annular ligament and abductor pollicis. The palmar surface is rough and triangular. The dorsal surface, being encroached upon by the superior and inferior convex articular surfaces, is reduced to a rough oblique groove. • Articulations. — Superiorly with the radius, inferiorly with the trapezium and trapezoid, and internally with the semilunar and os magnum. 'A MANUAL OF ANATOMY The Semilunar Bone. The semilunar or lunar bone is characterized by the crescentic concavity on its inferior surface. Superiorly it presents a quadri- lateral, convex, articular surface for the radius, which encroaches on the dorsal aspect. The inferior surface is deeply concave from before backwards. The greater part of it articulates with the upper surface of the head of the os magnum, and the narrow inner strip with the upper border of the unciform. The external surface, Internal Surface for Cuneiform For Unciform (on^ Inferior Surface) ^y Palmar Surface Dorsal Surface B Superior Surface for Radius Palmar Surface Inferior Surface for Os Magnum For Scaphoid (on External Surface) Fig. 114. — The Right Semilunar Bone. A, Internal View ; B, Supero-external View. narrow from above downwards, presents a crescentic facet for the scaphoid. The internal surface, which is inclined downwards and outwards, is deep from above downwards, and presents a, semi-oval facet for the cuneiform. The palmar and dorsal surfaces are rough, the former being large, convex, and quadri- lateral, and the latter small and flat. Articulations. — Superiorly v/ith the radius, inferiorly with the os magnum and unciform, externally with the scaphoid, and internally with the cuneiform. The Cuneiform Bone. The cuneiform or pyramidal bone is characterized by its resem- blance to a wedge, or pyramid, and it lies obliquely with the base ^Inferior Surface for Unciform -External Surface for Semilunar For Pisiform (on Anterior Surface) Anterior Surface • Fig. 115. — The Right Cuneiform or Pyramidal Bone (Anterior, External, and Inferior Surfaces). directed outwards and upwards. The external surface, which corresponds with the base, presents a semi-oval facet for the semi- THE BONES OF THE UPPER LIMB 203 lunar. The internal surface, which represents the rounded apex, is of hmited extent, and rough for the internal lateral ligament of the wrist- joint. The palmar surface presents a circular, slightly convex facet, which occupies rather more than the inner and lower half, and articulates with the pisiform, the rest of the surface being rough. The supero-posterior surface is divisible into two parts, outer and inner. The outer portion, which is close to the base, presents a convex facet for the inferior surface of the triangular interarticular libro-cartilage. The inner portion is marked by two rough oblique grooves, superior and posterior, separated by a ridge which is dorsally placed. The inferior surface presents a large triangular facet, concavo-convex from without inwards, for the unciform. Articulations. — Superiorly with the triangular interarticular libro-cartilage, inferiorly with the unciform, externally with the semi- lunar, and anteriorly with the pisiform. The Pisiform Bone. The pisiform bone is characterized by its resemblance to a pea, and is placed in front of the cuneiform, which constitutes its only articulation. It is irregularly round, except posteriorly, where it presents over its upper three-fourths a circular, slightly concave facet for the cuneiform, the lower fourth being non-articular. The Superior Aspect Ulnar Groove (on External Surface) For Cuneiform (on Posterior Surface) Fig. 116. — The Right Pisiform Bone (Postero-external View). long axis of the bone is directed downwards and slightly outwards. The palmar surface gives attachment superiorly to the flexor carpi ulnaris, inferiorly to the pisi-uncinate and pisi-metacarpal ligaments, and abductor minimi digiti, and extemall}' to a portion of the anterior annular ligament. The internal surface is irregularly convex, and the external presents the ulnar groove, which lodges the ulnar nerve and artery. The Trapezium. The trapezium is the external bone of the second row, and is characterized by a groove and ridge on its palmar surface, and a saddle-shaped facet on its inferior surface. It is polyhedral, 204 A MANUAL OF ANATOMY and its long axis is directed downwards and inwards. The superior surface presents a semi-oval, concave facet for the scaphoid. The inferior surface presents a saddle-shaped facet, concave from side to side, convex from before backwards, and directed outwards as well as downwards, for the base of the first metacarpal bone. The internal surface has two facets — an upper, which is large and concave, for the trapezoid, and a lower, which is small, for the base of the second metacarpal bone. The external surface is broad, pentagonal, and rough. The palmar surface, rough and elongated from above downwards and inwards, is broad above and narrow below. Superiorly it presents a deep groove, directed downwards and inwards, which transmits the tendon of the flexor carpi radialis, and external to this groove a prominent ridge, called the tuberosity, which gives attachment to the anterior annular ligament, abductor pollicis, and opponens pollicis. The Tuberosity Groove for Flexor Carpi Radialis Inferior Surface for 1st Metacarpal. ^ For Scaphoid (on Superior Surface) "For Trapezoid (on Internal Surface) For 2nd Metacarpal For 2nd Metacarpal (on internal Surface) Fig. 117. — The Right Trapezium. A, Antero-inferior View ; B, Supero-internal View. dorsal surface is broader than the palmar, and its inferior and internal angle is much elongated towards the base of the second metacarpal bone, with which it articulates by the small facet on its inner aspect. Articulations. — Superiorly with the scaphoid, inferiorly with the first metacarpal, and internally chiefly with the trapezoid, but also with the second metacarpal. The Trapezoid Bone. The trapezoid bone somewhat resembles the trapezium, but it is destitute of a groove and tuberositv. Its antero-posterior diameter is longer than the transverse. The palmar surface is small and pentagonal, and it gives origin to fibres oi the adductor obliquus pollicis. The dorsal surface is large and has its internal and inferior angle elongated towards the styloid process of the third meta- THE BONES OF THE UPPER LIMB 205 carpal bone. Both of these surfaces are rough for ligaments. The superior surface presents a quadrilateral, concave facet, elon- gated from before backwards, for the scaphoid. The inferior surface is characterized by a large saddle-shaped facet, convex from side to side and concave from before backwards, for the base of the second metacarpal bone. The external surface has a convex facet for the trapezium, below which there is a rough triangular surface with the base directed anteriorly. The internal surface is concave from before backwards, and its anterior portion presents a facet for the os magnum. For Trapcziain (on External Surface) / Superior Surface for Scaphoid ^"^k External Sor&ce ~~^ Part of Inferior Surface for snd Metacarpal Dorsal Snrface Part of Inferior Surface for 2nd Metacarpal -Internal Surface for Os Magnum L.' Dorsal Surface Fio. 118. — The Right Trapezoid Bone. A, External View ; B, Posterior View. Articulations. — Superiorly with the scaphoid, inferiorly with the second metacarpal, externally with the trapezium, and internally with the OS magnum. The Os Magnum. The OS magnum is the largest bone of the carpus, its distinctive characters being that it is composed of a head, neck, and bod}'. The superior and external aspects of the head are convex, and merge gradually into each other. The cartilage of the superior aspect is prolonged more behind than in front, and articulates with the semi- lunar. The external aspect of the head articulates with the scaphoid. The internal aspect of the head is flat, and presents the commence- ment of the facet for the unciform bone. The neck is mainly present in front and behind. The body is quadrilateral, and narrower in front than behind. The palmar and dorsal surfaces are rough, the former giving origin to fibres of the adductor obliquus poUicis. The external surface, which is con inuous with the outer convex aspect of the head, presents anteriorly a facet for the trapezoid. The internal surface presents at its back part the lower portion of the facet for the unciform, which is here narrow. The inferior surface is narrow in front, but broad behind, and the internal of the two posterior angles is elongated downwards and inwards. This surface presents 2o6 A MANUAL OF ANATOMY three facets. The middle one is the largest, and articulates with the third metacarpal bone. The external one is a narrow, concave strip for the second metacarpal bone. The internal one, small For 3rd Metacarpal For Scaphoid Head (for Semilunar For Trapezoid For Unciform — For 2nd Metacarpal For Unciform ^ B For 4th Metacarpal Fig. 119. — The Right Os Magnum. A, External Vrew ; B, Internal View. and circular, tips inferiorly the projecting postero-internal angle, and articulates with the fourth metacarpal bone. Articulations. — Superiorly with the semilunar, superiorly and externally with the scaphoid, inferiorly with the second, third, and fourth metacarpal bones, externally with the trapezoid, and internally with the unciform. The Unciform Bone. The unciform bone is characterized by a hook-like process on its palmar surface. It is triangular, or wedge-shaped, and lies with its base downwards. The superior extremity presents a narrow facet for the semilunar. The inferior surface is divided by an antero- posterior ridge into two quadrilateral facets, the outer of which articulates with the fourth, and the inner with the fifth, meta- carpal bone. The palmar surface, which is rough, presents at its lower and inner part a prominent curved projection, called the unci- form process. This process is laterally compressed, the external surface being concave and the internal convex, so that the direction of the curve is outwards. Its borders are superior, inferior, and anterior. The internal surface gives origin to the flexor brevis, and opponens, minimi digiti, and close to the root it presents the ulnar groove for the deep branches of the ulnar artery and nerve. The anterior border gives attachment to the anterior annular and pisi- uncinate ligaments. The dorsal surface is extensive and rough. The external surface presents an elongated facet, broad above .and narrow below, where it is confined to the back part, for articula- tion with the OS magnum. The supero-internal surface is con- cavo-convex from below upwards, and articulates with the cuneiform. The internal border, situated at the meeting of the supero-internal and inferior surfaces, is narrow and rough, its direction being from before backwards. THE BONES OF THE UPPER LIMB 207 Articulations. — Superiorly with the semilunar, sup ero -internally with the cuneiform, mjeriorly with the fourth and filth metacarpal bones, and externally with the os magnum. Unciform Process For 5 th Metacarpal. Inferior Aspect Unciform Proce For 4th Metacarpal For 5th Metacarpal Fig. 120. — The Right Unciform Bone. A, External View ; B, Supero-intemal View ; C, Inferior View. The carpus as a whole is narrower above than below. The dorsal aspect is irregularly convex, and the dorsal surfaces of the bones of the first row (exclusive of the pisiform) are narrow, but in the second row they are broad, this being reversed on the palmar aspect. It is to be noted that the postero-internal angles of the trapezium, trapezoid, and os magnum are distinctly elongated. The palmar aspect is rendered concave by the tuberosities of the scaphoid and trapezium externally, and the pisiform bone and unciform process internally. These projections give attachment to the anterior annular ligament, which with the palmar concavity forms a fibro- osseous canal for the passage of the flexor tendons and median nerve. The superior aspect, which is directed backwards as well as upwards, is convex, and articulates with the radius and triangular interarticular fibro-cartilage. The inferior or metacarpal aspect is somewhat undulating. The inferior surface of the first row is for the most part deeply concave, but externally it is convex. The superior surface of the second row is concavo-convex from without inwards, the concavity being formed by the trapezium and trapezoid, into which the scaphoid convexity above is received, whilst the con- 2o8 A MANUAL OF ANATOMY vexity is formed by the os magnum and unciform, and is received into the concavity above. Structure. — ^The carpal bones are each composed of cancellated tissue, covered by a thin shell of compact bone. Varieties. — The number of carpal bones is sometimes increased to nine, which is brought about in one or other of the following ways : (a) the scaphoid, semilunar, trapezium, or os magnum may be divided into two parts ; (b) the styloid process at the base of the third metacarpal, or the hook-like process of the unciform, may remain an independent ossicle ; or (c) there may be a persistent os centrale, situated on the dorsal aspect between the scaphoid, trapezoid, and os magnum. Ossification. — The carpal bones are all cartilaginous at birth. Each ossifies from one centre, in the following order, and at the following periods approximately : Os magnum, ist 5'^ear. Trapezium, 5 th year. Unciform, 2nd year. Scaphoid, 6th year. Cuneiform, 3rd year. Trapezoid, 7 th year. Semilunar, sthyear. Pisiform, 12th year. The Os Centrale. — This appeafs as an independent cartilage in the second month of in tra-u ferine life on the dorsal aspect of the carpus between the cartilaginous scaphoid, trapezoid, and os magnum. As a general rule it joins the cartilage of the scaphoid in the third month, but it may ossify independently, and remain persistent, as in the water tortoises and many apes. It is the representative of the navicular or scaphoid bone of the tarsus. The Metacarpus. The metacarpus supports the phalanges, and is composed of five long bones, which are Ucuned numerically from without inwards, that of the thumb being the first. Each bone is divisible into a shaft and two extremities, proximal and distal. The shaft is tri- angular, except in the first, in which it is compressed from before backwards. It is longitudinally concave on the palmar aspect, and presents three surfaces, two lateral and a dorsal. The lateral surfaces give attachment to interosseous muscles, and are separated from each other by an anterior border. The dorsal surface over its proximal third presents a median ridge, which in the case of the fifth metacarpal is placed towards the inner side. Over the distal two-thirds the ridge bifurcates, its divisions passing each to the dorsal tubercle on the side of the head, and enclosing between them a flat triangulcir surface. The head or distal extremity, which articulates with a first phalanx, is convex, and covered by cartilage, except laterally. The cartilage is prolonged farther on the palmar than on the dorsal surface, and terminates anteriorly in a concave border, the extremities of which form small cornua. Laterally the head is compressed, and presents at either side a dorsal tubercle and palmar depression for the lateral metacarpo-phalangeal ligament. The base or proximal extremity is irregularly quadrilateral, being broader on its dorsal than palmar surface, and it articulates THE BONES OE THE UPPER LIMB 209 superiorly with the carpus, and at either side with its fellows, except in the case of the first. The First Metacarpal Bone. — ^This is shorter than any of the others, and its shaft is compressed from before backwards. The palmar aspect, which has an inclination inwards, has the anterior border placed nearer the inner than the outer side. The outer margin and adjacent part of the palmar aspect give insertion to the opponens poUicis, and the inner margin over its proximal half gives origin to the outer head of the first dorsal inter- osseous. The dorsal surface is sUghtly convex, and is destitute of the ridge which characterizes the others. The head is elongated transversely, and presents on its palmar surface two shallow de- pressions for the sesamoid bones. The base is transversely oval. Head Fig. 121. .Grooves for Sesamoid Bones - - Medullary Foramen . . External Border for Opponens PoUicis I ntemal Border for ist Doisal Interosseoos (over proximal half) — Fcr Extensor Ossis Metacarpi PoDids Base -The First Right Metacarpal Bone (Palmar View). and has a saddle-shaped articular surface for the trapezium, which is concave from before backwards, and convex from side to side. Externally it presents a tubercle for the insertion of the extensor ossis metacarpi poUicis, and internally it gives origin to the deep head of the flexor brevis pollicis. Articulatioiis. — Superiorly with the trapezium, and inferiorly with the first phalanx of the thumb, and the two sesamoid bones. The Second Metacarpal Bone. — ^This is the longest. Its base, which is the largest, is deeply excavated superiorly for the trapezoid, being concave from side to side. Internal to this, it rises into a promi- nent border, which presents a faceted strip for the os magnum, and externally at the back part there is a small facet for the trapezimn. The inner side presents an antero-posterior facet, notched at the centre of its lower border, for the third metacarpal. The palmar aspect gives insertion to the principal part of the tendon of the flexor carpi radialis, and origin to a portion of the adductor obliquus 14 2IO A MANUAL OF ANATOMY pollicis. The dorsal aspect at its outer part gives insertion to the extensor carpi radiahs longior, and at its inner part to a small slip of the extensor carpi radialis brevior, there being a notch between the two impressions. The shaft gives origin to the first and second dorsal, and first palmar, interossei. Articulations. — Superiorly with the trapezium, trapezoid, and os magnum, internally with the third metacarpal, and inferiorly with the first phalanx of the index finger. Head Palmar Depression ^ Dorsal Tubercle ^ " Medullary Foramen Internal Surface.- External Surface For Trapezium For 3rd Metacarpal For Os Magnum For Trapezoid Fig. 122. — The Second Right Metacarpai. Bone. A, Internal View; B, External View. The Third Metacarpal Bone.— This is next in length to the second. Its distinctive character is the styloid process at the base. The superior surface of the base articulates with the os magnum. The outer side presents an antero-posterior facet, notched at its lower border, for the second metacarpal. The inner side presents two circular facets, separated by a rough vertical groove, for the fourth metacarpal. The palmar aspect gives insertion to a slip of the flexor carpi radialis, and origin to a portion of the adductor obliquus pollicis. The dorsal aspect externally gives insertion to the prin- cipal part of the extensor carpi radialis brevior, and it is projected upwards at its outer angle into the styloid process. The anterior border of the shaft, over its distal two- thirds, gives origin to the THE BONES OF THE UPPER LIMB 2ii adductor transversus pollicis, and the shaft also affords origin to the second and third dorsal interossei. Articulations. — Superiorly with the os magnum, and the second and fourth metacarpal bones, and inferiorly with the first phalanx of the middle finger. The Fourth Metacarpal Bone. — This is shorter than the third, and its base is small. The outer side of the base presents two circular facets, separated by a rough vertical groove, for the third metacarpal. The inner side has a semi-oval facet for the fifth metacarpal. The superior surface presents two facets. One is large for the unci- Intemal Surface. For 4th Metacarpal^rt:;^^:; For Os Magnum — External Surface Medullary Foramen •For 2nd Metacarpal Styloid Process Fig. 123. — The Third Right Metacarpal Bone. A, Internal View; B, External View. form, whilst the other, situated at the outer and posterior part, is small for the os magnum. The shaft gives origin to the third and fourth dorsal, and second palmar, interossei. Articulations. — Superiorly with the os magnum, unciform, and third and fifth metacarpals, and inferiorly with the first phalanx of the ring finger. The Fifth Metacarpal Bone.— This is shorter than the fourth, but longer than the first. The superior surface of the base presents a quadrilateral facet for the tmciform. The outer side has a semi-oval facet for the fourth metacarpal, and the inner side presents a rounded tubercle for the insertion of the extensor carpi ulnaris. The inner A MANUAL OF ANATOMY A B \ ^'J|_ _ External Surface and » 11' ' Medullary Foramen _^ For 3rd Metacarpal For Os Magnum For 5th Metacarpal Pig. 124.— The Fourth Right Metacarpal Bone. A, Internal View ; B. External View. B External Surface and — Medullary Foramen For Unciform For 4th Metacarpal . For 4th Metacarpal For Unciform Tubercle for Extensor Carpi Uinaris Fig. 1 2 5. —The Fifth Right Metacarpal Bone. A. External View ; B, Dorsal View. THE BONES OF THE UPPER LIMB 213 margin of the shaft gives insertion to the opponens minimi digiti, and the shaft also affords origin to the fourth dorsal, and third palmar, interossei. Articulations. — Superiorly with the unciform, externally with the fourth metacarpal, and inferiorly with the first phalanx of the little finger. Each metacarpal bone presents a medullary foramen, that of the first, and usually that of the second, being situated on the inner or ulnar side of each shaft, whilst those of the third, fourth, and fifth are situated on the outer or radial side* The foramen of the first and the canal to which it leads are directed downwards towards the head, but those of the other four are directed upwards towards the base. The medullary artery of the first metacarpal is furnished by the arteria princeps pollicis, those of the second and third are branches of the first palmar interosseous, that of the fourth is furnished by the second palmar interosseous, and that of the fifth by the third palmar interosseous, arteries. Structure. — ^The structure is that of a long bone. Tubetoaty k For ForOs Unciform Magnum Fig. 126. — The Bases of the Right Metacarpal Bones (Superior View). The metacarpus as a whole is concave from side to side, and also longitudinally, on its palmar aspect, whilst the dorsal aspect is con- vex. The first metacarpal stands off at an angle from its fellows, and occupies a more anterior plane, thus fitting it for the important movement of opposition on the part of the thumb. The other fovur metacarpals lie very nearly parallel with each other. They articu- late with one another by their bases, but diverge slightly towards their heads, where they are connected on their palmar aspects by the transverse met icarpal ligament. Between the five bones there are four intervals, called interosseous spaces, the first being that between the first and second bones. The Phalanges. The phalanges are also known as ossa internodia, from their position between the joints of the fingers. The fingers, of which they form the framework, are called poUex or thumb, index, middle, * Of 100 second metacarpal bones examined, 59 had the medullary foramen on the inner side, and 4 1 on the outer. -214 A MANUAL OF ANATOMY - • Ungual Process Proximal Extremity Proximal Extremity ring, and little, respectively. The number of phalanges is fourteen, three for each of the four inner fingers, and two for the thumb. They are arranged in rows, both longitudinally and transversely, and they diminish in length from above downwards. They are distinguished as first or proximal, second or intermediate, and third, distal, or ungual, except in the case of the thumb, where the second is wanting. The First Phalanx. — The shaft is compressed from before back- wards, fiat and concave longitudinally on the palmar aspect, and convex on the dorsal. The palmar surface presents at either side a rough border for the sheath of the flexor tendons. The proximal end or base is enlarged, and presents superiorly a concave articular sur- face, transversely oval, for the head of a metacarpal bone, and at either side a slight tubercular enlargement. The distal end is small, and presents a trochlear surface, grooved at the centre and elevated at either side of this into a small condyle, for articulation with the second phalanx, except in the case of the thumb, where it articulates with the ungual phalanx. The cartilage of the distal end is prolonged more on the palmar aspect than on the dorsal. At either side it presents a depression for the lateral inter- phalangeal ligament. The Second Phalanx. — ^This is shorter and smaller than the first, from which it is distinguished by having on its proximal end or base two shallow articular depressions, separated by a median antero- middle Finger (Dorsal View), posterior ridge, for the distal end of the first phalanx. The distal end resembles that of a first phalanx, except that it is smaller. The shaft resembles that of a first. Its palmar surface presents at the centre of the lateral borders two rough impressions, one at either side, which give insertion to the divisions of a superficial flexor tendon. The dorsal surface of the base is marked by a rough transverse ridge for the insertion of the middle division of a common extensor tendon. The Third Phalanx.— This is of small size. The proximal end or base resembles that of a second phalanx, and has in front a rough transverse ridge for the insertion of a deep flexor tendon, whilst the dorsal surface gives insertion to the two lateral divisions of a common extensor tendon. The distal end presents a rough, tapering, convex Proximal Extremity Fig. 127. — The Phalanges of the THE BONES OF THE UPPER LIMB 215 border, the roughness being continued for a little on the palmar aspect. This roughness, which is semilunar, is called the ungual process, and it supports the nail and the tissues forming the pulp of the finger. The two phalanges of the thumb are of large size. Special Muscalar Attachments. — The base of the proximal phalanx of the thumb gives insertion externally to the abductor poUicisand superficial head of the flexor brevis pollicis, internally to the deep head of the flexor brevis pol- licis, adductor obliquus pollicis, ' and adductor transversus poUicis, and posteriorly to the extensor brevis pollicis. The base of the distal phalanx gives insertion anteriorly to the flexor longus pollicis, and posteriorly to the extensor longus pollicis. The base of the proximal phalanx of the index finger gives partial insertion to the first dorsal interosseous externally, and the first palmar interosseous internally. The base of the proximal phalanx of the middle finger gives pjirtial insertion to the second dorsal interosseous ex- ternally, and the third dorsal interosseous internally. The base of the proximal 5th Year Year 6th Year , ^ ; i 7th Year 3rd Year /rr~^/ 5th Year i2th 1 ear 2nd Year .. . "^ Appear from the 3rd ] to the 5th Year. C .. J and join about 20 Appears from the 3rd to the 5th Year, and joins about 20 Appear abottt the 9th Week (intra-uterine) Fig. 128. — Ossification of the Bones of the Hand. A, 2nd Metacarpal ; B, ist Metacarpal ; C, ist Phalanx. phalanx of the ring finger gives partial insertion to the second palmar inter- osseous externally, and the fourth dorsal interosseous internally. The base of the proximal phalanx of the little finger gives partial insertion to the third palmar interosseous externally, and insertion to the abductor minimi digiti (partially) and flexor brevis minimi digiti internally. The medullary foramen of each phalanx is situated on the palmar aspect of the shaft, not far from the distal end. It may be single, in which case it is mesially placed, or there may be two, one close to each lateral border. In all cases the direction of the foramen and the canal to which it leads is downwards towards the distal end. The medullary arteries are furnished by the corresponding palmar digital arteries. Structure. — The structure is that of a long bone. In the terminal phalanges the medullary canal is replaced by cancellated tissue with wide meshes. 2i6 A MANUAL OF ANATOMY The Sesamoid Bones. — These are usually two in number, and are placed on the palmar aspect of the head of the first metacarpal bone. They are originally nodules of cartilage, one of which is developed in the tendon of insertion of the superficial head of the flexor brevis pollicis, and the other in that of the adductor obliquus pollicis. Similar ossicles are sometimes met with on the palmar aspects of the heads of the second and fifth metacarpal bones; Ossification of the Metacarpal Bones and Phalanges. — Each of these bones ossifies in cartilage from one primary, and one secondary, centre. The primary centre appears about the ninth week of intra-uterine life at the middle of the shaft, except in the case of the ungual phalanges, in which it appears at the distal end. In the inner four metacarpal bones the epiphysis is placed at the distal end or head, but in the first metacarpal bone (that of the thumb), and in all the phalanges, it is placed at the proximal end or base. The secondary centre in each case appears from the third to the fifth year, and the epiphyses are united to their respective shafts about the twentieth year. The first metacarpal bone has sometimes a thin distal epiphysis, as well as a proximal, which begins to ossify about the eighth year, and joins soon thereafter ; and the second metacarpal bone has sometimes a proximal epiphysis, as well as a distal. The first metacarpal bone, being a phalanx as regards its epiphysial ossification, is regarded by some as the proximal phalanx of the thumb, according to which view the bone wanting in the thumb is the metacarpal bone. The stjdoid process of the third metacarpal bone has sometimes a special centre, and, instead of joining the rest of the bone, it may remain persistent as a supernumerary bone of the carpus, or it may unite with the postero-internal angle of the trapezoid. The Hand as a Whole. The hand presents two surfaces — dorsal and palmar — -two borders ■ — outer and inner — and two extremities — proximal and distal. The dorsal surface is convex, both longitudinally and trans- versely. The palmar or volar surface is concave, both longitudinally and transversely. The outer or radial border is in line with the thumb or pollex, and is constructed by the scaphoid or navicular, trapezium, and the phalanges of the thumb. The inner or ulnar border is in line with the little finger, and is constructed by the cuneiform or pyramidal, unciform, and the phalanges of the Httle finger. This border presents the tubercle on the inner side of the proximal end or base of the fifth metacarpal bone for the tendon of the extensor carpi ulnaris. The proximal extremity is formed by the scaphoid or navicular, semilunar, and cuneiform or pyramidal bones. The distal extremity is formed by the third or ungual phalanges. It is to be noted (i) that the thumb is the shortest of all the digits ; (2) that it stands off at an angle from its fellows ; and (3) that it occupies a more anterior plane than its fellows, in which respects it presents a striking contrast to the great toe. The palmar aspect of the carpus is rendered concave by the THE BONES OF THE UPPER LIMB 217 tuberosities of the scaphoid and trapezium externally, and the pisiform and the hook of the unciform internally. These four pro- jections give attachment to the anterior annular Ugament. This ligament, along with the palmar concavity of the carpus, constructs a fibro-osseous passage, called the anterior palmar canal. This canal transmits (i) the tendons of the flexor sublimis, and flexor profundus digitorum, and the median nerve lying within the large inner compartment of the great palmar bursa ; and (2) the tendon of the flexor longus poUicis lying wittiin the small outer cofnpartment of the great palmar bursa. The tuberosity of the scaphoid gives partial attachment to the anterior annular ligament, and partial origin to the abductor pollicis muscle. The tuberosity of the trapezium, which has the form of a ridge, gives partial attachment to the anterior annular ligament, and partial origin to (i) the abductor pollicis, (2) the opponens pollicis, and (3) the superficial head of the flexor brevis pollicis. The groove on the palmar surface of the trapezium transmits the tendon of the flexor carpi radiaHs, which lies in a special compart- ment in the outer part of the anterior annular Ugament, and is invested by a special synovial membrane. The pisiform bone gives attachment to (i) part of the anterior annular Ugament, (2) the tendon of the flexor carpi ulnaris, (3) the pisi-uncinate and pisi-metacarpal ligaments, and (4) the abductor minimi digiti muscle. The hook of the unciform gives attachment anteriorly to part of the anterior annular Ugament and the pisi-uncinate Ugament, and internally partial origin to the flexor brevis minimi digiti and opponens minimi digiti. The ulnar groove on the internal surface of the hook, close to its root, transmits the deep branches of the ulnar artery and nerve. 2i8 A MANUAL OF ANATOMY Pisi-uncinate Ligament Abductor Pollicis Opponens Pollicis , Superficial Head of Flexor --^Ji Brevis Pollicis / •- Ext. Ossis Metacarpi Poll. ---_ Deep Head of Flex. Brevis Pollicis Flexor Carpi Radialis Opponens Pollicis" ~, Abd. Pollicis and Superf. Head of Flex. Brev. Poll. Extensor Brevis Pollicis Deep Head of Flex.Brevr' Poll., Add. Obliq. Poll., and Add. Trans. Poll. Extensor Longus Poll. Flexor Longus Poll. • ^ Flexor Carpi Ulnaris - -Abductor Minimi Digiti - _ Adductor Obliquus Pollicis Flex. Brev. and Oppon. Mii Pisi-metacarpal Ligament _ — Adduct. Transvers. P __Opponens Minimi Digiti Abductor Minimi Di and Flexor Brevi Minimi Digiti Flexor Sublimis Digitorum.^- Flexor Profundus Digitorum Fig. 129. — The Right Hand ^Palmar Surface). THE BONES OF THE UPPER LIMB 219 Semilnnar Cuneiform Pisiform Scai>hoid Os JNIagnum Trapezoid _ Trapezium Extensor Carpi Radialis Longior _ _ Extensor Ossis Metacarpi PoUicis - - Extensor Carpi Radialis Brevior Extensor _Bre\is PoUicis Deep Head of Flexor *Brev. PoU., Adductor Obliquus Poll., and Add. Transversus PoU . Extensor Longus PoUids y Eztoisor Communis Digitorum Fig. 13b. — ^The Right Hand (Dorsal Surface). 220 A MANUAL OF ANATOMY IV. THE BONES OF THE LOWER LIMB. The lower limb is arranged in four divisions, namely, hip, or pelvic girdle, thigh, leg, and foot. The pelvic girdle consists of the OS innominatum ; the thigh comprises the femur, with which is associated the patella ; the leg is composed of the tibia and fibula ; and the foot is subdivided into a tarsus, consisting of seven bones, a metatarsus, comprising five bones, and phalanges, which are fourteen in number. The Os Innominatum. The OS innominatum (os coxae) forms the lateral, and one half of the anterior, wall of the pelvis. It is much twisted, quadrilateral, and constricted about the centre. The external surface is charac- terized by the acetabulum, and below and internal to this is the obturator foramen. In early life the bone is composed of three parts — ilium, ischium, and os pubis — which unite in the acetabulum, and in the adult it is described under these three divisions. The ilium is the expanded portion above the acetabulum, of which it forms rather less than the upper two-fifths. It presents three borders and two surfaces. The superior border or crest is thick over its anterior and posterior thirds, but thin over the middle third. It presents two curves — anterior with the concavity directed inwards, and posterior with the concavity outwards. Anteriorly it terminates in the anterior superior spine, which gives attachment to Poupart's ligament and a portion of the sartorius. Posteriorly it ends in the posterior superior spine, which gives attachment to the oblique sacro-iliac ligament. The crest has two lips and an inter- vening space. The outer lip presents a tubercular prominence about 3 inches from the anterior superior spine. Over its whole extent this lip gives attachment to the iliac fascia lata ; for i|- inches in front, to the tensor fasciae femoris ; over its anterior half, to the obliquus externus abdominis ; and a little behind this, to the latis- simus dorsi. The intervening space over its anterior two-thirds gives origin to the obliquus internus abdominis, and over its pos- terior fifth, to the erector spinse. The inner lip over its anterior two- thirds gives origin to the transversalis abdominis, and for about 2 inches posteriorly, to the ilio-lumbar ligament and quadratus lumborum. Immediately within the inner lip, over its anterior two- thirds, the fascia transversalis and fascia iliaca take attachment. The anterior border extends from the anterior superior spine to the ilio-pectineal eminence. Superiorly it presents the anterior inter- spinous notch, the upper part of which gives partial origin to the sartorius. Below this notch is the anterior inferior spine, which gives origin anteriorly to the straight head of the rectus femoris, and inferiorly, to the ilio-femoral ligament. Internal to this spine THE BONES OF THE LOWER LIMB 221 Transversalis Abdominis Obliquus Intemus Abdominis Middle Gluteal Line Gluteus Medius Latissimus Dors! Crest Obliquns Externus Abdominis iperior Gluteal Line luteus Maximus asterior Superior.. Iliac Spine Posterior Inferior Iliac Spine Pjrriformis. Great Sciatic Notch Ischial Spine- Gemellus Superior Gemellus Inferior Obturator Groove, Quadratus Femoris Semimembranosus— Semitendinosus and Long Head of, Biceps Tuber Ischi Gluteus Minimus , Tensor Fasciae Femoris ^Anterior Superior Iliac Spine .Inferior Gluteal Line Anterior Inferior Spine _ and Straight Head of Rectus Femoris Reflected Head of Rectus ..Acetabulum Cotyloid Notch - Pectineus • Pubic Spine Pubic Crest and Rectus AMominis Pubic Angle Adductor Longus — Symphysis Pubis Gracilis Adductor Brevis Descending Pubic Ramtu Adductor Magnus Adductor Magnus Obturator Externus Ischial Ramus Fig. 131. — The Right Os Innominatum (External View). 222 A MANUAL OF ANATOMY there is a groove for the passage of the iHo-psoas, and internal to the groove is the ilio -pectineal eminence, which marks the junction of the ilium and superior pubic ramus. This eminence gives attach- ment to the ilio-pectineal intermuscular septum, and, it may be, partial insertion to the psoas parvus. The posterior border extends from the posterior superior spine to a point a little below the deepest part of the great sciatic notch, where there is usually a faint transverse line on the external surface, indicating the place of junction of the ilium and ischium. Superiorly it presents the posterior interspinous notch, and below this the posterior inferior spine, which gives attachment to the great sacro-sciatic ligament, whilst immediately below this it gives origin to fibres of the pyriformis. Inferiorly the posterior border forms the upper part of the great sciatic notch, over which the pyriformis passes as it leaves the pelvis. The external surface or dorsum ilii, concavo-convex from behind forwards, is traversed by three ridges, called the superior, middle, and inferior gluteal, or curved, lines. The superior gluteal line commences at the outer lip of the crest about 2 inches in front of the posterior superior spine, and passes downwards and forwards to the upper part of the great sciatic notch. The surface which it cuts off is semilunar, and its upper part is rough for the origin of fibres of the gluteus maximus. The middle gluteal line commences at the outer lip of the crest i^ inches behind the anterior superior spine, and passes backwards and downwards to the upper part of the great sciatic notch, where it terminates close to the superior line. The surface included between the middle gluteal line, crest, and superior gluteal line, which is falciform, gives origin to the gluteus medius. The inferior gluteal line commences at the lower part of the anterior interspinous notch, whence it passes back- wards to the deepest part of the great sciatic notch. The space between the inferior and middle gluteal lines gives origin to the gluteus minimus. Between the front part of the inferior gluteal line and the margin of the acetabulum there is a short transverse groove, which gives origin to the reflected head of the rectus femoris. The iliac portion of the bone is very thin and translucent toward the upper part of the middle third, where it is sometimes perforated, and it presents a strong rounded ridge, leading upwards from the margin of the acetabulum to the tubercular eminence on the outer lip of the crest. There is also a strong bar of bone extending from the upper margin of the acetabulum to the auricular surface on the internal aspect. The internal surface is divisible into an anterior, and a posterior, portion. The anterior division, which represents two-thirds, is sub- divided into a small lower, and large upper, part by the iliac portion of the ilio-jjectineal line, the direction of which is forwards and down- wards. The part below and behind the line enters into the lateral wall of the pelvis, and gives origin to a portion of the obturator internus. The part above the line is extensive and concave, and THE BONES OF THE LOWER LIMB 223 forms the iliac fossa, which lodges the iliacus muscle. The iliac portion of the ilio-pectineal line gives attachment to the fascia iliaca, and for about an inch posteriorly to the parietal pelvic fascia. It may also give partial insertion to the psoas parvus near the ilio-pectineal eminence. The posterior division is subdivided into auricular, ligamentous, and muscular portions. The auricular division, anteroinferior in position, is broad in front and narrow behind, where it extends over the inner aspect of the posterior inferior spine. It is covered by cartilage in the recent state, and articulates with the auricular surface of the sacrum. The liga- mentous division, situated above and behind the auricular, presents an elevation, called the tuberosity, for the posterior sacro-iliac ligament, its surface being marked by several pits. The muscular division, placed superiorly, gives origin to fibres of the multifidus spinae. The ischium forms the lower and back part of the bone, and is divisible into a body, tuberosity, and ramus. The body con- tributes rather more than two-fifths to the acetabulum, and forms the greater portion of its non-articular part. It is some- what triangular, the truncated apex being directed downwards, and its surfaces are internal, external, and posterior. The internal surface extends from near the centre of the ilio-pectineal line to the ischial spine, and is narrow above, but widens inferiorly before reaching the spine. Its place of junction with the ilium is indicated by a line passing from the Uio-pectineal eminence back- wards and downwards to a point a little below the deepest part of the great sciatic notch. Its junction with the superior pubic ramus is marked by a line passing from the ilio-pectineal eminence down- wards to the posterior margin of the obturator foramen about I inch below its upper end. This surface gives origin to part of the obturator intemus. The external surface enters into the acetabulum, and between that cavity and the tuberosity it presents an obturator groove for the tendon of the obturator externus. The upper part of this groove gives attachment to the ischio- capsular ligament. The posterior surface is limited externally by the brim of the acetabulum, behind by the posterior border, and below by the upper border, of the tuberosity. At the lower part it presents a portion of the obturator groove, and it supports the pyriformis, and the sciatic nerves and vessels. The borders, like the surfaces, are internal, external, and posterior. The internal border forms a portion of the posterior margin of the obturator foramen, and is sharp for the obturator membrane. It separates the internal from the external surface. The external border forms the posterior part of the margin of the acetabulum, and gives attachment to a part of the cotyloid ligament. The posterior border is continuous with that of the ilium. Superiorly it forms the lower part of the great sciatic notch, below which it presents a projection, called the spine, which has an inward curve towards the pelvis, and gives attachment to the 224 A MANUAL OF ANATOMY following structures : the small sacro- sciatic ligament at the tip, the levator ani, coccygeus, and white line of the pelvic fascia on the inner surface, and the gemellus superior along the lower border. The external surface (back) supports, from within outwards, the pudic nerve, internal pudic vessels, and nerve to the obturator internus. Crest and Obliquus Interims Abdominis Transversalis Abdominis Quadratus Lumborum I Tuberosity Ligamentous Surface Erector Spinae Multifidus Spinae Anterior Superioi Iliac Spine Iliacu9 Anterior Inferior Iliac Spine Iliopectineal Line - Psoas Parvus ~ Ilio-pectineal Eminence Obturator Groove Superior Pubic Ramus Pubic Spine . Pubic Crest Pubic Angle Pubic Body Symphysis Pubis Levator Ani Descending Pubic Ramu Posterior Superior Iliac Spine Posterior Inferior Iliac Spine Auricular Surface ^ Great Sciatic Notch — — Coccygeus -Ischial Spine Levator Ani Small Sciatic Notch Obturator Internus Tuber Ischii Transversus Perinaei Ischio-cavernosus Ischial Ramus Fig. IJ2.— The Right Os Innominatum (Internal View). Below the spine is the small sciatic notch, which is covered by car- tilage in the recent state for the play of the tendon of the obturator internus. The tuberosity (tuber ischii) forms the thick dependent part, and supports the body in the sitting posture. The upper border limits inferiorly the obturator groove and small sciatic notch, and THE BONES OF THE LOWER LIMB 225 in the latter situation it gives origin to the gemellus inferior. The inner border is prominent and sharp, and gives attachment to the great sacro-sciatic ligament. The outer border gives origin to the quadratus femoris. The anterior border is sharp and prominent, and forms the lower part of the posterior margin of the obturator foramen. The siu'faces are postero-inferior, external, and internal. The postero-inferior surface lies between the outer and inner borders, and is di^^ded into two parts. The posterior portion is somewhat quadrilateral, and is subdi\'ided into two parts by a diagonal line directed downwards, forwards, and outwards. The upper and outer part gives origin to the semimembranosus, and the lower and inner, to the conjoined long head of the biceps and semitendinosus. The inferior portion, which is in line with the inner margin of the ramus, is rough and triangular, and gives origin to fibres of the adductor magnus. The external surface is situated between the outer and anterior borders, and supports the obtiu-ator externus. The internal surface is placed between the inner and anterior borders. It looks towards the ischio-rectal fossa, and gives origin to fibres of the obtiu^ator intemus. The ramus is the compressed portion which extends upwards and inwards, from the tuberosity, on the anterior aspect of the obturator foramen, where it joins the inferior pubic ramus, the ?lace of meeting being indicated externally by a rough ridge, he outer border is sharp for a portion of the obturator membrane, and forms part of the anterior margin of the obturator foramen. The inner border is thick, and anteriorly it is rough and everted, more so in the male than in the female, for the attachment of the fascia of Colles, cms penis, and ischio-cavemosxis muscle. In the female this part gives attachment to the crus cUtoridis and erector clitoridis. Elsewhere the inner border gives attachment to the triangular ligament and compressor urethrae. The outer surface gives origin, from within outwards, to portions of the adductor magnus and obturator externus. The inner or pelvic surface gives attachment to part of the obturator intemus and parietal pelvic fascia. At its lower part, near the inner border, there is a sharp ridge which gives attachment to the falciform process of the great sacro-sciatic ligament. The OS pubis lies in the anterior wall of the pelvis, and is composed of a body and two rami, superior and inferior. The body is compressed from before backwards, and occupies an oblique plane, which is directed downwards and backwards. It presents three surfaces — anterior, posterior, and internal. The anterior or femoral surface has an inclination downwards. At its upper and inner part, below and external to the pubic angle, it gives origin to the adductor longus, and, lower dowTi, to the following muscles, in order from within outwards — ^gracilis, adductor brevis, a small portion of the adductor magnus, and obturator externus. The posterior or pelvic surface has an inclination upwards, and gives attachment from without inwards to the obturator intemus, 1=; 426 A MANUAL OF ANATOMY parietal pelvic fascia, levator ani, and pubo-prostatic ligament. The internal surface is oval, and occupies an oblique plane, which is directed downwards and backwards. It is covered by cartilage, and articulates with its fellow to form the symphysis pubis, a plate of fibro-cartilage intervening. The borders are external and superior. The external border, which is sharp, looks into the obturator foramen, and gives attach- ment to part of the obturator membrane. The superior border or crest is thick, and about an inch long. At its outer extremity is the pubic spine, which may be blunt or sharp, for the attach- ment of Poupart's ligament, and internally is the puhic angle, which surmounts the internal surface. The crest gives attachment to the conjoined tendon, pyramidalis, and outer head of the rectus abdominis. The inferior ramus passes downwards and outwards, and corre- sponds in all respects with the ischial ramus, which it joins. Its anterior surface gives origin, from within outwards, to the gracilis, adductor brevis, adductor magnus, and obturator externus. The structures attached to the posterior surface are portions of the obturator internus and parietal pelvic fascia. The superior ramus extends outwards and upwards from the body to the ilio - pectineal eminence and anterior part of the acetabulum, of which latter it forms one-fifth. It lies above the obturator foramen, and is triangular. Superiorly, at the back part, is a prominent ridge, representing the pectineal portion of the ilio -pectineal line, which leads to the pubic spine, and gives attach- ment to the following structures : the pubic lamina of the fascia lata, pectineus, Gimbernat's ligament, and conjoined tendon. In front of this line is the superior or pectineal surface, which is sloped downwards and forwards, and is triangular. It supports the pectineus, and is limited antero-inferiorly by the obturator crest, which extends from the pubic spine to the anterior margin of the cotyloid notch. The inferior surface presents the obturator groove for the obturator vessels and nerve, the direction of which is down- wards, forwards, and inwards. The posterior surface gives partial origin to the obturator internus. The acetabulum or cotyloid cavity is situated on the outer surface of the bone, and is directed downwards, outwards, and forwards. It is deep and circular, and articulates with the head of the femur. The ischium forms rather more than two-fifths of it, the ilium rather less, and the os pubis the remaining fifth. It is surmounted by a prominent brim, upon which the cotyloid ligament is set, except at the anterior and inferior part, where there is the cotyloid notch, this being bridged over by the cotyloid and transverse ligaments; The capsular ligament is attached to the bone just outside the brim. The interior is divided into two parts — articular and non- articular. The articular portion is covered by cartilage, which is arranged in the form of a horseshoe, and surrounds the circum- ference, except opposite the cotyloid notch. The non-articular part, THE BONES OF THE LOWER LIMB 227 which is formed mainly by the ischium, is depressed, and lodges the Haversian gland of the hip-joint. The obturator or thyroid foramen hes below, and internal to, the acetabulum, its boundaries being formed by the ischium and os pubis. Its long diameter is directed downwards and outwards, and it is oval in the male, but triangular, with rounded angles, in the female. Its circumference is sharp for the obturator membrane, which closes the opening, except opposite the obturator groove superiorly, where it converts that groove into the obturator canal. The great and small sciatic notches are situated on the posterior border of the bone, and are separated from each other by the spine of the ischium. The great notch is formed partly by the ihirni, and partly by the ischium; and the small notch hes between the ischial spine and tuber ischii. In the recent state these notches are converted into foramina by the great and small sacro-sciatic hgaments. For the structures which pass through these foramina, see the description of the gluteal region. Appears about the 8th Week ... (intra-uterine) Appears about the 5th Month ,»=«!■> ^ '• (intra-uterine) Vv.y^^ I V lir . - ''"" THE BONES OF THE LOWER LIMB 23 1 upper border of the symphysis pubis. The brim is therefore directed upwards and forwards. An idea of this obliquity may be obtained by placing a pelvis against a wall in such a way that the anterior superior iliac spines and the upper border of the symphysis pubis will touch the wall so as to lie in the same vertical plane. A line connecting the tip of the cocc5rx with the lower border of the symphysis pubis forms with the horizontal an angle of about 11 degrees, and the tip of the coccyx is about f inch above the sub- pubic angle. The direction of the outlet is downwards and back- wards, principally downwards when the coccyx is extended. The plane of the symphysis pubis forms with the horizontal an angle of from 35 to 40 degrees. It is worthy of note that the sacro- vertebral angle is estimated at 117 degrees in the male, and as much as 130 in the female. The Axes of the Pelvis. — ^The axes represent imaginary lines intersecting the planes of the brim, ca\aty, and outlet at right angles through their central points. The axis of the brim corresponds with a line drawn from the umbihcus to the sacro-coccygeal articu- lation, and its direction is downwards and distinctly backwards. The axis of the outlet represents a line drawn from the sacral promontory through the centre of the outlet, and its direction is downwards and very slightly backwards. The axis of the cavity intersects planes having different inclinations, and is necessarily cvu^ved, the concavity being directed forwards. It is described as ' the perpendicular of a line drawn from the middle of the symphysis pubis to the centre of the sacro-coccygeal curve.' The average measurements of the axes of the female pelvis are as follows : Conjugate. Transverse. ObUqnei Brim 4i 5i 5 Cavity 5 5 5 J Outlet 5 4I 4I Sexual Differences. — ^The differences in the two sexes are as follows : Female. Male. Bones smoother and more slender. Bones rougher and more massive Acetabula wide apart. Acetabiila not so wide apart. True pelvis wider and shallower. True pelvis narrower and deeper. Obturator foramen triangular. Obturator foramen oval. Ischial tuberosities ^^^der apart and Ischial tuberosities not so wide apart everted. and inverted. Span of subpubic arch wide. " Span of subpubic arch narrow. Inner border of ischio-pubic ramus Inner border of ischio-pubic ramus comparatively smooth. strongly marked and everted. Brim transversely ovzd. Brim cordate. Ilia more vertical. Ilia less verticaL False pelvis narrower. False pelvis wider. Sacral promontory less projecting. Sacral promontory more projecting. Sacrum broader, shorter, and Sacrum narrower, longer, and more straighten curved. Coccyx more movably articulated Coccyx less movably articulated with sacrum. with sacrum. Symphysis pubis shallower. - Symphysis pubis deeper. 232 A MANUAL OF ANATOMY The Pelvis of the Child. — ^The pelvis is of small size in the child. The iliac alae are expanded, and the cavity is of small dimensions, so that a large part of the urinary bladder in both sexes lies in the hypogastric region of the abdomen. The sacro-vertebral angle is relatively greater, and the pelvis has consequently a greater inclination. The Femur. The femur extends from the hip to the knee, its direction being downwards, inwards, and slightly backwards. It is a long bone, and is divisible into a shaft and two extremities, upper and lower. The upper extremity presents a head, neck, and two trochanters, great and small, together with anterior and posterior intertro- chanteric lines. The head forms more than half a sphere, and its direction is upwards, inwards, and slightly forwards. Its surface is smooth and covered by cartilage, except at a point behind and below the centre, where it presents a rough depression. The ligamentum teres is attached to the upper part of this depres- sion, which presents a small foramen for the passage of a nutrient artery. The head encroaches more upon the upper surface of the neck than on the under. The neck forms with the shaft an angle of about 125 degrees on an average, the range being from no to 140. It is greater in the male than in the female. The direction of the neck is upwards, inwards, and slightly forwards. It is expanded at either extremity, especially towards the shaft, and it presents four aspects — anterior, posterior, superior, and inferior, of which the posterior and inferior are more extensive than the other two. The anterior aspect is on the same plane with the anterior surface of the shaft, from which it is separated by the anterior intertrochanteric line. This line passes downwards and inwards, and it presents at either extremity the superior cervical, and inferior cervical, tubercle. The anterior intertrochanteric line gives attachment along its cervical aspect to the anterior part of the capsular ligament of the hip- joint, including the ilio-femoral band. Its inferior relations are the vastus externus over about the upper third, and the crureus over about the lower two-thirds. The anterior aspect of the neck is entirely intracapsular, and is more or less ridged, being closely covered by the retinacula of the capsular ligament. The posterior aspect is of greater extent than the anterior, and is smooth and concave. It is separated from the shaft by the posterior inter- trochanteric line, which presents at its junction with the posterior border of the great trochanter the quadrate tubercle, whence the linea quadrati, for the quadratus femoris muscle, descends. Only the upper two-thirds of this aspect are intracapsular and covered by retinacula, the capsular ligament being very loosely attached along the junction of the middle and lower thirds. The lower THE BONES OF THE LOWER LIMB 233 Obturator Intemus and Gemelli ■ Anterior Intertrochanteric Line „ ., . / • jHead Pynformis • ' ^^---"^■~>^ i-> ■ c r ■ t ' ' /"^ ' ^\ - iJepression for Ligamentum \ I \ r '. \ ^'^ Teres Gloteus Minimus Vastus Eztemus Cnurens- '• ' Neck Jlio-psoas Small Trochanter — — --—-Vastus Intemus External Tuberosity - on External Condyle "** Subcrureus Adductor Tubercle Tendon of Adductor Magnus Internal Tuberosity on Internal Condyle Patellar Surface Fig. 137. — The Right Femur (Anterior View). 234 A MANUAL OF ANATOMY third is therefore extracapsular, and at its outer part it presents a horizontal groove which leads to the digital or trochanteric fossa, and lodges the tendon of the obturator externus. The superior aspect forms a short, almost horizontal border, which has a slight inclination downwards to the great trochanter. The inferior aspect forms a long, concave border, ending inferiorly at the small trochanter. The neck is pierced by numerous nutrient foramina, which are more abundant and of larger size above and behind than else- where. The head and neck receive their blood-supply from the obturator, sciatic, and external and internal circumflex, arteries. The great trochanter is a quadrilateral eminence continuous with the outer surface of the shaft. It presents three surfaces and four borders. The external surface is marked by an oblique impression which extends from the postero-superior to the antero-inferior angle, and gives insertion to the gluteus medius. The anterior surface presents, towards its lower part, an impression for the insertion of the gluteus minimus. The internal surface at its lower part presents the digital or trochanteric fossa for the insertion of the obturator externus, whilst above and in front of this it affords insertion to the obturator internus and gemelli. The superior border, which is almost horizontal, meets the posterior border at a right angle, the pointed projection thus formed being called the postero-superior angle. Near the centre of this border there is an oval impression for the insertion of the pyriformis. The inferior border gives origin to fibres of the vastus externus. The anterior border skirts the front of the great trochanter, and ends above at the superior cervical tubercle. It also gives origin to fibres of the vastus externus. The posterior border is prominent and con- tinuous with the posterior intertrochanteric line, the quadrate tubercle being situated at the junction of the two. The great trochanter is pierced by several nutrient foramina. The small trochanter is a conical projection which springs from the posterior and inner aspects of the bone where the neck and shaft join. It -gives insertion to the ilio-psoas, some of the fibres of the iliacus being inserted below and in front of it, where there is a depressed triangular surface lying between the prominence and the spiral line. The trochanters receive their blood-supply from the circumflex arteries. The shaft is longitudinally curved, the convexity being directed forwards. Its girth is least at the centre, and it expands at either end, more especially the lower. It is triangular in section in the middle third, the lateral angles being rounded off, and the posterior, formed by the linea aspera, prominent. Over its upper and lower thirds it is somewhat subcylindrical. The posterior aspect presents over its middle third a bold ridge, called the linea THE BONES OF THE LOWER LIMB Head ■ ■ Neck 235 Depression for Ligamenium Teres — '^ %. . Digital Fossa and Obturator Extemus 1 Quadrate Tubercle Quadiatus Femoris ■ nio-psoas — - Small Trochanter — • —Gluteus Medius ..Great Trochanter Portion of Iliacus— - Pectineus — Spiral Line . Adductor Brevis Vastus Intemus Adductor longus — j Inner Lip of Linea Aspera Adductor Magnus' . Gluteal Ridge and Gluteus Maximus -Medullary Foramen . Vastus Extemus -Summit of Linea Aspera .Ou^er Lip of Linea Asperj Crureus ^Femoral Head of Biceps Internal Supracondylar Ridge and Expansion from Tendon of Adductor Magnus External Supracondylar Ridge Adductor Tubercle and Adductor Magnus Internal Head of / Gastrocnemius Popliteal Surface Plantaris _ . External Head of Gastrocnemius _ External Tuberosity _ External Condyle Internal Tuberosity Internal Condyle Intercondylar Fossa Fig. 138. — The Right Femur (Posterior View). 236 A MANUAL OF ANATOMY as-pera, which has two lips, outer and inner, and a narrow inter- vening space. The outer lip gives attachment, from behind forwards, to the short head of the biceps, external intermuscular septum, vastus externus over its upper half, and crureus over its lower half. The inner lip gives attachment, from behind forwards, to the adductor magnus, adductor longus, internal intermuscular septum, and vastus internus. A little above the centre of the shaft, close to the inner lip, is the medullary foramen for a branch of the second, or third, perforating artery, the direction of the foramen and the canal to which it leads being upwards towards the head. Over the upper third of the shaft the lips of the linea aspera diverge. The outer lip is prolonged to the base of the great trochanter pos- teriorly, and over about its lower 3 inches it is conspicuously rough, this portion being known as the gluteal ridge, which gives insertion to the lower part of the gluteus maximus. Close to the outer side of this ridge the vastus externus takes origin, and close to its inner side the upper fibres of the adductor magnus take insertion. The inner lip bifurcates. One division is prolonged in a winding manner round the inner aspect of the shaft, passing in front of the small trochanter and terminating at the inferior cervical tubercle, where it passes into the anterior intertrochanteric line. This winding division is called the spiral line, and it gives origin to the upper fibres of the vastus internus. The other division is prolonged to the back of the small trochanter, and it gives insertion over its upper third to the pectineus, and over its whole extent to the adductor brevis, the latter being behind the former. The relation of muscles at the back of the upper end of the shaft, from the small trochanter outwards to the outer margin of the gluteal ridge, is as follows : ilio-psoas; pectineus; adductor brevis; lower fibres of quadratus femoris ; adductor magnus ; gluteus maximus ; and vastus externus. The narrow intervening space of the linea aspera between its two lips is in line with the linea quadrati above. Over the lower third of the shaft the lips of the linea aspera diverge widely, and are prolonged to the condyles as the external and internal supracondylar ridges. These enclose between them a flat triangular area, called the popliteal surface, which is also known as the trigonum femoris. Over this region the periosteum is very thin, and this part of the bone is predisposed to necrotic changes. The popliteal surface forms the upper part of the floor of the popliteal space. The external supracondylar ridge gives attachment over its whole extent to the external intermuscular septum, and over about its upper two-thirds to the short head of the biceps and the crureus. For a short distance below, it gives origin to the plantaris, and immediately external to this, to fibres of the outer head of the gastroc- nemius. The internal supracondylar ridge is interrupted about an inch below its commencement by a slight groove, which is produced by the femoral vessels, and at its lower extremity, close to the internal condyle, there is a projection called the adductor tuberch, for the THE BONES OF THE LOWER LIMB 237 insertion of the tendon of the adductor magnus. Superiorly, for about an inch, this ridge gives insertion to a portion of the adductor magnus, and below the femoral groove to an expansion from its tendon. The shaft presents three surfaces, anterior and two lateral, but these merge gradually into one another, except posteriorly in the situation of the linea aspera over the middle third. The anterior and external surfaces over about their upper three-fourths give origin to the crureus. The internal surface is non-muscalar, and presents a characteristic elongated bare strip, which is merely covered by the vastus internus. The lower fourth of the anterior surface at its upper part gives origin to the subcrureus, and lower External Tuberosity External Ci^ndyle Interna] Tuberosity Internal Condyle Patellar Facet (in extreme flexion) Intercondylar Fossa Fig. 139. — The Lower Extremity of the Right Femur. down is cov^ered by the suprapatellar bursa, and the pouch which the s3aiovial membrane of the knee-joint sends upwards above the patellar surface of the bone. The lower end of the shaft presents many nutrient foramina for the passage of branches of the anastomotica magna of the super- ficial femoral, and the articular branches of the popliteal, arteries. The lower extremity presents an extensive articular surface, which is divided into three parts — anterior or patellar, and two postero-inferior or condylar. All three surfaces are continuous in front, but the condylar surfaces are widely separated behind by the intercondylar fossa. The patellar surface is trochlear, and presents a vertical groove with a convexity on either side. The groove is to the inner side of th^ centre, and the part external to it is broader, more prominent, and extends higher, than the internal part. The 238 A MANUAL OF ANATOMY upper border is therefore sloped inwards and slightly downwards. The greater forward prominence of the outer part of the surface explains why the patella is inclined inwards in extension of the knee-joint. The condyles are convex from before backwards and from side to side. Posteriorly they become prominent, and on this aspect the external condyle extends a little higher than the internal. As viewed from below the external condyle is broad and short, the internal being long and narrow. When the femur is held vertically the internal condyle projects lower down than the external, and this brings the two condyles upon the same horizontal plane when the bone occupies its natural sloping position. The outer border of the external condyle is very nearly in the same line with the outer border of the patellar surface, and the outer border of the internal condyle is in the same line with the inner border of the patellar surface. The inner border of the internal condyle has a convex outline, and at its anterior part it turns outwards to the patellar surface. For the most part the condyles are parallel, the exception being the front part of the internal condyle, which inclines outwards to meet the patellar surface. The demarcation between the condylar surfaces and the patellar surface is clearly marked at either side. The external condyle is separated from the patellar surface by a slightly elevated line and groove, extending outwards and slightly forwards from the front and outer part of the intercondylar fossa to the outer border of the cartilaginous surface, where there is a depression which receives the anterior part of the external semilunar fibro-cartilage during extension of the knee-joint. The internal condyle is separated from the patellar surface by a line and groove, extending from near the front and inner part of the intercondylar fossa forwards and slightly inwards to the inner border of the cartilaginous surface, at a point about i inch below the inner end of the upper border of the patellar surface. At this latter point there is a depression which receives the anterior part of the internal semilunar fibro-cartilage during extension of the knee-joint. The line and groove just referred to do not extend quite close to the intercondylar fossa. The groove subsides, but the line sweeps backwards in a curved manner along the outer part of the inner condylar surface, thus marking off a narrow semilunar zone from the general tibial surface. This zone lies close to the inner part of the intercondylar fossa, and is known as the patellar facet. In extreme flexion of the knee- joint, as in the position assumed by the miner when at work, the patella by its inner vertical zone articulates with this facet, which may be called the miner's facet. The outer surface of the external condyle towards the back part presents the external tuberosity, which gives attachment to the long external lateral ligament of the knee-joint. Immediately above and behind the tuberosity is an impression ^r the outer head of the gastrocnemius, and behind and below it there is a groove, called the popliteal groove^ which is directed downwards and forwards. THE BONES OF THE LOWER LIMB 239 The tendon of the popUteus cirises from the front part of the hori- zontal portion of the groove, and it is lodged in the groove only when the knee is flexed. The inner surface of the internal condyle presents at its centre a large blunt eminence, called the internal tuberosity, for the attachment of the internal lateral ligament. Posteriorly, where the internal supracondylar ridge joins the internal condyle, the adductor tubercle is situated, and the line of origin of the inner head of the gastrocnemius extends almost transversely outwards from this tubercle above the internal condyle. Fig. 140. — Longitudinal Section through the Upper End of the Femur, SHOWING THE PRESSURE LaMELL^E AND TENSION LaMELL/E. The markings in connection with the intercondylar fossa are for the crucial ligaments. The impression for the anterior crucial ligament is at the back part of the inner surface of the external condyle, whilst that for the posterior crucial ligament is at the front part of the outer surface of the internal condyle, and adjacent portion of the front of the intercondylar fossa. At the front of that fossa in the middle line the ligamentum mucosum is attached. Articulations. — Superiorly with the acetabulum of the os inno- minatum, and inferiorly with the head of the tibia below, and the patella in front. 240 A MANUAL OF ANATOMY Structure. — The structure is that of a long bone. The marrow canal extends from a point just below the small trochanter to the level of the apex of the trigonum femoris. Above and below these points the bone is composed of cancellated tissue, except externally, where there is a shell of compact bone. The cancellated tissue at the upper extremity has its lamellae arranged in a series of curves disposed in two systems, one of which represents the pressure lamellae, and the other the tension lamellae. The pressure lamellce extend from the lower part of the neck and upper part of the shaft internally in a radiating manner, some, which are very strong, passing inwards to the head, whilst others pass outwards to the great trochanter. The tension lamellce are disposed almost at right angles to the pressure lamellae, and arch upwards and inwards from the outer aspect of the shaft, below the great trochanter, to the head and lower part of the neck. Additional strength is afforded by an almost vertically disposed plate of compact bone, called the calcar femorale, which runs upwards and downwards in front of, and above, the small trochanter, and lies in the line in which weight is transmitted. The cancellated tissue at the lower extremity has its lamellae arranged in obliquely decussating lines which enclose somewhat rectangular meshes. Varieties. — (i) The gluteal ridge may assume the form of a depression, called the /055a hypotrochanterica. (2) There may be a third trochanter, situated at the upper part of the gluteal ridge. (3) The linea aspera may be unduly prominent owing to muscular ■^X— ist Year, and joins at 19 .-tth Year, and joins at 18 ..14th Year, and joins at 17 . Appears in the 7th Week (intra-uterine) Appears just before birth, and joins at 20. Fig. 141. — Ossification of the Femur. action, this condition being known as the pilastered femur. (4) A pressure facet is sometimes met with, as in miners, at the upper end of the front of the neck, close to the cartilage of the head, with which it is continuous, this facet being due to prolonged mainten- ance of the flexed posture. The Femur of the Female. — (i) The bone is smoother than in the male. (2) The angle formed by the neck with the shaft is about no degrees. (3) The bones are farther apart above, more sloped inwards, and nearer to each other below, than in the male. Ossification. — The femur ossifies in cartilage from one primary, and four secondary, centres. The primary centre appears at the middle of the shaft in the seventh week of intra-uterine life. The centre for the lower extremity appears ;ms/ before birth in the bottom THE BONES OF THE LOWER LIMB 241 of the intercondylar fossa. At birth the shaft is ossified, and the lower epiphysis is showing signs of ossification, but the three upper epiphyses are cartilaginous. The centre for the head appears in the first year, that for the great trochanter in the fourth year, and that for the small trochanter in the fourteenth year. The small trochanter joins the shaft at seventeen, the great trochanter at eighteen, the head at nineteen, and the lower epiphysis at twenty. The neck is ossified from the centre for the shaft. The hne indicating the junction ot the lower epiphj'sis and shaft cuts the adductor tubercle into two, one portion belonging to the lower epiphysis, and the other to the shaft. The Patella. The patella, rotula, or knee-cap, is situated in front of the knee- joint, where it articulates with the patellar surface of the femur. It is originally a sesamoid cartilage developed in the tendon of the quadriceps extensor cruris. The bone is triangular with the apex downwards, and is compressed from before backwards. The SuperMM- Border External Border Vertical Femoral Facet (ia extreme flexion) .,' Anterior Surface Upper Transverse Femoral Facet Middle do., do. —Lower do., do. - Ligamentum Patelbe Fig. 142. — The Right Patella. A, Anterior Surface ; B, Posterior Surface. superior border or base is broad, and its plane is inclined forwards and slightly downwards. It gives insertion anteriorly to the rectus femoris and crureus, in this order from before backwards, and posteriorly it is covered by a portion of the s\movial mem- brane of the knee-joint. The lateral borders are sloped towards the apex, the outer being at first rather more prominent than the inner. The outer border over its upper third gives insertion to a portion of the vastus extemus, and the inner over its upper half to a 16 243 A MANUAL OF ANATOMY portion of the vastus internus. The apex is blunt, and, together with the adjacent marginal parts, gives attachment to the ligamentum patellae, by which the bone is connected with the tubercle of the tibia. The anterior surface, which is slightly convex, is vertically striated and covered by a prolongation of the tendon of the quadri- ceps extensor cruris. It is perforated by numerous nutrient fora- mina, and is subcutaneous, being separated from the integument by the prepatellar bursa. The posterior surface is divided into two parts — articular and non-articular. The non- articular part represents the lower fourth, and is rough and depressed. It lodges a collection of fat covered by synovial membrane. The articular part corresponds with the upper three-fourths, and is divided into two unequal parts by a round vertical ridge, which is received into the groove of the patellar surface of the femur. The external division is broad and concave from side to side, whilst the internal is narrow and convex in the transverse direction. Excluding a narrow vertical zone at the inner part of the inner division, each division is subdivided by two slight transverse ridges into three horizontal zones — upper, middle, and lower, of which the middle is the largest and broadest. These six horizontal facets articulate with the patellar surface of the femur, the lower facets being in contact with the upper part of the patellar surface in extension of the knee-joint, the middle patellar facets with the middle portion of the patellar surface of the femur in semiflexion, and the upper patellar facets with the lower parts of the patellar surface of the femur in flexion of the knee-joint. The vertical zone at the inner part of the inner division of the articular surface (close to the inner border of the bone) constitutes a seventh facet, which may be called the miner's facet. In extreme flexion of the knee-joint this facet articulates with the semilunar facet (miner's facet) on the outer part of the tibial surface of the internal condyle of the femur close to the intercondylar fossa, whilst the upper and outer horizontal facet is in contact with the front part of the external condyle. The patella receives its arteries from the superficial branch of the anastomotica magna of the femoral, inferior articular branches of the popliteal, and anterior tibial recurrent. Structure. — The patella, being a short bone, is composed princi- pally of dense cancellated tissue with close meshes, surrounded by compact bone, which is much thicker in front than behind. Ossification. — The original cartilage is deposited in the tendon of the quad- riceps extensor cruris in the third month of intra-uterine life. In this cartilage^ a single centre appears in the third year, and ossification is completed about : the age of puberty. The Tibia. The tibia, or shin-bone, is the inner and larger of the two bones of the leg, and alone transmits the weight of the body to the foot. The posterior surfaces of the shafts of the tibia andj THE BONES OF THE LOWER LIMB 343 fibula are on the same horizontal plane above and below, but over about the middle three-fifths the fibula projects slightly farther back on account of its cur\'e. Anteriorly the tibia is on a more anterior plane than the fibula, a point to be borne in mind in making flaps by transfixion. The tibia is a long bone, and is divisible into a shaft and two extremities, upper and lower. The upper extremity, known as the head, is broader from side to side than from before backwards. Antero-laterally it is convex, but posteriorly it is rendered concave by the popliteal notch at its centre. The enlargements of the bone on either side of the head are called the tuberosities, external and internal. The external tuberosity is rather smaller than the internal, and at its posterior and under aspect it presents a flat circular facet, directed downwards. Anterior Comu of Internal Fibro-Cartilage Tuberde Anterior Cmcial Ligament *' Intemal Condylar Surfac-: Anterior Comu of External Fibro-Cartilage External Tabeick at Spine External Condylar Stirface Intemal Tubercle of Spint- Posterior Coma of Intemal Fibro-Cartilage i Popliteal Notch Posterior Crucial Ligament Posterior Comu of External Fibro-Cartfl age Fig. 143 The Head of the Right Tibia (Superior View). backwards, and outwards, which articulates with the head of the fibula. The cartilage of this facet is occasionally continuous with that of the external condylar surface. At the junction of its anterior and outer surfaces the external tuberosity presents an elevation, which usually assumes the form of a ridge, for the attachment of the ilio-tibial band of the fascia lata. The internal tuber nsiiy is larger than the external, and has a distinct inclina- tion backi^'ards as well as inwards, a point to be noted in setting fractures of this bone. On its posterior aspect it presents a hori- zontal groove for the insertion of the chief portion of the tendon of the semimembranosus muscle. On the anterior aspect of the superior extremity, at the junction of the head and shaft, there is a well-marked projection, called the tubercle or anterior tuberosity. It is fully I inch in length, and its upper border is about | inch 244 A MANUAL OF ANATOMY below the level of the upper surface of the head. It is divisible into two nearly equal parts, upper and lower. The lower division is rough, and is usually strongly ridged in the vertical direction for the attachment of the ligamentum patellae. The upper division is smooth, and is separated from that ligament by a synovial bursa. The superior surface of the head presents the two condylar articular surfaces, separated from each other by an irregular interval, which, amongst other markings, presents the bifid tibial spine. Each surface surmounts the corresponding lateral tuberosity. The external condylar surface is broad from side to side, and is almost circular. It is concave from side to side, and concavo- convex from before backwards. Its cartilage rises towards the middle line to coat the external surface of the outer tubercle of the tibial spine, and posteriorly it dips down for a little on the outer part of the back of the external tuberosity, where the tendon of the popliteus glides over it. It is in this situation where the carti- lage is occasionally continuous with that of the fibular facet. The internal condylar surface is oval and concave, being elongated from before backwards, but narrow from side to side. The cartilage of this surface rises towards the middle line to coat the internal surface of the inner tubercle of the tibial spine. Each condylar surface is deepened by a semilunar fibro-cartilage, which is placed round its peripheral part. The interspace between the condylar surfaces presents the spine, which is distant from the posterior border about one-third of the antero-posterior measurement. The spine is formed by an upward rising of the contiguous borders of the condylar surfaces, and is bifid, ending in two tubercles, of which the inner is the better marked and longer of the two. The interspace between these tubercles gives attachment to the posterior cornu of the external semilunar fibro-cartilage, which continues to be attached to a depression behind the outer tubercle. The surfaces of the tubercles which face each other are free from cartilage, but the other surfaces have each a cartilaginous covering. In front of the spine there is a rough depression where important structures are attached as follows : in front of the outer tubercle of the spine the anterior cornu of the external semilunar fibro- cartilage is attached, and in front of the inner tubercle the anterior crucial ligament is attached to the bone. At the extreme anterior and inner part there is an impression for the anterior cornu of the internal semilunar fibro-cartilage. On the outer side of the im- pression for the anterior crucial ligament, and in front of that for the anterior cornu of the external semilunar fibro-cartilage, there is a depression which is partially occupied by a small collection of fat. At its outer part, however, there is a groove which receives a portion of the external semilunar fibro-cartilage in extension of the knee-joint. The immediately adjacent portion of the external condylar surface is specially facetted for the play of part of the THE BONES OP THE LOWER LIMB 245 external condyle of the femur in extension of the joint. Behind the tibial spine there is a more limited rough depression, which leads backwards to the popliteal notch. The posterior comu of the internal semilunar fibro- cartilage is attached to the inner part of this depression, and the posterior crucial hgament is attached to its back part, as well as to the popliteal notch. Order of Structures attached to the Head. — The structures, enumerated as nearly as possible in order from before backwards, are as foUows : I. Anterior comu of internal semilunar fibro-cartilage. '2. Anterior crucial ligament. 3. Anterior comu of external semilunar fibro-cartilage. 4. Posterior comu of external semUimar fibro-cartilage. 5. Posterior comu of internal semilunar fibro-cartilage. 6. Posterior cmcial ligament. The head is pierced all round by many nutrient foramina for branches of the inferior articular arteries of the popliteal, and of the posterior and anterior tibial recurrents of the anterior tibial. The shaft is massive and triangular. It diminishes in size from above downwards over its upper two-thirds, and then gradually enlarges towards its lower end. It presents three borders and three surfaces. The anterior border extends from the outer side of the anterior tuberosity above to the anterior margin of the internal malleolus below. Over the upper two-thirds, where it occupies the middle line, it is prominent, and is known as the crest or shin- ridge. This is doubly curved, the convexity of the upper curve being directed inwards, and that of the lower outwards. Over the lower third the anterior border inclines inwards, and the external surface of the shaft is thus allowed to come forwards. The crest is subcutaneous, and gives attachment to the deep fascia of the leg. The internal border extends from the inner and back part of the internal tuberosity to the posterior margin of the internal malleolus. For 3 or 4 inches superiorly it is rough, and gives attachment to the internal lateral ligament of the knee-joint. Over its middle third it is prominent, and it here gives origin to a portion of the soleus as low as the centre of the bone. The external or inter- osseous border extends from the front of the fibular facet above to a point about 2 inches from the lower end, where it bifurcates. The two divisions pass to the front and back of the sigmoid cavity, and enclose between them a rough triangular surface for the inferior interosseous ligament. This border is sharp and wiry, and gives attachment to the interosseous membrane. The internal surface is situated between the crest and internal border. It is for the most part subcutaneous, and slightly convex. Superiorly, where it becomes expanded and flattened, it presents a vertical rough area, behind the tubercle, for the insertion of the sartorius, and behind this two vertical rough impressions in the same line with each other, the upper of which gives insertion 246 A MANUAL OF ANATOMY External Tuberosity of Tibia -j Biceps Femoris-'-' Head of Fibula-I Peroneus Longus Extensor Longus Digitorum Extensor Proprius Hallucis Antero-external Border. . Postero-external Border .— Peroneus Brevis— -"V Internal Tuberosity of Tibia / M-UUf/- — Tubercle --mw Peroneus Tertius"" ^ Gracilis Sartorius Semitendinosus External Surface and Tibialis Anticus Anterior Border or Crest Internal Border Triangular Subcutaneous Surface External Malleolus-^- ■ , .^^^^^^ ^^^^^^^^^ Fig. 144.— The Right Tibia and Fibula (Anterior View). THE BONES OF THE LOWER LIMB M7 to the gracilis, and the lower to the semitendinosus. The external surface is situated between the crest and interosseous border. It is concave over its upper two-thirds, where it gives origin to the tibiaUs anticus. Over the lower third, where it is convex, it turns to the front and supports the extensor tendons, and anterior tibial vessels and nerve. The posterior surface lies between the inter- osseous and internal borders. Superiorly it is crossed by the popliteal or oblique line, which is rough, and extends from the fibular facet downwards and inwards to the internal border at about the junction of the upper third and lower two-thirds. This line gives attachment to the popliteal fascia and part of the soleus, whilst the triangular popliteal surface above gives insertion to the popUteus muscle. The posterior surface below the oblique line presents over its middle third a vertical ridge which divides it into two parts. The outer portion is narrow, and gives origin to the tibialis posticus as low as a point just below the centre of the bone. The inner portion is broad, and gives origin to the flexor longus digitorum over the middle two-fourths of the bone. A little below the oblique line, close to the outer side of the vertical ridge, is the medullary foramen for a large branch of the posterior tibial artery. This foramen, which is the largest of its class, and the canal to which it leads are directed downwards. The posterior surface in its lower third supports the flexor tendons, and posterior tibial vessels and nerve. The lower extremity presents a quadrilateral articular surface, concave from before backwards, and wider in this direction exter- nally than internally. It is broader in front than behind, and articulates with the superior surface of the astragcJus. The pos- terior border projects somewhat lower than the anterior. The anterior surface, immediately above the anterior border, is depressed and rough for the anterior ligament of the ankle-joint. The posterior border gives attachment to the posterior ligament of the ankle-joint as far inwards as the groove behind the internal malleolus. It presents the following grooves : one for the tendon of the flexor longus hallucis near the outer end ; one (very faint) near the centre for the posterior tibial vessels and nerve ; and one mainly situated on the back of the internal malleolus for the tendons of the tibialis posticus and flexor longus digitonmi. The inner aspect of the lower extremity presents the internal malleolus, which is a strong process having a downward direction. Its internal surface is rough, convex, and subcutaneous. The external surface is covered by cartilage, continuous with that which coats the lower extremity. The plane of this surface is vertical, and the cartilage coats it more deeply in front than behind. It articulates with the internal surface of the astragalus. The anterior border is rough and round for the attachment of the anterior and internal lateral ligaments of the ankle-joint. The lower border is indented by a notch, in front of which is the projection known as the tip, the internal lateral ligament being attached to both of these parts. 248 A MANUAL OF ANATOMY Tibial Spine Semimembranosus J \ Popliteal Notch ^•Styloid Process of Fibula Internal Tuberosity of Tibia- r-l Soleus Posterior Surface Postero external Bolder -Flexor Longus Hallucis . Medullary Foramen Peroneus Brevis \ Postero-exterjial Border ■ Antero-external Border Tip of Internal Malleolus , Groove for Tibialis Posticus and ,,^^ ^ Flexor Longus Digitorum ,• f^ Peroneal Groove ' Tip of External Malleolus Groove for Flexor Longus Hallucis Fig. 145.— The Right Tibia and Fibula (Posterior View). THE BONES OF THE LOWER LIMB *49 Posteriorly is the groove for the tendons of the tibialis posticus and flexor longus digitorum. The outer aspect of the lower extremity presents a concave facet for the fibula, cind above this a concave triangular rough sin-face about i^ inches long for the inferior inter- osseous ligament. The inferior extremity of the tibia presents many nutrient foramina for branches of the anterior and posterior tibial, internal malleolar, and anterior peroneal, arteries. Articulations. — Superiorly with the condyles of the femur above, and the head of the fibula postero-extemally, and inferiorly with the fibula externally, and the superior and intemaJ aspects of the astragalus below. Structure. — The structure is that of a long bone. The medullary canal extends above to a point about i^ inches below the lower margin of the anterior tuberosity, and inferiorly to a point about I inch below the lower extremity of the crest. The cancellated tissue of the upper epiphysis has its lamellae disposed somewhat vertically, whilst that of the upper end of the shaft has its lamellae arranged in the form of arches. In the lower part of the shaft the cancellous lamella; are disposed vertically, and the cancellated tissue of the lower epiphysis is closely meshed. Varieties. — (i) The tibia is sometimes much compressed laterally, which leads to an increase in its antero-posterior diameter. In these cases the vertical ridge posteriorly becomes unduly promi- nent, a condition which is associated with a large development of the tibialis posticus muscle. Such a bone is spoken of cis being platycnemic (broad -legged), and the condition is known as platycnemism (broadness of tibia). (2) The anterior aspect of the lower extremity of the bone sometimes presents a pressure facet at its outer part for articulation with the upper surface of the neck of the astragalus in extreme flexion of the ankle-joint. Ossification. — The tibia is ossified in cartilage from i primary and 3 secondary centres. The primary centre appears at the centre of the shaft about the jth week. The 3 secondary centres are disposed as follows: 2 are superior, one for the head, and the other for the tubercle ; and i is inferior for the lower extremity and inter- nal malleolus. Upper Extremity. — The centre for the head appears just before birth, and from it the external and in- ternal tuberosities are ossified, which constitute the superior epiphysis. The centre lor the tubercle appears about the 12th year. Soon afterwards it joins the superior epiphysis, which unites with the shaft about the 22nd year. In some cases the tubercle is entirely ossified from the centre for the head. In other cases th;; upper smooth part of the tubercle is ossified from the centre for the head, and the lower rough part derives its ossification from the primar}' centre for the shaft. Lower Extremity. — ^The centre for the lower ex- tremity and internal malleolus appears towards the end of the 2>Mf year, and this lower epiphysis joins about the iSth year. Appears just liefore birtb, and joins about 22 May appear about the 12th year, and joins soon thereafter Appears in the 7th week (intra-uterine) Fig. ;;^_ Appears at end of 2nd year, and joins about 18. 146. — Ossification of the Tibia. 2SO A MANUAL OF ANATOMY The Fibula. The fibula, or peroneal bone, is situated on the outer side of the tibia. It is very slender for its length, and is a rudimentary bone. It takes no part in transmitting the weight of the body, but serves chiefly to afford attachment to muscles, though it also forms part of the ankle-joint, and acts as a brace or support to the tibia. It is a long bone, and is divisible into a shaft and two extremities, upper and lower. The upper extremity, or head, is enlarged and knob-like, its upper surface being somewhat flattened and sloping. It is situated about f inch below the level of the head of the tibia. Posteriorly it is prolonged upwards into the styloid process, to the tip of which the short external lateral ligament of the knee-joint is attached. In front of this process the upper surface of the head is sloped downwards and forwards, and is divisible into an articular and a non-articular part. The articular division is internal in position, and takes the form of a flat circular facet, which is directed upwards, inwards, and forwards, to articulate with the facet on the posterior and under aspect of the external tuberosity of the tibia, by which latter it is overhung. The non-articular division is external in position, and takes the form of a rough depression, into which the tendon of the biceps femoris, previously divided into two parts by the long external lateral ligament, takes insertion. Posteriorly the head gives origin to the soleus. Externally it gives origin to the peroneus longus, and at a point nearly ^ an inch anterior to the styloid process its outer margin gives attachment to the long external lateral ligament. Anteriorly it gives origin to the extensor longus digitorum. The constricted part below the head is called the neck. The upper extremity presents several nutrient foramina for branches of the inferior external articular of the popliteal, and superior fibular of the anterior tibial, arteries. The lower extremity is prolonged downwards into a massive pro- jection, called the external malleolus, which is not only larger, but lower down and farther back, than the internal malleolus. It is triangular or pyramidal, the base being directed upwards. The external surface is rough, convex, and subcutaneous. The internal surface is divisible into two parts, articular and non- articular. The articular division is anterior in position, and occupies about two-thirds of the surface. It is triangular and convex, and it mainly articulates with the outer surface of the astragalus. Superiorly, however, for about \ inch, it assumes a some- what semilunar outline, and this portion articulates with the outer aspect of the tibia. The non-articular division is posterior in position, and occupies about one-third of the surface. It is rough, depressed, and triangular, and is known as the digital fossa. Superiorly it gives attachment to the transverse ligament of the inferior tibio-fibular joint, and interiorly to the posterior fasciculus THE BONES OF THE LOWER LIMB of the external lateral ligament of the ankle-johit. Above the external malleolus on the inner aspect there is a rough, convex, triangular surface about i^ inches long for the inferior interosseous ligament. The anterior border projects at first forwards, and then slopes downwards and back- wards to the tip. The projecting part gives attachment to the anterior ligament, and the lower portion of the sloping part to the anterior fasciculus of the external lateral ligament of the ankle- joint. The posterior border is shorter than the anterior, and is vertical. It presents the peroneal groove for the tendons of the peroneus longus and peroneus brevis. The tip is the most dependent part, and is situated at the meeting of the posterior border and the lower sloping part of the anterior border. It gives at- tachment to the middle fasciculus of the external lateral ligament. The lower extremity presents several nutrient foramina for branches of the anterior and posterior peroneal, and external malleolar, arteries. The shaft is slightly curved, the convexity being directed backwards in the upper part, and inwards lower down. It is quadrilateral in its upper three-fourths, where it presents four borders and four surfaces, but it is somewhat triangular in the lower fourth. The ant era- external border, which is the most prominent, commences in front of* the head, and passes straight downwards until it reaches the lower fifth, where it bifurcates. One division passes to the anterior margin of the ex- ternal malleolus, and the other to -Styloid Process - Tibial Faxret on Head -—Neck .- Tibialis Posticus Medullary Foramen J|. Postero-intemal Border Antero-intemal or Interosseous Border . _Antero-external Border -- Postero-extemal Border Triangular Area for Inferior Interosseous Ligament __ Facet on External Malleolus for Astragalus "~ Digital Fossa Fig. 147. — The Right Fibula (Internal View). 252 A MANUAL OF ANATOMY the posterior margin, external to the peroneal groove. These two divisions enclose between them a triangular area which is continuous with the outer surface of the external malleolus. This border gives attachment to the antero-external intermuscular septum. The antero-internal or interosseous harder, which gives attachment to the interosseous membrane, also commences in front of the head, where it is very near to the antero-external border. As it descends it keeps near to that border at first, but beyond the upper third it gradually diverges from it, and on reaching a point about 2 inches above the external malleolus it bifurcates. One division passes to the anterior margin of the malleolus, becoming incorporated with one of the divisions of the antero-external border, whilst the other passes to the posterior margin of the malleolus, internal to the upper end of the peroneal groove. The two divisions, as they diverge, enclose a rough triangular area, which is slightly convex and gives attachment to the inferior interosseous ligament. The postero-internal border commences on the inner side of the head, not far from the antero-internal. It descends in a backwardly- curved manner, gradually leaving the antero-internal border, but subsequently approaching it, until on reaching the junction of the upper two-thirds and lower third it ends by joining it. This border gives attachment to an intermuscular septum, which separates the tibialis posticus from the soleus and flexor longus hallucis. The postero-external border extends from the back of the head to the back of the external malleolus, internal to the peroneal groove, and in its lower part it turns inwards. It gives attachment to the postero-external intermuscular septum. The anterior surface is situated between the antero-external and antero-internal or interosseous borders. It is very narrow over about its upper half, but becomes wider below. It gives origin over about its upper three-fourths to the extensor longus digitorum, over its lower fourth (except about i inch below) to the peroneus tertius, and over about its middle two-fourths to the extensor proprius hallucis, which is nearest to the antero-internal border. The internal surface is situated between the antero-internal and postero-internal borders. It is concave and fusiform, being narrow above and below, but wide at the centre, and it gives origin to the tibialis posticus. The posterior surface is limited by the postero- internal and postero-external borders, and in its lower fourth it undergoes a twist, and turns round to become internal. Over its upper third it gives origin to a part of the soleus, and over its lower two-thirds, except the last inch or more, to the flexor longus hallucis. The external surface lies between the antero-external and postero- external borders. It is the broadest, and in muscular subjects is deeply grooved over rather more than its upper half. Inferiorly it undergoes a twist, and turns round to become posterior, where it leads directly to the peroneal groove on the back of the external malleolus. In this manner the two peroneal tendons are guided to this groove. The upper two-thirds of this surface give origin to THE BONES OF THE LOWER LIMB 253 the peroneus longus, and the lower two-thirds, except the last 2 inches, to the peroneus brevis, these two muscles overlapping towards the centre of the bone. The medullary foramen, which is small, is usually situated on the posterior surface, but may be on the internal, a little above the centre, and there may be an additional one a little higher up. It is for a branch of the peroneal artery, and the direction of the foramen and the canal to which it leads is downwards towards the ankle. Articulations. — Superiorly with the external tuberosity of the tibia, and inferiorly with the outer aspect of the tibia, and the ex- ternal surface of the astragalus. Structure. — ^The structure is that of a long bone, and the marrow canal is limited to about the middle three-fifths of the shaft. ^ Appears about the 4th Year, and joins about 23 |l.. Appears in the 8th Week (intra-uterine) Ossification. — The fibula ossifies in cartilage from one primary, and two secondary, centres. The primaiy centre for the shaft appears in the eighth week of intra-uterine Ufe. At birth the shaft is ossified, but the extremities are cartilaginous. The centre for the lower extremity appears in the second year, and that for the upper extremity about the fourth year. The lower epiphysis joins the shaft about twenty, and the upper about twenty-three. The fibula forms an excep- tion to the general law of ossification apphcable to long bones with an epiphysis, or epiphyses, at either end, which may be here restated as follows : ' The epiphysis or epiphyses, at the end towards which the medullary foramen and the canal to which it leads are directed, are the last to show signs of ossification, but they are the first to join the shaft.' In the fibula the lower epiphysis not only joins the shaft first, but it is the first to show signs of ossification — due to the fact that this extremity is the least rudimentary part of the bone. At about the seventh month of intrauterine hfe the tibial and fibular malleoh are of nearly equal proportions, but by the second year. previous to the appearance of its centre of ossification, the fibular malleolus hcis attained the large relative size which characterizes it throughout Ufe. Fig. Appears m the 2nd Year, and joins about 20 148. — Ossification of THE Fibula. The Tarsus. The tarsus is composed of seven short bones, namely, the astragalus, os calcis, navicular or scaphoid, three cuneiforms, and cuboid. The first two constitute the proximal row, the astragalus l5dng above the os calcis, and the last four comprise the distal row, the order from the inner or tibial to the outer or fibular side being in- ternal, middle, and external cuneiform bones, and cuboid. The navicular occupies an intermediate position. 254 A MANUAL OF ANATOMY The Astragalus. The astragalus, or talus, is characterized by having a head, neck, and body. It is situated between the tibia above and the os calcis below, is grasped laterally by the tibial and fibular malleoli, and has the navicular in front. It is the only tarsal bone which receives directly the weight of the body, and it lies with its long axis directed forwards and inwards. In point of size it comes next to the os calcis. The head forms the anterior part of the bone, and presents an extensive convex articular surface, which looks forwards and also downwards. It is divided into three facets, called navicular, sustentacular, and ' spring.' The navicular facet, which is placed on the anterior surface, is pyriform, and its long axis is directed downwards and inwards. The sustentacular facet, continuous with the foregoing, is situated on the inferior surface. It is convex and eDiptical, and its long axis is directed forwards and outwards. It is often crossed by an elevated ridge a little anterior to the centre, and it articulates with the sustentacular facet on the upper surface of the OS calcis. The spring facet is situated on the inner aspect of the inferior surface, and is in contact with the superior surface of the inferior calcaneo-navicular or ' spring ' ligament. The neck is the constricted part behind the head. It is con- spicuous superiorly, and passes inferiorly into the interosseous groove. This groove is directed forwards and outwards, its inner part being narrow and deep, and the outer wide and shallow. It gives attachment to the strong interosseous ligament which binds the astragalus to the os calcis. The neck is perforated all round with numerous nutrient foramina for offsets of the dorsalis pedis artery and its tarsal branch. The body is quadrilateral, and presents four surfaces and a pos- terior border. The superior surface presents an extensive trochlear facet, which is concave from side to side, and convex from before backwards. Posteriorly it slopes downwards, and in this situation it usually presents a transverse groove for the play of the transverse ligament. The inner border is straight' and slightly depressed, and as a rule it extends rather farther back than the outer, which latter is somewhat sinuous. The surface is broader in front than behind. The external surface is deep, and presents a large triangular facet for the external malleolus, the apex being downwards. It is concave from above downwards, and, immediately in front of it, the anterior fasciculus of the external lateral ligament of the ankle-joint takes attachment. The internal surface pre- sents superiorly a falciform facet, broad in front and pointed behind, for the internal malleolus. This facet in the foetus en- croaches on the inner side of the neck, a condition which is associ- ated with the inversion of the foot at that period of life. This sometimes occurs in the adult, and, if it does so to any marked extent, it usually accompanies the condition known as talipes varus. THE BONES OF THE LOWER LIMB 255 The inferior surface presents a large oval facet, concave from within forwards and outwards, for articulation with the os calcis. The posterior border is short, stout, and oblique, its direction being inwards and forwards. It presents a groove, which is directed down- Head Neck — Jfc>-;: For Internal Malleolus .. For Tibia -•' Internal Tubercle Groove for Flexor Longus Hallucis For External Malleolus External Tubercle Navicular Facet . Facet for Spring Ligament For Os Calcis •= -1 Interosseous Groove ^ For Os Calcis Fig. 149. — The Right Astragalus. A, Superior View ; B, Inferior View. wards and inwards, for the tendon of the flexor longus hallucis. On either side of this groove there is a tubercle, the internal being rudimentary, whilst the external is well developed and gives attach- ment superiorly to the posterior fasciculus of the external lateral ligament of the ankle-joint. 2S6 A MANUAL OF ANATOMY The astragalus derives its blood-supply from branches of the dorsalis pedis artery. Articulations. — Superiorly with the shaft, and infernally with the internal malleolus, of the tibia ; externally with the external malle- olus of the fibula ; inferiorly with the os calcis ; and anteriorly with the navicular, and occasionally with the lower and inner angle of the cuboid. Structure. — The astragalus, being a short bone, is composed of cancellated tissue, surrounded by a thin shell of compact bone. The lamellae of the cancellated tissue are arranged in a curved manner, and in two sets. Some pass downwards and backwards from the superior surface to the posterior calcaneal facet, whilst others arch downwards and forwards from the superior surface to the neck, these being the directions in which weight is transmitted. Varieties. — (i) The external tubercle on the posterior border may form a separate ossicle, called the os trigonum. (2) There may be a pressure facet on the upper surface of the neck at its outer part, due to prolonged contact with the anterior margin of the lower end of the tibia. The Os Calcis. The OS calcis, or calcaneum, is the largest bone of the tarsus, and is characterized by its elongation, lateral compression, and en- largement posteriorly into a tuberosity. It is situated below the astragalus, and behind the cuboid, where it lies with its long axis directed forwards and outwards. It presents two extremities and four surfaces. The posterior extremity, which is enlarged, forms the tuberosity or tuber calcis, and constitutes the prominence of the heel. Posteriorly it is divided into three zones — an upper, which is smooth and separated from the tendo Achillis by a bursa ; a middle, rough and vertically ridged, for the insertion of the tendo Achillis ; and a lower, which is continuous with the tubercles on the plantar aspect, and supports the fat of the heel. In front of the tuber calcis there is a constriction, called the neck. The anterior extremity presents a large, somewhat triangular facet, narrow towards the sole, which is concave from above down- wards and outwards, and convex from side to side, for articulation with the cuboid. The superior surface presents over its anterior part two facets for the astragalus, separated by an oblique groove, and posteriorly a non-articular surface. The antero-internal or sustentacular facet surmounts the sustentaculum tali. It is concave and somewhat elliptical, its long axis being directed forwards and outwards. It is constricted in front of the centre, and is sometimes broken up into two facets by a rough groove The postero-external facet is large, oval, and convex from behind forwards and outwards. The intervening groove, which is directed forwards and outwards, becomes wide and shallow externally, and in front of the outer THE BQNES OF THE LOV/ER LIMB ^^57 part of the groove the upper surface gives origin to a portion of the extensor brevis digitorum, and the fundiform ligament of Retzius, When the astragalus is in position this groove is converted into a short tunnel, called the sinus tarsi, which is occupied by the inter- osseous ligament. The superior surface behind the articular portion is rough, and supports a collection of fat. For Astragalus For Astragalus For Astragalus Interosseous Groove Peroneal Spine _ Tubercle for Middle Fasciculus of External Lateral Ligament ,For Bursa For Tendo Achillis For Cuboid I i ! Anterior Tubercle Internal Tuberck Internal Surface Sustentaculum Tali, with Groove below it for Flexor Longus Hallucis Fig. 150. — The Right Os Calcis. A, Superior View ; B, Internal View. The inferior surface is narrow and rough. Posteriorly it presents two tubercles, the outer of which is small but prominent, whilst the inner is large and blunt. The outer tubercle gives attach- ment to the external division of the plantar fascia, and a portion of the abductor minimi digiti, whilst the inner gives attach- ment to the central and internal divisions of the plantar fascia, 17 2S8 A MANUAL OF ANATOMY the outer head of the abductor hallucis, the flexor brevis digitorum, and a portion of the abductor minimi digiti. The greater part of the inferior surface gives attachment to the long plantar ligament, and anteriorly it presents a small round eminence, called the anterior tubercle, to which the short plantar ligament is attached. The internal surface is concave, and is overhung at -its antero- superior part by the sustentaculum tali. This latter is concave and articular above for the astragalus, and below it presents a groove for the flexor longus hallucis. Anteriorly it gives attachment to the inferior calcaneo-navicular or ' spring ' ligament, below which a slip of the tibialis posticus takes insertion, and its inner margin gives attachment to fibres of the internal lateral ligament of the ankle- joint. The general concavity of the internal surface supports the tendon of the flexor longus digitorum and the plantar vessels and nerves, and anteriorly it affords origin to the inner head of the flexor accessorius. The external surface is for the most part fiat. Towards its anterior and lower part it presents a short oblique ridge, called the peroneal spine or ridge, which separates two grooves. The upper groove transmits the tendon of the peroneus brevis, and the lower that of the peroneus longus. Behind and a little above this spine there is a small tubercle, about the centre of the surface, for the middle fasciculus of the external lateral ligament of the ankle-joint. The OS calcis is pierced by many nutrient foramina for offsets of the calcaneal branches of the posterior tibial and external plantar, and the internal and external malleolar branches of the anterior tibial, arteries. Articulations. — Superiorly with the astragalus, and anteriorly with the cuboid. Structure.— rThe structure is that of a short bone. Some of the lamellae of the cancellated tissue arch downwards and backwards from the large postero-external facet on the superior surface to the prominence of the heel. In addition to these, there are other lamellae which pass in an antero-posterior direction just above the layer of compact bone which forms the plantar surface. In the region of the groove for the sinus pedis, especially towards the outer part, the upper compact layer is thicker than elsewhere. Ossification. — The os calcis ossifies in cartilage from one primary, and one secondary, centre. The primary centre appears in the sixth month of intra- uterine life. The secondary centre appears in the tenth year, and forms a thin epiphysial scale over the posterior surface of tfie tuber calcis, wliich joins in the sixteenth year. This epiphysis includes the outer, and a large part of the inner, tubercle on the under surface, and it may include the whole of the posterior surface, or only the lower two-thirds. The Navicular Bone. The navicular or scaphoid bone is distinguished by its resemblance to a boat. It is situated on the inner side of the foot, where it is placed in front of the astragalus, and behind the three cuneiform THE BONES OF THE LOWER LIMB 259 bones. It is compressed from before backwards, and its long axis is directed inwards and downwards. The anterior surface presents a large convex articular surface, divided into three facets by two ridges which converge inferiorly. The inner facet, for the internal cuneiform, is pyriform, with the narrow end upwards. The middle facet, for the middle cuneiform, is triangular, with the truncated apex downwards. The outer facet, for the external cunei- form, resembles the middle, except that it is rather shorter and has a rounder apex. The posterior surface is characterized by a large concave, pyriform facet for the front of the head oi the astragalus, its narrow end being directed downwards and inwards. The Dorsal Surface Tuberosity. For External Cuneiforin._l| — Posterior Surface for Head of Astragalus Spring Tubercle on Plantar Surface For Middle Cuneiform _^For Internal Cuneiform Spring Tubercle Fig. 151. — The Right Navicular Bone. A, Postero-superior View ; B, Antero-inferior View. dorsal surface, extensive and rough, is sloped downwards and inwards. The plantar surface, narrow and rough, gives attachment to the inferior calcaneo-navicular or ' spring ' ligament, and about its centre there is usually a knob-like projection, called the spring tubercle. The external surface is broad and rough, and it sometimes presents a small facet for the cuboid, contiguous to the outer facet on the anterior surface. The inner extremity (prow of the boat) is inclined downwards, and forms a stout, round projection on the inner side of the sole, called the tuberosity, which gives insertion to the principal portion of the tendon of the tibialis posticus. 26o A MANUAL OF ANATOMY Articulations. — Posteriorly with the astragalus, anteriorly with the three cuneiform bones, and sometimes with the cuboid externally. Structure. — The structure is that of a short bone. Variety. — The tuberosity sometimes forms a separate ossicle. The Cuneiform Bones. The cuneiform bones are three in number, namely, internal, middle, and external. They are situated between the navicular and the inner three metatarsal bones, and are characterized by their Dorsal Surface Anterior Surface for ist Metatarsal Ji Posterior Surface for Navicular - For Tibialis Anticus Posterior Surface for Navicular.-:^. — ■ For 2nd Metatarsal "---■-For Middle Cuneifom B Fig. 152. — The Right Internal Cuneiform Bone. A, Internal View ; B, External View. wedge shape. The internal cuneiform is the largest, and the middl is the smallest. The internal cuneiform bone is situated on the inner side of tl foot, where it lies with the narrow end of the wedge upwards, and supports the first metatarsal. The dorsal surface is narrow anc rough. The plantar surface is thick and convex, and posteriorly it presents an eminence for a slip of the tendon of the tibiali> posticus. The internal stuface is traversed by an oblique groove, directed downwards and forwards, for the tendon of the tibialis THE BONES OF THE LOWER LIMB 261 anticus, the principal portion of which is inserted into an impression situated at the lower part of the groove. The external surface presents, close to its superior and posterior borders, an L-shaped facet for the middle cuneiform, at the anterior extremity of which there is a small facet for the inner side of the base of the second metatarsal. When the bone is held in its proper position, the L is placed thus F in a right bone, and thus 1 in a left. The rest of the surface is concave and rough for strong ligaments, except at the lower and anterior part, where it gives insertion to a slip of the tendon of the peroneus longus. The anterior surface is deep, and presents a convex reniform facet for the first metatarsal, the concave border being directed outwards. The posterior surface, much smaller than the anterior, is characterized by a concave pyriform facet for the navicular, the narrow end being upwards. Articulations. — Posteriorly with the navicular, anteriorly with the first metatarsal, and externally with the middle cuneiform and second metatarsal. Variety. — The internal cuneiform may be divided into two parts, dorsal and plantar. The middle cuneiform bone lies with the broad end of the wedge upwards, and it supports the second, metatarsal. The dorsal A Dorsal Surface Anterior Surface / for 2nd Metatarsal — \ For Internal Cuneiform Q Posterior Surface for Navicular For External Cuneiform Fig. 153. — The Right Middle Cuneiform Bone. A, Internal View ; B, External View. surface is rough and nearly square. The -plantar surface, also rough, is narrow, and give? insertion to a slip of the tendon of the tibiaJis posticus. The internal surface presents, close to its superior and pos- terior borders, an L-shaped facet for the internal cuneiform, placed thus 1 for a right bone, and thus f for a left, the remainder of the surface being rough and ligamentous. The external surface has a vertical facet posteriorly for the external cuneiform, and elsewhere it is rough and ligamentous. The anterior and posterior surfaces are triangular and covered by cartilage, the former articulating with , the second metatarsal, and the latter with the navicular. They I are distinguished from each other in the following manner : the i anterior surface is convex, whilst the posterior is concave; the ; apex of the anterior surface is more pointed than that of the pos- 262 A MANUAL OF ANATOMY terior ; and the posterior surface is rather broader than the anterior, and has one of the limbs of the L facet close to it. Articulations. — Posteriorly with the navicular, anteriorly with the second metatarsal, internally with the internal cuneiform, and externally with the external cuneiform. The external cuneiform bone, like the middle, lies with the broad end of the wedge upwards, and it supports the third metatarsal. The dorsal surface is rough, quadrilateral, and elongated from before backwards. The plantar surface, also rough, is narrow, and gives insertion to a slip of the tendon of the tibialis posticus. The internal surface presents a vertical facet posteriorly for the middle cuneiform, and two semi-oval facets anteriorly for articiilation with the proximal pair of facets on the outer side of the base of the second metatarsal. The remainder of the surface is rough and ligamen- tous. The external surface has a large, almost circular, facet near the postero-superior angle for the cuboid, and there may be a For 2nd Metatarsal .Posterior Surface for Navicular For Middle Cuneiform — ^For 2nd Metatarsal For 4th Metatarsal (inconstant) __For Cuboid ■Anterior Surface for 3rd Metatarsal Fig. 154. — The Right External Cuneiform Bone. A, Internal View ; B, External View. small semi-oval facet at the antero-superior angle for the inner sid< of the base of the fourth metatarsal, but this facet is not constant Elsewhere the surface is rough and ligamentous. The anterio\ and posterior surfaces are triangular, and covered by cartilag the former articulating with the third metatarsal, and the latt with the navicular. They are distinguished from each other in th following manner : the anterior facet is deeper than the posterior and its apex is more pointed ; the cartilage of the anterior surface extends over its entire length, but the lower part of the posterior surface is non-articular ; the anterior facet is slightly concavo- convex from below upwards, but the posterior is concave, and it has the large, almost circular, facet on the external surface con- tiguous to it. Articulations. — Posteriorly with the navicular, anteriorly with the third metatarsal, internally with the middle cuneiform and outer side of the base of the second metatarsal, and externally with the cuboid, and, it may be, with the inner side of the base of the fourth metatarsal. THE BONES OF THE LOWER LIMB 263 Structure of the Cuneiform Bones. — ^The structure of each is that of a short bone. \\'hen the cuneiform bones are in position their posterior surfaces are on the same transverse plane, but the anterior surfaces of the Dorsal Aspect For 4th Metatarsal (inconstant) Anterior Surface of External' Cuneiform for 3rd Metatarsal ' For 2nd Metatarsal' I Anterior Surface of Internal i Cuneiform for ist Metatarsal 'For 2nd Metatarsal Anterior Surface of Middle Cuneiform for 2nd Metatarsal Fig. 155. — The Right Cuneiform Bones (Axtero-scperior View). internal and external project farther forwards than that of the middle. In this manner a recess is formed, into which the base of the second tnetatarsal bone is received. The Cuboid Bone. The cuboid bone is characterized by its irregularly cubical shape, and by the groove and ridge on its plantar aspect. It is situated on the outer border of the foot, where it lies between the os calcis and the fourth and fifth metatarsal bones. The anterior surface has its cartilage divided by a vertical ridge into two facets — an inner quadrilateral for the fourth metatarsal, and an outer triangular for the fifth metatarsal. The posterior surface presents a large, somewhat triangular, facet, narrow towards the sole and deep in- ternally, which is convex from above downwards and outwards, and concave from side to side. It articulates with the os calcis, and its internal and inferior angle, called the calcaneal process, projects backwards for a little beneath that bone. Below and inside the calcaneal process there may be a facet for the head of the astragalus. The internal surface, which is extensive and vertically disposed, presents a large, almost circular, facet for the external cuneiform, near the centre and extending to the dorsal surface. Behind this, and usually continuous with it, there may be a small facet for the navicular, the remainder of the surface being rough and ligamentous. The external surface, which is really a 264 A MANUAL OF ANATOMY border, is very short and narrow, and presents a notch leading to the peroneal groove on the plantar surface. The dorsal surface is rough, and is directed upwards and outwards. The plantar surface presents in front the deep peroneal groove, which is directed inwards and forwards, and lodges the tendon of the'peroneus longus. Behind the groove is a stout, oblique ridge for the long plantar ligament. This ridge becomes enlarged externally into a tubercle, which is covered by cartilage on its anterior and outer aspects for the play of the sesamoid cartilage, or bone, usually present in the tendon of the peroneus longus. The surface behind the ridge gives attachment to the short plantar ligament, a slip of the tendon of the tibialis posticus, and some fibres of the flexor brevis hallucis, but the latter may spring from the internal surface. Dorsal Surface I Posterior Surface for , Os Calcis Calcaneal Process For 4th Metatarsal - For External Cuneiform Posterior Surface for Os Calcis Fig. 156. — The Right Cuboid Bone. A, External View ; B, Internal View. Articulations. — Posteriorly with the os galcis, anteriorly with the fourth and fifth metatarsal bones, internally with the external cuneiform, and sometimes with the navicular, and at the lower and inner angle occasionally with the astragalus. Structure. — ^The structure is that of a short bone. The tarsus as a whole is convex superiorly, and concave interiorly, from before backwards as well as from side to side. The part in front of the astragalus and os calcis constitutes the instep, and the entire tarsus forms two columns — an inner, comprising the astrag- alus, navicular, and three cuneiform bones, and an outer, representing the OS calcis and cuboid. Varieties. — The number of tarsal bones is sometimes increased to eight, \vhich is brought about in one or other of the following ways : (i ) the external tubercle on the posterior border of the astragalus may form a separate ossicle, called the 05 trigonum : {2) the tuberosity of the navicular may form a THE BONES OF THE LOWER LIMB 265 separate ossicle ; (3) the internal cuneiform may be divided into two parts, dorsal and plantar ; or (4) there may be an additional ossicle in the space at the antero-intemal part of the os calcis, or between the internal cuneiform and the second metatarsal. Ossification. — The tarsal bones ossify in cartilage, each from one centre, (except the os calcis, which has one primary, and one secondary, centre), and at the following periods approximately : Os calcis, 6th month (intra-uterine). External cuneiform, ist year. Astragalus, 7th month (intra-uterine). Internal cuneiform, 3rd year. Caboid, 9th month (intra-uterine). Middle cuneiform, 4th year. Navicular, 4 th year. For the secondary centre of the os calcis, see page 258. The external tubercle on the posterior border of the astragalus has some- times a secondary centre, and then it remains separate as the os trigonum. The Metatarsus. The metatarsus is composed of five long bones, which are named nuiherically from within outwards, that of the great toe being the first. Each bone is di\'isible into a shaft and two extremities, proximal and distal. The shaft, which is triangular, is massive in the first, slender and much compressed laterally in the second, third, and fourth, and compressed from above downwards in the fifth. Each shaft, except that of the first, is longitudinally convex on its dorsal aspect, and they are all longitudinally concave on their plantar aspects. The shaft presents three borders and three surfaces. In the outer four bones the borders are two lateral, and a plantar. The lateral borders, external and internal, extend from the sides of the proximal end or base, close to the dorsal aspect, to the dorsal tubercle on either side of the distal end or head, and their outline is sharp. The plantar border, rotmd behind, but sharp in front, extends from the centre of the plantar aspect of the base forwards in the middle line to near the head, where it bifurcates, the divisions passing to the comua on the plantar aspect of the head. The dorsal surface lies between the external and internal borders, and is narrow. Each lateral surface is situ- ated between the lateral and plantar borders. The lateral surfaces, which are extensive and sloped, boiuid the interosseous spaces, and give attachment to the interosseous muscles. The shaft of the first metatarsal has its borders disposed as supero- external, infero- extemal, and internal. The dorsal surface is convex, and is directed upwards and inwards. The plantar surface is concave, and sup- ports the tendon of the flexor longus, and the flexor brevis hallucis. The external surface, which is practically vertical, is narrow in front, but wide behind. The heads of the four outer metatarsal bones are much compressed laterally. The cartilage is prolonged more on the plantar than on the dorsal aspect, and in the former situation it ends in a concave 266 A MANUAL OF ANATOMY border, surmounted at either side by a prominent cornu . On either side the head presents a dorsal tubercle and plantar depression for the lateral metatarso- phalangeal ligament. The head of the first metatarsal is of large size, and elongated transversely. On its plantar aspect it presents two well-marked grooves, separated by a median antero-posterior ridge, forr the sesamoid bones in the heads of insertion of the flexor brevis hallucis. The bases of the metatarsal bones articulate with the tarsus and with each other, except, as a rule, in the case of the first, and they present distinctive characters in each case. First Metatarsal Bone. — This supports the great toe, and is the thickest and most massive of the series. The base is of large size, and presents a concave reniform surface, with the concavity out- Head -^Grooves for Sesamoid Bones External Surface For 2nd Metatarsal (inconstant) , Plantar Surface Medullary Foramen For Tibialis Amicus For Peroneus Longus Tuberosity Fig. 157. — The First Right Metatarsal Bone (Plantar View). wards, for the internal cuneiform. Inferiorly it presents a pro- jection, called the tuberosity, which gives insertion, by its outer aspect, to the principal part of the tendon of the peroneus longus, and by its inner aspect to a slip of the tendon of the tibialis anticus. There is usually no facet on its outer surface, but sometimes it presents one for the second metatarsal, and it always gives origin to the inner head of the first dorsal interosseous. Articulations. — Posteriorly with the internal cuneiform, and some- times externally with the second metatarsal ; anteriorly with the first phalanx of the great toe ; and inferiorly with the two sesamoid bones. Second Metatarsal Bone. — ^This supports the second toe. Its base is wedge-shaped, with the broad end upwards. It recedes between the internal and external cuneiform bones, and posteriorly THE BONES OF THE LOWER LIMB 207 presents a concave triangular facet for the middle cimeiform. On the inner side, close to the dorsal aspect, there is a small facet for the internal cimeiform, and sometimes there is an additional facet, below and in front of this, for the first metatarsal. The outer side presents two facets, dorsal and plantar, separated by a rough antero- posterior groove, each of these being subdivided by a vertical ridge into two semi-oval facets. There are thus four facets in all — Dorsal Tabercl< Plantar Depressionr' External Surface— Medullary Foramen—-- • For 3rd Metatarsal-' Internal Smface .. For ist Metatarsal (inconstant) - For Internal Cuneiform For External Cuneiform For Middle Cuneiform Fig 158. — The Second Right Metatarsal Bone. A, Extemkl View ; B, Internal View. a posterior pair for the inner side of the external cimeiform, and an anterior pair for the inner side of the base of the third metatarsal. The plantar surface of the base gives insertion to a slip of the tendon of the tibialis posticus, and origin to a portion of the adductor obliquus hallucis. The shaft gives partial origin to the first and second dorsal interossei. Articulations. — Posteriorly with the middle cuneiform, internally with the internal cuneiform, and sometimes with the first metatarsal, externally with the external cuneiform and third metatarsal, and anteriorly with the first phalanx of the second toe. Third Metatarsal Bone. — ^This supports the third toe. The base resembles in shape that of the second, the broad end being upwards. Posteriorly it presents a triangular facet, concavo-convex from above downwards, for the external cuneiform. The iimer side of 268 A MANUAL OF ANATOMY the base presents two semi-oval facets, dorsal and plantar, separ- ated by a rough antero-posterior groove, for the anterior pair of facets on the outer side of the base of the second metatarsal. On the outer side there is a large semi-oval facet, dorsally placed, for the inner side of the base of the fourth metatarsal. The plantar surface of the base gives insertion to a slip of the tendon of the tibialis posticus, and origin to a portion of the adductor External Surface Medullary Foramen- For 4th Metatarsal.. -.Internal Surface V For and Metatarsal For External Cuneiform Fig. 159. — The Third Right Metatarsal Bone. A. External View ; B, Internal View. obliquus hallucis. The shaft gives origin to the first plantar interosseous, and partial origin to the second and third dorsal interossei. Articulations. — Posteriorly with the external cuneiform, internally with the second metatarsal, externally with the fourth metatarsal, and anteriorly with the first phalanx of the third toe. Fourth Metatarsal Bone. — ^This supports the fourth toe. The base is quadrilateral, and is somewhat broader above than below. Posteriorly it presents a quadrilateral facet for the cuboid. On the inner side there is a large semi-oval facet for the third meta- tarsal, and this is sometimes prolonged to the extremity of the base, thus forming an additional facet for the outer side of the external cuneiform. On the outer side there is a large semi-oval facet, dorsally placed, for the inner side of the base of the fifth metatarsal, and below this there is a deep rough groove. The plantar surface of the base gives insertion to a slip of the tendon THE BONES OF THE LOWER LIMB 269 of the tibialis posticus, and origin to a portion of the adductor obliquus hallucis. The shaft gives origin to the second plantar External Sur&oe -- Medullary Foramen .Jbitemal Surface _ .&. - For 3rd Metatarsal For External Cuneiform (inconstant) For 5th Metatarsal For Cuboid Fig. 160. — The Fourth Right Metatarsal Bone. A, External view; B, Internal view. interosseous, and partial origin to the third and fourth dorsal interossei. Articulations. — Posteriorly with the cuboid, infernally with the third metatarsal, and sometimes with the external cuneiform, externally with the fifth metatarsal, and anteriorly with the first phalanx of the fourth toe. Fifth Metatarsal Bone. — ^This supports the little toe. The base is elongated from side to side, and compressed from above down- wards. Its leading characteristic is a stout, mammillary process, situated on its outer aspect, called the tuberosity, which is directed outwards and backwards, and gives insertion to the tendon of the peroneus brevis. The posterioi surface presents a triangular facet for the cuboid, the plane of which is inclined inwards and forwards. This facet does not encroach upon the tuberosity. The inner sur- face presents a large semi-oval facet for the outer side of the base of the fourth metatarsal. The dorsal surface, which is rough and slightly convex, gives insertion, as a rule, to the tendon of the per- oneus tertius. The plantar surface, which is rough and concave, gives origin to the flexor brevis minimi digiti. The shaft gives origin to the third plantar interosseous, and partial origin to the fourth dorsal interosseous. Articulations. — Posteriorly with the cuboid, internally with the fourth metatarsal, and anteriorly with the first phalanx of the little toe. Each metatarsal bone presents a medullary foramen, that of 270 A MANUAL OF ANATOMY the first and second, and usually that of the third and fourth, being situated on the outer side of each shaft, whilst that of Internal Surface Medullary Foramen For 4th Metatarsal Dorsal Surface For Peroneus Tertius Tuberosity for Peroneus Brevis For Cuboid Fig. 161. — The Fifth Right Metatarsal Bone (Supero-internal View). the fifth is situated on the inner side.* The foramen of the first and the canal to which it leads are directed downwards towards the head or distal end, but that of each of the other four is directed For Middle Cuneiform For Internal Cuneiform \ For External Cuneiform A\ For Cuboid TuberoMty Tuberosity Fig, 162. — The Bases of the Right Metatarsal Bones (Posterior View). Upwards towards the base or proximal end. The first metatarsal receives its nutrient artery from the arteria magna or princeps hallucis, the second from the fourth digital artery, the third usually * Of 100 third, and an equal number of fourth, metatarsal bones examined, 73 third metatarsals had the medullary foramen on the outer side, and 27 on the inner side ; and 60 fourth metatarsals had it on the outer side, and 40 on the inner side. THE BONES OF THE LOWER LIMB 271 from the third digital, and the fourth and fifth from the second digital artery. Structure. — ^The structure is that of a long bone. Varieties. — (1) The tuberosity on the outer side of the base of the fifth metatarsal, or the tuberosity on the plantar surface of the base of the first, may form a separate ossicle. (2) An additional ossicle is sometimes met -with between the bases of the first and second metatarsals. The metatarsus as a whole is convex on its dorsal aspect from side to side, and also longitudinally. The transverse convexity is due to the broad ends of the bases of the second, third, and fourth metatarsals being directed upwards. On its plantar aspect it is concave from side to side, and also longitudinally. All five bones are nearly parallel with each other, being slightly divergent in front. The interosseous spaces are as in the hand, the first being the innermost. The Phalanges. The phalanges are fourteen in number — three to each of the four outer toes, and two to the great toe. The toes, from within out- wards, are called great toe or hallux, second, third, fourth, and fifth or httle toe. In their general characters the phalanges so closely resemble those of the hand that a detailed description is unnecessary. The phalanges of the great toe, called proximal and distal, are characterized by their large size and great length, which, with the length of the first metatarsal bone, places, the great toe on a level with those next it. The first phalcinx of the four outer toes is characterized by being slender, and much compressed from side to side over its shaft, the proximal end being of large size, and almost triangular. The second phalanx is short, and compressed from above downwards. The ungual phalanx is very small. Fig. 163. The Phal.\xges of THE Second Toe (Plaxt.\r View). Special Moseular Attachments. — The base of the proximal phalanx of the great toe, which presents a tubercular enlargement at either side, gives insertion internally to the abductor hallucis and inner head of the flexor brevis hallucis ; externally, to the outer head of the flexor brevis hallucis, adductor obUquus hallucis, and adductor transversus hallucis ; and on its dorsal surface there is a rough transverse ridge for the innermost tendon of the extensor brevis digi- torum. The base of the ungual phalanx of the great toe gives insertion, on its dorsal surface, to the extensor proprius hcdlucis, and, on its plantar surface, to the flexor longus hallucis. The base of the first phalanx of the second toe gives pcirtial insertion internally to the first dorsal interof?seous, and externally to the second dorsal interosseous. The base of the first phalanx of the third toe gives partial insertion internally to the first plantar interosseous, and eactemally to the third dorsal interosseous. The base of the first phalanx of 272 A MANUAL OF ANATOMY the fourth toe gives partial insertion internally to the second plantar inter- osseous, and externally to the fourth dorsal interosseous. The base of the first phalanx of the fifth toe gives partial insertion internally to the third plantar interosseous, and externally insertion to the abductor minimi digiti and flexor brevis minimi digiti. The second and ungual phalanges of each of the four outer toes give insertion to extensor and flexor tendons, as in the case of the corresponding bones of the four inner fingers. The medullary foramen and the canal to which it leads are, in each phalanx, directed towards the distal end. The nutrient arteries are derived from the corresponding plantar digital arteries. Structure. — The structure of each phalanx resembles that of the corresponding bone in the hand. Varieties. — Ankylosis of the ungual and second phalanges of the fifth toe is of frequent occurrence, and may even involve those of other toes, up to and including the second. Sesamoid Bones. — These are two in number, and are of large size. They are associated with the two heads of insertion of the flexor brevis hallucis, and lie on the plantar aspect of the head of the first metatarsal bone. Appears in the loth Year, and joins at i6 Appears at 6th Month ,J (intra-uterine) gth Month (intra-uterine) I St Year 7th Month (intra-uterine). 4th Year 4th Year 3rd Year Appears between 4th and 8th Year and joins about 19 gth Week (intra-uterine) Appears between 4th and 8th Year and joins about 19 Same as for Metatarsals :} Epiphysis Primary Centre Fig. 164. — Ossification of the Bones of the Foot. Ossification of Metatarsal Bones and Phalanges. — Each bone ossifies in cartilage from one primary, and one secondary, centre, which closely agree with those of the corresponding bones of the hand in their disposition. The primary centres for the shafts appear about the ninth week of intra-uterine life, whilst the secondary centres appear between the fourth and eighth year. Each epiphysis joins its shaft about the nineteenth year. THE BONES OF THE LOWER LIMB 273 Tuber Calcts Os Calcis (Neck) - Tubercle for Middle Fasciculus , of External Lateral Ligament Peroneal Spine or Ridge _. Extensor Brevis Digitonim-- --l--^- Cuboid Peroneus Brevis. Peroneus Tertius • External Cuneiform - Extensor Longus Digitorum "^- — Astragalus Navicular (Scaphmd) - Groove for Tibialis Aoticus - Internal Cuneiform- •- Middle Cuneiform Innermost Tendon of Extensor Brevis Uigitorum - Extensor Proprius Hallucis Fig. 165.— The Right Foot (Dorsal Surface). 18 274 A MANUAL OF ANATOMY The Foot as a Whole. The foot presents two surfaces — •dorsal and plantar — two borders — inner and outer — and two extremities — anterior and posterior. The dorsal or superior surface is arched, both longitudinally and transversely, and the superior surface of the astragalus constitutes its summit. The astragalus is the only bone of the tarsus which articulates with the tibia and fibula. The plantar surface is concave, both longitudinally and trans- versely, in conformity with the longitudinal and transverse arches. When an articulated foot is placed upon a table, with the plantar surface downwards, the parts in contact with the table are as follows: Posteriorly, the internal and external tubercles on the plantar aspect of the tuber calcis, and anteriorly the heads of the metatarsal bones. The plantar surface presents important projections and grooves, which will be enumerated, as nearly as possible, in order from behind forwards. 1. The internal and external tubercles on the plantar aspect of the tuber calcis. The internal tubercle gives attachment to the following struc- tures : (i) Internal division of plantar fascia (part of). (2) Central division of plantar fascia. (3) Outer head of abductor hallucis (part of). (4) Flexor brevis digitorum (part of). (5) Abductor minimi digiti (part of); The external tubercle gives attachment to the following struc- tures : (i) Outer division of plantar fascia. (2) Abductor minimi digiti (part of). 2. The anterior tubercle of the os calcis, which gives attachment to the short plantar ligament. 3. The sustentaculum tali of the os calcis, close to the inner border i of the foot, which is grooved inferiorly for the tendon of the flexor longus hallucis, the groove being continuous with that on the pos- terior border of the astragalus. Anteriorly, the sustentaculum talij gives attachment to the inferior calcaneo-navicular or spring liga-| ment. 4. The tuberosity of the scaphoid or navicular hone, close to the inner border of the foot, which gives insertion to the principn' portion of the tendon of the tibiahs posticus. 5. The spring tubercle on the plantar surface of the naviculai hone, for the spring hgament. 6. The eminence on the plantar surface of the internal cuneifori' hone, close to the inner border of the foot, for a slip of the tendo. of the tibialis posticus. THE BONES OF THE LOWER LIMB 275 Tuber Calcis Outer Head of Abductor Hallucis Flexor Brevis Digitonini Inner Head of Flexor Accessorius Sustentaculum Tali Tibialis Posticus _ Peroneus Longusv,^ Tibialis Anticut^rfcT Abductor Hallucis and Inner Head of Flexor Brevis Hallucis Outer Head of Flexor - Bre\-is Halhicis. Adduc- tor Obliquus Hallucis. and Adductor Trans- versus Hallucis Flexor Longus Hallucis '' Abductor Minimi Digiti Outer Head of Flexor Accessorius Fkzor Brevis Hallucis Tuberosity of 5th .. Metatarsal and Peroneus Brevis ■ - Flexor Brevis Minimi Digiti Adductor Obliquns Hallucis — . Abductor Minimi Digiti and Flexor Bre\-is Minimi Digiti ; Flexor Brevis Digitormn Flexor Longtis Digitorum Fig. 166— The Right Foot (Plantar Surface). 276 A MANUAL OF ANATOMY 7. The peroneal ridge on the outer surface of the os calcis, above which is the groove for the peroneus brevis, whilst that for the peroneus longus is below it. 8. The peroneal notch and groove on the outer border and plantar surface of the cuboid bone for the tendon of the peroneus longus. The ridge behind the groove gives attachment to the long plantar ligament. 9. The tuberosity on the plantar aspect of the proximal end or base of the first metatarsal bone, which gives insertion internally to a sUp of the tendon of the tibialis anticus, and externally to the main part of the tendon of the peroneus longus. (A slip of the latter tendon is inserted into the lower and anterior part of the external surface of the internal cuneiform bone.) The inner or tibial border of the foot is in line with the great toe, or hallux. It is constructed by the os calcis, astragalus, navicular, internal cuneiform, the first metatarsal, and the phalanges of the great toe. The sustentaculum tali of the os calcis, the tuberosity of the navicular bone, and the eminence on the plantar surface of the internal cuneiform bone, pertain to this border. The internal surface of the internal cuneiform bone presents an oblique groove, directed downwards and forwards, for the tendon of the tibiahs anticus, the principal part of which is inserted into an impression at the lower and posterior part of the groove. The outer or fibular border of the foot is in hne with the Httle toe. It is constructed by the os calcis, cuboid, fifth metatarsal, and the phalanges of the little toe. Its markings, enumerated from behind forwards, are as follows: 1. The tubercle for the middle fasciculus of the external lateral ligament of the ankle-joint, situated about the centre of the outer surface of the os calcis. 2. The peroneal ridge, situated a little below and anterior to the preceding tubercle, and lying between two grooves. The upper groove transmits the tendon of the peroaeus brevis, and the lower groove transmits the tendon of the peroneus longus, whilst the ridge gives attachment to the fibrous septum, which separates the two peroneal sheaths. 3. The peroneal notch, situated on the outer border of the cuboid bone, and leading to the peroneal groove, on the plantar surface of the bone, for the tendon of the peroneus longus. 4. The tuberosity on the outer side of the proximal end or base of the fifth metatarsal bone, which gives insertion to the tendon of the peroneus brevis. (The peroneus tertius is usually inserted into the dorsal surface of the base of this metatarsal bone.) The anterior extremity of the foot is formed by the third or ungual phalanges. It is to be noted that the great toe or hallux is almost as long as, and parallel to, the second toe, in which respects it presents a striking contrast to the thumb or pollex. THE BONES OF THE LOWER LIMB 277 The posterior extremity of the foot is formed by the tuber calcis. Posteriorly this tuberosity presents three transverse zones — -upper, for a synovial bursa ; middle, for the insertion of the tendo Achillis ; and lower, for the fat of the heel. The posterior border of the astragalus, though it stops short of the posterior extremity of the foot, may be referred to. The markings which it presents are a groove and two tubercles. The groove, which is directed downwards and inwards, transmits the tendon of the flexor longus hallucis, and leads to the groove on the under aspect of the sustentaculum tali of the os calcis. The external tubercle, of large size, gives attachment superiorly to the posterior fasciculus of the external lateral Ugament of the ankle-joint. The internal tubercle, which is small, gives attachment internally to a few fibres of the internal lateral or deltoid ligament of the ankle- joint. The sinus tarsi or astragalo-calcaneal canal is the obhque tunnel which Ues between the astragalus and the os calcis. Its direction is outwards and forwards, and it is occupied by a strong inter- osseous ligament, within which is the bursa sinus tarsi. For the Arches of the Foot, see p. 577. APPROXIMATE HOMOLOGIES OF THE BONES OF THE LIMBS. Upper Limb. Lower Limb. I. Shoulder Girdle and Pelvic Girdle. Scapula - - - =r Ilium. Coracoid - - - — Ischium. Precoracoid of mono- ^ _ n w tremata and reptUes ) ~ us pubis Clavicle ... Absent. (If, however, the clavicle is the morphological representative of the pre- coracoid of monotremata and reptiles, then it is homologous with the os pubis.) Upper Limb. Lower Limb. Special Homologies of Scapula and Ilium (Flower). Scapula. Ilium. Inferior angle - - = Anterior superior spine. Superior angle - - = Posterior superior spine. Base - - . - = Crest. Axillary border - - - Anterior border. Superior border - - = Posterior border. Supraspinous fossa - = Sacral surface. Infraspinous fossa - = Iliac fossa. Spine and acromion - = Ilio-pectineal line. Subscapular fossa - = Gluteal surface (dorsum ilii). Glenoid cavity - - = Cotyloid cavity. 278 A MANUAL OF ANATOMY I!. Arm, Forearm, Thigh, and Leg. Humerus- - = Femur. Absent - - = Patella. Radius - - = Tibia. Ulna - - = Fibula. Special Homologies of Humerus and Femur. Humerus, Femur. Great tuberosity - - = Small trochanter. Small tuberosity - - = Great trochanter. External epicondyle and \ _ internal condvle capitellum - - -/ ~ internal condyle. Internal epicondyle and \ t-. * i j i trochlea - - - ) = External condyle. III. Hand and Foot. Hand. Foot. Carpus - - - = Tarsus. Metacarpus - - = Metatarsus. Digital phalanges - ~ Digital phalanges. PoUex - - . = Hallux. Homologies of Carpus and Tarsus. Carpus. Tarsus. Scaphoid (except the part re- ^ presented by the embryonic I _ . , , supernumerary cartilage), T ~ ^ raga us. and semilunar - - • - j Cuneiform or pyramidal - - = Os calcis. (The pisiform is generally regarded as the rudiment of a suppressed digit.) The part of the scaphoid ] formed by the embryonic 'r = Navicular or scaphoid, supernumerary cartilage - J (In apes and water- tortoises there is an additional carpal bone, called the OS centrale, which represents the navicular of the tarsus.) Trapezium - - = Internal cuneiform. Trapezoid - - = Middle cuneiform. Os magnum - - = External cuneiform. Unciform - - = Cuboid. ARTHROLOGY An articulation or joint is the connection between two or more parts of the skeleton in the recent condition. In most joints the parts are osseous, but in certain cases cartilage forms the basis. The manner in which the parts are connected and the amoimt of movement allowed between them vary, and joints are accordingly divided into three classes, namely, synarthrosis, amphiarthrosis, and diarthrosis. Synarthrosis. — This is direct union, there being only a small amount of intervening tissue without any joint cavity, and the joint is immovable. There are two varieties of this class — s3mchondrosis and suture. 1. Synchondrosis. — In this joint a thin plate of hyaline cartilage intervenes between the component parts, as, for example, between the diaphysis or shaft and epiphyses of a long bone. It is essentially a temporary joint. 2. Suture. — In this variety the bones are separated by a small amount of fibrous tissue, which is continuous with the peri- osteiun. Such joints are only met with in the skull. There are three forms of suture, called true, false, and grooved. When the margins of the bones present a number of projections with inter- vening depressions, so that they become closely interlocked, the suture is called true. WTien the opposed margins are more or less flat, so that there is merely apposition without interlocking, the suture is spoken of as false \\^en one margin presents a ridge and the other a cleft into which the ridge is received, it is known as a grooved suture. True sutures are of three kinds— serrated, dentated, and limbous. In the serrated suture the margins of the bones are saw-like, as in the frontal suture ; in the dentated suture the margins present projections like teeth, as in the interparietal suture ; and in the limbous suture the margins of the bones are ridged and bevelled so that they overlap, as in the lower and mesial parts of the fronto- parietal suture. False sutures are of two kinds — squamous and harmonic. In the squamous suture the margins are bevelled so that one overlaps the other, as in the squamo-parietal suture. In the harmonic suture the surfaces, which are rough, are in direct apposition, as between 279 28o A MANUAL OF ANATOMY the superior maxillae. In the grooved suture a ridge on one bone is received into a cleft on another. Such a suture is known as schindylesis, and it is exemplified in the articulation between the rostrum of the sphenoid and the vomer. Amphiarthrosis.-;-In this class the opposed surfaces are connected either by a disc of fibro-cartilage, or by an interosseous ligament, and the joint is partially movable. When the connecting medium is a disc of fibro-cartilage the name of symphysis is given to the joint, as between the bodies of the vertebrae, the bodies of the pubic bones, and between the presternum and mesosternum. When the con- necting medium is an interosseous ligament the joint is called syndes- mosis, as in the inferior tibio-fibular articulation. Union by means of an interosseous membrane is also a form of syndesmosis. Diarthrosis. — While there is more or less continuity at a syn- arthrosis and an amphiarthrosis, there is none at a diarthrosis. The articular ends of the bones are free, and the joint is freely movable. The ends of the bones are smooth and polished, being covered by articular cartilage; they are connected by ligaments; and the interior of the joint is lined with a synovial membrane, except over the articular cartilages. This membrane secretes the synovia, which lubricates all parts of the interior. There are five varieties of diarthrosis. 1. Enarthrosis or Ball-and-socket Joint. — In this variety one articular end is spherical, and the other is hollowed into a socket for its reception, as in the shoulder- and hip-joints. 2. Condylarthrosis or Condylar Joint.— This is akin to enarthrosis. One articular end has the form of a condyle, and the other presents a shallow cavity, as in the metacarpo- and metatarso-phalangeal joints. 3. Trochlearthrosis, Ginglymus, or Hinge Joint.— In this variety one articular end has the form of a trochlea or pulley, and the other is so shaped as to adapt itself to it, as in the elbow- and ankle-joints. 4. Arthrodia or Gliding Joint. — In this joint the surfaces are almost plane, or in some cases concavo-convex, as in the joints between the articular processes of vertebrae, and the carpal and tarsal joints Under this variety is to be included the reciprocal or saddle joint, where the articular surfaces are saddle-shaped and mutually adapt themselves to each other, as between the trapezium and the first metacarpal bone. 5. Trochoides or Pivot Joint. — In this joint one articular end forms a pivot, and the other is so arranged as to rotate around it, as between the atlas and the odontoid process of the axis. Ligaments. — These are composed of white fibrous tissue, and, as their name implies, they bind the bones together. At a diarthrosis their chief use is to control movement, the bones being maintained in position by the muscles and atmospheric pressure. At their attach- ments they are intimately associated with the periosteum. When the fibrous tissue is arranged continuously round the joint the ligament is called a capsular ligament. In other cases the tissue is disposed as round cords, and in a third variety it forms flattened bands. ARTHROLOGY 281 Synovial Membranes. — These membranes are so named because they secrete a fluid, viscid Hke white of egg, which is called synovia. They serve to diminish friction and so facilitate movement Their situations are therefore associated with movable structures, such as joints, gliding tendons, and the integument over bony projections. Accordingly there are three kinds of synovial membrane — namely, articular, tendon or vaginal, and bursal. The articular synovial membranes line the interior of diarthrodial joints, except where there is articular cartilage, and they stop at the margin of this cartilage. In some joints they give rise to folds, some of which contain adipose tissue. Such folds are known as Haversian mucilaginous glands. The tendon or vaginal synovial membranes, also known as synovial sheaths, invest those tendons which have to glide within fibrous sheaths. They are met with around the ankle, particularly behind the external and internal malleoli, and upon the palmar aspect of the fingers. The bursal synovial membranes, commonly caUed synovial bursae, are synovial sacs which are situated between the integument or a muscle and some bony projection. They may be deep- seated or subcutaneous. The deep-seated burscB are situated between a muscle, or its tendon, and the contiguous bone,— e.g., the tendon of the biceps brachii and the anterior part of the bicipital tuberosity of the radius. The subcutaneous hurscB are placed beneath the in- tegument, which they separate from some bony projection — e.g., the prepatellar bursa. Stractare. — A synovial membrane consists of connective tissue, which is destitute of an endothelial Uning properly so called. At intervals it may pre- sent scattered groups of branched cells, but these are not endothelial. There are many capillary bloodvessels, and lymphatic vessels are described as being present. The nerves are described as terminating in corpuscles of the nature of end-balls, in a plexiform manner, and in Pacinian corpuscles. Development. — Synovial membranes are developed from the axial mesenchyme of the limb-buds, in the intervals between contiguous bones, which are being formed from that mesenchyme. Interarticular Fibro-carMlages. — These are met with in certain joints either in the form of plates separating the articular ends, or as bands placed around cavities, which they serve to deepen, or around fiat surfaces, which they render concave. They are known as menisci. When the fibro-cartilage takes the form of a plate it is spoken of as an interarticular meniscus. Such occur at the temporo-mandibular, stemo-clavicular, and radio-carpal joints. They act as buffers to break shock, and they compensate for .rregularities of the opposed surfaces. When the fibro-cartilage is iimited to the margin of a cavity, or the circumference of a surface, it is called a marginal meniscus, such as the glenoid ligament of the shoulder-joint, the cotyloid hgament of the hip-joint, and the [Semilunar fibro-cartilages of the kjiee-joint. Movements.— The different kinds of movement at diarthrodial oints are angular, circumduction, rotation, and gliding. 282 A MANUAL OF ANATOMY Angular Movement. — This increases or diminishes the angle between two or more bones. When it takes place in a forward and backward direction, so as to bend or straighten a joint, it is spoken of as flexion and extension. When it takes place laterally, away from or towards the median plane of the body, it is called abduction and adduction. In the case of the hand the median line from or towards which abduction and adduction take place is a line passing through the centre of the middle finger, and in the case of the foot, through the centre of the second toe. Circumduction. — This consists of the four forms of angular movement, occurring successively in such sequence as flexion, abduction, extension, and adduction. It occurs at ball-and-socket and condylar joints, and during the movement a part of the limb describes a cone, the apex of which is formed by the proximal end at the moving joint, whilst the base is described by the distal end. Rotation.- — This is movement of a bone round its axis without much disturbance of its position. It occurs at enarthrodial and trochoidal joints, and also at the knee-joint, which is a ginglymus. Gliding Movement. — This consists of a simple to-and-fro or sliding movement of two articular surfaces, as between the articular surfaces of vertebrae, and at the carpal and tarsal joints. When the gliding is combined with a certain amount of turning or rolling, so as toj bring different parts of the articular surfaces successively intoJ contact in different positions of the joint, the movement is known | as coaptation, as at the femoro-patellar joint. A description of the different articulations will be found in con-| nection with the regions to which they belong. THE UPPER LIMB THE BACK. Landmarks. — ^The middle line of the neck presents a median furrow, called the nuchal groove, which lies over the line of the ligamentum nuchae. It is due to the shortness of most of the cervical spinous processes and the prominence at either side, caused principally by the complexus muscle. At the upper end of this groove the strong bifid spine of the axis may be felt by sinking the finger deeply, but the spines of the third, fourth, and fifth cervical vertebrae cannot be detected, as these fall short of the surface so as to allovv of dorsal flexion of the neck. At the lower end of the groove the spine of the seventh cervical or vertebra prominens can readily be felt, and usually also that of the sixth, and succeeding to these are the thoracic and lumbar spines. The spine of the first thoracic vertebra is, as a rule, the most conspicuous of the series. Along the middle line of the thoracic and lumbar regions there is an elongated furrow, called the spinal groove, which is produced by the promi- nence formed by the erector spinae on either side. This groove is best marked in the lower thoracic and upper liunbar regions, and it subsides about the level of the third sacral spine. The outline of the scapula may be made out, unless in very muscular persons. It will be found to extend from the second to the seventh rib, and the spine and acromion process are usually readily felt. The root of the spine is on a level with the third thoracic spine, and the inferior angle coincides with the seventh rib. The crest of the ihmn can be felt at the lower part of the back, its greatest promi- nence being on a level with the fourth lumbar spine. Fascia. — ^The superficial fascia is thick, graniilar, and fatty, and in it the cutaneous nerves and vessels are met \vith. The deep fascia is thin and membranous, but firm. It contains no fat, and forms sheaths for the muscles. Cutaneous Nerves. — ^These are most readily met with at the level of the deep part of the superficial fascia, and the cutaneous vessels serve as the best guide to them. They are derived from the posterior primary divisions of the spinal nerves, which, with a few exceptions, divide each into an external and internal branch. 283 A MANUAL O^ A N ATOMY In the thoracic region the internal branches of the upper six nerves become cutaneous near the spines of the vertebrae, and then turn outwards in the integument. The branch of the second is character- ized by its great length, and it can be traced well outwards over the scapula. The external branches of the upper six thoracic nerves end in the muscles. The internal branches of the lower six thoracic nerves are muscular, and the external branches become Trapezius Deltoid Cutaneous ^ Nerves ; I of \ .If Back. ,Teres Major —Triceps Latissimus Dorsi _Obliquus Externus Abdominb . Gluteal Cutaneous Branches from first three — j Lumbar Nerves Gluteus Medius Gluteus Maximus Fig. 167. — The Superficial Dissection of the Back. cutaneous along the course of the angles of the ribs. In the lumbai region the internal branches end in the muscles. The externa branches of the first three nerves furnish cutaneous offsets whicl descend over the iliac crest in front of the outer border of tM erector spinae to the gluteal integument, supplying in their cours^ the integument of the lumbar region. The external branches 01 the lower two nerves end in the deep muscles. In all cases thf THE UPPER LIMB 285 distribution of the cutaneous nerves is at a lower level than their origin. The cutaneous arteries which accompany the cutaneous nerves of the thoracic and lumbar regions are derived from the dorsal branches of the intercostal and liunbar arteries. Muscles. Trapezius. — This muscle is so named because, along with its fellow, it presents a four-sided appearance like a table. The two muscles have also a resemblance to a monk's hood or cowl ; hence the name ciwullaris. Origin. — (i) The inner third of the superior curved line of the occipital bone, and the external occipital protuberance ; (2) the ligamentmn nuchae ; and (3) the spinous processes and supra- spinous ligaments of the last cervical, and, as a rule, all the thoracic vertebrae. The origins of the two muscles are markedly tendinous between the second cer\'ical and third thoracic spines, where they give rise to an elliptical area, widest opposite the sixth cer\'ical spine. Insertion.— (i) The posterior border of the outer third of the clavicle; (2) the inner border of the acromion process, and upper lip of the posterior border of the spine, of the scapula ; and (3) the tubercle which projects at the inner end of the upper lip of the spine near the root. The lower fibres end in a special tendon which glides over the triangular surface at the root of the spine, being separated from it by a synovial bursa. Nerve- supply. — (i) The spinal accessory nerve (spinal portion), and (2) branches from the cervical plexus, which are derived from the anterior primary divisions of the third and fourth cervical nerves. The nerves enter the deep smrface of the muscle after passing beneath its anterior border a little above the clavicle, and the spinal acces- sory, having become connected with the spinal nerves, can be traced over nearly the whole extent of its deep surface, where it lies about 2 inches from the spines of the vertebrae. Blood-supply. — ^There is one specially-named artery, called the sup>erficial cervical, which is a branch of the transverse cervical, and, like the nerves, enters the deep surface of the muscle. The upper fibres of the muscle are directed do\^Tiwards, outwards, and forwards ; the middle fibres pass more or less horizontally outwards ; and the lower fibres pass upwards and outwards. Action. — ^The upper fibres, acting from their origin, elevate the outer end of the clavicle and the point of the shoulder. Acting from their insertion they extend the head and incline the neck towards the same side, the face being directed towards the opposite side. The middle fibres a] proximate the scapula to the spine, and the lower fibres draw it downwards and inwards, both of these sets of fibres also producing rotation of the bone, so as to elevate the point of the shoulder. The entire muscle draws the scapula to the spine, and produces a certain amoimt of rotation of the bone, the point of the shoulder being raised, as in the act of shrugging the ; shoulders. 286 A MANUAL OF ANATOMY Ligamentum Nuchae. — This is a fibrous band, or intermuscular septum, which occupies the median line of the neck. Its superficial fibres are attached above to the external occipital protuberance, and below to the spine of the seventh cervical vertebra. Its deep fibres are attached to the external occipital crest, and to the spines of cervical vertebrae from the second to the sixth inclusive. They also extend into the interspinous intervals between the inter- spinales muscles, where they represent interspinous ligaments. Latissimus Dorsi — Origin. — (i) The spinous processes and supra- spinous ligaments of the lower six thoracic vertebrae; (2) the posterior lamina of the lumbar aponeurosis, through means of which it is attached to the lumbar and sacral spines, and the posterior fourth of the outer lip of the iliac crest ; (3) the outer lip of the iliac crest a little behind the centre for about 2 inches ; (4) the outer surfaces of the last three or four ribs external to their angles by fleshy slips, which interdigitate with slips of the obliquus externus abdominis ; and (5) the back of the inferior angle of the scapula, the last origin being inconstant. Insertion. — The floor of the bicipital groove of the humerus about its middle third for about i^ inches. Nerve-supply. — The middle or long subscapular nerve from the posterior cord of the brachial plexus, its fibres being derived chiefly from the seventh cervical nerve. The nerve is only seen during the dissection of the axillary space, and it enters the muscle on its deep aspect. Blood-supply. — Branches of the subscapular artery. The upper fibres of the muscle pass horizontally outwards, and cross the inferior angle of the scapula, which they bind to the chest wall ; the succeeding fibres pass obliquely upwards and outwards ; and those from the iliac crest and lower ribs pass almost vertically upwards. Action. — The arm being raised, the muscle draws it downwards and backwards, producing at the same time internal rotation, as when the hands are crossed behind the back. When the muscle acts from its insertion, it raises the pelvis and trunk after the out- stretched arms, as in the act of climbing a pole. It also elevates the last three or four ribs, as in forced inspiration. At the inferior angle of the scapula the muscle is behind the teres major ; it then winds round the lower border of that muscle; and eventually it is placed in front of it. The lower borders of the tendons of these muscles near their insertions are closely con- nected, but ultimately they become separated, a synovial bursa intervening between the two. Between the upper border of the latissimus dorsi, the lower border of the trapezius, and the base of the scapula, there is a triangular area in which are exposed a portion of the rhomboideus major, the sixth rib, and the sixth intercostal space. Triangle of Petit. — The anterior border of the latissimus dorsi, between the iliac crest and last rib, may or may not overlap the THE UPPER LIMB ' 287 posterior border of the obliquus externus abdominis. If it does not do so, a small space is left, called the triangle of Petit, which is situ- ated immediately above the centre of the iliac crest. It is bounded in front by the posterior border of the obliquus externus abdominis, behind by the anterior border of the latissimus dorsi, and below by the iliac crest near the centre. It is covered only by skin and fascia, and its floor is formed by a part of the obliquus intemus abdominis. In this situation a lumbar hernia may occur, or a lumbar abscess may find its way to the surface. Levator Anguli Scapulae — Origin. — By four tendinous slips from the posterior tubercles of the transverse processes of the first four cervical vertebrae. Insertion. — The base of the scapula from the superior angle to the triangular surface at the root of the spine. Nerve-supply. — Branches of the cerv^ical plexus, which are derived from the third and fourth cervical nerves, and a branch from the nerve to the rhomboids. The muscle is directed downwards, back\vards, and slightly outwards. Action. — Acting from its origin the muscle elevates the superior angle of the scapida, thereby rotating the bone and causing the point of the shoulder to be depressed. Acting from its insertion it is a lateral flexor of the neck. Rhomboideus Minor — Origin. — ^The lower part of the ligamentum nuchjE. and the spines and supraspinous ligament of the seventh cervical and first thoracic vertebrae. Insertion.— The base of the scapula opposite the triangular surface at the root of the spine. Rhomboideus Major — Origin. — ^The spines and supraspinous liga- ments of thoracic vertebrae from the second to the fifth inclusive. Insertion. — ^The base of the scapula from the triangular surface at the root of the spine to the inferior angle. The insertion takes place by means of a tendinous expansion, which is firmly attached near the inferior angle. Elsewhere the expansion is connected with the base of the bone by connective tissue, so that the muscle can be detached to a large extent without injury. Nerve-supply of the Rhomboids. — ^The nerve to the rhomboids, which is a branch of the fifth cervical. This nerve, having pierced the scalenus medius, gives a branch to the levator anguli scapulae, and passes beneath the upper border of the rhomboideus minor about I inch from the base of the scapula. Having given a branch to the deep surface of that muscle, it passes beneath the rhomboideus major and enters its upper part. The direction of the rhomboid muscles is downwards and outwards. Action. — ^The muscles draw the scapula backwards and upwards, and rotate the bone so as to depress the point of the shoulder. Posterior Scapular Artery. — ^This vessel is usually a branch of the transverse cervical, but it may arise from the third part of the sub- 288 A MANUAL OF ANATOMY clavian. It passes backwards beneath the levator anguH scapulae, and then downwards beneath the rhomboid muscles, lying close to the base of the scapula. It gives off branches to the adjacent muscles, and several offsets to the front and back of the scapula, which latter take part in the scapular anastomoses of arteries. At the upper border of the scapula a limited view is obtained of the posterior belly of the omo-hyoid muscle, and the suprascapular artery and nerve. The former arises from the upper border of the bone inside the suprascapular notch, as well as from the supra- scapular or transverse ligament. The suprascapular artery passes to the supraspinous fossa over the ligament, and the suprascapular nerve to the same region beneath it. The artery in this part of its course furnishes its supra- acromial branch to the upper surface of the acromion process. The transverse cervical artery is seen, at a higher level than the suprascapular, dividing into its superficial cervical and posterior scapular branches. The former passes superficial to the jf levator anguli scapulae, and the latter beneath that muscle. It will now be convenient to continue the description of the back to its termination, except the structures more immediately involved in the head and neck. Serratus Posticus Superior — Origin. — The lower part of the liga- mentum nuchae, and the spines and supraspinous ligaments of the last cervical and first two thoracic vertebrae. Insertion. — By fleshy and tendinous slips into the upper borders and outer surfaces of the second, third, fourth, and fifth ribs, external to their angles. Nerve-supply. — The second, third, and fourth intercostal nerves. The origin of the muscle is aponeurotic, and continues so over about half its length. The direction of the fibres is downwards and outwards. Action. — ^The muscle elevates the ribs into which it is inserted, and is therefore a muscle of inspiration. Serratus Posticus Inferior — Origin. — The posterior lamina of the lumbar aponeurosis, through means of which the muscle is attached to the spines and supraspinous ligaments of the lower two thoracic and upper two or three lumbar vertebrae, under cover of the latissimus dorsi. Insertion. — By four fleshy slips into the lower borders of the last four ribs. Nerve-supply. — The ninth, tenth, and eleventh intercostal nerves. The serrations of insertion overlap each other from above down- wards ; the second is the broadest, and the third to a large extent conceals the fourth. The direction of the fibres is upwards and outwards. Action. — (i) To draw backwards and slightly depress the lower four ribs, the effect of which is to increase the capacity of the lower part of the thoracic cavity ; and (2) to steady the lower four ribs, and thus to act as an auxiliary to the diaphragm. In both cases it acts as a muscle of inspiration. THE UPPER LIMB 289 Posterior Lamina of the Lumbar Aponeurosis.— The lumbar aponeurosis is the posterior aponeurosis of the transversahs ab- dominis muscle, and is composed of three laminae — anterior, middle, and posterior, the latter of which is alone fully exposed in this region. It is of considerable strength, and is attached to the spines of the lumbar and sacral vertebrae, and the posterior fourth of the outer lip of the iliac crest. It affords origin to a portion of the latis- simus dorsi and to the serratus posticus inferior, and lies behind the erector spinae, where it forms the posterior wall of its sheath. At the outer border of that muscle it blends with the middle lamina, which may be partially seen by raising the border. Superiorly it is joined by the vertebral aponeurosis. Erector Spirut Transverse Process Posterior l-amina of Ltimbar Aponeurosis Middle lamina of Lombtur Aponeurosis Qoadratus Lumborum Anterior Lamina of Lumbar Aponeurosis Lattssimus Dorsi Body of 3rd Lumbar Vertebra Fascia Transversalis/ Psoas Magnus, covered by Psoas Fascia I ; Obliquus Ext. Abd. I Obliquus' Int. Abdominis I'ransversalis Abdominis Fig. 168. —Diagram of the Lumbar Apokeurosis. Vertebral Aponeurosis. — This is a thin aponeurotic sheet v/hich covers the erector spinae. Its fibres are chiefly arranged trans- versely, being attached internally to the spines of the vertebrae, and externally to the angles of the ribs. Superadded to the transverse fibres there are a few which are longitudinal. Superiorly the aponeurosis passes beneath the serratus posticus superior, and becomes continuous with the deep cervical fascia as that ensheathes the splenius. Inferiorly it blends with the posterior lamina of the lumbar aponeurosis. Splenius. — This muscle is so named because it straps or binds down the muscles beneath it. It is single at its origin, but at its insertion it is divided into two parts — splenius capitis and splenius colli. 19 290 A MANUAL OF ANATOMY Origin. — (i) The lower two-thirds of the ligamentum nuchae, and (2) the spines of the last cervical and first six thoracic vertebrae. Insertion — (a) Splenius Capitis. — (i) The lower part of the outer surface of the mastoid process of the temporal bone, and (2) the occipital bone below the outer third of the superior curved line, in each case under cover of the sterno-cleido-mastoid. (b) Splenius Colli. — ^The posterior tubercles of the transverse processes of the first two or three cervical vertebrae, internal to the levator anguli scapulae, and in line with the cervicalis ascendens. Nerve-supply. — ^The posterior primary divisions of the cervical nerves below the third, and of the upper five thoracic. The direction of the fibres is upwards and outwards. Action. — The muscle extends the head and flexes the neck to its own side, the face being turned to the same side. Erector Spinae. — This composite muscle is single below in the region between the last rib and iliac crest, where it is strongly tendinous internally, and fleshy externally. It subsequently, how- ever, resolves itself into three columns — outer, middle, and inner, there being three muscles in each of the outer and middle columns, and one in the inner column, thus making seven muscles in all. Origin. — (i) The spines of the last two thoracic, all the lumbar, and the upper four sacral vertebrae ; (2) the back of the fourth sacral vertebra ; (3) the posterior sacro-iliac ligament ; and (4) the posterior fifth of the iliac crest. The insertion of the muscle is represented by the columns into which it divides. On approaching the last rib it presents a groove on its surface, which indicates its division at this stage into an outer and inner column, the latter representing the combined middie and inner columns. Outer Column. — ^This column is composed of three muscles, which, from below upwards, are named ilio-costalis, musculus accessorius ad ilio-costalem, and cervicalis ascendens. Ilio-costalis. — ^This is the direct continuation of the outer part of the erector spinae, and it is inserted by fleshy and tendinous bundles into the angles of ribs from the seventh to the eleventh, and into the lower border of the twelfth rib. Musculus Accessorius ad Uio-costalem. — This muscle prolongs the ilio-costalis from the lower six to the upper six ribs. It arises by tendons, internal to the slips of insertion of the ilio-costalis, from the angles of ribs from the seventh to the eleventh, and from the outer surface of the twelfth rib, and it is inserted by tendons into the angles of the upper ribs from the second to the sixth, and into the outer border of the first rib external to the tubercle. Cervicalis Ascendens. — ^This continues the musculus accessorius from the upper ribs to the neck. It arises by tendinous slips from the third, fourth, fifth, and sixth ribs, internal to the tendons of insertion of the musculus accessorius, and it is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae, where it is in line with the splenius colli. THE UPPER LIMB 291 Action. — The muscles of the outer column act as extensors and lateral flexors of the vertebral column, and as depressors of the ribs, as in expiration. Middle Column. — This column, like the outer, is composed of three muscles, which, from below upwards, are named longissimus Coraplexus Cervicaljs Ascendens — - Scrratus Posticus Superior Musculus Accessorius —^-JL. Loogissimus Dofsi -, Fig. 169. — The Deep Muscles of the Back. dorsi, longissimus cervicis (transversahs cervicis), and trachelo- mastoid (longissimus capitis). Longissimus Dorsi. — ^This is the direct continuation of the inner part of the erector spinae, and it is inserted in a twofold manner. The inner insertions take the form of round, tapering tendons, which are attached to the accessory processes of the lumbar vertebrae and the extremities of the transverse processes of the thoracic vertebrae. 292 A MANUAL OF ANATOMY The outer insertions are fleshy, and are attached to the backs of the transverse processes of the lumbar vertebrae, and the outer surfaces of the lower ten ribs external to the tubercles. Transversalis Cervicis (longissimus cervicis). — ^This continues the longissimus dor si to the neck. It arises from the transverse pro- cesses of the upper five or six thoracic vertebrae, and is inserted into the posterior tubercles of the transverse processes of cervical vertebrae from the second to the sixth inclusive, where it is internal to the splenius colli and cervicalis ascendens. Trachelo-mastoid (longissimus capitis). — ^This muscle has been so named because it extends from the neck to the mastoid process, and it continues the longissimus dorsi to the head. It arises from the transverse processes of the upper five or six thoracic vertebrae in close connection with the longissimus cervicis, and from the articular processes and capsular ligaments of the lower three cervical vertebrae. Its insertion is into the lower part of the outer surface of the mastoid process under cover of the splenius capitis. Towards its insertion this muscle is very narrow and ribbon-like, and it is marked by a tendinous intersection. Action. — The muscles of the middle column act as extensors and lateral flexors of the vertebral column. They also extend the head and flex the neck to one side, the face being turned to the same side. Inner Column. — ^This consists of the spinalis dorsi, which is intimately associated with the inner part of the longissimus dorsi. It arises from the lower two thoracic and upper two lumbar spines, and it is inserted by tendinous slips into the upper thoracic spines — sometimes the upper four, sometimes as many as the upper eight. Action. — ^This muscle is an extensor of the thoracic portion of the vertebral column. Nerve-supply. — ^The erector spinas and its component muscles are supplied by the posterior primary divisions of the spinal nerves. Between the iliac crest and the last rib the erector spinae is enclosed in a sheath, the posterior wall of which is formed by the posterior lamina of the lumbar aponeurosis, affording origin to the latissimus dorsi and serratus posticus inferior, whilst the anterior wall is formed by the middle lamina of that aponeurosis. On the back of the sacrum its tendon gives origin deeply to fibres of the multifidus spinae, whil t superficially, between the sacrum and the iliac crest, a few fibres of the gluteus maximus arise from it. Complexus — Origin. — (i) The extremities of the transverse pro- cesses of the upper six thoracic and last cervical vertebrae ; and (2) the backs of the articular processes and capsular ligaments of three or four cervical vertebrae above the seventh. The muscle may receive a fleshy slip from the spine of the seventh cervical. Insertion. — The occipital bone between the superior and inferior curved lines, commencing at the crest and extending outwards for about 2 inches. The inner fibres of the muscle are interrupted about the level of the sixth cervical vertebra by an elongated tendinous intersection, having the appearance of a tendon, with a fleshy belly THE UPPER LI2JB 293 at either extremity, from which circumstance this part is known as the biventer cervicis. About the level of the axis the muscle usually presents another faint transverse intersection. Nerve-supply. — (i) The posterior primary division of the first cervical or suboccipital nerve ; (2) the great occipital ; and (3) the posterior primary divisions of cervical nerves below the second. The innermost and longest fibres pass almost vertically upwards. .Trachelo-mastoid V- Tracbelo-niastoid TransTCTsalis Cervicis Semi^Nnalls Colli Semispinal is Dorsi. - ^\^ S^ ^\;\.f:^^-^\0, Longissimus Doisi (turned outn-ards) Fig. 170. — The Middle Column of the Erector Spin^, and the Semispinales Muscles. whilst the outer and upper fibres, which are short, pass upwards and inwards. Action. — To extend the head ind incline it to one side, the face being turned to the opposite side. A small part of the complexus may appear superficially in the upper part of the posterior triangle of the neck, this portion being pierced by the great occipital nerv^e. As high as the axis spine the muscle rests upon the semispinalis colh, and in this situation an arterial anastomosis takes place between the deep cervical of the superior intercostal from the second part of the subclavian and the 294 A MANUAL OF ANATOMY deep branch of the ramus cervicahs princeps of the occipital from the external carotid. Above the level of the axis spine it covers the recti capitis postici and obliqui capitis muscles, and forms the roof of the suboccipital triangle. Semispinalis Dorsi — Origin. — ^The extremities of the transverse processes of thoracic vertebrae from the sixth to the tenth inclusive. Insertion. — ^The spines of the last two cervical and upper four thoracic vertebrae. Semispinalis Colli — Origin. — ^The extremities of the transverse processes of the upper five thoracic vertebrae. Insertion. — The spines of cervical vertebrae from the second to the fifth inclusive. The bundle of fibres inserted into the axis spine is the largest, and the bundles overlap one another from above downwards. Nerve-supply of the Semispinales. — The posterior primary divisions of the cervical and upper thoracic nerves. The fibres of the two muscles are directed upwards and inwards. Action. — ^The muscles are extensors and lateral flexors of the vertebral column. The semispinalis colli and the cervical portion of the semispinalis dorsi also rotate the cervical vertebrae towards the opposite side. Multifidus Spinae. — This muscle lies deeply in the groove by the sides of the spines of the vertebrae. Origin. — (i) The sacral groove, and the deep surface of the tendon of the erector spinae ; (2) the posterior sacro-iliac ligament, and the inner lip of the iliac crest at its back part ; (3) the mammillary tubercles of the lumbar vertebrae ; (4) the transverse processes of the thoracic vertebrae ; and (5) the articular processes of the lower four cervical vertebrae. Insertion. — The spines of the vertebrae from root to tip. The superficial fibres from any given origin pass over three or four vertebrae before taking insertion, the succeeding fibres pass over two or three, and the deeper fibres pass over one. Nerve-supply. — ^The posterior primary divisions of the spinal nerves. Action. — ^The muscle is an extensor and lateral flexor of the spinal column, producing at the same time rotation towards the opposite side in the cervical and thoracic regions. Rotatores Spinae. — These muscles are really the deepest fibres of the multifidus spinae in the thoracic region. They are eleven in number. Origin. — The upper and back part of a transverse process. Insertion. — The lower border of the lamina of the vertebra imme- diately above. Nerve-supply. — ^The posterior primary divisions of the spinal nerves. Action. — To rotate the vertebrae towards the opposite side. Interspinales. — These muscles are usually confined to the cervical and lumbar regions, where they are arranged in pairs between the spines, one on either side of the middle line. In the neck they are limited to the region of the apices of the spines, but in the THE UPPER LIMB 495 lumbar region they extend very nearly over their whole length. In the neck the muscles of each pair are separated by a deep process of the ligamentum nuchae, representing an interspinous hgament, and in the lumbar region they are separated by the interspinous ligaments themselves. Muldfidas Spiiue Levator Costae Rotator Spinae Levator Costs Longior Fig. 171.- -The Multifidus Spin.« and Levatores Costarum Muscles. j Nerve- supply. — Posterior primary divisions of spinal nerves. j Action. — ^To extend the vertebrae. Intertransversales. — ^These muscles occur chiefly in the cervical i and lumbar regions, where they are arranged in pairs in each space. ' In the neck they extend between the anterior and posterior tubercles of adjacent vertebrae. In the liunbar region the muscles of each pair are arranged as lateral and mesial. The intertransversales laterales extend between two given transverse processes, and the 296 A MANUAL OF ANATOMY intertransversales mediates extend from the accessory process of one vertebra to the mammillary process of the vertebra below. Sometimes intertransversales muscles are met with in the lower thoracic region. Nerve-supply. — Posterior primary divisions of spinal nerves. Action. — ^The muscles act as lateral flexors of the vertebral column. Levatores Costarum. — ^These are twelve in number on either side. Origin. — The highest muscle arises from the tip of the transverse process of the seventh cervical vertebra, and the succeeding eleven arise from the tips of the transverse processes of the thoracic verte- brae from the first to the eleventh inclusive. Insertion. — Each muscle is inserted into the outer surface of the rib below, from the tubercle to the angle. In the case of the lower two or three muscles the more superficial fibres pass over the first rib below and take insertion into the next rib, these fibres con- stituting the levatores costarum longiores. Nerve-supply. — ^The intercostal nerves. The muscles are directed downwards and outwards. Action. — ^To elevate the ribs, as in inspiration. Each muscle is somewhat fan-shaped, and contains an admixture of aponeurotic fibres. In direction the muscles coincide with the external intercostals, with which they are closely incorporated by their outer borders. They are covered by the erector spinae, and by their deep surfaces they are related to the external inter- costals. Posterior Primary Divisions of Spinal Nerves. — These nerves in the thoracic region pass backwards, each through a four-sided space bounded below by the neck of a rib, above by the transverse process of the upper vertebra, externally by the superior costo-transverse ligament, and internally by the body of a vertebra. Between the transverse processes each divides into an internal and external branch. The internal branches incline inwards on the superficial surface of the multifidus spinae, and the upper six become cutaneous near the spines of the vertebrae, whilst the lower six end in the deep muscles. The external branches pass outwards beneath the middle column of the erector spinae, and, on reaching the interval between the middle and outer columns of that muscle, they end differently in the upper and lower parts of the back. The upper six end in the deep muscles, but the lower six become cutaneous along the line of the angles of the ribs. In the lumbar region the posterior primary divisions pass backwards, each through a space bounded externally by the quadratus lumborum muscle, internally by the intortransversalis lateralis muscle, and above and below by a transverse process. Their further disposition is as in the thoracic region, but the external branches of the first three only furnish cutaneous nerves, and, as already stated, these are principally gluteal in their distribution. THE UPPER LIMB Zqrj The arteries of the thoracic region are the dorsal branches of the intercostal arteries. Each dorsal branch passes backwards in com- pany with the corresponding posterior primary division of a spinal nerve. Before passing through the quadrangular space it gives off a spinal branch, which enters the spinal canal through the inter- vertebral foramen. After passing backwards it divides into an internal and external branch, which have a distribution similar to those of the nerve. The veins of the thoracic region terminate in the intercostal veins. The arteries of the lumbar region are the dorsal branches of the lumbar arteries. Each accompanies the corresponding posterior primary division of a spinal nerve, and its distribution is as in the thoracic region. The veins of the lumbar region terminate in the inferior vena cava. THE PECTORAL REGION AND AXILLARY SPACE. Landmarks — The outline of the clavicle cind acromion process of the scapula are readily made out, and, in connection with the acromion, it is to be borne in mind that the acromial epiphysis may remain permanently detached from the spine, and so simulate a fracture. The roundness of the shoulder is to be noted, this being due largely to the deltoid muscle, but also in part to the head of the humerus. Below the clavicle, at a point external to its centre, is a depression, called the infraclavicular fossa, which indicates the separation between the deltoid and pectoralis major. \Vhen the arm is abducted and the finger pressed into this hollow, the inner border of the coracoid process will be felt, and, if the finger be carried outwards under the deltoid, the tip of that process can be made out. In this region it is possible to compress the axillary artery against the second rib, but this requires deep pressure. The coinrse of this artery may be indicated by a line dra\NTi from the centre of the clavicle to the inner border of the coraco-brachialis, the arm having been raised to a right angle with the trunk, so as to define clearly the outline of that muscle. The anterior and posterior folds of the axi'la are to be observed, the anterior being formed by the lower border of the pectorahs major, which practically coincides with the line of the fifth rib, and the posterior by the latissimus dorsi winding round the lower border of the teres major. The hollow between these folds indicates the position of the axillary space, and it will be seen to be narrow towards the arm, but wide towards the thoracic wall. In the female the prominence formed by the manunary gland is usually apparent on the surface of the pectorahs major. Its vertical extent is from the second to the sixth rib, and it reaches transversely from the side of the sternum to the anterior fold of the axilla, except at the lower and outer part, where it extends beyond this fold upon the serratus magnus. A little below and internal to the centre of the mammary prominence is the nipple, which is sur- 498 ^ MANUAL OF ANATOMY rounded by a coloured circle, called the areola. The exact position of the nipple is subject to variation. As a rule it may be said to lie over the fourth intercostal space about 4 inches from the mid- sternal line, but in corpulent persons, and in females with pendulous mammae, it is lower in position. Along the middle line the sternum can readily be made out, and about 2 inches below its upper border the transverse ridge, called the sternal angle, may be felt, which is the guide to the second costal cartilage at. either side. Above the centre of the upper border of the sternum is a depression, known as the jugular fossa. Below the lower border of the mesosternum there is the infrasternal depression, which is situated between the seventh pair of costal cartilages, where it lies over the meta- sternum. Cutaneous Nerves. — ^These nerves are arranged in three groups — descending, anterior, and lateral. The descending nerves are branches of the cervical plexus, and are derived from the third and fourth cervical nerves. They are three in number — suprasternal or internal, supraclavicular or middle, and supra- acromial or external — and, as they descend, they lie beneath the platysma myoides. The suprasternal nerve crosses the inner end of the clavicle, and its branches are distributed to the sub- jacent integument, as well as to that over the upper part of the sternmn. The supraclavicular nerve crosses the centre of the bone, and its branches have a fairly wide distribution to the pectoral in- tegument. The supra-aeromial nerve crosses the outer end of the clavicle, and its branches are distributed to the integument over the upper half of the deltoid. The anterior cutaneous nerves are the terminal branches of the upper six intercostal nerves, and they pierce the pectoralis major close to the sternum. They furnish small twigs to the integument over that bone, but the principal part of each nerve takes an out- ward course and supplies the pectoral integument. The branch of the first nerve is sometimes absent. The lateral cutaneous nerves are branches of the intercostal nerves from the third to the sixth inclusive. The first inter- costal nerve gives no lateral cutaneous branch. The lateral cutaneous of the second intercostal nerve is undivided, and crosses the axillary space to the brachial region, under the name of inter- costo-humeral. The succeeding lateral cutaneous nerves emerge from their intercostal spaces by piercing the external intercostal muscles not far from the lower border of the pectoralis major. Each then divides into an anterior and a posterior branch, which pass out between the digitations of the serratus magnus, being separated from each other by a slight interval. The anterior branches wind round the lower border of the pectoralis major to supply the pectoral integument, whilst the posterior branches pass backwards to supply the integument over the anterior border of the latissimus dorsi. The anterior aad lateral cutaneous nerves are accompanied by THE UPPER LIMB 299 corresponding arteries, the anterior being the perforating branches of the internal mammary, and the latered being branches of the intercostal arteries. Fascia. — ^The superficial fascia is continuous ov^er the clavicle \%-ith the superficial fascia of the neck, and it is noteworthy in two respects. - .- -; Intercosto-bumeTal -Additional Intercosto- bninetal Lateral Cutaneoos 12th Thoracic Iliac Branch of Ilio hypogastric Hypc^astric Branch. „ w Ilio-hypogastric i Fig. 172. — Cutaneous Nerves of the Trunk (Antero-lateral View) (after Henle). I-I2. Anterior Cutaneous ; 2-12, Lateral Cutaneous. (In the first place, just below the clavicle it has a faint reddish coloxir, due to the fact that over the cla\-icular portions of the pectoralis major and deltoid it gives origin to fibres of the platysma myoides, which can be seen on incising it. In the second place, in the region of the mammary gland it divides into t\vo laminae, which jensheathe that gland. These laminae send processes into the sub- 300 A MANUAL OF ANATOMY stance of the gland which support its lobes, and from the anterior lamina fibrous bands pass to the integument, these being known as the ligamenta suspensoria of Cooper. Interiorly the superficial fascia is continuous with that over the anterior abdominal wall, and externally it is prolonged over the floor of the axillary space to become continuous with the superficial fascia of the brachial region. The deep fascia is thin and membranous, and it closely invests the pectoralis major. Superiorly it is attached to the front of the clavicle above the origin of that muscle, internally it is fixed to the front of the sternum, externally it is continuous with the deep fascia over the deltoid, and interiorly it joins the axillary fascia at the lower border of the pectoralis major. The axillary fascia is a firm membrane which stretches from the anterior to the posterior fold of the axilla, and forms the floor of that space. It is continuous in front with the deep pectoral fascia, and behind it blends with the deep fascia which ensheathes the latissimus dorsi. Externally it is continuous with the deep fascia of the brachial region, and internally with the fascia covering the serratus magnus. Its upper surface is convex, due to the fact that it receives, near the pectoralis major, the clavi-pectoral fascia, to be afterwards described. In this way the axillary fascia is drawn upwards into the space. It is of considerable strength, and is capable of affording much resistance to the pointing of an axillary abscess in this direction. Mammary Gland. — ^This gland is situated on the surface of the pectoralis major. It is somewhat hemispherical, and extends vertically from the second to the sixth rib, and transversely from the side of the sternum to the anterior fold of the axilla, except below and externally, where it passes over that fold upon the serratus magnus. A little below, and internal to, the centre of the gland is the corrugated nipple, lying in the centre of a coloured circle, called the areola. There is no fat beneath the nipple and areola, and the skin of these parts is provided with plain muscular tissue disposed circularly, which, by its contraction, contributes to erection of the nipple by compressing its veins. The summit of the nipple is perforated by the openings of the lactiferous ducts. The skin of the areola presents a number of small projections due to sebaceous glands, which are known as the glands of Montgomery. The mamma is a compound race- mose gland, which is composed of about twenty lobes, these in turn consisting of lobules, and all being connected by a fibrous stroma. The entire gland is ensheathed by the splitting of the superficial pectoral fascia into two laminae, and these send processes into its interior which support its component lobes. The posterior layer of the sheath is loosely connected to the deep pectoral fascia covering the pectoralis major, and sometimes deep processes of tht gland penetrate into the substance of the muscle. The lobes an pyramidal, and their apices converge toward the nipple. Each oi THE UPPER LIMB 301 Lactiferous Duct' Ampulla'ti'nt them is distinct, and has its own duct. A lobe is made up of lobules, and each lobule is composed of a cluster of tubes, called alveoli or acini, which represent the secreting parts of the gland, and are lodged in spaces known as lociili. The alveolar tubes are lined with cubical epithelium, the cells of which contain fat globules during the period of the functional activity of the organ. The ducts of the lobes are about twenty in number, and are called the lactiferous or galactOphOrOUS duets. Mammilla Areola They are lined with col- umnar epithelium, and, as they approach the nipple, each presents a dilatation, called the sinus or ampulla. There- after each duct becomes narrow, and enters the nipple to terminate by a minute pore on its summit. The mam- mary glands are present in both sexes, but in the male their development, as a rule, is arrested, so that they are in a rudi- mentan^' condition. Bloodvessels of the fig. Mamma. — The arteries are as follows: long thoracic (external mammary) of the second part of the axillary; anterior cutaneous or perforating of the internal mammary; and branches from the intercostal arteries of the spaces over which the gland lies. The veins pass to the axillary and internal mammary veins. Lsrmphatics. — The principal lymphatic vessels of the mammary gland arise in the fibrous stroma, and pass towards the nipple, lying in their course between the galactophorous ducts. In the region around the nipple they terminate beneath the areola in a plexus, called the subareolar plexus. This plexus also receives the cutaneous l^onphatics of the nipple and areola. The efferent vessels from this plexus pass to the antero-internal or pectoral group of axillary glands, more particularly to those on a level with the third rib. ■ There are, however, other paths by which lymph is conveyed I away from the mammary gland, (i) Some IjTnphatics emerge ifrom about the outer two-thirds of the gland, and pass to the Ifedoral group of axillary glands, either directly, or after having [joined the principal honphatics. (2) Other lymphatics (one or 173. — The Female Mamma during Lactation (after Luschka). 302 A MANUAL OF ANATOMY more) emerge from the deep part of the gland. These pierce the pectoralis major muscle, and terminate in one of the infra-clavicular glands. (3) A third set of lymphatics emerge from about the inner third of the gland. These pierce the pectoralis major muscle near the lateral border of the sternum, the anterior intercostal aponeu- rosis, and the interchondral portions of the internal intercostal muscles, after which they terminate in the internal mammary glands, otherwise known as the anterior intercostal or sternal glands. Nerves. — ^These are derived from the supraclavicular branch of the cervical plexus, and the anterior and lateral cutaneous branches of the upper intercostal nerves. Accessory mammae are sometimes met with on the upper, lower, and inner outskirts of the main gland, and more rarely in the axilla, or on the upper part of the anterior abdominal wall. Structure of the Mamma. — The mammary gland belongs to the class of acino-tubular or compound racemose glands. It consists of — (i) glandular tissue, and (2) a fibrous connective-tissue stroma, which together constitute a firm light red mass, known as the corpus mammce. The glandular element is composed of large lobes, varying in number from fifteen to twenty. There is no firm fibrous capsule, such as that possessed by the parotid salivary gland, but the superficial pectoral fascia, within which the mammary gland is embedded, sends inwards fatty processes between the lobes, the supporting fibrous tissue of these processes being continuous with the sustentacular tissue of the gland. Each lobe is tapering in outline, and is provided with its ov.^ duct, the various lobes being disposed in a radiating^ manner from the nipple. ^ A mammary lobe, being large, is made up of smaller lobes, and each small' lobe consists of a group of lobules, the structure of which furnishes the key' to the structure of the entire gland. A mammary lobule consists of from one to three acini, and these have one- duct in common. This duct is one of the radicles of the main duct of a given mammary lobe. The radicle duct breaks up into two or three somewhat dilated excretory passages, the walls of each of which are convoluted. This convoluted character is due to the fact that the walls are distended into a series of pouches, called alveoli, which beset all parts of the wall of the acinus, including its caecal end, thus giving it somewhat of the appearance of a grape — hence the name acinus. The wall of each alveolus consists of a delicate basement membrane, which is invested by capillary bloodvessels, and lined with cubical or short columnar epithelium. From one to three acini, as: stated, constitute a lobule, and they are consequently appendages of a lobular duct. Contiguous lobular ducts unite and form the duct of a small lobe, and the contiguous ducts of small lobes unite, and form the duct of a large lobe.. The number of main ducts corresponds to the number of main lobes — namely, from fifteen to twenty. They are referred to as the lactiferous or galacto-i phorous ducts. The main lactiferous ducts converge towards the nipple. As they lie beneath the areola, each. duct expands into a somewhat spindle-shaped dilatation, called the ampulla or lactiferous sinus, which serves as a reservoir for the milk during lactation. Thereafter the duct becomes narrow, and having traversed the nipple, it opens upon its summit at the bottom of a small depression or foveola. The orifice of the duct is of smaller size than the excretory tube leading to it. The arrangement of orifices at the summit of the nipple may be compared to the arrangement of the orifices of the excretory tubes of the kidney at the apex of a given Malpighian pyramid. The walls of the ducts consist of areolar and elastic tissue, and they are lined with columnar epithelium. The elastic tissue is disposed both longi- tudinally and in a circular manner. THE UPPER LIMB 303 Development of the Mammary Glands. — The mammary glands are of ecto- dermic origin. In the course of the second month of intra-uterine life a circular thickening of the epidermis (ectoderm) makes its appearance in the region of the future gland. This thickening projects into the subjacent mesodermic corium, and the superficial cent? al cells of the thickening becom- ing shed, the thickened area is now depressed. From the deep surface of the thickened ectodermic area solid columns of cells grow into the subjacent mesodermic corium, which give oflE lateral offshoots. These cell columns become hollow, and form the lactiferous or galactophorous ducts, which open upon the area corresponding to the circular thickening of epidermis. The lateral offshoots of the cell columns give rise to the lobes, lobules, and alveoli or acini of the gland. Indeed, each lateral offshoot gives rise to a mammary gland in miniature. The nipple and areola are developed from the glandular area — that is to say, the area of the original thickening of epidermis. The depression of this area disappears, and its central portion becomes elevated to form the nipple. This consists of epidermis, and contains the terminal parts of the lactiferous ducts, bloodvessels, and connective tissue. The remainder of the glandular area forms the areola. The corium corresponding to the nipple and areola is provided with unstriped muscular itssue. The connective-tissue stroma of the gland is developed from the mesoderm of the corium. Pectoralis Major — Origin. — (i) The anterior surface of the clavicle over its inner half, and the anterior stemo-clavicular ligament; (2) one-half of the anterior surface of the sternum as low as the metastemum; (3) the anterior surfaces of the upper six costal cartilages, and slightly from the bony part of the sixth rib; and (4) the upper portion of the external oblique aponeurosis. Insertion. — The outer bicipital ridge of the humerus over its lower three-fourths. The muscle is divisible into two portions, clavicular and sterno- costal, which are separated by a slight interval extending down- wards and outwards from the stemo-clavicular joint. The tendon of insertion is folded upon itself so as to be composed 3f two layers, anterior and posterior, the former of which is the shorter, and both being continuous below. The anterior layer receives the stemo-costal fibres above the third costal cartilage, md it also receives superficially the claviciilar fibres, which latter lescend lowest at their insertion, where they are intimately con- lected with the tendon of the deltoid. The posterior layer receives ill the fibres from the third costal cartilage downwards, and the owest of these fibres, as they pass outwards and upwards, become uccessively folded underneath the fibres above. The result is hat the fibres arising lowest reach the highest part of the posterior :iyer of the tendon, whilst the fibres above these reach its lowest part. The posterior layer ascends higher on the outer bicipital idge than the anterior, and from its upper border a tendinous xpansion passes to the great tuberosity of the humerus and the apsular hgament of the shoulder-joint, which conceals the long "udon of the biceps brachii. From the lower border of the tendon n expansion is given to the deep fascia of the arm. Nerve-stipply. — (i) The external anterior thoracic from the outer jprd of the brachial plexus, (its fibres coming from the fifth, sixth, ad seventh cerviccd nerves), the branches of which nerve enter 304 A MANUAL OF ANATOMY the deep surface of the clavicular and upper sterno-costal portions ; and (2) the internal anterior thoracic, the branches of which enter the deep surface of the sterno-costal portion, after having pierced the pectoralis minor. Blood-supply. — Branches of the thoracic axis. The upper fibres pass downwards and outwards, the middle transversely outwards, and the lower upwards and outwards. Action. — Acting from its origin the muscle adducts the arm, draws it forwards — that is to say, flexes it at the shoulder- joint Clavicular part of Pectoralis Major Clavicular part of Deltoid ^ Coraco-brachialis Sterno-costal part of Pectoralis Major Latissimus Dorsi and Teres Major Biceps Long Head of Triceps Brachialis Anticus Supinator Radii Brevis Bracbio-radialis Obliquus Ext. Abdominis Serratus Magnus Internal Head of Triceps Brachialis Anticus ..Pronator Radii Teres .Flexor Carpi Radial is Palmaris Longus — - Flexor Carpi Ulnaris Fig, 174. — The Superficial Muscles of the Front and Inner Side OF THE Pectoral and Brachial Regions. (by its clavicular portion), and rotates it inwards. Acting from its insertion it raises the trunk after the outstretched arm, as in climbing a pole, and it elevates the upper ribs in forced inspiration. The upper border of the muscle is related to the deltoid, from which it is separated by a triangular interval for a short distance below the clavicle, and the cephalic vein and humeral artery inter- vene between the two. The lower border forms the anterior fold of the axilla. Sometimes there is a muscle, called the sternalis, THE UPPER LIMB 305 present, on one or both sides. It lies over the sternal fibres of the pectorahs major, and is connected below with the external oblique aponeurosis, whilst above it may terminate in the sternal head of the stemo-cleido-mastoid, or on the presternum. Clavi-pectoral Fascia. — ^This is situated beneath the pectoralis major. Superiorly it is disposed in two laminae, which are attached to the anterior and posterior lips of the subclavian groove of the clavicle, and embrace the subclavius muscle. At the lower border of that muscle they unite to form the costo-coracoid membrane, which, on reaching the upper border of the pectoralis minor, divides to ensheathe it. At the lower border of the muscle the two layers unite to form a single sheet, which joins the axillary fascia, and acts as a suspensory ligament. Section of Clavicle Axillary Artery and its Sheath Clavicular Portion of Pectoralis Major (turned up) -Subclavius -Costo-coracoid Membrane . Pectoralis Miwv ■ Lower Portion of Clavi- pectoral Fascia . Lower Portion of Pectoralis Major Axillary Fascia Fig. 175. — Diagram of the Clavi-pectoral Fascia and the Costo-coracoid Membrane. Costo-coracoid Membrane. — This name is given to that portion of the clavi-pectoral fascia which extends from the lower border of the subclavius to the upper border of the pectoralis minor. The lower portion of the membrane is tense and cord-like, and is known Eis the costo-coracoid ligament. It is attached internally to the ipper surface of the first rib at its sternal extremity in connection .vith the tendon of the subclavius, and externally it is attached to :he posterior part of the antero-intemal border and adjacent portion )f the upper surface of the coracoid process. This membrane is »nnected by its deep surface with the axillary sheath ; it is covered >y the clavicular portion of the pectoralis major ; and it is pierced )y the cephalic vein, the thoracic axis, and the external anterior uoracic nerve. 20 3o6 A MANUAL OF ANATOMY The costo-coracoid ligament represents the ventral end of the coracoid bar of cartilage, the dorsal end of which forms the coracoid process. Pectoralis Minor — Origin. — ^The upper borders and outer surfaces of the third, fourth, and fifth ribs near their anterior extremities, as well as from the fascia covering the adjacent external intercostal muscles. Insertion. — ^The anterior half of the antero-internal border of the coracoid process of the scapula and the adjacent portion of its upper surface, where it is intimately connected with the common origin of the coraco-brachialis and short head of the biceps. Nerve-supply. — ^The internal anterior thoracic nerve, which is a branch of the inner cord of the brachial plexus, its fibres being derived from the eighth cervical and first thoracic. The branches of the nerve enter the muscle on its deep surface, and a few of them pierce it to enter the deep surface of the pectoralis major. Blood-supply. — The thoracic axis. The direction of the fibres is upwards and outwards. Action. — Acting from its origin the muscle draws the scapula downwards and forwards, the point of the shoulder being at the same time depressed. Acting from its insertion it elevates the ribs from which it arises, as in forced inspiration. Subclsivius— Origin. — By a rounded, tapering tendon from the upper surface of the first rib and its cartilage. Insertion. — The subclavian groove on the under surface of the clavicle, extending from the rhomboid impression internally to the interval between the conoid tubercle and trapezoid ridge externally. Nerve-supply. — The nerve to the subclavius, which arises from the front of the upper trunk of the brachial plexus, its fibres being derived from the fifth cervical. The nerve descends from the neck behind the clavicle, and enters the deep surface of the muscle. Blood-supply. — The thoracic axis. The direction of the fibres is upwards and outwards. Action. — (i) To depress the clavicle and draw it slightly forwards, and (2) to support the sterno-clavicular joint by bracing the clavicle in an inward direction. Axillary Space. — The axillary space is situated between the upper part of the arm and upper part of the thoracic wall. It has the form of a four-sided p5n-amid, and presents an apex, a base or floor, and four walls — anterior, posterior, inner, and outer. It is of much greater extent towards the thoracic wall than towards the arm, on account of the convergence in the latter direction of the structures forming the anterior and posterior walls. The apex is the narrowest part of the space, and is directed upwards towards the root of the neck. It is somewhat triangular, and lies between the clavicle, first rib, and upper border of the scapula. The base or floor is of considerable extent, and is formed directly by the axillary fascia, which, as stated, is drawn upwards into the space by the clavi- pectoral fascia. The anterior wall is formed over its whole extent by the pectoralis major, and, under cover of this, by the pectoralis THE UPPER LIMB 307 linor over about its middle third. Above the latter muscle the osto-coracoid membrane enters into the anterior wall. The lower (Order of the anterior wall, formed by the pectoralis major, con- titutes the anterior fold of the axilla. The posterior wall is formed rom above downwards by the subscapularis, teres major, and latis- imus dorsi. Towards the arm the tendon of the latissimus dorsi ies in front of the teres major, the latter muscle extending a little ower down. The posterior wall is longer than the anterior, and its Dwer border, formed by the folding of the latissimus dorsi round the eres major to get in front of it, forms the posterior fold of the axilla, rhe inner wall is formed by the upper four or five ribs, with their Qtercostal muscles, and the corresponding serrations of the serratus Brachial Plexus Cejphalic Vein \ Muscnlo-cutaneoas Nerve Deltoid Trapezius Suprascapular Vessels Transverse Cer\-ical Artery Posterior Belly of Omo-hj-oid Scalenus Anticus Stemo-ckido-iiiastcnci ""Clavicle in section I " Snbclavius --Axillary Artery ^- Axillary Vein ^~ Pectoralis Major (cut) 'Pectoralis Minor '\ ^ ' \ \ Outer Head of Median Nerve Nerve of Wrisberp \ N ^ ^ Axillary Vein \ \ Inner Head of Median Nerve Ulnar Nerve Internal Cutaneous Nerve 176. — ^The Axillary Space, after Reflection of the Pectoralis Major, and the Subclavian Triangle. fagnus. The outer wall, which is very circumscribed, is formed by le upper part of the humerus and the common origin of the coraco- rachialis and short head of the biceps. Contents and their Position. — The axillary vessels and the nerves bich arise from the brachial plexus lie for the most part along the iter wall. The thoracic axis and the long thoracic artery pass to le anterior wall, the former above the pectoralis minor, where it erces the costo-coracoid membrane, the latter along the lower irder of that muscle. The subscapular artery lies on the posterior ^all, where it passes inwards on the lower border of the subscapu- ^ris. The posterior circumflex artery lies for a short distance on the 1)sterior wall, but soon passes back\vards between the subscapularis 1 teres major. The anterior circumflex artery passes outwards 3o8 A MANUAL OF ANATOMY in front of the humerus beneath the coraco-brachialis and biceps. The superior thoracic artery is above the thoracic axis, where it takes a course inwards to the thoracic wall. The external anterior thoracic nerve pierces the costo-coracoid membrane to enter the deep surface of the pectoralis m*ajor. The internal anterior thoracic nerve enters the deep surface of the pectoralis minor, and sends branches through it to the major. The posterior thoracic nerve descends upon the inner wall, resting on the serratus magnus. The intercosto-humeral nerve pierces the second intercostal space, and crosses the axilla to the inner side of the arm. Below this nerve, on the thoracic wall, the succeeding lateral cutaneous branches of intercostal nerves pierce the intercostal spaces, and the posterior branch of the lateral cutaneous of the third intercostal gives a branch which crosses the axilla to the inner side of the arm, communicating in its course with the intercosto-humeral. The three subscapular nerves lie upon the posterior wall, and supply the muscles which form it. The circumflex nerve lies with the posterior circumflex artery, which it accompanies in its backward course. The musculo-spiral nerve descends behind the axillary artery, and eventually turns to the back of the humerus, but, before doing so, it gives off its internal cutaneous branch. The median nerve is upon the outer side of the main artery, and the ulnar nerve is internal to it, between it and the vein. The lesser internal cutaneous nerve is on the inner side of the vein, and the internal cutaneous nerve is usually met with partly over the line of the main artery and partly on its inner side. The axillary lymphatic glands are disposed in four groups. The external or humeral glands lie on the outer wall, where they form a chain along the axillary vein. The antero-internal or pectoral glands lie along the long thoracic artery at the lot&er border of the pectoralis minor, resting upon the serratus magnus. The posterior or subscapular glands lie on the posterior wall along the subscapular artery. The central glands are situated towards the base of the space. Axillary Artery. — ^The axillary artery is the continuation of the subclavian, and it extends from the outer border of the first rib to the lower border of the teres major, where it becomes the brachial. When the arm is by the side of the trunk the vessel describes a curve with the convexity upwards, but, when the limb is abducted to the position of a right angle to the trunk, its course is almost straight. Ir the latter position of the limb its course may be indicated by a line drawn from the centre of the clavicle to the inner border of tht, coraco-brachialis. The artery is crossed by the pectoralis minor! and is thus divided into three parts — first, second, and third. | First Part. — The first part extends from the outer border of thtj first rib to the upper border of the pectoralis minor, and it is abon I inch long. Relations. — Anteriorly it is covered by the skin, superficial fascia THE UPPER LIMB 309 origin of the platysma myoides, deep fascia, clavicular part of the pectoralis major, costo-coracoid membrane, axillary sheath, and the lower border of the subclavins when the shoulder is de- pressed. It is also crossed by the cephalic and acromio- thoracic veins, and the commimicating loop between the external and internal anterior thoracic nerv^es. Posteriorly it rests upon the first intercostal space, the first serration of the serratus magnus, and the upper portion of the second rib, with the intervention of g 10 ti 12 13 Long Head of Biceps Tendon of Pectoralis Major Short Head of Biceps Coraco-brachialis Posterior Circumflex Arterj- Deltoid Subscapular Arterj' Musculo-cutaneous Nerve Cephalic Vein Thoracic Axis Pectoralis Minor ao 19 18 17 16 12 Pectoralis Major (Clavicular Portion) 13 Subclavius 14 PectoralLs Major (Sterno- costal Portion) 15 Long Thoracic Artery 16 Serratus Magnus 17 Posterior Thoracic Nerve iS Long Subscapular Nerve 19 Subscapolaris ao Lower Subscapular Nerve 21 Dorsalis Scapulae Artery 22 Intercosto-humeral Nerve 23 Axillary Vein 24 Latissimus Dorsi 25 Teres Major 26 Nerve of Wrisberg 27 Ulnar NeiA-e 28 Axillarj- Artery 29 Median Nerve 30 Internal Cutaneous Nerve Fig. 177. — The Axillary Space. (The Pectoralis Major has been in great part removed.) the axillary sheath, and the posterior thoracic and internal anterior thoracic nerves lie behind it. Externally, and above it, are the three cords of the brachial plexus. Internally, and slightly over- |lapping it, is the axillary vein. Second Part. — The second part lies under cover of the pectoralis minor, and it is about i^ inches long. I Relations. — Anteriorly it is covered by the integument, and the pectoralis major and minor muscles. Posteriorly is the posterior cord 310 A MANUAL OF ANATOMY of the brachial plexus, behind which is a quantity of fat, separating the vessel from the subscapularis. Externally is the outer cord of the brachial plexus. Internally are the inner cord of the brachial plexus, the internal anterior thoracic nerve, and the axillary vein. Third Part. — ^The third part extends from the lower border of the pectoralis minor to the lower border of the teres major, and its length is about 3 inches. The upper half of this part is under cover of the pectoralis major, but the lower half is free from muscular covering, which is due to the posterior wall of the axilla being longer than the anterior. Relations. — Anteriorly over its upper half it is covered by the integument and pectoralis major, and over its lower half only by the integument of the arm. The inner root of the median nerve crosses it obliquely from within outwards, and the external vena comes of the brachial artery crosses it from without inwards. Posteriorly it rests, from above downwards, upon the subscapularis, tendon of the latissimus dorsi, and lower part of the teres major, and the cir- cumflex and musculo -spiral nerves descend behind it. Externally is the coraco-brachialis, which sometimes slightly overlaps it. The outer root of the median nerve lies on its outer side, as does also the musculo-cutaneous. Internally is the axillary vein, and, for a short distance below, the internal vena comes of the brachial artery. Between the axillary vein and the artery are the inner root of the median nerve and the ulnar nerve ; internal to the vein is the lesser internal cutaneous nerve ; and the internal cutaneous nerve is partly on the artery and partly to its inner side. Branches. — The first part gives off the superior or short thoracic, and the thoracic axis or acromio-thoracic artery. The second part furnishes the inferior or long thoracic, and the alar thoracic, which is very inconstant as a separate branch. The third part gives off the subscapular, the anterior circumflex, and the posterior circumflex. Branches of the First Part. — The superior or short thoracic artery is a small branch which arises just below the subclavius. Its course is inwards and downwards behind the axillary vein to the first two intercostal spaces, where it anastomoses with branches of the first and second intercostal arteries. It supplies the adjacent intercostal muscles, upper part of the serratus magnus, and occasionally the pectoral muscles. The thoracic axis or acromio-thoracic artery is a short, but large, trunk which arises immediately above the upper border of the pectoralis minor. Passing straight forwards it pierces the costo-coracoid membrane, and then divides into radiating branches, called thoracic, acromial, humeral, and clavicular. Tlie thoracic branches descend between the two pectoral muscles which they supply. The acromial branches pass outwards over the cora- coid process to the deltoid, in which some of them end, whilst others pierce that muscle, and so reach the upper surface of the acromion process, where they anastomose with branches of the suprascapular and posterior circumflex. The humeral {descending) branch passes THE UPPER UMB 3" downwards with the cephalic vein between the pectoralis major and deltoid, to the contiguous parts of which muscles it is distributed. The clavicular branch passes upwards to end in the subclavius. Branches of the Second Part. — ^The inferior or long thoracic artery, also called the external mammary, is directed downwards and inwards along the lower border of the pectoralis minor to the thoracic wall. It is distributed to the pectoral muscles, serratus magnus, and intercostal muscles, and it sends branches round the lower border of the pectoralis major to the mammary gland. It also gives branches to the pectoral group of axillary glands, and it anastomoses with branches of the aortic intercostals and internal mammary. The alar thoracic artery is distributed to the axillary glands. It is seldom a special branch, its place being usually taken by branches of the long thoracic and subscapular. Branches of the Third Part. — ^The subscapular artery, which is the largest of all the branches of the vessel, arises opposite the lower border of the subscapularis, along which it courses downwcurds and inwards to the lower angle of the scapula, in company with the long subscapular ner\'e, where it anastomoses with the posterior scapular and long thoracic. Besides giving branches to the muscles on the posterior wall, the serratus magnus, and the posterior group of axillary glands, it gives off near its origin a large branch, called the dorsalis scapula. This vessel at once passes backwards through the triangular space bounded above by the subscapularis, below by the teres major, and externally by the long head of the triceps. There- after it winds round the back of the axillary border of the scapula, piercing the origin of the teres minor and groov'ing the bone, and so it reaches the infraspinous fossa beneath the infraspinatus. Here it breaks up into numerous branches, which supply that muscle and the bone, and which anastomose with the suprascapular and dorsal branches of the posterior scapular. As it passes through the tri- angular space it furnishes a ventral branch (infrascapular), which ramifies in the venter of the scapula beneath the subscapularis, and- anastomoses with the ventral branches of the suprascapular and posterior scapular. Before piercing the teres minor it gives off a descending or teres branch, which passes downwards between the teres maj or and minor as far as the lower angle of the scapula, where it anastomoses with the terminal part of the posterior scapular. The dorsalis scapulae sometimes arises directly from the axillary. The anterior circumflex artery, which is of small size, arises from the outer side of the vessel a little below the subscapular and opposite the posterior circumflex. It passes outwards in front of the surgical neck of the humerus, and beneath the coraco-brachiaJis and biceps. On reaching the bicipital groove it gives off an ascend- ing or bicipital branch, which passes upwards in the groove with the long head of the biceps, to be distributed to the shoulder- joint and head of the humerus. Thereafter it continues its winding course to the outer side of the bone, where it anastomoses with the pos- ( terior circumflex. 312 A MANUAL OF ANATOMY The posterior circumflex artery, which is of large size, arises from the back of the vessel a little below the subscapular. Its course is backwards in company with the circumflex nerve through the quadrangular space, which is bounded above by the teres minor (subscapularis in front), below by the teres major, internally by the long head of the triceps, and externally by the surgical neck of the humerus. In its course it winds round the inner and posterior aspects of the neck of the bone, and it furnishes many branches, most of which enter the deep surface of the deltoid. A special acromial branch reaches the upper surface of the acromion process, and there anastomoses with the suprascapular and acromial branches of the thoracic axis. On the outer side of the neck of the bone the artery anastomoses with the anterior circumflex, and in this way an arterial circle is formed which closely embraces the surgical neck. Some of the branches supply the muscles bounding the quadrangular space, and one or two pass downwards between the long and outer heads of the triceps, where they anastomose with the superior profunda of the brachial. The posterior circumflex artery is subject to certain variations, (i) It may arise in common with the sub- scapular. (2) Its origin may be transferred to the superior pro- funda of the brachial, in which case it ascends behind the teres major. (3) It may give off the anterior circumflex, superior pro- funda, or dorsal is scapulae. Varieties of the Axillary Artery. — (i) The subscapular, circumflex, and profunda; of the brachial may arise by a common trunk. (2) The artery may give origin to a large branch, which may be the radial, ulnar, vas aberrans, or the interosseous trunk of the forearm. The part of the axillary artery most accessible for surgical interference is the lower half of the third part, which is covered only by the integument of the arm. Axillary Vein. — ^The axillary vein is the continuation of the basilic vein of the arm. It extends from the lower border of the teres major to the outer border of the first rib, where it becomes the sub- clavian vein. It is of large size, and throughout its entire course it lies to the inner side of the artery. Most of its tributaries corre- spond with the arterial branches, but the following two are specially noteworthy : (i) a little above its commencement it receives the trunk formed by the union of the venae comites of the brachial artery, and (2) below the clavicle it is joined by the cephalic vein. Axillary Sheatli. — The axillary vessels and the brachial plexus of nerves are enclosed in a loose, infundibuliform sheath, which is called the axillary sheath. It is a downward prolongation of the deep cervical fascia, and it blends with the deep surface of the costo-coracoid membrane. It has been compared to the crural sheath of the femoral vessels, but it is in no sense such a defined structure. Brachial Plexus. — ^The brachial plexus is situated in the lower part of the posterior triangle of the neck, behind the clavicle, and in the upper part of the axilla. Its complex formation is rendered simple THE UPPER LIMB 313 by arranging it into four stages, namely, (i) nerve roots, (2) nerve trunks, (3) divisions of nerve trunks, and (4) nerve cords. First Stage. — ^The nerves which form the plexus are the anterior primary divisions of the fifth, sixth, seventh, and eighth cer\'ical, and the greater part of that of the first thoracic. Superiorly the plexus is reinforced by a small descending branch from the fourth cervical, which joins the fifth, and interiorly it is occasionally reinforced by a branch from the second thoracic, which joins the first. As regards the first thoracic nerve, the part of it which does not join the plexus, and which is of small size, enters the first intercostal space to become the first intercostal nerve. The nerves, as they emerge at the side of the neck, are placed between the scalenus anticus and scalenus medius. Second Stage. — The fifth and sixth cervical nerves join at the outer border of the scalenus anticus to form the upper trunk ; the seventh cervical remains meanwhile single, and forms the middle trunk ; and the eighth cervical and greater part of the first thoracic unite between the scalene muscles to form the lower trunk. There are thus three trunks — upper, middle, and lower. Third Stage. — A little above the clavicle each of the three tnmks breaks up into an anterior and a posterior division. Fourth Stage. — ^The anterior divisions of the upper and middle trunks unite to form the outer cord of the plexus ; the anterior division of the lower trunk, which is of large size, forms the inner cord ; and all three posterior divisions (that of the lower trunk being of small size) unite to form the posterior cord. As a variety, the anterior division of the middle trunk may subdivide into two branches, one entering the outer cord and the other the inner. There are thus three cords — outer, inner, and posterior. Branches of the Plexus. — ^The branches are conveniently divided into two groups — supraclavicular, arising above the clavicle and coming from nerve roots and nerve trunks ; and infraclavicular, arising below the clavicle and coming from nerve cords. Supraclavicular Branches. — ^These are as follows : Muscular branches from the four cervical nerves to the scalene muscles and longus colli. One root of the phrenic nerve (inconstant) from the front of the fifth cervical. The Nerve to the Rhomboids. — ^This branch arises from the back of the fifth cervical close to, or along with, the highest root of the posterior thoracic, and it takes a backward course through the scalenus medius. The Posterior Thoracic Nerve or External Respiratory Nerve of Bell. — This branch arises by three roots from the back of the fifth, sixth, and seventh cervical nerves. The upper two roots pierce the scalenus medius below the nerve to the rhomboids, either conjointly or separately, whilst the lowest root passes in front of the scalenus medius, and joins the trunk formed by the others near the first rib. The ner\'e then courses behind the first part of the axillary artery, II 3U A MANUAL OF ANATOMY and subsequently descends upon the axillary surface of the serratus magnus, supplying branches to all its serrations. The Nerve to the Subelavius. — ^This small branch arises from the front of the upper trunk, its fibres being derived from the fifth cervical. It descends over the third part of the subclavian artery, and, passing behind the clavicle, it enters the subelavius muscle on its deep aspect. This nerve sometimes communicates with the phrenic nerve. The Suprascapular Nerve. — ^This is a large nerve which arises To Cervical Plexus 1 To Brachial Plexus^ 4.C. Third Root of Phrenic (inconstant) Nerve to the Rhomboids Nerve to Subelavius \ Suprascapular \ External Anterior Thoracic Circumflex Musculo-spiral Outer Root of Median Musculo-cutaneous Median ' Posterior Thoracic (Ext. Respiratory N. of Bell). First Intercostal i_ ■ Upper or Short Subscapular \ \ "Internal Anterior Thoracic ^. Middle or Long Subscapular > Lower Subscapular \ Nerve of Wrisberg N Inner Root of Median Internal Cutaneous 'Ulnar Fig. 178. — The Brachial Plexus. VeJlow= Spinal Nerves and their Branches; Blue = Trunks; Red = Outer Cord ; Purple = Inner Cord ; Grey = Posterior Cord . from the back of the upper trunk, its fibres being derived from the fifth and sixth cervical. It is directed downwards, outwards, and backwards beneath the trapezius and posterior belly of the omo- hyoid to the upper border of the scapula, on approaching which it gets in company with the suprascapular artery. It is distributed to the supraspinatus, infraspinatus, and shoulder-joint. Infraclavicular Branches.— -Outer Cord. — The branches of this cord are the external anterior thoracic, musculo-cutaneous, and outer root of the median. The external anterior thoracic, which derives its fibres from the THE UPPER LIMB 3i5 fifth, sixth, and seventh cervical, crosses ovei the first part of the axillary artery from without inwards, and gives a branch to the internal anterior thoracic. Thereafter it pierces the costo-cora- coid membrane, and is distributed to the pectoralis major. The musculo-cutaneous or perforating nerve of Casserius, which derives its fibres from the fifth, sixth, and seventh cervical, arises about the level of the pectoralis minor. For a short distance it lies on the outside of the axillary artery, but it soon leaves the vessel, and pierces the coraco-brachialis in a direction dowTiwards and outwards. Before reaching the muscle it parts with a branch to it, which usually enters it in two divisions. The fibres of this branch are derived from the seventh cervical. The subsequent course of the musculo-cutaneous will be described later on. The outer root of the median passes slightly on to the axillary artery, where it is joined by the inner root. Inner Cord. — ^The branches of this cord are the internal anterior thoracic, the lesser internal cutaneous or nerve of Wrisberg, the internal cutaneous, iimer root of the median, and ulnar. The internal anterior thoracic nerve, which derives its fibres from the eighth cervical and first thoracic, passes behind the first part of the axillary artery, and then comes forwards between the artery and the axUlary vein. Having received a branch from the external anterior thoracic nerve, which forms a loop over the first part of the artery, it breaks up into branches which enter the deep surface of the pectoralis minor, a few of them piercing that muscle to enter the deep surface of the pectoralis major. The lesser internal cutaneous or nerve of Wrisberg, which derives its fibres from the first thoracic, is at first placed behind the axillary vein, but subsequently descends on its inner side, where it communi- cates with the intercosto-humeral nerve. This nerve is sometimes absent. The internal cutaneous, which derives its fibres from the eighth cervical and first thoracic, descends partly on the axillary artery and partly to its inner side. The inner root of the median, which is of smaller size than the outer, passes obUquely over the axillary artery, and joins the outer root a little below the lower border of the pectoralis minor. The tnmk of the nerve, which derives its fibres from all the nerves of the plexus, then descends on the outer side of the third part of the artery. The ulnar nerve is the largest bremch of the iimer cord, of which it is the continuation, and it derives its fibres from the eighth cervical and first thoracic. It appears at the lower border of the pectoraHs minor, and then descends, lying deeply between the third part of the axillary artery and the vein. Posterior Cord. — ^The branches of this cord are the three sub- scapular nerves, circumflex, and musculo-spiral. The subscapular nerves are distinguished as upper or short, middle or long, and lower. The upper or short subscapular nerve, 3i6 A MANUAL OF ANATOMY which is of small size, derives its fibres from the fifth and sixth cervical. It is situated high up on the posterior wall of the axilla, and after a short course it enters the upper part of the subscapu- laris. The middle or long subscapular nerve derives its fibres chiefly from the seventh cervical, but to a certain extent also from the sixth and eighth. It descends along with the subscapular artery to the latissimus dorsi, which it supplies. The lower sub- scapular nerve derives its fibres from the fifth and sixth cervical. On approaching the lower border of the subscapularis it breaks up into branches, some of which enter the lower part of that muscle, whilst others pass to the teres major. The circumflex nerve derives its fibres from the fifth and sixth cervical. For a short distance it lies behind the axillary artery, resting on the subscapularis, but, at the lower border of that muscle, it passes backwards through the quadrangular muscular space in company with the posterior circumflex artery. In doing so it furnishes an articular branch to the shoulder- joint, and then breaks up into an upper or anterior and a lower or posterior division. The upper or anterior division accompanies the posterior circumflex artery, and divides into a number of branches which enter the deep surface of the deltoid over its anterior part. Some of the branches, piercing the muscle, supply the integument over about its middle third. The loiver or posterior division gives branches to the posterior part of the deltoid, a branch to the teres minor, and a cutaneous branch, which latter turns round the posterior border of the deltoid to be distributed to the integument over its lower third. The nerve to the teres minor presents a small reddish swelling, which has the appearance of a ganglion, but is really a fibrous thickening. In connection with the distribution of the circumflex nerve Hilton's law may be here stated as follows : a nerve trunk, supply- ing a given joint, also supplies the muscles moving that joint, and the integument covering their insertions. For example, the circum- flex nerve supplies the shoulder- joint, the deltoid, and the integu- ment covering its insertion. This law, however, is not universally applicable. The musculo-spiral nerve is the largest of all the branches of the plexus, and is the continuation of the posterior cord. It derives its fibres from the last four cervical nerves, and sometimes from the first thoracic. It descends behind the third part of the axillary artery, resting upon the subscapularis, latissimus dorsi, and teres major. Whilst in the axillary space it gives off muscular and cutaneous branches. The muscular branches are destined for the long and inner heads of the triceps, those for the long head entering it high up, whilst those for the inner head enter it at different levels. One of the latter, which is remarkable for its length, descends in company with the ulnar nerve to enter the inner head low down, this branch being known as the ulnar collateral nerve (Krause). The internal cutaneous branch usually arises in common THE UPPER LIMB ' 31^ with one of the muscular branches, and it takes a backward course behind the in tercos to-humeral nerve to be distributed to the integument of the back of the arm, reaching nearly as low as the elbow. Intercosto-humeral Nerve. — The intercosto-humeral nerv^e is the undivided lateral cutaneous branch of the second intercostal, and it represents the posterior branch of the other lateral cutaneous ner\'es. Emerging from the second intercostal space it appears between two serrations of the serratus magnus, and then crosses the axillary space. In its course it usually Conununicates with a branch of the posterior division of the lateral cutaneous of the third intercostal, and towards the arm it also communicates with the nerve of Wrisberg and the internal cutaneous of the musculo-spiral. On reaching the arm it is distributed to the integument of the inner and back part over the upper half. Sometimes there is another intercosto-humeral nerve, which is the undivided lateral cutaneous branch of the first intercostal nerve. When this is so the nerve of Wrisberg is absent. The lateral cutaneous nerves have been previously described in connection with the cutaneous nerves of the pectoral region on page 279. It may be stated, in addition, that the posterior branch of the lateral cutaneous of the third intercostal, as a rule, gives a branch across the axiUa to the inner side of the arm, which communicates in its course with the intercosto-humeral, and may largely replace it, if it is small. Axillary Lymphatic Glands. — ^The axillary glands are very numer- ous, and He embedded in the loose adipose tissue of the axillary space. They are disposed in four groups — external, or humeral ; antero-intemal, or pectoral ; posterior, or subscapular ; and central. The external or humeral glands are about six in number, and lie upon the outer wall of the space, where they form a chain along the axiUary vein. Their afferent vessels represent (i) most of the superficial cind deep lymphatics of the upper limb, (2) some of the efferent vessels of the pectoral axillary glands, and (3) some of the efferent vessels of the subscapular glands. Their efferent vessels pass to (i) the central axillary glands, (2) the infraclavicular glands, and (3) the* supraclavicular glands. The antero-intemal or pectoral glands are about six in number^ and are situated along the inferior or long thoracic artery at the lower border of the pectoralis minor muscle, and therefore within the anterior fold of the axilla. They lie upon the serratus magnus, in the angle between it and the pectoral muscles, and they extend from the level of the second to the level of the fifth intercostal space. They receive their afferent vessels from (i) the anterior and lateral parts of the thoracic waU, and the supra-umbilical portion of the abdominal wall, and (2) the outer two-thirds of the mammary gland. Their efferent vessels pass to (i) the external axillary glands, (2) the central axillary glands, and (3) the infra-clavicular glands. The posterior or subscapular glands are about five in number, and are situated upon the posterior wall of the axilla. They lie along 3i8 A MANUAL OF ANATOMY the lower border of the subscapularis muscle, in contact with the subscapular artery. Their afferent vessels are derived from (i) the superficial lymphatics of the lower and back part of the neck, (2) the superficial lymphatics of the posterior part of the trunk, and (3) some of the superficial lymphatics of the supra-umbilical portion of the lateral wall of the abdomen. Their efferent lym- phatics pass to (i) the external axillary glands, (2) the central axillary glands, and (3) the infra-clavicular glands. The central glands are about five in number, and are situated at the base of the axilla. They lie upon the axillary fascia, and between the external, pectoral, and subscapular groups. They receive as afferent vessels some of the efferent vessels of the external, pectoral, and subscapular glands. Their efferent vessels pass to the infra-clavicular glands. Serratus Magnus — Origin. — The outer surfaces of the first eight or nine ribs about midway between the angles Subscapularis ^nd costal Cartilages, by means of fleshy serrations which are curved with their convexities forwards. Each ser- ration arises from one rib, ex- cept the first, which arises from the first and second ribs and a fibrous arch between them. Insertion. — ^The anterior Obhquu. surface of the base of the Externus i r ,, ,. , . scapula from the superior Abdominis i i^, • r • , ^ to the mferior angle. Nerve - supply. — The posterior thoracic nerve, which arises by three roots from the fifth, sixth, and seventh cervical. The nerve descends on the axillary surface of the muscle. The muscle is arranged in three parts. The upper part is formed by the first serration, which is of large size, and it is inserted into the triangular area on the front of the superior angle of the scapula. The middle part forms a thin, expanded sheet, which is formed by the broad second and the third serrations, and it is inserted into the long, linear impression on the front of the base, reaching to near the superior angle and extending down to near the inferior angle. The lower part, which is formed by the lower five or six serrations, is fan-shaped, and towards the scapula is thick and stout, its insertion being into the expanded area in front of the inferior angle. The lower four or five serrations interdigitate with the obliquus externus abdominis. Action. — ^The muscle draws the base of the scapula forwards, as Fig. 179.- -The Serratus Magnus Muscle. THE UPPER LIMB 319 in pushing, and the strong lower fibres, acting upon the lower angle, rotate the bone so as to elevate the point of the shoulder. In this latter action the muscle is auxiUary to the trapezius. An im- portant use of the muscle is to steady the scapula, more particularly the glenoid cavity, this condition being necessary before the deltoid can elevate the humerus. The muscle by its contraction serves to keep the lower angle of the scapula in contact with the chest wall. When the shoulder is fixed, the lower part of the muscle may elevate the ribs from which it arises. When the serratus magnus muscle is paralyzed (in association with the rhom- boid muscles), the condition known as winged scapula is produced. The lower angle and vertebral border of the scapula are displaced backwards when an effort is made to abduct the arm or to thrust it forwards. THE SCAPULAR REGION. Cutaneous Nerves. — ^The cutaneous nerves of the shoulder are derived from the supra-acromial of the cervical plexus and the cir- cumflex. The supra-acromial nerve, having descended over the outer part of the clavicle and trapezius, divides into numerous branches, which supply the integument over the upper third of the deltoid. The circumflex nerve sends branches through the muscle which supply the integmnent over about its middle third. It also furnishes a special cutaneous branch which turns roimd the posterior border of the muscle a little below the centre, and supplies the integument over its lower third. Deep Fascia. — ^The deep fascia is well marked over the infra- spinatus, where it is strongly aponeurotic. It sends septa between that muscle and the teres muscles, and then passes forwards over them to the posterior border of the deltoid, where it splits into two layers which encase that muscle. Deltoid — Origin. — (i) The anterior border of the outer third of the clavicle ; (2) the outer border of the acromion process ; and (3) the lower lip of the posterior border of the spine of the scapula. Insertion. — ^The deltoid impression on the outer aspect of the humerus, commencing at the centre, and extending upwards for 2 inches or more. Nerve-supply. — ^The circmnflex nerve, which is a branch of the posterior cord of the brachial plexus, its fibres being derived from the fifth and sixth cervical. Blood-supply. — ^The posterior circumflex and acromio- thoracic arteries. The muscle, which has very coarse fasciculi, is triangular, the base being upwards. The clavicular portion passes downwards and outwards, the acromial downwards, and the spinal downwards and forwards. Action. — ^The acromial portion abducts the arm to the position of a right angle with the trunk ; the clavicular portion draws it for- wards ; and the spinal portion draws it backwards. The acromial portion of the muscle, besides arising from the bone. 320 A MANUAL OF ANATOMY springs to a large extent from the sides of four fibrous septa, which descend into that part, and the fibres arising in this manner are inserted into the sides of three fibrous septa, which ascend from below. The origin of the muscle corresponds with the insertion of the trapezius. The anterior border is related to the pectoralis major, the cephalic vein and humeral artery lying between the two. The posterior border is to a large extent bound down by the splitting of the deep fascia over the infraspinatus. The muscle covers the shoulder- joint, subacromial bursa, coracoid process, coraco-brachi- alis, biceps, tendons of insertion of the supraspinatus, infraspinatus, and teres minor, parts of the long and outer heads of the triceps, teres major, tendon of insertion of the pectoralis major, circumflex nerve, and posterior circumflex artery. Subacromial Bursa. — This is a large bursa which intervenes between the acromion process and deltoid, on the one hand, and the upper part of the capsular ligament and the tendons inserted into the great tuberosity of the humerus, on the other. Supraspinatus — Origin. — The inner two- thirds of the supra- spinous fossa of the scapula, and the aponeurosis covering the muscle. Insertion. — The upper impression on the great tuberosity of the humerus, its tendon being closely connected with the upper part of the capsular ligament, and with that of the infraspinatus. Nerve-supply. — ^The suprascapular nerve, which arises from the back of the upper trunk of the brachial plexus, its fibres being derived from the fifth and sixth cervical. The direction of the muscle is outwards and downwards. Action. — To abduct the arm in association with the deltoid. Posterior Belly of the Omo-hyoid — Origin. — The upper border of the scapula internal to the suprascapular notch, and, as a rule, the adjacent portion of the suprascapular or transverse ligament. Infraspinatus — Origin. — (i) The infraspinous fossa of the scapula over about its inner two-thirds, the parts excepted being those for the teres muscles, and a portion at the upper and outer part of the fossa ; and (2) the deep fascia covering the muscle. Insertion. — The middle impression on the great tuberosity of the humerus, its tendon being closely connected with the back part of the capsular ligament, from which it is sometimes separated by a bursa. The tendon, which is fan-shaped, is at first concealed within the muscle. Nerve-supply. — The suprascapular nerve. The direction of the muscle is outwards. Action. — When the arm is by the side of the trunk the muscle is an external rotator. When the arm is raised the muscle carries it backwards in association with the deltoid. Suprascapular Artery. — ^The suprascapular artery ( trans versalisj humeri) is a branch of the thyroid axis of the first part of the sub- THE UPPER LIMB 321 clavian. Having coursed transversely outwards behind the clavicle, it reaches the upper border of the scapula in company with the suprascapular nerve. The artery then passes backwards over the suprascapular ligament, whilst the nerve passes beneath it, and it descends into the supraspinous fossa beneath the supraspinatus, where it parts with several branches. Thereafter it passes behind the neck of the scapula through the great scapular notch, beneath the spino-glenoid ligament, into the upper and outer part of the infraspinous fossa under cover of the infraspinatus, where it anastomoses with the dorsalis scapulae and posterior scapular. Branches. — ^These are as follows : muscular, in the neck, to the sterno-cleido-mastoid and subclavius ; suprasternal, over the inner end of the clavicle, to the integument over the presternum ; medullary to the clavicle ; supra-acromial, which pierces the trapezius to reach the upper surface of the acromion process, where it anastomoses with branches of the acromio- thoracic and posterior circimiflex ; articular to the acromio-clavicular and shoulder- joints ; ventral to the belly of the scapula, given off as it passes backwards over the suprascapular ligament, this branch anasto- mosing with the ventral branches of the dorsalis scapulae and posterior scapular ; supraspinous to the fossa and its muscle ; and infraspinous to the fossa and its muscle. Suprascapular Nerve. — ^This nerve passes backwards beneath the suprascapular ligament into the supraspinous fossa, where it gives branches to the supraspinatus, and articular branches to the acromio- clavicular and shoulder- joints. It then accompanies the artery through the great scapular notch, beneath the spino-glenoid ligament, to the infraspinous fossa, where it ends in branches to the infra- spinatus. Teres Minor — Origin. — (i) The dorsimi of the scapula close to the axillary border for its upper two-thirds, and (2) the septa between it and the infraspinatus and teres major. Insertion. — ^The lower impression on the great tuberosity of the humerus, and the surgical neck of the bone for a short distance below, its tendon being closely connected with the back part of the capsular ligament. Nerve-supply. — ^The circumflex nerve, the branch of which has a reddish enlargement presenting the appearance of a ganglion, but being in reality a fibrous thickening. The direction of the muscle is outwards and slightly upwards. Action. — ^The muscle is an external rotator of the arm when it is abducted, and it also helps in depressing the arm. The muscle is pierced by the dorsalis scapulae artery. Teres Major — Origin. — (i) From an oval impression at the lower and outer part of the infraspinous fossa, which extends on to the lower angle, and reaches upwards on the axillary border for about its lower third ; and (2) the septa between it and the teres minor, infraspinatus, and subscapularis. 2X 322 A MANUAL OF ANATOMY Insertion. — The inner lip of the bicipital groove of the humerus for 2 inches over about its lower two-thirds. Nerve-supply. — The lower subscapular nerve, which is a branch of the posterior cord of the brachial plexus, its fibres being derived from the fifth and sixth cervical. The direction of the muscle is outwards. - Infraspinatus Teres Minor Teres Major Teres Branch of Dorsalis' ScapuljE Artery Dorsalis Scapulae Artery in^ Triangular Space Nerve to Teres Minor, with-' Gangliform Enlargement - Posterior Circumflex Art and Circumflex Nerve Quadrangular Space -Pectoraiis M< " - - Deltoid Fig. i8o. — Dissection of the Scapular and Upper Brachial Regions FROM Behind. (The Deltoid has been turned down, and the Triangular and Quadrangular Muscular Spaces, with their contents, are shown.) A ction.— The muscle adducts the arm. When the arm is abducted it acts as an internal rotator. The latissimus dorsi winds round the lower border of the muscle, and is subsequently placed in front of it. The two tendons are 3t first closely connected by their lower borders, but are after- THE UPPER LIMB 323 wards sep^ated by a bursa, and there is usually a bursa behind the teres major at its insertion. Subscapularis — Origin. — (i) The venter of the scapula, except near the neck, and along the front of the base where the serratus magnus is inserted ; and (2) the sides of tendinous septa which intersect the muscle and are connected with the ridges on the venter. Insertion. — ^The small tuberosity of the humerus, and the surgical neck of the bone for a short distance below. Nerve-supply. — The upper or short, and part of the lower, sub- scapular ner\'es, which are branches of the posterior cord of the brachial plexus, their fibres being derived from the fifth and sixth cervical. The direction of the muscle is outwards. Action. — When the arm is by the side of the tnmk the muscle is an internal rotator, and, when it is raised, it carries it forwards and do\^Tiwards. The muscle is closely connected with the front of the capsular hgament. Between its upper border and the coracoid process and neck of the scapula there is a bursa, which usually communicates with the synovial membrane of the shoulder- joint through an opening in the capsule. Triangular and Quadrangular Spaces. — When the long head of the triceps is cut and displaced a large triangular space is seen, which, as viewed from behind, is bounded above by the teres minor, below by the teres major, and exUrnally by the surgical neck of the humerus. As viewed from before, the subscapularis replaces the teres minor. Wlien the long head of the triceps is in position it descends in front of the teres minor, and behind the teres major. It therefore passes through the triangular space and divides it into two, one triangular and the other quadrangular. Triangular Space. — This, as viewed from behind, is bounded above by the teres minor, below by the teres major, and externally by the long head of the triceps. As viewed from before, the sub- scapularis replaces the teres minor. The dorsalis scapulae artery passes back\vards through this space, so long as the subscapularis forms one of its boundaries, but thereafter, and as seen from behind, it only hes in it preparatory to piercing the teres minor and winding round the axillary' border. Quadrangular Space. — ^This space, as viewed from behind, is bounded above by the teres minor, below by the teres major, i«- ternally by the long head of the triceps, and externally by the surgical neck of the humerus, the subscapularis replacing the teres minor in front. The structures which pass through it are the circumflex nerv'e and posterior circumflex vessels. It is covered by the deltoid. Scapular Anastomoses of Arteries. — ^The anastomoses of arteries apon the scapula are divided into tNVO sets — scapular proper, and acromial. i 324 A MANUAL OF ANATOMY Scapular Anastomoses Proper. — The arteries which take part in these anastomoses are (i) the suprascapular and posterior scapular, representing the subclavian; and (2) the dorsalis scapulae of the subscapular, representing the third part of the axillary. The suprascapular is a branch of the thyroid axis of the first part of the subclavian, and the posterior scapular arises from the transverse cervical, which is also a branch of the thyroid axis. The suprascapular is distributed to the supraspinous and infra- spinous fossae and venter, and so also is the posterior scapular. The subscapular is distributed by its dorsalis scapulae branch to the infraspinous fossa and venter. In the supraspinous fossa the suprascapular anastomoses with the posterior scapular. In the infraspinous fossa the suprascapular anastomoses with the dorsalis scapulae, as does also the posterior scapular. In the venter of the bone the ventral branches of the suprascapular and posterior scapular anastomose with the ventral branch of the dorsalis scapulae. At the lower angle of the bone the posterior scapular anastomoses with the descending or teres branch of the dorsalis scapulas. Acromial Anastomosis. — The arteries which take part in the acromial anastomosis or rete on the upper surface of the acromion process are as follows : (i) the supra-acromial branch of the supra- scapular ; (2) branches of the acromio-thoracic artery of the first part of the axillary ; and (3) a branch of the posterior circumflex of the third part of the axillary. The importance of the scapular anastomoses comes into play after ligature of the subclavian artery in the third part of its course. THE ARTICULATIONS OF THE CLAVICLE. Sterno - clavicular Joint. — ^This joint belongs to the class di- arthrosis, and to the subdivision arthrodia. The articular surfaces are the inner end of the clavicle and the clavicular impression on the upper border of the presternum. The articular surface of the clavicle is of larger size than that on the presternum, and the two are separated by an interarticular fibro-cartilage. The joint is surrounded by a complete capsule, which is weak above and below, but strong in front and behind, where it constitutes the anterior and posterior sterno-clavicular ligaments. Besides these there are the interclavicular and costo-clavicular or rhomboid ligaments. The anterior sterno-clavicular ligament is broad, and its fibres extend obliquely downwards and inwards from the front of the clavicle to the front of the presternum. The sternal head of origin of the sterno-cleido-mastoid is in contact with it. The posterior sterno-clavicular ligament resembles the anterior, and is similarly disposed behind the joint. The sterno-hyoid muscle THE UPPER LIMB 325 Snpra-acToinial Branch Suprascapuiai 1 Saprascapiilar Ligament Supraspinous Branch of Suprascapular \ Acromial Rete Infraspinous Branch of Suprascapular ^Porsalis Scapulae Teres Branch of VDorsalis Scapube Posterior Scapular <-^ Fig. 181.— The Anastomoses of Arteries on the Dorsum and Acromion Process of the Scapula. 326 A MANUAL OF ANATOMY arises in part from it. The interclavicular ligament is a well- marked, curved bundle of fibres, which is attached at either side to the upper and back part of the inner end of the clavicle. In crossing between the two bones it curves downwards to be attached to the interclavicular notch on the upper border of the presternum. The costo-clavicular or rhomboid ligament is a strong, quadrilateral band of fibres, which extends from the upper surface of the first costal cartilage to the rhomboid impression on the under surface of the clavicle, its direction being upwards, backwards, and outwards. The interarticular fibro-cartilage is a nearly circular, flattened plate, which is thinner at the centre and lower part than elsewhere. It is attached superiorly to the upper and back part of the inner end of the clavicle, and interiorly to the inner end of the first costal car- tilage, where it inclines slightly outwards to form part of a socket Interclavicular Ligament Anterior Sterno-clavicular Ligament j Interarticular Fibro-cnitilage CLAVICLE ^^ Costo-clavicular __WKJjji.o. s^^^lis^'Ss or Rhomboifl >\v5^^»^-v:^sr%^'^ Ligament 'fffi-'}!^^~^^ Fig. 182. — The Sterno-Clavicular Joints. . (The Left Anterior Sterno-clavicular Ligament has been remove^.) for the lower portion of the inner end of the clavicle. Its circura-- ference is connected with the fibrous capsule of the joint. The plate sometimes presents a perforation at its centre. There are two synovial membranes at this joint, one on eitherj side of the interarticular fibro-cartilage. When the latter is per- forated these are continuous with each other. Arterial Supply. — The suprasternal branch of the suprascapular,] and the internal mammary. Nerve-supply. — The suprasternal branch of the cervical plexus. Movements. — These take place in an upward, downward, forward, and bacW ward direction. There is also circumduction. In the upward and downwaro movements the clavicle moves on the fibro-cartilage, and the forward and backward movements take place between the fibro-cartilage and the pre-^ sternum. In the downward movement of the bone the interarticular ligamenl is put upon the stretch, and the upward movement is limited by the costoJ clavicular ligament. Acromio-clavicular Joint. — This belongs to the class diarthrosis, and to the subdivision arthrodia. The articular surfaces arc the outer end of the clavicle and the facet on the acromion process. THE UPPER LIMB 32? These surfaces are sometimes partially separated by an inter- articular fibro-cartilage, and the joint is surrounded by a complete capsule, which forms the superior and inferior ligaments. The superior and inferior acromio-ciavicular ligaments extend between the contiguous margins of the bones on their upper and under surfaces, the former being strengthened by aponeurotic fibres from the trapezius and deltoid. The interarticular fibro- cartilage, when present, is hmited to the upper part of the joint, where it is attached to the superior ligament. It may divide the joint into two synovial compartments, but there is usually only one. The eoraco-clavieular ligament, which is to be regarded as acces- sory to this joint, connects the clavicle with the coracoid process, Capsule of Acromio-clavicnlar Joint Coraco-acrombtl ligament Trapezoid Ligament Conoid Ligament Long Head of Biceps - Glenoid Lig^aroent Capsular Ligament (cut) Fig. 183.— The Riglt Glenoid Cavity, and the Adjacent Ligaments, and is composed of two parts — conoid and trapezoid. The conoid ligament, internal and posterior in position, is attached below by its apex to an impression at the back part of the antero-internal border of the coracoid process, and above by its base to the conoid tubercle of the clavicle, its direction being upwards and backwards. The trapezoid ligament, external and anterior in position, is some- what quadrilateral. It is attached below to the trapezoid ridge on the back part of the upper surface of the coracoid process, and above to the trapezoid ridge on the under surface of the clavicle, its d.rection being upwards; backwards, and outwards. Between the two ligaments there is a slight interval, in which there may be a bursa. Arterial Supply. — The suprascapular and acromio- thoracic arteries. Nerve-supply. — ^The suprascapular and circumflex nerves. 328 A MANUAL OF ANATOMY Movements. — The movements at this joint are Umited, and are principally of a gliding nature in an upward and downward, and forward and backward, direction. The Ligaments of the Scapula. These are three in number — suprascapular, coraco- acromial, and spino-glenoid. The suprascapular or transverse ligament extends from the upper border of the scapula, internal to the suprascapular notch, to the root of the coracoid process. It is thin and flat, and it bridges over the notch, which it converts into a foramen. It usually gives origin to some fibres of the posterior belly of the omo-hyoid, and the supra- scapular nerve passes backwards beneath it and the suprascapular artery over it. This ligament sometimes undergoes ossification. The coraco-acromial ligament, which is triangular, is attached by its apex to the tip of the acromion process, and by its base to the postero-external border of the coracoid process. Its superior surface is covered by the deltoid, and the inferior surface overhangs the shoulder-joint, the subacromial bursa intervening. The acro- mion process, coraco-acromial ligament, and coracoid process form the coraco-acromial arch, within which the head of the humerus fits when the arm is abducted. The arch therefore forms an auxiliary socket for the head of the bone. The spino-glenoid ligament consists of a few fibres which extend from the outer border of the spine to the adjacent part of the margin of the glenoid cavity. It arches over the suprascapular artery and nerve as they pass through the great scapular notch on their way to the infraspinous fossa. Movements of the Scapula. — These movements take place at the acromio-clavicular joint, and are associated with movements of the clavicle. They are of two kinds — namely, gliding and rotation. Gliding Movements. — These take place upwards, downwards, out- wards or forwards, and inwards or backwards. During their occur- rence the scapula moves over the dorsal wall of the thorax in such a manner as to describe the arc of a circle. The centre of this circle corresponds to the sterno-clavicular joint, and the clavicle repre- sents a ray of the circle. In the inward or bacl^ward movement the base of the scapula is drawn towards the vertebral column, and in the outward or forward movement the base is drawn away from the vertebral column. Rotatory Movements. — Rotation takes place inwards and out- wards. During internal rotation the acromion is elevated, the superior angle is depressed, and the inferior angle moves slightly outwards. In internal rotation the conoid ligament is tightened. During external rotation the superior angle is elevated, the acromion is depressed, and the inferior angle moves slightly inwards. In external rotation the trapezoid ligament is tightened. THE UPPER LIMB 329 On account of the existence of the acromio- clavicular joint, the direction of the glenoid cavity of the scapula remains unaltered during the movements of the bone. Chief Muscles concerned in the Movements. — Elevation of Entire Scapula : Cervical part of the trapezius, and the levator anguli scapulae. Depression of Entire Scapula : The lower fibres of the trapezius, which end upon the somewhat triangular tendon, and the pectoraUs minor. Outward or Forward Movement of Entire Scapula : The serratus magnus. Inward or Backward Movement of the Entire Scapula : The middle and lower parts of the trapezius, and the rhomboid muscles. Special Movements. — Elevation of Acromion : Cervical pari of the trapezius. Elevation of Superior Angle: Levator anguli scapulae, aided by the rhomboid muscles. The inferior angle of the scapula is kept in contact with the dorsal wall of the thorax by the upper horizontal fibres of the latissimus dorsi muscle, which pass over its dorsal aspect. The base of the scapula is kept in contact with the dorsal wall of the thorax by the serratus magnus and rhomboid muscles. THE ARM. Landmarks. — ^The front of the brachial region presents a well- marked elongated prominence, due to the biceps, which reaches from the anterior fold of the axilla to near the elbow. Internal to this prominence, above, is another swelling caused by the coraco- brachialis. On either side of the bicipital prominence is a groove, that on the outer side indicating the position of the cephalic vein, and that on the inner side the position of the basilic vein, brachial artery, and median nerve. External to the bicipital prominence, for a short distance above the elbow, is the prominence formed by the brachio-radialis and extensor carpi radialis longior. At the elbow the internal and external epicondyles of the humerus and the olecranon process of the ulna are to be noted. The internal epicondyle forms a very distinct projection, having an inclination backwards, and behind it, close to the olecranon, is the ulnar nerve. The external epicondyle, which is not well marked, may be felt in Semiflexion of the joint. The olecranon process can easily be felt at the back. In extension of the joint the summit of the olecranon is on the same line with the two epicondyles. When the arm and forearm are placed in the position of a right angle, the summit of the olecranon falls below a line connecting the epicondyles. In extreme flexion of the elbow the summit of the olecranon is anterior to a line connecting the epicondyles. The posterior surface of the olecranon is covered by a subcutaneous bursa. The head of the radius can be felt, in extension of the joint, at the bottom of a de- pression situated at the outer and back part, where it lies just below 330 A MANUAL OF ANATOMY the external epicondyle. It is most readily felt when the forearm is alternately pronated and supinated. In front of the elbow there is a slight hollow indicating the position of the anticubital fossa, and in this region the outlines of the median basilic and median cephalic veins may be visible, especially the former. On the back of Ihe Supraclavicular Anterior Branches of Lateral Cutaneous Supra -acromial Suprasternal Cutaneous Branch of. Circumflex Upper External Cutaneous of Musculo-spiral Branch of Radial . Anterior Cutaneous ~~-.Twig of Internal Cutaneous "^^-Intercosto-humeral ..Anterior Branch of Internal Cutaneous _. Posterior Branch of Internal Cutaneous — Anterior Branch of Musculo-cutaneous Twig of Ulnar (occasional) Palmar Cutaneous of Ulnar Palmar Cutaneous of Median Fig. 184. — Diagram of the Cutaneous Nerves of the Upper Limb (Anterior Aspect). forearm the posterior border of the ulna can readily be felt. It leads superiorly to the subcutaneous bursa on the back of the ole- cranon, and inferiorly it conducts to the styloid process of the bone, which is situated mainly on its posterior aspect. On the outer side of the lower end of the radius its styloid process can easily be felt. ;^v^iTV Or /v^j;^ ANATOMY THE UPPER LIMB 331 Supra-acromial which projects lower down than that of the ulna, and in front of it is the radial artery. On the back of the radius, about its centre, is the radial tubercle, which bounds externally the groove for the tendon of the extensor longus pollicis. Olecranon Bursa. — ^This bursa is situated subcutaneously over the posterior triangular surface of the olecranon process of the ulna. Cutaneous Nerves. — ^The inter- costo - humeral nerve, having crossed the axillary space, ramifies in the integument of the inner and back part of the arm over its upper half. It may be accompanied by an off- set of the posterior branch of the lateral cutaneous of the third intercostal. The lesser internal cutaneous or nerve of Wrisberg is dis- tributed to the integument of the inner side of the arm, as low as the interval between the internal epicondyle and olecranon. The internal cutaneous nerve furnishes one or more branches, which, piercing the deep fascia close to the axilla, are dis- tributed to the integument over the biceps. The nerve itself pierces the deep fascia a little below the centre of the arm, and then divides into an anterior and a posterior branch. The an- terior branch descends behind the median basilic vein, giving one or two twigs over it, and it is distributed„±o-theL integu- ment of the^'anterior aspect of the inner side of the forearm. The posterior branch passes downwards and inwards on the inner >ide of the basilic vein, and over the internal epicondyle, after which it turns backwards to supply the integument over the back of the inner side of the forearm. The internal cutaneous of the musculo-spiral is distributed to the integument of the back of the arm, almost as low as the olecranon. Cutaneous Branch of Circumflex Internal Cutaneous of Musculo spiral -- 'Intercosto-bumeral Lower External Cutaneous of Musculo-spiral Nerve of Wrisberg , -- Posterior Branch of Internal Cutaneous Posterior Branch of Musculo- cutaneous -Radial : Dorsal Bianch of Ulnar Fig. 18 Diagram of the Cutaneous Nerves of the Upper Limb (Posterior Aspect). lO 332 A MANUAL OF ANATOMY The external cutaneous branches of the musculo-spiral are two in number — upper and lower. They leave the main trunk towards the lower end of the spiral groove, just before the nerve passes through the external intermuscular septum, and the two branches pierce the deep fascia about | inch apart. The upper branch, of small size, descends with the cephalic vein to the front of the elbow, giving branches to the integument of the outer and anterior aspects of the arm in its lower half. The lower branch, of larger size, descends behind the external epicondyle into the forearm, where it is distributed to the integument on the posterior aspect of the outer side as low as the wrist. The cutaneous branch of the musculo -cutaneous pierces the deep fascia on the outer side of the biceps a little above the elbow. It descends behind the median cephalic vein, giving one or two twigs over it, and then it divides into two branches. One supplies the integument on the anterior aspect of the outer side of the forearm, and the other gives branches to the integument on the posterior aspect. The cutaneous branch of the ulnar, which arises about the centre of the forearm, pierces the deep fascia, and has a limited distribution to the integument just below the centre, internal to the median line. This branch is inconstant. Superficial Veins. — There are four principal superficial veins in the forearm, namely, the median, radial, anterior ulnar, and fJosterior ulnar. I The median vein is formed by the union of a few radicles which originate in the venous plexus in front of the wrist, and its course is upwards in front of the forearm. As it ascends it takes uj several veins, and often receives a large tributary from the bad of the limb. It is also in free communication with the radial anc anterior ulnar veins. On arriving at the hollow in front of th« elbow it receives a short but large branch, called the deep medial vein, which establishes a communication between it and the deej venae comites. Thereafter it divides into median cephalic anc median basilic, which diverge from each other as they ascenc' somewhat like the capital letter V. The median cephalic vein, th< smaller of the two, passes upwards and outwards in the interv^ between the biceps and brachio-radialis, having the cutaneou part of the musculo-cutaneous nerve behind, and a^ few of it twigs over it. A little above the external epicondyle it receive the radial vein, the resulting trunk being called the cephalic veil The median basilic vein, the larger of the two, passes inwards am upwards, crossing the bicipital fascia, which separates it from the^j brachial artery, and the anterior branch of the internal cutaneous j nerve descends behind it, a few of its twigs passing over it. Just above the internal epicondyle it receives the anterior and posterior ulnar veins, either separately or as a common trunk, and the resulting vessel is called the basilic vein. THE UPPER LIMB Pectoralis Major. Axillary Vein , Cephalic Vein , Pectoralis Minor>.^ fJL^ 333 Cephalic Vein.-- - Median Cef)halic Vein Radial Vein Superficial Median Vein.'-'' __ Basilic Vein ^, Internal Epicondylar Glands [^ , Median Basilic Vein Posterior Ulnar Vein \- Deep Median Vein Anterior Ulnar Vein Palmar Venous Arch Fig. i86. — The Superficial Veins of the Upper Limb (Anterior View). 334 ^ MANUAL OF ANATQMY The radial vein commences in the outer part of the plexus on the back of the hand, and it ascends at first on the back of the outer side of the forearm, but gradually inclines to its outer aspect. . A little above the external epicondyle it joins the median cephalic vein. The anterior ulnar vein commences on the inner aspect of the front of the wrist, and it ascends in front of the inner side of the fore- arm, to end either in the median basilic or by joining the posterior ulnar vein. The posterior ulnar vein, of large size, commences in the inner part of the plexus on the back of the hand, and it ascends along the back of the inner side of the forearm to join the median basilic, either separately or having previously taken up the anterior ulnar vein. The principal superficial veins of the brachial region are the cephalic and the basilic. The cephalic vein is formed by the union of the median cephalic and the radial a little above the external epicondyle. It then ascends, lying at first in the groove along the outer border of the biceps, and then between the pectoralis major and deltoid. There- after it crosses the first part of the axillary artery, and, piercing the costo-coracoid membrane and axillary sheath, opens into the axillary vein above the pectoralis minor. The basilic vein is formed by the union of the median basilic, anterior ulnar, and posterior ulnar, just above the internal epicon- dyle. It then ascends in the groove along the inner border of the biceps, lying inside the line of the brachial artery. In the lower half of the arm it is superficial to the deep fascia, but about the centre it pierces it, and becomes the axillary vein at the lower border, of the tendon of the teres major. In contact with the basilic vein, just above the internal epicondyle, there are one or two lymphatic; glands. FRONT AND INNER ASPECT OF BRACHIAL REGION. Deep Fascia. — The deep fascia or aponeurosis forms a continuous investment to the arm, its fibres being principally disposed trans^ versely, but others run more or less longitudinally. It is continuoi above with the axillary fascia and the fascial investments of th^ pectoralis major and deltoid, the tendons of which give expansior to it. It is thin over the biceps, and somewhat thicker over thd triceps, but it becomes specially strong in the region of the elbow| where it is attached to the epicondyles of the humerus and olecranoi process of the ulna. In front of the elbow it receives a considerably accession of fibres from the bicipital or semilunar fascia. At abouj the centre of the arm, on its inner aspect, it presents an opening fc the passage of the basilic vein. The deep fascia is connected wit the lower part of the humerus on either side by two deep processes called intermuscular septa. The external septum is attached to thi THE UPPER LIMB 335 external epicondyle, and external supracondylar ridge as high as a point posterior to the lower part of the tendon of insertion ot the deltoid, with which it is connected. It gives origin posteriorly to fibres of the inner head of the triceps, below where it is pierced by the musculo-spiral nerve, and above that point to fibres of the external head. Anteriorly, from above downwards, it gives origin to a small part of the brachialis anticus, brachio-radialis, and extensor carpi radialis longior. It is pierced from behind forwards by the musculo- spiral nerve and the anterior terminal branch of the superior profunda artery, the posterior terminal branch descending behind it. The internal septum is stronger than the external, and is attached to the internal epicondyle, and internal supracondylar ridge as high as a point behind the insertion of the coraco-brachialis. It gives origin anteriorly to the brachialis anticus, and posteriorly to the inner head of the triceps. It is pierced, at its upper part, from before back- wards by the ulnar nerve and inferior profunda artery, and, a little above the elbow, by the posterior branch of the anastomotica magna artery. Connected with the internal septum there is a fibrous band, known as the internal brachial ligament (Struthers), which extends from the humerus below the tendon of insertion of the teres major to the internal epicondyle. The two intermuscular septa divide the lower half of the arm into two compartments — anterior and posterior. The anterior compartment contains the biceps, brachialis anticus, brachio-radialis, extensor carpi radialis longior, basilic vein, brachial vessels, median nerve, ulnar nerve for a short distance above, internal cutaneous nerve, nerve of Wrisberg, and musculo-spiral nerve after it has pierced the external septum. The posterior compartment contains the triceps and a smaH part of the musculo-spiral nerve. Internal Epicondylar Lymphatic Glands. — ^These glands, usually two in number, are situated about li inches above the internal epicondyle of the humerus. They lie superficial to the deep fascia, and in close proximity to the commencement of the basilic vein. Their afferent vessels are derived from (i) the inner three fingers, (2) the inner part of the palm, and (3) the ulnar side of the forearm. Their efferent vessels ascend with the basilic vein, and, about the centre of the arm, they pass with the basilic vein through an opening in the deep fascia. Thereafter they join the deep hTnphatics along the brachial artery, which terminate in the external axillary glands. Anticubital Lymphatic Glands. — ^These are very inconstant. When present they are about two in nimiber, and lie opposite the bend of the elbow, superficial to the deep fascia. They receive their afferent vessels from the centre of the palm and the front of the forearm. Their efferent vessels ascend superficially along the inner border of the biceps brachii, and, piercing the deep fascia, they terminate in the external axillary glands. Coraco-brachialis — Origin. — (i) The tip of the coracoid process of the scapula ; and (2) the inner aspect of the tendon of the short head of the biceps for 3 inches or more. 336 A MANUAL OF ANATOMY Insertion. — The inner side of the humerus at its centre for about an inch and a half. Some of the upper fibres are inserted into a fibrous band, which ascends in front of the tendons of the latissimus dorsi and teres major to be attached to the humerus below the small tuberosity. Nerve-supply. — ^The musculo-cutaneous nerve, by a branch which derives its fibres from the seventh cervical. The muscle is directed downwards, outwards, and slightly back- wards. Action. — ^To adduct and flex the humerus. It also braces the head of the bone against the glenoid cavity. The muscle is pierced by the musculo-cutaneous nerve. Biceps Flexor Cubiti — Origin. — (i) The short head arises from the tip of the coracoid process of the scapula in association with the coraco-brachialis ; (2) the long head arises from the supraglenoid tubercle of the scapula by a rounded tendon, which lies within the capsular ligament of the shoulder- joint, and is continuous on either side with the glenoid ligament. Insertion. — ^i) The posterior rough portion of the bicipital tuberosity of the radius, being separated from the anterior smooth portion by a bursa ; and (2) the deep fascia covering the muscles arising from the internal epicondyle of the humerus by means of the bicipital or semilunar fascia. The short head arises by a short tendon, and the tendon of the long head is about 4 inches in length. This latter tendon arches over the head of the humerus, and leaves the interior of the joint by entering the bicipital groove, beneath the transverse humeral ligament. Within the joint it is invested by a tubular sheath formed by the synovial membrane, which accompanies it for a short distance in the bicipital groove, and is then reflected upwards to become continuous with the synovial lining of the capsular ligament. After leaving the bicipital groove the tendon is replaced by a conical bundle of fleshy fibres, and these join the fibres derived from the short head about the centre of the arm, giving rise to an elongated, oval, fleshy belly. At the level of the epicondyles of the humerus the belly gives place to the strong tendon of insertion, which sinks into the anti- cubital space, and undergoes a quarter of a turn before reaching its insertion. From the inner side of the tendon, towards its upper part, a strong band of fibres is given off, which passes to the deep fascia covering the muscles arising from the internal epicondyle. It is called the bicipital or semilunar fascia, and it passes over the brachial artery, whilst the median basilic vein lies upon it. Nerve-supply. — The musculo-cutaneous nerve, which is a branch of the outer cord of the brachial plexus, its fibres being derived from the fifth, sixth, and seventh cervical. Action. — (i) To flex the elbow-joint ; (2) to supinate the forearm ; (3) by its short head to adduct and flex the arm, and (4) by its long head to raise the arm at the shoulder. Internal to the muscle in the upper half is the coraco-brachialfe. THE UPPER LIMB 337 and in the lower half the brachial artery and median nerve. Ex- ternal to it is the cephalic vein. The biceps sometimes has a third head, which usually arises from the inner side of the humerus at or near the insertion of the coraco-brachialis. As a rule, it Deltoid . Biceps . Coraco-brachialis . Musculo-cutaneous Nerve ._ Brachialis Anticns. Musculo-spiral Nerve—.. Brachio-radialis Radial Nerve — Posterior Interosseous Nen-e Supinator Radii Brevis Ulnar Artery Radial Artery , Latissimus Dorsi Teres Major Ulnar Collateral Nerve of Krause Ulnar Nerve Long Head of Triceps Brachial Artery Median Ner%-e Inner Head of Triceps Internal Intermuscular Septum Internal Epicondyle Flexor Carpi Radialis .Palmaris Longus .Flexor Carpi Ulnaris ^ Pronator Radii Teres Fig. 187. — Dissection of the Right Brachial Region, and Bend of the Elbow. 3 external to the brachial artery, but sometimes it crosses the yessel. I Brachialis Anticus— Or/gm.— (i) The lower half of the front of •he humerus ; (2) the front of the internal intermuscular septum over he whole of its extent ; and (3) the front of the external intermus- l-ular septum for a short distance above. 338 A MANUAL OF ANATOMY Superiorly the muscle sends a pointed projection upwards on either side of the lower part of the insertion of the deltoid. Insertion. — ^The inner part of the rough triangular surface on and below the coronoid process of the ulna. Nerve-supply. — (i) The musculo-cutaneous nerve, and (2) a twig from the musculo-spiral nerve. Action. — ^The muscle is a direct flexor of the elbow- joint. Brachial Artery. — ^The brachial artery is the continuation of the axillary, and it extends from the lower border of the teres major to a point just below the bend of the elbow, where it divides opposite the upper part of the neck of the radius into the radial and ulnar arteries. It is at first internal to the humerus, but gradually inclines to the front of the bone, and at the elbow it is equally distant from the two epicondyles. The course of the vessel is indicated by a line drawn from a point midway between the anterior and posterior folds of the axilla at the humerus to a point midway between the epicondyles of the bone. The artery is accompanied by two vense comites, one on either side, which communicate with each other over the vessel at frequent intervals. It is for the most part superficial, being only slightly overlapped . by the coraco- brachialis and biceps. At the bend of the elbow, however, it sinks deeply under cover of the semilunar fascia, and lies in the anti- cubital space. Relations — Superficial. — Skin, superficial and deep fasciae, median nerve about the centre of the arm, semilunar fascia of the biceps, and, superficial to this, the median basilic vein. Deep. — ^The long head of the triceps, with the intervention of the musculo-spiral nerve and superior profunda artery, inner head of the triceps, insertion of the coraco-brachialis, and brachialis anticus. External. — The coraco- brachialis and biceps, both of which slightly overlap the vessel, external vena comes, and the median nerve in the upper half of the arm. Internal. — ^The internal vena comes, internal cutaneous nerve (which may be slightly over the vessel) as low as the centre of the arm, ulnar nerve also as low as the centre, median nerve in the lower third, and basilic vein, which is superficial to the deep fascia in the lower half, but beneath it in the upper half. The nerve most intimately related to the artery is the median, which lies on its outer side in the upper half of the arm, in front of it for a little at the centre, and on its inner side in the lower third. Branches. — ^The vessel gives off from its outer side a series of branches which are distributed to the muscles and integument of the front of the arm. The named branches arise from the inner and back part of the trunk. They are called superior profunda, inferior profunda, nutrient, and anastomotica magna. The superior profunda artery is a large vessel which arises from the back of the brachial near its commencement. It passes ' downwards and backwards with the musculo-spiral nerve between < the long and inner heads of the triceps, and it then winds round the back of the humerus, lying with the nerve in the spiral groo^•^ THE UPPER LIMB 339 between the outer and inner heads of that muscle. Towards the lower end of the groove it divides into two terminal branches — interior and posterior. The anterior branch accompanies the tousculo-spiral nerv^e through the external intermuscular septum, and then descends between the brachio-radialis and brachialis anticus to anastomose with the radial recurrent artery. The pos- terior branch descends behind the external intermuscular septum, and anastomoses behind the external epicondyle with the posterior interosseous recurrent, and across the back of the humerus above the olecranon fossa with the anastomotica magna. Besides the two terminal branches the superior profunda gives off the follow- ing offsets : muscular to the triceps ; an ascending branch, which passes upwards between the long and outer heads of the triceps to anastomose with a branch of the posterior circmnflex ; and a nutrient branch, which enters a foramen on the back of the humerus. The superior profvmda may arise from the third part of the axillary, and it may give off the posterior circumflex. The inferior profunda artery arises from the brachial about the centre of the arm, or sometimes from the superior profimda. It accompanies the ulnar nerve through the internal intermuscular septum, and then descends with it on the inner head of the triceps to the back of the internal epicondyle, where it anastomoses with the anastomotica magna and posterior ulnar reciurent arteries. In its course it gives muscular onsets to the triceps. The nutrient or medullary artery arises from the brachial opposite the lower border of the insertion of the coraco-brachialis, or it may come off from the inferior profunda. Its course is downwards, and it enters the medullary foramen of the bone to be distributed to its interior. ; The anastomotica magna artery arises about 2 inches above the albow. It passes inwards on the brachialis cmticus, and divides into two branches — a small anterior and large posterior. The anterior branch descends beneath the pronator radii teres, and anastomoses vvith the anterior ulnar recurrent artery. The posterior branch )ierces the internal intermuscular septum, and then passes outwards )eneath the triceps, resting upon the back of the humerus above the olecranon fossa, where it forms an arch with the posterior branch of he superior profunda artery. It gives a branch to the back of the ntemal epicondyle. which anastomoses with the inferior profunda nd posterior ulnar recurrent arteries. Varieties. — i . The brachial artery may divide above the normal level. In lost cases the vessel given off earlier than usual is the radial ; more rarely it the ulnar, and in these cases the interosseous trunk arises from the radial ; .till more rarely the premature branch is the interosseous trunk, or a large vas iberrans. The level at which a high division takes place is most frequently fi the upper third of the arm, less so in the lower third, and it is of rarest Iccurrence in the middle third. When two arteries are present they usually e side by side in the position of the normal vessel. When a vas abejxans I present it usually arises from the upper part of the brachial artery, and rminates below by joining, most commonly, the radial artery. 340 A MANUAL OF ANATOMY 2. In rare cases the brachial artery divides high up into two vessels of equal size, which become reunited into one trunk a little above the elbow. 3. When a supracondylar process is present the brachial artery, along with the median nerve, may descend towards the internal epicondyle until i1 gets below the level of the process, round which it turns forward to the front of the elbow. This is the normal course taken by the artery in the Felidcs, in which there is a supracondylar foramen. Collateral Circulation. — When the brachial artery has been ligatured above the centre of the arm, the collateral circulation is carried on by the superior profunda artery, which anastomoses below with (i) the radial recurrent, (2) the posterior interosseous recurrent, and (3) the anastomotica magna. When the artery has been ligatured in the vicinity of the elbow, the inferior profunda and anastomotica magna assist the superior profunda by anasto- mosing with the anterior and posterior ulnar recurrent. Brachial Venae Comites. — These are two in number, and they closely accompany the artery, one being placed on either side of it. Along the course of the vessel they communicate with each other across it at frequent intervals. Superiorly the external vena comes crosses inwards over the lower portion of the third part of the axillary artery to join the internal vena comes, and the resulting trunk opens into the axillary vein near the lower border of the subscapularis. The internal cutaneous nerve and the nerve of Wrisberg are situated on the inner side of the brachial artery, the former slightly encroaching upon it. The median nerve lies on the outer side of the artery as low as the centre of the arm, where it passes over it, and then descends on its inner side in the lower third. Instead of crossing over the vessel it may pass behind it. It gives off no branch in the arm, but it sometimes receives a branch from the musculo-cutaneous. The ulnar nerve lies on the inner side of the artery as low as the insertion of the coraco-brachialis. Here it meets with the inferior profunda artery, and with it pierces the internal intermuscular septum from before backwards. It then descends on the inner head of the triceps to the interval between the! olecranon and internal epicondyle. It gives off no branch in thai arm. The musculo-cutaneous nerve, having pierced the coraco-' brachialis, passes downwards and outwards between the biceps and brachialis anticus. A little above the elbow it appears at the outer border of the biceps, whence it descends to its cutaneous distribution, already described. Before piercing the coraco- brachialis, it gives off the branch to that muscle, and, as it cours between the biceps and brachialis anticus, it furnishes branches : them. It sometimes gives a communicating branch to the mediai nerve. Anticubital Space. — This is the name given to the triangul hollow in front of the elbow- joint. The roof of the space is fornn by the integument, median basilic and median cephalic vein anterior division of the internal cutaneous nerve, cutaneous pai of the musculo-cutaneous nerve, deep fascia, and semilunar fascia THE UPPER LIMB 341 rhe floor is formed by the brachialis anticus and a small part of the iupinator radii brevis. The base is represented by an imaginary ine connecting the epicondyles of the humerus. The outer boundary s formed by the brachio-radialis, and the inner by the pronator radii teres, the apex being constructed by the former muscle overlapping ntemal Cutaneous Nerve Basilic Vein Median Nen-e Brachial Artery and Vense Comites Posterior Branch ol Internal Cutaneous Ner\- Posterior Ulnar Vein Anterior Branch of Oternal Cutaneous Nerve Median Basilic Vein _ Bicipital Fascia Ulnar Artery and VensE Comites Anterior Ulnar Vein Pronator Radii Teres -- _j_ Median Cephalic Vdn Radial Vein Deep Median Vein Radial Recurrent Artery Radial Artery and Venjc Coimtes Median Vein Brachio-radialis -Superficial Dissection of the Front of the Left Elbow. he latter. The space contains the terminal part of the brachial, nd the commencement of the radial and ulnar, arteries, with their Jspective venae comites. On the outer side of the brachial artery •• the tendon of the biceps, and on its inner side is the median erve. Under cover of the brachio-radialis are the radial and •osterior interosseous branches of the musculo-spiral nerve. 342 A MANUAL OF ANATOMY BACK OF THE BRACHIAL REGION. Triceps Extensor Cubiti — Origin. — (i) The long head arises fron the infraglenoid ridge of the scapula, where it is superficially ten dinous. (2) The external head arises from (a) the outer part of th posterior surface of the humerus, reaching as high as the insertioi of the teres minor, and as low as the spiral groove ; and (b) th back of the external intermuscular septum above the point wher it is pierced by the musculo- spiral nerve. (3) The internal heai arises from (a) the whole of the posterior surface of the humeru below the spiral groove, reaching upwards on the inner side of th groove, in a tapering manner, as high as a point about ^ inch above and posterior to, the lower border of the insertion of the tere major ; (&) the back of the internal intermuscular septum ove its whole extent ; and (c) the back of the external inter muscular septum below where it is pierced by the musculo-spira nerve. Insertion. — (i) The back part of the upper surface of the olecranoi process of the ulna ; (2) the deep fascia covering the anconeus ; an< (3) slightly into the posterior ligament of the elbow- joint. The long and external heads terminate in a broad fiat tendon which occupies about the lower half of the arm, the fibres of tb long head ending on its inner side, and those of the external hea( on its upper and outer parts. Most of the fibres of the interna head terminate on the deep surface of the tendon, but some ar< inserted directly into the olecranon. The deepest and lowest fibre of this head are inserted into the posterior ligament of the elbow joint, and form the so-called subanconeus. There is usually ; bursa over the front part of the upper surface of the olecranon separating the tendon of the muscle from the posterior ligamen of the elbow-joint. The long head is related to the lower part of the capsular ligamen of the shoulder- joint. Nerve-supply. — The musculo-spiral nerve, which is a branch o the posterior cord of the brachial plexus, its fibres being derivec from the last four cervical, and sometimes from the first thoracic. Action. — ^The external and internal heads are simple extensor; of the elbow-joint. The long head also extends the elbow-joint and from its relation to the shoulder- joint it depresses the arir upon the scapula. Musculo-spiral Nerve. — ^This nerve at first lies behind the thirc part of the axillary artery, and then behind the upper part of the brachial. Thereafter it passes downwards and backwards, with the superior profunda artery, between the long and internal heads ol the triceps. It next winds round the back of the humerus in th( spiral groove, between the external and internal heads of the triceps. Having pierced the upper part of the external intermusculai septum, it descends in the groove between the brachio-radiali- and brachialis anticus to a point a little above the external epi- THE UPPER LIMB 343 ;ondyle, where it terminates by dividing into the radial and posterior interosseous nerves. Branches— /«/^«a/ Branches —These, which arise on the inner Latissimus Dorai ^^ Teres Major Long Head of Triceps Internal Head of Triceps Inar Nerve behind Internal Epicondyle Teres Minor External Head of Triceps Musculo-spiral Nerve and Superior Profunda Artery --Tendon of Triceps —External Epicondyle Anconeus Fig. 1 89. — Dissection of the Back of the Brachial Region. 'External Head of the Triceps has been divided and reflected outwards to show the contents of the Spiral Groove.) ide of the humerus, are muscular and cutaneous. The muscular tranches supply the long and internal heads of the triceps, ihose for the long head entering it high up, whilst those for the nternal head enter it at different levels. One of the latter, which 344 A MANUAL OF ANATOMY is remarkable for its length, descends, along with the ulnar nerve, to enter the internal head low down, this branch being known as the tdnar collateral nerve (Krause). The internal cutaneous branch usually arises in common with one of the muscular branches, and is distributed to the integument of the back of the arm, reaching nearly as low as the back of the elbow. Posterior Branches. — ^These arise behind the humerus, and are distributed to the external and internal heads of the muscle and to the anconeus, the nerve to the latter, which is long and slender, descending in the internal head. External Branches. — These arise on the outer side of the humerus, and are cutaneous, muscular, and articular. The upper and lower external cutaneous nerves have been already described. The muscular branches are distributed to the brachio-radialis, extensor carpi radialis longior, and brachialis anticus, the latter branch being a small twig. The articular branches, one or two in number, are distributed to the elbow- joint. THE SHOULDER-JOINT. The shoulder-joint belongs to the class diartkrosis, and to the subdivision enarthrosis (ball-and-socket). The articuW surfaces are the glenoid cavity of the scapula and the head of the humerus ; and the ligaments are the capsular, coraco-humeral, gleno-humeral, and glenoid. The capsular ligament is attached to the scapula around the margin of the glenoid cavity close to the glenoid ligament, with which many of its fibres are connected. Superiorly it extends to the root of the coracoid process, and inferiorly it is related to the long head of the triceps. At the himienis it is attached to the anatomical neck, its fibres descending for a little on the inferior aspect. The ligament is very loose, so that, when the muscles in contact with it have been divided, the head of the humerus drops away from the glenoid cavity for over an inch. The ligament presents two openings. One, called the foramen ovale, is situated on its anterior aspect, behind the upper border of the subscapular is. Through this opening a protrusion of the synovial membrane of the joint takes place beneath the upper border of the subscapu- laris, where it forms the subscapular bursa. The other opening is placed between the great and small tuberosities of the humerus at the commencement of the bicipital groove, and it allows the long | tendon of the biceps, with its synovial investment, to leave the interior of the joint, beneath the transverse humeral ligament. There is sometimes a third opening of small size on the posterior aspect of the capsule, which allows the synovial membrane io protrude and form a bursa beneath the infraspinatus. The coraco-humeral ligament is a strong band which extends ; THE UPPER LIMB 345 from the outer border of the coracoid process, near the root, across the upper part of the capsule, with which it is closely connected, to the great tuberosity of the humerus. The gleno-humeral bands are three in number, and are thickened parts of the capsule which project in an inward direction. The superior band is known as the gleno-humeral ligament, and is regarded as representing the ligamentum teres of the hip-jomt. It extends from the apex of the glenoid cavity, and the root of the coracoid process, of the scapula to the small tuberosity of the humerus, where it lies on the inner side of the bicipital groove. The middle band, called Flood's ligament, extends from the anterior Coraco-acromial Ligament -Foramen Ovale Subscapularis (reflected) — ^f Capsular Ligament Long Head of Biceps Fig. 190. — The Right Shoulder-Joint (Anterior View). margin of the glenoid cavity to the lower part of the small tuber- osity of the humerus. The inferior band, called Schlemm's liga- ment, extends from the lower part of the glenoid cavity to the lower part of the neck of the humerus. The gleno-humeral bands are best seen when the joint is opened from behind. Associated with the capsule there is also the transverse humeral ligament, which bridges over the upper end of the bicipital groove between the great and small tuberosities. The glenoid ligament is a dense iibro-cartilaginous band which is implanted on the edge of the glenoid cavity, and so deepens it for the head of the humerus. Externally it is connected with the capsular ligament, and superiorly each lateral division blends with the long head of the biceps. The long head of the biceps is to be regarded in the light of a 346 A MANUAL OF ANATOMY ligament, inasmuch as it arches over the head of the humerus, and tends to prevent upward displacement of the bone. The synovial membrane lines the inner surface of the glenoid ligament, and is reflected from it over the inner surface of the capsule. From this it passes to the anatomical neck of the humerus, which it covers as far as the margin of the articular cartilage of the head. It protrudes through the opening in the front of the capsule to form the subscapular bursa, and it sometimes protrudes through an opening behind to form a bursa beneath the infra- spinatus. The long head of the biceps, in passing from the supra- glenoid tubercle to the bicipital groove, receives a tubular invest- ment from it. This accompanies the tendon for a short distance in Capsule of Acromioclavicular Joint Coraco-acromial Ligament Trapezoid Ligament Conoid Ligament Long Head of Biceps Glenoid Ligament Capsular Ligament (cut) Fig. 191. — The Right Glenoid Cavity, and the Adjacent Ligaments. the bicipital groove, after which it is reflected upwards to become continuous with the synovial membrane lining the capsule. Muscular Relations. — The capsular ligament is closely related to the following muscles : superiorly, the supraspinatus ; pos- teriorly, from above downwards, infraspinatus and teres minor ; inferiorly, long head of the triceps ; and anteriorly, subscapularis. Arterial Supply. — ^The suprascapular, and anterior and posterior circumflex, arteries. Nerve-supply. — ^The suprascapular and circumflex nerves. Movements. — Seven movements are allowed at the shoulder-joint, namely forward flexion, as in shaking hands, extension, backward flexion, abduction, adduction, rotation, and circumduction. THE UPPER LIMB 347 Mnseles eoneerned in the Movements — Forward Flexion. — The clavicular parts of the pectoralis major and deltoid, short head of the biceps, and coraco- brachiaUs. Extension. — ^The spinal portion of the deltoid, teres major, and latissimus dorsi. Backward Flexion. — This movement being a continua- tion backwards of extension, the muscles concerned are the same as for that movement. Abduction. — The acromial portion of the deltoid and supra- spinatus. Adduction. — The stemo-costal portion of the pectoraUs major, short head of the biceps, coraco-brachiaUs, teres major, and latissimus dorsi. Suprascapular Nerve Snprascapular Artery C^isular Ligament Transverse Lig. Post. Belly of \ 1 Omohyoid \ \ \ fj^ ' ^^^^^-'t-^"^^^^^^?^^ >^,^J^-. Supra- spinatus Spino-glenoid Ligament Long Head of Triceps Fig. 192. — The Right Shoulder-Joint (Posterior View). External Rotation. — Infraspinatus and teres minor. Internal Rotation. — Subscapularis, pectorahs major, teres major, and latissimus dorsi. Circum- duction.— This movement, being a combination of flexion, abduction, exten- sion, and adduction, is effected by the various muscles concerned in these movements. Bursae at Shoulder-Joint. — The bursae in the vicinity of the shoulder- joint are as follows: Subscapular. Subacromial. Infraspinatus. Latissimus dorsi. Teres major. Coraco-clavicular ligament. Bicipital intertubdrcular. The subscapular bursa Ues between the upper border of the tendon of the subscapularis muscle and the upper part of the front of the capsular hgament. It is continuous with the synovial membrane of the joint, which protrudes through the foramen ovale in the capsule. The subacromial or subdeltoid bursa, which is of large size, is 348 A MANUAL OF ANATOMY situated beneath the acromion process of the scapula, the coraco- acromial hgament, and the acromial portion of the deltoid muscle. It covers the upper part of the capsular hgament, and the tendons inserted into the great tuberosity of the humerus. Occasionally it is multilocular. It has no communication with the synovial cavity of the shoulder-joint. The bursa of the infraspinatus muscle, which is not constant, is situated between the tendon of that muscle and the back part of the capsule. It may communicate with the synovial cavity of the joint through an opening in the back part of the capsule. The bursa of the latissimus dorsi muscle is situated between the back of the tendon of insertion of that muscle into the floor of the bicipital groove of the humerus and the front of the tendon of insertion of the teres major muscle into the inner bicipital ridge. It has no communication with the synovial cavity of the shoulder- joint. The bursa of the teres major muscle is situated directly behind the tendon of insertion of that muscle into the inner bicipital ridge of the humerus. It has no communication with the synovial cavity of the shoulder- joint. The bursa of the coraco-clavicular ligament is situated between the conoid and trapezoid portions of that hgament, which extend between the outer part of the clavicle and the root of the coracoid process of the scapula. It has no communication with the synovial cavity of the shoulder-joint. The bicipital intertubercular synovial sheath invests the long tendon of the biceps in the upper part of the bicipital groove of the humerus. It is a prolongation of the synovial membrane of the shoulder- joint. THE FOREARM AND HAND. Cutaneous Nerves. — Along the front of the outer side of the fore- arm is the anterior branch of the cutaneous part of the musculo- cutaneous, and along the back are its posterior branch and the lower external cutaneous branch of the musculo- spiral. Along the front and back of the inner side are the anterior and posterior divisions of the internal cutaneous. All these nerves have been already de- scribed. A small cutaneous branch of the ulnar nerve is given off from it about the centre of the forearm, which, after piercing the deep fascia and communicating with the anterior branch of the internal cutaneous, has a limited distribution to the integument just below the centre, internal to the median line. This branch is not constant. The integument of the palm of the hand is supplied by the palmar cutaneous branches of the ulnar, median, and radial. The THE UPPER LIMB 349 palmar cutaneous branch of the ulnar arises in common with the branch to the integument of the forearm and descends on the ulnar artery, keeping beneath the deep fascia until it approaches the wrist, where it becomes cutaneous on the outer side of the tendon of the flexor carpi ulnaris. It then passes over the anterior annular ligament, and is distributed to the integument of the inner part of the palm. The palmar cutaneous branch of the median arises a little above the wrist, and pierces the deep fascia just above the anterior annular ligament, in the interval between the tendons of the flexor carpi radialis and palmaris longus. It then descends Radial Dorsal Branch of Ulnar ., , Twigs of Median Fig. 193. — Diagram of the Nerves of the Hand (Dorsal Aspect). over the anterior annular ligament, and is distributed to the in- tegument of the outer part of the palm, and slightly to that of the thenar erhinence. It communicates internally with the palmar cutaneous of the ulnar, and externally with that of the radial. The palmar cutaneous branch of the radial arises from the external division of the nerve which passes to the outer side of the thumb. It is joined by a twig from the anterior branch of the musculo- cutaneous, and is distributed to the integument of the thenar eminence. The integument of the dorsum of the hand and fingers is supplied 350 A MANUAL OF ANATOMY by the radial nerve and the dorsal branch of the ulnar. The radial nerve winds backwards beneath the tendon of the brachio- radialis about 3 inches above the wrist, and then divides into two branches — external and internal. The external branch passes to supply the outer side of the thumb, giving off in its course the palmar cutaneous branch. The internal branch, having com- municated with the posterior branch of the musculo-cutaneous, and having given a branch to the back of the wrist which communicates with the dorsal branch of the ulnar, divides into four digital nerves. The first supplies the inner side of the thumb, the second the outer side of the index finger, the third bifurcates at the cleft between the index and middle fingers into two collateral branches for the supply of their contiguous sides, and the fourth passes to the cleft between the middle and ring fingers. The latter in its course is reinforced by an offset from the dorsal branch of the ulnar, and then it divides into two collateral nerves for the supply of the contiguous sides of the middle and ring fingers. The dorsal branch of the ulnar nerve arises about 2^ inches above the wrist, and winds backwards beneath the tendon of the flexor carpi ulnaris. It then gives a branch to the back of the wrist, which communicates with a branch of the radial, and there- after is distributed as follows : one branch supplies the inner side of the little finger ; a second branch passes to the cleft between the little and ring fingers, giving an offset to the innermost digital branch of the radial, and it divides into two collateral branches for the supply of the contiguous sides of these fingers ; whilst a third branch is distributed to the integument of the back of the hand. The distribution of the dorsal digital nerves is as follows : on the thmnb they extend as far as the nail, on the index finger to the distal end of the second phalanx, on the middle finger to near the distal end of the first phalanx, on the ring-finger to near the distal end of the second phalanx, and on the little finger as far as the nail. The portions of integument not supplied by the dorsal digital nerves derive their innervation from branches which pass backwards from the palmar digital branches" of the median and ulnar nerves. Veins. — ^The superficial veins of the forearm, already described, are the radial, median, anterior ulnar, and posterior ulnar. On the back of the hand is the dorsal venous plexus, and in front of the anterior annular ligament is the anterior plexus, of small size. The dorsal venous plexus receives the superficial digital veins, which com- mence in plexuses in the region of the nails. They are two in number to each finger, one being placed on each side towards the dorsal aspect. These veins form cross arches above and below the inter- phalangeal joints on the backs of the fingers. At the clefts the collateral veins unite to form in each case a single trunk, and these trunks end in the dorsal venous plexus. The superficial digital vein from the inner side of the little finger passes to the commence- THE UPPER LIMB 35' ment of the posterior ulnar vein, and is known as the vena salvatdla or ' saving vein.' The blood is conveyed away from the outer side of the dorsal venous plexus by the radial vein, and from the inner side by the posterior ulnar vein. The radial vein receives a com- municating branch from the venae comites of the deep palmar arch at the proximal end of the first interosseous space. The posterior ulnar vein receives a communicating branch from the venae comites of the profunda branch of the ulnar artery, which passes beneath the abductor minimi digiti muscle. The anterior venous plexus receives its radicles from the palm, and the blood is conveyed away from it by the median vein . The anterior ulnar vein, as stated, commences on the inner aspect of the front of the wrist. Deep Fascia of the Forearm. — The deep fascia is of considerable strength, its fibres being principally transverse, though some are disposed longitudinally and obliquely. Superiorly, below the internal epicondyle, it receives the semilunar fascia of the biceps, and behind it gets an accession of fibres from the tendon of the triceps. In front of the elbow it presents an opening for the passage of the deep median vein. In the region of the epicondyles it serves as a common tendon of origin to the muscles arising from these prominences, and it sends between them strong intermuscular septa which afford additional origin to them, and are readily recognised on the surface by white hues. It is attached above to the epicondyles of the humerus and the margins of the triangular surface on the back of the olecranon process of the ulna, and along the forearm to the posterior border of the latter bone. Anteriorly it sends an ex- pansion between the superficial and deep muscles, and it acts in a similar manner on the posterior aspect, where the fascia is stronger than in front. At the wrist it blends with the anterior annular liga- ment, and posteriorly it forms the posterior annular ligament. FRONT OF THE FOREARM. Muscles. — The muscles of the front of the forearm are arranged in three layers — first or superficial, second or intermediate, and third or deep. First Layer. — The muscles comprising this layer are, in order from without inwards, the pronator radii teres, flexor carpi radialis, palmaris longus (inconstant), and flexor carpi ulnaris. I. Pronator Radii Teres. — This muscle arises by two heads — superficial or humeral, and deep or coronoid. The superficial head, which is of large size, arises from (i) the front and upper part of the internal epicondyle, and lower part of the internal supracondylar ridge, of the humerus ; (2) the common tendon ; and (3) the inter- muscular septa between it and the flexor carpi radialis externally, and flexor sublimis digitorum deeply. The deep head, which is of small size, arises from the inner margin of the coronoid process of the 352 A MANUAL OF ANATOMY ulna, and, after a short course, it joins the deep surface of the super- ficial head at an acute angle. Insertion. — By means of a flat tendon, about i| inches broad, into the rough impression on the outer surface of the radius at its centre, where the curve of the bone is most prominent. Nerve-supply. — The median nerve, which arises from the outer and inner cords of the brachial plexus, its fibres being derived from the last four cervical and first thoracic nerves. The branches are given off just before the median nerve passes between the two heads of origin of the muscle. The muscle is directed downwards and outwards. Action. — (i) To pronate the forearm, and (2) to assist inflexion of the elbow- joint. The median nerve passes between the two heads of the muscle, and the ulnar vessels beneath its deep head. The muscle may have a third head, arising from the internal inter- muscular septum of the arm, or from a supracondylar process, and, when this is so, it bridges over the brachial artery and median nerve. 2. Flexor Carpi Radialis — Origin. — (i) The front of the internal epicondyle by means of the common tendon ; (2) the deep fascia covering the muscle ; and (3) the intermuscular septa separating it from the pronator radii teres externally, palmaris longus internally, and flexor sublimis digitorum deeply. Insertion. — The front of the base of the second metacarpal bone, and by a small slip into the front of the base of the third. The muscle presents a fusiform, fleshy belly in the upper half of the forearm, which is replaced in the lower half by a strong, flat tendon. Nerve-supply. — ^The median nerve. The direction of the muscle is downwards and outwards. Action. — (i) To flex the wrist-joint, and (2) to assist in flexion of the elbow- joint. The tendon of the muscle passes through a special compart- ment of the anterior annular ligament, where it traverses the groove on the palmar surface of the trapezium, and the radial vessels lie upon the outer side of the tendon in the lower half of the forearm. 3. Palmaris Longus — Origin. — (i) The front of the internal epi- condyle by means of the common tendon ; (2) the deep fascia cover- ing the muscle ; and (3) the intermuscular septa separating it from the flexor carpi radialis externally, flexor carpi ulnaris internally, and flexor sublimis digitorum deeply. Insertion. — (i) The upper part of the central division of the palmar fascia, and (2) the front of the anterior annular ligament at its lower part. Nerve-supply. — ^The median nerve. Action. — (i) To render tense the central division of the palmar fascia ; (2) to assist in flexing the wrist-joint ; and (3) to assist feebly in flexing the elbow- joint. THE UPPER LIMB 553 The palmaris longus is the representative of an original super- ficial flexor of the fingers, the expanded portion of the tendon of which remains as the palmar fascia. 4. Flexor Carpi Ulnaris. — ^This muscle arises by two heads. One Biceps Bracbialis Anticus Biachio-iadialis Flexor Sublimis Digitorum Flexor Longus Pollicis Pronator Quadratus Anterior Annular Ligament - Pronator Radii Ter'is . Fle.vor Carpi Radialis . Palmaris Longus - Flexor Carpi Ulnaris Palmaris Brevis Fig. 194. — The Superficial Muscles of the Front of THE Forearm. head arises from (i) the front of the internal epicondyle by means of the common tendon ; (2) the deep fascia ; and (3) the inter- j muscular septa between it and the palmaris longus and flexor sub- I limis digitorum. The other head arises from (i) the inner aspect of the olecranon process, and (2) the upper two-thirds of the posterior 23 3S4 A MANUAL OF ANATOMY border, of the ulna, by an aponeurosis common to it, the flexor profundus digitorum, and extensor carpi ulnaris. Insertion. — ^The pisiform bone. From the tendon of insertion two prolongations are given off, known as the pisi-uncinate and pisi- metacarpal ligaments, the former being attached to the anterior border of the hook of the unciform bone, and the latter to the front of the base of the fifth metacarpal. The tendon also gives off laterally a band to the anterior annular ligament. Nerve-supply. — The ulnar nerve, which is a branch of the inner cord of the brachial plexus, its fibres being derived from the eighth cervical and first thoracic. The fibres are directed downwards and forwards, and terminate on the posterior aspect of the tendon which appears about the centre of the forearm. Action. — (i) To flex and adduct the wrist-joint, and (2) to flex feebly the elbow- joint. The ulnar nerve and posterior ulnar recurrent artery pass between the two heads of the muscle. Second Layer. — Flexor Sublimis Digitorum (flexor perforatus) — Origin. — The upper part arises from (i) the internal epicondyle ; (2) the intermuscular septum between it and the first layer ; (3) the internal lateral ligament of the elbow-joint ; and (4) the tubercle on the inner margin of the coronoid process of the ulna. The lower part, broad and thin, arises from the anterior oblique line of the radius. Insertion. — By four tendons into the sides of the second phalanges of the four inner fingers, at their centre and on their anterior aspect. The muscle in the lower part of the forearm is replaced by four tendons which pass beneath the anterior annular ligament in pairs. The tendons of the anterior pair are for the middle and ring fingers, whilst those of the posterior pair are for the index and little fingers. In this situation, as well as for a little above the wrist, and as low as about the centre of the palm, they are invested, along with the deep flexor tendons, by the great palmar bursa, to be afterwards described. In the palm the four tendons diverge, and each is accom- panied by a tendon of the flexor profundus digitorum, which lies beneath it. At the commencements of the digits each pair of tendons enters the sheath on the palmar aspect of a finger, which binds them to the first and second phalanges. Towards the distal end of the first phalanx the flexor sublimis tendon splits into two parts to allow the flexor profundus tendon to pass through. The two divisions of the superficial tendon are folded round the deep tendon, and unite beneath it at the proximal end of the second phalanx. Beyond this point the superficial tendon is grooved to support the deep tendon, and then divides into its two parts of insertion. The sheath and its accessories will be afterwards described. Ntrve-supply. — The median nerve. Action. — (i) To flex the second phalanges of the four inner fingers ; THE UPPER LIMB 355 Biceps Brachio-radiali Brachial Artery Median Nerve . ^Brachialis Auticus Superficial Head of Pro- nator Radii Teres (cut) Radial Nerve^. Radial Recurrent Artery- Radial Artery ._ Superficial Head of Pronator- Radii Teres (cut) Flexor Longus Pollicis-. Radial Artery- Brachio-radialis- Flexor Carpi Radialis— Pronator Quadratus Extensor Ossis M«tacarpi~ Pollicis Abductor Pollicis — Superficial Head of Flexor -. Brevis Pollicis ^ Flexor Carpi Radialis --Ulnar Artery — Palmaris Longus '•-Deep Head of Pronator Radii Teres — - - — Flexor Carpi Uloaris Flexor Sublimis Digitorum —Median Nerve Palmaris Longus — —Ulnar Artery — Ulnar Nerve -Flexor Carpi Ulnaris Palmaris Brevis Palmar Fascia Fig. 195. -The Front of the Forearm, and Palm of the Hand. 356 A MANUAL OF ANATOMY (2) to flex their metacarpo-phalangeal joints ; (3) to flex the wrist- joint ; and (4) to assist in flexion of the elbow- joint. Radial Artery. — ^The radial artery is one of the terminal branches of the brachial, from which it arises in the anticubital space, opposite the upper part of the neck of the radius. It is smaller than the ulnar, which is the other terminal branch, and in point of direction the vessel is the continuation of the brachial. Its destination is the palm, to reach which it passes at first downwards and slightly outwards, as low as the styloid process of the radius. Here the vessel passes to the back of the wrist beneath the styloid process and upon the external lateral ligament, after which it sinks between the two heads of the abductor indicis muscle. In this way it reaches the palm, where it anastomoses with the profunda branch of the ulnar artery, and so forms the deep palmar arch. The vessel is divided into three parts. The first part lies in front of the fore- arm, the second on the back of the wrist, and the third in the palm. First Part. — This part extends from the origin to the styloid pro- cess of the radius. Its direction is downwards and slightly outwards, and its course may be indicated by a line drawn from a point just below the bend of the elbow, midway between the epicondyles of the humerus, to a point about | inch internal to the styloid process of the radius. In the upper third the vessel lies between the brachio-radialis externally and pronator radii teres internally, being overlapped by the fleshy belly of the former. Thereafter it is placed between the brachio-radialis externally and flexor carpi radialis internally, and in the lower half of the forearm, where these muscles are replaced by their tendons, the vessel is quite superficial. Relations — Superficial. — ^The integument, and margin of the brachio-radialis in the upper third, or more. Branches of the musculo-cutaneous nerve are distributed over the line of the vessel. Deep. — From above downwards it lies upon (i) the tendon of inser- \ tion of the biceps ; (2) the supinator radii brevis ; (3) the tendon of i insertion of the pronator radii teres ; (4) the radial origin of the flexor j sublimis digitorum ; (5) the flexor longus poUicis ; (6) the pronator quadratus ; and (7) the lower end of the radius. External. — The \ brachio-radialis throughout the whole of the forearm, and the I external vena comes. The radial nerve in the upper part lies a little (1 to the outer side of the vessel ; at the centre it is closer to it ; and in | the lower part the nerve leaves the artery by turning backwards i*: beneath the tendon of the brachio-radialis. Internal. — The in-[j ternal vena comes, pronator radii teres in the upper third, and 5 thereafter the flexor carpi radialis. H Branches of the First Part. — The first part gives off the following i branches, namely, radial recurrent, muscular, anterior radial If, carpal, and superficial volar. The radial recurrent artery, usually of large size, arises from the I outer side of the radial close to its commencement, and passes out-lji wards beneath the brachio-radialis, where it rests on the supinator'i i THE UPPER LIMB 357 radii brevis. Here it divides into branches which come into relation with the musculo-spiral nerve and its terminal divisions. Most of these are distributed to the muscles arising from the ex- ternal epicondyle, and they anastomose with the posterior inter- osseous recurrent. One branch, however, ascends with the musculo- spiral nerve between the brachio-radialis and brachialis anticus, and anastomoses with the anterior terminal branch of the superior profunda of the brachial. The radial recurrent also gives articular twigs to the elbow-joint. The muscular branches arise at frequent intervals along the forearm. The anterior radial carpal artery, of small size, arises from the inner side of the radial at the level of the lower border of the pro- nator quadratus, along which it passes inwards, lying deeply beneath the flexor tendons. At the middle hne it anastomoses with the an- terior ulnar carpal artery to form the anterior carpal arch. This arch is reinforced from above by the anterior branch of the anterior interosseous artery, and from below by the recurrent branches of the deep palmar arch. In this manner the anterior carpal arch is con- verted into a rete, the branches of which are distributed to the wrist - joint, and the carpal articulations and bones. The superficial volar artery arises either below the preceding, or sometimes above it. It passes downwards over, or through, the thenar muscles, in which, if of small size, it terminates. When large, it reaches the palm, and anastomoses with the ulnar artery to complete the superficial palmar arch. Varieties of the First Part.— (i) The artery may arise high up from the brachial, or axillary. (2) When of high origin, it may descend superficial to the semilunar fascia of the biceps and deep fascia of the forearm. (3) The I artery may turn backwards over the brachio-radialis just below the centre jof the forearm. (4) It may be joined by a vas aberrans from the brachial, jor axillary. (5) It may terminate at the lower part of the forearm, its dis- itribution being taken up by the ulnar, median, or anterior interosseous. 1 The second and third parts of the radial artery will be afterwards I described. Radial Venae Comites. — ^The radial artery is accompanied by two ; venae comites, which are placed one on either side of the vessel, and I they communicate at frequent intervals by transverse branches jing upon it. They terminate above by uniting to form the external brachial vena comes. Radial Nerve. — ^The radial nerve is one of the terminal branches of the musculo-spiral, its fibres being derived from the sixth cervical, -ind sometimes from the fifth and seventh. It passes straight down- kvards under cover of the brachio-radialis, lying at first a little to ithe outer side of the radial artery, then getting closer to it at the l:entre of the forearm, and finally leaving the vessel in the lower bart by turning backwards beneath the tendon of the brachio- ladialis on its way to its cutaneous distribution, which has been iilready described. It is a sensory nerve, and gives ofE no branches kntil it reaches the back of the limb. 3S8 A MANUAL OF ANATOMY Posterior Interosseous Nerve. — This is the other and larger terminal branch of the musculo -spiral, its fibres being derived from the sixth, seventh, and sometimes the eighth, cervical. After a short downward course under cover of the brachio-radialis, it winds round the outer side of the radius, passing through the supinator radii brevis. Having reached the back of the limb near the lower border of that muscle, it descends, in company with the posterior interosseous artery, between the superficial and deep groups of muscles. At the upper border of the extensor longus pollicis it leaves the artery and passes beneath that muscle, where it meets the posterior branch of the anterior interosseous artery on the back of the interosseous membrane. Thereafter it passes through the groove on the back of the radius for the extensor communis digi- torum and extensor indicis, lying beneath the tendons and the posterior annular ligament. It terminates on the back of the wrist in a gangliform enlargement, from which branches are given off to the wrist- joint and carpal articulations. Branches. — ^The branches are muscular and articular. Muscular Branches. — Before piercing the supinator radii brevis the nerve gives branches to that muscle and to the extensor carpi radialis brevior. After reaching the back of the forearm, it supplies the extensor communis digitorum, extensor minimi digiti, extensor carpi ulnaris, the three extensors of the thumb, and the extensor indicis. Articular Branches. — ^These irise from the terminal gangliform' enlargement, and are distributed to the wrist- joint and carpal articulations. Ulnar Artery. — ^The ulnar artery is the larger of the two termini branches of the brachial, and it arises in the anticubital space opposite the upper part of the neck of the radius. Its destinatioi is the palm, which it reaches by passing over the anterior annulai^ ligament, and there it forms the superficial palmar arch. It ig at first directed downwards and inwards beneath both heads ol the pronator radii teres, flexor carpi radialis, palmaris longusJ and flexor sublimis digitorum, and it here describes a slight curve^ the convexity of which is directed inwards. Having gained th^ front of the ulna it meets the ulnar nerve a little above the centre of the forearm, and it then descends on the outer side of the nerve both structures resting on the flexor profundus digitorum, anc being overlapped by the flexor car^n ulnaris. A little above th^ wrist the artery lies superficially on the outer side of the tendo^ of that muscle. It then crosses over the anterior annular ligament lying close to the outer side of the pisiform bone, with the inter vention of the ulnar nerve, and shortly thereafter it turns outwarc" in the palm towards the thenar muscles. The vessel is divide into three parts — first, second, and third. First Part. — This part extends from the origin to the upinr border of the anterior annular ligament. On account of the curve of the vessel at first no definite line can be given to indicate its* THE UPPER LIMB 359 Biceps ._ Musculo-spiral Nerve - - Brachio-radialis Radial Nerve - Radial Recurrent Artery,. Posterior Interosseous Nerve -- Ulnar Artery. _ Supinator Radii Brevis Radial Artery - Pronator Radii Teres . Flexor Longus Pollicis Anterior Interosseous Nerve Brachio-radialis Superficial Volar Artery — ~ Extensor Ossis Metacarpi Pollicis Opponens Pollicis Superficial Head of Flexor Brevis Pollicis j^iiUy-iL- IJrachialis Anticus LLii--\- Median Nerve Brachial Arterj- Pronator Radii Teres - Flexor Carpi Radialis Palmaris Longus Flexor Carpi Ulnaris AI-- Ulnar Nerve - Ulnar Artery __ Flexor Profundus Digitorum Anterior Interosseous Artery Pronator Quadratus — Median Nerve Abductor Pollicis iiperficial Palmar Arch Fig. 196. — Deep Dissection of Front of Right Forearm, AND Superficial Dissection of Palm. 36o A MANUAL OF ANATOMY entire course, but in the lower half of the forearm the border of the flexor carpi ulnaris is the guide. Relations — Superficial. — In the upper half of the forearm the artery is deeply placed, being covered by both heads of the pronator radii teres, flexor carpi radialis, palmaris longus, and flexor sub- limis digitorum. In the lower half it is overlapped by the tendon of the flexor carpi ulnaris, except for a little above the wrist, where it lies superficially on the outer side of that tendon. The palmar cutaneous branch of the ulnar nerve descends over the artery in the lower half. Deep. — Brachialis anticus for about i inch, and thereafter the flexor profundus digitorum. External. — ^The external vena comes, and, in the lower half, the flexor sublimis digitorum. Internal. — ^The internal vena comes, ulnar nerve for rather more than the lower half, and the tendon of the flexor carpi ulnaris for a little above the wrist. The nerves related to the first part of the artery are the median, ulnar, and palmar cutaneous branch of the ulnar. The median nerve lies for a little at first on the inner side of the vessel, but, at the point where the vessel passes beneath the deep head of the pronator radii teres, the nerve crosses it, being separated from it by the deep head of that muscle, and so gains its outer side. The ulnar nerve, having come from behind the internal epicondyle, is widely separated from the artery for rather more than the upper third of the forearm. A little above the centre the nerve and artery meet, and then descend in close contact, the nerve being on the inner side, with the intervention of the internal vena comes. The palmar cutaneous branch of the ulnar nerve, as stated, descends over the lower half of the vessel. Branches of the First Part. — The first part gives off the following branches, namely, anterior ulnar recurrent, posterior ulnar re- current, common interosseous (giving off anterior and posterior interosseous), muscular, posterior ulnar carpal, and anterior ulnar carpal. The anterior ulnar recurrent artery, of small size, passes upwards and inwards on the brachialis anticus and beneath the superficial head of the pronator radii teres, to supply these muscles and anastomose with the anterior branch of the anastomotica magna of the brachial. The posterior ulnar recurrent artery, of large size, arises just below the preceding, or sometimes in common with it. It passes inwards beneath the flexor sublimis digitorum, and then ascends with the ulnar nerve between the two heads of the flexor carpi ulnaris to the interval between the internal epicondyle and olecranon process. It supplies the adjacent muscles, ulnar nerve, and elbow- joint, and it anastomoses with the inferior profunda and posterior branch of the anastomotica magna. It also gives twigs over the back of the olecranon, which anastomose with the posterior inter- osseous recurrent, thus forming the olecranon rete. The common interosseous artery is a short, thick trunk, which arises, below the preceding, about i inch from the commencement THE UPPER LIMB 361 of the ulnar. It is directed backwards to the upper border of the interosseous membrane, where it divides into the anterior and posterior interosseous arteries. (i) The anterior interosseous artery descends on the front of the interosseous membrane, having a vena comes on either side of it, and the anterior interosseous nerve on its outer side. It lies between the flexor longus pollicis externally and the flexor profundus digitorum internally, both of which overlap it, and at the upper border of the pronator quadratus it divides into two terminal branches, anterior and posterior. Branches. — ^These are as follows : the median artery (comes nervi mediani) is a long, slender branch which arises from the commencement of the vessel. It at once gets in contact with the median nerve, which it accompanies beneath the flexor sublimis digitorum, supplying the nerve and that muscle. If of large size, it passes beneath, or over, the anterior annular ligament into the palm, where it may join the superficial palmar arch, or if that should be abnormal, it furnishes certain digital arteries. Muscular branches are given off to the deep layer of muscles, and to the extensor muscles of the thumb on the back of the interosseous membrane. The branches to the latter muscles pierce the mem- brane. The nutrient or medullary arteries enter the radius and ulna. The anterior terminal branch descends beneath the pro- nator quadratus and joins the anterior carpal arch. The posterior terminal branch, which, passing backwards through the interosseous membrane, and having anastomosed with the posterior interosseous, descends beneath the extensor tendons and the posterior annular ligament to the back of the wrist, where it joins the posterior carpal arch. (2) The posterior interosseous artery passes backwards between the upper border of the interosseous membrane and the oblique ligament. At the back of the forearm it appears between the supinator radii brevis and extensor ossis metacarpi pollicis, where it is joined by the posterior interosseous nerve. The artery, with the nerve, then descends between the superficial and deep group of muscles until it reaches the upper border of the extensor longus pollicis. Here the artery leaves the nerve, and passes over that muscle and the extensor indicis. At the lower border of the latter muscle it anastomoses with the posterior terminal branch of the anterior interosseous, and then ends in articular branches to the wrist- joint, though it may pass to join the posterior carpal arch. Branches. — ^These are as follows : the posterior interosseous re- current arises as soon as the vessel reaches the back of the forearm. It passes upwards beneath the anconeus to the back of the external epicondyle, where it anastomoses with the posterior branch of the superior profunda of the brachial. It also gives twigs over the back of the olecranon process which anastomose with branches of the posterior ulnar recurrent, and so form the olecranon rete. 362 A MANUAL OF ANATOMY In addition, it anastomoses with the muscular branches of the radial recurrent. Muscular branches supply the adjacent muscles. Articular branches are given off to the wrist-joint. The muscular branches of the first part of the ulnar artery arise at frequent intervals along the forearm. The posterior ulnar carpal artery arises a little above the pisiform bone, and passes backwards beneath the tendon of the flexor carpi ulnaris to the back of the wrist. Here it turns outwards beneath Brachial Arterj Rrachialis Amicus Anastomotica Magna Artery Tendon of Biceps Brachio-radialis Radial Recurrent Artery Supinator Radii Brevis... Ext. Carpi Radialis Longior Radial Artery Common Interosseous. Artery Tricepf Int. Intermuscular Septum Posterior Branch of Anastomotica Magna Anterior Branch of Anastomotica Magna . Pron. Radii Teres Common Origin of Superf. Flexors . Anterior Ulnar Recurrent Arterj' Posterior Ulnar Recurrent Artery Flexor Profundus Digitorum Ulnar Artery Fig. 197. — Deep Dissection of the Front of the Right Elbow (after Tiedemann). the extensor tendons, and anastomoses with the posterior radial carpal and posterior branch of the anterior interosseous to form the posterior carpal arch. It may give off the dorsal digital artery of the inner side of the little finger. The anterior ulnar carpal artery arises opposite the lower border of the pronator quadratus. It passes outwards along the lower border of that muscle beneath the flexor profundus digitorum, and anas- tomoses with the anterior radial carpal, the anterior branch of the anterior interosseous, and the recurrent branches of the deep palmar arch, to form the anterior carpal arch or rete. Anastomoses round the Elbow-Joint. — ^The anastomoses of THE UPPER LIMB 363 arteries round the elbow-joint are very free. In front of the internal epicondyle of the humerus the anterior branch of the anastomotica magna of the brachial anastomoses with the anterior ulnar recurrent. Behind the internal epicondyle the inferior profunda and the posterior branch of the anastomotica magna (both of the brachial) anastomose with the posterior ulnar recurrent. In front of the external epicondyle the anterior ter- minal branch of the superior profunda of the brachial anastomoses with the radial recurrent. Behind the external epicondyle the Inferior Profunda Posterior Branch of Anastomotica Magna Internal Epicondyle. Olecranon Rete Posterior Ulnar Recurrent Superior Profunda Posterior Branch) Arterial Arch External Epicondyle ""-.-.• Branches of Radial Recurrent Posterior Interosseous Recurrent Posterior Interosseous Fig. 198. — The Anastomoses round the Right Elbow-Joint (Posterior View) (after Tiedemann). posterior terminal branch of the superior profunda anastomoses with the posterior interosseous recurrent. Upon the back of the shaft of the humerus, immediately above the olecranon fossa, a transverse anastomosis takes place between the posterior branches of the superior profunda and anastomotica magna, both of the iirachial. Upon the back of the olecranon process is the olecranon 1 terial rete, which is formed by branches of the posterior inter- sseous recurrent and posterior ulnar recurrent. Varieties. — (i) The ulnar artery may arise high up from the bracliial, or xillary. In cases of high origin the vessel usually descends over the muscles 364 A MANUAL OF ANATOMY arising from the internal epicondyle of the humerus, and beneath the deep fascia, though it may be superficial to it. In such cases the common inter- osseous is a branch of the main trunk, and it furnishes the anterior and posterior ulnar recurrent arteries. (2) The artery, though normal in origin, may pass superficial to the muscles arising from the internal epicondyle. Second Part of the Ulnar Artery. — The second part lies upon the anterior annular ligament, and extends from its upper to its lower border. It has a vena comes on either side of it, and the ulnar nerve on its inner side. It lies on the outer side of the pisiform bone, by which it is overhung, and on the inner side of the hook of the unciform bone, where it is under cover of the pisi-uncinate ligament. Relations — Superficial. — The integument, the expansion from the flexor carpi ulnaris tendon to the front of the anterior annular ligament, and the pisi-uncinate ligament. Deep. — ^The anterior annular ligament. External. — ^The external vena comes, and hook of the unciform bone. Internal. — ^The internal vena comes, ulnar nerve, and pisiform bone. The branches of this part are unimportant. The third part of the ulnar artery will be described in connection with the palm. Ulnar Venae Comites. — ^The ulnar artery in the first and second parts of its course is accompanied by two venae comites, one being placed on either side of the vessel, and the two communicate at frequent intervals by transverse branches which lie upon it. They commence in the venae comites of the inner parts of the superficial and deep palmar arches, and they terminate above by uniting to form the internal brachial vena comes. Ulnar Nerve. — ^The ulnar nerve enters the forearm by passing through the interval between the internal epicondyle and olecranon process, where it lies between the two heads of the flexor carpi ulnaris. It then descends under cover of that muscle, lying upon the flexor profundus digitorum. A little above the centre of the forearm it meets with the ulnar artery, upon the inner side of which it subsequently lies. On approaching the wrist it escapes from beneath the flexor carpi ulnaris, and lies, with the artery, close to the outer side of its tendon. It then passes over the anterior annular ligament close to the outer side of the pisiform bone, by which it is overhung, and subsequently on the inner side of the hook of the unciform bone. Thereafter it enters the palm, where it divides into its two terminal branches, superficial and deep. Branches. — These are articular, muscular, and cutaneous. The articular branches, two or three in number, are given off to the elbow-joint as the nerve passes between the internal epicondyle and olecranon process. The muscular branches arise in the upper part of the forearm, and are distributed to the flexor carpi ulnaris and the inner portion of the flexor profundis digitorum. THE UPPER LIMB 3^5 The cutaneous branches are three in number, and have been already described. The ulnar nerve in the palm will be afterwards described. Median Nerve. — The median nerve lies at first in the anticubital space, where it is placed on the inner side of the brachial and ulnar arteries. On leaving the space it passes between the two heads of the pronator radii teres, where it crosses the ulnar artery, the deep head of that muscle intervening between the two. It then passes beneath the radial origin of the flexor sublimis digitorum, and descends under cover of that muscle in the middle line, until it approaches the wrist. Here it escapes from beneath the muscle, and lies between its tendons and that of the flexor carpi radialis, where it parts with its palmar cutaneous branch. Thereafter it passes under the anterior annular ligament into the palm, where it will be afterwards described. The nerve is accompanied by the median artery, which is a branch of the anterior interosseous near its origin. Branches. — The branches of the nerve in the forearm are articular, muscular, and cutaneous. The articular branches, one or two in number, enter the elbow- joint on its anterior aspect. The muscular branches supply all the muscles on the front of the forearm, except the flexor carpi ulnaris and the inner portion of the flexor profundus digitorum. The branch, or branches, to the pronator radii teres arise from the nerve before it passes between the two heads of that muscle. The branches for the flexor carpi radiahs, palmaris longus, and flexor sublimis digitorum arise lower down. The flexor longus polUcis, outer portion of the flexor profundus digitorum, and pronator quadratus are supplied by the anterior interosseous branch. This long branch arises from the median just below the neck of the radius, and it descends on the front of the interosseous membrane, lying on the outer side of the anterior interosseous artery, both being overlapped by the contiguous borders of the flexor profundus digitorum and flexor longus pollicis. On reaching the upper border of the pronator quadratus the nerve passes beneath that muscle, and ends in two branches, one of which enters the deep surface of the muscle, whilst the other passes to supply the wrist-joint. The branch to the outer portion of the flexor profundus digitorum arises high up, and it communicates in the muscle with the branch of the ulnar nerve to its inner portion. The anterior interosseous nerve in its course furnishes an interosseous branch, which is distributed to the interosseous membrane, and gives off medullary filaments which accompany the medullary arteries of the radius and ulna. Third Layer of Muscles. — ^The muscles comprising the third or deep layer are three in number, namely, the flexor profundus digitorum, flexor longus pollicis, and pronator quadratus. I. Flexor Profundus Digitorum (flexor perforans) — Origin. — (i) The upper three-fourths of the anterior surface of the ulna; 3^6 A MANUAL OF ANATOMY (2) the inner half of the front of the interosseous membrane ; (3) the upper two-thirds of the inner surface of the ulna ; and (4) the posterior border of the bone for a similar extent, by an aponeurosis common to it, the flexor carpi ulnaris, and extensor carpi ulnaris. Insertion. — ^The front of the bases of the distal phalanges of the four inner fingers. The tendinous part of the muscle makes its appearance about the centre of the forearm, and the index-finger tendon is usually separate from the rest of the tendinous mass over the greater part of its extent. The other three tendons become separate beneath the anterior annular ligament, so that in the palm there are four diverging tendons, connected with which are the lumbricales. Each deep flexor tendon accompanies a superficial flexor tendon, beneath which it lies, and both enter the sheath on the palmar aspect of a finger. Opposite the distal end of the first phalanx the deep tendon passes through the cleft in the superficial tendon, and so reaches its more distant point of insertion. Nerve- supply. — (i) The anterior interosseous branch of the median supplies that portion of the muscle which acts upon the index finger, and in part the portion acting upon the middle and ring fingers ; and (2) the ulnar nerve supplies that portion which acts upon the little finger, and in part the portion acting upon the ring and middle fingers. Sometimes the anterior interosseous nerve supplies the whole of the portion acting upon the middle finger. Action. — (i) To flex the distal phalanges of the four inner fingers ; (2) to assist in flexing the second phalanx and metacarpo-phalangeal joint ; and (3) to assist in flexing the wrist-joint. 2. Flexor Longus PoUicis — Origin. — (i) The anterior surface of the radius, from the anterior oblique line above to the upper border of the pronator quadratus below ; (2) the outer half of the front of the interosseous membrane ; and (3) as a rule by a tendinous slip from the inner margin of the coronoid process of the ulna, or from the internal epicondyle of the humerus. Insertion. — The front of the base of the distal phalanx of the thumb. The tendon appears on the front of the muscle about the centre of the forearm, and receives fleshy fibres until it is near the wrist. Nerve-supply. — ^The anterior interosseous nerve. Action. — (i) To flex the distal phalanx of the thumb ; (2) to assist in flexing its metacarpo-phalangeal joint ; and (3) to act as an auxiliary flexor of the wrist-joint. 3. Pronator Quadratus — Origin. — ^The front of the ulna over its lower fourth. Insertion. — The front of the radius for about 2 inches at its lower end, and the anterior part of the inner surface. Nerve-supply. — ^The anterior interosseous nerve. The fibres are disposed, for the most part, transversely, and the muscle is covered by a firm aponeurosis over about its inner third. Action. — To pronate the radius upon the ulna. THE UPPER LIMB 367 FRONT OF THE WRIST AND PALM. Landmarks. — Below, and internal to, the styloid process of the radius the tuberosity of the scaphoid can be felt, and below this the tuberosity of the trapezium. On the inner aspect of the front of the wrist the pisiform bone can easily be felt, and below, and external to, it, the hook of the unciform bone. The interval between these two projections indicates the position of the ulnar vessels and nerve. The centre of the palm presents a triangular hollow, the apex of which is directed upwards and inwards towards the wrist, and the base downwards towards the roots of the fingers, in which latter situation there is a transverse prominence, broken up by grooves leading to the four inner digits. The palmar hollow is bounded above and externally by the thenar eminence, and internally by the hypo thenar eminence. The integument of the palm presents four furrows, two being disposed transversely, and two more or less longitudinally. The lower transverse furrow is about i inch above the roots of the inner three digits, and is most conspicuous when the fingers are flexed. It commences at the inner border of the palm, and, passing outwards in a slightly arched manner, it terminates at the cleft between the index and middle fingers. It is produced by the flexion of the me tacarpo- phalangeal joints of the inner three fingers. These joints are situated about midway between this line and the roots of the fingers when these are extended. The upper transverse furrow commences at the outer border of the palm about f inch above the root of the index finger, and it passes inwards and slightly upwards to the inner border of the palm, lying about ^ inch above the lower furrow. The outer part of this furrow is due to flexion of the metacarpo-phalangeal joint of the index finger, and the remainder to complete flexion of the metacarpo-phalangCcJ joints of the inner three fingers. One of the longitudinal furrows commences about the centre of the wrist, and curves downwards and outwards to meet the upper transverse furrow. It is produced by flexion of the joint between the trapezium and metacarpal bone of the thumb during the movement of opposition. The other longitudinal furrow runs downwards from the wrist internal to the preceding, and meets the lower transverse furrow. It is due to the movement of opposi- tion of the little finger. The front of each of the four inner fingers presents three transverse furrows. The distal pair correspond with the interphalangeal joints, but the proximal furrow is about \ inch beyond the metacarpo-phalangeal joint. The front of the thumb presents only two transverse furrows. The position of the superficial palmar arch corresponds with a line drawn across the palm from the web between the thumb and index finger (the thumb being abducted) to the outer side of the pisiform bone. This line is slightly arched, with the convexity towards the fingers. From the convexity of the arch the three compound 368 A MANUAL OF ANATOMY digital arteries pass forwards in line with the webs of the fingers, and they lie over the interosseous spaces. An incision, therefore, may be made with safety in the palm in the direction of the middle line of a finger, but it should not be carried nearer the wrist than the line indicating the position of the superficial palmar arch. The deep palmar arch lies about | inch nearer the wrist than the superficial. The digital arteries are placed on the lateral aspects of the fingers. On the back of the hand the radial tubercle may be felt about the centre of the lower end of the bone, and the heads of the meta- carpal bones, which form the knuckles, are conspicuous when the fingers are flexed. Below and behind the styloid process of the radius there is a well-marked triangular hollow, the base of which is directed upwards, in which, by sinking the finger deeply, pulsa- tion may be felt in the second part of the radial artery in the living subject. At the upper part the tendons of the radial extensors of the wrist may also be felt. The hollow is bounded internally by a prominence formed by the tendon of the extensor longus pollicis, externally by a prominence due to the tendons of the extensor ossis metacarpi pollicis and extensor brevis pollicis, and above by the lower end of the radius. The scaphoid and trapezium lie in its floor, and the radial vein and branches of the radial nerve are in its roof. This hollow is known as the anatomical snuff-box (Cloquet). The middle line of the hand, from and towards which abduction and adduction take place, represents a longitudinal line drawn through the centre of the middle finger. Superficial Fascia. — ^The superficial fascia, especially over the hollow of the palm, is lobulated, the lobules being separated by fibrous processes which pass between the skin and the central division of the palmar fascia. Palmaris Brevis. — ^This is a thin, flat, subcutaneous muscle, of quadrilateral outline, and usually arranged in two or three bundles, separated by fat. Origin. — (i) The front of the anterior annular ligament at its lower and inner part, and (2) the inner margin of the central division of the palmar fascia at its upper part. Insertion. — ^The integument of the inner border of the hand at its inner part. Nerve-supply. — ^The superficial division of the ulnar nerve. Action. — ^To draw the integument into which it is inserted towards the middle line of the hand, thus giving rise to a wrinkled depression on the inner border at its upper part. The muscle lies in the superficial fascia over the upper part of the hypothenar eminence, and covers the ulnar vessels and nerve, which it guards against pressure. Superficial Transverse Ligament. — This ligament is composed of a bundle of transverse fibres, contained within the folds of skin which form the clefts of the four inner fingers. THE UPPER LIMB 369 Palmar Fascia. — The palmar fascia is arranged in three divisions — central and two lateral. The central division is triangular, the apex being towards the wTist, where it is continuous with the tendon of the palmaris longus, and attached to the front of the anterior annular ligament close to its lower border. The superficial fibres of this division are longitudinal, and the deep fibres transverse, the latter being most conspicuous between the diverging digital processes. The base is directed towards the roots of the four inner fingers, on approaching which the fascia divides into four digital processes. These diverge and pass to join the sheaths of the flexor tendons on the fronts of the fingers. Each process gives fibres to the superficial transverse liga- ment and skin of the clefts of the fingers. Each also gives ofl a deep expansion at either side, which joins the transverse metacarpal ligament at either lateral margin of the head of a metacarpal bone. In this way short canals are formed for the superficial and deep flexor tendons on their way to the fronts of the fingers. Between the diverging digital processes three intervals are left, in which the digital arteries and nerv^es and limibricales muscles make their appearance ; and, as stated, the transverse fibres are here conspicuous, where they lie superficial to these structures. The central division is bound to the skin by fibrous processes which enclose spaces containing the lobules of the superficial fascia. Its deep surface is related to the great palmar bursa. At either side it gives off a deep septimi which joins the interosseous fascia. The outer septum is placed betw^een the thenar muscles and the centre of the palm, where the flexor tendons and digital vessels and nerves lie, and it is. pierced by the digital nerves for the sides of the thumb and index finger. The inner septum is placed between the hypothenar muscles and the centre of the palm, and it is pierced by the digital branches of the ulnar nerve, and by a portion of the superficial palmar arch. In this way a large central fascial canal is formed, which contains 1 the superficial palmar arch and its digital branches, the digital I nerves, the superficial and deep flexor tendons, and the limibricales. On either side of this central canal are the thenar and hypothenar j canals, containing the short muscles of the thumb and of the little finger. The central division of the palmar fascia serves as j an important protection to the superficial palmar arch and the ' digital arteries and nerves. From its great strength and capability ' of resistance it has an important bearing on the course taken by ■ t pus in a palmar abscess. 1 The central division represents the expanded portion of the : i tendon of an original superficial flexor muscle of the fingers. The external or thenar division is thin, and covers the thenar ; I muscles. Superiorly it is connected with the tendon of the palmaris 1 [ longus and anterior annular ligament, and it receives an accession I of fibres from the tendon of the extensor ossis metacarpi pollicis. 'Inferiorly it blends with the sheath of the tendon of the flexor longus 'pollicis on the front of the thumb. 24 3/0 A MANUAL OF ANATOMY The internal or hypothenar division, also thin, is connected above with the anterior annular ligament, and terminates below over the muscles inserted into the inner side of the base of the first phalanx of the little finger. Third Part of the Ulnar Artery. — ^The third part of the vessel forms the superficial palmar arch. It descends for a little under cover of the palmaris brevis, and then turns outwards across the palm in an arched manner. About the middle of the thenar eminence it is joined by the superficial volar of the radial, or by a branch of the arteria radialis indicis, or, failing these, by a branch of the arteria princeps pollicis, and so the arch is completed externally. Its con- vexity is directed towards the fingers, and its course may be indicated by a line drawn across the palm from the web between the thumb and index finger (the thumb being abducted) to the outer side of the pisiform bone, the line being slightly arched, with the convexity towards the fingers. Relations — Stiperfidal. — The integument, the palmaris brevis for a short distance internally, and the central division of the palmar fascia. Deep. — From within outwards it rests upon the opponens minimi digiti, the digital branches of the ulnar nerve, the flexor, tendons, and the digital branches of the median nerve. The arch, lies within the great palmar bursa. Branches. — The branches of the arch are cutaneous to the integu- ment of the. palm, muscular to the adjacent superficial muscles, thej profunda branch, and the digital branches. The profunda artery is given off from the commencement of theT arch, opposite the lower border of the anterior annular ligament. It at once passes deeply, in company with the deep division of the ulnar nerve, between the abductor and flexor brevis minimi digiti, then through the opponens minimi digiti, and it terminates by anastomosing with the third part of the radial artery, thereby completing the deep palmar arch. In its short course it gives branches to the hypothenar muscles. The digital arteries arise from the convexity of the arch, and are four in number. They are destined for the sides of the inner three and a half fingers, and are called first, second, third, and fourth, from within outwards. The first is a single arteiy, but the other three are compound, each ultimately dividing into two. The first digital artery, of small size, passes downwards and inwards over the hypothenar muscles, to which it gives twigs, and then it passes along the inner side of the little finger. The second, third, and fourth digital arteries, which are compound, pass downwards over the fourth, third, and second interosseous spaces to near the clefts between the little and ring, ring and middle, and middle and index fingers, where each divides into two collateral digital arteries, which pass along the contiguous sides of these fingeffl. These four digital arteries account for the blood-supply of the sides of the inner three and a half fingers. The outer side of the indfflc finger and both sides of the thumb are supplied by the arteria j THE UPPER LIMB 371 Flexor Carpi Radialis Radial Arter>- Superficial Volar Arter>- . Abductor Pollicis. uperf. Head of lex. Brev. Poll. Id. Obliq. Poll.._ dd. Trans. ._ Pollicis 1st Dorsal iterosseou Flexor Caipi Ulnaris Ulnar Nerve 'i {■-...Ulnar Artery Anterior Annular Ligament ^^Median Nerve __Abd. Min. Dig. Oppon. Min. Dig. Flexor Bre vis Minimi DigitL Superficial - -Palmar Arch Fig. 199. — The Palmar Aspect of the H.\nd, (The Palmar Fascia has been jemoved.) 372 A MANUAL OF ANATOMY radialis indicis and arteria princeps pollicis of the radial. As the digital arteries pass towards the fingers they lie between the flexor tendons, and superficial to the digital nerves and lumbricales muscles. Along the sides of the fingers, however, the digital nerves are superficial to the arteries. Just before the outer three digital arteries divide into their collateral branches each is joined by a palmar interosseous artery from the deep palmar arch, and, it may be, by the inferior perforating branches of the dorsal inter- osseous arteries. The innermost digital artery receives its com- municating branch from the innermost palmar interosseous about the centre of the hand. As the arteries pass along the sides of the fingers they anastomose with each other across the front of the phalanges to form arches, which are placed on the proximal side of the interphalangeal joints. Each also supplies the flexor tendons with their sheaths, and gives off a few dorsal branches. In front of each terminal phalanx the arteries of each finger unite to form an arch, from which many twigs are given off to supply the pulp of the finger and matrix of the nail. The varieties of the superficial palmar arch will be afterwards described. Veins. — The superficial palmar arch is accompanied by two venae comites, and so are the digital arteries. The venae comites of the digital arteries unite at the clefts of the fingers to form single vessels, and these end in the venae comites of the superficial palmar arch. The venae comites of the inner part of the arch unite, and so do those of the inner part of the deep palmar arch, and in this way the venae comites of the ulnar artery are formed. Those from the outer side of the superficial arch go with the superficial volar artery, and, with those from the outer side of the deep arch which accompany the second part of the radial artery, form the radial venae comites. Median Nerve in the Hand. — The median nerve enters the palm by passing beneath the anterior annular ligament, where it lies within the great palmar bursa along with the superficial and deep flexor tendons, giving off articular twigs to the wrist- joint. Close to the lower border of the ligament it presents an enlargement, and breaks up into two divisions — external and internal. The external division gives off a muscular branch and three single digital nerves. The muscular branch passes outwards, and divides to supply the abductor pollicis, opponens pollicis, and superficial head of the flexor brevis pollicis. The three single digital nerves are distributed to the outer and inner sides of the thumb and the outer side of the index finger, and the latter nerve gives a l)ranch to the first, or most external, lumbricalis. The internal division breaks up into two compound digital nerves. The outer of these passes to near the cleft between the index and middle fingers, where it divides into two collateral digital nerves for the supply of the contiguous sides of these fingers. In its course it gives a branch to the second lumbricalis. The inner passes to near the cleft THE UPPER LIMB 373 between the middle and ring fingers, where it also divides into two collateral digital nerves, which supply their contiguous sides. In its course it communicates with the outer digital branch of the ulnar nerve. In the palm the digital nerves lie beneath the super- ficial palmar arch and its digital branches, but along the sides of the fingers the nerves are superficial to the arteries. Occasionally a digital artery may pass through a digital nerve. On the sides of the fingers the nerves, which present small swellings, called Pacinian bodies, give branches to the integument of the palmar aspects of the finger,, and the metacarpo-phalangeal and inter- phalangeal joints. At the extremities of the fingers each nerve Ulnar ; Median \ Anterior Branch of Musculo-cutaneoii< '^ Deep Branch of Ulnar -,iy 1 Branches to Hypothenar Muscle.<: ■/-^: Branches to 2 J Thenar Muscles Branch to ist Lumbricalis ''' Branch to 2nd Lumbricalis.'' Branch connecting Mediar. '' and Ulnar Fig. 200. — Diagram of the Nerves of the Palm. nds in branches for the pulp and matrix of the nail. The digital lerves also give branches which turn backwards to the dorsal aspects f the fingers. These, for the most part, supply the integument s follows : (i) the matrix of the thumb-nail ; (2) the back of the Jrminal phalanx of the index finger ; (3) the back of the second nd terminal phalanges of the middle finger ; and (4) the back of the ^rminal, and distal end of the second, phalanges of the ring finger. Summary of the Median Nerve. — Muscular. — It supplies (i) all the muscles 1 the front of the forearm, except the flexor carpi ulnaris and inner portion the flexor profundus digitorum; {2) two and a half muscles of the thenar ninence, namely, the abductor, opponent;, and superficial head of the ;xor brevis, poUicis ; and (3) the outer two lumbricales. Cutaneous. — It iipplies the outer part of the palm, and the outer three and a half digits. rticular. — It supplies branches to the elbow- and wrist-joints, as weU as to : al joints of the hand. 374 A MANUAL OF ANATOMY Ulnar Nerve in the Hand. — ^The ulnar nerve enters the hand by passing over the anterior annular ligament, where it lies on the inner side of the ulnar vessels, and is overhung by the pisiform bone. It then breaks up into two divisions — superficial and deep. The superficial division passes downwards beneath the palmaris brevis, which it supplies, and it ends in two digital nerves. The inner is a single nerve, and is distributed to the inner side of the little finger. The outer, which is compound, passes to near the cleft between the ring and little fingers, where it divides into two collateral digital nerves for the supply of their contiguous sides. This nerve communicates with the innermost digital branch of the median. The distribution of the nerves on the fingers corresponds with that of the median, and the branches which turn to the backs of the fingers are for the most part distributed as follows : (i) to the back of the terminal, and distal end of the second, phalanges of the ring finger, and (2) to the matrix of the nail of the little finger. The deep division of the ulnar nerve, along with the profunda branch of the ulnar artery, passes between the abductor and flexor brevis minimi digiti, and then through the opponens minimi digiti. There- after it accompanies the deep palmar arch, above which it lies, to the thenar region, and it has an extensive muscular distribution, as follows : it supplies the abductor, flexor brevis, and opponens, miniini digiti, the inner two lumbricales, the seven interossei, and two and a half muscles of the thenar eminence — namely, the deep head of the flexor brevis poUicis, adductor obliquus pollicis, and adductor transversus pollicis. It also gives articular twigs to the wrist-joint, and several of the joints of the hand. Summary of the Ulnar Nerve. — Muscular. — In the forearm it supplies the flexor carpi ulnaris and inner portion of the flexor profundus digitorum; and in the hand it supplies (i) the palmaris brevis, (2) the three hypothenar muscles, (3) the inner two lumbricales, (4) the seven interossei, and (5) two and a half muscles of the thenar eminence, namely, the deep head of the flexor brevis, adductor obliquus, and adductor transversus, pollicis. Cutaneous. — It supplies the integument of (i) the front of the forearm for a little below the centre, and internal to the middle line ; (2) the inner portion of the palm ; and (3) the inner one and a half fingers. Articular. — It supplies branches toi the elbow- and wrist-joints, and several of the joints of the hand. j I Great Palmar Bursa. — ^This bursa has two compartments, inner] and outer. I The inner compartment, which is large and loose, invests the? superficial and deep flexor tendons and median nerve as they pas<' beneath the anterior annular ligament. It extends upwards ini the forearm for rather more than an inch above the ligament, an downwards to about the centre of the palm. It is shut off from tin synovial sheaths of the flexor tendons of the index, middle, and rin fingers, but internally it is prolonged downwards \o be, as a nil continuous with the synovial sheath of the flexor tendons of tlii little finger. The outer compartment, which is long and narrow, invests t! tendon of the flexor longus pollicis beneath the anterior annul. THE UPPER LIMB 375 ligament, and reaches upwards to the same height as the inner compartment. Interiorly it is prolonged uninterruptedly along the tendon to its insertion, so that it is continuous with its synovial sheath on the thumb. The disposition of the great palmar bursa in relation to the thumb and little finger is to be carefully noted in connection with whitlow of these fingers. It will be evident that pus could readily burrow upwards from the thumb and little finger into the lower part of the forearm, passing in its course beneath the anterior annular ligament. Anterior Annular Ligament Synovial Sheath of Thumb Great Palmar Bursa _ . SjTiovial Sheath of Little Fingtr Fig. 201. — The Great Palmar Bursa, and the SyNOViAi, Sheaths of the Flexor Tendons. Sheaths of the Flexor Tendons. — As the superficial and deep flexor tendons pass along the fronts of the four inner fingers each pair is ■-ontained in a fibro-osseous canal. The osseous wall is formed by the palmar aspects of the first and second phalanges, and the fibrous .vail by a sheath. This sheath, over the greater parts of the first ind second phalanges, is thick and strong, and these parts of it ,ire known as the vaginal ligaments. The fibres of these ligaments j"un transversely, and are attached to the rough lateral margins of he palmar surfaces of the phalangeal shafts. Opposite the joints, n order not to interfere with flexion, the vaginal ligaments are -^laced by thin membranes, superadded to which are obliquely 376 A MANUAL OF ANATOMY Flexor Profundus Flexor Sublimis _Ligamentum Longum decussating fibres. Each fibro-osseous canal is lined by synovial membrane, which is reflected over the contained tendons in such a manner as to furnish a separate investment for each. The synovial sheaths of the index, middle, and ring fingers extend into the palm as far as the heads of the metacarpal bones, and they have no connection with the great palmar bursa. The synovial sheath of the little finger, however, is as a rule con- tinuous with the large inner compartment of that bursa. The synovial membranes of the sheaths form ce.tain bands, called vincula accessoria tendinum, which are of two kinds — ligamenta brevia and ligamenta longa. The ligamenta brevia are two in number — one for the superficial and one for the deep flexor tendon. They are broad, laterally compressed, triangular bands which connect each tendon, close to its insertion, with the distal end of the phalanx above that into which it is inserted. The liga- menta Imtga, few and inconstant, are narrow cords which pass between the tendons and the phalanges, or from one tendon to the other. The fibro-osseous canal for the tendon of the flexor longus pollicis isj similar to those of the other flexor tendons,j and its synovial membrane is continuoi with the outer compartment of the great palmar bursa. Lumbricales. — ^These are four tapering muscles which are con- nected with the deep flexor tendons in the palm, and they receive numerical names, the most external being the first. The first anc' second arise each from the outer side of the deep flexor tendon for the index and middle fingers, and the third and fourth arise from the adjacent sides of the two deep flexor tendons between which eacl lies, the tendons involved being those for the middle, ring, anc little fingers. Each muscle tapers off, and ends in a tendon whichJ turning round the outer side of a metacarpo-phalangeal jointj expands, and is inserted into the outer side of the broad expansioi of the extensor tendon on the back of the first phalanx. Nerve-supply — First. — ^The digital branch of the median to th€ outer side of the index finger. Second. — The digital branch of th€ median, which divides to supply the contiguous sides of the indej and middle fingers. Third and Fourth. — The deep division of the ulnar nerve. Action. — (i) To flex the metacarpo-phalangeal joint, and (2) to extend the interphalangeal joints. Anterior Annular Ligament. — This is a strong fibrous band which bridges over the concavity on the palmar aspect of the carpus, Fig. 202. — The Flexor Tendons of a Finger. THE UPPER LIMB i77 and converts it into a fibro-osseous canal. Externally it is attached to the tuberosities of the scaphoid and trapezium, and internally to the pisiform and hook of the unciform. Its upper border is con- tinuous with the deep fascia of the front of the forearm ; its lower border is connected with the palmar fascia ; at its upper and inner part it receives an expansion from the tendon of the flexor carpi ulnaris ; and near its lower border it gives partial insertion to the tendon of the palmaris longus. The ligament is crossed by the last- mentioned tendon and the ulnar vessels and ner\'e, the latter structures lying close to the pisiform bone, where they are overhung by it, and overlapped by a slip from the flexor carpi ulnaris. At either side the ligament affords origin to muscles of the thenar and hypothenar groups. The fibro-osseous canal formed by the liga- ment and front of the carpus gives passage to the tendons of the flexor sublimis and flexor profundus digitonun, the tendon of the flexor longus poUicis, and the median nerve. The tendon of the flexor carpi radialis does not pass through this canal, but traverses a special compartment in the outer part of the ligament as it passes through the groove on the front of the trapezium, where it is invested by a special synovial sheath. Thenar Muscles. — ^The short muscles of the thumb are five in number, namely, the abductor, opponens, and flexor brevis, pol- licis, the adductor obliquus pollicis, and the adductor transversus polUcis. 1. Abductor Pollicis — Origin. — (i) The front of the anterior annular ligament ; (2) the tuberosity of the scaphoid ; and (3) the tuberosity of the trapezium. Insertion. — (i) The outer side of the base of the first phalanx of the thumb, in association with the superficial head of the flexor brevis pollicis ; and (2) the outer margin of the tendon of the ex- tensor longus poUicis on the back of the first phalanx. Nerve-supply. — ^The median nerve. The muscle, which is triangular, is directed downwards and out- wards. Action. — (i) To abduct the thumb, and (2) to assist in flexing its first phalanx, the result being that the thumb is drawn forwards and a little inwards. It also assists in extending the distal phalanx. The muscle rests upon the opponens pollicis, and the superficial head of the flexor brevis pollicis hes on its inner side. 2. Opponens Pollicis — Origin. — (i) The front of the anterior annular ligament, and (2) the tuberosity of the trapezium. Insertion. — ^The outer border of the shaft of the metacarpal bone of the thumb, and the adjacent part of its palmar surface. Nerve-supply. — ^The median ner\-e. The muscle, which is triangular, is directed downwards and outwards. Action. — ^To flex the first metacarpal bone, the result being that the thumb is drawn forwards and inwards across the palm, so as to oppose its tip to the tips of the four inner fingers. Ii7^ A MANUAL OF ANATOMY The muscle supports the abductor poUicis, and has the superficial head of the flexor brevis pollicis along its inner border. 3. Flexor Brevis Pollicis. — This muscle arises by two heads — a large superficial or outer, and a small deep or inner. The super- ficial head arises from the outer two-thirds of the lower border of the anterior annular ligament, and the tuberosity of the trapezium. The deep head (interosseus primus volaris) arises from the proximal extremity of the first metacarpal bone on its inner aspect. Insertion. — The superficial head, along with the abductor pollicis, is inserted into the outer side of the base of the first phalanx of the thumb, a sesamoid bone being contained within it. The deep head joins the adductor obliquus pollicis, and, along with it, is inserted into the inner side of the base of the first phalanx of the thumb. Nerve-supply. — The superficial head is supplied by the median nerve, and the deep head by the deep division of the ulnar nerve. Action. — To flex the metacarpo-phalangeal joint of the thumb, and so to assist in opposition. 4. Adductor Obliquus Pollicis — Origin. — By several bundles from (i) the fronts of the bases of the second and third metacarpal bones ; (2) the fronts of the trapezoid and os magnum ; and (3) the sheath of the tendon of the flexor carpi radialis. Insertion. — ^The muscle, having received the small deep head of the flexor brevis pollicis, is inserted, along with the adductor trans- versus pollicis, into the inner side of the base of the first phalanx of the thumb, a sesamoid bone being contained within it. In its course the muscle detaches, from its outer side, a large fleshy bundle, which passes outwards behind the tendon of the flexor longus pollicis and joins the superficial head of the flexor brevis pollicis. Nerve-supply. — The deep division of the ulnar nerve. The muscle is directed downwards and outwards. Action. — To adduct the thumb and assist in opposition. The muscle has the superficial head of the flexor brevis pollicis on its outer side, the tendon of the flexor longus pollicis lying between the two, and the adductor transversus pollicis along its inner and lower aspect, the radial artery passing between the two. 5. Adductor Transversus PoUicis — Origin. — ^The distal two-thirds of the anterior border of the shaft of the third metacarpal bone. Insertion. — (i) The inner side of the base of the first phalanx of the thumb, along with the adductor obliquus pollicis and deep head of the flexor brevis pollicis ; and (2) the inner margin of the tendon of the extensor longus pollicis on the back of that phalanx. Nerve- supply. — The deep division of the ulnar nerve. The muscle, which is triangular, is directed outwards. Action. — ^To adduct the thumb and assist in opposition. It also assists in extending the distal phalanx. The tendon of the flexor longus pollicis on its way to its insertion THE UPPER LIMB 379 has on its outer side the superficial head of the flexor brevis pollicis, and on its inner side the adductor obhquus polhcis. Hypothenar Muscles. — The short muscles of the little finger are three in number, namely, the abductor, flexor brevis, and opponens, minimi digiti. -- Flexor Carpi Radialis .l__lS. Flexor Longus Pollicis [1 Abductor Pollicis (cut) Head of Flexor Pollicis Flexor Carpi Ulnaris Flexor Sublimis Digitcrum Anterior Annular Ligament Abductor Minimi Digiti Flexor Brevis Minimi _ "' Digiti JUJi, Opponens Minimi '• ^ ' Digiti 3rd Palmar Inteross. 4th Dorsal Inteross. 2nd Palmar Inteross. 3r Dorsal Inteross.-'" 2nd Dorsal Inteross.,-" --ist Dorsal Interosseous — -ist Palmar Interosseous ^.ist Lumbricalis Fig. 203. — The Thenar and Hypothenar Muscles. I. Abductor Minimi Digiti — Origin. — ^The lower part of the pisi- form bone. Insertion. — (i) The inner side of the base of the first phalanx of the little finger, in common with the flexor brevis minimi digiti ; and (2) the inner margin of the tendon of the extensor minimi digiti on the back of the phalanx. Nerve-supply. — The deep division of the ulnar nerve. 380 A MANUAL OF ANATOMY Action. — (i) To abduct the little finger, and flex its metacarpo- phalangeal joint ; and (2) to assist in extending the second and third phalanges. 2. Flexor Brevis Minimi Digiti — Origin. — (i) The inner surface of the hook of the unciform bone close to its tip, and (2) the front of the adjacent portion of the anterior annular ligament. Insertion. — The inner side of the base of the first phalanx of the little finger, in common with the abductor minimi digiti. Nerve-supply. — The deep division of the ulnar nerve. Action. — To flex the metacarpo-phalangeal joint of the little finger. This muscle is of small size, and lies on the outer side of the ab- ductor minimi digiti, from which it is separated, close to its origin, by the profunda branch of the ulnar artery and deep division of the ulnar nerve. 3. Opponens Minimi Digiti — Origin. — (i) The inner surface of the hook of the unciform bone underneath the preceding muscle, and (2) the adjacent part of the anterior annular ligament. Insertion. — ^The inner margin of the shaft of the fifth metacarpal bone. Nerve-supply. — ^The deep division of the ulnar nerve. Action. — ^To flex and adduct the fifth metacarpal bone. The muscle supports the abductor and flexor brevis minimi digiti, and its deep surface is related to the interosseous muscles of the fourth space. The deep branches of the ulnar artery and nerve pass through it on their way to the deep part of the palm. Tliird Part of the Radial Artery. — The third part, which forms the greater portion of the deep palmar arch, extends from the upper part of the first interosseous space to about the base of the fifth metacarpal bone, where it is joined by the profunda branch of the ulnar. It enters the palm by passing between the two heads of the abductor indicis, and then it crosses the palm, resting upon the bases of the second, third, and fourth metacarpal bones, and the adjacent interosseous muscles. In its course it describes a slight arch, the convexity of which is directed towards the fingers, and it is about ^ inch nearer the wrist than the superficial palmar arch. The deep division of the ulnar nerve lies close above it. The third part of the vessel is at first under cover of the adductor obliquus pollicis ; it then passes between that muscle and the adductor transversus pollicis ; and thereafter it lies beneath the superficial and deep flexor tendons and lumbricales, where it forms the deep palmar arch. Branches. — ^These are the arteria princeps pollicis, arteria radialis indicis, three palmar interosseous, recurrent, and superior per- forating, the last three coming from the deep palmar arch. The arteria princeps pollicis arises from the vessel immediately after it emerges from between the two heads of the abductor indicis, and it passes downwards along the first metacarpal bone, lying upon the abductor indicis and under cover of the adductor obliquus pollicis. On reaching the head of the bone it divides, under cover of the tendon THE UPPER LIMB 381 of the flexor longus pollicis, into two collateral digital arteries for the sides of the thumb, which appear on either side of the long flexor tendon, between the superficial head of the flexor brevis pollicis and adductor obliquus pollicis. Their distribution is similar to that of the other digital arteries. The arteria princeps pollicis may give a branch to complete the superficial palmar arch. The arteria radialis indicis passes downwards along the outer side of the second metacarpal bone, lying upon the abductor indicis and under cover of the adductor obliquus, and adductor transversus, Anterior Radial Carpal Anterior Ulnar Carpal Ulnar Artery Radial Artery Superficial Volar Princeps Pollicis ,. Deep Branch of Ulnar _ _ Recurrent Branches _ Deep Palmar Arch ist Digital Artery from Superficial Palmar Arch Radialis Indicis' ' ist Palmar Interosseus 4th Digital Artery from Superficial Palmar Arch Fig. 204. — The Radial Artery in the Palm (Deep Palmar Arch) (after Spalteholz). pollicis, and it becomes the digital artery of the outer side of the index finger. It may give a branch to complete the superficial palmar arch. Branches of the Deep Palmar Arch. — ^The palmar interosseous arteries, three in number, arise from the convexity of the arch, and pass downwards over the second, third, and fourth inter- osseous spaces. Near the clefts of the corresponding fingers, they terminate by joining the three compound digital arteries of the superficial palmar arch. The innermost palmar interosseous, as a rule, gives off a communicating branch to join the single digital 382 A MANUAL OF ANATOMY artery from the superficial arch to the inner side of the Uttle finger, the junction taking place about the centre of the palm. In those cases where the digital arteries from the superficial arch are awanting, the palmar interosseous arteries may take their place. The recurrent branches, few and small in size, arise from the concavity of the arch, and pass upwards to take part in the anterior carpal rete. The superior perforating arteries, three in number, pass through the upper ends of the inner three interosseous spaces between the two heads of the corresponding dorsal interosseous muscles, and on the back of the hand they join the dorsal interosseous arteries. Varieties of the Ulnar and Radial Arteries in the Hand. — i. The ulnar artery may be deficient in the number of digital branches furnished by the superficial palmar arch, or the vessel may end as the profunda artery, in which latter case there would be no superficial arch. Under these circumstances the deficiencies are usually supplied by the palmar interosseous branches of the deep arch, but sometimes by a large median and large superficial volar artery. 2. The radial artery may be deficient in its normal branches, and the arteria princeps poUicis and arteria radialis indicis may arise from the superficial arch, from a median, or from a superficial volar, artery. Veins. — The deep palmar arch is accompanied by two venae comites, which receive tributaries corresponding to the branches of the arch. The destination of these venae comites on either side has been already described in connection with the superficial palmar arch. Summary of the Palmar Arches. — The superficial palmar arch is formed mainly by the ulnar artery, being completed by the superficial volar of the radial, or, if this fails, by a branch from the arteria radialis indicis, or arteria princeps pollicis. Its digital branches lie over the interosseous spaces, so that, to avoid them, incisions in the palm should be made in line with the centre of a finger, and should not be prolonged farther upwards than the line indicating the position of the superficial palmar arch. On the fingers the digital arteries are placed laterally, so that in cases of whitlow an incision should be made along the middle line of a finger. The superficial palmar arch is sometimes joined by a large median artery, which is a branch of the anterior interosseous high up in the forearm. In such cases, if the arch were to be punctured, and if the haemorrhage could not be arrested by the graduated compress, it is evident that ligature neither of the ulnar nor radial artery would suffice. In order to arrest the circulation through a large median artery the ligature would require to be placed on the brachial artery. The deep palmar arch is formed mainly by the radial artery, and is com- pleted by the profunda branch of the ulnar. It lies about ^ inch above the superficial arch. BACK OF THE FOREARM AND HAND. The cutaneous nerves, already described, are as follows : the posterior branch of the musculo-cutaneous and the lower external cutaneous branch of the musculo-spiral to the outer part, and the posterior division of the internal cutaneous to the inner part. The deep fascia of the back of the forearm has been described in connection with the anterior aspect, and the posterior annular ligament will be presently referred to. THE UPPER LIMB 383 Muscles of the Outer Side of the Forearm. — ^These are three in number, namel^^ the brachio-radialis, extensor carpi radialis longior, and extensor carpi radialis brevior. 1. Brachio-radialis (supinator radii longus) — Origin. — (i) The upper two-thirds of the external supracondylar ridge of the humerus, and (2) the front of the external intermuscular septum over a corresponding extent. Insertion. — The outer side of the radius close above the base of the styloid process. Nerve-supply. — The musculo-spiral nerve. Action. — Though called a supinator, the muscle is a flexor of the forearm, acting most directly when the limb is in a state of semi- pronation. An important use of the muscle is to maintain the forearm in the flexed position, as in holding a book. When the forearm is fully pronated the muscle is a feeble supinator, but only to the extent of semisupination. When the forearm is fully supi- nated it produces sem.ipronation. The muscle presents a fleshy belly to near the middle of the fore- arm. Thereafter it is replaced by a flat tendon, which first appears on the deep surface of the muscle. Superiorly the surfaces are directed outwards and inwards, but afterwards they look forwards and backwards. 2. Extensor Carpi Radialis Longior — Origin. — (i) The lower third of the external supracondylar ridge of the humerus, and (2) the front of the external intermuscular septimi for a correspond- ing extent. Insertion. — The back of the base of the second metacarpal bone over its outer half, a small bursa lying beneath the tendon. Nerve-supply.— The musculo-spiral nerve. Action. — (i) To extend the wrist- joint, and (2) to assist in ex- ternal lateral flexion (abduction) of that joint. The muscle presents a fleshy belly to near the middle of the fore- arm, and thereafter a tendon which descends at first upon, and then on the outer side of, the tendon of the extensor carpi radialis brevior. These two tendons pass beneath the posterior annular ligament, and occupy the outermost groove on the back of the lower end of the radius. The surfaces of the muscle are at first directed outwards and inwards, and then forwards and backwards. 3. Extensor Carpi Radialis Brevior — Origin. — (i) The external epicondyle of the humerus by the common tendon ; (2) the external lateral ligament of the elbow- joint ; and (3) the intermuscular septa between it and adjacent muscles. Insertion. — ^The back of the base of the third metacarpal bone over its outer half, and often by a small slip into the back of the base of the second metacarpal over its inner part. A small bursa is placed beneath the tendon. Nerve-supply. — The posterior interosseous nerve. Action. — (i) To extend the wrist-joint, and (2) to assist in external lateral flexion (abduction) of that joint. 3^4 A MAlJUAL OP ANATOMY The tendon appears about the centre of the forearm, and becomes free from fleshy fibres in the lower third. It descends beneath the tendon of the long radial extensor, except near its insertion, where it lies internal to that tendon. It accompanies the long tendon beneath the posterior annular ligament, and passes with it through the outermost groove on the back of the lower end of the radius. Muscles of the Back of the Forearm. — ^These are arranged in two layers — superficial and deep. Superficial Layer. — ^The muscles of this layer, which are serially continuous with those of the outer side of the forearm, are four in number, namely, the extensor communis digitorum, extensor minimi digiti, extensor carpi ulnaris, and anconeus. The first three have a common tendon of origin, which they share with the extensor carpi radialis brevior. • I. Extensor Communis Digitorum — Origin. — (i) The external epi- condyle of the humerus by the common tendon ; (2) the deep fascia ; and (3) the intermuscular septa between it and adjacent muscles. Insertion. — ^The muscle ends in four tendons, which pass beneath the posterior annular ligament to the dorsum of the hand. Here they diverge and pass to the four inner fingers, that for the index finger being accompanied internally by the tendon of the extensor indicis. Having crossed the metacarpo-phalangeal joints, where they give fibres to their lateral ligaments, the tendons form broad expansions covering the backs of the first phalanges, which give insertion to the lumbricales and interossei. Towards the distal end of the first phalanx the expansion divides into three parts — central and two lateral. The central part is inserted into the back of the base of the second phalanx. The two lateral parts unite on the back of the second phalanx, and are inserted into the back of the base of the distal phalanx. The index and middle finger tendons are connected by a weak band of fibres. The ring- finger tendon is connected by a strong band of fibres with the tendon on either side of it, which explains the very limited amount of extension of which the ring-finger is capable, unless the middle and little fingers are extended along with it. The little finger tendon may divide into two parts, one joining the ring-finger tendon and the other the tendon of the extensor minimi digiti. Nerve-supply. — ^The posterior interosseous nerve. Action. — (i) To extend the first phalanges of the four inner fingers, and also the second and third phalanges slightly, these being extended principally by the interossei and lumbricales ; and (2) to assist in extension of the wrist-joint. The common extensor tendons, along with that of the extensor indicis, in passing beneath the posterior annular ligament, occupy the broad innermost groove on the back of the radius. 2. Extensor Minimi Digiti — Origin. — (i) The external epicondyle of the humerus by the common tendon; (2) the deep fascia; and (3) the intermuscular septum on either side. Insertion. — Having passed beneath the posterior annular liga- THE UPPER LIMB 385 ment, where it occupies the groove between the radius and ulna, the tendon divides into two parts, the outer part being joined by the common extensor tendon to the httle finger, or by its inner division. Both parts end in a broad expansion on the back of the first phalanx, Biceps ■ "^^^ Brachio-radialis- / ^■. -^'~r -Triceps Extensor Carpi Radialis Longior— - — Extensor Carpi Radialb Brevior Extensor Ossis Metacarpi Pollids Extensor Brevis Pollicis Extensor Longus Pollicis extensor Carpi Radialis Longior Extensor Indicis hi: 1) U '" Anconeus T15& Extensor Carpi Ulnaris Extensor Communis Digitorum .-Extensor Carpi Ulnaris UL Extensor Minimi Digit! 'Ll^ Posterior Annular Ligament Extensor Carpi Radialis Brevior Extensor Minimi Digit! (in two parts) Connecting Band Fig. 205. — The Muscles of the Radial Side and Back of the Forearm. and the ultimate insertion is as in the case of the common extensor tendons. Nerve-supply. — ^The posterior interosseous nerve. Action. — ^The muscle is the special extensor of the little finger, 25 386 A MANUAL OF ANATOMY as in inserting that finger into the ear canal. It also acts as a feeble auxiliary extensor of the wrist- joint. 3. Extensor Carpi Ulnaris — Origin. — (i) The external epicondyle of the humerus by the common tendon ; (2) the deep fascia ; (3) the intermuscular septum on either side ; and (4) the upper two-thirds of the posterior border of the ulna by an aponeurosis which is common to it, the flexor carpi ulnaris, and the flexor profundus digitorum. Insertion. — ^The tubercle on the inner side of the base of the fifth metacarpal bone. 'Nerve-supply. — ^The posterior interosseous nerve. Action. — (i) To extend the wrist-joint, and (2) to assist in internal lateral flexion (adduction) of that joint. The muscle rests upon the inner half of the posterior surface of the shaft of the ulna, and its tendon, in passing beneath the posterior annular ligament, occupies the groove on the back of the ulna. 4. Anconeus — Origin. — ^The back of the external epicondyle of the humerus at its lower part. Insertion. — The outer surface of the olecranon process, and the upper third of the posterior surface of the shaft, of the ulna. The muscle, which is continuous with the internal head of the triceps, is triangular, the upper fibres being short and transverse, whilst the others pass obliquely downwards and inwards. Nerve-supply. — ^The musculo-spiral nerve, by means of a long branch which descends in the internal head of the triceps, and enters the muscle on its deep surface near the upper border. Action. — ^To assist the inner head of the triceps in extending the elbow. The posterior interosseous recurrent artery ascends beneath the muscle to the back of the external epicondyle. The posterior interosseous nerve will be found described on p. 358, and the corresponding artery on p. 361. Deep Layer. — ^There are five muscles in this layer, namely, the supinator radii brevis, extensor ossis metacarpi pollicis, extensor brevis pollicis, extensor longus pollicis, and extensor indicis. I. Supinator Radii Brevis — Origin. — (i) The external lateral ligament of the elbow-joint ; (2) the orbicular ligament of the radius ; (3) the back part of the bicipital hollow, and the supinator ridge, of the ulna ; and (4) the aponeurosis covering the upper part of the muscle. Insertion. — ^The shaft of the radius on its anterior, outer, and posterior aspects over about the upper third. Anteriorly the muscle descends as low as the anterior oblique line, externally as low as the insertion of the pronator radii teres, and posteriorly as low as the posterior oblique line. It closely invests the radius over about its upper third, except on its inner aspect. Nerve-supply. — The posterior interosseous nerve. Action. — To supinate the radius upon the ulna. The muscle is pierced by the posterior interosseous nerve, and, THE UPPER LIMB 387 Triceps .. Anconeas Extensor Commuiiis — | . Digitorum Extensor Minimi Digit! , Extensor Carpi Ulnaris — Dorsal Branch of. Ulnar Nerve Posterior Aiuiular ligament Extensor Minimi Digits (in two parts) Biceps x^racbio-radialis Extensor Carpi Radialis Longior Extensor Carpi Radialis Brevior Supinator Radii Brevis Posterior Interosseous Nerve Extensor Ossis Metacarpi Pollids Ejttensor Brevis Pollicis Radial Nerve Extensor Longus Pollicis Extensor Indicis Extensor Brevis PoIUcis Extensor Indicis Extensor Longus FoUids Fig. 206.— Deep Dissection of the Back of the Forearm (The Radial Nerve and the Dorsal Branch of the Ulnar Nerve are also shown). 388 A MANUAL OF ANATOMY in doing so, the nerve passes between the small superficial and large deep lamina, of which the muscle is composed. 2. Extensor Ossis Metacarpi PoUicis — Origin. — (i) The posterior surface of the shaft of the radius for fully 2 inches below the posterior oblique line, where it meets the supinator radii brevis ; (2) the ad- jacent portion of the interosseous membrane ; and (3) the outer part of the posterior surface of the shaft of the ulna for a short distance below the oblique line, which limits the insertion of the anconeus. Insertion. — ^The outer side of the base of the metacarpal bone of the thumb. The muscle passes downwards and outwards, and its strong tendon is closely accompanied by that of the extensor brevis pollicis. Both of these tendons cross those of the radial extensors of the wrist, and traverse the groove on the outer side of the styloid process of the radius, where they occupy the outermost compartment of the posterior annular ligament. The tendon at its insertion gives a slip to the thenar portion of the palmar fascia, which gives it a double appearance. Nerve-supply. — The posterior interosseous nerve. Action. — (i) To extend and abduct the metacarpal bone of the thumb, and (2) to abduct the wrist-joint (external lateral flexion). 3. Extensor Brevis Pollicis (extensor primi internodii pollicis) — Origin. — ^The posterior surface of the shaft of the radius, and the inter- osseous membrane, for a short distance below the preceding muscle. Insertion. — The back of the base of the first phalanx of the thumb. The muscle closely accompanies the extensor ossis metacarpi pollicis. Nerve-supply. — The posterior interosseous nerve. Action. — (i) To extend the metacarpo-phalangeal joint of the thumb, and (2) to act as a feeble auxiliary to the extensor ossis metacarpi pollicis. 4. Extensor Longus Pollicis (extensor secundi internodii pollicis) — Origin. — (i) The outer part of the posterior surface of the shaft of the ulna over about its middle third, commencing immediately below the extensor ossis metacarpi pollicis ; and (2) the adjacent portion of the interosseous membrane. Insertion. — ^The back of the base of the distal phalanx of the thumb. The muscle is directed downwards and outwards, and its tendon passes beneath the posterior annular ligament, where it occupies the narrow oblique groove on the radius, internal to the radial tubercle. Nerve-supply. — ^The posterior interosseous nerve. Action. — ^To extend the distal phalanx of the thumb. Thereafter the muscle, which acts strongly, assists in extending the first phalanx and metacarpal bone, the thumb being drawn backwards. It is also an auxiliary extensor of the wrist-joint. 5. Extensor Indicis — Origin. — (i) The outer part of the posterior surface of the shaft of the ulna, commencing just below the middle THE UPPER LIMB 389 Extensor Ossis Metacarpi Pollids Extensor Brevis PoUicis — Posterior Annular Ligament Ext. Carpi Radialis Brevior Ext. Carpi Radialis Longior Extensor Brevis PoUicis .. Extensor Longus PoUicis ist Dors. Interosseous - (.\bductor Indicis) Add. Obliquus, and . Add. Transversus, PoUicis Extensor Carpi UInaris_ Extensor Minimi Digiti Extensor Indicis Extensor Communis Digitorum EztCDSor Minimi JDigiti (in two parts Connecting Band Extensor Indicts Fig. 207. — The Muscles and Tendons of the Back of THE Wrist and Hand. I., II., III., IV., Tendons of Extensor Communis Digitorum. 390 A MANUAL OF ANATOMY third, and reaching to near the lower end of the bone ; and (2) the lower part of the interosseous membrane. Insertion. — The inner side of the common extensor tendon of the index finger, which it joins at the metacarpo-phalangeal joint. The muscle is directed downwards and outwards, and its tendon passes beneath the posterior annular ligament, where it occupies the innermost groove on the back of the radius, in company with the common extensor tendons, beneath which it lies. Nerve-supply. — The posterior interosseous nerve. Action. — (i) The muscle is the special extensor of the index finger, as in pointing ; and (2) it acts as a feeble auxiliary extensor of the wrist- joint. The muscle is covered by the extensor communis digitorum, extensor minimi digiti, and extensor carpi ulnaris. Posterior Annular Ligament. — ^This is a thickened portion of the deep fascia of the back of the forearm, and it lies obliquely on the back of the wrist. It is attached externally to the lower part of the anterior border of the radius, and internally to the inner and back part of the cuneiform and pisiform bones, as well as to the hypo- thenar portion of the palmar fascia. Its direction is inwards and downwards, and it bridges over the various grooves in this region, sending deep processes to be attached to the ridges which separate them. In this manner these grooves are converted into fibro- osseous canals for the passage of the extensor tendons. These canals are six in number, four being on the radius, one between that bone and the ulna, and one on the ulna. Proceeding from without inwards, the first canal corresponds with the groove on the outer '"''..--/""■/'/'-' :^ ■'"I oid process of the radius, and it contains the surface ol tn^* ^^'^-^^ ^'"^ metacarpi pollicis and extensor brevis tendons of the extensor 'bsfe^^'-^^ds with the outer broad groove pollicis. The second canal correspoi ^e tendons of the extensor on the -back of the radius, and it contains'lP^'^^i^lis brevior. The carpi radialis longior and extensor carpi "1^'^^^^^"^ groove on inird canal corresponds with the narrow deeo^^'^^^c^ °^^^^^"g^ the back of the radius, internal to the radial tubTr'cre'^ P^^^^^^^- ^he L^f^rl ""J"^^'"' *^^ *""^°" «f the extensor longusT^^ °" ^^'' fourth canal corresponds with the broad innermosT^^^ extensor back of the radius, and it transmits ^h^ tendZ of^V^ the pos- communis digitorum and extensor indids tog^^^^^^^^ tenor interosseous nerve and posterior branch of the ant^^*^^^" osseous artery The fifth canal corresponds with the^^^^^^^^^^^ the radius and ulna, and it contains th^ Z.ii\: ^/^u ^ve on trltk'1^^;. ^1'^ ^1^*^ can^l c^es^t^s^wZlhf^^^^^^^ the back of the ulna, between the styloid process and hfnH^^""- bone and it transmits the tendon of the^eSensor carnf1,f ^*^' Deep Fascia of the Back of the Hand tko a x ■ ■ Cand region is continuous above w^tVfl^e ^^^ttToI^LfS fc^ THE UPPER LIMB 391 at either side with the thenar and hypothenar portions of the pabnar fascia. It covers the extensor tendons, with which it is intimately connected. Besides this fascia there is another fascial investment, which is placed beneath the extensor tendons. This deeper layer covers the dorsal interosseous muscles, and, in the intervals between them, it is attached to the dorsal aspects of the shafts of the meta- carpal bones. Second Part of the Radial Artery. — ^The second part of the vessel winds backwards below the styloid process of the radius to the back of the wrist. It extends from a point on the front of the radius about ^ inch internal to the stj'loid process to the upper end of the Posterior Annular Ligament _ , 1 1 Extensor Minimi Digiti^ // Extensor Carpi Ulnaris - - - -Extensor Communis Digitonim , Radial Carpal Exleasors Extensor Brevis Pollicis -~ Extensor Long^s Pollicis Fig. 208. —The Synovial Sheaths of the Extensor Tendons (after L. Testut's 'Anatomie Humaine'). first interosseous space on its posterior aspect, where it dips between the two heads of the abductor indicis muscle, and ends in the third part. Its course is at first backwards and then downwards. Relations — Superficial. — The mtegument, radial vein, branches of the radial nerve, tendons of the extensor ossis metacarpi pollicis, extensor brevis pollicis, and extensor longus pollicis, the latter crossing the vessel just before it disappears between the two heads of the abductor indicis. At first it is deeply placed, but afterwards it is superficial, and, in the living subject, pulsation may be felt in it m the triangular hollow below and behind the radial styloid 392 A MANUAL OF ANATOMY process. Deep. — ^The external lateral ligament of the wrist- joint, and the scaphoid and semilunar bones. It is accompanied by two venae comites. Branches. — The branches are the posterior radial carpal, first dorsal interosseous, two arteriae dorsales pollicis, and arteria dorsalis indicis. The posterior radial carpal artery, of small size, arises from the radial as it lies upon the external lateral ligament. It passes in- Extensor Carpi Radialis Brevior , Extensor Carpi Radialis Longior Post. Branch of Ant. Inteross. Artery __. Posterior Radial Carpal Artery --• ist Dorsal Interosseous Artery Radial Artery at Wrist Ext Carpi Ulnans — Posterior Ulnar Carpal Artery 2nd and 3rd Dors. Inteross. Arteries Superior Perforating Artery »_ Extensor Brevis Pollicis __- Arteria Dorsalis Pollicis — __ Extensor Longus Pollicis Fig, 209, — The Arteries of the Back of the Wrist and Hand (after L. Testut's ' Anatomie Humaine '). wards on the back of the wrist beneath the extensor tendons, and anastomoses with the posterior ulnar carpal and posterior branch of the anterior interosseous to form the posterior carpal arch. The first dorsal interosseous artery arises from the preceding, or from the radial a little lower down. It passes to the upper end of the second interosseous space, where it receives a superior THE UPPER LIMB- 393 perforating branch from the deep pahnar arch. It then descends over that space towards the cleft between the index and middle fingers, where it may send forward an inferior perforating branch to join the fourth or outermost digital artery from the superficial palmar arch. Thereafter it divides into two dorsal collateral digital arteries for the contiguous sides of the index and middle fingers. The second and third dorsal interosseous arteries are branches of the posterior carpal arch. They descend over the backs of the third and fourth interosseous spaces, at the upper ends of which each receives a superior perforating branch from the deep palmar arch. Near the clefts between the middle and ring, and ring and little fingers, they may send forwards inferior perforating branches to join the second and third digital arteries from the superficial palmar arch, and thereafter each divides into two dorsal collateral digital arteries for the contiguous sides of the middle and ring, and ring and little fingers. The dorsal digital artery of the inner side of the little finger arises from the third (innermost) dorscd interosseous, or from the posterior ulnar carpal. The arterise dorsales polllcis, two in nmnber, arise separately or by a common trunk, from the radial opposite the base of the first metacarpal bone, and are distributed to the sides of the thumb. The arteria dorsalis indicis arises below the preceding, just before the radial dips between the two heads of the abductor indicis. It descends on the outer side of the second metacarpal bone, and sup- plies the outer side of the index finger. The distribution of the dorsal digital arteriesceases, as a rule, about the level of the first interphalangeal joint. The Interosseous Muscles. The interosseous muscles ire seven in number, and ire arranged in two groups —three palmar and four dorsal. The palmar inter- Dssei are seen only on the palmar aspect, but the dorsal interossei are seen on Fig. 210,— The Palmar Interosseous •oth aspects of the hand. Muscles of the Right Hand. 394 A Manual of anatomy The palmar interossei belong to the index, ring, and Httle fingers, and they are named from without inwards — first, second, and third. Each is connected only with one metacarpal bone. The first arises from the mner aspect of the shaft of the second metacarpal bone, and the second and third from the outer aspects of the shafts of the fourth and fifth metacarpals. The fi-rst is inserted partly into the inner side of the base of the first phalanx of the index finger, and partly into the- expansion of the extensor tendon on the dorsal aspect of that phalanx. The second and third are inserted in a similar manner in the case of the ring and little fingers, except that each is inserted into the outer side of the base of the first phalanx. The palmar interossei are covered by a thin fascia, called the interosseous fascia. At either side it joins the thenar and hypo- thenar portions of the palmar fascia, and interiorly it is connected with the transverse metacarpal and anterior metacarpo-phalangeal ligaments. Two septa pass between it and the central portion of the palmar fascia. The dorsal interossei, which are four in number, belong to the index, middle, and ring fingers, the middle finger having two. They are named from without inwards — first, second, third, and fourth, the first being specially called the abductor indicis. Each muscle arises by two heads from the contiguous sides of the shafts of the metacarpal bones between which it is placed, and always more ex- tensively from the bone belong- ing to the finger upon which the muscie acts. The fibres of each muscle end upon a tendon which is placed in the centre, and this tendon is in- serted partly into the side of the base of the first phalanx of a finger, and partly into the expansion of the extensor tendon on the back of that phalanx. The first or abductor indicis is of large size. Its outer large head arises from the proximal half of the inner margin of the first metacarpal bone, and its inner small head from the whole length of the outer aspect of the shaft of the second metacarpal. It is inserted Fig. 211.— The Dorsal Interosseous Muscles of the Right Hand. THE UPPER LIMB 395 into the outer side of the base of the first phalanx of the index finger, and the expansion of the extensor tendon on the back of that phalanx. The second is inserted into the outer side, and the third into the inner side, of the base of the first phalanx of the middle finger, and both into the expansion of the extensor tendon on the back of that phalanx. The fourth is inserted into the inner side of the base of the first phalanx of the ring-finger, and into the expansion of the extensor tendon on the back of that phalanx. Nerve-supply. — All the interossei are supplied by the deep division of the ulnar nerve. Action. — (i) The palmar interossei are adductors, the fingers which they adduct being the index, ring, and little. (2) The dorsal interossei are abductors, the fingers which they abduct being the index, middle, and ring, the middle finger having two abductors, inasmuch as it can be drawn to either side of the middle line which passes through its centre. In speaking of adduction and abduction reference is made to an imaginary line passing through the centre of the middle finger, adduction being movement towards that line, and abduction from it. There is another very important action of all seven interossei, in the performance of which they are assisted by the lumbricales. This action is as follows : (i) to flex the metacarpo-phalangeal joints, in virtue of their insertion into the first phalanges of the four inner fingers, and (2) to extend their interphalangeal joints, in virtue of their insertion into the expansions of the extensor tendons. This action is well illustrated in making the hair- or up- stroke in writing. Between the two heads of the abductor indicis superiorly is an interval for the passage of the radial vessels, and between the two heads of each of the other dorsal interossei superiorly there is an interval for the passage of a superior perforating artery from the deep palmar arch. Lymphatic Vessels of the Upper Limb. The lymphatic vessels of the upper limb are arranged in two groups — super- ficial and deep. The superficial lymphatics lie in the subcutaneous tissue, and the deep lymphatics accompany the deep bloodvessels. Superficial Lymphatics. — (i) Digital. — There are very rich networks of lymphatics in the fingers, especially over their palmar aspects. The efferent lyinphatics from the digital networks form two digital vessels, on either side which he on each side of each finger, in contact with the corresponding digital artery. At the roots of the fingers these vessels pass to the dorsal aspect of the hand, and, after having communicated with each other and formed a dorsal net\vork, they pass to the back of the wrist. (2) Palmar. — ^There is a very rich network of lymphatics in the palm, from which several vessels emerge and pass in various directions — out- wards, inwards, downwards, and upwards. The external efferent vessels pass upwards and outwards over the thenar eminence, and join the lymphatics from the thumb. The internal efferent vessels pass inwards, and, having turned round the inner border of the hand, they join the lymphatics from the little finger. The inferior efferent l^'mphatics pass downwards to the clefts between the fingers, where they turn backwards and join the digital efferent lymphatics. The superior efferent vessels ascend to the front of the wrist. 396 A MANUAL OF ANATOMY (3) Carpal. — The carpal lymphatics form two groups — palmar and dorsal, which derive their vessels from the palmar and dorsal networks of the hand. {4) Antibrachial. — The superficial lymphatics of the front of the forearm are arranged in three groups — radial, median, and ulnar, which accompany the corresponding veins. As the radial and ulnar lymphatics ascend they are joined at intervals by efferent vessels from the dorsal plexus of the hand, which wind round the radial and ulnar borders of the forearm from its dorsal aspect. The radial lymphatics in part ascend into the arm and accompany the cephalic vein, and in part join the median lymphatics. The median lymphatics may terminate in the anticubital glands, if these are present. When these are absent, they join the ulnar lymphatics, which terminate in the supra-trochlear gland or glands. (5) Brachial. — The superficial lymphatics of the brachial region form two groups — -inner and outer. The inner lymphatics, which are very numerous, lie along the inner border of the biceps brachii. They largely represent the efferent vessels of the supra-trochlear gland or glands, and anticubital glands, if present, and they lie at first superficial to the deep fascia. Subsequently, however, they pierce that fascia and pass to the external or humeral axillary glands, in association with the deep brachial lymphatics. The outer lymphatics, which are reinforced by some of the radial lymphatics, lie on the outer side of the biceps brachii, along the course of the cephalic vein. They then ascend in the groove between the deltoid and pectoralis major muscles, where they may traverse on© or two very minute deep lym- phatic glands. Ultimately they pass to the infra-clavicular glands, but one or two of them may ascend over the clavicle, and terminate in one of the supra-clavicular glands. Deep Lymphatics. — ^These, as stated, accom- pany the deep bloodvessels, and they form five groups — radial, ulnar, anterior interosseous, posterior interosseous, and brachial. In con- nection with each artery there are usually two lymphatic vessels, and those accompanying the radial, ulnar, anterior interosseous, and brachial arteries occasionally traverse one or two deep lymphatic glands, which are some- times met with along the course of each of these arteries. The brachial lymphatics are formed by the union of the radial, ulnar, an- terior interosseous, and posterior interosseous lymphatic vessels. About the centre of the Fig. 212. — The Superficial arm they are reinforced by the efferent vessels Lymphatics of the Upper of the supra-trochlear gland or glands, and Limb (Anterior View). they terminate in the external or humeral axillary glands. Summary of the Lymphatic Glands of the Upper Limb. — ^The lymphatic gHnds of the upi er limb form two groups — superficial and deep. The superflcial glands embrace the internal epicondylar or supra-trochlear; THE UPPER LIMB 397 and, it iflay be. the anticubital glands; but the latter are inconstant. There are no 'uperficial h-mphatic glands in the hand or forearm. The deep glands principedly represent the axillary and infra-clavicular glands. A few deep lymphatic glands, however, of very small size are some- times met with in connection with the deep lymphatic vessels which accom- pany the arteries of the forearm and the brachial artery. One or two deep lymphatic glands are also sometimes met with in the groove between the deltoid and pectoralis major muscles, along the cephalic vein. Ssperficial Glands. Deep Glands. 1. Internal epicondylar. i. Axillary. 2. Anticubital (inconstant). 2. Infra-clavicnlar. 3. Radial (inconstant). 4. Ulnar (inconstant). 5. Anterior interosseous (inconstant). 6. Brachial (inconstant). 7. Cephalic (inconstant). Development of Arteries of Upper Limbs. The arterial stem of the left upper hmb is developed entirely from the seventh left cervical segmental artery, in association with the left vertebral artery. The component arteries of this stem, from above downwards, are as follows: (i) The subclavian artery; (2) the axillary artery; (3) the brachicil artery; and (4) The anterior interosseous artery. The arterial stem of the right upper hmb is developed from the fourth right arterial arch, a portion of the right dorsal aorta, and the seventh right cervical segmental artery, in association with the right vertebral arter\'. The component arteries of this stem are as on the left side. Before the adult condition of the arteries is reached, several stages of development have to be passed through. (i) As the anterior interosseous artery becomes diminished, another artery springs from the brachial a short distance below the elbow-joint. This new vessel accompanies the median nerve, and is called the median artery. (2) The medizin artery superiorly furnishes a branch, which becomes the ulnar artery. (3) As the median artery becomes diminished, a vessel springs from the brachial artery about the centre of the brachial region. This vessel is called the primary radial artery, and it accompanies the radial nerve. (4) As the upper part of the primary radial artery atrophies, the brachial artery gives off another branch just below the elbow -joint, which soon joins the primjiry radicd, and so the permanent radial artery is formed. Development of Veins of Upper Limbs. The veins of each upper hmb form two groups — superficial and deep. The superficial veins are developed prior to the deep, the latter accompanying the arteries. The primitive vein is the primary ulnar or postaxlal vein, which receives distaUy the digital veins, and opens proximally into the anterior cardinal vein. At a later period the cephalic vein is formed as an outgrowth from the external jugular vein, but it subsequently acquires its permanent connection with the upper part of the axillary vein. The distal portion of the primary ulnar vein disappears. Its proximal portion persists and gives rise to the basilic, axillary, and subclavian veins. From the distal end of the basilic vein the anterior and posterior ulnar veins and the median basilic vein are developed. The radial and median cephalic veins grow distally from the cephalic vein. The median vein is developed from the median basihc and median cephalic 398 A MANUAL OF ANATOMY THE ELBOW-JOINT. The elbow-joint belongs to the class diarthrosis and to the subdivision ginglymus. The articular surfaces are the trochlea and capitellum of the humerus above, and the great sigmoid cavity of the ulna and the cup-shaped depression on the head of the radius below. The trochlea articulates with the great sigmoid cavity, and the humeral capitellum with the head of the radius. The joint is surrounded by a capsule, which is made up of four ligaments — ^anterior, posterior, external lateral, and internal lateral. Anterior Ligament .. Internal Epicondyle Orbicular Ligament ^^g Tendon of Biceps . (reflected) — Brachialis Anticus (reflected) .Oblique Ligament Fig. 213. — The Right Elbow-Joint (Anterior View). The anterior ligament is broad and thin, the central portion "being the strongest. Its fibres are attached superiorly to the front of the humerus above the coronoid and radial fossae, and interiorly to (i) the front of the coronoid process of the ulna, and (2) the orbicular ligament of the radius. Some of its fibres nm vertically and others obliquely, the latter chiefly passing downwards and outwards super- ficial to the former. The ligament is closely covered by the brachialis anticus muscle. THE UPPER LIMB 399 The posterior ligament is thin and membranous. Superiorly it is attached to the upper part and sides of the olecranon fossa of the humerus, and interiorly to (i) the front part of the summit of Fig. 214. — The Posterior Ligament of the Elbow-Joint. the olecranon process of the ulna, and (2) the orbicular ligament of the radius. The most of its fibres are disposed vertically, but a few pass transversely between the margins of the olecranon fossa. External Lateral Ligament Orbicular Ligament Posterior Ligament Posterior Fibres of External Lateral Ligament Fig. 215. — The Right Elbow-Joint (External View). The ligament is related to the tendon of insertion of the triceps, some of the fibres of the internal head being inserted into it, under the name of the subanconeus. 400 A MANUAL OF ANATOMY The external lateral ligament is a short, stout, flat band, which is attached superiorly to the lower part of the external epicondyle of the humerus, and inferiorly to the outer part of the orbicular ligament of the radius. A few of its posterior fibres pass over the orbicular ligament, and are attached to the outer margin of the ulna. It is intimately related to the origins of the extensor carpi radialis brevior and supinator radii brevis muscles. The internal lateral ligament is triangular, with the apex upwards. It is attached superiorly to the anterior, inferior, and posterior parts of the internal epicondyle of the humerus, and inferiorly to the inner margin of the great sigmoid cavity of the ulna. It is divisible into three portions — anterior, posterior, and middle. The Orbicular Ligament Tendon of Biceps Oblique Ligament Superior Hiatus .. Internal Lateral Ligament (Anterior portion) Internal Lateral Ligament (Posterior portion) Internal Lateral Ligament (Middle portion) Fig. 2i6. — The Right Elbow- Joint (Internal View). anterior portion is attached superiorly to the front and lower part of the internal epicondyle, and inferiorly to the inner margin of the coronoid process. The posterior portion is attached superiorly to the lower and back part of the internal epicondyle, and inferiorly to the inner margin of the olecranon process. The middle portion consists of fibres which pass transversely from the olecranon to the coronoid process, and blend with the fibrous band bridging over the notch on the inner margin of the great sigmoid cavity between these two processes. The ligament is intimately related to the origin of the flexor sublimis digitorum. The synovial membrane lines the internal surface of the capsule, and inferiorly is continued into the superior radio-ulnar joint, where it lines the internal surface of the orbicular ligament and THE UPPER LIMB 40I upper part of the neck^f the radius. It also lines the coronoid, radial, and olecranon fossae of the humerus, which contain small cushions of fat. Muscular Relations. — ^The capsule is closely related to the fol- lowing muscles: anteriorly, the brachialis anticus; posteriorly, the triceps; externally, the extensor carpi radialis brevior and supinator radii brevis; and internally, the flexor sublimis digitorum. Arterial Supply. — ^The superior and inferior profundae, anasto- motica magna, anterior and posterior ulnar recurrent, radial recurrent, and posterior interosseous recurrent, arteries. Nerve-supply. — ^The musculo-spiral, musculo-cutaneous, median, and ulnar nerves. Movements. — Two movements are allowed, namely, flexion and extension, these being limited by the tension of the structures related to the joint, and flexion also by the coining into contact of the fleshy parts of the forearm and arm. Muscles concerDed in the Movements — Flexion. — This is produced by the biceps, brachiahs anticus, brachio-radiahs, and. as auxiliaries, the muscles arising from the internal epicondyle of the humerus. Extension. — This is produced by the triceps and anconeus, and, as auxiliaries, the muscles arising from the external epicondyle. Bursa at Elbow-Joint. — The bursae in the vicinity of the elbow- joint are four in number, as follows: Subcutaneous olecranon. Bicipito-radial. Deep olecranon. Epicondylar. The subcutaneous olecranon bursa is situated between the integu- ment and the posterior triangular surface of the olecranon process of the ulna. WTien this bursa becomes inflamed, it constitutes the affection known as miner's elbow. It has no communication with the synovial cavity of the elbow- joint. The deep or subtendinous olecranon bursa, which is of small size, is situated upon the front part of the upper surface of the olecranon. It separates the tendon of insertion of the triceps muscle from the posterior ligament of the elbow-joint, and it has no communication with the synovial cavity of the joint. The bicipito-radial bursa is situated between the tendon of insertion of the biceps muscle and the anterior smooth portion ot the bicipital tuberosity of the radius. It has no communication with the synovial cavity of the elbow-joint. The epicondylar bursae are not constant. There may be two }esial over the internal or mesial epicondyle of the humerus, and teral over the external epicondyle. THE RADIO-CARPAL OR WRIST-JOWT. ,The wrist-joint belongs to the class diarthrosis, and to the sub- ^vision condylarthrosis.— - The articular surfaces are the carpal rface of the radius and the triangular fibro-cartilage above, and jie superior facets of the scaphoid, semilunar, and cuneiform, as bU as the interosseous ligaments on either side of the semilimar, 26 402 A MANUAL OF ANATOMY below. The carpal surface of the radius, -which presents an outer or scaphoid and an inner or semilunar division, and the triangular fibro- cartilage form a socket, which is concave from side to side and from before backwards. The superior facets of the carpal bones extend more upon the dorsal than palmar aspects, and they present a convexity. The ulna is entirely excluded from this joint by the triangular fibro-cartilage. The joint is surrounded by a capsule, which is made up of four ligaments, namely, anterior, posterior, external, and internal. The anterior ligament is a broad, strong membrane, the fibres of which are attached posteriorly to the front of the lower end of the radius, close above the anterior border, and to the anterior margin Radius - — /— Anterior Ligament - External Lateral Ligament - Ligaments of ist Row External Lateral Ligaments of 1st and 2nd Rows Ligaments of 2nd Ro Capsule of Carpo- metacarpal Joint of Thumb — Interosseous Membrane Ulna Anterior Radio-ulnar Ligament ^ Internal Lateral Ligament _ Flexor Carpi Ulnaris Pisiform Bone ~~" Ligaments of ist & 2nd Rows — Pisi-uiicinate Ligament — Pisi-metacarpal Ligament Hook of Unciform Intermetacarpal Ligaments 2.M 5.M 4.M Fig. 217. — The Ligaments of the Radio-carpal, Carpal, Carpo- metacarpal, AND Intermetacarpal Joints (Anterior View). of the triangular fibro-cartilage. Interiorly they are attached to the palmar surfaces of the scaphoid, semilunar, and cuneiform bones. The fibres for the most part are directed downwards and inwards. The posterior ligament is a broad, weak membrane, the fibres of which are attached superiorly to the posterior border of the radius and triangular fibro-cartilage, and interiorly to the dorsal surfaces of the scaphoid, semilunar, and cuneiform bones, especially the latter. Its fibres are directed downwards and inwards. The external lateral ligament is a strong, flattened band, which extends from the tip of the styloid process of the radius to the outer aspects of the scaphoid and trapezium. It supports a portion of the second part of the radial artery. I THE UPPER LIMB 403 Radius Uloa The internal lateral ligament is a strong, round cord, which extends from the tip of the styloid process of the uhia to the cunei- form and pisiform bones. The synovial membrane lines the internal surface of the capside and the upper surfaces of the interosseous hgaments on either side of the semilunar. In cases where the triangular libro-cartilage is perforated it is continuous with the sjTiovial membrane of the in- ferior radio-ulnar joint, but it is distinct from that of the carpal articu- lations. Muscular Relations — A nterior. — From with- in outwards, the flexor carpi ulnaris, flexor pro- fundus digitorum, flexor longus pollicis, and flexor carpi radialis. Posterior. — From within outwards, the extensor carpi ulnaris, extensor minimi digiti, extensor communis digi- tormn with the extensor indicis, extensor longus pollicis, extensor carpi radialis brevior, and ex- tensor carpi radialis longior. External. — The extensor ossis metacarpi pollicis and extensor brevis pollicis. Arterial Supply. — The anterior and posterior carpal retia. Nerve-supply. — The median, ulnar, and posterior interosseous, nerves. Movements. — Six movements are allowed, namely, palmar flexion, dorsal flexion, ulnar flexion or adduction, radial flexion or abduction, extension, and circumduction. In all forms of flexion an angle is produced between the hand and forearm. Extension is straightening, so as to efface the angle produced by flexion. Clrcumdactlon is a combination of all the foregoing movements occurring in alternate succession. Adduction is more extensive than abduction, the stj'loid process of the radius limiting the latter move- ment. When the hand is in line with the forearm, the scaphoid division of the carpal articular surface of the radius articulates with the scaphoid bone, and the semilunar di\'ision of the carpal articular surface of the radius, together with the triangular fibro-cartilage, articulates with the semilunar bone, the fleeted part of the upper surface of the cuneiform being in contact with the ; mer portion of the capsule. When, however, the hand is adducted — that is >_ say, flexed in an inward direction — the faceted part of the upper surface of the cuneiform articulates with the triangular fibro-cartilage, the semilunar bone partially articulates with the scaphoid surface of the radius, and the scaphoid bone partially articulates with the outer portion of the capsule. ^»«i^ ^ J" FlG. 217A. — Radio-carpal and Carpal Synovial Membranes. i 404 A MANUAL OF ANATOMY THE RADIO-ULNAR JOINTS. The radius and ulna are united by a superior and an inferior radio-ulnar joint, and there is an intermediate connection between their shafts. Superior Radio-ulnar Joint. — This joint belongs to the class diarthrosis, and to the subdivision trochoides. The articular sur- faces are the deep inner part of the head of the radius, and the small sigmoid cavity of the ulna. There is one ligament at this joint, namely, the orbicular or annular ligament. This is a strong fibrous band, which forms about four-fifths of a circle, and surrounds the circumference of the head of the radius, which it retains in contact with the small sigmoid cavity. Its extremities are attached to the anterior and posterior margins of the small sigmoid cavity. The ligament is smaller below than above, and so it maintains the head of the radius in position. Its lower border is attached to the neck of the radius by loosely- disposed fibres. It gives attachment to (i) the external lateral ligament of the elbow- joint externally, (2) the outer fibres of the anterior ligament anteriorly, and (3) a portion of the posterior ligament posteriorly. The synovial membrane is con- tinuous with that of the elbow- joint, and lines the inner surface of the orbicular ligament and upper part of the neck of the radius. Muscular Relations. — Extensor carpi radialis brevior and supinator radii brevis. Arterial Supply. — The radial recurrent and posterior interosseous recurrent arteries. Nerve-supply. — The musculo-cutaneous and musculo - spiral nerves. Inferior Radio-ulnar Joint. — This joint belongs to the class diarthrosis, and to the subdivision trochoides. The articular sur- faces are the sigmoid cavity of the radius, and the outer side of the head of the ulna. The ligaments are anterior and posterior, and the triangular fibro-cartilage. The anterior and posterior radio-ulnar ligaments consist of scat- tered fibres in front of and behind the joint, which are attached to the adjacent portions of the radius and ulna. The bones, however, Fig. 218. — The Upper End OF THE Ulna, and the Orbicular Ligament. THE UPPER LIMB 405 are chiefly connected by the triangular flbro-cartilage, which is a strong plate. It is attached by its base to the ridge on the radius which separates the sigmoid cavity from the carpal articular surface, and by its apex to the pit on the lower end of the ulna at the root of the styloid process. It is thicker at the circumference than at the centre, and its anterior and posterior borders are connected with the anterior and posterior ligaments of the wrist- joint. Its upper surface is related to the lower end of the ulna, and its lower surface enters into the wrist- joint, articulating with the semilunar bone when the hand is in line with the forearm, and with the faceted part of the upper surface of the cuneiform bone when the hand is adducted. It sometimes presents a perforation. The synovial membrane is very loose, and is known as the mem- brana sacciformis. It consists of two parts, vertical and hori- zontal, which are continuous with each other. The vertical part extends upwards between the head of the ulna and the sigmoid cavaty of the radius, and the horizontal part lies between the lower end of the ulna and the upper surface of the triangular fibro-cartilage. When the fibro-cartilage is perforated the membrana sacciformis is continuous with the radio-carpal synovial membrane. Arterial Supply. — ^The anterior and posterior ulnar carpal arteries. Nerve-supply. — The anterior and posterior interosseous nerves. Intermediate Connection between the Radius and Ulna. — This is a variety of syndesmosis. The shafts of the two bones are connected by two ligaments, namely, the interosseous membrane and the oblique ligament. The interosseous membrane is a strong expansion which ex- tends between the interosseous borders of the shafts of the radius and ulna. Its fibres pass principally downwards and outwards from the radius to the ulna, but some pass in the opposite direction. Superiorly it reaches to a point about i inch below the bicipital tuberosity of the radius, and inferiorly to the upper part of the sigmoid cavity of that bone. The posterior interosseous artery passes backwards between the two bones over its upper border, and the posterior branch of the anterior interosseous artery pierces it a little above its lower end. The membrane, besides connecting the shafts of the two bones, serves to give origin to muscles of the front and back of the forearm. Relations — Anterior. — ^The flexor profundus digitorum and flexor longus poUicis, with the anterior interosseous vessels and nerve lying between the two, as low as the lower fourth, where the pronator I quadratus forms the anterior relation. Posterior. — From above down- i wards, the supinator radii brevis, extensor ossis metacarpi pollicis, 1 extensor brevis pollicis, extensor longus pollicis, extensor indicis, 1 and, for a short distance below, the posterior interosseous nerve and posterior branch of the anterior interosseous artery. The oblique ligament is a narrow band which extends from the j tuberosity of the ulna to the radius, close below the lower and back j part of the bicipital tuberosity. Its fibres are directed downwards 4o6 A MANUAL OF ANATOMY and outwards. The interval between it and the upper border of the interosseous membrane gives passage to the posterior inter- osseous vessels. Movements. — The movements allowed are pronation and supination, the latter being the stronger. In pronation the lower part of the radius, carrying with it the hand, crosses over the lower part of the ulna so as to lie on its inner side, the dorsum of the hand being directed upwards. In supination the radius and hand retrace their steps, so that the lower part of the radius lies on the outer side of the ulna, the palm of the hand being directed upwards. At the superior radio-ulnar joint the head of the radius rotates upon the capi- tellum of the humerus within the orbicular ligament, and comes into closest relation with the capitellum in semiflexion of the elbow-joint and semi- pronation of the forearm. At the inferior radio-ulnar joint the radius, carrying with it the triangular fibro-cartilage, rotates upon the head of the ulna, the movement being one of limited circumduction around an axis passing from the centre of the head of the radius to the styloid process of the ulna. There is also a limited amount of circumduction on the part of the ulna, the lower end of that bone moving outwards and backwards in pronation, and inwards and forwards in supination. Muscles concerned in the Movements — (i ) Pronation. — The principal pronator muscles are the pronator radii teres and pronator quadratus. (2) Supination. — The principal supinator muscles are the biceps and supinator radii brevis. The brachio-radialis is also a feeble supinator, but it only acts as such to the extent of semisupination. The biceps is enabled to act as a supinator in virtue of its insertion into the back part of the bicipital tuberosity of the radius. THE ARTICULATIONS OF THE HAND. Carpal Joints. — The carpal joints are divided into those of the first row, those of the second row, and the transverse carpal joint. Joints of the First Row. — ^These belong to the class diarthrosis,, and to the subdivision arthrodia. The bones of the first row, with! the exception of the pisiform, are united by two dorsal, two palma^ and two interosseous ligaments. The dorsal and palmar ligament extend transversely from the front and back of the semilunar to th^ corresponding surfaces of the scaphoid and cuneiform. The twc interosseous ligaments are placed one on either side of the semilunar and they connect it with the scaphoid and cuneiform. They an situated high up on the lateral surfaces of the bones, and thei upper surfaces form part of the lower wall of the radio-carpal joint The synovial membrane is continuous with that of the transversi. carpal joint. Pisiform Joint. — The pisiform bone is united to the front of th cuneiform by a capsular ligament, which surrounds the joint and i attached to the bones at the circumference of their opposed articula surfaces. Superiorly the capsule is connected with the tendon C' insertion of the flexor carpi ulnaris, and interiorly with two prolongs tions of that tendon, called the pisi-uncinate and pisi-metacarfx ligaments. The former is attached to the hook of the unciform bon^ and the latter to the base of the fifth metacarpal. These ligamen THE UPPER LIMB 407 act by keeping the pisiform bone fixed during the action of the flexor carpi ubiaris. The pisiform joint has a special synovial membrane. Joints of the Second Row. — These belong to the class diar- throsis, and to the subdivision arthrodia. The four bones of the second row are connected by three dorsal, three palmar, and three interosseous ligaments, which are disposed similarly to those of the first row. - , , , , The s\Tiovial membrane is continuous with that of the transverse carpal joint. , . . , ^1. /- ^ Transverse Carpal Joint.— This is the joint between the first and second rows. It belongs to the class diarthrosis, and partly to Interosseous Membrane __/ — Ulna / Posterior Radio-ulnar g. — Ligament Internal Lateral Ligament Ligaments between ist.=^ and 2nd Rows Ligaments of and Row.-:.- Dctacarpal Ligament Radius Styloid Process of Raditis ——---= Posterior Ligament Ext. Lateral Ligament ""^"^^^ Ligaments of ist Row Ext. Lateral Ligament of ist and znd Rows J. V^ _ Carpo-metacarpal " Ligaments Capsule of Carpo- metacarpal Joint umb :tacarpal of TnuE 5.M 4.M. 5.M. IG. 219. — Ligaments of the Radio-c.vrpal, Carpal, Carpo-metacarpai,. AND Intermetacarpal Joints (Posterior View). le subdivision arthrodia and partly to the subdivision condyl- throsis. The opposed surfaces of the two rows are each concavo- )nvex, the first in a direction from within outwards, and the second rom without inwards. The convexity of the first row is formed by irt of the scaphoid, and the concavity by part of the scaphoid, Bmilunar, and cimeiform. The concavity of the second row is led by the trapezium and trapezoid, and the convexity by the of the OS magnum and part of the unciform. The two rows connected by dorsal, palmar, and lateral ligaments. The dorsal lents are very indefinite and pass in different directions. The ilmar ligaments for the most part radiate from the os magnum, 4o8 A MANUAL OF ANATOMY though a few pass from the other bones of the second row. The external lateral ligament connects the scaphoid with the trapezium, and the internal lateral connects the cuneiform with the unciform. Carpal Synovial Membrane. — This membrane lines the transverse carpal joint, and gives off vertically- disposed processes. Two of these pass upwards, one on either side of the semilunar as far as its interosseous ligaments. Three pass downwards — one between the trapezium and trapezoid, another between the trapezoid and os magnum, and a third between the os. magnum and unciform. There- after the synovial membrane is continued into the inner four carpo- metacarpal joints, and this latter portion of it sends processes into the joints between the bases of the inner four metacarpal bones. Arterial Supply.— The anterior and posterior carpal retia. Nerve-supply. — The median, ulnar, and posterior interosseous nerves. Movements. — The movements between the bones of each row are extremely limited, and are of a gliding nature. The movements at the transverse carpal joint are more free, and take the form of flexion and extension in associa- tion with the corresponding movements at the radio-carpal joint. The number of the carpal articulations imparts to this part of the hand consider- able strength and elasticity, and so enables it to disperse shock. Carpo-metacarpal Joints. — Inner Four Joints. — These belong to class diarthrosis, and to the subdivision arthrodia. The bones con- cerned are the trapezium, trapezoid, os magnum, and unciform above, and the bases of the inner four metacarpal bones below. The ligaments are dorsal, palmar, and interosseous. The second, third, and fourth metacarpal bones receive each two dorsal liga- ments as a rule, and the fifth receives one, namely, from the unci- form. The palmar ligaments are usually one to each bone. There is only one interosseous ligament, which connects the adjacent parts of the os magnum and unciform with the inner aspect of the base of the third metacarpal bone towards its palmar aspect. The synovial membrane is a continuation of that of the carpus. These joints derive their arterial supply from the radial and ulnar arteries, and their nerve-supply from the deep division of the ulnar, and posterior interosseous, nerves. Movements. — The movements are those of flexion and extension, the former being most free in the case of the fifth metacarpal, as in the formation of the ' palmar cup.' Carpo-metacarpal Joint of the Thumb. — This belongs to the class diarthrosis, and to that variety of the subdivision arthrodia which is called the reciprocal or saddle-joint. The bones which enter into this important joint are the trapezium and the base of^ the first metacarpal. The articular surfaces are saddle-shaped, j and are connected by a capsular ligament, which is attached round! the margin of each articular surface, being strongest on the dorsal and outer aspects. This ligament is sufficiently loose to allow of considerable movement. THE UPPER LIMB 409 The synovial membrane is peculiar to the joint. Arterial Supply. — The arteria princeps pollicis of the radial. Nerve-supply. — ^The median ner\^e. Movements. — The movements allowed are flexion, extension, abduction, adduction, and circumduction. It is at this joint where the important move- ment of opposition takes place, whereby the tip of the thumb can be opposed in succession to the tip of each of the four inner fingers. Intermetacarpal Joints. — The basal intermetacarpal joints belong to the class diarthrosis, and to the subdivision arthrodia. The bones concerned are the inner four metacarpals, the first metacarpal bone standing off from the second, with which it has no articula- tion. The ligaments are dorsal, palmar, and interosseous. The dorsal ligaments are composed of stout fibres, which pass trans- versely between the contiguous aspects of the bases. The palmar ligaments are similarly disposed in front. The interosseous liga- ments are strong bundles which pass between the opposed surfaces of the bases to which they are attached on the distal sides of the articular facets. Nerve-supply. — ^The deep division of the ulnar nerve. Arterial Supply. — ^The palmar and dorsal interosseous arteries. The synovial membrane is a downward prolongation from that of the carpus. The heads of the inner four metacarpal bones are connected by the transverse metacarpal (deep transverse) ligament. It extends transversely across the palmar aspects of the heads, and its fibres are attached to the fibrous plates on the palmar surfaces of the metacarpo-phalangeal joints. It receives the deep expansions of the digital processes of the central division of the palmar fascia, and the digital arteries and nerves pass in front of it, and the in- terosseous muscles behind it. It is to be noted that the transverse metacarpal ligament excludes the head of the first metacarpal bone, whereas the corresponding ligament of the foot includes the head of the first metatarsal. The synovial membranes from the inferior radio-ulnar joint down to the intermetacarpal joints are five in number, as follows : 1. Inferior radio-ulnar or membrana sacciformis. 2. Radio-carpal. 3. Pisiform. 4. Carpal, composed of carpal proper, carpo-metacarpal, and intermetacarpal portions, all continuous with one another. 5. Carpo-metacarpal of the thumb. Metacarpo-phalangeal Joints. — These belong to the class diar- throsis, and to the subdivision condylarthrosis, which is a modifi- cation of enarthrosis or ball-and-socket joint. In each joint the round head of a metacarpal bone articulates with the cup- shaped depression on the proximal end of a first phalanx. Inner Four Metacarpo-phalangeal Joints. — Each of these joints has three hgaments — two .lateral, and a palmar. The lateral 4IO A MANUAL OF ANATOMY metacarpo-phalangeal ligaments are strong bands which are attached above to the dorsal tubercle and palmar depression on either side of the head of a metacarpal bone, and below to each side of the base of a first phalanx, and also to the lateral margin of the palmar fibrous plate. Each is connected with a deep expansion of a digital process of the central division of the palmar fascia. The palmar ligament takes the form of a fibrous plate. It is closely attached at either side to the lateral ligaments, interiorly to the palmar aspect of the base of the first phalanx, and superiorly, where it is connected with the transverse metacarpal ligament, it is slightly attached to the palmar aspect of the head of a metacarpal bone, close above the articular cartilage. It increases the extent of the phalangeal socket for the head of a metacarpal bone, and it forms part of the tunnel for the passage of a pair of flexor tendons. Its deep surface is lined by the synovial membrane of the joint. There is no dorsal ligament, its place being taken by the extensor tendon. Each joint is provided with a synovial membrane, which is looser in front than behind. Arterial Supply. — The digital arteries from the superficial palmar arch, or the palmar interosseous from the deep palmar arch. Nerve-supply. — ^The deep division of the ulnar nerve. Movements. — The movements are flexion, extension, abduction, adduction, and circumduction. Flexion is particularly free, and is combined with adduction. Extension is associated with abduction, and dorsal flexion is prevented by the palmar fibrous plates and flexor tendons. Metacarpo-phalangeal Joint of the Thumb. — ^The lateral liga- ments of this joint are similar to those of the other joints, but there is no palmar fibrous plate, its place being taken by two sesamoid bones. Each of these bones resembles a split pea. The palmar surface is convex, whilst the deep surface is almost flat and covered by cartilage, to play upon a groove on the palmar surface of the head of the first metacarpal bone. The two bones are united by fibres which pass between their contiguous surfaces, and are related i superficially to the tendon of the flexor longus pollicis. Interiorly j they are connected by fibres with the palmar aspect of the base ofj the first phalanx. At either side they are connected with the lateralf ligaments, and posteriorly they are slightly connected with the head; of the first metacarpal above the articular cartilage. The outeri; sesamoid bone is closely associated with the superficial head of the i flexor brevis pollicis, and the inner with the adductor obliquus;; pollicis. The place of a dorsal ligament is taken by the tendonsf^ of the extensor brevis, and extensor longus, pollicis. I Arterial Supply. — ^The arteria princeps pollicis of the radial. | Nerve-supply. — ^The median nerve. 1 Movements. — Flexion, extension, and lateral movement, the latter onljji when the joint is partially flexed. ( Interphalangeal Joints. — These belong to the class diarthrosisf and to the subdivision ginglymus. The ligaments are similar iff THE UPPER LIMB 411 those of the inner four metacarpo-phalangeal joints, namely, two lateral, and an anterior fibrous plate, the extensor tendon taking the place of a dorsal ligament. Each joint is provided with a sjTiovial membrane, and the arterial and nerve supply are derived from the digital arteries and nerves. Each of the inner four fingers has two interphalangeal joints, but the thumb, being destitute of a middle phalanx, has only one, and its dorsal hgament is represented by the tendon of the extensor longus pollicis, whilst its fibrous plate is grooved by the tendon of the flexor longus pollicis. Movements. — The only movements allowed are flexion and extension, the former being very free. Joints with Interarticular Fibro-cartilages. — ^The joints of the upper Umb which have interarticular fibro-cartilages are as follows : 1. The stemo-clavicular joint. 2. The acromio-clavicular joint (inconstant). 3. The triangular fibro-cartilage of the inferior radio-ulnar articulation is to be regarded as an interarticular fibro-cartilage between the ulna and cuneiform bone at the radio-carpal joint. The shoulder-joint has a circumferential fibro-cartilage, namely, the glenoid ligament. GUIDE TO THE UPPER LIMB. The Back. — To remove the skin, the following incisions may be made : one along the middle line from the seventh cervical spine to the second sacral spine ; another from the upper end of this incision outwards to the acromion process, and thence downvsards over the back of the shoulder in a curved manner to meet the posterior fold of the axilla ; and a third from the lower end of the mesial incision outwards along the iUac crest. The cutaneous nerves will be found near the spines of the upper six thoracic vertebrae and near the angles of the lower six ribs. Tliree branches from the first three lumbar nerves are fto be shown descending over the ihaic crest to the gluteal region. The trapezius muscle is to be cleaned, and, in doing so, as well as in the deep ^Stages of this dissection, it is advisable that the dissector of the upper Umb 'lould work in concert with the dissector of the head. The spinal accessory serve will be found passing beneath the anterior border of the trapezius. 1.Tie latissimus dorsi is next to be cleaned, and turning backwards round its iter border will be found the posterior ofisets of the lateral cutaneous branches Df the intercostal nerves. Between the contiguous borders of the latissimus iorsi and obhquus extemus abdominis, just above the centre of the iUac crest, triangle of Petit is to be shown. The region between the trapezius, itissimus dorsi, and base of the scapula, and the parts contained therein, are to be studied. The trapezius is to be divided about i inch from the spines of 'lie vertebrae, and the spinal accessory nerve, with branches of the thnrd and lourth cervical nerves, and the superficial cervical artery, are to be dissected on Its deep surface. The latissimus dorsi is to be divided by an incision carried iownwards from its upper border about 3 inches from the spines of the vertebrae the back part of the iliac crest internal to the iUac origin of the muscle, fso as to leave undisturbed its sUps of origin from the lower three or four ribs, well as its ihac origin. In reflecting inwards the inner portion of the muscle re is to be taken not to injure the serratus posticus inferior, and, in turning Jutwards the outer portion, the serratus magnus is not to be interfered with. The levator anguli scapulae and rhomboid muscles are to be dissected, and the nerve to the rhomboids is to be looked for deeply between these two 4l« A MANUAL OF ANATOMY muscles about i inch from the base of the scapula. The disposition of the rhomboideus major at its insertion is to be noted, and the fibrous band or arch shown. The levator anguli scapulae is to be divided about its centre, and the rhomboids about i inch from the spines of the vertebrae, which will bring into view the posterior scapular artery lying close to the base of the scapula. A branch to the levator anguli scapulae from the nerve to the rhomboids is to be looked for, and a very hmited view will be obtained of the posterior belly of the omo-hyoid at the upper border of the scapula. In association with it the suprascapular nerve and artery may just be seen, but this dissection is not to be pushed. The serratus posticus superior is next to be dissected, followed by that of the serratus posticus inferior, and before reflecting these muscles the vertebral aponeurosis is to be studied, and the posterior lamina of the lumbar apo- neurosis, which gives origin to the latissimus dorsi and serratus posticus inferior. At this stage the internal or deep surface of the serratus magnus is to be examined. The serratus posticus superior is to be cut about i inch from the spines of the vertebrae, and each serration of the serratus posticus inferior is to be divided just below the rib into which it is inserted. The vertebral aponeurosis is also to be carefully removed. In this manner the erector spinae muscle is exposed. Before dissecting this muscle, however, the splenius is to be studied, in concert with the dissector of the head, and divided about i inch from its origin. Underneath the splenius will be found the complexus, the inner portion of which is known as the biventer cervicis, and external to the complexus is the narrow, ribbon-like trachelo-mastoid or transversalis capitis. The dissector should now replace over the lower part of the erector spinae the posterior lamina of the lumbar aponeurosis, having attached to it the latissimus dorsi and serratus posticus inferior. At the outer border of the erector spinae he should notice a portion of the middle lamina of the lumbar aponeurosis, of which more will come into view by raising the outer border of the muscle. He will thus see that the lower part of the erector spinae is enclosed in a sheath, the posterior wall of which is formed by the pos- terior lamina, and the anterior wall by the middle lamina, of the lumbar aponeurosis. The anterior lamina is not visible at this stage. The obliquus internus abdominis may be seen to arise from the lumbar aponeurosis between the iliac crest and the last rib. The dissection of the erector spinae is now to be proceeded with. The separation between the outer and middle columns of the muscle will be ap- parent a little below the twelfth rib as a cellular interval, through which nerves emerge, and in line with which, higher up, nerves, accompanied bv arteries and veins, also appear. Dealing first with the outer column, and dissecting it from below upwards, the sUps of insertion of the ilio-costalis into the angles of the lower six ribs are to be shown. These are then to be turned outwards, and the slips of origin of the musculus accessorius lying internal to them are to be displayed, followed by the slips of insertion of that muscle into the upper ribs. The latter having been turned outwards, the slips of origin of the cervicaUs a.scendens will be found, and this muscle is to be followed up into the neck, where its three slips of insertion are to be brought out. In dealing with the middle column the dissector should first artificially separate from it the inner column, the connection between the two being very close, and he may at once dispose of the inner column or spinalis dorsi. Its four fleshy and tendinous origins below should be shown, and its tendons of insertion above, varying from four to eight in number. The series of arches formed by the tendons o/ this muscle should be noted. The middle column is next to be dissected, and the two series of insertions of the longissimus dorsi shown, the outer, fleshy, passing to the lumbar transverse processes and ribs, and the inner, round and tendinous, passing to the lumbar accessory processes and thoracic transverse processes. At the upper part of the back the dissector will find that the longissimus dorsi is prolonged into the neck by the transversalis cervicis, and to the head by the trachelo-mastoid. It is at this stage that the complexus is most advantageously studied. This muscle having been cut high up by the dissector of the head, the semispinalis dorsi and semispinalis colli are to be THE UPPER LIMB 4^3 dissected. The semispinales and longissimus dorsi having been removed, the multifidus spinae is to be studied, and an eflEort made to show its deepest fibres, called the rotatores spinae. The levatores costarum are to be carefully dissected, and the intertransversales and interspinales are to be looked to, chiefly in the cer\'ical and lumbar regions. Pectoral Region and Axillary Space. — To remove the skin, the following incisions should be made : a mesial incision along the sternum ; another from the upper end of this along the clavicle to the acromion process, and thence downwards over the front of the shoulder to the inner side of the arm close to the anterior fold of the axilla ; and a third transversely outwards from the lower end of the sternum. In the case of a female subject, a circular incision should be made around the margin of the areola. In removing the skin from over the mammary gland the fibrous processes, known as the Ugamenta suspensoria of Cooper, which pass between the superficial fascia in front of the gland and the skin, are to be noted. The following cutaneous nerves are to be displayed: (i) the suprasternal, supraclavicular, and supra-acromial branches of the cervical plexus, which descend over the clavicle beneath the platysma myoides ; (2) the anterior cutaneous branches of the intercostal nerves, which emerge through the upper six intercostal spaces close to the sternum ; and (3) the anterior offsets of the lateral cutaneous branches of intercostal nerves below the second, which turn round the anterior fold of the axilla. If the subject is a female, the mammary gland should now receive careful attention. Its relation to the superficial fascia, which ensheathes it, is to be studied, and also its relation to the deep fascia covering the pectorahs major. The thin skin of the areola is to be carefully raised towards the nipple, and the galactophorous ducts, each presenting a dilatation or ampulla, are to be shown. An endeavour should be made to display the glandular structure and loculi. The pectorahs major and anterior portion of the deltoid are to be dissected, and in the groove between the two the cephahc vein and humeral branch of the acromio- thoracic artery are to be shown. Ljing deeply in the upper part of this groove, just below the clavicle, the infraclavicular glands, two or three in number, are to be looked for. The clavicular part of the pectorahs major should now be divided and reflected. In doing so, the cephalic vein, external anterior thoracic nerve, and branches of the acromio- thoracic artery are to be preserved. The region now being dissected (infraclavicular) hes between the clavicle, pectorahs minor, and upper border of the sterno-costal portion of the pectorahs major. The costo-coracoid membrane, which is a part of the clavi-pectoral fascia, is to be shown, and the stout portion of it, called the costo-coracoid hgament, is to be noted. Having studied the connections of the costo-coracoid membrane and the various structures piercing it, the membrane, along with the axillary sheath beneath it, is to be carefully removed, and the first part of the axillary artery, with its branches, the axillary vein, and the trunks of the brachial plexus are to be displayed. The internal anterior thoracic nerve will be found coming for- wards between the artery and the vein, and a communication between it and the external anterior thoracic nerve is to be looked for over the artery'. The posterior thoracic nerve, which hes behind the artery, is to be carefully preserved. The removal of the costo-coracoid membrane will also expose the subclavius muscle. Without further disturbing the pectorahs major mean- while, the axillary space is now to be dissected from below. The axillary fascia forming the floor of the space, and its relations to the fascial investments of the pectorahs major and latissimus dorsi and fascia of the arm are to be noted. The fascia will be seen to be drawn up towards the space, this being due to the insertion of the clavi-pectoral fascia into its upper surface. The axillary fascia having been dissected, the adipose tissue in the space is to be removed with the greatest care. The lateral cutaneous branches of the inter- costal nerves (except the first) will be found on the inner wall between the serrations of the serratus magnus. The lateral cutaneous branch of the second intercostal is to be followed as the intercosto-humeral nerve across the space 414 A MANUAL OF ANATOMY to the inner and back part of the arm. The lateral cutaneous branches of the succeeding intercostal nerves are to be shown in two divisions — anterior and posterior. The axillary glands are to be carefully looked for. They will be found in three groups, namely, pectoral, within the anterior fold and on the adjacent part of the inner wall ; subscapular, on the posterior wall ; and external, on the outer wall. The posterior thoracic nerve is to be followed out upon the serratus magnus, the long thoracic artery will be found along the lower border of the pectoralis minor, and the subscapular artery on the posterior wall. The dorsalis scapulae branch of the subscapular artery is to be shown. The alar thoracic is seldom a special artery. The middle or long and lower sub- scapular nerves will be found on the posterior wall, the former, with the subscapular artery, going to the latissimus dorsi, the latter, farther out, supplying the teres major and adjacent part of the subscapularis. The upper or short subscapular nerve should not be looked for at present, as it Ues too high up. The structures along the outer wall are next to be shown, namely, the axillary artery, giving off its subscapular, anterior circumflex, and posterior circumflex branches ; the axillary vein ; and the nerves arising from the cords of the brachial plexus. The internal cutaneous branch of the musculo-spiral nerve should be shown at this stage, and preserved. When the tributaries of the axillary vein have been noted in the course of the foregoing dissection they should be removed. The sterno-costal portion of the pectoralis major is now to be divided and reflected, in doing which twigs of the internal anterior thoracic nerve will be seen entering its deep surface, after having pierced the pectoralis minor. The latter muscle is now to be dissected, the fascia, removed in preparing it, being continuous above with the costo-coracoid membrane, and being inserted below into the upper surface of the axillary fascia. The internal anterior thoracic nerve is to be shown entering the deep surface of the muscle. The pectoralis minor having been cut, the axillary space will be fully exposed. The second part of the axillary artery is to be dissected, and it will be found, as a rule, to give off the long thoracic, but the alar thoracic is very inconstant. The cords of the brachial plexus and their relation to the second part of the artery are to be noted, and the upper or short subscapular nerve may now be seen at the upper part of the posterior wall of the space, where it immedi- ately enters the upper part of the subscapularis. The origins of the branches of the cords of the brachial plexus are to be shown as follows : external anterior thoracic, musculo-cutaneous, and outer root of the median from the outer cord ; internal anterior thoracic, lesser internal cutaneous or nerve of Wrisberg, the internal cutaneous, inner root of the median, and ulnar from the inner cord ; and the three subscapular nerves, circumflex, and musculo-spiral from the posterior cord. The next duty of the dissector is to study the sterno-clavicular joint. There- after the clavicle is to be sawn through at its centre, and tlie subclavius muscle divided. At this stage the dissectors of the upper limb and head should work in concert. A full view will be obtained of the continuity between the sub- clavian and axillary arteries, and the nerve trunks and individual nerves of the brachial plexus, as well as the supra- clavicular branches of that plexus. The suprascapular artery and nerve, and the posterior belly of the omo-hyoid will also be seen. The vessels and nerves are then all to be included in two ligatures placed i inch apart, and divided between them, and the lower ligature is to be firmly secured to the outer cut end of the clavicle. The serratus magnus is to be studied, and it will be put upon the stretch if the shoulder is pressed outwards. The limb is then to be removed by dividing the serratus magnus, posterior belly of the omo-hyoid, and levator anguli scapulae, if the latter has not been already cut. Scapular Region. — After removal of the limb, the dissector is to trim the various scapular muscles already dissected, and the arrangement of the tendon of insertion of the pectoralis major is to be shown. The shoulder being sup- ported on a block, the skin is to be removed from over the deltoid, and the cutaneous nerves shown, namely, the su])ra-acromial over the upper third, and a large cutaneous branch of the circumflex turning round the postcriui THE UPPER LIMB 415 border of the muscle near its centre. In cleaning this border the relation to it of the deep fascia over the infraspinatus is to be observed. The deltoid having been fully dissected, and twigs of the circumflex nerve which pierce it having been noted, the muscle is to be divided about i inch below its origin. In turning it down the subacromial bursa and the circumflex nerve and posterior circumflex artery are to be shown, the latter two entering its deep surface. The infraspinatus, teres minor, teres major, and long head of the triceps are then to be dissected, and the gangUform enlargement on the branch of the circumflex nerve to the teres minor is to be observed. The quadrangular and triangular muscular spaces, ^^ith their contents, are to be exposed, and the substitution of the subscapularis as a boundary in front for the teres minor behind is to be noted. The dorsaUs scapulae artery- is to be shown winding round the axiUary border of the scapula through the origin of the teres minor. The supraspinatus is next to be dissected, and, to follow the muscle to its insertion, the acromion process may be sa\\Ti through. At the upper border of the muscle will be found the posterior belly of the omo-hyoid and the suprascapular nerve and artery. The subscapularis is to be cleaned, and at this stage the upper or short subscapular nerve will be fully seen. The supraspinatus, infraspinatus, and teres minor are to be stripped carefuUy from the bone and dissected up to their insertions, in doing which the intimate connection between their tendons and the upper and back parts of the capsule of the shoulder- joint will arrest attention. Between the infraspinatus tendon and the capsule a small bursa may be found. The careful removal of these muscles will allow the dissector to follow out the suprascapular artery and nerve, and the dorsaUs scapulae artery. The subscapularis is also to be stripped from the bone and dissected to its insertion, to do which the muscle must be raised from beneath the coraco-brachiaUs and short head of the biceps. The close connection between its tendon and the front of the capsule is to be noted, as well as the opening in the capsule through which the sjTiovial membrane protrudes to form the subscapular bursa. The teres major and latissimus dorsi are to be followed to their insertions, the varjdng relations between the two are to be made clear, the intervening bursa shown, and in some cases a small bursa behind the tendon of the teres major close to the bone. Before leaving this region the dissector should carefully study the scapular anasto- moses of arteries, the muscular relations of the capsule of the shoulder-joint, and the actions of the scapular muscles, with their ner\'e-supply. Cataneoas Nerves and Veins of the Arm and Forearm. — The skin should be at once reflected as low as the wrist by a median incision down the front of the hmb, and transverse incisions at the elbow and wrist. In reflecting it from over the back of the olecranon process the subcutaneous bursa, there situated, is to be attended to. The following cutaneous nerves are to be fol- lowed out to their distribution, care being taken to preserve the cutaneous veins : (i) the in tercos to-humeral to the inner and back part of the arm in its upper half ; (2) the internal cutaneous of the musculo-spiral to the back of the arm ; (3) the nerve of Wrisberg to the lower half of the arm on its inner aspect ; (4) twigs of the internal cutaneous to the front of the arm in its upper part ; and (5) the upper external cutaneous branch of the musculo-spiral (which appears a Uttle below the centre of the outer side of the arm) to the outer side and front of the arm over about its lower half. At the junction of the upper two-thirds and lower third of the arm on its iimer side the internal cutaneous nerve will be found piercing the deep fascia in two divisions, separ- ately or conjointly, and from this point the two divisions, anterior and posterior, are to be followed downwards along the inner part of the forearm, as low as the wrist in the case of the anterior. The lower external cutaneous branch of the musculo-spiral is to be followed from the outer side of the arm, a little below the centre, down the back of the outer side of the forearm as low as the wrist. The cutaneous part of the musculo-cutaneous wiU be found at the outer border of the biceps a httle above the elbow, and it is to be traced down the outer side of the forearm as low as the wrist in two divisions, anterior and posterior. In front of the forearm, just below the centre and internal to the middle line. 4i6 A MANUAL OF ANATOMY a cutaneous branch of the ulnar nerve may be met with, and towards the wrist the palmar cutaneous branches of the median and ulnar are to be shown. In the lower third of the forearm, posteriorly and on its outer aspect, the radial nerve is to be shown, as well as the dorsal branch of the ulnar nerve on its inner aspect. The cutaneous veins to be dissected are the radial, median, and anterior and posterior ulnar veins in the forearm ; the median basilic and median cephalic at the bend of the elbow, with the deep median joining the superficial median close to its termination ; and the basilic and cephalic in the arm, the basilic being superficial to the deep fascia in the lower half, but subsequently piercing it, and the cephalic being superficial throughout. In connection with the median basiUc vein the semilunar fascia of the biceps is to be shown, and one or two supracondylar glands are to be carefully looked for a little above the internal epicondyle, close to the basilic vein. Front and Inner Side of the Brachial Region. — The deep fascia of the arm is to be studied, and, as the dissection proceeds, the external and internal inter- muscular septa, with the structures related to them, are to be noted. The biceps and coraco-brachialis are to be dissected, and, in connection with the tendon of insertion of the latter muscle, a fibrous band should be looked for passing upwards to the humerus below the small tuberosity, and forming an arch over the latissimus dorsi and teres major. The internal brachial ligament of Struthers is to be looked for, extending from the humerus near the insertion of the teres major to the internal epicondyle. The musculo-cutaneous nerve is to be shown piercing the coraco-brachialis, and, by raising the biceps, the nerve is to be followed between that muscle and the brachialis anticus to the outer border of the biceps, where it becomes cutaneous, and its muscular branches are to be shown. It may be found to give a communicating branch to the median. The semilunar fascia of the biceps is to be carefully dissected, and its relation to the brachial artery and median basilic vein is to be observed. The brachial artery is next to be dissected, and the vense comites on either side of it shown. These will be found to join above, and terminate in the lower part of the axillary vein. The median nerve is to be shown lying at first on the outer side of the artery, then crossing it just below the centre of the arm, and thereafter lying on its inner side. It gives off no branches in the arm, but it may receive one from the musculo-cutaneous. The branches of the brachial artery are to be shown as follows : (i) the superior profunda arises high up from the inner and back part of the vessel, and accompanies the mus- culo-spiral nerve to the back of the arm ; (2) the inferior profunda arises from the inner side a Uttle lower down than the preceding, and accompanies the ulnar nerve through the internal intermuscular septum to the interval between the internal epicondyle and the olecranon ; (3) the nutrient or medullary artery arises from the inner side about the lower border of the tendon of insertion of the coraco-brachialis, and passes downwards to enter the medullary foramen of the humerus ; (4) the anastomotica magna arises from the inner side about 2 inches above the elbow, and divides into two branches — anterior, passing j downwards in front of the internal epicondyle beneath the pronator radii 1 teres, and posterior, piercing the internal intermuscular septum to reach the interval between the internal epicondyle and the olecranon ; and (5) several muscular branches arising from the outer side of the vessel. The musculo-spiral nerve is to be shown lying, for a little, behind the upper part of the brachial artery, and the branches which it here gives off, namely, internal cutaneous to the back of the arm, and muscular to the long and internal heads of the triceps, are to be noted. One of the latter descends with the ulnar nerve, as the ulnar collateral nerve of Krause, to enter the internal head of the muscle low down. The ulnar nerve is to be dissected as low as the internal epicondyle and the olecranon, and it is to be shown piercing thf internal intermuscular septum. It gives off no branches in the arm. Th« internal cutaneous nerve and the nerve of Wrisbcrg are also to be noted. Th< brachialis anticus is to be dissected by displacing the biceps outwards, and it h to be separated from the brachio-radialis. In this way a part of the musculo spiral nerve will be exposed, and it is to be followed carefully downwards ti near the external epicondyle, where its two terminal branches, radial ant THE UPPER LIMB 4^7 posterior interosseous, are to be shown. In this part of its course the nerve will be found to furnish branches to the brachio-radialis and extensor carpi radiaUs longior, and a twig to the brachiaUs anticus, the latter arising high up in the spiral groove. Descending with the musculo-spiral nerve in this groove will be found the anterior terminal branch of the superior profunda artery, and coming up from below to anastomose with it a branch of the radial recurrent. The anticubital space or triangular hollow in front of the elbow is next to be dissected, and its roof, floor, boundaries, and contents carefully studied. If the brachio-radialis is held aside, the posterior interosseous nerve will be seen piercing the supinator radii brevis ; and, if the superficial head of the pronator radii teres is raised, the anterior ulnar recurrent artery, of small size, will be found ascending to the front of the internal epicondyle, where it anastomoses with the anterior branch of the anastomotica magna. The mode of insertion of the tendon of the biceps is to be carefully noted, and its action in this connection studied. Back of the Brachial Region. — The triceps is to be dissected, and its three heads clearly shown. The long head is obvious, but the external and internal heads require careful dissection. The dissector should pull upon the musculo- spiral nerve to make evident its winding course round the back of the humerus, and he should then make an incision through the muscle over the course of the nerve, avoiding its long head. When the cut parts of the muscle are separated, the spiral groove of the humerus is laid bare, with the musculo- spiral nerve and superior profunda artery lying in it. The portion of the muscle above and external to the groove is the external head, and the small, peaked portion inside the groove and all the fibres arising from the back of the humerus below the groove represent the internal head. The branches of the musculo-spiral nerve behind the humerus are to be shown, and one long branch to the anconeus, which descends in the internal head of the triceps, is to be followed out. The nerve, on leaving the spiral groove, will be seen to pierce the external intermuscular septum from behind forsvards, along with the anterior branch of the superior profunda artery. This artery is also to be dissected, and its posterior terminal branch is to be shown descending behind the external intermuscular septum to the back of the external epicondyle, where it anastomoses with the posterior interosseous recurrent. The internal head of the triceps may now be cut into interiorly, in order to show its deepest fibres, under the name of the subanconeus, taking insertion into the back part of the capsule of the elbow- joint. Acromio-clavicuiar Joint. — In connection with this joint the coraco- clavicular Ugament is to be displayed in two parts — conoid and trapezoid — and between these will be found a little fat and a small bursa. The ligaments of the joint itself are next to be dissected, and, when the joint is opened, an incomplete interarticular libro-cartilage may be found within it at the upper part. Special Ligaments of the Scapula. — The suprascapular or transverse Ugament is to be made evident, with the suprascapular nerve passing backwards beneath it, the suprascapular artery over it, and fibres of the posterior belly of the omohyoid arisii^ from it. The coraco-acromial or deltoid hgament is next to be dissected, and its relation to the capsule of the shoulder-joint care- fully noted. The spino-glenoid hgament is to be shown passing between the outer border of the spine and the adjacent part of the margin of the glenoid cavity. It will be seen to bridge over the suprascapular artery' and nerve on their way to the infraspinous fossa. Shotllder-Joint. — The dissector should first revise the subacromial bursa and the muscular relations of the capsule of this joint. The capsular Ugament is then to be studied, and the coraco-humeral hgament is to be noted incor- porated with its upper aspect. Two openings in the capsule are to be observed. One is situated in front, behind the upper border of the tendon of the subscapularis, and through this opening the sjTiovial membrane wiU be found protruding to form the subscapular bursa. The other opening is situated between the tuberosities of the humerus, at the entrance to the bi- 27 4i8 A MANUAL OF ANATOMY cipital groove, this being for the passage of the long tendon of the biceps. The transverse humeral ligament will be found bridging over this part of the bicipital groove. The joint should now be opened by removing the posterior part of the capsule, and the three gleno-humeral ligaments are to be looked for. They are situated on the inner and anterior aspect of the capsule. The front part of the capsule should now be removed and the glenoid ligament examined. The tendon of the long head of the biceps, as it arches over the head of the humerus, is to be noted, and its relation to the glenoid ligament at the apex of the glenoid cavity is to be shown. The synovial membrane and movements are then to be studied. Front ol the Forearm. — The deep fascia is to be examined and removed, except the part covering the muscles arising from the internal epicondyle. These muscles are to be dissected, from without inwards, in the following order : pronator radii teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor subUmis digitorum. Having noted the common tendon of origin of these muscles, what is left of the deep fascia is to be removed, and the muscles carefully separated from each other up to their origins. In doing so, the strong intermuscular septa are to be noted. The small, deep head of the pronator radii teres is to be displayed, with the median nerve passing between the two heads of the muscle, and the ulnar artery beneath its deep head, and it should be noted that the median nerve, which is at first internal to the ulnar artery, crosses it to get to its outer side. The muscular branches of the median nerve are to be caught high up, as well as its anterior interosseous branch, in connection with which latter care is to be taken to preserve the median branch of the anterior inter- osseous artery, which is usually of small size. The ulnar nerve is to be shown entering the forearm between the two heads of the flexor carpi ulnaris, where it lies between the internal epicondyle and olecranon, and gives off articular twigs to the elbow- joint. Thereafter its branches to the flexor carpi ulnaris and inner portion of the flexor profundus digitorum should be displayed high up. The radial artery is next to be dissected as low as the wrist, its venae comites being noted. The branches to be shown are the radial recurrent, close to the origin, muscular down the forearm, and anterior radial carpal and superficial volar near the wrist. The radial nerve is also to be dissected until it turns to the back of the forearm beneath the tendon of the brachio- radialis. The ulnar artery is then to be dissected as low as the wrist, and, descending over its lower half, the palmar cutaneous branch of the ulnar nerve is to be preserved. The branches of the vessel to be shown are the anterior and posterior ulnar recurrents, the interosseous trunk, soon divid- ing into anterior and posterior interosseous, the former of which gives off the median artery (all of these branches arising high up), muscular down the forearm, and posterior and anterior ulnar carpals near the wrist. The pos- terior interosseous artery is to be shown passing backwards between the radius and ulna, and the median branch of the anterior interosseous artery is to be carefully studied, as it is sometimes of large size and may be continued into the palm to join the superficial palmar arch. The ulnar nerve is to be dis- sected as low as the wrist. Its occasional branch to the front of the forearm below the centre is to be looked for, and the palmar cutaneous and dorsal branches are to be shown, the former arising a little below the centre of the forearm and the latter about 2 inches above the wrist, after which it turns backwards beneath ±he tendon of the flexor carpi ulnaris. The flexor sublimis digitorum is then to be raised and held aside, to show j the median nerve, with the median artery, descending in close contact with | its deep surface as far as a little above the wrist, where the nerve comes to lie on the outer side of the muscle, and gives off its palmar cutaneous branch. I At this stage the dissector should carefully note that the great palmar bursa j is prolonged upwards round tho flexor tendons for fully an inch above the | anterior annular ligament, and the arrangement of the superficial flexor j tendons in pairs before they pass beneath that ligament is to be shown. By I pulling upon the individual tendons, those of the anterior pair will be seen THE UPPER LIMB 4^9 to belong to the middle and ring fingers, and those of the posterior pair to the index and little fingers. The deep muscles of the front of the forearm are next to be dissected, namely, the flexor profundus digitorum, flexor longus polUcis, and pronator quadratus. The anterior interosseous nerve and artery, the latter having two venae comites, are to be followed down the front of the interosseous membrane beneath the pronator quadratus. In this latter situation the nerve should be shown to supply the pronator quadratus, and give an articular branch to the wrist- joint. The artery should be here shown to divide into anterior and pos- terior branches, the former descending to take part in the anterior carpal rete, and the latter piercing the interosseous membrane to reach the posterior carpal rete. Front of the Hand. — The various landmarks are to be carefully studied. Thereafter the skin is to be removed by a median incision from the centre of the wrist to the cleft between the middle and ring fingers, and a transverse incision across the roots of the fingers. Median incisions are also to be made down the centre of the thumb and each finger, and the skin removed from these parts. In removing the skin from the palm fibrous processes will come into view, which connect it with the central division of the palmar fascia. The lobulated condition of the superficial fascia of the palm is to be noted, and the superficial transverse ligament is to be looked for as a few scattered transverse fibres lying within the skin at the roots of the fingers. The palmar cutaneous branches of the median and ulnar nerves are to be followed out, and twigs of the radial ners-^e, reinforced by tAvigs from the musculo-cutaneous, are to be shown over the thenar eminence. The palmaris brevis muscle is to be care- fully dissected, as it is subcutaneous and arranged in bundles. The expansion from the tendon of the flexor carpi ulnaris to the anterior annular Ugament is to be noted, as well as the pisi-uncinate and pisi-metacarpal expansions, which are known as ligaments. The ulnar artery and nerve are then to be followed over the anterior annular Ugament till they disappear beneath the palmaris brevis, and their relation to the pisiform bone and hook of the unciform are to be noted. The palmar fascia should now receive careful attention. Its thenar and h>*pothenar divisions, which are thin, are to be noted, but attention is to be concentrated on the central division. Its triangular shape, great strength, and the longitudinal direction of most of its fibres are to be observed. Some of the fibres, however, will be seen to be disposed transversely, especially towards the roots of the fingers. In this latter situation it should be shown dividing into four digital processes, which pass to become incorporated with the sheaths of the flexor tendons of the inner four fingers. The thenar and hypothenar divisions of the fascia are removable with ordinary care in order to expose the muscles, and no important structure is in danger. The central division, however, must be removed with the greatest care. In doing so the dissector should particularly note its great strength, which will show him how it would resist the pointing of a palmar abscess, and the necessity of early incision to give vent to the pus. As this division is being removed a deep lateral expansion is to be looked for at either side of it, these expansions passing to join the more deeply placed interosseous fascia. The result is that a great central fibrous tunnel is formed in the palm, which contains the superficial palmar arch, digital arteries and nerves, and flexor tendons, all enclosed in the great palmar bursa. In reflecting the digital processes of the central division deep lateral expansions should be looked for, which, along with them and the anterior fibrous plates of the metacarpo-phalangeal joints, form short tunnels for each pair of flexor tendons. On removal of the central division of the palmar fascia the great paln\ar bursa is to be thoroughly mastered. The superficial palmar arch is then to be dissected, and its position and branches are to be carefully studied. The profunda branch is to be shown coming off from the commencement (inner part) of the arch, and, along with the deep division of the ulnar nerve, it will be seen to disappear between the abductor, and flexor brevis, minimi digiti. Four digital arteries are to be followed from the convexity of the 420 A MANUAL OF ANATOMY arch, the inner one being single and the other three compound, for the suppl} of the inner three and a half fingers. It should be noted that the digita arteries, in passing to the fingers, lie over the interosseous spaces and super ficial to the digital nerves. About the centre of the palm the inner arterj will be found to be reinforced by a communicating branch from the deeply placed innermost palmar interosseous, and the outer three arteries, close tc their points of bifurcation, will be found to be joined each by a palmar inter osseous artery. The possible presence of a large median artery joining th< superficial palmar arch is to be borne in mind. The median and ulnar nerves are next to be dissected in the palm as far a; the roots of the fingers. The median nerve, after emerging from beneath th( anterior annular ligament, will be found to present an enlargement, and thei to break up into outer and inner divisions. The outer division is to be showi giving off a muscular branch which supplies the abductor poUicis, opponeni pollicis, and superficial head of the flexor brevis pollicis, and then to arrang< itself into three single digital nerves to both sides of the thumb and outer sid< of the index finger, the last branch giving a twig to the first or outermos lumbricalis muscle. The inner division furnishes two compound digital nerves each of which divides near the clefts of the fingers into two branches for th( supply of the contiguous sides of the index and middle, and middle and rinj fingers. The compound digital nerve to the cleft between the index anc middle fingers will be found to give a twig to the second lumbricalis, and tha to the cleft between the middle and ring fingers communicates by a cros! branch with the compound digital branch of the ulnar nerve to the clef between the ring and little fingers. The ulnar nerve is next to be dissected as far as the fingers. Its divisioi into a superficial and deep branch is to be shown, the latter accompanying the profunda artery between the abductor, and flexor brevis, minimi digiti The superficial division will be found to supply the palmaris brevis anc then to divide into two digital nerves — an inner single to the inner side o the little finger, and an outer compound for the supply of the contiguous side: of the little and ring fingers. The digital arteries and nerves are now to b« followed along the sides of the fingers, where the nerves will be seen to b< superficial to the arteries, and to present minute swellings, called Paciniar bodies. In dissecting the digital nerves on the outer side of the index fingei and both sides of the thumb the arteria radialis indicis and the two branche; of the arteria princeps polhcis are to be shown. The sheaths of the flexor tendons are now to be examined. The strong almost cartilaginous, vaginal ligaments over the first and second phalanges art to be noted, and the weak membrane opposite the interphalangeal joints, with its obliquely-decussating fibres, is to be shown. The sheath being opened, the synovial lining is to be studied, and the insertions of the superficial and deep flexor tendons are to be examined. In connection with the synovial lining the vincula accessoria tendinum are to be displayed, namely, the ligamenta longa and ligamenta brevia. The sheath of the tendon of the flexor longus pollicis is to be examined in a similar manner. The relations of the synovial sheaths of the flexor tendons on the digits to the great palmar bursa are to be carefully studied. The thenar muscles are now to be dissected. The most superficial is the abductor pollicis, and beneath this is the opponens pollicis. The super- ficial head of the flexor brevis pollicis lies internal to the opponens pollicis and close to the outer side of the tendon of the flexor longus pollicis, anc the adductor obliquus pollicis is close to the inner side of that tendon. Th« adductor transversus pollicis lies beyond the obliquus, from which it is separ ated by the radial artery. The deep head of the flexor brevis pollicis ii difficult to show. It Ues deeply, and arises from the inner side of the base o the first metacarpal bone, and it joins the adductor obliquus pollicis. A larg< bundle of fibres should be looked for passing from the adductor obliquui pollicis to the superficial head of the flexor brevis pollicis, and in each of thesi muscles at its insertion a small sesamoid bone will be met with. The medial, nerve will be found to supply the abductor, opponens, and superficial head O THE UPPER LIMB 421 the flexor brevis pollicis. the others being supplied by the deep division of the ulnar nerve. The three hypothenar muscles are then to be dissected. The profunda branch of the ulnar artery and deep division of the ulnar nerve pass between the abductor, and flexor brevis, minimi digiti, and then pierce the opponens minimi digiti, these three muscles being suppUed by the deep division of the nerve. The anterior annular Ugament is now to be dissected, the structures related tc it superficially are to be revised, and the ligament is then to be divided in order to examine the contents of the fibro-osseous canal which it forms with the front of the carpus. The great palmar bursa is to be carefully noted passing upwcirds beneath it, and descending will be found the super- ficial and deep flexor tendons, tendon of the flexor longus pollicis, and median nerve. Lying in a special compartment of the Ugament, at its outer part, will be found the tendon of the flexor carpi radialis, as it traverses the groove on the palmar aspect of the trapezium. The superficial flexor tendons may then be divided in the palm, to enable the deep flexor tendons to be raised and placed over the handle of a scalpeL The lumbricales, arising from these deep tendons, are then to be dissected, and their ner\'e- supply noted, namely, the deep division of the ulnar for the inner two, and the median for the outer two. The deep flexor tendons are to be cut and turned downwards with the lumbricales, in order to expose the radial artery in the palm, where it forms the deep palmar arch, wiiich is completed by the profunda branch of the ulnar. The arteria princeps poUicis and arteria radiahs indicis are to be shown cirising from the radial as it passes to the front of the hand, and the palmar interosseous, recurrent, and superior perforating branches of the deep palmar arch are to be dissected. The deep division of the ulnar nerve is next to be followed out, and its extensive muscular distribution is to be carefully studied. Baek of the Forearm and Hand. — The skin having been carefully removed, the dorsal venous arch, with its tributaries, is to be shown on the back of the hand, and the radial nerve and the dorsal branch of the ulnar nerve are to be followed to their digital distributions. In removing the deep fascia from the back of the forearm, care should be taken to leave intact the thickened portion of it on the back of the wrist which forms the posterior annular liga- ment. The muscles on the outer side of the forearm are to be dissected first, in the follo\^nng order : brachio-radiaUs, extensor carpi radialis longior, and extensor carpi radialis brevior. The superficial layer of muscles on the back of the forearm are then to be dissected as follows : extensor com- munis digitorum, extensor minimi digiti, extensor carpi ulnaris, and anconeus. Without disturbing meanwhile the posterior annular ligament, the extensor tendons are to be followed over the back of the hand to their insertions. In doing this, the thin, deep fascia on the dorsum, continuous above with the posterior annular ligament, is to be noted, and care is to be taken to preserve the dorsal arteries. The dissector will find the tendon of the extensor indicis lying inside the common extensor tendon to the index finger, and the tendon of the extensor minimi digiti will usually be found to be double. The flat bands which connect the ring-finger tendon with that on either side of it are to be showTi, as well as a band connecting the middle-finger tendon with the common extensor tendon to the index finger. The expansions of the common extensor tendons over the backs of the first phalanges are to be shown, and it will be seen that these receive the insertions of the lumbricales and interossei. The mode of insertion of the extensor tendons is then to be examined. Returning to the back of the forearm, the superficial muscles are to be held well aside, and the posterior interosseous nerve and artery dissected. The nerve, having wound round the outer side of the radius in the supinator radii brevis, will be found emerging from that muscle behind near its lower border, and a little below this the artery meets it, after having passed back- wards between the radius and ulna. The nerve is now to be followed down- wards between the superficial and deep muscles, and then beneath the extensor longus pollicis, but no lower in the meantime, and its muscular distribution 422 A MANUAL OF ANATOMY is to be noted. The posterior interosseous artery will be found to give of its posterior interosseous recurrent branch as soon as it reaches the back o the forearm. This branch is to be followed upwards beneath the anconeu! to the back of the external epicondyle, where it anastomoses with the posterio: terminal branch of the superior profunda. If well injected, it will be founc to give branches to the back of the olecranon process, which anastomose with branches of the posterior ulnar recurrent to form the olecranon rete The posterior interosseous artery, as it descends with the nerve, gets verj small, and usually ceases before reaching the wrist, where its place is taker by the posterior branch of the anterior interosseous, with which it anas tomoses. The muscles of the deep layer are then to be dissected in the following order supinator radii brevis, extensor ossis metacarpi pollicis, extensor brevii poUicis, extensor longus pollicis, and extensor indicis. The posterior annula: ligament is next to be carefully dissected, and, by opening it up, the fibro osseous canals which it forms with the grooves on the lower ends of the radiu; and ulna are to be studied. The localization of the various tendons in thes( canals is to be mastered, and careful attention is to be given to their synovia! sheaths. The mode of termination of the posterior interosseous nerve is alsc to be shown at this stage. It will be found to end beneath the tendons o: the extensor communis digitorum in a gangliform enlargement, from whicl articular twigs are given ofE to the adjacent joints. The radial artery or the back of the wrist and its branches are next to be dissected, and th( dissector is to note that the artery, just before it dips between the two heads of the abductor indicis, is crossed by the tendon of the extensor longus pollicis In connection with the posterior radial carpal artery, the posterior ulnar carpa' is to be shown, as well as the posterior carpal arch, beneath the extensoi tendons. The inner two dorsal interosseous arteries are to be shown arising from this arch, and they are to be followed downwards over the inner twc interosseous spaces to near the clefts between the middle and ring, and ring and little fingers, where each divides into two dorsal collateral digital branches The inner of the two arteries may give a branch to the inner side of the little finger, or this may arise from the posterior ulnar carpal. The first dorsal interosseous artery is to be followed from the radial over the second inter- osseous space to near the cleft between the index and middle fingers, where it also divides into two dorsal collateral digital arteries. The superior perforating branches of the deep palmar arch are to be shown after they have pierced the upper ends of the inner three interosseous spaces between the two heads oi the dorsal interosseous muscles, where each joins a dorsal interosseous artery. Each of these dorsal interosseous arteries may give off an inferior perforating branch, before it bifurcates, to join a digital artery from the superficial palmar arch. The arteria dorsalis pollicis is next to be shown, and it will be found to divide into two branches (which sometimes arise separately) for the sides of the thumb. Lastly, the arteria dorsalis indicis, which arises from the radial just before it leaves the back of the wrist, is to be followed along the outer side of the second metacarpal bone to the outer side of the index finger. The interosseous muscles are next to be dissected. In cleaning the palmar interossei the interosseous fascia is to be noted, and its relation to the central division of the palmar fascia is to be revised. In cleaning the dorsal inter- ossei a thin, deep dorsal fascia will be removed. It will also be necessary tc dissect the transverse metacarpal (deep transverse) ligament, which stretches across the heads of the four inner metacarpal bones on their palmar aspects. This having been cut, the muscles are now to be fully dissected, and theii nerve-supply and actions carefully studied. Elbow- Joint. — The muscles related to this joint are to be replaced, and theiii relation to it noted. The adjacent nerves are also to be observed, and th«! anastomoses of arteries around the joint are to be thoroughly mastered. Thti ligaments which compose the capsule, namely, anterior, posterior, externa)! lateral, and internal lateral, are to be dissected, and the joint is then to be| opened. The articular surfaces are to be examined, the pads of fat noted) and the synovial membrane and movements studied. \ THE UPPER LIMB 423 Wrist-Jofnt. — This joint is to be studied in the same way as the elbow-joint. Radlo-ulnar Joints. — The superior radio-uhiar joint has only the orbicular or annular Ugament, and its synovial membrane is continuous with that of the elbow-joint. The chief bond of union at the inferior radio-ulnar joint is the triangular fibro-cartilage, which is to be carefully examined, along with the sjTiovial membrane, which is called the membrana sacciformis. As regards the intermediate connection between the radius and ulna, the interosseous membrane is to be dissected, and its anterior and posterior relations studied. The opening in it near its lower part for the posterior branch of the anterior interosseous artery is to be shown. The obUque Ugament at the upper end is to be examined, and between it and the upper border of the interosseous membrane will be seen the interval for the passage of the posterior interosseous vessels. The movements of pronation and supination are to receive close attention, and the dissector is to make himself thoroughly famiUar with the muscles concerned in these important movements. Carpal Joints. — The transverse carpal joint is to be dissected first, and the ligaments and movements are to be studied. The pisiform joint is next to be examined, and its capsular Ugament shown. The dorsal, palmar, and inter- osseous Ugaments of the other three bones of the first row are next to be examined, foUowed by those of the second row. The carpo-metacarpal joints are to be studied, and special attention should be directed to the joint between the trapezium and first metacarpal bone. The intermetacarpal (basal) joints follow next. The deep transverse Ugament which connects the palmar aspects of the heads of the four inner metacarpal bones has been already dissected. The metacarpo-phalangeal joints, followed by the interphalangeal, are next to be dissected. The strong anterior fibrous plate is to be noted, and the absence of a dorsal Ugament, its place being taken by the extensor tendon. In the metacarpo-phalangeal joint of the thumb no anterior fibrous plate will be found, its place being taken by two sesamoid bones. Special attention is to be given to the arrangement of the s\-novial membranes, from the inferior radio-ulnar joint above, wth its membrana sacciformis, to the intermetacarpal (basal) joints below. The number of these synovial membranes and the complexity of that of the carpus are to be noted. THE LOWER LIMB THE GLUTEAL REGION. Landmarks. — The crest of the ilium is almost entirely obscured by the prominence of the abdominal muscles above it and the gluteus medius below it, so that as a rule its position is indicated by a groove. This groove conducts the finger to the posterior superior iliac spine, which is on a level with the second sacral spine and the centre of the sacro-iliac synchondrosis. The spinous processes of the sacral vertebrae, usually four in number, may be distinguished as separate projections, or they may be fused into one median ridge. The fifth sacral spine being undeveloped, no median projection can be felt, but at either side of the middle line the sacral comua may be made out. The coccyx is felt in the natal cleft between the buttocks. The tuber ischii is obscured by the lower border of the gluteus maximus when the hip- joint is extended, but, when that joint is flexed, the prominence is easily made out. The great trochanter is felt at the lower and outer part of the gluteal region, and behind it there is a natural depression. The prominence of the natis or buttock is formed by the gluteus maximus, covered by a large amount of adipose tissue. The fold of the natis is produced by a fold of the skin and fascia, and is very perceptible when the hip-joint is extended. It takes the form of a transverse furrow, which commences internally a little below the lower border of the gluteus maximus, and terminates externally on the surface of that muscle, having crossed its lower border. The fold is hori- zontal in direction, whilst the lower border of the gluteus maximus is oblique. It is possible to feel the great sciatic nerve in this fold, but that nerve lies deeply at a point very nearly midway between the great trochanter and tuber ischii, being rather nearer the latter than the former. Cutaneous Nerves. — ^These are met with in the following situations : (i) line of origin of gluteus maximus ; (2) iliac crest ; {3) outer and lower part of gluteus maximus ; and (4) lower border of gluteus maximus. I. Line of Origin of Gluteus Maximus. — The cutaneous nerves met with in this situation are divisible into three sets. 424 THE LOWER LIMB 425 (a) Two or three twigs from the external branches of the posterior primary divisions of the first three sacral nerves. These external branches form two sets of loops, one set being situated deeply on the back of the sacrum, and the other set more superficially on the posterior surface of the great sacro-sciatic ligament. It is from this latter set of loops that the two or three cutaneous twigs are derived, and their direction is chiefly outwards. {h) One or two t\\igs from the undivided posterior primary divisions of the last two sacral nerves and the coccygeal nerve. These divisions form a loop on the back of the sacrum, from which the cutaneous twigs are derived, their distribution being confined to the coccygeal integument. (c) Twigs from the so-called coccygeal plexus, which is situated on the pelvic surface of the coccygeus muscle. These twdgs pierce that muscle and the small sacro-sciatic hgament, as well as the gluteus maximus, and are distributed to the coccygeal integument. 2. Ulac Crest. — The cutaneous nerves in this situation from behind forwards are also divisible into three sets. (fl) Three offsets from the external branches of the posterior primary divisions of the first three lumbar nerves, which descend over the Hiac crest, in front of the outer border of the erector spinae muscle. (h) Ihac branch of the Uio-hypogastric nerve, which crosses the ihac crest at the jimction of the middle and anterior thirds. (c) Undivided lateral cutaneous or ihac branch of the anterior primary division of the twelfth thoracic (subcostal) nerve. This is a large and long nerve which descends over the anterior part of the ihac crest, i inch behind the anterior superior ihac spine, and is distributed to the integument of the anterior part of the gluteal region as low as the great trochanter. 3. Outer and Lower Part of Gluteus Maximus. — The cutaneous nerves appearing in this situation are branches of the posterior division of the external cutaneous nerve, which is derived from the lumbar plexus. 4. Lower Border of Gluteus Maximus. — ^The cutaneous nerves met with in this locahty are as follows : (a) Three or forn: recurrent branches from the small sciatic nerve, which supply the integmnent over the lower and outer part of the gluteus maximus. (6) Perforating cutaneous branch of the sacral plexus, more particularly from the back of the second and third sacral nerves, which supphes the integument ov^er the lower and inner part of the gluteus maximus. Fasciae. — ^The superficial fascia is very thick, and loaded with adipose tissue. It is continuous over the ihac crest with the super- ficial fascia of the back of the trunk, and it contributes to the prominence of the natal region. Between the ihac crest and the upper border of the gluteus maximus there is a considerable accession of adipose tissue to the deep siurface of the superficial 426 A MANUAL OF ANATOMY fascia, and so the depression in that region is filled up. The deef fascia forms a part of the fascia lata. Over the fleshy part o: the gluteus maximus it is thin, but, at the insertion of the muscle and over the anterior two-thirds of the gluteus medius, it is dense In these latter situations it gives insertion to a considerable par' of the gluteus maximus, and origin to the superficial fibres of th( gluteus medius in its anterior two-thirds. In passing from th( gluteus medius on to the gluteus maximus it straps down the uppei border of the latter muscle. Muscles. Gluteus Maximus — Origin. — (i) The posterior 2 inches of the outer lip of the iliac crest ; (2) the upper part of the rougl surface on the dorsum ilii between this part of the crest and th( superior gluteal line ; (3) the posterior lamina of the lumbal aponeurosis ; (4) the lateral part of the back of the fourth anc fifth sacral vertebrae ; (5) the back of the upper three coccygea vertebrae close to the lateral border ; and (6) the superficial surface of the great sacro-sciatic ligament. Insertion. — (i) Rather more than the upper half of the muscle is inserted between two laminae of the fascia lata on the upper anc outer part of the thigh ; (2) the superficial fibres of rather less thar the lower half are also inserted into the fascia lata, but the deej fibres of this portion are inserted into the gluteal ridge of the femur The part of the fascia lata which gives insertion to the gluteus maximus is known as the ilio- tibial band. Nerve-supply. — ^The inferior gluteal nerve from the sacral plexus which enters the muscle on its deep or anterior surface in its lowei third. The direction of the coarse fasciculi of the muscle is downwards and outwards. Action. — Acting from its origin the muscle extends the thigh upor the pelvis, as in rising from the sitting posture, or ascending a stair. The upper part, acting alone, would abduct the thigh, and the lower part would adduct it and rotate it outwards. The muscle also takes part in the completion of extension of the knee-joint, and in the maintenance of extension, as in standing, through means of the ilio-tibial band of the fascia lata. Acting from its insertion the muscle extends the pelvis upon the thigh, as in raising the trunk from the stooping posture. The gluteus maximus, which is quadrilateral, has a short uppeij border which is bound down to the gluteus medius by the fascic lata, and a long lower border which is free. | Deep Relations. — ^These, from above downwards, are as follows the posterior fleshy third of gluteus medius ; superficial divisioi of gluteal artery ; extrapelvic part of pyriformis ; great and smal sciatic nerves ; inferior gluteal nerve ; sciatic and internal pudi< arteries ; pudic nerve ; nerve to obturator internus, supplying branch to gemellus superior ; common nerve to gemellus inferior am quadratus femoris ; gemellus superior ; extrai)elvic part of obturate internus ; gemellus inferior ; quadratus femoris ; crucial anastomosi THE LOWER LIMB 427 of arteries ; upper horizontal part of adductor magnus ; origins of hamstring muscles from tuber ischii ; portion of vastus externus, just below the great trochanter ; and great sacro-sciatic ligament, Biceps Semttendlnosus Semimembranosus Crureus Gracilis Intemal Popliteal Nerve -- Sartorius — — Gastrocnemius — Soleus< _ Ilio-hypogastric Nerve Lateral Cutaneous .of I2th Thoracic Nerve Posterior Divisions of first three Ltimbar Nerves Posterior Divisions of Sacral Nerves Post. Div. of Cocc. N. Perforating Cutan. N. Oluteal Branches of :3niall Sciatic Nerve Post. Branch of Ext. Cutaneous Nerve Small Sciatic Nerve (Outline) Femoral Branches of Small Sciatic Nerve Ext. Cutaneous N. (iVnterior Branch) . Small Sciatic Nerve Posterior Branch of Int. Cutaneous Ner\'e Lateral Cutaneous of External Popliteal Nerve Ramus Commim. Fib. Ramus Commun. Tib. . Ext. Saphenous Nerve Branches of Internal Saphenous Nerve Flexor Longus Digitorum tPeroneus Longus Tendo Achillis ^ Tibialis Posticus -, Plantaris :FiG 2-0. — Muscles and Cutaneous Nerves of the Lower Limb (Posterior Aspect). pierced by the coccygeal branch of the sciatic artery, the sacral branch of the internal pudic artery, and the perforating cutaneous branch of the sacral plexus. 428 A MANUAL OF ANATOMY Three synovial bursne are found underneath the muscle. One, which is single, is situated between the lower border of the muscle and the tuber ischii. Its importance consists in the fact that it is concerned jn the condition known as 'lighterman's bottom.' A second lies between the muscle and the great trochanter, this one being multilocular. The third is found between the muscle and the upper part of the vastus externus, just below the great trochanter. Gluteus Medius — Origin.— (i) The dorsum ilii between the crest, superior gluteal line, and middle gluteal line ; and (2) the fascia lata covering the anterior two- thirds of the muscle. Insertion. — The oblique impression on the outer surface of the great trochanter, extending from the postero-superior angle down- wards and forwards to the antero-inferior angle. Nerve-supply. — The superior gluteal nerve. The direction of the anterior fibres of the muscle is downwards and slightly backwards, and of the posterior fibres downwards and forwards. The fibres of the muscle converge from their origin to the fan-shaped tendon of insertion, and they correspond in direction with those of the gluteus minimus. Action. — Acting from its origin the muscle abducts the thigh. The anterior fibres also act as an internal rotator, and the posterior fibres as an external rotator, of the thigh. Acting from its insertion it balances the pelvis upon the thigh, as in standing upon one leg, and it is also a lateral flexor of the pelvis. The gluteus medius is triangular. The posterior fleshy third is covered by the gluteus maximus, and the anterior two- thirds by the fascia lata. The muscle covers the gluteus minimus except posteriori}^ the deep division of gluteal artery, and the superior gluteal nerve, and a synovial bursa intervenes between it and the upper part of the great trochanter. Gluteus Minimus — Origin. — The dorsum ilii between the middle and inferior gluteal lines. Insertion. — ^The lower part of the anterior surface of the gieat trochanter. Nerve- supply. — The lower division of the superior gluteal nerve. The fibres of the muscle correspond in direction, for the most part, with those of the gluteus medius. Action. — Acting from its origin the muscle is an abductor and internal rotator of the thigh. Acting from its insertion it balances the pelvis upon the thigh, and is a lateral flexor of the pelvis. The gluteus minimus is fan-shaped, and the tendon of insertion spreads out into an aponeurotic expansion over its lower part. It is covered by the gluteus medius except at the posterior part, where the pyriformis rests upon it. Its deep surface is related to the capsular ligament of the hip- joint and the posterior or reflected head of the rectus femoris. The tendon of insertion of the muscle THE LOWER LIMB 429 is separated from the great trochanter by a synovial bursa, and is connected with the upper part of the capsular ligament of the hip- joint by a strong arched band of fibres. The anterior portion of the gluteus minimus is sometimes detached from the rest of the muscle, and, when this occurs, the separated part represents the gluteus quartus or musculus scansorius (cUmbing muscle) of certain animals. Pyriformis — Origin. — (i) By three fleshy shps from the anterior surfaces of the second, third; and fourth sacral vertebrae, which are interposed between, and lie external to, the adjacent anterior sacral foramina ; (2) the deep surface of the great sacro-sciatic liga- ment ; and (3) the posterior border of the iliirni immediately below the posterior inferior iliac spine. Insertion. — The upper border of the great trochanter near its centre. Nerve-supply. — ^Two branches from the sacral plexus, which enter the intrapelvic part of the muscle. The branches come from the dorsal divisions of the first and second sacral nerves. Action. — External rotator of the thigh. The pyriformis, in emerging from the pelvis through the great sacro-sciatic foramen, divides that foramen into a small upper and a large lower compartment. Through the upper compartment the gluteal vessels and superior gluteal nerv-e pass. Through the lower compartment the following structures are transmitted : the sciatic and internal pudic vessels, great and smaU sciatic nerves, inferior gluteal nerve, pudic nerve, nervx to obturator intemus, and common nerv^e to gemellus inferior and quadratus femoris. The extra- pelvic part of the pyriformis is sometimes pierced by the external popliteal nerve. Gemellus Superior — Origin. — The lower border and adjacent portion of the external surface of the spine of the ischium. Insertion. — The upper border of the tendon of the obturator intemus. Nerve-supply. — Branch from the nerve to the obturator intemus, which enters the muscle on its anterior or deep surface near the upper border, close to the origin. The gemellus superior is sometimes absent. Obturator Intemus — Origin. — (i) The internal surface of the obturator membrane ; (2) the posterior smiace of the body of the OS pubis, descending pubic ramus, and ascending ramus of the ischium ; (3) the inclined plane of the ischium, extending as far back as the great sacro-sciatic foramen, and nearly as high as the iUac portion of the ilio- pectineal line ; and (4) the parietal pelvic fascia covering the muscle. Insertion. — The inner surface of the great trochanter, above and in front of the digital fossa. Nerve-supply. — The nerve to the obturator intemus from the sacral plexus. Action. — External rotator of the thigh. 430 A MANUAL OF ANATOMY The intrapelvic and extrapelvic parts of the muscle form very nearly a right angle with each other. It emerges from the pelvis through the small sacro-sciatic foramen, and the deep surface of its tendon is here broken up into from three to five columns, separated from each other by grooves. The small sciatic notch is covered by cartilage, which presents as many grooves as there are columns on the deep surface of the tendon, these grooves being separated by slight ridges. The grooves lodge the columns of the tendon, and the ridges are received into the grooves between the tendinous columns. A bursa intervenes between the tendon and the cartilage covering the notch. Gemellus Inferior — Origin. — The upper part of the tuber ischii, and the lower margin of the small sciatic notch. Insertion. — ^The lower border of the tendon of the obturator internus. Nerve-supply. — Branch from the nerve to the quadratus femoris, which enters the muscle on its deep or anterior surface near the upper border, close to the origin. The gemelli muscles are merely extrapelvic origins of the obtu- rator internus, of which they form accessory parts. As they take insertion into the upper and lower borders of the obturator tendon they are folded over it, so as to overlap and partially conceal the tendon on its superficial aspect. They are auxiliary to the obturator internus in action. Small Sacro-sciatic Foramen. — The structures which pass through this foramen are as follows : (i) obturator internus ; (2) nerve to the obturator internus ; (3) pudic nerve ; and (4) internal pudic artery with its venae comites. Quadratus Femoris — Origin. — The outer border of the tuber ischii. Insertion. — The linea quadrati of the femur, extending as low as the small trochanter. Nerve-supply. — ^The nerve to the quadratus femoris from the sacral plexus, which enters the muscle on its deep or anterior surface near the upper border, close to the origin. Action. — External rotator of the thigh. The muscle conceals part of the obturator externus and the small trochanter of the femur, from which latter it is separated by a small bursa. When the gemellus inferior and quadratus femoris are separated, part of the obturator externus comes into view. Between the lower border of the muscle and the upper border of the adductor magnus the transverse branch of the internal circumflex artery appears, which here takes part in the crucial anastomosis. When the lower border of the muscle is raised, the small trochanter comes into view with the tendon of insertion of!' the ilio-psoas. Arteries. — The chief arteries of the gluteal region are the gluteal, sciatic, and internal pudic. Gluteal Artery. — This vessel arises from the posterior division;, of the internal iliac^^iUwyf ""TlF'pci»g.^e parietal pelvic fascia, itf' THE LOWER LIMB 431 Gluteus Maxunns ..M' //■ (origin) ""f"^/ Gluteal Artery J,l_'i> iperior Gluteal Xer\-e Pyrifonnis nternal Pudic Artery and Pudic Nerve Nerve to Obturator Intemus Great Sacro-sciatic Ligameut Sciatic Artery It Sciatic Nerve and nes Xervi Ischiad. wig Pudendal Nerve Hamstring Muscles (origin) Wductor Magnus cluo-pubic portion) • art of Adductor Magn from Tuber Ischii to Adductor Tubercle Lower Part of "^eat Sciatic Ner\e t- Popliteal Nen-e ^^ J-llfiJ Popliteal Vein Popliteal Artery . . Femoral Opening ., Tendon of Mdnctor Magnus Glutens Medins (reflected) Lower Branch of Deep Div. of Gluteal Artery ^ — Glutens Maximus ^-^ (insertion) - Obturator Interaus and Gemelli - Quadratus Femoris SmaU Sciatic Nerve - Crucial Anastomosis --- First Perforating Artery - Vastus Extemns .- Second Perforating Artery - Third Perforating Artery -- Fourth Perforating Artery - FemoraJ Head of Biceps External Popliteal Nerve Tendon of Insertion of Biceps Fio. 2.X.-THE Gluteal Region.. axd Back op the Thioh (Deep Dissection-^ ^^ii^h 432 A MANUAL OF ANATOMY passes between the lumbo-sacral cord and the anterior primary; division of the first sacral nerve, after which it emerges through the upper compartment of the great sacro -sciatic foramen above the pyriformis, and breaks up into two divisions — superficial and deep. The superficial division passes backwards between the posterior border of the gluteus medius and the pyriformis, and then enters the deep or anterior surface of the gluteus maximus near its origin. Some of its branches become cutaneous by piercing the muscle, and they anastomose with the posterior branches oi the lateral sacral arteries from the posterior division of the internal iliac. The deep division passes beneath the gluteus medius, where it subdivides into an upper and a lower branch. The uppet branch courses along the upper border of the gluteus minimus, in company with the upper division of the superior gluteal nerve. It supplies the ilium and adjacent muscles, and anasto- moses with the deep circumflex iliac of the external iliac and the ascending branch of the external circumflex of the arteria profunda femoris. The lower branch passes forwards over the centre of the gluteus minimus, in company with the lower division of the superior gluteal nerve. It supplies the gluteus medius and gluteus minimus muscles. It also gives an articular branch to the hip- joint, and a branch to the digital fossa which anastomoses with the sciatic, the ascending branch of the internal circumflex, and a branch of the first perforating of the arteria profunda femoris. The lower branch of the deep division also anastomoses with the ascending branch of the external circumflex. The place of emergence of the gluteal artery from the pelvis! is indicated as follows : the thigh being rotated inwards, draw £| line from the top of the great trochanter -to the posterior superion iliac spine, and take a point in this line at the junction of the innei third and outer two-thirds. The gluteal vein terminates in the internal iliac vein. Sciatic Artery. — ^This vessel arises from the anterior division o the internal iliac artery. It descends, usually behind the interna i pudic, upon the pyriformis and sacral nerves, and emerges througl: the lower compartment of the great sacro-sciatic foramen below thf pyriformis. It then passes between the great trochanter and tubef ischii, lying under cover of the gluteus maximus, on the inm^ side of the great sciatic nerve, and resting upon the gemellj^ obturator internus, and quadratus femoris. On leaving this hollovl it descends upon the posterior surface of the upper part of tH adductor magnus, where it terminates. I For the intrapelvic portion of the artery, see dissection of tl pelvis. Branches. — ^The extrapelvic branches are as follows : coccyger inferior gluteal, muscular, anastomotic, articular, gluteal cutaneoi and comes nervi ischiadici. The coccygeal branch pierces the great sacro-sciatic ligame THE LOWER LIMB 433 and gluteus maximus, and is distributed over the back of the cocc5nc. The inferior gluteal branch enters the deep surface of the gluteus maximus with the inferior gluteal ner\"e, and it anastomoses in the muscle with the superficial division of the gluteal artery. The muscular branches are distributed to the adjacent external rotator muscles and the origins of the hamstrings. In the latter muscles an anastomosis takes place with the external terminal branch of the obturator artery. The anastomotic branches are two in number. One passes to the digital fossa, where it anastomoses with the gluteal, ascending branch of the internal circumflex, and first perforating arteries. The other passes to the interval between the quadratus femoris and adductor magnus, where it anastomoses with the transverse branch of the internal circumflex, the transverse branch of the external circumflex, and the first perforating arteries, This fourfold anasto- mosis is called the crucial anastomosis. The articular branches are two or three in number. They pass beneath the gemelli and obturator internus with the nerve to the quadratus femoris, and pierce the back part of the capsular ligament of the hip- joint. The gluteal cutaneous branches pass round the lower border of the gluteus maximus with the gluteal cutaneous branches of the small sciatic nerve, and are distributed to the integument over the lower part of the muscle. The comes nervi ischiadici is a long branch which descends for some distance with the great sciatic nerve, to which it is dis- tributed, and in which it anastomoses with the perforating branches of the arteria profunda femoris. After ligature of the femoral artery in the upper third of the thigh this branch becomes much enlarged. The place of emergence of the sciatic artery from the pelvis is indicated as follows : draw a line from the posterior superior iliac spine to the outer border of the tuber ischii, and take a point in this line at the junction of the middle with the lower third. The sciatic vein terminates in the internal iliac vein. The sciatic artery in the early embryo is the leading arterial trunk of the lower limb. As the femoral artery is developed it forms a junction with the sciatic in the neighbourhood of the knee, and so becomes the chief artery, and the part of the primitive sciatic between the knee and the gluteal region for the most part disappears. Internal Pudic Artery. — ^This vessel arises from the anterior division of the internal iliac, and at first Hes within the pelvic cavity. It is only the second part of the vessel which is seen in the gluteal region, and which will be described here. Having emerged from the pelvis through the lower compartment of the great sacro- sciatic foramen below the pyriformis, the artery passes downwards for a short distance, and crosses over the back of the spine of the ischium. It then courses through the small sacro-sciatic foramen, and is lost to view. 28 434 A MANUAL OF ANATOMY Relations — Superficial or Posterior. — Gluteus maximus. Deep or Anterior. — Posterior surface of spine of ischium. On either side of the artery is a vena comes. The pudic nerve Hes on the inner side, and the nerve to the obturator internus on the outer side. Branches. — Muscular, to gluteus maximus, and sacral, which pierces the great sacro-sciatic ligament, and ramifies over the back of the lower end of the sacrum, where it anastomoses with the coccygeal branch of the sciatic artery. The position of the second part of the internal pudic artery upon the back of the spine of the ischium, which spine is about 4 inches below the posterior superior iliac spine, is ascertained as follows : the thigh being rotated inwards, draw a line from the upper border of the great trochanter to the junction of the sacrum with the coccyx, and take a point in this line at the junction of the inner third and outer two-thirds. Relation of Structures on Back of Spine of Ischium. — The relation from within outwards is as follows: (i) pudic nerve, (2) internal vena comes, (3) second part of internal pudic artery, (4) external vena comes, and (5) nerve to obturator internus muscle. Deep Nerves. Superior Gluteal Nerve. — ^This nerve arises from the sacral plexus, more particularly from the dorsal divisions of the descending branch of the fourth lumbar, the fifth lumbar, and the first sacral nerves. It passes through the upper compartment of the great sacro-sciatic foramen, above the pyriformis, with the gluteal artery, and then beneath the gluteus medius, where it divides into a small upper and large lower branch. The upper branch accompanies the corresponding division of the deep part of the gluteal artery along the upper border of the gluteus minimus, and it supplies the gluteus medius. The lower branch passes outwards over the centre of the gluteus minimus with the lower division of the deep part of the gluteal artery. It supplies the gluteus medius and gluteus minimus, and terminates by supplying the tensoi fasciae femoris. Inferior Gluteal Nerve. — ^This nerve arises from the sacral plexus, more particularly from the dorsal divisions of the fifth lumbar, and first and second sacral nerves. It passes through the lower com-i partment of the great sacro-sciatic foramen, below the^ pyriformis | in close contact with the small sciatic nerve. It then divide;^ into several branches which enter the deep surface of the gluteu: maximus in its lower third. Nerve to Obturator Internus. — This nerve arises from the sacra, plexus, more particularly from the ventral divisions of the fiftl' lumbar, and first and second sacral nerves. It passes through th lower compartment of the great sacro-sciatic foramen, below th pyriformis, internal to the great sciatic nerve ; over the posterior sui face of the spine of the ischium, where it lies to the outer side of th internal pudic vessels ; and through the small sacro-sciatic foram(> to the intrapelvic part of the obturator internus. At the 1o\m THE LOWER LIMB 435 border of the pyriformis it gives a branch to the gemellus superior, which enters that muscle on its deep surface near the upper border, close to the origin. Nerve to Quadratus Femoris. — This nerve arises from the sacral plexus, more particularly from the ventral divisions of the descend- ing branch of the fourth lumbar, the fifth lumbar, and the first sacral nerves. It passes through the lower compartment of the great sacro -sciatic foramen, below the pyriformis, where it lies in close contact with the deep surface of the great sciatic nerve. It then passes, in succession, beneath the gemellus superior, obturator intemus, gemellus inferior, and quadratus femoris, entering the last muscle on its anterior or deep surface near the upper border, close to the origin. As it passes beneath the gemellus inferior, it parts with its branch to that muscle, which enters its deep surface near the upper border, close to the origin. The nerve to the quadratus femoris also supplies, as a rule, an articular branch to the back of the hip- joint. Lymphatics. — ^The superficial lymphatics of the gluteal region terminate in the inguinal glands (superior or oblique superficial inguinal glands). Tiie deep lymphatics enter the pelvis, and terminate in the internal iliac glands. For the great and small sacro-sciatic ligaments see the description of the pelvis in Abdomen Section. THE TfflGH Back of the Thigh and Popliteal Space. Landmarks. — The hamstring muscles give rise to a prominence along the back of the thigh, but they cannot be individually recognised until they reach the popliteal space. The great sciatic nerve is deeply placed, being under cover of the long or ischial head of the biceps femoris, but its course may be indicated by drawing a line from the centre of the back of the knee-joint to a point between the great trochanter and the tuber ischii, rather nearer the latter than the former. The upper two-thirds of this line correspond with the great sciatic nerve, and the lower third with the internal popliteal ner\'e. The situation of the popliteal space behind the knee-joint is indicated by a depression when the joint is flexed. The strong tendon of the biceps femoris can be felt on the outer side, as it descends to reach the head of the fibula, and in front of it the long external lateral hgament of the knee-joint can be distinguished by its tense, cord-like feel. Anterior to this ligament the lower part of the ilio-tibial band of the fascia lata may be felt. The external popliteal nerve is close to the inner side of the biceps tendon. Lower down it can be felt just below the head of the fibula. On the inner side of the pophteal space, over the back of the inner 436 A MANUAL OF ANATOMY condyle, three tendons may be felt; The most superficial one is that of the semitendinosus, which, though firm, is narrow, and is traceable for some distance above the knee-joint. Underneath it is the tondon of the semimembranosus, and, internal to this, is the slender tendon of the gracilis. The course of the popliteal artery practically coincides with the middle line of the popliteal space, but the vessel can only be felt when the joint is well flexed. During this manipulation the popliteal lymphatic glands, if enlarged, may be detected. Back of the Thigh. — ^There is nothing noteworthy in the super- . ficial fascia. The deep fascia will be described in connection with the fascia lata. Small Sciatic Nerve. — This nerve arises from the sacral plexus, more particularly from the back of the first, second, and third sacral nerves. It emerges through the lower compartment of the great sacro-sciatic foramen, below the pyriformis. It then passes down- wards between the great trochanter and tuber ischii, resting upon the superficial surface of the great sciatic nerve, and being under cover of the lower part of the gluteus maximus. After escaping from beneath this muscle, it descends in the middle line super- ficial to the hamstring muscles, and beneath the deep fascia cover- ing them, and, passing over the popliteal space, it pierces the deep fascia at the back of the knee-joint. It then enters the back of the leg, and descends as low as about the centre of the calf, in company with the external or short saphenous vein. The nerve is entirely sensory. Branches. — ^The branches are gluteal cutaneous, long pudendal nerve of Soemmering, femoral cutaneous, and sural cutaneous. The gluteal cutaneous branches are three or four in number, and take a recurrent course, winding round the lower border of the gluteus maximus, and supplying the integument over its lower and outer part. The long pudendal nerve of Soemmering arises at the lower border of the gluteus maximus, and winds inwards towards the anterior part of the perineum, lying a little below the tuber ischii and crossing behind the origins of the hamstring muscles from that prominence. It then pierces the fascia lata fully i inch in front of the tuber ischii, and, passing over the ischio-pubic ramus and through Colles' fascia, it courses forwards and inwards, in company with the two superficial perineal nerves and the superficial perineal artery, to the scrotum in the male and the labium majus in the female. In the anterior part of the perineum it communicates with the two superficial perineal nerves, and with them forms the three long scrotal (or labial) nerves. Its branches are femoral cutaneous, to the upper and inner part of the thigh on its posterior aspect ; and scrotal or labial, to the scrotum or labium majus, according to the sex. The femoral cutaneous branches of the small sciatic supply the integument of the back of the thigh as low as the knee-joint. The sural cutaneous branches are the terminal branches of the nerve. THE LOWER LIMB 437 They supply the integument of the back of the leg as low as about the centre of the calf, and communicate with branches of the ramus communicans tibialis from the internal pophteal. Muscles. — The muscles of the back of the thigh are called the hamstring muscles, and are three in nmnber, namely, biceps femoris, semitendinosus, and semimembranosus. Biceps Femoris or Biceps Flexor Cruris — Origin. — The muscle arises by two heads — long or ischial, and short or femoral, (i) Long or Ischial Head. — This arises, in conjunction with the semitendinosus, from the lower and inner impression on the posterior surface of the tuber ischii. (2) Short or Femoral Head. — This arises from (i) the outer hp of the linea aspera, (2) the upper two- thirds of the external supracondylar ridge, and (3) the external intermuscular septum. Insertion. — The upper surface of the head of the fibula in front of the styloid process, by means of a rotmd tendon which sends an expansion downwards to the deep fascia covering the peroneus longus. A few fibres are also inserted into the external tuberosity of the tibia. The long external lateral hgament of the knee-joint passes through the tendon of insertion, and divides it into two parts, from which the ligament is separated by the bursa wrapped around it. The two divisions of the tendon are anterior and posterior, the anterior, which is the stronger, being inserted into the external tuberosity of the tibia, as well as into the head of the fibula. The expansion to the deep fascia of the leg is derived from the posterior division of the tendon. Nerve-supply. — Great sciatic nerve. The long or ischial head receives branches from the internal popliteal part of the nerve, and the short or femoral head from the external popliteal part. Action. — Acting from its origin the muscle is an extensor of the ip- joint and a flexor of the leg upon the thigh, and, having flexed le knee-joint, it acts as an external rotator of the leg. The long 3r ischial head alone extends the hip- joint. Acting from its iaser- ion the muscle, by means of its long or ischial head, is an extensor )f the pelvis upon the thigh. In virtue of its double insertion into "le head of the fibula and external tuberosity of the tibia, the biceps smoris contributes materially to the strength of the superior tibio- ibular joint by bracing the bones together. In rare cases the biceps femoris has a third head of origin, which lay arise from the tuber ischii, hnea aspera, or internal supra- condylar ridge. Semitendinosus — Origin. — ^The lower and inner impression on the jsterior surface of the tuber ischii, in conjunction with the long or :hial head of the biceps femoris. Insertion. — ^The upper part of the internal surface of the shaft of le tibia, behind the sartorius and below the gracilis. From the mdon of insertion an expansion is given to the deep fascia of the leg. Nerve-supply. — Great sciatic nerve. The branches come from the iternal popliteal part of the nerve. 438 A MANUAL OF ANATOMY Action. — Acting from its origin the muscle is an extensor of the hip- joint and a flexor of the leg upon the thigh, and, having flexed the knee-joint, it acts as an internal rotator of the leg. Acting from its insertion it is an extensor of the pelvis upon the thigh. The semi- tendinosus is intimately connected with the long or ischial head of the biceps femoris in the upper fifth of the thigh, and its belly is crossed at its centre by an oblique tendinous intersection. In the lower third of the thigh the muscle has a long, narrow, round tendon, which broadens out at its insertion, and crosses the internal lateral ligament of the knee-joint. A bursa intervenes between it and that ligament, and also between it and the tendon of the sartorius. Semimembranosus — Origin. — By means of a broad, flat tendon from the upper and outer impression on the posterior surface of the tuber ischii. Insertion. — The insertion is threefold, as follows : (i) the chief insertion is by means of a strong tendon into the horizontal groove on the posterior surface of the internal tuberosity of the tibia ; (2) by an expansion which passes upwards and outwards to the upper and back part of the external condyle of the femur, and which forms a large part of the posterior ligament of the knee-joint, known as the ligamentum posticum Winslowii ; (3) by a broad expansion, which passes downwards and outwards to the oblique or popliteal line on the posterior surface of the shaft of the tibia. This ex- pansion covers the popliteus muscle, and is called the popliteal fascia. Nerve-supply. — Great sciatic nerve. The branches come from the internal popliteal part of the nerve. Action. — Acting from its origin the muscle is an extensor of the hip- joint and a flexor of the leg upon the thigh, and, having flexed the knee-joint, it acts as an internal rotator of the leg. Acting from its insertion it is an extensor of the pelvis upon the thigh. The strong tendon of origin is prolonged downwards for some distance upon the outer side of the muscle, and the chief tendon of insertion is prolonged upwards for some distance upon its inner side The belly of the muscle is composed of short, oblique fasciculi, an arrangement which gives it great power of action, but a limited range of movement. The chief tendon of insertion is under cover of the posterior border of the internal lateral ligament of the knee- joint. Previous to this it is separated from the interned head of the gastrocnemius by the popliteal bursa, which frequently communi- cates with the synovial membrane of the knee-joint through an opening often present in the posterior ligament. The chief tendon of insertion is also separated by a bursa from the upper lip of the groove on the posterior surface of the internal tuberosity of the tibia. The hamstring muscles descend in close contact through the upper three-fourths of the thigh, being held together by the fascia lata. When, however, they reach the lower fourth, they part THE LOWER LIMB 439 company, the biceps femoris passing downwards and outwards, and the semitendinosus and semimembranosus downwards and inwards ; and so the popUteal space begins to open out. Great Sciatic Nerve. — ^This nerve arises from the sacral plexus, more particularly from the descending branch of the fourth lumbar, the fifth lumbar, and the first, second, and upper branch of the third sacral nerves. It emerges from the pelvis through the lower compartment of the great sacro-sciatic foramen, below the pyri- formis, and descends between the great trochanter and tuber ischii, being somewhat nearer the latter than the former. It then passes down the middle line of the back of the thigh, under cover of the long or ischial head of the biceps femoris, and, about the junction of the middle and lower thirds, it terminates by dividing mto internal and external popliteal nerves. The great sciatic nerve is about f inch broad. Its course may be indicated as follows : draw a Une from the centre of the back of the knee-joint to a point between the great trochanter and tuber ischii, rather nearer the latter than the former. The upper two-thirds of this line correspond with the great sciatic nerve, and the lower third with the internal popliteal nerve. Chief Relations. Superficial or Posterior. — Gluteus maximus, small sciatic nerve, and long or ischial head of the biceps femoris. Deep or Anterior. — From above downwards the nerve is in contact with the following structures : the ischium, the ner^'e to the quadratus femoris, gemellus superior, obturator internus, gemellus inferior, quadratus femoris, and posterior surface of adductor magnus. Internal. — Semimembranosus. Branches. — The branches are muscular and terminal. The muscular branches arise in the upper part of the thigh, with the exception of the branch to the short head of the biceps femoris, which arises about the centre. They supply the ham- string muscles, and also that part of the adductor magnus which descends from the tuber ischii to the adductor tubercle of the lemur. The branch to this part of the adductor magnus arises in common with the nerv'e to the semimembranosus. The branch to the ehort head of the biceps femoris is derived from the external popliteal part of the great sciatic nerve, but all the other muscular branches come from the internal popliteal part. The terminal branches are the internal and external popliteal nerves. They arise about the junction of the middle and lower thirds of the thigh, and will be described in connection with the popliteal space. The great sciatic nerve supplies an articular branch to the hip- joint in those cases where the nerve to the quadratus femoris faUs to do so. Blood-supply. — ^The nerve is supphed by the arteria comes nervi ischiadici from the sciatic, and the perforating branches of the arteria profunda femoris. The great sciatic nerve is not infrequently replaced by the external 440 A MANUAL OF ANATOMY and internal popliteal nerves. Under these circumstances the external popliteal nerve often pierces the pyriformis. Popliteal Space. — ^The pophteal space or ham* is situated behind the knee-joint, whence it extends upwards to the junction of the upper three-fourths and lower fourth of the thigh, and down- wards to the junction of the upper sixth and lower five-sixths of the leg. In shape the space resembles a diamond. Boundaries. External — (a) Above the Knee-joint. — Biceps femoris. {h) Below the Knee-joint. — External head of the gastrocnemius, and plantaris. Internal — {a) Above the Knee-joint. — Semitendinosus, semimem- branosus, gracilis, sartorius, and tendon of the adductor magnus, in the order named from behind forwards, (b) Below the Knee- joint. — Internal head of the gastrocnemius. The superior median angle of the space corresponds with the divergence of the hamstring muscles, the inferior median angle by the approximation of the external and internal heads of the gastrocnemius, the external angle by the meeting between the biceps femoris and external head of the gastrocnemius, and the internal angle by the meeting between the semimembranosus and internal head of the gastrocnemius. The roof is formed by the integument. It contains the small sciatic nerve, and, in its lower part, the terminal portion of the external or short saphenous vein. The floor is formed, from above downwards, by the popliteal surface or trigone of the femur, the posterior ligament of the knee- joint, and the popliteus muscle, covered by the popliteal fascia. Contents. — The contents are the popliteal artery and its branches, the popliteal vein and its tributaries (including the termination of the external or short saphenous vein), the internal popliteal nerve and its branches, the external popliteal nerve and some of its branches, the geniculate branch of the obturator nerve (inconstant), lymphatic glands, and a large amount of fat. Popliteal Artery. — This vessel is the continuation of the femoral artery. It extends from the posterior margin of the femoral opening, which is in connection with the adductor magnus, to the lower border of the popliteus muscle, where it divides into anterior and posterior tibial arteries. The division takes place on a level ; with the lower border of the tubercle of the tibia, and fully , i| inches below the level of the upper surface of the head of that j bone. The vessel at first passes downwards and outwards until it j reaches the middle line of the limb. It then takes a straight course downwards between the condyles of the femur, and finally it sinks! * The word ham is derived from a Teutonic verb signifying ' to be curved; or crooked,' and it has been appUed to the popUteal space because that space' is situated behind the ' crook,' ' curve,' or bend of the knee. By a later; extension of the word ham it came to be appUed to the whole of the back of the thigh — hence the name hamstring, which is given to the muscles of that region. THE LOWER LIMB 441 beneath the approximation of the external and internal heads of the gastrocnemius. General Relations. Superficial or Posterior. — Skin, superficial and deep fasciae, small sciatic ner\'e, terminal part of the external or short saphenous vein, fat, semimembranosus for about i inch after the artery enters the space, approximation of the external and internal heads of the gastrocnemius, and the plantaris, which crosses the artery from without inwards. Deep or Anterior. — Fat, pophteal surface or trigone of the femur, posterior hgament of the knee-joint, and pophteus muscle, covered by the pophteal fascia. Cnirens — Internal Popliteal Nerve Popliteal V Popliteal Biceps ■perior Ext. Artjcniar .\rtery External Popliteal Nerve E vtemal Head of Gastrocnemius- — External Popliteal Ner\-e- Ramus Commnnicans Fibolaris — Lateral Cutaneous Branch of- External Popliteal Nerve Middle Cutaneous Sural .Artery Small Sciatic Nerve (cut) -Semimembranosus Gracilis Semitendinosns Internal Popliteal Nerve Internal Head of Gastrocnemius Sartorius Ramus Communlcans Tibialis •Short Saphenous Vein (cut) Fig. 222. — ^The Popliteal Space (Superficial Dissection). Special Relations. — In the upper part of the space the pophteal is close behind, and on the outer side of, the artery, and the ^temal pophteal nerv-e is close behind, and on the outer side of, the 1, so that they overlap one another. In the middle of the space le pophteal vein is entirely behind the arter}-, and the internal )pliteal ner\-e is directly behind the vein. In the lower part the space the pophteal vein is close behind, and on the inner side f, the artery, and the internal pophteal ner^^e is close behind, and the inner side of, the vein, a relation which is the reverse of that the upper part of the space. The geniculate branch of the obtu- Itor nerve (when present), having pierced the adductor magnus 442 A MANUAL OF ANATOMY close above the femoral opening, descends at first upon the inner side of the popliteal artery, and then in front of it as low as the origin of the central or azygos artery, where the nerve leaves the main vessel and passes, with that branch, through the posterior ligament of the knee-joint to the interior of the articulation. Branches. — ^The branches are (i) muscular and cutaneous, and (2) articular. The muscular and cutaneous branches are divided into a superior and an inferior set. The superior set are purely muscular, and are distributed to the lower parts of the hamstring muscles. They anastomose with the lower two perforating branches of the arteria profunda femoris. The inferior or sural set are partly muscular and partly cutaneous. The muscular branches supply both heads of the gastrocnemius and the plantaris. The cutaneous branches are three in number, and supply the integument over the upper half of the calf. The middle cutaneous branch lies in the groove between the two heads of the gastrocnemius with the external or short saphenous vein. This branch is sometimes of large size, and in these cases, under the name of the external saphenous artery, it descends to the back of the external malleolus. The articular branches are five in number — two superior, external and internal, one central or azygos, and two inferior, external and internal. The superior external articular artery courses outwards close above the external condyle of the femur, passing beneath the biceps femoris and through the external intermuscular septum into the crureus muscle, where it breaks up into branches. These anastomose with the following arteries : (i) descending branch 01 the external circumflex ; (2) inferior external articular ; (3) deep branch of the anastomotica magna ; (4) superior internal articular ; and (5) fourth or lowest perforating branch of the arteria profunda femoris. The superior internal articular artery courses inwards close above the internal condyle of the femur, and, having passed beneath the tendon of the adductor magnus, it enters the vastus internus, where it divides into branches. These anastomose with the following arteries : (i) inferior internal articular ; (2) deep branch of the anastomotica magna ; and {3) superior external articular. The central or azygos articular artery, if a separate branch, arises from the front of the main artery, but it is often a branch of the superior external articular. It passes through the posterior ligament of the knee-joint to supply the synovial membrane and ligaments within the joint. The inferior external articular artery courses horizontally out- wards beneath the tendon of the biceps femoris and the long external lateral ligament of the knee-joint to the outer side of the THE LOWER LIMB 443 irticulation, where it divides into branches. These anastomose with the following arteries : (i) superior external articular ; (2) inferior internal articular ; (3) anterior tibial recurrent ; and (4) posterior tibial recurrent (inconstant). The inferior internal articular artery courses at first obliquely downwards and inwards along the upper border of the popliteus muscle, and then passes inwards below the level of the internal tuberosity of the tibia, where it lies beneath the internal lateral ligament of the knee-joint. On reaching the inner side of the articulation, it divides into branches which anastomose with the following arteries: (i) superficial branch of the anastomotica magna ; (2) superior internal articular ; (3) inferior external articu- lar ; (4) anterior tibial recurrent ; and (5) posterior tibial recurrent (inconstant). Varieties of Popliteal Artery. — i. The vessel may divide into its anterior and posterior tibial branches at the upper border of the popliteus muscle. 2. The terminal branches may be three in number instead of two, the additional branch being the peroneal artery. 3. In very rare cases the popliteal arterj- divides high up into two branches of equal size, which subsequently unite prior to the normal termination of the vessel. Popliteal Vein. — ^This vessel commences at the lower border of the popliteus muscle, where it is formed by the union of the venae comites of the anterior and f)Osterior tibial arteries, and it termi- nates at the posterior margin of the femoral opening, which is in connection with the adductor magnus, where it becomes the femoral vein. The relations of the vessel have already been described. Its tributaries correspond with the branches of the pophteal artery, with the addition of the external or short saphenous vein. Internal Popliteal (Tibial) Nerve. — ^This nerve is one of the ter- minal branches of the great sciatic, and it derives its fibres from the ventral divisions of the descending branch of the fourth lumbar, the fifth lumbar, the first and second sacral, and the upper branch of the third sacral ner\'es. It extends from the superior angle of the pophteal space to the lower border of the pophteus muscle, where it becomes the posterior tibial nerve. The relations. of this nerve have been given in connection with the popliteal artery. Branches. — ^The branches are articular, cutaneous, and muscular. The articular branches are three in number (sometimes two), as follows : superior (inconstant), accompanj.'ing the superior internal articular artery ; central or azygos, going with the corre- sponding artery ; and inferior, accompanying the inferior internal articular artery. . The cutaneous branch is called the ramus communicans tibialis. I It descends in the middle line beneath the deep fascia as far as the centre of the calf. Here it pierces the deep fascia, and shortly after\vards it is joined by the ramus communicans fibularis ; from the external popliteal. In this manner the external or short 1 saphenous nerve is formed. 444 A MANUAL OF ANATOMY - ^ astus Internus Superior Internal Articular Nerve Superior Internal Articular Artery Int. Head of Gastrocnemius Semimem- branosus Semitendinosus Sartorius Gracilis Inferior Internal Articular Artery - Internal Popliteal Nerye Tendon of Plantaris Fig. 22$. — The Popliteal Space (Deep Dissection). THE LOWER LIMB 445 The muscular (sural) branches are usually five in number, which are distributed as follows : one to the external head of the gastrocnemius, one to the plantaris (which sometimes comes from the preceding), one to the internal head of the gastroc- nemius, one to the soleus, and one to the popliteus. The nerve to the popliteus descends over the popliteal fascia, lying to the outer side of the popliteal vessels. On arriving at the lower border of the popliteus, it turns round that border and enters the deep surface of the muscle. This ner\-e, besides supplying the popUteus, fmnishes the following branches : articular to the superior tibio-fibular joint ; medullary, which enters the large nutrient or medullary foramen on the back of the tibia ; vascular to the anterior and posterior tibial arteries ; and interosseous. The interosseous branch is a long nerve which descends in the interosseous membrane to terminate in the inferior tibio-fibular joint. External Popliteal or Peroneal (Fibular) Nerve. — ^This nerve is the other terminal branch of the great sciatic, and it derives its fibres from the dorsal divisions of the descending branch of the fourth lumbar, the fifth Irnnbar, and the first and second sacral nerves. It commences at the superior angle of the popliteal space, and descends obliquely downwards and outwards as low as the back of the neck of the fibvila, where it passes forwards between the bone and the peroneus longus, to end on the outer side of the fibular neck in its terminal branches. The nerve lies at first close to the inner border of the biceps femoris, and then it rests upon the back of the external head of the gastrocnemius, between which and the biceps tendon it may be regarded as lying. Branches. — ^The branches are articular, cutaneous, and terminal. The articular branches are three in number, as follows : superior, accompanying the superior external articular artery ; inferior, going with the inferior external articular artery, which it reaches as the vessel is about to pass beneath the biceps tendon ; and recurrent articular, accompanying the anterior tibial recurrent artery. The cutaneous branches are two in number, as follows : lateral cutaneous branch, which supplies the integmnent of the outer side of the leg over about its upper two- thirds, as well as the adjacent integument of the sural region ; and ramus communicans fibularis, which passes downwards and inwards over the external head of the gastrocnemius and beneath the deep fascia to the centre of the calf, where it pierces the deep fascia and shortly afterwards joins the ramus communicans tibialis, to form the external or short saphenous nerve. The terminal branches are three in number, as follows : recurrent articular, already referred to ; anterior tibial (see p. 509) ; and musculo-cutaneous (see p. 503). For the geniculate branch of the obturator nerve, see p. 474. . Popliteal Lymphatic Glands. — These are usually four in niunber, jand lie in close contact with the popliteal artery, one being 446 A MANUAL OF ANATOMY superficial to the vessel, one beneath it, and the remaining two bein^ disposed laterally. They receive their afferent lymphatics from the following sources: (i) sole of the foot; (2) deep part of the back ol the leg ; (3) some of the superficial lymphatics accompanying the ex- ternal or short saphenous vein ; and (4) the two efferent lymphatics which proceed from the anterior tibial lymphatic gland on the front of the interosseous membrane at its upper part. The course of these two efferent lymphatics is backwards above the interosseous membrane, or through the superior hiatus in it. The efferent lymphatics of the popliteal glands ascend to become the afferent lymphatics of the deep femoral glands, which lie in con- tact with the femoral vein near Poupart's ligament. Front and Inner Side of the Thigh. Landmarks. — Thigh. — The anterior superior spinous process of the ilium is situated at the anterior extremity of the iliac crest, and can readily be felt. It is the point from which the measurement of the lower limb is taken. It is also a guide to the great trochanter of the femur, that prominence being situated about 4 inches below the spine, and about 4 inches behind a line let fall vertically from it. The crest of the ilium extends backwards in a curved manner from the anterior superior spinous process. Poupart's ligament passes between the anterior superior iliac spine and the pubic spine. It can be felt as a tense, firm band, especially when the thigh is extended, abducted, and rotated outwards. Immediately below it the inguinal lymphatic glands may be felt. Poupart's! ligament, when traced inwards, conducts the finger to the pubic' spine, which is situated at the lower and inner part of the anterior abdominal wall about i;^ inches outside the upper part of the symj physis pubis. It is sometimes a sharp-pointed process, and then iii can readily be felt beneath the integument. In most bodies, howl ever, it takes the form of a more or less indistinct tubercle, andj especially in corpulent bodies, it cannot be felt. In such cases th< Psoas Magnus ' /^'- PA/-'V^i , Pectineus -f:^-/ JiV-iX^''-'^. * I * Sartorius j- 111-,'/- -V Adductor Longus -l-CL-^- --^A- J|>- Graci Rectus Femoris Ilio-tibial Band - Vastus Externus -- Vx^tus Intemus Ligamentiim Patella- Gastrocnemi Peroneus Longus \^\ Soleus '^ Kxt. Longus Digitorum Kxt. Proprlus Hallucis Tibialis Amicus --- \\\y- Peroneus Tertius — _jJ Ii\ Anterior Annular Ligament t undiform Ligament of Retzius rTta Ext. Cutaneous Nerve Femoral Branch of Genito- femoral Nerve ^ Inguinal Nerve ~. Saphenous Opening ;iMid. Cutaneous Nerve - ,^-- Int. Saphenous Vein .. Int. Cutaneous Nerve (Outline) -. Ant. Branch of Internal j^7 Cutaneous Nerve Patellar Plexus of Nerves ... Patellar Branch of Interna! Saphenous Nerve _ Int. Saphenous Nerve Int. Saphenous Vein Post. Branch of Internal Cutaneous Nerve Cutaneous Part of Musculo- cutaneous Nerve Calcaneo-plantar Nerve - Int. Saphenous Nerve ,A. (Terminal Part) liG. 224. — Muscles .\nd Cutaneous Nerves of the Lower Limb (.\nterior .\spect). 452 A MANUAL OF ANATOMY The nerves which take part in it are as follows : the patellar branch of the long saphenous ; both divisions of the middle cutaneous ; the anterior division of the internal cutaneous ; and the anterior division of the external cutaneous (which, however, is not constant). Subsartorial Plexus. — This plexus is situated in the middle third of the thigh on its internar aspect, and lies beneath the sartorius upon the aponeurotic covering of Hunter's canal. The nerves which take part in its formation are as follows : the long saphenous ; the posterior division of the internal cutaneous ; and the superficial or anterior division of the obturator. The branches furnished by this plexus are distributed to the integument of the inner side of the thigh for about its middle third. Superficial Fascia. — The only point to be noted in connection with the superficial fascia is that, for about 3 inches below Poupart's ligament, it is divisible into two layers — subcutaneous and deep. The subcutaneous layer is fatty, and, when traced upwards, becomes continuous with the fascia of Camper on the anterior abdominal wall. The deep layer is a very delicate membrane, which is best seen on the inner side of and beneath the long saphenous vein, as that vessel lies between it and the subcutaneous layer. It can be traced upwards to a line about \ inch below Poupart's ligament, where it blends with the fascia lata. In passing upwards it covers the saphenous opening, to the outer margin of which it is closely bound by fibrous bands, more especially over the middle third. The part of this layer which lies over the saphenous opening is called the cribriform fascia, because it presents numerous foramina for the passage of the following structures : (i) the long saphenous vein ; (2) the efferent lymphatics of the inguinal and superficial femoral glands ; (3) the superior external pudic artery ; and (4) the superficial epigastric and superficial circumflex iliac arteries. The latter two vessels, however, sometimes pierce the fascia lata forming the outer margin of the saphenous opening. Lymphatic Glands. — ^The glands of the upper part of the front of the thigh are arranged in two groups — superficial and deep. Superficial Group. — The glands which comprise this group are arranged in two sets — inguinal and superficial femoral or saphenous. The inguinal glands are otherwise called the superior or oblique superfi^cial inguinal glands. They are situated immediately below Poupart's ligament, and lie underneath the subcutaneous layer of the superficial fascia, their long axes being oblique. They are usually from six to eight in number, and the innermost two or three, which lie internal to the upper part of the saphenous opening in the vicinity of the pubic spine, are spoken of as the pubic glands. The inguinal glands receive their aHerent lymphatics from the following sources : 1. The superficial lymphatics from the infra-umbilical portion of the> anterior wall of the abdomen, except those from the suprapubic region. 2. The superficial lymphatics from the outer two- thirds of the gluteal region.! THE LOWER LIMB 453 3. The superficial lymphatics from the outer and back parts of the thigh superiorly. The pubic glands receive their afferent vessels from the following sources : 1. The superficial lymphatics from the suprapubic region of the anterior wall of the abdomen. 2. The superficial lymphatics from the upper and inner parts of the thigh. 3. Some of the superficial lymphatics from the inner one-third of the gluteal region. 4. Most of the lymphatics from the scrotum. 5. The lymphatics from (a) the integument of the penis, including the prepuce and most of the penile portion of the urethra, (6) the prepuce of the clitoris, (c) the labium majus, and (d) the labium minus or nympha. (A few of these lymphatics may pass to the superficial femoral glands.) 6. The superficial lymphatics from the perineum (a few of which may pass to the superficial femoral glands). 7. The lymphatics of the lower part of the anal canal below the anal valves, and of the anus (a few of which occasionally pass to the superficial femoral glands) . 8. Some of the lymphatics from the lower one-third of the vagina. 9. A few lymphatics from the body of the uterus. The efferent lymphatics of both the inguinal and pubic glands pierce the cribriform fascia and anterior wall of the femoral sheath. Thereafter most of them end in the deep femoral glands, most of which lie within the middle compartment of the femoral sheath. A few of them, however, may ascend into the abdomen, and end in the lower external iliac glands. Blood-Supply. — ^The inguinal glands are supplied by the super- ficial circumflex iliac and superficial epigastric branches of the common femoral artery; and the pubic glands are supplied by the superior external pudic branch of that vessel. The superficial femoral or saphenous glands are otherwise called the inferior or vertical superficial inguinal glands. They are situated at the lower end of the saphenous opening, where they lie, with their long axes vertical, on either side of the terminal part of the internal or long saphenous vein, underneath the subcutaneous layer of the superficial fascia. They are usually from four to six in number, and they receive their afferent lymphatics from the following sources : 1. The superficial lymphatics of the foot and leg {internal saphenous lymphatics), except the external saphenous lymphatics which pass to the popUteal glands. 2. The superficial efferent lymphatics of the popUteal glands. 3. The superficial femoral lymphatics, except (i) those from the outer and back parts of the thigh superiorly, which pass to the inguinal glands; and (2) those from the upper and inner parts of the thigh, which pass to the pubic glands. 4. Some of the lynnphatics of the knee-joint. 5. Some of the superficial lymphatics from the inner one-third of the gluteal region. 6. Occasionally some of the lymphatics from (a) the perineum, (b) the scrotum, (c) the integument of the external genital organs (see Pubic Glands), and (d) the lower part of the anal canal and the anus. 454 A MANUAL OF ANATOMY Fig. 225. — The Superficial Lymphatics of the Lower Limb. THE LOWER LIMB 455 The efferent lymphatics of the superficial femoral or saphenous glands pierce the cribriform fascia, and terminate in a manner similar to those of the inguinal glands. Blood- supply. — ^These glands derive their arterial supply from two or three saphenous branches of the superficial femoral artery. Deep Group. — ^These are called the deep femoral glands {deep inguinal glands) . They are from three to four in number, and are situated within the femoral sheath. One of them (the gland of Cloquet) lies in the femoral canal at its upper end,, being attached to the inferior surface of the septum femorale. The other glands are situated in the middle compartment of the femoral sheath on the inner side of the femoral vein. The glands receive their afferent Ijinphatic vessels from the following sources: 1 . The inguinal glands. 2. The superficial femoral or saphenous glands. 3. The deep lymphatics of the knee and thigh. 4. The popliteal glands. The efferent lymphatics of the deep femoral glands enter the abdo- minal cavity, where they become the afferent lymphatics of the external iliac glands. Blood-supply. — ^The deep femoral glands derive their arterial supply from the superior or superficial external pudic branch of the common femoral artery. Internal or Long Saphenous Vein. — ^This vessel arises from the inner end of the venous arch on the dorsum of the foot. It passes in front of the internal malleolus and along the inner side of the leg, where it lies about a finger's breadth from the internal border of the tibia. It then covuses along the inner side of the knee-joint, being situated behind the most prominent part of the internal condyle of the femur, and so it enters the thigh. Thereafter it ascends along the inner side of the thigh superficial to the sartorius, until it reaches the upper third of that division of the limb. Here it turns to the front of the thigh, and in its subsequent course lies at the junction of the inner fourth and outer three-fourths. On reaching a point i| inches below Poupart's ligament it pierces the cribriform fascia and anterior wall of the crural sheath, and terminates in the femoral vein. Throughout its whole course the vein is superficial to the deep fascia. It receives many tributaries from the front and back of the leg and thigh, and it communicates at frequent intervals with the venae comites of the anterior and posterior tibial arteries, these communicating branches being intermuscular. Two tributaries in the upper part of the thigh are specially noteworthy from their size and constancy. One, collecting the blood from the front of the thigh, is called the external femoral cutaneous, or anterior saphenous, vein. The other returns the blood from the inner and back parts of the thigh, and is called the internal femoral cutaneous, or posterior saphenous, vein. These two tributaries terminate in the long saphenous vein near the 456 A MANUAL OF ANATOMY saphenous opening. It is to be noted that the external femoral cutaneous or anterior saphenous vein lies over the sartorius muscle at the apex of Scarpa's triangle, where it is liable to be cut in operating in this situation. Before piercing the cribriform fascia the internal or long saphenous vein receives as final tributaries the following veins : the superficial circumflex iliac ; the superficial epigastric ; the superior or superficial external pudic ; and the inferior or deep external pudic. The long saphenous vein has usually about fifteen valves. One of these is found in the vein just before it pierces the cribriform fascia, and another at its opening into the femoral vein. The guide to the vein in the femoral part of its course is a line drawn from a point immediately behind the most prominent part of the internal condyle of the femur to a point on the front of the thigh i| inches below Poupart's ligament, at the junction of the inner fourth and outer three-fourths of the limb. The vein is occasionally double in the femoral part of its course. This condition is brought about by the vein dividing into two branches shortly after it enters the thigh, which ascend close together and unite to form one trunk close to the saphenous opening. Deep Fascia or Fascia Lata. — The fascia lata is a very strong fibrous membrane which forms a continuous tubular sheath swathing the powerful muscles in this region. Superiorly it is attached as follows : (i) to Poupart's ligament as far inwards as the pubic spine ; (2) to the outer lip of the iliac crest, where it covers the anterior two- thirds of the gluteus medius ; (3) to the posterior lamina of the lumbar aponeurosis ; (4) to the back of the lower end of the sacrum and coccyx ; (5) to the lower border of the great sacro-sciatic ligament ; (6) to the tuber ischii ; (7) to the ischio- pubic ramus ; (8) to the anterior or femoral surface of the body of the OS pubis close to the symphysis ; and (9) to the anterior lip of the pubic crest as far outwards as the pubic spine. Inferiorly, in the region of the knee, the fascia lata is disposed as follows : (i) on the outer side it is attached to the head of the fibula and external tuberosity of the tibia ; (2) anteriorly it is attached to the lateral borders of the patella, in which latter situations it forms the larger portions of the so-called lateral patellar ligaments ; from its attachments to the lateral borders of the patella an expansion is sent over that bone and downwards to the head of the tibia, which confines the prepatellar bursa ; (3) posteriorly it is continued un- interruptedly into the back of the leg, covering the popliteal space as it descends, and becoming continuous with the deep fascia : (4) internally it is continued into the inner side of the leg, taking a limited attachment to the internal tuberosity of the tibia, and becoming continuous with the deep fascia. The fibres of the fascia lata interlace freely, some of them being circular and others longitudinal. It is pierced by a large THE LOWER LIMB 457 number of minute foramina for the passage of bloodvessels and nerves. The fascia is strongest upon the outer side of the thigh, where it gives insertion superiorly to a large part of the gluteus maximus, and lower down to the tensor fasciae femoris. It is also strong over the popliteal space and prepatellar region, receiving in the former situation accessions of fibres from the ham- string tendons, and, in the latter, similar accessions from the tendons of the muscles which form the quadri- ceps extensor cruris. Upon the inner side of the thigh the fascia is very thin. The portion upon the outer side of the thigh, between the fore part of the iliac crest and the anterior part of the external tuberosity of the tibia and outer border of the patella, is spoken of as the ilio-tibial band. At the insertion of the tensor fasciae femoris it gives off a deep lamina which passes upwards on the deep sur- face of the muscle to be attached to the bottom of the groove on the dorsum of the ilium above the acetabulum, where the posterior or reflected head of the rectus femoris takes its origin. This deep lamina is intimately con- nected with the capsular ligament of the hip-joint and the tendon of the gluteus minimus. The fascia lata on the front of the thigh divides at a point i^ inches below the inner third of Poupart's ligament into two laminae, iliac and pubic. The iliac lamina passes up- wards to be attached to Poupart's ligament, lying superficial to the outer portion of the anterior wall of the crural sheath. The pubic lamina is on a deeper or more posterior plane than the iliac, and passes upwards upon the flat pectineus muscle to be attached to the pectineal portion of the ilio-pectineal line and anterior Anterior Sapbenoas Fig. 226. — The Internal Saphenous Vein and its Tributaries. 458 A MANUAL OF ANATOMY lip of the pubic crest. This pubic lamina, when followed out- wards, passes behind the crural sheath and ends by blending with its posterior wall. It will thus be seen that the iliac lamina is superficial or anterior to the femoral vessels enclosed in the crural sheath, and that the pubic lamina is on a plane deeper than, or posterior to, the femoral vessels. Processes of the Fascia Lata. — ^These processes, which for the most part are indicated on the surface by white lines, pass between the muscles, forming intermuscular septa, and taking part in the muscular sheaths. Three of them are specially noteworthy, and are called external, internal, and posterior. The external inter- muscular septum is a deep expansion from the ilio- tibial band, and it is attached to the outer lip of the linea aspera and external supracondylar ridge of the femur in its whole extent. It separates the vastus oxternus and crureus in front from the femoral head of the biceps behind, and it gives partial origin to these muscles. The internal intermuscular septum is a delicate process, which is attached to the inner lip of the linea aspera, especially in its lower part. Over the internal supracondylar ridge its place is taken by an expansion from the tendon of the adductor magnus. This septum separates the vastus internus in front from the adductor longus and adductor magnus behind. The posterior intermuscular septum is a very delicate process which is attached to the summit of the linea aspera. It is situated behind the adductor magnus, which it separates from the femoral head of the biceps. Saphenous Opening. — This is an opening in the fascia lata for the passage of the long saphenous vein, and it is of importance surgically inasmuch as a femoral hernia may protrude through it. It is situated on the front of the thigh below and outside the pubic spine, just below the inner third of Poupart's liga- ment. It is not so much an opening as an oval depression in the fascia lata, formed by the division of that fascia into its iliac and pubic laminae, the iliac lamina passing upwards superficial to the outer part of the anterior wall of the crural sheath, and the pubic lamina passing upwards on a plane posterior to the posterior wall of the crural sheath, with which it becomes continuous. The average length of the opening is i| inches, and its breadth is from ^ to f inch. The lower border of the opening is called the inferior cornu, and over this the long saphenous vein passes. It is firm, sharp, and crescentic, with the concavity directed upwards. The inner part, formed by the pubic lamina of the fascia lata, is for the most part flat, the fascia being here spread out upon the pectineus muscle, whence it passes outwards to blend with the posterior wall of the crural sheath. Over the lower fourth, however, the opening has a distinct inner border, which is continuous with the inferior cornu. The outer border, formed by the iliac lamina of the fascia lata, is on a plane superficial to the outer part of the anterior wall of the crural sheath, to which it is bound by fibrous bands. In- THE LOWER LIMB 459 feriorly this border is continuous with the inferior cornu. Superiorly it curves inwards over the anterior wall of the crural sheath. The whole border is concave or semilunar, the concavity being directed inwards and shghtly downwards. The upper border is the portion in front of the anterior wall of the crural sheath, and it lies immedi- ately below Poupart's hgament. It is called the superior cornu. Superficial Circumflex Iliac Artery Superfidal Circumflex Iliac Vein Superficial Episastric Vessels , y Femoral Vein Falciform Process of Bums and Superior Cornu ^. Internal Saphenous Veinv^ ' Superior External Pudic VesseU Inferior Cornu of Saphenous Opening -'' Posterior Saphenous Vein — Anterior S iphenous Vein — Internal Saphenous Vein - ^ (In this case double) f mu-^^m F"iG. 227. — The Left Internal Saphenous Vein in the Thigh, with its Tributaries, and the Saphenous Opening. It is triangular, and is continuous with the outer border. Superiorly it is attached to the inner part of Poupart's ligament, extending inwards as far as the pubic spine, and a few of its fibres join the antero- inferior or femoral surface of Gimbemat's hgament. The inner portion of the superior cornu is internal to the femoral vein, and lies in front of the crural canal. It is this portion, inside the 46o A MANUAL OF ANATOMY femoral vein, which has been called the falciform process of Burns (John),* or the femoral ligament of Hey. The importance of this process or ligament is that it impresses upon a femoral hernia its final change in direction, inasmuch as it causes the protrusion to turn upwards over Poupart's ligament upon the anterior abdominal wall, or upwards and outwards towards the anterior superior iliac spine. The saphenous opening is covered by the cribriform fascia, which is more intimately attached to the outer border than elsewhere. Parts concerned in Femoral Hernia. Poupart's Ligament or the Superficial Femoral Arch. — This is the thickened lower border of the aponeurosis of the external oblique muscle. It is folded upon itself in a backward direction, and is attached externally to the anterior superior iliac spine and internally to the pubic spine. Gimbernat's Ligament. — This is the reflection of Poupart's ligament from the pubic spine along the ilio-pectineal line for i inch. It is triangular, and presents a free base which is sharp, wiry, and concave, and is situated immediately to the inner side of the crural or femoral ring. Deep Femoral Arch. — ^This is a thickening of the fascia trans- versalis, due to an accession of fibres as it is prolonged downwards beneath Poupart's ligament. It extends from the centre of that ligament on its deep aspect to the pectineal portion of the ilio- pectineal line, where it is attached behind Gimbernat's ligament near its base. Falciform Process of Burns. — ^This has just been described in connection with the superior comu of the saphenous opening. Femoral Slieath. — ^This sheath extends from Poupart's ligamicnt to a point about i| inches below it, where it blends with the special sheath of the femoral vessels. The outer wall is straight, but the inner is oblique, being sloped downwards and outwards. In shape the sheath resembles a funnel, from "which circumstance the term infundibuliform has been applied to it. The anterior wall is formed by the fascia transversalis, and the posterior wall by the fascia iliaca, both of which fasciae are prolonged downwards beneath Poupart's ligament. The outer wall is formed by the union of these two fasciae close to the outer side of the femoral artery. The imier wall is formed by their union at a point ^ inch to the inner side of the femoral vein. Within the sheath there are two septa, external and internal, both of which extend from the anterior to the posterior wall, the external septum being close to the outer side of the femoral vein, and the internal septum close to its inner side. By means of these two septa the interior of the sheath is divided into three distinct compart- * Edinburgh Medical and Surgical Journal, July i, 1806, p. 269. THE LOWER LIMB 461 ments — outer, middle, and inner. The outer compartment contains the common femoral artery and the femoral branch of the genito- femoral nerve for a short distance at its upper part, where the nerve lies immediately external to the arter\'. The middle com- partment contains the femoral vein and three of the deep femoral glands. The inner compartment is called the crural or femoral canal, and it contains one of the deep femoral glands and a certain amount of adipose tissue, the gland lying at the upper end of the canal. Femoral Canal. — ^This is the inner compartment of the femoral sheath, and it is \ inch in length. Its upper end forms the crural or femoral ring, and is on a level with the base of Gimbemat's ligament. Its lower end is just below the superior comu of the saphenous opening. The boundaries of the canal are as follows: the anterior wall is formed by the fascia transversalis ; the post^ior wall by the fascia iliaca ; the inner wall by the junction of the fascia transversalis and fascia iliaca; and the outer wall by the internal septum within the sheath. Femoral Ring. — ^This is by no means a patent opening, but is bridged over by the subperitoneal areolar tissue of the abdominal wall. The septum thus formed between the crural canal and abdominal cavity is called the septum femorale (fascia of Cloquet). It protrudes slightly into the canal, and the l\Tnphatic gland which lies at the upper end of the canal is attached to its under convex surface, ^^'hen the septum crurale has been removed from the femoral ring, the apertiure presents an oval shape, with the long measiu*ement lying transversely, in which direction it measures I inch. It readily admits the little finger, and it is som.e- what larger in the female than in the male. The situation of the ring is close to the outer side of the base of Gimbemat's ligament, and its position may be ascertained in one of two ways. (i) Draw a line from the pubic spine horizontally outwards across the front of the thigh, and take a point in this line fully i inch to the outer side of the pubic spine. (2) Find the central point between the anterior superior iliac spine and the s\Tnphysis pubis; then take a point on Poupart's ligament rather more than | inch to the inner side of this central point. Boundaries — Anterior. — ^The inner part of Poupart's ligament, and the deep femoral arch. Posterior. — The pubic lamina of the fascia lata, joined by Cooper's ligament;* the pectineus muscle; and the superior pubic ramus. Internal. — The base of Gimbemat's * The pubic ligament of Cooper is a strong bundle of fibres extending between the iUo-pectineal eminence and the pubic spine, between which points it is attached to the pectineal portion of the ilio-pectineal line. It has the pectineal border of Gimbemat's ligament immediately behind it, and is closely incorporated with the pubic lamina of the fascia lata, where that is attached to the pectineal portion of the ilio-pectineal line. ■ 462 A MANUAL OF ANATOMY ligament. External. — ^The upper extremity of the internal septum within the femoral sheath. Normal Relation of Bloodvessels to the Femoral Ring — Anterior. — The pubic branch of the deep epigastric artery, as it courses inwards behind the inner half of Poupart's ligament. Supero- anterior. — ^The vessels of the spermatic cord in the male, or of the round ligament of the uterus in the female. Supero-external. — ^The deep epigastric vessels. External. — ^The femoral vein, becoming the external iliac vein, and separated from the ring by the upper extremity of the internal septvmi within the femoral sheath. There are normally no vessels behind the ring, nor internal to it. Under no circumstances are there ever any vessels behind it, but in certain cases there may be a vessel on its inner side, namely, an abnormal obturator artery. Abnormal or Aberrant Obturator Artery. — The obturator, artery normally arises from the anterior division of the internal iliac, and under these circum- stances it has no relation to the femoral ring. In about 30 per cent, of cases, however, the obturator arises from the deep epigastric artery near its com- mencement. This origin is more common in the female than in the male, and is rarely bilateral. In most of these cases the aberrant obturator passes backwards close to the inner side of the commencement of the external iliac vein, and therefore upon the outer side of the femoral ring. In a few cases the aberrant vessel passes backwards across the centre of the femoral ring. In very rare cases it passes inwards behind Poupart's ligament, and then arches backwards either close to the base of Gimbernat's ligament, or a line or two inwards from it, and therefore upon the inner side of the femoral ring. If a femoral hernia should occur under these latter circumstances, the aberrant obturator artery would lie upon the inner side of the neck of the sac, and it would thus be endangered in the operation for the reUef of the strangulation. This very rare position of an aberrant obturator artery is more frequent in the male than in the female, and, according to Lawrence, it occurred once in a hundred cases. The origin of an aberrant obturator artery from the deep epigastric is due to a more or less complete obliteration of a normal obturator at its origin, and an enlargement of the normal anastomosis which takes place between the pubic branches of the deep epigastric and obturator arteries behind the body of the os pubis. Femoral Hernia. — This is a protrusion of an abdominal viscus, or part of a viscus, through the crural or femoral ring. The course of the hernia is as follows: entering the crural ring by elongating the septum crurale, it descends through the femoral canal, on reaching the lower end of which it is placed in the upper part of the saphenous opening, immediately below the falciform process of Burns or femoral ligament of Hey. This structure now impresses upon the hernia the following change in its course: the front part of the hernia being arrested in its downward course by that structure. the posterior part, which is free, comes down, and, passing forwards, turns upwards upon the anterior abdominal wall, or upwards and outwards, along Poupart's ligament. The course of a femoral hernia, when com- plete, is thus at first downwards through the femoral ring and femoral canal, then forwards through the upper part of the saphenous opening, and finally either upwards or upwards and outwards. Coverings of a Femoral Hernia. — The coverings, from within outwards, are as follows: 1. Peritoneum, which forms the sac. 2. Septum femorale. THE LOWER LIMB 463 Deep Circumflex Iliac Artery Internal Abdominal Ring • Deep Epigastric Artery External Iliac Vein Gimbemat's Ligament , Abnormal Obturator ^ Artery External Iliac Artery \ Obturator Ner>-e Obturator Canal Fig. 228. — Diagrams of Abnormal Obturator Artery (The red X indicates the position of the Femoral Ring). [A and B after Gray]. \, Artery external to Femoral Ring; B, Artery internal to Ring, and close to Base of Gimbernat's Ligament; C, Artery internal to Ring, and one or two lines from Base of Gimbernat's Ligament. 464 A MANUAL OF ANATOMY 3. Anterior wall of the femoral sheath, or fascia transversalis. 4. Cribriform fascia. 5. Subcutaneous layer of superficial fascia. 6. Skin. The septum crurale is usually inseparably united with the anterior wall of the femoral sheath, thus forming the fascia propria of Cooper. The neck of the sac is on a level with the base of Gimbernat's ligament, which is the most common cause of strangulation. Prepatellar Bursa. — ^This bursa, which is of large size, is situated on the anterior surface of the patella beneath the integument. When it becomes inflamed the condition is known as housemaid' s knee. There may be another subfascial bursa, between the fascia lata over the patella and the bone. Anterior Femoral Muscles. Sartorius — Origin. — (i) The anterior superior iliac spine, and (2) the upper part of the anterior inter- spinous notch of the ilium. Insertion. — ^The internal surface of the shaft of the tibia immedi- ately behind the tubercle. From the tendon of insertion two expansions are given off — one from the upper border to the capsule of the knee-joint, and another from the lower border to the deep fascia of the leg. Nerve-supply. — ^The anterior division of the anterior femoral nerve, the branches from which, arising in common with the middle cutaneous nerve, enter the muscle near the apex of Scarpa's triangle. Action. — Acting from its origin the muscle is (i) a flexor of the knee-joint, and an internal rotator of the leg ; and (2) a flexor of the hip-joint, and an external rotator and abductor of the thigh. Acting from its insertion it is a flexor of the pelvis upon the thigh. The sartorius is a long ribbon-like muscle, the fasciculi of which are the longest of any muscle in the body. The muscle, therefore, has a wide range of movement, but comparatively little power. It is at first directed downwards and inwards over the front of the thigh, where it forms, by its inner border, the outer boundary of Scarpa's triangle. Having crossed the superficial femoral artery at a point about 3^ inches below Poupart's ligament, the muscle passes vertically downwards as far as the internal condyle of the femur. Beyond this point, it curves forwards to its insertion, where it covers the subjacent tendons of the gracilis and semi- tendinosus, from which it is separated by a bursa. This bursa is a prolongation oi that which lies between the internal lateral ligament of the knee-joint and the more superficially placed tendons of the gracilis and semitendinosus. The muscle, in its lower part, is usually pierced by the patellar branch of the long saphenous nerve. The two most important relations of the sartorius are as follows : (i) it crosses the superficial femoral artery from without inwards at a point about 3| inches below Poupai"t's ligament ; and (2) it covers the superficial femoral artery in Hunter's canal. Tensor Fasciae Femoris. — Although this muscle is on the same plane as the gluteus maximus, it may be described in this place. THE LOWER LIMB 465 Origin. — (i) The outer lip of the crest of the ilium for i^ inches at its anterior part ; (2) the dorsum ilii for \ inch close to the upper part of the anterior interspinous notch ; and (3) the fascia lata covering the muscle. Insertion. — ^The angle of division of the ilio;- tibial band of the fascia lata into a superficial and deep lamina, at the junction of the upper fourth and lower three-fourths of the thigh. Nerve-supply. — ^The lower di\Tsion of the superior gluteal nerve from the sacral plexus, the branch of which enters the muscle on its deep surface. Action. — (i) Abductor and internal rotator of the thigh ; and (2) extensor of the knee-joint. The muscle, in association with, the gluteus maximus, takes part in the completion of extension of the knee-joint, and in the maintenance of extension through means of the ilio-tibial band, as in standing. The tensor fasciae femoris is a flat, strap-like muscle, the direc- tion of which is downwards, with a slight inclination outwards and backwards. Ilio-Psoas. — The femoral portion of this muscle is alone described in this place. For a full description of the psoas magnus and iliacus, see Abdomen Section. The ilio-psoas is inserted into the small trochanter of the femur, the outer fibres of the iliacus taking insertion into the triangular surface which is situated below and in front of the small trochanter, between it and the spiral line. The outer portion of the muscle, which is fleshy, represents the ihacus, and the inner portion, which is tendinous, represents the psoas magnus. Lying deeply between the two is the anterior crural nerve ; tlie femoral arten»', enclosed within the femoral sheath, rests upon the psoas magnus; and the femoral vein, similarly enclosed, lies between the psoas magnus and pectineus. The ilio- psoas covers the front of the capsular ligament of the hip- joint, a bursa inter\'ening between the psoas portion and the ligament. Pectineus — Origin. — (i) The pectineal portion of the ilio-pectineal line of the os pubis ; (2) the adjacent portion of the upper or pec- tineal surface of the superior pubic ramus ; and (3) the pubic lamina of the fascia lata, as it covers the muscle in this situation. Insertion. — The upper third of the line which leads from the back of the small trochanter of the femur to the inner lip of the linea aspera. Nerve-supply. — ^The anterior division of the anterior femoral nerve, the branch from which passes inwards behind the femoral sheath, and enters the superficial surface of the muscle close to its outer border. The pectineus sometimes receives an additional nerve from the anterior division of the obturator, or from the accessory obturator (when present), which enters the deep surface of the muscle. Action. — (i) Flexion of the hip-joint, and (2) adduction and xternal rotation of the thigh, as, for example, in crossing one leg over the other. The pectineus is a flat, four-sided muscle, which is directed doMm- 30 i 466 A MANUAL OF ANATOMY wards, outwards, and backwards. The surfaces at first look forwards and backwards, but, towards its insertion, the muscle undergoes a slight twist, and its surfaces are then external and internal. Its deep surface is related to the capsular ligament of the hip- joint, the anterior division of the obturator nerve, and the adductor brevis. Quadriceps Extensor Cruris. — This is a composite muscle, which consists of the rectus femoris, vastus externus, crureus, and vastus internus. The rectus femoris arises from the os innominatum, Twelfth Rib Quadratus Lumborum — Psoas Parvus Psoas Magnus Pyriformis - ^Iliacus Small Sacro-sciatic Ligain£nt Great Sacro-sciatic r - Ligament Obturator Externus Fig. 229. — The Psoas, Iliacus, and Quadratus I.umborum Musci.es. whilst the other three muscles take origin from the femur, the crureus being situated between the vastus externus and vastus internus. I. Rectus Femoris — Origin. — By two strong tendinous heads- anterior or straight, and posterior or reflected. The anterior or straight head arises from the anterior inferior iliac spine. The posterior or reflected head arises from the groove on the anterior part of the dorsum ilii immediately above the brim of the aceta- bulum, where it is under cover of the gluteus minimus. The two heads unite at an angle of about 60 degrees. THE LOWER LIMB 4^7 Insertion. — The anterior part of the upper border of the patella by a flat tendon, which is free from fleshy fibres in its lower 3 inches. Nerve-supply. — ^The posterior division of the anterior femoral nerve, the branch from which furnishes an offset to the hip-joint. Action. — (i) The muscle is a powerful extensor of the knee-joint ; and (2) it is a flexor of the hip-joint. In extending the knee-joint the rectus femoris acts entirely from its anterior or straight head when the hip- joint is extended ; but, when the hip- joint is flexed^ the muscle in extending the knee-joint acts from its posterior or reflected head. The fibres which form the fleshy belly are very short, and, spring- ing in a bipenniform manner from the common tendon of origin, they pass obhquely to end upon the tendon of insertion as low as a point 3 inches above the patella. This arrangement gives the muscle great power of action, but hmited range of movement. Superiorly the muscle is related to the capsular Ugament of the hip- joint. 2. Vastus Externus — Origin. — (i) The upper third of the anterior intertrochanteric line of the femur ; (2) the anterior and inferior borders of the great trochanter ; (3) the outer side of the gluteal ridge ; (4) the outer hp of the linea aspera in its upper half ; (5) the adjacent portion of the shaft of the femur ; and (6) the upper part of the external intermuscular septum. Insertion. — (i) The outer half of the upper border of the patella posterior to the rectus femoris ; (2) the upper third of the outer border of the patella ; and (3) very shghtly into the outer border ^of the tendon of the rectus femoris. Nerve-supply. — The posterior division of the anterior femoral nerve, the branch from which furnishes an offset to the knee-joint. The vastus externus at its origin is aponeurotic, and the aponeurosis spreads downwards upon the superficial surface of the muscle for a considerable distance. The fibres are directed downwards and forwards or inwards. The anterior border is free. 3. Crureus — Origin.^i) The lower two-thirds of the anterior intertrochanteric line ; (2) the anterior and external surfaces of the shaft of the femur over about their upper three-fourths ; (3) the outer lip of the linea aspera in its lower half ; (4) the upper two- thirds of the external supracondylar ridge, as well as the immediately adjacent portion of the bone ; and (5) the contiguous part of the external intermuscular septum. Insertion. — ^The inner half of the upper border of the patella behind the rectus femoris, where it has many of the fibres of the vastus intemus associated with it. Nerve-supply. — The posterior division of the anterior femoral ner\'e, the branches from which are two or three in number. The most internal of these branches furnishes an offset to the knee- ijoint, which in its course supplies the subcrureus muscle. ! The direction of the fibres of the crureus is chiefly downwards. 468 A MANUAL OF ANATOMY except in the loM^er and outer part of the muscle, where they pass forwards. 4. Vastus Internus— Ongm.— (i) The part of the spiral line of the femur which extends from the inferior cervical tubercle to the inner Ligamentum Teres -j;--^- Capsular Ligament Ilio-Psoas Crureus Bare Area of Femur Vastus Internus ._ Anterior Intertrochanteric Line Vastus Externus Tendon of Rectus Femoris Fig. 230. — Dissection of the Quadriceps Extensor Cruris Muscle. lip of the linea aspera ; (2) the inner lip of the linea aspera in it whole extent ; (3) the internal intermuscular septum ; and (4) tli front of the tendon of the adductor magnus almost as low as tli adductor tubercle. Insertion. — (i) The inner half of the upper border of the patella J THE LOWER LIMB 409 in close association with the cnireus ; (2) the upper half of the inner border of the patella ; and (3) very slightly into the inner border of the tendon of the rectus femoris. Nerve-supply. — ^The posterior division of the anterior femoral nerve by a branch called the nerve to the vastus intemus. This ner\-e descends in close contact v.ith, and on the outer side of, the long saphenous nerve, and with that nerve it traverses the upper half of Hunter's canal. Jt furnishes a large offset to the knee-joint. The direction of the fibres of the muscle is downwards and for- wards or outwards. WTulst the vastus extemus is easily separable from the crureus, the vastus intemus and crureus appear at first sight to be one muscle. A cellular interval, however, can be traced directly upwards from the inner border of the patella to the inferior cervical tubercle of the femur, along the course of which the two muscles can be distinctly separated. When this separation has been eifected, a characteristic elongated strip of the femur is laid bare upon the inner side of the shaft, which is free from muscular fibres. Suprapatellar Tendon. — ^This is the common tendon in which the four muscles constituting the quadriceps extensor cruris terminate. The part of it which belongs to the rectus femoris is inserted into the anterior part of the upper border of the patella, whence an expansion of fibres descends over the front of that bone to blend with the fibres of the ligamentum patellae. The tendon of the crureus is behind that of the rectus femoris, where it has many of the fibres of the vastus intemus associated with it, the rest of the last-named muscle terminating partly upon the upper half of the inner border of the patella, and partly upon the inner border of the tendon of the rectus femoris. The vastus extemus is partly behind the rectus tendon, and in part it joins the outer border of that tendon, and terminates upon the upper third of the outer border of the patella. Beneath the suprapatellar tendon there is a bursa, called the suprapatellar bursa. It is continuous with the pouch which the synovial mem- brane of the knee-joint sends upwards above the patellar surface of the femur. Adion of the Vasti and Crureus, — ^These three muscles act as powerful extensors of the knee-joint, the lowest fibres of the vastus intemus at the same time d^a^^'ing the patella inwards. Subcrureus. — ^This muscle is in reahty the lowest and deepest portion of the crureus. Viewing it as an independent muscle, it arises in tvvo bundles from the front of the femur about 4 inches above the patellar surface, and it is inserted into the suprapatellar bursa, which is continuous with the upward prolongation of the sjTiovial membrane of the knee-joint above the patellar surface of the femiu". Nerve-supply. — The articular branch to the knee-joint which comes from the innermost muscular branch to the crureus. Action. — The subcrureus is a tensor of the synoxnal membrane of the knee-joint. ■ 470 A MANUAL OF ANATOMY Ligamentum Patellae (infrapatellar tendon).— This ligament is really a continuation of the common tendon of the quadriceps extensor cruris, the patella being originally a sesamoid cartilage developed in that tendon. It is a very strong, flat, broad ligament, about 2 inches in length. It is attached superiorly to the blunt apex and adjacent margins of the lower part of the patella, and inferiorly to the lower rough half of the tubercle of the tibia, a bursa intervening between the tendon and the upper smooth half of that tubercle. Anterior Femoral Nerve. — ^This is the largest branch of the lumbar plexus, its fibres being derived from the dorsal divisions of the second, third, and fourth lumbar nerves. In the abdomen the nerve lies deeply between the psoas magnus and iliacus muscles, and in this position it passes into the thigh beneath Poupart's ligament. In the upper part of Scarpa's triangle it continues to lie deeply between these two muscles, being outside the femoral sheath md about J inch to the outer side of the common femoral artery. In this situation the nerve becomes broad and flat, and, at a point about f inch below Poupart's ligament, it breaks up into two divisions. One of these is called the superficial or anterior division, and it is partly muscular and partly cutaneous ; the other is called the deep or posterior division, and it is principally muscular and articular, only one . cutaneous nerve, namely, the long saphenous, arising from it. Branches. — ^These are conveniently divided into intra-abdominal and extra-abdominal or femoral. The intra-abdominal branches arise from the trunk of the nerve, and are as follows : muscular, three or four in number, to the iliacus ; and an arterial branch to the coats of the femoral artery. The extra-abdominal or femoral branches arise from the two terminal divisions of the nerve in Scarpa's triangle. The branches of the superfieial or anterior division are muscular to the sartorius and pectineus, and cutaneous, namely, middle cutaneous and internal cutaneous, to the integument of the front and inner side of the thigh, and of the inner side of the leg in its upper half. The branches of the deep or posterior division are muscular to the rectus femoris, vastus externus, vastus internus, crureus, and subcrureus ; articular to the hip-joint and knee-joint (see nerve- supply of quadriceps extensor cruris) ; and the long saphenous nerve, already described. Internal Femoral Muscles. Gracilis (adductor gracilis) — Origin.— | (i) The anterior or femoral surface of the body of the os pubis in its lower half, close to the symphysis ; and (2) the front of the descend-j ing pubic ramus close to its inner border. Insertion. — The upper part of the inner surface of the shaft of the tibia, above the semitendinosus, and under cover of the sartorius. THE LOWER LIMB 471 Nerve-supply. — The anterior or superficial division of the obturator nerve. Action. — The muscle is an adductor of the thigh, and a flexor of the knee-joint. Having flexed the knee-joint, it acts as an internal rotator of the leg. The gracilis is flat and strap-like in the upper third of the thigh. In the middle third it becomes thick and narrow, and it graduzdly tapers into a long, narrow, round tendon which expands towards its insertion. The surfaces are directed inwards and outwards, the borders looking forwards and backwards. In the lower third of the thigh the tendon has the sartorius in front of it, and the semi- tendinosus behind it, and it is separated from the internal lateral hgament of the knee-joint by a bursa. Adductor Longus— -Ori'gm. — ^The upper and inner part of the anterior or femoral surface of the body of the os pubis, immediately below and external to the pubic angle. Insertion. — ^The inner hp of the hnea aspera of the femur. Nerve-supply. — The anterior or superficial division of the obturator nerve. Action. — The muscle is an adductor and external rotator of the thigh, and a flexor of the hip- joint. The adductor longus is a flat, triangular muscle, the direction of which is doNvnwardSj outwards, and backwards. It hes to the inner side of the pectineus, and rests upon the adductor brevis, the anterior or superficial diWsion of the obturator nerve, and the adductor magnus. The superficial femoral artery is superficial to it, and the arteria profunda femoris beneath it. Adductor Brevis — Origin. — (i) The anterior or femoral surface of the body of the os pubis for rather less than its lower half, immedi- ately external to the gracflis ; and (2) the front of the descending pubic ramus, where it is likewise external to the gracihs. Insertion. — The line leading from the back of the small trochanter to the inner lip of the Unea aspera. Nerve-supply. — The anterior or superficial division of the obturator nerve (occasionally the posterior division). Action. — The muscle is an adductor and external rotator of the thigh, and a flexor of the hip- joint. The adductor brevis is quadrilateral, and is directed downwards, outwards, and backwards. It hes behind the pectineus and ad- ductor longus, and upon the adductor magnus. The anterior or superficial division of the obturator nerve is in front of it, and the posterior or deep division behind it. It is pierced by the first two perforating branches of the arteria profunda femoris. Adductor Magnus — Origin. — (i) The anterior or femoral surface of the body of the os pubis in its lower fourth, betvs'een the adductor brevis internally and the obturator extemus externally ; (2) the front of the ischio-pubic ramus ; and (3) the inferior portion of the postero-inferior surface of the tuber ischiL ■ 472 A MANUAL OF ANATOMY Insertion. — (i) The inner side of the gluteal ridge of the femur ; (2) the inner lip of the linea aspera, and the upper part of the internal supracondylar ridge for fully i inch ; and (3) the adductor tubercle, by means of a narrow, round tendon which gives a fibrous expansion to the internal supracondylar ridge below the femoral groove. Nerve- supply. — The posterior or deep division of the obturator nerve. The postero-inferior part of the muscle, representing the fibres which arise from the tuber ischii, is supplied by the branch of the great sciatic nerve to the semimembranosus. Action. — The muscle is a powerful adductor of the thigh. The part inserted into the shaft of the femur also acts as an external rotator of the thigh, and the part extending from the tuber ischii to the adductor tubercle as an extensor of the hip-joint. The adductor magnus is triangular or fan-shaped. The upper- most fibres are hori- zontal ; the succeeding fibres are oblique ; and those which arise from the tuber ischii are al- most vertical. The part of the muscle which is inserted into the inner vastus side of the gluteal ridge intemus-- usually forms a distinct portion, which is tri- angular in shape, and is sometimes called the adductor minimus. The insertion of the muscle into the shaft of the femur is interrupted by four tendinous arches, which give passage to the perforating branches of the arteria profunda femoris. Between the tendon which descends to the adductor tubercle and the part of the muscle which is inserted into the upper end of the internal supracondylar ridge there is an aperture, called the femoral opening, for the passage of the superficial femoral vessels. It is triangular, with the apex rounded off, and is tendinous in front, but fleshy behind. It is of larger size than is necessary for the passage of the vessels, being so adapted that the vessels are not in any way interfered with during the action of the muscle. The muscle supports the adductor brevis, adductor longus, and posterior or deep division of the obturator nerve. Its posterior surface is related to the hamstring muscles and the great sciatic nerve. Patella. - Tibia Sartorius Gracilis Semimembranosus Semitendiiiosus Gastrocnemiuis Fig. 231.— The Tendons of the Inner Side OF THE Knee. THE LOWER LIMB 473 The adductor muscles come into action.in riding upon horseback, enabling the rider to grasp the saddle with his thighs, and they are hence called ' the rider's muscles.' In this act the adductor longus is specially subjected to strain, and its narrow round tendon of origin is occasionally ruptured. At the seat of rupture ossification sometimes takes place, thus giving rise to the so-caUed ' rider's bone.' Obturator Externus — Origin. — (i) The external surface of the obturator membrane over its inner half ; (2) the adjacent portion of Obturator Externus Quadntus Femoris Adductor Brevis k _ Adductor Magnus Toidon of Adductor Magnus Fig. 232. — The Right Internal Femoral Muscles (.\nterior View). I, 2, 3, 4, Openings for the Perforating Arteries. the anterior or femoral surface of the body of the os pubis ; and !3) the front of the ischio-pubic ramus close to the obturator fora- men. Insertion. — The digital or trochanteric fossa of the femur. Xerve-supply. — ^The deep or posterior division of the obturator nerve as it passes through the upper part of the muscle. : Action. — The muscle is an external rotator and adductor of the fhigh. 474 ^ MANUAL OF ANATOMY The obturator ©xternus is somewhat triangular, and is directed at first outwards, and then backwards and upwards. Its round tendon of insertion is closely applied to the back of the neck of the femur, which it slightly grooves in its lower or extracapsular part. The superficial or anterior division of the obturator nerve passes over the upper border of the muscle, and the deep or posterior division pierces the upper part of it. The muscle is in close contact with the lower and back part of the capsular ligament of the hip- joint, a bursa being usually interposed. Obturator Nerve. — This nerve is a branch of the lumbar plexus, and generally arises by three roots from the ventral divisions of the second, third, and fourth lumbar nerves, but the root from the second may be absent. For a description of the nerve within the abdo- men and pelvis, see these sections. It escapes from the pelvic cavity by passing through the obturator canal, in which it breaks up into two divisions — superficial or anterior, and deep or posterior. The superficial or anterior division passes over the upper border of the obturator externus, and then descends in front of the adductor brevis, but behind the pectineus and adductor longus. This division communicates with the accessory obturator nerve (when present). The deep or posterior division pierces the upper part of the obturator externus, and then passes behind the adductor brevis and in front of the adductor magnus. Branches — Superficial or Anterior Division. — The branches of this division are as follows : articular to the hip- joint, which arises in the obturator canal, and enters the joint through the cotyloid foramen ; muscular to the gracilis, adductor longus, adductor brevis as a rule, and occasionally to the pectineus ; arterial to the coats of the femoral artery ; and cutaneous. This last branch commences at the lower border of the adductor longus, and, after a short course downwards, it pierces the fascia lata between the posterior border of the sartorius and the anterior border of the gracilis, to be distributed to the integument of the inner side of the thigh for a variable extent about the centre. Before this branch pierces the fascia lata it gives one or two twigs which communicate with branches of the long saphenous and the posterior division of the internal cutaneous beneath the sartorius, to form the subsartorial plexus. Deep or Posterior Division.— This division furnishes the follow- ing branches : muscular to the obturator externus, adductoiF magnus, and adductor brevis (provided the latter is not suppliecp by the superficial or anterior division) ; and articular to the kneej : joint, called the geniculate branch. This latter branch descends upor i the adductor magnus, which it subsequently pierces close abovM^ the femoral opening, and so reaches the popliteal artery. It accom j^ panies that artery, lying at first on its inner side and then in front ot it, as low as the origin of the central or azygos branch. Here th<' ; nerve leaves the main artery, and passes with its central or azygo,;* branch through the posterior ligament of the knee-joint to th THE LOWER LIMB 475 interior of the articulation. The geniculate nerve is frequently absent. Accessory Obturator Nerve.— This nerve is present in about 30 per cent, of bodies. It is comparatively small in size, and arises by two roots from the anterior primary divisions of the third and fourth lumbar nerves, the roots being interposed between those of the anterior crural and obturator nerves. It descends along the inner border of the psoas magnus, close to the brim of the pelvis, imderneath the external iliac vessels. It then passes over the superior pubic ramus, where it passes beneath the pectineus, and so emerges on to the thigh beneath Poupart's ligament. Under cover of the pectineus it divides into the following three branches : (i) articular to the hip- joint ; (2) muscular to the deep surface of the pectineus ; and (3) a reinforcing branch to join the superficial or anterior division of the main obturator nerve. Scarpa's Triangle. — ^This triangle is situated on the front of the thigh below Poupart's ligament. The base, which is directed upwards, is formed by Poupart's hgament. The outer boundary is formed by the inner border of the sartorius in its upper fourth, and the inner boundary is constructed by the internal border of the adductor longus in its upper part. The apex is about 3^ inches below Poupart's ligament, and is formed by the overlapping which there takes place between the superficially placed sartorius and the more deeply placed adductor longus. The roof is formed by the skin, two layers of the superficial fascia, and fascia lata. The following structures also he in the roof; the femoral branch of the genito-femoral nerve; the inguinal and superficial femoral or saphenous glands ; the cutaneous branches of the common femoral artery (except the inferior external pudic), with their correspond- ing veins ; the saphenous opening ; and the terminal part of the long saphenous vein, with the anterior and posterior saphenous veins joining it. The floor contains the following muscles, in order from within outwards : adductor longus ; pectineus ; psoas magnus ; and iliacus (the latter two being here united to form one muscle, called the ilio-psoas). Occasionally a small part of the adductor brevis is seen between the adductor longus and pectineus, and, when this is so, the superficial or anterior division of the obturator nerve may be seen in part. Contents. — ^The contents are as follows : the common femoral artery and its branches ; the first part of the superficial femoral artery and its branches ; the upper part of the femoral vein and its tributaries ; and the anterior femoral nerve, with its divisions and their branches. Hunter's Canal.* — ^This is a somewhat triangular, musculo- aponeurotic canal, which occupies the middle two- fourths of the thigh on its inner aspect. * The canal has received this complimentary name because John Hunter was the first surgeon who tied the superficial femoral artery in this part of its course for popliteal aneurism in the year 1785. 47t A MANUAL OF ANATOMY Obliquus Externus Abdominis — Ext. Cutaneous Nerve Sup. Circumflex Iliac Art. Tensor Fascia Femoris _ lliacus Ant. Femoral Nerve Femoral Vein Mid. Cutaneous. - Nerve L. Saphenous Vein Sartorius ilisAA Femoal Branch of Genito-femoral Nerve I Superficial Epigastric Artery I i \^\ Common Femoral An ^ ^ Hypogastric] • / of Ilio-hypo] Nerve ,Pectineus Sup. Ext. 1 (■ Arter Rectus Femoris Spermatic ' Inf. Ext. Pudic Ar Adductor Longus . Cutaneous Branch of Obturator Nerve - Internal Cutaneous Nerve Vastus Internus Fig. 233. — The Front of the Thigh (Scarpa's Triangle). THE LOWER LIMB 477 Boundaries — External. — The vastus intemus, closely covering the inner surface of the femur as far back as the inner lip of the linea aspera. Internal and Posterior. — ^The adductor longus and subse- quently the adductor magnus, both of which extend back to the inner hp of the linea aspera, where they meet the vastus intemus and so form the apex of the triangle. Anterior or Superficial. — ^This boundary is commonly called the roof of the canal. It represents the base of the triangle, and is formed by an aponeurotic expansion which extends from the adductor longus and adductor magnus on the inner side to the vastus intemus on the outer side. Superficial to this expansion in its whole length is the middle portion of the sartonus, and the subsartorial plexus of ner\'es lies between the two in the middle third of the thigh. The aponeurosis is com- paratively weak over the upper half of the canal, but over the lower half it is strong, and, below, it is continuous \vith the anterior margin of the femoral opening in connection with the adductor magnus. Contents. — ^These are sls follows : the superficial femoral artery in the second part of its course, and its branches ; the first portion of the femoral vein, and its tributaries ; the long saphenous nerve ; and the nerve to the vastus intemus muscle in the upper half of the canal. Femoral Artery. — ^This vessel extends from the lower border of Poupart's ligament to the posterior margin of the femoral opening, which is in connection with the adductor magnus. It is the direct continuation of the external ihac artery, and at its termination becomes the pophteal. It occupies the upper three-fourths of the thigh, and its direction is downwards and inwards. The coiuse of the vessel is indicated in the following manner : the thigh being partially flexed upon the abdomen, and at the same time shghtly abducted and rotated outsvards, draw a line from a point midway bet^veen the anterior superior ihac spine and the symphysis pubis to the adductor tubercle of the femur, or, if this tubercle cannot be felt, to the internal tuberosity on the inner surface of the internal condyle. This line over its upper three-fourths represents the course of the vessel. At a point about 3 J inches below Poupart's Ugament the sartorius takes up a position over the artery, and from this point onwards that muscle continues to lie over the vessel. For at least the first i^ inches of its course the vessel corresponds in size with the external iliac artery. WTien, however, it reaches a point from i^ inches to 2 inches below Poupart's hgament it gives off a large branch, called the arteria profunda femoris, after which it under- goes a sudden diminution in size. The part of the vessel between Poupart's ligament and the origin of the arteria profunda femoris is known as the common femoral ; the part beyond the origin of that large branch is called the superficial femoral ; and the arteria profunda femoris is spoken of as the deep femoral ; that is to say, the common femoral artery is regarded as dividing into superficial 478 A MANUAL OF ANATOMY femoral and deep femoral at a point from i^ inches to 2 inches below Poupart's ligament. For convenience of description, the femoral artery (meaning thereby the whole of the leading artery of the thigh) is divided into two parts — first and second — the first part lying in Scarpa's triangle, and the second part occupying Hunter's canal. First Part. — The first part of the femoral artery extends from the lower border of Poupart's ligament to the apex of Scarpa's triangle, within which triangle it lies. Relations — Superficial or Anterior. — ^The skin; superficial fascia in two layers; fascia lata; anterior wall of the femoral sheath for the first I J inches, and subsequently the anterior wall of the special sheath; internal cutaneous nerve crossing the vessel from without inwards, either as one nerve or in its two divisions, just above the apex of Scarpa's triangle and outside the special sheath; two or three cutaneous branches of the internal cutaneous nerve on their way to the inner side of the thigh ; superficial circumflex iliac vein near Poupart's ligament ; and external cutaneous femoral or anterior saphenous vein just above the apex of Scarpa's triangle. Deep or Posterior. — ^The posterior wall of the femoral sheath for the first i-| inches, and subsequently the femoral vein; branch of the anterior femoral nerve passing inwards to the pectineus muscle, and lying close behind the femoral sheath ; psoas magnus in the upper part and pectineus in the lower part, the artery being separated from the latter muscle by the femoral vein and profunda femoris vessels, the femoral vein being nearest to the artery. External. — ^The femoral branch of the genito-femoral nerve for a short distance below Poupart's ligament, where the nerve is within the crural sheath; anterior femoral nerve for about | inch below Poupart's ligament, and separated from the artery by an interval of about ^ inch ; long saphenous nerve and nerve to the vastus internus muscle, the former being nearest to the artery, and both being outside the special sheath ; and the arteria profunda femoris for about ^ inch at its commencement. Internal. — For about 2 inches below Poupart's ligament the femoral vein lies to the inner side of the artery, with the intervention of the external septum of the femoral sheath. Thereafter the vein gradually leaves the inner side of the artery to take up its position behind it, towards the apex of Scarpa's triangle. The femoral artery immediately below Poupart's ligament is anterior to the inner part of the head of the femur, but in the rest of its course the vessel is situated on the inner side of that bone. Second Part. — The second part of the artery (superficial femoral) extends from the apex of Scarpa's triangle to the posterior margin of the femoral opening in connection with the adductor magnus, where it becomes the popliteal. In this part of its course the I superficial femoral lies in Hunter's canal, and passes over the adductor longus, whilst the deep femoral is behind that muscle. THE LOWER LIMB 479 Relations — Superficial or Anterior. — The skin ; superficial fascia ; long saphenous vein ; fascia lata ; sartorius ; subsartorial plexus of nerves ; the aponeurotic covering of Hunter's canal ; and the long saphenous nerve in the act of crossing the vessel from its outer to its inner side. External. — The vastus intemus, covering the inner surface of the femur ; and the long saphenous nerve and the nerve to the vastus internus, both in the upper half of the canal. Internal. — At first the adductor longus, and lower down the adductor magnus, both of which muscles also lie behind the artery. In Hunter's canal the femoral vein still maintains its position close behind the artery until the lower end of the canal is reached, when the vein inclines a little to the outer side of the artery. The superficial femoral artery in Scarpa's triangle, as well as in Hunter's canal, is surrounded by a sheath, which also contains the femoral vein. Branches of the Femoral Artery. — The branches are as follows : superficial epigastric ; superficial circumflex Hiac ; superior or supei-ficial external pudic ; inferior or deep external pudic ; arteria profunda femoris or deep femoral (aU from the common femoral) ; muscular (from the superficial femoral in Scarpa's triangle and in Hunter's canal) ; saphenous (from the superficial femoral in Scarpa's triangle) ; and anastomotica magna (from the superficial femoral in Hunter's canal). The superficial epigastric artery arises from the common femoral about \ inch below Poupart's ligament. It then pierces the femoral sheath and the cribriform fascia, or the outer border of the saphenous opening, after which it turns upwards over Poupart's ligament a little to the inner side of the centre, and ramifies in the integmnent of the anterior abdominal wall as high as the umbilicus. In its course it supplies branches to the inguinal glands, and anastomoses with branches of the deep epigastric of the ex- ternal iliac. The superficial circumflex iliac artery frequently arises in common with the superficial epigastric. Having pierced the femoral sheath and the outer border of the saphenous opening, it passes outwards below the outer half of Poupart's ligament to the anterior part of the iliac crest, where it ramifies in the integument of that neighbourhood. In its coiu"se it supplies branches to the iliacus, sartorius, and outer inguinal glan(fc, and anastomoses with the deep circvmiflex iliac of the external iliac, and the gluteal of the internal iliac. The superior or superficial external pudic artery arises from the common femoral about | inch below Poupart's ligament. Having pierced the femoral sheath and cribriform fascia, it emerges through the saphenous opening, after which it passes inwards and upwards over the spermatic cord, or round ligament of the uterus, according to the sex, to be distributed to the integument of the suprapubic region, the adjacent portion of the scrotiun in the male, and the labium majus in the female, and the dorsimi of the I 48o A MANUAL OF ANATOMY Superficial Epigastric and Superficial Circumflex Iliac Arteries Common Femoral Artery ' Femoral Vein Sartorius #b//II| Anterior Femoral Nerve Iliacus Ext. Circumflex Artery Rectus Femoris Nerve to Vastus - Internus Superf. Femoral Artery in Hunter's Canal Long Saphenous - Nerve Anastomotica Magna Artery Long Saphenous Vein (cut) Patellar Branch of Long Saphenous Nerve Fig. 234. — The Front and Inner Side of the Thigh (The Sartorius has been in great part removed). THE LOWER LIMB 481 penis by a branch which extends as far as the prepuce in the vicinity of the corona glandis, Ijdng in its course external to the dorsalis penis artery. The vessel in its course gives branches to the inner inguinal or pubic glands, the deep femoral glands, and the cover- ings of the spermatic cord or of the round hgament of the uterus. It anastomoses ^vith (i) the cremasteric branch of the deep epigastric, in crossing the spermatic cord, that branch being represented in the female by the artery of the round hgament of the uterus ; (2) its fellow of the opposite side ; (3) the inferior or deep external pudic ; and (4) the dorsalis penis artery, which is a branch of the internal pudic from the internal iliac. The inferior or deep external pudic artery arises from the common femoral a little lower down than the preceding. Unlike the superior branch, it does not pass through the saphenous opening, but, after piercing the femoral sheath, it passes inwards on the pectineus and adductor longus, under cover of the fascia lata. Having reached the inner side of the thigh, it pierces the fascia lata to be distributed to the side of the scrotmn in the male and the labiiun majus in the female. In its course it gives branches to the muscles upon which it rests, and anastomoses with (i) the superior or superficial external pudiic, (2) the cremasteric, and (3) the superficial perineal, which is a branch of the internal pudic. The four arteries just described are spoken of as the cutaneous arteries of the groin. Arteria Profunda Femoris or Deep Femoral Artery. — ^This im- portant vessel is one of the terminal branches of the common femoral, arising from the outer and back part of that artery at a point from i^ inches to 2 inches below Poupart's ligament. At first it lies for about | inch on the outer side of the superficial femoral, where it rests upon the iliacus. It then bends sharply, and passes inwards over the pectineus, where it hes immediately behind the superficial femoral vessels and its own vein, the latter being nearest to it. Thereafter it descends behind the adductor longus, resting, in succession, upon the adductor brevis and adductor magnus, and, having become comparatively small, it terminates in the fourth or last perforating artery. As the profunda vessel passes behind the adductor longus, it is separated by that muscle from the super- ficial femoral artery. Branches. — ^The branches are as follows : external circumflex ; internal circumflex ; and perforating, which are four in number. The external circumflex artery, which is of large size, arises from the arteria profunda femoris close to its origin. Its direction is outwards beneath the sartorius and rectus femoris, and between the nerves arising from the posterior division of the anterior femoral, supplying in this part of its course branches to the sur- rounding muscles, and resting upon the crureus. It terminates by i dixiding into three sets of branches — ascending, transverse, and I descending. 31 A MANUAL OF ANATOMY lliacus ' Tensor Fasciae Femoris Sartorius (cut) Gluteus Medius - Rectus Femoris (cut) Ext. Circumflex Artery, Arteria Profunda Femoris Vastus Externus '' Long Descending Branch of- Ext. Circumflex Artery Adductor Longus (cut) Vastus Intemus Superficial Femoral Artery Deep Branch of Anastomotica Magna Artery Tendon of Rectus Femoris Psoas Magnus Commencement of Common , ' Femoral Artery , Pectineus (cut) Superf. Div. of Obt. Nerve DeepDiv. of Obt. Nerve piercing Obt. Ext. Adductor Longus Gracilis (cut) Adductor Brevis Adductor Magnus \nastomotica IMagna Artery Geniculate Branch of Obturator Nerve Tendon of Adductor Magnus Azygos Artery Semimembranosus , Gracilis Semitendinosus Tendon of Sartorius Fig, 235,— The Front and Inner Side of the Thigh (Deep Dissection). THE LOWER LIMB ^ 483 The ascending branch passes upwards beneath the tensor fasciae femoris to the fore part of the gluteal region. Its branches supply the tensor fasciae femoris and the anterior portions of the gluteus medius and gluteus minimus. It also supplies an articular branch to the hip-joint, which reaches the articulation under cover of the rectus femoris. The ascending branch anasto- moses with the gluteal of the posterior di\asion of the internal iliac, and the deep circumflex iliac of the external ihac. The transverse branches are at least two in number. They enter the vastus externus, in which they wind round the outer part of the femur, supplying that muscle in their course. One of them, piercing the femoral insertion of the gluteus maximus, reaches the back of the thigh, where it anastomoses with the first perforating artery, the sciatic, and the transverse branch of the internal circum- flex, thus forming the crucial anastomosis. The descending branches are three or four in number. They pass downwards with the nerve to the vastus externus, l5ang along the anterior border of that muscle, and supplying in theii course the rectus femoris, vastus externus, and crureus. One of them is long, and descends upon the vastus externus as low as the knee-joint, where, piercing that muscle, it anastomoses with the superior external articular of the popliteal, the fourth or lowest perforating of the arteria profunda femoris, the deep branch of the anastomotica magna of the superficial femoral, and the lowest muscular branch of the superficial femoral. The other descending branches anastomose in the crureus with the lower two perforating arteries. The internal circumflex artery is of smaller size than the external. Arising from the inner and back part of the arteria profunda femoris, opposite the origin of the external circmnflex, it passes backwards round the inner side of the femur towards the small trochanter. In this course it passes, in succession, between the pectineus and psoas magnus, and between the adductor brevis and obturator externus, gi\'ing off branches to the obturator externus and adductor muscles. On reaching the inter\'al be- tween the adductor brevis and obturator externus, it terminates in two branches — ascending or anterior, and transverse or posterior. The ascending or anterior branch passes with the obturator externus to the digital fossa of the femur, where it anastomoses with the gluteal and sciatic of the internal iliac, and the first perforating, thus forming the digital anastomosis. The transverse or posterior branch continues the course of the main artery backwards, passing between the upper border of the adductor magnus and lower border of the quadratus femoris, in which situation it anastomoses with one of the transverse branches of the external circumflex, the first perforating, and the sciatic of the internal iliac, thus forming the crucial anasto- mosis. The branches which the iniernal circumflex gives to the I 484 A MANUAL OF ANATOMY obturator externus anastomose in that muscle with the obturator artery, which is a branch of the internal iliac. The perforating arteries are four in number — first, second, third, and fourth. They pass backwards round the inner side of the femur, and under the tendinous arches of the adductor magnus. The first and second arteries pierce the adductor brevis and adductor magnus, whilst the third and fourth pierce the adductor magnus only. On reaching the back of the thigh, all four arteries give off the following branches : muscular, to the hamstring muscles ; branches to the great sciatic nerve ; and cutaneous, to the integument of the outer and back parts of the thigh. The first perforating also gives branches to the lower part of the gluteus maximus, and the second (or third) furnishes the chief nutrient or medullary artery of the femur. The perforating arteries, now much reduced in size, wind round the back and outer side of the femur. In this course the first pierces the femoral insertion of the gluteus maximus, and the second, third, and fourth pierce the femoral head of the biceps and the external intermuscular septum. The first and second terminate in the vastus externus, and the third and fourth in the crureus, all four anastomosing with branches of the external circumflex, the fourth also taking part in the deep geniculate arterial rete. At the back of the thigh the perforating arteries anastomose freely with one another. The first perforating also anastomoses with the gluteal, sciatic, and ascending branch of the internal circumflex in the digital fossa, thus forming the digital anastomosis, and with the sciatic and transverse branches of the internal and external circumflex between the adductor magnus and quadratus femoris to form the crucial anastomosis. The lower two perforating arteries anastomose at the back of the thigh with the superior muscular branches of the popliteal. The branches of the per- forating arteries to the great sciatic nerve anastomose with the comes nervi ischiadici branch of the sciatic. The muscular branches of the superficial femoral artery arise partly in Scarpa's triangle and partly in Hunter's canal. The lowest of these branches, which is somewhat large and very constant, is given off at the lower end of Hunter's canal. It passes outwards behind the femur, piercing the external inter- muscular septum and the femoral head of the biceps, and it termi- nates in the crureus, in which it anastomoses with the long descending branch of the external circumflex, the fourth perforating, and the superior external articular of the popliteal. The saphenous branches are two or three in number, and arise from the superficial femoral in Scarpa's triangle. They supply the superficial femoral or saphenous glands and the structures around the terminal part of the long saphenous vein. The arteria anastomotica magna arises from the superficial femoral at the lower end of Hunter's canal, and at once divides into a superficial and deep branch. In many cases these branches arise independently from the main vessel. The superficial bransh THE LOWER LIMB 485 pierces the aponeurotic covering of Hunter's canal, and descends in company with the long saphenous nerve between the sartorius and gracilis, where it lies beneath the fascia lata. It subsequently pierces that fascia, and enters the leg on its inner aspect, to be distributed to the integument over the upper third. This branch anastomoses with the inferior internal articular of the pop- liteal. The dee-p branch at once enters the vastus internus, in which it descends anterior to the tendon of the adductor magnus. It gives branches to the vastus internus and crureus, and anasto- moses with the superior internal articular of the popliteal. It also furnishes a cross branch, which passes outwards in front of the femur above the patellar siuface to form an arch with a branch of the superior external articular of the popliteal. Additional anasto- moses are formed with the long descending branch of the external circiunfiex, and the lowest perforating branch of the arteria pro- funda femoris. Varieties ol the Femoral Artery — I. The Trunk.-— (1) In rare cases the femoral artery may be found on the back of the thigh in company with the great sciatic nerve. In such cases the vessel is derived from the internal iliac, and may be regarded as a large sciatic arterj'. Under these conditions the external ihac artery ends as the arteria profunda femoris. (2) Occasionally the superficial femoral artery divides just below the origin of the arteria profunda femoris into two branches of equal size, which descend in close contact, and subsequently unite to form one trunk before reaching the femoral opening in connection with the adductor magnus. n. The Branches — (i) Arteria Profunda Femoris. — In normal cases this artery arises from the common femoral from i^ to 2 inches below Poupart's Ugament. The common femoral arter>-, however, may di\4de into superficial femoral and deep femoral at any point between this and Poupart's hgament. The superficial and deep femoral arteries may even spring from the lower part of the external iliac a httle above Poupart's Ugament, in which case two large arteries would pass out beneath that Ugament, instead of one. More rarely, the division of the common femoral into superficial and deep femoral may take place lower down than the normal level, even as low as 4 inches below Poupart's Ugament. (2) External Circumflex Artery. — This vessel is very Uable to variation. It may arise from the common femoral instead of the deep femoral, as in cases of low origin of the latter vessel, or it may arise in two branches, one from the deep femoral and one from the common femoral, or both from the deep femoral, or both from the common femoral. (3) Internal Circumflex Artery. — This vessel is not so Uable to variation as the external circumflex. It may arise along \\ith the external circumflex ; it may spring from the common femoral ; it may be a branch of the deep epigastric ; or it may be derived from the external iliac. In cases of low origin of the deep femoral, the external and the internal circumflex arteries usuaUy spring from the common femoral. (4) Arteria Anastomotica Magna. — In very rare cases the superficial branch of this artery assumes considerable length, and, under the name of the internal saphenous artery, accompanies the internal saphenous vein down the inner side of the leg as far as the internal malleolus. Unusual Branches. — The deep epigastric, the deep circumflex iUac, or an abnormal obturator arter^', may arise from the common femoral near Poupart's ligament. Collateral Circulation after Occlusion of the Femoral Artery. — i. The Common Femoral Artery. — (a) The superficial perineal and dorsaUs penis arteries, both from the internal pudic of the internal iUac, anastomose ^^^th the superior and inferior external pudics of the common femoral. 486 A MANUAL OF ANATOMY (b) The cremasteric from the deep epigastric of the external iliac anastomoses with the superior external pudic of the common femoral. (c) The obturator of the internal iliac anastomoses with the internal circum- flex of the arteria profunda femoris. (d) The deep circumflex iliac from the external iliac and the gluteal from the internal iliac anastomose with the ascending branch of the external circumflex from the arteria profunda femoris. (e) The sciatic of the internal iliac anastomoses with the transverse branch of the internal circumflex, the transverse branch of the external circumflex, and the first perforating artery, all branches of the arteria profunda femoris. (/) The sciatic and gluteal, both branches of the internal iliac, anastomose in the digital fossa with the ascending branch of the internal circumflex of the arteria profunda femoris. 2. The Superficial Femoral Artery below the Origin of the Arteria Profunda Femoris. — (a) The descending branch of the external circumflex of the arteria profunda femoris takes part in the deep geniculate arterial rete. (b) The third and fourth perforating branches of the arteria profunda femoris anastomose at the back of the thigh with the superior muscular branches of the popliteal. (c) The fourth perforating artery and the descending branch of the external circumflex, both from the arteria profunda femoris, anastomose with the lowest muscular branch of the superficial femoral. A continuous anastomotic chain of arteries extends from the gluteal region down the back of the thigh to the region of the knee, and it is formed in the following manner : the gluteal anastomoses with the sciatic, the sciatic with the external and internal circumflex, the gluteal, sciatic, external circumflex, and internal circumflex with the perforating branches of the arteria profunda femoris, and the perforating branches of the arteria profunda femoris with the upper muscular and articular branches of the popliteal. This chain is of special importance after occlusion of the common femoral artery, and the comes nervi ischiadici branch of the sciatic is particularly liable to enlarge- ment. Femoral Vein. — This vessel extends from the posterior margin of the femoral opening, which is in connection with the adductor magnus, to the lower border of Poupart's ligament, where it becomes the external iliac vein. In the lower part of Hunter's canal it lies close behind the superficial femoral artery, with a slight inclination to the outer side. In ascending, however, it soon takes up a position behind the artery, which it main- tains until it has entered Scarpa's triangle. The vein now gradually inclines to the inner side of the artery, and for about 2 inches below Poupart's ligament it is quite to its inner side, but on the same plane, being separated from the artery by the external septum of the femoral sheath, and lying here between the pectineus and psoas magnus. Tributaries. — ^These are as follows : the venae comites of the anastomotica magna artery at the lower end of Hunter's canal ; the venae comites of each of the muscular branches of the super- ficial femoral artery; the profunda femoris vein at a point about if inches below Poupart's ligament ; and the long saphenous vein at a point about i^ inches below Poupart's ligament, and above the point where the profunda vein terminates. The long saphenous vein has been previously reinforced by the anterior saphenous or external cutaneous femoral, the posterior sa])henous or internal cutaneous femoral, the superficial circumflex iliac, the THE LOWER LIMB 487 superficial epigastric, and the superior and inferior external pudic veins. The profunda femoris vein is formed by the venae comites which accompany each of the branches of the arteria profunda femoris. It is a large vessel, and is provided with several valves. Common Iliac Artery Elxtemal Iliac Artery Internal Iliac Artery Femoral Vein Poupart's Ligament ' External Abdominal Ring ^. W ^""^ ' '"''''*^ Femoral Branch of Genitofemoral Nerve ^trnannnnTT^ Psoas Magnus ___VK1j1L. Common Origin of Superficial _ '*" Epigastric and Superficial Circumflex Iliac Arteries Common Femoral Artery j-- Internal Saphenous Vein i._ Arteria Profunda Femoris External Circumflex Artery \w//mW//' l!>,ifm. ... . ^ Membrane Fig. 236. — Deep D*ssection of Scarpa's Triangle. 'he femoral vein is provided with five pairs of valves. Three of ^hese are situated in the part of the vessel below the point where it receives the profunda femoris vein. Of the other two, one is placed immediately above the termination of the profunda femoris vein, and the other at the point where the femoral vein ends in the 488 A MANUAL OF ANATOMY external iliac. This last valve is known as the ilio-femoral valve of Bennett. Varieties of the Femoral Vein. — i. The vein is sometimes absent from Hunter's canal. In such cases, instead of passing through the femoral opening in cpnnection with the adductor magnus, it ascends for some distance upon the posterior surface of that muscle, which it subsequently pierces, and so enters Scarpa's triangle. 2. The vein may be double, simulating the arrangement known as venae comites, in which case the femoral artery would have a vein on either side of it, with communicating branches passing between the two at frequent intervals over the vessel. Obturator Artery .^r-This vessel normally arises from the anterior division of the internal iliac, and for the most part is placed on the outer wall of the pelvic cavity. The artery, having passed through the obturator canal, divides at once into its two terminal branches, internal and external. These descend upon the anterior surface of the obturator membrane under cover of the obturator externus, the internal branch coursing along the inner margin, and the external along the outer margin, of the membrane. The internal branch supplies the obturator externus and adjacent adductor muscles. The external branch divides into two at the lower part of the obturator membrane. One of these divisions passes inwards and anastomoses with the internal branch, thus completing an arterial loop at the circumference of the membrane. The other division takes an outward course below the acetabulum to the region of the tuber ischii, where it supplies the origins of the ham- string muscles and anastomoses with the sciatic artery. This latter division supplies an articular branch to the hip- joint, which passes beneath the transverse ligament. The external branch, in addi- tion to the foregoing offsets, supplies the obturator externus, in which both terminal branches anastomose with the internal circumflex of the arteria profunda femoris. The obturator vein terminates in the internal iliac vein. THE HIP-JOINT. The hip-joint belongs to the class diarthrosis, and to the sub- division enarthrosis. The articular surfaces are the head of the femur and the acetabulum of the os innominatum. The ligaments are the capsular ligament, with its accessory parts, the ligamentum teres, the cotyloid ligament, and the transverse ligament. The capsular ligament is of great strength, and completeh' surrounds the joint. It is tight-fitting, and hardly admits ol separation taking place between the articular surfaces. Its superior attacliments are as follows : above and behind it is attached to the os innominatum immediately external to the coty- loid ligament and about three lines from the brim of the acetabulum. In front it is attached to the base of the anterior inferior ihac THE LOWER LIMB 489 spine ; the outer surface of the cotyloid hgament ; the ilio- pectineal eminence ; the outer extremity of the obturator crest of the superior pubic ramus ; and the adjacent portion of the obturator membrane. Antero - infer iorly (opposite the cotyloid notch) it is attached to the outer surface of the transverse ligament. Inferiorly it is attached to the upper part of the groove between the acetabulum and the tuber ischii. Its inferior attachments are as follows : superiorly it is attached to the anterior part of the upper border of the great trochanter of the femur and the superior cervical tubercle. Anteriorly it descends as low as the anterior intertrochanteric line, into which it is firmly implanted as low as the inferior cervical tubercle. Inferiorly and internally it is attached to the femur about | inch in front of the small trochanter. Anterior Inferior Iliac Spine Iliofemoral Band (Y Ligament of Bigelow) Pubo-femoral Band Anterior W.. ^7' \^/a Intertrochanteric V^* If^ \ ' /'t ' Line Obturator Membiane Fig. 237.— The Right Hip-Joint (Anterior View). Posteriorly it is attached very loosely to the neck of the femur at the junction of the middle and lower thirds. The majority of the fibres of the ligament are disposed longi- tudinally, but some are circular. The circular fibres are best inarked at the posterior and inferior parts of the capsule, where they form a band, nearly i inch in depth, called the zona orbicularis. In certain situations the longitudinal fibres form thickened bands which constitute the accessory portions of the capsule. These accessory bands, usually designated as special ligaments, are as lolJows : iho-femoral, iho-trochanteric, ischio-capsular, and pubo- lemoral. The illo-femoral ligament has been compared to an inverted Y, and IS knowTi as the Y-shaped ligament of Bigelow. It is situated on the anterior aspect of the capsule, and is attached superiorly 4 go A MANUAL OF ANATOMY to the inferior aspect of the anterior inferior iliac spine below the origin of the straight head of the rectus femoris. The lateral fibres as they descend form two strong bands, outer and inner, which diverge very slightly from each other. The inner band passes almost vertically to be attached to the lower end of the anterior intertrochanteric line of the femur and the inferior cervical tubercle. The outer band, shorter than the inner, passes obliquely downwards and outwards to be attached to the upper end of the anterior intertrochanteric line and the superior cervical tubercle. The central fibres are attached to the middle portion of the anterior intertrochanteric line, and the part of the capsule covered by them is comparatively weak. The ilio-trochanteric ligament is situated immediately external to the outer part of the ilio-femoral ligament. It is attached superiorly Digital Fossa -t\.. Great Trochanter It ^"~ Zona Orbicularis ""•^Extracapsular part of Neck of Femur Tuber Small Trochante FiCx. 238. — The Right Hip-Joint (Posterior View). to the lower and anterior part of the dorsum ilii immediately abovel the acetabulum, close to the upper attachment of the ilio-femorall ligament, and inferiorly to the great trochanter in the region ofl the superior cervical tubercle. The ischio-capsular ligament is a thickened band which extends! from the upper part of the obturator groove (just below thej acetabulum) to the zona orbicularis. The pubo-femoral ligament is the weakest of the three accessor}! ligaments. Its fibres are attached in a somewhat scattered manner to the ilio-pectineal eminence, the outer part of thiJ obturator crest, and the adj acent portion of the obturator membrane| From these points the fibres converge to be attached to the anterionl inner, and lower parts of the capsular ligament, where they lie clos|j|-^ to the inner band of the ilio-femoral ligament. Il^ THE LOWER LIMB 491 In addition to the accessory ligaments, the capsule receives ex- pansions from the reflected head of the rectus femoris and gluteus minimus. When the hip- joint is opened the innermost fibres of the capsular ligament are seen to be reflected upwards from their femoral attachments upon the neck of the femur as far as the margin of the articular cartilage of the head. The longitudinal folds thereby produced are called retinacula. Three of these are specially well marked, two being situated anteriorly, and corre- sponding in position with the outer and inner bands of the ilio- femoral ligament, and the other being situated at the upper and back part of the neck. The capsular ligament is strongest anteriorly and superiorly. The thinnest part is situated between the ilio- femoral and pubo- femoral ligaments. In fhis region there is some- times an opening in the capsule which allows the bursa beneath the ilio-psoas to communicate with the synovial membrane of the joint. The capsule is also thin where it is attached to the posterior surface of the neck of the femur and to the transverse ligament. It is to be noted that, though the anterior surface of the neck of the femur is entirely covered by the capsular ligament, and is therefore intracapsular, the posterior surface of the neck is only intracapsular in its upper two- thirds, the lower third being wholly extracapsular. The ligamentum teres is also called the inter articular ligament. Its femoral extremity, which is single and somewhat flattened, is attached to the upper part of the rough pit on the head of the femur behind and below its centre. On approaching the cotyloid notch, the ligament becomes expanded and divides into two bands, which are attached to the margins of the notch and to the under surface of \ the transverse ligament. The direction of the ligament is down- ^ wards from the femur to the cotyloid notch, and it rests upon the ; Haversian gland in the bottom of the acetabulum. It is invested by the synovial membrane of the hip-joint, which forms a tubular ! prolongation around it. A small nutrient artery is conducted by ' the ligament to the head of the femur. Fig. 239. — Interior of the Left Hip-Joint. I. Head of Femur; 2, Ligamentum Teres; 3, Haversian Gland ; 4, Cartilage of Acetabulum ; 5, Cotyloid Ligament. 492 A MANUAL OF ANATOMY Two views may be stated regarding the morphology of the Ugamentum teres. 1. It may be regarded as a part of the capsule of the hip-joint which has been cut off by the outgrowth of the articular surface of the head of the femur (Keith). 2. It may be I'egarded as the separated tendon of the pectineus muscle (Bland-Sutton). The cotyloid ligament is a firm annular band of fibro-cartilage which is implanted upon the brim of the acetabulum, thereby deep- ening that cavity and bridging over the cotyloid notch. Its fibres are oblique in direction, and are for the most part attached to the outer and inner surfaces of the brim, but opposite the cotyloid notch they are attached to the transverse ligament. The outer surface of the cotyloid ligament is convex, whilst the inner surface is concave and is closely applied to the head of the femur. Both surfaces are covered by the synovial membrane. The ligament is triangular, the base being iinplanted on the brim of the acetabulum, and the apex representing the free margin, which is incurved so as to grasp the head of the femur. The transverse ligament bridges over the cotyloid notch. It is somewhat complex in structure, being composed of three bundles of fibres intimately blended with one another. The superficial bundle is formed by that part of the cotyloid ligament which stretches over the notch. The other two bundles are more deeply placed, and are arranged as two decussating bands extending between the margins of the notch, and blending closely with the superficial bundle. The transverse ligament does not completely fill up the cotyloid notch, a space being left between the ligament and the bottom of the notch for the passage of articular vessels and nerves. The synovial membrane covers the anterior surface of the neck of the femur and the upper two- thirds of the posterior surface, passing over the retinacula and extending as high as the margin of the cartilage covering the head. From the neck it is reflected over the inner surface of the capsular ligament, which it com- pletely invests. After leaving the capsular ligament at its acetabular attachments it passes over the cotyloid ligament, and covers both of its surfaces. Thereafter it is reflected over the Haversian gland in the bottom of the acetabulum, from which it is prolonged as a tubular sheath around the ligamentum teres as far as : the pit on the head of the femur. In those cases where the capsular j ligament presents an opening between the ilio-femoral and pubo-' femoral ligaments, the synovial membrane is in communication! through that opening with the bursa beneath the ilio-psoas. It is; to be noted that the ligamentum teres, though intracapsular, is extrasynovial. Further, the synovial membrane is visible from' the exterior of the joint at the lower part of its posterior aspect, | on account of the very slight attachment of the capsular ligament] to the back of the neck of the femur. The so-called synovial or Haversian gland occupies the rough THE LOWER LIMB 493 pit in the bottom of the acetabulum, and is simply a collection of adipose tissue covered by the synovial membrane. The hga- mentum teres rests upon it, and the synovial membrane which covers it is thicker and more vascular than elsewhere. It serves as a cushion for the head of the femur. Mu5cular Relations. — Commencing at the inner aspect of the capsular hgament and passing over its anterior, outer, and posterior surfaces to its lower part, the muscles in contact with the hgament are as follows : (i) pectineus on the inner aspect and adjacent part of the anterior surface ; (2) iho-psoas in front ; (3) the two heads of the rectus femoris, with the tendon formed by their union, and the gluteus minimus on the outer and upper aspects ; (4) pyri- formis, gemellus superior, obturator intemus, and gemellus inferidr on the upper and posterior aspects ; and (5) obturator extemus on the posterior and inferior aspects. Between the iho-psoas and the ligament there is a bursa, which sometimes communicates with the synovial membrane of the joint through an opening in the capsule. Arterial Supply. — The hip- joint receives its arterial supply from the following sources : 1. The transverse branch of the internal circumflex. 2. The ascending branch of the external circumflex. 3. The external terminal branch of the obturator. 4. The inferior branch of the deep division of the gluteal. 5. The sciatic. Nerve-supply. — The hip- joint receives its nerves from the following sources : 1. The nerve to the rectus femoris, which is a branch of the pos- terior division of the anterior femoral. 2. The anterior or superficial division of the obturator nerve, or the accessory obturator when it is present. 3. The nerve to the quadratus femoris, or, if that nerve does not supply an articular branch, the great sciatic. The first two nerves are branches of the lumbar plexus, and the others are derived from the sacral plexus. Movements. — These are as follows : flexion, extension, abduction,- adduc- tion, rotation, and circumduction. Flexion. — This is of two kinds — ventral and dorsal. In ventral flexion the thigh is dra^^Ti upwards towards the cinterior abdomiucd wall. In dorsal flexion the thigh is carried backwards beyond the perpendicular. The extent of ventral flexion depends upon the condition of the knee-joint, being greater when that joint is flexed and more hmited when it is kept extended. Assuming the knee-joint to be flexed, ventrcd flexion is hmited by the coming into contact of the fleshy parts of the front of the thigh and anterior abdominal wall. \Mien the knee-joint is kept extended, ventral flexion is checked earUer by the tension of the hamstring musclee. Dorsal flexion is in most persons soon checked by the tightening of the front part of the capsulai- hgament. Extension. — In extending the hipnjoint from the position of ventral flexion the movement is limited by the tightening of the front part of the capsular ligament. When a person stands at rest the hip-joint is in a state of exten- sion. The vertical Une passing through the centre of gravity then falls behind the centre of rotation at the hir -joint, and there is thus a tendency on the 494 A MANUAL OT ANATOMY part of the pelvis to fall backwards. This tendency, however, is counter- acted by the tightening of the capsular ligament in front, and so the erect attitude is maintained without any muscular effort. Abduction. — This movement is controlled by the tightening of the pubo- femoral ligament and the lower part of the capsule ; the locking which takes place between the upper border of the neck of the femur and the adjacent margin of the acetabulum ; and the tension of the adductor muscles. Adduction. — This movement is controlled by the outer band of the ilio- femoral Ugament and upper part of the capsule, and the lo^dng which takes place between the inner part of the neck of the femur and the anterior margin of the acetabulum. If the hip-joint is flexed adduction is also controlled by the tightening of the ligamentum teres. Rotation. — This consists in movement of the femur round its longitudinal axis without much change of position. The axis of rotation is represented by a line passing through the centre of the head of the femur to meet the vertical line of the centre of gravity of the lower limb at a point corresponding with the middle of the intercondylar notch when the knee-joint is extended. Rotation may take place outwards or inwards. External rotation is con- trolled by the tightening of the outer band of the ilio-femoral ligament. Internal rotation is checked by the tightening of the ischio-capsular ligament ; by the zona orbicularis ; and by the muscles in contact with the back of the joint. The range of rotation is about 60 degrees, Circumduction. — This is a composite movement, consisting of flexion, abduction, extension, and adduction, following each other in rapid succession, the result being that the femur describes a cone, the head of the bone forming the apex and the lower extremity describing the circumference of the base. Ligamentum Teres. — This ligament is loose in the state of extension of the hip-joint, but becomes tightened in flexion and adduction. Muscles concerned in the Movements — Flexion. — lUo-psoas, rectus femoris, sartorius, pectineus, adductor longus, and adductor brevis, the ilio-psoas being the most powerful flexor. Extension. — Gluteus maximus, biceps femoris by its iscliial head, semitendinosus, semimembranosus, and adductor magnus by the fibres which extend from the tuber ischii to the adductor tubercle. Abduction. — Gluteus medius, gluteus minimus, gluteus maximus by its upper fibres, tensor fasciae femoris, and sartorius. Adduction. — Adductores gracilis, longus, brevis, et magnus, pectineus, gluteus maximus by its lower fibres, and obturator externus. Internal Rotation. — Gluteus medius by its anterior fibres, gluteus minimus, tensor fasciae femoris, and adductor magnus by the fibres which extend from the tuber ischii to the adductor tubercle. External Rota- tion.— Gluteus maximus by its lower fibres, gluteus medius by its posterior fibres, pyriformis, obturator internus and gemelli, quadratus femoris, pectineus, adductores longus, brevis, et magnus (the latter by the fibres which are inserted into the shaft of the femur), obturator externus, and sartorius. Relation of Muscles on the Femoral Aspect of the Body of the Os Pubis. Commencing at the symphysis pubis, and passing outwards as far as the inner margin of the obturator foramen, the relation of muscles is as follows : (i) gracilis, (2) adductor brevis, (3) a small portion of the adductor magnus, and (4) obturator externus. The adductor longus does not take part in this relation, its origin being at the upper and inner part of the anterior or femoral surface of the body of the OS pubis, from an impression which can be covered with the point of the Uttle finger. Relation of Muscles at the Back of the Upper End of the Shaft of the Femur. Commencing at the small trochanter, and passing outwards over the back 1 of the femur as far as the outer margin of the gluteal ridge, the relation j of muscles is as follows: (i) ilio-psoas, (2) pectineus, (3) adductor brevis, j THE LOWER LIMB 495 (4) lower fibres of the quadratus femoris, (5) adductor magnus, (6) gluteus maximus, and (7) vastus extemus. Relation of Muscles along the Linea Aspera of the Femur. — Commencing at the outer lip of the linea aspera, and passing inwards as far as the inner Up, the relation of muscles is as follows: (i) vastus externus and crureus in one hne; (2) short head of biceps femoris; (3) adductor magnus; (4) adductor longus; and (5) vastus internus. Borsae at Hip-Joint. — The bursse in the vicinity of the hip-joint are as follows : Psoas. Trochanteric {3). Sabtrochanterie. The psoas bursa is situated between the tendon of the psoas muscle and the anterior part of the capsule of the hip-joint, between the ilio-femoral and pubo-capsular accessory hgaments, this portion of the capsule being weak. The bursa may be continuous with the synovial membrane of the hip- joint through an opening in the capsule which is sometimes present (one in ten). The trochanteric bursae are three in number, and are associated with the great trochanter and the three gluteal muscles. The bursa of the gluteus maximus, which is of large size and multilocular, is situated between the fascial insertion of that muscle and the outer surface of the great trochanter of the femur. The bursa of the gluteus medius is situated between the tendon of insertion of that muscle and the outer surface of the great trochanter above, and in front of, the insertion. The bursa of the gluteus minimus is situated between the tendon of insertion of that muscle and the anterior surface of the great trochanter above the insertion. The subtrochanteric bursa is situated directly below the bursa of the gluteus maximus, and is also associated with that muscle. It Ues between the insertion of the muscle into the gluteal ridge of the femur and the tendinous vastus externus muscle as it skirts the base of the great trochanter. The trochanteric and subtrochanteric bursae have no communica- tion with the synovial cavity of the hip- joint. i 4Q6 A MANUAL OF ANATOMY THE LEG. Landmarks. — The sharp sinuous anterior border of the tibia, being entirely subcutaneous, can readily be felt, and will guide the finger to the tubercle, which is situated at its upper end, where it gives attachment to the ligamentum patellae. The lower border of the tubercle corresponds with the division of the popliteal artery into anterior and posterior tibial vessels. The head of the fibula forms a prominent landmark on the outer side of the leg, and is situated about i inch below the level of the upper surface of the external tuberosity of the tibia. The shaft of the fibula is for the most part obscured by muscles. It can be felt, however, over its lower fourth. The bone occupies a more posterior plane than the tibia. The prominence along the front of the leg in its upper two- thirds is mainly due to the fleshy belly of the tibialis anticus. The internal and external malleoli form bold projections at the lower end of the leg, the internal being formed by the tibia, and the external by the fibula. The malleoli are upon the same plane posteriorly, but the internal malleolus proj ects further forwards than, and does not descend so low as, the external malleolus ; that is to say, the internal malleolus is a little higher up and further forwards than the external, but the two project equally far back. This has to be borne in mind in Syme's amputation at the ankle-joint. It should be carefully noted that, whilst the internal malleolus looks directly inwards, the internal tibial tuberosity has a slight in- clination backwards as well as inwards. The tendons of the tibialis posticus and flexor longus digitorum may be felt behind the internal malleolus, the former being the larger and in close contact with the bone. If the inner border of the foot is raised so as to invert the sole, the tendon of the tibialis posticus will be more readily felt. The tendons of the peroneus longus and peroneus brevis are situated behind the external malleolus, where they lie one upon the other, the brevis tendon being in close contact with the bone. Several tendons can readily be felt in front of the ankle-joint. From within outwards they are as follows : tibialis anticus ; extensor proprius hallucis ; extensor longus digitorum ; and peroneus tertius. All these tendons are best felt in the Uving subject when the foot is flexed upon the leg — that is to say, when the foot is raised. The back of the leg is characterized by the prominence of the calf, which is produced by the gastrocnemius and soleus muscles. This prominence gives place inferiorly to the tendo THE LOWER LIMB 497 Achillis, which stands out boldly beneath the integument, and subsides at the tuber calcis. Upon either side of the projection formed by the tendo Achilhs there is an elongated furrow. The furrow on the outer side indicates the situation of the short saphenous vein and nerve and the peroneal artery, whilst that on the inner side corresponds with the position of the posterior tibial vessels and nerve. The course of the anterior tibial artery on the front of the leg is indicated by a hne drawn from the superior tibio-fibular articula- tion to the centre of the front of the ankle-joint, midway between the two malleoU. This practically coincides with the outer border of the tibiahs anticus. The course of the posterior tibial artery corresponds with a line drawn from the centre of the popliteal space to a point midway between the tip of the internal malleolus and the inner part of the point of the heel. It is to be noted that another large artery is situated upon the back of the leg. This is the peroneal branch of the posterior tibial, and in operations it will be caught upon the back of the fibula, the posterior tibial being between the tibia and fibula, except in the lower part of the leg, where it hes on the back of the tibia. The anterior and posterior tibial arteries can readily be com- pressed with one hand by placing the thumb in front of the ankle- joint midway between the two malleoh, and the middle finger midway between the tip of the internal malleolus and the inner part of the point of the heel. The long saphenous vein may be visible in front of the internal malleolus, and from this point it may be traceable upwards along the internal subcutaneous surface of the tibia. The short saphenous vein is rarely perceptible. It hes behind the external malleolus, then in the hollow upon the outer side of the tendo Achillis, after emerging from which it soon gains the middle line, where it lies in the groove between the two heads of the gastrocnemius. Deep Fascia. — The deep fascia is in part a prolongation of the fascia lata of the thigh, the continuity being estabUshed at the inner and posterior aspects of the knee-joint. Elsewhere it is attached superiorly to the head of the fibula, external tuberosity of the tibia, lower part of the patella, ligamentum patellae, and tubercle, and front of the internal tuberosity, of the tibia. In the leg it is attached to the crest of the tibia, from which it is prolonged back- wards over the inner surface to be attached to the internal border. It is also attached to the antero-extemal and postero-external borders of the fibula. At the ankle the deep fascia is attached to the internal and external malleoli. Over the inner surface of the tibia and at its malleolar attachments it becomes closely incorporated with the periosteum. The chief direction of the fibres of the fascia is vertical. There are, however, superadded transverse fibres behind the knee-joint and in the vicinity of the ankle-joint, in which latter region important annular hgaments are formed. 498 A MANUAL OF ANATOMY The part of the fascia behind the knee-joint presents an opening for the passage of the short saphenous vein. In the region of the gastrocnemius and over the inner surface of the tibia the deep fascia is very thin. Over the front and outer parts of the leg, however, more especially in the upper half, it attains considerable strength and density, and there it gives origin by its deep surface to the super- ficial fibres of the muscles which it covers. In the region of the knee-joint it receives many strong accessions of fibres from the tendons of the quadriceps extensor cruris, biceps femoris, sartorius, gracilis, and semitendinosus. Four expansions are given off from its deep surface, whkh are called intermuscular septa — anterior, antero - external, postero- external, and posterior or transverse. The anterior intermuscular septum is limited to the upper third of the leg, where it extends between the tibialis anticus and extensor longus digitorum, to both of which muscles it gives partial origin. The antero -external inter- muscular septum is attached to the antero-external border of the fibula, and extends between the extensor longus digitorum and peroneus tertius on the anterior surface, and the peroneus longus and peroneus brevis on the external surface. The postero-external intermuscular septum is attached to the postero-external border of the fibula, where it extends between the peroneus longus and peroneus brevis on- the external surface, and the soleus and flexor longus hallucis on the posterior surface. The peroneus longus and peroneus brevis are thus completely shut off from the adjacent muscles by the two external intermuscular septa. These septa, along with the deep fascia at the surface and the external surface of the shaft of the fibula, form a long fibro-osseous canal which contains the peroneus longus and peroneus brevis. The posterior or transverse intermuscular septum is a broad expansion which passes transversely between the postero-external border of the fibula and the internal border of the tibia. It lies beneath the soleus and upon the deep muscles of the back of the leg, as well as upon the posterior tibial vessels and nerve, binding down the structures which it covers. Annular Ligaments. — These are situated in the region of the ankle-joint, and are thickened portions of the deep fascia. They serve to confine and maintain in position the strong tendons in that vicinity, and are three in number — external, internal, and anterior. The external annular ligament extends between the posterior border of the external malleolus and the outer border of the tuber calcis and adjacent portion of its outer surface. Its direction is downwards and backwards over the peroneal groove behind the external malleolus. The tendons of the peroneus longus and peroneus brevis pass beneath it, and are thereby kept in position. The tendon of the peroneus brevis is close to the bone, and that of the peroneus longus is directly behind the brevis tendon, both being invested by one common synovial sheath. The external annular ligament at its anterior border is continued forwards to THE LOWER LIMB 499 form two distinct fibrous sheaths for the peroneal tendons, which are here lying one above the other (the peroneus brevis tendon being the upper one) as they traverse the outer surface of the os calcis. Each tendon has now its own synovial investment, the common synovial sheath beneath the external annular ligament having sent forward two prolongations. The internal annular ligament is chiefly formed by a thicken- ing of the posterior or transverse intermuscular septum, but super- ficial to it there is also the proper deep fascia, though that is here very thin. This annular ligament extends between the posterior border of the internal malleolus and the internal border of the tuber calcis, and is directed downwards and backwards. Its upper border is continuous principally with the posterior intermuscular Tibialis Posticus -,. Flexor Longus Digitorum Posterior Tibial Artery and Vense Comites ^ Pt.~-- Posterior Tibial Nerve Flexor Longus Hallucis Plantaris Abductor Hallucis Internal Annular Ligament Fig. 240. — The Structures between the Internal Malleolus AND the Heel. septum. Its lower border gives origin on its deep aspect to the inner head of the abductor hallucis, and on its superficial aspect it is in part continuous with the lower limb of the Y division of the anterior annular ligament. The internal annular ligament passes over the grooves on the back of the lower end of the tibia, and converts these into canals for the flexor tendons and posterior tibial vessels and nerve. There are in all four canals, three of them being fibro-osseous and one fibrous. The relation of structures beneath this ligament, from the internal malleolus outwards to the tuber calcis, is as follows : (i) the tendon of the tibialis posticus, lying in the groove behind the internal malleolus close to the bone, and occupying one of the fibro-osseous canals ; (2) the tendon of the flexor longus digitorum, lying behind, and slightly external to, that of the tibialis posticus, and occupying the 500 A MANUAL OF ANATOMY fibrous canal ; (3) the internal vena comes, posterior tibial artery, external vena comes, and posterior tibial nerve, all occupying a second fibro-osseous canal ; (in cases of an early division of the posterior tibial nerve into external and internal plantar nerves these two nerves are found in this canal, the internal on the inner side of the internal vena comes, and the external on the outer side of the external vena comes) ; (4) the tendon of the flexor longus hallucis, occupying the third fibro-osseous canal, and lying in the groove at the outer part of the posterior border of the lower end of the tibia. Each of the three tendons mentioned is invested by a special synovial sheath. The internal annular ligament is pierced by the calcaneo-plantar branch of the posterior tibial nerve and the internal calcaneal branch of the posterior tibial artery. The anterior annular ligament is composed of two divisions. One division is situated on the front of the leg above the ankle- Tibialis Amicus Li Extensor Proprius Hallucis Tibialis Posticus Flexor Longus Digitorum _. Flexor Longus Hallucis Fig. 241. — The Synovial Sheaths at the Ankle (Internal View) (after L. Testut's 'Anatomie Humaine'). joint, and is called the superior anterior annular ligament. The other division lies in front of the bend of the ankle, and is called the inferior anterior annular ligament, anterior annular ligament proper, or lambdoid ligament. The superior anterior annular ligament is a broad band extending transversely between the anterior borders of the tibia and fibula, and measuring about 2 inches from above downwards. Imme- diately beyond it the deep fascia is exceedingly thin. The structures passing beneath it, in order from within outwards, are (i) tibialis anticus, (2) extensor proprius hallucis, (3) internal vena 2omes, (4) anterior tibial artery, (5) external vena comes, (6) anterior tibial nerve, (7) extensor longus digitorum, and (8) peroneus tertius. These structures occupy one common compartment, thCj tibialis anticus tendon alone being surrounded by a synovial sheath. THE LOWER LIMB 501 Tibialis Amicus Extensor Longiis _ Digitorum which is continuous with that investing it as it passes through the lambdoid ligament. The inferior anterior annular or lambdoid ligament is a more defined structure than the superior. Being placed in front of the ankle-joint, it serves to strap down the extensor tendons as they are entering upon their horizontal course on the dorsum of the foot. It may be likened either to the capital letter -< placed upon its side as indicated, or to the Greek letter '< (lambda), also laid upon its side, as shown. From the former resemblance it may be called the Y annular liga- ment. The outer part, which is a single narrow band, is attached to a depre'ssion on the upper surface of the os calcis at its anterior and outer part, immediately in front of the interosseous groove. This part forms a loop through which the tendons of the extensor longus digitorum and peroneus tertius pass, invested by one synovial sheath. From the fact that it forms a loop it has been called by Retzius the fundi form ligament. It gives partial origin to the extensor brevis digitorum, and at its inner end it is continued into two diverg- ing bands, upper and lower. The upper band is attached to the internal malleolus, and the tendon of the extensor proprius hallucis passes underneath it, being surrounded by a synovial sheath. The tendon of the tibialis anticus passes throu^ it, the main portion of the band being underneath that tendon, and a small expansion from it passing superficial to the tendon. The tendon of the tibialis anticus has its own synovial sheath, which is prolonged upwards from this point along the tendon, to be continuous with the synovial Veath investing it as it passes behind the superior anterior Fig. 242. — The Synovial Sheaths at the Ankle (Anterior View) (after L. Testut's 'Anatomie Humaine'). i 502 'A MANUAL OF ANATOMY annular ligament. The lower band of the lambdoid ligament is a comparatively weak structure which passes to the inner border of the foot, where it joins partly the plantar fascia and partly the lower border of the internal annular ligament. The tendons of the extensor proprius hallucis and tibialis anticus both pass underneath it. There are thus three distinct synovial sheaths in connection with the lambdoid ligament — one for the extensor longus digitorum and peroneus tertius, one for the extensor proprius hallucis, and one for the tibialis anticus, the latter being continuous with that which invests the tendon beneath the superior annular ligament. The dorsalis pedis artery, with its venae comites, and the dorsalis pedis nerve pass underneath or behind both bands of the fundiform ligament. Internal Aspect of the Leg. The internal surface of the tibia, except at its upper end, is sub- cutaneous. The deep fascia is here very thin, and is intimately incorporated with the periosteum. The structures met with on this aspect are the long saphenous vein and nerve, the posterior division of the internal cutaneous nerve, and the superficial branch of the anastomotica magna artery. The long saphenous vein lies about a finger's breadth from the internal border of the tibia, and it receives many tributaries from the anterior and posterior aspects of the leg. The long saphenous nerve lies immediately behind it. The posterior division of the internal cutaneous nerve is confined to the upper half of the inner aspect of the leg, and the superficial branch of the anastomotica magna artery ramifies in the upper third. At the upper end of the internal surface of the tibia the tendons of insertion of the sartorius, gracilis, and semitendinosus are met with, as well as the internal lateral ligament of the knee-joint. Proceeding in a direction backwards from the tubercle of the tibia to the internal border of the bone, the relation of these structures is as follows : (i) tendon of the sartorius ; (2) tendons of the gracilis and semitendinosus in the same vertical line, the gracilis being the higher of the two, and both being under cover of the sartorius ; and (3) the internal lateral ligament of the knee-joint. The tendons of the gracilis and semitendinosus cross the internal lateral ligament in a forward direction, and are separated from it and the subjacent bone by a bursa, which furnishes an expansion to separate them from the more superficially placed sartorius. The portion of the internal lateral ligament met with in this region is a long, flat, expanded band, attached to the internal border, and adjacent portion of the internal surface, of the tibia, upon which it descends for fully 3 inches. The inffrior internal articular artery passes transversely forwards underneath it, below the internal tuberosity of the tibia ; and beneath the posterior border of the ligament the chief tendon of the semimembranosus passes to be inserted into the horizontal groove on the posterior surface of the internal tuberosity. THE LOWER LIMB 503 Musculo- cutaneous i Anterior Aspect of the Leg and Dorsum of the Foot Musculo-cutaneous Nerve (Superficial Peroneal). — This nerve is one of the terminal branches of the external popliteal, arising from that nerve on the outer side of the neck of the fibula, where it lies between the bone and the peroneus longus. It then descends in the antero-external intermuscular septum, lying between the extensor longus digitorum in front, and the peroneus longus and peroneus brevis behind. When it reaches the junction of the upper two- thirds and lower third of the leg, it becomes cutaneous by piercing the deep fascia, and almost immediately afterwards it divides into its two terminal branches, internal and external. Branches. — The branches of the nerve are as follows : muscular to the peroneus longus and peroneus brevis ; and cutaneous to the integument of the front of the leg in its lower third, which arises as soon as the nerve pierces the deep fascia. The internal terminal branch descends to the dorsum of the foot, lying superficial to both divisions of the anterior annular hgament. It then divides into two branches, inner and outer. The inner branch supplies twigs to the integument of the internal malleolus and inner side of the foot, which communicate with the terminal part of the long saphenous nerve, and it then becomes the dorsal digital nerve of the inner side of the great toe. It gives a communicating branch to the dorsalis pedis nerve as that lies upon the first dorsal interosseous muscle. The outer branch passes to the cleft between the second and third toes, where it divides into two dorsal collateral digital nerves for the supply of the contiguous sides of these toes. The external terminal branch, like the internal, descends to the dorsum of the foot, and also lies superficial to both divisions of the anterior annular ligament. On the dorsum of the foot it divides into two branches, inner and outer. The inner branch passes to the cleft between the third and fourth toes, and the Older to the cleft between the fourth and fifth toes. At these clefts the inner and outer branches divide each into two dorsal collateral digital nerves for the supply of the contiguous sides of the third and fourth, and fourth and fifth toes. The outer branch in its course supplies twigs to the integument of the Fig. 243.— ^Diagram of the Nerves of the Foot (Dorsal Aspect). 504 A MANUAL OF ANATOMY external malleolus and outer border of the foot which communicate with the terminal part of the short saphenous nerve. Summary of the Distribution of the Musculo-cutaneous Nerve. — The nerve is distributed to the peroneus longus, peroneus brevis, integument over the front of the leg in its lower tliird, integument of the malleolar regions and outer and inner borders of the foot, and the integument of (i) the inner side of the great toe, and (2) the contiguous sides of the second and third, third and fourth, and fourth and fifth toes, all on their dorsal aspects. The dorsal digital nerve of the outer side of the fifth toe is the terminal part of the short saphenous nerve. The dorsal collateral digital nerves for the supply of the contiguous sides of the great toe and second toe are derived from the dorsalis pedis nerve, which is the continuation of the anterior tibial nerve. Muscles. Tibialis Anticus— Ongw.— (i) The external tuberosity of the tibia at its lower part ; (2) the upper two-thirds of the external surface of the shaft of the tibia and adjacent portion of the anterior surface of the interosseous membrane ; and (3) the deep fascia, and the anterior intermuscular septum which lies between it and the extensor longus digitorum in the upper third of the leg. Insertion. — ^The tendon, having traversed the groove on the inner surface of the internal cuneiform bone, divides into two slips. The posterior slip is inserted into an oval impression at the lower part of the inner surface of the internal cuneiform bone, and the anterior slip is inserted into the inner surface of the tuberosity on the plantar aspect of the base of the first metatarsal bone. Nerve-supply. — The anterior tibial nerve. Action. — (i) To flex the foot upon the leg, and (2) to raise the inner border of the foot, thereby inverting the sole. Extensor Proprius or Longus Hallucis— Ongm. — The middle two- four ihs of the anterior surface of the shaft of the fibula, and the adjacent portion of the anterior surface of the interosseous mem- brane. Insertion. — ^The dorsal surface of the base of the distal phalanx of the great toe. Nerve-supply. — ^The anterior tibial nerve. Action. — (i) To extend the distal phalanx of the great toe, and (2) to flex the foot upon the leg. The extensor proprius hallucis is a very narrow muscle which lies deeply between the tibialis anticus and extensor longus digitorum, both of which conceal it until its tendon appears on the fiont of the lower part of the tibia. Extensor Longus Digitorum. — Origin. — (i) The external tuber- osity of the tibia ; (2) the head and upper three-fourths of the anterior surface of the shaft of the fibula ; (3) the anterior surface of the interosseous membrane in its upper fourth ; (4) the inter- muscular septa between it and adjacent muscles ; and (5) the deej) fascia. Insertion. — ^The second and distal phalanges of the four outer toes. The four tendons pass to the dorsal aspects of the metatarso- phalangeal joints of the four outer toes. At this point they broaden THE LOWER LIMB 505 out into expansions which receive the tendons of the lurabricales and interosseous muscles. In the case of the tendons destined for the second, third, and fourth toes, their expansions are also joined by the outer three tendons of the extensor brevis digitorum. Each tendinous expansion passes forwards over the dorsum of the first phalanx, and at its distal end divides into three 'bands. The middle band is inserted into the dorsal aspect of the base of the second phalanx. The two lateral bands, having united, are inserted into the dorsal aspect of the base of the distal phalanx. Nerve-supply. — The anterior tibial nerve. Action. — (i) To extend the second and distal phalanges of the four outer toes, and (2) to flex the foot upon the leg. Peroneus Tertius--Ong'm. — (i) The anterior surface of the shaft of the fibula in its lower fourth, except for an inch or more below, and (2) the adjacent portion of the anterior surface of the inter- osseous membrane, and the antero-external intermuscular septum between the muscle and the peroneus brevis. Insertion. — ^The dorsal surface of the base of the fifth metatarsal bone. Nerve-supply. — The anterior tibial nerve. Action. — (i) To flex Vie foot upon the leg, and (2) to raise the outer border of the foot slightly. The peroneus tertius is to be regarded as a detached portion of the extensor longus digitorum. Anterior Tibial Artery. — This vessel is one of the terminal branches of the popliteal artery. It commences at the lower border of the popliteus muscle on a level with the lower border of the tubercle of the tibia (fully ij inches below the level of the upper surface of the head of that bone), and it terminates on the anterior liga- ment of the ankle-joint midway between the two malleoli by becoming the dorsalis pedis artery. Being placed at its commence- ment on the back of the leg, the vessel passes at first forwards between the two heads of the tibialis posticus, and over the upper border of the interosseous membrane, where it lies below the superior tibio-fibular articulation. (The artery sometimes passes through an aperture in the upper part of the interosseous membrane, called the superior hiatus.) Having reached the front of the leg, the vessel changes its course somewhat abruptly, and then descends in close contact with the anterior surface of the interosseous mem- brane, until it reaches the junction of the upper two-thirds and lower third of the leg. Beyond this point it gradually inclines towards the anterior aspect of the tibia, and in the lower fourth it lies upon that surface, and finally upon the anterior ligament of- the ankle-joint. The course of the vessel on the anterior aspect of the leg corresponds with a line drawn from the superior tibio- fibular articulation to the centre of the front of the ankle-joint midway between the two malleoli. Relations — On the Back of the Leg. — The artery lies here between the two heads of the tibialis posticus, having the lower border of the I 5o6 A MANUAL OF ANATOMY popliteus muscle above it, and being under cover of the gastro- cnemius. On the Front of the Leg — Superficial. — In the upper three-fourths the artery is deeply placed, and is covered by the integument, and the meeting between the tibialis anticus on the inner side and the extensor longus Recurrent Articular Nerve Ext. Popliteal Nerve -Musculo-cutaneous N. Anterior Tibial Nerve Anterior Tibial Artery and Nerve digitorum and exten- sor proprius hallucis on the outer side. In the lower fourth the vessel is compara- ■tively superficial, the muscles having now ended in their ten- dons, and it is covered by the integument, upper division of the anterior annular liga- ment, and extensor proprius hallucis, the tendon of the latter muscle crossing it from without inwards about 3| inches above the ankle-joint. Deep. — Anterior surface of the interosseous mem- j brane (to which it is ' bound by fibrous tissue), anterior sur- face of the tibia in lower fourth, and the anterior ligament ofii the ankle-joint. Ex-t ternal. — E x t e n s o r| longus digitorum irj| the upper fourth olf the leg, extensor pro|> prius hallucis in th(| middle two - fourths| and extensor longu | digitorum again iif the lower fourth. /«| ternal. — Tibialis anticus in the upper three- fourths, and extensG| pro|)rius hallucis in the lower fourth. | The artery is accompanied by two venae comites, which closel| , embrace its sides and communicate with each other at frequer|,i intervals by transverse branches, crossing superficial to the vesse| i These venae comites, having passed backwards over the upp<| ; Peroneus. Tertius .Extensor Proprius Hallucis . Extensor Longus Digitorum .Musculo-cutaneous N. (Cutaneous Portion) \ Peroneus Brevis . Peroneus Longus Fig. 244. -The Front of the Left Leg (Deep Dissection). THE LOWER LIMB 507 border of the interosseous membrane (or through a superior hiatus in it), join to form one trunk, which unites with the trunk formed by the junction of the venae comites of the posterior tibial artery to form the pophteal vein. The anterior tibial artery in the upper fourth of the leg is separated from the anterior tibial nerve by the fibula and the extensor longus digitorum, the artery having passed forwards between the tibia and fibula, and the nerve having wound obliquely round the outer side of the bone. At the junction of the upper fourth and lower three- fourths of the leg the nerve, having pierced the antero-extemal intermuscular septum and extensor longus digitorum, comes into contact with the artery, along the outer side of which it descends for a short distance. It then lies on the artery for a little, and finally it again takes up a position upon the outer side of the vessel in the lower fourth of the leg. Branches. — The branches from above downwards are as follows : posterior tibial recurrent ; superior fibular ; anterior tibial re- current ; muscular ; internal malleolar ; and external malleolar. The posterior tibial recurrent artery is an inconstant branch. When present it arises from the anterior tibial artery whilst on the back of the leg. Its course is upwards beneath the popliteus muscle, and it is distributed to that muscle, the posterior liga- ment of the knee-joint, and the superior tibio-fibular articulation. It anastomoses with the external and internal inferior articular arteries on the back of the leg. The superior fibular artery also arises from the anterior tibial whilst on the back of the leg. Its course is outwards behind the neck of the fibula, where it pierces the soleus, and it is distributed to that muscle, the peroneus longus, and the adjacent integument. The anterior tibial recurrent artery arises from the anterior tibial whenever it reaches the front of the leg. Entering the upper part of the tibialis anticus, to which, as well as to the superior tibio-fibular joint, it gives branches, it ascends to the external tuberosity of the tibia, in company with the recurrent articular branch of the external popliteal nerv^e. Its terminal branches anastomose with the external and internal inferior arti- cular arteries. The muscular branches are very numerous, and are distributed chiefly to the muscles on the anterior aspect of the leg. Some offsets, however, reach the integument, and others, piercing the interosseous membrane, terminate in the tibialis posticus, in which I they anastomose with branches of the posterior tibial artery. ! The internal malleolar artery is a small branch which arises I from the inner side of the anterior tibial near the lower end of the I tibia. Its course is inwards beneath the tendon of the tibialis anticus, and it is distributed over the internal malleolus, where it i anastomoses with (i) the internal malleolar branches of the pos- 5o8 A MANUAL OF ANATOMY terior tibial, (2) the superior internal tarsal branch of the dorsalis pedis, and (3) branches of the internal plantar, thus forming the internal malleolar anastomosis. The external malleolar artery arises from the outer side of the anterior tibial at a slightly lower level than the internal malleolar. Its course is outwards beneath the tendons of the extensor longus digitorum and peroneus tertius, and it is distributed over the external malleolus, where it anastomoses with (i) the anterior peroneal, (2) the posterior peroneal, and (3) the external tarsal branch of the dorsalis pedis, thus forming the external malleolar anastomosis. The veins which accompany the branches of the anterior tibial artery are, in each case, arranged as venae comites, and they termi- nate as tributaries of the anterior tibial venae comites. Varieties — i . Origin. — The vessel may arise from the pophteal at the upper border of the popUteus muscle. In these cases it may descend on the posterior surface of that muscle (this being the more frequent position), or it may pass deeply in front of it. 2. Course. — The vessel in the lower fourth of the leg may be found upon the fibula instead of the tibia, in which cases it makes a sudden bend at the ankle-joint to become the dorsalis pedis artery. In very rare cases the vessel may become superficial at the centre of the leg instead of in the lower fourth. 3. Size. — The vessel is occasionally very small, and, if the diminution in size is very pronounced, it may fail to furnish the dorsalis pedis artery, in which cases that vessel is supplied by the anterior peroneal. Anastomoses round the Knee- Joint. — ^The arteries which take part in these anastomoses are as follows : (i) the two superior, and the two inferior, external and internal articular branches of the popliteal ; (2) the long descending branch of the external circum- flex of the profunda femoris ; (3) the anastomotica magna of the superficial femoral: ; (4) the fourth perforating of the profunda femoris ; and (5) the posterior tibial recurrent (inconstant), and the anterior tibial recurrent, both of which are branches of the anterior tibial artery. For the special anastomoses of the foregoing arteries see the descriptions of the individual vessels, and Fig. 251. The anastomoses are divided into superficial and deep, the former being placed superficial to the patella, and the latter being in contact with the lower end of the femur and the head of the tibia. Three transverse arches are to be noted anteriorly as follows : one lies in the substance of the crureus, just above the patellar i, surface of the femur, and is formed by branches of the superior [i external articular of the popliteal, and the deep branch of the | anastomotica magna of the superficial femoral. A second arch ji lies in front of the head of the tibia, near the superior surface, jj and is formed by branches of the inferior external articular, ij and the superior internal articular. A third arch lies in front ^ff of the tibia just above the tubercle, and is formed by branches % of the anterior tibial recurrent, and the inferior internal articular ?; artery. THE LOWER LIMB 509 The terminal part of the anterior peroneal artery, having reached the front of the leg by passing through the inferior hiatus in the interosseous membrane, descends in front of the inferior tibio- fibular articulation under cover of the peroneus tertius, to both of which it furnishes branches. It finally takes part in the external malleolar anastomosis, along with (i) the external malleolar of the anterior tibial, (2) the external tarsal of the dorsalis pedis, and (3) the posterior peroneal. Anterior Tibial Nerve (Deep Peroneal). — ^This nerve is one of the terminal branches of the external popliteal. It commences upon the outer side of the neck of the fibula, where it lies between the bone and the peroneus longus, and it terminates at the anterior ligament of the ankle-joint, where it becomes the dorsalis pedis nerve. At first it is directed downwards, forwards, and inwards through the antero-external intermuscular septum and extensor longus digitorum, and it comes into contact with the anterior tibial artery at the junction of the upper fourth and lower three- fourths of the leg. It then descends in close contact with that artery as far as its termination, lying at first external to the vessel, then in front of it, and finally again on its outer side. The general relations of the nerve closely correspond with those of the artery on the front of the leg. Branches. — ^These are muscular and articular. The muscular branches supply the tibialis anticus, extensor longus digitorum, extensor proprius hallucis, and peroneus tertius. The articular branches arise from the lower part of the nerve, and are distributed to the ankle-joint and inferior tibio-fibular articulation. Anterior Tibial Gland. — This lymphatic gland is situated in front of the interosseous membrane at its upper part in close proximity to the anterior tibial artery. Its afferent vessels take up l5miph from the dorsum of the foot and anterior aspect of the leg in its more deeply-placed parts. The efferent vessels, which are usually two in number, pass backwards either above the interosseous membrane or through a superior hiatus in it, lying along the anterior tibial artery, and they become afferent vessels to the popliteal glands. Dorsum of the Foot. Deep Fascia. — This is a delicate membrane which is prolonged for\vards from the lambdoid ligament over the long extensor tendons. Two other thin layers of deep fascia are met with, one covering the extensor brevis digitorum, and the other covering the dorsal interosseous muscles and the dorsal surfaces of the metatarsal bones. Extensor Brevis Digitorum — Origin. — (i) The anterior part of the upper surface, and adjacent part of the external surface, ;of the OS calcis ; and (2) the outer single portion of the lower division of the anterior annular ligament — that is to say, the fundi- form ligament of Retzius. I Insertion. — Into the four inner toes, namely, the great toe, J second, third, and fourth, by means of four tendons in the following I 5IO A MANUAL OF ANATOMY manner ; the innermost tendon has a special insertion into the dorsal surface of the first phalanx of the great toe near its base. The other three tendons join the outer borders of the long extensor tendons which go to the second, third, and fourth toes, the union taking place at the metatarso-phalangeal joints. Nerve- supply. — The external branch of the dorsalis pedis nerve. Action. — (i) Innermost tendon. — ^This tendon extends the great toe at the metatarso-phalangeal joint, and it also acts as an adductor of that toe. (2) Second, third, and fourth tendons. — ^These extend the corresponding toes in conjunction with the long extensor tendons. In doing so they tend, by the obliquity of their direction, to draw the toes outwards, and in this way they counteract the opposite tendency of the long extensor tendons, which of themselves would incline the toes inwards. The muscle lies obliquely upon the dorsum of the foot, and is directed forwards and inwards. The innermost fleshy bundle is always the largest, and separates from the parent muscle sooner than the others. It has accordingly been regarded as a separate muscle, and as such is called the extensor brevis hallucis. Dorsalis Pedis Artery. — This vessel is the continuation of the anterior tibial artery. It commences at the anterior ligament of the ankle-joint, midway between the two malleoli, and terminates at the proximal end of the first interosseous space, where it divides into two branches, plantar or perforating, and arteria dorsalis hallucis or first dorsal interosseous artery. The course of the vessel is along the inner part of the dorsum of the foot, and is indicated by a line drawn from the centre of the front of the ankle-joint, midway between the two malleoli,, to the proximal end of the first interosseous space. Relations — Superficial. — ^Theskin, superficial fascia, lower division of anterior annular ligament, deep fascia, and innermost tendon of the extensor brevis digitorum, which crosses it from without inwards near its termination. Deep. — Upper border of the head of the astragalus, navicular, middle cuneiform, base of second meta- tarsal, and the corresponding ligaments. External. — External vena comes, dorsalis pedis nerve, innermost tendon of the extensor longus digitorum, and, near its termination, the innermost tendon of the extensor brevis digitorum as it is about to cross the artery. Internal. — Internal vena comes, tendon of the extensor proprius hallucis, and, near its termination, the innermost tendon of the extensor brevis digitorum after it has crossed the vessel. The artery is firmly bound down by connective tissue to the subjacent bones and ligaments. It is .accompanied by two venae comites, one on either side, which communicate with each other by transverse branches lying superficial to the vessel, and ultimately become the vense comites of the anterior tibial artery. Branches. — The branches are as follows : internal tarsal, external tarsal, metatarsal, arteria dorsalis hallucis or first dorsal THE LOWER LIMB 5" interosseous, and plantar or perforating, which latter divides in the sole of the foot into arteria magna or princeps hallucis, or first plantar interosseous, and plantar communicating, which latter completes the plantar arch. The internal tarsal arteries are two or three in number, and supply the adjacent structures on the inner border of the foot, where they anastomose with branches of the internal plantar Anterior Peroneal Artery External Malleolar Artery External Malleolus Tarsal Artery Metatarsal Artery ._ Posterior Perforating Artery Second, Third, and. Fourth Dorsal Interosseous Arteries Anterior Tibial Artery Internal Malleolar Artery Internal Malleolns Tibialis Anticus Dorsalis Pedis Artery -----Internal Tarsal Arteries Plantar Branch of Dor- salis Pedis Artery . First Dorsal Interosseous Artery . Anterior Perforating Artery Fig. 245. — The Arteries on the Dorsum of the Right Foot (.\FTER L. Testut's ' Anatomie Humaine '). artery. The highest of them also takes part in the internal malleolar anastomosis. The external tarsal artery passes outwards beneath the extensor ■ IS digitorum. It suppUes the adjacent structures, and at the outer border of the foot it anastomoses with the metatarsal and external plantar arteries. It also takes part in the external malleolar stomosis. n 512 A MANUAL OF ANATOMY The metatarsal artery arises on a level with the bases of the metatarsal bones, over which it passes on its way to the outer border of the foot, being under cover of the extensor brevis digitorum. At the outer border it anastomoses with the tarsal and external plantar arteries. The vessel forms a slight arch with the convexity directed forwards. From the concavity of the arch a few recurrent branches are given off to the tarsal articulations. From the convexity three dorsal interosseous arteries- are given off, which pass forwards over the outer three interosseous spaces. Kt the level of the metatarso-phalangeal joints each divides into two dorsal collateral digital arteries, which supply the contiguous sides of the second and third, third and fourth, and fourth and fifth toes. The most external dorsal inter- osseous artery, before it divides into its two collateral branches, furnishes a single dorsal digital artery to the outer side of the fifth or little toe. At the proximal end of the second, third, and fourth interosseous spaces the three dorsal interosseous arteries (in them- selves small) are reinforced each by a posterior perforating artery, the three posterior perforating arteries being branches of the plantar arch. At the distal end of these interosseous spaces the three dorsal interosseous arteries are usually further reinforced each by an anterior perforating artery, the three anterior perforating arteries being branches of the three compound plantar digital arteries from the plantar arch. The arteria dorsalis hallucis is the first dorsal interosseous artery. Arising from the terminal part of the dorsalis pedis artery, it continues the direction of that vessel, and passes forwards over the first interosseous space. On reaching the cleft between the great toe and the second it divides into two dorsal collateral digital branches for the supply of the contiguous sides of these two toes, and it furnishes a small single dorsal digital artery for the supply of the inner side of the great toe. The dorsalis hallucis artery is not reinforced by any posterior perforating branch. Before, how- ever, dividing into its digital branches it receives an anterior per- forating artery, which is derived from the arteria magna or princeps hallucis in the sole. The dorsal digital arteries as they pass along the sides of the toes communicate with each other across their dorsal aspects, and also with the corresponding plantar digital arteries. The plantar or perforating artery will be described in connection with the sole of the foot. Varieties of Dorsalis Pedis Artery— i. Origin.— The vessel maybe the con- tinuation of the anterior peroneal artery. 2. Course. — The vessel often describes a considerable curve outwards before it reaches the proximal end of the first interosseous space. In these cases the artery may terminate at the back of the second interosseous space instead of the first. 3. Branches. — There is considerable deviation from the normal in respect of branches. The branch most affected is the metatarsal artery. This may arise in common with the tarsal branch. The metatarsal arch is often very i THE LOWER LIMB -513 indefinite. The metatarsal arterj- is sometimes absent, and when this occurs the dorsal interosseous arteries of the outer three interosseous spaces are usually furnished by the three posterior perforating arteries from the plantar arch, or, it may be, by the tarsal artery. Dorsalis Pedis Nerve.— This nen-e is the continuation of the anterior tibial. It commences at the anterior hgament of the ankle-joint, and terminates at the distal end of the first inter- osseous space by dividing into two dorsal collateral digital nerves Peroneus Brevis Peronetis Longus txtenjor Longas Digitorum Ext. Malleolar .-Vnastomosis Peroneus Tertius ■ - Metatarsal .Artery Musculo-cutaneous Nerx-e j,__i_:-^i Upper Band of Anterior ^ ^ ^^^ Annular Ligament Extensor Proprius Hallucis TiiA iTTni Tibialis .Anticus Lower Band of Anterior .-Vnnular Ligament External Branch of Dorsalis Pedis Nerve Extensor Brevis Digitorum ^T' Internal Tarsal Arteries Dorsalis Pedis Nerve Dorsalis Pedis Artery Communicating Branch between Musculo-cutaneous and Dorsalis Pedis Nerves First Dorsal Interosseous Artery Fig. 24*^. — Dissection of the Dorsum of the Right Foot. for the supply of the contiguous sides of the great toe and the second. Its relations correspond with those of the dorsalis pedis artery, on the outer side of which it lies, with the inter\^ention of the external vena comes. As the nerve passes over the dorsal aspect of the first interosseous space it is reinforced by an offset from the inner branch of the internal division of the musculo-cutaneous Jier\-e, I 33 5M A MANUAL OF ANATOMY Branches. — The branches are as follows : external or tarsal, interosseous, and terminal. The external or tarsal branch arises from the dorsalis pedis nerve as soon as it emerges from beneath the lower division of the anterior annular ligament. It passes outwards beneath the extensor brevis digitorum, and in that situation it presents a gangliform enlargement from which branches are furnished to the extensor brevis digitorum and the tarsal articulations. Three interosseous branches also arise from it, which pass over the dorsal aspects of the three outer interosseous spaces, supply- ing the adjacent tarso-metatarsal and metatarso-phalangeal articulations. The interosseous branch, which lies over the second interosseous space, usually sup- plies a small twig to the dorsal inter- osseous muscle of that space. The interosseous branch passes over the dorsal aspect of the first interosseous space, supplying the adjacent tarso-meta- tarsal and metatarso-phalangeal articula- tions. It also gives a twig to the first dorsal interosseous muscle. The terminal branches are the dorsal collateral digital nerves for the con- tiguous sides of the great toe and the second. Dorsal Venous Arch. — ^This arch is superficial to the deep fascia, and is situated well forward upon the dorsum of the foot, being about 2 inches from the webs of the toes. The convexity of the arch, which is but slight, is directed forwards. It receives (i) the dorsal digital veins, (2) small veins from the dorsum of the foot, and (3) the efferent interdigital veins which come from the plantar transverse venous arch situated near the clefts of the toes. The blood is carried away from the dorsal venous arch by the two saphenous veins. The internal or long saphenous vein arises from the inner end of the arch, and, having received branches from the superficial plantar venous plexus which turn round the inner border of the foot, it passes in front of the internal malleolus, and thus reaches the inner side of the leg. Its further course has been previously described. The external or short saphenous vein arises from the outer ends of the arch, and, having received branches from the superficial Fig. 247. — The External Saphenous Vein and its Tributaries. THE LOWER LIMB 515 plantar venous plexus which turn round the outer border of the foot, it passes below and behind the external malleolus, and thus reaches the back of the leg. It then passes upwards and inwards, lying at first to the outer side of the tendo Achillis. On reaching the middle line of the calf, it ascends in the groove between the two heads of the gastrocnemius until it arrives at the interval between the condyles of the femur. Up to this point the vein is superficial to the deep fascia. It now, however, passes through an opening in that fascia, and terminates in the pophteal vein. As high as the centre of the calf the vein is accompanied by the short saphenous nerve, which Ues on its outer side. From the centre of the calf up to where the vein pierces the deep fascia it is accompanied by the terminal part of the small sciatic nerve and the middle superficial or cutaneous sural artery. It receives many tributaries from the calcaneal region, and from the outer and back parts of the leg, and it communicates at intervals with the venae comites of the posterior tibial and peroneal arteries. Just before it pierces the deep fascia a communicating branch passes upwards and inwards from it to join the long saphenous vein. The external or short saphenous vein is provided with about ten valves. External Aspect of the Leg. In this region the lateral cutaneous branch of the external pop- liteal nerve is met with. It supplies the integument of the outer side of the leg over about its upper two- thirds, as well as the adjacent integument of the sural region. Muscles. Peroneus Longus — Origin. — (i) The external aspect of the head of the fibula ; (2) the adjacent part of the external tuberosity of the tibia ; (3) the upper two-thirds of the external surface of the shaft of the fibula ; (4) the "antero-external and postero- external intermuscular septa; and (5) the deep fascia. Insertion. — ^The tendon of insertion divides into two parts. The main part is inserted into the outer side of the tuberosity on the plantar surface of the base of the first metatarsal bone, and the other into the lower and anterior part of the outer surface of the internal cuneiform bone. Nerve-supply. — ^The musculo-cutaneous nerv^e. Action. — (i) To extend the foot upon the leg ; (2) to abduct or turn out the fore part of the foot ; (3) to depress the inner border of the foot, the efiect of which is to raise the outer border and produce eversion of the sole ; and (4) to support and strengthen the transverse arch of the foot. The tendon descends behind that of the peroneus brevis, and, ; along with it, passes through the groove behind the external mal- leolus and beneath the external annular Ugament, the two tendons ' having one synovial sheath in common. After leaving the malleolar groove, the tendon passes forwards on the outer surface of the os 5i6 A MANUAL OF ANATOMY calcis, where it occupies the groove below the peroneal spine or ridge. In this part of its course the tendon is surrounded by a fibrous sheath, which is derived from the lower border of the external annular ligament, and it is here invested by a special synovial sheath, which is a prolongation of that beneath the external annular ligament. It then turns round the peroneal notch on the External Popliteal Nerve Tendon of Biceps Long External Lateral Ligament Peroneus Longus Peroneus Brevis Tendo Achillis Extensor Proprius Halluois Extensor Longus Digitoruni Peroneus Tertius Upper Division of Ant. Annular Ligament ^ Lower Division of Ant. Annular Lig. ^Extensor Brevis Digitorum Tendon of Peroneus Tertius Fig. 248. — Muscles of the Leg (External View). outer border of the cuboid, and traverses the peroneal groove on the plantar surface of that bone, which is converted into a fibro- osseous canal by an expansion derived from the long plantar ligament. Finally, after leaving this fibro-osseous canal, in which it is invested by a special synovial sheath, the tendon crosses th sole of the foot to its twofold insertion, taking a direction forwartl I THE LOWER LIMB 5^1 and inwards. In that part of the tendon which turns round the outer border of the cuboid a sesamoid fibro-cartilage is found. Peroneus Brevis — Origin. — (i) The lower two-thirds of the ex- ternal surface of the shaft of the fibula, except the last 2 inches ; (2) the antero-extemal and postero-external intermuscular septa ; and (3) the deep fascia. Insertion. — ^The tuberosity on the outer side of the base of the fifth metatarsal bone. From the tendon of insertion a slip is often given to the long extensor tendon of the httle toe. Nerve-supply. — ^The musculo-cutaneous nerve. Action. — (i) To extend the foot upon the leg, but in a feeble manner ; (2) to abduct or turn out the fore part of the foot ; and (3) to raise directly the outer border of the foot, thus producing eversion of the sole. The middle third of the external surface of the fibula is occupied by both peroneus longus and peroneus brevis, the former arising from the posterior half, and the latter from the anterior half, so that the two muscles overlap. The tendon of the peroneus brevis passes through the groove behind the external malleolus with the tendon of the peroneus longus, which is directly behind it. Both tendons lie beneath the external annular ligament, where they have one synovial sheath in common. After leaving the malleolar groove the tendon of the peroneus brevis passes forwards on the outer surface of the os calcis, where it occupies the groove above the peroneal spine or ridge. In this part of its course the tendon is surrounded by a fibrous sheath, which is derived from the lower border of the external annular ligament, and it is here invested by a special synovial sheath, which is a prolongation of that beneath the external annular ligament. After leaving the outer surface of the OS calcis the tendon passes over the cuboid bone, and so reaches its insertion. On the outer surface of the os calcis the two peroneal tendons are completely separated from each other, that of the brevis being above that of the longus. The separation is effected partly by a strong fibrous septum, and partly by the peroneal spine or ridge. The peroneus longus and peroneus brevis are contained in a fibro- osseous canal formed by the deep fascia, the intermuscular septum on each side, and the external surface of the shaft of the fibula. Posterior Aspect of the Leg. Superficial Structures. — The following superficial structures are met with in this region : the external or short saphenous vein, the cutaneous sural branches of the pophteal artery, the terminal part of the small sciatic ner\'e, the ramus communicans tibialis nerve, the ramus communicans fibularis nerve, and the external or ?hort saphenous nerve. These, except the last named, have been already described. 5i8 A MANUAL OF ANATOMY External or Short Saphenous Nerve. — This nerve is formed by the union of the ramus communicans tibiahs of the internal pop- Hteal and the ramus communicans fibularis of the external pop- liteal. The union takes place at, or just below, the centre of the calf, and superficial to the deep fascia. The nerve descends on the outer side of the short saphenous vein, and external to the tendo AchilHs. It then passes behind and below the external malleolus, and so reaches the outer border of the foot, along which it passes to the outer side of the little toe, of which it is the dorsal digital nerve. The nerve supplies the integument of the back of the leg in its lower half, the external malleolar region, the outer side of the calcaneum, and the outer border of the foot and outer side of the little toe. It also furnishes articular branches to the ankle- joint, and the astragalo-calcaneal articulation. Muscles. — The muscles of the back of the leg are divided into two groups — superficial and deep. Superficial Group. — This group comprises the gastrocnemius, soleus, and plantaris, which are collectively called the sural (calf) muscles. Gastrocnemius. — This muscle is so named because it forms the ' belly of the leg,' that is to say, the fleshy enlargement at the back of the leg which is called the calf. Origin. — ^The external head arises from (i) the outer surface of the external condyle of the femur immediately above the commence- ment of the popliteal groove, and close behind and above the external tuberosity ; and (2) the adjacent part of the posterior surface of the femur, vertically, for at least an inch immediately external to the lower part of the external supracondylar ridge. The internal head arises from (i) an oblique impression on the posterior surface of the femur immediately above the internal condyle, and extending inwards for fully an inch as far as the adductor tubercle ; and (2) the lower extremity of the internal supracondylar ridge for a short distance. Insertion.— The fleshy part of the muscle gives place to a flat tendon, which joins the subjacent tendon of the soleus at the centre of th» leg to form the tendo Achillis. Through this latter the gastrocnemius is inserted into the middle zone on the posterior surface of the tuber calcis, a bursa intervening between the tendon and the upper zone. Nerve-supply. — ^The internal popliteal nerve, which furnishes two branches, one for each head. Action. — Acting from its origin, the muscle is a powerful extensor of the foot upon the leg, thus raising the heel. Acting from its insertion, as when the ankle-joint is fixed by the muscles of the anterior aspect of the leg, the gastrocnemius is a flexor of the knee-joint, flexing the femur upon the tibia. The two heads come into contact at the junction of the upper sixth and lower five-sixths of the leg, and so they limit the lower part of the popliteal space. After coming together they are sepa- THE LOWER LIMB 519 rated superficially by a longitudinal groove, and when the lips of this groove are held apart a tendinous band or raphe is seen to he between them. The fleshy fasciculi of both heads are short and oblique, and they terminate upon the lower tendon, which extends upwards upon the deep or anterior surface of the muscle in the form of an expanded aponeiuosis. The shortness of the fleshy bundles gives the muscle great power of action, but the range of movement is limited. The internal head is separated from the tendon' of the semimem- branosus by a large bursa, called the popliteal bursa, which fre- quently (one in five) communicates with the synovial membrane of the knee-joint. Another small bursa is situated a little higher, between the internal head and the posterior surface of the femur. In the external head a sesamoid fibro-cartilage is occasionally met with. Soleus. — ^This flat muscle has been so named from its resemblance to a sole-fish. Origin. — (i) The posterior surface of the head, and the upper third of the posterior surface of the shaft, of the fibula ; (2) the postero-external intermuscular septum ; (3) the fibrous arch thrown over the popliteal vessels and internal popliteal nerve ; (4) the oblique or popliteal line of the tibia ; and (5) the internal border of the tibia over its middle third. Insertion.^-The tendon joins that of the gastrocnemius at the centre of the leg to form the tendo Achillis, which is inserted into the middle zone on the posterior surface of the tuber calcis. Nerve-supply. — (i) The internal popliteal nerve, the branch from which enters the muscle on its superficial or posterior surface near the upper border ; and (2) the posterior tibial nerve, the branch from which enters the muscle on its deep or anterior surface near the centre of the leg. Action. — Acting from its origin the muscle is a powerful extensor of the foot upon the leg, thus raising the heel. Acting from its insertion, as when the ankle-joint is fixed by the muscles of the anterior aspect of the leg, the soleus steadies the leg upon the foot. The fasciculi of this muscle are short and oblique, like those of the gastrocnemius. It has therefore great power of action, but its range of movement is limited. Only a hmited number of the fibres of the soleus spring directly from the bony surfaces. The majority arise from two aponeurotic laminae, which are almost entirely concealed within the muscle, and which descend, one from the fibula, and the other from the oblique line of the tibia and the fibrous arch over the popliteal vessels. The fibres which arise from the anterior surfaces of these two laminae terminate upon a [ median tendinous band or raphe, which is deeply placed, and those i arising from their posterior surfaces end upon a broad expanded aponeurosis, which covers the superficial or posterior surface of 1 the muscle, giving it an appearance similar to that of the deep or anterior surface of the gastrocnemius. This aponeurosis is 520 A MANUAL OF ANATOMY simply an upward expansion of the tendon of insertion of the muscle. Tendo Achillis.* — This very strong tendon is formed by the union of the tendons of the gastrocnemius and soleus. It extends from the centre of the leg to the prominence of the heel, and is inserted into the middle zone on the posterior surface of the tuber calcis, a bursa intervening between it and the upper zone. The tendo Achillis is at first broad and comparatively thin. As it descends, it becomes narrower and thicker until it reaches a point about i| inches above the tuber calcis, beyond which it again broadens to its insertion. The short saphenous vein and nerve lie on its outer side, the tendon of the plantaris and the posterior tibial vessels and nerve on the inner side, and a large quantity of fat beneath it. Plantaris — Origin. — (i) The lower 2 inches of the external supracondylar ridge of the femur, internal to the external head of the gastrocnemius ; and (2) the adjacent part of the posterior ligament of the knee-joint. Insertion. — The middle zone on the posterior surface of the tuber calcis immediately to the inner side of the tendo Achillis, with which it is closely connected. It may, however, terminate upon the inner border of the tendo Achillis, in the deep fascia of the leg, upon the internal annular ligament, or in the plantar fascia. Nerve-supply. — ^The internal popliteal nerve. Action. — (i) The plantaris acts as a very weak auxiliary to the gastrocnemius. (2) From its connection with the posterior liga- ment of the knee-joint the muscle has a slight action as a retractor of that ligament during flexion of the joint, and thus it guards the ligament against being nipped or pressed upon by the articular surfaces of the femur and tibia. The fleshy belly of the muscle is limited to the upper sixth. The tendon is very narrow and descends inwards between the gastrocnemius and soleus. It is also very extensible, so that when grasped by the fingers and stretched laterally it can be drawn out into a ribbon of about 2 inches in breadth. The plantaris, which is sometimes absent, is a vestigial muscle, being the crural remains of a superficial flexor of the toes, the plantar portion of the tendon of which, having been divorced, remains persistent as the central f division of the plantar fascia. The homologue of the plantaris in the upper limb is the palmaris longus. Deep Group. — The muscles which comprise this group are four ■:; in number, namely, the popliteus, flexor longus digitorum, tibialis [i posticus, and flexor longus hallucis. The popliteus muscle is i; covered by the popliteal fascia, which is one of the modes of inser- j; tion of the semimembranosus. The other muscles, together with | * Being inserted into the heel, it has been called the tendo Achillis, becausie it was believed that the heel was the only part in which the Greek hero, Achilles, j Qould be wounded. ' | THE LOWER LIMB 521 the posterior tibial vessek and ner\'e, are covered by the posterior or transverse intermuscular septum. Popliteus — Origin. — (i) By a narrow round tendon from the front part of the horizontal portion of the popliteal groove on the outer surface of the external condyle of the femur, and (2) slightly from the posterior ligament of the knee-joint. Insertion. — (i) The popliteal surface of the tibia, and (2) the popliteal fascia which covers the muscle. Nerve-supply. — ^The internal popliteal nerve. The branch from this ner\e descends over the posterior surface of the muscle, and, turning round its lower border, enters the deep or anterior surface in its lower part. Action. — ^The muscle is a feeble flexor of the leg upon the thigh, and, when the knee-joint has been flexed, it acts as an internal rotator of the leg. The tendon of origin is within the capsular Ugament, and beneath the long external lateral hgament, of the knee-joint. Whilst within the joint it is in contact with the posterior and outer aspect of the external semilunar fibro-cartilage, which it grooves. It then pierces the capsule, and the fleshy 'ibres spread out in the manner of a fan as they diverge do^vn wards and inwards. The popliteal "fascia, which covers the muscle, represents part of the insertion of the semimembranosus muscle, and it is attached to the oblique or popliteal line of the tibia. Flexor Longus Digltorum (flexor perforans) — Origin. — (i) The inner division of the posterior surface of the shaft of the tibia, commencing at the oblique or popliteal line, and extending down- wards over the middle two-fourths of the bone ; (2) the posterior intermuscular septum which covers the muscle ; and (3) the inter- muscular septum bet\veen it and the tibiahs posticus on its outer side. Insertion. — By means of four tendons which go to the four outer toes, where each is inserted into the plantar surface of the base or proximal end of the distal phalanx. Nerve-supply. — ^The jxjsterior tibial nerve. Action. — (i)The muscle acts as a flexor of the distal phalanges of the four outer toes, and (2) when these have been flexed, it acts as an extensor of the foot upon the leg. The muscle crosses behind the tibiahs posticus obliquely from within outwards in the lower third of the leg. The tendon passes behind the internal malleolus and beneath the internal annular I ligament, Mng behind and slightly external to the tendon of the i tibialis posticus, and occupying a special, purely fibrous compart- ; ment, in which it is invested by a distinct synovial sheath. It I then enters the sole of the foot, where it passes for\s'ards and out- i wards to the middle line, crossing beneath the tendon of the flexor 1 longus hallucis, from which it receives a slip. On reaching the i middle hne it gives insertion to the flexor or musculus accessorius, ] and immediately afterwards it divides about the centre into four to 522 A MANUAL OF ANATOMY tendons which, after having given origin to the four lumbricales muscles, go to the four outer toes. Each tendon, as it passes along the plantar surface of a toe, has a tendon of the flexor brevis digitorum lying close beneath it as far as the second phalanx, the two tendons occupying a fibro-osseous canal lined by a synovial membrane, which furnishes a separate investment to each tendon. Opposite the first phalanx the brevis tendon divides into two parts, and the longus tendon passes through the cleft thus formed (hence the name flexor perforans) on its way to the distal phalanx. The fibro-osseous canals and their synovial membranes, with the vincula accessoria tendinum of the latter, namely, ligamenta brevia and ligamenta longa, correspond with those of the fingers. In the leg the muscle occupies a fibro-osseous canal formed by intermuscular septa and the posterior surface of the shaft of the tibia. Tibialis Posticus — Origin. — (i) The. outer division of the posterior surface of the shaft of the tibia, extending as high as the commence- ment of the oblique or popliteal line, and ceasing just below the centre of the bone ; (2) the posterior surface of the interosseous membrane, except the lower 2 inches ; (3) the internal surface of the shaft of the fibula ; (4) the posterior or transverse intermuscular septum, as it covers the muscle ; and (5) the intermuscular septa on either side, separating it from the flexor longus digitorum internally and the flexor longus hallucis externally. Insertion. — The tuberosity of the navicular or scaphoid bone. From this insertion eight expansions are given off. One passes backwards to the anterior part of the under surface of the susten- taculum tali of the os calcis. The other seven pass forwards, and are attached as follows : three to the internal, middle, and external cuneiform bones, one to the cuboid bone, and three to the bases of the second, third, and fourth metatarsal bones, all on their plantar aspects. Nerve-supply. — ^The posterior tibial nerve. Action. — (i) The muscle inverts the sole of the foot ; (2) it is an extensor of the foot upon the leg ; and (3) it contributes in a material degree +0 the support of the longitudinal arch of the foot, and so helps to guard against the condition known as flat foot, being in this respect auxiliary to the inferior or internal calcaneo-navicular or spring ligament. In the lower third of the leg the muscle passes obliquely in- wards in front of the flexor longus digitorum. The tendon passes through the groove behind the internal malleolus, where it is beneath the internal annular ligament, occupying one of the fibro- osseous canals, and having the tendon of the flexor longus digi- torum (enclosed within its fibrous canal) lying behind and slightly external to it. In this part of its course the tendon has a special synovial investment, which is also prolonged forwards around it as far as the navicular bone. As it ])asses over the head of the astragalus and spring ligament it contains a sesamoid fibrocartilage. i THE LOWER LIMB 523 The greater part of the muscle in the leg is contained in a fibro- osseous canal formed by the posterior or transverse intermuscular septum, the interosseous membrane, the intermuscular septa on either side, and the surfaces of the tibia and fibula from which it arises. Flexor Longus Hallucis — Origin. — (i) The lower two-thirds of the posterior surface of the shaft of the fibula, except the last inch or more ; (2) the postero-extemal intermuscular septum, which separates the muscle from the peroneus longus and peroneus brevis ; (3) the intermuscular septum between it and the tibiaUs posticus ; and (4) the posterior or transverse intermuscular septum, as it covers the muscle. Insertion. — ^The plantar surface of the base of the distal phalanx of the great toe. Nerve-supply. — ^The posterior tibial nerve. Action. — (i) The muscle acts as a flexor of the distal phalanx of the great toe ; (2) it is an extensor of the foot upon the leg ; (3) it contributes to the support of the longitudinal arch of the foot ; and (4) by means of the slip which it gives to the tendon of the flexor longus digitorum in the sole it is an auxihary of that muscle, more especially in flexing the second and third toes. The tendon passes through the groove on the back of the lower end of the tibia at its outer part, where it lies beneath the internal annular ligament, occupying one of the fibro-osseous canals, and having a special s^niovial investment. Beyond this point it passes in succession through the groove on the posterior border of the astragalus, and through that on the under surface of the sustenta- culum tali of the os calcis. Each of these grooves is converted into a fibro-osseous canal by a fibrous expansion, and in each case the tendon has a synovial investment. In the sole the tendon is crossed superficially or inferiorly, and from within outwards, by that of the flexor longus digitorum, to which it gives a slip. In most cases this slip is incorporated with the long flexor tendons of the second and third toes (Turner). As it passes along the first phalanx it is contained in a fibro-osseous canal lined by synovial membrane, which also invests the tendon and gives rise to a liga- mentum breve. In the leg the flexor longus hallucis is contained within a fibro-osseous canal formed by intermuscular septa and the posterior surface of the shaft of the fibula. Posterior Tibial Artery. — ^This vessel is the larger of the two terminal branches of the popliteal, the other being the anterior tibial. It commences at the lower border of the popliteus muscle on a level wi h the lower border of the tubercle of the tibia, fully if inches below the upper surface of the head of that bone, and it terminates at the lower border of the internal annular Hgament by dividing into the internal and external plantar arteries. The termination of the vessel is situated midway between the inner part of the point of the heel and the tip of the internal malleolus. In the upper two- thirds of the leg it is deeply 524 A MANUAL OF ANATOMY Superior Internal Articular Artery...^ Internal Head of Gastrocnemius.- Inferior Internal Articular- - Artery Popliteus Posterior Tibial Nerve Medullarj' Artery of Tibia Soleus (cut) Tibialis Posticus Flexor Longus Digitorum Posterior Tibial Nerve ^ ^ Posterior Tibial Artery Flexor Longus Digitorum Tibialis Posticus Internal Popliteal Nerve Popliteal Artery Superior External Articular Artery External Head of Gastrocnemiu ; - - - Plantaris -- Inferior External Articular Artery --- Anterior Tibial Artery - Posterior Tibial Artery -.Peroneal Artery Tibialis Posticus Peroneus Longus Flexor Longus Hallucis Peroneus Brevis Flexor Longus Hallucis Peroneus Longus Peroneus Brevis Tendo AchilUs (reflected) ■ Fig. 249 .-The Back of the Right Leg (Deep Dissection). THE LOWER LIMB 523 placed, being situated between the superficial and deep muscles, and over the interval between the tibia and fibula. It then inclines inwards, and in the lower third of the leg it lies over the back of the tibia and to the inner side of the tendo Achillis, where it is com- paratively superficial. The course of the vessel may be indicated by drawing a line from the centre of the lower part of the popliteal space to a point midway between the inner part of the point of the heel and the tip of the internal malleolus. Relations — Superficial or Posterior. — In the upper two-thirds the vessel lies beneath the gastrocnemius, soleus, and posterior or transverse intermuscular septum ; and, in the lower third, it is covered by the skin, superficial fascia, deep fascia, and the internal annular ligament. Anterior or Deep. — ^The tibialis posticus (to which it is bound by the posterior or transverse intermuscular septum), flexor longus digitormn, posterior surface of the tibia, and internal lateral ligament of the ankle-joint (in this order from above downwards). External. — The tendo Achillis in the lower part of the leg. The artery in this part of its course lies about midway between the inner border of the tendo Achillis and the internal border of the tibia. As the vessel passes beneath the internal annular ligament it occupies a special fibro-osseous canal along with its venae comites and the posterior tibial nerve, the latter being on the outer side. In this situation the tendons of the tibialis posticus and flexor longus digitorum lie on the inner side of these structures, and the tendon of the flexor longus hallucis on their outer side. The artery is accompanied by two venae comites, which closely embrace its sides, and communicate with each other at frequent intervals by transverse branches crossing superficial to the vessel. These venae comites ultimately join to form one trunk, which unites with that formed by the junction of the venae comites of the anterior tibial artery to form the popliteal vein, the union taking place at the lower border of the popliteus muscle. The posterior tibial nerve is at first internal to the artery for about ij inches. It then crosses over the vessel just below the origin of the peroneal branch, and from this point onwards it hes on its outer side. Beneath the internal annular ligament the artery has frequently a nerve upon either side of it, an arrangement which is brought about by an early division of the posterior tibial nerve into its internal and external plantar branches. Branches. — ^These are as follows : peroneal, muscular, medullary or nutrient, cutaneous, communicating, internal malleolar, internal calcaneal, and terminal. The description of the peroneal artery, from its large size and numerous branches, will be deferred to the last. The muscular branches are numerous, and are distributed to the deep group of muscles and to the soleus. The medullary or nutrient artery is the largest of all the arteries bearing that name. Arising from the upper part of the posterior 526 A MANUAL OF ANATOMY tibial, it pierces the tibialis posticus and enters the medullary foramen of the tibia, accompanied by the medullary branch of the nerve to the popliteus. The cutaneous branches are distributed to the integument of the inner and back part of the leg. The communicating branch arises about an inch above the ankle- joint. It passes transversely outwards between the tibia and flexor longus hallucis, and anastomoses with the communicating branch of the peroneal artery. The internal malleolar branches are usually two in number. Passing inwards beneath the tendons of the flexor longus digitorum and tibialis posticus, they reach the front of the internal malleolus, where they take part in the internal malleolar anastomosis. The internal calcaneal branch arises beneath the internal annular ligament, which it pierces near the lower border to be distributed over the inner surface of the os calcis, where it anastomoses with the internal calcaneal branches of the external plantar artery. The terminal branches are the internal and external plantar arteries, which will be afterwards described. Peroneal Artery. — ^This vessel, which is of large size, arises from the posterior tibial fully i inch below its commencement. It is at first directed downwards and outwards over the tibialis posticus to the back of the fibula. Having reached that bone, it descend.s along its posterior surface close to the postero-internal border, lying between the bone and the flexor longus hallucis, or within that muscle, or in a fibrous canal between that muscle and the tibialis posticus. About 2 inches above the ankle-joint it escapes from beneath the flexor longus hallucis, and divides into anterior and posterior peroneal arteries. Branches. — ^The branches are as follows : muscular, medullary or nutrient, cutaneous, communicating, and terminal. The muscular branches are distributed to the adjacent muscles. The medullary or nutrient artery enters the medullary foramen of the fibula. The cutaneous branches are distributed to the integument on the outer and back part of the leg. The communicating branch arises about i inch above the ankle- joint. It passes transversely inwards and anastomoses with the communicating branch of the posterior tibial artery. The terminal branches are the anterior peroneal and posterior peroneal. The anterior peroneal artery arises from the peroneal artery near the lower part of the interosseous membrane, and passes forwards through the inferior hiatus in it. Having reached the front of the leg, it descends under cover of the peroneus tertius, and takes part in the external malleolar anastomosis, along with the external malleolar of the anterior tibial, the external tarsal of the dorsalis pedis, and the posterior peroneal. THE LOWER LIMB 52? The posterior peroneal artery is the continuation of the peroneal artery. It passes behind the external malleolus, and along the outer border of the foot for a variable distance. Its branches are chiefly distributed over the outer surface of the os calcis, and these external calcaneal branches take part in the external malleolar anastomosis. Over the prominence of the heel they anastomose freely with the internal calcaneal branches of the external plantar, and on the outer border of the foot the pos- terior peroneal again anastomoses with branches of the external plantar. The peroneal artery is accompanied by two venae comites, which ultimately join the posterior tibial venae comites; Varieties of the Posterior Tibial Artery. — The vessel is sometimes very small, in which cases the peroneal artery is of large size, as well as the communicating branch normally given off about i inch above the ankle-joint, and so the small posterior tibial artery- is reinforced. In rare cases the vessel does not reach the ankle, and it may even be entirely absent, in which cases there is always a large peroneal artery to make good the deficiency. Varieties ol the Peroneal Artery. — The level at which this vessel arises from the posterior tibial is subject to variety. Its normal origin is fully i inch below the commencement of the posterior tibial, but it may arise lower down or higher up, or it may even spring from the pophteal, or from the anterior tibial. In some cases it is of large size, in order to compensate for a small posterior tibial. In other cases the peroneal artery may stop short of the ankle, its place being taken by a branch of the posterior tibial. The anterior peroneal branch is sometimes of large size, in order that it may reinforce a small anterior tibial, or even furnish the dorsahs pedis artery. Posterior Tibial Nerve. — ^This nerve is the continuation of the internal pophteal. It commences at the lower border of the popliteus muscle, and its normal termination corresponds with the lower border of the internal annular ligament, where it divides into internal and external plantar nerves. The division, however, frequently takes place at the upper border of the internal annular ligament, or as the nerve passes beneath it. The nerve closely accompanies the posterior tibial artery throughout the whole of its course. It lies at first on the inner side of the artery, with the intervention of the internal vena comes, but it only maintains this position for about i| inches. It then crosses over the vessel, and descends upon its outer side, the external vena comes intervening. The general relations of the nerve are similar to those of the corre- sponding artery. Branches. — These are muscular, fibular, calcaneo - plantar, articular, and terminal. The muscular branches are given off from the upper part of the nerve, and supply the flexor longus digitorum, tibiahs posticus, flexor longus hallucis, and soleus, the branch to the last muscle entering it on its deep or anterior surface near the centre of the leg. The fibular branch is a long nerve which is usually associated at its origin with the branch to the flexor longus hallucis. It accompanies the peroneal artery, and furnishes (i) a medullary 528 A MANUAL OF ANATOMY branch, which goes with the medullary artery into the interior of the fibula ; (2) periosteal branches to the fibular periosteum ; and (3) twigs to the coats of the peroneal artery. The calcaneo-plantar branch arises from the posterior tibial whilst it is beneath the internal annular ligament. Having pierced the ligament, it divides into internal calcaneal and plantar branches. The former supply the integument of the inner side of the heel, and the latter are the cutaneous nerves of the inner and posterior part of the sole. The articular branches, two or three in number, arise from the posterior tibial close to its termination, and enter the ankle-joint on its inner aspect by piercing the internal lateral ligament. The terminal branches are the internal plantar and external plantar nerves, which will be afterwards described. THE KNEE-JOINT. The knee-joint belongs to the class diarthrosis, and to the sub- division ginglymus. Though the chief movements are flexion and extension, there is also a certain amount of gliding or to and fro movement, as well as rotation. The joint, therefore, partakes of the nature of an arthrodial joint. It is really made up of three joints, namely, one into which the patella and the patellar surface of the femur enter (femoro-patellar), and other two into each of which a femoral condyle and a tibial condylar surface enter (femoro- tibial). These three joints in man communicate freely with one another. The articular surfaces are (i) the condyles and patellar surface of the femur, (2) the upper three-fourths of the posterior surface of the patella, and (3) the condylar articular surfaces of the tibia. The ligaments are divided into two groups, external and internal. I I. External Ligaments. — These are as follows : anterior or liga- j mentum patellae, posterior, external lateral, internal lateral, and ; capsular. ' The anterior ligament or ligamentum patellae is attached ; superiorly to the apex and adjacent margins of the lower part of | the patella, and inferiorly to the lower roygh portion of the 1 tubercle of the tibia, a bursa intervening between it and the ; upper smooth portion of the tubercle. It is a very strong, flat, ' broad ligament, the lateral margins of which are connected with | the lateral patellar ligaments. The posterior ligament is really a part of the capsular ligament. It covers the back parts of the femoral condyles, and; extends between the external and internal lateral ligaments. Superiorly it is attached to the upper margin of the intercondylar! THE LOWER LIMB 529 fossa, and at either side of this to the back of the femur immediately above each condyle. Inferiorly it is attached to the posterior border of the head of the tibia. It constitutes a broad membranous ligament, which in itself is thin, but it receives a considerable accession of fibres from the tendon of the semimembranosus, rhese fibres form a strong prominent bundle, which represents one mode of insertion of that muscle, and is known as the ligamentum -Ligamectam Mocosom -Post. Crucial Ligament Ant. Crucial Ligament - Internal Alar Ligament ^_ Tendon of Quadriceps Extensor Cruris Fig. 250. — Interior of the Left Knee-Joint (Anterior View). osticum Winslowii. It is directed upwards and outwards from le tendon of the semimembranosus towards the outer condyle of le femur' and outer head of the gastrocnemius. Internally the posterior Hgament blends with the internal lateral hgament, and eternally (regarding it as a part of the capsular ligament) it sends 1 expansion over the long external lateral ligament. The posterior .^ament presents a number of openings for the passage of nutrient ;:'ssels and nerves, the largest of these being at its centre for the 34 530 A MANUAL OF ANATOMY azygos artery, accompanied by a branch of the internal pophteal nerve and, it may be, the geniculate branch of the obturator nerve. At the outer part of the ligament there is a«special opening for the tendon of the popliteus. Another opening is frequently present over the upper and back part of the inner condyle, and, when this is so, the popliteal bursa between the semimembranosus and the inner head of the gastrocnemius communicates with the synovial membrane of the joint. The upper and outer part of Plantaris - External Head of Gastrocnemius Long Ext. Lat. Lig. — Short Ext. Lat. Lig. . _ Jjij Popliteus --^ Tendon of Biceps Tendon of Adductor Magnus Internal Head of Gastrocnemius ..Posterior Ligament Ligamentum Posti- cum Winsiowii Tendon of Semimem- branosus Expansion to Popliteal Fascia Popliteus (cut) Fig. 251. — The Left Knee-Joint (Posterior View). the posterior ligament gives origin to some of the fibres of thi plantaris. The external lateral ligament consists of two divisions — anterioi and posterior. The anterior division is the proper external latera ligament, and is known as the long external lateral ligament. It i firm and cord-like, and passes vertically downwards, lying clear c the joint. It is attached superiorly to the external tuberosity c the femur, and interiorly to the outer margin of the head of tb fibula about \ inch anterior to the styloid process. The ligam€ crosses the tendon of the popUtgugj^^and, near the head of the fibi /<5>>> — '■■-■. -^ THE LOWER LIMB 53i it pierces the tendon of the biceps femoris, being there provided with a synovial investment. The inferior external articular vessels and nerve pass beneath it. The long external lateral ligament repre- sents the original tendon of origin of the peroneus longus from the femur. The posterior division of the hgament, which is known as the short external laterals ligament, lies a little behind the long, and is not weU defined. If distinct, it is attached above to the external condyle close to the outer head of the gastrocnemius, where it blends with the posterior ligament, its inferior attachment being to the styloid process of the fibula. Its direction is downwards and forwards, and it is to be regarded as an expansion in that direction of the posterior ligament. The internal lateral ligament is a long, flat, strong band of unequal width, being broader at the centre than at either end. It is attached superiorly to the internal tuberosity of the femur, and inferiorly to the internal border and adjacent part of the internal surface of the shaft of the tibia, extending from the internal tuberosity downwards for fully 3 inches. Its posterior border covers the chief part of the tendon of the semimembranosus, and blends with the posterior ligament. As the ligament passes over the inner side of the knee-joint it is closely adherent to the internal semilunar fibro-cartilage, and, lower down, the inferior articular vessels and nerve pass beneath it. The internal lateral ligament represents the original insertion of the adductor magnus into the tibia. The capsular ligament is formed to a large extent by expansions derived from the tendons of the vastus extemus, vastus intemus, sartorius, and semimembranosus, and from the fascia lata. It surrounds the joint except above the patella, where its place is taken by the suprapatellar tendon. The posterior part of the capsule, which forms the posterior ligament, is specially strong, being reinforced by the ligamentum posticum Winslowii. In other situations it is comparatively thin. It furnishes a thin expansion over the ligamentum patellae, and on either side of the patella it forms the lateral patellar ligaments. ExtemaUy, where it is closely incorporated with the ilio- tibial band of the fascia lata, it covers the long external lateral hgament. Internally, where it receives accessions of fibres from the sartorius and semimembranosus, it ; blends with the internal lateral hgament. ;' The lateral patellar ligaments are two in number, external and internal, and they take the form of flat membranous bands, :;jometimes called the retinacula. The external extends between the i!Outer border of the patella and the anterior margin of the outer r Tuberosity of the tibia. It is intimatel}^ connected with, and in ipart formed by, the iho-tibial band of the fascia lata. The internal -xtends between the inner border of the patella and the anterior nargin of the inner tuberosity of the tibia. 2. Internal Ligaments. — The internal hgaments, properly so ailed, are as follows : the two crucial ligaments ; the two 532 A MANUAL OF ANATOMY semilunar fibro-cartilages, with their coronary hgaments ; and the transverse hgament. There are other structures, within the joint, designated as hgaments, namely, the ligamentum mucosum and ligamenta alaria ; but, as these are merely folds of the synovial membrane, they will he described in connection with it. Crucial Ligaments. — These are two in number, anterior or external, and posterior or internal, and they bind the condyles of the femur to the head of the tibia. They are very powerful, somewhat round bundles situated in the centre of the joint, and so disposed as to form a cross. Posterior Crucial Ligaim Patellar Facet ..^ Internal Condyle Internal Semilunar. - Fibro-cartilage External Condyle . Anterior Crucial Ligament -External Semilunar Fibro-cartilage Long External Lateral Ligament -Transverse Ligament Anterior Superior ■ Tibio-fibular Ligament Fig. 252.- -The Crucial Ligaments of the Left Knee- Joint (Anteetior View). The anterior or external crucial ligament is attached inferiorly tci the inner part of the rough depression on the upper surface of th({ head of the tibia in front of the inner tubercle of the spinel Superiorly it is attached to the depression on the posterior pari of the internal surface Of the external condyle of the femur. Itf direction is upwards, backwards, and outwards. At its tibial attachs ment it has the anterior cornu of the internal semilunar fibro-cartilagl in front of it, and the anterior cornu of the external semilunar fibrc| cartilage behind and to its outer side. The anterior crucial) ligament is tense in extension of the knee-joint, and prevents oveiJ extension. It is also tense in internal rotation of the leg. Th ligament is at one period the internal lateral ligament of tlie extern«J femoro- tibial joint. THE LOWER LIMB 533 The posterior or internal crucial ligament is attached inferiorly to the back part of the rough depression on the head of the tibia behind the spine, and to the pophteal notch. Superiorly it is attached to the anterior part of the external surface of the internal condyle of the femur, close to the front part of the intercondylar fossa, upon which it slightly encroaches. Its direction is upwards, forwards, and shghtly inwards. It is stronger, but shorter, than the anterior crucial ligament, and is not so oblique. At its tibial Anterior Crucial — Ligament External Semilunar Fibro-cartilage Synovial Membrane — ] Long External Laterals Ligament Posterior Superior Tibio-fibular Ligament Internal Semilunar Fibro-cartilage Synovial Membrane Internal Lateral Ligament Post. Accessory Bundle Posterior Crucial Ligament Fig. 253. -The Crucial Ligaments of the Left Knee-Joint (Posterior View) (after Spalteholz). attachment it is behind the posterior comua of both semilunar 5bro-cartilages, the posterior cornu of the internal one being more immediately in front of it and to its inner side. j The posterior crucial ligament is tense in flexion of the knee- ijoint, and checks over-flexion. It is at one period the external llateral ligament of the internal femoro-tibial joint. i Two views may be stated as to the origin of the crucial ligaments, i) According to Keith, they are originally parts of the capsule of the knee- toitit, but have become separated from that structure tis the result of the 534 A MANUAL OF ANATOMY outgrowth of the condyles of the femur. (2) According to Bland-Sutton, they are modifications of muscles, but there are no certain facts as to which muscles they originally belonged. The semilunar flbro-cartilages are two in number — internal and external. They are lunated plates, of very firm consist- ence, which are placed upon the peripheral parts of the condylar articular surfaces of the tibia so as to deepen them for the reception of the condyles of the femur. They also serve as cushions, which mitigate pressure and diminish shock. Each presents two surfaces, superior and inferior ; two borders, outer and inner ; and two extremities or cornua, anterior and posterior. The superior surface is slightly concave to adapt itself to a femoral condyle, being sloped from the outer to the inner border. The inferior surface is flat, and rests upon a condylar surface of the tibia at its circumference. Both these surfaces are covered by the synovial membrane of the joint. The outer border is convex and thick, and it is attached to the margin of the corresponding tuber- osity of the tibia by fibres which are really a part of the capsular ligament, but which have received the name of coronary ligament (one for each fibro-cartilage). The external semilunar fibro- cartilage is more loosely attached in this manner than the internal. Partly on this account, and partly by reason of the close proximity of its two cornua, the external fibro-cartilage is more movable than the internal. The inner border of each fibro-cartilage is very thin, sharp, and concave. It is quite free, and covered by the synovial membrane. The extremities or cornua are thin fibrous bands, which have the following attachments : the anterior cornu of the internal semilunar fibro-cartilage is attached to the rough depression in front of the spine of the tibia at its anterior and inner part ; or, to put it in another way, it is attached to the upper surface of the head of the tibia in front, and to the outer side, of the internal condylar surface. It has the anterior crucial ligament directly behind it. The posterior cornu is attached to the inner part of the rough depression behind the spine of the tibia, where it has the posterior crucial ligament behind it. The internal semilunar fibro- cartilage is semicircular, and may be likened to the capital letter C, its cornua being wide apart, and embracing between them the cornua of the external semilunar fibro-cartilage. It is intimately connected with the internal lateral ligament. The anterior cornu of the external semilunar fibro-cartilage is attached to the head of the tibia immediately in front of the outer | tubercle of the spine, where it is placed on the outer side of andj behind the anterior crucial ligament. The posterior cornu isj attached to the rough depression between the two tubercles of thej spine, and also to a depression immediately behind the outer jj tubercle. The external semilunar fibro-cartilage is almost circular,,; thus O, its cornua being very close together, and being embraced; by the cornua of the internal semilunar fibro-cartilage. The pos-;^ I THE LOWER LIMB 535 tenor and outer aspect of the external semilunar fibro-cartilage is ^ooved by the tendon of the pophteus, and this tendon separates it from the long external lateral ligament, whilst posteriorly it is connected with the posterior ligament. The semilunar fibro-cartilages move forwards when the knee- joint is extended, and backwards when it is flexed, the external more so than the internal. The so-called coronary ligaments are really portions of the capsular ligament. They represent fibres which connect the outer convex borders of the semilunar fibro-cartilages to the margins of the tuberosities of the tibia, more loosely in the case of the external than the internal. Tubercle Anterior Crucial Ligament Ant. Comu of Internal^ Semilunar Fibro-cartilage \^ Transverse Ligament Ant.Comu of External Semilunar Fibro-cartilage -Ext. Semilunar Fibro-cartilage Post. Comu of Internal Semilunar Fibro-cartilage Post. Comu of External Semilunar Fibro-cartilage Posterior Crucial Ligament Fig. 254. — The Ligaments and Fibro-Cartilages on the Head of the Right Tibia. In connection with the external semilunar fibro-cartilage there are two accessory bundles, anterior and posterior. The posterior bundle extends from the back part of the external semilunar fibro-cartilage to the external surface of the internal condyle of the femur, where it is attached close to the posterior crucial ligament. It is thick and strong, and may be double, in which case the two bundles are disposed one in front of, and the other behind, the posterior crucial Ugament. If single it may be in front of that ligament, or behind it, and it may be closely connected with the tibial attachment of the ligament. It serves as a kind of anchor to the back part of the external semilunar fibro-cartilage, and so prevents too much displacement of it during ; rotation. The anterior bundle constitutes the transverse Ugament. 1' The external semilunar fibro-cartilage is to be regarded as originating from the biceps femoris, and the internal from the semimembranosus, certain tex- tural alterations having taken place in the course of the metamorphosis. The transverse ligament is a narrow band which extends I from the front of the external semilunar fibro-cartilage to the 53(> A MANUAL OF ANATOMY front of the internal. It prevents the front part of the external semilunar fibro-cartilage from moving too far backwards during flexion of the joint. The synovial membrane invests the inner surface of the capsular ligament. On reaching the semilunar fibro-cartilages it is reflected over their upper and under surfaces, and is then conducted by the coronary ligaments to the margins of the tuberosities of the tibia. Between the front of the head of the tibia and the patella the membrane covers a collection of fat, known as the infrapatellar Suprapatellar Bursa Quadriceps Extensor Cruris Pouch of Synovial — Membrane of Knee-joint Patella Popliteus. Long External Lateral Ligament Semilunar Fibro-cartilage Ligamentum Patellae Bursa beneath Ligamentum Patellae Fig. 255. — The Synovial Membrane of the Right Knee-Joint (External View) (after Spalteholz). pad, and in this situation it is raised into certain folds, called ligaments, namely, the ligamentum mucosum and ligamenta alaria, to be presently described. Above the patella the membrane extends upwards in the form of a large pouch upon the front of the shaft of the femur for about 2 inches above the upper border of the patellar surface of the bone. This pouch lies beneath the suprapatellar tendon of the quadriceps extensor cruris, and communicates with the suprapatellar bursa, which is situated immediately above it, and which extends upwards for about i inch ; beneath the suprapatellar tendon. i THE LOWER LIMB 537 From the posterior ligament the sjmovial membrane is reflected forwards in the form of two laminae, one of which passes over the outer surface of the anterior crucial ligament, and the other over the inner surface of the posterior crucial ligament. After having done so, these two laminae become continuous with each other in front of the crucial ligaments. It will thus be evident that the following parts of these hgaments are destitute of synovial membrane : (i) the posterior surface of each Ugament, and (2) that part of the anterior surface of the posterior ligament which is in contact with the anterior ligament. In connection with the posterior ligament of the knee-joint it is to be noted that there is a narrow median vertical zone which is destitute of synovial membrane, on account of the forward reflec- tion of that membrane in two laminae. This interlaminar zone is covered by a certain amount of fat. The synovial membrane furnishes an investment to the tendon of the popliteus, which separates that tendon from the long external lateral ligament. This prolongation also extends in a downward direction between the posterior part of the external semilunar fibro-cartilage and the outer tuberosity of the tibia, so as to facilitate the movement of the tendon of the popliteus at that point. It may extend so far down as to become continuous with the synovial membrane of the superior tibio-fibular joint. At the back of the joint the synovial membrane frequently communicates with the popliteal bursa between the semimembranosus and inner head of the gastrocnemius. The synovial membrane, as it covers the infrapatellar pad of fat, forms three folds — the ligamentum mucosum and ligamenta alaria. The ligamentum mucosum, which contains a little fat, extends backwards to be attached to the front part of the inter- condylar fossa of the femur. It is narrow and pointed at its femoral attachment, but over the infrapatellar pad of fat it widens out and becomes triangular. The lateral borders of this latter part of the ligamentum mucosum constitute the so-called ligamenta alaria, which extend for a short distance in an upward direction along the lateral margins of the patella. The ligamentum mucosum, which serves to adjust the infra- patellar pad of fat to the different positions of the joint, is the remains of the double synovial partition which originally separates the femoro-tibial articulations. The articular fat forms two chief collections, called infrapatellar and suprapatellar, which represent the Haversian glands of the knee-joint. The infrapatellar pad is the larger of the two, and fills up the space between the lower end of the femur, the head of the tibia, and the patella with its ligament. It adapts itself to the different positions of the joint, and the ligamentum mucosum acts as its regulator. The suprapatellar pad is situated around the suprapatellar bursa and the pouch which the synovial membrane sends upwards above the patellar surface of the femur. 538 A MANUAL OF ANATOMY Muscular Relations.— The muscular relations are as follows : Anterior. — The quadriceps extensor cruris. External. — ^The biceps femoris. Posterior. — The popliteus, plantaris, and outer head of the gastrocnemius externally, and the inner head of the gastrocnemius and semimembranosus internally. Internal. — The sartorius, gracilis, semitendinosus, and semi- membranosus. Arterial Supply. — The joint receives its arterial supply from the following sources : (i) the long descending branch of the external circumflex of the arteria profunda femoris ; (2) the deep branch ol Crureus Subcrureus Posterior Ligament .- Posterior Crucial Ligament Anterior Crucial Ligament- Suprapatellar Bursa Pouch of Synovial Membrane of Knee-joint — Prepatellar Bursa — Ligamentum Patellfe — Ligamentum Mucosum — Infrapatellar Pad of Fat Bursa beneath Ligamentum Patellae -Skin Fig. 256. — Sagittal Section of the Right Knee-Joint, viewed FROM THE Outer Side. the anastomotica magna of the superficial femoral ; (3) the superior and inferior external and internal articular and the central or azygos articular branches of the popliteal ; and (4) the anterior tibial recurrent and posterior tibial recurrent (inconstant) branches of the anterior tibial. Nerve-supply. — ^The joint receives its nerves from the following sources : (i) the external and internal popliteal, both from the great sciatic; (2) the anterior femoral; and {3) the obturator. Tlie external popliteal nerve furnishes three articular branches, one with the superior external articular artery, one with the inferior external articular, and a recurrent branch with the anterior tibial recurrent. The internal popliteal nerve furnishes three (sometimes THE LOWER LIMB 539 two) articular branches, one with the superior internal articular artery (inconstant), one with the central or azygos articular, and one with the inferior internal articular. The anterior femoral nerve furnishes articular branches as follows: (i) the nerve to the vastus externus furnishes one articular branch ; (2) the most internal of the branches to the crureus furnishes another articular branch, which in its course supplies the subcrureus ; and (3) the nerve to the vastus internus furnishes a third articular branch, which is of large size, and ultimately accom- panies the deep branch of the anastomotica magna artery. The obturator nerve, by its deep or posterior division, furnishes an articular branch called the geniculate nerve. This branch, how- ever, may be absent. If the nerve-supply of the knee-joint is compared with that of the hip-joint, it will be evident that there is a nervous sympathy between these two articula- tions. Anastomotica Magna (Deep Branch) Superior Internal Articular Superior xtemal Articular Inferior Int Articular Inferior -Ext. Articular Head of Fibula Anterior Tibial Recurrent Fig. 257. — The Deep Anastomoses round the Knee-Joint (Anterior View) (Tiedemann). Movements — Femoro- tibial Joints. — The movements between the condyles of the femur and the condylar ar- ticular surfaces of the tibia are of two kinds, namely, flexion and ex- tension, and rotation, the latter movement being only possible when the knee-joint is flexed. Flexion and Extension. — These movements are complicated by the spiral outUne of the femoral condyles, and they partake partly of gliding and partly of rolling. During extension the two condyles move parallel to each other up to a certain stage, namely, towards the end of extension. When this stage has been reached, the anterior part of the outer condyle is in contact with the outer tibial articular surface. The inner condyle, however, being longer than the outer, continues to glide backwards so as to bring its oblique anterior part into contact with the inner tibial articular surface. The result is that the femur is rotated inwards on the tibia. Hence, at the very com- 540 A MANUAL OF ANATOMY mencement of flexion, the femur is rotated outwards on the tibia. When the joint is completely extended, the following ligaments are rendered tense : (i) anterior crucial, (2) posterior ligament, and (3) long external lateral and internal lateral ligaments. Over-extension is checked (i)by the tightening of the anterior crucial, the posterior ligament, and the two lateral ligaments ; (2) by the anterior portions of the semilunar fibro-cartilages being pressed into the depressions of the femoral condyles ; (3) by the locking which takes place between the anterior crucial ligament and the front part of the inter- condylar fossa ; and (4) by the locking which takes place between the inner depression of the outer femoral condyle and the front of the outer tubercle of the tibial spine (Bruce Young). At the end of extension the outer con- dyle pushes the anterior and inner part of the external semilunar fibro-cartilage over the anterior and inner border of the outer condylar surface of the tibia. When this has been done, the depression at the inner end of the groove on the outer condyle comes into contact with the front of the outer tubercle of the tibial spine, and with a special facet in front of that tubercle (at the anterior and inner part of the outer condylar surface of the tibia), and so the locking takes place. In flexion of the knee-joint the external ligaments are relaxed, except the ligamentum patellae. Over-flexion is checked by (i) the stretching of the quadriceps extensor cruris ; (2) the meeting of the fleshy parts of the calf and back of the thigh ; (3) the tightening of the posterior crucial ligament ; and (4) the extreme posterior and outer part of the inner condyle (which here presents a special facet) being pressed against the back part of the inner tubercle of the tibial spine (Cleland). In extension of the joint the semilunar fibro-cartilages move forwards, and in flexion they move backwards. Rotation. — This movement is impossible in extension of the knee-joint, owing to the tightening of the anterior crucial and the external ligaments, except the ligamentum patellae. In semiflexion, however, a fair amount of rotation is allowed. Internal rotation is checked by the anterior crucial ligament, and external rotation by the internal lateral ligament. The range of rotation is about 40 degrees. Assuming that all the muscles and external ligaments are cut, in which case the femur and tibia would be connected only by the crucial ligaments, if the femur is grasped firmly and the tibia rotated inwards the movement will be seen to be arrested by the tightening of the anterior crucial ligament. If, however, the tibia is rotated outwards neither crucial ligament interferes with the movement, so that the tibia can be made to describe half a circle, thus directing the front of the head of the bone backwards. Muscles concerned in the Movements — Flexion. — The muscles which pro- duce flexion are the biceps femoris, semitendinosus, semimembranosus, sar- torius, gracilis, and popliteus. If the ankle-joint is fixed, the gastrocnemius, with the plantaris as a feeble auxiliary, acts as a flexor. Extension. — The chief extensor is the quadriceps extensor cruris. The gluteus maximus and tensor fasciae femoris, however, take part in the completion of extension by means of the ilio-tibial band of the fascia lata. Internal Rotation. — This movement is produced by the popliteus, semitendinosus, semimembranosus, gracilis, and sartorius, in each case after flexion has been effected. External Rotation. — This movement is produced by the biceps femoris after it has flexed the joint. Femoro - patellar Joint. — The movement at this joint is of a gliding or to-and-fro nature, associated with a certain amount of rolling of the patella, the result of which is to bring different parts of the opposed articular surfaces into contact in different positions of the joint. This combination of gliding and rolling constitutes the movement called coaptation. In extension of the knee, when the patella is drawn up by the quadriceps extensor cruris, the inferior pair of patellar facets are in contact with the upper part of the patellar surface of the femur. In semiflexion the middle pair of patellar facets are in contact with the middle part of the patellar surface of the femur. In ordinary flexion the upper pair of patellar facets are in contact with the THE LOWER LIMB 541 lower part of the patellar surface of the femur. In extreme flexion, as in the position assumed by the miner when at work, the patella is entirely off the patellar surface of the femur, and, being turned outwards by the internal condyle, the inner vertical facet of the patella articulates with the semilunar facet on the outer part of the tibial surface of the internal condyle close to the intercondylar fossa, and the upper and outer horizontal patellar facet is in contact with the front part of the external condyle of the femur. When the patella is turned inwards in extension of the joint, the outer lateral patellar hgament is put upon the stretch, and so prevents over-displacement inwEirds. When the patella is turned outwards in flexion by the internal condyle, the inner lateral patellar hgament is put upon the stretch, and so prevents over- displacement outwards. When a person stands erect with both feet upon the ground, the vertical line of the centre of gravity faUs in front of the axis of movement at the knee-joint. There is thus a tendency to over-extension, which, however, is resisted by the tension of the Ugaments. In the erect attitude the knee-joint is, therefore, mjiintained in a state of extension to a large extent without muscular effort. This is proved by the fact that each patella is freely movable. When, however, one Umb is raised from the ground, muscular effort now becomes necessary to maintain extension, and the patella of each hmb becomes fixed. The gluteus maximus and tensor fasciae femoris muscles, acting through the iho- tibial band of the fascia lata, contribute to the maintenance of extension at the knee-joint, as in standing. Bursae at Knee-Joint. — The region of the knee-joint abounds in bursae, and in this respect surpasses other articular regions. The bursae are as follows: Suprapatellar. Popliteal. Subcrureal. Of popliteal tendon. Prepatellar. Of semimembranosus tendon. Infrapatellar. Gastrocnemiai, mesial. Anserine. Gastrocnemiai, lateral. Bicipital. The suprapatellar bursa is a large pouch of the synovial mem- brane of the knee-joint, which extends upwards upon the front of the shaft of the femur for about 2 inches above the upper border of the patellar articular surface of the bone. It lies beneath the suprapatellar tendon of the quadriceps extensor muscle, and its cavity is necessarily continuous with that of the sjTiovial membrane of the knee-joint. In cases of extensive effusion into that joint this bursa becomes distended with fluid, and forms a large swelling, which readily admits of palpation. Superiorly it usually com- municates with the subcrureal bursa. The subcrureal bursa hes upon the front of the femur above, or higher up than, the suprapatellar bursa. It is situated beneath the subcrureus muscle, and usually communicates with the suprapatellar bursa, of which it may be regarded as a differentiated part. The prepatellar bursae are situated in front of the patella. There may be three of these — namely, subcutaneous, subfascial, and sub- tendinous— or there may only be one — namely, subcutaneous. The subcutaneous prepatellar bursa is situated beneath the integu- ment, in front of the lower part of the pateUa and upper part of the hgamentum patellae. It may be more or less multilocular, and it is the seat of the condition known as housemaid's knee. This bursa is always present. 542 A MANUAL OF ANATOMY The subfascial and subtendinous prepatellar bursae are incon- stant. When present, they may be regarded as deep differentia- tions of the subcutaneous bursa, with which they usually com- municate more or less freely, and might therefore be involved in housemaid's knee. They may, however, form distinct bursae. The subfascial prepatellar bursa is situated between the fascia lata, which covers the patella, and the tendinous expansion which the suprapatellar tendon of the quadriceps extensor muscle sends downwards over the patella. It may extend downwards over the upper part of the ligamentum patellae, and it may be multilocular. The subtendinous prepatellar bursa is the most deeply placed. It is situated between the tendinous expansion of the suprapatellar tendon over the patella and the periosteum of the bone, and it is limited to the front of the bone. The prepatellar bursae have no communication with the synovial cavity of the knee-joint, and it is therefore necessary to discriminate between prepatellar bursitis and synovitis of the knee-joint. The infrapatellar bursae are two in number — subcutaneous and deep. The infrapatellar subcutaneous bursa is situated beneath the integument, and lies over the lower rough half of the tubercle or anterior tuberosity of the tibia, which half gives attachment to the lower end of the ligamentum patellae. The deep infrapatellar bursa is situated between the lower part of the ligamentum patellae and the upper smooth half of the tubercle or anterior tuberosity of the tibia. It is on a slightly higher level than the subcutaneous infrapatellar bursa, and neither the sub- cutaneous nor the deep bursa has any communication with the synovial cavity of the knee-joint. The bursa anserina is connected with the expanded tendons of insertion of the sartorius, adductor gracilis, and semitendinosus muscles into the upper portion of the inner surface of the shaft of the tibia, on a level with the tubercle or anterior tuberosity of the bone. It is also related superficially to the internal lateral liga- ment of the knee-joint, and it has no communication with the synovial cavity of that joint. It is called the anserine bursa, because the tendons of the muscles to which it is related are dis- posed somewhat in the form of a goose's foot, known as the pes anserinus cruris, as distinguished from the pes anserinus faciei, formed by the facial nerve on emerging from the parotid gland. The popliteal bursa, which is of large size, is situated at the posterior and inner aspect of the knee-joint. It lies between the inner head of the gastrocnemius and the semimembranosus muscle, and frequently (one in five) communicates with the synovial cavity of the joint. Under these circumstances, if effusion should take place into the knee-joint, this bursa might form a fluctuating swelling, which might be palpated at the posterior and inner part of the joint. The synovial sheath of the popliteal tendon is derived from the THE LOWER LIMB 543 synovial membrane of the knee-joint, as the tendon Ues \\'ithin the joint. It Ues over the lower part of the outer aspect of the external condyle of the femur, and it accompanies the tendon as the latter passes beneath the long external lateral ligament. This bursa may communicate with the superior tibio-fibular joint. The bursa of the semimembranosus tendon Ues between the chief tendon of insertion of that muscle and the upper lip of the horizontal groove on the posterior surface of the internal tuberosity of the tibia. This bursa has no communication with the synovial cavity of the knee-joint. The mesial gastrocnemial bursa, of small size, is situated between the inner head of the gastrocnemius and the posterior surface of the femur, just above the inner condyle. The lateral gastrocnemial bursa is situated between the outer head of the gastrocnemius and the adjacent part of the capsule of the knee-joint at its posterior and outer part, just above the external condyle. The two gastrocnemial bursae, being so close to the knee- joint, may communicate with its synovial cavity. The bicipital bursa invests the long external lateral Ugament of the knee-joint as that Ugament passes through the tendon of inser- tion of the biceps femoris muscle. It lies close above the outer aspect of the head of the fibula, and it has no conmiunication with the synovial cavity of the knee-joint. SOLE OF THE FOOT. Landmarks. — Along the inner border of the foot there are several important bony landmarks which can be made out without much difficulty. The internal maUeolus is a good starting-point. One inch below this projection the sustentaculum tali of the os calcis can be felt, and a little in front of it is the tuberosity of the navicular or scaphoid bone. The navicular tuberosity is situated about 1 1 inches in front of the internal malleolus, and on a lower level. The recess between the sustentaculum tali and the navicular tuberosity is bridged over by the spring ligament and the tendon of the tibiaUs posticus, the latter being the more superficial. Immediately in front of the navicular tuberosity the eminence on the plantar surface of the internal cvmeiform bone may be felt, and anterior to it is the tuberosity on the plantar aspect of the proximal end of the first metatarsal bone. Along the outer border two projections can be felt, namely, the external malleolus and the tuberosity on the outer side of the proximal end of the fifth metatarsal bone. The guide to the astragalo-navicular joint on the inner side of the foot is the tuberosity of the navicular bone, the joint being situated immediately behind that tuberosity. The guide to the calcaneo-cuboid joint on the outer side of the foot is a point midway 544 ^ MANUAL OF ANATOMY between the external malleolus and the tuberosity on the outer side of the proximal end of the fifth metatarsal bone. The astragalo- navicular and calcaneo-cuboid joints lie in the same transverse plane, and are the joints at which disarticulation is performed in Chopart's operation. The guide to the joint between the internal cuneiform and first metatarsal bones is a point i^ inches in front of the navicular tuberosity. This is to be remembered in connection with the tarso -metatarsal operations of Lisfranc and Hey. The joint between the cuboid and fifth metatarsal bones is situated immediately behind the tuberosity on the outer side of the proximal end of the fifth metatarsal bone. The course of the external plantar artery is complicated by the fact that it first crosses the sole of the foot from within outwards, and afterwards from without inwards. The former course is indicated by a line drawn from a point midway between the inner part of the point of the heel and the tip of the internal malleolus to a point about i inch internal to the tuberosity on the outer side of the base of the fifth metatarsal bone. A line drawn from the latter point to the proximal part of the first interosseous space indicates the position of the artery as it recrosses the foot. To indicate the course of the internal plantar artery start from the same point as for the commencement of the external plantar vessel, and draw a line to the centre of the metatarso-phalangeal joint of the great toe. The skin of the sole is characterized by great thickness over the bony prominences of the heel and balls of the toes, in which situations bursae are frequently developed. The superficial fascia is coarse and granular. It forms a thick pad composed of lobules of fat, which lie between, and are supported by, processes of fibrous tissue passing between the skin and the plantar fascia. Plantar Bursae. — These bursae are as follows: Calcaneal. Fifth metatarsal. First metatarsal. Navicular. Peroneal. ♦ The calcaneal bursa is placed over the plantar aspect of the tuber calcis, which has two tubercles — inner and outer. This bursa is but little developed, unless in those persons who have to stand for long periods of time. The first metatarsal bursa is situated over the plantar aspect of the head of the first metatarsal bone, which supports the two phalanges of the great toe or hallux. The head of this bone is of large size, and its plantar surface is rendered prominent by two large sesamoid bones. Another first metatarsal bursa is sometimes formed over the internal or medial aspect of the metatarso-phalangeal joint of the great toe. This occurs in cases of hallux valgus, which is an external displacement or subluxation of the great toe or hallux at the meta tarso-phalangeal joint. The hallux may be displaced outwards to THE LOWER LlMS 545 such an extent as to be overlapped by the second toe. Under these circumstances the inner part of the head of the first metatarsal bone and the inner part of the proximal end of the first phalanx give rise to a prominence on the inner aspect of the metatarso- phalangeal joint of the great toe. Over this prommence a synovial bursa is formed, and, when this bursa becomes enlarged, the most common form of bun ion is the result. I f suppuration should ensue, the metatarso-phalangeal joint of the great toe may become involved. The filth metatarsal bursa is situated over the plantar aspect of the head of the fifth metatarsal bone, which supports the phalanges of the httle toe. This bursa is of small size, and is due to the fact that the external pillar of the longitudinal arch of the foot is nearer the ground than the internal pillar. Another fifth metatarsal bursa is sometimes formed over the prominent tuberosity on the outer surface of the base or proximal end of the fifth metatarsal bone. This occurs in cases of talipes varus, in which the inner border of the foot is raised. The navicular bursa is not common. It may be formed over the tuberosity of the navicular or scaphoid bone, about ij inches in front of the internal malleolus — e.g., in cases of talipes valgus, in which the outer border of the foot is raised. The tendon-sheath of the peroneus longus invests the tendon of that muscle as it traverses the fibro-osseous canal formed by the long plantar ligament and the peroneal groove on the plantar sur- face of the cuboid bone. It is deeply placed. Plantar Fascia or Aponeurosis. — The plantar fascia is connected to the skin by fibrous processes, which enclose and support the lobules of the superficial fascia, and it presents two longitudinal grooves, along the course of which intermuscular septa pass deeply into the sole. These grooves indicate the division of the plantar fascia into three portions — central and two lateral. The central division covers the flexor brevis digitorum, and is of considerable strength. It is triangular, being somewhat pointed behind and expanded in front. Posteriorly, where it is narrow and thick, it is attached to the inner tubercle on the plantar aspect of the tuber calcis. From this point the fibres pass forwards towards the toes, the central division meanwhile widening out and becoming thinner. At the heads of the metatarsal bones it divides into five digital processes, one for each toe. The direction of its fibres is longitudinal — that is to say, they nm from heel to toes, but towards the balls of the toes transverse fibres make their appearance. Moreover, in the webs of the toes there are other superadded transverse fibres, which constitute the superficial transverse ligament. This ligament arch«s over the digital vessels, nerves, lumbricales muscles, and digital processes. Each of the five digital processes forms an arch over the flexor tendons as I these are about to pass to the plantar aspects of the toes. The 1 final disposition of each process is as follows : (i) it is attached superficially to the skin ; (2) it joins the vaginal hgament of the ' 35 546 A MANUAL OF ANATOMY Abductor Hallucis.. Flexor Longus Hallucis Flexor Brevis Hallucis.- _ Flexor Brevis Digitoriim -Abductor Minimi Digiti . Flexor Brevis Minimi Digiti Lumbricales Fig. 258. — The Plantar Fascia, and First Layer of Muscles (in part) THE LOWER LIMB 547 flexor sheath anteriorly ; and (3) at each side of the flexor tendons it sends a deep process upwards, which joins the transverse meta- tarsal (deep transverse) ligament connecting the heads of the metatarsal bones, and is also attached to the corresponding lateral metatarso-phalangeal ligament. There is thus formed a tunnel for the passage of the flexor tendons. The lumbricales muscles and the digital vessels and nerves make their appearance between the diverging digital processes. The central division contributes to the maintenance of the longitudinal arch of the foot by its tendency to approximate the toes to the heel. When it becomes contracted it gives rise to an exaggeration of the longi- tudinal arch, a condition known as pes cavus. Morphologically it represents the divorced plantar portion of the tendon of the plantaris. The external division is weaker than the central. It is attached posteriorly to the outer tubercle on the plantar aspect of the tuber calcis, whence it passes forwards over the abductor minimi digiti muscle. Internally it is continuous with the central division along the line of attachment of the external intermuscular septum ; externally it is continuous round the outer border of the foot with the deep fascia of the dorsum ; and anteriorly, having become very thin, it is attached to the proximal end of the first phalanx of the little toe on its outer aspect. This division forms a specially strong band between the outer tubercle of the os calcis and the tuberosity on the outer side of the base of the fifth metatarsal bone, which is the remains of the abductor ossis metatarsi quinti, or Wood's muscle. ■ The internal division is the weakest of the three. It is attached posteriorly to the internal aspect of the inner tubercle on the plantar surface of the tuber calcis, and to the lower border of the internal annular ligament, whence it passes forwards over the abductor hallucis muscle. Externally it is continuous with the central division along the hne of attachment of the internal intermuscular septum ; internally it is continuous round the inner border of the foot with the deep fascia of the dorsum ; and anteriorly, where it becomes very thin, it is attached to the proximal end of the first phalanx of the great toe on its inner aspect. The intermuscular septa are two in number, external and internal, and they extend upwards into the sole at either side of the central division along the course of the longitudinal grooves. They are situated on either side of the flexor brevis digitorum, the internal septum lying between that muscle and the abductor hallucis, j and the external septum intervening between it and the abductor minimi digiti. Each septum giv^es partial origin to the muscles between which it hes. The plantar fascia and the two inter- I muscular septa form three muscular compartments — inner, middle, ' and outer. Cutaneous Nerves. — The cutaneous nerves are as follows : 548 A MANUAL OF ANATOMY calcaneo-plantar, branches of the internal plantar, and branches of the external plantar. The calcaneo-plantar nerve is a branch of the posterior tibial whilst that nerve is beneath the internal annular ligament. Having pierced that ligament, the nerve divides into internal calcaneal and plantar branches. The former supplies the integu- ment of the inner side of the heel, and the latter the inner and posterior part of the sole. The plantar cutaneous branches of the internal plantar nerve appear along the groove between the abductor hallucis and flexor brevis digitorum, and, having pierced the plantar fascia, are distributed to the integument of the inner half of the sole. The plantar cutaneous branches of the external plantar nerve appear along the groove between the flexor brevis digitorum and abductor minimi digiti, and, having pierced the plantar fascia, are distributed to the integument of the outer half of the sole. It is to be noted that the integument of the outer side of the heel and outer border of the foot, including the outer side of the little toe, is supplied by the short saphenous nerve, the external branch of the musculo-cutaneous nerve also taking part in the supply of the outer border, whilst the integument of the inner border of the foot is supplied by the long saphenous, and by the internal branch of the musculo-cutaneous nerve. The cutaneous arteries of the sole are branches of the internal and external plantar vessels, and in their course and distribution they accompany the corresponding cutaneous nerves. There is a very copious supply of arteries to the integument of the heel, repre- sented by the internal calcaneal branches of the external plantar and posterior tibial arteries on the inner side, and the external calcaneal branches of the posterior peroneal artery on the outer side. Superficial Veins. — The superficial veins are very numerous, and are for. the most part arranged in the form of a plexus, which lies immediately beneath the skin. Besides this plexus, there is a transverse venous arch situated near the clefts of the toes. The destination of the venous blood of the plexus and transverse arch is the dorsum of the foot. The blood is conveyed away from the plantar subcutaneous plexus by anterior efferent and lateral efferent vessels. The anterior efferent vessels terminate in the transverse venous arch near the clefts of the toes. The lateral efferent vessels turn round the outer and inner borders of the foot, the external set terminating in the short saphenous vein, and the internal set in the long saphenous vein, just where these vessels are springing from the extremities of the dorsal venous arch. The transverse venous arch near the clefts of the toes receives the anterior efferent vessels of the plantar subcutaneous plexus, and the jjlantar digital veins. The blood is conveyed away from it by means of elferent veins, called inter digital, which pass upwards to the dorsum of the THE LOWER LIMB 549 foot, where they terminate in the dorsal venous arch. The super- ficial veins of the sole are all furnished with valves, which are so placed as to direct the flow of blood to the dorsum of the foot. Muscles. — ^The muscles of the sole are divided into four layers — first, second, third, and fourth. First Layer. — The first layer consists of the following three muscles, named in order from within outwards : abductor hallucis, flexor brevis digitorum, and abductor minimi digiti. All three lie immediately beneath the corresponding divisions of the plantar fascia, each muscle having a compartment to itself. Abductor Hallucis — Origin. — The outer head arises from (i) the internal aspect of the inner tubercle on the plantar surface of the tuber calcis ; (2) the deep surface of the internal division of the plantar fascia ; and (3) the internal intermuscular septum, which separates it from the flexor brevis digitorimi. The inner head arises from (i) the lower border of the internal annular ligament on its deep aspect ; and (2) the fibrous structures along the adjacent part of the inner side of the sole, such as the tendon of the tibialis posticus and some of its expansions. Insertion. — ^The tubercular enlargement on the inner side of the base of the first phalanx of the great toe. Nerve-supply. — ^The internal plantar nerve. Action. — (i) To abduct the great toe from the imaginary middle line of the foot, which passes through the centre of the second toe ; and (2) to flex the metatarso-phalangeal joint of the great toe. The tendon of the muscle receives on its outer and deep aspect the fleshy inner head of the flexor brevis hallucis. Flexor Brevis Digitorum (flexor perforatus) — Origin. — (i) The front of the inner tubercle on the plantar surface of the tuber calcis ; (2) the deep surface of the central division of the plantar fascia ; and (3) the intermuscular septum on either side. Insertion. — By means of four tendons which go to the four outer toes, where each is inserted into the sides of the shaft of the second phalanx at its centre and on its plantar aspect. Nerve-supply. — ^The internal plantar nerve. Action. — (i) To flex the second phalanges of the four outer toes, and (2) to flex the metatarso-phalangeal joints. Each tendon, as it passes along the plantar surface of a toe, has a tendon of the flexor longus digitorum above it as far as the second phalanx, the two tendons occupying a fibro-osseous canal lined by a synovial membrane which furnishes a separate invest- ment for each tendon. Opposite the first phalanx the brevis tendon divides into two parts, and the longus tendon passes through the cleft thus formed; hence the name flexor perforatus for the brevis muscle. Thereafter the two divisions of the brevis tendon unite by their adjacent margins on the upper or d6ep surface of the longus tendon, but they soon separate and take insertion into the sides of the shaft of the second phalanx at its centre and on its plantar aspect. Each brevis tendon has a ligamentum breve 550 A MANUAL OF ANATOMY Abductor Minimi Digiti. •, Outer Digital Branch of External Plantar Nerve. ,__ External Plantar._ Artery Inner Digital Branch of. External Plantar Nerve Communicating Nerve • Flexor Brevis Minimi Digiti Central Division of Plantar Fascia (cut) _. Abductor Hallucis Flexor Brevis Digitorum Internal Plantar Nerve and Artery i» Flexor Brevis Hallucis .Tendon of Flexor ^ Longus Hallucis Fig. 259.— The First Layer of Plantar Moscles (Left Foot). THE LOWER LIMB 551 which passes between its upper surface near its final division and the distal end of the first phalanx. The fibrous sheaths of the tendons, as they pass along the plantar aspects of the toes, as well as the accessories of these sheaths, correspond with those of the fingers." As the long and short flexor tendons are about to pass to the plantar aspects of the respective toes, and before entering the fibro - osseous canals, each pair of tendons passes through a short fibrous tunnel, corresponding in position with the balls of the toes, and constructed in the following manner : superiorly or deeply it is formed by a portion of the transverse metatarsal ligament ; inferiorly or superficially by a digital process of the central division of the plantar fascia ; and on either side by the deep expansion of the digital process which joins the transverse metatarsal Ugament and lateral metatarso-phalangeal hgament. Abductor Minimi Digit! — Origin. — (i) The outer side and front of the outer tubercle on the plantar aspfect of the tuber calcis ; (2) the front of the inner tubercle ; (3) the external intermuscular septum ; and (4) the external division of the plantar fascia, more particularly the strong band which extends between the outer tubercle of the os calcis and the tuberosity on the outer side of the base of the fifth metatarsal bone. Insertion. — ^The outer side of the base of the first phalanx of the httle toe, in conjunction with the flexor brevis minimi digiti. It often takes attachment also to the base of the fifth metatarsal bone on the outer aspect of its plantar surface. Nerve- sup ply. — ^The external plantar nerve. Action. — (i) To abduct the Uttle toe, and (2) to flex its metatarso- phalangeal joint. Occasionally a fourth muscle is met with in the first layer, called the abdactor ossis metatarsi quintl or Wood's muscle. It arises from the outer tubercle on the plantar aspect of the tuber calcis, and from the adjacent portion of the plantar fascia, and it is inserted into the tuberosity on the outer side of the base of the fifth metatarsal bone. In most cases, however, this muscle has undergone degeneration, and is only represented by the strong band of the external division of the plantar fascia, which extends between the outer calcaneal tubercle and the tuberosity on the outer side of the base of the fifth metatarsal bone. Second Layer. — ^This layer consists partly of tendons and partly of muscles. They are as follows : the tendon of the flexor longus ■ hallucis ; the tendon of the flexor longus digitorum ; the flexor or musculus accessorius ; and the lumbricales. Tendons of Flexor Longus Hallucis and Flexor Longus Digitorum. — The tendon of the flexor longus hallucis, after leaving the groove on the under surface of the sustentaculum tali of the OS calcis, is directed forwards and inwards, lying in its course between the two heads of the flexor brevis hallucis, and the tendon of the flexor longus digitonun is directed forwards and out- trds towards the middle line of the sole. The two tendons^ 552 A MANUAL OF ANATOMY Abductor Minimi. Digiti Long Plantar.. Ligament Outer Head of Flexor. Accessorius External Plantar. Artery External Plantar Nerve Peroneus Longus. Tuberosity of Fifth Metatarsal r 61^ Abductor Minimi . Digiti Flexor Brevis . Minimi Digiti Fourth Lumbri- , calls Tendon of Flexor. Brevis Digitorum Flexor Brevis Digitorum Inner Head of Flexor Accessorius -.Internal Plantar Nerve Internal _, Plantar Artery WWUW Flexor Accessorius 'y» Flexor Longus Digitorum _ .Abductor Hallucis .Inner Head of Flexor Brevis Hallucis Flexor Longus Hallucis Fig, 260.— The Second Layer of Plantar Muscles (Left Foot). THE LOWER LIMB 553 therefore, cross each other, that of the flexor longus hallucis being above, or on the deep surface of, the other, and giving a slip to it. The tendon of the flexor longus digitorum, on reaching the middle line of the sole, receives the flexor or musculus accessorius, and thereafter terminates in four tendons for the four outer toes, with which tendons the lumbricales are associated. Flexor or Musculus Accessorius. — This muscle is so named because it is accessory to the long flexor. It arises by two heads, inner and outer, which embrace between them the os calcis and the long plantar ligament. Origin. — ^The inner head arises from the internal concave surface of the OS calcis below the groove on the under surface of the susten- taculum tali. The outer head arises from (i) the junction of the external and plantar surfaces of the os calcis in front of the outer tubercle ; and (2) the adjacent portion of the long plantar ligament. Insertion. — ^The outer border and upper surface of the tendon of the flexor longus digitorum about the centre of the sole. Nerve-supply. — The external plantar nerve. Action. — (i) To flex the terminal phalanges of the four outer toes, and (2) to counteract the tendency of the long flexor tendons to draw the toes inwards during flexion. In performing this latter action, the muscle keeps the long flexor tendon in the middle line, so that its four divisions act in a straight line upon the toes. The inner head of the muscle is broad and fleshy, whilst the outer head is narrow, pointed, and tendinous. This muscle is to be regarded as a detached portion of the flexor longus digitorum, forming an additional tarsal origin for the purpose of counteracting the obliquity of its tendons. Lumbricales. — These muscles are four in number. Origin. — From the tendons of the flexor longus digitorum where these begin to diverge, the outer three taking origin each from the contiguous sides of the tendons between which it lies, and the most internal springing only from the inner side of the long flexor tendon destined for the second toe. Insertion. — ^The tendons, having passed round the inner sides of the metatarso-phalangeal joints of the four outer toes, take insertion each into the expansion formed by the extensor tendon on the dorsal aspect of the first phalanx. Xerve-siippiy. — ^The most internal or first lumbricalis is supplied by the internal plantar nerve, more particularly by its second digital branch on its way to the cleft between the great toe and the second. The outer three lumbricales, or the second, third, and fourth, are supplied by the deep division of the external plantar nerve. Action. — (i) To flex the metatarso-phalangeal joint, and (2) to extend the interphalangeal joints. The muscles are to be regarded as detached portions of the flexor longus digitorum. Third Layer. — ^The third layer consists of the following four 554 A MANUAL OF ANATOMY Third Plantar_ Interosseous ~ Abductor Minimi Digiti. Fl«xor Brevis Minimi.—'' Digiti Adductor Transversus, Hallucis _\ ___.:Flexor Brevis Digitorum External Plantar Artery External Plantar Nerve Internal Plantar Nerve Abductor Hallucis ^ — Internal Plantar Aitery ^^. Tendon of Flexor Longus i\\\\\\ , Digitorum Tendon of Flexor Longus Hallucis Itll ilWIll — Origin of Flexor Brevis Hallucis Adductor Obliquus Halluci Abductor Hallucis Inner Head of Flexor Brevis Hallucis Outer Head of Flexor Brevis Hallucis Tendon of Flexor Longus Hallucis Fig. 261, — The Third Layer of Plantar Muscles (Left Foot). THE LOWER LIMB 555 nuscles: flexor brevishallucis; adductor obliquus hallucis ; adductor ransversus hallucis ; and flexor brevis minimi digiti. Flexor Brevis Hallucis — Origin. — (i) The inner part of the plantar urface of the cuboid bone (sometimes the internal surface), and 2) the expansions of the tibialis posticus tendon to the middle and ;xtemal cuneiform bones. Insertion. — By means of two heads, outer and irmer. The inner lead is inserted into the tubercular enlargement on the inner side )f the base of the first phalanx of the great toe, in conjvmction with :he abductor hallucis. The outer head is inserted into the tuber- :ular enlargement on the outer side of the base of the first phalanx )f the great toe, in conjunction with the adductor obUquus hallucis ind adductor transversus hallucis. Nerve-supply. — ^The internal plantar nerve, more particularly its iirst or most internal digital branch. Action. — ^To flex the metatarso-phalangeal joint of the great toe. It may at the same time act as a very slight adductor of that toe. The flexor brevis hallucis lies along the outer side of the tendon af the abductor hallucis. It is tendinous and narrow behind, but soon becomes fleshy and divides into an inner and outer head of insertion, between which is the tendon of the flexor longus haUucis. In each head there is a sesamoid bone. Adductor Obliquus Hallucis — Origin. — (i) The sheath of the tendon of the peroneus longus, and (2) the plantar surfaces of the bases of the second, third, and fourth metatarsal bones. Insertion. — The tubercular enlargement on the outer side of the base of the first phalanx of the great toe, in conjunction with the outer head of the flexor brevis hallucis on the inner side and the adductor transversus hallucis on the outer side. Nerve-supply. — ^The deep division of the external plantar nerve. Action. — (i) To adduct the great toe, and (2) to flex the meta- tarso-phalangeal joint. The muscle lies obhquely on the outer side of the flexor brevis hallucis. Adductor Transversus Hallucis (transversalis pedis) — Origin. — (i) The inferior metatarso-phalangeal ligaments of the third, fourth, and fifth toes, and (2) the transverse metatarsal Ugament. Insertion. — ^The tubercular enlargement on the outer side of the base of the first phalanx of the great toe, in conjunction with the ^adductor obhquus hallucis. i Nerve-supply. — ^The deep division of the external plantar nerve. I Action. — (i) To adduct the great toe, and (2) to approximate jthe toes to each other. i The muscle consists of three fleshy bundles which join into one, and it lies transversely upon the heads of the four outer metatarsal bones. It is to be regarded as a detached portion of the adductor obliquus hallucis, which has become shifted forwards Id the balls of the toes. 556 A MANUAL OF ANATOMY Flexor Brevis Minimi Digiti — Origin. — (i) The plantar surface of the base of the fifth metatarsal bone, and (2) the sheath of the tendon of the peroneus longus. Insertion. — The outer side of the base of the first phalanx of the little toe, in conjunction with the abductor minimi digiti. A few of the fibres also take attachment to the plantar surface of the shaft of the fifth metatarsal bone over its anterior part. These fibres represent the muscle called opponens minimi digiti, the origin of which corresponds with those fibres of the flexor brevis minimi digiti which spring from the sheath of the tendon of the peroneus longus. Nerve-supply. — The superficial division of the external plantar nerve, and usually the outer digital branch of that division to the outer side of the little toe. Action. — To flex the metatarso-phalangeal joint of the little toe. The muscle is a small fleshy slip which lies upon the plantar surface of the fifth metatarsal bone, under cover of the abductor minimi digiti. It is liable to be taken for a plantar interosseous muscle, lying, as it does, in close contact with the most external plantar interosseous. Plantar Triangle. — This is a muscular triangle in connection with the third layer of muscles, the boundaries of which are as follows : Anterior or Base. — Adductor transversus hallucis. Internal.— Adductor obliquus hallucis. External. — Flexor brevis minimi digiti. Floor. — Portions of the plantar and dorsal interosseous muscles, covered by the interosseous fascia. Roof .—The long flexor tendons and the lumbricales. Contents. — (i) A limited portion of the deep part of the external plantar artery ; (2) some of the digital branches of the plantar arch, especially the second and third, and the corresponding veins ; and (3) a limited portion of the deep division of the external plantar nerve. Fourth Layer. — The fourth layer consists of the interosseous muscles ; the tendon of the peroneus longus ; and the tendon of the tibialis posticus. Interosseous Muscles. — The interosseous muscles are seven in num.ber, and are arranged in two groups — plantar, of which there are three, and dorsal, of which there are four. The plantar muscles are seen only in the sole, but the dorsal muscles are seen on the dorsum of the foot as well as in the sole. The plantar aspects of the muscles are covered by the thin interosseous fascia which joins anteriorly the transverse metatarsal ligament. Plantar Interossei. — These belong to the three outer toes, and are named first, second,, and third from within outwards. Origin. — (i) The inner surfaces of the shafts of the third, fourth, and fifth metatarsal bones, and (2) the sheath of the tendon of the peroneus longus. Insertion. — (i) The inner sides of the bases of the first phalanges of the third, fourth, and fifth toes, and (2) the expansions formed by the long and short extensor tendons (in the case of the fifth toe THE LOWER LIMB 557 long extensor only) on the dorsal aspects of the first phalanges of the same toes. Dorsal Interossei.— These belong to the second, third, and fourth toes, the second toe having two. They are named first, second, third, and fourth, from within outwards. Origin. — Each muscle arises by two heads from the adjacent lateral surfaces of the shafts of the metatarsal bones between which it is situated, but more extensively from the metatarsal bone of the toe upon which the muscle acts than from the other bone. In the case of the first (most internal) muscle its inner head is comparatively small, and arises from the outer side of the base of the first meta- tarsal bone, as weU as from the adjacent portion of the internal cuneiform. Fig. 262. — The Interosseous Muscles of the Right Foot. A, Plantar; B, Dorsal. Insertion. — ^The dorsal interossei are inserted in a manner pre- cisely similar to the plantar interossei. The first and second dorsal interossei belong to the second toe, one on either side ; the third belongs to the outer side of the third toe ; and the fourth to the outer side of the fourth toe. In the case of all the interosseous muscles the insertion into a first phalanx is comparatively slight, the chief insertion being into the expansion of the extensor tendon on the dorsal aspect of the first phalanx. Nerve-supply. — The external plantar nerve in the following manner : the deep division of the nerve usually supplies the inter- osseous muscles, with the exception of the two which occupy the fourth (most external) interosseous space, namely, the fourth dorsal and third plantar. These two are usually supplied by the outer digital branch of the superficial division of the external plantar 558 A MANUAL OF ANATOMY nerve to the outer side of the Httle toe. Sometimes, however, the deep division of the nerve supphes all seven interosseous muscles. In all cases the nerves enter the muscles on their plantar aspects. Action — Plantar Interossei. — These are adductors, the toes which they adduct being the third, fourth, and fifth. Dorsal Interossei. — These are abductors, the toes which they abduct being the second, third, and fourth. In speaking of adduction and abduction in the case of the foot, reference is made to an imaginary line passing through the centre of the second toe, adduction being movement towards that line, and abduction movement from it. The first and second dorsal interossei, acting both upon the second toe, abduct it from the imaginary line passing through its centre, the first abducting it to the inner side and the second to the outer side. The third and fourth dorsal interossei abduct the third and fourth toes. The interosseous muscles, aided by the lumbricales, also act as follows : (i) they flex the metatarso-phalangeal joints of the four outer toes, and (2) they extend the interphalangeal joints of these toes. The tendons of the peroneus longus and tibialis posticus have been already described. Plantar Nerves. — The plantar nerves are two in number, internal and external. They are the terminal branches into which the posterior tibial nerve divides on a level with the lower border of the internal annular ligament, though the division frequently takes place on a level with the upper border of that ligament, or at some point beneath it. The internal plantar is the larger of the two nerves, and it accompanies the internal plantar artery, which is the smaller of the two plantar arteries. The external plantar nerve accompanies the external plantar artery. Internal Plantar Nerve. — This nerve has a wider cutaneous, but a more limited muscular, distribution than the external plantar. From its origin it passes forwards on the outer side of the internal plantar artery, being at first under cover of the abductor hallucis, and subsequently lying between that muscle and the flexor brevis digitorum. About the middle (in length) of the foot it divides into its terminal branches. Branches. — ^These are muscular, articular, plantar cutaneous, and digital. The muscular branches supply the abductor hallucis and flexor brevis digitorum. The articular branches are distributed to the astragalo-navicular and naviculo-cuneiform articulations. The plantar cutaneous branches are distributed to the integu- ment of the inner half of the sole. The digital branches are four in number, and are named first, second, third, and fourth from within outwards. The first is a single nerve, but the other three are compound. The first digital THE LOWER LIMB 559 nerve is distributed to the inner side of the great toe, and it furnishes a branch to the flexor brevis hallucis muscle. The second digital ner\'e gives off a twig to the first lumbricalis, and near the cleft between the great toe and the second it divides into two collateral plantar digital nerves, which supply the contiguous sides of these two toes. The third digital ner\^e divides near the cleft between the second and third toes into two collateral plantar digital nerves, which supply the contiguous sides of these two toes. The fourth digital nerve also divides near the cleft between the third and fourth toes into two collateral plantar digital ner\-es, which supply the contiguous sides of these two toes. Before dividing, it communicates by a twig \\dth that digital branch of the superficial division of the external plantar which supphes the con- Calcaneo-plantar of Posterior .^i- Tibial Internal Plantar Branches of Internal Saphenous; Branch to Flexor Brevis Hallucis. _ Branch to First Lumbricali: Branches of External Saphenous External Plantar Superficial Branch Deep Branch Fig. 263. — Diagram of the Nerves of the Foot (Plantar Aspect). tiguous sides of the fourth and fifth toes. The nerves on the sides of the toes are placed below the digital arteries. They furnish articular branches to the joints of the toes and cutaneous branches to the plantar and dorsal surfaces of the toes. Finally each ter- minates in two branches — one to the matrix of the nail, and the other to the pulp of the toe. The branches of the digital nerves are beset with numerous Pacinian bodies. Summary of the Internal Plantar Nerve. — Museular branches to abductor hallucis. flexor brevis digitorum. flexor brevis hallucis, and first lumbricalis. Cutaneous branches to the integument of the inner half of the sole and the inner three and a half toes. Articular branches to the astragalo-navicular, naviculo-cuneiform, and digital articulations. The internal plantar nerve in its digital distribution corresponds closely 56o A MANUAL OF ANATOMY with the median nerve in the hand. There is this difference, however, between these two nerves : the internal plantar has one single digital nerve and three compound digital nerves, whereas the median has three single digital nerves and two which are compound. External Plantar Nerve. — This nerve has a more hmited cutaneous, but a wider muscular, distribution than the internal plantar. From its origin it is directed forwards and outwards to the base of the fifth metatarsal bone, where it breaks up into two divisions, super- ficial and deep. In this course it lies at first between the flexor brevis digitorum and flexor or musculus accessorius, and subse- quently in the groove between the former muscle and the abductor minimi digiti. It is close to the inner side of the external plantar artery, and occupies the concavity of the curve described by that vessel. This part of the nerve is spoken of as the trunk. Branches of the Trunk. — The branches are as follows : muscular to the flexor or musculus accessorius and abductor minimi digiti ; articular to the calcaneo-cuboid articulation ; cutaneous to the integument of the outer half of the sole ; and terminal. The terminal branches are two in number, superficial and deep, and they spring from the trunk at the base of the fifth metatarsal bone. The superficial division furnishes two digital nerves, outer and inner. The outer digital nerve is single, and is distributed to the outer side of the little toe, supplying branches to the flexor brevis minimi digiti and, as a general rule, to the interosseous muscles of the fourth interosseous space, namely, the fourth dorsal and the third plantar. It may, however, fail to supply these two interosseous muscles, in which case they derive their nerve-supply from the deep division of the external plantar nerve. The inner digital nerve is compound. In its forward course it communicates by a twig with the most extegrnal digital branch of the internal plantar nerve which supplies the contiguous sides of the third and fourth toes, and near the cleft between the fourth and fifth toes it divides into two collateral plantar digital nerves, which supply the contiguous sides of these two toes. The digital branches of the superficial division of the external plantar nerve resemble in all respects those of the internal plantar. The deep division is muscular and articular in its distribution. It sinks deeply into the sole with the external plantar artery as that vessel forms the plantar arch. Its direction is inwards and forwards on the deep or superior surface of the musculus acces- sorius, long flexor tendons and lumbricales, and adductor obliquus hallucis, and lying upon the bases of the second, third, and fourth metatarsal bones. Branches. — The branches of the deep division are muscular, articular, and perforating. The muscular branches supj)ly (i) the interosseous muscles, plantar and dorsal, with the exception, as a general rule, of the two which occupy the fourth interosseous space, namely, the THE LOWER LIMB S6\ fourth dorsal and third plantar — though these two may be in- cluded ; (2) the outer three lumbricales ; (3) the adductor trans- versus hallucis ; and (4) the adductor obliquus hallucis. The articular branches supply the tarsal and tarso-metatarsal articulations. They sometimes also supply the metatarso-phalangeal articulations. The perforating branches pass upwards through the proximal parts of the interosseous spaces, and join the interosseous branches of the dorsalis pedis nerve. Snmmary of External Plantar Nerve. — Muscular branches to the flexor or musculus accessorius, abductor minimi digiti, flexor brevis minimi digiti, all seven interossei, outer three lumbricales, adductor transversus hallucis. and adductor obliquus hallucis. Cutaneous branches to the integument of the outer half of the sole and the outer one and a half toes. Articular branches to the tarsal, tarso-metatarsal, and, in some cases, metatarso-phalangeal articulations. Perforating branches to join the interosseous nerves on the- dorsum of the foot. The external plantar nerve corresponds with the ulnar nerve in the hand. Plantar Arteries. — ^The arteries of the sole of the foot are three in number, namely, the internal plantar, the external plantar, and the plantar branch of the arteria dorsalis pedis. The internal and external plantar arteries are the terminal branches into which the posterior tibial divides on a level with the lower border of the internal annular ligament. The internal plantar is much smaller than the external, and each vessel is accompanied by the corre- sponding plantar nerve. Internal Plantar Artery. — This vessel passes forwards along the inner side of the sole with the internal plantar nerve, which lies on its outer side, and it usually terminates on the inner aspect of the metatarso-phalangeal joint of the great toe by anastomosing with the digital branch of the arteria magna or princeps hallucis to the inner side of that toe. It is at first under cover of the abductor hallucis, and subsequently lies between that muscle and the flexor brevis digitorum. It is accompanied by two venae comites. Branches. — ^These are as follows : Muscular to the muscles in its immediate vicinity. Cutaneous to the integument of the inner half of the sole. Articular to the articulations along the inner side of the foot. The internal tarsal branches pass inwards beneath the abductor hallucis to the inner border of the foot, where they anastomose with the internal tarsal branches of the arteria dorsahs pedis. The superficial digital arteries are three in number, and are usually very small. They accompany the three compound digital branches of the internal plantar nerve to the clefts where these nerves divide into their collateral branches, and there they terminate by joining the inner two digital arteries from the plantar arch and the arteria magna or princeps hallucis. 36 562 A MANUAL OF ANATOMY External Plantar Artery. — This vessel, which is much larger than the internal plantar, arises from the posterior tibial artery on a level with the lower border of the internal annular ligament, External Plantar Artery Internal Calcaneal Artery , Posterior Tibial Artery ^ Internal Plantar Artery Tibialis Posticus Peroneus Brevis... Posterior Perforating. Artery First Digital Artery Plantar Arch. Second Digital A.. Third Digital A. Fourth Digital A. Anterior Perforating, Artery — -.Flex. Longus Digitorum Flex. Longus Hallucis _\i . Flexor Accessorius --Tendon of Abd. Hallucis Plantar Branch of -.Dorsalis Pedis Aitery Communicating Branch - Arferia Magna Hallucis Fig. 2G4. — The Plantar Arteries (Left Foot) (after L. Testut's ' Anatomie Humaine'). and terminates at the proximal part of the first interosseous space by anastomosing with the communicating branch of the plantar division of the arteria dorsalis pedis. THE LOWER LIMB 5^3 The artery is accompanied by the external plantar nerve through- out its whole course, and by two venae comites. At its origin it is situated on the inner surface of the os calcis, from which point it is directed outwards and forwards across the sole to the base of the fifth metatarsal bone. It here describes a sharp bend, and, sinking deeply, it recrosses the sole on its way to the proximal part of the first interosseous space. The vessel is divided into two parts, first and second. These two parts together describe one great curve, the concavity of which looks inwards and is occupied by the external plantar nerve. The first part extends from the lower border of the internal annular ligament to the base of the fifth metatarsal bone. Its course may be indicated by drawing a hne from a point midway between the tip of the internal malleolus and the inner tubercle on the plantar aspect of the tuber calcis to the base of the fifth metatarsal bone. The direction of this part is outwards and forwards. Relations. — It is covered in succession by the abductor hallucis, flexor brevis digitorum, and finally only by the skin, superficial fascia, and plantar fascia. It rests upon the os calcis and the musculus accessorius. It is to be noted that this part of the vessel is very superficial for a short distance close to the base of the fifth metatarsal bone, where it lies between the flexor brevis digitorum and abductor minimi digiti. The second part extends from the base of the fifth metatarsal bone to the proximal part of the first interosseous space. Its course may be indicated by a line connecting the limits of this part of the vessel. It is directed inwards and forwards in a slightly curved manner, with the convexity of the cur\^e forwards, and thus it forms the plantar arch, which is completed by the communicating branch of the plantar division of the arteria dorsalis pedis. The second part is accompanied by the deep division of the external plantar nerve, and is very deeply placed. Relations. — It is covered by the skin, superficial fascia, central division of the plantar fascia, flexor brevis digitorum, flexor longus digitorum, lumbricales, and adductor obhquus hallucis. It rests upon the bases of the second, third, and fourth metatarsal bones cind the corresponding interosseous muscles. Branches of the First Part. — ^The branches are as follows : Muscular to the muscles in its immediate vicinity. The internal calcaneal branches are two or three in number. After piercing the origin of the abductor hallucis, they reach the inner surface of the os calcis, where they anastomose with the internal calcaneal branch of the posterior tibial artery. Over the prominence of the heel they also anastomose freely with the external calcaneal branches of the posterior peroneal artery. Cutaneous to the integument of the outer half of the foot. Branches also turn round the outer border of the foot, where they anastomose with the tarsal and metatarsal branches of the arteria dorsalis pedis and with the posterior peroneal artery. 564 A MANUAL OF ANATOMY Branches of the Second Part. — The branches of the second part, or plantar arch, are as follows : articular, posterior perforating, and digital. The articular branches arise from the concavity of the arch, and pass backwards to supply the tarsal articulations. The posterior perforating arteries, which are three in number, arise from the upper aspect of the arch. They pass upwards through the proximal parts of the three outer interosseous spaces, and between the two heads of the corresponding dorsal interosseous muscles. On reaching the dorsum of the foot they anastomose with the dorsal interosseous branches of the metatarsal artery, which is a branch of the arteria dorsalis pedis. The digital arteries are four in number — first, second, third, and fourth, from without inwards. They arise from the front or convexity of the arch and pass forwards. The first, which is a single artery, lies over the fifth metatarsal bone and flexor brevis minimi digiti. The second, third, and fourth, which are compound arteries, are placed over the fourth, third, and second interosseous spaces respectively, where they lie upon the corresponding inter- osseous muscles. The first is distributed to the outer side of the little toe, of which it is the plantar digital artery. The second, third, and fourth pass over the deep surface of the adductor transversus hallucis, and bifurcate near the clefts between the four outer toes, each dividing into two collateral plantar digital arteries. Those of the second supply the contiguous sides of the fourth and fifth toes, those of the third the contiguous sides of the third and fourth toes, and those of the fourth the contiguous sides of the second and third toes. Each of the inner three digital arteries at its point of bifurcation gives off an anterior perforating artery. These anterior perforating arteries pass upwards through the distal ends of the outer three interosseous spaces, and, on reaching the dorsum of the foot, anastomose with the dorsal interosseous arteries. The inner two (third and fourth) digital arteries are joined near the clefts of the toes by the outer two superficial digital branches of the internal plantar artery. On the sides of the toes the plantar digital arteries furnish branches to the flexor tendons and their sheaths, and anastomose freely with the dorsal digital arteries. Near the distal end of the first and second phalanx, and on the plantar aspect of each, the plantar digital arteries of opposite sides form arches from which articular twigs are given to the interphalangeal articulations, and on the plantar aspect of the terminal phalanx they end by forming another arch. From this latter arch branches are furnished to the pulp of the toe and matrix of the nail. Each digital artery is accom- panied by two vencB comites. The external plantar artery corresponds with the deep branch of the ulnar artery in the palm. It has been seen that the plantar arch, by means of its four digital branches, supplies the outer three and a half toes. There THE LOWER LIMB 5^5 thus remain one and a half to be accounted for, namely, both sides of the great toe and the inner side of the second toe. Plantar or Perforating Branch of Arteria Dorsalis Pedis. — ^This artery is one of the terminal branches of the arteria dorsalis pedis. Having entered the sole through the proximal part of the first interosseous space, between the two heads of the first dorsal inter- osseous muscl^, it immediately divides into two branches — com- municating and arteria magna or princeps hallucis. The communicating branch is a short vessel, which ends by joining the second part of the external plantar artery to complete the plantar arch. The arteria magna or princeps hallucis is the fifth plantar digital artery. Commencing at the proximal end of the first inter- osseous space it passes forwards over the plantar aspect of that space and the corresponding dorsal interosseous muscle towards the cleft between the great toe and second toe. In this part of its course it furnishes a single plantar digital artery, which, having crossed the first metatarsal bone, beneath the tendon of the flexor longus hallucis, is distributed to the inner side of the great toe. Near the cleft between the great toe and second toe it receives the innermost superficial digital branch of the internal plantar artery, and then divides into two collateral plantar digital arteries for the supply of the contiguous sides of these two toes. Before dividing, it communicates with the arteria dorsaUs hallucis by an anterior perforating branch, which passes through the distal end of the first interosseous space. Varieties — i. Internal Plantar Artery. — This vessel is sometimes very small, and it may then terminate in the flexor brevis hallucis. In other cases it is of fairly large size, and then it may replace the arteria magna or princeps hallucis, and furnish the plantar digital branches for both sides of the great toe and the inner side of the second toe. In very rare cases the internal plantar artery communicates with the external plantar, and so forms a super- ficial plantar arch. In such cases the superficial digital arteries arise from this arch. 2. External Plantar Artery. — This artery is liable to be diminished in size, and this may occur to such an extent as to exclude it from any share in the plantar arch. Such deficiencies are compensated for by an enlargement of the arteria dorsaUs pedis and its plantar branch. The posterior perforating branches of the plantar arch are sometimes of comparatively large size, and then they furnish the dorsal interosseous arteries after they reach the dorsum of the foot. For the tendon of the peroneus longus in the sole see p. 516. Tendons Involved in Club-loot. The chief varieties of club-foot are as follows : talipes equinus, talipes varus, talipes equino-varus, talipes valgus, taUpes calcaneus, and tahpes calcaneo- valgus. Talipes Equinus. — In this variety the foot is extended upon the leg, the heel being raised from the ground, so that the person walks upon the toes. The chief tendons involved are (i) the tendo Achillis, and (2) the plantaris tendon. The latter, however, is insignificant. Talipes Varus. — In this variety the inner border of the foot is raised so as to invert the sole, and the foot is at the same time slightly extended upon 566 A MANUAL OF ANATOMY the leg, so that the person walks upon the outer border of the foot. The chief tendons involved are those of the tibialis anticus and tibialis posticus. Talipes Equino-varus. — This is a combination of talipes equinus and talipes varus, the heel being raised as well as the inner border of the foot. The chief tendons involved are as follows : (i) tibialis posticus, (2) tibialis anticus, (3) tendo Achillis, and (4) plantaris. In addition to these tendons the abductor hallucis and the plantar fascia are usually implicated. Talipes Valgus. — In this variety the outer border of the foot is raised so as to evert the sole, and the person walks upon the inner bdrder of the foot. The tendons involved are those of the peroneus longus and peroneus brevis. Talipes Calcaneus. — In this variety the foot is flexed upon the leg, the toes being raised, so that the person walks upon the heel. The tendons involved are as follows : (i) extensor longus digitorum, (2) peroneus tertius, (3) extensor proprius hallucis, and (4) tibialis anticus. Talipes Calcaneo-valgus. — This is a combination of talipes calcaneus and talipes valgus, the foot being flexed and the outer border of the foot raised. The tendons involved are those which are implicated in talipes calcaneus and talipes valgus. Summary of the Veins of the Lower Limb. The veins of the lower limb are divided into two groups — superficial and deep. Superficial Veins. — In the sole of the foot there are (i) a plantar sub- cutaneous plexus, and (2) a transverse venous arch situated near the clefts of the toes, which receives the plantar digital veins. The blood is carried away from the plantar subcutaneous plexus by anterior and lateral efferent vessels. The anterior efferent vessels terminate in the transverse venous arch near the clefts of the toes. The lateral efferent vessels turn round the outer and inner borders of the foot, the external set terminating in the short saphenous vein, and the internal set in the long saphenous vein, where these vessels spring from the dorsal venous arch. The blood is conveyed away from the transverse venous arch by means of efferent veins, called interdigital, which pass upwards to the dorsum of the foot, where they terminate in the dorsal venous arch. The dorsal venous arch is situated well forward upon the dorsum of the foot, being about 2 inches from the webs of the toes. It receives (i) the dorsal digital veins, (2) small veins from the dorsum of the foot, and (3) the efferent interdigital veins from the plantar transverse venous arch. Tiie blood is carried away from the dorsal venous arch by the long and short saphe- nous veins. The long saphenous vein arises from the inner end of the arch, and, having received branches from the plantar subcutaneous venous plexus, passes in front of the internal malleolus, and thus reaches the inner side of the leg. Its subsequent course is upwards along the inner side of the leg, knee, and thigh, and finally, having reached the front of the thigh, it passes through the saphenous opening i^ inches below Poupart's ligament, and ter- minates in the femoral vein. It receives many tributaries in its course ; in the leg it communicates at frequent intervals with the venae comites of the anterior and posterior tibial arteries by intermuscular branches ; and near its termination it is reinforced by the posterior saphenous, anterior saphenous, superficial circumflex iliac, superficial epigastric, and superior and inferior external pudic veins. The short saphenous vein arises from the outer end of the dorsal venous arch, and, having received branches from the plantar subcutaneous venous plexus, it passes below and behind the external malleolus, and thus reaches the back of the leg. It then passes upwards and inwards, and subsequently straight upwards until it arrives at the interval between the condyles of the femur. Here it passes through an aperture in the fascia lata, and terminates in the jjopliteal vein. It receives many tributaries from the calcaneal region and the outer and back parts of the lo^ ; it communicates at intervals with the ven;c comites of the posterior tibial THE LOWER LIMB 567 and peroneal arteries ; and near its termination it communicates with the long saphenous vein. Deep Veins. — The deep veins accompany the various arteries and their branches. Below the level of the pophteus muscle they are arranged in pairs along the arteries which they accompany, this arrangement being known as venae comites. Opposite the lower border of the popliteus muscle the posterior tibial venae comites, having pre- \aously received the peroneal venae comites, unite with the anterior tibial venae comites, and so the popUteal vein is formed, which is continued into the femoral vein. Lymphatic Vessels of the Lower Limb. The lymphatic vessels of the lower limb are arranged in t^vo groups — superficial and deep. Superficial Lymphatics. — These form two sets, which are conveniently designated as internal saphenous and external saphenous from the veins which they accompany. 1. Internal Saphenous Lymphatics. — On the plantar aspect of each toe there is a digital lymphatic plexus, from which four Ijnnphatic vessels emerge, these being arranged in pairs on either side of the toe. They pass to a plexus on the dorsal aspect of the foot, and this plexus is reinforced by lymphatics from the plantar region which reach it at the clefts bet\veen the toes. From the dorsal plexus tvvo sets of vessels issue — internal and external. The internal vessels receive their lymph from about the inner one- third of the dorsal plexus and from the inner two toes. They also receive the internal plantar and internal calcaneal lymphatic vessels, and there- after they accompany the internal saphenous vein and finally empty into the superficial femoral glands. The externa! vessels of the dorsal plexus receive their lymph from about the outer two- thirds of the plexus and from the outer three toes. They also receive some Ij^mphatic vessels from the external plantar region. Thereafter they pass in front of the external malleolus, and, as they ascend in front of the leg, they soon inchne inwards and join the internal vessels of the dorsal plexus, which by this time form the internal saphenous lymphatics. 2. External Saphenous Lymphatics. — These ves- sels come from the outer border of the foot, over about its posterior half, and from the outer side of the heel. They accompany the external saphenous vein, and, as they ascend, they take up lymphatics from the superficial structures of the back of the leg. Finally they pierce the deep fascia over the popUteal space, and terminate in the popliteal glands, very often in that gland which hes close to the termination of the external saphenous vein. The superficial femoral lymphatics from (i) the lower and outer parts, (2) the front, (3) the lower and inner parts, and (4) the posterior parts of the thigh pass to the superficial femoral glands. The Fig. 265. — Superficial Lymphatics of tiIe Lower Limb. 568 A MANUAL OF ANATOMY lymphatic vessels from the knee-joint pass, for the most part, to the popliteal glands, but some ascend to the superficial femoral glands. The supeyficial lymphatics from the outer and back parts of the thigh supe- riorly pass to the inguinal glands, and those from the upper and inner parts of the thigh terminate in the pubic glands. The superficial gluteal lymphatics from the outer two-thirds of the gluteal region pass to the inguinal glands; and those from the inner one-third ter- minate partly in the pubic glands and partly in the superficial femoral glands. Deep Lymphatics of Lower Limb. — The deep lymphatic vessels accompany the main arteries. They form groups as follows: (i) Dorsalis pedis and anterior tibial; (2) plantar and posterior tibial; (3) peroneal; (4) femoral; (5) sciatic; (6) gluteal; and (7) obturator. The dorsalis pedis and anterior tibial lymphatics arise in the deep structures of the sole of the foot, and they reach the dorsum of the foot along the plantar or perforating branch of the dorsalis pedis artery. They then accompany the dorsalis pedis and anterior tibial arteries, taking up the deep lymphatics of the dorsum of the foot and front of the leg. Thereafter they terminate in the anterior tibial gland, the efferent vessels of which pass to the popliteal glands. The plantar and posterior tibial lymphatics arise, like the preceding group, in the deep structures of the sole of the foot, and they accompany the two plantar arteries, especially the external -plantar artery. . Thereafter they pass along the posterior tibial artery and terminate in the popliteal glands. The peroneal lymphatics arise in (i) the back part of the outer border of the foot, (2) the outer surface of the heel, and (3) the front of the external malleolus. They accompany the peroneal artery, taking up lymphatics from the deep structures on the back of the fibula, and in the upper part of the leg they terminate in the posterior tibial lymphatics. The deep femoral lymphatics represent (i) the efferent vessels of the popliteal glands, which accompany the superficial femoral artery, and (2) the lym- phatic vessels which accompany the arteria profunda femoris and its branches. They take up lymphatics from the deep structures on the inner and front aspects of the thigh, and they terminate in the deep femoral glands. The sciatic lymphatics return lymph from the structures supplied by the sciatic artery, which they accompany. Their destination is the internal iliac glands within the pelvis. The deep gluteal lymphatics arise in the gluteal muscles and other deep structures of the gluteal region. They accompany the gluteal artery, and, within the pelvis, they terminate in the internal iliac glands. The obturator lymphatics arise in the obturator membrane, obturator externus muscle, and upper portions of the adductor muscles. They accom- pany the obturator artery as that vessel passes through the obturator canal, and they terminate in the obturator gland, which, when present, lies in the obturator canal. If this gland is absent, they pass to the middle gland of the internal set of the external iliac glands. Summary of the Lymphatic Glands. — The lymphatic glands of the lower limb form the following groups : 1. InguinaL 4- Deep Femoral. 2. Pubic. 5 Popliteal. 3. Superficial Femoral, or Saphenous. 6. Anterior TibiaL Development of Arteries of Lower Limbs. The primary arterial stem of each lower limb is formed by the following arteries, in order from above downwards: (i) The sciatic artery, which accom- panies the great sciatic nerve; (2) the popliteal artery; and (3) the peroneal artery. A little below the knee-joint the popliteal artery gives off the anterior tibial artery, which is reinforced inferiorly by a branch of the peroneal artery. The arterial stem, as in the upper limb, is segmental in origin. The common iliac arteries represent a fifth pair of abdominal segmental arteries, and each THE LOWER LIMB 569 sciatic artery is developed from the hypogastric portion (subsequently internal iliac portion) of a common iliac artery. The external iliac and femoral arteries are formed at a later period, the external iliac being a secondary outgrowth from the common ihac at a higher level than the origin of the sciatic artery. The external iliac artery is con- tinued into the femoral, and the femoral artery joins the pophteal artery at the place where the sciatic artery is continued into that vessel. The sciatic artery now undergoes retrogression, and the part of it between the popliteal artery and the gluteal region for the most part disappears. The upper part of the primitive vessel, however, persists, and forms the sciatic cirtery (arteria gliitea inferior) of adult Ufe. Before the femoral artery joins the popliteal it gives off a fairly large branch, which accompanies the internal saphenous vein, and is called the internal saphenous artery. This vessel for the most part atrophies, but its upper portion persists and represents the superficial branch of the arteria anastomotica magna. The posterior tibial artery is developed from the upper part of the peroneal artery. Development of Veins of Lower Limbs. The veins of the lower limb form two groups — superficial and deep. The superficial veins are developed prior to the deep, the latter accompanying the arteries. The primitive vein of each lower limb is the primary fibular, or post-axial, vein, which opens proximally into the posterior cardinal vein. From the primary fibular vein a temporary anterior tibial vein is developed. The long saphenous vein grows distally from the posterior cardinal vein. A temporary posterior tibial vein is developed from the long saphenous vein. The primary fibular vein, which is originally continuous with the sciatic vein, loses its connection with that vessel, and persists as the short saphenous vein. THE ANKLE-JOINT. The ankle-joint belongs to the class diarthrosis, and to the sub- division ginglymus. The articular surfaces are the lower extremity of the shaft and the outer surface of the internal malleolus of the tibia, the inner surface of the external malleolus of the fibula, and the superior and both lateral surfaces of the astragalus. The ligaments are anterior, posterior, internal lateral, and external lateral. The anterior ligament is a thin membrane which covers the joint in front. Superiorly it is attached from within outwards to the anterior border of the internal malleolus, anterior surface of the lower end of the tibia two or three lines above the anterior border, anterior inferior tibio-fibular ligament, and anterior border of the external malleolus. Inferiorly it is attached to a groove on the upper aspect of the head of the astragalus, immediately behind the cartilaginous surface and in front of the neck. The fibres of the' ligament are chiefly disposed in a transverse direction. In addition to the tendons which lie upon it, this ligament is related to the anterior tibial vessels and nerve. Its deep surface is covered by the synovial membrane of the joint, and inferiorly is in contact with a collection of fat which lies in the hollow on the upper surface of the neck of the astragalus. A MANUAL OF ANATOMY The posterior ligament is weaker and less defined than the anterior. Superiorly it is attached from without inwards to the posterior aspect of the external malleolus internal to the peroneal groove, posterior inferior tibio-fibular ligament, and posterior border of the tibia as far inwards as the groove behind the internal malleolus. Inferiorly it is attached to the upper aspect of the posterior border of the astragalus immediately behind the superior articular surface, where it extends between the posterior fasciculus of the external lateral ligament and the internal lateral hgament. Its fibres are disposed obliquely, and radiate in an inward direction from the external malleolus. - -Interosseous Membrane Internal Malleolus - Astragalus - Internal Lateral Ligament- Groove for Flexor. Longus Hallucis Int. Astragalo-calcaneal Ligament Tuber Calcis Posterior Tibio-fibular Ligament -External Malleolus Posterior Band of External Lateral Ligament Ext. Astragalo-calcaneal Ligament Middle Band of External Lateral Ligament Fig. 266. — The Right Ankle-Joint (Posterior View). (The Posterior Ligament has been removed.) The internal lateral ligament is also known as the deltoid ligament. It is a strong, flat, triangular structure, which is attached superiorly to the lower border, tip, and anterior border of the internal malleolus, in which latter situation it is superficial to the fibres of the anterior ligament. A strong bundle of fibres springs from the notch which indents the lower border of the internal malleolus. From the superior attachment the fibres diverge in a radiating manner. The posterior fibres, strong and short, descend with an inclination backwards to be attached to the rough, de- pressed inner surface of the astragalus below the internal facet, where they extend as far back as the inner tubercle on the posterior border of the bone. The anterior part of the ligament, somewhat thinner and more radiating than the jjosterior, is attached to THE LOWER LIMB 571 ihe inner border of the sustentaculum tali of the os calcis, inner border of the internal calcaneo-navicular or spring ligament, and inner part of the dorsal surface of the navicular bone. The external lateral ligament is composed of three distinct fascicuh — anterior, middle, and posterior. The anterior fascicidus {astr a galo- fibular) is flat, and extends from the lower part of the anterior border of the external malleolus to the outer surface of the astragalus immediately in front of the external facet. Its direction is forwards and inwards, and it is the shortest of the three fasciculi. The middle fasciculus {calcaneo- fibular) , which is round, is attached superiorly to the tip of the external malleolus, and interiorly to a tubercle on the outer surface of the os calcis situated about the centre, behind and above the peroneal spine. Its direction is down- Internal Lateral Ligament Posterior Ligament of Ankle Posterior Astragalo- calcaneal Ligament Long Plantar Ligament Inferior Calcaneo-navicular Ligament Fig. 267. — Ligaments of the Right Foot (Internal View). wards and backwards, and it is related to the tendons of the peroneus longus and peroneus brevis. The posterior fasciculus {astragalo -fibular) is the strongest bundle of the three. It is attached by one extremity to the lower part of the digital fossa on the inner surface of the external malleolus behind the articular facet. The other extremity is attached to the upper surface of the outer tubercle on the posterior border of the astragalus. Its direction is inwards and slightly backwards. The synovial membrane lines the inner surfaces of the liga- ments in a loose manner, and it covers collections of fat (Haver- sian glands) at the front and back of the joint, where it forms folds 572 A MANUAL OF ANATOMY which project between the astragalus and the tibia. It is also prolonged into the inferior tibio-fibular articulation so as to line the anterior and posterior ligaments of that joint. Tendinous Relations of the Ankle- Joint — Anterior. — From within outwards these are the tibialis anticus, extensor proprius hallucis, extensor longus digitorum, and peroneus tertius. External. — Peroneus longus and peroneus brevis. Posterior. — From without inwards these are the peroneus longus and peroneus brevis, tendo Achillis and plantaris, with the intervention of a large amount of fat, flexor longus hallucis, and flexor longus digitorum and tibialis posticus. Internal. — ^Tibialis posticus. Posterior Inferior — Tibio-fibular Lig. \^|^ Posterior Band of. Ext. Lat. Lig. Middle Band of .^ Ext. Lat. Lig. Peroneus Longus Peroneus Brevis Fig. 268. — Ligaments of the Right Inferior Tibio-fibular, Ankle, Tarsal, and Taiiso-metatarsal Joints (External View). Arterial Supply.— The anterior tibial, external and internal malleolar, anterior peroneal, posterior tibial, and posterior peroneal arteries. Nerve-supply.— The posterior tibial, short saphenous, and external division of the dorsahs pedis nerve, or the anterior tibial nerve itself. Movements. — The chief movements at the ankle-joint are flexion and extension. When, however, the foot is extended a certain amount of lateral movement is allowed. The foot is said to be flexed when it is raised from the ground towards the front of the leg, as in standing upon the heels, and it is said to be extended when the hsel is raised towards the back of the leg. THE LOWER LIMB 573 as in standing npon the toes. In flexion of the foot the broad anterior part of the superior articular surface of the astragalus is carried backwards into the narrow posterior part of the tibial socket, and lateral movement is then impossible. Flexion is limited by (i) the tension of the posterior and middle portions of the internal lateral Ugament ; (2) the tension of the posterior and middle fasciculi of the external lateral ligament ; and (3) the locking which takes place between the upper surface of the neck of the astragalus and the anterior border of the lower end of the tibia. In extension of the foot the narrow posterior part of the superior articular surface of the astragalus is carried forwards into contact with the broad anterior part of the tibial socket, and a certain amount of lateral movement can now take place. Exten- sion is limited by (i) the tension of the anterior part of the internal lateral hgament ; (2) the tension of the anterior and middle fascicuU of the external lateral Ugament ; (3) the tension of the anterior ligament, particularly of its inner part ; and (4) the locking of the posterior part of the astragcilus against the posteror border of the lower end of the tibia. The range of movement in the direction of flexion and extension is about 90 degrees, and it takes place round a transverse axis passing through the body of the astragalus in a direction forwards and outwards. At the end of extension there is a tendency to abduction or turning in of the foot, due to the following factors : (i) the greater length posteriorly of the inner border of the superior articular surface of the astragalus ; (2) the greater depression of the corre- sponding part of the outer border of the astragalus ; and (3) adduction at the astragalo-calcaneal joint. The vertical hne of the centre of gravity falls in front of the axis of move- ment at the ankle-joint. There is thus a tendency to over-flexion, which, however, is counteracted by a certain amount of muscular effort on the part of the sural muscles. Muscles concerned in the Movements — Flexion. — This is produced by the tibiaUs anticus, peroneus tertius, extensor longus digitorum, and extensor proprius hallucis. Extension. — This is produced by the gastiocnemius and soleus by means of the tendo AchilUs, plantaris, tibialis posticus, flexor longus digitorum, flexor longus hallucis, peroneus longus, and peroneus brevis. Abduction. — The foot is everted by the peroneus longus and peroneus brevis. Adduction. — The foot is inverted by the tibialis anticus and tibialis posticus. Bursae and Tendon-Sheaths at Ankle-Joint. — ^The synovial borsae in the vicinity of the ankle-joint are as follows: Internal malleolar. Tendo Achlllis. External malleolar. Sinus tarsi. The malleolar bursae are not constant. There may be two mesial over the internal malleolus of the tibia, and lateral over the external malleolus of the fibula. The bursa of the tendo Achillis, which is constant, is situated between the lower part of this tendon and the upper smooth hori- zontal zone on the posterior surface of the tuber calcis. It Ues directly above the insertion of the tendon into the middle rough horizontal zone. The bursa sinus tarsi is situated within the sinus tarsi, between the inferior surface of the astragalus and the superior surface of the OS calcis. It hes within the strong interosseous hgament which binds these two bones together, and it partially separates the anterior and posterior laminae of which the interosseous ligament is composed. None of the foregoing bursae communicate with the sj'novial cavity of the ankle-joint. 574 A MANUAL OF ANATOMY The synovial or tendon-sheaths around the ankle-joint are very numerous and of great importance. In all there are nine sheaths, three of which are in front of the ankle-joint, three behind the internal malleolus between it and the tuber calcis, one behind the external malleolus, and two on the outer surface of the os calcis. The anterior tendon-sheaths, from within outwards, are as follows : Sheath of tendon of tibiahs anticus. Sheath of tendon of extensor longus hallucis. Sheath of tendons of extensor longus digitorum and peroneus tertius. These sheaths, which have no communication with the ankle- joint, frequently become the seat of teno-vaginitis or tenosynovitis. The sheath of the tendon of the tibialis anticus Hke the tendon which it invests, passes through a special compartment in the superior division of the anterior annular ligament, which lies just above the ankle-joint, through a special compartment in the upper band of the inferior division of that ligament, and beneath its lower band, the inferior division of the ligament being placed just in front of the ankle-joint. It is the only synovial sheath within the superior division, and it ceases beneath the lower band of the inferior division, on a level with the scaphoid or navicular bone. The sheath of the tendon of the extensor longus hallucis only invests that tendon as it passes through a special compartment in the upper band of the inferior division of the anterior annular liga- ment. It is not present beneath the superior division of the liga- ment. It commences just above the upper band of the inferior division of the ligament, and it terminates about the level of the joint between the internal cuneiform and first metatarsal bone. The common sheath of the tendons of the extensor longus digi- torum and peroneus tertius only invests these tendons as they pass through a special compartment in the outer single portion (fundi- form ligament of Retzius) of the inferior division of the anterior annular ligament. It is not present beneath the superior division of the ligament. It commences a little above the fundi,form liga- ment of Retzius, and it terminates about the level of the front part of the cuboid bone. The internal malleolar tendon-sheaths are situated between the posterior part^f the internal malleolus and the tuber calcis. They are three in number, and are quite independent of one another. The tendons to which they belong are (i) the tendon of the tibialis posticus, (2) the tendon of the flexor longus digitorum, and (3) the tendon of the flexor longus hallucis. All three sheaths lie beneath the internal annular ligament, which extends between the posterior border of the internal malleolus and the internal border of the tuber calcis. They commence about 2 inches above that ligament, and extend forwards beyond it for about 2 inches in advance of the internal malleolus. These three sheaths are frequently the seat of tenosynovitis. THE LOWER LIMB 575 The external malleolar tendon-sheath is situated behind the external malleolus. It is a common sheath for the tendons of the peroneus longus and peroneus brevis, as they lie one upon the other in the peroneal groove. It is situated beneath the external annular hgament, which extends between the posterior border of the ex- ternal malleolus and the outer border of the tuber calcis, and it com- mences about 2 inches above that ligament. After escaping from beneath the hgament the single sheath now forms two independent sheaths, one for the peroneus longus tendon, and the other for the peroneus brevis tendon, as these two tendons pass fonvards over the outer surface of the os calcis. The two sheaths terminate about I inch behind the level of the tuberosity on the outer side of the base of the fifth metatarsal bone. Teno-synovitis is not uncommon in the sheath behind the external malleolus. All the synovial bursae and tendon-sheaths in the vicinity of the ankle-joint are quite distinct from the synovial cavity of that joint. THE TIBIO-FIBULAR JOINTS. The superior and inferior extremities of the tibia and fibula form direct articulations, and the shafts are connected by means of an interosseous membrane and inferior interosseous ligament. Superior Tibio-fibular Joint. — This joint belongs to the class diarthrosis, and to the subdivision arthrodia. The articular sur- faces are the facets on the head of the fibula and on the external tuberosity of the tibia, and the ligaments are two in number, namely, anterior and posterior. Their fibres pass downwards and outwards from the outer tuberosity of the tibia to the head of the fibula, and they completely cover the joint in front and behind. Superiorly and inferiorly they meet, and thus construct a capsule for the joint. The anterior division of the tendon of the biceps femoris is closely related to the anterior ligament, and contributes materially to the strength of the joint, the more so because that division has an insertion into the outer tuberosity of the tibia as well as into the upper surface of the head of the fibula. The synovial membrane is usually distinct from that of the knee- joint. Occasionally, however, it is in communication with it posteriorly by means of the synovial investment which surrounds the tendon of the popliteus. Arterial Supply. — ^The arterial supply is derived from the inferior external articular, posterior tibial recurrent (inconstant), and anterior tibial recurrent arteries. Nerve-supply. — ^The inferior external articular and recurrent articular, both branches of the external popliteal, and the nerve to the popliteus muscle, which is a branch of the internal p)opliteal. Movements. — The movements are extremely limited, and are of a gliding or to-and-fro nature in an upward and downward direction. The knee being 57<5 A MANUAL OF ANATOMY almost fully extended, if the fingers are placed over the head of the fibula whilst the foot is alternately flexed and extended, the head of the bone will be felt to glide upwards during flexion and downwards during extension of the foot. Inferior Tibio-fibular Joint. — This joint belongs to the class diarthrosis, and to the subdivision arthrodia. The articular sur- faces are the upper part of the facet on the inner surface of the external malleolus of the fibula and the sigmoid cavity on the outer aspect of the lower end of the tibia. The ligaments are an- terior, posterior, inferior interosseous, and transverse. The anterior ligament is a strong, fiat band, the fibres of which pass obliquely downwards and outwards from the tibia to the fibula. It is related anteriorly to the peroneus tertius, and posteriorly is in contact with the inferior interosseous ligament. The posterior ligament, which is disposed like the anterior, is in contact with the transverse ligament inferiorly, and with the inferior interosseous ligament anteriorly. The inferior interosseous ligament is an important ligament, and is of considerable strength. It consists of short fibres which pass directly between the opposed rough triangular surfaces at the lower ends of the shafts of the tibia and fibula. It is continuous above with the interosseous membrane, and its extent is about i^ inches. Anteriorly and posteriorly it is in part related to the anterior and posterior inferior tibio-fibular ligaments. The part of the inferior tibio-fibular joint occupied by the inferior, inter- osseous ligament belongs to the class amphiarthrosis, and to the subdivision syndesmosis. The transverse ligament, which is strong, narrow, and somewhat round, extends almost horizontally from the posterior border of the lower end of the tibia to the upper part of the digital fossa of the external malleolus. Externally it lies along the lower border of the posterior inferior tibio-fibular ligament, by which it is slightly overlapped. It fills up a slight hollow between the tibia and fibula, and it plays across the back part of the upper articular surface of the astragalus, where it usually gives rise to a transverse groove. The transverse ligament completes the back part of the tibial socket for the upper surface of the astragalus. The synovial membrane is continuous with that of the ankle- joint. Arterial Supply. — The posterior and anterior peroneal arteries, and the external malleolar of the anterior tibial. Nerve-supply. — The interosseous branch of the nerve to the pop- liteus muscle, and the external division of the dorsalis pedis nerve. Movements. — These are very limited, and are of a gliding nature, chiefly upwards and downwards, the fibula moving on the tibia. Though the bones are firmly bound together by the inferior interosseous ligament, there is yet a certain amount of lateral separation allowed during flexion of the foot. Intermediate Connection between the Tibia and Fibula. — The union between the shafts of the tibia and fibula is effected by The lower limb 577 means of an interosseous membrane. This kind of union is a form of syndesmosis (union by an interosseous ligament). The inter- osseous membrane extends from the external border or interosseous ridge of the tibia to the antero-internal border or interosseous ridge of the fibula. The chief direction of the fibres is do^vn\vards and outwards from the tibia to the fibula, but a few pass in the opposite direction. Superiorly it terminates about i inch below the superior tibio-fibular joint in a sharp concave margin, the concavity of which is directed upwards. An interval is thus left above the membrane for the passage of the anterior tibial vessels and the efferent lymphatics of the anterior tibial gland. Sometimes these structures pass through a distinct aperture in the membrane, called the superior hiatus. Interiorly it becomes continuous with the inferior interosseous hgament, and in this neighbourhood it presents a small opening or inferior hiatus for the passage of the anterior peroneal vessels. The interosseous membrane serves as a surface of origin to muscles. Relations — Anterior. — Tibiahs anticus, over the upper two- thirds of the inner half ; extensor longus digitorum, over the upper fourth of the outer half ; extensor proprius hallucis, over the middle two- fourths of the outer half ; peroneus tertius, over the lower fourth of the outer half ; anterior tibial vessels, over the upper two- thirds in the middle line ; and anterior tibial nerve, over the middle third. Posterior. — Tibialis posticus. Arterial Supply. — ^The anterior tibial and peroneal arteries. Nerve-supply. — ^The interosseous branch of the nerve to the pop- liteus muscle, which descends within it to terminate in the inferior tibio-fibular joint. THE ARCHES OF THE FOOT. The foot presents two arches — antero-posterior or longitudinal and transverse (see Figs. 165, 166). The longitudinal arch has two piers— posterior or calcaneal and anterior or metatarsal. The calcaneal pier is formed by the internal and external tubercles on the plantar aspect of the tuber calcis, and the metatarsal pier is formed by the heads of the metatarsal bones. The longitudinal arch consists of two pillars^intemal and external. The internal pillar is constructed by the os calcis, astragalus, navicular, three cuneiforms, and inner three metatarsal bones. Its calcaneal pier is formed by the internal and external tubercles on the plantar aspect of the tuber calcis, and its metatarsal pier is formed by the heads of the inner three metatarsal bones. The summit of the internal pillar corresponds to the upper articular surface of the astragalus, and through the medium of that bone the greater part of the superincumbent weight is transmitted to the internal pillar. This pillar is much arched, and is character- ized by great strength and elasticity. The part of it most sub- 37 S^S A MANUAL OF ANATOMV jected to pressure is the astragalo-navicular joint. This joint, however, is powerfully braced inferiody by (i) the elastic inferior calcaneo-navicular or spring ligament, which blends internally with the anterior part of the internal lateral, or deltoid, ligament of the ankle-joint; and {2) the strong tendon of the tibialis posticus muscle, which hes on the inferior or plantar aspect of the spring ligament, and acts as a strong auxiliary to it. The external pillar of the longitudinal arch is constructed by the OS calcis, cuboid, and outer two metatarsal bones. Its calcaneal pier is formed by the internal and external tubercles on the plantar aspect of the tuber calcis, and its metatarsal pier is formed by the heads of the outer tivo metatarsal bones. The summit of the ex- ternal pillar corresponds to the highest part of the postero-external facet on the superior surface of the os calcis. Through the medium of the OS calcis the external pillar receives from the astragalus a small part of the superincumbent weight. This pillar is only slightly arched, and is characterized by its stability. The part of it most subjected to pressure is the calcaneo-cuboid joint. This joint, however, is powerfully braced inferiorly by the inferior calcaneo- cuboid ligaments — namely, the long and short plantar ligaments. The two pillars of the longitudinal arch receive material strength from the plantar fascia. The transverse arch of the foot is most conspicuous at the tarso- metatarsal joints. In this situation it is due to (i) the broad aspects of the middle and external cuneiform bones being dorsally placed, and (2) the broad aspects of the wedge-shaped bases of the second, third, and fourth metatarsal bones being also dorsally placed. The arch is braced inferiojly by plantar and interosseous ligaments, and by the tendon of the peroneus longus muscle. The arches of the foot serve the following purposes: (i) They impart strength and elasticity to the foot; (2) they protect the important structures which occupy the sole or plantar region; and (3) they allow of the heel-to-toe movement in walking. THE ARTICULATIONS OF THE FOOT. The articulations of the foot are divided into tarsal, tarso-meta- tarsal, intermetatarsal, metatarso-phalangeal, and interphalangeal. The Tarsal Articulations. I. Astragalo-calcaneal Joints. — The astragalus is connected with the OS calcis by two synovial joints, anterior and posterior, both of which belong to the class diarthrosis, and to the subdivision arthrodia. Posterior Astragalo-calcaneal Joint. —The ligaments are inter- osseous, ])osterior, internal, and external. The interosseous ligament passes between the oblique grooves separating the two articular surfaces of each bone, and forming THE LOWER LIMB 579 b}- their apposition the tunnel called the sinus tarsi. It is very strong, and is to be regarded as the anterior hgament of the posterior astragalo-calcaneal joint. The posterior ligament extends from the posterior aspect of the outer tubercle on the posterior border of the astragalus to the adjacent upper and inner surfaces of the os calcis. It is thin and membranous, and its fibres are arranged in a radiating manner. The internal ligament is a narrow band which passes from the inner tubercle on the posterior border of the astragalus to the back of the sustentaculum tali of the os calcis. It is related to the tendon of the flexor longus hallucis. The external ligament extends from the lower part of the outer surface of the astragalus, below the facet, to be attached to the adjacent part of the outer surface of the os calcis. It is under cover of, and parallel with, the middle fasciculus of the external lateral ligament, which, along with the internal lateral ligament of the ankle-joint, contributes to the strength of this articulation. The synovial membrane of this joint is peculiar to it. Arterial Supply. — The arterial supply is derived from the posterior tibial, external malleolar of the anterior tibial, posterior peroneal, and external tarsal of the dorsaUs pedis artery. Nerve-supply. — The short saphenous and the posterior tibial, or it may be the external plantar, nerves. Anterior Astragalo-calcaneal Joint. — This joint has a lateral liga- ment at either side, and a posterior, but it is continuous anteriorly with the astragalo-navicular joint. The ligaments are interosseous or posterior, internal astragalo-calcaneal, and external or superior calcaneo-navicular. The interosseous or posterior ligament has already been described in connection with the posterior astragalo-calcaneal joint. The internal astragalo-calcaneal ligament extends from the inner surface of the neck of the astragalus to the upper margin of the inner border of the sustentaculum tali of the os calcis. It blends posteriorly with the inner end of the interosseous ligament, and anteriorly with the upper border of the internal calcaneo-navicular or spring hgament. It is strengthened by the internal lateral ligament of the ankle-joint. The internal or inferior calcaneo-navicular or spring hgament is also an internal hgament of this joint, but, inasmuch as it ranks as a ligament of the astra- galo-navicular joint, it will be described in connection with that articulation. The external or superior calcaneo-navicular ligament is placed on the outer side of the joint. It also ranks as an external lateral ligament of the astragalo-navicular joint. It is strong, and extends from the anterior part of the upper surface of the os calcis, external to the anterior facet, to a depression on the outer surface of the navicular bone near its posterior margin. Inferiorly it blends with the internal calcaneo-navicular ligament, and superiorly with the superior astragalo-navicular hgament. 58o A MANUAL OF ANATOMY The synovial membrane, though distinct from that of the posterior astragalo-calcaneal joint, is continuous in front with that of the astragalo-navicular articulation. The arterial supply and nerve-supply are the same as for the astragalo-navicular articulation. Movements between the Astragalus and Os Calcis. — The movements at the astragalo-calcaneal joints are abduction, adduction, and rotation. In abduction the foot and toes are turned outwards, and in adduction they are turned inwards, these movements being associated with a certain amount of rotation round an axis passing from the inner side of the neck of the astra- galus downwards, backwards, and outwards to the lower and outer part of the tuber calcis. In adduction or inversion the posterior facet of the os calcis moves forwards and downwards upon the astragalus, and the front part of the os calcis is carried slightly inwards. During the movements the navicular bone rotates on the head of the astragalus, and the cuboid bone moves along with the os calcis. II. Astragalo-navicular Joint. — This belongs to the class diarthrosis, and to the subdivision enarthrosis. It is in direct continuity behind with the anterior astragalo-calcaneal joint, with which it shares its synovial membrane, and the two articulations are sometimes described as one composite joint under the naiAe of the astragalo-calcaneo-navicular joint. The ligaments are astragalo- navicular, external or superior calcaneo-navicular, and internal or inferior calcaneo-navicular, or spring, ligament. The astragalo-navicular ligament is a thin membrane which covers the joint on its dorsal aspect. It is attached posteriorly to the upper margin of the head of the astragalus close behind the cartilage, and also to its outer and inner surfaces. Anteriorly it is attached to the dorsal surface of the navicular bone. Its fibres are arranged in a radiating manner, and converge towards the navicular bone. At the attachment to the astragalus they frequently form three bands, outer, dorsal, and inner, which, however, are continuous with one another. The external or superior calcaneo-navicular ligament has been described in connection with the anterior astragalo-calcaneal joint, of which it ranks as the external ligament. The internal or inferior calcaneo-navicular ligament is one of the most important ligaments of the foot, and is known as the spring ligament. It is a broad, thick, strong band of the consistence of fibro-cartilage, and is composed of fibrous and elastic tissues. Posteriorly it is attached to the front of the sustentaculum tali and the adjacent portion of the plantar surface of the os calcis. Anteriorly it is attached to (i) the plantar surface of the navicular bone, (2) the back of its tuberosity, and (3) the inner part of its dorsal surface. It is directed forwards and inwards, and covers the joint on its inner and lower aspects. Internally it blends with the anterior part of the internal lateral ligament of the ankle-joint and the astragalo-navicular ligament, and externally it blends with the external calcaneo-navicular ligament. The superior or deep surface of the ligament is in contact with a special THE LOWER LIMB 5S1 facet on the internal aspect of the inferior surface of the head of the astragalus. This surface of the ligament is covered by synovial membrane, and forms part of the articular socket for the head of the astragalus. It has a smooth, polished appearance, and presents no indication of its fibrous structure. The inferior or superficial surface, on the other hand, has the ordinary fibrous appearance of a ligament, and is in close contact with the tendon of the tibialis posticus, which is a powerful auxiliary to the ligament in supporting the antero-posterior arch of the foot. The spring ligament sometimes contains a sesamoid fibro-cartilage, which occasionally becbmes ossified. External Calcaneo-navicular Ligament Facet for Spring Ligament Fig. 269.- Tendon of Tibialis Posticus Inferior Calcaneo-navicular or * Spring Ligament ■.Interosseous Lig^ament ■The Inferior Calcaneo-n.wicular or Spring Ligament OF THE Left Foot (Superior View), The astragalo-navicular, external or superior calcaneo-navicular, and internal or inferior calcaneo-navicular ligaments form together a capsule for the astragalo-navicular joint. The synovial membrane is continuous with the sjnovial mem- brane of the anterior astragalo-calcaneal joint. Arterial Supply. — ^The anterior tibial, external tarsal branch of the dorsalis pedis, and internal plantar arteries. Nerve-supply. — ^The internal plantar and the external division of the dorsalis pedis ner\'e. The movements at this joint will be described with those at the calcaneo-cuboid joint. 582 A MANUAL OF ANATOMY III. Calcaneo-cuboid Joint. — This belongs to the class diar- throsis, and to the subdivision reciprocal or saddle-joint. The liga- ments are dorsal, internal or interosseous, long plantar, and short plantar. The dorsdJ ligament is a broad, flat band which passes between the superior surfaces of the os calcis and cuboid. The internal or interosseous ligament is a strong band which lies deeply in the hollow between the fore parts of the astragalus and OS calcis, where it is connected with the external calcaneo- navicular ligament. Its attachments are to the adjacent inner portions of the os calcis and cuboid. The long plantar (long inferior calcaneo-cuboid) ligament is very strong, and is attached posteriorly to the plantar surface of the os calcis, upon which it extends from the inner and outer tubercles to the anterior tubercle. Anteriorly most of its fibres are attached to the ridge on the plantar surface of the cuboid bone behind the peroneal groove. Some of them, however, are continued forwards to be attached to the plantar aspects of the bases of the second, third, fourth, and fifth metatarsal bones. These latter fibres, as they pass over the peroneal groove, cover the tendon of the peroneus longus, and so complete its fibro-osseous canal. The short plantar (short inferior calcaneo-cuboid) ligament is more deeply placed than the preceding. Posteriorly it is attached to the plantar surface of the os calcis in front of the anterior tubercle, as well as to the fore part of that tubercle, and anteriorly to the plantar surface of the cuboid bone behind the ridge. The long and short plantar ligaments are in early life continuous with the tendo Achillis, but they become subsequently separated from it as the result of the backward growth of the heel. The synovial membrane of this joint is peculiar to it. Arterial Supply. — ^The external tarsal branch of the dorsalis pedis and the external plantar artery. Nerve-supply. — ^The external plantar and the external division of the dorsalis pedis nerve. Movements at the Astragalo-navicular and Calcaneo-cuboid Joints.— The movements at these joints are flexion and extension, combined with abduction, adduction, and rotation. Flexion occurs during extension of the ankle-joint, and extension during flexion of that joint. The axis of these movements passes from the inner side of the neck of the astragalus obliquely down- wards, outwards, and backwards to the lower and outer part of the tuber calcis. During flexion and extension of the astragalo-navicular joint rota- tion of the navicular bone on the head of the astragalus takes place. The most free movement at this joint is downwards and inwards, or upwards and outwards. In adduction and abduction of the foot movement takes place at this joint as well as at the astragalo-calcaneal articulations. In adduction or inversion the navicular bone moves downwards and inwards, and so also does the cuboid at the calcaneo-cuboid joint, the result being that the antero-posterior arch of the foot is diminished. In abduction or eversion the navicular and cuboid bones move upwards and outwards, and the antero-posterior arch is increased. In walking the head of the astragalus tends to sink upon the spring ligament, THE LOWER LIMB 58^ and a certain amount of abduction or eversion of the foot takes place. When a person stands erect with both feet upon the ground, abduction or eversion is prevented by the astragalo-calcaneal Ugaments. If, however, the spring ligament is in a weak condition, the tendon of the tibialis posticus is not of itself sufficient to prevent displacement of the head of the astragalus down- wards and inwards. Displacement accordingly takes place in that direction, and so the condition known as fiat foot (pes planus) is produced. At the calcaneo-cuboid joint, besides the movements of flexion and exten- sion combined with adduction and abduction, movement takes place down- wards and inwards, or upwards and outwards. The astragalo-navicular and - Tuber Calcis Groove for Flexor Longus Hallucis Sustentaculum Tali^ External Calcaneo- navicular Ligament Tibialis Posticus _ Inferior Calcaneo-^ aavicular (Spring) Ligament Short Plantar Ligament _ Naviculo-cuboid Ligament — Navicular Bone \ Naviculo-cuneiform f " Ligaments ( _ Internal Cuneiform , Bone Insertion of Peroneus Longus Capsule of ist Tarso metatarsal Joint .Long Plantai Ligament _, Peroneus Longus Peroneus Brevis - Cubo-mctatarsal Ligament Fig. 270. — Ligaments of the Right Foot (Pl.^ntar Aspect). calcaneo-cuboid joints together constitute the transverse tarsal articulation, the direction of which is in a straight Une across the foot. It is at this trans- verse tarsal joint where disarticulation is performed in Chopart's operation. IV. Naviculo-cuboid Joint. — ^This belongs to the class diarthrosis, and to the subdivision arthrodia, but only in those cases where the two bones articulate directly with each other by faceted surfaces. The ligaments are dorsal, plantar, and interosseous. The dorsal ligament passes from the outer part of the dorsal 584 A MANUAL OF ANATOMY surface of the navicular bone to the middle third of the inner border of the dorsal surface of the cuboid. The plantar ligament is a strong band which extends from the outer part of the plantar surface of the navicular bone to the internal part of the plantar surface of the cuboid. Its direction is forwards and outwards. The interosseous ligament is also a strong band which extends between the contiguous surfaces of the two bones. The navicular and cuboid bones do not, as a rule, articulate directly with each other by cartilaginous surfaces, and under these circum- stances there is no synovial membrane at this joint. Sometimes, however, the two bones come into actual contact, and then each has a special articular facet, that on the navicular bone being situated on its outer extremity, adjacent to the facet for the external cunei- form, and that on the cuboid being situated on its internal surface, behind the normal facet for the external cuneiform. When the two bones are thus in actual contact the joint is provided with a S5movial membrane which is continuous with that of the naviculo- cuneiform articulation. V. Naviculo-cuneiform Joint. — This belongs to the class diar- throsis, and to the subdivision arthrodia. The ligaments are dorsal, plantar, and internal. The dorsal ligament is a strong, continuous sheet of fibres passing from the dorsal surface of the navicular bone to the dorsal surfaces of the three cuneiform bones. The plantar ligament extends between the plantar surface of the navicular bone and the plantar surfaces of the three cuneiform bones. To a large extent it derives its fibres from the adjacent expansions of the tendon of the tibialis posticus. The internal ligament passes between the tuberosity of the navi- cular bone and the inner surface of the internal cuneiform, and it blends with the dorsal and plantar ligaments. VI. Intercuneiform Joints. — These belong to the class diarthrosis, and to the subdivision arthrodia. The ligaments are dorsal, inter- osseous, and plantar. The dorsal ligaments are two in number, and their fibres pass transversely between the dorsal aspect of the middle cuneiform and the dorsal aspects of the internal and external cuneiform bones. The interosseous ligaments are also two in number, and are very strong. They are deeply placed, and pass between the sides of the middle cuneiform and the contiguous sides of the internal and external cuneiform bones in front of the articular facets. They constitute the chief bond of union between the three bones. The ligament between the middle and external cuneiform is attached to the entire vertical extent of the contiguous surfaces, whilst that between the middle and internal cuneiform is generally limited to the inferior and anterior portions of the contiguous surfaces. THE LOWER LIMB 585 The plantar ligament passes between the inner aspect of the eminence on the plantar surface of the internal cuneiform and the plantar aspect of the middle cuneiform. VII. Cubo-cuneiform Joint. — ^This belongs to the class diarthrosis, and to the subdivision arthrodia. The ligaments are dorsal, plantar, and interosseous. The dorsal ligament passes between the dorsal surface of the external cuneiform bone ind the dorsal surface of the cuboid. The plantar ligament passes from the plantar aspect of the external cuneiform bone to the internal surface of the cuboid over its anterior half, close to the plantar surface. The interosseous ligament, which is strong and deeply placed, passes bet\veen the entire vertical extent of the contiguous surfaces of the two bones in front of the articular facets. Synovial Membrane of the Naviculo-cuneiform, Intercuneiform, and Cubo-cuneiform Joints. — The naviculo-cuneiform synovial mem- brane is usually prolonged into the cubo-cuneiform joint, though Interosseous Ligament Fig. 271. — The SYNO\aAL Cavities of the Tarsal and Tarso-metatarsal Joints. occasionally the latter has a synovial sac pecuhar to it. It is also continued into the naviculo-cuboid joint in those cases where these two bones articulate by facets. Further, it sends forwards two prolongations, one on either side of the middle cuneiform. The prolongation between the middle and external cuneiform and that between the external cuneiform and cuboid are entirely shut off from the sjmovial cavity of the middle tarso-metatarsal joint (the joint between the cuneiform bones and the second and third meta- tarsal bones). The explanation of this is that the interosseous hgaments between the middle and external cuneiform and between the external cuneiform and cuboid, which are placed in front of the articular surfaces, are attached over the entire vertical extent of the contiguous surfaces from the dorsal ligaments above to the plantar below. The prolongation, however, between the middle S^^ A MANUAL OF ANATOMY and internal cuneiform is usually continuous in front with the synovial membrane of the middle tarso-metatarsal joint, because the interosseous ligament between these two bones is generally limited to the inferior and anterior portions of the contiguous surfaces. If this ligament should reach the dorsal surface, the naviculo-cuneiform synovial membrane would be entirely isolated from that of the middle tarso-metatarsal joint. Arterial Supply. — ^The arterial supply . of the naviculo-cuboid, naviculo-cuneiform, intercuneiform, and cubo- cuneiform joints is derived from the metatarsal branch of the dorsalis pedis and the internal and external plantar arteries. Nerve-supply. — ^The dorsalis pedis, internal plantar, and external plantar nerves. Movements at the Naviculo-cuneiform, Intercuneiform, and Cubo-cuneiform Joints.— The movements at these joints are very limited, and are of the gliding or to-and-fro variety. They do not affect the position of the foot as regards flexion and extension, or inversion and eversion, but they influence the transverse arch by increasing or diminishing its span. Downward gliding would increase the span, and upward gliding would diminish it. The portion of the transverse arch which is formed by the three cuneiform and cuboid bones has the following muscles attached to its various parts — tibialis posticus, flexor brevis hallucis, adductor obliquus hallucis, peroneus longus, flexor brevis minimi digiti, and tibialis anticus. The first four muscles diminish the span, and so deepen the arch, whilst the tibialis anticus increases the span, and so renders the arch wider. The Tarso-metatarsal Joints. The tarso-metatarsal joints are divided into internal, middle, and external. They all belong to the class diarthrosis, and to the subdivision arthrodia. I. Internal Tarso-metatarsal Joint. — ^This is the joint between the internal cuneiform and the first metatarsal bone. The dorsal and plantar ligaments of this joint are so disposed as to meet upon its inner and outer aspects, and thus a complete capsule is formed round the articulation, which capsule is stronger inferiorly and internally than elsewhere. The synovial membrane of this joint is peculiar to it. II. Middle Tarso-metatarsal Joint. — The bones which enter into this joint are the three cuneiforms and the bases of the second and third metatarsals (sometimes a part of the base of the fourth also). The ligaments are dorsal, plantar, and interosseous. The dorsal ligaments. — ^The dorsal surface of the base of the second metatarsal bone receives three dorsal ligaments, one from each cuneiform. The dorsal surface of the base of the third meta- tarsal bone receives a dorsal ligament from the external cunei- form. Moreover, the external cuneiform is connected by a dorsal ligament with the dorsal surface of the base of the fourth metatarsal bone. The plantar ligaments are three in number. One passes between the base of the internal cuneiform and the plantar aspects of the THE LOWER LIMB $87 bases of the second and third metatarsals, having the shps of the tendon of the tibiahs posticus behind it ; a second passes between the middle cuneiform and the base of the second metatarsal ; and a third passes between the external cuneiform and the base of the third metatarsal, the latter two also having the slips of the tendon of the tibialis posticus behind them. The interosseous ligaments are three in number — internal, middle, and external. The internal interosseous ligament* extends from the anterior and upper part of the outer surface of the internal cuneiform to the inner surface of the base of the second metatarsal. In each case it is attached below and in front of the articular facet, and it separates the internal from the middle tarso-metatarsal joint. It is a very strong ligament, and offers considerable resistance to the knife in the performance of Lisfranc's operation. The middle inter- osseous ligament extends from the anterior part of the inner surface of the external cuneiform, between the two semi-oval facets, to the groove on the outer surface of the base of the second metatarsal which separates the two facets. The external interosseous ligament extends from the anterior part of the outer surface of the external cuneiform, below the inconstant antero-superior facet, to the outer side of the base of the third metatarsal below the facet. It is also attached to the inner side of the base of the fourth metatarsal, and it ranks as the interosseous ligament of the cubo-meta tarsal joint. The synovial membrane of the middle tarso-metatarsal joint is usually continuous with that of the naviculo-cuneiform joint, the continuity taking place between the internal and middle cuneiform bones. Sometimes, however, they are quite distinct from each other. It sends prolongations forward between the bases of the second and third and third and fourth metatarsals. III. External Tarso-metatarsal or Cubo-metatarsal Joint. — ^The bones which enter into this joint are the cuboid and the fourth and fifth metatarsals. The ligaments are dorsal, plantar, and inter- osseous. The dorsal ligament passes from the dorsal surface of the cuboid to the dorsal surfaces of the bases of the fourth and fifth metatarsals. The plantar ligament extends between the plantar surface of the cuboid in front of the peroneal groove and the plantar aspects of the bases of the fourth and fifth metatarsals. It is closely asso- ciated with the forward expansion of the long plantar Ugament and with one of the sMps of the tendon of the tibialis posticus. The interosseous ligament is the same as the external interosseous ligament of the middle tarso-metatarsal joint. The dorsal, plantar, and interosseous ligaments construct a capsule round the cubo-metatarsal joint. The synovial membrane is peculiar to this joint, and sends a prolongation between the bases of the fourth and fifth metatarsals. Arterial Supply.— The tarso-metartarsal joints derive their arterial * Lisfranc's ligament. 588 A MANUAL OF ANATOMY supply from the dorsalis pedis artery and its metatarsal branch, the internal plantar artery, and the plantar arch. Nerve-supply. — ^The dorsalis pedis, internal plantar, and external plantar nerves. Movements at the Tarso-metatarsal Joints. — The movements allowed are flexion and extension. At the internal tarso-metatarsal joint flexion is associated with a certain amount of abduction, whilst extension is accom- panied by sUght adduction. At the middle tarso-metatarsal joint flexion and extension are allowed, but no lateral movement. At the cubo-metatarsal joint flexion and extension, combined with abduction and adduction, are allowed, lateral movement being tolerably free in the case of the fifth meta- tarsal. A certain amount of gliding or to-and-fro movement is also per- missible at the tarso-metatarsal joints in the following manner : the third metatarsal base can glide upwards, whilst the pair on either side of it can glide downwards, the effect being to diminish the span of the transverse arch of the foot. When the reverse movement takes place the span of the arch is increased. The portion of the transverse arch which is formed by the bases of the metatarsal bones has the following muscles attached to its various parts : tibialis posticus, adductor obliquus hallucis, peroneus longus, flexor brevis minimi digiti, and tibialis anticus. The first three muscles diminish the span, and so deepen the arch, whilst the tibialis anticus increases the span, and so renders the arch wider. Surgical Anatomy of the Tarso-metatarsal Joints. — It is in this situation where Lisfranc's and Hey's amputations are performed. The guide to the line of articulation on the outer border of the foot is the tuberosity on the outer side of the base of the fifth metatarsal, which can always be felt without difficulty. The joint between the cuboid and the fifth metatarsal is situated immediately behind this tuberosity. The guide to the line of articulation on the inner border of the foot is a point i^ inches in front of the tuberosity of the navicular bone. The line of articulation is in no sense transverse, its inner part being about i inch further forwards than the outer part. The tarso-metatarsal joints are remarkable for their irregularity, which is due to two causes. In the first place, the anterior surfaces of the three cuneiform bones do not present an even frontage. The internal and external cuneiform project further forwards than the middle cuneiform, and so a recess is formed which receives the base of the second metatarsal as that extends backwards to articulate with the middle cuneiform. The base of the second metatarsal thus becomes locked between the internal and external cuneiform. In the second place, the external cuneiform extends a Uttle further forwards than the cuboid. The line of the tarso-metatarsal articula- tions, from the inner border of the foot to the outer border, is as follows : (i) outwards, between the internal cuneiform and first metatarsal ; (2) back- wards, for about ^ inch (at this stage a very strong interosseous ligament has to be divided, as it passes between the internal cuneiform and the inner side of the base of the second metatarsal ; (3) outwards, between the middle cuneiform and second metatarsal ; (4) forwards, for about | inch ; (5) outwards, between the external cuneiform and third metatarsal ; (6) backwards, for about J inch ; and (7) outwards and backwards, between the cuboid and the fourth and fifth metatarsals. The Intermetatarsal Joints. The basal intermetatarsal joints belong to the class diarthrosis, and to the subdivision arthrodia. The bones concerned are the outer four metatarsals. The first metatarsal bone does not usually articulate with the second, but sometimes it does. The ligaments are dorsal, plantar, and interosseous. . THE LOWER LIMB 589 The dorsal ligaments are short transverse bands, three in number, which pass between the dorsal aspects of the bases of the second and third, third and fourth, and fourth and fifth metatarsals. The plantar ligaments are disposed in a similar manner to the preceding on the plantar aspects of the bases of the four outer metatarsals. The interosseous ligaments, which are three in number, are deeply placed and of considerable strength. They constitute a very firm bond of union between the contiguous sides of the bases of the outer four metatarsals, to the non-articular parts of which they are attached. Synovial Membrane. — In the case of the joints between the bases of the second and third and third and fourth metatarsals' the synovial membrane is a forward extension of that of the middle tarso-metatarsal joint, which sends forward two prolongations. , Interosseous Ligament Fig. 272. — The Synovial Cavities of the Tarsal and Tarso-metatarsal Joints. In the case of the joint between the bases of the fourth and fifth metatarsals the synovial membrane is a forward prolongation of that of the cubo-metatarsal joint. As regards the contiguous sides of the bases of the first and second metatarsals, if they should articulate, a special synovial bursa is usually provided which some- times communicates with the sjniovial membrane of the internal tarso-metatarsal joint. The arterial supply and nerv^e-supply are derived from the same sources as in the case of the tarso-metatarsal joints. Movements. — These are of a purely gliding or to-and-fro nature, so as to increase or diminish the span of the transverse arch of the foot. The heads of all the metatarsal bones are cormected by the transverse metatarsal (deep transverse) ligament, which extends across their plantar aspects. Its fibres are attached to the fibrous plates on the plantar surfaces of the metatarso-phalangeal joints, 590 A MANUAL OF ANATOMY and it receives the deep expansions of the digital processes of the central division of the plantar fascia. It is to be noted that the transverse metatarsal ligament includes the head of the first metatarsal bone, whereas the corresponding ligament in the hand (transverse metacarpal) excludes the head of the first metacarpal bone. Summary of the Tarsal and Tarso- metatarsal Synovial Membranes. — These are usually six in number. 1. Posterior astragalo-calcaneal. 2. Astragalo-calcaneo-navicular. 3. Calcaneo-cuboid. 4. Naviculo-cuneiform, cubo-cuneiform, cubo-navicular (incon- stant), intercuneiform, and middle tarso-metatarsal. 5. Internal tarso-metatarsal. 6. External tarso-metatarsal or cubo-metatarsal. Sometimes the middle tarso-metatarsal synovial membrane is distinct from the naviculo-cuneiform and intercuneiform synovial membrane, in which case the number would be increased to seven. Occasionally the cubo-cuneiform synovial membrane is distinct from the naviculo-cuneiform and intercuneiform, in which case there would be eight synovial membranes. In addition to these, there may be a synovial bursa between the contiguous sides of the bases of the first and second metatarsals if these articulate with each other, as they sometimes do. The Metatarso-phalangeal Joints. These joints belong to the class diarthrosis, and to the subdivision condylarthrosis or condyloid joint. They are formed by the heads of the metatarsal bones and the proximal ends of the first phalanges. The ligaments of the four outer joints are three in number, two lateral and an inferior or plantar fibrous plate. In the metatarso-phalangeal joint of the great toe the plantar fibrous plate of the other joints is replaced by two sesamoid bones, which are closely associated with the ■ heads of insertion of the flexor brevis hallucis. In the case of each joint the expansion of an extensor tendon serves the purpose of a dorsal ligament. Each joint is provided with a synovial membrane. The ligaments, synovial membranes, and movements of these joints closely correspond with those of the metacarpo-phalangeal joints. Abduc- tion, adduction, and circumduction, however, are much more limited. Arterial Supply. — ^The plantar digital and dorsal interosseous arteries. Nerve-supply. — ^The deej) division of the external plantar nerve (either directly or through its branches to the interosseous muscles), or the adjacent digital nerves. THE LOWER LIMB 591 The Interphalangeal Joints. These joints belong to the class diarthrosis, and to the subdivision ginglymus. They are formed by the distal end of one phalanx and the proximal end of the adjoining phalanx. The hgaments are three in number, two lateral and an inferior or plantar fibrous plate, the extensor tendon taking the place of a dorsal ligament. Each joint is provided with a synovial membrane. The ligaments, Fig. 273. — Sagittal Section of Ankle and Foot, passing through THE Great Toe. I, Spring Ligament ; 2, Inner Sesamoid Bone. synovial membranes, and movements of these joints closely corre- spond with those of the interphalangeal joints of the hand. The only joint in the lower limb which has interartieolar fibro-eartilages is the knee-joint. The hip-joint has a circumferential fibro-cartilage, namely, the cotyloid ligament. Development of the Limbs. In the third week of embr>'onic life two longitudinal ridges make their appearance, one on either side, external to the mesodermic somites. The rudiments of the fore- and hind-limbs (exclusive of the i>ectoral and pelvic girdles) appear as processes of these ridges. These prominences cissume the form of distinct outgrowths, which are called the limb-buds. The limb-buds undergo elongation, and each bud becomes divided into two segments by means of a transverse groove. The distal segment represents the nianus or pes, as the case may be. The proximal segment soon becomes differentiated by means of another groove into two parts — namely, antibrachium and brachiutn for the fore-limb, and leg and thigh for the hind-hmb. Stractare of a Limb-Bud. — Each limb-bud consists of the following ele- ments: (1) A core of mesenchyme (covered with ectoderm), derived from several of the contiguous somites; (2) muscular tissue, derived from the muscle-plates of several contiguous somites; and (3) prolongations (anterior primary- divisions) from the contiguous spinal nerve-segmentsl The bones are developed from the core of mesenchyme, which first undergoes chondrification and subsequently os.sifi cation. The mesenchyme in the intervals between the osseous frsuneworks assumes a hollow condition, and 524 A MANUAL OP ANATOMY so gives rise to the joint-cavities, the synovial membranes and ligaments being formed by the surrounding mesenchyme. The muscular tissue, originally derived from the muscle-plates of the somites, or perhaps from the mesenchyme which forms the core of the limb- bud, becomes differentiated into the limb-muscles. The prolongations from the spinal nerve-segments become differentiated into the limb-nerves. Position of the Limbs. — At first the fore- and hind-limbs are disposed with their longitudinal axes parallel with the longitudinal axis of the trunk. As the limbs undergo elongation and division into their ultimate component parts, a change in their position takes place. They become bent in a ventral direction, so that their longitudinal axes are now at right angles to the longi- tudinal axis of the trunk. The radial or preaxial side of the antibrachium and the pollex, on the one hand, and the tibial or preaxial side of the leg, and the hallux, on the other, are directed towards the cephalic region ; the palmar and plantar surfaces of the hands and feet are directed towards the trunk; the elbows are directed outwards and slightly backwards; and the knees are directed outwards and slightly forwards. Towards the end of the sixth week a second change in the position of the limbs takes place, and their permanent condition is thereby brought about, in which their longitudinal axes coincide with the longitudinal axis of the trunk. This change consists in a rotation of each limb round its longittidinal axis. In the case of the fore-limbs the rotation takes place in an outward direction, but in the case of the hind-limbs the rotation is inwards. The permanent results of these rotations are as follows: Fore-Limbs [Ex- ternal Rotation): (i) The radial or preaxial side of the antibrachium and the pollex are directed outwards; (2) the elbow becomes entirely posterior; and (3) the ventral or flexor aspect of the limb is now anterior, the extensor aspect being posterior. Hind-Limbs [Internal Rotation): (i) The tibial or preaxial side of the leg and the hallux are directed inwards; (2) the knee becomes entirely anterior; and (3) the ventral or flexor aspect of the hmb is now posterior, the extensor aspect being anterior. From the preceding changes it will be evident that, in the adult, the anterior aspect of the upper limb corresponds to the posterior aspect of the lower Umb; the outer aspect of the upper hmb to the inner aspect of the lower limb; and so on. GUIDE TO THE LOWER LIMB. Gluteal Region. — The landmarks having been studied, the skin is to be re- moved by making the following incisions : one extending from the level of the spine of the fifth lumbar vertebra outwards along the iliac crest as far as the position of the body will allow, and another extending from the fifth lumbar spine downwards in the middle line as low as the coccyx, after which it is prolonged outwards and downwards to the outer side of the thigh at a point about 5 inches below the great trochanter. The skin having been reflected, the gluteal cutaneous nerves are to be exposed in the following situations : (i) line of origin of gluteus maximus ; (2) iliac crest ; (3) outer and lower part of gluteus maximus ; and (4) lower border of gluteus maximus. The super- ficial fascia should now be removed, and the deep fascia examined. It will be seen that, in passing from the gluteus medius to the gluteus maximus, it firmly straps down the upper border of the latter muscle to the former. When the gluteus maximus has been reflected, the fascia will be seen to divide into two laminae, which embrace and give insertion to rather more than the upper half of that muscle. tHE LOWER LIMB 5$^ The gluteus maximus should be cleaned in the direction of its coarse fasciculi, and in connection with its lower border the bursa between it and the tuber ischii should be displayed. The muscle is to be divided about ij inches from its origin. As the greater part of it is being reflected outwards, the follo\N'ing arteries should be exposed entering its deep surface : the superficial branch of the gluteal, the inferior gluteal branch of the sciatic, and branches of the first perforating of the arteria profunda femoris. The inferior gluteal nerve should also be shown entering the deep surface of the muscle in its lower third. Between the great trochanter and the insertion of the muscle into the fascia lata a large multilocular bursa will be found, and another single bursa should be noticed between its insertion and the vastus extemus just below the great trochanter. The twofold inser- tion of the muscle should be noted. The origin of the muscle is now to be removed so as to expose the great sacro-sciatic Ugament and the structures piercing it, namely, the coccygeal branch of the sciatic artery, the sacral branch of the internal pudic arterj', and the perforating cutaneous branch of the sacral plexus of nerves. On the superficial surface of the Ugament will be found the plexiform loops formed by the external branches of the posterior primary divisions of the first three sacral nerves. The fascia lata should next be removed from the anterior part of the gluteus medius, and in doing so it should be noted that the superficial fibres of the muscle arise from the deep surface of the fascia. The various structures underneath the gluteus maximus are to be cleaned from above downwards, as follows : the posterior fleshy part of the gluteus medius, gluteal vessels, pyriformis, great and small sciatic nerves, sciatic vessels, pudic nerve and internal pudic vessels, nerve to the obturator intemus, furnishing a branch to the gemellus superior, common nerve to the gemellus inferior and quadratus femoris, gemellus superior, tendon of the obturator intemus, gemellus inferior, quadratus femoris, upper horizontal part of the adductor magnus, origins of the hamstring muscles from the tuber ischii, and the upper tendinous fibres of the vastus extemus. The digital and crucial anastomoses should be looked for, the former in the digital or tro- chanteric fossa, and the latter between the quadratus femoris and adductor magnus. The small sciatic nerve should be displayed so as to show its long pudendal branch, and the great sciatic nerve is to be exposed in the hollow between . the tuber ischii and the great trochanter. The sciatic artery and its branches are to be followed out. The pudic nerve, the internal pudic vessels, and the nerve to the obturator intemus (with its branch to the gemellus superior) are to be shown as they cross the back of the spine of the ischium. The tendon of the obturator intemus should be divided to show the columns on its under surface, the synovial bursa between the tendon and the small sciatic notch, and the cartilage facing that notch, with its grooves and ridges for the columns of the tendon. The sacro-sciatic Ugaments, great and small, should be studied. The mode of formation of the great and small sacro-sciatic foramina should be made out, and the various structures passing through each should be noted. The upper border of the quadratus femoris is to be displaced downwards so as to show the obturator externus and the ascending branch of the internal circumflex artery, both on their way to the digital fossa. The lower border of the quadratus femoris should be raised to show the small trochanter and the insertion of the ilio-psoas in part. The common nerve to the gemellus inferior and quadratus femoris wiU be found at first underneath the great sciatic nerve, and subsequently passing beneath the gemelh, obturator internus, and quadratus femoris. Its articular branch to the hip-joint should be looked for. If absent, its place will be taken by a branch from the great sciatic nerve. The gluteus medius (except its anterior fibres) should now be stripped from the dorsum ilii, and the bone cleaned by scraping, so as to show the exact bony origin of the muscle. The pyriformis being also divided, the gluteus minimus is to be cleaned, along with the upper and lower branches of the deep divisions of the gluteal artery and superior gluteal nerve. One of each 38 5^4 ^ MAIfUALOF A tf ATOMY of these structures will be found coursing along the upper border of the gluteus minimus, and crossing outwards over its centre. The latter branch (lower) of the artery should be shown to give a branch to the digital fossa to take part in the digital anastomosis, and the corresponding branch of the superior gluteal nerve should be followed outwards to the outer aspect of the thigh as far as possible on its way to the tensor fasciae femoris, which it supplies. The gluteus minimus (except its anterior fibres) is to be stripped from the bone, after which the surface thereby exposed should be cleaned. The posterior or reflected head of the rectus femoris is to be shown arising from the dorsum ilii immediately above the brim of the acetabulum. The muscular relations of the capsular ligament of the hip-joint should be carefully attended to in so far as the position of the body will allow. Popliteal Space. — This space should be dissected before the structures on the back of the thigh are disturbed. The landmarks having been studied, the skin is to be removed by the following incisions : ( i ) a median vertical incision extending from the junction of the upper two- thirds and lower third of the thigh to the junction of the upper fourth and lower three-fourths of the leg ; and (2) two transverse incisions, one at either end of the median incision. The small sciatic nerve is to be displayed after it pierces the fascia lata at the back of the knee-joint, and it should be followed to its terminal distribution over the upper part of the back of the leg. The upper part of the external or short saphenous vein is to be dissected, and in connection with it the following two veins should be noticed : (i) a fairly large tributary vessel, which descends from the lower part of the back of the thigh ; and (2) a communicating branch, which passes upwards and inwards to join the long saphenous vein. Three cutaneous sural arteries (branches of the popliteal) may be looked for — an external, over the outer head of the gastrocnemius ; an internal, over the inner head ; and a middle, accompanying the short saphenous vein. The fascia lata should next be cleaned, and the accession of strength which it here receives from superadded transverse fibres should be observed. Above the level of the knee-joint the small sciatic nerve will be found in the middle line beneath the fascia lata. This fascia is now to be removed, and the boundaries of the popliteal space are to be cleaned. The principal contents of the space are to be displayed by the removal of a large amount of fat. The great sciatic nerve should be exposed close to the upper median angle, and its external and internal popliteal branches cleaned downwards from that point. The external popliteal nerve is to be followed along the inner border of the biceps femoris as far as a point just below the head of the fibula. In cleaning this nerve, the dissector should look for the following branches, namely, (i) superior articular, to accom- pany the superior external articular artery ; (2) inferior articular, to accompany the inferior external articular artery ; (3) lateral cutaneous, to the integument of the outer side of the leg over about its upper two-thirds ; and (4) ramus communicans fibularis, which passes downwards and inwards to the middle line of the calf on its way to join the ramus communicans tibiaUs, and so form the external or short saphenous nerve. The internal popliteal nerve is to be followed through the centre of the space as low as the interval between the heads of the gastrocnemius. In cleaning it, the following branches should be looked for : (i) superior articular (inconstant), to accompany the superior internal articular artery ; (2) central or azygos articular, to accompany the corresponding artery ; (3) inferior articular, to accompany the inferior internal articular artery ; (4) ramus communicans tibiahs, which takes a straight course downwards to the calf, where it forms the chief part of the external or short saphenous nerve ; and (5) four or five muscular (sural) branches, as follows : (a) one to the outer head of the gastrocnemius ; (b) one to the plantaris (which sometimes comes from the preceding branch) ; (c) one to the inner head of the gastrocnemius ; {d) one to the soleus ; and (e) one to the popliteus. The nerve to the popliteus should be preserved with great care. The internal popliteal nerve should be hooked to one side, and the popliteal THE LOWER LIMB 595 vein exposed, its varying relation to the more deeply-placed popliteal artery being noted. The tributaries of the popliteal vein, when dissected, should be cut. These correspond with the branches of the pophteal artery, the short saphenous vein being a special tributary'. The vein should next be hooked to one side, which will prepare the popUteal artery for dissection. In order to expose the vessel fully to its termination, the inner head of the gastrocnemius may be di\nded. In cleaning the artery, the geniculate branch of the obturator ner\e should be looked for. If present, it \^-ill be found piercing the adductor magnus close above the femoral opening, after which it usually descends at first upon the inner side of the artery and then in front of it, until it comes into contact with the central or cizygos branch, which it accompanies through the posterior Ugament of the knee-joint to the interior of the articulation. During this dissection the popliteal lymphatic glands may come into view in the interval between the femoral condyles, one gland being superficial to the artery, one beneath it, and one on either side. The branches of the artery are to be carefully cleaned, as follows: (i) muscular, to the hamstring and sural muscles ; (2) cutaneous, to the upper part of the back of the leg ; and (3) the following five articular arteries : (a) two superior, external and internal, above the knee-joint, usually close above the femoral condyles and lying very deeply ; (6) central or azygos, at the back of the joint, and coming either from the front (deep) surface of the main vessel, or in many cases from the superior external articular ; and (c) two inferior, external and internal, below the level of the joint. The floor of the popUteal space should next be cleaned and examined, as follows: (i) the popliteal surface or trigone of the femur ; (2) the posterior ligament of the knee-joint, wth the Hgamentum posticum Winslowii ; eind (3) the popliteal fascia covering the popliteus muscle. Back of the Thigh. — The landmarks having been studied, the skin is to be removed by making a single vertical incision in the middle line. In the superficial fascia the femoral cutaneous branches of the small sciatic nerve are to be looked for, along the inner and outer aspects. At the upper and inner part of the back of the thigh twigs may be met with from the long pudendal branch of the small sciatic nerve. The superficial fascia having been removed, the deep fascia or fascia lata should be studied. The deep fascia having been removed, the small sciatic nerve should be shown, and the hamstring muscles, namely, the biceps femoris, semitendinosus, and semimembranosus, should be cleaned and studied. The relation of the long head of the biceps to the great sacro- sciatic ligament should be noted. The great sciatic nerve is also to be cleaned to its division into external and internal popUteal nerves, which latter nerves sometimes take the place of the great sciatic. The muscular branches of the great sciatic should be dissected, and it should be noted that, with one exception, they are derived from the internal popUteal part of the nerve. The exception is the branch to the femoral head of the biceps, which is derived from the external popUteed part of the nerve. It should cdso be noted that the nerve to the semimembra- nosus gives a branch to that part of the adductor magnus which extends frona the tuber ischii to the adductor tubercle of the femur. The whole course and relations of the great sciatic nerve should be thoroughly mastered. The posterior surface of the adductor magnus should next be cleaned, showing the four arches with the four perforating arteries passing bactwards under them, and the femoral opening where the femoral artery becomes the popUteal. The distribution and anastomoses of the perforating arteries on the back of the thigh should be carefuUy studied, and it should be noted that they com- municate above with the sciatic and gluteal, and below \v-ith the popUteal. It should further be noted that the perforating arteries do not terminate on the back of the thigh, and for this purpose an effort should be mads to show aU four passing outwards preparatory to their \s-inding round the outer side of the femur to the outer side of the thigh, in which situation they end. The relation of muscles at the gluteal ridge of the femur should be studied, as weU as the relation of muscles along the linea asppra. 596 /4 MANUAL OF ANATOMY Front Ol the Thigh. — The dissector should make himself thoroughly familiar with the landmarks of the front of the thigh and of the knee. The first dissection should be limited to the upper 4 inches in connection with the parts involved in femoral her-nia. For tlus purpose three incisions are required for the removal of the skin, as follows : one along the line of the groin from the anterior superior iliac spine to the pubic angle, a second extending from the pubic angle vertically downwards along the inner side of the thigh for 4 inches, and a third extending from the lower end of the second incision transversely across the front of the thigh as far as its outer aspect. It is to be desired that the subsequent dissection, which has to do with the superficial fascia and cutaneous vessels, should be undertaken in concert with the dissector of the abdomen. The superficial fascia in this region should be shown to be divisible into a subcutaneous fatty layer and a deep thin mem- branous layer, which correspond with Camper's and Scarpa's fasciae of the lower part of the anterior abdominal wall. In order to reflect the subcu- taneous layer, a transverse incision should be carefully made across the thigh, the depth of this incision coinciding internally with the long saphenous vein, which lies between the two layers of the superficial fascia. Another incision should be made vertically upwards on the inner side of the thigh, and extending only through the subcutaneous layer. Acting simultaneously with the dissector of the abdomen, the dissector of the thigh can now reflect outwards the subcutaneous layer, and both dissectors will see that it is continuous over Poupart's ligament with Camper's fascia of the anterior abdominal wall. Care should be taken not to disturb the lymphatic glands of this region. The inguinal glands (including the pubic glands) and the superficial femoral or saphenous glands are next to be dissected. The former will be found lying with their long axes obHque just below Poupart's Ugament, and the latter with their long axes vertical along the terminal part of the long saphenous vein. The cutaneous arteries of the groin, with their corresponding veins, are to be dissected, namely, the superficial epigastric, superficial circumflex iliac, and superior external pudic. The inferior external pudic, being beneath the fascia lata, is not to be dissected at present. The terminal part of the long saphenous vein should be shown, up to the level of the saphenous opening, and the following tributaries should be displayed joining it, namely, the external femoral cutaneous or anterior saphenous from the front of the thigh, the internal femoral cutaneous or posterior saphenous from the inner and back parts of the thigh, and the cutaneous veins of the groin, namely, the superficial epigastric, superficial circumflex iliac, and superior and inferior external pudic. The deep layer of the superficial fascia is next to be raised towards Poupart's ligament. It lies immediately beneath the long saphenous vein, and upon the deep fascia or fascia lata. When raised towards the groin it will be seen to cover the saphenous opening, and thereafter to be firmly bound down to the fascia lata about ^ inch below Poupart's ligament. The portion of it which covers the saphenous opening should be carefully studied. It is called the cribriform fascia, and it should be shown to be closely attached to the outer border of the saphenous opening, but only loosely to the inner part. It will be obvious that a hernia in passing through the saphenous opening must receive a covering from the cribriform fascia. The following nerves should now be dissected, namely, (i) branches of the inguinal nerve (so-called ilio-inguinal), which will be found on the inner aspect of the thigh; (2) the femoral branch of the genito-femoral, appearing immediately external to the femoral artery just below Poupart's hgament, after having pierced the outer part of the femoral sheath ; and (3) the external cutaneous nerve, which will be found emerging beneath the outer end of Poupart's ligament. The fascia lata is next to be cleaned, and the saphenous opening exposed, which should be carefully dissected. The best starting-point is the in- ferior cornu, which will readily come into view by raising the long saphenous vein. The cribriform fascia, is to be carefully removed, and the various THE LOWER LIMB 597 parts of the opening displayed. Before disturbing the opening, the dis- sector should note that a part of the anterior waU of the femoral sheath is seen lying within it. Having studied the saphenous opening, the dissector should now separate the outer border of the opening from the anterior wall of the femoral sheath by dividing the fibrous processes which connect them. The superior comu is next to be detached from Poupart's Hgament, and turned downwards and outwards along with the outer border of the opening. This will bring fully into view the anterior wall of the femoral sheath. The deep femoral arch should be shown at this stage as a bundle of fibres extending from the centre of Poupart's hgament on its deep aspect inwards over the anterior wall of the femoral sheath to the pectineal portion of the iUo-pectineal hne, where it is attached behind Gimbemat's hgament. Having studied the sheath as it now appears, and having observed that the femoral branch of the genito-femoral nerve pierces the outer part of the sheath just below Poupart's ligament, three vertical incisions are to be made in its anterior wall — one over the femoral artery, another over the femoral vein, and a third a Une or two internal to the vein. The interior of the sheath should then be shown to be divided into three compartments by means of two septa, which pass backwards on either side of the femoral vein. The femoral artery and, for a very Umited distance, the femoral branch of the genito-femoral nerve should be shown in the outer compartment, whilst the femoral vein, having on its inner side two or three of the deep femoral (deep inguinal) glands will be found in the middle compartment. The inner compartment is called the femoral canal. It is of considerable surgical importance, and should be studied with the closest attention. It will be seen to contain a little fat, and at its upper end one of the deep femoral glands will be found. The dissectors of the thigh and abdomen, who should be working in concert at this stage, should now thoroughly explore the canal. The httle finger should be inserted into it, and carried upwards to a point beneath Poupart's hgament. At the upper end of the caUcJ the finger will detect the septum femorale, which shuts off the canal from the abdominal cavity. By breaking down this septum, the point of the finger will lie in the femoral ring, and the sharp wiry base of Gimbernat's hgament will readily be felt on the inner side of the ring, this being the usu£d cause of stricture in femoral hernia. Behind the finger as it Ues in the femoral ring is Cooper's ligament. This structure, however, can only be shown by making a deep dissection of the parts beneath Poupart's hgament, in con- junction with the dissector of the abdomen. The parts around the femoral ring should be studied with the greatest care, as it is through this ring and the femoral canal that femoral hernia may occur. The remainder of the skin of the thigh is now to be removed by making a vertical incision down the inner side of the thigh to a point just below the level of the patella, and carrying this incision transversely across the front of the leg immediately below the patella on to the outer aspect of the hmb. This will enable the dissector to reflect the skin from the patella as well as from the front of the thigh. The prepatellar bursa will be found lying in front of the bone, where it is confined by an expansion which the fascia lata sends over the bone from its lateral borders. A complete dissection of the cutaneous nerves and the femoral part of the long saphenous vein is now to be made. The external cutaneous nerve, which has been already caught, should now be followed out. Its small posterior division and large anterior di\'ision should be shown, and it should be noted that the latter is contained in a tube of fascia lata for about 4 inches before it enters the integument. The middle cutaneous nerve will be found piercing the fascia lata (usually in two divisions) about 4 inches below Poupart's hgament, and both should be followed down to the patellar plexus. It has been seen that the inguinal nerve is distributed to the integument of the inner aspect of the thigh in its upper third. In dissecting the long saphenous vein in the middle third of the thigh, twigs of the internal cutaneous nerve will be met with along the course of that vein. There may also be found branches of the subsartorial plexus ramifying in this region (middle third). Another nerve which should be looked for at this level is the cutaneous 598 A MANUAL OF ANATOMY branch of the superficial or anterior division of the obturator nerve. When present it will usually be found piercing the fascia lata at about the centre of the inner side of the thigh, between the posterior border of the sartorius and the anterior border of the gracilis. The two divisions of the internal cutaneous nerve, anterior and posterior, should next be dissected. The anterior division will be found piercing the fascia lata at the junction of the middle and lower thirds of the thigh. It should then be followed to the inner side of the knee and patellar plexus. The posterior division will be found piercing the fascia lata at the level of the inner condyle, after which it descends to the inner side of the leg, where it will be afterwards dissected. The patellar branch of the internal or long saphenous nerve is to be shown. It pierces the sartorius and the fascia lata at the level of the inner condyle, and should be followed to the integument over the patella and patellar plexus. The patellar plexus itself is to be carefully dissected. The fascia lata is now to be cleaned and examined. Its deep processes will only come into view as it is being removed to expose the muscles. The muscles of the front and inner side of the thigh are to be cleaned by removing the fascia lata. A strip of this fascia, the so-called ilio- tibial band, about 2 inches broad, and extending from the fore part of the iliac crest to the front of the external tuberosity of the tibia, should be preserved. In removing the fascia lata from the pectineus and adductor longus the inferior external pudic artery is to be dissected. The boundaries of Scarpa's triangle should be defined. In the triangle the following muscles should be cleaned from without inwards, namely, the iUacus, psoas magnus, pectineus, and adductor longus. The contents of the triangle are now to be cleaned and studied, namely, (i) the anterior femoral nerve; (2) the common femoral and superficial femoral arteries; (3) the origins of the superficial epigastric, superficial circumflex iliac, superior external pudic, and inferior external pudic arteries; (4) the origin of the arteria profunda femoris, and its external circumflex and internal circumflex branches, and (5) the femoral vein and its tributaries. In cleaning the anterior femoral nerve its branch to the pectineus should be noted as it passes inwards behind the femoral sheath. Having completed the superficial dissection of Scarpa's triangle, the remainder of the sartorius should be cleaned. The following muscles should also be cleaned in the order named : tensor fasciae femoris, rectus femoris, and gracilis. In cleaning the tensor fasciae femoris the branch of the superior gluteal nerve entering its deep surface should be shown by dissecting between the muscle and the gluteus medius, the ilio-tibial band should be studied, and a strong lamina of the fascia lata should be shown passing upwards on the deep surface of the muscle to the dorsum of the ilium. The two heads of the rectus femoris should be exposed. The sartorius should now be held aside in the middle two-fourths of the thigh, in order to study Hunter's canal and its contents. The aponeurotic covering or roof of the canal should be shown as an upward expansion from the tendinous anterior margin of the femoral opening in connection with the adductor magnus. It should be observed that this tendinous roof is strong over the lower part of the canal, where it is pierced by a branch of the long. saphenous nerve to the subsartorial plexus, and by the arteria anastomotica magna. An endeavour should be made at this stage to expose the subsartorial plexus as it lies upon the aponeurotic covering of Hunter's canal. This covering should now be removed, and the contents and boundaries of the canal exposed. It should be observed that the nerve to the vastus internus is only contained in the upper half of the canal, and that the arteria anastomotica magna arises from the superficial femoral at the extreme lower end of the canal. The deep dissection of Scarpa's triangle should now be undertaken. A slight interval may be noted between the lower part of the pectineus and adductor longus, in which a partial view may be obtained of the adductor brevis and the superficial or anterior division of the obturator nerve. The superficial femoral artery should be divided just below the origin of the arteria profunda femoris, as well as the femoral vein. The arteria profunda femoris THE LOWER LIMB 599 should now be studied as far as the upper border of the adductor longus, and this will be facilitated by dividing the corresponding vein. Its external circumflex branch should be followed out in its ascending, transverse, and descending branches, and the anastomoses of these branches should be care- fully studied. An articular offset to the hip-joint from the ascending branch should be looked for. The long descending branch of this artery to the geniculate arterial rete should be noted. The branches of the anterior or superficial and posterior or deep divisions of the anterior femoral nerve should be dissected, and the following articular nerves should be looked for, namely, one to the hip-joint from the nerve to the rectus femoris, and three to the knee-joint, as follows : one from the nerve to the vastus extemus ; one from the most internal of the branches to the crureus, supplying in its course the subcrureus ; and one from the nerve to the vastus intemus, which ultimately accompanies the deep branch of the arteria anastomotica magna. The vastus extemus, crureus, and vastus intemus are next to be dissected. The vastus intemus and crureus are to be separated by dissecting along the course of a cellular interspace, which extends upwards in the direction of a line drawn from the inner border of the patella to the inferior cervical tubercle of the femur. When the vastus intemus is reflected inwards, a bare strip along the inner aspect of the shaft of the femur, devoid of muscular fibres, is to be noted. The crureus should next be turned aside in two halves by making a vertical incision down the centre of the muscle. This will show the lower Umit of origin of the muscle, and it will bring into view the sub- crureus. The bursa beneath the suprapatellar tendon and the prolongation of the synovial membrane of the knee-joint, which is continuous with it, should be shown. In dissecting the lower part of the vastus intemus the deep branch of the arteria anastomotica magna and an articular branch to the knee-joint from the nerve to the vastus intemus should be followed out. The pectineus and adductor longus should be divided and reflected. When the pectineus has been reflected it should be noted that a portion of the capsular ligament of the hip-joint (including the pubo-femoral hgament) is exposed. This will bring fully into view the adductor brevis, with the anterior or superficial division of the obturator nerve resting upon it, and the obturator extemus lying above it. The continuation of the arteria profunda femoris is also exposed. The four perforating branches of this vessel should be shown, the first and second piercing the adductor brevis and adductor magnus, whilst the third and fourth pierce only the adductor magnus. The internal circumflex artery should be studied at this stage. Replacing the pectineus, the artery should be traced backwards between that muscle and the psoas magnus, and then between the adductor brevis and obturator extemus. In this latter situation the artery should be shown to divide into its two terminal branches, namely, (a) ascending, or anterior, passing with the obturator extemus to the digital fossa ; and (b) transverse or posterior, passing backwards between the quadratus femoris and upper border of the adductor magnus, and furnishing in its course an articular branch to the hip-joint which enters beneath the transverse hgament. It should be observed that the internal circumflex artery gives branches to the obturator ex- temus, which anastomose in that muscle with branches of the obturator artery. The adductor brevis should be divided without injuring the anterior division of the obturator nerve, and the obturator extemus should be dissected. Its relation to the neck of the femur and the capsular ligament should be noted, as also its relation to the obturator nerve. This nerve is now to be dissected. An articular branch to the hip-joint from the anterior division should be looked for, and the termination of this division in cutaneous and vascular branches should be noted. The posterior division should be followed out in the expectation of finding it terminating in the inconstant geniculate branch. An accessory obturator nerve may be found emerging over the superior pubic ramus beneath the pectiueus,i after which it wiU be seen to end in thceq 6oo A MANUAL OF ANATOMY branches, as follows : one to the hip-joint, one to the pectineus, and one to reinforce the anterior division of the normal obturator nerve. The obturator externus is next to be cut and reflected, in order to expose the obturator membrane and obturator artery. The artery should be shown to divide into an internal and external branch (the latter furnish- ing an articular branch to the hip-joint), and the arterial loop formed by these two branches at the circumference of the obturator membrane should be made out. The anastomosis in the obturator externus between the obturator and internal circumflex arteries will now be readily under- stood. The adductor magnus is next to be fully studied. Its division into three parts is to be shown, as well as the four tendinous arches under which the four perforating arteries pass. The relation of the muscle to Hunter's canal is to be noted, and the femoral opening for the passage of the superficial femoral artery and corresponding vein is to be dissected. The dissector should now replace the adductor brevis, adductor longus, and pec- tineus, and the relative positions of these muscles should receive attention. The anterior portions of the gluteus medius and gluteus minimus should be cleaned by removing the fascia lata, and when they are reflected the bursae between them and the great trochanter should be shown, as well as the strong arched band of fibres which connects the tendon of the gluteus minimus with the upper part of the capsule of the hip-joint. Hip-Joint. — A careful study of the hip-joint should now be made, pre- paratory to the removal of the limb, and this should be done in the following order: (i) The muscular relations of the capsular ligament should be care- fully noted, the muscles not yet cut should be divided, the bursa beneath the ilio-psoas should be observed, and the two heads of the rectus femoris should be again studied. The actions of the various muscles upon the joint should also be studied. (2) The capsular ligament should be cleaned, and an occa- sional opening in it should be looked for underneath the ilio-psoas bursa. The various accessory bands should be attended to, and their influence over the movements of the joint should be observed. The attachments of the capsule to the femur in front and behind are to be noted, and the difference in direction of the anterior and posterior fibre*?, as well as their relative strength, observed. The effect of different positions of the Umb upon the head of the femur should be attended to. (3) The capsular Ugament should be divided, and the ligaments within the joint studied, namely, (a) the cotyloid ligament, (b) the transverse ligament, and (c) the ligamentum teres. The synovial or Haversian gland is also to be noted. As regards the ligamentum teres, a good plan to adopt is as follows : the dissector of one limb should examine the hip-joint in the usual manner, namely, from the front, and the dissector of the other Umb should avail himself of this examination. The dissector of the other Umb should saw through the upper part of the shaft of the femur, and leave the hip-joint undisturbed in the meantime. Subsequently, when the pelvis has been sufficiently dissected, the dissectors of the abdomen, in conjunction with the dissectors of the lower limbs, should open into the hip-joint on the side on which it has been left undisturbed by operating upon the smooth incUned pelvic aspect of the ischial portion of the hip-bone. This dissection wiU enable the dissectors to study the action of the ligamentum teres with the capsular Ugament left undisturbed. (4) The synovial membrane of the joint is to be studied. (5) The bony articular surfaces are to be examined. (6) The movements at the joint, and the muscles by which these are effected, are to be thoroughly mastered, and the arterial supply aiid nerve-supply are to be reviewed. The relations of structures to the anterior intertrochanteric Une should next receive attention, and the obturator canal and its contents should be examined. The relative position of the muscles from the symphysis pubis outwards to the obturator foramen should be noted. Finally, the relative positions of the tendons of insertion of the sartorius, gracilis, and semi- tendinosus, and the bursa in connection with them, should be examined. The dissector is now prepared to remove the limb. Any muscles passing between the pelvis and the thigh are to be cut, and the ligamentum teres is THE LOWER LIMB 601 to be divided, after which the limb can be separated. The first duty of the dissector is to trim the femoral muscles, and revise their attachments and relations. On the inner side of the knee-joint, if not previously displayed, he should show the long saphenous vein and nerve, the posterior division of the internal cutaneous nerve, and the superficial branch of the arteria anastomotica magna. The deep branch of the last-named artery, if not previously dissected, should now be followed out. The relation of the long external lateral hgament of the knee-joint to the tendon of insertion of the biceps femoris, as well as the bursa in this situation, and the expansion from the tendon to the deep fascia of the leg, should be shown. Front and Sides of the Leg and Dorsum ol the Foot. — The dissector is to make himself thoroughly familiar with the landmarks of the leg and foot. The skin is then to be removed by making the following incisions : a vertical incision along the anterior border of the tibia, and along the dorsum of the foot as far as the web between the second and third toes ; a transverse incision at the ankle- joint, and another at the webs of the toes ; a median incision along the dorsum of each toe ; and a transverse incision across the dorsum of each toe close to the nail. The skin is to be reflected to either side, and the following structures should be exposed on the inner aspect of the tibia : ( i ) the long saphenous vein, which should be shown passing 'in front of the internal malleolus, and traced as far as the inner end of the dorsal venous arch ; (2) the long saphenous nerve, accompanjdng the foregoing vein as far as the centre of the inner border of the foot ; (3) the posterior division of the internal cutaneous nerve, ramify- ing in the integument of the upper half of the leg ; and (4) the superficial branch of the arteria anastomotica magna, ramifying in the upper third. Communications are to be sought for between the long and short saphenous veins, and also between the former and the deep-seated veins on the front of the leg. The venous arch on the dorsum of the foot should next be displayed, care being taken to preserve the cutaneous nerves. The long saphenous vein will conduct to it, and the small tributary veins from the superficial plantar venous plexus may be shown turning round the inner border of the foot to join the long saphenous vein. The short saphenous vein should be traced from the outer end of the arch to a point below and then behind the external malleolus ; the small tributary veins from the superficial plantar venous plexus may be shown turning round the outer border of the foot to join it ; and an endeavour may be made to show the following tributaries of the dorsal venous arch, namely, (i) the dorsal digital veins; (2) smaU veins from the dorsum of the foot ; and (3) the efferent or interdigital veins from the plantar transverse venous arch. The dissector should now display the musculo-cutaneous nerve. He will find it piercing the deep fascia on the outer side of the leg about the junction of the upper two-thirds and lower third. Branches should be traced to the integument of the front of the leg in its lower third, and the main nerve should be followed on in two divisions, to be distributed to the inner side of the great toe and the contiguous sides of the second and third, third and fourth, and fourth and fifth toes, as well as to the integument of the malleoli and dorsum of the foot. The external or short saphenous nerve should next be dissected along the outer border of the foot as far as the outer side of the Uttle toe. Upon the outer side of the leg the dissector will find the lateral cutaneous branch of the external popliteal nerve, which ramifies in the integument of about the upper two- thirds. The deep fascia of the front and sides of the leg should next be studied. Three intermuscular septa are to be noted, namely, anterior, antero-extemal, and postero-extemal. In the region of the ankle- joint the follo\ving parts of the deep fascia are to be specially dissected, namely, (i) the external annular Ugament, strapping down the tendons of the peroneus longus and peroneus brevis ; and (2) the anterior annular liga- ment, which will be found in two divisions — one above the ankle-joint and the other in front of it. The following points are to be specially noted in connection wth the two divisions of the anterior annular Ugament, namely. 6o2 A MANUAL OF ANATOMY (i) the number of compartments in each division ; (a) the tendons passing beneath each, and their relative position ; and (3) the number of synovial sheaths. The anterior tibial muscles are next to be dissected to their inser- tions in the following order, namely, the tibialis anticus, extensor longus digitorum, peroneus tertius, and extensor proprius hallucis. In connection with the expansions formed by the long extensor tendons on the dorsal aspects of the metatarso-phalangeal joints, the tendons of insertion of the lumbricales and interossei are to be carefully preserved. The anterior tibial nerve will be found coming into contact with the outer side of the anterior tibial artery about the junction of the upper fourth and lower three-fourths of the leg, and it should be followed from this point as far as the front of the ankle-joint. The anterior tibial artery is now to be shown lying deeply upon the interosseous membrane over about the upper two-thirds, but upon the anterior surface of the tibia in the lower fourth. In dissecting the upper part of the artery, the anterior tibial lymphatic gland should be looked for, and the venae comites accompanying the artery should be noted. The following branches of the artery should be shown, namely, anterior tibial recurrent, muscular, internal malleolar, and external malleolar. In dissecting the anterior tibial recurrent artery, the recurrent articular branch of the external popliteal nerve should be looked for. The terminal part of the anterior peroneal artery should be exposed as it appears through the inferior hiatus in the interosseous membrane, and it should be followed downwards under cover of the peroneus tertius and in front of the inferior tibio-fibular articulation, to take part in the external malleolar anastomosis. The dissector should now turn his attention to the dorsum of the foot. The deep fascia should be examined. The extensor brevis digitorum is to be dissected, and the insertion of its innermost tendon and its relation to the arteria dorsalis pedis are to be noted. The arteria dorsalis pedis and its venae comites are to be dissected, and the following branches of the artery are to be followed out, namely, internal tarsal, external tarsal, metatarsal, and arteria dorsaUs hallucis. The arch formed by the metatarsal branch is to be noted, and three dorsal interosseous arteries are to be dissected forwards from it. The dorsaUs pedis nerve (the continuation of the anterior tibial nerve) is next to be dissected as far as the cleft between the great toe and second, where it will be found to divide into two collateral dorsal digital branches for the supply of the contiguous sides of these two toes. The offset which it receives from the branch of the musculo-cutaneous nerve to the inner side of the great toe is to be shown, and the external branch of the nerve is to be followed beneath the extensor brevis digitorum. In this situation its gangli- form enlargement is to be looked for, and the offsets arising therefrom may be followed out. The four dorsal interosseous muscles should now be dissected. In connec- tion with the first dorsal interosseous the plantar or perforating branch of the arteria dorsalis pedis is to be noted, and in connection with the second, third, and fourth, the posterior and anterior perforating arteries should be looked for. The dissector should now turn his attention to the external aspect of the leg, where the peroneus longus and peroneus brevis are to be dissected. The latter muscle should be dissected throughout its entire course, but the former should only be followed meanwhile as far as the groove on the outer border of the cuboid bone. In dissecting these muscles, the fibro-osseous tunnel in which they lie is to be noted. The musculo-cutaneous and anterior tibial nerves are now to be traced upwards to their origin from the external popliteal at the level of the neck of the fibula. In doing so, in the case of the musculo-cutaneous nerve, both peroneal muscles are to be cut in so far as may be necessary, and in the case of the anterior tibial nerve the extensor longus digitorum and peroneus longus are to be cut. The mode of ending of the external popliteal nerve will now be made manifest, its terminal branches being the anterior tibial, musculo-cutaneous, and recurrent articular. Back of the Leg. — A transverse incision having been made over the heel, the THE LOWER LIMB '603 skin is to be reflected from the back of the leg. The terminal distribution of the small sciatic nerve having been revised, the dissector should trace the ramus communicans tibiahs and ramus communicans fibularis nerves to the centre of the calf, the former lyang in the median groove of the gastrocnemius, and the latter descending obUquely inwards over the outer head of that muscle. At or about the centre of the calf these two nerves will usually be found to unite, and so form the external or short saphenous nerve. This ner\'e, along \v-ith the short saphenous vein, should be followed superficial to the deep fascia downwards and outwards along the outer side of the tendo Achillis (the nerve meanwhile gi\'ing branches to the integument of the lower half of the back of the leg), then behind and below the external malleolus (in which situation the nerve suppUes calcaneal and malleolar branches), and subsequently along the outer border of the foot. Communications between the short saphenous vein and the long saphenous vein are to be sought for, as well as communications between the former and the deeply-seated veins which accompany the posterior tibial and peroneal arteries. The deep fascia of the back of the leg is next to be dissected, and thereafter the gastrocnemius muscle is to be studied. The inner head of the muscle having been previously cut in connection with the dissection of the lower part of the popliteal space, the outer head is now to be divided, and both heads are to be reflected upwards in order to show the exact origin of each, that of the inner head lying obUquely, whilst that of the outer head Ues vertically. The popUteal bursa, which separates the inner head from the semimembranosus, should be sought for, and its relation to the synovial membrane of the knee - joint examined. In the outer head of the muscle will be found a sesamoid fibro-cjirtilage (sometimes ossified). The belly of the gastrocnemius and its tendon is to be reflected downwards as far as the commencement of the tendo Achilhs. The plantaris is then to be dissected, and its long, narrow tendon should be taken between the index-finger and thumb of each hand and stretched laterally to demonstrate its distensibihty. The soleus is next to be dissected, and the fibrous arch over the posterior tibial vessels is to be shown, with fibres of the muscle springing from it. A branch from the internal popUteal nerve is to be found entering the superficial surface of the muscle near its upper border. The other nerve-supply from the posterior tibial will only come into view as the muscle is being reflected. The tendon of the soleus is to be shown joining that of the gastrocnemius to form the tendo AchilUs. The aponeurotic appearance presented by the deep surface of the gastrocnemius and the superficial surface of the soleus is to be noted. The tendo AchilUs is to receive careful attention. Before the soleus is disturbed, the hollow on either side of the tendo Achillis is to be noted. In the outer hollow the short saphenous vein and nerve have been already dissected, their position being here superficial. Lying deeply in the hoUow on the inner side of the tendon are the posterior tibial vessels and nerve. A Umited opening should be made in the deep fascia to show the exact position and relations of these structures. The soleus is now to be stripped from its tibial and fibular origins and turned downwards. In the course of this dissection a branch from the posterior tibial nerve is to be shown entering the deep surface of the muscle about the centre of the leg. The tendo AchilUs having been tur^^ed downwards, the large quantity of fat beneath it is to be observed, and the bursa between the tendon and the upper zone of the posterior surface of the tuber calcis is to be shown. By dissecting into the deep surface of the soleus, the arrangement of its very short fibres will be brought into view. The lower part of the popUteal vessels and internal popUteal nerve, though previously dissected, should now be revised. The di\'ision of the artery into anterior tibial and posterior tibial at the lower border of the popUteus muscle should be noted. The commencement of the anterior tibial artery is to be dissected, shovdng the vessel passing forwards between the two heads of the tibialis posticus, and between the tibia and fibula. Its branches in this situa- tion are to be shown, namely, posterior tibial recurrent (inconstant), and superior fibular. The nerve to the popUteus from the internal popUteal, if 6o4 A MANUAL OF ANATOMY not previously dissected, is to be followed out. The inferior external and inferior internal articular arteries are to be studied. The popliteal fascia covering the popliteus muscle is to be inspected, noting that it is one of the modes of insertion of the semimembranosus. The fascia is now to be removed, in doing which it should be noted that the superficial fibres of the popUteus muscle take insertion into its deep surface. In the meantime, the exact origin of that muscle cannot be shown, so that the dissector should content himself with showing the tendon after its escape from the interior of the knee-joint, when it is almost immediately replaced by fleshy fibres. The sural muscles having been completely turned aside, the expansion of the deep fascia, called the posterior or transverse intermuscular septum, is to be studied. In connection with it the internal annular ligament is to be dis- played (but not opened up as yet) between the internal malleolus and the tuber calcis. In doing so, care must be taken to preserve the calcaneo-plantar branch of the posterior tibial nerve and the internal calcaneal branch of the posterior tibial artery, both of which pierce the ligament. The deep muscles of the back of the leg are to be cleaned, and at the same time the posterior tibial vessels and nerve are to be dissected. The muscles from within outwards are the flexor longus digitorum, tibialis posticus, and flexor longus hallucis. It should be observed that the tibiaUs posticus is covered superficially by a strong aponeurotic expansion, which stretches across between the muscles on either side of it. In dissecting the lower portions of these muscles in the neighbourhood of the ankle-joint, the internal annular ligament is now to be opened, when it will be seen to contain four canals, three of which are fibro- osseous, and one (for the flexor longus digitorum) purely fibrous. The relation of the tendons, posterior tibial vessels, and posterior tibial nerve as they traverse these canals is to be studied, and the synovial sheaths are to be noted. The branches of the posterior tibial artery and nerve are to be displayed. As regards the branches of the artery, they should be dissected in the following order from above downwards, namely, (i) peroneal, of large size, and arising about i inch below the commencement of the posterior tibial ; (2) medullary, for the tibia (of large size) ; (3) muscular ; (4) communicating or transverse, near the ankle, and passing transversely outwards to join a similar branch of the peroneal ; (5) internal malleolar, usually two in number, and passing beneath the tendons behind the internal malleolus to take part in the internal malleolar anastomosis ; (6) internal calcaneal ; and (7) the two terminal branches, internal and external plantar arteries. Two venae comites are to be dissected with the posterior tibial artery, which communicate at frequent intervals by transverse branches placed superficial to the vessel. These venae comites should be shown to join those of the anterior tibial artery at the lower border of the popliteus muscle, and so form the popUteal vein. The peroneal branch of the posterior tibial artery requires special dissection. After reaching the back of the fibula, it sinks deeply and disappears from view, its course being either between the fibula and the flexor longus hallucis, or in that muscle, or in a fibrous canal between that muscle and the tibiaUs posticus. It will next be found becoming superficial about 2 inches above the ankle, where it should be shown to end by dividing into an anterior and a posterior peroneal branch. Two venae comites are to be dissected with the peroneal artery, which end by joining those of the posterior tibial. The following branches of the peroneal artery are to be dissected from above downwards, namely, (i) muscular; (2) medullary to fibula; (3) communi- cating or transverse ; (4) anterior peroneal, disappearing through the inferior hiatus in the interosseous membrane ; and (5) posterior peroneal. The last- named artery is to be shown passing behind the external malleolus on to the outer border of the foot for a variable distance. It will be seen to give off external calcaneal branches, which take part in the external malleolar anasto- mosis, and anastomose across the heel with the internal calcaneal branches of the external plantar. On the outer border of the foot it will be seen again to anastomose with branches of the external plantar. Knee-Joint. — The knee-joint is to be dissected before proceeding with the sole of the foot. The muscular and tendinous relations of the joint are to be THE LOWER LIMB 605 studied, and the threefold insertion of the semimembranosus is to be displayed. The arteries entering into the geniculate arterial rete are to be studied as fully as possible. All the external Ugaments of the joint are now to be dissected, namely, (i) the hgamentum patellse ; (2) the lateral patellar Ugaments; (3) the internal lateral ligament, with the inferior internal articular artery passing beneath it, and the medn division of the tendon of the semimem- branosus overlapped by it posteriorly ; (4) the long and short external lateral ligaments, with the inferior external articular arten,- passing beneath the long ligament ; (5) the posterior hgament, with its thickened part, known as the hgamentum posticum Winslowii ; and (6) the capsular ligament. In con- nection with the hgamentum patellze, the bursa between it and the upper part of the tubercle of the tibia should be shown. The exact origin of the tendon of the pophteus is to be displayed, and its relation to the joint and the long external lateral hgament noted. The expansion of the sj-novial mem- brane of the joint upwards above the patella and beneath the suprapatellar tendon is to be again studied. The zirticulation is now to be open«i from before by cutting transversely down through the sjTio\ial membrane just above the patella. This bone, along with the hgamentum patellae, having been turned downwards, underneath them will be seen a collection of fat covered by the synovial membrane, and representing the Haversian gland of the joint. In connection with this portion of the sj-novial membrane, the following so-called Ugaments are to be studied, namelj% the hgamentum mucosum and the hgamenta alairia. The crucial Ugaments are next to be examined in situ, as well as the semilunar fibro-cartilages. The sjTiovial membrane is to be examined, and thereafter the following external Ugaments, are to be cut, namely, the capsular and the posterior, thus leaving only the two lateral Ugaments intact. The joint is now to be placed in different positions — e.g., flexion, extension, internal rotation, and external rotation — and the conditions of the crucial and lateral Ugaments, as weU as of the semilunar fibro-cartilages, are to be carefuUy attended to. The lateral Ugaments are then to be cut, when the femur wiU be boimd to the tibia only by the crucial Ugaments, which should be completely mastered. The femur should be firmly grasped and the tibia rotated inwards in order to see the effect of this upon the anterior crucial Ugament. The tibia should next be rotated outwards, and it wiU then be made to describe hglf a circle, neither crucial Ugament interfering with this movement. In connection with the posterior comu of the external semilunar fibro-cartilage, the posterior acces- sory- bundle is to be observed, and thereafter the crucial Ugaments are to be divided. The upper surface of the head of the tibia being now fuUy exposed, the semilunar fibro-cartilages are to be studied, and in connection with their anterior aspects the transverse Ugament is to be examined. Lastly, the bony articular surfaces are to be examined. Sole of the Foot. — The skin is to be removed from the sole and plantar aspects of the toes by making the foUowing incisions : a median incision from the heel to the roots of the toes, a transverse incision across the roots of the toes, a median incision along the plantar aspect of each toe, and a transverse incision across the tip of each toe. Within the skin of the webs of the toes a bundle of transverse fibres, called the superficiad transverse Ugament, is to be dissected. The superficiad faiscia should be examined, and the calcaneal and plantar di\isions of the calcaneo-plantar branch of the posterior tibial nerve are to be followed out to their distribution. The superficial fascia is now to be removed so as to expose the dense deep fascia, known as the plantar fascia. In dissecting the three di\isions of this important fascia, care is to be taken to display the foUowing structures : (i) cutaneous branches of the internal plantar a^ter^- and ner\'e, which appear in the groove between the inner and middle di\isions'; and (2) cutaneous branches of the external plantar artery- and nerve, which appear in the groove between the middle and outer di\isions. The three divisions of the fascia are then to be carefuUy studied, and the grooves between them, indicating intermuscular septa, are to be noted. In the outer groove, near the base of the fifth metatarsal bone, the external plantar arterv should be exposed. 6o& A MANUAL OF ANATOMY and its superficial position noted. Special attention is to be directed to the middle division of the fascia. On being followed towards the toes, it should be shown to divide into five digital processes, one for each toe. The longitudinal direction of the fibres (from heel to toes) should be observed, but towards the toes superadded transverse fibres are to be displayed. In the interval between the diverging digital processes the plantar digital vessels and nerves are to be sought for and followed along the sides of the toes. The manner in which the digital processes are disposed is to be studied, and the bearing of the middle division of the plantar fascia upon the deformity known as pes cavus is to be carefully noted. In connection with the outer division of the fascia attention should be paid to the strong band which passes between the outer tubercle of the os calcis and the tuberosity on the outer side of the base of the fifth metatarsal bone, and which may be represented by a muscle known as the abductor ossis metatarsi quinti or Wood's muscle. The plantar fascia is now to be removed in the following manner : (i) the thin inner division is to be removed in the ordinary way so as to expose the abductor hallucis muscle, which it covers ; (2) the stronger outer division is also to be removed in the usual way so as to expose the abductor minimi digiti, which lies underneath it ; (3) the very strong middle division, which closely covers the flexor brevis digitorum, is to be carefully divided transversely about i inch in front of the heel, the posterior narrow part is to be dissected backwards, and the expanding anterior part is to be reflected for- wards. This dissection will bring into view the flexor brevis digitorum, and it will show the extent to which the superficial fibres of that muscle take origin from the deep surface of the middle division of the fascia. In dissecting the tendon of insertion of the abductor hallucis, the inner head of the flexor brevis hallucis is to be shown joining it, and a branch from the internal plantar nerve is to be looked for entering the abductor hallucis on its deep aspect about the centre. In dissecting the flexor brevis digitorum, it should be shown to end in four tendons for the four outer toes. Each tendon will be found to Ue superficial to a tendon of the long flexor of the toes, and the canal in which each pair of tendons lies before passing along the toes should be studied. The sheaths which confine the flexor tendons as they pass along the plantar aspects of the toes are next to be dissected. Upon one or more toes the sheaths are to be laid open, the insertions of the tendons made out, and the vincula accessoria tendinum (ligamenta longa and ligamenta brevia) shown. A similar dissection is to be made in connection with the tendon of the flexor longus hallucis. The intermuscular septum on either side of the short flexor is to be noted, and twigs from the internal plantar nerve are to be looked for entering the muscle on its deep surface. In dissecting the abductor minimi digiti, twigs from the external plantar nerve are to be looked for entering the deep surface of the muscle at its back part. The muscles of the first layer are to be divided near their origins and thrown forwards. The tendons of the flexor longus digitorum and flexor longus hallucis are now to be dissected, the former passing forwards and outwards, and the latter forwards and inwards. The crossing between these two tendons should be noted, that of the flexor longus hallucis being uppermost, and the slip which this tendon furnishes to that of the long flexor of the toes should be displayed. The tendon of the flexor longus hallucis is to be followed out to its insertion, and the vincula accessoria tendinum shown within its sheath on the great toe. The flexor or musculus accessorius is to be dissected in connection with the tendon of the long flexor of the toes previous to its division. In dissecting the musculus accessorius the external plantar vessels and nerve are to be carefully preserved as they cross the sole, and twigs of the nerve are to be looked for entering the inferior surface of the muscle at its back part. The four lumbricales muscles are to be dissected in connection with the four tendons of the long tte.xor of the toes. It should be noted tliat the innermost lumbricahs arises only from one tendon, whilst the other three arise each from the contiguous sides of two tendons. A branch from the second digital nerve of the internal plantar should be shown THE LOWER LIMB 607 entering the innermost lumbricalis, whilst the other three will be found to receive their nerve-supply from the deep part of the external plantar nerve. The internal plantar nerve is now to be dissected, as well as the internal plantar artery. The small size of the artery and the large size of the nerve are to be noted, and each is to be followed out to its distribution. The external plantar artery and nerve are next to be dissected in the first part of their course as they cross the sole from within outwards. The large size of the artery is to be noted, and the nerve is to be sho\vn suppl>-ing the mus- culus accessorius and abductor minimi digiti, besides giving off articular and cutaneous branches. The superficicil terminal branch of the external plantar nerve is also to be followed out, showing its two digital nerves, the outer- most of which suppUes the flexor brevis minimi digiti, and, as a rule, the interosseous muscles of the fourth space. The tendons of the flexor longus hallucis and flexor longus digitorum and the musculus accessorius are now to be divided near the ankle and turned forwards, but the plantar vessels and nerves are to be left undisturbed. The dissector is then to display the third layer of muscles in the following order from within outwards : flexor brevis hallucis, adductor obhquus hallucis, and flexor brevis minimi digiti. Ljing across the heads of the four outer metatarsal bones will be found the adductor transversus haUucis (transver- saUs pedis). In dissecting the flexor brevis hallucis its single origin and double insertion are to be noted, and a sesamoid bone is to be looked for in each head of insertion. Its nerve is to be found coming from the first or most internal digital branch of the internal plantar. The nerve of the adductor obUquus hallucis is to be found coming from the deep part of the external plantar nerve. In dissecting the flexor bre\is minimi digiti care must be taken to sepsirate it from the most external plantar interosseous, close to which it Ues, and with which it is apt to be confounded. Its nerve is usually to be found coming from the outer digital branch of the superficial part of the external plantar. In dissecting the adductor transversus hallucis it should be noted that the digital nerves on their way to the toes Ue superficial to the muscle, whilst the digital vessels Ue on its deep surface. The nerve-supply of this muscle is to be found coming from the deep part of the external plantar. The dissector should now show the relation of muscles which take insertion into the base of the first phalanx of the great toe, as follows: inner side — abductor hallucis and inner head of flexor brevis hallucis ; outer side^ — outer head of flexor brevis hallucis, adductor obhquus hallucis, and adductor transversus hallucis. The plantar triangle and its contents should next be examined. The further stage of the dissection of the sole consists in dividing the flexor brevis hallucis and adductor obhquus hallucis, in order to expose (i) the deep parts of the external plantar artery and nerve, (2) the plantar (and dorsal) interossei muscles, and (3) the plantar or perforating branch of the arteria dorsahs pedis. In the case of the deep part of the external plantar nerve, muscular, articular, and perforating branches are to be looked for. It is to be noted that the deep part of the external plantar nerve gives branches to the outer three lumbricales. In the case of the deep part of the external plantar artery the plantar arch and its branches are to be dissected. The plantar or perforating branch of the arteria dorsahs pedis is to be found appearing at the proximal part of the first interosseous space, and the following branches are to be dissected, namely, arteria magna or princeps hallucis, and communicating to the plantcir arch. The external plantar arter>- and nerve may now be cut to enable them to be laid fully aside, and the plantar interosseous muscles are to be dissected. Care must be taken not to confoimd the most external plantar interosseous with the flexor brevis minimi digiti. At this stage of the dissection the inser- tion of the lumbricales is to be studied. The innervation of the interossei will be found to come from the deep part of the external plantar nerve, except in the case of the interossei of the fourth space, which usually get their nerve- supply from the outer digital branch of the superficial part of the external plantar. The dissector should now revise the insertion of all the tendons connected \vith the foot, and, if any have not yet been followed out to their ^8 A MANUAL OP ANATOMY insertions, this should now be done. The actions of the muscles to which these tendons give insertion should be mastered, with special reference to the different varieties of club-foot, and an articulated foot should be before the dissector to enable him to illustrate these varieties and the actions of the muscles involved in producing them. Attention is now to be directed to the remaining articulations, namely, the tibio-fibular joints, the ankle-joint, and the joints of the foot. Before removing the muscles of the front of the leg and the deep muscles of the back, the anterior and posterior relations of the interosseous membrane should be studied, and the muscular relations of the ankle-joint mastered. Thereafter the muscles are to be removed, and attention is to be directed first to the superior tibio-fibular joint. The relation of the tendon of insertion of the biceps femoris to the joint is to be noted, as well as the relation of the tendon of the popliteus. More especially, the relation of the anterior division of the biceps tendon to the anterior ligament of the joint is to be studied. Having dissected the ligaments (anterior and posterior), the joint is to be opened and the synovial membrane examined. The bony articular surfaces are also to be inspected, and the movements of which the joint is capable are to be studied. The interosseous membrane is next to be dissected. The large deficiency left at its upper part for the passage of the anterior tibial vessels and. lymphatics is to be noted, and the anterior tibial lymphatic gland, if not previously dissected, is now to be shown. In the lower part of the interosseous membrane a small opening is to be displayed for the passage of the anterior peroneal vessels. The inferior tibio-fibular joint is next to be examined, pursuing the same order as in the examination of the superior. The ligaments to be dissected are anterior, posterior, inferior interosseous, and transverse, special attention being directed to the inferior interosseous ligament. The joint having been opened, the synovial membrane (which is continuous with that of the ankle-joint) is to be examined. Attention should next be directed to the bony articular surfaces and the movements of which the joint is capable. The ankle-joint should now be carefully examined. The dissector should first revise the muscular relations of the joint, and thereafter he should dissect the following Ugaments : anterior, posterior, internal lateral or del- toid, and external lateral in three fasciculi, anterior, middle, and posterior. The anterior and posterior Ugaments are then to be cut and the synovial mem- brane examined. Its continuity with the synovial membrane of the inferior tibio-fibular joint is to be noted, and collections of fat covered by it (Haversian glands) are to be shown at the front and back of the joint. The bony articular surfaces are to be examined, and special attention is to be given to the move- ments of which the joint is capable, and the muscles by which these are effected. The longitudinal and transverse arches of the foot should now receive careful attention, and a review of the different varieties of club-foot and the tendons involved will prove advantageous. Thereafter the articulations of the foot are to be dissected, and in doing so it is advisable that the dissector should have before him an articulated foot and the individual bones, all belonging to the same side as that which he is dissecting. The tarsal articulations are to be studied first, in the following order: (i) astragalo - calcaneal ; (2) astragalo-navicular ; (3) calcaneo-cuboid ; (4) naviculo-cuboid ; (5) naviculo- cuneiform ; (6) intercuneiform ; and (7) cubo-cuneiform. Before pursuing this order the dissector should make himself familiar with the transverse tarsal articulation — that is to say, the conjoined astragalo-navicular and calcaneo-cuboid joints, where disarticulation is performed in Chopart's operation. He should also study the expansions from the tendon of insertion of the tibialis posticus, and he should at this stage revise the tendon of the peroneus longus as it crosses the sole of the foot. In connection with the astragalo-calcaneal articulation two joints are to be recognised — posterior and anterior. The following ligaments are to be studied in connection with the posterior joint : interosseous, posterior, internal, and external. Only a lateral view of the interosseous ligament will be obtained at this stage, as it lies in the sinus pedis. It is to be noted that this joint has a synovial membrane peculiar to it. The anterior astragalo-calcaneal joint is next to THE LOWER LIMB 609 be dissected, and the following ligaments studied : interosseous, internal astragalo-calcaneal, and external or superior calcaneo-navicular. It is to be noted that the synovial membrane of this joint is continuous with that of the astragalo - navicular articulation. The bony articular surfaces of the astragalo-calcaneal joints cannot be studied until the astragalus is removed, which should presently be done. Meanwhile, by removing all the Ugaments, except the interosseous, and dividing the synovial membranes, the movements between the astragalus and os calcis are to be studied. The astragalo-navicular joint should now be examined. Inasmuch as this is one of the most important joints of the foot, it should receive careful study. The Ugaments to be dissected are as follows : astragalo-navicular, dorsally placed ; external or superior calcaneo - navicular ; and internal or inferior calcaneo-navicular, a most important Ugament, commonly spoken of as the spring hgament. The last-named Ugament is to be studied from two points of view, namely, from below, by removing the tendon of the tibiaUs posticus, and from above, by removing the astragalus. In performing the latter dissec- tion the interosseous astragalo-calcaneal Ugament is to be studied, and it is to be observed that, whilst it is the anterior Ugament of the posterior astragalo-calcaneal joint, it is the posterior Ugament of the anterior astragalo- calcaneal joint. An exceUent view is obtained from above of how the spring Ugament supports and forms a part of the socket for the under aspect of the head of the astragalus, and from below it can be well seen how the tendon of the tibiaUs posticus serves as an important strengthening adjunct to the Ugament. It is to be noted that the synovial membrane of the astragalo- navicular joint is continuous behind with that of the anterior astragalo- calcaneal. The movements at the astragalo-navicular articulation are to be carefully studied, and the manner in which pes planus may be brought about is to be observed. Attention should also be directed to the support which the spring Ugament, aided by the tendon of the tibiaUs posticus, gives to the inner longitudinal arch of the foot. The bony articulcir surfaces are also to receive attention. The calcaneo-cuboid joint is next to be studied. The Ugaments to be dis- sected are dorsal, internal or interosseous, long plantar, and short plantar. On opening the joint the sjTiovial membrane wiU be found to be pecuUar to it, and the movements of which the £U"ticulation is capable are to be studied. Attention is also to be given to the bony articular surfaces. The naviculo- cuboid joint is next to be attended to, the Ugaments being dorsal, plantar, and interosseous. The remaining tarsal articulations are to be studied in the foUowing order : naviculo-cuneiform, intercuneiform, and cubo-cuneiform, and the compUcated synovial membrane of these articulations should be examined. The bony articular surfaces and movements are cilso to be studied. The dissector should next direct his attention to the tarso-metatarsal articulations, which should be studied in the following order: (i) internal tarso-metatarsal, (2) middle tarso-metatarsal, and (3) external tarso-meta- tarsal. Special notice should be taken of the internal inteirosseous Ugament of the middle tarso-metatarsal joint. It wiU be found extending between the outer surface of the internal cuneiform and the inner surface of the base of the second metatarsal bone. The synovial membranes, bony articular surfaces, and movements of these articulations are to be attended to, and their surgery is to be caret uUy studied in connection with Lisfranc's operation. The intermetatarsal articulations are to be studied next, attention being directed to the basal intermetatarsal joints, and the union between the heads of the metatarsal bones. The tarsal and tarso-metatarsal synovial membranes should be reviewed at this stage. The metatarso-phalangeal articulations are now to be dissected, the Ugaments being two lateral and an inferior or plantar fibrous plate. The synovial membranes, bony articular surfaces, and movements are to be studied. Lastly, the interphalangeal articulations are to be dissected in a similar manner and to a Uke extent. 39 THE ABDOMEN MALE PERINEUM. Landmarks. — The tuber ischii can be felt on either side, as well as the ischio-pubic ramus ; but the great sacro-sciatic ligament cannot be felt, on account of the thickness of the lower border of the gluteus maximus. The tip of the coccyx is very accessible to the finger. The perineum practically corresponds with the outlet of the pelvis, and is somewhat lozenge-shaped, having the subpubic angle in front, the tip of the coccyx behind, and the tuber ischii on either side. It is conveniently divided into two parts by a line con- necting the ischial tuberosities, each division being triangular. The anterior represents the uro-genital or urethral division, this being the perineum proper, and the posterior the ischio-recteil or anal division. The skin of the mo-genital division presents an antero-posterior median elevation, called the perineal raphe, which extends over the posterior and anterior surfaces of the scrotum, and along the under surface of the penis. The position of the deeply- placed central tendinous point of the perineum is indicated by taking a point in this raphe very nearly i inch in front of the anus. The anus is the external opening of the anal canal. It is situated posterior to a line connecting the front parts of the ischial tuber- osities, and about li inches from the tip of the coccj^. A delicate white line surrounds the anus where the skin cind mucous mem- brane meet, which indicates the separation between the external and internal sphincter muscles (Hilton). The position of each ischio-rectal fossa is indicated by a slight depression between the anus and tuber ischii. Deep Boundaries of the Perineum — Anterior. — ^The subpubic angle and subpubic ligament. Posterior. — ^The coccyx. Lateral. — From behind forwards, the inferior border of the great sacro- sciatic ligament, tuber ischii, and ischio-pubic ramus. Ischio-Rectal Division. Cutaneous Nerves. — These are (i) the hemorrhoidal or perineal branch of the lower part of the anterior primary division of the 6n 6l2 A MANUAL OF ANATOMY fourth sacral, and (2) the inferior hemorrhoidal nerve, which is a branch of the pudic. The former supplies the integument between the tip of the coccyx and the back of the anus, and the latter the integument between the anus and tuber ischii. Fascia. — ^The fascia of this division is very thick, and is prolonged into the ischio-rectal fossa, where it forms an elastic pad for the lower part of the rectum and the anal canal. There is no deep fascia. Ano-coccygeal Body. — ^This is a collection of fibrous and muscular tissues situated between the coccyx and anal canal, the muscular element being connected with the levatores ani and sphincter ani muscles (Symington). Its importance lies in the fact that it gives support to the anal canal. Muscles. — ^The muscles in this division are the sphincter ani externus, corrugator cutis ani, levator ani, and coccygeus. Sphincter Ani Externus — Origin. — ^The tip of the coccyx and the integument over it. Insertion. — ^The greater part of the muscle is inserted into the central tendinous point of the perineum. The more superficial fibres, however, are inserted into the skin, and a certain amount of decussation takes place across the middle line. Nerve-supply. — ^The part of the muscle between the coccyx and the anus is supplied by the hemorrhoidal or perineal branch of the fourth sacral, and the remainder by the inferior hemorrhoidal and the deep branch of the perineal nerve, both of which are derived from the pudic. Action. — ^To keep the anal aperture closed, at the same time producing a wrinkled condition of the skin. The muscle is situated immediately beneath the skin, and is elliptical. Behind and in front of the anus it is single, but around that aperture it is arranged in two symmetrical halves, which are intimately connected with the middle portions of the levatores ani. Corrugator Cutis Ani (Ellis). — ^This muscle is represented by a very delicate sheet of involuntary muscular fibres, which pass in a radiating manner from the submucous tissue of the anal aperture to be inserted into the surrounding skin. Action. — (i) To throw the integument around the anus into wrinkles ; and (2) to invert the mucous membrane of the lower end of the anal canal after it has been everted during defaecation. For the levator ani and coccygeus, see pp. 862 and 863. Iscliio-rectal Fossa. — ^This is a deep fossa which is situated on either side between the ischium and rectum. It measures nearly 2^ inches in depth, 2 inches from before backwards, and i inch from side to side. In transverse section it is triangular, the base being directed downwards and the apex upwards. The outer wall, which is vertical, is formed by the lower part of the obturator internus muscle covered by the obturator fascia. The inner wall, which is oblique and longer than the outer, is formed by the lower part of the rectum, the anal canal, the levator ani muscle covered by the anal fascia, and the sphincter ani externus. The base is THE ABDOMEN 613 formed by the skin and fascia which extend between the tuber ischii and anus. The roof is just below the white line, where the anal fascia springs from the obturator fascia. Anteriorly the fossa is partially limited by the reflection of the fascia of Colles round the posterior border of the superficial transverse perineal muscle to join the base of the triangular ligament of the urethra. Abov^e this junction there is a forward prolongation of the fossa, called the anterior diverticulum, which extends almost to the symphysis pubis. It lies between the postero-superior layer of the triangular ligament and the inferior surface of the anterior part of the levator ani muscle. Scrotum Fascia of Colles (right halO Superficial Perineal/ Nerves 1 f Long Pudendal Nerve of -Cii Scemmering Superficial Transverse -/ Perineal Muscle //^ Inferior Hemorrhoidal Nerve Gluteal Cutaneotis .«-■ Branches of Small Sciatic Ner\'e Perforating Cutaneous Nerve ' - Central Tendinous Point Superficial Perineal Artery - Transverse Perineal Artery Internal Pudic Artery in Alcock's Canal Inferior Hemorrhoidal Artery Gluteal Cutaneous Branches of Sciatic Artery Hemoirhoidal or Perineal Brandi of 4th Sacral Nerve Fig. 274. — Dissection of the Male Perineum (On the left side the bulbo-cavemosus has been removed, and the cms penis cut). and its lateral limits are the prostate gland and pubo-prostatic ligament internally, and the ischio - pubic ramus externally. Posteriorly the fossa is partially limited by the margin of the great sacro-sciatic ligament and the lower border of the gluteus maximus muscle. Between these two structures it is prolonged backwards for a short distance in the form of a posterior diverticulum, which extends outwards towards the tuber ischii, and inwards towards the upper part of the coccyx. Position of Contents. — ^The internal pudic vessels and the perineal and dorsalis penis branches of the pudic nerve lie upon the outer 6i4 A MANUAL OF ANATOMY wall about i^ inches above the lower part of the tuber ischii, and they are contained in Alcock's canal. The inferior hemor- rhoidal vessels and nerve cross the fossa transversely from the outer wall to the anal canal. The superficial perineal vessels and nerves on their way forwards lie for a short distance in the front part. At the back part of the fossa, winding round the lower border of the gluteus maximus, the gluteal cutaneous branches of the small sciatic nerve and sciatic artery, as well as the perforating cutaneous branch of the sacral plexus, are met with. The fossa is filled with loose fat, which also extends into the anterior and posterior diverticula. This fat is badly supplied with bloodvessels, and its vitality is therefore low. As a consequence, an ischio-rectal abscess is of not infrequent occur- rence. When an abscess forms, the pus has a tendency to discharge itself in two directions, namely, through the skin forming the floor of the fossa, and through the wall of the anal canal about half an inch above the anus. When this happens a complete fistula in ano is the result. The severe pain which accompanies an ischio-rectal abscess is due to pressure upon the following nerves : (i) the inferior hemorrhoidal ; (2) the two superficial perineal nerves ; and (3) the gluteal cutaneous branches of the small sciatic. Uro-Genital Division. Superficial Fascia. — ^The superficial fascia resembles that over the lower part of the anterior wall of the abdomen in being divisible into two layers, which are called the subcutaneous layer and the deep layer or fascia of Colles. The subcutaneous layer is fatty and granular. When followed backwards on either side it forms the floor of the ischio-rectal fossa. At the middle line it is continuous with the corresponding layer of the opposite side. Externally it passes freely over the ischio-pubic ramus, and is continuous with the superficial fascia of the inner side of the thigh. Anteriorly it passes into the scrotum, where it joins the deep layer or fascia of Colles. The resultant fascia, now free from adipose tissue, contains involuntary muscular tissue, and forms the tunica dartos. The subcutaneous layer represents the fascia of Camper of the lower part of the anterior abdominal wall. The deep layer constitutes the fascia of Colles. It is mem- branous and strong. Externally, it is attached to the anterior everted lip of the inner border of the ischio-pubic ramus, as far back as the tuber ischii, immediately outside the attachment of the crus penis. Internally, the fascia of one side is continuous with that of the other along the middle line. Posteriorly, the fascia turns round the posterior border of each superficial transverse perineal muscle, and joins the base of the triangular ligament. Anteriorly, it passes into the scrotum, where it joins the sub- cutaneous layer, the two forming the tunica dartos. The fascia of Colles represents the fascia of Scarpa of the anterior abdominal wall. It encloses a space over the anterior division of the perineum, called the perineal pouch. This pouch is partially THE ABDOMEN 615 subdivided into two compartments by an incomplete septum, which extends upwards from the deep or superior surface of the fascia of Colles to be attached to the median raphe above. This septum is only complete for a short distance at the back part ; elsewhere it is very imperfect, and is continued forwards into the scrotum. When air is blo\vn beneath the back part of the fascia of Colles on one side of the middle line, the fascia of that side and the correspond- ing half of the scrotum become distended. As more air is blown in, the fascia of the opposite side and the corresponding half of the scrotum also become distended. It is into the perineal pouch that urine is extravasated in rupture of the urethra in the perineum. In such cases the urine cannot pass into either ischio-rectal fossa, its backward course being arrested at the posterior borders of the superficial transverse perineal muscles, where the fascia of Colles, as a whole, turns round to join the base of the triangular ligament. Neither can the urine make its way down the inner side of the thigh, its passage in this direction being stopped at the ischio-pubic ramus to which the fascia of CoUes is attached. The only course, therefore, which is impressed upon the extravasated urine is fonvards into the scrotal wall and on to the penis, in each case beneath the dartos tunic, whence it passes upwards along the spermatic cord to the anterior wall of the abdomen, in which situation it lies beneath the fascia of Scarpa. The fascia of Colles covers the following structures : the crura penis, covered by the ischio - cavemosi muscles ; the bulb of the urethra, covered by the bulbo-cavernosi muscles ; the superficial transverse perineal muscles ; the superficial perineal vessels of each side ; the three long scrotal nerves of each side ; and the deep perineal triangle of each side, in the area of which is one half of the antero-inferior layer of the triangiilar ligament. Muscles — Transversus Perinaei Superflciaiis — Origin. — ^The inner aspect of the tuber ischii above the origin of the ischio-cavernosus. Insertion. — ^The central tendinous point of the perinemn. Nerve-supply. — ^The deep division of the perineal branch of the pudic nerve. Action. — ^To draw back and fix the central tendinous point, and so' to aid the action of the bulbo-cavemosus. The muscle is directed obliquely inwards and forwards, being accompanied by the transverse perineal artery, and it forms the base of the deep perineal triangle. Ischio-cavernosus (erector penis) — Origin. — (i) The inner aspect of the tuber ischii close below the origin of the superficial transverse perineal muscle ; and (2) the inner border of the ramus of the ischium on either side of the crus penis. Insertion. — The under surface of the fibrous sheath of the crus penis in its front part, and the outer and upper surfaces of the fibrous sheath of the corpus cavernosum penis, in which latter situation it is continuous with the fascial investment of the penis and with the insertion of the suspensory ligament of that organ. Nerve-supply. — ^The deep division of the perineal branch of the pudic nerve. 6i6 A MANUAL OF ANATOMY Action. — The muscle compresses the crus penis against the ischio- pubic ramus, and, by retarding the return of venous blood, it helps to maintain the penis in a state of erection. It also contributes to the maintenance of erection by compressing the dorsalis penis vein. The anterior and outer part of the muscle is sometimes detached, and forms a separate muscle, called the compressor venae dorsalis penis. This arises from the descending pubic ramus, anterior to the origin of the ischio- cavernosus, and it terminates in an aponeurotic expansion which joins its fellow of the opposite side over the dorsal vein of the penis. Ischio-cavernosus Bulbo-cavernosus Membranous Urethra (exposed) ,. Crus Penis . - Bulb (uncovered) -- Antero-inferior Layer of Triangular Ligament Levator Ani (cut) Gluteus Maximus Anus Fig. 275. — Deep Dissection of the Male Perineum (The rectum has been turned back). Bulbo-cavernosus (accelerator or ejaculator urinae) — Origin. — (i) The central tendinous point of the perineum ; and (2) the median raphe, which is continued forwards from that point towards the symphysis pubis. Insertion. — ^The muscle, as regards its insertion, is conveniently divided into three parts, namely, the chief part, the anterior part and the posterior part. Chief Part. — ^The fibres of this part ascend between the crus penis and the side of the bulb to be inserted into the median raph6 on the upper surface of the bulb, where they meet the fibres of the corre- sponding part of the opposite muscle. THE ABDOMEN 617 Anterior Part. — ^The fibres of this part become somewhat detached and form the muscle of Houston. They are inserted partly into the outer surface of the fibrous sheath of the corpus cavernosimi penis in front of the ischio-cavernosus, and partly by means of a tendinous expansion into the fascial investment of the penis beneath which the dorsal vein of the penis lies. Posterior Part. — ^The fibres of this part arch outwards and back- wards to be inserted into the antero-inferior layer of the triangular ligament neeir its base. Nerve-supply. — ^The deep division of the perineal branch of the pudic nerve. Action. — (i) The chief part of the muscle, acting with its fellow, compresses the bulb. These portions of the t^vo muscles, therefore, come into play at the end of the act of micturition, when they expel the last drops of urine from this part of the urethra. A further action is to contribute to the maintenance of erection of the penis by compressing the veins of the bulb. (2) The anterior part compresses the dorsal vein of the penis, and so contributes to the maintenance of erection. (3) The posterior part tends to fix the bulb and maintain it in position. The chief f)ortions of the bulbo-cavernosi muscles completely surround the bulb, and may be regarded as forming a sphincter muscle to it. Compressor or Constrictor Urethral. — ^This muscle is also called the muscle of Guthrie. It extends transversely from the inner border of the ischio-pubic ramus of one side to the inner border of the opposite ischio-pubic ramus, lying in each case behind the attachment of the antero-inferior layer of the triangular liga- ment of the urethra. At the middle line the muscle divides into two layers, which, passing above and below the membranous part of the urethra, form a sphincter muscle to it, the lower layer also ensheathing the glands of Cowper. The posterior fibres of the muscle, which lie close to the base of the triangular ligament, are known as the transversa s perinaei profundus (Henle). The highest fibres are connected on either side with the pelvic surface of the descending pubic ramus at its upper part, and they join each other below the membranous portion of the urethra. These highest fibres, which are oblique in direction, constitute the levatores urethrae muscles, or muscles of Wilson. Nerve-supply. — ^The dorsal nerve of the penis. Action. — (i) To constrict the membranous part of the urethra. The muscle comes into play at the end of micturition, and it assists the bulbo-cavemosus in emptying the urethral canal. (2) To con- tribute to the maintenance of erection of the penis by compressing the plexus of veins, in the muscle, which receives its tributaries from the corpora cavernosa and bulb. (3) To compress Cowper's glands, and so aid in the expulsion of their secretion. The compressor urethrae muscle lies between the two layers of the triangular ligament of the urethra. Close to its attachment to 6i8 A MANUAL OF ANATOMY the ischio-pubic ramus it contains within its substance the internal pudic vessels and the dorsal nerve of the penis. Central Tendinous Point. — Nearly i inch in front of the anus there is a short transverse tendinous septum, about ^ inch long. At its centre it presents a thickening, to which the name of central tendinous point is given. The muscles which meet at this point are as follows : (i) the sphincter ani externus, coming from behind ; (2) the bulbo-cavernosi, coming from before ; (3) the superficial transverse perineal muscles, coming from either side ; and (4) the anterior portions of the levatores ani, which here lie above the posterior portions of the bulbo-cavernosi. The pointed process at the centre of the base of the antero- inferior layer of the triangular ligament of the urethra is also attached to the central tendinous point. Bulb of the Urethra. — ^This is the first part of the corpus spon- giosum penis, and is so named from its presenting a bulbous enlarge- ment. It measures about ij inches in length, and about | inch in breadth at its posterior part. Its posterior extremity rests upon the antero-inferior layer of the triangular ligament, and extends as far back as the central tendinous point, where it lies nearly I inch in front of the anus. This part extends fully J inch farther back than the bulbous part of the urethra. It here presents on its under surface, in the middle line, a faint groove indicative of a tendency to a bipartite division at this point. The bulb is invested by a fibrous sheath derived from the circumference of the urethral opening in the antero-inferior layer of the triangular ligament, superficial to which lie the fibres of the chief parts of the bulbo-cavernosi muscles. Each lateral wall of the bulb is pierced by Cowper's duct, which, with its fellow of the opposite side, opens upon the floor of the bulbous part of the urethra fully I inch in front of the antero-inferior layer of the triangular ligament. Crus Penis (crus corporis cavernosi penis). — ^This is the posterior attached portion of the corpus cavernosum penis. It is attached to the anterior everted lip of the inner border of the ischio-pubic ramus, superficial to the antero-inferior layer of the triangular ligament. Inferiorly and laterally it is covered by the ischio- cavernosus, and it lies beneath the fascia of Colles. The artery of the corpus cavernosum, having pierced the antero-inferior layer of the triangular ligament, passes between the attached surface of the crus and the ischio-pubic ramus, and enters the deep surface of the crus, to be continued forwards in the centre of the corpus cavernosum. Deep Perineal Triangle — Boundaries — External. — ^The crus penis, covered by the ischio-cavernosus muscle. Internal. — ^The bulb of the urethra, covered by the bulbo-cavernosus muscle. Posterior, or Base. — ^The superficial transverse perineal muscle. The floor is formed by the fascia of Colles, with the superficial perineal vessels and the three long scrotal nerves. In the undisturbed position of THE ABDOMEN 619 the parts the area of the triangle is concealed by the approximation of the bulbo-cavernosus and ischio-cavernosus muscles. When, however, these muscles are held apart there is seen lying deeply in the area one half of the antero-inferior layer of the triangular ligament of the urethra. Subpubic Ligament (ligamentum arcuatum). — ^This is a thick band which lies at the antero-superior part of the subpubic arch, where it fills up the subpubic angle. It is attached superiorly to the lower part of the interpubic disc, and laterally to the adjacent parts of the inner lips of the descending pubic rami. It is about \ inch in depth, and is slightly arched. Transverse Pelvic or Perineal Ligament. — This band extends transversely between the descending pubic rami two or three lines below the subpubic ligament. Inferiorly it is closely connected with the truncated apex of the antero-inferior layer of the triangular ligament. Between its upper border and the subpubic ligament there is the opening for the backward passage of the dorsalis penis vein. Triangular Ligament of the Urethra. — ^This ligament occupies the subpubic arch, which it fills, except at its antero-superior part where it is replaced by the subpubic and transverse pelvic or perineal ligaments. It is composed of two distinct layers, called antero-inferior (perineal) and postero-superior (pelvic). These two layers are united by their bases, but elsewhere they are separated by an interval of about | inch, in which the membranous part of the urethra in the male, and the vagina and urethra in the female, along with other structures to be presently enumerated, lie. The antero-inferior layer is also called the subpubic, or deep perineal, fascia. It is triangular, the apex being truncated. The apex is closely connected with the transverse pelvic or perineal ligament, which may be regarded as a part of its fibres. Each lateral margin is attached to the inner border of the ischio-pubic ramus, behind its everted hp, on which it extends as far back as the tuber ischii, lying between the attachments of the crus penis and ischio-cavernosus anteriorly and the compressor urethrae posteriorly. In this direction it measures fully 2 inches. The base is directed downwards and backwards, and is joined by the base of the postero - superior layer and the fascia of Colles. In the middle line the base is pro- jected into a slight process, which is connected with the central tendinous point of the perineum. On either side of this median process the base presents a concave margin where it sweeps down- wards and outwards to the tuber ischii. The length of the antero- inferior layer in the middle line is about ij inches. Its fibres are chiefly disposed transversely. The structures which pierce this layer are as foUows : the urethra, the arteries of the bulb, the arteries of the corpora cavernosa penis, the dorsal arteries and the dorsal nerves of the penis, the superficial perineal vessels and nerves, and the ducts of Cowper's glands. Urethral Opening. — ^This apertiire is situated in the middle line 620 A MANUAL OF ANATOMY fully I inch below the subpubic angle, and it gives exit to the membranous part of the urethra. From the circumference of the opening an expansion is given off, which forms a fascial investment for the bulb. Openings for the Arteries of the Bulb. — ^These are two in number, right and left, and are situated one on either side of the upper part of the urethral opening. Openings for the Arteries of the Corpora Cavernosa Penis. — ^These are two in number, right and left, and each is situated in the lateral attached border, under cover of the crus penis, about i inch below the level of the subpubic angle. Openings for the Dorsal Arteries and Nerves of the Penis. — These are two in number on either side, and are situated high up, Crus Penis (cut) Artery of Corpus Cavernosum Opening for Artery of the Bulb Opening for Cowper's Duct Antero-inferior Layer of --^ Triangular Ligament Openings for SOperficiaL Perineal Vessels and Nerves Urethral Opening '\ Base of Triangular Ligament Fig. 276. — The Triangular Ligament of (The antero-inferior layer has been removed Opening for Dorsalis Penis Vein -.-Dorsalis Penis Artery ^, Artery of the Bulb Dorsalis Penis Nerve- \ Internal Pudic Vessels Postero-snperior Layer of Triangular Ligament THE Urethra on the left side). being near the subpubic angle, and close to the descending pubic ramus, the opening for the artery being internal to that for the nerve. It is to be noted that the dorsal vein of the penis has a special opening, which is situated in the median line between the subpubic and transverse pelvic or perineal ligaments. Openings for the Superficial Perineal Vessels and Nerves. — ^These are situated, on either side, in the base at the line of junction with the fascia of CoUes. Openings for the Ducts of Cowper's Glands. — Each of these is situated on either side of the urethral aperture a little behind and below the opening for the artery of the bulb. Chief Relations — Antero-inferior. — ^The bulb of the urethra, and the crura penis, covered by their respective muscles, the superficial transverse perineal muscles, and the fascia of Colles. Postero- THE ABDOMEN 621 superior. — ^The membranous part of the urethra, the glands of Cowper, and the compressor urethrae muscle. The postero-superior layer is weak, and is formed by the parietal pelvic fascia. It lies about J inch above and behind that layer, and extend.s inwards to the urethra from the inner aspect of each ischio-pubic ramus near the posterior lip, where it is behind the compressor urethrae muscle. Superiorly it is attached to the transverse pelvic or perineal ligament, and its base joins that cf the antero-inferior layer. At each ischio-pubic ramus it is con- tinuous with the parietal pelvic fascia. When it arrives at the urethra it changes its course, and passes backwards over the anterior border of the levator ani muscle to blend with that portion of the visceral pelvic fascia which ensheathes the prostate gland. The postero-superior layer of the triangular ligament is to be regarded as a part of the parietal pelvic fascia. Antero-inferiorly it is in contact with the membranous part of the urethra and compressor urethrae muscle, whilst postero-superiorly it is related to the anterior fibres of the levator ani of each side, and forms the floor of the anterior diverticulum of the ischio-rectal fossa. The structures which pierce this layer are as follows : the membranous part of the urethra in the male, and the vagina and urethra in the female ; and the internal pudic vessels and dorsal nerves of the penis. Urethral Opening. — ^Tlus is often a mere cleft, in which cases the postero-superior layer may be described as being arranged in. two symmetrical halves. At this opening or cleft it becomes con- tinuous superiorly with the capsule of the prostate gland. openings for the Internal Pudic Vessels and Dorsal Nerves of the Penis. — These are situated close to the base, on either side, near the ischial ramus. Structures between the Layers of the Triangular Ligament. — These are as follows : 1. The membranous portion of the urethra in great part. 2. The glands of Cowper. 3. The compressor urethrae muscle. 4. The internal pudic arteries, each lying close to the ischio- pubic ramus in the compressor urethrae muscle, and each giving off the following branches : (a) the artery of the bulb, which in turn gives off the artery of a Cowper's gland ; (6) the artery of the corpus cavemosiun ; and (c) the dorsal artery of the penis. 5. A plexus of veins which receives its tributaries from the cms (corpus cavernosum) and bulb, and in which the internal pudic venae comites take their origin. 6. The deep lymphatics of the penis. 7. The dorsal nerves of the penis, each of which lies external to the corresponding internal pudic artery. Glands of Cowper. — ^These glands are two in number, right and left. They are situated between the two layers of the triangidar ligament, where they lie above the bulb and behind the mem- branous portion of the urethra, one on either side of the median 622 A MANUAL OF ANATOMY line. Each gland is a firm, round, and lobulated mass about the size of a small pea. Both glands are ensheathed by the lower layer of the compressor urethrae muscle, and within this there is the special fibrous capsule which has an admixture of plain muscular tissue. The glands belong to the class of racemose or acino-tubular glands, and each is composed of several lobules. The alveoli or acini are lined with columnar cells. The ducts are two in number, right and left. They are lined with cubical epithelium, and their walls contain plain muscular tissue. Each duct pierces the antero- inferior layer of the triangular ligament on either side of the urethral opening, a little behind and below the artery of the bulb. The duct then pierces the side of the bulb, and opens, with its fellow, upon the floor of the bulbous part of the urethra, fully i inch in front of the antero-inferior layer of the triangular ligament. Each gland receives a branch from the artery of the bulb. Cowper's glands are developed from the epithelial lining of the uro-genital sinus or canal. Internal Pudic Artery. — ^This vessel is one of the terminal branches of the anterior division of the internal iliac, the other and larger terminal branch being the sciatic. Lying at first within the pelvis, the artery passes downwards over the pyriformis muscle and sacral nerves, having the sciatic artery usually behind it, and it emerges from the cavity through the lower compartment of the great sacro- sciatic foramen. It then crosses the back of the spine of the ischium, after which it passes through the small sacro-sciatic foramen, and so enters the ischio-rectal division of the perineum. The vessel now courses along the outer wall of the ischio-rectal fossa, where, contained in Alcock's canal, it lies about li inches above the lower part of the tuber ischii. On approaching the anterior part of the fossa the artery gradually becomes more superficial, and, after leaving the fossa, it enters the interspace between the two layers of the triangular ligament of the urethra by piercing the postero-superior layer close to its base and near the ischial ramus. It now passes forwards and upwards, embedded in the compressor urethrae muscle, and lying close to the ischio-pubic ramus, where it is comparatively superficial. Having given off the artery of the bulb about ^ inch above the base of the triangular ligament, the vessel finally divides, about i inch below the subpubic angle, into its two terminal branches, the artery of the corpus cavernosum and the dorsal artery of the penis. In considering the relations and branches of the internal pudic artery it is convenient to divide the vessel into four parts — first, second, third, and fourth. The first part represents the intrapelvic portion of the vessel, and will be found described on p. 843 . The second part is the portion of the vessel which lies upon the 1 back of the spine of the ischium. For a description of it see p. 433. I THE ABDOMEN 623 The third part is the part of the vessel which lies on the outer wall of the ischio-rectal fossa. It is here contained in Alcock's canal, and is situated about i^ inches above the lower part of the tuber ischii. For its relations see Alcock's canal. Branches. — ^These are as follows : the inferior hemorrhoidal, the superficial perineal, and the transverse perineal. The inferior hemorrhoidal artery arises, either singly or in two or three branches, from the internal pudic immediately after it has taken up its position in Alcock's canal. The branches pass inwards to the anal canal through the loose fat which fills the ischio-rectal fossa. They are distributed to the external sphincter, levator ani, wall of the anal canal, and superficial structures of one half of the ischio-rectal division of the perineum, and they anastomose with the middle and superior hemorrhoidal arteries, and the inferior hemorrhoidal branches of the opposite side. The superficial perineal artery arises from the internal pudic at the anterior part of the ischio-rectal fossa. It pierces the base of the antero-inferior layer of the triangular ligament, and passes superficial to (sometimes on the deep surface of) the superficial transverse perineal muscle. Its subsequent course is forwards under cover of the fascia of Colles, where it lies in the floor of the deep perineal triangle, in company with the three long scrotal nerves. On approaching the scrotum it di\ddes into several long slender branches, which supply the back of the scrotum and anastomose with the external pudic branches of the common femoral artery. The transverse perineal artery, as a rule, arises in common with the superficial perinccJ, of which it is sometimes regarded as a branch. It may, however, arise directly from the internal pudic immediately in front of the origin of the superficial perineal. It is directed inwards and forwards to the central tendinous point lying superficial to the superficial transverse perineal muscle, and beneath the fascia of Colles. It supplies the muscles which meet at the central tendinous point, and anastomoses with its fellow of the opposite side. Alcock's Canal. — ^This canal is situated in the outer wall of the ischio-rectal fossa, and is formed by the obtiuator fascia. Its contents from below upwards are as foUows : (i) the perineal division of the pudic nerve ; (2) the lower vena comes ; (3) the third part of the internal pudic artery ; (4) the upper vena comes ; and (5) the dorsal nerve of the penis. The fourth part of the internal pudic artery lies between the two layers of the triangular ligament. It enters this interspace by piercing the postero-superior layer of that ligament close to its base and near the ischial ramus. It is embedded in the compressor urethrae muscle, and is comparatively superficial. As it Ues near the ischio-pubic ramus it has a vena comes on either side of it, and the dorsal nerve of the penis is external to it. Branches. — ^These are as follows : the artery of the corpus 624 A MANUAL OF ANATOMY spongiosum, the artery of the corpus cavernosum, and the dorsal artery of the penis. The artery of the corpus spongiosum (artery of the bulb) arises from the internal pudic about ^ inch above the base of the triangular ligament, and passes transversely inwards in the sub- stance of the compressor urethrse muscle. On approaching the urethra it turns forwards, and, having pierced the compressor urethrae, it passes through an opening in the antero-inferior layer of the triangular ligament at the side of the urethral aperture. It then enters the bulb, and is continued onwards in the corpus spongiosum as far as the glans penis, the erectile tissue of which parts it supplies. It anastomoses with its fellow of the opposite side and with the dorsal arteries of the penis. Whilst between the two layers of the triangular ligament the artery furnishes a branch to Cowper's gland of the corresponding side. The artery of the corpus cavernosum is one of the two ter- minal branches of the internal pudic, and is somewhat larger than the dorsal artery of the penis, which is the other terminal branch. It arises about i inch below the subpubic angle, and immediately thereafter pierces the compressor urethrse muscle and the antero-inferior layer of the triangular ligament close to the ischio-pubic ramus. It then passes between the bone and the crus, and, entering the crus on its deep surface, it is continued on- wards in the centre of the corpus cavernosum as far as the distal end of that body, the erectile tissue of which it supplies. The dorsal artery of the penis is the continuation of the internal pudic. For a very short distance it lies between the two layers of the triangular ligament embedded in the compressor urethrae muscle, its course here being upwards. It then turns forwards, and, having pierced that muscle and the antero-inferior layer of the ligament very near its upper part, it ascends between the crus and the symphysis pubis. Its subsequent course is between the two layers of the suspensory ligament of the penis, and then along the dorsum of the organ, where it has the centrally-placed dorsal vein on its inner side and the dorsal nerve of the penis on its outer. On arriving at the neck of the penis it ends in branches for the supply of the glans and prepuce, where it anastomoses with its fellow of the opposite side and the arteries of the corpus spon- giosum. In its course along the dorsum of the penis the artery gives off many branches, some of which supply the integument and anastomose with the superior external pudic of the common femoral, whilst others pierce the fibrous sheath of the corpus cavernosum to supply its erectile tissue, these latter anastomosing with the artery of the corpus cavernosum. Varieties of the Internal Pudic Artery — i. Trunlj. — The vessel is occasionally of small size, and may terminate in the artery of the bulb, or in the super- ficial perineal artery. In these cases an accessory pudic artery is present, which supplies the deficiencies. This vessel usually arises from the first or intrapelvic part of the internal pudic, though it may spring from an inferior THE ABDOMEN 625 vesical arter^^ Its course is forwards along th^side of the bladder, then along the side of the prostate gland to the triangular ligament of the urethra, which it pierces above the membranous part of the canal, and so reaches the root of the penis. The accessory pudic furnishes the artery of the corpus cavemosum and the dorsal arter>' of the penis, and in some cases the artery of the bulb. 2. Artery ol the Corpus Spongiosum (Artery of the Bulb). — Sometimes two arteries are present on one side ; sometimes the artery is absent on one side ; and sometinies it is of very small size. A much more important variety of this artery affects its origin. It may arise from the fourth part of the internal pudic close to the base of the triangular ligament, and even from the third part at the front of the ischio-rectal fossa. In these cases the artery cannot escape division in the operation of lateral lithotomy. In other <:ases it may arise from an accessory pudic artery, when it will lie higher up and further forwards than usual. 3. Dorsal Artery of the Penis. — This vessel may arise from the obturator artery in the obturator canal, or from one of the external pudic branches of the common femoral artery. Veins. — Lying in each compressor urethrje muscle there is a plexus of veins, which receives its tributaries from the corresponding corpus cavemosum and one half of the corpus spongiosum and bulb. The internal pudic venae comites arise on either side from this plexus, and accompany the internal pudic artery as far back as the upper border of the spine of the ischium, one lying on either side of the vessel. Here they join to form one trunk, which enters the pelvis through the lower compartment of the great sacro-sciatic foramen, and terminates in the internal iliac vein. They receive as tribu- taries the transverse perineal, superficial perineal, and inferior hemorrhoidal veins, as well as a few veins from the gluteus maximus and external rotator muscles. The inferior hemorrhoidal veins take their origin in a plexus of veins which is situated on the outer surface of the external sphincter muscle. Having crossed the ischio-rectal fossa through its loose fat, and being ultimately reduced to two or three in number, they join the internal pudic venae comites. It is to be noted that, though there are two dorsal arteries, there is only one dorsal vein, which takes the following course : after leaving the dorsum of the penis it passes through an opening between the subpubic and transverse pelvic or perineal ligaments, where it communicates on either side with the venous plexus in each half of the compressor urethfae muscle. Haxang entered the cavity of the pelvis, it divides into two branches, right and left, which join the prostatic plexus of veins. Lymphatics. — ^The superficial lymphatics of the perineum, as well as those of the anus and lower part of the anal canal, pass to the inguinal glands, which lie inunediately below Poupart's ligament, whilst the deep lymphatics pass to the internal iliac glands. Pudic Nerve. — ^The pudic nerve is one of the terminal branches of the sacral plexus, and derives its fibres from the ventral division of the second, the lower branch of the third, and the upper branch of the fourth sacral nerves, the majority of its fibres being derived from the lower branch of the third. Leaving the pelvis through the lower compartment of the great sacro-sciatic foramen, the nerve 40 626 A MANUAL OF ANATOMY crosses the back of the spine of the ischium, where it lies under cover of the gluteus maximus and on the inner side of the internal pudic vessels. It then passes through the small sacro-sciatic foramen, and so enters Alcock's canal in the outer wall of the ischio- rectal fossa. Immediately after doing so, it divides into three branches, namely, inferior hemorrhoidal, perineal, and dorsal nerve of the penis. The inferior hemorrhoidal nerve passes inwards across the ischio- rectal fossa to the region of the anus, and is distributed to the external sphincter muscle and the integument which covers the ischio-rectal fossa. Scrotum Fascia of Colles (right halO *"'~->^_ Superficial Perineal/ '~~----___ ff ^ Nerves \ ~77 '^ ■ M Long Pudendal Nerve of- — ^-^ Soemmering Superficial Transverse-- ». Perineal Muscle /// Inferior Hemorrhoidal Nerve Gluteal Cutaneous •-«-■ Branches of Small Sciatic Nerve Perforating Cutaneous Nerve — Central Tendinous Point . Superficial Perineal Artery — Transverse Perineal Artery -- Internal Pudic Artery in Alcock's Canal -Inferior Hemorrhoidal Artery - Gluteal Cutaneous Branches of Sciatic Artery Hemorrhoidal or Perineal Branch of 4th Sacral Nerve Fig. 277. — Dissection of the Male Perineum (On the left side the bulbo-cavernosus has been removed, and the crus penis cut). The perineal nerve is a large branch which passes forwards in Alcock's canal, being the lowest of its contents. It ultimately divides into superficial and deep branches. The superficial branches are two in number, and are called the external or posterior, and internal or anterior, superficial perineal nerves. Both nerves, having emerged from Alcock's canal, pass forwards and pierce the base of the antero-inferior layer of the triangular ligament. They then run forwards with the superficial perineal artery under cover of the fascia of Colles, and on approach- THE ABDOMEN 627 ing the back of the scrotum they divide into long slender branches which supply the scrotal integument. In the anterior division of the perineum the two superficial perineal nerves communicate freely, and are accompanied by the long pudendal nerve of Soemmering, which is a branch of the small sciatic. This nerve, having pierced the fascia lata about i inch in front of the tuber ischii, passes inwards over the ischio-pubic ramus and through the fascia of Colles. It then runs forwards and inwards beneath that fascia to the scrotum, to take part in the supply of its integument, and it communicates with the external or posterior superficial perineal nerve. The two superficial perineal nerves and the long pudendal nerve are known as the long scrotal nerves. The deep branch of the perineal nerve furnishes offsets which, with one exception, are muscular in their distribution, and supply the anterior part of the external sphincter, the anterior part of the levator ani, the superficial transverse perineal, the ischio-caver- nosus, and the bulbo-cavernosus. The non-muscular branch, called the nerve of the bulb, pierces the bulbo-cavernosus muscle and the wall of the biilb, to be distributed to the erectile tissue of the corpus spongiosum and the mucous membrane of the spongy part of the urethra. The dorsal nerve of the penis is at first contained in Alcock's canal, where it lies above the internal pudic vessels. Having emerged from that canal, it pierces the postero-superior layer of the triangular ligament near its base. It then passes for- wards and upwards, with the fourth part of the internal pudic artery, between the two layers of the triangular ligament, in which situation it lies on the outer side of the internal pudic vessels, and close to the ischio-pubic ramus, being embedded in the compressor urethrse muscle. Its subsequent course is similar to that of the dorsal artery of the penis, which it accompanies. On the dorsum of the penis, where it. lies external to the dorsal artery, it is con- tinued as far as the glans, where it ends in branches for the glans and prepuce. As the nerve lies between the two- layers of the triangular ligament, it gives branches to the compressor urethrae muscle, and it also furnishes the ner\'e of the corpus cavemosum. This latter nerve, having pierced the compressor urethrae and antero-inferior layer of the triangular ligament, enters the crus, and is continued forwards in the corpus cavernosum to supply the erectile tissue of these parts. As the nerve passes along the dorsum of the penis, it supplies numerous branches to the integu- ment of that organ. Structures divided in Left Lateral Litliotomy. — The structures divided in this operation are as follows : (i) the skin ; (2) the subcutaneous layer of the superficial fascia ; (3) the deep layer of the superficial fascia or the fascia of Colles; (4) the transverse perineal vessels; (5) the superficial transverse perineal muscle ; (6) the inferior hemorrhoidal vessels and nerve ; (7) the basal part of the antero-inferior layer of the triangular ligament ; (8) the compressor urethrae muscle and the plexus of veins embedded in it ; (-9) the 628 A MANUAL OF ANATOMY membranous part of the urethra; (lo) the postero-superior layer of the triangular ligament; (ii) the anterior fibres of the levator ani muscle.; (12) a portion of the left lateral lobe of the prostate gland, with its capsule, and some of the veins of the prostatic plexus ; and (13) the neck of the bladder. Structures to be avoided. — The structures to be avoided are as follows : ( i ) the rectum; (2) the internal pudic vessels as they lie in Alcock's canal; (3) the artery of the bulb ; and (4) the common ejaculatory duct FEMALE PERINEUM. The female perineum is divided into three regions^ — uro-genital, perineum proper, and ischio-rectal. The uro-genital division is situated at the anterior part, and comprises the pudendum and uro- genital cleft. The perineum proper is situated between the posterior part of the uro-genital cleft and the anus. The ischio-rectal division is situated as in the male. Uro-genital Division. The uro-genital division contains the external uro-genital organs. These collectively constitute the pudendum, and comprise the following parts : the mons Veneris ; labia majora ; labia minora, or nymphse ; clitoris ; vestibule ; meatus urinarius ; vaginal orifice, including the hymen, or the carunculae myrtiformes ; frgenulum pudendi ; fossa navicularis ; bulbi vestibuli ; and glands of Bar- tholin or of Duverney. The mons Veneris is an eminence situated in front of and above the upper part of the symphysis pubis. It is produced by a col- lection of adipose tissue, the skin over which is more or less freely provided with hair after the age of puberty. The labia majora are two thick, round folds of integument, which are directed from before backwards, with a slight inclination down- wards. The length of each is about 3 inches. Posteriorly they become thin, and join each other at the anterior part of the perineum proper, about i inch in front of the anus. The junction receives the name of the posterior commissure, and is somewhat pointed. Anteriorly they retain their thick, round character, and here also they join and become continuous with the mons Veneris. This latter junction is called the anterior commissure. Each labium majus has two surfaces, outer and inner. The skin covering the outer convex surface is somewhat dark in colour, like that of the scrotum, and contains numerous sebaceous glands of large size. It is also more or less freely provided with hair after the age of puberty, except towards the posterior part. The inner flat surface forms the lateral boundary of the uro-genital cleft, and touches that of the opposite side. The skin covering this surface is smooth and free from hair, and presents the openings of the ducts of sebaceous glands. Each labium majus contains adipose and areolar tissues, and a small amount of dartos tissue. The round ligament of the THE ABDOMEN 62^^ ^>Vn UF i6,v4>^ k -^-/-v^^^/ THE ABDOMEN 631 The clitoris is the homologue of the penis, from which it differs in the following respects : (i) the only part of a corpus spongiosum which it possesses is the glans (the part of the corpus spongiosum of the male which lies between the bulb and the glans penis being represented in the female by the fars intermedia of the bulbi vesti- buii); (2) it does not contain the female urethra; and (3) its com- ponent parts are much smaller than those of the penis. In reality the chtoris is a diminutive penis, minus the corpus spongiosum and the urethra. It is developed from the genital eminenee. Lymphatics. — The lymphatics of the prepuce of the chtoris accompany those of the labia majora, and pass to the pubic group of inguinal glands, and, it may be, to the superficial femoral or saphenous glands. The lymphatics of the glans clitoridis run on the dorsum of the clitoris towards the front of the symphysis pubis, where they form a network. The vessels which emerge from either side of this network have the following destinations: (i) Some pass to the deep femoral glands, which he within the femoral canal; and (2) one or two traverse the inguinal canal, and terminate in the lowest or retro-femoral gland of the outer chain of the external iliac glands. The lymphatics of the corpora cavernosa probably pass to the internal iliac glands on either side. The vestibule is the space which is enclosed by the labia minora, and is so called because it is the ' porch ' of the vagina. It is triangular, the apex, which is in front, being formed by the glans clitoridis, the lateral boundaries by the labia minora, and the base, which is directed backwards, by an imaginary line passing trans- versely in front of the external orifice of the vagina and behind the meatus urinarius. It is about i inch in length, and presents a smooth surface formed by mucous membrane, which is covered by stratified squamous epithelium. At its posterior extremity, in the middle line, and immediately in front of the external orifice of the vagina, there is a slight prominence, with somewhat irregular margins. Upon this prominence the meatus urinarius is situated at a point i inch behind the clitoris. The irregular prominence serv^es as a guide to this opening. The vestibule represents the remains of the uro-genital sinus. The external orifice of the vagina is situated immediately behind the vestibule. It is an antero-posterior cleft, having an elliptical shape when partially dilated. The portion of the vagina close above it is the narrowest part of the passage. For the description of the vagina, see Female Pelvis. The hymen in its normal condition is a thin semilunar fold of mucous membrane which is stretched across the posterior third, or half, of the external orifice of the vagina. Its concave border^ which is free, is directed for^vards and upwcirds. Sometimes the hymen completely surrounds the circumference of the orifice, an aperture being left in its centre. In other cases it stretches over the entire opening, but is perforated by apertures which give it a cribriform appearance. In rare cases it is an entire membrane, completely shutting off the vaginal canal from the uro-genital space, and it is then spoken of as an imperforate hymen. In some cases, even in the virgin, it is.«otii:e^ ralSieuW^ ^::-::^ la vr-o';?'^?^ 632 A MANUAL OF ANATOMY The hymen begins to appear about the fifth month of intra-uterine hfe as a fold of the mucous membrane at the point where the vagina opens into the uro-genital sinus. The carunculse myrtiformes are small elevations which repre- sent the remains of the hymen after its disappearance. Though called carunculcB (fleshy), they are really mucous excrescences. The fourchette, or fraenulum pudendi, is a crescentic fold of the uro-genital lining membrane which is situated a little in front of the posterior commissure, and it is best marked in early life. The fossa navicularis is a small depression which lies between the posterior commissure and the fourchette. Vestibule ^ Meatus Urinarius.^ Bulbus Vestibul Dorsal Vein of the Clitoris ., Pars Intermedia Glans Clitoridis Crus Clitoridis Sphincter Vaginae Right Gland of Bartholin and its Duct Vagina Fig. 279. — Dissection showing the Bulbi Vestibuli and Glands OF Bartholin (Modified from Kobelt) (The cross on either side of the Vaginal Orifice shows the position of the opening of the Duct of Bartholin's Gland). The bulbi vestibuli are two ovoid masses of erectile tissue i inch in length, which are situated on either side of the external orifice of the vagina and vestibule beneath the mucous membrane. Each bulb is covered by a delicate fibrous capsule derived from the antero-inferior layer of the triangular ligament, superficial to which the bulb of either side lies. The outer surface is convex, and is covered by one half of the sphincter vaginae muscle. The inner surface is slightly concave, and is covered by the vaginal mucous membrane. Posteriorly the bulbs diverge, and anteriorly, having become narrow, they ]:)ass upwards and forwards, and ultimately meet in the middle line, where they are attached to the antero- THE ABDOMEN 633 inferior layer of the triangular ligament. In front of the bulbs there is a plexus of veins which is continuous behind with their erectile tissue, and in front with that of the glans clitoridis. This plexus of veins is kno\sTi as the pars intermedia of Kobelt. It receives its veins from the labia minora, and its blood is conveyed into the vaginal plexus. The bulbi vestibuU, together, represent the bulb of the male urethra, which latter presents on its imder surface a faint groove in the middle line, indicating a tendency to a bipartite division. The pars intermedia of Kobelt is regarded as representing that part of the male corpus spongiosum which extends from the bulb to the glans penis. The glands of Bartholin or of Duvemey belong to the class of racemose or acino-tubular glands. They are two in number, right and left, and each resembles a small bean. They lie on either side of the external orifice of the vagina towards its back part, immedi- ately behind the posterior extremities of the bulbi vestibuli, and superficial to the base of the triangular ligament. The duct of each gland is about | inch long, and opens in the angle between the attached border of the njonpha posteriorly and the hymen or its remains, close to the centre of the margin of the vaginal orifice. These glands are homologous with the glands of Cowper, and their structure is similar. The glands of Bartholin are developed iiova the lining epithelium of the uro-genital sinus. The external uro-genital organs of the female have received the name of vulva. As this word, however, literally signifies ' a covering,' it is strictly applicable only to the labia majora, which by their approximation form a covering for the uro-genital space and its contents. Development of the External Genital Organs. In the early stages no sexual differences are apparent in the de- velopment of the external genital organs. The chief parts concerned are — (i) the genital eminence, (2) the genital groove, (3) the internal genital folds, and (4) the external genital folds. Female External Organs. — ^The surface-depression corresponding to the cloacal membrane, which bounds the cloaca postero-inferiorly, is known as the cloacal depression. As the cloaca becomes divided into two compartments — dorsal or intestinal, and ventral or uro- genital— ^by the cloacal or uro-rectal septmn, the cloacal membrane is also divided into two parts — dorsal or anal, and ventral or uro- genital. Moreover, the superficial cloacal depression is likewise divided into two parts — dorsal, which is called the anal depression or proctodeum ; and ventral, which is known as the uro-genital depression, and is somewhat cleft-like. When the uro-genital portion of the cloacal membrane ruptures the uro-genital sinus or canal communicates with the exterior by means of the uro-genital opening or cleft. 634 A MANUAL OF ANATOMY In the female the urinary bladder is developed from the cephalic part of the uro-genital sinus. The entire urethra of the female is developed from the cephalic part of the uro-genital sinus, in succes- sion to the urinary bladder. The caudal part of the uro-genital sinus, becoming expanded, gives rise to the vestibule, into the cephalic part of which the urethra opens, whilst the external orifice of the vagina is caudal, or posterior, to it. The female external genital organs are developed around the uro- genital opening. At the cephalic part of the primitive vestibule a small tubercle, called the genital eminence, makes its appearance in the median line. On the lower, or vestibular, surface of this eminence a furrow, called the genital grove, is formed. The lips of this groove, which are laterally disposed, are called the internal genital folds. On either side of the genital eminence, external to the corresponding internal genital fold, a prominent ridge makes its appearance. These ridges are known as the external genital Male. Raphi of Penis Glans Penis Female. Glans Clitoridis Genital (Labial) Fold Anus Uro-genit;:' Aperture Coccyx Coccyx Fig. 280. — Development of the External Genital Organs. folds. They are continuous with each other on the ventral aspect of the genital eminence, and they extend dorsalwards, lying on either side of the vestibule, and finally meeting behind in the perineum. The genital eminence undergoes lengthening, and gives rise to the clitoris. The terminal extremity of the eminence becomes enlarged, and forms the glans clitoridis, whilst the remainder gives rise to the corpora cavernosa clitoridis. The internal genital folds, which in the male fuse, enclosing the spongy part of the urethra, and forming the corpus spongiosum penis, remain separate in the female, and form the labia minora, or nymphcB. The external genital folds, which in the male fuse and form the scrotum, remain separate in the female, and give rise to the labia major a. The ventral portions of the external genital folds, which are continuous with each other on the ventral aspect of the genital eminence, form the mons veneris. THE ABDOMEN 635 The hymen appears as a semilunar fold of mucous membrane, extending as a rule over the dorsal part of the external orifice of the vagina. The glands of Bartholin are developed laterally as evaginations of the epithelial lining of the caudal part of the uro-genital sinus, which part, when expanded, forms the vestibule. The bulhi vestibuli and the pars inter media of Kobelt are developed as masses of erectile tissue close to the labia minora or n^nnphae and clitoris. Male External Organs. — In the male the genital eminence under- goes considerable lengthening, and gives rise to the corpora cavernosa penis, the terminal enlargement of the eminence forming the glans penis. As the genital eminence elongates, the genital groove on its lower surface undergoes proportionate elongation, and at the same time deepens. The internal genital folds, which form the lateral lips of this groove, and which in the female remain separate from each other as the labia minora, come together in the male, and fuse over the genital groove. This groove is thus transformed into a canal, which constitutes the spongy part of the male urethra. The line of fusion of the internal genital folds is indicated, in adult life, by the median raphe, which traverses the under, or scrotal, aspect of the penis. The portion of the urethra within the glans penis is developed from a collection of ectodermic cells, forming the so-called urethral septum or plate. These cells become tun- nelled into a canal, which is continuous with the spongy urethra, developed as stated from the genital groove. The spongy part of the urethra extends as far as the uro-genital sinus, from the lower part of which the prostatic and membranous purls of the canal are developed. In rare cases the internal genital folds fail to unite over some portion of the genital groove. In such cases the spongy urethra opens externally on the under, or scrotal, aspect of the penis, and the condition is known as hypospadias. The internal genital folds, which enclose the spongy part of the urethra, acquire erectUe tissue and constitute the corpus spongiosum penis. The genital eminence, having lengthened considerably, and having acquired erectile tissue, gives rise by its greater part to the corpora cavernosa penis, whilst its terminal enlargement forms the glans penis. As just stated, the corpus spongiosum penis is formed by the fusion of the two internal genital folds, this fusion converting the genital groove into the spongy part of the urethra. The external genital folds, which in the female remain separate and form the labia majora, unite in the male and give rise to the scrotum. The line of fusion is indicated, in adult life, by the scrotal raphe. It is to be noted that, whilst the prostatic and membranous portions of the male urethra are developed from the lower part of the urogenital sinus, and are therefore non-penile, the spongy portion of the canal is developed from (i) the genital groove on the 636 A MANUAL OF ANATOMY lower surface of the genital eminence, and (2) the internal genital folds. The spongy part of the urethra is therefore penile. The bulb of the corpus spongiosum penis represents the bulbi vestibuli of the female, and the portion of the corpus spongiosum penis between the bulb and the glans penis represents the pars intermedia of Kobelt in the female. Metamorphoses of the Structures concerned in the Development of the External Genital Organs. Structures. Female. Male. Genital eminence. Clitoris. Corpora cavernosa penis and glans penis. Internal genital folds. Labia minora and bulbi Corpus spongiosum and vestibuli. spongy uretlira. External genital folds. Labia majora. Scrotum. Uro-genital sinus. Bladder, urethra, vesti- Bladder, prostate gland, bule, and glands of prostatic and mem- Bartholin. branous urethra, and glands of Cowper. Perineum Proper. The perineum proper is the region which lies between the anus and the posterior commissure, and it presents a raphe in the middle line. It is in this division that the perineal body is situated, as well as the central tendinous point. The latter, being similar to that of the male, requires no special description. Perineal Body. — ^This body is peculiar to the female perineum. It is situated between the anus and the posterior commissure, and it may be regarded as a deep expansion of the central tendinous point. It is triangular, and is about i^ inches in breadth. It is bounded in front by the posterior wall of the vagina, behind by the anterior wall of the anal canal, and inferiorly by the integu- ment. The perineal body is produced by a thickening of connective tissue, with a free admixture of elastic tissue, and a few muscular fibres derived from the external sphincter, levatores ani, and sphincter vaginae muscles. It serves as a support to the posterior wall of the vagina. During parturition it becomes greatly stretched, but its elastic tissue usually guards it against rupture. Triangular Ligament. — The triangular ligament resembles that of the male in being composed of two layers, antero-inferior and postero-superior , The antero-inferior layer, on account of the greater width of the subpubic arch in the female, is broader than in the male, though it is more indefinite on account of its being pierced by the vagina. It is attached at either side to the inner border of the ischio-pubic ramus, and superiorly to the transverse pelvic or perineal ligament. In the middle line, where it is pierced by the vagina, it blends with the wall of that canal. Its base is joined by a somewhat indefinite layer of fascia representing the fascia of THE ABDOMEN 637 Colles in the male, and by the postero-superlor layer. The openings in the antero-inferior layer are similar to those in the male, with this exception, that the ducts of the glands of Bartholin do not pierce it as the ducts of the glands of Cowper do in the male, the glands of Bartholin being situated superficial to this layer. The urethral opening is situated i inch below the symphysis pubis. The opening for the vagina, which is of large size, lies below the urethral orifice, from which it is separated by a few fibres. The openings for the arteries of the bulbi vestibuli are situated one on either side of the vaginal opening. The openings for the artery of the corpus cavernosum clitoridis, for the dorsal artery and nerve of the clitoris, and for the superficial perineal vessels and nerves, all of each side, are situated as in the male. It is to be noted that the dorsal vein of the clitoris, like the corresponding vessel in the male, passes between the subpubic and transverse pelvic or perineal ligaments. The postero-superior layer is similar to the corresponding layer in the male, and it presents openings for the urethra, vagina, and internal pudic vessels and pudic nerves of each side. Ischlo-rectal Division. The chief characters of the ischio-rectal division in the female are as follows : the aperture of the anus is somewhat nearer the coccyx than in the male, the distance between the ischial tuber- osities is greater than in the male, and the ischio-rectal fossae are wider and shallower than in the male. Muscles. — ^The muscles of the female perineum, as compared with those of the male, present certain differences. Levatores Ani. — ^The anterior fibres of these muscles embrace the vagina instead of the prostate gland, as in the male. Iscliio-cavernosus (erector clitoridis). — ^This muscle replaces the erector penis, and is of small size. Bulbo-cavernosus or Sphincter Vaginae. — ^This muscle arises from the central tendinous point, where it meets the external sphincter and superficial transverse perineal muscles. It then passes forwards and divides into two symmetrical parts which surround the vaginal orifice and vestibule, each part closely embracing the outer surface of the corresponding bulbus vestibuli. Anteriorly the two parts become very narrow, and each is inserted into the fibrous sheath of the corpus cavernosum. A few fibres are here detached to be inserted into a tendinous expansion on the dorsum of the clitoris covering the dorsal vein, which vessel would be thereby compressed when the muscle is in action. Some of the inner fibres of the sphincter vaginae are inserted into the mucous membrane of the vestibule. The sphincter vaginae is homologous with the bulbo-cavemosi in the male. Compressor or Constrictor Urethrae.— This muscle, as in the male, lies between the two layers of the triangular ligament. It is 638 A MANUAL OF ANATOMY attached, on either side, to the inner margin of the ischio-pubic ramus, and in the middle Hne it is almost completely divided into two parts by the vagina. The anterior part passes transversely across the subpubic arch in front of the urethra, whilst the posterior and larger part passes inwards, partly transversely and partly obliquely, to blend with the vaginal wall. The external sphincter and superficial transverse perineal muscles are similar to those in the male. Internal Pudic Artery. — ^This vessel is of smaller size than in the male, but it takes a similar course. The difference, therefore, in the two sexes affects chiefly the branches of the artery. The superficial perineal artery is larger than in the male, and is distributed to the labium majus. The artery of the bulb is of comparatively small size, and is distributed to the bulbus vestibuli. The artery of the corpus cavernosum clitoridis, having pierced the antero-inferior layer of the triangular ligament, enters the crus clitoridis, and is then continued onwards in the centre of the corpus cavernosum. The dorsal artery of the clitoris, like the preceding, is compara- tively small in size. Having pierced the antero-inferior layer of the triangular ligament, it passes between the crura clitoridis, and also between the two layers of the suspensory ligament of the clitoris. It is then continued along the dorsum of that organ as far as the glans, having the dorsal vein of the clitoris on its inner side, and the dorsal nerve of the clitoris on its outer side. On reaching the glans, it divides into branches for the supply of the glans and its prepuce. As it passes along the dorsum of the clitoris it gives off several branches, which enter the corpus cavernosum by piercing its fibrous sheath. The veins of the female perineum are so similar to those in the male as not to require any special description. An exception, however, has to be made in the case of the dorsal vein of the clitoris. This vein is formed by branches which return the blood from the glans and prepuce, and also to a certain extent from the corpora cavernosa. It passes backwards in the groove between the corpora cavernosa, where it has on either side of it the dorsal artery, and external to this the dorsal nerve, of the clitoris. In this part of its course it receives tributaries from the corpora cavernosa. On reaching the root of the organ it passes between the two layers of the suspensory ligament of the clitoris, and then between the subpubic and transverse pelvic or perineal ligaments, and so it enters the pelvic cavity, where it terminates in the plexus of veins at the neck of the bladder. Lymphatics. — The lymphatics of the labia majora, the super- ficial lymphatics of the clitoris, including those of its glans, and the lymphatics of the lower third of the vagina and of the urethra terminate in the inguinal glands, which lie immediately below Poupart's ligament. The lymphatics of the upper two-thirds of THE ABDOMEN 639 the vagina terminate in the internal iliac glands, and the deep h-mphatics of the corpora cavernosa clitoridis, having accompanied the dorsal vein of the cHtoris, also terminate in the internal iliac glands. The pudic nerve and its branches are similar to those in the male, the superficial perineal nerves being distributed to the labia majora. ABDOMINAL WALL. Landmarks. — ^The position of the linea alba is indicated by the mid-abdominal groove, which extends from the ensiform process of the sternum to the umbilicus, and the mid-abdominal line, which extends from the umbilicus to the upper part of the s^Tnphysis pubis. After removal of the integument the linea alba presents a dense white appearance, and is slightly depressed below the level of the adjacent surfaces. It is produced by the decussation of the aponeuroses of the abdominal muscles of opposite sides, except the recti, and it is divided into two parts, supra-umbilical and infra- umbilical. The supra-umbilical part is about ^ inch broad, the recti being here separated to that extent. The infra- umbilical part is only about ^ inch wide on account of the approximation of the recti in this situation. Over the whole extent of its posterior or abdominal surface it is invested by the parietal peritoneum, unless in cases of abnormal distension of the bladder, when the peritoneum is stripped from the lower part to an extent corresponding with the height to which the distended bladder ascends. The anterior abdominal wall is thinner and less vascular along the linea alba than at any other part. This line is therefore selected for such operations as suprapubic lithotomy, tapping a distended bladder above the symphysis pubis, and ovariotomy. The structures which axe divided in opening the abdominal cavity along the linea alba are as follows : the integument, the decussating fibres of the aponeuroses of opposite sides, fascia transversalis, subperitoneal areolar tissue, and parietal peritoneum. There are no bloodvessels of any importance in this situation. The posterior aspect of the linea alba has important visceral relations. The left lobe of the liver lies behind it for about 2 inches below the ensiform process of the sternum. The relation of the stomach to it is variable. When the viscus is moderately distended it lies behind the linea alba below the margin of the liver. In the empty condition, however, it recedes from the linea alba, and this gives rise superficially to the epigastric depression, or scrohiculus cordis (' small trench of the heart '). The transverse colon, covered by the great omentum, as it crosses from right to left, usually lies behind the linea alba just above the imibilicus. The coUs of the jejunum and ileum, also covered by the great omentimi, lie behind it below the umbilicus. 640 A MANUAL OF ANATOMY In young persons the upper part of the bladder, being extra- pelvic, lies behind the lowest part of the linea alba. In adults the upper part of that viscus, when abnormally distended, also lies behind the lowest part of this line. The umbilicus takes the form of a cicatricial depression which is situated in the linea alba at the junction of the upper three- fifths and lower two-fifths. As seen from before it is irregu- larly circular, the skin being more or less puckered according to the state of distension of the abdomen. When viewed from behind it is smaller in size, and its long measurement lies transversely. Besides cicatricial tissue and fat, the lower part of it contains the upper ends of the urachus and obliterated hypogastric arteries, whilst the upper part is occupied by part of the obliterated runbilical vein. The upper part is weaker than the lower. The umbilicus is on the same horizonal plane as the disc between the bodies of the third and fourth lumbar vertebrae. During intra-uterine life the umbilicus is an opening by which the hypogastric arteries leave the abdomen of the foetus on their way to the placenta, and by which the umbilical vein, on its way from the placenta, enters the abdomen. A few days after birth, however, the opening becomes permanently closed. The linese semilunares coincide with the outer borders of the recti abdominis. The position of each is indicated by a line drawn from the lowest part of the eighth costal cartilage to the pubic spine. This line is curved, with the convexity outwards, and at the level of the umbilicus it is about 3 inches from it. Over the upper three-fourths of the rectus abdominis it indicates the splitting of the aponeurosis of the internal oblique into two laminae, which encase that extent of the muscle in a sheath. Over the lower fourth it indicates where the aponeuroses of the external oblique and internal oblique and the anterior aponeurosis of the transversalis abdominis pass in front of the rectus. The linese transversae are usually three in number, on either side. They are tendinous intersections or inscriptions which cross the rectus in the following situations : one at the level of the umbilicus, one at the level of the lower part of the ensiform process of the sternum, and one about midway between these two. The positions of the linege transversae are indicated by three faint grooves. The anterior wall of the sheath of the rectus is closely bound down to the tendinous intersections, and so each muscle above the level of the umbilicus is mapped out into two quadrangular areas, and the interior of the sheath, anterior to the muscle, is also divided into two distinct compartments. An abscess may form in one or other of these compartments, or there may be a spasmodic contraction of one or other of these quadrangular areas of the muscle, a condition in each case which would necessarily have a circumscribed limit, and might lead to error in diagnosing affections really having their seat within the abdominal cavity. The spino-umbillcal lines are two in number, right and left, THE ABDOMEN 641 and each extends from the anterior superior iliac spine to the umbilicus. The anterior superior spinous process of the ilium is situated at the anterior extremity of the iliac crest, and, being very super- ficial, it can be readily felt. It is on the same level with that of the opposite side, and therefore a line connecting the two should be quite horizontal. The plane of this interspinous line is rather lower than the promontory of the sacrum. The anterior superior iliac spine is the point from which the measurement of the lower limb is taken, the other point being the internal malleolus. This spine is also a good ready guide to the position of the great tro- chanter, which is situated about 4 inches below it, and about 4^ inches behind a line let fall vertically from it. The pubic spine is situated at the lower and inner part of the anterior abdominal wall about i\ inches outside the upper part of the symphysis pubis. It is sometimes a sharp-pointed process, and then it can readily be felt beneath the integument. In most persons, however, it takes the form of a more or less indistinct tubercle, and cannot readily be made out. In such cases the scrotal integument may be invaginated with the finger, and so the adipose tissue raised from over the spine. If it cannot be felt in this way the thigh should be well abducted to render prominent the adductor longus muscle, the tendon of origin of which will serve as a guide to the spine, which lies above and to the outer side of it. The pubic spine is the guide to the external abdominal ring, the crural or femoral ring, and the saphenous opening. The external abdominal ring is situated immediately above, and to the outer side of, the pubic spine. In exploring the ring the best way to proceed is to invaginate the scrotal integument, and carry the examining finger up the inner side of the spermatic cord, when the ring will be reached. In normal circumstances it should admit the point of the little finger. In making this examination the spermatic cord is readily felt, and the vas deferens can be distinguished as a firm cord-like structure lying at its back part, and easily separable from the other constituents of the cord. In the female the round liga- ment of the uterus takes the place of the spermatic cord, but, being a very ill-defined structure, it usually escapes detection. The femoral ring is situated fully i inch external to the pubic spine in a line drawn transversely outwards from that spine across the front of the thigh. The saphenous opening is situated below, and a little external to, the pubic spine. The pubic crest extends transversely inwards for about i\ inches from the pubic spine, and it terminates in the pubic angle which surmounts the internal surface of the pubic body, and is usually a rudimentary tubercle. The crest may be felt with the finger as the external abdominal ring, of which it forms the base, is being explored. Poupart's ligament can be felt as a tense band, especially when the thigh is extended, abducted, and rotated outwards, 41 642 A MANUAL OF ANATOMV passing between the anterior superior iliac spine and the pubic spine. The internal abdominal ring is situated midway between the symphysis pubis and the anterior superior iUac spine, and | inch above Poupart's Hgament. The inguinal canal extends obliquely downwards, forwards, and inwards from the internal to the external abdominal ring, and is situated immediately above the inner half of Poupart's ligament. Topography of Arteries, Triangles, and Iliac Fossae. — ^The bifur- cation of the aorta into right and left common iliac arteries usually takes place opposite the centre of the body of the fourth lumbar vertebra, a finger's breadth to the left of the middle line. The position of the bifurcation is indicated in one of two ways : (i) a point fully i inch below the umbilicus and a finger's breadth to the left of the linea alba pretty nearly corresponds with the point of bifurcation ; (2) a more definite guide is a point in the line which connects the highest parts of the iliac crests a finger's breadth to the left of where it intersects the linea alba. The common and external iliac arteries are indicated by a line drawn from a point midway between the anterior superior iliac spine and the symphysis pubis to the point corresponding to the bifurcation of the aorta. This line should be slightly curved, with the convexity directed outwards. Its upper 2 inches indicate the course of the common iliac artery, and the remainder represents the external iliac. The deep epigastric artery, in its first or oblique part, is indicated by a line drawn from the inner border of the internal abdominal ring to the outer border of the rectus abdominis at a point midway between the upper border of the symphysis pubis and the umbilicus. The subsequent course of the vessel is represented by a line corre- sponding to the centre of the rectus abdominis, and reaching to a point about 2 inches above the umbilicus. This latter line is about i| inches distant from the linea alba. The triangle of Hesselbach is situated on the inner side of the first or oblique part of the deep epigastric artery, and above the inner half of Poupart's ligament. The triangle of Petit is situated immediately above the centre of the iliac crest. In this region a lumbar hernia may protrude, and a lumbar abscess may come to the surface at this point. The right iliac fossa contains the terminal part of the ileum, the caecum, the ileo-csecal valve, and the vermiform appendix in part. The left iliac fossa contains the iliac colon. McBurney's point is situated in the right spino- umbilical line between i| and 2 inches from the anterior superior iliac spine. According to McBurney it corresponds very accurately in the living subject to the base of the vermiform appendix. Practically it coincides with the centre of the right iliac fossa. Monro's point is situated at the centre of the spino-umbilical line. Its distance from the anterior superior iliac spine a 2-6 inches. THE ABDOMEN 643 Upon the right side McBurney's point and Monro's point very nearly coincide. Both of these points are now regarded as indicat- ing approximately the situation of the ileo-caecaJ valve, and not the base of the vermiform appendix. The guide to the base or opening of the appendix is a point on an average rather more than I inch below the ileo-caecal valve — that is to say, the base or open- ing of the vermiform appendix is rather more than i inch below McBurney's point.* Anterior Abdominal Fasciae. — ^The superficial fascia of the anterior wall of the abdomen, from Poupart's ligament to a line drawn trans- versely from the anterior superior iliac spine to the linea alba, resembles the superficial fascia of the uro-genital division of the perineum in being divisible into two layers. The layer immediately beneath the skin is called the subcutaneous layer or fascia of Camper, and the other layer is called the deep layer or fascia of Scarpa. The subcutaneous layer or fascia of Camper is composed of areolar tissue containing adipose tissue in its meshes. When traced upwards it blends with the deep layer above the level of the line connecting the anterior superior iliac spine with the linea alba. \\Tien followed inwards it is continuous with the corre- sponding layer of the opposite side. In a downward direction it is freely continuous over Poupart's ligament with the subcutaneous layer of the superficial fascia of the front of the thigh. When traced downwards and inwards it passes along the spermatic cord into the scrotal wall and over the penis, in which situations, more especially the former, it contains involuntary muscular fibres, which replace its adipose tissue, and so, with the deep layer which it here joins, it forms the tunica dartos. In the female Camper's fascia passes along the romid ligament of the uterus into the labium majus. The deep layer or fascia of Scarpa is a strong membrane which contains yellow elastic tissue. It is separated from Camper's fascia by the superficial epigastric vessels, and, in the region of Poupart's ligament, by the inguinal glands. Its deep aspect is loosely connected by areolar tissue to the subjacent aponeurosis of the external oblique muscle. Superiorl)', above the line con- necting the anterior superior iliac spine with the linea alba, it blends with Camper's fascia. At the middle line it is firmly bound down by fibrous bands to the linea alba. Interiorly it blends with the inner part of Poupart's ligament, but external to this it passes over that ligament, to which it is bound by fibrous bands, and immediately ' thereafter it becomes incorporated with the fascia lata of the thigh. When traced downwards and inwards it passes along the spermatic cord into the scrotal wall, and over the penis. In the former situation it forms, along with the subcutaneous layer, the tunica dartos. In the female Scarpa's * Sir Frederick Treves, based upon observations made by Dr. C. Addison and Dr. Arthur Keith. 644 A MANUAL OF ANATOMY fascia passes along the round ligament of the uterus into the labium majus. The fascia of Camper is continuous, through the tunica dartos, with the subcutaneous layer of the superficial fascia of the uro- Hypogastric Branch of Ilio-hypogastric Intercosto-humeral Additional Intercosto- humeral Lateral Cutaneout^ 11. 1 2th Thoracic -Kii Iliac Branch of Ilio- hypogastric Fig. 28i. — Cutaneous Nerves of the Trunk (Antero-lateral View) (after Henle). I -1 2, Anterior Cutaneous ; 2-12, Lateral Cutaneous. :oi to ")0l tht :he .re le genital division of the perineum, and the fascia of Scarpa is simi- • larly continuous with the deep layer of the superficial fascia, or the fascia of Colles, of that division, •• The disposition of Scarj)a's fascia at the line of the groin explains , - why, in cases of extravasation of urine beneath Colles's fascia, tf^^^i^ urine, when it reaches the anterior abdominal wall, does not pa*^®^s THE ABDOMEN 645 downwards to the front of the thigh, but takes an upward course. The fascia of Scarpa represents the tunica abdominalis of quadrupeds, which is composed almost entirely of elastic tissue, and serves as an important adjunct to the abdominal parietes. The deep fascia resembles that in other parts of the body in being membranous. Laterally, where the external oblique is fleshy, this fascia is well marked, but, as it approaches the confines of the aponeurosis of that muscle, it becomes very delicate, and ultimately disappears. Over the external oblique aponeurosis, therefore, there is really no deep fascia properly so called, so that the deep layer of the superficial fascia or fascia of Scarpa lies directly upon the external oblique aponeurosis, to which it is loosely connected by areolar tissue. Cutaneous Nerves. — The anterior cutaneous nerves are the terminal branches of the lower five intercostal nerves and of the anterior primary division of the twelfth thoracic nerve (subcostal nerve). Having emerged through the anterior wall of the' sheath of the rectus abdominis in a straggling manner, they give a few twigs inwards, and then turn outwards to supply the anterior abdominal integument, in which they communicate with the anterior branches of the lateral cutaneous nerves. The hypogastric branch of ilio-hypogastric nerve pierces the external oblique aponeurosis about i inch above the external abdominal ring, and is distributed to the integument of the supra- pubic region. It is serially continuous with the anterior cutaneous nerves. The skin below the ensiform process is supplied by the seventh thoracic nerve ; that on a level with the umbilicus by the tenth thoracic ; and that over the lower half of the infra-umbilical region by the twelfth thoracic, and the iUo-hypogastric. The lateral cutaneous nerves are branches of the lower fi.ve intercostal nerves. Having emerged between the serrations of the external oblique muscle in the mid-axillary line, each divides into an anterior and a posterior branch. The posterior branch turns backwards to supply the integument over the lower part of the back. The anterior branch passes forwards to supply the anterior abdominal integument, in which it communicates wdth an anterior cutaneous nerve. Cutaneous Arteries. — The superior or superficial external pudic artery arises from the common femoral about J inch below Poupart's Ugament, after which it pierces the crural sheath and cribriform fascia. Having emerged through the saphenous opening, it passes inwards and upwards over the spermatic cord, or round hgament of the uterus, according to the sex, to be distributed to the integument of the suprapubic region, the adjacent portion of the scrotum in the male and the labium majus in the female, and the dorsum of the penis by a branch which extends as far as the prepuce, lying external to the dorsalis penis artery. The vessel in its course gives branches to the pubic glands, the deep femoral glands, and the coverings of the spermatic cord, or of the round Ugament of the uterus. It anasto- 646 A MANUAL OF ANATOMY moses with the following arteries : (a) the cremasteric branch of the deep epigastric, in crossing the spermatic cord, that branch being represented in the female by the artery of the round ligament of the uterus ; {b) its fellow of the opposite side ; (c) the inferior or deep external pudic ; and {d) the dorsalis penis. The venaj comites of this artery terminate in one vessel which joins the long saphenous vein. The superficial epigastric artery arises from the common femoral about ^ inch below Poupart's ligament. Having pierced the crural sheath and cribriform fascia, or the outer border of the saphenous opening, it turns upwards over Poupart's ligament a little to the inner side of the centre, and then ascends in the abdominal integument as high as the level of the umbilicus. As it turns upwards it supplies branches to the inguinal glands, and on the abdominal wall it anastomoses with branches of the deep epi- gastric artery. There are at first two venaj comites with this artery, but these eventually join to form one vessel which terminates in the long saphenous vein. The radicles of these venae comites communicate \tith the following vessels : the parumbilical veins in the region of the umbilicus, which lie on the surface of the round ligament of the liver, and communicate with the branches of the vena porta; ; the inferior or long thoracic and subscapular veins, upon the side of the thorax, which are tributaries of the axillary vein ; and the superior epigastric veins, which are tributaries of the internal mammary veins. In the superficial epigastric vein and its tributaries the blood can flow in either direction. The anastomoses of the tributaries of the vein explain why they become engorged- in cases of portal obstruction and obstruc- tion of the inferior vena cava. The superficial circumflex iliac artery often arises in common with the superficial epigastric from the common femoral about \ inch below Poupart's ligament. Having pierced the crural sheath and the outer border of the saphenous opening, it passes outwards below the outer part of Poupart's ligament to the anterior part of the iliac crest, where it is distri- buted to the adjacent abdominal integument. In its course it gives branches to the iliacus and sartorius muscles and the outer inguinal glands, and it anastomoses with {a) the deep circumflex iliac of the external iliac, and (b) the gluteal of the internal iliac. The vein corresponding to this artery terminates in the long saphenous vein. The anterior cutaneous arteries are derived from the deep and superior epigastric arteries. They emerge through the anterior wall of the sheath of the rectus abdominis in an irregular manner, and accompany more or less closely the anterior cutaneous nerves. The veins corresponding to these arteries terminate in the deep and superior epigastric veins. The lateral cutaneous arteries are branches of the lower five aortic inter- costal and subcostal arteries, and they emerge with the lateral cutaneous nerves between the serrations of the external oblique muscle in the mid- axillary line. The veins corresponding to these arteries are tributaries of the lower five intercostal and subcostal veins. Superficial Lymphatics. — The superficial lymphatics helow the level of the umbilicus accompany the superficial epigastric vessels, and terminate in the inguinal glands. Those above the level of the umbilicus pass to the axillary glands. The superficial lymphatics of the lateral abdominal wall terminate in two ways. Some accom- pany the superficial circumflex iliac vessels, and terminate in the inguinal glands ; others accompany the abdominal branches of the lumbar arteries, and terminate in the deeply-]:)laced lateral group THE ABDOMEN 647 of lumbar glands. For the deep lymphatics of the antero-lateral abdominal wall, see p. 664. Penis. Coverings. — The skin at the free extremity of the glans, being doubled upon itself, passes backwards until it reaches the constriction behind the corona glandis called the cervix. Here it is reflected forwards, closely investing the cervix, corona glandis, and body of the glans. On reaching the lips of the meatus urinarius it becomes continuous with the mucous membrane of the urethra. The skin covering the glans is provided with papillae, but these do not appear on the surface. The duplicature, which the skin forms in the region of the glans, is called the prapidiiim penis, or prepuce. The under part of the prepuce is connected to the imder surface of the glans by a median, laterally compressed, triangular fold, called the frenum prcepiitii, which extends as far as the lower pai t of the meatus urinarius. The skin of the cervix, corona glandis, and adjacent part of the inner surface of the prepuce contains large sebaceous glands, called the glands of Tyson. Their secretion is a whitish curdy substance, and is strongly odorous, from. which character the glands have been called the glanditicB odorifercB, the secretion being called the smegma prcBpuiii (unguent of the prepuce). The dartos tunic is situated immediately beneath the skin, and is destitute of adipose tissue. It is continuous with Camper's and Scarpa's fascise of the anterior abdominal wall, and with the tunica dartos of the scrotum, like which latter it contains involuntary muscular tissue. The fascial investment or sheath covers the penis, with the exception of the glans. It is situated beneath the dartos tunic, and at the cervix blends with the skin of the glans. Towards the root of the organ it receives expansions from the ischio-cavemosi and bulbo-cavernosi, and it covers the dorsal vessels and nerves. In this way the dorsal vein is com- pressed during the action of the ischio-cavemosi and bulbo- cavernosi. At the root of the organ the fascial investment blends with the two layers of the suspensory ligament. Suspensory Ligament. — ^This ligament, which is strong and tri- angular, is composed of fibrous and elastic tissues. It is attached superiorly to the front of the symphysis pubis, where it is single, and interiorly it divides into two laterally-disposed, diverging laminae, which blend with the fascial sheath of the penis. The interval between the two laminae is occupied by the dorsal vessels and nerves. The dorsal arteries. — For the description of these arteries, see p. 624. In addition to the dorsal artery, the integument of the organ is supplied by the superior or superficial external pudic arteries, the branch from each of these vessels lying external to the dorsaUs penis artery. Deep Dorsal Vein. — ^The tributaries which give rise to this vein come from the glans and corpora cavernosa. They form at first two dorsal veins, but these soon imite into one vessel, which passes backwards in the middle line, occup^ang the g?oove between the corpora cavernosa, where it is under cover of the fascial sheath 648 A MANUAL OF ANATOMY of the penis. At the root of the organ it passes between the two laminae of the suspensory ligament, and then between the subpubic and transverse perineal or pelvic ligaments. In this part of its course it communicates with the venous plexus in the compressor urethrge muscle in which the internal pudic venae comites arise. On entering the pelvis it divides into two branches, which terminate in the right and left portions of the prostatic plexus of veins. In addition to the deep dorsal vein, there are two superficial dorsal veins which take up blood from the glans and integument. Each accompanies a branch of the superiot external pudic artery, and opens into the superior external pudic vein. For a description of the dorsal nerves of the penis, see p. 627. The relation of the structures on the dorsum of the penis, from the middle line outwards, is as follows: deep dorsal vein, dorsal artery, and dorsal nerve. Composition of the Penis. — ^The penis has tv/o surfaces, upper or dorsal and under or scrotal. Viewed as a whole the organ is composed of three cylindrical bodies, namely, two corpora cavernosa and a corpus spongiosum, closely applied to each other. It is divisible into a root, body, cervix, and glans. The root is formed by the crura of the corpora cavernosa, which are attached to the inner margins of the ischio-pubic rami. The upper surface of the root is also connected to the symphysis pubis by the suspensory ligament; The upper or dorsal surface of the body is formed by the corpora cavernosa, the under or scrotal surface being formed by the corpus spongiosum in the middle line and the corpora cavernosa at either side. The corpora cavernosa and corpus spongiosum at their meeting become flattened, and so the shape of the body is subcylindrical. The corpora cavernosa terminate in round ex- tremities, in front of which the corpus spongiosum turns upwards, and, becoming much enlarged, forms the glans penis. The cervix is the constriction between the body and the glans. The glans penis is formed by the corpus spongiosum. It is somewhat conical, and has been likened to an acorn, from which circumstance it has been called the balanus. At the base there is a wheel-like rim, called the corona glandis. The part anterior to the corona is called the body of the glans, and this terminates in a small round tip, which presents a vertical fissure called the nf-aius urinarius. For the structure of the penis, see p. 856. Lymphatics. — ^These are divided into a superficial and deep set. The superficial lymphatics of the prepuce, having formed a plexus, pass to the cervix, which they surround in the form of a ring. Those of the glans, having also formed a plexus, pass along with those of the spongy portion of the urethra to the foregoing ring. From this ring three lymphatic trunks proceed towards the symphysis pubis. One of these is median and dorsally placed, whilst the other two are disposed one on either side. The median trunk, when it reaches the suspensory ligament of the penis, divides into two branches, right and left. Each of these passes with the corresponding lateral trunk to the groin of the same THE ABDOMEN 649 side, where both terminate in the pubic group of the inguinal ghnds. The position of the foregoing three lymphatic trunks accomits for the red hnes which are often seen along the dorsum and sides of the penis when septic matter is absorbed from a venereal sore on the prepuce or glans. Their mode of termination also explains the occurrence of induration, or of suppuration, in the inguinal glands as the result of such sores, or of gonorrhoea. The deep lymphatics return the lymph from the substance of the penis, and accompany the dorsalis penis vein into the pelvis, where they terminate in the internal iliac glands. The lymphatics of the clitoris correspond with those of the penis. Scrotum. — ^The wall of the scrotum is complex, and its con- stituent parts will be made more evident if they are enumerated in the order in which the testes receive them in their original descent from the abdominal cavity. It may be premised that the descent of each testis is preceded by a process of peritoneum, called the processus vaginalis, the lower part of which remains permanent as the tunica vaginalis scroti. The constituent parts of the scrotal wall, enumerated from within outwards, are as follows : timica vaginalis scroti, subperitoneal areolar tissue, internal spermatic fascia, cremasteric or middle spermatic fascia, intercolvmmar or external spermatic fascia, tunica dartos, and skin. Skin jTj/i Tunica Vaginalis Scroti '^'^•■' Subperitoneal Areolar Tissue Internal Spermatic Fascia Middle Spermatic Fascia External Spermatic Fascia Tunica Dartos Fig. 2 J -Scheme of the Structures forming the Wall of the Scrotum (Transverse Section). The tunica vaginalis scroti is the parietal layer of the tunica vaginalis. The sabperitoneal areolar tissue is composed of areolar and adipose tissues and a certain amount of plain muscular tissue, its muscular element being known as the middle cremaster. The internal spermatic fascia is derived from the fascia transversalis at the margins of the internal abdominal ring, in which vicinity it is called the infundibuliform lascia. In association with the subperitoneal areolar tissue it forms the fascia propria of Cooper. The cremasteric, or middle spermatic, fascia is composed of striated muscular tissue, forming the cremaster muscle (external cremaster), and of ^'^^olsLT and elastic tissues. It is traceable superiorly to the lower border ° -I- h '^*^"^^^ oblique and the centre of Poupart's ligament on its deep aspect. Ihe intercolumnar, or external spermatic, fascia is composed of connec- tive tissue, and is derived from the intercolumnar fibres which extend between the columns of the external abdominal ring. The internal, middle, and external spermatic fasciae are closely incorporated with one another. 650 A MANUAL OF ANATOMY The tunica dartos lies immediately within the skin. It is derived from the fasciae of Camper and of Scarpa of the anterior abdominal wall. It is chiefly composed of plain muscular tissue, but it also contains fibro-areolar and elastic tissues, and it has a brick-red colour. The skin is thin, very extensible, somewhat dark in colour, and pro- vided with hairs, sweat-glands, and sebaceous glands. It is more dependent on the left side on account of the lower position of the left testis. In the middle line it presents a raphe, which is continuous behind with that of the anterior part of the perineum, and in front with that on the under surface of the penis. This raphe is an external indication of the bilateral symmetry of the scrotum. On either side of the raphe the skin is thrown into a number of transverse rugae, the corrugated condition being due to the plain muscular tissue of the tunica dartos. The interior of the scrotum is divided into two compartments, each of which lodges the corresponding testis. This division is effected by the septum scroti, formed by the fusion of the con- tiguous walls of the two scrotal chambers, except the skin, which forms one continuous investment to both. Inferiorly the septum is attached to the bottom of the scrotal chamber, and superiorly to the under surface of the root of the penis. Blood-supply. — ^The scrotum receives its chief arterial supply from the superior and inferior external pudic branches of the common femoral of each side, and the superficial perineal branches of the internal pudic arteries. The veins corresponding to these arteries terminate in the long saphenous and internal pudic veins. The cremasteric branch of the deep epigastric of each side also takes part in the supply of the scrotal wall, the venous blood being returned into the deep epigastric vein, which at its termination is single. Lymphatics. — ^The most of the lymphatics of the scrotum termi- nate in the pubic inguinal glands, but those from the back part pass to the internal iliac glands. Nerve-supply. — The nerves of the scrotum are as follows : (i) the external or posterior and internal or anterior superficial perineal branches of the pudic; (2) the long pudenal nerve of Soemmering from the small sciatic; (3) the inguinal nerve (ilio-inguinal) from the lumbar plexus; and (4) twigs of the genital branch of the genito-crural nerve from the lumbar plexus. The two superficial perineal nerves and the long pudendal nerve are known as the long scrotal nerves. Development. — The external genital folds. Muscles of Abdominal Wall. Obliquus Externus Abdominis — Origin. — ^The outer surfaces of the lower eight ribs by means of eight fleshy slips, the upper five of which interdigitate with slips of the serratus magnus, and the lower three with slips of the latissimus dorsi. Insertion. — (i) The anterior half of the outer lip of the iliac crest by fleshy fibres. (2) By means of an aponeurosis into {a) the linea alba ; (6) the pubic spine and crest of the opposite side through means of the triangukir fascia ; (c) the front of the symphysis pubis ; {d) the pubic spine of the same side ; {e) the first inch THE ABDOMEN 651 of the ilio-pectineal line ; and (/) the anterior superior iliac spine. Nerve-supply. — ^The lower five intercostal nerv^es and the sub- costal nerve. Action. — (i) The two muscles, acting conjointly, diminish the size of the abdominal cavity, and so compress the viscera, as in defaecation. (2) The two muscles, acting conjointly from their origins, raise the front part of the pelvis and flex it upon the thorax. (3) Acting conjointly from their inser- tions, they flex the thorax upon the pelvis, the vertebral column being also flexed in the lower thoracic and lumbar regions ; but, if the column is fixed, the two muscles depress the lower eight ribs. (4) One muscle, acting from its origin, is a lateral flexor of the pelvis. When it acts from its insertion it flexes the thorax towards its own side and rotates it to the opposite side. The most of the fibres of the external oblique pass downwards and forwards, coinciding in direction with those of the external intercostal muscles. The only parts of the muscle which are free are the part between the last rib and the iliac crest, and the part opposite the pubic crest. The aponeurosis attains its greatest width and strength at. and below, the level of the anterior superior iliac spine, and it is narrowest opposite the umbilicus. Superiorly it gives origin to fibres of the pectoralis major. Crossing the fibres of the aponeurosis in an upward and inward direction there are several superadded fibres. In the lower part of the abdominal wall these are specially well marked, and are here spoken of as the intercolumnar fibres. Under this name they spring from the outer third of Poupart's ligament, whence they pass upwards and inwards in a curved manner, the convexity being downwards. On arriving at the upper and outer part of the external abdominal ring they extend from one column to the other. They round off and close the ring, and are prolonged upon the spermatic cord to form the intercolumnar or external spermatic fascia. The following parts of the external oblique aponeurosis require special description : Poupart's ligament, Gimbernat's ligament, the triangular fascia, the external abdominal ring, and the linea alba. Poupart's ligament, also known as the superficial femoral arch, is the thickened lower border of the external oblique aponeiu"osis, which is folded backwards. Externally it is attached to the anterior superior iliac spine, and internally to the pubic spine, from which it is reflected outwards and backwards upon the ilio-pectineal line for fully i inch to form Gimbernat's ligament. The ligament is curved, the convexity being directed down- wards and outwards, which is due to the attachment of the iliac lamina of the fascia lata to its lower border. The con- vexity is greatest when the thigh is extended, abducted, and rotated outwards, in which position the fascia lata on the front of the thigh is tightened. Relations — Superficial. — Sldn ; Camper's and Scarpa's fasciae ; super- ficial epigastric vessels, a little to the inner side of the centre; super- ficial circumflex iliac vessels just below its outer part ; and the inguinal 652 A MANUAL OF ANATOMY glands along its lower border. Deep. — Internal oblique along the outer half, and transversalis abdominis along the outer third. Along the outer half the fascia transversalis and fascia iliaca are attached, and form a canal containing the deep circumflex iliac vessels. The fascia transversalis continues to be attached to the inner part, but loosely and only as far inwards as the base of Gimbernat's ligament. The deep crural arch is also a deep Pectoralis Major Serratus Magnus —Si, 1 Latissiraus Dorsi Obliquus Extemus Abdominis Middle Linea Transversa Petit's Triangle ! Rectus ALdominis -.Anterior Superio.- Iliac Spine Poupart's Ligament Spermatic Cord at ~ Kxternal Abdominal Ring Fig. 283. — The External Oblique Muscle. relation. Poupart's ligament, along with the irregularly concave border of the OS innominatum, forms a large fibro-osseous canal. This region is known as the lacunar region. The deep femoral arch is a thickening of the fascia transversalis as it passes downwards beneath Poupart's ligament to form the anterior wall of the crural sheath. The thickening is due to superadded fibres which extend inwards from the centre of Poupart's ligament on its deep aspect to the ilio-pectineal line, where they are attached behind Gimbernat's ligament near its base. THE ABDOMEN 653 Gimbernat's ligament is the reflection of Poupart's ligament from the pubic spine along the ilio-pectineal line. Its. length is fully I inch, and it is triangular, the apex being at the pubic spine. It presents three borders and two surfaces. Two of the borders are fixed, one, called the Pou-part border, being continuous wdth the inner end of Poupart's ligament, and the other, called the pectineal border, being implanted on the pectineal portion of the ilio-pectineal line. The third border is free, and is called the base. It is sharp, wiry, and concave, and is situated immediately to the inner side of the crural or femoral ring. The surfaces of the ligament are femoral and abdominal. They occupy an oblique plane, the femoral surface looking downwards, forwards, and slightly out- wards, whilst the abdominal surface looks upwards, back\vards, and slightly inwards. This latter surface, along its line of junction with Poupart's ligament, forms the floor of the inguinal canal in its lower third, where it supports the spermatic cord in the male, and the round ligament of the uterus in the female. The fascia transversalis takes attachment to the base of the ligament on its abdominal aspect, and the conjoined tendon and fascia transversalis are behind it at the ilio-pectineal line. A few of the fibres of the superior cornu of the saphenous opening terminate on the femoral surface of the ligament, and the pectineus muscle and pubic lamina of the fascia lata are in front of its pectineal attachment. The triangular fascia, also known as the ligament of CoUes, is situated behind the spermatic cord and internal pillar of the external abdominal ring. Its fibres are derived from the external oblique aponeurosis of the opposite side, and, having crossed the linea alba, they take insertion into the pubic spine and crest. A portion of the fascia is seen Ipng in the lower and inner part of the external abdominal ring. The external abdominal ring is an opening in the aponeurosis of the external oblique, and it is situated immediately above, and to the outer side of, the pubic spine. It serves for the passage of the spermatic cord in the male, and the round ligament of the uterus in the female. In the natural condition no opening is per- ceptible, the intercolumnar fibres rounding it off, and being pro- longed downwards upon the transmitted structure. When the intercoliunnar fibres and fascia have been removed, the ring is seen to be formed in the following manner : the fibres of the external oblique aponeurosis, as they approach the os pubis, are disposed in two diverging bundles. One bimdle, which repre- sents the inner end of Poupart's ligament, is fixed to the pubic spine. The other bundle passes to be attached to the front of the s\-mphysis pubis, where its fibres decussate with those of its feUow of the opposite side, the fibres from the right side being superficially placed. An interval is thus left between these diverging bimdles, which is widest at the lower and inner part, where it corresponds with a portion of the pubic crest. This interval is the external abdominal ring. Its direction is upwards and outwards, and 654 A MANUAL OF ANATOMY it is parallel with the inner part of Poupart's ligament. Its length is from i inch to i| inches, and its breadth at the base about ^ inch. It is triangular, the base being formed by part of the pubic crest, and the apex being directed upwards and outwards. The margins of the ring are called pillars or columns. From the oblique position of the ring one pillar is external and inferior, the other being internal and superior. The internal or superior pillar, which is thin and straight, passes to be attached to the front of the symphysis pubis. The external or inferior pillar is at first thin, but it soon becomes thick and prismatic, and is fixed to the pubic spine. It presents superiorly a concavity which lodges the sper- matic cord in the male and the round ligament of the uterus in the female. The intercolumnar or external spermatic fascia is attached to both pillars, and it here lies upon the spermatic cord. Underneath the cord this fascia is attached along the pubic crest between the pillars of the ring. These attachments of the fascia explain why urine, extravasated into the perineum, does not find its way into the inguinal canal. Within the lower and inner part of the ring is the triangular fascia, and directly behind the ring is the conjoined tendon, which strer^thens what would otherwise be a weak part of the abdominal wall. The ring is smaller in the female than in the male. The linea alba has been already described (see p. 639). The triangle of Petit is only present when the latissimus dorsi and external oblique do not meet. It is situated immediately above the centre of the iliac crest, and is bounded in front by the posterior border of the external oblique, behind by the anterior border of the latissimus dorsi, and below by the central portion of the iliac crest. It is covered only by skin and fascia, and its floor is formed by a part of the internal oblique. In this situation a lumbar hernia may occur, or a lumbar abscess may find its way to the surface. Obliquus Internus Abdominis — Origin. — (i) The deep or abdo- minal surface of Poupart's ligament over its outer half; (2) the summit of the iliac crest over its anterior two-thirds ; and (3) the posterior aponeurosis of the transversalis abdominis. Insertion. — (i) The lower borders of the cartilages of the lower three or four ribs ; (2) the lower borders of the cartilages of the seventh and eighth ribs, and the side of the ensiform process of the sternum ; (3) the linea alba in its whole length ; (4) the front of the pubic crest ; and (5) the pectineal portion of the ilio-pectineal line for \ inch. Nerve-supply. — This is similar to that of the external oblique, with the addition of twigs from the inguinal nerve and hypogastric branch of the ilio-hypogastric, both of which are derived from the lumbar plexus, more particularly the first lumbar nerve. Action. — This is similar to that .of the external oblique. When the right internal oblique acts simultaneously with the left external oblique, the trunk is rotated to the right side, and vice versa. To THE ABDOMEN 655 ■understand this action, it is to be noted that the fibres of the internal obHque of one side coincide in direction with those of the external oblique of the opposite side. The most of the fibres pass upwards and forwards across those of the external oblique, and coinciding with those of the internal intercostal muscles. The Poupart fibres, however, pass downwards and inwards, and join the corresponding fibres of the transversahs Pectoralis Major Lumbar Aponeurosis - |-~ [' —Middle Linea Transversa .- Obliquus Extemus Abdominis (reflected) Obliquus Intertills Alxijminis ''y" - Rectus Abdominis Anterior Superior Iliac Spine Poupart 's Ligament Fig. 284. — The Internal Oblique Muscle. abdominis to form the conjoined tendon. The aponeurosis is broader above than below. Along the outer border of the rectus abdominis, over about its upper three-fourths, it divides into two laminae, one of which passes in front of the muscle and the other behind it. The anterior lamina joins the aponeurosis of the external oblique, and the posterior lamina joins the anterior aponeurosis of the transversalis abdominis. It is this latter lamina which has an inser- tion into the seventh and eighth costal cartilages and ensiform 656 A MANUAL OF ANATOMY process. Over about the lower fourth of the rectus the aponeu- rosis remains single, and passes in front of the muscle. The Poupart fibres of the muscle, as they leave the ligament, are in front of the spermatic cord as it lies in the upper third of the inguinal canal. They then arch over it, and finally descend behind it as it lies in the lower two-thirds of the inguinal canal. In this latter situation the fibres have terminated in the conjoined tendon. Cremaster — Origin. — ^The deep aspect of Poupart's ligament in its inner part. A few fibres are also derived from the lower border of the internal oblique. The fibres descend in a series of loops upon the outer and anterior aspects of the spermatic cord. The lowest loops reach the tunica vaginalis of the testis, upon the upper part of which they spread out in an arched manner, some of the fibres terminating on it. The other loops are successively shorter from below upwards, and ascend on the inner and posterior aspects of the cord, where they become tendinous and indefinite, to take insertion into the pubic spine and anterior lip of the pubic crest. The loops of the muscle are separated by intervals occupied by areolar tissue. This combination of muscular loops and areolar tissue forms the cremasteric or middle spermatic fascia. The cremaster muscle lies in series with the lower border of the internal oblique, and is peculiar to the male. It is occasionally represented in the female by a few fibres which descend on the round ligament of the uterus in the inguinal canal. Nerve-supply. — ^The genital branch of the genito-femoral nerve from the lumbar plexus, more particularly from the first, and the ventral division of the second, lumbar nerves. Action. — ^To support and raise the testis towards the external abdominal ring. The fibres composing the muscle are of the striated variety, but the action is involuntary, and of a reflex character. Cremasteric Reflex. — The afferent nerve involved in the cremasteric reflex is either the inguinal, which is distributed to the side of the scrotum and inner side of the thigh, or the femoral branch of the genito-femoral, which is distributed to the integument over Scarpa's triangle. The efferent nerve is the genital branch of the genito-femoral. Transversalis Abdominis — Origin. — (i) The deep aspect of Poupart's ligament over its outer third ; (2) the inner lip of the iliac crest over its anterior two-thirds ; (3) the lumbar aponeurosis, which, by its posterior lamina, is connected with the spinous processes of the lumbar and sacral vertebrae, and the posterior fourth of the outer lip of the iliac crest, by its middle lamina with the tips of the lumbar transverse processes, and, by its anterior lamina, with the fronts of the lumbar transverse processes near their tips ; and (4) the inner surfaces of the cartilages of the lower six ribs by six slips which interdigitate with slips of the diaphragm. Insertion. — (i) The linea alba ; (2) the front of the pubic crest ; and (3) the pectineal portion of the ilio-pectineal line for i inch.. THE ABDOMEN 657 Nerve-supply. — ^This is similar to that of the internal oblique. Action. — ^To diminish the capacity of the abdominal cav-ity, and so compress the viscera. To a limited extent the two muscles aid the external and internal oblique muscles in elevating the pelvis, flexing the thorax, and depressing the ribs. The most of the fibres pass transversely for^vards, and terminate in the anterior aponeurosis. The Poupart fibres, however, pass -Posterior Wall of Sheath of Rectus Posterior Aponeurosis of r Tranversalis Abdominis ~^ Semilunar Fold of Douglas Band of Hei.le Rectus Abdominis (cut) Fig. 285. — The Transversalis Abdominis Muscle. flownwards and inwards, and join the corresponding fibres of the internal oblique to form the conjoined tendon. The anterior aponeurosis is narrow above, but broad below. Over about the upper three-fourths of the rectus abdominis it passes behind the mascle, but over about the lower fourth it passes in front of it. The transversalis abdominis is continuous superiorly with the triangularis sterni muscle, and its lower border is free where it arches over the spermatic cord, or the round ligament of the uterus. 42 658 A MANUAL OF ANATOMY For the posterior aponeurosis of the muscle, see p. 765. Conjoined Tendon. — This is the tendon which gives a common insertion to the Poupart fibres of the internal oblique and trans- versalis abdominis muscles. It is inserted into (i) the front of the pubic crest, and (2) the pectineal portion of the ilio-pectineal line for I inch. The tendon is formed principally by the transversalis abdominis, which extends for i inch along the ilio-pectineal line, whilst the internal oblique only extends along that line for I inch. Relations — Supeirficial. — The structures in front of the conjoined tendon, from the middle line outwards, are as follows : the lower part of the in- ternal pillar of the external abdominal ring ; the triangular fascia ; the insertion of the cremaster ; Gimbernat's ligament ; the inner part of Poupart's ligament ; and the spermatic cord. Deep. — The fascia transversalis. The conjoined tendon varies greatly in development, and in many cases is hardly distinguishable. As a rule, it covers the inner two-thirds of the floor of Hesselbach's triangle, where it lies behind the inner two-thirds of the inguinal canal and has the spermatic cord, or the round ligament of the uterus, as a superficial relation. It also lies directly behind the external abdominal ring, and so strengthens what would otherwise be a weak part of the abdominal wall. In some cases the conjoined tendon is divisible into two parts, the outer being known as the ligament of Hesselbach, and the inner as the ligament of Henle. ReQected Tendon of Cooper. — In normal circumstances the conjoined tendon is limited to the first inch of the pectineal portion of the ilio-pectineal line. Sometimes, however, the anterior aponeurosis of the transversalis abdominis is prolonged outwards beyond the normal limit of the conjoined tendon, in the form of a thin semilunar expansion which extends as far as the inner and lower parts of the internal abdominal ring, and is attached inferiorly to the deep crural arch. This semilunar expansion of the con- joined tendon is known as the reflected tendon of Cooper. Its concavity is directed outwards, and, when present, it covers the outer third of the floor of Hesselbach's triangle, where it lies behind the spermatic cord, and is closely connected with the subjacent fascia transversalis, to which it imparts strength. An inspection of the external oblique, internal oblique, and transversalis abdominis muscles shows that they cross each other at different angles, the external oblique passing downwards and forwards, the internal oblique upwards and forwards (these two muscles thus crossing like the limbs of the letter X), and the trans- versalis horizontally forwards. They thus form an intricate lattice-work which renders the abdominal wall very strong, and is a powerful safeguard against hernial protrusions. Rectus Abdominis — Origin. — This muscle arises by two heads, both of which are tendinous. The external head, broad and flat, arises from the pubic crest, and the internal head, narrow and some- what round, from the fibrous structures in front of the symphysis pubis, where it is closely connected with its fellow of the opposite side. The two heads join about i inch above the symphysis pubis. Insertion. — By means of three flat slijjs, which are at first fleshy and subsequently tendinous, into the anterior surfaces of the fifth, sixth, and seventh costal cartilages. The most internal slip is THE ABDOMEN 659 sometimes partially inserted into the side of the ensifoim process of the sternum. Nerve-supply. — ^The lower five intercostal nerves and the sub- costal nerve. Action. — ^The action is similar to that of the two oblique and transversalis muscles, with the exception that it does not produce lateral rotation of the thorax. The muscle is long, flat, and strap-like, its fibres being directed vertically upwards by the side of the linea alba. It is narrow below and broad above, its greatest breadth being about 3 inches. Below the umibilcus the two muscles are very near each other, the interval between them being not more than about | inch. Above the umbilicus, however, the muscles are separated by an interval of about \ inch. Each muscle is marked by tendinous intersections or inscriptions, which cross it in a somewhat irregular manner at certain intervals. They are usually three in number, and are situated as follows : one at the level of the umbilicus, a second opposite the tip of the ensiform process, and a third about midway between these two. Sometimes there is a fourth inscription, which crosses the muscle a little below the umbilicus, but this one is faint, and does not usually extend the whole width. These inscriptions, which do not usually penetrate to the posterior surface, map out the upper part of the muscle into two quadrangular areas, and are firmly boimd to the anterior wall of its sheath. Above the level of the umbiUcus, therefore, the interior of the sheath, anterior to the muscle, is divided into two distinct compeurtments. The tendinous inscriptions are the remains of the septa which separated the primitive myotomes or muscle-segments, and by some they are regarded as indicating the abdominal ribs of cert:ain animals, such as the crocodile. Pyramidalis Abdominis — Origin. — ^The front of the pubic crest. Insertion. — ^The linea alba for 2 inches or more above the sjnm- physis pubis. Nerve-supply. — The subcostal nerve. Action. — To render tense the linea alba. The muscle is sometimes present only on one side ; sometimes it is absent on both sides ; and sometimes it is double on one or both sides. In man it is a small muscle, and vestigial like the plantaris ; but it attains a large size in marsupials, and especially in omithorhynchus. Sheath of Rectus Abdominis. — Over about the upper three-fourths of the muscle the anterior wall is formed by the anterior lamina of the internal oblique aponeurosis and the external oblique aponeu- rosis, the two being closely connected ; and the posterior wall is formed by the posterior lamina of the internal oblique aponeurosis and the anterior aponeurosis of the transversalis abdominis, thpse two being likewise closely connected. Over about the lower fourth the anterior wall is formed by the external oblique aponeurosis, the undivided internal oblique aponeurosis, and the 66o A MANUAL OF ANATOMY anterior aponeurosis of the transversalis abdominis, in this order from before backwards, all three being closely connected. Ov&c this extent the sheath is deficient posteriorly, and the muscle rests upon the fascia transversalis, with an exception to be presently stated. The lower border of the posterior wall presents a free curved margin, with the concavity downwards, called the semilunar fold of Douglas, over which the deep epigastric artery passes. This fold is usually situated about the junction of the upper fourth and lower three-fourths of the infra-umbilical portion of the linea alba. Sometimes the anterior aponeurosis of the transversalis abdominis, though passing in front of the lower fourth of the rectus, sends scattered fibres behind it, which would thus intervene between the muscle and the fascia transversalis for a variable distance below the fold of Douglas. In such cases the posterior wall of the sheath presents another curved semilunar fold, situated from i to 2 inches below the semilunar fold of Douglas, and known as the band of Obliquus Externus Abdominis Obllquus Internus Abdominis ._ ] Transversalis Abdominis Lumbar Fascia '•, Rectus Abdominis —Linea Alba ""--.Fascia Transversalis Fig. 286. — Diagram showing the Sheath of the Rectus Abdominis. A, Over the upper three-fourths ; B, over the lower fourth. Henle, over which the deep epigastric artery passes. The contents of the sheath are as follows : the rectus abdominis, pyramidalis abdominis, deep epigastric vessels, superior epigastric vessels, and terminal parts of the lower five intercostal, and subcostal, nerves. Relation of Structures at the Pubic Crest. — The relation of structures from before backwards is as follows : 1. The triangular fascia. 2. The conjoined tendon. 3. The pyramidalis. 4. The outer head of the rectus abdominis. 5. The fascia transversalis. A few fibres of the cremaster are inserted into the pubic crest close to the pubic spine. Relation of Structures at the Pectineal Portion of the Ilio-pectineal Line.— The relation of structures from before backwards is as follows : I. The pubic laniina of the fascia lata, incorporated with which is the pubic ligament of Cooper. i. The pectineus. 3. Gimbernat's ligament. 4. The conjoined tendon. 5. The fascia transversalis and the deep femoral arch. THE ABDOMEN 66i Deep Nerves of the Abdominal WalL— The lower ttve intercostal nerves, after leaving the intercostal spaces, lie between the in- ternal oblique and transversalis abdominis, and pass downwards and forwards to the outer border of the rectus. Here they pierce, in succession, the posterior wall of the sheath, the rectus, and the anterior wall of the sheath, after which the}!- terminate in the anterior cutaneous nerves. In their course they supply the two oblique, the transversalis, and the rectus muscles. Each nerve gives off a lateral cutaneous branch in the mid-axillary line. These lateral cutaneous branches, having pierced the internal oblique, appear between the slips of the external oblique and divide into anterior and posterior branches. The subcostal nerve is the anterior primary div^ision of the twelfth thoracic nerve. It is in series with the eleventh inter- costal, but is not ranked as an intercostal nerve, inasmuch as it lies along the lower border of the twelfth rib. It is commonly spoken of as the last dorsal nerve. Its abdominal relations, course, and distribution are similar to the preceding nerves, wdth an addi- tional distribution to the pyramidalis abdominis. Its lateral cutaneous or iliac branch, which is undivided, having pierced the internal and external oblique muscles, descends over the anterior part of the iliac crest, i inch behind the anterior superior iliac spine, and is distributed to the integument of the anterior part of the gluteal region as low as the great trochanter of the femur. The ilio-hypogastric nerve, having pierced the posterior part of the transversalis abdominis a little above the iliac crest, furnishes its iliac branch (lateral cutaneous), which perforates the internal and external oblique, and, having crossed the iliac crest at the junction of its middle and anterior thirds, is distributed to the integument of the adjacent part of the gluteal region. The nerve then continues its course forwards between the internal oblique and transversalis, supplying branches to these muscles and com- municating \\'ith the inguinal nerve. About i inch in front of the anterior superior iliac spine it pierces the internal oblique, and runs forwards between the Poupart fibres of that muscle and the external oblique aponeurosis. Finally, it pierces that aponeurosis about I inch above the external abdominal ring, and is distributed to the integument of the suprapubic region, where it is in series with the anterior cutaneous nerv^es. The inguinal nerve (ilio-inguinal), as it passes forwards, lies internal to the inner lip of the iliac crest, beneath the transver- salis and upon the iliac fascia and iliacus muscle. Near the anterior part of the iliac crest it pierces the transversalis, and here com- municates wdth the hypogastric branch of the ilio-hypogastric. It subsequently perforates the Poupart fibres of the internal oblique, after which it descends through the lower two-thirds of the inguinal canal, and emerges through the external abdominal ring where it lies external to the spermatic cord. Finally, it is distributed to the integument of the inner side of the thigh in its upper third. 662 A MANUAL OF ANATOMY and to the integument of the scrotum, or labium majus, according to the sex. The nerve in its course suppHes branches to the internal oblique and transversalis muscles. Deep Arteries of the Abdominal Wall. — ^The deep epigastric artery arises from the inner side of the external iliac, about J inch above Poupart's ligament. For a very short distance at first it passes inwards between Poupart's ligament and the lower border of the internal abdominal ring. It then changes its course, and passes upwards and inwards, lying close to the inner side of the internal abdominal ring, only the external vena comes intervening. On arriving at the outer border of the rectus abdominis, at a point about midway between the upper border of the symphysis pubis and the umbilicus, the artery passes beneath the muscle and enters the sheath over the semi- lunar fold of Douglas. It then changes its course, and ascends vertically between the muscle and the posterior wall of the sheath, as high as the umbilicus. Thereafter it enters the muscle, and, about 2 inches above the umbilicus, it ends in its terminal branches, which anastomose with branches of the superior epigastric artery. The deep epigastric lies at first in the subperitoneal areolar tissue, having the. parietal peritoneum on its deep surface, and the fascia transversalis superficial to it. Shortly after passing the internal abdominal ring the vessel pierces the fascia transversalis, and in its course to the outer border of the rectus it forms the outer boundary of Hesselbach's triangle. As the vessel turns from the lower border to the inner side of the internal abdominal ring it has the spermatic cord in front of it, and the vas deferens here hooks round its outer side. The course of the vessel in its first or oblique part is indicated by a line drawn from the inner border of the internal abdominal ring to the outer border of the .rectus abdominis at a point about midway between the umbilicus and the upper border of the symphysis pubis. The course of the second or vertical part of the vessel is represented by a vertical line corresponding with the centre of the rectus, and distant from the linea alba about i^ inches. Branches. — ^These are as follows : cremasteric, pubic, muscular, cutaneous, peritoneal, and terminal or anastomotic. The cremasteric artery enters the spermatic cord and supplies the cremaster muscle and the other coverings of the cord. It anastomoses with the spermatic artery, the superior and inferior external pudic arteries, and the superficial perineal artery. The cremasteric artery is replaced in the female by the artery of the round ligament of the uterus. The pubic artery passes inwards behind the inner half of Poupart's ligament to the back of the body of the os pubis, where it anastomoses with the pubic branch of the obturator artery and its fellow of the opposite side. The muscular branches arise chiefly from the outer side of the deep epigastric, and supply the two oblique, transversalis, and THE ABDOMEN 66x rectus muscles. They anastomose with the lower two intercostal arteries, the subcostal arter}', the abdominal branches of the lumbar arteries, and the lateral or intermuscular epigastric (so called ' ascending branch ') of the deep circumflex iliac arterj'. The cutaneous branches perforate the rectus and the anterior wall of its sheath, to be distributed to the integument in which they anastomose \\-ith branches of the superficial epigastric. The peritoneal branches pierce the posterior wall of the sheath of the rectus, to be distributed to the adjacent parietal peritoneimi. The terminal or anastomotic brandies enter the rectus above the level of the umbilicus and anastomose with the superior epi- gastric of the internal mammary. For an abnormal or aberrant obturator artery, see p. 462, There are two venae comites with the deep epigastric artery, one on either side. These ultimately join to form one vessel, which terminates in the external iliac vein. The superior epigastric artery is one of the teitninal branches of the internal mammary from the first part of the subcla\'ian. It descends behind the seventh costal cartilage, passing between the sternal and costal portions of the diaphragm, and enters the sheath of the rectus, where it lies at first bet^veen the muscle and the posterior wall of its sheath. It then enters the muscle and anastomoses with the deep epigastric. Its branches are as follows : melasternal, which crosses in front of the meta- stemum and anastomoses with its feUow of the opposite side ; phrenic, to the diaphragm ; muscular to the muscles of the abdo- minal wall ; anterior cutaneous to the integument ; falciform or hepatic (present only on the right side), which passes to the liver in the falciform ligament and anastomoses with the hepatic artery ; and peritoneal, which pierce the posterior wall of the sheath of the rectus, to be distributed to the adjacent parietal peritoneum. The vessel is accompanied by two venae comites, which terminate in those of the internal mammarj' artery. The deep circumflex iliac artery arises from the outer side of the external iliac nearly opposite the origin of the deep epigastric. It passes outwards and upwards behind the outer half of Poupart's ligament, where it is contained in a canal formed at the jimction of the fascia transversalis and fascia iliaca. Having arrived at the anterior superior iliac spine, it pierces the fascia transversalis, and courses outwards and backwards along the iliac crest on its iimer aspect. At its termination it anastomoses with the lumbar branch • of the ilio-lumbar from the internal iliac. Over about the anterior half of the iliac crest the artery lies beneath the transversalis mtiscle, but about the centre of the crest it pierces that muscle, and subsequently lies between it and the internal oblique. Branches. — In the first part of its course the vessel gives branches to the ilio-psoas, sartorius, and tensor fasciae femoris, in which latter muscle it anastomoses with the ascending branch of the external circumflex from the arteria profunda femoris. 664 A MANUAL OF ANATOMY As it courses along the iliac crest it furnishes branches to the muscles of the abdominal wall, some of which reach the gluteal region, where they anastomose with the gluteal of the internal iliac and the superficial circumflex iliac ot the common femoral. It also gives branches to the iliacus muscle, which anastomose with the iliac branch of the ilio-lumbar from the internal iliac. One of the muscular branches of the artery is very constant and of large size. It springs from the vessel near the anterior superior iliac spine, and, having pierced the fascia transversalis and transversalis muscle, it ascends vertically between that muscle and the internal oblique, where it anastomoses with the abdominal branches of the lumbar arteries. This branch is usually spoken of as the ascending branch, but it may be called the lateral or intermuscular epigastric. The deep circumflex iliac artery is accompanied by two venae comites. These ultimately join to form one vessel, which crosses the external iliac artery from without inwards about | inch above Poupart's ligament, and terminates in the external iliac vein. The lower two intercostal arteries ultimately leave the tenth and eleventh intercostal spaces and pass towards the rectus muscle, lying in their course between the internal oblique and transversalis. They anastomose with the superior epigastric, deep epigastric, and subcostal arteries. The subcostal artery lies below the last rib, and is in series with the aortic intercostal arteries above and the lumbar arteries below. On the abdominal wall it anastomoses with the last intercostal, the abdominal branch of the first lumbar, and the superior epigastric, arteries. The abdominal branches of the lumbar arteries pass forwards towaids the rectus abdominis. They anastomose with the deep epigastric, subcostal, and lateral or intermuscular epigastric of the deep circiimflex iliac. The veins corresponding to the lower two intercostal arteries terminate in the corresponding intercostal veins. The subcostal vein of the right side terminates in the right azygos vein, and that of the left side in the lower left azygos vein. The veins accom- panying the abdominal branches of the lumbar arteries terminate in the lumbar veins, which are tributaries of the inferior vena cava. Deep Lymphatics. — The deep lymphatics of the lower part of the anterior abdominal wall accompany the deep epigastric and deep circumflex iliac vessels, and terminate in the external iliac glands ; those of the upper part accompany the superior epigastric artery, and terminate in the sternal glands. The deep lymphatics of the lower part of the lateral abdominal wall accompany the abdominal branches of the lumbar arteries and the ilio-lumbar artery, and terminate in the lateral group of lumbar glands ; those of the upper part accompany the adjacent anterior intercostal and musculo-phrcnic arteries, and terminate in the sternal glands. THE ABDOMEN 665 For the superficial lymphatics of the antero-lateral abdominal wall, see p. 646. Fascia Transversal is. — ^The fascia transversalis is situated imder- neath the transversalis abdominis muscle. It is of greatest strength over the lower part of the abdominal wall, particularly between the lower free border of the transversalis and Poupart's ligament. When traced upwards to the costal margin it becomes very thin, and is there continuous with the fascia which covers the abdominal surface of the diaphragm. Along the linea alba it is continuous with the fascia of the opposite side. In the lumbar region it is continuous with the anterior wall of the sheath of the quadratus lumborum. In the region of the iliac crest it is attached to the anterior two-thirds of the crest immediately internal to its inner lip, where it meets and becomes continuous with the fascia iliaca, both of these fasciae being here interposed between the transversalis and iliacus muscles. The most important disposition of the fascia is along the line of the groin, where its attachments are as follows : along the outer half of Poupart's ligament it is firmly attached to that ligament on its deep aspect, and over that extent it meets and is continuous with the fascia iliaca, the two fasciae here forming a canal, which contains the deep circumflex iliac vessels. In the situation of the external iliac vessels, and as far inwards as the base of Gimbernat's ligament, it is only loosely attached to Poupart's ligament, and is here prolonged downwards beneath the ligament to the thigh, where it lies in front of the common femoral vessels, and forms the anterior wall of the crural sheath. As the fascia is prolonged beneath Poupart's ligament it is strengthened by superadded fibres, which are known as the deep crural arch. In the region of Gimbernat's ligament the fascia is attached in succession to the pectineal portion of the ilio-pectineal line behind the conjoined tendon, and to the pubic crest. Behind the symphysis pubis the fascia descends into the pelvis, and becomes continuous with the pubo- prostatic, or anterior true, ligaments of the bladder. The strongest part of the fascia transversalis, as before stated, is between the lower free border of the transversalis muscle and Poupart's ligament, this part of the abdominal wall being uncovered by muscular structures. It is in this situation where the fascia is pierced by the spermatic cord in the male and the roxmd ligament of the uterus in the female. Internal Abdominal Ring. — ^This ring is situated in the fascia transversalis at a point midway between the symphysis pubis and the anterior superior iliac spine, and h inch above Poupart's liga- ment. It serves for the passage of the spermatic cord in the male and the round ligament of the uterus in the female. As viewed from before no opening is visible in the undissected state, because the fascia transversalis is prolonged from the margins of the aper- ture round the spermatic cord as the infundibuliform or internal spermatic fascia. Wlien fully dissected the ring is oval, with the long axis lying vertically, in which direction it measures f inch, 666 A MANUAL OF ANATOMY the transverse measurement being i inch. The deep epigastric artery Hes at first below, and then on the inner side of, the ring, the vessel being here beneath the fascia transversahs. The reflected tendon of Cooper may be upon the inner side of, and below, the ring. On the outer side of the ring are the Poupart fibres of the internal oblique, and above is the lower free border of the transver- sahs. The fascia at the outer and lower parts of the ring is stronger than elsewhere. , E.O.A. O.I. A. Intcrcolumnar Fibres Saphenous External Abdominal Opening Ring Reflected Tendon of Cooper Fig. 287 — Superficial and Dbep Dissection of the Lower Part OF THE Anterior Abdominal Wall (after Cooper). E.O.A. External Oblique Aponeurosis O.I. A. Obliquus Internus Abdominis T.A. Transversalis Abdominis F.T. Fascia Transversalis I.A.R. Internal Abdominal Ring B.C. Spermatic Cord D.E.V. Deep Epigastric Vessels X. Triangular Fascia Inguinal Canal. — ^The inguinal canal is the oblique passage in the lower part of the anterior abdominal wall, which transmits the spermatic cord, or round ligament of the uterus, according to the sex, and also the inguinal nerve in its lower two-thirds. It is situated immediately above the inner half of Poupart's ligament, its direction being downwards, forwards, and inwards, and. it is ij inches in length. The inlet to the canal is the internal abdominal ring, the outlet being the external abdominal ring. Its component parts are a floor, a roof, an anterior wall, and a posterior wall. The floor in its upper two-thirds is formed by the meeting between the fascia transversalis and Poupart's ligament. This portion of it presents a groove, which lodges the spermatic cord. In the lower third the floor is formed by the THE ABDOMEN 667 abdominal surface of Gimbemat's ligament along its line of jimc- tion with Poupart's ligament. The roof is formed by the apposition of the external and internal oblique muscles, and also by the lower borders of the internal oblique cind transversalis. The anterior wall is formed by the following structures from before backwards : (i) the skin ; (2) fascia of Camper ; (3) fascia of Scarpa ; (4) external oblique aponeurosis (all of these four structures extending over the whole length of the anterior wall) ; and (5) the Poupart portion of the internal oblique over the outer third. The posterior wall is formed by the following structures, in order from behind forwards : (i) the parietal peritonemn ; (2) subperitoneal fat ; (3) fascia Obliquus Intemus Abdominis Transversalis - Abdominis Obliquus Extemas ^ Abdominis fectii Sartorius Adductor Longus !..' Fig. 2 5 .■L' Rectus Abdominis —— Spermatic Cord I Suspensory Liga- ment of Penis r~-~Inguinal Nerve -Dissection of the Inguinal Region. transversalis; (4) conjoined tendon over the inner two-thirds, and it may be, the reflected tendon of Cooper over the outer third ; and (5) the outer portion of the triangular fascia (provided that fascia is well developed), which lies over the extreme inner part of this wall. In early life the inguinal canal is very short. Indeed, at one period of life it is non-existent, inasmuch as the internal abdominal ring in very early life lies directly behind the external ring. As the pehns, however, increases in breadth, the internal ring is gradually shifted outwards, and so the inguinal canal becomes formed. The inguinal canal in the female differs from that in the male in 668 A MANUAL OF ANATOMY being of smaller size, and in containing the round ligament of the uterus. Triangle of Hesselbach. — This triangle is situated at the lower part of the anterior abdominal wall above the inner half of Poupart's ligament. Boundaries — Internal. — ^The outer border of the rectus abdominis over about its lower 2 inches. External. — The deep epigastric vessels. Inferior (base). — ^The inner half of Poupart's ligament. The apex corresponds with the point where the deep epigastric vessels pass beneath the outer border of the rectus. The floor is covered over its whole extent by the fascia transversalis, superficial to which, over the inner two-thirds, is the conjoined tendon, and over the outer third, sometimes the reflected tendon of Cooper. The floor is, therefore, conveniently divided into an inner two-thirds, where the conjoined tendon lies, and an outer third, where the re- flected tendon of Cooper may be situated. The triangle is covered superficially by the skin, the fasciae of Camper and of Scarpa, and the external oblique aponeurosis. Spermatic Cord. — ^The spermatic cord extends from the internal abdominal ring to the upper part of the posterior border of the testis. For the fii^st i^ inches of its course it lies in the inguinal canal, and is directed downwards, forwards, and in- wards. After passing through the external abdominal ring it enters the scrotum, in which it descends almost vertically. The relations of the cord in the inguinal canal will be understood on referring to the description of that canal. In the lower two-thirds of the canal it is accompanied by the inguinal nerve. The spermatic cord is composed of the following structures : the vas deferens or excretory duct of the testis ; three arteries, namely, the spermatic artery, the artery of the vas deferens, and the cremasteric artery ; the spermatic or pampiniform plexus of veins ; the lymphatics of the testis and epididymis ; the spermatic plexus of sympathetic nerves ; and the genital branch of the genito- crural nerve. These structures are connected by areolar tissue, and the cord receives certain coverings to be presently described. The vas deferens is the excretory duct of the testis. It com- mences at the lower end or globus minor of the epididymis, and terminates at the base of the prostate gland by joining the duct of the vesicula seminalis to form the common ejacu- latory duct. This latter duct, having passed through the prostate gland for about i inch, opens upon (sometimes within) the margin of the opening of the sinus pocularis or prostatic vesicle on the floor of the prostatic portion of the urethra. The vas deferens at its commencement is slightly tortuous, but it soon becomes straight. It lies at first on the inner side of the epididymis, and along the pos- terior border of the testis. After entering the cord it is placed behind all the other elements, where it can be readily felt. It main- tains this position until it arrives at the internal abdominal ring, where it lies on the inner side of the other elements of the cord. THE ABDOMEN 669 After passing through the internal abdominal ring it hooks round the outer side ot the deep epigastric artery, and, having crossed the external iliac vessels from without inwards, it dips down on the inner side of the external iliac vein, and so enters the pelvis under cover of the peritoneum, where it will be afterwards described. The vas deferens in its natural state measures about i foot in length, but when straightened it attains a length of from i^ to 2 feet. Mucosa and Columnar Epithelium " Iter Longitudinal Muscular Fibres Inner Longitudinal Muscular Fibres Middle Circular Muscular Fibres Fig. 289. -Transverse Section of the Vas Deferens, showing its Minute Structure. Structure ol the Vas Deferens. — The vas deferens has a very thick wall, and feels like a piece of whip cord. Its outer coat consists of fibrous tissue. Within this there is a thick muscular coat composed of plain muscular tissue, which is arranged in three la^-ers — an outer longitudinal, a middle circular (both of which are thick), and an inner thin longitudinal layer. Within the muscular coat is the mucosa, which is covered by non-ciliated columnar epithelium. Development. — From the lower part of the Wolffian duct. The artery of the vas deferens, or deferential artery, is usually a branch of the superior vesical of the internal iliac, though it may arise from the inferior vesical, and it diN-ides into a descending and an ascending branch. The descending branch passes downwards to supply the lower part of the vas deferens and the vesicula seminalis. The ascending branch accompanies the vas deferens through the inguinal canal to the testis, suppling the vas deferens, and giving a few tungs to the globus minor of the epididymis, in which latter situation it anastomoses with the epidid\Tnal branch 670 A MANUAL OF ANATOMY of the Spermatic artery. The deferential artery is sometimes of large size, and then it takes the place of the spermatic artery when that vessel is absent. The deferential vein opens into the vesical plexus of veins, and thence into the internal iliac vein. The spermatic artery arises from the abdominal aorta about I inch below the renal artery. On approaching the upper part of the testis it divides into testicular and epididymal branches, the former supplying the testis and the latter the epididymis. As Spermatic Artery Artery of the Vas Deferens Vas Deferens Pampiniform Plexus of Veins Epididymal Branch of Spermatic Artery I'esticular Branch of Spermatic Artery Hydatids of Morgagni . Pampiniform Plexus of Veins - Digital Fossa Fig. 290. — Dissection of the Spermatic Cord, showing the Blood- vessels AND Duct of the Testis (after Sappey). the artery descends in the spermatic cord it supplies branches to its coverings which anastomose with the cremasteric artery, and its epididymal branches anastomose with the deferential artery. For the cremasteric artery, see p. 662. The spermatic veins issue from the testis along its posterior border. In the cord they form a copious ple.xus, called the pampiniform plexus. At the internal abdominal ring two veins emerge from this plexus, which range themselves on either side of the spermatic artery. These, as they ascend, soon join to form one vessel, that of the right side opening into the inferior vena cava, and that of the left side into the left renal vein. The veins of THE ABDOMEN 671 the spermatic plexus have valves, but they are not competent. There is, however, a competent valve as a rule at the termination of each spermatic vein. The lymphatics of the testis and spermatic cord, the spermatic plexus of sympathetic nerves, and the genital branch of the genito- crural nerve will be afterwards described. Coverings of the Spermatic Cord. — ^The coverings, enumerated from within outwards, are as follows : 1. The subperitoneal areolar tissue, which is continuous with that of the abdominal wall through the internal abdominal ring. It contains a certain amoimt of muscular tissue, which is known as the middle cremaster. 2. The fascia transversalis, prolonged from the margins of the internal abdominal ring, and known as the uUernal spermatic fascia. This covering near the ring is funnel-shaped, and is thence called the infundibuliform fascia, but lower down it becomes incorporated with the subperitoneal areolar tissue, and forms the fascia propria of Cooper. 3. The cremasteric fascia, or middle spermatic fascia. 4. The intercolumnar fascia, or external spermatic fascia. 5. The tunica dartos. 6. The skin. Within the innermost of these coverings there are a few scattered muscular fibres, which constitute the internal cremaster of Henle, and which are regarded as representing the inverted lateral bands of the gubernaculum testis. It is to be noted that the middle cremaster is the muscular tissue contained in the subperitoneal areolar tissue on the surface of the cord, whilst the external cremaster is the more distinct muscular structure which is derived from the lower border of the internal oblique. The fibres of the external cremaster are of the striated variety, but those of the middle and internal are of the plain variety. Descent of Testis and Formation ol Inguinal Canal. — The testis originally lies in the lumbar region of the abdomen upon the psoas magnus muscle, on a level with the last thoracic and first lumbar vertebrae. It is situated on the mesial side of the Wolffian body or mesonephros and behind the peritoneum, the epitheUal cells of the peritoneum being the superficial cells of the germinal epithelium. In order to understand the descent of the sexual organ (testis or ovary) it is necessary to refer to certain embryological structures. As stated, the testis (as well as the ovary) is situated on the mesial side of the Wolffian body. The sexual organ is attached to the mesial part of the Wolffian body by a short peritoneal fold, called the meso-testis or mesorchium in the male, and the mesovarium in the female. The Wolffian body is attached to the posterior abdominal wall by a peritoneal fold, the so-called Wolffian mesentery (more strictly Wolffian ligament). External to the Wolffian body there are (i) the Wolffian duct, which gives origin to the epi- didymis, vas deferens, and common ejaculatorj' duct, and (2) the Miillerian duct, from which the uterus and vagina are developed. These two ducts — Wolffian and Miillerian — he within a fold of peritoneum, called the urogenital lold, by which they are attached to the outer part of the Wolffian bod}', the Miillerian duct, at this level lying upon the outer side of the Wolffian duct. k 672 A MANUAL OF ANATOMY In addition to the mesorchium or mesovarium, according to the sex, the testis and ovary are each provided with two other peritoneal folds — superior and inferior. The superior testicular fold, which ascends towards the dia- phragm, is called the plica vascularis, and it contains the bloodvessels of the spermatic cord. In the female it forms the ovario-pelvic ligament. The inferior testicular (or ovarian) fold joins the urogenital fold at the lower part of the Wolffian body, and will be presently referred to. After atrophy (to a large extent) of the Wolffian body the mesorchium, or mesovarium, and the urogenital fold become incorporated with the Wolffian mesentery (Hgament) and form the urogenital mesentery (ligament), which may be regarded as an augmented secondary mesorchium. A fold of the urogenital mesentery ascends to the diaphragm, and is known as the dia- phragmatic ligament of the mesonephros or Wolffian body. It is not con- cerned in the migration of the sexual organ, and may therefore be disregarded. Gubernaculum Testis. — At the lower part of the Wolffian body the uro- genital fold is joined by the inferior testicular fold, as stated. After this junction has taken place the urogenital fold furnishes a peritoneal fold which extends to the inguinal region at a point corresponding to the situation of the ,-rrn^-ll-... Fig. 291 — Diagram showing the Descent of the Testis. A, First Stage ; B, Second Stage ; C, Final Stage. 1. Testis (in Abdomea) 2. Primitive Peritoneum (Tunica Adnata) 3. Parietal Peritoneum 3'. Processus Vaginalis 4. Subperitoneal Areolar Tissue 5. Fascia Transversalis 6. Internal Abdominal Ring 7. Integument future internal abdominal ring. This offshoot of the urogenital fold is called the plica gubernatrix or plica inguinalis. In the female this fold, as it descends, becomes connected with the corresponding Miillerian duct at the level where this duct fuses with its fellow to form the rudiment of the uterus and vagina. Within the plica gubematrrx fold a fibro-muscular cord is developed, con- sisting of connective tissue and plain muscular tissue. This cord is called the gubernaculum testis. Inferiorly it is attached, at first, to the posterior surface of the anterior abdominal wall in the inguinal region, at a point corresponding to the situation of the future internal abdominal ring, whence it, or the greater part of it, ultimately extends to the bottom of the cor- responding scrotal chamber. Superiorly its attachment is twofold: (i) It is principally attached to the lower part of the epididymis, at the junction of the globus minor and vas deferens. (2) A portion of it ascends within the inferior testicular fold to be attached to the caudal end of the testis. Accord- ing to some authors the lower part of the gubernaculum testis is reinforced by striated muscular fibres derived from the internal oblique and transversalis abdominis muscles. These fibres, which form the so-called inguinal cone, are superadtled to the fibro-muscular cord, just referred to, which constitutof- the core of the gubernaculum. Superiorly these superadded fibres from the THE ABDOMEtt 673 inguinal cone are described as being attached to the testis and epididj-mis. Tqferiorly, three attachments are ascribed to them, as follows: (i) The outer ■undle is attached to the deep aspect of Poupart's hgament near its centre; (2) the middle or principal bundle accompanies the gubemaculum testis to the bottom of the scrotal chamber; and (3) the inner bundle is attached to the pubic crest. T-wo views are thus entertained regarding the structure of the gubemaculum testis. - According to one \'iew it consists solely of plain muscular tissue and connective tissue arranged as a cord within the peritoneal fold, called the plica gubematrix or plica inguinalis. According to the other \-iew, in addi- tion to these fibro-muscular elements, there are superadded striated muscular fibres derived from the internal obhque and transversalis abdominis muscles in the form of the inguinal cone. However constituted, the gubemaculum testis soon becomes a stout thick cord, the final destination of which will be presenth' referred to. Descent of the Testis. — As stated, the testis originally hes in the abdomen on a level with the last thoracic and first lumbar vertebrae, being placed behind the peritoneum which forms its mesorchium. As it descends it takes Parietal Peritoneum Nodule Spermatic Cord Tunica Albuginea Testis Tunica Vaginalis Scroti Tunica Vaginalis Testis Fig. 292. — Varieties of the Tunica Vagin.\lis. A, Normal Type ; B, Congenital Type ; C, Infantile Type. along with it the superficial cells of its germinal epithehum, and the mesor- chium also accompanies it. The descent, or more properly the migration, of the organ commences about the third month of intra -uterine hfe, and its usual destination is the corresponding scrotal chamber. The migration is accomplished in jour stages — pelvic, inguinal, intraparietal, and scrotal — and throughout all these stages it follows the lead of the gubemaculum, which necessarily undergoes shortening. The pelvic stage soon brings the testis into the ihac fossa, where it Ues near the brim of the true pelvis, having the epididymis externally and the vas deferens internally, the latter dipping into the peRic ca\ity. The inguinal stage takes the testis to the posterior aspect of the inguinal portion of the anterior abdominal wall, at a point corresponding to the future internal abdominal ring, where it arrives about the sixth month. Inasmuch as there are no abdominal rings and no inguinal canal at this period, a pause now takes place in the migration of the testis, in order to pemiit of a path being cleared for its progress. In the immediate vicinity of the lower or inguinal end of the gubemaculum testis a peritoneal depression is formed, and the principal part of the inguinal end of the gubemagulum now slowly penetrates the compact anterior abdominal wall in the inguinal region, thus giving rise to the ioguinal canal and abdominal rings. In pre- 43 674 ^ MANUAL OF ANATOMY paring this path for the testis, its gubernaculum takes with it the parietal peritoneum forming the peritoneal depressioh, just alluded to, which accord- ingly constitutes a peritoneal process, called the processus vaginalis. This process may be likened to the finger of a glove, being open towards the peri- toneal or abdominal cavity, but closed at its distal end. The principal part of the gubernaculum lies behind the processus vaginalis, which latter aids the stout gubernaculum in the formation of the inguinal canal. As the processus vaginalis penetrates the inguinal portion of the abdominal wall, it elongates before it the several elements which compose the wall, in the following order from within outwards : 1. Subperitoneal areolar tissue. 2. Fascia trans versalis. 3. Lowermost Poupart fibres of internal oblique muscle (cremaster). 4. External oblique aponeurosis. 5. Scarpa's and Camper's fasciae (tunica dartos). 6. Skin of scrotum. In the foregoing manner the internal abdominal ring, inguinal canal, and external abdominal ring are formed by the gubernaculum testis and pro- cessus vaginalis. Beyond the external abdominal ring these two structures enter the corresponding scrotal chamber, the lower part of the processus vaginalis forming a serous lining for it. The lower part of the gubernaculum extends lower down than the lower end at the processus vaginalis, and this portion is attached to the fundus of the scrotal chamber. The intraparietal stage in the migration of the testis consists in the passage of the organ through the inguinal canal. This stage commences about the seventh month of intra-uterine life, and the testis follows the lead of the middle or principal bundle of the gubernaculum testis, gliding along the posterior wall of the processus vaginalis, and being post-vaginal in position. The scrotal stage consists in the entrance of the testis into the corresponding scrotal chamber, which usually takes place about the end of the eighth month of intra-uterine life. The organ still lies behind the lower part of the processus vaginalis, which it invaginates from behind, to form the tunica vaginalis. The middle or principal bundle of the gubernaculum testis has now become very short, and is ultimately represented by an indefinite fibrous bundle, spoken of as the remnant of the gubsinaculum, which connects the lower parts of the epididymis and testis to the fundus of the scrotal chamber. As the testis descends into the scrotum, the outer or Poupart and inner or pubic bundles of the gubernaculum testis, according to the view that there is a conus inguinalis, are drawn downwards on the sides of the spermatic cord. There are two theories regarding the migration of the testis, which may be called developmental and muscular. According to the developmental theory the migration is not an active process, due to muscular contraction, but is brought about by developmental changes, of the nature of disproportionate or unequal growth, which take place in the lumbar, iliac, and inguinal regions of the trunk. According to the muscular theory, maintained by those who favour the existence of a conus inguinalis, the migration is brought about by muscular contraction, as follows: All three bundles of the muscular inguinal cone would draw the testis down to the inguino-pubic region, and thereafter the middle bundle would draw it down into the scrotal chamber, the outer and inner bundles being elongated downwards. The non-striated muscular fibres in the core of the gubernaculum may also take part in the descent, and the descent may be aided by the ' retraction ' of the connective tissue of the gubernacular core. Metamorphoses of the foregoing Peritoneal Folds — Male. — The plica guber- natrix or plica inguinalis in the male contains the gubernaculum testis. The inferior testicular fold forms part of the plica gubernatrix. The superior testicular fold or plica vascularis contains the elements of the- spermatic cord. The mesorchium, derived from the greatly reduced urogenital nleL^cnte^y, connects the testis and epididymis. THE ABDOMEN 675 Female. — The portion of the plica gubernatrix or plica inguinalis (of which pHca the embryonic inferior ovarian fold forms a part) between the caudal end of the ovar\' and the fusion of the Mullerian duct with its fellow to form the rudiment of the uterus, represents the hgament of the ovary; and the part which extends from the Miillerian fusion through the inguinal canal to the labium majus contains the round ligament of the uterus, which is the homologue of part of the gubemaculum testis. In other words, the entire plica gubernatrix in the male contains the gubemaculum testis; whereas in the female it pertains to (i) the ligament of the ovan,-, and (2) the round ligament of the uterus. The embrjonic superior ovarian fold represents the ovario-pelvic ligament. The urogenital mesentery of either side, which is formed by the mesovarium. Wolffian mesenterj-, and urogenital fold (within which latter the Mullerian duct Ues along with the Wolffian duct) becomes the corresponding broad ligament of the uterus. Metamorphosis of the Processus Vaginalis. — As stated, the processus vaginalis is originally a tubular process or diverticulum of the parietal peri- toneum of the inguinal region, resembling the linger of a glove, which pre- cedes the descent of the testis, and behind which the testis descends, following the lead of the middle bundle of the g^abemaculum testis. After the testis has reached the scrotal chamber, it invaginates the processus vaginalis from behind, to form the tunica vaginalis, and that process now undergoes certain changes. To understand these changes familiarity with the following facts is necessary- : (i) The processus vaginalis is closed below and open above; (2) the lumen of the process is simply a diverticulum of the cavity of the peritoneum; (3) the part of the process related to the testis is called the testicular potion ; and (4) the part in front of the spermatic cord is referred to as the funicular portion. The changes are as follows: (i) About the period of birth the processus vaginalis usually becomes constricted and closed superiorly at the internal abdominal ring, and then the process is an elongated tube, closed at each end, its lumen being now shut off from the cavity of the peritoneum. (2) A few days after birth the process usually becomes constricted and closed a little above the testis. (3) The- funicular portion of the process usually becomes impervious and converted into a fibrous thread, which as a rule disappears in the course of the first month after birth. (4) The testicular portion of the process persists as a shut serous sac, called the tunica vaginalis. Normally the persistent remains of the embryonic processus vaginalis in the adult are (i) the testicular portion, which forms the tunica vaginalis, and (2) a small nodule on the parietal peritoneum immediately behind the internal abdominal ring. Instead of a mere nodule, however, a slender fibrous thread, called the ligamentuni vaginale, may extend downwards from this part of the parietal peritoneum in front of the spermatic cord as low as the external abdominal ring, and sometimes as low as the tunica vaginalis. In the female the processus vaginalis is represented by a tubular process of the peritoneum which hes in front of the round hgament of the uterus for a short distance in the inguinal canal. When this process remains open superiorly, it is known as the canal of Xuck. Abnormal Conditions of the Processus Vaginalis — Congenital Type. — (i ) The processus vaginalis may remain permanently open throughout, under which circumstances the cavity of the tvmica vaginahs is in direct communication with the general peritoneal cavity. (2) The processus vaginalis may be closed just above the tunica vaginahs, but it may remain as a permanently open tube above this point. Infantile or Funicular Type. — (i) The processus vaginahs may be closed only at its upper end near the internal abdominal ring. In these cases the tunica vaginalis, instead of being limited to the region of the testis, is pro- longed upwards as an elongated tube in front of the spermatic cord into the inguinal canal. (2) The processus vaginalis may be closed above, near the internal abdominal ring, and also below, just above the tunica vaginalis, the portion of it inter\-ening between these two points remaining as an elongated tube, closed at either end, and lying in front of the spermatic cord. 676 A MANUAL OF ANATOMY The funicular portion of the processus vaginalis is sometimes closed at intervals along the course of the spermatic cord, and, when serous fluid accumulates in the intervening patent portions, the condition is known as encysted hydrocele of the cord. Abnormal Positions of Testis. — (i) The testis may remain permanently in the abdominal cavity. (2) Its descent may be arrested in the inguinal canal, or at the external abdominal ring. Such conditions constitute the condition known as cryptovchismus. Ectopia Testis. — The testis may occupy unusual situations, (i) It may be found in the anterior part of the perineum. (2) It may be found on the front of the thigh in the region of the saphenous opening, in which cases it might simulate a femoral hernia. For the structure and development of the testis, see pp. 683, 684. Subperitoneal Fat or Areolar Tissue. — ^This is situated between the fascia transversahs and the parietal peritoneum. Its con- dition is subject to much variety, being fairly well marked in some bodies, and in others hardly perceptible. Internal to the external iliac vein at Poupart's ligament it forms the septum crurale, which closes the upper end of the crural canal, and at the internal abdominal ring it is carried downwards round the spermatic cord underneath the infundibuliform fascia. Parietal Peritoneum. — This is the innermost covering of the abdominal wall, and it is connected with the fascia transversahs by the subperitoneal areolar tissue. Behind the internal abdominal ring it forms a slight projection, which in some cases enters the ring, the corresponding depression on its abdominal aspect at this point being known as the digital fossa. The projecting part of the parietal peritoneum corresponds with. the upper end of the original processus vaginalis, and presents a slight nodule, or it may be a slender thread-like process. It is here in the female where a diverticular process may extend for a short distance into the inguinal canal in front of the round ligament of the uterus, forming the canal of Nuck. Peritoneal Plicse and Inguinal Fossse. — ^The peritoneum lining the posterior surface of the anterior abdominal wall below the umbilicus presents plicse or folds and fossae or pouches. The plicse are five in number, one being situated in the middle line, and two on either side. The median plica extends from the apex of the bladder to the umbilicus, and contains the urachus. It is called the plica urachi. Of the two lateral plicae the more internal one contains the obliterated hypogastric artery, and is called the plica hypogastrica. It is oblique in direction, and meets the plica urachi and its fellow of the opposite side at the umbilicus. It corresponds to the junction of the inner two-thirds and outer third of Hesselbach's triangle. The external of the two lateral plicae is produced by the deep epigastric artery, and is called the plica epigastrica. The inguinal fossse are six in number, three right and three left, and are called internal, middle, and external. The internal inguinal fossa is situated bet-ween the plica urachi and plica hy])o- gastrica, and lies behind the inner two- thirds of Hesselbach's THE ABDOMEN 677 triangle, the conjoined tendon, and the external abdominal ring. The middle inguinal fossa is situated between the plica hypo- gastrica and plica epigastrica, and lies behind the outer third Umbilictis Plica Urachi Plica Hypogastrica Plica Epigastrica External Inguinal Fossa Anterior Crural Nerve Bladder External Iliac Artery External Iliac Vein Middle Inguinal Fossa Fig. 293 Internal Inguinal Fossa . — The Plic.e and Fossae on the Posterior Surface of THE Anterior Abdominal Wall. of Hesselbach's triangle. The external inguinal fossa is situated on the outer side of the plica epigastrica, and its lower and inner part is behind the internal abdominal ring. INGUINAL HERNIA. By an inguinal hernia is meant a protrusion of a viscus (usually bowel, or, it may be, great omentum) from the abdominal cavity in the inguinal region. This region is predisposed to such an occurrence from the presence of the two abdominal rings and inguinal canal, and the inguinal fossae. All forms of inguinal hernia, if complete, ultimately protrude through the external abdominal ring, and thereafter enter the scrotum. Relatively to the deep epigastric artery there are two varieties of inguinal hernia, namely, external and internal, the former leaving the abdominal cavity external to that vessel, and the latter escaping internal to it. Inasmuch, however, as the region inside the deep epigastric artery, namely, Hesselbach's triangle, is divisible into an inner two-thirds and an outer third, there may be two forms of internal hernia. Viewing, therefore, inguinal hernia in its relation to the abdominal wall, there are three varieties, namely, external oblique, internal direct, and internal oblique. External Oblique Inguinal Hernia. This variety is called external because the hernia, as it leaves the abdominal cavity, is external to the deep epigastric artery, and oblique, from its oblique course. The course of the hernia is as follows : it enters the external inguinal fossa, and elongates 678 A MANUAL OF ANATOMY before it the peritoneum forming that fossa. It then passes through the internal abdominal ring, and traverses the entire length of the inguinal canal, from which it emerges through the external abdominal ring into the scrotum, thus forming a complete external oblique inguinal hernia. Throughout its entire course the hernia lies in front of the spermatic cord, and its descent is arrested at the upper part of the testis, which can be felt at its lower and back part. The bowel may be arrested at any part of the inguinal canal, the hernia being then called incomplete, and forming what is known as a bubono- cele. In its descent the bowel elongates and carries before it certain invest- ments from the structures to which it is related, these investments being called the coverings of the hernia. The first covering of this form of hernia, as of the other varieties, is derived from the parietal peritoneum, the par- ticular part being that which forms the external inguinal fossa, and this constitutes the sac. The other coverings are simply those of the spermatic cord, which are all superadded to the sac. The coverings, enumerated in order from within outwards, are as follows : 1. Parietal peritoneum, which forms the sac. 2. Subperitoneal fat or areolar tissue. 3. Fascia transversalis, from the margins of the internal abdominal ring, forming the infundibuliform or internal spermatic fascia. 4. Cremasteric or middle spermatic fascia, at the lower border of the internal oblique muscle. 5. Intercolumnar or external spermatic fascia, from the pillars of the external abdominal ring. 6. Tunica dartos. 7. Skin. A short distance below the internal abdominal ring the subperitoneal fat and infundibuliform fascia become united, and are known as the fascia propria. The sac is composed of the following parts : (i) the moxith, which is the opening by which its interior communicates with the general peritoneal cavity ; (2) the neck, which is the constricted part immediately beyond the mouth ; and (3) the body. The neck of the sac is on a level with the margins of the internal abdominal ring, and the deep epigastric vessels lie immediately on its inner side. The seat of stricture may be (i) at the external abdominal ring ; (2) at the Icrwer border of the internal oblique muscle; or (3) at the neck of the sac, the last being the most common situation. Internal Direct Inguinal Hernia. — This variety is called internal because the hernia, as it leaves the abdominal cavity, is internal to the deep epigastric artery, and direct, from its straight course through the abdominal parieties. The course of this variety is as follows : the hernia enters the internal inguinal fossa, elongating before it the peritoneum forming that fossa. It then passes through the inner two-thirds of Hesselbach's triangle, and so reaches directly the external abdominal ring without traversing the inguinal canal. Having emerged through the external ring it descends into the scrotum, thus forming a complete internal direct inguinal hernia, which is in front of, and internal to, the spermatic cord. It is to be noted (i) that there is no natural opening in the fascia transversalis over the inner two-thirds of Hesselbach's triangle, as there is external to the deep epigastric artery, and (2) that the conjoined tendon covers the inner two-thirds of Hesselbach's triangle. The coverings of this variety, enumerated in order from within outwards, are as follows : 1. Parietal peritoneum. 2. Subperitoneal fat or areolar tissue. 3. Fascia transversalis. 4. Conjoined tendon. 5. Intercolumnar or external spermatic fascia. 6. Tunica dartos. 7. Skin. If the hernia occurs suddenly, rupture of the conjoined tendon may take place, in which cases the bowel would pass through the fissure. The seat of THE ABDOMEN 679 stricture in an internal direct inguinal hernia may be (i) at the external abdominal ring, (2) at the fissure in the conjoined tendon, if that structure should be ruptured, or (3) at the neck of the sac. The latter situation is the most common, and it is to be noted that the deep epigastric vessels lie on the cuter side of the neck of the sac. Internal Oblique Inguinal Hernia. — This variety is called internal because the hernia, as it leaves the abdominal cavity, is internal to the deep epigastric- artery, and oblique, because it has to descend through the lower two-thirds of the inguinal canal. The course of this variety is as follows : the hernia enters the middle inguinal fossa, elongating before it the peritoneum forming that fossa. It then passes through the outer third of Hesselbach's triangle and descends through the lower two-thirds of the inguinal canal, from which it emerges through the external abdominal ring into the scrotum, thus forming a complete internal oblique inguinal hernia. Practically the only difference between the course of an internal oblique and an external oblique inguinal hernia is that the external oblique variety enters the inguinal canal by its natural inlet, namely, the internal abdominal ring, whereas the internal oblique variety obtrudes itself into the upper part of the inguinal canal through its posterior wall. It is to be noted (i) that there is no natural opening in the fascia transversalis over the outer third of Hesselbach's triangle, as there is external to the deep epigastric artery, and (2) that there is no conjoined tendon over the outer third of Hesselbach's triangle. The coverings of tliis variety, enumerated in order from within outwards, are as follows : 1. Parietal peritoneum. 2. Subperitoneal fat or areolar tissue. 3. Fascia transversalis. 4. Cremasteric or middle spermatic fascia. 5. Intercolumnar or external spermatic fascia. 6. Tunica dartos. 7. Skin. If the coverings of an external oblique, and an internal oblique, inguinal hernia are compared with each other, it will be seen that the former has a tube of fascia transversahs already prepared for it. namely, the infundibuliform fascia, whereas the latter has to elongate before it a fresh portion of fascia transversalis. In some cases the fascia transversahs over the outer third of Hesselbach's triangle is covered by an expansion from the conjoined tendon, which is known as the reflected tendon of Cooper. In such cases that reflected tendon must be added as a covering of internal obUque inguinal hernia, its position being immediately superficial to the covering formed by the fascia transversalis. The relation of an internal oblique inguinal hernia to the spermatic cord is similar to that of an external obUque, and the possible seats of stricture are also similar. The neck of the sac is the most common situa- tion, and the deep epigastric vessels he immediately on its outer side. The extreme difficulty which must be experienced in diagnosing between an external obhque and an internal obUque hernia is explained by the fact that the former leaves the abdominal cavity immediately external to the deep epigastric vessels, and the latter immediately internal to them. Hence, the practical rule followed in operating is to cut upwards and not transversely. The propriety of this rule is further enhanced if it be remembered that an external oblique inguinal hernia of old standing may so drag upon the internal abdominal ring as to displace it do\\Tiwards and inwards to a point behind the external ring, and thus a hernia which is really external oblique may simulate one of the internal direct variety. Varieties of External ObUque Inguinal Hernia. — There are two varieties of this form of hernia, the special features of which depend upon abnormal conditions of the processus vaginalis (see p. 673). These varieties are named congenital and infantile.' Congenital Hernia.^There are two forms of congenital hernia, (i) The processus vaginalis may remain permanently open throughout, in which case the bowel descends within that process into the ca\aty of the tunica vaginaUs at its lower extremit\\ The tunica vaginalis thus represents the 68o A MANUAL OF ANATOMY sac of the hernia, and this form is therefore spoken of as a hernia into the tunica vaginalis. In such cases the bowel more or less completely envelops the testis. (2) The processus vaginalis may be shut off only just above the testis, the part above this remaining as a funicular process communicating above with the general peritoneal cavity. In such cases the bowel descends into the funicular process, which thus forms the sac of the hernia. This form is therefore spoken of as a hernia into the funicular process. Infantile Hernia.— There are two forms of infantile hernia, infantile hernia proper and encysted hernia. In both there is a funicular process which is closed above, towards the internal abdominal ring. It may also be closed below just above the testis, being thus distinct from the tunica vaginalis, or it may simply be an upward extension of the tunica vaginalis. In either case it is situated in front of the spermatic cord. In infantile hernia proper the bowel, having elongated the parietal peritoneum to form a sac, descends between the spermatic cord and the funicular process. Its importance con- sists in the fact that, before the bowel can be exposed in operating, three serous layers must be divided, two of these belonging to the funicular process and the other representing the wall of the hernial sac. In this form the descent of the bowel is arrested at the upper part of the testis. In encysted hernia the bowel, having elongated the parietal peritoneum to form a sac, pushes against the upper part of the funicular process so as to invaginate it in a downward direction in the form of a cup, in which the bowel, enclosed in its sac, lies. The condition of matters is therefore very much like an egg set in its cup, assuming that the top of the shell is removed, and that the wall of the cup is formed of two layers. To bring out this simile, the contents of the egg may be taken as representing the bowel, the shell of the egg being the sac of the hernia, and the assumed two layers of the wall of the cup repre- senting the two serous layers of the doubled down or invaginated funicular process, the cavity thus formed representing the inside of the cup. In this form, as in infantile hernia proper, three serous layers must be divided before the bowel is exposed in operating, two of these belonging to the invaginated funicular process and the other representing the wall of the hernial sac. Umbilical Hernia (Exomphalos). — By an umbilical hernia is meant a pro- trusion of bowel or of great omentum from the abdominal cavity through the umbilicus. The protrusion occurs through the upper part of the umbilicus, which, containing only the obliterated umbilical vein, is weaker than the lower part where the obliterated hypogastric arteries and the urachus lie. The coverings of an umbilical hernia are as follows : 1. Parietal peritoneum. 2. Subperitoneal fat or areolar tissue. 3. Fascia transversalis. 4. An expansion from the decussating fibres of the aponeuroses of the abdominal muscles of opposite sides. 5. Superficial fascia. 6. The cicatricial cutaneous umbilical tissue. There is no vessel liable to be injured in operating on this form of hernia, the deep epigastric artery being about i^ inches from the linea alba. The congenital form of umbilical hernia consists in a protrusion of bowel or omentum through the centre of the umbilicus into the umbilical cord, in which it may descend for some distance. Its possible presence will show the propriety of carefully examining the cord before ligaturing it after birth. The anterior abdominal wall above the umbilicus presents pos^ teriorly a median fold of parietal peritoneum, which represents a part of the upper border of the falciform ligament of the liver. This fold contains a portion of the obliterated umbilical vein, which is now spoken of as the round ligament of the liver. It extends upwards from the umbilicus to the interlobar or umbilical THE ABDOMEN 68i notch on the anterior border of the liver, through which it passes to enter the umbilical fissure on the under surface of the viscus. As the round ligament ascends to the liver the peritoneum, within which it lies, is being gradually elongated in the form of two closel}^ applied laminae, which thus project to form a part of the falcifonu ligament. The apex of this ligament is therefore at the umbilicus. The Tunica Vaginalis and Testis. Tunica Vaginalis. — ^This is a closed serous sac, behind which the testis lies. It is formed by the lower part of the processus vaginalis, or peritoneal diverticulum, which precedes the descent of the testis from the abdomen. Like all serous membranes, it is composed of two layers, parietal and visceral. The parietal layer is known as the tunica vaginalis scroti, from the circumstance that it lines the scrotal chamber of its own side. It is much larger and looser than the visceral layer, with which it is continuous along the posterior border of the testis and on the spermatic cord about J inch above the organ. The visceral layer is known as the tunica vaginalis testis. It closely invests the tunica albuginea of the testis, to Spermalic Cord „. Organ of Giraldes Tunica Vaginalis Scroti ^ Epididymis Digital Fossa Hydatids of Morgagni Fig. 294.— The Testis and its Coverings. which it is inseparably united. It also invests the epididyinis except at its posterior border, where the constituents of the spermatic cord enter or leave the testis. Between the epi- did\Tnis and the testis it forms a recess, called the digital fossa, and it extends upwards on the spermatic cord for about i inch above the testis. Along the posterior border of the organ, where this layer becomes continuous with the parietal layer, there is a narrow strip which is free from serous investment. The portion of the tunica vaginalis which is related to the spermatic cord is called the fitnictilar pen . When fluid accumulates between the parietal and visceral layers, the condition is known as hydrocele of the tunica vaginalis. 682 A MANUAL OF ANATOMY Testis. — ^The testis is suspended obliquely by the spermatic cord in its scrotal compartment, to the bottom of which it is loosely attached by the fibrous remains of the gubernaculum testis. The left testis is a little lower than the right. The organ is oval, and compressed from side to side. Its exterior, which is smooth, is closely invested by the visceral layer of the tunica vaginalis, except where the constituents of the cord enter or leave the organ. The surfaces are external and internal, the former looking slightly back- wards, and the latter forwards. The extremities are superior and inferior, the former being inclined forwards, and the latter back- waids. The borders are anterior and posterior. The anterior border looks slightly downwards and oiitwards, and is free. The posterior border looks upwards and inwards, and is attached. The average weight of the testis is about 7 drachm ',. Epididymis. — This is an elongated narrow body, composed of the convolutions of the excretory duct, and lying along the posterior border and adjacent portion of the external surface of the testis. its upper extremity, which is above the upper end of the testis, is enlarged, and is called the caput or globus major ; the lower and smaller end is called the tall or globus minor ; and the intervening narrow portion represents the body. The globus major and globus minor are connected to the testis by fibrous tissue, and by a reflec- tion of the tunica vaginalis, the former being further connected to the organ by the efferent ducts. The body, except at its posterior border, is free, being separated from the testis by the digital fossa. The epididymis is almost completely invested by the visceral layer of the tunica vaginalis except at its posterior border, where there is a duplicature of that membrane containing bloodvessels and attaching it to the testis. Hydatids of Morgagni. — These are two small pyramidal bodies which are situated on the anterior aspect of the globus major at its lower part, or on the front of the upper end of the testis below the globus major, one of them being pedunculated and the other sessile. Each is composed of connective tissue and bloodvessels, covered by the visceral layer of the tunica vaginalis. The hydatids are vestiges of Miiller's duct. These small bodies are two in number. One is pedunculated or stalked, and is situated on the front of the caput epididymis at its lower part. The other hydatid is sessile, and is placed on the upper end of the testis below the caput epididymis. Organ of Giraldes or Paradidymis. — ^This organ is situated on the front of the spermatic cord, immediately above the globus major, and under cover of the funicular part of the tunica vaginalis. It consists of a few irregular nodules of convoluted tubules, which are lined with ciliated columnar epithelium. These nodules are remains of the Wolffian body. Development. — The organ of Giraldds represents a portion of the caudal part of the Wolffian body. THE ABDOMEN 683 Arterial Supply of the Testis and Epididymis. — The testis derives its arterial supply from the testicular branch of the spermatic (which enters the posterior border of the organ), and the epidid\Tnis derives its supply from the epidid\Tnal branch of the spermatic, which vessel arises from the abdominal aorta about i inch below the renal artery. The globus minor of the epidid\-mis also receives a few twigs from the deferential artery, which is usually a branch of the superior vesical from the internal iliac. The veins of the testis issue at the upper part of the posterior border, and, along with those of the epididjTnis, enter the spermatic cord, where they form the pampiniform plexus. The right sper- matic vein, in which the right plexus ultimately ends, opens directly into the inferior vena cava, and the left into the left renal vein. Lymphatics. — ^These ascend in the spermatic cord, and accompany the spermatic vessels as high as the lateral and median groups of lumbar glands in which they terminate. Nerve-supply. — ^The spermatic plexus of the s\Tnpathetic system which derives its fibres from the aortic and renal plexuses. The testis is homologous to the ovary of the female (testis muliebris) . General Structure of the Testis and Epididymis.— The testis is an aggregation of seminiferous tubules collected into lobules, which are encased within a capsule called the tunica albugmea. This tunic is a dense, bluish white, in- elastic membrane, composed of bundles of fibrous tissue. Its outer surface is closely covered by the tunica Wall of Sciotum vaginalis testis . I ts inner sur - face is invested by a copious vascular network, known as the tunica vasculosa of Cooper. At the posterior border of the testis the tunica albuginea passes for a certciin distance into the interior, this inflec- tion being called the corpus Highmorianum, or mediasti- num testis. This mediastinum extends into the organ for one-fourth of its antero-pos- terior measurement, and from its sides and anterior border a number of trabeculae, con- taining plain muscular tissue, pass off, which extend in various directions as far as the inner surface of the tunica albuginea, to which they are Tunica Vaginalis Scroti ' _ Tunica Vaginalis Testis .Tunica Albuginea bulus Testis _ Mediastinum Testis Digital Fossa Hpididymis - . Spermatic .-Vrtery Vas Deferens ; Spermatic Veins Artery of the Vas Deferens Fig. 295. — Diagram showing a Transverse Section of the Testis and Scrotum. attached. By means of these the interior of the testis is mapped out into a number of loculi. the trabeculae which enclose them contain- ing the branches of the spermatic arterj- as they make their way to the tunica vasculosa. These compartments contain the seminiferous tubules collected into bundles, called the lobuli testis, which vary in number from 300 to 400. Each lobule contains from t^vo to four tubules, and is conical, the base being directed towards the circumference of the testis and the apex 684 A MANUAL OJ^ ANATOMY towards the mediastinum. Each tubule is about ^fo inch in diameter and IS convoluted. When the coils are undone the tubule measures about 2 teet m length. The tubules of each lobule unite into one and the tubules of adjacent lobules unite in turn, and so give rise to the tuhuli recti, each of which IS about ^i^y inch m diameter, and about -^\ inch in length These tubuh recti enter the mediastinum, where they form by their division a net- work, called the rete testis. From this rete tubules, called vasa efferentia proceed, which are about ^V inch in diameter, their number varying from twelve to twenty. These leave the testis at the upper part of its posterior border. For a short distance thereafter they remain straight, but they are soon thrown into convolutions, which form conical masses, called coni vasculost. The length of each conus vasculosus is about ^ inch and its apex IS directed towards the testis. When the convolutions are undone the tube assumes a length of about 8 inches, its diameter gradually diminishing from about A inch at its commencement to about ^\ inch at its termination Ihe com vasculosi open by separate orifices into the canal of the epididymis. Globus Major Coni Vasculosi Body of Epididymis Vas Deferens , Mediastinum Testis (Corpus Highmorianum) L.LobuIus Testis ■"•Tunica Albuginea Vas Aberrans Globus Minor Fig. 296. — The Structure of the Testis and Epididymis. The epididymis consists of one tube, having a diameter of about iV inch in the globus major, where it commences in a blind extremity. In the body it diminishes a httle in diameter, and in the globus minor it again enlarges. The tube presents a great number of convolutions, which, being folded upon themselves and connected together by loose tissue, give rise to a series of lobules. When the convolutions are undone the length of the epididymis has been variously estimated at from 12 to 20 feet. At its upper extremity it receives the coni vasculosi, and beyond the globus minor it terminates in the vas deferens. At the point where it terminates in the vas deferens there is a diverticulum connected with it, called the vas aberrans of H alter, which extends upwards in a convoluted manner between the epididymis and the adjacent part of the vas deferens. The vas aberrans, when the coils are undone, is from 8 to 1 2 inches in length. Minute Structure. — The tubuli seminiferi are composed of a hyaline base- ment membrane, lining which there are several layers of epithelial cells, (i) The most external layer consists of cubical cells, known as the parietal cells. They line the basement membrane of the tubule, and are of two kinds. The majority of them give rise to the spermatozoa, and these are called the spermatogenic cells, or spermatogonia. Others arc of a supporting nature, and are called the sustentacular cells, or cells of Sertoli, which subsequently THE ABDOMEN 6S5 form the columns of Sertoli. (2) The spermatogonia undergo mitotic division, and give rise to a second layer of cells, called the primary spermatocytes, or mother-cells. (3) The primary spermatocytes also undergo mitotic division, and give rise to a third layer of cells, called the secondary spermatocytes, or daughter-cells. (4) The secondary sper- matocytes also undergo mitotic division, and give rise to a fourth layer of cells, called the spermatoblasts, or spermatids. These spermatids, having undergone considerable modifications, give rise to the spermatozoa. These spermatozoa lie with their heads buried between the more deeply placed cells, and their long tails projecting free into the lumen of the tubule. The enlarged ends or heads of the spermatozoa, whilst they lie buried between the deeper cells, are connected with the sustentacular cells of the lining epithelium. The tubuli recti are composed of a basement membrane lined with a single layer of cubical epithelium. The tubules of the rete testis are destitute of a basement membrane, its place being taken by the connective tissue of the mediastinum. The lining membrane of the tubules consists of a single layer of cubical cells. The vasa eflerentia and coni vasculosi are composed of a basement membrane, external to which there is a layer of plain muscular fibres arranged in a circular manner. The lining epithelium is of the ciliated columnar variety. The structure of the epididymis is similar to that of the vasa eflerentia and coni vasculosi. Fig. 297. — The Tubuli Semini lERi OF THE Testis (magni- fied). Development of the Internal Sexual Organs. The testis and the ovary do not present any distinctive sexuzd characters in the earliest stage of their development, and this stage, in each case, is therefore spoken of as the indifferent stage. Indifferent Stage. — The first indication of a sexual organ is the appearance of a thick longitudinal fold on the inner surface of the Wolffian body. This fold is called the genital ridge, and it is formed by (i) a thickening of the coelomic epithelium which covers the inner surface of the Wolffian body, and (2) the subjacent mesodermic tissue. The genital ridge presents three regions — namely, anterior or rete region. middle or sex-gland region, and posterior or mesenteric region, the last-named taking no part in the development of the sexual organ. The ccelomic epithelium of the genital ridge constitutes the germinal epithelium, and the cells of this epithelium over the sex-gland region of the genital ridge invade the subjacent mesoderm in the form of strands called the sex-cords. The cells of these strands are of two kinds, some being small epithelial cells, whilst others are large primitive sexual cells. As the stage of differentiation proceeds, these sexual cells give rise to spermatozoa, or seminal cells, in the case of the testis, and to ova in the case of the ovary. The indifferent sexual organ is thus represented by the genital ridge, the mesodermic basis of which is invaded by sex-Cords, the cells of which are partly epithelial and partly sexual. Moreover, the indifferent organ hes on the inner side of the Wolffian body. The stage of differentiation now commences. 686 A MANUAL OF ANATOMY Development of the Testis and its Excretory Apparatus. — The embryonic rudiments pertaining to the development of the testis are as follows: Genital ridge. Sex-cords. Anterior tubules of the meso- Rete-cords. nephros, or Wolffian body. Wolffian duct. The cells of the germinal epithelium of the sex-gland region of the genital ridge which invade the mesoderm are, as stated, small epithelial cells and large sexual cells, and they are arranged as cylindrical columns, which, as stated, are known as the sex-cords. These cords become separated from the epithelium of the genital ridge when the tunica albuginea of the testis is formed from connective tissue derived from ' the basal nuclei of the sex- cords.' They are broken up into spherical masses which, like the sex-cords, consist of small epithelial cells and large sexual cells. These masses become hollow, and, after undergoing elongation, they give rise to the secreting seminiferous tubules. The sexual cells of the masses become spermatogonia, or primordial sperm-cells, from which the spermatozoa are derived, whilst the small epithelial cells are probably transformed into the cells of Sertoli. For spermatogenesis, or the formation of spermatozoa, see Index. The excretory tubules (tubuli recti and rete testis) are usually regarded as being developed from the anterior or sexual tubules of the mesonephros, or Wolffian body. From the epithelium of the Malpighian corpuscles of these tubules solid cords of cells, called the rete-cords, grow into the developing testis. These cords become tubular, and they give off branches which acquire connections with the secreting seminiferous tubules. In this manner the tubuli recti and rete testis are formed. The vasa efferentia are developed from the anterior or sexual tubules of the Wolffian body. Another view is that the rete-cords arise from the cells of the germinal epithelium over the anterior or rete-region of the genital ridge, being serially homologous with the sex-cords. The rete-cords are at first solid, but subse- quently acquire a lumen. They extend posteriorly into the proper glandular substance, formed by the sex-cords. As they do so, they give off branches, each of which passes to one of the spherical masses into which the sex-cords are broken up. Within this mass it becomes continuous with a secreting seminiferous tubule. The proximal ends of the rete-cords become detached from the epithelium of the rete-region of the genital ridge. They then come into close contact with the capsules of Bowman of the Malpighian corpuscles belonging to the anterior or sexual tubules of the mesonephros or Wolffian body, which tubules give rise to the vasa efferentia of the testis. The contact may be direct, or through means of evaginations of the walls of Bowman's capsules. In either case fusion takes place, and the proximal ends of the rete-cords (rete-tubules open into the capsules of Bowman, and become continuous with the anterior or sexual tubules (vasa efferentia of the testis) of the mesonephros. These mesonephric tubules open into the Wolffian duct, which gives rise to the epididymis, vas deferens, and common ejaculatory duct. The convoluted canal of the epididymis, the vas deferens, and the common ejaculatory duct are developed from the Wolffian duct. The vesicula seminalis is formed as a blind diverticulum of the caudal part of the Wolffian duct; and the vas aberrans is a slender diverticulum of that portion of the Wolffian duct which forms the globus minor, or tail, of the epididymis. Summary. — The testis, genetically considered, consists of (i) secreting seminiferous tubules and seminal cells, and (2) excretory tubules. The secreting seminiferous tubules and their seminal cells are developed from the sex-cords of that portion of the germinal epitheUum which covers the sex-gland region of the genital ridge. The tubuli recti and rete testis are de- veloped from the epithelium of the Malpighian corpuscles of the anterior or sexual tubules of the mesonephros, or Wolffian body, which covers the anterior or scA-Ma/^/rt«rfy<^gjow, or from the germinal epithelium of the rete-region of the genital ridge. The vasa efferentia are developed from the anterior or sexual tubules of the mesonephros or \\'olffian body. The epididymis, vas deferens, THE ABDOMEN 687 vas aberrans, vesicula seminaJis, and common ejaculatorj- ducts are all de- veloped from the Wolffian duct. The interstitial stroma of the testis is developed from the mesoderm of the genital ridge. The tunica albuginea is formed from connective tissue de- rived from ' the basal nuclei of the sex-cords.' Development of the Ovary. — The embryonic rudiments pertaining to the development of the ovary are as follows: Genital ridge and germinal epithelium. Egg-columns or egg-tubes of Medullary cords. Pfluger (sex-cords). Rete-cords. The ovary, like the testis, is developed from the indifferent sexual orgain. Whilst in the case of the testis the anterior or sexual tubules of the meso- nephros or Wolffian body and the Wolffian duct pertain to its development, inasmuch as the excretors- tubules of the male sexual gland are associated with the epithehum of their Malpighian corpuscles ; in the case of the ovary the Wolffian tubules and the Wolffian duct become vestigial. The ovary is developed from the sexual cords and the mesoderm of the genital ridge. The epithelial cells of the genital ridge, as in the male, constitute the germinal epithelium. The deep cells of the epithehum of the sex-gland region of the genital ridge invade the mesoderm of the ridge, and are disposed as cellular cords, which are separated by ingrowths of connective tissue, derived from the mesoderm of the genital ridge. These cellular cords cire called the egg-columns, or egg -tubes of Pfluger (sex-cords). These egg-columns con- sist of small epithehal ceUs (foUicular cells) and large sexual cells or primitive ova. They become separated from the epithehum of the genital ridge when the somewhat indefinite tunica albuginea of the ovary is formed from the con- nective tissue derived from ' the basal nuclei of the medullary- cords.' The sexual cells of the egg-columns increase in size, and each column, being invaded by connecti\e tissue, is thereby broken up into groups of cells, known as cell-nests, which form the primary Graafian folhcles. Each of these folhcles consists of one sexual cell, or primitive ovum, and numerous small epithehal cells, with an external investment of connective tissue. These small cells are disposed as a single layer around the o\-um, which layer represents the membrana granulosa, and the investing connective tissue forms the theca folliculi. At a later period the cells of the membrana granu- losa undergo prohferation, and so give rise to several layers. A fluid, called liquor folliculi, is then formed by these cells; the o\Tim is thereby displaced to one side of the foUicle; and the mass of cells, within which it is embedded, forms the discus proligerus. The egg-columns (egg-tubes of Pfliiger) form the cortical part of the ovary. The medullary Cor(£, which contribute to the medullary part of the ovary, hke the sex-cords of the testis, are probably developed from the germinal epithehum of the sex-gland region of the genital ridge. They bear a re- semblance to the egg-columns, bj" which they aire succeeded, and contain follicular cells and primitive ova. They become broken up into a number of primary- Graafian folhcles, but these soon degenerate. In the meduUar)- part of the ovary they give rise to groups of foUicular cells, and these subse- quently become converted into connective tissue. The rete-cords are developed, as in the male, from the germinal epithehum of the rete-region of the genital ridge. They differ from the rete-cords of the male inasmuch as they do not become hollow, so as to form tubules, but remain solid. They resemble the medullary cords, and, along with the re- mains of these cords, they form the medullary part of the ovarj', giving rise to groups of foUicular cells, which subsequently become converted into con- nective tissue. This arrangement is known as the rete ovarii. The epithehum, which covers the surface of the ovary, in adult hfe repre- sents the superficial cells of the germinal epithelium, which take no part in the formation of the egg-columns. The ceUs of this epithehum differ in a marked manricr from those of the adjacent peritoneum inasmuch as they are columnar, whilst the adjacent cells are the usual endothelial cells of a serous membrane. 688 A MANUAL OF ANATOMY Summary-. — -The cortical part of the ovary, with its Graafian folHcles and their contents, is developed from the cell-nests formed by the ovarian ends of the egg-columns or egg-tubes of PflUger, which arise from the germinal epi- thelium of the sex-gland region of the genital ridge. The medullary part of the ovary is formed by the ovarian ends of the medullary cords and rete-cords, which are now transformed into a connective- tissue stroma, the latter cords constituting the so-called rete ovarii. The medullary cords have a similar origin to that of the egg-tubes of Pfliiger; and the rete-cords arise from the germinal epithelium of the rete-region of the sex-gland. The tunica albuginea of the ovary is developed from the connective tissue derived from ' the basal nuclei of the medullary cords.' The columnar epithelium, which covers the surface of the adult ovary, represents the superficial cells of the embryonic germinal epithelium. Mesorchium and Mesovarium. — The Wolffian body is attached to the dorsal wall of the body-cavity by a fold of peritoneum, which is spoken of as its 'mesentery,' but is really its ligament. -This ligament is prolonged to the diaphragm, under the name of the diaphragmatic ligament, and externally it blends with the uro-genital fold, which contains the Wolffian and Miillerian ducts. From the caudal part of the Wolffian body another fold of peri- toneum, containing connective tissue and plain muscular tissue, extends to the inguinal region. This fold is called the inguinal ligament. As the genital ridge, or indifferent sexual organ, which lies on the inner side of the Wolffian body, becomes differentiated into the testis and the ovary, it retains its connection with the Wolffian body, and is attached to the dorsal wall of the body-cavity by a fold of peritoneum, which acts as a suspensory hgament. This fold forms the mesorchium and mesovarium, respectively, and at the level of the caudal part of the Wolffian body it blends with the uro-genital fold, the latter having previously fused with the Mgament (' mesentery ') of the Wolffian body. The sexual gland is retro-peritoneal ; that is to say, it lies behind the peritoneum. As the caudal tubules of the Wolffian body become atrophied, the in- guinal ligament acquires a connection with the caudal end of the sexual organ. In the male it constitutes the gubernaculum testis, which is referred to in connection with the descent of the testis. In the female the inguinal liga- ment, as it descends, becomes connected with the Miillerian duct at the level where this duct fuses with its fellow to form the uterus and vagina, and there- after it continues its course to the inguinal region, traversing the inguinal canal, and terminating within the labium majus. The part of the inguinal ligament between the ovary and the uterus forms the ligament of the ovary, and the part which extends from the uterus through the inguinal canal to the labium majus constitutes the round ligament of the uterus. The descent of the inguinal ligament through the inguinal canal is preceded, or accompanied, by a small diverticulum of the peritoneum, which lies in front of the inguinal ligament. This diverticulum generally becomes obliterated. In rare cases, however, it remains pervious as a blind diverticulum, communi- cating only with the peritoneal cavity, and known as the canal of Nuck. Development of the Epoophoron. — The longitudinal tube, which lies parallel to the Fallopian tube, is a persistent part of the ^^'olffian duct, and repre- sents the canal of the epididymis in the male. In some animals, e.g., the sow, the Wolffian duct remains persistent, and, under the name of the duct or canal of Gartner, can be traced from the broad ligament of the uterus along the side of that organ to the lateral wall of the vagina in its upper part, where it disappears. In the human female it sometimes takes a similar course, and the portion of it on the uterine and vaginal walls is to be regarded as rcpre- sentmg the vas deferens in the male. The transverse tubules of the epoophoron extending from the region of the ovary to the longitudinal tube (so-called duct of Gartner), into which they open at right angles, arc vestiges of the anterior segmental tubes of the Wolffian body, and represent the tubuU recti, rete testis, vasa efferentia, and coni vasculosi of the testis in the male. Development of the Paroophoron. — These vestigial tubules arc derived from the more posterior segmental tubes of the Wolffian body, and they represent the paradidymis or organ of Giraldcs in the male. THE ABDOMEN 689 ABDOMINAL CAVITY. The abdominal cavity is somewhat ovoid, the vertical measm^e- ment greatly exceeding the transverse. Its superior boundary is formed by the diaphragm, which here presents a concave surface. The inferior boundary is formed by the levatores ani and coccygei muscles, covered superiorly by the visceral pelvic fascia and inferiorly by the anal fascia. This boundary is concave on its upper aspect. The superior and inferior boundaries, being fleshy, are capable of con- tracting and relaxing alternately. During contraction the diaphragm descends on each side, and the levatores ani ascend, thus diminishing the vertical measurement of the cavity. During relaxation the reverse takes place, the diaphragm ascending and the levatores ani descending, and so the cavity is increased in its vertical measure- ment. The anterior and lateral boundaries are partly osseous and partly musculo-aponeurotic. The osseous boundaries are formed by the lower ribs above, and the pelvis below. Elsewhere these boun- daries are formed by the musculo-aponeurotic planes of the abdominal muscles. The posterior boimdary is formed by the bodies and discs of the lumbar vertebrse, psoas magnus and quadratus lum- borum muscles with their fascial investments, sacrum, and coccyx. The cavity is divided into two regions, the abdomen proper and the pelvis. The abdomen proper is limited below by the brim of the pelvis, and its visceral contents are the abdominal portion of the alimentary canal, with the exception of the pelvic colon and rectum, the liver, pancreas, spleen, kidneys, and suprarenal bodies. The pelvis is situated below the level of the brim, and contains the pelvic colon, rectum, and internal uro-genital organs. Abdomen Proper. Division into Regions. — The abdomen proper is divided into .nine regions by means of two horizontal and two vertical lines, with their corresponding planes. The horizontal lines are called subcostal and intertubercular. The subcostal line encircles the abdomen proper on a level with the lowest parts of the tenth costal cartilages, and the plane corresponding to it is called the subcostal plane. The intertubercular line connects the highest points of the iliac crests which can be felt from the front, where there is usually a tubercle on the outer lip about 3 inches from the anterior superior iliac spine. The plane corresponding to this line is called the intertubercular plane. The vertical lines are called the Poupart lines, right and left, and each extends vertically upwards from the centre of Poupart's ligament. The planes corresponding to these lines are known as the Poupart planes. The subcostal and inter- tubercular lines, with their corresponding planes, map out the abdomen proper into three horizontal zones, called subcostal, umbilical, and hypogastric. The two Poupart lines, with their 44 ego A MANUAL OF ANATOMY corresponding planes, subdivide each of these zones into three regions, two lateral, right and left, and a central. The abdomen proper is thus eventually divided into nine regions, three in each of the three horizontal zones, as follows : the subcostal zone is sub- divided into right hypochondriac, epigastric, and left hypochondriac regions ; the umbilical zone is subdivided into right lumbar, um- bilical, and left lumbar regions; and the hypogastric zone is sub- divided into right iliac, hypogastric, and left iliac regions. Superficial View of the Contents. — On taking a superficial view of the contents of the abdomen proper the sharp anterior border of the liver is seen on the right side projecting beyond the right costal margin, and also beyond the ensiform process. The great bulk of the . organ, however, lies concealed in the right hypochondrium, and the extent to which it passes into the left hypochondrium usually corresponds to the left mammary line. In the middle line it projects beyond the ensiform process for about 2 inches, but along the right costal margin it does not usually project more than about ^ inch. The anterior border presents two notches. One, which is well defined, is called the interlobar or umbilical notch. It is situated fully i inch to the right of the middle line, and transmits the obliterated umbilical vein or round ligament. The other, which is situated about 2 inches to the right of the interlobar notch, is usually somewhat indefinite, and is called the cystic notch. It allows the fundus of the gall-bladder to come forward opposite the ninth right costal cartilage at a point coincid- ing with the outer border of the right rectus muscle. The falciform or suspensory ligament is conspicuous as it takes attachment to the supero-anterior surface of the liver, which it divides into two lobes, right and left. On the left side a portion of the stomach is visible, though a large part of the viscus lies deeply in the left hjqjochondrium. The portion which is seen in the epigastrium is partially covered by the left lobe of the liver, but a part of it is in contact with the anterior abdominal wall, provided the viscus is not empty. Descending from the great curvature of the stomach there is an extensive fold of peritoneum, which hangs down in the form of a curtain, and so conceals the jejunum and ileum. This fold is called the great or gastro-colic omentum. In normal circumstances it descends as low as the level of the sacral promontory upon the left side, but it stops a little short of that level on the right side. The condition of the great omentum is subject to much variety. In some bodies it is very narrow, and much puckered in the vertical direction, so as to leave exposed the viscera which are normally covered by it. In other cases it is displaced to one or other side, or it may even be raised into the left hypochondrium. In normal circumstances a few coils of the ileum are visible beyond the great omentum on the right side, and, more especially in the female, one or two loops of the. ileum may descend into the pelvic cavity to occupy the pouch of THE ABDOMEN 691 Douglas. In the right iliac fossa the caecum is in part seen, and in the left iliac fossa the iliac colon is partially visible. When the great omentum is raised and laid over the costal margin, the coils of the jejunvmi and ileum come into view, occupy- ing the umbilical and hv-pogastric regions, and extending into the right and left lumbar, and iliac, regions. The transverse colon is also seen crossing in an arched manner from the right to the left h^-pochondriac regions. \\Tien moderately distended, the stomach is Pyrxform and curved. It presents for consideration the following parts: Two extremities, two surfaces, two curvatures, and two orifices. Extremities. — ^The extremities are left and right. The left ex- tremity is knowTi as the cardiac or splenic end or fundus. It is large (ESO^MACUS OUOOCMO- PVLOWIC CONSTRICTION,' Sulcus intermeoius' Fig. 298. — The Stomach (External Vibw). and round, and forms a cul-de-sac. Its direction is upwards, hack- li-ards, and to the left, and it is related to the left half of the diaphragm posteriorly and the spleen. The right extremity is knowTi as the Pyloric end. It Ues beneath the quadrate lobe of the hver, and is directed backwards. It is narrow, and is continuous with the first part of the duodenum. Its position is indicated superficially by a well-marked, circular constriction, called the duodeno-pyloric con- striction. Surfaces. — ^These are antero-superior and postero-inferior. The antero-superior surface is convex, and, though mainly directed up)- wards, it has a sUght incUnation forwards. It is closely related to (i) the under surface of the left lobe of the Uver, (2) the left half of the diaphragm, and (3) the anterior abdominal wall. The postero- 692 A MANUAL OF ANATOMY inferior surface is somewhat flat, and has a slight inclination back- wards. Its relations are as follows: 1. The diaphragm. 2. The gastric surface of the spleen. 3. The left suprarenal capsule. 4. The gastric area at the upper part of the front of the left kidney. 5. The antero-superior surface of the pancreas. 6. The transverse colon. 7. The upper surface of the transverse mesocolon. Curvatures. — The curvatures, also known . as borders, are small and great. The small curvature, or posterior border, extends downwards and to the right from the right side of the lower end of the oesophagus to the duodeno-pyloric constriction. It is con- cave, and is directed backwards and towards the right. The small or gastro-hepatic omentum connects the small curvature with the lips of the portal fissure of the liver, and between the two layers of the gastro-hepatic omentum, along the small curvature, there are the gastric artery and the pyloric branch of the hepatic artery, with the corresponding veins. Towards its pyloric extremity the small curvature presents a notch, which is produced by the stomach being bent upon itself. This notch is called the incisura angularis. It indicates the division of the stomach into cardiac and pyloric parts. The great curvature, or anterior border, extends from the left side of the lower end of the oesophagus to the duodeno-jejunal constriction. It is convex, and much arched. At first it arches over the fundus, passing upwards, backwards, and to the left. Thereafter it passes downwards and forwards, and finally it extends from left to right. The direction of the greater part of the great curvature is forwards and towards the left. It gives attachment to two omenta — namely, the great or gastro-colic omentum, and the gastro- splenic omentum. The gastro-colic omentum is attached to the greater part of the great curvature, from which it depends. Between its two layers there are the right gastro-epiploic artery and the left gastro-epiploic artery, together with the gastro-epiploic veins, right and left. The gastro-splenic omentum is attached to the great curvature to the left of the attachment of the gastro-colic omentum. The transverse colon lies immediately below the great curvature, under cover of the great omentum. About ij inches from the pyloric end the great curvature presents a notch, called the sulcus intermedius, which indicates the subdivision of the pyloric part of the stomach into a pyloric canal and a pyloric vestibule. Orifices. — These are two in number — namely, oesophageal and pyloric. The oesophageal orifice is also known as the cardiac orifice, or cardia, and through it the oesophagus opens into the stomach. It is situated at the upper and left extremity of the small curvature, fully 2 inches to the right of the highest part of the fundus. The pyloric or duodenal orifice, through which the stomach communicates with the duodenum, is narrow, and is THE ABDOMEN 693 situated at the right extremity of the stomach. It is directed backwards, and is guarded by the pyloric valve, which will be described in connection with the structure of the stomach. Its position is indicated superficially by the duodeno-pyloric constric- tion already referred to. Divisions of the Stomach. — ^The stomach is divided into two parts — cardiac and pyloric — by means of a line connecting the incisura angtilaris on the small curvature with the opposite point on the great curvature. The cardiac part lies to the left of this line, and is of large size. It consists of the fundus and body of the stomach, the separa- tion between these two parts being indicated by a line connecting the cardia with the opposite point on the great curvature. The pyloric part, which is short, is subdivided into two portions — namely, the pyloric canal and the pyloric vestibule — ^by means of the sulcus intermedius on the great curvature. The Pyloric canal adjoins the duodeno-pyloric constriction. It is about i\ inches in length, and is narrow and cylindrical in outline, hke a portion of the small intestine. Its walls are thick, and it is directed backwards. The pyloric vestibule, or antrum pylori, is a dilatation, situated to the left of the pyloric canal, from which it is separated by the sulcus intermedius. Its direction on the great curvature is downwards. Position of the Stomach. — When the stomach is empty it is com- paratively small, which is due to the contracted state of its walls during Ufe. It is situated horizontally in the left hypochondrium and the left part of the epigastrium, emd is falciform in outUne. The fundus is directed backwards; the cardiac portion, somewhat saccular, is directed for%vards and sUghtly to the right ; the pyloric portion, tubular in outhne, passes to the right; the pylorus Ues about I inch to the right of the median Hue; the surfaces look upwards and downwards; and the great curvature looks forwards, and the small curvature backwards. When the stomach becomes distended, it usually assumes an oblique position, its long axis being directed downwards, forwards, and to the right. The organ increases in length; the pylorus is carried towards the right side, assuming a position from i^ to 2 inches on the right side of the median plane; the pyloric canal is bent backwards; the fundus becomes enlarged and directed upwards and towards the left; and the upper surface acquires an inclination forwcirds, and the under surface an inchnation back- wards. The position of the cardia is practically unaltered. The stomach still occupies the left hypochondrium and the epigastrium, but, when much distended, part of it may enter the umbiHcal and left lumbar regions. Occasionally the stomach, when distended, retains the horizontal position occupied by it when empty. Topography of the Stomach. — The cardiac orifice, or cardia, is situated to the left of the median Une about i inch below the sternal attachment of the seventh left costal cartilage. It is about 4 inches distant from the anterior abdominal wall, and is on a level with the upper part of the body of the eleventh thoracic vertebra. 694 A MANUAL OF ANATOMY The Pyloric orifice, or pylorus, is on a lower level and more anterior plane than the cardia, and, moreover, it usually lies to the right of the median line. Relatively to the vertebral column it is on a level with the upper part of the body of the first lumbar vertebra, and it is opposite the tip of the ninth right costal cartilage. When the stomach is empty, the pylorus usually lies about | inch to the right of the median line, but this distance is increased during distension to i^ or 2 inches, or even more. The pylorus may be said to lie about 4 inches below the junction of the seventh right costal cartilage with the sternum. Its level may also be stated as being midway between the interclavicular notch on the upper border of the manubrium sterni and the upper border of the sym- physis pubis. Peritoneal Relations. — The stomach is almost completely invested by peri- toneum, the anterior surface deriving its covering from the peritoneum of the general cavity, and the posterior surface from that of the small sac. The parts uncovered by peritoneum are as follows : a narrow line along the small curvature between the two layers of the gastro- hepatic omentum for the passage of the gastric and pyloric arteries ; a narrow line along the great curvature between the two layers of the gastro-colic omentum for the passage of the right and left gastro-epiploic arteries ; and the uncovered area or trigone. This latter area is situated on the posterior surface, bslow, and a little to the left of, the cardiac orifice. It is about 2 inches in breadth, and rather less from above downwards, its shape being triangular. This part of the stomach is in contact with the left crus of the diaphragm, and sometimes with the left suprarenal capsule. The reflection of the peritoneum around this area from the stomach to the diaphragm is known as the gastro-phrenic liga- ment, which lies on the left side of the lower end of the oesophagus. For the structure and development of the stomach, see pp. 781, 798. Position, Connections, and Component Parts of the Intestinal Canal. — The intestinal canal commences at the pyloric end of the stomach and terminates at the anus. It is divided into small intestine and large intestine. The small intestine commences at the pyloric extremity of the stomach, and terminates in the right iliac fossa by opening obliquely into the large intestine. It measures fully 23 feet in length, and is divided into three parts, which, from above downwards, are called the duodenum (twelve fingers' breadth), jejunum (' empty '), and ileum (' coiled'). The duodenum is from 10 to 11 inches in length, and its limits are the pyloric extremity of the stomach, and the left side of the body of the second lumbar vertebra. Being very deeply placed, its position and connections will be described further on (p. 731). Of the remainder of the small intestine the upper two-fifths represent the jejunum, and the lower three-fifths the ileum. There is no evident external mark of separation between the three divisions of the small intestine, so that they merge imper- ceptibly into each other; but there are internal characters which serve to distinguish these divisions. On the left side of the body of the second lumbar vertebra, where the duodenum terminates in the jejunum, the bowel describes a bend in a downward and for- THE ABDOMEN 695 ward direction, called the duodeno-jejunal flexure, which is sus- pended from the left crus of the diaphragm by a fibro-muscular band, called the musculus suspensorius duodeni. The jejunum and ileum are very much convoluted, their coils being covered to a greater or less extent by the great omentum. They lie below the transverse colon, and occupy the umbilical, hypogastric, right and left lumbar, and right and left iliac regions. A few coils of the ileum sometimes dip into the pelvis, and when this occurs they occupy, in the female, the pouch of Douglas. The jejunum and ileum are attached to the vertebral column by a fold of peri- toneum, called the mesentery proper, which contains their blood- vessels, nerves, and lymphatics, and which is of such a nature as to permit of great mobility in this part of the intestinal tube. They are surrounded by peritoneum except along a narrow interval corresponding with the attachment of the mesentery proper, this border of the bowel being csJled the attached or mesenteric border, as distinguished from the free or anti-mesenteric border. The small intestine is a smooth cylindrical tube, which gradually diminishes in size from above downwards. The terminal portion of the ileum, as it is about to join the large intestine, is directed upwards and to the right, with a slight inclination backwards. Meckel's DiTerticulam. — This is a protrusion which is sometimes found con- nected with the free or anti-mesenteric border of the ileum about 3 feet above the ileo-caecal valve. It represents the persistent proximal j>art of the vitel- line or vitello-intestinal duct, which connects the yolk-sac with that portion of the primitive aUmentary canal from which the lower part of the ileum is formed. It usually measures from 2 to 3 inches in length, and its calibre generally corresponds with that of the tube from which it springs. In most cases it resembles the finger of a glove, but occasionally it is reduced to the condition of a cord. It is rarely provided with a mesentery. The large intestine commences in the right iliac fossa, and termi- nates at the anus. It measures about 6 feet in length, and gradually diminishes in size from its commencement to its termi- nation. It is composed of the colon and the rectmn. The colon is subdivided into the caecum (with the vermiform appendix), ascending or right colon, hepatic flexure, transverse or middle colon, splenic flexure, descending or left colon, iliac colon, and pelvic colon. Caecum. — ^The caecum (caput caecum coli) is the commencement of the large intestine. It represents that part of the gut which extends below the ileo-caecEil orifice, and is situated in the right iliac fossa, where it rests upon the ilio- psoas muscle with the intervention of the fascia iliaca. Its lower end or fundus has an inclination inwards towards the pelvic brim, close to which it usually lies. The average length of the caecum is about 2^ inches, its breadth being about 3 inches. When empty it is more or less covered by coils of the ileum. In the distended state it comes into contact with the anterior abdominal wall, and at the same time it descends as low as the outer half of Poupart's ligament. At its inner and back part, at a point about 2h inches from its ^696 A MANUAL OF ANATOMY lower end, it receives the termination of the ileum, the opening being guarded by the ileo-caecal valve. The position of this valve corresponds with a point in the right spino-umbilical line between i^ and 2 inches from the anterior superior iliac spine {McBurney's point). In normal cases the caecum is very movable, being com- pletely covered by peritoneum. The line of reflection of the peritoneum posteriorly may correspond with the level of the ileo- caecal orifice. In some cases, however, the peritoneum, after having invested the posterior aspect of the caecum, gives a covering to the posterior wall of the ascending colon for if inches (Treves), after which the reflection takes place. The line of reflection may be transverse or oblique, and the peritoneum so reflected is continuous with the left or inferior layer of the mesentery proper. In a few cases (about 6 per cent.) the upper part of the posterior surface of the caecum is destitute of peritoneum, and is bound down by connective tissue to the subjacent fascia iliaca. Under these circumstances its mobility is more or less curtailed. Varieties of Caecum. — The caecum is characterized by extreme variableness as regards form, but the variations may be grouped into the following four principal types (Treves) : First Type. — In the foetus the caecum is conical, the vermiform appendix springing from the apex of the cone. The three longitudinal muscular taeniae are disposed as follows : one is situated on the postero-internal aspect ; a second lies along the postero-extemal aspect ; and the third is placed on the anterior aspect. They are nearly equally distant from each other, and meet at the apex of the caecum. Second Type. — The caecum is quadrilateral. The lower end presents two sacculi, and the vermiform appendix springs from the interval between them. The taeniae are situated as in the preceding type. Third Type. — In this variety the part of the caecum to the right ai the anterior taenia becomes more developed, and consequently more prominent, than the part to the left of that band, and the anterior wall undergoes greater growth than the posterior wall. During these changes the apex is being gradually shifted backwards and to the left, until finally it takes up a position near the ileo-caecal junction, where it corresponds with the origin of the vermiform appendix. The part to the right of the anterior taenia becomes so much developed, especially in a downward direction, as to give rise to a false apex. This is the most common form of caecum, the origin of the appendix being transferred to the left and posterior aspect. Fourth Type. — In this variety the part to the right of the anterior taenia undergoes excessive development, and the part to the left becomes much atrophied, and in many cases practically disappears. This causes the anterior taenia to terminate at the lower part of the ileo-caecal junction, and the vermiform appendix arises immediately posterior to that point. Vermiform Appendix. — ^The vermiform appendix is a small diverticulum of the caecum, which opens into its inner and back part rather more than i inch below the ileo-caecal orifice. The caecal end of the appendix is called its base, and the guide to it is rather more than i inch below McBurney's point. Its diameter corre- sponds with that of an ordinary goose-quill, and its length varies from 2 to 6 inches, or more. Its outline is serpentine, and the lumen is usually confined to its caecal half, though it may extend throughout its entire length. The opening by which the appendix THE ABDOMEN 697 communicates with the caecum is occasionally guarded by a fold of mucous membrane, which is known as the valve of Gerlach. The appendix is provided with a mesentery, caJled the appendicular mesentery or meso- appendix. It seldom reaches more than half or two-thirds along the appendix, which latter is thus rendered more or less convoluted or serpentine. The meso-appendix and its variations will be found described on p. 725. The position occupied by the appendix is extremely variable. According to Lockwood and RoUeston, the normal positions may be tabulated as follows : 1. The vermiform appendix often lies under the left or iaferior layer of the mesentery, where it takes a course upwards and to the left in the direction of the spleen. (According to Treves this is its usual position.) 2. It may lie on the brim of the pelvis, or it may project into the pelvic cavitv. 3. If the appendicular mesentery is long, the appendix may lie to the right of the caecum and ascending colon, in which situation it may ascend over the right kidney towards the right lobe of the liver. 4. It may lie free over the caecum and ascending colon. 5. It may he free underneath the caecum. (This is the second most common situation according to Treves.) As regards abnormal positions of the vermiform appendix, it may, amongst other situations, be found lying in the retro-caecal, or in the ileo-caecal, fossa. It has been found extending horizontally across the vertebral column at the level of the lumbo-sacral angle, with its tip resting on the left psoas magnus muscle (Treves). Ascending or Right Colon. — ^This extends from the caecum, on a level with the ileo-caecal orifice, to the under surface of the right lobe of the liver at a point to the right of the gall-bladder. Here it describes a bend, called the hepatic flexure, which indents the liver, and so gives rise to the impressio colica. The ascending colon occupies a part of the right iliac, right lumbar, and right hypochondriac regions, in which it lies deeply, being in contact with the posterior abdominal wall. Posteriorly it rests upon a portion of the right iliacus muscle covered by the fascia iliaca, the right quadratus lumborum invested by its sheath, and the front of the right kidney in its lower and outer part. Anteriorly it is more or less covered by the coils of the jejunum and ileum. Internally, it has the coils of the jejunum and ileum, and the right psoas magnus muscle, covered by its fascia. The ascending colon in most cases is covered by peritoneum in front and at the sides, but not behind. Sometimes, however, it is completely invested by the serous membrane, which then forms behind it a mesentery, called the ascending meso-colon. Occasionally a peritoneal fold is met with, which extends from the right side of the ascending colon to the abdominal wall at, or a little above, the -level of the iliac crest. It is called the sustentaculum hepatis, and occurs in about 18 per cent, of cases (Treves). It presents anteriorly a free con- cave border, and it measures about i^ inches in width, and about 2 inches from before backwards. Hepatic Flexure. — ^This is the bend formed by the gut between 698 A MANUAL OF ANATOMY the termination of t-he ascending colon and the commencement of the transverse colon. The bend takes place in a direction forwards and to the left, and so brings the bowel in front of the second or vertical part of the duodenum. The hepatic flexure has the impressio colica on the inferior surface of the right lobe of the liver above it, the sharp anterior margin of the liver on its outer side, and the second part of the duodenum on its inner side. Posteriorly it is in contact with the right kidney in the same locality as the upper part of the ascending colon, and it is here uncovered by peritoneum. Transverse or Middle Colon. — ^This, which is comparatively long and very arched, commences in the right hypochondrium in front of the second part of the duodenum, and terminates in the left hypochondrium in the splenic flexure. Its extremities are deeply placed, the right being a little lower and more superficial than the left, and both being comparatively fixed on account of the shortness of the transverse meso-colon at these points. The greater part of it descends into the umbilical region, where it usually lies just above the umbilicus. The transverse colon is completely invested by peritoneum, except occasionally for i inch or more posteriorly at its right extremity. The serous membrane forms an extensive fold behind it, called the transverse meso-colon, which passes backwards to the anterior border of the pancreas, and is of very limited extent at its right and left extremities. The transverse colon is covered in front by the great omentum. Above it, from right to left, are the liver, gall-bladder, great curvature of the stomach, inferior surface of the pancreas, and basal surface of the spleen; behind it are the second part of the duodenum, head of the pancreas, and transverse meso-colon ; and below it are the coils of the jejunum. Splenic Flexure. — ^This is situated in the left hypochondrium in contact with the basal surface of the spleen, and behind the cardiac end of the stomach. It occupies a higher and deeper position than the hepatic flexure, and its posterior surface is un- covered by peritoneum. Connected with its left aspect there is a triangular fold of the serous membrane, which attaches it to the diaphragm opposite the tenth or eleventh left rib. This fold is called the phreno-colic or costo-colic ligament, and it forms a platform upon which the basal surface of the spleen rests : hence the name sustentaculum lienis (' support of the spleen '). It will be found described on p. 720. Descending or Left Colon. — ^This, which is of comparatively small calibre, commences in the left hypochondrium at the splenic flexure, and terminates in the lower part of the left lumbar region on a level with the back part of the iliac crest, where it passes into the iliac colon. It lies deeply in the left hypochondriac and left lumbar regions, being directed at first downwards and slightly inwards, and subsequently vertically downwards. Posteriorly it is in contact, from above downwards, with the front of the left kidney at its lower and outer part, and the left quadratus lumborum muscle invested by its sheath. Anteriorly it is covered by coils THE ABDOMEN 699 of the jejunum and ileum. Internally coils of the jejunimi and ileum form a superficial relation, whilst more deeply there are the lower part of the left kidney and the left psoas magnus muscle covered by its fascia. The descending colon in most cases is covered by peritoneum in front and at the sides, but not behind. Sometimes, however, it is completely invested by the serous membrane, which then forms behind it a mesenterj', called the descending meso-colon. The ascending, transverse, and descending parts of the colon form an arch, within the concavity of which the coils of the jejunum and ileum are disposed. Iliac Colon.— This commences at the lower extremity of the descending colon on a level with the back part of the iliac crest, and terminates at the inner border of the left psoas magnus, anterior to' the left sacro-iliac articulation. At this point it enters the pelvic cavity and becomes the pelvic colon. It is situated in the left iliac fossa, where it lies upon the ilio-psoas muscle with the inter- vention of the fascia iliaca, its direction being downwards and inwards. Anteriorly it is covered, when empty, by coils of the ileum, but when distended it lies in contact with the anterior abdominal wall. The iliac colon in most cases is covered by peritoneum in front and at the sides, but not behind. Sometimes, however, it is completely invested by the serous membrane, which then forms behind it a mesentery, called the iliac meso-colon. For the pelvic colon and rectum, see p. 859. The large intestine, with the exception of the vermiform appendix and rectum, is characterized by weU-marked sacculations, which present a striking contrast to the smooth cylindrical contour of the wall of the small intestine. These sacculations are due to the longitudinal muscular fibres being gathered into three longitudinal bands, called teenies coli (ligaments of the colon), which are shorter than the portion of bowel to which they are applied. The saccula- tions are separated from each other by constrictions filled with fat. Another characteristic of the greater part of the large intestine is the presence, at frequent intervals, of small projections of the peritoneal coat containing fat, called appendices epipioicce. These characteristics will be found described in connection with the structure of the large intestine on p. 795 . For the structure and development of the intestinal canal, see Index. Position, Connections, and Component Parts of the Spleen.— The spleen (lien) is a ductless gland which lies deeply in the left hypochondrium opposite the ninth, tenth, and eleventh ribs, and extending from about the level of the ninth thoracic spine to that of the eleventh. The organ can only be seen when the stomach is drawn out from the left hypochondrium. It is soft, spongy, easily torn, and exceedingly vascular, and it has a dark red colour. It is so liable to become enlarged that it is subject to much variety as regards dimensions and shape. The following statement, therefore. JOO A MANUAL OF ANATOMY of its dimensions is only to be accepted as approximately accurate. The average length of the spleen may be said to be about 5 inches, its breadth, at the widest part, being about 3 inches, and its thick- ness about ij inches. The weight, which is very variable, is about 6 ounces. The organ occupies an oblique position, its long axis being directed downwards, outwards, and forwards. Its lower two- thirds are situated in the left hypochondrium, and the upper third in the epigastrium. When it has been hardened in situ its shape resembles that of an irregular tetrahedron (Cunningham) — that is to say, it resembles a solid figure enclosed by four equilateral triangles. The following description is based upon this view of its shape. Apex. — ^This corresponds with the upper end, "and lies in the epigastrium, about 2 inches from the median line. It is directed upwards, inwards, and slightly forwards. Surfaces. — One aspect of the organ is directed towards the diaphragm, the other looking towards the abdominal cavity and its viscera. The former aspect re- presents the parietal or^ ex- ternal surface, which is convex, and adapts itself to the concavity of the diaphragm. It is called the phrenic surface, and its direction is outwards, Hilum „ .. Anterior Basal Angle Pancreatic Impression Fig. 299. — The Spleen (Visceral Are;e). Internal Basal Angle backwards, and upwards. It is in contact with the diaphragm opposite the ninth, tenth, and eleventh ribs, the left pleural sac descending for some distance between that part of the diaphragm and the adjacent ribs. A part of the base of the left lung, very thin and covered by pleura, also descends for a short distance so as to intervene between the upper part of this surface of the spleen and the exterior. The abdominal or visceral aspect is complex, and presents three surfaces, which are separated from each other by more or less well-marked ridges, radiating from the internal basal angle (Cunningham). These surfaces are called gastric, renal, and basal. The gastric surface is large, concave, and somewhat semilunar. Its direction is forwards, inwards, and downwards, and it accu- rately adapts itself to the fundus of the stomach on its posterior aspect. It is limited anteriorly by the sharp anterior border of the spleen, which separates it from the phrenic surface, and THE ABDOMEN lo\ posteriorly it is separated from the renal surface by the ridge which extends from the internal basal angle upwards to the apex. A little in front of this ridge, and therefore situated on the gastric surface, there is a fissure, called the hilum, for the passage of the splenic vessels, lymphatics, and nerves. Instead of a hilum there is sometimes a row of foramina. The narrow portion of the gastric surface behind the hilum is, at its lower end, in contact with the tail of the pancreas. The renal surface, which is posterior to the gastric surface, is narrow. It is directed inwards and downwards, and is in contact with the front of the left kidney at its upper and outer part, close to the external border. It is separated from the gastric surface by the ridge already referred to, and is limited behind by the posterior border, which separates it from the phrenic surface. Interiorly it is separated from the basal surface by the ridge which extends from the internal basal angle to the posterior angle. The basal surface is the small triangular surface which looks, downwards and inwards. It rests upon the splenic flexure of the colon and upper surface of the sustentaculum lienis or peritoneal platform formed by the costo-colic ligament. It is separated from the renal surface by the ridge already referred to, and from the gastric surface by the ridge which passes between the internal and anterior basal angles. The angles of this surface are called internal, posterior, and anterior, the last being the most prominent. Borders. — These are anterior, posterior, and inferior. The anterior border is situated between the phrenic and gastric surfaces. It is sharp, and usually presents several notches. The posterior border is situated between the phrenic and renal surfaces. It is blunt, and its position and direction practically coincide with the lowest left intercostal space. The inferior border separates the phrenic and basal surfaces, and is somewhat sharp. Peritoneal Relations. — ^The spleen is surrounded by peritoneum, except at the hilvun, and where the gastro-splenic omentum and phreno-splenic ligament are connected with it. The serous mem- brane forms three folds, called gastro-splenic omentum, lieno-renal ligament, and phreno-splenic ligament. The gastro-splenic omen- tum is attached by one extremity to the gastric surface of the spleen just in front of the hilum, the other extremity being connected with the cardiac end of the stomach on its posterior aspect and the left border of the great omentum. The lieno-renal ligament is attached by one extremity to the gastric surface along the line of the hilum, the other extremity being attached to the front of the left kidney at its upper and outer part. The phreno-splenic or lieno-phrenic ligament extends between the spleen near its upper extremity and the contiguous part of the diaphragm. Occasionally small accessory spleens, var>nng in number from one to twenty, are found in the gastro-splenic omentum in the neighbourhood of the hilum, or more rarely in the great omentum. 702 A MANUAL OF ANATOMY Area of Splenic Dulness. — ^This area is limited posteriorly by the mid-scapular line between the ninth and eleventh left ribs, and anteriorly by the mid-axillary line as it crosses the ninth, tenth, and eleventh ribs, or by a line connecting the left sterno-clavicular joint with the tip of the eleventh left rib. The length of the area is about 3 inches, and its breadth from 2 to 2J inches. For the structure and development of the spleen, see Index. Position, Connections, and Component Parts of the Liver. — ^The liver (hepar), which is the largest gland in the body, occupies almost all the right hypochondrium, a great part of the epigastrium, and a small part of the left hypochondrium, in which latter direction it usually extends as far as the left Poupart plane. It is maintained in position by the following peritoneal ligaments : the posterior or coronary ligament, the right and left lateral or triangular liga- ments, and the falciform or suspensory ligament. Topography. — The size of the liver is such a variable factor that the following statement of its limits is only to be regarded as 'approximately accurate. In the right mammary line it extends from a point about J inch below the right nipple to a point about \ inch below the tip of the bony part of the tenth right rib, being covered by the right ribs from the fifth to the tenth inclusive. In the mid-axillary line the right aspect of the organ extends from the seventh to the eleventh rib, and in [the scapular line its superior and inferior limits are on a level with the ninth and eleventh thoracic spinous processes respectively, the ribs to which it is here related being the ninth, tenth, and eleventh. The left limit of the organ usually corresponds to the left Poupart plane. In mapping out the upper limit the middle line may be taken as the starting- point. In this situation the limit is indicated by a line crossing the sternum at the level of the sixth costal cartilages, this line being slightly arched downwards. The line should then be prolonged to the left, with a slight curve upwards, to a point about 2 inches to the left of the left border of the sternum. In continuing the line to the right it should be carried upwards so as to reach a point about h inch below the right nipple. The line, on being pro- longed from this point towards the right side, must be carried slightly downwards so as to reach the mid-axillary line at the level of the seventh right rib. The lower limit of the organ extends from a point about | inch below the tip of the bony part of the tenth right rib to the left extremity of the line indicating the upper limit. The direction of the line indicating the lower limit is upwards and to the left. Summary of Outline of Liver. — Commencing 2 inches from the left border of the sternum and i inch below the nipple, draw a line downwards and to the right to the left border of the sternum at the level of the sixth costal cartilage, next across the sternum with a slight curve downwards, then upwards and to the right to a point about | inch below the right nipple. From this point carry the line downwards and to the right as far as the seventh rib in the right mid-axillary line, then downwards and backwards to the ninth rib on a level with the ninth thoracic spine, whence the line is carried downwards to the THE ABDOMEN 703 eleventh rib on a level with the eleventh thoracic spine. From this latter point the line should proceed forwards and sUghtly upwards to a point about ^ inch below the tip of the bony part of the tenth right rib. and finally upwards and to the left to reach the starting-point. The liver is to a very large extent under cover of the lower ribs and costal cartilages of the right side, the ensiform process, and the sixth, seventh, and eighth, costal cartilages of the left side. It is accurately moulded on the under surface of the diaphragm, which separates it from the base of the right lung covered by pleura, and the heart enclosed in the pericardium. The thin marginal part of the base of the right lung, with its pleural investment, descends in the angular interval between the diaphragm and the thoracic wall, and so partially covers the liver, a relation which has to be borne in mind in percussing the organ. In the right mammary line the lung descends as low as the sixth rib, whilst the liver ascends to the upper border of the fifth. In the right mid-axillary line the limg descends as low as the eighth rib, whilst the liver ascends as high as the seventh. In the right scapular line (inferior angle of scapula) the lung descends as low as the tenth rib, whilst the liver ascends as high as the ninth. The liver comes nearest to the surface beyond the right costal margin and ensiform process. In the former situation it projects about \ inch, and in the latter about 2 inches, and in each situation is in contact with the anterior abdominal parietes. Various circumstances aflfect the position of the liver. ^ During respiration, the hver descends in inspiration and ascends in expiration. In the horizontal posture it ascends, and in the sitting or upright posture it descends. In distension of the stomach and intestines, as well as in ascites, it ascends. In right hydro-thorax, hypertrophy of the heart, and hydro-pericardium it descends. Long-continued pressure, as in tight lacing, causes the liver to be displaced downwards. Finally, when the abdomen proper is encroached upon by the gravid uterus or by an ovarian tumour the liver is displaced upwards. The liver has a reddish- brown colour, and presents for the most part a smooth surface. It is firm to the touch, but under pressure is friable, that is to say, easily crumbled. The dimensions of the organ can only be stated approximately. In the transverse direction (from right to left) it measures from 7 to 10 inches, the measurement from before backwards at its right extremity being about 6 inches, which also represents its vertical measurement at the thickest part of the right lobe. Its weight in the adult ranges from 45 to 60 ounces, or from 3 to 4 pounds, the weight in the female being rather less, and its relation to the body weight being in the proportion of one to forty in the adult. In early life the liver is proportionately larger than in the adult, and in a child at the period of birth its relation to the body weight is as one to twenty. Surfaces. — ^These are superior, anterior, inferior, right lateral, and posterior. It is not to be supposed, however, that these surfaces are all clearly separated from one another by well-defined borders, only one margin being in reality distinct, namely, the anterior border, which has a very sharp outline. 704 A MANUAL OF ANATOMY The superior surface is markedly convex in its right portion, and accurately adapts itself to the concavity of the diaphragm with which it is in contact. To the left of this convex part there is a depression, called the impressio cardica, produced by the heart with the intervention of the diaphragm. To the left of this im- pression the superior surface again becomes convex, and adapts itself to the concavity of the left half of the diaphragm. The superior surface is separated from the posterior, anterior, and right lateral surfaces by round, somewhat indistinct, borders. Right Lateral Surface Suspensory Ligament Round Ligament Fundus of Gall-bladder Fig. 300. — ^The Liver (Antero-superior View). The anterior surface looks forwards and is triangular. The apex is directed towards the left extremity of the liver, whilst the base is towards the right extremity. One side of the triangle corresponds to the anterior border, the other side being formed by the round border which separates the anterior from the superior surface. The anterior surface is mainly in contact with the diaphragm and the right and left costal margins, but at the middle line it is in relation with the ensiform process, and, for about 2 inches below that process, it is in contact with the anterior abdominal wall. The superior and anterior surfaces are divided into two lateral parts by the falciform ligament, the part to the right of this ligament being called the right lobe, and the part to the left the left lobe. The right lobe forms about four-fifths of the entire supero-anterior surface in the adult, but in early life the two lobes are very nearly of equal size. The inferior surface looks downwards with an inclination to the left. It is divided into two parts, right and left, by the umbilical fissure. The part to the left of this fissure represents a portion of the left lobe. It lies in front of the cardiac orifice THE ABDOMEN 705 of the stomach, and the anterior surface of that organ close to the small curvature. The part related to the cardiac orifice presents an impression, called the impressio gastrica. The part to the right of this impression, close to the back part of the umbilical fissure, presents a smooth round eminence, called the tuher omentale. This eminence projects in a backward direction over the small curvature of the stomach, and so abuts against the anterior layer of the gastro-hepatic omentum : hence the name, tuber omentale. The part of the inferior surface to the right of the umbilical fissure presents, as its most striking object, the gall-bladder, which occupies the cystic fossa. This fossa extends from the anterior border to the Inferior Vena Cava Lobus Caudatus Lobus Spigeln Venosal Fisiure Esophageal Groove Impressio Suprarcnalis Uncovered Area of Right Lobe Impressio Duodenalis Impressio Renolis na Portae Cystic Duct mpressio Gastric on Left Lobe Tuber Omentale / Hepatic Artery / [ ' ; I Impressio Colica Hepatic Duct ' , I Gall-bladder ! j Lobus Quadratus Round Ligament Ductus Communis Choledochus Fig. 301. — The Inferior Scrface of the Liver. portal or transverse fissure. It has the quadrate lobe on its left side, and a large part of the right lobe on its right side. The por- tion of the inferior surface of the right lobe to the left of the gall- bladder includes the following parts : the quadrate lobe, the portal or transverse fissure, the caudate lobe, and the lower margin of Spigel's lobe. The quadrate lobe, which is elongated from before backwards, is bounded anteriorly by the anterior border of the liver ; posteriorly, by the portal or transverse fissure ; on the right side by the gall- bladder and cystic fossa ; and on the left by the umbilical fissure. It is in contact with the pyloric end of the stomach and first part of the duodenum. 45 706 A MANUAL OF ANATOMY The portal or transverse fissure forms a right angle with the back part of the umbilical fissure, from which it extends over the inferior surface of the right lobe for a distance of about 2 inches. It is bounded in front by the quadrate lobe, and behind by the caudate lobe and the lower margin of Spigel's lobe. The two layers of the gastro-hepatic omentum are attached to its anterior and posterior lips. It serves for the passage of the following structures, in order from before backwards : (i) the hepatic duct ; (2) the hepatic artery, accompanied by the hepatic sympathetic plexus of nerves and lymphatic vessels ; and (3) the vena portse, all surrounded by the capsule of Glisson. The caudate lobe is the narrow portion 01 liver substance which connects the right extremity of the lower margin of Spigel's lobe with the adjacent part of the inferior surface of the right lobe. It lies behind the portal fissure, and has the vena portae in front of it, and the inferior vena cava behind it. It forms the upper boundary of the foramen of Winslow. The lower margin of Spigel's lobe, like the caudate lobe, is situated behind the portal fissure. It is divided by a notch into two eminences of unequal size. The right eminence, which is the smaller of the two, is continuous with the caudate lobe. The left eminence is of large size, and is known as the tuber papillare. The part of the inferior surface of the right lobe which lies' to the right of the gall-bladder is of large extent, and presents three impressions, namely, impressio colica, impressio renalis, and impressio duodenalis. The impressio colica, which looks downwards, is situated in front, where it lies to the right side of the body of the gall-bladder. It is in contact with the hepatic flexure of the colon. The impressio renalis, which is of large size, looks backwards as well as down- wards, is posterior to the impressio colica, and is in contact with a large part of the front of the right kidney. The impressio duode- nalis is situated on the inner side of the impressio renalis, just external to the neck of the gall-bladder. It is in contact with the commencement of the second part of the duodenum. The umbilical fissure is so named because it contains the re- mains of the umbilical vein, now known as the round ligament of the liver. It commences at the anterior border of the organ in the umbilical or interlobar notch, and extends as far back as the left extremity of the portal fissure, with which it forms a right angle. It separates the quadrate lobe from the inferior surface of the left lobe. Sometimes the fissure is more or less completely bridged over by a portion of hepatic substance, which thus forms a pons hepatis. The obliterated umbilical vein terminates by joining the left division of the vena portae, and posteriorly the left division of the vena portae is joined by the obliterated ductus venosus. The right lateral surface is convex, and is in contact with the diaphragm and right ribs from the seventh to the eleventh, the margin of the base of the right lung and pleura here descending between the ribs and diaphragm as low as the eighth rib. There is THE ABDOMEN 707 no well-marked line of demarcation between this surface and the posterior, superior, and anterior surfaces, but it is distinctly separated from the inferior surface by the right portion of the anterior border. The posterior surface presents a concavity corresponding with the convexity of the bodies of the tenth and eleventh thoracic vertebrae. It is related to the diaphragm, and its component parts from left to right are as follows : the posterior part of the left lobe ; the venosal fissure for the ductus venosus ; Spigel's lobe, except its lower margin ; the caval fossa for the inferior vena cava ; and the un- covered area of the right lobe. The posterior part of the left lobe at its left extremity is a mere margin, but elsewhere it presents a distinct surface marked by Falciform Ligament Posterior Area of Left Lobe CEsophageal Iinpreision ' Ligamentum Ductus Venosi ' (in Venosal Fossa) _/ Lobus SpigeliJ I \ Bare Area of Right Lobe • Rigbt Suprarenal Impression Inferior Vena Ca\-a (in Caval Fossa) Fig. 302. — The Posterior Surface of the Liver. the a'sophageal groove, which is in contact with the right side of the lower end of the oesophagus. The venosal fissure lies vertically on the posterior surface, having Spigel's lobe on its right, and the oesophageal groove of the left lobe on its left. Inferiorly it meets the left extremity of the portal fissure and the posterior extremity of the umbilical fissure, and superiorly it meets the caval fossa. It lodges the obliterated ductus venosus, which is connected below with the left division of the vena portse, and above with the inferior vena cava. The venosal and umbilical fissures separate the right and left lobes on the posterior and inferior surfaces respectively. Spigel's lobe, with the exception of its lower margin, lies vertically on the posterior surface. It is bovmded on the right side by the caval fossa, on the left by the venosal fissure, and inferiorly bj' the portal or transverse fissure. It looks backwards and a little 7o3 A MANUAL OF ANATOMY inwards, and is in contact with the right crus of the diaphragm opposite the tenth and eleventh thoracic vertebrae. Its lower margin has been already described (p. 706). The lobe lies at the upper end of the small cavity of the peritoneum. The caval fossa lodges a part of the inferior vena cava. It lies vertically, and somewhat deeply, on the posterior surface, having the uncovered area of the right lobe on its right side, Spigel's lobe on its left side, and the caudate lobe below. This fossa is sometimes bridged over by a portion of liver substance, called a pons hepatis. At the upper part of this fossa the hepatic veins open into the inferior vena cava. The uncovered area of the right lobe represents its back part. It measures from 2j to 3 inches in the transverse direction, and fully 2 inches from above downwards, except at the extreme right, where it tapers to a point. It is destitute of peritoneum, and is enclosed between the two serous layers which form the coronary ligament, being attached to the diaphragm by areolar tissue. Its direction is backwards and a little inwards. The extreme left end of this area, at a point immediately to the right of the lower end of the caval fossa and near the caudate lobe, presents a somewhat triangular impression, called the impressio suprarenalis, for the right suprarenal body. Borders. — ^The chief borders are three in number, namely, postero- superior, postero-inferior, and anterior. The postero-superior and postero-inferior borders give attachment to the two layers of peri- toneum which form the coronary ligament, and they enclose between them the posterior surface. The anterior border is sharp. At its right extremity it passes backwards so as to separate the inferior from the right lateral surface. At its left extremity it also passes backwards, and so forms the thin left margin of the left lobe. Its anterior portion presents two notches, umbilical or interlobar and cystic. The umbilical or interlobar notch is situated fully i inch to the right of the middle line, and transmits the obliterated umbilical vein or round ligament. The cystic notch, often hardly perceptible, is situated about 2 inches to the right of the umbilical notch, and allows the fundus of the gall-bladder to come into contact with the anterior abdominal wall. Peritoneal Relations. — ^The liver is covered by peritoneum except in the following regions : the uncovered area of the right lobe ; a small triangular area at the posterior extremity of the hepatic attachment of the falciform ligament ; the portal fissure ; and the cystic fossa, unless in those cases where the gall-bladder is completely invested by peritoneum. For the ligaments of the liver, see Index. Excretory Apparatus of the Liver. — ^This consists of the hepatic duct, the gall-bladder, the cystic duct, and the common bile-duct. The hepatic duct is formed by the union of a right and left branch which issue from the respective lobes at the portal fissure. It is the most anterior of the structures in that fissure^ and, after THE AB DOMES 709 a course of rather more than i inch downwards and to the right, it joins the cystic duct, and so gives rise to the common bile-duct. The diameter of the hepatic duct is about \ inch. The gall - bladder is a reservoir for the bile. It is pyriform, and is situated obliquely on the inferior surface of the right lobe, where it occupies the cystic fossa, having the quadrate lobe on its left side, and a large part of the right lobe on its right side. It extends from the anterior border of the liver to near the portal fissure, and presents a fundus, body, and neck. The fundus, which is round, looks downwards, forwards, and to the right. It occupies the cystic notch on the anterior border, and is in contact Neck Cystic Duct and Valves of Heister I .^^ ^ ~~ Pancreatic Duct (Duct of Wirsiing) ■~- Ampulla of Vater Duodenum (2nd part) Fig. 303. — ^The Excretory Apparatus of the Liver. with the anterior abdominal wall opposite the ninth right costal cartilage, at the outer border of the right rectus abdominis muscle. The body is directed upwards, backwards, and to the left. Its inferior and lateral surfaces are free, but superiorly it is attached by areolar tissue to the cystic fossa. It rests upon the right end of the transverse colon and the first part of the fluodenum. The neck describes two curves like the letter S, after which it is continued into the cystic duct. The gall-bladder is usually covered by peri- toneum, except on its upper surface. Sometimes, however, the serous membrane entirely surrounds it and forms a ligamentous fold above it, by which it is loosely and movably suspended 7IO A MANUAL OF ANATOMY from the cystic fossa. The gall-bladder measures about 3 inches in length, its breadth at the widest part being i| inches. Its capacity is from i to i| ounces. For the structure of the gall- bladder, see Index. The cystic duct is about i| inches long, its diameter being about ^L- inch. Its course is backwards, downwards, and to the left, and it ends by joining the hepatic duct near the portal fissure to form the common bile-duct. The common bile-duct (ductus communis choledochus) is formed by the union of the hepatic and cystic ducts near the portal fissure. Its length is fully 3 inches, its diameter being about J inch. It passes downwards between the two layers of the gastro-hepatic omentum in front of the foramen of Winslow, where it has the hepatic artery on its left side, and the vena portae behind. It afterwards descends behind the first part of the duodenum, and subsequently between the second part of the duodenum and the head of the pancreas on their posterior aspect. It then enters the wall of the second part of the duodenum in company with the duct of the pancreas, and runs obliquely in the wall for | inch. Thereafter it joins the pan- creatic duct, and the resulting duct forms a dilatation, called the ampulla of Vater, which, having become constricted, pierces the mucous membrane and opens on the tip of the bile-papilla at the junction of the inner and posterior walls of the second part of the duodenum, where the upper two-thirds and lower third of that part meet. The distance of this opening from the pylorus is about 4 inches. The common bile-duct sometimes opens into the duodenum independently of the pancreatic duct, but close to it. It is in the ampulla of Vater where a gall-stone may become lodged and delayed in its downward progress towards the duodenum. Liver in Early Life. — The size of the liver in early life is much greater than in the adult, the left lobe in particular assuming large dimensions. As age advances, however, the left lobe undergoes a marked diminution in size. For the structure and development of the liver, see Index. Peritoneum. — ^The peritoneum is the serous membrane which lines the abdominal parietes, and invests more or less com- pletely most of the viscera. It is composed of two layers, parietal and visceral, the contiguous surfaces of which are smooth and moist. In the male the interval between the two layers forms a shut sac, but in the female, at the fimbriated extremity of each Fallopian tube, the sac communicates with the lumen of that tube, and through it with the cavity of the uterus and the vagina. It is at the margin of the fimbriated extremity of each Fallopian tube where the endothelium of the peritoneum undergoes a sudden transition into the columnar ciliated epithelium of the Fallopian tube. The peritoneum forms certain reflections or folds which are ol three kinds, namely, omenta, mesenteries, and ligaments. THE ABDOMEN 711 An omentum is a double fold of peritoneum passing between two abdominal viscera. The omenta are three in number, namely, the great or gastro-colic omentum (epiploon), which passes between the great curvature of the stomach and the transverse colon, the small or gastro- hepatic omentum, which passes between the small curva- ture of the stomach and the portal fissure of the liver, and the gastro-splenic omentum, which passes between the posterior sur- face of the cardiac end of the stomach and the gastric surface of the spleen. A mesentery is a double fold of peritoneum passing between a portion of intestine and the abdominal wall. The mesenteries in the adult are normally as follows : the mesentery proper, which connects the jejunum and ileum to the vertebral column ; the appendicular mesentery or meso- appendix, which is connected with the vermiform appendix ; the transverse meso-colon, which extends between the transverse colon and the posterior wall of the abdomen at the anterior border of the pancreas ; and the pelvic meso-colon, which connects the pelvic colon to the anterior surface of the sacrum as low as the third sacral vertebra. Occasionallj' the ascending colon, descending colon, and iliac colon are each provided with a mesentery, called respectively the ascending meso-colon, descending meso-colon, and iliac meso-colon. A ligament is a fold of peritoneum which connects a viscus net intestine to the abdominal or pelvic parietes. The peritoneal liga- ments are as follows : (i) the ligaments of the liver, namely, the falciform ligament, the coronary ligament, and the right and the left lateral or triangular ligaments ; (2) the gastro-phrenic ligament ; (3) the lieno-phrenic ligament ; (4) the false ligaments of the urinary bladder, namely, two posterior, two lateral, and superior ; and (5) the broad ligaments of the uterus. Course of the Peritoneum. — ^The parietal and visceral layers of the peritoneum are in unbroken continuity with each other, and this continuity is shown by tracing the membrane in the vertical and transverse directions. Vertical Course. — Commencing at the portal fissure of the liver two layers of peritoneum descend to the small curvature of the stomach, forming the gastro-hepatic omentum. On reaching the small curvature these two layers separate, one passing over the anterior surface, and the other over the posterior surface, of the stomach. At the great curvature they come together, and descend in the form of a curtain over the coUs of the jejunum and ileum to the lower part of the abdomen, forming the two anterior or descending layers of the gastro-colic omentum. These two layers are then folded backwards and ascend to the transverse colon, thus forming the two posterior or ascending layers of the gastro- colic omentum. On reaching the transverse colon they separate, one layer passing in front of, and above, the bowel, and the other layer below and behind it. Having enclosed the transverse colon, the two layers meet, and are prolonged backwards to the posterior 712 A MANUAL OF ANATOMY wall of the abdomen at the anterior border of the pancreas, thus forming the transverse meso-colon. On reaching the anterior border of the pancreas the two layers of the transverse meso-colon take leave of each other, and form an ascending and a descend- ing layer. The ascending layer passes upwards over the anterior surface of the pancreas, the second part of the duodenum, and the posterior portion of the under surface of the diaphragm. Outline of Diaphragm Parietal Peritoneum Gastro-hepatic Omentum _ Transverse Meso-colon , I Great Omentum , I The Mesentery Parietal Peritoneum Vesicula Seminalis Fig. 304. — Diagram of the Peritoneum in the Adult Male (Vertical Section). S. Stomach S.J. .Small Intestine P. Pancreas B. Urinary Bladder D. Duodenum R. Rectum 'I'.C. Transverse Colon The arrow is through the Foramen of Wiiislow. from which it passes to the postero-inferior border of the liver, thus forming the inferior layer of the coronary ligament. Having covered Spigel's lobe, it arrives at the posterior li]> of the portal fissure, where it is continuous with the posterior layer of the gastro- hepatic omentum. The descending layer of the transverse meso-colon passes at first backwards upon the inferioi surface of the pancreas, and then downwards over the third part of the duodenum, at the lower border of which it is conducted off to the jejunum and ileum by the THE ABDOMEN 7' 3 superior mesenteric vessels. Having surrounded these portions of the small intestine it passes to the posterior abdominal wall upon the other aspect of the superior mesenteric vessels, and so forms the mesentery proper. It then descends over the abdominal aorta and inferior vena cava into the pelvis, where its course will be subse- quently traced. From the apex of the urinary bladder this layer of the peritoneum is reflected on to the posterior surface of the anterior abdominal wall, after lining which it passes to the anterior portion of the under surface of the diaphragm, whence it is reflected on to the postero- superior border of the liver, thus forming the superior layer of the coronary ligament. It then passes over the superior and anterior surfaces of the liver, and, turning round its anterior border, it arrives at the anterior lip of the portal fissure, where it is continuous with the anterior layer of the gastro-hepatic omentum. Transverse Course. — The peritoneum may be traced in the transverse direction at two levels, namely, above the trans- verse colon, or at the level of the foramen of Winslow, which is situated behind the right or free border of the gastro-hepatic omentum, and below the transverse colon, or at the level of th^ umbilicus. • Above the Transverse Colon, or at the Level of the Foramen of Winslow. — In front of the foramen of Winslow there are the two layers of peritoneum, anterior and posterior, which form the right or free border of the gastro-hepatic omentum, and which contain between them the common bile-duct, the hepatic artery, and the vena portae. Tracing the gastro-hepatic omentum from this point to the left, its two layers separate to enclose the stomach, after whi^h they pass to the gastric surface of the spleen as the gastro-splenic omentum. The two layers of this omentum are anterior and posterior, and they contain between them the vasa brevia of the splenic artery. At the spleen the two layers are immediately in front of the hilum. The anterior layer now takes temporary leave of the posterior layer, and turns completely round the spleen, covering its gastric, ba^al, phrenic, and renal surfaces in succes- sion. On leaving the renal surface of the organ it again passes to the gastric surface, but it is now behind the hilum. Here it meets the posterior layer of the gastro-splenic omentum, which had remained meanwhile stationary immediately in front of the hilum. These two layers now pass backwards to the anterior surface of the left kidney at its upper extremity, and close to its external border, thus forming the lieno-renal ligament. The two layers of this ligament are disposed as right and left, and between them are the splenic branches of the splenic artery. The right layer corresponds with the posterior layer of the gastro-splenic omentum, and the left layer with the anterior layer of that omentum. The right layer of the lieno-renal ligament, after leaving the left kidney, passes to the right over the aorta and inferior vena cava. As it covers the latter vessel it is placed behind the foramen of Winslow, 7M A MANUAL OF ANATOMY It then continues its course to the right, and, having given a partial covering to the front of the right kidney, it passes over the right lateral and anterior wall of the abdomen as far as the middle line. The left layer of the lieno-renal ligament, after leaving the left kidney, passes over the left lateral and anterior wall of the abdomen, and, on arriving at the middle line, it becomes continuous with the right layer, which has just been traced as far as the middle line. Along the posterior surface of the anterior wall of the abdo- men in the middle line, above the level of the umbilicus, the peri- toneum meets with the obliterated umbilical vein or round ligament Stomach Visceral Peritoneum \ Parietal Peritoneum Gastro-hepatic Omentum ^ Hepatic Artery Vena Portse mmon Bile-duct Left Kidney Abdominal Aorta I 12th Thoracic Vertebra \ Right Kidney Inferior Vena Cava Fig. 305. -Diagram of the Peritoneum at the Level of the Foramen OF WiNSLOw (Transverse Section). of the liver, around which it is reflected, and here it is carried ofi from the abdominal wall to form part of the falciform or suspensory ligament. Another way to trace the peritoneum transversely at the level of the foramen of Winslow is to commence just behind that fora- men. Beginning at this point, the peritoneum, which covers the inferior vena cava, passes to the right, and, having given a partial covering to the front of the right kidney, it is continued over the right lateral wall of the abdomen, and thence over the right half of the anterior wall. At the middle line, above the level of the umbilicus, it meets with the obliterated umbilical vein or round ligament of the liver, around which it is reflected, and here it is carried off from the abdominal wall to form part of the falciform or suspensory ligament. It then continues its course over the left THE ABDOAfEN 715 half of the anterior abdominal wall and the left lateral wall, whence it passes on to the front of the left kidney at the upper part, close to the external border. From this point it passes to the right over the posterior wall ot the abdomen, covering the aorta and inferior vena cava, and so it arrives at a point behind the foramen of Winslow. Between the left kidney and the hilum of the spleen the peritoneum forms the lieno-renal ligament, and between the gastric surface of the spleen, just in front of the hilum, and the posterior aspect of the cardiac end of the stomach it forms the gastro-splenic omentum. The two layers of this omentum, having separated, enclose the stomach. They then meet at the small curvature to form the gastro-hepatic omentum, the layers of which, when followed to the right, arrive at the front of the foramen of Winslow. Small Intestine Abdominal Aorta , The Mesentery , Parietal Peritoneum , Inferior Vena Cava Descending Colon / Ascending Colon Section of Lumbar Vertebra Fig. 306. — Diagram of the Peritoneum at the Level of the Umbilicus (Transverse Section). Below the Transverse Colon, or at the Level of the Umbilicus. — Commencing at the middle line and passing to the right, the peri- toneum covers the right half of the anterior abdominal wall and the right lateral wall as far as the lumbar region. It then covers the right side, anterior surface, and left side of the ascending colon, whence it passes over the front of the right kidney at its lower and inner part. Thereafter it is reflected over the inferior vena cava, and, meeting with the superior mesenteric vessels, it is carried off by them to the jejunum and ileum, both of which it invests. It is then conducted back again to the vertebral column by the superior mesenteric vessels, thus forming the mesentery proper. It next passes to the left over the aorta, and, having partially covered the front of the left kidney at its lower and inner part,' it meets with the descending colon in the left lumbar region, which it covers on the right side, anterior surface, and left side. Thereafter it is 71 6 A MANUAL OF ANATOMY reflected over the left lateral and left half of the anterior wall of the abdomen as far as the middle line. The relations of the peritoneum to the duodenum, pancreas, and kidneys will be described when these viscera fall to be considered. Omenta. — ^The great or gastro-colic omentum (epiploon) extends from the great curvature of the stomach and first inch of the first part of the duodenum to the transverse colon, descending in its course usually as low as the pelvic brim, and lower on the left side than on the right, which accounts for the greater frequency of an omental hernia on the left side. It covers the coils of the jejunum and ileum. At the great curvature of the stomach it contains between its two layers the right and left gastro-epiploic arteries, and the epiploic branches of these vessels, which are long and slender, descend into it. The great omentum is often of small size, thus leaving many of the coils of the small intestine uncovered, or it may even be displaced into the left hypochondrium. It is composed of four layers of peritoneum, two of which descend from the great curvature of the stomach, inseparably united, to the region of the pelvic brim, these being called the anterior or descend- ing layers. The other two layers, also inseparably united, ascend from the region of the pelvic brim to the transverse colon, these being called the posterior or ascending layers. Between the two anterior and the two posterior layers there is usually, in healthy persons, a space which represents a part of the small cavity of the peritoneum, and is known as the bag or sac of the great omentum. In many cases, however, this space is scarcely demonstrable on account of adhesions. It is most conspicuous a little below the great curvature of the stomach. The small or gastro-hepatie omentum extends from the small curvature of the stomach and first inch of the first part of the duodenum to the portal fissure of the liver, and also to the venosal fissure. It is composed of two layers of peritoneum which, at the small curvature of the stomach, contain between them the anterior and posterior branches of the gastric and pyloric arteries. For the most part its two layers are inseparably united, but at its right border, which is free, it contains between them the following structures : (i) the common bile-duct to the right side ; (2) the hepatic artery, invested by the hepatic plexus of sympathetic nerves, to the left side ; (3) the vena portae, which lies between these two, and on a plane posterior to both ; and (4) lymphatic vessels. This right or free border, with the foregoing contents, lies in front of the foramen of Winslow. The left border of the gastro-hepatie omentum is short on account of the oblique position of the stomach, and is attached to the diaphragm between the caval and oesophageal openings. The anterior layer of the small omentum is formed by peritoneum belonging to the great sac, and the posterior layer by that belonging to the small sac, these two layers becoming continuous with each other round the right or free border of the omental fold in front of the foramen of Winslow, THE ABDOMEN 7^7 The gastro-splenic omentum extends between the posterior surface of the cardiac end of the stomach and the gastric surface of the spleen just in front of the hilum. It is composed of two layers, anterior and posterior, which are continuous with the t^vo anterior layers of the great omentum. The anterior layer is formed by peritoneum belonging to the great sac, and the posterior layer by that belonging to the small sac. The fold contains between its two layers the vasa brevia of the splenic artery. Mesenteries. — The mesentery proper is the fold of peritoneum which attaches the jejunum and ileum to the vertebral column. Its vertebral border is called the root, and is comparatively short, measuring from 5 to 6 inches in length. Its line of attach- ment extends from the commencement of the jejunum on the left side of the body of the second lumbar vertebra, at the anterior border of the pancreas, to the termination of the ileum in the right iliac fossa, near the right sacro-iliac articulation. This line of attachment passes obliquely from left to right, and in this course the root of the mesentery proper crosses in succession the third part of the duodenum, aorta, infeiior vena cava, and right psoas magnus. The other border of the mesentery proper is called the intestinal border, and is attached to the jejunum and ileum throughout their whole length. This border is of considerable length, and equals that of the jejunum and ileum. The widening of the mesentery proper takes place gradually, so that it is thrown into a number of folds, an arrangement which accounts for the coils of the jejunum and ileum. I to average breadth, from the root to the intestinal border, is about 8 inches. The fold is composed of two layers of peritoneum, right or superior, and left or inferior. The right or superior layer is continuous with the inferior layer of the transveise meso-colon, and with the peritoneum which covers the ascending colon, whilst the left or inferior layer is continuous with the peri- toneum which covers the descending colon. Both layers are formed by peritoneum belonging to the great sac. The two layers contain between them the following structures: (i) the superior mesenteric vessels, and the rami intestini tenuis ; (2) the superior mesenteric plexus of sympathetic nerves, and its secondary off- shoots ; (3) the lacteal vessels ; and (4) the mesenteric lymphatic glands. In some cases the mesentery proper presents one or more openings, known as mesenteric holes, which may be congenital or traumatic. If a portion of intestine slipped through one of these holes a mesen- teric hernia wovild result, and, if the hole is situated in one layer only^ the herniated portion of intestine would take up a position in the space between the two layers. These openings are liable to be met with in that portion of the mesentery proper which is attached to the lower part of the ileum, within the arch formed by the ileo-colic branch of the superior mesenteric arterv and the last ramus intestini tenuis (Treves). The appendicular mesentery or meso-appendix is a fold of 71 8 A MANUAL OF ANATOMY peritoneum which is derived from the left or inferior layer of the mesentery proper near the terminal part of the ileum. It is triangulai, and usually lies obliquely. Its right end reaches in a pointed manner to the ileo-caecal junction, and its left end forms a concave free border which transmits the appendicular vessels and sympathetic plexus of nerves. It seldom extends for more than half or two-thirds along the appendix, which is thus rendered more or less convoluted or serpentine. It may, however, extend along its entire length. In some cases it lies vertically, and then it loses its hold upon the mesentery proper, its attachment being transferred to the caecum, or right fascia iliaca, or even to the back of the ascending colon. The base of the appendix is sometimes destitute of a mesentery, in which cases that portion of it is closely connected to the posterior aspect of the caecum. Occasionally the entire meso-appendix is awanting, and then the appendix is found adhering to the back of the caecum. The meso-appendix may present a small opening through which a portion of bowel may pass and become strangulated. In very rare cases the meso-appendix is disposed in such a manner as to divide the ileo-caecal fossa into an upper and a lower compartment. The transverse meso-colon is a broad fold of peritoneum which extends between the transverse colon and the posterior abdominat wall at the anterior border of the pancreas. Its layers contain between them the middle colic vessels, sympathetic nerves, and the lymphatics of the transverse colon. Mesenteric holes may be present in the transverse meso-colon, under which circumstances a meso-colic hernia may occur. The pelvic meso-colon is a fold of peritoneum which attaches the pelvic colon to the front of the sacrum. It extends from the inner border of the left psoas magnus (covered by the left fascia iliaca) near the left sacro-iliac articulation to the front of the third sacral vertebra, and its length is such as to render the pelvic colon freely movable. Its line of attachment posteriorly extends obliquely from left to right, and it is composed of two layers disposed laterally, and containing between them the superior hemorrhoidal vessels, sympathetic nerves, lymphatic vessels, and a certain amount of fat. The ascending colon, descending colon, and iliac colon are each, in normal circumstances, devoid of a mesentery. Occasionally, however, an ascending meso-colon, a descending meso-colon, and an iliac meso-colon are present. Peritoneal Ligaments — Ligaments of the Liver. — The peritoneal ligaments of the liver are four in number (the round ligament not being regarded as of a peritoneal nature), and they are as follows : the falciform ligament, the coronary ligament, the right lateral ligament, and the left lateral ligament. The falciform ligament is also known as the ligamentum latum and suspensory ligament. It extends between the inferior surface of the diaphragm and the posterior surface of the anterior abdominal THE ABDOMEN 7»9 wall on the one hand and the superior and anterior surfaces of the liver on the other. Its base, which is free, extends from the um- bilicus to the interlobar notch of the liver, and contains between its two layers the obliterated umbilical vein or round ligament. The line of attachment of the ligament to the anterior and superior surfaces of the liver map the organ out into a right and left lobe, and along tliis line the two layers of the ligament separate from each other, the right layer extending over the right lobe and the left qver the left lobe. Near the postero-superior border of the liver the two layers of the ligament diverge somewhat abruptly, and leave between them a small triangular area which is destitute of peritoneum. Thereafter they become continuous, on either side, with the superior layer of the coronary ligament. The coronary ligament is also known as the posterior ligament. It is composed of two layers of peritoneum, superior and inferior, which are attached to the postero-superior and postero- inferior borders of the liver on the one hand, and the diaphragm on the other. These layers are separated from each other by an interval, which corresponds with the uncovered area of the right lobe of the liver. The superior layer is continuous with the falciform ligament, and the inferior layer is continuous with the peritoneum which covers the inferior vena cava and the fiont of the right kidney. The right and left lateral or triangular ligaments are situated at the extreme right and ^left ends of the coronary ligament, and are formed by the meeting, at these points, of the two layers of that ligament. The round ligament of the liver, though not a peritoneal ligament, may here be described. It is a fibrous cord formed by the obliterated umbilical vein, and is contained \\ithin the base of the falciform ligament between the umbilicus and the interlobar notch of the liver, its course between these points being upwards, backwards, and to the right. At the interlobar notch it enters the umbilical fissure on the inferior surface of the liver, and terminates by joining the left branch of the vena portae. A minute portion of the lumen of the left umbilical vein remains pervious within the round Ugament of the Uver. This per\'ious portion communicates at the portal fissure of the liver with the left division of the portal vein, and at the umbihcus it is connected with the epigastric veins of the anterior abdominal wall. It thus forms a channel of communication between the left division of the portal vein and the systemic veins of the anterior abdominal wall. Through this pervious portion of the left umbiUcal vein the blood can flow towards the umbihcus. The anastomosis thus estabhshed between the left umbihcal vein and the epigastric veins of the anterior abdominal wall explains the enlargement of the veins of the anterior abdominal wall in cases of portal obstruction within the liver. A small portion of the right primitive umbiUcal vein near the umbilicus also remams pervious, and this portion hkewise forms an anastomosis with the epigastric veins of the anterior abdominal wall. On the surface of, or within, the round hgament of the Uver there are a few very smaU veins, called parambilical veins. These anastomose at the um- bihcus with the epigastric veins of the anterior abdominal wall, and superiorly mey are connected with the left division of the portal vein. They are also concerned in the enlargement of the veins of the anterior abdominal wall in cases of portal obstruction within the Uver. 7^<> A MANUAL OF ANATOMY The ligament of the stomach is called the gastro-phrenic liga- ment. It is of small size, and extends between the region of the uncovered trigone of the stomach and the inferior surface of the diaphragm, lying immediately to the left of the lower end of the oesophagus. The ligaments of the spleen are two in number, namely, phreno- splenic or lieno-phrenic, and lieno-renal. The phreno-splenic or lieno-phrenic ligament is also called the suspensory ligament. It extends between the spleen, near its upper extremity, and the contiguous part of the diaphragm. The lieno- renal ligament extends from the hilum of the spleen to the front of the left kidney at its upper and outer part. Its direction is backwards, and it is composed of two layers of peritoneum, right and left, which contain between them the splenic branches of the * splenic artery. The right layer coiresponds with the posterior layer of the gastro-splenic omentum, and the left with the anterior layer of that omentum. The phreno-colic or costo-colic ligament {sustentaculum lienis) extends between the splenic flexure of the colon and the diaphragm opposite the tenth or eleventh left rib. It is triangular, and its surfaces are superior and inferior, its anterior border being free. It forms a platform upon which the basal surface of the spleen rests. The sustentaculum hepatis is a fold of peritoneum which is sometimes met with in connection with the ascending colon. (Treves found it in eighteen out of one hundred bodies.) When present it extends from the right side of the ascending colon to the abdominal wall at a point a little above the level of the iliac crest. Its free border looks forwards, and it forms a shelf which supports the right margin of the liver. Cavity of the Peritoneum. — The peritoneal cavity is divided into two compartments, great and small, which communicate with each other through the foramen of Winslow behind the right or free border of the gastro-hepatic omentum. The great cavity or sac is the space which is exposed to view after opening the abdominal cavity. It is separated from the small sac by the liver, gastro-hepatic omentum, stomach, gastro-colic omen- tum, gastro-splenic omentum, lieno-renal ligament, and transverse meso-colon. The small cavity or sac is an offshoot from the great sac, the introversion taking place at the foramen of Winslow. It extends upwards behind the stomach to the posterior part of the inferior surface of the diaphragm and the Spigelian lobe of the liver, and downwards into the gastro-colic omentum, the part of it within that omentum being known as the bag or sac of the great omentum. Boundaries of the Small Sac — Anterior. — From below u]nvards, the two anterior or descending layers of the gastro-colic omentum, the posterior surface of the stomach, the gastro-hepatic omentum, and the posterior surface of the Spigelian lobe of the liver. Posterior. — From below upwards, the two posterior or ascending layers of the gastro-colic omentum, the transverse colon, the transverse meso- colon, and the asceftding layer of the transverse mcso-colon. THE ABDOMEN 721 Superior. — The posterior part of the inferior surface of the diaphragm. Inferior. — ^The bend of the gastro-colic omentum, where the two anterior or descending layers are folded backwards to become the two posterior or ascending layers. Left. — The spleen ; the gastro-splenic omentum ; the lieno-renal ligament ; and the left border of the gastro-colic omentum. In a great many cases that part of the small sac which is con- tained within the gastro-colic omentum is very limited in its down- ward extent, on accoxmt of adhesions having formed between the layers of the great omentum. Foramen of Winslow. — ^This is the opening by which the great and small sacs of the peritoneum communicate with each other. It is situated behind the right or free border of the gastro-hepatic omentum, on a level with the body of the 12th thoracic vertebra. Its direction is fonvards and to the right, and it admits of the passage of one finger, and in some cases of two fingers. It is, however, often blocked by inflammatory products. Boundaries — Anterior. — ^The right or free border of the gastro- hepatic omentum, containing bet^veen its two layers (i) the common bile-duct, to the right side ; (2) the hepatic artery, invested by the hepatic plexus of sympathetic nerves, to the left side ; (3) the vena |x>rtae, which lies between these two, on a plane posterior to both ; and (4) lymphatic vessels. Posterior. — ^The inferior vena cava covered by peritoneum. Superior. — ^The caudate lobe of the liver. Inferior. — ^The first part of the duodenum, and the hepatic artery in the first part of its course, as it curves forwards and up- wards from the coeliac axis. Wlien the foramen is blocked by inflammatory products, if fluid should be effused into the small sac the condition known as hydrops saccatus would result. It is possible for a loop of bowel to pass through the foramen, thus forming one variety of internal hernia. Peritoneal Fosss or Pouches. — The peritoneum presents in certain situa- tions small pockets, which are known as peritoneal fossae or pouches. Their importance consists in the fact that a small portion of intestine may enter one or other of them and become strangulated, thus constituting an internal hernia, which, except in the cases of the inguinal pouches, is called a retro-peritoneal hernia. The fossae, according to their situation, are called duodenal, duodeno-jejunal, peri-caecal, and intersigmoid. Duodenal Fossae. — Four varieties of duodenal fossae are met with in con- nection with the terminal part of the duodenum, namely, inferior duodenal, superior duodenal, para-duodenal, and retro-duodenal (Jonnesco). The inferior duodenal fossa is the most common and largest. It is situated on the left side of the terminal part of the duodenum -^nd opens upwards. It is bounded in front by a thin triangular portion of ; ..itoneum, called the inferior duodenal fold, which presents a free cresceudc border or base superiorly. The fossa may admit the thumb, and may be nearly an inch deep. It is said to be present in 75 per cent, of cases (Jonnesco). The superior duodenal fossa is less constant, and of smaller size, than the inferior, and lies about an inch above it. It opens downwards, and its orifice faces that of the inferior duodenal fossa. It may admit the tip of a finger. It is bounded in front by a thin triangular portion of peritoneum, called the superior duodenal fold, which presents a free crescentic border or base in- feriorly. The fossa is said to be present in 50 per cent, of cases (Jonnesco). 40 722 A MANUAL OF ANATOMY The para-duodenal fossa is situated a little to the left of the terminal part of the duodenum. It is bounded on the left side by a faint fold of peri- toneum, called the inferior mesenteric fold, which is produced by the inferior mesenteric vein. The retro-duodenal fossa is si uated behind the terminal part of the duodenum. Duodeno-jejunal Fossa.— This fossa is situated on the left side of the duodeno-jejunal flexure, and leads upwards and towards the left side. It is bounded by two free portions of peritoneum, called the duodeno-raesocolic folds, and it has the pancreas above, the left kidney on the left, and the aorta on the right. It is of small size, and may admit the tip of the httle linger. It is said to be present in from 15 to 20 per cent, of cases. Perl-Caecal Fossae. — These fossae are three in number, namely, ileo-coHc, ileo-caecal, and retro-caecal, Superior Duodenal Fossg Inferior Duodenal Fossa Fig. 307. — Duodenal Foss.^. The ileo-colic fossa is situated in the angle between the termination of the ileum and the commencement of the ascending colon, in front of the adjacent part of the mesentery proper. It opens inwards, and is bounded in front by a portion of the peritoneum, called the ileo-colic fold, which is produced by the anterior caecal artery; behind, by the mesentery proper; below, by the ileum ; and, on the right side, by the commencement of the ascending colon. In size and depth the fossa is small. The ileo-csecal fossa is situated in the angle of junction of the ileum and caecum, and opens downwards and inwards. It may extend upwards for a variable distance behind the ascending colon, and sometimes is capable of admitting two fingers. It is bounded anteriorly and infcriorly by a portion of peritoneum, called the ileo-csecal told (bloodless fold of Treves) ; posteriorly, by the meso-appendix; externally, by the caecum; and superiorly, by the posterior aspect of the terminal part of the ileum and the inferior layer of the mesentery proper. The importance of this fossa consists in the fact that it often contains the vermiform appendix, or a portion of it. The retro-csecal fossa is situated behind the caecum, on the outer side of the meso-appendix. It may extend upwards for a variable distance behind the ascending colon, and is sometimes divided into an external and internal com- partment. It occasionally contains the vermiform appendix, or a portio^i of it. Intersigmoid Fossa. — This fossa is of rare occurrence in the adult, but is frequently present in early infancy. It is situated on the left side of the pslvic meso-colon near the bifurcation of the left common iliac artery, and THE ABDOMEN Ileocolic Fold Ileo-colic Fossa 723 \ Iloo-CEcal Fossa Ileo-caecal Fold Vermifomi Appendix Fig. 308. -The Ileo-colic and iLEo-CitCAL Foss«. Vermiform Appendix ■ ' Ileo-csecal Fossa Retro-caecal Fossa Fig. 309. — The Retro-cjecal and Ileo-c^cal Foss/E. 724 A MANUAL OF ANATOMY is produced by a fold of peritoneum which contains the sigmoid artery. It opens downwards and towards the left side. In early life the alimentary tube is very short and straight. Its ventral and dorsal aspects are attached to the ventral and dorsal body-walls by meso- dermic folds, which constitute the primitive ventral and dorsal mesenterjes. The primitive ventral mesentery extends from the pharynx to the duodenum. Its cephalic or cardiac portion gives rise to the ventral and dorsal cardiac mesenteries or mesocardia. Its caudal or posterior part forms the ventral or anterior gastro-duodenal mesentery. The primitive dorsal mesentery connects the dorsal aspect of the entire primitive alimentary tube to the dorsal body-wall. The ventral gastro-duodenal mesentery extends from the ventral aspect of the primitive stomach and upper part of the duodenum to the ventral body- wall on the cephalic side of the umbilicus. It is closely associated with the lower layer of the septum transversum, within which the liver undergoes development. As the liver descends, it carries with it the ventral gastro- duodenal mesentery, which it divides into two parts. The part between the liver and (i) the ventral portion of the diaphragm, and (2) the ventral wall of the abdomen as low as the umbilicus, forms the falciform ligament of the liver ; and the part between the liver (portal fissure) and stomach (small curvature) forms the small or gastro-hepatic omentum. The primitive dorsal mesentery receives names corresponding to the parts of the alimentary tube with which it is connected. Thus, in the abdomen, there are the mesogastrium, mesoduodenum, mesojejunum, meso-ileum, meso- appendix, mesocolon (ascending, descending, iliac and pelvic), and meso-rectum. As development proceeds, these mesenteric folds undergo important changes. Mesogastrium. — This is the primitive posterior mesentery of the stomach, and, as stated, is a portion of the primitive dorsal mesentery. It consists of two layers of peritoneum, which extend between the great curvature of the stomach (at this period directed backwards) and the dorsal body-wall, where the two layers enclose the pancreas. As the stomach changes its position, the pyloric end being tilted forwards, and the whole organ along with the duodenum turning round upon its right side, the great curvature, which originally looked backwards, is now directed downwards and towards the left side. During this change the mesogastrium becomes stretched. Thereafter a gradual extension of the mesogastrium takes place in a downward direction from the great curvature of the stomach over the transverse colon, jejunum, and ileum; and in this manier the great omentum is formed. At first the two posterior or ascending layers of the great omentun^ pass over the front and upper part of the transverse colon without separating to enclose it, and then pass backwards to the posterior abdominal wall, where they enclose the pancreas. The lower layer is now reflected ventralwards from the posterior abdominal wall until it meets with the transverse colon. Having invested this part of the gut, it retraces its steps to the posterior abdominal wall, thus forming the two layers which constitute the primitive transverse meso-COlon. On referring to Fig. 310, it will be seen that, in this region, there are four layers of peritoneum at this stage. The upper two layers are contin- uous with the two posterior or ascending layers of the great omentum, and represent the original mesogastrium. The lower two layers belong to the primitive transverse mesocolon. Subsequently the lower of the upper two layers and the upper of the lower two layers unite and disappear. There are thus left only two layers of peritoneum, which constitute the transverse meso- colon of the adult, the lower layer of which is part of the primitive transverse mesocolon, whilst the upper layer is part of the great omentum. In fact, both layers are ultimately derived from the two posterior or ascending layers of the great omentum. As the result of these changes, the pancreas comes eventually to lie behind the peritoneum, whereas it was originally contained between the two layers of the mesogastrium. The remaining portions of the primitive dorsal mesentery are disposed as follows : THE ABDOMEN 725 Transverse Meso\xoden\JiVa.; primitive intestinal tube. T.C. Transverse Colon ; S.I. Small Intestine. Blood-suppIy of the Intestinal Canal. — ^The intestinal canal receives its blood-supply from the superior and inferior mesenteric arteries, with the exception of the upper portion of the duodenum, and a portion of the rectum. Superior Mesenteric Artery. — ^This vessel springs from the front of the abdominal aorta about \ inch below the coeliac axis. It is at first directed downwards behind the body of the pancreas and the splenic vein. It then passes downwards and forwards in front of the uncinate process of the pancreas and third part of the duodenum, at the lower border of which latter it takes up its position between the two layers of the mesentery proper. The vessel then passes downwards near the root p^^ 311.— End o- of the mesentery, its course being slightly thelium of a Serous curved with the convexitv towards the left :Membrane. 726 A MANUAL OF ANATOMY side, and it terminates near the ileo-caecal junction in the last ramus intestini tenuis, which anastomoses with the ileal branch of the ileo-colic artery. The vessel is surrounded by a tough sheath formed by the superior mesenteric sympathetic plexus. Branches — Left Branches. — These are called the rami intestini tenuis, and are at least twelve in number. They pass downwards Fig. 312. — The Superior Mesenteric Artery and its Branches (after Tiedemann). 1. Superior Mesenteric Artery 2. Rami Intestini Tenuis 3. Ileo-colic 4. Right Colic 5. Middle Colic 6. Inferior Pancreatico-diiodenal 7. Duodenum 8. Jejunum 9. Ileum 10. Caecum 11. Ascending Colon 12. Transverse Colon and to the left between the two layers of the mesentery proper, and supply the jejunum and ileum. After a course of about 2 inches each divides into two branches, which by their junction with con- tiguous branches give rise to primary arches. From the convexities of these arches small branches are given off, which act in a similar manner, and give rise to secondary arches. This disposition of arteries goes on so as to form tertiary, quaternary, and even THE ABDOME}i '/*7 quinary arches. The minute vessels arising from the arches of the last tier enter the wall of the jejunum and ileum along the mesen- teric border, where each divides into two branches, which encircle the bowel beneath its serous covering. From the rings thus formed branches penetrate deeply to reach the mucous coat. Each ramus intestini tenuis, as well as its various branches, conducts to the bowel an offshoot of the superior mesenteric sympathetic plexus. Right Branches — Ileo-colic Artery. — ^This vessel is the lowest of the right branches, and in many cases it arises in common with the right colic. Its course is downwards and out\vards towards the right iliac fossa behind the peritoneum, and it divides into two branches, colic and ileo-caecal. The colic branch passes upwards and forms an arch with the descending branch of the right colic, from which branches proceed to the lower part of the ascending colon. The ileo-ccecal branch passes to the upper part of the ileo-caecal junction, where it furnishes the following branches: ileal, to the terminal part of the ileum, where it anastomoses with the last ramus intestini tenuis ; appendicular, which, descending behind the terminal part of the ileum, passes between the two layers of the meso-appendix, and so reaches the vermiform appendix; anterior ccecal, to the front of the caecrim ; and posterior ccecal, to its posterior aspect. Right Colic Artery.— This is the second branch in order from below upwards, and in many cases it arises in conmion with the ileo-colic. Its course is transversely to the right behind the peritoneum, and it divides into two branches, descending and ascending. The descend- ing branch anastomoses with the colic branch of the ileo-colic, and the ascending branch with the right branch of the middle colic. The arches thus formed furnish branches to the ascending colon, which in their course form secondary and tertiary arches. Middle Colic Artery. — ^This vessel arises from the right side and front of the main trunk about 2 inches above the right colic, on a level with the lower border of the third part of the duodenum. Its course is forwards between the two layers of the transverse meso- colon, and it divides into a short right and a long left branch. The right branch anastomoses with the ascending branch of the right colic, and the left branch with the ascending branch of the left colic from the inferior mesenteric. The arches thus formed fuirnish branches to the middle colon, which in their course form secondary and tertiary arches. Inferior Pancreatico-duodenal Artery. — ^This small vessel usually arises from the right side of the main trunk opposite the upper border of the third part of the duodenum, but it may spring from the first ramus intestini tenuis. Its course is to the right behind the superior mesenteric vein, and between the head of the pancreas and the third part of the duodenum. Thereafter it ascends for a little between the head of the pancreas and the second part of the duodenum, and anastomoses with the superior pancreatico- duodenal of the gastro-duodenal from the hepatic. It supplies the 728 A MANUAL OP ANATOMY adjacent portions of the pancreas and duodenum. The vessel is accompanied by an offshoot from the superior mesenteric sym- pathetic plexus, and, when it arises from the first ramus intestini tenuis, it passes behind the superior mesenteric artery. Superior Mesenteric Vein. — This vein is formed by tributaries which return the blood from the parts of the intestinal canal supplied by the superior mesenteric artery, and it receives in addition the right gastro-epiploic vein. It ascends on the right side of the superior mesenteric artery. After leaving the mesentery it passes over the third part of the duodenum and uncinate process of the pancreas, and finally behind the neck of the latter organ, where it joins the splenic vein to form the vena portae. The vessel and its tributaries are destitute of valves, so that the blood can regurgitate in cases of portal obstruction. Superior Mesenteric Sympathetic Plexus. — ^This plexus is derived from the solar plexus. It closely surrounds the superior mesenteric artery in the form of a tough sheath, and it furnishes offshoots which accompany all the branches of that vessel. Lymphatic Vessels of Small Intestine. — ^These which are called lacteals, originate in the villi of the mucous mem- brane of the small Fig. 313. — Portion of Jejunum with its Mesentery, i^^^estine (see p. showingLacteal Vessels AND Mesenteric Glands. 79^)- They leave the wall of the bowel at the mesenteric border, those of the jejunum exceeding in number those of the ileum . Within the mesentery they take a course inwards and upwards, becoming, in succession, the afferent and efferent vessels of the groups of mesenteric glands. At the root of the superior mesenteric artery the lacteals, which have now emerged from the innermost mesenteric glands, terminate in from one to four lymphatic trunks, which open into the receptaculum chyli. Superior Mesenteric Glands. — ^These are about 150 in number, and are situated within the mesentery proper and along the course of the trunk of the superior mesenteric artery. In health their average size is about that of a small pea, except along the course of the main artery, where they are somewhat larger, and they are more numerous in the jejunal than in the ileal mesentery. They receive the lacteals from the lower part of the duodenum, the jejunum, and the ileum, and also the lymphatics from the ascending and transverse colon. There are no glands in the portion of mesentery close to the intestine THE ABDOMEN 749 for about 2 inches. In the ileo-colic angle there is a special group of glands, called the ileo-colic glands. These receive afferent vessels from the terminal part of the ileum, the caecxun, and the vermiform appendix, and their efferent vessels pass to the innermost group of superior mesenteric glands. Lymphatic Vessels of Ascending and Transverse Colon. — ^The l\-mphatics of the ascending colon terminate in two ways, as follows: those from the lower part pass to the innermost group of superior mesenteric glands, whilst those from the upper part go to the mesocolic glands . The lymphatics of the transverse colon become afferent vessels of the me- so-colic glands, the efferent ves- sels of which join the terminal in- testinal l\Tnpha- tic trunks from the superior mes- enteric glands. Inferior Mes- enteric Artery. — Tliis vessel arises from the front of the abdominal aorta towards its left side, about 1 2- inches above the bifurcation. Its course is downwards and to the left to- wards the left iliac fossa. It is behind the peritoneum, and Ues first upon the aorta, and then on its left side, where it is supported by the psoas magnus. Subsequently it is continued as the superior hemorrhoidal artery over the left common iliac vessels. The artery is surroimded by the inferior mesenteric sympathetic plexus. Branches— Left Colic Artery. — This vessel passes transversely to the left, behind the peritonevun and over the lower part of th3 Fig. 314. — The Inferior Mesenteric Artery and ITS Branches (after Tiedemann). 1. Superior Mesenteric Artery 2. Middle Colic 3. Inferior Mesenteric 4. Left Colic 5. Arteriae Sigmoide«e 6. Superior Hemorrhoidal 7. Transverse Colon 8. Descending Colon 9. Iliac Colon 10. Peh-ic Colon 730 A MANUAL OP ANATOMV left kidney, and it divides into two branches, ascending and descending. The ascending branch anastomoses with the left branch of the middle colic, and the descending branch with the ascending branch of the superior sigmoid artery. The arches thus formed supply branches to the left extremity of the transverse colon and the descending colon, which in their course form secondary and tertiary arches. Sigmoid Arteries. — ^These are usually three in number, superior, middle, and inferior, but they frequently arise as a single trunk. They pass downwards and to the left over the psoas magnus, and supply the lower part of the descending colon, the iliac colon, and the pelvic colon. The superior sigmoid artery, which lies, as a rule, behind the peritoneum, divides into two branches, ascending and descending. The ascending branch forms an arch with the descending branch of the left colic, and the descending branch passes between the two layers of the pelvic meso-colon, where it anastomoses with the middle sigmoid artery. The middle and inferior sigmoid arteries pass between the two layers of the pelvic meso-colon, where they form arches with the descending branch of the superior sigmoid, with one another, and with the superior hemorrhoidal artery. The branches of these arches form secondary, or even tertiary, arches before the terminal branches are given off. The superior hemorrhoidal artery is the continuation of the inferior mesenteric, and will be found described on p. 875, inferior Mesenteric Vein. — ^This vein is formed by tributaries which return the blood from the parts of the large intestine supplied by the inferior mesenteric artery. It lies at first near the left side of its artery, but soon leaves it and ascends on the left psoas magnus, where it lies on the left side of the aorta behind the peri- toneum. In this course it crosses the left spermatic artery and left renal vein. It finally passes behind the pancreas with an inclination to the right, and usually terminates in the splenic vein. It may, however, open into the angle of junction of the splenic and superior mesenteric veins, or into the superior mesenteric vein, near its termination. The inferior meseftteric vein and its tributaries are destitute of valves, so that the blood can regurgitate in cases of portal obstruction. Inferior Mesenteric Sympathetic Plexus. — This plexus is derived from the left half of the aortic plexus. It forms a tough sheath round the artery, and furnishes offshoots with its branches. Inferior Mesenteric Glands. — These glands are situated around the root, and along the trunk and branches, of the inferior mesenteric artery. Those around the root of the vessel constitute the inferior mesenteric group of the pre-aortic glands. Their afferent vessels are derived from (i) the lower part of the descending colon, (2) the iliac colon, (3) the pelvic colon, and (4) some of the lymphatics of the rectum. Their efferent vessels pass to the inferior mesenteric group of pre- aortic glands. THE ABDOMEN 731 Lymphatic Vpssels of Descending, Iliac, and Pelvi Colon. — The lymphatics of the descending colon terminate in two ways, as follows : those of the upper part pass to the meso-colic glands, whilst those of the lower part join the left lymphatic trunk from the median lumbar glands. The lymphatics of the iliac and pelvic colon also join the left hnnphatic trunk from the median Itmibar glands. Lymphatic Glands of Large Intestine (colic glands). — These glands are arranged in groups, named according to the portion of intestine to which they are related, and they are situated behind the respective parts, except those belonging to the transverse colon which lie between the two layers of the transverse meso-colon, and are known as the meso-colic glands. Position and Connections of the Duodenum. — The duodemmi is the first part of the small intestine. It measures from 10 to 11 inches in length, and is the widest and least movable part. It extends from the pylorus to the left side of the body of the second lumbar vertebra, where it ends in the jejimtun. It describes a somewhat U-shaped cur\'e with the concavity directed upwards and to the left in close adaptation to the head of the pancreas. It is devoid of a mesentery, and is divided into three parts, first, second, and third. First or Superior Part. — ^The first part extends from the pylorus to the right side of the neck of the gall-bladder. It lies in the epi- gastric region, and is about 2 inches in length, its direction being upwards, backwards, and to the right when the stomach is empty, but directly backwards when that organ is distended. The gastro- hepatic omentum furnishes a complete covering to about the first inch, and the remainder is covered by peritoneum only in front. The first part is therefore comparatively movable. Relations — Superior and Anterior.— The quadrate lobe of the liver and the gall-bladder. Posterior. — ^The vena portae, gastro- duodenal artery, common bile-duct, and neck of the pancreas. Inferior. — ^The head of the pancreas. The first part lies below the foramen of Winslow. Second or Descending Part. — This part extends from the right side of the neck of the gall-bladder to the right side of the body of the third (sometimes fourth) lumbar vertebra. It lies at first in the epigastric, and subsequently in the umbilical, region ; its length is from 3 to 4 inches, and its direction is almost vertically downwards behind the right extremity of the transverse colon. The anterior surface is covered by peritoneum, except opposite the transverse colon. If there is no transverse meso-colon at this point, there is a distinct strip near the centre left uncovered and connected to the colon by areolar tissue. If, however, there is a transverse meso-colon present at this point, the bare area is trifling. The posterior surface is destitute of peritoneum. The second part is therefore very immovable. Relations — Anterior. — From above downwards the gall-bladder near its neck, the right extremity of the transverse colon, and some coils of the small intestine. Posterior. — ^The anterior sm-face of the right kidney near the hilwn, and the inferior vena cava. Right. — 734 A MANUAL OF ANATOMY The hepatic flexure of the colon, and the right lobe of the liver. Left. — ^The head of the pancreas, with the common bile-duct behind, and the superior pancreatico-duodenal artery in front. The common bile-duct and pancreatic duct enter the wall of this part at the junction of the inner and posterior aspects, a little below the centre. Third or Inferior Part. — This part extends from the right side of the body of the third (sometimes fourth) lumbar vertebra to the left side of the body of the second on a level with its upper border. At this point it makes a sharp bend forwards, and terminates in the jejunum, thus forming the duodeno- jejunal flexure. It lies at first in the umbilical, and subsequently in the epigastric, region ; its length is about 5 inches, and its direction is at first obliquely to the left and upwards, and afterwards vertically upwards. Its anterior surface is covered by peritoneum derived from the descend- ing layer of the transverse meso-colon, except where it has the superior mesenteric vessels in front of it. There is no peritoneum behind it, and consequently it is fixed in position. Relations — Anterior. — The superior mesenteric vessels and the upper part of the root of the mesentery, with portions of the small intestine on either side of these. Posterior. — The inferior vena cava, aorta (below the origin of the superior mesenteric artery), left renal vein, left psoas magnus, and left crus of the diaphragm. Superior. — The lower part of the head of the pancreas (mcluding its uncinate process), and the inferior pancreatico-duodenal artery. The terminal portion of the third part is sometimes spoken of as the fourth or ascending part of Treves. It is covered by peri- toneum on the left side, as well as in front, and in cases where a retro- duodenal fossa is present it is partially covered by peri- toneum behind, towards the left side. The duodenal fossae of the peritoneum are met with on the left side of this portion. The duodeno- jejunal flexure is suspended from the left crus of the diaphragm by a fibro-muscular bundle, called the musculus sus- Pensorius duodeni. Blood and Nerve Supply of the Duodenum. — ^The arteries of the duodenum are as follows: (i) The pyloric branch of the hepatic; (2) the superior pancreatico-duodenal branch of the gastro-duodenal of the hepatic; and (3) the inferior pancreatico-duodenal branch of the superior mesenteric. The veins terminate in the superior mesenteric and splenic veins. The nerves are derived from the hepatic and superior mesenteric sympathetic plexuses. The lymphatic vessels of the first part of the duodenum pass to the retro-pyloric glands, and those of the second and !hird pa.Tis pass to the pre-pancreatico-duodenal and retro-pancrcatico-duodenal glands. Position and Connections of the Pancreas. — The pancreas is a long narrow gland which is situated behind the stomach, on a level with the first and second lumbar vertebrae. Its right extremity occupies the duodenal curve, and its somewhat pointed left ex- THE ABDOMEN 733 tremity is in contact with the spleen. The greater part of the organ Hes in the epigastric region, but its left extremity is situated in the left hypochondrium. The antero-superior surface is covered by the ascending layer of the transverse meso-colon, and the inferior surface by the descending layer, but the posterior surface is destitute of serous covering. The length of the organ is from 6 to 8 inches, its depth from i to i^ inches, except at the right and left extremities, and its thickness from ^ to | inch. Its weight is about 3^ ounces. Hepatic Artery Gastric Arter>- Splenic Artery furnishing the Vasa Brevia Pyloric Artery Right Gastroepiploic Artery Vena Portae Common Bile-duct [N stro-duodenal Artery | Superior , Pancreatico- / duodenal /~~~~ Artery Gastro-epiploic Artery Superior Mesenteric Vein Superior Mesenteric Artery I Inrerior Pancreatico-duodenal Artery Fig. 315. — The Arteries of the Stomach, Duodenum, Pancreas, AND Spleen. It has been likened in shape to the capital letter J laid thus C (Birmingham). For convenience of description it is divided into a head, neck, body, and tail. The head is the enlarged flattened right extremity. It chiefly corresponds with, and is closely attached to, the second and third parts of the duodenum as far almost as the duodeno- jejunal flexure. The expansion of the head to the left along the upper part of the third portion of the duodenum is called the uncinate process. Relations — Anterior. — The transverse colon with its meso-colon, and the superior mesenteric vessels crossing the uncinate process. 734 A MANUAL OF ANATOMY Posterior. — ^The inferior vena cava, right crus of the diaphragm, aorta, and left renal vein. Superior. — The first part of the duo- denum. Inferior. — ^The third part of the duodenum, and the inferior pancreatico-duodenal artery. Right. — The second part of the duodenum, with the common bile-duct behind, as low as a little below the centre, and the superior pancreatico-duodenal artery in front. The neck may be defined as the part in front of the origin of the vena portae and the termination of the superior mesenteric vein. It springs from the anterior surface of the head near its upper part, and is about i inch in length. Its direction is upwards and to the left, and it forms the connecting link between the head and body. The gastro-duodenal and superior pancreatico-duodenal arteries occupy a groove on its right side, and the commencement of the first part of the duodenum is in front of it, whilst the origin of the vena portae and the termination of the superior mesenteric vein are behind it. The body passes to the left, with a slight inclination backwards after it has crossed the aorta. It is triangular, and presents three surfaces — antero-superior, posterior, and inferior, and three borders — superior, anterior, and posterior. The antero-superior surface, which is covered by peritoneum, is in relation with the posterior surface of the stomach. At its right extremity, just below the coeliac axis, it presents a prominence, called the omental tuberosity from its relation to the gastro-hepatic omentum. The posterior surface, which is destitute of peritoneum, is related to the following structures : the aorta below the coeliac axis, with a portion of the solar plexus ; the origin of the superior mesen- teric artery ; the left suprarenal capsule ; and the left kidney with its vessels. The splenic vein passes from left to right in contact with this surface near the superior border. The inferior surface, which is covered by peritoneum, is moulded on the duodeno-jejunal flexure, some coils of the jejunum, and the left extremity of the transverse colon. The coeliac axis projects forwards over the superior border above the omental tuberosity. To the left of this axis the splenic artery pursues its tortuous course to the spleen, and to the right of it the hepatic artery lies for a short distance. The transverse meso- > colon is attached to the anterior border along which its separation into ascending and • descending layers takes place, the former covering the antero-superior surface of the organ, and the latter, on its way backwards, investing the inferior surface. The posterior border presents nothing noteworthy. The tail corresponds with the left extremity where the pancreas is narrowest, and is in contact with the lower end of the gastric surface of the spleen behind the hilum. For the structure and development of the pancreas, see pp. 8og, 812. Solar or Epigastric Plexus of the Sympathetic System. — The solar plexus is of large size, and is situated deeply in the epigastric region, behind the stomach and in front of the crura of the diaphragm and the aorta close to the origins of the coeliac axis and THE ABDOMEN Aorta 735 Great Splanchnic Nervo ihragmatic Plexus Plexus mic N Qchnicf 1 Plexus ^CEsophagus ^Diaphragm .Left Vagus i^^^a>^ .Stomach (cut) •-Gastric Plexus Splenic Plexus Cceliac Plexus Right Semilunai i4-/' ' Ganglion S^i^'-L -Sup. Mesenteric Plexus ■Aortico- renal Ganglion Sympa- Cord permatic • Plexus } Aortic Plexus — I lio-h>-pcga stric Nerve _ Inguinal Nerve .In«. Mesenteiic Plexus Ext. Cutanecu: Nerve Ureter (cut - Right Pelvic Plexus Communications between Pelvic Sympathetic Cords Sacral Plexus Pelvic Sympathetic Cord— Ganglion Impar Fig. 316. -The Sympathetic System in the Abdomen and Pelvis (HiRSCHFELD AND LeVEILL)£). R.K. Right Kidney ; R.T. Right Tesris. 736 A MANUAL OF ANATOMY superior mesenteric artery. It extends from one suprarenal capsule to the other, and is composed of nerve-fibres and ganglia, with an admixture of adipose tissue. The plexus receives its chief fibres from the great and small splanchnic nerves of each side, which contain a large number of spinal fibres. The great splanchnic nerve is formed by roots derived usually from the fifth to the ninth thoracic sympathetic ganglia inclusive, and it enters the abdomen by piercing the crus of the diaphragm. The small splanchnic nerve arises by two roots from the tenth and eleventh thoracic ganglia, and it also enters the abdomen by piercing the crus of the diaphragm. The plexus also receives fibres from the right pneumogastric nerve. Two of the ganglia of the solar plexus are of large size, and are situated one at either lateral pole. They are called the semilunar ganglia, right and left. Each lies over the corresponding crus of the diaphragm close to the suprarenal body, that of the right side being under cover of the inferior vena cava, and each receives at its upper part the great splanchnic nerve. The lower part of each ganglion is more or less detached, and is known as the aortico-renal ganglion, which lies over the root of the renal artery, and in which the small splanchnic nerve terminates. From each semilunar ganglion branches proceed in a radiating manner upwards, out- wards, downwards, and inwards. The inner group of fibres extend from one ganglion to the other, embracing the coeliac axis as they cross the aorta, and forming the cceliac plexus, which receives fibres from the right pneumogastric nerve, and contains numerous small ganglia. The coeliac plexus furnishes three secondary plexuses — gastric, splenic, and hepatic. The gastric plexus accompanies the corre- sponding artery to the small curvature of the stomach, and supplies branches to the adjacent portions of the anterior and posterior surfaces of that organ. The splenic plexus goes with the splenic artery, and receives branches from the right pneumogastric nerve. It is distributed, with the branches of the artery, to the pan- creas, cardiac extremity of the stomach, left half of its great curva- ture and adjacent portions of its surfaces, and the spleen. The hepatic plexus accompanies the artery of that name, and receives branches from the left pneumogastric nerve. Its distribution corresponds with that of the artery, and its offshoots are as follows : pyloric to the small curvature of the stomach ; gastro-duodenal, dividing into right gastro-epiploic to the great curvature of the stomach, and superior pancreatico-duodenal to the head of the pancreas, and the first and second parts of the duodenum ; cystic to the gall- bladder ; and hepatic to the liver. The diaphragmatic or phrenic plexus receives its fibres from the upper part of the semilunar ganglion, and it accompanies the inferior phrenic artery to the diaphragm, giving branches in its course to the suprarenal plexus. The suprarenal plexus receives its fibres from the semilunar ganglion and coeliac plexus. It contains small ganglia, and is THE ABDOMEN 737 SEIMILUMAR CANGUON Fig. 317. — Scheme of the Sympathetic Nerve in the Abdomen AND Pelvis (Flower). S.C. Sympathetic Cord 1,2,3,4. Lumbar Ganglia n,h,c,d. Pelvic Ganglia G.I. Ganglion Impar G.S. Great Splanchnic S.S. Small Splanchnic L.S. Least Splanchnic D. P. Diaphragmatic Plexus S.R.P. Suprarenal Plexus R,P. Renal Plcvus S.P. Spermatic Plexus A. P. .\ortic Plexus \. M. P. Inferior Mesenteric Ple.xus L.C. P. Left Colic Plexus S.P. Sigmoid Plexus S. H. P. Superior Hemorrhoidal Plexus H.P. Hypogastric Plexus R.I.P. Rami Intestiiii Tenuis Plexuses P.P. Pelvic Plexus E.P. Epigastric Plexus C.P. Coeliac Plexus S.P. Splenic Plexus Pa. P. Pancreatic Plexus L.G. P. Left Gastro-epiploic Plexus B.S. Branches to Spleen G.P. Gastric Plexus H.P. Hepatic Plexus Py LP. Pyloric Plexus . G. D.P. Gastro-duodenal Plexus C.P. Cystic Ple-xus B. L. Branches to Liver S.M.P. Superior Mesenteric Plexus I. C.P. Ileo-colic Plexus R.C.P. Ru;ht CoUc Plexus M.C. P. Middle Colic Plexus 47 738 A MANUAL OF ANATOMY joined from above by branches from the diaphragmatic plexus, and below by branches from the renal plexus. It is distributed to the suprarenal capsule. The renal plexus derives its fibres from the aortico-renal ganglion, the coeliac and aortic plexuses, and the least splanchnic nerve when present. (The least splanchnic nerve arises from the twelfth thoracic ganglion, and enters the abdomen behind the ligamentum arcuatum internum, or through the crus of the diaphragm). The fibres of the renal plexus, which contain ganglia here and there, are distributed with the renal artery to the kidney, branches being also given to the suprarenal plexus, spermatic plexus (ovarian in the female), and to the ureter. The superior mesenteric plexus is a continuation of the coeliac plexus, and also receives fibres from the semilunar ganglia. It contains a ganglion, called superior mesenteric, in contact with the origin of the artery of that name, and it accompanies that vessel and its branches to be distributed to the intestinal canal from (and including) the third part of the duodenum to the commencement of the descending colon. Its secondary plexuses are as follows : rami intestini tenuis, ileo-colic, right colic, middle colic, and inferior pan creatico -duodenal. The aortic plexus derives its fibres from the semilunar ganglia, and the coeliac and superior mesenteric plexuses. It extends along the aorta, beyond the origin of the superior mesenteric artery, in the form of two lateral strands which communicate freely with one another over the vessel by many interlacing fibres. It is reinforced laterally by branches from the lumbar portion of the gangliated sympathetic cord. The two lateral strands of the plexus ultimately cross the common iliac arteries, and unite in front of the body of the fifth lumbar vertebra to form the hypogastric plexus. The aortic plexus furnishes, on either side, branches to the renal and spermatic (or ovarian) plexuses, and supplies the coats of the aorta. The right strand gives branches to the inferior vena cava, and the left furnishes the chief fibres of the inferior mesenteric plexus. The spermatic plexus derives its fibres from the renal and aortic plexuses, and accompanies the spermatic artery to the testis. In the female it is called the ovarian plexus, which goes with the artery of that name to the ovary. The inferior mesenteric plexus is derived chiefly from the left strand of the aortic plexus, and contains a ganglion, called inferior mesenteric, which lies below the root of the inferior mesen- teric artery. The plexus accompanies the inferior mesenteric artery, and furnishes left colic, sigmoid, and superior hemorrhoidal plexuses, which supply the descending colon, iliac colon, pelvic colon, and rectum. The hypogastric plexus is formed by the fusion of the two halves of the aortic j^lexus after these have crossed the common iliac arteries. It is reinforced by branches from the lumbar ganglia, and is THE ABDOMEN 739 situated in front of the body of the fifth lumbar vertebra between the common iliac vessels. It is a large fiat plexus, measuring about ih inches in breadth, and it ends in two divisions, which become the right and left pelvic plexuses. Coeliac Axis. — ^The coeliac axis is a short thick trunk which arises from the front of the aorta between the crxua of the diaphragm just below the aortic opening. Its direction is straight forwards over the superior border of the body of the pancreas, and, after a course of about \ inch, it divides into three radiating branches — gastric, splenic, and hepatic. Of these the splenic is the largest, except during foetal life when it is exceeded by the hepatic. The branches of the axis supply the stomach, duodenum, pancreas, spleen, liver, and gall-bladder. Relations. — ^The right lobe of the liver above, the superior border of the body of the pancreas below, the gastro-hepatic omen- tum in front, and a semilunar ganglion on either side, with the Spigelian lobe of the liver as an additional right relation. The axis is closely surrounded by the coeliac sympathetic plexus. The gastric (coronary) artery is directed upwards and to the left as far as the small ciirvature of the stomach on the right side of the oesophagus. It then bends sharply forwards and downwards, and descends in two divisions from left to right along the small curvature towards the pylorus, where it anastomoses with the two divisions of the pyloric branch of the hepatic. The artery is at first behind the small sac of the peritoneum, but along the small curvature it lies between the two layers of the gastro-hepatic omentum, and is surrounded by the gastric sympathetic plexus. Branches. — ^These are oesophageal, cardiac, and gastric. The oesophageal branches arise when the artery reaches the small curva- ture, and they ascend through the oesophageal opening of the diaphragm to anastomose on the gullet with the lower oesophageal branches of the thoracic aorta. The cardiac branches are distributed to the cardiac end of the stomach, where they anastomose with the vasa brevia of the splenic. The gastric branches arise from the two divisions of the artery on the small curvature, and pass to the front and back of the stomach, where they anastomose with branches of the gastro-epiploic arteries. " The gastric vein ascends from right to left along the small curvature of the stomach as far as the oesophagus, where it receives a few oesophageal tributaries, after which it turns to the right and opens into the vena portae. The splenic artery takes a tortuous course to the left along the superior border of the body of the pancreas behind the small sac. On reaching the front of the left kidney it breaks up into several splenic branches which enter the spleen through the hilum. The artery is invested by the splenic sympathetic plexus, and the splenic vein hes below it, and behind the pancreas. Branches. — These are pancreatic, left gastro-epiploic, vasa brevia, 740 A MANUAL OF ANATOMY and splenic. The pancreatic branches arise at intervals along the superior border of the pancreas, which they enter. One of them, known as the arteria pancreatica magna, enters the organ towards its left end, and passes from left to right, lying a little above the pancreatic duct. The left gastro- epiploic artery arises near the spleen, and passes within the gastro-splenic omentum to the great curvature of the stomach, along which it descends from left to right Gastro-duodenal Artery- Vena Portae j Pyloric Artery Ductus Communis Cholcdochus Round Ligament of Liver '■ Inferior Phrenic Arteries Cystic Artery Duodenum superior Pancreatico- duodenal Artery Right Gastro-epiploic Artery (Esophagus Coeliac Axis / Gaslric Artery Hepatic Artery Splenic Artery Fig. 318. — The Arteries of the Stomach, Liver, and Spleen (after Merkel). between the two layers of the gastro-colic omentum as far as the centre, where it anastomoses with the right gastro-epiploic. It furnishes gastric branches to the front and back of the stomach, which anastomose with branches of the gastric artery, and epiploic branches, which descend into the gastro-colic omentum, these latter being long and slender. The vasa brevia arise from the terminal part of the splenic and from its splenic branches. They are about five in number, and, having passed within the gastro- splenic omentum to the cardiac extremity of the stomach, they THE ABDOMEN 741 anastomose with branches of the left gastro-epiploic and gastric arteries. The splenic branches are about five in number, and pass to the spleen within the lieno-renal ligament. The splenic vein is formed by the imion of about five veins which emerge from the spleen. It is of large size, and passes from left to right behind the pancreas near its superior border, where it lies below the splenic artery. Having crossed the aorta, it joins the superior mesenteric vein to form the vena portae behind the neck of the pancreas. The vein takes up the following tributaries : the vasa brevia, the left gastro-epiploic, many pan- creatic veins, and the inferior mesenteric (as a rule). The hepatic artery passes at first to the right along the superior border of the pancreas for a short distance, where it lies behind the small sac. It then turns forwards below the foramen of Winslow to the upper border of the first part of the duodenum near the pylorus, and it subsequently ascends between the two layers of the gastro-hepatic omentum in front of the foramen of Winslow towards the portal fissure of the liver, on approaching which it divides into a right and left hepatic branch. The vessel is accompanied by the hepatic sympathetic plexus. As it ascends between the two layers of the gastro-hepatic omentum it has the common bile-duct on its right side, the vena portae being behind both. Branches. — ^These are pyloric, gastro-duodenal, and right and left hepatic. The Pyloric artery, of small size, arises near the pylorus, and passes to the small curvature of the stomach, where it divides into two branches. These lie between the two layers of the gastro-hepatic omentmn, and supply offsets to the front and back of the stomach. They anastomose with the two divisions of the gastric artery. The gastro-duodenal artery also arises near the pylorus, and descends behind the first part of the duodenum, having the common bile-duct on its right, and the vena portae behind it. Having reached the lower border of the first part of the duodenum, it occupies a groove on the right of the neck of the pancreas, and here divides into its two terminal branches — right gastro-epiploic and superior pancreatico-duodenal. The right gastro-epiploic artery passes from right to left along the great curvature of the stomach as far as its centre between the two layers of the gastro-colic omentum, and its distribution and anastomoses are similar to those of the left gastro-epiploic artery. The superior pancreatico-duodenal artery descends anteriorly between the head of the pancreas and the second part of the duodenum, towards the lower end of which latter it anastomoses with the inferior pancreatico- duodenal of the superior mesenteric. It supplies the first and second parts of the duodenum, and furnishes branches to the adjacent portion of the pancreas. The hepatic branches are the terminal divisions of the trunk. The right, which is the larger, enters the portal fissure at its right end, whilst the left, small in size, enters that fissure at its left end, having previously furnished a branch to 742 A MANUAL OF AN ATOM V the Spigelian lobe. The right branch gives off the cyslic artery, and this divides into two branches, superior and inferior, which ramify on the upper and under surfaces of the gall-bladder. The pyloric vein passes from left to right, and opens into the vena portse near the pylorus. The right gastro-efiploic vein passes from left to right, and opens into the superior mesenteric vein near its termination. The fancreatico-duodenal vein takes up blood from the right end of the pancreas and from the duodenum, and opens into the superior mesenteric vein near its termination. The cystic vein usually, ends in the right division of the vena portae. All the veins which return the blood from the stomach, duodenum, pancreas, and spleen are destitute of valves, so that the blood can regurgitate in cases of portal obstruction. Coeliac Glands. — The glands of this group are numerous. They surround the coeliac axis, and extend over the aorta as low as the origin of the superior mesenteric artery. They receive their afferent vessels from the gastric, pancreatic, splenic, and hepatic glands, and their efferent vessels either join the intestinal lymphatic trunk (or trunks) of the superior mesenteric glands, or open inde- pendently into the receptaculum chyli. Gastric Lymphatic Glands. — These are arranged in two groups, superior and inferior, the former lying along the small curvature of the stomach, and the latter along the great curvature. They receive their afferent vessels from the stomach, and their efferent vessels pass to the coeliac glands. Pancreatic Glands. — ^These lie along the superior border of the pancreas. They receive their afferent vessels from that organ, and their efferent vessels pass to the coeliac glands. Splenic Glands. — These are numerous, and are situated near the hilum of the spleen in contact with the tail of the pancreas. They receive their afferent vessels from the spleen, and their efferent vessels, having been joined by some of those from the left half of the great curvature of the stomach, pass to the coeliac glands. Hepatic Glands. — These are situated between the two layers of the gastro-hepatic omentum near the portal fissure. They receive as afierent vessels those of the deep lymphatics of the liver which accompany the branches of the portal vein, and also some of the superficial lymphatics of the inferior surface of the liver, and their efferent vessels pass to the coeliac glands. Vena Portae. — ^This vein is formed by the union of the superior mesenteric and splenic veins, and is about 3 inches in length. It commences on a level with the body of the first lumbar vertebra a little to the right of the middle line, where it lies behind the neck of the pancreas. It ascends behind the first part of the duodenum, and then between the two layers of the gastro-hepatic omentum in front of the foramen of Winslow, where it has anterior to it the hepatic artery and common bile-duct, the artery being THE ABDOMEN 743 on the left of the duct. WTien the vessel arrives at the right extremity of the portal fissure of the liver it presents a slight en- largement, called the portal sinus, and then divides into two branches, right and left, the former being the larger and shorter of the two. The right branch, having received the cystic vein, enters the right lobe of the liver. The left branch, having trav^ersed the portal fissure from right to left, and furnished branches to the quadrate and Spigelian lobes, crosses the longitudinal fissure, and Fig. 319. — ^Vena Port/E and its Tributaries. I. Vena Portae 12. Pancreaticoduodenal 2. Right Division 13. Superior Hemorrhoidal 3- Left Division 14. Sigmoid A- Superior Mesenteric 15. Left Colic 5- Splenic 16. Splenic VeiiK 6. Inferior Mesenteric 17. Vasa Brevia 7- Rami Intestini Tenuis 18. Left Gastroepiploic 8. Ileo-Colic 19. Pancreatic 9- Right Colic 20. Pyloric 10. Middle CoUc 2i. Gastric II. Right Gastio-epiploic 22. Cystic enters the left lobe. As it crosses this fissure it is joined in front by the round ligament of the liver, which is the remains of the umbilical vein of foetal life. Posteriorly, and slightly to the right of this point, it is connected with the fibrous cord which represents the foetal ductus venosus. The vena portae near the pj'lorus receives the pyloric and gastric veins. The distinctive character of the vessel is that it behaves like an artery, its blood ultimately entering the intralobular plexuses in the liver. The sources from which the vein receives its blood are as follows : 744 A MANUAL OF ANATOMY (i) the stomach, (2) the small and large intestine, except a portion of the anal canal, (3) the pancreas, (4) the spleen, and (5) the gall- bladder. Summary of the Tributaries of the Vena Portse. — (i) The superior mesenteric vein, which takes up (o) the right gastro-epiploic, (b) the pancreatico-duodenal, (c) the rami intestini tenuis, (d) the ileo-colic, (e) the right colic, and (/) the middle colic. (2) The splenic vein, which takes up {a) the gastric vasa brevia, (6) the left gastro-epiploic, (c) many pancreatic veins, and (d) the inferior mesenteric (as a rule), which in turn takes up the superior hemorrhoidal, sigmoid, and left colic veins. (3) The pyloric vein. (4) The gastric vein. (S) The cystic vein. The portal vein and its tributaries are destitute of valves, so that the blood can regurgitate in cases of portal obstruction. Development of the Vena Portse. — The lower portion of the vein results from the union of the two vitelline veins. The upper portion is developed from the left half of the lower venous ring and the right half of the upper venous ring, formed by the vitelline veins around the primitive duodenum. For a description of the common bile-duct, see p. 710, Kidneys. — ^The kidneys are two in number, right and left, and are situated deeply at the posterior part of the abdomen, where they lie behind the peritoneum. They chiefly occupy portions of the epigastric and hypochondriac regions, but also extend slightly into the umbilical and lumbar regions. Relatively to the vertebral column they extend from the level of the upper border of the last thoracic vertebra to about the centre of the body of the third lumbar, the right kidney being usually somewhat lower than the left. The long axis of each organ is directed downwards and slightly outwards, so that their upper ends are rather nearer the middle line than the lower. The superior limit of the right kidney is usually the lower border of the eleventh rib, whilst that of the left is usually the upper border of the eleventh rib. Inferiorly the organs ap- proach the iliac crests, from which they are distant about 2 inches, the right being the nearer of the two. Each kidney is surrounded by a quantity of areolar and adipose tissues, constituting the adipose capsule, which, along with the adjacent viscera, anchors the organ. The length of a kidney is about 4 inches, the breadth about 2^ inches, and the thickness about i|^ inches. The right kidney is usually shorter and broader than the left. The weight of the organ is about 5J ounces. In form the kidney is bean-shaped. It presents two smooth surfaces, two extremities, and two borders. The anterior surface looks outwards as well as forwards, and presents important visceral impressions, whilst the posterior surface looks inwards as well as backwards, and presents muscular impressions. The extremities are enlarged and round, the superior more so than the inferior, the latter often assuming a somewhat pointed appearance. The external border has an inclination backwards, and is convex and free. The internal border has an inclination forwards, is concave, and is connected with the renal vessels and the pelvis of the kidney. THE ABDOMEN 745 Relations — Anterior Surface of the Right Kidney. — ^This surface is overlapped by the right suprarenal capsule for a very short distance at its upp-^r and inner part. It presents three visceral areas — hepatic, duodenal, and colic. The hepatic area lies somewhat obliquely, and occupies about the upper two- thirds, being in contact with the impressio renalis on the under siuface of the right lobe of the liver. CE^phagus Diaphragm. Superior Capsular - i;i Arteries i Suprarenal Body d. Capsular Artery . if. Capsular Artery . Renal Artery. [nfeiior Vena Cava_ It Spermatic Artery '! Right Ureter— - Aorta Right Common Iliac.. Artery j^-^iplnf. Phrenic Arteries L^jJ-Coeliac Axis I' Jjl^Superior Mesenteric Artery '^ / , .Lumbar Artery _ .Qnadratns LtunboruiF Magnus 1-1-.-. _Hli.. Inferior J Mesenteric Artery -i-..IIiacus --.Left Spermatic Artery Left Common Iliac Vein '-.Middle Saaral Artery External Iliac Artery External Iliac Vein Rectum Bladder Fig. 320. — Dissection of the Posterior Abdominal Wall. It is covered by peritoneum. The duodenal area corresponds with an elongated narrow strip lying close to the hUum, and reaching a little above and below it. It is in contact with the posterior wall of the second part of the duodenum, both being destitute of peri- toneum. The colic area lies below the hepatic, and, like it, is oblique. It is in contact with the upper end of the ascending colon and the hepatic flexure without the inter\'ention of peritoneum. Between the lower part of the duodenal and the colic impression, 746 A MANUAL OF ANATOMY that is, at the lower and inner part of the anterior surface, there is a small area covered by peritoneum which is in contact with a portion of the small intestine. Anterior Surface of the Left Kidney. — ^This surface is overlapped by the left suprarenal capsule for a very short distance at its upper and inner part. It presents five visceral areas — splenic, gastric, pancreatic, colic, and jejunal. The splenic area is situated at the upper and outer part, close to the external border, and is in contact with the renal surface of the spleen, the peritoneum of the great cavity intervening. The gastric area, somewhat triangular, lies at the upper end, between the splenic and capsular areas, and above the pancreatic area. It is in contact with the postero-inf erior surface Right Suprarenal Body Duodenal Area Splenic Area Area for Portion of Small Intestine Inferior Vena Cava I Left Ureter L'jft Uenal Vessels Aorta Fig. 321. — The Visceral Areas of the Kidneys (In this case the right renal vein was higher than usual). of the stomach with the intervention of the peritoneum of the small sac. The pancreatic area lies transversely below the gastric area, and extends as low as about the centre of the hilum. It is in relation with the posterior surface of the body of the pancreas and the splenic vessels, without peritoneum. The colic area is situated at the lower and outer part, and is in contact with the splenic flexure and the commencement of the descending colon, without peritoneum. At the lower and inner part there is a small area covered by peritoneum, which is related to a part of the jejunum. Posterior Surface. — This surface is readily recognised by ob- serving the posterior position of the pelvis of the kidney at the THE ABDOMEN 747 hilum, with which it coincides. The inner portion of it rests upon [a) the psoas magnus and its sheath, and [b) the crus of the diaphragm. The outer portion rests, from above downwards, upon {a) the twelfth rib (in the case of the left kidney the eleventh rib also), [b) the diaphragm, and (c) the quadratus lumborum, covered Subcostal Artery and Nerve Fig. 322.— Diagram showing the Relations of the Kidneys from Behind. R.L. Right Lung L.L. Left Lung S. Spleen R.K. Right Kidney L.K. Left Kidney IX. Ninth Rib X. Tenth Rib XI. Eleventh Rib XII. Twelfth Rib I.L. First Lumbar Vertebra ILL. Second Lumbar Vertebra I ILL. Third Lumbar Vertebra IV. L. Fourth Lumbar Vertebra V. L. Fifth Lumbar Vertebra by the anterior lamina of the lumbar aponeurosis. An important surgical relation of the upper part of this division of the posterior surface is that the pleura, in descending between the diaphragm and the twelfth rib, lies behind the kidney. Three nerves pass down- wards and outwards behind the organ, namelj^, the subcostal, ilio-hypogastric, and inguinal. The superior extremity is capped by the suprarenal capsule, which also extends for a little over the anterior surface and adjacent portion of the internal border. The external border, which is convex, rests on the pos- terior aponeurosis of the transversalis abdominis. The external border of the right kidney, over about its upper two- thirds, is in contact with the liver, whilst the external border of the left kidney at its upper end is in contact with the spleen. The internal border of the right kidney lies very near the 748 A MANUAL OF ANATOMY inferior vena cava, whilst that of the left is situated fully I inch from the aorta. This border is concave, and presents a longitudinal fissure, called the hilum, which extends over about its middle third. It presents two somewhat thick lips, anterior and posterior, and it leads to a cavity within the organ, called the sinus. It transmits the following structures in order from before backwards : the branches of the renal vein, the branches of the renal artery, with branches of the renal sympathetic plexus and lymphatics, and the pelvis of the kidney. The side to which a kidney belongs may be ascertained in the following way : if the organ is held with that end dowTiwards towards which the ureter is naturally inclined, and that surface backwards which coincides with the pelvis at the hilum, the convex border will then indicate the side to which the organ belongs. Varieties — Form. — The kidneys may be much elongated, or somewhat round, or triangular. The lobulated condition, which is characteristic of the kidney in early life, may persist in the adult. Size. — One kidney may be diminished in size, in which cases there is a proportionate increase in the other organ. Position. — It is very rare to find the kidneys higher than usual, but one or both not infrequently extend into the iliac fossa, or over the pelvic brim. Number — Diminution. — One kidney (usually the left) may be entirely suppressed, in which cases the solitary kidney usually occupies its normal position, and may, or may not, be of large size. Increase. — The number may be increased to three, the additional organ being lateral, or median, in position. Horseshoe Kidney. — This condition is brought about by the fusion of the lower parts of the organs, the connecting band of renal substance extending across the vertebral column. Preternatural Mobility. — The kidney is usually anchored in its normal position by its capsule and the adjacent viscera, but it is sometimes movable, which may be due to one of two causes : (i) the capsule may be very loose, giving rise to the condition known as movable kidney ; or (2) the organ may be attached to the posterior abdominal wall by a peritoneal fold, called the meso-nephron, in which case the condition known as floating kidney occurs, this being said to be more frequent on the right side. For the structure and development of the kidney, see Index. Ureter.- — The ureter is the excretory duct of the kidney, and it conveys the urine to the bladder. It is a cylindrical, thick-walled tube, like a goose-quill, its average length being about 12 inches, and its diameter about ^ inch. The ureter proper commences, towards the lower end of the kidney, where it is the continuation of the pelvis, and it terminates in the bladder. The pelvis is funnel- shaped and flattened from before backwards. It lies partly in the sinus, where it receives the calices, and partly outside the hilum, where it lies behind the other transmitted structures. Its direc- tion is downwards and inwards, and, having become narrow, it passes into the ureter proper towards the lower end of the kidney. The ureter proper passes downwards and inwards behind tht peritoneum, in contact with the posterior abdominal wall. T rests at first upon the psoas magnus and its sheath, being hen crossed superficially by the spermatic (or ovarian) vessels, whici THE ABDOMEN 749 are taking a course downwards and outwards, and deeply by the genito-crural nerve, which is taking a similar course. In this part of its course the right duct has the inferior vena cava near it on its inner side, whilst the left duct has the aorta on its inner side, but at some little distance. The ureter next crosses the terminal part of the common iliac artery (or the commencement of the external iliac), after which it enters the pelvic cavity, the right ureter being crossed by the lower part of the root of the mesentery proper, and the left by a portion of the pelvic meso-colon. In the pelvis the lureter passes downwards and forwards in front of the internal iliac artery to the outer wall of the pelvis, lying beneath the peritoneum, and crossing internally the obturator vessels and nerve, and the obliterated hypogastric artery. It subsequently passes inwards to the bladder, being crossed internally by the vas deferens. Having arrived at the lateral or ureteric angle of the bladder, it commences to pierce the vesical wall anterior to the upper free end of the vesicula seminalis, being here about 2 inches distant from its fellow, and about ij inches from the base of the prostate gland. It now pursues an oblique course through the wall of the bladder, lying in it for about | inch, and it finally opens into the interior by a very small slit-like aperture placed obliquely at one angle of the base of the internal trigone, where it is distant from its fellow and from the urethral orifice by about ij inches. In the female the ureter, in its pelvic covu^se, passes along the side of the cervix uteri and upper part of the vagina. Varieties. — (i) The pelvis may be absent, its place being taken by two, or three, tubes. (2) Double Ureter. — ^The foregoing tubes may remain separate for some distance beyond the hilum, or even as low as the bladder, thus giving rise to a double ureter. A triple ureter is extremely rare. (3) Dilated Ureter. — This condition is liable to result in such cases as urethral stricture, enlarged prostate, and vesical calculus. For the structure of the ureter, see Index. Suprarenal Capsules or Bodies. — The suprarenal capsules (adrenals) are two in number, right and left, and are situated in the epigastric region. Each is compressed from before backwaj-ds, and broad from side to side. It is set upon the superior extremity of the correspond- ing kidney, to which it is bound by connective tissue. Each cap- sule encroaches upon the adjacent parts of the anterior surface and internal border of the kidney, the left being mainly situated upon the internal border. The dimensions of the organ are so variable that they can only be stated approximately as foUows : the height is about ij inches, and the breadth rather less than 2 inches. The weight, on an average, is about 2 drachms. The right capsule is rather smaller than the left, and is triangu- lar. It is wedged in between the diaphragm and the jxtsterior surface of the right lobe of the liver, and its surfaces are anterior and posterior, the former having an inclination outwards, and the latter inwards. The anterior surface, close to the inner border, is in contact with the inferior vena cava, and elsewhere it is related to the pos- 750 A MANUAL OF ANATOMY terior surface of the right lobe of the liver. At its upper and inner part there is a small fissure, called the hilum, through which the right suprarenal vein emerges. The peritoneum gives a partial covering to this surface at its lower part. The posterior surface is in contact with the diaphragm and the upper part of the anterior surface of the right kidney. The right semilunar ganglion lies on the inner side of the right capsule. The left capsule is somewhat semilunar. The anterior surface is related above to the postero-inferior surface of the stomach, with the intervention of the small sac, which furnishes it with a peritoneal covering. Below this it is related to the posterior surface of the body of the pancreas and the splenic vessels, without peritoneum. The hilum, through which the left suprarenal vein emerges, is situated at the lower and inner part of this surface. The posterior surface at its upper part is in contact with the left crus of the diaphragm, and, below, it rests upon the upper and inner part of the front of the left kidney, as well as upon its internal border. For the structure and development of the suprarenal capsule see Index. Abdominal Aorta. — The abdominal aorta commences at the aortic opening of the diaphragm on a level with the lower border of the body of the twelfth thoracic vertebra, where it lies in the middle line, and it usually terminates opposite the centre of the body of the fourth lumbar vertebra, a finger's breadth to the left of the middle line, by dividing into the right and left common iliac arteries. The position of the bifurcation may be indicated in one of two ways, as follows : (i) by taking a point fully i inch below the umbilicus and a finger's breadth to the left of the linea alba ; or (2) by taking a point in the line which connects the highest parts of the iliac crests a finger's breadth to the left of where it intersects the linea alba. The bifurcation may take place a little lower down or higher up than the normal level. The length of the vessel is about 5 inches. It occupies the epigastric and umbilical regions, where it lies very deeply behind the peritoneum, and its direction is downwards with a slight inclination to the left. Relations — Anterior. — ^The direct anterior relations, from above downwards, are as follows : the origins of the inferior phrenic arteries, the coeliac axis, coeliac glands, and solar plexus, the ascend- ing layer of the transverse meso-colon, the pancreas and splenic vein, the root of the superior mesenteric artery, the third part of the duodenum and left renal vein, the origins of the spermatic (01 ovarian) arteries, the aortic plexus, the median group of lumbar glands, the peritoneum of the general cavity, and the origin of the inferior mesenteric artery. The more remote anterior relations are the gastro - hepatic omentum, stomach, transverse colon with its meso-colon, coils of the small intestine, root of the mesentery proper, and gastro-colic omentum. Posterior. — ^The disc between the twelfth thoracic and first lumbar, vertebnu, the bodies and discs of the upper four lumbar vertebra}, and THE ABDOMEN 751 the anterior common ligament, the left lumbar veins, and the origins of the lumbar and middle sacral arteries. Right. — ^The right crus of the diaphragm, with the receptaculum chyli and right vena azygos lying deeply between the vessel and the right crus, the former being nearest the aorta, and slightly covered by it ; and the inferior vena cava. Left, — ^The left crus of the diaphragm, the left semi- GElsophagus Diaphragm . superior Capsular Arteries Suprarenal Body - . Capsular Artery - '. Capsular Artery -. Renal Artery . iferior Vena Cava .. Sperniatic Arterj-... Right Ureter — Aorta — ^ight Common Iliac.. Ariery r-Mr^-l-Inf. Phrenic Arteries !-- fT-Cceliac Axis t' ;jj —Superior Mesenteric Ariery ^./ . .Lumbar Artery Quadratus Lumboruni . . Psoas Magnus --Inferior Mesenteric Artery . ..Iliacus — Left Spermatic Artery External Iliac Arterj' External Iliac Vein >^-i^ Left Commoo Iliac Vein *-. Middle Sacral Ariery Rectum Bladder Fig. 323. — Dissection of the Posterior Abdominal Wall. lunar ganglion, the terminal portion of the third part of the duodenum (ascending part of Treves), and the left svmpathetic gangliated cord. Branches. — ^These are nine in number, and are arranged in two [ groups, visceral and parietal, four of them being single, and five i arranged in pairs. The four single branches are the cceliac axis, superior mesenteric, inferior mesenteric, and middle sacral. The five pairs are the inferior phrenic, middle capsular, renal, spermatic j^i A MANUAL OF ANATOMY (ovarian in the female), and the lumbar. Excluding the lumbar arteries, the order of origin of the branches is as follows : (i) inferior phrenic, (2) coeliac axis, (3) superior mesenteric and (4) middle capsular, both on same level, (5) renal, (6) spermatic (or ovarian), (7) inferior mesenteric, and (8) middle sacral. In what follows the letter P after an artery signifies parietal, and V visceral. The inferior phrenic arteries (P) are two in number, right and left, and they are called inferior to distinguish them from the superior phrenic of the internal mammary, right and left. They arise, either separately or by a common trunk, from the front of the aorta, whenever the vessel has passed through the aortic opening of the diaphragm. They at once diverge, each passing outwards and upwards over the crus of the diaphragm, the right vessel lying behind the inferior vena cava, and the left behind the oesophagus. Each ends by dividing into two branches, anterior and external. The anterior branch passes forwards and inwards in a curved manner in front of the central tendon, and anastomoses with its fellow of the opposite side, and the superior phrenic and musculo-phrenic of the internal mammary. The external branch passes outwards, and anastomoses with the musculo-phrenic and the lower inter- costal arteries. Each inferior phrenic artery furnishes a superior capsular branch (or branches) to the suprarenal capsule, the right vessel also giving off a few branches to the inferior vena cava, whilst the left supplies a few branches to the oesophagus. The right inferior phrenic vein opens into the inferior vena cava, and the left terminates in the left supraienal vein, left renal vein, or inferior vena cava. The coeliac axis (V) and superior mesenteric artery (V) will be found described on pp. 725, 739. The middle capsular arteries (V) are of small size, and are two in number, right and left, each arising from the side of the aorta on a level with the origin of the superior mesenteric artery. The vessel passes outwards and upwards over the crus of the diaphragm to the suprarenal capsule, in which it anastomoses with the superior capsular of the inferior phrenic and the inferior capsular of the renal. The right suprarenal vein opens into the inferior vena cava, and the left into the left renal vein. The suprarenal veins originally open into the cardinal veins. The right suprarenal vein becomes transferred to the upper segment of the inferior vena cava (above the right renal vein). The left suprarenal vein, after the obliteration of the adjacent jxirtion of the left cardinal vein, becomes trans- ferred to the loft renal vein. The renal arteries (V) are remarkable for their large size, and are two in number, right and left. They arise from the side of the aorta about ^ inch lielow the superior mesenteric on a level with the body of the first lumbar vertebra, the right artery being usually a little lower than the left. They form right angles with THE ABDOMElsf 753 the aorta, and cross the crura of the diaphragm on their way to the hila of the kidneys, the right vessel passing behind the inferior vena cava, second part of the duodenum, and head of the pancreas, whilst the left passes behind the body of the pancreas. Each vessel has its own vein in front of it, and the aortico-renal ganglion lies over its root. On approaching the renal hilum each vessel divides into three or four branches, one of which usually passes behind the pelvis of the kidney, whilst the others lie between the renal vein in front and the pelvis behind. For the subsequent distribution of the branches in the kidney, see p. 822. Before breaking up into its proper renal branches the vessel gives oS an inferior capsular artery to the suprarenal capsule, peri-renal branches to the capsule, and ureteric to the upper part of the ureter. Differences between the Renal Arteries. — (i) The right artery is rather lower than the left. (2) The right is rather longer than the left, on accoimt of the inclination of the aorta to the left of the middle line. (3) The right passes behind the inferior vena cava, second part of the duodenum, and head of the pancreas, whilst the left passes behind the body of the pancreas. Varieties. — 1. Very often there is an accessory renal artery present, arising close to the main vessel, and usually above it. 2. The renal artery may divide into its renal branches close to its origin. 3. There may be an aberrant renal artery, which may arise frofti the inferior phrenic, spermatic (or ovarian), inferior mesenteric, common or external iUac, or middle sacral. 4. In cases of variations, or even in the normal condition, one or more of the renal branches may fail to enter the hilum, and may pierce the kidney on its anterior surface, or near the upper or lower end. The renal veins, like the arteries, are of large size. Each lies in front of its artery, and receives tributaries from the adipose tunic and the upper part of the ureter. The vessels are tributaries of the inferior vena cava, which they join almost at a right angle, the left a little higher than the right. The left vein crosses in front of the aorta, taking up in its course the left suprarenal and left spermatic (or ovarian) veins. In some cases there is a single semilunar valve at the lower part of the opening of each renal vein into the inferior vena cava. Difference between the Renal Veins. — (i) The left vein is longer than the right, on account of the position of the inferior vena cava on the right side. (2) The left is rather higher than the right. (3) The left crosses in front of the aorta. (4) The left receives the left suprarenal and left spermatic (or ovarian) veins. The renal veins originally open into the cardinal veins. Subsequently the right renal vein opens into the junction of the upper and lower segments of the inferior vena cava. \\Tien the left cardinal vein becomes obliterated, in great part the left renal vein becomes continuous with the left division of the primitive inferior vena cava. The mesial portion of the left renal vein is developed from the left division of the priaiitive inferior vrua ca'a. 48 754 ^ MANUAL OF ANATOMY The spermatic arteries (V) are two in number, right and left, and they arise from the front of the aorta about i inch below the renal arteries. If they arise separately they are close to each other, but they sometimes spring by a common trunk. They are long, slender, somewhat tortuous vessels, which at once diverge, each passing obliquely downwards and out- wards behind the peritoneum. In this course the vessel rests upon the aorta for a short distance, and then upon the psoas mag- nus and its sheath, where it crosses the ureter. The right artery passes in front of the inferior vena cava and behind the terminal part of the ileum, whilst the left passes behind the iliac colon. Subsequently the artery, on its way to the internal abdominal ring, lies upon the terminal part of the external iliac. At the internal ring it approaches the vas deferens to form, with other structures, the spermatic cord. The vessel then passes through the internal abdominal ring, along the inguinal canal, and through the external abdominal ring into the scrotum, where it divides into testicular and epididymal branches. In the abdomen the spermatic artery furnishes ureteric branches to the ureter, and in the scrotum it gives off cremasteric branches to the coverings of the spermatic cord, which anastomose with the cremasteric branch of the deep epigastric. During foetal life the vessel is very short, and takes a transverse course to the testis, which is then lying below and behind the kidney. As the testis, iiowever, descends into the scrotum the vessel gradually becomes much elongated. Varieties. — ( i ) One or both spermatic arteries may be absent, in which cases the testis is supplied chiefly by the deferential artery. (2) A spermatic artery may arise from a renal artery. The spermatic veins spring from the pampiniform plexus of the spermatic cord at the internal abdominal ring, and are at first two in number on each side, which lie one on either side of the corresponding artery. They subsequently unite to form a single vessel, which on the right side opens at an acute angle into the inferior vena cava, and on the left at a right angle into the left renal vein. There is usually a valve at the point of termination of each vein, though this may be absent. In the left spermatic vein, where it joins the left renal vein, the valve directs the current of blood entering by the spermatic vein in the direction of the inferior vena cava. It also prevents the blood in the left renal vein from entering the spermatic vein by directipg the current over the mouth of the latter vessel. The left spermatic vein is rather longer than the right. The spermatic veins orif^inally open .into the lower cardinal veins. The right spermatic vein opens into that portion of the right cardinal vein wliich persists as the lower segment of the permanent inferior vena cava. The upper part of the left spermatic vein is formed from that portion of the left cardinal vein which lies immediately below the left renal vein. In this manner the difference in the mode of termination of the two spermatic veins in the adult is accounted for. I THE ABDOMEN 755 The ovarian arteries (V), in the female, take the place of the spermatic arteries in the male, and their com-se and relations in the abdomen correspond with those of the spermatics. The ovarian arteries are, however, shorter than the spermatics, and they do not pass out through the inguinal canal, but enter the pelvis by crossing the commencement of the external iliac artery. In the pelvis each vessel becomes very tortuous, and passes between the two layers of the broad ligament of the uterus to be distributed to the ovary. In the abdomen the artery supplies branches to the ureter, and in the pelvis it furnishes the following offsets : tnhal to the Fallopian tube ; a uterine branch to the side of the uterus ; and a ligaynentous branch to the round ligament of the uterus, which it accompanies as far as the inguinal canal. The ovarian arteries, like the spermatic, are very short and transverse in direction during foetal life, when the ovary occupies a position similar to that of the testis. They, however, gradually become elongated as the ovary descends to its future abode in the pelvis. The ovarian veins spring from the ovarian or pampiniform plexus between the two layers of the broad ligament, close to the ovary. After emerging therefrom their subsequent course and mode of termination resemble those of the spermatic veins. . . For the inferior mesenteric artery (V) and vein, see p. 729 ; for the middle sacral artery (P) and vein, see p. 86i ; and for the lumbar arteries (P) and veins, see p. 772. Inferior Vena Cava. — The inferior vena cava commences opposite the upper border of the body of the fifth lumbar vertebra a little to the right of the middle line, where it is formed by the union of the right and left common iliac veins, and it terminates at the postero-inferior angle of the right auricle of the heart. It ascends along the right side of the aorta, resting upon the anterior and right aspects of the lumbar yertebrse as high as the level of the second. Beyond this point it" diverges from the aorta, and is supported by the right cms of the diaphragm. It then occupies the caval fossa on the posterior surface of the right lobe of the liver. On leaving this fossa it passes through the caval opening in the central tendon of the diaphragm, and, almost immediately thereafter, it opens into the postero-inferior angle of the right auricle of the heart. As the vein passes through the caval opening its walls are connected with the margins of that opening, and so the patency of the vessel is maintained. Relations — Anterior. — From below upwards, the right common iliac artery, lower part of the root of the mesentery proper, right spermatic (or ovarian) vessels, third part of the duodenum, head of the pancreas, origin of the vena portae, first part of the duodenum, foramen of Winslow, and posterior surface of the liver. Posterior. — ^The bodies, discs, and anterior common ligament of the lower thiee lumbar vertebrae, the corresponding right lumbar vessels, inner border of the right psoas magnus and its sheath, 756 A MANUAL OF ANATOMY right sympathetic ganghated chain, right renal artery, right semi- lunar ganglion, right crus of the diaphragm, right suprarenal capsule, and right infeiior phrenic artery. Right. — From below upwards, the right ureter and the internal border of the right kidney. Hepatic Veins Right Inferior Phrenic ^*^J Right Suprarenal ^j/ Right Renal - -^-^--^ Right Spermatic Lumbar Veins <; Position of Caval Opening in Diaphragm .,Left Inferior Phrenic 'f//- Left Suprarenal Left Renal ---Left Spermatic Left Ascending Lumbar Right Common Iliac ,JL— Right Internal Iliac Right External Iliac Right Deep Circumflex Iliac Middle Sacral ^r Right Deep Epigastric Fig. 324. — Scheme of the Inferior Vena Cava and its Tributaries. Left. — From below upwards, the aorta and the right crus of the diaphragm. Tributaries. — ^These are as follows : the right and left common iliac veins, right and left lumbar veins, the right spermatic (or ovarian) vein, the right and left renal veins, the right suprarenal vein, the right inferior phrenic vein (and sometimes the left), and the hepatic veins at the caval fossa of the liver. Chief Varieties. — (i) The vessel may be found on the left side of the aorta in its lower part, in which cases it subsequently crosses that vessel to take up THE ABDOMEN 7^7 its usaal position on its right side. This may be due to a transposition of viscera, or to a permanent patency of the lower part of the left cardinal vein oi foetal life. (2) The inferior vena cava, in very rare cases, may terminate in a large right azygos vein, and, through means of that, in the superior vena cava. Under these circumstances the hepatic veins open into the right auricle of the heart. Development. — The postrenal segment of the inferior vena cava is usually regarded as being developed from the lower portion of the right posterior cardinal vein. The prerenal segment is developed from (i) the upper portion of the right subcardinal vein; (2) the hepatic sinusoids, and (3) the vena hepatica communis (Lewis). Aortic Lymphatic Glands. — ^These glands are very numerous, and are arranged in four groups, which lie around the abdominal aorta. The groups are spoken of as pre-aortic, lateral aortic, right and left, and retro-aortic, respectively. Pre-aortic Glands. — ^These are usually disposed in three sets, namely, (i) coeliac glands, which constitute a very distinct set around the origin of the coeliac axis; (2) superior mesenteric glands, in the region of the origin of the superior mesenteric artery, and along the trunk of the vessel ; and (3) inferior mesenteric glands, in the region of the origin of the inferior mesenteric artery. The afferent vessels of the pre-aortic glands are derived from the following sources : 1. Rectum. 8. Vermiform appendix. 2. Pelvic colon. 9. Small intestine. 3. Iliac colon. lo. Stomach. 4. Descending colon. 11. Liver. 5. Transverse colon. 12. Pancreas. 6. Ascending colon. 13. Spleen. 7. Caeciun. 14. Lateral aortic glands. The coeliac glands, more particularly, receive their chief afferent vessels from the following glands : 1. Coronar}^ or gastric glands. 3. Hepatic glands. 2. Retro-pyloric glands. 4. Splenic glands. 5. Pancreatic glands. The efferent vessels of the pre-aortic glands usually unite to form one trunk, called the intestinal lymphatic trunk, which opens into the receptaculum chyli, a few of them having traversed the retro- aortic glands. Lateral Aortic Glands (Lateral Lumbar Glands). — ^These are dis- posed in two groups — right and left. The right lateral aortic glands lie both in front of, and behind, the inferior vena cava ; whilst the glands of the left side form a single chain on the left side of the abdominal aorta. The lateral aortic glands, of either side, receive their afferent vessels from the following sources : 1. Common iliac glands. 4. Ovar>% Fallopian tube, and ad- 2. Limibar (lateral limibar) jacent half of body of uterus. glands. 5. Suprarenal body. 3. Testis. 6. Kidney. 758 A MANUAL OF ANATOMY Their efferent vessels, for the most part, unitC) on either side, to form a lateral aortic lymphatic trunk, right and left, which opens into the receptaculum chyli. Some pass to the pre-aortic glands, and others to the retro-aortic glands. Retro-aortic Glands. — ^These glands are about four in number, and they lie behind the abdominal aorta. Their afferent vessels are derived from the pre-aortic and lateral aortic glands, as well as from the vertebral bodies and ligaments to which they are related. Thexv efferent vessels unite to form a single trunk, called the retro- aortic lymphatic trunk, which opens into the receptaculum chyli. Diaphragm — Origin — Sternal Portion. — By two fleshy slips from the back of the ensiform process close to its lower end. Costal Portion. — By six fleshy slips, at either side, from the inner sur- faces of the lower six costal cartilages, which interdigitate with slips of the transversalis abdominis. Vertebral Portion. — From the external and internal arcuate ligaments, and the fronts of the bodies of lumbar vertebrae, as well as the intervertebral discs and anterior common ligament, by two crura, the right crus reaching usually as low as the disc between the third and fourth lumbar bodies, and the left as low as the disc between the second and third. Insertion. — ^The central tendon on all sides. Nerve-supply. — ^The right and left phrenic nerves, each of which springs chiefly from the anterior primary division of the fourth cervical nerve, and usually receives a branch from the third, and sometimes from the fifth. Each phrenic nerve, on approaching the diaphragm, divides into branches which pierce 'its muscular part separately in front of the central tendon, and are distributed on the abdominal surface of the muscle. In the right half of the muscle a communication takes place between the right phrenic nerve and the right inferior phrenic sympathetic plexus, a small ganglion, called the ganglion diaphragmaticum, being situated at the place of com- munication. A similar connection is established on the left side, but no ganglion is present. Arterial Supply. — (i) The inferior phrenic branches of the abdominal aorta ; (2) the superior phrenic (comes nervi phrenici) and musculo-phrenic, both branches of the internal mammary of each side ; (3) the phrenic branch of the superior epigastric of the internal mammary of each side ; and (4) branches from the lower intercostal arteries. Lymphatics. — ^These pass to the sternal, anterior mediastinal, posterior mediastinal, intercostal, and lumbar glands. Action. — ^The diaphragm by its contraction increases the vertical diameter of each half of the thorax, and is therefore a muscle of inspiration. The middle portion of the central tendon is fixed by reason of the fibrous portion of the pericardium, which is implanted into it, being connected above with the deep cervical fascia. The fleshy portion, however, becomes flattened, and descends towards the abdomen, displacing the viscera, and so increasing the vertical THE ABDOMEN 759 diameter of each half of the thorax. .The diaphragm also elevates the lower ribs, except the last. Metastemum Stemal Origin Central Tendon Caval Opening CEsophageal Opening Ltgamentum Arcuatum •'' Externum Quadratus Lumborum ^ Ligamentum Arcuatum Internum ' Psoas Magnus Right Cms Intervertebral Disc Fig. 325. — The Diaphragm (Inferior View). The muscular fibres pass in an arched manner upwards and inwards to the central tendon, upon which they converge from all points. The stemal portion is separated on either side from the costal portion by a small interval occupied by areolar tissue, through which the superior epigastric vessels and some of the superficial lymphatics of the upper surface of the liver pass. Above and below this interval are the pleura and peritoneum respectively. In this situation a diaphragmatic hernia may take place, involving one or other of the abdominal viscera. Between the lowest costal fibres and the corresponding external arcuate ligament there is sometimes another areolar interval of small size. The crura are strong, thick musculo-tendinous bundles disposed verticallj', the left being the smaller, shorter, and more posterior of the two. Each crus is fleshy externally, and strongly tendinous internally, the lower extremity of each being entirely tendinous. On a level with the lower border of the body of the twelfth thoracic vertebra the inner tendinous fibres of the crura are connected by a fibrous band, called the middle arcuate ligament, which lies in front of the aorta. The muscular fibres of the crura pass upwards in a diverging manner to be inserted into the posterior border of the central tendon. The innermost muscular fibres on either side, reinforced by fibres springing from the middle arcuate ligament, decussate before reaching the central tendon and enclose between them the oesophageal opening. In the decussation the bundle derived from the right crus passes in front of th t from the left, which latter is of small size. The central tendon is also called the cordiform or trefoil tendon. It is much elongated from side to side, convex in front, and con- 76o A MANUAL OF ANATOMY cave behind. It is divided into three lobes or alae, right, middle, and left, of which the right is the largest, and the left the smallest and narrowest. The separation into lobes is indicated by two small notches situated in the course of the anterior convex border. The diaphragm presents three foramina, namely, aortic, caval, and oesophageal. The aortic opening is situated in the middle line between the upper portions of the crura, and in front of the disc between the bodies of the twelfth thoracic and first lumbar vertebrae. It is bounded on either side by a crus, in front by the middle arcuate ligament, and behind by the anterior common ligament of the Central Tendon I L I V CEsophageal Opening Right Crus ' > Aortic Opening Ixft Crus Fig. 326, — The Diaphragm (Superior View) (After L. Testut's "Anatomic Humaine "). vertebral column. It is therefore not really an opening in the diaphragm, but is situated behind it. It transmits the aorta, thoracic duct, and right azygos vein, in this order from left to right. The caval opening (foramen quadratum) is situated in the central tendon close to its posterior border, and at the junction of the right and middle lobes. It is somewhat four-sided with rounded angles, and transmits the inferior vena cava and some of the deep lymphatics of the liver. The oesophageal opening is situated in the fleshy part of the muscle. It is elliptical, and lies in front, and a little to the left, of the aortic opening, being separated from it behind by the inner decussating fibres of the crura. It transmits the oesophagus, the THE ABDOMEN 761 right and left pneumogastric nen'es, and the oesophageal branches of the gastric artery. In addition to the foregoing foramina, the diaphragm presents certain small fissures, as follows : each crus is pierced by the great and small splanchnic nerves, and sometimes by the least. The left crus is also pierced by the lower left azygos vein. The musculo-phrenic artery pierces the costal portion, and the branches of the phrenic nerve are also transmitted through the muscle. The arcuate ligaments are five in number, as follows : external, right and left ; internal, right and left ; and middle. The external arcuate ligament is a thickening of the upper part of the anterior wall of the sheath of the quadratus lumborum, and extends from the last rib to the tip of the transverse process of the first lumbar vertebra. The subcostal artery and nerve pass downwards and outwards behind it. The internal arcuate ligament is a thickening of the upper part of the sheath of the psoas magnus, and extends from the tip of the transverse process of the first lumbar vertebra to the side of its body. The gangliated cord of the sympathetic passes into the abdomen behind it, and sometimes the least splanchnic nerve. The middle arcuate ligament is a fibrous band which connects the innermost tendinous fibres of the crura on a level with the lower border of the body of the twelfth thoracic vertebra, and it arches over the aorta. Relations of the Diaphragm — Superior. — The right and left pleurae with the lungs, and the pericardium with the heart. Inferior. — The peritoneum, except opposite the uncovered area of the posterior surface of the liver ; the liver with its suspensory, coronary', and right and left lateral or triangular ligaments ; the stomach ; spleen ; pancreas ; kidneys ; and suprarenal capsules. Development. — The diaphragm is develop)ed in two parts — ventral and dorsal. The ventral part, which is the first to appear, is developed from the upper layer of the septum transversum. It shuts off the pericardial cavity from the peritoneal cavity, leaving t^vo passages, one on each side of the primitive ahmentary tube, which are called the thoracic prolongations of the peritoneal cavity, and which are destined to form the pleural cavities. The dorsal part of the diaphragm is developed from the two plearo-peri- toneal membranes, formed by the pleuro-peritoneal folds, which grow from the dorsal and lateral body-walls, and which close the primitive pleuro-peri- toneal openings on either side. The fusion betsveen these pleuro-peritoneal membranes and the ventral part of the diaphragm may be incomplete on one or other side, in which cases a communication is left between the thoracic and abdominal cavities, through which a diaphragmatic hernia may occur. Gangliated Cord of the Sympathetic. — ^This cord enters the abdo- men behind the inner portion of the internal arcuate ligament. It then descends along the inner border of the psoas magnus, where it lies in front of the bodies of the lumbar vertebrae, and, having passed behind the common iliac artery, it enters the pelvis. The right lumbar cord is under cover of the inferior vena cava, whilst the left lies a little to the left of the aorta, and the lumbar vessels of each side pass beneath the corresponding cord. Each cord usually contains four ganglia. Branches. — These are arranged in two sets, namely, rami com- municantes, and branches of distribution. The rami communic antes, which are long, are of two kinds, white and grey, the latter being 762 A MANUAL OF ANATOMY the more numerous. The white rami are composed of medullated nerve-fibres, and are not more than three in number. They are derived from the anterior primary divisions of the first three lumbar nerves, and proceed to the ganglia. The grey rami pass from all four ganglia to join the anterior primary divisions of the five lumbar nerves. Both white and grey rami pass together beneath the fibrous arches of the psoas magnus in company with the lumbar vessels, and the communications with the lumbar nerves are estab- lished close to the intervertebral foramina. The branches of distribution proceed partly from the ganglia and partly from the connecting cord, and are distributed to the coats of the aorta, the bodies and ligaments of the lumbar vertebrae, and the hypogastric plexus, the last branches crossing the common iliac artery. Receptaculum Chyli. — ^This is the dilated commencement of the thoracic duct. Tt is situated deeply at the upper part of the posterior abdominal wall in front of the bodies of the first and second lumbar vertebrae, where it has the aorta on its left side and slightly in front, and the right azygos vein on its right side. It is overlapped by the right crus of the diaphragm. It is somewhat elliptical, being about ^ inch broad at its widest part, and about 2 inches in length. Superiorly it becomes narrow, and is continued into the thoracic duct, which enters the thorax through the aortic opening of the diaphragm. It receives the following afferent vessels from below upwards : the right and left lumbar lym- phatic trunks from the median lumbar glands, which join its lower narrow end ; some of the efferent vessels from the lateral lumbar glands ; and the intestinal lymphatic trunk (or trunks) from the mesenteric glands, which sometimes takes up the efferent vessels of the coeliac glands, though these may enter the receptaculum chyli independently. Azygos Veins. — ^These are three in number, namely, the vena azygos major, or right azygos vein, the vena azygos minor or lower left azygos vein, and the upper left, or accessory, azygos vein. The vena azygos major or right azygos vein usually commences in the right ascending lumbar vein, which is formed by longitudinal anastomosing branches passing between the lumbar veins in front of the lumbar transverse processes, and so disposed as to form one vein which communicates with the inferior vena cava and with one or other of the following veins of the right side : the common iliac, the internal iliac, the ilio-lumbar, or the lateral sacral. Sometimes, however, the right azygos vein springs from the posterior aspect of the inferior vena cava close to the right renal vein, or from that renal vein itself, or from the first right lumbar vein. It ascends upon the body of the first lumbar vertebra, where it lies on the right side of the receptaculum chyli under cover of the right crus of the diaphragm, and it enters the thorax through the aortic open- ing of that muscle. For its subsequent course in the thorax, where it terminates in the superior vena cava, sec the section of the thorax. The vena azygos minor or lower left azygos vein commences in THE ABDOMEN 763 the kit ascending lumbar vein, through which it has communications sunHar to those of the right azygos vein. It may, however, spring from the left renal vein, or the first left lumbar vein. It enters Right Lj-mphatic Duct Right Innominate Vei: . - S\ Superior Vena Ca\ Right Superior Intercostal Vei Right Azygos Vein Thoracic Duct Posterior Intercostal Glan<1s ._ Receptaculum Chyli_ Right Ascending Lumbar Ve Inferior lor Vena Cav3.__:.j.^ ■ • _ Thoracic Duct Left Innominate Vein .-._ Left Superior Intercostal Vein L Arch of Aorta _ Upper Left Azygos Vein L'pper Transverse Azygos Vein Lower Transverse Arj'gos Veir Ninth Intercostal Vein : Lower Left Azygos Vein 1.4^— Left Subcostal Vein ■Quadratus Lumbonui -Left Ascending Lumbar Vein -;... Abdominal Aorta ■ 7 vn- ^'V^^g^— Iliac Crest —V L— Psoas Magnus "A Common Iliac Arteries Fig. 327. — The Thoracic Duct, Azygos Veins, and Posjerior Intercostal Glands. the thorax through the left crus'of the diaphragm, and subsequently terminates in the right azygos vein. The right and lower left azygos veins are persistent portions of the right and left cardinal veins of foetal life. The right and lower left azygos veins, through their connections with the ascending lumbar veins, establish communications with 764 ' A MANUAL OF ANATOMY the inferior vena cava, and with the common iliac veins or some of their tributaries. They therefore form important channels by which a considerable quantity of blood is returned from the lower limbs and abdominal wall in cases of obstruction of the inferior vena cava. The upper left, or accessory, azygos vein will be found described in connection with the thorax. FasciaB of the Posterior Abdominal Wall — Iliac Fascia. — ^This fascia covers the iliacus and psoas magnus muscles. Above the level of the iliac crest it is related only to the psoas magnus, and the part covering that muscle is spoken of as the psoas sheath. Superiorly it forms the internal arcuate ligament, which extends between the tip of the first lumbar transverse process and the side of the body of that vertebra. Internally it is attached to (a) the intervertebral discs and contiguous margins of the bodies of the lumbar vertebrae, and (h) the fibrous arches over the lumbar vessels opposite the centre of each lumbar body. Externally, near the tips of the lumbar transverse processes, it blends with the anterior lamina of the lumbar aponeurosis which covers the quadratus lumborum. Below the level of the iliac crest the iliac fascia covers the iliacus as well as the psoas magnus. This part of it is known as the fascia iliaca, and it passes uninterruptedly from the iliacus on to the psoas magnus. Externally it is attached to the anterior two-thirds of the iliac crest immediately within its inner lip, and internally to the ala of the sacrum and the iliac portion of the ilio-pectineal line. Inferiorly it is disposed in the following manner : along the outer half of Poupart's ligament on its deep aspect the fascia is firmly attached to that ligament, and joins the fascia transversalis, the two constructing a canal which contains the first part of the deep circumflex iliac artery. Opposite the external iliac vessels the fascia passes downwards behind them and Poupart's ligament to form the posterior wall of the crural sheath. Internal to the external iliac vessels it is continuous with the pubic lamina of the fascia lata, as that covers the upper part of the pectineus. From the point of junction between the iliac fascia and the pubic fascia lata an intermuscular septum (ilio-pectineal) passes backwards between the pectineus and the psoas magnus to be attached to the ilio-pectineal eminence and the front of the capsular ligament of the hip- joint. The importance of the iliac fascia has reference to the course taken by pus in cases of lumbar (psoas) abscess. The pus cannot pass outwards over the quadratus lumborum without bursting through the psoas sheath, because the psoas sheath is bound down to the anterior wall of the sheath of the quadrajtus lumborum at the outer border of the psoas muscle. It cannot pass across the vertebral column on account of the attachments of the psoas sheath in that situation. The usual course, therefore, taken by the pus is to diffuse itself downwards within the psoas sheath. On reaching the iliac fossa it may diffuse itself outwards beneath the iliac fascia as that covers the iliacus muscle, but it cannot enter the pelvic cavity on account of the attachment of the iliac fascia to the pelvic brim, unless it bursts through the psoas sheath. Subsequently the pus usually treks along the psoas magnus THE ABDOMEN 765 witlriii its sheath, and, passing behind Poupart's ligament and the femoral vessels encased in the crural sheath, it usually points over the saphenous opening on a level with the small trochanter, where it may simulate a femoral hernia. Lumbar Aponeurosis. — This is situated between the last rib and the iliac crest, and is to be regarded as the posterior aponeurosis of the transversalis abdominis muscle. When followed backwards it divides into three laminae, anterior, middle, and posterior. The anterior lamina, which is thin, covers the quadratus limiborum, and is attached internally to the fronts of the transverse processes of the lumbar vertebrae near their tips. In this situation it is inter- posed between the quadratus Imnborvun and psoas magnus, and receives the iliac fascia which forms the psoas sheath. At the outer Erector Spinae Lumbar Spine Transverse Process Posterior Lamina of Lumbar Aponeurosis Middle Lamina of Lumbar Aponeurosis Quadratus Lumborum Anterior Lamina of Lumbar Aponeurosk Latissimus Dorsi Body of 3rd Psoas Magnus, covered Lumbar Vertebra by Psoas Fascia Obliquus Ext. Abd. Obliquus Int. Abdominis Transversalis Abdominis Fig. 328. — Diagram of the Lumbar Aponeurosis. border of the quadratus lumborum it joins the middle lamina, and is here also continuous with the fascia transversalis. Superiorly it forms the external arcuate ligament, which extends between the last rib and the tip of the first Ivunbar transverse process. Inferiorly it is attached to the ilio-lumbar ligament and the contiguous part of the inner lip of the iliac crest. The middle lamina, which is of considerable strength, is attached internally to the tips of the lumbar transverse processes, and externally, at the outer border of the quadratus lumborum, it is joined by the anterior lamina, whilst at the outer border of the erector spinae it receives the posterior lamina. Superiorly it is attached to the lower border of the last rib, and inferiorly to the back part of the summit of the iliac crest. The middle lamina lies between the quadratus limiborum and the 766 A MANUAL OF ANATOMY erector spinae. The posterior lamina, which is also very strong, is attached to the spinous processes of the lumbar and sacral vertebrae, and the posterior fourth of the outer lip of the iliac crest. It lies behind the erector spinae, at the outer border of which it blends with the middle lamina, and so the muscle is enclosed in a sheath. The posterior lamina is joined by the vertebral aponeurosis, and affords attachment to the latissimus dorsi and serratus posticus inferior. Muscles of the Posterior Abdominal Wall — Psoas Magnus — Origin. — (i) The fronts of the transverse processes of the lumbar vertebrae ; (2) the lateral aspects of the intervertebral discs, and of the adjacent borders of the twelfth thoracic, and all the lumbar, vertebrce ; and (3) a series of fibrous arches which cross the lumbar vessels at the centres of the bodies of the lumbar vertebrae. Insertion. — The small trochanter of the femur, by a tendon which receives, on its outer side, the greater part of the iliacus. Nerve-supply. — ^The lumbar plexus. The branches come more particularly from the anterior primary divisions of the second and third lumbar nerves. Action. — Acting from its origin the muscle is a powerful flexor of the thigh upon the pelvis, coming into play in walking, or ascending a stair. Acting from its insertion it is a flexor of the Imnbar portion of the vertebral column upon the pelvis, and of the pelvis upon the thigh, as in the act of stooping. The muscle of one side, acting from its insertion, is capable of producing lateral flexion of the lumbar portion of the vertebral column. As the muscle descends close to the pelvic brim the fibres of the iliacus begin to join the outer side of its tendon, and they continue to do so as far as the insertion, thus giving rise to a conjoined muscle known as the ilio-psoas. Psoas Parvus. — This muscle is present in man on one or both sides in about 45 per cent, of bodies. It arises from the lateral aspect of the intervertebral disc between the twelfth thoracic and first lumbar vertebrae, and from the - -+iofuous borders of their bodies, by means of a small fleshy belly, which is con-cjjiL 01 1*^ 2 inches long. It is then replaced by a long, narrow, flat usually about,, T^^jjjg ^^ -^^ ^g about to take insertion into the middle of the tendon which exp.. , „ the ilio-pectineal eminence, in which latter situation iho-pectmeal line and ^tineal intermuscular septum. It blends with the ilio-pewu ^qj. primary division of the first lumbar aerve. The nerve-supply is the ante. ,^ (^^^^ ^^ ^^^ ^^^ l^-^ ^ ^^^ vertebral Acting from its origin the muscu . ^^^^^^^ ^^^^^ f ^.^^ i^s insertion it column, and is a tensor of the psoas rcx.^art of the thoracic portion, of the tends to flex the lumbar portion, and lower i,„^^^gj.ig^i^, ^^^^^ fg g^g^ j^ ^hei vertebral column upon the pelvis. Its chare. .^.^^ ^^^ ^^^ ^f leaping, that! position assumed by saltatory animals preparatoryi ;^ ^^^ vertebral column,] position consisting in a drawing forwards of the pelvl ^^ psoas magnus close The psoas parvus lies along the anterior aspect of t^^i*^ ;,.3(jed tendon turns to its inner border, except at the pelvic brim, where its expai..^ to the inner side of that muscle. * Iliacus— On;?m.— (I) The upper surface of the ala of i^?^^^^'"""^ (2) the anterior sacro-iliac, ilio-lumbar, and lumbo-sacral life^*^^"! ^ J and (3) the upper half of the iliac fossa, reaching anteriorly,' ^ °^'^ as the anterior inferior iliac s]Mne. THE ABDOMEN 767 Insertion. — (i) The outer aspect of the tendon of the psoas magnns ; (2) the triangular surface which is situated below, and in front of, the smcJl trochanter of the femur (between it and the spiral line) ; and (3) the iho-femoral ligament. The fibres inserted into the ilio- femoral ligament are those which arise in the region of the anterior inferior iliac spine. They are sometimes separated from the rest of the muscle, and are then known as the iliacus minor or Uio-capsiilaris. Nerve-supply. — ^The anterior femoral nerve. JW Twelfth Rib Quadratus Lumbonun - PyrifiWTiiis Small Sacro-sciadc - - Ligament Great Sacro-sdatic r - Ligament Obturator Eztemus Fig. 3-29. — The Psoas, Iliacus. and Quadratos Lumboruh Muscles. - Action. — Acting from its origin the muscle is a flexor of the thigh upon the pelvis. Acting from its insertion it is a flexor of the peh-is upon the thigh. Quadratus Lumborum— Ong'tn.— (i) The ilio-lumbar ligament; (2) the inner lip of the crest of the iliiun for about 2 inches behind and outside the Uio-lumbar ligament ; and (3) the tips of the trans- verse processes of the lower three or four lumbar vertebrae. Insertion. — (i) The lower border of the last rib along its inner half, and {2) the tips of the transverse processes of the upper three or 768 A MANUAL OF ANAtOMY four lumbar vertebrae, by tendinous slips which lie behind the slips of origin. Nerve-supply. — ^The subcostal nerve and the anterior primary divisions of the first two lumbar nerves. Action. — Acting from its origin the muscle depresses and fixes the last rib, and is therefore a muscle of inspiration, inasmuch as it is auxiliary to the diaphragm. In depressing the last rib the muscle is also capable of producing lateral flexion of the vertebral column. Acting from the last rib it will produce lateral flexion of the pelvis. The muscle is encased in a sheath, the anterior wall of which is formed by the anterior lamina of the lumbar aponeurosis, and the posterior wall by the middle lamina. Lumbar Plexus. — ^The lumbar plexus is situated deeply in front of the transverse processes of the first three lumbar vertebrae, where it lies in the psoas magnus. It is formed by the anterior primary divisions of the first three lumbar nerves and the greater part of that of the fourth. In addition, the anterior primary division of the first lumbar is usually reinforced by a small com- municating branch from the subcostal nerve, called the dorso- lumbar nerve. The nerves coricerned in the lumbar plexus first furnish the following branches : (i) the first gives twigs to the psoas parvus when present ; (2) the first and second supply branches to the quadratus lumborum ; (3) the second and third give branches to the psoas magnus ; and (4) the upper two or three furnish white rami communicantes to the lumbar sympathetic gangliated cord. The mode of formation and branches of the plexus are as follows : The first lumbar, having been, as a rule, reinforced by the dorso- j 'umbar from the subcostal, furnishes, from above downwards, the .^.- rnuscie^ff.astric and inguinal, and then it descends to join a branch ilio-hyp^^. _ _ _ThiTljPu second, third, and that part of the fourth ^^^1,* second. x_ itame^'v. break up into a small anterior or which enters into the plex\nracic ai/iorsal division. The descending ventral, and a large posterior or'^J^Y "^'^ from the ventral division of branch from the first joins a brancn^^^^^^^^nerve, which arises next in the second to form the genito-femoral i-minenious nerve arises by two order to the inguinal. The external cutafftr septond and third. The roots from the dorsal divisions of the sei^^°^ ^' the dorsal divisions anterior femoral nerve arises by three roots from!,tw ^ third being the of the second, third, and fourth, the root from thethde roots from the largest Ihe obturator nerve arises usually by thre^ ^^^t the root from ventral divisions of the second, third, and fourth '■ ^^^P^ nerve, when nresenr".ri ""^^ ^! ''^''"*- ^^' ^^^^^^«^y obtm-at.'^'prth, which are present, arises by two roots from the third and fou i^ and main interposed between the roots of the anterior crui^^ ^^ obturator nerves. ^"^"^ acrai ^^ follows • The branches of the lumbar plexus are accordinfflv^^^'"^ ^^"^bar. I. Muscular to psoas parvus (when present), from fir^^ ^nd second ^^^2.Juscular to quadratus lumbofmn, from first \ THE ABDOMEN 769 3. Muscular to psoas magnus, from second and third lumbar. 4. Two or three white rami communicantes, to the lumbar sympathetic gangliated cord, from the upper two or three lumbar. 5. Ilio-hypogastric and inguinal, from first lumbar. 6. Genito-f emoral, from first and ventral division of second lumbar. 7. External cutaneous, from dorsal divisions of second and third lumbar . 8. Anterior femoral, from dorsal divisions of second, third, and fourth limibar. g. Obturator, from ventral divisions of second, third, and fourth lumbar. 10. Accessory obturator (when present), from third and fourth lumbar, between the roots of the anterior cnual and main obturator. Lurabo-sacral Cord Fig. 330. — Diagram of the Right Lumbar Plexus. The illo-hypogastrie nerve, having pierced the outer border of the psoas magnus near its upper part, passes outwards and down- wards over the quadratus lumborum, lying below the subcostal nerve and behind the kidney. It then pierces the posterior part of the transversalis abdominis a little above the iliac crest, and furnishes its iliac or lateral cutaneous branch, which, perforating 49 no A MANUAL OF ANATOMY the internal and external oblique, crosses the iliac crest at the junction of its middle and anterior thirds to be distributed to the integument of the adjacent part of the gluteal region. The nerve continues its course forwards between the internal oblique and transversalis abdominis, supplying branches to these muscles and communicating with the inguinal nerve. About i inch in front of the anterior superior iliac spine it pierces the internal oblique, and then runs forwards between the Poupart fibres of that muscle and the external oblique aponeurosis. • Finally it pierces that aponeurosis i inch above the external abdominal ring, and is distributed to the integument of the suprapubic region, where it is in series with the anterior cutaneous nerves. The ilio-hypogastric nerve is serially continuous with the intercostal nerves, like which it gives off a lateral cutaneous branch, called iliac, and then ends as an anterior cutaneous nerve. The inguinal nerve (ilio-inguinal), having pierced the outer border of the psoas magnus lower down than, but close to, the ilio-hypogastric, passes obliquely outwards and downwards over the quadratus lumborum, where it may lie below the lower end of the kidney or behind it. It then passes forwards internal to the inner lip of the iliac crest beneath the transversalis abdominis. In this part of its course it rests upon the iliac fascia and iliacus muscle. Near the anterior part of the iliac crest it pierces the transversalis, and here communicates with the hypogastric branch of the ilio-hypogastric. It subsequently perforates the Poupart fibres of the internal oblique, after which it descends through the lower two- thirds of the inguinal canal, and emerges through the external abdominal ring, where it lies external to the spermatic cord. Finally, having pierced the intercolumnar fascia, it is distri- buted to the integument of the inner side of the thigh in its upper third, and the integument of the scrotum, or labium majus, according to the sex. The inguinal nerve in its course supplies branches to the internal oblique and transversalis abdominis muscles. It differs from the ilio-hypogastric and intercostal nerves in the following two respects : it does not give off any iliac or lateral cutaneous branch, and it is not distributed to the integument of the abdominal wall. The genito-{emoral nerve passes forwards through the psoas magnus, and appears on its superficial surface about the level of the body of the third lumbar vertebra, where it lies close to the inner border of the muscle. It sometimes pierces the muscle in two parts, due to an early division of the nerve into its genital and crural branches. It then descends upon the psoas sheath, passing slightly outwards, and crossing behind the ureter. At a variable distance above Poupart's ligament (sometimes in the psoas magnus) the nerve divides into two branches, genital and crural. The genital branch lies upon the external iliac artery close above Poupart's ligament, and enters the inguinal canal through the internal abdominal ring to be distributed to the cremaster muscle. The crural branch descends on the outer side of the external iliac artery THE ABDOMEN m\ and passes out behind Poupart's ligament, having, just prior to this, crossed the deep circumflex iliac artery. On entering the thigh it lies for about \ inch within the crural sheath, and subse- quently, piercing the outer wall of that sheath, it is distributed to the integument over Scarpa's triangle. The external cutaneous nerve pierces the outer border of the psoas magnus near its centre, and takes a direction downwards and outwards over the back part of the iliac crest into the iliac fossa. It then crosses the iliacus under cover of the fascia iliaca towards the anterior superior iliac spine, where it emerges on to the thigh behind the outer end of Poupart's ligament. For the distri- bution of the nerve in the thigh, see p. 449. The anterior femoral nerve pierces the outer border of the psoas magnus about the level of the back part of the pelvic brim. It then passes forwards, lying deeply between the psoas magnus and iliacus, and emerges on to the thigh behind Poupart's ligament. Whilst in the abdominal cavity it gives branches to the iliacus muscle. The course and distribution of the nerve in the thigh will be found on p. 470. The obturator nerve pierces the inner border of the psoas magnus at the back part of the pelvic brim, and it lies upon the ala of the sacrum, having the lumbo-sacral cord on its inner side. Passing deeply behind the common iliac artery it enters the pelvic cavity, and passes along the outer wall a little below the pelvic brim, where it lies above the obturator artery. It then emerges on to the thigh through the obturator canal. For the course and distri- bution of the nerve in the thigh, see p. 474. The accessory obturator nerve (when present) pierces the inner border of the psoas magnus close to the main obturator nerve, but, unlike it, does not enter the pelvic cavity. Its course is forwards along the inner border of the psoas magnus underneath the external iliac vessels, and it emerges on to the thigh by passing over the superior pubic ramus beneath the pectineus muscle. Under cover of that muscle it divides into the following three branches : articular to the hip-joint ; muscular to the deep surface of the pectineus ; and a reinforcing branch to join the superficial or anterior division of the main obturator nerve. Varieties of the Lumbar Plexus. — These assume the form of two types, high or prefixed, and low or postfixed. In the prefixed type the anterior primary division of the third lumbar is a nervus furcalis, and takes part in the sacral plexus, whilst in the postfixed type the anterior primary division of the fifth lumbar is a nervus furcalis, and takes part in the lumbar plexus. Lumbo-sacral Cord. — This is formed by the union of the ventral and dorsal divisions of the descending branch of the fourth lumbar nerve with the ventral and dorsal divisions of the anterior primary division of the fifth lumbar. It is a large double tnmk, which rests upon the ala of the sacrum, being at first under cover of the psoas magnus, and subsequently lying on its inner side, where it has the obturator nerve external to it. In its course it passes behind the common and internal iliac vessels, and in the pelvis, its two divisions having joined those of the anterior primary division of the first sacral nerve, it takes part in the sacral plexus, entering 77^ A MANUAL OF ANATOMY more particularly the upper or outer band of that plexus which is continued into the great sciatic nerve. The anterior primary division of the fourth lumbar nerve is known as a nervus furcalis from the fact that it is distributed partly to the lumbar and partly to the sacral plexus. Lumbar Arteries. — These are branches of the abdominal aorta, being parietal in their distribution, and they are serially continuous with the aortic intercostal and subcostal arteries. They are eight in number, four right and four left, and they arise in pairs, separately or conjointly, from the posterior aspect of the parent trunk. They occupy the grooves at the centres of the bodies of the first four lumbar vertebrae. As each artery winds round a vertebral body it passes beneath one of the fibrous arches of the psoas magnus and the lumbar sympathetic gangliated cord. It then passes behind the psoas magnus and lumbar plexus, and, on reaching the interval between two adjacent lumbar transverse processes, it divides into two branches, dorsal and abdominal. The upper two arteries pass beneath the corresponding crus of the diaphragm, and those of the right side also pass beneath the receptaculum chyli and right azygos vein. All four arteries on the right side pass beneath the inferior vena cava. The trunk of each lumbar artery gives off a few vertebral branches to the body and ligaments of the adjacent vertebra, and muscular branches to the psoas magnus. The dorsal branch passes backwards between the adjacent transverse processes, in company with the posterior primary division of a spinal nerve, and it divides into an internal and external branch. The internal branch supplies the multifidus spinse, and the external branch supplies the erector spinse, giving also cutaneous branches which accompany the cutaneous nerves to the integument. Opposite an intervertebral foramen the dorsal branch furnishes a spinal branch, which enters the spinal canal through the foramen, to be distributed to the spinal cord and its coverings, as well as to the wall of the canal. The abdominal branch is to be regarded as the continuation of a lumbar artery. These branches usually pass behind the quadratus lumborum, with the exception, as a rule, of that of the fourth. At the outer border of that muscle they pierce the posterior aponeurosis of the transversal is abdominis, and pass forwards between that muscle and the internal oblique, as far as the lower part of the rectus abdominis, which they enter. They furnish the following offsets, in order : muscular to the quadratus lumborum ; capsular to the capsule of the kidney, which anastomose with branches of the renal artery ; subperitoneal to the subperitoneal areolar tissue, which anastomose therein with branches of the ilio-lumbar, the mferior phrenic, and the hepatic, colic, and renal arteries, thus forming the subperitoneal arterial plexus of Turner ; muscular to the abdominal muscles, which anastomose above with the lower two intercostal and subcostal arteries, below witli the lateral or intermuscular epigastric of the deep circumflex iliac, and ilio-lumbar, THE A BDOMEN 773 and in front with the deep epigastric. Sometimes there are five lumbar arteries on each side, the fifth pair coming usually from the middle sacral artery. Each of these passes beneath the correspond- ing common iliac vessels, and, ha\Tng furnished a dorsal branch, usually to the gluteus maximus, it is distributed over the lateral mass of the sacrum and ends in the iliacus, where it anastomoses with the deep circumflex iliac artery. The lumbar veins open into the inferior vena cava, those of the left side passing behind the abdominal aorta. The vessels of each side are connected by a series of longitudinal anastomosing veins in front of the lumbar transverse processes, and the longi- tudinal vessel thus formed is called the ascending lumbar vein. Subcostal Artery. — This vessel is the last parietal branch of the thoracic aorta. It lies below the last rib, and is in series with the aortic intercostals above and the lumbar arteries below. It winds roimd the side of the body of the twelfth thoracic vertebra, and courses along the lower border of the twelfth rib with the subcostal nerve, passing behind the external arcuate ligament of the diaphragm and in front of the quadratus lumborum. This part of the vessel is behind the kidney and the ascending or descending colon, according to the side. Its subsequent course corresponds with that of the abdominal branches of the lumbar arteries. It anastomoses with the lower two intercostal arteries, the abdominal branches of the lumbar arteries, the lateral or intermuscular epi- gastric of the deep circumflex iliac, and the deep epigastric artery. This vessel has to be borne in mind in such operations as nephrotomy, nephrorrhaphy, and nephrectomy. The subcostal vein of each side enters the thorax behind the external arcuate ligament of the diaphragm, the right opening into the right azygos vein, and the left into the lower left azj'gos vein. Subcostal Nerve. — This is the anterior primary division of the twelfth thoracic nerve, and is in series with the eleventh or last intercostal. It accompanies the subcostal artery, and ultimately enters the sheath of the rectus abdominis, which muscle it pierces from behind forwards to become an anterior cutaneous nerve. In its course it gives off an undivided lateral cutaneous or iliac branch, which pierces the internal and external oblique muscles, and descends over the iliac crest to be distributed to the integument of the anterior part of the gluteal region. Besides this branch it furnishes the following offsets: (i) dor so - lumbar to the anterior primary division of the first lumbar nerve ; and (2) branches to the quadratus lumborum, transversalis abdominis, internal oblique, and pyramidalis abdominis. Lumbar Glands. — ^These are very numerous, and are divided into three groups — median, and two lateral, right and left. The median lumbar glands are about twelve in number, and lie behind the parietal peritonemn, in front of, behind, and along the sides of the aorta (as high as the root of the superior mesenteric artery) and inferior vena cava. A few of the lower glands lie along 77 f A MANUAL OF ANATOMY the common iliac arteries, and these are sometimes spoken of as the eommon iliac glands. The median lumbar glands receive their afferent vessels from the following sources : (i) the external iliac glands ; (2) the internal iliac glands ; (3) the sacral glands ; (4) the efferent lymphatics of the testes in the male, and of the ovaries, Fallopian tubes, and upper end of the uterus in the female ; (5) the kidneys ; (6) the suprarenal capsules ; (7) the vertebral part of the diaphragm ; and (8) some of the efferent vessels of the lateral lumbar glands. Their efferent vessels unite to form two lumbar lymphatic trunks, right and left, which open into the lower end of Inferior Vena Cava Suprarenal Lymphatics I Renal Lymphatics Median Group of Lumbar Glands ^\M^\i jL \v. 11(1 11 tM 4 Mi' ''iliiA f Fig. 331, — Lymphatics of the Abdomen (after Mascagni). the receptaculum chyli on a level with the body of the second lumbar vertebra. The left trunk receives the lymphatics of the lower part of the left colon, iliac colon, and pelvic colon. The lateral lumbar glands are small but very numerous, being about twenty in number. They are situated behind the psoas magnus, where they lie between the lumbar transverse processes, and they receive their afferent vessels from the following sources : (i) the posterior abdominal wall and deep muscles of the back, and (2) the spinal canal. Some of their efferent vessels join the right and left lumbar lymphatic trunks, whilst others open independently into the lower end of the receptaculum chyli. Common Iliac Arteries. — These vessels are the terminal THE ABDOMEN 775 branches of the abdominal aorta. They arise from that vessel opposite the centre of the body of the fourth lumbar vertebra, a finger's breadth to the left of the middle line, and they at once diverge from each other. Their course is obliquely downwards and outwards over the lower portion of the body of the fourth and the whole of that of the fifth Imnbar vertebra, as well as the disc between the two. Each artery, on arriving opposite the lirnibo- sacral articulation, ends by dividing into external and internal iliac arteries. The length of the right common iliac is about 2 inches, and that of the left about i| inches. The left vessel is less oblique in direction than the right, and the course of each may be indicated in the following manner : draw a line from a point fully I inch below the umbilicus, a finger's breadth to the left of the middle line, to a point at the groin midway between the anterior superior iliac spine and the symphysis pubis, and let this line be slightly cur\'ed with the convexity directed outwards. About the upper 2 inches of this line indicate the course of the conunon iliac artery, and the remainder that of the external iliac vessel. Relations — Anterior. — ^The peritoneiun, coils of the small intes- tine, one half of the aortic sympathetic plexus, and the ureter, which latter crosses the artery close to its termination, though it may be transferred to the commencement of the external iliac vessel. An additional superficial relation of the left common iliac artery is that it is crossed by the superior hemorrhoidal vessels. Posterior. — Each artery rests upon the lower half of the body of the fourth and the whole of that of the fifth lumbar vertebra, as well as the disc above and below the latter, and the gangliated s\TTipathetic chain. The right vessel is separated from the fore- going structures by the commencement of the inferior vena cava, the terminal part of the left common iliac vein, and the right common iliac vein, whilst the left vessel is free from posterior venous relations. Lying deeply behind each artery there are the obturator nerve, lumbo-sacral cord, and ilio-lumbar artery. External. — On the outer side of the right vessel there are, from above downwards, the inferior vena cava, right common iliac vein, and psoas magnus. On the outer side of the left vessel is the psoas magnus. Internal. — On the inner side of the right vessel, from below up- wards, there are the right common iliac vein, the left common iliac vein, and the hypogastric sympathetic plexus. Oh the inner side of the left vessel there are the left common iliac vein, and the hypogastric plexus. It is to be noted that the left artery is related only to its own vein, which lies on its inner side. The right artery, on the other hand, is related to three veins as follows : the inferior vena cava, which lies partly behind its upper end and partly on its outer side ; the terminal part of the left conunon iliac vein, which lies partly on its inner side and partly behind it : and the right common iliac 776 A MANUAL OF ANATOMY vein, which, from below upwards, lies first on its inner side, then behind it, and finally on its outer side. Branches. — ^These are as follows : peritoneal to the peritoneum and subperitoneal areolar tissue ; muscular to the psoas magnus ; ureteric to the ureter (all of small size and unimportant) ; external iliac ; and internal iliac. In some cases the common iliac gives of^ one or other of the following vessels : ilio-lumbar, middle sacral, lateral sacral, lumbar, or an aberrant renal artery. Varieties. — The chief variety affects the length of the vessel. It may be very short, which is due either to a low bifurcation of the aorta or a high bifurcation of the artery itself ; or it may be very long, which is due to exactly opposite causes. When abnormally long, the vessel is usually more or less tortuous. Collateral Circulation. — After ligature of a common iliac artery, the chief channels by which the circulation is carried on are as follows : ( i ) the superior epigastric of the internal mammary from the first part of the subclavian anasto- moses with the deep epigastric of the external iUac ; (2) the lumbar branches of the aorta anastomose with (a) the lateral or intermuscular epigastric of the deep circumflex iliac from th^-eKternal iliac, and (b) the ilio-lumbar of the internal iliac ; (3) the superior hemorrhoidal of the inferior mesenteric from the aorta anastomoses with (a) the middle hemorrhoidal of the internal iliac, and (b) the inferior hemorrhoidal of the internal pudic from the internal iliac ; (4) the middle sacral from the aorta anastomoses with the lateral sacral branches of the internal iliac ; and (5) the pubic branches of the obturator from the internal iliac and of the deep epigastric from the external iliac, both of one side, anastomose across the middle line with the corresponding branches of the opposite side. The vesical, and middle and inferior hemorrhoidal arteries of one side anastomose in a similar manner with those of the opposite side. Common Iliac Veins. — Each vein is formed by the union of the external and internal iliac veins opposite the corresponding sacro- iliac articulation, on a level with the brim of the pelvis. They unite to form the inferior vena cava opposite the upper border of the body of the fifth lumbar vertebra a little to the right of the middle line, behind and on the right side of the right common iliac artery. The right vein is necessarily shorter than the left, and it ascends almost vertically, lying at first internal to, then behind, and finally on the outer side of its own artery. The left vein ascends very obliquely from left to right, lying internal to its own artery, and then behind that of the right side. It crosses the middle sacral artery, and is crossed by the superior hemorrhoidal vessels and the left half of the aortic plexus. The common iliac veins are usually destitute of valves. Tributaries. — These are chiefly the external iliac, internal iliac, and ilio-lumbar. In addition, the left vein receives the middle sacral vein. The left common iliac vein is mainly the persistent and enlarged transverse branch (transverse iliac) which connects the right and left cardinal veins of the embryo above the back part of the pelvic brim. Its commencement, however, is developed from a portion of the left cardinal vein. The right common iliac vein is developed from the part of the right cardinal vein which intervenes between the termination of the right external iliac vein and the right extremity of the transverse iliac vein. THE ABDOMEN 777 Common Iliac Lymphatic Glands. — ^These glands are about nitie in number, and are arranged in three groups — external, posterior, and internal — which lie along the common iliac artery. The afferent vessels of the external group are derived from the external iliac glands; those of the posterior group come from the internal iliac glands ; and the afferent vessels of the internal group proceed from (i) the prostate gland, (2) the base of the bladder, (3) the lower part of the vagina, and (4) the cervix uteri. The efferent vessels of all* the common iliac glands of one side pass to the lateral aortic glands of the same side. External Iliac Artery.— This vessel is the larger of the two ter- minal divisions of the common iliac in the adult. It extends from the lumbo-sacral articulation to the lower margin of Poupart's ligament, where it is continued into the common femoral artery. Its course is along the pelvic brim, and at the groin it passes through the vascular lacuna at a point midway between the anterior superior iliac spine and the symphysis pubis. The course of the vessel may be indicated in the following manner: Draw a line from a point fully I inch below the umbilicus, a finger's breadth to the left of the middle line, to a point at the groin midway between the anterior superior iliac spine and the symphysis pubis, and let this line be slightly curved with the convexity directed outwards. About the upper 2 inches of this line indicate the course of the common iliac artery, and the remainder that of the external iliac vessel. The line indicating the course of the vessel corresponds to the lower part of that which has been given as indicating the course of the common iliac. The vessel is from 3I to 4 inches long, and its direction is downwards, outwards, and forwards. Relations — Anterior. — The artery is covered by the parietal peri- toneum and subperitoneal areolar tissue, the portion of the latter which is related to it being known as Abernethy's fascia. The right vessel at its commencement is crossed by the terminal part of the ileum, and sometimes by the v^ermiform appendix, whilst the left at its commencement is crossed by the pelvic colon, and each may be crossed by the ureter. In the female both arteries are crossed superiorly by the ovarian vessels. Near Poupart's ligament each vessel is crossed by the deep circumflex iliac vein, and the genital branch of the genito-crural nerve lies upon it. The spermatic vessels in the male also lie for a short distance upon it in this situa- tion, and the vas deferens (or round ligament of the uterus) arches over it from without inwards. The external iliac glands lie along the artery. Posterior. — ^The artery rests upon the iliac fascia at the pelvic brim, except for a little above Poupart's ligament, where it lies upon the psoas muscle with the intervention of the iliac fascia, as that forms its sheath. The right artery at its commencement has its own vein behind it for a short distance, and each vessel may have the accessory obturator nerve as a deep posterior relation. External. — ^The psoas magnus covered by the iliac fascia, the genito- crural nerve, and its crural branch Internal. — ^The peritoneum, 778 A MANUAL OF ANATOMY the subperitoneal areolar tissue (Abernethy's fascia), which binds the artery with its vein to the iliac fascia, the external iliac vein (except for a short distance above on the right side, where the vein is behind its artery), and the vas deferens near Poupart's ligament. Branches. — These are as follows : muscular to the psoas magnus ; glandular to the external iliac glands (both unimportant) ; deep epigastric; and deep circumflex iliac. For the latter two, see pp. 662, 663. Varieties of the Branches. — (i) The origin of the deep epigastric may be transferred to the common femoral, or to the arteria profunda femoris, and the deep circumflex iliac may be transferred to the common femoral. (2) The internal circumflex, obturator, or arteria profunda femoris may arise from the external iliac, in which latter case two large arteries would emerge on to the thigh beneath Poupart's ligament. The external iliac vein is the continuation of the femoral vein. It extends from the lower border of Poupart's ligament to the sacro-iliac articulation on a level with the brim of the pelvis, where it joins the internal iliac, and so forms the common iliac vein. The right vein lies at first internal to its artery, and then behind it. The left vein lies internal to its artery throughout. Its chief tribu- taries are the deep epigastric and deep circumflex iliac veins. The external iliac vein of adult life is preceded in function by the sciatic vein of the embryo, which is the primitive vein of the lower limb. In the process of development the upper part of the femoral and the whole of the external iliac vein of the adult are continued upwards from the long saphenous vein to the cardinal portion of each common iliac vein, and the sciatic vein is now a tributary of the internal iliac. Collateral Circulation. — When the external iliac artery is ligatured, the collateral circulation is carried on through the following channels : ( i ) the superior epigastric of the internal mammary from the first part of the subclavian anastomoses with the deep epigastric of the external iliac ; (2) the pubic branch of the obturator from the internal iliac anastomoses with the pubic branch of the deep epigastric ; (3) the ilio-lumbar and gluteal, both from the internal iliac, and the abdominal branches of the lumbar arteries from the aorta anastomose with the deep circumflex iliac of the external iliac ; (4) the obturator from the internal iliac anastomoses with the internal circumflex of the arteria profunda femoris ; ( 5 ) the sciatic from the internal iliac anastomoses with the internal and external circumflex, and the first perforating of the arteria profunda femoris ; (6) the gluteal anastomoses with the external circumflex and the ascending branch of the internal circumflex from the arteria profunda femoris ; (7) the arteria comes nervi ischiadici of the sciatic anasto- moses with the perforating branches of the arteria profunda femoris ; and (8) the superficial perineal and dorsalis penis of the internal pudic from the internal iliac anastomose with the superior and inferior external pudics of the common femoral. External Iliac Lymphatic Glands. — ^These glands are related to the external iliac vessels, and are about twelve in number. They are usually arranged in three chains — outer, middle, and inner — there being about four glands in each chain. The outer chain lies on the THE ABDOMEN 779 outer side of the external iliac arten', between it and the psoas magnus muscle, except the lowest gland, which lies upon that muscle. The middle chain lies in front of the external iliac vessels. The inner chain lies below the level of the external iliac vein, upon the upper part of the lateral wall of the pelvis, above the obturator nerve. One of the glands of this chain may lie within the pelvic entrance to the obturator canal, and is spoken of as the obturator gland, but it is not constant. The lowest gland of each chain lies close to the deep aspect of Poupart's ligament, and these are known as the retfo- femoral glands — external, middle, and internal respec- tively. The afferent vessels of the external iliac glands convey IjTnph from the following sources : 1. The deep femoral glands, 2. Some of the inguinal and superficial femoral glands. 3. The deep structures of the antero-lateral abdominal wall hdow the umbilicus. 4. To a certain extent the glans penis, or glans clitoridis, these hTTiphatics passing along the inguinal canal. 5. The adductor muscles. 6. The prostate gland and prostatic urethra, in part. 7. The bladder. 8. Part of the membranous and the bulbar portions of the urethra. 9. The upper part of the vagina. 10. The body and cersix of the uterus. The efferent vessels of all the external iliac glands pass to the common iliac glands. Lacunar Region. — ^The lacunar region is situated between Poupart's ligament and the anterior margin of the os innomi- natum, and is divided into two compartments — ^muscular and vascular. The muscular lacuna is subdi\nded into two portions, external or iliac, and internal or pectineal, by the ilio-peciine^l septum, which separates the psoas magnus from the pectineus. This septum passes between the ilio-pectineal eminence and the fascia ihaca at its point of junction with the upper part of the pubic portion of the fascia lata. The iliac compartment, which is of large size, is bounded in front by the outer part of Poupart's ligament and the iliac fascia, behind by the anterior margin of the iliiun, and internally by the ilio-pectineal septum. It transmits (i) the ilio- psoas muscle, (2) the external cutaneous nerve, and (3) the anterior femoral ner\'e. The pectineal compartment is situated between the superior pubic ramus behind, and the upper part of the pubic lamina of the fascia lata in front, the ilio-pectineal septum being external to it. It contains the origin of the pectineus muscle, and is shut off from the abdominal ca\nty by the attachment of the pubic lamina of the fascia lata to the pectineal portion of the ilio- pectineal line. In connection with this portion of the fascia lata 78o A MANUAL OF ANATOMY there is a bundle of fibres, known as the pubic ligament of Cooper. This ligament extends between the ilio-pectineal eminence and the pubic spine, between which points it is attached to the pectineal portion of the ilio-pectineal Ime in front of Gimbernat's ligament, being closely incorporated with the pubic lamina of the fascia lata. t. Pubic Spine 7- Psoas Magnus 12. Iliacus 2. External Abdominal Ring 8. Femoral Artery 13- External Cutaneous Nerve 3- Gimbernat's Ligament 9- Femoral Branch of Genito- 14. Ant. Superior Iliac Spine 4- Pectineus femoral Nerve IS- Acetabulum 5- Crural or Femoral Ring lO. Anterior Femoral Nerve 16. Obturator Foramen 6. Femoral Vein II. Poupart's Ligament Fig. 332. — Poupart's Ligament and the Lacunar Region. The vascular lacuna is situated anterior to the other two. It is bounded posteriorly by the connection between the iliac fascia and the pubic lamina of the fascia lata, whilst anteriorly it is bounded by the central portion of Poupart's ligament and the downward prolongation of the fascia transversalis to form the anterior wall of the femoral sheath, that fascia being here strengthened by the deep femoral arch. It gives passage to (i) the external iliac vessels, the THE ABDOMEN 781 vein being internal to the arter\', and (2) the femoral branch of the genito-femoral nerve, which lies close to the outer side of the artery. The part of this lacuna internal to the external iliac vein forms the crural or femoral ring, which is closed by the septum femorale. STRUCTURE AND DEVELOPMENT OF THE ABDOMINAL VISCERA Structure of the Stomach. The wall of the stomach is composed of four coats — serous, muscular, submucous, and mucous. The serous coat is formed by the peritoneum, which covers every part of the organ except (i) along the great and small CEsophagus Longitudinal Muscniar Layer s Pyloric Sphincter V Fig. 333. — Dissection showing the Muscular Layers of the Stomach. *s I curvatures, and (2) the uncovered trigone, situated on the posterior |, surface, below and a little to the left of the cardiac orifice. The muscular coat {muscidaris externa) is composed of plain muscular tissue disposed in three layers external or longitudinal, middle or circular, and internal or oblique. The external or longi- titdinal fibres are continuous with the longitudinal fibres of the oesophagus, and at the pyloric end of the stomach they are continuous with the longitudinal fibres of the duodenum. They are most abundant along the small curvature. The middle 782 A MANUAL OF ANATOMY or circular fibres completely surround the stomach from the fundus to the pyloric end. At first they are thin and irregular in position, but over the pyloric canal they are thick. At the pylorus they become augmented, and are gathered together into a thick muscular ring, called the sphincter pylori, which lies within a circular fold of the mucous membrane. The outermost fibres of this ring become continuous with the circular fibres of the duodenum. Some of the circular fibres appear to be continuous with the superficial circular fibres of the right side of the lower end of the oesophagus. The internal or oblique fibres are continuous with the circular fibres of the left side of the lower end of the oesophagus. They loop over the stomach immediately to the left of the cardia, and run very Cardiac Orifice CEsophagus Fundus Small Curvature Hepatic Duct^ Cystic Duct Pylorus Ductus Communis - Choledochus Great Curvature Duct of Wirsung Duodenum Fig. 334. — The Stomach and Duodenum opened. obliquely downwards and to the right for a considerable distance on both surfaces of the organ . They cannot be traced as far as the pylorus, but end by inclining downwards to the great curvature, where they blend with the circular fibres. The submucous coat is situated between the muscular and mucous coats. It is composed of loose areolar tissue, and serves partly as a connecting medium, and partly as a bed in which the arteries subdivide before entering the mucous coat. The mucous coat is covered by a single layer of columnar epi- thelium, many of the cells being mucus-secreting goblet cells. It is solt and pulpy, and in the empty state of the viscus is thrown into rugae, which are for the most part longitudinal, and are due to the* loose connection between the muscular and mucous coats. These,! however, are readily effaced when the stomach becomes distended.! THE ABDOMEN 7^i It is thickest towards the pyloric end, and in healthy adults it has a light crimson colour, while in early life this is heightened into a bright rosy tint. After death, however, it presents a mottled appearance, being marked with grey- brown patches. When examined w ith a lens, it presents a great number of polygonal depressions, varying in diameter from y^^ to gi-^ inch, the largest being near the pylorus. These impart to it a honeycomb appearance. The mucous mem- brane surrounding them is elevated into ridges by subjacent capillary networks, and in the region of the pylorus these ridges present processes, called pliccB villosce. The polygonal depressions are beset with minute pores. Duct which are the orifices of the gastric glands. These glands, which belong to the tubular variety, are placed per- pendicularly in the mucous coat, and are closely packed together like upright stakes. They are of two kinds, cardiac and pyloric, between which there are certain differences. The cardiac glands are situated in the cardiac two- thirds. The duct of each forms about one- third of the entire length of the gland. It is lined with a single layer of columnar epithelium. The deep end of the duct is connected with two or three gland- tubes, which represent y Mucosa with Cardiac Glands Muscularis Mucosae ^^-^^^^g Submucosa Muscular Coat Peritoneal Coat Fig. 335. — The Cardiac Glands of the Stomach (highly magnified). two- thirds of the entire gland. Each gland-tube is divisible into a neck, body, and fundus. The neck is the part connected with the duct, and it forms one- third of the length of the gland- tube. It is narrower than the body, and is lined with coarsely granular polyhedral cells, which almost completely fill it, thus leaving a very small lumen. These are called the central or chief cells. Between these and the basement membrane there are interposed large oval or spherical granular cells, each having a clear nucleus. These, which are called the parietal or oxyntic (' acid- forming ') cells, do not form a continuous layer, but are placed at intervals, and they give rise to small swellings on the wall of the neck. The body is wider than the neck, and forms two-thirds of 784 A MANUAL OF ANATOMY the length of the gland-tube. It is lined by a prolongation of the central or chief cells of the neck, which almost completely fill it, and which have now become somewhat columnar and transparent. Between these cells and the basement membrane there are a few parietal or oxyntic cells here and there. The parietal cells of the neck and body impart the characteristic beaded appearance to the gland- tube. The fundus is the blind deep end of the gland-tube. The pyloric glands are situated in the pyloric third. The duct of each forms one half of the entire length of the gland. It is lined with a single layer of columnar epithelium. The deep end of the duct is con- nected with two or three gland-tubes, which re- present one half of the entire gland. The neck of each tube is com- paratively short, and the body is branched at its deep extremity. The neck and body are lined with cubical granular cells, representing the central or chief cells of the cardiac glands, and they are not so crowded as in the cardiac glands, so that there is a very distinct lumen. There is an entire absence of parietal or oxyntic cells, and the body of each gland- tube has an undulating, convoluted outline. The pyloric glands are serially continuous with Brunner's glands of the small intestine. Mucosa with Pyloric Glands Muscularis Mucosse Submucosa Muscular Coat Z Peritoneal Coat Fig. 336. — The Pyloric Glands of Stomach (highly magnified). Summary of the Cardiac and Pyloric Glands. Cardiac Glands. Ducts short. Gland-tubes long. Gland-tubes almost filled with coarsely granular polyhedral cells, called central or chief cells. I>umen very small. Gland - tubes have parietal or oxyntic cells between the central cells and the basement mem- brane. Pyloric Glands. Ducts long. Gland-tubes short. Gland-tubes lined with cubical granular cells. Lumen distinct. Gland-tubes destitute of parietal or oxyntic cells. THE ABDOMEN 783 At the deepest part of the mucous coat, and forming a part of it, there is a stratum of plain muscular tissue, called the muscularis mucoscB {muscularis interna), which is disposed in two layers — outer longitudinal, and inner circular. The mucous membrane is also provided with lymphoid tissue in the interspaces between the deep ends of the gastric glands. In the cardiac part of the stomach this lymphoid tissue occurs in the form of isolated collections, called lymph follicles, which bear a resemblance to the solitary glands of the intestinal mucous membrane. In the neighbourhood of the pylorus these lymph follicles become aggregated, and so resemble somewhat the agminated glands or Peyer's patches of the small intestine. Blood-supply — Arteries. — Along the small curvature there are (i) the gastric branch of the coeliac axis in two divisions, and (2) the pyloric branch of the hepatic, also in two divisions. Along the great curvature there are (1) the right gastro-epiploic of the gastro- duodenal of the hepatic from the cceliac axis, and (2) the left gastro- epiploic of the splenic from the coeliac axis. At the fvmdus there are the vasa brevia of the splenic artery. The branches arising from all these arteries enter the muscular coat without piercing the peritoneum. They subsequently make their way inwards to the submucous coat, where they break up into branches which freely anastomose with one another. Fine branches then enter the mucous coat, which rim upwards between the closely- packed gastric glands, round which they form by their anastomoses a delicate capillary network with its meshes elongated in the direction of the gland-tubes. From this network somewhat larger vessels proceed upwards, which by their anastomoses form a coarser and more superficial network around the orifices of the ducts of the glands. Veins. — ^These arise from the superficial network of capillaries round the orifices of the ducts of the glands. They take a down- ward course between the gland- tubes, and on reaching their deep ends they form a plexus. From this plexus branches proceed outwards to the submucous coat, in which they form another plexus. The branches arising from this latter plexus, having passed through the muscular coat, terminate in the following veins : (i) the right gastro-epiploic, which opens into the superior mesen- teric ; (2) the left gastro-epiploic and vasa brevia, which open into the splenic ; (3) the gastric ; and (4) the pyloric, the latter two opening directly into the vena portae. The veins of the stomach contain numerous valves, which are sufficiently competent in early life to oppose the return of venous blood, but in the adult [ they are incompetent. j Lymphatics. — These commence near the free surface of the mucous j membrane either in loops or in enlargements, and they take a down- I ward course between the gland- tubes, where they open into a net- work of lacunar spaces. The branches which proceed from this network on reaching the deep ends of the glands form a plexus, 50 7»6 A MANUAL OF ANATOMY i'and the vessels issuing from this plexus on entering the submucous coat form another plexus, the lymphatics of which are furnished with valves. The vessels which emerge from this latter plexus accompany the bloodvessels, and pass to the small and great curvatures, and the vicinity of the hilum of the spleen. At the curvatures they are connected with the superior and inferior gastric lymphatic glands, whilst those which accompany the vasa brevia arteries pass through the splenic glands, the efferent vessels of all these glands ultimately passing to the coeliac glands. In addition to the lymphatic vessels just described there is a subperitoneal lymphatic plexus. Nerves. — ^These are derived from (i) the two pneumogastric nerves, and (2) sympathetic plexuses from the solar plexus. The right pneumogastric nerve descends upon the posterior surface of the stomach, whilst the left nerve descends upon the anterior surface. The sympathetic -plexuses closely accompany the arteries. The nerves form two gangliated plexuses composed of non-medullated nerve-fibres. One of these is situated between the longitudinal and circular fibres of the external muscular coat, and corresponds to the plexus myentericus of Auerbach of the intestine. The other plexus is situated in the submucous coat, and corresponds to the plexus of Meissner of the intestine. . The explanation of the right pneumogastric nerve descending upon the posterior surface, and the left upon the anterior surface, of the stomach is found in the position assumed by the stomach in the early embryo. Briefly stated, at that period of life the stomach is a straight tube, and its surfaces are right and left. The two pneumogastric nerves, therefore, right and left, naturally descend on the right and left surfaces of the viscus. When, however, the stomach turns over on its right side, the surface which was originally right becomes posterior, and the surface which was originally left becomes anterior. Thus the right nerve eventually descends on the posterior (originally the right) .•surface, and the left nerve descends on the anterior (originally the left) sur- face. Pylorus. — ^The opening between the pyloric end of the stomach and the duodenum is provided with a sphincter muscle, called the sphincter Pylori, This is formed by an aggregation of the circular muscular fibres, which causes the mucous membrane to project in the form of an annular fold, thus giving rise to the pyloric valve. The sphincter pylori is only relaxed when the contents of the stomach are being passed into the duodenum. At all other times, it is in a condition of firm contraction, and the pyloric orifice then takes the form of a cleft. The. average length of the stomach is about 12 inches, and its average width at the widest part about 5 inches. I t weighs about 4J ounces, and its capacity, which is very variable, ranges from 3 to 5 pints. THE ABDOMEN 787 Structure of the Intestinal Canal. Small Intestine. — The wall of the small intestine, which is cylindrical, is composed of four coats — serous, muscular, sub- mucous, and mucous. The serous coat is formed by peritoneum derived from the mesen- tery proper. In the case of the duodenum it is incomplete, but it forms a complete investment to the jejunum and ileum, except along a narrow interval corresponding to the mesenteric border of the bowel, where the peritoneal investment becomes continuous with the two layers of the mesentery proper. The muscular coat {mitscidaris externa) is composed of plain muscular tissue, disposed in two layers, external or longitudinal, and internal or circular. The external or longitudinal fibres are continuous with the corresponding fibres of the stomach, and they are best marked along the an ti- mesenteric border. The internal or circular fibres are continuous with the outermost fibres of the sphincter pylori, and form a much thicker layer than the longitu- dinal. The muscular coat .attains its greatest thickness in the duodenum, whence it gradually diminishes. Between the two muscular layers there is a gangliated plexus of non-medullated ner\'e-fibres, called the plexus myentericus of Auerbach, and also a plexus of Hinphatic vessels. The submucous coat is situated between the muscular and mucous coats. It is composed of loose areolar tissue, and serves partly as a connecting medium and partly as a bed in which the arteries subdivide. It contains a gangliated plexus of non-medul- lated nerve-fibres, called the plexus of Meissner, and a plexus of l5nnphatic vessels. In the duodenum this coat lodges Brunner's glands, and the deep ends of the solitary glands project into it throughout. The mucous coat is red and thick in the upper part of the small intestine, but pale and thin in the lower part. It is covered by a single layer of columnar epithelium, many of the cells being mucus- secreting goblet cells. The protoplasm of the cells is longitudinally fibrillated, and their free ends are covered by a delicate striated basilar border, the striations being vertically disposed. Underneath the epithelium there is a basement membrane, known as the stib- epithelial endothelium, and underneath this is the main part of the mucous coat, which is essentially composed of adenoid tissue, that is to say, retiform tissue containing in its meshes lymph corpuscles. At the deepest part of the mucous coat, and forming a part of it, there is a stratum of plain muscular tissue, called the muscularis mucosce {muscidaris interna), which in many situations is disposed in two layers — outer longitudinal, and inner circular. 2 PR A MANUAL OF ANATOMY In some places, however, only the outer longitudinal layer is present. The mucous coat is beset all over with minute projections, called villi, and is sometimes called the villous coat. These villi impart to it a woolly appearance like the nap of velvet. It diminishes in thickness from above downwards, and is characterized by the following structures : (i) valvulae conniventes, (2) villi, (3) Brunner's glands, (4) crypts or follicles of Lieberkiihn, (5) solitary glands, and (6) agminated glands or Peyer's patches. Of the foregoing structures the valvulae conniventes, villi, and Peyer's patches constitute the macroscopical (naked-eye) characters of the mucous membrane, the others forming its microscopical characters. The valvulae conniventes (valves of Kerkring) are permanent folds of the mucous membrane, which cannot be effaced. They are absent from the first part of the duodenum for a distance of from I to 2 inches from the pylorus. Commencing about the . upper end of the second part of the duodenum as small straggling folds, they become large and distinct at the place of entrance of the ductus communis choledochus and pancreatic duct (about 4 inches from the pylorus). Throughout the rest of the duodenum and in the upper part of the jejunum they are still prominent, and are placed close to each other. In the lower part of the jejunum they become smaller, and are placed farther apart. In the upper part of the ileum they become still smaller and more irregular, and they finally disappear just beyond the centre of the ileum. They are crescentic folds placed across the bowel, and each consists of two layers of mucous membrane applied back to back, with a little submucous areolar tissue intervening. Their average length is about 2 J inches, and the average breadth of each. is about J inch. The majority of them extend round the bowel for from one-half to two-thirds of its circumference. Some, how- ever, describe complete circles, whilst a few are arranged in a spiral manner so as to describe from one to three turns round the tube. Some of them begin and terminate in bifurcated extremities, whilst others present abrupt single ex- tremities. The purpose served by the valvulae conniventes is a 1 twofold one. In the first place they increase the extent of the ; absorbing and secreting surface of the mucous membrane, and in ' the second place they delay the passage of the intestinal contents, 1 and so afford time for digestion and absorption. i In connection with the valvulae conniventes of the duodenum the common orifice of the ductus communis choledochus and : Fig. 337.— The Val VVLM Conniventes, THE ABDOMEN 789 Goblet CeU pancreatic duct has to be noted. At the junction of the inner and posterior aspects of the second part of the duodenum where the upper two- thirds and lower third of that part meet, there is a small eminence of the mucous membrane, called the bile papilla. It lies at the lower end of a vertically-placed valvula connivens, which bifurcates so as to form a kind of cap for it. From the lower part of the papilla a fold extends downwards for some distance, which acts as a bridle, and gives the apex a downward direction. On the summit of this papilla there is an opening which represents the common orifice of the two ducts. These ducts, having traversed the wall of the second part of the duodenum obliquely for | inch, unite to form one duct which, before piercing the mucous coat, presents an enlargement called the ampulla of Vater, but subse- quently narrows at its final ending. In the ampulla of Vater a gallstone may become lodged and delayed in its dovvTiward progress toward the duodenum. About i inch above the bile papilla there is another small papilla upon which there is another minute opening. This represents the orifice of the accessory pancreatic duct, or duct of Santorini. The villi commence at the beginning of the duodenum on the outer side of the pylorus, and extend as far as the margins of the segments of the ileo-cgecal valve. They are minute projec- tions of the mucous mem- brane, to which they impart a woolly appearance, and may be visible to the naked eye, but are more readily seen with the aid of an ordinary lens if a portion of bowel is floated in water. They are closely set upon the mucous membrane (vahnilae conni- ventes included), except over the solitary glands. Their total number is said to be about four millions (Krause). The villi are conical, cylindri- cal, leaf-like or finger-like pro- cesses, varying in length from aV to To inch. They are larger and more numerous in the lower part of the duodenum and in the jejunum, especially at its upper part, than in the ileum, and they diminish both in size and mmiber from above downwards, becoming somewhat filiform in the ileum. Each villus is an elevation of the mucous membrane covered by a single layer of columnar epithelium. It is composed of (i) adenoid tissue, (2) a capillary network of Fig. 338. — Two Villi. A. Villus, showing Striated Basilar Border, Columnar Epithelium, Goblet Cells, and Lacteal Vessel. B. Villus, showing the Capillary Bloodvessels. 7?o A MANUAL OF ANATOMY bloodvessels, (3) one or more lacteal vessels ensheathed by plain muscular tissue ; and (4) arborisations of nerve-fibrils derived from the plexus of Meissner. Between the columnar epithelial cells of the free surface, many of which are mucus-secreting goblet cells, there are amoeboid lymph corpuscles. Beneath the epithelium is a basement membrane composed of flattened cells, and known as the subepithelial endo- thelium. The cells of this basement membrane send processes outwards between the columnar cells of the free surface, and they also send processes inwards which are connected with the branched cells of the retiform tissue of the adenoid tissue. One artery (sometimes two) enters the base of the villus and ascends to near the centre. Here it breaks up into a number of branches, which form a copious capillary network. From this plexus the blood is returned by one or two venous radicles, which leave the villus at its base, where they open into the venous plexus of the mucous membrane. In the centre of the villus there is a lacteal vessel, which commences near the tip in a blind bulbous extremity, or, if there should be two lacteals, they originate in the form of a loop. The wall of the lacteal vessel is formed by a single layer of endo- thelial plates, which are connected by processes with the branched cells of the retiform tissue of the adenoid tissue. The vessel is ensheathed by longitudinal plain muscular fibres derived from the muscularis mucosae, their fibre-cells being connected with the base- ment membrane of the villus. The villus is pervaded by adenoid tissue — that is to say, retiform tissue with its meshes filled with amoeboid lymph corpuscles. The branched cells of this retiform tissue are connected by processes on the one hand with the endo- thelial plates which compose the wall of the lacteal vessel, and on the other hand with the cells of the basement membrane near the surface, and these latter in turn send out processes between the columnar epithelial cells of the free surface. The villi play a most important part in absorption, partly through their copious capillary networks, and partly through their lacteals. The lacteals serve specially for the absorption of fats, which is probably effected in the following manner : the columnar epithelial cells at the free surface take up the saponified and emulsified fats, which they transfer to the amoeboid lymph corpuscles between them. These corpuscles then carry the fats inwards through the adenoid tissue into the lacteal vessel. Brunner's glands are confined to the duodenum, and are serially continuous with the pyloric glands of the stomach. They are very numerous in the commencement of the duodenum, where they form a continuous layer of gland tissue extending as low as the entrance of the common bile-duct and pancreatic duct. Beyond this point they gradually diminisU in number, and ultimately disappear near the duodeno-jejunal flexure. They belong to the class of racemose or acino-tubular glands, and they differ from the pyloric glands of the stomach in having their tubules THE ABDOMEN 791 Otherwise the stnic- Brunner's glands lie Brunner's Glands more branched, and in having longer ducts ture of the two kinds of glands is similar embedded in the submucous coat, and their long ducts pass through the whole thickness of the mucous coat, upon the surface of which they open between the crypts of Lieberkiilin. Some of them, however, open into these crypts. The glands can easily be displayed by re- moving the peritoneal and muscular coats of the duodenum and a little of the submucous areolar tissue, when they appear as small, round, grey-coloured masses like millet seeds, varying in dia- meter from ^V to ^jj inch. The crypts or follicles of Lieberkuhn are foimd in large numbers over the whole of the mucous membrane of the small intestine, as well as that of the large bowel. They belong to the class of simple tubular glands, and are to be regarded as small diverticula o the mucous membrane. Each crypt takes the form of a simple tube, which is closed and slightly enlarged at its fig. 339.— Section of the deep extremity, and opens by its other Duodenum, showing end on the surface between the villi. Brunner's Glands The crypts are present on the valvule (highly magnified). conniventes as well as in the intervening parts. They are placed vertically and close together, and are confined entirely to the mucous coat, in which they extend from the free surface to the muscularis mucosae. In length they vary from ^^5- to yi^ inch. Each crypt is composed of a basement membrane lined with colimrmar epithelium, many of the cells being mucus-secreting goblet cells, and the Imnen is of large size. The solitary glands are present over the whole extent of the mucous membrane of the small intestine. They assume the form of small white round or oval nodules, which project by their deep ends into the submucous coat, whilst their superficial ends give rise to slight elevations of the free surface, where they have the openings of the cr^'pts of Lieberkiihn placed around them. They are found upon, as well as between, the valvulae conniventes. In structure each solitary gland is composed of adenoid tissue containing large numbers of l\Tnph corpuscles, and permeated by capillary networks. Each gland is surroimded at its deep part by a copious plexus of lymphatic vessels, or by l^niphatic sinuses. The solitary glands are simply lymphoid nodules. The agminated glands or Peyer's patches are pecuhar to the 7y2 A MANUAL OF ANATOMY small intestine, and average about thirty in number in the adult, being more numerous in early life. They are situated along the free or anti-mesenteric border of the bowel, which must, therefore, be opened along its attached or mesenteric border in order to preserve them. They are largest, best marked, and most plentiful in the lower half of the ileum. In the upper part of the ileum and Villus — Lieberkuhn's Crypt — '1^ Solitary Gland- . Muscularis Mucosae Submucosa— -5 Circular Muscular Fibres Longitudinal Muscular Fibres Mucosa Peritoneal Coat — - — —r. Fig. 340. — Vertical Transverse Section of the Small Intestine (highly magnified). lower part of the jejunum they become smaller and more scarce, and they disappear as a rule above the centre of the jejunum. They vary in length from ^ inch to 4 inches, their breadth ranging from I inch to i inch. They are for the most part oblong, their long axis coinciding with that of the bowel. In the upper part of the ileum and lower part of the jejunum, however, thev are somewhat circular. Each patch is composed of a group of solitary glands or lymphoid nodules, surrounded by lymphatic plexuses or lymphatic sinuses. The area of each patch is slightly elevated, and there are no villi over the lymphoid nodules, whilst the openings of the crypts of Lieberkiihn are arranged in a circular manner round each nodule. There are no valvulse conniventes over Peyer's patches. The patches are best marked in young persons. Towards middle life they fade away, and in old persons they are usually only distinguishable as discoloured portions of the mucous membrane. i IHE ABDOMEN 793 Bloodosupply — Arteries. — The duodenum receives its arteries from the superior pancreatico-duodenal of the gastro- duodenal from the hepatic, and the inferior pancreatico- duodenal of the superior mesenteric. The jejimum receives its arteries from the rami intestini tenuis of the superior mesenteric. The ileum also receives its arteries from the rami intestini tenuis, and its terminal part in addition receives its arterial supply from the ileal branch of the ileo-colic from the superior mesenteric. Veins. — The destination of the venous blood of the small intestine is the superior mesenteric vein, and thereafter the vena portae. The veins are provided with valves which are competent in early life, but in the adult they are incompetent, and therefore allow regurgi- tation of blood to take place towards the small intestine, as happens in cases of portal obstruction. Lymphatics. — ^These form a copious plexus of valved vessels, which is situated in the fig. 341.— A Peyer's submucous coat. This plexus receives the Patch. lymphatics of the mucous membrane and the lacteals of the villi, and it surrounds the deep ends of the solitary glands. Its efferent vessels pierce the muscular coat, and in doing so they take up the l^onph from an intramuscular plexus of lymphatics, which lies between the longitudinal and circular layers. They then leave the bowel at the mesenteric border, where they pass between the two layers of the mesentery, and on their way to the receptaculum chyli they traverse the superior mesenteric glands. Nerves. — ^These are derived fiom the superior mesenteric sympa- thetic plexus, and they form two gangliated plexuses of non- medullated nerve-fibres. One of these is situated in the muscular coat between the longitudinal and circular layers, and is known as the plexus myentericus of Auerbach (plexus of the muscular coat of the intestine). The other is situated in the submucous coat, and is called the plexus of Meissner. The branches of this latter plexus are distributed to the muscularis mucosae and the mucous membrane with its villi. Characters of Different Parts of the Small Intestine — Duodenum— Pcm- tonetim. — There is no mesentery and only a partial investment of peritoneum. Muscular Coat. — This is very thick. Submucous Coat. — This contains the tubular portions of Brunner's glands. Mucous Coat. — The characters of this coat are as follows : ( i ) valvulae conniventes. except in the first i or 2 inches, (2) villi, (3) Lieberkiihn's cr^'pts. (4) solitary glands. (5) ducts of Brunner's glands, (6) common orifice of the ductus communis choledochus and pancreatic duct, and (7) orifice of the accessory pancreatic duct, or duct of Santorini. 794 A MANUAL OF ANATOMY The diameter of the duodenum is from i J to 2 inches. Jejunum — Peritoneum. — There is a mesentery, and the bowel is sur- rounded by peritoneum except along its mesenteric border. Muscular Coat. — This is comparatively thin. Mucous Coat. — This has the following characters : (i) valvulse conniventes, (2) villi in abundance, (3) Lieberkiihn's crypts, (4) solitary glands, and (5) Peyer's patches in its lower half. The diameter of the jejunum is about i^ inches. Ileum — Peritoneum. — In this respect the ileum resembles the jejunum. Muscular Coat. — This is very thin. Mucous Coat. — The characters of this coat are as follows: (i) valvulae conniventes in upper half, but small and sparse, there being none in the lower half; (2) villi, but in fewer numbers; (3) Lieberkiihn's crypts; (4) solitary glands; and (5) Peyer's patches. The diameter of the ileum is about j^ inches. Large Intestine. — ^The wall of the large intestine, which is sac- culated, is composed of four coats — serous, muscular, submucous, and mucous. The serous coat forms a complete investment to the vermiform appendix, caecum, transverse colon, and pelvic colon. As regards the ascending colon, descending colon, and iliac colon, it is incom- plete, being absent behind. The muscular coat {muscularis externa) is composed of plain muscular tissue, disposed in two layers — external or longitudinal, and internal or circular. The longitudinal muscular fibres are for the most part collected into three flat bands, called taeniae coli, or ligaments of the colon, except upon the rectum. In the intervals between these bands there are some longitudinal fibres, but they are very few and scattered. The taeniae, which are about ^ inch in breadth, commence upon the caecum at the base of the vermiform appendix, and they extend along the several parts of the large intestine as far as the rectum, where they spread out and form a continuous covering, which com- pletely surrounds that part of the bowel . Upon the caecum, ascend- ing colon, descending colon, and iliac colon the taeniae from their disposition are called anterior, postero-internal, and postero- external. Upon the transverse colon they are so placed as to be called anterior or omental (great omentum), postero-inferior, and superior or meso-colic (transverse meso-colon). They are shorter than the bowel to which they are applied, with the result that the tube is drawn together or puckered, and thus thrown into sacculi. There being three taeniae, there are three rows of sacculi between them, and, inasmuch as the taeniae are placed at nearly equal distances from each other, the sacculi are pretty much of equal dimensions. Between the successive sacculi there are cohstrictions, usually containing fat. The sacculi give rise internally to large pouches, and the constrictions between the sacculi produce internally sharp crescentic rugae, which separate the pouches from each other. When the taeniae are divided, the sacculi and constrictions entirely disappear, and the large bowel becomes elongated into a smooth cylindrical tube. Along- the course of the taeniae there are a number of small processes of peritoneum containing fat, called appendices epiploicae. THE ABDOMEN 795 Except in the case of the transverse colon, these are chiefly found along the postero- internal taenia, but in the case of the transverse colon they are principally met with along the postero-inferior taenia. The circular fibres are thin and scattered over the sacculi, but in the constrictions between them they become aggregated. Upon the rectum and anal canal they form a thick layer, which in the latter situation is known as the sphincter ani intemus. The submucous coat is in all respects similar to that of the small intestine. The mucous coat is pale and greyish in colour, except in the rectum, where it is red. Its epithelium is similar to that of the small intestine. It is destitute of valvulae conniventes and villi, and consequently presents a smooth surface. It contains large numbers of the cr\'pts or follicles of Lieberkiihn, which abound in mucus-secreting goblet cells. It also contains solitary glands or lymphoid nodules, which are especially prevalent in the vermiform appendix and caecum. The deepest part of the mucous coat is formed by the muscularis mucoscB {muscularis interna). Blood-supply — Arteries. — These are as follows : (i) appendicular, for the vermiform appendix ; (2) anterior and posterior caecal, for the caecmn : (3) colic of ileo- colic, and right colic, for the ascending colon ; (4) middle colic, for the transverse colon (all branches of the superior mesenteric) ; (5) left colic, for the descending colon ; and (6) sigmoid arteries, for the iliac colon and pelvic colon (the latter two being branches of the inferior mesenteric). Veins. — ^The destination of the venous blood of the vermiform appendix, caecum, ascending colon, and transverse colon is the superior mesenteric vein, whilst the blood of the descending colon, iliac colon, and pelvic colon is carried into the inferior mesenteric vein. In both cases the further destination of the blood is the vena portae. As in the small intestine, the veins have valves which are competent in early life, but not so in the adult. The lymphatics will be found described on pp. 729 and 730- Nerves. — These are derived from the superior mesenteric sympa- thetic plexus, and the inferior mesenteric plexus, which latter is an offshoot from the aortic plexus. The disposition of the nerves corresponds with that in the small intestine. The large intestine diminishes gradually in size from its com- mencement to its termination. Its diameter varies in different parts, the extremes being 2h inches and i inch. Characters of the Large Intestine — Peritoneal Coat. — This presents at fre- quent intervals small projections called appendices epiploicae. Muscular Coat. — The longitudinal fibres are for the most part arranged in three taeniae. Mucous Coat. — This is destitute of (a) valvulae conniventes, (b) villi, (c) Brunner's glands, and (d) Peyer's patches, but it is provided with (i) Lieberkuhn's crypts, and (2) solitary glands or lymphoid nodules. Outline of Tube. — The bowel presents three rows of sacculi, except in the vermiform appendix and rectum. 796 A MANUAL OF ANATOMY Structure of the Vermifdrm Appendix. — The vermiform appendix is entirely covered by peritoneum, which forms a more or less complete meso- appendix or appendicular mesentery. It has a muscular coat, composed of an external longitudinal and internal circular layer, both of which completely surroimd it. The Circular Muscular Fibres Longitudinal Muscular Fibres Peritoneal Coat Submucosa Mucosa with Lieberkiihn's Crypts Fig. 342. eso-appendix Lymphoid Nodules -Transverse Section of the Vermiform Appendix (highly magnified). submucous coat contains, in great abundance, lymphoid nodules (solitary glands) of large size, and the mucous coat contains a few lymphoid nodules, as well as a few crypts of Tieberkiihn. The base of the appendix is situated at a point on an average rather more than i inch below the ileo-caecal valve according to Treves. The opening by which the appendix communicates with the caecum is occasionally guarded by a fold of mucous membrane, which is known as the valve of Gerlach. The vermiform appendix is usually regarded as the remains of the herbi- vorous caecum. It is also looked upon as an appendage of the lymphoid system, and as such it would belong to the class of structures represented by Peyer's patches, namely, lymphoid organs. In its typical form it is peculiar to man, the higher apes, and the marsupial wombat. In certain rodents, however — e.g., the rabbit and hare — the verv lirui cnmcious ca'cum shows an approach to a vermiform appendix at its lown i \tri mily. THE ABDOMEN 79-: Ileo-caecal or Ileo-colic Valve (valve of Tulpius). — This valve is situated at the point where the terminal part of the ileum opens into the junction between the caecum and ascending colon. The orifice, as seen from the interior of the large intestine, has the form of a slightly oblique cleft about h inch long, and rimning in an antero- posterior direction. It is boimded above and below by the two segments which form the valve, and which project into the large intestine. The upper or ileo-colic segment is prominent, and occu- pies an almost horizontal plane. The lower or ileo-ccecal segment, longer than the upper, is concave superiorly, and occupies an oblique plane. The anterior part of the cleft is rounded off, whilst the Ascending Colon Frenum of Ileo-caecal VaWe Frenum of IIeo-_, caecal Valve Ileum Orifice of Vermiform ' Appendix Venniform Appendix Pi^*- 343- — The Interior of the Cjecum and the Ileo-c^cal Valvk. posterior part tapers to a point. The segments meet in front of and behind the cleft, and form two prominent folds, which are prolonged round the wall of the bowel for some distance. These folds are known as the frena or retinaciila of Morgagni. Each segment is composed of two layers of mucous membrane, one of which belongs to the ileum, and the other to the caecum or colon as the case may be. These two layers are continuous with each other at the free margin of the segment, and they contain between them submucous areolar tissue and circular muscular fibres, both of which are derived partly from the ileum and partly from the large intestine. The longitudinal muscular fibres and the serous or peritoneal coat take no part in the formation of the segments, being continued uninterruptedly from the ileum to the large 798 A MANUAL OF ANATOMY intestine. The mucous membrane which covers the opposed surfaces of the segments belongs to the ileum, and is, therefore, provided with villi. The mucous membrane of the other surfaces, that is to say, the surfaces which look away from each other (down- wards and upwards respectively), belong to the cacum and colon, and are destitute of villi. The villi thus disappear at the margins of the segments. The valve may be described as being formed by an inversion of the terminal part of the ileum into the large intestine. That part of the ileum, having passed upwards and to the right with a slight inclination backwards, enters the large intestine. As it does so, it leaves behind its serous and longitudinal muscular coats, and takes with it its circular muscular, submucous, and mucous coats, the corresponding coats of the large intestine accompanying it in the inversion. The ileo-csecal valve prevents the regurgitation of the contents of the caecum into the ileum. It is generally believed that the mode of action of the valve is as follows : when the caecum becomes distended the fraena or retinacula of the valve are stretched, and exercise traction upon its segments, which are thereby brought together, very much as an old-fashioned purse is closed by pulling upon the two strings. For the structure of the rectum, see Index. Development of the Stomach and Intestinal Canal. — The primitive gut, or archenteron, consists of splanchnopleure — that is to say, entoderm covered externally by splanchnic mesoderm — and it extends from the head-fold to the tail-fold, lying on the ventral aspect of the notochord. It is divided into three parts — namely, the fore-gut, mid-gut, and hind-gut. The lore-gut gives rise to (i) the tongue and back part of the oral cavity, (2) the pharynx, (3) the oesophagus, (4) the stomach, (5) the greater part of the duodenum, and (6) the organs developed as outgrowths from the foregoing parts. The mid-gut gives rise to (i) a small part of the duodenum, (2) the jejunum, (3) the ileum, and (4) the colon, except a small portion at its lower end. The hind-gut gives rise to (i) a small portion of the colon at its lower end, (2) the rectum, and (3) the portion of the anal canal above the anal valves. The anus and the portion of the anal canal below the anal valves are developed from the proctodcBum, which is an invagination of the ectoderm at the caudal end of the trunk to meet the intestinal entoderm . The cephalic end of the primitive gut is closed, and is separated from the stomodseum, or primitive mouth (which is developed from an invagination of the ectoderm), by a septum, known as the pharyngeal membrane. This septum consists of two layers, one of which is formed by the ectoderm of the stomodaeum, whilst the other consists of entoderm belonging to the cephalic or anterior end of the primitive gut (pharyngeal portion). The primitive gut is also closed near its caudal end by a septum, called the cloacal membrane. This membrane, from its mode of formation, bears a close resemblance to the pharyngeal membrane. It consists of two layers, one of which is formed by the ectoderm of the exterior, whilst the other is formed by the entoderm of the hind-gut. The mid-gut remains for some time in free communication with the yolk- sac. This communication is at first wide, but a constriction takes place on a level with the umbiUcal aperture, so that the mid-gut and yolk-sac now com- municate by a narrow neck, called the vitelline, vitello-intestihal, or umbilical duct. * The ventral body-wall being now formed, and the yolk-sac being extra- embryonic, this duct extends inwards, along the umbilical cord, through the umbilical aperture, and, after entering the embryonic coelom or body-cavity, THE ABDOMEN 799 ^- Lung CEsophagus Stomach Bile duct it opens into the mid-gut. The part of the mid-gut which is connected with this duct gives rise to the lower portion of the ileum. The duct, as a rule, becomes closed and disappears. In some cases, however, its intestinal portion retains its communication with the gut, and gives rise to a bhnd evagination of the gut, which is known as Meckel's diverticulum. In very rare cases the intestinal portion of the vitelline duct undergoes no closure, under which cir- cumstances it is pervious throughout, opening internally into the gut, and externally into the cavity of the umbilical cord. Such a condition of matters gives rise to a congenital umbilical feecal fistula. The primitive gut is lined throughout with entoderm, from which the future intestinal epithelium is developed, as well as the epithelium of the gland-ducts which open into the gut. This entoderm is covered externally by splanchnic ■mesoderm, these t^vo combined layers forming the splanchnopleure. The splanchnic mesoderm gives origin to the tissues which form the other coats of the gut. The primitive gut, thus constituted, is separated from the body-wall, which is composed of somatopleure (ectoderm and somatic mesoderm combined) by the coelom or body-cavity, which becomes partitioned ofE into pericardial, pleural, and peritoneal ca\'ities. Stomach. — The primitive gut is a straight tube up to about the fourth week of intra-uterine hfe. About that time the first indication of the stomach shows itself as a spindle-shaped dilatation of the primitive gut in the neighbourhood of the embryonic heart, this dilatation being at first straight. After the stomach descends into the abdominal cavity its dorsal aspect undergoes greater develop- ment than the ventral, and the organ becomes curved. The convexity of this curve is, at this period, directed dorsal- wards, and the concavity ventralwards. The surfaces of the organ are right and left, and they thus naturally receive, at this period, the corresponding pneumo- gastric nerves. The pyloric end, which is directed caudalwards, is now tilted for- FiG. 344. — The Alimentary wards towards the ventral body-wall, and Canal of the Embryo (His). it carries the duodenal portion of the gut along with it, the duodenal loop being thereby produced. Thereafter the stomach undergoes parried rotation round its long axis towards the right side, and the cephalic or cardiac end is carried to the left of the median line. The stomach, as it rotates, carries with it the lower part of the oesophagus and the duodenal loop, which latter thus takes up a position on the right side of the median hne. The original right surface of the stomach now becomes dorsal or posterior, and the original left surface becomes ventral or anterior. This change in the direction of the surfaces explains why the right pneumogastric nerve is dis- tributed to the posterior surface of the stomach in the adult, and the left pneumo- gastric nerve to the anterior surface of the organ. The partial rotation of the lower part of the oesophagus towards the right also explains why, in the adult, the right pneumogastric nerve lies behind the lower part of the oesophagus, and the left in front of the lower part of that tube. The great curvature of the stomach, which was originally directed dorsal- wards, is now directed caudalwards and towards the h ft ; whilst the small curva- ture, which originally looked ventralwards, is now directed cephalicwards or upwards, and towards the right. 8oo A MANUAL OF ANATOMY Intestinal Canal. — This canal is at first very short and almost straight, and, as has been stated, it communicates freely with the yolk-sac. At this stage there is no indication of a division into small and large intestine. When the wide opening leading to the yolk-sac becomes constricted and converted into the vitelline duct, the intestinal canal undergoes lengthening, and a con- spicuous loop is formed, which projects into the cavity of the proximal part of the umbilical cord, this cavity being a direct projongation of the coelom or body-cavity. This loop is spoken of as the U"loop. The convexity of the bend of the loop is directed ventralwards, and the vitelline duct is connected with the convexity. The loop has two limbs, which lie at first parallel to each other. One limb is cephalic, upper, or proximal, and leads from the duodenal loop of the gut; the other limb is caudal, lower, or distal, and leads to the caudal end of the gut. Upon the distal limb a bud makes its appearance. This assumes the form of a blind diverticulum, or cul-de-sac, which is the rudiment of tlie caecum. The appearance of the caecal evagination is the first indication of the division of the intestinal canal into small and large intestine. The primitive small intestne is the part on the proximal side of the rudimentary caecum, and the primitive large intestine is the part extending from the rudi- mentary caecum to the caudal end of the gut. The U"loop soon undergoes rotation in such a manner that the distal limb bearing the caecal diverticulum crosses obliquely over, or ventral to, the proximal limb, so that the original distal or lower limb now becomes proximal or upper. The part of the gut which is crossed ventrally by a portion of the distal limb represents the future descending part of the duodenum. This crossing accounts for the fact that, in the adult, the commencement of the transverse colon lies in front of the descending part of the duodenum. The U-loop is occupied by a mesentery, which represents the mesentery proper of the adult. Close to the point of crossing of the two limbs of the loop, its mesentery contains the superior mesenteric artery. The loop itself, as stated, lies in the cavity of the proximal part of the umbilical cord. At a later period (about the ninth week of embryonic life) it is withdrawn from its original extra-embryonic position into the body-cavity (abdomen). In rare cases the prolongation of the coelom into the proximal part of the um- bilical cord may persist at birth, and so predispose to the occurrence of a congenital umbilical hernia. The elongation of the jejunal and ileal portions progresses after withdrawal of the U'loop. ai^d takes place more rapidly than that of the large intestine. Moreover, the small intestine outgrows in length the body-cavity, in conse- quence of which the jejunum and ileum are thrown into coils. These coils are placed, at first, on the right side of the median line. The primitive large intestine is represented by (i) the caecum, which is its initial part, (2) a short transverse colon, (3) a descending colon, and (4) a terminal part, which subsequently forms an iliac colon, pelvic colon, rectum, and upper two-thirds of the anal canal. There is no ascending colon at this stage. These initial parts (caecum and colon) lie, at first, on the lejt side of the median line, the caecum being underneath the left part of the liver. The caecum gradually shifts to the median line, and then to the right side, still lying beneath the liver, and, as it thus alters its position, the transverse colon undergoes elongation. Finally, the caecum, as a rule, descends slowly to its permanent abode in the right iliac jossa. During this descent the ascending colon becomes formed. The large intestine having, like the small, outgrown the body-cavity, now has the form of an arch or loop, in the concavity of which the coiled jejunum and ileum lie. In the course of these changes in the position of the caecum, the jejunum and ileum are also shifting their position. Originally, as stated, they lie on the right side of the median line, but they, along with the lower part of the duodenum, are gradually shifted (but not entirely) towards the left side, so as to be brought within the loop of the large intestine. The foregoing transposition of parts is brought about by the twist which has been referred to as occurring in the U-l"oP- ^^is twist, or rotation, involves not only the loop itself, but also its mesentery, and it takes place THE ABDOMEN Sot from left to right round an axis, represented by the superior mesenteric artery. Inasmuch as the mesentery of the U"lo<^P ^^ involved in this rotation, the original right side of the mesentery becomes, after rotation, the left side, and vice versa. Caecum and Vermiform Appendix. — The caecum appears about the fifth week of embryonic Ufe as a bud in connection with the distal hmb of the U-loop of intestine. It assumes the form of a bhnd diverticulum, which is at first of uniform dimensions. It soon, however, becomes conical. The proximal part undergoes enlargement, and represents the permanent caecum. The distal part remains long and narrow, and represents the vermiform appendix, whicn ultimately becomes connected with the left and posterior part of the caecum. The various positions occupied by the caecum and its migration to the right iliac fossa have just been referred to. Suffice it to say that it lies, at first, on the left side of the median line, then it crosses to the right side, being at this stage high up below the liver, and finally it sinks into its usual permanent abode. The descent of the caecum, however, may be arrested at any stage. For the development of the rectum and anal canal, see Index. Development of the Peritoneal Cavity and Peritoneum. — The peritoneal cavity is one of the four divisions of the coelom or body-cavity. The other three divisions — namely, the pericardial cavity and the two pleural cavities, are contained within the thorax, and are separated from the peritoneal cavity by the diaphragm. The parietal peritoneum is formed by the somatic mesoderm of the somato- pleure of the body-wall, and the visceral peritoneum is derived from the splanchnic mesoderm of the splanchnoplettre of the primitive intestinal tube. The opposed surfaces of these two layers cire lined with mesothelium, the flattened cells of which give rise to the lining endothelium of the peritoneal cavity. In early life the entire alimentary tube is characterized by its shortness and straightness. Its ventral and dorsal aspects are attached to the ventral and dorsal body-walls by mesodermic folds, called primitive mesenteries. These mesenteries are two in number — namely, ventral and dorsal — and they establish a continuity between the splanchnic mesoderm of the alimentary tube and the somatic mesoderm of the body-wall. The primitive ventral mesentery extends from the pharynx to the upper part of the duodenum, and consists of splanchnic mesoderm. The cephalic part is known as the cardiac portion. The heart and pericardium are de- veloped within it, and it gives rise to the ventral and dorsal mesocardia. The caudal or posterior part of the ventral mesentery- forms the ventral, or anterior, gastro-diiodenal mesentery. The primitive dorsal mesentery is the fold which attaches the dorsal aspect of the primitive alimentary' tube, over its entire length, to the dorsal body-wall. Like the ventral mesentery, it consists of splanchnic mesoderm. The primitive mesenteries are thus two in number — namely, ventral and dorsal. The ventral gastro-duodenal mesentery extends from the ventral aspects of the primitive stomach and upper part of the duodenum to the ventral body- wall on the cephalic side of the umbilicus. As the liver, which is undergoing development within the caudal or hepatic layer of the septum transversum, descends, it separates from the middle or diaphragmatic layer of that septum', which gives rise to the ventral portion of the diaphragm; and as it descends it passes between the two layers of the gastro-duodenal mesentery. This mesentery is now divided into two parts by the developing Uver. The part between the liver and (i) the ventral portion of the diaphragm and {2) the ventral wall of the abdomen as low as the umbilicus becomes the falciform ligament of the liver; and the part between the liver (future portal fissure) and (i) the stomach (future small curvature); and (2) the duodenum (future first part for about an inch) becomes the small or gastro-hepatic omentum. The dorsal mesentery receives names corresponding to the parts of the ahmentary tube with which it is connected. Thus, in the abdomen, there are 51 8o2 A MANUAL OF ANATOMY the mesogastrium, mesoduodenum, mesojejunum, meso-ileum, mesocolon, and mesorectum. In the course of development these various parts of the primitive dorsal mesentery undergo marked changes. I. Mesogastrium. — The mesogastrium is that portion of the primitive dorsal mesentery which extends vertically between the great curvature of the stomach, which at this period is directed dorsalwards, and the dorsal body- wall. It is at first comparatively short, but it undergoes lengthening as the stomach turns round on its right side. During this partial rotation of the stomach the mesogastrium is somewhat doubled upon itself, and forms a pouch, which is directed downwards and to the left. This pouch is the initial stage in the formation of the small sac of the peritoneum. The pouch is bounded ventrally by (i) the small or gastro-hepatic omentum, and (2) the dorsal surface of the stomach (originally the right surface) ; dorsally by the dorsal body-wall; and caudalwards by the somewhat doubled mesogastrium. During the rotatory movement of the stomach, the small or gastro-hepatic omentum, the direction of which was originally sagittal — that is, dorso- ventral — now assumes a coronal or transverse position. In this manner, combined with a slight doubling of the mesogastrium, a small part of the peritoneal cavity is incompletely partitioned off, and this is the portion which constitutes the upper part of the small sac, lying, as just stated, dorsal to the small omentum and dorsal surface of the stomach. This upper part of the small sac communicates with the general peritoneal cavity (from which it has been partitioned off) by an opening, called the foramen of Winslow, which is situated behind the right or free border of the small or gastro-hepatic omentum. This opening is at first large, but, as the liver grows, it becomes considerably curtailed. The great, or gastro-collc, omentum is developed from the mesogastrium, which increases slowly in size downwards. When fully developed, it forms the extensive sheet which descends from the great curvature of the stomach, and lies ventral to the transverse colon and the coils of the jejunum and ileum. As the great omentum grows downwards, the pouch, which represents the upper part of the small sac, increases in size and also grows downwards. This downward extension of the small sac occupies the interval between the two anterior, or descending and the two posterior, or ascending, layers of the great omentum, this part of the small sac being known as the bag or sac of the great omentum. For the changes which this curtain undergoes, prior to assuming its con- dition in the adult, see the Peritoneum in the Foetus. The gastro-splenic omentum and lieno-renal ligament are associated with the development of the spleen (lien) in the mesogastrium. The portion of the mesogastrium between the stomach and spleen gives rise to the gastro- splenic omentum, whilst the portion between the spleen and the left kidney forms the lieno-renal ligament. It is to be noted that the great or gastro-colic omentum is developed from the mesogastrium, which is a portion of the primitive dorsal mesentery, whilst the small or gastro-hepatic omentum is formed, as stated, by that portion of the ventral gastro-duodenal mesentery which extends between the liver (the future portal fissure) and the stomach (the future small curvature). As the development of the abdominal portion of the alimentary tube proceeds, it undergoes considerable changes, which impress modifications upon the peritoneum, and impart to it a remarkably complicated character. The stomach appears at first as a spindle-shaped dilatation of the alimentary tube, which, together with the duodenal portion of the intestinal tube, is at first straight. For the subsequent changes in form and position of the stomach and intestinal canal, see their development. It is sufficient in this place to state that the stomach becomes curved, and turns round on its right side, carrying the duodenum along with it, whilst the intestinal tube undergoes elongation and becomes very tortuous. The primitive ventral gastro-duodenal mesentery, as stated, gives rise to — (1) the falciform ligament of the liver, and (2) the sirtall or gastro-hepatic omentum. THE ABDOMEN 803 The mesogastrium (part of the primitive dorsal mesentery), as stated, gives rise to — (i ) the great or gastro-colic omentum ; {2) the gastro-splenic omentum ; and (3) the heno-renal ligament. 2 . Mesoduo-ienum. — This fold disappears, so that the duodenum, except for about an inch at its commencement, is retroperitoneal. 3. Meso jejunum and Meso-ileum. — These folds persist and constitute the mesentery proper. Its dorsal end contains the superior mesenteric artery, and is of hmited extent. As the jejunum and ileum increase in length, the intestinal end of the mesentery prop>er acquires a much greater length than the vertebral end. Moreover, as these parts of the intestinal tube become coiled, the mesentery- proper towards its intestinal end becomes curv'ed, and presents a number of segments of circles, which impart to it an undulating outline. 4. Caecum. — The csecum, being originally a bud or outgrowth of the gut, has no mesentery, and is entirely surrounded by peritoneum. 5. Vermiform Appendix. — The vermiform appendix, being originaUj- the bhud narrowed end of the caecum, or, in other words, a diverticulum of the caecum, is also destitute of a mesentery, properly so called, and is invested by an extension of the peritoneal envelope of the caecum. There is, however, in most cases a fold of peritoneum pertaining to the vermiform appendix, which extends along it for about | or § of its length. This fold is called the meso- appendlx or appendicular mesentery, and it is derived from the left or inferior layer of the mesenten.- proper, close to the ileo-cohc junction. 6. Ascending Mesocolon. — This fold, in most cases, disappears. 7. Transverse Mesocolon. — This fold is persistent. 8. Descending Mesocolon. — ^This fold, hke the ascending mesocolon, in most cases disappears. 9. Iliac Mesocolon. — This fold in most cases disappears. 10. Pelvic Mesocolon. — This fold is persistent. Ti. Mesorectum. — This fold disappears. Structure of the Liver. The liver has two coats, external and internal. The external or serous coat is formed by the peritoneum, and is incomplete (see p. 708). Within the serous coat is the fibrous or areolar coat, which is kno^vn as the fibrous capsule of the organ. It is for the most part thin, except where the peritoneal coat is deficient. It is continuous all over the surface with the scanty amoimt of areolar tissue which pervades the interior of the organ and connects the hepatic lobules. At the portal fissure it surrounds the hepatic duct, hepatic artery, and vena portae, under the name of the capsule of Glisson. The subdivisions of this capsule accompany the various branches of the duct, artery, and vein as these ramify throughout the liver in the portal canals. The liver-substance is composed of a great number of small polyhedral masses, called hepatic lobules, which are closely packed together, and are set, each by one surface, on the walls of the sublobular veins, to which they are attached by means of intralobular or central veins. In man there is very little areolar tissue between the lobules, which are therefore for the most part confluent. In some animals, however, notably the pig and camel, there is a very distinct amount of areolar tissue between the lobules, which, therefore, stand clearly apart from each -Other. 8o4 A MANUAL OF ANATOMY The average diameter of a hepatic lobule is v,^^ inch. One of its surfaces is called the base. It is by this surface that the lobule is set upon the wall of a sublobulai vein, and the intralobular or central vein, having emerged from the lobule through the centre of its base, opens at once into the sublobular vein. The lobules, therefore, relatively to the sublobular veins, on which they are ranged, are sessile. When a sublobular vein is opened and viewed from within, an appearance something like mosaic work presents itself, the closely-set bases of the lobules being visible through the thin wall of the vein, and the minute openings of the intralobular or central veins appearing in the centre of each base. Each lobule is com- posed of hepatic cells, permeated by capillary networks of blood- vessels and bile capillaries. Bloodvessels. — The liver derives its blood from two sources, namely, the vena portae, and the hepatic artery. These two vessels, together with the hepatic duct, are invested by the capsule of Glisson at the portal fissure. Their several branches, ensheathed by prolongations of Glisson's capsule, ramify from this point throughout the liver, being contained in the system of canals, known as portal canals. Each of these canals contains (i) a branch of the vena portae, (2) a branch of the hepatic artery, accompanied by a plexus of nerves, (3) lymphatic vessels, and (4) a minute duct, all these being loosely surrounded by a pro- longation of Glisson's capsule. The vena portae ramifies within the liver like an artery. In the portal canals its branches receive as tributaries small cap- sular and vaginal veins, and they go on ramifying until they arrive at the inter- lobular areas. Here they anastomose freely with one another around the lobules, and so form the interlobular plexuses. The branches which arise from these plexuses enter the lobules on all sides except their bases, and form in the interior of each lobule an intralobular plexus. From this plexus a few radicles converge towards the centre of the lobule, where they form by their union the intralobular or central vein. The portal blood, though dark in colour, is very rich, being derived from, amongst other sources, the stomach and small intestine. The hepatic artery is a branch of the coeliac axis. As its branches traverse the portal canals they give off capsular branches to the fibrous capsule of the liver, and vaginal branches, which supply the walls of the vessels in the portal canals, as well as their Glis- sonian sheaths. The branches of the artery finally end as minute interlobular arteries, which supply the walls of the interlobular Fig. 345. — Section of THE Liver, showing A Large Hepatic Vein and its Tribu- taries (after Kier- nan). THE ABDOMEN 805 veins and bile-ducts. According to some authorities they send minute capillary branches into the interior of each lobule to join the intralobular plexus of the venae portae, but this view is not held by others. The function of the hepatic artery and its branches is to nourish the tissues of the liver, whilst the portal blood suppUes the materials which are elaborated by the hepatic cells. The hepatic veins commence in the centre of each lobule as an intralobular or central vein. The intralobular veins open into the suhlohular veins, which are closely adherent to the bases of the lobules. The sublobular veins join to form larger sub- lobular veins, and these in turn terminate in the hepatic veins, which are not in direct contact with the lobules. The hepatic veins pass to the caval fossa on the posterior surface of the liver, towards which they con- verge, taking up sublobular veins in their course. The passages which contain the veins are known as the hepatic canals. On arriving at the upper part of the caval fossa they are reduced to two or three in number, which pour their contents directly into the inferior vena cava. It is to be noted that the hepatic veins converge to the caval fossa on the posterior surface, whilst the branches of the vena portae radiate in all directions from the portal fissure. The hepatic veins are accompanied only by lymphatic vessels, and are surroimded by a very scanty amount of areolar tissue, which explains why they present open mouths when cut across. Distinguishing Characters of the Hepatic and Portal Veins — Hepatic Veins. — (i ) These present open mouths when cut across. (2) They are accompanied only by Ij-mphatic vessels. (3) Their waUs are very thin, and are practically in direct contact Avith the substance of the liver. {4) They converge towards the caval fossa on the posterior surface. Portal Veins. — (i) The mouths of these veins are practically closed or collapsed when cut across. (2) The veins are accompanied by branches of the hepatic arter\', and by ducts. (3) Their walls are fairly tliick, and are separated from the substance of the Uver by the sheaths derived from Glisson's capsule. (4) They radiate in all directions from the portal fissure in portal canals. Hepatic Cells. — ^These are situated within the lobules. They are polj'hedral. granular cells, having a diameter of ybW inch, and each contains a round nucleus. They have no cell-wall, properly Fig. 346. — Two Hepatic Lobules (highly magnified). A, Lobule showing the Intralobular Plexus ; B, Lobule showing the Hepatic Cells. 806 A MANUAL OF ANATOMY SO called, and they are connected by a delicate supporting tissue. The cells, which are capable of amoeboid movement, lie between, and around, the capillary vessels, where they are arranged in radiating rows converging towards the centre of the lobule. Bile-ducts. — ^These commence within the lobules as bile-capillaries or bile-canaliculi, which are in reality intercellular passages. They have a very delicate wall, and are bounded on all sides by the hepatic cells — hence the name intercellular passages. According to Pfiiiger and Kupffer, the cells contain vacuoles, which communicate by intracellular passages with the bile-capillaries. The hepatic cells intervene between the bile-capillaries and the capillary blood- vessels. At the circumference of the lobule the bile-capillaries pass into the small interlobular bile-ducts. These join to form larger ducts, and these in turn go on joining until, on arriving at the portal fissure, only two ducts result, which emerge one from each lobe. These now join to form the hepatic duct, and this joins the cystic duct to form the common bile-duct. The walls of the interlobular ducts are very thin, being composed of a basement membrane lined with polygonal epithelium. The larger ducts in the portal canals have thicker walls, which, from without inwards, are composed of a fibro-elastic coat, containing plain muscular tissue, arranged longitudinally and circularly, and a mucous coat lined with columnar epithelium. The mucous 'membrane of the larger ducts presents numerous openings, which lead into blind mucus-secreting recesses. The structure of the hepatic and common bile-ducts is similar to the preceding, though on an increased scale. Lymphatics. — ^The lymphatic vessels of the liver are arranged in two groups— superficial and deep. Superficial Lymphatics. — ^These form plexuses beneath the peri- toneal coat, and have different destinations. Supero-anterior Surface. — (i) The lymphatics from the vicinity of the falciform ligament enter that ligament, and, passing through the diaphragm into the thorax, they terminate in the anterior mediastinal glands. (2) The lymphatics from the right part of the superior surface and those from the right lateral surface enter the right lateral ligament, and, passing through the diaphragm, they terminate in the middle diaphragmatic glands of the right sida (3) The lymphatics from the left part of the superior surface and those from the left extremity enter the left lateral ligament, and pass to the peri-cesophageal glands in relation to the lower end of the oesophagus, the efferent vessels of which terminate in the cceliac glands. (4) The lymphatics from the anterior part of the supero-anterior surface, except those from the vicinity of the falciform ligament, turn round the anterior border of the liver, and end in the hepatic glands within the small omentum. (5) The lymphatics from the posterior surface of the right lobe pass between the two layers of the coronary ligament, and, having pierced the diaphragm, they terminate in the caval glands within the thorax. Inferior Surface. — (i) The lymphatics from the greater part of the inferior surface of the right lobe, including those of the quadrate THE ABDOMEN 8^7 lobe, pass to the hepatic glands. (2) The lymphatics from the posterior part of the inferior surface of the right lobe pierce the diaphragm, and end in the caval glands. (3) The lymphatics from the greater part of Spigel's lobe pierce the diaphragm, and end in the caval glands ; whilst those from the lower part of this lobe pass to the hepatic glands. (4) The lymphatics from the inferior surface of the left lobe pass to the hepatic glands. Deep Lymphatics. — ^These vessels form two distinct sets. Some of them accompany the branches of the portal vein, and, having emerged through the portal fissure, they terminate in the hepatic glands. Others pass with the hepatic veins to the caval fossa of the liver, and thereafter they enter the thorax along with the inferior vena cava, their destination being the caval glands. Nerves. — The nerves of the liver are derived from the hepatic plexus, which is an offshoot of the coeliac plexus, that in turn being derived from the solar plexus of the sympathetic system. The coehac plexus, though principally composed of sympathetic fibres, is reinforced by a few twigs from the right pneumogastric nerve. The hepatic plexus accompanies the hepatic artery to the portal fissure, where it receives branches from the left pneumogastric nerve, which have ascended from the antero-superior surface of the stomach between the two laj-ers of the gastro-hepatic omentum. In the liver the nerves, which are chiefly non-medullated, are dis- tributed to the walls of the bloodvessels and ducts, penetrating as far as the interspaces between the hepatic cells. DevelopmeDt of the Liver. Liver. — The hepatic cells and the epithelium of the bile-ducts are of ento- dermic origin, whilst the connective tissue of the gland and its vascular con- stituents are developed from the mesoderm. The rudiment of the liver appears as a longitudinal groove on the inner aspect of the ventral wall of the duodenal portion of the primitive gut. This groove gives origin to a diverticulum or evagination of the entoderm of the ventral duodenal wall, called the hepatic diverticulum or liver-bud, which has at first a wide communication with the gut. At a later period this com- munication becomes constricted, and forms a pedicle, which, after undergoing elongation, gives rise to the common bile-duct. From this pedicle, close to the duodenal wall, the ventral diverticulum of the pancreas arises. The hepatic diverticulum or liver-bud invades the lower or caudal layer of the septum transversum, composed of mesoderm, within which it bifurcates, the two divisions representing the right and left hepatic ducts. The cells of these two divisions of the hepatic diverticulum undergo pro- liferation within the mesoderm of the lower layer of the septum transversum, and thereafter each division breaks up into a number of solid trabeculae, which are known as the hepatic cylinders. These cylinders give off secondary solid trabeculae, and these again ramify extensively. The subdivisions of the various trabeculae anastomose freely, and in this manner intricate networks are formed around the vitelline and umbilical veins, which veins traverse the septum transversum as they pass to the sinus venosus. The hepatic cylinders invade these veins, carrying the endothelial walls of the vessels before them. The veins are thus freely .subdivided into blood-channels, which are known as sinusoids. These sinusoids form capillary networks, which occupy the meshes of the net\vorks formed by the hepatic cylinders. Many of the solid trabeculae become tubular, and give rise to the bile- capillaries or bile-canaliculi, and bile-ducts. Others give rise to the hepatic 8o8 A MANUAL OF ANATOMY cells. The liver thus consists originally of intricate reticula of solid cellular trabecul'S, or hepatic cylinders, disposed around the vitelline and umbilical veins. As the liver increases in size it projects downwards, carrying with it the lower layer of the septum transversum, which forms its capsule and connective tissue. The organ now lies between the two layers of the ventral or gastro- duodenal mesentery, which gives rise to — (i) the falciform ligament; (2) the posterior or coronary ligament; and (3) the gastro-hepatic or small omentum. About the middle of intra-uterine life the liver occupies a large part of the abdominal cavity, and the right and left lobes are of equal size. In the latter half of intra-uterine life, however, the right lobe gradually attains greater size than the left. About the period of birth the liver extends almost as low as the umbilicus. After birth it undergoes diminution in size, the circulation of placental blood through it, by the umbilical vein, having been permanently arrested at birth. At an early period in its development the liver presents four lobes — two vitelline and two umbilical. The vitelline lobes represent the parts which are developed around the vitelline veins, whilst the umbilical lobes are developed around the umbilical veins. As, however, development proceeds the lobar condition characteristic of the full-grown liver is gradually assumed. Neck Cystic Dact and Valves of Heister Body of Gall-bladder Right Hepatic Duct -•Left Hepatic Duct '^ Common Hepatic Duct Ductus Communis Choledochus ^^ ~- Pancreatic Duct (Duct of Wirsung) ~"^- Ampulla of Vater Duodenum (2nd part) Fig. 347, — ^The Excretory Apparatus of the Liver. Structure of the Gall-bladder.— The wall of the gall-bladder is composed of three coats — serous, fibro- muscular, and mucous. The serous coat is formed by the peritoneum, and is usually incom- plete, being confined to the inferior and lateral surfaces. Some- times, however, the peritoneum completely surrounds the organ, and attaches its superior surface to the cystic fossa of the liver by a ligamentous fold. k THE ABDOMEN 809 The fibro-muscular coat is composed of fibrous and plain muscular tissues. The fibrous bands are disposed in all directions, and inter- lace freely with one another. The muscular fibres, which inter- mingle with the fibrous bands, are arranged both longitudinally and transversely. The mucous coat is covered by colmnnar epithelium. Its surface presents a great number of small ridges, which interlace in all direc- tions and enclose polygonal depressions or alveoli of various sizes. This pitted appearance bears a resemblance to honeycomb, and the mucous membrane of the vesiculas seminales in the male is similarly arranged. The mucous coat is richly provided with mucous glands. In the neck of the gall-bladder, which describes two curves like the letter 3» there are two fibro-mucous folds, which project into the interior, one opposite each curve, and serve as valves. Structure of the Cystic Duct. — ^The wall of the duct is composed of a fibro-elastic and muscular coat, and a mucoiis coat. The former resembles that of the gall-bladder. The mucous coat, which is covered by columnar epithelixun, presents several crescentic folds, disposed obliquely round the wall in a spiral or somewhat cork- screw manner, and succeeding each other at frequent intervals. When the duct is distended, its exterior presents a series of spiral constrictions with intervening swellings. The spiral folds in the interior serve as valves, which are known as the valves of Hetster, or of Amussat. Blood-supply. — ^The gall-bladder is supplied by the cystic artery, which is a branch of the right di\nsion of the hepatic. Its course is forwards between the hepatic and cystic ducts to the neck of the organ, where it divides into two branches, superior and inferior. The superior branch ramifies on the upper surface of the organ, between it and the cystic fossa of the liver, whilst the inferior branch is distributed over the inferior surface beneath the peri- toneiuTi. The cystic vein, which is formed by the vmion of superior and inferior branches, usually opens into the right division of the vena portae. Lymphatics. — ^These pass between the two layers of the gastro- hepatic omentum to the hepatic glands. Nerves. — These are derived from the hepatic sympathetic plexus. Development of the Gall-bladder and Cystic Duct. — These are formed in the course of the second month as a diverticulum from the common bile-duct. Structure of the Pancreas. The pancreas belongs to the class of compound racemose or acino- tubular glands, and bears a close resemblance to a serous or true salivary gland, e.g., the parotid. It has a greyish-pink colour, and is somewhat soft in consistence. It is from 6 to 8 inches long, from I to 1 1 inches deep, except at the right and left extremities, and from i to | inch thick. Its weight is about 3.^ oimces. It is Sio A MANUAL OF ANATOMY destitute of a fibrous capsule, properly so called, and is invested merely by a thin connective- tissue covering, which readily allows the outline of the lobules to be seen. It is composed of a number of lobules, which are loosely held together by ducts and areolar tissue. Each lobule consists of a group of alveoli or acini which are long, tubular, and convoluted, wherein they differ from the saccular alveoli of such a gland as the parotid. From each lobule a duct passes off, which unites with the ducts of adjacent lobules in the left extremity of the gland to form the commencement of the principal duct. Within the lobule the lobular duct divides into junctional ducts, each of which belongs to an acinus, and is lined with flattened cells. Islets of Langerbans Alveoli Fig. 348. — Structure of the Pancreas (highly magnified). The alveoli or acini are each composed of a basement membrane, reticular in structure, and lined with secreting columnar epithelium, the basement membrane being continuous with the wall of the junctional duct. The lumen of each acinus is small, and is usually occupied by spindle-shaped cells, known as the centro-acinar cells of Langerhans, which are continuous with the cells of the junctional duct. The connective tissue which covers the pancreas sends ex- pansions inwards between the lobules, along which the bloodvessels are conducted. Further, the interlobular connective tissue pene- trates into the lobules, and so conducts the bloodvessels into their interior. The inter alveolar connective tissue has a loose disposition, and in certain parts contains small groups of epithelium-like cells, THE ABDOMEN 8ll sunounded by large convoluted capillary vessels. These groups constitute the islets of Langerhans, which are characteristic of the pancreas. Excretory Apparatus of the Pancreas.— There is one principal duct, called the pancreatic duct or duct of Wirsung. It is buried in the substance of the gland, and is readily recognised by its white colour. It lies nearer the posterior than the anterior surface, and rather nearer the lower than the upper part of the gland. It commences in the tail, whence it runs through the body as far as the neck, receiving in its course a great many tributaries. On arriving at the neck it gets a branch from the accessory pancreatic duct, and then it describes a bend, and passes into the head in a direction dowTiwards, backwards, and to the right. Finally, on leaving the pancreas it meets with the common bile-duct, and the two, entering the wall of the second part of the duodenum, terminate in the manner already described (see p. 710). The accessory pancreatic duct or duct of Santorini is com- paratively small, and varies much in size. If well developed, it commences in the lower part of the head, where it takes up the ducts of the lobules of that part. It then passes upwards with an inclination to the right, and divides into two branches. One of Pancreatic Duct (Duct of Wirsung) Accessory Duct (Duct of Santorini) Ductus Communis Choledochus Uncinate Process Dnct of \\'ursung Fig. 349. — The Pancreas and its Ducts (Posterior View). these joins the duct of Wirsung in the neck, whilst the other opens into the second part of the duodenum at a point about i inch above the common opening of the common bile-duct and duct of Wirsung. The secretion conveyed by the duct of Santorini in early life is usually regarded as flowing into the duodenmn, whilst in the adult it is diverted into the duct of Wirsung. The tributaries of the principal duct, as well as of the accessory duct, when followed into the pancreas, become in succession inter- lobular and intralobular ducts. The intralobular ducts pass wathin the lobules, and end in intermediary, jundiofial, or intercalary* ducts, with which the alveoli or acini are directly connected. The part of the duct between the intermediary and the intralobular duct is called the neck. The walls of the intermediary ducts are thin, and are formed of a basement membrane covered by flattened * Interposed or inserted between the alveoli and the intralobular ducts. 8l2 A MANUAL OF ANATOMY epithelial cells, the neck being Uned by polyhedral cells. In the larger ducts a connective- tissue coat is superadded to the basement membrane, which is now covered by columnar epithelium. The duct of Wirsung, though of comparatively large size, has a thin wall destitute of muscular fibres, and composed of two coats — external fibrous and internal mucous. The mucous coat is smooth and covered by columnar epithelium. Varieties — (i) Small Pancreas. — This consists in a permanent detachment of the unciform process, or that part of the pancreas which extends along the tipper aspect of the third part of the duodenum and has the superior mesenteric vessels in front of it. (2) The head of the pancreas may surround the second part of the duodenum more or less completely. (3) Accessory Pancreas. When an accessory pancreas is present it is usually met with in the wall of the upper part of the duodenum, but it may be found in the wall of the stomach. (4) The duct of Wirsung sometimes opens into the duodenum independently of, but close to, the common bile-duct. Blood-supply. — The pancreas derives its arteries from (i) the pancreatic branches of the splenic artery, one of which accom- panies the principal duct from left to right, and is known as the artetia pancreatic magna; (2) the superior pancreatico- duodenal of the gastro-duodenal from the hepatic ; and (3) the inferior pancre- atico-duodenal of the superior mesenteric. The veins are (i) the pancreatic veins, which open into the splenic vein, and (2) the pancreatico-duodenal vein, which terminates in the superior mesenteric vein. All the pancreatic venous blood eventually passes into the portal vein. Lymphatics. — These commence as Ijonphatic clefts around the alveoli, and pass chiefly to the cceliac glands. Some of them, how- ever, terminate first in the superior mesenteric glands in contact with the upper part of the superior mesenteric artery. Nerves. — ^These are derived from offshoots of the hepatic, splenic, and superior mesenteric plexuses, and accompany the arteries. They are chiefly composed of non-medullated fibres. Development or the Pancreas. — The tubular portion of the pancreas is of entodermic origin, but its connective tissue and vascular elements are developed from mesoderm. The pancreas is developed from two entodermic diverticula — dorsal and ventral. The dorsal diverticulum is an evagination of the entoderm of the dorsal wall of the duodenal portion of the primitive gut. The ventral diverticulum springs from the primitive hepatic diverticulum close to the ventral wall of the duodenum, which diverticulum subsequently forms the common bile-duct. The dorsal diverticulum extends between the two layers of the mesogastrium, where it comes into relation with the developing spleen. This diverticulum gives off lateral epithelial tubes, which ramify freely, and so build up an acino- tubular gland. The acini appear as enlargements of the walls of the terminal tubes. By means of the ramifications of the dorsal diverticulum, the greater part of the head, body, and tail of the adult pancreas are formed. The ventral diverticulum, which is small, gives rise to ramifying epithelial tubes, like the dorsal diverticulum, and these form the lower part of the head of the adult pancreas. The ventral diverticulum, an evagination, as stated, from the future coinnion bile-duct, gives rise to the principal duct of the pancreas, or duct of Wirsung, and the dorsal diverticulum forms the accessory pancreatic duct, or duct of Santorini. which consequently opens directly into the duodenum. THE ABDOMEN 813 The ventral and dorsal parts of the pcincreas join, and the dorsal diverti- culum (duct of Santorini) and ventral diverticulum now communicate by freeh- anastomosing branches. Thereafter the duodenal portion of the duct of Santorini usually atrophies and disappears. It may, however, persist, and open, as an independent duct, into the second part of the duodenum. The duct of Wirsung is persistent, and constitutes the principed duct of the fully developed pancreas. From its mode of development it necessarily opens into the common bile-duct. The islands of Langerhans, which are characteristic of the pancreas, are formed of cells derived from the walls of the original epithelial tubes. These cells become differentiated, and by their multipUcation. they give rise to isolated cell-groups, l>Tng in the mesodermic connective tissue between the lobules of the gland, where they are soon permeated by bloodvessels. Pylorus Duct of Santorini Common Bile-duct^ Orifice of Common Bile-duct and Pancreatic Duct. Duct of Wirsung Dorsal Pancreas - - Duodeno-jejunal Flejrare --•■ Superior Mesenteric Vessds Ventral Pancreas Fig. 350. — The Pancreas in Early Life. The development of the pancreas, as stated, proceeds within the meso- gastrium. It occupies a mesial position at this stage, and is completely invested by the mesogastrium. When, however, the stomach and duodenum undergo partial rotation towards the right, the pancreas also turns on its right side. The head of the gland incUnes towards the right, and occupies the U-shaped curve described by the duodenum. The body and tail pass to the left, the body coming to lie in front of the left kidney, and the tail appljong itself to the spleen. The entire gland, therefore, now Ues across the dorsal body-wall. The dorsal layer of the mesogastrium. covering the dorsal surface of the pancreas, becomes absorbed, and consequently the pancreas of adult Ufe is situated behind the peritoneum, and is therefore spoken of as being retro- peritoneal. Structure of the Spleen. The spleen is the largest ductless gland in the body. It has two coats, serous and fibrous, inseparably connected together. The serous coat is formed by the peritoneum. The fibrous coat or tunica -propria is composed of fibrous tissue, with a con- siderable admixture of elastic tissue, and a certain amount of 8i4 A MANUAL OF ANATOMY Capsule Trabecula plain muscular tissue, all of which build up a strong distensible tunic. The organ is composed of a trabecular network, the spleen pulp, bloodvessels, and Malpighian corpuscles. The tunica propria sends into the organ a number of trabeculae which, like the tunica propria, are composed of fibrous, elastic, and plain muscular tissues. These divide and subdivide, and unite with one another, as well as with processes de- rived from the sheaths which the bloodvessels carry in with them at the hilum. There is thus formed a trabecular network which pervades the interior, and contains in its meshes the spleen pulp, capil- lary tufts, and Malpighian corpuscles. The spleen pulp occupies the meshes of the network formed by the trabeculge. It is soft, and has a dark red colour, which, however, be- comes brighter on exposure to the air. The matrix of the spleen pulp is reticular, and is formed by branched con- nective-tissue corpuscles, which constitute the susten- tacular cells of the organ. The matrix is, therefore, in reality retiform tissue. The interstices of the reticulum contain blood, in which there is a large number of white corpuscles, and also special cells characteristic of the spleen, and called the splenic cells. These latter are of large size, and are amoeboid. They contain pigment, and red blood-corpuscles in various stages of disintegration. Bloodvessels and Malpighian Corpuscles— Arteries.— The splenic artery furnishes five or six large branches which enter the organ at the hilum, and carry in with them trabecular sheaths from the tunica propria. In the interior they divide and subdivide, and finally terminate in pencil-like clusters of capillary vessels, by which time they have laid aside all their coats except the endothelial lining. The endothelial cells then become separated from each other by spaces, and, being continuous with the sustentacular cells of the spleen pulp, the blood flows directly into the interstices of the reticulum of the pulp. The arteries, which are at first accom- panied by trabecular sheaths, ultimately lose these sheaths, and Malpighian Corpuscle Spleen Pulp Fig. 351. — Section of the Spleen. THE ABDOMEN 815 enter the spleen pulp to end in clusters of capillaries. Before they terminate in these clusters their external coat undergoes an important modification, which consists in its transformation into lymphoid or adenoid tissue. This Ijonphoid tissue forms at intervals small round or oval enlargements, called the Malpighian corpuscles, which on section appear as minute white specks in the dark red spleen pulp. These corpuscles are simply localized expansions of the Honphoid tissue which forms the external coat of the small arteries. The expansion may be confined to one side of the artery, or it may include the whole of its circumference. Each corpuscle receives minute twigs from the artery on which it is set, and contains large numbers of Ijnnph corpuscles, as well as capillary bloodvessels. Veins. — The arterial blood, on leaving the capillary vessels, flows directly into the interstices of the reticular matrix of the spleen pulp, and from these it is taken up by radicle veins which commence in a manner similar to that in which the capillaries end. Endo- thelial cells, continuous with the sustentacular cells of the pulp, come together and cohere, so as to form very delicate tubular vessels, having closed walls. As these radicle veins unite and become larger the usual other coats are superadded to the endo- thelial lining. Ultimately five or six veins leave the spleen at the hUmn, which unite to form the splenic vein, this in turn uniting with the superior mesenteric vein to form the vena portae. It is to be noted that, in the circulation through the spleen, the arterial blood leaves tubular vessels and flows through the inter- stices of the reticulum of the spleen pulp, where it bathes the Malpighian corpuscles, after which it enters tubular vessels of the nature of veins. The cells of the spleen are of three kinds as follows : (i) the sustentacular cells of the retiform tissue of the spleen pulp ; (2) the splenic cells ; and (3) lymphoid corpuscles. Lymphatics. — These are arranged in two groups — trabecular and perivascular. The trabecular lymphatics are contained in the trabeculae, and communicate with a lymphatic network in the tunica propria underneath the peritoneal coat. The 'perivascular lymphatics commence in the lymphoid tissue which forms the external coat of the smaller arteries. At the hilum both sets of lymphatics meet and pass to the splenic glands, and thence to the cceliac glinds. Nerves. — These are derived from the splenic plexus, >yhich is an offshoot from the coeliac plexus of the solar plexTis. The fibres, which are mosth' non-medullated, are derived parti v from the svm- pathetic system and partly from the right pneimaogastric nerve. Development of the Spleen. — The spleen is usually regarded as being de- veloped from the mesoderm between the two layers of the mesogastrium. It is in close proximity to the developing pancreas, which, howe^^e^, is of ento- dermic origin. Towards the end of the second month the mesenchyme becomes thickened by an accumulation of lymphoid cells. This mass is in- creased by the addition of cells which migrate from the surface-cells of the mesogastrium, and it becomes permeated by bloodvessels. The cells give off processes, and these interlace, thus giving rise to the trabecular network. 8i6 A MANUAL OF ANATOMY At a later period the Malpighian corpuscles make their appearance. These are formed from lymphoid cells, which are grouped around the small branches of the splenic artery, before these branches terminate in their clusters of capillaries. As the spleen grows towards the left side it carries with it the left layer of the mesogastrium, and from this are formed the gastro-splenic omentum, the lieno-renal omentum, and the lieno-phrenic, or phreno-splenic ligament. Zona Glomerulosa Structure of the Suprarenal Capsules. The suprarenal capsules or bodies (adrenals) belong to the so-called ductless glands. Each capsule is enclosed in a thin sheath of con- nective tissue, from the deep part of which processes are given off into the interior, where they form a supporting stroma. The propel substance of the capsule is divided into an external or cortical, and internal or medullary part. The cortical part has a somewhat yellowish tint, and is com- posed of cells supported by a fibrous stroma. The cells being variously arranged in different parts, the cor- tex is divisible into three zones, named, from without inwards, zona glomerulosa, zona fasci- culata, and zona reticu- laris. The zona glomexulosa, which is narrow, lies immedi- ately within the ex- ternal capsule, and is so named because its component cells are grouped in such a manner as to form glomeruli, which are em- bedded in a fibrous stroma. The cells are polyhedral, and each contains a clear round nucleus. The zona fasciculata forms the chief part of the cortex, and is so named because its component cells are arranged in columns or Fig- 352.— Section of the Suprarenal Capsule. fasciculi. The cells are similar to those of the zona glomerulosa, and the cell-columns are separated from one another by fibrous trabeculae, which act as carriers of the bloodvessels, nerves, and lymphatics. The zona reticularis, which is narrow, lies within the zona fasciculata, and is so named because its component groups of polyhedral cells are con- nected with one another in such a manner as to form a reticulum. •Zona Fasciculata i S Zona Reticularis Medulla ~ THE ABDOMEN 817 The medullary part is confined to the centre of the capsule in the adult, is soft in consistence, and has a reddish-brown colour, due to the contained venous blood. The supporting fibrous stroma of the cortex pervades it, and is arranged in a reticular manner. The meshes of this reticulum are occupied by cells, resembling somewhat epithelial cells, and larger and more irregular than those of the cortex, some of them being branched. Blood-supply — Arteries. — ^These are (i) the superior capsular of the inferior phrenic or diaphragmatic from the abdominal aorta, (2) the middle capsular from the abdominal aorta, and (3) the inferioi capsular from the renal. The veins of each capsule eventually unite to form one supra- renal vein. This vessel emerges through the hilum, and on the right side it opens directly into the inferior vena cava, whilst on the left side it terminates in the left renal vein. The lymphatics terminate in the lateral lumbar glands. Nerves. — The suprarenal capsules are very richly supplied with nerves, which are derived from (i) the inferior or diaphragmatic plexus from the semilunar ganglion of the solar plexus, (2) the suprarenal plexus from the semilunar ganglion and coeliac plexus, and (3) offshoots from the renal plexus. According to Bergmann, the suprarenal capsules also receive fibres from the phrenic and pneumogastric nerves. The fibres, which are chiefly non-medullated, form rich plexuses in the medullary part, where they have numerous ganglion cells connected with them. Development. — The suprarenal capsule makes its appearance internal to the Wolffian body. The cortex is of mesodermic origin, and the medulla is developed from the ganglia of the primitive abdominal sympathetic chain. The cortex is developed from cellular outgrowths of the mesotheUum of the coelom or body-cavity, on the mesial aspect of the mesonephros, or Wolffian body. These outgrowths soon become separated from the ccelomic meso- thelium, and unite to form a soUd mass, which constitutes the cortex. The medulla is derived from the ganglia of the primitive abdominal sympa- thetic chain. Groups of cells grow out from the gangUa (these cells being consequently of ectodermic origin), and they invade the cortex. They lose their connection with the sympathetic ganglia, and become differentiated into two groups. The cells of ope group are chromaffin cells, and stain a dark yellow colour with chromic acid salts. The cells of the other group are ganglion cells. All the cells developed from the sympathetic ganglia gradually pass to the centre, where they constitute the medulla. The suprarenal body thus develops in two parts — cortex, derived from the ccelomic mesothelium (mesoderm), and medulla, derived from the abdominal sympathetic gangUa, and therefore of ectodermic origin. Structure of the Kidneys. The kidneys are compound tubular glands. Each organ is in- vested by a capsule, composed of fibrous tissue with a certain amount of elastic fibres. The deep surface of this capsule is attached to the peripheral portion of the renal substance by fine fibrous processes and small bloodvessels. Underneath it there is a certain amount of plain muscular fibre-cells, arranged in a somewhat plexiform manner. At the hilum on the inner border it 52 8tS A MANUAL OF ANATOMY Malpighian Pyramid Cortex Cahx - - Pelvis is prolonged inwards to line a cavity to which the hilum leads, called the sinus, where it becomes continuous with the fibrous coats of the calices. When a kidney is cut into two halves by a longitudinal incision carried from the outer to the inner border, it is seen to be composed of two parts — cortical and medullary. The medullary part, which is internal in position, is arranged in conical bundles, termed the pyramids of Malpighi, which vary in number from eight to eighteen, the average number being about twelve. The bases of these pyramids are directed towards the cir- cumference, whilst their apical parts, called papillce, project into the sinus, where they are grasped by the calices. Each Malpighian pyramid is divided into three parts, namely, the boundary zone or basal part, the papillary zone, and the apex. The bound- ary zones of the pyra- mids form collectively the boundary or inter- mediate layer of the kidney. They abut against the cortical substance, which sends prolongations between them, called septula renum or columncB Bertini. Ureter jhesc prolougatious extend as far as the commencement of the apical parts of the papillary zones, where the}^ cease, so that these apical parts project into the calices free from cortical in- vestments. Each Malpighian pyramid is composed of straight, slightly diverging uriniferous ■ tubules {tubuli recti) and straight bloodvessels, the number of tubules being very much greater in the boundary zone or basal part than elsewhere. This straight arrangement of tubules and bloodvessels imparts to each pyramid a longitudinally striated appearance from apex to base. The boundary zones or basal parts have a dark reddish-brown colour, which becomes brighter in the papillary zones. The cortical part of the kidney is mainly situated within the fibrous capsule. It has a reddish-brown colour and, as already stated, sends prolongations between the Malpighian pyramids. Like tlie medullary part, it is composed of uriniferous tubules and bloodvessels, but the tubules are principally convoluted (tubuli Fig. 353. — Diagram of the Kidney in Longitudinal Section. THE ABDOMEN 819 contorti), though there are also bundles of straight tubules {tubuli recti) which have issued from the Malpighian pyramids, and form the medullary rays or pyramids of Ferrein. Cortex. — The cortical part is composed of the labyrinth and the medullary rays or pyramids of Ferrein. Labyrinth. — ^This portion of the cortex is so named from the very complicated arrangement of its tubules. It is situated in the interspaces between the medullary rays, and is composed of convo- luted uriniferous tubules, bloodvessels, and Malpighian corpuscles, each of which corpuscles is enclosed within a capsiile of Bowman. Uriniferous Tubules, — Each tubule commences in the labyrinth of the cortex in a spherical dilatation, called the capsule of Bowman, within which there is a tuft of convoluted capillary bloodvessels, known as a glomerulus (Ruysch) or Malpighian corpuscle. Bowman's capsule presents two poles. One of these is formed by two bloodvessels, afferent and efferent, which pierce the capsule at separate points, but close to each other. At the other pole Bowman's capsule becomes constricted, and forms the neck of a cylindrical tubule. After the tubule has passed the neck it becomes convoluted, and forms the first or proximal convo- luted tubule. The basement membrane and lining epithelium of Bowman's capsule are continuous with the basement membrane and lining epithelium of the proximal convoluted tubule, and the space between Bowman's capsule and the glomerulus is con- tinuous with the lumen of the tubule. The proximal convoluted tubule soon becomes straight, though slightly wavy, and, entering a medullary ray, it forms the spiral tubule. This tubule, on reaching the junction of the cortex and boundary layer, becomes suddenly very narrow, and traverses the boundary zone of a Malpighian pyramid. It is known as the descending tubule of Henle. On leaving the boundar^'^ zone it enters the papUlary zone, and after a short course it describes a very sharp bend, called the loop of Henle's tubule. It now retraces its steps from the papillary zone into the boundary zone of a Malpighian pyramid, in which latter situation it becomes suddenly enlarged. This part, which retraces its steps, is called the ascending tubule of Henle. It re-enters the cortex, where it becomes narrower, and passes into a medullary ray, in which it lies for a short distance. It subsequently, however, leaves the ray, and, entering the labyrinth, winds between the convoluted tubules as the irregular or zigzag ttibule, which has become slightly enlarged. This zigzag tubule then passes into the second or distal convoluted (intercalary) tubule. This tubule, becoming narrow, passes into the junctional or collecting tubule, which is slightly wavj\ The junctional tubule leads into the straight collecting ttcbule which is slightly enlarged, and is situated in a medullary ray. This straight collecting tubule now passes to the boundary zone of a Malpighian pyramid, taking up in its course other junctional tubules from the labyrinth. In passing through the various parts of a Malpighian pyramid the straight collecting tubules unite at 820 A MANUAL OF ANATOMY acute angles, and so become less numerous and at the same time larger. They run in straight, slightly converging lines towards the apex of a papilla, where they are very much reduced in numbers. Cortex Papillary Portion Fig. 354. — Diagram of the Uriniferous Tubules of the Kidney (Klein> a and a', Outer and Inner Zones of Cortex, which are free from Malpighian Corpuscles. 1. I. Capsule of Bowman 4. 4. Spiral Tubule 2. 2. Neck of Capsule 5. 5. Descending Limb of Henle s Loop 3. 3. Proximal Convoluted Tubule 6. 6. Loop of Henle 7. 7., 8. 8., 9. 9., Ascending Limb of Henle's Loop 10.10. Irregular Tubule 13., 14. Straight Collecting Tubule 11. II. Distal Convoluted Tubule 15. Excretory Tube or Duct of Belhni 12. 12. Junctional Tubule but of large size. In this final part of their course each straight collecting tubule forms the excretory tube or duct of Bellini. These excretory tubes open on the apex of a papilla, where there is often THE ABDOMEN 821 a foveola or small depression, and through these openings the urine escapes into a calix. The diameter of the excretory tubes or ducts of Bellini is about the 25^ inch. Sammary of a Tubule from Beginning to End. 1. The capsule of Bowman, containing a glomerulus or Malpighian corpuscle, in the labyrinth. 2. The neck, in the labyrinth. 3. The flrst or proximal convoluted tubule, in the labyrinth. 4. The spiral tubule, in a medullary ray. 5. The descending tubule of Henle (small), in a boundary zone, and in part of a papillary zone, of a Malpighian pyramid. 6. The loop of Henle' s tubule, in a papillary zone. 7. The ascending tubule of Henle (large), in part of a papillary zone, a boundary zone, and the cortex, in which latter it is in a medullary ray. 8. The irregular or zigzag tubule, in the labyrinth. 9. The second or distal convoluted (intercalary) tubule, in the labyrinth. 10. The junctional tubule, in the labyrinth on its way to a medullary ray. 11. The straight collecting tubule, in a medullary ray of the cortex, and in a boundary zone of a Malpighian pyramid. 12. The excretory tube, or duct of Bellini, in a papillary zone of a Malpighian pyramid. Structure of the Uriniferous Tubules.— The tubules are composed of a base- ment membrane lined with a single layer of epitheUal cells. The basement membrane itself consists of flattened epithelial cells. The tubules vary in size, but theur average diameter may be stated as ,^ inch. The characters of the Uning epithelial cells present differences in the different tubules, which will now be considered in order. 1. The capsule of Bowman is lined with a single layer of flattened epi- thelium, which is reflected over the glomerulus or Malpighian corpuscle, where it is more distinct in early Ufe than in the adult. 2. The neck is Uned with cubical epithelium. 3. The first or proximal convoluted tubule is also lined with cubical epi- thelium, but the cells, which are thick, are peculiar. The inner part of each cell — that is the part next the lumen of the tubule, including the spherical nucleus, has granular protoplasm, whilst the outer part — that is, the part next the basement membrane — has its protoplasm striated or fibrillated, owing to the presence of rod-shaped fibrils disposed vertically to the basement membrane (Heidenhain). These fibrillated cells are provided laterally with processes, by which they embrace one another. The lumen of the tubule is distinct. 4. The spiral tubule is lined with epitheUum similar to that of the proximal convoluted tubule, and its lumen is distinct. 5. The descending tubule of Henle is lined with clear, thin, flattened cells. The tubule, though narrow, has a distinct lumen. 6. The loop Of Henle's tubule is lined with epithelium which resembles that of the descending tubule. 7. The ascending tubule of Henle is Uned with fibrillated, cubical epithelial cells like those of the proximal convoluted and spiral tubules. Though it is of conaparatively large size, its lumen is small. 8. The irregular or zigzag tubule is lined with cubical epithelial cells, which are markedly fibrillated, and its lumen is minute. 9. The second or distal convoluted tubule is lined with epithelium which resembles that of the proximal convoluted tubule, with the following differ- ences : (a) the cells are longer ; and (b) they are highly refractive. In size it corresponds with the proximal convoluted tubule. 10. The junctional tubule is hued with clear flattened, cubical epithelial cells, and its lumen is large. 822 A MANUAL OF ANATOMY 11. The straight collecting tubule is lined with epithelial cells, which, in its earlier part, are clear and cubical, but in its later part they are columnar, and the lumen is very distinct. 12. The excretory tube or duct of Bellini is lined with epithelial cells which are clear and columnar. Medullary Rays or Pyramids of Ferrein. — ^These take the form of pyramidal bundles of uriniferous tubules, which are separated from each other by portions of the labyrinth. The tubules are straight, and emerge from the boundary zones of the Malpighian pyramids. As these medullary rays are followed from the boundary zones to the periphery, each gradiially diminishes in breadth, and ultimately tapers to a point, which stops a short distance from the fibrous capsule, being separated from it by a portion of the labyrinth. The rays are thus conical, their bases being at the boundary zones of the Malpighian pyramids, and their apices near the fibrous capsule — hence the name ' pyramids.' The explanation of this shape is that the tubules at the circumference of a medullary ray enter the labyrinth sooner than those in the centre, which latter form the apex of the ray. Summary of a Medullary Ray. — Each contains the following tubules : (i) spiral tubules; (2) ascending tubules of Henle ; and (3) straight collecting tubules. Medulla of the Kidney. — The medullary portion has been already generally described. It is composed of Malpighian pyramids, con- sisting of uriniferous tubules and bloodvessels (true and false). The tubules in the various parts of the Malpighian pyramids are as follows : 1. Boundary Zone. — ^This contains the following tubules : Portions of the descending tubules of Henle. Portions of the ascending tubules of Henle. Straight collecting tubules. 2. Papillary Zone. — ^This contains the following tubules : Portions of the descending tubules of Henle. The loops of Henle's tubules. Portions of the ascending tubules of Henle. The excretory tubes or ducts of Bellini. 3. Apex of the Papillary Zone. — This contains only the excretory tubes or ducts of Bellini. Bloodvessels of the Kidneys — Arteries. — Each kidney receives a large amount of blood from the renal artery, which is a branch of the abdominal aorta. This vessel, as it approaches the hilum, divides into four or five branches, which enter the sinus, where they are embedded in fat along with the calices. They then subdivide into interlobar branches, which pass between the Mal- pighian pyramids, where they continue to subdivide. On arriving at the junction of the cortex and boundary layer they form a series of arches, which are independent of one another, and are called the cortico-medullary arches. Alongside of these there are venous arches, which, unlike the arterial arches, anastomose freely with THE ABDOMEN 823 one another. The convexities of the incomplete arterial arches are directed towards the cortex, and the concavities towards the Malpighian p\Taniids. The branches of the arches are inter- lobular and arteriae rectae. The interlobular arteries (cor- tical) arise from the convexities of the arches and enter the laby- rinth of the cortex, in which they pass outwards between the medullary rays. They give off afferent and capsular branches. The afferent branches are so named because they carry blood to the glomeruli or Malpighian corpuscles. They arise from the interlobular arteries at frequent intervals, and each passes to a capsule of Bowman without giving ofi any branch. Having pierced the capsule at one pole, the afferent vessel breaks up into a number of convoluted capillary vessels, which form a small vascular ball, called a glomerulus or Malpighian cor- puscle. The blood is conveyed away from the glomerulus b}' an efferent vessel, which is variously regarded as an artery and a vein. This efferent vessel is smaller than the afferent artery. Tt pierces Bowman's capsule at the same pole as the afferent artery, but separate from, though close to, it. Thereafter it breaks up into a network of capillary vessels, which invest the corre- sponding proximal convoluted uriniferous tubule, the meshes of the network being polygonal. The efferent vessels of those glomeruli which lie nearest to the Malpighian pyramids are disposed in a different manner. They break up into bundles of straight vessels, called false vasa recta, which enter the boundary zones or basal parts of the pyramids, where they supply to a large extent the uriniferous tubules, upon the walls of which they form capillary networks with elongated meshes. It is, however, to be noted that the Malpighian pyramids also receive true arteriae rectae from the cortico-medullary arterial arches. Fig. 355. — Diagram of the Blood- vessels OF THE Kidney. A, Cortex ; B, Medulla, 1. Arterial Arch 2. Interlobular Artery 3. Afferent Artery of Glomerulus 4. Capsular Branches 5. Efferent Vessel of Glomerulus 6. Malpighian Corpuscle 7. Proximal Convoluted Tubule 8. True Arteria Recta q. False Arteria Recta 10. Venous Arch It. Interlobular Vein 12. Venae Stellatse 13. Venae Rectse 824 A MANUAL OF ANATOMY Malpighian Corpuscles. — A. Malpighian corpuscle of the kidney is a glomerulus or small ball of convoluted capillary bloodvessels, having two vessels connected with it, one of which is an afferent artery and the other an efferent vessel. The vessels of many of the corpuscles are col- lected into bundles, an arrangement which renders these corpuscles lobulated, the number of lobules varying from two to five. Each corpuscle lies within a capsule of Bowman, and the flattened epithelium of the capsule is reflected over the corpuscle from the points of entrance and exit of the afferent and efferent vessels. The epithelial cells covering the corpuscle are thicker and less flattened than those lining the capsule of Bowman, and are better marked in early life than in the adult. In the case of the lobulated corpuscles the epithelial investment dips in between the component lobules. The epithelium of Bowman's capsule and the epithelium of the corpuscle, which in each case forms a single layer, are separated from one another by a slight interspace. The diameter of a Malpighian corpuscle is about .j^^^ inch. The corpuscles are confined to the cortex of the kidney, where they lie in rows in the labyrinth between the medullary rays. There is a narrow zone immediately within the ex- ternal capsule, and another narrow zone close to the Malpighian pyramids, from both of which Malpighian corpuscles are absent. The capsular branches of the interlobular arteries supply the external fibrous capsule of the kidney, in which they anastomose with branches of the lumbar arteries from the abdominal aorta. The arteriae rectae (medullary), or vasa recta (true), arise from the concavities of the cortico - medullary arterial arches, and at once enter the boundary zones or basal parts of the Malpighian pyramids. Here they break iip into bundles of straight, slightly diverging arterioles, which run between the bundles of straight, slightly converging uriniferous tubules, a mutual arrangement which imparts to the Malpighian pyramids a longitudinally-striated appearance. The capillary networks formed by these arterioles have necessarily elongated meshes. It is to be noted that the Malpighian pyramids derive their blood-supply from two sources, namely, (i) the arteriae rectae, or vasa recta (true), from the cortico- medullary arterial arches, and (2) the false vasa recta from the efferent vessels of those glomeruli which lie nearest the Malpighian pyramids. It is also to be noted that a Malpighian corpuscle of Fig. 356. — Diagram SHOWING A Malpig- hian Corpuscle of THE Kidney with its Afferent and Ef- ferent Vessels, and A Proximal Convo- luted Tubule with its Venous Plexus (Bowman). !• Glomerulus 2. Bowman's Capsule 3. Uriniferous Tubule 4. Interlobular Artery 5. Afferent Vessel 6. Efferent Vessel 7. Venous Plexus around Tubule 8. Interlobular Vein i THE ABDOMEN 825 the kidney is a ball of convoluted capillary bloodvessels, which is enclosed within a capsule of Bowman, whereas a Malpighian corpuscle of the spleen is a collection of lymphoid or adenoid tissue which is a localized expansion of the external or lymphoid coat of the small arteries in the interior of that organ. Veins — Veins of the Cortex. — These are called the interlobular veins. Some of them commence on the surface of the kidney beneath the capsule, from which they return blood, and these are called vencB stellatce, because the venous radicles which give rise to them converge to a point, and so present a star-like appearance. Others originate in the plexuses around the uriniferous tubules. The interlobular veins terminate by joining the convexities of the venous arches, which are situated between the cortex and the Malpighian pyramids. Veins of the Medulla. — ^The veins of the Malpighian pyramids commence in plexuses which surroimd the excretory tubes or ducts of Bellini in the apical parts of the papillary zones, and they are called vencB rectcB. As these traverse the pyramids they are collected into bundles of straight vessels, which open into the concavities of the cortico-medullary venous arches, Cortico-medullary Venoits Arches. — ^These arches, w^hich are com- plete, are situated between the cortex and the Malpighian pyramids, where they lie alongside of the incomplete arterial arches. They derive their blood from the interlobular veins of the cortex, and the vense rectae of the Malpighian pyramids. The veins which proceed from these arches pass between the pyramids to the sinus of the kidney, where they unite to form the renal vein, which termi- nates in the inferior vena cava. Lymphatics. — ^These consist of two groups, superficial and deep. The superficial lymphatics, which are few in number, form a plexus in the fibrous capsule, and communicate with lymph spaces between the uriniferous tubules in the outer part of the cortex. They terminate by joining the deep lymphatics at the hilum. The deep lymphatics accompany the bloodvessels, and communicate with lymph spaces between the uriniferous tubules of the cortex and boimdary layer. On emerging at the hilum they receive the superficial lymphatics, and then pass to the lateral group of lumbar glands. Nerves. — ^The kidney receives numerous nerves from the renal plexus, which derives its fibres from (i) the aortico-renal ganglion, in which the small splanchnic nerve terminates ; (2) the coeliac plexus ; and (3) the aortic plexus. If there is a least splanchnic nerve present it reinforces the renal plexus. The nerve-fibres are partly sympathetic, partly spinal through the small and least splanchnic nerves, and in part derived from the right pneumo-gastric through the coeliac plexus. They accompany the arterial branches, and ramify upon the walls of the vessels and uriniferous tubules. Excretory Apparatus of the Kidney.— This consists of the calices or infundibula, pelvis, and ureter. 826 A MANUAL OF ANATOMY Ureter. — ^This is the excretory duct of the kidney, and it has the form of a cylindrical tube, like a goose-quill, its colour being a dull white. Its length varies from 12 to 16 inches, and its diameter is about i inch. At its lower extremity it opens into the bladder, and at the hilum of the kidney it presents a dilatation called the pelvis of the kidney, which is funnel-shaped, being wide above and narrow below. The pelvis is flattened from before backwards, and lies partly in the sinus and partly outside the hilum, its direction being downwards and inwards. It breaks up into two or three primary divisions within the sinus, and these again form secondary divisions, the resulting tubes being called ealices or infundibula, which vary in number from 7 to 13. The number of ealices thus falls short of the number of Malpighian pyramids (8 to 18), the explanation being that one calix grasps two papillae or even three. The ealices embrace the papillae of the Malpighian pyramids, which thus project into them, and they receive the urine as it oozes through the pores on the apices of the papillae, these pores being the openings of the excretory tubes or ducts of Bellini. The interspaces between the ealices in the sinus are occupied by the branches of the renal bloodvessels and by fat. Structure of the Ureter. — The ureter is a thick-walled muscular tube, lined with mucous membrane, and it consists of three coats — external or fibrous, middle or nmscular, and internal or mucous. The fibrous coat is composed of fibrous tissue, very compactly arranged, and it contains the bloodvessels and nerves, which here subdivide. The muscular coat is composed of plain muscular tissue, which is disposed in three layers — otiter longitudinal, middle circular, and internal longitudinal. The outer longitudinal layer is best marked in the lower half of the ureter, where it forms a continuous investment. In the upper half of the tube its bundles are some- what scattered. The mucous coat superiorly is continued over the papillae of the Malpighian pyramids, and inferiorly becomes continuous with the mucous membrane of the bladder. It is covered by stratified transitional epithelium, the cells being ar- ranged in four layers. In the most superficial layer (nearest the lumen of the tube) the cells are cubical, and present depressions on their deep surfaces, which receive the round ends of the pyriform cells of the layer beneath. In the second layer the cells are pyriform, the round superficial ends being capped by the cubical cells of the first layer, and the narrow deep ends projecting between the deeper cells. In the third and fourth layers the cells are round or oval. The mucous membrane is thrown into longitudinal folds, and the lumen of the tube, which is of small size, presents under the micro- scope a branched appearance in cross section. Blood-supply — Arteries. — ^The ureter receives branches from the renal, spermatic (ovarian in the female), common iliac, and superior vesical, arteries. The veins terminate in the vessels corresponding to these arteries. THE ABDOMEN 827 Lymphaties. — These pass to the lateral group of lumbar glands, and to the internal iliac glands. Nerves. — ^These accompany the arteries, and are derived from the renal, spermatic (ovarian in the female), and pelvic plexuses. The fibres form plexuses in the fibrous and muscular coats, which contain small ganglia. Middle Circular Muscular Fibres Outer Longitudinal Mnscnlar Fibres Inner Longitudinal Muscular Fibres Transitional Epithelium Mucosa Fig. 357. — Transs^rse Section of the Lower Part of the Ureter, SHOWING ITS Minute Structure. Structure of the Pelvis and Calices.— The structure of these parts of the excretory apparatus resembles that of the ureter, with the exception that they have only two layers of plain muscular tissue, instead of three as in the ureter. The layer which is wanting is the outer longitudinal layer. The calices are attached to the bases of the papillae, and in these situations their fibrous coats become continuous with that part of the fibrous capsule of the kidney which is prolonged inwards through the hilmn to line the sinus. The internal longitudinal muscular fibres disappear towards the papilla, but the circular muscular fibres accompany a calix to its termination, where they are arranged in the form of a circular band, which surrounds the base of a papilla at the line of attachment of a calix. The stratified transitional epithelium of the mucous coat of a calix is prolonged over the apex of each papilla. Stroma of the Kidneys. — Between the uriniferous tubules and bloodvessels there is a certain amount of connective tissue, which is present in greatest abundance in the region of the papillary zones. 828 A MANUAL OF ANATOMY Genital Gland (Testis or Ovary) Peritoneal Infundibulum Glomeruljis of Mesonephros.-J Glomerulus of Pronephros Miillerian Duct Permanent Kidney / Ureter Urinary Bladder--" Wolffian Duct } Pronephros ._{. Miillerian Duct .1.. Wolffian Duct \ Mesonephros 1 Canaliculi of _!__ Mesonephros j Artery of 't Mesonephros _i Glomerulus of Mesonephros j Metanephros ^(Permanent I Kidney) Fig. 358. — Development of the Kidney: Schematic (Testut). THE ABDOMEN • 829 This constitutes what is known as the fibrous or interstitial stiooia, of wliich there is a very small amount. Early Condition of the Kidneys. — The kidneys of a child at the period of birth are lobulated, each lobule representing a Malpighian pyramid sur- rounded by cortical substance. In this respect they resemble the permanently lobulated kidneys of certain animals, e.g., the ox. The lobules first become apparent towards the end of the third month of intra- uterine life, and aU traces of them have usually disappeared by the eighth or teaith year. They may, however, remain persistent to a greater or less extent throughout life, though this condition is of very rare occurrence. It is, however, not un- common to find the surface of an adult kidney marked by faint grooves indicative of its original lobulated condition. The disappearance of the lobulated condition is brought about by the adjacent lobules coalescing, this being accompanied by an increased development of cortical substance at the surface. The portions of cortical substance which remain in the spaces between the medullary pyramids (except their apical parts) represent the septula renum or columnae Bertini. Development of the Kidney and Ureter. The kidneys are of mesodermic origin, and are developed in connection with the intermediate cell-mass, which appears along the groove separating tHe mesodermic somites of the paraxial mesoderm from the latereil plate of mesoderm. The intermediate cell-mass, Uke the paraxial mesoderm, under- goes segmentation, its segments being known as nephrotomes, each of which is a sohd cord of cells. In the course of the development of the urinary system in vertebrates, three sets of organs have to be considered — namely: (i) the pronephros, (2) the mesonephros. and (3) the metanephros. The pronephros, fore-kldiiey, or head-kidney, which is functional in lower vertebrates, originates on either side as a thickening of the lateral part of the corresponding intermediate cell-mass, called the Wolffian ridge, which projects into the coelom or body-cavity. The Wolffian ridge consists of soUd cords of cells, which soon become tubular and give rise to a longitudinal canal, called the pronephrie or s^mental daet. This duct extends from the region of the heart anteriorly to tibe cloaca posteriorly, into the ventral com- partment, of which latter it opens. Associated with the cephahc end of this duct there are two epithelial tubules, known as the pronephrie tnboles, which he at right angles to it. By one end these tubules open into the pronephrie duct in those vertebrates in which the pronephros is functional, but in the human embryo they do not communicate with the pronephrie duct. By their other extremities they open into the ccelom or body-cavity (peri- toneal ca\ity), the openings being known as nephrostotnata. In the neigh- bourhood of the nephrostomata, but independent of them, there are tufts of capillar^' bloodvessels, covered by epithehum. These are called the pronephrie glomeruli. In those vertebrates m which the pronephros is well developed — e.g., cer- tain Fishes, and Amphibia during the larval stage, the urinary secretion makes its way from the pronephrie glomeruU into the coelomic cavity, from which it passes' through the nephrostomata into the pronephrie tubules, and thence into the pronephrie duct. The latter duct conveys it to the cloaca. In most vertebrates the pronephros is a rudimentary structure, and its tubules soon atrophy. The pronephrie duct, however, persists as the Wolffian duct, which belongs to the mesonephros. The mesonephros, mid-kidney, or Wolffian body consists of (i) a series of transverse tubules, called the mesonephric or Wolffian tubules, and (2) the Wolffian duct. The Wolffian tubules are developed from the intermediate ceU-mass, which, as stated, is broken up into segments, called nephrotomes. Each solid 830 A MANUAL OF ANATOMY nephrotome becomes hollow and gives rise to a mesonephric tubule, other- wise known as a segmental tubule. These tubules open by one end into the pronephric duct, now called the mesonephric or Wolffian duct. Their other extremities open into the ccelom by nephrostomata, but these soon become closed. The Wolffian duct extends from the region of the heart to the cloaca, into the ventral compartment of which it opens — that is to say, the uro-genital sinus or canal. The Wolffian duct on either eide lies external to the Wolffian body, and the MuUerian duct is on the outer side of the Wolffian duct. These two ducts lie within a fold of mesoderm, called the uro-genital fold, by which they are connected with the outer part of the Wolffian body. Anteriorly the uro-genital folds, right and left, are wide apart, but posteriorly they converge and fuse. By this fusion a dense fold of mesoderm is formed, called the genital cord, which contains the four ducts — namely, the right and left Wolffian ducts and the right and left Miillerian ducts. The Miillerian duct of either side having crossed over the Wolffian duct, the two Miillerian ducts lie close together at the median line within the genital cord, and in this situa- tion they blend to form the rudiment of the uterus and vagina (utricle or uterus masculinus in the male) . Each Wolffian tubule presents a saccular dilatation towards its coelomic end, which dilatation is invaginated by a tuft of capillary bloodvessels. Miillerian Duct — Wolffian Duct-- Suprarenal Testis -4 — !-"=■ Mesonephros or Wolffian Body Gubernaculum Fig. 359. — Mesonephros and Contiguous Structures of the Embryo Pig: Schematic (B. M. Allen). This tuft represents a glomerulus, and the saccular part of the tube invaginated by it represents a capsule of Bowman, the glomerulus and capsule of Bowman corresponding to a Malpighian corpuscle of the permanent kidney. The glomerular part of the tube is the secreting part; and the portion opening into the Wolffian duct is the excretory part, which becomes convoluted. The Wolffian tubules just described are known as the primary tubules. Sub- sequently secondary and tertiary tubules are formed. These tubules have no communication with the coelomic cavity. At one end, which is bhnd, they acquire Malpighian corpuscles, and their other ends join the excretory parts of the primary tubules, and so form collecting tubes. The mesonephros or Wolffian body persists in Fishes and Amphibia, and constitutes the functional kidney. In Mammals, Birds, and Reptiles it soon atrophies, and is largely replaced by the metanephros or permanent kidney. The fate of the Wolffian body will be afterwards referred to. The metanephros (after-kidney), or permanent kidney, is developed from (i) the renal diverticulum, which springs from the dorsal aspect of the caudal or posterior end of the Wolffian duct close to the uro-genital sinus of the cloaca, and probably (2) the metanephric blastema. The renal diverticulum elongates into a tube which grows cephalicwards, lying dorso-mesial to the Wolffian duct. Its cephalic end extends into the intermediate cell-mass, and is surrounded by mesodermic tissue, known as the metanephric blastema, where it undergoes enlargement. The caudal part of the diverticulum repre- -jrtaVU^-'^^J^j'' Vv ; <'>^ ANATOMY i THE ABDOMEN 831 sents the primitive ureter, and its cephalic enlargement corresponds to the primitive renal pelvis. The pelvic enlargement furnishes secondary diver- ticula, which grow into the metanephric blastema, and represent the calices. These, in turn, give off tubular branches, which, becoming extended and subdivided, give rise to the excretory tubules of the medullary part of the kidney. j v 1 The comphcated system of tubules in the cortical part, beyond the col- lecting or excretory tubules — namely, the secretory tubules — are developed from the metanephric blastema, which surrounds the enlarged cephahc extremity of the renal diverticulum. The tissue of this blastema becomes differentiated into two zones — outer and inner. The mesodermic tissue of the outer zone furnishes the connective-tissue stroma and capsule of the kidney as well as the columns of Bertini. Suprarenal Bodies HuUerian Duct f f\j| y*>j /v^ fikrr-r V,Mullerian Duct . Kidneys .Rudiments of Sex-Organs Wolffian Body \3^^^r{7 k^r^CM^&J— Wolffian Body I. Intestine Wolffian Duct ..\2^S^^)I| ~ l\lfS^«K<^ ^°'®*° ^"*^' Mullerian Duct Genital Cord Uro-genital Sinus Cloa'.-a Fig. 360. — ^The Wolffian Bodies : Wolffian and Mullerlan Ducts, and Contiguous Parts (Allen Thomson). The mesodermic tissue of the inner zone gives rise to solid outgrowths, which at a later period become hollow and separated from the inner zone. These outgrowths are called the renal vesicles. Each vesicle becomes elongated, and forms an S-shaped tubule. One end of the S becomes connected with the contiguous collecting tubule, into which it opens. The other end pertains to a Malpighian corpuscle. Within the lower loop of the S a collection of mesenchyme appears, and within this a glomerulus is developed. This glomerulus invaginates a portion of the upper wall of the lower limb of the S. and the part thus invaginated forms Bowman's capsule. The remainder of the lower limb represents the commencement of the proximal convoluted tubule. As the S tubule elongates it forms several curves, and thus gives rise to ( i ) the remainder of the proximal convoluted tubule, (2) the spiral tubule, (3) Henles looped tubule, (4) the irregular, or zigzag tubule, (5) the second convoluted tubule, and (6) the junctional tubule. 832 A MANUAL OF ANATOMY Ligjment ladder is anterior in position, being situated behind the bodies of the pubic bones, and resting by its base upon the rectum. The vesiculae seminales and the lower portions of the vasa deferentia lie in contact with the base of the bladder, between it and the rectum. The prostate gland surrounds the neck of the bladder and the prostatic part of the urethra. Peritoneum. — ^The disposition of the peritoneum will be simplified THE ABDOMEN 83: by defining the limits of the pelvic colon and rectum, and the different parts of the bladder. The pelvic colon extends from the inner border of the left psoas magnus, just anterior to the left sacro-iliac articulation, to the level of the third sacral vertebra. The rectum extends from the third sacral vertebra to a point i^ inches in front of and below the tip of the coccjoc, where it pierces the pelvic diaphragm to terminate in the anal canal, which is the part of the large gut surrounded by the sphincter muscles. The bladder, when empty, or only moderately distended, presents the following parts : (i) an apex, which is directed forwards, and lies behind the upper part of the symphysis pubis, where it has connected with it the fibrous cord representing the urachus ; (2) a Pelvic Colon Line of Peritoneal Reflection Ureter Vas Deferens Vesicula Seminalis Bladder / Urachus 'j/i—il ^Symphy^ Pubis -^-! — U-,— Triangular Ligament " "^ of Urethra ^^~. Corpus Cavemosum ^ Corpus Spongiosum \ Bulb and Bulbo-cavemosus '\ Colles' Fascia ^^^^^^ . Perineal Pouch Levator Ani (cut) / ^7 \ ^ Membranous Urethra , • Cowper s Gland Anus ProsUte Gland and Capsule Fig. 362. — The Viscera of the Male Pelvis (Lateral View). base or fundus, directed backwards and downwards towards the rectum, from which it is separated by the vesiculae seminales and vasa deferentia ; (3) a body, which has a superior surface, an inferior surface, and three borders, two being lateral and one posterior ; and (4) a neck. The jDeritoneum, having descended from the posterior waU of the abdomen over the common iliac vessels, enters the back part of the pelvic cavity, where it invests the pelvic colon, forming behind it an expanded, wavy mesentery, called the pelvic meso-colon, which attaches it to the front of the sacrum as low as the third sacral vertebra. The peritoneum is then prolonged upon the rectum, the upper third of which it covers anteriorly and laterally, but not posteriorly, the middle third being covered by it only anteriorly, whilst the lower third is destitute of peritoneal covering. 836 A MANUAL OF ANATOMY The point at which the peritoneum leaves the rectum is fully 3 inches above the anus. The membrane is now carried forwards to the upper ends of the vesiculae seminales, and the adjacent portions of the vasa deferentia, which it covers. Thereafter it passes forwards over the superior surface of the bladder, which it completely covers as far as the apex. Here it meets with the urachus, and by this it is conducted from the bladder to the posterior surface of the anterior abdominal wall. Along each lateral border of the bladder the peritoneum is reflected over the correspond- ing lateral wall of the pelvis. In passing from the rectum to the upper part of the base of the bladder, the peritoneum forms the recto- vesical pouch. The bottom of this pouch is, as a rule, fully i inch distant from the base of the prostate gland, thus leaving the part of the base of the bladder, called the external trigone, quite free from peritoneum. The peritoneum, as it passes to and from the bladder, forms certain folds, which constitute the false ligaments of the viscus. These are five in number, as follows : iiejo posterior, which represent the laterally-disposed lips of the mouth of the recto-vesical pouch ; two lateral, right and left, which represent the reflection of peri- toneum from each lateral border of the bladder to the correspond- ing lateral wall of the pelvis ; and superior, which is the reflection of the peritoneum from the apex of the bladder to the posterior surface of the anterior abdominal wall along the urachus. The parts of the bladder which are left uncovered by peritoneum are (i) the inferior surface, and (2) the external trigone. The pelvic peritoneum on either side of the bladder and rectum presents three fossae when these viscera are empty, which are named, from before backwards, paravesical, paravesicular, and pararectal. Retro-pubic Pad of Fat. — ^This is a collection of areolar and adipose tissues which lies between the posterior aspect of the bodies of the pubic bones, the bladder, and the pubo-prostatic ligaments. Pelvic Fascia. — ^This fascia clothes the inner wall of the pelvis, and furnishes inward expansions, which have an intricate con- nection with, and serve to support, the contained viscera. It is divisible into two portions — parietal and visceral. Parietal Portion. — Over the posterior wall of the pelvic cavity the parietal portion of the pelvic fascia, which is here very thin, covers the intrapelvic portion of each pyriformis muscle and the corresponding sacral plexus, this portion being known as the fascia of the pyriformis. Over the lateral wall the fascia attains considerable strength, and is attached superiorly to the back part of the iliac portion of the ilio-pectineal line for a short distance, where it becomes continuous with the iliac fascia. In front of this the fascia falls short of the ilio-pectineal line, and is fixed to the lateral wall of the pelvis a little below the line, its attachment being oblique, and accurately following the upper border of the obturator internus muscle. When it arrives at the upper part of THE ABDOMEN 837 the obturator foramen, there is a break in the osseous attachment of the fascia, which here joins the upper border of the obturator membrane over the upper border of the obturator intemus, and so converts the obturator groove into a canal for the passage of the obturator vessels and nerve. At the upper and inner part of the obturator foramen the fascia resumes its osseous attachment, but falls more and more short of the pelvic margin, its connection with the back of the body of the os pubis being in a direction down- wards and inwards till it reaches a point just below the lower part of the symphysis pubis. The fascia descends from the foregoing line of attachment, closely covering the obturator internus, to be Parietal Pelvic Fascia Visceral Pelvic Fascia Levator Ani Anal Fascia Obturator Internus Parietal Pelvic Fascia Prostate Gland, with Urethra Alcock's Canal Fig. 363. — The Pelvic Fascia (Anterior View). attached as follows from before backwards : (i) to the pelvic aspect of the ischio-pubic ramus near the subpubic arch, where it lies on the mesial side of the obturator internus ; (2) to the inner margin of the falciform process of the great sacro-sciatic ligament at the lower part of the ischial ramus, and also to the great sacro-sciatic ligament itself, where that is attached to the inner margin of the tuber ischii ; and (3) to a portion of the great sacro-sciatic ligament near its ischial attachment, and to the anterior margin of the great sciatic notch. The lateral portion of the parietal pelvic fascia, from its relation to the obturator intemus muscle, is sometimes called the obturator fascia. From its lower attachment the fascia is continued backwards and inwards over the great sacro-sciatic foramen, pyriformis, and sacral plexus to the sacnun, as the fascia of the pyriformis. As it covers the foramen it is perforated by the gluteal, sciatic, and internal pudic vessels. At the anterior part of the pelvic cavity the fascia, after taking attachment to the pelvic surface of the ischio-pubic ramus near the subpubic arch, is continued inwards over that arch, where it lies behind the .compressor urethrae muscle, and forms one half of the postero-superior or deep layer of the triangular ligament, the other half being formed by the corresponding portion of the fascia of the opposite side. When it arrives at the urethra, it changes its course, and passes backwards over the anterior border of the 838 A MANUAL OF ANATOMY levator ani to blend with that portion of the visceral pelvic fascia which ensheathes the prostate gland. In the direction of a line passing from the inner aspect of the ischial spine to the back of the body of the os pubis, near its lower end and close to the symphysis, the lateral pelvic fascia is strength- ened by fibres which impart to it a white colour. This part is called the white line, and it serves to divide the fascia into two portions, upper or pelvic proper, and lower or perineal. The pelvic portion looks into the pelvic cavity, and covers the upper part of the obturator internus, whilst it is itself covered by the peritoneum. The perineal portion covers the lower part of the obturator internus, and lies on the outer wall of the ischio-rectal fossa, where it con- structs Alcock's canal. The under aspect of the white line affords extensive origin to the levator ani muscle. Parietal Pelvic Fascia Levator Ani ... Anal Fascia ^^ij^'Wr.?: Obturator Internus- Parietal Pelvic Fascia-''' 1 ^i" Alcock's Canal Visceral Pelvic Fascia ^— ..Vesicula Seminalis Vas Deferens Fig. 364. — Diagram of the Pelvic Fascia from Behind. Visceral Portion of the Pelvic Fascia. — ^The visceral portion is destined to support the lower part of the bladder, vesiculae seminales, terminal portions of the vasa deferentia, prostate gland, and rectum. It is a laminar offshoot of the parietal portion, from which it springs along the white line. Though, however, this is its piincipal source, it has an independent origin anteriorly on either side of the middle line from the posterior aspect of the body of the OS pubis near the lower part of the symphysis. In this latter situation it lies a little above the attachment of the parietal por- tion, the anterior fibres of the levator ani taking origin from the portion of bone between the two fasciae. Though the visceral por- tion forms one continuous sheet along its pelvic attachment, its ultimate disposition is so intricate that it is convenient to consider its arrangement under three divisions. I. opposite the Madder, vesicula seminalis, and rectum. In this region the visceral portion of the fascia passes inwards as far as the outer border of the vesicula seminalis. In doine: so it covers THE ABDOMEN 839 the upper surfaces of the levator ani and coccygeus, and is in turn covered by the peritoneum. At the outer border of the vesicula seminalis it divides into three laminae — upper, middle, and lower. The upper or vesical lamina ascends upon the lateral aspect of the bladder for a short distance, and ultimately loses itself in the muscular tissue of the vesical wall. This portion at each side forms the lateral true ligament of the bladder. The middle or recto- vesical lamina passes inwards betvveen the base of the bladder and the rectum, and is continuous with the corresponding lamina of the opposite side. As it passes inwards it furnishes a sheath to the vesicula seminalis and adjacent portion of the vas deferens, closely strapping these structures to the base of the bladder. The lower or rectal lamina descends upon the side of the rectum, and passes to its posterior surface, where it is continuous with the rectal lamina of the opposite side. 2. Opposite the neck of the bladder and prostate gland. In this situation the visceral portion of the fascia also divides into three laminae — upper, middle, and lower. The upper or prostatic lamina passes inwards over the anterior surface of the prostate gland, and is continuous with the prostatic lamina of the opposite side. The middle or recto - prostatic lamina passes inwards between the posterior surface of the prostate gland and the rectum, and is continuous with the corresponding lamina of the opposite side. The lower or rectal lamina is imaltered in its disposition. The upper or prostatic and middle or recto-prostatic laminae furnish a stout sheath to the prostate gland. 3. Between the pubic bodies and the upper aspect of the neck of the bladder. The portion of the visceral fascia in this region represents the upper lamina in the other regions, and may be called the pubo-prostatico-vesical lamina. It is arranged in the form of two stout cords, which are kno\\Ti as the pubo-prostatic ligaments or the anterior true ligaments of the bladder. Each is attached anteriorly to the posterior aspect of the body of the os pubis, near the lower part of the sjmiphysis, and a little above the attachment of the parietal portion of the pelvic fascia in this region, the anterior fibres of the levator ani taking origin from the portion of bone between the two fasciae. As the cord-like fascial bands pass backwards they are connected by a portion of the visceral fascia which covers the dorsal vein of the penis and lies deeply, thus giving rise to a small pouch, which is capable of admitting the point of a finger. This pouch is filled with fat, which is continuous with the retro-pubic pad of fat. The anterior portion of the visceral fascia lies upon the anterior surface of the prostate gland, and on reaching the neck of the bladder it passes forwards to its inferior surface, where it soon disappears in the muscular tissue of the vesical wall. The pubo-prostatic ligaments are largely composed of plain muscular tissue, which is derived from the longitudinal fibres on the inferior surface of the bladder as they pass to take attachment to the back of the bodies of the pubic bones on either 840 A MANUAL OF ANATOMY side of the middle line. These fibres constitute the so-called ■picbo-vesical muscles. Anal Fascia. — ^This very thin sheet of fascia is an offshoot from the parietal pelvic fascia just below the white line and the origin of the levator ani. It closely covers the ischio-rectal surface of that muscle and of the coccygeus, upon which it descends to the region of the anus, where it blends with the aponeurotic investment of the sphincter ani externus. Sympathetic Plexuses in the Pelvis. — ^These are derived from the hypogastric plexus, which is formed by the fusion of the two lateral strands of the aortic plexus after they have crossed the common iliac arteries. It is reinforced by branches from the ganglia of the lumbar sympathetic cords, and is situated in front of the body of the fifth lumbar vertebra between the common iliac vessels. It is a large, flattened plexus, measuring about i| inches in breadth, and it breaks up into two divisions, which form the right and left pelvic plexuses. Each of these enters the pelvis on the inner side of the internal iliac artery, and takes up a position on the side of the rectum. The pelvic plexus of each side is reinforced by branches from the upper one or two ganglia of the pelvic sym- pathetic chain, and by spinal fibres from the anterior primary divisions of the third and fourth sacral nerves (sometimes also the second), therKJbeing very small ganglia at the places of junction. From each plexus the following secondary plexuses are given off, which accompany the corresponding branches of the internal iliac artery : hemorrhoidal, vesical, prostatic, vesicular, and deferential, the latter three being replaced in the female by the vaginal and uterine plexuses. Internal Iliac Artery. — ^This vessel arises from the common iliac opposite the lumbo-sacral articulation, and terminates opposite the upper border of the great sciatic notch by dividing into an anterior and a posterior division. The length of the vessel is about i| inches, and its direction is downwards and backwards. Relations — Anterior. — ^The artery is covered by the peritoneum, and the ureter descends over it. The terminal part of the ileum forms an anterior relation of the right vessel, whilst the pelvic colon is similarly related to the left. Posterior. — ^The vessel rests chiefly upon its own vein, but near its origin it is placed over the commencement of the common iliac vein. Behind the veins there are the lumbo-sacral cord and ala of the sacrum. External. — ^The psoas magnus, with the intervention of the external iliac vein, and subsequently the lateral wall of the pelvis, with the intervention of the obturator nerve. Internal. — ^The peritoneum. Varieties. — ^Ihe chief variety affects the length of the vessel. It may be shorter or longer than usual, according as the common iliac is longer or shorter than normal, or according to the height at which the internal iUac ends in its two divisions. Foetal Condition. — During foetal life the internal iliac is represented by the hypogastric and umbilical arteries, the size of which greatly exceeds that of the external iliac. The function of these arteries is to carry the impure blood THE ABDOMEN 841 from the foetus to the placenta of the mother. The hypogastric artery- passes forwards to the posterior surface of the anterior wall of the abdomen, being crossed by the vas deferens. It then ascends to the lower part of the um- bilicus, where it leaves the abdomen with its fellow. Beyond the umbihcus the hypogastric is known as the umbilical arter>', and the two umbilical arteries, together with the umbilical vein, form the umbilical cord, in which the arteries describe spiral coils around the vein. The arteries convey the impure blood to the placenta, where it is purified, after which it is returned to the abdomen of the foetus by the umbilical vein. After birth, there being no further use for the placental circulation, the umbilical cord is tied, and the child separated from the mother. Thereafter the hypogastric arteries become impervious, and each is converted into a fibrous cord. The obliteration, however, does not involve the first I ^ inches of the vessel, which persist as the internal iUac artery of the adult. Moreover, the proximal end of the fibrous cord representing the obliterated hypogastric remains pervious also, and, being connected with the anterior division of the internal iliac, it furnishes the superior vesical artery or arteries. This pervious portion lies along the side of the pelvis beneath the peritoneum, where it is crossed by the vas deferens in the male, and the round Ugament of the uterus in the female. The foetal hypogastric artery gives off the sciatic, which is the primitive main artery of the lower Umb, until the external iliac, which becomes the femoral, is developed. Branches. — ^These are subject to much variation. In normal cases they arise from the two terminal divisions, anterior and posterior, some of them being parietal in their distribution, which will be indicated by the letter P, whilst others are visceral, which wiU be indicated by the letter V. The branches are las follows : Anterior Division. Posterior Division. Visceral. Parietal. Parietal. Superior vesical. Obturator. Ilio-lumbar. Inferior vesical. Internal pudic. Lateral sacral. Middle hemorrhoidal. Sciatic. Gluteal. In the female the inferior vesical artery may be replaced by the vaginal, or the vaginal may be an independent branch, and the uterine artery is always a special branch. Anterior Division. — ^The superior vesical artery (V) arises from the pervious portion of the fibrous cord which represents the foetal hypogastric artery, and at once breaks up into several twigs which frequently have independent origins. They are distributed to the upper portion of the bladder, and anastomose with the vesical of the obturator, and the inferior vesical of the same side, and with the superior vesical of the opposite side. The superior vesical furnishes the following branches : urachal to the urachus ; ureteric to the lower end of the ureter ; and deferential (as a rule) to the vas deferens, though this branch may arise from the inferior vesical. The deferential artery, which is usually of small size, divides into a descending and an ascending branch. The descending branch passes downwards to supply the ampulla of the vas deferens, and the vesicula seminalis. The ascending branch accompanies the vas deferens through the internal abdominal ring and inguinal canal into the scrotum, supplying the vas deferens, and giving a few twigs 842 A MANUAL OF ANATOMY to the globus minor of the epididymis, in which latter situation it anastomoses with the epididymal branch of the spermatic artery. In the spermatic cord it also anastomoses with the cremasteric branch of the deep epigastric. The deferential artery is sometimes of large size, and then it takes the place of the spermatic artery, if that vessel should be absent. One of the branches of the superior vesical artery is sometimes spoken of as the middle vesical. Small Sacro-sciatic Ligament Great Sacro-s Ligamei Internal Pudic Inferior Hemorrhoidal Superficial Perineal 1 Transverse Perineal Common Iliac Anterior Superior Iliac Spine Internal Iliac Ilio-lumbar Posterior Division External Iliac Anterior Division Superior Vesical Inferior Vesical Deep Circumflex Iliac Deep Epigastric Obturator Nerve Obturator Artery Obturator Vein Obturator Membrane .Symphysis Pubis Dorsal Artery of Penis Artery of Corpus Cavernosum Artery of the Bulb Fig. 365.— The Left Internal Iliac Artery and its Branches. The inferior vesical artery (V) takes an inward course to the lower portion of the bladder, which it supplies, giving branches to the vesicula seminalis, ampulla of the vas deferens, and prostate gland, and in the female to the vagina. It sometimes gives off the deferential artery, and it may give origin to an accessory j pudic. It anastomoses with the superior vesical and middle | hemorrhoidal of its own side, and with its fellow of the opposite side. . , The middle hemorrhoidal artery (V) often arises in common with THE ABDOMEN 843 the inferior vesical. It is distributed to the rectum, and gives branches to the vesicula seminalis, ampulla of the vas deferens, and prostate gland. The anastomoses which it establishes are with the superior hemorrhoidal of the inferior mesenteric, the inferior hemorrhoidal of the internal pudic, the inferior vesical of its own side, and its fellow of the opposite side. The obturator artery (P) passes along the outer wall of the pelvic cavity on its way to the obturator canal, lying between the parietal pelvic fascia and the peritoneum. It has the obturator nerve above it, and its o\^ti vein below it. In entering the obturator canal, by which it emerges from the pelvis, the artery does not pierce the parietal pelvic fascia, but passes over its upper border, where that joins the upper part of the obturator membrane. As the artery passes along the pelvic wall it furnishes the following branches : muscular to the obturator internus ; iliac to the iliac fossa, which supply the bone, psoas magnus, and iliacus, and anastomose with the iliac branch of the ilio-lumbar ; vesical, which reaches the side of the bladder within the lateral false ligament ; and fuhic to the back of the body of the os pubis, where it anastomoses with the pubic branch of the deep epigastric from the external iliac, and its fellow of the opposite side. For the distribution of the obturator artery outside the pelvis, see p. 488. The obturator artery sometimes arises from the deep epigastric ; see p. 426. The internal pudic artery (P) is one of the terminal branches of the anterior division. It descends with the sciatic artery upon the pyriformis and sacral nerves, and emerges from the pelvis through the lower compartment of the great sacro-sciatic foramen, having previously pierced the parietal pelvic fascia. The intrapelvic branches of the vessel are unimportant, and are distributed to the pyriformis, coccygeus, obturator internus, and pelvic fascia. For the further course and distribution of the artery, see the gluteal region and the perineum, pp. 433 and 622. The sciatic artery (P) is the other and larger terminal branch of the anterior division. It descends, usually behind the internal pudic, upon the pyriformis and sacral nerves, and emerges from the pelvis through the lower compartment of the great sacro- sciatic foramen, having previously pierced the parietal pelvic fascia. Within the pelvis the artery gives off branches to the pjrriformis, levator ani, coccygeus, rectum, bladder, vesicula seminalis, and prostate gland. For the extrapelvic course and distribution of the vessel, see P- 432. Posterior Division. — The ilio-lumbar artery (P) passes upwards and outwards in front of the sacro-iliac articulation, between the lumbo- sacral cord and obturator nerve. In its course it passes behind the external iliac, or, it may be, the common iliac, vessels, and also behind the psoas magnus and iliacus. On reaching the back part 844 A MANUAL OF ANATOMY of the iliac fossa, it divides into two branches, iliac and lumbar, The iliac branch, passing transversely, ramifies in the iliacus and ilium, and anastomoses with the iliac branch of the obturator and branches of the deep circumflex iliac from the external iliac. The lumbar branch ascends beneath the psoas magnus on to the quadratus lumborum, where it anastomoses with the terminal part of the deep circumflex iliac, and the last lumbar of the ab- dominal aorta. In its course it furnishes a spinal branch, which enters the spinal canal through the intervertebral foramen between the fifth lumbar and first sacral vertebrae, to be distributed in a manner similar to the other spinal arteries. The lateral sacral arteries (P) are usually two in number, superior and inferior. They course downwards and inwards to the front of the lateral mass of the sacrum, passing in front of the pyriformis and sacral nerves. Upon the sacrum both arteries lie external to the anterior sacral foramina, the superior being confined to the region of the first two foramina, whilst the inferior descends as low as the coccyx, where it anastomoses with the middle sacral artery. They are distributed to the pyriformis and sacral nerves, and furnish spinal branches, which enter the anterior sacral foramina, and so reach the sacral canal, where they supply its contents. Each spinal branch, before entering the sacral canal, gives of? a posterior branch, which emerges through the posterior sacral foramen, and anastomoses with branches of the gluteal, sciatic, and internal pudic. The lateral sacral arteries anastomose with each other and with the middle sacral. The gluteal artery (P) is a large vessel, which is the continuation of the posterior division. It is destined for the supply of the gluteal region, and lies within the pelvis for a very short dis- tance. Its direction is backwards through the parietal pelvic fascia, and between the lumbo-sacral cord and the anterior primary division of the first sacral nerve, its escape from the pelvis being through the upper compartment of the great sacro- sciatic foramen. The branches of the artery within the pelvis are unimportant. For the extrapelvic course and distribution of the vessel, see p. 430. The branches of the internal iliac, with one exception, have to pierce the pelvic fascia. The exception is the obturator artery, which, as stated, passes over the upper border of the parietal pelvic fascia at the obturator canal. Internal Iliac Vein. — This vessel results from the union of branches which correspond, for the most part, with branches of the internal iliac artery. The ilio-lumbar vein, however, is an exception, inas- much as it is a tributary of the common iliac vein. Moreover, during foetal life the umbilical vein, which corresponds to the hypogastric (subsequently umbilical) artery, passes to the liver after entering the abdomen of the foetus. The internal iliac vein extends from the upper part of the great sciatic notch to the sacro- THE ABDOMEN 845 iliac articulation on a level wnth the pel vac brim, where it joins the external iliac, and so the common iliac vein is formed. In its course it lies behind the corresponding artery. There are no valves in the vein itself, but its branches are freely provided with them. The internal iliac vein is developed from the lower part of the cardinal vein. Internal Iliac Lymphatic Glands. — These glands are about ten in number, and are associated with the origins of the branches of the internal iliac arter}^ One of them lies near the side of the rectum, in relation with the middle haemorrhoidal artery, and is spoken of as the middle hcemorrhoidal gland. The afferent vessels of the internal iliac glands return lymph from the parts supplied by the branches of the internal iliac artery. Thus, they receive afferent vessels from the following parts; 1. Upper part of the anal canal, above the anal valves. 2. Lower part of the rectum. 3. Bladder. 4. Vesicular seminalis and vas deferens. 5. Prostate gland. 6. Prostatic, membranous, and bulbar portions of the urethra, in part. 7. Uterus (cer\4x). 8. Vagina (central part). 9. Deep structures of gluteal region, supplied by gluteal artery. 10. Deep structures of upper part of back of thigh, supplied by sciatic artery. 11. Deep structures of perineum. The efferent vessels of the internal iliac glands pass to the posterior group of common iliac glands. Anterior Primary Divisions of the Sacral and Coccygeal Nerves. — ^There are five sacral nerves and one coccygeal nerve on either side. The anterior primary divisions of the first four sacral nerves emerge into the pelvis through the anterior sacral foramina, and that of the fifth sacral passes between the inferior lateral angle of the sacrum and the transverse process of the first coccygeal vertebra, through the coccygeus muscle. The anterior primary division of the coccygeal nerve enters the pelvis below the trans- verse process of the first coccygeal vertebra, through the coccy- geus muscle. The first and second sacral nerves are of large size, and their course is obliquely downwards and outwards. Beyond the second they diminish rapidly in size, and pass more horizontally. They receive grey rami communicantes from the adjacent ganglia of the pelvic sympathetic cord, and the third and fourth nerves (sometimes also the second) furnish white rami communicantes to the corresponding pelvic plexus. The anterior primary divisions of the first and second sacral nerves divide each into an anterior or ventral and a posterior or dorsal branch. The anterior primary division of the third sacral nerve divides into an upper and a lower 846 A MANUAL OF ANATOMY branch, and is known as the nervus bigeminus. The anterior primary division of the fourth sacral nerve also divides into an upper and a lower branch, and it is known as a nervus furcalis. The lumbo-sacral cord in two divisions, ventral and dorsal, the anterior primary divisions of the first two sacral nerves, the upper and lower branches of the third sacral, and the small upper branch of the fourth sacral form the sacral plexus, whilst the large lower branch of the fourth sacral, the fifth sacral, and the coccygeal form the sacro-coccygeal plexus. Sacral Plexus. — ^This plexus, formed as stated, is a large flattened To Lumbar Plexus CREAT "" SCIATIC Pudic Fig. 366.— a, The Sacral Plexus A 1, I, I. Nerve to Quadratus Femoris 2, 2, 2. Nerve to Obturator Internus 3, 3, 3. Small Sciatic Nerve Perforating Cutaneous To Coccygeal Plexus B, The Sacro-Coccygeal Plexds. B 4.S. Fourth Sacral, giving a Branch to Sacral Plexus V. Visceral Branches M. Muscular Branches T.C. Terminal Cutaneous Branches mass, lying upon the pyriformis muscle, and behind the parietal pelvic fascia, which separates it from the sciatic and pudic vessels. The mass ultimately forms two bands, upper and lower. The upper or sciatic band, which is the larger of the two, receives the lumbo-sacral cord, first sacral, larger portion of the second sacral, and upper branch of the third sacral nerves. It is fiat and somewhat triangular, and is continued into the great sciatic nerve, which leaves the pelvis through the lower part of the great sacro-sciatic THE ABDOMEN 847 foramen below the pyriformis, without piercing the parietal pelvic fascia. The upper band and its contributory nerves are sometimes spoken of as the sciatic plexus. The lower or pudic band, the smaller of the two, receives fibres from the second, lower branch of the third, and upper branch of the fourth sacral nerves, and is continued into the pudic nerve, which leaves the pelvis, like the great sciatic, through the lower compartment of the great sacro-sciatic foramen without piercing the parietal pelvic fascia. The lower band and its contributory nerves are sometimes spoken of as the pudic plexus. The great sciatic and pudic nerves are thus the terminal branches of the sacral plexus. The reason of the name nervus bigeminus, as applied to the third sacral nerve, is because it enters into the sciatic band by its upper branch, and into the pudic band by its lower branch. Branches. — ^The branches of the sacral plexus are arranged in two groups — collateral and terminal. Collateral Group. — The branches of this group form three sets — visceral, muscular, and cutaneous. Visceral Branches. — ^These are derived from the third sacral and that part of the fourth which enters into the sacral plexus (some- times also from the second). They are white rami communicantes, which reinforce the pelvic plexus of the sympathetic, a few of them being traceable independently to the pelvic viscera. They are known as the pelvic splanchnics. Muscular Brandies. — The superior gluteal nerve arises by three roots from the dorsal divisions of the descending branch of the fourth lumbar, fifth lumbar, and first sacral nerves. It passes outwards and backwards, and leaves the pelvis with the gluteal artery through the upper compartment of the great sacro-sciatic foramen, to be distributed to the gluteus medius, gluteus minimus, and tensor fasciae femoris muscles. The inferior gluteal nerve arises by three roots from the dorsal divisions of the fifth lumbar and first and second sacral nerves. It leaves the pelvis through the lower compartment of the great sacro-sciatic foramen, below the pyriformis and superficial to the great sciatic nerve, to be distributed to the gluteus maximus. It is usually intimately associated with the small sciatic nerve. The nerves to the pyriformis, which are usually two in number, spring from the dorsal divisions of the first and second sacral nerves. The nerve to the obturator internus and gemellus superior arises by three roots from the ventral divisions of the fifth lumbar and first and second sacral nerves. It leaves the pelvis through the lower compartment of the great sacro-sciatic foramen, crosses the back of the ischial spine, where it lies external to the internal pudic vessels, and then passes through the small sacro-sciatic foramen to the outer wall of the ischio-rectal fossa, where it enters the inner or pelvic surface of the obturator internus. In the gluteal region it gives a branch to the gemellus superior when that muscle is present. 848 A MANUAL OF ANATOMY The nerve to the quadratus femoris and gemellus inferior arises by three roots from the ventral divisions of the descending branch of the fourth lumbar, fifth lumbar, and first sacral nerves. It leaves the pelvis through the lower compartment of the great sacro-sciatic foramen, and then lies between the ischium and the great sciatic nerve. It subsequently descends over the back of the capsular ligament of the hip- joint, to which it usually gives a branch, and beneath the gemelli and obturator internus to the deep surface of the quadratus femoris, in which it ends, having previously given a branch to the gemellus inferior. Cutaneous Branches. — The small sciatic nerve arises by three roots from the posterior aspects of the first, second, and third sacral nerves. It leaves the pelvis through the lower compartment of the great sacro-sciatic foramen, and is distributed to (i) the lower and outer part of the gluteal region by its gluteal cutaneous branches, (2)] the integument of the scrotum by the long pudendal nerve of Soemmering, (3) the integument of the back of the thigh, and (4) the integument of the back of the leg as low as about the centre of the calf. The perforating cutaneous nerve arises by two roots from the posterior aspects of the second and third sacral nerves. It passes backwards through the great sacro-sciatic ligament, after which it turns round the lower border of the gluteus maximus near the coccyx to be distributed to the integument over the lower and inner part of that muscle. Terminal Group. — ^This group is comprised of two nerves, namely, the great sciatic and the pudic. The great sciatic nerve is the continuation of the upper or sciatic band of the sacral plexus. In reality it is made up of the two divisions in which it ultimately ends, namely, the external and internal popliteal, which lie close together within the same sheath. Sometimes, however, these two divisions arise separately from the sacral plexus, in which cases the external popliteal nerve may pass through the pyriformis. Again, though the great sciatic nerve may be apparently single, a careful dissection of it, after the removal of its sheath, will reveal the external and internal popliteal nerves, which can be shown to have independent origins. The external popliteal nerve derives its fibres from the dorsal divisions of the descending branch of the fourth lumbar, fifth lumbar, and first and second sacral nerves;; and the internal popliteal nerve derives its fibres from the ventral divisions of the foregoing nerves, and in addition from the upper branch of the third sacral. The great sciatic nerve leaves the pelvis through the lower com- partment of the great sacro-sciatic foramen below the pyriformis. The pudic nerve is the continuation of the lower or pudic band of the sacral plexus. It arises by three roots from the ventral division of the second, the lower branch of the third, and the upper branch of the fourth sacral, the root from the third being the largest. The nerve leaves the pelvis through the lower compart- THE ABDOMEN 849 ment of the great sacro-sciatic foramen, crosses the back of the ischial spine, where it lies internal to the internal pudic vessels, passes through the small sacro-sciatic foramen, and then traverses the outer wall of the ischio-rectal fossa. Having given off the inferior hemorrhoidal ner\'-e, it divides into the perineal and dorsalis penis nerves, which with the internal pudic vessels are contained in Alcock's canal. The sacral plexus and its branches being situated behind the parietal pelvic fascia, the branches do not pierce that fascia as they leave the pelvis. The branches of the internal iliac artery, on the other hand, being placed on the superficial surface of the parietal pelvic fascia, have to pierce it, with the single exception of the obturator artery. Sacro-coccygeal Plexus. — The nerves which fIi branch of the genito-crural nerve and the cremasteric branch of the deep epigastric artery- are to be noted, and the cremasteric fascia is to be studied. The internal oblique is to be removed in the following manner : make an incision carefully through the muscle just in front of the anterior superior iliac spine, and expose the lateral or intermuscular epigastric branch (so-called ascending branch) of the deep circumflex iliac artery. This is the best guide to the separation between the internal oblique and transversalis abdominis. Now carry an incision inwards through the internal oblique towards the linea alba, and leave the Poupart fibres undisturbed" in the meantime. The internal oblique is next to be detached from the iliac crest, from the posterior aponeu- rosis of the transversalis abdominis, and from the lower three or four costal cartilages, and the muscle, with its aponeurosis, is to be thrown forwards as far only as the outer border of the rectus abdominis. During the reflection of the muscle care must be taken to preserve the following structures, namely, the lower five intercostal nerves ; the anterior primary division of the twelfth thoracic nerve (subcostal nerve) ; the hypogastric branch of the ilio - hy-pogastric nerve ; the inguinal (so-called ilio-inguinal) nerve ; the lateral or intermuscular epigastric artery ; the abdominal brajjches of the lumbar arteiies ; and the lower two intercostal arteries. The transversalis abdominis is next to be cleaned and studied. The lower five intercostal nerves and the anterior primary division of the twelfth thoracic nerve are to be followed forwards as far as the outer border of the rectus abdominis, where they disappear by piercing the sheath to get behind the muscle. The posterior aponeurosis of the muscle (which forms the lumbar aponeurosis) cannot be displayed in the present position of the body, but the anterior aponeurosis should be dissected as far as the outer border of the rectus abdominis, where it will be further studied in connection with the sheath of that muscle. The dissector should now direct his attention to the Poupart fibres of the internal obhque and transversalis abdominis. He will find that the Poupart fibres of the two muscles are intimately connected together, but a careful dissection wiU show that, whilst the internal oblique arises from the outer half of Poupart's ligament on its abdominal aspect, the transversalis abdominis arises only from the outer third. The former muscle, then, reaches lower down along Poupart's ligament than the latter. An incision having been made through the transversalis abdominis in a transverse direction inwards from the anterior superior iliac spine, the Poupart fibres of the two muscles are to be detached from the ligament, and, in the course of reflecting them inwards without injuring the fascia transversalis, the dissector should observe their varying relations to the spermatic cord and internal abdominal ring, and also the lower border of each muscle. These fibres of the two muscles will be found to end in the conjoined tendon, and this structure should be followed to its insertion and studied. It will be found that the anterior aponeurosis of the transversalis abdominis contributes more to the con- joined tendon than the aponeurosis of the internal oblique. The relation of the conjoined tendon to Hesselbach's triangle will be presently seen. Meanwhile the dissector is to observe that the tendon lies behind the sper- matic cord (or round ligament of the uterus), and that it also lies behind the external abdominal ring, thereby strengthening an otherwise weak part of the abdominal wall. The dissector should look for the reflected tendon of Cooper. If present, it will be found as a thin semilunar expansion, extending outwards from the outer border of the conjoined tendon to the inner and lower part of the internal abdominal ring, where it is attached to the deep crural arch. Its relation to Hesselbach's triangle, as well as to the inguinal canal, will be seen further on in the dissection. At this stage the dissector of the abdomen should associate himself with the dissector of the lower limb in order to make a dissection of the deep crural arch. The anterior wall of the sheath of the rectus abdominis is now to be opened and reflected by making a vertical incision through it about an inch and a half from the linea alba, and turning one half inwards and the other outwards, preserving at the same time the transmitted nerves. In doing so the close 912 A MANUAL OF ANATOMY connection between the anterior wall of the sheath and the tendinous inscrip- tions of the muscle is to be noted at the following levels, namely, at the umbilicus, opposite the tip of the ensiform process, and about midway between these two points. Occasionally a fourth connection is established a little below the umbilicus. The anterior wall of the sheath having been reflected, the pyramidalis muscle should be dissected. If present, it will be found in front of the lower part of the rectus abdominis. The rectus itself is then to be fully dissected. Its two heads of origin and three slips of insertion are to be shown, and the three (sometimes four) tendinous inscriptions are to be studied. The varying relation of the inner border of the muscle to its fellow along the linea alba is to be observed, and both borders of the muscle are to be freed from their connections. In freeing the outer border, the lower five intercostal nerves and the anterior primary division of the twelfth thoracic nerve are to be shown on their way to the back of the muscle (within the sheath). The deep epigastric artery is to be displayed, disappearing beneath the outer border of the muscle at a point about midway between the upper border of the symphysis pubis and the umbilicus. Before further disturbing the muscle, the triangle of Hesselbach is to be studied. It will be found between the lower fourth of the rectus abdominis and the deep epigastric vessels. The relation of the conjoined tendon to the triangle, and the manner in which it divides the triangle into two compartments are to be noted. If the reflected tendon of Cooper should be present, its relation to the triangle is also to be noted. The rectus abdominis is now to be raised from its sheath, but not yet divided. As this is being done, the lower five intercostal nerves and the anterior primary division of the twelfth thoracic nerve will be seen making their way from behind forwards through the muscle to become anterior cutaneous nerves. At this stage also the superior epigastric artery is to be shown entering the deep surface of the upper part of the muscle from behind the seventh costal cartilage. The continuation of the deep epigastric artery in the substance of the muscle is to be dissected from behind to a point about 2 inches above the umbilicus, and the anastomosis between it and the superior epigastric at that level may be shown. The sheath of the rectus is next to be studied, the muscle itself having been previously divided a little above the umbilicus. The splitting of the internal oblique aponeurosis into two laminae anterior and posterior, along the outer border of the muscle is to be shown. This, however, will be found to cease at a point a little above the level of the anterior superior iliac spine, below which point the undivided aponeurosis will be found to pass in front of the muscle. The anterior aponeurosis of the transversalis abdominis will be seen to pass behind the rectus for a similar extent to that over which the splitting of the internal oblique aponeurosis takes place ; but, over the lower part of the muscle (below a point a little above the level of the anterior superior iliac spine), it passes in front of it. The deficiency of the sheath posteriorly over its lower fourth is to be noted, and the semilunar fold of Douglas, with the deep epigastric artery passing over it, is to be studied. Sometimes the anterior aponeurosis of the transversalis abdominis will be found to send scattered fibres behind the rectus for a variable distance below the semilunar fold of Douglas. In such cases another curved semilunar fold, known as the band of Henle, is to be looked for from i to 2 inches below the semilunar fold of Douglas. The com- position of the sheath in front and behind is to be mastered ; the different attachments superiorly of the anterior and posterior walls are to be noted ; the contents of the sheath are to be studied ; and the linea alba should be thoroughly revised. The dissector should next direct attention to that part of the deep epigastric artery which forms the outer boundary of Hesselbach's triangle, showing its relations to the internal abdominal ring and fascia transversalis, and also its two vena; comites. The cremasteric and pubic branches of the artery are to be shown, but the artery itself is not to be followed, at this stage, to its origin from the external iliac. The deep epi- gastric artery should now be studied throughout its course, its branches should be mastered, and the anastomoses of the vessel should be carefully attended to. THE ABDOMEN 913 The next stage of the dissection consists in (i) detaching the transversalis abdominis from the iliac crest, (2) cutting through posterior aponeurosis in the region between the ihac crest and the last rib, and (3) dividing the muscle as it escapes from beneath the costal margin. Wten the muscle has been reflected forwards to the outer border of the rectus, the various nerves on its surface having been divided in front and turned outwards, and the ilio-hypogastric and inguinal nerves being carefully preserved in the region of the iliac crest, a good view will be obtained of the fascia transversalis. Before proceeding to study this fascia, however, it will well repay the dis- sector to .replace for a moment the external oblique, internal oblique, and transversalis abdominis, in order to show the intricate piece of lattice-work which these muscles construct by the var5nng direction of their fibres, a cir- cumstance which adds materiaJly to the strength of the abdominal wall. The fascia transversahs should be followed upwards beneath the costal margin, where, now very thin, it becomes continuous with the areolar investment of the diaphragm. Towards the lower part of the abdominal wall it becomes better marked. Its disposition along the Unea alba and along the iliac crest is to be studied ; its arrangement along the line of Poupart's ligament should be carefully attended to ; the deep crural arch is to be revised in connection with it ; its relation to Hesselbach's triangle is to be noted ; and the internal abdominal ring, with the infundibuliform fascia prolonged from its margins, is to receive the closest attention. To see the ring the spermatic cord (or round ligament of the uterus) should be puUed upon, and a circular incision made through the infundibuliform fascia close to the ring. In performing this dissection, it will be seen that the infundibuliform fciscia is prolonged upon the cord as the internal spermatic fascia. If the cord be pulled upon it will be seen to receive a covering from the sub- peritoneal fat or areolar tissue through the internal ring. The internal abdominal ring in all its bearings is to be fully studied, and the relation of the deep epigastric vessels to it carefully noted. At this stage the deep circumflex iliac artery should be dissected in the first part of its course. It will be found in a canal behind the outer half of Poupart's ligament formed by the meeting of the fascia transversalis and fascia iUaca, but it should not be dissected at this stage beyond the anterior superior iliac spine, in which region it will be found to pierce the fascia transversalis. The inguinal canal is next to be attended to, and its boundaries and relations studied. The spermatic cord, or round ligament of the uterus, according to the sex, is to be observed traversing it throughout, and the inguinal nerve will be found in the lower two-thirds of the canal, after which it wUl be seen to emerge through the external abdominal ring external to the spermatic cord. Hesselbach's triangle should be revised at this stage, and the relation of the conjoined tendon to the inguinal canal is to be noted. Further, if the reflected tendon of Cooper should be present, its relation to the canal is to be observed. The spermatic cord is next to be dissected. Lying in front of its upper part for a variable distance may be found a thread-like prolongation of the peritoneum. The various coverings of the cord are to be studied, and the dissector is to note that there are three sj>ermatic fasciae. By teasing and separation the various constituents of the cord are to be shown. Certain of these will not be easily made out, such as the spermatic plexus of nerves and the lym- phatics of the testis, but the vas deferens can be separated without difficidty. The spermatic artery (in the centre of the cord), the pampiniform plexus of veins, and the deferential artery are to be looked for. The round Ugament of the uterus (a very variable structure in this part of its course) requires very Uttle dissection, and may be followed into the labium majus. A few fibres, representing the cremaister muscle in the male, should be looked for in front of the round ligament. The fascia transversahs is now to be removed as carefully as possible, and in doing so the dissector should observe that it is connected to the underK-ing peritoneum by the subperitoneal fat or areolar tissue. In connection with this tissue two points have to be noted, namely, (i) internal to the external ihac vein it forms the septum crurale, closing the crural or femoral ring, which should be studied in conjunction with the 914 A MANUAL OF ANATOMY dissector of the lower limb ; and (2) at the internal ring it is carried downwards with the spermatic cord. The parietal peritoneum is now to be examined. It will be readily recog- nised by its bluish-white colour, and upon it a small nodule is to be looked for just behind the internal abdominal ring, representing the upper end of the original processus vaginalis. Instead of a mere nodule the dissector may find a fibrous thread descending for a variable distance on the spermatic cord, and sometimes containing a canal in the female, known as the canal of Nuck. The disposition of the fascia transversalis and fascia iliaca along the outer half of Poupart's ligament, and in the region of the external iliac vessels at the groin is to be attended to, the deep crural arch being at the same time revised. Gimbernat's ligament may be looked to at this stage, but its com- plete examination should be postponed till a later period. The abdominal cavity is now to be opened. This is to be done only partially at first by means of the following incisions : commencing immediately below the umbilicus, an incision is to be made downwards and outwards, on either side, to Poupart's ligament at the junction of its inner two-thirds and outer third. In this manner a triangular portion of the anterior abdominal wall below the umbilicus can be thrown down. The parietal peritoneum lining this portion having been sponged, the following plica; and fossa; are to be studied : (i) Folds. — (a) plica urachi, in the middle line ; (b) plica hypogas- trica ; and (c) plica epigastrica, which is usually a little external to the plica hypogastrica, though sometimes the two correspond. (2) Fossae. — These are the internal, middle, and external inguinal fossae. The relations of the internal and middle fossae to the two divisions of Hesselbach's triangle are to be noted, as well as the relation of the external fossa to the internal abdo- minal ring. At this stage the dissector should study the descent of the testis, and the abnormal conditions of the processus vaginalis. A complete revisal of all the structures of the abdominal wall in the region of Poupart's ligament should now be made, and thereafter inguinal hernia is to receive careful attention in the following order : external oblique hernia ; internal direct hernia ; internal oblique hernia ; congenital hernia ; and infantile hernia. Having mastered these varieties of hernia, the dissector should now turn his attention to umbilical hernia, or exomphalos. The relation of structures at the pubic crest is next to be mastered, as well as the relation of parts at the pectineal portion of the ilio-pectineal line. It will be proper to dissect the testis at this stage, if it is in proper con- dition. If not, it should be delayed until the organ has been sufficiently hardened by immersion in spirit. The testis, along with the lower part of the spermatic cord, is to be removed and laid upon a board, and the parts are to be kept in position by pins. The tunica vaginalis is to be studied, and the dissector should note that the lower fibres of the cremaster spread out in a scattered manner over its upper part. An attempt should be made to inflate it, by making an aperture in it, just large enough to admit the small end of a blow-pipe. If this is successfully done, an instructive view of the membrane will be obtained. The tunica vaginalis is then to be divided by a vertical incision, when its two parts will come readily into view, namel5^ tunica vaginalis scroti and tunica vaginalis testis. These two parts having been studied, attention is next to be directed to the following structures : ( I ) the body of the testis, closely invested by the dense tunica albuginea, which, in turn, is closely covered by the tunica vaginalis testis ; (2) the epididymis, which will be seen lying along the posterior border and adjacent portion of the external surface of the testis ; and (3) the digital fossa, which is a recess formed by the tunica vaginalis testis between the testis and the epididymis. The epididymis will be seen to be composed of a head or globus major, situ- ated at the upper end ; a body, succeeding to the head, long and narrow : and a tail or globus minor, situated at the lower end of the body. Before proceeding further, the dissector should look carefully for the following vestiges of embryonic structures, namely (i) the hydatids of Morgagni, which will usually be seen on the front of the globus major, or on the front of the testis just below the globus major ; (2) the organ of Giraldes or para- THE ABDOMEN 915 didymis, situated on the front of the spermatic cord immediately above the globus major, beneath the visceral layer of the funicular portion of the tunica vaginalis ; and (3) the vas aberrans of Haller, situated at the point where the globus minor passes into the vas deferens. The tissue between the globus major and the testis should be carefully unravelled, and an effort made to show the coni vasculosi entering the globus major after leaving the testis. The vas deferens should be shown as it passes off from the globus minor, and the tortuosity wluch it here presents is to be noted. The tunica albuginea is next to be opened by making a vertical, median, anterior incision. On separating the t'.vo halves from the substance of the testis the dissector is to observe the fibrous processes, thereby torn, which pass into the interior of the organ between the lobuU testis. An attempt should now be made to show the lobuli testis by teasing out the glandular tissue, which may bring into view the tubuli seminiferi. A transverse incision should next be made through the testis, in order to show the forward projection of the tunica albuginea from the back part of the testis into the interior for a short dis- tance, known as the corpus Highmorianum, or mediastinum testis. The abdominal wall above the umbilicus is to be removed by making a vertical incision through it at either side of the middle Une, thus preser\-ing meanwhile a median strip. The lateral parts of the waU are then to be divided along each costal margin as far back as the position of the body will allow. Reverting to the median vertical strip, the dissector should study on its posterior surface a median fold of parietal peritoneum, representing a part of the falciform Ugament of the liver, which contains the obUterated umbilical vein. The umbilicus and this peritoneal fold are to be preserved. Without in any way disturbing the contents of the abdominal cavity, the dissector should remove with a sponge any fluid which may have accumu- lated. He should then make himself acquainted with the various regions into which the cavity is divided, and the lines and planes by which these divisions are effected. He should also study the boundaries of the cavity. The succeeding stages of the dissection being very complicated, it is ad'/ isable that the dissector should exercise considerable method in his mode of pro- cedure. His first duty is to take a superficial view of the contents of the abdomen in their undisturbed position, and this should be done in the following order : the liver, the stomach, and the great omentum, depend- ing from the great curvature of the stomach. It should be noted that the great omentum descends lower on the left side than on the right, and that a few coils of the ileum are visible beyond it on the right side. The caecum will be partly seen in the right iliac fossa, and the iliac colon is partly visible in the left iliac fossa. The great omentum is next to be raised and laid over the costal margin, when the coils of the jejunum and ileum will come into view. The trans- verse colon will also be seen crossing from the right to the left hj'po- chondrium. If the urinary bladder should be distended, a part of it would be seen in the h\-pogastrium. The foregoing represent the contents which are seen on taking a superficial view. The coils of the jejunum and ileum should now be carried over to the left side, and the ascending colon examined. Superi )rly it will lead to the hepatic flexure, and, without disturbing the parts, the right kidney should be felt. The caecum %\-ill now be fully exposed at the lower end of the ascending colon, and the vermiform appendix, and the mode of ending of the ileum in the large intestine, should be carefully examined. The coils of the jejunum and ileum are then to be carried over to the right side, and the descending colon, commencing above at the splenic flexure and terminating below in the iliac colon, is to be examined. The left kidney is to be felt for, and, if the jejunum is followed upwards, the duodeno jejunal flexure will be exposed. The dissector should now study (i) the position and connections of the stomach, and {2) the position and connections of the intestinal canal (except the duodenum, pelvic colon, and rectu-n). In connection with the small intestine the possible presence of Meckel's diverticulum, about 3 feet from the ileo-OEcal valve, is to be borne in mind. In studying the laige intestine. 916 ^ MANUAL OF ANATOMY special attention should be paid to the caecum, including its varieties, and the vermiform appendix. The ascending, transverse, descending, and iliac colon should next be studied in the order named. The position and connections of the spleen are next to be studied, and for this purpose the stomach is to be well drawn out from the left hypochondrium. It is to be remembered that occasionally accessory spleens are met with in the gastro-splenic omentum, or in the great omentum. The dissector is next to turn his attention to the position, connections, ligaments, and component parts of the liver, in so far as they can at present be made out. The gall-bladder is to be included in this examination. A study of the foregoing structures will have prepared the dissector for the examination of the peritoneum. The description given of this mem- brane and its various folds should be read, and it should be compared with, and verified from, the dissection. In a great number of bodies, however, verification is rendered impossible by the existence of adhesions, but the dissector should do his best. The continuity between the parietal and visceral peritoneum is to be shown in two ways, namely, in the vertical direction, and in the transverse direction. The continuity can be demon- strated in the vertical direction without much difficulty, and the best starting-point is the portal fissure of the liver. The peritoneum is to be traced in the transverse direction at two levels, namely, above the transverse colon, or at the level of the foramen of Winslow, and below the transverse colon, or at the level of the umbilicus. The former is difficult of accomplishment, but the dissector should try his best. The latter will not cause much trouble. The various folds formed by the peritoneum, namely, omenta, mesenteries, and ligaments, are next to be studied in the following order : (i) the great omentum ; (2) the small omentum ; (3) the gastro-splenic omentum ; (4) the mesentery proper ; (5) the appendicular mesentery or meso-appendix ; (6) the transverse meso-colon ; (7) the pelvic meso-colon (wliich, however, belongs to the pelvis) ; (8) the peritoneal ligaments of thi; liver ; (9) the peritoneal ligament of the stomach, namely, the gastro- phrenic ligament ; (10) the peritoneal ligaments of the spleen, namely, the lieno-phrenic and lieno-renal ligaments ; and (11) the peritoneal ligament of the splenic flexure of the colon, namely, the phreno-cohc or costo-colic liga- ment (sustentaculum lienis). In connection with the ascending colon, a peritoneal fold, known as the sustentaculum hepatis, may be met with. The cavity of the peritoneum is next to be studied, attention being given first to the great cavity, and then to the small cavity. The boundaries of the small cavity are to be studied, which will be facilitated by making an incision through the descending layers of the great omentum about an inch below the great curvature of the stomach. The hand should then be introduced through the incision into the small cavity, and, unless there are adhesions, the dis- sector will be able to insinuate it downwards between the descending and ascen ling layers of the great omentum until it is arrested where that omentum describes its bend. In this way the bag or sac of the omentum (great) is demonstrated He should also pass his hand upwards behind the stomach and gastro-hepatic omentum, and he will feel Spigel's lobe of the liver at the upper end of the small cavity. Thereafter the foramen of Winslow should be mastered. It will be found behind the right or free border of the gastro- hepatic omentum. In order to familiarize himself with this opening, the dissector should again pass his hand into the small cavity through the incision already made below the stomach, keeping the thumb outside in the general cavity. If the hand (except the thumb) is now carried upwards behind the stomach and gastro-hepatic omentum, the index finger can easily be pushed through the foramen of Winslow (unless it is blocked by inflammatory pro- diicts) into the great cavity, where it can be made to meet the thumb. Again the index finger of one hand should be passed through the foramen into tl>. small cavity, and the thumb of the same hand should be brought down upon the right or irc-e border of the gastro-hepatic omentum. This having been done, the dissector will have two layers of peritoneum between the index finger and thumb, one of which belongs to the small cavity, and the other THE ASDOMBK 917 to the great cavity. The structures contained between these two layers are to be noted. As the finger Ues in the foramen of Winslow the caudate lobe of the Uver will be felt above it. It is possible for a hernia to occur through this foramen. The relation of the duodenum to the peritoneum should next be attended to. Certain peritoneal fossae are to be studied in the following order : ( 1 ) the duodenal and duodeno-jejunal fossae ; (2) the peri-caecal fossae, namely, ileo-colic, ileo-caecal, and retro-caecal ; and (3) the intersigmoid. The study of the peritoneum in the adult having been concluded, the dissector should attend to the condition of the peritoneum in the foetus. The dissection of the mesentery proper should now be proceeded with. The great omentum, with the transverse colon, is to be raised and laid over the costal margin, and the jejunum and ileum are to be carried over to the left side. The dissector is to place portions of the mesentery successively upon a platter, and remove the right or upper layer. The trunk of the superior mesenteric artery is to be dissected beyond the point where it escapes from under cover of the pancreas, and the superior mesenteric sympathetic plexus around it is to be noted, as well as the superior mesenteric vein on its right side. About twelve rami intestini tenuis are to be shown arising from the left side of the parent trunk, and these are to be followed out to their primary, secondary, and at least tertiary arches, attention being given at the same time to the accom- panying sympathetic plexuses and veins. During this dissection the mesen- teric glands are to be sho\vn, and an effort should be made to display the lacteals, which enter the glands as afferent vessels, and emerge from them as efferent vessels. The*right side of the superior mesenteric artery will be found to give off, in order from above downwards, the inferior pancreatico-duodenal, middle colic, right coUc, and Ueo - colic branches, but they should be followed out from below upwards. The ileo-colic is to be shown dividing into a colic and an ileo-caecal branch, the latter of which will be found to give off appendicular, anterior caecal, posterior caecal, and ileal branches. The right coUc and middle colic are to be shown, each dividing into two branches, the latter lying between the two layers of the transverse meso-colon. Throughout this dissection the tributaries of the superior mesenteric vein are to be noted, as well as the offshoots from the superior mesenteric sj^mpathetic plexus. The inferior pancreatico-duodenal artery should not be followed out at this stage. The jejunum and ileum are now to be carried over to the right side, and the left branch of the middle colic artery is to be followed to its termination. This will guide the dissector to the descending branch of the left cohc artery, and, as he follows this down, he wiU readily expose the trunk of the inferior mesenteric artery, arising from the aorta about li inches above the bifurcation. In doing so, he is to note that the artery is behind the parietal peritoneum. It will be found to give off a left colic branch, one, two, or three sigmoid branches, and a superior hemorrhoidal branch. The inferior mesenteric sympathetic plexus and ganglion, and the offshoots from the plexus should be noted. The left colic and superior sigmoid arteries are to be followed to their distribution, and the superior hemorrhoidal is to be shown crossing the left common iUac vessels on its way to the pelvis, where it disappears between the two layers of the pelvic meso-colon. The superior hemorrhoidal, sigmoid, and left colic veins will be found to form the inferior mesenteric vein, which is to be followed upwards on the left psoas magnus as high as the pancreas, care being taken to show that it crosses the left spermatic artery and left renal vein. The intestines are now to be removed in the following manner : a double ligature is to be placed upon the jejunum at its commencement, and another double ligature at the point where the ihac colon passes into the pelvic colon. The gut is then to be divided between each of these double ligatures, and the jejunum and ileum are to be separated from the mesentery propxer by dividing the latter with a knife, or clipping it with scissors. When this has been done, the large intestine should be forcibly drawn out from its deep position, any adhesions which it has formed being severed with a knife. The parts of intestine left behind are (i ) the duodenum, and (2) the pelvic colon and rectum. I 9i8 A MANUAL OF ANATOMY The portion of gut removed is to be cleansed by allowing water to flow through it, and small portions are to be separated, inflated, and dried for future inspection. These portions are to be taken from the following regions : (i) the upper and lower ends of the jejunum ; (2) the upper end, and near the lower end, of the ileum ; and (3) two pieces from the ascending colon. One of these pieces, from the small intestine, is to be dissected in the inflated and moist condition, in order to show the longitudinal and circular muscular fibres. One of the pieces from the ascending colon, when inflated, should also be dissected in the moist condition. The sacculated appearance and the three muscular taeniae having been noted, the peritoneum is to be carefully removed, and the arrangement of the muscular fibres studied. Thereafter the three taeniae are to be divided, and the elongation which then takes place in the wall of the gut is to be observed. The small intestine is to be opened along the mesenteric border by means of a pair of scissors, one of the points of which has been guarded with a piece of cork. The gut is then to be spread out upon a board, and the characters of the mucous membrane are to be studied. A small portion should be examined under water with the aid of an ordinary lens, which will make clear the villi. With the exception of the caecum and the first 2 inches of the ascending colon, the large intestine is to be treated in a similar manner. The cscum and 2 inches of the ascending colon, along with the last 2 inches of the ileum, are to be treated in a different manner. The bowel is to be filled with water from the colic end, the ileal end being left free. It will then be seen that, in distension of the caecum, no water escapes into the ileum, thus demonstrating the action of the ileo-caecal valve. The exact attachment of the base of the vermiform appendix should be noted, and the meso-appendix should receive attention. The caecum and colon are then to be laid open along the right wall, or that opposite the ileum, and the ileo-caecal valve is to be studied. The opening of the vermiform appendix should be examined, and the valve of Gerlach, guarding it, noted. The extent to which the appendix is pervious should also be attended to. It is advisable that the dissectors should associate themselves with the dis- sectors of another abdomen, in order that the caecum and parts of the ascending colon and ileum from one abdomen may be inflated and dried, so as to allow of the ileo-caecal valve being examined in the dried state. The intestines having been studied, the dissector is to cut away the remainder of the mesentery proper, leaving only small portions of the superior mesenteric vessels, as well as of the inferior mesenteric vein, for future refer- ence. A blow-pipe having been introduced into the small portion of the jejunum which has been left, the duodenum and stomach are to be moderately inflated, and the stomach is to be turned upwards. When this has been done, the position and connections of the duodenum are to be studied, the musculus suspensorius duodeni is to be shown passing between the duodeno-jejunal flexure and the left crus of the diaphragm, and the peritoneal fossae in this region are to be revised. The position and connections of the pancreas are next to receive attention, followed by the spleen and the liver. The blood-supply of the foregoing viscera should be shown bj' displa^dng the coeliac axis without injuring the important plexus of nerves which sur- rounds it. The axis will be found appearing at the superior border of the pancreas, where it breaks up into gastric, splenic, and hepatic branches, which are to be followed out in the order named. The gastric artery will be seen to pass upwards and to the left behind the small cavity of the peritoneum, and it is to be followed out. The splenic artery is recognised by taking a tortuous course to the left along the superior border of the pancreas, and its pancreatic, left gastro-epiploic, vasa brevia, and proper splenic branches are all to be shown. The hepatic artery is next to be dissected as far as the portal fissure of the liver. In displaying the vessel in front of the foramen of Winslow, opportunity is to be taken to show the common bile-duct descending on its right side, and the vena porta; ascending behind the two. The follow- ing branches are to be shown arising from the hepatic artery, all of which are to be followed out: (i) pyloric; (2) gastro-duodenal, dividing into superior THE ABDOMEN 9t9 pailcreatico-duodenai aud right gastro-epiploic ; and (3) right and left hepatic. The right hepatic branch will be found to give off the cystic artery, which divides into superior and inferior branches. It is at this stage that the inferior pancreatico-duodenal artery is to be studied. In dissecting the foregoing arteries, the following groups of lymphatic glands are to be noted : (i) the coeliac glands surrounding the coeliac axis; {2) the gastric glands arranged in two sets — superior, along the small curvature of the stomach, and inferior, along the great curvature ; (3) the pancreatic glands along the superior border of the pancreas ; (4) the splenic glands near the hilum of the spleen ; and (5) the hepatic glands within the gastro-hepatic omentum. The veins corresponding to the arteries are to be preserved, if possible, in connection wth the portal system. The vena portae is to receive careful attention. Its mode of formation behind the neck of the pancreas is to be noted, and its mode of termination at the right extremity of the pprtal fissure of the liver, where it presents the portal sinus, is to be shown, with the cystic vein joining its right branch. The sources from which the vena portae receives its blood should be thoroughly mastered. The common bile-duct is next to be studied. Its formation by the union of the hepatic duct with the cystic duct is to be dissected, and the hepatic duct itseJt is to be shown as formed by the union of two ducts, one issuing from the right, cind the other from the left, lobe of the Uver. The duct is to be followed down in front of the foramen of Winslow, behind the first part of the duodenum, and between the head of the pancreas and the second part of the duodenum on their posterior aspect, to about as low as the junction of the upper two- thirds and lower third of the second part. Its mode of termination in the interior of the second part will fall to be noted when the duodenum is opened for inspection. The liver is now to be removed, in doing which the inferior vena cava should be ligatured below it, ani then divided. It must also be divided above the liver, close to the diaphragm. The viscus is then to be thoroughly studied in all its aspects, and so also is the gall-bladder, the interior of which is to be examined to display the reticulated mucous membrane. An effort should be made at this stage to display the right and left pneumogastric nerves as they enter the abdomen through the oesophageal opening of the diaphragm. The right nerve may be followed to the posterior surface of the stomach, and the left to the anterior surface. The stomach, duodenum, pancreas, and spleen are then to be removed en masse, the oesophagus having been previously tied below the seat of divasion. These organs are now to be care- fully studied. After washing out the stomach and duodenum, they are to be opened and their interior examined. The main pancreatic duct, or duct of Wirsung, is to be shown by dissecting the pancreas from behind, and an effort should be made to find the small pancreatic duct, or duct of Santorini, in the head of the gland. The junction of the duct of Wirsung with the common bile-duct in the duodenal wall is to be displayed, and the common internal opening of the two ducts is to be examined. The spleen is to be studied, and sections of it should be made and washed, with pressure, under a stream of water, in order to remove the pulp, and show the trabecular framework. Posterior Wall of the Abdomen. The prevertebral sympathetic plexuses, namely, the epigastric or solar and hj'pogastric, with their secondary offshoots, are to be carefully dissected. The dissector will find the great splanchnic nerve piercing the cms of the diaphragm, and it will guide him to the semi-lunar gangUon. These gangUa, two iu number, lie at either lateral pole of the solar plexus, close to each suprarenal capsule, that of the right side being under cover of the inferior vena cava. The lower part of each ganghon will be found to be semi-detached as the aortico-renal ganglion, which lies over the root of the renal artery, and terminating in this ganglion will be found the small splanchnic nerve, after it has pierced the crus of the diaphragm. The least splanchnic nerve, if present, may pierce the crus, or it may pass behind the Ugamentum 920 A MANUAL OF ANATOMY arcuatum internum, to terminate in the renal plexus. Passing inwards from each semilunar ganglion a matted leash of nerve-fibres, mixed with minute ganglia, is to be dissected. These fibres meet in front of the aorta, and invest the coeliac axis and root of the superior mesenteric artery, in which latter situation is the superior mesenteric ganglion. The offshoots from the solar plexus to be shown are as follows : inferior phrenic ; coeliac, furnishing gastric, splenic, and hepatic ; superior mesenteric ; capsular ; renal ; aortic ; spermatic (ovarian in the female) ; and inferior mesenteric. The spermatic plexus will Ije seen to come from the renal and aortic plexuses, and the aortic plexus is to be shown in two halves, right and left, which communicate freely with each other over the front of the aorta. The inferior mesenteric plexus will be found to arise chiefly from the left half of the aortic plexus, and the inferior mesenteric ganglion is to be looked for in it, near the root of the artery of that name. The various secondary plexuses will be found to accompany the corresponding branches of the abdominal aorta. The two halves of the aortic plexus, reinforced by branches from the ganglia of the lumbar sympathetic chains, are to be followed over the common iliac arteries, after which they will be found to blend, in the angle between these vessels, to form the hypogastric plexus. This latter is to be shown dividing into the right and left pelvic plexuses. Attention is next to be directed to the kidneys and suprarenal capsules. The adipose tunic of the kidney is to be carefully removed, and the suprarenal capsule preserved on the upper part of the organ. The great vascularity and copious nerve-supply of the suprarenal capsule are to be noted, and only one vein is to be looked for, emerging from each through an anterior hilum, that of the right side opening into the inferior vena cava, and that of the left into the renal vein of that side. The structures at the hilum of the kidney are to be shown, and the relations of the organ carefully studied, the visceral areas on the anterior surface of each being noted. The inferior vena cava is next to be dissected, and its tributaries shown, one of these on the right side being the spermatic, or ovarian, vein, whilst the vein of the left side, in each sex, is a tributary of the left renal. The abdominal aorta and its branches are to be dissected, followed by the common iliac vessels. Along the front of the aorta the median lumbar glands should be looked for, and along each common iliac artery the so-called common iliac glands. By drawing aside the right crus of the diaphragm, the receptaculum chyli will be found on the right of the aorta, in front of the first and second lumbar vertebra?, and, on the right of it, the right azygos vein. The ureter is to be dissected as low as the pelvic brim, and the pelvis at its upper end is to be shown. The renal vessels are to be studied, and the kidney is then to be removed. The organ is to be divided into two halves by a vertical incision carried from the outer to the inner border. This will show the fibrous capsule (which should be stripped off), sinus, calices, Malpighian pyramids, and cortex. The diaphragm is next to be dissected. Its central tendon, crura, ligamenta arcuata, and openings are to be studied. The iliac fascia is next to be dissected, with its upward prolongation on the psoas magnus, known as the Esoas fascia. Its mode of attachment to the vertebral column and pelvic rim are to be noted, and its disposition at the outer border of the psoas magnus above the iliac crest is to be carefully studied. The nerves on the posterior wall are now to be shown. Emerging from beneath the ligamentum arcuatum externum, and passing along the lower border of the twelfth rib, will be found the anterior primary division of the twelfth thoracic nerve (subcostal nerve), and with it the subcostal vessels. The genito-crural nerve pierces the psoas magnus close to its inner border, singly or in two branches, genital and crural, and these are to be followed, the former to the cremasteric muscular covering of the spermatic cord, and the latter to Poupart's ligament, beneath which it escapes on to the front of the thigh, close to the outer side of the external iliac artery. The ilio-hypogastric and inguinal nerves appear at the outer border of the psoas magnus, and cross the quadratus lumborum close together, the inguinal being the lower of the two. The external cutaneous nerve also appears at the outer border of the psoas magnus below THE ABDOMEN 92 1 the preceding, and is readily recognised by crossing the iliac fossa to a point beneath the outer end of Poupart's ligament, where it passes out to the thigh. The anterior crural nerve will be found lying deeply in the groove between the psoas magnus and iliacus, and the obturator nerve will be found lying deeply on the inner side of the psoas magnus, on its way to the lateral wall of the pelvis. If an accessory obturator nerve is present, it will usually be found passing deeply along the inner side of the psoas magnus, close to the peh'ic brim, and then coursing over the superior pubic ramus, where it passes beneath the pectineus. The psoas magnus is now to be dissected, and a psoas parvus is to be looked for. The nerves are tlien to be followed upwards and inwards to their origins, by cutting through the psoas magnus. In this manner the lumbar plexus will be exposed, which should be carefully dissected, the lumbo-sacral cord being shown, at the same time, descending to take part in the sacral plexus. The gangliated cord of the sympathetic is to be displayed in front of the bodies of the lumbar vertebrae, and the length of its rami communi- cantes, which accompany the lumbar arteries, is to be noted. The lumbar branches of the aorta are now to be dissected as far back as the intervals between the lumbar transverse processes, where the lateral lumbar glands should be looked for. If the lumbar veins have not been previously dissected, this should now be done. In connection with these veins, at either side, the ascending lumbar vein is to be shown, that of the right side ending as the right azygos vein, and that of the left side ending as the lower left azygos vein. The posterior aponeurosis of the transversahs abdominis and the quadratus lumborum are next to be dissected, and, if that muscle is cut, it will be seen to be encased in a sheath which is formed by the anterior and middle laminae of the aponeurosis. The iliacus muscle and the external iliac vessels are now to be dissected, and the relation of the vessels to the peritoneum, sub- peritoneal tissue, and iliac fascia is to be carefuUy noted, as well as their relation to the genito-crural nerve and constituents of the spermatic cord. The principal branches of the artery, namely, the deep epigastric and deep circumflex iliac, are to be shown, and related to the artery will be found the external iUac glands, three of them being placed just above Poupart's liga- ment, one on the outer side, another on the inner side, and a third in front of the vessel. The deep circumflex iUac artery' is to be followed behind the outer half of Poupart's ligament, and along the iliac crest, and its anastomoses are to be studied. The lacunar region, which lies between Poupart's liga- ment and the front of the hip-bone, is to be examined, and its two muscular lacunae, outer and inner, A^ath the vascular lacuna in front of them, are to be sliown, with the structures lying in each. Pelvis. The pelvis is to be separated by cutting through the disc between the third and fourth lumbar bodies, and then applying the saw. The various muscles connected with the exterior having been trimmed, the bladder is to be partially inflated, and the general position of the viscera and their relations are to be studied, as far as possible, in situ. The extent of the pelvic colon is to be noted, and its extensive mesentery, with the superior hemorrhoidal vessels between its two layers, observed. The reflections of the peritoneum are then to be examined. If a male subject, the relation of the peritoneum to the bladder is to be thoroughly mastered, and the false ligaments, which it forms for the viscus, noted. The recto-vesical pouch of the peritoneum is also to be observed. If a female subject, the relation of the peritoneum to the uterus is to be studied, and the recto-uterine pouch, or pouch of Douglas, is to be carefully examined, which usually contains a few coils of the ileum, and, it may be, a prolapsed ovary. The broad ligament of the uterus, formed by two layers of peri- toneum, is to be studied. The position of the Fallopian tube along its upper border, of the ovary with its ligament in a backward extension of it, and of the round ligament of the uterus in a forward extension of it, are to be observed. 922 A MANUAL OF ANATOMY The exact position of the ovary should receive special attention, andthecofpus fimbriatum of the Fallopian tube, with its ovarian fimbria, is to be noted. The peritoneum is now to be stripped from the walls of the pelvis to expose the pelvic fascia. On the lateral wall of the cavity the obturator vessels and nerve are to be shown on their way to the obturator canal, through which they pass. The pelvic fascia is then to be carefully examinea. This fascia will be seen to line the lateral wall, where it covers the obturator internus, and the posterior wall, where it forms the fascia of the pyriformis. To see it in front, the bladder must be drawn well backwards. The lining portion of the fascia is called the parietal pelvic fascia. To study it more fully the dissector should remove a large part of the os innominatum by means of the following cut : place the saw over the back part of the iliac crest and over the pubic bone, keeping as near as possible to the pelvic brim, but external to it. The bone is now to be sawn downwards in such a manner as to remove a large part of the tuber ischii, but the great and small sciatic notches are to be avoided. The obturator externus muscle is then to be carefully removed from the outer surface of the obturator membrane, and the obturator artery is to be shown in two branches, which form a loop upon the membrane round its circumference. The obturator membrane is then to be removed, which will expose a portion of the obturator internus. When this part of that muscle is taken away, a good view of the parietal pelvic fascia from the outside will be obtained through the obturator fora- men. The thickened portion of the fascia, known as the white line, is to be observed extending from near the lower part of the symphysis pubis to the spine of the ischium. On looking deeply into the pelvic cavity, the bladder having been well displaced to one side, the parietal pelvic fascia, along the white line, will be seen to send inwards its visceral layer, and the portion of the parietal fascia below the white line will be seen, from the perineal point of view, to line the outer wall of the ischio-rectal fossa, where it contains Alcock's canal. From the under aspect of the white line the levator ani muscle arises, and immediately below this the parietal pelvic fascia gives off the anal fascia, which covers the perineal surface of the levator ani. The dissector will now understand what structures separate the pelvic cavity, on either side of the bladder, from the ischio-rectal fossa, this partition being formed, from above downwards, by the visceral pelvic fascia, the levator ani, and the anal fascia. At the upper part of the obturator foramen the parietal pelvic fascia should be shown, on the side not yet dissected, to join the upper border of the obturator membrane over the obturator internus muscle, thus converting the obturator groove on the under surface of the superior pubic ramus into a fibro-osseous tunnel, called the obturator canal. Through this canal the obturator vessels and nerve will be seen to pass, and it will be evident that the obturator artery escapes from the pelvic cavity without piercing the parietal pelvic fascia. As the parietal fascia is attached along the ischio-pubic ramus, at either side, it is continued inwards until it meets with the urethra. This portion of it, with its fellow, forms the postero-superior layer of the triangular ligament. From the urethra the fascia is continued backwards over the anterior border of the levator ani to the prostate gland, where it becomes continuous with the visceral layer of the fascia, which ensheathes that gland. The visceral layer of the fascia is now to be followed inwards to the bladder, rectum, and prostate gland. Opposite the vesicula seminalis it divides into an upper or vesical, a middle or recto-vesical, and a lower or rectal layer, the vesical layer forming the lateral true ligament of the viscus. Opposite the prostate the visceral fascia divides into prostatic, recto-prostatic, and rectal layers. In the female the visceral fascia divides into four layers, namely, vesical, vesico- vaginal, recto-vaginal, and rectal. The bladder being pulled well backwards, two stout bands of the visceral pelvic fascia will be seen to extend from the lower part of the body of each pubic bone over the anterior surface of the prostate gland to the bladder. These constitute the anterior true ligaments of the bladder, and each will be found to contain some of its external longitudinal muscular fibres. Between these two ligaments a well- THE ABDOMEN 923 marked depression, occapied by fat, is to be shown. To facilitate this dis- section, the pelvic brim may be removed on one side. The prostate gland is now to be exposed, and the anterior fibres of the levator ani shown on its side. Within its fascicd sheath wiU be found the prostatic venous plexus, which receives the dorsal vein of the penis in two divisions. If the subject is a female, a portion of the vagina is to be shown. The ureter, vas deferens, and obliterated hypogastric artery are to be dis- played, and their relations noted. The ureter will be found on the lateral wall of the pelvis in front of the internal iliac arterj', and, as it curves inwards to the lateral angle of the bladder, it will be seen to be crossed by the vas deferens. In the female, before reaching the bladder, it should be shown to he on the side of the extravaginal portion of the cervix uteri, and for a short distance on the lateral waU of the vagina at its upper part. The obUterated hv-pogastric artery wiU be found passing forwards from the anterior division of the internal iliac artery over the lateral waU of the pelvis towards the apex of the bladder. Thereafter the internal iliac artery and its branches are to be dissected, as follows : from the anterior division, the pervious portion of the obUterated hypogastric, giving off two or three superior vesical arteries ; inferior vesical, usuaUj' gi\'ing off middle hemorrhoidal ; obturator ; internal pudic ; and sciatic ; and, from the posterior division, the iUo-lumbar ; two or three lateral sacral ; and gluteal. The special branches in the female are the uterine and vaginal arteries. The arteries are accompanied by offshoots from the pelvic sympathetic plexus. In dissecting the branches of the artery, care is to be taken of the nerves which arise from the sacral plexus. By displacing the viscera, this plexus and its branches are to be dissected, including the lumbo-sacral cord. In dissecting the plexus, the nerves which form the lumbo-sacral cord, the cord itself, and the first two sacral nerves are to be shown, by careful dissection, in two divisions, ventral and dorsal, and the third sacral (nervus bigeminus) is to be shown dividing into an upper and a lower branch. The fourth sacral is a nervus furcaUs. The sciatic and pudic bands of the plexus are to be displayed. The branches will be found to arise as follows : superior gluteal, by three roots from the dorsal divisions of the descending branch of the fourth lumbar, the fifth lumbar, and the first sacral ; inferior gluteal, by three roots from the dorsal di\'isions of the fifth lumbar, and first and second sacral ; muscular branches to the pyriformis, from the dorsal divisions of the first and second sacral ; nerve to the obturator intemus and gemellus superior, by three roots from the ventral divisions of the fifth lumbar, and first and second sacral ; nerve to quadratus femoris and gemellus inferior, from the ventral divisions of the descending branch of the fourth lumbar, fifth lumbar, and first sacral ; visceral branches to the bladder, from the third and part of the fourth sacral ; small sciatic, by three roots from the posterior aspect of the first, second, and third sacral ; perforating cutaneous, by two roots from the posterior aspect of the second and third sacral ; great sciatic, which is the continuation of the upper or sciatic band of the plexus ; and pudic, which is the continuation of the lower or pudic band. The sacro-coccygeal plexus, formed by part of the fourth sacral, fifth sacral, and coccygeal nerves, is to be dissected, and the pelvic sympathetic cord is to be displayed with the ganglion impar on the first coccygeal vertebra. The middle and lateral sacral arteries are to be followed out, and an effort should be made to show the coccygeal gland of Luschka near the tip of the coccyx. Branches of the middle sacral artery may help to guide the dissector to it. The pyriformis, levator ani, and coccygeus muscles are to be dissected, and the relation of the latter two to the pelvic floor is to be noted. The obturator intemus is also to be studied. Viscera of the Pelvis. — The position of the rectum, and its relations to the bladder and prostate gland in the male, and uterus and vagina in the female, having been studied as far as possible in situ, the viscera are to be removed en masse along with the superior hemorrhoidal vessels. The bladder, if empty, should be partially inflated, and the rectum and anal canal slightly distended with tow, as well as the vagina.if the subject is a female. The relations of the 924 ^ MANUAL OF ANATOMY rectum are now to be more fully examined, after which the gut is to be separated from the other structures, and subjected to a special dissection. The superior hemorrhoidal artery is to be followed out in two divisions, laterally disposed. The tow having been removed, and one end securely tied, the gut is to be in- flated from the other end, which is then to be ligatured. The arrangement of the longitudinal and circular muscular fibres are to be shown, and the thicken- ing of the latter along the anal canal, which gives rise to the internal sphincter, is to be noted. The gut is now to be laid open from end to end, and its interior examined. The valves of Houston, three in number, are to be looked for as transverse crescentic folds. One will be found on the right side fully 3 inches above the anus, and two on the left side about i inch above and below the right valve. The part of the bowel surrounded by the internal sphincter muscle is to be studied as the anal canal. The longitudinal folds seen here, called the columns of Morgagni, are to be examined, and a little above the anus these columns will be seen to be connected by circularly- disposed semilunar folds, known as the anal valves. The entire blood-supply of the rectum should be carefully revised. The bladder is next to be dissected, showing the ureters at the lateral angles, and the vesiculae seminales and vasa deferentia at the fundus. The commence- ment of each common ejaculatory duct is also to be shown, this being formed by the union of a vesicula seminalis and vas deferens. The limited area on the fundus, bounded on either side by these structures, and called the external trigone, is to be studied. The peritoneum having been removed from the upper surface of .the bladder, the muscular fibres of the viscus are to be displayed as well as possible. They will be found to be arranged as an external longitudinal, a middle circular, and an internal longitudinal, layer, the last being very indefinite. The fibrous cord, representing the urachus, is "to be shown passing from the apex of the bladder. The prostate gland is now to be fully examined, and, if not previously dissected, its recto-vesical capsule and the prostatic venous plexus are to be shown. At the base of the gland the dissector should look for the middle lobe, which is represented by the small part lying between the common ejaculatory ducts and the wall of the bladder, the rest of the organ being disposed as two lateral lobes. The membranous part of the urethra is to be shown succeeding to the apex of the prostate gland. A vesicula seminalis may now be cut into, in order to show the reticulated arrangement of its mucous lining. The bladder is to be opened, and its interior carefully examined. The openings of the ureters and the urethral opening are to be noted, and the smooth internal trigone examined, which lies within ridges connecting these openings. The prostate gland is also to be laid open along its anterior surface, and the whole penis is to be laid open, so as to expose the interior of the corpora cavernosa, and the urethra contained in the corpus spongiosum. In the prostatic urethra the central dilatation and the constriction at either end are to be observed, as well as the following mark- ings : the crest, along the posterior wall ; the sinus pocularis, having on the lateral margins of its opening, or just within them, the openings of the common ejaculatory ducts ; and the prostatic sinus, on either side of the crest, in which the prostatic ducts open. The spongy urethra is next to be examined, and the dilatation towards its centre, and also in the glans, are to be observed, the latter being called the fossa navicularis. The openings of the glands of Littre and the lacunae of Morgagni are to be noted. The septum pectini- forme of the corpora cavernosa, and their trabecular tissue, which supports the erectile tissue, are to be observed. In the female the bladder is to be examined as in the male. The absence of a prostate gland is to be noted, and the urethra is to be laid open, its short- ness and distensibility being observed. The vagina is to be opened from end to end by an incision along the lateral wall. Its mucous rugae are to be examined, as well as the carunculae myrtiformes at its external orifice, and the lower part of the cervix uteri, which is received into its anterior wall at the upper end. The transverse slit of the os uteri externum is to be studied, along with its anterior and posterior lips. The recesses formed by the vagina around the lower part of the cervix uteri, called the fornices, are to be THE ABDOMEN 925 explored, and, on introducing the finger into the posterior fornix, the dissector will find that he can palpate the recto-uterine pouch of peritoneum or pouch of Douglas. The uterus is next to be carefully examined, and its relations, peritoneal included, are to be revised. The fundus, body, isthmus, and cervix are to be attended to. On each side of the upper part of the vagina and cervix uteri a collection of fat, called the parametrium, is to be shown. The body of the uterus is now to be laid open from before by a triangular incision, the apex of which is on a level with the isthmus, whence the two limbs diverge upwards and outwards to each lateral angle. The thick, triangular flap of the anterior wall thus formed having been raised, the cavity of the body is to be examined. The smoothness of the mucous lining is to be observed, and the uterine openings of the Fallopian tubes at each lateral angle, as well as the os uteri internum at the isthmus, are to be studied. The cers'ix is then to be opened along its anterior wall on one side of the middle line, and the arrangement of the mucous membrane, known as the arbor vitae uterina, is to be noted. The Fallopian tube, with the corpus fimbriatum at its outer end, is to be studied, followed by the round ligament of the uterus. The ovary is next to be fully examined, and the scarred condition of its surface noted. The part of the broad ligament between the ovaryand Fallopian tube, called the mesosalpinx, on being held up to the light, may be seen to contain the epoophoron (paro- varium, or organ of Rosenmuller). la a young subject a few other tubules may be seen nearer the uterus, which are knowm as the paroophoron. The ovarian and uterine arteries, if injected, are to be followed to their distribution. Articulations of the Pelvis. — The sacro-vertebral joint is to be examined, and the sacro-vertebral and ilio-lumbar ligaments dissected. The symphysis pubis is to receive careful attention, and the oblique direction of the joint is to be noted. Its ligaments are to be shown, and the interarticular fibro-cartilage is to be examined. Occasionally an interspace will be found in it towards the upper and back part, in which there may be a Uttle fluid. The movement at this joint is only of a very slight yielding nature, except in the female during parturition. The sacro-iliac joint or synchondrosis is next to be examined. Its anterior ligament is weak. The posterior ligament, however, which is to be studied by partially separating the bones, is of considerable strength, and the part which it takes in supporting weight is to be carefully studied. The great and smaU sacro-sciatic ligaments are to be studied, and the manner in which they convert the sciatic notches on the posterior border of the hip- bone into foramina is to be noted. The dissector is to observe the cartila- ginous facing of the small sciatic notch, and the grooves, with intervening ridges, which it presents, for the columns on the under surface of the tendon of the obturator intemus. Finally, the sacro-coccygeal and intercoccygeal joints are to be examined. THE THORAX Thoracic Wall. Muscles — Intercostal Muscles. — These are two in number in each space, external and internal, and they are arranged as thin sheets of obliquely-disposed muscular fibres, with a large admixture of tendinous fibres. External Intercostal Muscles — Origin. — ^The lower border of the upper rib. Insertion.- -The outer margin of the upper border of the lower rib. . Internal Mammary Artery External Intercostal Muscle Interosseous Part of Internal Intercostal Muscle Interchondral Part of Interi'al Intercostal Muscle External Intercostal Muscle Fig. 380. — Diagram of the Intercostal Muscles and Intercostal Arteries (A small portion of the external intercostal muscle has been divided and reflected). Nerve-supply.- -The intercostal nerve of the corresponding space. The fibres of each muscle are directed downwards and forwards, and in this respect coincide with those of the obliquus externus abdominis. The muscles, as a rule, extend as far forwards as the junction of the ribs with their cartilages, but sometimes they stop short of this point, especially in the upper spaces. From the 920 THE THORAX 927 point where the fibres cease the upper six muscles are continued inwards to the side of the sternum by a thin delicate membrane, called the anterior intercostal aponeurosis. This occupies the spaces between the true costal cartilages. Posteriorly the muscles extend as far as the tubercles of the ribs. Internal Intercostal Muscles — Origin. — The upper margin of the subcostal groove of the upper rib. Insertion. — ^The inner margin of the upper border of the lower rib. Nerve-supply. — ^The intercostal nerve of the corresponding space. The fibres of each muscle are directed downwards and backwards, and in this respect coincide with those of the obliquus intemus abdominis. The upper six muscles extend as far inwards as the side of the sternum, and the lower two are continuous anteriorly with the obliquus internus abdominis. Posteriorly the muscles extend as far back as the angles of the ribs. In this situation each is replaced by a delicate membrane, called the posterior intercostal aponeurosis, which lines the adjacent portion of the external inter- costal muscle, and blends behind with the anterior or external superior costo-transverse ligament. The internal intercostal muscles are covered internally by the parietal pleura. Action of the Intercostal Muscles. — ^This subject has given rise to much discussion and difference of opinion. Three views are enter- tained, (i) According to Haller, the external and internal intercostal muscles both act as elevators of the ribs, and are therefore muscles of inspiration. Inasmuch as the fibres of the two muscles decus- sate, they must, according to this view, act on the principle of the parallelogram of forces. The common nerve-supply of the two muscles tends to favour this view. (2) According to Hamberger, the external intercostal muscles are elevators of the ribs, and therefore muscles of inspiration, whilst the internal intercostal muscles are depressors of the ribs, and therefore muscles of expiration, (3) According to Hutchinson, the external intercostal muscles and the inter chondral portions of the internal intercostal muscles act as elevators of the ribs, and are therefore muscles of inspiration, whilst the interosseous portions of the internal intercostal muscles act as depressors of the ribs, and are therefore muscles of expiration. When a rib is elevated, its lower border is at the same time everted. For the levatores costanim muscles, see Indax. Intercostal Nerves. — ^Tbese are eleven in number on each side, and are the anterior primary divisions of the upper eleven thoracic spinal nerves. The anterior primary division of the twelfth thoracic spinal nerve is not an intercostal ner\'e, but lies along the lower border of the twelfth rib, and is known as the subcostal nerve (* last dorsal nerve '). The lower five intercostal nerves ultimately leave the intercostal spaces and pass on to the anterior abdominal wall. Upper Six Intercostal Nerves. — Each of these nerves, as it enters the back part of an intercostal space, lies between the posterior 928 A MANUAL OF ANATOMY intercostal aponeurosis and the parietal pleura. About the level of the angle of the rib it pierces the posterior intercostal aponeurosis, and passes forwards in the subcostal groove of the upper rib' lying between the intercostal muscles. It continues its forward course in this position, in company with the aortic intercostal artery and intercostal vein, the order of these from above downwards being intercostal vein, aortic intercostal artery, and intercostal nerve. The nerve is concealed by the overlapping lower border of the upper rib. Having reached a point about midway between the vertebral column and the side of the sternum, the nerve gives off Fig. 381. — Scheme of an Intercostal Nerve. S.C. Spinal Cord 1. Anterior Root of Spinal Nerve 2. Posterior Root, with Ganglion 3. Spinal Nerve A.P.i). Anterior Primary Division (Intercostal Nerve) S.G. Sympathetic Ganglion R.C. Rami Communicantes L.C. Lateral Cutaneous Nerve A.B. Anterior Branch P.B. Posterior Branch A.C. Anterior Cutaneous Nerve P.P.D. Posterior Primary Division E.B. External Branch I.B. Internal Branch a large branch, called the lateral cutaneous nerve. The intercostal nerve itself, now reduced in size, leaves the intermuscular space hitherto occupied by it, and enters the internal intercostal muscle, in the substance of which it continues its forward course. Having arrived at the anterior extremity of the osseous rib, the nerve cmreges from the internal intercostal muscle and passes inwards on its deep surface, lying at first upon the parietal pleura, and subsequently upon the triangularis sterni muscle, crossing in. its course the internal mammary vessels. On reaching the side ofj the sternum it passes straight forwards, to become an anteriori TBE THORAX 9^9 cutaneous nerve, piercing in succession the following structures : the interchondral portion of the internal intercostal muscle ; the anterior intercostal aponeurosis ; the pectoralis major muscle ; and the deep fascia. Branches. — ^These are muscular, lateral cutaneous, and anterior cutaneous. The muscular branches supply the following muscles : the levatores costarum, serratus posticus superior, subcostal muscles, intercostal muscles, and triangularis stemi. The lateral cutaneous nerves arise about midway between the vertebral column and the side of the sternum. They pierce the external intercostal muscles, and make their appearance between the digitations of the serratus magnus. The first intercostal nerve, as a rule, gives off no lateral cutaneous branch, and that of the second is known as the intercosto-humeral ner\'e. The anterior cutaneous nerves are the terminal branches of the upper six intercostals, that of the first being sometimes absent. For their description, see Index. Intercostal Arteries. — These vessels are arranged in two sets — posterior and anterior. Posterior Series. — The intercostal arteries of the first two spaces are derived from, the superior intercostal artery (see Index). The intercostal arteries of the lower nine spaces are branches of the descending thoracic aorta, and are called the aortic intercostal arteries. Each at first lies between the posterior intercostal aponeurosis and the parietal pleura. About the level of the angle of the rib it pierces the posterior intercostal aponeurosis, and gives off its collateral intercostal branch, which inclines downwards. These two arteries now pass forwards between the two intercostal muscles, the main aortic intercostal lying in the subcostal groove of the upper rib, where it has the intercostal vein above it and the intercostal nerve below it, and the collateral intercostal lying along the upper border of the lower rib. These two vessels, in the case of the upper nine spaces, terminate by anastomosing with the anterior intercostal arteries, which are two in number in each of these spaces, and will be presently described. These anastomoses take place a little in front of the mid-point between the vertebral Column and the side of the sternum. Branches. — These are dorsal, collateral intercostal, and lateral cutaneous. The dorsal branch passes backwards to the muscles and integument of the back, giving off in its course a spinal branch, which enters the spinal canal through the intervertebral foramen. The collateral intercostal branch, as stated, arises about the level of the angle of the rib, and inclines dowTiwards to the upper border of the lower rib, along which it passes between the intercostal muscles. The lateral cutaneous branch accompanies the corresponding lateral cutaneous nerve. 59 930 A MANVAL OF ANATOMY The aortic intercostal and collateral intercostal arteries give branches to the intercostal muscles and ribs. Those of the third, fourth, and fifth spaces, at least, furnish branches to the mammary gland and pectoral muscles, which anastomose with the thoracic branches of the acromio-thoracic artery from the first part of the axillary, and with the long thoracic from the second part of that vessel. The first aortic intercostal artery, as it enters the third intercostal space, gives off a branch which ascends to the back part of the second intercostal space, and anastomoses with the branch of the superior intercostal artery to that space. Anterior Series, — The internal mammary artery furnishes two anterior intercostal arteries to each of the upper six intercostal spaceSy and the musculo-phrenic branch of the internal mammary furnishes two anterior intercostal arteries to each of the seventh, eighth, and ninth in tercostar spaces. The arteries of the upper six spaces lie at first upon the triangularis sterni muscle, and then upon the parietal pleura, being under cover of the internal inter- costal muscle. Afterwards all the anterior intercostal arteries pass between the external and internal intercostal muscles. In each space they anastomose with the aortic intercostal and collateral intercostal arteries, and also with the corresponding intercostal arteries of the upper two spaces. Branches. — ^These are distributed to the intercostal muscles, ribs, mammary gland, and pectoral muscles. The lower two intercostal spaces are not furnished with anterior intercostal arteries. The aortic intercostal arteries of these spaces, after leaving them, enter the abdominal wall, and pass forwards between the internal oblique and transversalis muscles to the rectus abdominis, in which they anastomose with the superior epigastric and deep epigastric arteries. Intercostal Veins. — ^These veins accompany the corresponding arteries. The chief intercostal vein passes backwards in the subcostal groove of the upper rib, in company with the aortic intercostal artery, above which it lies. In the region of the angle of the rib it is joined by the collateral intercostal vein, which accompanies the correspond- ing artery. Close to the vertebral column the chief intercostal vein receives a large dorsal branch, which returns blood from the muscles and integument of the back, the dorsal spinal venous plexus, and the spinal canal. The mode of termination of the chief intercostal veins differ on each side, and will be described in connection with the dissection of the posterior wall of the thorax. The anterior intercostal veins accompany the anterior intercostal arteries. Those of the upper six intercostal spaces pass to the internal mammary, and those of the succeeding three spaces pass to the musculo-phrenic, veins. Intercostal Lymphatics. — ^The lym]:)hatic vessels of the intercostal spaces pass partly to the posterior intercostal glands, which lie at the back parts of the intercostal spaces, and partly to the anterior /^" THE THORAX 931 intercostal or sternal glands, which lie along the course of the internal mammary' arter\\ Internal Mammary Artery. — ^This vessel arises from the lower portion of the first part of the subclavian artery, and it passes down- wards, forwards, and inwards behind the inner part of the clavicle and the first costal cartilage. It then descends vertically behind the succeeding costal cartilages as low as the sixth intercostal space, where it terminates by dividing into two branches, namely, the superior epigastric and the musculo-phrenic. The artery lies about \ inch from the margin of the stermma. Cervical Relations — Anterior. — ^The clavicular portion of the sterno-cleido-mastoid muscle, and the internal jugular and sub- clavian veins. The phrenic nerve crosses it superficially from without inwards. Posterior. — ^The dome of the pleura. Thoracic Relations — Anterior. — ^The pectoralis major ; upper six costal cartilages ; anterior intercostal aponeuroses ; internal inter- costal muscles ; and upper six intercostal nerves. Posterior. — ^The pleura above, and subsequently the triangularis sterni muscle. Lateral. — ^The artery has a vena comes on either side of it. The anterior intercostal or sternal glands lie along the course of the vessel. Branches. — The artery gives off no branches in the neck. In the thoracic part of its course it furnishes the following branches : Superior phrenic. Anterior intercostal. Mediastinal. Perforating. Pericardial. Musculo-phrenic. Sternal. Superior epigastric. The superior phrenic artery, long and slender, arises high up, and accompanies the phrenic nerve to the diaphragm, from which cir- cumstance it is known as the comes nervi phrenici. It gives twigs to the pericardium and pleura, and in the diaphragm it anastomoses with the inferior phrenic branch of the abdominal aorta and with the musculo-phrenic branch of the internal mammary. The mediastinal branches are distributed to the contents of the anterior mediastinum, namely, the remains of the thymus body, anterior mediastiucd glands, and areolar tissue. The pericardial branches supply the front part of the pericardium. The sternal branches are distributed to the sternum and triangularis sterni muscle. The anterior intercostal arteries are two in number to each of the upper six intercostal spaces. For their description, see Index. The perforating branches are six in number, one arising opposite each of the upper six intercostal spaces. Each vessel pierces the internal intercostal muscle, anterior intercostal aponeurosis, and pectoralis major. Thereafter it gives a few twigs to the front of the sternum, and then turns outwards to supply the pectoral integu- nient. The second, third, fourth, and fifth perforating branches give offsets to the inner portion of the mammary gland. ' The musculo-phrenic artery is one of the terminal branches of the 932 A MANUAL OF ANATOMY internal mammary. It arises from that vessel in the sixth inter- costal space, and passes obliquely downwards and outwards behind the seventh, eighth, and ninth costal cartilages. About the level of the tenth rib it perforates the diaphragm and terminates in the lateral wall of the abdomen, where it anastomoses with the lateral epigastric branch (ascending branch) of the deep circumflex iliac artery. It gives off anterior intercostal and muscular branches. The anterior intercostal arteries are two in number to each of the seventh, eighth, and ninth intercostal spaces, in which they are Sterno-hyoid Muscle Sterno-thyroid Muscle Subclavian Artery (First Part) Internal Mammary Artery Anterior Intercostal Arteries Sternal Glands Superior Epigastric Artery Musculo-phrenic Artery Fi&. 382. -Dissection of the Anterior Wall of the Thorax (Posterior View). disposed in a manner similar to the anterior intercostal branches of the internal mammary. The muscular branches are distributed to the diaphragm and lateral wall of the abdomen. In the diaphragm they anastomose with the inferior phrenic branch of the abdominal aorta and the superior phrenic branch of the internal mammary. The superior epigastric artery is the other terminal branch of the internal mammary, of which it is the continuation. It descends behind the seventh costal cartilage, and passes through the areolar interval between the sternal and costal portions of the diaphragm THE THORAX 933 In this manner it enters the sheath of the rectus abdominis, l^'ing at first behind the muscle, but afterwards entering it. In the muscle it anastomoses with the deep epigastric artery, which is a branch of the external iliac. The branches of the superior epigastric artery will be found described on p. 663. The internal mammary veins {vence comites) are two in number, and lie one on each side of the artery. They are formed, respectively, by the union of the venae comites of the musculo-phrenic and superior epigastric arteries. In their course they receive tributaries corresponding to the branches of the artery. About the level of the first intercostal space the outer vein crosses over the artery and joins the inner vein to form a single vessel, which opens into the corresponding innominate vein. The internal mammary veins are provided with valves at intervals. Sternal or Internal Mammary Lymphatic Glands. — These glands form a chain along the course of the internal mammary vessels on either side, there being one, or it may be two, in the anterior ex- tremity of each of the upper six intercostal spaces. They receive their afferent vessels from (i) the inner third of the mammary gland, {2) the anterior half of the costal pleura, (3) the anterior halves of the external and internal intercostal muscles, (4) the lymphatics which accompany the superior epigastric artery, and (5) the anterior diaphragmatic glands. Their efferent vessels pass to the thoracic duct, or to the rigJit lymphatic duct, according to the side on which the glands lie. Triangularis Sterni — Origin. — (i)'The deep surface of the ensiform process and body of the stemiun, close to the lateral border, and extending as high as the level of the third costal cartilage ; and (5) the deep surfaces of the lower two or three true costal cartilages at their sternal ends. Insertion. — ^The deep surfaces and lower borders of the costal cartilages from the sixth to the second. The insertion takes place by separate slips, and one or two of the upper slips may be partially attached to the rib itself. Nerve-supply. — The intercostal nerves of the adjacent spaces. The lowest fibres of the muscle are horizontal ; the succeeding fibres pass obliquely upwards and outwards ; and the upper fibres are almost vertical. Action. — ^To depress the anterior extremities of the ribs, and so take part in expiration. The muscle forms a thin musculo-tendinous sheet, which is situated on the deep surfaces of the costal cartilages and side of the sternum, and it is serially continuous with the transversalis ab- dominis muscle. It supports the internal mammary vessels, sternal glands, and certain of the intercostal nerves, whilst its deep surface rests upon the parietal pleura. 934 A MANUAL OF ANATOMY Thoracic Cavity. Contents and their General Position. — ^The thoracic cavity is chiefly occupied by the lungs and heart . The lungs are situated one in each half of the cavity, and each lung is provided with a serous membrane, called the pleura. The heart lies obliquely between the lungs, projecting more to the left of the sternum than to the right, and it is enclosed within a fibro-serous sac, called the pericardium. Each lung is free to expand except at the hilum pulmonis, which is situated on its inner surface. Through this hilum the bronchus, pulmonary artery, and pulmonary veins pass, along with other structures, and the pedicle so formed is called the root of the lung. The upper part, or apex, of the lung rises into the root of the neck, where it is covered by the dome of the pleura, that in turn being covered by Sibson's fascia. The lower part, or base, of the lung rests upon the corresponding half of the diaphragm, the heart lying upon the central tendon of that muscle. The pulmonary artery springs from the base of the right ventricle of the heart, and the aorta from the base of the left ventricle, being at first covered by the pulmonary artery. The left innominate vein courses along the upper aspect of the arch of the aorta in front of the origins of the innominate, left common carotid, and left sub- clavian arteries, and it unites with the right innominate vein behind the sternal end of the first right costal cartilage to form the superior vena cava. This latter vessel opens into the postero-superior angle of the right auricle of the heart, and, just before piercing the pericardium, it receives the right azygos vein, which arches forwards over the right bronchus. The inferior vena cava, having entered the thorax through the foramen quadratum in the central tendon of the diaphragm, almost immediately opens into the postero- inferior angle of the right auricle of the heart. The phrenic nerve, on each side, descends in front of the root of the lung, and is intimately related to the pericardium, especially on the left side. The small anterior pulmonary plexus of nerves lies in front of the root of each lung. The pneumogastric nerve, on each side, descends behind the root of the lung, and forms in that part of its course the much larger posterior pulmonary plexus. The following important nerves descend in front of the arch of the aorta : the left phrenic, the left pneumogastric, the upper cervical cardiac branch of the left sympathetic, and the lower cervical eardiac branch of the left pneumogastric. The left superior inter- costal vein lies in front of the back part of the aortic arch. The superficial cardiac plexus of nerves lies within the concavity of the arch of the aorta, and the deep cardiac plexus lies behind the arch and in front of the trachea, close to its bifurcation into the two bronchi. The left recurrent laryngeal nerve passes backwards under THE THORAX 935 the arch, and then ascends behind it. Within the concavity of the aortic arch the trunk of the pulmonary artery breaks up into its right and left divisions, and the ligamentum ductus arteriosi extends from the root of the left pulmonary artery to the back part of the con- cavity of the aortic arch, immediately beyond the origin of the left subclavian artery. The gangliated cord of the sympathetic lies very deeply, and descends over the heads of the ribs close behind the parietal pleura, and the two, or three, splanchnic ner\''es lie obliquely on the sides of the bodies of the lower thoracic vertebrae. The oesophagus lies in contact with the front of the vertebral column, and the trachea is anterior to it. The descending thoracic aorta lies very deeply, being situated at first on the left side of the vertebral column, but subsequently in front of it. The thoracic duct ascends on its right side, and the right azygos vein ascends on the right side of the thoracic duct, both structures being under cover of the oesophagus. The two left azygos veins, upper and lower, as well as the two transverse azygos veins, upper and lower, are closely related to the vertebral column. The thoracic cavity contains the following sets of lymphatic glands : the anterior mediastinal, in front of the pericardium ; the superior mediastinal, above the pericardium, along the arch of the aorta and innominate veins ; the posterior mediastinal, behind the pericardium ; the posterior intercostal, in the back parts of the intercostal spaces ; and the bronchial, in the interval between the diverging bronchi, and also at the root of each lung. In early life a portion of th? thymus body, which is then of large size, lies behind the upper part of the sternum, whence it extends into the lower part of the neck. Pleurae. — ^The pleurae are the two serous sacs which invest the lungs, and line the adjacent parietes. Each forms a shut sac, which is quite distinct from its fellow. Like other serous membranes, the pleura consists of two portions — parietal and visceral — which, however, are continuous with one another. The parietal pleura lines the parietes, and is divisible into five portions, namely, costal, diaphragmatic, pericardial, cervical, and mediastinal. The costal pleura lines the inner surfaces of the ribs and internal intercostal muscles. The diaphragmatic pleura covers the upper surface of one-half of the diaphragm. Th& pericardial pleura is in intimate contact with the pericardium. The cervical pleura forms what is known as the dome, and rises into the neck for about I inch above the clavicle, being a little higher on the right side than on the left, on account of the projection formed by the liver. The mediastinal pleura of each side bounds the media'^tinum thoracis. The visceral pleura closely invests the lung, and is known as the pulmonary pleura. It is intimately connected with the limg sub- stance, and extends into the fissure, or fissures, which map out the lung into lobes. Below the root of each lung it forms a fold, called the ligamentum latum pulmonis, which descends to the diaphragm, and is connected with the pericardium. 936 A MANUAL OF ANATOMY Continuity and Reflections of the Pleura. — (i) In the transverse direction. — Commencing at the deep surface of the sternum, the parietal pleura of each side passes backwards to the pericardium, the two being in contact except for a little inferiorly. They form the lateral boundaries of the space which is called the anterior mediastinum. When they reach the pericardium the two pleurae separate, each keeping to its own side of that sac, and so forming the pericardial pleura, which bounds laterally the space known as the middle mediastinum. Each pleura in this manner reaches the anterior aspect of the root of the corresponding lung, where it becomes the visceral pleura. This covers the front of the root of the lung, and then invests the entire organ, dipping into its fissure or fissures, as the case may be, and giving a covering to the posterior Fig. 383. — Diagram showing the Reflections of the Pleura (Transverse Section). aspect of the root. On leaving the back of the root of each lung, the two pleurae pass backwards, slightly over the pericardium, trachea, and oesophagus, and over the descending thoracic aorta, to the lateral aspects of the bodies of the thoracic vertebrae. These portions form the lateral boundaries of the space which is called the posterior mediastinum. From the vertebral column each pleura passes out- wards over the gangliated cord of the sympathetic, and then lines the inner surfaces of the ribs, as well as the internal intercostal muscles. In this manner it reaches the deep surface of the sternum. From the foregoing description it will be evident that the pleura, in passing from the deep surface of the sternum to the vertebral column, meets with, and is reflected over, the lung and its root THE THORAX 9yj At the level of the manubrium sterni the pleura passes uninterrup- tedly backwards to the vertebral column. That of the right side passes over the side of the superior vena cava, innominate artery, right innominate vein, and trachea ; whilst that of the left side passes over the side of the left common carotid and left subclavian arteries, oesophagus, and thoracic duct. The two pleurae, as they pass back- wards at this level, form the lateral boundaries of the space which is called the superior mediastinum. Below the level of the root of the lung the aatero-posterior reflec- tion of the pleura is complicated by a triangular fold, called the ligamentum latum pulmonis. This fold consists of two layers of pleura, in close apposition, which are continuous superiorly with the anterior and posterior pleural investments of the root of the lung. It extends, on the one hand, between the lower border of the root of the lung and the diaphragm, to which latter it is aiiached, and, on the other hand, between the pericardium and the inner surface of the lung below the level of the root. In the last-named situation its two layers separate, to encase the lung at that level. Its lower border is free and concave. (2) In the vertical direction. — Superiorly the parietal pleura of each side rises, in the form of a dome, into the root of the neck for about I inch above the clavicle, where it is covered by Sibson's fascia. This fascia is attached, on the one hand, to the internal border of the first rib, and, on the other, to the front of the transverse process of the seventh cervical vertebra. The subclavian artery and innominate vein are intimately related to the dome of the pleura internally and anteriorly, the artery being the higher of the two. Inferiorly the parietal pleura of each side is reflected from the thoracic wall on to the upper surface of the corresponding portion of the diaphragm, which it covers where the base of the lung rests upon it. The intervening portion of the diaphragm (central tendon) is covered by the serous portion of the pericardium. In- ternally the diaphragmatic pleura becomes continuous with the mediastinal pleura. Lines of Reflection of the Pleurae — Sternal Reflection. — Behind the manubrium sterni the right and left pleurae are separated from each other by an interspace which represents the superior medi- astinum. At the levd of the junction of the manubrium and body of the sternum they meet each other, and descend behind the body of the bone, in close contact and inclining slightly to the left of the median line. At the level of the lower border of the fourth costal cartilage the left pleura parts company with the right, and passes outwards and downwards close to the left border of the sternum, and in intimate relation with the pericardium. There is, however, a small triangular area of that sac which is uncovered by the pleura, and lies in direct relation to the anterior thoracic wall. The left pleura continues its downward course as far as the inner surface of the sixth costal cartilage, lying not far from the left border of the sternum. At this level it again passes outwards and downwards, 938 A MANUAL OF ANATOMY to be reflected on to the diaphragm. The right pleura pursues an undeviating course downwards behind the sternum as far as the junction of the body and ensiform process. At this level it leaves the bone, and passes obliquely outwards, downwards, and back- wards over the inner surface of the seventh costal cartilage, from which it is reflected on to the diaphragm. Costo-diaphragmatic Reflection. — The level of this reflection may be considered in the first place as it affects certain definite vertical lines. In the left sternal line it takes place at the level of the sixth costal cartilage, and in the right sternal line at the level of the soventh costal cartilage. In the left mammary line it takes place at the level of the eighth costal cartilage, where it joins the osseous part of the rib, and on the right side at a similar level. In the left mid-axillary line it takes place on a level with the lower border of the tenth rib, this being the lowest point to which the pleura descends. In the right mid-axillary line it takes place on a level with the upper border of the tenth rtb, or, it may be, the lower border. Posteriorly, in the scapular line (inferior angle of the scapula), on each side, it takes place at the level of the lower border of the twelfth rib. From this point inwards to the vertebral column the line of pleural reflection is a little below the adjacent border of the twelfth rib, and is very nearly midway between the vertebral end of that rib and the first lumbar transverse process. From the foregoing description it will be evident that the pleura descends lowest in the mid-axillary line, and that posteriorly, close to the vertebral column, it actually descends below the level of the lower border of the twelfth rib. The direction of the line of costo-diaphragmatic reflection, from before backwards, is at first obliquely downwards and outwards, until the level of the tenth rib is reached. Thereafter the line passes backwards and upwards to the vertebral column. The costo-diaphragmatic pleural line is on a distinctly lower level than the margin of the base of the lung, but it is a little above the line of the costal attachment of the diaphragm. The portion of the diaphragm below the line is therefore in direct contact with the thoracic wall and adjacent internal intercostal muscles, without the intervention of the pleura, and the costo-diaphragmatic reflection is connected to these structures by a fascial expansion. The free surfaces of the parietal and visceral pleurae are, in health, in close contact. They are polished and moistened by a slight amount of serous fluid, so that they glide smoothly upon each other. In cases of pleurisy, however, certain changes take place. The free | surfaces are, in the first place, rendered dry, and thereafter theyj become roughened at intervals by the deposit of lymph. Under these circumstances the movement of the lung is accompanied by, the sound known as pleuritic friction. Adhesions are also frequently | formed, and a serous exudation takes place into the pleural sac,- which tends to compress the lung injuriously, the condition being j known as hydro-thorax. In cases of serous exudation the cavity of j the pleura, which is a shut sac, is clearly demonstrable, but in 'I THE THORAX 939 health no such cavity exists, the parietal and visceral pleurae being at all times in intimate contact with each other. The attached sur- faces of the parietal and visceral pleurae are roughened by fibrous processes, by means of which they are connected to the parts which they cover. The costal pleura is the thickest, and can readily be stripped fiom the inner surfaces of the ribs and internal intercostal muscles. There is a fairly thick laj-er of subserous areolar tissue on its attached surface. The diaphragmatic and pericardial pleurae are thinner than the costal pleura, and are more adherent to the sub- jacent structures. The pulmonarj^ pleura is the thinnest and most adherent. Beneath it there is a layer of subserous areolar tissue, containing much elastic tissue, and this is in continuity with the areolar tissue which pervades the lung. Differences between the Two Pleural Sacs. — The right pleural sac rises higher into the root of the neck, and is shorter and w-ider, than the left. These differences are due partly to the projection formed by the liver on the right side, and partly to the greater inclination of the heart to the left of the sternum than to the right. Blood-supply. — ^The parietal -pleura receives its arteries from (i) the aortic intercostals, and (2) the superior phrenic, anterior intercostal, anterior mediastinal, pericardial, and musculo-phrenic branches of the internal mammary. The veins pursue courses corresponding to the arteries. Nerve-supply. — ^The nerves are derived from the sympathetic and phrenic ner\'es. Lymphatics— Visceral or Pulmonary Pleura. — The lymphatic vessels of this part of the pleura open into the superficial lymphatics of the lungs. Parietal Pleura. — The lymphatics of the costal pleura open into the lymphatics of the internal intercostal muscles, which terminate in (i) the sternal or internal mammary' glands, and (2) the intercostal glands. The l\Tnphatics of the diaphragmatic pleura open into the lymphatics of the diaphragm. The Ijmiphatics of the mediastinal pleura open into (i) the anterior mediastinal glands, and (2) the posterior mediastinal glands. Structure. — The pleura is a typical serous membrane like the serous portion of the pericardium, the peritoneum, and the tunica vaginalis. Such mem- branes are called serous because their free surfaces are moistened by a small quantity of serous fluid. Briefly stated, the pleura consists of a homogeneous, connective-tissue basement membrane, containing elastic tissue, and lined with endothelium. It presents many stotnata, which communicate with the pleural cavity and with the pleural lymphatic vessels. Development. — The pleura is developed from the walls of the coelom, or body-cavity, which is the cleft in the mesoblast separating the splanchno- pleure and somatopleure. Mediastinum Thoracis. — ^The mediastinum thoracis is formed by the approximation of the two pleural sacs in the region of the median antero-posterior line of the thorax. The inter\-al between the two sacs is called the mediastinal space, and its boundaries are 940 A MANUAL OF ANATOMY as follows : in front, the sternum ; behind, the bodies of the thoracic vertebrae; and, on either side, the corresponding pleural sac. The mediastinal space contains structures so numerous as to necessitate its subdivision into four parts — superior, anterior, middle, and posterior. The superior mediastinum is situated above the pericardium, and its boundaries are as follows : in front, the deep surface of the manu- brium sterni, with the origins of the sterno-hyoid and sterno-thyroid muscles ; behind, the bodies of the upper four thoracic vertebrae and the lower portions of the longus colli muscles ; above, an imagi- nary plane corresponding to the superior aperture of the thorax ; below, an imaginary plane passing from the lower border of the manubrium sterni to the lower border of the body of the fourth thoracic vertebra ; and, laterally, the mediastinal pleura of each side as it extends from the deep surface of the manubrium sterni to the vertebral column. Contents. — ^These are as follows : (i) the arch of the aorta ; (2) the innominate artery, and the thoracic portions of the left common carotid and left subclavian arteries ; (3) the right and left innominate veins, and the upper half, or extrapericardial portion, of the superior vena cava ; (4) the phrenic, pneumogastric, left recurrent laryngeal, and cardiac nerves ; (5) the trachea, oesophagus, and thoracic duct ; (6) the superior mediastinal glands ; and (7) the remains of the thymus body. The anterior mediastinum is situated behind the body of the sternum, and its boundaries are as follows : in front, the deep surface of the body of the sternum, and the left triangularis sterni muscle ; behind, the pericardium ; and, laterally, the mediastinal pleura of each side as it extends from the deep surface of the body of the sternum to the lateral aspects of the pericardium. Its direction is downwards and to the left. At its upper part there is no interspace, because the two pleural sacs come into contact behind the first piece of the body of the sternum. Below this level, however, the left pleural sac diverges from its fellow, so as to leave an interspace. Contents. — ^These are the anterior mediastinal glands, some lymphatic vessels, the anterior mediastinal branches of the internal mammary artery, and areolar tissue. Anterior Mediastinal Glands. — These glands are situated within the areolar tissue of the lower part of the anterior mediastinum, between the lower part of the body of the sternum and the front : of the pericardium. They receive their afferent vessels from (i) the antero-mesial portion of the diaphragm, corresponding to the ensiform process of the sternum, (2) the supero-anterior surface of the liver, on either side of the falciform ligament, (3) the anterior part of the pericardium, (4) the anterior part of the mediastinal pleura, and (5) the lower sternal, or internal mammary, glands. Their efferent vessels ascend and open into the superior mediastinal or cardiac glands. THE THORAX 941 The middle mediastinum lies behind the anterior, and below the superior, mediastinum, and is the \\-idest part of the interpleural space. Contents. — These are as foUows: (i) the heart, enclosed in the pericardium; (2) the ascending aorta; (3) the trunk of the pul- monary artery; (4) the lower half, or intrapericardial portion, of the superior vena cava; (5) the phrenic nerves and the superior phrenic Parietal Pleura Pknral Interval Internal Mammary Vessels Pulmonarj- Pleura Left Vagu Nerve Right Vagus Nerve Thoracic Duct Right Azygos Vein Fig. 384. — Transverse Section of the Thorax through the Second Sternebra in Front and the Body of the Ninth Thoracic Ver- tebra Behind, showing the Reflections of the Pleura and the Position of the Viscera. S. Sternum A.M. Anterior Mediastinum A. A. Ascending Aorta P.A. Pulmonarj- Artery R.A.A. Right Auricular Appendix R.A. Right Auricle M.M. Middle Mediastinum L..A. Left Auricle P.M. Posterior Mediastinum O. CE^phagus D.A. Descending Thoracic Aorta . T.V. Thoracic Vertebra M. Middle Lobe of Right Lung R.U. Right Upper Lobe R.L. Right Lower Lobe L.U. Left Upper Lobe L.L. Left Lower Lobe vessels; (6) the bifurcation of the trachea; and (7) the roots of the lungs. The posterior mediastinum is situated behind the pericardium, and below the posterior part of the superior mediastinum, with which latter it is continuous. Its boundaries are as foUows: in front, the pericardium, and below this the posterior part of the diaphragm; behind, the bodies of the thoracic vertebrae below the level of the lower border of the body of the fourth; and laterally, the mediastinal pleura of each side as it extends from the back of the root of the lung to the side of the vertebraj colmmi. 942 A MANUAL OF ANATOMY Contents. — These are as follows: (i) the descending thoracic aorta; (2) the oesophagus, and the two pneumogastric nerves; (3) the thoracic duct ; (4) the right azygos vein ; (5) the upper and lower left azygos veins, with the corresponding transverse azygos veins; (6) the great splanchnic nerves, right and left; and (7) the posterior mediastinal glands. Phrenic Nerve. — ^This nerve arises chiefly from the anterior primary division of the fourth cervical nerve. It usually receives a small root from the anterior primary division of the third cervical, and, as a rule, an additional root from that of the fifth cervical. Having descended on the superficial surface of the scalenus anticus muscle to the root of the neck, it crosses the internal mammary artery superficially from without inwards. Thereafter it enters the thorax and descends in front of the root of the lung, in close contact with the side of the pericardium, and under cover of the mediastinal pleura. Having reached the diaphragm, the nerve divides into several branches, which pierce that muscle to be distributed to its abdominal surface. The terminal branches of each nerve are con- nected, in the diaphragm, with filaments of the corresponding inferior phrenic plexus of the sympathetic, which is an offshoot from the solar plexus. At the place of junction of the two sets of fibres on the right side there is a small ganglion, called the ganglion diaphragmaticum. In the thorax the phrenic nerve occupies the superior and middle mediastinal spaces. The right phrenic nerve lies, in succession, on the outer side of the right innominate vein and superior vena cava, and then descends in front of the root of the right lung. The left phrenic nerve descends in the interval between the left common carotid and left subclavian arteries, where it crosses the left pneumogastric nerve from without inwards. Thereafter it passes behind the left innominate vein, and crosses over the arch of the aorta, after which it descends in front of the root of the left lung. Each nerve is accompanied by the superior phrenic artery, which is a branch of the internal mammary artery. Branches. — The nerve of each side furnishes twigs to the peri- cardium and the mediastinal pleura, its principal branches being distributed to the diaphragm. Differences between the two phrenic nerves — (i) The right nerve is shorter than the left, because the right half of the diaphragm, having the bulk of the liver below it, is higher than the left half. (2) The right nerve is straighter than the left, because the heart, enclosed in the pericardium, projects less to the right side than to the left. (3) The right nerve occupies a deeper position in the upper part of the thorax than the left. Pericardium. — ^The pericardium is the fibro-serous sac which loosely surrounds the heart in the middle mediastinum. It is some- what conical, loeing wide below, where it is in contact with the dia- phragm, and narrow above, where it surrounds the great vessels connected with the base of the heart. On each side it is intimately related to the mediastinal pleura, and is embraced by the inner THE THORAX 943 surfaces of the lungs anterior to their roots. The phrenic nerve, on each side, descends in very close contact with it. In front of it are the body of the sternum and the sternal ends of the correspond- ing costal cartilages. Its anterior surface is, to a greater or less extent, encroached upon by the adjacent portions of the anterior margins of the limgs and by the two pleurae. There is, however, a small portion of this surface which is immediately related to the stermmi below the Ie\el of the lower border of the fourth left costal cartilage at its sternal end. Posteriorly, the pericardium hes in front of the posterior mediastinum, and the oesophagus is here related to it opposite the posterior aspect of the left auricle of the heart. Arch of Aorta Superior Vena Cava Ascending Aorta Right Auricular Appendix Pericardium (cut) Right Auricle Pulmonary Artery Left Auricular Appendix Diaphragm Left Ventricle -• Pericardium (cut) Central Tendon of Diaphragm Apex Fig. 385 The Heart (Anterior View) and Pericardium (The anterior part of the pericardium has been removed). The pericardium consists of two portions — an external or fibrous, and an internal or serous. The fibrous portion is strong and dense. Inferiorly it is attached to the central tendon of the diaphragm, and slightly to its muscular part on the left side. Superiorly it ensheathes the great vessels connected with the base of the heart, with the single exception of the inferior vena cava. These sheaths are eight in number. One, which is the strongest, invests the whole of the ascending aorta; two invest the right and left pulmonary' arteries; one surrounds the lower half of the 944 A MANUAL OF ANATOMY superior vena cava; and the remaining four invest the pulmonary veins. The inferior vena cava receives no sheath from the fibrous portion, because that vessel opens into the right auricle of the heart almost immediately after it passes through the foramen quadratum in the central tendon of the diaphragm. The fibrous layer is attached to the sternum by two fibrous bands, which are known as the superior and inferior sterno-peri- cardial ligaments of Luschka, the former being attached to the deep surface of the manubrium, and the latter to the deep surface of the ensiform process. The serous portion is a typical serous membrane, and consists of two layers, parietal and visceral, which together form a shut sac. The parietal portion lines the inner surface of the fibrous part, to which it is closely adherent, and it also intimately covers the upper surface of the central tendon of the diaphragm. The visceral portion, known as the epicardium, closely invests the heart, and also the great vessels at its base more or less com- pletely. The continuity between the parietal and serous portions is established inferiorly along the inferior vena cava. Superiorly the continuity is established along the great vessels at the base of the heart about i| inches above it. In this situation the serous portion forms an arterial sheath which encloses within it the ascending aorta and trunk of the pulmonary artery, for, as stated, about ij inches, this being the only complete sheath formed by the serous portion. Behind this sheath, with its contents, and in front of the auricular portion of the heart, there is a passage, called the transverse sinus of the pericardium, which leads from the right to the left side of the serous sac. The serous portion is also related to the superior vena cava and the pulmonary veins, but it only covers them in front and at the sides. The serous portion of the pericardium forms a triangular fold, called the vestigial fold of Marshall, which is situated between the left pulmonary artery and the upper left pulmonary vein. Its base is directed towards the left, and its surfaces are anterior and posterior. Between its two delicate layers there is a small fibrous cord, which is a vestige of the left duct of Cuvier. The free surfaces of the parietal and visceral layers of the serous portion are smooth, polished, and lubricated by serous fluid to allow of free movement on the part of the heart. In the course of pericarditis they become at first dry, and then roughened by deposits of lymph, thus giving rise to the pericarditic friction murmur, and, it may be, to adhesions. They may also become separated from each other by effusion into the pericardial sac, thus giving rise to the condition known as hydro-pericardium. Blood-supply. — The fibrous portion of the pericardium and the parietal layer of the serous portion receive their arteries from (i) the pericardial and superior phrenic branches of the internal mammary, and (2) the descending thoracic aorta. The visceral layer of the serous ])ortion receives arterial twigs from the coronary arteries of the heart- THE THORAX 945 The veins pass to the internal mammary, superior phrenic, and azygos veins. Nerve-supply. — The phrenic, pneimiogastric, and sympathetic nerves. Lymphatics. — ^These pass to the anterior, superior, and posterior mediastinal glands. Structure. — The fibrous portion of the pericardium is composed of fibrous tissue, and is very dense, but not very extensible. The serous portion consists of a homogeneous, connective-tissue basement membrane, con- taining some elastic fibres, and lined with endothelium. The parietal layer is much thicker than the visceral, and the latter is intimately connected with the cardiac muscular tissue, except along the grooves which are occu- pied by adipose tissue and bloodvessels. Development. — The serous portion of the pericardium is developed from the walls of the coelom, or body-cavity, which is the cleft in the mesoblast separating the splanchnopleure and somatopleure. Thymus Body (Gland). — ^This body is present only in the foetus and young child. It attains its greatest size at the period of birth, and forms a very conspicuous object in the dissection of a child during the first year or two of life. It soon, however, begins to diminish. In its fully - developed condition it is situated partly in the thorax, and partly in the neck. In the former situation it occupies the superior and anterior media- stinal spaces, extending as low as about the level of the fourth costal cartilages, and lying in front of the great bloodvessels and upper part of the pericardium, the upper part of the sternum being in front of it. In the neck it extends as high as the lower part of the thyroid body, being imder cover of the sterno-hyoid and sterno-thyroid muscles. In this situation it embraces the front and sides of the trachea, completely concealing it from view, and it encroaches upon the carotid sheath on either side. Its length is about 2j inches, and its breadth, which is greatest in- teriorly, is about i^ inches. Its colour is pinkish ; it is soft in con- sistence ; and its surface shows indications of lobulation. It consists of two asymmetrical lateral lobes, each of which is pyramidal. In some cases the left lobe is the larger, and in other cases the right. These lobes are in close contact, but are still quite distinct. Some- times a third lobe is present, occupying an intermediate position between the other two. Blood-supply. — ^The arteries are chiefly derived from the internal mammar}^ inferior thyroid, and superior thyroid. The veins open into the right and left innominate and thyroid veins. Nerve-supply, — The nerves are derived from the sympathetic and pneumogastric. Structure.— Each lobe has a capsule of fibrous tissue, from which trabe- culae pass into the interior. These trabeculae map out each lobe into large and small lobules. Each lobule consists of an outer cortical, and an inner medullary, portion. The cortex is composed of lymphoid tissue, the lymphoid element predominating over the retiform, and it is surrounded by a capillary net- work of bloodvessels, which contains many lymph corpuscles. The lymphoid tissue of the cortex is incompletely subdivided into nodules by means of trabeculae. 60 946 A MANUAL OF ANATOMY The medulla is more transparent than the cortex, the retiform element of the lymphoid tissue is more conspicuous, and the lymph corpuscles are less numerous. In addition, the medulla contains small groups of cells, more or less concentrically arranged, which are known as the concentric corpuscles of Hassall. According to one view these cells are remains of the diverticula from which the thymus body is developed ; but another view is that they are concerned with the formation of bloodvessels and connective tissue. Development. — The thymus body is developed in two lateral parts from the entodermic epithelium of the pharyngeal portion of the primitive gut. The epithelium of the third visceral cleft, on either side, becomes evaginated, and gives rise to a hollow diverticulum. This diverticulum has a thick epithelial wall, but a small lumen, and it grows in a downward direction. Its distal end, which lies ventral to the pericardium, forms a solid enlarge- ment, and the proximal end loses its connection with the third visceral cleft. The enlarged distal end gives off numerous solid epithelial buds, which are invested with mesoderm. This budding gradually extends to the proximal part of the diverticulum. The solid buds ramify freely and give rise to the corresponding lobe of the thymus. The original diverticulum thus assumes a lobulated appearance, and resembles a racemose gland. The buds or acini, however, are soUd, and not hollow, as in racemose or acinous glands. The acini are separated by connective tissue and bloodvessels, which are developed from the surrounding mesoderm. Lymphoid tissue is also developed around the acini, and this tissue forms the greater part of the adult thymus. The epithelial elements of each lobe are subordinate to the lymphoid tissue, and are ultimately represented by the concentric corpuscles of Hassall. Thymus Body in the Adult. — Only the remains of the thymus body are present in the form of a collection of adipose and areolar tissues, which lies in the superior mediastinum in front of the innominate and left common carotid arteries, above the arch of the aorta. This mass receives a few twigs from the mediastinal branches of the internal mammary artery, and it usually contains a certain amount of the original lymphoid tissue. Lungs. — The lungs are two in number — right and left. They are spongy in consistence, float in water, and are readily compressed. When pressed between the fingers crepitation is elicited, this being due to the displacement of air. When the lung is incised, similar crepitation is heard, and a muco-serous fluid, mixed with air, exudes. They possess considerable elasticity, their colour is that of a dark slate, and they are usually mottled, this being due to carbonaceous matter. In early life, however, the colour is rose- pink. The lungs occupy the greater part of the thoracic cavity. Nor- mally they are at all times in close contact with the thoracic walls, the pleurae intervening. Unless adhesions have formed during life between the visceral and parietal pleurae, the surface of each lung is quite free except in two situations, namely, at the root, which occupies a limited area of the inner surface, and at the attachment of the ligamentum latum. Each lung is conical, the base being directed downwards. It presents for consideration an apex, a base, two surfaces, outer and inner, and two borders, anterior and posterior. The apex is blunt, and rises out of the thoracic cavity into the THE THORAX 947 root of the neck for about ij inches. It is here covered by the dome of the pleura, and a Httle below its highest point it presents a groove on its internal and anterior aspects. In the case of the right lung this groove is produced by the innominate and right subclavian arteries, and, in the case of the left lung, by the sub- clavian artery of that side. Below this groove there is another groove, produced on either side by the innominate and subclavian veins. The base is extensive, semilunar in outline, and concave in adapta- tion to the upper arched surface of the diaphragm, upon which it Two FoUides Trabecula Medulla Cortex Fig. 386. — Transverse Section of a Lobule of the Thymus Gland of A Kitten (The concentric corpuscles of Hassall are shown in the medulla). rests, with the intervention of the pleura. The base of the right lung is related to the right lobe of the Uver, and that of the left lung to the left lobe of the hver, the stomach, and the spleen, the diaphragm intervening in each case. The margin of the base is thin and sharp, and it extends into the costo-diaphragmatic space, reaching lowest behind, but nowhere as low as the line of the costo- diaphragmatic reflection of the pleura. The outer surface is extensive and convex, and in health it is closely applied to the inner surfaces of the ribs and of the internal intercostal muscles. The inner surface is of much more Umited extent than the outer. 948 A MANUAL OF ANATOMY The greater part of it is concave in adaptation to the heart, enclosed in the pericardium, the concavity being greater m the case of the left lung on account of the projection of the heart to the left side. About the junction of the anterior two-thirds and posterior third this surface presents a vertical fissure, called the hilum pul- monis, at which the root of the lung is situated. The inner surface of the right lung, behind the hilum, is related to the oesophagus, and the corresponding portion of the inner surface of the left lung presents part of the aortic groove, vertically placed and produced by the descending thoracic aorta. Anterior to the lower part of this groove the left lung is related to the oesophagus, but less Fig. 387. — Diagram showing the Heart and Lungs in Situ. 1. Tricuspid Orifice 3. Mitral Orifice 2. Pulmonary Orifice. 4. Aortic Orifice X, Region of Latham's Circle intimately than the right lung. The inner surface of the right lung presents the following grooves above the level of the hilum, named in order from below upwards : (i) azygos, for the right azygos vein ; (2) caval and innominate, for the superior vena cava and right innominate vein ; and (3) arterial, for the innominate artery. The inner surface of the left lung presents the following grooves above the level of the hilum : (i) the commencement of the aortic groove, transversely disposed, for the arch of the aorta ; (2) the subclavian groove, for the left subclavian artery, leading upwards from the preceding ; and (3) an indefinite groove, anterior to the subclavian groove, for the left innominate vein. The borders are anterior and posterior. The anterior border is thin and short, and overlaps the jxjricardium, more .so during THE THORAX 949 inspiration than expiration, but leaving an area of the pericardium uncovered, which is known as the area of precordial diilness. The anterior border of the right lung keeps behind the sternum as low as the sixth right costal cartilage. The corresponding border of the left lung, beyond the lower border of the fourth left costal cartilage, presents a deep V-shaped notch, called the cardiac notch, for the reception of the apical portion of the heart, enclosed in the pericardium. The posterior border is elongated, thick, and round, and it occupies the pulmonary groove of the tnorax, by \\v^ side of the thoracic portion of the vertebral column. Each lung is divided into two lobes, upper and lower, by au extensive, oblique, and deep fissure, which penetrates almost to Groove for Subclavian Artery, Groove for Innominate Vein Upper Lobe ,Groove for Subclavian Artery _ Groove for Innominate Vein Upper Lobe Lower Lobe ' Interlobar Fissure Cardiac Notch Interlobar Fissure Lower Lobe Fig. 388. — The Lungs (Anterior View). A, the Right Lung ; B, the Left Lung. the hilum. So deep is this fissure that, unless adhesions have formed, the Irnig appears to consist of two halves. The fissure commences on the inner surface, near the posterior border, about 3 inches below the apex. It then turns round the posterior border, and passes obliquely downwards and forwards over the outer sur- face to the basal margin. In the case of the right Itmg the fissure joins the basal margin some little distance from the lower end of the anterior border ; but, in the case of the left lung, the fissure joins the basal margin distinctly farther forwards. A good ready guide to this fissure is the lower border of the pectoralis major muscle, as it forms the anterior fold of the axilla. 950 A MANUAL OF ANATOMY The upper lobe is comparatively small, and includes the apex, about the upper 3 inches of the posterior border, the anterior border, and, in the case of the left lung, practically all that can be auscultated anteriorly. The lower lobe is of large size, and lies behind and below the great pulmonary fissure. It includes the base, the posterior border except the upper 3 inches, and prac- tically all that can be auscultated posteriorly. By means of the great pulmonary fissure each lung, as stated, is divided into two iooes. In the case of the left lung the division proceeds no further. In the case of the right lung, however, there is an additional fissure, which extends from the chief fissure, at Right Bronchus Right Pulmonary^ Artery *^^ Right Pulmonary ,.-,-,^.\ , Veins ^^§{t\) . Left Pulmonary Artery Left Bronchus Fig. 389. — The Roots of the Lungs (Anterior View). the posterior border, horizontally forwards over the outer surface to the anterior border at about the level of the lower margin of the fourth right costal cartilage, which corresponds to the com- mencement of the cardiac notch on the anterior border of the left lung. This additional fissure cuts off from the upper lobe a tri- angular or wedge-shaped portion, which is called the middle lobe. Differences between the two lungs — (i) The right lung has two fissures and three lobes, whilst the left lung has only one fissure and two lobes. (2) The anterior border of the right lung is unin terrupted, whilst that of the left lung presents interiorly the cardia i THE THORAX 951 notch. (3) The right lung is larger and heavier than the left, the weight of the right being about 20 ounces and that of the left about 18 ounces. (4) The rigit lung is shorter than the left, this being due to the fact that the liver causes the right half of the dia- phragm to rise higher than the left half. (5; The right lung is broader than the left, because the heart projects more to the left side than to the right. Vertical Extent of the Lungs. — In the mammarj' line the right lung descends as low as the sixth rib ; in the mid-axillary line, as low as the eighth rib ; and, in the scapular line (inferior angle of the scapula), as low as the tenth rib. The lower limits of the left lung exceed those of the right by about the depth of a rib. Root of the Lung. — ^The root is situated at the hilum pulmonis on the inner surface. Its chief constituents are as follows : (i) the bronchus or air-tube ; (2) the pulmonary artery, which conveys venous blood to the lung ; and (3) the two pulmonary veins, which convey the arterial or oxygenated blood from the lung to the left auricle of the heart. In addition to these constituents there are (a) the bronchial arteries and veins, (6) the pulmonary' lymphatic vessels, (c) the pulmonary nerves, and (d) the bronchial Ijinphatic glands. All these constituents are connected by areolar tissue, and the entire root is invested by the pleura. Relations. — The following relations are common to both roots : in front, the phrenic nerv^e, with the superior phrenic artery, and the anterior pulmonary plexus of nenes ; behind, the pneumo- gastric nerve and the posterior pulmonary plexus of nerves ; and, below, the ligamentum latum pulmonis. Special Relations — Right Root — Anterior. — The superior vena cava and the upper part of the right auricle of the heart. Superior. — ^The right azygos vein, as it arches forwards over the right bronchus to open into the superior vena cava. Posterior. — The right azygos vein. Left Root — Superior.— The arch of the aorta. Posterior. — ^The descending thoracic aorta. Relative Position of the Chief Constituents.— The relation from before backwards is the same on each side, and is as foUows : (i) the upper of the two pulmonary veins ; (2) the pulmonary artery ; and (3) the bronchus. The relation from above downwards differs on the two sides. On the right side the relation is bronchus, pul- monary artery, and pulmonary veins ; and, on the left side, pul- monary artery, bronchus, and pulmonary veins. The difference in the position of the bronchus on each side is due to the fact that the right bronchus gives off a branch known as the eparterial bronchus, which lies above the right pulmonary artery, the larger portion of the right bronchus and the whole of the left bronchus being hyparterial. Straetare of the Langs — The trachea divides into two bronchi, right and left, the structure of which is similar to that of the trachea. The right bronchos, at about J inch from its origin, gives oflF superiorly a branch 952 A MANUAL OF ANATOMY called the cparterial bronchus, for the upper lobe of the right lung and beyond this point, where it is now hyparterial, it divides into two branches one for the middle, and the other for the lower, lobe. The left bronchus is entirely hyparterial. and divides into two branches, one for the upper and the other for the lower, lobe of the left lung. The structure of these primary divisions of the brorcni is similar to that of the bronchi themselves. Within each lung these^ primary divisions undergo subdivision, to a certain extent dichotomously, .^ut the ramifications are chiefly due to branches being given oil laterally, and these never anastomose. The ramifications of tlie air- tubes within the lungs are called the bronchial tubes, and their ultimate subdivisions within the lobules are known as the bronchioles. Each bron- chiole transmits air to and from a group of infundibula, or ultimate lobules. _ haen lobular bronchial tube, after entering a lobule, divides into as many Dronchioles as there are groups of infundibula or ultimate lobules. Each Infundibulum or Ultimate Lobule .-Bronchiole Intercellular Septum Air Cell Lobular Bronchial Tube * Vestibule Fig. 390.- -SCHEME OF A PuLMONARY LOBULE (AFTER L. TeSTUT's 'Anatomie Humaine'). bronchiole, on approaching a cluster of, say, two or three infundibula, pre- sents a dilatation, called the vestibule, and from this vestibule reception- chambers, known as the atria, proceed to the infundibula. An infundibulum or ultimate lobule is an irregular, funnel-shaped passage, closed at one end, and having its walls and closed extremity beset with air-cells or pulmonary alveoli, which also beset, though more sparsely, the walls of the atria. The bronchial tubes within the lungs are destitute of membranous walls posteriorly, and are cylindrical. This is due to the fact that their irregular plates of cartilage are disposed round the circumference of the wall. The muscular fibres are arranged in complete rings round the tubes, and the elastic tissue forms longitudinal bundles. The mucous membrane is freely provided with racemose mucous glands, and is covered with stratified ciliated columnar epithelium. When the tubes, by division, have attained a diameter of about vj>5 inch, the cartilaginous plates disappear, and the walls consist of a THE THORAX 95.^ fibro-elastic membrane and circularly-disposed muscular fibres, with a thin mucous coat, destitute of mucous glands, and covered with simple cihated columnar epitheUum, there being here and there patches of squamous, non- ciliated ceUs. The walls of the vestibule, atria, and air-ceUs are very thm and consist of areolar, elastic, and muscular tissues, the elastic element being specially developed at the margins of the orifices of the cells. This elastic tissue enables the ceUs to recoil after distension. The interior of the vestibule^ atria and air-cells is Uned with a single layer of squamous. non-cUiated epitheUum, which is of extreme delicacy in the air-cells. Upon the outer walls of the ceUs there are dense networks of capillary- bloodvessels, which also per- vade the septa between the cells, these septa being formed by infoldings of the contiguous cell-walls. Each septum contains only one capillary layer. The venous blood is thus brought into the most intimate relation \vath the air, all that separates the two being the very thin walls of the cells and the very delicate walls of the capillary blood- vessels. Moreover, there being only one capillary layer in each intercellular septum, the blood in the septal capillaries is exposed to the air on each side. Summary of the Structure of the Lung. — The lung consists of an im- niense number of lobules, irregularly polygonal in outline, and each of .these is provided with its own bronchial tube. A lobule is composed of groups of infundibula or ultimate lobules, and the lobular bronchial tube, on enter- ing the lobule, divides into as many bronchioles as there are groups of in- fundibula. Each bronchiole, on approaching a cluster of infundibula, presents a dilatation, called the vestibule, from which atria lead to the infundibula. The walls of the infundibula are freely beset with air-cells, which are also present, though more sparsely, on the walls of the atria. Upon the walls of the air-cells are dense networks of capillary bloodvessels, and each inter- cellulcLT septum contains a single capillciry layer. Bloodvessels of the Lungs. — ^Two sets of arteries are associated with each lung, namely, pulmonary and bronchial, the former having to do with the respiratory function of the organ, and the latter with the nutrition of its component tissues. The pulmonary arteries are two in number, right and left. They result from the bifurcation of the pulmonary trunk, and convey venous blood to the lungs. Each artery ramifies freely within the lung, its branches accompanying the bronchial tubes, but they never anastomose with one another. Ultimately they terminate in dense capillary networks which lie upon the walls of the air-cells, and also in the septa between adjacent cells. The pulmonary veins commence as radicles in the capillary net- works already referred to, and they pass to the root of each lung, where they give rise to two pulmonary veins, which proceed to the left auricle of the heart and convey to it arterial or oxygenated blood. The pulmonary veins and their tributaries are destitute of Fig. 391. — Section of Lung (injected). 954 ^ MANUAL OF ANATOMY valves. It is to be noted that the puknonary arteries carry venous blood, whilst the pulmonary veins carry arterial blood. The bronchial arteries convey arterial blood to the lungs for the nutrition of their component tissues. They will be described in connection with the descending thoracic aorta, with which they are associated. The bronchial veins return their blood chiefly into the right azygos and upper left azygos veins respectively. Lymphatics.— The lymphatic vessels of each lung are arranged in two sets — superficial and deep. At the hilum these two sets open into the interhronchial glands. The superficial set receives the lymphatics of the visceral or pulmonary pleura. Nerves. — These are derived from the anterior and posterior pulmonary plexuses, which are formed by the pneumpgastric nerves, aided by branches from the sympathetic. The nerves penetrate as far as the air-cells, upon the walls of which they are regarded as terminating in arborizations. The anterior and posterior pulmonary plexuses will be found described on p. gG/-. Development of the Respiratory Apparatus. The respiratory apparatus consists of the larynx, trachea, and lungs. The earliest indication of it is a median longitudinal groove on the inner aspect of the ventral wall of the oesophageal part of the fore-gut. This groove is called the pulmonary or laryngo-tracheal groove, and it produces an evagina- tion of the ventral wall of the oesophagus. It consists of entoderm, derived from that of the fore-gut, and it is covered by splanchnic mesoderm. This groove gradually deepens, and by the fusion of its lips a longitudinal diver- ticulum of the ventral wall of the oesophageal part of the fore-gut is formed, called the pulmonary or laryngo-tracheal diverticulum. It lies on the ventral aspect of the oesophagus, from which it becomes gradually separated in a caudo-cephalic direction. At the cephalic end, however, the separation is arrested, and a communication (superior laryngeal aperture) persists between this part of the pulmonary diverticulum and the pharyngo-oesophageal tube. The pulmonary diverticulum consists of (i) entoderm, derived from that of the fore-gut, and (2) mesoderm, which invests it. The condition of matters now is that there are two tubes, dorsal or pharyngo- CESOphageal, and ventral or pulmonary (laryngo-tracheal), which communicate freely cephalicwards. Larynx. — The larynx is developed from the cephalic or proximal part of the pulmonary or laryngo-tracheal diverticulum. (see the Larynx). Trachea. — The trachea is developed from the caudal or distal part of the pulmonary or laryngo-tracheal diverticulum, the cartilaginous rings, con- nective tissue and muscular tissue of the trachea being developed from the mcsodermic investment of the primitive diverticulum. Lungs. — The rudiments of the lungs appear as two lung-buds, right and left, which are formed by the bifurcation of the pulmonary diverticulum at its caudal end. Like the diverticulum itself, these buds consist of entoderm, invested by mesoderm. The entoderm of each lung-bud and of its various ramifications furnishes all the epithelial elements, bronchial and alveolar, of the corresponding lung. The mesoderm of the bud and of its various ramifi- cations gives rise to the bloodvessels, connective and muscular tissues, and cartilages of the bronchial tubes, as well as to the visceral pleura. The pedicles of the lung-buds give rise to the bronchi. The right lung-bud gives off three processes or vesicles, and the left lung-bud gives off two processes, and in this THE THORAX 955 manner the three-Iobed condition of the adult right lung and the two-lobed condition of the adult left lung are indicated. Each of these processes gives rise, by budding, to secondary processes, and these in turn give rise, successively, to other processes. This budding goes on very freely, and the ramifications constitute the palmonary lobes. All the buds or processes, which carry along with them an investment of mesoderm, give rise to the ramif^-ing system of bronchial tubes. The ter- minal ramifications form the bronchioles and infandibula. The air-cells or palmonary alveoli are formed as hollow sessile buds or evaginations of the walls of the infundibula, with the cavities of which they communicate freely. As stated, the epithelial cells of the lung-buds and of all their ramifications, as well as the epithelial cells of the pulmonary diverticulum, are developed from the entoderm of the fore-gut. Lungs of the Fcetus. — The lungs prior to birth, having been im- pervious to air, feel solid, Uke Uver, and they would at once sink if placed in a vessel containing water. Superior Mediastinal or Cardiac Glands. — These glands, which are numerous and important, are situated in the superior mediastinum, along the upper aspect of the arch of the aorta, in front of the lower end of the trachea, and along the right and left innominate veins. They receive their afferent vessels from (i) the anterior mediastinal glands, (2) the upper part of the pericardium, (3) the heart, and (4) the thymus body, in early Hfe. Their efferent vessels terminate in the thoracic duct and in the right lymphatic duct. Innominate Veins. — ^These vessels are two in number, right and left, and each is formed by the junction of the internal jugular and subclavian veins behind the inner end of the clavicle. They both lie in the superior mediastinum. The right innominate vein is about an inch in length, and passes downwards with a slight inclination inwards. At the level of the lower border of the first right costal cartilage, close to the sternum, it unites with the left innominate vein to form the superior vena cava. Externally it is closely related to the right phrenic nerve and right pleura ; its internal relation is the upper part of the innominate artery ; and, behind it, is the right pnevmiogastric nerve. The left innominate vein is about 3 inches in length, and passes obliquely inwards and dowTiwards from left to right. As stated, it joins its fellow of the right side to form the superior vena cava. In front of it there are the upper part of the manubrium sterni, the origins of the sterno-hyoid and sterno-th\Toid muscles, and the remains of the thymus body. Behind it are the origins of the innominate, left common carotid, and left subclavian arteries, the left pneumogastric and left phrenic nerves, and two superficial cardiac nerves from the cervical portions of the left pneumo- gastric and left sympathetic. Below it there is the arch of the aorta. There are no valves in the innominate veins. Tributaries. — Each vein receives the following tributaries : (i) the vertebral vein ; (2) the inferior thyroid vein ; (3) the internal 956 A MANUAL OF ANATOMY mammary vein ; and (4) the first intercostal vein. The last-named vessel, however, sometimes opens into the vertebral vein, and occasionally the right inferior thyroid vein opens into the left innominate vein. The left innominate vein receives, as an addi- tional tributary, the left superior intercostal vein. Development. — The right innominate vein is developed from that portion of the right anterior cardinal vein which intervenes between the place where it receives the right subclavian vein and the place where the transverse j ugular vein joins it. The left innominate vein is developed from the transverse jugular vein. Right Bronchus Right Pulmonary^ Artery Left Pulmonary Artery Left Bronchus Cu^^ , Left Pulmo- r\-. i\\ .' jj^y Veins Fig. 392. — The Roots of the Lungs (Anterior View). Superior Vena Cava. — This vessel is formed by the union of the right and left innominate veins behind the lower border of the first right costal cartilage, close to the sternum. It is about 3 inches in length, and descends almost vertically to the level of the upper border of the third right costal cartilage, where it opens into the postero-superior angle of tfie right auricle of the heart. In its course it pierces the fibrous portion of the pericardium. The upper half of the vessel is extrapericardial, and lies in the superior medias- tinum ; but the lower half is intrapericardial, and lies in the middle mediastinum. Relations — Upper Half — External. — The right phrenic nerve and the right pleura. Internal. — ^The lower part of the innominate artery. Lower Half — Internal. — ^The ascending aorta. Postcrior.- The root of the right lung. The serous portion of the pericardium THE THORAX 957 covers the lower part of the vessel except over about its posterior fourth. The superior vena cava is destitute of valves. Tributaries. — ^The chief tributary is the right azygos vein, after it has arched forwards over the right bronchus. It opens into the superior vena cava immediately before that vessel pierces the fibrous portion of the pericardimn. Other minute tributaries are pericardial and mediastinal veins. Development. — The portion of the superior vena cava above the right azygos vein is developed from that part of the right primitive jugular vein which lies below the point where it is joined by the transverse jugular vein ; and the portion below the right azygos vein is developed from the right duct of Cuvier. Inferior Vena Cava. — ^This vessel enters the thorax through the foramen quadratum in the central tendon of the diaphragm, and immediately thereafter it is received within the fibrous portion of the pericardium. Its course in the thorax is practically nil, as it may be said to open at once into the postero-inferior angle of the right auricle of the heart. Thoracic Aorta. — The thoracic aorta extends from the base of the left ventricle of the heart to the level of the lower border of the body of the twelfth thoracic vertebra. At this point it passes through the aortic opening of the diaphragm, and thereafter enters upon the abdominal part of its course. It passes at first upwards and to the right ;. thereafter it sweeps, in an arched manner, up- wards, backwards, and to the left, over the root of the left lung ; and finally it descends in close contact with the vertebral column, lying at first upon its left side, but subsequently in front of it. It is therefore conveniently divided into three parts, namely, the ascending aorta, the arch of the aorta, and the descending aorta. Ascending Aorta. — ^The ascending aorta commences at the base of the left ventricle of the heart, behind the left border of the sternum, on a level with the lower margin of the third left costal cartilage, and it terminates at a point behind the right border of the sternum on a level with the upper margin of the second right costal cartilage. Its course is upwards and to the right, with an inclination forwards. It lies in the middle mediastinum, and within the fibrous pericardimn, which ensheathes it, and, for about the first i| inches of its course it is enclosed, along with the ad- jacent portion of the pulmonary arterj^ in a sheath formed by the serous part of the pericardium. The ascending aorta measures about 2 inches in length. At its commencement it presents three bulgings, which correspond to the sinuses of Valsalva in the interior and lie opposite the segments of the aortic valve. The bulgings are disposed as right antero-lateral, left antero-lateral, and posterior respectively. Along the right side of the vessel there is another somewhat extensive dilatation, called the great sinus of the aorta. Relations — Anterior. — ^The root of the pulmonary artery and the right auricular appendix, at first, and subsequently the first piece 958 A MANUAL OF ANATOMY of the body of the sternum, from which it is separated by the peri- cardium, right pleura, and anterior margin of the right lung. Posterior. — The right pulmonary artery and the left auricle. Right. — The superior vena cava, and the right auricle. Left. — ^The trunk of the pulmonary artery. Branches. — ^These are the two coronary arteries, right and left. The right coronary artery arises from the right antero-lateral sinus of Valsalva. Passing forwards between the right auricular appendix and the root of the pulmonary artery, it enters the right auriculo-ventricular groove, which it traverses from front to back as far as the commencement of the inferior interventricular groove. At this point it divides into two branches, transverse and descend- ing. The transverse branch enters the posterior part of the left auriculo-ventricular groove, in which it anastomoses with the transverse branch of the left coronary artery. The descending branch traverses the inferior interventricular groove as far as the region of the apex, where it anastomoses with the descending branch of the left coronary artery. The right coronary artery furnishes branches to the right auricle and to both ventricles. One, of large size, called the right mar- ginal branch, passes along the right border, or margo acutus, towards the apex. The left coronary artery arises from the left antero-lateral sinus of Valsalva, and is at first concealed by the root of the pulmonary artery. It then passes forwards between the pulmonary artery and the left auricular appendix, and divides into two branches, transverse and descending. The transverse branch enters the left auriculo-ventricular groove, which it traverses from front to back, anastomosing posteriorly with the transverse branch of the right coronary artery. The descending branch traverses the antero- superior interventricular groove as far as the region of the apex, where it anastomoses with the descending branch of the right coronary artery. The left coronary artery furnishes branches to the left auricle and to both ventricles. One, of large size, called the left marginal branch, springs from its transverse branch and passes along the left border, or margo obtusus, towards the apex. Development. — The ascending aorta, along with the trunk of the pul- monary artery, is developed from the aortic bulb. Arch of the Aorta. — ^The arch of the aorta commences behind the right border of the sternum, on a level with the upper maigin of the second right costal cartilage, and it terminates on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes the descending aorta. It passes upwards, backwards, and to the left, sweeping over the root of the left lung, and, when it reaches the left side of the body of the fourth thoracic^ vertebra, it descends. The height to which the arch reaches cor-' responds to the centre of the manubrium sterni, which is about THE THORAX ^59 I inch below the upper border of the manubrium. It lies in the superior mediastinum, and its left side is in close relation with the left pleura. Relations — Anterior. — ^The left phrenic and left pneumogastric ... Left Common Carotid Arttry Scalenus Anticus Muscle Left Pneumogastric Nerve Left Subclavian Artery (Third Part) Left Phrenic Nerve Left Superior Intercostal Artery Cervical Cardiac Branches of Left Symp. and Vagus Superficial Cardiac Plexus Left Bronchus Fig. 393. — Dissection of the Posterior Wall of the Thorax. nerves, the former being on the right side of, and anterior to, the latter. Between these two nerves are the superior cervical cardiac branch of the left sympathetic and the inferior cervical cardiac branch of the left pneumogastric, both on their way to the super- 96o A MANUAL OF ANATOMY ficial cardiac plexus, which they form. All these nerves are over- laid by the left pleura. Farther back than these nerves is the left superior intercostal vein. The remains of the . thymus body constitute an additional anterior relation. Posterior. — ^The trachea, deep cardiac plexus of nerves, oesophagus, thoracic duct, and left recurrent laryngeal nerve. Superior. — The left innominate vein, and the origins of the following three great arteries, named in order from right to left, and also from before backwards : the innominate, the left common carotid, and the left subclavian. Inferior. — The left bronchus, the bifurcation of the pulmonary artery, the superficial cardiac plexus of nerves, the left recurrent laryngeal nerve, and the ligamentum ductus arteriosi. The last- named fibrous cord is attached to the back part of the concavity of the arch, immediately beyond the level of the origin of the left subclavian artery. The arch presents a constriction immediately beyond the origin of the left subclavian artery, called the aortic isthmus, and this is succeeded by a short fusiform dilatation, known as the aortic spindle of His. These conditions are best marked in the foetus. Branches. — ^These are three in number, namely, the innominate, left common carotid, and left subclavian arteries. They arise in the order named, proceeding from before backwards, and also from right to left. Innominate Artery. — ^This vessel is the first and largest of the three branches which arise from the arch of the aorta. It springs from the upper aspect of the arch rather above the level of the upper border of the second right costal cartilage, and it terminates behind the upper border of the right sterno-clavicular joint by dividing into the right common carotid and right subclavian arteries. It is from i| to 2 inches in length, its direction is upwards and outwards, and it lies in the superior mediastinum. Relations — Anterior. — ^The right half of the manubrium sterni, ■ with the origins of the right sterno-hyoid and sterno-thyroid muscles ; the left innominate and the right inferior thyroid veins ; the right sterno-clavicular joint ; and some remains of the thymus body. Posterior. — ^The trachea at first, but, as the artery ascends obliquely to the right, it leaves the front of the trachea and is placed on its right side. The three cervical cardiac branches of the right sjnnpathetic also lie behind the artery on their way to the deep cardiac plexus. Right. — ^The right pleura ; the innominate vein, with the right pneumogastric nerve behind it ; the sui:)erior .vena cava ; and the right phrenic nerve. Left. — ^The left common carotid artery, and the trachea, in this order from below upwards. Branches. — These are terminal, and are two in number, namely, the right common carotid and the right subclavian. The artery, as a rule, gives off no branches in its course. Occasionally, how- ever, it gives origin to a vessel, of variable size, called the arteria ihyroidea ima (lowest thyroid artery). The interest attached to this occasional branch is that, in ascending to the isthmus of the THE THORAX 961 thyroid body in the neck, it lies in front of the trachea, and would be endangered in perfoiming the low operation of tracheotomy. Varieties. — (i) The innominate artery may be shorter or longer than usual. (2) In cases of high bifurcation the artery may so encroach upon the trachea as to be endangered in performing the low operation of tracheotomy. Left Common Carotid Artery in the Thorax. — This vessel arises from the upper aspect of the arch of the aorta, just to the left of, and posterior to, the origin of the iimominate artery. It lies in the superior mediastinum, and its direction is upwards and to the left. Having reached the posterior aspect of the left sterno- clavicular joint, it enters upon the cervical part of its course. Relations — Anterior. — ^The left half of the manubrium stemi, with the origins of the left stemo-hyoid and sterno-thyroid muscles, but these structures lie at a little distance from the vessel ; the left innominate vein ; and some remains of the thymus bod}'. Pos- terior.— ^The trachea at first, and subsequently the oesophagus (which here deviates slightly to the left of the trachea), and the thoracic duct. Right. — ^The innominate artery at first, and there- after the trachea. Left. — ^The left pneimiogastric and left phrenic nerves, with the superior cervical cardiac branch of the left sympa- thetic and the inferior cervical cardiac branch of the left pneumo- gastric ; and the left pleura and lung. The thoracic portion of the left subclavian artery is on the left of, and posterior to, the vessel, but at a little distance from it. The thoracic portion of the left common carotid artery gives off no branches. First Part of the Left Subclavian Artery in the Thorax.— This vessel arises from the upper aspect of the arch of the aorta, a little to the left of, and posterior to, the origin of the left common carotid artery. It lies deeply in the superior mediastinum, and is almost parallel to the thoracic portion of the left common carotid, its course being nearly vertical. Relations — Anterior. — ^The left common carotid artery ; the left pneumogastric and left phrenic nerves, with the superior cervical cardiac branch of the left sympathetic and the inferior cervical cardiac branch of the left pneumogastric, all these nerves lying between it and the left common carotid artery ; and the left in- nominate vein. Posterior. — ^The oesophagus, and the thoracic duct. Right. — ^The trachea, and the left recurrent laryngeal nerve. Left. — The left pleura, and the inner aspect of the left lung, the latter being grooved by the vessel. The thoracic portion of the left subclavian artery gives off no branches. Varieties of the Aorta — i. Position. — (a) The arch of the aorta may rise IS high as the upper border of tlie manubrium stemi, or it may stop short of the level of the centre of the manubrium, (b) It may be a right aortic arch, instead of a left, in which cases there may, or may not, be a transposition of the viscera. The presence of a right aortic arch is due to its formation from the fourth right arterial arch, and the persistence of the right primitive dorsal aorta. 61 962 A MANUAL OF ANATOMY Fig. 394. — ^The Aorta in the Thorax, and the Principal Arteries of THE Head and Neck. 1. Arch of the Aorta 2. Aortic Isthmus .1 Aortic Spindle 4. Descending; Aorta 5. Coronary Arteries (from Ascending Aorta) 6. Innominate Artery 7. Left Common Caroti'l 8. Left Suliclavian 9. Right Common Carotid 10. Right Subclaviarj 11. External Carotid 12. Internal Carotid 13. Internal Maxillary 14. Superficial Temporal 15. Vertebral >6. Internal Mammary 17. Thyroid Axis 18. Inferior Thyroid 19. Transverse Cervical 20. Suprascapular 21. Superior Thyroid 22. Lingual 23. Facial 24. Occipital 25. Posterior Auricular 96. Ascending Pharyngeal 27. Transverse Facial 28. Aortic Intercostals 29. Lig. Ductus .\rteriosi THE THORAX 9^3 2. Branches ol the Arch and their Positions. — Varieties in these respects are very numerous. The normal number of branches arising from the arch is three. There may, however, be four. The most common additional branch is the left vertebral artery, its place of origin being between the left common carotid and left subclavian arteries. The right vertebral artery sometimes arises from . the arch, but this is somewhat rare. An arteria thyroidea ima may arise from the arch betw-een the innominate and left comm.on carotid arteries. In rare cases the internal mammary artery, or the inferior thyroid, may spring from the arch. The innominate artery may be absent, in which cases the right subclavian and right common carotid have independent origins. Under these circumstances the right subclavian artery may be the last of the branches from the upper part of the arch, and, when this is so, in order to reach the right side of the neck, it crosses in front of the vertebral column, lying behind the oesophagus, or between the trachea and the oesophagus. Development of the Arch of the Aorta and its Branches. — As already stated, the ascending aorta is developed, along with the pulmonary artery, from the aortic bulb. The arch of the aorta is developed chiefly from the fourth left arterial arch, but slightly also from the root of the left primitive ventral aorta, that is, the part as high as the fourth left arterial arch. The innominate artery is developed from the root of the right primitive ventral aorta — that is, the part as high as the fourth right arterial arch. The left common carotid artery is developed from that portion of the left primitive ventral aorta which lies between the fourth and third left arterial arches. The left subclavian artery is developed from a segmental artery. For the description of the descending aorta, see p. 1023. Pulmonary Artery. — ^This is the great vessel which, by means of its right and left divisions, carries the venous blood from the right ventricle of the heart to the lungs. It is therefore an example of an artery which conveys venous blood, and in this respect resembles the hypogastric and umbilical arteries of the foetus. It arises from the infundibulum, or conus arteriosus, of the right ventricle of the heart, on a level with the upper margin of the third left costal cartilage at its junction with the sternum. It is directed upwards and backwards, and, after a course of about 2 inches, breaks up into two divisions, right and left, within the concavity of the arch of the aorta. The vessel lies in the middle mediastinum, and, along with the ascending aorta, it is contained within the pericardium, the serous portion of which forms one common sheath for the two arteries over about the first i^ inches of their course. Relations — Anterior. — ^The sternal extremity of the second left intercostal space and second left costal cartilage ; and the left pleura and left lung. Posterior. — ^The root of the ascending aorta ; the commencement of the left coronary artery ; and the left auricle of the heart. Right. — ^The right coronary artery ; the right auricular appendix ; and the ascending aorta. Left. — ^The left coronary artery ; and the left auricular appendix. The only branches of the artery are the two terminal divisions. The right pulmonary artery passes outwards to the right, behind the ascending aorta and superior vena cava, to the root of the right lung, where it divides into two branches, upper and lower. The upper branch is distributed to the upper lobe, and the lower branch, which is the larger of the two, is distributed to the middle and lower lobes. cj64 A MANUAL OF ANATOMY The left pulmonary artery passes outwards to the left, in front of the left Ijronchus and descending aorta, to the root of the left lung, where it divides into two branches, one for the upper, and the other for the lower, lobe. The ligamentum ductus arteriosi is attached to the upper aspect of its root. The right pulmonary artery is larger and longer than the left. Development. — The trunk of the pulmonary artery, along with the ascending aorta, is chiefly developed from the aortic bulb, but a small portion of it is formed by the commencement of the sixth left arterial arch, which remains con- nected with that portion of the aortic bulb which becomes partitioned off to form the pulmonary trunk. The right and left pulmonary arteries are developed as branches from the sixth left arterial arch near its commencement, the remainder of that arch giving rise to the ductus arteriosus of the foetus. Ligamentum Ductus Arteriosi. — ^This is a fibrous cord which is the remains of an important vessel, peculiar to foetal life, called the ductus arteriosus. It extends from the upper aspect of the root of the left pulmonary artery to the under surface of the arch of the aorta, immediately beyond the level of the origin of the Teft subclavian artery. Its direction is upwards, backwards, and slightly to the left. During foetal life the right and left pulmonary arteries are of small size, and the ductus arteriosus conveys the greater part of the venous blood from the right vfentricle of the heart into the aorta at a point beyond the origin of the left subclavian artery. None of this blood, therefore, can pass into the great vessels which spring from the upper aspect of the arch of the aorta. Development. — The ductus arteriosus is developed from the dorsal part of the sixth left arterial arch. Pulmonary Veins. — ^These vessels carry the arterial or oxygenated blood from the lungs to the left auricle of the heart. Though they are called veins, they contain arterial blood, and in this respect resemble the umbilical vein of the foetus. They are four in num- ber, two right and two left, and, at the root of each lung, the upper of the two is on a more anterior plane than the lower. The right veins pass behind the superior vena cava and the right auricle, and the left veins pass in front of the descending aorta. All four vessels open into the left auricle on its posterior aspect. On leaving the roots of the lungs the veins are said to receive small bronchial tributaries from the adjacent bronchial tubes and glands. The right pulmonary veins are larger and longer than those of the left side. Pneumogastric Nerves in the Thorax. — ^These nerves, right and left, differ so much from each other in their course and relations as to require separate descriptions. The right pneumogastric, or vagus, nerve, having descended in front of the first part of the. right subclavian artery," and having given off its inferior or recurrent laryngeal branch at the lower border of that vessel, enters the thoracic cavity. It then descends in the superior mediastinum behind the innominate vein, and, inclining backwards, it reaches the right side of the trachea, alontj which it courses to the posterior aspect of the root of the right lung. THE THORAX 965 p.f?,'? AJ^ Behind the root of the right lung the nerve becomes flattened out and breaks up into numerous branches, which are disposed in a plexiform manner, and constitute the right posterior pulmonary plexus, from which branches are given off to the right lung. From the lower part of this plexus the nerve issues in the form of two cords, which descend in the posterior mediastinum upon the right side of the oesophagus, or gullet, and communicate freely with the corresponding cords of the left side. In this manner a plexus is formed, which is called the plexus gulce. Subsequently the two cords of the right side unite to form a single ner\^e, which descends on the posterior surface of the oesophagus, and enters the abdomen through the oeso- phageal openingof the diaphragm to be distributed to the posterior surface of the stomach. The left pneumcgastric, or vagus, nerve enters the thoracic cavity between the left common carotid and left subclavian arteries, and descends in the superior mediastinmn behind the left innominate vein. It then passes in front of the arch of the aorta, having the left phrenic nerve on its right side and an- terior to it, with the intervention of the superior cervical cardiac branch of the left sympathetic and its own inferior cervical cardiac branch. At the lower border of the arch it gives off its inferior or recurrent laryn- geal branch, and then passes to the posterior aspect of the root of the left lung. Behind the root of the left lung the nerve, as on the right side, becomes flattened out and breaks up into numerous branches, which are disposed in a plexiform manner, and constitute the left posterior pulmonary plexus, from which branches are given off to the left lung. Frori the lower part of this plexus the nerve, as on the right side, issues in the form of two cords, which descend m the posterior mediastinum upon the left side of the oesophagus or gullet, and communicate freely with the corresponding cords of the right side. In this manner, as stated, a plexus is formed, which IS called the plexus gulce. Subsequently the two cords of the left side unite to form a single nerve, which descends on the anterior )7i!i. 395. — Scheme of Pneumogas- TRic Nerve in Thorax and Abdomen (Flower). C.P. Branches to Cardiac Plexus P. P.P. Branches to Posterior Pul- monary Plexus A. P. P. Branches to Anterior Pul- monarj' Plexus T.S.G. Branches from Upper Thoracic Ganglia of Sympathetic P.O. Plexus fiute G. B. Gastric Branches 966 A MANUAL OF ANATOMY surface ol the oesophagus, and enters the abdomen through the oesophageal opening of the diaphragm, to be distributed to the anterior surface of the stomach. Differences between the Right and Left Pneumogastrie Nerves. Right Pneumogastrie Nerve. 1. Descends in front of first part of right subclavian artery. 2. Gives off its recurrent laryngeal branch at lower border of right subclavian artery. 3. Lies behind right innominate vein. 4. Lies on right side of trachea. 5. Lies at first on right side of oesophagus, and then behind it. 6. Ramifies on posterior surface of stomach. Left Pneumogastrie Nerve. 1. Descends between left common carotid and left subclavian arteries. 2. Passes behind left innominate vein. 3. Crosses in front of arch of aorta. 4. Gives off its recurrent laryn- geal branch at lower border of arch. 5. Lies at first on left side of oeso- phagus, and then in front of it. 6. Ramifies on anterior surface of stomach. Branches. — ^These are as follows : the left inferior or recurrent laryngeal ; cardiac, from the right nerve ; pulmonary ; oesophageal ; and pericardial. The lefl inferior or recurrent laryngeal nerve arises from the left pneumogastrie in front of the arch of the aorta, on a level with its lower border. It passes backwards within the arch at the place of attachment of the ligamentum ductus arteriosi, and then it turns upwards behind the arch. Having reached the groove between the trachea and the oesophagus, it ascends therein to the neck, where its subsequent course and distribution will be described. In the thorax the nerve, which contains fibres derived from the bulbar or accessory portion of the spinal accessory nerve, furnishes a few cardiac branches to the deep cardiac plexus as it winds round the arch of the aorta. The right inferior or recurrent laryngeal nerve is extra-thoracic, inasmuch as it arises from the right pneumogastrie at the root of the neck, and it winds round the first part of the right subclavian artery. The recurrent course of the right and left recurrent laryngeal nerves is brought about by the change in position which the heart and great vessels undergo in the course of development. In early embryonic life each recurrent laryngeal nerve passes inwards to the larynx below the corresponding sixth arterial arch. This arch on the right side, together with the fifth, disappears, and the right recurrent laryngeal nerve then becomes related to the fourth right arterial arch, from which the first part of the right subclavian artery is developed. The sixth left arterial arch gives rise to the ductus arteriosus, which, however, becomes obliterated, and then the left recurrent laryngeal nerve becomes related to the fourth left arterial arch (the fifth having dis- appeared) at the place where it receives the ductus arteriosus, and from this fourth left arch the arch of the aorta is developed. As the heart and great vessels descend from the neck into the thorax each recurrent laryngeal THE THORAX 967 nerve is necessarily dra\v-n downwards, and the right nerve becomes recurrent round the first part of the right subclavian artery (the original fourth right arterial arch), whilst the left nerve becomes recurrent round the arch of the aorta (the original fourth left arterial arch) at the place of attachment of the ligamentum ductus arteriosi. The cardiac branches of the right pneumogastric are two or three in number, and they descend upon the trachea to the deep cardiac plexus. (The cardiac branches on the left side are derived, as stated, from the left recurrent laryngeal nerse as it winds round the arch of the aorta.) The pulmonary branches are arranged in two sets, anterior and posterior. The anterior fidmonary branches are two or three in number, and arise from the parent trunk before it disappears behind the root of the lung. They pass to the anterior aspect of the root, and, being joined by sympathetic twigs, they form the anterior pulmonary plexus, which is reinforced by twigs from the deep cardiac plexus, and, in the case of the left anterior pulmonary plexus, by twigs from the superficial cardiac plexus. The branches of the anterior pulmonary plexus enter the limg, and accompany the ramifications of the bronchial tubes. The posterior pulmonary branches arise from the pneumogastric nerve behind the root of the lung. They are larger and more numerous than the anterior branches, and, being joined by twigs from the second, third, and fourth thoracic sympathetic ganglia, they form the posterior pulmonary plexus. The iDranches of this plexus, like those of the anterior, enter the limg, and accompany the ramifications of the bronchial tubes. The (esophageal branches arise chiefly from the plexus guise, below the level of the roots of the lungs, and they are distributed to the portion of the oesophagus which occupies the posterior mediastinum. Other oesophageal branches, however, arise above the level of the roots of the lungs, and are distributed to the portion of the oeso- phagus which occupies the superior mediastinum. The pericardial branches arise from the plexus guise, and are dis- tributed to the pericardium, which they enter from behind. Summary ol Branches. Right Pneumogastric Nerve. Left Pneumogastric Nerve. Cardiac. Recurrent Lar^-ngeal (which gives off Anterior Pulmonary. Cardiac branches). Posterior Pulmonary. Anterior Pulmonary. QEsophageal. Posterior Pulmonary'. Pericardial. (Esophageal. Pericardial. Cardiac Plexus. — ^The cardiac plexus is one of three large pre- vertebral plexuses associated with the s^Tupathetic system, the other two, namely, the epigastric or solar and the hypogastric, being situated in the abdominal cavity. The plexus is situated partly in the concavity of the arch of the aorta, and partly upon 968 A MANUAL OF ANATOMY the trachea above the bifurcation and behind the aortic arch. It is formed by branches of the pneumogastric and sympathetic nerves, and consists of two portions, superficial and deep, which communicate with each other. The superficial cardiac plexus, which is comparatively small,, is situated in the concavity of the arch of the aorta, between the ligamentum ductus arteriosi and the right pulmonary artery. It is formed by (i) the superior cervical cardiac branch of the left sympathetic, and (2) the inferior cervical cardiac branch of the left pneumogastric, nerves. These two nerves descend over the arch of the aorta, lying between the left phrenic and left pneumogastric nerves. At the place where the two nerves join there may be a small ganglion, which is known as the ganglion of Wrisberg. Branches. — ^The plexus gives branches to the left anterior pul- monary plexus, and, having received a considerable accession of fibres from the right half of the deep cardiac plexus, it is prolonged into the right coronary plexus. The deep cardiac plexus, of larger size than the superficial, is situated upon the trachea immediately above the bifurcation and behind the arch of the aorta. It is formed by (i) all the cervical cardiac branches of the right sympathetic, namely, superior, middle, and inferior, and of the right pneumogastric, namely, superior and inferior ; (2) one or two cardiac branches from the right recurrent laryngeal nerve ; (3) one or two thoracic cardiac branches from the right pneumogastric ; (4) the middle and inferior cervical cardiac branches of the left sympathetic ; (5) the superior cervical cardiac branch of the left pneumogastric ; and (6) the thoracic cardiac branches of the left recurrent laryngeal nerve. It is arranged in two halves, right and left, which communicate with each other ; the right half also gives a considerable accession of fibres to the superficial cardiac plexus. Each half receives the following branches : Right Half. Left Half. 1. The three cervical cardiac i. The middle and inferior cervical branches of the right sympa- cardiac branches of the left thetic. sympathetic. 2. The two cervical cardiac 2. The superior cervical cardiac branches of the right pneumo- branch of the left pneumo- gastric. gastric. 3. The cardiac branches of the 3. The cardiac branches of the right recurrent laryngeal. left recurrent laryngeal. 4. The thoracic cardiac branches of the right pneumogastric. Branches. — ^The right half of the deep cardiac plexus gives off (i) branches to the right anterior pulmonary plexus ; (2) branches to the right auricle of the heart ; (3) branches to reinforce the right coronary plexus, which is deprived, as stated, from the suj^erficial cardiac plexus ; and (4) a few branches to the left coronary plexus. The left half of the deep cardiac plexus gives off (i) brcinches to the THE THORAX 969 Fig. 396. — Scheme of the Sympathetic Nerve in the Neck, and of the Cardiac Plexus (Flower). LC.G. Inferior Cervical Ganglion. 7c, 8c. To Seventh and Eighth Cervical Nerves V.P. To Vertebral Plexus S.P. To Subclavian Plexus I.C.N. Inferior Cardiac Nerve S.C.O. Superioi Cervical Ganglion. P.N. and G.P. Branches to Pneumogastric and Glosso-pharyngeal ic, 2C, 3c, 4c. Branches to Upper Four Cervical Nerves C P. Carotid Plexus Cav. P. Cavernous Plexus C.G. Branch to Ciliary Ganglion G.D.P. Great Deep Petrosal G.S.P. Great Superficial Petrosal V.N. Vidian Nerve P.N. To Ganglion of Trunk of Pneumogastric H. To Hypoglossal E.C.P. To External Carotid Plexus P.P. To Pharyngeal Plexus S.C.N. Superior Cardiac Nerve M.C.G. Middle Cervical Ganglion. 5c, 5c. To Fifth and Sixth Cervical Nerves I.T.P. To Inferior Thvroid Plexus M.C.N Middle Cardiac Nerve F.T.G. Firit Thoracic GanglioB Cardiac Plezns C.B.Pn. Cardiac Branches of Pneumogastric S.C.P. Superficial Cardiac Plexus G.W. Ganglion of Wrisherg D.C.P. Deep Cardiac Plexus R.A.P.P. Right Anterior Pulmonary Plexus L. A.P P. l.<;ft Anterior Pulmonary Plexus R.C.P. Right Coronary Plexus L.C.P. Left Coronary Plexus 970 A MANUAL OF ANATOMY left anterior pulmonary plexus ; (2) branches to the left auricle of the heart ; and (3) the left coronary plexus. Coronary Plexuses. — ^These are two in number, right and left. The right coronary plexus is formed by branches from (i) the superficial cardiac plexus, and (2) the right half of the deep cardiac plexus. It accompanies the right coronary artery, and furnishes branches to the right auricle and right ventricle of the heart. The left coronary plexus is formed by branches which are derived chiefly from the left half of the deep cardiac plexus, but it also receives a few branches from the right half. It accompanies the left coronary artery, and furnishes branches to the left auricle and left ventricle of the heart. Ganglia are met with in the coronary plexuses, and in the course of the fibres which supply the walls of the auricles. They are also present on the fibres which supply the walls of the ventricles in the region of the auriculo- ventricular groove, but nowhere else. In the heart of the calf the nerves are easily recognised beneath the visceral layer of the pericardium, as they pass across the muscular fibres in an oblique manner. Heart. — ^The heart is a hollow, nmscular organ, which, enclosed within the pericardium, is situated in the middle mediastinum, where it lies obliquely between the two lungs. It is conical in shape, and is free to move within its pericardial sac, except at the base, where it is connected with the great bloodvessels. Its relation to the thoracic wall, during life, is influenced by posture and by the respiratory movements. When a person lies upon the left side, or when the prone position is assumed, the organ is more intimately related to the thoracic wall than in the opposite postures ; and during inspiration it is less intimately connected with the thoracic wall than during expiration. General Relations and Topography. — ^The heart lies obliquely behind the lower three-fourths of the body of the sternum. About two-thirds of the organ are contained in the left half of the thoracic cavity, and about one-third in the right half. The base is directed upwards, backwards, and to the right, and lies opposite the bodies of the middle four thoracic vertebrae, namely, the fifth, sixth, seventh, *and eighth. The apex is directed downwards, for- wards, and to the left, and, during life, it strikes the thoracic wall in the fifth left intercostal space, i| inches below the left nipple, and about J inch within the left mammillary line. This point represents the apex-beat, and is about 3J inches from the median line of the sternum. The antero-superior surface, which is convex, lies behind the lower three-fourths of the body of the sternum and the corresponding costal cartilages, right and left, namely, the third, fourth, fifth, and sixth, more particularly those of the left side. This surface is encroached upon by the pleurae and the thin anterior margins of the lungs. Opposite the cardiac notch on the anterior margin of the left lung there is a small portion which is uncovered by lung, unless during deep inspiration, and this cor- THE THORAX 971 responds with the area of precordial dtdness. Latham's circle is taken as defining this area, and the directions for describing the circle are as follows : ' Make a circle of 2 inches in diameter roimd a point midway between the left nipple and the end of the ster- mma.' Strictly speaking, the area of precordial dulness is tri- angular in conformity to the V-shaped cardiac notch on the anterior margin of the left limg, and it may be mapped out by the following lines : one drawn from the position of the apex-beat to the median line of the sternum on a level with the fourth left costcd cartilage ; another drawn from the position of the apex-beat to the median line of the stemvun at the junction of the body and ensiform pro- cess ; and a third connecting the mesial ends of these two lines, and extending along the middle of the stemvun. The inferior or diaphragmatic surface, which is flat, is directed do\\Ti wards, and rests upon the upper surface of the central tendon of the diaphragm, covered by the serous portion of the pericardiimi. The outline of the heart, in reference to the anterior wall of the thorax, may be indicated, with approximate accuracy, in the following manner : Base. — Draw a line across the sternum on a level with the upper border of the third right, and the lower border of the second left, costal cartilages, and prolong this line for | inch to the right of the sternum, and i inch to the left of it. Inferior (Right) Border, or Margo Acutus. — Draw a line from the sternal end of the sixth right costal cartilage to the position of the apex-beat. This line corresponds to the lower limit of the heart. Right Limit. — Draw a line from the upper border of the third right costal cartUage, ^ inch from the sternum, to the sternal end of the sixth right costal cartilage. This line should be curved outwards to such an extent that its greatest convexity will be i| inches distant from the median line of the sternum. It cor- responds with the right limit of the right auricle. Left Border, or Margo Obtusus vel Rotundus. — Draw a line from the lower border of the second left costal cartilage, i inch from the sternum, to the position of the apex-beat. This line should be slightly curved outwards, but it must not include the left nipple. It corresponds to the left limit of the heart. Course of the Circulation. — The interior of the heart is divided by two septa (interauricular and interventricular) into two halves, right and left, and each half is subdivided by a transverse con- striction into two chambers, cin upper or auricle, and a lower or ventricle, right and left respectively. The auricles, except in the foetus, are completely separated from each other by a septum, and so also are the ventricles ; but the auricle and ventricle of each side communicate freely with each other by the auriculo-ventricular orifice. The right auricle receives the venous blood chiefly from the superior and inferior venae cavae and the coronary sinus. From the right auricle the blood passes into the right ventricle, and thence into the trunk of the pulmonary artery. The right and 972 A MANUAL OF ANATOMY left pulmonary arteries convey it to the lungs, and in passing through the pulmonary capillaries it is oxygenated and becomes arterial blood. It is then taken up by the pulmonary venous radicles, and conveyed to the pulmonary veins, which carry it to the left auricle of the heart. From the left auricle it passes into the left ventricle, whence it is driven into the aorta. The aorta and its various ramifications convey the arterial blood to the different parts of the body, and thereafter it is returned as venous blood to the right auricle of the heart. Exterior of the Heart.— The exterior of the heart presents dis- tinct indications of its division internally into four chambers. Superior Vena Cava Aorta Right Auricular Appendix-, Right Auric'e Right Coronary Artery .Pulmonary Artery ,Conus Arteriosus (Infundibulum) ,,- I>eft Auricular Appendix Left Ventricle . Left Coronary Artery Apex Fig. 397. — The Heart (Anterior View). These take the form of grooves, namely, auriculo-ventricular, interauricular, and interventricular. - The auriculo-ventricular groove, which is deep, divides the heart into auricular and ventricular portions, and it surrounds the organ except in front, where the roots of the aorta and pulmonary artery are situated. The auricular portion is posterior and sujx'rior in jwsition, whilst the ventricular portion is anterior and inferior. The right half of the auriculo-ventricular groove contains (1) the right coronary artery, and (2) the right or small cardiac vein, which latter lies chiefly in its posterior part. The left half of the auriculo- ventricular groove contains (i) the transverse branch of the left coronary artery, {2) the transverse branch of the right coronary THE THORAX 973 artery, which lies in its posterior part ; (3) a portion of the great cardiac or coronary vein, which lies in its anterior part, and also slightly in its posterior part ; and (4) the coronary sinus, which lies in its posterior part. The auricular portion of the heart has the form of a crescent, the horns of which represent the auricular appendices, and are directed forwards. The concavity of the crescent is also directed forwards, and it lodges the roots of the aorta and pulmonary artery, the latter being the more anterior of the two. The walls of the auricular portion are thin, and it is divided into two auricles, right and left. The external indication of this division is the inferauricular groove, which is situated vertically on the posterior surface, to the left of the openings of the superior and inferior venae cavae. This grooA-e corresponds to the posterior attachment of the interauricular septimi in the interior. The greater part of the posterior surface of the auricular portion is formed by the left auricle. The large posterior part of each auricle is called the atrium (' reception- chamber '), and projecting forwards from the anterior and upper part of each atrium there is the auricular appendix. The two auricular appendices embrace between them the roots of the aorta and pulmonary artery'. The right auricle forms the anterior and right part of the base of the heart, and is quadrangular. The superior vena cava enters its atrium at the postero-superior angle, and the inferior vena cava at the postero- inferior angle. Near the latter vein the coronary sinus also opens into the atrium. The right auricular appendix is prolonged forwards from the antero-superior ang^s of the atrium, and inclines to the left in front of the root of the ascending aorta. It is shorter, broader, and less curved than the left auricular appendix, and its margin is notched, but not so much so as in the left appendix. The right auricle is traversed by a groove, called the sulcus terminalis, which extends from the front of the ter- mination of the superior vena cava to the right side of the termina- tion of the inferior vena cava. This groove indicates where the saccus reuniens of embryonic life meets the primitive auricle. The left auricle forms the posterior and left part of the base of the heart. It is quadrilateral, and the greater part of it lies flattened behind the ascending aorta and trunk of the pulmonary artery. The pulmonary veins, two right and two left, open into the posterior part of its atrium. The left auricular appendix is prolonged for- wards from its left aspect, and inclines to the right over the left side of the root of the pulmonary artery. It is longer, narrower, and more curved than the right auricular appendix, and its margin is more deeply notched. The back of the left auricle is related to the oesophagus, with the intervention of the pericardimn, and the small oblique vein of Marshall passes downwards and inwards upon it, to open into the coronary sinus. The ventricular portion of the heart is conical, its walls are thick, and it is divisible into two ventricles, right and left. The ex- 974 A MANUAL OF ANATOMY ternal indication of this division is the interventricular groove, which corresponds to the attachment of the interventricular septum in the interior. This groove consists of two parts, antero- superior and inferior. The aniero-superior interventricular groove extends over the antero- superior surface of the heart from the left side of the root of the pulmonary artery to the inferior border, or margo acutus, to the right of, and near, the apex. At this point it becomes continuous with the inferior interventricular groove. It contains, besides fat, (i) the descending branch of the left coronary artery, and (2) a part of the great cardiac or coronary vein (more Pulmonary Artery Left Pulmonary Veins -- 'J Great Cardiac Vein -j Left Ventricle Superior Vena Cava Right Pulmonary Veins ... Right Auricle Inferior Vena Cava Coronary Sinus .. Right Coronary Artery Right Ventricle The Heart (Posterior View). properly called the antero - superior interventricular vein in this region). The inferior interventricular groove is situated on the in- ferior surface of the heart, and, as stated, is continuous with the preceding. It contains, besides fat, (i) the descending (inferior) branch of the right coronary artery, and (2) the middle cardiac vein (more properly called the inferior interventricular vein). The ventricular portion of the heart presents an apex, a base, two surfaces, and two borders. The apex is directed downwards, forwards, and to the left, and forms the apex of the heart. The left ventricle alone enters into its formation. The base is directed upwards, backwards, and to the right, and is connected with the THE THORAX 975 atria of the auricles and the origins of the aorta and pulmonary ari:ery, the former being behind, and the latter in front. The surfaces are antero-superior and inferior. The antero- superior surface is convex, and is traversed by the antero-superior interventricular groove. As this groove lies near the left border, the greater part of this surface (about two-thirds) is formed by the right ventricle, and the remainder by the left ventricle. In post- mortem examinations, therefore, when the pericardium is opened, the right ventricle is chiefly exposed for inspection. On this aspect of the right ventricle there are the anterior cardiac veins. Its upper and left part is somewhat conical, and is called the in- fundibiilum or conus arteriosus. It gives origin superiorly to the trunk of" the pulmonary artery. The inferior surface is flat, and is traversed by the inferior interventricular groove. As this groove lies near the inferior border, the greater part of this surface (about two-thirds) is formed by the left ventricle, and the remainder by the right ventricle. On this aspect of the left ventricle there are the posterior cardiac veins. The borders are inferior (right) and left. The inferior border is comparatively long, and extends from right to left. It is formed by the right ventricle, and is sharp in outline, from which circum- stance it is known as the margo acutus. The marginal branch of the right coronary artery and one of the anterior cardiac veins lie along it. The left border is shorter than the inferior, and is blunt and round, from which circumstances it is known as the margo obtusiis vel rotundtts. The marginal branch of the left coronary artery lies along it. Interior of the Heart — Right Auricle. — The wall of the auricular appendix is marked by a number of muscular elevations, arranged as closely-set, vertical, parallel bands, like the teeth of a comb, from which circumstance they are called the musculi pectinati. These bands, relatively to each other, are more or less reticular. They are also present on the right wall of the atrium, being more comb-like here than in the appendix, and they terminate posteriorly at a vertical ridge, called the crista terminalis. This crest cor- responds in position to the sulcus terminalis externally, and it has the same significance. Internally and posteriorly the walls of the auricular atrium are destitute of musculi pectinati, and present a smooth appearance. The atrium of the right auricle presents the following openings : the opening of the superior vena cava ; the opening of the inferior vena cava ; the opening of the coronary sinus ; the foramina Thebesii ; and the auriculo- ventricular opening. The orifice of the superior vena cava, which is destitute of a valve, is situated at the postero-superior angle of the atrium. It is directed downwards and forwards, and the upper part of the crista terminalis is continuous with its anterior margin. The orifice of the inferior vena cava is situated at the postero- inferior angle of the atrium, and is directed upwards and inwards. In front of the orifice, and to a certain extent overlapping it, there 976 A MANUAL OF ANATOMY is a crescentic fold of endocardium, which is the remains of the Eustachian valve of foetal life. The convexity of the crescent is continuous with the anterior margin of the orifice of the vein, and the inner horn of the crescent is continuous with the anterior limb of the annulus ovalis, to be presently described. The fold is a somewhat indefinite structure in the adult, being subject to much variety as regards size, and sometimes presenting several small openings. During foetal life, however, the Eustachian valve is of the utmost importance, inasmuch as it directs the blood entering by the inferior vena cava through the foramen ovale into the left auricle. The orifice of the coronary sinus is situated between the vestigial Eustachian valve and the auriculo-ventricular orifice. It is Arch of Aorta Superior Vena Cava Right Pulmonary^' Veins ^^ Pulmonary Artery Right Auricle ._ Pulmonary Orifice — Inferior Vena Cava Left Pulmonary Veins Left Auricle - — Aortic Orifice .Interventricular Septum Fig. 399. — Diagrammatic View of the Interior of the Heart (after Milne Edwards). guarded by a delicate semicircular fold of the endocardium, called the coronary valve, or valve of Thebesius, which, however, is function- ally incompetent. The foramina Thebesii represent several minute openings on the wall of the atrium. Some of these are simply blind recesses, whilst others are the orifices of minute veins, called the vencr minimcB cordis, which return the blood from the wall of the auricle. The auriculo-ventricular, or tricuspid, orifice is situated in the lower and anterior ]xart of the atrium, in front of the orifice of the inferior vena cava, with the intervention oi that of the coronary sinus. It is oval, and, in health, the index, middle, and ring fingers, THE THORA>t '^7*1 held close together and side by side, can be passed through it with- out difficulty. Through this opening the blood passes from the right auricle into the right ventricle, its return being prevented by the tricuspid valve, whi^h will be described in connection with the right ventricle. The so-called hiberde of Lower is an unimportant slight projec- tion, which is situated on the interauricular septum, just below the opening of the superior vena cava and behind the upper part of the fossa ovalis. The posterior wall of the atrimn corresponds to the interauricular septum, and it presents for consideration the fossa ovalis and the annulus ovalis. The fossa ovalis is an oval depression which is situated upon the lower part of the interauricular septum, a little above and to the left of the orifice of the inferior vena cava. It indicates the position of the foramen ovale of the foetal heart, which is a conmiunication between the t\vo auricles through which the blood entering the right auricle by the inferior vena cava passes into the left auricle. The floor of the fossa ovalis is very thin, and is bounded above and at the sides by a prominent, crescentic margin, called the annulus ovalis. The annulus is deficient below, and the concavity of the crescent is directed downwards. Its anterior limb is continuous with the vestigial Eustachian valve. In some cases a minute oblique communication between the two auricles persists in the adult, being situated imder cover of the upper portion of the annulus ovalis. Interior of the Right Ventricle. — WTien exposed to view in the ordinary way the interior of the right ventricle is triangular, the base being directed backwards and upwards, and the apex for- wards and downwards. It is completely separated from the left ventricle by the inter\'entricular septum, which forms the posterior wall of the ventricle, and bulges into it so as to be convex towards it. In transverse section, therefore, the right ventricle is semilunar. Its wall, which is about three times thinner than that of the left ventricle, is thickest at the base, and becomes thinner towards the apex. The capacity of the ventricle is about 4 ounces. Its upper and left part forms the infimdihuluni or coitus arteriosus, from the upper part of which the trunk of the pulmonary artery' springs. The walls of the infundibulum are smooth, but elsewhere the walls of the ventricle are elevated into muscular bands, called columnce carnece. These project into the cavity, and, from their reticular arrangement, they render the wall verj- irregular. According to the manner in which the columnae comeae are attached to the wall, they are arranged in three sets : (i) some are simple elevations, which are attached to the wall by their entire length, as well as by their extremities ; (2) some are attached to the wail only by their extremities, being free elsewhere ; and (3) others are attached only by one extremity. These latter are called musculi fapillarcs. They are conical, and their bases are attached to the 62 978 A MANUAL OF ANATOMY wall of the ventricle. Their free extremities are connected with a number of filiform processes, called chordce tendinece, which pass to the margins and ventricular surfaces of the segments of the auriculo-ventricular valve. When the ventricle contracts, the musculi papillares also contract, and, by tightening the chordae tendineae, they prevent the segments of the auriculo-ventricular valve from being driven back into the auricle. The segments are therefore maintained in contact during the ventricular systole, and no regurgitation of blood from the ventricle into the auricle is allowed, in health. The musculi papillares are arranged in two groups, anterior and posterior, and their bases are attached to the Superior Vena Cava Aoita Annulus Ovalis Fossa Ovalis ^ Pulmonary Artery (opened) Pulmonary Valves Interventricular Septum Left Ventricle Eustachian Valve - Orifice of Coronary - Sinus Thebesian Valve ■'\\ Inferior Vena Cava Tricuspid Valve' Chordae Tendineje Musoulus Papillaris Fig. 400. — The Interior of the Right Auricle and Right Ventricle. wall of the ventricle in the region of the apex of the cavity. The anterior musculus papillaris is of large size, and the posterior is^ usually broken up into two or more secondary papillary muscles. In most hearts a fleshy column, called the moderator hand, is| met with in the right ventricle, which extends from the inter- ventricular septum to the base of the anterior papillary muscle. It is regarded as controlling distension of the right ventricle, which' it effects by the influence it exerts upon the anterior wall. The openings connected with the right, ventricle are two in number, namely, the auriculo-ventricular and jnilmonary. They are situated at the base of the cavity, and are guarded by most important valves. The auriculo-ventricular orifice is situated on the THE THORAX 979 right and posteriorly, whilst the pulmonary orifice is situated on the left and anteriorly, being also on a higher level than the other. Vence minima cordis are said to open into the right ventricle. The auriculo-ventricular, or tricuspid, orifice is, as already stated in connection with the right auricle, oval, and it readily admits the index, middle, and ring fingers held close together. It allows the venous blood to flow from the right auricle into the right ventricle, and, in order to prevent regurgitation of blood from the ventricle into the auricle during the ventricular systole, it is guarded by an important valve, called the right auriculo-ventricular or tricuspid valve. This valve is composed of three segments or cusps, which are covered with endocardium. These project into the cavity of the ventricle, and are triangular. The bases of the cusps are con- tinuous with one another, and form a ring, which is attached to the margin of the auriculo-ventricular orifice. The largest cusp is situated in front, and to the left, of the auriculo-ventricular orifice. It inter\-enes between that orifice and the infrmdibulum, and is known as the left or infundibular cusp. Another cus pis situated behind the auriculo-ventricular orifice, and is in contact with the interventricular septum. It is called the posterior or septal cusp. The third cusp is situated to the right, near the margo acutus, and is called the right or marginal cusp. In the angular intervals between the basal parts of the three large cusps there are usually three small cusps. Each cusp consists of two layers of endocardium, with fibrous tissue between them, especially at their central parts. The middle portion of each cusp is therefore thicker than the marginal portions, these latter being thin and transparent. The margins themselves are notched. The auricular surfaces of the cusps are smooth, but their ventricular surfaces are roughened by the chordae tendineae, which are also attached to the margins. The chordae tendinese are filiform, fibrous processes which are connected, on the one hand, with the wall of the ventricle, and, on the other, with the cusps of the auriculo-ventricular valve. Most of them spring from the two papillary muscles, but a few of them arise from the inter\'entricular septum and from small papillary eminences upon it. Those which are connected with the anterior papillary muscle pass to the internal between the infundibular and marginal cusps ; those which are connected with the posterior papillary muscle and its subdivisions pass to the interval between the septal and marginal cusps ; and those which are connected with the interventricular septum pass to the interval between the infundibular and septal cusps. The connection of the chordae tendineae with the cusps of the valve is of a threefold nature, as follows : (i) the most numerous are connected with the marginal parts of the cusps ; (2) others are connected with the thickened central portion of each cusp ; and (3) a few pass to the basal portion of each cusp, where they are connected with the fibrous ring around the auriculo-ventricular orifice. 98o A MANUAL OF ANATOMY The pulmonary valve guards the orifice of the pulmonary artery, and prevents regurgitation of blood from the trunk of the pulmonary artery into the right ventricle during the elastic recoil of the arterial wall. It is composed of three semilunar or sigmoid segments, and the wall of the artery, opposite each segment, presents a recess, these recesses being called the sinuses of Valsalva. The valve and the sinuses of Valsalva are similar to corresponding structures in connection with the aortic orifice, and will be fully described along with that orifice. Interior of the Left Auricle. — ^The musculi pectinati are present only in the auricular appendix, whereas in the right auricle they are Pulmonary Artery , Lunula ^^Pulmonary Veins Ascending Aorta (opened) - Aortic Seniilunar Valves Interventricular Septum -Chordae Tendinex — Musculus Papillaris Columnje Carneae Fig. 401. — The Interior of the Left Auricle and Left Ventricle. present both in the auricular appendix and on the right wall of the atrium. The wall of the left atrium is entirely smooth. The atrium presents five openings, namely, the openings of the four pulmonary veins, and the auriculo-ventricular opening. The orifices of the four pulmonary veins are situated on the pos- terior wall at either side, two right and two left, and they are destitute of valves. The auriculo-ventricular, or mitral, orifice is situated in the anterior part of the floor of the atrium. It is oval, and, in health, it admits two fingers held side by side, and in close contact. V'ence minimce cordis arc said to open into the left auricle. THE THORAX o8i The inter auricular septum presents a slight depression, limited inferiorly by a faint crescentic ridge, the concavity ot which is directed upwards. These indicate the position of the foramen ovale of the fcetal heart. Interior of the Left Ventricle. — ^The cavity of the left ventricle extends quite to the apex of the heart, and is longer and narrower than that of the right ventricle. It is somewhat conical, the base being directed backwards and upwards. The interventricular septum recedes from the cavity, and is concave towards it. In transverse section, therefore, the left ventricle is oval, or nearly circular. The wall of the left ventricle is about three times thicker than that of the right, the difference being readily accounted for by the fact that the left ven- tricle is concerned with the systemic circulation, whilst the right ventricle has to do with the pulmonary circula- tion, the latter involving a much shorter circuit. The wall of the left ventricle attains its maximum thick- ness about the junction of the upper fourth and lower three- fourths, and it is thin- nest in the region of the apex. The capacity of the ventricle is about 4 ounces. The portion of the cavity immediately below the aortic orifice is known as the aortic vestibule, the walls of which are fibrous. The left ventricle, like the right, is provided with columnae cameae. They are arranged in a very intricate manner, more particularly in the region of the apex and over the posterior wall. The aortic vestibule, and the interventricular septum, at least over its upper part, are destitute of columnse cameae, and present a smooth appearance. The musculi papillares are much larger than those in the right ventricle ; they are two in number, anterior and pos- terior ; and they are attached by their bases to the respective walls of the ventricle, whilst their free ends are connected with the chordae tendineae. The openings connected with the left ventricle are two in number, namely, auriculo-ventricular and aortic. They are situated at the base of the ventricle in close proximity to each other, and are guarded b}^ important valves. The auriculo-ventricular orifice is Interventricular Sepium Ventricle Fig. 402. — Transverse Sections of THE Heart. A, Through Apex (Superior View): B, Through Ventricles (Inferior Vie.v). gSz A MANUAL OF ANATOMY situated on the left and posteriorly, whilst the aortic orifice is situated on the right and anteriorly. The aortic orifice is also the higher of the two. Vence minimce cordis are said to open into the left ventricle. The auriculo-ventricular, or mitral, orifice is oval, and, in health, it admits two fingers held side by side. It allows the arterial blood to flow from the left auricle into the left ventricle, and, in order to prevent regurgitation of blood from the ventricle into the auricle during the ventricular systole, it is guarded by an important valve. This valve is called the left auriculo-ventricular, mitral, or bicuspid valve. It is composed of two large segments or cusps, with two small cusps in the angular intervals between their basal parts. The cusps are similar in shape and structure to those of the tricuspid valve, but, on account of the nature of their work, they are thicker and stronger. They are disposed obliquely, and are of unequal Pulmonary Orifice and Valves Left Coronary Artery.^ Left Ventricle- Section of Left Auricle Mitral Orifice and Valve | Secondary Segment of Mitral Valve Aortic Orifice and Valves Right Coronary Artery ^.... Right Ventricle Tricuspid Orifice and Valve I Section of Right Auricle Fig. 403. — TrtE Auriculo-Ventricular and Arterial Orifices of the Heart, with their Valves (Superior View). (The Auricles have been removed.) size. The larger of the two is placed in front, and to the right, of the orifice. It intervenes between the auriculo-ventricular and aortic orifices, and is known as the anterior or aortic cusp. The smaller cusp is placed behind, and to the left, of the orifice, and is known as the posterior or marginal cusp. The chordae tendinese are attached to the cusps, as in the case of the tricuspid valve. They are, however, fewer in number, and of greater thickness and strength, than on the right side. Function of the Tricuspid and Mitral Valves. — These valves serve to prevent regurgitation of blood from the ventricles into the auricles during the ventricular systole. Whilst the ventricle is being filled, some of the blood gets behind the segments of the auriculo-ventricular valve, that is to say, between each segment and the wall of the ventricle, and the segments are thus carried towards the auriculo-ventricular orifice. When the ventricle is THE THORAX 983 filled with blood, the segments are in contact, and the ventricular systole now takes place. At the same time the musculi papillares contract. Blood is forced against the segments of the valve, but it cannot, in health, enter the auricle, because the segments are maintained in close contact, and are prevented from being driven back into the auricle, by the chordae tendineae, which are under the control of the musculi papillares. If there were no musculi papillares, in which case the chordae tendineae would spring directly from the wall of the ventricle, then the segments of the valve would not be held tight, but would, under the pressure of the blood, be driven back into the auricle, and regurgitation of blood would of necessity occur. The explanation of this lies in the fact that when the ventricle contracts a kind of screwing up or wringing movement takes place in its wall, as, so to speak, in wringing a wet towel. The effect of this peculiar action is to approximate successive parts of the ventricular wall to the auriculo-ventricular orifice, and this would have the effect of relaxing the chordae tendineae, and so allowing the segments of the valve to be driven back into the auricle. The chordae tendineae, however, spring from musculi papillares, and these are elevations of the wall of the ventricle, directed towards the auriculo-ventricular orifice. During the wringing movement, therefore, of the ventricular wall in systole the musculi papillares, as stated, contract, and so maintain the chordae tendineae taut, or tightly drawn. When the mitral valve opposes the entrance of blood into the left ventricle the cardiac affection is known as mitral obstruction (stenosis). When the mitral valve is incompetent, and allows regurgitation of blood to take place from the left ventricle into the left auricle, the cardiac affection is known as mitral regurgitation (incompetence). The aortic orifice is circular, and is separated from the auriculo- ventricular orifice by the anterior or aortic cusp of the mitral valve. It is guarded by the aortic valve, which, by means of its segments, prevents regurgitation of blood from the aorta into the left ventricle during the elastic recoil of the arterial wall. It is composed of three semilunar or sigmoid segments, consisting of fibrous tissue, covered on their ventricular surfaces by endocardium, and on their Orifice of Corpus Arantii Lunula Orifice of Coronary Artery J Coronarj- Artery Fig. 404. — The Aortic Semilunar Valves. arterial surfaces by the endothelial lining of the arter}-. Each segment is attached by its convex border to the wall of the artery at the place where it springs from the ventricle. The other border of the segment is free, and is directed away from the ventricle. Each segment, therefore, is so disposed as to allow the blood to pass freely into the aorta from the left ventricle. The free border of each segment is strengthened by a band of fibrous tissue, and at 9^4 A MANUAL OF ANATOMY the centre of the border there is a small swelling, called the nodule or corpus Arantii. This gives rise to a slight projection, and on either side of it the border is concave. The attached convex border of each segment is also strengthened by fibrous tissue. In addition to these fibrous thickenings, fibrous tissue pervades each segment from the nodule to the attached border, with the exception of the portions immediately below the lateral concave parts of the free border. These portions, in each segment, are semilunar, and are called the lumtlce. They are the thinnest parts of the segment, and are transparent, consisting prac- tically of endocardium and the endo- thelial lining of the artery. The interior of the wall of the aorta presents three well - marked recesses, each of which is placed opposite a segment of the valve. These recesses are called the sinuses of Valsalva, and they are disposed as right antero-lateral, left antero- lateral, and posterior, respectively. The right antero-lateral sinus of Valsalva presents the orifice of the right coronary artery, and the left antero-lateral sinus of Valsalva pre- sents the orifice of the left coronary artery. Each sinus of Valsalva, together with the corresponding segment of the aortic valve, forms a small pocket, and the three pockets open away from the left ventricle, that is to say, in a direction corresponding to the normal blood-flow. Function of the Aortic Valve. — This valve serves to prevent regurgitation of blood from the aorta into the left ventricle during the elastic recoil of the arterial wall close to the heart. During the ventricular systole, when the blood is being driven through the aortic orifice, the aortic valve is passive, and its three seg- ments are applied to the arterial wall. During the elastic recoil of the arterial wall, however, the valve is in action. The first effect of the elastic recoil is to force sufficient blood backwards towards the left ventricle to close the aortic valve. This blood enters the pockets formed by the sinuses of Valsalva and the segments of the valve. The segments are pressed towards the centre of the aortic orifice, and they come into contact in the following manner: the three nodules or corpora Arantii come into close contact at the centre of the aortic orifice, and so close what would otherwise be a small space, and the respective lunula; are closely pressed against one another. In this manner the aortic orifice is completely closed, and regurgitation of blood into the left ventricle is, in health, effectually guarded against. It will be evident that the strain of the backward pressure of blood must be borne by those portions of the segments which are strengthened by fibrous tissue extending from each ijodule to the attached border of each segment. Though the lunul.Te are thin and weak, nevertheless, being, so to speak, doubled up against one another, the more they are pressed upon the more closely they fit together. When the aortic valve offers opposition to the entrance of blood into the aorta, the cardiac affection is called aortic obstruction (stenosis). On the Fig. 405. — The Semilunar Valves of the Aorta (Superior View). I, Left Antero-lateral Sinus of Valsalva ; 2, Right Antero- lateral Sinus of Valsalva; 3, Posterior Sinus of Valsalva ; 4, Right Coronary Artery ; 5, Left Coronary Artery. THE THORAX 985 lather hand, when the aortic valve is incompetent, and allows regurgitation 6i blood to take place into the left ventricle, the cardiac affection is called aortic regurgitation (incompetence). The pulmonary valve, which guards the orifice of the pulmonary artery, is similar to the aortic valve, and the preceding description is, for the most part, applicable to it. The segments of the pul- monary valve are, however, weaker than those of the aortic valve, and the sinuses of Valsalva are destitute of any arterial orifices. These sinuses are disposed as anterior, right postero-lateral, and lejt Postero -lateral, respectively. The function of the pulmonary valve is similar to that of the aortic valve. Interventricular Septum. — This septum completely separates the right and left ventricles. The external indications of its attach- ments are the antero-superior and inferior interventricular grooves. It is thick and, for the most part, fleshy. It is thickest in the region of the apex, and becomes thinner towards the base of the ventricles. It bulges into the right ventricle, so as to be convex on that aspect, whilst it recedes from the left ventricle, so as to be concave towards it. The upper or basal part of the septum pre- sents anteriorly a small portion which is destitute of muscular fibres. This portion is thin, and consists of fibrous tissue, covered on either side by endocardium. It is known as the pars mem- branacea septi, and is developed from the lower part of the septum which divides the aortic bulb into the ascending aorta and trunk of the pulmonary artery. It forms part of the aortic vestibule of the left ventricle. In rare cases the interventricular septum is deficient in the region of the pars membranacea, and a communica- tion thus exists between the right and left ventricles. Topography of the Orifices of the Heart. — The pulmonary orifice is situated on a level with the upper margin of the third left costal cartilage at its junction with the sternum. The aortic orifice, which is more deeply placed than the pulmonary, is situated behind the left border of the sternum on a level with the lower margin of the third left costal cartilage. The tricuspid orifice lies behind the body of the sternum opposite the fourth intercostal spaces and fourth and fifth costal cartilages. The mitral orifice, which is placed very deeply, is situated behind the left border of the sternum on a level with the fourth left costal cartilage. Cardiac Bloodvessels — Arteries. — ^The nutrient vessels of the heart are the coronary arteries, right and left, which arise from the root of the ascending aorta. For a description of these vessels, see p. 958r Veins. — The cardiac veins are as follows : the great or left cardiac or coronary vein ; the coronary sinus ; the posterior cardiac veins ; the middle cardiac vein ; the right or small cardiac or coronary vein ; the anterior cardiac veins ; the oblique vein of Marshall ; and the vense minimae cordis or smallest cardiac veins. With the 986 A MANUAL OF ANATOMY exception of the last-named cardiac veins (vense minimae cordis), all the others are seen upon the exterior of the heart. The great or left cardiac or coronary vein commences at the apex of the heart, and ascends in the antero-superior inter- ventricular groove alongside of the descending branch of the left coronary artery. In this part of its course it is more properly called the antero-superior interventricular vein. It is of large size, and receives tributaries from both ventricles and from the inter- FiG. 406. — Diagram showing the Position of the Heart and its Valvular Orifices in relation to the Anterior Wall of the Thorax. R.A. Right Auricle R.V. Right Ventricle L. A. Left Auricle L.V. Left Ventricle A.A. Arch of Aorta In. Innominate Artery R.S. Right Subclavian Artery R.C.C. Right Common Carotid Artery L.C.C. Left Common Carotid Artery L.S. Left Subclavian Artery S.V.C. Superior Vena Cava Numbers on Sternum. 1. Tricuspid Orifice 2. Pulmonary Orifice 3. Mitral Orifice 4. .\ortic Orifice ventricular septum. On reaching the auriculo-ventricular groove, it enters the left division of that groove, in which it courses along with the transverse branch of the left coronary artery. Having turned round the left margin of the heart, it joins the left extremity of the coronary sinus, with which it is continuous. The name coronary is strictly applicable to this vessel only where it lies in the left auriculo-ventricular groove. The coronary sinus (see Fig. 398, p. 974) is the dilated terminal THE THORAX 987 part of the great cardiac vein. It is about i inch in length, and occupies a portion of the posterior part of the left auriculo-ven- tricular groove. Its left extremity is continuous with the great cardiac vein, and its right extremity opens into the right auricle between the vestigial Eustachian valve and the auriculo-ventricular orifice, the opening being guarded by the Thebesian valve. At the place where the coronary sinus is continuous with the great cardiac vein there is a valve, which is composed of two segments. The coronary sinus is the persistent terminal part of the left duct of Cuvier and left lateral cornu of the sinus venosus. The posterior cardiac veins ascend upon the inferior surface of the left ventricle, arid open partly into the coronary sinus, and partly into the contiguous portion of the great cardiac vein. One of them is known as the left marginal vein. The middle cardiac vein (more properly called the inferior inter- ventricular vein), which is of large size, commences at the apex of the heart, and passes along the inferior interventricular groove with the descending branch of the right coronary artery. It re- ceives tributaries from the adjacent surface of the right ventricle and from the interventricular septum, as well as a few from the left ventricle, and it opens into the right extremity of the coronary sinus. The right or small cardiac or coronary vein occupies the right auriculo-ventricular groove, in company with the right coronary artery, and it opens into the right extremity of the coronary sinus. It is subject to some variation, but it usually receives tributaries from the contiguous parts of the right auricle and right ventricle, including the anterior cardiac veins. The anterior cardiac veins ascend on the front of the right ventricle, and open into the right cardiac vein. One of them is known as the right marginal vein. The oblique vein of Marshall, which is a persistent part of the left 'duct of Cuvier, passes downwards and inwards over the posterior aspect of the left auricle, and opens into the left extremity of the coronary sinus, its orifice being destitute of a valve. Development. — The oblique vein of Marshall represents the portion of the left duct of Cuvier which adjoins the terminal part, this latter part giving rise to the coronary sinus. Tributaries of the Coronary Sinus. — ^These are as follows : (i) the great or left cardiac vein ; (2) some of the posterior cardiac veins, others of these veins opening into the great cardiac vein ; (3) the middle cardiac vein ; (4) the right cardiac vein ; and (5) the oblique vein of Marshall. With the exception of the last-named tributary, all the others are provided with valves at their terminal orifices, but elsewhere they are destitute of valves. The smallest cardiac veins, or vence minimce cordis, also known as the vencB Thebesii, are not visible upon the exterior of the heart. They are very minute, and they open into the right auricle, their orifices constituting some of the foramina Thebesii. Similar 988 A MANUAL OF ANATOMY minute veins are said to open into the left auricle, and also into both ventricles. Lymphatics.— The lymphatic vessels of the heart form two net- works— subendocardial and subpericardial. The vessels are ulti- mately collected into two trunks, right or posterior, and left or anterior. The right trunk receives the lymphatics of the right side of the heart, and the left trunk takes up those of the left side. Each trunk accompanies the corresponding coronary artery, and both pass backwards on either side of the common pulmonary artery. Having pierced the pericardium, they terminate in the superior mediastinal or cardiac glands. Nerves. — ^The nerves of the heart are derived from the super- ficial and deep cardiac plexuses, and, through these, from the pneumogastric and sympathetic nerves. The branches to the auricles are derived partly from the deep cardiac plexus, and partly from the coronary plexuses. They form a gangliated plexus on the surface of each auricle beneath the epicardium, and from this plexus branches proceed to the muscular wall. The branches to the ventricles are derived from the right and left cor- onary plexuses. These branches lie upon the surface of each ventricle beneath the epicardium, and in the heart of the calf they are readily recognisable as delicate, thread-like streaks. Minute ganglia are met with, at intervals, on these nerves in the region of the base of the ventricles, but none on those nerves which lie over the lower two-thirds of each ventricle. The branches which enter the muscular, substance of the ventricular walls form plexuses, but are destitute of ganglia. Structure of the Heart. — The cardiac wall is composed of muscular tissue, which is known as the myocardium. This is intimately covered by the visceral layer of the serous portion of the pericardium, this layer being called the epicardium, and the cavities of the heart are lined with a membrane which is known as the endocardium. The epicardium resembles a serous membrane in structure, and is covered by endothelium. It is provided with stomata, which establish a communica- tion between its lymph-canalicular system and the cavity of the pericardium.^ Beneath the epicardium there is a variable amount of fat, which is chiefij met with in the auriculo-ventricular and interventricular grooves. The endocardium is a smooth, delicate membrane, destitute of blood-- vessels, and covered on its internal surface by endothelium. It consists of a connective-tissue basement membrane, containing elastic fibres, and is continuous, through the arterial and venous orifices, with the tunica intitnc of the vessels. It enters into the formation of the segments of the auriculo-' ventricular and semilunar valves. Fibrous Tissue. — The auriculo-ventricular and arterial orifices of the heart are each surrounded by a ring of fibrous tissue, and these rings, in the case of the auricles and ventricles, connect them together. The fibrous tissue of these rings furnishes that which is met with in the segments of the various valves. In the triangular interval between the aortic and the two auriculo- ventricular orifices there is a collection of dense fibrous tissue, of the con- sistence of fibro-cartilage, which is connected with the fibrous rings just referred to. When a heart is boiled, the fibrous tissue is dissolved, and the auricular portion can be separated from the ventricular portion. Myocardium. — The muscular tissue of the auricles is mostly distinct from THE THORAX 989 that of the ventricles, the fibrous rings at the auriculo-ventricular orifices inter\'ening between the two, and serving to connect them. Auricles. — The muscular fascicuU of the auricles are arranged in a super- ficial set, common to both auricles, and a deep set, confined to each auricle. The superficial fasciculi £ire disposed transversely, and some of them enter the interauricular septum. They are best marked in front. The deep fasciculi are arranged in two sets, looped Jind circular. The looped fasciculi arch vertically over the auricle, their extremities being attached to the ring of fibrous tissue which surrounds the auriculo-ventricular orifice. The circular fasciculi are present in the auricular appendix, around the venous orifices, and around the fossa ovaUs. The walls of the auricles, though muscular, are thin. Ventricles. — ^The muscular fasciculi of the ventricles are. as stated, mostly distinct from those of the auricles, and are disposed in a very complicated manner. They spring, for the most part, from the rings of fibrous tissue which surround the auriculo-ventricular orifices. The superficial fasciculi descend obliquely towards the apex, where they are disposed in a twisted or whorled manner, after which they pass on to the inner surface of the left ventricle. Some of them become continuous with the musculi papillares of that ventricle, whilst others ascend as a vertical layer on the inner surface of the ventricle to be attached to the left auriculo-ventricular fibrous ring. The superficial fasciculi are common to both ventricles. This figure is planned after oae of Luschka's, but its details were chiefly taken from an original preparation. The aorta, b', and pulmonary artery, a', have been cut short close to the semilunar valves, so as to show the anterior fibres of the auricles, a, superficial layer of the fibres of the right ventricle ; b, that of the left ; c, c, anterior interventricular groove ; d, right auricle ; d', its appendix, both showing chiefly perpendicular fibres ; e, upper part of the left auricle ; between e and b', the transverse fibres which behind the aorta pass across both auricles ; e", appendix of left auricle ; /, superior vena cava, around which, near the auricle, circu- lar fibres are seen ; g, g', right and left pulmonarj- veins with circular bands of fibres sur- rounding them. Fig. 407. — Anterior View of He.\rt of a Young Subject dissected AFTER Long Boiling, to show the Superficial Muscular Fibres (Allen Thomson). §. (From Quain's 'Anatomy.') The remaining fasciculi are very numerous, and must be described sepa- rately for each ventricle. The principal fascicuU of the left ventricle spring from the left auriculo-vent.icular fibrous ring, and they pass more or less obliquely towards the apex. In their course they turn" inwards, and enter the front part of the interventricular septum inferiorlv. Some of them now pass upwards to the base of the ventricle to be attached to the collection of dease fibrous tissue, of the consistence of fibro-cartilage, already described ; 99° A MANUAL OF ANATOMY others pass across to the postero -inferior wall of the right ventricle, where they partly end in a musculus papillaris, and partly pass to be attached to the right auriculo -ventricular fibrous ring; whilst a third set pass to the postero-inferior wall of the left ventricle, where they become circular in direction. The principal fasciculi of the right ventricle are, like the super- ficial fasciculi, continuous with those of the left ventricle, and they spring from the fibrous rings around the auriculo-ventricular and pulmonary orifices. Those on the postero-inferior surface of the right ventricle pass into the interventricular septum, and, having traversed it obliquely forwards and upwards, they issue from it, and become continuous with the deep fibres of the left ventricle. Those on the antero-superior surface of the right ventricle also pass into the interventricular septum, and having traversed it obliquely backwards and downwards, they pass on to the postero-inferior wall of the left ventricle. Those from the inferior aspect of the right ventricle enter the lower part of the interventricular septum, and ascend in the septum to the collection of dense fibrous tissue of the consistence of fibro-cartilage at the base. Although the ventricular muscular fasciculi are disposed for the most part obliquely, there are some circular fasciculi, but these are confined to the thickest part of each ventricular wall. Fibres of Purkinje. — These fibres are situated between the endocardium and the cardiac muscular tissue. They consist of elongated cells, united at their ends so as to form chains. The central part of each cell contains granular protoplasm, within which there are two nuclei; and the peripheral part presents transverse striations. These cells are probably vestiges of an early condition of cardiac muscular fibres. Fig. 408.- -The Superficial Muscular Fibres of the Heart in the Region of the Apex (C. Gegenbaur). The whorled arrangement is well shown. Auriculo-Ventricular Bundle. — This bundle constitutes the only auriculo- ventricular muscular connection, and functionally it is of a conducting nature. It may be described in three sections — auricular (atrial), nodal, and ventricular. The auricular section consists of fibres which are derived from (i) the circular fibres of the right auricle, just above the base of the septal cusp of the tricuspid valve, and (2) the muscular tissue of the interauricular septum at a point situated at the lower and anterior part of the septum on its right side, just above the anterior end of the base of the septal cusp of the tricuspid valve. These auricular fibres (circular and septal) enter the central fibrous body of the heart, which is situated between the aortic and the two : auriculo-ventricular orifices. The nodal section is situated within the central fibrous body. It is a small knot, consisting of an intricate network of muscular fibres, intermingled j with, and embedded in, fibrous tissue. The ventricular section emerges from the nodal section as a single bundle, which represents the main stem of the auriculo-ventricular bundle. This stem passes forwards along the upper margin of the muscular portion of the interventricular septum, lying immediately below the pars membranacea \ septi, and beneath the anterior part of the base of the septal cusp of the tricuspid valve. In this situation the main stem breaks up into two divisions? — right and left. Each of these divisicms enters the septal wall of the corre-' THE THORAX 991 spending ventricle, and divides into branches which ramify beneath the endo- cardium, where they form part of the system of Purkinje's fibres. Ultimately the terminal ramifications blend with the muscular fibres of the ventricles and musculi papillares. The fibres of the auriculo-ventricular bundle are pale, and are furnished with nerve-fibres and ganglia. The clinical significance of the bundle has reference to Stokes-Adams disease, or heart-block. (Kent, His junior, Tawara, and Keith and Flack.) Structure of the Cardiac Valves. — Each segment of the tricuspid and mitral valves consists of two layers of endocardium, enclosing between them fibrous tissue which is derived frbm the fibrous ring around the corresponding auriculo- ventricular orifice. Each segment of the aortic and pulmonary valves also consists of two layers of endocardium, enclosing between them fibrous tissue which is derived from the fibrous ring around the corresponding arterial orifice. The segments of all the valves are destitute of bloodvessels. Minute Structure of the Myocardium. — Cardiac muscle is composed of transversely striated fibres, but these differ so much from ordinary striated Fig. 409. — Cardiac Muscular Fibres showing their Transverse Stri.*., Divisions, Junctions, and Position of the Nuclei. voluntary muscular fibres as to require a special description. They possess no sarcolemma; they branch freely, and adjacent branches unite, so that an intricate network is formed by them ; and the transverse striae are fainter and less regular than those of voluntary muscle. Each fibre and its branches are broken up into a series of short quadrangular muscle-corpuscles, arranged in rows or chains, and separated from one another by cross-marks. Each muscle-corpuscle contains one nucleus, which occupies the centre of the cor- puscle and the corpuscle presents longitudinal striae as well as transverse. A cardiac muscular fibre, as well as its branches, is therefore a chain of muscle- corpuscles, each of which has a nucleus at its centre, and there is an absence of sarcolemma. Weight of the Heart. — The average weight of the heart of the adult male is 10. I ounces, and of the adult female 8.V ounces. Size. — The size of a normal heart has been compared to the closed hand of the individual person. Development of the Heart. — The heart makes its first appearance as two tubes, which are hollowed out in the splanchnic mesoderm of the peri- cardial region (cardiac portion of the ventral mesentery). These tubes are yya A MANUAL OF ANATOMY at first separated from each other, but subsequently they come together and fuse, giving rise to a single longitudinal tube, composed of splanchnic meso- derm, which represents the primitive heart, this tube being situated mesially along the ventral aspect of the pharyngeal portion of the fore-gut. It thus occupies the region which subsequently becomes the neck. The lumen of each of the two primitive tubes is lined with mesothelium, which becomes part of the cardiac endothelium. The mesenchyme, which lies outside the lining mesothelium, gives rise to the following cardiac tissues: (i) the myocardium, or cardiac muscular tissue; (2) the epicardium, or visceral layer of the serous portion of the pericardium; and (3) the connective-tissue element of the endocardium. ♦ After the fusion of the two tubes, which represent the cardiac rudiments, the primitive heart has the form of a longitudinal tube. At the caudal end of the tube is the sinus venosus. Mesocardial Folds. — At this stage the primitive heart is connected dorsally with the ventral wall of the pharyngeal portion of the fore-gut, and ventrally with the somatopleuric body-wall, by means of splanchnic mesoderm, dis- posed in two layers. These bilaminar mesodermic folds form the dorsal mesocardium and ventral mesocardium, which are of the nature of mesenteries. They soon disappear, the ventral folds entirely and the dorsal folds to a large extent. After the disappearance of these folds the cardiac tube is for the most part free, its ends being more or less fixed. Fig. 410. — Scheme showing Four Successive Stages in the Develop- ment OF THE Heart (L. Testut's ' Anatomie Humaine '). I. Arterial Bulb. 2. Ventricle. 4. Veins opening into the Sinus Venosus, 3. Auricle. Further Development of the Heart. — The cardiac tube soon presents two constrictions, which indicate its drl'ision into three parts — namely, auricular (atrial), ventricular, and bulbar. The auricular portion pertains to the venous end of the doubly-bent cardiac tube; and the ventricular and bulbar portions belong to the arterial end, the bulbar portion being differentiated from the primitive heart as the aortic bulb or hulhus arteriosus (bulbus cordis). The ventricular portion is therefore intermediate in position between the auricular and bulbar parts. The auricular division is closely associated with the sinus venosus, which will be described presently, and which, though not a division of the primitive cardiac tube, becomes ultimately merged into its auricular portion. The constriction between the auricular and ventricular portions gives rise internally to a passage called the auricular, or atrial canal ; and the constriction between the ventricular and bulbar portions gives rise internally to a passage known as the /return Halleri or strait of Haller. The primitive sinuous cardiac tube Ihus becomes differentiated into three chambers — namely: (i) the primitive auricle, (2) the primitive ventricle, and (3) the aortic bulb, or bulbus arteriosus. Whilst these differentiations are in progress, the tube undergoes two bends, and now resembles a capital S, laid somewhat thus — (J . The \enous loop THE THORAX 993 IS directed dorsahvards, and migrates cephalicwards, whilst the arterial loop is directed ventrahvards, and migrates caudahvards. Transformation of the Single Heart into the Doable Heart. — The double function of the permanent heart is concerned in (1) the pulmonary circula- tion, and (2) the systemic circulation. In order to prepare the organ for the performance of this t^vofold function, the primitive single heart tindergoes a series of changes, which result in the dix-ision of its auricular and ventricular portions each into two halves, and of the aortic bulb into the ascending aorta and trunk of the pulmonary artery. The permanent heart, therefore, is a double organ, consisting of a right or pulmonary half, and a left or systemic half. The transformation of the single auricle into two halves, right and left, is of a compHcated nature. Prior to the commencement of the transformation the single auricle presents a pocket-like dilatation or diverticulum on either side of the median line. These two diverticula represent the right and left auricular appendices. A groove then mcikes its appearance on the upper and dorsal walls of the single auricle. This groove indicates the position internally of a falciform fold, which grows downwards and forwards within the auricular cavit>'. The lamina is called the septum primiim (interauricular septum) or septum superius, and it eventually joins the upper part of the septum intermedium, to be presently described. It may here be stated, however, that the septum intermedium di\"ides the auricular canal into two parts, right and left, which represent the permanent auriculo-ventricular orifices. In the foregoing manner the primitive single auricle and the single auricular canal are divided each into t\vo — right and left. The two auricles, right and left, are for the most part separated by the septum primum, and the two auriculo-ventricular orifices are separated by the septum intermedium. The septum primum is incomplete, and the two auricles communicate with each other by an opening, called the ostium ititerauriculare primum, which is situated between the septum primum and septum intermedium. This ostium, however, is soon closed by the fusion of the septum primum with the septum intermedium. At the dorsal attachment of the septum primum a new opening, called the foramen ovale or ostium interauriculare secundum, makes its appearance, which establishes a communication between the two auricles. Another septum, called the septum secundum, is also developed. It grows downwards from the roof of the right auricle, and hes on the right side of, and parallel with, the septum primum. This secondary septum ends in a semilunar or falciform border, which bounds the foramen ovale above, in front, and below, and forms the annulus ovalis or limbus Vieussenii. The portion of the septum primum within the free semilunar border of the septum secundum projects slightly into the cavity of the left auricle, and is so dis- posed as to allow blood to pass freely from the right auricle into the left, but it guards against regurgitation. This portion of the septum primum is consequently called the valve of the foramen ovale. About the period of birth the ventral margin of this valve becomes as a rule adherent to the left side of the annulus ovalis, and the foramen ovale is thereby closed. Therccifter the valve (a portion of .the septum primum) forms the floor of the depression known as the fossa ovalis. In some cases the union of the valve with the left side of the annulus ovalis is incomplete, and in these circumstances a patent foramen ovale persists, giving rise to the condition known as morbus ccsruleus. Transformation of tiie Auricular Canal. — The auricular canal, which is the narrow communication between the auricular and ventricular divisions of the primirive cardiac tube, undergoes invagination into the ventricular chamber. Internally it presents two thickenings of endocardium, called the endocardial cushions, one of which is situated ventrally and the other dorsally. As these cushions grow they come together and fuse, thus giving rise to the septum intermedium. This septum divides the auricular canal into two compartments, which represent the right and left auriculo-ven- tricular orifices. The upper part of the septum intermedium, as stated, joins the lower pait of the septum primum, a temporary opening, known 63 594 A MANUAL OF ANATOMY as the ostium interauriculare primum, being situated between the two, prior to complete fusion. The right auriculo- ventricular orifice now pertains to the right auricle, and the left auriculo-ventricular orifice to the left auricle. Transtormatlon of the Single Ventricle. — The division of the single ven- tricular chamber into two ventricles, right and left, is effected by the forma- tion of a partition, called the interventricular septum, or septum inferius. .The position of this septum internally coincides with a groove externally, called the interventricular groove, which traverses the ventral and dorsal surfaces of the ventricular division. The interventricular septum appears first in the lower part of the ventricular chamber, and grows in an upward and backward direction. The dorsal part of its upper border blends with the dorsal part of the lower border of the septum intermedium. The ventral part of its upper border falls short of the root of the aortic bulb, so that the interventricular septum is incomplete in this region. The two ventricles therefore communicate with each other at this stage by a somewhat oval aperture, called the ostium interventnculare, which is situated between the root of the aortic bulb and the ventral part of the upper border of the inter- ventricular septum. This aperture, however, becomes closed by the down- ward growth of the membranous aortic septum, which divides the aortic bulb into the ascending aorta and trunk of the pulmonary artery. As the membranous aortic septum grows downwards, it closes the ostium inter- ventriculare by meeting, and fusing with, the ventral part of the upper border of the interventricular septum. The partition between the two ventricles is then complete. The interventricular septum is thus partly muscular and partly membranous. The membranous portion, comparatively small, is formed by the downward growth of the aortic septum, and this part of the interventricular septum is known as the pars membranacea septi. The superior connections of the interventricular septum, as stated, are twofold, as follows: ventrally, it blends with the downward growth of the aortic septum, and, dorsally, it joins the dorsal part of the lower border of the septum inter- medium. Cases have been recorded in which the pars membranacea septi has been found perforated, or, in other words, in which the original ostium interven- triculare has not been completely closed by the downward growth of the aortic septum. Wherever such a condition exists, an intercommunication between the venous blood in the right ventricle and the arterial blood in the left ventricle is allowed. The ostium interventriculare represents the normal communication which exists between the two ventricles in the hearts of some Reptilia — e.g., Lizards and Chelonia (Tortoises and Turtles). Transformation of the Aortic Bulb. — The aortic bulb or bulbus arteriosus is divided into the ascending aorta and the trunk of the pulmonary artery by a partition, which is called the aortic septum. This septum is formed by the meeting and fusion of two longitudinal endocardial ridges which appear on opposite walls of the aortic bulb internally. It is first developed in the upper part of the bulb, and in this situation the formative ridges appear on the ventral and dorsal walls of the bulb. The septum is therefore disposed at first antero-posteriorly. As the endocardial ridges grow downwards in a spiral manner, they become disposed laterally, as right and left ridges. This accounts for the ascending aorta and the trunk of the pulmonary artery lying side by side superiorly (aorta to the right, and trunk of the pulmonary artery to the left), whilst inferiorly, close to the heart, the trunk of the pulmonary artery is anterior, and the aorta lies behind it. The aortic membranous septum, as it grows downwards, meets, and fuses with, the ventral part of the upper border of the interventricular septum. In so doing, as stated, it closes the ostium interventriculare, and forms that part of the interventricular septum which is known as the pars membranacea septi. Two grooves appear on the exterior of the aortic bulb, which coincide with the attached borders of the aortic septum. As these grooves deepen, the aortic bulb becomes divided into (i) the ascending aorta, and (2) the trunk of the pulmonary artery. THE THORAX 995 Sinus VenosUs. — The sinus venosus (saccus reuniens) is at first an appendage of the auricular division of the primitive heart, below and behind which it lies. Subsequently, however, it becomes merged into the right auricle, and forms the posterior part of that chamber of the adult heart. Into it the following veins discharge their blood: (i) The t^vo ducts of Cuvier, from the body of the embrj-o; (2) the two xatelline veins from the yolk-sac; cind (3) the two umbihcal or allantoic veins from the chorion. It is elongated transversely, and its lateral portions, where the ducts of Cuvier open into it, are spoken of as the lateral cornua. The communication bet\veen the sinus venosus and the auricular chamber soon becomes small, and it shifts towards the right side, to a point between the right lateral comu and the right half of the auricular chamber. Ulti- mately, when the auricular chamber has become divided into two auricles, the sinus venosus opens entirely into the right auricle. The narrow opening is guarded by two endocardial folds, right and left, which axe known as the venous valves. These valves are continuous superiorly with a ridge called the septum spurium, on the roof of the atrium. The left venous valve dis- appears, but the right venous valve persists, and gives rise to (i) the Eustachian valve, and (2) the Thebesian valve. The venous valves, right and left, are situated at the opening of the sinus venosus into the right auricular cavity, and they are formed by the margins of the opening which project sUghtly into the right auricular cavity. The upper end of the right venous valve is continuous with a fold, called the septum spurimn, situated on the roof of the right auricular ca\dty on the right side of the septum primum. The right venous waive gives rise to the Eustachian and Thebesian valves. The left venous valve is continuous with the septum secundum, which bounds the foramen ovale above, in front, and below. The semilunar border of the septum secundum, together with the left venous valve, forms the annulus ovaUs. The right lateral cornu, which receives the right duct of Cuvier, undergoes enlargement, and, along with the central portion of the sinus venosus, it forms the atrium of the right auricle. The right lateral comu carries with it the right duct of Cuvier, or right superior vena cava. The left laterad comu which receives the left duct of Cuvier, is not merged into the right auricle, but remains connected with it, forming the coronary sinus, which is the persistent and pervious cardiac end of the left duct of Cuvier, or left superior vena cava. Whilst the right auricle receives the sinus venosus, the left auricle receives the trunk formed by the union of the pulmonary veins, but these latter vessels are, at this stage, of little importance, the pulmonary circulation l>»ng merely of a nutritive nature. The common orifice of the pulmonary veins becomes enlarged and forms the atrium of the left auricle; and subsequently the veins open into the atrium by four orifices, t%vo right and two left. Formation of the Valves ol the Heart. — The muscular tissue of the ven- tricular walls of the heart is at first loosely arranged in the form of trabeculae, which are disposed in a reticular manner. This muscular reticulum, including its meshes, is lined with endocardium. The superficial trabecuLB soon come together, and form a compact muscular wall, but towards the interior the reticular arrangement is retained. Muscular bundles, of different kinds, are therefore formed — e.g.,columncs carnece, tnusculi papillares, and moderator bands. In the portions of the ventricular walls around the auriculo-ventricular orifices the muscular tissue is replaced by fibrous tissue. This fibrous tissue gives rise to thin, somewhat triangular lamellae, and these become the segments of the aurieulo-ventricular valves. The chordcB tendinis represent musculzir trabeculae, which, at their valvular ends, have been replaced by fibrous tissue, whilst their ventriculiir ends retain their muscular character, and form the tnusculi papillares. The aortic and pulmonary semilunar valves are developed in connection with the ventricular end of the aortic bulb, prior to its division into the ascending aorta and trunk of the pulmonary artery. They appear as four fibrous cushions on the inner wall of the ventricular end of the aortic bulb, and are anterior, posterior, and right and left lateral respectively, ^^"hen the 996 A MANUAL OF ANATOMY aortic bulb is divided into the ascending aorta and trunk of the pulmonary artery, each lateral cushion is divided into two equal segments — anterior and posterior — by the aortic septum as it descends. The aortic and pul- monary orifices are thus provided each with three valves. The pulmonary valves are disposed as follows: One is anterior in position, and it represents the original anterior cushion of the lower end of the undivided aortic bulb; whilst two are postero-lateral, right and left, and they represent the anterior segments of the lateral cushions of the lower end of the undivided aortic bulb. The aortic valves are disposed as follows: Two are antero-lateral, right and left, and they represent the posterior segments of the lateral cushions of the lower end of the undivided aortic bulb ; whilst one is posterior in position, and it represents the posterior cushion of the lower end of the undivided aortic bulb. At this stage the root of the pulmonary artery is in front of the root of the aorta, and the segments of the pulmonary and aortic valves occupy the PULMONARY ARTERY PULMONARY ARTERY Endocardial Cushions of Primitive Aortic Bulb Aortic Bulb undergoing Division : Segmentation of Lateral Cushions R.P.L. = Right Postero-Lateral R,A.L. = Right Antero- Lateral Fig. 411. — Development of Aortic and Pulmonary Valves. positions which have just been assigned to them. Towards the end of intra- uterine life, however, the heart undergoes a rotation from right to left to such an extent as to place the root of the pulmonary artery in front, and to the left, of the root of the aorta. The aorta, as well as the pulmonary artery, is involved in this rotation, and the segments of the pulmonary and aortic valves are now permanently altered in position. The relations of the various segments in the adult are as follows: The pulmonary valves are disposed as two antero-lateral, right and left, and one posterior; whilst the aortic valves are one anterior and two postero-lateral, right and left. The rotation, just referred to, also explains why the left ventricle of the adult heart is chiefly postero-inferior in position, comparatively Uttle of it appearing on the antero- superior surface of the adult heart. Peculiarities of the Foetal Circulation. — The structures peculiar to the foetus in connection with the circulation of the blood are as follows : I. Foramen ovale, 3. Eustachian valve. 3. Ductus arteriosus. 4. Hypogastric and umbilical arteries. 5. Umbilical vein. 6. Ductus venosus. The foramen ovale is an oval opening in the interauricular septum. Up to the fourth month of intra-uterine life it is quite free, but after that joeriod the valve of the foramen ovale gradually extends upwards on the left side of, and beyond, the annulus ovalis, and acts as a valve during the latter months of foetal life. The blood can then THE THORAX 997 onl}' flow from the right auricle into the left, its return being pre- vented by this valve. The Eustachian valve is of large size during foetal life, and is associated with the orifice of the inferior vena cava at the postero- inferior angle of the right auricle. It is a crescentic fold of the endocardium, which extends between the anterior margin of the orifice of the inferior vena cava and the anterior horn of the annulus ovalis. Its situation is such as to direct the blood entering the right auricle by the inferior vena cava to the foramen ovale. The ductus arteriosus connects the trunk of the pulmonary artery to the arch of the aorta at a point immediately beyond the origin of the left subclavian arter\', and it conveys the most of the blood from the right ventricle to the descending thoracic aorta. The hypogastric arteries, right and left, are prolonged from the common iliac arteries to the umbilicus, through which they leave the body of the foetus, and, under the name of the umbilical arteries, they pass along the umbilical cord to be distributed to the foetal part of the placenta. They convey the impure blood of the foetus to the placenta. The umbilical vein extends from the foetal part of the placenta through the umbilicus to the inferior surface of the liver, where it traverses the umbilical fissure, and gives off right and left branches to the right and left lobes, which join the branches of the vena portae. After parting with its right and left branches the mnbilical vein is prolonged, under the name of the ductus venosus, to the inferior vena cava, which it joins at the caval fossa of the liver. The umbilical vein conveys pure blood from the placenta into the body of the foetus. Foetal Circulation. — ^The right auricle receives blood from the superior and inferior venae cavse, and from the coronary sinus. The superior vena cava returns the venous blood from the head and neck, the upper limbs, and the thoracic portion of the trunk ; and the inferior vena cava returns the blood from the lower limbs, the abdominal portion of the trunk, and the placenta. The placental blood is pure, and reaches the inferior vena cava in two ways : (i) a large quantity of it is conveyed directly into the inferior vena cava by the ductus venosus ; and (2) some of it cir- culates through the liver in the branches of the vena portae, and is thereafter conveyed to the inferior vena cava by the hepatic veins. The blood entering the right auricle by the inferior x^ena cava is necessarily of a mixed nature, being partly placental and partly venous. The impure blood which enters the right auricle by the superior vena cava, having received a small quantity of the mixed blood which enters by the inferior vena cava, passes through the right auriculo-ventricular orifice into the right ventricle, and from thence is driven into the trunk of the pulmonary artery. A small quantity of it is conveyed to the lungs by the right and left pul- monary arteries, which at this period are of small size, and it is 998 A MANUAL OF ANATOMY returned from the lungs to the left auricle by the pulmonary veins. By far the greater part of the right ventricular blood, however, enters the ductus arteriosus, and is conveyed by it to the aorta immediately beyond the origin of the left subclavian artery. None of this blood, therefore, enters the three great vessels which spring from the arch of the aorta. The whole of it descends in the de- scending thoracic and abdominal portions of the aorta, and has a Internal Jugular Vein Subclavian Vessels^'fQ'^: Superior Vena Cava Foramen Ovale Orifice of Inferior Vena Cava Eustachian Valve Inferior Vena Cava Hepatic Veins zzT^ Inferior Vena Cava Aorta Common Iliac Vein External Iliac Vessels Common Carotid Artery '^^Wi^ Ductus Arteriosus , Pulmonary Artery Left Auricle Left Ventricle . Right Ventricle Ductus Venosus Left Branch of Vena Portae Right Branch of . ^ Vena Portse Vena Poitae Umbilical Vein . . Umbilicus - Umbilical Arteries -. Umbilical Vein l^^mbilical Cord Hypogastric Arteries Fig. 4n. — Diagram of the Organs of Circulation in the Fcetus (The arrows indicate the course of the Circulation). twofold destination. Part of it is distributed to the abdominal and pelvic viscera, and the lower limbs, whence it is returned by the vena portae and inferior vena cava ; but the greater part of it is conveyed out of the body of the fcKtus to the placenta by means of the hypogastric and umbilical arteries. Having been purified in the placenta, it is returned thence by the umbilical vein into the body of the foetus. This placental blood, as stated, reaches the inferior vena cava in two ways, partly directly by means of the THE THORAX 999 ductus venosus, and partly indirectly by means of the hepatic veins after having circulated through the liver. A small quantity of the mixed blood which enters the right auricle by the inferior vena cava mingles with the venous blood which enters that cavity by the superior vena cava ; but by far the greater part of it is directed by the Eustachian valve to the foramen ovale, through which it passes into the left ventricle. Here it receives the blood which has been returned from the lungs by the pulmonary veins, and then it passes through the left auriculo- ventricular orifice into the left ventricle. From the left ventricle it is driven into the aorta, and the greater part of it passes into the innominate, left common carotid, and left subclavian arteries to be distributed to the brain, head and neck, and upper limbs, as well as to the substance of the heart by the coronary arteries. A small quantity, however, of this mixed blood passes into the de- scending thoracic aorta, and mixes with the venous blood entering by the ductus arteriosus. The blood is returned to the right auricle of the heart from the brain, head and neck, and upper limbs, by the superior vena cava, and from the substance of the heart by the coronary sinus. Changes at Birth. — At birth respiration is established, and the lungs perform their respiratory function ; the right and left pul- monary arteries undergo rapid enlargement ; and the placental circulation is entirely arrested. The hypogastric arteries become obliterated and transformed into fibrous cords, except at their roots, where they persist as the internal iliac arteries. The um- bilical vein becomes obliterated, and is now known as the round ligament of the liver. The ductus venosus becomes transformed into a fibrous cord, called the ligamentwn ductus venosi, which occupies the venosal fissure of the liver. The foramen ovale is closed by the valve of the foramen ovale becoming adherent to the margin of the annulus ovalis or limbus Vienssenii on its left side. In some cases, however, this union is incomplete, and a ndnute opening persists, through which a small probe may be passed. In yery rare cases a fairly large opening may remain, as in the con- dition known as morbus ccertdeus. As viewed from the interior of the left aiu-icle, the upper crescentic border of the valve of the foramen ovale is visible upon the interauricular septum, and above this border there is a slight depression. The ductus arteriosus becomes obliterated, and persists as a fibrous cord, called the ligamentum ductus arteHosi, which passes from the root of the left pulmonary artery to the arch of the aorta immediately beyond the origin of the left subclavian artery. The closure of all the peculiar structures associated with. the fcetal circulation is usually complete from the eighth to the tenth day after'birth. Development of the Principal Arteries. — In the embryo the aortic bulb or bulbus arteriosus divides into two vessels, called the primitive ventral aorts, right and left, which pass cephalicwards on the ventral aspect of the fore-gut. looo A MANUAL OF ANATOMY From each of these vessels two arterial arches are given off, and from the aortic bulb there spring four arterial arches on either side, the bulb repre- senting their common stem. Subsequently two of the bulbar arterial arches, on either side, are transferred to the ventral aortae, whilst the other two maintain their connection with the bulb. There are thus six arterial arches on either side, four of which spring directly from the corresponding ventral aorta, these being the cephalic four, whilst the caudal pair, on either side, arise directly from the aortic bulb. These six arches arc called first, second, third, fourth, fifth, and sixth, in this order from the cephalic region caudal- wards. The fifth arch, on either side, is rudimentary and of temporary dura- tion, and it takes no part in the development of permanent bloodvessels. The arterial arches traverse the visceral arches, and, in doing so, they sweep from before backwards on either side of the fore-gut. They are sometimes spoken of as the visceral arch arteries. Fig. 413. — Diagram of the Heart and Primitive Vessels of the Embryo Chick, as seen from below and enlarged (after Allen Thomson, IN Quain's ' Embryology '). A, Auricle ; B, Ventricle ; C, Bulbus Arteriosus ; D, Primitive Ventral Aortae ; E, E, Primitive Dorsal Aortae ; F, Single Dorsal Aorta ; G, Continuations of the Dorsal .\ortaE beyond the origins of the Vitelline Arteries; i to 5, Aortic Arches; 6, 6, Vitelline Arteries; 7, 7, Vitelline Veins. Each arterial arch, after having swept dorsalwards, opens into the cor- responding primitive dorsal aorta. These primitive dorsal aortae are two in number — right and left, and each is continuous with the corresponding primitive ventral aorta through means of the first arterial arch of its own side. The series of arterial arches therefore establish direct communications between the ventral and dorsal aorta?, and the extremities of each arterial arch are referred to as ventral and dorsal roots respectively. The primitive dorsal aortae pass caudalwards on either side of the noto- chord, and each gives off a series of vessels, which are known as segmental arteries. In the cervical region there are seven segmental arteries; and in the thoracic and lumbar regions there are the intercostal and lumbar arteries respectively, all of which belong to the segmental type. The ujiper two or three thoracic segmental arteries disajjpear, and the anastomotic loop between them forms, on either side, the superior intercostal artery. THE THORAX Caudahvards each primitive dorsal aorta furnishes the vitelline or omphalo- mesenteric artery, which is its principal mode of termination. The tvvo vitelline arteries pass to the yolk-sac. Another branch of each primitive dorsal aorta, however, passes caudalwards, which, though small, is really the continuation of the corresponding dorsal aorta. After retrogression of the yolk-sac, the vitelline arteries are replaced by the allantoic arteries. At a subsequent period the two primitive dorsal aortae unite at about the level of the future fourth thoracic vertebra, and so give rise to one vessel, namely, the dorsal aorta. This vessel is continued onwards as the median caudal aorta, which is ultimately known as the middle sacral artery. The arterial arches, as stated, are caUed first, second, third, fourth, fifth External Carotid Ventral Aorta Internal Carotid Common Carotid Right Subclavian Artery Right Pulmonary. Artery Trunk of Pulmonary Artery Aortic Arch Ductus Arteriosus \'ertebral Artery Left Pulmonary Artery Fig. 414. — Scheme of the Aortic Arches and their Destination (MODIFIED FROM KOLLMANN) (FROM GrAY'S 'AnaTOMY'). (rudimentary and temporary), and sixth. As the development of the prin- cipal arteries proceeds, important changes take place in these arches. Keep- ing in view the fact that, according to some authorities, the arterial arches are five in number, and not six, the following description will be equally applicable to each view, provided the sixth arch of the view adopted is re- garded as being equivalent to the fifth arch of the other view. The first, second, and fifth arches disappear, on either side. The sixth right arch disappears. The part of the left dorsal aorta between the dorsal roots of the third and fourth left arches disappears. The part of the right dorsal aorta, which extends from the dorsal root of the third right arch to the place of junction of the two dorsal aortas, disap- 1002 A MANUAL OF ANATOMY pears, except the small portion which contributes to the formation of the right subclavian artery. Permanent Vessels. — The development of these vessels is here described, in a caudo-cephalic order, or from behind forwards. The ventral portion of the sixth left arch gives rise to the right and left pulmonary arteries respectively, which pass backwards to the lungs. The dorsal part of the sixth left arch — ^that is to say, the part beyond the origin of the right and left pulmonary arteries — persists up to birth, and forms the important vessel called the ductus arteriosus (duct of Botalli), which joins the left dorsal aorta. After birth the ductus arteriosus undergoes obliteration, and is converted into a fibrous cord, known as the ligamentum ductus arteriosi. Fig. 415. -Development of Cervical, Segmental, and Vertebral Arteries, The root, or proximal part, of the left ventral aorta — that is to say, the part between the aortic bulb and the ventral root of the fourth left arch — forms the part of the arch of the aorta between the innominate and left common carotid arteries. The fourth left arch forms the part of the arch of the aorta between the left common carotid artery and the point of entrance of the ductus arteriosus. As development proceeds, the fourth left arch gradually descends, along Avith the heart, into the cavity of the future thorax, and so comes to occupy a lower plane than the fourth right arch. The root, or proximal part, of the right ventral aorta — that is to say, the part between the aortic bulb and the ventral root of the fourth right arch — ■ gives rise to the innominate artery. The fourth right arch contributes to the formation of the rie;ht subclavian THE THORAX 1003 artery. Two other factors, however, are to be taken into account in connection with this vessel — namely: (i) the part of the right dorsal aorta between the dorsal roots of the fourth and sixth right arches, and (2) the seventh right cervical segmental artery, which arises from the right dorsal aorta at the level of the dorsal root of the sixth right arch. This segmental artery furnishes the root of the right vertebral artery. The vertebral artery is at first larger than the subclavian, which latter appears then to be a branch of the vertebral, but as the right subclavian arter\' grows out into the corresponding upper limb-bud to become the right axillary artery, it becomes larger than the vertebral artery. The orgin of the left subclavian artery is much more simple than that of the right vessel. The left subclavian artery is a lateral branch of the seventh left cervical segmental artery, which arises from the left dorsal aorta at the level of the dorsal root of the sixth left arch. This segmental artery furnishes the root of the left vertebral artery, which latter vessel is, as on the right side, at first larger than the subclavian. As the left subclavian vessel, however, grows out into the left upper limb-bud to become the left axillary, it becomes larger than the vertebral artery. Another subsequent factor in the forma- tion of the left subclavian is the root of the seventh left cervical segmental artery, which thus brings the left subclaNnan vessel on to the arch of the aorta, and makes the left vertebral now a branch of it, though originally the vertebral artery was really its parent. Developmental Differences between the two Subclavian Arteries. (Fourth right arterial arch. Portion of right dorsal aorta. Seventh right cervical segmental artery. Left Artery = Seventh left cervical segmental artery. The part of each ventral aorta between the ventral roots of the third and fourth arches forms the corresponding common carotid artery. The part of each ventral aorta above the ventral root of the third arch gives rise to the corresponding external carotid artery. The third arch and the part of the dorsal aorta above its dorsal root give rise, on either side, to the internal carotid artery. Summary. Right Ventral Aorta. — (i) The root, or part between the aortic bulb and the ventral root of the fourth right arch, gives rise to the innominate artery. (2) The part between the ventral roots of the third and fourth right arches forms the right common carotid artery. (3) The part above the ventral root of the third right arch gives rise to the right external carotid artery. Left Ventral Aorta. — (i) The root, or part bet^veen the aortic bulb and the ventral root of the fourth left arch forms the part of the arch of the aorta between the innominate and left common carotid arteries. (2) The part between the ventral roots of the third and fourth left arches gives rise to the left common carotid artery. (3) The part above the ventral root of the third left arch forms the left external carotid artery. Ri^nt Dorsal Aorta. — (i) The part between the dorsal root of the third right arch and the place of junction of the two dorsal aortae disappears, except the small portion which contributes to the formation of the right subclavian artery. (2) The part above the dorsal root of the third right arch persists and forms part of the right internal carotid artery. Left Dorsal Aorta. — (i) The part between the dorsal roots of the third and fourth left arches disappears. (2) The part above the dorsal root of the third left arch persists and forms part of the left internal carotid artery. (3) The part between the dorsal root of the sixth left arch and the place of junction of the two dorsal aortae forms the commencement of the descending aorta. I004 A MANUAL OF ANATOMY Arterial Arches. — (i) The first, second, and fifth arches, on either side, disappear; and the sixth right arch also disappears. (2) The third arch, on each side, persists and forms part of the corresponding internal carotid artery. (3) The fourth right arch forms part of the right subclavian artery. (4) The fourth left arch forms the part of the arch 0! the aorta between the left common carotid artery and the point of entrance of the ductus arteriosus. (5) The ventral portion of the sixth left or pulmonic arch gives rise to the right and left pulmonary arteries respectively. (According to some authorities, the right pulmonary artery arises from the ventral part of the sixth right arch, which would then be a pulmonic arch like the sixth left.) (6) The dorsal part of the sixth left arch — :that is to say, the part beyond the origin of the right and left pulmonary arteries — persists up to birth, and forms the ductus arteriosus. Summary of the Permanent Aorta. — (i) The ascending aorta is developed from the aortic bulb or bulbns arteriosus, along with the trunk of the pul- monary artery. (2) The part Of the arch of the aorta between the innom- inate and left common carotid arteries is developed from the root of the left ventral aorta — that is to say, the part between the aortic bulb and the ventral root of the fourth left arch. (3) The part of the arch of the aorta between the left common carotid artery and the point of entrance of the ductus arte- riosus is developed from the fourth left arch. (4) The descending aorta is formed from above downwards by (a) a portion of the left dorsal aorta, and {b) the fusion of the right and left dorsal aortae. Summary of the Pulmonary Artery. — (i) The trunk of the pulmonary artery, otherwise spoken of as the common pulmonary artery, is developed from the aortic bulb or bulbus arteriosus, along with the ascending aorta. (2) The right and left pulmonary arteries are developed from the ventral portion of the sixth left arch. Development of the Segmental, Vertebral, and Left Subclavian Arteries. — Each primitive dorsal aorta in the cervical part of its course gives off seven arteries, which are called the cervical segmental arteries. There are thus seven pairs of these arteries, serially arranged. The first or highest lies between the occiput and the atlas, and is therefore suboccipital ; and the seventh or lowest corresponds to the interval between the sixth and seventh cervical vertebrae. These seven vessels, on either side, are connected by interseg- mental anastomotic vessels, which, by their continuity, establish a longi- tudinal anastomotic chain. Superiorly this chain is prolonged through the foramen magnum into the cranial cavity, where it terminates by anas- tomosing with the corresponding internal carotid artery. The upper six cervical segmental arteries soon disappear, but the seventh segmental artery and the longitudinal anastomotic chain persist, on either side. The first part of the vertebral artery is developed from the seventh cervical segmental artery. The second part of the vertebral artery, which traverses the upper six costo-transverse, or vertebrarterial, foramina, represents the persistent longitudinal anastomotic chain, except its cephalic part. The third, or suboccipital, and fourth, or intracranial, parts of the artery are devel- oped from the cephalic part of the longitudinal anastomotic chain, which, as stated, is prolonged through the foramen magnum into the cranial cavity. The seventh cervical segmental artery, on either side, is of special importance for two reasons. In the first place it gives origin to the vertebral artery, which takes a course cephalicwards. In the second place, it gives origin, on the left side, to the left subclavian artery, and on the right side it contributes to the formation of the right subclavian artery. Each subclavian artery takes an outward course to the corresponding upper limb-bud. The seventh left cervical .segmented artery thus constitutes a common stem for the left vertebral and left subclavian arteries, whilst the seventh right cervical seg- mental artery forms a common stem for the right vertebral artery and a part of the right subclavian artery. The origin of a vertebral artery precedes that of the corresponding sub- THE THORAX 1005 clavian artery, so that the subclavian artery is originally a lateral branch of the vertebral artery. As development proceeds, however, the subclavian artery increases in size, and greatly exceeds the vertebral artery, the latter vessel being now regarded as a branch of the subclavian, whereas originally it is the parent trunk. The thoracic and abdominal segmental arteries have been already referred to in connection with the dorsal aortae. Development of the Principal Veins. The primitive veins form tv:6 groups. One group returns the blood from the yolk-sac and the placenta; and the other group returns the blood from the head and neck, anterior limbs, body-wall. Wolffian bodies, and posterior limbs. The first group comprises: (i) The vitelline veins, in connection with which the portal vein is developed; and (2) the umbihcal or allantoic veins. The second group consists of (i) the anterior cardinal veins; (2) the posterior cardinal veins ; and (3) the subcardinal or supracardinal veins. The veins of each group are arranged in pairs, right and left, as follows: Two Vitelline Veins. Two Anterior Cardinal Veins. Two Umbilical Allantoic Veins. Two Posterior Cardinal Veins. Two Subcardinal or Supracardinal Veins. Vitelline or Omphalo-Mesenteric Veins and Vena Port». — These veins are developed first, and they return the blood from the yolk-sac. They enter the lody of the embrj'o along the vitelUne duct, and finally open into the sinus venosus, after traversing the septum transversum. Within the body they ascend, parallel with each other, at first in front of, and subsequently on either side of, the duodenal portion of the primitive intestinal tube. In the latter region, on the caudal side of the hepatic bud, they become con- nected by three transverse anastomotic vessels, tr^vo of which he across the ventral aspect of the gut, and one being placed on its dorsal aspect. The first or lowest anastomotic vessel hes on the ventral aspect of the gut; the second or middle vessel is dorsal to the gut; and the third or highest, like the first or lowest, is ventral to the gut. By means of these three anastomotic vessels two venous rings — lower, or caudal, and upper, or cephalic — are formed around the duodenal portion of the primitive intestinal tube, these rings constituting the sinus annularis. During their formation the two divisions of the hver-bud are breaking up into hepatic cylinders, and these are giving off secondary cyUnders. Owing to these hepatic developments the vitelline veins cease to communicate directly with the sinus venosus. The portions of the vitelline veins above the upper duodenal venous ring (shown in Fig. 417 to proceed from its sides) become surrounded by the hepatic cylinders, and invaded by the secondary cylinders. In this manner these portions of the vitelline veins are freely subdivided into blood-channels, which are known as sinusoids (Minot). These sinusoids form a netsvork which occupies the meshes of the netvvork formed by the branches of the hepatic cylinders. The veins which convey blood from the upper duodenal ring to the hepatic sinusoids are now known as the vencs hepaticcE advehentcs, and they become the right and left divisions of the portal vein. The veins which carr>' the blood from the hepatic sinusoids to the sinus venosus are known as the vence hepatic^ revehentes, and they become the hepatic veins. Trunk of the Portal Vein. — The portions of the two vitelline veins which ascend in front of the primitive duodenum he close together and parallel with each other. These portions fuse for a short distance, and form a single venous stem, which opens into the first, or lowest, ventral anastomotic vessel, or, in other wordS; into the lower part of the lower duodenal venous ring. This short stem receives the veins of the primitive intestinal tube, and it forms the root of the portal vein. The primitive portal vein, therefore, receives loo6 A MANUAL OF ANATOMY A Fig. 416. A, Scheme of the Development of the Principal Veins. B, Scheme of the Primitive Veins which open into the Primitive Heart. 1. External Jugular Vein (Primitive Jugular) 2. Internal Jugular Vein 3. Subclavian vein 4. Right Innominate Vein 5. Left Innominate Vein 6. Superior Vena Cava 7. Left Superior Intercostal Vein 8. Right Superior Intercostal Vein 9. Right Azygos Vein 10. Lower Left Azygos Vein 11. Upper Left Azjgos Vein 12. 13. Transverse Azygos Veins 14. Left Duct of Cuvier (Remains oQ B 1, 1. Primitive Jugular Veins 2, 2. Cardinal Veins 3, Right Duct of Cuvier Coronary Sinus Inferior Vena Cava 18. Inferior Vena Cava Mesial Part of Left Renal Vein Right Renal Vein Lateral Part of Left Renal Vein Suprarenal Vein Spermatic Vein (Ovarian Vein) Lumbar Veins Transverse Iliac Vein Common Iliac Vein Internal Iliac Vein External Iliac Vein 4, Left Duct of Cuvier 5, 5. Vitelline Veins 6, 6. Umbilical Veins THE THORAX 1007 its blood from (i) the yolk-sac, and (2) the primitive intestinal tube, within the abdomen. As the yolk-sac atrophies the portions of the vitelline veins between it and the commencement of the portal vein £dso atrophy, and the tributaries of the portal vein gradually assume their condition in adult Ufe. ' The following parts of the sinus annularis, or double duodenal venous ring, undergo atrophy: 1 . Right half of lower ventral anastomotic vesseL 2. Right half of lower duodenal ring. 3. Left half of upper duodenal ring. The following parts of the sinus annularis persist: 1 . Left half of lower ventral anastomotic vesseL 2. Left half of lower duodenal ring. 3. Middle or dorsal anastomotic vessel. 4. Right half of upper duodenal ring. 5. Upper ventral anastomotic vessel. These persistent portions, with the exception of the upper ventral anasto- motic vessel, form t\ie greater part of the trunk of the portal vein. The upper ventral anastomotic vessel represents a part of the left division of the portal vein. The portal vein has originally a spiral relation to the duodenal portion of the primitive intestinal tube — that is to say, it winds round the left side and dorsal aspect of the duodenum, and then appears on its right side. Divisions of the Portal Vein. — These are connected with the upper duodenal venous ring. As previously stated, thp veins which convey the blood from this ring to the hepatic sinusoids are known as the venee hepatioB advehentes, right and left. The right division of the portal vein is formed by the right vena hepatica advehens, which springs from the right half of the upper duodenal venous ring. The left division is formed by (i) the upper ventrjil anastomotic vessel, and (2) the left vena hepatica advehens. Summary of the Development of the Portal Vein. Root=Fusion of vitelline veins ventral to the primitive duodenum. fi. Left half of lower ventral anastomotic vessel. _ 2. Left half of lower duodenal ring, of Trunk 1 3. Middle or dorsal anastomotic vessel. V 4. Right half of upper duodenal ring. Right Division= Right vena hepatica advehens. Toftniuicinn — / ^- Uppcr vcutral anastomotic vesscl. i.ei; uivision -y^ j^eft vena hepatica advehens. According to some authorities the common stem formed by the fusion of the vitelline veins in front of the duodenal portion of the intestinal tube, together with the left half of the lower duodenal ring, gives rise to the superior mesenteric vein, which is joined by the splenic vein. According to this view, the portal vein is formed by (i) the middle or dorsal transverse anastomotic vessel, and (2) the right half of the upper venous ring. Summary of the Vitelline Veins. The vitelline veins, which are developed first, return the blood from the yolk-sac to the sinus venosus. They enter the body of the embryo along the vitelline duct. At first they ascend in front of the duodenal portion of the primitive intestinal tube, hing close to, and parallel with, each other. Subsequently they ascend on either side of the duodenal gut. The portions of the veins in front of the duodenal gut fuse and form the root or lower part of the portal vein, which receives the veins of the primitive intestinal tube. The portions on either side of the duodenal gut become connected by three ioo8 A MANUAL OF ANATOMY transverse anastomotic vessels, two of which, lower and upper, lie across the ventral aspect of the duodenal gut, and one — middle — dorsal to it. A double venous ring {sinus annularis) is now formed, the rings being known as lower or caudal and upper or cephalic, and these embrace the duodenal gut. The portions of the tw^ vitelline veins above the upper venous ring cease to be connected directly with the sinus venosus, owing to the develop- mental changes which are now taking place in the hepatic diverticulum or liver-bud. They are invaded l5y the hepatic cylinders, and are freely sub- divided into sinusoids. The veins which carry the blood from the upper venous ring to these sinusoids are called the vencs hepatica; advehentes, and the veins which carry the blood from the sinusoids to the sinus venosus are Fig. 417.— The Venous Trunks of the Human Embryo (His). P.J.V. Primitive Jugular Vein X.X. Upper separated portions of Umbilical Veins C.V. Cardinal Vein R.U.V. Right Umbilical Vein R.S.V.C. Right Superior Vena Cava L.U.V. Left Umbilical Vein L.S.V.C. Left Superior Vena Cava V.P. Vena Portse V.V. Vitelline Veins called the vencB hepatices revehentes, the latter giving rise to the hepatic veins of adult life. A summary of the portal vein has just been given. The initial portions of the vitelline veins atrophy. The vitelline veins thus give rise to (i) the portal vein and its ramifications, and (2) the hepatic veins. Umbilical or Allantoic Veins. — The two umbilical veins return the blood from the placenta to the sinus venosus. They are of small size during the period of the vitelline circulation, but become enlarged as the yolk-sac atrophies and as the allantois undergoes increase in size. The two veins unite and form a single trunk within the umbilical cord. At the umbilicus this trunk enters the body of the embryo, and immediately divides into two umbilical veins, right and left, which traverse the septum transversum and open into the sinus venosus. As they traverse the septum transversum they are intimately related to the developing liver. The two umbilical veins soon lose their connection with the sinus venosus, and they are now subdivided, like the vitelline veins, into hepatic sinusoids THE THORAX 1009 by the hepatic cylinders. At this stage the blood of the umbihcal veins flows through the hepatic sinusoids, from which it is taken up by the venae hepaticae revehentes. or hepatic veins, and these veins convey it to the sinus venosus. At a later period the right umbihcal vein, for the most part, atrophies. A portion of it, however, near the umbihcus, persists, and estabhshes a con- nection with the epigastric veins of the abdominal wall. In this persistent portion the blood can flow towards the umbihcus. As the right umbilical vein undergoes atrophy, the left umbihcal vein becomes enlarged. Imme- diately below the developing Uver it joins the upper duodenal venous ring, formed by the vitelline veins. Meanwhile a vein is being developed, which passes from the convexity of the upper duodenal venous ring — that is to say, from the left division of the portal vein — to the right vena hepatica revehens, or right hepatic vein, near the sinus venosus. This new vein constitutes the ductus venosus, or duct of Arantius, and through this channel the greater part of the pure placental blood passes directly to the heart, without circu- lating through the liver. A certain amount of pure placental blood, however, reaches the liver through the left vena hepatica advehens, which, as pre- viously stated, forms a part of the left division of the portal vein. The left vena hepatica revehens, or left hepatic vein, loses its connection with the sinus venosus, and now opens into the right vena hepatica revehens, or right hepatic vein, at the level where the latter receives the ductus venosus. A common venous stem is now formed, representing (i) the right hepatic vein, (2) the left hepatic vein, and (3) the ductus venosus. This stem is known as the vena hepatica cowmunis, and it gives rise to the terminal or cardiac portion of the prerenal division of the inferior vena cava. The left umbihcal vein and the ductus venosus remain pervious, and are important vessels, until the period of birth, being concerned in the placental circulation. After the cessation of this circulation both vessels atiophy, the ductus venosus entirely, and the left umbihcal vein almost entirely. The obliterated ductus venosus is known as the ligamentum ductus venosi, and the obliterated left umbilical vein forms the round ligament of the liver. A minute portion of the lumen of the left umbilical vein remains pervious within the round ligament of the hver. This pervious portion communicates at the liver with the left division of the portal vein, and at the umbihcus it is connected with the epigastric veins of the abdomiucd wall. It thus forms a channel of communication between the left division of the portal vein and the systemic veins of the anterior abdominal wall. In this pervious portion the blood can flow towards the umbUicus. This anastomosis betiveen the portal and systemic circulations accounts for the enlargement of the veins of the anterior abdominal wall in cases of ported obstruction within the Uver. Summary of the Umbilical Veins. The umbilical veins return the blood from the placenta to the sinus venosus. The two veins unite and form a single trunk within the umbUical cord. At the umbihcus this trunk enters the body of the embr^-o, and immediately divides into two umbihcal veins, right and left, which traverse the septxun transversum and open into the sinus venosus. They soon lose their con- nection with this sinus, and become broken up into sinusoids by the hepatic cylinders. At a later period the right umbUiccd vein, for the most part, atrophies ; but a portion of it, near the umbilicus, persists and conveys blood towards the umbihcus, where it communicates with the epigastric veins of the abdominal wall. The left umbilical vein now enlarges, and, immediately below the developing hver, it joins the upper duodenal venous ring. Mean- while a vein is being developed, which passes from the convexity of the upper duodenal ring — that is to say, from the left division of the portal vein — to the right hepatic vein. This new vessel is the ductus venosus, and through it the greater part of the pure placental blood passes directly to the heart. The 64 loio A MANUAL OF ANATOMY left hepatic vein loses its connection with the sinus venosus, and opens into the right hepatic vein at the level where that vein receives the ductus venosus. The common stem, thus formed, is known as the vena hepatica communis, which forms the terminal part of the inferior vena cava. The left umbilical vein and the ductus venosus persist throughout foel^l life. Thereafter the ductus venosus atrophies and forms the ligamentum ductus venosi. The left umbilical vein atrophies almost entirely, and gives rise to the round ligament of the liver. A minute portion of its lumen, how- ever, remains pervious at the centre of the round ligament of the liver, and this portion forms an anastomotic channel between the left division of the portal vein and the epigastric veins of the abdominal wall. In this pervious portion the blood can flow towards the umbilicus. Anterior Cardinal Veins. — These veins are two in number — right and left — and they return the blood from the head and fore-limbs. Each vein consists of two parts — intracranial and extracranial. The intracranial, part gives rise, directly and indirectly, to the intracranial sinuses, whilst the extra- cranial part, which is the true anterior cardinal vein, becomes the internal jugular vein. The intracranial part is known as the vena capitis medialis. This vein lies at first on the mesial side of the primitive cranial nerve-roots. In this position it is connected with venous loops which embrace the nerve- roots. The mesial portions of these loops disappear, and their lateral por- tions become connected by an anastomotic vessel, which forms another tem- porary vein, known as the vena capitis lateralis. This vein commences just beyond the primitive Gasserian ganglion, and it leaves the cranial cavity in company with the primitive facial nerve, becoming thereafter continuous with the extracranial part of the anterior cardinal vein. Vena Capitis Medialis. — This primitive vessel extends as far as the Gasserian ganglion, lying, as stated, on the mesial side of the primitive cranial nerve-roots. The portion of it on the mesial side of the Gasserian ganglion gives rise to the cavernous sinus, and the remainder disappears. Vena Capitis Lateralis. — This temporary vein receives three chief intra- cranial tributaries — anterior, middle, and posterior cerebral. The primitive anterior cerebral vein derives its blood from the optic vesicle (eye), fore- brain, and mid-brain. Certain of the tributaries of the anterior cerebral vein, of each side, become connected longitudinally by an anastomotic vessel, lying close to the median line. These two anastomotic vessels, right and left, constitute the rudiment of the superior longitudinal sinus, which sinus is consequently in two halves originally. Subsequently, however, the two anastomotic vessels blend, and so give rise to one superior longitudinal sinus. The primitive middle cerebral vein derives its blood from the cerebellum, and the primitive posterior cerebral vein derives its blood from the medulla oblon- gata. The posterior cerebral vein issues from the cranial cavity through the primitive jugular foramen, prior to joining the vena capitis lateralis, whilst the anterior and middle cerebral veins, having joined the vena capitis lateralis, necessarily issue from the cranial cavity along with the facial nerve through a temporary foramen. Subsequently anastomotic connections are formed between the three primitive cerebral veins. The vena capitis lateralis, which, as just stated, leaves the cranial cavity along with the facial nerve, undergoes atrophy, and the venous blood of the entire encephalon issues from the cranial cavity through the jugular foramen. Subsequent Metamorphoses. — The superior longitudinal sinus, originally in two halves and developed from certain of the tributaries of the anterior cerebral veins, acquires two anastomotic connections, first with the cephalic end of the middle cerebral vein, and afterwards with the posterior cerebral vein. The latter anastomosis gives rise to the greater or transverse part of the lateral sinus, the posterior cerebral vein forming the sigmoid part of that sinus. The middle cerebral vein becomes the superior petrosal sinus. The inferior petrosal sinus is developed from an anastomotic connection between the dorsal part of the cavernous sinus and the distal part of the lateral sinus. THE THORAX loil The extracranial part of the anterior cardinal vein, after the obUteration of the vena capitis lateralis, commences at the jugular foramen, whence it extends caudalwards, receiving in its course the cervical segtnental veins. In the vicinity of the sinus venosus it meets the posterior cardinal vein of its own side, with which it unites. The venous trunk thus formed is called the duct ol Cuvier, of which they are two — right and left. These two ducts pass transversely, one on either side, to the sinus venosus, into which they open. At this stage the sinus venosus also receives the vitelline and um- bilical veins of each side. The ducts of Cuvier form the primitive right and left superior venae cavse. As the heart descends from the region of the fore-gut, the ducts of Cuvier become vertical, and are in line with the anterior cardinal veins. When the sinus venosus becomes merged into the right auricle, and the heart undergoes a shght rotation from right to left, the left duct of Cuvier is placed dorsal to the left auricle, before opening into the right auricle. Each anterior cardinal vein is joined, near its caudal extremity, by the corresponding subclavian vein. Close to the junction the subclavian vein receives the external jugular vein. This vein is a secondary formation, and is probably derived from a posterior auricular vein, being subsequently reinforced by a pre-auricular vein. A transverse anastomotic vessel is now formed, called the transverse jugular vein. It extends from the junction of the left anterior cardinal and left subclavian veins to the right anterior cardinal vein at a point a little below the place where it receives the right subclavian vein. This transverse jugular vein, which extends obliquely from left to right, with a downward inclination, gives rise to the left innominate vein. The venous blood from (i) the left side of the head and neck and (2) the left fore-hmb now passes through the left innominate vein into the permanent superior vena cava. The right innominate vein is formed by the short portion of the right anterior cardinal vein which intervenes between the place where it receives the right subclavian vein and the place where the transverse jugular vein joins it. The portion of the right anterior cardinal vein, which lies immediately below the place where the transverse jugular vein joins it, forms the upper or extra- pericardial part of the permanent superior vena cava — that is to say, the part above the point where the right azygos vein opens into it. The lower or intrapericardial part of the superior vena cava is developed from the right duct of Cuvier. The permanent superior vena cava therefore represents (i) the lower part of the right anterior cardinal vein, and (2) the right duct of Cuvier. The portion of the left anterior cardinal vein immediately below the left extremity of the transverse jugular vein forms the upper part of the left superior intercostal vein, thus accounting for the ending of that vein in the left innominate vein, which, as stated, is formed by the transverse jugular vein. The left duct of Cuvier undergoes partial obliteration. Its terminal part, along with the left lateral comu of the sinus venosus, gives rise to the coronary sinus. The portion next the terminal part also persists in the form of a very minute vein, called the oblique vein of Marshall, which lies over the posterior aspect of the left auricle. The obliterated portion is represented by the vestigial fold of Marshall, which is contained within a small triangular fold of the serous portion of the pericardium, in front of the root of the left lung. Posterior Cardinal Veins. — These are two in number — right and left — and they return the blood from the Wolffian bodies, body-wall, and hind-hmbs. They he on either side of the aorta, dorsal to the mesial part of the Wolffian bodies. The caudal end of each vein receives the sciatic vein, which is the primitive vein of the hind-Hmb. A little above this point it is joined, at a later period, by the external iliac vein, which, along with the femoral vein, has now been developed. The cephalic end of each posterior cardinal vein joins the corresponding IOI2 A MANUAL OF ANATOMY anterior cardinal vein, and the trunk so formed is called the duct of Cuvier (right and left), which opens into the sinus venosus. Amongst other tributaries, the posterior cardinal veins receive segmental veins, such as the lumbar and intercostal veins, and veins from the inter- mediate cell-mass, and they are connected with each other by transverse retro-aortic vessels, which constitute the transverse retro-aortic posterior cardinal anastomoses. One of these, situated in the lower lumbar region, enlarges and forms the transverse iliac vein. This vessel extends some.what obliquely from the left posterior cardinal vein, at a point a little above the place where it receives the left external iliac vein, to the right posterior car- dinal vein, its incHnation in crossing being upwards. The transverse iliac vein gives rise to the greater part of the left common iliac vein, the com- mencement of the latter vessel being formed by that portion of the left posterior cardinal vein which intervenes between the place where it receives the left external iliac vein and the left extremity of the transverse iliac vein. After the formation of the transverse iliac vein, the blood from the left half of the pelvis and left hind-limb is now diverted through the transverse iliac vein into the right posterior cardinal vein. In the thoracic region, two (sometimes one) of the retro-aortic posterior cardinal anastomoses persist as the lower and upper transverse azygos veins. Between the anterior cardinal veins, and also between the posterior cardinal veins, there are, as stated, several transverse anastomotic vessels. Four (sometimes three) of these are of special importance, and may be here summed up as follows, in order from above downwards : 1. Transverse jugular between anterior cardinals, forming the left in- nominate vein. 2. Upper retro-aortic posterior cardinal anastomosis in thorax, forming the upper transverse azygos vein. 3. Lower retro-aortic posterior cardinal anastomosis in thorax, forming the lower transverse azygos vein. 4. Transverse iliac, between posterior cardinals in lower lumbar region, forming greater part of left common iliac vein. The posterior cardinal veins constitute a somewhat circuitous route to the heart. Moreover, in the region of the Wolffian bodies they become, to a certain extent, subdivided into sinusoids. New and more direct channels are therefore formed. New Secondary Venous Channels. — As the development of the hind-Hmbs proceeds, two new secondary venous channels are formed, which are auxiliaries of the posterior cardinal veins, and relieve the obstruction caused by the developing Wolffian bodies. They are called the subcardinal veins (F. T. Lewis). Each subcardinal vein is formed by a longitudinal anastomotic vessel, which connects the small veins passing from the mesentery to the posterior cardinal veins, and it lies ventral to the mesial part of the Wolffian body. The subcardinal veins run parallel with the posterior cardinal veins, on their ventral aspect, and each extends from the caudal end of a posterior cardinal vein to near its cephalic end, being connected with the posterior cardinal at either extremity. Between these points the two veins (posterior cardinal and subcardinal) are connected, at frequent intervals, by dorso- ventral anastomoses. Each vein is also connected with its fellow of the opposite side by transverse anastomoses, those between the posterior cardinal veins being retro-aortic, whilst those between the subcardinal veins are pre- aortic. The subcardinal anastomotic vessels, for the most part, disappear, but one of them becomes large, and lies below the root of the superior mesen- teric artery, in front of the aorta and opposite the future renal veins. It is known as the great pre-aortic transverse subcardinal anastomotic vessel. It also forms an indirect anastomosis between the adjacent parts of the pos- terior cardinal veins. At the level of this anastomotic vessel each renal vein opens into the corresponding posterior cardinal vein. One of the dorso-ventral anastomotic vessels on the right side connects THE THORAX 1013 the subcardina vein with the posterior cardinal vein, opposite the future right renal vein. The right subcardinal vein becomes connected superiorly, behind the liver and within the caval mesentery, with hepatic veins by means of a fusion betsveen hepatic and subcardinal sinusoids. In this manner a venous channel is formed, which leads to the common hepatic vein and thence to the heart. The right subcardinal and posterior cardinal veins being in free commimica- tion with each other, much of the venous blood from the caudal pjirt of the body can flow through the new channel, formed in the caval mesentery by the fusion of the hepatic and subcardinal sinusoids, into the common hepatic Posterior Cardinal Vein Fig. 418. — The Development of the Vena Cava Inferior (Early Stages). Cardinal and Subcardinal Veins, etc. (Frederick T. Lewis, in the American Journal of Anatomy.) vein, and thence to the heart. The blood of the posterior cardinal veins can therefore now reach the heart through two channels — namely: (i) the upper part of the right subcardinal vein, the new path within the caval mesentery, and the common hepatic vein; and (2) the duct of Cuv-ier. The first channel is taken by the blood of the lower parts of the posterior cardinal veins, and the second channel by the blood from the upper parts of the posterior cardinal veins, above the Wolffian bodies. The subcardinal and posterior cardinal veins of each side are divided into two parts — lower and upper — by the great transverse pre-aortic anastomotic vessel. The lower parts of the two subcardinal veins atrophy. The upper part of the right subcardinal vein persists, and forms a portion of the IOI4 A MANUAL OF ANATOMY inferior vena cava of adult life, and the part of the left subcardinal vein above the great transverse pre-aortic anastomotic vessel forms the terminal portion of the left suprarenal vein. The great transverse pre-aortic anas- tomotic vessel persists, and forms the mesial part of the left renal vein of adult life. Additional important changes take place in the course of development, which will now be stated. Metamorphoses of Left Posterior Cardinal Vein. — (i) The part below the left extremity of the transverse iliac vein persists, and forms from above down- wards: (fl) the commencement of the left common iliac vein, and {b) the left i'fiternal iliac vein, into which latter the left external iliac vein subsequently opens. 2. The part between the left extremity of the transverse iliac vein and the place of entrance of the left spermatic vein undergoes atrophy. 3. The part between the place of entrance of the left spermatic (or ovarian) vein and the future left renal vein persists, and forms the upper, or terminal, part of the left spermatic (or ovarian) vein. This circumstance explains why the left spermatic (or ovarian) vein opens into the left renal vein, whereas the right spermatic vein opens into the inferior vena cava. 4. The part immediaiiely above the left renal vein disappears. 5. The remainder of the left posterior cardinal vein persists, and gives rise to (a) the lower left azygos vein, {b) the upper left azygos vein, and (c) the lower portion of the left superior intercostal vein, the upper portion of which is formed by that part of the left anterior cardinal vein which lies immediately below the left extremity of the transverse jugular vein. 6. The part between the lower and upper left azygos veins, and the part between the upper left azygos and left superior intercostal veins may, or may not, undergo obliteration. Metamorphoses of the Right Posterior Cardinal Vein. — (i) The part below the right extremity of the transverse iliac vein persists, and forms from above downwards {a) the right common iliac vein, and (6) the right internal iliac vein, into which latter the right external iliac vein subsequently opens. 2. The part between the right extremity of the transverse iliac vein and the future right renal vein persists, and forms the lower, or postrenal, division of the inferior vena cava. Into this part, superiorly, the right spermatic vein opens, which explains the mode of ending of that vein in the adult, as compared with the mode of ending of the left spermatic vein, which, as stated, opens into the left renal vein. 3. The part immediately above the right renal vein disappears. 4. The remainder of the right posterior cardinal vein persists, and gives rise to the right azygos vein, which, superiorly, takes up the right superior intercostal vein. The right superior intercostal vein is developed from the anastomotic channels which connect the upper three thoracic segmental veins of the right side. The right and left posterior cardinal veins, in the thoracic region, are con- nected by two transverse retro-aortic anastomotic vessels. The lower of these cross- branches persists, and forms the lower transverse azygos vein, which diverts the blood from the lower left azygos vein into the right azygos vein. The upper cross-branch also persists, and gives rise to the upper transverse azygos vein, which diverts the blood from the upper left azygos vein likewise into the right azygos vein. There may only be one transverse azygos vein. Metamorphoses of the Subcardinal Veins — Right Subcardinal. — (i) The right subcardinal vein, as stated, becomes connected with the hepatic veins by a fusion between hepatic and subcardinal capillaries dorsal to the liver and within the caval mesentery. (2) The portion of it which lies above the large transverse anastomotic vessel, connecting the subcardinal and posterior cardinal veins below the level of the root of the superior mesenteric artery, persists, and forms part of the prerenal division of the inferior vena cava. (3) The portion of it on the caudal side of the large transverse anastomotic vessel disai^pears. THE THORAX 1015 Left Subcardinal. — ^The left subcardinal vein, in the cephalic direction, has no connection with the liver. The part above the level of the great transverse pre-aortic subcardinal anastomosis persists as the left suprarenal vein ; and its lower part, below the level of the anastomosis just named, atrophies. Development ol the Inferior Vena Cava. The inferior vena cava, as regards its development, consists of t^vo divisions — lower, or postrenal, and upper, or prerenal. As previously stated, the posterior cardined tind subcardinal veins of the right side are connected by the great transverse pre-aortic anastomotic vessel below the root of the superior mesenteric artery, and at the level where the right renal vein opens into the right posterior cardinal vein. The part of the right posterior cardinal below this anastomotic vessel comes into line with the part of the right subcardinal above it, and so one channel is formed. The postrenal division of the inferior vena cava is formed by the lower portion of the right posterior cardinal vein — that is to say, the portion below the great transverse pre-aortic anastomotic vessel, which forms a part of the left renal vein. The prerenal division is more compUcated in its development. As pre- viously stated, the upper part of the right subcardinal vein becomes con- nected with the hepatic veins by a fusion between the hepatic and subcardinal sinusoids, dorsal to the liver and within the caval mesentery, a new channel being thereby formed to the common hepatic vein and heart. (The common hepatic vein is formed by the union of the right and left hepatic veins and ductus venosus.) The prerenal division of the inferior vena cava is formed, from below upwards, by (i) the upper portion of the right subcardinal vein — that is to say, the portion above the great transverse pre-aortic anastomotic vessel, (2) the fusion of hepatic and right subcardinal sinusoids within the caval mesentery, (3) the right hepatic vein, and (4) the common hepatic vein, which is connected with the heart. Summary of Development of Inferior Vena Cava. Postrenal Division = Portion of right posterior cardinal between right renal and transverse iUac veins. 1. Anastomotic connection between right posterior cardinal and right subcardinal veins at level of right renal vein. 2. Upper portion of right subcardinal vein — that is to say, the portion above the great transverse pre- aortic anastomotic vessel. 3. Fusion of hepatic and right subcardinal capilleiries within the caval mesentery. 4. Right hepatic vein. 5. Common hepatic vein. Development of Renal Veins. — ^Each renal vein is originally a segmental vein of the corresponding intermediate cell-mass, in which the renal organs are developed. The right vessel has no other source, but the terminal part of the left renal vein is formed by the great transverse pre-aortic anastomotic vessel, which lies across the aorta below the root of the superior mesenteric artery. Development of Suprarenal Veins. — Each vessel probably originates as a segmental vein of the suprarenal area of the corresponding intermediate cell- mass. The right vessel has no other source, but the terminal part of the left vein s formed by the part of the left subcardinal vein above the great trans- verse pre-aortic anastomotic vessel, which persists as the mesial part of the left renal vein. Development of Lumbar Veins. — The right and left lumbar veins are origin- ally the segmental veins of the lumbar region. The right vessels have no further Prerenal Division =■( ioi6 A MANUAL OF ANATOMY source, but those portions of the left lumbar veins, which cross behind the abdominal aorta to reach the inferior vena cava, represent the persistent transverse retro-aortic posterior cardinal anastomotic vessels. Development of Azygos System ol Veins. — The right vena azygos represents the, upper part of the right posterior cardinal vein, above the level of the future right renal vein. The lower and upper left azygos veins are developed from the thoracic portion of the left posterior cardinal vein. The lower and upper transverse azygos veins are persistent transverse retro-aortic posterior cardinal anastomotic vessels. Development of Spermatic and Ovarian Veins. — Each of these veins is originally a segmental vein of the corresponding intermediate cell mass, in which the sexual glands are developed. The vessels of the right side have no other source, but the terminal part, of each left vein is formed by that portion of the left posterior cardinal vein which extends between the point of entrance of the left spermatic (or ovarian) vein and the future left renal vein. Development of the Lymphatic System. The lymphatic system consists of lymphatic vessels and lymphatic glands or nodes. There is also lymphoid or adenoid tissue, as in the thymus body, lymphoid follicles and villi of the intestinal mucous membrane, Malpighian corpuscles of the spleen, palatine tonsils, and pharyngeal tonsil. There are two stages in the development of the lymphatic system — primary and second- ary. The primary stage is concerned in the formation of lymph-sacs, and the secondary stage consists in the formation of lymphatic vessels and lymph- glands. Lymph Sacs. — There are two pairs of lymph-sacs and two single sacs, eis follows : 1. Cervical or jugular (2). 2. Retro -peritoneal or pre-aortic (i), 3. Receptaculum or cisterna chyli (i). 4. Caudal or sciatic (2), Opinions differ as to the development of these lymph-sacs. The view of Florence R. Sabin will be stated first. According to this lady the sacs are developed as sproutings from the endothelial lining of veins, and this constitutes the primary stage in the development of the lymphatic system. Jugular Sacs. — The jugular lymph-sacs, right and left, are the first to appear. Each is situated on the outer side of the lower part of the primitive anterior cardinal vein, which becomes the internal jugular vein. It is formed from part of a capillary venous plexus, connected in early life with the anterior cardinal vein. A large part of this plexus disappears, whilst the connection of the remainder with the anterior cardinal vein is severed. There thus results a detached collection of capillaries, lined with endothelium and in close proximity to the outer side of the lower part of the anterior cardinal vein. These capillaries become dilated, and subsequently join to form the jugular lymph-sac of each side, which is lined with endothelium, and which establishes a fresh connection with the lower part of the anterior cardinal vein, where it is joined by the subclavian vein, a valve being formed at the venous junction by a protrusion of part of the lymph-sac at the place of junction. The jugular sac of each side is connected externally with per- ipheral lymphatic vessels which extend to the head, neck, and fore-limb bud of the same side. The caudal end of the left sac becomes connected with the thoracic duct, whilst the caudal end of the right sac becomes connected with the right lymphatic duct. The dorsal part of the sac becomes converted into a plexus of lymphatic vessels, from which chains of lymph-glands are de- veloped. Retro-Peritoneal Sac. — The retro-peritoneal or pre-aortic lymph-sac is single, and is formed from a capillary venous plexus in the root of the mesentery, which plexus is connected with the great pre-aortic transverse anastomotic vessel which extends between the two subcardinal veins. The capillary THE THORAX 1017 plexus in the root of the mesentery becomes converted into a lymph-sac, without any venous connection, jind this constitutes the retro-peritoneal or pre-aortic sac, which establishes a communication with the receptaculum or cistema chyh, and through it with the thoracic duct. It is ultimately replaced by a plexus of l>Tnphatic vessels, and from this plexus chains of h-mphatic glands are developed which he along the ventral aspect of the abdominal aorta. From the retro-peritoneal sac lymphatic vessels pass within the mesentery along the branches of the superior mesenteric artery, and these form another lymphatic plexus, from which the mesenteric lym- phatic (lacteal) glands are developed. Subsequently lymphatic (lacteal) vessels enter the wall of the small intestine. Seiatic Saes. — ^The sciatic lymph-sacs, right and left, are developed from capillar>' venous plexuses in connection with the two primitive sciatic veins. On either side the sac extends from near the caudal end of the receptaculum chyU along the outer side of the primitive sciatic vein. It ultimately becomes converted into lymphatic glands. Reeeptacalum Chyli.— The receptaculum or cistema chyli is a single sac, situated at the caudal end of the thoracic duct. It is developed from, and replaces, a venous plexus. The thoracic duct connects the receptaculum chyh with the left jugular lymph-sac, and the receptaculum chyU communi- cates with each sciatic sac. From each jugula? sac a vessel grows caudal- wards. On the right side this vessel constitutes the right lymphatie tronk, aad on the left side it forms the thoraeie daet. As the thoracic duct ap- proaches the developing aortic arch it divides and gives rise to two thoracic ducts, which embrace that arch and then pass to join separately the recep- taculum chyh opposite the WoLQ&an bodies. Subsequently these two ducts fuse, and one duct is formed. The thoracic duct is developed from a series of venous capillaries, originally having a connection with veias. Lymphatie Vessels. — ^The formation of these vessels, along with that of Ij-mph-glands, constitutes the second stage in the development of the Ijrm- phatic system. According to Sabin, the lymphatic vessels are formed from the endothelial lining of the lymph-sacs, whilst the Ijmph-glands are developed from plexuses of lymphatic capillaries. The development of the thoracic daet, as stated, takes place from several groups of venous capiUciries. It is the largest lymphatic vessel, and it connects the receptaculum chyli with the left jugular sac. The IjTuphatics derived from the jugular Ijonph-sacs pass to the head, neck, and fore-Umb buds; those from the sciatic lymph sacs extend to the hind-limb buds; and those from the retro-peritoneal (mesenteric) Ij-mph- sac enter the mesentery', within which lymph-glands (mesenteric) are devel- oped in connection with them. From these mesenteric glands, in succession, fresh Ijmiphatic vessels pass to the intestinal tube. The other view of the development of the lymphatic system, held by Hunt- ington amongst others, is that the connection of the Ijonphatic vessels with the venous sj'stem is secondary, and not primary-, as Sabin holds. According to this other \-iew the Ij-mphatic vessels spring from lymph-spaces, which are formed in the mesoderm (mesenchyme), and are linedwitii mesathelium. The endothehal cells of the lymphatic vessels are derived from this mesothehum, and not from the venous endotheUum according to Sabin, and the vessels estabhsh a connection with the venous s>^tem at a later period. Lymph-Glands. — Some of these are formed in connection with the lymph- sacs, whilst others are formed in connection with peripheral lymphatic vessels. There are three stages in the development of a h-mph-gland. The first stage consists in the formation of a plexus of lynnphatic capillaries pervaded by connective-tissue septa. The second stage consists in the invasion of these septa by blood-capillaries, stirrounded by lymphocytes. The third stage consists in the formation of a lymph-sinos from the original plexus of Ijtu- phatic capillaries. The essential elements of a lymph-gland are thus threefold — namely: ioi8 A MANUAL OF ANATOMY (i) a plexus of lymph-capillaries, (2) blood-capillaries, surrounded by lym- phocytes, within connective-tissue septa, and (3) a lymph-sinus. Each lymph-gland is connected with several lymphatic vessels. Those which enter the gland are known as afferent vessels, and they open into the peripheral or cortical part of the lymph-sinus. Those which emerge from the gland are termed efferent vessels, and they arise in the central or medullary part of the lymph-sinus. In no case does a lymphatic vessel pass uninter- ruptedly through a lymph-gland. The gland is a station in the path of a lymphatic vessel, which represents the terminus of that vessel, but not the terminus of the lymph. That fluid, after leaving the afierent vessel, flows Afferent Lymphatics Fibrous Coal Efferent Lymphatics Fig. 419. — Diagrammatic Section of Lymphatic Gland (Sharpey, from Quain). in succession through the cortical and medullary parts of the lymph-sinus, and from the medullary part it flows into the efferent vessels. It is there- fore, so far as the lymph is concerned, a case of, so to speak, changing car- riages at a glandular station. During this process any injurious matter is taken up by the branched cells (phagocytes) of the lymph-sinus, and the lymph is furnished with a contingent of lymphocytes Structure of Lymphatic Vessels. A l3niiphatic vessel, of large size, consists of three coats — inner, middle, and outer. The inner coat (tunica intima) consists of a longitudinal network of elastic fibres, lined with endothelial cells. The middle coat [tunica media) consists of plain muscular and elastic tissues, disposed for the most part transversely. The outer coat [tunica externa) consists of (i) longitudinal bundles of connective tissue, and (2) plain muscular and elastic fibres, dis- posed for the most part longitudinally, lined with endothelium. Lymphatic vessels are furnished with bloodvessels and nerves. Most of them are also provided with valves, similar to those of the veins. Each valve consists of two semilunar segments, facing one another, which are foldings of the inner coat, containing connective and elastic tissues. They project slightly towards each other, and their free edges are directed in the course of the lymph-stream. The valves are situated at short intervals, and they serve to prevent reflux of lymph. When a lymphatic vessel becomes distended it THE THORAX 1019 presents a beaded appearance, with constrictions between the projections, these constrictions corresponding to the attached margins of the valvular segments. Development. — According to Sabin the lymphatic vessels are developed from the endothelial lining of the primitive lymph-sacs (see Development of Lymphatic System). Strneture of Lymphatic Glands. A lymphatic gland consists of a capsule, which encloses the glandular substance. The capsule is composed of connective tissue, containing elastic fibres. The glandular substance presents two parts — superficial or cortical, and central or medullary. Each of these parts is permeated by a supporting framework of trabecula; derived from the capsule. These trabecula? are composed of connective tissue, with a few plain muscular fibres. They sub- divide the cortex into follicles, between which they form incomplete septa. In the medulla the trabeculae are arranged in a reticular manner. The glandular substance is formed by lymphoid or adenoid tissue, which consists of retiform tissue, with lymphocytes in its meshes. In the cortex of the gland this lymphoid tissue is disposed as lymph-follicles, and in the medulla it forms lymph-cords. In both parts of the gland there are spaces between the glandular substance and the supporting trabecular framework. These spaces, which are for the passage of lymph, constitute the lymph-sinus. This sinus is broken up at all parts of the gland by retiform tissue, the meshes of which are partially lined with branched cells of the nature of phagocytes. The glandular substance, except the lymph-sinus, are permeated by blood- capillaries. Lymphatic glands are furnished with bloodvessels, nerves, and lymphatic vessels. The arterioles pass to the glandular substance, being at first en- sheathed by the supporting trabeculae of connective tissue, and subsequently by the retiform tissue of the glandular substance. The nerves are destined for the plain muscular tissue of the trabeculae and bloodvessels. The lymphatic vessels are of two kinds — afferent and efferent. The afferent vessels enter the gland over its surface, whilst the efferent vessels emerge at a definite part of the gland, where there is a shght depression, called the hilum. The afferent vessels convey lymph to the cortical part of the lymph-sinus, whilst the efferent vessels convey lymph from the medullary part of that sinus. Inasmuch as the medullary part of the gland extends quite to the surface at the place where the depression, known as the hilum, exists, the efferent vessels emerge from the gland through this hilum, which also gives passage to the arteries and veins. Development. — Lymphatic glands are developed partly from the primitive lymph-sacs, and partly from peripheral lymphatic vessels (see Development of Lymphatic System). Trachea in the Thorax. — ^The thoracic portion of the trachea extends from the level of the upper border of the manubrium sterni to the level of the intervertebral disc between the bodies of the fourth and fifth thoracic vertebrae, where it divides into the two bronchi, right and left. It occupies a median position in the superior mediastinum, and its length is about 2J inches. As in the neck, it is cylindrical and firm in front and at the sides, but posteriorly it is flattened and membranous, where it rests upon the oesophagus. Relations — Anterior. — ^The manubrium sterni, and the origins of the sterno-hyoid and sterno-thyroid muscles ; the remains of the thymus body ; the origins of the innominate and left common carotid arteries, and the left innominate vein; and the arch of the aorta, which lies upon it immediately above its bifurcation into the Ioa> A MANUAL OF ANATOMY two bronchi, with the intervention of the deep cardiac plexus of nerves. Posterior. — ^The oesophagus, which inclines partially to the left of the trachea. Right. — ^The right pneumogastric nerve ; the innominate artery, after it has left the front of the trachea ; and the right pleural sac. Left. — ^The arch of the aorta and the left common carotid artery, after these have left the front of the trachea ; the left subclavian artery ; and the left recurrent laryngeal nerve. Bronchi.— The bronchi, right and left, commence at the bifurca- tion of the trachea, and each passes to the hilum of the correspond- ing lung, where its ramifications commence. As in the trachea, each bronchus is cylindrical and firm in front and at the sides, but posteriorly it is flattened and membranous. There being certain differences between the bronchi, a separate description is required for each. The right bronchus is about i inch in length up to the point where it gives off its first, or eparterial, branch. It has about six cartilaginous rings, and is larger than the left bronchus. It is more vertical than the left bronchus, and therefore coincides with the direction of the trachea to a greater extent than its fellow. Relations — Superior. — ^The right azygos vein arches over it to open into the superior vena cava. Posterior. — ^The right pneumo- gastric nerve. Inferior. — ^The right pulmonary artery, which sub- sequently lies anterior to it. About I inch from its commencement the right bronchus gives off a branch from its outer side which passes to the upper lobe of the right lung. This branch is known as the eparterial bronchus, because it arises above the right pulmonary artery. The rest of the right bronchus is spoken of as being hyparterial. The left bronchus is about 2 inches in length. It has about twelve cartilaginous rings, and is smaller than the right bronchus on account of the smaller size of the left lung. Its course is more oblique than that of its fellow, and it is directed downwards and outwards beneath the arch of the aorta to the hilum of the left lung. Relations — Anterior.— The. left pulmonary artery, which subse- quently lies above it. Posterior. — The oesophagus and the descend- ing thoracic aorta. The left bronchus has no eparterial branch. When the interior of the trachea is viewed from above, as in using the laryngoscope, the openings of the two bronchi are seen to be separated by a ridge which is situated to the left of the median line, and more of the interior of the right bronchus than of the left is visible. Partly on this account, and partly by reason of the more vertical direction of the right bronchus, as well as its larger size, a foreign body getting into the trachea is more apt to descend into the right bronchus than into the left. THE THORAX X02X The structure of the trachea will be described in connection with the description of the windpipe in the neck. (Esophagus in the Thorax. — The oesophagus or gullet extends from the pharjTix to the stomach. In the first part of its course it hes in the neck, and this portion \sill be found described in connection with that region. The thoracic part (see Fig. 422) extends from the level of the upper border of the manubrium stemi to the level of the body of the twelfth thoracic vertebra, where it passes through Epiglottis Great Coma of Hyoid Bone. Small Comu of Hyoid Bone. i . Body of Hyoid Bone... l Thyro-hyoid Membrane- — Levator GIandube\ ___ Thyroidetween the external and internal intercostal muscles, it enters the sub- costal groove of the upper rib. In this position it courses forwards, and ends by anastomosing with the upper anterior intercostal branch of the internal mammary artery, or of its musculo-phrenic branch, according to the level. The companion intercostal vein lies above the artery, and the corresponding intercostal nerve lies below it. The order of struc- tures, therefore, in the subcostal groove, from above downwards, is as follows : intercostal vein, intercostal artery, and intercostal nerve. The upper seven aortic intercostal arteries are confined to the intercostal spaces which they occupy ; but the lower two, namely, those in the tenth and eleventh intercostal spaces, ulti- mately leave these spaces, and pass into the abdominal wall, where they have been described in connection with the abdomen. Branches. — ^These are dorsal, giving off a spinal branch ; collateral ; and lateral cutaneous. The dorsal branch arises from the aortic intercostal artery as that vessel enters the posterior extremity of an intercostal space. It passes backwards, in company with the posterior primary division of the corresponding spinal nerve, between the adjacent transverse processes, where it lies internal to the superior costo-transverse ligament. Opposite the intervertebral foramen it gives off its spinal branch, which enters the spinal canal through the foramen to be distributed to its osseous and ligamentous walls, as well as to the spinal cord and its membranes. The dorsal branch, con- tinuing its course baclcwards, divides into an internal and external branch, which supply the muscles and integument of the back. The collateral intercostal artery arises from the main aortic inter- costal opposite the angle of the rib. It passes obliquely downwards and outwards to the upper border of the lower rib, along which it courses, lying between the external and internal intercostal muscles. Anteriorly it ends by anastomosing with the lower anterior inter- costal branch of the internal mammary artery, or of its musculo- phrenic branch, according to the level. The lateral cutaneous branches accompany the lateral cutaneous branches of the corresponding intercostal nerves to the integu- ment. The first aortic intercostal artery, namely, that which lies in the third intercostal space, furnishes a branch, of varitible size, which ascends over the neck of the third rib to the second inter- costal space. This branch anastomoses with the second intercostal THE THORAX 1027 axter\', which is a branch of the superior intercostal, and may even replace it. The subcostal arteries, right and left, are the last branches of the descending thoracic aorta. They are serially continuous with the aortic intercostal arteries above, and with the lumbar arteries below. Each vessel winds roimd the side of the body of the twelfth thoracic vertebra, and, passing beneath the external arcuate ligament of the diaphragm, it enters the wall of the abdomen, where it lies along the lower border of the t^^'elfth rib. These vessels will be found described in connection with the abdomen (see p. 773). The first and second intercostal spaces receive their arteries from the superior intercostal artery, which is a branch of the second part of the subclavian on the right side, and of the first part on the left side. Having descended in front of the neck of the first rib to the posterior extremity of the first intercostal space, the vessel furnishes the first intercostal artery to that space, and it also gives off the second intercostal artery, which descends in front of the neck of the second rib to the second intercostal space. As stated, the second intercostal artery receives a branch from the third intercostal artery, which ascends over the neck of the third rib, the third inter- costal being the first aortic intercostal. Development of the Descending Aorta. — The upper portion of the descend- ing aorta is developed from that part of the left primitive dorsal aorta which lies between the fourth left arterial arch and the place of junction of the two primitive dorsal aortae. The greater portion of it, however, results from the union of the two primitive dorsal aortae. The intercostal arteries are developed from thoracic segmental arteries. Intercostal Veins. — ^The intercostal veins are eleven in number on either side, and each lies in the subcostal groove above the corresponding aortic intercostal artery. In the region of the angle of the rib each vein receives the collateral intercostal vein, which accompanies the artery of that name. At the posterior extremity of an intercostal space each vein receives a large dorsal branch, which returns blood from the muscles and integument of the back, the dorsal spinal venous plexus, and the spinal canal. With the exception of the upper three or four veins, all the other intercostal veins pass inwards, behind the . corresponding sympa- thetic cord, on to the bodies of the thoracic vertebrae, from which they receive small twigs. Their mode of termination differs on the two sides. On the right side the veins, hav'ing passed behind the oesophagus, terminate in the right azygos vein. On the kft side the lower four veins, namely, the eighth, ninth, tenth, and eleventh, open into the lower left azygos vein ; and the succeeding three (or four), namely, the fifth, sLxth, and seventh (and, it may be, the fourth also), open into the upper left azygos vein. The first intercostal vein of each side accompanies the corre- sponding superior intercostal artery, and terminates in the inno- minate vein, or, it may be, in the vertebral vein, of its own side. The second and third intercostal veins (and, it may be, the fourth) I028 A MANUAL OF ANATOMY of each side unite to form the superior intercostal vein. The right superior intercostal vein, after a downward course, joins the upper part of the right azygos vein. The left superior intercostal vein ascends over the back part of the arch of the aorta, and opens into the left innominate vein. It sometimes receives the left bronchial vein as a tributary. Summary of the Intercostal Veins — Right Intercostal Veins. — The first opens into the right innominate vein, or sometimes into the right vertebral vein. The second and third (and, it may be, the fourth also) unite to form the right superior intercostal vein, which opens into the right azygos vein. The lower eight (sometimes the lower seven) are direct tributaries of the right azygos vein. Left Intercostal Veins. — The first opens into the left Innominate vein, or sometimes into the left vertebral vein. The second and third (and it may be the fourth also) unite to form the left superior intercostal vein, which opens into the left innominate vein. The fifth, sixth, and seventh (and, it may be, the fourth also) terminate in the upper left azygos vein. The eighth, ninth, tenth, and eleventh are tributaries of the lower left azgyos vein. The left superior intercostal vein is developed from two sources. The upper part is formed by the portion of the left primitive jugular vein below, and adjacent to. the commencement of the transverse jugular vein. The lower part is formed by the upper portion of the left cardinal vein. Intercostal Glands. — These glands form a chain on either side of the vertebral column, in line with the heads of the ribs. The main glands of each chain lie in the posterior parts of the intercostal spaces, and one or two glands accom- pany each posterior intercostal artery for a very short distance. The intercostal glands receive their afferent vessels from (i) the posterior half of the costal pleura, (2) the posterior halves of the external and internal intercostal muscles, (3) the deep muscles of the back, and (4) the spinal canal. Their efferent vessels, on either side, pass to the thoracic duct. The efferents of the upper right intercostal glands sometimes open into a right broncho -mediastinal lymphatic trunk, which terminates in the right lymphatic duct. The right superior intercostal vein is developed from the anastomotic channels which connect the upper three thoracic segmental veins of the right side. Azygos Veins. — ^These are three in number, one right and two left. The vena azygos major or right azygos vein commences in the abdomen as the right ascending lumbar vein, and enters the thorax through the aortic opening of the diaphragm, lying on the right side of the aorta, the thoracic duct intervening. It then ascends, under cover of the oesophagus, upon the bodies of the thoracic vertebrae, crossing in its course the right aortic intercostal arteries. Having reached the level of the fifth thoracic vertebra it leaves the vertebral column, and, arching forwards over the right bronchus, it opens into the superior vena cava, just before that vessel pierces the pericardium. In the thorax the right azygos vein continues to lie on the right side of the aorta, the thoracic duct intervening. Tributaries. — ^These are as follows : 1. The right subcostal vein. 2. The lower seven (sometimes the lower eight) right intercostal veins. THE THORAX 1029 3. The right superior intercostal vein. 4. The right bronchial vein. 5. Some oesophageal veins. • 6. Some pericardial veins. 7. The lower and upper transverse azygos veins Right Lymphatic Duct Right Innominate Vein— ^!3^ZA Superior Vena Ca Right Superior Intercostal Vein_^ Right Azj-gos \ c Thoracic Dutt ^ Posterior Intercostal Glands- — _ — Reoeptaculum Cbyli ■; V t / / Right Ascendug Lumbar Vein. .--j^^,^^}. Inferior Vena Cava Thoracic Duct Left Innominate Vein ^ Left Superior Intercostal Vein 5. . Arch of Aorta .Upper Left Azygos Vein SSs^_<.^3L_Upper Transverse Azygos Vein ■ Lower Transverse Az>'gos Vein ._ Ninth Intercostal Vein _ Lower Left Azygos Vein Si^-Left Subcostal V«n # ■ Quadrafais Lumborum i — A-^'l^^ Left Ascending Ltimbar Vein ■ \^ - ^ --Abdominal Aorta . Iliac Crest *"'■!— Psoas Magnus 'i^...Iliacus -.-w Common Iliac Arteries Fig. 423. — The Thoracic Dcct, Azygos Veins, and Posterior Intercostal Glands. The vena azygos minor or lower left azygos vein commences in the abdomen as the left ascending lumbar vein, and enters the thorax by piercing the left cms of the diaphragm. It ascends upon the vertebral column to the level of the eighth thoracic ver- I030 A MANUAL OF ANATOMY tebra, lying in front of the lower aortic intercostal arteries, and it takes up the lower four left intercostal veins. It then crosses the vertebral column from left to" right, under the name of the lower transverse azygffs vein, passing behind the descending aorta and thoracic duct, and thereafter it opens into the right azygos vein. Tributaries. — These are as follows : 1. The left subcostal vein. 2. The lower four left intercostal veins. 3. Some oesophageal veins. The upper left, or accessory, azygos vein is formed by the union of the fifth, sixth, and seventh left intercostal veins (sometimes also the fourth). At the level of the seventh thoracic vertebra it crosses the vertebral column from left to right, under the name of the upper transverse azygos vein, passing behind the descending aorta and thoracic duct, and thereafter it opens into the right azygos vein. It communicates above with the left superior inter- costal vein, and below with the lower left azygos vein. Tributaries. — ^These are as follows : 1. The fifth, sixth, and seventh left intercostal veins (sometimes also the fourth). 2. The left bronchial vein, as a rule. 3. Some oesophageal veins. The lower and upper left azygos veins, which are subject to much variation, sometimes unite to form one transverse azygos vein. Summary of the Azygos Veins — Right Azygos Vein. — This vessel receives (i) the right subcostal vein; (2) the lower seven (sometimes the lower eight) right intercostal veins ; (3) the right superior intercostal vein ; (4) the right bronchial vein ; (5) some "oesophageal veins ; (6) some pericardial veins ; and (7) the lower and upper transverse azygos veins. Lower Left Azygos Vein. — This vessel receives (i) the left subcostal vein; (2) the lower four left intercostal veins ; and {3) some cesophageal veins. Upper Left Azygos Vein. — This vessel receives (i) the fifth, sixth, and seventh (sometimes also the fourth) left intercostal veins ; (2) the left bronchial vein, as a rule; and (3) some oesophageal veins. The right azygos vein and the lower left azygos vein, through their connections with the ascending lumbar veins, establish com- munications with tjie inferior vena cava and with the common iliac veins or some of their tributaries. They therefore form important channels by which a considerable quantity of blood is returned from the lower limbs and abdominal wall in cases of obstruction of the inferior vena cava. Development. — The right azygos vein is developed from the thoracic portion of the right cardinal vein. The lower and upper left azygos veins are developed from the thoracic portion of the left cardinal vein. Subcostal Veins. — These are two in number, right and left, and they are serially continuous with the intercostal veins. Each vessel enters the thor^^-f fOffiT the' abd>omen by passing behind the A M A THE THORAX 1031 external arcuate ligament of the diaphragm. As stated, the right vein opens into the right azygos vein, and the left into the lower left azygos vein. Anterior Primary Divisions of the Thoracic Spinal Nerves. — These are twelve in number on each side. The first eleven enter inter- costal spaces, and are called the intercostal nerves. The last, which belongs to the abdomen, lies along the lower border of the twelfth rib, and is called the subcostal nerve (' last dorsal nerve '). At the posterior extremities of the intercostal spaces the intercostal nerves are near the gangliated cord of the sympathetic, and each nerve is connected with the adjacent sympathetic ganglion by two rami comnmnicantes, which are necessarily very short. One of these rami, being composed of spinal fibres, is white, and the other, which consists of sympathetic fibres, is grey. Each intercostal nerve lies below the corresponding artery, and, like it, lies between the parietal pleura and the posterior intercostal aponeurosis, as far as the angle of the rib. Its subsequent course corresponds to that of the artery. The first intercostal nerve is of small size, because the greater part of the anterior primary division of the first thoracic nerve takes part in the formation of the brachial plexus. The second intercostal nerve sometimes gives off a small branch which ascends to join the portion of the anterior primary division of the first thoracic nerve which takes part in the brachial plexus. The further course and distribution of the intercostal nerves belong to the thoracic and abdominal walls, in connection with which they will be found described. Thoracic Duct. — ^The thoracic duct commences in the abdomen in a dilatation, called the receptaculum chyli, which is situated in front of the bodies of the first and second lumbar vertebrae, and it terminates by opening into the angle of junction of the internal jugular and subclavian veins of the left side. It is about 18 inches in length, and enters the thorax from the abdomen by passing through the aortic opening of the diaphragm, where it lies between the aorta on the left and the right azygos vein on the right. In this position it ascends in the thorax, resting upon the vertebral column, the right aortic intercostal arteries, and the lower and upper transverse azygos veins, being under cover of the oesophagus. Up to the level of the fourth or fifth thoracic vertebra it occupies the middle line. At this level it passes behind the arch of the aorta, inclining to the left of the middle line. Thereafter it ascends in close contact with the left side of the oesophagus, and behind the thoracic portion of the left subclavian artery. In this position it enters the root of the neck on the left side, where it ascends upon the left side of the oesophagus, between the left common carotid and left subclavian arteries. At about the level of the seventh cervical vertebra it describes a curve, and passes outwards, for- wards, and downwards, in contact with the dome of the left pleura. Thereafter it inclines inwards, and terminates by oj^ening into the angle of junction between the internal jugular and subclavian veins I032 A MANUAL OF ANATOMY Of the left side In the lower part of the thorax the thoracic duct is nL.'^if/'' ""^^'^r l^^" i" '^^ "PP^^ P^^t- Its course is somewhat esDecall^?; fhp ''^'" ^^'^^^^'^ ^' P^'^^^^*^ ^ beaded appearance especially in the upper part, due to the number of valves with which It is provided. Sometimes the duct divides into two branches m the lower part of the thorax, which reunite at a higher kvel The duct IS freely provided with valves, especially in its upper part* and at its termination there is an important vllve, con^sfsting of two segments, which are so directed as to prevent effectually the reflux of chyle, or the flow of blood, into the duct ^ «;onrrP. "JxtTi, '1''^ '^""T^l lymphatic vessels from the following sources . (i) the lower limbs ; (2) the abdomen and its viscera except sonae of the lymphatics from part of the upper surface of th^ tT^: ?^ 'AV'^i^ ^"^^ °^ '^' ^^°^^^^^ ^^" ' f4) the^eft kng and the left half of the heart ; (5) the left upper limb ; and (6) th! left b.tf 1/1?%^""^ and neck. Most of the lymphatics of the right aiiall of the thorax and those of the right lung and right half of the hearr uiP- ° ^J "?h* lymphatic duct, for the description of which see the sectionr'ii^^^^^ng ^jjh the neck. Thoracic Lymphatic'"^<^i-^^^s-~These are arranged in several groups, as follows : anterior intb^'^^ostal or sternal, posterior inter- costal, superior mediastinal, anterior ^'i^ediastinal, posterior medias- tinal, bronchial, and caval. The anterior intercostal or sternal glands will' be found described on p. 933. They receive their afferent vessels fron'il (i) the anterior parts of the upper six intercostal spaces ; {2) the iui'ier portion of the mammary gland ; (3) the lymphatics accompanying uhe superior epigastric artery from the upper part of the anterior afrdominal wall ; and (4) the l^nrntphatics accompanying the musculo- phrenic artery from the anterior parts of the seventh, eighth, and ninth intercostal spaces, and from a portion of the diaphragm. The efferent vessels of the right glands terminate in the right lymphatic duct, and those of the left glands in the thoracic duct. The posterior intercostal glands are situated on either side of the vertebral column, where they lie in the intercostal spaces, thers being from one to three in each space. They receive their afferen*^ vessels from (i) the posterior parts of the intercostal spaces ; (2) the parietal pleura ; (3) the spinal canal ; and (4) the deep muscles of the back. The efferent vessels of the left intercostal glands open into the thoracic duct. On the right side the efferent vessels from the lower glands pass to the thoracic duct, but those from the upper glands open into the right lymphatic duct. The superior mediastinal glands lie in the superior mediastinum in relation to the arch of the aorta and the innominate veins, and they are continuous with the posterior mediastinal and bronchial glands. They receive their afferent vessels from the pericardium, the heart, and the thymus body in early life, and their efferent vessels pass to the thoracic duct and right lymphatic duct. The anterior mediastinal glands lie in the lower part of the anterior Auriculo temporal Nerve Facial Nerve { Posterior Auricular Nerve •, • ^^a* lom. Car. Art. and Symp. Plexus - -/jm^^^^fngB^^^MK^l---"- ' Superior Laryngeal Nerve •i^i^^\JI^^^^M^^^^SKmj Ganglion Sympathetic Gangliated JS^BB^^r-^ ^^^^^5^' ' : Small Splanchnic Nerve— A - ' ' ' "" i ST""' \ Branches of Vagus A f on Stomach Great Splanchnic Ner\ ■ fcjS, W^ Least Splanchnic Nerv , -> mBBSS^^Bm^'W ^^gjf^gj^^^l^^j^^-- Right Semilnnar Ganglion \S| ^: '': ^' " ^il^tjajj^^^gJT^- — Epigastric Plexus ^i HrflHpPWBP^'^—^^'*** Superior Mesenteric Artery Renal Artery and Plexus Abdominal Aorta S.V.C. Superior Vena Cava Fig. 424, — Nerves of the Right Side of the Face, Neck, and Thorax (HiRSCHFELD AND LeVEILL^). 1034 A MANUAL OF ANATOMY mediastinum, in front of the pericardium. They receive their afferent vessels from (i) the mesial portions of the right and left lobes of the liver in the vicinity of the falciform ligament ; (2) the adjacent portion of the diaphragm ; (3) the anterior part of the pericardium ; and (4) the lower anterior intercostal or sternal glands. Their efferent vessels pass to the thoracic duct and right lymphatic duct. The posterior mediastinal glands are situated in the posterior mediastinum, along the course of the descending aorta and oeso- phagus. They receive their afferent vessels from the oesophagus, the posterior part of the pericardium, and the vertebral portion of the diaphragm. Their efferent vessels pass, for the most part, to the thoracic duct. The bronchial glands are very numerous, and are situated partly between the two bronchi, where these spring from the trachea, and partly at the root of each lung. They are very dark in colour, and receive their afferent vessels from the lungs and the visceral pleurae. Their efferent vessels pass to the thoracic duct and right lymphatic duct. The caval glands are situated in contact with the limited thoracic portion of the inferior vena cava. They receive their afferent vessels from the uncovered area of the posterior surface of the liver, and also those deep lymphatics of that organ which accompany the hepatic veins to the caval fossa. Their efferent vessels pass to the thoracic duct. . Gangliated Cord of the Sympathetic. — ^The sympathetic system in the thorax consists of (i) two gangliated cords, right and left, and (2) a prevertebral plexus, namely, the cardiac plexus. The latter plexus has been already described. The gangliated cord lies on each side of the vertebral column behind the parietal pleura, and superficial to the intercostal vessels. It presents, as a rule, twelve ganglia, but the first is frequently united with the inferior cervical ganglion, in which cases the number is reduced to eleven. The upper ten ganglia are placed upon the heads of the correspond- ing ribs, but the lower two lie upon the sides of the bodies of the eleventh and twelfth thoracic vertebrae. The first thoracic ganglion is the largest of the thoracic series, and is known as the ganglion stellatum. The sympathetic cord leaves the thorax by passing behind the inner part of the internal arcuate ligament of the diaphragm, and so enters the abdomen. Branches — i. Of Communication. — ^These are called the rami conimunic antes. Two of these, one white and the other grey, pass between each ganglion and the adjacent intercostal nerve. The white fibres are of spinal, and the grey of sympathetic, origin. From the proximity of the ganglia to the intercostal nerves the rami communicantes are characterized by their shortness, 2. Of Distribution. — From the upper five ganglia small vascular branches are given off, which are distributed to the coats of the thoracic aorta. From the second, third, and fouith ganglia pid- THE THORAX t035 monary branches are given off to the posterior pulmonary plexus. From the fifth ganglion downwards the three splanchnic (' visceral ') nerves — great, small, and least — are given off. The great splanchnic nerve arises by five separate roots from the fifth, sixth, seventh, eighth, and ninth ganglia, the fibres of the upper roots being traceable in the sympathetic cord as high as the second ganglion. The roots arch obliquely forwards and downwards upon the sides of the bodies of the adjacent vertebrae, and by their union they form a large nerve, which pierces the crus of the diaphragm and terminates in the semilunar ganglion of the epi- gastric or solar plexus. The great splanchnic nerve contains a large number of spinal fibres, which impart to it a white colour and firm consistence. The right nerve presents a small ganglion just be- fore it leaves the thorax, called the splanchnic ganglion, and there may be one on the left nerve. The great splanchnic nerve gives vascular branches to the lower part of the thoracic aorta. The small splanchnic nerve arises by two roots from the tenth and eleventh ganglia. It pierces the crus of the diaphragm, and termi- nates in the aortico-renal ganglion of the epigastric or solar plexus. The least splanchnic nerve, which is sometimes absent, arises by one root from the twelfth ganglion. It either passes behind the internal" arcuate ligament of the diaphragm or through the crus, and it termi- nates in the renal plexus. When the least splanchnic nerve is ab- sent, its place may be taken by a branch from the small splanchnic nerv^e. Subcostal Muscles. — These are small indefinite muscular sheets, which lie on the inner surfaces of the ribs in the region of the angles. They coincide in direction with the internal intercostal muscles, and are best developed interiorly. They are attached to the inner surfaces of the ribs Fig. 425. — Scheme of the Gang- LiATED Cord of the Sympa- thetic IN THE Thorax (after Flower). I to 12. Thoracic Ganglia R.C. Rami Communicantes B.D. Branches of Distribution from Upper Ganglia G.S. Great Splanchnic Nerve and Ganglion S.S. Small Splanchnic Nerve L.S. Least Splanchnic Nerve 1036 A MANUAL OF ANATOMY near the angles, and each muscle crosses over one, or it may be two, intercostal Spaces. They are supplied by the intercostal nerves. The diaphragm will be found described in connection with the abdomen. The Articulations of the Vertebral Column. I. Articulations of the Bodies of the Vertebrae. — ^These joints belong to the class amphiarthrosis and subdivision symphysis. The ligaments are as follows: the anterior common ligament, the pos- terior common ligament, and the intervertebral discs. The anterior common ligament is a dense band of white glistening fibres, which extends over the anterior surfaces of the bodies of Posterior Band of Superior Costo-transverse Ligament Anterior Band of Superior Costo-transverse Ligament . Anterior Common Anterior Costo-central , or Stellate Ligament I Interarticulnr Ligament Fig. 426. — Ligaments of the Bodies of the VERTEBRiE and Right Costo-central Joints. the vertebrae and intervertebral discs. It extends from the axis to the first segment of the sacrum, and its fibres are disposed longi- tudinally. The most superficial fibres extend from a given vertebra to the fifth below it ; the intermediate fibres pass from a given vertebra to the third below it ; and the deepest fibres pass from a given vertebra to the one immediately below it. The fibres are firmly attached to the intervertebral discs and margins of the vertebral bodies, but very loosely to the centres of the bodies, on account of the presence of bloodvessels. The anterior common ligament is broadest in the lumbar region, and thickest in the THE THORAX X037 thoracic region. It is thicker opposite the centres of the bodies than elsewhere, and in these situations it fills up the concavities, and so renders the front of the column less undulating than it otherwise would be. Over the lateral surfaces of the bodies a few scattered fibres are present, which pass from one vertebra to that below. In the sacral region the anterior common ligament is lost in the periosteum of the bone, but it reappears lower down as the anterior sacro-coccygeal ligament. The anterior common ligament is serially continuous superiorly with the anterior atlanto- axial ligament. The posterior common ligament is situated within the spinal canal, and extends over the posterior surfaces of the bodies of the Fig. 427. — Posterior Common Liga- ment OF THE Bodies of the Vertebrae. Fig. 428. — Intervertebral Discs (Anterior View). vertebrae and intervertebral discs. It is broader above than below, and consists of glistening fibres, which extend from the axis to the first coccygeal vertebra, its sacral part, however, being very narrow and delicate. Its fibres are firmly attached to the intervertebral discs and margins of the vertebral bodies, but they are separated from the centres of the bodies by the transverse venous com- munications between the anterior intraspinal veins. In the cervical region the ligament is of almost uniform breadth, being expanded over the vertebral bodies, as well as over the intervertebral discs. In the thoracic and lumbar regions, however, it is narrow opposite the vertebral bodies, and broad opposite the inter\'ertebral discs. Its margins, therefore, present dentations, which give it a denticu- lated appearance. The arrangement of its fibres is similar to the I038 A MANUAL OF ANATOMY Fig. 429. — Intervertebral Disc (Transverse Section). arrangement of those of the anterior common ligament. The posterior common ligament is serially continuous superiorly with the posterior occipito-axial ligament. The intervertebral discs are situated between the adjacent sur- faces of the bodies of the vertebrae, and they constitute the chief bondof union between them. Their outline corresponds to ^'""■^' "'^ Fibro-lambar Portion that of the bodies between which they are placed, and they are elastic and com- pressible. Except in early life, the first or highest disc is situated between the bodies of the axis and the third cervical vertebra, and in the adult the last or lowest disc is situated be- tween the bodies of the fifth lumbar and first sacral ver- tebrae. Each disc is composed of a circumferential fibrous part, disposed in the form of superimposed laminae, and a central portion, which is soft and pulpy. The external laminar part forms more than half of the disc, and is composed of fibrous tissue and fibro-cartilage. As seen in transverse section the laminae are arranged concentrically around the central pulp, Fibro-laminar Portion ^j^-^j^ ^^^^ ^j^^^jy CmbraCC i ?'"'P and compress. The fibres />VL'i.v..'!^;r:c#'^Mi;;i;;.. A of which they are composed are arranged in parallel bundles, which extend obliquely between the adja- cent surfaces of the verte- bral bodies, being attached to the layer of hyaline car- tilage which covers them. The fibres of successive laminae pass obliquely in opposite directions, and are disposed thus X. The outer laminae consist of fibrous tissue, but the majority are composed of white fibro-cartilage. As seen in vertical section the outermost laminae are bent outwards, and those around the central pulp are bent inwards towards it, this arrangement contributing to Capsule of rtic. Processes Fig, 430. — Vertical Sagittal Section of Two Intervertebral Discs. THE THORAX X039 the elasticity of the vertebral column. The central portion of the disc consists of a soft, elastic, pulpy substance, having a lobate arrangement. Being surrounded and compressed on all sides by the external laminar part, when a section of a disc is made the pulp, being relieved from pressure, projects beyond the level of the cut surface. It is composed of a cellular reticulum, supported by a delicate fibrous stroma. The pulp is a persistent portion of the notochord. The intervertebral discs form about one -fourth of the length of the vertebral colunm, and are thickest in the lumbar region. In the cervical and lumbar regions they are deeper in front than be- hind, and they give rise to the curve forwards in the cervical region, whilst they increase the forward curve in the lumbar region. In the thoracic region they are of uniform depth. Throughout the Fig. 431. — LIGAME^rTA Subflava in the Lumbar Region (Anterior View) (The Pedicles have been sawn through, and the Vertebral Bodies removed). column they are intimately connected with the anterior and pos- terior common ligaments, and, in the thoracic region, with the anterior costo-central or stellate ligaments and the interarticular ligaments of the heads of most of the ribs. In the cervical region the discs are not present at either lateral aspect of the opposed surfaces of the bodies. In these regions there is a synovial space on either side, between the projecting lateral lip of the upper surface of the lower body and the bevelled lateral margin of the lower surface of the upper body. The opposed surfaces are covered by cartilage, and there is an indistinct capsular ligament. 2. Ligaments of the Laminse. — ^These are called the ligamenta subflava. They are strong, thick plates of yellow, elastic tissue, which connect the laminae together, and they extend from the axis to the first sacral segment. They are best seen from the interior I040 A MANUAL OF ANATOMY of the spinal canal, and as they extend between the neural arches they close in the canal in these situations. Each ligamentura subflavum extends from the root of the articular process to the place where the lamina joins its fellow to form the spinous process. At this point it comes into relation with the ligament of the opposite side, a small interval being left between the two for the passage of veins. Superiorly the ligament is attached to the anterior surface of the upper lamina a little above its lower border, and inferiorly it is attached to the upper border, and adjacent part of the posterior surface, of the lower lamina. The ligamenta subflava are wider in the cervical and lumbar regions than in the thoracic region, and over the greater part of the latter region, as viewed from the exterior, they are concealed from view by the imbricated laminae. Their importance consists in their great elasticity, which enables them to maintain the vertebral column erect, and to restore it to the erect position after it has been bent forwards. 3. Ligaments of the Articular Processes. — ^The joints between the articular processes belong to the class diarthrosis, and to the sub- division arthrodia. The articular surfaces are covered by cartilage, and the joint is surrounded by a capsular ligament, lined with a synovial membrane. These ligaments are disposed more loosely in the cervical region than elsewhere. 4. Ligaments of the Spinous Processes. — ^These are supraspinous and interspinous. The supraspinous ligament consists of longitudinal fibres which connect the extremities of the spinous processes. It extends from the spine of the seventh cervical vertebra to the spine of the fourth sacral segment, and its fibres are arranged in a manner similar to those of the anterior common ligament. In the cervical region the supraspinous ligament is replaced by the ligamentum nuchae. The interspinous ligaments, which are thin and membranous, are situated between adjacent spinous processes, to the margins of which they are attached from root to tip. They are strongest in the lumbar region, and in the neck they are replaced by deep pro- cesses of the ligamentum nuchas. 5. Ligaments of the Transverse Processes. — ^These consist of scattered fibres, which pass between the extremities of the trans- verse processes in the thoracic and lumbar regions. In the neck they are replaced by the intertransversales muscles. Movements. — The movements allowed in the vertebral column are flexion, extension, lateral movement, rotation, and circumduction. Flexion and extension are freely allowed in the cervical and lumbar regions. In the thoracic region these movements are very limited on account of (i) the small amount of intervertebral substance, and (2) the imbrication of the lamina?. Lateral flexion is allowed in the cervical, thoiacic, and lumbar regions, but in the neck it is associated with rotation. During these com- bined movements of lateral flexion and rotation in the neck one inferior articular process glides upwards and forwards on that which is opposed to it, whilst the other inferior articular process glides downwards and backwards on the one opposed to it. Pure rotation is allowed in the thoracic region round an axis corresponding with the centre of a circle of which the surfaces THE THORAX It^t of the articular processes form segments. This centre is necessarily anterior to the articular processes, and corresponds pretty nearly with the centres of the bodies of the vertebrae. In the lumbar region rotation is impossible, for the following two reasons: (i) the centre of the circle of which the articular processes form segments is posterior to these processes ; and (2) the articular processes are so disposed as to be locked. In the lumbar region circumduction is allowed, which consists in a combination of flexion, extension, and lateral movements. Summary of Movements — Cervical Region. — (i) Flexion and extension; and (2) a combination of lateral flexion and rotation. Thoracic Region. — (i) Flexion and extension, but only to a limited extent ; (2) lateral flexion ; and (3) pure rotation. Lumbar Region. — (i) Flexion and extension ; {2) lateral flexion ; and (3) circumduction. The articulations of the atlas, axis, and occipital bone will be found described in the section dealing with the head and neck. THE ARTICULATIONS OF THE RIBS, COSTAL CARTILAGES, AND STERNUM. I. Ribs — Costo-vertebral Articulations. — These are divided into costo-central and costo-transverse. Costo-central Articulations. — ^These unite the heads of the ribs to the centra or bodies of the thoracic vertebrae, and they are some- times spoken of as the capiitdar joints. They belong to the class diarthrosis, and to the subdivision condylarthrosis. The articular surfaces are the demi-facets on the heads of the ribs and the demi- facets on the sides of the bodies of the thoracic vertebrae, that is to say, the lower demi - facet of the vertebra above and the upper demi-facet of the vertebra below, the intervertebral disc intervening between the two. In the case of the ist, (some- times the loth), the nth, and the 12th vertebrae there is only one facet, and the corresponding intervertebral discs do not enter into the joints, unless in the case of the ist joint, into which the disc between the 7th cervical and ist thoracic vertebrae may enter. Ligaments. — ^These are as follows : anterior costo-central, capsular, and interarticular. The anterior costo-central ligament consists of strong white fibres which are attached to the anterior margin of the head of the rib. From this point the fibres radiate inwards in three bands, one of which passes upwards to be attached to the body of the vertebra above, a second horizontally inwards to be attached to the inter- vertebral disc, and a third downwards to be attached to the body of the vertebra below. From the radiating disposition of these bands the ligament is known by the name of stellate or radiate. In the case of the ist, loth, nth, and 12th joints, into each of which only one vertebra enters, the ligament is composed of two bands, instead of three. In the ist joint the lower band passes to the 66 1042 A MANUAL OF ANATOMY body of the ist thoracic vertebra, and the upper band to the body of the 7th cervical. In each of the loth, nth, and 12th joints the lower band passes to the body with which the head of the rib articulates, and the upper band to the body of the vertebra above. The capsular ligament is incomplete, and consists of thin loose fibres, which cover the posterior, superior, and inferior aspects of the joint. The interarticular ligament consists of short stout fibres, which extend from the ridge on the head of the rib, separating the two facets, to the intervertebral disc. It divides the joint into two complete synovial cavities, and it is wanting in the ist, loth, nth, and 12th joints. There are two distinct synovial membranes in those joints which are provided with an interarticular ligament, namely, from the Posterior Band of Superior Costo-transverse Ligament Anterior Band of Superior Costo-transverse Ligament Anterior Costo-centralV or Stellate Ligament T Interarticular Ligament Anterior Common Ligament. .Intervertebral Disc Fig. 432. — Ligaments of the Bodies of the Vertebrae and Right costo-central joints. 2nd to the gth . inclusive, one being above the ligament and the other below it. In those joints in which the interarticular ligament is absent, namely, the ist, loth, nth, and 12th, there is only one synovial membrane. Arterial Supply. — Branches from the intercostal arteries. Nerve-supply. — Branches from the intercostal nerves. Costo-transverse Articulations.— These belong to the class diar- throsis, and to the subdivision arthrodia. The articular surfaces are the facet on the tubercle of the rib and the facet on the anterior aspect of the extremity of the transverse process of the thoracic vertebra. THE THORAX 1043 Ligaments. — ^These are as follows: posterior costo-transverse, middle costo-transverse, superior costo-transverse, and capsular. The posterior costo - transverse ligament is a strong flat band, situated on the posterior aspect of the joint, and extending from the extremity of the transverse process to the non-articular part of the tubercle of the rib. The direction of its fibres is upwards and outwards. The middle costo-transverse or interosseous ligament consists of short strong fibres which pass between the posterior surface of the neck of the rib and the anterior surface of the adjacent transverse process, namely, that with which the tubercle of the rib articulates. Its fibres, which are disposed horizontally, extend from the costo- central to the costo-transverse joint. This ligament is rudimentary in the nth and 12th ribs. The superior costo-transverse ligaments are two in number, anterior and posterior. The anterior ligament is a broad flat band, external in position, the fibres of which pass from the crest on the upper border of the neck of the rib to the lower border of the trans- verse process immediately above, in the vicinity of its tip. Its fibres are directed upwards and outwards, and its outer border is continuous with the posterior intercostal aponeurosis. The pos- terior ligament is a narrow band, internal to the preceding, and extending from the back of the neck of the rib, below the crest, to the lower aspect of the transverse process immediately above, close to its base. The superior costo-transverse ligaments are wanting in the case of the ist rib. The capsular ligament is formed in part by the posterior costo- transverse ligament, and elsewhere by a thin loose membrane, the fibres of which are attached external to the articular processes. It is absent in the case of the nth and 12th ribs. The synovial membrane is single and small. Arterial and Nerve Supply. — Offsets from the posterior branches of the intercostal arteries and nerves. The costo-transverse articulations are wanting in the case of the nth and 12th ribs, and sometimes in the case of the loth. Costo-chondral Articulations. — These belong to the class syn- arthrosis. The outer extremity of the costal cartilage is implanted in the oval pit on the anterior extremity of the rib, and the union is effected by the continuity which takes place between the peri- osteum of the rib and the perichondrium of the cartilage. 2. Costal Cartilages — Chondro-sternal Articulations. — ^These belong to the class diarthrosis, and to the subdivision ginglymus, except in the case of the ist joint, which belongs to the class synarthrosis. The cartilages which take part in these joints are the first seven on either side, these being received into the costal pits or facets on the side of the sternum. The ligaments are anterior, posterior, superior, and inferior, and, in the case of the 2nd joint at least, interarticular. I044 A MANUAL OF ANATOMY The anterior chondro-sternal ligament is a triangular band, the upper fibres of which ascend upon the sternum, and the lower descend, whilst the intervening fibres pass horizontally forwards. They decussate with those of the opposite side, and blend with the tendinous fibres of origin of the pectoralis major muscle. The posterior chondro-sternal ligament is disposed in a manner similar to the anterior ligament. The superior and inferior chondro-sternal ligaments pass from the upper and lower borders of the costal cartilage to the side of the sternum. The interarticular ligament is present in the 2nd joint, and may be present in some of those succeeding to it. Its fibres extend horizontally between the centre of the sternal end of the 2nd costal cartilage and the plate of fibro- cartilage between the manu- FiG. 433.— The Chondro-sternal Joints (Anterior View). The Secoi.- ^^-^^^^^ ^nd Fourth Joints of the Left Side are seen in Section. brium and ^°^^^^^^g^;\ties+ernum. It divides this joint into two The ist io;i;t ^^f^i"^ synov^. ^^^^^^^^^^ ^^^ ^^^^ ^^^^^^ cartilage being directly um^ ^ial membic.ium sterni. The 2nd joint, as stated, ^^^^Jr^"- V-^^r ligament. 1 one above and the other below ^^f^^'l'l'lovi^X membrane, bx. .^eceeding joints have each usually one sy ometimes one or more of them may have two ■ or perfoi Arterial ^^^^f^"^' ng branches of the interchondral Articu^^^^^^^ T,, ^he class diar- throsis, and to tne s _^^^ ^^^^^ ^^^ cartilages involved are usually the btti, 7 . ^^^.^^^ J^^ ^^^ ^^^^ THE THORAX 1045 and it may be the 5th, and even the loth. The lower border of each cartilage projects downwards, and comes into contact wath the upper border of the cartilage below. Each joint is surrounded by fibres disposed in the form of a capsule, and it is provided with a sjTiovial membrane. Arterial Supply. — The musculo-phrenic branch of the internal mammary arterj'. Nerve-supply. — The adjacent intercostal nerves. 3. Sternal Articulations. — The joint between the manubrium and body of the sternum belongs to the class amphiarthrosis, and sub- division symphysis. The opposed surfaces are covered by hyaline cartUage, and a plate or disc of fibro-cartilage is interposed between them, which is connected at either side with the interarticular hga- ment of the second chondro-stemal joint. This disc may contain a small cavity. In front of and behind the joint there are Hga- mentous fibres which are disposed longitudinally. The entire sternum is strengthened by its dense periosteum, by the radiating fibres of the chondro-stemal hgaments, and by the tendinous fibres of origin of the pectoralis major muscles. Movements ol the Ribs. — The movement allowed at the eosto-eentral and costo-transverse joints is of a gliding nature, and takes place in an upward and do%\Taward direction. During this movement the rib rotates round the eosto-vertebral axis, which corresponds to a line passing obliquely through the costo-central joint, the neck of the rib, and the costo-transverse joint. 0\\'ing to the curve and downward inclination of the rib, the result of this rotation is that the anterior and lateral parts of the rib are elevated. Simul- taneously, on account of the obliquity of the axis of rotation, the anterior part of the rib is carried forwards, and along with it the sternum, thus in- creasing the antero-posterior diameter of the thorax. The lateral part of the rib, and to a certain extent the anterior part also, are carried outwards, thus giving rise to eversion of the lower border of the rib, and at the same time the angle between the rib and its costal cartilage is opened out. In this manner an increase in the transverse diameter of the thorax is produced. During the elevation of the anterior and lateral parts of the rib and the ever- sion of its lower border the movement takes place round the costo-sternal axis, which corresponds to a line drawn from the costo-central joint of one side to the corresponding chondro-stemal joint. It is usual to liken this movement to the movement of the handle of a bucket. In the case of the first rib elevation and depression are the chief move- ments allowed, the amount of eversion being trivial, inasmuch as the axis of rotation is almost transverse. In the case of the second, third, fourth, fifth, and sixth ribs elevation and depression, along with eversion, are allowed, the axis of rotation in each case becoming successively more oblique. The seventh, eighth, ninth, and tenth ribs, in which the costo-transverse articular surfaces are almost flat, besides rotating round the costo-vertebral axis, also rotate round the costo-sternal axis. In the case of these ribs elevation is accompanied by a backward movement, and depression by a forward move- ment. These backward and forward movements take place more freely in the case of the eleventh and t%velfth ribs, which have no costo-transverse joints. At the chondro-stemal joints the movement is limited, and consists in elevation and depression, together with forward and backward movement. At the interchondral joints slight gliding movement is allowed. Muscles concerned in Respiration. — In ordinary quiet inspiration the muscles concerned are as follows : (i) the diaphragm ; (2) the external and internal intercostal muscles, assuming Haller's view to be correct ; (3) the I046 -> A MANUAL OF ANATOMY levatores costarum ; (4) the serratus posticus superior ; (5) the serratus pos- ticus inferior ; and (6) the quadratus lumborum, as being auxiliary to the diaphragm, the serratus posticus inferior being also auxiliary. Ordinary quiet expiration is due to (i) the elastic recoil of the lungs, (2) the elastic recoil of the thoracic wall (costal cartilages and sternum), (3) the triangularis sterni muscle, and (4) the muscles of the antero-lateral wall of the abdomen, which press mildly upon the abdominal viscera, and thereby push the diaphragm upwards towards the thorax. In forced inspiration the following muscles come into play : (i) the scaleni ; (2) the sterno-cleido-mastoid ; (3) the serratus magnus ; (4) the pectoralis major and pectoralis minor ; and (5) the latissimus dorsi. As auxiliary muscles Fig. 434. — Diagram showing the Axes of Rotation of the Ribs (from Halliburton's 'Handbook of Physiology'). A, B, Axis passing from Costo-central to Chondro-sternal Joint ; a, b, Axis passing through Costo-transverse and Costo-central Joints. (The movement round the axis A, B resembles the raising of the handle of a bucket.) there are the trapezius, levator anguli scapulae, and rhomboid muscles, which, by their action upon the scapula, fix the shoulder. In forced expiration the muscles of the antero-lateral wall of the abdomen act with considerable strength, and now depress those ribs with which they are connected, and necessarily also the sternum. By some authorities the serratus posticus inferior is regarded as being concerned. In inspiration the thoracic cavity is enlarged in its vertical, antero-posterior, and transverse diameters. The increase in the vertical diameter is due to the contraction and descent of the diaphragm ; the increase in the antero-posterior diameter is caused by the anterior parts of the ribs, and along with them the sternum, being carried forwards ; and the increase in the transverse diameter is brought about by the eversion of the lower borders of the ribs, and the opening out of the angles between the ribs and their costal cartilages. GUIDE TO THE THORAX. Thoracic Wall. — The upper limb having been separated from the trunk, the dissector should remove the remains of the following muscles : the pec- toralis major, pectoralis minor, tendon of origin of the subclavius, serratus magnus, obliquus externus abdominis, latissimus dorsi, and rectus abdominis. In removing the remains of the pectoralis major the anterior cutaneous nerves THE THORAX 1047 should be preserved, as well as the perforating branches of the internal mam- mary artery. In removing the serrations of the serratus magnus the lateral cutaneous nerves and arteries^ which appear between them, should also be preserved. The insertions of the scalenus anticus and scalenus medius into the first rib, and of the scalenus posticus into the second rib, are to be left intact in the meantime. If the sternum has not been interfered with, for the purpose of injecting the subject from the ascending aorta, the dissector should make himself familiar with the sternal angle at the junction of the manubrium and body of the sternum. In this connection he should note that the angle serves as the guide to the second rib, the cartilage of which articulates partly with the manubrium, and partly with the body of the bone. The external intercostal muscle is to be dissected in at least two inter- costal spaces. The direction of its fibres is to be carefully observed, and it is to be noted that the muscle does not extend farther forwards than the junction of the osseous rib with its costal cartilages ; indeed, in some cases not so far as this. The anterior intercostal aponeurosis is also to be shown in the intervals betsveen the costal cartilages. In one or more spaces a small portion of the external intercostal muscle is to be carefully divided trans- versely, and reflected upwards and do\vnwards in two pieces. This dissec- tion will expose a limited portion of the internal intercostal muscle, and it will enable the dissector to contrast the diflference in direction of the two muscles. In another space as much of the external intercostal muscle as possible should be detached from the upper border of the lower rib, and turned upwards with great care, preserving at the same time the lateral cutaneous nerve and artery. The anterior intercostal aponeurosis of the same space should also be carefully removed, care being taken to preserve the anterior cutaneous nerve and perforating artery. This dissection will expose the internal intercostal muscle, the intercostal nerve, and the various intercostal arteries. The direction of the fibres of the internal intercostal muscle is to be observed, and it is to be noted that the muscle extends quite up to the lateral border of the sternum, where it is pierced by the anterior cutaneous nerve. The intercostal nerve will be found under cover of the lower border of the upper rib, where it lies in the subcostal groove, having the aortic intercostal artery above it, the intercostal vein being in turn above the artery. It is well, therefore, to make slight traction upon the nerve before attempting to display it, and for this purpose the lateral cutaneous nerve wiU suffice, which is one reason for preserving that nerve. The first intercostal nerve, as a rule, gives off no lateral cutaneous branch, and those of the succeeding nerves will be found piercing the external intercostal muscles about midway between the vertebral column and the sternum. Up to this point the intercostal nerve will be met with between the two intercostal muscles, but subse- quently it lies in the substance of the internal intercostal muscle, and finally, between the costal cartilages, it is placed beneath the internal intercostal muscle. The arteries to be dissected in each space are as follows : (i) the aortic intercostal and its collateral intercostal branch, both passing forwards, the former within the lower border of the upper rib, above the nerve, and the latter along the upper border of the lower rib ; and (2) the anterior intercostal arteries, two in each space, except the lower t^vo spaces, one lying along the lower border of the upper rib, and the other along the upper border of the lower rib. The internal intercostal muscle should now be carefully removed, aiter which an instructive view of the parietal pleura will be obtained. This, however, must be left intact. The dissector is next to turn his attention to the internal mammary vessels and anterior intercostal or sternal glands. These structures are to be dis- played in a different manner on the two sides. On one side the costal cartilages are not to be interfered with in the mean- time, and on the other side the second, third, fourth, fifth, cind sixth costal cartilages are to be cut through at their inner and outer ends, and then lifted 1048 A MANUAL OF ANATOMY out. On both sides the anterior intercostal aponeuroses and interchondral fibres of the internal intercostal muscles should be removed. The internal mammary artery and its branches, along with its venae comites, and the anterior intercostal or sternal glands are then to be dissected. The artery will be found about ^ inch from the side of the sternum, and its superior phrenic branch (comes nervi phrenici) is to be preserved until a later period. The venae comites are also to be subsequently shown uniting superiorly to form one vessel. In the sixth intercostal space the internal mammary artery is to be shown dividing into its two terminal branches, namely, mus- culo-phrenic and superior epigastric. The triangularis sterni muscle is then to be dissected from before. On the side on which the costal cartilages have been left intact they are now\ to be cut through from the second to the sixth inclusive, close to the osseous ribs. Thereafter the ribs corresponding to these costal cartilages on each side are to be divided with the bone-forceps, and this should be done as far back as possible by turning the subject round on either side. The divided ribs are then to be bent backwards, the parietal pleura having been carefully separated from them. The sternum, meanwhile, is to be left undisturbed, with whatever costal cartilages are attached to it. The parietal pleura is then to be carefully studied. By way of showing that it does not descend as low as the lins of attachment of the diaphragm, the external and internal intercostal muscles of one or two of the lowest spaces should be removed, when it will be seen that the diaphragm comes into view without any trace of parietal pleura. The manubrium sterni is next to be partially sawn through near its lower border, the seventh costal cartilage on each side is to be cut through, and the great bulk of the sternum is then to be bent upwards in such a manner that it can be replaced when required. If the bone should break, the two parts should be connected by wire sutures. The relations of the anterior borders of the two pleural sacs to the sternum, to each other, and to the pericardium, are now to be carefully studied. The anterior mediastinum and the remains of the thymus body are to be inspected, and the area of the pericardium which is uncovered by the left pleura, and is directly related to the thoracic wall, is to receive special attention. At this stage an opening should be made in the cervical portion of the trachea, and a blow-pipe, provided with a stop-cock, should be introduced and tied firmly in position. The lungs are now to be inflated through the blow-pipe, the stop-cock is to be turned, and the following points are to be accurately observed : (i) the extent to which the lungs encroach upon the heart, enclosed within the pericardium ; and (2) the extent to which they descend between the diaphragm and the ribs. By reversing the stop-cock the lungs will be seen to collapse and recede from the precordial area. During these observations the greater part of the sternum should be alternately raised and lowered. The chief part of the sternum is now to be removed, along with whatever costal cartilages are connected with it. On the side on which the cartilages remain in connection with the bone the triangularis sterni and the internal mammary vessels are to be dissected from behind. The chondro-sternal joints may be dissected at this stage, or it may be convenient to preserve the sternum for their future dissection. Phrenic Nerves, Pleurae, Pericardium, and Lungs. — Before the further stages of the dissection are entered upon, it is necessary that the dissector should have some knowledge of the general position of the structures to be exposed. From their complicated nature it is not possible to lay down hard-and-fast directions, and in his mode of procedure he must keep a careful look-out. The phrenic nerve is to be dissected, and its close relation to the pericardium is to be noted, as well as its course in front of the root of the lung. Possibly the superior phrenic branch (comes nervi phrenici) of the internal mammary artery may be found coming into contact with the nerve high up in the thorax. The reflections of the pleura are to be studied both in the transverse and in the vertical directions. If any adhesions are present, these should be separated with the fingers, and any fluid which has accumulated must be THE THORAX 1049 removed, and the parts thoroughly cleansed. The Imes of the sternal and costo-diaphragmatic reflections of the pleura are to be carefully studied. In examining the antero-posterior reflections of the membrane the ligamentum latum pulmonis, below the root of the lung, is to be noted, and the medias- tinum thoracis, with its divisions, is to receive ver>' careful attention, these divisions being anterior, superior, middle, and posterior. The two pleural sacs which form the lateral boundaries of the anterior mediastinum are to be separated, when the middle mediastinum \^-ill be exposed, with the peri- cardium, enclosing the heart, l\"ing in it. The lungs are next to be studied. They have been already examined in their inflated and collapsed conditions, but attention is now to be directed to their form, component parts, fissure or fissures, and lobes. The difierences between the t\vo lungs are also to be noted, which impress corresponding differences upon the pleural sacs. The roots of the lungs are not to be dis- sected at this stage. The superior mediastinum should now be examined, without disturbing the pericardium, and the remains of the thymus body, together with the superior mediastinal glands, are to be dissected. The right and left innominate veins are next to receive attention, and their inferior thjToid and internal mammarj' tributaries, with, in some cases, the first intercostal vein, are to be noted. The left superior intercostal vein is to be displayed as an additional tributary of the left innominate vein, which it joins not far from its commencement, after having crossed the back part of the arch of the aorta. The superior vena cav^a, formed by the junction of the two innominate veins, is to be showTi and followed down to where it pierces the pericardium, but no farther in the meantime. The right azygos vein is to be displayed arching over the root of the right lung, and opening into the superior vena cava just before that vessel pierces the pericardium. The pericardium is now to be studied from the exterior. Connected with its anterior wall parts of the superior and inferior stemo-pericardial ligaments of Luschka are to be looked for. The relation of the fibrous portion of the pericardium to the diaphragm is to be looked to, and its disposition upon the great vessels at the base of the heart, for which it forms sheaths, is to receive attention. The intimate relation of the phrenic nerves to the pericardium has been already noted. The pericardium is now to be laid open by means of a vertical median incision, extending over its entire length, and a transverse incision opposite the roots of the lungs. The serous portion of the pericardium is then to receive careful attention. It is to be observed that, being a serous membrane, it is composed of parietal and viscercil portions, which enclose between them a shut sac. The close relation of the parietal portion to the fibrous part is to be noted, and the disposition of the visceral portion upon tha ascending aorta and trunk of the pulmonary artery is to be carefully studied. It will be seen to form a single sheath for them, and to rise upon the ascending aorta for from i to i^ inches. The tiansverse sinus of the pericardium should be explored with the finger. It will be found lying behind the ascending aorta and trunk of the pulmonary arter5% and in front of the auricular portion of the heart. In connection with the serous portion of the pericardium the triangular fold, called the vestigial fold of Marshall, is to be looked for in front of the root of the left lung, between the left pul- monary artery and the subjacent pulmonary vein. XMien this fold is care- fully dissected it will be found to contain a delicate fibrous cord, \s'iiich is a vestige of the left duct of Cuvier of embryonic life. The pericardium is now to be removed, which will show the lower part of the superior vena cava. The heart, being now exposed, should receive the most careful attention. Its external form and component parts are to be observed, and the relations of these parts to the thoracic wall must be thoroughly mastered. More especially the relation of the valvular orifices of the heart to the thoracic wall calls for the closest observation. The trunk of the pulmonary arterj' is to be studied, as it springs from the conus arteriosus I050 A MANUAL OF ANATOMY at the base of the right ventricle, and it is to be noted that it conceals the origin of the aorta from the base of the left ventricle. Further, it will be seen that both of these vessels are embraced by the auricular appendices. The right and left coronary arteries, each accompanied by the corresponding coronary plexus of nerves, are to be displayed as they come forwards on either side of the root of the pulmonary artery. The superior vena cava is to be shown opening into the postero-superior angle of the right auricle, and, by raising the heart, the inferior vena cava will be seen to open into the postero- inferior angle of the right auricle. The four pulmonary veins, two right and two left, will be found to open into the back part of the left auricle. The ascending aorta is to be dissected, and in conjunction with it the trunk of the pulmonary artery, the superior vena cava being also kept in view. The arch of the aorta is next to be dissected, along with the innominate artery, and the thoracic portions of the left common carotid and left sub- clavian arteries. Crossing iii front of the aortic arch will be found the left phrenic and left pneumogastric nerves, and between them the superior cervical cardiac branch of the left sympathetic and the inferior cervical cardiac branch of the left pneumogastric, both of these two small nerves being on their way to the superficial cardiac plexus. The left recurrent laryngeal nerve is to be shown arising from the left pneumogastric opposite the lower margin of the arch of the aorta, and passing backwards beneath the arch, and then upwards behind it, where it gives off one or two cardiac branches to the deep cardiac plexus. The left superior intercostal vein will be seen crossing over the back part of the arch on its way to the left innominate vein. Within the concavity of the arch, in addition to the left recurrent laryngeal nerve, the superficial cardiac plexus of nerves and the ligamentum ductus arteriosi fall to be dissected. The superficial cardiac plexus lies in front of the trunk of the pulmonary artery, close to its bifurcation, and on the right side of the ligamentum ductus arteriosi, and it requires the most careful dissection. The best way to proceed is to follow downwards from the front of the arch of the aorta the superior cervical cardiac branch of the left sym- pathetic and the inferior cervical cardiac branch of the left pneumogastric, both of which will conduct to the plexus. In this plexus a small ganglion, called the ganglion of Wrisberg, is to be looked for. The plexus itself will be found to furnish delicate filaments to the left anterior pulmonary plexus, after which it is prolonged into the right coronary plexus, which latter is reinforced by fibres from the right half of the deep cardiac plexus. The ligamentum ductus arteriosi will be found extending from the root of the left pulmonary artery to the under aspect of the arch of the aorta immediately beyond the place of origin of the left subclavian artery. The left lung is now to be turned well forwards, and fixed in that position by hooks. The trunk of the left pneumogastric nerve is to be followed down- wards behind the root of the left lung. Before reaching that point it is to be shown furnishing a few branches which pass to the front of the root, and there form the small anterior pulmonary plexus. Behind the root of the left lung the nerve will be found to become flattened, and to break up into a number of branches, which form the posterior pulmonary plexus. From this plexus the nerve is to be shown issuing as two cords which pass down- wards to the oesophagus, where they are to be left in the meantime. The right pneumogastric nerve will be found behind the right innominate vein, and on the right side of the right innominate artery and trachea. A little above this point the nerve has crossed over the first part of the right sub- clavian artery, and parted with the right recurrent laryngeal nerve opposite the lower margin of that vessel. The right pneumogastric nerve will be seen to occupy a much deeper position than the left. A branch to the deep cardiac plexus should be looked for coming from it, and the main nerve is to be followed downwards behind the root of the right lung, that organ having been turned well forwards, and kept in that position by hooks. Behind the root of the right lung the right pneumogastric nerve acts in a manner similar THE THORAX 1051 to the left nerve, and forms the right posterior pulmonary plexus, from which it emerges as two cords, and these, as on the left side, descend to the oeso- phagus. The lungs having been replaced in position, the root of each is now to be fully dissected, the bronchus, pulmonary artery, and pulmonary veins being clearly separated from each other all round the root. In performing this dissection the anterior and posterior pulmonary plexuses of nerves, already referred to, are to be studied, and the bronchial lymphatic glands are to be displayed. These glands are usually quite black, this being due to the deposit of carbonaceous matter in them. The general relations of each root, and the special relations of the chief constituents, are to be thoroughly mastered. The right and left pulmonary arteries should now be examined from their origin from the main trunk to the root of each lung, and their relations are to be noted, as well as the ligamentum ductus arteriosi in connection with the root of the left pulmonary artery. The pulmonary veins on each side are also to be followed from the root of the lung to the back part of the left auricle of the heart. In the dissection of the roots of the lungs the bronchial arteries, one right and two left, and the bronchial veins are to be kept in view. Exterior of the Heart. — The dissection of the heart is now to be proceeded with. Its external form is to be carefully examined ; the directions of the base, apex, and borders are to be observed ; and the grooves by which it is divided into auricular and ventricular portions, and these, in turn, into right and left auricles, and right and left ventricles, are to be noted. The apex will be seen to be formed entirely by the left ventricle. The right and left coronary arteries are to be fully dissected, and their origins from the root of the ascending aorta clearly shown, the trunk of the pulmonary artery being displaced as may be required. The right coronary artery is to be followed along the front and back of the right auriculo-ven- tricular groove, and its marginal branch is to be shown passing along the margo acutus. On the back of the heart the main vessel will be found to divide into two terminal branches, transverse and descending. The trans- verse branch is to be followed into the back part of the left auriculo-ven- tricular groove, where it anastomoses \vith the transverse branch of the left coronary artery ; and the descending branch is to be followed along the inferior interventricular groove as far as the region of the apex, where it anastomoses with the descending branch of the left coronary artery. The left coronary artery is to be shown dividing very early into a trans- verse and descending branch on the left side of the root of the pulmonary artery. The transverse branch is to be followed round the left auriculo- ventricular groove, and its marginal branch is to be shown parsing along the margo obtusus vel rotundus. The descending branch is to be followed along the antero-supericH" interventricular groove as far as the region of the apex. In dissecting the coronary arteries the right and left coronary plexuses of nerves are to be kept in view, and the various cardiac veins are to be at the same time displayed. In the back part of the left auriculo-ventricular groove the coronary sinus, about I inch leng, will be found, and its dUated condition is to be noted. The great cardiac or coronary vein (anterior interventricular vein) will be found in the antero-superior interventricular groove, along with the de- scending branch of the left coronary artery. On entering the front part of the left auriculo-ventricular groove (where it is now strictly the great cardiac or coronary vein), it should be followed, in company with the transverse branch of the left coronary artery, to the back part of the groove, where it will be found to become continuous with the coronary sinus. The middle cardiac vein (posterior interventricular vein) \\'ill be met \\-ith in the inferior interventricular groove, where it accompanies the descending branch of the right coronary artery, and it should be shown to join the right extremity of the coronary sinus. The right or small cardiac or coronary vein will be I052 A MANUAL OF ANATOMY found in the back part of the right auriculo-ventricular groove, and, it may be, in the front part of it. The anterior cardiac veins wiU be found on the front of the right ventricle and along the margo acutus, and they are to be traced to the right coronary vein. The posterior cardiac veins will be found on the inferior surface of the left ventricle, and they are to be followed to the lower border of the coronary sinus. The oblique vein of Marshall is to be carefully looked for on the back of the left auricle, along which it passes downwards and inwards to open into the left extremity of the coronary sinus. The tributaries of this sinus are now to be fully reviewed, and there- after it is to be laid open with scissors. This will bring into view a valve, composed of two segments, which is situated at the place where the great cardiac or coronary vein opens into the sinus, namely, about i inch from the ending of the sinus in the right auricle. The very delicate nerves derived from the coronary plexuses course upon the surfaces of the ventricles, but in the human heart they do not lend them- selves very readily to inspection. The heart of the calf is much more favourably disposed for their examination. Interior of the Heart. — In this dissection the best way to proceed is to follow the course of the blood through the heart. The right auricle is to be laid open by two incisions as follows : (i) a vertical incision is to be made from the auricular extremity of the superior vena cava to near the point of entrance of the inferior vena cava, keeping clearly in front and to the left of it, in order not to injure the vestigial Eustachian valve which is associated with its orifice ; and (2) an oblique incision is to be made from the auricular appendix to about the centre of the vertical incision. Having removed the venous blood and sponged the interior of the auricle, the following points are to receive attention : (i) the musculi pectinati, situated on the wall of the auricular appendix and the adja:cent portion of the right wall of the atrium ; (2) the crista terminalis ; (3) the fossa ovalis and annulus ovalis on the inter- auricular septum ; (4) the so-called tubercle of Lower ; (5) the vestigial Eustachian valve in connection with the orifice of the inferior vena cava ; (6) the opening of the coronary sinus, and the Thebesian valve ; (7) the fora- mina Thebesii ; and (8) the auriculo-ventricular orifice. It is to be noted that no valve guards the opening of the superior vena cava. In connection with the annulus ovalis a very minute opening may be found under cover of it, leading into the left ventricle. Its possible presence may be determined by exploring with a fine probe. Three fingers, held side by side, should be passed through the auriculo-ventricular orifice, and, if normal, it will be found to admit them readily. The right ventricle is to be opened by means of two incisions, the left fore- finger having previously been passed through the auriculo-ventricular orifice. A transverse incision is to be carried along the upper part of the ventricle, just below and parallel to the auriculo-ventricular groove. This incision is to be prolonged as far as a point below the root of the pulmonary artery. The other incision is to commence at the left end of the foregoing incision, and is to be carried downwards just to the right of the antero-superior inter- ventricular groove. In this manner a triangular flap, representing the front wall of the right ventricle, can be turned down, and the cavity fully exposed. The second incision, just stated, may be replaced by one extending along the margo acutus to the lower end of the antero-superior interventricular groove, and then a triangular flap would be raised towards the left. After cleansing the ventricle, the dissector is to observe (i) that its cavity is excluded from the apex of the heart, (2) that it is prolonged to the root of the pulmonary artery as the infundibulum or conus arteriosus, and (3) that the interventricular septum bulges into it, so as to be convex on its right aspect. The fleshy elevations, called columnae carneae, are to receive attention, their various kinds are to be noted, and special attention is to be given to the variety known as the musculi papillares. These latter will be found to be disposed in two groups — anterior and posterior. The absence of columnae carneae from the infundibulum is to be noted, and the moderator band is to be looked for extending from the anterior papillary muscle to the interven- THE THORAX 2053 tricular septum. The tricuspid valve is next to receive attention, and its three main segments are to be carefully studied, the smcdl secondary seg- ments l>Tng between their basal parts being noted. The chordae tendineae and their relations to the segments of the tricuspid valve should be closely examined, and the function of that valve is to receive careful consideration. The study of the pulmonary valve, which guards the orifice of the pulmonary artery, is to be postponed till a later period. On account of the posterior position of the left auricle, and preparatory to opening it, the inferior vena cava may be divided in order to liberate the heart from the diaphragm. The heart is then to be turned over to the right side, and also upwards. A transverse incision may then be made above and parallel to the auriculo-ventricular groove, and any other which may suggest itself to the dissector, who is supposed to know by previous study the intemzd arrangement of the parts. The interior having been cleansed, it will be at once apparent that the musculi pectinati are confined entirely to the region of the auricular appendix. On examining the left surface of the interauri- cular septum the position of the foramen ovale of the foetal heart, and the remains of the valve which originally closed it, will be recognised as a slight depression, which is limited inferiorly by a crescentic border with the con- cavity' directed upwards. It may be compared to the imprint of a finger- nail. The orifices of the pulmonary veins on the posterior wall — two right and two left — are to be examined, and the absence of valves noted. The left auriculo-ventricular orifice is next to receive attention. If two fingers, held side by side, are passed through the orifice, it will be found, if normal, to admit them readily. The left ventricle is to be opened by two incisions, one carried transversely across the ventricle, just below and parallel to the auriculo-ventricular groove, and the other extending from the right end of the preceding incision to the lower part of the ventricle on the left side of the apex. The ventricle having been cleansed, the great thickness of its wall is to be noted, and the dissector is to observe (1) that its cavity extends quite to the apex of the heart, and (2) that the interventricular septum recedes from it, so as to be concave on this aspect. The portion of the cavity adjacent to the aortic orifice is to receive attention, this part, which is known as the aortic vestibule of Sibson, having fibrous walls. The columnae cameae and their varieties are to be studied as on the right side, their very intricate arrange- ment being noted, and special attention is to be directed to the musculi papillares, which are anterior and posterior. The two large cusps of the mitral valve, with two small cusps placed between their basal parts, are to be carefully studied, and the relation of the anterior or aortic cusp to the aortic orifice is to be noted. The chordae tendineae, and their relations to the segments of the valve, should be closely examined, and the function of the vadve is to receive careful consideration. The auriculo-ventricular and aortic orifices are to be studied, but the aortic valve is to be left over for future consideration. Before leaving the study of the interior of the heart, the relations of its auriculo-ventricular and arterial valvular orifices to the thoracic wall should be thoroughly mastered. Deep Cardiac Plexus. — To expose this plexus the ascending acrta should be divided near its upper end, and the superior vena cava is to be divided a Uttle below the point where it receives the right azygos vein. The arch of the aorta is then to be displaced towards the left side, and kept out of the way by hooks. If necessary, the ligamentum ductus arteriosi should be divided, but the superficial cardiac plexus is to be left intact. This dissec- tion will expose the thoracic portion of the trachea, in front of which the deep cardiac plexus is situated, just above the bifurcation into the two bronchi. By very careful dissection the nerves forming this plexus cire to be shown passing dowTiwards and inwards on the sides of the trachea to its anterior aspect, where they end in the plexus. The deep cardiac plexus is arranged in two halves, right and left, which are in free communication with each other. The contributory nerves to the right half of the plexus are I054 ^ MANUAL OF ANATOMY (i) the upper, middle, and lower cervical cardiac branches of the right sym- pathetic ; (2) the upper and lower cervical cardiac branches of the right pneumogastric ; (3) one or two branches from the right recurrent laryngeal nerve ; and (4) one or two thoracic cardiac branches from the right pneumo- gastric nerve. The contributory nerves to the left half of the plexus are (i) the middle and lower cervical cardiac branches of the left sympathetic ; (2) the upper cervical cardiac branch of the left pneumogastric ; and (3) branches from the left recurrent laryngeal nerve. As regards the upper cervical cardiac branch of the left sympathetic, and the lower cervical cardiac branch of the left pneumogastric, they have already been followed over the arch of the aorta into its concavity, where they have been seen to form the superficial cardiac plexus. The connection between the two halves of the deep cardiac plexus is to be made out, as well as that between the right half and the superficial cardiac plexus. The right coronary plexus is to be shown coming from the superficial and right half of the deep cardiac plexus. From the right half of the deep cardiac plexus branches are to be looked for passing to the right anterior pulmonary plexus, and also to the right auricle. The left coronary, plexus is to be shown coming from the left half of the deep cardiac plexus, of which it forms the chief prolongation. Branches are also to be looked for passing to the left anterior pulmonary plexus, and to the left auricle. The heart is now to be removed by dividing the trunk of the pulmonary artery and the pulmonary veins. The aorta and pulmonary artery are, in succession, to be attached to a water-tap, and by turning the stop-cock the flow of water will demonstrate the action of the arterial valves. The three bulgings on the exterior of each vessel close to the corresponding ventricle, and produced by the sinuses of Valsalva in the interior, will be at the same time shown. The auricular portion of the heart should now be separated from the ventricular portion. There is no continuity between the auricular and ventricular muscular fibres, these being only connected through the medium of the fibrous rings round the auriculo-ventricular orifices. A heart usually requires to be boiled in the first place, in order to dissolve the fibrous tissue, but the separation of the auricular from the ventricular portion is possible by careful dissection. After its completion an instructive view will be obtained of the orifices at the base of the ventricular portion. The auriculo- ventricular orifices will be seen to lie side by side, the aortic orifice being in front of and between them, and the pulmonary orifice being in front of the aortic. In the angle between the auriculo-ventricular and aortic orifices a collection of dense fibrous tissue, of the consistence of cartilage, will be found, and processes are to be shown passing from it to the fibrous rings which sur- round the auriculo-ventricular and aortic orifices. The pulmonary artery is next to be laid open by an incision passing between two of the three segments of which the pulmonary valve is composed. The segments of the valve and the sinuses of Valsalva are to be examined, but these admit of much better observation in the case of the aortic valve. The aorta is also to be laid open, observing the same precaution as in opening the pulmonary artery, and the segments of the aortic valve are to receive most careful attention. The two lunulae and corpus Arantii of each seg- ment are to be noted, the direction of the free margins of the segments is to be observed, and the sinuses of Valsalva are to be looked to. The orifices of the right and left coronary arteries are to be examined, that of the right being connected with the right antero-lateral sinus of Valsalva, and that of the left with the left antero-lateral sinus of Valsalva. Lastly, the function of the aortic and of the pulmonary valves is to be carefully studied. For the purpose of examining the arrangement of the muscular fasciculi of the auricles and ventricles a sheep's heart may be obtained and boiled for a short time in order to dissolve the fibrous tissue. Posterior Mediastinum. — The thoracic part of the trachea is now to be dissected, and its bifurcation into two bronchi, right and left, is to be shown, as well as some bronchial glands which lie within the angle of bifurcation. The greater size of the right bronchus and the greater length of the left THE THORAX 1055 bronchus are to be observed, and it is to be specially noted that the right bronchus is more in line with the trachea than the left. The trachea is then to be carefully divided a little above its bifurcation, and the lower part of it, with the two bronchi and two lungs, is to be removed. The right bronchus is to be dissected, and its eparterial and hypaxterial divisions are to be shown. The ramifications of the bronchial tubes within the lungs are then to be followed out. The difference bet^veen the main bronchus and its pulmonary ramifica- tions, as regards the extent of the cartilaginous rings in their walls, should attract attention. The bronchial tubes are to be laid freely open, and their mucous lining is to be inspected. The lung is also to be incised at different parts, and the cut surfaces examined. A portion of healthy lung should be put into a dish of water, and the result should be noted. The thoracic part of the oesophagus is next to be displayed. The dissector is to note that it lies at first on the right side of the descending aorta, then in front of it, and finally slightly to its left side. The right and left pneumogastric nerves will be found in very close contact with the gullet, the right nerve gradually inclining from the right side of the tube to its pos- terior aspect, and the left nerve gradually inclining from the left side of the tube to its anterior aspect. The plexus gulae, formed by branches of these two nerves, should be displayed, and the oesophageal branches of the descend- ing aorta are to be borne in mind. The oesophagus is to be displaced, and the thoracic duct is to be dissected. The dissectors should remember that this duct is sometimes double in the thorax. It \%-ill be found lying close to the right side of the descending aorta, between it and the right azygos vein. It is to be carefully followed up beneath the arch of the aorta and along the left side of the oesophagus, on its way to the root of the neck on the left side. The dissectors of the thorax should now associate themselves with the dissectors of the head and neck, in order to follow the thoracic duct to its termination in the angle of junction between the left internal jugular and left subclavian veins. The descending aorta falls to be dissected next, along with its branches. The aortic intercostal arteries are to be shown on either side, and they are to be followed into the back parts of the intercostal spaces. At this stage the dissector should display the delicate posterior intercostal aponeurosis between which and the parietal pleura each intercostal artery passes. The corresponding intercostal vein and nerve are to be shown in position, and near the angle of the rib the aortic intercostal artery will be found to give off its collatercil intercostal branch, having previously, on its entrance into the space, given off its dorsal branch. In dissecting the descending aorta the bronchial arteries which nourish the lungs are to be looked for behind the corresponding bronchus. There' is usually one right bronchial artery, which arises either from the descending aorta or from the first right aortic intercostal artery, and there are two left bronchial arteries, which spring from the parent trunk. The azygos veins are next to receive attention. The right azygos vein will be found under cover of the oesophagus, where it has the thoracic duct on its left side, and it is to be followed up to its termination in the superior vena cava, a tag of which vessel has been specially preserved. The following tributaries are to be shown enteiing the right azygos vein : (1) the lower seven, or it may be eight, right intercostal veins ; (2) the lower and upper transverse azgyos veins ; and (3) the right superior intercostal vein, which takes up the second and third, and it may be the fourth, intercostal veins of the right side. The first right intercostal vein opens into the correspond- ing innominate vein, or sometimes into the vertebral vein. The lower and upper left azygos veins are then to be dissected, along with the lower and upper transverse azygos veins ; and the left superior intercostal vein, if not previously dissected, is to be followed over the back part of the arch of the aorta, and shown entering the left innominate vein. The first left intercostal vein is disposed similarly to its feUow of the right side. The superior intercostal artery on either side is to be dissected, and its I056 A MANUAL OF ANATOMY distribution to the first and seond intercostal spaces shown. The vessel will be found descending in front of the neck of the first rib. A branch from the first aortic intercostal artery — that, namely, to the third space — should be looked for ascending over the neck of the third rib to join the second inter- costal artery, which it sometimes replaces. The thoracic portion of the gangliated cord of the sympathetic should now be dissected. It will be found lying over the heads of the ribs under cover of the parietal pleura, and gradually inclining inferiorly on to the side of the vertebral column. Two rami communicantes are to be shown passing between each ganglion and the adjacent intercostal nerve, and it is to be noted that these rami are very short. The vascular branches of distribution of the upper ganglia, as well as the branches to the posterior pulmonary plexus of nerves, are not easy of dissection, but the splanchnic nerves admit of this readily, the great and small splanchnic nerves being constant, but the least being frequently absent. The upper surface of the diaphragm is next to be dissected, and attention should be directed to (i) its thoracic relations, (2) the central tendon, (3) the foramen quadratum, (4) the aortic and oesophageal openings, and (5) the relation of the sympathetic cords and splanchnic nerves to it. The diaphragm may now be laid open, in association with the dissectors of the abdomen, and the thoracic duct is then to be followed down to its commencement in the receptaculum chyli. Thereafter the subcostal muscles should be dis- sected. They will be found over the back parts of the ribs in the vicinity of the angles. Articulations. — i. Vertebral Column. — The part available for the dissec- tion of the ligaments is the portion below the first thoracic vertebra, and probably as low as the tenth or eleventh thoracic vertebra. The ligaments to be dissected are (i) the anterior common ligament, which is easily dis- played ; (2) the posterior common ligament, to show which th? neural arches of the vertebrae must be removed by sawing through the pedicles ; (3) the intervertebral discs, which are to be dissected by means of transverse and vertical sections ; (4) the ligamenta subflava, which connect the laminae, and are readily seen after removal of the neural arches ; (5) the capsular liga- ments, which connect the articular processes ; (6) the supraspinous and inter- spinous ligaments ; and (7) the intertransverse ligaments. The movements of the vertebral column are to be carefully studied. 2. Ribs — Costo-central Joints. — The ligaments to be dissected are (i) the anterior costo-central or stellate, easily recognised ; and (2) the inter- articular, which is only seen on opening the joint, and which is absent in the first, sometimes the tenth, the eleventh, and twelfth joints. The two synovial cavities are to be noted, except in the case of the joints just enume- rated as having no interarticular ligament. Costo-transverse Joints. — The ligaments to be dissected are the posterior, middle, and superior costo-transverse. Within the posterior costo-trans- verse ligament the synovial membrane of the joint is to be shown. The middle costo-transverse or interosseous ligament can only be studied properly by sawing horizontally through the neck of the rib and the adjacent trans- verse process. The superior costo-transverse ligaments are to be displayed as two distinct bands — anterior or external, which is large ; and posterior or internal, which is small. The continuity of the outer border of the anterior ligament with the posterior intercostal aponeurosis is to be shown. Costo-chondral Joints. — Each rib is connected to its cartilage by the con- tinuity which takes place between the periosteum of the rib and the peri- chondrium of the cartilage. Sterno-chondral Joints. — The ligaments to be dissected are anterior, pos- terior, superior, and inferior. In the case of the second joint, and it may be in some of the succeeding joints, there is an interarticular ligament, which divides the joint into two distinct synovial compartments. The direct con- nection of the first costal cartilage with the manubrium sterni is to receive attention. Interchondral Joints. — These are met with from about the fifth to the THE THORAX 1057 ninth or tenth costal cartilages. They are pro\4ded with capsular ligaments and synovial membranes. 3. Sternam. — The manubrium and body are connected by ligamentous fibres, disposed longitudinally in front and behind, and by a plate of fibro- cartilage which is interposed between the articular surfaces. It is to be noted that the entire sternum is strengthened by its dense periosteum, by the radiating fibres of the chondro-stemal ligaments, zmd by the tendinous fibres of origin of the pectoralis major muscles. The movements of the ribs are to be studied with the greatest care, and the muscles concerned in these movements are to be specially noted. 67 THE HEAD AND NECK BACK OF THE SCALP AND NECK Landmarks. — ^The external occipital protuberance can, as a rule, readily be made out, and the superior curved line, if well developed, may be felt extending outwards from it. The mastoid process of the temporal bone can be distinguished without difficulty behind the auricle. The occipital artery, with the great occipital nerve on its inner side, lies a little internal to the centre of a line connect- ing the external occipital protuberance and the tip of the mastoid process. The occipital lymphatic gland, or glands, may be felt, when enlarged, over the upper part of the trapezius or complexus muscle. The spine of the seventh cervical vertebra, or vertebra prominens, can easily be felt, and that of the sixth may also be made out. Extending from the external occipital protuberance to the seventh cervical spine there is an elongated depression, called the nuchal furrow, which indicates the position of the ligamentum nuchas. It is possible to feel the strong bifid spine of the axis by sinking the finger deeply into the upper part of the nuchal furrow, near the occipital bone, but the spines of the third, fourth, and fifth cervical vertebrae lie too deeply for detection. The lymphatic glands, known as the gland ulae concatenatae, may be felt, when en- larged, along the posterior border of the sterno-cleido-mastoid muscle. Back of the Neck — Fasciae. — ^The superficial fascia presents nothing worthy of note. The deep fascia closely invests the cervical portion of the trapezius, and is then prolonged over the posterior triangle of the neck to the posterior border of the sterno- cleido-mastoid, where it divides to ensheathe that muscle. It will be described in connection with the deep cervical fascia. Nerves. — ^The nerves of this region are as follows : the great occipital ; the least or third occipital ; the internal branches of the posterior primary divisions of the third, fourth, and fifth cervical spinal nerves ; the small occipital ; the great auricular ; the super- ficial cervical ; the spinal accessory ; and the descending superficial branches of the cervical plexus, namely, the suprasternal, supra- clavicular, and supra-acromial. 1058 THE HEAD AND NECK 1059 The great occipital nerve is the internal branch of the posterior primary division of the second cervical ner\'e. It pierces the upper part of the complexus muscle, and sometimes the trapezius, about \ inch from the middle line. It then turns upwards, with an inclination outwards, and accompanies the occipital artery to the cranial integument, lying on the inner side of that vessel. Its branches are long, and have an extensive distribution, reaching as far as the vertex of the skull. Externally it commimicates with the small occipital nerve, and internally with the least occipital. The least or third occipital nerve is a small offset from the internal branch of the posterior primary division of the third cervical nerve. Having pierced the trapezius, it ascends internal to the great occipital nerve, with which it communicates, and has a limited distribution to the occipital integument inside that nerve. The internal branches of the posterior primary divisions of the third, fourth, and fifth cervical nerves appear through the trapezius close to the middle line, and turn outwards to supply the skin of the back of the neck, that of the third furnishing, as just stated, the least occipital nerve. The small occipital nerve is one of the ascending superficial branches of the cervical plexus, and arises from the anterior primary division of the second cervical nerve, sometimes receiving a branch from that of the third. It appears at the posterior border of the stemo-cleido-mastoid muscle, and ascends along that border to the occipital region. Here it divides into mastoid and occipital branches, which supply the skin of the mastoid, outer part of the occipital, and adjacent portion of the parietal, regions. It furnishes an auricular branch to the skin of the inner surface of the auricle, and it communicates with the great occipital, the mastoid and auricular branches of the great auricular, and the posterior auricular branch of the facial. The small occipital nerve is sometimes double, and in these cases one portion of it usually pierces the anterior border of the trapezius. The great auricular nerve, like the small occipital, is one of the ascending superficial branches of the cervical plexus, and arises by two roots from the anterior primary divisions of the second and third cervical nerves. It turns round the posterior border of the stemo-cleido-mastoid immediately below the small occipital nerve, and passes upwards and forwards upon that muscle towards the lobule of the auricle, on approaching which it divides into mastoid, auricular, and facial branches. The mastoid branch is distributed to the skin over the mastoid region ; the auricular branch supplies the skin of the inner surface of the auricle, and sends one or two twigs through the cartilage of the auricle to the skin covering its outer surface ; and the facial branch is distributed to the skin over the parotid gland. The mastoid and auricular branches communicate with the small occipital and posterior auricular nerves, and the facial branch commimicates in the parotid gland with the cervico-facial division of the facial nerve. ro^o A MANUAL OF ANATOMY The superficial or transverse cervical nerve, like the small occipital and great auricular, is a superficial branch of the cervical plexus, and arises by two roots from the anterior primary divisions of the second and third cervical nerves. It appears at the posterior border of the stemo-cleido-mastoid, close below the great auricular, Attrahens Auriculam Attollens Auriculam Retrahens Auriculam Occipitalis Great Occioital Nerved Complexus — -y-, Small Occipital Nerve— Splenius Capitis Levator Anguli Scapulae.. Great Auricular Nerve ._ Spinal Accessory Nerve ..^j Branches from Third and Fourtn 11 1. Cervical Nerves to Trapezius " Scalenus Medius Supra-acromial Nerve Trapezius Scalenus Anticus Posterior Belly of Omo-hyoid Frontalis >■ Orbicularis Palpebrarum Levator Labii _ Superioris Ala;que Na j_.Levator Labii Superio Zygomaticus Minor ?t'— Zygomaticus Major — . Masseier —I Orbicularis Oris ^Depressor Labii Inferior --Depressor Anguli Oris —Levator Menti Anterior Belly of Digastric m/._ Sterno-hyoid ,. Anterior Belly of Omo-hyoid Sterno-cleido-mastoid .Superficial Cervical Nerve ..Suprasternal Nerve —Supracluvicular Nerve Subclavian Artery (third part) Fig. 435. — The Right Side of the Head and Neck. (The Platysma Myoides has been removed, and the Nerves are shown), and turns over that muscle to reach the front of the neck, where it will be afterwards described. The spinal accessory nerve [spinal portion) appears at the posterior border of the sterno-cleido-mastoid near its centre, below the super- ficial cervical, and then crosses the posterior triangle of the neck downwards and backwards to the anterior border of the trapezius, beneath which it passes. It is accompanied by two small branches THE HEAD AND NECK 1061 of the anterior primary divisions of the third and fourth cervical ner\-es, which lie below it, and it forms a plexiform communication with them beneath the trapezius, to which muscle it is distributed. The descending superficial branches of the cervical plexus appear at the posterior border of the stemo-cleido-mastoid, below the spinal accessor}', usually as a single trunk which arises by two roots from the anterior primary divisions of the third and fourth cervical ner\-es. This trunk, as it descends, divides into three nerves, namely, suprasternal, supraclavicular, and supra-acromial, which pass downwards over the clavicle, and will be afterwards referred to. Muscles — Cervical Portion of the Trapezius — Origin. — (i) The inner third of the superior curved line of the occipital bone, and the external occipital protuberance ; and (2) the ligamentum nuchae. Insertion. — (i) The posterior border of the outer third of the clavicle ; and (2) the inner border of the acromion process of the scapula. Nerve- supply. — (i) The spinal accessory nerve (spinal portion) ; and (2) branches from the cervical plexus, which are derived from the anterior primary divisions of the third and fourth cervical nerves. The nerves enter the deep surface of the muscle after passing beneath its anterior border a little above the clavicle, and they here form a plexiform communication with each other. Blood- supply. — ^There is one specially named artery, called the superficial cervical artery, which is a branch of the transverse cer- vical, and, like the ners^es, enters the deep surface of the muscle. The fibres are directed downwards, forwards, and outwards. Action. — ^The cervical fibres, acting from their origin, elevate the outer end of the clavicle and the point of the shoulder. Acting from their insertion they extend the head, and incline the neck towards the same side, the face being directed towards the opposite side. The anterior border of the muscle forms the posterior boundary of the posterior triangle of the neck. Occasionally a small muscle, called the transversns naehs, is met with, extending from the external occipital protuberance to the tendon of insertion of the stemo-cleido-mastoid. It may be fleshy or tendinous. Ligamentum Nuchae. — This is a strong fibrous band which occupies the median line of the neck. Its superficial fibres are attached superiorly to the external occipital protuberance, and inferiorly to the spine of the seventh cervical vertebra. Its deep fibres are attached to the external occipital crest, and to the spines of cervical vertebrse, from the second to the sixth inclusive. They also extend into the interspinous intervals, bet^veen the interspinales muscles, where they represent interspinous ligaments. Insertion and Posterior Border of the Stemo-cleido-mastoid.— This muscle is inserted into (i) the outer surface of the mastoid process of the temporal bone, and (2) the superior curved line of io62 A MANUAL OF ANATOMY the occipital bone over about its outer half, or more. The posterior border of the muscle forms the anterior boundary of the posterior triangle of the neck, and has the following nerves related to it : (i) the small occipital ascends along it to the head ; (2) the great auricular passes upwards and forwards over it towards the lobule of the auricle ; (3) the superficial cervical crosses it in a forward direction ; (4) the spinal accessory appears from behind it, along with the branches of the third and fourth cervical nerves to the trapezius ; and (5) the descending superficial branches of the cervical plexus emerge from underneath it. The glandulsB concatenatae belong to the deep cervical glands, and are situated along the posterior border of the sterno-cleido- mastoid muscle. They will be afterwards described. The levator anguli scapulae, rhomboids, serratus posticus superior, splenitis, complexus, transversalis cervicis, trachelo-mastoid, semi- spinalis colli, intertransversales, and interspinals muscles will be found described in connection with the muscles of the back, see p. 287 et seq. Second and Third Parts of the Occipital Artery.— At the mastoid process this vessel lies very deeply. Having crossed the rectus capitis lateralis muscle, it enters the occipital groove on the inner aspect of the mastoid process, where it is covered by the following structures, in order from the surface downwards : (i) stemo-cleido- mastoid ; (2) splenius capitis ; (3) trachelo-mastoid ; (4) mastoid process ; and (5) the posterior belly of the digastric. In its back- ward course the vessel rests, in succession, upon the insertions of the obliquus capitis superior and complexus, and it escapes from beneath the muscles covering it in the following order : posterior belly of the digastric, trachelo-mastoid, splenius capitis, and stemo- cleido-mastoid. After emerging from beneath the last-named muscle, it lies for a little in the posterior triangle, close to the apex, and then, piercing the occipital origin of the trapezius, it enters upon the third part of Us, course. This part ascends, along with the great occipital nerve, to the occipital region, where it divides into several long tortuous branches. Branches. — ^The branches of the second and third parts are as follows : mastoid, posterior meningeal, arteria princeps cervicis, communicating, muscular, and terminal. The mastoid artery passes through the arterial fissure on the outer surface of the mastoid process, and supplies the diploe and mastoid cells, as well as the adjacent dura mater. The posterior meningeal artery enters the cranial cavity through the jugular foramen, and takes part in the supply of the dura mater of the posterior fossa. The arteria princeps cervicis arises under cover of the splenius capitis, and at the outer border of the complexus it divides into a superficial and deep branch. The superficial branch is distributed to the splenius capitis and trapezius, and anastomoses, in the latter muscle, with the superficial cervical artery. The deep branch passes beneath the complexus, and anastomoses, upon the semispinalis THE HEAD AND NECK 1063 colli, with (i) the deep cervical of the superior intercostal of the second part of the subclavian, and (2) branches of the vertebral artery. The communicating branches enter the suboccipital triangle, where they anastomose with branches of the vertebral artery. The muscular branches supply the contiguous muscles. The terminal branches are at first two in number, but these soon divide into several long tortuous branches, which supply the occipitalis and the integument as high as the vertex. They anas- tomose with the posterior auricular, the posterior division of the superficial temporal, and their fellows of the opposite side. The occipital venous plexus communicates with the posterior auricular, and the posterior branch of the superficial temporal, veins. It receives the parietal emissary vein, which emerges through the parietal foramen, and so a' communication is established with the superior longitudinal sinus. Sometimes it receives a small occipital emissary vein, which emerges through an opening at the external occipital protuberance, and then a communication would be established with the torcular Herophili. Two or three occipital veins emerge from the occipital plexus. The external vessel is known as the posterior jugular vein. It receives the mastoid emissary vein, which emerges through the mastoid foramen, and so an important communication is established with the lateral sinus. Having been reinforced by tributaries from the superficial structures at the upper part of the back of the neck, the posterior jugular vein passes on to the stemo-cleido-mastoid, where it opens into the external jugular. The middle occipital vein (inconstant) accompanies the occipital artery, and usually opens into the internal jugular. The internal occipital vein, having in some cases pierced the trapezius, passes beneath the complexus, and enters the suboccipital triangle. In this situation it joins the suboccipital plexus, from which the deep cervical and vertebral veins emerge. Occipital Glands. — ^These glands are usually two in number, and lie over the occipital portion of the trapezius, or over the upper part of the complexus. They receive their afferent lymphatics from the back part of the scalp, and their efferent lymphatics pass to the deep cervical glands. Deep Cervical Artery. — This vessel is a branch of the superior intercostal of the second part of the subclavian. Having passed backwards between the transverse process of the seventh cervical vertebra and the neck of the first rib, it ascends upon the semi- spinalis colli, under cover of the complexus, towards the level of the spine of the axis, where it anastomoses with the deep branch of the arteria princeps cervicis of the occipital. In its course it furnishes a spinal branch, which enters the spinal canal through the intervertebral foramen for the eighth cervical nerve, and muscular branches, which anastomose with branches of the vertebral artery. The deep cervical vein commences, within the suboccipital triangle, in the suboccipital plexus, which receives the internal occipital io64 A MANUAL OF ANATOMY vein. It descends, in company with the deep cervical artery, to the lower part of the neck, where it passes forwards between the transverse process of the seventh cervical vertebra and the neck of the first rib, and ends by joining the vertebral vein just before that vessel terminates in the innominate vein. In addition to the muscular branches of the occipital and deep cervical arteries, the deep muscles of the back of the neck receive twigs from the second part of the vertebral artery, which traverses the costo-transverse foramina of the upper six cervical vertebrae. These twigs pass backwards through the intertransverse spaces, and anastomose with branches of the arteria princeps cervicis and deep cervical arteries. Suboccipital Region — Muscles — Rectus Capitis Posticus Major — Origin. — One of the tubercles in which the spine of the axis terminates. Insertion. — ^The outer part of the inferior curved line of the occipital bone, and the subjacent area. Nerve-supply. — ^The posterior primary division of the suboccipital nerve. The direction of the fibres is upwards and outwards. Action. — (i) To rotate the head towards the same side ; and (2) to extend the head. The muscle is triangular, and its insertion is slightly overlapped by the obliquus capitis superior. Rectus Capitis Posticus Minor — Origin. — ^The posterior arch of the altas, close to, and encroaching upon, the posterior tubercle. Insertion. — ^The inner third of the inferior curved line of the occipital bone, and the subjacent area as low as the foramen magnum. Nerve-supply. — ^The posterior primary division of the suboccipital nerve. The direction of the fibres is upwards in an expanded manner. Action. — ^To extend the head. The muscle is fan-shaped, and lies deeper than, and internal to, the rectus capitis posticus major. Obliquus Capitis Inferior— Or^gm. — One of the tubercles in which the spine of the axis terminates. Insertion. — ^The lower surface of the extremity of the transverse process of the atlas at its back part. Nerve-supply. — ^The posterior primary division of the suboccipital nerve. The direction of the fibres is outwards and slightly upwards. Action. — ^To rotate the atlas, along with the head, towards the same side. The muscle is thick and fleshy. At its origin it is interposed between the rectus capitis posticus major superiorly and the highest bundle of the semispinalis colli interiorly. The great occipital nerve winds round its lower border. Obliquus Capitis Superior — Origin. — ^The upper surface of the THE HEAD AND NECK 1065 extremity of the transverse process of the atlas at its back part. Insertion. — ^The occipital bone between the outer parts of the superior and inferior curved lines. Nerve-supply. — ^The posterior primary division of the suboccipital nerve. The direction of the fibres is upwards and inwards. Action. — (i) To extend the head ; and (2) to act as a slight lateral flexor of the head. * The muscle is triangular. Suboccipital Triangle. — ^This triangle is situated under cover of the upper part of the complexus, close below the occipital bone. Recti Capitis Postici Minores A Rectus Capitis Posticus Major Posterior Tubercle of Atlas Spinous Process of Axis Interspinales^-v;."' .Suboccipital Triangle Obliquus Capitis Superior -Mastoid Process ~ Vertebral Artery - — ,_ (Third Part) ■-■^^ ~" — Posterior Division of ^^^^ Suboccipital Nerve "^ Transverse Process of -,^ Atlas '■"•^^Obliquus Capitis Inferior Great Occipital Nerve ___J'.raSemispinalis Colli (upper " two bundles) Fig. 436. — The Suboccipital Triangle. Boundaries — Sup era-internal. — ^The rectus capitis posticus major. Super 0- external. — ^The obliquus capitis superior. Inferior. — ^The obliquus capitis inferior. The roof is formed by the complexus, and the floor by half of the posterior arch of the atlas, and half of the posterior occipito-atlantal ligament. The contents are (i) the third part of the vertebral artery, (2) the suboccipital plexus of veins, and (3) the posterior primary division of the suboccipital nerve. Third Part of the Vertebral Artery. — The vertebral artery, having emerged from the costo-transverse foramen of the atlas, enters upon the third part of its course, and takes a winding course back- wards and inwards. It lies in the vertebrarterial groove of the atlas, the posterior primary division of the suboccipital nerve being beneath it, and it passes under an arched band of the io66 A MANUAL OF ANATOMY posterior occipito-atlantal ligament. It leaves the suboccipital triangle by piercing the duca mater, and enteis the cranial cavity through the foramen magnum. The third part of the vessel fur- nishes muscular branches to the adjacent muscles which anastomose with the arteria princeps cervicis of the occipital, and the deep cervical of the superior intercostal. Suboccipital Plexus of Veins. — ^This plexus is formed by branches which proceed from (i) the intraspinal venous plexus, (2) the ad- jacent muscles, and (3) the occipital periosteum. It receives the internal occipital vein, and the blood is conveyed away from it by the deep cervical vein, already described, and the vertebral vein, which will be afterwards considered. Posterior Primary Division of the Suboccipital Nerve. — ^This divi- sion passes backwards, as a single nerve, in the vertebrarterial groove of the atlas, lying between the bone and the third part of the vertebral artery. On entering the suboccipital triangle it divides into branches which supply the obliqui, recti postici, and complexus muscles. Posterior Primary Divisions of the Cervical Spinal Nerves. — The cervical nerves are eight in number, the first being known as the suboccipital nerve. Each breaks up into an anterior and a pos- terior primary division. The posterior primary division of the first or suboccipital is single, and has just been described. The posterior primary divisions of the lower seven arise in the inter- vertebral foramina, and each soon divides into an external and internal branch. The external branches of all are distributed to the deep muscles, and do not become cutaneous. The internal branch of the posterior primary division of the second, which is of large size, constitutes the great occipital nerve. It winds round the lower border of the obliquus capitis inferior, and pierces the complexus, to which it gives branches. Thereafter it may pierce the trapezius to reach its cutaneous distribution, which has been already described. The internal branches of the third, fourth, and fifth are directed inwards upon the semispinalis colli, to which, as well as to the complexus, they give branches. Close to the cervical spinous processes they pass backwards, internal to the biventer cervicis (part of the complexus), and, having pierced the trapezius, they reach the integument, which they supply. The internal branch of the posterior primary division of the third, before piercing the trapezius, gives off a small ascending branch, known as the least or third occipital. It passes upwards, lying at first under cover of the trapezius, and then passing through it, to reach the occipital integument. The internal branches of the posterior primary divisions of the sixth, seventh, and eighth are directed in- wards towards the cervical spinous processes beneath the semi- spinalis colli, and are distributed to the adjacent muscles. They do not furnish any branches to the integument. THE HEAD AND NECK 1067 The Scalp and Temporal Region. Scalp — Fascia. — ^The superficial fascia is firm and granular, and is separated into lobules by fibrous processes which pass between the skin and the epicranial aponeurosis. The deep fascia is repre- sented by the epicranial aponeurosis of the occipito-frontalis muscle, to be presently described. Nerves of the Scalp Proper. — ^The great, small, and least or third occipital nerves, and the mastoid branch of the great auricular have been already described. In the fronto-parietal region two sensory nerves are met with, namely, the supra-orbital and supra- trochlear, both of which are derived from the frontal nerv^e, which is one of the branches of the ophthalmic division of the fifth cranial nerve. The supra-orbital nerve, which is of large size, leaves the orbit through the supra-orbital foramen. It then ascends, lying at first beneath the upper part of the orbicularis palpebrarum and the frontalis muscles, but subsequently piercing the latter muscle in two branches, outer and inner. The outer branch is the larger of the two, and its offsets extend well back over the parietal region. As the supra-orbital nerve passes through the supra-orbital foramen it furnishes one or two twigs to the mucous membrane of the frontal air-sinus and to the diploe of the frontal bone, and, after emerging from the foramen, it sends downwards palpebral branches to the integument of the upper eyelid. Thereafter the nerve supplies the integument of the fronto-parietal region. The outer and inner branches of the supra-orbital nerve sometimes emerge from the orbit separately, the outer branch passing through the supra-orbital foramen, and the inner branch passing over the frontal notch. The supratrochlear nerve, which is of small size, is internal to the supra-orbital nerve. It leaves the orbit close to the internal angular process of the frontal bone, where it lies above the trochlea or pulley of the superior oblique muscle of the eyeball. It then ascends beneath the upper part of the orbicularis palpebrarum and the frontalis muscles, and, piercing the latter muscle, it has a limited distribution to the frontal integument close to the median line. As the nerve leaves the orbit it furnishes palpebral twigs to the inner part of the integument of the upper eyelid. Arteries. — ^The third part of the occipital artery has been already described. The arteries of the fronto-parietal region are three in number, namely, the supra-orbital, frontal, and anterior branch of the superficial temporal. The supra-orbital artery is a branch of the ophthalmic, and emerges from the orbit with the supra-orbital nerve. It is dis- tributed to the structures covering the frontal bone, and anasto- moses with the frontal, and the anterior division of the superficial temporal, arteries. In the supra-orbital foramen it furnishes one or two branches to the mucous membrane of the frontal air-sinus and to io68 A MANUAL OF ANATOMY the diploe of the bone, and, after emerging from the foramen, it sends downwards palpebral branches to the integument of the upper eyelid. The supra-orbital vein passes downwards and inwards to a point just above the inner canthus, where it joins the frontal vein. In this manner the angular vein is formed, which is the commence- ment of the facial vein. The supra-orbital vein receives tributaries from the frontal region and the upper eyelid, and in the region of the inner canthus it communicates with the superior ophthalmic vein. It also communicates with the superior ophthalmic vein through the supra-orbital notch, and this communication receives the frontal diploic vein, which returns the blood from the diploe of the frontal bone and mucous membrane of the frontal air-sinus. The frontal artery, like the supra-orbital, is a branch of the ophthalmic, and emerges from the orbit with the supratrochlear nerve. It is distributed to the structures over the frontal bone internal to the supra-orbital artery, with which it anastomoses, as well as with its fellow of the opposite side. The frontal vein, of large size, passes downwards near the median line, and at a point just above the inner canthus is joined by the supra-orbital vein, the resultant vessel being the angular vein. At the root of the nose it communicates with its fellow of the opposite side by a transverse vessel, called the transverse nasal vein. The supra-orbital and frontal veins communicate with each other, and with the tributaries of the anterior branch of the super- ficial temporal vein. The anterior branch of the superficial temporal artery will be described in connection with the temporal region. Occipito-frontalis. — ^This muscle consists of the following parts : (i) the occipitalis, (2) the frontalis, and (3) the epicranial aponeurosis. Occipitalis. — ^This consists of two thin fleshy bellies, right and left. Origin.— (i) The outer parts of the highest and superior curved lines of the occipital bone ; and (2) the outer surface of the mastoid process of the temporal bone, immediately above the insertion of the sterno-cleido- mastoid muscle. Insertion. — ^The epicranial aponeurosis. Each belly forms a thin, broad sheet, the length of the fasciculi being about i| inches. The two bellies, right and left, are sepa- rated towards the median line by a portion of the epicranial aponeu- rosis, which here dips down between them. Frontalis.— This consists of two parts, right and left, which are separated superiorly by a narrow angular portion of the epicranial aponeurosis, but interiorly, and for the most part, they are in con- tact. Origin. — (i) The subcutaneous tissue of the eyebrow and root of the nose, where the fibres blend with the upper part of the orbicularis palpebrarum and the corrugator supercilii ; and (2) slightly from the external angular process of the frontal bone, and from the nasal bone. Insertion. — The epicranial aponeurosis, a little below the level of the fronto-parietal suture. THE HEAD AND NECK Io6q The fasciculi are about 3J inches long, and the innermost fibres inferiorly are regarded by some as being prolonged downwards upon the nasal bone as the pyramidalis nasi muscle. Epicranial Aponeurosis. — This is the intermediate tendon of the occipito-frontalis muscle. It forms an aponeurotic stratum be- neath the superficial fascia, and is connected to the skin by fibrous processes, which separate the superficial fascia into lobides. Its deep surface is loosely connected by areolar tissue to the subjacent Stensen's Duct.- Baccinator Muscle... Facial Artery .. Submental Artery ._ Lingtial Artery - Sup. Lar. Art. and Nerve- Thyro-hyoid Muscle . Superior Thyroid Artery Post. Belly of Omo-hyoid *^^i^'±'^ Subclavian Artery.- ^'' /'/-Li (third part) Transverse Facial Artery Superficial Tem- porcl Artery Internal Maxillary Artery Posterior Auricular Artery -_.^. Occipital Artery 7^W7^mttif— Stylo-byoM Muscle " -^frrji'l P°^*- ^*"y °'" Digastric ._^\^'|. Hypoglossal Nerve ^:V «; I Descendens Cervicis 1 J Nerve External Carotid Artery n— ~ Stemo-ckido-mastoid ^*^ — TrapezitK ___Transverse Cervi- cal Artery - . Suprascapular Artery feii'iiii.Aui Fig. 43/. — The Left Side of the Head and Neck. (The Platy'sma Myoides has been removed). periosteum. Posteriorly it gives insertion to the two bellies of the occipitalis muscle, and, in the interval between these, it dips down to be attached to the inner part of the highest curved line of the occipital bone and the external occipital protuberance. Anteriorly it gives insertion to the two halves of the frontalis muscle. Laterally, below the superior temporal ridge, it is prolonged downwards over the temporal fascia as a delicate expansion, which gives origin to the attollens auriculam and attrahens auriculam muscles. Nerve- supply. — ^The occipitalis muscle is supplied by the pos- I070 A MANUAL OF ANATOMY terior auricular branch of the facial nerve, and the frontalis muscle is supplied by the temporal branches of the tempore -facial division of the facial nerve. Action. — ^The two bellies of the occipitalis draw backwards the epicranial aponeurosis, and along with it the scalp. The two halves of the frontalis, acting from below, draw forwards the epi- cranial aponeurosis, and along with it the scalp. Acting from above they elevate the eyebrows, and throw the skin of the frontal region into transverse wrinkles. When the occipitalis and frontalis act simultaneously the scalp is drawn backwards, and the eye- brows are forcibly raised. When the two muscles act alternately the scalp is drawn backwards and forwards. Pericranium. — ^This is the periosteum of the cranium, and it is loosely connected by areolar tissue to the superjacent epicranial aponeurosis. Temporal Region — Nerves. — ^These are as follows : (i) the tem- poral branches of the tempo ro- facial division of the facial nerve ; (2) the auriculo-temporal nerve ; and (3) the temporal branch of the orbital or temporo-malar nerve. The temporal branches of the temporo-facial division of the facial nerve pass upwards a little in front of the auricle, and supply the following muscles : the frontalis, upper part of the orbicu- laris palpebrarum, corrugator supercilii, attollens auriculam, and attrahens auriculam. They communicate with the auriculo-tem- poral, temporal branch of the orbital, and supra-orbital nerves. The auriculo-temporal nerve is a branch of the posterior division of the inferior maxillary nerve, which is the third division of the fifth cranial nerve. It emerges from the upper part of the parotid gland, and ascends immediately in front of the auricle, in company with the superficial temporal artery, lying between that vessel and the auricle. Branches. — In this part of its course the nerve furnishes the following branches : (i) two meatal branches to the meatus audi- torius externus, which enter the canal between its osseous and cartilaginous walls, and supply the integument of the meatus, the upper of the two branches giving an offset to the membrana tympani : (2) two anterior auricular branches, which supply the skin of the tragus and outer aspect of the auricle over its upper half ; and (3) temporal branches, which supply the integument above and in front of the auricle, and of the temporal region generally. The temporal branch of the orbital or temporo-malar nerve from the superior maxillary is of small size, and pierces the temporal fascia about i inch above the anterior part of the zygoma, and close behind the marginal process of the malar bone. Having communi- cated with one of the temporal branches of the facial nerve, it has a limited distribution to the integument of the anterior part of the temporal region. The superficial temporal artery is one of the terminal branches of the external carotid artery, from which it arises within the parotid gland on a level with the neck of the lower jaw. Emerging from the THE HEAD AND NECK 1071 gland it ascends in front of the auricle, in company with the auriculo-temporal nerve, which lies between the vessel and the auricle, and, after a course of about 2 inches, it divides into its two terminal branches. Branches. — These are as follows: (i) transverse facial; (2) articular ; (3) anterior auricular ; (4) middle temporal ; (5) orbital ; and (6) terminal, namely, anterior temporal and posterior temporal. The transverse facial branch will be described in connection with the face. It arises within the parotid gland, and in its course Transverse Facial Supra4>rbital Frontal Superficial Temporal Occipital - Internal Maxillary Posterior Auricular Lateral Nasal Occipital Internal Carotid External Carotid Inferior Labial '' Submental * ^^ Submaxillary Gland \ Facial Lingual Superior Thyroid Fig. 438. — The Arteries of the Right Side of the Head (after L. Testot's ' Anatomie Humaine '). furnishes glandular branches. The articular branches supply the temporo-mandibular joint. The anterior auricular branches supply the outer aspect of the auricle, and in part the meatus auditorius extemus. The middle temporal branch pierces the temporal fascia and temporal muscle immediately above the zygoma, and then ascends in a groove on the outer surface of the squamous part of the temporal bone. It gives branches to the temporal muscle, and anastomoses with the deep temporal arteries, which are branches of the internal maxillary. The orbital branch passes forwards close above the zygoma, where it lies between the two layers of the temporal fascia. It is distributed to the outer part of the orbi- cularis palpebrarum muscle. The anterior temporal branch passes forwards and upwards in a tortuous manner, and is distributed I072 A MANUAL OF ANATOMY to the structures covering the frontal bone, where it anastomoses with the supra-orbital and frontal branches of the ophthalmic artery, and with its fellow of the opposite side. The posterior temporal branch takes an arched course upwards and backwards above the auricle, supplying the adjacent structures, and anasto- mosing with the posterior auricular and occipital arteries, and with its fellow of the opposite side. The superficial temporal vein is formed in front of the auricle by the union of an anterior and a posterior branch, the former "com- municating freely with the supra-orbital and frontal veins, and the latter with the posterior auricular vein and the occipital venous plexus. Above the zygoma it is joined by the middle temporal vein, which originates in a plexus in the temporal fossa, and pierces the temporal muscle and temporal fascia, receiving in its course the orbital vein. The superficial temporal vein then descends over the zygoma and enters the parotid gland, within which it receives the anterior auricular, articular, and transverse facial veins. Finally, it joins the internal maxillary vein about the level of the neck of the lower jaw to form the temporo-maxillary vein. Extrinsic Muscles of the Auricle. — ^These are three in number, as follows : (i) attollens auriculam ; (2) attrahens auriculam ; and (3) retrahens auriculam. Attollens Auriculam — Origin. — ^The lateral part of the epicranial aponeurosis. Insertion. — ^The inner or cranial surface of the auricle over the convexity corresponding to the fossa of the antihelix on its outer surface. Nerve-supply. — ^The temporal portion of the temporo-facial division of the facial nerve. The posterior part of the muscle may be supplied by the posterior auricular branch of the facial nerve. The muscle is very thin, pale, and fan-shaped, and its fibres con- verge in a downward direction. Action. — ^To raise the auricle. Attrahens Auriculam — Origin. — The lateral part of the epi- cranial aponeurosis in front of the attollens auriculam, with which muscle it is continuous. Insertion. — ^The anterior part of the helix of the auricle. Nerve-supply. — ^The temporal portion of the temporo-facial division of the facial nerve. The muscle is directed backwards. Action. — ^To draw forwards the auricle. Retrahens Auriculam— Ongiw. — The upper part of the outer surface of the mastoid process of the temporal bone. Insertion. — The inner or cranial surface of the auricle over the convexity of the concha. Nerve-supply. — ^The posterior auricular branch of the facial nerve. The muscle is directed forwards. A ction. — To draw back the auricle. The retrahens auriculam is more distinct than the other two muscles, and is usually arranged in two bundles. THE HEAD AND NECK 1073 Posterior Auricular Nerve. — ^This is a branch of the facial nerve immediately after it emerges from the aqueduct ot Fallo- pius through the stylo-mastoid foramen. It passes upwards between the mastoid process and the auricle, where it lies deeply in company with the posterior auricular artery, and it divides into two branches — auricular and occipital. The auricular branch supplies the retrahens auriculam muscle on its deep aspect, and those intrinsic muscles of the auricle which lie on its inner or cranial aspect. It may also send a branch upwards beneath the retrahens auriculam to supply the posterior part of the attollens auriculam. The occipital branch passes backwards, and supplies the corresponding half of the occipitalis muscle. The posterior auricular nerve com- municates with the small occipital and great auricular ner\'es, and also with the auricular branch (Arnold's nerve) of the pneumo- gastric. Nerve of Arnold. — ^This is the auricular branch of the ganglion of the root of the pneumogastric ner\-e. Ha\'ing traversed the auricular canaliculus in the petrous part of the temporal bone, it emerges through the auricular or tjnipano-mastoid fissure, between the mastoid process and tympanic plate, and thereafter divides into two branches — auricular and communicating. The auricular branch takes part in the supply of the inner or cranial surface of the auricle, and also supplies the lower and back part of the meatus auditorius extemus ; and the communicating branch joins the posterior auricular ner\'e. Posterior Auricular Artery. — ^This vessel is one of the t\vo pos- terior branches of the external carotid artery, the other branch being the occipital artery. Having passed backwards and upwards under cover of the parotid gland, it lies deeply bet\veen the mastoid process and the auricle, in close relation to the posterior auricular nerve, and divides into two branches — auricular and mastoid. The auricular branch supplies the inner or cranial surface of the auricle and adjacent structures, and it anastomoses with the pos- terior branch of the superficial temporal artery. The mastoid branch passes backwards to the corresponding half of the occipitalis muscle, and anastomoses with the occipital artery. The posterior auricular vein is of fairly large size, and returns the blood from the lateral portion of the scalp posteriorly, and the inner surface of the auricle. Its radicles communicate with the occipital plexus and with the posterior branch of the superficial temporal vein. The vessel passes downwards and forwards over the upper part of the stemo-cleido-mastoid muscle, and terminates about the level of the angle of the lower jaw by joining the posterior division of the temporo -maxillary vein to form the external jugular vein. Posterior Auricular, or Mastoid, Glands. — These glands lie close to the insertion of the stemo-cleido-mastoid muscle. They receive their afferent hmphatics from the lateral part of the back of the scalp and the back of the auricle, and their efferent IjTiiphatics pass tu the superficial cervical glands. 68 to74 A MANUAL OF ANATOMY Temporal Fascia. — ^This is a strong aponeurosis which covers the temporal muscle. Superiorly it is attached from before backwards to the temporal border of the malar bone, the superior temporal ridge of the frontal and parietal bones, and the supramastoid crest of the temporal bone. Inferiorly it divides into two laminae, which are attached to the outer and inner margins of the upper border of the zygomatic arch. Between these two laminae there are a small amount of adipose tissue and the orbital branch of the superficial temporal artery. Superficial to the fascia there are the delicate prolongation of the lateral portion of the epicranial aponeurosis and the attollens and attrahens auriculam muscles. Superiorly the fascia gives origin, by its deep surface, to superficial fibres of the temporal muscle, but it is separated from that muscle towards the zygoma by adipose tissue. Temporal Muscle — Origin. — (i) The temporal fossa, extending as high as the inferior temporal ridge of the frontal and parietal bones, and as low as the infratemporal crest on the external surface of the great wing of the sphenoid ; and (2) the deep surface of the temporal fascia over its upper part. The muscle is fan-shaped. The anterior fasciculi descend almost vertically ; the posterior fasciculi pass almost horizontally for- wards ; and the intervening fasciculi descend with varying degrees of obliquity. A complete description of the temporal muscle will be found on p. 1200. Lymphatic Vessels of the Scalp — Frontal Region. — These pass to the intraparotid lymphatic glands. Temporo-parietal Region.^ The anterior lymphatics pass to the intraparotid glands, and the posterior lymphatics terminate in the mastoid, or posterior auricular, glands. The Cranial Cavity. The meninges of the encephalon, namely (i) the dura mater, with its septa and venous sinuses, (2) the arachnoid membrane, and (3) the pia mater, will be found described in Index. Cranial Nerves at the Base of the Skull. — ^The cranial nerves are arranged in twelve pairs, and as they leave the cranial cavity they receive sheaths from the meninges of the encephalon. The olfactory bulb rests upon one-half of the cribriform plate of the ethmoid bone. Through the foramina of that plate it receives about twenty olfactory filaments, which arise as the axons of the olfactory cells of the olfactory mucous membrane of the nasal fossa. The nasal nerve passes forwards and inwards beneath the dura mater on one-half of the cribriform plate of the ethmoid bone to the nasal slit. The optic nerve passes forwards and outwards from the optic commissure to the optic foramen, through which it enters the orbit. It is accompanied by the ophthalmic artery, which lies beneath it. The third or oculo-motor nerve pierces the dura mater, which THE HEAD AND NECK 1075 forms the outer wall of the cavernous sinus, a little in front of the posterior clinoid process of the sphenoid bone. The fourth or trochlear nerve, of small size, pierces the dura mater at a point a little behind the posterior clinoid process of the sphenoid bone, external to the third nerve, and beneath the free margin of FzxHital Air-Sinus Optic Nerve-^ ithalmic Artery Third Ner Fourth Nerve,/- ;]/ Region of J^ Meckel's Cave ' Fifth Nerve Facial Nerve lUditory Nerve >so-phary ngeal . Nerve Pneumogastric Nerve Spinal Accessory Anterior Fossa Sylvian Border of Smai. Wing of Sphenoid \ Ant. Pt. of Circ. Sinus v\ , (Ant. Intercav. Sinus^ V ^ Pituitary Body Cavernous Sinus Sixth Nerve '^^V-^ i-'fr^ " Middle Fossa WaVL. w l..>-4l4i-- Basilar Sinus -v,-^--"^^_ ,- , I M Sinus '^'\^ '%."""""-'"^— M Inf. Petrosal ' ' 0 j Sinus ->i- Lateral Sinus Cerebellar Fossa Lateral Sinus Cerebral Fossa Spinal Cord, ■' Torcular Herophili Occipital Sinus Fig. 439, — The Internal Base of the Skull, showing the Cranial Nerves and Venous Sinuses. the tentorium cerebelli. Thereafter it traverses the outer wall of the cavernous sinus. The fifth or trigeminal nerve consists of two roots — sensory and motor. These two roots pierce the dura mater at the apex of the petrous part of the temporal bone, and enter a recess of the dura mater, called Meckel s cave, where they will be presently described. The sixth or abducent nerve pierces the dura mater at the outer border of the dorsum sellse of the sphenoid bone, a little below.the I076 A MANUAL OF ANATOMY posterior clinoid process, where it occupies a notch on the bone. It lies a little to the inner side of the fifth nerve. The seventh or facial nerve, the eighth or auditory nerve, and the pars intermedia of Wrisberg, accompanied by the internal auditory artery, enter the meatus auditorius internus. The ninth or glosso-pharyngeal nerve, the tenth or pneumogastric nerve, and the eleventh or spinal accessory nerve pass through the middle compartment of the jugular foramen. This foramen is divided into three compartments, namely, antero-internal, middle, and postero -external. The antero-internal compartment gives passage to the inferior petrosal sinus. The middle compartment transmits the glosso-pharyngeal, pneumogastric, and spinal acces- sory nerves, in this order from before backwards. The glosso- pharyngeal nerve pierces the dura mater separately, and receives special sheaths from the dura mater and arachnoid membrane. The pneumogastric and spinal accessory nerves pass through the same aperture in the dura mater, and receive common sheaths from the dura and arachnoid membrane. The postero -external com- partment transmits the lateral sinus, which terminates in the internal jugular vein. The twelfth or hypoglossal nerve pierces the dura mater in two bundles, which pass through separate apertures. As these bundles pass through the anterior condylar foramen they unite to form one nerve. Structures passing through the Foramen Magnum. — (i) The medulla oblongata, with its membranes, passes out and becomes the spinal cord. (2) The spinal portion of the spinal accessory nerve, of either side, having ascended from the interval between the posterior roots of the cervical spinal nerves and the ligamentum denticulatum, enters the cranial cavity. It then turns outwards to the middle compartment of the jugular foramen, where it meets • the bulbar portion of the nerve, with which it Ijecomes closely connected as it passes through the foramen. (3) The vertebral artery of each side enters the cranial cavity, after having left the vertebrarterial groove on the upper aspect of the posterior arch of the atlas. (4) The two anterior spinal branches of the vertebral arteries descend on the front of the medulla oblongata, and, inclining inwards towards each other, they unite in passing through the foramen magnum to form the anterior spinal artery. (5) The two posterior spinal branches of the vertebral arteries pass outwards through the foramen magnum. (6) Parts of the cerebellar amygdahc. Gasserian Ganglion. — ^The Gasserian ganglion occupies the Gas- serian depression on the superior surface of the petrous part of the temporal bone near the apex, where it lies in a recess of the dura mater, called Meckel's cave. It is somewhat semilunar, being con- vex in front and conca,ve behind, and measures fully | inch from before backwards. It is associated with the sensory root of the fifth nerve, which, before entering the posterior concave aspect of the ganglion, becomes expanded, its fasciculi at the same THE HEAD AND NECK 1077 time becoming separated and assuming a plexiform arrange- ment. Internally the ganglion is intimately related to the back part of the cavernous sinus and the internal carotid artery at the foramen lacerum medium, and on this aspect it receives delicate filaments from the carotid sympathetic plexus. The motor root of the fifth nerve, small in size, lies in close contact with the deep surface of the ganglion ; but there is no blending of the two sets of fibres, the motor root passing independently in an out\vard direction to the foramen ovale. The great superficial petrosal nerve, on its way to the foramen lacerum medium, passes beneath the ganglion. The ganglion contains cells similar to those of a spinal ganglion, and it receives its blood from the middle and small meningeal arteries. Branches. — ^The branches of the ganglion arise from its anterior convex aspect, and are known as divisions. They are as follows : the first or ophthalmic division ; the second or superior maxillary division ; and the third or inferior maxillary division. The oph- thalmic and superior maxillary nerves are entirely sensory, but the inferior maxillary nerve, being joined by the motor root, is both sensory and motor. The first division of the fifth nerve, or the ophthalmic nerve, is the smallest of the three branches of the ganglion. It passes forwards in the outer wall of the cavernous sinus, where it lies below the fourth ner\'e. On approaching the sphenoidal fissure it parts with its chief branches, in the following order fro.m behind forsvards : (i) nasal, (2) lachrymal, and (3) frontal, the last-named representing the continuation of the nerve. All these three branches enter the orbit through the sphenoidal fissure. As the ophthalmic nerve passes forwards it receives a communicating branch from the cavernous sympathetic plexus, and it furnishes a recurrent men- ingeal branch to the tentorium cerebelli. It also communicates with each of the third, fourth, and sixth nerves. The second division of the fifth, or the superior maxillary nerve, passes horizontally fonvards for a short distance in the lower part of the outer wall of the cavernous sinus, and it leaves the cranial cavity through the foramen rotundum, which leads to the spheno- maxillary fossa. Before leaving the cranial cavity it furnishes a delicate recurrent meningeal branch to the dura mater of the middle fossa. The third division of the fifth, or the inferior maxillary nerve, is the largest of the three branches of the ganglion. It passes down- wards to the foramen ovale, through which it leaves the cranial cavity, and so enters the zygomatic fossa. It is accompanied by the motor root of the fifth nerve, which joins it as it passes through the foramen ovale. The recurrent meningeal branch of the inferior maxillary nerxe is not given off until after the parent trunk has issued through the foramen ovale, and it enters the cranial cavity through the foramen spinosum, in company with the middle meningeal artery. It then divides into t\vo offsets, one of which supplies the dura mater over the great wing of the sphenoid bone, 1078 A MANUAL OF ANATOMY and the other passes through the fissure between petrous and squamous parts of the temporal bone to supply the mucous mem- brane of the mastoid cells. Great Superficial Petrosal Nerve. — This nerve is a branch of the geniculate ganglion of the facial nerve in the aqueduct of Fallopius. It enters the middle fossa of the base of the skull through the hiatus Fallopii, and passes forwards and inwards in a groove on the superior surface of the petrous part of the temporal bone. Having passed beneath the Gasserian ganglion, it enters the upper part of the foramen lacerum medium, where it is placed on the outer side of the internal carotid artery, and it joins the great deep petrosal nerve from the carotid sympathetic plexus. In this manner the Vidian nerve is formed, which enters the pterygoid or Vidian canal by its opening on the g,nterior aspect of the foramen lacerum medium, and so reaches Meckel's ganglion in the spheno-maxillary fossa. The great super- ficial petrosal nerve is accompanied by the petrosal branch of the middle meningeal artery. Small Superficial Petrosal Nerve. — This nerve represents the continuation, through the tympanic plexus, of the tympanic branch (Jacobson's nerve) of the glosso-pharyngeal nerve. It is reinforced by a small branch from the geniculate ganglion of the facial nerve, which joins it as it traverses a small canal in the petrous part of the temporal bone, beneath the canal for the tensor tympani muscle. The nerve enters the middle fossa through the accessory hiatus on the superior surface of the pars petrosa. It then passes for a little forwards and inwards, and leaves the cranial cavity through the canaliculus innominatus (when present), or through the fissure between the pars petrosa and the great wing of the sphenoid, or, it may be, through the foramen ovale, after which it terminates in the otic ganglion. External Superficial Petrosal Nerve. — This nerve, which is inconstant, passes from the sympathetic plexus on the middle meningeal artery back- wards and outwards on the superior surface of the petrous part of the tem- poral bone, and it leaves the cranial cavity through a minute aperture situated within the thin margin of the hiatus Fallopii. It terminates in the geniculate ganglion of the facial nerve. Interior of the Cavernous Sinus. — ^The interior of this sinus is broken up by a number of delicate trabeculse, which are arranged in a reticular manner. The outer wall of the sinus contains the follow- ing cranial nerves, in order from above downwards : the third, the fourth, the ophthalmic division of the fifth, and the superior max- illary division of the fifth. These nerves, as they pass forwards, are separated from the blood-current by the endothelial lining of the outer wall of the sinus. The cavity of the sinus is traversed by (i) the cavernous part of the internal carotid artery, accom- panied by the cavernous sympathetic plexus, and (2) the sixth cranial nerve, which lies in close contact with the outer side of the internal carotid artery. These structures are also separated from the blood-current by the endothelial lining of the sinus. For the processes and other sinuses of the dura mater see Index. Cavernous Part of the Internal Carotid Artery. — ^This part of the internal carotid artery lies within the cavernous sinus, which occupies the cavernous groove on the lateral aspect of the body of the sphenoid bone. It is separated from the blood-current by the endothelial lining of the sinus. The course of the vessel is at first upwards, between the lingula sphenoidalis and the posterior petrosal THE HEAD AND NECK 1079 process of the sphenoid ; then forwards, as far as the anterior clinoid process of the sphenoid ; and, finally, upwards internal to the anterior clinoid process. In the latter situation it pierces the dura mater which forms the roof of the cavernous sinus, and enters upon the cerebral part of its course. The vessel is accompanied by the cavernous sympathetic plexus, and the sixth cranial nerve lies in close contact with its outer side, all being invested by the endothelial lining of the sinus. Branches. — ^These are as follows : pituitary, to the pituitary body ; ganglioyiic to the Gasserian ganglion ; cavernous, to the wall of the cavernous sinus, and to the third, fourth, fifth, and sixth cranial nerves ; meningeal, to the dura mater of the middle cranial fossa ; and the ophthalmic artery. The latter vessel arises from the cavernous part of the internal carotid on the inner side of the anterior clinoid process, and it enters the orbit, with the optic Internal Carotid Artery Sixth Nerve i ; Sella Turcica Third Nerve Fourth Nerve Ophthalmic Nerve Superior Maxillary Nerve Left Sphenoidal .Air-Sinus Fig. 440, — Diagram of the Left Cavernous Venous Sinus and its Outer Wall, showing the Relative Positions of the Contained Struc- tures (Posterior View). nerve, through the optic foramen, lying at first beneath the nerve, and then on its outer side. Cavernous Sympathetic Plexus. — ^This plexus is situated prin- cipally on the inner and lower aspects of the bend which the cavernous part of the internal carotid artery describes internal to the anterior clinoid process. Its branches are as follows : (i) vas- cular, to the internal carotid artery and its branches ; (2) pituitary, to the pituitary body ; (3) communicating, to the third, fourth, ophthalmic division of the fifth, and sixth cranial nerves ; and (4) the sympathetic root of the ciliary ganglion. The last-named branch enters the orbit through the sphenoidal fissure. The pituitary body [hypophysis cerebri) is a small oval mass which is situated in the pituitary fossa, or sella turcica, of the sphenoid bone. It lies under cover of a circular fold of the dura mater, called the diaphragma sellce, in the centre of which is an opening for the passage of the infundibulum. Its long measurement extends transversely, and it consists of two lobes — anterior or buccal, and posterior or cere- bral. The anterior lobe is the larger of the tvvo, and the posterior loSo A MANUAL OF ANATOMY lobe is connected with the anterior part of the tuber cinereum by means of the infundibulum. The infundibulum projects downwards from the anterior part of the tuber cinereurh to the posterior lobe of the pituitary body. Its upper part is hollow, and contains a funnel-shaped diverti- culum of the cavity of the third ventricle. Structure. — The anterior lobe consists of several tubules, lined with epi- thelium, and invested by capillary bloodvessels. The posterior lobe, though developed from the brain, is destitute of nervous elements. It is composed of a reticulum of connective tissue, which contains branched cells. Development. — The anterior lobe is developed from a diverticulum of the buccal or stomatodseal epiblast, which is known as the pouch of Rathke. The diverticulum grows upwards, and, when the cranio-pharyngeal canal of early life becomes closed, the connection of the diverticulum with the buccal epiblast is severed. The diverticulum thereafter becomes converted into tubules, which form the anterior lobe. The posterior lobe of the pituitary body and the infundibulum, which is connected with it, are developed as a diverticulum which grows downwards from that part of the thalamencephalon or diencephalon which forms the floor of the third ventricle. The cavity of the diverticulum remains permanent in the upper part of its infundibular portion, but elsewhere it becomes obliterated. The lower part of the diver- ticulum thereafter becomes converted into a reticulum of connective tissue, with branched cells, which forms the posterior lobe. Side of the Neck. The side of the neck has a quadrilateral outline, the boundaries of which are as follows : superior, one half of the base of the inferior maxilla, and a line prolonged from the angle of that bone over the mastoid process to the inner third of the superior curved line of the occipital bone; inferior, the clavicle, and one half of the upper border of the manubrium sterni ; anterior, the middle line of the neck, that is to say, a line connecting the symphysis of the inferior maxilla with the centre of the upper border of the manubrium sterni ; and posterior, a line connecting the inner third of the superior curved line of the occipital bone with the outer third of the clavicle. Landmarks. — ^The base and angle of the inferior maxilla can easily be felt, and the clavicle, together with the upper border of the manubrium sterni, is conspicuous, A deep depression, called the suprasternal or jugular fossa, is perceptible above the upper border of the manubrium sterni, lying between the sternal heads of origin of the sterno-cleido-mastoid muscles. The outline of the sterno- cleido-mastoid muscle is readily discernible when the head is turned so as to direct the face towards the opposite shoulder. The muscle extends in a diagonal direction from the sterno-clavicular joint to the mastoid process and outer half or two-thirds of the superior curved line of the occipital bone, and it divides the side of the neck into two triangles — anterior and posterior. A small triangular interval may be felt between the sternal and clavicular heads of origin of the sterno-cleido-mastoid, just above the inner end of the clavicle, in which the common carotid artery and internal jugular vein lie deeply. The external THE HEAD AND NECK lo8i jugular vein crosses the stemo-cleido-mastoid muscle in the direc- tion of a line extending from a point just behind the angle of the inferior maxilla to a point above the centre of the cla\'icle, and it is accompanied by the superficial cervical glands. The common carotid artery lies under cover of the anterior border of the stemo- cleido-mastoid muscle, in the direction of a line drawn from the stemo-clavicular joint to a point midway between the angle of the inferior maxilla and the tip of the mastoid process of the temporal bone. The vessel extends along this line as high as the level of the upper border of the thyroid cartilage, and thereafter it is replaced by the external carotid artery. The internal jugular vein is close to the outer side of the common carotid artery, and the pneumo- gastric ner\-e lies deeply between the two vessels. If deep pres- sure is made over the common carotid artery, on a level with the cricoid cartilage of the larynx, the tubercle of the costal process of the sixth cervical vertebra (commonly spoken of as the anterior tubercle of the transverse process) may be felt. It is known as the carotid tubercle of Chassaignac. The commencement of the right innominate vein and the bifurca- tion of the innominate artery' lie behind the upper border of the right stemo-cla\4cular joint ; and the commencement of the left innominate vein and the left common carotid artery lie behind the left stemo-clavicular joint. Near the middle line of the neck the anterior jugular vein descends vertically. The spinal portion of the spinal accessory nerve passes downwards and outwards beneath the anterior border of the stemo-cleido-mastoid to pierce the deep part of that muscle at about the junction of the upper fourth and lower three-fourths. The ner\'e is met with fuUy i inch below the tip of the mastoid process, and in the direction of a line let fall vertically from the mastoid tip. It is very nearly on a level with the body of the hyoid bone. Along the posterior border of the stemo-cleido-mastoid the IjTnphatic glands, known as the glandulae concatenatae, may be felt. Important structures occupy the middle line of the neck, and can be usually distinguished without difficulty. These are as follows, in order from above downwards : (i) the body of the hyoid bone, lying just below the inferior maxilla, and having the great comu projecting backwards and upwards on either side ; (2) the thyro-hyoid membrane ; (3) the th\Toid cartilage, with its prominent angle or isthmus (pomum Adami) in the middle line, leading up to the V-shaped thyroid notch on the upper border, and its expanded ala on either side, each of which terminates posteriorly in a superior and an inferior comu ; (4) the crico-thjToid membrane ; (5) the narrow, anterior part of the cricoid cartilage, which coincides with the level at which the anterior belly of the omo-hyoid muscle crosses the carotid sheath : and (6) the rings of the trachea, which, however, are covered superiorly by the isthmus of the thjToid body, and inferiorly by the stemo-hyoid and stemo-thyroid muscles and adipose tissue. io82 A MANUAL OF ANATOMY The lateral lobes of the thyroid body may be felt on either side of the larynx and trachea as low as about the fifth ring ; and, in young children, the thymus body extends upwards upon the trachea for some distance above the manubrium sterni. The great cornu of the hyoid bone is the guide to the lingual artery for operative purposes, the vessel lying just above the great cornu. The upper border of the thyroid cartilage is on a level with the disc between the bodies of the third and fourth cervical vertebrae. The narrow anterior part of the cricoid cartilage is on a level with the disc between the bodies of the fifth and sixth cervical vertebrae, at which level the pharynx terminates in the oesophagus. In this situation a foreign body, when swallowed, is liable to become impacted. Above the middle third of the clavicle, between the sterno- cleido -mastoid and trapezius muscles, there is a depression known as the supraclavicular fossa, which indicates the position of the sub- clavian or supraclavicular triangle, with the third part of the sub- clavian artery and the trunks of the brachial plexus of nerves. Platysma Myoides — Origin. — ^The superficial fascia which covers the clavicular parts of the pectoralis major and deltoid muscles. Insertion. — (i) The outer aspect of the base of the inferior maxilla from the symphysis to the anterior border of the masseter muscle ; and (2) the angle of the mouth, where the fibres blend with those of the depressor anguli oris and orbicularis oris. Nerve- supply. —The inframandibular (cervical) branch of the cervico-facial division of the facial nerve, which communicates with branches of the superficial cervical nerve. The fibres are directed upwards and forwards or inwards over the clavicle and side of the neck. Action. — (i) To draw the angle of the mouth downwards and out- wards ; (2) to act as a feeble depressor of the inferior maxilla ; (3) to raise the skin of the neck and upper pectoral region, as far out as the acromion process, throwing it into obliquely-disposed folds. By diminishing pressure upon the external jugular vein during forced inspiration the muscle contributes to the return of blood through that vessel. The muscle forms an extensive, thin, pale sheet, which is embedded within the superficial fascia. In the region of the symphysis of the inferior maxilla the innermost fibres decussate across the middle line with those of the opposite side, the fibres of the right muscle being superficial. The muscle covers the external and anterior jugular veins, the superficial branches of the cervical plexus of nerves, the subclavian triangle, and the sterno-cleidc- mastoid, sterno-hyoid, omo-hyoid, and digastric muscles. The platysma myoides in man is a remnant of a subcutaneous muscular sheet, called the panniculus carnosus, which exists in many animals, and by which the twitching of the skin is produced. Jugular Veins. — ^The jugular veins are four in number on eithei" side, namely, anterior, external, posterior, and internal. THE HEAD AND NECK 1083 The anterior jugular vein commences in the roof of the sub- maxillary or digastric triangle, where it is formed bj^ the union of radicles which communicate with the submental vein, and are joined by radicles which have descended from the structures over the body of the inferior maxilla. It descends vertically near the median line, Ijdng at first superficial to the deep cervical fascia, but sub- /jk_ / ^~J^'^^^ \ jj -~^^^^ \ tMk Frontal Vein f ^O ' T( v'^t^^-SfecR Supra-orbital Vein :rior Auricubr Lym- ,C Y/ ij A\ v ■ /;k^/'^ /^^^^^VN Superficial Temporal phatic Glands P^4>k >i \ (;. r^^T^TfnT' '"" OcdpiulVein4^jn^ (^^\^^ Occipital Lymphatic ---T^^^T^ i A^^^^i^^^MM^HliL'' ' •' ' ' l^i ^^^^ GUnd \ PX mW^^IB^R^''' '" ' — 1^7:} -W Temp.-Maxillary Vein :erior Auricular Vein \ t--^----— v?PWH '"'. nt^H^<^ ) _ \ T^X \^V ' »]S?'=^-i^ Facial Vein Posterior Division of . N KA V- VV^JS^ ^y - ^ Temp<^^Maxillary \\^ \ -JF/^'J^^Wi^S^T ^nt. Div. of Temporo- Superficial Cervical -c-r^-'-'-'-T^^'^^^S^ ij I \-^^^^^^^^I~' Submax. Lymph. Gland Lymphatic Glands "'"--^^ i Uf, -^X--/ f \ ^S~~~~~^~f^ ~i - - ~ Common Facial Vein ~"">-»^ / VVA^I 1 , \^"^r-~^7~ "---""" Internal Jugular Vein / W -^ ""^^ L^^CM^ J 7^" -- ~~~ Lingual Vein rtemal Jugular Vem mrrrySfr/S^^ ^"^^--Middle Thyroid Vein Transv^C«vical..._ /|/ll^Ll^;^ "^C V I ....V'-V-V.-- Anterior Jugular Vein >4; i'' ! \\ \a7/' ' A C^r "X^- Suprasternal Lynr yr-I'lii) 1 ^\\\\!:^,::0y^ ■■ -^ ^\ phaticGland Suprascapular Vein and Supraclavicular Lymphatic Glands Fig. 441. — The Superficial Veins and Superficial Lymphatic Glands OF THE Right Side of the Head and Neck. (The Platysma Myoides Muscle has been removed) . sequently entering the suprasternal interfascial space, or space of Bums. It then describes a bend, and, passing out%vards behind the stemo-cleido-mastoid muscle, and in front of the scalenus anticus, it opens into the lower part of the external jugular vein. It may, however, open into the subclavian vein. It communicates with the external jugular vein by one or more branches, and it usually receives a branch from the facial vein which descends along the anterior io84 A MANUAL OF ANATOMY border of the sterno-cleido-mastoid and joins it towards the lower part of the neck. Further, it communicates with its fellow of the opposite side by a transverse branch which crosses in front of the trachea, and lies in Burns's space. The anterior jugular veins are usually asymmetrical, one or other being of small size. Occasionally there is only one vein, which is mesially placed, and, under these circumstances, it divides into two vessels interiorly. The anterior jugular vein is destitute of valves. The external jugular vein commences close behind the angle of the inferior maxilla in the substance of the parotid gland, where it is formed by the union between the posterior division of the temporo- maxillary vein and the posterior auricular vein. Having emerged from the parotid gland it descends almost vertically to a point above the centre of the clavicle. In its course the vessel crosses the sterno- cleido-mastoid muscle, lying superficial to its sheath, and beneath the superficial fascia containing the fibres of the platysma myoides. At this level the main part of the superficial cervical nerve courses forwards beneath the vein, and offsets of the nerve pass over it. Having crossed the sterno-cleido-mastoid muscle, the vein descends not far from its posterior border, where it lies in the roof of the sub- clavian or supraclavicular triangle, over the third part of the sub- clavian artery. Up to this point the vessel is superficial to the deep cervical fascia, but it now pierces that fascia and opens into the subclavian vein. The course of the external jugular vein is indicated by a line drawn from a point close behind the angle of the inferior maxilla to a point above the centre of the clavicle. Its tributaries are as follows : (i) posterior jugular, which joins it about the middle of the neck ; (2) transverse cervical ; (3) suprascapular ; and (4) anterior jugular, the latter three joining it not far from its termination. It also communicates with the anterior jugular vein by one or more branches. The vessel is provided with valves, both at its termina- tion and about ij inches above this point, and the transverse cervical and suprascapular veins are also furnished with valves, where they open into the external jugular vein, or near their orifices. The external jugular vein is sometimes very small, or even absent ; and it may communicate with the cephalic vein by a vessel which passes over the clavicle. Development. — The external jugular vein is usually regarded as being developed from the primitive jugular vein; but according to some authorities the primitive jugular vein gives rise to the internal jugular vein, the external jugular being of later development. . The posterior jugular vein represents the most external occipital vein, and is formed by tributaries which issue from the outer part of the occipital plexus, reinforced by veins from the superficial structures at the back of the neck. Having usually received the mastoid emissary vein, it passes downwards and forwards, and joins the external jugular vein about the middle of the neck. THE HEAD AND NECK 1085 The internal jugular vein will be found described on p. 1113. Superficial Cervical Glands. — ^These are about six in number, and they lie upon the stemo-cleido-mastoid muscle, along the course of the external jugular vein, and beneath the superficial fascia and platysma myoides muscle. They receive their afferent lymphatics from the adjacent superficial structures, the occipital and mastoid glands, and some of those of the parotid and submaxillary lym- phatic glands. Their efferent lymphatics pass to the deep cervical and supraclavicular glands. Deep Cervical Fascia. — The deep cerA-ical fascia is divided into (i) a superficial layer, which completely invests the neck in the form of a collar, and (2) deep processes or laminae, which invest the muscles, viscera, and chief bloodvessels and nerves. Superficial Layer. — ^This layer is attached posteriorly to the liga- mentum nuchas ; superiorly to (i) the superior curved line of the occipital bone ; (2) the mastoid process of the temporal bone ; (3) the zygomatic arch : and (4) the base of the inferior maxilla, under cover of the platysma myoides, as far forwards as the sym- physis ; and interiorly to the clavicle and upper border of the manubrium sterni, being pierced above the centre of the clavicle by the external jugular vein. Along the middle line of the neck anteriorly it is continuous with the superficial layer of the opposite side. The superficial layer invests the cervical portion of the trapezius, and from the anterior border of that muscle it passes forwards over the posterior triangle of the neck to the posterior border of the stemo-cleido-mastoid. In doing so it furnishes a deep process, which ensheathes the posterior belly of the omo-hyoid muscle. This process also embraces the intervening tendon of that muscle, after which it passes downwards and inwards to be attached to the back of the inner end of the clavicle and the first rib. In this manner the horizontal position of the posterior belly of the omo- hyoid is accounted for. When the superficial layer of the deep cervical fascia reaches the posterior border of the stemo-cleido- mastoid it splits into two laminae which ensheathe that muscle, the superficial lamina being underneath the external jugular vein and platysma myoides. At the anterior border of the stemo-cleido- mastoid the two laminae reunite, and the fascia passes forwards over the anterior triangle of the neck to the median line, where it is continuous with the corresponding layer of the opposite side. Between the upper part of the anterior border of the stemo- cleido-mastoid and the angle of the inferior maxilla the super- ficial layer is of considerable strength, and draws that border of the muscle forwards and upwards, so as to render it convex and keep it over the line of the leading vessels. Between the mastoid process and the angle of the inferior maxilla the superficial layer is prolonged upwards over the parotid gland as the parotid fascia, which is very dense, and is attached superiorly to the lower border ^i>i the zygomatic arch. I08G A MANUAL OF ANATOMY Below the level of the thyroid body the superficial layer divides into two laminae, anterior and posterior, both of which are super- ficial to the depressor muscles of the hyoid bone. At the middle line these laminae are continuous with those of the opposite side, and inferiorly they are attached to the anterior and posterior margins of the upper border of the manubrium sterni. Between them there is an interfascial interval, called the suprasternal space, or space of Burns. This interval contains areolar tissue, one or more lymphatic glands, the lo\\:er portions of the anterior Superficial Lamina of Fascia Anterior Belly of Omo-hyoid \ Pretracheal Lamina of Fascia Prevertebral Lamina of Fascia Carotid Lamina of Fascia Scalenus Anticus Burns's Space Sterno-thyroid ' ^ i_ Sterno-hyoid ' Trachea Scalenus Medius Anguli Scapulae Muscular Compartment ,- Lateral Lobe of Thyroid Body , CT^sophagus Descendens Cervicis Nerve ^'JZommon Carotid Artery "'" Internal Jugular Vein - Pneumogastric Nerve ^-Platysma Myoides ;iri Sympathetic Nerve -Longus Colli .Sterno-cleido-mastoid External Jugular Ve •Vertebral Vessels Complexus Splenius Trapezius Semispinalis Fig. 442. — Diagram of a Transverse Section of the Neck at the Level of the Sixth Cervical Vertebra, showing the Arrange- ment OF THE Deep Cervical Fascia, and the Positions of Other Structures. jugular veins, with the transverse vessel which here connects them, and the sternal heads of the sterno-cleido-mastoid muscles. Deep Processes or Laminse. — The deep laminae, as stated, invest the muscles, viscera, and chief bloodvessels and nerves. The most important are derived from that lamina of the superficial layer which forms the posterior wall of the sheath of the sterno- cleido-mastoid muscle, and they "are three in number, namely, carotid, pretracheal, and prevertebral, all of which have an intimate initial connection. The carotid lamina splits to form the carotid sheath, which con- tains, in separate compartments (i) the common carotid artery and descendens cervicis nerve, (2) the internal jugular vein, and (3) the THE HEAD AND NECK 1087 pneumogastric nerve, the latter being contained within the back part of the septum, which separates the artery from the vein. The pretracheal or visceral lamina, which is at first intimately connected with the anterior wall of the carotid sheath, passes for- wards behind the depressor muscles of the hyoid bone, in which situa- tion it splits to ensheathe 1 he thyroid body, trachea, and oesophagus, and then it passes to the median line, where it is continuous with the pretracheal lamina of the opposite side. The pretracheal lamina is attached superiorly to the body of the hyoid bone, and inferiorly it descends over the trachea and bloodvessels into the superior mediastinum of the thorax, where it blends with the fibrous layer of the pericardium. The prevertebral lamina, which is at first intimately connected with the posterior wall of the carotid sheath, passes forwards behind the pharynx and oesophagus, and in front of the prevertebral muscles. It is known as the prevertebral fascia. At the middle line it is continuous with the corresponding lamina of the opposite side ; superiorly it is attached to the base of the skull ; and inferiorly it descends over the longus colli muscle into the posterior medi- astinum of the thorax. Along a line corresponding to the inner wall of the carotid sheath the pretracheal lamina furnishes a secondary lamina, called the bucco-pharyngeal fascia, which covers the constrictor muscles of the pharynx and the buccinator muscle. Between the bucco-pharyngeal and prevertebral fasciae there is an interval, called the retro-pharyngeal space, which contains the loosely arranged connective tissue uniting the two fasciae. This space extends as high as the base of the skull, and inferiorly is con- tinuous with the posterior mediastinum of the thorax. Another process of the prevertebral fascia passes downwards and outwards in front of the scalenus anticus muscle. Thereafter it invests the third part of the subclavian artery and subclavian vein, together with the nerve-trunks of the brachial plexus, and, passing behind the clavicle, it becomes continuous with the axillary sheath, which latter blends with the posterior aspect of the costo-coracoid mem- brane. In the region of the subclavian triangle there is an inter- fascial space between this process of the pretracheal fascia and the superficial layer of the deep cervical fascia. This space extends downwards behind the clavicle to the point where the axillary sheath and costo-coracoid membrane join. It contains the pos- terior belly of the omo-hyoid muscle, the suprascapular and trans- verse cervical vessels, the lower part of the external jugular vein, and the terminal portion of the anterior jugular vein. Interfascial Compartments. — It has been stated that the deep cervical fascia reaches the median line of the neck anteriorly in three layers, namely, anterior or superficial in (two divisions), pre- tracheal, and prevertebral. It is therefore evident that there are four interfascial compartments, as follows : (i) the suprasternal space, or space of Burns, which is situated between the two divisions of the anterior or superficial layer, and contains the structures io88 A MANUAL OF ANATOMY already enumerated ; (2) the muscular compartment, which is situ- ated between the anterior or superficial layer and the pretracheal layer, and contains the depressor muscles of the hyoid bone ; (3) the visceral compartment, which lies between the pretracheal and pre- vertebral layers, and contains the larynx, trachea, thyroid body, pharynx, oesophagus, and carotid sheath, the retro -pharyngeal space being in the subdivision of this compartment behind the bucco-pharyngeal fascia ; and (4) the vertebral compartment, which lies between the prevertebral layer and the attachment of the fascia to the ligamentum nuchae posteriorly, and contains the vertebral column, spinal cord, and prevertebral and postvertebral muscles. The suprasternal and muscular compartments are shut off from the thoracic cavity. The visceral compartment, in front of the trachea, is continuous with the superior mediastinum of the thorax, and behind the oesophagus it, along with the retro-pharyngeal space, is continuous with the posterior mediastinum. Parotid Process of the Deep Cervical Fascia. — ^This process is given off a little below the angle of the inferior maxilla, and it passes upwards on the deep surface of the parotid gland to the skull. Along with the parotid fascia superficial to the gland it forms a dense sheath which closely invests the glandular substance. The parotid process furnishes sheaths to the posterior belly qf the digastric, styloid, and pterygoid muscles, and it also gives an investment to the superficial part of the submaxillary gland. Con- nected with the parotid process there are several bands, usually called ligaments, which are as follows : (i) spheno- mandibular ; (2) stylo -mandibular ; (3) pterygo-mandibular ; and (4) pterygo- spinous. The spheno-mandibular ligament will be described in connection with the temporo-mandibular joint, of which it ranks as the internal lateral ligament. The stylo-mandibular ligament extends from the styloid process of the temporal bone, near its tip, to the angle and adjacent part of the posterior border of the ramus of the inferior maxilla, where it is placed between the masseter and internal pterygoid muscles. The pterygo-mandibular ligament is a narrow band which extends from the hamular process of the internal pterygoid plate of the sphenoid bone to the posterior extremity of the mylo-hyoid ridge of the inferior maxilla, close to the last molar alveolus. Anteriorly it gives origin to fibres of the buccinator muscle, and posteriorly to fibres of the superior constrictor muscle of the pharynx. The pterygo-spinous ligament is a narrow band which extends from a sharp spine on the posterior border of the external pterygoid plate of the sphenoid bone, towards its upper part, to the spinous process of the sphenoid. This ligament is liable to become ossified. Sterno-cleido-mastoid — Origin. — ^The sternal head, which is narrow and round, arises from the upper and outer part of the anterior surface of the manubrium sterni. It is tendinous in front, THE HEAD AND NECK 1089 and fleshy behind. The clavicular head, which is broad and flal, arises from a rough ridge about ij inches long on the upper surface of the clavicle at its inner end, near the postero-superior border. Insertion. — (i) The outer surface of the mastoid process of the temporal bone, and (2) the superior cur\ed line of the occipital bone over about its outer half or two-thirds. Nerve-supply. — (i) The spinal portion of the spinal accessory ner\-e, and (2) a branch from the cervical plexus, more particularly from the anterior primary division of the second cervical nerve. The spinal portion of the spinal accessory nerve passes beneath the anterior border of the muscle fully i inch below the tip of the mastoid process, and, in passing downwards and backwards, it pierces the deep part of the muscle, gi\Tng off, as it does so, its branches to it. The muscle is directed upwards, outAvards, and backwards. Action. — (i) To flex the head towards the side on which the muscle is placed, the face being turned towards the opposite side. This is the position of the head in torticollis or ury-neck, a con- dition which may be due to an organic contraction of the muscle, affecting both heads, or, it ma\^ be, the sternal head alone. (2) WTien both muscles act together from their origin they flex the head towards the thorax. (3) When both muscles act together from their insertion they elevate the upper part of the anterior thoracic wall in forced inspiration. The sternal and clavicular heads are separated by a triangular cellular interv-al for a short distance above the stemo-clavicular joint, and before their junction the fibres of the clavicular head to a large extent pass behind those of the sternal head, so that over- lapping takes place. The muscle is surrounded by a strong sheath, which is formed by the deep cer\-ical fascia. The platysma myoides covers a large part of it, and the external jugular vein, the super- ficial cervical and great auricular ner\'es, and the superficial cervacal glands are related to its superficial surface, under cover of the platysma mj-oides. The principal deep relations are as follows : in the lower part of the neck it covers the first and second parts of the subclavian artery, the stemo-hyoid, stemo-thyroid, omo- hyoid, and scalenus anticus muscles, with the phrenic nerve l>dng upon the last-named muscle. In this situation it also covers the anterior jugular vein, and the transverse cervical and suprascapular arteries. Higher up it covers the cervical plexus of ner\-es, the levator anguli scapulae, scalenus medius, and scalenus posticus muscles, and the spinal portion of the spinal accessory and the hypo- glossal nerves. At its insertion it covers the splenius capitis, trachelo-mastoid, and posterior belly of the digastric muscles, and a portion of the occipital artery, in this order from the surface downwards. The anterior border of the muscle forms the posterior boundary of the anterior triangle of the neck, and covers the carotid sheath, with its contents, as high as the level of the upper border of the thyroid cartilage ; and abo\e that level it covers the togd A MANUAL OF ANATOMY external and internal carotid arteries. This border also overlaps slightly the lateral lobe of the thyroid body. The posterior border forms the anterior boundary of the posterior triangle of the neck, and along it there lie the following structures : the glandulse con- catenate, the small occipital nerve, great auricular^ superficial cervical, spinal portion of the spinal accessory, and the descend- ing superficial branches of the cervical plexus of nerves, and a por- tion of the external jugular vein. Stensen's Duct Buccinator Muscle ^ Facial Artery Submental Artery Lingual Artery-^ Sup. Lar. Art. and Nerve Thyro-hyoid Muscle -- Superior Thyroid Artery Post. Belly of Onio-hyoid _ Subclavian Artery. «. (third part) Transverse Facial Artery Superficial Tem- poral Artery Internal Maxillary Artery / Posterior Auricular Artery '1/—^-. Occipital Artery II. Stylo-hyoid Muscle ' Post. Belly of Digastric Hypoglossal Nerve -- Descendens Cervicis Nerve External Carotid Artery Sterno-cleido-mastoid ^Trapezius ...Transverse Cervi- cal Artery Suprascapular Artery Fig. 443.— The Left Side of the Head and Neck. (The Platysma Myoides has been removed). The sterno-cleido-mastoid muscle, from its diagonal position upon the side of the neck, divides the quadrilateral space into two triangles— posterior and anterior. Posterior Triangle.— This is the region which lies behind the sterno-cleido-mastoid muscle. Boundaries — Anterior. — ^The posterior border of the sterno- cleido-mastoid. Posterior. — ^The anterior border of the trapezius. Inferior (base).— The middle third of the clavicle. The apex is at THE HEAD AND NECK 1091 the superior curved line of the occipital bone, where the stemo- cleido-mastoid and trapezius may meet, but the apex is usually truncated. The roof is formed by the skin, superficial and deep fasciae, and, for a short distance inferiorh^ by the platysma myoides. The small occipital nerve lies in the upper part of the roof, and the descending superficial branches of the cervical plexus and the external jugular vein lie in the lower part of the roof. The floor is formed by the following muscles, in order from above down- wards : (i) a small angle of the complexus, provided the trapezius is not well developed at the occiput ; (2) the splenius capitis ; {3) the levator anguli scapulae ; (4) the scalenus medius and scalenus posticus ; (5) the posterior belly of the omo-hyoid ; and (6) the scalenus anticus. The posterior triangle is subdivided by the posterior belly of the omo-hyoid into a large upper portion, called the occipital triangle, and a small lower portion, called the subclavian or supraclavicular triangle. Occipital Triangle — Boundaries — Anterior. — ^The posterior border of the sterno-cleido-mastoid. Posterior. —The anterior border of the trapezius. Inferior (base). — ^The posterior belly of the omo- hyoid. The muscles in its floor are (i) a small angle of the com- plexus (inconstant), (2) splenius capitis, (3) levator anguli scapulae, and (4) scaleni medius et posticus. The contents are the super- ficial branches of the cervical plexus, the spinal accessory nerve, the branches of the cervical plexus to the levator anguli scapulae and trapezius, a small part of the occipital artery close to the apex, and the glandulae concatenatae. Cervical Plexus. — ^The cervical plexus is situated under cover of the upper part of the sterno-cleido-mastoid muscle, and lies immediately in front of the slips of origin of the scalenus medius. It is formed by the anterior primary divisions of the first three cervical nerves and the greater part of that of the fourth, a small branch of the latter descending to join the anterior primary division of the fifth, and so taking part in the brachial plexus. Each of the anterior primary divisions of the first four cervical nerves is connected with the superior cervical ganglion of the sympathetic by a grey ramus communicans. The anterior primary division of the first cervical nerve lies at first in the vertebrarterial groove of the atlas under cover of the verte- bral artery. It then passes forwards in a groove on the outer surface of the superior articular process of the atlas, having the vertebral artery on its outer side. It next emerges between the rectus capitis lateralis muscle (to which it gives a branch) and the rectus capitis anticus minor, and descends in front of the root of the costal process of the atlas to join the ascending branch of the second nerve. From the loop so formed branches are given to the recti antici muscles, major and minor, and one or more branches pass to the hypoglossal nerve, the destination of their fibres being the descendens cervicis and thjiro-hyoid ner\^es. I092 A Manual of anatomy The anterior primary divisions of the second, third, and fourth cervical nerves, having emerged between the corresponding inter- transversales muscles, divide each into an ascending and a descend- ing branch, which unite with adjacent branches to form loops. The descending branch of the fourth nerve, as stated, joins the fifth, and enters into the brachial plexus. The cervical plexus is therefore a looped plexus, the number of loops being three. PHRENIC Fig. 444. — Scheme of the Cervical Plexus of Nerves. The Descendens Cervicis Nerve is also shown. ic, 2C, 3c, \ Anterior Primary Divisions of 4c, 5c. ; Upper Five Cervical Nerves " R.L. To Rectus Lateralis G.A. Great Auricular S.O. Small Occipital S.C.M. To Sterno-cleido-mastoid Sup.C. Superficial Cervical S.M., S.M. To Scalenus Medius las' \'^° Levator Anguli Scapulje Tk.,'Tr. To Trapezius S.A. SupVa-acromial S.C. Supraclavicular S.S. Suprasternal Sv. Branches to Sympathetic R.A. To Rectus Capitis Anticus Major et Minor H. To Hypoglossal Pn. To Pneumogastric (Ganglion of Trunk) C.C., C.C. Communicantes Cervicis DC. Descendens Cervicis A.B.O.H. To Anterior Belly of Omo-hyoid A. C. Ansa Cervicis S.H. To Sternohyoid S.T. To Sterno-thyroid P.B.O.H. To Posterior Belly of Omo-hyoid Branches. — ^These are divided into two groups— superficial and deep. Superficial Group. — ^The nerves of this group are ascending, transverse, and descending. The ascending and transverse nerves arise from the second and third cervical nerves. The ascending nerves are the small occipital and great auricular (sec p. 1059). The transverse nerve is the superficial (transverse) cervical. THE HEAD AND NECK 1093 The superficial or transverse cervical nerve arises by two roots from the anterior primary divisions of the second and third cervical nerves, and, turning round the posterior border of the sterno- cleido-mastoid muscle, it passes forwards over the muscle, lying beneath the platysma myoides and the external jugular vein. Having reached the anterior triangle of the neck, it divides into two branches, upper and lower, which are distributed to the integu- ment over the anterior triangle. The offsets of the upper branch communicate freely with the inframandibular branch of the facial nerv^e beneath the platysma myoides. The descending nerves are the suprasternal, supraclavicular, and supra-acromial, and they arise in common from the third and fourth cervical nerves. As they descend they form distinct nerves, which lie in the roof of the subclavian triangle under cover of the platysma myoides. For their distribution, see p. 298. Deep Group. — ^The nerves of this group are arranged in two sets — external and internal. External Set. — ^The nerves of this set are muscular, (i) The second nerve furnishes a branch to the stemo-cleido-mastoid, which communicates in that muscle with the branch of the spinal portion of the spinal accessory nerve. (2) The third and fourth nerves furnish {a) two branches to the trapezius, which communicate in a plexiform manner with the spinal portion of the spinal accessory nerve beneath the upper part of the muscle ; (b) two branches to the levator anguli scapulae ; and (c) branches to the scalenus medius. Internal Set. — ^The nerves of this set are communicating and muscular. The communicating branches are as follows : (i) connecting branches (grey rami communicantes) pass from the upper cervical ganglion of the sympathetic ; (2) communicating branches pass to the pneumogastric and hypoglossal nerves from the highest loop of the plexus ; and (3) two rami communicantes cervicis pass from the second and third nerves forwards and downwards, usually over, but sometimes underneath, the internal jugular vein, and ter- minate by joining the descendens cerv'icis, conjointly or separately, thus forming the ansa cervicis (ansa hypoglossi). The muscular branches are distributed to the rectus capitis lateralis, recti antici, major and minor, upper part of the scalenus anticus, longus colli, and the diaphragm. The ner\'e to the dia- phragm is the phrenic nerve (internal respiratory ner^'e), and, from its importance, it requires a special description. The phrenic nerve arises, as a rule, by two roots, the larger .of which is derived from the anterior primary division of the fourth cervical nerve, and the other from that of the third. In some cases the fifth cervical nerv^e, which enters into the brachial plexus, furnishes an additional small root. In the neck the nerve descends upon the scalenus anticus muscle, which it crosses obliquely downwards and inwards, passing beneath the tendon of the omo-hyoid muscle, the transverse cerv^ical and supra- I094 A MANUAL OF ANATOMY scapular arteries, and the anterior jugular vein. At the root of the neck the nerve/ having left the scalenus anticus, passes behind the terminal part of the subclavian vein, and crosses over the internal mammary artery from without inwards. Having come into con- tact with the inner surface of the dome of the pleura, it disappears behind the inner end of the clavicle, and enters upon the thoracic part of its course (see p, 942). The right nerve at the root of the neck is superficial to the second part of the right subclavian artery, with the intervention of the scalenus anticus muscle. The left nerve at the root of the neck is anterior and parallel to the first part of the left subclavian artery, and lies behind the terminal part of the thoracic duct. The phrenic nerve is sometimes reinforced towards the root of the neck by a branch from the nerve to the subclavius muscle, and, when this takes place, the root from the fifth cervical nerve is usually absent. Before leaving the neck the phrenic nerve receives a twig from the middle, or lower, cervical ganglion of the sympathetic. No branches arise from the phrenic nerve in the neck. Supraclavicular Group of Deep Cervical Glands. — These glands lie in the anterior part of the supraclavicular triangle, and are related superficially to the clavicular nerve, and deeply to the upper and middle trunks of the brachial plexus. Superiorly they are con- tinuous with the external chain of the substerno-mastoid glands. They receive their afferent vessels from the following sources : 1. The back of the neck. 2. The external group of axillary glands. 3. The upper part of the pectoral region. 4. Occasionally the lymphatics along the cephalic vein, which may ascend over the clavicle. Their efferent vessels unite, on either side, with those of the internal chain of substerno-mastoid glands (superior and inferior groups) to form the common jugular lymphatic trunk. Subclavian or Supraclavicular Triangle. — ^The subclavian triangle is the lower division of the posterior triangle of the neck, and is separated from the upper division, or occipital triangle, by the posterior belly of the omo-hyoid muscle. It is situated above the middle third of the clavicle, and is of small size until the deep cer- vical fascia, which ensheathes the posterior belly of the omo-hyoid, has been divided. Boundaries — Superior.— ^he posterior belly of the omo-hyoid muscle. Inferior. — The middle third of the clavicle. Anterior. — The clavicular part of the sterno-cleido-mastoid muscle. Roof. — The skin ; superficial fascia and platysma myoides muscle ; supra- sternal, supraclavicular, and supra-acromial nerves ; a part of the external jugular vein ; and the deep cervical fascia. Floor. — ^The scalenus medius and scalenus posticus muscles. The extent of the triangle is affected by (i) the height to which the posterior belly of the omo-hyoid ascends above the clavicle, and (2) the extent of the clavicular attachments of the sterno-cleido- mastoid and trapezius muscles. The depth of the triangle is in- . THE HEAD AND NECK 1093 fluenced by the position of the shoulder, being greater when the shoulder is raised and carried forwards, and less when it is depressed and carried backwards. Contents. — The contents are as follows: (i) the greater portion of the third part of the subclavian artery ; (2) small portions of the transverse cervical artery and vein ; (3) the lower portion of the external jugular vein ; (4) the nerve-trunks of the brachial plexus ; and (5) the nerve to the subclavius muscle, and the supra- scapular and posterior thoracic nerves. Third Part of the Subclavian Artery. — ^This part of the vessel extends from the outer border of the scalenus anticus muscle to the outer border of the first rib, where it becomes the axillary artery. Its course is downwards and outwards, and, for the greater part ot its extent, it lies in the subclavian triangle. Subsequently, however, it passes under cover of the clavicle and subclavius muscle. Brachial Plexus Cephalic Vein \ Musculo-cutaneous Nerve Deltoid ^ Trapezius ' Suprascapular Vessels I \ Transverse Cervical Artery Posterior Belly of Omo-hyoid Scalenus Anticus Stemo J^-r-^-:^- Occipital Artery '-^^^^4 Descendens Cervids JPlWT ^ ^'erve ~ ""■ — J External Carotid Artery Stemo^leido-mastoid ~. Trapezius .Transverse Cervi- cal Artery . Supra.<;capular Artery Fig. 447, — ^The Left Side of the Head and Neck. (The Platysma Myoides has been removed). transverse cervical nerve, and the inframandibular branch of the facial nerve. The anterior triangle is divided into three triangles by the anterior belly of the omo-hyoid muscle inferiorly, and the two bellies of the digastric muscle superiorly. The subdivisions from below upwards are called muscular, carotid, and digastric or submaxillary. The muscular triangle (inferior carotid) is bounded anteriorly by the middle line of the neck ; posteriorly by the anterior border of the stemo-cleido-mastoid ; and superiorly by the anterior belly of the omo-hyoid. "oo A MANUAL OF ANATOMY The carotid triangle (superior carotid) is bounded inferiorly by the anterior belly of the omo-hyoid ; superiorly by the posterior belly of the digastric and stylo-hyoid ; and posteriorly by the anterior border of the sterno-cleido-mastoid. The digastric or submaxillary triangle is bounded postero-inferiorly by the posterior belly of the digastric and stylo-hyoid ; antero- inferiorly by the anterior belly of the digastric ; and superiorly by one half of the base of the inferior maxilla, and a line drawn from the angle of that bone to the mastoid process. Contents of the Triangles — Muscular Triangle. — ^The area of this triangle is occupied by the sterno-hyoid and sterno-thyroid muscles ; hence the name muscular triangle. Under cover of these muscles there are the carotid sheath with its contents, the lateral lobe of the thyroid body, the trachea, and the larynx. The oesophagus lies behind the trachea, with a slight inclination towards the left side at the root of the neck, and the inferior or recurrent laryngeal nerve lies in the groove between the trachea and the oesophagus. The inferior thyroid artery pursues a tortuous course inwards behind the lower part of the carotid sheath, and the gangliated cord of the sympathetic descends behind the sheath. Carotid Triangle. — ^This triangle contains the upper part of the common carotid, and the commencements of the external and internal carotid, arteries, all of these being overlapped by the anterior border of the sterno-cleido-mastoid, when the deep fascia which ensheathes that muscle is undisturbed. The common carotid and internal carotid arteries, together with the pneumo- gastric nerve, are contained within the carotid sheath, and the descendens cervicis nerve lies upon the sheath, or within it, being situated in either case over the common carotid artery. The sterno-cleido-mastoid artery and the superior thyroid vein cross the sheath near the bifurcation of the common carotid artery, and the carotid body lies behind the vessel about the same level. The deep cervical glands lie along the course of the internal jugular vein. The origins of the superior thyroid, lingual, facial, and occipital arteries are contained in this triangle, and the ascending pharyngeal branch of the external carotid lies deeply between that vessel and the internal carotid. The internal jugular vein in this triangle receives the common facial, lingual, and superior thyroid veins. The hypoglossal nerve lies along the lower border of the posterior belly of the digastric muscle, and it here gives off, from behind forwards, the descendens cervicis and thyro-hyoid nerves, the former passing downwards over, or within, the carotid sheath, and the latter passing forwards and downwards at an acute angle with the parent trunk. The internal branch of the superior laryngeal nerve lies deeply behind the bloodvessels, and the ex- ternal laryngeal branch of that nerve descends internal to them, and passes beneath the depressor muscles of the hyoid bone. The pneumogastric nerve is within the carotid sheath, and the gangli- ated cord of the sympathetic is behind it. The spinal portion of the spinal accessory nerve lies deeply, its course being downwards THE HEAD AND NECK i loi and backwards beneath the stemo-cleido-raastoid, the deep portion of which it pierces. Digastric or Submaxillary Triangle. — ^This triangle is divided into two parts, anterior and posterior, by the stylo-mandibular liga- ment. The anterior part contains the superficial part of the sub- maxillary gland, the facial vein being superficial to it, and the facial artery being embedded in its upper and back part. In this triangle the facial artery gives off its inferior or ascending palatine, tonsillar, glandular, and submental branches. The muscles in the floor of the anterior part of the triangle are the mylo-hyoid, and a part of the hyo-glossus. The superficial part of the sub- maxillary gland rests upon the mylo-hyoid muscle, and conceals the mylo-hyoid nerve and submental artery, which are in direct contact with the muscle. The hypoglossal nerve lies upon that part of the hyo-glossus muscle which appears in the anterior part of the triangle, but it soon disappears beneath the posterior free border of the mylo-hyoid muscle, in company with the deep part of the submaxillary gland and the lingual nerve. The posterior part of the digastric triangle contains a portion of the parotid gland, and under cover of this part is the external carotid artery, which here furnishes its posterior auricular branch. The anterior jugular vein and the superficial or transverse cer- vical neri'e have been already described (see pp. 1083 and 1093). The inframandibular branch of the facial nerve will be found described on p. 1175. Submaxillary Lymphatic Glands. — These glands lie upon the super- ficial surface of the submaxillary salivary gland, under cover of the deep cervical fascia. They form a chain beneath the corresponding half of the base of the mandible, which extends from near the angle of the bone to near the origin of the anterior belly of the digastric muscle. The central gland of the chain is closely related to the facicd artery as that vessel is about to ascend over the base of the mandible. They receive their afferent vessels from the following sources ; 1. The side of the nose. 7. The subjacent portion of the 2. A few from the lower eyelid. floor of the mouth. 3. The lower part of the cheek. 8. Half of the upper gum. 4. Half of the upper lip. 9. The lateral part of the lower 5. The lateral part of the lower gum. lip. 10. The superficial facial glands. 6. The anterior third of the lat- 11. The submaxillary and sub- eral border of the tongue. Ungual saUvary glands. Their efferent vessels pass to those glands of the internal group of the substemo-mastoid glands which are on a level with the upper border of the th3Toid cartilage of the larynx. The suprahyoid or submental glands are situated beneath the chin in the submental triangle, and are two or three in nvunber. They receive their afferent lymphatics from the tip of the tongue, the front of the floor of the mouth, and the inner part of the lower II02 A MANUAL OF ANATOMY lip; and their efferent lymphatics pass to the submaxillary lym- phatic glands. The prelaryngeal glands, when present, are situated in front of the crico-thyroid membrane, and are one or two in number. They receive their afferent lymphatics from the interior of the larynx, below the rima glottidis, and from the adjacent part of the thyroid body. Their efferent lymphatics pass to the inferior group of deep cervical glands. The pretracheal glands lie in front of the cervical portion of the trachea, from which, as well as from the adjacent part of the thyroid body, they receive their afferent lymphatics. Their efferent lymphatics pass to the inferior group of deep cervical glands. Occasionally a few lymphatic glands are met with along the course of the anterior jugular vein. Deep Cervical Glands. — ^These glands lie beneath the sterno- cleido-mastoid muscle, and are about twenty-five in number. They are arranged in two groups, superior and inferior. The superior group lie along the internal jugular vein above the level of the upper border of the thyroid cartilage. They receive their afferent lymphatics from the cranial cavity, the internal maxillary glands, some of the parotid and submaxillary lymphatic glands, the root of the tongue, the upper part of the thyroid body, the larynx, and the lower part of the pharynx. Their efferent lymphatics pass to the glands of the inferior group. The inferior group lie along the lower part of the internal jugular vein, and extend outwards and backwards beneath the sterno- cleido-mastoid, as far as its posterior border, where they give rise to a chain known as the glandules concatenatce. The glands of this chain are continuous interiorly with the supraclavicular glands, and, through these,, with the external axillary glands. They receive their afferent lymphatics from the superior group of deep cervical glands, the upper superficial cervical glands, the lower part of the thyroid body, and the cervical portions of the trachea and oesophagus. Their efferent lymphatics unite to form a single vessel, called the jugular lymphatic trunk, which opens on the left side into the thoracic duct, and on the right side into the right lymphatic duct. Infrahyoid Muscles. — ^These are four in number, on either side, as follows : the omo-hyoid, sterno-hyoid, sterno-thyroid, and thyro- hyoid. Omo-hyoid. — This muscle consists of two bellies, anterior and posterior, and an intervening tendon. Origin. — By means of the posterior belly from (i) the upper border of the scapula close to the inner side of the suprascapular notch, and (2) the supra- scapular or transverse ligament, which bridges over the supra- scapular notch. Insertion. — By means of the anterior belly into the outer third of the lower border of the body of the hyoid bone, immediately external to the insertion of the sterno-hyoid muscle. THE HEAD AND NECK 1103 Nerve-supply. — The anterior belly is supplied by the descendens cenicis nerve, and the posterior belly derives its branches from the ansa cervicis (ansa h^^joglossj). The posterior belly is contained in the posterior triangle of the neck, and separates' the occipital from the subclavian or supra- clavicular triangle. Its course is forwards and slightly upwards, and it passes beneath the stemo-cleido-mastoid muscle, where its fibres terminate in the intervening tendon. It is ensheathed by a deep process of the deep cer^'ical fascia, as that fascia crosses the posterior triangle, and this process is attached to the back of the inner end of the clavicle and the first rib, which explains the almost horizontal position occupied by the "posterior belly. The anterior belly proceeds from the intervening tendon, and passes upwards and slightly inwards to the body of the hyoid bone. As it emerges from beneath the anterior border of the stemo- cleido-mastoid muscle the anterior belly crosses the carotid sheath on a level with the narrow anterior part of the cricoid cartilage, and in the anterior triangle of the neck it forms the separation between the muscular (inferior carotid) and carotid (superior carotid) triangles. Sterno-hyoid — Origin. — (i) The posterior surface of the manu- brium sterni at its upper and outer part ; (2) the posterior sterno- clavicular ligament ; and, it may be, (3) the posterior surface of the clavicle at its inner end. Insertion. — The inner two-thirds of the lower border of the body of the hyoid bone, extending from the middle line to the insertion of the anterior belly of the omo-hyoid. Nerve- supply. — ^The ansa cer\'icis (ansa hj-poglossi). The muscle is flat and ribbon-like, and rests upon the sterno- thyroid and th\To-hyoid. Sterno-thyroid — Origin. — (i) The posterior surface of the manu- brium steini at its upper and outer part, below the origin of the sterno-hyoid ; and (2) the posterior surface of the first costal cartilage. Insertion. — ^The oblique line on the outer surface of the ala of the thyroid cartilage. Nerve-supply. — The ansa cervicis (ansa hypoglossi). The muscle is broader, but shorter, than the sterno-hyoid, under- neath which it lies. Within the thorax the right muscle lies in front of the innominate artery, and the left in front of the left com- mon carotid artery and left innominate vein. In the neck each muscle rests upon the carotid sheath and the corresponding lateral lobe of the thyroid body. The sterno-hyoid muscles as they emerge from the thorax are separated by an interval, in which situation the sterno-thyroid muscles lie in close contact. As the muscles ascend, the sterno- hyoids converge,, but the sterno- thyroids diverge. Thyro-hyoid — Origin. — ^The oblique line on the outer surface of the ala of the thyroid cartilage. Insertion. — (i) The outer half of the lower border of the body of 1I04 A MANUAL OF ANATOMY the hyoid bone; and (2) the basal half of the great cornu of that bone. Nerve- supply. — ^The thyro-hyoid nerve, which is a special branch of the hypoglossal. The nerve enters the deep surface of the muscle close to its posterior border. The muscle is quadrilateral. Its superficial surface supports the anterior belly of the omo-hyoid and the sterno-hyoid muscles, and its deep surface is related to the ala of the thyroid cartilage, the thyro-hyoid membrane, the internal branch of the superior laryngeal nerve, and the superior laryngeal artery. The nerves which supply the infrahyoid group of muscles are regarded as being of spinal origin. Action of the Infrahyoid Muscles — Omo-hyoid. — (i) To depress the hyoid bone ; and (2) to render tense the deep cervical fascia in the lower part of the neck. Sterno-hyoid. — To depress the hyoid bone. Sterno-thyroid. — To depress the thyroid cartilage. Thyro-hyoid. — (i) To depress the hyoid bone ; arid (2) to elevate the thyroid cartilage, as in the production of high notes, or in deglutition. Structures in the Median Line of the Neck.— The median line of the neck is divisible into two regions, suprahyoid and infrahyoid. Great Corau Small Cornu - - Hyo-glossus Body - • Chondro-glossus Genio-hyo-glossus Digastric Stylo-hyoid Omo-hyoid (Ant. Belly) Thyro-hyoid Mylo-hyoid Sterno-hyoid Genio-hyoid Fig. 448. — The Hyoid Bone, showing its Muscular Attachments. Suprahyoid Region. — The innermost fibres of the two platysma myoides muscles decussate at the median line for a short distance below the chin. On either side of the median line, under cover 0/ the platysma myoides, is the anterior belly of the digastric muscle. The anterior bellies of opposite sides are near each other at the chin, but, as they descend with an inclination outward:, they diverge THE HEAD AND NECK XX05 from each other and leave between them a triangular interval, called the submental triangle. The base of this triangle is formed by the body of the hyoid bone, and each lateral boundary is con- structed by the anterior belly of the digastric, the apex being placed at the chin. The area of the triangle is occupied by the anterior portions of the mylo-hyoid muscles, which meet at the median line in a tendinous raphe, and superficial to these muscles there are the suprahyoid or submental glands. Immediately underneath the mesial portions of the mylo-hyoid muscles are the genio-hyoid muscles, these two latter muscles being in very close contact at the median line. Beneath each genio-hyoid muscle is the inferior portion of the genio-hyo-glossus. Posterior Belly of Digastric and Stylo-hyoid Hyo-glossus Aluscle and Hypoglossal Nerve Ster. Head of St.-cleido-mas Crico-thyroid Muscle -. Cricoid Cartilage Lat. Lobe of Thyroid Body Trapezius — CHavicular Head of-_^> Sterno-cleido-mas. //// Brachial Plexus -_'/.' Subclavian Artery - (third part) Clavicle In . - Anterior Belly of Digastric ■ Mylo-hyoid -Body of Hyoid Bone .interior Belly of Omo-hyoi( Stemo-hyoid Ji'^-.'i '- -iLilX-^?- -Isthmus of Thyroid Cartilai ^ ' • ^mi-nn- -Stemo-thyroid -^SSJrJi'i --Anterior Belly of Omo-hyoi -rr ySSltlM^n Cricc-thyroid Membrane ■' ■ ^^'"iSSn- Stemo-hyoid Isthmus of Thyroid Body Inferior TTiyroid Flex of Veins Cla. HeadofSt.-cI.-m; Stemo-thyroid Sternal Head of Sterno- deido-mastoid Stemo-thyroid Fig. 449. Sterno-hyoid -Dissection of the Front of the Neck. (The area bounded on either side bv the Anterior Belly of the Digastric and below by the body of the Hyoid Bone is the Submental Triangle.) The relation of structures in the suprahyoid region, from the surface downwards (in a deep direction), is as follows: 1. Platysma myoides. 3. Genio-hyoid. 2. Mylo-hyoid. 4. Genio-hyo-glossus. Submental, or Suprahyoid, Lymphatic Glands. — These glands, usually two in number. He in the submental triangle, beneath the 70 iio6 A MANUAL OF ANATOMY Great Cornu of Hyoid Bone _ Small Cornu of Hyoid Bone._ Body of Hyoid Bone.. Thyro-hyoid Membrane -- Levator Glandulae \ Thyroidae Muscle / " Thyroid Cartilage - - Crico-thyroid Membrane __ Pyramid - - Cricoid Cartilage Lateral Lobe of Thyroid Body Isthmus Trachea chin and above the body of the hyoid bone, one being on either side of the median Hne. Each gland receives its afferent vessels from (i) the mesial portions of the lower lip and lower gum; (2) the tip of the tongue and adjacent portion of the floor of the mouth; and (3) the integument of the chin. Their efferent vessels pass to (i) the submaxillary lymphatic glands, and (2) that gland of the internal group of the substerno-mastoid glands which lies on a level with ,, . . . the cricoid cartilage of the Ep.glott.s j^y^^ Infrahyoid Region. — The re- gion from the hyoid bone down- wards to the interclavicular notch on the upper border of the manubrium sterni is of con- siderable importance in connec- tion with bronchocele or goitre, laryngotomy, and tracheotomy. The body of the hyoid bone is a well-marked structure, along with the great cornu on either side of it. Below the hyoid bone there is the thyro-hyoid membrane, which passes up- wards within the lower border of the hyoid bone. The next structure is the thyroid carti- lage, the upper border of which presents a well-marked median notch, whilst its two alse form by their union the prominent isthmus, or pomum Adami. Succeeding to the thyroid cartilage there is a narrow interval, which is occupied by the crico-thyroid mem- brane, and immediately below this membrane is the narrow anterior part of the cricoid cartilage. The crico-thyroid membrane is only exposed close to the median line, being elsewhere covered by the two crico-thyroid muscles. The exposed part of the membrane is crossed by the crico-thyroid arterial arch, which is situated midway between the thyroid and cricoid cartilages, and lying upon the membrane there may be one or two prelaryngeal lymphatic glands. Laryngotomy may be performed in the crico-thyroid region, and the crico-thyroid arterial arch has to be borne in mind. Succeeding to the cricoid cartilage is the trachea, which, as it descends, inclines backwards, and therefore becomes somewhat Right Bronchus Eparterial Bronchus, Hyparterial Bronchus.^ Left Bronchus Fig. 50. — The Hyoid BiONE, Larynx, Trachea, Bronchi, and Thyroid Body (Anterior View). THE HEAD AND NECK rioy inaccessible. The thyroid body is intimately related to it superiorly. Each lateral lobe closely embraces it laterally as low as about the fifth ring, and the isthmus lies in front of the second and third rings as a rale, but its position is liable to variation. Crossing the upper border of the isthmus there is one of the branches of the superior thyroid artery, known as the artery of the isthmus. There is nothing of any importance in front of the trachea above the isthmus of the thyroid body. Below the isthmus there is a more or less copious plexus of veins, called the inferior thyroid plexus, from which the right and left inferior thyroid veins descend. Occasionally a small artery, called the arteria thyroidea ima, ascends directly in front of this part of the trachea, in the median line, to reach the isthmus of the thyroid body. The innominate, and even the right common carotid, artery, and the left innominate vein sometimes encroach upon the front of the trachea towards the root of the neck. In early life the upper part of the thymus body covers the front of the trachea. The foregoing structures are covered by the stemo-thyroid and stemo-hyoid muscles in the following manner : the two stemo-thyroid muscles are in contact with each other for a short distance above the manubrium stemi, so as to cover the trachea, but the two stemo-hyoid muscles are here separated by an interval ; superiorly the two stemo-thyroid muscles diverge, and the two stemo-hyoid muscles come very nearly together. The operation performed upon the trachea is tracheotomy. According as it is performed above or below the isthmus of the thyroid body, it is spoken of as the high operation, or the low ope ation. In the high operation there is no anatomical obstacle, unless it be a close attachment of the isthmus of the thyroid body to the tracheal rings which it covers. In the low operation the following obstacles are presented : (i) the trachea is here less accessible, because it recedes from the surface ; (2) the inferior thyroid plexus of veins might prove troublesome ; (3) an arteria thyroidea ima may be present ; (4) the innominate and right common carotid arteries, and the left innominate vein may be endangered ; and (5) in young children the thymus body would be in the way. Descendens Cervicis (Descendens Hypoglossi) Nerve. — ^The de- scendens cervicis nerve arises from the hypoglossal nerve as the latter hooks round the occipital artery, its fibres being derived from the communicating branch which the hypoglossal receives from the loop between the first and second cervical nerves. The nerve, which is long, passes downwards and slightly forwards, lying upon, or within, the carotid sheath, and in either case directly over the line of the common carotid artery. Before reaching the centre of the neck it fumishes a branch to the anterior belly of the omo-hyoid muscle. Thereafter it is joined by a branch which is formed by the union of the two rami communicantes cervicis from the anterior primary divisions of the second and third cervical nerves. These two rami, however, sometimes join it separately. In this manner a loop is formed, which is called the ansa cervicis iio8 A MANUAL OF ANATOMY (ansa hypoglossi). The convexity of the loop is directed downwards, and from it branches are given off to (i) the sterno-hyoid, (2) the stemo-thyroid, and (3) the posterior belly of the omo-hyoid, muscles. The fibres of the descendens cervicis nerve are regarded as being of spinal, act hypoglossal, origin. For the rami communicantes cervicis, see Cervical Plexus. Thyro-hyoid Nerve. — ^This nerve, which is composed of spinal fibres, derived from the loop between the first and second cervical nerves, arises from the hypoglossal at the lower border of the GH& I.J.V. P.N. S.N. ,o.H. Fig. 45 IB. — Carotid Sheath. I.J. v., internal jugular vein; P.N., pneumogastric nerve; S.N., sym- pathetic nerve ; C.C.A., common carotid artery; C.S., carotid sheath ; S., septum ; D.C.N., descendens Fig. 451A. — Scheme of the Hypoglossal cervicis nerve. Nerve, showing its Conkections with Cervical Spinal Nerves. Sy., twig from sympathetic ; Pn., communicating with pneumogastric ; ic, ac, 3c, first, second, and third cer- vical ; C.H., oommunicans hypoglossi ; C.C., communi- cantes cervicis; D.C., descendens cervicis; A.B.O.H., to anterior belly of omo-hyoid ; A.C., ansa cervicis; S.H., to sterno-hyoid ; S.T., to stemo-thyroid ; P.B.O.H., to posterior belly of omo-hyoid; T.H., to thyro-hyoid; G.H., to genio-hyoid ; G.H.G., to genio-hyo-glossus ; H.G.. to hyo-glossus ; S.G., to stylo-glossua. posterior belly of the digastric. It passes forwards and downwards, forming an acute angle with the parent trunk, and it disappears beneath the posterior border of the thyro-hyoid muscle, immediately after which it enters its deep surface. Carotid Sheath. — The carotid sheath, as stated in connection with the deep cervical fascia, is derived from the posterior lamina of the sheath of the stemo-cleido-mastoid muscle, and is intimately connected anteriorly with the pretracheal process, and posteriorly with the prevertebral process, of the deep cervical fascia. The interior of the sheath is divided into three compartments — outer. THE HEAD AND NECK 1109 Fig. 452, — The Aorta in the Thorax, and the Principal Arteribs of THE Head and Neck. 1. Arch of the Aorta 2. Aortic Isthmus 3. Aortic Spindle 4. Descending Aorta 5. Coronary Arteries (from Ascending Aorta) 6. Innominate Artery 7. Left Common Carotid 8. Left Subclavian 9. Right Common Carotid 10. Right Subclavian 11. External Carotid 12. Internal Carotid 13. Internal Maxillary 14. Superficial Temporal 15. Vertebral 16. Internal Mammary 17. ThjToid Axis 18. Inferior Thyroid 19. Transverse Cervical 20. Suprascapolar 21. Superior Thyroid 22. Lingual 2^ Facial 24. Occipital 25. Posterior Auricular 26. Ascending Pharyngeal 27. Transverse Facial 28. Aortic Intercostals 29. Lig. Ductfls Arteriosi "lo A MANUAL OF ANATOMY inner, and posterior, the latter being mesially placed. The outer and inner compartments are separated from each other by a mesial septum, the inner compartment containing the common carotid artery and, it may be, the descendens cervicis nerve, and the outer compartment the internal jugular vein. The posterior compart- ment is situated within the back part of the septum, and contains the pneumogastric nerve. The descendens cervicis nerve may lie upoii the sheath, or within it, and the gangliated cord of the sympa- thetic descends behind, and in intimate relation with, it. Common Carotid Arteries. — ^The right common carotid artery arises from the innominate artery behind the upper border of the right stemo-clavicular joint, and the left common carotid artery arises from the upper surface of the arch of the aorta, in close proximity to the origin of the innominate artery. The vessel of the right side is therefore entirely cervical, whilst that of the left side is partly thoracic and partly cervical. The thoracic part of the left common carotid artery has already been described in connection with the thorax (see p. 961). In the neck the common carotid artery of each side extends from the back of the corresponding stemo-clavicular joint to the level of the upper border of the thyroid cartilage of the lar5aix, which corresponds to the disc between the bodies of the third and fourth cervical vertebrae. At this level the vessel divides into the external and internal carotid arteries. The place of bifurcation is sometimes opposite the body of the hyoid bone, and, more rarely, on a level with the cricoid carti- lage of the larynx. The vessel is about 3I inches long, and its course is upwards and outwards in the direction of a line drawn from the stemo-clavicular joint to a point midway between the angle of the inferior maxilla and the mastoid process of the temporal bone. This line, as high as the level of the upper border of the thyroid cartilage, represents the course of the common carotid artery. At the root of the neck the two common carotid arteries are not very far apart, and the trachea lies in the intervening space. As the two vessels ascend they become more divergent, on account of the projection of the lateral lobes of the thyroid body and the thyroid cartilage. The artery, along with the intemal jugular vein and pneumo- gastric nerve, and, it may be, the descendens cervicis nerve, is con- tained within the carotid sheath, already described. Opposite the cricoid cartilage it is crossed by the anterior belly of the omo- hyoid muscle. Below this level it lies deeply in the region of the muscular triangle, being under cover of the stemo-hyoid and stemo- thyroid muscles, in addition to the platysma myoides and the anterior border of the sterno-cleido-mastoid. Above this level it is situated in the carotid triangle, being here more superficially placed, its only muscular coverings being the platysma myoides and the anterior border of the sterno-cleido-mastoid. Relations — Anterior. — ^The skin ; superficial fascia and platysma THE HEAD AND NECK mi myoides ; superficial layer of the deep cervical fascia ; anterior border of the stemo-cleido-mastoid ; stemo-hyoid ; stemo- thyroid ; anterior belly of the omo-hyoid ; and the anterior wall of the carotid sheath. Three veins cross the artery from without inwards, as follows : the anterior jugular vein crosses it immediately above the clavicle, superficial to the stemo-hyoid and stemo-thyroid muscles ; the middle thyroid vein crosses it just below the level of the cricoid Socia Paroddis Stensen's Duct : Transveise Facial Artery Parotid Gland Mental Arter>- Facial Artery Lingual Artery- External Caroti'' Arterj-..- Soperjor Laryngeal Artery _ / i \' \ Superior Thyroid Artery. ^^I*.^ Pneumogastric Nerve I ' ' Internal Jugular Vein Common Carotid Artery Anterior Belly of Omo-fayoid Ascending Cervical Artery Inferior Thyroid Artery ' __ ^Saper6cial Tempoial Artery ^ Intercal Maxillary Artery Posterior Auriculai Artery lOcdpital Artery Great OcciiMta] Nerve — Icteroal Carotid Artery k »De^ Cervical Glands - Phrenic Nerve -Scalenus Anticus Muscle -Transverse Cervical Artery • \ Snbdavian Artery (first part) \ _ ^ , , \ rtnprascaiNilar Artery Thyroid Axis Fig. 453. — Deep Dissection of the Left Side of the (after Spalteholz). Neck cartilage ; and the superior th5n-oid vein crosses it near its bifur- cation. The stemo-cleido-mastoid branch of the superior thyroid atrtery, which is of smaH size, passes obliquely downwards and outwards over the carotid sheath in the carotid triangle. The descendens cervicis nerve descends upon, or it may be within, the carotid sheath, lying directly over the artery, and the ansa cer\^icis (hypoglossi) lies upon the sheath. Posterior. — The posterior wall of the carotid sheath ; the cervical I1I2 A MANUAL OF ANATOMY transverse processes as high as the level of the fourth ; the longus colli, scalenus anticus, and part of the rectus capitis anticus major, muscles ; the gangliated cord of the sympathetic, which is inti- mately related to the posterior wall of the carotid sheath ; the recurrent laryngeal nerve ; and the inferior thyroid artery, both of which latter structures pass inwards and upwards behind the lower part of the sheath. The carotid body lies behind the vessel close to its bifurcation. External. — ^The internal jugular vein and the pneumogastric nerve, the latter lying between the artery and the vein, on a plane posterior to both. At the lower part of the neck, on the right side, the internal jugular vein diverges from the common carotid artery, so as to leave a slight interval^ in which the right pneumogastric nerve appears as it is about to pass over the first part of the right subclavian artery. On the left side, however, the internal jugular vein is very closely related to the common carotid artery, and more or less overlaps it. Internal. — From below upwards (i) the trachea and oesophagus, with the recurrent laryngeal nerve and the inferior thyroid artery lying in the intervening groove ; (2) the lateral lobe of the thyroid body, upon which the vessel impresses a groove, and by which it may be slightly overlapped ; and (3) the lar3mx and pharynx. The common carotid artery, as a rule, gives off no branch. The superior thyroid artery, however, may arise from it superiorly, and in some cases the ascending pharyngeal artery. Surgery — Compression. — ^The part of the vessel most favourably situated for compression lies in front of the tubercle of the costal process of the sixth cervical vertebra, this tubercle, known as the carotid tubercle of Chassaignac, being on a level with the cricoid cartilage of the larynx. Ligation. — ^The part of the vessel most favourably placed for ligation is situated on a level with the cricoid cartilage, just above the point where it is crossed by the anterior belly of the omo-hyoid muscle. The structures to be avoided in the operation are as follows : (i) the descendens cervicis nerve, upon, or it may be within, the sheath ; (2) the internal jugular vein and pneumogastric nerve, both of which are within the sheath, and upon the outer side of the artery ; and (3) the gangliated cord of the sympathetic, which lies behind, and in close contact with, the sheath. The small stemo-cleido-mastoid artery will probably be cut, as it passes obliquely downwards and outwards over the sheath in the carotid triangle. Ligation of the artery below the level of the cricoid cartilage is attended with difficulty, the vessel being here covered by the stemo-hyoid and stemo-thyroid muscles, in addition to the platysma myoides and stemo-cleido-mastoid. On the left side the internal jugular vein would constitute an additional difficulty. Collateral Circulation after Ligation. — (r) Cross anastomoses take THE HEAD AND NECK iii3 place freely between the external and internal carotid arteries of opposite sides. (2) The inferior thyroid artery of the side operated upon anastomoses freely with the superior thyroid of the same side, which is a branch of the external carotid. (3) The deep cervical branch of the superior intercostal, which latter is a branch of the second part of the subclavian artery on the right side, and of the first part on the left side, anastomoses with the ramus cer\dcaJis princeps of the occipital, which is a branch of the external carotid. (4) The vertebral artery undergoes much enlargement. Carotid Body or Ganglion. — This small body is situated behind the common carotid artery close to its bifurcation. It is composed of a few lobules, united by connective tissue, and it receives minute twigs from the adjacent part of the common carotid artery. The lobules consist of groups of polyhedral cells, permeated by blood- capillaries and sympathetic nerve-filaments. Some of the cellular constituents are chromaffin cells, similar to those which are met with in the medulla of the suprarenal body and in the sympathetic gangHa. These cells are derived from the contiguous ganglia of the sympathetic system. The carotid body of each side is similar to the coccygeal body and organs of Zuckerkandl. The carotid body may be regarded as being developed in part from the sympathetic system, and as belonging also to the lymphatic system. Development. — The common carotid arteries are developed from the parts of the ventraJ aortae which are situated between the third and fourth arterial arches. Internal Jugular Vein. — ^The internal jugular vein is the con- tinuation of the intracranial lateral sinus. It commences in the postero-extemal compartment of the jugular foramen, and termi- nates behind the inner end of the clavicle by joining the subclavian vein to form the innominate vein. At its commencement it presents a slight dilatation, called the bulb. The vein descends vertically, lying at first on the outer side of the internal carotid artery, and subsequently on the outer side of the common carotid artery, the pneimiogastric nerve being interposed in each case, and all being enclosed within the carotid sheath. The relations of the vessel for the most part correspond to those of the arteries which it accompanies. Tributaries. — ^These are as follows : Inferior petrosal sinus. Pharyngeal. Common facial. Superior thyroid. Lingual. Middle thyroid. A small vein accompanying the occipital artery may occasionally open into it. The inferior petrosal sinus leaves the cranial cavaty through the antero-mtemal compartment of the jugular foramen, and opens into the internal jugular vein close to the base of the skull. Development. — The internal jugular vein is developed from the anterior cardinal or primitive jugular vein. tll4 A MANUAL OF ANATOMY The pneumogastric nerve in the neck will be found described in [ndex. External Carotid Artery. — The external carotid artery is one of the terminal branches of the common carotid, the other being the internal carotid artery. The two vessels are called external and internal, the one because it is extracranial in its distribution, and the other because it is intracranial. The external carotid artery, as regards position, is the internal of the two vessels, and it lies anterior to, and nearer the median line than, the internal carotid. It extends from a p3int on a level with Hypoglossal Nerve Second Cervical Nerve / Spinal Accessory , Nerve / Occipital Artery Small Occipital Nerve Great Auricular ^-"^^fe Nerve """ " ° — Communicantes Cervicis •{ Fourth Cervical Nerve scending Branch of Fourth Cervical Nerve Descending Branches of Cervical Plexus External Jugular Vein (cut) / j Nerve to Subclavius Pneumogastric Nerve Nerve to Thyro-hyoid Muscle i!/Ti rminal Branches of Hypoglossal Nerve Internal Laryngeal Nerve External Laryngeal Nerve --.Descendens Cervicis Nerve Nerve to Anterior Belly of Omo-hyoid Ansa Cervicis Anterior Jugular Vein Internal Jugular Vein Subclavian Vein Fig. 454. — Deep Dissection of the Right Side of the Neck (after HiRSCHFELD AND LeVEILLE). I, Upper Part of Sterno-cleido-mastoid ; 2, Trapezius ; 3, Tendon of Omo-hyoid. the upper border of the thyroid cartilage to a point immediately behind the neck of the inferior maxilla, where it divides, in the substance of the parotid gland, into the superficial temporal and internal maxillary arteries. It is about 2h inches in length, and its direction is upwards and slightly backwards. At first the artery lies in the carotid triangle, and is comparatively super- ficial. As it leaves this triangle it is more deeply placed, being THE HEAD AND NECK 1115 crossed by the posterior belly of the digastric and stylo-hycid muscles, and the hypoglossal nerve. Thereafter the vessel is em- bedded in the substance of the parotid gland, where it is crossed from behind forwards by the facial nerve. Relations — Anterior. — ^The skin ; superficial fascia ; platysma myoides ; deep fascia ; anterior border of the stemo-cleido-mastoid ; the lingual and common facial veins ; the hypoglossal nerve (all the foregoing being anterior relations, whilst the artery lies in the superior carotid triangle) ; the posterior belly of the digastric and stylo-hyoid muscles ; the greater part of the parotid gland ; the temporo-maxillary vein ; and the facial nerve. Posterior. — ^The Transverse Facial Supraorbital Frontal Angular ■X „„ > „ . v^ . ... .>.-, . . .>.^^_^^__> -^ . ,- Lateral Nasal Superficial Temporal Occipital - Internal Maxillary Posterior Auricular — Superior Coronary Inferior Cornnary T, Inferior Labial Occipital ,■ Internal Carotid' ~" Submental Submaxillary Gland Eternal Carotid Facial Lingual Superior Thyroid Fig. 455. — The Arteries of the Right Side of the Head (after L. Testut's ' Anatomie Humaine '). chief posterior relations are as follows : (i) the stylo-pharyngeus muscle, glosso-pharyngeal nerve, and styloid process of the tem- poral bone, all of which intervene between the vessel and the in- ternal carotid (the latter now lying behind the external carotid) ; and (2) a small portion of the parotid gland. External. — The internal carotid artery for a short distance. Internal. — ^The pharynx and hyoid bone ; the superior laryngeal nerve ; a portion of the parotid gland ; and the posterior border of the ramus of the inferior maxilla. The external carotid artery has no vein in the sense of a com- Iii6 A MANUAL OF ANATOMY panion vessel, but the temporo-maxillary vein descends in front of it, in the parotid gland, to near the angle of the inferior maxilla, beyond which point the artery has no vein. The course of the vessel may be indicated by a line drawn from the side of the cricoid cartilage of the larynx to the tragus of the auricle. Development. — The external carotid artery is the persistent part of the ventral aorta above the level of the third arterial arch. Branches. — ^These are arranged in four sets, anterior, posterior, ascending, and terminal, and are as follows ; Anterior. Posterior. Ascending. Terminal. Superior thjnroid. Occipital. Ascending Superficial temporal. Lingual. Posterior auricular, pharyng^il. Internal maxillary. Facial. Superior Thyroid Artery. — ^This vessel arises in the carotid triangle from the front part of the external carotid close to its commencement. It takes an arched course forwards and down- wards, passing under cover of the depressor muscles of the hyoid bone. On reaching the apex of the lateral lobe of the thyroid body it breaks up into its terminal branches, which enter the lobe on its superficial aspect, and anastomose freely, within it, with branches of the inferior thyroid artery, and, in the isthmus, with its fellow of the opposite side. Branches. — ^These are £is follows ; Infrahyoid. Crico-tli5rroid. Stemo-cleido-mastoid. Glandular. Superior laryngeal. Muscular. The infrahyoid artery passes inwards on the thyro -hyoid membrane, beneath the thyro -hyoid muscle, and close to the lower border of the hyoid bone. It anastomoses at the middle line with its fellow of the opposite side, and with the supra- hyoid branch of the lingual artery of the same side. The sierno- cleido -mastoid artery passes obliquely downwards and outwards, over the upper part of the carotid sheath, to enter the deep surface of the muscle from which it takes its name. It is liable to be cut in ligation of the common carotid artery. The superior laryngeal artery accompanies the internal laryngeal nerve, and passing beneath the outer border of the thyro-hyoid muscle, it pierces the thyro-hyoid membrane, to be distributed to the interior of the lar57nx. The crico-thyroid artery passes transversely inwards upon the crico-thyroid membrane, and anastomoses with its fellow of the opposite side to form the crico-thyroid arch. This arch is situated midway between the cricoid and thyroid cartilages, but, notwithstanding this position, it may be in danger in the operation of laryngotomy. The glandular branches are distributed to the lateral lobe of the thyroid body. They anastomose freely with THE HEAD AND NECK 1117 branches of the inferior thyroid of the same side, and with branches of its fellow of the opposite side. One very constant branch, known as the artery of the isthmus, courses along the upper border of the isthmus, and anastomoses with its fellow of the opposite side. The muscular branches are distributed to tlie depressor muscles of the hyoid bone. The superior thyroid vein issues from the upper part of the lateral lobe of the thyroid body, and crosses in front of the common carotid artery, near its bifurcation, to open into the internal jugular vein. Its tributaries for the most part correspond to the branches of the artery, amongst these being the crico-thyroid and superior laryngeal veins. Lingual Artery. — The lingual artery arises from the front part of the external carotid, a little above the origin of the superior thyroid, and opposite the great comu of the hyoid bone. From its com- Dorsum of Tongue Sublingual Gland (turned up) Stylo-glossus Muscle ■*>. Lingual Nerve , Submaxillary Ganglion _ Submaxillarj' Gland (deep part) Facial Artery Mandible ,_ (in section) Genio-hyo-glossus Muscle Genio-hyoid Muscle • i Sublingual Artery \ Ranine Artery \i_^.. Lingual Artery y;,je^~^- Sup- Thy. Artery \ \^- Ext. Car. Arterj- \ Ranine Vein Hypoglossal Nerve Fig. 456. Iftliarton's Duct Deep Dissection of the Left Submaxillary Region. plicated course it is convenient to divide the artery into three parts. First Part. — The first part of the vessel ascends for a Httle, and then, bending sharply, descends to the great comu of the hyoid bone, passing beneath the posterior belly of the digastric and stylo- hyoid muscles. So far the vessel lies in the carotid triangle and the bend which it describes is crossed by the hypoglossal nerve. It is for the most part comparatively superficial. Second Part. — The second part passes horizontally forwards along the upper border of the hyoid bone beneath the hyo-glossus muscle, the hypoglossal nerve and ranine vein being superficial to that muscle. At the anterior border of the hyo-glossus it enters upon the third part of its course. The second part lies deeply in Lesser's triangle, the boundaries of which are as follows : the base, which is directed upwards, is formed by a portion of the hypo- I "8 A MANUAL OF ANATOMY glossal nerve ; the two sides are formed by the tendon of the digastric, which is here disposed in the form of a V ; and the floor is formed by the hyo-glossus muscle. The artery lies under cover of that muscle, and rests upon the middle constrictor of the pharynx. Third Part. — Near the anterior border of the hyo-glossus muscle the lingual artery describes another sharp bend in an upward direction, and ascends almost vertically to the under surface of the tongue, resting upon the genio-hyo-glossus, and being under cover of the anterior border of the hyo-glossus. Having reached the tongue, the artery passes forwards on its under surface in a tortuous manner, under the name of the ranine artery. Branches. — ^These are as follows : 1. Suprahyoid. 3. Sublingual. 2. Dorsalis linguae. 4. Ranine. The suprahyoid artery arises from the lingual at the posterior border of the hyo-glossus, and passes inwards along the upper border of the hyoid bone to supply the adjacent structures. At the median line it anastomoses with its fellow of the opposite side, and with the infrahyoid branch of the superior thyroid of the same side. The dorsalis linguce artery arises under cover of the hyo-glossus muscle, which it pierces, and so reaches the posterior third of the dorsum of the tongue. It is distributed to the mucous membrane and substance of the tongue, the tonsil, and the soft palate, and it anastomoses with its fellow of the opposite side. The sublingual artery arises close to the anterior border of the hyo-glossus muscle. It supplies the sublingual gland, the adjacent muscles, and the mucous membrane of the floor of the mouth. One of the lateral branches anastomoses at the median line with a corre- sponding branch of the opposite artery, and another of them is loiown as the artery of the frenum lingua. The ranine artery is the terminal part of the lingual. It passes forwards on the under surface of the tongue, lying immediately external to the insertion of the genio-hyo-glossus, between it and the inferior lingualis. It is more or less embedded in the substance of the tongue, and its course is tortuous in adaptation to the mobility of the organ to which it is so intimately related. Towards the tip of the tongue the vessel is very superficially placed, lying close by the side of the frenum linguae, and it anastomoses with its fellow of the opposite side near the tip. Elsewhere the cross anastomoses are un- important. The ranine artery furnishes branches freely to the substance of the tongue. Its close relation to the frenum linguae is to be carefully noted in connection with the operation for relief of tongue-tied children. The lingual veins are as follows : (i) the ranine vein, which is of large size, commences under the tip of the tongue, and passes THE HEAD AND NECK iiiToid Axis i3. Inferior Thyroid 19. Traosverse Cervical 30. Suprascapular 21. Superior Thyroid 22. Lingual 23. Facial 34. Occipital 25. Posterior Auricular 26. Ascending Pharyngeal 27. Transverse Facial 28. Aortic Intercostals 29. Lig. Ductus Arteriosi ii40 A MANUAL OF ANATOMY nerves also cross it superficially, namely, the pneumogastric and its cervical cardiac branches, the cervical cardiac branches of the sympathetic, and the nerve -loop known as the ansa Vieussenii. Posterior. — ^The recurrent laryngeal nerve, gangliated cord of the sympathetic, fat, longus colli muscle, first thoracic vertebra, dome of the pleura, and apex of the lung. Inferior. — ^The recurrent laryn- geal nerve, part of the ansa Vieussenii, and the pleura. The right subclavian and right internal jugular veins unite anterior to this part of the vessel to form the right innominate vein. First Part of the Left Subclavian Artery. — ^This part extends from the upper aspect of the arch of the aorta, towards its back part, to the inner border of the scalenus anticus muscle. It is therefore placed at first in the thoracic cavity. Its course is almost vertical until it reaches the root of the neck, where it curves sharply outwards upon the dome of the pleura, and so reaches the scalenus anticus. The relations of the intrathoracic portion have been described in connection with the thorax (see p. 961). Cervical Relations — Anterior. — ^Th,e skin, superficial fascia and platysma myoides, deep cervical fascia, clavicular origin of the sterno-cleido-mastoid, sterno-hyoid and sterno-thyroid muscles, and the thoracic duct which arches over it. The left internal jugular and subclavian veins unite in front of it to form the left innominate vein, and the left vertebral vein descends in front of it under cover of the left internal jugular vein. Posterior. — ^The gangliated cord of the left sympathetic with the inferior cervical ganglion, fat, and the left longus colli muscle. Right. — ^The trachea, oesophagus, left recurrent lar5mgeal nerve, and thoracic duct. The varieties in origin of the subclavian artery have been described in connection with the arch of the aorta (see p. 963). Second Part of the Subclavian Artery. — ^This portion of the vessel is situated behind the scalenus anticus muscle. It lies about J inch above the clavicle, and forms the highest part of the arch described by the vessel. Relations — Anterior. — ^The skin, superficial fascia and platysma myoides, deep cervical fascia, clavicular part of the sterno-cleido- mastoid, scalenus anticus, phrenic nerve on the right side, and subclavian vein, the latter vessel being on a lower level than the artery, and separated from it by the scalenus anticus. Posterior. — The pleura. Superior. — ^The nerve-roots of the brachial plexus. Inferior. — ^The pleura. In some cases the second part of the vessel passes through the scalenus anticus, and in rare cases it passes in front of the muscle. For the third part of the subclavian artery, see p. 1095 . Development. — The right subclavian artery, as far as the origin of the internal mammary arterj', is developed from the fourth right arterial arch. The left subclavian artery is developed from the seventh left segmental artery. Branches of the Subclavian Artery. — These are four in number, namely the vertebral, internal mammar5^ thyroid axis, and THE HEAD AND NECK 1141 superior intercostal. The first three arise from the first part of the artery towards its termination, and the last arises from the second part on the right side, and from the first part on the left side. Vertebral Artery. — This is the first branch in order. On the right side it arises from the upper and back part of the artery about an inch from its origin, and on the left side from the vessel just after it enters the root of the neck. It passes for a short distance upwards, backwards, and slightly outwards, and disappears from view by entering through the costo-transverse (vertebrarterial) foramen in the transverse process of the sixth cervical vertebra as a rule. It then ascends vertically through the successive costo-transverse foramina above that of the sixth vertebra, and in passing from that of the axis to that of the atlas it describes a bend outwards. Having traversed the costo-transverse foramen of the atlas, it passes back- wards and inwards, lying in the vertebrarterial groove on the upper surface of the posterior arch of the atlas behind the superior articular process. Thereafter it pierces the dura mater and arachnoid, and, having reached the side of the spinal cord, it turns upwards in the subarachnoid space, and enters the cranial cavity through the foramen magnum. Being now related to the medulla oblongata, it gradually inclines from its lateral to its ventral aspect, and at the lower border of the pons Varolii it joins its feUow to form the basilar artery. On account of its complicated course, the vertebral artery is divided into four parts, namely, first or cer\'ical, second or costo- transverse, third or suboccipital, and fourth or intracranial. The first or cervical part extends from the origin of the vessel to the costo-transverse foramen in the transverse process of the sixth cervical vertebra. It lies between the scalenus anticus and longus colli muscles, having the internal jugular and vertebral veins in front of it ; being crossed by the inferior thyroid artery ; and having the sympathetic gangliated cord and the transverse process of the seventh cervical vertebra behind it. The vessel of the left side has the thoracic duct as an additional anterior relation. The first part gives off no branches. The second or costo-transverse part traverses the costo-transverse foramina of the cervical vertebrae from, as a rule, the sixth upwards. It is surrounded by the vertebral venous plexus, and by the vertebral plexus of the sympathetic, and it lies in front of the cervical spinal nerves as these emerge from the intervertebral foramina. Branches. — ^These are as follows : lateral spinal and muscular. The lateral spinal branches enter the spinal canal through the inter\'ertebral foramina. The muscular branches supply the deep muscles of the neck, and anastomose with the deep cervical, ascend- ing cervical, and occipital arteries. For the third or suboccipital, and the fourth or intracranial, parts of the vertebral artery, see Index. Varieties. — (i) The left vertebral artery occasionally arises from the arch of the aorta between the origins of the left common carotid and left subclavian 1142 A MANUAL OF ANATOMY arteries, (2) The vessel may pass the costo-transverse foramen of the sixth cervical vertebra, and may enter that of the fifth, or even that of the fourth. (3) The vessel has been found in rare cases to enter the costo-transverse foramen of the seventh cervical vertebra. Development. — The vertebral artery is developed from (i) the seventh cer- vical segmental artery, and (2) the longitudinal anastomotic chain which connects the seven cervical segmental arteries. Internal Mammary Artery. — ^This vessel is so named in contra- distinction to the external mammary, or long thoracic, which is a branch of the second part of the axillary artery. It arises from the lower aspect of the first part of the subclavian artery very nearly opposite the thyroid axis. Its course is downwards, forwards, and slightly inwards, and it disappears behind the sternal end of the clavicle and first costal cartilage. For its subsequent course and relations, see p. 931. Relations of Cervical Part — Anterior. — ^The clavicular part of the sterno-cleido-mastoid, and the internal jugular and subclavian veins. The phrenic nerve crosses the vessel superficially from without inwards. Posterior. — ^The pleura. No branches arise from this part of the vessel. Thyroid Axis. — ^This is a short trunk which springs from the front of the first part of the subclavian artery close to the inner border of the scalenus anticus muscle. It almost immediately divides into three diverging branches, namely, inferior thyroid, transverse cervical, and suprascapular. The inferior thyroid artery passes upwards and inwards in a tortuous manner in front of the vertebral artery, and b'ehind the carotid sheath and sympathetic nerve, the middle cervical ganglion of which latter rests upon it. Having reached the lower part of the lateral lobe of the thyroid body, the artery breaks up into its terminal branches, which enter the lobe on its deep aspect, and ramify in it, anastomosing with the superior thyroid, and with its fellow of the opposite side in the isthmus. As the vessel ascends it is intimately related to the recurrent laryngeal nerve, which usually lies behind it. Branches. — ^These are as follows : muscular, ascending cervical, inferior laryngeal, tracheal, and oesophageal. The muscular branches supply the scalenus anticus, longus colli, depressor muscles of the hyoid bone, and inferior constrictor of the pharynx. The ascending cervical artery arises from the inferior thyroid as it passes inwards behind the carotid sheath. It ascends in front of the transverse processes of the cervical vertebrae, lying between the scalenus anticus and rectus capitis anticus major, and having the phrenic nerve on its outer side. It anastomoses with branches of the vertebral, occipital, and ascending pharyngeal arteries. It may furnish some spinal branches which enter the spinal canal through the intervertebral foramina, to be distributed in a manner similar to the other spinal arteries. The inferior laryngeal artery accompanies the recurrent laryngeal nerve to the larynx. The tracheal and oesophageal branches are distributed as their names suggest. THE HEAD AND NECK 1143 The transverse cervical artery passes transversely outwards in front of the scalenus anticus and phrenic nerve, and behind the clavicular part of the stemo-cleido-mastoid, lying a little above the clavicle, and also above the suprascapular artery. It then enters the subclavian triangle, which it soon leaves by passing beneath the posterior belly of the omo-hyoid. Thereafter it passes in front of, or between, the nerve-trunks of the brachial plexus, and beneath the trapezius muscle. Having reached the anterior border of the levator anguli scapulae, it divides into its two terminal branches — superficial cervical and posterior scapular. The superficial cervical artery passes superficial to the levator anguli scapulae, and is distributed to the trapezius, levator anguli scapulae, splenius, and the adjacent lymphatic glands. The pos- terior scapular artery passes backwards beneath the levator anguli scapulae to the superior angle of the scapula. Thereafter it descends along the base of the bone, imder cover of the rhomboid muscles, as far as the lower angle, where it anastomoses with the teres branch of the dorsalis scapulae of the subscapular from the third part of the axillary artery. The artery gives branches to the adjacent muscles, and ventral and dorsal branches to the scapula, which take part in the scapular anastomoses proper (see p. 325). The posterior scapular artery is frequently a branch of the third part of the subclavian, in which cases there is no transverse cervical artery, the superficial cervical artery taking its place and arising from the thyroid axis. The suprascapular artery (transversalis humeri) passes downwards and outwards in front of the scalenus anticus and phrenic nerve, and behind the clavicular part of the stemo-cleido-mastoid. Having reached the back of the clavicle, it courses outwards behind that bone, passing in front of the third part of the subclavian artery and the trunks of the brachial plexus. It then passes to the upper border of the scapula, in company with the suprascapular nerve. For the further course of the vessel see p. 320 ; and for the scapular anastomoses of arteries see Index. Branches in the Neck. — ^These are as follows : muscular, supra- sternal, and medullary. The muscular branches supply the stemo- cleido-mastoid and subclavius. The suprasternal branch descends over the inner end of the clavicle to supply the integument over the manubrium stemi. The medullary artery of the clavicle is directed outwards, and enters the medullary foramen of that bone. Superior Intercostal Artery. — ^This vessel arises from the second part of the subclavian on the right side, and from the first part on the left side, in each case from the posterior aspect of the parent trunk. On the right side it is therefore behind the scalenus anticus, and on the left side close to the inner border of that muscle The vessel at first passes backwards for a short distance, and then descends in front of the neck of the first rib. At the posterior extremity of the first intercostal space it furnishes the first inter- costal artery to that space, and then descends in front of the neck II44 A MANUAL OF ANATOMY of the second rib to become the second intercostal artery. The superior intercostal artery, therefore, furnishes the first and second intercostal arteries for the first and second intercostal spaces, their distribution being similar to that of the succeeding aortic inter- costal arteries. Besides these two branches, the vessel gives off the deep cervical artery. This branch, which is homologous with the dorsal branch of an aortic intercostal artery, arises from the superior intercostal before it descends in front of the neck of the first rib. It passes backwards between the transverse process of the seventh cervical vertebra and the neck of the first rib, and then ascends between the complexus and semispinalis colli muscles to about the level of the axis. In this latter situation it anastomoses with the deep branch of the ramus cervicalis princeps of the occipital from the external carotid. . The deep cervical in its course gives off muscular branches which anastomose with branches of the vertebral and ascending cervical arteries. It also furnishes a spinal branch which enters the spinal canal through the intervertebral foramen between the seventh cervical and first thoracic vertebrae. The superior intercostal artery on each side is developed from the anasto- motic loop between the upper two or three thoracic segmental arteries. Subclavian Vein. — ^This vessel, which is the direct continuation of the axillary vein, extends from the outer border of the first rib to the back of the inner end of the clavicle, where it unites with the internal jugular to form the innominate vein. It lies in front of, and on a lower plane than, the subclavian artery, and it passes in front of the scalenus anticus muscle and phrenic nerve. In rare cases the vein has been met with passing behind the scalenus anticus. Its principal tributary is the external jugular vein (some- times also the anterior jugular). The external jugular vein joins it close to the outer border of the sterno-cleido-mastoid. The thoracic duct opens at the angle of junction of the left sub- clavian and left internal jugular veins, and the right lymphatic duct opens into the angle of junction of the corresponding veins on the right side. Vertebral Vein. — ^This vein commences in the suboccipital venous plexus within the suboccipital triangle. It passes through the costo-transverse foramen in the atlas, and accompanies the ver- tebral artery through the succeeding costo-transverse foramina as low as the sixth, forming a plexus around the vessel. This plexus is ultimately replaced by a single vein, which emerges through the costo-transverse foramen in the sixth cervical vertebra (sometimes the seventh). It then descends in front of the first part of the subclavian artery, under cover of the internal jugular vein, and opens into the back part of the innominate vein, the opening being provided with a single or double valve. The chief tributaries of the vertebral vein are as follows : muscular, spinal, anterior vertebral, and deep cervical. It also, as a rule, receives the first intercostal vein. No vein accompanies the cervical part of the internal mammary THE HEAD AND NECK 1145 artery. The inferior thyroid vein, which does not accompany the corresponding artery, will be found described in connection with the thyroid body. The transverse cervical and suprascapular veins return the blood from the parts supplied by the corresponding arteries, and are tributaries of the lower part of the external jugular vein. The deep cervical vein (posterior vertebral vein) commences in the suboccipital venous plexus wdthin the suboccipital triangle. It descends in company with the deep cervical artery, and passes forvv'ards between the transverse process of the seventh cervical vertebra and the neck of the first rib to terminate in the vertebral vein. The anterior vertebral vein commences in a plexus in front of the upper cervical transverse processes. It descends in company with the ascending cervical branch of the inferior thyroid arter^', receiving muscular tributaries in its descent, and it opens into the lower part of the vertebral vein. Collateral Circulation after Ligation of the Third Part of the Sub- clavian Artery. — (i) The suprascapular and the posterior scapular branch of the transverse cervical, both branches of the thjToid axis from the first part of the subclavian, take part in the scapular anastomoses, and anastomose freely with branches of the first and third parts of the axillary artery. (2) The internal mammary from the first part of the subclavian anastomoses with the long thoracic from the second part of the axillary. Collateral Circulation after Occlusion of the First Part of the Subclavian Artery. — (i) The vertebral artery of one side anastomoses with that of the opposite side. (2) The internal mammary anasto- moses with the deep epigastric from the external iliac, and with the aortic intercostal arteries. (3) The inferior thjToid anastomoses with the superior thyroid from the external carotid. (4) The superior intercostal anastomoses with the first aortic intercostal. (5) The deep cervical of the superior intercostal anastomoses with the deep branch of the ramus cervicalis princeps of the occipital from the external carotid. (6) The scapular branches of the thyroid axis anastomose with branches of the axillarj' artery. (7) The thoracic branches of the axillary artery anastomose with the aortic intercostals. Cervical Part of the Thoracic Duct. — ^This part of the thoracic duct occupies the root of the neck on the left side, and lies upon the side of the oesophagus, between the left common carotid and left subclavian arteries. In this position it ascends to about the level of the seventh cervical vertebra, and then it describes a cune and passes outwards, forwards, and downwards in contact with the dome of the left pleura. Thereafter it inclines inwards, and, after receiving the left jugular and axillary- Ijonphatic trunks, terminates in the angle of jimction of the intemaJ jugular and subclavian veins of the left side. The terminal orifice of the duct is guarded by a valve composed of two segments, which are so II46 A MANUAL OF ANATOMY directed as to effectually prevent the reflux of chyle, and the flow of blood, into it. The duct crosses the left vertebral artery, and subsequently the left subclavian artery. Right Lymphatic Duct. — ^The position of this duct corresponds to that of the thoracic duct on the left side. It is about | inch in length, and is formed by the union of the right axillary lymphatic trunk and right jugular lymphatic trunk. Besides returning lymph from the right side of the head and neck and the right upper limb, it receives the lymphatic vessels from the right side of the heart, the right lung, the upper part of the right half of the thoracic wall, and some of those from the supero-anterior surface of the liver. It terminates in the angle of junction of the internal jugular and subclavian veins of the corresponding side, its orifice being guarded by a double valve. Cervical Portion of the Lung — The apex of the lung projects into the root of the neck for from i to i^ inches. It is covered by the dome of the pleura, on the inner and anterior aspects of which the subclavian artery arches outwards. The dome of the pleura is covered by Sibson's fascia, which extends from the internal border of the first rib to the front of the transverse process of the Seventh cervical vertebra. This fascia is probably derived from the adjacent scalene muscles, and it may contain some muscular fibres. The Orbit. The contents of the orbit are as follows : (i) the eyeball and the optic nerve ; (2) the capsule of Tenon ; (3) seven muscles, six of which belong to the eyeball, namely, the four recti and two obliqui, whilst the seventh belongs to the upper eyelid, and is called the levator palpebrae superioris ; (4) the third, fourth, and sixth cranial nerves, the three branches of the ophthalmic division of the fifth cranial nerve, namely, frontal, lachrymal, and nasal, and the orbital or temporo-malar branch of the superior maxillary division of the fifth cranial nerve ; (5) the ciliary, len- ticular, or ophthalmic ganglion ; (6) the lachrymal gland ; and (7) a quantity of soft fat. The foregoing contents are surrounded by a fibrous sheath which is formed by the periosteum. Periosteum. — ^The periosteum of the orbit is continuous pos- teriorly with the dura mater through the sphenoidal fissure. An- teriorly it becomes continuous with the pericranium of the frontal bone, and the periosteum of the superior maxillary and malar bones. Along the supra-orbital and infra-orbital margins the superior and inferior palpebral ligaments blend with it. The periosteum is loosely attached to the bony walls of the orbit, and forms a sheath for the contents of the cavity, which is incomplete in front. Lachrymal Gland. — This gland lies at the anterior and outer part of the orbit superiorly, where it occupies the lachrymal fossa on the inner side of the external -angular process of the frontal THE HEAD AND NECK ii47 bone. It is almond-shaped. Its upper surface is convex, and its under surface is concave in adaptation to the eyeball. The anterior part of the gland is more or less detached, and is known as tlie palpebral portion, the chief part being known as the orbital portion. The ducts, which issue from both portions, are about twelve in number, and they open in a row into the outer part of the superior fornix conjiinctivce. Blood-supply. — ^The lachrymal artery. Nerve-supply. — ^The lachrymal nerve, and sympathetic filaments. The structure of the gland is similar to that of the parotid gland. Development. — The lachrymal gland, hke the Meibomian glands and glands of Moll, is developed as solid epitheUal cords from the conjunctiva. The solid epithelial cords spring from the upper and outer part of the conjunctiva, where it is reflected from the inner surface of the upper eyelid on to the front of the eyeball. The solid cords grow into the contiguous mesoderm, and give off lateral processes. Cords and processes, at first solid, soon become hollow, and so give rise to the alveoU, or acini, and ducts of the lachrymal gland. Muscles. — These are seven in number, as follows : levator pal- pebrae superioris, superior rectus, inferior rectus, internal rectus, external rectus, superior oblique, and inferior oblique. Levator Palpebrse Superioris — Origin. — ^The under surface of the roof of the orbit above, and in front of, the optic foramen. Insertion. — By a broad membranous expansion, which divides into three layers. The middle layer, which represents the chief insertion, and consists largely of involuntary muscular fibres, is attached to the upper margin of the superior tarsal plate. The upper or superficial layer, which is fibrous, passes over, or in front of, the superior tarsal plate, lying between it and the palpebral fibres of the orbicularis palpebrarum. Its fibres pierce the superior palpebral ligament, and, having passed between the bimdles of the palpebral portion of the orbicularis palpebrarum, they are attached to the skin of the upper eyelid. The lower or deep layer, which is also fibrous, is attached to the conjunctiva along the superior fornix. The outer and inner margins of the broad membranous expansion are attached to the outer and inner margins of the orbit close to the external and internal tarsal ligaments, and at the inner angle a slip is detached to the pulley of the superior oblique muscle. Nerve-supply. — ^The upper division of the third cranial nerve, the branch from which enters the deep or ocular surface of the muscle near its origin. Action. — To raise the upper eyelid. The muscle is the antagonist of the superior palpebral fibres of the orbicularis palpebrarum. Relations. — Superiorly, the frontal ner\'e and the supra-orbital artery. Inferiorly, the superior rectus and the conjunctiva. Recti Muscles — Superior Rectus — Origin. — ^The upper part of the fibrous ring in relation to the optic foramen. Insertion. — By a thin expanded tendon into the upper surface of the sclerotic about three or four lines from the margin of the cornea. ri48 A MANUAL OF ANATOMY Nerve-supply. — ^The upper division of the third cranial nerve, the branch from which enters the deep or ocular surface of the muscle near its origin. The muscle is flattened from above downwards, and its direction is forwards and slightly outwards. Action. — ^To elevate the eyeball, so as to direct the cornea up- wards. The muscle imparts a certain amount of inward move- ment to the eyeball, accompanied by slight rotation. Relations. — Superiorly, the levator palpebrae superioris, which is the narrower of the two muscles. Inferiorly, the soft fat of the orbit. Internal Rectus — Origin. — ^The upper and lower parts of the fibrous ring in relation to the optic foramen, the origin being wide, Supra-orbital Nerve (in two divisions-) Supratrochlear Nerve Infratrochlear of Nasal^" Olfactory Bulb.^ Nasal Nerve3 Fig. 471. — A, The Ciliary Ganglion ; B, The Nerves of the Orbit (External View) (Hirschfeld and Leveille). 1. Cavernous Plexus 2. Ophthalmic Nerve 3. Nasal Nerve 4. Sympathetic Root of Ciliary Ganglion 1. Gasserian Ganglion 2. Third Nerve 3. Sixth Nerve 4. Internal Carotid Artery 5. Optic Nerve 6. Fibjous King for Recti 5. Sensory Root of Ciliary Ganglion 6. Long Ciliary Nerves 7. Branch of Third Nerve to Inferior Oblique B 7. Levator Palpebrae Superioris 8. Superior Rectus g. Frontal Nerve 10. External Rectus 11. Inferior Oblique 12. Inferior Rectus 13. Short Ciliary Nerves 8. Motor Root of Ciliary Gang- lion 9. Ciliary Ganglion 10. Infratrochlear Branch of Nasal Nerve 11. Short Ciliary Nerves 14. Branch of Third Nerve to Inferior Oblique 15. Ciliary Ganglion 16. Ophthalmic Nerve 17. Superior Maxillary Nerve 18. Inferior Maxillary Nerve is a very minute nerve which is derived from the cavernous plexus of the sympathetic, and it usually reaches the ganglion in company with the long root. It may, however, join the ganglion separately, and then it does so in close proximity to the entrance of the long root. The branches of the ciliary ganglion are called the short ciliary nerves. They are from six to eight in number, and come off, in two groups, from the antero-superior and antero-inferior angles. The 1158 A MANUAL OF ANATOMY nerves of the lower group usually exceed those of the upper in number. As they pass forward above and below the optic nerve they divide, and give rise to from sixteen to twenty delicate filaments. Having reached .the back of the eyeball, they pierce the sclerotic around the entrance of the optic nerve. They then pass forwards between the sclerotic and the choroid, giving twigs to the latter, and they are finally distributed to the ciliary muscle, the iris, and the cornea. The short ciliary nerves thus convey to the eyeball sensory fibres from the ophthalmic division of the fifth nerve, motor fibres from the third nerve, and sympathetic fibres from the cavernous plexus of the sympathetic. Frontal Artery Internal Palpebral Arteries Nasal Artery Trochlea of Superior Oblique Anterior Ethmoidal Artery, Posterior Ethmoidal Artery Jffl Arteria Centralis Retinae (in outline) ' Y;|\ Superior Oblique AIJ Superior Rectus (cut). Levator Palpebrje Superioris (cut). Optic Nerve -,^ Optic Commissure (right half) — Lachrymal Gland -^ Jl — Supra-orbital Artery External Ciliary Arteries Lachrymal Artery External Rectus (cut) Ophthalmic Artery Right Optic Tract Fig. 472. — Dissection of the Right Orbit from above, showing the Optic Nerve, Ophthalmic Artery, and Superior Oblique Muscle. Summary of the Ophthalmic Nerve. — This nerve is entirely sensory. It supplies (i ) the skin of (a) the frontal region and top of the skull, (b) the upper eyelid, and (c) the root, tip, and lower part of the side of the nose ; (2) the caruncula lacrimalis and lachrymal sac ; (3) the mucous membrane of the nasal fossa, and the palpebral conjunctiva; (4) the eyeball; and (5) the lachrymal gland. Summary of the Ciliary Ganglion. — The branches of this ganglion supply the cornea, iris, and ciliary muscle. The fibres which supply the sphincter pupillSB are derived from the third or oculo-motor nerve, through means of the motor root of the ganglion. The fibres which supply the dilator pupillse are derived from the sympafhetic, through means of the sympathetic root of the ganglion, which is derived from the cavernous sympathetic plexus. Branch of the Superior Maxillary Division of the Fifth. — The orbital or temporo-malar nerve, of small size, arises from the superior maxillary in the spheno-maxillary fossa. It enters the orbit through the spheno-maxjllary fissure, and soon divides into two THE HEAD AND NECK It^g branches, temporal and malar. The temporal branch ascends upon the outer wall of the orbit, and, having received a communicating twig from the lachrjnmal nerve, it leaves the cavity by passing through the temporal canal in the malar bone. Its destination is the skin of the anterior part of the temporal region. The malar branch passes forwards in the angle between the outer wall and floor of the orbit, and leaves the cavity by passing through the malar canal, from which it subsequently emerges through the malar foramen. It is distributed to the skin over the malar bone. Ophthalmic Artery. — ^This vessel arises from the internal carotid artery on the inner aspect of the anterior clinoid process, and it enters the orbit through the optic foramen, lying beneath the optic nerve. Within the orbit it is situated for a short distance on the outer side of the optic nerve, and then it passes obliquely inwards and forwards in a tortuous manner over the nerve to the inner wall of the orbit. Thereafter it passes forw^ards to the region of the internal angular process of the frontal bone, near which it divides into its two terminal breinches, nasal and frontal. Branches. — These are as follows : 1. Arteria centralis, retinae. 6. Posterior ethmoidal. 2. Posterior ciliary. 7. Anterior ethmoidal. 3. Lachrymal. 8. Palpebral (two). 4. Muscular. 9. Nasal. 5. Supra-orbital. 10. Frontal. The arteria centralis retinae arises from the ophthalmic at the back part of the orbit below the optic nerve. Its direction is forwards beneath the nerve, and, at a point about J inch behind the eyeball, it enters the nerve, and passes forwards in its centre to the retina, upon which it ramifies. The posterior ciliary arteries arise from the ophthalmic whilst it is below the optic nerve. They are arranged in two sets, external and internal, which pass forwards on either side of the optic nerve to the back part of the eyeball. Here they pierce the sclerotic, and the majority of them enter the choroid coat under the name of the short ciliary arteries. Two of them, however, are fairly large, and are known as the long ciliary arteries. They pass forwards between the sclerotic and the choroid, one on each side, and are distributed to the ciliary muscle and iris. The lachrymal artery arises from the ophthalmic on the outer side of the optic nerve, and passes fonvards along the upper border of the external rectus muscle to the lachrymal gland. In its course it furnishes the following branches : (i) a recurrent meningeal branch, which passes through the outer part of the sphenoidal fissure to the middle cranial fossa, where it anastomoses with the middle meningeal artery ; (2) muscular and anterior ciliary branches, the latter piercing the sclerotic very near the corneal margin ; ti6o A MANUAL OF ANATOMY (3) temporal and malar offsets, which pass through the temporal and malar canals of the malar bone to the face and temporal region, in company with the temporal and malar branches of the temporo- malar or orbital nerve ; (4) two external palpebral arteries, superior and inferior, which pass inwards in the upper and lower eyelids, and anastomose with the internal palpebral branches of the ophthalmic, thus forming arterial arches ; and (5) glandular branches to the lachrymal gland. The muscular branches arise from the ophthalmic in two sets. outer and inner, and also from some of its branches, e.g., the lach- rymal and supra-orbital. They furnish a few of the anterior ciliary arteries. The supra-orbital artery arises from the ophthalmic as it crosses Internal Palpebral Arteries Frontal Artery Nasal Artery Anterior Ethmoidal Artery Posterior Ethmoidal Artery Ophthalmic Artery Internal Ciliary Arteries Ophthalmic Artery (in Optic Foramen) Lachrymal Gland } External Palpebral Arteries upra-orbital Artery Lachrymal Artery Muscular Arteries """~ Arteria Centralis Retinae External Ciliary Arteries Internal Carotid Artery Fig. 473. — Diagram of the Ophthalmic Artery and its Branches. inwards over the optic nerve. It courses foiivards to the supra- orbital notch, through which it passes, with the corresponding nerve, to the forehead. It supplies the upper eyelid and the frontal region, and anastomoses with the superficial temporal and frontal arteries. The posterior ethmoidal artery, a small vessel, passes through the posterior ethmoidal canal on the inner wall of the orbit, and is distributed to the mucous membrane of the posterior ethmoidal cells, and the mucous membrane of the upper and back part of the outer wall of the nasal fossa. The latter branches pass through foramina in the cribriform plate. The anterior ethmoidal artery is larger than the preceding. It THE HEAD AND NECK ll6t passes through the anterior ethmoidal canal along with the nasal nerve, and enters the anterior fossa of the base of the skull. Here it crosses the cribriform plate of the ethmoid bone to the nasal slit by the side of the crista galli. It then descends through this slit, still in company with the nasal nerve, traverses the nasal groove on the posterior surface of the nasal bone, and finally emerges between the lower border of the nasal bone and the upper lateral nasal cartilage to the tip of the nose. Its branches supply the dura matei in the anterior cranial fossa, the mucous membrane of the anterior ethmoidal cells and corresponding frontal sinus, the mucous membrane of the upper and anterior parts of the nasal fossa, and the skin of the tip of the nose. The palpebral arteries (internal) are two in number, superior and inferior, and are distributed to the eyelids. They arise, separately or conjointly, from the ophthalmic close to the pulley of the superior oblique muscle, and each takes an outward course in the correspond- ing eyelid. They anastomose with the superior and inferior palpe- bral branches of the lachrjTnal artery, thus forming arterial arches. The nasal artery is one of the terminal branches of the ophthalmic. It emerges from the orbit above the internal tarsal ligament, and is distributed to the upper part of the side of the nose in the region of the root, where it anastomoses with the angular and lateral nasal branches of the facial artery. The frontal artery is the other terminal branch of the ophthalmic. It emerges from the orbit at the inner angle, and then ascends to the frontal region, along with the supratrochlear nerve, to be dis- tributed to the integument by the side of the median line. It anastomoses with the supra-orbital artery and its fellow of the opposite side. Ophthalmic Veins. — ^These are two in number, superior and inferior. The superior ophthalmic vein, of large size, commences at the inner angle of the orbit, where it communicates freely with the angular vein, which is the commencement of the facial vein. It accompanies the ophthalmic artery, passing outwards and back- wards over the optic nerve. Having reached the inner end of the sphenoidal fissure, the vessel passes between the two heads of the external rectus muscle, and through the fissure, after which it opens into the anterior part of the cavernous sinus. Its tributaries correspond for the most part to the branches of the ophthalmic artery. It does not, however, receive the frontal vein, nor the supra-orbital vein, but it is in communication with the latter by means of a small branch through the supra-orbital foramen. The inferior ophthalmic vein arises in connection with the lower posterior ciliary and lower muscular veins. It passes backwards along the floor of the orbit, and, as a rule, it joins the superior ophthalmic vein before that vessel passes between the two heads of the external rectus, thus giving rise to what is known as the common ophthalmic vein. It may, however, leave the orbit separately and open inde- pendently into the anterior part of the cavernous sinus. It com- Ii62 A MANUAL OF ANATOMY municates freely with the pterygoid plexus of veins through the spheno-maxillary fissure, and that plexus sometimes represents its mode of termination. Structures passing through the Sphenoidal Fissure. — ^These struc- tures are as follows : 1. The third nerve. 2. The fourth nerve. 3. The nasal, lachrymal, and frontal nerves. 4. The sixth nerve. 5. The sympathetic root of the ciliary ganglion. 6. The two ophthalmic veins. 7. The orbital branch of the middle meningeal artery. 8. The recurrent branch of the lachrymal artery, g. A process of the dura mater. The lachrymal, frontal, and fourth nerves enter the orbit above the external rectus muscle, in the order named from without inwards. The third nerve, the nasal nerve, and the sixth nerve enter the orbit between the two heads of the external rectus muscle, the third , Small Wing of Sphenoid Lachrymal Nerve . Frontal Nerve --"\^. ^n^^^^V^^- Optic Nerve Fourth Nerve... Upper Division of Third Nerve Nasal Ner\e. Lower Division of Third Nerve Sixth Nerve Ophthalmic Vein Fig. 474. — Diagram of the Left Sphenoidal Fissure, showing the Transmitted Structures (Posterior View). nerve having previously broken up into two divisions ; and the two ophthalmic veins leave the orbit between the two heads of the external rectus. The order of parts between the two heads of the external rectus, from above downwards, is as follows : 1. The superior division of the third nerve. 2. The nasal nerve. 3. The inferior division of the third nerve. 4. The sixth nerve. 5. The ophthalmic veins (or vein). The sympathetic root of the ciliary ganglion passes through the sphenoidal fissure independently, or along with the nasal nerve, or sometimes with the third nerve. THE HEAD AND NECK H^S THE FACE. Landmarks. — ^The nasal eminence or glabella of the frontal bone can be felt just above the root of the nose, and extending outwards from it on either side is the superciliary ridge, behind the inner part of which is the corresponding frontal air-sinus. Below the super- ciliary ridge the supra-orbital arch can readily be felt, and at the junction of its inner third and outer two-thirds is the supra-orbital notch, or foramen, for the passage of the supra-orbital ner\-e and artery. A line drawn from the position of the supra-orbital notch to the base of the inferior maxilla, in such a manner as to pass between the lower bicuspid teeth, crosses in succession the infra- orbital and mental foramina. The infra-orbital foramen lies in this line at a point about ^ inch below the infra-orbital margin, and it indicates the exit of the infra-orbital nerve and artery from the infra-orbital canal. The mental foramen in the adult lies midway between the alveolar and basilar borders of the inferior maxilla, and it indicates the exit of the mental nerve and artery from the inferior dental canal. In line with the tragus of the auricle the zygomatic arch can be felt, and leading back%vards from it above the orifice of the meatus auditorius extemus is the posterior root of the zygoma. This root is continued into the supramastoid crest, which corresponds to the level of the tegmen antri. In connection with the supra- mastoid crest it is important to note the position of the suprameatal triangle of Macewen. This triangle is bounded above by the supra- mastoid crest, below by the postero-superior part of the meatus auditorius extemus, and behind by a vertical line cormecting the upper and lower boundaries, this line being continuous with the posterior part of the meatus auditorius extemus. The superficial temporal artery and auriculo-temporal nerve lie directly in front of the tragus, the division of the artery into its anterior and posterior branches taking place about the level of the upper part of the auricle. The anterior branch of the artery lies nearly an inch above the external angular process of the frontal bone, and the posterior branch about an inch above the upper part of the auricle. The parotid gland is situated in front of the auricle. It is limited above by the zygoma, behind by the auricle, and interiorly it extends for a limited distance into the digastric triangle of the neck. Anteriorly it extends for a short distance over the masseter muscle, and Stensen's duct issues from its anterior border. The course of this duct may be indicated by a line drawn from the incisura inter- tragica, or from the junction of the lobule and cartilage of the auricle, to a point midway between the nostril and the red margin of the upper lip. About the middle third of this line corresponds to the duct. Above it is the transverse facial artery, and below it are the infra-orbital branches of the facial nerve. The course of the 1164 ^ MANUAL OF ANATOMY facial nerve through the parotid gland may be indicated by a line drawn forwards from the lobule of the auricle parallel to the line indicating the course of Stensen's duct. The posterior border of the ramus of the inferior maxilla can readily be felt. It leads superiorly to the condyle and temporo- mandibular joint, and inferiorly to the angle of the bone. Extend- ing forwards from the angle is the basilar border, which, about 2 inches from the angle, supports the facial artery, pulsation being readily felt, during life, in this part of the vessel, in front of the masseter muscle, the facial vein intervening between the two. In this situation a lymphatic gland lies in contact with the artery. From this point the facial artery extends, in a tortuous manner, to the inner canthus of the eye, passing close to the angle of the mouth, the facial vein pursuing a comparatively straight course. In the median line of the face the structures to be noted are the nasal bones, nasal cartilages, dorsum and tip of the nose, alse nasi, columella nasi, and the philtrum, which latter is the median groove leading from the columella nasi to the upper lip. For the component parts of the auricle, see p. 1192. The palpebrge or eyelids are to be noted, along with the palpebral fissure between them, and the canthi, outer and inner, at either extremity. The tarsal plates of the upper and lower eyelids can easily be felt, and connected with their inner extremities is the internal tarsal ligament, or tendo oculi. This latter may be made tense by approximating the eyelids, and drawing them outwards. It crosses the lachrymal sac a little above the centre. The eyelids being everted, the outlines of the Meibomian glands may be seen, these being arranged in a linear manner, and being placed per- pendicular to the palpebral margins. The eyelashes, or cilia, on the margins of the eyelids are to be noted, and within these are the orifices of the ducts of the Meibomian glands, which are arranged in a row. Along the line of the eyelashes the skin of the eyelid becomes continuous witH the palpebral conjunctiva, and along the line of reflection of the palpebral conjunctiva on to the eyeball the recess, known as the fornix, is to be noted. At the inner canthus, where the eyelids do not meet, there is a recess between the lids and the eyeball, which lodges a small red fleshy protuberance, called the caruncula lacrimalis, which is provided with a few delicate hairs. In this situation there is the fold called the plica semilunaris. Upon the eyelids at their inner ends the papillse lacrimales are visible, and on each papilla is a minute orifice, called the punctum lacrimale. The lower papilla is larger than the upper, and is placed a little farther out. Each punctum leads into the lachrymal canal, and by these canals the tears are conveyed into the lachrymal sac, and thence by the nasal duct into the inferior meatus of the nose. The position of the lachrymal sac may be indicated by drawing the eyelids outwards, so as to render tense the tendo oculi, which, as stated, crosses the sac a little above its centre. THE HEAD AND NECK H65 Muscles of the Face. Orbicularis Palpebrarum^Orbital Portion — Origin. — (i) The inner part of the internal tarsal ligament ; (2) the outer surface of the nasal process of the superior maxilla ; and (3) the internal angular process of the frontal bone. Insertion. — ^This corresponds to the origin, there being no attach- ment to the outer part of the orbit. Palpebral Portion — Origin. — ^The upper and lower surfaces of the internal tarsal ligament. Insertion. — ^The upper and lower surfaces of the external tarsal ligament. Nerve-supply. — ^The facial nerve. Action — Orbital Portion. — (i) The upper half depresses the eyebrow, and antagonizes the frontalis muscle ; (2) the lower half elevates the skin of the infra-orbital region. Palpebral Portion. — ^This closes the eyelids, as in winking, the upper lid being depressed and the lower raised, the former movement being more free than the latter. Through means of its con- nection with the internal tarsal ligament the palpebral portion draws forwards the front part of the lachrymal sac, and so con- tributes to the removal of the tears. When the entire muscle con- tracts the lids are forcibly closed, and drawn slightly inwards. The upper part of the muscle is related by its deep surface to the frontalis, the supra-orbital vessels and nerve, and the supratrochlear nerve. The chief deep relations of the lower part are the levator labii superioris, and, beneath that, the infra-orbital nerve. Internal Tarsal Ligament. — ^This is also called the tendo ociili, or tendo palpebrarum. It is attached internally to the outer surface of the nasal process of the superior maxilla, immediately in front of the lachrymal groove. Its direction is outwards in front of the lachrymal sac, and it bifurcates at the inner canthus, the divisions diverging, and taking attachment to the inner extremities of the tarsal plates. As the ligament passes in front of the lachrymal sac it is in intimate contact with that sac, and it gives origin to the palpebral portion of the orbicularis palpebrarum, which ex- plains the action of that portion of the muscle upon the lachrymal sac. External Tarsal Ligament. — ^This is attached externally to the frontal process of the malar bone. Its direction is inwards, and it bifurcates at the outer canthus, the divisions taking attachment to the outer extremities of the tarsal plates. Tensor Tarsi {Muscle of Horner) — Origin. — ^The crest of the lachrymal bone, behind the lachrymal sac. Insertion. — By means of two slips into the inner extremities of the tarsal plates, where the fibres become continuous with the ciliary ftbres of the orbicularis palpebrarum. Nerve-supply. — ^The facial nerve. The direction of the muscle is outwards and forwards, and its (two slips pass behind the lachrymal canals. Ii66 A MANUAL OF ANATOMY Action. — ^To draw backwards the outer part of the internal tarsal ligament, and in this manner compress the lachrymal sac, the effect of which is to propel the tears into the nasal duct. Corrugator Supercilii — Origin. — ^The inner extremity of the super- ciliary ridge of the frontal bone. Insertion. — ^The deep surface of the skin of the eyebrow at the centre. Nerve-supply. — The facial nerve. The direction of the muscle is outwards and upwards, and to reach the skin the fibres pass through the upper part of the orbicu- laris palpebrarum and the adjacent portion of the frontalis. Action. — ^To draw the skin of the eyebrow inwards and down- wards, giving rise to verffccal wrinkles between the eyebrows, as in frowning. The muscle is under cover of the inner portion of the upper half of the orbicularis palpebrarum, and it conceals the supratrochlear nerve as it emerges from the orbit. Muscles of the Nose — Pyramidalis Nasi — Origin.— The aponeurosis of the compressor naris over the lower part of the nasal bone. Insertion. — ^The deep surface of the skin over the glabella of the frontal bone. Some of the fibres become continuous with the mesial portion of the frontalis. Nerve-supply. — ^The facial nerve. Action. — ^To draw downwards the skin between the eyebrows, giving rise to transverse wrinkles. Compressor Naris — Origin. — ^The superior maxilla between the canine fossa and the nasal notch. Insertion. — By means of an expanded aponeurosis which blends with its fellow of the opposite side over the cartilaginous portion of the nose, and gives origin superiorly to the pyramidalis nasi. Nerve- supply. —The facial nerve. Action. — ^To depress the cartilaginous portion of the nose. The muscle is triangular, and at its origin is under cover of the levator labii superioris alaeque nasi. Levator Labii Superioris Alaeque Nasi — Origin. — The outer surface ol the nasal process of the superior maxilla by a pointed extremity. Insertion. — By means of two slips. The inner or nasal slip is inserted into the skin of the ala of the nose. The outer or labial slip is inserted into the skin of the upper lip, some of its fibres blending with the levator labii superioris, and others with the upper part of the orbicularis oris. Ne/ve- supply. — ^The facial nerve. Action. — (i) To raise the upper lip, and (2) to raise, and dilate, the ala of the nose. The muscle is triangular, and covers the origin of the compressor naris. Depressor Alae Nasi — Origin. — ^The incisor fossa of the superior maxilla. THE HEAD AND NECK 1 167 Insertion. — ^The posterior part of the ala, and the adjacent part 0 f the septum, of the nose. Nerve- supply. — ^The facial nerve. Action. — ^To depress the ala of the nose. Attrahcns Auriculam Attollens Auriculam Retrahens Auriculam Occipitalis Great Occioital Ne^ve^ Complexus"- Small Occipital Nerve. Le\-ator Anguli Scapute. Great Auricular Nerve Spinal Accessory Nerve Branches from Third and Fourtn Cervical Nerves to Trapezius " J^ Scalenus Medius Supra-acromial Nerve Trapezius Splenius CapitL Frontalis Orbicularis Palpebrarum Levator Labii Superioris Abeque Nasi ,Le\-ator Labii Superioris Zygomaticus Minor *iC.Zygomatictis Major -—.Masseter I . Orbicularis Oris .Depressor Labii Inferioris —•Depressor Anguli Oris -.Levator Menti ^Anterior Belly of Digastric '^ '■ .. Anterior Belly of 0_mo-hyoid ~7_ J* _. Stemo-cleido-mastoid Superficial Cervical Nerve r\>itsit3'4^ .Suprasternal Nerve _:i Ml Supraclavicular Nerve Scalenus Anticus Posterior Belly of Omo-hjroid Subclavian Artery (third part) Fig. 475. — ^The Right Side of the Head and Neck. (The Platysma Myoides has been removed, and the Nerves are shown). Dilator Maris Anterior — Origin. — ^The cartilage of the aperture of the nose. Insertion. — The deep surface of the skin over the ala of the nose. Nerve-supply. — ^The facial nerve. Action. — To dilate the nostril. Dilator Maris Posterior — Origin. — (i) The margin of the nasal notch of the superior maxilla ; and (2) the accessory or sesamoid cartilages of the nose. Ii68 A MANUAL OF ANATOMY Insertion. — ^The skin over the back part of the ala of the nose. Nerve-supply. — ^The facial nerve. Action. — ^To dilate the nostril. Levator Labii Superioris — Origin. — ^The superior maxilla between the infra-orbital foramen and the lower margin of the orbit. Insertion. — ^The skin of the upper lip. Nerve-siipply. — ^The facial nerve. Action. — To raise the upper lip. The muscle is quadrilateral. At its origin it is overlapped by the lower half of the orbicularis palpebrarum, and it covers the infra-orbital nerve and artery as they emerge from the infra-orbital foramen. At its insertion the fibres interlace with those of the upper half of the orbicularis oris. Its inner border is joined by some of the fibres of the outer or labial slip of the levator labii superioris alaeque nasi, and its outer border is joined by some fibres of the zygomaticus minor. Levator Anguli Oris — Origin. — ^The upper part of the canine fossa of the superior maxilla, under cover of the levator labii superioris. Insertion. — ^The angle of the mouth, where some of the fibres are inserted into the skin, whilst others decussate with those of the depressor anguli oris, and enter the lower lip, mingling with those of the lower half of the orbicularis oris. Nerve-supply. — ^The facial nerve. The direction of the muscle is downwards and slightly outwards. Action. — To raise the angle of the mouth, and at the same time to draw it slightly inwards. The infra-orbital nerve and artery are superficial to the muscle. Zygomaticus Minor — Origin. — ^The anterior and lower part of the malar bone, close to the superior maxilla. Insertion. — ^The skin of the upper lip immediately external to the levator labii superioris, with the outer border of which muscle some of its fibres blend. Nerve-supply. — ^The facial nerve. The muscle is directed downwards and inwards. Action. — ^To raise feebly the upper lip, and at the same time to draw it slightly outwards. Zygomaticus Major — Origin. — ^The outer surface of the malar bone near the zygomatic suture. Insertion. — ^The skin at the angle of the mouth, where its fibres blend with those of the orbicularis oris. Nerve-supply. — ^The facial nerve. The muscle is directed downwards and inwards. Action. — ^To draw the angle of the mouth upwards and out- wards. Risorius of Santorini — Origin.— ^h.e deep fascia which covers the masseter muscle and parotid gland. Insertion. — ^The skin at the angle of the mouth, where its fibres blend with the orbicularis oris. Nerve-supply. — The facial nerve. THE HEAD AND NECK iie>9 The direction of the muscle is inwards, some of its fasciculi cilso ascending. Action. — To draw the angle of the m.outh outwards and slightly downwards. It is not a muscle of laughter, but is expressive of scorn or pain. The muscle consists of a few scattered fasciculi, which are em- bedded in the adipose tissue over the buccinator, and it is to be regarded as a detached portion of the platysma myoides. Buccinator — Origin. — (i) The outer surfaces of the alveolar borders of the superior and inferior maxillae, opposite the three molar alveoli ; and (2) the anterior aspect of the pterygo-mandibular ligament. Insertion. — ^The orbicularis oris at the angle of the mouth. Long Buccal Nerve (cut) Upper Head of External Pterygoid Capsule of Temporo- mandibular Joint Lower Head of External Pterj-goid Pteryeo-mandibular Ligament i:;. . Stensen's Duct .Buccinator Internal Pterygoid Fig. 476. — The Pterygoid and Buccinator Muscles. The central fibres decussate, those from above entering the lower lip, and those from below entering the upper lip. The highest and lowest fibres take no part in this decussation, the highest passing directly into the upper lip, and the lowest into the lower lip. Nerve-supply. — ^The short buccal nerves, which are derived from (i) the infra-orbital branches of the temporo- facial division of the facial, and (2) the buccal branches of the cervico-facial division of the facial, nerve. Action. — (i) To draw the angle of the mouth outwards, and press the lips against the teeth, thus preventing the food from accumulat- ing between the lips and the teeth during mastication ; and (2) to regulate the expulsion of air from the buccal cavity when the buccal aperture is narrowed, as in playing the flute, or in whistling. The muscle is expanded over the cheek, but towards the angle 74 1170 A MANUAL OF ANATOMY of the mouth it becomes narrow and thick. It is pierced by Stensen's duct opposite the second upper molar tooth, and the long buccal nerve also passes through it on its way to the mucous membrane of tUe cheek. Externally the muscle is overlapped by the anterior border of the masseter, from which it is separated by the buccal pad of fat. Buccal Pad of Fat. — ^This is a well-defined collection of fat which is situated upon the buccinator muscle close to the anterior border of the masseter. It is continuous with the fat of the zygomatic fossa, and is well developed in young children. Depressor Anguli Oris {triangularis menti) — Origin. — ^The external oblique line of the inferior maxilla, from about the level of the canine alveolus to about the level of the first molar alveolus. Insertion. — ^The angle of the mouth, where some of the fibres are attached to the skin, whilst others decussate with those of the levator anguli oris and enter the upper lip, in which they mingle with the upper part of the orbicularis oris. Nerve-supply. — The facial nerve. Action. — ^To depress the angle of the mouth. Internally the muscle overlaps a portion of the depressor labii inferioris. Depressor Labii Inferioris {quadratus menti) — Origin. — ^The lower part of the outer surface of the body of the inferior maxilla, com- mencing almost close to the symphysis, and extending outwards to a point just below the mental foramen. Insertion. — ^The skin of the lower lip. Nerve-supply. — ^The facial nerve. The muscle is directed upwards and inwards. Action. — ^To draw the lower lip downwards and slightly outwards. The muscle is overlapped externally by a portion of the depressor anguli oris, and internally it is in contact superiorly with its fellow of the opposite side. The deep surface is related externally to the mental foramen and the mental nerve and vessels, and internally to part of the levator menti. In the lower lip its fibres pass amongst those of the lower part of the orbicularis oris. Levator Menti, or Levator Labii Inferioris — Origin. — ^The incisor fossa of the inferior maxilla. Insertion. — ^The skin of the chin. Nerve-supply. — ^The facial nerve. The muscle is directed downwards and forwards. Action. — (i) To raise the integument of the chin ; and (2) to elevate and protrude the lower lip. It gives rise to a proud or imperious expression, and has been hence called the musculus superbus. Superiorly the muscle is under cover of the depressor labii in- ferioris. Interiorly it appears along with its fellow, between the two depressor labii inferioris muscles. Orbicularis Oris. — This is a complex muscle, being composed of three strata. The superficial stratum consists of fibres which are prolonged from the elevators and depressors of the angles of the THE HEAD AND NECK 1171 mouth, and extend as far as the centre of the lip, but are not continuous with those of the opposite half. They are inserted into the skin, and are partially reinforced by fibres from the elevators of the upper lip, the zygomatic muscles, the risorius, the posterior fibres of the platysma myoides, and the depressor labii inferioris. The intermediate stratum consists of fibres which are derived from the buccinator muscles. These fibres are disposed transversely, and those of opposite sides are directly continuous. The fibres of this stratum extend quite to the margins of the lips. The foregoing fibres are destitute of bony and cartilaginous attachments. The deepest stratum consists of fibres which are so disposed as to constitute specially-named muscles. These are four in number for the upper lip, two for each half, namely, the musculus incisivus superior and the musculus naso-labialis ; and two for the lower lip, one for each half, namely, the musculus incisivus inferior. The musculus incisivus superior arises from the incisor fossa of the superior maxilla, and turns outwards in the upper lip towards the angle of the mouth, where the fibres blend with the orbicularis oris. The musculus naso-labialis arises from the back part of the nasal septum, and, like the preceding, turns outwards in the upper lip to blend with the orbicularis oris. The musculus incisivus inferior arises from the incisor fossa of the inferior maxilla, and turns outwards in the lower lip towards the angle of the mouth, where the fibres blend with the orbicularis oris. In addition to the foregoing fibres there are oblique fibres which extend between the skin and the mucous membrane. Nerve-supply. — ^The facial nerve. Action. — (i) To close the oral aperture ; and (2) to press the lips against the alveolar margins. The muscle is not a sphincter muscle, properly so called, inasmuch as the upper and lower fibres are not directly continuous at the angles of the mouth. It is separated from the buccal mucous membrane by the coronary arteries and the labial mucous glands. The labial mucous glands, which are racemose, or acino-tubular, are numerous, and each is about the size of a small pea. They are situated on the deep surface of the mucous membrane of the lips, where they lie in the loose areolar tissue between the mucous membrane and the orbicularis oris. Their ducts open into the vestibule of the mouth. The buccal mucous glands, also racemose, or acino-tubular, are situated between the mucous membrane of the cheek and the buccinator. The molar mucous glands, also racemose, or acino-tubular, lie upon the buccinator in the vicinity of the terminal part of Stensen's duct. They are four or five in number, and their ducts, having pierced the buccinator, open into the vestibule of the mouth opposite the molar teeth. 1 172 A MANUAL OF ANATOMY Nerves of the Face. The nerves of the face are thirteen in number on either side. Twelve of these are sensory nerves, and one is motor, namely, the facial nerve. The facial or seventh cranial nerve {portio dura) will only be described here after its emergence from the aqueduct of Fallopius in the petrous part of the temporal bone. It emerges from that Temporo-facial Division of Facial Nerve Temporal Branches of Facial Nerve Malar Branches of Facial Nerve Branch of Lachrymal Nei Supra-orbital Nerve " (in two divisions) .- Infratrochlear Nerv« Malar Nerve Term. Br. of Ne . Infra-orbital Infra-orbital Branches of Facial Nervi . . Long Buccal Nerve Mental Nerve Parotid Gland Buccal Branches of Facial Nerve Supramandibular Brs. of Facial Nei Inframandibular (Cervical) Branches 1. of Facial Nerve External Jugular Vein Auriculo-temporal Nerve Posterior Auricular Nerve-- Great Occipital Nerve,--— Facial Nerve at Stylo-,, mastoid Foramen Digastric Branch of • Facial Nerve Cervico-facial Division of ■ Facial Nerve Small Occipital Nerve Great Auricular Nerve Superficial Cervical Nerve Fig. 477. — Superficial Dissection of the Right Side of the Head and Upper Part of the Neck (Hirschfeld and Leveill£). I, Sterno-cleido-mastoid ; 2, Trapezius. aqueduct through the stylo-mastoid foramen, after which it passes downwards and then forwards into the parotid gland. Near the posterior border of the ramus of the inferior maxilla it breaks up into two terminal parts, called the temporo-facial and cervico- facial divisions. Branches. — These are as follows : the posterior auricular, digastric, stylo-hyoid, and the two terminal divisions, namely, temporo-facial, and cervico-facial- THE HEAD AND NECK 1173 The posterior auricular nerve arises from the facial close to the stylo-mastoid foramen. It ascends between the auricle and the mastoid process, where it lies deeply, and divides into two branches, auricular and occipital. The auricular branch passes upwards behind the auricle and beneath the retrahens auriculam, to be distributed to that muscle, and it may be to the attollens auriculam, as well as to the small intrinsic muscles on the inner aspect of the auricle. The occipital branch passes backwards to supply the occipitalis muscle. The posterior -auricular nerve com- municates with the great auricular, the small occipital, and the auricular branch (Arnold's nerve) of the pneumogastric. The digastric nerve is directed downwards, and breaks up into branches which enter the posterior belly of the digastric muscle. One of the digastric branches communicates with the glosso-pharyn- geal nerve. The stylo-hyoid nerve usually arises in common with the preceding. It is of some length, and, passing forwards, it enters the stylo-hyoid muscle about its centre. The terminal divisions, as stated, are called temporo-facial and cervico-facial. Both divisions continue to pass forwards in the parotid gland, crossing superficially the temporo-maxillary vein and the external carotid artery, the direction of these vessels being vertical. In this part of their course these divisions receive the following branches ; the temporo-facial division receives two branches from the auriculo- temporal nerve, and the cervdco- facial division receives branches from the great auricular nerve. The temporo-facial division, which is the larger of the two, traverses the upper part of the parotid gland, and the cervico-facial division passes through the gland in a forward and downward direction. Each division breaks up, within the gland, into three branches, and, as these pass in various directions over the face and upper portion of the neck, they ramify freely. The branches frequently communicate with each other in a plexiform manner, both in the parotid gland and on the face, the plexus thus formed being known as the pes anserinus or goose's foot. The ramifications also com- municate with the branches of the three divisions of the fifth nerve which appear on the face, these being sensory nerves. The temporo-facial division furnishes three sets of branches, namely, temporal, malar, and infra-orbital. The temporal branches ascend over the zygomatic arch to the temporal region, and are distributed to the following muscles : the attrahens and attollens auriculam, the intrinsic muscles on the outer surface of the auricle, the frontalis, the upper part of the orbicularis palpebrarum, and the corrugator supercilii. The temporal branches communicate with the supra-orbital and lachrymal branches of the ophthalmic, the temporal branch of the orbital from the superior maxillary, and the auriculo-temporal of the inferior maxiUary, all of these being sensory nerves. The malar branches pass forwards over the malar bone towards : "74 A MANUAL OF ANATOMY the outer angle of the orbit, and supply the outer part of the orbicularis palpebrarum. They form communications with the lachrymal branch of the ophthalmic, with the malar of the orbital, and with the infra-orbital, both these latter being branches of the superior maxillary, and all of them being sensory nerves. The infra-orbital branches, the largest of this group, pass forwards to the region between the lower margin of the orbit and the upper lip. They supply the lower part of the orbicularis palpebrarum. Fig. 478. — Scheme of the Facial Nerve (Flower). C.A. Communicating Twigs with Auditory A.T. G.G. Geniculate Ganglion G.S.P. Great Superficial Petrosal T.F. S.S.P. Branch to Small Superficial Petrosal T. E.S.P. External Superficial Petrosal M. S, Branch to Stapedius Muscle I.O. C.T. Chorda Tympani G.A. A. Auricular Branch (Arnold's Nerve) S.M.F. Stylo-mastoid Foramen C.F. P. A. Posterior Auricular B. S.H. Branch to Stylohyoid Muscle S.M. D. Branch to Posterior Belly of Digastric I.M. Communicating Branches from Auriculo-temporal Temporo-facial Division Temporal Branches Malan Branches Infra-orbital Branches Communicating Branches from Great Auricular Cervico-facial Division Buccal Branches Supramandibular Branches Inframandibular Branches the muscles of the nose, the elevators of the upper lip, the upper part of the orbicularis oris, and the buccinator. They communicate with the following .sensory nerves : the infra-orbital of the superior maxillary, the infratrochlear of the nasal, and the terminal cutaneous branch of the nasal, from the ophthalmic. The com- munications with the infra-orbital nerve take place under cover of the levator labii superioris muscle, and form a somewhat intricatej plexus, called the infra-orbital plexus. The cervico-facial division likewise furnishes three sets of I THE HEAD AND NECK "75 branches, namely, buccal, supramandibular, and inframandibular or cervical. The buccal branches pass forwards over part of the masseter and the buccinator muscles to the angle of the mouth. They supply the buccinator and the outer part ot the orbicularis oris, and are connected with the infra-orbital branches of the temporo-facial division, and with the long buccal nerve, which is a branch of the inferior maxillary division of the fifth nerve. The latter communica- tions take the form of a plexus situated on the superficial surface of the buccinator muscle, called the buccal plexus. The supramandibular branches pass forwards over the mandible to the region below the lower lip. They supply the lower part of the orbicularis oris, depressor anguli oris, depressor labii inferioris, Fig. 479. — Diagram of the Sensory Nerves of the Right Side OF THE Head. 1. Supra-orbital 2. Supratrochlear 3. Infratrochlear 4. Nasal 5. Lachrymal 6. Temporal of Orbital 7. Malar of Orbital 8. Infra-orbital g. Auriculo-temporal 10. Long- Buccal 11. Mental 12. Great Auricular 13. Small Occipital 14. Great Occipital and levator menti muscles. They communicate with the mental branch of the inferior dental from the inferior maxillary nerve, under cover of the depressor anguli oris. The inframandibular or cervical branch descends beneath the upper part of the platysma myoides and the deep cervical fascia to the suprahyoid region. Having pierced the deep fascia, it divides into branches which curve forwards and supply the platysma on its deep surface. It communicates freely with the upper branch of the superficial cervical nerve from the cervical plexus. Summary of the Facial Nerve. — The facial nerve, after its emergence from the aqueduct of Fallopius through the stylo-mastoid foramen, supplies the following muscles : ( i ) the extrinsic and intrinsic muscles of the auricle ; (2) the posterior belly of the digastric and the stylo-hyoid ; (3) the muscles of the scalp, namely, the occipitalis and the frontalis ; (4) the superficial II76 A MANUAL OF ANATOMY muscles of the face, including the buccinator, but not the masseter, nor the levator palpebr^ superioris ; and (5) the platysma myoides. All these muscles, except the posterior belly of the digastric and the stylo-hyoid, are spoken of as muscles of expression. The nerve establishes free communications with all three divisions of the fifth nerve, which are sensory. It also communicates with the small occipital, great auricular, and superficial cervical, which are branches of the cervical plexus. Sensory Nerves of the Face. — ^These, as stated, are twelve in number on either side. With one exception they are derived from the fifth cranial (trigeminal or trifacial) nerve, the exception being in the case of the great auricular, which is a branch of the cervical plexus. Most of them reach their distribution as independent nerves, but some sensory fibres reach the skin of the face through their connection with the branches of the facial nerve, as, for example, in the case of the auriculo-temporal and great auricular nerves. The sensory nerves are as follows : A. Branches of the Fifth Cranial Nerve. Distal Sources. I. Ophthalmic nerve. 2. Superior maxillary nerve. 3. Inferior maxillary nerve. Proximate Sources. (a) Frontal division. -j (fe) Lachrymal division, (c) Nasal division. (a) Superior maxillary. /Orbital, or ^ ' (^Temporo-malar. (a) Anterior division. (b) Posterior division. {c) Inferior dental of posterior division. Nerves. Supra-orbital. Supratrochlear. Superior palpebral. Infratrochlear. External terminal branch of nasal. Infra-orbital. Temporal. Malar. Long buccal. ' Auriculo-temporal. Mental. B. Facial Branches of the Great Auricular Nerve. Branches of the Fifth Cranial Nerve. — The supra-orbital and supratrochlear nerves 'have been already described (see Index). The former is distributed to the skin of the frontal region and the upper part of the scalp ; and the latter to the skin of the lower and central portion of the frontal region. Both these nerves furnish twigs to the skin of the upper eyelid. The superior palpebral branch of the lachrymal nerve pierces the superior palpebral ligament, and is distributed to the skin and conjunctiva of the outer part of the upper eyelid, as well as to the skin in the immediate vicinity of the external angular process of the frontal bone. The infratrochlear branch of the nasal nerve emerges from the orbit below the pulley of the superior oblique muscle, and furnishes twigs to the skin and conjunctiva of the inner parts of the eyelids, THE HEAD AND NECK "77 the side of the root of the nose, the lachrymal sac, and the caruncula lacrimalis. The external terminal branch of the nasal nerve emerges betvi'^een the lower border of the nasal bone and the upper lateral nasal cartilage, and descends beneath the compressor naris muscle to the tip of the nose. Its twigs supply the skin of the tip, and lower part of the side, of the nose. The infra-orbital nerve is the terminal part of the superior maxil- lary division of the fifth. It emerges from the infra-orbital canal through the infra-orbital foramen, where it is under cover of the levator labii superioris. In this situation it communicates with the infra-orbital branches of the facial, forming the infra-orbital plexus, and it divides into three sets of branches, namely, inferior palpebral, lateral nasal, and superior labial. The inferior palpebral branches ascend to supply the skin and conjunctiva of the lower eyelid. The nasal branches pass inwards, and are distributed to the skin of the side of the nose. The superior labial branches, long and large, descend to supply the skin and mucous membrane of one half of the upper lip. As they descend they furnish twigs to the skin between the infra-orbitaJ foramen and the upper lip. The temporal branch of the orbital or temporo-malar nerve is of small size. Having traversed the temporal canal in the malar bone, it pierces the temporal fascia about i inch above the front part of the zygoma, and behind the marginal process on the postero-superior or temporal border of the malar bone, and is distributed to a limited portion of the skin over the anterior part of the temporal region. The malar branch of the orbital or temporo-malar nerve is of small size, and emerges from the malar canal in the malar bone through the malar foramen. It is distributed to the skin over the malar bone. The long buccal nerve is a branch of the anterior division of the inferior maxillary nerve. It emerges from beneath the anterior border of the masseter on to the superficial surface of the buccinator, where it divides into branches which communicate freely with the buccal branches of the facial nerve, forming the buccal plexus. Its final distribution is to the skin and mucous membrane of the cheek, the branches to the latter piercing the buccinator. The auriculo-temporal nerve, which is a branch of the posterior division of the inferior maxillary nerve, has been already described as regards its cutaneous distribution (see p. 1070). The mental nerve is one of the terminal branches of the inferior dental, which, in turn, is a branch of the posterior division of the inferior maxillary nerv^e. It emerges from the dental canal in the inferior maxilla through the mental foramen, under cover of the depressor anguli oris, and in line with the interval between the two lower bicuspid alveoli. Its branches supply the skin and mucous membrane of one half of the lower lip, and the skin over one half of the body of the inferior maxilla. The supra-orbital, infra-orbital, and mental nerves, being fre- II78 A MANIJAL OF ANATOMY quently the seat of neuralgia, their positions for purposes of operative treatment can readily be ascertained in the following manner : A line drawn upwards from the position of the mental foramen, which is in line with the interval between the two lower bicuspid alveoli, to the supra-orbital notch, which is situated at the junction of the outer two-thirds and the inner third of the supra-orbital arch, will coincide with the infra-orbital foramen. This line, therefore, is over the points of emergence of these three important sensory nerves. Branches of the Great Auricular Nerve. — ^The facial branches of the great auricular nerve, which is a branch of the cervical plexus, are distributed to the skin over the parotid gland. They send twigs into the gland which communicate with the cervico-facial division of the facial nerve. Arteries of the Face. The arteries of the face are as follows : Sources. External carotid. Ophthalmic, from internal carotid. Arteries. Sources. ^Facial. Superficial Nasal. temporal. Frontal. Supra-orbital. ' Internal Internal palpebral maxillary. (superior and inferior). Terminal branch of an- terior ethmoidal. f External palpebral (superior and inferior). Arteries. (Transverse facial. Anterior temporal. Orbital. \ Infra-orbital. /Buccal. Inferior dental, 'i internal maxU- J-Mental. lary. J Lachrymal, ophthalmic. iMakS!''^^^ The chief of these arteries are the facial and the transverse facial. Facial Artery. — ^The facial artery [external maxillary) is one of the three anterior branches of the external carotid, being the highest in order. It is situated at first in the upper portion of the anterior triangle of the neck, where it has been previously described (see p. 1119). It leaves the neck and enters upon its facial course by mounting over the base and body of the inferior maxilla, in front of the anterior border of the masseter, where it is very superficial, being covered only by the platysma myoides and the integument. From this point it extends to the inner canthus of the eye, where it pierces the levator labii superioris alaeque nasi, or becomes embedded in it, and terminates in its angular branch. Its course is upwards and forwards, and it describes many bends, being remarkable for its tortuosity, this being in adaptation to the great mobility of the surrounding parts. Though embedded in the fat, and covered by certain muscles, the facial part of the vessel is in no sense deeply placed. Relations — Superficial. — The integument and platysma myoides, the risorius, the zygomatic muscles, and branches of the facial THE HEAD AND NECK 1179 nerve. Its relation to the levator labii superioris is variable. It may be under cover of, or over, that muscle. Deep. — ^The body of the inferior maxilla (where pulsation can readily be felt in the vessel), the buccinator, the levator anguli oris, and the infra- orbital nerve. External. — ^The facial vein, which is at a little distance from it, except at the body and base of the mandible, where the vein lies close to the outer side of the vessel. Facial Branches. — (i) Muscular branches, of small size, arise from the outer side of the vessel, and are distributed to the structures in the masseteric, buccal, and infra-orbital regions, where they anastomose with the buccal, transverse facial, and infra-orbital arteries. (2) The inferior labial artery passes forwards over the body of the mandible, and beneath the depressor anguli oris, to supply the structures between the lower lip and the base of the mandible. It anasto- moses with the inferior coronary, mental, and submental arteries. (3) The inferior coronary artery arises just below the angle of the mouth, and passes inwards beneath the depressor anguli oris. In the lower lip it lies near the margin, between the orbicularis oris and the mucous membrane, and it anastomoses with its fellow of the opposite side, and with the inferior labial. (4) The superior coronary artery, of larger size than the inferior, arises just above the angle of the mouth, under cover of the zygomaticus major. Its position in the upper lip is similar to that of the inferior coronary in the lower lip, and it anastomoses with its fellow of the opposite side. Near the middle line it furnishes the artery of the septum nasi, which ramifies on the columella nasi as far as the tip of the nose. The superior and inferior coronary arteries of each side sometimes arise together. The vessels of each side, superior and inferior, form in each lip a tortuous arterial arch, which is necessarily divided in operations upon one or other lip. (5) The lateral nasal arteries arise opposite the nose, upon the side of which they ramify. They anastomose with the nasal branch of the ophthalmic, the artery of the septum, the terminal branch of the anterior ethmoidal artery, and its fellow of the opposite side. (6) The angular artery is the terminal branch of the facial at the inner canthus of the eye. It lies either beneath, or embedded in, the levator labii superioris alaeque nasi, and supplies the side of the root of the nose and the adjacent part of the orbicularis palpebrarum. It anastomoses with the nasal branch of the ophthalmic artery. The facial vein commences above the inner canthus of the eye in the angular vein, which is formed by the union of the frontal and supra-orbital veins. The course of the vessel is downwards and outwards, external to the artery and at a little distance from it, except over the body and base of the inferior maxilla, where it lies close to its outer side and in contact with the anterior border of the masseter. The vein is much less tortuous than the artery, and in the lower part of its course descends almost vertically. The cervical part of the vein, which terminates in the internal jugular, has been already described. The muscular ii8o A MANUAL OF ANATOMY relations of the vein correspond pretty much with those of the artery. Its tributaries are as follows : (i) the frontal vein ; (2) the supra-orbital vein, which communicates with the ophthalmic vein ; (3 the angular vein, which receives internally the lateral nasal veins, and externally a few superior palpebral veins, whilst posteriorly it communicates with the commencement of the superior ophthalmic vein, and internally with its fellow of the opposite side by means of the transverse nasal vein, which lies over the bridge of Transverse Facial Supra-orbital \ , Frontal Superficial Temporal Occipital Internal Maxillary Posterior Auricular Angular -. Lateral Nasal .— . Superior ^oronary . Inferior Coronary Inferior Labial Occipital Internal Carotid'' External Carotid "~ Submental I ^^ Submaxillary Gland \ Facial Lingual Superior Thyroid Fig. 480, — The Arteries of the Right Side of the Head (after L. Testut's ' Anatomie Humaine '). the nose ; (4) a few inferior palpebral veins, which are in communi- cation with the infra-orbital vein ; (5) the superior labial vein, which issues from a plexus in the upper lip (the blood from the similar plexus in the lower lip being chiefly conveyed by a few vessels to the roof of the digastric triangle of the neck, where they take part in the formation of the anterior jugular vein) ; (6) the deep facial vein, of large size, which, emerging from the pterygoid plexus, appears from behind the anterior border of the ramus of the inferior maxilla and of the masseter muscle, and passes forwards over the buccinator ; and (7) parotid, masseteric, and buccal branches. THE HEAD AND NECK ll8l Superficial Facial Lymphatic Glands. — These glands lie on the face along the course of the superficial facial artery and vein. Some are situated upon the mandible, beneath the platysma myoides, one of them being placed upon the base of the mandible, close to the facial vessels; others [buccal) rest upon the fascia covering the buccinator muscle; and the remaining glands of this group are met with be- tween the angle of the mouth and the inner canthus. They receive their afferent vessels from the adjacent structures, and their efferent vessels pass to the submaxillary lymphatic glands. Transverse Facial Artery. — This vessel arises from the superficial temporal in the parotid gland, and passes horizontally forwards. After emerging from beneath the anterior border of the gland it crosses the masseter, having the zygoma above it and Stensen's duct below it, the infra-orbital branches of the facial nerve being, in turn, below Stensen's duct. The order of structures from above downwards is, accordingly, artery, duct, and nerves. The artery is distributed to the parotid gland, the masseter muscle, and the structures on the side of the face, and it anastomoses with the infra-orbital, malar, facial, and buccal arteries. The transverse facial vein opens into the superficial temporal vein. The nasal artery is one of the terminal branches of the ophthalmic, and emerges from the orbit at the inner canthus above the internal tarsal ligament. It is distributed to the lachrjnnal sac and the side of the root of the nose, and anastomoses with the angular and lateral nasal arteries. It gives off a transverse nasal branch, which crosses the root of the nose and anastomoses with its fellow of the opposite side. The transverse nasal vein connects the two angular veins over the root of the nose, and the other veins corresponding to the nasal artery open into the angular and superior ophthalmic veins. The supra-orbital and frontal arteries have been already described (see Index). The internal palpebral arteries, superior and inferior, arise from the ophthalmic, and emerge from the orbit at the inner canthus, one passing above, and the other below, the internal tarsal ligament. Their course is outwards between the palpebral fibres of the orbi- cularis palpebrarum and the tarsal plates, and they anastomose, and form arches, with the palpebral branches of the lachrymal artery. They are distributed to the palpebral structures, the lachrymal sac, and the caruncula lacrimalis. The corresponding veins from the upper eyelid open into the angular vein, and those from the lower eyelid into the facial vein. The terminal branch of the anterior ethmoidal artery emerges, along with the terminal branch of the nasal nerve, between the lower border of the nasal bone and the upper lateral nasal cartilage. It is distributed to the skin of the tip, and the lower part of the side, of the nose. ii82 A MANUAL OF ANATOMY The external palpebral arteries, superior and inferior, are branches of the lachrymal artery within the orbit. Their course is inwards between the palpebral fibres of the orbicularis palpebrarum and the tarsal plates, and they anastomose, and form arches, with the palpebral branches of the ophthalmic. The external palpebral veins terminate in the orbital vein, which opens into the middle temporal vein, this in turn joining the super- ficial temporal vein. The temporal and malar arteries are branches of the lachrymal, and they accompany the temporal and malar branches of the temporo-malar or orbital nerve. The orbital and anterior temporal arteries have been already described (see Index). The infra-orbital artery arises from the third part of the internal maxillary in the spheno-maxillary fossa. Having passed horizon- tally forwards, with the infra-orbital nerve, through the infra- orbital canal it emerges with that nerve through the infra-orbital foramen, lying under cover of the levator labii superioris muscle. It then gives branches upwards to the lower eyelid, inwards to the side of the nose, and downwards towards the upper lip. It anasto- moses with the inferior palpebral, facial, transverse facial, and buccal arteries. The infra-orbital vein, having traversed the infra-orbital canal, opens into the pterygoid plexus. The buccal artery is a branch of the second part of the internal maxillary. It accompanies the long buccal nerve to the super- ficial surface of the buccinator muscle, and is distributed to that muscle and to the mucous membrane of the cheek. It anastomoses with branches of the facial artery. The mental artery is one of the terminal branches of the inferior dental from the first part of the internal maxillary, and it emerges from the dental canal of the inferior maxilla, along with the mental nerve, through the mental foramen, lying under cover of the de- pressor anguli oris muscle. It supplies the structures in this vicinity, and anastomoses with the inferior coronary, inferior labial, and submental arteries. The mental vein joins the inferior dental vein, which opens into the pterygoid plexus. Lymphatics. — ^The lymphatics of the face are arranged in two sets, superficial and deep. The superficial lymphatics for the most part take a course similar to that of the facial vein, and terminate in the submaxillary lymphatic glands. They receive the lymphatics of (i) the inner portion of the frontal region at the inner canthus ; (2) the inner portions of the eyelids ; (3) the side of the nose ; (4) the portion of the face between the lower eyelid and upper lip ; and (5) the upper and lower lips. The lymphatics from the temporal and outer part of the frontal regions, from the front of the auricle, from the outer portions of the eye- THE HEAD AND NECK 1183 lids, and from the outer part of the cheek terminate in the parotid lymphatic glands. The deep lymphatics, including those of the orbit, anterior part of the nasal cavity, roof of the mouth, and temporal and zygomatic fossae, terminate in the internal maxillary glands. Parotid Lymphatic Glands. — These glands are arranged in two groups — superficial parotid and intraparotid. The superficial parotid or pre-auricular lymphatic glands [lympho- glandidcB auriculares anteriores) lie upon the superficial surface of the parotid salivary gland, immediately beneath the parotid fascia, and in front of the tragus of the auricle. They receive their afferent vessels from the following sources: 1. The outer surface of the auricle. 2. The anterior wall of the external auditory meatus. 3. The eyebrow, and upper and lower eyehds. 4. The root of the nose. 5. The upper part of the cheek. Their efferent vessels pass to (i) the upper superficial cervical, or external jugular, glands, and (2) the superior deep cervical glands. The intraparotid lymphatic glands {lympho-glandulca parotidecs) lie within the parotid salivary gland, along the terminal part of the external carotid artery. They receive their afferent vessels from the following sources: 1. The tympanic cavity, in part. 2. The frontal region of the scalp. 3. The anterior temporo-parietal region of the scalp. 4. The parotid salivary gland. 5. The deep facial, or internal maxillary, glands. Their efferent vessels pass to the superior deep cervical glands. Buccal Lymphatic Glands. — ^These glands are situated on the buccinator muscle. They receive their afferent lymphatics from the malar region and the lateral aspect of the face, and their efferent lymphatics pass to the parotid and submaxillary lymphatic glands. Parotid Gland. — ^This salivary gland, which is of large size, is situated on the side of the face immediately in front of the auricle, and also below the auricle, where it occupies the space between the ramus of the lower jaw and the stemo-cleido-mastoid muscle. Its limits are as follows : superiorly, the zygoma ; inferiorly, the stylo -maxillary ligament, in the direction of a line drawn from near the tip of the styloid process of the temporal bone to the angle of the inferior maxilla, this ligament separating it from the submaxillary gland ; and posteriorly, the external auditory meatus, the mastoid process, and the anterior border of the stemo-cleido- mastoid muscle. The anterior border rests upon the posterior part of the masseter, and it is from this border, above its centre, that the parotid duct emerges. The duct is usually accompanied by a IIJ A MANUAL OF ANATOMY small portion of the gland, which lies above it, and may take the form of a distinct lobe. It is known as the pars or glandula socia parotidis. The superficial surface of the gland, which presents the usual lobulated appearance of compound racemose or acino-tubular glands, is covered by the parotid fascia, which is an upward ex- tension of the deep cervical fascia. It is very dense, and conse- quently a parotid abscess is subjected to considerable tension. Lying beneath it, on the surface of the gland, there is the super- ficial set of parotid lymphatic glands. The deep connections of the gland are very intricate. It extends deeply between the mastoid process and sterno-cleido-mastoid behind, and the pos- terior border of the ramus and angle of the inferior maxilla in front. Stensen's Duct arton's Duct Fig. 481.^ — The Salivary Glands of the Right Side. Superiorly, a deep extension of the gland, known as the glenoid portion, occupies the posterior part of the glenoid fossa, formed by the tympanic plate, and lying behind the fissure of Glaser. Lower down it extends both in front of, and behind, the styloid process and styloid muscles, and is here intimately related to the internal carotid artery, internal jugular vein, and glosso- pharyngeal, pneumogastric, spinal accessory, and hypoglossal nerves. The deep surface of the gland is invested by an upward extension of the deep cervical fascia, which, with the parotid fascia, forms a capsule for the gland. Anteriorly, the gland ex- tends deeply behind the posterior border of the ramus of the lower jaw, as far at least as the posterior border of the internal pterygoid muscle, or it may be for a short distance between that muscle and the external pterygoid. THE HEAD AND NECK I185 Several important structures traverse the gland, (i) The external carotid artery ascends deeply in it as high as the level of the neck of the inferior maxilla, where it divides into the superficial temporal and internal maxillary arteries, which are at first embedded in the gland. Whilst in the gland the superficial temporal artery gives off its transverse facial and auricular branches. (2) The super- ficial temporal and internal maxillary veins unite in the gland, at the level of the neck of the inferior maxilla, to form the temporo- maxillary vein, which descends from that level within the gland, lying superficial to the external carotid artery, and close to the lower border of the gland it breaks up into an anterior and a pos- terior division. (3) The external jugular vein is formed in the lower part of the gland by the union of the posterior auricular vein with the posterior division of the temporo-maxillary vein. (4) The facial nerve traverses the gland from behind forwards, and, in doing so, breaks up into its temporo-facial and cervico-facial divisions, the branches of which emerge from the gland anteriorly and superiorly. The nerve is superficial to the external carotid artery and temporo-maxillary vein. (5) Entering the lower part of the gland are branches of the great auricular nerve, which communicate within the gland with the facial nerve. (6) The auriculo-temporal nerve is related to the deep surface of the upper part of the gland, where it gives branches to it which communicate with the facial nerve. Parotid Duct. — ^This excretory tube, which feels dense and tough, is usually called the duct of Stensen or Steno. It emerges from the anterior border of the gland, and passes forwards on the masseter muscle, lying fully | inch below the zygomatic arch. In this part of its course it is accompanied, for a short distance, by the pars or glandula socia parotidis, which, with the transverse facial artery, lies above it, whilst the infra-orbital branches of the facial nerv^e are placed below it. After leaving the surface of the masseter muscle the duct dips deeply through the fat covering the buccinator, and pierces that muscle. Thereafter it passes forwards for a very short distance beneath the buccal mucous membrane, which it finally pierces to terminate in a minute opening on a small papilla situated opposite the crown of the second upper molar tooth. The duct is about the size of a crow-quill, its diameter being about | inch, except at its buccal orifice, where it becomes narrow. It is about 2 inches in length, and its course ma}' be indicated by a line drawn from the incisura intertragica, or from the junction of the lobule and cartilage of the auricle, to a point midway between the nostril and the red margin of the upper lip. About the middle third of this line corresponds to the duct. Blood-supply. — ^The arteries are derived from (i) the external carotid, (2) the superficial temporal, (3) the transverse facial, and (4) the posterior auricular. Lymphatics.. — ^These pass to the superficial and deep cervical 75 :i86 A MANUAL OF ANATOMY glands, having previously traversed the parotid lymphatic glands, and, in the case of some, the submaxillary lymphatic glands. Nerve-supply. — (i) The auriculo- temporal nerve, which conveys to the gland secretory fibres of the glosso-pharyngeal nerve through its tympanic branch (Jacobson's nerve), the small superficial petrosal nerve, and the otic ganglion ; (2) the great auricular nerve ; (3) the sympathetic plexus on the external carotid artery ; ^/^^^^Ig^fr^^l^M^e^^ and (4) the facial nerve. ^t^^^^v^^^^y^^^^^^ Fig. 482. — Structure of the Parotid Gland. Structure. — The parotid gland is a com- pound racemose or acino-tubular gland, and is composed of large lobules, which are united by connective tissue. Each of these is made up of smaller lobules, likewise con- nected by connective tissue. Each small lobule is a gland on a minute scale, and is made up of a group of more or less saccu- lated tubules, called alveoli or acini. A duct passes from each small lobule, which unites with adjacent ducts, and these in turn unite, larger and still larger • ducts being formed, the resultant being the principal duct, called Stensen's duct. Each alveolus is serous or albuminous as regards the nature of its secretion, and is composed of a basement membrane continuous with the wall of the duct, and surrounded by a plexus of capillaries. The alveolus is lined with polyhedral cells, which contain albuminous granules, and almost com- pletely fill the tube, leaving only a small lumen. The first portion of the duct, called the intercalary duct, is lined with flattened epithelium. Beyond this the duct becomes constricted into a neck, which is lined with cubical cells, these being replaced in the intralobular duct by columnar cells. These cells are granular towards the lumen of the tube, but striated in the outer part. Each of the larger ducts is composed of a basement membrane, strengthened externally by a layer of connective tissue, superadded to which there is a stratum of plain muscular fibres. Development 0! the Salivary Glands. — ^The salivary glands — parotid, sub- maxillary, and sublingual — are of ectodermic origin. They appear as solid outgrowths of the epithelium of the stomodaeum, or primitive buccal cavity, which grow into the adjacent mesodermic connective tissue. The epithelial constituents of each gland are derived from the stomodaal ectoderm, whilst the capsule and connective-tissue elements are of mesodermic origin. Each solid epithelial outgrowth ramifies very freely, and these ramifications, as well as the primary outgrowth, become tubular. The hollowing process commences in the primary outgrowth, and extends thence throughout its numerous ramifications. The primary outgrowth represents the principal duct of each gland, and the acini, or alveoli, appear as dilatations of the walls of the terminal ramifications. The sublingual gland, from its numerous ducts, is to be regarded as a cluster of small alveolo-lingual glands. A few of these glands are developed from diverticula of Wharton's duct, which is the duct of the submaxillary gland. The majority of them, however, like the parotid and submaxillary glands, are developed from solid epithelial outgrowths of the ectoderm of the stomo- daeum. THE HEAD AND NECK 1187 Ocular Appendages. The appendages of the eye consist of the eyelids and the lachnTnal apparatus. Eyelids. — The eyelids, or palpebrae, are two movable curtains, placed in front of the eyeball, to which they form an important protection. The inner surface of each is covered by mucous membrane, which constitutes the conjunctiva. The upper eyelid is larger than the lower, and, when closed, covers the transparent part of the eye or cornea. It is also more movable than the lower, being provided with a special elevator muscle, namely, the levator palpebrae superioris. The elliptical interval between the lids is called the fissura palpebrarum, and the lateral extremities of this fissure are called the outer canthus and inner canthus. The outer canthus is formed by the junction between the two lids. At the inner canthus the lids are separated by a recess, called the lacus lacrimalis, in which there is a small body, called the caruncula lacrimalis. In this region the eyelids are separated from the eyeball by a vertical, semilunar fold of the conjunctiva, called the plica semilunaris. The margin of each eyelid presents, at the com- mencement of the lacus lacrimalis, a slight conical elevation, called the papilla lacrimalis, .the apex of which presents a small orifice, termed the punctum lacrimale, its direction being towards the eyeball. Each punctum is the entrance to a passage, called the canaliculus lacrimalis, by which the tears are conveyed from the surface of the eyeball into the lachrymal sac, and thence, through the nasal duct, into the inferior meatus of the nasal fossa. The free margins of the eyelids, external to the puncta lacrimalia, are provided with hairs, called the cilia or eyelashes. They are short, stout, and cun-ed, and are arranged in two rows. Those of the upper lid are more numerous and larger than those of the lower. The upper eyelashes are curved upwards, and the lower downwards, and in this manner intermingling is avoided. Within the lines of attachment of the eyelashes there is a row of modified sweat-glands, known as the glands of Moll, the openings of which are associated with the follicles of the eyelashes, and with the condition known as stye. Structure of the Eyelids. — Each eyelid is composed of the following structures, in order from without inwards : 1. Skin. 4. Tarsal plate. 2. GDunective tissue. 5. Meibomian glands. 3. Palpebral fibres of 6. Conjunctiva. the orbicularis palpebrarum. In addition to the foregoing structures the upper eyelid contains the tendinous insertion of the levator palpebrae superioris muscle. The skin is very thin, and at the ciliary margins of the eyelids it becomes continuous with the conjunctiva, which is a mucous membrane. The subcutaneous connective tissue is very loose, and Ii88 A MANUAL OF ANATOMY devoid of fat. The palpebral fibres of the orbicularis palpebrarum form a very delicate, pale sheet. The tarsal plate, or tarsus, one for each eyelid, is a fibrous plate, and is composed of compact fibrous tissue. The superior tarsal plate is larger than the inferior, and is semilunar, its depth at the centre being about I inch. Its upper and anterior part gives insertion to the levator palpebrae superioris. The inferior tarsal plate is narrow, and is almost of the same depth throughout. The ciliary margins of the tarsal plates are free, straight, and comparatively thick. The orbital margins are attached to the circumference of the orbit by mem- branous expansions, called the superior and inferior palpebral ligaments. The superior palpebral ligament is attached above to the upper part of the circumference of the orbit, where it blends with the periosteum, and below it blends with the tendon of insertion of the levator palpebrae superioris on the superior tarsal plate. The inferior palpebral ligament extends between the lower part of the circumference of the orbit and the lower margin of the inferior tarsal plate. The superior and inferior palpebral ligaments together constitute a partition, called the septum orbitale, which intervenes between the superficial and deep palpebral structures. Externally and internally the tarsal plates have attachments by means of the tarsal ligaments, which are two in number, external and internal. The external tarsal ligament is formed by the junction of the superior and inferior palpebral ligaments, and is attached to the malar bone. The internal tarsal ligament, tendo palpebrarum, or tendo oeuli, is independent of the palpebral ligaments. Internally it is attached to the external surface of the nasal process of the superior maxilla in front of the lachrymal groove. From this point it passes horizontally outwards for about ^ inch, and then divides into two laminae, which are attached to the superior and inferior tarsal plates. It passes in front of the lachrymal sac, and furnishes an offset, which passes behind the sac to be attached to the lachrymal crest of the lachrymal bone. The ligament gives origin to a few fibres of the orbicularis palpebrarum. The Meibomian glands are situated on the internal surface of each tarsal plate, and lie between the plate and the conjunctiva at right angles to the ciliary margin. There are about thirty in the upper eyelid, and about twenty in the lower, and they are arranged in parallel rows, which occupy grooves on the ocular surface of each tarsal plate. Each gland opens by an independent orifice, and these orifices are arranged in a single row, lying a little behind the ciliary margin of the eyelid. Structure. — The Meibomian glands are sebaceous glands, and their secretion lubricates the margins of the eyelids, and prevents them from adhering. Each consists of a tube, closed at one end, aiad having its sides beset with diverticula. The wall of the tube is composed of a basement membrane, which is lined with cubical epitlielium throughout the greater part of the gland, but close to the orifice this is replaced by stratified epithelium. THE HEAD AND NECK 1189 In the vicinity of the closed ends of the Meibomian glands there are some convoluted tubules, which are known as the posterior tarsal, or accessory lachrymal, glands, the orifices of which are placed close to the fornix conjunctivae. Conjunctiva. — ^This is the mucous membrane which covers the ocular surfaces of the eyelids and the front of the eyeball. It consists of two parts — palpebral and ocular. The palpebral conjunctiva lines the ocular or inner surfaces of the eyelids, and, at their ciliary margins, it is continuous with the skin on their outer surfaces. It is also continuous, through the puncta lacrimalia, with the lining membrane of the lachrymal canals, lachrymal sac, nasal duct, and inferior meatus of the nose. In the region of the inner canthus it gives rise to the plica semi- lunaris, and at the outer part of the upper eyelid it is continuous with the lining membrane of the lachrymal ducts. The palpebral conjunctiva is fairly thick and highly vascular, and it presents numerous papillae. The ocular conjunctiva consists of two portions — sclerotic and corneal. It is continuous with the palpebral conjunctiva, and the line of reflection from the eyelids is known as the fornix conjunctivae, superior and inferior respectively. In this vicinity the orifices of the posterior tarsal, or accessory lachrymal, glands are met with. The sclerotic conjunctiva covers the part of the sclerotic which is adjacent to the cornea. It is loosely connected to the sclerotic, is thin, non-papillary, and transparent, and contains only a few blood- vessels, the whiteness of the sclerotic being unaffected by it. The corneal conjunctiva is very thin, and consists only of the conjunctival epithelium. The palpebral conjunctiva is covered by columnar epithelium, which, at the ciliary margin, passes into the stratified epithelium of the skin ; the sclerotic conjunctiva is also covered by colunmar epithelium ; but the corneal conjunctiva is represented by the stratified epithelium of the cornea. The conjunctiva is supplied with blood by offsets from the palpebral branches of the ophthalmic artery and its lachrymal branch. The vessels are disposed in a tortuous manner, and are movable upon the eyeball when the conjunctiva is pressed upon and displaced. The nerves are numerous, and form plexuses. The lymphatics commence close to the corneal margin in a network, from which vessels proceed to a network in each eyelid behind the tarsal plate. The efferent vessels ultimately reach the parotid and submaxillary lymphatic glands. The caruncula lacrimalis occupies the lacus lacrimalis in the region of the inner canthus. It is a small, reddish, spongy bodv, consisting of a detached portion of skin, containing modified sweat and sebaceous glands. The latter open into the follicles of very delicate hairs with which the surface of the caruncle is provided, and they furnish the white secretion which may accumulate at the inner canthus. iigo A MANUAL OF ANATOMY The plica semilunaris is a vertical, semilunar fold of the con- junctiva which is situated on the outer side of the caruncle, its concave margin being directed outwards. It corresponds to the membrana nictitans, or third eyelid, of some animals. Development of the Eyelids and Meibomian Glands. — The eyelids make their appearance as two folds of skin, above and below the developing eyeball. Each fold contains some mesodermic tissue which gives rise to the connective- tissue element and tarsal plate of the lid. The ectoderm of the posterior sur- faces of the lids acquires the characters of mucous membrane, and forms the conjunctival epithelium. In the course of the third month the eyelids grow together and unite along their margins, a space being thereby enclosed be- tween thelids and the front of the developing eyeball. The union affects the epithelium only, and persists until near the end of intra-uterine life. During the period of fusion of the eyelids the Meibomian glands and the cilia or eyelashes are formed. The Meibomian glands are developed from the epi- thelium along the line of fusion of the lids. Solid rods of epithelial cells are formed which grow into the mesodermic tissue of the two lids and give off lateral processes. These solid rods beqome hollow, and so form the Meibomian glands. Some of the epithelial rods give rise to the glands of Moll. A short time before birth the eyelids become separated, and the palpebral fissure is thereby formed. The plica semilunaris is developed as a vertical fold of conjunctiva near the inner canthus of the eye, external to the caruncle, but it attains little develop- ment in man. The caruncle is developed from that portion of the margin of the lower eyelid which intervenes between the inferior punctum lacrimale and the inner canthus. The Meibomian glands in this region become modified, and the tissue containing these modified glands becomes raised, and forms the reddish, spongy caruncle. Lachrymal Apparatus. — The constituent parts of the lachrjonal apparatus are as follows: 1. The lachrymal gland. 3. The lachrymal sac. 2. The lachrymal canaliculi. 4. The nasal duct. The lachrymal gland will be found described on p. 1146. The lachrymal canaliculi are two in number, superior and inferior. They commence at the puncta lacrimalia on the summit of the papillae lacrimales, which latter are situated on the ciliary margins of the eyelids, close to the lacus lacrimalis. The superior canali- culus at first ascends vertically for about yV inch, after which it makes a sudden bend, and passes inwards and downwards to the lachrymal sac. The inferior canaliculus at first descends vertically for about ^^ inch, after which it makes a sudden bend and passes almost horizontally inwards to the lachrymal sac. The two canali- culi open into the lachrymal sac, either close together or by a common orifice, and their mucous membrane is hned with stratified squamous epithelium. The two slips of the tensor tarsi muscle are closely related to the horizontal portions of the canaliculi. The lachrymal sac is the dilated upper part of the passage by which the tears are conveyed from the lachrymal canaliculi to the inferior meatus of the nose. It occupies the lachrymal groove of the lachrymal bone and nasal process of the superior maxilla. THE HEAD AND NECK I191 Superiorly it presents a round, closed extremity, and inferiorly it opens into the nasal duct. Externally it receives the lachrymal canaliculi, separately or conjointly, and anteriorly it is crossed by the tendo palpebrarum or internal tarsal ligament, which furnishes an offset round it. Posteriorly it is related to the tensor tarsi muscle. The guide to the lachrymal sac is the lachrymal tubercle or spine of the superior maxilla, which is situated at the point of continuity of the infra-orbital margin of the bone and the crista lacrimalis anterior on the outer surface of the nasal process. The lachr^-mal sac lies immediately intemaUto this tubercle. In many cases, however, the tubercle or spine is very rudimentar}'. The nasal duct extends from the lower end of the lachr^inal sac to the anterior part of the inferior meatus of the nose, under cover of the front part of the inferior concha. Its length is about | inch, Lachrymal Gland • ?''<» Semilunaris Ladirymal Ducts^ Xfxjt^ ^ „i Superior Punctum Lacrimale " ' ' ' ' Caruncula Lacrimalis Superior Lachrymal Canal A' y^^ Lachrymal Sac ^~ Inferior Lacbrynal Canal _ Nasal Duct Inferior Punctum Lacrimale . Fig. 483. — The Lachrymal Apparatus of the Right Eye. (The Meibomian Glands of the Upper Eyelid are also shown.) and its diameter about ^ inch. It is directed downwards, outwards, and backwards, and its opening into the anterior part of the inferior meatus of the nose is usually guarded by an imperfect mucous fold, kno\\'n as the valve of Hasner. The nasal orifice of the duct is about i\ inches from the anterior nasal aperture. Structure of the Lachrymal Sac and Nasal Duct. — The wall is composed of fibro-elastic tissue, which adheres closely to the periosteum of the bones, and is covered by mucous membrane. The epithelial hning is of the columnar variety, and at intervals the cells are furnished with ciUa. The mucous membrane is continuous superiorly with the conjunctiva through the lach- r>'mal canaUculi and puncta, and inferiorly it is continuous with the nasal mucous membrane. In the nasal duct it may present one or f:s"o folds. Development of the Nasal Duct and its Appendages. — The efferent lachrymal apparatus consists of (i) the lachr>'mal canaliculi, (2) the lachrymal sac, and (3) the na-sal duct. In the course of the development of the face, the maxillary' process and the lateral nasal process, of either side, are separated by a groove which extends 1 192 A MANUAL OF ANATOMY from the inner angle of the eye to the olfactory pit. This groove is called the naso-optic, or oculo-nasal, groove, and it indicates, deeply, the position of the lachrymal duct. In the bottom of this groove a solid epithelial cord makes its appearance, which, becoming hollow, forms the nasal duct. The upper extremity of the duct bifurcates, its two divisions becoming connected with the margins of the eyelids hear their inner ends, and forming the lachrymal canaliculi. The lower end of the nasal duct, after the completion of develop- ment, opens into the lower part of the nasal cavity. The lachrymal sac is the upper expanded extremity of the nasal duct. Auricle. The auricle, or pinna, is that part of , the external ear which projects from the side of the head. It is somewhat pyriform, with the broad end upwards, and it presents two surfaces, outer and inner. Darwin's Tubercle , Scaphoid Fossa . (Fossa of Helix) Helix Antihelix^ Concha' Crus Antihelicis Superior Fossa Triangularis '%< ^''(Fossa of Antihelix) Helix Crus Antihelicis Inferior Crus Helicis 'sL Tragus _ Orifice of External Auditory Meatus -~»,Incisura Intertragica *\Antitragus Lobule Fig. 484. — The Right Auricle (External View). The outer surface is irregularly concave, and presents certain elevations and depressions. About its centre there is a largo deep fossa, called the concha, which leads to the meatus auditorius extemus. Towards the upper and anterior part of the concha there is an elevation, called the crus helicis, which is directed upwards and forwards to the anterior border of the auricle. The concha is thus divided into two parts, upper and lower. In front of the concha there is a small, somewhat conical, prominence, called the tragus, which projects slightly backwards over the orifice of the meatus auditorius externus, and is provided with hairs on its inner aspect. A short distance behind the tragus, and on a lower level than it, there is another prominence, called the antitragus, which is separated from the tragus by a deep notch, called the incisura intertragica. The skin over the antitragus is also provided with hairs. Below the antitragus and incisura intertragica is the most dependent part of the auricle, called the lobule, which is compara- THE HEAD AND NECK 1193 lively soft in consistence. The prominent rim of the amicle is called the helix. It is incurved, and commences at the upper and anterior part of the concha in the cms helicis, already referred to. There- after it surrounds the upper part of the anterior margin, and the superior and posterior margins, of the auricle, and subsides below in the back part of the lobule. In some cases the helix presents a projection, called the tubercle of Darwin, which is situated on the incurved margin, slightly above the level where the antihelix, to be presently described, bifurcates into its crura. This projection is well developed in the ears of quadrupeds, and forms the point or tip. A short distance within the helix there is another curved elevation, called the antihelix. This commences interiorly at the back part of the antitragus and ascends behind the concha, above which it divides into two diverging crura, upper and lower. Between the helix and the antihelix is an elongated, narrow fossa, called the fossa of the helix, or the scaphoid fossa, and between the diverging crura of the antihelix there is a depression, called the fossa of the antihelix, or the triangular fossa. The inner or cranial surface of the auricle presents convexities corresponding to the fossae on the outer surface, the convexity opposite the concha being especially prominent. Structure of the Auricle. — ^The auricle, with the exception of the lobule, is composed of a plate of yellow elastic fibro-cartilage covered by skin. This plate imparts firmness and elasticity to it, and is provided with hgaments and intrinsic muscles. The skin is thin, and adheres closely to the fibro- cartilaginous plate. It is provided with hairs, which are most plentiful in the regions of the tragus and antitragus. The cartilage of the auricle is rolled upon itself so as to form the outer or cartilaginous part of the meatus audi- torius externus. This portion of it is attached internally to the external auditory process of the temporal bone by fibrous tissue. The rolled or tubular portion presents a deficiency at the anterior and upper part, between the tragus and the commencement of the helix, which is occupied by a fibrous membrane. It also presents a variable number of transverse clefts, called the fissures of Santorini, which are filled with fibrous tissue. The lower ex- tremity of the cartilage of the helix is separated from the cartilage of the antiheUx by a deep cleft. The part of the cartilage of the heUx behind this cleft is known as the processus caudatus helicis. At the upper and anterior part of the auricle, where the helix begins to curve backwards, the cartilage presents a small sharp projection, called the spine of the helix. Ligaments of the Auricle. — These are two in number, anterior and posterior. The anterior ligament extends from the spine of the helix to the z\goma of the temporal bone close to its root. The posterior ligament extends from the cranial aspect of the concha, under cover of the retrahens auriculam muscle, to the mastoid process. Intrinsic Muscles. — These muscles, which are very thin and pale, are confined to the auricle and are six in number, four being situated on the outer surface, and two on the inner surface. Muscles on Outer Surface. — These are as follows : (i) the musculus helicis major; (2) the musculus helicis minor; (3) the musculus tragicus ; and (4) the musculus antitragicus. "94 A MANUAL OF ANATOMY The musculus helicis major extends from the spine of the hehx along the anterior part of the hehx as high as the level at which it curves backwards. The musculus helicis minor lies upon the crus hehcis. The musculus tragicus lies upon the outer surface of the tragus, its fibres being almost vertical. The musculus antitragicus extends from the outer surface of the antitragus backwards and slightly upwards, to be attached to the processus caudatus of the hehx. Attrahens Auriculam Musculus Helicis Major.. ^ Musculus Helicis Minor Musculus Tragicus _ — Attollens Auriculam '^Retrahens Auriculam Fig. Processus Caudatus of Helix Musculus Antitragicus 485. — The Outer Surface of the Left Auricle and its Muscles (Arnold). Muscles on Inner Surface. — These are as follows: (i) the musculus transversus, and (2) the musculus obliquus. The musculus transversus extends over the depression which corresponds to the antihelix on the outer surface, its attachments being to the convexity of the concha on the one hand, and the convexity of the fossa of the helix on the other. The musculus obliquus extends over the depression corresponding to the lower crus of the antihelix on the outer surface. Action of the Intrinsic Muscles. — The musculus tragicus and musculus antitragicus diminish the orifice of the meatus auditorius externus, and the muscles of the helix, major and minor, have an opposite effect. THE HEAD AND NECK 1 195 Nerve-supply. — The facial nerve. Blood-supply of the Auricle.— The arteries are derived from (i) the posterior auricular branch of the external carotid. {2) the anterior auricular branches of the superficial temporal, and (3) the deep auricular branch of the first part of the internal maxillary, the last named giving offsets to the cartilaginous part of the meatus auditorius externus. The veins terminate in the posterior auricular, superficial tem- poral, and internal maxillary veins, and one or two of them may open into the mastoid emisscury vein. ,..j\^^'rlt;,, (I i jj { / ; Attollens Auriculam TTTlTJll '" ^Attrahens Auriculam /^Mu -cuius Obliquus Auriculae jRfiw^ Eminence of Concha External Auditory Meatus Processus Caudatus of Helix Fig. 486. — The Inner Surface of the Left Auricle and its Muscles (Arnold). The lymphatic vessels of the inner surface of the auricle pass chiefly to the mastoid, or posterior auricular, glands ; but a few end in the superior deep cervical glands. The lymphatics of the lobule pass to (i) the superficial cervical, or external jugular, glands, and (2) the superior deep cervical glands. The lymphatics of the outer surface of the auricle pass to the superficial parotid, or anterior auricular, lymphatic glands. Nerve-supply. — The inner surface receives three cutaneous nerves, as follows: the great auricular supplies about the lower three- fourths, the small occipital about the upper fourth, and the auricular branch (Arnold's nerve) of the pneumogastric supplies II96 A MANUAL OF ANATOMY the integument over the convexity of the concha. The outer surface is supphed by two cutaneous nerves, as follows: the auriculo-temporal nerve supplies the upper two-thirds, and the great auricular supplies the lower third. The motor nerve of the intrinsic muscles is, as stated, the facial nerve. The Nose. The nose, as it appears upon the face, presents a root, situated belo\y the glabella of the frontal bone; a tip, or point, situated inferiorly; and a dorsum, which occupies an intermediate position. The upper part of the dorsum is known as the bridge of the nose. At the lower part of the nose there are the openings of the nostrils, or anterior nares. The outer margin of each nostril is slightly prominent and curved, and is called the ala. The nostrils are separated from each other by a septum, called the columella nasi, Nasal Bone \\ _:.„Nasal Process of Superior Maxillary Bone ^\NV;... Upper Lateral Cartilage 2 Cartilage of Septum .linor Cartilages Subcutaneous Fat Cartilage of Aperture Fig. 487. — The Cartilages of the Nose (Anterior View) (Arnold). which, as well as the ala, is composed of fibrous tissue and skin. Within the circumference of each nostril there are several stout hairs or vibrissa. The superficial or facial aspect of the nose derives its arteries from (i) the lateral nasal and angular branches of the facial, and (2) the nasal branch of the ophthalmic. The nerves are derived from the nasal and infra-orbital nerves, the branches from the nasal being the infratrochlear and the terminal cutaneous offsets. The cutaneous lymphatics of the root of the nose pass to the super- ficial parotid, or anterior auricular, lymphatic glands. Those from the greater part of the nasal integument pass to the submaxillary lymphatic glands, the superficial facial glands forming gland- stations in their path. The framework of the nose is both osseous and cartilaginous. THE HEAD AND NECK 1 197 Cartilages of the Nose. — The nasal cartilages are five in number, as follows : Upper lateral, right and left. Lower lateral,, right and left. Septal. Nasal Bone Nasal Process of Superior _ Maxillary Bone Upper Lateral Cartilage Lower Lateral Cartilage Minor Cartilage:- Subcutaneous Fat' Fig. 488. — The Cartilages of the Nose (Lateral View) (Arnold). The upper lateral cartilages are situated immediately below the nasal bones. They are triangular, and their anterior borders are continuous with each other, and with the anterior margin of the Cartilage of Aperture ^_ Crus Mediale 1 \ ..Cms Laterale i_\ Anterior Naris ..Minor Cartilages Subcutaneous Fat Cartilage of Septum Fig. 489. — The Cartil.\ges of the Nose (Inferior View) (Arnold). septal cartilage, in each case superiorly. Inferiorly, the anterior borders are separated by a slight interval, in which the anterior margin of the septal cartilage is visible. The posterior border of each cartilage is attached to the lower sloping border of the nasal bone, and also to the upper part of the nasal notch on the mesial 1198 A MANUAL OF ANATOMY border of the superior maxilla. The lower border is connected by fibrous tissue to the upper margin of the lower lateral cartilage. The lower lateral cartilages are also known as the cartilages of the apertures. They are situated below the upper pair, and each is bent so as to lie in front, and on each side, of the nostril, which it keeps open. Its outer portion is called the crus laterale, and its inner portion the crus mediale. Frontal Air-Sinus Nasal Bone Perpendicular^'' Plate of Ethmoid Palatal Process of Palate ' Bone (in section) Cartilage of Aperture Septal Cartilage Cartilage of Jacobson Palata Process of Superior Maxilla (in section) Fig. 490. — The Osseous and Cartilaginous Nasal Septum (Right Lateral View). The crus laterale is attached by fibrous tissue to the upper lateral j cartilage, and to the lower part of the nasal notch on the mesial; border of the superior maxilla. The crus mediale is folded back-, wards, and is contiguous to its fellow of the opposite side. It lies] along the upper part of the columella nasi, and along the antero- inferior border of the cartilage of the septum. Anteriorly it is^ separated from its fellow by a notch. In the fibrous tissue which connects the crus laterale to thej superior maxilla two or more isolated portions of cartilage are met] with, called the sesamoid or minor cartilages. THE HEAD AND NECK 1 199 Development. — The lateral nasal cartilages are derived from the cartilaginous core of the lateral nasal process. The cartilage of the septum is mesially placed, and is usually inclined slightly to one side, most frequently the left. It forms a large part of the nasal septum anteriorly, and has the form of an irregularly four-sided, laterally-compressed plate. Its anterior border is attached to the back of the nasal bones, along the course of the intemasal suture; below this it is connected to the anterior borders of the upper lateral nasal cartilages ; and below these it lies between the middle crura of the lower nasal cartilages. Its pos- terior border is accurately applied to the irregular anterior margin of the perpendicular plate of the ethmoid bone. Its inferior border is received into the front part of the groove on the anterior border of the vomer. The antero-inferior border passes upwards and for- wards from the front part of the inferior border to the anterior border. In early life the septal cartilage is prolonged backwards to the body of the sphenoid bone in the form of a narrow strip, which intervenes. between the lower border of the perpendicular plate of the ethmoid and the vomerine groove. This portion is known as the sphenoidal or posterior process. Along the inferior border of the septal cartilage, between it and the anterior border of the vomer, there are two narrow, elongated strips of cartilage, right and left, which are called the cartilages of Jacobson, or the vomerine car- tilages of Buschke. Development. — The septal cartilage is derived from the chondrocranium. The Temporal and Ptergyo-maxillary Regions. Muscles of Mastication. — ^These are four in number, namely, the masseter, temporal, external pterygoid, and internal pterygoid. Masseter — Origin — (i) Superficial Portion. — The anterior two- thirds of the lower border of the zygomatic arch. (2) Deep Portion. — ^The posterior third of the lower border, and the whole of the deep or internal surface of the zygomatic arch. Insertion. — ^The superficial portion is inserted into the lower half, and the deep portion into the upper half, of the outer surface of the ramus of the inferior maxilla. The superficial fibres extend as far as the angle, and the deep fibres encroach on the coronoid process. Nerve-supply. — ^The masseteric branch of the anterior portion of the inferior maxillary division of the fifth cranial nerve. This branch emerges from the pterygoid region by passing over the sigmoid notch of the inferior maxilla, below the zygoma, and it therefore enters the muscle on its deep surface, accompanied by the masseteric artery. The superficial portion of the muscle is directed downwards and slightly backwards, and the deep portion downwards and very slightly forwards. 1200 ■ A MANUAL OF ANATOMY Action. — To elevate the inferior maxilla. The superficial portion also draws it slightly forwards. Relations — Superficial. — ^The parotid gland and Stensen's duct, branches of the facial nerve, the transverse facial artery, the risorius, and the platysma myoides. Deep. — ^The ramus of the infarior maxilla, and the masseteric nerve and artery. The anterior border overlaps the buccinator, from which it is separated by the buccal pad of fat. Temporal Muscle — Origin. — (i) The temporal fossa, extending as high as the inferior temporal ridge of the frontal and parietal bones, and as low as the infratemporal crest on the external surface of the great wing of the sphenoid, but excluding the portion of the fossa formed by the malar bone ; and (2) the deep surface of the temporal fascia over its upper part. Insertion.— {1) The internal surface, summit and anterior border of the coronoid process of the inferior maxilla; and (2) the elongated triangular surface on the internal surface of the ramus of the inferior maxilla, close within the anterior border, and ex- tending as low as a point on the inner side of the last molar alveolus. Nerve-supply. — ^The deep temporal nerves, usually three in number, which are branches of the anterior portion of the inferior maxillary division of the fifth cranial nerve, and which enter the deep surface of the muscle. The muscle is fan-shaped. The anterior fibres descend almost vertically ; the middle fibres pass obliquely downwards and for- wards ; and the posterior fibres pass forwards almost horizontally. Action. — ^To raise the inferior maxilla, that is, to draw it upwards into contact with the superior maxilla, as in closing the mouth. The posterior fibres also retract the inferior maxilla, and act in opposition to the external pterygoid, which protracts it. RelSitions—Superficial. — ^The temporal fascia, supporting the attrahens and attolleris auriculam muscles ; the superficial tem- poral artery, auriculo-temporal nerve, and temporal branches of the facial nerve ; the zygoma ; and fat, which is continuous with the buccal pad. Deep. — ^The temporal fossa, the deep temporal arteries and nerves, and the external pterygoid muscle. The long buccal nerve passes downwards and forwards under cover of the muscle close to the anterior border of the ramus of the inferior maxilla, and the masseteric nerve and artery pass out- wards close to the posterior border in the region of the sigmoid notch of the inferior maxilla. For the temporal fascia, see Index. External Pterygoid — Origin — (i) Upper Head. — ^The zygomatic division of the outer surface of the great wing of the sphenoid, below the infratemporal crest. (2) Lower Head. — ^Tlie outer surface of the external pterygoid plate of the sphenoid. The upper head is small, and the lower head is of large size. Insertion. — (i) The depression on the front of the neck of the THE HEAD AND NECK I20I inferior maxilla ; and (2) the front-of the interarticularfibro- cartilage of the tempo ro -mandibular joint. Nerve-supply. — ^The external pterygoid nerve, which is a branch of the long buccal nerve, that, in turn, being a branch of the anterior portion of the inferior maxillary division of the fifth cranial nerve. The direction of the muscle is backwards and slightly outwards. Action. — (i) To draw forwards the neck and condyle of the in- ferior maxilla, and also the interarticular fibro-cartilage. When the muscles of opposite sides act in concert the inferior maxilla is protruded, and the lower incisor and canine teeth project beyond the level of those of the superior maxilla. The muscles of opposite sides, however, usually act in reciprocal succession, as in the Long Buccal Nerve (cut) Upp«r Head of External Pterygoid Capsule of Tempore mandibular Joint Lower Head of External Pterygoid Pterygo-mandibular Ligament ^^i^_Stensen's Duct ^~ Buccinator Internal Pterygoid Fig. 491. — The Pterygoid and Buccinator Muscles. oblique or grinding movement, the lower molars of one side being carried forwards and inwards upon the corresponding upper molars, and vice versa. At the same time the elevators of the inferior maxilla are in action. (2) To take part in opening the mouth by drawing the condyle of the inferior maxilla and interarticular fibro- cartilage forwards on to the eminentia articiilaris of the temporal bone. The external pterygoid is antagonistic to the posterior portion of the temporal muscle. Relations — Superficial. — Part of the ramus of the inferior maxilla, the lower part of the temporal muscle, part of the pterygoid plexus of veins, the long buccal nerve, and, it may be, the second part of the internal maxillary artery. Deep. — ^The upper portion of the internal pterygoid muscle, the spheno-mandibular ligament, in !?ome cases the second part of the internal maxillary artery, the middle meningeal artery, a part of the pterygoid plexus of veins, 76 I202 A MANUAL OF ANATOMY the inferior maxillary nerve, the otic ganglion, and the chorda tympani nerve. Superior. — ^The masseteric and middle and pos- terior deep temporal nerves. Inferior. — ^The inferior dental and lingual nerves, and the spheno-mandibular ligament. The long buccal nerve, with the anterior deep temporal nerve, makes its appearance between the upper and lower heads, and the internal maxillary artery may sink between them. Internal Pterygoid — Origin. — (i) The inner surface of the external pterygoid plate of the sphenoid, and the portion of the tuberosity of the palate bone which forms the lower part of the pterygoid fossa ; and (2) the outer surface of the tuberosity of the palate bone, and the adjacent portion of the tuberosity of the superior maxilla. Insertion. — (i) The inner aspect of the angle of the inferior maxilla f and (2) the back part of the inner surface of the ramus, between the angle and the dental foramen. Nerve-supply. — ^The internal pterygoid branch of the anterior portion of the inferior maxillary division of the fifth cranial nerve. The direction of the muscle is downwards, backwards, and out- wards. Action. — (i) To elevate the inferior maxilla ; and (2) to draw it forwards. Relations — Superficial. — ^The external pterygoid muscle to a slight extent superiorly, the spheno-mandibular ligament, the internal maxillary and inferior dental vessels, and the inferior dental and lingual nerves. Deep. — ^The tensor palati muscle, and the superior constrictor muscle of the pharynx. For a description of the spheno-mandibular ligament, see Index. Internal Maxillary Artery. — ^This vessel is the larger of the two terminal branches of the external carotid. It arises from that artery opposite the neck of the inferior maxilla, and within the parotid gland. Its course is at first forwards and inwards behind the neck of the mandible, and superficial to the spheno-mandibular ligament. It then inclines upwards and forwards through the zygomatic fossa, usually passing superficial to the external pterygoid muscle, though in many cases it passes beneath it. Having reached the interval between the two heads of the external pterygoid, it sinks deeply between them, and, passing through the pterygo- maxillary fissure, it enters the spheno-maxillary fossa, where it gives off its terminal branches. In those cases where the artery passes beneath the external pterygoid muscle, it forms a pro- jecting curve between the two heads of the muscle. The course of the vessel is very tortuous in adaptation to the mobility of the surrounding structures. Owing to its complexity it is convenient to divide the artery into three parts, namely, first, second, and third. The first, or mandibular, part is situated between the neck of the inferior maxilla and the spheno-mandibular ligament, and its course is horizontally forwards and inwards. It is accompanied by the internal maxillary vein, and THE HEAD AND NECK 1203 lies along the back part of the lower border of the external pterygoid muscle, crossing in front of the inferior dental nerve. The second, or pterygoid, part usually lies upon the lower head of the external pterygoid, and under cover of the insertion of the temporal muscle. Its course through the zygomatic fossa is upwards and forwards, and it sinks between the two heads of the external pterygoid on its way to the pterygo-maxillary fissure. In many cases, however, the second part of the vessel passes beneath the lower head of the external pterygoid, crossing in front of the internal pterygoid muscle and lingual nerve. Under these circumstances it forms a projecting curve between the two heads of the external pterygoid beneath the long buccal nerve. The third, or spheno-maxillary, part is situated in the spheno-maxillary fossa, which it enters by passing through the pterygo-maxillary fissure. In this fossa the vessel and its branches are intimately related to the superior maxil- lary nerve and Meckel's ganglion, with its branches. Branches. — ^These are as follows : First Part. Deep auricular. Tympanic. Middle meningeal, giving ofE small meningeal. Inferior dental. Second Part. Masseteric. Internal pterygoid. External pterygoid. Posterior deep temporal. Anterior deep temporal. Buccal. Third Part Posterior dental. Infra-orbital. Descending palatine. Vidian. Pterygo-palatine. Spheno-palatine. Branches of the First Part. — ^The deep auricular artery, of small size, ascends within the parotid gland, just behind the temporo- mandibular joint, and pierces the anterior cartilaginous wall of the meatus auditorius extemus. It supplies the cutaneous lining of that passage, and the outer surface of the membrana tympani. The tympanic artery may be associated with the preceding at its origin. It ascends beneath the external pterygoid, and enters the t5mipanic cavity by passing through the fissure of Glaser. It is distributed to the structures within the tympanum, and to the inner surface of the membrana tympani. Around the circum- ference of that membrane it forms an arterial ring with an offset of the stylo-mastoid artery, which is a branch of the posterior auricular. The middle meningeal artery, of large size, ascends beneath the external pterygoid muscle, and, passing between the two roots of origin of the auriculo-temporaJ nerve, it enters the cranial cavity through the foramen' spino sum in the sphenoid bone. It then passes upwards and forwards to the inner aspect of the antero- inferior angle of the parietal bone, where it divides into two branches, anterior and posterior, which ramify in the branching grooves on the inner surface of the parietal bone. The artery is accompanied by a plexus of sympathetic nerves, and by two veins. For the distribution of the vessel within the cranium, see Index. Before disappearing through the foramen spinosum the middle meningeal I204 A MANUAL OF ANATOMY artery usually gives off the small meningeal artery, which enters the cranial cavity through the foramen ovale. The inferior dental artery arises nearly opposite the middle meningeal artery, and descends upon the spheno-mandibular liga- ment in company with the inferior dental nerve, lying on its pos- terior and outer side. Having reached the inferior dental foramen, it gives off the small mylo-hyoid artery, and then it passes through the inferior dental foramen and enters the inferior dental canal which it traverses as far as the level of the mental foramen, where Posterior Division of Middle Meningeal Anterior Division of ,.- Middle Meningeal Posterior Deep Temporal Anterior Deep \^ Temporal Infra-orbital Superficial Temporal TW V" Deep Auricular. \ '^ \, Tympanic. — -V" Internal Maxillary--' External Carotid/ Inferior Dental ' Pterygoid Mental ^Middle Meningeal giving off Small Meningeal Fig. 492. — The Internal Maxillary Artery and its Branches. (The Ramus of the Mandible and one half of the Calvaria liave been removed). I. External pterygoid muscle. 2. Internal pterygoid muscle. it ends by dividing into its mental and incisor branches. Within the inferior dental canal the artery is accompanied by the inferior dental nerve and inferior dental vein. Branches. — ^The mylo-hyoid artery, of small size, arises at the level of the inferior dental foramen. In company with the mylo- hyoid nerve it pierces the spheno-mandibular ligament, and descends in the mylo-hyoid groove to be distributed to the under surface of the mylo-hyoid muscle. The molar, bicuspid, and canine branches arise within the inferior dental canal, and supply the pulps of these teeth, which they reach by passing through the foramina on the extremities of their fangs. The mental artery emerges from the THE HEAD AND NECK 1205 inferior dental canal through the mental foramen, and has been already described (see Index). The incisor artery suppUes the pulps of the incisor teeth of one side. Branches of the Second Part. — The branches of this part are muscular in their distribution. The masseteric artery passes out- wards, with the corresponding nerve, over the sigmoid notch of the inferior maxilla, and enters the deep surface of the masseter. The internal and external pterygoid branches are distributed to the corresponding muscles. The posterior and anterior deep temporal arteries pass upwards to the posterior and anterior parts of the temporal fossa beneath the temporal muscle. They supply the muscle and the bones forming the fossa, and anastomose with the middle temporal artery, which is a branch of the superficial temporal. The anterior deep temporal artery also anastomoses with the lach- rymal artery by twigs which pass through minute foramina in the outer wall of the orbit. The buccal artery passes downwards and forwards in company with the long buccal nerve, and is distributed to the buccinator muscle and the buccal mucous membrane which lines it internally. Branches of the Third Part. — ^The posterior dental artery arises from the internal maxillary as it is about to pass through the pterygo- raaxillary fissure into the spheno-maxillary fossa, and is sometimes associated with the infra-orbital artery at its origin. It descends upon the zygomatic surface of the superior maxilla, posterior to the malar process, and its principal branches traverse the posterior dental canals to supply the pulps of the upper molar teeth of one side. It also furnishes twigs to the mucous lining of the antrum of Highmore, and to the gum. The infra-orbital artery arises in the spheno-maxillary fossa, sometimes in common with the posterior dental. It passes through the spheno-maxillary fissure in company with the superior maxillary nerve, and traverses the infra-orbital groove and canal on the floor of the orbit, the accompanying nerve being now called the infra-orbital nerve. From this canal it emerges through the infra-orbital foramen on to the face, where it has been already described (see Index). The artery is accompanied by the infra- orbital vein. As the artery traverses the infra-orbital canal it furnishes (i) orbital branches to the structures on the floor of the orbit ; and (2) the middle and anterior dental arteries, which descend in the middle and anterior dental canals in the superior maxilla, in company with the corresponding nerv^es, to supply the pulps of the upper bicuspid, incisor, and canine teeth of one side, and the mucous lining of the antrum of Highmore. The descending palatine artery passes downwards in the posterior palatine canal, in company with the great or anterior descending palatine ner\'e, to the hard palate, where it passes forwards and inwards to the anterior palatine fossa. In this situation it furnishes a branch which ascends through the incisor canal, or canal of Stensen, to anastomose with the naso-palatine artery. As the artery i2o6 A MANUAL OF ANATOMY traverses the posterior palatine canal it gives off a posterior and an external branch, which accompany corresponding nerves in the posterior and external accessory palatine canals, and supply the soft palate and tonsil. The Vidian artery passes backwards through the Vidian canal in company with the Vidian nerve, and its branches are : (i) pharyngeal, to the upper part of the pharynx ; (2) Eustachian, to the Eustachian tube ; and (3) tympanic, to the tympanum. The pterygo-palatine artery, of small size, passes backwards through the pterygo-palatine canal, in company with the pharyngeal nerve, and is distributed to the upper part of the pharynx, the Eustachian tube, and the mucous lining of the corresponding sphenoidal air-sinus. The spheno-palatine artery enters the superior meatus of the nasal fossa through the spheno-palatine foramen. Its branches are distributed extensively on the outer wall of the nasal fossa, and supply the mucous membrane of the antrum, ethmoidal cells, and frontal air-sinus. One branch, called the naso-palatine artery, or artery of the septum, descends upon the septum to the incisor foramen, where it anastomoses with the ascending branch of the descending palatine artery. Pterygoid Plexus of Veins. — ^This is a large plexus which surrounds the external pterygoid muscle. Its tributaries correspond, for the most part, to the branches of the internal maxillary artery, and are chiefly as follows : the deep auricular, tympanic, two middle meningeal, inferior dental, masseteric, pterygoid, deep temporal, buccal, superior dental, infra-orbital, palp.tine, and spheno-palatine. The blood is conveyed away from the plexus by two veins, namely, the internal maxillary and the deep facial. The internal maxillary vein is a short vessel which issues from the posterior part of the plexus, and accompanies the first part of the internal maxillary artery. Opposite the neck of the inferior maxilla it joins the superficial temporal vein within the parotid gland to form the tempo ro-maxillary vein. The deep facial vein issues from the anterior part of the pterygoid plexus, and, passing downwards and forwards, it emerges from behind the mandibular ramus and masseter muscle, and joins the facial vein on the buccinator muscle. The pterygoid plexus establishes the following important connections superiorly : it com- municates with the intracranial cavernous sinus by means of emissary veins, which pass through the foramen ovale, foramen Vesalii, and foramen lacerum medium ; and it communicates with the inferior ophthalmic vein at the spheno-maxillary fissure. Internal Maxillary, Deep Facial, or Zygomatic Lymphatic Gland {LymphoglandulcB faciales profundce). — These glands lie upon the external pterygoid muscle. Their afferent vessels are derived from (i) the zygomatic and temporal fossae; (2) the orbit; (3) the palatal mucous membrane; (4) the nasal fossa, in part; (5) the cerebral dura mater; and (6) the tympanic cavity. Their efferent vessels pass to THE HEAD AND NECK 1207 (i) the intraparotid lymphatic glands, and {2) the superior deep cervical glands. Inferior Maxillary Nerve. — This is the third division of the fifth nerve. It is a mixed nerve, and consists of two roots — sensor^' and motor. The sensory root, which is of large size, arises from the Gasserian ganglion, and the motor root represents the entire motor root of the fifth nerve. Both roots leave the cranial cavity through the foramen ovale, and immediately after their exit they unite to form a mixed nerve, that is to say, a nerve composed of both sensory and motor fibres. This nerve is very short, and lies deeply in the zygomatic fossa, under cover of the external pterygoid muscle, where it gives off two branches, namely, a recurrent branch, and the internal pterygoid nerve. Thereafter it immediately breaks up into two parts, known as the anterior and posterior divisions. The recurrent branch enters the cranial cavity through the foramen spinosum, along with the middle meningeal artery, and divides into two branches — anterior and posterior. The anterior branch is distributed to the adjacent dura mater, and the posterior branch passes through the fissure between the petrous and squamous parts of the temporal bone, to be distributed to the mucous lining of the mastoid cells. The internal pterygoid nerve arises from the deep surface of the undivided inferior maxillary nerve, and passes downwards to enter the deep surface of the internal pterygoid muscle. Close to its origin it is intimately related to the otic ganglion. Anterior Division of the Inferior Maxillary Nerve. — This division is smaller than the posterior, and is principally motor in function, the only sensory branch furnished by it being the long buccal nerve. Its branches are as follows: (i) masseteric, furnishing the posterior deep temporal; (2) middle deep temporal; and (3) long buccal, giving off the external pterygoid and anterior deep temporal, after which it is purely sensory. The masseteric nerve passes upwards beneath the upper head of the external pterygoid muscle, where it furnishes the posterior deep temporal nerve. It then passes outwards over the upper border of the external pterygoid, and over the sigmoid notch of the lower jaw, behind the temporal muscle, to enter the upper part of the masseter on its deep surface. The deep temporal nerves are three in number — anterior, middle, and posterior. The antertor deep temporal nerve usually arises from the long buccal after it has emerged between the two heads of the extemcd pterj'goid. It passes upwards, superficial to the upper head of that muscle, and enters the anterior part of the temporal muscle on its deep surface. The middle deep temporal nerve is a direct branch of the anterior division of the inferior maxL[lar\', and it ascends beneath the external pterygoid to enter the middle part of the temporal muscle on its deep surface. The posterior deep temporal nerve springs from the masseteric nerve beneath the I208 A MANUAL OF ANATOMY upper head of the external pterygoid, and, passing upwards, it enters the posterior part of the temporal muscle on its deep surface. The long buccal nerve passes outwards between the two heads of the external pterygoid, and then downwards and forwards in contact with the inner surface of the temporal muscle at its insertion. Having emerged from underneath the mandibular ramus and anterior border of the masseter, it is received upon the outer surface Posterior Deep Temporal Nerve Masseteric Nerve, Auriculo -Tempo ral Nerve Facial Nerve — S^ Mylo-hyoid Nerve. Inferior Dental Nerve Anterior Deep Temporal Nerve .„ Long Buccal Nerve Short Buccal Nerve .. Lingual Nerve Mental Nerve Fig. 493. — The Nerves of the Temporal and Pterygo-maxillary Regions (HiRSCHFELD AND LeVEILL£). I, Temporal Muscle ; 2, External Pterygoid ; 3, Internal Pterygoid ; 4, Masseter ; 5, Buccinator. of the buccinator, where it communicates with the short buccal branches of the facial nerve to form the buccal plexus. Thereafter its terminal branches are distributed to the skin over the buccinator muscle and the mucous membrane which lines it. The long buccal nerve furnishes two branches, namely, the external pterygoid nerve and the anterior deep temporal nerve. The external pterygoid nerve is detached from it near its origin, and enters the external pterygoid muscle on its deep surface. The anterior deep temporal nerve arises from it after it has emerged between the two heads of the external THE HEAD AND NECK 1209 pterygoid. These two branches conduct away all the motor fibres from the long buccal ner\'e, which thereafter is entirely sensory. Posterior Division. — ^This division is larger than the anterior, and is almost entirely sensory, the only motor fibres which it con- tains being destined for the mylo-hyoid branch of the inferior dental nerve. Its branches are three in number, namely, (i) auriculo- temporal, (2) inferior dental, and (3) lingual (gustatory). Auriculo-temporal Nerve. — ^This nerve, which is sensory, arises by two roots, between which the middle meningeal artery ascends to the foramen spinosum. Thereafter the two roots join, and the nerve is directed backwards under cover of the external pterygoid muscle. Having passed close behind the temporo-mandibular joint to the interval between that joint and the auricle, it enters the upper part of the parotid gland. It then changes its course, and passes upwards through the upper part of the gland, after emerging from which it crosses tne zygoma and ascends close behind the superficial temporal artery to end in its terminal tem- poral branches. Branches of Communication. — (i) Each root of the auriculo- temporal nerve receives a small branch from the otic ganglion. These branches contain fibres of the glosso-pharyngeal nerve, through means of (a) its tympanic branch (Jacobson's nerve), (b) the tympanic plexus, and (c) the small superficial petrosal nerve, which latter is reinforced by a branch from the geniculate ganglion of the facial nerve. These glosso-pharyngeal fibres are destined for the parotid gland. (2) Two communicating branches pass to the temporo-facial division of the facial nerve in the parotid gland. Branches of Distribution. — (i) Articular branches enter the tem- poro-mandibular joint through the back part of the capsule. (2) Glandular branches are distributed to the parotid gland, to which they conduct fibres of the glosso-pharyngeal nerve. (3) Meatal branches, upper and lower, enter the meatus auditorius extemus between its cartilaginous and osseous parts, and supply the skin which lines it, the upper branch also giving twigs to the outer layer of the membrana t^Tnpani. (4) Anterior auricular branches are distributed to the skin of the tragus and the upper part of the outer surface of the auricle. The distribution of the : meatal and auricular branches explains why .pain, due to affections I of the lower teeth, may be referred to the ear canal and auricle. ! (5) The temporal branches are terminal. They accompany the I branches of the superficial temporal artery, and supply the skin of the temporal region as high as the vertex of the skull. They communicate with the temporal branches of the facial, and the temporal branch of t le temporo-malar from the superior maxillary nerve. Inferior Dental Nerve. — This nerve, though chiefly sensory, con- tains motor fibres, which, however, leave it in its mylo-hyoid branch. It passes downwards, being at first under cover of the external pterygoid muscle. After escaping from beneath that muscle, it I2IO A MANUAL OF ANATOMY descends upon the spheno-mandibular ligament and internal pterygoid muscle to the inferior dental foramen, through which it passes into the inferior dental canal, after having parted with its mylo-hyoid branch. The lingual nerve is anterior and internal to it, and the inferior dental artery is posterior and external to it. Within the dental canal the nerve is accompanied by the inferior dental artery, and, having arrived at the level of the mental foramen, it terminates by dividing into two branches, mental and incisor. Branches. — (i) The mylo-hyoid nerve is given off from the parent trunk just before it passes through the inferior dental foramen. It conducts away all the motor fibres from the parent trunk, and in company with the mylo-hyoid artery pierces the lower part of the spheno-mandibular ligament, and then passes downwards and forwards in the mylo-hyoid groove of the inferior maxilla. The nerve and artery are maintained in position within this groove by an expansion from the lower part of the spheno-mandibular liga- ment, which is attached to the lips of the groove. Thereafter the nerve passes forwards on the inferior surface of the mylo-hyoid muscle, under cover of the superficial part of the submaxillary gland. Having furnished twigs to the mylo-hyoid muscle, it ter- minates in the anterior belly of the digastric. (2) The dental branches arise from the parent trunk, whilst it traverses the inferior dental canal. They communicate with each other to form a delicate plexus, from which branches are given oft to the pulps of the lower molar and bicuspid teeth, as well as to the adjacent part of the gum. The pulp-branches correspond in number to the fangs of the teeth, and each enters through a minute opening on the extremity of the fang. (3) The mental nerve is one of the two terminal branches. It emerges from the inferior dental canal through the mental foramen. For its distribution, see p. 1177. (4) The incisor nerve represents the termination of the inferior dental. It commences at the level of the mental foramen, and passes almost as far as the middle line. Its dental branches com- municate in a plexiform manner, and supply the pulps of the lower canine and incisor teeth, as well as the adjacent portion of the gum. Lingual Nerve. — This nerve is sensory. It descends under cover of the external pterygoid muscle, lying anterior and internal to the inferior dental nerve. Whilst under cover of that muscle it receives near its origin the chorda tympani nerve, which joins it from behind at an acute angle, in a direction downwards and for- wards, after emerging from the tympanum through the iter chordae anterius, or canal of Huguier. After issuing from beneath the external pterygoid muscle the lingual nerve j^asses downwards and forwards between the internal pterygoid muscle and the mandibular ramus, and over the mandibular fibres of the superior constrictor muscle. Below the level of the third lower molar tooth it lies im- mediately beneath the mucous membrane of the mouth, and is THE HEAD AND NECK here accessible for operative purposes. Thereafter it crosses the stylo-glossus, and passes forwards over the hyo-glossus close to the side of the tongue. Upon the latter muscle it describes a slight curve with the convexity downwards. It then passes beneath the mylo-hyoid muscle, where it lies above the deep part of the sub- maxillary gland and Wharton's duct, and has the submaxillary ganglion suspended from it. Finally, having crossed Wharton's duct from above downwards, it continues its course as far as the tip of the tongue. As it passes along the side of the tongue the nerve is immediately beneath the mucous membrane. Branches of Communioation. — (i) Chorda tympani (sensory of facial) ; (2) two branches to the submaxillary ganglion ; and (3) one Sixth Nerve Internal Carotid Artery with • Sympathetic Plexuses ; Facial Nerve in Aqueduct of Fallopius y Superior Maxillary Nerve Internal Carotid .\rtery Third Nerve ; ■■ ■. I Optic Nerve Chorda Tympani ^ Glosso-pharyngeal T Inferior Dental-- -J- Spinal Accessory— y — Mylo-hyoid Hypoglossal Pneumogastric Supra-orbital Nerve Supratrochlear Frontal Infra trochlear Nasal Lachrymal (cut) Ophthalmic Infra-orbital Meckel's Ganglion Anterior Dental --Middle Dental ~-^ J- Posterior DentaJ ' Otic Ganglion >^ "■ Lingual Submaxillary Ganglion Ner\-e to Thyro-hyoid Muscle Fig. 494. — General View of the Fifth Cranial Nerve (Hirschfeld and Leveille). I, Sterno-cleido-mastoid ; 2, Mylo-hyoid ; 3, Internal Pterygoid. or two filaments to the hypoglossal nerve at the anterior border of the hyo-glossus muscle. Branches of Distribution.— (i) Buccal, to the mucous membrane of the floor of the mouth and of the gums ; (2) glandular, to the sublingual gland ; and (3) lingual, to the mucous membrane of the sides and dorsum of the tongue over its anterior two-thirds. These lingual branches pierce the muscular tissue of the tongue, and are destined chiefly for the conical and fungiform papillae. Otic Ganglion. — ^The otic ganglion, or Arnold's ganglion, is a small oval body, of a pinkish colour, which is situated close to the foramen ovale, on the deep surface of the inferior maxillary nerve at the place of origin of the internal pterygoid nerve, with which it is closely connected. It has the middle meningeal artery I2I2 A MANUAL OF ANATOMY behind it, and the cartilaginous part of the Eustachian tube on its inner side. The ganghon has three roots. One root (motor- sensory) is derived from the internal pterygoid nerve, and conveys to the ganglion motor fibres, and probably also sensory fibres. A second root (sensory-motor) is represented by the small superficial petrosal nerve, which joins the back part of the ganglion. This root also conveys to the ganglion sensory and motor fibres. The sensory fibres come from the glosso-pharyngeal, through means of (i) the tympanic nerve or nerve of Jacobson, (2) the tympanic plexus, and (3) the small superficial petrosal. The motor fibres conveyed by this root come from the geniculate ganglion of the facial nerve, through means of the branch which that ganglion gives Nasal Nerve Frontal Nervl Lachrymal Nerve, \ Ciliary Ganglion , \ * Internal Carotid Artery \ Lachrymal Gland Ciliary Nerves Ophthalmic Nerve Gasserian Ganglion ^- Great Superficial Petrosal Ner\-e ,, Branch to Small Sup. Pet. N Facial Nerve in Aqueduct ^ of Fallopius Posterior Auricular Nerve Facial Nerve Internal Carotid Artery /' Chorda Tympani Nerve '' / / ,' Inferior Maxillary Nerve / / Inferior Dental Nerve ' / Otic or Arnold's Ganglion' Lingual Nerve Branch of Third Nerve to Inferior Oblique Sup. Maxillary Nerve Meckel's Ganglion Naso-palatine Nerve Ant. Palatine Nerve Submaxillary Ganglion Fig. 495. Sublingual Ganglion -Scheme of the Fifth Cranial Nerve and its Ganglia (HiRSCHFELD AND LeVEILLE). to join the small superficial petrosal nerve. The third root (sympa- thetic) comes from the sympathetic plexus around the middle meningeal artery. Branches — (i) Of Communication. — (a) Two branches pass to the auriculo-temporal nerve, one to each root. These convey to that nerve glosso-pharyngeal fibres which are destined for the parotid gland, (b) A branch joins the chorda tympani. (c) A branch joins the Vidian nerve. (2) Of Distribution. — Muscular branches are given to the tensor tympani and tensor palati. Submaxillary Ganglion.— This ganglion is of small size, and is connected with the lingual nerve in the submaxillary region. It is situated upon the upper part of the hyo-glossus muscle, between the lingual nerve and the deep part of the submaxillary gland, and under cover of the posterior part of the mylo-hyoid muscle. It is THE HEAD AND NECK 1213 suspended from the lingual nerve by two connecting branches, posterior and anterior, which stand apart from each other. The posterior connecting branch, sometimes broken up into two or three twigs, conveys to the ganglion sensory fibres from the chorda t^inpani (sensory portion of the facial) and lingual nerves, the latter being a branch of the inferior maxillary division of the fifth cranial nerve. The anterior connecting branch represents fibres passing front the ganglion to the lingual nerve. The posterior branch consists of fibres which are derived from the chorda tympani of the facial, and from the lingual nerve. This posterior branch may exist as two twigs. The anterior branch Pars Intermedia of Wrisberg Geniculate Ganglion Facial Nerve Nerve to Stapedius. Chorda Tympani Great Superficial Petrosal Small Superficial Petrosal . Great Deep Petrosal Great Superf. Petrosal Vidian Nerve Spheno-palatine ^ Nerves Meckel's Ganglion Descending Palatine Nerves Otic Ganglion Arnold's Ner\e _ / Internal Carotid .Artery and .Sympath. Plexus Pneumogastric Tympanic or Jacobson's Nerve Petrous Ganglion of Glosso-pharyngeal Fig. 496 — The Facial Nerve in the Aqueduct of Fallopius, etc. (HiRSCHFELD AND LeVEILL£). may be regarded as an offset from the ganglion to join the lingual. The sympathetic root of the ganglion is derived from the plexus on the cervical portion of the facial artery. Roots of the Submaxillary Ganglion. Secretory. Sensory. Sympathetic. From chorda tjinpani From lingual. From plexus on cervical portion o' facial. of facial artery. The submaxillary ganglion has three roots— secretor>% sensory and sympathetic. The secretory root comes from the chorda tympam ner\'e; the sensory root from the Ungual nerv^e; and the sympathetic root from the plexus on the cervical portion of the facial artery. The secretory and sensory roots represent the pos- terior connecting branch of the ganglion. Branches.— These proceed from the lower and anterior parts of the ganghon, and are as follows: (i) glandular to the submaxiUary I2I4 A MANUAL OF ANATOMY gland; (2) branches to Wharton's duct; (3) buccal, to the mucous membrane of the floor of the mouth ; and (4) an anterior connecting branch, which passes to the lingual nerve. The anterior connecting branch probably consists of both chorda tympani and Hngual fibres, and it accompanies the lingual nerve to the tongue. It furnishes twigs to the sublingual gland, and a small ganglion associated with these twigs has been described under the name of the sublingual ganghon. Summary of the Inferior Maxillary Nerve — i. Cutaneous Distribution. — It supplies (i) a portion of the dura mater, and the mucous membrane of the mastoid cells ; (2) the skin over the greater part of the temporal region ; (3) the skin of the external auditory meatus, and the outer surface of the membrana tympani ; (4) the skin of the tragus, and of the upper part of the outer surface of the auricle ; (5) the skin over the body of the inferior maxilla, including the skin of the chin and lower lip, as well as the mucous membrane of the lower lip ; (6) the mucous membrane of the floor of the mouth, and the lower giim ; and (7) the sides and, dorsum of the tongue over its anterior two-thirds. 2. Articular Distribution. — It supplies the temporo-mandibular joint. 3. Dental Distribution. — It supplies the pulps of all the lower teeth of one side, and the mucous membrane of the outer surface of the lower gum of one side. 4. Glandular Distribution. — It gives branches to the parotid, submaxillary, and sublingual glands. 5. Muscular Distribution. — It supplies (i) the muscles of mastication, namely, the masseter, temporal, external pterygoid and internal pterygoid ; (2) the mylo-hyoid and anterior belly of the digastric ; and (3) the tensor palati and tensor tympani. The Temporo-mandibular Joint. The temporo-mandibular (temporo-maxillary) joint belongs to the class diarthrosis, and to the subdivision condylarthrosis. The articular surfaces are (i) the anterior part of the glenoid fossa, in front of the fissure of Glaser, and (2) the condyle of the mandible or inferior maxilla. Ligaments. — ^These are as follows : the external lateral, capsular, internal lateral, stylo-mandibular, and interarticular fibro -cartilage. The external lateral ligament is a short strong bundle of fibres, which is attached above to the tubercle and adjacent portions of the outer surface and lower border of the zygoma, and below to the condylar tubercle and the outer and back part of the neck of the mandible. Its fibres are directed obliquely downwards and back- wards. This ligament forms the external portion of the capsular ligament. The capsular ligament consists of scattered fibres which form a thin loose investment to the joint on its anterior, internal, and posterior aspects, being completed on the outer aspect by the external lateral ligament. The internal lateral, or spheno-mandibular, ligament is a long flat band, which stands off from the joint, and therefore has no direct relation to it. It is somewhat triangular, being narrow above and broad below. Superiorly it is attached to the spinous process of the sphenoid bone, and interiorly to the lingula and the inner margin of the inferior dental foramen of the mandible. Its fibres are directed downwards and slightly forwards. Superiorly it is covered by the external pterygoid muscle ; subsequently the first THE HEAD AND NECK I2I5 part of the internal maxillan,'^ arter^'- rests upon it, and separates it from the neck of the mandible; and inferiorly the inferior dental vessels and ner\e and the auriculo-temporal nerve intervene between it and the ramus of the mandible. At its lower attachment it is spread over the upper end of the mylo-hyoid groove, and is here pierced by the mylo-hjoid nerve and artery. This ligament is sometimes spoken of as the long internal lateral ligament, in con- tradistinction to the internal portion of the capsule, which is regarded as the short internal lateral ligament. The spheno-mandibular ligament represents a portion of the fibroas invest- ment of Meckel's cartilage. The stylo-mandibular ligament is a stout process of the deep cervical fascia, which extends from the styloid process of the temporal bone near its tip to the angle and adjacent portion of the posterior border of the ramus of the mandible. Superiorly it gives origin to a few fibres of the styloglossus, and inferiorly it is implanted between the masseter and internal pterygoid muscles. It separates the sub- maxillary gland from the lower portion of the parotid gland. Capsular Ligament Styloid Process Zygoma Coraooid Process Spheno-mandibular (Internal Lateral) Ligament Stylo-mandibalar Ligament— ~— — Mylo-hyoid Groove Fig. 497. — The Temporo-Mandibolar Joint (Internal View). The interarticular fibro-cartilage is an oval plate which is inter- posed between the t\vo articular surfaces. It is thinnest at the centre, where it is occasionally perforated, and thickest posteriorly. Its superior surface is concavo-convex from before backwards, in adaptation to the convexity of the eminentia articularis and the concavity of the glenoid fossa. Its inferior surface is concave, and fits upon the condyle of the mandible. Its circumference is con- nected with the capsular ligament, and anteriorly it gives partial I2l6 A MANUAL OF ANATOMY insertion to the external pterygoid muscle. It divides the joint into two compartments, upper and lower, which are usually distinct. The synovial membranes are two in number, upper and lower, one being above and the other below the plate of fibro-cartilage. The upper synovial membrane is larger and looser than the lower, and, when the plate of fiibro-cartilage is perforated at the centre, the two synovial membranes are continuous through the perforation. Arterial Supply. — ^The superficial temporal artery chiefly. Nerve-supply. — ^The auriculo- temporal nerve and offsets from the masseteric nerve. Movements. — These are as follows : (i) depression, (2) elevation, (3) pro- traction, (4) retraction, and (5) lateral movements. There being two divisions of the joint, upper and lower, different movements occur in each. The move- ment in the upper compartment is of a gliding character, whilst in the lower compartment it is of a ginglymoid or hinge character. When the mandible is depressed, as in opening the mouth, the condyle and the plate of fibro- cartilage move forwards on to the eminentia articularis. In cases of over- depression, as in violent yawning, or forcing too large a body into the mouth, the condyle is apt to slip over the eminentia articularis into the zygomatic fossa, and, when this takes place, dislocation of the mandible is the result. Meatus Auditorius Externus Condyle (in section)i Coronold Process Mastoid Process Styloid Process Fig. 498. — The Temporo-Mandibular Joint Opened (External View). The movement of forward gliding on the part of the condyle and plate of fibro-cartilage during depression takes place in the upper compartment "of the joint. Another movement, however, of a ginglymoid or hinge character is taking place in the lower compartment of the joint, namely, between the condyle and the interarticular plate. This consists in the condyle rotating on the under surface of the plate round a transverse axis. When the mandible is elevated, as in shutting the mouth, the changes which occur in both compartments of the joint are the reverse of those just described as taking place in depression. The condyle and fibro-cartilage glide backwards into the glenoid cavity, and at the same time the condyle rotates back to its previous position. In protraction, as when the lower incisors are protruded beyond the upper, and in retraction, the movement mainly takes place in the upper compartment of the joint, and consists in the condyle and plate of fibro- cartilage gliding forwards and backwards. When these movements are per- THE HEAD AND NECK 1217 formed alternately on each side the lateral oblique movements, as in grinding or chewing, take place, and the condyle and iibro-cartilage of one side move forwards and backwards, whilst the other condyle and fibro-cartilage move in the opposite direction. During these movements oblique rotation is taking place in the lower compartment of the joint. Muscles Concerned in the Movements. — Depression is effected by the platysma myoides, mylo-hyoid, anterior belly of the digastric, and genio- hyoid muscles ; and elevation by the anterior fibres of the temporal, masseter, and internal pterygoid muscles. Protraction is produced by the external pterygoid, the superficial fibres of the masseter, and slightly by the internal pterygoid ; and retraction by the posterior fibres of the temporal, and the deep fibres of the masseter. The grinding movement is effected by the external pterygoid muscles acting alternately. The Superior Maxillary Nerve. The superior maxillary nerv'e is the second division of the fifth cranial nerve, and in size is intermediate between the inferior maxil- lary and the ophthalmic. It is entirely sensory, and arises from the Gasserian ganglion. Its course is forwards to the foramen rotundum, by which it leaves the cranial cavity. Thereafter it enters the posterior part of the spheno -maxillary fossa, and then crosses the upper part of that fossa to the spheno-maxillary fissure, through which it passes on to the floor of the orbit. It now takes on the name of the infra-orbital nerve, and traverses the infra-orbital groove, and then the infra-orbital canal, on the floor of the orbit. Finally, it emerges from this canal through the infra- orbital foramen, under cover of the levator labii superioris, and ends in its terminal branches. The course of the superior maxillary nerve (and its continuation under the name of the infra-orbital ner\^e) is almost directly forwards, there being a slight inclination outwards. Branches. — ^These are as follows : Intracranial. In Infra-orbital Canal. Recurrent meningeal. Middle superior dental. Anterior superior dental. In Spheno-maxillary Fossa. Facial. Orbital or temporo-malar. Inferior palpebral. Spheno-palatine. Lateral nasal. Posterior superior dental. Superior labial. The recurrent meningeal branch supplies the dura mater of the middle cranial fossa. The orbital or temporo-malar nerve is the first branch of the superior maxillary in the spheno-maxillary fossa. It arises from its upper surface, and enters the orbit through the spheno-maxillary fissure. For its further course, see p. 1082. The spheno-palatine nerves are two in number. They arise from the lower aspect of the parent trunk, and, after a very short de- scending course, they end for the most part in Meckel's ganglion, to which they convey sensory fibres, and of which they are the 77 1218 A MANUAL OF ANATOMY sensory roots. Many of their fibres, however, pass clear of the grey matter of the ganglion, and are prolonged into the nasal and de- scending palatine branches of the ganglion. The posterior superior dental nerve arises from the superior maxillary as it is about to pass through the spheno-maxillary fissure, and soon divides into two branches, which sometimes arise separately. They descend in grooves on the zygomatic surface of the superior maxilla, in company with branches of the posterior dental artery, and give off branches to the gum and con- tiguous part of the mucous membrane of the cheek. Thereafter they traverse the posterior dental canals, and within the substance of the bone they communicate with each other and with the middle superior dental nerve to form a delicate plexus, from which branches are given off to the pulps of the three upper molar teeth. Slender filaments are also furnished to the mucous membrane lining the antrum of Highmore. The middle superior dental nerve arises from the main trunk as it lies in the infra-orbital groove near the spheno-maxillary fissure. It descends, in company with the middle dental artery, in the middle dental canal of the superior maxilla. Its branches communicate with each other, and with the posterior superior and anterior superior dental nerves within the substance of the bone, to form a delicate plexus, from which branches are given to the pulps of the upper two bicuspid teeth and to the gum. This nerve also furnishes delicate filaments to the mucous membrane lining the antrum of Highmore. Two enlargements are described in connec- tion with the middle superior dental nerve. One is situated at its communication with the posterior superior dental nerve, and is known as the ganglion of Valentin ; and the other at its communi- cation with the anterior superior dental, this one being known as the ganglion of Bochdalek. The anterior superior dental nerve arises from the infra-orbital nerve near the front part of the infra-orbital canal, and descends, in company with the anterior dental artery, in the anterior dental canal. Its branches communicate with each other and with the middle superior dental nerve to form a delicate plexus, from which branches are given to the pulps of the upper canine and incisor teeth. This nerve also furnishes delicate filaments to the mucous membrane lining the antrum of Highmore, and a nasal branch, which enters the nasal fossa and supplies the mucous membrane of the anterior part of the inferior meatus and adjacent portion of the inferior concha. The facial branches of the infra-orbital nerve, namely, inferior palpebral, lateral nasal, and superior labial, have been already described, see p. 1177. It is to be noted that there are three superior dental nerves, right and left, the posterior being a branch of the superior maxillary, and the middle and anterior being branches of the infra-orbital ; whilst there is only one inferior dental nerve, which is a branch of the inferior maxillary. THE HEAD AND NECK 1219 Spheno-palatine Ganglion. — This is also called Meckel's ganglion. It is a small triangular, somewhat reddish body, situated on the upper part of the spheno-maxillary fossa, close to the spheno- palatine foramen, which leads through the inner Wall of the fossa to the superior meatus of the nasal fossa. It is suspended from the superior maxillary nerve by some of the fibres of the two spheno-palatine branches of that nerve, many fibres of these two branches, as stated, passing clear of the grey matter of the ganglion into its nasal and descending palatine branches. The fibres con- veyed to the grey matter of the ganglion by the two spheno- palatine nerves represent its sensory root or roots. The ganglion has sensory and sympathetic roots, but no motor root. The sensory roots are derived from two sources — superior Suoerior Nasal Nerves Olfactory Filaments I Spheno-palatine Nerves from Superior Maxillary ij Vidian Nerve Internal Carotid Arterj- Great Superficial Petrosal Nerve Great Deep Petrosal Nervo Meckel's Ganglion Post. Descending Palatine Nei vc Ext. Descending Palatine Nerve — Ant.Descending Palatine Nerve Inferior Nasal Nerves Fig. 499. — Nerves of the Nasal Fossa, and the Spheno-palatine or Meckel's Ganglion, with its Branches (Internal View) (Hirsch- feld and Leveilt.e). maxillary and facial. The superior maxillary sensory root-fibres form two bundles, and represent portions of the two spheno-palaiine nerves, by which the ganglion is suspended from the trunk of the superior maxillary nerve in the spheno-maxillary fossa. The facial sensory root-fibres are represented by the great superficial petrosal nerve, which is a branch of the ^niculate ganglion of the facial nerve. The sympathetic root is formed by the great deep petrosal nerve from the carotid plexus of the sympathetic. The facial sensory root (great superficial petrosal) and the sym.- pathetic root (great deep petrosal) join to form the Vidian nerve in the foramen lacerum medium. After traversing the Vidian canal from behind forwards, the Vidian nerve enters the spheno-maxillary fossa and joins the back part of Meckel's gangUon. In the Vidian I220 A MANUAL OF ANaTOMY canal the Vidian nerve gives off one or two nasal branches, which pass through the floor of the canal, and are distributed to the mucous membrane of the posterior part of the roof of the nasal fossa and adjacent part of the septum. Branches of the Spheno-palatine Ganglion. — ^These are arranged in four sets, and are as follows : Ascending. Posterior. Internal. Descending. Orbital. Pharyngeal or pterygo-palatine. Vidian. Superior nasal. Naso-palatine. Great or anterior palatine. Small or posterior palatine. External palatine. Ascending Branches. — These are called the orbital branches. They are two or three in number, and enter the orbit through the spheno -maxillary fissure, to be distributed to the periosteum. They have been described by Luschka as sending filaments through the inner wall of the orbit to supply the mucous membrane of the posterior ethmoidal cells and the sphenoidal air-sinus. Posterior Branches. — ^These are the pharyngeal and the Vidian nerves. The pharyngeal nerve passes backwards in the pterygo- palatine canal, along with the pterygo-palatine artery, and is dis- tributed to the mucous membrane of the upper part of the pharynx in the region of the Eustachian orifice. The Vidian nerve (just described), if it is to be regarded as a posterior branch of the ganglion, establishes a communication between it and (i) the geniculate ganglion of the facial, through means of the great superficial petrosal, and (2) the carotid plexus of the sympathetic, through means of the great deep petrosal. Internal Branches. — ^These are the superior nasal and naso- palatine nerves. The superior nasal nerves are of small size, and derive some of their fibres from the spheno-palatine nerves. They are about six in number, and, springing from the inner part of the ganglion, they enter the superior meatus of the nose through the spheno-palatine foramen. They supply the mucous membrane of the superior and middle conchae, the superior meatus, the posterior ethmoidal cells, the middle meatus, and the upper and back part of the septum. The naso-palatine nerve {nerve of Cotunnius) enters the nasal fossa along with the superior nasal nerves. It crosses the roof of the fossa, and then passes downwards and forwards upon the septum, lying in the groove on the lateral surface of the vomer. Having arrived at the region of the incisor crest, the left naso-palatine nerve descends through the anterior foramen or canal of Scarpa, and the right descends through the posterior. Having reached the anterior palatine fossa in this manner, the two nerves communicate in a plexiform manner, and delicate filaments are furnished to the mucous membrane of the hard palate behind the incisor teeth. In this situation communications are established with the great or anterior descending palatine nerve of each side. As the naso- i THE HEAD AND NECK 1221 palatine nerve traverses the groove on the lateral surface of the vomer, it furnishes twigs to the mucous membrane of the nasal septum, and in this part of its course it is accompanied by the naso- palatine artery (artery of the septum) ; but this artery does not accompany it through the foramen or canal of Scarpa. Descending Branches. — ^These are the great or anterior, the small or posterior, and the external palatine nerves. They arise from the lower part of the ganglion, usually by a common trunk, and they derive some of their fibres from the spheno-palatine nerves. The great or anterior palatine nerve descends in the posterior pala- tine canal, and escapes from it through the posterior palatine foramen. Thereafter it divides into branches which pass forwards and inwards, occupying grooves on the hard palate, to the mucous membrane and glands of which, as well as to the mucous membrane of the upper gum on its inner aspect, they are distributed. In the region of the anterior palatine fossa this nerve communicates with the naso-palatine nerve. As it descends in the posterior palatine canal, it furnishes two inferior nasal nerves, which enter the nasal fossa, and are distributed to the mucous membrane over the inferior concha, except anteriorly, and to that of the adjacent por- tion of the inferior meatus. The small or posterior palatine nerve descends in the posterior accessory palatine canal, after emerging from which it is distributed to the mucous membrane of the soft palate and tonsil. It may furnish branches to the levator palati and azygos uvulae muscles, the fibres of these branches being derived from the geniculate ganglion of the facial through means of the great superficial petrosal, which contributes to the formation of the Vidian nerve, and conveys motor fibres to Meckel's ganglion. The two muscles in question, however, are most probably supplied by the bulbar part of the spinal accessory nerve through the pharyngeal plexus. The external palatine nerve descends through the external accessory palatine canal, after emerging from which it is distributed to the mucous membrane of the outer portion of the soft palate and tonsil. Summary of the Superior Maxillary Nerve and Meckel's Ganglion — I. Cutaneous Distribution. — (i) The skin of the anterior part of the temporal region, and over the malar bone ; (2) the skin from the lower eyelid down to the upper lip, including the skin of the side of the nose ; (3) the mucous membrane of the naso-pharynx in the vicinity of the Eustachian orifice ; (4) the mucous membrane of the nasal fossa ; (5) the mucous membrane of the antrum of Highmore ; (6) the mucous membrane of the soft palate and tonsil ; and (7) the mucous membrane of the hard palate, with its glands, and that of the inner surface of the upper gum. 2. Dental Distribution. — The pulps of all the upper teeth of one side, as well as the mucous membrane of the outer surface of the upper gum. In addition to the foregoing, the superior maxillary nerve supplies the periosteum of the orbit, and the dura mater of the middle cranial fossa. Deep Dissection of the Neck. Stylo-pharyngeus — Origin. — ^The base of the styloid process of the temporal bone on its inner aspect. 1222 A MANUAL OF ANATOMY Insertion.— {i) The superior and posterior borders of the ala of the thyroid cartilage, and (2) the lateral Wall of the pharynx, its fibres blending with those of the palato-pharyngeus and middle constrictor muscles. Nerve-supply. — ^The glosso-phar3mgeal nerve. The muscle is directed downwards and inwards. Action. — To elevate the pharynx and larynx. The muscle passes between the superior and middle constrictor muscles. The glosso -pharyngeal nerve lies at first along its lower border, and then crosses over it on its way to the posterior part of the tongue. Internal Carotid Artery. — ^The internal carotid artery is one of the terminal branches of the common carotid. It commences on a level with the upper border of the thyroid cartilage, and passes vertically upwards to the under surface of the petrous part of the temporal bone. Here it enters the carotid canal within the pars petrosa, and, after traversing this canal, it enters the cranial cavity. The vessel is divided into three parts — extracranial or cervical, petrous, and intracranial or cavernous. Extracranial or Cervical Part. — ^This part of the vessel extends from the level of the upper border of the thyroid cartilage to the foramen caroticum on the inferior surface of the petrous part of the temporal bone. Its coruse is vertically upwards, and at first it lies in the carotid triangle, where it is placed external to, and behind, the external carotid artery. Relations — Anterior. — ^This part of the vessel is comparatively superficial, being covered by the integument, platysma myoides, and stemo-cleido-mastoid, the latter overlapping it. After leaving the carotid triangle the artery becomes deeply placed, and passes beneath the posterior belly of the digastric and stylo-hyoid muscles, parotid gland, styloid process, and stylo -pharyngeus muscle. In this part of its course the vessel is crossed by the hypoglossal, glosso-pharyngeal, and pharyngeal branch of the pneumogastric, nerves, and by the occipital and posterior auricular arteries. The relation of the artery to the external carotid here undergoes a change. The level where the change takes place is as the internal carotid passes beneath the styloid process of the temporal bone, and the change consists in the external carotid taking up a position directly anterior to the internal carotid. The two arteries are, however, separated from each other by the following structures : (i) the styloid process ; (2) the stylo-pharyngeus muscle ; (3) the glosso-pharyngeal nerve ; and (4) the pharyngeal branch of the pneumogastric nerve. Posterior. — ^The rectus capitis anticus major, the superior cervical ganglion of the sympathetic, and the superior laryngeal branch of the pneumogastric nerve. External. — ^The internal jugular vein and pneumogastric nerve, the nerve being on a plane posterior to both artery and vein. These three structures are still surrounded by a sheath which is an upward extension of the carotid sheath, previously described. Close to the THE HEAD AND NECK 1223 base of the skull the glosso-pharyngeal, spinal accessory, and h>-po- glossal nerves lie between the internal carotid artery and the internal jugular vein. The glosso-pharyngeal nerv^e soon passes forwards superficial to the artery, the spinal accessory nerve passes back- wards superficial to the vein, and the hypoglossal nerve passes forwards superficial to the artery at the lower border of the posterior belly of the digastric muscle. Internal. — ^The ascending pharyngeal artery, the lateral wall of the pharynx, the tonsil, and the superior laryngeal nerve. Development. — The internal caxotid artery is developed from the third arterial arch and the part of the dorsal aorta above it. The Glosso-pharyngeal Nerve. The glosso-phar\Tigeal or ninth cranial nerve is a mixed nerve, consisting of both afferent or sensory and efferent or motor fibres. It emerges from the cranial cavity through the middle compartment of the jugular foramen, along with the pneumogastric and spinal accessory nerves, but enclosed in a separate sheath of the dura mater, and lying on the outer side of, and anterior to, these two nerves. In passing through the jugular foramen, the nerve presents two ganglia, the upper one, which is small and situated in the upper part of the foramen, being called the jugular ganglion ; and the lower one, which is rather larger, being called the petrous ganglion. The latter is about \ inch in length, and lies in the lower part of the foramen, where it occupies a groove on the petrous portion of the temporal bone. After emerging from the jugular foramen, the nerve at first descends between the internal carotid artery and internal jugular vein, being external to the line of the pneumogastric nerve. It then passes downwards and forwards in front of the internal carotid artery, and under cover of the styloid process, stylo- pharyngeus muscle, and external carotid artery. It next cun^es round the lower border of the stylo-pharyngeus, and crosses its superficial surface in a forward direction. Finally, it passes beneath the hyo-glossus muscle, and so reaches the posterior third of the tongue, where it divides into its terminal branches. The jugular ganglion, as stated, is very small, and involves only a few of the fibres of the nerve, the other fibres passing clear of, but close to, the ganglion, and being continued into the nerve beyond it. This ganglion neither gives nor receives any branches, and is sometimes absent. The petrous ganglion, unlike the jugular, involves all the fibres of the nerve, and it furnishes connecting branches and the t5mipanic nerve. Branches of the Glosso-pharyngeal Nerve — i. From the Petrous Ganglion — {a) Branches of Communication. — ^These are three in number, as follows : one to the superior cervical ganglion of the sympathetic ; one to the auricular branch of the ganglion of the root of the pneumogastric ; and one to the ganglion of the root of the pneumogastric. 1224 A MANUAL OF ANATOMY (b) Branch of Distribution. — ^This is called the tympanic nerve, or nerve of Jacobson. After leaving the petrous ganglion, it ascends, in company with the tympanic branch of the ascending pharyngeal artery, through the tjnnpanic canaliculus. In this way it enters the tympanic cavity at the junction of the inner wall and floor, and ascends upon the inner wall. Being joined by the carotico- tympanic branch of the carotid plexus of the sympathetic, it breaks up into branches which occupy grooves upon the promon- tory, and form the tympanic plexus. From this plexus the tym- panic nerve emerges under the name of the small superficial petrosal nerve, which leaves the tympanic cavity and traverses a minute canal in the petrous bone, passing in its course beneath the upper portion of the canal which lodges the tensor tympani muscle. Whilst in this canal, it is joined by a communicating branch from the geniculate ganglion of the facial nerve. It emerges from the canal through the accessory hiatus on the superior surface of the petrous bone, which is external to the hiatus Fallopii, and then passes forwards and inwards beneath the dura mater. Thereafter it passes through the canaliculus innominatus, when present, or through the fissure between the pars petrosa and great wing of the sphenoid, or sometimes through the foramen ovale, into the zygo- matic fossa, where it joins the otic ganglion, to which it conducts glosso-pharyngeal and facial fibres. For a description of the tympanic plexus, see Index. 2. From the Trunk of the Nerve. — (i) A communicating branch sometimes passes from the nerve a little below the petrous ganglion to join the digastric branch of the facial nerve. (2) A carotid branch passes to the sympathetic plexus on the internal carotid artery. (3) Pharyngeal Branches. — ^These are about four in number. Three of them unite, over the middle constrictor of the pharynx, with the subdivisions of the phar5mgeal branch of the ganglion of the trunk of the pneumogastric, and with branches of the superior cervical ganglion of the sympathetic, to form the pharyngeal plexus. The other pharyngeal branch pierces the superior constrictor, and is distributed to the mucous membrane of the upper part of the pharynx. (4) A muscular branch to the stylo-pharyngeus muscle, some of the fibres of which pierce the muscle to supply the mucous membrane of the pharynx. (5) Ton- sillar branches are given off near the tongue, which are distributed to the tonsil and the anterior and posterior pillars of the fauces. (6) Lingual or Glossal Branches. — Under cover of the hyo-glossus muscle, the terminal part of the nerve divides into two branches, dorsal and lateral. The dorsal branch passes to the dorsum of the tongue, and is distributed to the circum vallate papillae and the mucous membrane over the posterior third, extending as far back as the front of the epiglottis. The lateral branch is distributed to the mucous membrane of the side of the tongue over about its posterior half. THE HEAD AND NECK 1225 Auriculotemporal Nerve Facial Nerve ; Posterior Auricular Nerve •. •• Glosso-pharyngeal N^rve Spinjl Accessory Nerve Great Occipital Nerve Hj-poglossal Nerve \ Sup. Cer\'ical Symp. Ganglion External Carotid Artery Internal Carotid Artery Sjinpathetic Cord Lin. Car. Art. and Symp. Plexus Phrenic Ner\-e Right Ansa Vieusseni First Thoracic Ganglion Right Posterior — Pulmonary Plexus Right Azygos Vein Vascular Brandi Intercostal Vessels/ ' ? and Nerve \ Ramus Communicans Sympathetic Gangliated Cord Small Splanchnic Ner\-e. Great Splanchnic Ne; Least Splanchnic Nerve^-W Hypoglossal Nerve ] Superior Laryngeal Nerve Vagus Nerve Middle Cer\-ical Sympathetic Ganglion Recurrent Laryngeal Nerve Cardiac Branches of Vagns Phrenic Nerve :|. R: -t of Right Lung Right Vagus Nerve on CEsophagus -xus Guls Liver (cut) -- Left Vagus Nerve ^::7^?^^^^^^~^^^^^"'l">g Aorta ---5: — ^ -—-^^^-^ Thoracic Duct 1 Branches of Vagns f on Stomach •jj — Xight Semilunar Ganglion Epigastric Plextis Suoerior Mesenteric .Artery and Plexus Renal Artery and Plexus Abdominal Aorta S.V.C. Superior Vena Cava Fig. 500.— Nerves of the Right Side of the Face, Neck, and Thorax (HiRSCHFELD AND LeVEILlS). 1226 A MANUAL OF ANATOMY Summary of the Glosso-pharyngeal Nerve — i. Cutaneous Distribution. — It supplies (a) the mucous membrane of the tympanum, the posterior third of the tongue, the pillars of the fauces, and the pharynx ; and (b) the tonsil. 2. Muscular Distribution. — It supplies the stylo-pharyngeus. 3. Glandular Distribution. — Through means of (i ) its tympanic, subsequently small super- ficial petrosal, branch, {2) the otic ganglion, and (3) the auriculo-temporal nerve, it furnishes secretory branches to the parotid gland. The Pneumogastric Nerve. The pneumogastric (vagus) or tenth cranial nerve is a mixed nerve, consisting of both afferent and efferent fibres. It emerges from the cranial cavity through the middle compartment of the jugular foramen, being enclosed in the same sheath of dura mater as the spinal accessory, and, with that nerve, lying on the inner side of, and slightly posterior to, the glosso-pharyngeal. In the foramen it presents a small enlargement, called the ganglion of the root. After emerging from the foramen, it is joined by the accessory portion of the spinal accessory nerve, and it here presents another enlargement, called the ganglion of the trunk. This ganglion is larger and longer than that of the root, measuring fully | inch in length, and presenting a somewhat plexiform appearance. In this part of its course the nerve lies between the internal carotid artery and the internal jugular vein, the glosso-pharyngeal nerve being in front of it, and the spinal accessory behind it. The hypo- glossal nerve lies at first deeply behind it, but subsequently turns round the outer side of the ganglion of the trunk. The pneumo- gastric then descends within the carotid sheath, lying at first between the internal carotid artery and the internal jugular vein, and then between the common carotid artery and the internal jugular vein, being on a plane posterior to both vessels. Within the sheath the nerve occupies a special compartment, situated in the back part of the septum which separates the artery from the vein. Beyond the root of the neck the right and left nerves present important differ- ences in their course and relations (see p. 964). Branches — A. Ganglion of the Root — i. Branches of Communi- cation.— (a) It receives two filaments from the bulbar or accessory portion of the spinal accessory nerve, (b) It communicates by a small twig with the petrous ganglion of the glosso-pharyngeal nerve, (c) It communicates with the facial, and with the posterior auricular branch of the facial, through means of its auricular branch of dis- tribution (Arnold's nerve), (d) It receives a twig from the superior cervical ganglion of the sympathetic. 2. Branches of Distribution. — (a) The meningeal branch takes a recurrent course, and, after entering the cranial cavity, supplies the dura mater which lines the cerebellar fossa of the occipital bone. {b) The auricular branch, or nerve of Arnold, is of small size, and is soon reinforced by a twig from the petrous ganglion of the glosso- phar5mgeal. It enters the auricular canaliculus through an aperture on the posterior part of the outer wall of the jugular fossa. In this THE HEAD AND NECK 1227 canaliculus it traverses the petrous portion of the temporal bone, crossing in its course the inner aspect of the descending portion of the aqueduct of Fallopius a little above the stylo-mastoid foramen, where it forms its first communication with the facial nerve. It then emerges from the pars petrosa through the auricular or tjTnpano-mastoid fissure, between the mastoid process and the tympanic plate, and thereafter divides into two branches. One of these joins the posterior auricular branch of the facial nerve, and the other is distributed to (a) the skin of the inner surface of the auricle, and (b) the skin of the lower and back part of the external auditory meatus. B. Ganglion of the Trunk — i. Branches of Communication. — (a) The most important branch of conmiunication is the bulbar or accessory portion of the spinal accessory nerve, which passes over the surface of the ganglion in intimate contact with it. Most of the bulbar fibres are continued into the pharyngeal and superior laryn- geal nerves, but some of them descend in the main trunk of the pneumogastric, and pass into its cardiac and inferior laryngeal branches. The bulbar fibres are to be regarded as of two kinds, namely, motor, for the muscles of the soft palate, pharynx, and larynx, and cardiac inhibitory, [b) Branches pass between the ganglion of the tnink and the hypoglossal nerve, (c) A communi- cating branch is received from the superior cervical ganglion of the sympathetic. 2. Branches of Distribution. — ^These are two in number, namely, pharyngeal and superior laryngeal. The pharyngeal nerve arises from the upper part of the ganglion of the trunk, its fibres being chiefly derived from the bulbar or acces- sory portion of the spinal accessory nerve. It passes forwards and downwards over the internal carotid artery, and divides into branches opposite the middle constrictor muscle, which join the pharyngeal branches of the glosso -pharyngeal and superior cervical ganglion of the sympathetic to form the pharyngeal plexus. The pharyngeal plexus is situated upon the middle constrictor muscle of the pharjmx. It is formed by (i) the pharyngeal branch of the ganglion of the trunk of the pneumogastric ; (2) the pharyn- geal branches of the glosso-pharyngeal ; and (3) the pharyngeal branches of the superior cervical ganglion of the sympathetic. Branches. — ^These are distributed to (i) the constrictor muscles of the pharynx ; (2) the mucous membrane of the pharynx ; and (3) the palato-glossus, palato-pharyngeus, levator palati, and azj-gos uvulae muscles. Branches of communication pass betu-een the plexus and the superior laryngeal and external laryngeal nerves, and another branch, known as the lingual branch of the vagus, passes to the hypoglossal nerve. Superior Laryngeal Nerve. — This nerve, which is principally sensory, arises from the ganglion of the trunk of the pneimiogastric near its centre, and contains fibres of the bulbar or accessory portion of the spinal accessory nerve. It passes downwards and 1228 A MANUAL OF ANATOMY forwards behind the internal carotid artery, having previously received communicating branches from the superior cervical ganglion of the sympathetic and from the pharyngeal plexus. As it passes behind the internal carotid artery, it divides into two branches, internal and external. The internal laryngeal nerve, which is sensory, passes forwards, in company with the superior laryngeal branch of the superior thyroid artery, to the thyro-hyoid membrane, which it pierces under cover of the posterior border of the thyro-hyoid muscle. Having reached the interior of the larynx, it divides into branches which supply the mucous membrane of the epiglottis, with its folds, the mucous membrane of the lar5mx as low as the true vocal cords, and that covering the lateral and posterior portions of the cricoid cartilage. One branch descends over the inner surface of the ala of the thyroid cartilage, and joins a branch of the inferior or recurrent laryngeal. The external laryngeal nerve, of small size, descends beneath the sterno-thyroid muscle to the crico-thyroid muscle, which it supplies. It furnishes some twigs to the inferior constrictor, and a filament which joins the superior cardiac branch of the sympathetic. It receives a communicating branch from the superior cervical ganglion of the sympathetic, and one or two branches from the pharyngeal plexus. Inferior or Recurrent Laryngeal Nerve. — ^This nerve is mainly motor, and is the principal motor nerve of the intrinsic muscles of the larynx. It contains fibres of the bulbar or accessory portion of the spinal accessory nerve. The right nerve arises from the pneumo- gastric at the root of the neck in front of the first part of the sub- clavian artery, round the lower border of which it bends, and then ascends behind it. Thereafter it passes upwards and inwards behind the carotid sheath and inferior thyroid artery to the groove between the trachea and the oesophagus. The left nerve arises in the thorax from the pneumogastric in front of the arch of the aorta, on a level with its lower border. It passes backwards within the arch at the place of attachment of the ligamentum ductus arteriosi, and then it turns upwards behind the arch. Having reached the groove between the trachea and the oesophagus, it ascends therein to the neck. The right and left nerves pass upwards in the groove between the trachea and the oesophagus, on each side, lying behind the corresponding inferior thyroid artery. At the level of the cricoid cartilage each nerve passes beneath the lower border of the inferior constrictor muscle, and enters the larynx behind the crico-thyroid joint. Extralaryngeal Branches. — (i) Communicating twigs pass between the recurrent laryngeal nerve and the inferior cervical ganglion of the sympathetic ; (2) cardiac branches, which contain bulbar fibres from the spinal accessory, are furnished to the deep cardiac plexus ; (3) tracheal and (esophageal branches are supplied to these tubes ; and (4) muscular offsets pass to the lower part of the inferior con- strictor. Intralaryngeal Branches. — ^These are chiefly muscular, and \ apply THE HEAD AND NECK 1229 the intrinsic muscles of the lajynx, except the crico-thyroid, which is supplied by the external laryngeal nerve. Sensory branches, however, are given to the laryngeal mucous membrane below the true vocal cords, except over the lateral and posterior portions of the cricoid cartilage. Within the larynx the ner\-e communicates with a branch of the internal laryngeal nerve, under cover of the lower part of the ala of the thyroid cartilage. For the explanation of the recurrent course of each inferior Iar}-ngeal ner\-e, see p. 966. Cervical Cardiac Branches. — ^These are subject to variation as regards numbers. As a rule, there are two, upper and lower, both of which contain bulbar fibres from the spinal accessory. Those of the right side pass behind the first part of the subclavian artery, and end in the deep cardiac plexus. On the left side the upper nerve passes to the deep cardiac plexus, but the lower nerve ter- minates in the superficial cardiac plexus. Sammary of the Pneumogastric Nerve in the Neck — i. Motor Distribution. — The nerve supplies (i) the muscles of the soft palate, except the tensor palati ; (2) the constrictor muscles of the pharynx ; (3) the intrinsic muscles of the larynx ; and (4) the muscular tissue of the oesophagus and trachea. 2. Sensory Distribution. — It supplies (i) the pharynx, oesophagus, and trachea ; (2) a limited portion of the dura mater ; and (3) a small portion of the skin on the inner surface of the auricle, as well as of the lower and back part of the external auditory meatus. 3. Communications. — Each pneumo- gaistric nerve forms connections with the facial, glosso-pharyngeal, spinal accessory, hypoglossal, and sympathetic nerves. It is also connected with the loop between the first and second cervical spinal nerves. Its most im- portant connection is that which is established with the bulbar or accessory portion of the spinal accessory nerve. The bulbar fibres of the nerve are probably chiefly concerned in the innervation of the muscles of the soft palate (except the tensor palati), pharynx, and larynx, but also to a certain extent in the innervation of the heart. Spinal Accessory Nerve. The spinal accessory or eleventh cranial nerve consists of two parts, bulbar or accessory, and spinal. In the jugular foramen these two parts either unite to form one trunk, or freely intermingle, and a communication is established between the accessory part and the ganglion of the root of the pneumogastric by means of two twigs. The nerve emerges through the jugular foramen, being enclosed in the same sheath of dura mater as the pneumogastric, behind which it lies. Immediately beneath the jugular foramen the two parts of the nerve separate from each other. The bulbar or accessory part passes over, but in intimate contact with, the ganglion of the trunk of the pneumogastric, and its fibres are continued partly into the pharyngeal and superior laryngeal branches of the ganglion of the trunk, and partly into the trunk of the vagus below the ganglion. These latter fibres are ultimately prolonged into the cardiac and recurrent lar^Tigeal branches of the nerve. The bulbar or accessory fibres of the spinal accessory are regarded as (i) the motor nerves of (a) the muscles of the soft I230 A MANUAL OF ANATOMY palate, except the tensor palati, (b) the constrictor muscles of the pharynx, and (c) the intrinsic muscles of the larynx ; and (2) the inhibitory fibres of the heart. The spinal part of the spinal accessory nerve passes backwards and downwards either behind or in front of the internal jugular Fig. 501. — Scheme of the Glosso-pharyngeal, Pneumogastric, and Spinal Accessory Nerves (Flower). G.P. Glosso-Pharyngeal. J.G. Jugulrj: Ganglion P.O. Petrous Ganglion Ty. Tympanic Branch (Jacobson's Nerve) C.Ty. Carotico-tympanic Nerve T.P. Tympanic Plexus T.B. Branches to Tympanum S.S.P. Small Superficial Petrosal S.D.P. Small Deep Petrosal G.D.P. Branch to Great Deep Petrosal Sv. Communicating from Sympathetic D.F. Twig from Digastric Branch of Facial S.P. Branch to Stylo-pharyngeus Muscle T. Tonsillar Branches L.B. Lingual Branches PN. Pneumogastric. G.R. Ganglion of Root A. Auricular Branch (Arnold's Nerve) G.T. Ganglion of Trunk Sv. Communicating from Sympathetic ic. Branch from First Cervical H. Communicating with Hypoglossal P. Pharyngeal Branch P.P. SL. I.L. M.B. E.L.. I.C.P. T.G. C.T. S.C. I.e. R.L. I. M.B. C.P. T.Pn. Pharyngeal Plexus Superior Laryngeal Internal Laryngeal Branches to Mucous Membrane of Larynx External Laryngeal Branch to Inferior Constrictor Muscle Branches to Thyroid Body Branch to Crico-thyroid Muscle Superior Cardiac Branch Inferior Cardiac Branch Recurrent Laryngeal Branches to Intrinsic Laryngeal Mus- cles (except Crico thyroid) To Cardiac Plexus Thoracic Pneumogastric SP.A. Spinal Accessory. Sp.P. Spinal Portion of Spinal Accessory 2C. From Second Cervical S.C.M. To Sterno-cleido-mastoid 3c. From Third Cervical 4c. From Fourth Cervical Tr. To Tmpezius vein. It then pierces the deep surface of the sterno-cleido-mastoid, which it supplies along with a branch of the second cervical nerve. Thereafter it crosses the posterior triangle of the neck obliquely downwards and backwards to the anterior border of the trapezius, beneath which it passes, supplying the muscle, in company with branches from the third and fourth cervical nerves. THE HEAD AND NECK 1231 Summary. — The spinal portion of the spinal accessory nerve supplies two muscles, namely, the trapezius and the stemo-cleido-mastoid. The bulbar portion, through its connection with the pneumogastric nerve and its branches, supplies (i) the muscles of the soft palate, except the tensor palati ; {2) the constrictor muscles of the pharynx ; and (3) the intrinsic muscles of the larynx. It also furnishes the inhibitory fibres of the heart, which reach that organ through the cardiac branches of the pneumogastric. Hypoglossal Nerve. The hypoglossal or twelfth cranial nerve consists at first of two bundles, which pierce the dura mater separately. In passing through the anterior condylar foramen these t%vo bundles unite to form one trunk. After emerging from that foramen the nerve lies deeply under cover of the internal carotid artery and internal jugular vein. It then turns roimd the outer side of the ganglion of the trunk of the pneumogastric, with which it is closely connected, and passes forwards between the internal carotid artery and internal jugular vein. Thereafter it descends to the lower border of the posterior belly of the digastric, at which level it hooks round the occipital artery from without inwards, and crosses in front of the external carotid artery and its lingual branch. In this part of its course the nerve lies in the superior carotid triangle. It next courses forwards above the hyoid bone, passing beneath the tendon of the digastric and the lower part of the stylo-hyoid muscle, and resting on the hyo-glossus. Thereafter it disappears beneath the mylo-hyoid, still resting upon the hyo-glossus, where it is accom- panied by the ranine vein, and lies below the deep part of the submaxillary gland. At the anterior border of the hyo-glossus it is connected with the lingual nerve, and then enters the genio-hyo- glossus. Branches — i. Of Communication. — After emerging from the anterior condylar foramen, the hypoglossal nerve communicates with the ganglion of the trunk of the pneumogastric. It then receives a branch from the superior cervical ganglion of the sympa- thetic, and one from the first cervical nerve, or the loop between the first and '=;econd. As it hooks round the occipital artery, it receives the lingual branch of the vagus from the pharyTigeal plexus ; and at the anterior border of the hyo-glossus it is connected with the lingual ner\^e. 2. Of Distribution. — One or two meningeal branches arise from the nerve in the anterior condylar foramen, which take a recurrent course, and enter the cranial cavity to supply the dura mater in the vicinity of the foramen. The descendens cervicis (descendens hypoglossi) nerve has been already described (see Index. The thyro-hyoid nerve will be found described on p. 1108. The muscular branches are given off from the nerve as it lies upon the hyo-glossus imder cover of the mylo-hyoid. These supply the stylo-glossus, hyo-glossus, genio-hyo-glossus, and genio-hyoid. The 1232 A MANUAL OF ANATOMY nerve to the genio-hyoid is generally regarded as being composed of spinal fibres, derived from the first, second, and third cervical nerves. The terminal or glossal branches pierce the under surface of the tongue, and are distributed to its muscular tissue. The hypoglossal nerve receives many spinal fibres. Those derived from the first cervical nerve, or the loop between the first and second, soon become applied to it, and the most of them pass off to form the descendens cervicis nerve. A few of these, however, still pass along the main trunk. The spinal fibres derived from the second and third cervical nerves in part ascend in the descendens cervicis nerve, and then pass off from it to be applied to the main trunk in its onward course. Summary — i. Distribution. — Tlie h5^oglossal fibres of the nerve supply the stylo-glossus, hyo-glossus, genio-hyo-glossus, and intrinsic muscles of the tongue. The spinal fibres supply both bellies of the omo-hyoid, the sterno- hyoid, sterno-thyroid, thyro-hyoid, and genio-hyoid muscles. The hypo- glossal nerve also supplies the dura mater in the vicinity of the cranial aspect of the anterior condylar foramen. 2. Connections. — It establishes connec- tions with (i) the ganglion of the trunk of the vagus ; (2) the superior cervical ganglion of the sympathetic ; (3) the first, second, and third cervical nerves ; (4) the pharyngeal plexus, through means of the lingual branch of the vagus ; and (5) the lingual nerve from the inferior maxillary division of the fifth cranial nerve. Gangliated Cord of the Sympathetic. Cervical Portion. — ^This portion of the sympathetic cord extends from the base of the skull, at the foramen caroticum on the under surface of the petrous part of the temporal bone, to the root of the neck, where it enters the thorax, passing, on the right side, behind the subclavian artery. It lies directly behind the carotid sheath, and in front of the transverse processes of the cervical vertebrae, resting upon the rectus capitis anticus major and longus colli muscles. The cord presents three ganglia — superior, middle, and inferior. Superior Cervical Ganglion. — ^This ganglion is elongated and fusi- form. It is regarded as representing four ganglia united into one, and corresponding to the first four cervical nerves. It is situated in front of the transverse processes of the second and third cervical vertebrae, and lies upon the rectus capitis anticus major, the pneu- mogastric nerve being external to it. At either end it tapers, being continued superiorly into its ascending branch, and interiorly into the descending cord. Branches. — ^These are numerous and complicated. They may be conveniently arranged into ascending, external or communi- cating, internal or pharyngeal, superior cardiac, and anterior or vascular. The ascending branch enters the carotid canal in the petrous part of the temporal bone, in company with the internal carotid artery, THE HEAD AND NECK "33 Fig. 502. — Scheme of the Sympathetic Nerve in the Neck, and of the Cardiac Plexus (Flower). S.C.G. Superioi CerTical Ganglion. P.N. and G.P. Branches to Pneumogastric and Glosso-pharyngeal ic, 2C, 3c, 4c. Branches to Upper Four Cervical Nerves C p. Carotid Plexus Cav. P. Cavernous Plexus C.G. Branch to Ciliary Gangliou G.D.P. Great Deep Petrosal G.S.P. Great Superficial Petrosal V.N. Vidian Nerve P.N. To Ganglion of Trunk of Pneumogastric H. To Hypoglossal E.C.P. To External Carotid Plexus P.P. To Pharjngeal Plexus S.C.N. Superior Cardiac Nerve M.C.O. Middle Cervical Ganglion. 5C, 5c. To Fifth and Sixth Cervical Nerves I.T.P. To Inferior Thyroid Plexus *'.C.N. Middle Cardiac Nerve LC.G. Inferior Cervical Ganglion, 7c, 8c. To Seventh and Eighth Cervical Nerves V.P. To Vertebral Plexus S.P. To .Subclavian Plexus I.C.N. Inferior Cardiac Nerve F.T.G. First Thoracic Ganglion Cardiac Plexus. C.B.Pn. Cardiac Branches of Pneumogastric S.C.P. Suf-erficial Cardiac Plexus G.W. Ganglion of VVrisberg D.C.P. Deep Cardiac Plexus R.A.P.P. Right .\nterior Pulmonary Plexus L.A.P.P. Left Anterior Pulmonary Plexus R.C.P. Right Coronary Plexus L.C.P. Left Coronary Plexus 78 t234 A MANUAL OF ANATOMY and divides into two parts. The external division lies upon the outer side of the artery, and its subdivisions form by their interlacement the carotid plexus. From this plexus several communicating branches are given o&. (i) The carotico-tympanic nerve enters the tympanum, and joins the tympanic branch (Jacobson's nerve) of the glosso-phar5mgeal, to take part in the tympanic plexus, (2) The great deep petrosal nerve joins the great superficial petrosal from the geniculate ganglion of the facial, in the upper part of the fora- men lace rum medium, to form the Vidian nerve, which passes through the Vidian canal to join Meckel's ganglion. (3) A branch (or branches) passes to join the sixth cranial nerve. (4) One or more branches pass to join the Gasserian ganglion. The carotid plexus furnishes filaments to the coats of the internal carotid artery, and it receives the small deep petrosal nerve from the tympanic plexus. The internal division of the ascending branch of the superior cervical ganglion lies upon the inner side of the internal carotid artery, to which it furnishes twigs, and its subdivisions form by their interlacement the cavernous plexus. This plexus lies in contact with the internal carotid artery as it traverses the cavernous sinus. Its communicating branches pass to join the third, fourth, and ophthalmic division of the fifth cranial nerves, and the. ciliary or lenticular ganglion. The last-named branch forms the sympa- thetic root of the ciliary ganglion, and enters the orbit through the sphenoidal fissure. It is the source of the motor supply of the dilator pupillse muscle. The cavernous plexus furnishes filaments to the coats of the internal carotid artery, and offsets which accom- pany the branches of that artery, around which they are disposed as plexuses. The external branches are communicating, and pass to (i) each of the upper four cervical nerves ; (2) the petrosal ganglion of the glosso-pharyngeal ; (3) the ganglion of the root, and the ganglion of the trunk, of the vagus ; and (4) the hypoglossal nerve. The internal branches are pharyngeal and cardiac. The pharyn- geal branches, two or three in number, unite with the pharyngeal branches of the glosso-pharyngeal and vagus to form the -phsxyn- geal plexus (see p. 1227). The superior cardiac nerve arises by two roots from the lower part of the superior cervical ganglion, and descends behind the carotid sheath, lying internal to the main sympathetic cord. The nerve of the right side passes either over or beneath the first part of the subclavian artery, and then along the innominate artery, to ter- minate in the deep cardiac plexus. In its course down the neck it receives twigs from the external laryngeal nerve, and is joined by the upper cervical cardiac branch of the pneumogastric nerve. As it enters the thorax, it receives a filament from the recurrent laryngeal nerve. The nerve of the left side within the thorax accompanies the left common carotid artery, and passes over the arch of the aorta to terminate in the superficial cardiac plexus. THE HEAD AND NECK 1235 The anterior branches are vascular, and pass to the external carotid artery, upon which and its branches they form delicate plexuses. Middle Cervical Ganglion. — ^This ganglion is situated opposite the sixth cervical vertebra, and usually lies close to the inferior thyroid artery. It is the smallest of the three, and probably repre- sents two ganglia united into one. Occasionally it is absent. It is connected by grey rami with the fifth and sixth cervical ner\'es, and its branches of distribution are thyroid and middle cardiac. The thyroid branches accompany the inferior thyroid artery to the thyroid body, and they communicate with the external and recur- rent laryngeal nerves. The middle cardiac nerve of each side terminates in the deep cardiac plexus. The nerve of the right side passes either in front of, or behind, the first part of the right sub- clavian artery. It then descends in front of the trachea, and joins the right half of the deep cardiac plexus. The nerve of the left side enters the thorax between the left common carotid and left subclavian arteries, and it joins the left half of the deep cardiac plexus. Inferior Cervical Ganglion. — ^This ganglion is situated between the transverse process of the seventh cervical vertebra and the neck of the first rib, where it lies behind the root of the vertebral artery. It is intermediate in size between the superior and middle ganglia, and, like the middle, it probably represents two ganglia united into one. It is frequently fused with the first thoracic ganglion. One or two cords establish a communication between it and the middle cervical ganglion, passing in front of the first part of the subclavian artery. The cord or cords in front of the vessel form a loop around it, called the ansa Vieussenii, or ansa subclavia. The inferior cervical ganglion is connected by grey rami with the seventh and 'eighth cervical nerves, and its branches of distribution are vascular and in- ferior cardiac. The vascular branches accompany the vertebral artery in the form of the vertebral plexus, which gives filaments to the vessel and offshoots along its various branches. The plexus is continued along the basilar artery and its branches, and on to the posterior cerebral arteries. The inferior cardiac nerve on each side joins the deep cardiac plexus. The nerve of the right side passes behind the first part of the right subclavian artery, and then in front of the trachea. It is connected with the middle cardiac and recurrent laryngeal nerves. The nerve of the left side in many cases joins the middle cardiac nerve, and so reaches the deep cardiac plexus. Constitution of the Cervical Sympathetic Cord. The sympathetic cord in the neck contains the following important groups of fibres, namely, (i) dilator pupillae, (2) vaso-constrictor ajid vaso-dilator, (3) secretory, and (4) accelerator. The dilator pupillae fibres axe derived from the upper three thoracic nerves, and ascend in the sympathetic cord to the superior cervical ganglion, in which they terminate. From this ganglion they are continued as sjTnpathetic 1236 A MANUAL OF ANATOMY fibres to the cavernous plexus, through this plexus to the ciliary ganglion, and thence to the dilator pupillae muscle. The vaso-constrictor fibres are derived from a variable number of thoracic nerves, commencing at the second and terminating at the eighth. The origin of the vaso-dilator fibres is not definitely known. The vaso-constrictor fibres ascend to the superior cervical ganglion, in which they terminate. From this ganglion they are continued as sympathetic fibres into the plexus around the external carotid artery, and thence along the branches of that vessel. The secretory fibres are destined for the submaxillary gland, and are derived chiefly from the second and third thoracic nerves. They also ascend to the superior cervical ganglion, in which they terminate. They are thence con- tinued as sympathetic fibres into the external carotid plexus, from that into the facial plexus, and thence into the submaxillary ganglion, from which they pass into the submaxillary and sublingual glands. The accelerator fibres of the heart are chiefly derived from the second and third thoracic nerves, but some also spring from the first, fourth, and fifth nerves. The spinal fibres pass to the middle and lower cervical ganglia, from each of which they are continued as sympathetic fibres. The Mouth. The mouth, or buccal cavity, extends from the ritna oris in front, where it opens externally on the face, to the isthmus faucium behind, where it opens into the pharynx. It is divided by the upper and lower dental arches into two compartments, the anterior of which is called the vestibule and the posterior the mouth proper. The vestibule is bounded anteriorly and externally by the lips and cheeks, and internally by the dental arches and gums. Superiorly and interiorly it is bounded by the reflection of the mucous mem- brane from the lips and cheeks on to the gums. In the median line, above and below, the mucous membrane forms a small vertical fold, called the frenulum lahii. On the inner surface of each cheek the vestibular mucous membrane presents a small papilla opposite the second upper molar tooth, and on this is the minute opening of Stensen's duct. The mouth proper lies within the dental arches. It communicates with the vestibule by the interval between the upper and lower teeth, and also by an opening at either side situated behind the last molar tooth. Anteriorly and externally it is bounded by the dental arches and gums, and posteriorly it opens into the pharynx by means of the isthmus faucium. The roof, which is arched, is formed by the hard palate and the velum pendulum palati, or soft palate. The fioor is formed by the tongue, and the reflection of mucous membrane from the inner surface of the lower dental arch on to its under surface. In the region of the tip of the tongue the lateral reflections of mucous membrane from the two sides of the lower dental arch are continuous across the median line. In the median line the mucous membrane forms a prominent fold, called the frenum lingua, which is connected above with the under surface of the tongue a little distance from the tip. In some children it may extend quite to the tip, impairing the utility of the organ, and giving rise to the condition known as ' tongue-tied.' Close to each side of the frenum there is a small papilla, on which is the THE HEAD AND NECK 1237 opening of Wharton's duct, and near to this is the opening of the duct of Rivini or of Bartholin, which comes from the outermost lobule of the sublingual gland. A little posterior to this is a fold of the mucous membrane, at either side, produced by the upper border of the subjacent sublingual gland. This fold is known as the plica sublingualis, and it extends from the side of the tongue to the dental arch. It is upon this plica that the majority of the ducts of Walther (sublingual ducts) open. The lips are covered by skin externally, and mucous membrane internally. Between these two layers are the muscular fibres Descending Palatine Artery .Palatal Raph6 .Uvula [''' _.Post. Pillar of Fauces -Ant. Pillar of Fauces Tonsil I Posterior Wall of Pharynx^ '^ Dorsum of Tongue Fig. 503. — The Buccal Cavity and Isthmus Faucium. (The Maxillae are widely separated). of the orbicularis oris, blended with which are the fibres of the buccinator, and, in the case of the upper lip, fibres of the depressor anguli oris, whilst in the case of the lower lip there are the fibres of the levator anguli oris. Between the mucous mem- brane and the muscular element there are a number of small race- mose glands, called the labial glands, the ducts of which open on the inner surface of each lip. The tortuous coronary arteries are embedded in each lip, and those of opposite sides anastomose at the median line. Between the upper lip and the columella nasi there is a groove, called the philtrum. The lymphatic vessels of the npper lip pass, on either side, to the submaxillary lymphatic glands. The Ijonphatic vessels of the lateral portion of the lower lip also pass, on either side, to the sub- maxillary lymphatic glands; and those of the mesial portion pass to the submental, or suprahyoid, gland of the corresponding side. 1238 A MANUAL OF ANATOMY The cheeks are covered externally by skin, and internally are lined with mucous membrane. The muscular element consists of the buccinator, which is covered by the buccal fascia. Posteriorly this fascia is continuous with the pharyngeal fascia, Which is derived from the deep cervical fascia, the two being known as the bucco-pharyngeal fascia. Superiorly and interiorly it is attached to the dental arches. The lymphatic vessels of the cheek pass to (i) the superficial parotid or pre-auricular lymphatic glands, and (2) the submaxillary lymphatic glands, the buccal lymphatic glands being a gland-station in the path of the latter. The buccal pad of fat is situated upon the buccal fascia, and is Well developed in young children. It is of soft consistence, and is continuous With the fat beneath the temporal muscle under cover of the ramus of the lower jaW. The buccal fascia, buccinator, and lining mucous membrane are pierced by Stensen's duct. Between the buccinator and the mucous membrane there are several racemose buccal glands. In addition to these there are three or four molar glands, mucous in character, which are situated superficial to the buccal fascia in the angle between the masseter and buccinator. The masseteric fascia is an upward prolongation of the deep cervical fascia. It is attached superiorly to the zygoma, and externally is continuous with the parotid fascia. The dental arches are formed by the alveolar borders of the superior and inferior maxillae, the teeth, and the gums. The gums (gingivae) consist of dense fibrous tissue, which is covered by mucous membrane and is closely connected with the periosteum of the alveolar borders of the superior and inferior maxillae. The mucous membrane, which is very vascular, is con- tinuous with the labial and buccal mucous membrane on the one hand, and with that of the floor of the mouth on the other. Close to the necks of the teeth it is beset with vascular papillae. The lymphatic vessels of the upper gum pass, on either side, to the submaxillary lymphatic glands. The lymphatic vessels of the lateral portion of the lower gum also pass, on either side, to the sub- maxillary lymphatic glands ; and those of the mesial portion pass to the submental or suprahyoid gland of the corresponding side. The mucous membrane of the gums is separated from the subjacent periosteum by dense connective tissue, which connects the two in such a close manner that the mucous membrane is immovable. Close to the necks of the teeth it is beset with papillae. The mucous membrane of the hard palate, like that of the gums, is separated from the periosteum by a thick layer of dense connective tissue, which binds the two so closely that the mucous membrane is immovable. It presents a median raphe, which is continued over the soft palate, and ends in front at the anterior palatine fossa in a small papillary elevation, knoWn as the incisor papilla. On either side of the raphe anteriorly there are a few transverse rugae. Each lateral half of the hard palate is traversed by the ramifications of THE HEAD AND NECK 1239 the descending palatine artery, the branches of which extend forwards and inwards from either lateral angle posteriorly. The mucous membrane of the hard palate is provided with racemose palatal glands of a serous character, which are arranged in two symmetrical groups laterally disposed. The lymphatic vessels of the mucous membrane of the hard palate pass to (i) the deep facial, or internal maxillary, glands, and (2) the superior deep cervical glands. Nerves. — The great or anterior palatine nerve descends in the posterior palatine canal, from which it emerges through the posterior palatine foramen. Thereafter it divides into branches which pass forwards in grooves on the hard palate, and supply the mucous membrane, glands, and inner aspect of the upper gum. The naso-palatine nerve is distributed to the mucous membrane behind the incisor teeth, where it communicates with twigs of the great or anterior palatine nerve. To reach the hard palate the nerve of the right side passes through ih.e posterior foramen of Scarpa, whilst the left nerve passes through the anterior foramen. The mucous membrane of the cheek is supplied by the long buccal nerve, which is a branch of the inferior maxillary division of the fifth cranial nerve. The mucous membrane of the floor of the mouth derives its nerves from the submaxillary ganglion. Arteries. — These are the right and left descending palatine branches of the third part of the internal maxillary. Each descend- ing palatine artery takes the same course as, and has a similar distribution to, the great or anterior palatine nerve. At the anterior palatine fossa it terminates in a small branch which ascends through Stensen's canal, and anastomoses at the upper end of that canal with the naso-palatine branch of the spheno-palatine artery. Development of the Mouth, Lips, and Gums. The rudiment of the mouth appears as an invagination of the ectoderm of the ventral aspect of the embryo between the fore-brain (which is folded downwards) and the pericardial region. This invagination gives rise to a depression, called the oral fossa or stomodseum. As the stomodaeum deepens, the invaginated ectoderm approaches the phar^'ngeal end of the fore-gut, with which it unites. There is thus formed a bilaminar stratum, called the bucco-pharyngeal membrane, one layer of which is formed by the stomodcsal ectoderm, whilst the other layer consists of the er.toderm of the fore-gut (pharynx). This membrane forms a septum between the pharyngeal part of the fore-gut and the stomodaeum. In the course of the fourth week this septum ruptures and disappears, and thereafter the pharynx communicates freely with the stomodaeum. The formation of the stomodaeum and bucco-pharyngeal membrane bears a close resemblance to the formation of the anal fossa or proctodaeum and cloacal membrane, at the caudal end of the hind-gut. The primitive oral cavity, or stomodaeum, includes the cephalic part of the pharynx, and from the stomodaeum the permanent oral cavity or mouth and the naisal cavities are formed. The boundaries of the stomodaeum are as follows: Dorsally, the bucco- pharyngeal membrane; superiorly and ventrally, the fronto-nasal process; tnferiorly and behind, the two mandibular arches; and, laterally, the corre- sponding maxillary process. 1240 A MANUAL OF ANATOMY Annexed to the stomodgeum there are (i ) the pouch of Rathke, (2) the tongue (3) the saUvary glands, (4) the tonsils, and (5) the teeth. The pouch ol Rathke is an evagination or diverticulum of the roof of the ectodermic stomodaeum, ventral to the bucco-pharyngeal membrane. It grows in a cephalic direction, and gives rise to the anterior lobe ol the pituitary body, or hypophysis cerebri, the posterior lobe of which is developed from a diverticulum of the floor of the third ventricle of the cerebrum. The development of the tongue, salivary glands, tonsils, and teeth will be found after the description of each of these organs. The stomodceum becomes divided into two chambers — upper or nasal and lower or oral — this division being effected by the formation of the hard palate. The nasal chamber becomes transformed into the two nasal fossae, and the oral chamber constitutes the oral cavity or permanent mouth. The permanent oral cavity is much more circumscribed than the primitive oral cavity or stomodaeum. The latter, as already stated, includes the cephalic part of the pharynx, but that part of the pharynx is, in adult life, shut off from the permanent oral cavity by the velum pendulum palati or soft palate. The development of the hard palate is described in connection with the visceral arch skeleton of the face, but it may be here briefly restated. Globular Process . Maxillary Palatal Process Maxillary Process Oral Cavity Palatal Processes of Globular Processes t Aperture of Olfactory Pit Lens . Eye Palatal Shelf Pouch of Rathke Fig. 504 — Roof of Mouth (Marshall, after His). The horizontal or palatal plate of the palate bone and the greater part of the palatal plate of the superior maxilla, of either side, are developed from the palatal shelf of the corresponding maxillary process of the first visceral, or mandibular, arch. The incisor or premaxillary portion of the psJatal plate of the superior maxilla — that is to say, the portion ventral to the incisor or premaxillary suture on the under aspect — is developed, on either side, from the nasal lamina of the corresponding globular process of the mesial nasal process of the fronto-nasal process. The formation of the hard palate is completed about the end of the third month. Lips [labia oris) and Gums [gingiva;). — Shortly after the fusion of the max- illary and globular processes to form the superior maxilla, a groove, produced by an ingrowth of epithelium, appears along each of these processes, on either side. The margins of this groove, which form parallel ridges, are external and internal, relatively to the oral cavity. The external, or labial, ridge gives rise to the upper lip, the globular portion of the ridge representing the pre- maxillary part of the lip, and the maxillary portion forming the remainder. The internal or gingival ridge is the rudiment of the upper gum. The philtrum is probably developed from the mesodermic investment of the united globular processes. A similar groove and similar ridges [labial and gingival) appear along each mandibular arch, and from the ridges the lower lip and lower gum are developed. The angles of the mouth correspond to the union between the two lips, on either side, and each originally represents the angle between a mandibular arch and maxillary process. THE HEAD AND NECK 1 241 The Tongue. The tongue is a muscular and very sensitive organ, covered by the buccal mucous membrane, and situated on the floor of the mouth. It is concerned in the sense of taste, mastication, deglu- tition, and speech, and it consists of a root or base, a body, and a tip. The root is attached to the hyoid bone. The tip is the anterior free extremity, which, in the quiescent state, hes behind the upper incisor teeth. The body presents an upper surface or dorsmn, an imder surface, and two lateral borders, right and left. The dorsiun is convex from before backwards, and pre- sents over its anterior two-thirds a median depression or raphe, on either side of which the surface is convex from side to side. This raphe terminates posteriorly in the foramen ccecum. In this region the dorsum presents a V-shaped groove, known as the stdctts terminalis. The point of the V is at the foramen caecum, and the two limbs pass outwards and forwards to the sides of the tongue, where the anterior pillars of the fauces are connected with it. The sulcus terminalis marks the union of the two portions, anterior and posterior, from which the tongue is developed. The portion behind it, representing one-third, is the basal, lymphoid, or pharyngeal portion. It occupies the buccal portion of the pharynx, and overhangs the epiglottis. The portion in front of the sulcus terminalis, representing two-thirds, is known as the buccal or papillary portion. Mucous Membrane. — ^The mucous membrane covering the basal or pharyngeal portion of the tongue is destitute of proper papillae, but is freely provided with lymphoid follicles similar to those of the tonsils, and with mucous glands. The follicles are ranged upon the walls of crypts, the mouths of which open upon the surface. The mucous membrane in this region forms the glosso-epiglottidean fold, or frenum epiglottidis, which is mesiaUy placed. On either side of this fold, between it and each pharyngo-epiglottidean fold, there is a pouch or depression, called the vallecula. In front of the sulcus terminalis the mucous membrane of the dorsum, borders, and tip of the tongue is freely covered by characteristic papillae, which, being visible to the naked eye, impart to this part its distinctive appearance. These papillae bear secon- dary papillae, which, however, are concealed by the epithelial covering. The mucous membrane on the under surface of the tongue in the median line forms, near the tip, a vertical fold, called the frenum linguce. A little external to the frenum, on either side, is an indistinct fringed fold, called the plica fimbriata. The two plicae converge as they pass forwards towards the tip, and inside each the outline of the ranine vein may be visible. On either side of the tongue, in the region of the limbs of the sulcus terminals, the mucous membrane presents a few ridges which represent the "papilla foliata of such animals as the rabbit. 1242 A MANUAL OF ANATOMY Papillae.— -These are of three kinds, namely, conical, fungiform, and circumvallate, and they are confined to the anterior two- thirds of the organ. The conical papillae are the most numerous, and are arranged in more or less parallel, closely-set rows, directed forwards and outwards from the median line, except towards the tip, where the rows tend to become transverse. On the sides of the tongue they are arranged in vertical parallel rows. In some Uvula Posterioi Pillar of Fauces Epiglottis Median Glosso- epiglottidean Fold Foramen Csecum A^ Lymphoid Tissue v Anterioi Pillar of Fauces Tonsil Median Raph# Fungiform Papilla: Fig. 505. — The Dorsum of the Tongue, and the Fauces. conical papillae the epithelium which caps the secondary papillae forms thread-like processes. Such are known as filiform papillae. The fungiform papillae are scattered amongst the conical, and are most numerous at the sides and tip, being rather sparse over the dorsum. Each is round and enlarged at the surface, but tapers at its deep end, and it bears secondary papillae, but there is no fili- form arrangement of the epithelial caps. The circumvallate papillae are conspicuous, and vary in number from seven to thirteen. They are arranged in two diverging rows TH£ HEAD AND NECK 12 41 which lie anterior to, and parallel with, the limbs of the sulcus tenni- nalis. The two rows converge backwards and inwards, and so form a capital V. In the median line, at the point of the V, there is a single circum vallate papilla, behind which is the foramen caecum. The free surface of each papilla is broad and flat, and bears secondary papillae, whilst the deep end is somewhat constricted, and is received into a circular pit of the mucosa. In this manner each papilla is surrounded by a space known as the trench. The outer wall of the trench projects slightly beyond the level of the free surface of the papilla, thus forming a circular elevation around it, called the vallum (rampart). It is from this circumstance that the papillae Epithelial Covering Papilla Fig. 506. — The Conicai. (Filiform) Papilla of the Tongue. have received the name ' circumvallate.' Their sides, as well as the wall of the vallum, contain the taste-buds. The tongue contains a number of acinous glands. Some of them open into the trenches around the circumvallate papillae, where taste- buds are present, and are serous in character, these being known as the glands of Ebner. Others open into the foramen caecum, into the crypts on the posterior third of the dorsum, and along the sides of the organ, these being mucous in character, and being known as the glands of Weber. Beneath the apex of the tongue, on either side of the median line, there is a small group of glands, partly serous and partly mucous. These two groups are known as the glands of Blandin, or of Kuhn. 1244 A MANUAL OF ANATOMY The muscular tissue of the tongue is of the striped variety. It forms two sets of muscles, namely, extrinsic and intrinsic. The extrinsic muscles are those which have their origins outside the tongue, and their insertions into it. They are as follows : (i) the genio-hyo-glossus, (2) the hyo-glossus (including the chondro- glossus), (3) the stylo-glossus, and (4) |:he palato-glossus, all of which have been already described. I'he intrinsic mttscles are those which are contained entirely within the tongue, and they are arranged in pairs on either side of the median fibrous septum, Taste-bud Fig. 507.— Vertical Section of a Circumvallate Papilla of the Tongue. A, Circumvallate Papilla, beset with Secondary Papillae ; B, Taste-bud; C, Gustatory Cell. which extends from the tip of the tongue as far back as the body of the hyoid bone. The intrinsic muscles are as follows : (i) the lingualis superficialis, (2) the lingualis inferior, (3) the lingualis transversus, and (4) the lingualis verticalis. The lingualis superficialis is an expanded sheet placed on the dorsum, immediately beneath the mucous membrane. Its fibres are disposed longitudinally, and the muscle extends from the tip backwards to the body of the hyoid bone. Posteriorly it is over- lapped by fibres of the hyo-glossus. Its fibres do not extend over the whole length of the tongue, but take attachment, at short intervals, to the mucous membrane. THE HEAD AND NECK 1245 The lingualis inferior is disposed as a round bundle on the inferior surface of the tongue. Posteriorly it lies between the insertions of the genio-hyo-glossus internally and the hyo-glossus externally, and anteriorly between the former muscle internally and the stylo-glossus externally. The muscle extends from the tip of the tongue to the body of the hyoid bone, with which it is connected. The lingualis transversus constitutes a layer of considerable thickness, which is placed between the lingualis superficialis and Fig. 5o8. — Longitudinal Section of the Tongue of a Cat (injected). 1. Mucosa 2. Lingiialis Superficialis 3. Lingualis Transversus et Verticalis 4. Lingualis Inferior lingualis inferior. It arises from the median septum, and extends outwards, the upper fibres cur^-ing upwards, to be inserted into the mucous membrane of the side of the tongue and adjacent portion of the dorsum. This muscular stratum is interspersed with fat, id is much broken up by fibres of the lingualis verticalis and genio- lyo-glossus. The lingualis verticalis extends from the mucosa of the dorsum to lat of the inferior surface. Its fibres describe cur\'es, having the )nvexities directed inwards, and they decussate freely with the ibres of the lingualis transversus. 1246 A MANUAL OF ANATOMY Septum Linguae. — The septum of the tongue is a fibrous partition, which extends in the median Une from the tip of the organ to the body of the hyoid bone. It divides the tongue into two sjmi- metrical halves, and the Hngualis transversus muscle arises from it on either side. Arteries. — These are as follows: (i) the ranine artery, which is a branch of the lingual, and is situated on the inferior surface, im- mediately external to the line of insertion of the genio-hyo-glossus muscle. It anastomoses with its fellow beneath the tip. (2) The dorsalis linguae artery, which is also a branch of the lingual. (3) The tonsillar branch of the cervical portion of the facial artery. (4) The palatine branch of the ascending pharyngeal artery. The veins pass to the internal jugular vein. Lymphatics. — The lymphatic vessels of the tongue are disposed in four groups — apical, marginal, basal, and central. The apical lymphatics issue from the tip, and are two in number, on either side. One passes to the submental, or suprahyoid, gland of the same side; and the other passes to one of the internal chain of substemo-mastoid glands, on a level with the cricoid cartilage of the larynx. The marginal lymphatics convey Ijnnph from the anterior two- thirds of the lateral border, and the marginal portion of the dorsum for a similar extent. The anterior lymphatics of this set pass through the mylo-hyoid muscle, and terminate in the anterior sub- maxillary lymphatic glands. The posterior lymphatics of this set pass to the superior deep cervical glands, and, more particularly, to those situated under cover of the posterior belly of the digastric muscle. The small lingual glands, which he upon the outer surface of the hyo-glossus muscle, serve as gland-stations in their path. The basal lymphatics return lymph from the posterior third of the tongue, and have the same termination as the posterior marginal lymphatics, just stated. The central lymphatics return the lymph from median part of the tongue, and pass to the deep cervical glands, which extend from the posterior belly of the digastric muscle to the level of the cricoid cartilage of the larynx. Nerves. — The sensory nerves are: (i) the lingual branch of the inferior maxillary division of the fifth cranial nerve, which is dis- tributed to the mucous membrane over the anterior two-thirds of the tongue, including the conical and fungiform papillce, upon which it confers common sensibility ; (2) the chorda tympani nerve, w'hich accompanies the lingual nerve to the anterior two- thirds of the tongue, of which it is usually regarded as the nerve of special sense; (3) the lingual branch of the glosso-pharyngeal nerve. Which is distributed to the mucous membrane of the posterior third and to the circumvallate papillce, of Which it is the nerve of special sense; (4) the internal branch of the superior laryngeal nerve, which furnishes a few twigs to the mucous membrane of the THE HEAD AND NECK 1247 root of the tongue, in the region of the epiglottis ; and (5) the hypo- glossal nerve, which supplies the lingual muscles. Sympathetic filaments are also conducted to the tongue by the various arteries. Taste-buds. — These constitute the gustatory organs. They are modified epitheUal cells, and are present in the following situations : (i) The sides of the circumvallate papillae, and the opposed surface of each vallum ; (2) the sides of the anterior two-thirds of the tongue, partly in connection with the fungiform papillae, and partly em- bedded in the stratified epitheHum; (3) the folds which form the papules foliates ; {4) the buccal surface of the soft palate ; and (5) the posterior surface of the epiglottis. They extend vertically through the epithehum from the free siuface to the corium of the mucosa. Each taste-bud is a flask-shaped body. The base rests upon the corimn of the mucosa, and gives passage to nerve-fibres. The apex or narrow end lies between the surface-cells of the epithehum, and it is perforated by a minute opening, called the gustatory pore, through which the peripheral processes of the gustatory cells in the interior of the bud project as gustatory hairs. Structure. — The wall of a taste-bud is composed of flattened, nucleated, epithehal cells, called the sustentacular or tegmental cells. These cells are elongated in the direction of the bud, they taper at either end, emd their margins are closely applied to each other. The interior of the bud consists of a bundle of gustatory cells. Each gustatory cell is nucleated and spindle-shaped. The body of the cell is prolonged, at either end, into a process — peripheral and central respectively. The peripheral process passes to the gustatory pore at the apex of the bud, through which it projects as a gustatory hair. The central process passes towards the base of the bud, which rests upon the corium of the mucosa. It is usually branched, and terminates in free extremities. It does not therefore become con- tinuous with ner\'e-fibres, and therein it differs from the correspond- ing process of an olfactory cell. The base of each taste-bud, as stated, gives passage to nerve-fibres. The fibres, as they enter the bud, lose their medullary sheaths, and their axons terminate within the bud in arborizations around the constituent gustatory ceUs. Nerve-fibrils also enter the epithehal wall of the bud, and remiify between the sustentacular or tegmental cells. Development. — ^The tongue is developed in the floor of the pharynx in t\vo parts — buccal and pharyngeal — which are separated from each other by the foramen caecum and V-shaped sulcus terminalis. The buccal or papillary part, which represents the anterior two-thirds, is developed from the ventral ends of the first or mandibular visceral arch, on either side of the tuberculum impar. It is therefore originally in two parts, right and left, which subsequently fuse and envelop the tuberculum impar. This eminence may give rise to the portion of the buccal part directly in front of the foramen caecum. The pharyngeal or basal part of the tongue, which represents the posterior one-third, behind the foramen caecum and sulcus terminalis, is developed from 1248 A MANUAL OF ANATOMY the ventral ends of the second, or hyoid, and third, or thyro-hyoid, visceral arches. The union between the buccal and pharyngeal parts is indicated by the V-shaped sulcus terminaUs, between the two limbs of which is the foramen ccccum, or upper end, of the thyro-glossal duct. This foramen represents the persistent upper extremity of the embryonic median diverticulum, called the ductus thyro-glossus, from the lower part of which the isthmus of the thyroid body is developed. The tuberculum impar makes its appearance as a round eminence in the median line, opposite and between the first visceral clefts. Behind it, and separated from it by a groove, is the furcula, which is a forked eminence, mesially placed opposite the second and third visceral arches, and resembling a horseshoe. It gives origin to the epiglottis and aryteno-epiglot- tidean folds. The ventral ends of the second and third visceral arches of either side coalesce, and the united ends of these arches join each other in the interval between the tuberculum impar and the furcula, forming the copula. It is from the copula that the root of the tongue is formed. It is developed from it as two elevations, which take an upward and forward direction, Tuberculum Impar Furcula — Fig. 509.— The Visceral Arches of the Embryo (Posterior View) (His). Mandibular Arch Hyoid Arch V. Fifth Arch III. Thyro-hyoid Arch IV. Fourth Arch diverging at the same time in a V-shaped manner, so as to embrace the buccal part. After the pharyngeal and buccal portions of the tongue have coalesced, a V-shaped groove persists for some time, indicating the line of union of the two parts of the organ; and in adult life this is represented by the sulcus ferminalis. The Soft Palate. The soft palate, or velum penduhim palati, is a movable musculo- aponeurotic curtain situated at the back part of the hard palate, w'here it projects dov^'n Wards and backwards into the pharynx. Anteriorly it is attached to the posterior border of the hard palate, laterally it is connected with the side of the tongue and the Wall of the pharynx, and postero-inferiorly it presents a free border. Its surfaces. Which occupy an oblique plane, are antero-inferior or buccal, which is concave, and postero-superior or pharyngeal. Which is convex and looks towards the naso-pharynx. The postero- inferior border at its centre presents a conical process, called the uvula. On either side of the base of the uvula there are two prominent folds of mucous membrane, which extend outwards and downwards in a diverging manner. These folds constitute the THE HEAD AND NECK 1249 anterior and posterior pillars of the fauces. Each posterior pillar belongs to the postero-inferior border of the soft palate, and it sweeps outwards, downwards, and backwards on the lateral wall of the pharynx. It is due to the palato-pharyngeus muscle. Each anterior pillar belongs to the buccal surface of the soft palate, and it sweeps outwards, downwards, and forwards to the back part of the side of the tongue. It is produced by the palato-glossus muscle. Between the diverging cinterior and posterior pillars, on either side, there is a triangular interval, which is occupied by the tonsil. The passage which leads from the buccal cavity into the pharynx is called the fauces or isthmus faucium. It is somewhat constricted, and is bounded above by the soft palate, below by the Descending Palatine Artery Palato-pharyngeus ^ ^ Palato-glossus Posterior Wall of PhatjTuc •'y Palatal Raph« Uvnla '1^^- Post. Pillar of Fauces ' Ant. Pillar of Fauces - Tonsil Dorsum of Tongue Fig. 510. — The Buccal Cavity and Isthmus Faucium. (The Maxillae axe widely separated), back part of the dorsum of the tongue, and on either side by the anterior pillar of the fauces. The buccal surface of the soft palate presents a faint mesial raphe. Structure. — ^The soft palate is composed of a double fold of mucous membrane, which contains between its two layers an aponeurosis, muscles, and many racemose glands, with bloodvessels and nerves. The mucous membrane on the buccal surface presents, as stated, a median raphe, which is continuous with that on the mucous membrane of the hard palate, and along which the originally separate halves of the soft palate unite. On the buccal surface and along the postero-inferior border it is covered by stratified squamous 79 I250 A MANUAL OF ANATOMY epithelium, but on the pharyngeal surface by ciliated columnar epithelium. The glands, which are racemose or acinous, are especi- ally abundant on the buccal surface beneath the mucous membrane, where they are closely packed together. The aponeurosis is attached anteriorly to the posterior border of the hard palate, and laterally it becomes continuous with the aponeurosis of the pharynx. It affords attachment to portions of the palatal muscles. Muscles. — These are arranged in pairs, and are as follows : palato-glossus, palato-pharyngeus, azygos uvulae, levator palati, and tensor palati. Palato-glossus (Constrictor Isthmi Faucium) — Origin. — ^The under surface of the palatal aponeurosis, its fibres being continuous across the middle line with those of the opposite muscle. Insertion. — ^The back part of the side of the tongue, where its fibres blend with the transverse muscular fibres of the tongue. Nerve-supply. — ^The pharyngeal plexus. The direction of the muscle is outwards, downwards, and forwards. Action. — (z) To depress the side of the soft palate, and (2) to draw the tongue upwards and backwards. The two muscles also approximate the anterior pillars of the fauces. By means of these combined actions, aided by the tongue, the isthmus faucium is closed, and the anterior part of the buccal cavity is shut off from the pharjmx at the commencement of the second stage of deglutition. The muscle forms the lowest layer in the soft palate, and it gives rise to the mucous fold, called the anterior pillar of the fauces. Palato-pharyngeus — Origin. — By two layers, upper and lower. The upper small layer arises from the aponeurosis of the soft palate above the azygos uvulae, its fibres decussating with those of the opposite side ; and the lower large layer arises from the posterior margin of the hard palate, as well as from the palatal aponeurosis, decussating with its fellow of the opposite side. Insertion. — (i) The superior and posterior borders of the ala of the thyroid cartilage, and (2) the lateral and posterior wall of the pharynx, its fibres blending with those of the stylo-pharyngeus. The muscle receives an accessory slip from the lower part of the cartilage of the Eustachian tube, which is known as the salpingo- pharyngeus muscle. Nerve-supply. — ^The pharyngeal plexus. The muscle is directed downwards and backwards. Action. — (i) To approximate the posterior pillar of the fauces to its fellow at the commencement of the second act of deglutition, and (2) to elevate the pharynx. The muscle gives rise to the mucous fold, called the posterior pillar of the fauces. Azygos Uvulae — Origin. — The side of the posterior nasal spine and the adjacent aponeurosis. I Insertion. — The submucous tissue of the uvula, having previously 1 united with its fellow of the opposite side. THE HEAD AND NECK 1251 Nerve-supply.— TYiQ pharyngeal plexus. The du-ection of the muscle is backwards and downwards. Action. — To elevate and shorten the uvula. The muscle is double at its origin, but single at its insertion. It lies above the levator palati, and beneath the upper layer of the palato-pharvngeus. . Levator Palati — Origin. — (i) The rough surface on the mfenor aspect of the petrous part of the temporal bone between the apex and the carotid foramen, and (2) the lower and posterior part of the cartilage of the Eustachian tube. Eustachian Cushion Posterior Border of the Vomer kight Posterior Naris / Levator Palati Salpingo- pharyngeus Azygos Uvulae Palato- pharyngeus" Tensor Palati . Internal Pterygoid Uwila -- Rooi of Tongue 1 Epiglottis Wall of Pharynx Sinus Pyriformis Arytsenoideus Obliquus Arytanoideus Transversus Crico-arytienoideus Posticus CEsophagus Fig 511. — The Pharynx opened from behind. Insertion. — ^The aponeurosis of the soft palate, its posterior fibres becoming continuous across the middle line with the corresponding fibres of the opposite muscle. Nerve-supply. — ^The pharyngeal plexus. Another view, however, is that the muscle is supplied by the posterior descending palatine perve from Meckel's ganglion, which conveys fibres of the facial nerve through the great superficial petrosal and Vidian nerves. The muscle is directed downwards, forwards, and inwards. Action. — (i) To raise the soft palate, and (2) to press upwards the membranous floor of the Eustachian tube, and so lead to closure of the Eustachian orifice during deglutition (Cleland). 1252 A MANUAL OF ANATOMY The muscle, which is round and fleshy, passes over the upper border of the superior constrictor and through the pharyngeal aponeurosis. At its origin it is closely related to the membranous portion of the Eustachian tube. Tensor Palati — Origin. — (i) The scaphoid fossa at the root of the internal pterygoid plate of the sphenoid ; (2) the spine of the sphenoid ; and {3) the outer side of the Eustachian tube. Insertion. — (i) The transverse ridge on the under surface of the horizontal plate of the palate bone, near the posterior border ; and (2) the aponeurosis of the soft palate. Nerve-supply. — A branch from the otic ganglion. Two views are maintained as to the source from which the nerve-fibres are derived. One view is that they come from the inferior maxillary division of the fifth cranial nerve, through the branch to the internal pterygoid muscle, which branch furnishes motor fibres to the ganglion. The nerve-supply of the tensor palati muscle is explained as follows: The Eustachian tube is developed from the first visceral cleft; the tensor palati muscle lies in front of the Eustachian tube, and is consequently associated with the first visceral, or mandibular, arch; and the nerve of that arch is the inferior maxillary division of the fifth cranial nerve. The muscle at first descends vertically as a flat fleshy band between the internal pterygoid plate and the internal pterygoid muscle, being in close contact with the mesial surface of the latter. As it ^^roaches the hamular process it ends in a tendon, which turns round that process, a synovial bursa intervening, and then passes horizontally inwards, expanding as it does so. From the fact that the muscle is bent around the hamular process it has been called the circumflexus palati. Action. — (i) To make tense the soft palate, and (2) to draw downwards and backwards the margins of the cartilage of the Eustachian tube, and so open the tube during deglutition. (See action of levator palati.) The muscle comes into play during the second stage of deglutition. Sensory Nerves. — ^These are (i) the posterior and external palatine nerves from Meckel's ganglion, and (2) the tonsillitic branches of the glosso -pharyngeal. Arteries. — ^The soft palate is supplied by the following arteries : (i) the inferior or ascending palatine of the cervical portion of the facial ; (2) the palatine branch of the ascending pharyngeal ; and (3) the posterior and external branches of the descending palatine artery from the internal maxillary, which descend in the posterior and external accessory palatine canals. Relation of Structures in the Soft Palate. — Supposing the soft palate to be transfixed from its buccal to its pharyngeal surface, the following structures would be pierced in the order stated : (i) the mucous membrane covering the buccal surface, (2) the layer of closely-set racemose glands, (3) the palato-glossus, (4) the lower layer of the palato-pharyngeus, (5) the palatal aponeurosis and tensor palati, (6) the levator palati, (7) the azygos uvulae, (8) the upper layer of the palato-pharyngeus, and (9) the mucous membrane covering the pharyngeal surface. THE HEAD AND NECK 1253 Development. — The soft palate is developed from a diflEerentiated portion of the palatal shelf or plate of the majcillary process of either side. This differentiated portion does not undergo ossification, but acquires muscular tissue. Like the hard palate, the soft palate and the uvula are developed in two symmetrical halves. The Tonsils. The tonsils {amygdalce) are two in number, right and left. Each is situated in the triangular depression between the anterior and posterior pillars of the fauces on either side, and, above it, is a small recess, known as the supratonsillar fossa, which is the remains of the inner portion of the second visceral cleft. The tonsil stands out as an oval enlargement, covered by mucous membrane, and it lies opposite the angle of the inferior maxilla, being under cover of it and I Lymphoid Follicle' ^""""**— — ^====^^^^^*^^ Buccal Epithelium Fig. 512. — Section through a Crypt of the Tonsil the adjacent portion of the ramus. The organ varies much in size, but on an average it measures about i inch in length, about f inch from before backwards, and about \ inch from within out- wards. The internal surface is pitted with a number of orifices, which lead into crypts in the interior. The outer surface, which has a fibrous covering, is related to the superior constrictor of the pharynx, some loose tissue intervening, and external to the superior constrictor is the internal pterygoid muscle. Two of the tonsillar arteries, namely, the tonsillar and inferior or ascending palatine, lie between the superior constrictor and internal pterygoid. The cervical portion of the facial artery in its course lies a little below the outer aspect of the tonsil. The internal carotid artery is situated about I inch from it on its outer and posterior aspect. Arteries. — ^These are as follows : (i) the tonsillar and inferior or ascending palatine branches of the cervical portion of the facial ; (2) the ascending pharyngeal branch from the external carotid; •(3) the dorsalis linguae from the Ungual; and {4) the posterior and external palatine offsets of the descending palatine artery from the third part of the internal maxillary. 1254 A MANUAL OF ANATOMY The veins form a plexus on the outer surface of the tonsil, from which the blood passes into the pharyngeal plexus. Lymphatics. — These passto the uppergroupof deepcervicalglands. Nerves. — The nerves are derived from (i) the glosso-pharyngeal, (2) the posterior and external palatine branches of Meckel's ganglion, and (3) the sympathetic. Structure . — The tonsils are composed of lymphoid follicles. The follicles are ranged upon the sides of the crypts which penetrate into the organ, these crypts being lined with mucous membrane, covered by stratified squamous epithelium. Lymph corpuscles migrate from the follicles into the crypts, and become salivary corpuscles. Development. — The tonsil of either side is developed from the epithelium of the corresponding second visceral cleft. About the fourth month a depression, known as the sinus tonsillaris, makes its appearance. Solid epithehal out- growths or buds then extend from this sinus into the surrounding mesoderm. These buds subsequently become hollow; the surface of the sinus becomes pitted ; and so the crypts of the tonsil are formed. The mesoderm in relation to the buds and crypts becomes pervaded with lymphoid cells, and in this manner is formed the lymphoid tissue which constitutes the bulk of the tonsil. The supratonsillar fossa is a remnant of the second visceral cleft. The Nasal Fossae. The nasal fossae extend from the anterior nares to the posterior nares. Anteriorly they open upon the face, and posteriorly they open into the naso-phar5mx. Each fossa is narrow above, but ex- panded below. It presents two walls, outer and inner, a roof, and a floor. The outer wall is rendered very irregular by three convoluted bony eminences, disposed antero-posteriorly, which bulge into the fossa. These are the superior and inferior turbinate processes of the ethmoid, and the inferior turbinate bone. They are also known as the superior, middle, and inferior spongy bones, or conchae. They overhang deep channels, which are known as the meatus — superior, middle, and inferior respectively. The superior meatus is confined to the back part of the outer wall, and lies between the superior and middle conchae. It is short and oblique, and opening into it there are (i) the spheno-palatine foramen, which leads from the spheno-maxillary fossa, and (2) the posterior ethmoidal cells, by one or more openings. Above and behind the superior concha is a depression, called the spheno- ethmoidal recess, into which the sphenoidal air-sinus opens. The middle meatus is situated between the middle and inferior conchae, is directed from behind forwards, and is overhung by the middle concha. Anteriorly it describes a bend, and passes upwards under cover of the front part of the middle concha, to be continued into the infundihulum, which leads from the frontal air-sinus of the corresponding side. The openings into the middle meatus are as follows: (i) the infundihulum, leading from the frontal air-sinus, with the opening of the anterior ethmoidal cells; (2) the opening of the maxillary air-sinus or antrum of Highmore; and (3) one or two openings of the middle ethmoidal cells. Ihese various openings THE HEAD AND NECK 1255 are concealed by the middle concha. When this is removed the lateral wall of the middle meatus is seen to present a deep curved groove, called the hiatus semilunaris, which is directed downwards and backwards from the lower end of the infundibulum. Behind and above this hiatus there is a round prominence, called the bulla ethmoidalis. The opening of the anterior ethmoidal cells is situated in the vertical portion of the hiatus semilunaris, and the opening of the antrum of Highmore, which is of small size, is placed FroQtal Air-Sinus Snperio: Meatus \ Superior Concha \ / Spheno-ethmoidal Recess Inferior Meatus Hard Palate (in section) Tongue Mandib!s (in section) ^.- Sphenoidal Air-Sintl3 Middle Concha ..Middle Meatus ..Inferior Concha Eustachian Orifice Salpingo-pharyngeal Fold ..Soft Palate "- Epiglottis Pharynx Gcnio-fayo-glossus Genio-hjrpid Vrntricle of Larynx y Thyroid Cartilage Cricoid Cartilage (Esophagus Tracb:= Fig. 513. — Sagittal Section through the Nasal Fossa, Mouth, Pharynx, (Esophagus, and Larynx. (The Outer Wall of the Right Nasal Fossa is shown). in its hori2ontal portion, whilst the middle ethmoidal cells open above the bulla ethmoidalis. In front of the middle meatus is the region known as the atrium, which communicates anteriorly with the vestibule, the latter being situated just within the ala of the nostril. The inferior meatus is situated below the inferior concha. Open- ing into its anterior part, under cover of the inferior concha, is the lower orifice of the nasal duct, which is provided with an imperfect mucous fold, called the valve of Hasner. The orifice is about i^ inches from the anterior nasal aperture. t256 A MANUAL OF ANATOMY The inner wall forms the septum nasi. The roof, which is narrow, is horizontal in its central part, the anterior portion being sloped downwards and forwards, and the posterior portion downwards and backwards. The floor is smooth, and at its anterior and inner part is the incisor foramen, into which a funnel-shaped portion of the mucous membrane extends. This region represents the wide communica- tion which existed in early life between the nasal and buccal cavities. Each nasal fossa is divided into three regions — vestibular, ol- factory, and respiratory. The vestibular region, or vestibule, forms the anterior and lower part contiguous to the nostril. It is covered by skin, which is provided with hairs or vibrissce. The olfactory Atrium Orifice of Nasal Duct^ Vestibule Frontal Air-Sinus ■ Infundibulum Opening of Anterior Ethmoidal Cells j Cut Margin of Middle Concha \i' ,' j Hiatus Semilunaris I / / Openuig of Middle Ethmoidal Cells )S>Z / / / Bulla Ethmoidalis V ' ' r'^^vte,^^'' , Spheno-ethmoidal Recess .Superior Meatus Sphenoidal Air-Sinus Opening of Antrum of Highmore — Eustachian Orifice Inferior Meatus I | Middle Meatus • Part of Inferior Concha g^^.^ p^,^^^ Fig. 514. — The Outer Wall of the Right Nasal Fossa. (The Superior and Middle Conchse and part of the Inferior Concha have been removed). region is situated superiorly, and corresponds to the superior concha and the upper third of the septum nasi. The respiratory region comprises the middle and inferior conchas, the middle and inferior meatus, and the corresponding part of the septum. Mucous Membrane. — With the exception of the vestibule, which is lined with skin, the nasal fossa is provided with a highly vascular and sensitive mucous membrane, called the pituitary or Schnciderian membrane. It is continuous through the posterior nares with the mucous membrane of the naso-pharynx ; with that of the nasal duct, lachrjonal sac, and lachrjonal canaliculi, and thence with the conjunctiva ; and with that of the various air-sinuses which communicate with the nasal fossa. It is thick and spongy over the conchae, especially along the lower borders of the middle THE HEAD AND NECK 1257 and inferior conchce, and also on the septum nasi, but over the floor, atrium, and meatus it is comparatively thin. It is freely provided with acinous glands, and contains a certam amount of l\nnphoid tissue. The epithelium varies in different regions. In the vestibular region, where the lining membrane is skin, the epithelium is of the stratified squamous variety ; in the respiratory region, as well as m -1 Frontal Air-Sinus Nasal Bone Perpendicular '^ Plate of Ethmoid Palatal Process of Palate Bone (in section) Cartilage of Aperture Septal Cartilage Cartilage of Jacobson Fig. 515. Palata Process of Superior Majdlla (in section) -The Osseous and Cartilaginous Nasal Septum (Right Lateral View). the air-sinuses, it is stratified, columnar, ciliated epithelium ; and in the olfactory region it is non-ciliated columnar epithelium. Olfactory Mucous Membrane. — In the olfactory region the mucous membrane is thick and pulpy, and has a yellowish-brown colour, due to pigment in the epithelial cells. It contains a copious plexus of olfactory nerve-fibres, and many serous glands, which are known as the glands of Bowman. The epithelium is thick, and, as just stated, is of the non-ciliated columnar variety, its free surface being covered by a delicate limiting membrane. The cells 1258 A MANUAL OF ANATOMY of which it is composed are of three kinds, (i) Long columnar nucleated cells, called the sustentacular cells, the deep ends of which are prolonged each into a branched process. (2) Between these sustentacular cells there are the olfactory cells, which are elongated and spindle-shaped. Each contains an almost spherical nucleus, and has a superficial and a deep process or pole. The superficial pole extends through the limiting membrane to the free surface, and projects slightly in the form of a tuft of delicate hair- like filaments called the olfactory hairs. The deep pole, which is a delicate varicose filament, extends towards the mucosa, where it becomes continuous with one of the nerve-fibrils of the olfactory Olfactory Filaments Olfactory Bulb / Olfactory Tract Fig. 516A. — The Nerves of the Nasal Septum (Hirschfeld and Leveille). Fig. 5 1 6b. — Cells of Olfactor- Mucous Membrane (Schultzi FROM Quain's 'Anatomy ')• plexus. (3) In the deep part of the epithelium there are in some places conical cells, the broad ends of which rest upon the basement membrane. • Olfactory Nerves. — ^These are from fifteen to twenty in number on each side. After leaving the inferior surface of the olfactory bulb, they pass through the foramina in the corresponding half of the cribriform plate of the ethmoid bone, and so reach the upper part of the nasal fossa, invested by prolongations of the membranes of the brain. Within the nasal fossa they are arranged in two groups, inner and outer. The nerves of the inner group are distributed' to the mucous membrane of the septum nasi over about its upper third. The nerves of the outer group are distributed to the mucous membrane in the region of the superior concha and olfactory sulcus. The nerves form a copionr. plexus in the mucous membrane, and the filaments which issue from this plexus become continuous, as i THE HEAD AND NECK »«59 stated, with the deep poles of the olfactory cells. The olfactory nerves are destitute of a medullary sheath. Nerves of Ordinary Sensation. — These axe derived from the ophthalmic and superior maxillary divisions of the fifth creinial nerve, and are as follows : 1. Superior nasal nerves. 2. Nasal branches of the Vidian nerve. ■I. Inferior nasal nerves. 4. Internal branches of the nasal nerve. 5. Nasal branch of the anterior superior dental nerve. 6. Naso-palatine nerve. The superior nasal nerves are derived from Meckel's ganglion. They enter the superior meatus through the spheno-palatine foramen, and are distributed to the mucous membrane (i) over the superior and middle conchae, (2) over the upper and back part of the septum nasi, and {3) within the posterior ethmoidal cells. The nasal branches of the Vidian nerve pierce the floor of the pterygoid or Vidian canal, and are distributed to the mucous membrane over the back part of the roof of the nasal fossa and the adjacent part of the septum. Posterior Ethmoidal Artery Spheno- Palatine Artery y AnteriOT EthnKudal Artery Soft Palate Fig. 517. — The Arteries of the Nasal Septum (Hirschfeld and Leveille). The inferior nasal nerves arise from the great or anterior descending pala- tine branch of Meckel's ganglion, as that nerve traverses the posterior pala- tine canal. They enter the nasal fossa through foramina in the vertical plate of the palate bone, and are distributed to the mucous membrane over the greater part of the inferior concha, and the corresponding parts of the middle and inferior meatus. The internal branches of the nasal nerve are two in number, septal and external. The septal branch is distributed to the mucous membrane over the anterior and upper part of the septum, and the external branch to that over the anterior portions of the middle and inferior conchae, and over the Outer wall in front of these. The nasal branch of the anterior superior dental nerve is distributed to the mucous membrane over the anterior part of the inferior meatus and the adjacent part of the floor of the nasal fossa. i25o A MANUAL OF ANATOMY The naso-palatine nerve, or nerve ol Cotunnius, arises from Meckel's gang- lion, and enters the nasal fossa through the spheno-palatine foramen. It then crosses the roof, and so reaches the septum, upon which it descends, with a forward inclination, occupying the groove on the outer surface of the vomer. Thereafter it passes downwards to the anterior part of the hard palate, the left nerve traversing the anterior foramen of Scarpa, and the right nerve the posterior foramen of Scarpa. As the naso-palatine nerve lies upon the septum nasi it furnishes branches to its mucous membrane. Arteries ol the Nasal Fossa. — These arteries are derived from the following sources : 1. The spheno-palatine. 2. The descending palatine. 3. The Vidian. Anterior Ethmoidal I 4. The anterior ethmoidal. 5. The posterior ethmoidal. 6. The superior coronary. Posterior Ethmoidal Naso-palatine (cut) Spheno-palatine m^'^P-Posterior Nasal Ascending Branch of Descending Palatine Soft Palate Fig. 518. — The Arteries of the External Wall of the Right Nasal Fossa (after Hirschfeld and Leveille). The spheno-palatine artery is the principal artery of the nasal fossa. Arising from the third part of the internal maxillary, it enters the fossa through the spheno-palatine foramen. Most of its branches are distributed to the outer wall ; but one, called the naso-palatine branch, accompanies the naso- palatine nerve. This branch gives offsets to the septum, and terminates by entering the incisor foramen, where it anastomoses with a branch of the descending palatine artery, which ascends from the palate in the incisor canal (Stensen's canal). The descending palatine artery arises from the third part of the internal maxillary. As it traverses the posterior palatine canal it gives off two or three branches which accompany the inferior nasal nerves through foramina in the vertical plate of the palate bone, to be distributed to the back part of the inferior concha and the adjacent parts of the middle and inferior meatus. The Vidian artery, arising from the third part of the internal maxillary, traverses the pterygoid or Vidian canal, and furnishes a few twigs which accompany the nasal offsets of the Vidian nerve, and supply the back part of the roof of the nasal fossa and the adjacent part of the septum. The anterior and posterior ethmoidal arteries are branches of the ophthalmic. The anterior ethmoidal enters the nasal fossa along with the nasal nerve, and furnishes branches to the anterior ^nd upper part of the septum, the front THE HEAD AND NECK 1261 part of the outer wall, and the anterior portions of the middle and inferior conchae. The posterior ethmoidal furnishes nasal branches which enter the nasal fossa through some of the foramina in one half of the cribriform plate of the ethmoid bone, and are distributed to the roof and upper part of the septum. The superior coronary artery, a branch of the facial, furnishes the artery of the septum, which suppUes the anterior part of the septum and the columella nasi. The veins form a copious plexus, especially over the inferior concha and the lower margin and back part of the middle concha. The vessels which carry away the blood from the plexus correspond to the various arteries, and their principal destination is threefold, namely, (i) the pterygoid plexus, (2) the superior ophthalmic vein, and (3) the facial vein. The ethmoidal veins, which open into the superior ophthalmic vein, communicate with the intra- cranial anterior meningeal veins and with the angular vein of the face by means of twigs which pass through minute apertures in the nasal process of the superior maxilla, and, it may be, through a small foramen in the nasal bone. In those cases where the foramen caecum is pervious it transmits an emissary vein which passes between the intracranial superior longitudinal sinus and the veins of the roof of the nasal fossa. The lymphatics of the atrium and vestibule pass to the submaxillary lym- phatic glands. The principcd l)anphatics pass to (i) the retro -pharyngeal glands; (2) the deep facial, or internal maxillary, glands; and (3) the superior deep cervical glands. The lymphatics of the air-sinuses end in a similar manner. The lymphatics of the nasal fossae communicate with lymphatic spaces which are related to the olfactory nerve-filaments ; and these lymphatic spaces in turn communicate with the intracranial, subdural, and subarachnoid spcices. Development of the Nose. The primitive oral cavity, or stomodaeum, becomes divided into two cham- bers, upper or nasal, and lower or oral, this division being effected by the formation of the hard palate. The oral chamber constitutes the permanent mouth, and the nasal chamber becomes transformed into the two nasal fossae. The first indications of the olfactory organ are the two olfactory areas. They consist of thickened ectoderm, and are placed on the ventral aspect of the anterior cerebral vesicle, on either side of the mesial nasal process of the fronto-nasal process, and on the cephaUc side of the orifice of the stomodaeum. Each olfactory area soon becomes depressed and forms the olfactory pit. The two pits, right and left, are situated one on each side of the mesial nasal process of the fronto-nasal process. Each pit has the corresponding globular process of the mesial nasal process internally, and the lateral nasal process externally, this position corresponding to the situation of the future anterior nans on either side. At this stage the olfactory pits communicate with the stomodaeum, and the orifice of each pit constitutes the corresponding primitive anterior naris. The lateral nasal process of the fronto-nasal process is at first separated from the maxiUary process by a groove, called the oculo-nasal, naso-optic, or lachrymal sulcus, which extends from the ocular pit on the outer side of the lateral nasal process (which forms the aJa of the nostril) to the olfactory pit. This sulcus indicates the position of the future lachrymal sac and nasal duct of the corresponding side. When the maxillary process (previously joined by the lateral nasal process) grows inwards to unite with the globular process, it lies below the olfactory pit. In this manner the orifice of the olfactory pit — namely, the primitive anterior naris — is cut off from com- munication with the stomodaeum. The blind olfactory pits now grow dorsalwards along the roof of the stomo- daeum, and so give rise to the nasal sacs which represent the primitive nasal fossae. As each pit grows dorsalwards it is deepened by the formation of a groove, called the nasal groove, which extends to the roof of the stomodaeum. This groove is bridged over by ectoderm, and is thus separated from the corresponding olfactory pit. VVhen the maxillary process (previously joined 1262 A MANUAL OF ANATOMY by the lateral nasal process) unites with the globular process, the nasal groove is obliterated, and the olfactory pit is cut off from the stomodaeum. By the development of the hard palate, on either side, the ectodermic covering of the nasal groove disappears. The posterior part of this covering con- stitutes the naso-stomodaal membrane. When this membrane ruptures, on either side, a dorsal aperture, called the primitive posterior naris, is formed, likewise on either side, which estabUshes a fresh communication between the olfactory pit (blind end) and the stomodaeum on the cephalic side of the corresponding palatal shelf. By the formation of the hard palate the nasal fossae are almost entirely shut off from the permanent mouth, and by the formation of the septum nasi the fossae are entirely separated from each other. The communications which originally existed between the olfactory pits and the stomodaeum become considerably curtailed as the hard palate is being formed, and they are per- manently represented, in man, by the canals of Stensen, in the region of the anterior palatine fossa. In certain animals — e.g., ruminantia — there is a wide passage on either side of the median line, between the ventral part of the hard palate and each nasal fossa, which passage leads to the organ of Jacobson. Septum Nasi. — ^The septal cartilage of the nose is derived from the eth- moidal division of the basal sheet of cartilage, called the chondrocranium, and the vomer is developed in the mesoderm which invests the posterior and inferior parts of the septal cartilage. The perpendicular plate ol the ethmoid is developed from the ethmoidal division of the chondrocranium, as is also the cribriform plate. The superior, middle, and inferior spongy bones, or conches, appear as folds of ectoderm which project from the outer wall of the nasal fossa. These folds contain mesoderm, and in this mesoderm cartilage, pertaining to the car- tilaginous nasal capsule, is formed. The cartilage undergoes ossification, and gives rise to the three conchae, the upper two forming part of the lateral mass of the ethmoid, whilst the inferior concha persists as an independent bone, usually spoken of as the inferior turbinate bone. Air-Sinuses. — ^The frontal, ethmoidal, sphenoidal, and maxillary air-sinuses are developed as evaginations of the nasal mucous membrane, which extend into spaces formed by absorption within the respective bones. The mastoid cells are developed as evaginations of the tympanic mucous membrane, which is continuous with the nasal mucous membrane through the Eustachian tube and naso-pharynx. Olfactory Organ. — The true olfactory organ is situated in the upper part, or olfactory region, of each nasal fossa. The olfactory epithelium, which covers the mucous membrane of this region, is developed from the upper part of the corresponding olfactory pit. External Nose. — The dorsum and tip of the nose, and the columella nasi are developed from the portion of the mesial nasal process which Ues between the globular processes. The upper and lower lateral nasal cartilages are derived from the cartilaginous core of the corresponding lateral nasal process. The anterior naris of each side represents, as stated, the external orifice of the corresponding olfactory pit. Organ ol Jacobson. — Jacobson's organ is rudimentary in man, but is Well developed in ruminantia. It takes the form of a blind pouch, Which is situated in the lower and anterior part of the septum nasi on either side. The minute orifice of the pouch lies above the recess or depression of mucous membrane which projects slightly into the upper end of Stensen's canal. The pouch extends upwards and backwards in the septum nasi for a very short distance, and terminates in a blind extremity. The cartilage of Jacobson lies underneath it. Jacobson's organ does not seem to perform any function in man. In those animals, however, in which it is Well developed, e.g., ruminantia, it receives two nerves, one of Whicli THE HEAD AND NECK 1263 is olfactory, the other being derived from Meckel's ganglion. More- over, its epithelial lining is similar to that of the olfactory region of the nasal fossa, inasmuch as it contains olfactory cells, the deep poles of which are continuous with olfactory filaments. In such animals it acts as a supplementary organ of smell. Development of Organ ol Jacobsoa. — ^This organ is developed as a diverticu- lum of a portion of the ectoderm of the olfactorj- pit. The diverticulum projects upwards and backwards into a recess situated laterally within the lower and anterior part of the septal nasal cartilage, just above the upper end of Stensen's canal (incisor canal). The Pharynx. The pharynx is situated behind the posterior nares, isthmus faucimn, and larynx, and it extends from the basilar region of the base of the skull to the level of the lower border of the cricoid cartilage of the larynx, where it becomes continuous with the oesophagus. It is a musculo-aponeurotic tube, about 5 inches long, and it attains its greatest width between the base of the skull and the hyoid bone. BeloW the latter level it narrows, and is flattened from before backwards, so as to assimae the form of a transverse cleft, except during the act of deglutition. Relations. — Posteriorly it rests upon the bodies and discs of the cersical vertebrae as low" as the sixth, and the prevertebral muscles covered by the prevertebral fascia. Between it and the last-named fascia is the retropharyngeal space. Which is occupied by connective tissue, but this is so loosely arranged that no obstacle is offered to the movement of the tube, and a post-pharyngeal abscess can readily diffuse itself. Anteriorly it communicates with (i) the nasal fossae through the posterior nares, (2) the Eustachian tubes, (3) the buccal cavity through the isthmus fauciimi, and (4) the larynx. On this aspect its attachments are effected by means of the con- strictor muscles in its w'alls. Laterally it is related to the principal bloodvessels and nerves of the neck, and comes into contact with the styloid muscles and the process from which they arise. Superiorly it is attached to the basilar region of the base of the skulL Inferiorly it is continuous with the oesophagus. The w'all of the pharjmx consists of the following four strata, in order from without inwards: (i) the pharjTigeal portion of the bucco-pharyngeal fascia, (2) the muscular coat, (3) the pharyngeal aponeurosis, and (4) the mucous coat. Pharyngeal Fascia. — This is an offshoot of the prevertebral lamina of the deep cervacal fascia along the mesial aspect of the carotid sheath. In front it becomes continuous with the fascia covering the buccinator muscle. In association with this fascial stratum there are many veins upon the posterior and lateral Walls of the pharjmx, which constitute the pharvTigeal venous plexus. . Muscular Coat. — This is composed, on either side, of the three constrictor muscles, inferior, middle, and superior, the stylo- phar\Tigeus, and the palato-pharyngeus (including the salpingo- pharyngeus). 1264 A MANUAL OF ANATOMY Inferior Constrictor — Origin. — (i) The side of the cricoid cartilage at its posterior part; (2) the inferior cornu and the obHque hne of the ala of the thyroid cartilage; and (3) the upper border of the ala behind the superior tubercle. Insertion. — The median raphe on the posterior wall of the pharynx, Where it meets its fellow of the opposite side. The lower fibres of the muscle are horizontal, but the upper fibres pass upwards and backwards more and more obliquely, and the highest fibres of the two muscles meet in the raphe to form a peak, which is about an inch below the basilar process of the occipital bone. The lower border of the muscle overlaps the upper end of Sinus of Morgagni Superior Constrictor . . Muscle Middle Constrictor Muscle External Pterygoid Muscle Styloid Process -C jndyle of Mandible 7...«,Spheno-mandibu- lar Ligament - Ramus of Mandible «,Stylo-phar. Muse. Stylo-hyoid Lig. .^.Internal Pterygoid Muscle Great Cornu of Hyoid Bone Angle of Mandible „. Median Raph^ of Pharynx Inferior Constrictor Muscle- CEsophagus Fig. 519. — The Posterior Wall of the Pharynx and Adjacent Structures. the oesophagus, and, to a hmited extent, some of the fibres are continuous With the oesophageal muscular fibres. The recurrent lar5mgeal nerve and inferior laryngeal artery pass upwards beneath the lower border behind the crico-thjnroid joint. The upper border, Which is very oblique, overlaps the lower portion of the middle constrictor, and the internal laryngeal nerve and the superior laryngeal artery, on their way to pierce the thyro-hyoid membrane, pass between the two muscles anteriorly. Middle Constrictor — Origin. — (i) The upper surface of the great cornu of the hyoid bone over its entire length, {2) the small cornu, and (3) the hyoid extremity of the stylo-hyoid hgament. TME HEAD AND NECK 1265 Insertion. — ^The median raphe on the posterior vrall of the pharynx, where it meets its fellow of the opposite side. The muscle is fan-shaped, and its fibres consequently diverge very much as they pass round to reach the raphe. The inferior fibres descend very obhquely, and are overlapped by the upper fibres of the inferior constrictor, the internal laryngeal nerve and superior lar5mgeal artery- passing to the thyro-hyoid membrane between the two muscles anteriorly. The middle fibres pass more or less transversely. The superior fibres ascend obhquely, and reach the basilar process of the occipital bone. They overlap the loWer portion of the superior constrictor, and the stylo-pharyngeus muscle and glosso-pharyngeal nerve pass between the two. The lingual artery rests upon the muscle at the great comu of the hyoid bone. Superior Constrictor — Origin. — (i) The lower third of the posterior border of the internal pterygoid plate, and the hamular process of the sphenoid bone; (2) the posterior aspect of the pterygo-mandi- bular ligament, along which it meets the buccinator muscle ; (3) the posterior extremity of the mylo-hyoid ridge of the lower jaw; (4) the mucous membrane of the mouth; and {5) the side of the tongue. Insertion. — The median raphe on the posterior wall of the pharynx, where it meets its fellow of the opposite side. A feW of the highest fibres are inserted into the pharyngeal tubercle on the under surface of the bcisilar process of the occipital bone. The muscle is somewhat four-sided. The fibres for the most part pass horizontally, but the lower fibres radiate in a downward direction, whilst the upper fibres curve backwards and upwards. The lower portion of the muscle is overlapped by the upper part of the middle constrictor, the stylo-phan^ngeus muscle and glosso- pharyngeal nerve passing between the two. Between the upper, concave border and the base of the skull there is an interval occupied by the pharyngeal aponeurosis, which is here stronger than elsewhere, and so compensates for the absence of muscular fibres. This interval is semilimar, and is known as the sinus of Morgagni. Nerve-supply of the Constrictor Muscles. — The nerves are derived from the pharyngeal plexus, which is formed by the pharyngeal branch of the pnevmiogastric, the pharyngeal branches of the glosso-pharyngeal, and sympathetic filaments. The motor fibres of the plexus are derived from the pharyngeal branch of the pneumogastric, but their ultimate source is the bulbar portion of the spinal accessory nerve. The inferior constrictor muscle also receives twigs from (i) the external larjTigeal branch of the superior larj-ngeal nerve, and (2) the inferior or recurrent larjoigeal nerve as it passes beneath the lower border of the muscle. Action. — The constrictor muscles are concerned in the act of deglutition. The superior constrictor and upper portion of the middle constrictor act upon the naso-pharynx, that is, the compart- ment of the pharynx which hes above the soft palate, and is in communication with the nasal fossje through the posterior nares. They narrow the naso-pharjTix in the lateral direction, and this 80 1266 A MANUAL OF ANATOMY movement, in conjunction with the action of the posterior pillars of the fauces, shuts off the naso-phar5mx, thus preventing regurgita- tion into and through the nasal fossae. The lower portion of the middle constrictor and the inferior constrictor diminish the calibre of the buccal compartment of the pharynx. Coming into action during the second stage of deglutition, they grasp the bolus of food and press it downwards into the oesophagus. The constrictor muscles contract rapidly, and in order from above downwards. Tensor Palati Levator Palati Pterygo-mandibular Ligament Stensen's Duct Stylo-hyoid Ligament (cut)._ Superior Constrictor Stylo-pharyngeas . Glosso-pharyngeal Nerve - Middle Constrictor ... Hypoglossal Nerve and Hyo-glossus Superior Laryngeal Nerve -- Superior Laryngeal Artery __ Inferior Constrictor Buccinator Muscle Mylo-hyoid Muscle — Crico-thyroid Muscle CEsophagus -liHWIBfllllir''''" "'"'""'!!'.. Trachea "■^fiii'r- '"''erior Laryngeal Nerve Inferior Laryngeal Artery Fig, 520. — Dissection showing the Cheek, Pharynx, Submaxillary Region, and Larynx (Right View). For a description of the stylo-pharyngeus and palato-pharyngeus muscles (including the salpingo-pharyngeus), see Index. Pharyngeal Aponeurosis. — This is situated between the muscular coat and the mucosa. Inferiorly it is weak and indistinct, but superiorly it acquires greater firmness and density, expecially whert; it is attached to the basi-occipital, the apex of the petrous part oi the temporal bone, the adjacent portion of the Eustachian tube, THE HEAD AND NECK 1267 and the internal pterygoid plate of the sphenoid bone. It receives an accession of strength in the median line from a strong bimdle of fibres which descends from the pharyngeal tubercle on the under surface of the basilar process of the occipital bone, and which forms the raphe of the pharynx. Interior of the Pharynx. — The mucous membrane, which forms the fourth stratum in the pharjoigeal wall, is of a papillary character, and has the following important continuations : (i) with the mucous membrane of the Eustachian tube, and thence with that of the Frontal Air-Sinus Superior Meatus S uperior Concha Inferior Meatus Hard Palate(insection)7rrir___j,_,.,-_- Tongue ^'\'!j '■ -^ Mandible (in section) _. Genio-hyo-g^ossus Genio-hyoid ■' Spheno-ethmoidal Recess ^,- Sphenoidal Air-Sinns Middle Concha Middle Meatus ^-LV Inferior Concha — .--I'l Eustachian Orifice -^- — Salpingo-pharyngeal Fold ...Soft Palate ^^ Epiglottis ^Mr Pharynx Ventricle of Larynx ,' Thyroid Cartilage Cricoid Cartilage te^ (Esophagns Trachea Fig. 521. — Sagittal Section through the Nasal Fossa, Mouth. Pharynx, (Esophagus, and Larynx. (The Outer Wall of the Right Nasal Fossa is shown.) tympanum or middle ear ; (2) With that of the nasal fossae through the posterior nares ; (3) with that of the buccal cavity through the isthmus faucium; {4) with that of the larynx through the superior laryngeal aperture; and {5) with that of the oesophagus. At its upper and back part it is richly provided with lymphoid tissue, to be presently referred to, and in the submucous tissue there are many acinous glands of a mucous character. The soft palate projects into the cavity of the pharynx in a down- ward and backward direction, and divides it into tWo regions, upper and lower. The upper region is known as the naso-pharynx. 1268 A MANUAL OF ANATOMY and is in communication with the nasal fossae and Eustachian tubes. It also communicates with the lower region by means of the pharyngeal isthmus. The lower region is subdivided into two parts, buccal and laryngeal. The buccal part is limited above by the soft palate, and below by the superior aperture of the larynx, and it communicates with the buccal cavity through the isthmus faucium. The laryngeal part is situated behind the larynx, with which it communicates, as Well as with the oesophagus inferiorly. Naso-pharynx. — This is entirely respiratory in function, and is consequently always pervious. It is bounded in front by the Eustachian Cushion Posterior Border of the Vomer ! Right Posterior Naris / Levator Palati Salpingo- pharyngeus Azygos Uvulae Tensor Palati - Internal Pterygoid . Uvula - Root of Tongue — Epiglottis _ Wall of Pharynx Sinus Pyriformis — Arytanoideus Obliquus — Arytaenoideus Transversus Crico-arytaenoideus Posticus CEsophagus Fig. 522. — The Pharynx opened from behind. posterior nares and the posterior border of the vometr ; behind, by the vertebral column; above, by the basilar process of the occipital and part of the body of the sphenoid ; and below by the soft palate, which can be elevated and depressed. Four openings communicate with the naso-pharynx. The anterior wall presents the oval openings of the posterior nares leading from the nasal fossas, and: separated from each other by the posterior border of the vomer. Each opening in the recent state measures about i inch from above downwards, and about \ inch from side to side. Through it, on the outer wall of the corresponding nasal fossa, are seen the posterior parts of the inferior turbinate bone and the inferior turbinate THE EtEAD AND NECK 1269 process of the ethmoid bone, covered b}- mucous membrane; and above and below the inferior turbinate bone are seen the posterior parts of the middle and inferior meatus. The orifice of the Eustachian tube is situated on each lateral wall, behind and external to the corresponding posterior naris, and on the same level as the posterior end of the inferior turbinate bone. It is somewhat oval, and presents, above and behind, a prominent round border, formed of cartilage, called the cushion. Behind the cushion there is a deep pouch on the lateral wall of the naso- pharynx, called the lateral pharyngeal recess, or fossa of Rosenmuller, which represents the upper part of the phar^mgeal portion of the second \asceral cleft. The mucous membrane extending between the lateral pharyngeal recesses, at the upper and back part, presents a number of folds containing a large amoimt of IjTnphoid tissue, which constitute the pharyngeal tonsil. When enlarged this mass is liable to obstruct the Eustachian orifices, and even the posterior nares. At the lower part of the phan/ngeal tonsil ther-^ may be seen a small median recess, called the pharyngeal bursa, which leads upwards and back\Vards towards the pharyngeal tubercle on the basilar process of the occipital bone. The mucous membrane is covered by ciliated columnar epithelium. Buccal Part of the Pharynx. — This part is situated between the soft palate and the superior aperture of the larynx. Anteriorly it commvmicates with the buccal cavity through the isthmus faucium, below which is the root of the tongue. Each lateral wall presents the posterior pUlar of the fauces, the interval between the two pillars corresponding to the pharyngeal isthmus. In front of each posterior pillar is a triangular depression which lodges the tonsil. Laryngeal Part of the Pharynx. — This part is situated behind the lar^Tix. Anterior to it there are the epiglottis, the superior aperture of the lar\Tix, on either side of which is a recess called the sinus pyriformis, and the posterior parts of the arytenoid and cricoid cartilages. With the muscles related to them. It communi- cates with the larynx anteriorly and the oesophagus inferiorly. The mucous membrane of the buccal and laryngeal portions is covered by stratified squamous epithelium. Blood-supply. — The arteries of the pharynx are derived from several sources, e.g., the ascending pharyngeal branch of the external carotid, the inferior or ascending palatine and tonsillar branches of the cervical part of the facial artery-, and the descending palatine and pterj'go-palatine breinches of the internal maxiUary. The veins form a copious pharyngeal plexus, which is disposed upon the lateral and posterior walls of the pharjTix. It com- j municates superiorly with the pter5'goid venous plexus, and receives ' tributaries from the soft palate, tonsils, and Eustachian tubes. ; Inferiorly the blood is conveyed from it into the internal jugular vein directly, or through means of the common facial vein. Lymphaties. — The lymphatic vessels from the upper part of the ^ pharynx pass to the internal maxiUary glands. Which are associated : with the lateral walls of the tube, and those from the remaining I270 A MANUAL OF ANATOMY part pass to the upper group of deep cervical glands. Some of the lymphatics from the upper part pass to the retropharyngeal gland, two in number, each of Which lies upon the upper part of the corresponding rectus capitis anticus major muscle. Development ol the Pharynx, and of the Pharyngeal Pouches or Visceral Clefts and Visceral Arches. The pharynx is developed from the anterior or cephalic part of the fore-gut. On the ventral wall of this part there are two elevations, the anterior of which is called the tuberculum impar, whilst the posterior is called the furcula. The latter has the form of a horseshoe, the open part of which is placed posteriorly. The furcula is "separated from the tuberculum impar in front, and from the lateral wall of the fore-gut on either side, by a groove called the sinus arouatus. The tuberculum impar gives origin to the anterior two-thirds, or buccal portion, of the tongue ; the anterior part or loop of the furcula gives rise to the epiglottis ; the posterior extremities of the furcula to the arytenoid cartilages ; and the depression within the furcula becomes deepened and developed into the larynx and trachea. Posterior to the furcula the foregut becomes dilated to form the rudimentary stomach, and as this descends the oesophagus is formed. Pharyngeal Pouches. The pharyngeal pouches (visceral clefts) are situated on each lateral wall of the pharyngeal part of the fore-gut, and are arranged in pairs from the cephalic region caudalwards. Their direction is dorso-ventral, or from behind forwards, and they are almost parallel with each other, there being a sUght convergence ventralwards. The number of pouches on either side is five in the human embryo. The fifth pouch is rudimentary, and is an appen- dage of the fourth, from which it projects in a caudal and ventral direction. The pouches are separated from each other by rounded bars, which represent the visceral arches. In order from the cephalic region caudalwards they are designated as first, second, third, fourth, and fifth pouches. Each pouch is developed as an outward protrusion of the entodermic lining of the pharyngeal part of the fore-gut. To meet each entodermic protrusion from the interior an inward extension of the ectoderm takes place from the exterior. In this manner furrows are formed on the exterior of the pharynx. The bottom of each pharyngeal pouch is closed, and is separated from the corresponding external furrow by an epithelial septum, which constitutes the closing membrane. This septum is bilaminar, its interned layer being entodermic, and its external layer ectodermic, both being in intimate contact. Metamorphoses of the Pharyngeal Pouches — First Pharyngeal Pouch. — The closing membrane at the bottom of this pouch separates it from the lirst external furrow which corresponds to it. The pouch itself, being pharyngeal, is entodermic, but the external furrow is ectodermic. From this pouch (ento- derm) the tympanitic cavity and the Eustachian tube are developed. The external furrow (ectoderm) becomes the external auditory meatus, and the lips of this furrow become differentiated into the component elements of the pinna. The closing membrane, originally bilaminar, becomes trilaminar, a third layer, consisting of mesoderm, having been developed between the two original entodermic and ectodermic laminae. So constituted, the closing membrane forms the membrana tympanl. Second Pharyngeal Pouch. — The remains of this pouch in the adult are — (i) The tonsil; (2) the supratonsillar fossa, a small depression which lie above the tonsil; and (3) the lateral pharyngeal recess or fossa of RosenmulU* behind the cushion of the pharyngeal orifice of the Eustachian tube. Third Pharyngeal Pouch. — This pouch disappears, but it furnishes a dive ticulum from which the corresponding lateral lobe of the thymus body developed. Fourth Pharyngeal Pouch. — ^This pouch likewise disappears, but, like third, it furnishes a diverticulum from which a portion of the correspondii THE HEAD AND NECK tvjx lateral lobe of the thyroid body is developed. It also gives rise to the sinus Pyriformis of the larynx. Visceral or Branchial Arches. — Between the pharyngeal ponches a thicken- ing of mesoderm takes place in the intervals between the entoderm and ectoderm. These thickenings give rise to elevated, rounded bars, which constitute the visceral or branchial arches. The number of these arches on either side is six. The sixth, however, which lies behind the fifth pharyngeal pouch, remains undifferentiated. Like the pharyngeal pouches, the visceral arches are arranged in pairs. The dorsal extremities of the arches, right and left, stand apart, and are attached to the sides of the head. The ventral extremities, on either side, approach the mesial Une of the future embryonic neck, and subsequently they become connected along the mesijd hne. Each arch projects into the pharyngeal part of the fore-gut, and the first four also form projections on the exterior, which increase the depth of the external Tuberculiun Impar Furcula Fig. 523. — The Visceral Arches of the Embryo (Posterior View) (His). I. Mandibular .Arch III. Thyro-hyoid Arch II. HyoidArch IV. Fourth Arch V. Fifth Arch furrows, corresponding to the visceral clefts. The names of the arches, from the cephaUc region caudalwards, are as follows : First, or mandibular, arch. Second, or hyoid. arch. Third ] Fourth I „ , . , . Fifth I Branchied arches proper. Sixth j The first arch on either side is situated between the first pharyngeal pouch and the stomodaeum or primitive oral ca\ity. By means of their mandibular and maxillary processes, right and left (the latter being supplemented by the fronto- nasal process), the first arches support the primitive oral cavity, forming its lower or posterior eind upper or iinterior boundaries. They are therefore known as the oral arches, the succeeding arches being post-oral. Each visceral arch, in its primitive condition, consists of (i) a central portion, or core, and (2) an epitheUal investment. The core consists of mesenchyme (mesoderm), and is peculiar to its own arch. The epitheUal investment is derived internally from the entoderm of the pharyngeal part of the fore-gut, and externally firom the ectoderm of the exterior. At a later stage each visceral arch acquires the following four elements: (i) An artery; (2) a cervical myotome or muscle-segment; (3) a nerve (or nerves) ; £ind (4) a rod of cartilage. The artery is known as a visceral-arch artery, and it is one of the primitive aortic arches, which arches, on either side, estabUsh a communication between the corresponding right and left primitive ventral and dorsal aortae. 1272 A MANUAL OF ANATOMY Myotomes ot Visceral Arches. — ^The cervical myotome in each arch gives rise to certain muscles. The myotome of the Jirst arch furnishes (i) the anterior belly of the digastric; (2) the mylo-hyoid; and (3) the muscles of mastication — namely, (a) masseter, (b) temporal, (c) external pterygoid, and (d) internal pterygoid. The myotome of the second arch furnishes (i) the posterior belly of the digastric; (2) the stylo-hyoid; and (3) the stapedius. From this myotome are also derived the muscles ol expression on the face and epicranial region, as well as the platysma. The myotome of the third arch furnishes the stylo-pharyngeus, and the middle constrictor ol the pharynx may be regarded as derived from it. The myotome of the fourth arch (and perhaps that of the fifth arch) may be regarded as furnishing the inferior constrictor of the pharynx. Nerves of Visceral Arches — First, or Mandibular (oral). Arch. — The common nerve of this arch is the fifth cranial, or trigeminal, nerve. The inferior maxillary or mandibular division belongs to the mandibular process of the arch, and to its muscles, and the lower teeth of one side ; the superior max- illary division belongs to the maxillary process of the arch, and to the upper teeth of one side; and the ophthalmic division belongs to the supplementary fronto-nasal process (one-half) . Second, or Hyoid, Arch. — The nerve of this arch and of the first pharyngeal pouch is the seventh cranial, or facial, nerve. The eighth cranial, or auditory, nerve may be included. Third, or Thyro-Hyoid, Arch. — ^The nerve of this arch and of the second pharyngeal pouch is the ninth cranial, or glosso-pharyngeal, nerve. Fourth Arch. — ^The nerve of this arch is the superior laryngeal nerve, which is a branch of the tenth cranial, or pneumogastric (vagus). Fifth Arch. — The nerve of this arch is the inferior, or recurrent laryngeal, nerve, which is a branch of the pneumogastric. The bar of cartilage, in each arch, is developed in the mesenchyme, which forms the core of the arch. Metamorphoses of the Visceral Arches. First Visceral, or Mandibular, Arch. — This arch is situated, as stated, between the first pharyngeal pouch and the stomodaeum or primitive oral cavity. Its artery is the first primitive aortic arch; its common nerve is the fifth cranial or trigeminal nerve; and its cartilaginous bar is known as Meckel's cartilage. The ventral end of this cartilage meets its fellow of the opposite side, and is joined to it by connective tissue. The dorsal end is related to the periotic cartilaginous capsule, and furnishes an offshoot, called the maxillary process. For a full account of the transformation of the first visceral arch see the Development of the Skull. It will be sufficient here to note the following points : 1. The upper or dorsal end of Meckel's cartilage, becoming ossified, gives rise to the malleus, and probably the incus. 2. The lovoer or ventral end of Meckel's cartilage gives rise to the indsor portion of the mandible. 3. The part of Meckel's cartilage between the upper and lower ends disap- pears. The membranous investment of the lower or mandibular portion of this part gives rise to the chief part of one-half of the body of the mandible, and the lower half of the ramus as high as the inferior dental foramen. The mem- branous investment of the upper portion, between the periotic cartilaginous capsule and the inferior dental foramen, forms the spheno-mandlbular liga- ment. 4. The maxillary process, aided by part of the fronto-nasal process — namely, the globular and lateral nasal processes, gives rise to the superior maxilla (see Development of the Skull). 5 . The upper end of the first arch gives rise to the tragus, and part of the heiix of the pinna. Second, or Hyoid, Arch. — This arch is situated, as stated, between the first and second pharyngeal pouches. Its artery is the second primitive aortic THE HEAD AND NECK 1273 arch ; its nerve is the seventh cranial, or facial, nerve, with the chorda tympani and the auditory nerves, and its cartilaginous bar is called the hyoid bar, or cartilage of Reichert. This bar ventrally is connected with its fellow of the opposite side ana with the thyro-hyoid bar of the same side by a transverse piece of cartilage, called the copula, which lies between the tuberculum impar and the loop of the furcula. The second arch becomes transformed into the following structures : 1 . The upper or dorsal segment of the hyoid bar gives rise to the head, neck, and crura of the stapes, the foot-piece of that ossicle being developed from the cartilaginous capsule of the labyrinth, within the fenestra ovalis. 2. The succeeding segment of the hyoid bar gives rise to (a) the tympano- hyal. and {b) the stylo-hyal, which collectively constitute the styloid process of the temporal bone. 3. The next portion of the hyoid bar becomes converted into fibrous tissue, and forms the stylo-hyoid ligament, which sometimes exisfts as an epi-hyal bone. 4. The lower or ventral segment of the hyoid bar gives rise to the cerato- hyal, or small cornu of the hyoid bone. The second arch also gives rise superiorly to the antihelix, antitragus, and lobule of the pinna ; and inferiorly, along with the third arch, to one-half of the posterior third of the tongue. Third, or Thyro-Hyoid, Arch. — This arch is situated between the second and third pharyngeal pouches. Its artery is the third primitive aortic arch ; its nerve is the ninth cranial, or glosso-pharyngeal nerve ; and its cartilaginous bar is known as the thyro-hyoid bar. This bar is connected ventrally with its fellow, and with the hyoid bar of the same side, by the copula already referred to. A large portion of the thyro-hyoid bar disappears, but its lower or ventral segment gives rise to the thyro-hyal or great cornu of the hyoid bone. The basi-hyal or body of the hyoid bone is developed from the copula. Fourth and Filth Visceral Arches. — The artery of the fourth arch is the fourth primitive aortic arch, and its nerve is the superior laryngeal nerve, wMch is a branch of the pneumogastric. The artery of the fifth arch is the fifth primitive aortic arch, and its nerve is the inferior, or recurrent, laryngeal hranch of the pneumogastric. The greater portions of these two arches disappear; but the lower or ventral ends of their cartilaginous bars are usually regarded as giving rise to the corresponding ala of the thyroid cartilage. Sixth Visceral Arch. — The artery of this arch is the sixth primitive aortic arch. The sixth arch itself, being undifferentiated, leaves no traces behind it. The metamorphoses of the pharyngeal pouches have been already described in connection with these pouches. The first external furrow, corresponding to the iirst internal pharyngeal pouch, gives rise, as stated, to the external auditory meatus, and the walls of this furrow become differentiated into the component parts of the pinna. Sinus Cervicalis and Cervical Fistula. — The first or mandibular and second or hyoid arches increase more rapidly in all directions than the succeeding branchial arches proper. The third and fourth branchial arches therefore become overlapped by the second or hyoid arch, and now lie at the bottom of a depression. This depression is called the sinus cervicalis. The lining membrane of the sinus is formed by the ectodermic constituents of the over- lapped branchial arches. The sinus is, as a rule, transitory, being soon obliterated as the second visceral arch grows backwards towards the fifth arch, the Ups of the sinus fusing. In rare cases, however, the sinus cer\-icalis may persist as an ectodermal cervical cyst. In other rare cases the ectoderm of the sinus may become ruptured, and then a communication might be established with a mucous canal — namely, the pharyngeal portion of the fore-gut, thus giving rise to the condition known as cervical fistula. Morphology of the Visceral Arches and Clefts. — In aquatic animals — e.g.. Fishes, and Amphibia at an early stage, but only in Perennibranchiata per- manently— these are called the branchial or gill-arches and clefts. The clefts range in number from five to eight, and they differ from those of Mammals and Birds inasmuch as they are complete clefts, the closing membrane being 1274 A MANUAL OF ANATOMY absent. They therefore establish free communications between the extericr and the fore-part of the alimentary canal, or throat, for the entrance and exit of water. The functional branchial arches are those which are post-oral, commencing with the second. The second branchial or gill -arch is not, however, a real branchial arch in the functional sense, but is opercular, giving rise, on either side, to the operculum or gill-cover. The real branchial or gill-arches, properly so-called functionally, are those which succeed to the second, of which the third and fourth are conspicuous. The mucous membrane of the real bran- chial arches is folded into parallel lamellae, which are placed close together, and are freely furnished with capillary bloodvessels, the blood being derived from the branchial -arch arteries. These lamellae constitute the branchiae or gills. Aquatic respiration consists in the passage of currents of water, containing oxygen, through the complete gill-clefts into the pharyngeal part of the fore-gut. As the water bathes the branchiae, or gills, its oxygen is taken up into the blood within the branchial capillaries, and the carbon dioxide of the capillary blood is yielded up to the water. Thereafter the water is ex- pelled through the gill-clefts, and is immediately replaced by a fresh current of respiratory water. The branchiae, or gills, of aquatic animals therefore correspond functionally to the lungs of Mammals and Birds, whose respiration is aerial. Eustachian Tube. The Eustachian tube leads from the tympanum to the naso- pharynx, and is about i^ inches in length. It is directed forwards, inwards, and slightly downwards, and is composed of two parts, osseous and cartilaginous. The osseous or postero-external part is about ^ inch long, and represents the lower or Eustachian com- partment of the canal situated in the angle between the petrous and squamous parts of the temporal bone. The cartilaginous or antero-internal part is about i inch in length, and lies in the groove between the great wing of the sphenoid and the apical portion of the petrous part of the temporal bone. It is at first narrow, but gradually enlarges, so as to resemble a trumpet. The narrowest portion of the whole tube is at the junction of the osseous and cartilaginous parts, this being known as the isthmus, and the widest part is at the pharyngeal orifice. The roof, inner wall, and upper part of the outer wall of the cartilaginous part consist of a triangular plate of cartilage, the margins of which are slightly rolled towards each other. The floor- and most of the outer wall are formed of a dense fibrous membrane. The pharyngeal orifice of the tube is expanded, and is situated on the lateral wall of the naso-pharjmx behind, and external to, the corresponding posterior naris, and on the same level as the posterior end of the inferior turbinate bone. It is somewhat oval, and presents, above and behind, a prominent border, formed by the thick margin of the cartilage, and called the cushion. Posterior to this is the lateral pharyngeal recess or fossa of Rosenmiiller. The tube is lined with mucous membrane, which is continuous with that of the tympanum on the one hand, and with that of the naso-pharynx on the other. It is thin in the osseous part of the tube, but in the cartilaginous part it is thick, and contains mucous THE HEAD AND NECK 1275 glands and lymphoid tissue. It is covered by stratified columnar ciliated epithelium. Muscles connected with the Eustachian Tube. — The levator palati has an origin from the lower margin of the cartilage of the tube, the tensor palati from the outer side of the cartilage, and the salpingo- pharyngeus is attached to the lower and front part of the tube. During deglutition the orifice of the tube is usually regarded as being kept open. According to Cleland, however, who had unusual opportunities of examining matters on the living person, ' the anatomical facts make it e\ndent that any dilating influence of the tensor palati is exercised on the hinder and smaller part of the tube, whilst the levator palati closes the anterior (that is, phar}^- geal) orifice ' by raising the membranous floor of the tube. Arteries. — These are derived from (i) the Vidian branch of the third part of the internal maxillary, and (2) the ascending pharyn- geal branch of the external carotid. Kerves. — ^The nerves are derived from (i) the tympanic plexus on the inner wall of the t3mipanum, and (2) the Vidian nerve. De?elopnient. — The Eustachian tabe is developed from the hypoblast of the first visceral cleft. The Larynx. The larynx is the upper part of the respiratory passage, being modified in structure so as to enable it to act as the organ of voice. It is situated in the median line of the neck above the trachea, and it lies opposite the fourth, fifth, and sixth cervical vertebrae. Superiorly it opens into the laryngeal portion of the pharynx, and interiorly into the trachea. It is covered in front by the integiunent and the deep cervical fascia, and the laryngeal portion of the pharynx lies behind it. On either side it is in relation with the upper part of the lateral lobe of the thyroid body, the stemo-hyoid, omo-hyoid, stemo-th5n:oid, and th5n:o-hyoid muscles, and the common carotid artery. Structure. — ^The larynx consists of a framework of cartilages, some of which are connected by joints and ligaments ; it is provided with special muscles, spoken of as intrinsic ; and it is lined with mucous membrane. Cartilages. — ^These are nine in number, three being single and three arranged in pairs. The single cartilages are the epiglottis, the thyroid, and the cricoid, and the three arranged in pairs are the arytenoid, the comicula laryngis, and the cuneiform. The epiglottis is a leaf-like plate of yellow elastic fibro-cartilage, which stands bolt upright between the base of the tongue and the superior aperture of the larjnix. Its lower part forms a narrow pedicle, which is attached to the receding angle of the thyroid cartilage, just below the median notch on its upper border, by means o*^ a fibro-elastic band, called the thyro-epiglottidean liga- ment. Superiorly it presents a broad, round, free margin. Each lateral border is free above, but its lower part is contained within 1276 A MANUAL OF ANATOMY the aryteno-epiglottidean fold of mucous membrane. The anterior or lingual surface is free over its upper part, where it faces the base of the tongue, and is covered by mucous membrane. This mem- brane is prolonged on to the base of the tongue as the glosso- epiglottidean fold, or frenum epiglottidis, which is mesially placed. It is also prolonged from the sides of the epiglottis on to the lateral walls of the pharynx as the pharyngo-epiglottidean folds. On either side of the frenum epiglottidis, between it and each Epiglottis- Superior Cornu of Thyroid . Cartilage Cuneiform Cartilage _ (Wrisberg) / Corniculum Laryngb^jr — | (Santorini) Arytaeno-epiglottideus_J (Arytaenoideus Obliiiuus) V, Arytaenoideus Transversus Crico-arytaenoideus Posticus Crico-thyroid Joint Cricoid Cartilage Trachea-—'' i Fig. 524. — The Intrinsic Muscles of the Larynx (Posterior View). pharyngo-epiglottidean fold, there is a depression or fossa, which is known as the vallecula. Lower down than these folds the anterior surface is connected to the back of the upper border of the body of the hyoid bone by an elastic, semilunar membrane, called the hyo-epiglottidean ligament. Above the upper border of the thyroid cartilage the anterior surface is separated from the posterior aspect of the thyro-hyoid membrane by a collection of adipose and elastic tissues, which is known as the periglottis (epi- glottidean gland). The posterior or laryngeal surface is free over its whole extent, and is covered by mucous membrane. It is con- cave from side to side, and concavo-convex from above down- wards. The lower convexity forms the cushion or pulvinar. When the mucous membrane is removed the epiglottis presents a number of small glandular pits. Development. — The epiglottis is developed from the loop of the lurcula. THE HEAD AND NECK 1277 Thyroid CariUage. — ^This cartilage is composed of two flat quadri- lateral ala, which meet in front by their anterior borders, but diverge widely behind. The angular projection formed by their imion is called the isthmus or pomum Adami. The xmion is confined to about the lower half of each anterior border, and there is left superiorly a deep triangular cleft called the thyroid notch. The posterior border, of greater length than the anterior, is round, and gives attachment to fibres of the palato-pharyngeus and stylo-pharj^n- geus muscles. At either extremity it is prolonged into a projection, the superior comu and inferior comu respectively. The superior cornu gives attachment to the lateral thyro-hyoid ligament, and the inferior cornu, which is slightly incurved, is facetted on its inner aspect to articulate with fiie cricoid cartilage. The superior border is for Thyrwd Notch Superior Conia of Thyroid Cartilage Saperior Tabercle of Ala Obliqae Line of Ala ~-~-. Isthmns (Pomum Adami) ^- Inferior Tuberde of Ala .Inferior Comu Cricoid Cartilage Crico-thyroiJ Menhrane Fig. 525. — The Thyroid and Cricoid Cartilages of the Larynx (Anterior View). the most part convex, and near its back part it presents a slight eminence, called the superior tubercle. The inferior border is almost horizontal, and presents an eminence about the jimction of the posterior third with the anterior two-thirds, called the inferior tubercle. Tt gives attachment to the median portion of the crico- thjToid membrane and the crico-thjToid muscle. The outer surface of the ala is marked by an oblique line, or, it may be, ridge, which extends downwards and forwards from the superior to the inferior tubercle. This line gives insertion to the stemo-th}Toid, and origin to the thjro-hyoid, muscles. It divides the outer surface into two imequal parts, an anterior three-fourths and a posterior fourth, the latter giving origin to fibres of the inferior constrictor muscle. The inner surface of the ala is smooth, slightly concave, and covered by mucous membrane. In the median line, behind the pomum Adami, there is a vertical depression known as the receding angle. Commencing just below the thyroid notch on the upper border and passing downwards, this region gives attachment to the 1278 A MANUAL OF ANATOMY following structures : (i) the thyro-epiglottidean ligament, (2) the superior thyro-arytenoid ligaments (false vocal cords), and (3) the inferior thyro-arytenoid ligaments (true vocal cords), in association with which are the fibres of the thyro-arytenoid muscles. Isthmus (Pomum Adami) Cricoid Cartilage Superior Cornu of Thyroid Cartilage .. Superior Tubercle of Ala . .Oblique Line of Ala Inferior Cornu «^Crico-thyroid Ligament Inferior Tubercle of Ala Fig. 526 — The Thyroid and Cricoid Cartilages of the Larynx (Lateral View). Arytenoid Facet Development of the Thyroid Cartilage. — The thyroid cartilage is regarded as being developed from the ventral portions of the skeletal cartilages of the fourth and fifth visceral arches of either side, which become united by a median plate. Cricoid Cartilage. — The cricoid cartilage is situated below the thyroid cartilage, and forms the lower part of the larynx. It bears some resemblance to a signet-ring, and it consists of two parts — an anterior arch and a posterior lamina. The anterior arch is narrow from above downwards as well as from side to side. The inferior border is horizontal, and is connected with the first ring of the trachea by a fibro- elastic membrane. The superior border is con- nected with the inferior border of thyroid cartilage by the median portion of the crico- thyroid membrane. The posterior lamina is quadrilateral and broad. It attains considerable depth, owing to the rapid elevation of the superior border of the anterior arch as it passes backwards. The inferior border is connected laterally with the first ring of the trachea by a fibro-elastic membrane, and mesially, where the tracheal rings are deficient, to the same membrane. The superior border presents a median notch, and on either side of this an oval Posterior Surface Fig. 527.— The Cri- coid Cartilage of the Larynx (Pos- terior View). THE HEAD AND NECK 1*79 convex facet for articulation with the base of the arytenoid carti- lage. The posterior surface is divided into two depressed areas by a median vertical ridge, which gives attachment to the longitudinal muscular fibres of the oesophagus. The depressed area on either side of this median vertical ridge gives origin to the posterior crico- arytenoid muscle. The oider surface of the cricoid cartilage presents posteriorly a circular facet for articulation with the inferior comu of the ala of the th)?roid cartilage. The upper sloping border of this part gives attachment, cJong its inner margin, to the lateral portion of the crico-thyroid membrane. The internal surface of the cricoid cartilage is lined with the mucous membrane of the larynx. Development. — The cricoid cartilage, like the rings of the trachea, is developed in the mesoblast of the respiratory tnbe. Arytenoid Cartilages. — These cartilages, which are two in number, surmoimt the superior border of the cricoid cartilage posteriorly. Each has the form of a three-sided pyramid, and measures about J inch in height, and about \ inch in width at the base. The apex looks upwards, and is curved in a backward and inward direction. It is surmoimted by the comiculum laryngis. The base looks down- wards, and is slightly concave and facetted to articulate with the superior border of the cricoid cartilage posteriorly. Two of the three angles of the base are promiaent, namely, the anterior and the external. The anterior angle, somewhat pointed, is directed Comicalum Laryngis straight forwards, and is known as ^^ the vocal process. It gives attach- /3 ment to the inferior thyro-ary- ^'t«'°»'B«**«*-y^— Anterior Borier tenoid ligament or true vocal cord. /J**" VVocai Pionss The external angle, thick and some- ^""^"^ ^*"*^ ^J^k>^ what round, has an inclination Base backwards, as weU as outwards, fig. 528.— The Right Arytenoid and IS known as the musciUar Cartilage and Cornicux,um ■process. Anteriorly it gives in- Laryngis (External View). sertion to the crico-arytaenoideus lateralis, and posteriorly to the crico-arytaenoideus posticus. The surfaces are antero-extemal, posterior, and internal. The antero- external surface, a little above the vocal process, gives attachment to the, superior thyro-arytenoid ligament or false vocal cord, and, above and external to the voCal process, to the thyro-arytaenoideus muscle. The posterior surface is triangular and conca\-e, and gives attachment to a portion of the arytaenoideus muscle. The internal surface faces its fellow of the opposite side, and is covered by mucous membrane. It forms the posterior part of the lateral boimdary of the rima glottidis. The borders are anterior, posterior, and ex- ternal. The anterior border separates the internal from the antero- extemal surface, and terminates below in the vocal process. The posterior border separates the internal from the posterior surface. i28o A MANUAL OF ANATOMY The external border separates the antero-external from the posterior surface, and terminates below in the muscular process. The thyroid and cricoid cartilages usually retain their cartilaginous con- dition up to about the twentieth year. In the case of the thyroid cartilage ossification proceeds from the inferior cornu, there being a special osseous nucleus in the region of the pomum Adami. The anterior part and lower margin of the cricoid cartilage remain carti- laginous for some time, but the remainder undergoes ossification simultane- ously with the thyroid cartilage. Ossification of the arytenoid cartilages takes place at a later date than in the case of the two preceding cartilages. Cornicula Laryngis or Cartilages of Santorini.— These are two small, somewhat conical nodules of yellow elastic cartilage which cap the apical parts of the arytenoid cartilages, their direction being backwards and inwards. Each lies within the aryteno- epiglottidean fold of mucous membrane, Cuneiform Cartilages or Cartilages of Wrisberg. — ^These are two nodules of yellow elastic cartilage, which are situated, one on either side, in the aryteno-epiglottidean fold of mucous membrane at its back part, not far from the cornicula laryngis. Development. — The arytenoid cartilages and the aryteno-epiglottidean folds are developed from the lateral parts of the furcula. The cornicula laryngis are offshoots of the arytenoid cartilages. The cuneiform cartilages are derived from the epiglottis. Ligaments of the Larynx — Thyro-hyoid Membrane. — This is a broad membranous sheet, which passes between the superior border of the thyroid cartilage and the back of the upper border of the body of the hyoid bone, as well as the deep surface of each great cornu. Its central and lateral portions are strong, and are composed chiefly of elastic tissue. The central portion is known as the middle thyro-hyoid ligament, its lower attachment being to the margins of the thyroid notch. The lateral portions, round and cord-like, are very elastic, and are known as the lateral thyro- hyoid ligaments. Each extends from the superior cornu of the thyroid cartilage to the tip of the great cornu of the hyoid bone, and enclosed within it, towards its upper part, there is a small nodule of cartilage called the cartilago triticea. Between the upper median portion of the thyro-hyoid membrane and the concave Eosterior surface of the body of the hyoid bone there is a synovial ursa. It is to be noted that the superior attachment of the thyro- hyoid membrane is such as to enable the upper part of the thyroid cartilage, when raised, to be received within the outline of the hyoid bone. The central portion of the membrane is subcutaneous, but on either side it is covered by the thyro-hyoid muscle. Beneath the posterior border of this muscle the internal laryngeal nerve and superior laryngeal artery pierce this membrane. Crico-thyroid Membrane. — ^This membrane is composed of a median and two lateral portions. The median portion is composed chiefly of elastic tissue, and is attached to the adjacent borders of the cricoid and thyroid cartilages. It is subcutaneous in the median THE HEAD AND NECK 1281 line, but laterally it is overlapped by fibres of the crico-thyroid muscles. Its centre is crossed by the crico-thyroid arterial arch, formed by the crico-thyroid branches of the superior thyroid arteries, and it presents a few openings for the passage of blood- vessels. Through this portion laiyngotomy may be performed. The lateral portion of the crico-thyroid membrane is connected below with the inner margin of the upper border of the lateral part of the cricoid cartilage. Superiorly it is not connected with the thyroid cartilage, but passes within its ala into the larynx, where it expands in an inward direction, and extends from the back of the ala of the thyroid cartilage in its lower part, close to the receding angle, to the under aspect of the vocal process of the arytenoid cartilage. Between these points it becomes continuous with the inferior thyro-arytenoid Ugament or true vocal cord. The lateral portion of the crico-thyroid membrane (within the ala of the thyroid cartilage) is covered by the lateral crico-arytenoid and thyro-arytenoid muscles. Superior Thyro-arytenoid Ligaments. — ^These form two small fibrous bands, one at either side, which lie within the folds of mucous membrane, called the false vocal cords. Each is attached . Superior Cornn of Thyroid Cartilage .Superior Tubercle of Ala • Oblique Line of .-Ua Isthmus (Pomum Adami) Cricoid Cartilage — Inferior Cornn »^ Crico-thyroid Ligament Inferior Tubercle of Ala Fig. 529. — The Thyroid and Cricoid Cartilages of the Larynx (Lateral View). in front to the receding angle of the th5n-oid cartilage immediately below the attachment of the thyro-epiglottidean ligament, and behind to the antero -external surface of the arytenoid cartilage a little alxDve the vocal process. Inferior Thyro-arytenoid Ligaments. — ^These important ligaments, covered by mucous membrane, constitute the true vocal cords, and each is continuous with the upper part of the expanded lateral portion of the crico-thyroid membrane. Each is composed of 81 1282 A MANUAL OF ANATOMY Root of Tongue yellow elastic tissue, and, with its fellow, is attached in front to the receding angle of the thyroid cartilage at its centre, and behind to the vocal process of the arytenoid cartilage. Its inner border, which is covered by mucous membrane, is free and clearly defined. In its front part there is a small nodule of elastic cartilage called the cartilage of Luschka (Klein). Crico-thyroid Joint. — This belongs to the class diarthrosis. The articular surfaces are the facet on the inner surface of the inferior cornu of the thyroid cartilage, and that on the outer surface of the cricoid cartilage posteriorly. The joint is surrounded by a capsular ligament, and this is lined with a synovial membrane. The move- ments allowed are as follows: (i) rotation of the thyroid cartilage round an axis passing transversely through both joints; and (2) ghding, in which the cricoid moves upwards and backwards, or downwards and forwards, this movement par- taking somewhat of a swinging character. The recurrent laryngeal nerve ascends close behind the crico-thyroid joint preparatory to entering the larynx. Crico-arytenoid Joint. — This belongs Epiglottis to the class diarthrosis. The articular surfaces are the convex facet on the superior border of the cricoid cartilage posteriorly, and the concave under surface of the base of the arytenoid cartilage. The joint is surrounded by a ^^caniiag^V'wHsberg capsular ligament, and this is lined with a s5niovial mem- brane. The movements allowed are as follows: (i) rotation, in which the arytenoid cartilage rotates on a nearly vertical axis, the effect being to invert, or evert, the vocal process; and (2) gliding in a lateral direction, in which one cartilage moves in- wards towards its fellow, or outwards away from its fellow. The cornicula laryngis are usually connected to the arytenoid cartilages by fibrous tissue, but in some cases there is a synovial articulation. Prelaryngeal Lymphatic Glands. — These glands are inconstant. When present, there may be one, or there may be two. They lie upon the median portion of the crico-thyroid membrane, in the interval between the crico-thjn-oid muscles. Their afferent vessels are derived from (i) the infraglottic portion of the larynx, the lymphatics from which pierce the crico-thyroid membrane; (2) the commencement of the trachea; and (3) the upper part of the isthmus of the thyroid body. Their efferent vessels pass either to the inferior deep cervical glands, or to the pretracheal glands as an intermediate gland-station. Aryteno- epiglottidean Fold ..False Vocal Cord Ventricle True Vocal Cord Vocal Process of Arytenoid Cartilage Rima Glottidis Cartilage of Santorini Fig. 530. — The Superior Aperture OF THE Larynx and Adjacent Parts. THE HEAD AND NECK 1283 Interior of the Larynx. — The superior aperture of the larynx is situated behind and below the epiglottis. It is triangular, being wide in front and narrow behind, and its plane is sloped obliquely downwards and backwards. Above and in front it is bounded by the epiglottis, and behind by the fold of mucous membrane which stretches bet^veen the arytenoid cartilages. On either side are the prominent ar\'teno-epiglottidean folds, which extend from the tips of the arytenoid cartilages to the sides of the epiglottis and contain muscular fibres. Each of these folds, close to the arytenoid cartilage, contains the comiculum laryngis or cartilage of Santorini, which gives rise to a slight elevation, and a little in front of this it presents another slight elevation produced by the cuneiform cartilage or cartilage of Wrisberg. Between the arytenoid cartilage and the back part of the aryteno-epiglottidean fold internally and the back part of the ala of the thyroid cartilage extemaJly there is a depression, opening upwards, called the sinus pyriformis. In this depression a foreign body may become lodged. The interior of the larynx commences at the superior aperture and terminates on a level with the lower border of the cricoid cartilage. It is divided into three compartments by means of two antero-posterior folds of mucous membrane, v.hich project into it from each lateral wall. The upper pair of folds are called Epigiouis the false vocal cords, and the lower pair the true vocal cords. The upper compartment is known as the vestibule, and it extends from the superior aper- ture down to the level of the false vocal cords. It is wider above than below, and its anterior depth exceeds the pos- terior. The middle or ventricular compartment is situated between the false vocal cords above and the true vocal cords below. On either side it presents a recess, called the ventricle of the larynx or laryngeal sinus. This is bounded above by a false vocal cord, and below by a true vocal cord. Its outer wall is covered externally by fibres of the thyro-arytenoid muscle. At the anterior part of the ventricle there is a small valvular aperture, which leads to a diverticulum of the ventricle, called the laryngeal saccule or pouch. This extends upwards between the false vocal cord and the ala of the thyroid cartilage, reaching as high as the upper border of the latter. On its inner aspect there are some muscular fibres. ^{^Vestibule Ala of Thyroid Cartilage — Middle Compartment Cricoid Cartilage Lower Compartment Tnu±ea Fig. 531. — Vertical Transverse Section of the Larynx, showing THE Posterior Surface of the Anterior Half of the Organ (Marshall). 1284 A MANUAL OF ANATOMY which are known as the compressor saccuhs laryngis or Hilton's muscle. The lower compartment of the larynx is compressed from side to side above, but becomes circular inferiorly, where it opens into the trachea. Vocal Cords. — ^These are arranged in two pairs, laterally disposed, called false and true, or superior and inferior. The superior or false vocal cords are two folds of mucous mem- brane, which extend at either side from the receding angle of the thyroid cartilage immediately below the attachment of the thyro- epiglottidean ligament to the antero-external surface of the arytenoid cartilage, a little above the vocal process. Each contains Hyoid Bone (in section)- Thyro-hyoid Membrane. Thyroid Cartilage.. True Vocal Cord. Crico-thyroid MembraneL-ir-' Cricoid Cartilage . (anterior part) _ -i .Epiglottis .False Vocal Cord .Ventricle ..Arytenoid Muscle (in section) .Arytenoid Cartilage .Cricoid Cartilage (posterior part) Trachea Fig. 532. — Sagittal Section of the Larynx and Trachea, showing THE Vocal Cords and Ventricle of the Right Side. some fibrous tissue forming the superior thyro- arytenoid ligament. The false vocal cords are widely separated from each other by an interval known as the false glottis, so that the true vocal cords are visible on looking into the larynx from above. The inferior or true vocal cords are concerned in the production of the voice. They are prominent folds at either side, which are rather less than an inch in length, and extend from the receding angle of the thyroid cartilage to the vocal process of each arytenoid cartilage. Each cord consists of the inferior thyro-arytenoid liga- ment, which is continuous with the upper part of the expanded lateral portion of the crico-thyroid membrane, and is composed of yellow elastic tissue. The mucous membrane covering the cord is thin, and firmly adherent to the elastic tissue of the ligament, THE HEAD AND NECK 1285 and it has a characteristic peariy white colour. The true \'ocal cords are much nearer to each other than the false, so that the latter are not visible when the larynx is viewed from below. Rima Glottidis. — ^The rima glottidis, or glottis vera, is the narrow fissure by which the upper and lower compartments of the larynx communicate with each other, and it is the narrowest part of the cavity. It is elongated from before backwards, and is narrow in front at the receding angle of the thyroid cartilage, but wider behind, where it is closed by the interarytenoid fold of mucous membrane. It is divisible into an interchordal portion, called the glottis vocalis, and an interarytenoid portion, called the glottis respiratoria. The glottis vocalis is narrow, and is bounded on either side by the true vocal cord. Its length, as stated, is rather less than an inch, and it forms about two-thirds of the entire glottis. Thyroid Notch Ala of Thyroid Cartilage Thyro-arytaenoideus True Vocal Cord Crico-arytaenoideus Lateralis Arytenoid Cartilage Fig. Crico-arytaenoideus Posticus Arytaenoideus 533. — Dissection of the Larynx, showing the Muscles, True Vocal Cords, and Rima Glottidis (Superior View). The glottis respiratoria is wider than the glottis vocalis, and is bounded on either side by the inner aspect of the base of the arytenoid cartilage. It is about ^ inch in length, and forms about one-third of the length of the entire glottis. The shape of the rima glottidis is subject to alteration, and has to be considered under three conditions. (i) During quiet respiration it has the form of an elongated triangle, the apex being in front at the thyroid cartilage, and the base behind at the interarytenoid fold of mucous membrane. (2) During a deep inspiration the rima is widely dilated, and assumes a somewhat diamond-shape, the widest part being opposite the tips of the vocal processes of the arytenoid cartilages, where the lateral angles of the diamond are placed, the posterior angle, at the interarytenoid fold of mucous membrane, being truncated. (3) During vocalization, phonation, and especicdly in singing high 1286 A MANUAL OF ANATOMY notes, the vocal cords become so closely approximated as to be practically parallel, and the glottis vocalis assumes the form of a narrow chink. Ventricle » Epiglottis and its Cushion False Vocal Cord _\ True Vocal Cord ., Cuneiform Cartilage Corniculum Laryngis — -" Tip of Arytenoid Cartilage -"' Trachea Right and Left Bronchi '*=" Fig. 534. — The Superior Aperture of the Larynx and the Rima Glottidis, as seen by the Aid of the Laryngoscope under I Different Conditions, ' (The Figures on the left side are copied from Czermak). A, Ordinary quiet inspiration B, Very deep inspiration C, Vocalization, especially in singing high notes R.G. Rima Glottidis Mucous Membrane of the Larynx. — ^This is continuous above with the mucous membrane of the pharynx, and below with that of the trachea. Above the level of the rima glottidis its subjacent attach- ment is of a loose nature on account of the presence of submucous areolar tissue, particularly in the vicinity of the aryteno-epiglottidean folds, a condition which favours the occurrence of oedema, but over the laryngeal surface of the epiglottis it is firmly attached. Over the true vocal cords it is very thin, and is firmly connected to the inferior thyro-arytenoid ligaments, which they contain. The membrane is covered by ciliated columnar epithelium, except (i) near the margin of the aryteno-epiglottidean folds, where it is of the stratified squamous variety, as in the laryngeal portion of the pharynx and the buccal cavity ; and (2) over the true vocal cords, where it is also of the stratified squamous variety. Bodies resembling the taste-buds of the tongue are met with on the THE HEAD AND NECK 1287 lar5mgeal surface of the epiglottis, the inner surfaces of the arytenoid cartilages and of the aryteno-epiglottidean folds, and over the margins of the false vocal cords. The mucous membrane contains a large number of acinous mucous glands, the ducts of which open freely on the surface, except over the true vocal cords, where there are no glands. They are arranged in groups, as follows : (i) epiglottidean, which are very numerous, and occupy the pits on the laryngeal surface of the epiglottis ; (2) arytenoidean, in front of the ar^-tenoid cartilages, and in the adjacent portions of the aryteno-epiglottidean folds ; (3) along the false vocal cords ; and (4) in the wall of the larj-ngeal saccule, where they are very numerous. Intrinsic Muscles. — ^These are the muscles by which the cartilages are moved upon each other so as to affect the condition of the L Epiglottis— Superior Comu of Thyroid- Cartilage Cuneiform Cartilage _ ' (Wrisberg) / CorniCTilum Laryngisw — (Santorini) bi \ Ary tieno-«piglottideas _* . (Arytinoideus Obliquus) \ Arytsenoideus Transversus Crico-arytienoideus Posticus_ Crico-thyroid Joint Cricoid Cartilage " Trachea b' 'd ^^G. 535. — The iNTkiNsic Muscles of the Larynx (Posterior View). vocal cords. They are as follows : the crico-th5n-oid, posterior crico-arytenoid, lateral crico-arytenoid, arytenoid, and arytaeno- epiglottideus. The arytenoid is a single muscle, but all the others are arranged in pairs. Crico-thyroid— Origtw. — ^The front of the anterior part of the cricoid cartilage, extending as far as the median line. Insertion. — (i) The lower margin of the ala of the thyroid cartilage, and (2) the front of the inferior comu 1288 A MANUAL OF ANATOMY Nerve-supply. — ^The external lar5mgeal branch of the superior laryngeal nerve. The fibres are directed upwards and backwards in a diverging manner, the posterior being horizontal and the anterior oblique. These two sets of fibres are usually distinct. Action. — To approximate the front parts of the cricoid and thyroid cartilages in the following manner : the posterior horizontal fibres draw the cricoid cartilage backwards, and the anterior oblique fibres elevate the anterior part of the cricoid cartilage, thus impart- ing a swinging movement to the cartilage. As a result of this movement the deep posterior part of the cricoid cartilage, with the arytenoid cartilages on its upper border, are depressed. In this manner the vocal cords are put upon the stretch, so that the muscles are tensors of the cords. Between the two muscles anteriorly there is a triangular interval about I inch wide, in which the central portion of the crico-thyroid membrane is visible, this portion being crossed at its centre by the crico-thyroid arch of arteries. In this region, just above the cricoid cartilage, laryngotomy may be performed. Posterior Crico-arytenoid — Origin. — The posterior surface of the cricoid cartilage on one side of the median vertical ridge. Insertion. — ^The posterior aspect of the muscular process or external angle of the base of the arytenoid cartilage. Nerve-supply. — The recurrent laryngeal nerve. The fibres of the muscle are directed upwards and outwards, the highest being short and nearly horizontal, the middle being oblique, and the lowest almost vertical. Action. — ^To draw the muscular process of the arytenoid cartilage backwards and inwards, thereby swinging the vocal process or anterior angle outwards, the result of which is to open or widen the rima glottidis. The muscle is, therefore, a dilator of the rima glottidis. The muscle is separated from its fellow by the median vertical ridge on the back of the cricoid cartilage. Lateral Crico-arytenoid — Origin. — ^The lateral portion of the cricord cartilage along its upper sloping border, extending as far back as the crico-arytenoid joint. Insertion. — ^The anterior aspect of the muscular process of the arytenoid cartilage, and the adjacent portion of the antero- external surface. Nerve-supply. — ^The recurrent laryngeal nerve. The fibres of the muscle are directed backwards and upwards. Action. — ^To draw the muscular process of the arytenoid cartilage forwards and inwards, thereby swinging the vocal process or anterior angle inwards, the result of which is to narrow the rima glottidis. The two muscles, therefore, approximate and relax the true vocal cords, and they come into action in vocalization. When the posterior and lateral crico-arytenoid muscles act together they assist the arytenoid muscle in approximating the arytenoid carti- THE HEAD AND NECK 1289 lages, and so the rima glottidis is closed. The lateral crico-arytenoid muscle is covered externally by the ala of the thjToid cartilage and the upper fibres of the crico-thyroid muscle, and internally by the lateral expanded portion of the crico-thjToid membrane. Epiglottis Left Ala of Thyroid. Cartilage Arytaenoideus. Muscular Process. Crico-arytaenoideu s . Posticus ^-Hyoid Bone Qd secticm) !^.«TbyTO-arytaeno-epigk>ttidetis .Ala of Thyroid Cartilage (in section) Thyro-arytaenoideus — Crico-arytienoideus Lateralis Ciic(»d Cartilage Fig. 536. — The Intrinsic Muscles of the Larynx (Lateral View). (The greater part of the Right Ala of the Thjroid Cartilage has been removed) Thyro-arytenoid. — This muscle consists of two portions, external and internal. External Portion — Origin. — (i) The lower half of the inner surface of the ala of the thyroid cartilage, and (2) the outer surface of the lateral portion of the crico-thyroid membrane. Insertion — ^The front of the muscular process and the adjacent part of the outer border of the arytenoid cartilage, a few of the fibres passing round the cartilage to become continuous with the arytaenoideus. The uppermost fibres of this portion pass upwards and backwards to the aryteno-epiglottidean fold, and thence to the epiglottis, under the name of the thyro-epiglottideus. Internal Portion — Origin. — (i) The receding angle of the thyroid cartilage, and (2) the cartilage of Luschka in the anterior part of the true vocal cord. According to Ludwig the deepest fibres of this portion, known as the ary-vocalis, spring from the anterior part of the true vocal cord. Insertion. — ^The outer surface of the vocal process of the arytenoid cartilage, and the adjacent portion of the antero-extemal surface. The fibres pass from before backwards, some of them having a slight inclination outwards, and the highest backwards. "90 A MANUAL OF ANATOMY Nerve-supply. — ^The recurrent laryngeal nerve. Action. — (i) Internal Portion. To draw forwards the arytenoid cartilage, and the posterior part of the cricoid cartilage, swinging the latter in an upward and forward direction. The result of this action is to relax the true vocal cords by approximating the arytenoid cartilage to the thyroid cartilage. This portion of the muscle is, therefore, the antagonist of the crico- thyroid. It is to be borne in mind, however, that one factor in relaxation of the true vocal cords must of necessity be elastic recoil. The fibres represent- ing the ary-vocalis muscle of Ludwig act, according to him, by rendering tense that part of the true vocal cord which is in front of them, and relaxing the part behind them. (2) External Portion. In virtue of its insertion into the muscular process of the arytenoid cartilage this portion will draw forwards that process, the effect of which is to swing inwards the vocal process. The fibres known as the thyro-epiglottideus have been supposed to assist in depressing the epiglottis. The outer portion of the muscle lies within the ala of the thyroid cartilage. Its lower border is contiguous to the lateral crico- arytenoid, and its upper fibres lie on the outer wall of the ventricle and saccule. The inner portion of the muscle is in close contact with the outer side of the true vocal cord. Arytenoid. — The arytenoid muscle lies across the posterior sur- faces of the arytenoid cartilages. It consists of two parts — super- ficial and deep. The superficial part is composed of two decussating bundles, each of which is known as the arytenoideus obliquus; and the deep part constitutes the arytenoideus transversus. Arytenoideus Obliquus. — Each of these muscles, which has the form of a narrow oblique bundle, arises from the back of the mus- cular process of the arytenoid cartilage. Its direction is upwards and inwards, and at the median line it decussates with its fellow of the opposite side, thus X. Having reached the summit of the opposite ar5d;enoid cartilage, a few of the fibres terminate upon it, but the majority enter the corresponding aryteno-epiglottidean fold. Being reinforced by a few fibres from the summit of the arytenoid cartilage, the fibres now constitute the aryteno-epiglottideus muscle, which passes forwards within the aryteno-epiglottidean fold to be inserted into the side of the epiglottis. Associated with the aryteno- epiglottideus there are those fibres of the external portion of the thyro-arytenoid muscle which are known as the thyro-epiglot- tideus. Nerve-supply. — The inferior or recurrent laryngeal nerve. Action. — The two muscles, having the arytenoid cartilages within their embrace, sweep these cartilages together, in which action they are aided by the transverse arytenoid muscle, and the superior aper- ture of the larynx is narrowed, very much after the manner of a sphincter muscle. Arytenoideus Transversus. — The fibres of this muscle extend trans- versely from the posterior surface and outer border of one arytenoid cartilage to the posterior surface and outer border of the other THE HEAD AND NECK 1291 cartilage. Some of the fibres are continuous with those of the external portion of the thyro-axytenoid muscle. Nerve-supply. — The inferior or recurrent laryngeal nerve. Action. — To draw the aiytenoid cartilages together, so as to approximate the true vocal cords, and even close the rima glottidis. The ar\tenoideus transversus muscle, clothed with mucous mem- brane internally, boimds the rima glottidis posteriorly; and its superficial or posterior surface supports the decussating arytenoidei obhqui muscles. Compressor Sacculus Laryngis, or Hilton's Muscle. — This is the name given to a thin layer of muscular fibres on the inner side and upper end of the sacculus lar^Tigis. The fibres are related superiorly to those of the arytaeno-epiglottideus, which are contained within the aryteno-epiglottidean fold. Summary of the Actions of the Laryngeal Muscles. — The intrinsic muscles of the larynx, by regulating the condition of the rima glottidis, contribute to vocalization, and modify the pitch of notes. In so doing they lengthen, so as to render tense, or shorten, so as to relax, the vocal cords ; and they also bring the cords together, or draw them apart. In other words, the intrinsic muscles bring about tension and parallelism of the true vocal cords, or give rise to the opposite conditions, namely, relaxation and divergence. Tension is effected by the crico-thjToid muscles, which swing the anterior part of the cricoid cartilage upwards and backwards towards the thyroid, the result being to increase the distance between the receding angle of the thyroid cartUage and the vocal processes of the arytenoid cartilages. In this manner the true V'ocal cords are stretched, and tension of them is produced. Parallelism of the true vocal cords is effected by (i) the lateral crico-arytenoid muscles, and (2) the arytenoid muscle, the latter also producing narrowing of the glottis respiratoria (interarytenoid portion of glottis). The lateral crico-arjrtenoid muscles draw forwards the muscular processes of the arytenoid cartilages, the result of which is to swing inwards the vocal processes, and so produce parallelism. The arytenoid muscle draws the arytenoid cartOages together, and so narrows the glottis respiratoria, con- tributing at the same time to the condition of parallelism. Relaxation of the true vocal cords is brought about by the thyro- arytenoid muscles, which draw the arytenoid cartilages, along with the posterior part of the cricoid cartilage, forwards. In this manner the distance between the receding angle of the thyroid cartilage and the arytenoid cartilages is diminished, and so relaxation of the true vocal cords is produced. They are at the same time shortened in virtue of their elastic recoU. The fibres of the thyro- arytenoid muscle, known as the ary-vocalis, act by rendering tense the part of the true vocal cord in front of them, and relaxing the part behind them (Ludwig). Divergence of the true vocal cords and opening of the rima glottidis is effected by the posterior crico-arj-tenoid muscles, which draw *^e muscular processes of the arytenoid cartilages backwards and 1292 A MANUAL OF ANATOMY inwards, the result of which is to swing the vocal processes outwards. The actions of the intrinsic muscles may be tabulated thus : Tension. Relaxation. Crico-thyroids. Thyro-arytenoids. Posterior crico-arytenoids. Lateral crico-arytenoids. Parallelism and Closure. Divergence and Opening. Lateral crico-ar5rtenoids. Posterior crico-arytenoids. Arytenoid. Function of the Epiglottis. — Two views are held as regards the function of the epiglottis, (i) According to one view it is folded down, like a Ud, over the superior aperture of the larynx. This Ud-like action is brought about by (a) the pressure exerted by the base of the tongue, {b) the action of the aryteno-epiglottidei muscles, and (c) the action of the thyro-hyoid muscles, which elevate the thyroid cartilage. (2) According to Anderson Stuart, the epiglottis is never folded down like a lid. The superior aperture of the larynx is, accord- ing to this author, closed during deglutition by the action of (i) the transverse arytenoid muscle, and (2) the external portions of the thyro-arytenoid muscles. The transverse ar5^enoid muscle approxi- mates the arytenoid cartilages, and the external portions of the thyro- ar5rtenoid muscles draw the arytenoid cartilages forwards, until their apical parts come into contact with the cushion of the epiglottis. The sphincter-like action of the aryteno-epiglottidei muscles upon the superior aperture of the larynx must, however, be taken into account. Prima facie the lid-like action appears to be the most natural one. The results, however, of ulceration of the epiglottis, and consequent loss of function, would tend to support Anderson Stuart's view. Nerves. — The nerves of the larynx are the superior and inferior, or recurrent, laryngeal, both of which are branches of the pneimio-gastric. The superior laryngeal nerve divides into two branches, external and internal. The external branch (external laryngeal nerve), which is comparatively small, supplies the crico-thyroid muscle, and also furnishes twigs to the inferior constrictor muscle of the pharynx. The internal branch (internal laryngeal nerve), which is sensory, passes beneath the posterior border of the thyro-hyoid muscle, and enters the larynx by piercing the th5n:o-hyoid membrane, in com- pany with the superior laryngeal artery, above which it lies. In the interior of the larynx it breaks up into branches, some of which ascend to the aryteno-epiglottidean fold and posterior surface of the epiglottis, a few of them passing through the latter to reach its anterior surface. The other branches descend to supply the laryngeal mucous membrane, and one of them joins a twig from the inferior or recurrent laryngeal nerve. The inferior or recurrent laryngeal nerve is the principal motor nerve of the larynx. On the rig/it side it arises from the vagus at the root of the neck, and hooks round the first part of the right sub- clavian artery. On the left side it arises from the vagus in the upper part of the thorax, and hooks round the arch of the aorta. THE HEAD AND NECK 1293 Having ascended in the groove between the trachea and oesoph- agus, it passes beneath the lower border of the inferior con- strictor muscle, and ascends upon the cricoid cartilage, lying close behind the crico-thyroid joint. Here it divides into two branches, anterior and posterior. The anterior branch ascends under cover of the thyroid cartilage, and is distributed to the lateral crico- ar^iienoid, thyro-arytenoid, thyro-epiglottideus, and aryteno-epi- glottideus muscles. The posterior branch passes upwards on the back of the cricoid cartilage beneath the posterior crico-arytenoid muscle, which it suppUes, and then it goes on to end in the arytenoid muscle. The recurrent laryngeal nerve furnishes some sensory branches to the mucous membrane of the larynx below the rima glottidis, and it communicates with the internal branch of the superior laryngeal. The motor fibres of the external branch of the superior laryngeal and of the inferior laryngeal are derived from the bulbar portion of the spinal accessory nerve. Summary ol the Laryngeal Nerves. — The superior laryngeal nerve, through its internal branch, is sensory, and its external branch supplies the crico- thyroid muscle, and, in part, the inferior constrictor muscle of the pharynx. The inferior or recurrent laryngeal nerve is chiefly motor, and it supplies the intrinsic muscles of the larynx, with the single exception of the crico-thyroid muscle. Arteries. — ^The arteries of the larynx are the superior and the inferior laryngeal. The superior laryngeal artery is a branch of the superior thyroid. It accompanies the internal larjTigeal nerve, below which it lies, and enters the larynx by piercing the thyro- hyoid membrane. The inferior laryngeal artery is a branch of the inferior thyroid, and it accompanies the inferior or recurrent laryngeal nerve. Veins. — The superior laryngeal vein opens into the superior thyroid, and the inferior laryngeal vein into the inferior thyroid vein. Lymphatics. — ^These are arranged in two sets — superior and inferior. The superior lymphatics come from the portion of the larynx above the rima glottidis. Having pierced the thyro-hyoid membrane, they pass to the upper group of deep cer\acal glands. The inferior lymphatics come from the portion of the larynx below the rima glottidis. Having pierced the crico-thyroid membrane, they pass to the lower group of deep cervical glands, having previously traversed the prelaryngeal glands. In early life the larynx occupies a higher position than it does in the adult, its descent, which is gradual, being completed by puberty. Up to that period the projection known as the pomum Adami is not present. After puberty important changes take place. The cartUages increase in size, the pomum Adami assumes marked development, especially in the male, and the true vocal cords undergo increase in length. These various changes account for the modifications which the voice undergoes at and after puberty. 1294 A MANUAL OF ANATOMY Development of the Larynx. — The larynx is developed from the upper part of a median diverticulum from the ventral aspect of the fore-gut, which diverticulum by its lower part gives rise to the trachea. The epiglottis, arytenoid cartilages, and aryteno-epiglottidean folds are developed from the furcula, which is an elevation, like a horseshoe, lying between the second, third, and fourth visceral arches of either side (see Fig. 523). The front part of the furcula gives origin to the epiglottis, the lateral parts to the aryteno- epiglottidean folds, and the back part (extremities of the horseshoe bend) to the arytenoid cartilages. The groove within the furcula represents the superior aperture of the larynx. Prevertebral Muscles. Rectus Capitis Anticus Major — Origin. — By four short tendons from the tubercles of the costal processes (anterior tubercles of the transverse processes) of the third, fourth, fifth, and sixth cervical vertebrae, where it coincides with the origin of the scalenus anticus. Insertion. — The inferior surface of the basilar process of the occipital bone, from the pharyngeal tubercle obliquely outwards and forwards for about ^ inch. Nerve-supply. — The cervical plexus. The muscle is directed upwards and inwards. Action. — ^To flex the head. Relations — Anterior. — ^The upper part of the common carotid, and the internal carotid, arteries, the internal jugular vein, the pneumogastric and sympathetic nerves, and the pharynx. Pos- terior.— A part of the longus colli, and a large portion of the rectus capitis anticus minor. Rectus Capitis Anticus Minor — Origin. — ^The front of the root of the costal process of the atlas. Insertion. — The inferior surface of the basilar process of the occipital bone, between the foramen magnum and the outer part of the insertion of the rectus capitis anticus major. Nerve-supply. — ^The anterior primary division of the first cervical nerve. The muscle is directed upwards and slightly inwards. Action. — To flex the head. Rectus Capitis Lateralis — Origin. — ^The upper aspect of the ex- tremity of the transverse process of the atlas at its front part. Insertion. — ^The inferior surface of the jugular process of the occipital bone. Nerve-supply. — The anterior primary division of the first cervical nerve. The muscle passes vertically upwards. Action. — ^To flex the head to one side. Longus Colli. — ^This complex muscle consists of three parts — upper oblique, vertical, and lower oblique. Upper Oblique Part — Origin. — ^The fronts of the tubercles of the i costal processes (anterior tubercles of the transverse processes) of 1 the third, fourth, fifth, and sixth cervical vertebrae. Insertion. — ^The lateral aspect of the anterior tubercle of the !^ atlas. i THE HEAD AND NECK 1295 The fibres are directed upwards and inwards. Vertical Part — Origin. — ^The fronts of the bodies of the last two cerv'ical and first three thoracic vertebrae. Insertion. — The fronts of the bodies of the second, third, and fourth cervical vertebrae. Lower Oblique Part — Origin. — The fronts of the bodies of the first three thoracic vertebrae in common with the lower portion of the vertical part. Rectus Capitis Antictis Minor Rectus Lateralis i, Basilar Process of Occipital Bone ^ Vertebral Artery /.•' (third part) Rectus Capitis Anticus Major Longus Colli (upper oblique part) Vertebral Artery (second part) Scalenus Anticus,, / Scalenus Medius^ Scalenus . Posticus .r. Longus Colli (vertical part) Vertebral Artery (first part) Longus Colli (lower oblique part) Scalene or Lisfranc's Tubercle Fig. 537. — The Right Prevertebral Muscles. (The Vertebral Artery is also shown). Insertion. — ^The fronts of the tubercles of the costal processes (anterior tubercles of the transverse processes) of the fifth and sixth cervical vertebrae. Nerve-supply. — ^The anterior primary divisions of the adjacent spinal nerves. Action. — ^To flex the cervical part of the vertebral column. 1296 A MANUAL OF ANATOMY Relations — Anterior. — ^The pharynx and oesophagus, the common and internal carotid arteries, and internal jugular vein ; the pneumo- gastric nerve, and the gangliated cord of the sympathetic ; the rectus capitis anticus major superiorly ; and the recurrent laryngeal nerve, inferior thyroid artery, and first part of the subclavian artery inferiorly. Posterior. — ^The bodies and discs of the adjacent vertebrae, and their transverse processes. Petrous Part of the Internal Carotid Artery.— This part of the internal carotid artery is contained within the carotid canal of the petrous part of the temporal bone. It is at first directed up- wards, and then, describing a bend, it passes forwards and inwards to the foramen lacerum medium, where it enters upon the cavernous part of its course. The vessel is surrounded by small tympanic veins, and is accompanied by the ascending branch of the superior cervical ganglion of the sympathetic nerve. This branch breaks up into two divisions. One of these lies on the outer side of the artery, and gives rise to the carotid sympathetic plexus, whilst the other lies on the inner side of the artery, and goes on to form the cavernous sympathetic plexus. Pars Intermedia of Wrisberg Geniculate Ganglion Facial Nerve Great Superficial Petrosal Small Superficial Petrosal Great Deep Petrosal Nerve to Stapedius Chorda Tympani Great Superf. Petrosal Vidian Nerve Spheno-palatine Nerves -Meckel's Ganglio - Descending Palat Nerves Arnold's Nerve _ ; Pneumogastric Otic Ganglion Internal Carotid Artery and Sympath. Plexus Tympanic or Jacobson's Nerve Petrous Ganglion of Glosso-pharyngeal Fig. 538. — The Facial Nerve in the Aqueduct of Fallopius, etc. (HiRSCHFELD AND LeVEILL6). As the artery ascends in the carotid canal it is situated in front of, and below, the tympanum and cochlea ; as it bends it has the Eustachian tube on its anterior and outer side ; and as it passes forwards and inwards it has the Gasserian ganglion above it, the partition between the two being for the most part membranous. Branches. — The petrous part gives oH a tympanic branch which enters the tympanum through the posterior wall of the carotid THE HEAD AND NECK 1297 canal, and it may furnish a petrosal branch to accompany the great deep petrosal nerve. For the cavernous part of the internal carotid artery, see p. 1078 . Petrous Part of the Faeial Nerve. — This part of the nerve extends from the orifice of the meatus auditorius intemus, on the posterior surface of the petrous part of the temporal bone, to the stylo- mastoid foramen, and it traverses (i) the meatus auditorius intemus, and (2) the aqueduct of Fallopius. Meatal Portion. — ^This portion of the nerve is directed outwards, and is accompanied by the pars intermedia of Wrisberg, the auditory nerve, and the internal auditory artery. It is placed upon the upper and anterior aspect of the auditory nerve, and the pars intermedia lies between the two, and here joins the facial nerve. At the deep end of the internal auditory meatus the facial nerve parts company with the auditory nerve, and enters the aqueduct of Fallopius. Branches. — ^Two branches connect the facial nerve with the auditory nerve. Portion in the Aqueduct of Fallopius. — ^The direction of this portion of the nerve corresponds to that of the aqueduct. It may con- veniently be divided into three stages — first, second, and third. In the first stage, which is very short, the nerve passes horizontally outwards, between the cochlea and vestibule, to the inner wall of the t\TTipanum, where it presents an enlargement, called the geniculate ganglion. It then describes a sharp bend, and in the second stage passes backwards, lying abov^e the fenestra ovalis. Thereafter it describes another abrupt bend, and in the third stage descends behind the posterior wall of the t^Tnpanum to the stylo- mastoid foramen, by which it escapes from the aqueduct. The hiatus Fallopii leads from near the commencement of the aqueduct to the superior surface of the pars petrosa . As the aqueduct descends it com- municates with the canal of the pyramid of the tjTnpanum, and below this it presents another opening, called the iter chordce poster ius. Branches. — ^These are as follows : {Great superficial petrosal (to Meckel's ganglion). Communicating branch to small superficial petrosal (to the otic ganglion). External superficial petrosal (to sympathetic plexus on middle meningeal artery). Nerve to the stapedius muscle. Chorda tympani nerve. Communicating branch to the auricular branch (Arnold's nerve) of the pneumogastric. The great superficial petrosal nerve arises from the geniculate ganglion and passes forwards through the hiatus Fallopii, by which it emerges from the aqueduct of Fallopius. It then courses inwards and forwards in a groove on the superior surface of the petrous part of the temporal bone, and passes beneath the Gasserian ganglion to the foramen laeerum medium. In the upper 82 1298 A MANUAL OF ANATOMY part of this foramen it joins the great deep petrosal nerve from the carotid plexus to form the Vidian nerve, which passes forwards through the Vidian canal into the spheno-maxillary fossa, and joins the back part of Meckel's ganglion. The great superficial petrosal nerve contains some motor fibres, but to a large extent it consists of sensory fibres. These represent peripheral branches of the unipolar cells of the geniculate ganghon, the central branches of which give rise to the pars intermedia of Wrisberg. A communicating branch passes from the geniculate ganglion to the small superficial petrosal nerve, which latter represents the tympanic branch (Jacobson's nerve) of the glosso-pharyngeal, after it has emerged from the tympanic plexus on the inner wall of the tympanum. Through means of the small superficial petrosal nerve this communicating branch is conducted to the otic ganglion. The external superficial petrosal nerve (sometimes absent) emerges at a point just within the orifice of the hiatus Fallopii, and passes to the sympathetic plexus around the middle meningeal artery. The nerve to the stapedius muscle arises from the facial nerve in the descending part of the aqueduct of Fallopius, opposite the pyramid of the tympanum. It enters a small canal in the p5n-amid, and so reaches the stapedius as that muscle lies within the canal. The chorda tympani nerve arises from the geniculate ganglion, and it remains closely associated with the motor portion of the facial nerve in the descending part of the aqueduct of Fallopius. A httle above the stylo-mastoid foramen it leaves the motor portion of the nerve, and passes upwards and forwards in a somewhat recurrent manner through a minute canal, called the iter chordcB posterius, by which it enters the tympanum. At first it is placed on the posterior wall of the tympanum, close to the posterior margin of the membrana tympani, and on a lower level than the pyramid. The nerve then passes forwards upon the membrana tympani, near its upper margin, lying between its mucous and fibrous layers, so as to be ensheathed by the mucous membrane. In this part of its course it passes over the inner aspect of the handle of the malleus. Having arrived at the inner end of the fissure of Glaser, it leaves the tympanum by passing through the iter chordce anterius or canal of Huguier. It then enters the pterygo-maxillary region, and passes , downwards and forwards imder cover of the external pterygoid I muscle, where it receives a communicating twig from the otic i ganglion, and thereafter joins the lingual nerve at an acute angle, under cover of the external pterygoid muscle. The subsequent! distribution of the nerve has been already described (see p. 1246).^ ! The chorda tympani is composed of fibres which are the peri-j pheral processes of the unipolar cells of the geniculate ganglion ofj the facial nerve. These represent the fibres which are distributed' to the sides and dorsum of the tongue over its anterior two-j thirds. They are, therefore, regarded as gustatory, or pertaining! to taste, and functionally are afferent. They belong to the same THE HEAD AND NECK 1299 group of fibres as compose the pars intermedia of Wrisberg, which represent the central processes of the unipolar cells of the geniculate ganghon of the facial nerve. In other words, the greater portion of the chorda t^Tupani and the pars intermedia are to be regarded as one nerve, with the imipolar cells of the geniculate ganghon interpolated in their course in the form of ceU-stations. The chorda tjTTipani nerve, however, also contains purely facial fibres, which are the secretory fibres of the submaxillary and sublingual glands. The ners'e is, therefore, a mixed nerve. A commumeating branch is given off from the facial nerve, just above the stylo-mastoid foramen, which connects it with the auricular branch (Arnold's nerve) of the pneiunogastric. Pars Intermedia of Wrisberg. — The fibres of this small nerve arise from the imipolar ceUs of the geniculate ganghon of the facial, being the central processes of these cells, the peripheral processes representing the principal fibres of origin of the chorda tympani. The pars intermedia is at first closely incorporated with the facial nerve, and passes from the aqueduct of Fallopius into the internal auditory meatus. Here it separates from the facial nerve, and Ues between it and the auditory nerve. After emerging through the orifice of the internal auditory meatus the pars intermedia passes to the lower border of the pons Varolii, where it enters the medulla oblongata, and terminates in the fasciculus solitarius and upper part of the glosso-pharyngeal nucleus. The chorda tympani and the pars intermedia of Wrisberg, with the geniculate ganglion interpolated, may be regarded as represent- ing the afferent or sensory root of the facial nerve. Geniculate Ganglion. — The geniculate ganghon is situated on the facial nerve in the aqueduct of Fallopius, at the point where the aqueduct, having reached the inner wall of the tympanum, makes a sharp bend before passing backwards. Like a spinal ganghon and the Gasserian ganghon, it consists of unipolar cells, each of which has a central process and a peripheral process. The ganghon is the nucleus of origin of the sensory fibres of the facicd nerve. The central processes of the unipolar cells form the pars intermedia of Wrisberg, and the majority of the peripheral processes form the chorda tympani nerve. Some of the peripheral processes, however, gi\e rise to (i) the great superficial petrosal nerve; (2) the communi- cating branch to the small superficial petrosal nerve; and (3) the external superficial petrosal nerve (inconstant). The faciaJ nerve is partly motor and partly sensory. The sensory portion, as stated, is represented by (i) the pars intermedia of Wris- berg; (2) the geniculate ganglion ; and (3) the chorda tympani nerve. The great superficial petrosal nerve is to be regarded as a branch of the sensory portion of the facial nerve. Summary of the Petrosal Nerves. — There are three superficial petrosal ner\es, namely, great, small, and external; and there are two deep petrosal aerves, namely, great and smalL 1300 A MANUAL OF ANATOMY Auditory Nerve in the Internal Auditory Meatus. — This nerve passes outwards in the internal auditory meatus in company with the pars intermedia of Wrisberg, the facial nerve, and the internal auditory artery. The facial nerve is placed upon its upper and anterior aspect, and the pars intermedia lies between the two. Two branches connect the auditory nerve with the facial. At the deep end of the meatus the auditory nerve breaks up into two divisions — an upper, called the vestibular nerve, and a lower, called the cochlear nerve. The vestibular nerve presents a ganglion, called the ganglion of Scarpa, which is situated at the deep end oi the meatus, its bipolar cells giving origin to the vestibular fibres. Thereafter it breaks up into two parts, upper and lower. The uppei portion furnishes branches which pass to the ampullae of the superior and external semicircular canals, and to the utricle. These pass through the foramina of the superior vestibular area of the upper fossa of the lamina crihrosa at the deep end of the meatus. The lower portion supplies branches to the ampulla of the posterior Fig. 539 — Scheme of the Auditory Nerve (Flower). C.F. Communicating with Facial E.S.C. To External Semicircular Canal C Cochlear Nerve U. To Utricle V. Vestibular Nerve S. To Saccule S.S.C. To Superior Semicircular Canal P.S.C. To Posterior Semicircular Canal semicircular canal and to the saccule. The former pass through the foramen singulare in the lower fossa of the lamina cribrosa, and the latter through the foramina of the inferior vestibular area of the lower fossa of the lamina cribrosa. The branches of the cochlear nerve pass through the foramina of the cochlear area of the lower fossa of the lamina cribrosa. Superficial Petrosal Nerves. — The great superficial petrosal nerve is a branch of the geniculate ganglion of the facial in the aqueduct of Fallopius. Aftei emerging from that aqueduct through the hiatus Fallopii, it passes to thi upper part of the foramen lacerum medium. Here it joins the great deej petrosal nerve to form the Vidian nerve, which passes forwards through th< Vidian canal into the spheno-maxillary fossa, and joins the back part oj Meckel's ganglion. I The small superficial petrosal nerve issues from the tympanic plexus on thi inner wall of the tympanum, and represents the continuation of the tympani«j branch (nerve of Jacobson) of the petrous ganglion of the glosso-pharyngeai nerve. As it traverses a canal in the petrous portion of the temporal boB' it is joined by a small branch from the geniculate ganglion of the facialj Emerging from this canal through the accessory hiatus, it passes througl the canaliculus innominatus, when present, or through the fissure between the pars petrosa and great wing of the sphenoid, or sometimes through th foramen ovale, into the zygomatic fossa, where it joins the otic ganglion, closi below the foramen ovale. \ The external superficial petrosal nerve (inconstant) is a branch of the genicu THE HEAD AND NECK 1 301 ite ganglion of the facial. It emerges from the petrous part of the tern- oral bone through a small opening (inconstant) close to the hiatus Fallopii, id joins the sympathetic plexus on the middle meningeal artery. Deep Petrosal Nerves. — The great deep petrosal nerve is a branch of the carotid lexus of the sympathetic. It joins the great superficial petrosal in the upper irt of the foramen lacerum medium to form the Vidian nerve, which, as ated, passes through the Vidian canal. into the spheno-maxillary fossa, and tins the back part of Meckel's ganglion. The small deep petrosal nerve is a branch of the tympanic plexus. It jsses forwards within the processus cochleariformis to the upper part of le foramen lacerum medium, where it joins the carotid plexus of the sympa- letic, and the great deep petrosal nerve, or, it may be, the great superficial Btrosal nerve. In this manner some of its fibres pass in the Vidian nerve ) Meckel's ganglion. The Articulations of the Atlas, Axis, and Occipital Bone. Atlanto-axial Joints. — These are three in number, and they belong 3 the class diarthrosis. One is mesially placed, the articular sur- ices being the atlantal facet on the anterior surface of the odontoid Anterior Tubercle of Atlas Posterior Sy novial Cavity Transverse Ligament ^ Anterior Syno\-ial Cavky , Odontoid Process of Axis Superior Articulcir Process of Atlas "--Posterior Tubercle of Atlas Spinous Process of Axis Fig. 540. -The Articulation between the Anterior Arch of the Atlas and the Odontoid Process of the Axis. •recess of the axis and the odontoid facet on the posterior surface ■f the anterior arch of the atlas. This joint belongs to the sub- ^vision trochoides or pivot- joint. The other two are placed one on either side, the articular surfaces of each being the inferior articular process of the atlas and the corresponding superior articular process )f the axis. These two joints belong to the subdivision arthrodia. Ligaments. — These are as follows: the transverse ligament, the capsular Hgaments, and the accessory ligaments. Besides these there are the anterior and posterior atlanto-axial ligaments, which ire not directly related to any of the joints. I302 • A MANUAL OF ANATOMY The transverse ligament is usually spoken of as the transverse ligament of the atlas. It represents the transverse portion of the cruciform ligament, to be presently referred to, and it constitutes a strong band, which is attached on either side to the tubercle on the inner aspect of the lateral mass of the atlas. It is arched back- wards behind the odontoid process, and at the median line it is connected on the posterior aspect with the crura of the vertical portion of the cruciform ligament. Between the ligament and the odontoid process there is an extensive synovial membrane, which extends well over each lateral aspect of the process, so as to come very near another synovial membrane between the front of the process and the anterior arch of the atlas. The capsular ligaments are loose sacs which surround the articula- External Occipital Crest ; Posterior Occipito-atlantal Ligament ^^ 1 ^^& ' Posterior Tubercle of Atlas .Vertebral Artery (third part) Atlanto-axial Capsule Posterior Atlanto-axial Ligament Spine of Axis Fig. 541. — The Occipital, Atlantal, and Axial Ligaments (Superficial Posterior View). tions between the inferior articular processes of the atlas and the superior articular processes of the axis. The accessory ligaments are two in number — right and left. Each! extends from the posterior surface of the body of the axis, close toi the root of the odontoid process, to the inner and posterior part of the lateral mass of the atlas. The direction of each ligament i< upwards and outwards, and it is closely related superiorly to tli' capsular ligament, which it strengthens internally and posteriori) The accessory ligaments are auxiliary in function to the check liga ments, and take part in limiting rotation of the atlas upon the axis The anterior atlanto-axial ligament, broad, thin, and mem branous, is attached superiorly along the lower margin of tin anterior arch of the atlas, and interiorly to the anterior aspect (> the body of the axis. It is serially continuous with the anteriu THE HEAD AND NECK 1303 common ligament of the bodies of the vertebrae, and its central portion is rendered thick by accessory fibres derived from the anterior common hgament. The posterior atlanto-axlal ligament, also broad, thin, and mem- branous, extends from the under aspect of the posterior arch of the atlas to the upper borders and adjacent portions of the outer sur- faces of the laminae of the axis. It is serially continuous with, and represents, the hgamenta subflava of succeeding vertebrae. Atlanto-occipital Joints. — These are two in number, right and left. They belong to the class diartlirosis and to the subdivision eondylartlirosis. The articular surfaces are the condyles of the occipital bone and the superior articular processes of the atlas. Posterior Occipito-axial Licameiit (Membrana Tectoiia) Basilar Groove of Occipital Bone_ Lateral Odontoid or . ir- \ - Check Ligament ; Superior Cms cf Cmdfonn Ligament Occipito- atlancal Capsule -- - Atlanto-axial Joint (opened) \ Inferior Cms of Cmcif<»m Ligament Fig. 54: SfHDoas Process of Axis -Occipital. Atlantal, and Axial Ligaments (Posterior View). Ligaments. — These are as follows: the capsular ligaments and the anterior and posterior occipito-atlantal hgaments, the latter two being indirectly connected with the joints. The capsular ligaments are loose sacs which directly surroimd the articulations. Their fibres are attached superiorly around the margins of the occipital condyles, and inferiorly to the lateral masses of the atlas, external to the circumference of the superior articular processes. The anterior atlanto-occipital ligament, thin and membranous, is attached inferiorly to the upper margin of the anterior arch of the atlas, and superiorly to the under surface of the basilar process of the occipital bone, close to the front part of the foramen magnum 1304 A MANUAL OF ANATOMY between the occipital condyles. In the median line it is rendered thick by the addition of a stout, round bundle of fibres, representing the accessory ligament, the fibres of which for the most part are attached below to the anterior tubercle of the atlas, but some of them are prolonged into the thickened anterior accessory part of the anterior atlanto-axial ligament. The posterior atlanto-occipital ligament, broad, thin, and mem- branous, is attached inferiorly to the upper margin of the posterior arch of the atlas, except in the region of the vertebrarterial grooves, and superiorly to the lower margin of the foramen magnum behind the occipital condyles. Over each vertebrarterial groove of the atlas this ligament forms an arch, beneath which the vertebral artery and suboccipital nerve pass. Posterior Occipito-axial Ligament (Membrana Tectoria) Superior Crus of Vertical Part of Cruciform Ligament Anterior Margin of jv. Foramen Magnum \ |>" Odontoid Process of Axis -1.1 A ^« .Basilar Groove of Occipital Bone •' , Middle Odontoid or Suspensory ;•>,'' Ligament , Anterior Condylar Foramen _ Lateral Odontoid or Check Ligament Occtpito-atlai> tal Joint (capsule) Atlanto-axial Joint (opened). Spinous Process of Axis Fig. 543. — The Occipital, Atlantal, and Axial Ligaments (Deep Posterior View). Occipito-axial Ligaments. — These are as follows: the posterior occipito-axial hgament; the lateral odontoid, or check, ligaments; the middle odontoid, or suspensory, ligament; and the vertical portion of the cruciform ligament. The posterior occipito-axial ligament, also called the membrana tectoria, is a broad membranous band, which is attached inferiorly to the posterior surface of the body of the axis, where it is con- tiiyious with the fibres of the posterior common ligament of the bodies of the vertebrae, and superiorly to the posterior part of the basilar groove of the occipital bone. It covers the odontoid pro- cess of the axis and the odontoid and cruciform ligaments, hence the name membrana tectoria. THE HEAD AND NECK 1305 The vertical portion ol the cruciform ligament consists of two parts, upper and lower, which are spoken of as the superior cms and inferior cms. The superior crus extends from the posterior surface of the transverse ligament at the median line to the pos- terior part of the basilar groove of the occipital bone, between the anterior margin of the foramen magnum and the superior attach- ment of the membrana tectoria, under cover of which latter it lies. This cms, as it ascends, is in contact with the posterior surface of the head of the odontoid process. The inferior crus extends from the posterior surface of the transverse ligament at the median line to the posterior surface of the body of the axis above the inferior attachment of the membrana tectoria. The transverse portion of the cruciform ligament constitutes the transverse ligament of the atlas, already described. The middle odontoid or suspensory ligament is a narrow round cord which is attached inferiorly to the ridge on the head of the odontoid process, and superiorly to the anterior margin of the foramen magnum in the median line. The lateral odontoid or alar ligaments, also known as the check ligaments, form two very strong bands which are attached in- feriorly to the lateral surfaces on the head of the odontoid process, and superiorly to an impression on the inner surface of each con- dylar part of the occipital bone. The direction of each Hgament is outwards and shghtly upwards. Movements — Atlanto-Axial Joints. — The movements are of a rotatory kind, the atlas, bearing the head, rotating on the axis, the odontoid process of which serves as a pivot. The extent of rotation is about 30 degrees, and it is Umited by the lateral odontoid Ugaments. aided shghtly by the accessory- atlanto-axial Ugaments. As stated in the section on Osteology, the superior articular pro- cesses of the axis are each divided by a sUght transverse elevation into t\vo parts — anterior and posterior. When the atlas hes directly over the axis, as when the face is directed straight forwards, the inferior articular processes of the atlas are not in accurate contact with the superior articular processes of the axis. Between the contiguous pairs there is a distinct interval all round. When, however, the atlas is rotated, the anterior division of the axial articular process of one side is brought into accurate contact with the corresponding atlantal articular process, and the posterior division of the opposite axial articuleir process into accurate contact with the atlantal articular process of that side. AUanto-oeeipital Joints. — The movements allowed at these joints are as follows: (i) Flexion; (2) extension; and (3) oblique movement. Flexion and extension constitute the forward and backward, or nodding, movements. In overextension (dorsi-flexion) the posterior margins of tiie superior articular processes of the atlas enter the posterior condylar fosses of the occipital bone, and locking takes place. In complete fonvard or ventral flexion the anterior margins of the superior articular processes of the atlas come into contact with the occipital bone in front of each condyle. Oblique movement occurs in the position of semiflexion ventralwards. As stated in the section on Osteology, the condyles of the occipital bone, like the superior articular processes of the axis, are each divided into two parts, anterior and posterior, by a sUght elevation, which, in the case of the occipital condyles, is disposed obUquely. During obhque movement the anterior division of one occipital condyle is in contact with the corresponding superior articular process of the atlas, whilst the posterior division of the opposite occi- pital condyle is in contact with the superior articular process of the atlas on that side. THE NERVOUS SYSTEM The nervous system is arranged in two divisions, cerebro -spinal and sympathetic. The sympathetic nervous system consists of (i) two gangliated cords, right and left, situated on either side of the vertebral column, and (2) three prevertebral plexuses, namely, the cardiac plexus, situated in the thorax ; the epigEistric or solar plexus ; and the hypogastric plexus, the latter two being situated in the abdomen. The cerebro-spinal nervous system or axis consists of the ence- phalon and the spinal cord, the former being situated within the cranial cavity, and the latter within the spinal canal. The continuity between these two divisions is established through the foramen magnum. The cerebro-spinal axis is central in position, and is connected with the various parts of the body by the cranial and spinal nerves. It is composed of two kinds o\ nervous matter, white and grey. The white matter consists chiefly of nerve-fibres, and the grey matter consists of nerve-cells, with their axis-cylinder processes or axons and dendrites, the pervading supporting tissue in each case being called neuroglia. In the brain the white matter is disposed in the interior as the tnedulla, and the grey matter forms the exterior or cortex. In the spinal cord the white matter is disposed externally in the form of three columns on either side, whilst the grey matter is situated in the interior. The cerebro-spinal axis is surrounded by three membranes, or meninges, which, from without inwards, are named the dura mater, arachnoid membrane, and pia mater. The Spinal Cord. Membranes of tlie Spinal Cord. — ^The membranes are three in number, namely, the dura mater, the arachnoid membrane, and the pia mater. Dura Mater. — ^This is the most external covering of the cord. 1306 THE NERVOUS SYSTEM Frontal Lobe 1307 B Temporal Lobe /_ Basilar Artery Vertebral Arteries Soperior Cervical_ Sympathetic Ganglion Cervical Plexvis Vertebral Artery Middle Cervical Ganglion Brachial Plexus Ganglion Stellatum 4th Intercostal Xerve Anterior Spinal Artery Thoracic Sympathetic Cc«d , , iN-fc> ^V" Spinal Ganglion ^r .4. ■■rk ■ Mir^ ^ -w - Subcostal Nerve Lumbar Sympathetic Cord . Lumbar Plexus I' lr'-i/\t \>bd-Ai_^— - Pelwc Sympathei HI P'^y>^ Z^— Sacral Plexus -\ r - vjanglion Impar tic Cord Fig 544. — ^The Cerebro-Sptxal and Sympathetic Systems (Anterior View) (Hxrschfeld and Leveille). i3o8 A MANUAL OF ANATOMY It forms a dense fibrous tube, known as the theca, which extends from the margin of the foramen magnimi of the occipital bone to the level of the second sacral vertebra. Inferiorly, where it has become tapering behind the second sacral vertebra, the theca is perforated by the filum terminale, and from this level the spinal dura mater is prolonged downwards around the filum terminale, with which it blends. Finally it is attached, along with the filum terminale, to the back of the first coocygeal vertebra, where it is incorporated with the periosteum. In this situation the spinal dura mater is firmly fixed. The theca surrounds the spinal cord very loosely, and it is separ- ated from the wall of the spinal canal by an interval, called the epidural spaee {cavum epidurale B.), which is occupied by venous plexuses and loose areolar tissue. Opposite the intervertebral foramina of each side the theca presents a series of openings, which are arranged in two parallel rows. The openings constituting each pair are placed side by side, but are distinct from each other, and they transmit the ventral or anterior and dorsal or posterior roots of the spinal nerves. Each of these roots, as it makes its exit, receives a tubular sheath from the margin of the corresponding thecal opening, and these sheaths remain distinct as far as the spinal ganglion of the dorsal root. Thereafter the contiguous sheaths fuse and form one sheath, which blends with the sheath of the corresponding spinal nerve. The spinal dura mater is maintained in position by several con- nections, (i) Superiorly it is fixed to the margin of the foramen magnum of the occipital bone. (2) Opposite the body of the axis it is firmly attached, anteriorly, to the posterior occipito-axial ligament. (3) Below the level of the axis it is loosely connected, anteriorly, with the posterior common ligament of the bodies of the vertebrae by fibrous bands. (4) Laterally it is connected with the sheaths of the spinal nerves by means of the tubular sheaths which it gives to the ventral and dorsal nerve-roots. (5) Inferiorly it blends with the periosteum over the back of the first coccygeal vertebra through means of the filum terminale. Posteriorly it is quite free from connections. The spinal dura mater differs from the cranial dura mater in the following respects : (i) It is destitute of an outer or periosteal layer ; (2) it does not send septa into the spinal cord; and (3) it does not contain venous sinuses. Blood-supply of Spinal Dura Mater. — ^The arteries are derived from (i) the spinal branches of the vertebral, intercostal, and lumbar arteries; and (2) the lateral sacral arteries, which are branches of the internal iliac trunk. Nerve-supply. — ^The nerves are partly spinal and partly sym- pathetic. Lymphatic Vessels. — There are no lymphatic vessels, their place being taken by perivascular lymph-spaces in connection with the arteries. THE NERVOUS SYSTEM 1309 Doia Mater (Theca) Strnetnre. — The spinal dura mater consists of fibrous tissue and some elastic tissue disposed in parallel longitudinal bundles. Its internal and external surfaces are covered by endothelial ceUs. Subdural Space. — Between the spinal dura mater and the arach- noid there is a narrow cleft-Hke interv^al, which is known as the subdural space {cavum suhdurale B.). It contains a small amount of fluid, and it communicates freely with the lymph-spaces or clefts in the sheaths of the spinal nerves. It has, however, no communi- cation with the subarachnoid space. Spinal Arachnoid Membrane.— This is a delicate transparent membrane which loosely surrounds the spinal cord between the theca externally and the pia mater intern- ally. It is separated from the theca by the /L^\ subdural space, and ^^ from the pia mater ) by the subarachnoid space. Superiorly it is continuous with the cranial arachnoid, and inferiorly it encloses the Cauda equina. On either side it forms sheaths for the pro- cesses of the ligamen- tum denticulatum as far as the inner sur- face of the theca . The ventral and dorsal roots of the spinal nerves also receive sheaths from it, which accompany them through the openir^s in the theca, but soon cease. Subarachnoid Space {Cavum Subarachnoi- dale B.). — ^This space, which is wide, is situated, as stated, between the arachnoid and pia mater. It contains cerebro-spinal fluid, and its dorsal part is continuous superiorly with the cistema magna of the cranial subarachnoid space, which communicates with the fourth ventricle by three openings (foramen of Magendie and fora- mina of Luschka). The subarachnoid space is partially divided into t\^^ compart- ments, ventral and dorsal, by ligamenta subflava, which form in- complete lateral septa. The ventral roots of the spinal nerves traverse the ventral compartment, and the dorsal roots traverse the ^ Arachnoid - -T— Ligamentum Dentictilatum Anteiior Nerve-Root Posterior Nerre-Root Pia Mater Sinnal Cord Anterior Nerve-Root (cot) OF THE Fig. 545. — Portion SHOWING THE Membranes, Dexticul.\ta, and Roots of Nerves. Spinal Cord, Ligamenta THE Spinal I3IO A MANUAL OF ANATOMY dorsal compartment. The dorsal compartment is partially sub- divided into two portions, right and left, by means of a third in- complete septum, called the septum posticum. This partition extends from the pia mater, as it crosses the dorsal median fissure of the spinal cord, to the dorsal part of the arachnoid at the median line. All the compartments of the subarachnoid space communicate freely with each other. The subarachnoid space has no communication with the subdural space. Structure of the Arachnoid Membrane. — ^The arachnoid consists of fine fibrous tissue, arranged in interlacing bundles, the intervals between these bundles being occupied by delicate cellular membranes. Several such layers, intimately blended together, form the membrane. Beneath the arachnoid, and constituting a part of it, there is a reticulum of subarachnoid trabecules. These trabeculae consist, as in the case of the arachnoid proper, of fine fibrous tissue, but the inter- trabecular spaces, instead of being occupied by cellular membranes, contain cerebro- spinal fluid. The trabecular reticulum connects the arach- noid with the subjacent pia mater. Spinal Pia Mater. — ^This is the most internal mem- brane of the spinal cord. It is very vascular and closely invests the cord, the substantia gelatinosa externa or glial sheath being situated immedi- ately beneath it. Su- periorly it is continuous with the cranial pia mater, the conus medullaris over .. Dura Mater (Theca) . lanea Splendens Ligamentum Denticulatum _L Pia Mater Anterior Nerve-Root Fig. 546. — A Portion of the Spinal Cord (Anterior View). (The Theca has been laid open, and the Arachnoid Membrane removed). and interiorly it is prolonged from the upper half of the intrathecal part of the filum terminale. On either side it forms tubular sheaths for the ventral and dorsal roots of the spinal nerves, which blend with the sheaths of the nerves. Along the course of the ventral median fissure of the cord it sends a vascular fold into that fissure. Along the course of the dorsal median fissure, over which it passes, the neuroglial septum occupying that fissure is attached to it. From the deep surface of the pia mater several septa are prolonged into the cord, which carry with them portions of the glial sheath. The pia mater is separated from the arachnoid by the subarach- noid space, and opposite the dorsal median fissure of the cord it is connected with the dorsal part of the arachnoid by the septum posticum. THE NERVOUS SYSTEM 13" Blood-supply. — The pia mater derives its arteries from (i) the anterior and posterior spinal arteries, and (2) the neural branches of the lateral spinal arteries. Nerve-supply. — ^The nerves are derived from the sympathetic system. Structure. — The spinal pia mater consists of two layers — outer and inner. The outer layer consists of fibrous tissue, which is disposed for the most part in parallel longitudinal bundles. The inner layer consists of areolar tissue, containing a great many bloodvessels, and its outer and inner surfaces are covered by endotheUal cells. Between the two layers there are narrow cleft- like lymphatic spaces, which communicate \vith the subarachnoid space, and with lymphatic clefts ciround the arteries of the pia mater. Dora Matet Pia Mater Arachnoid Ligamentum Denticulatum Subdural Space Subarachnoid Space Septum Posdcum Fig. 547. — Diagram of a Transverse Section of the Spinal Cord AND ITS Membranes. A.M.F. Anterior Median Fissure, with Process of Pia Mater P.M.F. Posterior Median Fissure A.C. Anterior Column L.C. Lateral Column P.C. Posterior Column A.R. Anterior Nerve-Root P.R. Posterior Ner\-e-Root G. Spinal Ganglion S.P. Spinal Nerve A.P.D. Anterior Primarj- Division P.P.D. Posterior Primary Divbion The spinal pia mater differs from the cranial pia mater in being thicker and more adherent to the ner\'ous matter. The greater thickness is due to the presence of the outer layer, the cranial pia mater representing the inner layer of the spinal pia mater.. Linea Splendens. — ^The pia mater presents a glistening vertical fibrous band, which hes over the ventral median fissure. This band is kno\\-n as the linea splendens, and it extends along the entire length of the cord and along the conus medullaris on to the filum terminale. Ligamentum Denticulatum. — This is a fibrous band which ex- tends along the spinal cord, on each side, opposite the corresponding lateral column. It lies between the ventral and dorsal roots of the spinal nerves, and extends from the margin of the foramen magmmi to the lower end of the cord. It lies within the subarachnoid space, and partially divides that space into two compartments — ^ventral and dorsal. 1312 A MANUAL OF ANATOMY Internally it forms an uninterrupted band which is attached to the pia mater along the lateral column of the cord. Externally it is denticulated. The denticulations (about twenty-one in number) carry with them sheaths from the arachnoid, and their pointed outer ends are attached to the inner surface of the theca in the intervals between each pair of openings for the exit of the ventral and .dorsal nerve-roots. The two ligamenta denticulata act as lateral supports to the spinal cord. Structure. — Each ligamentum denticulatum consists of fibrous tissue, which is continuous with the outer layer of the pia mater. External Characters of the Spinal Cord. — ^The spinal cord, or medulla spinalis, which is somewhat cylindrical, is that division of the cerebro-spinal axis which is situated within the spinal canal. It extends from the loWer margin of the foramen magnum in the occipital bone to about the level of the disc between the bodies ot the first and second lumbar vertebrae, and it is about i8 inches in length. Superiorly it is continuous with the medulla oblongata, and interiorly it terminates in a tapering portion, called the conus meduUaris. From the lower end of this cone a slender,- glistening thread, called the fllum terminale, is continued downwards between the bundles of lumbar, sacral, and coccygeal nerves of either side, which constitute the cauda equina, to be attached to the back of the first coccygeal segment. The spinal cord is of smaller dimensions than the spinal canal, and is therefore relieved from pressure during the ordinary move- ments of the vertebral column. It is surrounded by three membranes, already described, namely, the dura mater, the arachnoid membrane, and the pia mater, in this order from with- out inwards. Within its theca of dura mater the cord is sus- pended by means of the ligamenta denticulata, and the nerve- roots as they emerge through the openings in the theca. The spinal cord varies in shape in different regions. In the cervical region, as seen in transverse section, it is transversely oval, and is slightly flattened from before backwards. In the thoracic region it is somewhat circular, but the transverse diameter exceeds the antero-posterior. In the lumbar region it is still more circular than in the thoracic region. The cord presents two swellings, which are known as the cervical and lumbar enlargements, and which are associated with the numerous and large nerve-trunks- destined for the upper and lower limbs. The cervical enlargement extends from near the com- mencement of the cord to the second thoracic vertebra, and its breadth is greatest opposite the sixth cervical vertebra. The lumbar enlargement, which is less conspicuous than the cervical, extends from the level of the tenth thoracic vertebra to the conus medul- laris, and its breadth is greatest opposite the twelfth thoracic vertebra. THE NERVOUS SYSTEM 1313 Filum Terminale. — This delicate glistening thread is also known as the central ligament of the cord. It Ues in the median hne between the lumbar, sacral, and coccygeal nerves of either side, which constitute the cauda equina, and it extends from the apex of the conus meduUaris to the back of the first coccygeal segment. It is about 6 inches in length. As low as the back of the body of the second sacral segment it is situated within the theca, but at that level it pierces the theca, from which it receives an investment, and then passes to be attached to the back of the first coccygeal ^■xrtJ — Fiist Lumbar Vertebra Conns MeduUaris - Intratbecal Portion of Filum Terminale First Sacral Vertebra -' Eztiathecal Portion of Filiun Terminale Fig. 548. — Lumbar and Sacral Portions of Spinal Canal, showing Lateral View of Conus Medullaris, Filum Terminals, and Theca (Testut). segment, where it blends with the periosteum. The intrathecal portion is known as the fdutn terminale internum, and the extrathecal portion as the filum terminale externum. Structure. — The filum terminale internum in its upper half consists of pia mater, prolonged from the conus medullaris of the spinal cord. This encloses grey matter, within which, over about the upper third, there is a continuation of the central canal of the cord. The lower half consists chiefly of connective tissue. The filum terminale extemimi is a mere fibrous filament, invested by a prolongation of 83 I3I4 A MANUAL OF ANATOMY Linea Splendens ll|:.Cauda Equina — -Filum Terminale the theca which blends with it. It is also composed of pia mater prolonged downwards from the contis medullaris, and reinforced by fibres derived from the lower portions of the Hgamenta denticulata and linea splendens. Its lower part is purely fibrous. Cauda Equina. — ^This is situated within the lower part of the theca. It consists of the lumbar, sacral, and coccygeal nerves of each side, which are arranged in the form of a leash, and the filum terminale lies in the median line between the two nerve-leashes. On account of the high origins of the individual nerves, relatively to the positions of the inter- vertebral foramina through which they Conus Medullaris pass, the direction of the nerves is almost vertical until they reach the level of their respective foramina of exit. Fissures of the Spinal Cord.— The spinal cord, which is somewhat flattened in front and behind, is incompletely divided into two symmetrical halves by two median fissures, anterior and posterior. The anterior median fissure extends into the cord for one-third of its thick- ness from before backwards, and it con- tains a fold of the pia mater. At the bottom of the fissure the transverse * band of nerve-fibres, called the anterior m white commissure, crosses between the two halves of the cord. The posterior median fissure, though so named, is not an actual fissure like the anterior, and does not contain a fold of the pia mater. It is just wide enough to contain a septum formed by neuroglia, and it extends into the cord for about half of its thickness from before backwards. The posterior grey commissure lies at the bottom of the fissure. The anterior median fissure is more distinct and wider than the pos- terior, but it is not so deep. Each half of the cord presents a groove along the line of entrance o;f the fasciculi of the posterior nerve-roots, called the postero-Iateral sulcus, but there is no similar groove along the line of emergence of the fasciculi of the anterior nerve-roots, these being spread over an area of some breadth. By means of the postero-Iateral sulcus on the one hand and the area corresponding to the emergence of the fasciculi of the anterior nerve roots on the other, each half of the spinal cord is divided superficially into three columns, anterior, | lateral, and posterior. I The anterior column is situated between the anterior median Fig. 549. — The Terminal Part of the Spinal Cord, AND THE Cauda Equina. THE NERVOUS SYSTEM 1315 fissure and the most external fasciculi of the anterior nerve-roots ; the lateral column is the area between the most external fasciculi of the anterior nerve-roots and the postero -lateral sulcus ; and the posterior column lies between the postero-lateral sulcus and the posterior median fissure. Practically the anterior colrmin repre- sents the region in front of the anterior nerve-roots, the lateral column the region bet^^'een the anterior and posterior nerve-roots, and the posterior colmnn the region behind the posterior nerve-roots. According to some authorities there are only two columns, namely, antero-lateral and posterior, the former extending from the anterior median fissure to the postero-lateral sulcus, and representing the combined anterior and lateral colimms. In the cervical region the siurface of each posterior colmim presents a shght groove which is situated nearer the posterior median fissure than the postero-lateral sulcus. This groove is called the posterior intermedial or paramedian furrow. It contains a septimi of pia mater, and in this manner the posterior column of the cord is marked off into two tracts. The inner and smaller tract is called the postero-median column, or column of GoU, and the outer and larger is called the postero-extemal column, or column ol Burdach. These two columns extend throughout the cord, but it is only above the level of the mid-thoracic region that they are separated from each other by a septum of pia mater, known as the posterior ititermediate septum. Origin of the Spinal Nerves. — • There are thirty-one pairs of spinal nerves, which arise from the sides of the spinal cord. They are arranged in five groups, on either side, as follows: cervical, eight in number ; thoracic, twelve ; lumbar, five ; sacral, five ; and coccygeal, one. Each spinal nerve is attached superficially to the cord by two roots, anterior and posterior, the posterior root being the larger of the tw-o. The portion of the cord from which each pair of spinal nerves arise is spoken of as a segment of the cord. Each root is ensheathed by tubular prolongations of the coverings of the cord, namely, the pia mater, arachnoid, and dura mater, in this order from within outwards, and these sheaths ultimately blend with the perineurium. The roots are separated from each other by the lateral colimm of the cord and the ligamentum denticulatimi, and l^ey pass through separate openings in the theca of dura mater. The anterior roots are composed of efferent or motor fibres, and their fasciculi emerge from the cord in an irregular manner, being spread over an area corresponding in breadth to the caput of the anterior comu of the grey matter in the interior. The posterior roots are composed of afferent or sensory fibres, and their fasciculi enter the cord in a straight line along the course of the postero-lateral sulcus. Each posterior root presents an oval swelling, called the spinal ganglion. These gangUa are, for the most part, situated in tiie intervertebral foramina, and immediately beyond each ganglion the anterior and posterior roots unite to form I3i6 A MANUAL OF ANATOMY a spinal nerve, which is necessarily a mixed nerve, inasmuch as it is composed of afferent and efferent fibres. Each spinal nerve breaks up into an anterior and a posterior primary division. The upper cervical nerve - roots are short, and pass almost horizontally outwards. The succeeding nerve-roots, however, gradually increase in length, and incline downwards as they pass outwards. This downward inclination goes on increasing until it becomes almost vertical in the case of the limibar, sacral, and Fig. 550. — Two Segments of the Spinal Cord, showing the Attach- ments OF the Anterior and Posterior Nerve-Roots, and thb Spinal Ganglia. A, Superior View ; B, Anterior View. 1, I. Anterior Median Fissure 5, 5. Spinal Ganglion 2, 2. Posterior Median Fissure 6, 6. Spinal Nerve 3, 3. Anterior or Motor Nerve-Root 7, 7. Anterior Primary Division 4, 4. Posterior or Sensory Nerve-Root 8, 8. Posterior Primary Division 9, 9. External and Internal Branches of Posterior Primary Division coccygeal nerves, which constitute the cauda equina. From this disposition it follows that, in the majority of cases, the superficial origins of the spinal nerves art on a higher level than the inter- vertebral foramina through which they emerge from the spinal canal. Relation of the Spines of Vertebrae to the Bodies and to the Origins of the Nerves. — In the case of the cervical and the eleventh and twelfth thoracic vertebra; the extremities of the spinous processes correspond to the lower margins of the bodies of the respective vertebrae. In the case of the thoracic- vertebrae, from the first to the tenth inclusive, the extremity of each spinous, process corresponds to the upper margin of the body immediately below. In the case of the lumbar vertebra; the extremity of each spinous process corresponds to the centre of the body of its own vertebra. Each cervical spinous process is nearly opposite the lower fasciculi of the roots of the nerve below. The spinous process of the seventh cervical vertebraj THE NERVOUS SYSTEM ^xji? (vertebra prominens) is opposite the roots of the first thoracic nerve. From the third to the tenth thoracic vertebrae the spinous processes correspond to the second root below. The eleventh thoracic spine corresponds to the first and second lumbar nerves. The twelfth thoracic spine corresponds to the third, fourth, and fifth lumbar nerves. The first lumbar spine correspcmds to the first, second, and third sacral nerves. (Gowers, from an original investigation). Mode of distinguishing the Anterior and Posterior Surfaces of the Spinal Cord. — ^These surfaces may be recognised by attending to the following points : Anterior Surface. Posterior Surface. 1. Linea splendens in median line. i. Ganglion on each posterior nerve- root. 2. Anterior spinal artery in 2. Fasciculi of posterior nerve-roots median line. lie in a straight line, and enter through postero-lateral sulcus. 3. FascicuU of anterior nerve- 3. Arterial anastomotic chain be- roots spread over a wide hind and in front of the pos- area. tenor nerve-roots. Internal Structure of the Spinal Cord. — The spinal cord, as seen in transverse section, consists of a central portion com- posed of grey matter, and an external portion composed of white matter. Grey Matter. — ^This is arranged in the form of two irregular crescents, the concavities of which are directed outwards, and the convexities inwards, the latter being connected across the middle line by the grey commissure. The arrangement has been likened to the letter M . The grey commissure lies at the bottom of the posterior median fissure, and presents about its centre the minute opening of the central canal of the cord. The part of the commis- sure in front of this canal is known as the anterior grey commissure, and the part behind as the posterior grey commissure. In front of the anterior grey commissure there is a transverse band of white matter, called the anterior white commissure, which lies at the bottom of the anterior median fissure. Each crescent of grey matter consists of two comua, anterior and posterior, the former bemg in front of, and the latter behind, the grey commissure. The anterior cornu is broad and blvmt, and it stops short of the sur- face of the cord, being separated from the surface by white matter which is traversed by the fasciculi of the anterior ner\'e-roots. The blunt extremity of the anterior cornu is called the caput cornu, and the portion adjoining the grey commissure, which is slightly constricted, is called the cervix cornu. The posterior cornu is, for the most part, long, narrow, and tapering, and its pointed ex- tremity almost reaches the surface of the cord at the bottom of the postero-lateral sulcus. This pointed extremity is called the apex ccrnu, and it contains a translucent substance, known as the substantia gelatinosa of Rolando, which forms a cap for the caput 1^x8 A MANUAL OF ANATOMY comu posterioris. It contains a small amount of neuroglia, and numerous nerve-cells. The portion adjoining the grey commissure, which is slightly constricted, is called the cervix co^ynu, and the portion contiguous to the cervix, which is slightly enlarged, is called the caput comu. The part between the two cornua is called the body. About the centre of the concavity of the body crescent the grey matter projects outwards into the lateral column in the form of processes arranged in a reticular manner and enclosing white matter. This network is called the processus reticularis, and it is most conspicuous in the cervical region. In the thoracic region, more particularly in its upper part, the grey matter of each crescent forms a triangular projection, which extends outwards for a short distance immediately in front of the processus reticularis, and adjacent to the junction of the anterior cornu with the grey com- Central Canal Anterior Nerve-Root , 1 Mesial Group of Motor Cells Anterior Cornu Lateral Cornu Posterior Posterior Lateral Group of Motor Cells Cells of Lateral Cornu Clarke's Dorsal Nucleus bstantia Gelatinosa Rolandi Fig. S51. — Transverse Section of the Spinal Cord in the Upper Thoracic Region, showing the Arrangement of the Grey Matter AND Cells (Semi-diagrammatic) (after Poirier). missure. This projection is variously known as the lateral cornu, the intermedio-lateral tract of Lockhart Clarke, or the intermediate process of Gowers. When followed into the lower cervical and into the lumbar regions it blends with the anterior cornu, the thickness of which it increases, but it is again present above the level of the fourth cervical vertebra. The grey matter varies in amount in different parts of the cord. It is present in largest quantity in the lumbar enlargement, where the large nerve-trunks for the lower limbs arise, and next to this in the cervical enlargement, where the large nerve-trunks for the upper limbs arise. The cornua of the crescents of grey matter vary in shape in different regions. In the cervical region the anterior cornua are short, broad, and blunt, and the posterior cornua are long, narrow, THE NERVOUS SYSTEM 1319 and pointed. In the thoracic region both comua are narrow, though the posterior is more so than the anterior. In the lumbar region both comua are broad, though the anterior is more so than the posterior. These differences render sections of the spinal cord in the cervical, thoracic, and lumbar regions easily recog- nisable. As stated, the lateral comu is also a characteristic ol the cord in the thoracic region, more particularly in its upper part. Central Canal. — ^This minute canal is situated about the centre of the grey commissure, and extends throughout the entire length of the spinal cord. Superiorly it is continued into the lower half of the medulla oblongata, and it opens into the lower part of the fourth ventricle at the calamus scriptorius. Interiorly, near the apex of the conus medullaris, it becomes enlarged, and assumes the shape of an inverted T, thus ±. This enlargement is known as the ventrlculus terminalis of Krause. From this point it is prolonged for some distance into the filum terminale, and it ends in a closed extremity. In the cervical and thoracic regions the central canal Fig. 552. — Transverse Sections of the Spinal Cord in Different Regions. A, Cervical Region ; B, Mid-thoracic Region ; C, Lumbar Region ; D, Conus Medullaris. is nearer the anterior surface of the cord than the posterior, but in the lumbar region it occupies the centre. In the conus medullaris it is near the posterior surface. The canal is lined with ciliated columnar epithelium, the columnar cells being known as epend^Tnal cells. The central canal represents the lumen of the neural tube of epiblast from which the spinal cord is developed. White Matter of the Spinal Cord. — ^The white matter forms the outer part of the cord, and is arranged in three columns, anterior, lateral, and posterior. The anterior column is situated between the anterior median fissure and the anterior comu of grey matter, and extends as far as the most external fasciculi of the anterior nerve-roots. It therefore includes the superficial coating of the anterior comu, where it is traversed, over an area of some breadth, by the scattered fasciculi of the anterior ner\^e-roots. The lateral column is situated between the anterior and posterior comua of grey matter, in the concavity of the crescent. Its superficial limits are the most extemal fasciculi of the anterior nerve-roots and the fasciculi of the posterior nerve-roots at the postero-lateral sulcus. I320 A li^ANUAL OF ANATOMY The posterior column is situated between the posterior median fissure and the posterior cornu of grey matter, its superficial limit being the fasciculi of the posterior nerve-roots at the postero-lateral sulcus. The white matter increases in quantity from below upwards, and septa of pia mater and neuroglia fibres pass into it at various points. Chief Distinguishing Characters of the Spinal Cord in Different Regions^ as seen in Transverse Sections. Cervical Region. Thoracic Region. Lumbar Region. '• Transversely oval. I. Approaching to circular. I. Almost circular. 2. Anterior Cornu, 2. Anterior and Pos- 2. Anterior and Pos- short, broad, and terior Cornua terior Cornua both blunt. both narrow. broad, anterior Posterior Cornu, posterior more so more so than pos- long, narrow, and than anterior. terior. 3- tapering. Formatio Reticu- 3- Formatio Reticu- 3- Formatio Reticu- laris, well laris, not very laris, absent. marked. distinct. 4- Lateral Cornu, 4- Lateral Cornu, con- 4- Lateral Cornu, merged into an- terior, excapt above fourth cer- spicuous, especi- ally in upper part. merged into an- terior. vical vertebra. 5- White Matter, large s- White Matter, less s- White Matter, small in amount. in amount, but large in propor- tion to Grey Matter. in amount, and Grey Matter, large. 6. Central Canal, 6. Central Canal, 6. Central Canal, in nearer the ven- nearer the ven- the centre. tral than the dor- tral than the dor- sal surface. sal surface. 7- Postero - interme- 7- Postero - interme- 7- Postero - intermediat« diate Sulcus and diate Sulcus, ab- Sulcus and Septum Septum of pia mater, well sent, but Sep- tum of pia mater of pia mater, ab< sent. marked. recognisable. i Minute Structure of the Spinal Cord— Grey Matter.— The grey matter consists of nerve-cells, nerve-fibres, and neuroglia, and is very vascular. The nerve-cells are present in great numbers, and are multi- polar. Each cell sends off at various points several protoplasmic processes, one of which becomes the axis-cylinder of a nerve-fibre, and is called the axis-cylinder process, or axon. The other processes are known as the protoplasmic processes of Deiters, or de^idrites, and, after successive branchings, they terminate in free extremities. There are no anastomoses between the dendrites of the same cell, nor between those of contiguous cells. A multipolar nerve-cell, with its axon and dendrites, constitutes a neuron. The multipolar THE NERVOUS SYSTEM 1321 cells form longitudinal columns of various lengths, and, as seen in transverse sections of the cord, they are arranged in groups which occupy particular regions. These cell-columns or groups are three in number, namely, anterior or ventral, in the anterior comu of grey matter ; lateral, in the lateral comu of grey matter ; and posterior, constituting the posterior vesicular column of Lockhart Clarke, and being very conspicuous in the mesial portion of the cer\-ix of the posterior grey comu in the thoracic region. Besides these main columns or groups, other ner\'e-cells are present, which are scattered irregularly throughout the other portions of the grey matter. The anterior or ventral cell-column is situated, as stated, in the anterior comu of grey matter, and extends throughout the Anterior Nerve-Root Anterior Comu Central Canal Latetal Comu Mesial Group of Motor Cells Lateral Group of Motor Cells „ Cells of Lateral Comu Posterior Comu Posterior Nerve-Root Clarke s Dors^ Nucleus Substantia Gelatioosa Rolandi Fig. 553- — Transverse Section of the Spinal Cord in the Upper Thoracic Region, showing the Arrangement of the Grey Matter AND Cells (Semi-diagrammatic) (after Poirier). whole length of the spinal cord. Its cells are of large size and very conspicuous, and their axons, which are at first non-medul- lated, become medullated, and then constitute the fascicuH which emerge to form the anterior ner^-e-roots. These cells are therefore the sources from which the efferent or motor ner\'e-fibres proceed, and the ventral column is consequently spoken of as the motor or ganglionic column. The ventral or motor cells of this column are arranged in two groups, mesial and lateral. The mesial group occupies the mesial part of the anterior grey comu, and the lateral group is situated in its outer part. In the cer^ucal and lumbar enlargements of the cord the cells of the lateral group are very numerous, and are arranged in two sub-groups, ventro -lateral and dorso-lateral. The intermedio-lateral cell-column is situated, as stated, in the 1322 A MANUAL OF ANATOMY lateral comu of grey matter, and the cells constitute a column, known as the intermedio-lateral tract of Lockhart Clarke, or the dorsal nucleus of Stilling. This tract extends throughout the entire thoracic region of the cord, and for a short distance into the cervical and lumbar enlargements. The posterior vesicular cell-column is situated in the mesial part of the cervix of the dorsal cornu of grey matter. The cells con- stitute the posterior vesicular column of Lockhart Clarke, and they are of large size. Clarke's column exists chiefly in the thoracic portion of the cord. The cells of the grey matter differ as regards their axons, some having short, and others long, axons. The cells with short axons have their axons confined to the grey matter, in which they ramify not far from the parent-cells. They serve to bring contiguous cells into relation with one another. The cells with long axons are partly root-cells and partly association-cells, and their axons travel for some distance from the parent-cells. The axons of the root-cells leave the cord in the fibres of the ventral or motor nerve-roots. The axons of the association-cells constitute association-fibres, which are disposed in two ways: (i) Some enter the white matter of the same side of the cord, in which they divide into ascending and descending branches. Eventually they re-enter the grey matter, and terminate in arborizations at some distance from the parent-cells. (2) Other association-fibres cross to the opposite side in the ventral or white commissure. Some of these end in arborizations around the cells of the grey crescent, whilst others enter the white matter, in which they are disposed as on the side from which they have crossed. Destination of Axons of Cells of Grey Matter. Cells of Ventral Cornu. — (i) Many axons become the axis-cylinder processes of the efferent fibres of the ventral nerve-roots. (2) Other axons constitute association-fibres, which cross to the opposite side in the ventral or white commissure. After crossing, some end in arborizations around the cells of the ventral cornu ; others enter the white matter ; and a few are regarded by some authorities as entering the ventral nerve-roots of the side to which they have crossed. Cells of Lateral Cornu. — ^The axons of the cells of the intermedio-lateral tract of Clarke pass to the efferent fibres of the ventral nerve-roots, and they are regarded as furnishing the white rami communicantes of the sympathetic system. Cells of Dorsal Cornu. — The axons of the cells of the dorsal comu have various directions: (i) Some pass to the ventral cornu and ventral or white commissure. (2) The axons of the cells of Clarke's column pass to the lateral column, and are usually regarded as entering the dorsal cerebellar and ventro- lateral cerebellar tracts. (3) The axons of the cells of the substantia gela- tinosa of Rolando pass partly to the lateral column, adjacent to the dorsal horn, where they divide into ascending and descending branches, and partly into the posterior marginal bundle of Lissauer. (4) The axons of other cells in the lateral part of the cervix of the dorsal cornu pass to the lateral and ventral cornua, the ventral or white commissure, and the lateral column. (5) The axons of the cells of the caput cornu posterioris pass to the lateral column of the same side, and a few are regarded as passing to the opposite side in the ventral or white commissure. Dorsal or Grey Commissure. — This commissure lies at the bottom of the dorsal median fissure. It consists of (i) grey matter, con- taining a few small nerve-cells, and (2) meduUated nerve-fibres. These fibres pass across from one side to the other, and thereafter THE NERVOUS SYSTEM 1323 diverge in each grey crescent. They serve as association-fibres which bring the cells of opposite sides into relation with one another. This commissure contains the central canal of the cord, which for the most part is nearer the ventral portion of the commissure than the dorsal. The part of the commissure surrounding the central canal is called the substantia gelatinosa ceniralis. It consists of neuroglia, a few nerve-cells, and nerve-fibres ; and it is invaded by processes derived from the deep ends of the ciliated columnar epithelial cells which line the central canal. Summary ol the Gelatinoos Substances ol the Grey Matter. — These are — (i) The substantia gelatinosa of Rolando, which forms a cap for the caput comu posterioris; (2) the substantia gelatinosa centralis, which surrounds the central canal of the cord; and (3) the substantia gelatinosa externa, which forms the glial sheath of the cord beneath the pia mater. White Matter. — ^The white matter of the cord consists of longi- tudinal medullated nerve-fibres, traversed by septa of the pia mater, and embedded in neuroglia. The fibres have no primitive sheath or neurilemma. Ventral or White Commissure. — ^This commissure lies at the bottom of the ventral median fissure, and it is separated from the central canal of the cord by a part of the dorsal or grey commissure. It consists of medullated nerve-fibres, destitute of a" neurilemma, some of which pass transversely, but most of them decussate, entering the commissure ventrally on one side, and leaving it dor sally on the opposite side. The fibres, after crossing, enter the grey crescent and the ventral column. They are derived from (i) the direct pyramidal tract, or tract of Turck, (2) the processes of root-cells and of association-cells, and {3) the fibres of the spino- thalamic tract, to be presently described. Fibres of Roots of Spinal Nerves — Ventral or Anterior Nerve- Roots. — ^The fibres of the ventral nerve-roots arise within the cord from several sources, (i) Many of them are axons of the mesial cells of the ventral horn of grey matter of the same side. (2) Some are axons of the lateral cells of the ventral cornu. (3) Others are axons of the cells of the intermedio-lateral tract of Clarke of the same side. (4) A few are axons of cells in the dorsal cornu of grey matter of the same side. (5) A few are regarded as being axons of the mesial cells of the ventral cornu of the opposite side, which cross in the ventral or white commissure. All the axons receive their medullary sheaths near the parent-cells, and they form funiculi, which leave the white matter of the ventral column over an area corresponding to the caput of the ventral comu of grey matter, after which each fibre acquires its primitive sheath or neurilemma. The most of the axons of the fibres of the ventral nerv^e-roots belong to the ventral (motor) cells of the ventral comu of grey matter of the same side. . Dorsal or Posterior Nerve-Roots. — ^The fibres of the dorsal nerve- roots arise from the unipolar (originally bipolar) cells of the spinal ganglia. The single pole or process of each of these cells is T-shaped. 1324 A MANUAL OF ANATOMY One half of the horizontal limb of the T is central, and enters th( cord at the dorso-lateral sulcus between the dorsal and latera columns of white matter. The other half of the horizontal limb i peripheral, and passes outwards in the course of the nerve. Within the cord a few of the fibres enter the marginal bundle o Lissauer, and the dorsal cornu of grey matter, but the most of then Fig. 554- — Course of Nerve-Fibres in the Spinal Cord (from Halli- burton's ' Handbook OF Physiology' (after SchAfer). D. Ascending Branch of Fibre in the Spin Cord Pi, P2. Posterior Cornual Cells C (upper C). Cell of Clarke's Column 5. Collateral, passing directly to arborize aroui an Anterior Cornual Cell (2) 6. Collateral, with an Intermediate Cell-Slati< in a Posterior Cornual Cell (Po) 7. CoUateral.arborizing around a Cell of Clark( Column (upper C) 8. Continuation of Main Ascending Branch Fibre P. Pyramidal Tract I, 2, 3, 4. Anterior Cornual Cells A, A, A, A. Axons of Anterior Cornual Cells M. Muscular Fibre G. Unipolar Cell of a Spinal Ganglion, giving Origin to a Fibre of a Pos- terior Nerve-Root B. Peripheral Branch of Fibre S. Skin C (lower C) Central Branch of Fibre, passing into the Spinal Cord E. Descending Branch of Fibre in the Spinal Cord pass into the column of Burdach, close to the dorsal cornu of gre] matter. Within this column the fibres divide into two branchcs- ascending and descending. The descending branches, after a shor course, enter the dorsal cornu. These descending fibres are usuall; regarded as forming the ' comma tract of Schultz.' The ascendini branches are longer than the descending, and, at various levels they also enter the dorsal cornu. The ascending branches of th THE NERVOUS SYSTEM 1325 fibres of the dorsal roots of the lower spinal nerves enter the column of Goll. The ascending and descending branches give off numerous collateral fibrils, which enter the dorsal cornu. These collaterals have the following destinations : (i) The dorsal cornu of the same side, and that of the opposite side through the dorsal or grey com- missuje; and (2) the ventral and lateral cornua of the same side. In each case they come into close relation with the corresponding nerve-cells — e.g., the cells of the dorsal cornu, including Clarke's column, the ventral or motor-cells of the ventral cornu, and the cells of the intermedio-lateral tract of Clarke in the lateral cornu. Multipolar Cells of Anterior Cornu Fibres of Motor Root Compound Spinal Nerve { Efferent and Sensory Fibres of Ganglion ; Afferent Fibres of Ganglion Spinal Ganglion witb two Bipolar Cells Fig. 555. — Origin of Motor and Sensory Fibres of a Spinal Nerve. Spinal Ganglia. — These are situated on the posterior roots of the spinal nerves in the intervertebral foramina, and outside the theca, though invested by a prolongation from it. Each ganglion is oval, and consists of unipolar nerve-ceUs. The single pole of each cell divides into two processes, one of which is centripetal and forms part of the posterior nerve-root, whilst the other is centrifugal and passes into the spinal nerve. The pole and its inward and outward pro- cesses resemble the letter T. In early Ufe the cells are bipolar. The fibres of the posterior ner\-e-roots have their deep origins in the unipolar cells of the spinal gangUa, and they grow into the spinal cord. On the other hand, the fibres of the anterior nerve-roots have their deep origins within the spinal cord, where they arise as the axons of the multipolar nerve-cells of the anterior cornu of grey matter, and they grow outwards. Tracts of the Spinal Cord. Posterior Column. — The tracts of this column are ascending and descending, and they are as follows: Ascending Tracts. Descending Tract. Tract of GoII. Comma Tract ol Schultz. Tract of Burdach. Tract of Lissauer. This tract also belongs to the lateral column. 1326 A MANUAL OF ANATOMY Ascending Tracts.— The tract of GoU is situated close to the posterior median sulcus, and superiorly it is known as the funiculus gracilis. Its fibres are derived from the dorsal roots of the coccy- geal, sacral, lumbar, and lower thoracic nerves. They are at first contained in the tract of Burdach, but, as they ascend, they are gradually displaced inwards, and so form a special tract. The fibres terminate superiorly in connection with the cells of the nucleus gracilis of the medulla oblongata. aa. Fig. 556. — The Tracts of the Spinal Cord (L. Testut's HUMAINE'). Anatomie a. Anterior Median Fissure i. Posterior Median Fissure 1. Direct Pyramidal Tract 2. Crossed Pyramidal Tract 3. Anterior Ground Bundle 3'. Lateral Ground Bundle 10. Tract of Lissauer 4. Direct Cerebellar Tract 5. Tract of Gowers 6, 6'. Lateral Limiting; Zone 7. Tract of Burdach 8. Tract of Goll 9. Ventral Tract of Posterior Column The tract ol Burdach (known superiorly as the funiculus cuneatus) is situated on the outer side of the tract of Goll, next to the dorss horn of grey matter. Above the mid-thoracic region it is separated from Goll's tract by the dorsal intermediate or paramedian furrow and a septum o\ pia mater. Its fibres are derived from the dorsal nerve-rootsj Above the mid-thoracic region they are derived from the dorsa roots of the upper thoracic and cervical spinal nerves, and these fibres terminate superiorly in connection with the cells of the nucleus cuneaius of the medulla oblongata. Below the mid-thoracic region the fibres are derived from the lower dorsal nerve-roots, ant THE NERVOUS SYSTEM 1327 these, being displaced inwards into the tract of Goll, terminate in connection with the cells of the nucleus gracilis. The tract of Lissauer, or posterior marginal bundle, is close to the outer surface of the cord. It embraces the contiguous parts of the posterior and lateral colimms, and occupies the region of the dorso- lateral sulcus w^here the funiculi of the dorsal nerve-roots enter the cord. It lies between the substantia gelatinosa of Rolando and the surface of the cord. Its fibres are derived from the dorsal nerve-roots, and they ascend close to the substantia gelatinosa of Rolando, in which they terminate at different levels. Deseending Tract. — ^The comma tract of Scholtz is situated in the outer part of the tract of Burdach. Its fibres are usually regarded as being derived from the descending branches of the fibres of the dorsal ner\'e-roots, in which case they are exogenous. The other view, however, is that the fibres are intrinsic or endo- genous, 8ind spring from the cells of the dorsal comu of grey matter. AssoeiatiOD Fibres. — These fibres are also known as intrinsic, commissural, or intersegmental fibres. Unlike those just described, they are not derived from the dorsal nerve-roots, but spring from the cells of the dorsal comu of grey matter. They are therefore intrinsic or endogenous. Thereafter they enter the white matter of the posterior column and divide into ascending and descending branches. Subsequently these branches re-enter the grey matter of the dorsal comu at different levels, and terminate in connection with its cells. They serve to connect different segments of the cord, and they form ascending and descending bundles. The aseendlng bundle lies in the deep or ventral part of the posterior column, close to the dorsal or grey commissure and dorsal median fissure. The descending intrlnsie fibres are disposed in two bundles. One is known as the comn-commissural bundle. It is met with in the lumbo-sacral region, and is contiguous to the dorsal comu of grey matter and the dorsal or grey commissure. The other descending bundle occupies different positions in the cord at different levels, (i) In the sacral region it occupies a small triangular area in the postero-intemal part of Goll's column. (2) In the lumbar region it Ues contiguous to the centre of the dorsal median fissure and at the corre- sponding part of the dorsal surface of the cord. This bundle is known as the septo-marginal or oval bundle. (3) In the thoracic and cervical regions it may be represented by the comma ttaet of Sehultz, if the fibres of that tract are to be regarded as intrinsic. Antero-Lateral Column. — ^The tracts of this column are arranged into descending and ascending, and are as follows: Deseending Tracts. Ascending Tracts. Crossed Pyramidal Tract Dorsal Spino-cerebellar Tract. Direct Pyramidal Tract, Ventral Spino-cerebellar Tract Uncrossed Lateral Pyramidal Tract. Spino-thalamic Tract Anterior Marginal or Ground-Bundle. Spino-tectal Tract. -^ Prepyramidal or Rubro-spinal Tract. 1^ Bulbo-spinal Tract Descending Tracts.— The crossed or lateral pyramidal tract {jasci- culus ccrebro-spinalis lateralis Bj is a long descending tract, of large size, which is situated deeply in the dorsal part of the lateral 1328 A MANUAL OF ANATOMY column, directly in front of the dorsal cornu of grey matter. It is separated from the outer surface of the cord by the dorsal spino- cerebellar tract. It diminishes in size as it descends, and in the lumbar region it becomes superficial. At about the level of the third sacral nerve it terminates. The fibres of this tract have their origin in the pyramidal cells of the Roland ic or motor area of the cortex of the cerebral hemisphere of the opposite side. From this origin they descend through (i) the internal capsule of the corpus striatum, (2) the cms cerebri, and (3) the pons Varolii. On leaving the pons they enter the pyramid of the medulla oblongata on the side from which they have arisen. At the lower part of the pyramid they cross to the opposite side and take up their position deeply in the dorsal part of the lateral column of the spinal cord. The fibres of the crossed pyramidal tract of one side^ therefore come from the cerebral hemisphere of the opposite side, and they form the inner and larger part of the pyramid of the medulla oblongata, also of the opposite side. As this tract descends, fibres leave it in each segment of the cord. These fibres enter the ventral cornu of grey matter and end in close relation with the ventral or motor cells, the axons of manj' of which form the axis-cylinder processes of the fibres of the ventral or motor nerve-roots. The direct pyramidal tract {fasciculus cerebro-spinalis anterior B) is also known as the tract of Turck. It is of small size, and is situated in the anterior column, where it lies close to the ventral median fissure. It diminishes in size as it descends, and usually terminates about the centre of the thoracic region, but fibres have been traced as low as the fourth sacral nerve. The fibres of this tract, like those of the crossed pyramidal tract, have their origin in the pyramidal cells of the Rolandic or motor area of the cortex of the cerebral hemisphere, but in this case of the same side. The fibres of the direct pyramidal tract of one side therefore come from the cerebral hemisphere of the same side. They pursue a similar downward path as low as the pjnramid of the medulla oblongata of the same side, of which they form the outer and smaller part. They take no part, however, in the decussation of the pyramids, as do the fibres of the crossed pyramidal tract. Their course is directly downwards into the corresponding half of the spinal cord, where most of them take up their position in the anterior column, close to the ventral median fissure. The fibres of the direct pyra- midal tract, though they take no part in the decussation of the pyramids, cross to the opposite side at regular intervals as they descend in the anterior column of the cord. The crossing takes place in the ventral or white commissure, and, having entered the ventral cornu of grey matter of the opposite side, the fibres end, like those of the crossed pyramidal tract of that side, in close rela- tion with the ventral or motor cells, the axons of many of which pass to the ventral or motor nerve-roots. Most of the pyramidal fibres therefore cross from the side on which THE NERVOUS SYSTEM 1329 they arise to the opposite side. In the case of the crossed pyramidal tract the crossing takes place in the lower part of the medulla oblongata. In the case of the direct pyramidal tract the crossing takes place in the ventral median fissure of the spinal cord along the course of the tract. The uncrossed lateral pyramidal tract consists of a few fibres which descend from the corresponding pyramid of the medulla oblongata into the lateral column of the same side, where they mix with the fibres of the crossed lateral pyramidal tract. It differs from the crossed lateral, and direct, pyramidal tracts, inasmuch as its fibres never cross to the opposite side. It is therefore a direct motor path from the Rolandic motor area of the cerebral cortex of the same side. The anterior marginal or ground-bundle of Lowenthal {fasciculus anterior proprius B.) or tractus vestihulo-spinalis is situated in the anterior column, where it lies superficially. Its fibres are derived from the cells of the nuclei of Deiters in the medulla oblongata, chiefly on the same side as the bundle. These nuclei receive fibres of the corresponding vestibular nerve, and are closety related to the vestibular nuclei. The bundle descends through the meduUa oblongata and ventral column of the spinal cord as low as the lumbar region, and its fibres terminate in the anterior cornu of grey matter aroimd the ventral or motor cells. The nucleus of Deiters and the vestibular nucleus, of either side, are connected with small grey nuclei which lie in the white matter of the cerebellum, and in this manner an indirect connection is established between the cerebellum and the ventral or motor-cells of the ventral grey cornu of the spinal cord, as foUows : The grey nuclei within the cerebellimi are connected with the nuclei of Deiters, and the axons of the cells of Deiters represent the origin of the fibres of the anterior marginal or ground-bundle, which fibres terminate around the ventral or motor-cells of the ventral grey cornu of the spinal cord. The prepyramidal or rubrospinal tract, or bundle of Monakow, is situated in the lateral column, on the ventral aspect of the crossed pyramidal tract. Its fibres are chiefly derived from the red nucleus of the tegmentum or dorsal part of the cms cerebri of the opposite side, and they are regarded as terminating in the dorsal part of the ventral cornu of grey matter .- The bulbo-spinal tract, or bundle of Helweg, is confined to the cervical region of the cord, and is triangular. Its fibres are regarded as arising in the medulla oblongata behind the olive, but their mode of termination is not known. They lie near the surface of the cord opposite the lateral cornu of grey matter. Ascending Tracts.— The dorsal spino-cerebeUo tract, or direct cerebellar tract of Flechsig {fasciculus cerebello-spinalis B.), is situated in the lateral colimin. It lies in front of the dorso-lateral sulcus, between the crossed pyramidal tract and the outer surface 84 i33o A MANUAL OF ANATOMY of the cord . It commences in the lower part of the thoracic region, and superiorly it traverses the lower part of the medulla oblongata on its lateral aspect, after which it enters the restiform body, by which it is conducted to the vermis of the cerebellum. Its fibres are usually regarded as being derived from the posterior vesicular column of Clarke. The ventral spino-cerebellar tract, or tract of Gowers [fasciculus antero-lateralis superficialis B.), is situated chiefly in the lateral column, in front of the dorsal cerebellar tract close to the outer surface of the cord . It is comma-shaped in section, its dorsal part being broad, but, as it extends forwards between the funiculi of the ventral nerve-roots, it tapers and enters the ventral column super- ficially. It commences near the lumbar region of the cord. Superiorly it extends through the medulla oblongata and pons, and thereafter passes along the superior cerebellar peduncle into the cerebellum, terminating in the vermis. It therefore takes an indirect course as compared with that of the dorsal spino-cerebellar tract. Its fibres are usually regarded as being derived from the posterior vesicular colimin of Clarke. The ventral spino-cerebellar tract contains the spino-thalamic and spino-tectal tracts. The spino-thalamic tract consists of fibres which arise as the axons of cells of the dorsal grey comu, around which cells the fibres of the dorsal nerve-roots have terminated. The spino-thalamic fibres cross to the opposite side in the ventral or white commissure, thus giving rise to a spinal inferior sensory decussation or spino- thalamic decussation, as distinguished from the superior sensory decussation in the bulb, called the decussation of the fillets, which is produced by the deep arcuate fibres which arise from the cells of the nucleus gracilis and nucleus cuneatus. The spino-thalamic fibres, having crossed in the ventral white commissure, ascend in the tract of Gowers, and, after traversing the bulb and pons, they terminate in the optic thalamus of the side to which they have crossed as a cell-station. It is important to note that there are two sensory decussations — lower or spinal, and upper or bulbar. In unilateral lesions of the spinal cord there would only be partial anaesthesia on the opposite side; whereas in unilateral lesions of the bulb, involving both the fillet-fibres and the spino-, thalamic fibres, there would be complete anaesthesia on the opposite ' side. The spino-tectal tract is also an ascending tract. Its fibres are connected with the cells of the ventral comu of grey matter. Thej ascend in conjunction with the tract of Gowers and pass througi the formatio reticularis of the bulb and pons. Thereafter tliej decussate with those of the opposite side, forming the fountain^ decussation of Meynert, which lies between the two red nuclei, tc which nuclei the spino-tectal fibres furnish collaterals. After the decussation the fibres of either side pass to the corresponding superior colliculus of the corpora quadrigemina. THE NERVOUS SYSTEM 1331 The tracts of the antero-lateral column may be otherwise arranged as follows : Ventral or Anterior Colanin. Lateral Column. Direct Pyramidal Tract (descending). Crossed Pyramidal Tract (ieicenJmg). Anterior Marginal Bundle (Lowen- Dorsal Spino-cerebellar Tract (ascend- thal) {descending). »«o)- Ventral Part of Ventral Spiao-cere- Ventral Spino-cerebellar Tract (chief bellar Traet {ascending). part of) (ascending). Prepyramidal Tract (descending). The Spino-Thalamic and Spino-Tectal Tracts (ascending) are con- tained in the ventral spino-cerebellar tract. A part of the posterior marginal bundle (Lissauer's tract) lies superficially in the dorsal part of the lateral column, and it has been described in connec- tion with the dorsal column. Association-Fibres of Antero-Lateral Column. — The part of the antero- lateral column which is not occupied by the descending and jiscending tracts, is adjacent to the grey matter, and it constitutes the antero-lateral marginal or ground-bundle. It is di\'ided into two parts — anterior and lateral. The anterior marginal or ground-bundle of Lowentlial is situated in the ventral column, in front of the ventral coma of grey matter, and has been already described. The lateral marginal or ground-bundle (fasiculus lateralis proprius B.) occupies the lateral column, ventral and mesial to the crossed pyramidal tract. The portion of the ventro-lateral ground-bundle adjacent to the grey matter, and almost surrounding it, is known as the limiting zone. The fibres of the entire antero-lateral ground-bundle are association — or longitudinal commissural fibres, which serve to coimect the grey matter of successive segments of the spinal cord. They are derived from the cells of the grey matter of the same side, and also of the opposite side, the latter crossing in the ventral or white commissure. Arteries of the Spinal Canal and Spinal Cord — ^Arteries ol the Spinal Canal. — These vessels enter the spinal canal through the intervertebral and sacral foramina. In the cervical region they are branches of the vertebral and deep cervical arteries; in the thoracic and lumbar regions they are derived from the dorsal branches of the intercostal and Itunbar arteries ; and in the sacral region they come from the lateral sacral arteries. Within the spinal canal each spinal artery divides into three branches, namely, neural or central, and two parietal, anterior and posterior. The neural or central branch pierces the theca of the spinal cord. It supplies the coverings of the cord and the nerv-e-roots, and it anastomoses with the anterior and posterior spinal arteries on the cord. The neural branch is sometimes spoken of as the lateral spinal artery. The anterior parietal branch of each side passes to the back of the body of a vertebra, near the pedicle, and there it divides into two branches, ascending and descending. These anastomose with the adjacent offsets of the contiguous anterior parietal branches, and in this manner a lateral longitudinal anasto- motic chain is formed, which communicates, at frequent intervals, with its fellow of the opposite side by transverse branches. From these transverse branches ascending and descending offsets are 1332 A MANUAL OF ANATOMY given off, which anastomose with adjacent offsets of contiguous transverse branches, and in this manner a median longitudinal anastomotic chain is formed on the backs of the bodies of the vertebrae. There are thus three longitudinal chains on the posterior surfaces of the bodies of the vertebrae, one being median and two Lateral. From these chains branches are furnished to the bodies of the vertebrae and their ligaments. The posterior parietal branch of each side passes to the front of a lamina, where it acts in a manner similar to the anterior parietal branch. Two posterior longitudinal anastomotic chains are thus constructed in front of the laminae, one at either side, which communicate at frequent intervals by trans- verse branches, and from these sources offsets are furnished to the laminae and ligamenta subflava. Arteries of the Spinal Cord. — ^These are : (i) the anterior spinal artery ; (2) the posterior spinal arteries, right and left ; and (3) the lateral spinal arteries, right and left (neural or central branches just described in connection with the spinal canal). The anterior spinal artery is formed by the union of the anterior spinal branches, right and left, of the vertebral arteries. It descends along the front of the cord in the median line, and is reinforced at regular intervals by the lateral spinal arteries. In this manner an anterior longitudinal anastomotic chain is formed, which descends for some distance on the filum terminale. The posterior spinal arteries are two in number, right and left, and each is a branch of the corresponding vertebral artery. Each vessel descends on the side of the cord in two branches, one being in front of, and the other behind, the posterior nerve-roots. These are reinforced by branches from the lateral spinal arteries, and the lateral longitudinal anastomotic chains, formed in this manner, extend over the entire length of the cord. There are thus five longitudinal anastomotic arterial chains in connection with the cord, namely, one anterior, and two lateral on each side, of which one is in front of, and the other behind, the posterior nerve-roots. From these chains branches are freely given to the pia mater, and through it to the cord. Veins of the Spinal Column and Spinal Cord — Veins of the Spinal Column. — ^These veins, which form plexuses, are disposed in five sets, namely, (i)' dorsal, (2) veins of the vertebral bodies, (3) anterior intraspinal, (4) posterior intraspinal, and (5) anterior extraspinal. The dorsal spinous venous plexus is situated deeply upon the superhcial surface of the neural arches of the vertebrae, under cover of the multifidus spinae muscle. It receives its tributaries from the integument and muscles of the back, and it communicates with the posterior longitudinal intraspinal plexus by branches, which pierce the ligamenta subflava. In the neck the blood is conveyed away from the plexus by veins which open into the vertebral venous plexus around the vertebral artery of each side ; in the thoracic region by veins which join the dorsal branches of THE NERVOUS SYSTEM 1333 the intercostal veins; and in the lumbar region by veins which join the dorsal branches of the lumbar veins. The veins of the bodies of the vertebrae {vence basis vertehrce) are contained within the cancellated tissue of the vertebral bodies. They communicate in front with the anterior extraspinal veins, and posteriorly they terminate in two venous trunks which, emerging through the two foramina on the posterior surface of each vertebral body, open into the transverse communicating branch between the two anterior longitudinal intraspinal veins. The anterior longitudinal intraspinal veins form two anastomotic chains, which are situated on the posterior surfaces of the bodies of the vertebrae, one on either side. They communicate with each other opposite the centre of each body by transverse branches which receive the terminal trunks of the venae basis vertebrae. These transverse branches pass between the posterior common ligament and the bodies of the vertebrae. Superiorly the anterior intraspinal veins communicate with the vertebral and the trans- verse or basilar plexuses of veins, and laterally an offset passes outwards through each intervertebral foramen, which, with that of the posterior intraspinal vein, forms a plexus around the adjacent spinal nerve. The posterior longitudinal intraspinal veins are situated in front of the laminae, one on either side, and they are connected at frequent intervals by transverse branches. They communicate with the dorsal spinous venous plexus by branches which pierce the ligamenta subflava. Superiorly they communicate with the marginal sinuses, on either side of the foramen magniun and vermi- form fossa, which by their union form the occipital sinus. With the marginal sinuses and the anterior intraspinal veins they form a venous ring at the foramen magnum. Laterally each vein sends outwards through the corresponding intervertebral foramen an offset, which, with that of the anterior intraspinal vein, forms a plexus around the adjacent spinal nerve. The anterior and posterior intraspinal veins are situated between the theca of dura mater and the wall of the spinal canal. The anterior extraspinal veins form a plexus along the anterior aspect of the bodies of the vertebrae, which is most copious in the neck. On either side it communicates with the vertebral plexus, around the vertebral artery in the neck, the intercostal veins in the thoracic region, and the lumbar veins in the lumbar region. It is also connected with the venae basis vertebrae. Veins of the Spinal Cord. — ^These vessels lie within the substance of the pia mater, and are disposed as venous chains, one being in front, one behind, and two on either side. The anterior vessel lies over the anterior median fissure beneath the anterior spinal artery ; the posterior vessel is also m.esially placed ; and the two lateral vessels are situated one in front of, and the other behind, the posterior nerve-roots. Besides these principal chains the veins form a plexus on the surface of the cord. Laterally branches 1334 A MANUAL OF ANATOMY emerge through the intervertebral foramina, which along with the offsets of the anterior and posterior intraspinal veins, form plexuses around the spinal nerves. From these plexuses the blood is conveyed on either side into the vertebral plexus and deep cervical vein in the neck, and into the intercostal and lumbar veins in the corresponding regions. Lymphaties. — There are no l5aiiphatic vessels in the spinal cord. Their place is taken by spaces in the outer coat of the arteries, called perivascular spaces, which are in communication with the subajachnoid space. Development of the Spinal Cord. The spinal cord is developed from the wall of the neural tube, and the neural tube is developed from the neural plate. This plate, situated in the anterior part of the embryonic area, consists of ectodermic cells, and it presents Posterior Nerve-Root Spongioblasts Neuroblasts Anterior Nerve-Root Fk5. 557. — Section of the Spinal Cord of a Human Embryo of Four Weeks (His). a median longitudinal groove, called the neural groove. The lateral margins of the plate become elevated into two ridges, the neural folds, and these by their approximation and fusion give rise to the neural tube or canal. At either end the neural tube presents an opening — the anterior and posterior neuropore, but these openings soon become closed. The ectodermic cells of the wall of the tube undergo proliferation, the wall becomes thickened, and it consists of two kinds of cells — namely, (i) sus- tentacular or supporting cells, and (2) nerve-cells proper. The former con- stitute the ependyma and neuroglia of the spinal cord, and the latter give rise to the grey and white matter. The cells are loosely arranged, and form what is known as the myelospongium. The cells of this myelospongium become condensed internally and externally, and these condensed layers form the internal and external limiting membranes. The wall of the neural THE NERVOUS SYSTEM 1335 tube is arranged in three layers or zones — namely, (i) inner or ependymal, (2) intermediate or mantle zone, and (3) outer or marginal zone. The ependymal zone consists of a single layer of elongated cells, connected with the internal limiting membrane. Their bases are directed towards the lumen of the neural tube, and from their apices delicate radial fibres pass outwards to the external Umiting membrane. Amongst these there are some conspicuous cells, called germinal cells. These he close to the ■wall of the neural tube, and by their proliferation they give rise to (i) ependymal cells, (2) spongioblasts, and (3) neuroblasts. The latter two migrate outwards into the mantle zone. The mantle zone consists of branching cellular strands of myelospongium, which radiate from the centre to the periphery. It contains spongioblasts and neuroblasts, and it forms the rudiment of the grey matter of the spinal cord. The marginal zone consists of reticula of myelospongium, traversed by nerve-tracts. It is the rudiment of the white matter of the spinal cord. The cells of the Wcdl of the neural tube as they undergo differentiation form two groups — spongioblasts, which form neuroglia, and neuroblasts or ganglionic cells. Spongioblast GenninalCell Fig. Young Neuroblast . Axon of Neuroblast Spongioblast I Neuroblast 358. — The Celxs of the Spinal Cord of the Human Embryo (L. Testut's • Anatomie Humaine ') (after His). Development of Neuroglia. — ^This tissue consists of (i) ependymal cells, (2) neuroglia -cells, and (3) neurogha-fibres, all of which are derived from the spongioblasts. These spongioblasts traverse the entire thickness of the wall of the neural tube, and are disposed in strands which radiate outwards from the lumen of the tube, giving off lateral processes. The spongioblasts adjacent to the lumen of the tube form the ependymal cells, and these form the internal limiting membrane. The remaining spongioblasts form the neoroglla'-cells. NeurogUa-cells have many branches, and are spoken of as glia-cells or spider-cells. The neuroglia-Qbres are fibrillations of the peripheral protoplasm of the cells, from which they become differentiated. The neuroblasts lie in groups within the mantle layer, and they give rise to the nerve-cells of the spinal cord. Each cell is primarily unipolar and pear-shaped. It has a prominent nucleus, and the body is prolonged into a process or pole, whch represents the axon or axis cylinder process of a nerve- fibre. Subsequently the pear-shape is lost, due to the formation of secondary processes or dendrites, the cell being now multipolar. The lateral walls of the neural tube become thickened owing to cell-pro- liferation, but ventrally and dorsally it remains thin, these parts forming the 1336 A MANUAL OF ANATOMY floor-plate and roof-plate. Each lateral wall is divided into two plates — ventral and dorsal — by a longitudinal groove, called the sulcus limitans. The ventral plate, which is motor, is spoken of as the basal lamina, and the dorsal plate, which is sensory, is referred to as the alar lamina. The basal lamina is thick, and its mantle zone contains many cells from which the anterior cornu of grey matter is developed. The axons of these cells pass outwards through the marginal zone and form the anterior roots of the spinal nerves. The fibres of the posterior nerve-roots enter from the spinal gangUa at the sulcus limitans, and in the marginal zone of the alar lamina they form by their bifurcations longitudinal strands, which constitute the posterior column of the cord. Metamorphoses of the Primitive Spinal Cord. — ^The primitive spinal cord consists of (i) two lateral walls, (2) a ventral or floor-plate, and (3) a dorsal or roof -plate. Changes in Lateral Walls. — Each latereil wall, as stated, is subdivided into a ventral or basal lamina and a dorsal or alar lamina by the sulcus limitans. The ventral or basal lamina on either side gives rise to (i) the anterior cornu of grey matter, (2) the anterior or motor-nerve roots, and (3) the longitudinal funiculi of nerve-fibres, which form the anterior and lateral ground-bundles. The dorsal or alar lamina on either side gives rise to (i) the posterior cornu of grey matter, including the substantia gelatinosa of Rolando, and (2) the longitudinal funiculi of nerve-fibres which form the posterior column of the cord (Goll's column and Burdach's column), which receive most of the fibres of the entering posterior nerve-roots. Lumen of Neural Tube. — This constitutes the central canal of the spinal cord. At first it is a dorso-ventrally elongated slit, widest in the dorsal portion, and subsequently in the ventral region. At a later period the dorsal portion of the lumen becomes closed, but the ventral portion, now somewhat round, persists as the central canal of the cord. The closure of the dorsal portion of the lumen occurs during the development dorsalwards of the posterior comua of grey matter and posterior columns of the cord. The lateral walls of the dorsal portion, becoming approximated, fuse, the dorsal or roof-plate disappearing. Along the line of fusion neuroglia-fibres extend from the dorsal wall of the central canal to the dorsal surface of the cord at the median hne. This thin layer of neuroglia-fibres constitutes the posterior median septum. As the posterior columns of the cord undergo development the septum elongates dorsalwards, the dorsal or roof -plate disappearing. Anterior Median Fissure. — This fissure is the result of the growth ventral- wards of the anterior column of each side. During this ventral growth the ventral or floor-plate becomes depressed, and consequently a distinct cleft is produced, ventral to the depressed floor-plate, and intervening bet\veen the protuberant anterior columns. This cleft forms the anterior median Assure of the cord, which is occupied by an inflection of the pia mater. The floor-plate now lies at the bottom of the fissure, and that plate forms the anterior white commissure of the cord. It consists of decussating nerve- fibres, derived from the neuroblasts of the mantle layer of either side. For the development of the spinal ganglia and the sensory and motor roots of the spinal nerves, see Neural Crests under Development of the PeriphrEDULLA (L. Testut's * Anatomie Humaine '). a. Pons Varolii 6- Medulla Obloneata (anterior aspect) c. Decussation of the Pyramids d. Section of the Cervical Spinal Cord 1. Direct Pyramidal Tract 2. Crossed Pyramidal Tract 3. Sensory Tract 3'. Nucleus Gracilis et Nucleus Cuneatus 4. Antero-lateral Ground-Bundle S- Anterior Pyramid 6. Fillet 7. Posterior Longitudinal Bundle 8. Tract of Gowers 9. Direct Cerebellar Tiact alorg which the funiculi of the h\^glcssal nerve emerge. It con- stitutes the pyramid of the bulb. The two p^Tamids, right and left, represent the motor tracts of the bulb. As regards position, the pjTamid represents the anterior column of the spinal cord, and 1348 A MANUAL OF ANATOMY it consists of bundles of nerve-fibres, disposed longitudinally. Inferiorly it is somewhat narrow, but it widens superiorly. At the lower border of the pons Varolii it undergoes a slight constric- tion, after which it sinks into the pons. As it traverses the pons its funiculi become separated into several strata, and these are gathered together at the upper border of the pons into the crus cerebri of the corresponding side. Inferiorly each pyramid is disposed in two parts — inner and outer. The inner portion represents as a rule the inner three-fourths, and its fibres cross to the opposite side in the lower part of the ventral median fissure of the bulb. Thereafter they sink deeply into the dorsal part of the lateral column of the spinal cord on the side to which they have crossed, where they constitute the crossed pyra- midal tract. The intercrossing of fibres which takes place in the lower part of the ventral median fissure of the bulb is called the decussation of the pyramids, or the motor decussation, and, as stated, it usually involves the fibres of the inner three-fourths of the pyramid. The outer portion of the pyramid represents as a rule the outer fourth, and its fibres take no part in the decussation. The path of most of them is downwards into the anterior column of the spinal cord of the same side, where they lie close to the anterior median fissure of the cord and constitute the direct pyramidal tract. A few of them, however, descend into the lateral column of the same side, and constitute the uncrossed lateral pyramidal tract. The pyramid of the bulb, therefore, only corresponds topo- graphically with the anterior column of the spinal cord. The direct pyramidal tract of the anterior column of the cord forms the greater part of the outer fourth of the corresponding pyramid of the bulb ; and the crossed pyramidal tract of the lateral column of the cord forms the inner three-fourths of the pyramid of the oppo- site side. The remainder of the anterior column of the cord sinks deeply into the bulb and lies on the dorsal aspect of the pyramid. The ventral surface of each pyramid is crossed above the level of the decussation of the pyramids by the anterior superficial arcuate fibres, which emerge from the ventral median fissure and take an arched course outwards and then backwards to the restiform body. The sixth cranial nerve emerges close to the lower border of the pons Varolii, immediately external to the pyramid, and in line with the funiculi of the hypoglossal nerve as these emerge from the ventro-lateral sulcus. Lateral Area of the Medulla Oblongata. — This superficial area is situated between the ventro-lateral sulcus, with the funiculi of the hypoglossal nerve, and the dorso-lateral sulcus, with the funiculi of the glosso-pharyngeal, pneumogastric, and bulbar part of the spinal accessory nerves. Superiorly it presents an oval eminence, called the olive {oliva B.). Inferiorly it has the appearance of being a prolongation of the lateral column of the spinal cord, but this is not the case. The crossed pyramidal tract of the lateral THE NERVOUS SYSTEM 1349 column of the cord sweeps obliquely across to the opposite side, where it forms the greater part of the pyramid of that side. The parts, therefore, of the lateral column of the cord which form the lateral area of the bulb below the olive are (i) the dorsal or direct spino-cerebellar tract, (2) the ventral spino-cerebeUar tract, and (3) the lateral ground-bundle. The dorsal spino-cerebeDar tract as it ascends, soon inclines obliquely backwards to join the restiform body. The ventral spino-cerebellar tract and lateral ground- bundle ascend until they reach the lower end of the olive. They then for the most part sink deeply and ascend to the pons Varolii on the dorsal or deep aspect of the olive. A few of the fibres, however, remain on the surface and ascend in the small interval Middle Commissure Pineal Peduncle ; Third Ventricle (Habenula) \ : ^, Optic Thalamus Upper Quadrigeminal Body Lower Quadrigeminal Body ■^^^.Crus Cerebri ~""-- Frenulum Veli ^""-^ Valve of Vieussens ^ ~ --.Superior Peduncle of Cerebellum ■~-Do., do. (cut) ~~ Striae Acusticae "^ ^^ ^"-,Trigonum Acusticum (base) n>L^ ^"-^Trigonura Hypoglossi •19^^ ^-~ Trigonum Vagi ■/^ ^-^. Tubercle of Rolando -Clava — Funiculus Gracilis Funictilus Cuneatus Median Furrow Erainentia Teres Sujjerior Fovea, .^_ Stris Acusticae — Iv - Inferior Fovea Cnneate Tubercle— Fig. 564. — ^The Floor of the Fourth Ventricle and Adjacent Parts. which lies between the outer part of the olive and the funiculi of the glosso-pharyngeal and pneumogastric nerves. The lateral area of the bulb below the olive thus represents the dorsal or direct spino-cerebellar tract, ventral spino-cerebellar tract, and lateral ground-bundle of the lateral colrunn of the spinal cord of the same side. Superiorly, as stated, the lateral area presents an oval eminence, called the olive. It lies between the funiculi of the hypoglossal nerve on the one hand, and the funiculi of the glosso-pharyngeal and pneumogastric nerves on the other, with the intervention of some ascending fibres belonging to the ventral spino-cerebellar tract. Its long axis is placed vertically, and in this diiection it 135° A MANUAL OF ANATOMY measures about | inch. Superiorly it is separated from the pons Varolii by a deep transverse groove, and interiorly the anterior superficial arcuate fibres arch over its lower part. At the lower border of the pons Varolii, external to the upper end of the olive, the facial and auditory nerves make their appearance. The facial nerve is internal in position, and is in line with the funiculi of the glosso-pharyngeal nerve. The auditory nerve appears external to the facial nerve, and between the two is the small pars intermedia of Wrisberg. Dorsal or Posterior Area of the Medulla Oblongata. — ^This super- ficial area is limited in front by the dorso-lateral sulcus, containing the funiculi of the glosso-pharyngeal, pneumogastric, and bulbar part of the spinal accessory nerves. Posteriorly its lower half extends as far as the dorsal median fissure, and its upper half extends only as far as the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. Inasmuch as this area pertains to both the closed and open parts of the bulb it will be considered in two sections — Slower and upper. Lower Portion of Posterior Area. — This portion, as stated, is limited behind by the dorsal median fissure, and it is in direct continuity with the dorsal column of the spinal cord of the same side, which is composed of the columns of Goll and of Burdach. It presents three longitudinal eminences — ^namely, the funiculus gracilis, funiculis cuneatus, and funiculus of Rolando. The funiculus gracilis is a prolongation of Goll's column of the spinal cord, and lies close to the dorsal median fissure. The funi- culus cuneatus is a prolongation of Burdach's column of the cord, and lies external to the funiculus gracilis, from which it is separated by an upward continuation of the dorsal intermediate or para- median furrow of the cord. At the level of the calamus scriptorius each of these two funiculi becomes enlarged and terminates in a prominence or bulb. The enlargement formed by the funiculus gracilis is called the clava, and that formed by the funiculus cuneatus is termed the cuneate tubercle. The two clavse, right and left, lie on either side of the calamus scriptorius, and, as the bulb opens out dorsally at this level to form the lower or bulbar half of the floor of the fourth ventricle, each clava is displaced laterally. An angular interval now separates the two clavae, and the prolongation of the central canal of the spinal cord through the lower or closed part of the bulb opens into the fourth ventricle in the angle between the two clavse. The funiculus gracilis, with its clava, and the funiculus cuneatus, with its cuneate tubercle, are to a large extent produced by the collections of grey matter which they contain — ^namely, the nucleus funiculi graciHs and nucleus funiculi cuncati. The funiculus of Rolando is situated on the outer side of the funiculus cuneatus, between it and the funiculi of the bulbar part of the spinal accessory nerve. It is produced by the substantia gelatinosa of Rolando, which comes close to the surface in the THE NERVOUS SYSTEM 1351 lower or closed part of the bulb. Inferiorly the funiculus of Rolando is narrow, but it w'idens as it ascends, and superiorly it terminates in an enlarged extremity, called the tubercle of Rolando. The funiculus and tubercle of Rolando are covered by a thin layer of longitudinal ner\-e-fibres which represent the spinal or descending sensory root of the fifth cranial ner\'e. Upper Portion of Posterior Area. — This portion, as stated, per- tains to the upper or open part of the bulb, and extends as far as the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. It presents a prominent round tract, called the restiform body {corpus restiforme B.), which is situated between the lower half of the floor of the fourth ventricle and the funiculi of the pneumogastric and glosso-phar^mgeal nerves. Its direction is upwards, outwards, and backwards, and it enters the corresponding hemisphere of the cerebellum. It is otherwise known as the inferior cerebellar peduncle. The restiform body succeeds to the funiculus gracilis and funiculus cuneatus of the low-er portion of the posterior area of the bulb, but it is quite distinct from these funiculi, and receives no fibres from them. The sources of its fibres wall be stated in connection with the internal structure of the bulb. Meanwhile it may be stated that it constitutes the great tract of connection between the cere- bellar hemisphere, the bulb, and the spinal cord. The restiform body becomes conspicuous above the level of the cuneate tubercle, and forms the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. Internal Structure of the Medulla Oblongata. — Each half of the bulb is composed of grey nerv^ous matter and tracts of white nerv'ous matter. Grey Matter. — The grey matter lies largely in the interior. Over the dorsal aspect of the upper or open part of the bulb, however, it comes to the surface and covers the lower or bulbar half of the floor of the fourth ventricle. As compared with the grey matter of the spinal cord, it presents important modifications, and its component parts Eire as follows: 1. Substantia or formatio reticularis. 2. A thick layer of grey matter around the central canal in the lower or closed part of the bulb. 3. A thick layer of grey matter over the floor of the fourth ventricle in the upper or open part of the bulb. 4. Substantia gelatinosa of Rolando. 5. Nuclei of grey matter. The modifications undergone by the grey matter of the bulb in its lower or closed part are brought about by the decussation of the pjTamids. The ner\'e-funiculi of the crossed pyramidal tract of the spinal cord, on one side as they are traced upwards, pass through the ventral grey cornu of that side, and then cross in the lower part of the ventral median fissure of the bulb to the pyramid t3S2 A MANUAL OF ANATOMY of the opposite side, of which they form the inner and larger part. The nerve-funiculi of the crossed pyramidal tract of the other side are disposed in a similar manner. The ventral grey comu of either side is thus broken up by the corresponding crossed pyra- midal tract. Its basal pari remains on the ventral and lateral aspects of the central canal, but its caput is detached and displaced laterally by the pyramid and olive of the same side. The dorsal cornu of grey matter is gradually displaced laterally and ventralwards, in the lower or closed part of the bulb, by the funiculus gracilis and funiculus cuneatus. Its basal part remains on the dorsal and lateral aspects of the central canal; its cervix is broken up into a network by intersecting nerve-fibres ; and its caput is thereby detached. The caput lies close to the detached caput of the ventral cornu of grey matter, but does not blend with it. Substantia or Formatio Reticularis. — ^The grey matter of the de- tached caput of the ventral grey cornu is broken up into a network Fasciculus Solitaritif Tola Cboroidea Corpus Restiforme Formatio Reticu- laris Grisea Formatio Reticularis Alba Spinal Trigeminal Tract Rudiment of Middle Accessory Olivary Nucleus Fig. 565. — Transverse Section of Medulla Oblongata (Keibel and Mall) . by intersecting nerve-fibres, which run longitudinally and trans- versely. This reticulum, augmented by the network formed in the cervix of the dorsal grey cornu, constitutes the substantia or formatio reticularis of the bulb. It lies deeply within the bulb, dorsal to the olive and pyramid of the same side, and it consists of grey matter, longitudinal and transverse nerve-fibres, and some nerve-cells. The funiculi of the hypoglossal nerve, as they pass forwards to the ventro-lateral sulcus of the bulb, divide the formatio reticularis into two parts — ^lateral and mesial. The lateral portion is situated behind the olive, and is called the formatio reticularis grisea, from the large amount of grey matter, with nerve-cells, which it con- tains. The mesial portion is situated behind the pyramid, and is THE NERVOUS SYSTEM 1353 called the formatio reticularis alba. It contains little grey matter and few nerve-cells. Central Grey Matter. — ^The grey matter which surrounds the central canal in the lower or closed part of the bulb is derived from the basal portions of the ventral and dorsal grey comuaof the upper part of the spinal cord. In the upper or open part of the bulb this central grey matter spreads out and forms a thick layer over the lower or bulbar part of the floor of the fourth ventricle. The mesial part of this layer represents the basal part of the ventral giey comu, and it contains the hypoglossal nucleus. The lateral part represents the basal part of the dorsal grey cornu, and it contains pneumogastric, glosso-pharyngeal, and auditory nuclei. Fig. 566. — Section of the Medulla Oblongata at the I>evel of the Decussation of the Pyramids (L. Testut's * Anatomie Humaine '). 1. Anterior Median Fissure 2. Posterior Median Fissure 3. Motor Roots 4. Sensory Roots 5. Base of the Anterior Cornu from which the Caput, 5', has been detached by the pas- sage of the crossed Pyramidal Tract 6. Decussation of the crossed Pyramidal Tracts 7. Posterior Cornu 8. Nucleus Gracilis Substantia Gelatinosa of Rolando.— This caps the detached and displaced caput of the dorsal horn of grey mattei . Having increased in amount and lying close to the surface, it gives rise to the funiculus and tubercle of Rolando. Nuclei of Grey Matter.— The nuclei, which will be considered in this place, are as follows : 1. Nucleus gracilis, 2. Nucleus cuneatus. 3. Ohvary nuclei. 4. Arcuate nucleus. 5. Nucleus lateralis. The nucleus gracilis is a collection of grey matter within the funiculus gracilis. For the most part it is connected with the grey 1354 A MANUAL OF ANATOMY matter on the dorsal and lateral aspects of the central canal, and it may be regarded as being, in large part, an extension from the basal part of the dorsal grey cornu. It is elongated and increases in size as it ascends. It gives rise to the prominence of the funi- culus gracilis and to the clava, and the fibres of the funiculus gracilis, as they ascend, terminate at intervals around the cells of the nucleus. The nucleus cuneatus is a collection of grey matter within the funiculus cuneatus. It is a direct extension from the basal part of the dorsal grey cornu which lies on the dorsal and lateral aspects of the central canal. Like the nucleus gracilis it is elongated, and increases in size as it ascends. It gives rise to the prominence of Fig. 567. — Section of the Medulla Oblongata through the Lower Part of the Decussation of the Pyramids (L. Testut's 'Anatomie HUMAINE '). 1. Anterior Median Fissure 2. Posterior Median Fissure 3. Anterior Cornu 3; Anterior Nerve-roots 4. Posterior Cornu 4I Posterior Nerve-roots 5. Crossed Pyramidal Tract 6. Column of Burdach The red arrows, a, a', indicate the paths taken by the crossed Pyramidal Tracts at the level of the decussation of the Pyramids ; and the blue arrows, b, b', indicate the paths of the Sensory Fibres. the funiculus cuneatus and to the cuneate tubercle, and the fibres of the funiculus cuneatus, as they ascend, terminate at intervals around the cells of the nucleus. On the outer side of the nucleus cuneatus there is a small collection of grey matter, which is known as the external or accessory cuneate nucleus. It is on a higher level than the decussation of the pyramids, and it may be regarded as a detached portion of the substantia gelatinosa of Rolando. The olivary nuclei are associated with the olive, and are three in number — namely, inferior, and two accessory — mesial and dorsal. The inferior olivary nucleus, which is the chief nucleus, is situated within the olive. As seen in transverse sections through the olive, it appears as a wavy lamina of grey matter, curved in such a manner as to form an incomplete capsule, which encloses white matter. The open part of the capsule is called the hilum, and is directed THE NERVOUS SYSTEM 1355 towards the median line, but it stops short of either end of the nucleus. A great many nerve-fibres pass through the hilum, some inwards and others outwards, and these form what is known as the olivary peduncle. The wavy lamina is traversed by nerve-fibres. The superior olivary nucleus is situated in the dorsal or tegmental part ot the pons Varolii. The mesial accessory and dorsal accessory olivary nuclei are situated on the mesial and dorsal aspects, respectively, of the inferior or chief olivary nucleus, from which, however, they are distinct. Each consists of a band of grey matter, and the upper part of the mesial accessory nucleus lies opposite the hilum of the chief nucleus. 7 6 2 L.5' Fig. 568.— Transverse Section passing through thb Sensory Decussation (Schematic) (L. Testut's * Anatomie Humaine '). 1. Anterior Median Fissure 2. Posterior Median Fissure 3, 3'. Caput and Base of Anterior Cornu (in red) 4. Hypoglossal Nerve 5, 5. Caput and Base of Posterior Comu 6. Nuclen? Gracilis 7. Nucleus Cuneatus 8, 8. Fillet, or Sensory Tract 9. Sensory Decussation low Pyramidal Tract Structure of Inferior Olivary Nucleus. The wavy lamina consists of many small nerve-cells and nerve-fibres which traverse it. The axons of the nerve-cells leave the nucleus as nerve-fibres, and pass to the raphe of the bulb. Some of the nerve-fibres which traverse tlie wavy grey lamina terminate in connection with its cells, and other fibres pass through it. The inferior olivary nucleus receives a tract of fibres, called the thalamo-olivary tract, which descends from the optic thalamus through the central part of the tegmentum. The structure of the two accessory^ olivarj'^ nuclei corresponds to that of the chief or inferior olivary nucleus. Arcuate Nucleus. — ^This nucleus consists of a lamina of grey matter which lies upon the ventral aspect of the pyramid of the bulb, above the level of the decussation of the p^Tamids, and 1356 A MANUAL OF ANATOMY beneath the anterior superficial arcuate fibres as they arch out- wards over the pyramid after emerging from the ventral median fissure. Superiorly it lies over the mesial aspect of the pyramid, close to the ventral median fissure. It contains small nerve-cells, in connection with which some of the anterior superficial arcuate fibres terminate, whilst others arise as axons of the cells, and many of them pass over the nucleus without entering it. Nucleus Lateralis. — This is a special collection of nerve-cells in that portion of the formatio reticularis grisea which lies on the dorso-lateral aspect of the olive. It is situated deeply between the olive and the substantia gelatinosaof Rolando. White Matter of the Medulla Oblongata. — ^The white matter is situated chiefly on the surface. Over the dorsal aspect of the upper or open part of the bulb, however, the grey matter comes to the surface and covers the lower or bulbar half of the floor of the fourth ventricle. The white matter is disposed in tracts or strands which are chiefly longitudinal, but a few run transversely in an arched manner. The tracts are as follows : 1. Pyramidal tract, or p5n:amid. 2. Dorsal or direct spino-cerebellar tract. 3. Ventral spino-cerebeUar tract. 4. Restiform body. 5. Funiculus cuneatus. 6. Funiculus gracilis. 7. Dorsal or posterior, and ventral or anterior longitudinal, bundles. 8. Superficial arcuate tract. 9. Deep arcuate tract. 10. Fillet. 11. Olivo-cerebellar tract. The pyramid of either side, and the decussation of the pyramids, have been already described. It may, however, be again stated that the path of their motor nerve-fibres is downwards into the spinal cord. The fibres comprising about the inner three-quarters of a pyramid, having taken part in the decussation, enter the dorsal portion of the lateral column of the cord on the side to which they have crossed, and here they constitute the deeply placed crossed lateral pyramidal tract. The fibres comprising about the outer quarter of a pyramid take no part in the decussation. Most of them pursue a direct path downwards into the anterior column of the cord on the same side. Having entered the anterior column, they take up a position close to the ventral median fissure and constitute the direct or ventral pyramidal tract {tract of Turck) . A few of them, however, enter the lateral column of the same side, and constitute the uncrossed lateral pyramidal tract. The pyramidal tract has descended from the pons Varolii. Dorsal or Direct Spino-cerebellar Tract. — This tract extends upwards from the lateral column of the spinal cord. It traverses THE NERVOUS SYSTEM 1357 the lower part of the lateral area of the bulb nearly as high as the lower part of the olive, after which it passes backwards and upwards into the restiform body, of which it forms a part. Ventral Spino-cerebellar Tract. — ^This tract, like the dorsal or direct spino-cerebellar tract, extends upwards from the lateral column of the spinal cord. It is situated chiefly on the dorsal aspect of the olive, but some of its fibres appear close to the outer Fig. 569. — The Formatio Reticularis of the Medulla Oblongata, shown BY a Horizontal Section passing through the Middle of the Olivary Body (Demi-Schematic) (L. Testut's ' Anatomie Humaine '). 1. Anterior Median Fissure 2. Fourth Ventricle 3. Formatio Reticularis 3 . Reticularis Alba 3". Reticularis Grisea 4. Raph6 5. Anterior Pyramid 6. Fillet 7. Inferior Olive, with the two Accessory Nuclei 7'. Peduncle of Olivary Body 13. 8. Hypoglossal Nerve 14. 8'. Hypoglossal Nucleus 14'. 9. Pneumogastric Nerve 9'. Terminal Nucleus of Pneu- 15. mogastric Nerve 16. 10. External Dorsal Auditory Nucleus 16'. 11. Nucleus Ambigutis 17. 12. Nucleus Gracilis 18. Nucleus Cuneatus Caput of Posterior Comu Lower Sensory Root of Fifth Nerve Fasciculus Solitarius External Anterior Arcuate Fibres Arcuate Nucleus Lateral Nucleus Nucleus of Fasciculus Teres side of that body. Whilst the dorsal spino-cerebellar tract passes into the restiform body and so reaches the cerebellar hemisphere directly, the ventral spino-cerebellar tract is continued upwards into the pons Varolii before reaching the cerebellar hemisphere. Restiform Body. — ^The restiform body is situated on the dorsal aspect of the bulb in its upper or open part, the funiculus gracilis and funiculus cuneatus occupying the dorsal aspect in its lower or closed part. It succeeds to the clava and cuneate tubercle in which 1358 A MANUAL OF ANATOMY these two funiculi respectively end, but it receives no nerve-fibres from the funiculi. It makes its first appearance in relation to the nucleus cuneatus, and above the cuneate tubercle it is a conspicuous massive bundle, which forms the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. Its course is up- wards, outwards, and backwards. It sinks into the corresponding hemisphere of the cerebellum, and is otherwise known as the inferior cerebellar peduncle. The restiform body is composed of fibres which are derived from the following sources : 1. The olivo-cerebellar fibres of the inferior olivary nucleus of the opposite side. 2. The direct cerebellar tract of the lateral column of the spinal cord of the same side. 3. The anterior superficial arcuate fibres from the nucleus gracilis and nucleus cuneatus of the opposite side. 4. The posterior superficial arcuate fibres from the nucleus gracilis and nucleus cuneatus of the same side. 5. Vestibular fibres from the vestibular nuclei of the vestibular division of the auditory nerve. The restiform body, from its composition, serves as an important means of connection between the cerebellar hemisphere superiorly and the medulla oblongata and spinal cord interiorly. Funiculus Cuneatus and Funiculus Gracilis. — ^These tracts are prolonged upwards from the posterior column of the spinal cord. As stated, each contains a grey nucleus, around the cells of which the corresponding sensory nerve-fibres terminate at intervals as they ascend. Towards the clava and cuneate tubercle the fibres become few and are spread over the clava and cuneate tubercle, finally ending in connection with the cells of the grey nuclei which give rise to these prominences. Dorsal or Posterior Longitudinal Bundle.— The fibres of this bundle {fasciculus longitudinalis medialis B.), when followed down- wards into the anterior column of the spinal cord on the same side, represent the fibres of (i) the ventral ground-bundle and (2) the anterior marginal bundle of Lowenthal. As these fibres are followed into the lower part of the bulb they form a bundle, which lies close to the median raphe and directly dorsal to the corresponding pyramid. This strand represents the dorsal longitudinal bundle in the lower part of the bulb. The deep arcuate fibres, to be presently described, pass obliquely through it to the median line, where they decussate with those of the opposite side. This de- cussation takes place in the interval between the right and left dorsal longitudinal bundles. Having now reached the other side, the deep arcuate fibres take an upward course, close to the median line, as the mesial fillet. The dorsal longitudinal bundle and fillet are therefore now closelv related to one another in the lower part of the bulb, both lying dorsal to the pyramid, the fillet lying close to the raphe. In the upper part of the bulb the two tracts become distinct. THE NERVOUS SYSTEM 1359 The dorsal longitudinal bundle is displaced dorsalwards during the formation of the fillet, and it comes into contact with the grey matter on the floor of the fourth ventricle ; whilst the fillet lies on the dorsal aspect of the p^Tamid. The dorsal longitudinal bundle is prolonged into the ventral column of the spinal cord on the same side, where it is represented, as stated, by the ventral ground-bundle and anterior marginal bundle of Lowenthal. A ventral or anterior longitudinal bundle (tecto-spinaJ tract) is described as lying on the ventral aspect of the dorsal or posterior longitudinal bundle. This bundle, however, is not well defined. It descends into the anterior column of the spinal cord, and is accompanied by the ponto-spinal tract, the fibres of which spring from the cells of the formatio reticularis of the pons. Arcuate Tracts. — These tracts form two groups — superficial and deep. The superficial arcuate fibres are arranged in two sets — anterior and posterior. The anterior superficial arcuate fibres arise from the nucleus gracilis and nucleus cuneatus of the opposite side, and a few arise from the arcuate nucleus of the same side. At the median line they decussate with those of the opposite side, and emerge at the ventral median fissure, where many of them arch over the mesial and ventral aspects of the pyramid. Others pierce the pjrramid, whilst some emerge at the ventro-lateral sulcus between the p\Tamid and olive. The fibres now pass outwards and dorsal- wards, some arching over the lower part of the olive, and they finally enter the restiform body. The posterior superficial arcuate fibres arise from the nucleus gracilis and nucleus cuneatus of the same side, and they enter the restiform body also of the same side. The deep arcuate fibres are disposed in two sets — ^lemniscal and olivo-cerebeUar. The lemniscal deep arcuate fibres arise from the nucleus gracilis and nucleus cimeatus of the same side. They sweep fon^'ards and inwards towards the raphe, passing obliquely through the dorsal longitudinal bundle. At the median line they decussate with those of the opposite side above the level of the decussation of the pyTamids. Having reached the opposite side, the deep arcuate fibres change their course, and now pass upwards. The ascending tract thus formed constitutes the mesial fillet or lemniscus. The decussation which takes place between the deep arcuate fibres in the median line, immediately above the decussation of the pwamids, is called the decussation of tlie fillets {decussatio lemnis- coruni B.). or the superior sensory decussation, as distinguished from the inferior sensory- or spino-thalamie decussation, which takes place in the spinal cord. The olivo-cerebellar deep arcuate fibres arise from the inferior oUvary nucleus of the same side. Emerging through the hilum, they pass across the median line to the opposite side. They then 1360 A MANUAL OF ANATOMY pass over, or through, the inferior olivary nucleus of that side, on the dorsal aspect of which they are collected into a distinct tract. This tract, arching backwards, applies itself to the restiform body, on its deep aspect, and is thereby conducted to the cerebellar hemisphere. Its fibres terminate in the cortex of the vermis and cerebellar hemisphere. The olivo-cerebellar arcuate fibres con- stitute the olivo-cerebellar tract, which connects the inferior olivary nucleus of one side with the cerebellar hemisphere of the opposite side. Fillet. — ^The fillet, or lemniscus, as present in the bulb, is a well- marked tract of fibres which lies on the dorsal aspect of the pyramid close to the raphe. As just stated, its fibres are derived from the lemniscal deep arcuate fibres of the opposite side. In the lower part of the bulb the fillet and dorsal longitudinal bundle are closely related. In the upper part of the bulb, however, as previously stated, the dorsal longitudinal bundle is displaced dorsalwards by the developing fiUet, and the fillet, now distinct from the dorsal longitudinal bundle, lies on the ventral aspect of that bundle, and on the dorsal aspect of the pyramid. The ventral region of the bulb is thus traversed by three longitudinal tracts, all of which lie close to the median line. These tracts are related to each other in the following order from before backwards : Pyramid. Fillet. Dorsal longitudinal bundle. Olivo-cerebellar Tract. — ^This tract has already been described in connection with the olivo-cerebellar deep arcuate fibres. Raphe of tlie Medulla Oblongata. — ^The raphe of the bulb occupies the median plane above the decussation of the pyramids, and is composed of fibres which, for the most part, cross obliquely from one side to the other. These fibres represent (i) the anterior superficial arcuate fibres, (2) the lemniscal deep arcuate fibres, and (3) the olivo-cerebellar deep arcuate fibres. A few fibres pass ventro-dorsally, and some are disposed longitudinally. The fibres are therefore arranged in an intersecting manner. Central Canal of tlie Medulla Oblongata. — ^The central canal of the spinal cord is prolonged upwards through the lower or closed part of the bulb. As it ascends it is gradually displaced backwards, first by the decussation of the pyramids, and afterwards by the decussation of the fillets. It is surrounded by a thick layer of grey matter, which is derived from the basal portions of the ventral and dorsal grey cornua of the spinal cord. Superiorly, at the level of the calamus scriptorius, it opens into the lower part of the fourth ventricle in the angle between the two diverging clavse. The grey matter which surrounds the canal is now spread out and forms a thick covering over the lower part of the ventricular floor, as pre- viously stated. Areas of Flechsig. — These areas involve the whole substance of the bulb, and aie mapped out by the funiculi of the hypoglossal and pneumogastric THE NERVOUS SYSTEM 1361 nerves. As seen in transverse section, these funiculi lie near each other as they arise from their nuclei in the grey matter of the lower part of the floor of the fourth ventricle. As the funicuh of the hypoglossal nerve pass forwards and those of the pneumogastric nerve outwards, they diverge from each other, and the substance of the bulb is thereby divided into three seg- ments, which constitute the areas of Flechsig — ventral, lateral, and dorsal. The ventral area lies bet^veen the raphe of the bulb and the funiculi of the hypoglossal nerve. Throughout its thickness this area contains the following structures : The pvramid and arcuate nucleus. The fillet. The dorsal or posterior longitudinal bundle. The formatio reticularis alba. The lateral area Ues between the funicuh of the hypoglossal nerve and those of the pneumogastric nerve. Throughout its thickness this area con- tains the following structures : The oUve and inferior oUvary nucleus. The nucleus laterahs. The nucleus ambiguus (to be afterwards described). The formatio reticularis grisea. The dorsal area is the region behind the funicuh of the pneumogastric nerve. Throughout its thickness this area contains the following structures: The restiform body. • The upper part of the cuneate nucleus. The descending root of the vestibular nerve | ^ ^ afterwards The fasciculus solitanus r \i K^ri The spinal root of the fifth cranial nerve J aescriDed. The substantia gelatinosa of Rolando. Course of Chief Nerve-FunicuU of Spinal Cord through Medulla Oblongata. Spinal Cord. Medulla Oblongata. Posterior Column. Column of Goll. Funiculus Gracilis and Nacleas Gracilis. Column of Burdaeh. Funiculus Cuneatus and Nucleus Cuneatus. Lateral Column. Crossed Lateral Pyramidal Tract. Inner three - quarters of opposite Pyramid. Uncrossed Lateral Pyramidal Tract. Outer one-quarter of Pyramid of same side. Dorsal or Direct Spino - cerebellar Lateral Area below Olive, and Resti- Tract. form Body. Ventral or Indirect Spino-cerebellar \ Tract I Lateral Area below Olive, and For- Prepyramidal or Rubro-spinal Tract j matio Reticularis. Lateral Ground-Bundle J Anterior Column. Direct Pyramidal Tract. Outer one - quarter ol Pyramid of same side. Ventral Ground-Bundle ^ Anterior Marginal Bundle of Lowen- - Dorsal Longitudinal Bundle, thai I Development of Medulla Oblongata.— The bulb is developed from the myelencephalon, which is the caudal division of the rhomben- cephalon. 86 1362 A MANUAL OF ANATOMY 2, The Pons Varolii. The pons Varolii is situated above the medulla oblongata, anc between the hemispheres of the cerebellum. With the exceptior of the restiform bodies, all the other parts of the medulla oblongata are prolonged into it. The pons presents two surfaces, ventral anc dorsal, and two borders, upper and lower. The ventral surfacf rests upon the upper part of the basilar groove of the occipital bon( and the dorsum sellse of the sphenoid. It is convex from side tc side, and from above downwards, and has a transversely-striatec appearance, due to the disposition of its superficial fibres. Alon^ the median line it presents the basilar groove, which extends fron the lower to the upper border, and lodges the basilar artery. Or either side of this groove the ventral surface is rendered prominen- by the prolongation upwards of the pyramids of the medulli oblongata, and the basilar groove is chiefly due to this circumstance 1 he sensory and motor roots of the fifth nerve, lying close together appear on the lateral aspect of the ventral surface, the small moto: root being the upper of the two. The portion external to these two nerve-roots constitutes the middle peduncle of the cerebellum It is composed of the transverse fibres of the pons, these on eithei side being collected into a large bundle, which passes backward: and outwards into the corresponding cerebellar hemisphere. The dorsal surface is directed towards the cerebellum. II presents a triangular area which is covered with grey matter. This area is continuous with the dorsal surface of the upper or open pari of the medulla oblongata, and it forms the upper or pontine pari of the floor of the fourth ventricle. On either side it is boundec by the superior peduncle of the cerebellimi as it passes upwards anc inwards. The upper border is slightly depressed at the centre, and on eithei side of the median depression it slopes outwards and downwards towards the middle peduncle of the cerebellum. The crura cerebri right and left, sink into the pons at the upper border. Internal Structure of the Pons Varolii. — The pons is composed 01 a large ventral and a small dorsal part. Ventral Part. — This portion consists of: (i) bundles of transversa fibres, (2) bundles of longitudinal fibres, and (3) a large amount ol grey matter. The bundles of transverse fibres intersect the bundles of longi- tudinal fibres, and on either side they are collected into the middle peduncle of the cerebellum, which enters the corresponding cere- bellar hemisphere. Some of the transverse fibres arise in the cortex of the cerebellum as the axons of the cells of Purkinje, and these terminate in the pons in arborizations around the cells of the nucleus pontis, mostly on the opposite side to that on which thej arise. Other transverse fibres arise in the pons as the axons of the cells of the nucleus pontis on one side. They then cross to the other side, and enter the cerebellar hemisphere of that side, where thej THE NERVOUS SYSTEM 1363 terminate in arborizations in the cortex. The fibres, therefore, of which the middle peduncle of the cerebellmn is composed may be regarded as being of two kinds, namely, efferent and afferent. The efferent fibres arise in the cerebellar cortex and terminate in the pons, whilst the afferent fibres arise in the pons and terminate in the cerebellar cortex. The bundles of longitudinal fibres in each half of the ventral part of the pons are derived from the breaking up of the crusta or pedal portion of the corresponding crus cerebri, which enters the pons at its upper border. Most of these bundles are collected together at the lower border of the pons, and form the pyramid of the medulla oblongata on the same side. Certain of the fibres of the crusta of the cms cerebri, however, terminate in the pons, as follows: (i) some end in arborizations around the cells of the motor nucleus of the fifth cranial nerve, the nucleus of the sixth cranial nerv^e, and the nucleus of the seventh cranial, or facial, ner\e ; and (2) others end in arborizations around the cells of the nucleus pontis, all of the same side. The grey matter of the pons, which is large in amount, occupies the intervals between the intersecting transverse P, Right Pyramid ; O.B., Right Olivary Body, and longitudinal bun- dles, and contains small multipolar nerve-cells. It is kno\vn as the nucleus pontis, and is continuous with the arcuate nuclei of the medulla oblongata. Corpus Trapezoides or Trapezium. — ^The trapezium represents a group of transverse fibres, on either side, which have no connection with the corresponding middle peduncle of the cerebellum. The fibres are situated in the lower part of the pons, dorsal to the pjTa- midal bimdles. Within the trapezium are large multipolar cells, which constitute the nucleus of the trapezium. The fibres of the trapezium arise chiefly as the axons of the cells of the ventral cochlear nucleus and also of the lateral cochlear nucleus or tuber- culum acusticum, in which nuclei the fibres of the cochlear di\nsion of the auditory ner\'e terminate. Some of the fibres arise from the superior olivary nucleus; others are the axons of the cells of the nucleus of the trapezium; whilst a third set {strice acusticce) arise Corpora Albicantia Crusta of Crus Cerebri ___,." \^\Jug Locus Perforatus Postic'jf "" Aiwy Right Pyramidal Tract Transverse Fibres of Pons Varolii Middle Peduncle of Cerebellum Decussation of the Pyramids — - — 1, I Fig. 570. — Dissection of j.^.^ ^ ,:.s Varolii, showing the course of the pyramidal Tracts of the Medulla Oblongata (HiRSCHFELD AND LeVEILL^). 1364 A MANUAL OF ANATOMY from the tuberculum acusticum of the opposite side. Certain of the fibres of the trapezium terminate in the superior olivary nucleus, but the majority cross the median plane, where they decussate with those of the opposite side. Having crossed to the opposite side, they become longitudinal, and form a well-marked ascending tract in the dorsal part of the pons Varolii, called the lateral fillet, which lies on the outer side of the main or mesial fillet. Fig. 571. — Vertical Transverse Section through the Upper Part of THE Pons Varolii (from L. Testut's 'Anatomie Humaine,' after Stilling). 1. Fourth Ventricle 2. Valve of Vieussens 3. Superior Root of Fifth Nerve 4 Nerve-cells which accompany this Root 5. Posterior Lonptudinal Bundle 6. Formatio Reticul.iris 7. Lateral Fissure of Isthmus 8. Section of Superior Cerebellar Peduncle 9, 9 . Mesial and Lateral Portions of the Fillet 10, 10. Transverse Fibres of the Pons 11, II. Longitudinal Fibres of the Pons 12. RaphiTrigonum Acosticum (base) ^-^Trigonum Hypoglossi f/^^ ^^Trigonum Vagi "~^,Tubercleof Rolando "-.Clava -- Funiculus Gracilis Funiculus Cuncatus Fig. 577. — The Floor of the Fourth Ventricle and Adjacent Parts. free margin there is the ependymal epithelium of the ventricle, covered, as stated, by pia mater. This portion of pia mater is called the tela choroidea inferior. The epithelial part of the roof presents superficially three laminse of white nervous matter — namely, the obex and the ligulae. The obex is a thin triangular lamina which is situated at the point of the calamus scriptorius, being attached laterally to the diverging clavse. The ligulce are two in number, right and left. Each ligula is a narrow band which is continuous inferiorly with the obex. It is attached inferiorly to the clava and the cuneate tubercle. It then passes transversely outwards over the dorsal aspect of the restiform body. The transverse part of the ligula forms the lower boundary of the lateral recess of the ventricle. 1380 A MANUAL OF ANATOMY Openings in the Roof.— ^These openings are three in number — one median and two lateral. They are situated in the non-nervous part of the roof — ^that is to say, the part formed by the ependymal epithelium of the ventricle, covered by pia mater, called the tela choroidea inferior; and they penetrate both of these layers fepi- thelial and pia-matral). The median opening is known as the foramen of Magendie, and is situated immediately above the obex. The lateral openings, right and left, constitute the foramina of Lusclilta. Each is situated in the roof of the corresponding lateral recess, where that recess terminates. By means of these three foramina — ^foramen of Magendie and foramina of Luschka, right and left — ^the cavity of the fourth ventricle communicates with the cisterna magna of the cranial subarachnoid space, which in turn is continuous with the dorsal part of the spinal subarachnoid space. , Upper Quadrigeminal Body , Lower Quadrigeminal Body ^. Superior Peduncle of Cer«bellum Right Hemisphere of Cer» bellum (m oblique section) Strise Acusticae Fig. 578. — The Fourth Ventricle and Right Hemisphere of the Cerebellum (in Section) (Hirschfeld and Leveill^). Choroid Plexuses of Fourth Ventricle. — ^These are two in number, right and left. Each is a longitudinal inflexion of the pia mater which forms the tela choroidea inferior, and it invaginates the ependymal epithelium of the lower part of the roof of the ventricle, by which it is covered on its ventricular surface. Each choroid plexus consists of two parts — ^longitudinal and transverse, and the two plexuses are disposed somewhat thus: "]f. The longitudinal parts lie on either side of the median line, and extend upwards from the region of the foramen of Magendie. Each transverse part ex- tends outwards into the corresponding lateral recess of the ventricle. Development of Fourth- Ventricle. — ^The lower or bulbar part is developed from the myelencephalon ; and the upper or pontine part is developed from the metencephalon, these being the two divisions of the rhombencephalon. THE NERVOUS SYSTEM 1381 TELENCEPHALON. Cerebral Hemispheres. The cerebral hemispheres are two in number, right and left. Each is semi-ovoid, and presents two extremities and three surfaces. The extremities are anterior and posterior. The anterior ex- tremity is thick and round, and its most projecting part is called Great Longitudinal Fissure Inferior Frontal Gyrus Sulcus Occipitalis^ Lateralis Sulcus Occipitalis"' Sulcus Occipitalis Transversus' External Parieto-occipital Fissure Fig. 579. — The Cerebral Hemispheres (Superior View). the frontal pole. The posterior extremity is narrow and pointed, and its most projecting part is called the occipital pole. The surfaces are external, internal, and inferior. The external surface is convex, in adaptation to the concavity of the cranial vault. The internal surface is flat and vertical, and it forms the lateral boundary of the great longitudinal fissure. For the most part it is in contact with the falx cerebri. The inferior surface is irregular, being adapted to the corresponding lateral divisions of the anterior and middle fossae of the interior of the base of the skull and the upper surface of the tentorium cerebelh. It is crossed transversely by a deep cleft, representing the stem of the fissure of Sylvius. The 1382 A MANUAL OF ANATOMY portion in front of this fissure is known as the orbital area, and is concave, in adaptation to the convexity of the orbital plate of the frontal bone, upon which it rests. The extensive portion behind the stem of the Sylvian fissure is known as the tentorial area, and is prominent and arched. Its anterior portion is received into the lateral division of the middle cranial fossa, and its posterior portion rests upon the tentorium cerebelli. The borders of each hemisphere are four m number, namely, supero-mesial, infero -lateral, superciliary, and internal occipital. The supero-mesial border separates the external from the internal surface. The infer o-lateral border separates the external surface from the tentorial area of the inferior surface. The superciliary border separates the front part of the external surface from the orbital area of the inferior surface. The internal occipital border separates the internal surface from the tentorial area of the inferior surface, and it extends from the occipital pole to the splenium of the corpus callosum. The exterior of each hemisphere is broken up into tortuous eminences, called gyri or convolutions, and these are separated from each other by clefts, called sulci or fissures. The exterior is com- posed of grey matter, which is spoken of as the cerebral cortex, and the interior is occupied by white matter, which forms the medullary centre. The breaking up of the hemispheres into gyri, with the intervening sulci, greatly increases the amount of cerebral cortex and, to a proportionate extent, of pia mater. The fissures are of two kinds — complete and incomplete. The complete fissures are produced by infoldings of the entire wall of each cerebral hemi- sphere, and corresponding to each of these fissures there is a projection on the wall of the lateral ventricle. The complete fissures are as follows : (i) The fissure of Sylvius, giving rise to the corpus striatum; (2) the choroidal fissure, giving rise to the choroid plexus of the lateral ventricle; (3) the hippocampal fissure, giving rise to the hippocampus major; (4) the calcarine fissure (anterior part), giving rise to the calcar avis or liippocampus minor; and (5) the collateral fissure (middle part), giving rise to the eminentia collateralis. The parieto-occipital fissure, though it gives rise to no internal projection, may be regarded as a complete fissure. The incomplete fissures are merely furrows on the suriace of the hemisphere, formed in association with the growth of the gyri. Each hemisphere presents six principal fissures, called interlobar fissures, and by means of these it is divided into six lobes. The fissures and lobes are as follows : Interlobar Fissures. Lobes. 1. Fissure of Sylvius. 1. Frontal. 2. Fissure of Rolando. 2. Parietal. 3. Parieto-occipital. 3. Occipital. 4. Calloso-marginal. 4. Temporal. 5. Collateral. 5. Island of Reil or Insula. 6. Circular or Limiting. 6. Limbic. Interlobar Fissures. — ^The fissure of Sylvius, which is the first fissure to appear in the course of development, commences on the inferior surface of the hemisphere at the locus perforatus anticus in a depression, called the vallecula Sylvii. From this point it passes THE NERVOUS SYSTEM 1383 horizontally outwards to the Sylvian point on the external surface of the hemisphere, where it divides into three diverging branches. It is a deep cleft, which is overhung posteriorly by the front part of the temporal lobe, and it separates the orbital surface of the frontal lobe from the temporal lobe. The posterior or Sylvian border of the small wing of the sphenoid bone faces the fissure, which lodges the middle cerebral artery. The limbs into which the fissure divides at the Sylvian point are, as stated, three in number, namely, anterior horizontal, anterior ascending, and posterior horizontal. The anterior horizontal limb passes forwards into the frontal lobe, its length being about | inch. The anterior ascending limb passes upwards and slightly forwards into the frontal lobe for about i inch, but its length is variable. The posterior horizontal limb is the longest and most conspicuous. It passes backwards on the external surface of the hemisphere for at lejist 2 inches, having portions of the frontal and parietal lobes above it, and the temporal lobe below it. Finally it turns upwards into the parietal lobe for a very short distance. The fissure of Rolando, also known as the cen£ra/sM/c«s, com- mences at the supero-mesial border of the hemisphere, alif fle behind its mid-point, and terminates above the centre of the posterior horizontcd limb of the fissure of Sylvius. It does not usually open into this limb, but may do so. Superiorly the fissure in most cases intersects the supero-mesial border to reach the internal surface of the hemisphere, upon which it passes backwards for a very short distance. The direction of the fissure of Rolando is irregularly downwards and forwards over the external surface of the hemisphere, and it separates the frontal from the parietal lobe. It describes t^'o bends. The upper genu has its concavity directed forwards, and is situated about the junction of the upper and middle thirds of the fissure. The lower genu has its concavity directed backwards, and is situated on a more anterior plane than the upper genu. Below the lower genu the direction of the fissure is almost vertical, with a slight inclination backwards. The parieto-occipital fissure is situated about 2 inches behind the upper end of the fissure of Rolando, and it separates the parietal from the occipital lobe. It is composed of two limbs, external and internal, which are continuous with each other at the supero-mesijQ border of the hemisphere, where they form a right angle. The external limb is situated on the external surface of the hemisphere, [- upon which it passes transversely outwards for about | inch, when it is arrested by the convolution which connects the parietal and occipital lobes. The internal limb appears as a deep, almost vertical, deft on the internal surface of the hemisphere, which opens into the calcarine fissure a short distance behind the splenium of the corpus callosum. The calloso-marginal fissure is situated on the internal surface of the hemisphere. It commences below the rostrum of the corpus callosum, contiguous to the locus perforatus anticus, and, bending round the genu, it passes backwards above the corpus callosum. 1384 A MANUAL OF ANATOMY from which it is separated by the callosal gyrus. At a point a Uttle behind the centre of the internal surface of the hemisphere it turns upwards and terminates at the supero-mesial border, a short distance behind the upper end of the fissure of Rolando. The calloso- marginal fissure lies between the frontal and limbic lobes, the marginal gyrus being above it and the callosal gyrus below it. The collateral fissure is situated on the mferior surface of the hemisphere. It commences near the occipital pole, and extends forwards to near the temporal pole. Posteriorly it has the calcarine fissure above, and in line with, it, and anteriorly it has the hippor campal gyrus on its mesial side. It separates the temporal lobe from the hippocampal portion of the limbic lobe. The middle Fig. 580. — The Left Cerebral Hemisphere (Superior Surface). Red = Frontal Lobe. Orange = Parietal Lobe. Blue = Occipital Lobe. portion of the collateral fissure gives rise to the eminentia collateralis in the floor of the lateral ventricle. The circular or limiting fissure is situated deeply in the anterior part of the posterior horizontal limb of the fissure of Sylvius. It almost surrounds the convolutions which constitute the island of Reil or insula, and is composed of three parts — superior, inferior, and anterior. The superior part separates the insula from the frontal and parietal lobes, the inferior part separates it from the temporal lobe, and the anterior part separates it from the frontal lobe. The circular fissure is deficient in the region of the apex of the insula. THE NERVOUS SYSTEM 1385 Lobes of the Cerebral Hemisphere — Frontal Lobe. — ^This is of large size. On the external surface of the hemisphere it is bounded behind by the fissure of Rolando, and below by the posterior horizontal limb of the fissure of Sylvius. On the inferior surface it is bounded behind by the stem of the fissure of Sylvius. On the internal surface it is bounded by the calloso - marginal fissure. The frontal lobe has three surfaces — external, inferior, and internal. External Surface. — ^This surface presents three principal sulci, namely, precentral, superior frontal, and inferior frontal. The precentral sulcus is more or less parallel to the fissure of Rolando, the ascending frontal or precentral gyrus inter^'ening between the two. It may be a single fissure, but it more frequently consists of two parts, superior and inferior. The superior part is usually joined above by the superior frontal sulcus. The inferior j»f"^^' ^\ Fig. 581 . — The Right Cerebral and Cerebellar Hemispheres (External Surface). Red = Frontal Lobe. Blue = Occipital Lobe. Orange = Parietal Lobe. Green = Temporal Lobe. Purple = Cerebellar Hemisphere. part passes superiorly into the middle frontal gyrus for a short distance in a forward and upward direction. The superior and inferior frontal sulci extend forwards from the precentraj sulcus. The gyri of the external surface are as foDows : ascending frontal, superior frontal, middle frontal, and inferior frontal. The ascending frontal or precentral gyrus is bounded behind by the fissure of Rolando or central sulcus, and in front by the superior and inferior parts of the precentral sulcus. It extends from the supero-mesial border of the hemisphere to a little behind the Sylvian point, which corresponds to the place where the stem of the fissure of Sylvius appears on the external surface of the hemisphere, and divides into its three branches. Below the lower end of the fissure of Rolando it is, as a rule, connected with the ascending parietal or postcentral gyrus by an annectant gyrus. 1386 A MANUAL OF ANATOMY The superior or first, middle or second, and inferior or third frontal gyri are arranged in tiers, which are disposed antero-posteriorly, the first and second being usually each subdivided, so as to make five tiers in all. They are separated from the ascending frontal or precentral gyrus by the superior and inferior parts of the pre- central sulcus. The superior frontal gyrus is narrow, and lies between the supero- mesial border of the hemisphere and the superior frontal sulcus. It is continuous with the marginal gyrus on the internal surface of Cerebral Hemisphere Fig. 582. — The Encephalon (Right Lateral View) (Hirschfeld AND Leveille). 6. Ramus Horizontalis. 7. Ramus Occipitalis. 8. Transverse Occipital Sulcus. 9. Lateral Occipital Sulcus. 10. External Part of Occipito- Parietal Fissure. 11. Superior Temporal, or Parallel, Sulcus. 12. Inferior Temporal Sulcus. 1 . Fissure of Rolando. 2. Posterior Horizontal IJmb of Fissure of Sylvius. 3. Anterior Ascending Limb of Fissure of Sylvius. 4. Anterior Hoiizontal Limb of Fbsure of Sylvius. 5. 5. Intraparietal Sulcus. the hemisphere, and is partially broken up into two parts, upper and lower. The middle frontal gyrus, which is broad, lies between the superior and inferior frontal sulci, and is usually connected with the ascend- ing frontal or precentral gyrus by an annectant gyrus. It is broken up anteriorly into two parts, upper and lower, by an antero-posterior secondary sulcus ; and it is cut into behind by the upper portion of the inferior part of the precentral sulcus. THE NERVOUS SYSTEM 1387 The inferior frontal gyrus lies below the inferior frontal sulcus, and in front of the lower part of the precentral sulcus. The anterior horizontal and the ascending hmbs of the fissure of Sylvius enter it and subdivide it into three parts, namely, pars orbitaUs, pars triangularis, and pars basilaris. The pars orhitcdis lies below the anterior horizontal limb of the fissure of Sylvius ; the -pars triangu- laris is situated between the anterior horizontal and the ascending limbs of the fissure of Sylvius ; and the pars basilaris is placed between the ascending limb of the fissure of Sylvius and the lower part of the precentral sulcus. The inferior frontal gyrus is connected posteriorly with the lower end of the ascending frontal or precentral gyrus by an annectant gyrus. The inferior frontal gyms of the left side is specially important, inasmuch as the speech-centre is assigned to the portion of it which forms the pars triangularis (le cap of Broca). Inferior or Orbital Surface of the Frontal Lobe. — ^This surface pre- sents two sulci, olfactory and orbital. The olfactory sulcus is parallel to the mesial border, from which it is separated by the gyms rectus. It lodges the olfactory tract and olfactory bulb. The orbital sulcus (triradiate sulcus of Turner) is of very variable form, but, as a rule, bears some resemblance to the letter M. It has therefore three limbs — inner, outer, and transverse. The inner limb is separated from the olfactory sulcus by the internal orbital gyrus. The oiiter limb is curved, and has external to it the orbital part of the inferior frontal gyrus. The transverse limb passes in a more or less curved manner between the inner and outer limbs. The gyri of the orbital surface are as follows : gyrus rectus, in- ternal orbital gyrus, anterior orbital gyrus, external orbital gyrus, and posterior orbital gyrus. The gyrus rectus lies between the olfactory sulcus and the mesial border. The internal orbital gyrus is placed between the olfactory sulcus and the inner limb of the orbital sulcus. The external Fig. 583. — The Inferior Surface OF THE Left Cerebral Hemi- sphere, SHOWING THE GYRI AND Sulci. 1388 A MANUAL OF ANATOMY orbital gyrus is external to the outer limb of the orbital sulcus. The anterior orbital gyrus is situated in front of the transverse limb of the orbital sulcus. The posterior orbital gyrus Hes behind the transverse limb of the orbital sulcus. Internal Surface of the Frontal Lobe. — ^The internal or mesial surface presents only one convolution, namely, the marginal gyrus, which is situated between the supero-mesial border of the hemisphere and the calloso-marginal sulcus. It is continuous with the superior frontal gyrus, and anteriorly is broken up by one or two sulci. Its posterior part is almost completely detached, and forms the paracentral lobule, which contains the upper end of the fissure of Rolando. Corpus Callosum Anterior Pillar of Fornix Septum Lucidum Pineal Body, Splenium ^ Gena passing into Rostrua V oramen of Monro -^ Anterior Commissure Optic Thai, and Mid. Com. Optic Nerve Pkuitary Body Tuber Cinereum Corpus Albicans Cerebellum Fourth Ventricle Third Nerve ' Pons Varolii Crus Cerebri /A Aqueduct of Sylvius Medulla Oblongaai Fig. 584. — The Mesial Surface of the Left Cerebral Hemisphere {HiRSCHFELD AND LF.VEILLlfe). Parietal Lobe. — This lobe lies between the large frontal and small occipital lobes, and above the temporal lobe. It is bounded an- teriorly by the fissure of Rolando, which separates it from the frontal lobe. Posteriorly it is bounded by (i) the external part of the parieto-occipital fissure, and (2) a line drawn across the external surface of the hemisphere from the extremity of this fissure towards the pre-occipital notch on the infero-lateral border of the hemisphere, from i^ to 2 inches in front of the occipital pole. The parietal lobe has two surfaces — external and intemaL THE NERVOUS SYSTEM ' 1389 External Surface. — ^This surface presents the following sulci : the intraparietal sulcus, composed of four parts ; and the ter- minal portions of (a) the posterior limb of the fissure of Sylvius, (b) the first temporal or parallel sulcus, and (c) the second temporal sulcus. The intraparietal sulcus (Turner) is composed of four parts, namely, inferior postcentral, superior postcentral, ramus hori- zontalis, and ramus occipitalis. The inferior and superior postcentral sulci may be distinct, or continuous with each other. They he behind the fissure of Rolando, with which they are parallel, and from which they are separated by the ascending parietal or postcentral gyrus. The ramus horizontalis passes backwards and slightly upwards from the upper end of the inferior postcentral sulcus. It has the superior parietal gyrus above it, and the inferior parietal gyms below it. The ramus occipitalis lies behind the ramus horizontalis, with which it is usually connected. It forms the outer boundary of the gyrus which arches round the external part of the parieto- occipital fissure, namely, the arcus parieto-occipitalis (first annectant convolution). Posteriorly the ramus occipitalis divides into two short sulci, which diverge, one ascending, and the other descend- ing, in the occipital lobe. The terminal portions of (a) the posterior limb of the fissure of Sylvius, (6) the first temporal or parallel sulcus, and (c) the second temporal sulcus, are confined to the lower part of the external surface of the parietal lobe, where they lie in the order named, from before backwards. The gyri of the external surface are as follows : ascending parietal ; superior parietal ; and inferior parietal, with its supramarginal, angular, and postparietal gyri. The ascending parietal or postcentral gyrus is situated unmediately behind the fissure of Rolando, which separates it from the ascending frontal or precentral gyrus in front of that fissure. Posteriorly it is limited by the superior and inferior postcentral sulci. It extends from the supero-mesial border of the hemisphere to the posterior horizontal limb of the fissure of Sylvius, and it lies parallel to the ascending frontal or precentral gyrus, with which it is connected below the fissure of Rolando. The superior parietal gyrus is situated between the ramus hori- zontalis and the supero-mesial border of the hemisphere, where it is continuous with the quadrate lobule, or praecuneus, of the internal surface. Anteriorly it is limited by the superior postcentral sulcus, round the upper end of which it is continuous with the ascending parietal gyrus. Posteriorly it is bounded by the external part of the parieto-occipital fissure, round the extremity of which it is connected with the occipital lobe by the arcus parieto-occipitalis (first annectant convolution). The inferior parietal gyrus is situated behind the inferior post- I390 A MANUAL OF ANATOMY central sulcus, and below the ramus horizontalis and ramus occi- pitalis. It is broken up into three gyri, namely, supramarginal, angular, and postparietaJ, in this order from before backwards. The supramarginal gyrus arches round the ascending extremity of the posterior limb of the fissure of Sylvius. It is continuous in front with the ascending parietal gyrus below the lower end of the inferior postcentral sulcus ; posteriorly with the angular gyrus ; and postero-inferiorly with the first temporal gyrus. The angular gyrus arches round the ascending extremity of the first temporal or parallel sulcus, and is continuous with the second temporal gyrus. The postparietal gyrus arches round the ascending ex- tremity of the second temporal sulcus, and is continuous with the third temporal gyrus. Internal Surface of the Parietal Lobe.— The internal or mesial Fimbria Gyrus Dentatus Fig. 585. — The Mesial Surface of the Right Cerebral Hemisphere (HiRSCHFELD AND LEVEILL^). surface is of quadrilateral outline, and constitutes the quadrate lobule or praecuneus. It is bounded in front by the upturned posterior extremity of the calloso -marginal sulcus, behind by the internal part of the parieto-occipital fissure, and below by the postlimbic sulcus and a portion of the limbic lobe. Occipital Lobe. — ^This lobe lies behind the parietal and temporal lobes, and forms the posterior part of the cerebral hemisphere. Externally the lobe is bounded in front by the external part of the parieto-occipital fissure, and a line connecting this fissure with the pre-occipital notch on the infero-lateral border of the hemi- sphere. Internally it is bounded in front by the internal part of the parieto-occipital fissure, which separates it from the quadrate lobule, or precuneus, of the parietal lobe. Inferiorlv it is continuous with the temporal and limbic lobes, but the separation may be indicated by a line connecting the pre-occipital notch with the THE NERVOUS SYSTEM 1391 portion of the limbic lobe which lies below the splenium of the corpus caUosum, this portion being known as the isthmus of the limbic lobe. The occipital lobe is pjTamidaJ, and presents an apex and three surfaces — external, internal, and inferior. The apex forms the occipital pole of the cerebral hemisphere. External Surface. — This surface presents t\vo sulci, transverse occipital and lateral occipital. The transverse occipital sulcus is formed by the bifurcation of the posterior end of the ramus occipitalis of the intrapanetal sulcus, and it crosses the upper part of the occipital lobe transversely. Its upper limb Ues a Uttle behind the external part of the parieto-occipital fissure, from which it is separated by a portion of the arcus parieto-occipitlais ; and its lower limb is behind the post-parietal gyrus. The lateral occipital sulcus is situated on the external surface of the occipital lobe, and extends almost horizontally from behind forwards. It divides the external surface of the lobe into two parts, upper and lower, which are connected with the parietal and tempor£il lobes by annectant gyri. Internal Surface. — The internal or mesial surface presents the calcarine fissure. This is a deep cleft which commences on the internal aspect of the occipital pole in a bifurcated manner. It takes a curved course forwards, pcissing at first upwards and then downwards, and it terminates by entering the limbic lobe beneath the splenium of the corpus callosum. It is joined at a point anterior to its centre by the internal part of the paneto-occipital fissure, and between the two fissures is the cuneus. The calcarine fissure may be regarded as being composed of two parts, anterior, representing the portion in front of the internal part of the parieto- occipital fissure, and posterior, representing the portion behind that fissure. The anterior calcarine fissure gives rise to the hippo- campus minor, or calcar avis, on the inner wall of the posterior comu of the lateral ventricle. The gyri of the internal surface are two in number, namely, the cuneus and the gyrus lingualis. The cuneus is triangular, and is wedged in between the posterior calcarine fissure and the internal part of the parieto-occipital fissure. The gyrus lingualis (infracalcarine gyrus) is situated between the calcarine fissure above and the posterior part of the collateral fissure below. Anteriorly it becomes narrow, and joins the hippocampal gyrus. The lower portion of this gyrus is visible on the inferior surface of the lobe. Inferior Surface. — ^The inferior or tentorial surface presents the posterior part of the occipito-temporal gyrus, internal to which is the posterior part of the collateral fissure, and internal to this again there is the lower portion of the gyrus lingualis. Temporal Lobe. — ^The temporal (temporo-sphenoidal) lobe is prominent, and of large size. It is situated below the posterior horizontal limb of the fissure of Syhius, and behind the stem of that fissure. Superiorly it is bounded by (i) the horizontal portion 1392 A MANUAL OF ANATOMY of the posterior limb of the fissure of Sylvius, and (2) a line pro- longing this limb backwards to meet the posterior boundary of the parietal lobe. Anteriorly it is bounded by the stem of the fissure of Sylvius, which separates it from the orbital area of the frontal lobe. Posteriorly it is continuous with the occipital lobe, but the separation may be indicated by the following lines : externally by a line connecting the extremity of the external part of the parieto- occipital fissure with the pre-occipital notch, and inferiorly by a line connecting the pre-occipital notch with the portion of the limbic lobe which lies below the splenium of the corpus callosum (isthmus of the limbic lobe). Inferiorly it is separated from the hippocampal gyrus by the collateral fissure. The temporal lobe is somewhat pyramidal, the rounded apex being directed forwards. The apical part forms the temporal pole, and it overhangs from behind the stem of the fissure of Sylvius. The uncus of the hippocampal gyrus lies on its inner side, but on a more posterior level, and separated from it by the temporal sulcus. The lobe presents three surfaces — superior, external, and inferior. The superior or opercular surface is concealed within the fissure of Sylvius, and is directed towards the island of ReU. The external surface presents two horizontaJ sulci and three convolutions, the latter being disposed in horizontal tiers. The sulci are called first temporal and second temporal, respectively. The first temporal sulcus is parallel to the posterior limb of the fissure of Sylvius, from which circumstance it is called the parallel sulcus. It commences near the temporal pole, and posteriorly it turns upwards into the parietal lobe, where the angular gyrus arches round it. The second temporal sulcus is parallel to the first, below which it lies, and it is usually broken up into two or more parts by annectant gyri. Posteriorly it turns upwards into the parietal lobe, where the postparietal gyrus curves round it. The gyri of the external surface, as stated, are arranged in hori- zontal tiers, and are three in nimiber, first, second, and third, in this order from above downwards. The first temporal gyrus is situated between the posterior limb of the fissure of Sylvius and the parallel sulcus. Posteriorly it is continuous with the supramarginal, and slightly with the angular, gyri of the parietal lobe. The second temporal gyrus lies between the parallel and second temporal sulci, and posteriorly is continuous with the angular and postparietal gyri of the parietal lobe. The third temporal gyrus lies below the second temporal sulcus, and posteriorly is continuous with the lower part of the external surface of the occipital lobe. The inferior or tentorial surface of the temporal lobe presents the occipito-temporal sulcus and the occipito-temporal gyrus. The occipito-temporal sulcus extends from before backwards, lying near the infero-lateral margin of the hemisphere, and external to the collateral fissure. It is usually broken up into parts by annectant THE NERVOUS SYSTEM i393 convolutions. The occipito-temporal gyrus is situated bet^veen the occipito-temporal sulcus and the collateral fissure, and extends from the occipital pole to the temporal pole. External to the occipito-temporal sulcus there is the narrow inferior or tentorial surface of the third temporal gyrus. Island of Reil, Central Lobe, or Insula. — ^This lobe is situated deeply within the fissure of Syhnus, and is concealed from view by the opercular gyri, to be presently described. It is triangular, the apex being directed downwards towards the vallecula Sylvii and locus perforatus anticus. The cir- cular or limiting sulcus being here absent, the grey matter of the apex is continuous with that of the locus perforatus anticus, this point being called the linwn insula. Elsewhere the island of Reil is sur- rounded by the circular or limiting sulcus, which has been already described. The insula presents several sulci, which diverge as they pcLss from the apical region to the base, and these map it out into gyri. One of these sulci is known as the sulcus centralis Insulse. It extends from the apex to the base in an upward and back- ward direction, almost in line %vith the fissure of Rolando, and it divides the insula into two lobules, precentral and postcentral. The precentral lobule is com- posed of three short gyri, called the gyri breves, which converge as they descend from the base, but they do not reach the apex or pole of the precentral lobule. The postcentral lobule is formed by the gyrus longus, which is usually broken up into two gyri towards the base of the insula. The direct internal or mesial rela- tion of the insula is the claustrum, internal to which there are, in succession, the external capsule, the nucleus lenticularis, the internal capsule, and the nucleus caudatus. The insula and the corpus striatum represent the stem of the cerebral hemisphere, whilst the remainder of the hemisphere is known as the palUum or mantle. 88 Fig. 586. — The Inferior Surface OF THE Left Cerebral Hemi- sphere, SHOWING THE GyRI AND Sulci. 1394 A MANUAL OF ANATOMY Opercula Insulse. — ^The parts of the cerebral hemisphere which bound the three hmbs of the fissure of Sylvius and overhang the insula are called the opercula insulae. They are four in number, namely, fronto-parietal, temporal, frontal, and orbital. The fronto-parietal operculum forms the upper lip, and the temporal operculum forms the lower lip, of the posterior limb of the fissure of Sylvius. The frontal operculum represents the pars triangularis of the inferior frontal gyrus — that is to say, the part which lies between the ascending and the anterior limbs of the fissure of Sylvius. The orbital operculum represents the pars orbitalis of the inferior frontal gyrus, and lies below the anterior limb of the fissure of Sylvius. Limbic Lobe. — ^This lobe is situated on the internal or mesial surface of the cerebral hemisphere. It is composed of two convo- Fissure of Rolando Superior Part of Limiting Sulcus^ Anterior Part of Limiting Sulcus Postero-inferior Part of ''OLE I Limiting Sulcus Central Sulcus Fig. 587. — The Left Island of Reil (Poirier, from Eberstaller). 1, 2, 3, Gyri Breves ; 4, 5, Gyri Longi ; x , Limen Insulae. lutions, namely, the callosal gyrus, or gyrus fomicatus, and the hippocampal gyrus, so disposed as to form an almost complete ring round the corpus callosum and subjacent parts. The open part of the ring, which is very small, is situated at the locus perforatus anticus, and is occupied by the roots of the olfactory tract. Around its circumference the limbic lobe is bounded superiorly by the calloso-marginal fissure, posteriorly by the postlimbic sulcus, and inferiorly by the anterior part of the collateral fissure and the incisura temporalis. The callosal and hippocampal gyri become con- ■ tinuous beneath the splenium of the corpus callosum, the connecting portion, which is narrow, being known as the isthmus of the limbic lobe. The callosal gyrus, or gyrus cinguli, arches round the corpus callosum: hence the name gyrus fornicatus. It commences at the THE NERVOUS SYSTEM 1395 locus perforatus anticus, below the rostrum of the corpus callosum, and it terminates below the splenium of that body. Between these two points it pursues a sweeping course, passing forwards beneath the rostrum, upwards in front of the genu, backwards above the body of the corpus callosum, and finally curving roimd the splenium, to be continued into the hippocampail gyrus through the isthmus. It is bounded superiorly by the calloso-marginal fissure, which separates it from the marginal gyrus and paracentral lobule, and, posterior to the latter, it is partially separated from the praecuneus by the postlimbic sulcus. The caUosal gyrus is separated from the corpus callosmn by the eallosal sulcus. The hippocampal gyrus constitutes the lower part of the limbic lobe, the upper part being formed by the eallosal gyrus. Posteriorly, below the splenium of the corpus callosum, it is continuous above with the eallosal g}Tiis throiigh means of the isthmus, and behind and below with the lingual gyrus. As it passes forwards it has the hippocampal or dentate fissure above it, and the anterior part of the collateral fissure below it. Anteriorly, near the apex of the temporal pole and close behind the locus perforatus anticus, it forms an enlargement, known as the caput gyri hippocampi, which is separated from the temporal pole by a slight fissure, called the incisura temporalis. From the caput a hook-hke process, known as the uncus, passes backwards fcr a short distance above the Jinterior part of the hippocampal or dentate fissure. The caput represents the largely-developed lobus pyriformls of many mam- mals, and it constitutes the olfactory centre of the cerebral cortex. Along with the uncus it forms part of the rhinencephalon or rhino- paUium, the rest of the hippocampal gyrus belonging to the neo- pallium. The part of the gyrus which hes below the hippocampal fissure is known as the subiadum. The incisura temporalis, which, as stated, separates the caput gyri hippocampi from the temporal pole, represents the rhinal fissure, which bounds the weU-developed rhinencephalon in some animals The cingiilum is connected with the limbic lobe, which is com- posed of the eallosal and hippocampal gyri. According to Cajal, its fibres arise as the axons of cells of the caUosal gyrus, upon the under sm-face of which gyrus the cinguliun hes. On entering the cingulima some fibres pass forwards, and others backwards, whilst a few are described as branching into forward and backward branches. The anterior branches pass as far as the caput of the corpus striatum, where they are described as blending with the fibres which enter the internal capsule. Some may even pass to the cortex of the prefrontal region. The posterior branches turn round the splenimn and then he upon the subiculum, or upper part of the hippocampal g>Tus, as far forwards as the caput and uncus. The posterior fibres are described as ending in the cortex of (i) the subiculmn hippocampi and (2) occipital lobe. The cingulum belongs to the class of long association fibres. 1396 A MANUAL OF ANATOMY Hippocampal or Dentate Fissure. — This fissure commences behind the splenium of the corpus callosum, where it is continuous with the callosal sulcus. It is directed forwards, lying between the gyrus dentatus above and the hippocampal gyrus below, and it terminates within the uncus of the hippocampal gyrus. The hippocampal fissure is a complete fissure. It appears in the course of the fifth week, and is parallel to the temporal portion of the choroidal fissure, below which it lies. The portion of the vesicular waU between these two fissures represents the gyrus dentatus, and the portion below the hippocampal fissure forms the hippocampal gyrus. The hippocampal fissure, being complete, gives rise to an internal elevation, namely, the hippocampus major, on the wall of the de- scending comu of the lateral ventricle. Gyrus Dentatus {Fascia Dentata of Tarinus) . — The gyrus dentatus is situated above the hippocampal gyms, and below the fimbria. It is separated from the hippocampal gyrus by the hippocampal fissure, and from the fimbria by a slight groove, called the fimhrio- dentate sulcus. The dentate gyrus is narrow, and its free margin is indented or notched : hence the name dentatus. It commences behind the splenium of the corpus callosum, and is directed forwards above the hippocampal gyrus into the curve of the uncus. Here it describes a bend, after which it emerges from the curve of the uncus, and, crossing the recurved part, is lost on its outer aspect. This portion of the dentate gyrus is called the frenulum Giacomini. Posteriorly it is continuous round the splenium with the rudimen- tary gyrus supracallosus, which contains the mesial and lateral longi- tudinal stricB of one half of the upper surface of the corpus callosum. Fimbria. — ^The fimbria is the prolongation of the posterior pillar of the fornix. It is situated above the g5mis dentatus, from which it is separated by the fimbrio-dentate sulcus. Posteriorly it turns upwards round tiie posterior extremity of the optic thalamus, and so becomes continuous with the posterior pillar of the fornix. Anteriorly it enters the uncus. Development of the Cerebral Hemispheres. — Each hemisphere is developed from the wall of the cerebral vesicle, which is a hollow protrusion from the upper and lateral part of the telencephalon, one of the divisions of the prosen- cephalon. The anterior wall of that portion of the telencephalon which lies between the two cerebral vesicles is called the lamina terminalis. The hemispheres grow out of proportion to the other parts of the encephalon in a forward, upward, and backward direction. Their backward growth is so great that they completely cover the other parts of the encephalon by the seventh month of intra-uterine life. The sulci and gyri of the hemispheres first appear about the fifth month of intra-uterine life. Development of the Insula and Fissure of Sylvius. — The insula, or island of Reil, appears as a depression, called the Sylvian lossa, on the lateral aspect df the cerebral vesicle. The wall of this fossa becomes developed into the opercula insulce, and, as these grow, they cover the insula, and give rise to the limbs of the fissure of Sylvius. THE NERVOUS SYSTEM ,397 Olfactory Lobe. The olfactory lobe is rudimentary in man. It is composed of two lobules, anterior and posterior (His). Anterior Lobule. — ^This consists of the foUowmg parts : (i) the olfactory bulb ; (2) the olfactory tract, with its two roots, mesial and lateral ; (3) the trigonum olfactorium ; and (4) the area of Broca, The olfactory bulb is the enlarged anterior extremity of the olfactory tract. It is oval, and its upper surface is in contact with the orbital surface of the frontal lobe, whilst its lower surface rests upon one half of the cribriform plate of the ethmoid bone. The lower surface receives the olfactory nerves, which arise from the olfactory cells of the olfactory mucous membrane and pass through the foramina of the cribriform plate. The olfactory tract is a white band which extends backwards from the olfactory bulb, both of them occupying the olfactory sulcus on the inner part of the orbital surface of the frontal lobe. Pos- teriorly it di\ndes into two roots, inner and outer, which diverge and enclose between them the trigonum olfactorium. The inner or mesial root passes inwards, in a curved manner, behind the area of Broca. Some of its fibres pass into this area, and others enter the anterior extremity of the caUosal gyrus, or gyrus fomicatus. The outer or lateral root passes backwards and outwards over the outer part of the posterior lobule (locus perforatus anticus), and enters the anterior part of the hippocampal gyrus. The trigonum olfactorium is the area of grey matter which lies between the diverging mesial and lateral roots of the olfactory tract. It is sometimes described as the middle or grey root of the olfactory tract. The area of Broca is situated in front of the inner root of the olfactory tract. It is continuous with the commencement of the callosjd gjTTis. Posterior Lobule. — This portion of the olfactorj' lobe is otherwise known as the locus perforatus anticus. It is bounded anteriorly by the fissura prima of His, which separates it from the trigonum olfac- toriiun; posteriorly by the caput gyri hippocampi ; externally by the lateral root of the olfactory tract ; and internally by the anterior part of the optic tract and the laterail margin of the optic commis- sura Its openings give passage to the central or ganghonic branches of the anterior and middle cerebral arteries. The grey matter of the locus perforatus anticus is continuous superiorly with the grey matter of the lenticular nucleus and of the large anterior end of the nucleus caudatus. Development. — The olfactory lobe is developed as a hollow protrusion from the anteroinferior part of the cerebral vesicle. This protrusion becomes solid, and gives rise to the olfactory tract and olfactory bulb. 1398 A MANUAL OF ANATOMY Rhinencephalon. — The rhinencephalon consists of the olfactory lobe, uncus, gyrus dentatus, supracallosal and subcallosal gyri, half of the septum lucidum, half of the fornix, and hippocampus major. Development of the Olfactory Organ. The olfactory organ is developed in two parts — the olfactory lobe, and the olfactory epithelium. The olfactory lobe is intracranial, and is an outgrowth from the anterior part of the ventral aspect or floor of the telencephalon, Great Longitudiaai Fissure Forceps Minor ^ Genu of Corpus Callosum ".Median Raph^ Stria . Longitudinalis Mesialis Stria „ Longitudinalis I^ateralis Tapetuni Forceps Majof Great Longitudinal Fissure Splenium of Corpus Callosum Fig. 588. — The Corpus Callosum (Superior View) (Hirschfeld AND LEVEILLfe). which is the cephalic division of the prosencephalon, or fore-brain. It consti- tutes the olfactory lobe (rhinencephalon) of the brain, and it becomes trans- formed into several parts, which will presently be stated, its terminal portion being the olfactory bulb, which rests upon one-half of the cribriform plate of the ethmoid bone. The olfactory epithelium is intranasal, and occupies the upper part of the nasal fossa of either side. It represents a neuro-cpithelium, which is derived from an invagination of the surface-ectoderm. The axons of its sensory cells constitute the olfactory nerve-filaments, which pass upwards through the foramina of the cribriform plate, and enter the under surface of the olfactory bulb. THE NERVOUS SYSTEM 1399 Olfactory Lobe. — The olfactory lobe appears as a hollow protrusion of the anterior cerebral vesicle on its ventral aspect, and near its anterior part. The cavity of this protrusion, which is continuous with the lateral ventricle, soon undergoes obhteration, and the protrusion becomes solid. Its terminal extremity undergoes enlargement, and the entire protrusion becomes differ- entiated into the following parts: (i) The olfactory bulb; (2) the olfactory tract; (3) the inner or mesial, and outer or lateral, olfactory roots; (4) the trigonum olfactorium; (5) the area of Broca; and (6) the locus perforatus anticus. Of these parts, the olfactory bulb is the enlarged terminal extremity of the original protrusion, and, as stated, it rests upon one-half the cribri- form plate of the ethmoid bone, through the foramina of which half it receives the olfactory filaments, which are the axons of the sensory cells of the olfactory epithelium of the upper part of the nasal fossa. Corpus Callosum Anterior Pillar of Fornix Septum Lucidum Pineal Body Splenium Genu passing into Rostrum .Corpora Quadri Foramen of Monro -^ Anterior Commissure Optic Thai, and Mid. Com. Optic Nerve ■^ Pituitary Body Tuber Cinereum Corpus Albicans Cerebellum Fourth Ventricle Third Nerve Pons Varolii I Cms Cerebri Aqueduct of Sylvius Medulla Oblongata Fig. 589. — The Mesial Surface of the Left Cerebral Hemisphere (HiRSCHFELD AND LeVEILL6). Olfactory Epithelium. — The first indications of the olfactory organ are the two olfactory or nasal areas. They consist of thickened ectoderm, and are placed on the ventral aspect of the anterior cerebral vesicle, on either side of the mesial nasal process of the fronto-nasal process, and on the cephalic side of the orifice of the stomodaeimi. Each olfactory area soon becomes depressed, and forms the olfactory or nasal pit. The two pits, right and left, are situated one on each side of the mesial nasal process of the fronto-nasal process. Each pit has the corresponding globiilar process of the mesicJ nasal process internally, and the latercil nasal process externally, this position corresponding to the situation of the future anterior naris on either side. At this period the olfactory pits communicate with the stomodseum, and the orifice of each pit, slightly constricted, constitutes the corresponding primitive anterior naris. This naris, on either side, becomes separated from the stomo- dseum by the union of the maxillarj- process (previously joined by the lateral nasal process) with the globular process. I400 A MANUAL OF ANATOMY The blind olfactory pits now grow dorsalwards along the roof of the stomo- daeum, and so give rise to the nasal sacs, which represent primitive nasal fossae. As each pit grows dorsalwards it is deepened by the formation of a groove, called the nasal groove, which extends to the roof of the stomodaeum. This groove is bridged over by ectoderm, and is thus separated from the corresponding olfactory pit. When the maxillary process (previously joined by the lateral nasal process) unites with the globular process, the nasal groove is obliterated, and the olfactory pit is cut off from the stomodaeum. By the development of the hard palate on either side, the ectodermic covering of the nasal groove disappears. The posterior part of this covering constitutes the naso-stomodesal membrane. When this membrane ruptures on either side, a dorsal aperture, called the primitive posterior naris, is formed, hkewise on either side, which establishes a fresh communication between the olfactory pit (blind end) and the stomodaeum on the cephalic side of the corresponding palatal shelf. The olfactory epithelium is developed from the upper part of the nasal pit, and it is separated from the olfactory bulb by the cribriform plate of the ethmoid bone. The ectodermic cells of the upper part of the nasal pit con- stitute a neuro-epithelium, and each cell is prolonged into a slender process, which is an axis-cylinder process, or axon. These axons form the olfactory nerve-filaments, which are non-medullated, and they pass through the foramina in one-half of the cribriform plate. Having reached the under surface of the olfactory bulb, they enter the bulb and break up into arborizations, which intermingle with the arborizations of the mitral cells of the bulb. For the Development of the Organ of Jacobson see Index. Rhinencephalon. — ^The rhinencephalon or olfactory brain repre- sents the olfactory region of each cerebral hemisphere, and is feebly developed in man. It consists of the following closely associated parts : I. Olfactory lobe. 6. Mesial and lateral longitudinal 2. Caput et uncus gyri Iiippocampi. striae. .3. Fimbria. 7- Fasciola clnerea. 4- Fornix. 8. Gyrus dentatus. 5- Subcallosal gyrus. 9- Septum pellucidum. Morphologically considered, the cerebral hemisphere is composed of three parts — namely, the stem, rhinopallium, and neopallium. The stem or stalk is formed by the corpus striatum; the rhinopallium consists of the parts which compose the rhinencephalon; and the neopallium represents the remainder of the hemisphere. Corpus Callosum. — The corpus callosum connects the two cerebral hemispheres. It is situated at the bottom of the great longitudinal fissure, and extends nearer to the front than back of the hemispheres. It is arched and thicker in front and behind than at the centre, its greatest thickness being posteriorly, where more fibres cross in it than elsewhere, on account of there being more of the hemisphere behind it than in front of it. The superior surface is related to the falx cerebri, but is in contact with it only posteriorly. It is covered by a thin layer of grey matter, and presents a transversely-striated appearance, indicative of the direction of its fibres. In the median line there is a slight antero-posterior furrow or raphe, and on either side of this there is a white longitudinal band, called the stria longitudinalis mesialis. The two striae longitudinales mesiales, right and left, are sometimes THE NERVOUS SYSTEM 1401 spoken of as the nerves of Lancisi. External to each mesial stria, and situated under cover of the gyrus fomicatus or caUosal gyrus, there is another band, composed of grey matter, called the stria longitudinalis lateralis. Each lateral stria is sometimes spoken of as the tcsnia tecta (' covered taenia'), from the circumstance that it is covered by the callosal gyrus. The striae of each side may be traced posteriorly round the spleniiun into the corresponding gyrus dentatus. Anteriorly each mesial stria, along with the grey matter in which it lies, passes round the genu and backwards on the under surface of the rostrvun, under the name of the geniculate gyrus. This enters the sub- callosal gyrus, and finally passes to the temporal pole. The mesial and lateral longitudinal striae of each side, together with the thin layer of gray matter, represent a rudimentary convolation caUed the supracallosal gyras. The posterior extremity of the corpus callosum is called the splenium. It is ver^- thick, which is due, as stated, to the great number of fibres which cross in it, on account of there being more of the hemisphere behind it than in front of it. The splenium is rolled upon itself, so that its lower part is directed forwards. It lies over the mesencephalon. Anteriorly the corpus callosum is bent upon itself, and passes at first downwards and then backwards. The bent portion is called the genu, and the portion which passes backwards is termed the rostrum. The rostrum terminates in the median line by becoming connected with the lamina terminaUs, and on either side it passes into the peduncles of the corpus callosum, otherwise known as the subcallosal gyri. Each subcallosal gyrus, with the contained stria longitudinalis mesialis, now called, as stated, the geniculate gyrus, passes downwards on the internal surface of the cerebral hemisphere to the locus perforatus anticus, lying in front of the lateral portion of the lamina cinerea. The geniculate gyrus then passes backwards and outwards along the posterior margin of the locus perforatus anticus, and so reaches the temporal pole. The inferior surface of the corpus callosiun is divisible into a mesial and two lateral portions. The mesial portion is connected posteriorly with the fornix, and over the remainder of its extent with the septum lucidrun. Each lateral portion enters into the roof of the body and anterior comu of the corresponding lateral ventricle. Destination of the Callosal Fibres. — The transverse fibres of the corpus callosmn, on entering the white medullary substance of each cerebral hemisphere, traverse it in a radiating manner as they pass to the cerebral cortex. They constitute the radiatio corporis callosi, and intersect in their course the fibres which pass between the internal capsule and the cerebral cortex, which form the corona radiata. The fibres from the central portion or body and upper part of the splenium of the corpus callosum constitute the tapetum. This forms the roof of the body of the lateral ventricle. I402 A MANUAL OF ANATOMY the chief part of the roof and the outer wall of the commencement of the middle or descending comu, and the roof and outer wall of the posterior comu. The fibres of the tapetum ultimately pass into the temporal and occipital lobes. The fibres from the region of the genu curve forwards into the front part of the frontal lobe, and form the roof of the anterior comu of the lateral ventricle. They constitute the forceps minor. The fibres from the lower part of the splenium curve backwards into the occipital lobe, and give rise to an eminence on the inner wall of the posterior comu of the lateral ventricle. They constitute the forceps major. Development. — The corpus callosum may be regarded as being developed from the lamina terminalis. Fornix. — This is an arched lamina of white longitudinal fibres, which lies beneath the corpus callosum, with which it is connected posteriorly, but from which it is separated anteriorly by the septum lucidum. It is composed of two lateral halves, which are united together in the median line to form the body of the fornix ; but in front and behind they are separated from each other, and form the anterior and posterior pillars. The fornix is thus composed of a body, two anterior pillars, ctnd two posterior pillars. The body is triangular, being narrow in front, where it is con- tinuous with the anterior pillars, and broad behind, where it is prolonged into the posterior pillars. The superior surface of the body is connected posteriorly with the corpus callosum, and anteriorly with the septum lucidum. Each lateral border is well defined, and projects slightly into the lateral ventricle. The inferior surface rests directly upon the velum interpositum, beneath which, in the median line, is the third ventricle, and on either side the upper surface of the optic thalamus. The anterior pillars are two round bundles, which are continuous with the anterior part of the body, and are slightly separated from each other. They pass downwards in front of the foramina of Monro, traversing the grey matter on the sides of the third ventricle. On reaching the base of the brain each piUar becomes twisted in the form of a loop, and forms the white portion of the corresponding corpus albicans or mammillare. The fibres of the anterior pillar terminate in the grey nucleus of the corpus albicans, and from this nucleus a bundle of fibres, called the bundle of Vicq d'Azyr, passes upwards and backwards into the optic thalamus. The anterior commissure lies in front of the anterior pillars. The posterior pillars are prolongations of the posterior part of the body on either side. They are flattened bands, which at first adhere to the under surface of the corpus callosum. Subsequently however, each curves outwards and downwards round the posterior extremity of the optic thalamus, and enters the descending cornu of the lateral ventricle. Here the posterior pillar comes into contact with the hippocampus major, upon the surface of which some of its fibres become spread out, forming the alveus. The rest of the THE NERVOUS SYSTEM 1403 fibres are prolonged as a narrow band of white matter, called the fimbria, or taenia hippocampi, along the inner concave border of the hippocampus major, to which it is attached, as far as the uncus. As the two posterior pillars diverge from each other they enclose between them a small triangular space on the under surface of the corpus callosum posteriorly. This space is crossed by trans- verse fibres, and is known as the lyra or psalteriion, from its supposed resemblance to a lyre. The transverse fibres form a commissure between the two hippocampi majores, and the lyra is therefore known as the hippocampal commissure. Each lateral half of the fornix is to be regarded as establishing a communication between the hippocampus major, in which the majority of its fibres originate, and the optic thalamus of the same side through means of (i) the anterior pillar, {2) the corpus mammillare, and (3) the bundle of Vicq d'Azyr. Development. — The fornix may be regarded as being developed from the lamina terminalis. Anterior Commissure. — This is a round bundle of white fibres which crosses the middle line immediately in front of the anterior pillars of the fornix. Anteriorly its central portion is connected with the lamina terminalis, and posteriorly the central portion appears between the anterior pillars of the fornix, where it forms part of the anterior boundary' of the third ventricle, and is covered by the ventricular epend\Tna. On either side the commissure enters the cerebral hemisphere, and divides into two parts, olfactory and temporal. The olfactory portion is of small size, and enters the corresponding olfactory tract. Some of its fibres serve to connect the olfactory bulb of one side with that of the other side. The other fibres connect the olfactory bulb of one side with the temporal lobe of the opposite side. The temporal portion is of large size, and its fibres disappear in the white matter of the temporal lobe. The anterior commissure ser\^es to connect the olfactory bulbs and the temporal lobes. Septum Lucidum. — ^This is a thin vertical partition which is situated between the anterior comua of the lateral ventricles, as well as between the front parts of the bodies of these ventricles. It is triangular, being broad in front and narrow behind. Pos- teriorly it is attached above to the imder surface of the corpus callosum, and below to the upper surface of the body of the fornix. Anteriorly it occupies the concavity behind the genu of the corpus callosum, being attached above to the corpus callosum and below to the rostnun of that body. The septimi lucidum is composed of two delicate laminae. The outer surface of each lamina looks into the corresponding lateral ventricle, and is covered by the ventricular epend^Tna (epithelium). The inner surface faces that of its fellow, a narrow interval, representing the fifth ventricle, intervening between the two. Each lamina consists of white 1404 A MANUAL OF ANATOMY matter, which is covered by grey matter on the surface looking towards the fifth ventricle. The two laminse are formed from portions of the mesial walls of the two cerebral hemispheres which have become detached in the course of the development of the corpus callosum and fornix. Fifth Ventricle. — ^The fifth ventricle, or ventricle of the septum, is the narrow cleft-like interval between the two laminse of the septum lucidum. It is a closed space, and has therefore no com- munication with the other ventricles. It is destitute of any ependymal lining, and contains a very little fluid. Caudate Nucleus •*■-—.. Left Vein of Galen Vein of Corpus Striatum i Choroid Vein " Veins of Galen Choroid Plexus entering De- scending Cornu of Lateral Ventricle Septum Lucidum Fifth Ventricle Fornix ..Velum Inter - positum Vena ^fagna Galeni — Lyra Posterior Pillar of Fornix Fig. 590. — The Velum Interpositum and Veins of Galen. As regards development, it differs from the other ventricles, having been originally a part of the great longitudinal fissure. Velum Interpositum. — ^This is also known as the tela choroidea superior, in contradistinction to the tela choroidea inferior, which is the pia mater forming the roof of the lower part of the fourth ventricle. It lies immediately beneath the fornix, and rests upon the ependymal roof of the third ventricle, and also upon the ad- jacent portions of the optic thalami. It consists of two layers of pia mater, and is triangular, the apex being situated behind the anterior pillars of the fornix at the foramina of Monro and the base lying beneath the splenium of the corpus callosum. In the latter situation the two layers of the velum interpositum become THE NERVOUS SYSTEM 1405 continuous with the pia mater, which has entered through the transverse fissure, situated between the splenium of the corpus callosum and the corpora quadrigemina. Chi either side the velum interpositum projects beyond the lateral border of the fornix, and appears as a vascular fringe in the lateral ventricle, where it is covered by the ventricular epend^Tua. This fringe is known as the choroid plexus of the lateral ventricle. Posteriorly it is prolonged into the descending comu. Anteriorly it approaches its fellow of the opposite side, and the two unite in the median line behind the foramina of Monro. From this junction two other choroid plexuses extend backwards on the inferior surface of the velum interpo- situm, one on either side of the median line. They form the choroid plexuses of the third ventricle, and lie superficial to the ependjTnal roof of that cavity. The principal veins in connection with the velum interpositmn are the two choroid veins and the two veins of Galen. The choroid vein of each side is situated in the choroid plexus of the lateral ventricle. It passes fonvards and inwards to a point behind the corresponding foramen of Monro, where it joins the vein of the corpus striatum, which lies bet^veen the optic thalamus and the corpus striatum. In this manner the vein of Galen of one side is formed. The veins of Galen are two in number, right and left. Each vein is formed, as just stated, by the union between the choroid vein and the vein of the corpus striatum behind the corresponding foramen of Monro. The two veins of Galen pass backwards within the velum interpositiun, one on either side of the median line. At first they are near each other ; then they diverge ; but subsequently they again come together and unite to form one vessel, called the vena magna Galenl, which opens into the anterior extremity of the straight sinus. Each vein of Galen receives numerous tributaries from the corresponding choroid plexus of the third ventricle, optic thalamus, corpus callosima, corpora quadrigemina, and pineal body. Near its termination it is joined by the large basilar vein, which is formed at the locus perforatus anticus by the union of the anterior cerebral vein with the deep Sylvian vein. The vena magna Galeni receives tributaries from the upper surface of the cerebellum and from the occipital lobes of the cerebral hemispheres. Lateral Ventricles. The lateral ventricles are the ventricles of the cerebral hemi- spheres, and are two in number, right and left. They are of irregular shape, and each occupies about two-thirds of the length of the corresponding hemisphere. They are lined with ependyma (epithelium), and contain a certain amount of cerebro-spinal fluid. Each ventricle communicates with the third ventricle by the foramen of Monro of its own side, which is situated between the 1406 A MANUAL OF ANATOMY anterior pillar of the fornix and the front part of the optic thalamus. The lateral ventricle of either side consists of a body and three cornua — anterior, middle or descending, and posterior. The body extends from the foramen of Monro to the level of the splenium of the corpus callosum. The anterior cornu is situated in front of the foramen of Monro, and curves forwards and out- wards into the frontal lobe. The middle or descending cornu Genu of Corpus Callosum ^Anterior Cornu of Lateral Ventricle ^^Fifth Ventricle (within ^^ _^ ^^_ ' Septum Lucidum) Caudate Nucleus Left Foramen of Monro Taenia Semicircu- laris Optic Thalamus . Choroid Plexus of Body of Lateral Ventricle Choroid Plexus of Descending Cornu -Posterior Cornu of Lateral Ventricle Bulb of Posterior Cornu (due to Fibres of the Forceps Major) Cerebellum Fig. 591. — The Lateral Ventricles of the Cerebrum (after HiRSCHFELD AND LeVEILLE). enters the temporal lobe, and describes a remarkable curve as it sweeps round the posterior extremity of the optic thalamus. Its direction is backwards, outwards, downwards, forwards, and finally inwards to a point about i inch from the temporal pole. The posterior cornu curves backwards and inwards into the occipital lobe. The body of the lateral ventricle presents a roof, an inner wall. THE NERVOUS SYSTEM 1407 and a floor. The roof is formed by the corpus callosum (tapetum). The inner wall is formed by the posterior part of the septum lucidum, and, behind this, by the attachment of the body of the fornix to the under surface of the corpus callosum. Externally the body is limited by the meeting of the roof and floor. The floor presents the following structures, in order from within outwards : (i) the sharp lateral border of the fornix ; (2) the choroid plexus of the lateral ventricle ; (3) a portion of the upper surface of the optic thalamus ; (4) an oblique groove, extending forwards and inwards Third Ventricle ^,« Anterior Comu Descending C(»iia -Suprapineal Recess Fotuth Ventricle Lateral Recess of Fourth Ventricle Impression for Bulbus Comu Posterioris Posterior Comu Fig. 592. — Drawing of a Metal Cast of the Ventricles of the Brain of an Adult (Superior View) (Retzius). between the optic thalamus and nucleus caudatus, in which there are (a) a white band, called the taenia semicircularis, and (b) the vein of the corpus striatum, the latter being the more super- ficial of the two ; and (5) the narrow part of the nucleus caudatus of the corpus striatum. The anterior cornu has its roof formed by the corpus callosum (forceps minor}. Externally it is limited by the meeting of the roof and floor. Anteriorly where it is pointed, it is bounded by part of the posterior aspect of the genu of the corpus callosum. Its inner wall is formed iDy the anterior part of the septum lucidum. 1408 A MANUAL OF ANATOMY The floor presents a prominent swelling, which is the large round extremity of the nucleus caudatus of the corpus striatum. The posterior cornu has its roof and outer wall formed by the tapetum of the corpus callosum. The inner wall presents two elongated, curved eminences, upper and lower. The upper eminence is produced by the fibres of the forceps major as they sweep back- wards from the lower part of the splenium of the corpus callosiun to the occipital lobe. It is called the bulb of the posterior cornu. The lower eminence is called the calcar avis or hippocampus minor, Descending Cornu Hippocampus Major. Trigonum Ventriculi' Pes Hippocampi --Uncus Gyrus Dentatus "---Hippocampal Gyrus ~- Fimbria Posterior Pillar of Fornix 5- Splenium Buib of Posterior Cornu Hippocampus Minor, or Calcar Avis Posterior Cornu Fig. 593. — The Descending and Posterior Cornua of the Left Lateral Ventricle (after Hirschfeld and Leveill£). (The Descending Cornu has been laid open throughout its entire extent). and is produced by the anterior calcarine fissure on the mesial surface of the cerebral hemisphere. The middle or descending cornu is situated in the temporal lobe. Its roof is formed chiefly by the tapetum of the corpus callosum, and, at the deep end of the cornu, presents the amygdaloid tubercle, which is produced by a collection of grey matter, called the amyg- daloid nucleus. The narrow part or tail of the nucleus caudatus and the taenia semicircularis are prolonged into the roof, and extend in it as far as the amygdaloid nucleus. The floor of the descending cornu presents the following structures : (i) the hippo- campus major, or cornu Ammonis ; (2) the fimbria or taenia hippo- THE NERVOUS SYSTEM 1409 canipi ; {3) the ertlinentia collateralis, or pes accessorius ; and (4) the choroid plexus of the descending comu. The hippocampus major, or cornu Ammonis, is a prominent cur\'ed elevation which traverses the entire length of the descending comu, accurately adapting itself to its curves. It enlarges as it descends, and beneath the amygdaloid tubercle it terminates in a swelling, which is notched on the surface. This swelling is called the pes hippo- campi. The hippocampus major is produced by the dentate or hippo- campal fissure on the mesial surface of the cerebral hemisphere. The fimbria, or taenia hippocampi, is the continuation of the posterior pillar of the fornix. It lies adong the iimer concave border of the hippocampus major, to which it is attached, and it is com- posed of white fibres, some of which form the layer on the surface of the hippocampus major, called the alveiis. The emlnentia collateralis, or pes accessorius, is an elevation which is situated in the angle between the descending and posterior comua, where there is a small triangular space, called the trigonum ventriculi. It extends backwards into the posterior comu, and for a variable distance into the descending comu. The eminentia collateralis is produced by the central portion of the collateral fissure on the tentorial surface of the cerebral hemi- sphere. The choroid plexus of the descending cornu rests upon the surface of the hippocampus major, and is continuous with that of the body of the lateral ventricle. It is covered by the epend^Tna of the inner wall of the descending comu, which it invaginates. \Vhen the choroid plexus is removed its ependjinal covering comes away along with it, and the choroidal fissure then becomes apparent. The choroidal fissure is situated between the fimbria and the roof of the descending comu, and, curving round the back part of the optic thalamus, it is traceable as far forwards as the foramen of Monro of the same side. In the other direction it extends to the lower extremity of the descending comu. It is produced by an infolding or invagination of the epithehal mesial wall of the cerebral vesicle of one side over the choroid plexus of the descending comu of the lateral ventricle. On either side it is continuous with the lateral and lower part of the transverse fissure. When the choroid plexus is withdrawn from the descending comu of the lateral ventricle, the epithehal or ependjTnal covering of the plexus comes away with it, or is broken down. Under these circum- stances the descending comu opens freely upon the exterior. The choroidal fissure is a complete fissure, and the internal prom- inence corresponding to it is the choroid plexus in the descending cornu of the lateral ventricle. Development. — ^The lateral ventricles represent the cavities of the primitive cerebral vesicles. The choroidal fissure is developed as an invagination of the mesial wall of the cerebral vesicle; and the choroid plexus is developed from a growth of mesoblast into the choroidal fissure. 89 I4I0 A MANUAL OF ANATOMY Basal Ganglia of the Cerebral Hemispheres. The basal ganglia of each cerebral hemisphere are as follows: the nucleus caudatus and nucleus lenticularis of the corpus striatum, the claustrum, and the amygdaloid nucleus. Great Longitudinal Fissure . Anterior Cornu of Lateral Ventricle L), , Caudate Nucleus \y I I ^ Genu of Corpus Callosum Trigonum Habenulae Lower Quadrigeminal Body Fifth Ventricle (Ventricle of the Septum) Anterior Pillars of Fornix - Ant. Tub. of Optic Thalamus __, Taenia Semicircularis Middle Commissure iXV— -Stria Pinealis —\W- Third Ventricle Posterior Commissure Pineal Peduncle ^^^^X" (Habenula) ■ -A Thalamic Groove for Margin of Fornix ^- Pulvinar of Optic Thalamus Pineal Body Superior Peduncle of Cerebellum Upper Quadrigeminal Body Fig. 594. — The Third Ventricle, Portions of the Lateral Ventricles, Pineal Body, and Corpora Quadrigemina (Superior View) (Henle). (The Corpus Callosum, Fornix, and Velum Interpositum have been removed). The corpus striatum is a large ovoid mass, which is situated in front, and on the outer side, of the optic thalamus. It is composed of two collections of grey matter, one of which is intraventricular and the other extraventricular. The intraventricular portion is called THE NERVOUS SYSTEM 141 1 the nucleus caudatus. The extravovtricular portion is embedded in the white matter of the cerebral hemisphere, and is termed the nucleus lenticularis. Between these two nuclei there is a part of the thick tract of white fibres which constitutes the internal cap- sule ; and on the outer side of the nucleus lenticularis there is the thin lamina of white matter, called the external capsule. When a coronal section is made through the corpus striatiun on a level with the anterior part of the nucleus lenticularis, the white matter of the front part of the internal capsule is seen to be intersected by striae of grey matter which pass between the nucleus caudatus and nucleus lenticularis. From the striped appearance thus produced the body has received the name of corpus striatum. The nucleus caudatus is pyriform. The large round end is directed forwards, and projects into the anterior comu of the lateral ventricle. Entrance to Descending Comu of Lateral Ventricle Hippocampus Major Fig. 595 . — Horizontal Section of the Brain through the Genu AND SpLENIUM of THE CORPUS CaLLOSUM (DaLTON). The narrow portion is directed outwards and baclavards in the floor of the body of the lateral ventricle, where it lies on the outer side of the optic thalamus, from which it is separated by the taenia semicircularis. Its tapering tail is continued into the roof of the descending comu of the lateral ventricle, and is prolonged in the roof as far as the amygdaloid nucleus, in which it terminates. The 1 412 A MANUAL OF ANATOMY nucleus caudatus is composed of grey matter, and its cells are of the multipolar variety. The nucleus lenticularis is embedded in the white matter of the cerebral hemisphere, and lies on the outer side of the nucleus caudatus and optic thalamus, from both of which it is separated by the internal capsule. It is of more limited extent than the nucleus caudatus, and receives its name from the fact that, in horizontal section, it presents the appearance of a biconvex lens, the broadest part being on a level with the front of the optic thalamus. Anteriorly it is closely related to the front part of the nucleus caudatus, being continuous with it inferiorly, and con- nected with it superiorly by striae of grey matter which intersect the white matter of the front part of the internal capsule. The anterior part of the nucleus lenticularis, as seen in coronal section, Great Longitudinal Fissure Fifth Ventricle (within Septum Lucidum) Anterior Cornu of Lateral Ventricle Left Anterior . Pillar of Fornix Middle Com-', missure Third Ventricle -S§^-" Genu of Corpus Callosum Caudate Nucleus .Optic Thalamus Internal Capsule ^^ , External Caps Claustrum -Grey Matter ( Island of Rei ^ White Matter o Island of Reil Optic Tract (cut) Infundibulum Lenticular Nucleus Fig. 596. — Coronal Section of the Frontal Portions of the Cere- bral Hemispheres, passing through the Anterior Cornua of thb Lateral Ventricles (Posterior View). 1, Putamen of Lenticular Nucleus ; 2, 3, Globus Pallidus of Lenticular Nucleus. is somewhat semilunar. When such a section is made through the* centre, the nucleus presents a triangular outline, the base being directed towards the island of Reil, and having the external capsule, in loose connection with it, whilst the internal surface is in contact with the internal capsule. In such a section the nucleus is seen to be traversed vertically by two white bands, called the medullary lamina, which divide it into three zones. The outer zone, which has a dark reddish colour, is the largest, and is called the putamsn. THE NERVOUS SYSTEM 14^3 The inner two zones, which axe somewhat yellowish, are together known as the globus paUidus. The putamen and globus palhdus, which consist of grey matter, are traversed by white fibres. The grey matter of the nucleus caudatus and nucleus lenticularis comes to the surface at the base of the brain in the region of the locus perforatus anticus, where it is continuous with the grey matter of the cerebral cortex. The internal capsule is the thick tract of white matter which lies between the nucleus lenticularis externally, and the nucleus cau- datus, taenia semicircularis, and optic thalamus internally. As seen in horizontal section it describes a bend opposite the front part of the optic thalamus. This bend is called the genu, and its convexity is directed inwards. The part of the internal capsule in front of the genu is called the anterior limb. It forms about one-third of the entire capsule, and its direction is forwards and out- wards. The part behind the genu is called the posterior limb. It forms about two- thirds of the entire capsvde, and its direction is backwards and outwards. The anterior limb of the internal capsule is situated between the front part of the nucleus lenticularis and the nucleus caudatus. Anteriorly it is intersected by the striae of grey matter which pass between the two nuclei. The fibres which compose the anterior limb are partly corticipetal and partly corticifugal. The corticipetal fibres are as follows: (i) thalamo-frontal fibres, which pass from the optic thalamus to the cortex of the frontal lobe ; (2) thalamo-striate fibres, which pass from the optic thalamus to the corpus striatum (thalamo-caudate and thalamo-lenticular fibres) ; and (3) strio-frontal fibres, which pass from the corpus striatum to the cortex of the frontal lobe. The chief corticifugal fibres constitute the fronto-pontine tract. The fibres of this tract arise in the cortex of the prefrontal region. They traverse the anterior limb of the internal capsule, and then descend in the inner part of the crusta of the cms cerebri to the pons Varolii, within which they terminate in connection with the ceUs of the nucleus pontis. Other centrifugal fibres constitute fronto-thalamic, fronto-siriaie, and strio-thalamic tracts. The posterior limb of the internal capsule is situated between the back part of the nucleus lenticularis and the optic thalcimus, and is prolonged backwards for a little beyond the posterior limit of the nucleus lenticularis. It is therefore conveniently divided into two parts, lenticular, representing the anterior two-thirds, and postlenticular, representing the posterior third. The lenticular part of the posterior limb, like the anterior limb, is composed of centripetal and centrifugal fibres. The centripetal fibres arise in the optic thalamus, and their destination is the cerebral cortex. The centrifugal fibres represent the pyramidal or motor fibres, and they occupy the anterior portion of the lenticular part of the posterior limb of the internal capsule. These fibres descend from the Rolandic region of the cerebral cortex. Some of them pass to 1414 A MANUAL OF ANATOMY the nucleus of the facial nerve; others pass to the nucleus of the hypoglossal nerve; but the majority of them are destined for the motor cells in the anterior grey cornu of the spinal cord. The fibres which pass to the facial nucleus lie close to the genu, and those which pass to the hypoglossal nucleus lie close behind the facial fibres. The fibres of the pyramidal tract occupy the central portion of the crusta of the cms cerebri in their downward course. The postlenticular part of the posterior limb contains the following sets of fibres : (i) the fibres of the optic radiation, on their way from and to the optic thalamus, external geniculate body, and superior quadrigeminal body ; (2) the fibres of the auditory radia- tion, passing between the auditory region of the temporal lobe and the internal geniculate body ; and (3) ' the fibres of the temporo- pontine tract (cortico-protuberantial fibres), which pass from the cortex of the temporal lobe through the outer part of the crusta of the cms cerebri to the pons Varolii, where they terminate in the nucleus pontis. The internal capsule is continuous inferiorly with the crusta of the cms cerebri. Superiorly its fibres diverge in a radiating manner on their way to the cerebral cortex, forming the corona radiata, the fibres of which are intersected by those of the radiatio corporis caUosi. The external capsule is a thin lamina of white matter which is situated on the outer side of the nucleus lenticularis, where it lies between that nucleus and the claustmm. In front of and behind the nucleus lenticularis it is continuous with the internal capsule. The external capsule is, as stated, only loosely connected with the putamen of the nucleus lenticularis. The fibres of which it is composed are probably derived from the anterior white commissure and the optic thalamus. Connections of the Corpus Striatum. — (i) The nucleus caudatusand nucleus lenticularis are partly continuous with each other, and partly connected by striae of grey matter. (2) The corpus striatum is connected with the optic thalamus by strio-thalamic and thalamo-striate fibres. (3) The nucleus caudatus is said to be connected with the substantia nigra by a tract of fibres known as the stratum intermedium. (4) The nucleus lenticularis is connected with the optic thalamus by the ansa lenticularis. (5) The corpus striatum is connected with the cerebral cortex by cortico-striate fibres. Development. — The corpus striatum is developed as a thickening of the floor of the cerebral vesicle. The claustrum is a thin lamina of grey matter which is situated on the outer surface of the external capsule. It lies embedded in the white matter which occupies the region between the lenticular nucleus and the island of Reil. Superiorly it is narrow and tapering, but inferiorly it expand^ and reaches the surface at the base of the brain, in the region of the locus perforatus anticus. Its outer surface presents elevations and intervening depressions, which correspond to the sulci and gyri of the island of Reil. The claustrum is regarded as an isolated portion of the grey matter of the island of Reil. The amygdaloid nucleus is an oval collection of grey matter which is situated in the anterior part of the temporal lobe, where THE NBRVOVS SYStEM 1415 it lies in the roof of the deep extremity of the descending comu of the lateral ventricle. The putamen of the nucleus lenticularis hes above it; anteriorly it is continuous \vith the cerebral cortex; inferiorly it receives the narrow part or tail of the nucleus caudatus; and the taenia semicircularis arises from it. The taenia semicircularis is a narrow white band of fibres which, as just stated, arises from the amygdaloid nucleus. The band passes backwards in the roof of the descending comu of the lateral ventricle, and then it sweeps upwards and forwards into the body of the lateral ventricle, lying between the nucleus caudatus and the optic thalamus. Anteriorly, in the region of the foramen of Monro, it dips downwards towards the anterior pillar of the fornix and the anterior white commissure. In this situation its fibres are variously disposed. Some pass into the anterior pillar of the fornix ; others pass in front of the anterior commissure, and enter the grey matter between the head of the nucleus caudatus and the septum lucidum ; whilst a few are regarded as entering the nucleus caudatus. The vein of the corpus striatum hes superficial to the taenia semicircularis. Relation of Structures in the Region of the Corpus Striatum. — When a coronal section has been made the relation of structures, from within outwards, is as follows : 1. Nucleus caudatus. 4. External capsule. 2. Internal capsule. 5. Claustnun. 3. Nucleus lenticularis. 6. Island of Reil. THALAMENCEPHALON OR DIENCEPHALON. Tiiird Ventricle. The third ventricle is the cleft-like interval which is situated, in the median line, between the two optic thalami. It extends from the pineal body posteriorly to the anterior pillars of the fornix in front, is very narrow from side to side, and is deeper in front than behind. The cavity presents a roof, a floor, two lateral walls, an anterior botmdary, and a posterior boundary. The roof is formed by a delicate layer of epitheliiun which extends across between the upper margins of the lateral walls, and is con- tmuous with the ependymal lining of the ventricle. Superficial to this epithelial roof, and intimately connected with it, is the velum interpositimi, from the under surface of which the two choroid plexuses of the ventricle project downwards, one on either side of the middle line, each invaginating the epithehum of the roof. The epithelium of the roof is so intimately connected with the velum interpositum that, when the latter is removed, the epithelium comes away with it, and the cavity of the ventricle is exposed. Superficial to the velum interpositum is the body of the fornix, and, above this again, is the body of the corpus callosum. Summary of the Roof. — To expose the ventricle from above the following structures must be removed, in the order named : (i) the bodv of the corpus callosum ; (2) the body of the fornix ; and (3) the velum interpositum, along \vith the epithelium of the roof. t4i6 A MANUAL OF ANATOMY The floor, which is sloped downwards and forwards, is formed by the structures which lie within the interpeduncular space at the base of the brain, these being as follows, from behind for- wards: the locus perforatus posticus, the corpora mammillaria, and the tuber cinereum, with the upper end of the infundibulum. The tegmenta of the crura cerebri enter, to a certain extent, into the floor posteriorly, and the optic commissure lies across it anteriorly. Above the optic commissure the floor presents a depres- sion, called the optic recess, and behind this there is another depression or diverticulum, called the infundibular recess. The latter forms the upper part of the infundibulum which leads to the posterior lobe of the pituitary body. The lateral wall is slightly convex, and is formed, for the most part, by the inner surface of the optic thalamus, which has a thick Suprapineal Recess Posterior Comu Anterior Cornu - Foramen of Monro Position of Anterior Commissure Recess bulum Fourth Ventricle Lateral Recess of Fourth Ventricle Fig. 597. — Drawing of a Metal Cast of the Ventricles of the Brain of an Adult (Right Lateral View) (Retzius). covering of grey matter. Towards its centre it presents a furrow, which leads from the foramen of Monro in a backward direction towards the upper opening of the aqueduct of Sylvius. This groove is called the sulcus of Monro. At the upper part of the lateral wall there is a delicate band of white fibres, called the stria pinealis or medullaris, which represents the dorsal portion of the stalk of the pineal body, and passes to the anterior pillar of the fornix. Con- necting the two lateral walls (optic thalami), in front of the centre of the ventricle, there is a fragile band of grey matter, called the middle or soft commissure. At the anterior part of the lateral wall the corresponding anterior pillar of the fornix passes down- wards and backwards. The anterior boundary is formed inferiorly by the lamina termin- THE NERVOUS SYSTEM I4»7 afis, which extends upwards from the optic commissure to the ros- trum of the corpus callosum, and superiorly by the anterior pillars of the fornix and the central portion of the anterior commissure. The posterior boundary is formed by the pineal body and the posterior commissure, and under cover of the latter is the upper opening of the aqueduct of Sylvius. The posterior boundary pre- sents two recesses, pineal and suprapineal. The pineal recess passes backwards above the posterior conmiissure into the stalk of the pineal body, separating the stalk into two portions, dorsal and ventral. The suprapineal recess is connected with the back part of the epithelial roof of the ventricle, and passes backwards over the pineal body. The third ventricle has thus four diverticula, namely, the optic recess, the infundibular recess, (both of which recesses are associated with the floor), the pineal recess, and the suprapineal recess. The cavity communicates with the fourth ventricle by means of the aqueduct of Sylvius, and with the two lateral ventricles by means of the foramina of Monro. Foramina of Monro. — ^These are two in number, right and left, and they lead from the lateral ventricles into the third ventricle. Each foramen is situated between the anterior pillar of the fornix in front and the anterior tubercle of the optic thalamus behind. From this point the foramen of each side leads inwards and slightly downwards, and opens into the third ventricle at the anterior and upper part of the corresponding lateral wall. By means of the foramina of Monro the lateral ventricles communicate with the third ventricle, and, through that ventricle, with each other. The choroid plexuses of the lateral ventricles also become continuous with each other and with those of the third ventricle through these foramina. From each foramen a furrow, called the sulcus of Monro, leads, as stated, in a backward direction, over the inner surface of the optic thalamus towards the upper opening of the aqueduct of Syhaus. Development. — The posterior and greater part of the third ventricle repre- sents the cavity of the thalamencephalon or diencephalon ; and the antericH" part, in the region of the foramina of Munro, represents the mesial portion of the cavity of the telencephalon. The foramen of Monro, of each side, represents the original wide communi- cation between the cavity of the cerebral vesicle and the cavity of the mesial portion of the telencephalon. Optic Thalami. — ^The optic thalami are two large ovoid masses of grey matter which He obliquely, with their long axes directed backwards and outwards, for the most part on the sides of the third ventricle. Their anterior extremities are near each other, but their posterior extremities stand apart, the corpora quadrigemina being situated between them. Over their anterior two-thirds they are separated from each other by the third ventricle. The optic thalamus presents four surfaces — superior, inferior, ex- ternal, and internal ; and two extremities — anterior and posterior. The superior surface is limited externally by an oblique groove. I4i8 A MANUAL OF ANATOMY which separates it from the nucleus caudatus, and contains the taenia semicircularis and, anteriorly, the vein of the corpus striatum. Internally it is bounded, from before backwards, by (i) the stria pinealis, (2) the trigonum habenulse, and (3) the Great Longitudinal Fissure ^Genu of Corpus Callosum Anterior Cornu of Lateral Ventricle ^__li Caudate Nucleus Fifth Ventricle (Ventricle of the Septum) Anterior Pillars of Fornix _ Ant. Tub. of Optic Thalamus Tsenia Semicircularis - « Middle Commissure -Stria Pinealis ,__ Posterior Commissure Trigonum Habenulae Lower Quadrigeminal Body V Vr-.Third Ventricle ~Vi.,\ Pineal Peduncle ^'\~r~ (Habenula) ^■'AThalamic Groove for ;;>;,_^ ' Margin of Fornix ^>Pulvinar of Optic Thalamus \ "'Pineal Body \ ■*■ Superior Peduncle of Cerebellum Upper Quadrigeminal Body Fig. 598. — The Third Ventricle, Portions of the Lateral Ventricles, Pineal Body, and Corpora Quadrigemina (Superior View) (Henle). (The Corpus Callosum, Fornix, and Velum Interpositum have been removed). corpora quadrigemina. It is divided into two areas, outer and inner, by a groove which is directed backwards and outwards from the inner border, near the anterior extremity, to the outer end of the posterior extremity. This groove corresponds to the THE NERVOUS SYSTEM 1419 lateral margin of the body of the fornix. The outer area enters into the body of the lateral ventricle, and is covered by the epen- dvTna of that ventricle. The inner area is excluded from the lateral ventricle, and is covered by portions of the velum interpositura and body of the fornix. The superior surface is covered by a thin layer of white fibres, called the stratum zonale, these fibres being derived from the optic tract and optic radiation. The inferior surface lies posteriorly upon the upward prolongation of the tegmental fibres of the cms cerebri, which constitutes the subthalamic tegmental region, but anteriorly it rests upon the corpus mammillare and a portion of the tuber cinereum. The external surface is directly related to the posterior limb of the internal capsule, which separates it from the nucleus lenti- cularis. Many fibres emerge from this surface and enter the in- ternal capsule on their way to the cerebral cortex, whilst others from the cerebral cortex enter the optic thalamus through this surface. These fibres constitute the thalamic radiation. On the outer surface the fibres form a well-marked reticular layer of white matter, which is called the external fneduUary lamina. The internal surface faces its fellow of the opposite side, with which it is connected by means of the middle or grey commissure. It fonns the lateral wall of the third ventricle, zmd superiorly is limited by the stria pinealis or medullaris. As stated in connection with the third ventricle, it presents the sulcus of Monro. It is covered by a thick layer of grey matter, which is continuous with that around the aqueduct of Sylvius. The anterior extremity is marked by a prominence, called the anterior tubercle, which enters into the body of the lateral ventricle, and forms the posterior boundary of the corresponding foramen of Monro. The posterior extremity presents, at its inner end, a weU-marked prominence, called the posterior tubercle or pulvinar. It lies over the brachia of the corpora quadrigemina, which it almost conceals. Below and external to the pulvinar there is an oval swelling, called the corpus geniculatum externum. Below this body is the upper brachium of the corpora quadrigemina, and inferior to this is the corpus geniculatum internum. Metathalamus or Corpora Geniculata. — ^The corpora geniculata are two in number — external or lateral and internal or mesial. They are associated with the posterior extremity of the optic thalamus, and the internal also with that portion of the mesen- cephalon which constitutes the corpora quadrigemina. The corpus geniculatum externum is an oval eminence situated on the posterior extremity of the optic thalamus below, and external to, the pulvinar. Internally it is connected with the upper quadri- geminal body by the superior brachium. It consists of grey and white curved lamellae, which alternate with each other. The fibres of the white lamellae belong to the outer or visual root of the optic tract. The axons of the cells of the grey 1420 A MANUAL OF ANATOMY matter enter the optic radiation as corticipetal j5bres. The lateral or outer geniculate body is associated with the visual sense. The corpus geniculatum internum is a small oval eminence, which is situated below the pulvinar and on the lateral aspect of that portion of the mesencephalon which constitutes the corpora quadri- gemina. The inferior brachium, which is beneath it, connects it with the lower quadrigeminal body. • The inner geniculate body contains many nerve-cells, the axons of which become corticipetal fibres, their destination being the cortex of the temporal region of the brain. Through means of the lower quadrigeminal body and the internal brachium the inner geniculate body receives fibres from the lateral or acoustic fillet, which terminate in arborizations around its cells. The axons of these cells become corticipetal fibres, the destination of which is the cortex of the temporal region of the brain. The inner genicu- late body is associated with the auditory sense. Development. — The corpora geniculata appear as elevations on the lateral wall of the thalamencephalon or diencephalon. Structure of the Optic Thalamus. — The optic thalamus is composed chiefly of grey matter. Its superior surface is covered with a layer of white matter, known as the stratum zonule, and its lateral surface is covered with a reticular layer of white matter, called the external medullary lamina. The mesial surface has a thick coating of grey matter which is continuous with the grey matter around the aqueduct of Sylvius. The grey matter of the interior of the optic thalamus is traversed by a plate of white matter, called the internal medullary lamina, which divides it into two nuclear areas — lateral and mesial. The lateral nuclear area lies between the internal and external medullary laminae, and extends backwards as far as the pulvinar. The mesial nuclear area Ues between the internal medullary lamina and the thick layer of grey matter which coats the mesial surface of the optic thalamus. It extends backwards as far only as the habenular region, and anteriorly it is separated from the anterior tubercle by a lamina of white matter. The region of the anterior tubercle therefore constitutes a third or anterior nuclear area of grey matter. The grey nuclear areas are consequently three in number — lateral, mesial, and anterior. Lateral Nuclear Area. — This area includes the pulvinar, the geniculate bodies, and the radiate nucleus. The pulvinar and geniculate bodies have just been described. The radiate nucleus is associated with the fibres of the thalamic radiation, to be presently referred to. Anterior Nuclear Area. — This area includes the anterior tubercle, and is the chief sensory nucleus. It receives corticifugal fibres, and its cells furnish corticipetal fibres. It also receives many of the fibres of the lateral fillet, as well as those of the superior cerebellar peduncle, and the fibres of the bundle of Vicq d'Azyr. Mesial Nuclear Area. — ^This area contains the ganglion habenul^e, to be presently described. Connections of the Optie Thalamus. — (i) Viewing the optic thalamus as an aggregation of ' cell-stations ' in the course of the centripetal fibres of the tegmentum of the crus cerebri, the tegmental fibres probably all terminate in the thalamic cells. (2) Through means of the stratum zonale the optic thalamus is connected with the optic tract and optic radiation. (3) The cells of the anterior nucleus receive the fibres of the bundle of Vicq d'Azyr, which are continuous, through the corpus albicans, with the fibres of the anterior pillar of the fornix. (4) Thalamic Radiation. — This is composed of thalamo-cortical fibres which arise within the optic thalamus as the axons of the thalamic cells. They issue from its external and inferior surfaces, and pass to all parts of the cerebral cortex. They are conveniently arranged THE NERVOUS SYSTEM 1421 in four groups or stalks — frontal, parietal, occipital, and inferior or ventral, (a) The fibres of the frontal stalk, having emerged from the front part of the external surface, traverse the anterior limb of the internal capsule, and most of them pass to the cortex of the frontal lobe. Some of these fibres are thalamo-caudate and thalamo-lenticular, as regards their destination. {b) The parietal stalk, having issued from the external surface of the optic thalamus, passes for the most part through the internal capsule, but also, to a certain extent, through the external capsule, to the cortex of the parietal lobe, and the Rolandic region of the frontal lobe, (c) The occipital stalk issues from the outer part of the pulvinar, and, having traversed the postlen- ticular portion of the posterior limb of the internal capsule, it passes back- wards and outwards, external to the posterior comu of the lateral ventricle, and so reaches the cortex of the occipital lobe, (d) The inferior or ventral stalk emerges from the front part of the inferior surface of the optic thalamus, and its fibres arise as the axons of the cells of the outer and inner nuclei. The most superficial of these fibres constitute a band, called the ansa lenti- cularis, which enters the nucleus lenticulcuris, where it terminates. The remaining fibres pass outwards beneath the nucleus lenticularis to the cortex of the temporal lobe and island of Reil. Besides the thalamo-cortical fibres there are eortlco-thalamic fibres, which pass from the various parts of the cerebral cortex into the optic thalamus, where they terminate in arborizations around the thalamic cells. Development. — The optic thalamus is developed as a thickening of the lateral w^all of the thalamencephalon or diencephalon. Subthalamic Tegmental Region. — This region represents the upward prolongation of the tegmental fibres of the cms cerebri beneath the posterior portion of the optic thalamus. The parts to be noted are as follows : upward prolongations of the red nucleus and substantia nigra of the tegmentum of the cms cerebri; the mesial fillet ; the fibres of the superior peduncle of the cerebellum ; and the corpus subthalamicum, or nucleus of Luys. The red rMcleus and the substantia nigra gradually disappear, and are no longer visible at the level of the corpus albicans. The mesial fillet lies on the superficial and outer aspects of the red nucleus. The fibres of the superior pedimcle of the cerebellum partly ter- minate in connection with the cells of the red nucleus, but many of them surround it in the form of a capsule. Beyond the red nucleus the mesial fillet, fibres of the superior cerebellar peduncle, and fibres which issue from the red nucleus enter the inferior sur- face of the optic thalamus, and terminate in connection with the thalamic cells. Some of these fibres may pass through the optic thalamus into the internal capsule, and thence to the cortex of the Rolandic region of the cerebral hemisphere. The corpus sub- thalamicum or nucleus of Luys is a small lenticular mass of grey matter, surrounded by white fibres, which lies on the outer side of the substantia nigra. Epithalamus. — The epithalamus includes the following parts: 1. Pineal body. 3. Trigonum habenulae. 2. Strise medullares. 4. Posterior commissure. Pineal Body, or Epiphysis Cerebri. — The pineal body is so named because it resembles a pine-cone. It is situated on the dorsal or superior surface of the mesencephalon, and occupies the depression between the upper quadrigeminal bodies. It is of small size, dark 1422 A MANUAL OF ANATOMY red in colour, and somewhat conical in shape. Superiorly it is inti- mately related to the pia mater, as that membrane passes through the transverse cerebral fissure to form the velum interpositum, and the splenium of the corpus callosum lies above it with the inter- vention of the pia mater. Inferiorly it is in contact with the depres- sion between the upper quadrigeminal bodies. Its apex, which is directed downwards and backwards, is free. Its base is directed upwards and forwards, and contains the pineal recess, which is con- tinuous anteriorly with the cavity of the third ventricle. The portion of the base which lies below this recess is connected with the posterior commissure, which separates it from the upper opening* of the aqueduct of Sylvius. The portion above the recess contains the commissura habenularum and the superior commissure. Con- nected with either side of the base of the pineal body there is a bundle of white fibres. These two bundles constitute the peduncles or stalks of the pineal body. Each stalk passes outwards, and soon terminates in the trigonum habenulae. Structure ol the Pineal Body. — The pineal body is free from nervous con- stituents. It consists of a number of follicles, lined with epithelial cells, and containing a variable amount of calcareous matter, called acervulus cerebri or brain-sand, which is composed of calcium phosphate, calcium carbonate, magnesium phosphate, and ammonium phosphate. Development. — The pineal body is developed as a diverticulum of the posterior part of the dorsal aspect of the thalamencephalon or diencephalon. This diverticulum for the most part becomes solid, but a portion of it persists as the pineal recess of the third ventricle. The pineal body is regarded as representing the pineal eye of Uzards. Striae Medullares or Pineales. — Each stria meduUaris is a narrow strip of white longitudinal fibres, lying along the upper part of the mesial surface of the corresponding optic thalamus. It constitutes the habenula. Anteriorly, most of its fibres are derived from the olfactory lobe, more particularly the olfactory bulb and locus perforatus anticus. Some, however, may be derived from the anterior pillar of the fornix, and through the fornix from the cells of the hippocampus major. Posteriorly, the fibres are disposed in two ways, (i) The lateral fibres enter the ganglion habenulae, and terminate in connection with its cells. (2) The mesial fibres curve inwards towards the base of the pineal body, in which they cross to the opposite side, lying above the pineal recess. As they cross the median line they decussate with the mesial fibres of the opposite stria medullaris, and they terminate in the ganglion habenulae of the side to which they have crossed. Their decussation is known as the commissura habenularum. Trigonum Habenulae. — This is a small triangular area which is bounded posteriorly by the upper quadrigeminal body, internally by the posterior part of the stria medullaris, and externally by the adjacent part of the optic thalamus. It contains an important group of multipolar nerve-cells, known as the ganglion habenulae. This ganglion belongs to the mesial area of the optic thalamus. It receives some of the fibres of the stria medullaris, which come from THE NERVOUS SYSTEM 1423 the olfactory lobe, and, it may be, from the anterior pillar of the fornix. The axons of the ganglionic cells issue from the ventral surface of the ganglion and form a bundle, called the fasciculus retroflexus. This bundle passes downwards and forwards in the tegmentum of the cms cerebri, l>'ing on the mesial side of the red nucleus. Its fibres terminate in connection with the cells of the ganglion inter pedunculare, which is situated in the lower part of the locus perforatus posticus, directly above the pons Varolii. The ganglia habenulanun are connected with each other by fibres which constitute the sitperior commissure or commissure of the habenular ganglia. These nbres cross in the dorsal part of the base of the pineal body, and are on a higher plane than the posterior commissure. The striae medullares, or habenulae, and the ganglia habenulanun are associated with the rhinencephalon or olfactory brain. Posterior Commissure. — ^This is a band of white fibres which is situated at the back part of the third ventricle. It lies in the posterior wall of the ventricle, directly above the upper opening of the aqueduct of Sylvius, and underneath the base of the pineal body. Its fibres are regarded as arising from a nucleus in the grey matter of the lateral wall of the third ventricle, near the upper opening of the aqueduct of Sylvius. Some of the fibres of either side, after crossing, may descend in the tegmentum of the cms cerebri, as part of the dorsal longitudinal bundle of that side, and so reach the medulla oblongata. Hypothalamus. — ^The hypothalamus consists of two parts — mammillary and optic. The pars mammillaris hypothalami repre- sents the two corpora mammillaria. The pars optica hypothalami includes the following structures: 1. Tuber cinereum. 2. Infundibulum. 3. Posterior or cerebral lobe of the pituitary body. 4. Optic commissure. 5. Lamina terminalis. The corpora mammillaria are two small, white, pea-like bodies, which lie side by side directly in front of the locus perforatus posticus. Each is composed of white matter externally, and of a grey nucleus internally. The white matter is derived from the corresponding anterior pillar of the fornix, the fibres of which terminate in connection with the cells of the grey nucleus. This grey nucleus contains many cells, the axons of which give rise to two fascicuh, namely, the bundle of Vicq d'Azyr, and the peduncle of the corpus mammillare. The bundle of Vicq d'Azyr, which is appar- ently a continuation of the anterior pillar of the fornix, enters the optic thalamus, and its fibres terminate in connection with the cells of the anterior nucleus. The peduncle of tlie corpus mammillare passes downwards and backwards in the grey matter of the floor of the third ventricle to the tegmental region of the mesencephalon, but the mode of termination of its fibres is not known. 1424 A MANUAL OF ANATOMY Development. — ^I'he corpora mammillaria are developed from the ventral aspect of the thalamencephalon or diencephalon. Up to the fourth month of intrauterine life they are represented by a single corpus mammillare, but after that period this divides into two corpora. The tuber cinereum is an elevated area of grey matter which Ues in front of the corpora mammillaria and behind the optic commissure, the anterior portion of each optic tract being on either side. It is continuous anteriorly with the lamina terminalis, and on either side with the grey matter of the locus perforatus anticus. In the outer part of the tuber cinereum, in the vicinity of the optic tract, there is a collection of nerve-cells, which is variously spoken of as the basal ganglion of Meynert or the supra-optic nucleus of Cajal, and which is con- nected with the fibres of the commissure of Giidden. Behind the tuber cinereum, and in front of the corpora mammillaria, there is a small prominence, mesially placed, called the eminentia saccularis of Retzius, who regards it as the homologue of the saccus vasculosus of some lower verte- brates, e.g., fishes. Along the outer side of the tuber cinereum, close to the innermost fibres of the optic tract, there is a strand of grey matter containing nerve-ceUs. This collection of cells is known as the basal optic ganglion, or supra-optic nucleus. The infundibulum is a funnel-shaped stalk which extends down- wards from the anterior part of the inferior surface of the tuber cinereum to the posterior lobe of the pituitary body. Its upper part is hollow, and contains the infundibular recess or diverticulum of the cavity of the third ventricle. The infundibulum is the peduncle of the posterior lobe of the pituitary body. Lamina Terminalis. — This is a thin plate of grey matter which extends between the upper surface of the optic commissure and the rostrum of the corpus callosum near the genu. On either side it is connected with the grey matter of the locus perforatus anticus. It forms the lower part of the anterior wall of the third ventricle. Development. — The lamina terminalis represents the terminal part of the ventral wall of the embryonic neural tube, and it originally connects the anterior wall of the telencephalon with that of its fellow. For the pituitary body and infundibulum, see Index. Optic Nerve, Optic Commissure, Optic Tract, and Optic Radiation. The optic nerves, or nerves of sight, in the cranial cavity are connected together at the optic commissure, where some of the fibres decussate. From the back part of the commissure each nerve, under the name of the optic tract, passes backwards round the crus cerebri to its cerebral connections. The optic commissure or chiasma is somewhat quadrilateral, and rests upon the olivary eminence and optic groove of the sphenoid bone. It lies in front of the tuber cinereum and infundi- bulum, and its superior surface is connected with the lamina cinerea, and is intimately related to the anterior part of the floor THE NERVOUS SYSTEM M*5 of the third ventricle. Each extremity is connected anteriorly with the optic nerve, and posteriorly with the optic tract. On either side of the commissure is the locus perforatus anticus. The most of the fibres of the commissure proceed from each retina in the corresponding optic nerve, being afferent or centripetal ; but at the back part of the commissure there are the fibres of the inner roots of the optic tracts, which have no connection with either retina. The decussation of fibres in the commissure is only partial. The fibres which arise in the nasal or inner half of the retina cross and enter the optic tract of the opposite side. The fibres which arise in the temporal or outer half of the retina take no part in the decussation, but pass directly backwards into the optic tract of the same side. Occupying the back part of the commissure there are, as stated, some fibres which have no connection with either retina. These fibres constitute the commissure of Gudden. They lie behind the decussating fibres, and represent the fibres of the inner root of the optic tract of each side. They constitute the innermost fibres of each optic tract, and they connect the internal geniculate body of one side with its fellow of the opposite side. Summary. — The fibres which arise in the nasal or inner half of one retina cross in the optic commissure, and enter the optic tract of the opposite side. The fibres which arise in the temporal or outer half of one retina pass directly backwards into the optic tract of the same side. The fibres of the inner root of each optic tract cross in the back part of the commissure, and form the commissure of Gudden, the fibres of which have no connection with the optic nerves, but connect the two internal geniculate bodies, right and left. The optic commissure therefore consists of the following groups of fibres : (i) The crossed fibres, which axise in the nasal or inner portion of each retina ; (2) the uncrossed fibres, which arise in the temporal or outer portion of each retina, and occupy the outer part of the commissure ; and (3) the fibres of the commissure of Gudden, which occupy the back part of the commissure. The optic tract of each side is a flattened white band which passes backwards from the optic commissure. It cur\'^es round the cms cerebri, and in the region of the posterior extremity of the optic thalamus it divides into two roots, outer and inner. The outer or visual root is the larger of the two. It is chiefly com- posed of afferent fibres, which pass from the retina to the brain ; but it also contains efferent fibres, which pass from the brain to the retina. The afferent fibres are derived from (i) the temporal or outer half of the retina of the same side, and (2) the nasal or inner half of the retina of the opposite side, the latter having crossed in the optic commissure. The fibres of the outer root terminate in the external geniculate body, the pulvinar of the optic thalamus, and the upper quadrigeminal body, reaching the last-named body through the superior brachium. They form arborizations around the cells of these bodies which constitute the terminal nuclei or lower visual centres of the outer or visual root. These lower visual centres are connected with the higher or cortical visual centre by 90 1426 A MANUAL OF ANATOMY Fig. 599. — Scheme indicating the Course of the Optic Nerve-fibres FROM the Retina to the Cerebral Cortex (L. Testut's ' Anatomie HUMAINE '). a.s. Left Eye o.ii. Right Eye t. Temporal Zone of Retina ft. Nasal Zone of Retina T.N. Temporal and Nasal Por- tions of the Field of Vi- sion for the Left Eye T'N'. The corresponding por- tions of the Right Eye D. The Right Half, and S, the Left Half, of the Field of Vision 1. Optic Nerve 1'. Its Direct Fibres (in red) i". Its Crossed Fibres (in yel- low on left side, and blue on right side) 2. Optic Commissure 3. Optic Tract 3'. Direct Fibres of Optic Tract 3". Crossed Fibres of Optic Tract 3"'. Commissure of Gudden • Nuclei of Interruption Optic Radiation Direct Fibres Crossed Fibres Cerebral Cortex (Mesial Aspect of Occipital Lobe) Posterior Cornu of Lateral Ventricle THE NERVOUS SYSTEM I4»7 the strand of fibres forming the optic radiation, the higher visual centre being situated in the cortex of the cuneate and lingual gyri of the mesial surface of the occipital lobe. The inner or com- missural root of the optic tract passes beneath the internal genicu- late body, which represents the nucleus of most of its fibres. As stated, these fibres have no connection with the optic nerve. Having traversed the inner part of the optic tract, they cross in the back part of the optic commissure, behind the decussating fibres, and are continuous with the corresponding fibres of the opposite side. Taese are the fibres which constitute the commissure of Gudden. Summary of the Optic Tract. — ^The outermost fita-es of each optic tract form the outer portion of the optic nerve of the same side. Most of the other fibres cross in the optic commissure, and form the inner portion of the optic nerve of the opposite side. The innermost fibres cross in the back part of the optic commissure, and form the commissure of Gudden. Optic Radiation. — The strand of fibres which forms the optic or thalamo-occipital radiation of either side establishes a con- nection between the lower visual centres (extemal geniculate body, puhdnar, and upper quadrigeminal body) and the higher or cortical visual centre, which is situated (i) on the mesial surface of the occipital lobe, close to the calcarine fissure in the region of the cuneus and lingual gyrus, and (2) on the adjacent part of the extemal surface of the occipital lobe. The strand passes through the post-lenticular part of the internal capsule, and then passes backwards in the medullary substance of the occipital lobe, lying on the outer side of the posterior comu of the lateral ventricle. Thereafter the fibres pass in a radiating manner to the higher or cortical visual centre. The optic radiation consists of afferent or corticipetal and efferent or corticifugal fibres. The corticipetal fibres, for the most part, arise as the axons of the nerve-cells wdthin the pulvinar and extemal geniculate body, which are terminal nuclei of the retinal nerve- fibres, and they end in the higher or cortical visual centre. Some corticipetal fibres arise in the higher or cortical visual centre of the opposite side and cross in the splenimn of the corpus callosum. These fibres are of a commissural character. The corticifugal Jibres arise as the axons of the pyramidal cells of the cortex of the visual area of the occipital lobe, and they terminate in the pulvinar and upper quadrigeminal body. The lower visual centres are regarded as being connected with the nuclei of origin of the nerves which supply the ocular muscles, probably through means of the posterior longitudinal bundle. Mesencephalon. The mesencephalon is composed of the corpora quadrigemina, which form its upper or dorsal portion; the crura cerebri, which form its lower or ventral portion; and the aqueduct of Sylvius, which passes through it from the fourth ventricle below to the third ventricle above. 1428 A MANUAL OF ANATOMY Corpora Quadrigemina.— These are four rounded eminences, which, as just stated, form the dorsal portion of the mesencephalon. They are covered by the splenium of the corpus callosum, and are arranged m pairs, upper and lower, the upper pairs (nates) being larger than the lower pair (testes), but not quite so prominent. The four eminences are separated from each other by two grooves, longitudinal and transverse, which are arranged in a crucial manner! The longitudinal groove extends upwards as far as the posterior commissure, and it separates the upper and lower quadrigeminal bodies of one side from those of the other side. Its upper part lodges the pineal body, and from its lower part a band of white Middle Commissure Pineal Peduncle •» Third Ventricle (Habenula) < - Optic Thalamus Upper Quadrigeminal Body ' '"JS^— L'-'^^'' Quadrigeminal Body ^i^-**\- Crus Cerebri , ' Frenulum Veli -~ Valve of Vieussens ~«Superior Peduncle of Cerebellum ■■^Do., do. (cut) Striae Acusticse "^^^NTrigonum Acusticum (base) ^^^^Trigonum Hypoglossi ^^ Trigonum Vagi ■-^.Tubercle of Rolando "xClava - Funiculus Gracilis Funiculus Cuneatus Fig. 600. — The Floor of the Fourth Ventricle and Adjacent Parts. Eminentia Teres M^Jw' ' Superior Fovea ,_S«W ^ Striae Acusticae.Z^T^Z^^ Inferior Fovea Cuneate Tubercle - - fibres, called the frenulum veli, passes downwards to the superior medullary velum or valve of Vieussens, which lies below the lower pair of eminences. The transverse groove separates the upper pair of quadrigeminal bodies from the lower pair. Laterally each eminence is connected with a white band, called the brachium, the two brachia being separated by a continuation of the transverse groove. The superior brachium extends outwards and forwards from the upper quadrigeminal body to the external geniculate body and the outer root of the optic tract. It passes between the pulvinar of the optic thalamus and the internal geniculate body. Its fibres terminate within the internal geniculate body. These fibres are derived from the lateral or acoustic fillet, partly directly, and partly through the intervention of the lower quadrigeminal body. THE NERVOUS SYSTEM 1429 The superior brachium is associated with the vtsual apparatus. The inferior brachium, though connected with the internal genicu- late body, with which body the inner or commissural root of the optic tract (commissure of Gudden) is also connected, is associated with the acoustic apparatus. The superior brachium contains two sets of fibres, namel}^ retinal fibres, derived from the outer root of the optic tract, and (2) occipital fibres, from the cortex of the occipital lobe of the cerebrum. , , ^, , , . The inferior brachium passes upwards from the lower quadn- geminal body to the under aspect of the internal geniculate body. Optic Commissure ■ _ Optic Nerve Infundibulum Tuber Cinereum Corpus Albicans Mesial Root of Optic Tract Lateral Root of Optic Tract .i'^. External Geniculate BodyX. »• Locus Perforatus Posticus ^ Sixth Nerve Facial Nerve _ Pars Intermedia of Wrisberg. _" ~~ Auditory Nerve.. Glosso-pharyngeal Nerve Pneumogastric Nerve Superficial Arcuate Fibres - Spinal Accessory Nerve-" First and Second Cervical Nerves ' Optic Tract Third Nerve Fonrth Nerve Motor Root of Fifth Nerve Sensory Root of Fifth Nerve Middle Peduncle of Cerebellum Restiform Body Hypoglossal Nerve Anterior Median Fissure Decussation of the Pyramids Fig. 601. — The Medulla Oblongata, Pons Varolii, and Interpedunculak Region. C.C, Crus Cerebri ; P., Pyramid ; O.B., Olivary Body. which is a small oval mass on the lateral aspect of the mesen- cephalon, under cover of the pulvinar of the optic thalamus. Though the inner root of the optic tract is connected with the internal geniculate body, the inferior brachium passes clear of it, and the most of its fibres are traceable to the optic thalamus through the tegmentum. Structure of Corpora Quadrigemlna. — The lower quadrigeminal body [col- liculiis inferior B.) is composed of the following parts: 1 . A central nucleus of grey matter. 2. A dorsal layer of white matter. 3. A ventral layer of white matter. The central grey nucleus consists of many multipolar cells and nerve-fibres. The axons of the cells pass partly to the dorsal and partly to the ventral layers of white matter. The nerve-fibres are derived from the lateral or I430 A MANUAL OF ANATOMY acoustic ftUet, and they terminate in arborizations around the cells of the central nucleus. The dorsal white layer derives its fibres from the lateral fillet and from the axons of the cells of the central grey nucleus. The fibres pass into the inferior brachium, by which they are conducted to the internal geniculate body. The ventral white layer also derives its fibres from the lateral fillet and from the axons of the cells of the central grey nucleus. This layer separates the central nucleus from the subjacent grey matter of the aqueduct of Sylvius. Some of the fibres cross the median plane, and decussate with corresponding fibres of the opposite side, superficial to the roof of the aqueduct of Sylvius. Others enter the tegmentum of the crus cerebri of the same side and also of the opposite side, in which their course is downwards in the lateral fillet. The lower quadrigeminal body {colliculus inferior B.), which receives its fibres from the lateral or- acoustic fillet, is associated with the acoustic ap- paratus. The upper quadrigeminal body [colliculus superior B.) is composed of the following layers: 1. Stratum zonale. 3. Stratum opticum. 2. Stratum cinereum. 4. Stratum lemnisci. The stratum zonale is the most superficial layer, and probably consists of retinal fibres which are derived from the outer root of the optic tract. Many of these fibres pass into the stratum cinereum and terminate in connection with its cells. Others cross the median plane and decussate with corre- sponding fibres from the opposite side, superficial to the roof of the aqueduct of Sylvius. The stratum cinereum, or second layer, lies beneath the stratum zonale, and consists of a crescentic layer of grey matter, containing many nerve-cells. It represents the grey nucleus of the upper quadrigeminal body, and the axons of its cells pass to the more deeply seated strata. The stratum opticum is the third layer, and it consists of grey matter, which contains numerous nerve-cells and nerve-fibres. The fibres are con- ducted to this stratum by the superior brachium, and they are of two kinds : (i ) Many are retinal fibres and are derived from the outer root of the optic tract. (2) Others are coriicifugal fibres, which come from the higher visual centre in the cortex of the occipital lobe and form part of the optic radiation. The fibres pass into the stratum cinereum and terminate in arborizations around its cells. The axons of the cells of the stratum opticum pass into the stratum lemnisci. The stratum lemnisci is the deepest layer. Like the stratnm opticum, it consists of grey matter, which contains numerous nerve-cells and nerve- fibres. The fibres are derived from the following sources: (i) Many are derived from the mesial or main fillet; and (2) some are the axons of cells belonging to the stratum opticum and stratum lemnisci. The fillet-fibres terminate in the stratum lemnisci. The fibres formed by the axons of the cells of the stratum opticum and stratum lemnisci cross the median plane and decussate with the corresponding fibres of the opposite side. This decus- sation is known as the fountain-decussation of Meynert. The fibres, after crossing, form the ventral longitudinal bundle, or tectospinal tract, of that side, and this bundle or tract descends through the pons Varolii and medulla oblongata into the corresponding ventral or antei:y)r column of the spinal cord. The upper quadrigeminal body, through means of the superior brachium, is one of the three lower visual centres, the other two being the pulvinar and the external geniculate body, both of which belong to the optic thalamus. Development of Corpora Quadrigemina. — ^The corpora quadrigemina are developed from the dorsal wall or roof of the mesencephalon. Commissure of Meynert. — Tliis commissure or decussation con- .sists of fibres which issue Irom each upper quadrigeminal body and THE NERVOUS SYSTEM 1431 cross to the opposite posterior longitudinal bimdle, in which they descend towards the pons Varolii. Crura Cerebri. — The crura or pedunculi cerebri are two large strands which are situated above the pons Varolii. They He at first near each other, being separated by the interpeduncular fossa, but afterwards diverge as they pass upwards and outwards to the cerebral hemispheres. The inner surface of each cms looks towards the interpeduncular region, and it presents a furrow, called the ocido-motor sulcus, through which the funiculi of the third cranial, or oculo-motor, nerve emerge, near the pons. The outer surface looks towards the temporal lobe of the brain, which to a large extent overlaps the cms, and this surface also presents a furrow, called the sulcus lateralis. The slender fourth cranial nerve Ues upon this surface. Close to the cerebral hemisphere the ventral and outer aspects of the cms are embraced by the optic tract of the corresponding side. Each cms is composed of two parts — ventral and dorsal. The ventral part is variously known a^ the crosta, basis, or pes, and the dorsal part is called the tegmentum. The separation between these two parts is indicated superficially by the sulcus lateralis on the outer surface, and the oculo- motor sulcus on the inner SUr- ^^g^"^**^ Corpora Quadrigemina face. Within the cms the two /X\_^^T^ parts are separated by a mass (...l.-tA ) ^. tegmentum of dark grey matter, called the /^ ? A Lateral Sulcus substantia nigra. J ^ K The crusta is continuous su- / \ j\ periorly ^vith the internal cap- ( V yT ^""^'^ sule of the corpus striatum, and V Nv^/\..x^ --^— Crusta interiorly its fibres enter the ven- ^ — ^^^ ^^r;- — ^ tral part of the pons VaroUi. ^"tjcuio-Motor suicm The upward prolongation of the p^^ 602 -Topogr.^phy of the Cros tegmentum constitutes the sub- Cerebri (after Poirier). thalamic tegmental region. Structure of the Crusta, Basis, or Pes. — ^The crusta, as seen in transverse section, presents a crescentic outline, the concavity of the crescent being occupied by the convexity of the substantia nigra. It consists of longitudinal corticifugal fibres, which arise in the cells of the cerebral cortex. These fibres form two groups — • pyramidal and cortico-pontine. The pyramidal fibres, on either side, constitute the motor tract from the pre-Rolandic or motor region of the cortex of the frontal lobe, and they arise, for the most part, from the cells of that region, which control the muscles of the upper and lower limbs, as weU as the muscles of the face, though indirectly. Tegmentum.— The tegmentum is continuous interiorly with the formatio reticularis of the dorsal portion of the pons Varolii, which in turn, is continuous interiorly with the formatio reticularis of the medulla oblongata. The two tegmenta, right and left, are separated 1432 A MANUAL OF ANATOMY from each other by a median raphe, which is continuous with that of the pons VaroHi. In the lower part of the mesencephalon this raphe is indistinct on account of the decussation which takes place across the median plane between the superior cerebellar peduncles, underneath the lower pair of quadrigeminal bodies. The dorsal surface of each tegmentum extends on either side of the grey matter of the aqueduct of Sylvius, and becomes continuous with the basal parts of the upper and lower quadrigeminal bodies of the corresponding side. The ventral surface is separated from the crusta by the substantia nigra. Structure of the Tegmentum. — Each tegmentum, as stated, is continuous inferiorly with the formatio reticularis of the dorsal portion of the pons Varolii. It consists of bundles of longitudinal fibres, separated by bundles of curved fibres which pass trans- versely. The intervals between these bundles are occupied by grey matter. Grey Matter. — ^The grey matter of the tegmentum contains the red nucleus. The red nucleus {nucleus ruber) is a round reddish mass, which is situated in the centre of the upper part of the tegmentum, and it lies in the path of the superior cerebellar peduncle of the opposite side. It corresponds to the position of the upper quadrigeminal body, and is prolonged upwards into the subthalamic tegmental region. Some of the fibres of the superior cerebellar peduncle of the opposite side surround the red nucleus in the form of a capsule on their way to the optic thalamus. Other fibres of that peduncle enter the red nucleus and terminate in arborizations around its cells. The axons of the cells of the red nucleus form two sets of nerve- fibres — ascending and descending. The ascending fibres pass to the optic thalamus, in company with those fibres of the superior cere- bellar peduncle which encapsule the red nucleus. These ascending fibres form relays which carry on those fibres of the superior cere- bellar peduncle which terminate within the red nucleus, that nucleus being a cell-station in their path. The descending fibres constitute the rubrospinal tract, or bundle of Monakow. The fibres of this tract cross the median plane in the raph6, and by their decussation with those of the opposite side they constitute the fountain-de- cussation of Forel, in contradistinction to the fountain-decussation of Meynert. The latter decussation is on a higher level, and in- volves the fibres of the ventral longitudinal bundles, or tectospinal tracts, which derive their fibres from the cells of the stratum opticum and stratum lemnisci of the upper quadrigeminal bodies. The rubro-spinal tract of either side descends through the pons Varolii and medulla oblongata into the lateral column of the spinal cord, where each constitutes the prepyramidal tract, which lies on the ventro-lateral aspect of the crossed pyramidal tract. (The tecto- spinal tract, or ventral longitudinal bundle, on either side, descends into the anterior column of the spinal cord.) THE NERVOUS SYSTEM 1433 White Matter of the Tegmentum. — ^The principal tracts of the white matter on either side are as follows : 1. Superior cerebellar peduncle. 2. Dorsal longitudinal bundle. 3. Ventral longitudinal bundle, or tecto-spinal tract. 4. Rubro-spinal tract. 5. Mesial fillet (chief sensory tract). 6. Lateral (acoustic) fillet. Superior Cerebellar Peduncle. — ^The fibres of this peduncle emerge, for the most part, through the hilum of the nucleus dentatus in the cerebellar hemisphere. The two peduncles, right and left, having emerged from the hemispheres, pass upwards on the lateral parts of the dorsal surface of the pons Varolii in a converging manner towards the lower pair of the quadrigeminal bodies, being connected by the valve of Vieussens . On entering the mesencephalon, the two peduncles decussate across the raphe beneath the lower quadri- geminal bodies. This decussation extends as high as the upper quadrigeminal bodies, and it involves almost all the fibres of the two peduncles. Each peduncle, having gained the opposite side, ascends in the upper part of the tegmentum as a longitrudinal tract, and soon comes into contact with the red nucleus. Many of its fibres enter this nucleus and terminate in aborizations around its cells. Other fibres of the peduncle encapsule the nucleus, and then ascend through the subthalamic tegmental region to the anterior part of the optic thalamus, within which they terminate in arborizations around the cells of the anterior nuclear area (chief sensory nucleus). From the cells of the red nucleus relays of fibres proceed upwards, which carry on those fibres of the peduncle which terminate within the nucleus, and these relays ascend with those fibres of the peduncle which encapsule the red nucleus to the optic thalamus. From the cells of the optic thalamus other relays of theilamo-corticipetal fibres arise, which pass through the internal capsule to the cerebral cortex, more particularly the cortex of the ascending parietal or post-central gyrus, which lies directly behind the fissure of Rolando. The superior cerebellar peduncle of one side connects the cere- bellar hemisphere of that side with the post-Rolandic region of the cerebral cortex of the opposite side, the red nucleus and the optic thalamus being cell-stations in the path of the fibres. A few of the fibres of each superior cerebellar peduncle do not take part in the decussation beneath the lower pair of quadrigeminal bodies, but ascend to the red nucleus of their own side. Before the fibres decussate, or after the decussation has taken place, each of them furnishes a descending branch. These de- scending branches form the descending cerebeUar bundle of Cajal, which traverses the dorsal part of the pons Varolii and the medulla oblongata, giving off collaterals to the motor nuclei of these parts. According to Cajal, the fibres of this bundle enter the anterior 1434 ^ MANUAL OF ANATOMY column of the spinal cord, and are connected with the cells of the ventral cornu of grey matter. The superior cerebellar peduncle is almost entirely an ascending tract, but a few of its fibres are regarded as arising within the optic thalamus and as descending to the cerebellar hemisphere. Dorsal or Posterior Longitudinal Bundle. — ^This bundle occupies the dorsal part of the tegmentum, and is intimately related to the grey matter which forms the ventral wall or floor of the aqueduct of Sylvius. It lies close to the median raphe, as dofes its fellow of the opposite side, and across the raphe an interchange of fibres takes place between the two bundles. In the spinal cord it is represented by the anterior ground-bundle and the anterior mar- ginal bundle of Lowenthal. In the medulla oblongata it traverses the dorsal part of the pyramid, being separated fiom the pyramidal (motor) fibres by the mesial fillet or chief sensory tract. There- after it traverses the formatio reticularis of the dorsal part of the pons Varolii, and is continued upwards as one of the tracts of the .tegmentum of the cms cerebri. The fibres of the dorsal longitudinal bundle are regarded as being the axons of cells belonging to (i) the nucleus of Deiters, which is one of the terminal nuclei of the vestibular root of the auditory nerve, (2) the formatio reticularis of the medulla oblongata and pons Varolii, (3) the formatio reticularis of the tegmentum, (4) the sensory nucleus of the fifth cranial nerve, and (5) the nucleus of the dorsal longitudinal bundle. Inferiorly the fibres of the bundle ramify within the anterior column of the spinal cord in connection with the motor cells of the ventral cornu of grey matter. Superiorly its fibres are intimately related to the following important nuclei — namely, (i) the oculo-motor nucleus, or nucleus of the third cranial nerve; (2) the trochlear nucleus, or nucleus of the fourth cranial nerve; and (3) the abducent nucleus, or nucleus of the sixth cranial nerve, these being the nuclei which control the muscles of the eyeball and upper eyelid. The bundle furnishes numerous col- laterals to each of these nuclei, which terminate in arborizations around their cells. The bundle also establishes connections with the motor nuclei in the pons Varolii and medulla oblongata. The dorsal longitudinal bundle extends as high as a special nucleus, called the nucleus of the dorsal longitudinal bundle, which is situated in the grey matter of the ventro-lateral portion of the third ventricle, near the upper opening of the aqueduct of Sylvius, from the cells of which nucleus some of its fibres arise. The dorsal longitudinal bundle consists of ascending and descend- ing association-fibres, which form connections between the impor- tant nuclei just referred to. Probably the chief use of the bundle is to maintain a functional association between these nuclei, and insure harmonious action of the muscles which are supplied by the nerves arising from them. Ventral or Anterior Longitudinal Bundle. — ^This bundle consti- tutes the tectospinal tract, and it lies on the ventral aspect of the i THE NERVOUS SYSTEM 1435 dorsal longitudinal bundle. Its fibres are derived from the stratum opticum and stratum lemnisci of the upper quadrigeminal body of the opposite side. These fibres, as stated in connection with the upper quadrigeminal bodies, cross the median plane and decussate with the corresponding fibres of the opposite side, the decussation being known as the fcmntain-decussaiion of Meyneri. The fibres descend through the tegmentimi, Ipng close to the red nucleus, to which they furnish collaterals. Thereafter they traverse the formatio reticularis of the pons Varolii and medulla oblongata, still lying on the ventral aspect of the dorsal longitudinal bundle. From the medulla oblongata the fibres pass into the anterior ground-bimdle of the ventral column of the spinal cord, in associa- tion with the fibres of the dorsal longitudinal bundle, and they form arborizations around the motor cells of the ventral comu of grey matter. Rubro-Spinal Traet, or Bundle of Monakow.— The fibres of this tract are derived, as previously stated, from the axons of the cells of the red nucleus. They cross the median plane, decussating with the corresponding fibres of the opposite side, and constituting the fountain-decussation of Ford. The tract then descends through the pons Varolii and medulla oblongata into the lateral colvmm of the spinal cord, in which it constitutes the prepyramidal tract on the ventro-lateral aspect of the crossed p\Tamidal tract. Mesial FlUet. — ^The mesial or main fillet of either side, which represents the chief sensory tract, commences in the lower part of the medulla oblongata. It here constitutes the only fillet on either side, and its fibres are derived from the deep lemniscal arcuate fibres, which arise from the cells of the nucleus gracilis and nucleus cimeatus of the opposite side. The main fillet there- fore represents the upward continuation of the posterior column of the spinal cord (columns of Goll and of Burdach), and it is spoken of as the chief sensory traet. The deep lemniscal arcuate fibres, as previously stated, cross the median plane directly above the decussation of the pyramids {motor decussation), and they decussate with the corresponding fibres of the opposite side, thus constituting the decussation of the fillets (main fillets, or chief sen- sory tracts), or the sensory decussation. The fibres, after crossing the median plane, form the fillet of the side to which they have crossed. In the medulla oblongata it lies close to the median raphe, and at first is internal to the dorsal longitudinal bundle. Subsequently, however, the main fillet takes up a position in front of the dorsal longitudinal bundle, and directly behind the p^nramid. The main fillet then ascends through the dorsal part of the pons Varolii, its relative position remaining unchanged. In this situa- tion the lateral fillet, to be presently described, takes up its position on the outer or lateral aspect of the main or mesial fillet. The main fillet, on leaving the pons Varolii, enters the ventral part of the tegmenttmi, still having the lateral fillet on its outer side. As it encoimters the red nucleus, it is displaced outwards and back- 1436 A MANUAL OF ANATOMY wards, and then occupies the dorso-lateral part of the tegmentum, lying almost beneath the internal geniculate body. The fibres of the main or mesial fillet (chief sensory tract) termi- nate in two ways, (i) Some enter the upper quadrigeminal body, and these probably terminate in the stratum lemnisci. (2) Others traverse the subthalamic tegmental region and enter the anterior part of the optic thalamus, within which they terminate in arbori- sations around the cells of the anterior nuclear area (chief sensory nucleus). From these cells relays of thalamo-corticipetal fibres proceed to the cerebral cortex. It is convenient to refer to the main or mesial fillet as the sensory fillet. Lateral Fillet. — ^The main or mesial fillet being the sensory fillet, it is convenient to refer to the lateral fillet as the acoustic fillet. The fibres of this fillet are derived from the following sources: (i) The corpus trapezoides, the fibres of which come from the ventral cochlear nucleus, the nucleus trapezoides, and the superior olive of the opposite side, as well as from the superior olive of the same side; (2) the striae acusticse, which are derived from the lateral cochlear nucleus of the opposite side; and (3) the nucleus of the lateral fillet. The fibres of the right and left lateral fillets decussate across the median plane. Having crossed to the opposite side, the fibres become longitudinal and form a well-marked ascending tract in the dorsal part of the pons Varolii, which takes up a position on the lateral or outer side of the main or mesial fillet. In this part of its course the lateral fillet encounters a collection of grey matter, called the nucleus of the lateral fillet. Some of its fibres end in this nucleus. Others pursue their upward course, and are reinforced by relays of fibres which arise from the nerve-cells of the nucleus. On leaving the pons Varolii the lateral fillet enters the tegmentum, and its fibres terminate in (i) the nuclei of the lower quadrigeminal body, and (2) the cells of the internal geniculate body. The fibres destined for the lower quadrigeminal body, having curved round the outer aspect of the superior cerebellar peduncle, become super- ficial on the outer side of the tegmentum. The fibres destined for the internal geniculate body reach it through the inferior brachium, partly directly and partly through the intervention of the lower quadrigeminal body. The axons of the cells of the internal genicu- late body form corticipetal fibres which pass to the cortex of the first or superior temporal gyrus of the temporal lobe. The lateral fillet, as previously stated, is associated with the auditory apparatus. It is chiefly composed of ascending fibres. There are, however, some descending fibres which are probably derived from the lower quadrigeminal bodies. In addition to the foregoing tracts there other tracts. Fasciculus Retroflexus. — The fibres of this bundle, already described, arise from the cells of the ganglion habenulcB. They descend in the upper part of the tegmentum, internal to the red nucleus, and they terminate in arboriza- tions around the cells of the interpeduncular gangUon. THE NERVOUS SYSTEM 1437 Central Tract. — ^The fibres of this tract descend from the optic thalamus, or, it may be, from the nucleus lenticularis of the corpus striatum, through the pons Varolii into the medulla oblongata. Its fibres are regarded as terminating in connection with the inferior ohvjiry nucleus. Bundle ol Manzer. — The fibres of this tract descend from the lower quadri- geminal body to the formatio reticularis of the lateral part of the pons \'arolii. Spino-thalamlc Tract. — The fibres of this tract, as stated in connection with the tracts of the spinal cord, arise from the cells of the dorsal grey comu of the opposite side. Having crossed in the ventral or white commissure, they enter the antero-lateral or indirect cerebellar tract (tract of Gowers) in which they ascend through the medulla oblongata, pons Varolii, and tegmentum of the cms cerebri to the optic thalamus of the side to which they have crossed. Subthalamic Tegmental Region. — ^This region represents the up- ward prolongation of the tegmentum of the cms cerebri beneath the posterior part of the inferior or ventral surface of the optic thalamus. The prolongation contains (i) an upward extension of the red nucleus of the tegmentum, (2) the fibres of the superior peduncle of the cerebellum, and (3) the main or mesial fillet (chief sensory tract). The upnard extension of the red nucleus ceases about the level of the corresponding corpus mammillare. Some of the fibres of the superior peduncle of the cerebellum terminate, as stated, in the red nucleus, and others encapsule it, as they do in the tegmentum. Many fibres issue from the cells of the red nucleus, and these, along with the investing fibres of the superior cerebellar peduncle, enter the inferior or ventral surface of the optic thalamus. The main fillet (chief sensory tract), which lies on the dorso- lateral aspect of the red nucleus, also enters the inferior or ventral siurface of the optic thalamus. Development ol the Crura Cerebri. — ^The crura cerebri are de- veloped from the ventral wall of the mesencephalon. Crusta or Pes. — The crusta or pes is, as stated, the ventral portion of the cms cerebri, and it is separated from the tegmentum of the cms by a mass of dark grey matter, called the substantia nigra, which is situated in the interior. Externally the separation is indicated on the outer aspect by the lateral sulcus, and on the inner aspect by the oculo-motor sulcus, through which the fasciculi of the oculo- motor nerve emerge. The crusta is continuoiis with the internal capsvde of the corpus striatum, and it consists of longitudinal centri- fugal fibres, which arise in the cells of the cerebral cortex. These fibres are arranged in two sets, namely, pyramidal and cortico- pontine. The pyramidal fibres form the motor tract from the Rolandic region of the cerebral cortex; and the cortico-pontine fibres are arranged in two strands, namely, fronto-pontine and temporo-pontine. The pyramidal fibres form the motor tract from the Rolandic region of the cerebral cortex. They traverse the lenticular portion of the posterior limb of the internal capsule, and then occupy the middle three-fifths of the crusta. Thereafter they descend through the ventral portion of the pons Varolii and the pyramid of the H38 A MANUAL OF ANATOMY medulla oblongata. In the lower part of the pyrcimid they give rise to the crossed and direct pyramidal tracts. The crossed pyramidal tract, having taken part in the decussation of the pyramids, descends in the spinal cord, occupying the posterior part of the lateral column of the opposite side. The direct pyra- midal tract descends in the spinal cord, occupying the inner portion of the anterior column of the same side, and forming the column of Tiirck. Its fibres, however, cross at intervals to the opposite side. As the pyramidal tract descends through the pons Varolii and meduUa oblongata, some of its fibres pass to the motor nuclei of the cranial nerves in these regions. The cortico-pontine or cortico-protuberantial fibres are arranged in two strands, fronto-pcntine and temporo-pontine. The fibres Aqueduct of Sylvius, _A Corpora Quadrigemina Grey Matter around Aqueduct of Sylvius Red Nucleus of Tegmentum Temporo-Pontine Fibres —Locus Niger _ Pyramidal Fibres -.>^ Fronto Pontine Fibres Oculo-Motor Sulcus Fig. 603. — Transverse Section of the Crus Cerebri (after Poirier). of the fronto-pontine strand arise from the cells of the cortex of the anterior part of the frontal lobe, and, having traversed the anterior limb of the internal capsule, they are regarded as occupying the inner fifth of the crusta. The fibres of the temporo-pontine strand arise from the cells of the cortex of the temporal lobe, and, having traversed the postlenticular part of the internal capsule, they occupy the outer fifth of the crusta. In the ventral part of the pons both the fronto-pontine and the temporo-pontine fibres terminate in arborizations around the cells of the nucleus pontis, whereas the pyramidal fibres pass uninterruptedly through the ventral part of the pons. Summary of the Crusta. — The crusta is divided into three parts. The middle three-fifths contain the fibres of the pyramidal or motor tract, the inner fifth probably contains the fibres of the fronto-pontine strand, and the outer fifth contains the fibres of the temporo-pontine strand. Substantia Nigra. — This is a mass of dark grey matter which is situated between the tegmentimi and the crusta of the crus cerebri. IJke the crusta, it is semilunar or crescentic, as seen in transverse section. It contains many multipolar nerve-cells, which are deeply pigmented, and it extends from the upper border of the pons THE NERVOUS SYSTEM 1439 Varolii into the subthalamic tegmental region. Laterally it reaches the lateral sulcus on the outer asf)ect of the cms, where it is thin, and the oculo-motor sulcus on the inner aspect, where it is thick and is traversed by the fasciculi of the third cranial or oculo-motor nerve. Its tegmental surface is concave, and the surface directed towards the crusta is convex. From the latter surface prolonga- tions extend into the crusta. Aqueduct of Sylvius. — The aqueduct of Sylvius is the narrow passage which leads through the mesencephalon from the third to the fourth ventricle [iter a tertio ad quartutn ventriculum). It lies nearer the dorsal than the ventral aspect of the mesencephalon ; its direction is from above downwards; and its length is rather more than I inch. Its upper opening is situated on the posterior boundary of the third ventricle, immediately underneath the posterior com- missure, and its lower opening occupies the superior median angle of the floor of the fourth ventricle. In transverse section the aqueduct is T-shaped in its upper part, near the third ventricle, and triangular in its lower part, near the fourth ventricle. The passage is lined with ciliated columnar epitheUum, external to which there is a thick layer of grey matter, which is spoken of as the Sylvian grey matter. This is continuous superiorly with the grey matter of the floor and lateral walls of the third ventricle, and in- feriorly with that which covers the floor of the fourth ventricle. It contains numerous nerve-cells, disposed in a scattered manner, but, in addition to these, there are certain definite cell-groups. These groups constitute the nuclei of origin of the follo%ving cranial nerves: the third or oculo-motor, the fourth or trochlear, and the descending or mesencephalic root of the fifth nerve. The oculo-motor nucleus is situated in the ventral portion of the Sylvian grey matter, imdemeath the upper quadrigeminal body, and it extends upwards into the layer of grey matter on the adjacent portion of the lateral wall of the third ventricle. The trochlear nucleus is also situated in the ventral portion of the SyMan grey matter, but at a lower level than the oculo-motor nucleus, being placed imdemeath the upper part of the lower quadrigeminal body. The nucleus of the descending or mesencephalic root of the fiftii nerve is extensive, and is situated in the lateral portion of the Sylvian grey matter. Development — ^The aqueduct of Sylvius is the perststent remains of the cavity of the mesencephalon. Locus Perforatus Posticus. — This space has been previously described, in a general way, in connection with the base of the encephalon. It will here be considered more fully. It Ues at the bottom of a deep depression, called the interpeduncular fossa {fossa Tarini), which forms the back part of the mterpeduncular space. The fossa is boimded posteriorly by the median portion of the upper border of the pons VaroUi, and laterally bv the crura cerebri .4m- teriorly it is limited by the corpora mammillaria. t440 A MANUAL OF ANATOMY The locus perforatus posticus is a perforated lamina of grey matter which forms the floor of the interpeduncular fossa, the openings being for the passage of the postero-mesial central or ganglionic branches of the posterior cerebral arteries. This grey lamina extends between the tegmenta of the crura cerebri, and it is hence known as the pons Tarini. Ganglion Interpedunculare. — This is a collection of nerve-cells, situated mesially in the lower part of the grey lamina which con- stitutes the locus perforatus posticus. On either side it receives the fibres of the fasciculus retroflexus, which are derived from the ganglion habenulae. Structure of the Cerebral Hemispheres. The cerebral hemisphere is composed of grey and white matter. The grey matter is disposed externally, and forms the cerebral cortex. The white matter occupies the interior, and constitutes the medullary centre. Cerebral Cortex. — The grey matter forms a continuous covering to the entire hemisphere, dipping into the sulci, so as to cover the opposed surfaces of the gyri, as well as the bottom of the sulci. It is thicker over the superficial surfaces of the gyri than at the bottom of the sulci, and attains its greatest thickness over the upper portions of the precentral and post -central g5^i, whilst it is thinnest over the occipital lobe. The cerebral cortex is indistinctly divided into strata by means of layers of a whitish substance. When examined on section it therefore presents a stratified appearance, and is seen to consist of successive grey and white layers, alternating with each other. In most parts of the cerebral cortex there are four superimposed strata; but in certain situations, e.g. over the precentral gyrus, there are as many as six. These strata are as follows, from without inwards : 1. Superficial white layer (pale and narrow). 2. Superficial grey layer. 3. Outer white band of Baillarger. 4. Middle grey layer. 5. Inner white band of Baillarger. 6. Inner or deep grey layer, subjacent to which is the white matter of the medullary centre. The medullated fibres of the medullary centre pass into the stratified grey cortex in a radiating manner, and within the cortex their course, for the most part, is perpendicular to the superficial surface, and between the component cells of the cortex. Minute Structure of the Cerebral Cortex. — The cortex is com- posed of nerve-cells and nerve-fibres. Nerve-cells. — These are arranged in four layers, which are as follows from without inwards; (i) the molecular layer; (2) the THE NERVOUS SYSTEM 1441 Molecular | Flexifonn Layer Layer of Small ^ Pyramidal Cells Layer of Large ^ Pyramidal CelU Layer of Polymorphous ^ CelU Plexus of Exnei (Superficial TangeDtial Fibres) Deep Tangentia' Fibres White Medullary Centre Fig. 604. — Diagram showing the Minute Structure of the Cerebral Cortex (Poirier). The Fibres are shown on the right, and the Cells on the left. 91 1442 A MANUAL OF ANATOMY layer of small pyramidal cells; (3) the layer of large pyramidal cells ; and (4) the layer of polymorphous cells. The molecular or plexiform layer, which is the most superficial, is thin and consists of cells and fibres. Many of the cells are neuroglia-cells, the others being nerve-cells. These nerve-cells are for the most part fusiform, and are disposed horizontally. They are known as the horizontal cells of Cajal. Their dendrons and axons are long, the latter forming meduUated fibres which are disposed horizontally or parallel to the surface. These furnish minute branches which pass vertically towards the surface. The horizontal cells, according to Cajal, receive impulses from the corticipetal fibres which extend from the optic thalamus to the cerebral cortex. In addition to these Terminal Ramifications fibres there are many others which enter the molecular layer from deeper sources, and form a dense interlace- ment by their ramifi- cations. The sources from which these ex- traneous fibres are de- rived are as follows: (i) the terminal rami- fications of the apical dendrons of the pyra- midal cells (small and large) ; (2) the axons of the cells of Martin- otti; and (3) corticipe- tal fibres derived from the medullary centre of the gyrus. The pyramidal layers represent the second and third layers, and are composed of characteristic pyramidal cells which are peculiar to the cerebral cortex, those of the second layer being small, whilst those of the third layer are large. The layer of small pyramidal cells is narrow, but the layer of large pyramidal cells is of considerable thickness. There is no well-marked line of demarcation between these two layers, the one passing imperceptibly into the other. They con- stitute the chief part of the cerebral cortex. The apex of each pyramidal cell is directed towards the surface of the gyrus, and is prolonged into a long tapering dendrite, which passes into the molecular layer, giving off delicate collaterals in its course. Near the surface of the molecular layer it divides into terminal filaments, which are disposed horizontally and mingle with Apical Dendrite, giving off Collaterals ^-^— Body of Cell L/L Lateral Dendrites ..Axon, giving off Collaterals Fig. 605. — A Pyramidal Cell of the Human Cerebral Cortex (Ramon y Cajal). THE NERVOUS SYSTEM 1443 the tangential fibres. The base of the pyramidal cell is directed towards the medullary centre of the gyrus, and from its centre an axon is given off, which enters the medullary centre, giving off collaterals in its course. From each side of the body of the cell, as well as from each lateral angle of its base, dendrites are given off. The polymorphous layer is the deepest layer, and is composed of cells which have different shapes. Each cell gives off several den- drites, which pass towards, but do not enter, the molecular layer. The axon of each cell enters the medidlary centre as a nerve-fibre. In addition to the foregoing cells of the cerebral cortex, two other kinds of cells are met with amongst the pyramidal and poly- morphous cells, namely, the cells of Golgi and the cells of Martin- otti. The cells of Golgi are characterized by the fact that the axon of each almost immediately divides into several branches, which pass towards the surface, but soon terminate without entering the molecular layer. The cells of Martinotti are chiefly met with in the poljTnorphous layer. The axon of each cell passes towards the surface, and enters the molecular layer, where it divides into terminal branches, which form part of the tangential fibres of this layer. Nerve-fibres of the Cortex. — These are arranged in two groups — vertical and tangential. The vertical (radial) fibres are disposed in radiating bundles, which issue from the medullary centre, and traverse the poly- morphous and large pyramidal layers, after which they become indistinguishable. The pol^Tuorphous and large pjrramidal cells lie in the spaces between these bundles, and assume a columnar arrangement. The fibres of the radiating bundles gradually become less nmnerous, some of them becoming the axons of the polymorphous cells, but most of them becoming the axons of the large pyramidal cells. The radiating bundles contain centripetal cortical fibres, which pass into the molecular layer and end in terminal ramifications, forming part of its tangential fibres. The tangential fibres are disposed horizontally at different levels, and form the following strata: (i) the superficial tangential fibres (plexus of Exner), which occupy the superficial part of the mole- cular layer; (2) the band of Bechterew, which is situated in the superficial part of the small pyramidal layer; (3) the outer band of Baillarger {band of Vicq d'Azyr), which intersects the large pyramidal layer; (4) the inner band of Baillarger, which is situated between the large pyramidal and polymorphous layers; and (5) the deep tangential fibres [intra-cortical association fibres), yihich are situated in the deep part of the polymorphous layer. The tangential fibres are formed by (i) the collaterals of the polymorphous and pyramidal cells and of the cells of Martinotti; (2) the ramifications of the axons of the cells of Golgi; and (3) asso- ciation fibres. Medullary Centre of Cerebral Hemisphere. — The white matter of the medullary centre consists of medullated nerve-fibres, which 1444 A MANUAL OF ANATOMY pursue different courses, and are arranged in three groups, namely, projection-fibres, commissural fibres, and association-fibres. The projection-fibres connect the cerebral cortex with parts at a lower level, and they are of two kinds — corticipetal or afferent, and corticifugal or efferent. The commissural fibres pass from one hemisphere to the other and connect portions of the cerebral cortex of opposite hemispheres. The association-fibres are confined to one side of the median plane, and they bring different parts of the cerebral cortex of the same hemisphere into association with one another. Projection-Fibres. — These fibres, as stated, are both corticipetal and corticifugal, and the majority of them constitute the internal capsule of the corpus striatum, and the diverging arrangement of its fibres known as the corona radiata, which passes to all parts of the cerebral cortex. Some projection-fibres, however, do not traverse the internal capsule and corona radiata — e.g., the fibres of the ansa peduncularis. Corticifugal Fibres. — The corticifugal or efferent fibres constitute the following tracts : 1. Pyramidal or motor. 3. Fronto-pontine. 2. Cortico-thalamic. 4. Temporo-pontine. 5. Optic radiation. The pyramidal or motor tract derives its fibres from the axons of the pyramidal cells of the cortex of the precentral gyrus, which is situated in front of the fissure of Rolando. Having traversed the corona radiata, these fibres pass, in succession, through (i) the posterior limb of the internal capsule, (2) the middle three-fifths of the crusta of the cms cerebri, (3) the ventral portion of the pons Varolii, and (4) the pyramid of the medulla oblongata. The motor strand enters the spinal cord in three ways — partly as the direct pyramidal tract or column of Turck — partly as the uncrossed lateral pyramidal tract — but chiefly as the crossed lateral pyra- midal tract. Ultimately the fibres terminate at different levels in arborizations around the motor-cells of the ventral cornu of grey matter of the opposite side, from which cells the fibres of the motor nerve-roots proceed. The cortico-thalamic tract extends only between the cerebral cortex and the optic thalamus. Its fibres arise as the axons of the pyramidal cells of various parts of the cerebral cortex, and they terminate in arborizations around the cells of the optic thalamus. The fronto-pontine tract does not extend lower than the pons Varolii. It consists of fibres which arise as the axons of the pyra- midal cells of the cortex of the prefrontal region — that is to say, the region of the frontal lobe in front of the precentral sulcus. These fibres traverse the anterior limb of the internal capsule, and then descend through the inner or mesial fifth of the crusta of the crus cerebri into the pons Varolii. Within the pons they terminate in arborizations around the cells of the nucleus pontis. The temporo-pontine tract, like the preceding, does not extend THE NERVOUS SYSTEM 1445 lower than the pons Varolii. It consists of fibres which arise as the axons of the p^Tamidal cells of the cortex of the first and second temporal gyri. These fibres traverse the post -lenticular part of the posterior limb of the internal capsule, and then descend through the outer fifth of the crusta of the cms cerebri into the ventral part of the pons Varolii. Within this part of the pons they terminate in arborizations aroimd the cells of the n ml ens pontis. The corticifugal fibres of the optic radiation consist of fibres which arise as the axons of the p5^amidal fibres of the cortex of the occipital lobe. They traverse the post -lenticular part of the pos- terior limb of the internal capsule, and thereafter pass to the lower visual centres, namely, the external geniculate body, the puhonar of the optic thalamus, and the upper quadrigeminal body. Within these bodies they terminate in arborizations around their com- ponent cells. Corticipetal Fibres. — The corticipetal or afferent fibres belong to the following tracts: 1. Mesial fillet. 3. Thalamic radiation. 2. Saperior cerebellar peduncle. 4. Auditory radiation. 5. Optic radiation. The mesial fillet, or principal sensory tract, arises from the nucleus gracilis and nucleus cimeatus of the medulla oblongata, and is the upward prolongation of the posterior column of the spinal cord. Having decussated with its fellow, it ascends through the dorsal part of the pons Varolii, through the tegmentmn of the cms cerebri, and through the subthalamic tegmental region to the optic thalamus. Within this body its fibres terminate in arborizations around the thalamic cells. As the mesial fillet ascends towards the optic thalamus some of its fibres enter the upper quadrigeminal body, in which they end. From the optic thalamus the fillet-fibres are continued to the cerebral cortex by relays of thalamo-cortical fibres. The superior cerebellar peduncle, having decussated with its fellow, soon comes into contact with the red nucleus. Many of the fibres of the pedimcle enter this nucleus and terminate in arboriza- tions around its cells. Numerous fibres encapsule the nucleus, and continue their course upwards, traversing the subthalamic tegmental region, and finally entering the ventral aspect of the optic thalamus, within which they terminate in arborizations around the thalamic cells. As in the case of the fillet-fibres, they are con- tinued to the cerebral cortex by relays of thalamo-cortical fibres. The thalamic radiation is composed of thalamo-cortical fibres which arise as the axons of the cells within the optic thalamus, that body being regarded as an aggregation of cell-stations in the path of such corticipetal fibres as those of the mesial fillet and superior cerebellar pedimcle. These thalamo-cortical fibres, as stated in the description of th? optic thalamus, issue from that body in four groups or stalks — frontal, parietal, occipital, and inferior or ventral. The fibres o£ the frontal stalk traverse the 1446 A MANUAL OF ANATOMY anterior limb of the internal capsule, and most of them pass to the cortex of the frontal lobe. The fibres of the parietal stalk pass partly through the internal capsule and partly through the external cap- sule to the cortex of the parietal lobe and of the Rolandic region of the frontal lobe. The fibres of the occipital stalk pertain to the optic radiation, to be presently described. The fibres of the in- ferior or ventral stalk form the ansa lenticularis and ansa peduncu- laris. The ansa lenticularis enters the nucleus lenticularis, within which its fibres terminate. The ansa peduncularis passes beneath the nucleus lenticularis and traverses the external capsule, the destination of its fibres being the cortex of the temporal lobe and island of Reil. The auditory radiation consists of fibres which arise as the axons of the cells of the internal geniculate body. Having issued from that body they traverse the post-lenticular part of the posterior limb of the internal capsule, and pass to the cortex of the middle part of the first temporal gyrus of the temporal lobe. The corticipetal fibres of the optic radiation are associated with the corticifugal fibres, already described. The corticipetal fibres arise as the axons of the cells of the pulvinar, corpus geniculatum externum, and upper quadrigeminal body. They traverse the post-lenticular part of the posterior limb of the internal capsule, and thereafter pass to the cortex of the occipital lobe. Commissural Fibres. — ^These fibres are disposed transversely, and serve to connect the grey cortex of one hemisphere with that of the other. They constitute the following commissures : (i) the corpus callosum ; (2) the anterior commissure ; and (3) the lyra or psalterium, which is known as the hippocampal commissure. The fibres of the corpus callosum, as they enter each hemisphere, are disposed so as to form an extensive callosal radiation, and serve to connect the cortex of one hemisphere with that of the other. The individual portions of cortex so connected may be symmetrical, but to a large extent they are asymmetrical. The fibres arise on one side as (i) the axons of pyramidal or of poly- morphous cells, or (2) collaterals of projection or of association fibres ; and on the opposite side they tenninate in delicate arboriza- tions. The anterior commissure, which crosses from side to side in front of the anterior pillars of the fornix, divides on either side into two parts, olfactory and temporal. The olfactory portion enters the olfactory tract. Some of its fibres serve to connect the olfactory bulb of one side with that of the other side ; and other fibres con- nect the olfactory bulb of one side with the temporal lobe of the opposite. The temporal portion enters the white matter of the temporal lobe on either side. The lyra or psalterium consists of transverse fibres which con- nect the hippocampus major of one side with its fellow of the opposite side ; hence the name hippocampal commissure. Association Fibres. — These fibres serve to connect different parts THE NERVOUS SYSTEM 1447 of the cortex of the same hemisphere, and they are of two kinds, short and long. The short association fibres pass between contiguous gyri, ex- tending in their course across the bottom of the sulci. Some of them lie beneath the grey cortex, whilst others are contained within its deep part. The long association fibres pass between portions of the grey cortex, which are at some distance from each other. They are arranged in bundles, the chief of which are as follows : (i) the superior longitudinal fasciculus ; (2) the inferior longitudinal fasciculus ; (3) the perpendicular fasciculus ; (4) the uncinate fasciculus ; (5) the cingiilum ; (6) the occipito-frontal fasciculus ; and (7) the fornix. The superior longitudinal fasciculus consists of fibres which extend from the frontal to the occipital lobe. Posteriorly many of its fibres sweep downwards and forwards into the temporal lobe, and from this circumstance it is sometimes spoken of as the arcuate fasciculus. The inferior longitudinal fasciculus connects the occipital and temporal lobes, its fibres being disposed upon the outer walls of the posterior and descending comua of the lateral ventricle. The perpendicular fasciculus connects the inferior parietal gyrus with the occipito-temporal gyrus. The uncinate fasciculus crosses the stem of the fissure of Sylvius, and connects the frontal and temporal lobes. The cingulum is connected with the limbic lobe, and lies upon the under surface of the calloscd gyrus and the upper surface of the hippocampal gyrus. Its fibres connect the gyri of the limbic lobe with the cerebral cortex. The occipito-frontal fasciculus connects the frontal with the occipital and temporal lobes. According to Dejerine the tapetum of the corpus callosum belongs to this fasciculus, and not to the corpus callosmn. The fasciculus Ues internal to the corona radiata, in intimate relation to the nucleus caudatus, and, as the fibres pass backwards, they lie on the outer walls of the descending and pos- terior comua of the lateral ventricle. The fornix connects the hippocampus major of one side with the corresponding corpus albicans, and, through the latter, with the optic thalamus by means of the bundle of Vicq d'Azyr, the fibres of which arise in the corpus albic^is. Peculiarities of the Cerebral Cortex — i. Calearine Area. — This area is situated on the mesial surface of the occipital lobe, in close proximity to the calearine fissure, and it is known as the visual area. In this region the outer band of Baillarger is very conspicuous, whilst the inner band of Baillarger is absent. 2. Rolandic Area. — In this region, more especially in the cortex of the precentral gyrus, there are groups of very large pyramidal cells, which are known as the giant-cells of Betz, and nerve-fibres are present in large numbers. 3. Hippocampal Area. — The hippocampus major corresponds to the hip- pocampal or dentate fissure, and is produced by an infolding of the cerebral 1448 A MANUAL OF ANATOMY cortex. It is therefore composed chiefly of grey matter, and is covered superficially by a thin layer of white matter, called the alveus, which is con- tinuous with the fimbria. The hippocampus major is composed of the follow- ing layers, named in order from the ventricular surface outwards : (i) the alveus, composed of white matter, and covered by the ventricular ependyma ; (2) neurogliar layer, consisting of neuroglia fibres and cells ; (3) pyramidal layer, composed of large pyramidal cells ; (4) stratum radiatum, which is the outer part of the pyramidal layer, and is composed of the dendrites of the apical parts of the pyramidal cells, being thereby rendered striated in appear- ance ; (5) stratum laciniosum, composed of the ramifications of the foregoing apical dendrites, intimately intermixed ; (6) stratum granulosum, composed of many small cells ; and (7) the involuted medullary lamina, consisting of white fibres. Olfactory Tract and Olfactory Bulb.— These are developed as a hollow outgrowth from the anterior cerebral vesicle, more par- ticularly from the part of it which ultimately gives rise to the lateral ventricle, and is known as the telencephalon. In many animals the central cavity persists, and maintains its connection with the lateral ventricle ; but in man the cavity disappears, though traces of its ependymal lining remain. External to the vestigial epen- dyma there is a layer of white matter, and, superficial to this, there is a layer of grey matter. In the olfactory tract the layer of grey matter is very thin over the ventral or inferior aspect, but over the dorsal or superior aspect it is fairly thick. In the bulb the reverse is the case, the grey matter being thick over the ventral aspect, where it receives the olfactory filaments, but thin over the dorsal aspect. Structure of the Ventral Grey Matter of the Olfactory Bulb. — The grey matter consists of three layers, namely (i) the nerve- fibre layer, (2) the glomerular layer, and (3) the granular layer. The nerve-fibre layer is the most superficial layer, and is com- posed of olfactory nerve- fibres. These fibres are non-medullated, and arise as the axons of the olfactory cells of the olfactory mucous membrane of the nasal fossa. Having passed through the foramina of one half of the cribriform plate of the ethmoid bone, they enter the grey matter on the ventral aspect of the bulb, where they break up and form arborizations. These intermingle with the arborizations formed by the dendrites of the mitral cells, to be presently described. The glomerular layer is composed of round bodies or glomeruli, which are formed by the interlacements between the arborizations of the olfactory nerve-fibres and those of the dendrites of the mitral cells. The granular layer lies next to the layer of white matter, and is chiefly characterized by the presence of large mitral cells. These are pyramidal, and one dendrite from each cell passes into the glomerular layer, where it gives rise to a glomerulus in the manner just described in connection with the glomerular layer. Other dendrites intermingle with those of adjacent mitral cells. The axon of each mitral cell enters the white layer of the bulb, and passes along the olfactory tract to the cerebrum. THE NERVOUS SYSTEM 1449 Weight of the Brain. — ^The average weight of the brain of the adult male is about 48 ounces, and that of the adult female about 44 ovmces. Arteries of the Encephalon. Cerebral Part of the Internal Carotid Artery. — ^The internal carotid artery, having pierced the roof of the cavernous sinus, internal to the anterior clinoid process of the sphenoid bone, ascends between the second and third cranial nerves to the inner end of the stem of the fissure of Sylvius. Here it divides into its terminal branches, namely, anterior cerebral and middle cerebral. Branches. — These are as follows : posterior communicating anterior choroidal, anterior cerebral, and middle cerebral. The posterior communicating artery arises from the back part of the internal carotid, and passes backwards to anastomose with the posterior cerebral artery. It is usually of small size, but is occasion- ally large, and it furnishes twigs to the cms cerebri and inner aspect of the optic thalamus. The anterior choroidal artery arises from the back part of the internal carotid close to its termination. It passes backwards and outwards between the cms cerebri and the hippocampal gyms, and it enters the lower and anterior extremity of the descending comu of the lateral ventricle by passing through the choroidal fissure. In its course it gives twigs to the hippocampal gyms and cms cerebri, and it terminates in the choroid plexus of the lateral ventricle. Anterior Cerebral Artery. — This is the smaller of the two terminal branches of the internal carotid artery, and it has a more limited distribution than the other terminal branch, namely, the middle cerebral artery. It passes forwards and inwards, above the optic nerve, to the commencement of the great longitudinal fissure, where it is connected with its fellow of the opposite side by a short transverse vessel, called the anterior communicating artery. There- after it enters the great longitudinal fissure, along with its fellow, turns round the genu of the corpus callosum, and passes backwards over the upper surface of that body to the splenium, where it anas- tomoses with the posterior cerebral artery. Branches. — ^These are arranged in two groups, antero-mesial or ganglionic and cortical. The antero-mesial or ganglionic branches, smaU in size, pass through the lamina cinerea, along with twigs from the anterior com- municating artery, and supply the front part of the caudate nucleus. The cortical branches are as follows : (i) internal orbital, to the internal orbital gyms, olfactory lobe, and gyms rectus ; (2) anterior internal frontal, to the superior frontal gyms, the anterior two- thirds of the middle frontal gyms, and the anterior part of the marginal gyms ; (3) middle internal frontal, to the callosal gjn-us, the posterior part of the marginal gyrus, and the upper part of the precentral gyms ; and (4) posterior internal frontal, to the quadrate 1450 A MANUAL OF ANATOMY lobule and the corpus callosum, the branch to the latter being known as the artery of the corpus callosum. Anterior Communicating Artery. — This vessel connects the two anterior cerebral arteries at the entrance to the great longitudinal fissure, and lies over the lamina terminalis, in front of the optic commissure. It gives off a few twigs, which accompany the antero- mesial branches of each anterior cerebral artery. Middle Cerebral Artery. — ^This is the larger of the two terminal branches of the internal carotid artery, and it has a wider distribu- tion than the anterior cerebral artery. It enters the stem of the fissure of Sylvius, in which it passes outwards. Branches. — These are arranged in two groups, antero-lateral or Fig. 606. — Distribution of the Left Middle Cerebral Artery (Charcot). F.I. Superior Frontal Gyrus F.2. Middle Frontal Gyrus F.3. Inferior Frontal Gyrus F.A. Ascending Frontal Gyrus P. A. Ascending Parietal Gyrus L.P.S. Superior Parietal Gyru L.P.I. Inferior Parietal Gyrus P.C. Angular Gyrus L.O. Occipital Lobe L.T. Temporal Lobe S. Middle Cerebral Artery entering Fissure of Sylvius P. Lenticulo-striate Arteries 1. Artery to Broca's Gyrus (Inferior Frontal Gyrus) 2. Ascending Frontal Artery 3. Ascending Parietal Artery 4. Parieto-Temporal Artery 5. Arteries to Temporal Lobe ganglionic and cortical. The antero-lateral or ganglionic branches pass through the locus perforatus anticus, and form two sets, internaJ striate and external striate. The internal striate arteries represent the lenticular arteries of Duret, and they supply the globus pallidus (inner part) of the lenticular nucleus, the internal capsule, and the caudate nucleus. The external striate art jries represent the lenticulo-striate and lenticulo-optic arteries of Duret. The lenticulo-striate arteries supply the putamen (outer part) of the lenticular nucleus and the external capsule. One of the lenticulo- striate arteries is larger than the others, and is subject to rupture in cases of cerebral haemorrhage. It is known as the artery of cere- THE NERVOUS SYSTEM 1451 bral hemorrhage (Charcot). Its course is outwards and upwards round the outer aspect of the lenticular nucleus, between it and the external capsule, and then through the internal capsule to the caudate nucleus. The lenticulo-optic arteries supply the posterior part of the lenticular nucleus and the anterior part of the optic thalamus on its outer aspect. The cortical branches arise in the vicinity of the island of Reil, and are as follows : (i) inferior external orbital, to the orbital surface of the frontal lobe external to the internal orbital sulcus, and to the inferior frontal gyrus ; (2) ascending frontal, to the posterior Fig. 607. — Coronal Section of the Cerebral Hemispheres made Onb Centimetre behind the Optic Commissure (Charcot, from Duret). (The Arteries of this region axe shown). I. Area of Anterior Cerebral Artery II. Area of Middle Cerebral Artery III. Area of Posterior Cerebral Artery V. V. Section.s of Anterior Cornua of Lateral Ventricles P.P. Anterior Pillars of Fornix C.N. Caudate Nucleus L S.A. Lenticulo-Striate Arteries CL. Claustrum I.R. Island of Reil E.C. External Capsule L.N. Lenticular Nucleus I.e. Internal Capsule O.T. Optic Tract (cut) G.M. Grey Matter of Third Ventricle O.C. Optic Conunissure O.N. Optic Nerve A.C. Anterior Cerebral .Artery C. Internal Carotid Artery M.C. Middle Cerebral Artery L.A. Lenticular Arteries A.C.H. Artery of Cerebral Hemorrhage third of the middle frontal gyrus, and to the lower and greater part of the precentral gyrus ; (3) ascending parietal, to the postcentral gyrus and superior parietal g}Tus ; (4) parieto-temporal, which traverses the posterior horizontal limb of the fissure of Sylvius, and supplies the inferior parietal gyrus, and the posterior parts of the superior and middle temporal gyri ; and (5) the temporal branches, which emerge from the posterior horizontal limb of the fissure of Sylvius, and supply the anterior and greater parts of the superior and middle temporal g\Ti. Fourth or Intracranial Part of the Vertebral Artery.— The verte- 1452 A MANUAL OF ANATOMY bral artery, on leaving the suboccipital triangle, pierces the dura mater and arachnoid, and enters the cranial cavity through the foramen magnum. As it ascends, it lies at first on the side of the medulla oblongata, between the hypoglossal nerve and the anterior root of the suboccipital nerve. It then passes upwards on the ventral surface of the medulla, and, on reaching the lower border of the pons Varolii, it unites with its fellow of the opposite side to form the basilar artery. Branches. — These are as follows : posterior meningeal, posterior spinal, posterior inferior cerebellar, anterior spinal, and bulbar. The posterior meningeal artery arises from the vertebral artery just before it pierces the dura mater, and it enters the cerebellar fossa of the occipital bone where it supplies the dura mater. The posterior spinal artery arises from the vertebral artery immediately after it has pierced the dura mater. It descends upon the side of the spinal cord, in front of the posterior roots of the spinal nerves, and it gives off a branch which descends behind these roots. These two arteries, in themselves small, are reinforced by the spinal branches of the second part of the vertebral artery and of. the dorsal branches of the intercostal arteries. In this manner lateral anastomotic arterial chains are formed upon each side of the spinal cord, in front of, and behind, the posterior nerve- roots. The posterior inferior cerebellar artery, of large size, arises a little above the preceding branch. It passes backwards between the pneumogastric and spinal accessory nerves, and then over the restiform body to the vallecula of the cerebellum, where it divides into branches. Some of these supply the inferior verniis, and others ramify on the inferior surface of the cerebellar hemisphere, at the periphery of which they anastomose with branches of the superior cerebellar artery. The artery furnishes branches to the corresponding choroid plexus of the fourth ventricle and to the medulla oblongata. The anterior spinal branch of the vertebral artery arises from that vessel near its termination. It passes obliquely downwards and inwards over the ventral aspect of the medulla oblongata, and at the median line it unites with its fellow of the opposite side to form the anterior spinal artery of the spinal cord. It furnishes twigs to the medulla oblongata. The bulbar branches are distributed to the medulla oblongata. Basilar Artery. — ^This vessel is formed by the union of the two vertebral arteries. It extends from the lower to the upper border of the pons Varolii, occupying the median basilar groove on its ventral surface. It lies beneath the arachnoid membrane, within the cisterna fontis, and at the upper border of the pons it divides into the two posterior cerebral arteries. Branches. — ^These are as follows, on either side : transverse, internal auditory, anterior inferior cerebellar, superior cerebellar, and posterior cerebral. THE NERVOUS SYSTEM 1453 The transverse or pontine arteries are numerous, and pass out- wards on either side to supply the pons, the sensory and motor roots of the fifth cranial ner\-e, and the middle peduncle of the cere- bellimi. The internal auditory artery, long and slender, accompanies the auditory nerve through the internal auditory meatus, and is dis- tributed to the internal ear. The anterior inferior cerebellar artery arises from the centre of the basilar, and passes backwards to be distributed to the anterior part of the inferior surface of the cerebellar hemisphere. It anastomoses with the posterior inferior cerebellar arterj% which is a branch of the vertebral. The superior cerebellar artery arises from the basilar close to its 13 15 r4 Fig. 608. — The Arteries at the Base of the Brain, and the Circle of Willis. 1. Internal Carotid 2. Middle Cerebral 3. Anterior Cerebral 4. Anterior Communicating 5. Posterior Communicating 6. Posterior Cerebral 7. Basilar 8. Superior Cerebellar 9. Transverse Pontine 10. Internal Auditory- 11. .A.nterior Inferior Cerebellar 12. Posterior Inferior Cerebellar 13. Vertebral 14. Anterior Spinal 15. Posterior Spinal 16. Anterior Choroid 17. Posterior Choroid 18. Central or Ganglionic 19. Central or Ganglionic 20. Central or Ganglionic (Postero-mesial) 21. Central or Ganglionic (Postero- lateral) termination. It passes outwards, parallel to the posterior cerebral arterv% from which it is separated by the third cranial nerve. It then winds round the outer side of the cms cerebri, below the fourth cranial ners'e, and so reaches the superior surface of the cerebellar hemisphere, where it divides into branches. These supply the superior vermis, the valve of Vieussens, the velum interpositum, and the superior surface of the cerebellar hemisphere, at the peri- pher\' of which they anastomose with branches of the inferior cerebellar arteries. Posterior Cerebral Artery. — ^This is one of the terminal branches of the basilar arter^', at the upper border of the pons Varolii. It passes at first outwards, beneath the crus cerebri, and parallel to the superior cerebellar artery, from which it is separated by the 1454 A MANUAL OF ANATOMY third cranial nerve. It then winds round the outer side of the cms cerebri, lying between it and the hippocampal gyrus, and above the fourth cranial nerve. In this manner it reaches the tentorial or inferior and mesial surfaces of the occipital lobe of the cerebral hemisphere. It receives, not far from its commencement, the posterior communicating artery. Branches. — These are arranged in two groups — ganglionic and cortical. The ganglionic group includes three sets of branches, namely, postero-mesial, postero-lateral, and posterior choroidal. The postero-mesial ganglionic arteries pass internal to the crus cerebri, and pierce the locus perforatus posticus. They supply the inner part of the crus cerebri and the posterior part of the optic thalamus. The postero-lateral ganglionic arteries pass on the outer side of the crus cerebri, and supply the outer part of the crus, the posterior part of the optic thalamus, the corpora quadrigemina, and the corpora geniculata. The posterior choroidal arteries are two or three in number, and pass through the choroidal fissure to the velum interpositum, which they supply, together with the choroid plexus of the lateral ven- tricle, and the corresponding choroid plexus of the third ventricle. The cortical branches are as follows : (i) anterior temporal, to the anterior parts of the occipito- temporal and hippocampal gyri ; (2) posterior temporal, to the posterior parts of the occipito-temporal and hippocampal gyri, and the inferior temporal gyrus ; and (3) occipital, to the occipital lobe. One of the occipital branches is called the calcarine artery. It lies in the calcarine fissure, and supplies the lingual or infracalcarine gyrus and the cuneus. Circle of Willis. — ^This circle is formed by (i) the anastomoses which take place between (a) the internal carotid and posterior cerebral arteries, through means of the posterior communicating arteries, and (b) the anterior cerebral arteries, through means of the anterior communicating artery ; and (2) the connection between the two posterior cerebral arteries which is established by the basilar artery. It is situated at the base of the brain, and, though spoken of as a circle, it is reaJIy a heptagon — that is to say, it has seven sides and seven angles. The circle is formed in front by the anterior communicating artery, which connects the two anterior cerebral arteries ; behind, by the basilar artery, as it divides into the two posterior cerebral arteries ; and on either side by (i) the anterior cerebral artery, (2) the trunk of the internal carotid artery, (3) the posterior communicating artery, and (4) the posterior cerebral artery, in this order from before backwards. The circle of Willis furnishes twigs to the grey cortex of the interpeduncular region. It serves to equalize the blood-pressure in the cerebral arteries, and it also provides for the regular supply of blood to the brain in cases where one of the main arterial trunks may be obstructed. THE NERVOUS SYSTEM X455 The following parts are contained within the circle of Willis, in order from behind forwards : (i) the locus perforatus posticus ; (2) the corpora albicantia or mammillaria ; (3) the tuber cinereum and infundibulum ; and (4) the optic commissure or chiasma. Veins of the Encephalon. The cerebral veins are arranged in two groups — superficial and deep. The superficial cerebral veins are divided into two sets — superior and inferior. The superior cerebral veins return the blood from the upper parts of the outer surfaces of the cerebral hemispheres. They lie in the pia mater, and pierce the arachnoid membrane and inner layer of the dura mater, after which they open into the superior longitudinal sinus, having previously received the veins from the mesial surface of either hemisphere. Their direction, for the most part, is forwards and inwards, whilst the direction of the blood-current in the superior longitudinal sinus is backwards. The inferior cerebral veins return the blood from the lower parts of the cerebral hemispheres, and they terminate in the cavernous, superior petrosal, and lateral sinuses. One of these veins is known as the middle cerebral, or superficial Sylvian, vein. It passes along the fissure of Sylvius, and opens into the front part of the cavernous sinus. This vein commimicates posteriorly with (i) the superior longitudinal sinus, through means of the great or superior anasto- motic vein ; and (2) the lateral sinus, through means of the posterior anastomotic vein. The deep cerebral veins are as follows : (i) the choroidal veins ; (2) the veins of the corpora striata ; (3) the veins of Galen ; (4) the anterior cerebral veins ; (5) the deep Sylvian veins ; and (6) the basilar veins. The choroidal vein of each side commences in the choroid plexus of the descending comu of the lateral ventricle. It ascends at first, and then passes forwards in the lateral margin of the velum inter- positum to the foramen of Monro, where it unites with the vein of the corpus striatimi to form the corresponding vein of Galen. The vein of the corpus striatum is formed by branches which issue from the corpus striatimi and optic thalamus. It runs for- wards in the groove between these two bodies, hing superficial to the taenia semicircularis, and at the foramen of Monro it joins the choroidal vein to form, as stated, the corresponding vein of Galen. The vein of Galen, of each side, is formed close to the foramen of Monro by the union of the choroidal vein, and the vein of the corpus striatum. The two veins of Galen, right and left, pass back- wards between the two layers of the velum mterpositvun, and they unite, beneath the splenium of the corpus callosum, to form one vessel, called the vena magna Galenl, which opens into the front part of the straight sinus. Each vein of Galen receives tributaries from 1456 A MANUAL OF ANATOMY the optic thalamus, the corresponding choroid plexus of the third ventricle, the corpus callosum, and the corpora quadrigemina ; and, prior to joining its fellow, it takes up the basilar vein of its own side. The vena magna Galeni receives tributaries from the upper surface of the cerebellum. The anterior cerebral vein of each side is situated in the great longitudinal fissure, along with the corresponding artery. Having curved round the genu of the corpus callosum it passes to the region of the locus perforatus anticus, where it joins the deep Sylvian vein to form the basilar vein. The deep Sylvian vein returns the blood from the island of Reil, and lies deeply within the stem of the fissure of Sylvius. At the locus perforatus anticus it joins the anterior cerebral vein to form, as stated, the basilar vein. The basilar vein of each side commences at the locus perforatus anticus, where it is formed by the union of the anterior cerebral and deep Sylvian veins. It passes backwards round the cms cerebri, and opens into the vein of Galen of its own side, just before that vessel joins its fellow to form the vena magna Galeni. The basilar vein receives, close to its commencement, one or more inferior striate veins, which descend from the corpus striatum through the locus perforatus anticus. It also receives tributaries from the parts within the interpeduncular space. The cerebellar veins are arranged in two groups — superior and inferior. The superior cerebellar veins terminate in the vena magna Galeni, and in the straight, lateral, and superior petrosal sinuses. The inferior cerebellar veins pass to the lateral, inferior petrosal, and occipital sinuses. Blood-supply of the Different Parts of the Encephalon. The medulla oblongata is supplied by the vertebral, anterior spinal, and posterior inferior cerebellar arteries. The pons Varolii is supplied by the transverse or pontine branches of the basilar artery. The cerebellum is supplied inferiorly by the posterior inferior cerebellar branches of the vertebral arteries, and the anterior inferior cerebellar branches of the basilar artery. Superiorly it is supplied by the superior cerebellar branches of the basilar artery, and, to a limited extent, by the posterior inferior cerebellar arteries. The crus cerebri is supplied by the postero-mesial and postero-lateral branches of the posterior cerebral artery, and by the posterior communicating artery. The locus perforatus posticus is pierced by the postero-mesial branches of the posterior cerebral arteries. The corpora quadrigemina are supplied by the postero-lateral branches of the posterior cerebral arteries. The optic thalamus is supplied posteriorly by the postero-mesial and postero- lateral branches of the posterior cerebral artery. Anteriorly its outer part is supplied by the lenticulo-optic branches of the middle cerebral artery, and its inner part by the posterior communicating artery. The locus perforatus anticus is pierced by the antero-lateral ganglionic branches of the middle cerebral artery. THE NERVOUS SYSTEM 1457 Frontal Lobe. — The superior frontal gyrus, the axiterior two-thirds of the middle frontal g>Tus, and the upper portion of the precentral gyrus are supplied by cortical branches of the anterior cerebral artery. The posterior third of the middle frontal g\Tus, the inferior frontal gyrus, and the lower and greater part of the precentral gyrus are supplied by cortical branches of the middle cerebral artery. On the orbital surface the internal orbital gyrus, olfactory lobe, and gyrus rectus are supplied by the anterior cerebraJ artery, whilst the remainder is supplied by the middle cerebral artery. Parietal Lobe. — The whole of tlus lobe is supplied by the middle cerebral artery. Occipital Lobe. — This lobe is supplied by the posterior cerebral artery. Temporal Lobe. — The superior and middle temporal gyri are supplied by the middle cerebral artery, and the Fcxc-brain remainder is supplied by the pos- terior cerebral artery. Mesial Surface of the Cerebral Hemisphere. — The anterior cerebred cirtery has an extensive distribution to this surface, which it supplies as far back as the internal part of the parieto-occipital fissure. The parts behind this fissure, namely, the cuneus and the parts around the calcarine fissure, are supplied by the posterior cerebral artery. The corpus callosum is supplied by the anterior cerebral arteries. Corpus Striatum. — The nucleus caudatus and nucleus lenticularis are supplied, for the most part, by the antero-lateral or ganglionic branches of the middle cerebral artery, which pass through the locus perforatus anticus. According to Duret they form three sets — lenti- cular, lenticulo-striate, and lenti- culo-optic. The lenticular (internal striate) arteries supply the globus pallidus (inner part) of the lenticular nucleus, the internal capsule, and the caudate nucleus. The lenticulo- striate (external striate) arteries supply the putamen (outer part) of the lenticular nucleus, and the external capsule. One of the lenti- culo-striate arteries is larger than the others, and is subject to rup- ture in cases of cerebral haemor- rhage. It is known as the artery of cerebral hemorrhage (Charcot). Its course is outwards and upwards round the outer aspect of the lenticular nucleus, between it and the external capsule, and then through the internal capule to the caudate nucleus. The lenticulo-optic arteries supply the posterior part of the lenticular nucleus, and the anterior part of the optic thalamus on its outer aspect. The front part of the caudate nucleus is supplied by the antero-mesial branches of the anterior cerebral and anterior communicating arteries. The larger arteries occupy the subarachnoid space, where they divide into branches which enter the pia mater. These in turn give off smaller branches, which enter the cerebral substance, some of them being cortical, and others medullary, in their distribution. 92 -Optic Vesick — Mid-brain —Hind-brain Heart Vitelline Veins Protovertebral Somites Medullary Tube Fig. 60Q. — Anterior Part of an Em- bryo Chick at the End of the Second Day (Dorsal View) (Kol- liker). MsS A MANUAL OF ANATOMY Blood-supply of the Choroid Plexuses. — The choroid plexus ol the lateral ventricle derives its blood from (i) the anterior choroidal artery, which is a branch of the internal carotid ; and (2) the posterior choroidal arteries, which are branches of the posterior cerebral. The choroid plexuses of the third ventricle derive their blood from the posterior choroidal arteries. The choroid plexuses of the fourth ventricle derive their blood from the posterior inferior cerebellar arteries. The velum interpositum derives its blood from the posterior choroidal arteries and from the superior cerebellar eirteries. Lymphatics of the Brain. — There are no lymphatic vessels in the brain. Their place is taken by spaces in the outer coat of the arteries, called peri- vascular spaces, which are in communication with the subarachnoid space. Development of the Encephalon. The encephalon is developed from the cephalic part of the neural tube. This part of. the tube undergoes enlargement, and is divided by constrictions into three parts, called the anterior, middle, and posterior primary cerebral vesicles. The anterior primary cerebral vesicle forms the prosencephalon or Fig. 610. — Brain of an Embryo about Three and a Half Weeks Old. From Quain's 'Anatomy' (His). Telencephalon Thalamencephalon Mesencephalon Metencephaloii 5. Myelencephalon 6. Cervical Flexure 7. Spinal Cord Pontine Flexure 9 Olfactory Lobe t, 2 = Prosencephalon ; 3 = Mesencephalon ; 4, 5 = Rhombencephalon fore-brain ; the middle primary cerebral vesicle constitutes the mesencephalon or mid-brain ; and the posterior primary cerebral vesicle gives rise to the hind-brain, or rhombencephalon (rhomb-brain, from the rhomboid character of the floor of the fourth ventricle). The constriction between the mesen- cephalon and rhombencephalon is called the isthmus. It gives rise to the valve of Vieussens. From the lower part of each lateral wall of the anterior primary cerebral vesicle (telencephalon) a hollow protrusion is developed. These two protru- sions constitute the optic vesicles. Flexures of the Primitive Encephalon. — Prior to the subdivision of the three primary cerebral vesicles three flexures make their appearance, called cephalic THE NERVOUS SYSTEM 1459 pontine, and cervical. The eephalic flexure appears between the prosen- cephalon and mesencephalon, and by it the prosencephalon is bent ventral- ward; round the cephalic end of the notochord. on to its ventral aspect. By reason of this flexure the prosencephalon is lowered, and the mesencephalon occupies the summit of the encephalon. The cephalic flexure coincides with the head-fold of the embryo, and the concavity of the flexure is directed ventralwards. The pontine flexure, the concavity of which is directed dorsal- wards, appears on the ventral waU of the metencephalon, or cephalic sub- division of the hind-brain, in the region of the future pons Varolii. The cervical flexure appears between the myelencephalon, or caudal subdivision of the hind-brain, and the commencement of the spinal cord. Its concavity is directed ventralwards, like that of the cephalic flexure. Secondary Cerebral Vesicles. — The middle primary cerebral vesicle remains undivided, but the anterior and posterior primary cerebral vesicles are each subdivided into two parts by constrictions which appear on their lateral walls. The subdivisions of the anterior primary cerebral vesicle are known as the first and second secondary cerebral vesicles, the former being the anterior of the two. The middle primary cerebral vesicle, as stated, remains undivided, and forms now, in series, the third secondary cerebral vesicle. The subdivisions of the posterior primary cerebral vesicle are known as the fourth and fifth second- ary cerebral vesicles. There are thus five secondary cerebral vesicles, named first, second, third, fourth, 3x16^ fifth, of which the third is reaUy not secondary. The first secondary cerebral vesicle represents the telencephalon (end-brain), the second the diencephalon (inter-brain) or thalamencephalon (bedchamber- brain), the third the mesencephalon (mid-brain), the fourth the metencephalon (hind-brain), and the fifth the myelencephalon (marrow- or after-brain). Secondary Cerebral Vesicles. First ^, Telencephalon (end-brain). Second /Diencephalon (inter-brain) ; or •'■ \ Thalamencephalon (bedchamber-brain). Third ,, Mesencephalon (mid-brain). Fourth .. Metencephalon (hind-brain). Fifth .. Myelencephalon (marrow- or after-brain). The constrictions, which subdivide the anterior primary cerebra vesicle into telencephalon and diencephalon, are anterior to the origins of the optic vesicles, and consequently these vesicles pertain to the diencephalon. In a general way. the telencephalon gives origin to the cerebral hemispheres and the olfactory lobes. The diencephalon gives origin to the optic stalks and the structures around the third ventricle — e.g., the optic thalaml, pineal body, and posterior lobe of the pituitary body. The mesencephalon gives origin to the structures around the aqueduct of Sylvius — namely, the crura cerebri and corpora quadrigemina. The metencephalon gives origin to the cerebellum, pons Varolii, and pontine part of the fourth ventricle. The myelencephalon gives origin to the medulla oblongata and bulbar part of the fourth ventricle. The following table represents the formations just referred to: fTelencephal on = First secon- \ Diencephalon J vesicle Middle primarv "\ f Mesencephalon, 1 i-v j j 1 cerebral vesicle / = \ or mid-brain J Third secondary vesicle D ^ ■ ^ [Rhombencephalon.! (Metencephalon = Fourth secon- Posterior primary IT"^" ucui^cpixaauu, ■ j ^^^ dary vesicle cerebral vesicle / | hind-brain f 1 Myelencephalon = Fifth secon- v J \ dary vesicle 1460 A MANUAL OF ANATOMY The parts of the encephalon, formed from the foregoing subdivisions, are as follows : Telencephalon. Thalamencephalon, or Diencephalon. Cerebral hemispheres. Posterior part of third ventricle. Lateral ventricles. Optic thalami. Anterior part of third ventricle. Pineal body. Foramina of Monro. Interpeduncular structures. Olfactory lobes. Pituitary body. Optic nerve and retina. Mesencephalon. Hetencephalon. Myelencephalon. Corpora quadrigemina. Cerebellum. Medulla oblongata or bulb. Crura cerebri. Pons Varolii. Bulbar part of the fourth Aqueduct of Sylvius. Pontine part of the fourth ventricle, ventricle. Metamorphoses of the Secondary Cerebral Vesicles. Myelencephalon. — This is the fifth secondary cerebral vesicle, being the caudal subdivision of the rhombencephalon or posterior primary cerebral vesicle. Its walls give rise to the medulla oblongata or bulb, and its cavity forms the bulbar part of the fourth ventricle. The lateral walls of the myelen- cephalon correspond for the most part with those of the spinal portion of the neural tube, each consisting of three zones — ependymal, mantle, and mar- ginal, from within outwards. Moreover, the lateral walls are connected by two plates — dorsal or roof-plate, and ventral or floor-plate. Each lateral wall is composed of a ventral or basal lamina and a dorsal or alar lamina, these being separated by a longitudinal groove, called the sulcus limitans, as in the spinal portion of the neural tube. In the myelencephalon certain changes are effected. 1 . The roof -plate becomes much widened. 2. The basal and alar laminae of each lateral wall, which primarily occupy an almost vertical plane, spread outwards and occupy an almost horizontal plane, the roof plate meanwhile expanding. The basal and alar laminae now form the floor of the bulbar part of the fourth ventricle, the basal lamina being mesial to the dorsal lamina. 3. The lumen of the neural tube, which is a mere dorso-ventral cleft in the spinal portion of the tube, becomes wide in the region of the fourth ventricle. Roof-Plate. — This forms the roof-epithelium or ependyma of the bulbar part of the fourth ventricle, and it becomes thickened in certain situations (mesial and lateral), thus giving rise to (i) the obex (mesial), and (2) the ligula, right and left (lateral). The roof-plate is connected, on either side, with the dorsal margin of the corresponding alar plate, which margin becomes everted and forms the rhombic lip. Subsequently this lip fuses with the contiguous part of the outer surface of the alar lamina. The widened roof-plate is covered by vascular mesenchyme, representing pia mater. At the level of the pontine flexure the ependymal or epithelial roof is invaginated into the fourth ventricle in the form of a transverse fold — plica choroidea, containing pia mater, which extends between the lateral recesses of the ventricle. From this transverse fold two vertical folds, pliccs choroidecB, hkewise containing pia mater, extend vertically downwards into the ventricle, close to the median line. These ependymal folds, containing pia mater, form the two choroid plexuses of the lateral ventricle, thus — [J. Lateral Walls. — Each lateral wall, as stated, consists of three zones — ependymal, mantle, and marginal, from within outwards. On either side it presents two laminae — dorsal or alar, and ventral or basal, separated by the sulcus limitans. Moreover, as stated, these two laminae lie vertically, the dorsal margin of the alar lamina forming the rhombic hp. The axons of the neuroblasts of the mantle-layer of the basal lamina emerge as centrifugal or THE NERVOUS SYSTEM 1461 efferent nerve-fibres. The alar lamina, ventral to the rhombic lip, receives the centripetal or afferent fibres of the glosso-pharyngeal and vagus nerves, which terminate in a prominent oval area, representing the fasiculus solitarius, at first placed superficially. Subsequently, the two laminae spread outwards and then occupy a horizontal plane, the roof-plate meanwhile expanding. The basal and alar laminae now form, as stated, the floor of the bulbar part of the fourth ventricle, the basal lamina being mesial to the dorsed lamina. The two basal laminae, right and left, are connected by the floor-plate. The trigonum hypoglossi in the bulbar part of the floor of the fourth ventricle pertains to the basal lamina, whilst the trigonum vagi and trigonum acusticum belong to the alar lamina. When the rhombic hp has fused with the contiguous part of the alar lamina, a proUfic nest of neuroblasts is formed in this region. Many of these neuro- blasts pass ventralwards, embracing the fasciculus solitarius, which now hes deeply. These neuroblasts, on reaching the basal lamina, become differ- entiated into the olivary body. Other neuroblasts pass into the alar lamina, where they give rise to the nucleus gracilis and nucleus cuveatus. Each pyramid is a ventral bulging of that part of the basal lamina which is on the mesial side of the olivary body, and it is produced by the motor tracts as they descend from the Rolandic area of the cerebral cortex through the pons Varolii. The arcuate nucleus is developed from neuroblasts derived from the rhombic- lip-area of the alar lamina. The formatio reticularis, which lies on the dorsal aspects of the pyramid and oUvary body, is developed in connection with the mantle-layer of the basal lamina prior to the development of the pyramid. As the pyramids, right and left, bulge ventralwards, the floor-plate, which connects the basal laminae, sinks, and the anterior median fissure is formed, as in the development of the spinal cord. The spongioblastic floor-plate is now invaded by nerve-fibres, most of which cross from one side to the other, these fibres being (i) the anterior superficial arcuate fibres, (2) the deep arcuate fibres, and (3) the cerebello-ohvary fibres. In this manner the raphe of the bulb is formed, as in the development of the anterior or white commis- sure of the spinal cord. The cavity of the medullary or bulbar portion of the neural tube extends in early life as low as the cervical flexure, where it is continuous with the cavity of the spinal portion of the neural tube, and the calamus scriptorius of the fourth ventricle is, at this stage, on a level with the cervical flexure. As development proceeds, the basal and alar laminae, which had spread outwards so as to he horizontally on the ventral wall, resume their original position in the lateral wall of the lower half of the medullary portion of the neural tube on either side. In this manner the lower half of the bulb becomes closed dorsalwards, and so the lower half contains a prolongation of the central canal of the spinal cord. Metencephalon. — The metencephalon, which represents the fourth secondary cerebral vesicle, is the cephalic subdivision of the rhombencephalon, hind- brain, or posterior primary cerebral vesicle. From it are developed (i) the pons Varolii, (2) the cerebellum, (3) the superior and middle peduncles of the cerebellum, and (4) the superior medullary velum or valve of Vieussens and the inferior medullary velum. The cavity of the metencephalon forms the upper or pontine part of the fourth ventricle. The pons Varolii is developed from the ventral wall of the metencephalon. The cerebellum is developed from the dorso-lateral walls of the meten- cephalon. The rudiments of the eerebellum appear as thickenings of the right and left dorsal or alar lamines of the lateral walls of the metencephalon. These thickened alar laminae constitute the two lateral cerebellar plates, the cere- bellum being originally composed of two symmetrical halves, separated by a median furrow of the roof-plate of the metencephalon. The two cerebellar plates subsequently fuse across the median dorsal line, and, being now trans- verse, they form one transverse cerebellar plate. The central part of this plate 1462 A MANUAL OF ANATOMY gives rise to the vermis or middle lobe of the cerebellum, and the lateral parts give rise to the cerebellar hemispheres, or lateral lobes. The surface of the cerebellum is originally smooth and unbroken, but fissures or sulci afterwards appear. The earliest of these is the floccular fissure, of which there are two — right and left. At a later period many- other fissures make their appearance, which impart a laminated character to the lateral hemispheres and vermis. The floccular fissure of either side cuts off the dorsal part of each lateral cerebellar plate (lateral cerebellar hemi- sphere), and this part constitutes the flocculus. The parafiocculus on either side is developed from the lateral part of each lateral cerebellar plate, close to the rhombic lip. The two floccular fissures meet across the anterior part of the inferior vermis, giving rise to the post-nodular fissure, which cuts off the nodule from the anterior part of the inferior vermis. The flocculus and nodule are developed from the rhombic lip — the floccu- lus from the lateral part and the nodule from the median part. The cephalic portion of the roof-plate of the metencephalon, close to the isthmus, gives rise to the superior or anterior medullary velum {valve of Vieus- sens), and lower down it forms the inferior or posterior medullary velum, which is continuous with the ependymal or epithehal roof of the bulbar part of the fourth ventricle. On either side of the valve of Vieussens the roof-plate is thickened by the superior cerebellar peduncles. The superior peduncles of the cerebellum, right and left, arise from the cells of the nucleus dentatus of the corresponding lateral cerebellar hemisphere. Emerging from the anterior parts of the dentate nuclei, the peduncles give rise to two thickenings of the roof -plate of the metencephalon, one on either side of the valve of Vieussens. Thereafter they enter the mesencephalon or mid-brain, and after decussating, each passes to the corresponding red nucleus of the tegmentum of either crus cerebri, which constitutes its lower cell- station. The middle peduncles of the cerebellum [brachia pontis) are developed from the cells of the pontine nuclei of the pons Varolii, right and left. The fibres of each peduncle issue from the lateral portion of the corresponding pontine nucleus and enter the adjacent cerebellar hemisphere. The inferior peduncles of the cerebellum or restiform bodies are very com- plex, inasmuch as they derive their fibres from several sources. These sources are as follows : 1. The olivo-cerebellar fibres of the Inferior olivary nucleus of the opposite side. 2. The direct cerebellar tract of the lateral column of the spinal cord of the same side. 3. The anterior superficial arcuate fibres from the nucleus gracilis and nucleus cuneatus of the opposite side. 4. The posterior superficial arcuate fibres from the nucleus gracilis and nucleus cuneatus of the same side. 5. Vestibular fibres from the vestibular nuclei of the vestibular division of the auditory nerve. Mesencephalon. — The mesencephalon represents the third secondary cerebral vesicle, which also constitutes the middle primary cerebral vesicle. Its thickened walls give rise to the parts around the aqueduct of Sylvius — namely, (i) the crura cerebri, (2) the posterior perforated space, and (3) the corpora quadrigemina. Its cavity, very much diminished, persists as the aqueduct of Sylvius, or aqueductus cerebri. The crura cerebri and posterior perforated space are developed from the ventral wall or floor of the mesencephalon. The alar plates of the lateral walls encroach so much upon the roof-plate as to reduce it to a mere line. It presents a median longitudinal groove, which separates two rounded eminences, known as the corpora bigemina. At a later period a transverse groove appears, which divides each of the corpora bigemina into two, thus giving rise to the corpora quadrigemina. THE NERVOUS SYSTEM 1463 The cavity of the mesencephalon is largely encroached upon by the thick- enings undergone by its walls. A minute canal, however, is left, called the aquedoet ol Sylvius, or aqueductus cerebri, which constitutes a part of the cephalic prolongation of the central canal of the spinal cord. It is continuous below with the fourth ventricle, and above with the third ventricle. Dieneephalon or Thalameneephalon. — The diencephalon represents the second secondary cerebral vesicle, which is one of the subdivisions of the pros- encephalon, fore-brain, or anterior primary cerebral vesicle. Its walls give rise to the parts around the third ventricle — namely, (i) the greater part of the ependymal roof, with the velum interpositum and pineal body; (2) the optic thalami; and (3) the tuber cinereum, infundibulum, posterior lobe of the pituitary body, and corpora mammillaria. The diencephalon also gives origin to each optic stalk, from which the optic nerve is developed, the retina being developed from the optic vesicle. The cavity of the diencephalon forms the greater part of the third ventricle. The roof remains very thin, and consists merely of ependymal epithehum. This forms the direct roof of the third ventricle, and it is covered by two layers of pia mater, adherent to each other, and closely connected to the ependymal roof. One of these layers of pia mater belongs to the diencephalon, whilst the other belongs to the under surfaces of the developing cerebral hemispheres, which have expanded backwards so as to overlap the diencephalon. The two layers of pia mater constitute the velum interpositum, or tela choroidea superior, and, with the ependymal lamina, upon which they lie, they form the roof of the third ventricle. The pineal body, or epiphysis cerebri, is developed from the dorsal part of the ependymal roof of the third ventricle. It appears as a diverticulum of the ependymal roof, close to the mesencephalon, and it is directed backwards, so that it comes to lie over the corpora quadrigemina. The distal end is blind, and, in connection with it, a number of closed foUicles are formed which contain calcareous particles, forming the acervulus cerebri, or brain- sand. The proximal part of the diverticulum forms the stalk of the pineal body, which contains the pineal recess and opens into the third ventricle. The lateral walls of the diencephalon become much thickened and give rise to the optic thalami, the cavity of the third ventricle being thereby converted into a narrow cleft. The floor forms the tuber cinereum, and from the tuber cinereum a diver- ticulum, called the infundibulum, passes downwards. The lower part of the infundibulum becomes solid and forms the posterior lobe of the pituitary body, the anterior lobe of that body being developed from the poueh of Rathke, which is an upward diverticulum of the stomodeBal ectoderm. Caudal to the infundibulum the floor forms the mammillary recess, from the thickened walls of which the corpora mammillaria are formed. The optic vesicles are important appendages of the diencephalon, each vesicle growing out from the lateral part of its floor, in front of the level of the infundibulum. For a description of these vesicles see the Development of the Eye. Telencephalon. — ^The telencephalon represents the first secondary cerebral vesicle, which is one of the subdivisions of the prosencephalon, fore-brain, or anterior primary cerebral vesicle. It extends forwards and downwards from the diencephalon, and from it are developed the cerebral hemispheres and their associated structures, including the lateral ventricles, as well as the anterior portion of the third ventricle. The cerebral hemispheres make their appearance as hollow protrusions which grow out from the dorsal zones or alar laminae of the lateral walls of the telencephalon. These two lateral protrusions constitute the vesicles of the cerebral hemispheres, and their cavities are lateral extensions of the cavity of the telencephalon. This cavity, mesially placed, forms the anterior portion of the third ventricle. The vesicular cerebral hemispheres grow with great rapidity, and are separated from each other by a cleft called the interhemispherical fissure, which is the rudiment of the great longitudinal Assure. The direction of their 1464 A MANUAL OF ANATOMY Palliuir Optic Thalamus - growth is forwards, upwards, and backwards from the position of the foramen of Monro on either side. They soon cover the diencephalon, and, as their backward growth continues, they cover in succession the mesencepalon and rhombencephalon. The mesial wall of each vesicle is intimately related to the lateral wall of the diencephalon on either side. As the vesicles of the cerebral hemispheres grow backwards they are still separated by the interhemispherical fissure, and the roof of the diencephalon lies at the bottom of this fissure over a limited area, the corpus callosum and fornix eing as yet undeveloped. The cavity of each vesicle, which, as stated, is a lateral extension on either side of the cavity of the telencephalon, is the rudiment of the corresponding lateral ventricle; and the cavity of the telencephalon, mesially placed, forms, as stated, the anterior portion of the third ventricle. The communication between the cavity of the vesicle of the cerebral hemisphere and the cavity of the telencephalon persists throughout life on either side! It is the rudiment of each foramen ol Monro, and is at first of large size. The front part of the telencephalon now presents the anterior portions of the developing cerebral hemi- spheres right and left, and between them is the thin anterior wall of the telenceph- alon. This wall represents the terminal cephalic bound- ary of the embryonic neural canal, and it is known as the lamina terminalls, which con- nects the antero-mesial parts of the developing cerebral hemispheres. Inasmuch as the cavity of the telen- cephalon forms the anterior portion of the third ventricle, the lamina terminalis forms the anterior wall of that ventricle, the anterior pillars of the fornix and the anterior white commissure being subsequently developed in connection with it. The roof -plate of the telencephalon forms the anterior part of the roof of the third ventricle. The walls of the primitive cerebral hemispheres are very thin and consist of neuro-epithelium, the cells of which multiply very freely, the cavity (lateral ventricle) meanwhile diminishing. The innermost cells form the ependyma, which lines the lateral ventricles, but the majority form an extensive super- ficial mantle-layer, known as the neopallium, or mantle, which constitutes the grey cortex. The neuroblasts of the mantle multiply freely, the ven- tricular cavity meanwhile becoming diminished. Many of the axons of the neuroblasts pass towards the centre, and they give rise to the white matter which constitutes the medullary centre. The grey matter is not confined to the cortex, but exists also in the basal ganglia of each hemisphere — namely, the corpus striatum, claustrum, and amygdaloid nucleus of each side. The surface of each hemisphere-vesicle is at first smooth and unbroken. At a very early period, however, a depression makes its appearance at the lower part of each lateral surface of the vesicle. This depression, which is triangular, is called the Sylvian, or lateral cerebral, fossa. The cortical sub- stance over the floor of this fossa becomes much thickened, and its deep part projects into the cavity of the vesicle (lateral ventricle), giving rise to the Third Ventricle Middle Commissure Pineal Body _ Corpora ;' " Quadrigemina ', Valve of Vieussens Superior Cerebellar Peduncle XX Foramina of Monro Fig. 611. — Diagram of Primitive Fore- Brain AND Contiguous Structures. THE NERVOUS SYSTEM 1465 basal ganglia of the cerebral hemisphere^namely, the corpus striatum, claustrum, and amygdaloid nucleus of either side. The superficial part of the cortical substance represents the primitive insula, or island of Reil. The Syl ian fossa gradually extends across the ventral aspect of the hemisphere- vesicle towards the lower margin of its mesial surface, and the temporjil lobe grows forwards and downwards towards it. In this manner the stent of the Sylvian fissure is formed. The fossa also extends in a back\vard direction upon the lateral surface of the vesicle, and in this manner the rudiment of the posterior horizontal limb of the Sylvian fissure is formed. The anterior ascending and anterior horizontal limbs are formed at a later period. The elevated margins of the Sylvian fossa and of its back\vard extension, which gradually approach each other, and meet over the insula, represent the opercular region. The cerebral hemisphere on either side is disposed in the form of an in- complete ring around the Sylvian fossa, the break in the ring being formed by that fossa. The stalk of the hemisphere is located at the fossa, and cor- responds to the corpus striatum, with which is associated the optic thalamus. The remaining, and much larger, part of the hemisphere constitutes the neopallium. The insula, or island of Reil, as stated, is developed from the super- ficial part of the cortical substance which forms the floor of the Sylvian fossa. The grey matter becomes almost completely surrounded by a limiting fissure, and is then broken up by sulci into the component parts of the adult insula. _ _ The anterior part of the hemi- F^^. 612.— The Primitive Fissure of sphere-vesicle corresponds to the Sylvius. frontal lobe ; the lower part, as far forwards as the stem of the Sylvian fissure, becomes the temporal lobe, and the upper and posterior part represents the parietal lobe. The occipital lobe is formed at a later period as the hemisphere grows backwards. The limbic lobe is developed in connection with the mesial surface of the hemisphere. The olfactory lobe is developed as a hollow protrusion from the ventral aspect of the frontal portion of the hemisphere-vesicle. The surface of each hemisphere becomes very much broken up into gyri or convolutions, this being effected by means of fissures. The fissures are of two kinds — complete and incomplete. The incomplete fissures are merely sulci produced by the growth of the gyri, and they do not involve the entire thickness of the walls of the cerebral hemispheres. The complete fissures are infoldings of the walls of the cerebral hemispheres, and involve their entire thickness. They consequently give rise internally to certain prominences upon the wall of each lateral ventricle — namely, the corpus striatum, lateral choroid plexus, hippocampus major, calcar avis, and eminentia collateraUs. The complete fissures are as follows : SyK-ian. Calcarine (anterior part). Choroidal. Parieto-occipital. Hippocampal. Collateral (central part). With the exception of the Sylvian fissure, already described in connection with the Sylvian fossa, the other complete fissures appear on the mesial surface of the vesicle of the cerebral hemisphere. The choroidal fissure is not really a fissure, but merely a groove or sulcus produced by an infolding of the vesicular wall, which is here composed entirely of ependyma. It commences above and behind the foramen of Monro of the corresponding side, and it terminates close to the tip of the temporjil pole, where the inferior or descending comu of the lateral ventricle ends. Between these two points it passes backwards, downwards, and then forwards into 1466 A MANUAL, OF ANATOMY the future temporal lobe, in a crescentic manner, so as to embrace the stalk of the cerebral hemisphere. After the ependymal infolding has taken place, vascular mesenchyme dips in between its two folds, and so a plica choroidea is formed. From this choroidal fold the lateral choroid plexus of the cor- responding side is formed. This plexus projects into the lateral ventricle, but is excluded from the ventricular cavity by the ependyma of the wall, previously infolded. When the lateral choroid plexus is withdrawn, the thin ependymal covering of the plexus comes away with it, or is broken down. Under these circumstances the choroidal fissure is really a fissure, inasmuch as the lateral ventricle now opens upon the surface through it. The internal prominence produced by the choroidal fissure is the lateral choroid plexus, covered by ependyma, this prominence being very conspicuous. The other complete fissures will be found described in connection with the cerebral hemispheres. The incomplete fissures are very numerous. The first two to make their appearance are the calloso-marginal fissure, or sulcus cinguli, on the mesial surface of the cerebral hemisphere, and the central sulcus or fissure of Rolando on the external surface. These, along with the other incomplete fissures, will be found described in connection with the cerebral hemispheres. The cavity of the vesicle of the cerebral hemisphere forms on either side the lateral ventricle, which is very much curtailed by the thickening under- gone by the vesicular walls, and the internal prominences produced by the complete fissures. As the frontal lobe undergoes development the body of the ventricle extends forwards into it, and so the anterior cornu of the ventricle is formed. As the temporal lobe grows in a downward and forward direction, it carries with it an extension of the body of the ventricle, this extension constituting the inferior or descending cornu. As the occipital lobe becomes developed at a later period the body of the ventricle extends backwards into it, and so the posterior cornu is formed. Meanwhile the foramen of Monro on either side, originally large, is being gradually much diminished in size. Basal Ganglia. — ^The basal gangha of each cerebral hemisphere are as follows : Corpus striatum. Claustrum. Amygdaloid nucleus. They are all developed from the deep part of the much thickened cortical substance which forms the floor of the Sylvian fossa. The claustrum and amygdaloid nucleus remain of small size, but the nucleus caudatus of the corpus striatum forms a conspicuous prominence in the lateral ventricle, as it bulges into the anterior cornu of that cavity. Commissures. — The commissures are as follows: 1. Corpus callosum. 4. Anterior. 2. Fornix. 5. Posterior. 3. Hippocampal. 6. Middle. 7. Habenular. At an early period in the development of the cerebral hemispheres the interhemispherical (great longitudinal) fissure leads directly dow n to the roof of the diencephalon. At a later period the roof of the diencephalon is separated from the great longitudinal fissure by two commissures, placed one above the other. The upper commissure is the corpus cedlosum, and the lower one is the fornix. The corpus callosum and fornix are formed in connection with the lamina terminalis. This lamina, which is originally thin, becomes thickened, and the mesial walls of the hemispheres come together and fuse directly over and anterior to it. At the same time the united walls of the hemispheres blend with the upper margin of the lamina terminalis. The area of fusion of the walls of the hemispheres now extends both anteriorly and posteriorly, and this area forms a basis or plate for the formation of the corpus callosum and fornix. Transverse fibres are developed over the dorsal aspect of the area, which cross from the neopallium of one hemisphere to that of the other. fkE NERVOUS SYSTEM 1467 and these transverse fibres constitute the eorpas eallosam. The fibres of the tornix appear on the ventral aspect of the plate formed by the fused areas of the cerebral hemispheres. On either side they are developed from the hippocampus major, and they form, in succession, the fimbria, or tcsnia hippocampi, the posterior pillar, one Judf of the body, and the anterior pillar, of the fornix. The anterior pUlar passes downwards through the lamina terminahs to the base of the brain, where it becomes twisted in the form of a loop, and forms the white substance of the corresponding eorpas mammillare. Thereafter its fibres terminate in the grey nucleus of that body, and from this nucleus the bundle of Vieq d'Azyr passes upwards and backwards into the optic thalamus. Each half of the fornix is therefore a commissure between the hippocampus major and the optic thalamus of the same side. The hlppocampal eommissore appears on the back part of the ventral aspect of the plate formed by the fused areas of the cerebral hemispheres. Its fibres pass across from one hippocampus major to the other, and they correspond to the region known as the lyra or psalterium. The anterior commissure is formed in connection with the dorsal part of the lamina terminahs. over and anterior to which the mesial walls of the cerebral hemispheres fuse. The posterior commissure is formed in connection with the back part of the roof of the diencephalon, behind the pineal diverticulum. The so-called middle or grey eommissare is not a commissure properly so called, but is formed by the fusion, over a limited area, of the grey matter of the mesial surfaces of the optic thalami. The habenular commissure is produced by the decussating fibres of the striae pineales. these fibres, as they decussate, forming the dorsal part of the pedicle of the pineal body. Septum Lucidum and Ventricle of the Septum. — ^The anterior part of the corpus callosum and its genu and rostrum are separated from the anterior part of the fornix by a cleft-hke interval, which is a part of the great longi- tudinal fissure. This interval is bounded on either side by a limited portion of the thin mesial waU of the cerebral hemisphere. These portions of the mesial walls of the cerebral hemispheres, known as the trapezoid plates, con- stitute the t\%o laminap of the scptum lucidum, which septum forms a partition between the adjacent portions of the lateral ventricles. The interval bet».veen the two layers of tiie septum lucidum is called the ventricle of the septum, or the fifth ventricle. It is destitute of an ependymal lining, and its cleft-like space is entirely discoimected with the cephahc prolongation of the central canal of the spinal cord. It therefore difiers from the ependymal ventricles of the brain. As stated, it is an isolated portion of the great longitudinal fissure of the brain. Lumen of the Neural Tube. — In the development of the spinal cord from the spinal part of the neural tube it has been stated that the ventral portion of the lumen (neural canal) of that part of the neural tube. ha\-ing become modified, persists as the central canal of the spinal cord. The lumen of the cephahc part of the neural tube, from which the various parts of the encephalon are developed, also persists and remains in direct continuity with the central canal of the spinal cord. In the cephahc part of the neural tube, however, the limaen tmdergoes certain modifications. At the calamus scrip torius of the fotirth ventricle the central canal of the spinal cord opens into the fourth ventricle, thus pertaining to the myelenee- phalon and metencephalon. In the mesencephalon it becomes very narrow, jmd forms the aqueduct of Sylvius, or iter a tertio ad quartum ventriculum, which leads from the fourth to the third ventricle. In the diencephalon it forms the third ventricle. The third ventricle com- municates by the foramina of Monro with the two lateral ventricles, which belong to the telencephalon. The central canal of the spinal cord is thus in communication with all the cerebral ventricles, properly so called. As previously stated, it is not related to the ventricle of the septum (fifth ventricle), this not being an ependymal 1468 A MANUAL OF ANATOA^ ventricle, as the others are, but merely an isolated portion of the great longi- tudinal fissure. Meninges of the Encephalon. — The walls of all the cerebral vesicles are invested by mesoderm, and this tissue becomes differentiated into the three meninges — namely, the dura mater, arachnoid, and pia mater. Choroid Plexuses. — ^The choroid plexuses of the two lateral, third, and fourth ventricles are developed as infoldings of the ependymal walls of the ventricles. Vascular mesenchyme (mesoderm) dips in between the two layers of each infolding, and in this manner plicss choroidecs are formed. These choroidal folds give rise to the choroid plexuses which, as they project into the ventricles, carry the ependymal walls, already infolded, before them. Development of the Peripheral Nervous System. The peripheral nerves are arranged in two groups — namely, spinal, which are derived from the spinal cord, and cranial, which arise from the brain. The spinal nerves are composed of two kinds of fibres — efferent, centrifugal, or motor, and afferent, centripetal, or sensory. A motor spinal nerve-flbre arises as the axon of a neuroblast or nerve-cell in the mantle-layer of the neural tube. (See Development of the Spinal Cord.) A sensory spinal nerve-flbre is developed from a cell of a spinal ganglion, and these gangUa are developed from the corresponding neural crest. Neural Crest (Ectoderm) Neural Tube derm ce of Sen.sory Roots Fig, 613. — Development of the Neurai, or Ganglion Crest (Keibel AND Mall) (after Von Lenhossek and Kollmann). Neural Crests. — The neural or ganglionic crests, right and left, are ridges of ectodermic cells, which lie on either side of the neural tube. They are derived from a single crest of ectoderm, which is formed by the fusion of the ectoderm over each neural fold, this single crest being situated mesially on the dorsal aspect of the neural tube, along the line of fusion of the neurail folds to close the tube. Subsequently the mesial crest divides into right. and left halves, which migrate to the lateral aspects of the neural tube. ^* Each neural crest becomes broken up into a number of segments, or ganglia, there being four pairs for the head-region, and thirty-one pairs for the region of the trunk. Spinal Ganglia. — The spinal ganglia are arranged in thirty-one pairs, right and left. Each cell of a ganglion acquires two poles— afferent or centripetal, and efferent or centrifugal, and, at this stage, it is consequently a bipolar cell. THE NERVOUS SYSTEM 1469 The centripetal or proximal pole, which is the axon of a ganghonic cell. grows into the dorsal part of the wall of the neural tube and forms part of the dorsal or posterior root of a spinal nerve. Within the marginal layer of the neural tube the centripetal pole or nerve-fibre divides into two branches — ascending and descending, which give off collaterals and terminate in arboriza- tions. The centrifugal or distal pole joins the ventral or anterior nerve-root of the same segment of the spinal cord, on the distal side of the ganglion, to form a spinal nerve. Though the cells of a spinal gangUon are originally bipolar, they become in the course of growth unipolar, the single pole having a T-shape. This is brought about by an excessive growth of one wall of the bipolar cell, which brings the two original poles into contact, when they fuse, and are now con- nected with the cell by one stalk or pole, which divides into a centripetal and a centrifugal process. Whilst the fibres of the dorsal or posterior roots of the spinal nerves grow into the mantle-layer of the neural tube from the cells of the spinal gangUa, the fibres of the ventral or anterior roots arise within the mantle-layer as the axons of its neuroblasts or nerve-cells. The fibres of the anterior roots there- fore grow out from the neural tube. Cranial Nerves. — The development of the cranial nerves, with the exception of the olfactory and optic nerves, corresponds for the most part with the development of the spinal nerves. The motor cranial nerve-fibres arise as the axons of nerve-cells of the brain and grow into the brain, whereas the sensory cranial nerve-fibres grow into the brain from the cells of the cephalic gangha. Cephalic Ganglia. — The cephalic gangUa, like the spinal ganglia, are developed from the neural crests, and they constitute four pairs of ganghonic groups — namely, trigeminal, acoustico-facial, glosso-pharyngeal, and vagal. They are all comparable to the spinal ganglia The trigeminal or Gasserian ganglion is connected with the sensory root of the fifth cranial nerve. The centripetal poles of its nerve-cells pass inwards into the brain, forming the large sensory root of the nerve, and the centrifugal poles of its cells pass peripheradly, forming the ophthalmic, superior maxiUary. and sensory part of the inferior maxillary nerves. The Gasserian gangUon is thus clearly comparable to a spinal ganglion. The small motor root of the fifth nerve is homologous to the motor or anterior root of a spinal nerve, inasmuch as its fibres arise as the axons of nerve cells tvithin the brain. The acoustico-facial ganglion resolves itself into facial and acoustic parts. The facial ganglion, known as the geniculate ganglion, is coimected with the genu of the facial nerve in the aqueduct of Fallopius. The centripetal poles of the nerve cells of this ganghon form the sensory root of the facial nerve — namely, the pars intermedia of IVrisberg, which passes inwards to the fasciculus solitarius and upper part of the glosso-pharyngeal nucleus. Many of the centrifugal poles of the cells issue from the ganglion as the chorda tympani nerve, which passes to the anterior two- thirds of the tongue as a nerve of special sense. The acoustic ganglion is represented by the vestibular and cochlear ganglia in connection with the auditory nerve. The vestibular ganglion is connected with the vestibular division of the auditory nerve in the internal auditory meatus. As in the other gangha, the centripetal poles of the cells of this ganglion form the centripetal fibres of the vestibular nerve, which pass inwards to the brain. The centrifugal poles of the cells leave the ganghon and form the peripheral part of the nerve as regards its distribution. The cochlear ganglion, known as the ganglion spirale, is connected with the cochlear division of the auditory nerve, and is situated in the spiral canal of the modiolus. Its nerve-celk are related to nerve-fibres as in the case of the vestibular ganglion. The glosso-pharyngeal ganglion, which is broken up into a jugular ganglion and a petrous ganglion, is comparable to a spinal ganglion. The centripetal poles of the nerve-cells, which issue from the gangUon, represent the centri- petal sensory fibres of the glosso-pharjTigeal nerve, passing into the brain. I470 A MANUAL OF ANATOMY The centrifugal poles of the nerve-cells, issuing from the ganglion, represent the peripheral sensory fibres of the nerve. The vagal ganglion, which is broken up into the ganglion of the root and the ganglion of the trunk, is disposed to- wards the sensory fibres of the vagus or pneumogastric nerve as in the case of the other ganglia. Neural Crest eural Tube , Spinal Ganglion Deyelopment of the Sympathetic Nervous System. The sympathetic ganglia may be re- garded as being developed from the ventral aspects of the neural crests and spinal ganglia, and they are therefore of ectodermic origin, according to this view. Certain cells become detached from the neural crests and spinal ganglia, and migrate ventralwards towards the region of the aorta, where they form the ganglionic sympathetic chain. The gang- lionic cells proliferate and are furnished with processes which become fibrillar. These fibrillar processes give rise to the chain which connects the ganglia, and also to the grey rami communicantes ajid the various visceral branches. Migratory Cells from Ganglion Motor Root of Spinal Nerve Sympathetic Ganglion Aorta Fig. 614. — Development of Sym- (schematic.) PATHETIC Ganglia. MENINGES OF THE ENCEPHALON. Dura Mater. The dura mater is a strong fibrous membrane which surrounds the encephalon, and is composed of two layers — outer and inner. The outer or periosteal layer serves as the internal periosteum or endocranium of the cranial bones, and the inner or sustentacular layer supports the encephalon. It is more firmly adherent to the bones fonning the base of the skull than over the cranial vault, and it is also firmly attached along the course of the sutures. At the various openings it is prolonged outwards, blending with the sheaths of the transmitted nerves, and also becoming continuous with the external periosteum or pericranium. At the sphenoidal fissure it passes into the orbit to form the orbital periosteum. At the lower margin of the foramen magnum the two layers of which the dura mater is composed separate. The external layer blends with the periosteum of the occipital bone around the margin of the foramen magnum. The internal layer is prolonged into the spinal canal, and forms the theca of the spinal cord. The outer surface of the dura mater is rough and flocculent, owing to fibrous processes which connect it to the inner surfaces of the cranial bones. Its inner surface is smooth and covered by endothelium. Superiorly, on either side of the superior longitudinal sinus, there are several small granular nodules, called Pacchionian bodies, which are best marked in old age. They indent the parietal bone, and protrude into the superior longitudinal sinus, carrying with them prolongations from the endothelial lining of the sinus, which separate them from the blood. THE NERVOUS SYSTEM I47» The Pacchionian bodies are enlargements of the vilh of the aiachnoid membrane (see p. 1481). Stractare. — The dura mater consists of fibrous and elastic tissues, arranged as parallel bundles. The intracranial dura mater differs from the dura mater of the spinal cord in the following respects : (i) it consists of two layers — outer or periosteal, and inner or sustentacular — ^whereas the spinal dura mater has only one layer, representing the sustentacular layer; (2) it furnishes certain processes or septa, which project into the cranial cavity, and separate parts of the encephalon from each other, whereas the spinal dura mater sends no septa into the spinal cord ; and (3) it contains venous sinuses, which are absent in the spinal dura mater. Subdural Space. — ^This is the interval between the dura mater and the arachnoid membrane. There is really no space, but simply sufficient interval to contain a minute quantity of serous fluid for lubricating purposes. The dura mater and the arachnoid are there- fore practically in contact with each other. Blood-supply. — The cranial dura mater is supplied by the meningeal arteries, which are also distributed to the inner table and diploe of the cranial bones. These vessels cire very numerous, and the chief are as follows on either side, from before backwards : (i) anterior meningeal, two in number, from the anterior ajid posterior ethmoidal arteries ; (2) meningeal, from the cavernous part of the internal carotid artery ; {3) small meningeal, from the middle meningeal, or from the first part of the internal maxillary artery ; (4) middle meningeal, from the first pjui: of the internal maxillary ; (5) menin- geal branches of the ascending pharjmgeal artery ; (6) posterior meningeal branch of the occipital artery ; and (7) posterior meningeal, from the vertebral artery. The anterior meningeal branch of the anterior ethmoidal artery arises from that vessel as it accompanies the nasal nerve on the cribriform plate of the ethmoid bone, and it takes part in the supply of the dura mater of the anterior fossa. The anterior meningeal branch of the posterior ethmoidal artery arises from that vessel after it has entered the cranial cavity through a minute foramen between the cribriform plate of the ethmoid and the sphenoid. It has a limited distribution to the dura mater in this region. The meningeal branch of the internal carotid artery arises from the cavernous part of that vessel, and enters the middle fossa to supply the dura mater. The small meningeal artery is usually a branch of the middle meningeal, but it may arise from the first part of the internal maxillary artery. It enters the cranial cavity through the foramen ovale, and supplies the adjacent dura mater and the Gasserian ganglion. The middle meningeal artery, as stated, is a branch of the first part of the internal maxillary artery. It is of large size, and enters the cranicd cavity through the foramen spinosum in the sphenoid bone, after which it divides into two branches, anterior and posterior. The anUrior branch passes for- wards, outwards, and upwards in a groove on the upper surface of the great wing of the sphenoid bone to the inner aspect of the antero-inferior angle of the parietal bone, where there is a groove, or sometimes a short canal. The position of the middle meningeal sirtery at this level is ascertained by taking a point on the exterior of the skull i^ inches behind the external angular process of the frontal bone, and i^ inches above the zygomatic arch. From this point the artery ascends in a branching meningeal groove near the anterior border of the parietal bone, as high as the superior longitudinal sinus. 1472 A MANUAL OF ANATOMY In this part of its course it furnislies numerous branches forwards and back- wards. The posterior branch passes outwards and upwards on the squamous part of the temporal bone, and then on to the inner aspect of the inferior border of the parietal bone, where there is a meningeal groove about the centre. From this point it ascends in a branching groove as high as the superior longi- tudinal sinus, giving off branches forwards and backwards. The distribution of the middle meningeal artery extends as high as the superior longitudinal sinus, forwards on to the frontal bone, and backwards on to the occipital bone. Besides supplying the dura mater and the inner table and diploe of the bones, the vessel furnishes the following branches : (i) Gasserian to the Gasserian ganglion ; (2) a petrosal branch, which passes through the hiatus Fallopii to supply the facial nerve in the aqueduct of Fallopius, and anastomose with the stylo-mastoid branch of the posterior Anterior Temporal Diploic Vein Posterior Temporal Diploic Vein Occipital Diploic Vein Fig. 615. — The Veins of the Diploe. (The outer tables of the Cranial Bones have been removed). auricular artery ; and (3) an orbital branch, which enters the orbit through the sphenoidal fissure, and anastomoses with the ophthalmic artery. The meningeal branches ol the ascending pharyngeal artery, which is a branch of the external carotid, are three in number. One passes through the foramen lacerum medium into the middle fossa ; another passes through the jugular foramen into the posterior fossa ; and the third passes through the anterior condylar foramen, likewise into the posterior fossa. The posterior meningeal branch ol the occipital artery passes through the jugular foramen into the posterior fossa. The posterior meningeal branch of the vertebral artery passes through the foramen magnum into the cerebellar fossa of the occipital bone. Meningeal Veins. — The veins accompanying the middle meningeal ai-tery are two in number. They pass through the foramen spinosum, and terminate in the pterygoid plexus of veins. The other meningeal veins are disposed in one of two ways. Some of them accompany the corresponding arteries and terminate in extracranial veins ; whilst others terminate in the various intracranial venous sinuses, in part directly and in part through means of venous lacunae. THE NERVOUS SYSTEM 1473 Veins of the Diplo'e. — These vessels axe situated in the cancellated tissue between the outer and inner plates of the cranial bones, and are exposed after removal of the outer plate. They are destitute of valves, and are arranged in the form of a network, from which the blood is returned by four diploic veins on either side, namely, frontal, anterior temporal, posterior temporal, and occipital. These terminate partly in extracranial veins, and partly in the intracranial venous sinuses and meningeal veins. The frontal diploic vein passes downwards, and escapes through an open- ing in the outer plate of the frontal bone at the supra-orbital notch, where it joins the communicating vein which passes between the supra -orbital and ophthalmic veins. It receives radicles from the frontal air-sinus of the same side. The anterior temporal diploic vein is confined to the back part of the frontal and anterior part of the parietal regions, and descends to terminate in two ways. It partly joins one of the extracranial deep temporal veins, by passing through an opening in the outer plate of the great wing of the sphenoid, and in part it ends in a meningeal vein, or in the spheno-parietal, or, it may be, the cavernous, sinus. The posterior temporal diploic vein is confined to the parietal region, and descends to the postero-inferior angle of the parietal bone, where it pierces the inner plate of that bone, and terminates in the lateral sinus. The occipital diploic vein occupies the occipital region, and pierces the inner table of the occipital bone, to terminate in the lateral sinus. Nerves of the Dura Mater. — The dura mater receives nerves from (i) the sympathetic plexuses which accompany the arteries ; (2) the three divisions of the fifth cranial nerve ; (3) the ganglion of the root of the pneumogastric nerve ; and (4) the hypoglossal nerve. Processes cf the Dura Mater. — The dura mater, as stated, is com- posed of two layers — outer or periosteal, and inner or sustentacular. The processes are formed by the inner or sustentacular layer, and are four in number, namely, the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellse. The falx cerebri is an extensive falciform process, which occupies the great longitudinal fissure of the cerebnmi, where it lies between the two cerebral hemispheres. Anteriorly it is almost pointed, and is attached to the crista galli of the ethmoid bone. Posteriorly it is broad, and is attached to the upper surface of the tentorium cerebelli along the median line, the straight sinus being situated at the place of junction. The superior border is convex, and is attached in the median line to the frontal, parietal, and occipital bones, extending upon the latter bone only as low as the internal occipital protuberance. The superior longitudinal sinus is situated along this border. The inferior border is concave and free. It overhangs the upper surface of the corpus callosum. from which it is separated by a slight interv^al. The inferior longitudinal sinus is situated within this border. The lateral surfaces face the mesial surfaces of the cerebral hemispheres. The tentorium cerebelli is an extensive crescentic sheet which covers the cerebellum. Superiorly it supports the posterior parts of the cerebral hemispheres, and is elevated along the median line, whence it slopes towards the attached borders. Anteriorly it presents a free, sharp, concave border, which forms, with the dorsum sellae of the sphenoid bone anteriorly, an oval opening, called the incisura tentorii, within which the mesencephalon is 93 1474 A MANUAL OF ANATOMY placed. Posteriorly and laterally the tentorium cere belli is convex, and is attached as follows, from behind forwards : (i) to the hori- zontal ridge on the inner surface of the tabular part of the occipital bone, where the process contains the lateral sinus ; (2) to the inner aspect of the postero-inferior angle of the parietal bone, where the process also contains the lateral sinus ; and (3) to the superior border of the petrous part of the temporal bone, where the process contains the superior petrosal sinus. Close to the apex of the pars petrosa the outer and anterior borders of the tentorium cere- belli cross, the outer border passing inwards to be attached to the posterior clinoid process of the sphenoid bone, and the anterior Falx Cerebri Frontal.-— Air-Sinus Styloid Process Tentorium Cerebelli Mastoid Process Fig. 616. — The Falx Cerebri, Tentorium Cerebelli, and Venous Sinuses OF THE Dura Mater (Left View). 1. Superior Longitudinal Sinus 4. Lateral Sinus 2. Inferior Longitudinal Sinus 5. Superior Petrosal Sinus 3. Straight Sinus 6. Internal Jugular Vein border passing forwards to be attached to the anterior clinoid process of that bone. The falx cerebelli extends forwards into the posterior cerebellar notch, where it lies between the two cerebellar hemispheres. It is falciform in outline. Superiorly it . is attached to the posterior part of the inferior surface of the tentorium cerebelli in the median line. Posteriorly it is attached to the internal occipital crest, and this portion bifurcates interiorly, the two divisions being connected to the lateral margins of the vermiform fossa. Along this posterior THE NERVOUS SYSTEM 1475 attachment it contains the occipital sinus and its two divisions. Anteriorly it ends in a free border. The diaphragma sellae is a small circular fold, horizontally placed, which forms a roof for the sella turcica or pituitary fossa of the sphenoid tone, and almost entirely covers the pituitary body. At its centre there is a small opening for the passage of the infundi- bulum. Venous Sinuses of the Dura Mater. — These are blood-channels or spaces situated bet^veen the two layers of the dura mater, and lined with endothelium. They are as follows : Superior longitudinal sinus. Spheno-parietal sinuses (two). Inferior longitudinal sinus. Circular sinus. Straight sinus. Superior petrosal sinuses (two). Lateral sinuses (two). Inferior petrosal sinuses (two). Occipital sinus. Transverse or basUar sinus. Cavernous sinuses (two). Petro-squamous sinuses (two). The superior longitudinal sinus is situated in the median line within the superior convex border of the falx cerebri. It extends from the crista galli of the ethmoid bone to the internal occipital protuberance, where, as a rule, it turns sharply to the right, and opens into the right lateral sinus. It sometimes, however, turns to the left, and opens into the left lateral sinus. Its posterior extremity is dilated, and forms the torcular Herophlli, which usually occupies a depression on the right side of the internal occipital protuberance, and is connected with the dilatation at the posterior extremity of the straight sinus by a transverse vessel. It increases in size as it passes backwards, and its shape is triangular, the base being directed towards the cranial vault. The apex is directed downwards, and in this region the sinus is crossed by a number of delicate fibrous bands, called the chordae Willisii. Opening into the sinus on either side there are venous spaces, called lacunae laterales, which are situated within the dura mater, and projecting into these lacunse from below, or into the sinus itself, there are several Pacchionian bodies, covered by the endothelial lining. The sinus receives the superior cerebral veins and some of the meningeal veins of the falx cerebri. The former open into it from behind forwards, so that the blood-flow in these veins is opposed to the current of b.'ood in the sinus, which is from before back- wards. The superior longitudinal sinus frequently communicates an- teriorly with the veins of the roof of the nose through the foramen ccBciim, and it communicates with the veins of the scalp by means of an emissary vein, which passes through the parietal foramen of each side, when that is present. The inferior longitudinal sinus (vein) is of small size, and is. situated in the lower free border of the falx cerebri over its posterior two-thirds. Its direction is backwards, and it opens into the front part of the straight sinus at the anterior margin of the ten- torium cerebelli. It is circular, and increases in size as it passes M76 A MANUAL OF ANATOLI Y backwards. Its tributaries are derived from the lower part of the falx cerebri, and from the adjacent parts of the mesial surfaces of the cerebral hemispheres. The straight sinus is situated at the junction of the falx cerebri with the tentorium cerebelli, and is formed by the union between the inferior longitudinal sinus and the vena magna Galeni at the anterior margin of the tentorium. It is triangular, and increases in size from before backwards. Its course is downwards and backwards in the median line to the left side, as a rule, of the internal occipital protuberance, where it becomes slightly dilated, and is continued into the left lateral sinus. Its terminal dilatation is connected with the torcular Herophili by a transverse vessel. In those cases where the superior longitudinal sinus passes into the left lateral sinus, the straight sinus passes into the right lateral sinus. In addition to the inferior longitudinal sinus and the vena magna Galeni, the straight sinus receives some of the superior cerebellar veins and tributaries from the falx cerebri and tentorium cerebelli. The lateral sinuses are two in number, right and left. Each sinus extends from the internal occipital protuberance to the postero-external compartment of the jugular foramen, through which it passes, to terminate in the bulb of the internal jugular vein. The sinus pursues a curved course. It passes outwards in the transverse groove on the inner surface of the tabular part of the occipital bone as far as the inner surface of the postero- inferior angle of the parietal bone. Here it ascends for a little in a groove, and, having described a sharp curve, it passes down- wards and inwards in the sigmoid groove on the inner surface of the mastoid portion of the temporal bone. Finally, it turns for- wards in the groove on the upper surface of the jugular process of the occipital bone to the jugular foramen. As far as the postero- inferior angle of the parietal bone the lateral sinus is contained within the attached border of the tentoriimi cerebelli, and, just before leaving this, it receives the superior petrosal sinus. The right lateral sinus is, as a rule, foimed by the superior longitudinal sinus, and, in these circumstances, is larger than the left, which is usually formed by the straight sinus. The reverse, however, may be the case. As stated, the torcular Herophili and the terminal dilatation of the .straight sinus are connected by a transverse branch. The lateral sinus of each side, in addition to the superior petrosal sinus, receives tributaries from the posterior part of the cerebrum and the superior and inferior surfaces of the cerebellum. It also receives the posterior temporal and occipital diploic veins, and the petro-squamous sinus, when that sinus is present. Near its termination it communicate? with the marginal sinus of the same side. The sinus communicates with extracranial veins by means of two large emissary veins, posterior condylar and mastoid, which pass through the corresponding foramina. These foramina. THE NERVOUS SYSTEM 1477 however, being inconstant, the emissary veins referred to are sometimes awanting. The name ' lateral ' or ' transverse ' is strictly applicable only to that part of the sinus which is contained within the attached border of the tentorium cerebelli, and extends from the internal occipital protuberance to the postero- inferior angle of the parietal bone. Beyond this latter point the sinus is known as the sigmoid sinus. Fi(»itat Air-Sinus Anterior Fossa Optic Nerve ^^^ ^^ balmic Artery Third Nerve Fourth Nerve ~ri-,'L_^ Region of Meckel's Cave 1 4 Fifth Nerve TTI" Facial Nerve iiditory Nerve so-pharyngeal Nerve ?neumogastric Nerve Sylvian Border of Small Wing of Sphenoid Ant, Pt. of Circ. Sinus ' (Ant. Intercav. Sinus) Pituitary Body Cavernous Siniis \\_.- Sixth Nerve Middle Foss.-, Basilar Sinus Sup. Petrosal Sinus r\~ Inf. Petrosal Sinus -> — Lateral Sinus Cerebellar Fossa Lateral Sinus Spinal Accessory Nerve Hypoglossal Nerve Spinal Cord Occipital Sinus Cerebral Fossa Torcular Herophili Fig. 617. — The Internal Base of the Skull, showing the Crania:. Nerves and Venous Sinuses. The occipital sinus is situated within the falx cerebelli along its attachment to the internal occipital crest. It is of small size, and is formed inferiorly by the union of the two marginal sinuses (inferior occipital) which lie on either side of the vermiform fossa and foramen magnimi, where they communicate with the posterior intraspinal veins and the terminal part of each lateral sinus. Superiorly it In certain cases the marginal opens into the torcular Herophili. 1478 A MANUAL OF ANATOMY or inferior occipital sinuses remain separate, and then each opens into the corresponding lateral sinus. The occipital sinus receives tributaries from the falx cerebelli and the inferior surface of the cerebellum, and it establishes a communication between the com- mencement and termination of the lateral sinuses. The cavernous sinuses are two in number — right and left — and are so named because the interior of each is broken up by fibrous filaments, which import to it a reticular appearance. Each sinus is situated on the side of the body of the sphenoid bone, and extends from the inner extremity of the sphenoidal fissure to the apex of the petrous part of the temporal bone. Anteriorly it receives the ophthalmic vein, or veins, from the orbit, and posteriorly it ter- minates by dividing into the superior and inferior petrosal sinuses. In addition to the ophthalmic vein, or veins, the cavernous sinus receives the spheno-parietal sinus and some of the inferior cerebral veins. It communicates with the angular vein of the face through the superior ophthalmic vein ; with its fellow of the opposite side through the circular sinus ; with the lateral sinus by the superior petrosal sinus ; with the internal jugular vein by the inferior petrosal sinus ; with the pterygoid plexus through the inferior ophthalmic vein, and by an emissary vein which passes through the foramen ovale, or through the foramen Vesalii ; and with the pharyngeal p'exus by an emissary vein which passes through the foramen lacerum medium. The internal carotid artery, with the cavernous sympathetic plexus, lies in contact with the inner wall of the sinus, and the sixth cranial nerve is close to the outer side of the artery. In connection with the outer wall of the sinus there are the third, fourth, and ophthalmic and superior maxillary divisions of the fifth, cranial nerves. The spheno-parietal sinuses are two in number — right and left. Each is of small size, and is situated on the inferior surface of the small wing of the sphenoid bone. It generally commences in connection with the anterior temporal diploic vein, and termi- nates in the anterior part of the cavernous sinus. The circular sinus surrounds the pituitary body in the pituitary fossa. It is composed of two transverse sinuses — anterior inter- cavernous and posterior intercavernous — which lie in front of and behind the pituitary body, and establish communications between the cavernous sinuses. The superior petrosal sinus is situated along the superior border of the petrous part of the temporal bone, and lies within the attached margin of the tentorium cerebelli. It commences at the back part of the cavernous sinus, and, having passed outwards and backwards, it opens into the lateral sinus as that is about to enter the sigmoid groove of the pars mastoidea. It receives tributaries from the cerebellum and tympanum. The inferior petrosal sinus occupies the groove at the junction of the basilar process of th(; occipital bone with the petrous part of the temporal bone. It commences at the back part of the cavernous sinus, and, passing backwards and slightly outwards, it leaves the THE NERVOUS SYSTEM 1479 cranial cavity through the antero-intemal compartment of the jugu- lar foramen, to terminate in the bulb of the internal jugular vein. It receives tributaries from the inferior surface of the cerebellum, and from the internal ear. The transverse or basilar sinus is really a plexus of veins, situated within the dura mater over the basilar process of the occipital bone, and extending as low as the anterior margin of the foramen magnum, where it communicates with the anterior intraspinal veins. It connects the anterior ends of the inferior petrosal sinuses with each other. The petro-squamous sinuses are two in number — right and left — and are situated, on either side, along the junction of the petrous and squamous parts of the temporal bone. The direction of each is backwards, and it opens into the lateral sinus as that is entering the sigmoid fossa of the pars mastoidea. Each petro-squamous sinus represents the continuation of the lateral sinus, in early life, to terminate in the primitive jugular vein. Sometimes there are no traces of these petro-squamous sinuses. Emissary Veins. — These axe vessels which pass through foramina in the cranial wall, and serve to establish communications between the intracranial venous sinuses and the extracranial veins. The principal emissary veins are as follo^^-s : mastoid, nasal, posterior condylar, parietal, and occipital. In addition to these there are emissary veins, which pass through (i) the foramen ovale, {2) the foramen Vesalii (when present), and (3) the foramen lacerum medium. The lateral sinus, in many cases, has two emissary veins, mzistoid and posterior condylar. The mastoid emissary vein is of large size. It passes through the mastoid foramen, and usually opens into the posterior jugular vein, but it may open into the posterior auricular vein. The posterior condylar emissary vein passes through the posterior condylar foramen, and opens into the suboccipital plexus, from which the blood is carried away by the vertebral and deep cervical veins. The mastoid and posterior condylar veins are not constant. The superior longitudinal sinus hcis three emissary veins — nasal, parietal, and occipital. The nasal emissary vein passes through the foramen caecum, in front of the crista galli of the ethmoid bone, and it establishes a communication between the superior longitudinal sinus and the veins of the roof of the nose. The parietal emissary vein passes through the parietal foramen, and opens into the occipital plexus, or into radicles of the superficial temporal vein. The occipital emissary vein passes from the torcular Herophili to the occi- pital plexus, being transmitted through a minute foramen which pierces the external occipital protuberance. The nasal, parietal, and occipital emissai^r veins are inconstant. As previously stated, the cavernous sinus communicates with (i) the angular vein of the face, (2) the pterygoid plexus, and (3) the pharj-ngeal plexus. The marginal or inferior occipital sinus communicates with the pos- terior intraspinal veins, and the transverse or basilar sinus communicates with the anterior intraspinal veins. Arachnoid Membrane. This is a very delicate membrane which loosely surrounds the encephalon, and is situated between the dura mater and pia mater. 1480 A MANUAL OF ANATOMY It does not dip into the fissures, except in the case of the great longi- tudinal fissure, its general course being over the gyri and other eminences and depressions of the encephalon. It is conspicuous at the base of the encephalon in the region of the inter-peduncular space, pons Varolii, and medulla oblongata. Its outer surface is practically in close contact with the mner surface of the dura mater, the extremely slight interval containing a very little lubricating serous fluid, and being known as the subdural space. Between the arachnoid and the pia mater there is the interval known as the subarachnoid space. The membrane furnishes sheaths to the various cranial nerves. Subarachnoid Space. — This space, as stated, is situated between the arachnoid and the pia mater. It is crossed by delicate trabeculse of connective tissue, which pass between the two membranes in a reticular manner. The meshes of this reticulum contain the cerebro- spinal fluid. The subarachnoid space communicates with the ventricles of the brain by means of five openings. Three of these communicate with the fourth ventricle, namely, the foramen of Magendie, and the foramina of Luschka, the former being situated in the median line of the roof of the ventricle a little above the calamus scriptorius, and the latter being situated each in the roof of the lateral recess of the ventricle. The other two openings communicate with the descending cornua of the lateral ventricles, each being situated at the extremity of the corresponding cornu. In some situations — as, for example, over the gyri — the arachnoid and pia mater are in close contact ; but in other localities the two mem- branes are more or less widely separated by intervals, called cisternse. These are principally three in number, namely, the cistema magna, cisterna pontis, and cistema basalis. The cisterna magna lies between the posterior part of the inferior surface of the cerebellum and the medulla oblongata. It is of large size, the arachnoid, which here passes from cerebellum to medulla, being widely separated from the pia mater. It is con- tinuous through the foramen magnum with the posterior part of the subarachnoid space of the spinal cord. The cisterna pontis is situated on the ventral aspect of the pons Varolii. Interiorly it is continuous with the anterior part of the subarachnoid space of the spinal cord, and in the region of the medulla oblongata it is continuous posteriorly with the cisterna magna. It contains the basilar artery. The cisterna basalis is situated in front of the pons Varolii, in which situation the arachnoid extends over the interpeduncular space from one temporal lobe to the other. It contains the arteries which form the circle of Willis. This cisterna is prolonged outwards on each side into the stem of the fissure of Sylvius, each of these pro- longations containing the middle cerebral artery. Anteriorly it extends in front of the optic commissure into the great longitudinal fissure over the upper surface of the corpus callosum, this prolonga- tion containing the anterior cerebral arteries. The subarachnoid fluid can be drained away in two directions. THE NERVOUS SYSTEM 1481 It can enter the lymph-spaces of the cranial nerves upon which the arachnoid is prolonged outwards in the form of sheaths; and it can enter the lacunae laterales through the intervention of the Pacchionian bodies, and from these lacunae it can make its way into the superior longitudinal sinus. Structure of the Arachnoid Membrane. — The arachnoid consists of fine fibrous tissue, arranged in interlacing bundles, the intervals between these bundles being occupied by delicate cellular membranes. Several such layers, intimately blended together, form the membrane. Beneath the arachnoid, and constituting a part of it, there is a reticulum of subarachnoid trabecules. These trabeculae consist, as in the case of the arachnoid proper, of fine fibrous tissue, but the intertrabecular spaces, instead of being occupied by cellular membranes, contain cerebro-spinal (subarach- noid) fluid. The trabecular reticulum connects the arachnoid \\-ith the subjacent pia mater. The superficial surface of the arachnoid is covered ■w-ith a delicate layer of endothelium. The nerves of the arachnoid are derived from the sympathetic system. Pacchionian Bodies. — These are small fleshy-looking bodies which are situated along the course of the superior longitudinal sinus, into which some of them project. They are also met with in connection with other sinuses, e.g., the lateral and straight sinuses. Each Pacchionian body is a localized projection of the arachnoid mem- brane, with which it is connected by a narrow pedicle. As stated, some Pacchionian bodies project into the superior longitudinal sinus ; others project from below into the lacunae laterales. In all cases the bodies carry before them the lining of the sinus. Super- ficially the bodies give rise to the Pacchionian depressions on the internal surface of the parietal bone near the superior border. Each Pacchionian body, as stated, is a localized projection of the arachnoid membrane (enlarged villus — Luschka). It contains a prolongation of the subarachnoid space and reticulum. This is surrounded by a prolongation of the arachnoid membrane, and external to this is the endothelial lining of the sinus or of the lacuna. The Pacchionian bodies constitute channels through which the subarachnoid fluid can be drained away from the subarachnoid space into the lacunae laterales, and thence into the superior longi- tudinal sinus, as well as into the other sinuses, e.g., the lateral and straight sinuses. They are quite rudimentary in early life, and are most conspicuous in advanced life. Pia Mater. The pia mater is the most internal covering of the encephalon. It is a very vascular membrane, which invests, and is closely adherent to, the entire surface. From its internal surface delicate processes pass into the cerebral substance, which represent the minute bloodvessels, surrounded by pia-matral sheaths. The pia mater not only invests the external surface, but also dips into the sulci, and covers the opposed surfaces of the gyri. It also furnishes 1482 A MANUAL OF ANATOMY sheaths to the various cranial nerves, which blend with their perineurium. It gives rise to two web-like expansions, namely, the tela choroidea inferior and tela choroidea superior. The tela choroidea inferior is situated in the lower part of the roof of the fourth ventricle, and from it are derived the choroid plexuses of that ventricle. The tela choroidea superior, or velum interpositum, is an invagination of the pia mater through the trans- verse fissure beneath the splenium of the corpus callosum. It lies underneath the body of the fornix, and its deep surface is covered by the ependymal lining of the third ventricle, the latter forming the roof of that cavity. The tela choroidea superior furnishes the choroid plexuses of the two lateral and third ventricles. The pia mater of the encephalon differs from the pia mater of the spinal cord in being thinner and less adherent to the nervous substance-. The greater thinness is due to the fact that it is destitute of the outer layer which characterizes the spinal pia mater. Structure. — The pia mater of the encephalon consists of a single layer of areolar tissue, which contains a great many small bloodvessels, these being derived from the larger vessels, lying in the subarachnoid space. The Cranial Nerves. The cranial nerves are arranged in twelve pairs. They have received numerical names according to the order in which they leave the cranial cavity from before backwards, and they are alsa known by functional names. The different pairs of nerves are as follows, in order from before backwards : First, or olfactory. Seventh, or facial. Second, or optic. Eighth, or auditory. Third, or oculo-motor. Ninth, or glosso-pharyngeal. Fourth, or trochlear (pathetic). Tenth, or pneumogastric (vagus). Fifth, or trigeminal (trifacial). Eleventh, or spinal accessory. Sixth, or abducent. Twelfth, or hypoglossal. The cranial nerves are connected to certain parts of the encephalon. and these connections constitute their superficial or apparent origins. The fibres, however, can be traced to certain collections of grey matter, which are called nuclei. From the deep positions occupied by these nuclei they constitute the deep origins of the nerves. First or Olfactory Nerve. — ^This nerve is a complex structure, and consists of (i) the olfactory lobe, and (2) the olfactory filaments or nerves, which are about twenty in number. The olfactory lobe has been already described (see p. 1397). The olfactory nerves are non-medullated. They arise as the axons of the olfactory cells of the olfactory mucous membrane of the nasal fossa, and enter the cranial cavity through the foramina of one half of the cribriform plate of the ethmoid bone. Thereafter they enter the grey matter on the ventral or inferior aspect of the olfactory bulb, and terminate in arborizations which intermingle THE NERVOUS SYSTEM 1483 with the arborizations formed by the dendrites of the mitral cells, situated in the granular layer of the bulb (see p. 1448). The olfactory nerve is the ner\^e of smell. Second or Optic Nerve.— This nerve arises from the brain by means of the optic tract, the deep connections of which have been already described (p. 1424). Each optic tract passes forwards and inwards to the optic commissure or chiasma, which is situated in Olfactory Bulb Fissure of Sylvius Broca's Area Li-cns Perforatus Anticus .. Tuber Cinereiun Cocpns Albicans Crus Cerebri Locus Perfotatu Posticus Pons Varolii Fifth Nerve Sixth Nerve Facial Nerve -^ Pars Intermedia Auditory Nerve-'' bsso-pharyngeol Ner%-e - Pneumogastric Nerve Spinal Accessory Xene' Hypoglossal Nerve Medulla Oblongata Spinal Cord Fig. 61 S. — The Base of the Encephalox, and the Cranial Nerves. I . Frontal Lobe (Orbital Surface) ; 2, Temporal Lobe ; 3. Cerebellum. front of the interpeduncular space. The optic nerve of each side arises from the anterior part of the optic commissure. It courses forwards and outwards to the optic foramen, through which it passes into the orbit, piercing the dura mater, and re- ceiving a sheath from it, as well as from the arachnoid membrane. Having reached the back part of the eyeball, it pierces the sclerotic and choroid coats ^ inch to the nasal or inner side X)i the axis 1484 ^ MANUAL OF ANATOMY of the eyeball, and terminates in an expansion which forms the most internal layer of the retina, called the nerve-fibre or optic layer. The optic nerve is the nerve of sight. Third or Oculo-motor Nerve.— The fibres of this nerve arise from the oculo-motor nucleus, which is situated in the grey matter of the ventral aspect (floor) of the aqueduct of Sylvius, on a level with M \ ; ).i' ■% \ Fig 619. — Scheme showing the Different Cell-groups which consti- tute, ACCORDING TO PeRLIA, THE NUCLEUS OF OrIGIN OF THE ThIRD Cranial or Oculo-motor Nerve (L. Testut's ' Anatomie Humaine'). 1. Posterfor Dorsal Nucleus 6. Antero-external Nucleus i'. Posterior Ventral Nucleus 7. Trunk of Oculo-Motor Nerve 2. Anterior Dorsal Nucleus 8. Crossed Fibres 2'. Anterior Ventral Nucleus 9. Fourth Cranial Nerve 3. Central Nucleus 9'. Nucleus of Origin of Fourth Nerve 4. Nucleus of Edinger and Westphal 9". Intercrossingof Fourth Cranial Nerves 5. Antero-internal Nucleus 10. Third Ventricle M. Middle Line the upper quadrigeminal body, and extends superiorly, for a short distance, on to the lateral wall of the third ventricle. The nucleus is intimately related to the posterior longitudinal bundle, through means of which it is connected with the trochlear and abducent nuclei. All three nuclei receive collaterals from the posterior longitudinal bundle ; and in this manner a functional association between these nuclei is maintained, and harmonious action is insured on the part of the muscles which are supplied by the nerves THE NERVOUS SYSTEM I4S5 arising from them. It consists of several groups of cells. As many as seven groups are ascribed to each oculo-motor nucleus by Perlia, which correspond to the seven muscles supplied by the oculo-motor nerve, and are disposed symmetrically. In addition to these, there is a mesially-placed group, the cells of which furnish fibres to both ociilo-motor nerves. The fibres which arise from the individual groups of each nucleus are regarded as supplying particular orbital muscles. Certain of the oculo-m.otor fibres of one side arise from the nucleus of the opposite side, the fibres from either side decussating at the median line. Moreover, each oculo- motor nerve is said to receive fibres from the abducent nucleu; of the opposite side, which ascend in the posterior longitudinal bundle and cross to the other side. Two views are entertained in regard to the nerve supply of the internal rectus muscle. According to one view, the muscle of one side is supplied by those fibres which have crossed from the oculo- motor nucleus of the opposite side. The other view is that the muscle of one side is supplied by those fibres which have crossed from the abducent nucleus of the opposite side. According to this latter \-iew the nerve-fibres which supply the external rectus muscle of one side and those which supply the internal rectus muscle of the opposite side arise from the same nucleus, namely, the abducent nucleus, and vice versa. Fibres are conveyed by the posterior longitudinal bundle from the oculo-motor nucleus to the facial ner\-e, and thence to the orbicularis palpebrarum and corrugator supercilii muscles. Course of the Fibres of the Third Nerve. — The fibres pass forwards from their origin through the tegmentum, the red nucleus, and the inner portion of the substantia nigra, and thereafter make their superficial appearance at the oculo-motor sulcus on the inner aspect of the crus cerebri. The third or oculo-motor nerve supplies the following seven muscles : the levator palpebrae superioris ; the superior, inferior and internal recti ; the inferior oblique ; the sphincter pupillae ; and the ciliary muscle. Fourth, Trochlear, or Pathetic Nerve. — The fibres of this ner\'e arise from the trochlear nucleus, which is situated in the grey matter of the ventral aspect (floor) of the aqueduct of Syhnus. on a level with the upper part of the lower quadrigeminal body. The nucleus is intimately related to the posterior longitudinal bundle, through means of which it is connected with the oculo-motor nucleus. The fibres are at first directed outwards and backwards, and then downwards and mwards to the upper part of the superior medullary velvm, or valve of Vieussens, which they enter. Here the ner\'e crosses to the opposite side, decussating with its feUow. after which it emerges from the upper end of the superior medullary velum, close below the lower quadrigeminal body, and by the side of the frenulum veli. Thereafter the ner^-e turns outwards over the superior pedimcle of the cerebellum, and is then directed forwards i486 A MANUAL OF ANATOMY round the outer aspect of the cms cerebri, between which and the temporal lobe it makes its superficial appearance. The fourth nerve supplies the superior oblique muscle of the eyeball. Fifth Cranial, Trigeminal, or Trifacial Nerve. — The fifth cranial nerve resembles a spinal nerve in having two roots — sensory and motor — ^the former being large, and having a ganglion, called the Gasserian ganglion. Sensory Root. — ^The fibres of this root are derived from the central poles of the bipolar cells of the Gasserian ganglion. After entering the pons Varolii each fibre divides into two branches — ascending and descending, as in the case of the fibres of the dorsal ■or sensory root of a spinal nerve. The terminal nuclei of these ascending and descending sensory fibres are two in number — ^upper and lower. The upper sensory nucleus is situated in the outer portion of the dorsal part of the pons Varolii, where it lies close to the outer side of the pontine or principal motor nucleus of the nerve. The ascending sensory fibres, after a short course, enter this nucleus and terminate in arborizations around its cells. The lower sensory nucleus, which is a continuation of the upper sensory nucleus, is an upward prolongation of the substantia gelatinosa of Rolando from the tubercle and funiculus of Rolando in the medulla oblongata. The nucleus is traceable as low as the dorsal grey cornu of the spinal cord on a level with the second cervical spinal nerve, where it is close to the substantia gelatinosa of Rolando. The descending sersory fibres, which are numerous and constitute the spinal or descending sensory root of the fifth nerve, pass downwards through the pons and medulla oblongata into the spinal cord, as low as the level of the second cervical spinal nerve. They are accompanied by the lower sensory nucleus, and at different levels they enter this nucleus and terminate in arborizations around its cells. The most of the axons of the cells of the terminal sensory nuclei pass inwards to the raphe and cross to the opposite side. They then become longitudinal and ascend in company with the mesial fillet or chief sensory tract, their destination being the optic thalamus of the side to which they have crossed. They thus constitute a trigemino-thalamic ascending tract. From these fibres collaterals are furnished to (i) the facial nucleus, and (2) the ventral vago-glosso- pharyngeal nucleus, or nucleus ambiguus, from the cells of which latter the efferent or motor fibres of the pneumogastric or vagus nerve arise. A few of the axons, however, enter the pontine or chief motor nucleus, and also the mesencephalic or accessory motor nucleus, of the nerve, and terminate in arborizations around its cells. Motor Root. — ^The fibres of this small root are derived from two nuclei — pontine and mesencephalic. The pontine or chief motor nucleus is situated in the outer portion THE NERVOUS SYSTEM 1487 of the dorsal part of the pons Varolii, close to the inner side of the upper sensory nucleus, and beneath the floor of the upper or pontine part of the fourth ventricle. The axons of the ceUs of this nucleus form the larger part of the small motor root. The mesencephalic or accessory nucleus is situated in the grey matter on the lateral wall of the aqueduct of Syhnus. The fibres which arise from the axons of the cells of this nucleus constitute the mesencephalic, Sylvian, or descending motor fibres of the fifth nerve. They enter the pons Varolii, and join the more numerous fibres from the pontine or chief motor nucleus to form the motor root of the fifth nerve. As the mesencephalic fibres descend they furnish many collaterals to the pontine nucleus. The large sensory and small motor roots appear, close together, on the lateral aspect of the ventral surface of the pons Varolii, the motor root h'ing above, and slightly internal to the sensory root. The sensory root enters, and the motor root emerges from, the pons Varolii. Distribution. — ^The fifth cranial nerve has an extensive distribu- tion through means of its three divisions — ophthalmic, superior maxillary, and inferior maxillary. Ophthalmic Nerve (Sensory). — (i) The front part of the cranium; (2) the integument of (a) the upper eyelid and [b) the root and tip of the nose; (3) the anterior part of the nasal mucous membrane, and the conjunctiva; (4) the eyeball; and (5) the lachninal gland. Maxillary or Superior Maxillary Nerve (Sensory). — (i) The integu- ment of the malar and anterior part of the temporal regions; (2) the integument of (a) the lower eyelid, {b) the side of the nose, (c) the upper lip, and (i) the part of the face between the lower eyelid and the upper lip ; (3) the pulps of the upper teeth, and the mucous membrane of the upper gum ; (4) a large part of the nasal mucous membrane ; (5) the mucous membrane of the maxillary- air- sinus or antrum of Highmore ; (6) the mucous membrane of {a) the naso-pharynx, and (6) the soft and hard palate and the tonsil. Mandibular or Inferior Maxillary Nerve (Sensory and Motor), — The sensory distribution of this nerv^e is as follows: (i) The integu- ment of (a) the temporal region, (&) the outer surface of the pinna, and (c) the external auditory meatus; (2) the integument of the lower lip, and that which covers the mandible; (3) the temporo- mandibular joint; (4) the parotid salivary gland; (5) the mucous membrane lining the buccinator muscle, and the integument cover- ing that muscle (through means of the long or sensory buccal nerve) ; (6) the mucous membrane (fungiform and conical papillae) of the anterior two-thirds of the tongue (common sensation) ; (7) the sub- maxillary and sublingual salivary glands ; and (S) the pulps of the lower teeth, and the mucous membrane of the lower gum. The motor distribution of the inferior maxiUary ner\^e is as follows: (i) The muscles of mastication — namely, {a) the masseter, {b) the -temporal, and (c) the external and internal pterygoid muscles; (2) the mylo-hyoid muscle and anterior belly of the digastric ; (3) the 1488 A MANUAL OF ANATOMY tensor tympani muscle by means of a branch from the otic ganglion ; and (4) the tensor palati muscle, through the otic ganglion. Sixth or Abducent Nerve. — The fibres of this nerve arise from the abducent nucleus, which is situated in the dorsal part of the pons Varolii, close to the median line. It lies above the striae acusticag on the floor of the fourth ventricle, subjacent to the eminentia teres. The fibres emerge from the inner part of the nucleus, and pass through the lower part of the pons in a forward and slightly downward and outward direction to the point where the nerve makes its superficial appearance, namely, the lower border of the pons, just external to the pyramid of the medulla oblongata. The abducent nucleus receives collaterals from the dorsal or posterior longitudinal bundle, and a functional connection is thereby established between that nucleus and the oculo-motor nucleus. The internal rectus muscle of one side and the external rectus of the other side are thus associated muscles. The sixth nerve supplies the external rectus muscle of the eyeball. Seventh or Facial Nerve. — The facial nerve is composed of two parts. One of these consists of efferent or motor fibres, and is known as the facial nerve proper. The other part, of small size, consists of afferent or sensory fibres, and is called the pars inter- media of Wrisberg. The facial nerve proper arises from the facial nucleus, which is situated deeply in the dorsal part of the lower portion of the pons Varolii. The fibres of the nerve pursue an intricate course before appearing superficially. They at first pass backwards and inwards to the floor of the fourth ventricle. Here they turn upwards, lying close to the median line in the form of a single bundle. The nerve then makes a sharp bend outwards, and passes forwards through the pons in a downward and outward direction to its place of emergence. In its course within the pons the nerve is intimately related to the dorsal aspect of the abducent nucleus. The intrapontine part of the facial nerve proper is intimately related to the following structures : 1. The abducent nucleus. 4. The spinal root of the fifth 2. The superior olive. nerve. 3. The corpus trapezoides. 5. The dorsal or posterior longitudinal bundle. The motor facial nucleus receives fibres from the following sources: (i) The corpus trapezoides, being thereby brought into connection with the cochlear division of the auditory nerve ; (2) the spinal root of the fifth cranial or trigeminal nerve, which is the sensory nerve of the face ; and (3) the pyramidal tract of the opposite side, being thereby brought into connection with the pre-Rolandic motor area of the cerebral cortex. All the foregoing fibres terminate within the nucleus in arboriza- tions around its component cells. THE NERVOUS SYSTEM 1489 The pars intermedia of Wrisberg or sensory portion of the facial nerve arises from the central poles of the bipolar cells of the genicu- late ganglion on the facial nerve in the aqueduct of Fallopius. This ganglion resembles the Gasserian ganglion of the fifth nerve and the spinal ganglia, and most of the peripheral poles of its bipolar cells give rise to the chorda tympani nerve. The pars intermedia emerges from the aqueduct of Fallopius into the internal auditory meatus. After issuing from that meatus it passes to the lower border of the pons Varolii, where it hes between the facial nerve proper and the auditor}- nerve. The nerve then enters the medulla oblongata, and passes downwards to the upper part of the nucleus of the fasciculus solitarius (see Glosso-phar^ngeal Xerv^e), and its fibres terminate in arborizations around the cells of the upper part of that nucleus. In this situation it is closely associated with the terminal afferent or sensory fibres of the glosso-phaiymgeal nerve. The facial nerve proper emerges from the brain at the lower border of the pons Varolii in front of, and internal to, the auditory nerve ; and the pars intermedia of Wrisberg enters between the facial nerve proper and the auditory nerve. Distribution, Motor Part (Facial Nerve Proper). — (i) The muscles of the face, including the buccinator ; (2) the occipito-frontalis ; (3) the muscles of the auricle ; (4) the posterior belly of the digastric and the stylo-hyoid; (5) the platysma myoides; and (6) the stapedius muscle, within the tympanic cavity. Sensory Part (Pars Intermedia of Wrisberg and Chorda Tympani). — The anterior two-thirds of the tongue (sense of taste). The chorda tympani nerve conveys secretory and vciso-dilator fibres from the facial nerve proper to the submaxillary and sub- lingual salivary glands. The lai^e superficial petrosal nerve, from the geniculate ganglion of the facial nerve, is concerned in the supply of the mucous mem- brane of the soft palate, the path being as follows: (i) Large super- ficial petrosal nerve (facial fibres) ; (2) the Vidian nerve; (3) Meckel's ganglion ; and (4) the descending palatine nerves. Eighth, Auditory, or Acoustic, Nerve. — The auditory nerve is the nerve of hearing and of equilibrium. It is an afferent or centripetal nerve which conducts impressions from the membranous labvrinth (cochlea and vestibule) to the medulla oblongata and pons Varolii, and thence to the cerebrum and cerebellum. It consists of two divisions — ^namely, the cochlear nerve or root, and the vestibular nerv'e or root. The fibres of the cochlear nerve arise from the bipolar cells of the spiral ganghon in the spiral canal of the modiolus, the modiolus being the central pillar of the osseous cochlea. The fibres of the vestibular nerve arise from the bipolar cells of the ganglion of Scarpa at the deep end of the internal auditorv meatus. The two nerves or roots reach the brain at the lower border of the pons VaroHi, external to the facial ner\^e.and ventral to the restiform body. They have different central connections, and 94 1490 A MANUAL OF ANATOMY consequently take different courses. The cochlear nerve passes round the outer side of the restiform body, whilst the vestibular nerve passes backwards on the inner side of that body, and each root has special terminal nuclei. Cochlear Nerve. — ^The terminal nuclei of the cochlear nerve, which is the nerve of hearing, are two in number — ^ventral and lateral. The ventral or accessory nucleus lies on the ventral aspect of the restiform body, between the cochlear and vestibular nerves. The tr/'Vji} iiii laaqm'i Fig. 620. — Terminal Nuclei of the Vestibular Nerve, with their Superior Connections (Schematic) (L. Testut's ' Anatomie Humaine '). I. Cochlear Root, with its Two Nuclei 2 Accessory Nucleus 3. Lateral Nucleus, or Tuberculum Acusticum 4. Vestibular Root 5. Internal Dorsal Nucleus 6. External Dorsal Nucleus, or Nucleus of Deiters 7. Nucleus of Bechterew 8. Inferior or Descending Root of Auditory Nerve 9. Ascending Cerebellar Fibres 10. Fibres passing to Raph^ 11. Oblique Fibres 12. Fillet 13. Inferior Sensory Root of Fifth Cranial Nenre 14. Pyramidal Fibres 15. Raph^ 16. Fourth Ventricle 17. Inferior Peduncle of Cerebellum (Restiform Body) 18. Origin of Striae Acusticas lateral or dorsal nucleus, or tuberculum acusticum, is situated on the lateral and dorsal aspects of the restiform body. The fibres of the cochlear nerve or root enter these two nuclei, and terminate in arborizations around their component cells. Central Connections of the Ventral and Lateral Cochlear Nuclei. — The ventral and lateral nuclei constitute cell-stations in the path of the fibres of the cochlear nerve, and from these cell-stations two fresh nerve-tracts arise, one being ventral, which constitutes the corpus trapezoides, and the other dorsal, which forms the striae acusticae. THE XERVOUS SYSTEM 1491 Ventral ochlear Tract. — The relays, or fresh supplies, of nerve- fibres for this tract are furnished by the cells of the ventral nucleus. The axons of these cells give rise to the trapezium, or corpus trape- zoides, which is reinforced by the axons of the cells of the nucleus trapezoides, and fibres from the superior olive of the same side. The trapezoidal fibres cross the median plane, and thereafter con- stitute the lateral or acoustic fillet, being further reinforced by fibres from the superior olive of the side to which they have crossed, and from the nucleus of the lateral fillet. The fibres of this fillet termi- nate in the lower quadrigeminal body and internal geniculate body, both of the same side. Dorsal Cochlear Tract. — ^The relays of fibres for this tract are furnished by the cells of the lateral nucleus. The axons of its cells form the striae acusticae, which cross the dorsal aspect of the resti- form body and the floor of the fourth ventricle. At the median line they pass forwards, and then cross to the opposite side. There- after they join the lateral or acoustic fillet of the side to which they have crossed. The lateral or acoustic fillet, as previously stated, derives its fibres from the following sources : (i) The corpus trapezoides ; (2) the striae acusticae; (3) the superior olive of both sides; and (4) the nucleus of the lateral fillet. It serves as a path of connection between the ventral and lateraV cochlear nuclei of one side, and the lower quadrigeminal body and internal geniculate body of the opposite side. It is to be noted that the ventral and lateral cochlear nuclei are slightly connected with the lower quadrigeminal body of the same side, but not with the corresponding internal geniculate body. The axons of the cells of the internal geniciilate body form a corticifetal tract which passes to the cortex of the first or superior temporal gyrus of the temporal lobe of the brain. The complex nervous chain associated with the cochlear nerve may be tabulated as follows : 1. The bipolar eells of the spiral ganglion. 2. The fibres of the cochlear nerve. 3. The ventral and lateral cochlear nuclei. 4. The fibres of the corpus trapezoides, reinforced as stated. 5. The striae acusticae. 6. The internal geniculate body. 7. The corticipetal tract from the internal geniculate body to the superior temporal gyrus. The cell-stations connected with this nervous chain are as follows: 1 . The ventral cochlear nucleus. 5. The nucleus of the lateral 2. The lateral cochlear nucleus. fillet. 3. The nucleus trapezoides. 6. The lower quadrigeminal 4. The superior olive of each body. side. 7. The internal geniculate body. Some of the fibres of the chain terminate in these cell-stations, and others are derived from the axons of the cells which compose the stations. 1492 A MANUAL OF ANATOMY Vestibular Nerve. — ^The terminal nuclei of the vestibular nerve, which is the nerve of equilibrium, are three in number — ^namely, (i) the dorsal or principal nucleus, (2) the descending nucleus, and (3) the nucleus of Deiters, associated with which there is the nucleus of Bechterew. 6 14 -^^^ Z Fig. 621. — Terminal Nuclei of the Cochlear Nerve, with their Supe- RioR Connections (Schematic) (L. Testut's ' Anatomie Humaine '). (The vestibular root and its terminal nuclei, with the efferent fibres of these latter, have been suppressed. In order not to obscure the trapezoid body, the efferent fibres of the terminal nuclei of the right side have been in a great part of their extent resected. The trapezoid body is consequently composed of only half of its fibres — namely, those which come from the left). 6". Crossed Fijjres of the Striae Acusticae going to the Superior Olivary Body of the oppo- site side 7. Superior Olivary Body 8. Corpus Trapezoides . 9. Trapezoid Nucleus 10. Lateral Fillet 11. Raph6 12. Pyramidal Tract 13. Fourth Ventricle 14. Inferior Peduncle of Cerebellum (Restifom Body) The dorsal or principal nucleus is situated in the floor of the fourth ventricle underneath the area acustica and strice acusticcB. The descending nucleus is continuous with the lower end of the dorsal nucleus, and it accompanies the descending fibres of the vestibular nerve into the medulla oblongata. The nucleus of Deiters is situated external to the dorsal and descending nuclei, and the 1. Vestibular Root of Auditory Nerve 2. Cochltar Root 3. Accessory Nucleus of Auditory Nerve 4. Lateral Nucleus, or Tuberculum Acusticum 5. Efferent Fibres of Accessory Nucleus 6. Efferent Fibres of Lateral Nucleus, forming the Striae Acusticae 6'. Direct Fibres of the Striae Acusticx going to the Superior Olivary Body of the same side THE NERVOUS SYSTEM 1493 nucleus of Bechterew represents the upper and outer part of the nucleus of Deiters. As the vestibular nerve passes backwards on the inner side of the restiform body, some of its fibres, to be presently described, turn downwards. The majority, however, pass to the dorsal or principal nucleus, the nucleus of Deiters, and the nucleus of Bechterew, and terminate in arborizations around the cells of these nuclei. A few of the vestibular fibres are regarded as passing directly to the cerebelliun (superior vermis). Central Connections of the Nuclei of the Vestibular Nerve. — ^The fibres of the vestibular nerve terminate in the nuclei just stated. Median Line \- III. Nerve .-.IV. Nerve V. (Chief Motor Nucleus) VI. Nerve VII. (Facial) IX. and X. (Glosso-pharyn- eeal and Pneumogastric) XII. (Hj-poglossal) '^^ XI. (Spinal Accessory) • ist Cervical Nerve Fig. 622. — Scheme showing the Continuation of the Grey Matter of THE Spinal Cord into the Medulla Oblongata, Pons Varolii, and Crura Cerebri (Poirier). (The separation into two columns on either side and the breaking up of these into Cranial Motor Nuclei are indicated). The dorsal or principal nucleus and the nucleus of Deiters (including the nucleus of Bechterew), are intimately related to the superior vermis of the cerebellum, and especially to the rocf-nucleus, by means of cerebellar fibres. This communication represents the direct sensory cerebellar tract of Edinger, and it is contained within the inferior peduncle of the cerebellum. The axons of many of the cells of the nucleus of Deiters and nucleus of Bechterew pass into the dorsal or posterior longitudinal bundle, within which they divide into ascending and descending branches. In this manner the dorsal 1494 A MANUAL OF ANATOMY longitudinal bundle is brought into communication with the vestib- ular nerve. Through means of the dorsal longitudinal bundle, which represents the ventral ground-bundle and anterior marginal bundle of Lowenthal in the spinal cord, the nucleus of Deiters is brought into communication with the anterior or motor cornua of Ihe spinal cord. Through means of this bundle the nucleus of Deiters is also brought into communication with the nuclei which control the ocular muscles — ^namely, the oculo-motor, trochlear, and abducent nuclei. The complex nervous chains associated with the vestibular nerve may be tabulated as follows: Cerebellar Chain. 1. The bipolar cells of the ganglion of Scarpa. 2. The fibres of the vestibular nerve. 3. The dorsal vestibular nucleus, nucleus' of Deiters, and nucleus of Bechterew. 4. The secondary cerebellar vestibular tract, or the direct sensory cerebellar tract of Edinger, leading to the superior vermis and roof-nucleus of the cerebellum. Spinal and Oculo-Motor Chains. 1 . The bipolar cells of the ganglion of Scarpa. 2. The flbres of the vestibular nerve. 3. The nuclei of Deiters and of Bechterew. 4. The secondary vestibular tract from the nuclei of Deiters and of Bech- terew to the dorsal or posterior longitudinal bundle, and thence to the motor cornua of the spinal cord and the motor nuclei of the ocular muscles. The nucleus of Deiters thus has important connections as follows: 1. The membranous 3. The motor cornua of the vestibule. spinal cord. 2. The cerebellum. 4, The motor nuclei of the ocular muscles. Descending Fibres of the Vestibular Nerve. — ^As the vestibular nerve passes backwards on the inner side of the restiform body, some of its fibres, as stated, take a downward course. These descending fibres constitute the so-called descending root of the vestibular nerve. They descend through the lower part of the pons Varolii into the medulla oblongata as low as the level of the cuneate tubercle. They are accompanied throughout by the descending nucleus, and they are usually regarded as terminating in aborizations around the cells of that nucleus. Superiorly they are related to the nucleus of Deiters, and some authorities have regarded them as fibres passing between the nucleus of Deiters and the cuneate nucleus. The cochlear and vestibular nuclei originally form one acoustic or auditory nucleus, which is developed from the rhombic lip. Ninth or Glosso-pharyngeal Nerve. — ^This nerve consists chiefly of afferent or sensory fibres, which grow into the medulla oblongata. THE NERVOUS SYSTEM 1495 but it also contains a few efferent or motor fibres, which arise within the medulla oblongata. AfiFerent or Sensory Fibres. — These fibres arise from the central poles of the bipolar cells of the jugular and petrous ganglia, which are situated on the glosso-phar\-ngeal nerve as it passes through the jugular foramen. These ganglia resemble the Gasserian ganglion of the fifth nerve and the spinal ganglia. Ha\nng entered the medulla oblongata, the afferent fibres end in t«o terminal sensory nuclei — namely, the dorsal vago-glosso-pharyngeal nucleus, and the nucleus of the fasciculus solitarius. The dorsal vago-glosso-pharyngeal nucleus consists of two parts — upper and lower. The upper part is situated in the grey matter of the floor of the lower or bulbar part of the fourth ventricle, imder- neath the superficial area known as the trig07ium vagi {ala cinerea), and immediatelv exiertuU to the h}-poglcssal nucleus. The loTJcer part is situated in the lower or closed part of the bulb, and lies in the grey matter which forms the lateral wall of the central canal of the bulb, being here situated behijid the h^'pcglossal nucleus. The highest part of the dorsal vago-glosso-phan-Tigeal nucleus represents the portion associated with the glosso-phar^Tigeal nerve, and the remaining and greater part belongs to the vagus ner^-e. The nucleus of the fasciculus solitarius is a column of grey matter and nerve-cells which accompanies the fasciculus solitarius, to be presently described, throughout the whole length of the medulla oblongata. A few of the afferent fibres of the glosso-phar\Tigeal ners^e enter the highest part of the dorsal vago-glosso-phar\Tigeal nucleus, and terminate in arborizations around its cells. The most of the afferent fibres, however, descend along with a few of the afferent fibres of the vagus nerve, the two sets of descending fibres constituting a strand, called the fasciculus solitarius {iractus solitarius B.) or respiratory bundle. This strand descends throughout the whole length of the medulla oblongata. It hes external to the dorsal vago-glosso-phar\Tigeal nucleus, inclining towards the ventral aspect of the upper part of that nucleus, and towards the dorsal aspect of its lower part. It is accompanied throughout by the nucleus of the fasciculus solitarius, and the glosso-pharynigeal afferent fibres of the fasciculus solitarius terminate, at different levels, in arboriza- tions around its cells. The fasciculus soHtarius is formed chieflv, if not entirely, by glosso-phar\Tigeal fibres. The fasciculus soli- tarius and its nucleus are comparable to the spinal or descending fibres (root) and lower sensory nucleus of the fifth ner\'e. Efferent or Motor Fibres.— These fibres arise within the medulla oblongata as the axons of some of the cells of the ventral vago- glosso-pharyngeal nucleus or nucleus ambiguus. This nucleus is situated iu the formatio reticularis grisea of the medulla oblongata, and is in line ^\^th the facial motor nucleus which is placed in the dorsal part of the lower portion of the pons Varolii. Both of these nuclei correspond to the motor cells of the ventral grev comu of 1496 A MANUAL OF ANATOMY the spinal cord. The nucleus ambiguus is ventral in position to the dorsal vago-glosso-pharyngeal nucleus, and the axons of its cells, some of which form the glosso-pharyngeal efferent or motor fibres, pass dorsalwards towards the more superficially placed dorsal vago-glosso-pharyngeal nucleus. They then alter their course and pass ventralwards and outwards, and associate themselves with the afferent or sensory glosso-pharyngeal fibres. The tuniculi of the glosso-pharyngeal nerve appear in the dorso- lateral sulcus of the medulla oblongata, between the olivary and restiform bodies, and immediately below the facial nerve. Distribution. — ^The glosso-pharyngeal nerve is distributed to (i) the mucous membrane of the posterior third of the tongue, of which part it is the nerve of taste, as well as of common sensation ; (2) the mucous membrane of the pharynx, tonsil, and fauces ; (3) the mucous membrane of the tympanum ; and {4) the stylo-pharyngeus muscle. It also furnishes secretory and vaso-dilator fibres to the parotid gland through means of (i) its tympanic branch (Jacobson's nerve), (2) the tympanic plexus, (3) the small superficial petrosal nerve, (4) the otic ganglion, and (5) the auriculo-temporal nerve. Tenth, Pneumogastric, or Vagus Nerve. — ^This nerve consists of afferent or sensory fibres, which grow into the medulla oblongata; and efferent or motor fibres, which arise within the medulla oblongata . Afferent or Sensory Fibres. — ^These fibres arise from the central poles of the bipolar cells of the ganglion of the root and the ganglion of the trunk of the nerve, which resemble the glosso-pharyngeal ganglia (jugular and petrous), the Gasserian ganglion of the fifth nerve, and the spinal ganglia. Having entered the medulla oblon- gata, the afferent fibres pass to the same two terminal sensory nuclei as do the afferent fibres of the glosso-pharyngeal nerve — namely, the dorsal vago-glosso-pharyngeal nucleus and the nucleus of the fasciculus solitarius — which have just been described in con- nection with the glosso-pharyngeal nerve. The most of the afferent fibres of the vagus nerve pass to the vagal portion of the dorsal vago- glosso-pharyngeal nucleus, which represents its greater and lower part, the highest part of the nucleus receiving, as stated, a few of the afferent fibres of the glosso-pharyngeal nerve. Within the vagal part of the nucleus the afferent fibres of the vagus terminate in arborizations around its cells. A few of the afferent fibres, however, descend along with most of the afferent fibres of the glosso- pharyngeal nerve, the two sets of descending fibres constituting the strand called the fasciculus solitarius, already described in connec- tion with the glosso-pharyngeal nerve. These descending afferent vagal fibres terminate, like the corresponding glosso-pharyngeal fibres, in the nucleus of the fasciculus solitarius, which has been described in connection with the glosso-pharyngeal nerve. The dorsal vago-glosso-pharyngeal sensory nucleus, and the nucleus of the fasciculus solitarius, also sensory, are therefore shared in common by the afferent or sensory fibres of the glosso- THE NERVOUS SYSTEM 1497 pharvTigeal and vagus nerves, but in unequal proportions. Only a few glosso-pharyngeal afferent fibres go to the dorsal vago-glosso- pharyngeal nucleus, whereas most of the vagal afferent fibres pass to that nucleus. In the case of the nucleus of the fasciculus solitarius it is the reverse. Efferent or Motor Fibres. — ^These fibres arise within the medulla oblongata as the axons of most of the cells of the ventral vago- glosso-pharyngeal nucleus or nucleus ambiguus, which has been described in connection with the glosso-phar\-ngeal nerve. The fibres pass dorsalwards to the more superficially placed dorsal vago- glosso-pharyngeal nucleus. They then alter their course and pass ventralwards and outwards, and associate themselves with the afferent or sensory vagal fibres. The ventral vago-glosso-pharA.'ngeal nucleus or nucleus ambiguus, which is a motor nucleus, is shared in common by the efferent or motor fibres of the glosso-pharvTigeal and vagus nerves, especially the latter. The funiculi of the pneumogastric or vagus nerve appear in the dcrso-lateral sulcus of the medulla oblongata, between the olivary and restiform bodies, and immediately below the funiculi of the glosso-phar^Tigeal nerve. Distribution. — The vagus ner\'e has a very extensive distribution on either side, of which the following is a summar\' : Motor Distribution. — (i) The muscles of the soft palate (except the tensor palati) ; (2) the constrictor muscles of the phar\Tix ; (3) the intrinsic muscles of the lar\Tix; (4) the muscular tissue of the oesophagus and stomach; and {5) the muscular tissue of \a) the trachea, {h) the bronchi, and (c) the bronchial tubes. Sensory Distribution. — (i) The phar^-nx, oesophagus, and stomach ; (2) the lar\Tix, trachea, and bronchial tubes to their terminal rami- fications ; and (3) the skin on the inner surface of the pinna, as weU as of the lower and back part of the external auditory meatus. Cardiac Fibres. — ^The cardiac fibres of the nerve are inhibitory (efferent) and depressor (afierent). The most important connection of the vagus nerve is that which is established with the bulbar or accessory portion of the spinal accessory nerve. Glosso-pharyngeal and Vagal Nuclei. — ^These two nerves, as stated, consist of afferent or sensory and efferent or motor fibres. The afferent fibres of both ner\-es share in common two terminal nuclei — namely, the dorsal vago-glosso-pharyngeal nucleus and the nucleus of the fasciculus solitarius. Most of the glosso-pharyngeal afferent fibres terminate in the nucleus of the fasciculus solitarius, and most of the vagal afferent fibres terminate in the dorsal vago- glosso-phar^-ngeal nucleus. According to the description which has been given of the dorsal vago-glosso-pharyngeal nucleus, it is a nucleus of termination, or sensory nucleus. According to certain authorities, however, it is a mixed nucleus — ^that is to say, it is both a nucleus of termination, or sensory nucleus, and a nucleus of origin, 1498 A MANUAL OF ANATOMY or motor nucleus. In accordance with this view, the nucleus con- tains two sets of cells — sensory and motor — some of the afferent glosso-pharyngeal and most of the afferent vagal fibres terminating in arborizations around the sensory cells, and some of the efferent fibres of each nerve arising as the axons of the motor cells. The nucleus of the fasciculus solitarius is a nucleus of termination, or sensory nucleus. The fibres of the pars intermedia of Wrisberg or sensory portion of the facial nerve terminate in the upper part of the nucleus of the fasciculus solitarius. The efferent or motor fibres of the glosso-pharyngeal and vagus nerves arise as the axons of the motor cells of the ventral vago- glosso-pharyngeal nucleus, or nucleus ambiguus, which is a nucleus of origin, or motor nucleus. According to the description which has been given of this nucleus, it gives origin to all the motor fibres of the two nerves. If, however, the dorsal vago-glosso-pharyngeal nucleus is a mixed nucleus, then some of the efferent or motor fibres of the two nerves arise as the axons of its motor cells. The axons of the cells of the terminal sensory nuclei are disposed like those of the cells of the terminal sensory nuclei of the fifth nerve. They cross to the opposite side, become longitudinal, and ascend in company with the mesial fillet or chief sensory tract to the optic thalamus of the side to which they have crossed. They constitute the vago-glosso-pharyngeal ascending thalamic tract. •Eleventh or Accessory (Spinal-Accessory) Nerve. — ^This is a motor nerve, which is really a continuation of the pneumogastric or vagus. Its fibres arise from the accessory nucleus (dorsal vago-accessory nucleus), which is situated partly within the medulla oblongata or bulb, and partly within the cervical part of the spinal cord. This nucleus consists of a column of large cells which is continuous with the dorsal vago-glosso-pharyngeal nucleus. The column extends from the level of the lower part of the olivary body to the level of the sixth cervical nerve. The bulbar portion of the nucleus is situ- ated on the dorso-lateral aspect of the hypoglossal nucleus. The spinal portion is situated in the lateral part of the anterior grey cornu of the cervical spinal cord, and its cells lie directly behind the motor cells which give origin to the anterior roots of the upper five cervical nerves. The fibres which arise from the bulbar portion of the accessory nucleus constitute the bulbar part of the accessory nerve, and are accessory to the vagus nerve. The fibres which arise from the spinal portion of the accessory nucleus constitute the spinal part of the accessory nerve. Bulbar Part. — The fibres of this part arise as the axons of the cells of the bulbar portion of the accessory nucleus. They are directed at first dorsalwards, and then outwards through the lateral part of the medulla oblongata or bulb, from which they emerge in the form of about five funiculi, placed below, and in line with, the funicuH of the pneumogastric nerve. They then pass outwards, lying within THE NERVOUS SYSTEM 1499 the cranial ca\'itv, and they join the spinal part of the accessory nen-e (which has entered the cranial ca\ity through the foramen magnum), the accessory nerve subsequent!}- emerging from the cranial ca\'ity through the jugular foramen. Spinal Part. — ^The fibres of this part arise as the axons of the cells of the spinal portion of the accessory nucleus. They are directed at first dorsalwards, and then outwards through the lateral column of the spinal cord, from which they emerge as a series of funiculi which succeed to the funiculi of the bulbar part, the lowest spinal funiculus being on level with the fifth cer\'ical ners'^e. The funiculi of the spinal part ascend, l\Tng in the subdural space between the ligamentum denticulatum and the posterior roots of the upper five cervical nerves. They enter the cranial cavity through the foramen magnum, and join the funiculi of the bulbar part, to form the accessory nerve, which, as stated, emerges from the cranial ca\-ity through the jugular foramen. Distribution of Accessory Nerve. — After emerging from the jugular foramen, the accessory nerve divides into two branches — internal and external — ^the internal branch containing the fibres of the bulbar part, whilst the external branch contains the fibres of the spinal part. Spinal Distribution. — ^The external or spinal branch supplies the sterno-cleido-mastoid and trapezius muscles. Bulbar Distribution. — The internal or bulbar branch passes over, and in close contact with, the ganglion of the trunk of tiie pneumo- gastric nerve. Its fibres are continued into (i) the phar^iigeal and superior lar\Tigeal branches of the ganglion of the trunk of the vagus, and (2) the trunk of the vagus beyond the ganglion. The bulbar fibres, through their connection with the vagus nerve, are probably distributed to ^) the muscles of the soft palate, excluding the tensor palati; (2) the constrictor muscles of the phar^Tix; and (3) the intrinsic muscles of the lar^-nx. The bulbar fibres ma}' also furnish (a) the inhibitory fibres to the heart, (b) the motor fibres to the oesophagus, and (c) the motor fibres to the stomach. The bulbar fibres of the accessory nerve are regarded by some authorities as arising from the column of cells which constitutes the ventral vago-glo5so-phar\-ngeal nucleus, or nucleus ambiguus. Twelfth or Hypoglossal Nerve. — The fibres of the hypoglossal ner\-e arise from the axons of the cells of the hypoglossal nucleus, which is situated within the medulla oblongata. This nucleus represents a column of large multipolar motor-cells, which extends from the level of the striae acusticae superiorly to the level of the upper part of the decussation of the p\Tainids inferiorly. The lower part of the nucleus is situated within the lower or closed part of the medulla oblongata, and its upper part lies within the upper, open, or ventricular part. The lower part lies in the grey matter which forms the ventro-lateral aspect of the central canal of the medulla oblongata. The upper part hes in the grey matter which covers the bulbar part of the floor of the fourth ventricle, and is imdemeath the area known as the trigonum hypoglossi. I500 A MANUAL OF ANATOMY The nerve-fibres issue from the ventral aspect of the nucleus, and the nerve-funiculi pass through the medulla oblongata in a dorso- ventral direction, lying between its anterior and lateral areas, and between the formatio reticularis alba and formatio reticularis grisea. Having reached the bottom of the ventro -lateral sulcus between the pyramid and the olive, they emerge from the medulla oblongata in line with the sixth cranial nerve superiorly. The two hypoglossal nuclei, right and left, are connected with each other by commissural dendrons; and each nucleus receives collaterals from the pyramidal tract of the opposite side, being thereby brought into connection with the pre-Rolandic motor area ot the opposite cerebral hemisphere. Distribution. — ^The hypoglossal nerve is the motor nerve of the tongue, and supplies (i) the stylo-glossus, (2) the hyo-glossus, (3) the genio-hyo-glossus, and (4) the intrinsic muscles of the tongue. Cranio-cerebral Topography. The auricular point is the centre of the orifice of the meatus auditorius externus. The pre-auricular point is situated in the depression between the tragus of the auricle and the condyle of the mandible. The bregma, or point of junction of the sagittal and coronal sutures, corresponds to the centre of a line connecting the two auricular points (the centre of the orifice of the meatus auditorius externus) . The lambda, or meeting of the sagittal and lambdoidal sutures, is situated about 2f inches above the inion, or external occipital protuberance. The pterion, or region of the spheno-parietal suture, is situated about I J inches behind the external angular process of the frontal bone, and about if inches above the zygomatic arch. The asterion, or point where the parieto-mastoid, occipito- mastoid, and lambdoid sutures meet, is situated about 2 inches behind the auricular point, very nearly in line with the upper border of the zygomatic arch. The sagittal line represents the line which connects the nasion, or meeting of the two fronto-nasal sutures, with the inion. The sagittal suture corresponds to that part of the sagittal line which extends from the lambda to the bregma. The coronal suture is indicated on either side by a line extending from the bregma to the pterion. The lambdoid suture (occipito-parietal) corresponds to a line extending from the lambda to the asterion. The squamo-parietal suture, and its continuation backwards as the parieto-mastoid suture, are indicated by a curved line, with the convexity upwards, extending from the pterion to the asterion, ■ the highest part of the curve being about 2 inches above the zygo- matic arch. THE NERVOUS SYSTEM 1501 The superior longitudinal sinus corresponds to a line drawn from the glabella to the inion, or external occipital protuberajice. For the most part it occupies the median line, but, as it grooves the upper portion of the tabular part of the occipital bone, it deviates to one side, most commonly the right side. The toreular Herophili is usually situated on the right side of the inion. The occipital sinus corresponds to a line drawn downwards from the inion. The transverse sinus on either side is indicated by a line drawn outwards from a point immediately above, and external to, the inion to a point immediately above the asterion. This line is slightly curved, the convexity being upwards. The sinus grooves the inner surface of one-half of the tabular portion of the occipitaLbone, along the line of attachment of the tentorium cerebelli ; and in the region of the asterion, where the sinus, in altering its course, describes a curve, it grooves the inner aspect of the parietal bone, close to the postero-inferior angle, for a very short distance. Inasmuch as the superior longitudinal sinus usually opens into the right transverse sinus, the right sinus is usually larger than that of the left side. The sigmoid part of the transverse sinus grooves the inner surface of the mastoid portion of the temporal bone, and the superior surface of the jugular process of the occipital bone. It consists of two limbs and a genu. The superior limb passes horizontally for- wards, and the inferior limb passes downwards and inwards. The genu intervenes between the two limbs, and its convexity is directed forwards. The following line indicates approximately the course of the sigmoid part of the transverse sinus: (i) Draw a line hori- zontally forwards from the asterion for fully | inch to a point on the root of the mastoid process in line with the upper part of the meatus auditorius extemus; (2) the line now curves, and passes down- wards and inwards on the front part of the mastoid process towards its tip for I inch, lying close to the groove between the back of the pinna and the mastoid process (the level to which this line descends is J inch below the lower margin of the orifice of the meatus audi- torius extemus) ; and (3) the line finally passes forwards for h inch to meet the jugular foramen, through which the sigmoid part of the transverse sinus leaves the cranial cavity to become the internal jugular vein. Part (i) of the preceding line indicates the superior horizontal limb of the sigmoid sinus; part (2) the inferior descending limb; and part {3) the terminal portion of the sinus passing forwards to the jugular foramen. The genu and descending limb of the sigmoid sinus lie directly behind the mastoid or tympanic antrum, being separated from it only by a very thin plate of bone. In pyogenic affections of the tympanum and antrum the genu and descending Umb of the sigmoid sinus are consequently liable to become affected with thrombosis. I502 A MANUAL OF ANATOMY The convexity of the genu of the sigmoid sinus is on a level with the temporo-mandibular joint, and lies from | to J inch behind the base of the suprameatal triangle, or | inch behind the pre-auricular point. The right sigmoid sinus is usually larger than the left. In many cases the genu is scarcely perceptible, and the horizontal and vertical limbs under these circumstances are practically almost in direct continuity with each other. The genu lies at a depth from the surface varying from | to | inch. Fig. 623. — Diagram showing the Relations of the Chief Cerebral Fissures to the Exterior of the Head (Reid). B.C. Transverse Fissure D.E., F.G. Reid's Perpendicular Lines Sy. Fis. Sylvian Fissure Sy.a. Fis. Anterior Limb of .Sylvian Fissure Sy.h.Fis. Posterior Horizontal Limb of Sylvian Fissure p.o.Fis. External Parieto-occipital Fissure + Parietal Eminence A. Glabella B. Inion C Auricular Point E. Pre-auricular Point F. .Superior Rolandic Point G. Posterior Border of Root of Mastoid Process H. Inferior Rolandic Point The middle meningaal artery corresponds to the centre o4 the zygomatic arch. At a point from i to J inch above the centre of the arch it divides into its two terminal branches— anterior and posterior. The large anterior division of the middle meningeal artery, as it lies in the groove, or, it may be, short canal, on the internal aspect of the antero-inferior angle of the parietal bone, is indicated by taking a point i^ inches behind the external angular process of the frontal bone, and i^ inches above the zygomatic arch. From this THE NERVOUS SYSTEM 1503 point it ascends almost vertically towards the sagittal suture, lying about I inch behind the coronal suture. The small posterior division of the middle meningeal artery hes about 2 inches behind the anterior division. The Sylvian point coincides with the pterion, and is situated about li inches behind the external angular process of the frontal bone, and about 2 inches above the zygomatic arch. It indicates the division of the stem of the fissure of Sylvius into its three limbs — anterior, ascending, and posterior. The anterior limb of the fissure Fig. 624. — The Outer Surface of the Right Cerebral Hemisphere, SHOWING the Relations of its Gyri and Fissures to the Exterior OF the Cranium (from a Preparation made by the Author). passes horizontally forwards for about i inch, and the ascending limb upwards and slightly forsvards for a variable distance, from the Sylvian point. The pars orhitalis of the frontal lobe of the cerebrum lies helow the anterior limb ; the pars triangularis of the frontal lobe is situated between the anterior and ascending limbs ; and the pars basilaris of the frontal lobe is situated directly behind the ascending limb. The pars triangularis of the left side {le cap of Br oca) is the seat of the speech-centre. 1504 A MANUAL OF ANATOMY The posterior limb of the stem of the fissure of Sylvius is long, and is directed, for the most part, horizontally backwards for fully 2 inches, after which it turns upwards into the parietal lobe for a short distance. The line which indicates the course of the posterior limb is called the Sylvian line. It extends from the Sylvian point backwards for fully 2 inches, and then vertically upwards for about I inch towards the region of the parietal eminence. The parietal lobe and a small portion of the frontal lobe lie above the Sylvian line, and the temporal lobe lies below it. The superior Rolandlc point is situated ^ inch behind the centre of the sagittal line, which connects the nasion and the inion. This point approximately represents the upper extremity of the fissure of Rolando. The inferior Rolandic point is situated on the Sylvian line about I inch behind the Sylvian point, and 2 inches above the pre- auricular point. It indicates the point where the fissure of Rolando, if sufficiently prolonged, would meet the posterior limb of the stem of the fissure of Sylvius. The Rolandic line is represented by a line connecting the superior and inferior Rolandic points. The Rolandic angle is the angle which the Rolandic line forms with the sagittal line. It ranges from 65 to 70 degrees. The Rolandic line, if sufficiently prolonged, would cross the zygomatic arch at its centre. It indicates, in a general way, the course of the fissure of Rolando, but this fissure usually ceases at a point i inch above the Sylvian line. The cerebral convolutions directly in front of, and behind, the Rolandic line are (i) the precentral, or ascending frontal, convolution (motor area) in front, and (2) the post-central, or ascending parietal, convolution (sensory area) behind. The Rolandic line represents the boundary-line between the frontal and parietal lobes of the cerebral hemisphere. The base-line of Reid represents a line drawn backwards from the centre of the infra-orbital margin through the pre-auricular and auricular points to the inion. The fissure of Rolando may be deter- mined from Reid s base-hne in the following manner : Two lines are drawn upwards to the sagittal line perpendicular to the base-line, one from the pre-auricular point and the other from the posterior border of the mastoid process close to its root. These two lines, together with the sagittal and Sylvian lines, enclose a quadrilateral area, and the diagonal connecting the postero-superior and antero- inferior angles represents the fissure of Rolando except at its superior and inferior limits. The parietal eminence, which is usually indefinite, corresponds to the region situated | inch behind the centre of a line connecting the pre-Rolandic and pre-auricular points. It indicates the position of the supramarginal gyrus of the parietal lobe of the cerebral hemisphere. The frontal eminence corresponds to the middle frontal convo- lution. THE NERVOUS SYSTEM 1505 The foramen magnum, through which the medulla oblongata is continuous with the spinal cord, hes midway between the mastoid processes. Its posterior margin is 2 inches from the inion in a downward and forward direction. The tentorium cerebelli and superior surface of the cerebellum practically coincide with the level of the transverse sinus, as indi- cated by a line, slightly curved upwards, connecting the inion and asterion. The lower level of the cerebral hemisphere may be indicated by the following line: Commencing at a point J inch external to the nasion, the line passes outwards in an arched manner, with the convexity upwards, lying about ^ inch above the centre of the supra-orbital arch. It then inclines downwards and crosses the temporal ridge of the frontal bone about i inch above the fronto- malar suture, the guide to which is a point just above the outer canthus of the eyelids. Thereafter the line passes backwards and shghtly downwards to the Sylvian point, and thence to the upper border of the posterior part of the zygomatic arch. From this point the line passes backwards, Ipng about ^ inch above the upper margin of the orifice of the meatus auditorius extemus. It then crosses the supramastoid crest (posterior root of the zygoma), and passes to the asterion. Thereafter it nearly follows the line of the transverse sinus from the asterion to a point a little above, and external, to the inion. In other words, speaking generally, the cerebral hemisphere extends as low as the superior cur\-ed line of the occipital bone posteriorly, the upper border of the zygomatic arch laterally, and the upper part of the e3'ebrow anteriorly. The frontal lobe of the cerebral hemisphere is to a large extent in contact with the frontal portion of the frontal bone, but it is also related to the anterior part of the parietal bone as far back as the Rolandic line. The parietal lobe is related to the part of the parietal bone which lies behind the Rolandic line. The lobe extends as far back as the parieto-occipital fissure, which is usually situated opposite the lambda. The occipital lobe occupies the cerebral fossa of the tabular part of the occipital bone, its limits being the level of the lambda superiorly and the level of the inion inferiorly. The temporal lobe is under cover of the squamous portion of the temporal bone and the postero-inferior part of the parietal bone. The parallel sulcus, which separates the first and second temporal convolutions, is indicated by a line dra\NTi from the lambda to the marginal tubercle on the temporal or posterior border of the malar bone, about ^ inch below the fronto-malar suture. 95 THE EYE The eyeball is almost spherical. It consists of the segments of two spheres, namely, a large posterior or sclerotic segment, which is opaque, and a small anterior or corneal segment, which is trans- parent. The sclerotic segment forms five-sixths of the eyeball, and the corneal segment forms one-sixth. The centre of the Levator Palpebrae Superioris Hyaloid Canal ' (Canal of Stilling) Canal of Schlemm Hyaloid Membirne Retina . Choroid Rectus Superior ^.Sclerotic Arteria_ ; /Centralis /•• / Retinae Let Iris' Ciliary , i> Processes M Canal of Petit Rectus Inferior Fornix Conjunctivse Fig. 625. — Vertical Sagittal Section of the Eye and its Appendages (Hirschfeld and Leveill£). corneal segment is called the anterior pole, and the centre of the sclerotic segment is known as the posterior pole. The sagittal (antero-posterior) axis, or axis of vision, of the eyeball is repre- sented by a line connecting the anterior and posterior poles. The equator is represented by a line encircling the eyeball opposite the centre of the axis of vision, the diameter of the circle being 1506 THE EYE *507 about I inch. The plane of this circle would therefore divide the eyeball into two halves— an anterior half, consisting of the corneal segment and the front part of the sclerotic segment, and a posterior half, consisting of the back part of the sclerotic segment. The meridian is represented by a line encircling the eyeball at right angles to the equator, and passing through the anterior and pos- terior poles. Posteriorly the eyeball receives the optic nerve, which pierces the sclerotic coat at a point about |^ inch to the inner side of, and about ^^ inch below, the posterior pole. The eyeball is composed of three coats, concentrically arranged, as follows : (i) an external coat, consisting of an opaque part, called the sclerotic, and a transparent part, called the cornea ; (2) a middle coat, which is vascular, pigmented, and muscular, and consists of (a) a posterior part, called the choroid coat, {h) an anterior part, called the iris, and (c) an intermediate part, representing the ciliary body ; and (3) an internal coat, called the retina. These three coats enclose a cavity which contains the refracting media, these being three in number, as follows : (i) a fluid, called the aqueous humour, which lies between the cornea and the crystal- line lens, where it occupies the anterior and posterior chambers, into which this region is divided by the iris ; (2) a solid body, called the crystalline lens, which lies behind the aqueous humour ; and (3) a soft gelatinous body, called the vitreous body, which occupies the large space behind the crystalline lens. Coats of the Eyeball. Refracting Media. External = sclerotic and cornea. Aqueous humoior. Middle = choroid, ciliary body, Jind iris. Crj^alline lens. IntCTnal = retina. Vitreous body. External Coat. Sclerotic Coat. — The sclerotic (white of the eye) is a strong white fibrous coat of great density, which surrounds the posterior five- sixths of the eyeball, and maintains the shape of the organ. An- teriorly it unites, and becomes continuous, with the cornea, which it slightly overlaps. The junction of the two is indicated by a slight groove, called the sulcus sclerce, and the union is known as the corneoscleral junction. Posteriorly the sclerotic is pierced by the optic nerve, this part being known as the optic entrance. It is situated, as stated, at a point about ^ inch to the inner side of, and about ^ inch below, the posterior pole of the eyeball. The part of the sclerotic corresponding to the optic entrance is pierced by a number of openings for the passage of the fasciculi of the optic nerve, and is hence called the lamina cribrosa. Around the optic entrance there are numerous minute openings for the ciliary vessels and nerves, and in this situation the dura- matral sheath of the optic ner\'e blends with the sclerotic. About midway between the optic entrance and the comeo-scleral junction i5o8 A MANUAL OF ANATOMY the sclerotic is pierced by four openings for the passage of the vencB vorticoscB of the choroid. The sclerotic is thickest posteriorly around the optic entrance. It is also thick near the corneo-scleral junction, where it gives insertion to the recti muscles, from the tendinous expansions of which it receives accessions of fibres. The outer surface of the sclerotic is covered by a membranous investment, called the capsule of Tenon, and between the two there is the perisclerotie lymph-space or Tenon's space, which is broken up into a reticulum by processes of connective tissue which pass between the capsule of Tenon and the sclerotic. This space com- municates with the subdural and subarachnoid spaces. The inner surface is of a dark brown colour, and presents grooves for the ciliary vessels and nerves. It is lined with connective tissue containing pigment cells, this layer being called the lamina fusca. Processes from this layer pass to be attached to the choroid coat, and these processes, together with vessels and nerves, traverse an interval, which represents the perichoroidal lymph-space. This space communicates with the perisclerotie lymph-space through the vascular openings in the sclerotic. Anteriorly the sclerotic blends with the cornea at the corneo-scleral junction, the sclerotic slightly overlapping the cornea. Posteriorly, around the optic entrance the sclerotic blends with the dura-matral sheath of the optic nerve. Structure. — ^The sclerotic is composed of fibrous tissue, mixed with elastic fibres, and it contains many connective-tissue cor- puscles. The fibres are arranged in bundles, which are disposed longitudinally and transversely, and interlace with one another. The connective-tissue corpuscles occupy spaces between the fibres, which may be regarded as lymph-spaces. Arteries. — These are the short ciliary group of posterior ciliary arteries, and the anterior ciliary arteries, which are branches of the ophthalmic artery. The vessels belonging to the former group are disposed in the form of capillary networks ; whilst the vessels derived from the latter form a ring near the corneo-scleral junction beneath the conjunctiva, to which ring they converge in the sub- stance of the sclerotic. The sclerotic veins open into the anterior ciliary veins, and into the vencB vorticoscB of the choroid. Nerve-supply.— The ciliary nerves. The capsule of Tenon will be found described on p. 1151. Cornea. — ^The cornea is the transparent part of the external coat of the eyeball, of which it forms the anterior sixth, and it serves to transmit light. It is almost circular, its transverse measurement being slightly greater than the vertical. At its cir- cumference it is continuous with the sclerotic, by which it is slightly overlapped. The anterior surface is convex. The posterior surface is concave, and forms the anterior boundary of the anterior chamber of the eye. THE EYE 1509 Structure. — ^The cornea consists of five layers, which are as follows, from before backwards : 1. The conjtmctival epithelium. 2. The anterior elastic lamina. 3. The substantia propria. 4. The posterior elastic lamina. 5. A layer of endothelium. The eonjunctival epithelium is of the stratified variety, there being not less than five strata of cells, and it is continuous with the epitheUum which covers the free surface of the conjimctiva. The 1 Stratified Epithelium of / Conjunctiva ]~~ Membrane of Bowman or Anterior Elastic Lamina Substantia Pn^nia Posterior Elastic Lamina or MemlM^ne of Descemet Single Layer of Sc^uamous Epithelium linmg Descemet's Membrane Fig. 626. — Vertical Section of the Cornea (magnified). cells of the deepest stratum are columnar ; succeeding to these there are layers of polygonal cells ; and these in turn are overlaid by layers of squamous cells. The anterior elastic lamina (Bowman) is probably of the same nature as the fibrous portion of the substantia propria. It is closely connected with the substantia propria, is thin, and contains no corpuscles. The substantia propria is composed of modified connective tissue, arranged in bundles which form superimposed laminae. These laminae amount in number to about sixty: The fibres of alternate laminae cross each other at right angles, and at the circumference of the cornea they are continuous with the fibres of the sclerotic. I5IO A MANUAL OF ANATOMY The successive laminae are connected by cement substance, and within this substance there are branched spaces, called the corneal spaces or lacunae, which communicate with each other by very delicate canaliculi. Each of these spaces contains a nucleated connective- tissue corpuscle, called the corneal corpuscle. These corpuscles, like the spaces which they occupy, are branched, and the offsets of adjacent corpuscles communicate with one another. As seen in vertical sections of the cornea the corpuscles are spindle- shaped, but in horizontal sections they appear flattened out, and give off their branches. The posterior elastic lamina, or membrane of Descemet (mem- brane of Demours), covers the posterior surface of the substantia propria. It is thicker than the anterior elastic lamina, and is composed of an elastic homogeneous membrane, which is very brittle. When stripped from the substantia propria it comes away in shreds, and these curl up at their ends in such a manner that the anterior or attached surface of each shred is turned inwards. At the circumference of the cornea the posterior elastic lamina becomes broken up into fibres. The most posterior of these fibres pass in a radiating and reticular manner into the iris, and they form the ligamentum pectinatum iridis, the intervals between the fibres of which represent the spaces of Fontana. The layer of endothelium lines the posterior surface of the posterior elastic lamina, and consists of one stratum of cells. It is continued over the front of the iris, and into the spaces of Fontana. The cornea in the adult is non-vascular, except at the circum- ference, in which situation there are the conjunctival and sclerotic capillaries, which terminate in loops. Being destitute of blood- vessels, the nourishment of the cornea is maintained by the flow of lymph through its substance. Nerve-supply. — The nerves are derived from the ciliary nerves, and are very numerous. They enter the anterior part of the sclerotic, and form a plexus around the corneo-scleral junction. Offsets from this plexus enter the cornea, and form what is known as the plexus annularis. From this plexus delicate offsets are given off, which traverse the substance of the cornea and pass through the anterior elastic lamina. They then give rise to a fine plexus upon the surface of that lamina, called the subepithelial plexus. From this plexus, in turn, minute fibrils are given off, which pass amongst the cells of the conjunctival epithelium, and almost reach the surface, forming an intra-epithelial plexus. Ligamentum Pectinatum Iridis. — As stated, the posterior elastic lamina at its circumference breaks up into fibres. The most posterior fibres, which pass in a radiating and recfcicular manner into the iris, constitute the ligamentum pectinatum iridis, and they are covered by a prolongation of the endothelial layer of the cornea. Spaces of Fontana. — These spaces represent the irregular intervals which lie between the radiating and reticular fibres of the liga- mentum pectinatum iridis. They are lined by a prolongation THE EYE 15" of the endothelial layer of the cornea, and they communicate internally with the anterior chamber and the lymph spaces withm the iris, and externallv with the canal of Schlemm. Canal of Schlemm (canal of Fontana, simts circularis iridis, or sinus venosus sclerce).— This canal is situated deeply in the sclerotic, close to the comeo-scleral junction. It communicates internally with the anterior chamber through means of the spaces of Fontana, and with the veins of the iris, and externally with the veins of the sclerotic. Middle Coat. I. Choroid Coat. — ^This is a very vascular, deeply pigmented tunic of a dark brown colour, which lies between the sclerotic and the retina. It extends over the posterior five-sixths of the eyeball, Lamina Saprachoroidea{- Z^ Arterio- Venous Layer Membrana ChoricM;apil 1 aris Membrane ef Bruch Pigmentary Layer of the Retina Fig. 627. — Vertical Section of the Choroid Coat. (The Pigmentary Layer of the Retina is also shown). and reaches as far forwards as the ora serrata of the retina. An- teriorly it is connected with the circumference of the iris, and pos- teriorly it is pierced by the optic nerve. Its outer surface is con- nected to the inner surface of the sclerotic by means of the lamina fusca and its processes, as well as by vessels and nerves which cross the perichoroidal lymph-space. Its inner surface is in contact with the pigmentary layer of the retina. Structure. — ^The choroid coat consists of connective tissue, blood- vessels, and branched pigment cells. It is composed of three layers, which are as follows, from without inwards : ^i) the lamina suprachoroidea ; (2) the choroid proper ; and (3) the lamina basalis, or membrane of Bruch. The lamina suprachoroidea is composed of delicate, non-vascular lamellae, each of which is made up of elastic fibres, arranged in a reticular manner, and of branched pigment cells. The choroid proper consists principally of bloodvessels and pig- I5I2 A MANUAL OF ANATOMY ment-cells, supported by connective tissue. The bloodvessels are arranged partly as arteries and veins, and partly as capillaries. The choroid proper is therefore composed of two layers, namely, external or lamina vasculosa, and internal or lamina chorio- capillaris. The lamina vasculosa (arterio-venous layer) is composed of (i) branches of the short ciliary group of the posterior ciliary arteries, which pass forwards before they turn inwards to ter- minate in capillaries ; and (2) veins, which form the chief part of the lamina vasculosa, and are called the vense vorticosse. These veins are very closely set, and are arranged in a whorled manner. They ultimately converge and form about four vessels, which pierce the sclerotic nearly midway between the optic entrance and the comeo-scleral junction, at points equally distant from each other. Scattered throughout the lamina vasculosa there are branched pigment-cells. The lamina chorio-capillaris, or tunica Ruyschlana, is composed of a plexus of capillary bloodvessels, the arteries leading to it being derived from the short ciliary arteries. The lamina vasculosa and lamina chorio-capillaris are connected by fine elastic fibres, which form what is known as the stratum intermedium. The lamina basalis, or membrane of Bruch, is situated on the inner surface of the lamina chorio-capillaris, which it separates from the pigmentary layer of the retina. It is a very delicate membrane, without any very definite structure. Tapetum. — This is present in certain animals. It lies between the lamina vasculosa and the lamina chorio-capillaris in the stratum intermedium, and it gives rise to a rainbow-like appearance. In some animals it is fibrous in structure, and in others cellular. 2. Ciliary Body. — The ciliary body, as stated, connects the anterior part of the choroid to the circumference of the iris. It is composed of (i) the orbicularis ciliaris, (2) the ciliary processes, and (3) the ciliary muscle. The orbicularis ciliaris is a narrow zone which lies immediately in front of the anterior part of the choroid, with which it is con- tinuous. It presents plications which are radially disposed, and it separates the ciliary processes from the ora serrata of the retina. The ciliary processes, which are about seventy in number, are projections or infoldings of the anterior part of the choroid, and consist of the choroid proper and the membrane of Bruch. They constitute a series of rays, arranged in a circular manner, and converge as they pass inwards and forwards to the periphery of the crystalline lens on its anterior aspect. They are somewhat conical in outline. Their free extremities, which are round and prominent, lie behind the circumference of the iris upon the anterior aspect of the periphery of the crystalline lens. Their attached extremities are connected with the orbicularis ciliaris. THE EYE 1513 Anteriorly they are related to the posterior chamber of the eyeball at its circumference. Posteriorly they rest upon the zonule of Zinn, the folds of which fit closely in between them. Structure. — The ciliary processes are similar in structure to the choroid, but the pigment-cells are not so numerous. On their deep or posterior surfaces the processes are covered by the pars ciiiaris retinaB, which is prolonged from the pigmentary layer of the retina, and is continuous with the pars iridica retinae (uvea) on the posterior surface of the iris. The arteries of the ciliary processes are derived from those of the anterior part of the choroid, and from the anterior ciliary arteries. The veins pass to those of the choroid. Ciliary Muscle. — ^This muscle is composed of unstriped fibres. It forms a greyish-white ring, about ^ inch broad, which is Pupil Iris (dilator pOTtiao) Seven Ciliary Processes '''^^^;^^^^^5:>^^ ^n Ciliary Process reflected Fig. 628. — The Iris and Ciliary Processes (Posterior View) (HiRSCHFELD AXD LeVEILL^). situated at the anterior part of the choroid, opposite the ciliary processes. The fibres are arranged in two sets — radial and circular. The radial fibres arise from the deep surface of the sclerotic, close to the comeo-scleral junction, and behind the canal of Schlemm. From this origin they pass backwards in a radiating manner, and are inserted into the orbicularis ciiiaris and the attached ends of the ciliary processes. The circular fibres form a ring around the circumference of the iris, internal to the radial fibres. The ciliary muscle is supplied by the ciliary nerves, which are branches of the ciliary ganglion. Action. — The ciliary muscle is the muscle of accommodation, and adjusts the eye to the vision of near objects. When it contracts it draws forwards the choroid and the ciliary processes ; the suspensory ligament of the crystalline lens is thereby relaxed ; and, as a consequence, the anterior surface of the lens is rendered convex. I5I4 A MANUAL OF ANATOMY Anterior Wall of Capsule of Lens Sphincter Pupillje Membrane of Desceraet — rm-if'^ Epithelium of Cornea Canal of Schlemm or of Fontana Suspensory Ligament Middle Portion of Suspensory Ligament Posterior Portion of Suspensory Ligament Ciliary Muscle...!^ A (Radiating Fibres) H^^ Sclerotic . Fig. 629._Meridional Section through the Anterior Portion of THE Eye (magnified 16x1) (Fuchs). C.P., C.P.. Canal of Petit. THE EYE 1515 The circular fibres of the ciliary muscle are well developed in cases of hypennetropia, but are deficient in cases of myopia. . 3. Iris. — The iris forms the anterior part of the middle coat of the eyeball. It is a coloured contractile curtain, which is suspended in the aqueous humour between the cornea and the cr^'stalline lens. It is perforated by an almost circular aperture, called the pupil, which is situated slightly to the nasal or inner side of its centre, and serves for the transmission of light. The margin which surrounds the pupil is known as the pupillary margin. Its cir- cumference is continuous with the ciliary body, and is cormected with the posterior elastic lamina of the cornea by means of the ligamentum pectinatum iridis. The circumference is known as the ciliary margin. The surfaces of the iris are anterior and posterior. The anterior surface is directed towards the cornea. Its colour varies in different individuals, and it presents a striated appearance, the striae converging towards the margin of the pupil, and being produced by the underljdng vessels. The posterior surface is directed towards the crystalline lens and ciliary processes. It has a purple colour, and is covered by two layers of colunmar epithelium, the cells of which contain dark pigment. These two layers of pigmented cells constitute the pars iridica retinae {uvea), which is continuous with the pars ciliaris retinae. The iris divides the space between the cornea and the crystalline lens into two compartments, the anterior chamber and posterior chamber, both of which contain the aqueous humour. Structure. — The component parts of the iris are as follows : (i) a layer of endothelium ; (2) a connective-tissue stroma, with branched cells ; (3) muscular tissue ; and (4) pigment. The layer of endothelium covers the anterior surface of the iris, and is continuous with the endothelium which lines the posterior elastic lamina (membrane of Descemet) of the cornea. The connective-tissue stroma is composed of fibres which, for the most part, pass in a radiating manner towards the pupillary margin. Some, however, are disposed circularly at the ciliary margin. They support the bloodvessels and ner\-es, and scattered between their bundles there are branched cells. These cells con- tain pigment in dark coloured eyes (black, grey, or brown), but in blue eyes the\' are destitute of pigment. The muscular tissue is of the unstriped variety, and its fibres are arranged in two sets, circular and radiating. The circular fibres form a ring round the pupil, and are nearer the posterior surface than the anterior. They are known as the sphincter pupiilse. The radiating fibres converge from the ciliary margin of the iris towards the pupillary margin, where they blend with the circular fibres. The radiating fibres constitute the dilator pupiUse. Some authorities regard the radiating fibres as being elastic, and not muscular. The pigment of the iris is variously situated, according to the colour of the eye. In the eyes of ailbinos there is no pigment. I5i6 A MANUAL OF ANATOMY In other eyes pigment is contained in the cells of the two layers of columnar epithelium which line the posterior surface of the iris, and form the pars iridica retinae (uvea). In blue eyes the pigment is confined to this region, but in dark coloured eyes (black, grey, or brown), it is also present in the brajiched cells of the con- nective-tissue stroma. Blood-supply — Arteries. — ^The arteries of the iris are derived from (i) the long ciliary, and (2) the anterior ciliary, vessels. The long ciliary arteries are two in number, and belong to the posterior ciliary group of branches from the ophthalmic artery. They pierce the back part of the sclerotic, one on each side of the optic nerve, and pass forwards between the sclerotic and the choroid towards the ciliary margin of the iris. Here each vessel divides into two branches, upper and lower, which anastomose with those of the opposite side to form an arterial ring round the ciliary margin of the iris, called the circulus major. This ring is joined by some Long Ciliary Artery Anterior Ciliary Artery ,^-->==:::-^^ Short Ciliary Artery Arteries of Iris ,, ^j. r-^^u ^r-^^=»^ -•^tuins^.x « . , « , Portion of Sclerotic Optic Nerve __^ _ Short Ciliary Arteries Pupil "'" Ciiculus Major Fig. 630. — The Arteries of the Choroid and Iris (Lateral View). of the anterior ciliary arteries, and it gives offsets to the ciliary muscle and iris. The branches which enter the iris are supported by the connective-tissue stroma, and converge towards the pupillary margin, near which they form by their anastomoses another arterial ring, called the circulus minor. The anterior ciliary arteries are about six in number, and are derived from the muscular and lachrymal branches of the oph- thalmic artery. They are of small size and pierce the anterior part of the sclerotic, close to the corneo-scleral junction. Some of them supply the ciliary processes, and others join the circulus major. The veins of the iris accompany the arteries, and are in com- munication with the canal of Schlemm. Nerves of the Choroid Coat and Iris. — These are derived from the ciliary nerves, short and long, the former coming from the ciliary ganglion, and the latter from the nasal branch of the THE EYE 1517 ophthalmic or first division of the fifth cranial nerve. They are about sixteen in number, and pierce the back part of the sclerotic around the optic nerve. They then pass forwards between the sclerotic and choroid, giving branches to the latter coat, which become disposed in a plexiform manner amongst the bloodvessels. Having reached the comeo-scleral junction, the nerves enter the ciliary muscle, in which they form a plexus. From this plexus branches enter the iris at the ciliary margin. These branches accompany the vessels, and, by their subdivisions and communi- cations, they form a copious plexus of non-medullated fibres in the connective -tissue stroma of the iris. The sphincter pupillse is sup- plied by fibres which are derived from the oculo-motor or third Pupil ins ..Ciliarj- Muscle Ciliary Nerves ^-- "^^i^^B^P Vena Vorticosa Optic Nerve and Ciliary Nerves. --^H ' Portion of Sclerotic Fig. 631. — The Choroid and Iris, showing the Ven^ Vorticos.e AND Ciliary Nerves (after Hirschfeld and Leveille). (The Sclerotic and Cornea have been removed). cranial nerve, through means of the motor root of the ciliary ganglion. The dilator pupillae is supplied by fibres which are derived from the sympathetic through means of the sympathetic root of the ciliary ganglion. Membrana Pupillaris. — During intra-uterine life the pupil is closed by a delicate membrane, called the membrana pupillaris. This membrane is vas- cular, except at its centre, the arteries being derived from the cu-culus minor, and from those of the front part of the capsule of the crystalline lens. The vessels converge from the circumference of the membrane to near its centre, and terminate by forming loops. The membrana pupillaxis disappears shortly before birth. Internal Coat. Retina. — ^The retina is the internal or nervous tunic of the eye- ball. It is soft in consistence, translucent, and of a pinkish colour. Its mtemal surface is in contact with the hyaloid membrane, I5i8 A MANUAL OF ANATOMY which encloses the vitreous body, and its external surface is in contact with the choroid coat. Posteriorly it receives the fibres of the optic nerve. Anteriorly it extends almost to the ciliary body, where it presents a notched border, called the ora serrata. Here its nervous elements terminate, but its pigmentary layer is con- tinued over the deep or posterior surfaces of the ciliary processes on to the posterior surface of the iris, forming, with the addition of a layer of columnar epithelial cells, the pars ciliaris retinae and pars iridica retinae (uvea), respectively. The retina diminishes in thick- ness from behind forwards. The external surface is formed by a stratum of hexagonal pigment- cells, which send processes into the adjacent layer. When the 50 <& temporal ad sa TV he d v 'n &e jp curciu. Fig. 632. — Longitudinal Section through the Head of the Optic Nerve (14x1) (Fuchs). r. Retina b. Centre of Porus Opticus ch. Choroid s. Sclerotic so. Outer Part of Sclerotic si. Inner Part of Sclerotic ei. Ciliary Artery (in longi- tudinal section) nasal, Inner Side sd. SuVjdural Space sa. Subarachnoid Space n. Bundles of Nerve-fibres se. .Septa between the Nerve-bundles a. Arteria Centralis Retinae V. Vena Centralis Retinae p. Sheath formed by Pia Mater ar. Sheath formed by Arachnoid du. Sheath formed by Dura Mater temporal, Outer Side choroid is separated from the retina these processes are torn, and the stratum of pigment-cells remains attached to the choroid, being apparently a part of it. The pigmentary layer, however, really belongs to the retina. The internal surface presents, in the line of the visual axis of the eyeball, the macula lutea or yellow spot, where vision is most distinct. This spot is transversely oval, and measures about y\^ inch in the transverse diameter. At its centre there is a slight depression, called the fovea centralis. In this situation the retina is thinnest, and the dark colour of the hexagonal pigment- cells is visible through it, imparting to it the appearance of a fora- men. About \ inch to the inner side of the posterior pole of the THE EYE »5«9 eyeball, and about ^V ^^ch below its level, is the porus opticus, or optic disc. This is circular in outline, and its circumference is slightly elevated. It represents the point of entrance of the fibres of the optic nerve, and the centre of the disc is pierced by the arteria centralis retinae, which immediately divides into two branches — upper and lower. The optic disc consists entirely of nerve-fibres, and is known as the * blind spot,' vision being absent in this situation. Structure of the Retina. — ^The retina consists of eight super- imposed layers, seven of which are nervous and one pigmentary. Macula Lutea, with Fovea Centralis Poms Opticas Fig 633. -The Posterior Portion of the Right Retina (Anterior View). In addition to these, there are sustentacular fibres. The eight layers arfe as follows, from within outwards : 1. Stratum opticum, or layer of nerve-fibres. 2. Ganglionic layer, or layer of nerve-cells. 3. Inner molecular (inner plexiform) layer. 4. Inner nuclear or granular layer. 5. Outer molecular (outer plexiform) layer. 6. Outer nuclear or granular layer. 7. Layer of rods and cones, or bacillary layer. 8. Pigmentary laj'er. In addition to the foregoing layers, there are two very delicate membranes, which really belong to the sustentacular fibres of the retina, but are known as the membrana limitans interna and mem- brana limitans externa. The membrana limitans interna covers the retina on its internal surface, and the membrana limitans I520 A MANUAL OF ANATOMY externa intervenes between the outer nuclear layer and the bacillary layer. The layers of the retina are supported by fibres called the sustentacular fibres. I. Stratum Opticum. — ^This layer consists of the fibres of the optic nerve, and it extends from the optic disc to the ora serrata. The fibres are non-medullated, and are chiefly centripetal, but some are centrifugal. The centripetal fibres arise mainly as the axons of Pigmentary Layer Layer of Rods and Cones i. Membrana Limitans Externa . Outer Nuclear Layer LOuter Molecular Layer i ► Inner Nuclear Layer .Inner Molecular Layer .Layer of Nerve-cells (.Ganglionic Layer) Layer of Nerve-fibres Membrana Limitans Interna Fig. 634. — Diagrammatic Section of the Human Retina (Schultze). (Copied from Quain's ' Anatomy'). the cells of the ganglionic layer. The centrifugal fibres pass towards the inner molecular and inner nuclear layers. 2. Ganglionic Layer. — ^This layer consists of large, somewhat flask-shaped, multipolar ganglion-cells, which for the most part form a single layer. In the macula lutea, however, they form several layers. The round ends of the cells rest upon the stratum opticum, and from each of these ends an axon is given off, which enters the stratum opticum obliquely, and forms one of its component fibres. The tapering end of each cell sends off several dendrites, which enter The eye ts^ the inner molecuiax layer, within which they terminate in arboriza- tions. 3. Inner Molecular (Inner Plexiform) Layer. — This layer consists of the arborizations of the dendrites of (i) the cells of the ganglionic layer, and (2) the bipolar cells of the inner nuclear layer. The intercommunications between these two sets of dendrites give rise to five strata, according to Ramon y Cajal. Besides these, there are the arborizations of the processes of the spongioblasts of the inner nuclear layer, which are likewise arranged in strata. 4. Inner Nuclear or Granular Layer. — ^This layer consists of ceUs which are arranged in three groups, namely, (i) bipolar cells, (a) horizontal cells, and (3) spongioblasts, or amacrine cells. The Fig. 635. — Scheme of the Horizontal Cells and Spongioblasts of THE Retina (Ramon y Cajal). A. Rod-fibres ' 2. Inner Molecular Layer B. Cone-fibres /,r, A, ) Spongioblasts extending to I. Outer Molecular Laj-er j, L f different depths a, b. Horizontal Cells, with arborizations M(, n. Spongioblasts with diffuse processes c. Horizontal Cell, with deep processes o. Ganglionic Nerve-cell bipolar cells are the most numerous, and are nucleated. Each cell gives off two processes — internal and external. The internal processes of the cells enter the inner molecular layer, and terminate at different levels in arborizations. The external processes pass into the outer molecular layer, and terminate in arborizations in its outermost part, which are closely related to the terminal parts of the rods and cones of the bacillary layer. According to Cajal, the bipolar cells are of two kinds— rod-bipolars and cone-bipolars. The external processes of the rod-bipolars ramify around the ter- minal parts of the rod-fibres, and the internal processes arborize around the cells of the ganglionic layer. The external processes of the cone-bipolars form horizontal arborizations aroimd the terminal 96 X524 A MANUAL OF ANATOMY parts of the cone-fibres, and the internal processes termmate in arborizations in the inner molecular layer at diiferent levels. The horizontal cells occupy the outer part of the inner nuclear layer. Their dendrites enter the outer molecular layer, and come into relation with the terminal parts of the cone-fibres, whilst their axons run in a horizontal direction. The spongioblasts are situated in the innermost part of the inner nuclear layer. They are destitute of axons, and have been called amacrine cells, because each cell is ' without a long fibre or process.' Their dendrites enter the inner molecular layer, and terminate in arborizations, which are arranged in strata. 5. Outer Molecular (Outer Plexiform) Layer.— This layer is com- posed of the following structures : (i) the external processes of the Layer of Rods and Cones Membrana Limitans Externa Outer Nuclear Layer Outer Molecular Layer Inner Nuclear Layer Inner Molecular Layer Ganglionic Layer Nerve-fibre Layer Membrana Limitans Interna Fig. 636. — Section of the Retina as seen under the Microscope (magnified). rod-bipolars and cone-bipolars of the inner nuclear layer ; (2) the dendrites of the horizontal cells of the inner nuclear layer ; and (3) the terminal parts of the rod-fibres, and filaments from the foot- plates of the cone-fibres. 6. Outer Nuclear or Granular Layer. — This consists of granules, which are of two kinds, namely, rod-granules and cone-granules. The rod-granules are the more numerous, and are oval enlargements in the course of the rod-fibres, as these pass to the outer molecular layer. Each rod-fibre has only one rod-granule, and the granules lie at different levels. Each granule has a nucleus, which presents transverse striations, there being at least two clear bands. The external process of each rod-granule is continuous with one of the rods of the bacillary layer, and the internal process passes into the THE EYE 1523 outer molecular layer, where it comes into relation with the arboriza- tions of the external process of a rod-bipolar. The cone-granules are larger than the rod-granules, but not so numerous, and each contains an oval nucleus. They are situated in the outermost part of the outer nuclear layer, close to the mem- brana limitans externa. The outer end of each granule is con- tinuous with one of the cones of the bacillary layer. The inner end is prolonged into a cone-fibre, which passes into the outermost part of the outer molecular layer, where it expands into a foot- plate, from which filaments are given off. These filaments come into relation with the arborizations of the external process of a cone- bipolar cell. 7. Layer of Rods and Cones, or Bacillary Layer. — ^This layer consists of two elements, namely, rods and cones, the former being cylindrical, and the latter flask-shaped. The rods are much more numerous, longer, and narrower than the cones, and both are placed perpendicularly . Each rod and cone consists of two segments — outer and inner. In the case of the rods the two segments are of almost equal length, the inner segment being rather larger than the outer. The outer segment is the only seat of the colouring matter known as visual purple or rhodopsin. In the case of the cones, which, as stated, are flask-shaped, the inner segment of each forms two-thirds of the cone, and is of large size ; whGst the outer segment forms one-third, is narrow, and represents the tapering part of the flcisk. The outer segments of both rods and cones present faint transverse striations. The inner segments of both are subdivided into tvvo parts — outer and inner. The outer part is composed of delicate fibrils, longi- tudinally arranged, and therefore presents a longitudinally striated appearance. The inner part is faintly granular. The rods and cones are continued at their inner ends through the membrana limitans externa into the rod-fibres and cone-fibres, which belong to the outer nuclear layer. The outer ends of the rods project into the pigmentary layer. 8. Pigmentary Layer. — ^This is the most external layer of the retina, and it is in close contact with the choroid coat. It consists of a single layer of hexagonal epithelial cells, which contain pigment. The deep surfaces of the cells give off processes which extend into the interv^als between the outer ends of the rods and cones. Sustentacular Fibres, or Fibres of Miiller. — These fibres constitute the supporting tissue of the retina, and extend from its internal surface to the boundary-line between the outer nuclear layer and the layer of rods and cones. The inner ends of the fibres are ex- panded, and cohere by their edges so as to present the appearance of a distinct retinal layer, which is called the membrana limitans interna. Their outer ends, which are very numerous owing to the breaking up of the fibres, also expand, and form what is known as the membrana limitans externa, which lies between the outer nuclear layer and the layer of rods and cones. (The membrana limitans 1524 A MANUAL OF ANATOMY interna and membrana limitans externa are sometimes counted as layers of the retina, under which circumstances the retinal layers would be ien in number, instead of eight, as stated). From the membrana limitans externa delicate offsets enter the layer of rods and cones, in the innermost part of which they form fibre-baskets in connection with the deep ends of the rods and cones. As the sus- tentacular fibres pass through the inner nuclear layer each presents an oval nucleus, which contains a nucleolus. This nucleus is variously described as being situated on one side of the fibre, or as involving its whole circumference. Throughout their course the sustentacular Membrana Limitans Externa Outer Molecular^, Layer Nucleus of one of— — Miiller's Fibres Inner Molecular Layer Muller's Fibres Limitans Interna. Membrana Rods and Cones Outer Nuclear Layer Subepithelial Ganglion-cell Stellate Ganglion- cell _ Bipolar Ganglion Gai ell Centrifugal Nerve-fibre - Multipolar Ganglion-cell Multipolar Gangliou-cell ^ Layer of Nerve- "" fibres Fig. 637. — Diagram of the Elements of the Retina (Wiedersheim, AFTER Ph. St6hr). A, Nervous Elements ; B, Supporting Elements. fibres give off lateral offsets, which increase in number from within outwards. Structure of the Macula Lutea and Fovea Centralis.— The chief structural characters of the macula lutea and fovea centralis may be stated in the following tabular manner : Macula Lutea. 1. Cones only. 2. Outer nuclear layer has only cone- fibres, disposed obliquely. 3. Ganglionic ayer very thick, cells being several layers deep. 4. Stratum opticum not continuously disposed. Fovea Centralis. 1. Thinnest part of the retina. 2. Pigmentary layer thick. 3. Cones only. 4. Outer nuclear layer has only cone-libres. 5. Ganglionic layer absent. 6. Stratum opticum absent. THE EYE 1525 Structure of the Ora Serrata.— At the ora serrata, as previously stated, the nervous elements of the retina terminate, and its pig- mentary layer is continued over the deep or posterior surfaces of the ciliary processes. In this latter situation there is superadded to its deep or posterior surface a layer of columnar epithelial cells, and the two layers form the pars ciliaris retinae, which is continued Fig. 638. — Scheme of the Retina, showing the Connection between THE Layer of Rods and Cones and the Ganglionic Layer (Ramon y Cajal). A. Layer of Rods and Cones B. Outer Nuclear Layer C. Outer Molecular Layer E. Inner Nuclear Layer F. Inner Molecular Layer G. Ganglionic Layer H. Layer of Nerve-fibres M. Mailer's Fibre a. Rods b. Cones c. Granule of Cones d. Granule of Rods Bipolar Cells of Rods f. Bipolar Cells of Cones - r Ganglionic Corpuscles ramifymg at S.'°'''J different levels in Inner Molecular Layer Deep arborizations of Bipolar Cells s. Centrifugal Ner\-e-fibre t. Nnclens of MuUer's Fibre X. Deep ends of Rod-fibres amongst superficial arborizations of Bipolar Cells Z. Meeting of arborizations of Omks and Bipolar Cells into the pars iridica retinae (uvea). In the latter the cells of both layers are pigmented. Blood-supply of the Retina. — ^The retina is supplied with blood by the arteria centralis retinae, which is a branch of the ophthalmic artery. Within the orbit the artery pierces the vmder aspect of the optic nerve a little behind the eyebzill, and passes forwards in the centre of the nerve. It makes its appearance at the centre of the optic disc, £ind then divides into t^^'o branches, upper and lower. 1526 A MANUAL OF ANATOMY Each of these breaks up into two branches, nasal or internal, and temporal or external. The temporal branches keep clear of the macula lutea, but furnish small twigs to it, which, however, do not enter the fovea centralis, this part being non-vascular. As the branches pass inwards and outwards, respectively, towards the periphery of the retina, they ramify freely, and ultimately terminate in capillary networks. The arteries do not extend farther outwards than the inner nuclear layer. No anastomoses take place between the branches of the arteria centralis retinae. In the foetus the arteria centralis retinae furnishes a branch to the posterior part of the capsule of the crystalline lens, which reaches it through the canal of Stilling in the vitreous body. The veins are ultimately collected into two vessels, upper and lower, which pass through the optic disc, one above, and the other below, the artery. They then form one vessel which opens into the superior ophthalmic vein. The veins of the retina are destitute of muscular tissue, the wall of each being formed by a single layer of endothelial cells, external to which there is a perivascular lymph-space, this, in turn, being limited by another layer of endo- thelial cells. These lymph-spaces are in communication with those of the optic nerve. Relation of the retinal layers to one another. — ^The only two layers which are in direct continuity are the stratum opticum and ganglionic layer, some fibres of the former being the axons of the cells of the latter. As regards most of the strata, the constituent elements of successive layers are brought into communication by means of the interlacements which take place between the arboriza- tions formed by their various processes. These interlacements occur in the inner and outer molecular layers. In the inner molecular layer there are several strata of interlace- ments, by means of which the dendrites of the cells of the ganglionic layer are brought into communication with the internal processes of the bipolar cells of the inner nuclear layer. In the outer mole- cular layer there is a free intermingling between the external pro- cesses of the bipolar cells of the inner nuclear layer and the rod- fibres and cone-fibres. Nerve-cells of the Retina. — These are arranged in three strata, and are in communication with one another through interlacing arborizations. The outermost stratum consists of the rods and cones ; the middle stratum is formed by the bipolar cells ; and the innermost stratum represents the cells of the ganglionic layer. The axons of the ganglionic cells enter the stratum opticum as centripetal fibres, which pass in the optic nerve to the brain. The centrifugal fibres of the stratum opticum ramify in the inner molecular or inner nuclear layer. THE EYE «527 Refracting Media. Aqaeons Humour and Chambers of the Eye. — The aqueous humour occupies the space between the cornea and the front of the crystalline lens, which is divided by the iris into two chambers, anterior and posterior. It is a clear fluid, having an alkaline reaction, and is composed of H.2O, holding in solution a very small amount of sodium chloride. The anterior chamber is bounded anteriorly by the cornea, and posteriorly by the iris and the central portion of the crystalline Levator Palpebne Superioris Hyaloid Canal (Canal of Stilling) Canal of Schlemm Hyaloid Membrane Retina Choroid Rectus Saperior .Sclerotic Ciliary / Processes' Canal of Petit Inferior Fornix Conjnnctivae Fig. 639. — Vertical Sagittal Section of the Eye and its .\PPENDAGES (HiRSCHFELD AND LeVEILL£). lens, enclosed within its capsule. The anterior chamber com- municates with the spaces of Fontana, through them with the canal of Schlenun, and through this canal with the veins of the sclerotic. The posterior chamber, which is of limited extent, is bounded anteriorly by the iris, and posteriorly by the peripheral part of the crystalline lens and its suspensory ligament, and by the ciliary processes. The anterior and posterior chambers communicate with each other through the pupil ; with lymph-spaces in the iris ; and, through the latter spaces, with the perichoroidal lymph-space. I5i8 A MANUAL OF ANATOMY Crystalline Lens. — ^The crystalline lens is situated directly behind the pupil and iris, from which latter it is separated by the posterior chamber. It is a solid, transparent, biconvex body, the posterior surface being more convex than the anterior, and it is enclosed within a homogeneous, transparent envelope, called the capsule of the lens. The centre of the anterior surface is called the anterior pole, and that of the posterior surface the posterior pole. The line connecting these two poles constitutes the axis of the lens, and a line surrounding the periphery represents the equator. The trans- verse measurement of the lens is about ^ inch, and its axis measures about ^ inch. The anterior surface at its central part faces the pupil. External to this, the pupillary margin of the iris rests upon it, and, external to this again, is the posterior chamber. Fig. 640. — Fibres of the Crystalline Lens (highly magnified) (After Kolliker). A, Fibres of the Ox (seen on edge) ; B, Human fibres (seen on end). with part of the aqueous humour. The posterior surface is received into the patellar fossa on the anterior aspect of the vitreous body. The periphery is related to the suspensory ligament, the canal of Petit, and the ciliary processes. From the anterior and posterior poles delicate lines radiate towards the equator. In early life these are three in number on each surface. Those on the anterior surface are directed as follows : one vertically upwards, and the other two downwards and outwards in a diverging manner, thus X- Those on the posterior surface are directed as follows : one vertically downwards, and the other two upwards and outwards in a diverging manner, thus Y. These lines represent the free margins of septa within the lens, upon which the ends of the lens-fibres terminate. Structure. — ^The lens is laminar in structure. The outer laminae are soft in consistence, but the succeeding ones gradually become THE EYE 15*9 firmer, and the central portion, which constitutes the nucleus, is very firm and hard. The laminae are arranged concentrically, and, after boiling or immersion in alcohol, they may be peeled off, like the coats of an onion. The fibres of which the laminae are composed terminate upon septa within the lens, of which septa the radiating lines on the surfaces, already referred to, are the free margins. The concentric laminae are therefore not continuous all round, but are split up along these lines. The lens-flbres, which are disposed in a curved manner, are of small size, and have serrated edges, which fit closely to each other. In transverse section the fibres appear as hexagonal prisms. The fibres are the elongated cells which line the posterior part of the epiblastic vesicle (lens -vesicle), from which the lens is developed. In early life each fibre has a nucleus, but, after the lens has attained its full development, only the outermost fibres are nucleated. The lens is non-vascular in the adult. Capsule of the Lens. — ^This is a transparent, homogeneous, elastic, and brittle membrane, which surrounds and encloses the lens. Its anterior wall is thicker and more elastic than the posterior. In the adult it is non-vascular, but in the foetus it receives the hyaloid branch of the arteria centralis retinae, which reaches it through the canal of Stilling in the vitreous body. Epithelium of the Lens. — ^The posterior surface of the lens is devoid of epithelium, and is in direct contact with the posterior wall of the capsule. The anterior surface is covered by a single layer of columnar cells, which intervenes between the anterior surface and the anterior wall of the capsule. Towards the equator these cells become elongated, and pass into short fibres, which become continuous with the superficial lens-fibres. Crystalline Lens at Different Ages. — The characters of the lens at different ages are as follows : Foetal Lens. Adult Lens. Lens in Old Age. Almost spherical. Biconvex. Flattened. Pinkish colour. Colourless. Amber colour. Semitransparent. Transparent. Opaque, more or less. Soft in consistence. Firm in consistence. Very firm in consistence. Vitreous Body. — This body occupies about four-fifths of the space within the eyeball, and is situated between the crystalline lens and the retina. It is transparent, and gelatinous in consist- ence, and is composed of HoO, holding in solution a small quantity of sodium chloride and albuminous matter. It is surrounded by a transparent, homogeneous envelope, called the hyaloid membrane. This membrane is in contact with the retina, except anteriorly, in which latter situation it presents an excavation called the fossa fatellaris, into which the posterior surface of the crystalline lens is received. Towards its circumference the vitreous body is laminated, the laminae being arranged concentrically. Laminae are also saicj to I530 A MANUAL OF ANATOMY radiate from its antero-posterior axis towards the circumference. Scattered throughout the vitreous body there are some amoeboid corpuscles, and it is traversed from behind forwards by a minute passage called the hyaloid canal, or canal of Stilling (canal of Cloquet). This canal extends from the centre of the optic disc to the posterior wall of the capsule of the lens, and posteriorly it communicates with the lymph-spaces of the optic nerve. In the foetus the canal transmits a branch of the arteria centralis retinae, called the hyaloid artery, which supplies the capsule of the lens. No vessels enter the vitreous body, its nutrition being derived from the vessels of the retina and ciliary processes. Zonula of Zinn. — ^The zonula of Zinn, or zonula ciliaris, is the thickened portion of the hyaloid membrane which is situated in front of the ora serrata of the retina. From this point it extends in^yards behind the ciliary processes towards the periphery of the crystalline lens. Behind the ciliary processes it presents radial folds with intervening depressions. The depressions receive the ciliary processes, and the radial folds are separated from the intervals between the ciliary processes by lymph-spaces, which communicate with the posterior chamber of the eye. Suspensory Ligament of the Lens, and Canal of Petit. — ^The zonula of Zinn, as it approaches the periphery of the lens, divides into three layers, posterior, middle, and anterior. The posterior layer lines the fossa patellaris on the anterior aspect of the hyaloid membrane. The middle layer consists of a few scattered fibres which pass to the equator of the lens. The anterior layer is the thickest, and constitutes the suspensory ligament of the lens, which is attached to the anterior waJl of the capsule of the lens not far from the equator. When the radiating fibres of the ciliary muscle contract the suspensory ligament is relaxed, and the convexity of the anterior surface of the lens is increased. Behind the suspensory ligament of the lens there is a sacculated lymph-space, called the canal of Petit, which surrounds the equator of the lens. Development of the Eye. The retina, optic nerve, and crystalline lens are developed from the ecto- derm, the retina and optic nerve being derived from the ectoderm of the anterior primary cerebral vesicle, whilst the crystalline lens is developed from the ectoderm of the side of the head. The accessories of the eye — e.g., the sclerotic, cornea, choroid, ciliary body, and iris, are all developed from the mesoderm. The vitreous body, though developed to a certain extent from the mesoderm, is principally formed from the ectoderm. The earliest indication of the development of the eye is the formation of a hollow protrusion on either side, from the lower and lateral portion of that part of the anterior primary cerebral vesicle which forms the diencephalon or thalamencephalon, anterior to the level of the infundibulum. This protrusion, therefore, is an adjunct of the cavity of the diencephalon, which gives rise to the third ventricle. On the ventral aspect of the diencephalon, between the openings of the optic vesicles, there is a depression, called the optic recess, in the posterior margin of which the optic ohiasma or commissure is developed. The direction of each protrusion is outwards towards the ectoderm of the side of the head. Towards its distal end it becomes enlarged, this enlarge- THE EYE 1531 Anterior Wall of Capsule of Lens Suspensory ■ Ligament Middle Portion of Suspensory Ligament Posterior Portion of 'Suspensory Ligament inal of Schlemm or of Fontana .^ ^> ^ Ciliary Muscle . _ .^^_\!Vt^ ^^^ (Radiating Fibres) ^k^$^J^^\\^x\ ' \ft^W Chor- oid Fig. 641. — Meridional Section through the Anterior Portion of THE Eye (magnified 16x1) (Fuchs). C.P.. C.P.. Canal of Petit. 1532 A MANUAL OF ANATOMY ment being called the optic vesicle. The remainder of the protrusion consti- tutes a narrow, hollow pedicle, called the optic stalk, which is attached to the wall of the diencephalon, the cavity of the stalk communicating with the third ventricle. The enlargement formed by the optic vesicle lies beneath the ectoderm of the lateral surface of the head. The ectoderm corresponding to the optic vesicle becomes thickened and depressed, this depressed portion constituting the lens-area. The depressed ectoderm is deepened and converted into a kind- of cup, and, the mouth of the fossa becoming constricted, its lips unite. In this manner the lens-area becomes transformed into a closed ectodermic sac, called the lens-vesicle, from which the crystalhne lens is differentiated. The lens-vesicle now becomes completely separated from the surface-ectoderm, with which it was originally continuous. Coincident with the formation of the lens- vesicle, an important change takes place in the optic vesicle. The distal or outer wall of the optic vesicle is invaginated or pushed inwards towards the inner wall until the two walls come into contact, this being effected by the lens-vesicle. The optic vesicle thereby becomes transformed into the optic cup, the wall of which is com- posed of two layers — outer and inner. The lens-vesicle lies just within the mouth of the cup. The portion of the cup close to the margin represents the ciliary region, and the fundus of the cup forms the retinal region. The cup becomes surrounded by mesodermic tissue. During the formation of the optic cup it is not only the distal or outer wall of the optic vesicle which is invaginated, or pushed inwards, by the Lens Pit Lens Ectoderm | Optic Vesicle ; Optic Cup Optic Stalk - Re n- 1^6 K^ /-^ • o 11 J|&^ Pigmentary i M-^ Optic Stalk H^ ^tffi Layer of ' ^ " Optic Cup Retinal Layer of Optic Cup Fig. 642. — Development of Crystalline Lens and Optic Vesicle. lens-vesicle. The ventral wall of the optic vesicle, and the ventral wall of the part of the optic stalk, which is adjacent to the optic vesicle, are also invaginated. As the result of this extra invagination a cleft, of temporary duration, is left on the under surface of the optic cup, which is called the choroidal fissure. Through this fissure mesoderm enters the optic cup, posterior to the lens-vesicle. In this mesoderm a nutrient artery is developed, called the hyaloid artery, which furnishes the minute vessels conferring vas- cularity upon the capsule around the developing lens. As a rule the choroidal fissure becomes closed, and then the hyaloid artery is enclosed within the cavity of the optic stalk, and constitutes the arteria centralis retinse. In cases of non-closure of the choroidal fissure, the region of the lissure remains unpigmented, and one of two congenital deficiencies in the eye are met with, each being known by the general term coloboma. If the patent lissure affects the ventral wall of the optic cup, then the deficiency in pigment affects the choroid, and the condition is known as coloboma choroidea. If the patent fissure affects the lower margin of the optic cup, then the deficiency affects the lower part of the iris, and the condition is known as coloboma iridis. As stated, the wall of the optic cup consists of two layers. The outer layer, which is comparatively simple, gives rise to the pigmentary layer ol the Tetina. The inner layer is, on the other hand, very complicated. After much differentiation it gives rise to all the other layers ol the retina. The THE EYE JJ3J mesodermic tissue. Tfhich invests the optic cup. gives rise to the sclerotic, cornea, choroid, ciliary body (including the ciliary processes and ciliary muscle) and iris. Crystalline Lens. — The lens is of ectodermic origin. The surface-ectoderm on the lateral aspect of the head opposite the optic vesicle becomes thickened and depressed to form, as stated, the lens-area. The depressed ectoderm is deepened and converted into a kind of cup. The mouth of the cup becomes constricted, and its hps unite. In this manner the lens-area becomes trans- formed into a closed ectodermic sac, called the lens-vesiele, from which the crystalline lens is difierentiated. The lens-vesicle becomes completely sep. arated from the surface-ectoderm, with which it was originally continuous. It is now received into the optic cup, which has be«i formed in connection with the optic vesicle, its position being just within the mouth of the cup, the circumference of the margin projecting shghtly in advjmce of the vesicle. The anterior and posterior walls of the lens-vesicle at this stage consist of several layers oi cylindrical cells, and the vesicle contains a small central cavity. The anterior uall becomes gradually thin, and is ultimately formed of one layer of flattened cells, these cells constituting the anterior epithelium of the adult crystalline lens. The cells of the posterior waU become elongated in a forward direction, obhterating the cavity of the vesicle, and coming into contact with the anterior wall. By this process of cell-elongation the lens- fibres are formed. At the equator of the lens the cells of the anterior and posterior walls merge gradually into one another through the medium of a transitional zone of columnar cells. At this stage in its development the crystalline lens consists of (i) an anterior epithelial wall, and (2) a posterior wall composed of elongated cells forming the lens-fibres. As development proceeds, additional lens-filM-es are formed by the pro- liferation of cells at the equator of the lens. These fibres are laid down in successive layers, which are arranged concentrically. Capsule of the Crystalline Lens. — At an early period in its development the lens becomes invested by a mesodermic capsule, freely supphed with blood- vessels derived from the hyaloid artery and anterior ciliary arteries. This capsule is known as the tunica vasculosa. It persists throughout the period of active growth of the lens, and then undergoes retiogression to form the permanent lens-capsule. The portion of the tunica vasculosa which covers the front part of the lens is called the membrana pupillaris, but this usually disappears prior to birth. It may, however, be present at birth, giving rise to the condition kno^Ti as atresia pupillee. Towards the end of intra-uterine life the timica vasculosa undergoes retrogressicm, and becomes transformed, as stated, into the permanent iens-capsole, which is a transparent, homo- geneous, elastic membrane. » According to some authorities the lens-capsule is of mesodermic origin, whilst according to other authorities it is derived from the ceUs of the crystal- line lens. Development of the Optie Cap and Optic Stalk. — The optic cup. as stated, is formed by the invagination by the lens-vesicle of the distal or outer wall of the optic vesicle, the invagination also affecting the ventral wall of the optic vesicle and the ventral wall of the part of the optic stalk which is ad- jacent to the optic vesicle, thereby gi^•ing rise to the choroidal fissure. The mouth of the optic cup is directed towards the lateral aspect of the head, and the lens-vesicle hes just within the mouth. The margin of the cup projects shghtly over the lens-vesicle and the circumference of this margin represents tiie outline of the papiL The wall of the cup consists of two layers — namely, inner and outer, the inner representing the distal or outer wall erf the optic vesicle, which has now become invaginated, or pushed inwards. The cup is divisible into two regions — namely, (i ) the ciliary region, adjoiniag the margin of the cup, and (2) the fundus. The line of separation between these two regions corresponds to the ora serrata of the adult eye. The ciliary region of the optic cup is associated with the ciliary body (in- cluding the ciliary processes and ciliary muscle) and the iris, which ar« 1534 A MANUAL OF ANATOMY developed from the thickened anterior part of the choroid. The outer layer of the ciliary portion, as elsewhere, forms the pigmentary layer of the retina. The inner layer of the ciliary portion, which is very thin, forms (i) the pars ciliaris retinse, on the posterior surfaces of the ciliary processes, and (2) the pigmented pars iridica retinae {uvea) on the posterior surface of the iris. The fundus of the optic cup is the proper retinal region. The outer layer forms, as in the ciUary region, the pigmentary layer ol the retina. The inner or retinal, layer becomes differentiated into all the layers of the retina except the pigmentary layer. The changes which it undergoes are very complicated. Its thickness is considerably increased, and it subdivides into two layers — outer and inner — from which the various retinal strata (except the outer pigmentary layer) are specialized. The optic stalk is transformed into the optic nerve. The stalk is at first hollow, its cavity communicating with that of the optic vesicle on the one hand, and with the third ventricle of the brain on the other. As stated, the choroidal fissure involves the under surface of the optic stalk near the optic vesicle, as well as the under surface of the optic vesicle itself. When the choroidal fissure undergoes closure, the hyaloid artery, which passed through that fissure, becomes enclosed within the optic stalk, and forms the arteria centralis retina of adult life. By the closure of the choroidal fissure, and the consequent enclosure of the hyaloid artery, the cavity of the distal portion of the optic stalk becomes obliterated. Inasmuch as the ventral or lower wall of this part of the stalk has been previously invaginated, the wall of the stalk is now composed of two layers — outer and inner — the inner being formed by the invaginated ventral or lower wall. The outer layer of the optic stalk is now continuous with the outer layer of the optic cup, whilst the inner layer of the optic stalk is continuous with the inner layer of the optic cup. As regards the proximal part of the optic stalk, its cavity becomes gradually closed. The wall of the optic stalk becomes thickened, its cells proliferate, and they give rise to the neuroglial or sustentacular tissue of the future nerve. The nerve-flbres, which build up the optic nerve, are regarded as having two sources. The majority of them represent the a^ons of the ganglion-cells of the retina, which pass in the optic stalk to the diencephalon and mesencephalon. These are therefore centripetal fibres. Other fibres are regarded as being centrifugal, these arising in connection with the diencephalon and mesencepalon. Vitreous Body. — ^This body is formed within the optic cup, for the most part posterior to the lens-vesicle. It is principally developed from the ecto- derm, but the mesoderm also takes part in its formation. The ectodermic fibres are derived from those cells which pertain to the sustentacular fibres of the retina, or fibres of Miiller. These ectodermic fibres form a very delicate reticulum, which constitutes the primary vitreous body. In all probability the vitreous body is reinforced by fibres from the mesodermic tissue which enters the optic cup, along with the hyaloid artery, through the choroidal fissure on the ventral or under surface of the optic cup. The peripherad part of the vitreous body gives rise to the hyaloid membrane. The vitreous body soon becomes very vascular. The chief artery is the hyaloid artery, which enters the optic cup, along with mesoderm, through the choroidal fissure. The anterior ciliary arteries also contribute to its vascu- larity, these vessels gaining entrance between the margin of the optic cup and the lens-vesicle. The hyaloid artery occupies the centre of the vitreous body, lying in a passage, called the hyaloid canal, or canal of Stilling. On reaching the posterior part of the lens-capsule it breaks up into a number of branches. The arteries of the vitreous body at this stage confer great vas- cularity upon the lens-capsule, hence the name tunica vasculosa, and through it they contribute to the nourishment of the lens-vesicle during the period of its active development. The anterior part of this tunica vasculosa, as stated, gives rise to the membrana pupillaris. Towards the latter part of intra-uterine life the bloodvessels disappear, the hyaloid canal, or canal of Stilling, remaining permanent. The part of the hyaloid artery which becomes enclosed within the optic stalk forms the arteria centralis retina. THE EYE 1535 Derivatives ol the Mesodermic Envelope of the Optle Cap. — These are as follows: (i) Sclerotic, (2) cornea, {3) choroid, {4) ciliary body (including the ciliary processes and ciliary muscle), and (5) iris. The mesoderm which invests the outer surface ol the optic cnp is disposed in two layers — outer and inner. The outer layer has a fibrous character, and gives rise to the sclerotic, of which the eornea is a for\vard extension. The inner layer is vascular, cind gives rise to the choroid, ciliary body, and iris. The outer dense fibrous layer of the mesoderm of the outer surface of the optic cup, as stated, gives rise to the sclerotic. From its anterior margin a thick lamina of mesoderm is prolonged between the lens-vesicle and the surface ectoderm. This lamina di\-ides into two layers — superficial and deep. The superficial layer becomes differentiated into the eomea, which is thus genetic- ally continuous with the sclerotic. The deep layer becomes the anterior wall of the lens-capsule. Between these two layers there is an interval, which represents the aqueous chamber, this chamber being subsequently divided by the iris into the anterior and posterior aqueous chambers. The inner vascular layer of the mesoderm of the outer surface of the optic cap, as stated, gives rise to the choroid. The anterior margin ol the choroid, which adjoins the margin of the optic cup (ciliar}' region) becomes thickened, and gives rise to the ciliary body, in connection with which the ciliary processes and ciliary muscle are developed. The ciliary processes become covered posteriorly by the pars ciliaris refines, which is a thin retinal expansion from the ciliary region of the optic cup. The iris is also developed at the anterior margin of the choroid in the form of a ring of mesoderm. In this mesoderm the fibres forming the dilator pupillce and sphincter pupUlcB muscles are formed, and the back of the iris receives a pigmentary covering (uvea) from the pars iridica retina, which is a thin retinal extension from the ciliary region of the optic cup. THE EAR The organ of hearing is divided into three parts, namely, the external ear, the middle ear, and the internal ear. External Ear. The external ear consists of the auricle, or pinna, and the meatus auditorius externus. The auricle, or pinna, has been already described (see Index). The external auditory meatus extends from the bottom of the concha to the membrana tympani, and is about i inch in length. It consists of two parts — outer, or cartilaginous, and inner, or osseous. The cartilaginous part, which also consists of fibrous tissue, is about J inch in length, and the osseous part, which lies within the petrous portion of the temporal bone, is about § inch long. The widest part of the meatus is its orifice, which is oval, the long measurement being vertical. The narrowest part is situated in its osseous portion, about i inch from the membrana tympani, and it is known as the isthmus. There is another constriction of the canal situated near the deep end of the cartilaginous part, and produced by a projection which is placed antero-inferiorly. The chief direction of the canal is inwards and slightly forwards. At first it is also inclined upwards, then backwards, and finally downwards. The cartilaginous part is continuous with the cartilage of the auricle, and is attached to the external auditory process of the temporal bone. Its cartilage is folded so as to form a deep groove, which is open at its upper and back part, the cartilaginous de- ficiency being completed by fibrous tissue. The anterior wall of the cartilaginous part presents two clefts, called the fissures of San- torini, which are occupied by fibrous tissue. The osseous part has been described in connection with the temporal bone. At its deep end there is a narrow groove, called the sulcus tympanicus, which forms about five-sixths of a circle, the deficiency being placed superiorly, at the notch of Rivinus, where the ring is completed by the squamous part of the temporal bone. The membrana tympani is set obliquely within the sulcus tympanicus, being incHned downwards and towards the median line. The floor and anterior wall of the meatus are consequently longer than the roof and' posterior wall. The meatus is lined with skin, which is continuous with that of the auricle. In the osseous part of the canal the skin is very thin, and is provided with vascular papillae, but is destitute of glands and hairs. It is reflected over the outer surface of the membrana tympani, of which it forms the outer layer. In the cartilaginous part of the canal the skin is thicker, and is provided with hairs, connected with the follicles of which are sebaceous glands. In 1.536 THE EAR 1537 addition to these sebaceous glands, there are convoluted tubular glands, similar in structure to sweat-glands, and called the cerumi- nous glands, which secrete the ear-wax. Blood-supply. — The arteries are derived from the posterior auri- cular of the external carotid, the deep auricular of the first part of the internal maxillary, and the anterior auricular branches of the superficial temporal. The veins follow the course of the arteries. Lymphatics. — These pass to the mastoid glands and to the parotid lymphatic glands. r- Kerves. — (i) The auricuio-temporal nerve furnishes two branches io the meatus, upper and lov/er, which enter it by passing between Upper Part of — r-^ Helix t ^- Extemal T.igamfiit of the MalleiE Incns Semidicolar Caoak CoDcfaa External Auditory Meatus Malleus Vestibule ,/ Cochlea Tympantun Tensor Tympani Muscle Apex of Pet. Poriion of Temporal Bone . —Anterior Lig. of the Malleus Internal Carctfd Artery Tip of Styloid Process of Temporal Bone Membrana Tympani Fig. 643. — General View of the Right Organ of Hearing (after HiRSCHFELD AND LeVEILLE). (The External Ear and Middle Ear are seen in section). the cartila^ginous and osseous walls. The upper branch furnishes twigs to the skin over the upper part of the membrana tympani. (2) The auricular branch (Arnold's ner\-e) of the pneumogastric supplies the skin of the osseous part of the canal over its lower and back part, and also the skin over the lower part of the mem- brana tympani. Early Condition of the Meatus.^- At birth the osseous part of the canal is represented merely by the tympanic annidus and a small portion of the squamous part of the temporal bone. It is con- nected by fibrous tissue to the cartilaginous framework of the auricle, and within this fibrous tissue the osseous canal becomes formed by two outgrowths from the tvmpanic annulus. 97 1538 A MANUAL OF ANATOMY Middle Ear. The middle ear, or tympanum, is an irregular space within the petrous part of the temporal bone, which lies between the mem- brana tympani externally and the outer osseous wall of the internal ear or labyrinth internally. It is lined with mucous membrane, and it communicates with the naso-pharynx by means of the Eustachian tube, through which it receives air. It presents three parts, namely, (i) the t5niipanum proper, or cavum t)mipani ; (2) the attic, or epi- tympanic recess ; and (3) the tympanic or mastoid antrum. The tympanum proper, or cavum tympani, is situated between the membrana tympani and the outer wall of the internal eaj. Its contents are as follows : I. A chain of ossicles (malleus, 2. Muscles, incus, and stapes), with 3. Nerves. their ligaments. 4. Bloodvessels. The vertical and antero-posterior diameters (inclusive of the attic) are fully | inch. The transverse measurement is from I to 1^ inch, except opposite the centre of the membrana t5mipani,. where it is only Yt inch. The tympanic cavity presents six walls — outer, inner, roof, fioor,^ anterior, and posterior. The outer wall is formed (i) chiefly by the membrana tympani, which has the handle of the malleus fixed to it, and (2) slightly by the tympanic annulus, within the circumference of which there is a groove, called the sulcus tympanicus, in which the membrana tympani is set. The tympanic annulus and sulcus are interrupted superiorly by a notch, called the notch of Rivini. In front of the tympanic annulus is the open, inner extremity of the fissure of Glaser, which lodges the processus gracilis of the malleus, and trans- mits the tympanic branch of the internal maxillary artery. At the inner end of the fissure of Glaser is the opening of the iter chordcB anterius, or canal of Huguier, by which the chorda tympani nerve leaves the tympanum. The inner wall separates the tympanum from the internal ear or labyrinth. It is very irregular, and presents the following parts : 1. The fenestra ovalis. 3. The promontory. 2. Projection formed by part of the 4. The fenestra rotunda. aqueduct of Fallopius. 5. The sinus tympani. The fenestra ovalis is situated in a depression, called the fossula ovalis, at the upper part of the inner wall, and it leads into the cavity of the vestibule. It is irregularly oval, and is elongated from before backwards. It is occupied by the footpiece of the stapes, and the annular ligament which connects the circumference of the footpiece to the margin of the opening, the margin being covered by cartilage. The projection formed by part of the aqueduct of Fallopius is situated above the fenestra ovalis. The aqueduct, which contains the facial nerve, is here directed backwards. \'< THE E4R 1539 Mastoid Ancrum Pyram-d, with Open- ing for Stapedius Fenestra CK-alis Aqueduct of Fallopius at Hiatus Fallopii The promontory {tuber cochlea) is situated below ' the fenestra ovalis, between it and the fenestra rotunda, and slightly anterior to both. It is a rounded prominence which is produced hy the first turn of the cochlea, and it presents grooves for the nerves of the tympanic plexus. The fenestra rotunda is situated in a funnel-shaped depression, called the fossula rotunda, below and behind the promontory. It leads into the scala tympani of the cochlea, and in the recent state is closed by the secondary membrane of the tympanum. The sinus tympani is a depression situated behind the promontcwy,. and between the fossula ovalis and fossula rotunda. The roof of the tympanum is formed by a thin plate of bone,, called the legmen tympani, which forms part of the superior surface of the petrous- part of the temporal bone. The floor is formed by a thin plate of bone which separates the tympanum from the jugular fossa. The anterior wall is narrow, owing to the descent of the roof, and the inclination towards each other of the outer and inner waUs. It pre- sents the orifices of two canak, the upper of which lodges the tensor tympani muscle, whilst the lower is the osseous part of the Eustachian tube. The two orifices are separated by the margin of Xht processus cochlearifor mi s. The posterior wall is formed by the anterior or tympanic surface of the petrous part of the temporal bone. It presents, from above downwards, the following parts : (i) the opening of the mastoid antrum, which communicates with the attic of the tympanum, or epitympanic recess ; (2) a depression called the fossa inoudis, which receives the short process of the incus ; (3) a small conical projection, called the pyramid, the summit of which presents an opening for the passage of the tendon of the stapedius muscle ; (posteriorly the canal within the pyramid, which contains the stapedius muscle, passes downwards in the posterior wall of the tympanum, and communicates with the descending part of the aqueduct of Fallopius, which contains the facial nerve, thus ex- plaining how the branch of that nerve to the stapedius reaches the Outlet of Caiotid Canal Promontory Fenestra Rotunda Sinns Tympani bullet of Aqueduct of FallopitlS- at Stylo- mastoid Foramen Fig. 644.- — SECTtON THROUGH THE PeTROUS AND Mastoid Portions of the Tempor.\l Bone, showing the Tympanum and Mas- toid Cells. 1540 A MANUAL OF ANATOMY muscle) ; and (4) the iter chordae posterius, for the passage of the chorda tympani nerve. Membrana Tympani. — ^This is the membrane which closes the inner extremity of the meatus auditorius externus. It is situated on the outer wall of the tympanum, of which it forms the chief part, and it is set, for the most part, in the sulcus tympanicus, which marks the inner surface of the tympanic annulus. Superiorly, however, where the annulus is deficient, the membrane is attached to the notch of Rivini. This part of it is thinner and looser than the rest, and is called the membrana flaccida, or Shrapnell's membrane. The attachment of the membrana tympani to the sulcus tympanicus 'is effected by means of a thickened band of fibres, disposed in the form of a ring, called the annulus fibrosus. This annulus passes Superior Ligament of Malleus Head of Malleus Insertion of Tensor Tympani Chorda Tympani Nerve ' Eustachian Tube--— Superior Ligament of Incus Body of Ijicus /T ^^Attic of Tympanum I Short Process of -*" Incus '■''A'df Long Process of Incus _. Processus Orbicu- y & ; laris of Incus Handle of Malleus Membrana Tympani Fig. 645. — The Right Membrana Tympani, Malleus, and Incus (Internal, Posterior, and Superior View) (Spalteholz). from the extremities of the notch of Rivini to the short process of the malleus in the form of two bands, which are known as the anterior and external malleolar ligaments, and which form the lower boundary of the membrana flaccida. Opposite the notch of Rivini these annular fibres separate the membrana flaccida from the rest of the membrana tympani. The membrane is set obliquely in the sulcus tympanicus, so that its lower part forms an acute angle with the floor of the meatus auditorius externus, and its upper part an obtuse angle with the roof of the passage. The membrana tympani is somewhat oval. In the vertical direction it measures about 10 mm., and horizontally from 8 to 9 mm. The handle of the malleus lies between the mucous and fibrous layers of the membrane, and descends to a point a little below its centre, where it ends in a small knob, from which the radi- THE EAR 1541^ ating fibres of the membrane proceed. This knob is firmly attached, and, being directed inwards, the membrane is consequently drawn inwards at that point, and its outer surface presents a slight conical depression, the deepest part of which is called the umbo. Structure. — ^The membrana tympani consists of three layers — external, middle, and internal. The external or cutaneous layer is very thin, and is derived from the skin of the meatus auditorius extemus. It contains no glands, is freely provided with bloodvessels and nerves, and is covered by stratified squamous epithelium. The middle or fibrous layer forms the proper substance of the membrane, and consists of fibrous tissue. The fibres are arranged in two sets — radial and circular. The radial fibres lie beneath the cutaneous layer, and radiate from the handle of the malleus to the annulus fibrosus. The circular fibres are situated within the radial fibres, and are most numerous towards the circumference of the membrane. Both sets of fibres are absent from the membrana flaccida. The Internal or mucous layer is continuous with the mucous mem- brane of the tympanum, and is covered by a single layer of squamous epithelium. The membrana flaccida, or Shrapnell's membrane, is composed of two layers — cutaneous and mucous, there being no fibrous layer. These two layers are united by connective tissue, which is Very loosely arranged, and this renders the membrane flaccid. This part is very liable to perforation. Cone of Light. — Extending from the knob, in which the handle of the malleus terminates, downwards and inwards to the antero- inferior margin of the membrana tympani there is seen a specially bright reflection, triangular in outline, with the apex towards the umbo. This is called the cone of light. Arterial Supply of the Membrana Tympani. — (i) Deep auricular branch of the internal maxillary artery. This vessel, which passes through the anterior wall of the meatus auditorius extemus, supplies the cutaneous layer. It descends from the skin of the roof of the meatus along the course of the handle of the malleus to the umbo, where it divides into branches which radiate towards the circum- 'ference of the membrane. (2) The stylo-mastoid branch of the posterior auricular, and (3) the tympanic branch of the internal maxillary. The former artery enters the tympanum from the aqueduct of Fallopius, and the latter through the fissure of Glaser. Branches from them supply the mucous layer, and form an anasto- motic ring around the circumference of the membrane. The fibrous layer receives its arterial supply from the vessels of the cutaneous and mucous layers. The veins pass to the external jugular and internal jugular veins. Nerve-supply. — The nerves are derived from (i) the auriculo- temporal of the inferior maxillarj^ (2) the auricular branch (Arnold's 154^ A MANUAL OP ANATOMY nerve) of the pneumogastric, and {3) branches from the tympanic plexus. Secondary Membrane of the Tympanum.— -This membrane closes the fenestra rotunda on the inner wall of the tympanum, and sepa- rates the tympanic cavity from the scala tympani of the cochlea. It is concave towards the tympanum, and, like the membrana tympani, it consists of three layers. The external layer is formed by the tympanic mucous membrane ; the middle layer is fibrous ; and the internal layer is formed by the lining membrane of the cochlea. The mastoid antrum and mastoid air-cells will be found described in connection with the temporal bone, and a description of the Eustachian tube will be found on p. 1274. Facet for Incus Short Process Long Process,. Handle -•-'' Fig, 646. — The Malleus. I, Anterior View ; 2, Posterior View. r; _^. Ossicles of the Tympanum. The tympanum contains three small bones, arranged in the form of a chain which extends from the membrana tympani to the fenestra ovalis. The bones are the malleus, the incus, and the stapes. The malleus is related to the membrana tympani, the stapes to the fenestra ovalis, and the incus occupies an intermediate position between these two. The malleus is so named from its resemblance to a hammer. It is composed of a head, neck, handle, and two processes, namely, long and short. The head is the upper, enlarged, rounded end. Posteriorly it pre- sents a saddle-shaped facet, directed obliquely downwards and inwards, for articulation with the incus in a synovial joint. The neck is the constricted part below the head. The handle (manubrium) is directed downwards, inwards, and backwards from the neck ; it is compressed from before backwards, and slightly curved, and it terminates in a slight knob. It lies between the fibrous and mucous layers of the membrana tympani, descending, to a point a little below the centre of the membrane. It is firmly attached to the fibrous layer by its periosteum. The tensor tym- pani muscle is inserted into its inner part, close to its root. The long process (processus gracilis), which is slender, springs from the front of the neck, and is directed forwards and downwards to the fissure of Glaser, where it is embedded in fibres which form part of the anterior ligament of the malleus, and connect it to the margins of the fissure. The long process is in the adult for the most part replaced by fibrous tissue, except close to the neck of the malleus. In early life it is continuous with Meckel's cartilage. The short process (processus brevis) is situated immediately below the long process. It is directed outwards to the upper part of the membrana THE EAR 1543 Short Process Long Process Fig . J^nticular Process fot Head of Stapes The Ixccs. 647. ( Postero-intemal View). t^^npani, with which it is connected by the annulus fibrosus. It is also connected with the extremities of the notch of Rivini by those bands of the annulus fibrosus which are known as the anterior and posterior malleolar ligaments. The incus has been so named from its resemblance to an anvil. It consists of a body and two processes — short and long. The body is thick, somewhat four-sided, and laterally compressed. Anteriorly it presents a saddle-shaped articular sur- face for the head of the malleus, with which it forms a synovial joint. The short process is directed backwards, is tipped with cartilage, and articulates with the fossa incudis on the posterior wall of the tympanum. The long pro- cess is directed downwards and in- wards, behind and parallel to the handle of the malleus. Its lower ex- tremity is bent inwards, and becomes narrowed into a neck, upon which is placed a disc-like knob of bone, called the processus lenticularis seu orbicularis, which is covered by cartilage for articulation with the head of the stapes. In early life, and up to the sixth month of intra-uterine life, this process forms a separate ossicle, called the os orhicidare. The stapes is so named from its resemblance to a stirrup. It consists of a head, neck, two crura, and a ^ foot-piece or base. The head is directed outwards, is concave and covered by cartilage, and articulates with the pro- cessus lenticularis of the incus. The neck is the constricted part which lies immediately internal to the head. Pos- teriorly it gives insertion to the stapedius muscle. The crura are anterior and pos- terior respectively, and spring from the neck. They diverge as they pass in- wards, and are attached to the foot- piece near its extremities. The anterior cms is straighter and shorter than the posterior. The foot-piece or base is some- what oval, is directed inwards, and occupies the fenestra ovalis, which it almost completely fills; its circumference is covered by cartilage, being attached to the margins of the fenestra by annular ligamentous fibres. The arch formed by the crura and foot-piece is occupied by a delicate membrane, which is attached to a slight groove on the inner aspect of the arch. Development of the Tympanic Ossicles. — The malleus and incas are usually regarded as being developed from the proximal end of Meckel's cartilage. Head Stapes.- FiG. 648. — (i) The Stapes, AND (2) Tympanic Ossi- cles IN Position. ^544 A MANUAL OF ANATOMY which forms the cartilaginous bar of the first or mandibular arch. According to some authorities, however, the incus is developed from the hyoid bar. The stapes is developed from the dorsal part of the hyoid bar of the second visceral arch, its foot-piece being derived from the labyrinth-cartilage withia the fenestra ovalis. Ligaments of the Ossicles. — ^The synovial joints between the malleus and incus and between the incus and stapes are provided with thin capsular hgaments. The Hgaments which connect the ossicles to the walls of the tympanic cavity are five in number, three of them belonging to the malleus, one to the incus, and one to the stapes. The ligaments of the malleus are anterior, posterior, and superior. The anterior ligament is arranged in two parts, as follows: (i) the band of Meckel (formerly known as the laxator tympani muscle), which extends from the root of the long process to the fissure of Glaser, through which it passes to be attached to the spine of the sphenoid bone; and (2) the so-called anterior malleolar fold, which extends from the short process to the anterior extremity of the notch of Rivini. The posterior ligament extends from the short process to the posterior extremity of the notch of Rivini. The superior ligament extends from the head of the malleus to the roof of the attic or epitympanic recess. The ligament of the incus connects the short process, near its posterior extremity, to the fossa incudis. The annular ligament of the stapes connects the circumference of the foot-piece, which is covered by cartilage, to the margin of the fenestra ovalis, which is also covered by cartilage. Muscles of the Tympanum. — These are two in number, namely, the tensor tympani and the stapedius. Tensor Tympani — Origin. — (i) The cartilaginous part of the Eustachian tube, superiorly ; (2) the adjacent part of the great wing of the sphenoid ; and (3) the wall of the osseous canal through which the muscle passes. Insertion. — ^The inner aspect of the handle of the malleus, close to its root. Nerve-supply. — A branch from the otic ganglion, and, through it, from the internal pterygoid branch of the inferior maxillary division of the fifth cranial nerve. The muscle consists of a fleshy belly, about \ inch long, and a delicate tendon. In passing backwards to the tympanum it lies in a canal, the entrance to which is situated within the petro- squamous angle of the temporal bone. The canal is placed above the osseous part of the Eustachian tube, from which it is separated by the processus cochleariformis. On entering the tympanum the tendon of the muscle bends sharply over the edge of the processus cochleariformis, and then passes outwards to reach its insertion. The tendon forms very nearly a right angle with the fleshy belly. Action. — To render tense the membrana t5anpani by drawing THE EAR 1545 inwards the handle of the malleus, and, along with it, the mem- brane. Stapedius — Origin. — The wall of the canal within the pyramid, and of the continuation of this canal in front of the descending part of the aqueduct of Fallopius. The tendon emerges from the canal withia the pyramid through, a small orifice on the apex. Insertion. — The posterior aspect of the neck of the stapes. Nerve-supply. — The facial nerve. Action. — ^To draw the head of the stapes backwards. The result is that the front part of the foot-piece of the stapes is tilted away from the vestibule, and its back part is pressed inwards towards the vestibule. Movements of the Ossicles. — ^The malleus and incus move simul- taneously, the movement being one of rotation round an axis extending from the tip of the long process of the malleus to the tip of the short process of the incus. During the action of the tensor tympani muscle, when the handle of the malleus and the membrana tympani are drawn inwards, the long process of the incus is pushed inwards, and the stapes is thereby pressed inwards. The result is that the foot-piece of the stapes presses upDn the peri- lymph of the labyrinth, and the secondary- membrane of the tympanum is pressed outwards. Probably the stapedius tends to prevent undue pressure upon the perilymph of the labyrinth during strong contraction of the tensor tympani by the tilting action already ascribed to it. Mucous Membrane of the Tympanum. — ^The tympanic mucous membrane is continuous anteriorly with that of the naso-phar^Tix through the Eustachian tube. Posteriorly it is prolonged into the mastoid antrum, and thence into the mastoid cells. It forms the internal layer of the membrana t\^mpani, and the external layer of the secondary membrane of the tympanum. It also furnishes sheaths for the tendons of the tensor tympani and stapedius muscles, and for the chorda tympani ner\'e. Two folds extend downwards from the roof of the attic or epitympanic recess, one in front of, and the other behind, the superior ligament of the malleus. The former is connected with the head of the malleus, and the latter (sometimes described as the superior ligament of the incus) with the incus. Attic or Epitympanic Recess, and its Pouches. — ^The part of the tympanic cavity which lies above the level of the upper margin of the membrana tympani is called the attic or epitympanic recess, as distinguished from the atrium or tympanum proper. It contains the head and neck of the malleus, and the body and short process of the incus. These di\'ide it incompletely into two compartments — outer and inner. The outer attic is subdivided into t\vo pouches — superior and inferior. The superior pouch is partially separated from the inner attic by the two mucous folds which have been already referred to as descending from the roof 1546 A MANUAL OF ANATOMY of the attic in front of and behind the superior ligament of the malleus. The inferior pouch of the outer attic is known as the pouch of Prussak. It is bounded externally by the membrana fiaccida, superiorly by the external ligament of the malleus, which partially separates it from the superior pouch, and inferiorly by the short process of the malleus. The pouch communicates pos- teriorly with the tympanic cavity by an opening which is situated a little above the level of the bottom of the pouch. If fluid there- fore should accumulate in Prussak's pouch, it may readily lead to perforation of the membrana fiaccida or Shrapnell's membrane. Two other pouches are present, namely, the anterior and posterior pouches of Troltsch. These lie one in front of, and the other behind, the handle of the malleus, and are produced by the fold of mucous membrane which invests the chorda tympani nerve. The tympanic mucous membrane is covered, for the most part, by columnar ciliated epithelium, except over the ossicles and membrana tympani, where the epithelium consists of a single layer of squamous, non-ciliated cells. The tympanic or mastoid antrum is supplementary to the tym- panum proper, or cavum tympani, behind which it is situated. ' It communicates by a large irregular opening with the attic, and is lined with mucous membrane, which is continuous with that of the attic and cavum tympani. Opening from the antrum there are the mastoid cells, which are lined with mucous membrane, continuous with that of the antrum. The average measurements of the antrum are as follows : vertical, about 9 millimetres; antero-posterior, about ii millimetres; and transverse, about 8 millimetres. The roof is formed by the thin tegmen tympani, which enters into the formation of the middle fossa of the base of the skull, and is consequently related to the temporal lobe of the cerebrum and its meninges. The genu and descending limb of the sigmoid sinus lie behind the antrum, and a httle farther back is the cerebellum. The facial nerve, as it traverses the descending part of the aqueduct of Fallopius, lies in the posterior wall of the cavum tympani, close to the inner wall and in front of the mastoid antrum. This part of the nerve is on a plane anterior to the mastoid process, and is nearly flush with the opening of the antrum. The ampulla of the external semi- circular canal of the internal ear gives rise to a slight eminence on the inner i0all at its anterior part. The outer wall corresponds with the area of the suprameatal triangle of Macewen, and is formed by the posimeatal plate of the squamous portion of the temporal bone. For a description of this triangle, which is the region selected for mastoidectomy, and also for the mastoid cells, see the description of the Temporal' Bone. THE EAR 1547 Summary of Important Structures closely related to the Mastoid Antrum. r. Temporal lobe of cerebrum and its meninges (roof). 2. Genu and descending limb of sigmoid sinus, and farther back the cere- bellum 'posterior wall . 3. Facial nerve (posterior wall of cavum tympani. close to inner wall, and nearly flush with antral opening^ 4. External semicircular canal (anterior part of inner wall). The upper part of the antrum communicates, as stated, with the attic of the cavum tympani, but the lower part is shut off by bone from the cavity of the ca\'iun t^mpanL The mucous membrane of the mastoid antrum is continuous with that which hnes the mastoid cells. Anteriorly it is also con- tinuous, as stated, with the mucous membrane of the attic and ca\Tmi t\Tnpani or tympanum proper. The mucous membrane of the caviun t\Tnpani is continuous anteriorly with that of the Eustachian tube, and the mucous membrane of the Eustachian tube is continuous with that of the naso-pharynx. This extensive and continuous tract of mucous membrane is covered by columnar ciliated epitheliimi, except in the following regions: (i) the pro- montory; (2) the t^onpanic ossicles; (3) the membrani tympani; ^4) the mastoid antrum ; and (5) the mastoid cells. In these regions the epithelium consists of a single layer of squamous non-ciliated cells. It is of considerable importance to note that micro-organisms may pass from the naso-pharynx through the Eustachian tube into the cavum tympani and attic, and thence into the mastoid antrum and mastoid cells. Purulent affections of these regions may there- fore readily be caused in this manner. Such affections may sub- sequently involve (i) the temporal lobe of the cerebrum and its meninges, (2) the genu and descending limb of the sigmoid sinus, and (3) the internal ear or labyrinth. Arteries of the Tympanum. — The principal £u-teries are two in number, namely, (i) the tympanic branch of the internal maxillary, and {2) the stylo- mastoid branch of the posterior auricular. The tympanic artery enters through the fissure of Glziser, and supplies the membrana tympani and front part of the tympanum. The stylo-mastoid artery enters the aqueduct of Fallopius through the stylo-mastoid foramen, and passes from the descending part of the aqueduct into the tympanum. It supplies the back part of the cavity and the mastoid cells, and it forms, with the tympanic artery, a ring round the circumference of the membrana tympani. In addition to the foregoing two arteries, the following three £irteries enter the tympanic cavity : (i) the petrosal branch of the middle meningeal, which enters from the aqueduct of Fallopius, into which it passes through the hiatus Fallopii ; {2) the tympanic branch of the ascending pharyngeal, which accom- panies Jacobson's nerve through the tympanic canaliculus ; and (3) the tympanic branch of the internal carotid, which enters by a minute foramen on the posterior wall of the ascending part of the carotid cancil, in company with a sympathetic twig from the carotid plexus. The veins of the tympanum pass to the pterygoid plexus, the superior petrosal sinus, the internal jugular vein, and the pharyngeal plexus. 1548 A MANUAL OF ANATOMY Nerves of the Tympanum — i- Tympanic Plexus. — This plexus is situated on the inner wall of the tympanic cavity, more particularly over the pro- montory. It is formed by (a) the tympanic branch (Jacobson's nerve) of the petrous ganglion of the glosso-pharyngeal, and (6) the carotico-tympanic branch of the carotid plexus of the sympathetic. Branches. — These are distributed to the mucous membrane of the tym- panum, Eustachian tube, and mastoid cells. Besides these, there are two named branches, called the small superficial petrosal and the small deep petrosal. The small superficial petrosal nerve is to be regarded as the con- tinuation of Jacobson's nerve. After issuing from the tympanic plexus it leaves the tympanum at the upper part of the anterior wall, and traverses a small canal in the petrous part of the temporal bone, passing beneath the upper portion of the canal which lodges the tensor tympani muscle. Whilst in this canal it is joined by a small branch from the geniculate ganglion of the facial nerve, and it emerges from the canal through the accessory hiatus on the superior surface of the pars petrosa. It then passes forwards and inwards beneath the dura mater, and leaves the cranial cavity through the canaliculus innominatus, or through the fissure between the pars petrosa and the great wing of the sphenoid, or through the foramen ovale. Having entered the zygomatic fossa, it joins the otic ganglion, to which it conducts glosso- pharjmgeal fibres. The small deep petrosal nerve passes forwards through a minute canal within the processus cochleariformis to the upper aspect of the foramen lacerum medium, where it joins the carotid plexus of the sympathetic and the great deep petrosal, or, it may be, the great superficial petrosal, nerve. In this manner some of its fibres pass in the Vidian nerve to Meckel's gang- lion. 2. Chorda Tympani Nerve. — This nerve arises from the facial nerve in the lower portion of the descending part of the aqueduct of Fallopius. Having ascended for a little in the aqueduct, it leaves it by passing forwards through a minute canal, called the iter chordce posterius, which opens on the posterior wall of the tympanum, below the level of the pyramid. The nerve, invested by a fold of mucous membrane, now passes forwards internal to the mem- brana tympani, and over the upper part of the handle of the malleus. It then leaves the tympanic cavity through a passage situated at the inner end of the fissure of Glaser, called the iter chordce anterius, or canal ol Huguier^ after which it joins the lingual nerve. Internal Ear. The internal ear is the essential part of the organ of hearing, and is known as the labyrinth from its remarkable complexity. It consists of two parts, namely, the osseous labyrinth and the mem- branous labyrinth. Osseous Labyrinth. The osseous labyrinth is a cavity situated within the petrous part of the temporal bone, and it is divided into three parts, namely, the vestibule, the semicircular canals, and the cochlea. These divisions are lined with a delicate periosteum, between which and the contained membranous labyrinth there is a clear fluid, called the perilymph. Vestibule. — ^The vestibule is the central division of the osseous labyrinth. The semicircular canals lie behind it, and the cochlea is situated in front of it. The outer wall presents the fenestra ovalis, which is occupied by the foot-piece of the stapes and its annular THE EAR 1549 ligament. The inner wall presents anteriorly a depression called the fovea spherica, which corresponds to the lamina cribrosa at the deep end of the meatus auditorius internus. It is pierced by apertures for the passage of filaments of the auditory nerve to the saccule. Behind and above the fovea spherica there is a ridge, called the crista vestibuli, which lies obliquely. Posteriorly it bifurcates, and between its two divisions there is a small depression. Aqueduct of Fallopius Cupola of Cochlea ^ ; Petrous part of Tem- fxjral Bone Superior Semicircular Canal Fenestra Ovalis External Semicircular Canal Posterior Semicircular Canal Vestibule ^^_^. Fenestra Rotunda Superior Semicircular Canal Inner Wall of Canal ' of Cochlea Helicotrema' Lamina Spiralis Crus Commune of Sup. and Post. Semicircular Canals Posterior Semicircular Canal External Semicircular Canal ^- Fovea Elliptica Crista Vestibuli ^ Fovea Spherica 1 Orifice of Aqueductus Vestibuli Recessus Cochlearis Fenestra Rotunda Scala Vestibuli Scala Tympan Fig. 649. — The Osseous Labyrinth of the Left Side (External View). A, Entire ; B, Opened (Hirschfeld and Leveille. B, IModified). called the recessus cochlearis, which presents a few openings for the passage of nerve filaments to the canalis cochleae. Anteriorly it becomes some\vhat triangular, and forms the pyramid, which is pierced by foramina for the passage of nerves to the utricle. The roof of the vestibule, behind and above the crista vestibuli, presents an oval depression, called the fovea elliptica, which en- croaches on the inner wall and lodges the recessus utriculi. It is pierced by foramina for the passage of the nerves to the ampullae 1550 A MANUAL OF ANATOMY of the superior and external semicircular canals. Below the fovea elliptica is the opening of the aqueductus vestibuli, which leads to the posterior surface of the petrous part of the temporal bone, about \ inch external to the orifice of the meatus auditorius internus. It transmits the ductus endol5miphaticus and a minute vein. Anteriorly the vestibule communicates with the scala vestibuli of the cochlea, and posteriorly it presents the five openings of the semicircular canals. Semicircular Canals. — The osseous semicircular canals are situated behind the vestibule. They are three in number — -superior, pos- terior, and external — and they open into the vestibule by five circular apertures, the contiguous ends of the superior and posterior canals having a common orifice. Each canal forms about two- thirds of a circle, and each presents at one end an enlargement, called the ampulla. The superior semicircular canal occupies a vertical position, and lies transversely as regards the long axis of the petrous part of the temporal bone, giving rise to the eminentia arciiata on its superior surface. Its ampullary end (antero-external) opens independently into the upper part of the vestibule, above the ampullary orifice of the external canal. Its non-ampullary end unites with the non-ampullary end of the posterior canal, and the two open by a common orifice into the vestibule. The posterior semicircular canal arches backwards towards the posterior surface of the pars petrosa, with which it is almost parallel, and, like the superior, it occupies a vertical position. Its ampullary end (inferior) opens independently into the lower and back part of the vestibule, and its non-ampullary end, as just stated, joins that of the superior canal. The external semicircular canal arches outwards, and occupies a horizontal position. Its extremities are independent of those of the other two canals, and they open by separate apertures into the upper and back part of the vestibule. Its ampullary end is external. Cochlea. — ^The osseous cochlea is situated in front of the vesti- bule. It consists of a tube coiled spirally upon itself, like a snail's shell, and is of conical outline. Its base is opposite the lamina cribrosa at the deep end of the meatus auditorius internus ; and its apex, known as the cupola, is directed outwards and slightly for- wards towards the canal which contains the tensor tympani muscle. Its length from base to apex is about \ inch. It consists of (i) a winding tube, called the spiral canal of the cochlea; (2) a central pillar, called the modiolus, round which the spiral canal turns; and (3) a thin plate of bone, called the lamina spiralis, which winds spirally round the modiolus and projects into the spiral canal of the cochlea. The spiral canal of the cochlea (cochlear canal or tube) winds round the modiolus, which forms its inner wall. It descriljes two and three-quarter turns, and its basal turn or coil gives rise to the' promontory on the inner wall of the tympanum proper. At the THE EAR 1551 cupola it ends in a blind- extremity. It gradually diminishes in size from base to cupola; its length is about 32 millimetres; and its diameter is about 2 millimetres at the base, where it is greatest. The modiolus is the central pillar round which the spiral canal of the cochlea turns, and it forms the inner wall of that canal. It commences at the cochlear area of the lamina cribrosa at the deep end of the internal auditory meatus, and extends almost to the cupola, gradually tapering. It is traversed by minute canals for branches of the cochlear division of the auditory nerve. One of these canals occupies the centre of the modiolus, and is called the central canal of the modiolus. This canal commences at the foramen centrale of the cochlear area of the lamina cribrosa, and it transmits the nerve-filaments for the apical coil. The other canals, which have no special name, commence at the tr actus spiralis Fig. 650. — Median Section of the Left Osseous Cochlea of Man FROM Apex to Base (Arnold). S.V. Scala Vestibuli L.S.O. Lamina Spiralis Ossea S.T. Scala Tympani C.C. Central Canal of Modiolus M.A.I. Meatus Auditorius Internus foraminosus of the cochlear area of the lamina cribrosi, and they transmit the nerve-filaments for the other coils — middle and basal. At successive levels these canals change their direction, and pass outwards to the attached margin of the lamina spiralis, to be presently described. Here they coalesce and form a winding canal, called the spiral canal of the madiolus, which lodges the spiral ganglion or ganghon of Corti. From this canal secondary canals for nerve-filaments pass into the lamina spiralis. The lamina spiralis ossea is a thin plate of bone, which winds spirally round the modiolus, to which it is attached. It projects from the modiolus into the spiral canal of the cochlea throughout the windings of the latter, and it extends for about half-way towards the outer wall of the cochlear canal. It divides that canal incom- pletely into two passages or scal-cB — ^aa upper, or scala vestibuli. 1552 A MANUAL OF ANATOMY and a lower, or scala tympani, the commencement of which is at the fenestra rotunda. Close to the cupola the lamina spiralis ter- minates in a hook-like process, called the hamulus. The spiral lamina consists of two plates of bone, between which there are canals for nerve-filaments, these canals being offsets of the spiral canal of the modiolus, which, as stated, contains the spiral ganglion or ganglion of Corti. They extend to the free margin of the spiral lamina. The free margin of the lamina spiralis is, in the recent state, attached to the outer wall of the spiral canal of the cochlea by means of the basilar membrane, and the scala vestibuli and scala tympani are now completely separated, except in the region of the hamulus, where they communicate through an opening, called the helicotrema. The lamina cribrosa, at the deep end of the internal auditory meatus, will be found described in connection with the Temporal Bone. At the lower end of the scala tympani is the upper opening of the aqueductus cochleae, which passes downwards and inwards to ter- minate on the posterior border of the petrous part of the temporal bone. It transmits a small vein to the inferior petrosal sinus, and establishes a communication between the scala tympani and the subarachnoid space. Membranous Labyrinth. The membranous labyrinth is situated within the osseous laby- rinth, and its constituent parts receive the terminal branches of the auditory nerve. It is separated from the periosteal lining of the osseous labyrinth by the perilymph, and it contains the fluid known as the endolymph. In the case of the vestibule and the osseous semicircular canals the membranous labyrinth corresponds, more or less, with them; but in the case of the osseous cochlea it forms part of the septum between the scala tympani and scala vestibuli, and contains a passage called the membranous canal of the cochlea. Vestibular Part of the Membranous Labyrinth. — The vestibule contains two membranous sacs, namely, the utricle and the saccule, which are in close contact, but do not communicate with each other directly. These sacs contain endolymph. The utricle is the larger of the two sacs, and into it the mem- branous semicircular canals open. It occupies the upper and back part of the vestibule, a portion of it, known as the recessus utriculi, lying in the fovea elliptica. In the vicinity of the crista vestibuli the wall of this recess receives fibres of the auditory nerve and is thickened, this portion of it being called the macula acustica utriculi. From the anterior and inner part of the utricle a minute canal, called the ductus utriculi {ductus ulriculo-saccularis), passes to join the ductus sacculi, and so form the ductus endo- lymphaticus. THE EAR 1555 The saccule, which is somewhat oval, hes in front of the utricle, and occupies the fovea spherica, where it is contiguous to the open- ing leading into the scala vestibuli of the cochlea. Through the openings of the fovea spherica it receives filaments of the auditory nerve, and this portion of the saccule being thickened is known as the macula acustica sacculi. Inferiorly the saccule is connected with a small canal, called the canalis or ductus reuniens of Hensen, which opens into the canal of the cochlea, or ductus cochlearis, not far from its closed vestibular end. From the posterior part of the saccule a minute canal, called the ductus sacculi, passes off, which is soon joined by the ductus utricull, and so the ductus endolymphaticus is formed. This latter duct traverses the aqueductus vestibuli, and, having reached the posterior surface of the petrous part of the temporal bone, it ends in a small blind dilatation, called the sacculus endolymphaticus, which lies beneath the dura mater. The saccule and utricle are thus indirectly con- nected by means of the ductus sacculus and ductus utriculus ; and the saccule communicates with the ductus cochlearis by means of the canalis or ductus reuniens of Hensen. Semicircular Canals. — ^The membranous semicircular canals cor- respond in outline to the osseous semicircular canals, within which they lie ; they form about two-thirds of a circle ; and each presents an ampulla at one extremity, which is situated within the ampulla of the osseous canal. They are elliptical in transverse section, and open into the utricle by five orifices, the non-ampullary ends of the superior and posterior canals being imited, so that these two ends open by a common orifice. The convex wall of each canal is attached to the periosteal lining of the osseous canal, whilst the concave wall is practically free from the osseous wall, and is bathed by the perilymph. These canals contain endolymph. Structure. — ^The walls of the utricle, saccule, and membranous semicircular canals consist of three layers, namely, (i) an outer or fibrous layer, which is vascular ; (2) a middle layer, or membrana propria, which is translucent ; and (3) an inner or epithelial layer. In each ampulla the middle layer, or membrana propria, projects into the cavity of the canal from the peripheral wall, this projecting part being known as the septum transversum. It partially divides the interior of the ampulla into two compartments, and its free margin, which is covered by the auditory epithelium, is called the crista acustica. The epithelial layer consists of a single stratum of squamous cells, except in those regions to which the filaments of the auditory nerve are distributed. These regions are as follows : (i) the macula acustica utriculi ; (2) the macula acustica sacculi ; and (3) the crista acustica of each ampulla. The macula acustica utriculi is the thickened part of the antero- inferior wall of the recessus utriculi, and is lined with auditory epithelium. The macula is cohered by calcareous particles, called otoliths or otoconia, which consist of crystals of calcium carbonate. The macula acustica sacculi i>^ the thickened part of the anterior 98 ^^ A MANUAL OF ANATOMY wall of the saccule, and is also lined with auditory epithelium, covered by otoliths. The crista acustica, as stated, is the free margin of the septum transversum in each ampulla, and is covered by auditory epithelium. The auditory epithelium is of the columnar variety, and consists of two kinds of cells, auditory and sustentacular. The auditory €ells are nucleated, and each is provided at its free extremity with a slender, tapering, hair-like filament, which projects into the cavity. These filaments are sometimes spoken of collectively as auditory hairs, and the cells are hence called hair-cells. Their deep ex- tremities fall short of the membrana propria. The sustentacular €ells lie between the hair-cells, and are elongated and nucleated. Their deep extremities are attached to the membrana propria, and their free extremities give rise to a kind of limiting membrane. The auditory nerve-fibres pierce the membrana propria, and, having Superior Semicircular Canal External Semicircular Canal JjC^ \. Crus Commune of Superior and _>tT— Posterior bemicircular Canals Posterior Semicircular Canal /? VnV'') /\ Ampulla •A ^j j^-^/ fl^-f Nerve to Ampulla "^^^-^^f^Jli^r. Nerve to Utricle c^^^^Mjjt ^BI Nerve to Saccule ^VB\iW/^ Cochlear Nerve Facial Nerve '' ^Mlff Fig. 651.— The Membranous Semicircular Canals, showing the Dis- tribution OF THE Branches of the Auditory Nerve to their Ampullae (Breschet). lost their medullary sheaths, the axons terminate in arborizations around the deep ends of the auditory or hair cells. Membranous Cochlea. — The membranous cochlea is situated within the osseous cochlea, and completes the deficiency which is left by the lamina spiralis. It consists of two membranes, namely, the basilar membrane and the membrane of Reissner, which enclose between them the ductus cochlearis, or scala media. The osseous cochlea in the recent state is therefore divided into three spiral passages, namely, (i) the scala t3niipani, (2) the scala vesti- buli, and (3) the scala media. The scala vestibuli is continuous with the scala t5nTipani at the cupola through means of an aperture, called the helicotrema ; and at the base of the cochlea it opens upon the anterior wall of the vestibule. The scala tympani commences at the fenestra rotunda, and in the recent state is separated from the tympanic cavity by the secondary membrane of the tympanum. The scala media, or ductus cochlearis, communicates, near its lower end, with the saccule by means of the canalis or ductus reuniens of Hensen. The scala vestibuli and scala tympani contain peri- THE EAR ,553 lymph, which is continuous with the periI>Tnph of the vestibule ^srA osseous semicircular canals. The scala media contains endo- lymph, which is continuous with that of the saccule. Basilar Membrane. — The basilar membrane extends from the iree margin of the lamina spiralis to the crista basilans, or lower Modiolas Osseous Spiral T^'"'"» ''^^^SS^jfes Scala V'estibuli Membrane of Reissner .^^3=i^^2 ^^^S^^ Scala Media Basilar Membrane >^5 ^nV',?! ; .: ^-^ala Tympani Fig. 652. — Vertical Section of the Cochlea of a Fn-ngeal portion of the alimentary tube. The entoderm of the upper end of the cleft is elongated dorsalwards and out%vards. and its dorsal •extremity, becoming expanded, forms the cavity of the middle ear, or tym- panum, whilst the ventral portion of the entodermic diverticulum, remaining tubular, gives rise to the Eustachian tube, which necessarily opens from the pharynx. The entire entodermic diverticulum is invested by mesoderm ic iissue. The tissue surrounding the enlargement which forms the tympanum, as well as that surrounding the tympanic portion of the Eustachian tube, forms part of the periotic cartilaginous capsule, and when ossified, constitutes the osseous wall of the t)rmpanum, and the osseous upper part of the Eus- tachian tube. The mesodermic tissue surrounding the lower part of the Eustachian tube gives rise to the cartilage which characterizes that portion of the tube. Inasmuch as the tympanum is developed from the upper end of the first visceral cleft, it is intimately related to the upper ends of the first and second visceral arches. From the upper end of the skeletal bar of cartilage (Meckel's eartilage) of the first visceral, or mandibular, arch the malleus and the incus are developed; and from the upper end of the skeletal bar of cartilage (hyoid bar, or Reichert's cartilage) of the second visceral, or hyoid, arch the greater part of the incus is developed. These ossicles — namely, the malleus, incus, and stapes, constitute the tympanic ossicles of adult life. These three ossicles, together with the chorda tympani nerve, all lie external 1562 A MANUAL OF ANATOMY to the epithelial wall of the primitive tympanic cavity. After the periotic cartilaginous capsule has undergone ossification and formed the osseous wall of the tympanum, the malleus, incus, stapes, and chorda tympani nerve lie embedded in the mesodermic tissue which intervenes between the epithelial or mucous roof of the membranous tympanum and its osseous roof. This, mesodermic tissue disappears, and the mucous (orginally epithelial) lining of the tympanum now comes into direct contact with the malleus, incus, stapes, and chorda tympani nerve, all of which it encloses within folds. Though these structures apparently lie within the tympanic cavity, this is not their actual position. They are really outside the cavity, inasmuch as they lie external to the mucous lining of the cavity. This may be illustrated by stating that the handle or manubrium of the malleus and the chorda tympani nerve do not lie in the tympanic cavity, but are placed between the middle, or fibrous layer and the internal, or mucous, layer of the membrana tympani. External Ear. — The external ear consists of (i ) the external auditory meatus, including the membrana tympani, and (2) the pinna. The external auditory meatus is developed from the upper part of the first external or ectodermic furrow, which corresponds, in position, to the first internal visceral cleft. The membrana tympani is developed from the closing membrane which separates the first internal visceral cleft from the first external ectodermic furrow. This closing membrane is a trilaminar structure. Its inner layer consists of entoderm; its middle layer of mesoderm; and its outer layer of ectoderm. The membrana tympani, which is developed from it, is therefore trilaminar. The outer layer is ectodermic, and is continuous with the cuticular lining of the external auditory meatus; the middle layer is mesodermic, or fibrous ; and the inner layer is entodermic, or mucous, and is continuous with the mucous lining of the tympanic cavity. The component parts of the pinna are developed from six projections, consisting of mesoderm, covered by ectoderm. These appear on the upper ends of the first and second visceral arches, where these bound the upper part of the first external ectodermic furrow, which gives rise to the external auditory meatus. The helix is developed from two of these tubercles, and each of the other four gives rise to the antihelix, tragus, antitragus, and lobule^ The mesodermic tissue of the projections becomes differentiated into con- nective tissue and cartilage, and the ectoderm forms the integument. GUIDE TO THE HEAD AND XECK 156^ GUIDE TO THE HEAD AND NECK. Back of the Scalp and Neck. — The landmarks having been studied, the skin is to be removed by making the following incisions : one is to be carried along the median line from the level of the seventh cervical spinous process to the vertex of the skull, and this incision may be prolonged to the root of the nose ; a second is to be made from the upper part of the auricle, and a third from the acromial region, both of these meeting the first incision. On reflecting the flaps of skin thus marked out great care has to be exercised, as the skin and superficial fascia are very closely adherent. The cutting edge of the knife should be directed towards the sldn, so as to score it, and in doing so the roots of the hairs will be severed. At the same time the dissector will note the strong fibrous processes which bind the superficial fascia to the skin. The cutaneous nerves jire to be displayed at once, and followed to their terminations. The great occipital nerve, with the occipital artery lyiag external to it, will be met with piercing the complexus, and. it mav be, the trapezius, about ^ inch from the median line, and the occipital venous plexus is to be kept in view. The least, or third, occipital nerve, very minute, will be found internal to the great occipital, and the small occipital nerve is to^ be found along the posterior border of the stemo-cleido-mastoid muscle. The great auricular nerve lies immediately below the small occipital, and turns upwards and forwards over the upper part of the stemo-cleido-nicistoid towards the lobule of the auricle, where its mastoid, auricular, and facial branches are to be shown. The superficial or transverse cervical nerve can cnly be shown initially. It appears immediately below the great auricular,, and at once passes horizontally forwards over the stemo-cleido-mastoid, where it must be left in the meantime. The spinal accessory nerve is to be caught where it appears from beneath the posterior border of the stemo- cleido-mastoid, about its centre and below the superficial cervical. It is to- be followed downwards and outwards across the posterior triangle to the anterior border of the trapezius, beneath which it disappears. Accompany- ing it, and hnng on a lower level than it, an effort should be made to show the two branches which the anterior primary divisions of the third and fourth cervical nerves furnish to the trapezius. The descending superficial branches of the cervical plexus will be met with at the posterior border of the stemo- cleido-mastoid, immediately below the spinal accessory. If they appear as one trunk they will soon divide into suprasternal, supraclavicular, and supra- acromial ; but these nerves, in this position of the subject, can only be seen at their commencement. The internal branches of the posterior primary divisions of the third, fourth, and fifth cervical ner\-es are to be displayed as they pierce the trapezius close to the median line, and they are to be followed outwards. Behind the auricle, over the mastoid process, the mastoid glands are to be carefully looked for, and the occipital gland, or glands, will be met with over the cranial insertion of the trapezius, or, it may be, the complexus. Along the posterior border of the stemo-cleido-mastoid the glandulx concatenate are to be looked for. 15^4 A MANUAL OF ANATOMY The cervical part of the trapezius is to be dissected, and its anterior border clearly defined, with the spinal accessory nerve and branches of the third and fourth cervical nerves passing beneath it. The posterior portion of the upper part of the sterno-cleido-mastoid is also to be clearly defined. The interval between the trapezius and the sterno-cleido-mastoid, partially visible in this position of the subject, is the posterior triangle. Within it are to be partially dissected the following structures : a small angle of the complexus muscle pierced by the great occipital nerve, provided the trapezius is not well developed ; a portion of the splenius muscle, fiat and broad, and directed upwards and outwards ; and a portion of the levator anguli scapulae. The occipitalis muscle is next to be dissected, and the epicranial aponeurosis, upon which its fibres end, is to be displayed. The close connection between this aponeurosis and the superficial fascia is to be noted, whereas it is only loosely connected to the subjacent periosteum or pericranium. Behind the auricle the retrahens auriculam muscle is to be shown passing between the mastoid process and the convexity of the concha. Lying deeply in the hollow between the mastoid process and the auricle careful dissection will bring into view the posterior auricular nerve and artery, both of which are to be fol- lowed to their distribution. The posterior auricular vein is of importance, because, in conjunction with the posterior division of the temporo-maxillary vein, it forms the external jugular vein. Above the auricle the attoUens auriculam muscle is to be shown, lying upon the temporal fascia. In front of the auricle, and continuous with the preceding muscle, will be found the attrahens auriculam. The latter two muscles will be found to receive twigs from the temporo-facial division of the facial nerve. Frontal Region. — The dissection of the frontal region is next to be over- taken, the head being well raised upon a block. The frontalis muscle and front part of the epicranial aponeurosis are to be dissected. The supra- orbital nerve, of large size, is to be carefully displayed. It will be found ascending in line with the junction of the inner third and outer two-thirds ■of the supra-orbital arch, in company with the supra-orbital artery, and it lies at first beneath the upper part of the orbicularis palpebrarum and the frontalis muscles. Its twigs to the upper eyelid are to be looked for, and its main branches are to be followed towards the vertex of the skull. The supra- trochlear nerve, of small size, will be found internal to the supra-orbital, and in line with the inner canthus of the eye. It is accompanied by the frontal artery. The supra-orbital vein is to be shown passing downwards and inwards to join the frontal vein in the region of the inner canthus, the resultant vessel being the angular vein, which is the commencement of the facial vein. A communicating vessel is to be looked for passing from the supra-orbital vein to the supra-orbital notch, after traversing which it communicates with the superior ophthalmic vein within the orbit. Temporal Region. — The attollens and attrahens auriculam muscles have been already referred to. Directly in front of the tragus of the auricle there will be found the auriculo-temporal nerve and the superficial temporal artery and vein. The nerve lies between the tragus and the artery, and its meatal, anterior auricular, and temporal branches are to be shown, the first two sets of branches requiring considerable care in their display. The temporal branches of the temporo-facial division of the facial nerve are to be kept in view at this stage. The superficial temporal artery, in two divisions, anterior and posterior, is to be dissected, and special attention is to be given to the tortuous anterior division, which is of some surgical impor- tance. The temporal branch of the temporo-malar or orbital nerve (from the superior maxillary division of the fifth cranial nerve) will be met with piercing the temporal fascia about i inch above the anterior part of the zygoma, and close behind the marginal process on the temporal border of the malar bone. Its cutaneous distribution is somewhat limited. The temporal fascia, or aponeurosis, is next to be dissected. In the region of the zygomatic arch it will be found to consist of two laminae, between which, in addition to fat, will be found the orbital branch of the superficial temporal artery on its way to the outer part of the orbicularis palpebrarum GUIDE TO THE HEAD AND NECK 1565 muscle. In removing this fascia the dissector will note that its deep surface gives origin to the superficial fibres of the temporal muscle superiorly. The upper portion of the temporal muscle is then to be studied, but it cannot be followed at the present time beyond the level of the zygomatic arch. At this stage the dissector, in association with his companion, may take the steps necessary for the removal of the brain, the subject being now assumed to have lain for two days face downwards. It may, however, be preferable to complete the dissection of the back of the neck. The trapezius is to be divided by a vertical incision about i inch from the spines of the vertebrae, in association with the dissector of the upper limb. The spinal accessory nerve is then to be dissected along the deep surface of the muscle, in company with the superficial cervical artery, and the plexi- form communication between the spinal accessory and the branches from the anterior primary divisions of the third and .fourth cervical nerves is to^ be shown. The insertion of the stemo-cleido-mastoid is to be in great part detached and turned forwards towards the auricle. Assuming that the dis-r sector of the upper limb has paved the way by dividing and reflecting the rhomboid muscles and the serratus posticus superior, the splenius muscle is then to be fully dissected in co-operation A^dth the dissector of the upper limb. Its twofold condition at its insertion, namely, the splenius capitis and the splenius colli, is to be clearly brought out. The muscle is there- after to be divided by a vertical incision about i inch from the spines of the vertebrje, a procedure which will enable the dissector to display more fully the twofold condition of the muscle at its insertion. The trachelo-mastoid and complexus muscles fall next to be dissected, the former being very narrow and ribbon-like, whilst the latter is a large and powerful muscle, and is pierced by the great occipital nerve. Tendinous intersections are to be looked for in these muscles, one in each, and in the case of the complexus the condition of its mesial portion is to be carefully looked to. The dissector will note that this portion presents an intervening tendon, with a fleshy belly at either end, thus accounting for the name biventer cervicis, by which the inner portion of the complexus is known. At this stage the second part of the occipital artery falls to be dissected. Its princeps cervicis branch (arteria princeps cervicis) is to be dissected very carefully, and preserved for immediate further dissection. The trachelo- mastoid is to be divided, and the relation of structures in the mastoid region from the surface downwards is to be carefully noted. The complexus is to- be divided about 2 inches below its insertion, and on reflecting the muscle the dissector should follow downwards the cirteria princeps cervicis. About the level of the spine of the axis he will find that it anastomoses with the deep cervical artery, which, he will note, ascends beneath the complexus. The subsequent and final stage of this dissection consists in displaying the structures of the infra-axial arid supra-axial regions. Below the level of the spine of the axis the semispinalis colli muscle, as regards its fourfold in- sertion, is to be made clear. The origin of this muscle must be dissected in concert with the dissector of the upper limb. Ascending upon it there is, as stated, the deep cervical arter^'. Passing inwards upon it will be found the internal branches of the posterior primary divisions of the third, fourth, and fifth cervical spinal nerves, whilst those of the sixth, seventh, and eighth nerves pass inwards underneath the muscle. When the semispinalis colli is^ removed the upper part of the multifidus spinae falls to be dissected. The interspinales muscles, along with the ligamentum nuchae, are next to receive attention, and the tendinous slips of insertion of the cervicalis ascendens and transversalis cervicis into tubercles (posterior tubercles) of transverse pro- cesses are to be made evident. At this stage the dissector should familiarize himself with the relative position of muscles, proceeding from the tubercles (posterior tubercles) of cervical tiansverse processes, and passing backwards to the cervical spines. Above the level of the spine of the axis four muscles and the suboccipital triangle, with its contents, require very careful dissection. The obliquus- capitis inferior will be found extending obliquely outw^ards and upwards from 1566 ^V^-' A MANUAL OF ANATOMY the spine of the axis to the transverse process of the atlas, and the dissector will note that the great occipital nerve, preparatory to piercing the complexus, winds round the lower border of the inferior oblique in a backward direction. The obliquus capitis superior will be found extending upwards and inwards from the transverse process of the altas to the occipital bone between the outer parts of the superior and inferior curved lines. The rectus capitis posticus major is to be shown extending from the spine of the axis upwards and outwards to the outer part of the inferior curved line of the occipital bone and the subjacent area. The rectus capitis posticus minor is partially visible internal to the preceding muscle, but is also under cover of it. It will be recognised as a fan-shaped muscle, lying very deeply, and extending from the posterior arch of the atlas, close to the posterior tubercle, in a radiating manner upwards to the inner third of the inferior curved line of the occipital bone and the subjacent area. The suboccipital triangle will now be exposed, lying between the inferior oblique, superior oblique, and rectus capitis posticus major. Within this triangle the dissector, by exer- ■cising great care, should expose and study the following structures : (i) the posterior primary division (undivided) of the first cervical or suboccipital nerve, lying in close contact with the vertebrarterial groove of the atlas ; (2) the third part of the vertebral artery ; (3) the posterior occipito-atlantal ligament (one half), and one half of the posterior arch of the atlas. The suboccipital plexus of veins also occupies this triangle, from which the blood is conveyed away by the vertebral and deep cervical veins. Up to this stage of the dissection it m.ay be presumed that the period allowed for the subject to lie with its face downwards has expired. Removal of the Brain. — The brain may be removed whilst the subject lies upon its face, but there is no objection to removing it whilst the subject lies upon its back. The scalp having been previously dissected, together with the temporal fascia and the origin of the temporal muscle, the cranium is to be cleared for the saw by carrying a scalpel around it, passing about i inch above the orbits, and about ^ inch above the external occipital protuberance. The external table of the cranial bones is then to be sawn through, and there- after the internal table is to be cracked by means of a chisel and mallet. The calvaria is then to be eased all round by inserting the chisel, and forcibly raised from the dura mater, which is adherent to it. The dura mater, being now exposed, is to be carefully sponged and studied in situ. The superior longitudinal sinus, which runs in an antero-posterior direction in the median line, is to be laid freely open, and its interior examined. On either side of this sinus the outlines of the Pacchionian bodies are to be noted, and the ramifications of the middle meningeal artery are to receive attention. The dura mater is then to be divided on a level with the sawn margin of the skull, its mesial attachments in front and behind being left intact. On being raised towards the median line, the* subdural space will be freely ex- posed, and the arachnoid membrane and pia mateir are to be examined. The ■cerebral veins, as they pass to the superior longitudinal sinus, are to receive attention, and it should be noted that the direction of these veins is from behind forwards, so that the current of blood in them is opposed to that in the superior longitudinal sinus. The cerebral hemisphere is now to be slightly pulled away from the median line in order to expose the falx cerebri. When this process has been studied, its attachment to the crista galli is to be severed, and the process is to be thrown backwards towards the tentorium cerebelli, after which the brain is to be removed. Assuming the subject to be lying upon its face, the posterior cerebral lobes are to be raised, which will expose the tentorium cerebelli. This is to be divided near the superior border of the petrous part of the temporal bone, and for a short distance along the course of the lateral sinus on either side, but the sinus is not to be laid open. At the same time the fourth and fifth pairs of nerves are to be divided. Exactly in the median line the vena magna -mphatic glands. Emerging from the anterior border of the gland, and passing forwards over the meisseter muscle on to the buccinator, the parotid or Stensen's duct is to be shown, with the transverse facial artery above it, and the infra-orbital branches of the facial nerve below it. The pars or glandula socia parotidis is to be shown accom- panying Stensen's duct for a variable distance, and lying above it. The branches of the facial nerve are now to be followed into the parotid gland, cutting away the glandular substance in doing so. This will enable the dissector to trace the trunk of the facial nerve to the stylo-mastoid foramen, and to show its posterior auricular, digastric, and stylo-hyoid branches! The auriculo-temporal nerve is also to be shown within the upper part of the gland, and communications between this nerve and the temporo-facial division of the facial, as well as between the great auriculcir nerve and the cervico-facial division of the facial, are to be kept in view. The external 1576 A MANUAL OF ANATOMY carotid artery is to be shown within the gland, dividing into its superficial temporal and internal maxillary branches. The superficial temporal vein is to be followed downwards within the gland until it is joined by the internal maxillary vein, and the resultant vessel, namely, the temporo-maxillary vein, is thereafter to be followed downwards within the gland in front of the external carotid artery. The mode of termination of the temporo-maxillary vein is also to be shown, its anterior division joining the facial vein to form the common facial vein, and its posterior division joining the posterior auricular vein to form the external jugular vein. The foregoing dissections will have led to the removal of a large part of the parotid gland. The dissector will therefore be able to see that it extends inwards behind the ramus of the inferior maxilla, and deeply into the posterior part of the glenoid fossa of the temporal bone. Ocular Appendages. — The eyelids or palpebrae, with their tarsal plates, are to receive attention, as well as the eyelashes or cilia, and the canthi, outer and inner. At the inner canthus the lacus lacrimalis, caruncula lacrimalis, and plica semilunaris are to be studied, as are also the papillae lacrimales and puncta lacrimalia. The lachrymal canaliculi are to be opened up, and the lachrymal sac is to be shown lying in the lachrymal groove of the lachrymal bone and nasal process of the superior maxilla. The sac should be laid open, and a probe passed down the nasal duct. The superior and inferior palpebral ligaments, as well as the external tarsal ligament, are to be dissected. The internal tarsal ligament or tendo palpebrarum has been already seen. The conjunctiva, palpebral and ocular, is to be carefully studied, and the superior and inferior fornix noted. On the internal surface of each tarsal plate, between it and the conjunctiva, the outlines of the Meibomian glands will be seen, and their orifices may be visible, arranged in a row a little behind each ciliary margin. In this situation the glands of Moll are to be borne in mind. Auricle (Pinna). — The auricle is to be carefully studied and dissected. Its extrinsic muscles, namely, attrahens, attollens, and retrahens, auriculam have been already attended to. The component parts of the auricle are to be mastered, namely, the concha, helix, crus helicis, antihelix, tragus, anti- tragus, incisura intertragica, lobule, tubercle of Darwin, fossa of the helix (scaphoid fossa), and fossa of the antihelix (triangular fossa). The ligaments and intrinsic muscles are to be dissected, according to the description of them which is given in the text ; the blood-supply and nerve-supply of the auricle are to be reviewed ; and thereafter an effort is to be made to dissect the plate of yellow elastic fibro-cartilage which forms its framework. The meatus auditorius externus is to receive very careful study. Nose. — The cartilaginous framework of the nose is now to be dissected, and this should be overtaken by the two dissectors working in concert. The upper lateral nasal cartilages will be found immediately below the nasal bones. The lower lateral nasal cartilages, or cartilages of the apertures, are situated below the preceding, and each is bent so as to lie in front, and on each side, of the nostril. The crus laterale and crus mediate of each cartilage of the aperture are to be noted. Two or more sesamoid, or minor, cartilages are to be looked for in the fibrous tissue which connects the crus laterale to the superior maxilla. In dissecting the foregoing cartilages the dissectors should have before them the description given of them in the text. The cartilage of the septum is mesially placed, and can only be fully studied in connection with the interior of the nasal fossae. It is sufficient meanwhile to note that its anterior border is visible between the anterior borders of the upper lateral nasal cartilages inferiorly. Masseter Muscle. — Before leaving the dissection of the face the masseter is to be dissected. Its superficial and deep parts are to be clearly shown, and its relations thoroughly mastered. Orbit. — To prepare the cavity of the orbit for dissection the osseous roof must be removed. For this purpose a vertical cut is to be made with the saw through the frontal bone as low as a point just external to the fovea trochlearis. A second cut is to be made with the saw through the lateral wall of the skull from a point on a level with the auricle downwards and GUIDE TO THE HEAD AND NECK i577 forwards to the sphenoideil fissure. A large portion of the malar bone is to be removed, for which purpose the bone-pliers may suffice. In his further mode of procedure the dissector should be careful to leave intact the portion of bone immediately surrounding the optic foramen. The inner and outer saw-cuts are to be connected by using the chisel and mallet, one or two smart knocks being sufficient for this purpose. Thereafter the osseous roof of the orbit is to be tilted forwards by a smart knock ^^ath the mallet. The small wing of the sphenoid bone is next to be removed with the bone-pliers. In the foregoing manner the cavity of the orbit will be exposed, and the sphenoidal fissure will be opened from above. The periosteum of the orbit is to be examined, and then laid open. Exactly in the median line, and embedded in the soft fat of the orbit, the dissector will find the frontal nerve, which anteriorly is accompanied by the supra- orbital artery, and divides into supra-orbital and supra-trochlear. The supratrochlear nerve, before leaving the orbit, will be found to give oflE a small twig, which descends to form a loop with the infratrochlear branch of the nasal nerve. More deeply placed than the frontal nerve, but also in the median line, the levator palpebrae superioris muscle is to be dissected, and immediately beneath it the superior rectus. The branches of the upper division of the third or oculo-motor nerve to these two muscles are to be found entering the deep or ocular surface of each muscle. The superior oblique muscle is to be dissected along the inner wall of the orbit, where it lies superficially, and the dissector is to show the fourth nerve entering its superficijd or orbital surface far back. The muscle is to be fol- lowed forwards, and its tendon traced through the trochlea or pulley, and thereafter to its insertion. Underneath the superior oblique muscle will be found the internal rectus, in dissecting which the branch from the lower division of the third nerve is to be shown entering its deep or ocular surface. Between the superior oblique and interned rectus muscles will be found the nasal nerve and the anterior and posterior ethmoidal vessels. The lachrymal gland will be found at the anterior and outer part of the orbit. The lachrymal nerve, accompanied by the lachrymal artery, is to be found along the outer wall of the orbit, and is to be followed forwards to its distribution. A branch is to be looked for passing downwards from the lachrymal nerve to join the temporal branch of the orbital or temporo-malar nerve. Beneath this nerve the dissector will find the external rectus muscle. The frontal nerve and levator palpebrae superioris are to be divided, and to facilitate the dissection of the ocular muscles the eyeball may be inflated. This must be done with very great care, in order to leave intact important structures not yet dissected. The optic nerve is to be exposed by carefully pushing aside the jrielding structures which cover it. Having slipped a liga- ture round the nerve not far from the eyebaJl, a puncture is to be made in the nerve behind the ligature, and a blow-pipe is to be pushed into the nerve as far as its centre. The blow-pipe is then to be pushed forwards into the eyeball, and when the eyeball has been inflated through it the pipe is to be withdrawn, and the ligature made fast. It is possible to destroy the ciliary ganglion in inflating the eyeball, but that ganglion could easUy be dissected on the outer side of the optic nerve before taking the steps necessary for inflation. In the dissection of the ocular muscles the capsule of Tenon is to be kept in view. It forms a connective-tissue covering for the sclerotic coat of the eyeball, and extends from the point of entrance of the optic nerve to near the margin of the cornea, where it joins the ocular conjunctiva. Between the capsule of Tenon and the sclerotic a space can easily be demonstrated by puncturing the capsule, and introducing the handle of a scalpel. This is the periscl erotic space, or Tenon's space. The suspensory ligament of Lock- wood requires great care in dissection. It is a thickening of the lower part of Tenon's capsule, and extends between the malar and lachrymal bones. The capsule of Tenon is pierced by the ocular muscles, to which it furnishes sheaths. In connection with the sheaths of the recti muscles important forward 1578 A MANUAL OF ANATOMY expansions are to be noted. Those which are connected with the external and internal recti are strong, and are attached, respectively, to the orbital process of the malar bone and to the lachrymal crest of the lachrymal bone. The expansion connected with the superior rectus blends with the deep layer of the tendon of the levator palpebrae superioris, and that which is connected with the inferior rectus passes to the inferior tarsal plate. The external rectus muscle is to be fully exposed, with the sixth nerve entering its deep or ocular surface. The two heads of the muscle are to be made quite evident, with the following structures passing between them, in order from above downwards : (i) the upper division of the third nerve, (2) the nasal nerve, (3) the lower division of the third nerve, (4) the sixth nerve, and (5) the ophthalmic vein or veins. The superior rectus is to be divided and thrown forwards and backwards. On pushing aside and removing a quantity of fat the optic nerve will be exposed, and crossing it from without inwards is the ophthalmic artery. An effort should be made to show the numerous branches of this artery as detailed in the text. The nasal nerve is to be shown crossing the optic nerve from without inwards to the anterior ethmoidal canal, through which it leaves the orbit. The branches of the nerve to be looked for are as follows : (i) the long or sensory root of the ciliary ganglion, which arises from the nasal as it passes between the two heads of the external rectus ; (2) two long ciliary nerves, which communicate with the short ciliary nerves, and accom- pany them ; and (3) the infratrochlear nerve. The latter nerve is given off by the nasal at the anterior ethmoidal foramen, and it is to be followed for- wards to near the pulley of the superior oblique, where it receives a twig from the supratrochlear nerve. Thereafter it passes beneath the pulley, and emerges from the orbit at the inner canthus. The ciliary or lenticular gang- lion will be found on the outer side of the optic nerve. Its long or sensory root will be found coming from the nasal nerve, and its sympathetic root, from the cavernous plexus, usually reaches it through the sensory root. Its short or motor root comes from that branch of the lower division of the third nerve which supplies the inferior oblique muscle. Passing forwards from the ganglion are the short ciliary nerves, which will be seen to range themselves above and below the optic nerve, by which they are conducted to the back part of the sclerotic. The third cranial nerve is to be fully dissected. Its upper and lower divisions are to be shown, and the distribution of their branches made evident, those of the upper division supplying the levator palpebrae superioris and the superior rectus, and those of the lower division supplying the internal rectus, inferior rectus, and inferior oblique. The motor root of the ciliary ganglion comes from the branch to the last-named muscle. The dissector is to note that the branches of the third nerve enter the muscles which they supply on their deep or ocular surface, except in the case of the branch to the inferior oblique, which enters the posterior border of that muscle. In connection with the origins of the recti muscles the fibrous ring in the region of the optic foramen is to be examined ; and its upper part, or superior tendon of Lockwood, and lower part, or ligament of Zinn, are to be noted. The inferior oblique muscle is situated below the eyeball and also on its outer aspect. In order to expose this muscle the lower eyelid is to be everted, and the conjunctiva divided along the inferior fornix or line of reflection from the lower eyelid on to the eyeball. The origin of the muscle will be found at the anterior and inner part of the floor of the orbit, immediately external to the opening of the lachrymal canal. The orbital or temporo-malar nerve, which enters the orbit through the spheno-maxillary fissure, is to be looked for in two divisions — temporal and malar. The temporal branch receives a communicating twig from the lachrymal nerve, and ascends upon the outer wall of the orbit to the temporal canal. The malar branch passes forwards in the angle between the outer wall and floor to the malar canal. During the dissection of the orbit the ophthalmic artery and its branches, as well as the ophthalmic vein or veins, are to be kept in view. GUIDE TO THE HEAD AND NECK 1579 The structures which pass through the sphenoidal fissure are next to be carefully dissected, and their relative positions noted. Ptarygo-maxillary Region. — The temporal fascia and the part of the tem- poral muscle above the zygomatic arch have been already dissected. The masseter muscle has also been dissected. In order to expose the pter\'go- maxillary region the dissector must proceed in a definite order. The zygo- matic arch is to be divided in front of, and behind, the origin of the masseter. This is to be done at first with the saw and then with the bone-pliers. The zygomatic arch, bearing the origin of the masseter, is to be turned down- wards until the sigmoid notch of the inferior maxilla is exposed. At this stage the dissector is to show the masseteric nerve and artery emerging from the pterygo-maxillary region over the sigmoid notch and entering the deep sur- face of the masseter. The nerve and artery having been divided, the mas- seter is to be stripped from the outer surface of the ramus of the inferior maxilla as low as the angle of the bone. The extensive fleshy origin of the deep part of the muscle from the inner surface of the zygomatic arch is to be carefully noted. The dissector is next to turn his attention to the insertion of the temporal muscle, noting how it extends downwards within the anterior border of the mandibular ramus to the region of the third molar alveolus. The long buccal nerve and the buccal artery are to be caught just within the anterior border of the mandibular ramus as they pass forwards and down- wards, or, at all events, they are to be separated from the deep aspect of the insertion of the temporal muscle by pressure with the handle of the scalpel. The coronoid process of the mandible is then to be got rid of by means of the saw and bone-pliers in the following manner : ( i ) make a vertical cut from the centre of the sigmoid notch downwards for fully i inch ; and (2) make a horizontal cut from the anterior border of the mandibular ramus backwards to meet the vertical cut at a right angle. In addition to these cuts through the bone, the strongly tendinous fibres of the temporal muscle must also be divided. The coronoid process, bearing part of the insertion of the temporal muscle, is then to be turned upwards, and the muscle is to be stripped gradually from the lower part of the floor of the temporal fossa. The deep temporcd nerves, three in number, are to be looked for, as well as the anterior and posterior deep temporal arteries. An effort should also be made to expose the middle temporal artery, which, being a branch of the superficial temporal, has had to pierce the temporal fascia and temporal muscle to reach the tem- poral fossa. This artery ascends in the groove familiar to the dissector as marking the outer surface of the squamous peirt of the temporal bone. Two other horizontal cuts with the saw and bone-pliers still require to be made through the mandibular ramus. One is to be made immediately below the neck of the inferior maxilla, thus leaving intact the insertion of the ex- ternal pterygoid muscle. The other cut is to be made across the ramus from its anterior to its posterior border on a level with the summit of the crown of the third or last molar tooth, or, if this tooth be absent, as near that level as possible. This will keep the dissector free of the inferior dental foramen on the inner surface of the ramus, and will consequently leave intact the inferior dental nerve and artery. The structures to be dissected in connection with the pterygo-maxillary region are as follows : (i) the external and internal pterygoid muscles, the former passing horizontally to the front of the neck of the inferior maxilla, and the latter extending downwards and outwards to the inner surface of the mandibular ramus between the inferior dental foramen and the angle of the bone ; (2) the first and second parts of the internal maxillary artery, the second part of the vessel usually lying upon the external pterygoid muscle, but sometimes passing beneath it ; (3) the pterygoid plexus of veins around the external pterygoid muscle ; (4) the spheno -mandibular ligament (internal lateral ligament of the temporo-mandibular joint), emerging from beneath the external pterygoid muscle and resting upon the internal ptery- goid ; (5) the inferior dental and lingual nerves, emerging from beneath the lower border of the external pterygoid and passing downwards, the former, which is posterior in position, parting with it» mylo-hyoid branch close to 1580 A MANUAL OF ANATOMY the inferior dental foramen ; (6) the long buccal nerve emerging between the two heads of the external pterygoid, and giving upwards the anterior deep temporal nerve ; and (7) the middle deep temporal nerve and the masseteric nerve, emerging from beneath the upper border of the external pterygoid, the latter parting with the posterior deep temporal nerve. The first and second parts of the internal maxillary artery are to be dis- sected, as are also the pterygoid muscles. In dissecting the artery the internal maxillary lymphatic glands are to be borne in mind. The first part of the artery will be found to give off (i ) the deep auricular, (2) the tympanic, (3) the middle meningeal, furnishing the small meningeal, and (4) the inferior dental, giving off its mylo-hyoid branch. The second part gives off masseteric, deep temporal (anterior and posterior), pterygoid, and buccal branches. The posterior dental artery will be found coming off from the vessel as it is about to enter the spheno-maxillary fossa. The third part of the artery must be deferred to the time when the spheno-maxillary fossa is being dissected. The inferior dental (with its mylo-hyoid branch) and lingual nerves having been dissected in situ, the inferior dental canal is to be laid open, and the inferior dental nerve fully dissected to its distribution. In opening the canal the saw, chisel and mallet, and bone-pliers are to be used. This dissection will show the dissector how the pulps of the lower teeth are supplied with nerves, and it will also make evident the origin of the mental nerve at the level of the mental foramen. Before reflecting the external pterygoid muscle certain details may be looked to in connection with the temporo-mandibular joint. A complete dissection, however, of this articulation can only be made at the sacrifice of other structures. The dissector is therefore recommended to perform this dissection upon a specially reserved part. He should have little difficult}' in studying the external lateral ligament and the capsule. The capsule is to be opened and the interarticular fibro-cartilage noted. This will at once make evident the existence of two synovial membranes, upper and lower. Beyond this the dissector can hardly go, but he should read the description which is given of this joint in the text. The mandibular condyle is now to be disarticulated and turned forwards, along with the interarticular fibro-cartilage. In this manner the external pterygoid muscle will be reflected ; but, in disarticulating the condyle, the dissector should keep a sharp look-out for the auriculo-temporal nerve, which is in intimate contact with the back of the temporo-mandibular joint. The reflection of the external pterygoid muscle will enable the dissector to expose the following structures : (i) the inferior maxillary division of the fifth cranial nerve and its branches ; (2) the otic (Arnold's) ganglion ; (3) the chorda tympani nerve, passing forwards and downwards, and applying itself to the lingual nerve at an acute angle ; (4) the middle meningeal artery, parting, as a rule, with the small meningeal ; and (5) the upper part of the spheno- mandibular ligament. The middle meningeal artery will be found to pass, as a rule, between the two roots of origin of the auriculo-temporal nerve. The foregoing structures are to be dissected, as nearly as possible, in agreement with the description which has been given of them in the text. Admittedly the dissector >vilJ find the otic ganglion extremely difficult of dissection, but he should not refrain from attempting it. The ganglion lies behind the undivided trunk of the inferior maxillary nerve close to the foramen ovale, and the best plan is to trace upwards the internal pterygoid nerve, with which the ganglion is closely connected. The pterygo-mandibular ligament is to be examined, which separates the buccinator and superior constrictor muscles, giving origin to fibres of both muscles. Sublingual Region. — The structures in the submaxillary region have been previously dissected, e.g., the mylo-hyoid muscle, the structures covered by it, the genio-hyoid, and the hyo-glossus. This being so, the dissector is advised to saw through the inferior maxilla, say between the lateral incisor and canine alveoli. This should also be done on the other side by his partner. GUIDE TO THE HEAD AND NECK 1581 because at this stage it is most desirable that the two dissectors should work in concert. The foregoing cuts will isolate the symphysial portion of the inferior maxilla, and so preserve the attachments of the anterior belly of the digastric, genio-hyoid, and genio-hyo-glossus muscles. By a few touches of the knife the mucous membrane on the inner surface of the mandible can be cut. Thereafter a needle, threaded with a ligature, is to be pushed through the tip of the tongue and through the tip (or columella) of the nose. The needle having now been dispensed with, the ends of the ligature are to be tightly drawn and fixed. The object in this procedure will be at once obvious to the dissector, namely, to put the tongue as much upon the stretch as pos- sible. In the further stages of this dissection the ligature can easily be un- done so as to allow the tongue to retire to its normal position. The dissector will now recognise structures which he has been advised to dissect partially at a previous stage. The structures covered by the mylo-hyoid muscle are now to be completely dissected and mastered, namely, (i) the lingual nerve, with the submaxillary ganglion ; (2) the deep part of the submaxillary gland and WTiarton's duct ; (3) the hypoglossal nerve ; and (4) the sublingual gland, for the ducts of which the dissector is referred to the text. The genio-hyoglossus muscle now admits of complete dissection, and it will well repay the dissector to study it fully. Immediately extemeil to its extensive insertion into the side of the tongue he should expose the tortuous ranine artery. The genio-hyoid and hyo-glossus muscles have been already referred to. This region is admittedly one of extreme complication and perplexity, so that the dissector should not be surprised that no hard-and fast instructions can be submitted for his guidance. He may, however, show the stylohyoid ligament, the stylo-glossus muscle (already referred to at an earlier stage), the stylo-pharyngeus muscle, and, in connection with that muscle the glosso- pharyngeal nerve. The hyo-glossus muscle is to be divided near its origin and reflected towards the tongue. This will expose a portion of the lingual artery, which is now to receive the attention of the dissector, and may be fully studied with ad- vantage. The branches of the vessel are to be dissected in accordance with the text, and special attention is to be directed to the ranine artery. Superior Maxillary Nerve, Meckel's Ganglion, and Third Part of Internal Maxillary Artery. — This dissection is one of considerable difiiculty, and the dissector is advised to have before him for his guidance a section of the skull bearing upon this region. The contents of the orbit having been entirely removed, the skull is to be sawn through in a direction downwards and for- wards from a point above the meatus auditorius extemus to the region of the inner end of the sphenoidal fissure. This cut will pass through the squamous part of the temporal bone and the great wing of the sphenoid. A second cut with the saw is to be made in advance of the preceding, on a level with the anterior border of the great wing of the sphenoid, and this is to meet the first cut. The portion of bone included between these two cuts is to be removed. The foramen rotundum is to be carefully laid open with the bone- pliers, and the infra-orbital canal is to be opened with equal care. To open the posterior part of this canal the bone-pliers will be sufl&cient, but the anterior part of the canal, being somewhat deeply placed, will require the saw, or the chisel and mallet. The superior maxillary nerve is now to be studied, its straight course forwards through the foramen rotundum, upper part of the sphenomaxillary fossa, infra-orbital canal and infra-orbital foramen being conspicuous. Its orbital or temporo-malar branch is to be shown, as are also the two short sphenopalatine branches which descend to Meckel's ganglion. A little farther forwards the posterior superior dental nerve is to be shown. This at once divides into two branches which descend upon the zygomatic surface of the superior maxilla. Sometimes these two branches arise sepa- rately from the parent trunk. Within the infra-orbital canal, in order from behind forwards, the middle and cinterior superior dental branches are to be sho^vn by carefully raising the infra-orbital nerve. The dissector should exercise his own discretion as to the removal of bone to expose the course of these two nerves. 1582 A MANUAL OF ANATOMY Meckel's ganglion is now to be dissected. It is suspended from the trunk ot the superior maxillary nerve in the spheno-maxillary fossa by means of the two short spheno-palatine nerves, and lies close to the spheno-palatine foramen on the inner wall of the fossa. To understand the course of the branches of this ganglion it is absolutely necessary that the dissector should have an accurate knowledge of the foramina and canals which communicate with the spheno-maxillary fossa. With this knowledge his path will be comparatively smooth, but without it he is certain to become befogged. The spheno-maxillary fossa is so much hemmed in by bone that the dissection of Meckel's ganglion and its branches is one of the nicest dissections in the body. The dissector must act with discretion and osteological knowledge, and he will no doubt clear paths with the bone-pliers which will show the course of the nerves now to be mentioned. The spheno-palatine nerves have been already shown descending from the superior maxillary nerve to the ganglion, to which they convey sensory fibres. To understand the courses taken by the branches of the ganglion, it may be said that four paths lead from the spheno-maxillary fossa, namely (i) internal, representing the spheno-palatine foramen ; (2) inferior, representing the posterior palatine canal and its two byways — the posterior and externa) accessory palatine canals ; (3) posterior, representing (a) the Vidian or pterygoid canal and (b) the pterygo-palatine canal ; and (4) antero-superior, representing the spheno-maxillary fissure. The dissector will now, it is to be hoped, be able to follow the branches of Meckel's ganglion. Taking the internal path through the spheno-palatine foramen, he will find (i) the superior nasal Qerves, and (2) the naso-palatine nerve, or nerve of Cotunnius, all of which enter the nasal fossa. Traversing the inferior path and its two byways, he will find the three descending palatine nerves — great or anterior, small or posterior, and external. In following out the great or anterior descending palatine nerve through the posterior palatine canal the dissector is to show the two inferior nasal nerves which it gives off, and these can be traced without much difficulty to the nasal fossa by removing with the bone-pliers whatever of the vertical plate of the palate bone may be necessary. Pursuing the pos- terior paths, the dissector should look for (i) the Vidian nerve, which takes the Vidian or pterygoid route, and (2) the pharyngeal nerve, which passes through the pterygo-palatine canal. The orbital branch (or branches) of the ganglion takes the antero-Superior path, and, passing through the spheno-maxillary fissure, enters the orbit. The branches of the third part of the internal maxillary artery fall in the way of being dissected in the course of the foregoing very complicated dis- section. The dissector cannot possibly hope to show everything, so that, to a certain extent, he should rest satisfied with the description given in the text. The posterior dental artery has been already dissected. The infra- orbital artery may be available for dissection. If so, it will have become evident in the course of dissecting the infra-orbital nerve, of which it is the companion in all respects. The spheno-palatine, descending palatine. Vidian, and pterygo-palatine branches may be left with this enumeration of them. The course of the Vidian nerve, just referred to, may be exposed by re- moving the portion of bone which lies external to the foramen ovale, and laying open the Vidian canal. Like the preceding dissection, this is one of much nicety. The Vidian nerve, when followed backwards to the region of the foramen lacerum medium, will be found to divide into the great super- ficial petrosal and great deep petrosal nerves. The great superficial petrosal nerve may be followed beneath the Gasserian ganglion to the hiatus Fallopii, through which it enters the aqueduct of Fallopius to reach the geniculate ganglion of the facial nerve. The great deep petrosal nerve passes to the carotid plexus of the s)rmpathetic. The foramen ovale may now be laid open and the inferior maxillary nerve, with the motor root of the fifth cranial nerve, exposed. The internal ptery- goid nerve is to be shown arising from the back part of the inferior maxillary immediately after the latter has received the motor root, and, in intimate GUIDE TO THE HEAD AND NECK 15^5 relation with that branch of the parent trunk, the otic (Arnold's) ganglion falls to receive consideration. The relation of the ganglion to the smcill superficial petrosal and auriculo-temporal nerves is to be borne carefully in mind. The ganglion lies immediately below the foramen ovale, between the inferior maxUlary nerve and the cartilaginous part of the Eustachian tube, and the middle meningeal artery is situated behind it. The source of the motor root of the ganglion from the nerve to the internal pter\-goid muscle will be readily understood, but the dissector must not overlook the small superficial petrosal nerve, which conducts to the ganglion fibres of the glosso- pharyngeal and facial nerves. The cartilaginous part of the Eustachian tube in this vicinity may be made apparent by removing, at the discretion of the dissector, the portion of the great wing of the sphenoid bone which lies internal to the foramen ovale. This dissection will allow of the branches of the otic ganglion being displayed. One branch will be found to pass upwards and backwards to the tensor tympani muscle ; a second, downwards and for- wards to the tensor palati muscle ; branches to the auriculo-temporal nerve ; and a branch to the chorda tympani nerve. These, however, are extremely difficult of dissection ; nevertheless, an effort made will not be without its reward. Deep Dissection of the Neek. — A very complicated dissection has now to be overtaken. It is impossible to lay down hard-and-fast instructions for the guidance of the dissector. He is advised to make himself master of what has been carefully stated in the text. The structures referred to are (i) the glosso-pharyngeal, (2) the pneumogastric, (3) the spinal accessory, (4) the hypoglossal, (5) the superior cervical ganglion of the sympathetic, nerves, and (6) the cervical part of the internal carotid artery, along with the upper part of the internal jugular vein. After he has done his best to study these very important structures the dissector is to revise the styloid muscles and ligaments, and thereafter the styloid process of the temporal bone is to be nipped through, and turned downwards and forwards. This procedure may be advisable in the course of the immediately preceding dissection. Without doubt the dissector will find himself in very deep water here. He should, however, try his best. When he gets clear of the difficulties in the upper part of the neck near the base of the skull, his course is fairly clear. The spinal accessor}' nerve is to be completely mjistered, and its bulbar part, of considerable importance, is to be shown applying itself to the ganglion of the trunk of the pneumogastric. The distribution of the spinal part of the nerve must by this time be familiar to the dissector. The glosso-pharyngeal nerve is to be followed in accordance with the description which has been given of it in the text. The ganglion of the trunk of the pneumogastric nerve admits of easy dissection, but must receive careful study. Its pharyngeal and superior laryngeal branches demand most careful attention, and the relation to it of the bulbar part of the spinal accessory nerve is to be specially noted. The pharyngeal branch, conducting fibres of the bulbar part of the spinal accessory, will be found to contribute largely to the pharyngeal plexus, the other con- tributory nerves being derived from the glosso-pharyngeal and the superior cervical ganglion of the sympathetic. The superior laryngeal nerve has already been followed out in its internal and external laryngccil branches, but the dissector should note that it must contain some of the fibres of the bulbar part of the spinal accessory nerve. The parent trunk of the pneumogastric is now to be carefully studied in its course down the neck. The dissector will be already quite familiar with it. A superior aJid an inferior cervical cardiac branch are to be kept in view. As regards (i) the auricular branch of the pneamogastric, colloquially referred to as Arnold's nerve, and (2) the tjinpanic branch of the glosso- pharyngeal nerve (Jacobson's nerve), the dissector is recommended to accept these as described in the text, unless he desires to pursue a dissection of the most intiicate nature possible. The sympathetic cord is now to be dissected. The superior cervical ganglion, of great length and elliptical shape, can easily be shown, and an efifart 1584 A MANUAL OF ANATOMY should be made to show all its connections, especially its upward con- tinuation into the carotid canal of the pars petrosa. The middle and inferior cervical ganglia will probably have been met with in a previous dissection, the former being associated with the inferior thyroid artery, and the latter with the vertebral artery. From each ganglion, respectively, in order from above do^^iwards, there come the superior, middle, and inferior cervical cardiac branches ; but, though these are actually present, the dissector should not feel disheartened if he cannot verify their existence. Carotid Canal and its Contents. — The dissector is now getting into as deep water as it would be safe for him to enter. His knowledge of osteology should come to his aid. His object is to display the intrapetrous part of the internal carotid artery, and for this purpose he will remove whatever bone he deems desirable. In intimate association with this part of the internal carotid he will find the upward continuation of the cervical sympa- thetic cord. He may be able to show how this upward prolongation divides into two branches, external and internal, the former giving rise to the carotid plexus, and the latter going on to form the cavernous plexus. The dissector should carefully read the description given of these plexuses in the text. The foramen lacerum posterius, or jugular foramen, is next to be dissected. Its three compartments, already familiar to the dissector, namely (i) antero- intemal, transmitting the inferior petrosal sinus ; (2) middle, transmitting the glosso-pharyngeal, pneumogastric, and spinal accessory nerves ; and (3) postero-extemal, transmitting the lateral sinus, may now be completely verified by opening up the foramen referred to. PJiarynx, Solt Palate, and Mouth. — To prepare these important regions for dissection, the skull must be divided into two parts. The leading blood- vessels and nerves, as well as the trachea and oesophagus, are to be divided close to the root of the neck. The pharynx is then to be carefully separated from the prevertebral muscles quite up to the base of the skull, and the basilar region of the skull is to be divided with the chisel and mallet, aided by the saw. The front part of the skull) bearing the pharynx, along with the great bloodvessels and nerves, is to be separated from the back part, which bears the cervical portion of the vertebral column, with the pre- vertebral muscles. The pharynx having been distended with tow, the superior, middle, and inferior constrictor muscles are to be dissected, and whilst doing so the pharyngeal plexus of veins is to be noted. The manner in which the constrictor muscles overlap one another from below upwards is to be noted. The stylo-pharyngeus muscle and glosso-pharyngeal nerve are to be shown in the interval between the lower border of the superior constrictor and the upper border of the middle constrictor. Upon the surface of the middle constrictor muscle the dissector should make an effort to show the pharyngeal plexus of nerves, formed by the pharyngeal branches of the glosso-pharyngeal and pneumogastric, and branches from the superior cervical ganglion of the sympathetic. Be- tween the lower part of the middle constrictor and upper part of the inferior constrictor there will be found the internal laryngeal nerve and the superior laryngeal artery. The relation of the lower border of the inferior constrictor to the oesophagus is to be noted, and passing beneath this border of the hiuscle there are the inferior or recurrent laryngeal nerve and artery. The pharyngeal branch of the external carotid artery and the inferior palatine and tonsillar branches of the cervical part of the facial artery may admit of being dissected at this stage, but the injection often fails to enter these arteries. Above the upper border of the superior constrictor muscle the dis- .sector is to note the sinus of Morgagni and the pterygo-mandibular ligament, the latter separating the superior constrictor from the buccinator muscle. The wall of the pharynx, above the superior constrictor muscle, is then to be carefully opened, when the levator palati and tensor palati muscles will admit of dissection. The dissection of the exterior of the pharynx having been completed, the interior is to be shown by opening the pharynx by means of (i) a median GUIDE TO THE HEAD AND NECK 1585 vertical incision along its posterior wall, and (2) a transverse incision close to the base of the skull. The soft palate is to be studied, and the divisions of the pharynx noted, namely, the naso-pharynx, above the soft palate, and the buccal and laryngeal divisions below it. In connection with the naso- pharynx the posterior nares and the orifices of the two Eustachian tubes are to receive careful attention. The lateral pharyngeal recess, or fossa of Rosenmiiller, on the lateral wall of the naso-pharynx, is to be noted, and the pharyngeal tonsil at the upper and back part, unless the median vertical incision has interfered with it. The phar>Tigeal bursa, below the pharyngeal tonsil, is also to be examined. The isthmus faucium, superior aperture of the larynx, and oesophagus are next to be examined. The soft palate is now to receive careful attention. The anterior and pos- terior pUlars of the fauces are to be carefully examined, together with the uvula. The tonsU, lying between the anterior and posterior pillars, is to receive attention, and the supratonsillar fossa may be noted. The actual dissection of the tonsil, however, is to be postponed till the muscles of the soft palate have been dissected. The levator palati and tensor palati muscles are now to be fully dissected. The relation of the levator palati to the mem- branous floor of the lower part of the Eustachian tube is to be carefully studied. The relation of the tensor palati to the hamular process of the internal pterygoid plate of the sphenoid bone is to be specially noted. The palato-glossus and palato-phar>Tigeus muscles are to be dissected, and in connection with the latter muscle the salpingo-pharyngeus is to be looked for, descending from the lower part of the cartilage of the Eustachian tube. The dissection of the muscles of the soft palate is to be completed by showing the azygos uvulae, and the tonsil is then to be dissected. The mouth is to be carefully examined in detail. Its two divisions, namely, the vestibule and mouth proper, will have been under observation at a previous stage of the dissection. The tongue is to receive very careful attention. At its root will be seen the epiglottis and the folds of mucous membrane in this region, namely, median and two lateral, with the glosso-epiglottidean pouch, or vallecula, on either side of the median fold, are to be noted. The fold, known as the frenum linguae, should be carefully examined. It will be found on the under surface of the tongue a little distance from the tip. Close to each side of the frenum will be seen a small papilla, bearing the orifice of Wharton's duct, and near to this the orifice of the duct of Rivini or of Bar- tholin. A little posterior to this is the fold, known as the plica sublingualis, produced by the sublingual gland, and bearing the orifices of the majority of the ducts of Walther (sublingual ducts) . In connection with the tongue the three sets of papillae, namely, conical (and filiform), fungiform, and circum- vallate are to be noted. The V-shaped arrangement of the latter will attract notice, and attention is to be given to the foramen caecum. The limitation of the papillae to the anterior two-thirds of the tongue will be evident. The extrinsic muscles of the tongue are now to be carefully revised, and their dissection completed if necessary. The intrinsic muscles of the organ fall now to be dissected, namely, the lingualis superficialis, lingualis inferior, lingualis trajisversus, and linguahs verticalis. The ranine artery having been alreauiy dissected, the dissector should revise with the utmost care the nerves which aire distiibuted to the tongue. Nasal Cavities. — To expose these cavities the skull is to be sa\^Ti through vertically on one side of the median line. The septum nasi now admits of full study. Descending upon it, in a forward direction, will be found the naso- palatine nerve, or nerve of Cotunnius, from Meckel's ganglion, and accompany- ing this nerve may be seen the naso-palatine branch of the spheno-palatine artery. An effort should be made to follow the palatine branch of the naso- palatine nerve through the foramen of Scarpa to the anterior pau-t of the hard palate. The outer wall of the nasal fossa should be studied with the closest atten- tion. The three meatus — superior, middle, and inferior — and the three conchae (turbinate bones) admit of easy examination. The openings into the various meatus are to be inspected and compaired with the descriptions given 100 1586 A MANUAL OF ANATOMY of them in the text. To expose the middle meatus completely the middle concha is to be removed with the scissors. The dissector will then see the deep curved groove, called the hiatus semilunaris, at the upper and anterior part of which will be found the infundibulum. The bulla ethmoidalis will be evident, and the atrium and vestibule are to receive attention. By clipping away the anterior part of the inferior concha a view will be obtained of the lower orifice of the nasal duct, with its imperfect mucous fold, known as the valve of Hasner. The distance of the orifice of the nasal duct from the anterior nasal aperture should be carefully inspected. A probe should be passed through the nasal duct, and the direction taken by the probe noted. A Eustachian catheter should also be passed straight backwards through the inferior meatus, and the mode of introducing it into the lower orifice of the Eustachian tube should be inspected and practised. The dissection of the otic ganglion and of Meckel's ganglion may now be completely overtaken, it being left to the discretion of the dissector to remove whatever portions of bone may be necessary, after a perusal of the descrip- tions which are given of these ganglia and their branches in the text. Larynx. — The lar5nix, with the tongue, is to be separated from the superior maxilla and the lateral parts of the inferior maxilla. The superior aperture of the larynx and the epiglottis are to be carefully studied, and, on looking down through the superior aperture, the rima glottidis is to be inspected, with a true vocal cord on either side of it. A little above each true vocal cord the less distinct false vocal cord may be seen. In connection with the superior aperture, the comicula laryngis, or cartilages of Santorini, are to be noted, as well as the cuneiform cartilages, or cartilages of Wrisberg. Between the arytenoid cartilage and the back part of the ala of the thyroid cartilage the recess known as the sinus pjrriformis is to be looked for, and its downward direction is to receive attention, which accounts for a foreign body being liable to become lodged within it. The position of the great cornu of the hyoid bone on either side should also receive attention, inasmuch as from an external ex- amination of the upper part of the neck it might possibly be taken for, say, a fish- bone. In the dissection of the larynx, the dissectors, who must act in concert, should keep in view (i) the superior laryngeal nerve, its external, as well as its internal, branch; (2) the inferior or recurrent laryngeal nerve; and (3) the superior and inferior laryngeal arteries ; but the latter may not be sufficiently injected for dissection. The internal laryngeal nerve will be found piercing the [thyro-hyoid membrane, and the external laryngeal nerve is traceable to the crico-thyroid muscle and the lower part of the inferior constrictor muscle of the pharynx. The recurrent laryngeal nerve will be found close behind the crico-thyroid joint. The larynx being placed with its posterior surface upwards, the two posterior crico-arytenoid muscles will admit of easy dissection by removal of the mucous membrane. They will be found upon the extensive posterior surface of the cricoid cartilage. The median vertical ridge on the posterior surface of the cricoid cartilage will be found to give origin superiorly to the longitudinal muscular fibres of the oesophagus. In dissecting the arytenoid muscle, which extends between the posterior surfaces of the ary- tenoid cartilages, the dissector should first show the two decussating ary- taeno-epiglottidei muscles. To follow out each of these muscles, the outer layer of the aryteno-epiglottidean fold of mucous membrane requires to be carefully removed. The cornicula laryngis may now be shown. They will be found to cap the arytenoid cartilages, and not far from them the cuneiform cartilages may be exposed in the back part of the aryteno-epiglottidean folds of mucous membrane, already familiar to the dissector in connection with the superior aperture of the larynx. At this stage it may be said that the dissectors cannot possibly expect to obtain anything like a satisfactory knowledge of such an important struc- ture as the larynx from the dissection of one specimen. The larynx should be dissected several times. However, assuming that the time and oppor- tunities of the dissectors are limited, the cricoid and thyroid cartilages may now be studied, followed by the crico-thyroid and crico-arytenoid joints. The thjrro-hyoid membrane is to be dissected, and the epiglottis is to be GUIDE TO THE HEAD AND NECK i^B? examined. The crico-thyroid muscle is to be studied in so far as it can be seen without interfering with the thyroid cartilage, and its nerve- supply, namely, the external laryngeal nerve, is to be carefully noted. The part of the crico-thyroid membrane between the two crico-thyroid muscles has been already studied in connection with the operation of laryngotomy. The larynx being now placed upon its side, the greater part of the ala of the thyroid cartilage is to be removed by making (i) a vertical cut through it not far from the median line, and stopping short of the lower border, and (2) a horizontal cut extending backwards from the lower end of the vertical cut. A complete view will now be obtained of the crico-thjnroid muscle, which should be removed. Thereafter the following muscles fall to be dis- sected, namely, the lateral crico-arjrtenoid, the thyro-arytenoid, and the thyro-epiglottideus. An effort should be made to show the two portions of the thyro-arytenoid muscle, namely, internal and external ; and the close relation of the internal portion to the true vocal cord is to be noted. The lateral crico-arytenoid, and the whole of the thyro-arytenoid, muscles are to be very carefully removed. This will expose the lateral portion of the crico-thyroid membrane, the inferior thjrro-arytenoid ligament or true vocal cord, and the wall of the ventricle of the larynx. Above the wall of the ven- tricle the fibres of the superior thyro-arytenoid ligament, which enter into the false vocal cord, will be found. The mucous membrane above the true vocal cord may now be removed on the side which is being dissected, when the true and false cords of the opposite side may be examined, with the ventricle of the larynx lying between them. The saccule, which is connected with the anterior part of the ventricle, is to be explored with a probe. During the course of the foregoing dissections it is presumed that the dissectors, as recommended, have been keeping in view the nerves and arteries of the larynx. The ligaments of the larynx will have been displayed in the course of the dissection, these ligaments being the thyro-hyoid membrane, the crico- thyroid membrane, the superior thyro-arytenoid ligament, and the inferior thyro-arytenoid ligament. Two joints require close attention, namely, the crico-thyroid and the crico-arytenoid joints, and the movements allowed at these articulations are to be carefully studied. The varying conditions assumed by the rima glottidis will be found described in the text. The actions of the laryngeal muscles are to be studied with the closest attention, and the function of the epiglottis is to be considered. Prevertebral Muscles. — The scedene muscles — anticus, medius, and posticus, if not previously dissected, should now be examined, followed by the rectus capitis anticus major, rectus capitis anticus minor, rectus capitis lateralis, and longus colli. The vertebral artery, as it traverses the costo-transverse foramina of the upper six cervical vertebrae, is to be dissected, and the plexiform arrangement of veins around it is to be noted. The vertebral plexus of the sympathetic is also to be borne in mind. The Ear. — The meatus auditorius extemus is to be laid open with the chisel and bone-pliers, and the membrana tympani is to be carefully examined from the outside. The upper part of the membrane, called the membrana flaccida. or Shrapnell's membrane, which is attached to the notch of Rivini, is to receive special attention. The handle of the malleus will be observed extending between the mucous and fibrous layers of the membrane to a point a little below its centre, where the membrane is drawn inwards so as to give rise ex- ternally to a slight depression, known as the umbo. To expose the cavity of the tympanum, an opening is to be made through the thin lamina of bone, called the tegmen tympani, which is situated on the superior surface of the petrous portion of the temporal bone. If this opening is made external to the eminentia arcuata, it will expose the mastoid antrum. The opening is then to be enlarged with the bone-pliers, and the canal containing the tensor tympani muscle is to be laid open. The meatus auditorius intemus may also be laid open. The tympanic cavity, with its intricate contents, the tensor t>Tnpani muscle, and the osseous part of the Eustachian tube, are now available for examination. The contents of the meatus auditorius intemus are to be held over in the meantime. The ossicles of the tympanum, namely. 1588 A MANUAL OF ANATOMY the malleus, incus, and stapes, are to be studied in situ. The insertions ol the tensor tympani and stapedius muscles are to be made evident, and tlieir actions studied. The stapedius muscle will be found to enter the tympanum through an opening on the summit of the pyramid on the posterior wall. The dissector need not expect to be able to show the ligaments of the tym- panic ossicles, but he may make an effort to show the chorda tympani nerve. This nerve enters the tympanum through the iter chordae posterius on the posterior wall. It then passes forwards upon the membrana tympani, lying between its mucous and fibrous layers, and it leaves the tympanic cavity by passing through the iter chordae anterius, or canal of Huguier, at the inner end of the fissure of Glaser. The inner wall of the tympanum, with the fenestra ovalis, occupied by the foot -piece of the stapes and annular ligament, the promontory, and the fenestra rotunda, closed by the secondary membrane of the tympanum, is to receive careful attention. The dissector may note the position of the attic or epitympanic recess, which lies above the level of the upper margin of the membrana tympani, and which is divided incompletely into two compartments, outer and inner, by the head and neck of the malleus, and the body and short process of the incus. In connection with the oufer compart- ment, he may try and familiarize himself with the pouch of Prussak, which is bounded externally by the membrana flaccida, or Shrapnell's membrane. For the pouches of Troltsch, see the description of the tympanum in the text. The osseous part of the Eustachian tube is to be carefully studied, and the 'mastoid cells are to be examined. For the latter purpose the mastoid process of the temporal bone is to be laid open. The internal ear or labyrinth can only be effectually studied from specimens which have been specially prepared. By means of the chisel and bone-pliers, however, the dissector will obtain a fair amount of information regarding this exceedingly complicated region. The meatus auditorius internus having been already laid open, the roof of the labyrinth is to be removed in a fragmentary fashion. The coiled cochlea, with its two and a half turns, is to be noted, its base being directed towards the deep end of the meatus auditorius internus. Behind the cochlea will be found the vestibule, and at the back part of the vestibule the three semicircular canals are to be noted. Contents of the Meatus Auditorius Internus. — This meatus having been already laid open, the auditory nerve, the pars intermedia of Wrisberg, the meatal portion of the facial nerve, and the internal auditory artery are to be studied. The auditory nerve will be found to break up into two divisions — vestibular and cochlear. The meatal portion of the facial nerve will be found on the upper and anterior aspect of the auditory nerve ; and the pars intermedia of Wrisberg lies between the two. The auditory and facial nerves are connected by two branches. The internal auditory artery is seldom in- jected. Facial Nerve in the Aqueduct of Fallopius. — To make a complete dissection of this very intricate aqueduct, the temporal bone requires to be decalci- fied. An effort should, however, be made to display the aqueduct in the natural bone. The tympanic cavity having been already exposed, the posi- tion of the second portion of the aqueduct will be recognised by a ridge on the upper part of the inner wall of the tympanum above the fenestra ovalis. It is here to be laid open with the chisel and mallet. The first portion of the aqueduct, which leads from the deep end of the meatus auditorius internus, may also be laid open with the chisel and mallet in such a manner as to follow the course of the facial nerve, which is horizontally outwards between the cochlea and vestibule to the inner wall of the tympanum. The third or vertical part of the aqueduct, which descends behind the tympanum, to the stylo-mastoid foramen, can best be laid open by removing the mastoid process of the temporal bone. This process is to be sawn across in the vertical-trans- verse direction, posterior to the level of the stylo-mastoid foramen, into which a probe may be passed for guidance. Another cut is to be made from behind forwards, also in the vertical direction, to meet the preceding cut, close to the stylo-mastoid foramen. The included bone having been removed, the third part of the aqueduct may be reached and laid open with the chisel. In dissecting the facial nerve in the aqueduct, the following structures are to be GUIDE TO THE HEAD AND NECK 1589 shown: (i) the geniculate ganglion, giving off {a) the great superficial petrosal nerve, (b) a communicating branch to the small superficial petrosal nerve, and (c) the external superficial petrosal nerve (inconstant), all these being situated in the first portion of the aqueduct ; and (2) the following branches, arising in the third part of the aqueduct, namely, (a) the nerve to the stapedius muscle, (b) the chorda tympani nerve, and (c) a communicating branch to the auri- cular branch (Arnold's nerve) of the pneumogastric. Articulations of the Atlas, Axis, and Occipital Bone. — The ligaments of these joints are to be dissected according to the descriptions given of them in the text, and the movements allowed between the occipital bone and the atlas, and between the atlas and axis, are to be carefully studied. In particular, the following ligaments require special attention : (i) the transverse ligament of the atlas, with the extensive synovial membrane between it and the odontcid process of the axis ; (another synovial membrane is to be noted between the odontoid process and the anterior axch of the atlas) ; (2) the cruciform ligament, of which the preceding forms a part; (3) the lateral odontoid or alar liga- ments ; and (4) the posterior occipito-axial ligament, or membrana tectoria, which covers the other ligaments just enumerated. Certain of the ligaments under consideration admit of being dissected from the exterior. These are as follows : (i) the atlanto-axial — anterior, postei ior, and capsular ; and (2) the atlanto-occipital — anterior, posterior, and cap- sular. The others, however, are situated within the spinal canal, in relation to its anterior wall. These are as follows : (i) the posterior occipito-axial, or membrana tectoria ; (2) the accessory atlanto-axial ligaments ; (3) the cruciform ligament, of which the transverse ligament of the atlas constitutes a part ; (4) the lateral odontoid or alar ligaments ; and (5) the middle odontoid, or suspensory, ligament. In order to display the ligaments which are situatetl within the spinal canal, the posterior arch of the atlas and the neural arch of the axis should be cut through with the saw. The tabular part of the occipital bone is to be sawn across a little behind the occipital condyles, and the pos- terior arch of the atlas and the neural arch of the axis are also to be sawn through. After removal of the dura mater, the first ligament to be dissected is the posterior occipito-axial, or membrana tectoria, which, as stated, co%eis the others, and should be detached from the axis and turned upwards after it has been examined. The cruciform ligament having been studied, the final stage in this intricate dissection consists in detaching the superior crus of the vertical part of the cruciform ligament from the basilar groove of the occipital bone, and turning it carefully downwards. The Eyeball. — The dissection of the human eyeball can only be accom- plished on perfectly fresh specimens. In order to prepare himself for this the dissector is recommended to obtain several eyeballs of the ox, say five or six. The fat, ocular muscles, conjunctiva, and capsule of Tenon are to be removed by dividing, with the scissors, the capsule of Tenon and the conjunctiva in a circular manner at the comeo-scleral junction. The adjuncts of the sclerotic can then be stripped off in a backward direction towards the optic nerve. In detaching the capsule of Tenon from the sclerotic the perisclerotic lymph- space, or Tenon's space, is to be noted. The venae vorticosae will probably also be seen. These are usually four in number, and they pierce the sclerotic about midway between the optic entrance and the comeo-scleral junction, at points equally distant from each other. Near the comeo-scleral junction the anterior ciliary arteries may be seen piercing the sclerotic, and around the entrance of the optic nerve the ciliary nerves and posterior ciliary arteries may be seen piercing the sclerotic. It is well that the eyeballs should be prepared for dissection by keeping them in a 10 per cent, solution of formalin, which may sufficiently harden them. There being several ox's eyeballs at the disposal of the dissector, it will be to his advantage to make use of two of them in the following manner: (i) divide one eyeball into two halves, inner or nasal, and outer or temporal, by making an antero-posterior cut along the sagittal axis, or axis of vision — that is to say, a line connecting the anterior and posterior poles of the eyeball ; and (2) divide another eyeball into two halves, anterior and posterior, by making a cut along the course of the equator. These two sections *590 ^ MANUAL OF ANATOMY will afford the dissector a general knowledge of the component parts of the eyeball. Upon another ox's eyeball the sclerotic and cornea are to be examined. The sclerotic is to be carefully opened at a point in the course of the equator down to the level of the chocolate-coloured choroid. Thereafter the sclerotic is to be clipped completely round the eyeball in the course of the equator, which will divide it into two parts — anterior and posterior. These two parts are then to be carefully reflected, one forwards and the other backwards, which may be facilitated by clipping each into flaps. The dark brown tint of the inner surface of the sclerotic is to be noted, this being due to the connective-tissue layer, called the lamina fusca. Processes passing from the lamina fusca to the subjacent choroid coat will have been observed, these processes traversing the perichoroidal lymph-space. The sclerotic having been removed in the foregoing manner, the dissector will now obtain a view of the choroid or vascular coat, easily recognised by its chocolate colour. If the dissector can succeed in washing out the pigment from the choroid, he may obtain a view of the closely-set, whorled venae vorticosae, which converge to four points, and form four vessels. These vessels will then present a white appearance. Ciliary Process. — Upon another ox's eyeball a vertical-transverse section is to be made, anterior to the line of the equator. The posterior segment is to be laid aside in the meantime, for the examination of the posterior half of the retina. The vitreous body having been removed from the anterior segment, a good view will be obtained, from behind, of the ciliary processes, which radiate from the periphery of the crystalline lens. Iris. — To obtain a view of the iris, and also of the ciliary processes, from before, the cornea is to be clipped in another eyeball around the corneo-scleral junction, and removed. This opens up the anterior part of the aqueous chamber, and the iris can now be examined. The shape of the pupil in the ox's eye is to be noted, it being much elongated in the transverse direc- tion. Flaps of the anterior part of the sclerotic are then to be made with the scissors, by clipping from before backwards, and thereafter they are to be turned backwards. This may enable the dissector to obtain some knowledge of the ciliary muscle, which may be recognised as a white ring in the region of the corneo-scleral junction. In front of the ciliary muscle is the canal of Schlemm. To demonstrate the canal of Petit a blow-pipe may be introduced, close to the periphery of the crystalline lens, through the posterior layer of the zonula of Zinn, behind the ciliary processes (see the text). By blowing air in, the canal of Petit may become evident, and it may then present a sacculated appearance. The suspensory ligament of the lens will be recognised as lying in front of the canal of Petit. Crystalline Lens. — The iris having been removed, the anterior wall of the capsule of the crystalline lens is to be laid open, when the lens will escape. The outer portion of the lens will be felt to be soft, but the central portion, which constitutes the nucleus, is of firm consistence. The posterior segment of the eyeball, recently laid aside, is now to be examined by carefully removing the vitreous body. This will enable the dissector to examine the posterior part of the retina from the front. The foregoing dissections having been made upon the ox's eyeballs, the dissector should avail himself of the first opportunity of repeating them upon the human eyeball. For this purpose the eye of a child will suffice, or a human eye may possibly be obtained from the post-mortem room of a hospital. 1716 Spinal Cord. — To expose the spinal cord within the spinal canal, the vertebral and sacral grooves of the vertebral column are to be cleaned as well as possible by scraping away the muscles which occupy them. The laminas of the vertebrae, having been thereby exposed, are to be sawn through on either side in an inwardly slanting direction, and the ligamenta subflava, which connect the laminae, are to be divided. The chisel and mallet should also be used in this dissection. This will enable the dissector to remove the posterior wall of the spinal canal, which will be available for the dissection GUIDE TO THE HEAD AND NECK tsgx of the ligamenta subflava, and the interspinous and supraspinous ligaments. The spinal canal having been laid open, the dissector wnll expose the epidural space, occupied by loose areolar tissue, embedded in which there is a copiou3 plexus of veins and spinal arteries. The arteries of the spinal canal and spinal cord, though usually uninjected, are to be studied from the description given of them in the text, and, in association with the arteries, the veins are to receive attention. Meninges of the CorA. — The dura mater, forming the theca, the zu-achnoid, and the pia mater, are to receive the most careful attention. The outer surface of the dura mater will be readily exposed by removing the areoleir tissue and plexus of veins already referred to. The dissector will easily be able to show the tubular sheaths which the dura mater furnishes on either side to the spinal nerves as these pass through it, these sheaths being pro- longed into the intervertebral foramina. The dura matral theca is now to be carefully laid open along the middle line with a pair of scissors. This will expose the narrow interspace known as the subdural space. This space having been studied, attention is to be directed to the arachnoid membrane, beneath which is a wide interspace, called the subarachnoid space. In studying this space the dissector is to make himself familiar with its division into three compartments by means of the septum posticum, posteriorly, and the ligamenta denticulata, one on either side. The arachnoid membrane having been carefully removed, the pia mater is to be studied. Its very intimate relation to the spinal cord wUl be at once evident, and in connection with it the ligamenta denticulata, right and left, should receive careful attention. The manner in which the ligamenta denticulata act as suspensory ligaments to the spinal cord will be evident. The spinal cord, along with the dura mater, is now to be removed from the spinal canal. In doing so the dissector should be careful to remove, at the same time, the lateral prolongations of the dura mater ■■ into the inter- vertebral foramina, containing the spinal nerves. For this purpose the inter- vertebral foramina may be laid open with the bone-pliers, and the actual dissection of a spinal nerve may be accomplished at this stage, if the dis- sector prefers it. The external characters of the cord are then to receive the most careful attention. The glistening band, called the linea splendens, is to be noted on the anterior surface of the cord, over the course of the anterior median fissure. The cervical and lumbar enlargements are to be noted. The mode of origin of a spinal nerve by two roots is to be made evident, and the ganglion on the posterior root is to be shown. The union of the two roots immediately outside the ganglion, to form a spinal nerve, should be shown, as well as the division of the spinal nerve into anterior and posterior primary divisions. The anterior median and posterior median fissures, as well as the postero-lateral sulcus, are to receive attention. The antero-lateral and posterior colunms are to be studied, as well as the columns of GoU and of Burdach. At the lower end of the cord the conus meduUaris will be seen, and the aurrangement of nerves, known as the cauda equina, will attract attention, in the centre of which leash the filum terminaie can be shown without difiiculty. When the dissector has studied the external characters of the cord, he should endeavour to harden it by immersion in the ordinary fluid used for the preservation and hardening of the brain. This process will occupy three or four weeks, after which time transverse sections should be made through the cord at various levels. This will give the dissector some know- ledge of the internal structure of the cord. The Brain. — The brain, it is assumed, has been sufficiently hardened by immersion in the fluid used for this purpose. In their operations upon this organ it is absolutely necessary that the dissectors should treat it with the most scrupulous gentleness, supporting it on all sides where necessary, and always keeping those parts which are not under immediate dissection or observation covered with cloth saturated with the hardening fluid. With these general precautions the brain should be placed on a wooden platter. 1593 A MANUAL OF ANATOMY the base being at first downwards, and a kind of nest having been made for it on the platter with pieces of cotton wadding, saturated with the hardening fluid. Two small wedge-shaped blocks should also be in constant use, each being insinuated gently underneath the lateral aspect of the corresponding cerebral hemisphere. These blocks the dissectors will find to be of great utility in keeping the parts of the brain together. The superior surface of the brain is to receive the most careful attention, and the dissectors are recommended to study the description given of it in the text. The brain is now to be reversed, and placed in its nest with the base up- wards. In doing so it must be handled with the greatest gentleness. The dissectors have been already advised to study the base immediately after the removal of the brain from the cranial cavity. It will, however, well repay them to renew this examination in view of the importance of the parts here exposed for their careful study, e.g., (i) the component parts of the encephalon ; (2) the superficial origins of the cranial nerves, including the olfactory lobes ; (3) the arteries, including the circle of Willis ; (4) the cisternse beneath the arachnoid, and so on (see the description given of all these in the text). A careful effort may be made to follow out the leading arteries, but this is on no account to be pushed, as, to do so, might endanger structures of con- siderable importance. The branches of each vertebral artery may admit of reasonable dissection ; so also may those of the internal carotid. The dis- sectors will find a description of the arteries in the text, and their special attention is drawn to the lenticulo-striate arteries. If the fissure of Sylvius has not been already opened up, that should now be carefully done, in order to see the gyri operti of the insula or island of Reil, lying deeply at the bifurca- tion of the fissure. The bloodvessels and membranes are now to be carefully removed from the base of the brain, except in the interval between the cerebellum and medulla oblongata. For this purpose the forceps will be sufficient, aided occasionally by a pair of scissors. In doing so there is considerable risk of taking away the cranial nerves, but this must not be done. The inter- peduncular region may now be studied, and the superficial origins of the cranial nerves revised, the olfactory lobe also receiving attention. The dissectors are now advised to reverse the position of the brain, and to proceed with a systematic dissection of all its parts ; but they must be prepared to encounter considerable difficulties, as it is not an easy matter to lay down hard-and-fast directions. It may be further stated that the brain should be dissected several times, and in different ways. The brain being now placed with its base downwards, the fissures, lobes, and gyri of the cerebral hemispheres, in so far as they are visible, are to be thoroughly mastered, special attention being directed to (i) Broca's lobe; (2) the fissure of Rolando, and the gyri which bound it in front and behind ; (3) the parieto-occipital fissure ; and (4) the three limbs of the fissure of Sjivius. The opercula insulae are also to be studied. The cerebral hemispheres are then to be sliced away with a long knife until the level of the corpus callosum is reached. In doing so the dissector is to note the white matter in the centre, surrounded by the grey cortex. The corpus callosum is to be carefully inspected from above, the raph6, striae longitudinales mesiales, and striae longitudinales laterales being noted. The anterior cerebral arteries will also be seen sweeping backwards upon the corpus callosum. The forward and backward extent of the corpus callosum is also to be attended to. Lateral Ventricles. — These ventricles are to be opened by means of two longitudinal cuts through the corpus callosum, each cut being made about J inch from the median line. Each ventricle is then to be laid completely open, so as to show the anterior and posterior cornua, by removing as much of the hemisphere as may be necessary. The various structures exposed in the floor of the lateral ventricle are to be carefully studied, namely, (i) the nucleus caudatus of the corpus striatum in the anterior cornu ; (2) the taenia semicircularis, and the vein of the corpus striatum ; (3) a portion of the GUIDE TO THE HEAD AND NECK 1593 upper surface of the optic thalamus, resting upon which there are (a) the sharp lateral border of the fornix, and {h) the choroid plexus ot the lateral ventricle ; and (4) the bulb of the posterior comu, produced by the fibres of the forceps major, and beneath this the calcar avis, or hippocampus minor, produced by the anterior calcarine fissure on the mesial surface of the cerebral hemisphere. The middle or descending comu of the lateral ventricle, situated within the temporal lobe, is to be laid freely open by removing a large portion of that lobe. The remarkable course of this comu is to be noted, and the following structures, which occupy its floor, are to be studied : (i) the hippocampus major, or comu Ammonis ; (2) the fimbria, or taenia hippo- campi ; (3) the eminentia coUateralis, or pes accessorius ; and (4) the choroid plexus of the descending comu. The swelling in which the hippocampus major terminates, called the pes hippocampi, is to be noted ; and the choroidal fissure which extends from the foramen of Monro to the lower extremity of the descending cornu is to receive attention. The corpus callosum is now to be divided transversely about its centre. On raising the anterior part the septum lucidum will be exposed, as it extends vertically bet^veen the under surface of the corpus callosum and the upper surface of the body of the fornix. The relation of the septum lucidum to the lateral ventricles having been studied, the septum is to be carefully divided with a pair of scissors, and the interval beti^'een its two layers, called the fifth ventricle, or ventricle of the septum, is to be examined. It will be evident to the dissectors that this ventricle is a closed space. The posterior part of the corpus callosum may now be turned backwards. The fornix falls to be studied at this stage. Thereafter it is to be divided transversely about its centre, and the two parts are to be carefully raised from the subjacent velum interpositum, and turned forwards and back- wards. The two posterior pillars of the fornix will be seen to be at first connected with the under surface of the corpus callosum, but subsequently each enters the descending comu of the lateral ventricle under the name of the fimbria, or taenia hippocampi. On the under surface of the corpus cal- losum, between the diverging posterior pillars of the fornix, the dissector is to note the lyra, or psalterium. On turning forwards the anterior part of the fornix, its two anterior pillars will be seen descending towards the base of the brain, and in the interval between them a partial view will be obtained of the anterior commissure. After reflection of the fornix the velum inter- positum is exposed, in connection with which the two veins of Galen are to be studied, these subsequently joining to form the vena magna Galeni. The transverse fissure oi the brain, by which the pia mater enters, to form the velum interpositum, may be studied at this stage, its lateral portions being the choroidal fissures. Third Ventricle. — To expose this ventricle at the present stage the velum interpositum is to be removed with the greatest care. It is to be laid hold of with the forceps anteriorly, and turned bactwards. In doing so the two choroid plexuses of the third ventricle on the under surface of the velum interpositum, as well as the ependymal roof of the third ventricle, are neces- sarily removed. In reflecting the back part of the velum interpositum the dissector must be careful not to disturb the pineal body, which rests upon the mesencephalon at the back part of the ventricle. This dissection will expose fully (i) the upper surface of each optic thalamus ; (2) the chink -like cavity of the third ventricle, lying in the mesial line between the two optic thalami ; and {3) the middle, or grey, commissure, which extends between the inner surfaces of the optic thalami. This commissure, however, being very soft, often gives way. At this period the dissectors should make themselves familiar (by revision) with the various structiires which form the roof of the third ventricle. This ventricle itself is to be fully studied, and the relation of its sloping floor to the interpeduncular region at the base of the brain is to be carefully noted. The optic thalamus is to be studied, and in connection with it the following parts are to be noted : (i) the anterior tubercle ; (2) the posterior tubercle, or pulvinar ; (3) the corpus geniculatum externum ; emd (4) the stria pinealis, or mednUaris, as well as the sulcus of •1594 A MANUAL OF ANATOMY Monro, on its internal surface. The anterior pillars of the fornix and the anterior commissure are to be again looked to. The two foramina of Monro are to receive careful consideration, each being situated between the anterior pillar of the fornix in front and the anterior tubercle of the optic thalamus behind. It will be evident to the dissectors that the third ventricle com- municates freely with the two lateral ventricles by means of the foramina of Monro. If attention is now directed to the posterior part of the third ventricle, the dissectors will see the upper opening of the aqueduct of Sylvius, by which aqueduct the third ventricle communicates with the fourth ventricle. Above the upper opening of this aqueduct, and beneath the stalk of the pineal body, the dissectors will have no difficulty in seeing the posterior commissure. Pineal Body. — This body is situated upon the mesencephalon at the pos- terior part of the third ventricle, and should receive careful attention. In connection with it the following parts are to be noted : (i) the stalk, peduncle, or habenula, the dorsal portion of which forms the stria pinealis, or medul- laris, already referred to in connection with the internal surface of the optic thalamus ; (2) the pineal recess, which passes backwards above the posterior commissure into the stalk, or habenula, of the pineal body (but this recess, like the optic, infundibular, and suprapineal recesses, can Ijest be studied from plaster, or metal, casts of a mesial section through the brain) ; and (3) the trigonum habenula;, which will come more fully into view presently. Mesencephalon, or Mid-brain. — The mid-brain may be exposed from above by displacing backwards the anterior part of the cerebellum until the corpora quadrigemina are sufficiently exposed. This should be done with the greatest care, in order not to injure (i) the valve of Vieussens, immediately below the lower pair of quadrigeminal bodies, with the superior peduncle of the cere- bellum on either side ; and (2) the slender fourth cranial nerves, which issue from the valve of Vieussens, and thereafter turn round the crura cerebri, one on either side. The corpora quadrigemina now fall to be studied. They will easily be recognised as four rounded eminences, arranged in pairs, upper and lower, and the crucial groove which separates them from one another will attract attention. The internal geniculate body will be recognised as a small oval mass on the lateral aspect of the mesencephalon, under cover of the pulvinar of the optic thalamus. The superior and inferior brachia are to be examined, also upon the lateral aspect of the mesencephalon. A. reference to the text may guide the dissectors in their examination of these brachia. At this stage the dissectors are advised to read the description of the optic tract and its connections as given in the text. They are to make themselves familiar with the mesial and lateral roots of the optic tract, and are to note very carefully that (i) the pulvinar of the optic thalamus, (2) the external genicu- late body, and (3) the upper quadrigeminal body constitute the lower visual centres, as distinguished from the higher, or cortical, visual centre in the cortex of the cuneate and lingual gyri close to the calcarine fissure on the mesial surface of the occipital lobe. The trigonum habenulae, previously referred to, will now be fully exposed. To complete the dissection of the mesencephalon the crura cerebri are to receive the most scrupulous attention at this stage, and it will be necessary to carefully reverse the preparation for this purpose — at all events, for re- vision. The mesencephalon is now to be divided transversely between the upper and lower pairs of quadrigeminal bodies. This procedure will enable the dissectors to remove the following parts, namely, the pons Varolii, cerebellum, and medulla oblongata. On examining the cut surface the aqueduct of Sylvius will be seen in section. The division of each crus cerebri into two by the crescentic mass of grey matter, called the substantia nigra, may be evident, the upper or dorsal part being the tegmentum, and the lower or ventral part the crusta or pes. The oculo-motor sulcus on the inner surface of the crus for the third or oculo-motor nerve is to be noted, and on the outer surface will be seen the lateral sulcus. The description given of the crus cerebri in the text ia to be carefully read. GUIDE TO THE HEAD AND NECK 1595 Basal Ganglia of the Cerebral Hemispheres. — The pons Varolii, cerebellum, and medulla oblongata are to be laid aside in the meantime, and the dis- section of what is left of the cerebral hemispheres is to be overtaken. This should be divided into two parts by a mesial, antero-posterior incision, and one of these parts is to be used for the examination of the inferior surface of the cerebral hemisphere. (The mesial surface of the cerebral hemisphere should be studied on another brain.) In this connection the orbital surface of the frontal lobe will fall to be examined, with its olfactory sulcus, triradiate sulcus, and gyri. The inferior surfaces of the temporal and occipital lobes will also admit of being examined. The basal ganglia are then to be attended to, these being the nucleus caudatus and nucleus lenticularis of the corpus striatum, the claustrum, and the amygdaloid nucleus. Several sections through the cerebral hemispheres require to be made to obtain a knowledge of these important ganglia. On one side coronal, that is to say, vertical-transverse sections are to be made through the cerebral hemisphere from the level of the front part of the nucleus caudatus backwards to the posterior part of the optic thalamus. On the other side several horizontal sections are to be made through the structures which lie upon the floor of the lateral ventricle. In connection with these sections the dissectors are advised to read the description given of the basal ganglia, and also of the optic thalami, in the text. Medulla Oblongata. — The dissectors are to note carefully the superficial origins of the seventh, eighth, ninth, tenth, eleventh, and twelfth cranial nerves. Tke anterior median fissure, with the pyramid on either side, is to be examined, and an effort is to be made to show the decussation of the pjrramids. The olivary body and anterior superficial arcuate fibres are to receive attention. In connection with the posterior area of the medulla oblongata it is to be noted that it is divided into two portions, lower or closed, and upper or open. The lower portion presents in the median line the pos- terior median fissure, on either side of which are the following structures, in order from within outwards: (i) the funiculus gracilis, which is the con- tinuation of Goll's column of the spinal cord, and which terminates superiorly in the clava ; (2) the funiculus cuneatus, or continuation of Burdach's column of the spinal cord, terminating superiorly in the cuneate tubercle ; and {3) the funiculus of Rolando, terminating superiorly in the tubercle of Rolando. The calamus scriptorius, between the two clavae, is to be noted ; but the upper or open part of the medulla had better be postponed until the floor of the fourth ventricle is under consideration. Suffice it to say that it presents on either side the restiform body. The dissectors should at this stage make them- selves familiar with the cistema magna, in connection with the subarachnoid space, this cistema lying between the cerebellum and the medulla oblongata. Further dissection of the medulla oblongata should only be overtaken with proper assistance. Pons Varolii. — This will admit of easy examination, except as regards its dorsal surface and internal structure. The points to be noted are as follows : (i) the basilar groove; (2) the crura cerebri, emerging from its upper part ; (3) the middle peduncles, emerging from it laterally ; (4) the stout sensory, and slender motor, roots of the fifth cranial nerve, also emerging from it laterally ; and (5) the sixth, seventh, and eighth cranial nerves at its lower border. The dorsal surface of the pons is to be postponed for a short time, until the floor of the fourth ventricle is under examination. Cerebellam. — Like other parts of the encephalon, the cerebellum requires to be examined from several points of view. Assuming, however, that the dissectors desire to get as much as possible out of one brain (a desire to be strongly deprecated) , the component parts of the cerebellum are to be studied. On the superior surface the superior vermis and the upper surface of each hemisphere are to be examined. On the under surface the vallecula is to be noted, with the inferior vermis lying deeply in it. In connection with the inferior vermis the following parts are to be studied: (i) the tuber valvulze ; (2) the pyramid ; {3) the uvula, with the furrowed band on either side of it, covered by the amygdala ; and (4) the nodule, with the lateral portion of the inferior medullary velum on either side of it. On the under surface of each 1596 A MANUAL OF ANATOMY cerebellar hemisphere the following parts are to be noted : (i) the postero- inferior lobule, composed of (a) the lobulus gracilis, and {b) the inferior semi- lunar lobule ; (2) the biventral lobule ; (3) the amygdala ; and (4) the flocculus. The dissectors should also make themselves familiar with the peduncles of the cerebellum, namely, the superior, middle, and inferior peduncles, right and left. The superior peduncles will be seen to converge towards the lower pair of quadrigeminal bodies, after they emerge from the cerebellar hemi- spheres, the valve of Vieussens having been already observed extending between them. The middle peduncles, formed by the transverse fibres of the pons Varolii, sink into each cerebellar hemisphere. The inferior peduncles, which constitute the restiform bodies, connect the cerebellar hemispheres with the upper or open part of the medulla oblongata posteriorly. Fourth Ventricle. — This ventricle is to be laid open by making a median incision through the vermis of the cerebellum from above. This will bring into view the central collection of white matter called the corpus trapezoides. The two parts of the cerebellum are then to be gently separated, so as to expose the superior medullary velum, or valve of Vieussens, the inferior medullary velum, and the tela choroidea inferior, which lies lower down than the inferior medullary velum, and presents in the median line the foramen of Magendie. The obex is to be looked for in the lower part of the roof, where it overhangs from behind the upper opening of the central canal of the spinal cord, and on either side the ligula may be seen projecting over the epi- thelium of the roof for a short distance. When these structures have been divided, the floor of the fourth ventricle will be exposed. Its rhomboidal shape is to be noted. At the lower end the dissectors will observe the open- ing of the central canal of the spinal cord and the calamus scriptorius, and at the upper end the lower opening of the aqueduct of Sylvius. The longi- tudinal groove, traversing the floor between these two openings, is to be noted, and the striae acusticse crossing the floor towards its centre, on either side of this groove, are to receive attention. The floor is thus divided into two portions, lower and upper. The lower or medullary portion will be seen to be bounded on either side, from below upwards, by the clava, the cuneate tubercle, and the restiform body, which latter should now receive full con- sideration. The parts to be noted in connection with each half of the lower portion of the floor are as follows : (i) the fovea inferior, (2) the trigonum vagi, (3) the trigonum hypoglossi, and (4) the trigonum acusticum. The trigonum acusticum may be seen to be continued superiorly into a promi- nence called the tuberculum acusticum, over which the striae acusticae pass. The upper or pontine portion of the floor will be seen to be bounded on either side by the superior peduncle of the cerebellum, and the parts to be noted in connection with each half are as follows : (i) the fovea superior ; (2) the eminentia teres, produced by the subjacent fasciculus teres ; (3) the locus cseruleus ; and (4) an upward prolongation of the tuberculum acusticum. The lateral recess of the fourth ventricle is to be examined. It will be found as a lateral prolongation of the ventricle, on either side, round the upper part of the restiform body. In the roof of each lateral recess is the foramen of Kay and Retzius. The great horizontal fissure of one cerebellar hemisphere is now to be opened up, and the upper half of the hemisphere is to be removed. This will give the dissectors a view of the three cerebellar peduncles as they enter the white medullary substance in the centre of the hemisphere. This substance contains the corpus dentatum, which is a wavy lamma of grey matter en- closing white matter, and open at the upper and inner part. Through this opening many of the fibres of the superior cerebellar peduncle emerge. To expose the corpus dentatum a cerebellar hemisphere has to be cut through horizontally a little above the level of the centre. Sagittal sections are also to be made across the direction of the cerebellar laminae, when the appear- ance known as the arbor vitae cerebelli will become evident. Lastly, with proper assistance, sections should be made through the pons Varolii, with the view of obtaining some knowledge of its internal structure. GENERAL EMBRYOLOGY 1597 GENERAL EMBRYOLOGY. Embryology is a treatise on the embryo and the development of its tissues and organs from the stage of the fertilized ovimi to their mature condition. Two factors are concerned in the formation of the embryo — namely, (i) the male pronucleus, formed by the head and a portion of the middle piece of a spermatozoon or male germ-cell, and (2) the female pronucleus, which represents the mature ovum or female germ -cell. The Animal Cell. The animal cell is a mass of a living substance called protoplasm. The essential component parts of the cell are (i) a cell-body, and (2) a nucleus. The nucleus may contain one or more nucleoli, but these are not essential elements. The protoplasm of the cell-body is called the cytoplasm, or cell-protoplasm, and it may be enclosed (as in the ovum) within an envelope, called the cell-membrane, which is simply a condensation of the peripheral cytoplasm. The proto- plasm of the nucleus is called the karyoplasm, or nucleoplasm, ^^-s"!^?:;!?^??;^^ Centrosome and it is enclosed within an /^'^^^v-v'H^y^^^^ envelope, called the nuclear /' '" ' ' ' ''^ ' ■ >v '*'"^'°* membrane. The animal cell is - .>-4:' >\ therefore 'a mass of proto- ■ .^ ' '^^ plasm, containing a nucleus.' ^ ■;'=": Karyoplasm Cytoplasm. — The cytoplasm ^ , • x ". >^^^ ''^" ' t -^ l{"^ is the protoplasm of the cell- y -7 " ' ;>' ^-'i *°"* body, as distinguished from the \-^>*(, . >'' v ^ karyoplasm, which is the proto- ^ '•, -^, ; ^ " ' ' " plasm of the nucleus. It is /^ ^^ 1^^^ viscid, translucent, and more or ^^^^^ less granular. At the periphery Fig. 656. — The Animal Cell. it may be condensed to form a cell-membrane. The basis of the cytoplasm consists of a network of slender filaments, which is known as the sfongioplasm. The meshes of this reticulum are occupied by a semifluid substance called the hyaloplasm. The cytoplasm contains granules, which are called cyto-micro- somes. The hyaloplasm, in addition to the cyto-microsomes, con- tains several non-protoplasmic bodies — e.g., food-particles and pigment-granules — which are known as the dentopiasm. 1598 A MANUAL OF ANATOMY In most cells, usually close to the nuclear membrane, but external to it, there is a small spherical area of cytoplasm, from which lines radiate outwards into the cell-protoplasm. This area is called the centrosome or attraction-sphere, and the protoplasm around the area is known as the archoplasm. At the centre of the centrosome there are usually two small nodules of protein matter, called the central or aitraction-farticles, from which lines radiate outwards into the archoplasm and cjrtoplasm. The centrosome thus constitutes the aster, and it plays an important part in nuclear division by mitosis. The cell-nembrane, when present, is a condensation of the peri- pheral c5rtoplasm. In many cells, however, it is absent. The Nucleus. — 'The nucleus is usually situated eccentrically in the cytoplasm. Its protoplasm is called karyoplasm, and the nuclear elements are as follows : 1. Nuclear membrane. 3. Karyoplasm. 2. Nuclear reticulum. 4. Nucleoli. The nuclear membrane is a well-defined envelope which surrounds the nuclear contents and separates them from the cytoplasm. It consists of the elements of the nuclear reticulum — namely, nuclein containing chromatin, and linin. The nuclear reticulum, which corresponds to the spongioplasm of the cell-protoplasm, consists of nuclein, containing a stainable material called chromatin, arranged in granules. These granules are connected by threads of linin. The karyoplasm, which corresponds to the hyaloplasm of the cell -protoplasm, occupies the meshes of the nuclear reticulum, and contains granules, known as karyosomes. The nucleolus (sometimes absent) may be one or more in number. There are two kinds of nucleoli — ^true and false. The true nucleoli lie in the nuclear reticulum, or, it may be, in the karyoplasm. The false nucleoli are nodes which are connected with the filaments of the nuclear reticulum, where they intersect. Cell-Division. There are two kinds of cell-division — namely, karyokinetic or mitotic, which is indirect division, and akinetic or amitotic, which is direct division. Karyokinesis or Mitosis. — ^This kind of cell-division is of a very complicated nature, and the changes involved affect both the nucleus and the centrosome. It is convenient to consider it under four phases — namely, (i) the anaphase, (2) the metaphase, {3) the kataphase, and (4) the telophase. Anaphase. — ^The anaphase constitutes the preparatory stage, and it includes three phenomena, all of which lead ' up ' to the meta- phase, as follows: I. Formation of spireme. 2. Formation of chromosomes. 3. Formation of spindle. GENERAL EMBRYOLOGY 1599 Spireme. — ^The chromatin and linin of the nuclear reticulum and nuclear membrane become transformed into a coiled thread, called the spireme or skein. Chromosomes. — ^The spireme is broken up transversely into an even number of segments, called chromosomes, the number of these being constant and characteristic of the species of animal. These chromosomes usually assume the form of short rods, which resemble a V. Spindle. — ^Whilst the chromosome-stage is in progress, important changes take place in the stellate centrosome or aster. It divides into two segments, each division taking up a central or attraction- particle, and being furnished with radiating fibres. In this manner two centrosomes or asters are formed. Certain of the radiating fibres extend from one centrosome to the other in a fusiform manner, and these connecting fibres, called the spindle-fibres, constitute the spindle, which has a centrosome or aster at either pole. As the nucleus becomes elongated transversely, the two centrosomes take up positions one at either pole of the somewhat elliptical nucleus, the spindle-fibres becoming gradually elongated. Up to this point the spindle, with an astral centrosome at either pole, is external to the nuclear membrane, but when this membrane disappears the spindle becomes intranuclear, and the spindle-fibres extend from one pole of the nucleus to the other, where they are connected with the two astral centrosomes respectively. The foregoing phenomena conclude the anaphase or preparatory stage. Metaphase. — ^After the disappearance of the nuclear membrane, the chromosomes are brought into direct contact with the spindle, and he at first scattered between the spindle-fibres. Very soon, however, they congregate at the equatorial plane of the spindle, which corresponds to its widest part. Here they are arranged in a stellate manner, which constitutes the aster according to some authorities. Each chromosome now splits longitudinally into two equal parts, called daughter-chromosomes, the original nimiber of parent -chromosomes being thereby doubled. The formation of daughter-chromosomes constitutes the metaphase or chief stage. Kataphase. — ^The daughter-chromosomes at first form two rows at the equatorial plane of the spindle, lying close to each other. They soon, however, separate, those of each row travelling along (tnetakinesis) the corresponding spindle-fibres to either pole of the spindle, where they enter the centrosome or aster. These pheno- mena conclude the kataphase, or leading ' down ' stage. Telophase. — The daughter -chromosomes within each aster now imite end to end, and form a spireme, round which a new nuclear membrane is formed. The spireme gradually assumes the form of a chromatic reticulum, characteristic of a normal nucleus, and karyoplasm is formed within the meshes of the reticulum. Two daughter-nuclei are thus constructed, one in either centrosome, each of which contains one-half of the parent -chromosomes belong- i6oo A MANUAL OF AN4T0MY ing to the original cell. The cytoplasm of the parent-cell now becomes constricted at the equatorial plane, and by the deepening Fig. 657. — Stages of Karyokinesis (from E. B. Wilson's " Cell," by Permission of the Macmillan Company, New York). A, Resting-Cell B, Early Anaphase C, Later Anaph.-ise D, Later Anaphase E, Latest Anaphase V, Cell ready for Karyokinesis G, Meiaphase H, Kataphase I, Telophase J, Division complete of this constriction the cytoplasm is divided into two halves, which separate from e^Qh other, each half surrounding the nuclear mem- GENERAL EMBRYOLOGY 1601 brane of the corresponding daughter-nucleus. Two complete daughter-cells are thus formed, and the telophase or concluding stage is finished. The complex changes concerned in the mitotic division of the parent-cell are concluded with the formation of two complete daughter-cells. Summary of Karyokinesis, or Mitosis. — ^There are four phases — namely, anaphase, metaphase, kataphase, and telophase. The anaphase consists in (i) the conversion of the linin — and chromatin — reticulum of the nucleus into a spireme, or skein ; {2) the breaking up of this spireme into chromosomes ; and (3) the formation of a spindle from the spindle-fibres which connect the two centrosomes, these centrosomes gradually separating from each other, and the nuclear membrane disappearing. The metaphase consists in the congregation of the chromosomes at the equatorial plane of the spindle. The kataphase consists in (i) the splitting of each chromosome into two daughter-chromosomes, and (2) the migration of these daughter-chromosomes from either side of the equatorial plane of the spindle along the corresponding spindle-fibres to either pole of the spindle where they enter the aster. The telophase consists in (i) the formation of a daughter-nucleus within each aster, and (2) the cleavage of the cytoplasm of the parent-cell into two halves, each of which sur- rounds the corresponding daughter-nucleus, two daughter-cells being thereby formed. Amitosis. — This is direct cell -division. The nucleus is simply cleft into two daughter-nuclei, and this is accompanied by cleavage of the cyto- plasm. The Spermatozoon. The spermatozoon is the germ-cell of the male, distinguished from the ovum, which is the germ- cell of the female. A spermatozoon is essentially a cell, though it has undergone considerable modifications from the usual cell-type. It is an elongated body, which is endowed with remarkable power of movement, the movement being of a lashing or vibratory nature. It consists of the following parts: I. A head. 2. A middle piece. 3. A flagellum or tall. Fig. 658. — Sper- The head is short, and, as seen on the flat, is matozoon. oval. When, however, it is viewed in profile it is pyriform, the narrow end being directed forwards. It is pro- vided with a head-cap, which covers its anterior part. Over the apical, somewhat pointed, anterior part of the head this cap is lOI Head -Middle. Piece . FUgelluin. or Tail ■ Terminal Filameut i6o2 A MANUAL OF ANATOMY arranged in a lanceolate manner, and forms the perforaculum, which is well adapted for perforating. The head represents the nucleus of the parent-spermatid, the nucleus being elongated and oval. It consists of a dense collection of chromatin, and external to it there is a delicate layer of cytoplasm. The archoplasm of the parent-spermatid gives rise, at the anterior end of the nucleus, to the head-cap. The middle piece lies behind the head, and from its posterior end the fiagellum, or tail, is prolonged. The middle piece is developed from the cytoplasm of the parent-spermatid. It contains a ceniro- some, which is situated near the head. The flagellum or tail, is the slender filament of lashing move- ment, and is much elongated. It consists of a central fibril, or axial filament, which is prolonged from the centrosome in the middle piece. The filament is surrounded by a delicate sheath, which dis- appears towards the end of the tail. The relation of a spermatozoon to its parent-spermatid may be stated as follows : Spermatozoon. Head Head-cap Middle Piece Flagellum or Tall Parent-Spermatid. Nucleus. Archoplasm. Cytoplasm. Centrosome and Cytoplasm. Spermatogenesis. Spermatogenesis is the begetting formed in immense numbers within Primordial Germ-cell of spermatozoa, which are the tubuli seminiferi of the testes. Each . spermatozoon is developed from the ger- minal epithelium, its original source being known as the primordial germ- or sperm- cell, which is of large size. These cells undergo several mitotic divisions, and from the last generation spermato- gonia are developed, which correspond to the oogonia of the female. These spermato- gonia divide, by mitosis, and give rise to primary spermato- cytes, two for each spermato- gonium, and these corre- spond to the female primary oocytes. Each primary sper- matocyte divides, by mitosis, into two cells, which are known as the secondary sper- matocytes, and correspond to the female secondary oocytes. Each secondary spermatocyte, in turn, divides, by mitosis, into two cells, which are called spermatids, and each of these corresponds Primary Spermatocyte - Secondary Spermatocyte— -fl^ )t , Division- Period .Growth- Period Fig Spermatid d V 4 ▼ Spermatozoa, _..^ i i i 659. — Diagram showing Spermato GENESIS (after BoVERI). Maturation- Period GENERAL EMBRYOLOGY 1603 to the mature ovum of the female. Each spermatid now undergoes transformation into a spermatozoon, the change taking place within a cell or column of Sertoli (sustentacular cell). Prior to its full development a spermatozoon has passed through four stages — namely, (i) a spermatogonium; (2) a primary spermatocjle ; (3) a secondary spermatocele ; and (4) a spermatid. In all cases the cell- divisions are of the nature of a somewhat modified mitosis or kar\'o- kinesis, consisting in a reduction-division — ^that is to say, a reduction in the number of chromoses at each cell-division. From one primary spermatocyte (mother-cell) there thus result four grand-daughter cells of equal size, each of which is a spermatid. These spermatids subsequently imdergo transformation, each into an active spermatozoon, capable of fertilizing a mature o\ami. The Ovum. The ovum or oocyte, which is the female germ-cell, has all the characters of a typical cell, being specially remarkable for the large Genninal Spot (Nndeolns) Germinal Vesicle (Nuclens) Gsrona Radiata Zona Radiata Perivitelllne Space Vitellus or Yolk Perivitelline Membrane Fig. 660. — ^The Ovtm ied after Stricker). size of its nucleus and nucleolus. It is formed within a Graafian follicle of the ovary, and it has a diameter of y^ inch. Its com- ponent parts are as follows: 1. Cell- wall. 3. Nucleus. 2. Cell-body. 4. One or more nucleoli. The cell-wall is knowTi as the vitelline membrane. The vitelline membrane surrounds the vitellus, of which it is a peripheral condensation. External to the vitelline membrane is the zona pellucida, which is separated from the vitelline membrane f by a narrow interval, called the perivitelline space. When examined i6o4 A MANUAL OF ANATOMY under a high power of the microscope, it presents very delicate striae, which radiate across its breadth, and from this circumstance it is known as the zona radiata. These striae are regarded as minute pores or passages. External to the zona radiata there are several layers of cells, which are disposed in a radiating manner and constitute the corona radiata. These cells, like the zona radiata, are derived from the discus proligerus within the Graafian follicle, and the innermost cells send processes through the pores of the zona radiata to the cytoplasm of the ovum. The cell-body, as in an ordinary cell, consists of cytoplasm (ooplasm), and this presents the usual reticulum or spongioplasm, the meshes of which are occupied by hyaloplasm. The ooplasm constitutes the vitellus or yolk. Embedded in it there are several fat-globules and albuminoid granules. These granules constitute the denioplasm or nutritive yolk. According to some authorities, the vitellus contains, in the earlier stages, an attraction-sphere and centrosome, situated close to the nuclear membrane. The nucleus represents the germinal vesicle, and constitutes the essential part of the ovum. As will be presently described, it forms the mature ovum or female pronucleus, after extrusion of the two polar bodies. It is a large spherical body, situated at first at the centre of the ovum, but subsequently becoming eccentric. Its diameter is about -^-^ inch, and it consists of the following parts : 1. Nuclear membrane. 3. Karyoplasm. 2. Nuclear reticulum. 4. Nucleolus. The nuclear membrane is well marked, and is formed by the chromatin and linin of the nuclear reticulum. The nuclear reticu- lum resembles that of a typical cell. The karyoplasm occupies the meshes of the nuclear reticulum. ■ The nucleolus represents the germinal spot. Oogenesis. Oogenesis is the begetting of ova. Each ovum is developed from the germinal epithelium, the remnant of which epithelium covers the adult ovary. The original source of the ovum is known as the primordial germ-cell. These cells undergo many mitotic divisions, and from the last generation oogonia are developed, which corre- spond to the spermatogonia of the male. These oogonia divide by mitosis, and give rise to primary oocytes. Each primary oocyte represents the ovum as it leaves the Graafian follicle, and it corre- sponds to a male primary spermatocyte. In the process of develop- ment each primary oocyte undergoes two mitotic divisions, one after the other, both of which are unequal. In the first division the primary oocyte (mother-cell) extrudes the first polar body, and then it becomes a secondary oocyte, which corresponds to a secondary spermatocyte of the male. In other words, thq primary oocyte GENERAL EMBRYOLOGY 1605 Primordial Germ-ccfl OSgonia divides by mitosis into two cells— namely, (i) the first polar body, of small size ; and {2) the secondary ooc^-te. In the second division the secondary oocyte (daughter-cell) extrudes the second polar body, and then it becomes a mature ovum (female pronucleus) . In other words, the secondary oocv-te divides, by mitosis, into two cells— namely, (i) the second polar body, of small size ; and (2) the mature o\Tim (female pro- nucleus), which latter only undergoes further division if fertilized. Prior to its matura- tion, the ovum has passed through three stages — namely, (i) oogonium, (2) primary oocyte, and (3) secondary ooc\i:e. The mature ovum cor- responds to a male spermatid, the difference, in the case of the latter, being that the spermatid undergoes further transforma- tion into a spermatozoon. In all cases the cell-divisions are of the nature of a some- what modified mitosis or karyo- kinesis, consisting in a reduc- tion-division— that is to say, a reduction in the number of at each cell- 2nd Polar Body ist Polar Body Divisions of ist Polar Body Fig. 661. — Diagram SHOw^NG Oogenesis (after Boveri). primary ooc>i:e chromosomes division. From one (mother-cell) there thus finally result four grand-daughter cells, one large and three small — namely, the mature ovum (female pro- nucleus) of large size, and three small polar bodies, the first polar body, as a rule, having divided into two small cells. The mature o\-um is capable of fertilization, but the polar bodies (abortive ova) are inactive and disappear. Table of Comparison between the Hale and Female Germ-cells. Male. Spermatogonium Primary spermatocyte . . Secondary spermatocyte Spermatid Female. Oogonium. Primary oocyte. Secondary oocj'te. Mature ovum. Though there is a great resemblance between spermatogenesis and oogenesis, two differences are to be noted: (i) The final result in oogenesis is the formation of four cells — namely, {a) the mature oxTim, of large size, and capable of fertilization; and (6) three, as a rule, polar bodies, all small, quite inactive, and subsequentty ■ \ 1606 A MANUAL OF ANATOMY disappearing. In spermatogenesis, on the other hand, though four spermatids are formed at the same stage of cell-division as in oogenesis, they are all equal in size. (2) The mature ovum under- goes no further change, unless it becomes fertilized. Each sper- matid, on the other hand, becomes transformed into an active spermatozoon, capable of fertilizing a mature ovum. Spermato- genesis may therefore be said to comprise one stage more than oogenesis, but this additional stage is not one of cell-division, but is simply the transformation of a spermatid into a spermatozoon. Reduction-Division. — This process consists in the reduction, at each cell-division, of the nimiber of chromosomes or segments of the chromatic spireme within the nucleus. In the male and female germ-cells the chromosomes are arranged in groups of four, each quadruple group being called a tetrad. When a tetrad is split into two equal parts, two groups are formed, each containing two chromosomes, and each of these pairs is called a dyad. The number ' Division of ist Polar Body ist Polar ist Polar Spindle and Body Body -^ Elevation ^ >\ \ ' X' \ / First Stage Second Stage Third Snge Fig. 662. — Extrusion of Polar Bodies (modified after Hertwig). of individual chromosomes, which is always an even number, is constant and characteristic of each species of animal. Primary Oocyte (Ovum prior to Maturation). — ^The number of single chromosomes in the germinal vesicle, for the purpose of illus- trating reduction-division, may be assumed to be eight, these being disposed as two tetrads. At the first unequal cell-division, or extru- sion of the first polar body, each of these two tetrads is split into a dyad, four dyads being thus formed. Two dyads go with the first polar body, and two remain within the germinal vesicle.- Though, therefore, the cell-division is unequal, the reduction and dis- tribution'of the chromosomes is equal. When the first polar body subdivides (during the extrusion of the second polar body) one dyad goes with each subdivision. At the second unequal cell-division, or extrusion of the second polar body, each of the two dyads within the germinal vesicle splits into two chromosomes, and one chromosome of each dyad goes with GENERAL EMBRYOLOGY 1607 the second polar body, and one of each remains within the nucleus or germinal vesicle of the ovum, which latter is no\\\mature. Each of the four cells which finally result from the primary o6c\i:e — namely, the mature ovum and the three polar bodies — contains two single chromosomes. The preceding remarks, as illustrating reduction-division in chromosomes in the primary ooc}i;e, or o\'um prior to maturation, may be taken as applicable, for the purpose of illustration, to the primary spermatoc}i:e. Each of the ioui spermatids, resulting from a primary spermatocyte, will therefore contain two single chromosomes. Each of the two single chromosomes of the mature ovum and of the spermatid respectively represents one-quarter of one of the two tetrads present in the primary oocjrte and primary spemiatoc\i:e. Moreover, the number of single chromosomes in the mature oxiim and in the three polar bodies, as well as in each of the four sper- matids— namely, two — ^represents the number of tetrads of chromo- somes in the primary' o6c}i:e and primary spermatocyte respectively — namely, two. Reduction-div-ision, therefore, in the sexual germ-cells consists in (i) the division of tetrads into dyads, and (2) the allocation of dyads to cell-divisions. Ovulation. The ovum lies for some time within a Graafian follicle. At this period it is embedded within a heap of cells, kno\\Ti as the discus proligerus. The innermost cells of this discus, which are in direct contact with the o\'Tim, form the zona pellucida or zona radiata^ and two or three layers of the succeeding cells give rise to the corona radiata. Within the Graafian follicle, besides the discus proligerus and o\'um, there is some fluid, called the liquor folliculi. Ovulation is the extrusion of the ovum from the Graafian follicle. As a follicle becomes mature, it approaches the surface of the ovary, and, when quite mature, it lies close beneath the surface. This part of the follicle presents a slight projection, on which there is a pale spot, called the stigma. The stigma, becoming very much attenu- ated, ruptures. The liquor folliculi then escapes, carrvang with it the ovum, surrounded by the corona radiata and the zona pellucida or radiata, these, as stated, being derived from the discus proligerus. The expelled ovum is, as a rule, conducted by the grooved ovarian fimbria of the corpus fimbriatum to the ostium ahdominale of the Fallopian tube. Here it enters that tube, and is gradually conveyed into the cavity of the body of the uterus, where, if previously fer- tilized, it undergoes development into the embryo, and then into the foetus. Abnormal Conditions. — (i) The ovum may never leave the Fallopian tube, and, if fertilized, it would give rise to tubal pregnancy. (2) When expelled from the Graafian follicle and ovary, the o\Tim may drop into the abdominal cavity, and, if fertihzed under these conditions, it would give rise to abdominal i6o8 A MANUAL OF ANATOMY pregnancy. (3) In extremely rare cases the ovum may not leave the Graafian follicle, even though that follicle and the ovary should rupture in the usual way. If fertilized under these conditions, it would give rise to ovarian preg- nancy. These three abnormal conditions are spoken of as cases of extra- uterine pregnancy. The periods of ovulation, or extrusion of the ovum from the Graafian follicle and ovary, which occur at more or less regular successive intervals, are attended by certain changes in the mucous membrane of the cavity of the body of the uterus. These changes constitute menstruation. Maturation of the Ovum. The ovum, as it leaves a Graafian follicle, represents a primary oocyte. In order to become mature and capable of being fertilized it has to undergo certain changes which affect primarily the ger- minal vesicle or nucleus, these changes being of the nature of karyokinetic or mitotic cell-division. Briefly stated, the changes consist in the ovum undergoing two unequal cell-divisions. In other words, the ovum extrudes two polar bodies, one after the other, these being minute spherical globules, which are abortive ova. When the first cell - division Primaryoocytc ^^^^^ pj^^^g ^^iQ primary oocyto (ovum) divides into two cells of unequal size. The large cell is the secondary oocyte, and the small one is the first polar body. At the second cell-division the secondary oocyte likewise di- vides into two cells, of unequal size. The large cell is the mature ovum, or female pro- nucleus, and the small one is the second polar body. The first division may take place whilst the ovum is in a Graafian follicle, or, like the second, in the Fallopian tube. The polar bodies are ex- truded from the ovum, and, prior to the extrusion of the second, the first polar body usually undergoes an equal division, so that utimately there are three polar bodies. These, being abortive ova, so^n disappear. The final result of the foregoing two divisions is the formation of four cells. One of these, of large size, is the mature ovum, or female pronucleus, which is capable of activity, and the other three, of small size, are inactive polar bodies, or abortive ova, the first polar body having, as a rule, divided into two. Prior to the first cell- division, or extrusion of the first polar body, the germinal vesicle or nucleus moves towards the periphery of the primaty oocyte. Mature Ovum Derivatives of ist Polar Body Fig. 663. — Maturation of the Ovum. GENERAL EMBRYOLOGY 1609 After the second polar body has been extruded from the secondary o6c\i:e the mature o\ami, or female pronucleus, passes from the periphery to the centre, and there awaits the male pronucleus, pro\aded fertilization is to take place. Nature of the Changes. — ^The germinal vesicle, or nucleus, ha\'ing moved to the upper surface (animal pole) of the primary oocyte, undergoes division, of the nature of karyokinesis, or mitosis, slightly modified. Four phases have to be considered — namely, the anaphase, metaphase, kataphase, and telophase. Anaphase. — ^The anaphase comprises four stages, (i) A spireme, or skein, is formed from the chromatic reticulum of the germinal vesicle. (2) This spireme breaks up into chromoses, which are dis- FiG. 664. — ^Maturation of Ovum (Wilson, by Permission of THE MaCMILLAN COMPANY, NEW YORK). A, Initial Phase B, Equatorial Plate C, Rotation of Spindle D, Formation of First Polar Body E, Dyads F, Division of First Polar Body G, Second Polar Body H, Three Polar Bodies posed as short rods. (Meanwhile the nuclear membrane of the vesicle begins to disappear ; the germinal spot or nucleolus becomes disintegrated ; and the karyol\-mph flows into the \-itellus, or cyto- plasm.) (3) A spindle is formed, with a centrosome at each pole, and the rod-like chromosomes lie parallel to the spindle-fibres. (4) The chromosomes congregate at the equator of the spindle. At this stage the spindle lies parallel to the upper surface (animal pole) of the ovum. It now, however, undergoes rotation, and takes up a position at right angles to the animal pole of the ovum. The superficial or peripheral pole of the spindle produces a slight i6io A MANUAL OF ANATOMY projection of the vitellus, or cytoplasm, which is known as the polar bud. Metaphase. — The chromoses, being now close to the equator of the spindle, are broken up into daughter-chromoses. Kataphase. — The daughter-chromosomes now separate, half of them travelling along [metakinesis) the spindle-fibres to the upper pole of the spindle, where a centrosome awaits them, and half remain in the primary oocyte. Telophase. — Cell-division now takes place in the primary oocyte. The upper pole of the spindle, with its contained daughter-chromo- somes, is cut off and extruded as the first polar body, after the entrance of a spermatozoon. This takes with it the vitellus, or cytoplasm, forming the polar bud, as well as some filaments from the spindle, and those which connect the daughter-chromosomes. This concludes the first cell-division, which affects the primary oocyte. The interrupted spindle is now completed, and a new centrosome is formed. The spindle takes up a position at first parallel to the animal pole of the secondary oocyte, and then rotates to become at right angles to it. The daughter-chromosomes congregate at the equator of the spindle, and undergo splitting. Half of them pass to the upper pole of the spindle, and half remain in the secondary oocyte. The subsequent phases are as in the first cell- division. A second polar body is extruded, carrying with it some of the vitellus, and the remainder of the secondary oocyte, much the larger part, forms the mature ovum, or female pronucleus, which now takes up a central position. Fertilization of the Ovum. Fertilization is otherwise spoken of as impregnation, or fecundation. It :onsists in the conjugation or fusion of the male pronucleus, or head of a spermatozoon, with the female pronucleus, or mature ovum, and it constitutes the commencement of the development of a new individual to propagate the species. As a general rule, con- jugation takes place in the outer part of the Fallopian tube, or oviduct, into which spermatozoa have made their way through the vagina and uterus by the lashing movement of their tails. When the spermatozoa come into contact with the mature ovum one of them as a rule passes through the zona pellucida, or radiata, into the yolk. At the point of entrance the yolk forms a conical protuberance, called the receptive, or entrance cone. As the sperma- tozoon passes through this cone it parts with its tail, the surrounding vitellus becoming disposed in a radiating manner. Meanwhile a delicate membrane is formed round the yolk, called the vitelline membrane, which prevents the entrance into the yolk of other spermatozoa as a rule. The head, or nucleus, of the sperm.atozoon now constitutes the male pronucleus, or sperm-nucleus, and the middle piece contaiis GENERAL EMBRYOLOGY i6xx a centrosome, called the spermo-centre. The male pronucleus advances towards the centre of the ovum, near which, up till now, the mature o\-um. or female pronucleus, is l>-ing quiescent, being destitute of its original centrosome, which has disappeared. As the male pronucleus, along with its centrosome, advances, the centro- some leading the way, the female pronucleus shows receptive signs, and moves slightly to meet the approaching \'isitor. The two pronuclei then come into very near contact, not far from the centre of the ovum, but they do not as yet fuse. The male centrosome, or spermo-centre, now divides, and two centrosomes are formed, one First Stage Second Stage Third Stage Fig. 665. — Fertilization of Ovum. A, Entnnce of Spermatozoon B, Extrusion of Polar Bodies C, Male Pronaclcos D, Compound Nucleus (Male and Female Pronucleus) E, Female Pronucleus (Ovum) F, Female Pronucleus of which passes to the distal side of the female pronucleus. Con- jugation or fusion of the two pronuclei now takes place, and the mixed nucleus thus produced is called the segmentation, or cleavage- nucleus. This completes the stage of fertilization. A chromatic spireme, or skein, chromosome, and a spindle are subsequently formed within the segmentation-nucleus, and the segmentation-stage is entered upon — that is to say, cell-division of the nature of mitosis, or karyo- kinesis. takes place. Certain authorities maintain that the ovum, after parting with the second polar body, retains a centrosome, known as the ovo-centre. The male pro- nucleus, as stated, brings with it a centrosome or spermo-centre. Each ovo- centre and spermo-centre divides into two, and each division of the ovo- centre joins a di\-ision of the spermo-centre. When, therefore, fusion of the two pronuclei has been effected, the resultant segmentation-nucleus has two mixed centrosomes (male and female) , one on either side, or at each pole. Segmentation of the Ovum. Segmentation consists in the division of the fertilized ovum into a mass of cells. After the mature ovum, or female pronucleus, has been fertilized by fusion with the male pronucleus, mitotic or karyokinetic cell- division commences, and the o\'um is ultimately transformed into i6i2 A MANUAL OF ANATOMY a great number of cells, which are called blastomeres, or segmenta- tion-cells. At the first division, which affects primarily the seg- mentation nucleus, the ovum is cleft into two cells, which lie close together, the opposed surfaces being flattened. At the second division each of these cells is cleft into two, so that four blastomeres now occupy the interior of the ovum. Each of these, in turn, divides into two, thus giving rise to eight blastomeres. This process First Division Final Division Fig. 666. — Segmentation of Ovum. of cell-division goes on, sixteen blastomeres being formed, succeeded by thirty-two, and so on. Finally, the ovum, originally simple, becomes transformed into a heap of nucleated blastomeres, or seg- mentation-cells, the superficial cells being clear, whilst the more deeply placed cells are granular. These constitute a solid, spherical, mulberry-like mass, called the morula, and this stage is hence known as the morula-stage. Formation of the Blastodermic Vesicle and Blastoderm. After the morula-stage has been completed, fluid accumulates within the morula and a cavity is formed, called the segmentation- cavity or blastocoele. The ovum is now a vesicle, and is known variously as the blastula, or blastodermic vesicle. During the formation of the segmentation-cavity the blastomeres or cells of the morula become arranged in two groups — outer and inner. The cells of the outer group, which are clear, spread out and form a membrane, which is known as the enveloping layer, or irophoblast. This layer represents the primitive ectoderm, and it encloses (i) the inner group of cells, and (2) the segmentation-cavity. That portion of the enveloping layer which covers the inner group of cells at the upper pole of the blastodermic vesicle is known as Rauher's covering layer. The primitive ectoderm (enveloping layer), being extra- embryonic, gives rise to the foetal part of the placenta and the foetal membranes. The cells of the inner group, which are granular and spherical, and which originally filled the morula, become gradually collected into a round heap, known as the inner cell-mass. This mass is situated at the upper, embryonic, or germinal pole of the blasto- GENERAL EMBRYOLOGY 1613 dermic vesicle, where they are in intimate contact with the envelop- ing layer (this part of the enveloping layer being, as stated, Rauber's covering layer). Elsewhere, the inner cell-mass is separated from the enveloping layer by the segmentation-cavity and its fluid. The enveloping layer constitutes the blastoderm, which, at this stage, is unilaminar. The cells of the inner cell-mass, which lie next the segmentation- cavitv, now begin to spread out, and they ultimately form a layer which lines the enveloping layer. This lamina represents the primitive entoderm. The blastoderm is now bilaminar, its outer, or enveloping, layer representing the primitive ectoderm, whilst its inner layer corresponds to the primitive entoderm. Prior to the completion of the entodermic layer, certain changes take place within the remainder of the inner cell-mass. The lower cells form a thickened group, known as the embryonic bud, or disc, from which the embryo is devel- oped. Within the upper cells inner C*lI.MaM^^^^G«nninal Layer vacuoles appear, which rapidly increase and coalesce so as to form a cavity within the upper part of the inner cell-mass, which is called the amniotic cavity. The roof of this cavity is formed directly by the superficial cells of the inner cell - mass. Superficial to this lamina, at first, there is that part of the enveloping layer, or extra- embryonic ectoderm, which is known as Rauber's laj-er. The floor _ of the amniotic cavity is fomied p,^ eej-^S^TI^MEXTATioN by a layer of cells, derived from c.wity of Blastodermic those which form the amniotic sur- Vesicle. face of the embryonic bud, the cells of that bud being derived from the inner cell-mass. This floor- layer of cells and the direct roof-layer of cells, both of which are derived from the inner cell-mass, constitute the embryonic ectoderm, as distinguished from the extra-embryonic ectoderm, wJiich is repre- sented by the enveloping layer. The embryonic ectoderm, which surroim(6 the amniotic cavity, becomes continuous with the extra- embryonic ectoderm, or enveloping layer, at the periphery of the roof of the amniotic cavity; and that part of the enveloping layer which enters into the roof of the cavity (Rauber's laver) disappears. The upper pole of the blastodermic vesicle is now covered by embryonic ectoderm. GastrolatioD. — In Amphioxus the blastomeres or segmentation-cells of the fertilized ovum are disposed at an early period in one layer, and there is no morula-stage. This single layer of cells constitutes the unilaminar blasto- derm, which encloses a cavity, and the ovum is now a blastula or blasto- dermic vesicle. i6i4 A MANUAL OF ANATOMY Blastopore or Primitive Mouth Entoderm . Ectoderm Fig. 668. — The Gastrula of Am- PHioxus (modified after Wiedersheim). The unilaminar blastoderm becomes invaginated at one pole of the blastula, and the original cavity, being thereby gradually encroached upon, ultimately disappears. Another cavity, however, is formed within the invaginated portion of the unilaminar blastoderm, and this cavity is the archenteron or primitive intestinal cavity. The opening by which the archenteron com- municates with the exterior, and which is situated at the place where invagina- tion occurs, is called the blastopore. The result is that a double - walled sacciform body is formed, called the gastrula. The inner wall of the gastrula is formed by the invaginated portion of the unilaminar blastoderm, and this constitutes the entoderm. The outer wall of the gastrula consists of ectoderm. At the margins of the blastopore these two germinal layers are continuous with each other. This constitutes the gastrula-stage or gastrulation. In such animals the entoderm is entirely the result of a process of in- vagination. Moreover, the mesoderm is subsequently developed at the margins of the blastopore, and gradually insinu- ates itself between the ectoderm and entoderm. In Mammalia no such invagination takes place. The entoderm is formed from cells which are entirely within the blastula or blastodermic vesicle — namely, those which constitute the inner cell-mass. Embryonic Area. — ^The bilaminar blastodermic vesicle presents at the upper pole a dark region, which is called the embryonic or germinal disc, or embryonic shield. It is due to a thickening of the embryonic ectoderm, and its shape is at first circular, then oval, and subsequently pyriform, the narrow end being directed Neural Fold Neural Groove caudalwards. Over its caudal or posterior half a longitudinal streak appears, called the primi- tive streak, which extends for- wards in the median line to the centre of the embryonic area. The streak is due to a prolifera- tion of the deep cells of the ectoderm. Along the primitive streak a furrow is formed, known as the primitive groove, and immediately beneath the primitive streak there is ento- derm. As stated, the primitive streak extends only to the centre of the embryonic area. At the anterior end of the streak there is a definite dark spot, which is due to an accumulation of cells on the under aspect of the ectoderm, and is known as Hensen's node. In front of this node there is another dark linear marking, mesially placed Head Process Hensen's Node Neurenteric Canal Primitive Streak The Embryonic Area. GENERAL EMBRYOLOGY 1615 and in line with the primitive streak, which constitutes the head- process of the streak. Significance of the Head- Process and Hensen's Node. — The ectodermic cells, which lie over the head-process, give rise to the medullary plate, neural or medullary groove, medullar^' folds, and neural or medullary canal, the last named being the rudiment of the entire cerebro-spinal nervous system. The posterior end of the neural groove embraces the anterior end of the primitive streak and primitive groove. In this situation, where Hensen's node is located, a somewhat wide communication exists at an early period between the posterior end of the neural canal and the primitive intestinjil cavity. This communication, which is temporary, is known as the neoren- teric canal. It passes through Hensen's node, and it corresponds to the blastopore of Amphioxus. Along the under aspect of the ectodermic cells, which give rise to the neural canal, the cells of the subjacent entoderm become thickened and differentiated to form the notochordal plate. This plate gives rise to the cylinder of ceUs. called the notochord, which is the axis round which the vertebral column and its hgaments are developed. The posterior part of the primitive streak gives rise to the cloacal membrane, which is bilaminar, one layer consisting of ectoderm, and the other of entoderm. It forms the posterior boundary of the primitive alimentary tube, and is subsequently concerned in the formation of the anus. Formation of the Mesoderm. — On either side of the primitive groove the cells of the primitive streak become proliferous. Cell- proliferation also occurs on either side of the head-process. The new cells, thus formed, gradually extend, on either side, into the blastoderm, and insinuate themselves hetween its two layers, which consist of ectoderm and entoderm respectively. In this manner a third or middle layer is formed for the blastoderm, and this laver, which is of secondary formation, represents the primitive mesoderm. It is chiefly derived from the primitive streak and its head-process, which consist of embr^-onic ectoderm; but it is reinforced by cells from the subjacent entoderm. The mesoderm is thus a secondary formation, whilst the ectoderm and entoderm are of primary origin. Inasmuch as the embryonic ectoderm and entoderm are derived from the inner cell-mass, it follows that the inner cell-mass is con- cerned in the formation of all three germinal layers of the embryo. The blastodermic vesicle has now a trilaminar blastoderm, the layers, from without inwards, being the ectoderm, the mesoderm, and the entoderm. Summary of the Formation of the Germinal Layers. The germinal layers are three in number — namely, ectoderm, entoderm, and mesoderm. The ectoderm and entoderm are of primary origin, whilst the mesoderm is of secondary origin. The ectoderm is developed from the outer layer of blastomeres or segmentation-ceUs, which result from the segmentation of the fertilized ovum, and the entoderm is developed from the inner cell-mass. The mesoderm is developed chiefly from the primitive streak on the embryonic area of the blastodermic vesicle, the cells of which streak consist of ectoderm, but it also derives cells from the entoderm which lies close beneath the primitive streak. The mesoderm is also, in part, derived from the head-process of the primitive streak. I6i6 A MANUAL OF ANATOMY The blastoderm is the wall of the blastodermic vesicle, this vesicle repre- senting the fertilized ovum after segmentation has been completed, and after a cavity, called the segmentation-cavity or blastocoele, has been formed within the morula or mulberry-like mass of cells which results from the segmentation of the fertilized ovum. The blastoderm is at first unilaminar, and is formed by the outer cells of the morula, which spread out and form the enveloping layer. This layer represents the primitive ectoderm, and, being extra-embryonic, it gives rise to the foetal part of the placenta and the foetal membranes. Meanwhile, during the formation of the cavity of the blastodermic vesicle, the remaining cells of the morula become collected into a round heap, called the inner cell-mass, which is situated at the upper em- bryonic, or germinal pole of the blastoderm. The cells of the inner cell-mass which lie next the segmentation-cavity, spread out and ultimately form a layer, which lines the primitive ectoderm ftr enveloping layer. This lamina represents the primitive entoderm, and the blastoderm is now bilaminar. !Prior to the completion of this entodermic lamina, certain changes take place within the remainder of the inner cell-mass. Some of its cells give Neural Tube Ectoderm ^^^^^^S-. Myocoel Mesoderm^ >^^^!^^^ -' Lateral Mesoderm / Somatopleure Coelom ,^jg7%:S^Se)^<%1l^^ ^S/^^I^MbSS^^^ '' / Coelom i Dorsal Aorta ,'' • Dorsal Aorta Splanchnopieure Entoderm Notochord Fig. 670. — The Germinal Layers. rise to the embryonic bud or disc, which is the rudiment of the embryonic body. In others vacuoles appear, which coalesce and form a cavity within the upper part of the inner cell-mass, beneath Rauber's layer, called the amniotic cavity. The floor of this cavity is formed by cells derived from the embryonic bud. This layer of cells represents the embryonic ectoderm, which becomes con- tinuous with the extra-embryonic ectoderm forming the enveloping layer. Up to this stage the blastoderm has remained bilaminar. Formation of the Mesoderm. — On either side of the primitive streak and its head process, cell-proliferation takes place, and the new cells thus formed gradually extend, on either side, into the blastoderm, insinuating themselves between its two layers — ectodermic and entodermic. In this manner a third or intermediate layer is formed, which represents the primitive mesoderm, this being secondary as regards development. It receives its cells chiefly from the ectoderm of the primitive streak and its head-process, but it is rein- forced by cells derived from the subjacent entoderm. The blastoderm is now trilaminar, being composed, from without inwards, of ectoderm, mesoderm, and entoderm. Characters of the Germinal Layers. — ^The cells of the ectoderm are of an epithelial nature. In the region of the embryonic or germinal pole of the blastoderm they are somewhat columnar, but elsewhere they are flattened. The cells of the entoderm are also of an epithelial nature, and are all flattened in the first instance ; but subsequently they become columnar. The cells of the mesoderm are at first separated by intercellular vacuoles, containing fluid, and they are branched. GENERAL EMBRYOLOGY 1617 Structures derived from the Germinal Layers. Eetoderm. 1. The nervous s\^tem — ^that is to say, the spinal cord and enceptialon, the peripheral nen-es, and the s}Tnpathetic s\-stem. 2. The epithelial elements of the organs of sense, except the tongue — e.g., the epithelial elements of the olfactory region, internal ear, optic nerve, and retina. 3. The epithelial elements of the posterior lobe of the pituitary body, and those of the pineal body. 4. The cr\-stalline lens. 5. The epidermis and its appendages — e.g., the hairs and nails. 6. The epithelial elements of the sebaceous glands, sweat-glands, and mammary glands. 7. The plain muscular tissue connected with the hair-follicles, and arranged as the musculi arrectores pilorum, as well as the plain muscular tissue of the sweat-glands. 8. The epithelium of the roof and sides of the mouth, but not that which covers the tongue and back part of the floor of the mouth ; the epithehum of the salivary' glands ; the enamel of the teeth ; and the anterior lobe of the pituitar\' bod\-. 9. The epithelium of the nasal fossae and of the air-sinuses which communicate \viih them, as well as of the naso-phar\"nx. 10. The epithehum of the external auditory meatus and outer layer of the membrana t^-mpani. 11. The epithehum of the conjunctiva and front part of the cornea. 12. The epithelium (modified epidermis) of the anal canal below the anal valves. 13. The epithelium of the spongy part of the male urethra. Entoderm. 1. The epithehum of the alimentar\' canal, except the following parts: (a) The re of and sides of the mouth; (6) the naso-pharynx ; and (c) the anal canal below the anal valves. 2. The epithehum of the tongue (including that of the taste-buds) and of the back part of the floor of the mouth. 3. The epithelium of the glands which open into the alimentary canal (except the sahvary glands) — e.g., the hver and pancreas. The epithehmn of the gall-bladder is included. 4. The epithelium of the Eustachian tube and t\Tnpanum. 5. The epithelium of the th\Toid and thymus bodies. 6. The epithelium of the respirator^' tract — e.g., the lar5aix, trachea, bronchial tubes, and air-cells of the lungs. 7. The epithehum of the urinary* bladder, of the prostatic and membranous parts of the male urethra, and of the whole of the female urethra. 102 I6l8 A MANUAL OF ANATOMY Mesoderm. 1. The various connective tissues — e.g., bone, cartilage, dentine, cement, areolar tissue, fibrous tissue, and blood. 2. Muscular tissue, striated and plain, except the muscular tissue of the sweat-glands, that which constitutes the musculi arrectores pilorum in connection with the hair-follicles, and that of the iris. 3. The vascular and lymphatic systems, together with their endo- thelial linings. 4. The serous and synovial membranes, together with their endo- thelial linings, including all bursal sacs. 5. The kidneys and ureters. 6. The testes, and their complicated excretory equipments. 7. The ovaries, Fallopian tubes, uterus, and vagina. 8. The spleen. The mesoderm exists under two forms, called mesothelium and mesenchyme. Mesothelium is that form of mesoderm in which the cells are flattened and form a definite epithelial membrane or layer, known as endothelium, there being only a very small amount of inter- cellular substance. It lines serous membranes, as well as the chambers of the heart, the bloodvessels, and the lymphatic vessels. Mesenchyme is that form of mesoderm in which the cells are more or less scattered in a homogeneous ground-substance or matrix, as occurs, say, in the various connective tissues. The cells are stellate and non-epithelial. Formation of the Embryo. Early Stages. The early stages in the formation of the embryo take place in that part of the embryonic area which lies in front of the primitive streak. These stages are three in number — ^namely, (i) the forma- tion of the neural canal; {2) the formation of the notochord; and (3) the formation of the mesodermic somites. Neural Canal. — ^The ectodermic cells of the head-process, in front of the primitive streak, give rise to the neural plate, which very soon presents a median longitudinal furrow, called the neural groove. This groove is bounded on either side by a longitudinal ridge of ecto- derm, these two ridges being known as the neural or medullary folds. Anteriorly, these folds are continuous with each other in front of the neural groove; but, posteriorly, they are separate, and embrace between them the anterior end of the primitive streak and Hensen's node, through which node the neurenteric canal passes. That canal is therefore originally in direct communication with the neural groove, subsequently the neural canal, its other communica- tion being with the archenteron or primitive intestinal cavity. The neural folds, becoming elevated, incline towards each other, and eventually they unite over the neural groove. In this manner GENERAL EMBRYOLOGY 1619 Fore-Brain Opdc Vesicle Miti-Brain Hind- Brain Spinal Portion o( Neural Tube - Mesodermic Somite the groove is converted into a tube, which constitutes the neural canal. This canal forms the rudiment of the whole cerebro-spinal nervous system, and it consists entirely of ectoderm. The cephalic end of the canal becomes dilated, and gives rise to the three primary cerebral vesicles, which are the rudi- ments of the fore-brain, mid-brain, and hind-brain, including the cavities •of the cerebral ventricles. The re- mainder of the canal, from the wall of which the spinal cord is developed, persists as the central canal of the spinal cord. As previously stated, the neural canal originally communicates wath the primitive intestinal cavity by means of the neurenteric canal. At this point the ectoderm of the neuraj canal becomes continuous with the entoderm of the primitive intestinal ■cavity. The neurenteric canal, how- ever, is only of temporary duration. Notochord or Chorda Dorsalis. — Along the ventral aspect of the neural groove the cells of the entoderm be- come thickened and differentiated to form the notochordal plate, which constitutes the first stage in the for- mation of the notochord from the entoderm. For a description of the notochord, which forms the axis roimd which the vertebral column and its ligaments are developed, see Index. Mesodermic Somites. — After the formation of the mesoderm it becomes ■disposed in /o«r parts. Two of these form longitudinal columns, which lie not far from the median or axial line, one being placed on either side of the neural canal and notochord. These two columns constitute the paraxial mesoderm. The other two parts are disposed in the form of sheets, which are known as the lateral plates, each plate lying external to the corre- sponding paraxial column, with which it is at first in continuity. The lateral plates of mesoderm are each composed of several strata of cells, which form, on either side, a single compact sheet. Within each plate vacuoles form, which coalesce and so give rise to a cleft- like space. In this space fluid soon acciunulates, and a cavity is Fig. 671. — Embryo Chick, SHowaNG Cranial and Spi- nal Portions of Neural Tube and Mesodermic Somites (Kolliker). i62o A MANUAL OF ANATOMY formed. The mesoderm of each lateral plate becomes thereby dis- posed in two lamellae — outer or parietal, and inner or visceral. The parietal layer is called the somatic mesoderm, and the visceral layer is known as the splanchnic mesoderm. The somatic mesoderm joins the ectoderm, and so the somatopleure is formed. The splanchnic mesoderm joins the entoderm, and the two constitute the splanchnopleure. The cavity formed within each lateral plate, and dividing that plate into its somatic and splanchnic lamellae, is called the coelom or primitive body-cavity. It is also known as the pletiro-peritoneat cavity. It subsequently gives rise to the pleural, pericardial, and peritoneal serous cavities, and also to the cavity of each tunica Somatopleure Splanchnopleure Ccelum Entoderm -Neural Tube Notochord Fig. 672. — Transverse Section of Body of an Amphioxus (modified after Hatschek). vaginalis in connection with the testes. The mesodermic cells which line the coelom represent mesothellum, subsequently known as endothelium. The paraxial mesoderm, as stated, is disposed as two longitudinal columns of thickened mesoderm, one being situated on either side of the neural canal and notochord. Each of these columns under- goes segmentation, and is broken up into a number of primitive segments, called mesodermic somites, cervical, thoracic, lumbar,, sacral, and coccygeal respectively. The process of segmentation is preceded by the appearance of a series of transverse furrows along each column. In this manner there is formed, in each longi- tudinal column of paraxial mesoderm, a series of cubical somites. There are thus two parallel rows of mesodermic somites, one right and one left, situated one on either side of the neural canal and noto- chord . The somites on either side become gradually separated from the contiguous lateral plate of mesoderm by a longitudinal groove. Along this groove a row of cells appears, known as the intermediate cell-mass by which the somites are for some time connected with GENERAL EMBRYOLOGY 1621 the contiguous lateral plate. Eventually, however, the lateral plate becomes detached. The intermediate ceU-mass on either side gives rise to the internal genital and the renal organs. Each mesodermlc somite consists of cells, which are arranged in a laminar manner around a central cavity or myoccele, which is of temporary duration. These cells become disposed in three groups, two being internal, and one external. Of the two inner groups the mesial one, or that nearest to the neural canal and notochord, by its mesenchvTne, constitutes a sclerotome, and the lateral group, or that nearest to the temporary ca\'ity of the somite, forms a muscle- plate. The external group of cells is generally regarded as giving rise to the cutis- plate. The successive sclerotomes on either side proliferate and surroimd the notochord and superjacent neural canal, forming for them a selerotogenous or skeletogenous sheath of mesenchyme. This invest- ment, as regards the notochord, represents the membranous verte- bral column, and from it are developed (i) the vertebrae and their ligaments, and (2) the inter\'ertebral discs, except the central pulp of each, this piilp being a persistent part of the notochord. As regards the neural canal, the selerotogenous investment gives rise to the meninges of the brain and spinal cord. The successive muscle-plates give rise to myotomes (muscle- segments) , and from these the striated muscles of the trunk, at least, are developed. According to some authorities, they also give rise to the muscles of the limbs; but another \'iew is that the limb- muscles are developed from the core of mesenchyme in the centre of each limb-bud, which core gives rise to the skeletal framework of the limb. The cutis-plate, formed by the external group of somitic cells, gives rise to the cutis vera or corium, the epidermis being of ecto- dermic origin. According to some authorities, however, this group of cells is concerned in the formation of muscular tissue. Mesodermic Somites ol the Head. — The first or most anterior primitive or trunk mesodermic somite, derived as stated from the division of the column ■of paraxial mesoderm, occupies the future occipital region. In front of this region several head-somites or segments appear in lower vertebrates. They are regarded as being nine in number, but they are less numerous in the human embrj-o, there being probably three. They are formed bj' a segmen- tation of the mesoderm of the head, as distinguished from the paraxial meso- derm. Later Stages in the Fonn?.tion of the Embryo. The early stages in the formation of the embr\'o, just described, are threefold, as follows: (i) The formation of the neural canal from ectoderm, this canal being the rudiment of the entire cerebro-spina! ner\'ous system ; (2) the formation of the notochord or chorda dor- salis from entoderm, this chord constituting the axis roimd which the vertebral column and its ligaments are developed from the selerotogenous or skeletogenous sheath of the notochord, the chord 1622 A MANUAL OF ANATOMY itself only persisting as the central pulp of each intervertebral disc; and (3) the formation of the mesodermic somites from the paraxial mesoderm, these somites being arranged in two longitudinal rows, right and left, one on either side of the neural canal and notochord. The lateral plate of mesoderm on either side has been divided into two lamellae — ^namely, somatic and splanchnic, this being effected by the formation, within each lateral plate, of vacuoles, which coalesce and so give rise to a cleft -like space. Within this space fluid accumulates and a cavity is formed, called the ccelom, primitive- hody-cavity , or pleuro-peritoneal cavity. The somatic mesoderm joins the ectoderm, and forms the somatopleure, whilst the splanchnic mesoderm joins the entoderm, and forms the splanchnopleure. The cavity of the ccelom is therefore bounded on the one hand by somatopleure, and on the other by splanchnopleure. The cavity of the blastodermic vesicle, which is situated on the ventral aspect of the notochord, is single at this stage, and is bounded by splanchnopleure. This cavity represents the primitive intes- tinal cavity. Separation of the Embryo. — ^The primitive embryo, developed from the embryonic area of the blastodermic vesicle, becomes separated from the extra-embryonic part of that vesicle by a process of infolding of somatopleure ventralwards around the embryonic area. This infolding gives rise to certain grooves and folds. The grooves are cephalic, lateral, and caudal. In the chick (to which the following description applies) the cephalic or anterior groove lies, in a crescentic manner, in front of the head-end of the embryo, the concavity of the crescent being directed towards the head. The lateral grooves are disposed one on either side of the. embryonic area. The caudal or posterior groove is situated, in a crescentic manner, behind the tail-end of the embryonic area, the concavity of the crescent being directed towards the tail. By the coalescence of these four grooves one continuous groove is formed, . which surrounds the entire embryonic area, and is known as the marginal or circular groove. The folds lie external to the grooves, of which they are the elevated- outer lips, and they are spoken of as head-fold, lateral (right and left), and tail-fold. They consist of two layers of somatopleure, inner and outer, and constitute the amniotic folds. As the circular groove deepens, it encroaches, from all sides, upon the ventral aspect of the embryonic area as far as the central part, which coincides with the site of the future umbilicus. The head-, tail-, and lateral amniotic folds become more elevated, the embryo ^inks slightly, and the amniotic folds approach one another over the embryo. Subsequently these folds unite over the dorsal aspect of the embryo, and give rise to a sac, called the amnion, which sur- rounds the embryo. (In man the amnion is formed in a different manner, as will be presently described.) After fusion of the amniotic folds has taken place to form the amnion, the inner layer of somatopleure separates from the outer GENERAL EMBRYOLOGY 1623 layer, except at the caudal or posterior extremity of the embryo. The inner layer constitutes the amnion, whilst the outer layer, which is part of the general or extra-embryonic somatopleure, forms the chorion. As the circular groove encroaches from all sides upon the ventral aspect of the embryonic area, the somatopleure of the inner wall of the groove forms the lateral and ventral body-walls of the embryo, and, at the site of the future umbilicus, this somatopleure becomes continuous with that of the amnion. The subjacent splanchnopleure meanwhile encroaches upon the blastodermic cavity, and, as a result of this constriction, from all sides, the archenteron is incompletely divided into two unequal parts. The small dorsal compartment gives rise to the mid-gut (primitive gut), and the large ventral compartment constitutes the yolk-sac or umbilical vesicle. These two compartments communi- cate with each other at the site of the constriction by a narrow canal, called the vitelline duct or yolk-stalk. The walls of the Fore-Got Mid-Gut Hind Gm mid-gut and yolk-sac consist of splanchnopleure, and, like their cavities, they are continuous with one another. The mid-gut, which lies along the ventral aspect of the noto- chord, is originally a straight groove called the intestinal groove, which extends towards the cephalic and caudal ex- tremities of the embryo. It is, however, subsequently con- verted into a tube. At first it has only one opening — namely that of the vitelline duct or yolk-stalk — through which it communicates with the yolk-sac or umbilical vesicle. Its cephalic and caudal extremities are closed. The fore-gut is formed as a tubular recess or diverticulum from the anterior part of the blastodermic vesicle, and it lies within the downward bend formed by the head of the embryo. Posteriorly it opens into the mid-gut compartment of the blastodermic vesicle at the intestinal orifice of the vitelline duct, the opening being knowTi as the anterior intestinal portal. Anteriorly it is, at this stage, closed by the bucco-pharyngeal membrane, which consists of two layers — an outer or ectodermic, and an inner or entodermic. The hind-gut is formed, similarly to the fore-gut, as a tubular recess or diverticulum from the posterior part of the blastodermic vesicle, and it lies within the tail-fold. Anteriorly it opens into the mid-gut compartment of the blastodermic vesicle at the intes- tinal orifice of the vitelline duct, the opening being kno\vn as the posterior intestinal portal. The cephalic and caudal ends of the Fig. 673. — Yolk-Sac, Vitelline Duct, AND Embryo (Schematic). 1624 A MANUAL OF ANATOMY embryo become bent ventralwards, and these bent ends form the cephalic or head-fold and the caudal or tail-fold. Posteriorly the hind-gut is, at this stage, closed by the cloacal membrane, which, like the bucco-pharyngeal membrane at the cephalic end of the ali- mentary tract, consists of two layers — an outer or ectodermic, and an inner or entodermic. The entire primitive intestinal canal is therefore closed at either end, cephalic and caudal, by bilaminar membranes — ^bucco-pharjmgeal and cloacal — the internal lamina of each of which consists of entoderm. The wall of the primitive intestinal canal is formed by splanchno- pleure — that is to say, entoderm and the splanchnic lamella of the lateral plate of mesoderm — ^the tube being lined with entodermic cells. The unfolding processes, just described, accomplish the separation of the embryonic area on the dorsal aspect of the blastodermic vesicle, and that area now represents the primitive embryo. At this stage the embryo consists of three tubes and a solid cylinder of cells. The tubes are as follows: (i) The neural tube; (2) the primitive intestinal canal; and (3) the coelom, body-cavity, or pleuro-peri- toneal cavity. The solid cylinder of cells is the notochord. The order of these component parts dorso -ventralwards is as follows: Neural tube or canal. Notochord. Primitive intestinal canal, enclosed by splanchnopleure. Coelom or pleuro-peritoneal cavity, enclosed by somatopleure. The Appendages of the Embryo. The appendages or supplementary organs of the embryo are, for the most part, developed from the extra-embryonic area of the blastodermic vesicle, and they are as follows : 1. The amnion. 2. The yolk-sac and vitelline duct. 3. The chorion (representing a large part of the placenta). 4. The allantois (diverticulum and stalk). 5. The umbilical cord. Functionally they are (i) protective, (2) nutritive, (3) respiratory, and (4) excretory. All these appendages are dispensed with at birth, the umbilical cord being then divided. The Amnion. The amnion is one of the two fceial deciduous membranes, the other being the chorion. It is a closed membranous sac, the cavity' of which, called the amniotic cavity, contains a clear albuminous fluid, known as the liquor amnii. The amnion surrounds the embryo, which floats in the liquor amnii. When this fluid is present in ex- cessive quantity, the condition is known as hydramnios, or dropsy of the amnion. Rupture of the amnion and escape of the liquor amnii usually precede the birth of the child. GENERAL EMBRYOLOGY 1625 The following account of the mode of formation of the amnion in the chick, although referred to already, may here be re-stated. The amnion is developed from the somatopleure which forms the outer elevated lip of the marginal or circular groove round the embryonic area of the blastodermic vesicle, the appearance of which groove constitutes the first stage in the separation of the germinal disc. This somatopleure, which is disposed in two layers, inner and outer, gives rise to the amniotic folds. The circular groove deepens and encroaches, from all sides, upon the ventral aspect of the embryonic area as far as the site of the future umbilicus ; and the somatopleure of the inner wall of the groove forms the lateral and ventral body- walls of the embryo. Meanwhile the amniotic folds gradually encroach, from all sides, upon the dorsal aspect of the embryonic area in the form of cephalic, lateral, and caudal hoods. Subsequently these hoods meet and fuse. When this fusion has taken place, the inner layer of somatopleure separates from the outer layer (except at the caudal or posterior extremity of the embryo), and it constitutes a closed sac, which is the amnion, the outer layer of somatopleure giving rise to the chorion. The wall of the amnion is formed by somatopleure — that is to say, ectoderm and somatic mesoderm. The ectodermic layer is the inner of the two, and forms the lining of the amniotic cavity, whilst the layer of somatic mesoderm is situated externally. The body- wall of the embryo, as stated, also consists of somatopleure ; but in this case the ectoderm is external, and the somatic mesoderm lies on its inner aspect. The ectodermic layer of the wall of tl.e amnion, which is the inner layer, therefore faces the ectodermic laver of the body-wall of the embryo, which layer is situated on the exterior. At the site of the future tmibilicus, on the ventral aspect of the embryo, the somatopleure forming the wall of the amnion becomes continuous with the somatopleure which constitutes the body-wall of the embryo. In the human embryo the amnion is formed in a manner different from that which has just been described as applicable to the chick. In the chick the amnion, briefly stated, is formed from the amniotic folds, representing the outer elevated lips of the circular groove around the embryonic area. The four amniotic folds — namely, cephalic, two lateral, and caudal — come together over the embryonic area, and by their fusion give rise to the amnion, which is therefore not a closed sac at first. In the human embr\-o it is different. From the very commencement the amnion is a closed sac, and is formed within the inner ceU-mass of the blastodermic vesicle. Vacuoles form within the uppermost of these cells, the remainder of the cells forming the embryonic bud or disc. Bv the coalescence of these vacuoles the amniotic cavity is formed, "which is thus a closed cavity from the first. The cells surroimding this ca\'ity, and therefore forming its lining, are derived from the embrvonic ecto- derm, which forms the inner layer of the wall of the amnion. The outer layer of the waU, formed by somatic mesoderm, is derived i626 A MANUAL OF ANATOMY from the somatic mesoderm of the embryo, as well as from the meso- derm of the allantoic or body-stalk. The embryonic bud lies- originally below the amniotic cavity. As the periphery of the bud curves downwards or ventralwards, it carries with it the wall of the amnion where that is connected with the periphery of the bud. The roof of the amniotic cavity is formed by the superficial cells of the inner cell-mass, covered by that portion of the enveloping layer which is known as Rauber's layer. The floor is formed by the embryonic bud or disc. The cells on the amniotic surface of this bud spread out over the wall of the cavity and become continuous with the roof-cells derived from the inner cell-mass, forming the embryonic ectoderm, as distinguished from the extra-embryonia ectoderm, which is represented by the enveloping layer. The embryonic ectoderm thus lines the amniotic cavity, and it becomes continuous with the extra-embryonic ectoderm or enveloping layer at the periphery of the roof of the amniotic cavity, that part of the enveloping layer which forms Rauber's layer having disappeared. External to the lining layer of embryonic ectoderm there is a layer of somatic mesoderm, which is derived from the somatic mesoderm of the embryo, as well as from the mesoderm of the allantoic or belly-stalk. The wall of the amniotic cavity therefore consists of two layers — an inner, formed by embryonic ectoderm ; and an outer, formed by somatic mesoderm — both connected together. The embryonic bud or disc, as stated, lies originally in the floor of the amniotic cavity. As the periphery of the bud curves ventral- wards, it carries with it the wall of the amnion, where that is con- nected with the periphery of the bud. At the caudal or posterior extremity of the embryo the inner and outer layers of the amnion still remain connected. In. this region, the outer layer of the amnion, formed by somatic mesoderm, is continuous with the inner layer of the chorion, which also consists of somatic mesoderm. This connection gives rise to the allantoic or belly-stalk, and, as the amnion is continuous with the body-wall of the embryo, the allantoic stalk connects the embryo with that part of the chorion which subsequently forms, along with the meso- derm of the allantoic stalk, the foetal part of the placenta. The amnion is peculiar to Mammals, Birds, and Reptiles, these three classes of Vertebrata forming the group of Amniota. In Amphibia and Fishes the amnion is absent, and these two classes are consequently grouped as Anamnia. Pro-Amnion. — In front of the embryonic area of the blastodermic vesicle is the pro-amniotic area, the blastoderm, of which is bilaminar, the two layers consisting of ectoderm and entoderm. As the head of the embryo grows forwards, it comes to lie over the pro-amniotic region, and the embryo is meanwhile sinking slightly. The bilaminar blastoderm of the pro-amniotic region thus forms a hood for the head of the embryo, this hood being known as the pro-amnlon. At a later period the pro-amnion is invaded by somatic and splanchnic lamellae of mesoderm, and then it consists of somatopleure and splanchnopleure. Its somatopleuric constituent fuses with that division of the amniotic folds which is called the head-fold, and therefore forms part of the amnion. The pro-amnion is well marked in the chick, but in the human embryo, if present at all, it is only for a very brief period. GENERAL EMBRYOLOGY 1627 The Yolk-Sac and Vitelline Duct. The yolk-sac is the ventral compartment of the cav-ity of the original blastodermic vesicle. As the formation of the amnion is being completed, an infolding of splanchnoplenre takes place. The blastodermic vesicle is thereby gradually constricted, and its cavity is divided, at first incompletely, into two compartments — namely, dorsal and ventral. The dorsal compartment, which is the smaller of the two, gives rise to the mid-gut (primitive gut), and is situated within the body of the embryo. It is at first a groove, kno\\-n as the intestinal groove, but it is subsequently converted into a tube. The ventral compartment which is large and capacious, forms the yolk-sac or umbilical vesicle, and is extra-embryonic. The yolk-sac is at first in wide communication with the centre of the primitive mid-gut by a passage called the vitelline or vitello- intestinal duct (yolk-stalk) which passes through the umbilical opening, and is connected with the ventral aspect of the mid-gut. The wall of the yolk-sac and vitelline duct is continuous with that of the mid-gut, both consisting entirely of splanchnoplenre — ^that is to say, entoderm and splanchnic mesoderm, the entoderm forming the lining membrane. In the human embryo the yolk-sac contains fluid. Its wall presents a well-marked vascular area, with which the primitive bloodvessels are associated. These vessels are called the vitelline or omphalo-mesenteric vessels and are four in number, two arteries and two veins, which will be again referred to. The yolk-sac undergoes atrophy, but a remnant of it persists in the umbilical cord. The \'itelline duct also undergoes atrophy, and its lumen disappears. The part of the duct, however, which is connected with the mid-gut sometimes remains persistent, and so gives rise to an intestinal protrusion, known as Meckel's diverticulum. The Chorion. The chorion is the outer of the two foetal deciduous membranes, the one internal to it being the amnion. It is developed from the outer layers of the amniotic folds, and, like the amnion, is composed of somatopleure. Its external surface consists of extra-embryonic ectoderm, and the internal surface is formed by somatic mesoderm. The chorion is situated external to the amnion, and the somatic mesoderm of its inner surface faces the somatic mesoderm which forms the outer surface of the amnion. The interval between the chorion and the amnion is known as the chorionic cavity, and the embryo is now surrounded by two membranes, the inner of which is the amnion. The chorionic cavity represents the extra-embryonic portion of the coelom or body-ca\nty, and it contains (i) the embryo, enclosed within the amnion; and (2) the yolk-sac or umbilical vesicle. It is i628 A MANUAL OF ANATOMY further traversed by the allantoic stalk or belly-stalk, as that struc- ture extends from the umbilical orifice of the embryo to the placental area of the chorion, with which area the mesoderm of the allantoic stalk blends, and to which area that mesoderm conducts blood- vessels. The chorionic cavity becomes gradually obliterated as the amniotic sac expands, the chorion and amnion then being intimately related to each other. From the outer or ectodermic surface of the chorion small bud- like processes grow into the contiguous maternal blood-lacunae. These processes represent the rudimentary chorionic villi, and are at first entirely composed of ectoderm. Subsequently the meso- derm, which forms the inner layer of the chorion, grows outwards into these rudimentary villi, and forms for each of them a core. In this mesodermic core capillary bloodvessels are developed, which are continuous with the allantoic vessels through the mesoderm of the allantoic stalk, which fuses with the placental area of the chorion. The villi are now complete, and are somewhat club- shaped. A complete villus consists of the following parts: (i) An external envelope of ectoderm, the superficial layer of which con- sists of syncitium; (2) a vascular core of mesoderm; and (3) an arteriole, capillaries, and a venous radicle. The villi at first beset the entire outer surface of the chorion, and are of equal size. Subsequently, however, the villi of one particular area undergo enlargement and ramifications, whilst the others undergo retrogression, and become very small and scattered, ulti- mately becoming atrophied. The area over which retrogression of villi takes place becomes comparatively smooth, and this part of the chorion is consequently called the chorion leve. The limited area over which the villi become enlarged is rough and shaggy, and is known as the chorion frondosum or leafy chorion. This area of the chorion becomes intimately connected with the uterine mucosa, usually at the upper part of the posterior wall of the uterine cavity, close to the fundus. Along with the mesoderm of the adjacent part of the allantoic stalk, it forms the foetal part of the placenta. The villi of the chorion frondosum are numerous and large. Moreover, they ramify and so become arborescent. Some of them penetrate by filamentous processes into the uterine mucosa (decidua basalis or serotina) in the placental region, and these processes, or calkers, not only grip but become continuous with it. Such villi are known as fixation- or root-villi. Others project into, and lie free within, the maternal blood-lacunae, which are formed in connec- tion with the decidua basalis or serotina of the uterine mucosa, where they are freely bathed by the maternal blood. The uterine surface of the chorion frondosum has an epithelial covering consisting of ectoderm. This ectoderm is disposed at an early period in two layers — superficial and deep. The deep layer is distinctly cellular, and is known as the layer of Langhans. The i GENERAL EMBRYOLOGY 1629 villi pass through it, but have no connection with it. Subsequently its cells become grouped into patches, and finally disappear. The superficial layer becomes converted into a tissue, composed of nucleated protoplasm, but without any recognisable cells. This layer is known as the syncitial layer. It is also spoken of as the syncitium, being so named because it has no recognisable cells. In the case of the fixation — or root — vWh, this s\Ticitium accompanies them in the form of fihform processes, as they penetrate into the uterine mucosa. The villi of the chorion frondosiim, as they project from the surface, are separated by intervals, which constitute the maternal blood-spaces, -sinuses, or -lacunae. These intervals are also known as the intervillous spaces, and those villi which are free project into them. These spaces are lined with sjTicitium, which tissue conse- quently covers the surface of the chorion frondosum between the villi, as weU as the villi themselves. The Allantois. The allantois extends as a hollow tubular diverticulum from the dorsal waU of the yolk-sac to the inner surface of the chorion fron- dosum. The hind-gut has not been differentiated at this stage, but when this takes place the allantois becomes connected NN-ith the ventral waU of the hind-gut. At this point it is placed on the cephalic side of the cloacal membrane. It soon acquires an important relation to the cloaca, this latter being a blind chamber into which the hind-gut and urogenital ducts open. The allantois becomes connected with the ventral wall of the ventral or uro- genital compartment of the cloaca, the dorsal compartment per- taining to the rectum. The aUantois consists of splanchnopleure (entoderm and splanchnic, or visceral mesoderm), which is continuous with the splanchnopleure of the wall of the gut. It soon elongates towards the umbilical orifice, through which it leaves the body of the embryo, lying on the caudal side of the vitelline duct. At this open- ing the allantoic diverticulum enters the allantoic, or body-stalk. This stalk traverses the chorionic cavity*, and ends by blending with the inner surface of the chorion frondosum, which gives rise to the foetal part of the placenta. The allantois consequently establishes an important connection between the body of the embryo and the placenta. In order to understand the fimctions of the allantois it may be divided into two parts — ^intra-embryonic and extra-embryonic. The intra-emhryonic part is distinguished as the allantoic diverti- culum, and the extra-embryonic part is known as the allantoic, or body-stalk. The allantoic diverticulum has just been described. The allantoic stalk extends from the umbilical orifice to the placental area of the chorion. As has been incidentally stated, the amnion and chorion do not become completely separated at the .1630 A MANUAL OF ANATOMY caudal or posterior end of the embryo, their opposed surfaces, which consist of mesoderm, being here connected. From this mesoderm a peduncle is developed, and this mesodermic peduncle constitutes the allantoic stalk, in the centre of which is the remnant of the allantoic diverticulum, now without a lumen. After having tra- versed the chorionic cavity it blends, as stated, with the chorion frondosum, which gives rise to the foetal part of the placenta. The mesodermic tissue of the allantoic stalk contains the allantoic or umbilical bloodvessels (two arteries and two veins). This vascular stalk therefore establishes an important communication between the caudal or posterior extremity of the embryo and the foetal (chorionic) part of the placenta. Its vessels render the placental area of the chorion, and also the chorionic villi, vascular. Whilst the amnion and chorion are extra-embryonic, the allantois is both intra-embryonic and extra-embryonic. Functions of the Allantois. — ^The extra-embryonic part or allantoic stalk is concerned with respiration and nutrition, as regards the human embryo, through means of the allantoic arteries and veins. In the embryos of oviparous animals it also serves the purpose of excretion (urinary). Subsequent History of the Allantois. — The extra-embryonic part contributes fo the formation of the chorionic or foetal part of the placenta. The intra-embryonic part, or allantoic diverticulum, which is originally tubular, is connected, as stated, with the ventral or urogenital compartment of the cloaca. The urinary bladder is to be regarded as developed from the anterior or cephalic portion of this compartment, and perhaps from the root or cloacal end of the allantoic diverticulum. The portion of the allantoic divertic- ulum between the apex of the urinary bladder and the umbilicus loses its tubular character, and persists in the form of a fibrous cord, called the uracbus. The Umbilicus and Umbilical Cord. The umbilicus is the opening in the ventral body-wall, through which originally the vitelline duct or yolk-stalk enters the ccelom or body-cavity, of the embryo. The allantois also leaves the foetal body through it. As the somatopleure (somatic mesoderm and ectoderm) closes the ventral body-wall it divides the embryonic portion of the body-cavity from the extra-embryonic portion. When the somatopleure reaches the situation of the vitelline duct an aperture is left in it for the duct, this aperture being the primitive umbilicus. After entering the embryonic body-cavity, the vitelline duct is attached to the ventral aspect of the mid-gut. At the margins of the umbilicus the somatopleure becomes continuous dorsalwards with that of the amnion, and ventralwards it ensheathes the vitelline duct for a short distance towards the yolk-sac, which is extra-embryonic. The un^bil^p^al cord connects the foetus with the placenta, and, GENERAL EMBRYOLOGY , 163 1 amongst other structures, it contains the bloodvessels which convey (i) the impure blood from the body of the foetus to the placenta for purification, and {2) the blood, when purified in the placenta, from that organ back into the foetal body. Functionally it replaces the allantoic stalk. It extends, as a ' cord,' between the umbilical orifice and the foetal part of the placenta. In the later stages of pregnancy its average length is about 22 inches. This length is only attained after expansion of the amniotic sac, and it permits of ample freedom of movement on the part of the foetus in the amniotic fluid. Under these circumstances the placenta is not subjected to any influence of a dragging nature. The average length, however, may be exceeded, or it may be very much curtailed. The cord presents a spiral appearance, principally due to the winding of the two umbilical arteries around the umbilical vein. The constituents of the imibilical cord are as follows: 1. Two umbilical arteries. 2. One umbilical vein. 3. A remnant of the allantoic stalk. 4. A remnant ol the yolk-sac. 5. A remnant of the vitelline duct. 6. Mesoderm and Wharton's jelly. 7. An ectodermic envelope. As stated in connection with the allantois, the allantoic stalk consists of mesoderm, and contains two allantoic arteries and two allantoic veins, which bloodvessels it serves to conduct tc and from the placental area of the chorion (chorion frondosum). The two umbiUcal arteries replace the allantoic arteries ; and the single umbilical vein of the umbilical cord represents the two allantoic veins. The nmbilical arteries, within the abdomen of the foetus, are known as the hypogastric arteries, and the proximal li inches of these vessels represent the permanent internal iliac arteries. The remainder of each vessel, for the most part, constitutes the perma- nent obliterated hypogastric artery. The h\T50gastric and umbilical arteries carry impure blood from the foetus to the placenta. The umbilical vein undergoes no change in name on entering the abdomen of the foetus. It conveys pure blood from the placenta to the foetus, and, after entering the abdomen, it passes to the umbilical fissure of the liver. As regards its subsequent history, it is repre- sented by (i) the round ligament of the liver, and (2) the ligamentum ductus venosi. The remnant ol the allantoic stalk blends with the chorion fron- dosum. In rare cases the lumen of the allantoic diverticulum may persist for some time, thus giving rise to the condition which is known as an umbilical urinary fistula. The yolk-sac and vitelline duct are present as mere remnants. Mesoderm forms a large part of the umbilical cord. It supports and connects the various constituent elements, and consists of stellate cells, so arranged as to form a reticulum. The meshes of 1632 A MANUAL OF ANATOMY this reticulum are occupied by Wharton's jelly, which is composed of connective tissue, pervaded by a gelatinous fluid. The external epithelial covering of the cord consists of ectoderm, and at the placental end of the cord this ectoderm is continuous with that of the amnion. In early foetal life one or more loops of intestine protrude into the umbilical cord for a short distance, but this condition is of tem- porary duration. The Uterine Mucosa. The uterine mucosa, or mucous membrane of the cavity of the body of the gravid uterus, having undergone hypertrophy, is known as the membrana decidua. It consists of three parts — namely, decidua vera, decidua capsularis, or reflexa, and decidua basalis, or serotina. The ovum, after entering the cavity of the body of the uterus, becomes embedded in the uterine mucosa, the lining ciliated colum- nar epithelium of this part having disappeared, as well as the base- ment membrane and some of the superficial cells of the corium. The mucosa thus becomes excavated at the place where the ovum sinks into it, and the connection between the two is established through means of the fixation or root villi of the chorion frondosum. The usual site of attachment of the ovum is the upper part of the posterior uterine wall, close to the fundus uteri. The decidua vera represents the greater part of the uterine mucosa or membrana decidua. It lines the cavity of the body of the uterus, except where the ovum is attached, and it has no direct connection with the ovum. The decidua capsularis, or reflexa, is derived from the margins of the excavation formed at the site of attachment of the ovum, and it invests the ovum in the form of a capsule. . This maternal envelope lies outside the chorion leve, but does not encroach upon the chorion frondosum. It is at first separated from the decidua vera by a space. As, however, the embryo increases in size the decidua capsularis, or reflexa, comes into contact with, and joins, the decidua vera, one deciduous membrane being thereby formed, and the cavity of the body of the uterus being obliterated. The decidua basalis, or serotina, is that portion of the uterine mucosa which forms the floor of the excavation formed at the site of attachment of the ovum. It corresponds to the region of the chorion frondosum, with which it becomes incorporated, and it gives rise to the maternal part of the placenta, as distinguished from the ffjeial part. Structure of the Decidua Vera. — ^The mucosa which forms the decidua vera has undergone certain modifications in structure, (i) It has become very much thickened, and the covering layer of ciliated columnar epithelium has disappeared. (2) The uterine glands have undergone enormous development, and are now much elongated, dilated, and tortuous. (3) In the interglandular spaces GENERAL EMBRYOLOGY ^^33 there are many large spherical cells, called the decidual cells. These cells are present throughout the whole thickness of the decidua vera, but they are most numerous in its superficial stratum. The decidua vera is composed of three layers — namely, stratum compactum, stratimi spongiosum, and stratum profundum. The stratum compactum is the superficial layer, and lines the uterine cavity. The uterine glands, as they traverse it, are elon- gated, somewhat dilated, slightly tortuous, and parallel with each other. The epithehum Uning them consists of cubical or flat cells. Decidua Serotina Fundus Uteri Cotyledon Villi of Chorion Froodosum Chcrioo Frondosum F.mbryo and Allantoic Stalk Fallopian Tube- Decidua Chorion Os Internum Cavity of Cervix Os Externum Fig. 674. — The Gravid Uterus. This stratum contains many decidual cells, and has a compact structure. The stratum spongiosum, or cavernosum, is more deeply placed than the stratmn compactum. The uterine glands, as they traverse it, are much dilated, and very tortuous. It contains few decidual cells, and has a spongy or cavernous structure. As seen in section it presents a number of irregular spaces, or areolae, which represent the gland-cavities. The epithelium lining these cavities consists of cubical or flat cells. 103 1634 A MANUAL OF ANATOMY The stratum profundum lies next the muscular coat, there being no submucosa in the uterine wall. It contains the deep parts of the uterine glands, the blind ends of which project into the inner muscular layer, after having undergone in many cases dichotomous division. Structure of the Decidua Capsularis or Reflexa.— This contains no uterine glands, except where it is in continuity with the decidua vera. Essentially it consists of a matrix of connective tissue, per- meated by decidual cells, and it is devoid of epithelium. Structure of the Decidua Basalis or Serotina. — Prior to the fifth month of pregnancy the structure of the decidua basalis practically resembles that of the decidua vera. As the ovum sinks into it, certain changes occur. It loses its cihated columnar epithelium, basement membrane, and some of the superficial cells of the corium. After this loss there remain (i) the deep part of the stratum com- pactum, (2) the stratum spongiosum, presenting the usual irregular spaces or gland-cavities, and (3) the stratum profundum. The Decidua Vera, Reflexa, and Serotina after the Fifth Month of Pregnancy. Decidua Vera. — ^This membrane is now being subjected to pressure by the growing foetus, and it undergoes certain retrogressive changes, (i) The ciliated columnar epithelium disappears. (2) The portions of the uterine glands which lie in the stratum compactum lose their epithelial lining and, becoming obliterated, entirely disappear. The gland-cavities in the stratum spongiosum likewise lose their epi- thelial lining, but they persist, being now converted by pressure into narrow elongated clefts. (3) The gland-cavities in the portion of the stratum spongiosum which adjoins the stratum compactum likewise lose their epithelial lining, but those in the portion which adjoins the stratum profundum retain their epithelium. All these gland-cavities persist, but they now assume the form of elongated, narrow clefts, which lie parallel to the uterine wall. This change is brought about by the expansion of the uterus and the lateral stretching of the gland-cavities. (4) The decidua vera, now very thin, is joined by the decidua capsularis, or reflexa. Decidua Capsularis or Reflexa. — ^This membrane gradually ex- pands after the fifth month of pregnancy in adaptation to the grow- ing foetus, and it comes to press closely upon the decidua vera. The uterine cavity thereby becomes gradually occupied by (i) the foetus and its membranes, and (2) the placenta. Whatever glandular elements the decidua capsularis contains disappear, the membrane becomes extremely thin, and it fuses with the decidua vera. Accord- ing to some authorities, the membrane entirely disappears, in which case the chorion leve would come into contact with the decidua vera. Decidua Basalis, or Serotina. — ^The changes which this membrane has undergone prior to the fifth month of pregnancy have just been GENERAL EMBRYOLOGY 1635 Stated. As it is the source from which the maternal part of the placenta is formed, its future intra-uterine histor\' differs materially from that of the decidua vera and decidua capsularis. The changes, therefore, which this membrane undergoes after the fifth month are associated with the full development of the placenta, which see. Thev may, however, be stated here in continuity with the changes undergone by the decidua vera and decidua capsularis. (i) The gland-ca^^ties of the stratum spongiosum undergo changes similar to those which affect the corresponding stratum of the decidua vera. (2) In the remainder of the stratum compactum the uterine glands lose their epithelium and disappear. This vestigial stratum acquires great vascularity, and becomes conse- quently increased in thickness. (3) Superficially — that is to say. towards the region of the foetal part of the placenta — it gives rise to the maternal blood-lacunae, into which the maternal arterioles pour their blood. {4) Underneath — that is to say, on the uterine side of this region of maternal blood-lacunae — there is a layer of the vestigial stratum compactum, which is known a4 the basal layer. This layer adjoins the stratum spongiosum, and is very vascular. The decidua basalis will be again referred to in connection with the maternal part of the placeftta. The Placenta. The placenta is a ver\' vascular organ, which establishes an impor- tant connection between the body of the foetus and the maternal uterus. Its function is respiratory, nutritive, and excretory', during the last six months of intra-uterine life. Physical Characters of the Placenta at Full Tenn. — The placenta at full term has the form of a discoid cake, which is spongy in con- sistence. Its average width is about 7 inches, and its thickness at the centre is about i| inches, the circumference, which is the thinnest part, measuring about 23 inches. Its average weight is about 20 ounces. In all these respects, however, it is subject to much variety. It presents two surfaces — namely, foetal and maternal or uterine. The fcetal surface is smooth and concave, and is looselv covered by the amnion, through which the branches of the umbilical arteries can be seen as they di\nde and subdivide before entering the organ. It is connected with the abdominal wall of the foetus at the umbilical orifice by means of the umbilical cord, which is attached to the placenta at, or near, the centre, as a rule. Some- times, however, the mnbilical cord is attached to some part of the margin of the placenta, which then bears a resemblance to a battle- dore. Under these circumstances it is known as a battledore- placenta. The maternal or uterine surface is convex, and constitutes the ■vault of the placenta. It is very irregular, being broken up into a number of polygonal masses or lobes, called cotyledons, which are arborescent tufts of chorionic villi. 1636 A MANUAL OF ANATOMY At its circumference the placenta is connected with the chorion leve, decidua capsularis or reflexa, and decidua vera. The usual site of the placenta is the posterior wall of the cavity of the body of the uterus near the fundus. It may, however, be attached to any part of the internal surface of the body of the uterus. When it is implanted over the os uteri internum, it forms the lowest of the contents of the gravid uterus, and under these circumstances it gives rise to the condition called placenta prcevia, or placental presen- tation. In some of these cases the placenta is attached round the entire circumference of the os uteri internum, this condition being known as complete placenta prcevia, or placenta centralis. In other cases the attachment of the placenta in this region is incomplete, and such a condition is spoken of as partial placenta prcevia or placenta lateralis. The placenta consists of two parts — namely, foetal and maternal or uterine, which cannot be separated from each other. Fig. 675. —Placenta : Fcetal and Maternal Surfaces. Fcetal Part of the Placenta. — ^The foetal or chorionic part consti- tutes the largest portion of the placenta. It is formed by the chorion frondosum, which is joined by the chorionic end of the allantoic stalk. The chorion leve takes no part in its formation, the villi of the chorion leve, at first few and scattered, becoming atrophied. The villi of the chorion frondosum are of large size, and they undergo ramifications, forming, as stated, arborescent tufts or cotyledons. Some of these villi are attached to the maternal part of the placenta, with which they become continuous. Hence the foetal and maternal parts cannot be separated from each other. These attached villi are, as previously stated, called fixation- or root- villi. Other villi project into, and lie free within, the maternal blood-lacunae, where they are bathed by the maternal blood. Each villus, as stated in connection with the chorion, consists of the following elements: (i) An external covering of ectoderm, the superficial lamina of which is formed by syncitium, and (2) a core of GENERAL EMBRYOLOGY 1637 somatic mesoderm. This core contains an arteriole, capillaries, and a venous radicle. As the arteriole traverses the mesodermic core of the \'illus it gives off minute twigs, which form a rich capillary network, lying close beneath the surface, from which the blood passes into the venous radicle. At the free extremity' of the villus the arteriole is connected with the commencement of the venous radicle by a capillary loop. Maternal Part of the Placenta. — ^The maternal or uterine part forms a small portion of the entire placenta, corresponding to the ■convex uterine surface or vault, and it is developed from the decidua basalis or serotina of the uterine mucosa. The decidua basalis or serotina consists, at an early period, of the three strata which characterize the decidua vera — namely, the stratum compactum, stratum spongiosum, and stratum profundum. As the ovum sinks into the decidua basalis, in order to grip the uterine mucosa, the -mus; and (4) the embryonic liver. The blood-platelets may represent portions of disintegrated leuco- cytes, cr they may be fragments of the multi-nucleated giant-cells of bone-marrow. The organs concerned in the formation of blood-corpuscles are spoken of as hcematopoietic (blood-forming) organs. The process of vascularization invades the entire wall of the yolk- sac, and is brought about in a manner similar to that which afiects the vascular area. The splanchnopleure is invaded by cell-cords; the superficial cells of these cords form the endothelial linings of the vessels; and the contained ceU-cord, in each case, becomes hollowed out to form the lumen of the vessel. This process of vascularization extends along the vitelline duct, and in this manner the vessels are brought within the body of the embryo. Thereafter they become connected with the primitive heart, which at this stage is undergoing development. \Vhen this connection has been effected — direct as regards the vitelline veins, but indirect as regards the viteUine arteries — ^the vitelline circula- tion is established, by means of which nutritive materials are con- veyed from the yolk-sac to the embryo (chick or rabbit). The Vitelline Circulation. The bloodvessels concerned in the vitelline circulation are four in number — ^namely, (i) the two vitelline or omphalo-mesenteric veins, and (2) the two vitelline or omphalo-mesenteric arteries — ^there being an intervening system of vessels, of the nature of capillaries, and a blood-channel, called the sinus terminalis. The sinus terminalis surrounds the vascular area of the yolk-sac, and the numerous capillar^' vessels proceeding from it give rise by their confluence to the two vitelline veins. These veins, having entered the body of the embryo, pass along the primitive intestinal 1642 A MANUAL OF ANATOMY tube to the sinus venosus, which is situated close to the caudal or posterior end of the developing heart. The two vitelline arteries are branches of the two primitive dorsal aortcB, and are therefore connected with the developing heart only indirectly. The vitelline circulation is of little importance in Man, but it is a considerable factor in the case of oviparous animals — e.g., Birds — • the yolk in such animals being very abundant and specially nutri- tive. The Allantoic Circulation. As retrogression of the yolk-sac and vitelline circulation takes place, the nutritive and respiratory functions of the foetus are assumed by the allantois and allantoic circulation. The left vitel- line artery becomes entirely obliterated, but the proximal or intra-emhryonic portion of the right vitelline artery persists, and gives rise to the superior mesenteric artery. As previously stated, the allantois is a blind diverticulum from the ventral wall of the hind-gut. This diverticulum consists of splanchnopleure — ^that is to say, entoderm and splanchnic meso- derm— ^which is continuous with the splanchnopleure of the wall of the gut. This part of the allantois is known as the allantoic diver- ticulum. At the umbilical orifice it enters the allantoic stalk, which extends from the umbilicus to the placental area of the chorion, or chorion frondosum. The mesodermic tissue of the allantoic stalk contains the two allantoic arteries and the two allantoic veins. The allantoic arteries grow from the caudal ends of the two primitive dorsal aortcB. In the region of the chorion frondosum they divide into branches which enter the cotyledons or tufts of arborescent chorionic villi, and render these important structures vascular. In this manner the peripheral part of the allantoic stalk and the chorion frondosum are brought into continuity. The blood is conveyed from the primitive dorsal aortas to the chorion frondosum by the allantoic arteries, which leave the body of the foetus through the umbilical orifice; and, after having undergone the necessary changes, it is conveyed back into the body of the foetus by the allantoic veins. These veins enter the foetal body through the umbilical orifice, and, after passing along the intestinal tube, they open into the sinus venosus at the caudal or posterior end of the developing heart. The foregoing constitutes the allantoic circulation, which is of special importance in Birds, Reptiles, and Fishes. In Man, how- ever, this circulation is of a transitory nature, and soon gives place to the placental circulation. The Placental Circulation. The nature of the placental circulation has been described in connection with the placenta. It is sufficient to state in this place GENERAL EMBRYOLOGY 1643 that the bloodvessels concerned in it are the two umbilical arteries and the two timbilical veins (there being two such veins at an early period) . The umbilical arteries replace the allantoic arteries, and they originally grow from the caudal ends of the two primitive dorsal aorta. They carry impure blood from the foetus to the placenta, where it is purified and furnished with nutritive materials from the maternal blood b\- a process of osmosis. The umbilical veins replace the allantoic veins, and they convey pure blood from the placenta to the body of the foetus. At an early stage, to which this description only applies, they terminate in the sinus venosus. These umbilical veins have been already referred to in connection with the development of the veins. Development of the Pericardial, Pleural, and Peritoneal Cavities, Septum Transversum, and Diaphragm. The coelom, body-cavity, or pleuro-peritoneal cavity is the space which lies between the somatopletire of the body-wall and the splanchnopleure of the primitive alimentary tube. It is originally a single ca\'ity, but is subsequently divided into (i) the pericardial cavity ; {2) the pleural cavities, right and left ; and (3) the peritoneal ca\4ty. The pericardial and pleural cavities are situated in the thorax, and the peritoneal cavity is situated in the abdomen, the septum between the thorax and the abdomen being formed by the diaphragm. Pericardial Cavity. — In connection with the development of the heart, it has been stated that the rudiments of that organ take the form of two tubes, which are hollowed out in the splanchnic meso- derm. These two tubes, approaching each other, fuse and form a single longitudinal tube, or primitiv'e heart, which lies mesially along the ventral aspect of the phar>Tigeal part of the fore-gut. It has been further stated that the primitive heart is connected with the. ventral body-wall b}' a bilaminar fold of splanchnic mesoderm, called the ventral meoscardium, and with the phar^Tigeal part of the fore- gut by another similar fold, called the dorsal mesocardium. These folds soon disappear — the ventral mesocardium entirely, and the dorsal mesocardium to a large extent. There are also two lateral mesocardia — right and left — which are continuous with the ventral margin of the septum transversum, each of these containing a duct of Cuvier on its way to the sinus venosus of the heart. The heart is developed in the splanchnic mesoderm of the peri- cardial region (cardiac portion of the ventral mesentery), the portion of that mesoderm which is ventral to the primitive heart being the ventral mesocardium, whilst the portion dorsal to the primitive heart forms the dorsal mesocardium. The part of the coelom which corresponds to the pericardial region is known as the pericardio- thoracic cavity, and it gives rise to the pericardial cavity. This latter cavity is subsequently shut off from the peritoneal cavity by the i644 A MANUAL OF ANATOMY septum iransversum, which gives rise to the ventral portion of the diaphragm. The pericardial cavity is also shut off from the two pleural cavities by the formation of the pieuro-pei'icardial membrane. Finally, the pleural cavities are shut off from the peritoneal cavity by the pleuro-periioneal membranes, which give rise to the dorsal part of the diaphragm. Demarcation of the Pericardial Cavity. — ^The pericardial cavity is the first of the divisions of the coelom to be differentiated. As stated, it is cut off from the peritoneal cavity by the septum trans- versum, which gives rise ts the ventral portion of the diaphragm. Septum Transversum. — ^This is a thick, incomplete lamina of mesoderm, which is situated at the caudal end of the pericardial region on a level with the third and fourth cervical somites. It separates the sinus venosus of the primitive heart within the peri- cardial portion of the coelom or body-cavity from the primitive stomach and intestinal tube, within the peritoneal portion of the coelom. At first it occupies an almost horizontal plane, but, as the heart extends dorsal wards, it gradually assumes an oblique plane, the ventral attachment of the septum descending, so that the direction of the plane is do rso-ventral wards. As just stated, the septum is incomplete, the deficient part being situated dorsally, and its attachments are as follows: Ventrally (anteriorly) it is at- tached tp the ventral wall of the coelom, in which situation it receives the vitelline and umbilical veins on their way to the sinus venosus of the primitive heart. Laterally it is attached to the lateral wall of the coelom on either side (lateral mesocardia), where it receives the corresponding duct of Cuvier, these two ducts being likewise on their way to the sinus venosus. Dorsally the margin of the septum may be divided into three parts — ^mesial and two lateral, right and left. The mesial part faces, and is soon closely connected with, the ventral aspect of the primitive duodenum, at the place where the hepatic diverticulum makes its appearance. The lateral parts of the dorsal margin are free and form the ventral boundaries of the peritoneal openings of the two thoracic (pleural) recesses of the peritoneum. As development proceeds, the septum transversum becomes separated into three layers — cephalic, mesial, and caudal. The cephalic or pericardial layer becomes the diaphragmatic portion of the pericardial wall. The middle or diaphragmatic layer gives rise to the ventral portion of the diaphragm. The caudal or hepatic layer becomes separated from the middle or diaphragmatic layer, as the development of the liver from the hepatic diverticulum proceeds within it, and this layer gives rise to the connecting tissue of the liver. The deficiency left by the septum transversum dorsally is filled up by the two pieuro-peritoneal membranes, right and left, to be presently described, and in this manner the dorsal part of the dia- phragm is formed. ' '"''[' As stated, the septum transveiium is incomplete dorsally. On GENERAL EMBRYOLOGY 1645 either side of the fore-gut and its dorsal mesentery there is a pro- longation of the peritoneal cavity into the thorax. These thoracic prolongations are narrow cleft-like passages, known as the thoracic or pleural recesses, and they represent the primiiive pleural cavities. They communicate ventralwards with the dorsal aspect of the peri- cardial cavity by the pleuro-pericardial openings, and caitdalwards with the peritoneal cavity by the pleuro-peritoneal openings. The lung-buds of the pulmonary diverticula abut against these dorsally placed thoracic or pleural recesses in a ventro-lateral direction. As the lung-buds grow, the primitive pleural cavities (thoracic recesses) extend ventro-laterally, gradually displacing the pjirietal pericardium from the body-wall in a mesial direction. Subsequently they surround the pericardial ca\'ity, except on its ventral and cauda.! aspects. The coelom, or body-cavity, originally single, is now divided into four compartments — pericardial, two pleural, and peritoneal — all of which communicate with one another. The pericardial cavity is shut off from the pleural cavities by the formation of the pleuro-pericardial membrane. This membrane is derived from (i) the right and left lateral mesocardia, and (2) a portion of the dorsal mesocardiimi. The lateral mesocardia (pleuro- pericardial folds) grow in the form of two curtains towards the mesial line, and unite with a portion of the dorsal mesentery to form the pleuro-pericardial membrane. The pericardial cavity is now completely isolated from the pleural cavities. At an earlier date it is shut off from, the peritoneal cavity by the septum transversum. The parietal pericardium is derived from (i) the somatic mesoderm of the somatopleure of the body-wall, which has been displaced mesially by the growth of the lungs ; (2) the cephalic or pericardial layer of the septum transversum; and (3) the pleuro-pericardial membrane. The visceral pericardium is derived from the splanchnic mesoderm of the primitive cardiac tube. Pleural Cavities. — ^These cavities are formed by the thoracic or pleural recesses of the peritoneal cavity, on either side of the fore- gut and its dorsal mesentery. They originally communicate ven- trally with the dorsal aspect of the pericardial cavity by the pleuro- pericardial openings, and with the peritoneal cav'ity by the pleuro- peritoneal openings. As the lung -buds of the pulmonary diverticula grow, each carries along with it splanchnic mesoderm continuous with that of its diverticulum, and the superficial part of this splanchnic mesoderm ultimately forms the visceral pleura. This explains why the lungs lie behind the pleural sac. The parietal pleura is derived from the somatic mesoderm of the somatopleure of the body- wall. Closure of Pleuro-Peritoneal Openings. — The closure of these openings is effected by the pleuro-peritoneal membranes, each of which is formed by the growth ventralwards of the mesoderm of the dorsal body- wall. When this mesoderm reaches the ventral boundary of the pleuro-peritoneal opening on either side, it joins 1646 A MANUAL OF ANATOMY the free lateral portion of the dorsal margin of the septum trans- versum. In this manner the pleural compartments of the ccelom are shut off from the peritoneal compartment, and the diaphragm is completed dorsally. At an earlier date the pleural cavities are shut off from the pericardial cavity by the pleuro-pericardial mem- brane. The four divisions of the originally single coelom or body- cavity now constitute four serous sacs, quite independent of each other — namely, pericardial, pleural, right and left, and peritoneal. From what has been stated it will be evident that the pleural sacs or cavities are originally thoracic prolongations of the peritoneal cavity, from which they are shut off by the pleuro-peritoneal mem- branes. At the caudal end of the peritoneal cavity there are two somewhat similar scrotal prolongations, called the processus vaginales, one on either side. These prolongations are, as a general rule, shut off from the peritoneal cavity by the closure of their upper ends. The lower part of each process forms the tunica vaginalis. The corresponding prolongations in the female are known as the canals of Nuck. The diaphragm, as stated, is developed in two parts, ventral and dorsal. The ventral portion is formed from the middle layer of the septum transversum, whilst the dorsal portion is developed from the two pleuro-peritoneal membranes. In very rare cases the dorsal portion of the diaphragm may fail to unite with the ventral portion on one or both sides, due to an arrest in the development of one or both pleuro-peritoneal membranes, and this condition is spoken of as an arrest in the development of the diaphragm. Under such cir- cumstances a communication exists between the peritoneal and thoracic cavities. If a part of an abdominal viscus should protrude into the thoracic cavity through such an aperture, the condition is known as a congenital diaphragmatic hernia. Musculature of the Diaphragm. — ^As stated, the septum trans- versum is, at first, on a level with the third and fourth cervical somites. The muscular tissue of the diaphragm is, in part, derived from the myotomes of these segments, especially the fourth seg- ment, and, it may be, the fifth also, which explains why the muscle is supplied by the phrenic nerve, the two chief roots of that nerve being derived from the anterior primary divisions of the third and fourth cervical spinal nerves. 'mnJhs*T-fm! APPENDIX. ANATOMICAL NOMENCLATURE. OSTEOLOGY. (Skeletal System). Vertebral Column. ENGLISH. Odontoid facet of Atlas. Axis. Lateral mass of Sacrum. Auricular surface of „ LATIN (BASLE). Fovea dentis. Epistropheus. Pars lateralis. Facies auricularis. Thorax. False, or asternal, Ribs. Ensiform process of Sternum. Interclavicular notch of ,, Gestae spurige. Processus xiphoideus. Incisura jugularis. Bones of the Head. Occipital Bone. Anterior condylar foramen. Jugular process. Superior curved line. Inferior ,, ,, Groove for lateral sinus. Parietal Bone. Internal surface. Posterior border. Anterior ,, Superior „ Inferior „ Parietal eminence. Os Occipitale. Canalis condyloideus. Tuberculum jugulare. Linea nuchae superior, „ ,, inferior. Sulcus transversus. . Os Parietale. Facies cerebralis. Margo occipitalis. „ frontalis. „ sagittalis. „ squamosus. Tuber parietale. 1647 1648 APPENDIX ENGLISH. Frontal Bone. Frontal eminence. Superciliary ridge. Supra-orbital arch. External angular process. Temporal Bone. Fissure of Glaser. Glenoid fossa. Articular eminence. Mastoid Portion. Digastric groove. Petrous Portion. Aqueduct of Fallopius. Gasserian depression. Vaginal process. Aqueduct of the cochlea. Eustachian canal. Sphenoid Bone. Pituitary fossa. Olivary eminence. Carotid groove. Sphenoidal turbinate bones. Optic groove. External pterygoid plate. Internal „ „ Eustachian groove. Ethmoid Bone. Lateral mass. Os planum, or orbital plate. Superior Maxillary Bone. Orifice of the antrum. Lachrymal groove. Nasal process. Malar process. .; Incisor canal. Alveolar bordetje*? hO Malar Bone. Malar canal. Lachrymal Bone. Hamular process. LATIN (BASLE). Os Frontale. Tuber frontale. Arcus superciliaris. Margo supra-orbitalis. Processus zygomaticus. Os Temporale (Temporis). Fissura petrotympanica. Fossa mandibularis. Tuberculum articulare. Pars Mastoidea. Sulcus mastoideus. Pars Petrosa. Canalis facialis. Impressio trigemina. Vagina processus styloidei. Canaliculus cochleae. Semicanalis tubae auditorise. Os Sphenoidale. Fossa hypophysea. Tuberculum sellae. Sulcus caroticus. Conchae sphenoidales. Sulcus chiasmatis. Lamina lateralis. ,, medialis. Sulcus tubae auditoriae. Os Ethmoidale. Labyrinthus ethmoidalis. Lamina papyracea. Maxilla. Hiatus maxillaris. Sulcus naso-lacrimalis. Processus frontalis. „ zygomaticus. Canalis incisivus. Limbus alveolaris. Os Zygomaticum. Canalis zygomatico-orbitalis. Os Lacrimale. Hamulus lacrimalis. APPENDIX 1649 ENGLISH. LATIN (bASLE). Inferior Turbinate Bone. Concha Inferior. Palate Bone. Os Palati. Inferior turbinate crest. Superior „ „ Crista conchalis. „ ethmoidalis. Inferior Maxillary Bone. Mandibula. Condyle. Sigmoid notch. Inferior dental foramen. Processus condylaris. Incisura mandibularis. Foramen mandibulare. Hyoid Bone. Os Hyoideum. Teeth. The Teeth. Denies. Ivory. Enamel, Nasmyth's membrane. Dental arch. Wisdom tooth. Substantia ebumea. „ adamantina. Cuticula dentis. Arcus dentalis. Dens serotinus. Bones of the Upper Limb. Humerus. Humerus. Bicipital groove. Sulcus intertubercularis. Radius. Radius. Bicipital tuberosity. Sigmoid cavity. Tuber radii. Incisura ulnaris. Ulna. Ulna. Great sigmoid cavity. Incisura semilunaris. Hand. Manus. Carpus. Carpus. Scaphoid bone. Semilunar bone. Cuneiform or pyramidal Pisiform bone. Trapezium. Trapezoid. Os magnimi. Unciform bone. bone. Os naviculare manus. Os lunatum. Os triquetrum. Os pisiforme. Os multangulum ma jus. Os multangulum minus. Os capitatum. Os hamatum. Thumb. Index finger. Middle „ Ring Little Pollex. Index. Digitus medius. ,, minimo - proximus vel annularis. Digitus minimus. 104 1650 APPENDIX Bones of the Lower Limb. ENGLISH. LATIN (bASLE). Hip-bone. Os Coxae, Articular surface of acetabulum. Cotyloid notch. Facies lunata. Incisura acetabuli. Ilium. Os Ilii. Ilio-pectineal line. Linea arcuata. Ischium. Os Ischii. Os Pubis. Os Pubis. Pubic spine. Tuberculum pubicum. Pelvis. Pelvis. Brim. Outlet. Apertura superior. „ inferior. Femur. Os Femoris. Depression for ligamentum teres. Outer lip of linea aspera. Inner „ Popliteal surface. Fovea capitis. Labium laterale. „ mediale. Trigonum femoris. Foot. Pes. Tarsus. Tarsus. Scaphoid bone. Great toe. Sinus pedis. Os naviculare pedis. Hallux. Sinus tarsi. ARTHROLOGY. (Articulations or Joints). (L. = Ligamentum). Vertebral Column. Intervertebral discs. Circumferential fibro-laminar part of disc. Central pulp of disc. Anterior common ligament. Posterior „ „ Occipito-atlantal ligaments. Fibro - cartilagines interverte- brales. Annulus fibrosus. Nucleus pulposus. L. longitudinale anterius. L. „ posterius. Membranae atlanto-occipitales. APPENDIX 1651 BNGZJSH. Lateral odontoid, or alar, liga- ments. Middle odontoid ligament. Cruciform ligament. LATIN (BASLE). Ligamenta alaria. L. apicis dentis. L. cniciatum. Thorax. Anterior costo- central, or stel- late, ligament. Interarticular ligament. Middle costo- transverse ligament. Anterior and posterior costo- stemal ligaments. L. capitis costae radiatum, L. capitis costae interarticulare. L. cervicis costae. Ligamenta stemo-costalia radiata. Upper Limb. Interarticular meniscus. Suprascapiilar ligament, Spino-glenoid ligament. Glenoid ligament of shoulder- joint. Internal lateral ligament of elbow-joint. External lateral ligament of elbow-joint. Pisi-uncinate ligament. Pisi-metacarpal ligament. Discus articularis. L. transversum scapulae su- perius. L. transversiun scapulae in- ferius. Labrum glenoidale. L. coUaterale ulnare. L. coUaterale radiale. L. piso-hamatum. L. piso-metacarpale. Pelvis. Great sacro-sciatic ligament. Small „ „ Inferior or subpubic ligament. Interpubic disc. L. sacro-ischio-tuberans. L. sacro-ischio-spinosum. L. arcuatum. Lamina fibro-cartilaginea inter- pubica. Lower Limb. ■Cotyloid ligament of hip-joint. Pubo-femoral ligament. External lateral ligament of knee-joint. Internal lateral ligament of knee- joint. Mucous ligament {ligament um mucosum). Alar ligaments. Labrmn glenoidale. L. pubo-capsulare. L. coUaterale fibulare. L. coUaterale tibiale. Plica synovialis pateUaris, Plicae alares. 1652 APPENDIX ENGLISH. Complexus. MYOLOGY. (Muscular Sj^tem), (M,= Musculus). Muscles of the Back. LATIN (baSLE). Semispinalis capitis. Muscles of the Upper Limb. Serratus magnus. Biceps flexor cubiti. Brachialis anticus. Triceps extensor cubiti. Long head of „ ,, External „ „ „ Internal ,, ,, ,, Pronator radii teres. Supinator radii longus. Supinator radii brevis. M. serratus anticus. M. biceps brachii. M. brachialis. M. triceps brachii. Caput, longum. „ laterale. „ mediale. M. pronator teres. M. brachio-radialis. M. supinator. Muscles of the Lower Limb. Quadriceps extensor cruris. Vastus externus. Crureus. Vastus internus. Subcrureus. Biceps flexor cruris. Flexor, or musculus, accessorius. M. quadriceps femoris. M. vastus lateralis. M. ,, intermedins. M. ,, medialis. M. articularis genus. Biceps femoris. M. quadratus plantte. Muscles of the Abdomen. Poupart's ligament. Gimbernat's ligament. Triangle of Petit. Ligamentum inguinale. ,, lacunare. Trigonum lumbale. Muscles of the Thorax. Triangularis sterni. Foramen quadratum of dia- phragm. Muscles of the Head. M. transversus thoracis. Foramen venae cavae inferioris. Epicranial aponeurosis. Compressor naris. Dilator alae nasi. Galea aponeurotica. M. nasalis transversus. M. „ alaris. APPENDIX 1653 ENGLISH. Depressor alae nasi. Orbicularis palpebrarum. Tensor tarsi. Depressor labii inferioris. Palato-glossus. „ pharyngeus. Azygos uvulae. Lingualis superficialis, „ inferior. LATIN (BASLe). M. depressor septi. M. orbicularis oculi. Pars lacrimalis musculi orbicu- laris oculi. M. quadratus labii inferioris. M. glosso-palatinus. M. pharyngo-palatinus. M. uvulae. M. longitudinalis superior. M- „ inferior. ANGEIOLOGY. (Vascular and Lymphatic Systems). Heart. Auriculo-ventricular groove. Antero-superior surface. Inferior surface. Vestigial fold of Marshall. Auricle. Interauricular septum. Columnae cameae. Annulus ovalis. Foramina Thebesu. Tubercle of Lower. Eustachian valve. Thebesian valve. Cor. Sulcus coronarius. Facies stemo-costalis. „ diaphragmatica. Ligamentum venae cavae si- nistrae. Atrium. Septum atriorum. Trabeculae cameae. Limbus fossae ovalis. Foramina venanim minimarum. Tuberculum intervenosum. Valvula venae cavae inferioris. „ sin (is coronarii. Interventricular Septum. Pars membranacea. Tricuspid Valve. Right cusp. Left or infundibular cusp. Posterior or septal cusp. Mitral Valve. Semilunar or Sigmoid Valves. Corpus Arantii. Septum Musculare Ventricu- lar urn. Septum membranaceum ventri- culorum, Valvula Tricuspidalis. Cuspis medialis. „ anterior. „ posterior. Valvula Mitralis vel Bicuspidalis. ValvuliB Semilunar es. Nodulus valvulae semilunaris. 1654 APPENDIX ENGLISH. LATIN (bASLE). Arteries. Arteriae. (A. = Arteria vel Arteriae). Pulmonary artery. Arch of the Aorta. A. pulmonalis. Arcus Aortae. Right coronary artery. Left „ A. coronaria dextra. A. „ sinistra. Innominate artery. Common carotid artery. A. anonyma. A. carotis communis. External Carotid Artery. A. Carotis Externa. Ranine artery. Facial „ A. profunda linguae. A. maxillaris externa. Inferior coronary artery. Superior „ „ A. labialis inferior. A. labialis superior. Internal Maxillary Artery. Vidian artery. Circle of Willis. Subclavian Artery. Internal mammary artery, Superior phrenic artery. Thyroid axis. Suprascapular artery. Axillary Artery. Superior thoracic. Acromio-thoracic artery. Long thoracic artery. Dorsalis scapulae artery. Anterior circumflex artery. Posterior „ ,, Brachial Artery. Superior profunda artery. Inferior ,, „ Anastomotic artery. Radial Artery. Superficial volar artery. Anterior radial carpal arlery. Radialis indicis artery. Ulnar Artery. Common interosseous artery. Anterior . „ „ Posterior ,, ,, A. Maxillaris Interna. A. canalis pterygoidei. Circulus arteriosus. A. Subclavia. A. mammaria interna. A. pericardiaco-phrenica. Truncus thyreo-cervicalis. A. transversa scapulae. A. Axillaris. A. thoracalis suprema, A. thoraco-acromialis. A. thoracalis lateralis. A. circumflexa scapulae. A. circumflexa humeri anterior. A. ,, ,, posteriori! A. Brachialis. A. coUateralis superior. A. ,, media. A. „ inferior. A. Radialis. A. volaris superficialis. A. radialis carpea volaris. A. radialis volaris indicis. A. Ulnaris. A. interossea communis. A. „ volaris. A. ,, dorsalis. APPENDIX 1655 Anterior ulnar carpal artery. Posterior ,, „ Profunda artery. Superficial palmar arch. Deep palmar arch. Abdominal Aorta. Capsular arteries. Spermatic „ Coeliac axis. Gastric (coronary) artery. Splenic Artery. Vasa brevia. Hepatic Artery. Pyloric artery. Superior Mesenteric Artery. Rami intestini tenuis. Right colic artery. Middle „ LATIN (BASLE). A. ulnaris carpea volaris. A. „ „ dorsalis. A. volaris profunda. Arcus volaris super ficialis. Arcus „ profundus. Aorta Abdominalis. A. suprarenales. A. spermatic* intemse. A. coeliaca. A. gastrica sinistra. A. Lienalis. A. gastricae breves. A. Hepatica. A. gastrica dextra. A. Mesenterica Superior. A. intestinales. A. colica dextra. A. „ media. Inferior Mesenteric Artery, Left colic artery. Sigmoid arteries. Internal Iliac Artery. Gluteal artery. Sciatic „ Artery of the vas deferens. Internal Pudic Artery. Superficial perineal artery. Artery of the bulb. „ „ corpus caver- nosum. External Iliac Artery. Deep epigastric artery. Cremasteric artery. Femoral Artery. Anastomotic artery. A. Mesenterica Inferior, A. colica sinistra. A. sigmoideae. A. Hypogastnca. A. glutsea superior. A. ,, inferior. A. deferentialis. A. Pudenda Interna. A. perinaei. A. bulbi urethrae. A. profunda penis vel clitoridis. A. Diaca Externa. A. epigastrica inferior. A. spermatica externa. A. Femoralis. Arteria suprema genus. 1656 APPENDIX Popliteal Artery. Superior external articular artery. Superior internal articular artery. Middle or azygos articular artery. Inferior external articular artery. Inferior internal articular artery. Lower muscular or sural arteries. Plantar Arteries. Internal plantar artery. External „ ,, Dorsal Artery of Foot. Tarsal artery. Metatarsal artery. Veins. (V.=Vena Great cardiac or coronary vein. Small cardiac, or right conorary, vein. Middle cardiac vein. Smallest cardiac veins. Innominate veins. Vena azygos major, or Right azygos vein. Vena azygos minor inferior, or Lower left azygos vein. Vena azygos minor superior, or Upper left azygos vein. Facial vein. Temporo-maxillary vein. Common facial vein. Portal vein. Splenic vein. Internal iliac vein. Internal or long saphenous vein. External or short LATIN (BASLE). A. Poplitea. A. superior lateralis genus. A. ,, medialis „ A. media genus. A. inferior lateralis genus. A. ,, medialis „ A. surales. A. Plantares. A. plantaris medialis. A. „ lateralis. A. Dorsalis Pedis. A. tarsea lateralis. A. arcuata. Venae. vel Vense). V. magna cordis. V. parva ,, V. media ,, V. minimae „ V. anonymae, dextra et sinistra. V. azygos. V. hemi-azygos. V. „ accessoria. V. facialis anterior. V. „ posterior. V. ,, communis. V. portae. V. lienalis. V. hypogastrica. V. saphena magna. V. „ parva. Sinuses of the Dura Mater. Superior longitudinal sinus. Inferior „ „ Straight sinus. Circular „ Basilar „ Lateral „ Cavernous sinus. Sinus Durse Matris. (S. = Sinus). S. sagittalis superior. S. „ inferior. S. rectus. Sinfls intercavemosi. Plexus basilaris. S. transversus. S. cavemosus. APPENDIX 1657 Lymphatic System. Thoracic duct. Receptaculum chyli. Right l5maphatic duct. LATIN fBASLE). Systema Lymphaticum. Ductus thoracicus. Cistema chyli. Ductus lymphaticus dexter. (The Spinal Cord. Cervical enlargement. Lumbar „ Anterior column. Lateral „ Posterior „ G)lumn of Goll. ,, Burdach. Anterior comu. Posterior ,, Lateral „ Central canal. Clarke's column. NEUROLOGY. Nervous System). Medulla Spinalis. Intumescentia cervicalis. ,, lumbalis. Funiculus anterior. „ lateralis. „ posterior. gracHis. „ cuneatus. Colimana grisea anterior. „ „ posterior. „ „ lateralis. CanaJis centralis. Nucleus dorsalis. Tracts in the Spinal Cord. Tract of Goll. ,, Burdach. Direct cerebellar tract. Tract of Gowers. Pyramidal tract, lateral or crossed part. Pyramidal tract, anterior or direct part (column of Tvirck.) Antero-lateral descending cere- bellar tract. Anterior ground -bundle. Lateral Fimiculus gracilis. ,, cuneatus. Fasciculus dorso-lateralis cere- bello-spinahs. Fasciculus antero-lateralis cere- bello-spinaJis. Fasciculus cerebro - spinalis lateralis. Fasciculus cerebro-spinalis an- terior. Fasciculus cerebello-vestibulo- spinalis. Fasciculus anterior proprius. „ lateralis proprius. Encephalon. Bulb. Pyramid. Olivary body or eminence. Restiform Body. Fillet. Medulla Oblongata. Pjnramis. Corpus olivare vel Oliva. Corpus Restiforme. Lemniscus. 1658 APPENDIX Decussation of the Fillets, Superior medullary velum (Valve of Vieussens). Inferior medullary velum. Red nucleus. Superior quadrigeminal bodies. Inferior ,, „ Stratum cinereum. Aqueduct of Sylvius. Crusta or Pes of the Crus Cerebri. Pineal body. Ganglion habenulse. Middle or grey commissure. Corpora albicantia. Bundle of Vicq d'Azyr. Optic tract. Optic commissure. Nucleus of Luys. Great longitudinal fissure. Fissure of Sylvius. Fissure of Rolando. Quadrate lobule of Parietal Lobe. Island of Reil. Threshold of the Island of Reil. Convolution of the Corpus Cal- losum. Limbic Lobe. Uncus. Hippocampus major. Dentate Gyrus. Lyra or Psalterium. Cuneate Lobule. Radiation of the Corpus Callosum. Forceps minor. Forceps major. Anterior pillars of the Fornix. Posterior ,, ,, „ Septum lucidum. LATIN (BASLE). Decussatio lemniscorum. Velum meduUare superius vel anterius. Velum medullare inferius vel posterius. Nucleus ruber. CoUiculi superiores. „ inferiores. Stratum griseum. Aquaeductus cerebri. Basis pedunculi. Corpus pineale. Nucleus habenulse. Commissura mollis. Corpora mammillaria. Fasciculus thalamo-mammil- laris. Tractus opticus. Chiasma opticum. Corpus subthalamicum vel Nu- cleus hypothalamicus. Fissura interhemispherica. Fissura lateralis. Sulcus centralis. Praecuneus. Insula. Limen insulae. Gyrus fornicatus. Gyrus fornicatus et gyrus hip- pocampi. Uncus gyri hippocampi. Hippocampus. Fascia dentata hippocampi. Commissura hippocampalis. Cuneus. Radiatio corporis callosi. Pars frontalis. „ occipitalis. Columnae fornicis. Crura fornicis. Septum pellucidum. Lateral Ventricles. Anterior horn. Middle or Lateral horn. Posterior horn. Ventriculi Laterales. Cornu anterius. ,, inferius. „ posterius. APPENDIX 1659 ENGLISH. Third Ventricle, Fourth Ventricle. Fifth Ventricle. Meninges. Epidural space. Subdural ,, Subarachnoid space. Pacchionian Bodies. LATIN (basle). Ventriculus tertius. Ventriculus quartus. Ventriculus quint us vel Cavum septi peUucidi. Meninges. Cavum epidurale. „ subdurale. „ subarachnoidale. Granulationes arachnoidales. Cerebro-spinal Nerves. (N. = Nervus vel Nervi). Cranial Nerves. First or Olfactory nerve. Second or Optic nerve. Third or Oculo-motor nerve. Fourth or Trochlear nerve. Fifth or Trigeminal nerve. Superior maxillary nerve. Inferior „ ,, Sixth or Abducent nerve. Seventh or Facial nerve. Eighth or Auditory nerve. Ninth or Glosso-pharyngeal nerve. Jugular ganglion of ,, Petrous ganglion of ,, Jacobson's ner\x. Tenth or Pneumogastric nerve. Ganglion of Root of „ Ganglion of Trunk of ,, Arnold's nerve. Eleventh or Spinal Accessory nerve. Twelfth or Hypoglossal nerv^e. Descendens cervicis (hypoglossi). Cer\accd Plexus. Small occipital nerve. Great auricular nerve. Superficial or Transverse cervical nerve. First cervical nerve. Great occipital nerve. Third or Least occipital nerve. Phrenic nerve. N. Cerebrales. N. Olfactorius. N. Opticus. N. Oculo-motorius. N. Trochlearis vel Patheticus. N. Trigeminus. N. Maxillaris. N, Mandibularis. N. Abducens. N. Facialis. N. Acusticus. N. Glosso-pharyngeus. Ganglion superius. „ petrosum. N. Tympanicus. N. Vagus. Ganglion jugulare. Ganglion nodosum. N. Auricularis. N. Accessorius. N. Hypoglossus. N. cervicalis descendens. Plexus Cervicalis. N. occipitalis minor. N. auricularis magnus. N. cutaneus colli. N. suboccipitalis. N. occipitaJis major. N. ,, minimus N. phrenicus. i66o APPENDIX ENGLISH. Brachial Plexus. Nerve to the Rhomboid Muscles. Long thoracic nerve, or External respiratory nerve of Bell. Anterior thoracic nerves. Median nerve. Ulnar „ Circumflex nerve. Long subscapular nerve. Twelfth thoracic „ Lumbar Plexus. Genito-crural nerve. Crural branch of ,, Genital branch of „ External cutaneous nerve. Obturator nerve. Anterior crural nerve. Internal or long saphenous nerve. Sacral Plexus. Small sciatic nerve. Great „ External popliteal, or Peroneal, nerve. Lateral cutaneous branch of peroneal nerve. Fibular communicating nerve. Tibial Musculo-cutaneous nerve. Anterior tibial nerve. Internal popliteal, or Tibial, nerve-. External or short saphenous nerve. Internal plantar nerve. External „ „ Deep division of plantar nerve. Pudic nerve. LATIN (basle). Plexus Brachialis. N. dorsalis scapulae. N. thoracalis longus. N. thoracales anteriores. N. medianus. N. ulnaris. N. axillaris. N. thoraco-dorsalis. N. subcostalis. Plexus Lumbalis. N. genito-femoralis. N. lumbo-inguinalis. N. spermaticus externus. N. cutaneus femoris lateralis. N. obturatorius. N. femoralis. N. saphenus. Plexus Sacralis. N. cutaneus femoris posterior. N. ischiadicus. N. peroneeus communis. N. cutaneus surae lateralis. N. anastomoticus peronaeus. N. communicans tibialis. N. peronaeus superficialis. N. ,, profundus. N. tibialis. N. cutaneus surae medialis vel N. suralis. N. plantaris medialis. N. plantaris vateralis. Ramus profundus. N. pudendus. Mouth. Lips. Cheeks. SPLANCHNOLOGY. (The Visceral System). Digestive System. Cavum oris. Labia oris. Buccae. APPENDIX 1661 Gums. Hard palate. Soft „ , Anterior pillar of the fauces. Posterior „ „ „ Tongue. Dorsum of the tongue. Inferior surface of the tongue. Parotid gland. Parotid, or Stensen's, duct. Glandula socia parotidis, Wharton's duct. Pharynx. Tonsils. Crypts of the tonsil. Pharyngeal tonsil. Fossa of Rosenmiiller. Orifice of the Eustachian tube. Eustachian cushion. Gullet ((Esophagus). Stomach. Fundus (Cardiac end). (Esophageal orifice. Pyloric orifice. Plicae villosae. Small Intestine. Valvulae conniventes. Glands of Brunner. Crypts of Lieberkiihn. Solitary glands. Agminated glands, or Peyer's patches. Large Intestine. Ileo-colic, or ileo-caecal, valve. Upper segment of „ „ Lower segment of ,, „ Retinacula of ,, „ Vermiform appendix. Ascending colon. Hepatic flexure. Transverse colon. LATIN (basle). Gingivae. Palatum durum. „ molle vel Velum pen- dtilum palati. Arcus glosso-palatinus. „ pharyngo-palatinus. Lingua. Dorsum linguae. Facies inferior. Glandula parotica. Ductus paroticus. Glandula parotica accessoria. Ductus submaxillaris. Pharynx. Amygdalae, vel Tonsillae pala- tinae. Fossulae tonsillares. Tonsilla pharyngea. Recessus pharyngeus. Ostium pharyngeum tubae audi- toriae. Torus tubae auditorise. Gula. Ventriculus. Fundus ventriculi. Cardia. Pylorus. Plicae gastricae. Intestinum Tenue. Plicae circulares. Glandulae duodenales. Glandulae intestinales. Noduli lymphatici solitarii. aggregati. Intestinum Crassum. Valvula coli. Labium superius. „ inferius. Frenula valvulae coli. Processus vermiformis. Colon vel Colum dextrum. Flexura dextra coli. Colon transversum vel medium 1 652 APPENDIX Splenic flexure. Descending colon. Iliac colon. Pelvic colon. Sacculi of colon. Crescentic folds between the sacculi. Rectum, Rectal valves, or Valves of Houston. Anal canal. Columns of Morgagni. Liver. Suprarenal impression. Gastric „ Colic ,, Renal ,, Duodenal ,, Omental tuberosity. Quadrate lobe. Caudate lobe. Fossa of the inferior vena cava, ,, (fissure) of the ductus venosus. Umbilical fissure. Portal, or Transverse, fissure. Fossa of the gall-bladder. Round ligament. Hepatic duct. Capsule of Glisson. Gall-bladder. Cystic duct. Common bile-duct. Spleen. Diaphragmatic surface. , Gastric surface. Renal ,, Basal „ Kidneys. Muscular surface. Visceral ,, Pyramids of Malpighi. Columnae Bertini. LATIN (BASLE). Flexura sinistra coli. Colon sinistrum. Colon iliacum. Colon pelvicum. Haustra coli. Plicae semilunares coli. Intestinum rectum. Plicae transversales recti. Pars analis intestini recti. Columnae canalis analis. Hepar. Impressio suprarenalis. „ gastrica. ,, colica. ,, renalis. ,, duodenalis. Tuber omentale. Lobus quadratus. Lobus vel Processus caudatus. Fossa venae cavas inferioris. ,, ductus venosi. „ venae umbilicalis. Porta hepatis. Fossa vesicae felleae. Ligamentum teres hepatis vel Ligamentum venosum. Ductus hepaticus. Capsula fibrosa. Vesica Fellea. Ductus cysticus. „ communis choledochus. Lien. Facies diaphragmatica. ,, gastrica. „ renalis, ,, basalis. Renes (singular, Ren). Facies muscularis. ,, visceralis. Pyramides renales. Columnae renales. APPENDIX 1663 ENGLISH. Medullary rays. Labyrinth. Malpighian corpuscles. Uriniferous tubules. Renal arteries. Renal veins. Urinary Bladder. Base of bladder. Summit, or Apex, of bladder. Body of bladder. Urethral orifice of bladder. Fibrous cord of the urachus. Peritoneal coat. External muscular coat. Middle ,, „ Internal „ „ Sphincter muscle. Submucous coat. Mucous coat. Male Reproductive Organs. Testicles. Tunica vaginalis testis. Tunica ,, scroti. Globus major of Epididymis. Globus minor „ Organ of Giraldes. Digital fossa. Coni vasculosi. Vas deferens. Spermatic cord. Penis. Upper surface of penis. Under Body of penis. Prepuce. Glands of Tyson. Corpora cavernosa. Corpus spongiosum. Prostate Gland. Base of prostate gland. Apex of „ LATIN (BAELE). Pars radiata. „ convoluta. Corpuscula renis. Tubuli renales. Arteriae renis. Vense renis. Vesica Urinaria. Fundus vesicae. Vertex vesicae. Corpus vesicae. Orificium internum urethrse. Ligamentum umbUicale medium. Tunica serosa. Stratum musculare extemmn. „ „ medium. ,, ,, internum. Annulus urethralis. . Tela submucosa. Tunica mucosa. Organa Genitalia Virilia. Testes. Lamina visceralis. „ parietalis. Caput epididymis. Cauda ,, Paradidymis. Sinus epididymis. Lobuli epididymis. Ductus testis. Fimiculus spermaticus. Penis. Dorsum penis. Facies urethralis. Corpus penis. Praeputium. Glandulae praeputiales. Corpora cavernosa penis. Corpus cavemosum urethrae. Glandula Prostatica vel Prostadica. Basis prostadis. Apex prostadis. 1664 APPENDIX ENGLISH. Male Urethra. Prostatic part. Membranous part. Spongy part. Meatus urinarius. Glands of Cowper. Glands of Littre. Female Reproductive Organs. Ovary. Upper, or Tubal, pole of ovary. Lower, or Uterine, pole of ovary. Anterior border of ovary. Peritoneal fold of ovary. Ligament of ovary. Peritoneal fossa of ovary. Graafian follicles. Discus proligerus. Fallopian Tube. Duct of Gartner. Hydatids of Morgagni. Uterus. Anterior surface. Posterior ,, Cavity of the cervix. Plicae palmatse. Broad ligament. Round ,, Peritoneal coat. • Vagina. Lower part of anterior column. Vulva, or Pudendum. Fourchette. Female urethra. Meatus urinarius. Mammary Gland. Glands of Montgomery. Galactophorous ducts. Ampulla of galactophorous duct. LATIN (bASLE). Urethra Virilis. Pars prostatica vel prostadica. „ membranacea. ,, cavernosa. Orificium externum urethrae. Glandulge bulbo-urethrales. ,, urethrales. Organa Genitalia Muliebria vel FeminSa. Ovarium. Extremitas tubalis. ,, uterina. Margo mesovarii. Mesovarium. Ligamentum proprium ovarii. Fossa ovarii. Folliculi vesiculosi oopherii. Cumulus oopherii. Tuba Uterina. Ductus epoopherii longitudi nalis. Appendices vesiculosi. Uterus. Facies vesicalis. „ intestinalis. Canalis cervicis uteri. Arbor vitae uterina. Ligamentum latum uteri. teres „ Tunica serosa. Vagina. Carina urethral is. Pudendum muliebre vel femi- neum. Frenulum labiorum pudendi. Urethra muliebris vel feminea. Orificium externum urethrse. • Mamma. Glandulae areolares. DuctQs lactiferi. Sinus lactiferus. - ' APPENDIX 1665 Larynx. Thyroid cartilage. Oblique line. Cricoid cartilage. Arytenoid cartilages. Cartilages of Santorini. Cartilages of Wrisberg. Epiglottis. Tubercle, or Cushion, of epiglottis. Superior aperture of the larynx. Cavity of the larynx. Superior thyro-arytenoidligament. Inferior thyro-arytenoid ligament. False vocal cords. True ,, „ False glottis. True ,. Vocal glottis. Respirator}^ glottis. Ventricle of the lar\Tix. Saccule LATIN (BASLE). Larynx. Cartilago thyroidea. Linea obliqua. Cartilago cricoidea. Cartilagines arytaenoides. „ comiculatae. „ cuneatae. Epiglottis. Pulvinar epiglottideum. Aditus laryngis. Cav-um laryngis. Ligamentum ventriculosum. „ vocale. Plicae ventriculosae. „ vocales. Glottis spuria. Glottis vera, vel Rima glottidis. Pars intermembranacea. ,, intercartilaginea. Ventriculus laryngis. Appendix ventriculi. Organs of Sense. Eye. Eyeball. Capsule of Tenon. Sclerotic coat. Canal of Schlemm. Membrane of Bowman. Membrane of Descemet, Demours. Choroid coat. Membrane of Bnich. Ciliarx' body. Zonula of Zinn. Valve of Hasner. Oculus vel Org^num visus. Globus oculi. Fascia bulbi. Sclera. Sinus venosus sclerae. Lamina elastica anterior, or of „ „ posterior. Tunica chorioidea. Lamina basalis. Corpus ciliare. Zonula ciliaris. Plica lacrimalis. Ear. Auris Organum Auditus. External Ear (Auricle). Auris Externa (Auricula). Upper portion of concha, above Cymba conchae. crus helicis. Lower portion of concha, below Cavum conchae, crus helicis. Tubercle of Daruan. Tuberculum auriculae. 105 1666 APPElSlDlX ENGLISH, Fossa of the helix. Fossa of the antihelix. Eminence on cranial aspect of concha. Hairs of tragus and antitragus. External auditory meatus. Sweat-glands of auditory meatus. Middle Ear. Tympanic cavity. Outer wall of ,, Inner „ Anterior wall ,, Posterior ,, ,, Roof ,, ,, Floor „ „ Tympanic Membrane. Shrapnell's membrane. External layer of tympanic membrane. Middle layer of tympanic mem- brane. Internal layer of tympanic mem- brane. Fenestra ovalis. Fenestra rotunda. Secondary membrane of the tympanum. Mastoid antrum. Eustachian tube. Tympanic orifice of tube. Pharyngeal „ Tympanic Ossicles. Malleus. Handle. Long process. Short LATIN (bASLe). Scapha, Fossa triangularis. Eminentia conchae. Barba hircina. Meatus acusticus externus. Glandulae ceruminosae. Auris Media. Cavum tympani. Paries membranacea. labyrinthica. carotica. mastoidea. tegmentalis. jugular is. Membrana Tympani. Membrana vel Pars flaccida. Stratum cutaneum, Membrana propria (Stratum radiatum et stratum circu- lare). Stratum mucosum. Fenestra vestibuli. „ cochleae. Membrana tympani secundaria. Antrum mastoideum vel tym- panicum. Tuba auditoria. Ostium tympanicum. „ pharyngeum. Ossicula Auditus. Malleus. Manubrium. Processus longus. brevis. Incus. Long process. Short Incus. Crus longum. ,, breve. APPENDIX 1667 ENGLISH. Stapes. Anterior cms. Posterior ,, Foot-plate. Internal Ear. Osseous Labyrinth. Vestibule. Fovea spherica. „ elliptica. Cochlea. Base of cochlea. Apex ,, Modiolus. Spiral canal of the modiolus. Interned auditory meatus. Membranous Labyrinth. Canal of Hensen. Membranous cochlea. Membrane of Reissner. Basilar membrane. Nose. Cartilage of the septum. Vomerine cartilage. Upper lateral nasal cartilage. Lower lateral nasal cartilage. Outer plate of nasal cartilage. Inner plate of ,, „ Superior meatus. Middle ,, Inferior ,, Glands of Bowman. LATIN' (BASLE). Stapes. Cms anterius. ,, posterius. Basis. Auris Interna. Labyrinthus Osseus. Vestibulum. Recessus sphericus. „ ellipticus. Cochlea. Basis. Cupola. Columella. Canalis spiralis modioli. Meatus acusticus intemus. Labyrinthus Membranaceus. Ductus reunien*. „ cochlearis vel Scala media. Membrana vestibularis. „ basilaris. Nasus. CartUago septi nasi. Cartilago vomero-nasalis Jacob- soni. Cartilago nasi lateralis superior. „ _ inferior vel Cartilago aperturae nasi. Cms laterale. Cms mediale. Meatus nasi superior. „ ,, medius. ,, ,, inferior. Glajidulae olfactoriae. GLOSSARY Abdomen, probably from ahdo, I hide or conceal ; perhaps a corruption of adipomen, from adeps, the. soft fat of animals. Aberrant, wandering from the normal source. Acerviilus, a little heap. Acetabulum, a vessel for holding vinegar ; a juggler's cup. Acinus, any juicy berry with stones, e.g., the grape ; the kernel in the berry. Acrocephalus, pointed or conical head. Acromion, the point or summit of the shoulder, Acustieus, -a, -um, pertaining to sound, or to the sense of hearing. Adamantoblast, enamel-germ. Adenoid, glandular. Aditus, an approach or access. Adrenal, near to, or pertaining to, the kidney. Advehens, carrying to. Afferent, carrying to. Agger, a mound or rampart. Agminated, in groups. Ala, a wing. Albicans, white. Albuginea, whitish. Allantois, sausage-like. Alveolus, a little trough. Alveus, a trough. Amacrine, without a long fibre. Ambiguus, dark, obscure. Ameloblast, enamel-germ. Ammonis, cornu, horn of Ammon, who was represented as having the head of a ram. Amphiarthrosis, literally, articu- lation on both sides. Ampulla, a flask. Amygdala, an almond. Anastomosis, literally, an outlet ; the communication of branches of vessels with one another. Anconeus, pertaining to the elbow. Ankylosis, bony union between two bones which are normally separate. Annulus, a little ring. Ansa, a handle, haft, or brace. Anserinus, pertaining to a goose. Antecubital (Anticubital), before the elbow. Anticus, in front, anterior. Antinion, facing the inion. Antrum, a cave or cavity. Anus, a ring. Aorta, literally, the lower end of the trachea; a carrier. Aponeurosis, an expansion from a tendon. Apophysis (' grow from '), a process or swelling on a bone. Arachnoid, like a spider's web. Archenteron, primitive intestine. Arcuatus, curved. Areola, a small open place. Artery, literally, the trachea; a bloodvessel which carries the blood from the heart. 1668 GLOSSARY 1669 Arthrodia, from a Greek word meaning ' a joint ' ; gliding is implied. Arytenoid, pitcher-like. Aspera, rough. Asterion, a star. Astragalus, the ankle-bone ; a die (pi. dice). Atlas, a support. Atresia, imperf oration. Atrium, the hall in a Roman house. Attollens, raising up, elevating. Attrahens, drav/ing to or to- wards. Auditory, pertaining to the organ, or sense, of hearing. Auricle, the external ear. Azygos, without a yoke, single. Bacillary, pertaining to a small staff or rod. Balanus, an acorn. Barba, a beard. Basilar, belonging to the base. Basilic, royal, important. Basion, base. Biceps, having two heads. Bicornis, two-homed. Biventer, having two bellies. Brachium, the arm. Braehycephalic, short-headed. Bregma, from a Greek verb meaning ' to moisten.' Bronchial, pertaining to the windpipe. Bronchiole, a little bronchus. Bronchus, literally, a draught ; the windpipe. Bubonocele, a tumour in the groin. Buccinator, a trumpeter. Bulla, a knob. Bursa, a sac containing fluid. Cactimen, tip, peak, or end. Caecum, blind. Caeruleus, dark blue. Calamus, a reed-pen. Calcaneum, the heel. Calcar, a spur. Calcination, reduction to a pow- der (or lime) by heat. Calcis, of the heel. Calix, a cup or goblet. Callosum, hard, thick. Calvaria {calva, the bald scalp), the upper part of the skull. Cancellated, lattice-formed, re ticulated. Caninus, canine. Cwiithus, the angle of the eye. Capillary, pertaining to the hair : a vessel of hair-like minute- ness. Capitellum, a small head. Cardia, the opening of the stomach ; the heart. Cardiac, pertaining to the heart. Cardinal, principal or chief. Carina, a keel. Carneae, pertaining to flesh. Carotid, stupefying ; or perhaps from two Greek words mean- ing ' head ' and ' ear.' Carpus, the wTist. Caruneula, a little piece of flesh. Cauda, a tail. Caudal, pertaining to a tail. Caudate, pertaining to a tail. Cavernous, full of hollows or cavities. Centimetre (cm.), f of an English inch. Cephalic, pertaining to the head. Cerato, horny. Ceruminous, pertaining to wax. Chiasma, two lines placed like anX. Choana, a funnel. Choledochus, bile-receiving. Chondral, pertaining to carti* lage. Choroid (Chorioid), like skin. Cinereus, ash-coloured. Cingulum, a small girdle. Circumflexus, bent around. Cisterna, a cistern or reservoir. 1670 GLOSSARY Claustrum, a bolt, barrier, or inclosure. Clava, a club. Clavicle, from clavis, a key. Cleido-, pertaining to the clavicle. Clinoid, like the knob of a bed- post. Clitoris, from a Greek verb meaning ' I shut up ' or ' enclose.' Clivus, a slope. Cloaca, a sewer or drain. Coccyx, a cuckoo. Cochlea, a snail. Cochleariformis, spoon-like. C(Eliac, pertaining to the belly. CoUieulus, a little hill. Colon, the great gut. Comes, a companion. Complexus,, literally, folded to- gether; encompassing. Concatenatse, chained together. Concha, a shell. Condyle (' knuckle '), a small round prominence covered by cartilage. Conjunctiva, connecting. Conniventes, winking or blinking. Conoid, cone-like. Convoluta, rolled together. Coracoid, like a crow or raven. Cordiform, heart-shaped. Cornea, horny. Corniculum, a little horn. Coronal, literally, pertaining to a crown ; transverse. Coronary, encircling. Coronoid, like a crooked beak. Corrugator, a wrinkler. Cortex, tUe bark or outer cover- ing. Costal, pertaining to a rib. Cotyloid, cup-like. Coxa, the hip. Cranium, the skull. Crassum, thick, dense, or bulky. Cremaster, a suspender. Cretin, a simple-minded person. Cribriform, sieve-like. Cribrosa, perforated with sieve- like pores. Cricoid, like a ring. Crucial, pertaining to, or shaped like, a cross. Crural, pertaining to the leg. Cryptorchismus, concealment of the testis. Cryptozygous, hidden arches. Cubitum, the elbow. Cucullaris, pertaining to a cowl or hood. Culmen, the top or summit. Cuneate, wedge-shaped. Cuneus, a wedge. Cupola, a dome. Cymba, a boat or skiff. Cystic, pertaining to the gall- bladder. Cytoplasm, formative yolk. Dacryon, a tear. .Dartos, skinned or flayed. Deciduous, falling away. Deferens, carrying away. Detrusor, from detrudo, I drive away. Deutopiasm, nutritive yolk. Dia-, through or between. Diaphragm, a partition. Diaphysis (' grow between '), the shaft of a bone, or the part which grows between the epiphyses. Diarthrosis, an ' apart ' joint (without intervening , sub- stance). Diencephalon, the 'tween-brain or inter-brain. Digastric, having two bellies. Diploe, a doubling. Diverticulum, from diverto, ' I separate,' or ' part,' or ' go a different way.' Dolichocephalic, long-headed. Dorsal, pertaining to the back aspect. Dorsum, the back. Duodenum, twelve. GLUSSA R Y 1 671 Ebur, -oris, ivory. Eburnea, pertaining to ivory. Ectopia, a displacement. Efferent, carrying out. Emboliformis, beak-shaped or wedge-shaped. Emissary, sent out. Emulgent, milking, straining out. Eneephalon, the contents of the head or skull. Endocardium, ' within the heart ' : the lining membrane of the cardiac chambers. Endognathion, literally, inner jaw. Endostemn, ' within a bone ' ; the medullary membrane. Ensiform, sword-like. Entomion, a notch. Ependyma, from a Greek word meaning ' clothing.' Ephippium, a saddle. Epi-, upon or over. Epicardium, upon the heart. Epididymis, upon the testicle. Epiotic, upon or over the ear. Epiphysis (' grow upon ') ; a process of a bone which has a secondary^ centre of ossification. Epiploon, from a Greek verb meaning ' I sail upon.' Epipteric, upon a wing. Enoophoron, upon the egg-bear- ing organ. Erythroblast, red germ. Ethmoid, sieve-like. Exognathion, literally, outer jaw. Exomphalos, out of the navel. Facet (French, facette, a little face), a small plane articular surface. Falciform, sickle-like. Falx, a sickle. Fascia, a band. Fasciculus, a small bundle. Fastigium, a roof. • Fauces, the throat. Fel, f ellis, the gall-bladder. Femur, the thigh. . Fenestra, an opening, a window. Ferruginea, pertaining to iron- rust. Fibula, a buckle, clasp, or brace. Filum, a thread. Fimbria, a fringe. Fimbriatum, fringed. Fissure, a cleft or sHt. Fistula, a pipe or tube. Flocculus, a little lock of wool Follicle, a small bag or sac. Fontanelle, a small spring. Foramen, an aperture or a hole. Forceps, a claw of a beetle. Fomicatus, pertaining to an i aroh. ! Fornix, an arch or a vault. ; Fossa, a ditch or trench. i Fourchette, a fork. I Fovea, a small pit. I Foveola, a small pit. Frenum, a bridle. Frenulum, a small bridle. Frontal, pertaining to the fore- head. Fundiform, shng-like. Funicular, pertaining to a cord. Funiculus, a slender rope, a cord. Furcalis, pertaining to a two- pronged fork. Furcula, a small two-pronged fork. I Fusca, dark or dusky. i j Galactophorous, milk-carrying. ! Galea, a helmet. I Gallinaginis, of a woodcock. j Gallus, a cock. j Ganglion, a swelling or excres- cence. Gastric,pertainingto the stomach . Gastrocnemius,the belly of the leg. Cremellus, paired or double. Geminus, double or twofold Greniculate, knee-like. Crenio-, pertaining to the chin. Genu, the knee. i672 GLOSSARY Ginglymus, a hinge. Glabella, without hair ; smooth. Gladiolus, a small sword. Glenoid, like a shallow socket. Globosus^ round or spherical. Globus, a globe or sphere. Glomerulus, a small ball of thread. Glosso-, pertaining to the tongue. Glottis, the mouthpiece of a flute. Gluteal, pertaining to the buttock. Gnathic, per taming to the jaw. Gnathion, the jaw. Gomphosis, a bolting together. Gonion, an angle. Gracilis, slender. Grisea, grey. Gubernaculum, a rudder. Gula, the gullet. Gustatory, pertaining to taste. Guttural, pertaining to the throat . Gyrus, a circle ; a crook. Habenula, a small rein. Hallux, the great toe. Ham, see p. 440 (footnote). Hamular, hook-shaped. Harmonia, a fitting together. Haustrum, a machine for draw- ing water. Helicine, spiral. Helicotrema, hole of a spiral. Helix, a coil or spiral. Hemorrhoidal, pertaining to hemorrhoids or piles. Hepar, the liver. Hepatic, pertaining to the liver. Hernia, a sprout ; a rupture. Hiatus, a gap. Hilum, a little thing, a trifle. Hippocampus, a seahorse. Hircina, pertaining to a goat. Homodynamic, having the. same force or value. Homogenesis, one and the same generation. Homologous, agreeing in position or structure. Humerus, the upper part of the arm ; the shoulder. Hyaline, glassy. Hyaloid, like glass. Hydatid, a watery vesicle. Hydrocele, a watery tumour. Hymen, a thin skin or membrane. Hyoid, like the Greek letter upsilon. Hypo-, beneath or under. Hypophysis, ' grow beneath.' Hypothenar, beneath the palm of the hand. Ileum, implying twists or coils. Ilium, the flank. Ima, lowest. Impar, dissimilar (in number), unequal. Incisivus, cutting into. Infundibulum, a funnel. Infundibuliform, funnel-shaped. Inguinal, pertaining to the groin. Inion, literally, the occiput. Innominatum, unnamed. Insula, an island. Intercalary, inserted. Internodium, between two joints. Interpositum, placed between. Interstitial, belonging to inter- stices or small intervals sepa- rating the minute parts of bodies. Iris, the rainbow. Ischiatic, pertaining to the hip. Ischium, the hip. Iter, a passage or road. Jejunum, empty. Jugal, yolking. Jugular, pertaining to the throat. Jugum, a yolk. Labrum, a basin. Lachrymal, pertaining to tears. Laciniosum, full of folds, in- dented, jagged. Lacteal, pertaining to milk. Lactiferous, milk-carrying. GLOSS AKy 1673 Lacuna, a hollow or cavity. Lacunar, pertaining to a hollow or gap. Lamella, a small plate. Lamina, a plate. Lateral, external. Latissimus, broadest. Latum, broad. Lemniscus, a ribbon. Leptorhine, having small narrow nostrils. Levator, a lifter or raiser. Lien, the spleen. Lieno-, pertaining to the spleen. Ligament, a band. Ligula, a little tongue. Limbous, pertaining to a border. Limbus, a border. Limen, a threshold. Linea, a line. Lingual, pertaining to the tongue, Lingula, a little tongue. Longissimus, longest. Lumbar, pertaining to the loin. Lumbricalis, pertaining to an earth-worm. Lunar, pertaining to the moon. Lunula, a little moon. Luteum, muddy, like clay. Lymphatic, from lympha, pure or spring water ; lymph. Lyra, a lyre. Macula, a spot. Malar, pertaining to the cheek. Malleolus, a small hammer or mallet. Malleus, a hammer or mallet. Mamma, a breast or pap. Mammilla, a little breast or pap. Mandible, the chewing bone. Manubrium, a handle or hilt. Masseter, the chewing muscle. Mastoid, breast- or pap-like (nipple-like). Maxilla, jaw. Meatus (pi. meatus), a passage or canal. Mediastinum, standing in the middle. Medulla, marrow. Megacephalic, having a large head. Megaseme, great index. Meninges, membranes. Meniscus, a crescent. Mental, pertaining to the chin. Mesaticephalic, pertaining to a.i intermediate head. Mesencephalon, the mid-brain. Mesentery, middle intestine. Mesial, internal. Meso-, middle. Mesocephalic, pertaining to an intennediate head. Mesogastrium, middle belly. Mesognathion, middle jaw. Mesometrium, middle of womb. Meso-nephros, mid-kidney. Mesorhine, pertaining to an in- termediate nose. Mesosalpinx, middle of trumpet or tube. Mesoseme, intermediate index. Meta-, after or beyond. Meta-nephros, hind-kidney. Metencephalon, the after-brain. Metopic, pertaining to the fore- head. Metopism, persistence of the metopic or frontal suture. Microcephalic, pertaining to a small head. Microseme, small index. Millimetre (mm.), slightly less than -^ of an English inch. Minimae^ least, smallest. Mitral, resembling an Asiatic head-dress. Modiolus, the nave of a wheel. Molar, pertaining to a mill, or to grinding. Montanum, pertaining to a mountain. Monticulus, a smaD mountain. Morbus, a disease. Muliebris, pertaining to a woman, feminine. 1674 GLOSSARY Multifidus, many cleft; divided into many parts. Myelencephalon, marrow-brain. Myeloplaxes, marrow-plates. Myentericus, pertaining to the muscular tissue of the bowel. Myli;-, pertaining to a mill. Myccardium, the muscular tissue of the heart. Myrtiform, like a myrtle-berry. Naris (pi. nares), a nostril. Nasal, pertaining to the nose. Natal, pertaining to the buttock. Natis (pi. nates), the buttock. Navicular, pertaining to a boat. Nephros, a kidney. Neural, pertaining to a nerve. Neuroglia, * nerve and glue.' Nictitans, winking. Norma, a rule or measure, (aspect). Notochord, string or cord of the back. Nucha, the nape of the neck. Nucleus, a kernel. Nymphse, demi-goddesses, or in- ferior deities, of the fountains. Obelion, a horizontal line (per- haps a little spit). Obex, a bolt. Obturator, a stopper-up. Occipital, against the head. Odontoblast, a tooth-germ. Odontoid, tooth-like. Odoriferse, carrying odours. CEsophagus, food-carrier. Olecranon, head of the elbow. Olfactory, pertaining to smell. Olivary, pertaining to an olive. Omentum, a caul or net ; the fat-skin. Omo-, pertaining to the shoulder. Omphalo-, pertaining to the navel. Operculum, a covering, Ophryon, the eyebrow. Ophthalmic, pertaining to the eye. Opisthion, hinder or rear, Opisthotic, behind the ear. Optic, pertaining to sight, Ora, a border or margin. Orthognathous, pertaining to a straight or upright jaw. Os, oris, a mouth. Os, ossis, a bone. Osteoblast, bone-germ. Osteoclast, bone-destroyer. Osteogenetic, bone-begetting. Ostium, a door, entrance, or exit. Otic, pertaining to the ear. Otoconia, ear-dust. Otoliths, ear-stones. Ovary, egg-former. Oxyntic, producing acid. Palatum, the palate. Pallium, a covering. Palmar, pertaining to the palm, Palpebra, an eyelid. Pampiniform, tendril-like. Pancreas, literally, all flesh. Para-, near, by the side of. Paradidymis, near the testis. Parametrium, near the womb. Parietal, pertaining to a wall. Paroophoron, near the egg-bear- ing organ. Parotid, near the ear. Patella, a small dish ; a plate. Patheticus, affecting. Pecten, the os pubis. Pectinatus, pertaining to a comb. Pectiniform, comb-like. Pectineal or PeetinUus, pubic. Pectoralis, pertaining to the breast. Pelvis, a basin. Penicillus, a painter's brush. Penis, a tail. Peri-, around, about, or near. Pericardium, around the heart. Perineum, from a Greek verb meaning ' I dwell, or am situated, around.' Periosteum, around a bone. GLOSSARY 1675 Periotic, around the ear. Peritoneum, from a Greek verb meaning ' I stretch around.' Peroneal or Peroneus, pertain- ing to a buckle, clasp, or brace. Petrous, rocky. Phalanx, a rank of soldiers. Vharynx, the throat. Phenozygous, having visibh arches. Philtrum, a love potion. Phrenic, pertaining to the dia- phragm. Pineal, belonging to, or like, a pine-nut or pine-cone. Pinna, a kind of sheU-fish ; a feather or wing. Pisiform, like a pea. Pituitary, pertaining to phlegm or mucus. Placenta, a flat cake. Plagiocephalous, pertaining to an oblique or twisted head. Planta, the sole of the foot. Plantar, pertaining to the sole of the foot. Platycnemism, broadness of leg. Platyrhine, pertaining to a broad nose. Platysma, a broad sheet. Pleura, a side, or a rib. Plexus, a twining or network. Plica, a fold. Pneumogastric, pertaining to the breathing organs and stomach. Pocularis, pertaining to a cup. Pollex, the thtunb. Pons, a bridge. Popliteal or Popliteus, pertaining to the ham. Porta, a gate. Portal, pertaining to a gate. Postaxial, distal or caudal. Posticus, posterior. Prseputiura, the prepuce. Preaxial, proximal or cephalic. Proctodaeum, the threshold of the anus. Prognathous, pertaining to a projecting lower jaw. Proligerus, bearing offspring ; germinating. Pro-nephros, fore-kidney. Pro-otic, before the ear. Prosencephalon, the fore-brain. Prostate, stiinding before ; or, more probably, pertaining to a porch or vestibule. Psalterium, a psaltery or instru- ment of the lute kind. Psoas, the loin. Pterion, a wing. Pterotic, pertaining to a wing. Pterygoid, wing-like. Pubes, the hair which appears on the external genital organs at the age of puberty. Pubic, pertaining to the os pubis. Pudendal, pertaining to the pu- dendum. Pudendum, ' of which one ought to be ashamed.' Pudic, modest or chaste. Pulmo, a lung. Pulmonary, belonging to the lungs. Pulvinar, a couch or cushion. Putamen, that which is pruned off ; chippings. Pylorus, literally, a gate-keeper. Pyriformis, pear-shaped. Quadratus, square. Quadriceps, having four heads. Quadrigeminus, fourfold, four. Racemose, pertaining to a cluster of grapes ; full of clusters ; clustering. Radius, a staff or rod : the spoke of a wheel. Ramus, a branch. Ranine, pertaining to a frog. Raphe, a seam. 1676 GLOSSARY Receptaculum, a receptacle. Rectus, straight. Recurrent, running back. Refractory, breaking up. Ren, a kidney. Restiform, like a rope or cord. Rete, a net. Retina, from rete, a net. Retrahens, drawing back. Revehens, carrying back. Rhinencephalon, the ' nose ' or olfactory brain. Rhinion, a nose. Rhombencephalon, the rhomb- brain (hind-brain). Rima, a cleft or chink, Risorius, laughing. Rostrum, a beak. Rotula, a little wheel. Rugae, wrinkles. Sacrum, sacred. Sagittal, pertaining to an arrow ; antero-posterior. Salpinx, a trumpet or tube. Salvatella, saving, or making well. Saphenous, manifest. Sartorius, pertaining to a tailor. Scala, a ladder, flight of steps, or staircase. Scalenus, of unequal sides. Scansorius, of, or for, climbing. Scaphocephalous, pertaining to a head like a boat. Scaphoid, like a boat. Scapula, a spade ; probably from a Greek verb meaning ' I dig.' Schindylesis, a splitting or cleavage. Sciatic (identical with Ischiatic), pertaining to the hip. Scle];a, hard. Sclerotic, hard. Scrobiculus, a little ditch or trench. Scrotum, a skin-bag or -pouch ; a hide. Sebaceous, pertaining to grease. Sella, a seat ; a saddle. Seminalis, pertaining to semen. Septum, a fence or barrier. Serotinus, that comes or happens late. Serratus, saw-shaped. Sesamoid, like sesame (a kind of grain). Sigmoid, like the Greek letter 2 (sigma). Sinus, a cavity or hollow. Smegma, a cleanser. Solar, relating to the sun. Soleus, a sole or sandal ; a sole- Sperma, seed or semen. [fish. Spermatic, pertaining to semen. Spermatoblast, a seminal bud. Spermatozoa (plural), seminal animals. Sphenoid, wedge-like. Sphenotic, pertaining to the sphe- noid bone and ear-capsule. Sphincter, binding or closing tight. Splanchnic, pertaining to viscera. Splenium, a bandage or com- press. Splenius,pertaining to a bandage. Squamous, scaly. Stapes, a stirrup. Stellatum, starry. Stephanion, a crown or wreath. Sternebra, a segment of the sternum. Sternum, the breast or chest. Stomata, mouths or pores. StomatodEBum or Stomodseum, the threshold of the mouth. Styloid, pen-like. Subflava, somewhat yellow. Subiculum, an underlayer or support. SudorWerous, sweat-carrying. Sulcus, a furrow. Supercilium, an eyebrow. Sural, pertaining to the calf of the leg. Sustentaculum, a prop or support. Suture, a sewing together, a seam. GLOSSARY i67' Symphysis, growth together. Syn-, with ; together with, (union or harmony may be implied). Synarthrosis, literally, a ' to- gether with ' (direct) joint. Synchondrosis, ' with cartilage.' Syndesmosis, ' with a band ' or ' ligament.' Synovia, resemblance to the white of an egg. Taenia, a band or ribbon. Talus, a die (pi. dice) ; the ankle- bone. Tapetum, a carpet or coverlet. Tarsus, a broad flat surface ; the instep. Tectorius, pertaining to a cover. Tegmen, a covering. Tegmentum, a covering. Tela, a web. Telencephaion, the end-brain. Temporal, pertaining to time. Tendon, from tendo, ' I stretch.' Tentorium, a tent. Tenuis, slender, small. Teres, rounded. Testis, a witness. Thalameneephalon, the bed- chamber-brain, or inter-brain. Thalamus, a bed-chamber, situ- ated between two other rooms ; a marriage-bed. Theca, a cover, case, or sheath. Thenar, pertaining to the palm. Thorax, the breast or chest ; a breast-plate. Thymus, thyme. Thyroid, like a shield. Tibia, a pipe or flute ; the shin- bone. Tinea, a small fish, perhaps the tench. Torcular, a wine-press (twisting is implied). Torus, a protuberance. Trabecuia, a little beam. Trachea ('rough '), the wind-pipe. Trachelo-, belonging to the neck. Tragus, a goat. Trapezium, a table ; a four-sided figure, no two sides of which are parallel to one another. Trefoil, having three leaves. Triceps, having three heads. Trigeminus, threefold, triple. Trigonocephalus, a triangular head. Trigonum, a triangle ; triangular. Triquetrum, three-cornered ; tri- angular. Triticea, wheaten. Trochanter, from a Greek verb meaning ' I roll, turn, or revolve.' Trochlea, the wheel of a pulley. Trochlear, pulley-shaped. Trochlearthrosis, a pulley-joint. Trochoides, wheel-like. Tuba, a trum.pet. Tubarius, pertaining to a trumpet. Tubercle, a small swelling. Tuberosity, an exaggerated tubercle. Turbinate, whirled or coiled ; like a top. Turbo, a whirl or coil ; a top. Turcica, Turkish. Tympanum, a drum. Ulna, the elbow. Umbilicus, the nave!. Umbo, a boss or knob. Unciform, hook-like. Uncinate, furnished with a hook. Ungual, relating to a nail. Unguis, a nail. Unicornis, one-homed. Urachus, urine-holder. Ur6ter, from a Greek verb mean- ing ' I pass urine.' Urethra, the canal by which urine is passed. Uriniferous, urine-carrying. Uterus, the womb or. matrix. i6;8 GLOSSARY Utricle, a little womb or matrix. UvSa, from uva, a bunch of grapes ; a cluster. Uvula, a small bunch of grapes. Vagina, a scabbard or sheath. Vagus, strolling about, wander- ing, vagrant. Valgus, bent or turned outwards. Vallecula, a little valley. Vallum, a rampart. Varus, bent or turned inwards. Vas (pi. vasa), a vessel. Velum, a curtain or veil. Veneris, ' of Venus.' Ventral, pertaining to the belly. Vermiform, liice a worm. Vertebra, from verto, ' I turn.' Vertex, the top or crown of the head. Veru, a dart, javelin, or spear. Vesica, the urinary bladder. Vescial, pertaining to the urinary bladder. Vespertilio, a bat. Vestigial, pertaining to a trace. Vestigium, a trace or vestige. Vibrissa, a stiff hair of the nos- tril. Villus, shaggy hair ; a tuft of hair. Vinculum, a band or bond. Vitelline, pertaining to the yolk of an egg. Vitellus, the yolk of an egg. Vitreous, like glass, glassy. Vola, the palm of the hand. Volar, pertaining to the palm ; palmar. Vomer, a ploughshare. Vorticosse, full of whirlpools, eddying, coiled. Vulva, a wrapper or covering. Xiphoid, like a sword. Zygoma, a yoke. INDEX Abdomen, 6ii division into regions, 689 superficial view of contents, 690 Abernethy, fascia of, 777 Aberrans, vas, of Haller, 684 Accessory lachrymal glands, 1189 thyroids, 1122 Acervulus cerebri, or brain sand, 1422 Acetabulum, 226 Achillis, tendo, 520 Acromio-clavicular joint, 326 Acustica, area, 1378 Acusticae, striae, 1377 Acusticum, trigonum, 1378 tuberculum, 13 78 Adamantoblasts, 173 Adductor tubercle, 236 Air sinuses. 139 • Ala cinerea, 1378 Alae vespertilionis, 880 Alar thoracic artery, 311 Alcock, canal of, 623 Allantoic stalk, 1629 veins, 163 1 Allantois, 870, 1629 Alveus, 1409 Ambiguus, nucleus, 1495 Amitosis, 1601 Ammonis, cornu, 1409 Amnion, 1624 Amphiarthrosis, 280 AmpuUa of Vater, 710 Amygdala of cerebellum, 13 71 Amygdalae, or tonsils, 1253 Amygdaloid nucleus, 14 14 tubercle, 1408 Anal canal, of male, 861 development of, 877 of female, 890 lymphatics of, 877 structure of, 874 fascia, 840 membrane, 871 valves of Morgagni, 875 Anaphase, 1598 Anastomosis, digital (trochanteric), 483 femoral, 483 round elbow-joint, 362 knee-joint, 508 scapular, 323 1679 Anastomotica magna of brachial, 339 of femoral, 484 Anconeus muscle, 386 Angle, sacro-vertebral, 38 sternal, 48 Angular movement 281 Animal cell, 1597 matter of bone, 3 Ankle-joint, 569 Aimular ligament, anterior, of ankle, 500 external, of ankle, 498 internal, of ankle, 499 anterior, of hand, 376 posterior, of hand, 390 Annular (orbicular) ligament, 404 Annulus fibrosus, 1540 ovalis, 977 tympanicus, 80 Ansa cervicis, 1107 hypoglossi, 1108 lenticularis, 1421 subclavia, 1235 Vieussenii, 1235 Anterior triangle of neck, 1098 subdivisions of, 1099 Antibrachium, 175 Anticubital space, 340 Antinion, 133 Antrum of Highmore, 102 mastoid, 73 pylori, 693 Anus, 6ii imperforate, 878 Aorta, abdominal, 750 arch of, 958 development of, 963 primitive, dorsal, 1000 ventral, 1002 thoracic, descending, 1023 Aortic arches, 1000 isthmus, 960 orifice, 983 position of, 985 plexus, 738 spindle, 960 valves, 983 vestibule, 98 1 Aortico-renal ganglion, 736 Aponeurosis, epicranial, 1069 intercostal, anterior, 927 i68o INDEX Aponeurosis intercostal, posterior, 927 lumbar, 289, 765 posterior lamina of, 289 pharyngeal, 1266 of soft palate, 1250 vertebral, 289 Apparatus, lachrymal, 1190 Appendices epiploicae, 699, 794 Appendicular mesentery, 697 skeleton, i Appendix, vermiform, 696 Aqueduct of Sylvius, 1439 development of, 1439 grey matter of , 1439 Aqueductus cochleaj, 78, 1552 Fallopii, 75 vestibuli, 76 Arachnoid membrane, cranial, 1479 spinal, 1309 nerves of, 1481 structure of, 1481 Arantii, corpus, 984 duct of, 1009 Arbor vitae cerebelli, 1373 uterina, 888 Arc, longitudinal, of skull, 158 Arch, dental, 168 dorsal venous, of foot, 514 femoral, deep, 460, 652 superficial, 460, 651 hyoid, 1 2 71 mandibular, 127 1 palmar, deep, 380 superficial, 370 plantar, 563 thyro-hyoid, 1271 Arches, arterial, 1000 dental, 168, 1238 of foot, 577 longitudinal, 577 transverse, 578 visceral, 1271 ' first or mandibular, 163 second or hyoid, 165 third or thyro-hyoid, 165 development of, 1271 Meckel's cartilage, 1272 metamorphoses of, 1272 first or mandibular, 1272 second or hyoid, 1272 third or thyro-hyoid, 1272 fourth or fifth, 1273 sixth, 1273 morphtology of, 1273 Arcuate fasciculus, 1447 fibres of medulla, deep, 1359 superficial, 1359 nucleus, 1355 Arcuatum, ligamentum, 903 Arcus parieto-occipitalis, 1389 Area, cochlear, 75 embryonic, 161 4 inferior vestibular, 75 superior vestibular, 75 Areas, of Flechsig, 1360 dorsal, 1361 lateral, 1361 medulla, 1360 ventral, 1361 Areola of nipple, 300 Arm, 329 Arnold, nerve of, 1073, 1226 Arteria centralis retinae, 1159, 1525 princeps cervicis, 1062 deep branch of, 1062 • superficial branch of, 1062 thyroidea ima, 1123 Arteriae rectae, 824 Artery or Arteries — acromial rete, 324 acromio-thoracic, 310 alar thoracic, 311 allantoic, 163 1 anastomosis, crucial, 483 digital (trochanteric), 483 round elbow-joint, 362 knee-joint, 508 scapular, 323 anastomotica magna of brachial, 339 of femoral, 484 angular, 11 79 aorta, abdominal, 750 branches of, 751 guides to bifurcation of, 642 arch of, 958 development of, 963 ascending, 957 branches of, 958 development of, 958 great sinus of, 957 descending, 1023 development of, 1027 thoracic, 957, 1023 varieties of, 961 appendicular, 727 arch, palmar, deep, 380 superficial, 370 plantar, 563 articular, of popliteal, 442 auditory, internal, 1453, 1559 of auricle, 1 195 auricular, deep, 1203 posterior, 1073, 1120 branches of, 1073, 1120 axillary, 308 first part, 308 branches of, 3 10 INDEX l6Si Arter>' or Arteries {continued) — axillarj', second part, 309 branches of, 311 third part, 310 branches of, 311 varieties of, 312 axis, thoracic, 310 azygos, 442 basUar, 1342, 1452 branches of, 1342, 145^ brachial, 338 branches of, 338 collateral circulation after occlusion of, 340 varieties of, 339 bronchial, 1025 buccal, 1 1 82, 1205 of bulb, female, 638 male, 624 caecal, 727 calcarine, 1454 capsular, middle, 752 of liver, 804 carotid, common, mo collateral circulation, after hgation of , 1 1 1 2 left, in thorax, 961 surgery' of, IH2 external, 1114 branches of, 11 16 development of, ni6 relations of, 1115 internal, at base of brain, 1342, 1449 cavernous part of, 1078 cervical part of, 1222 development of, 1223 petrous part of, 1296 carpal, anterior radial, 357 posterior radial, 392 anterior ulnar, 362 posterior ulnar, 362 cerebellar, anterior inferior, 1453 posterior inferior, 1452 superior, 1453 cerebral, anterior, 1343. 1449 branches of, 1449 middle, 1343, 1450 branches of, 1450 posterior, 1453 branches of, 1454 of cerebral hemorrhage, 1450 cervical, ascending, 11 42 deep, 1063, 1 144 branches of, 1063 superficial, 1143 transverse, 285, 1096, 1143 choroidal, anterior, 1449 posterior, 1454 ciliary, anterior, 1516 long, 1159, 1516 Artery or Arteries (continued) — ciliary, posterior, 1159 short, 1 159 circle of Willis, 1343, 1454 parts contained within, 1455 circulus major, 15 16 minor, 1516 circamflex, anterior, of axillary, 3" posterior, of axillary, 312 varieties of, 312 external, of profunda fem- oris, 481 internal, of profunda fem- oris, 483 iliac, deep, 663 superficial, of femoral, 479. 646 clitoris, dorsal artery of, 638 cochlear, 1560 coeliac axis, 739 ' colic, left, 729 middle, 727 right, 727 comes n^^i ischiadici, 433 mediani, 361 phrenici, 931 communicating, anterior, 1450 posterior, 1449 coronary, of face, 1261 of heart, 958 of corpus callosum, 1450 cavernosum clitoridis, 638 penis, 624 spongiosum penis, 624 crico-thyroid, 11 16 cutaneous, anterior, of abdo- minal wall, 646 lateral, of abdominal wall, 646 plantar, 548 cystic, 742 deferential, 669, 841 dental, anterior, 1205 inferior, 1204 brcinches of, 1204 middle, 1205 posterior, 1205 digital, of foot, 564 superficial, 561 of hand, 370 dorsal, of penis, 624 dorsalis linguae, 1 1 1 8 scapulag, 311 of dura mater, cranial, 1471 spinal, 1308 of encephalon, 1449 at base of, 1342 epigastric, deep, 662 branches of, 662 guide to, 642 106 i682 INDEX Artery or arteries (continued) — epigastric, lateral or intermus- cular, 664 superficial, 479, 646 superior, 663, 932 branches of, 663 ethmoidal, anterior, 1160, 1260 posterior, 1160, 1261 of Eustachian tube, 1275 of face, 1 1 78 facial, in neck, 11 19 branches of, 11 19 on face, 11 78 branches of, 11 79 transverse, 1181 femoral, 477 first part, 478 second part, 478 branches of, 479 collateral circulation after occlusion of, 485 deep, 481 varieties of, 485 fibular superior, 507 of frenum lingua;, '418 frontal, 1068, 1161 ganglionic, 1449, 1454 gastric, 739 gastro-duodenal, 741 gastro-epiploic, left, 740 right, 741 gluteal, 430, 844 hallucis, arteria dorsalis, 512 magna or princeps, 565 helicine, 869 hemorrhoidal, inferior, 623, 876 middle, 842, 876 superior, 875 hepatic, 741 branches of, 741, 804 humeri, transversalis, 320 hypogastric, 840 iliac, circumflex, deep, 663 branches of, 663 superficial, 479, 646 common, 774 branches of, 776 collateral circulation, after ligation of, 776 guide to, 642, 775 varieties of, 776 external, 777 branches of, 778 collateral circulation after ligation of, 778 development of, 778 guide to, 642, 777 varieties of branches, 778 internal, 840 branches of, 841 Artery or Arteries [continued) — iliac, internal, foetal condition of, 840 varieties of, 840 ileo-caecal, 727 ileo-colic, 727 ilio-lumbar, 843 incisor, 1205 indicis, dorsalis, 393 radialis, 381 infra-hyoid, 11 16 infra-orbital, 11 82, 1205 branches of, 1205 innominate, 960 varieties of, 961 intercostal, 929, 1025 anterior, 930 aortic, 929 collateral, 1026 lower two, 664 superior, 1027, 1143 interlobar of kidney, 822 interlobular of kidney, 823 of liver, 804 interosseous, common, 360 anterior, 361 posterior, 361 first dorsal, of hand, 392 of iris, 15 16 of kidney, 822 afferent, 823 efferent, 823 labial, inferior, 11 79 of labyrinth, 1559 lachrymal, 1159 larjmgeal, inferior, 1142 superior, 11 16 of larynx, 1293 lenticular, of Duret, 1450 lenticulo-optic, of Du-et, 1451 lent.culo-striate, of Duret, 1450 lingual, II 17 branches of, 1 1 1 8 lumbar, 772 abdominal branches of, 664 branches of, 772 malar, 1182 malleolar, external, 508 internal, of anteriter tibial, 507 of posterior tibial, 498 mammary, extern M, 311 internal, cervical part of, 1142 thoracic part of, 931 branches of, 931 masseteric, 1205 mastoid, 1062 maxillary, internal, 1202 branches of, 1203 first part, 1203 INDEX 1683 Artery or Arteries [continued) — maxillary, internal, second part, 1205 third part, 1205 median, 361 meduUary, of clavicle, 1143 of femur, 484 of fibula, 526 of humerus, 339 of radius, 361 of tibia, 525 of ulna, 361 of membrana tj'mpani, 1541 meningeal, anterior, of eth- moidal, 1 471 of ascending pharyngeal, 1121, 1472 of internal carotid, 1471 middle, 1203, 1471 guide to, 1502 posterior, of occipital, 1062, 1472 small. 1204, 1471 of vertebral, 1452, 1472 mental, 1182 mesenteric, inferior, 729 branches of, 729 superior, 725 branches of, 726 metatarsal, 512 of mouth, 1239 musculo-phrenic, 931 mylo-hyoid, 1204 of nasal fossae, 1260 nasal, 1181 lateral, 1179 naso-palatine, 1260 of nose, facial aspect of, 1 196 obturator, 488, 843 aberrant or abnormal, 462 occipital, 1062, 1 120 branches of, 1062, 1120 olecranon rete, 363 ophthalmic, 1159 branches of, 1 159 ovarian, 755, 890 branches of, 755, 890 of palate, soft, 1252 palatine, descending, 1205, 1260 inferior, 11 19 of ascending pharyngeal, 1121 palmar arch, deep, 380 branches of, 381 interosseous of, 381 summary of, 382 superficial, 370 branches of, 370 palpebral, external, 1182 internal, 1161, 1181 Artery or Arteries [continued) — pancreatic magna, 740 pancreatico-duodenal, inferior, 727 superior, 741 pedis, dorsalis, 510 varieties of, 512 perforating of profunda femoris, 484 perineal, superficial, of female, 638 ofmale,623 transverse, 623 peroneal, 526 anterior, 509, 526 posterior, 527 varieties of, 327 petrosal, 1297 pharj-ngeal, ascending, 11 21 branches of, 11 21 of pharynx, 1269 phrenic, inferior, 752 superior, 931 of pia mater, 131 1, 1482 plantar or perforating, 565 external, 562 varieties of, 565 internal, 561 varieties of, 565 pollicis, dor sales, 393 princeps, 380 pontine, 1453 popliteal, 440 branches of, 442 varieties of, 443 profunda, inferior, of brachial, 339 profunda, superior, of brachial, 338 femoris, 481 of ulnar, 370 pterygo-palatine, 1206 pudic, accessor}', 624 pudic, external, inferior, of fem- oral, 481 superior, of fem- oral, 479, 645 internal, 433, 622, 843 branches of, 623 varieties of, 624 pulmonary-, 963 development of, 964 pyloric, 741 radial, 356 first part, 356 branches of, 356 second part, 391 branches of, 392 third part, ^80 branches of, 380 varieties of, 382 1 684 INDEX Artery or Arteries {continued) — rami intestini tenuis, 726 ranine, 11 18 recurrent, of forearm, posterior interosseous, 361 radial, 356 anterior ulnar, 360 posterior ulnar, 360 anterior, of tibial, 507 posterior, of tibial, 507 renal, 752 aberrant, 753 accessory, 753 branches of, 753, 822 rete, acromial, 324 olecranon, 363 sacral, lateral, 844 middle, 861 saphenous, external, 442 internal, 484 of scalp, 1067 scapulae, dorsaiis, 311 scapular, posterior, 287 sciatic, 432, 843 extrapelvic branches of, 432 of sclerotic, 1508 sigmoid, 730 spermatic, 754 terminal part of, 670 varieties of, 754 spheno-palatine, 1206, 1260 branches of, 1206 spinal, anterior, 1332, 1452 lateral, 1332 poster or, 1332, 1452 of spinal canal, 1331 of spinal cord, 1332 anterior, 1332 posterior, 1332 splenic, 739 sterno-cleido-mastoid, 11 16 striate, external, 1450 internal, 1450 stylo-mastoid, 1121, 1547 subclavian, first and second parts of, 1138.; 1 1 40 branches of, 1140 collateral circulation after ligation of first part of, 1145 third part of, 1095 collateral circulation after ligation of third part of, "45 left, in thorax, 961 subcostal, 773, 1027 sublingual, 11 18 submental, 11 19 subscapular, 311 suprahyoid, 11 18 supra- orbital, 1067, 1 160 Artery or Arteries {continued) — ■ suprascapular, 320, 1096 branches of, 321 temporal, anterior, deep, 1205 of lachrymal, 1182 posterior, deep, 1205 superficial, 1070 branches of, 1071 thoracic, alar, 311 axis, 310 inferior or long, 311 superior or short, 310 thyroiciea ima, 960 thyroid, inferior, 1142 branches of, 11 42 superior, 11 16 branches of, 1116 tibial, anterior, 505 branches of, 507 recurrent, 507 varieties of, 508 posterior, 523 branches of, 525 recurrent, 507 varieties of, 527 of tongue, 1246 of tonsils, 1233 tonsillar, of facial, iiiq trans versalis humeri, 320 tympanic, 1547 of ascending pharyngeal, 1121 of internal carotid, 1296 of internal maxillary, 1203 ulnar, 358 first part, 358 branches of, 360 second part, 364 third part, 370 branches of, 370 varieties of, 363 in hand, 382 umbilical, 840 uterine, 891 branches of, 891 vaginal, 892 azygos, 892 of liver, 804 vasa brevia, of splenic, 740 recta, false, of kidney, 823 true, of kidney, 824 vertebral, at base of brain, 1342 first part of, 1141 second part of, 1141 branches of, 11 41 third part of, 1065 branches of, 1066 fourth part of, 1451 branches of, 145^ vesical, inferior, 842 INDEX 1685 Artery or Arteries (continued) — vesical, superior, 841 vestibular, 1560 Vidian, 1206, 1260 branches of, 1 206 volar, superficial, 357 Arthrodia, 280 Arthrolog>', 279 Articulations. See Joints Arytaeno-epiglottidei muscles, 1290 Arytenoid cartilages, 1279 muscle, 1290 Ary-vocalis muscle, 1289 Aspera, linea, 236 Association fibres of cerebrum, 1446 Asterion, 142 Astragalo-calcaneal joint, anterior, 579 posterior, 578 • Astragalo-navicular joint, 580 Astragalus, 254 Atlanto-axial joints, 1301 ligaments of , 1302 accessor\% 1303 -occipital joints, 1303 ligaments of, 1303 accessory, 1303 Atlas, 14 ossification of, 29 transverse ligament of, 1302 Atresia ani, 878 Atria of lung, 951 Atrium of heart, 973 of middle meatus, 1255 Attic of tympanum, 1545 Attollens auriculam muscle, 1072 Attrahens auriculam muscle, 1072 Auditory artery, internal. 1453, 1559 cells, 1554 epithelium, 1554 hairs, 1554 meatus, external, 78, 1536 internal, 75 nerve. See Cranial Nerves process, external, 79 radiation, 1446 teeth, 1556 vesicle, 1560 Auerbach, plexus myentericus of, 793 Auricle, 1 192 blood-supply of, 1195 ligaments of, 11 93 IjTnphatics of, 1195 muscles of, extrinsic, 1072 intrinsic, 1193 nerve-supply of, 11 95 veins of, 11 95 Auricular appendix, 973 artery, deep, 1203 posterior, 1073, 1120 branches of, 11 20 Auricular canaliculus, 76 fissure, 77 glands, posterior, 1073 nerve, great, 1059 branches of, 1059, 11 78 posterior, 1073, 11 73 branches of , 11 73 point, 140 vein, posterior, 1073, 1121 Auriculo-temporal nerve, 1070, 1209 branches of, 1070, 1209 Auriculo-ventricular bundle, 990 Axial skeleton, i Axillary arterj', 308 varieties of, 312 first part, 308 branches of, 310 second part, 309 branches of, 311 third part, 310 branches of, 311 Axillaiy lymphatic glands, 317 afferent vessels, 317 efferent vessels, 317 trunk, 317 sheath, 312 space, 306 contents of, 307 vein, 312 Axis, 17 ossification of, 29 basi-bregmatic, 149 basi-cranial, 149 basi-facial, 149 cerebro-spinal, 1306 coeliac, 739 thoracic, or acromio - thoracic artery, 310 Axon, 1320 cylinder process. 1335 Azygos artery, 442 uvulae muscle, 1250 veins, 762 Bacillary layer of retina, 1523 Back, the, 283 Back of scalp and neck, 1058 landmarks of, 1058 BaiUarger, inner band of, 1440, 1443 outer band of, 1440, 1443 Ball-and-socket joint, 280 Bar, hyoid, 1272 Bartholin, glands of, 633 development of, 633 duct of (sublingual), 11 36 Basi-bregmatic axis, 149 Basi-cranial axis, 149 Basi-facial axis, 149 Basi-hyal, 165 Basi-occipital, 59 Basilar artery, 1342, 1452 1 686 INDEX Basilar artery, branches of, 1342, 1452 border, striatea, 739 groove, 59 membrane, 1555 process, 59 sinus, 1479 vein, 1456 Basilic vein, 334 median, 332 Basion, 148 Basket-cells of cerebellum, 1375 Bechterew, band of, 1443 nucleus of, 1493 Bell, external respiratory nerve of, 313 muscles of, 867 nerve of, 1098 Bellini, duct of, 820 Bergmann, fibres of, 1376 Bertin, bones of, 90 Bertini, columnae, 818 Betz, giant cells of, 1447 Biceps femoris (flexor cruris), 437 flexor cubiti, 336 Bicipital (semilunar) fascia, 336 groove, 186 hollow of ulna, 199 tuberosity of radius, 191 Bicuspid teeth, 167 valve, 982 Bigelow, Y ligament of, 489 Bile-canaliculi, 806 capillaries, 806 duct, common, 710 ducts, 806 interlobular, 806 Biventer cervicis muscle, 293 Biventral lobule, 1371 Bladder, urinary, male, 850 development of, 870 female, 889 infantile, 867 ligaments of, false, 836, 867 true, 867 lymphatics of, 868 orifices of, 866 peritoneal relations of, 851 structure of, 865 trigone, external, of, 851 internal, of, 866 Blandin, glands of, 1243 Blastoderm, 161 3, 1616 Blastodermic vesicle, 161 2 Bochdalek, ganglion of, 1218 Body cavity, primitive, 1620 Bone-cell, 7 Bones, classification of, 7 astragalus, 254 atlas, 1 1 axis, 17 of Bertin, 90 Bones, calcaneum or os calcis, 256 carpal, 201 clavicle, 175 coccyx, 36 cuboid, 263 cuneiform of carpus, 202 of tarsus, 260 endochondral, 162 epipteric, 142, 155 ethmoid, 92 femur, 232 fibula, 250 frontal, 65 of head, 56 humerus, 184 hyoid, 121 ilium, 220 innominate, 220 interparietal, 57, 61 ischium, 223 lachrymal, 108 of limbs, homologies of, 277 of lower limb, 220 lunar, 202 magnum, 205 malar, 104 maxillary inferior, 115 superior, 97 membranous or tegmental, i6z metacarpal, 208 metatarsal, 265 nasal, 107 navicular, 258 occipital, 57 palate, no parietal, 62 patella, 241 phalangeal of foot, 271 of hand, 213 pisiform, 203 pubic, 225 pyramidal, 202 radius, 191 ribs, 41 sacrum, 30 scaphoid of carpus, 201 of tarsus, 258 scapula, 178 semilunar, 202 sesamoid, of foot, 272 of hand, 216 sphenoid, 82 sternum, 47 supra-occipital, 57 tarsal, 253 temporal, 69 tibia, 242 trapezium, 203 trapezoid, 204 triquetral, 155 of trunk, 1 1 INDEX 1687 Bones, turbinate, inferior, 100 spheaoidal, 90 ulna, 197 unciform, 206 of upper limb, 175 vomer, 114 Wormian, 155 Bowman, capsule of, 819, 824 glands of, 1257 Brachia of corpora quadrigemina, 1428, 1429 Brachial artery, 338 branches of, 338 varieties of, 3 39 Brachial plexus, 312, 1096 infraclavicular branches of, 314 supraclavicular branches of, 313, 1098 branches of inner cord, 315 of outer cord, 314 of posterior cord, 315 region, back of, 342 front of, 334 Brachialis anticus, 337 Brachio-radialis, 383 Brachium, 175 Brachycephalic skulls, 132, 158 Brain, 1337 development of, 1458 lymphatics of, 1458 weight of, 1449 Bregma, 124 Bregmatic bone, 69, 155 Broca, area of, 1397 le cap of, 1387 Bronchial tubes, 952, 1020 Bronchioles, 952 Bronchus, eparterial, 1020 hyparterial, 1020 left, 1020 right, 1020 Bruch, membrane of, 15 12 Brunner, glands of, 790 Bryant's test-line, 447 Bubonocele, 678 Buccal artery, 1182, 1205 lymphatic glands, 11 83 nerve, long, 11 77, 1208 short, 1 169 Buccal pad of fat, 11 70 Buccinator muscle, 11 69 Bucco-pharyngeal fascia, 1087 Budin, hinge-joint of, 62 Bulb, 1345 olfactory, 1397 Bulbi vestibuli, 6^2 Bulla ethmoidal's, 1255 Bundle, anterior longitudinal, 1359 posterior longitudinal, 1358 Burdach. column of, 13 15, 1326 Bums, falciform process of, 460 space of, 1086 Bursa, great palmar, 374 olecranon, 331 pharyngeal, 1269 popliteal, 542 prepatellar, 464, 541 subacromial, 320 subscapular, 346, 347 suprapatellar, 541 Bursae, at ankle-joint, 573 at elbow-joint, 401 at hip-joint, 495 at knee-joint, 541 at shoulder-joint, 347 plantar, 544 Cacuminis, foUum, 136S Caecum, 695 peritoneal relations of, 696 varieties of, 696 Caeruleus, locus, 1378 Calamus scriptorius, 1377 Calcaneo-cuboid joint, 582 Calcaneo-navicular ligaments, 580 Calcaneo-plantar ner\'e, 548 Calcaneum, 256 ossification of, 258 Calcar avis, 1408 femora le, 240 Calcarine fissure, 1391 Calcination, 4 Calcis, OS, 256 tuber, 256 Calices of kidney, 826 Callosal gyrus, 1394 radiation, 1401, 1446 Calloso-marginal fissure, 1383 Calvaria, 149 Camper, fascia of, 643 Canal or canals — of Alcock, 623 carotid, 74 central, of medulla, 1360 of spinal cord, 1319 cranio-pharyngeal, 82, 92 dental, anterior and middle, 98 inferior, 118 posterior, 97 ethmoidal anterior, 68, 95 posterior, 68, 95 femoral, 461 of Fontana, 151 1 Haversian, 5 hepatic, 805 ofHuguier, 72, 1538 Hunter's, 475 hyaloid, of Stilling, 1530 incisor, loi infra-orbital, 98, 136 inguinal, 666 t6g8 INDEX Canal or Canals (continued) — intestinal, 694 malar, 105 naso-palatine, loi of Nuck, 881 palatine, posterior, or palato- maxillary, 112 accessory, external, 112 posterior, 112 of Petit, 1530 portal, 804 pterygoid or Vidian, 89 pterygo-palatine, 84, 113 spinal, 40 of Stensen, loi temporal, 105 Volkmann's, 6 Canaliculi of bone, 6 Canaliculus, auricular, 76, 148 innominatus, 87 lacrimalis, 1190 tympanic, 77 Canalis reuniens of Hensen, 1553 Cancellated bone, 7 Canine fossa, 97 ridge, 97 teeth, 167 Canthus, inner, 11 87 outer, 1 1 87 Capitellum of humerus, 189 Capsule, external, of brain, 1414 internal, of brain, 14 15 centrifugal fibres of, 141 3 centripetal fibres of, 141 3 genu of, 1 41 3 limb, anterior of, 141 3 posterior, of, 141 3 Caput gallinaginis, 855 Cardia, 693 position of, 693 Cardiac nerves, of pneumogastric, cervical, 1229 thoracic, 967, 968 of sympathetic, cervical, 1234, 1235 plexus, 967 deep, 968 superficial, 968 Carotico-clinoid foramen, 86 Carotid artery, common, 11 10 collateral circulation after ligation of, 1 1 1 2 development of, 11 13 left, in thorax, 961 surgery of, Iii2 external, 11 14 branches of, 1116 development of, 11 16 relations of, 11 15 internal, at base of brain, 1342, 1449 Carotid artery, internal, branches of, 1449 cavernous part of, 1078 branches of, 1079 cervical part of, 1222 development of, 1223 petrous part of, 1296 branches of. 1296 Carotid body, 11 13 plexus, 1234 sheath, 1108 triangle, 1100 Carotid foramen, 76, 148 groove of sphenoid, 84 notch of sphenoid, 85 tubercle, 20 Carpal artery, anterior radial, 357 posterior radial, 392 anterior ulnar, 362 posterior ulnar, 362 Carpal joints, 406 Carpi, extensor, radialis brevior, 383 longior, 383 extensor, ulnaris, 386 flexor, radialis, 352 ulnaris, 353 Carpus, 201 as a whole, 207 ossification of, 208 varieties of, 208 Cartilage, basal, 161 basi-occipital, 161 basi-sphenoid, 161 ethmoidal, 161 Reichert's, 165 Cartilages of larynx, 1275 of Santorini, 1280 of Wrisberg, 1280 Cartilago triticea, 1280 Caruncula lacrimalis, 11 89 Carunculas myrtiformes, 632 Casserius, perforating nerve of, 315 Cauda equina, 13 14 Caudatus, nucleus, 141 1 blood-supply of, 1457 Cavernous groove, 84 plexus, 1234 sinus, 1478 communications of, 1479 interior of, 1078 Cell division, 1598 Cells, ethmoidal, 96 Cement, 172 Centrale, os, 208, 278 Centro-acinar cells of Langerhans, 810 Cephalic index, 158 vein, 334 median, 332 Cerato-hyal, 165 INDEX i68g Cerebellar tract, antero-lateral as- cending, or indirect, of Gowers, 1330 antero-lateral descending, 1329 dorso-lateral ascending, or direct, 1328 CerebeUum, 1367 association and commissural fibres of, 1373 blood-supply of, 1456 development of, 1376 fissures of, 1371 great horizontal, 1367 hemispheres of, 1338, 1367 lobes and lobules of under sur- face of, 1370 lobes and lobules of upper sur- face of, 1368, 1369 monticulus, 1367 peduncles of, 1372 inferior, 1372 middle, 1372 superior, 1372, 1433 structure of, 1375 vallecula of, 1369 veins of, 1456 vermis, inferior, 1370 superior, 1367 Cerebral hemispheres, 1381 arteries of, 1450 artery of cerebral hemor- rhage, 1450 commissure, anterior, 1403 hippocampal, 1403 middle or grey, 14 16 posterior, 1423 convolutions or gyri of, 1382 cortex, 1440 cells of, 1440 Golgi, 1443 of Martinotti, 1443 corticefugal fibres, 1444 molecular layer, 1442 pyramidal layer, 1442 development of, 1396 fibres of, 1443 association, 1446 commissural, 1446 projection, 1444 fissures (interlobar) of, 1382 calloso-marginal, 1383 circular or limiting, 1384 collateral, 1384 parieto-occipital, 1383 of Rolando, 1383 of Sylvius, 1382 (For other fissures see special names) Cerebral ganglia, basal, of, 1410 lobes of — frontal, 1385 island of Reil, 1393 limbic, 1394 occipital, 1390 parietal, 1388 temporal, 1391 lobules of — > cuneus, 1391 paracentral, 1388 postcentral, 1393 praecuneus, 1390 precentral, 1393 quadrate, 1390 blood-supply of, 1457 pole, frontal, of, 1381 occipital, of, 13 81 temporal, of, 1392 veins, 1455 vesicles, primary, 1458 secondary, 1459 Cerebri, crura, 1338, 1431 Cerebro-spinal axis, 1306 Ceruminous glands, 1537 Cervical fascia, deep, 1085 compartments of, 1087 muscular, 1088 space of Burns, 1087 suprasternal space, 1086, 1087 vertebral, 1088 visceral, 1088 laminae of, 1086 carotid, 1086 pretracheal, 1087 prevertebral, 1087 * visceral, 1087 parotid process of, 1088 Cervical glands, deep, 1102 superficial, 1085 nerve, superficial, 1060, 1093 plexus, 1 09 1 branches of, deep, 1093 superficial, 1092 ascending, 1059 descending, 1061 spinal nerves, origins of, 1 3 1 5 posterior primary divisions of, 1066 Cervical vertebrae, 12 Cervicalis ascendens muscle, 290 Cervicis, transversalis, muscle, 292 Charcot, artery of cerebral hemor- rhage of, 1450 Chassaignac, carotid tubercle of, 20, 1081 Check ligaments of eyeball, 1 152 Cheeks, 1238 Chemical composition of bone, 3 Choanae, 140 1690 INDEX Chondrocranium, 160 Chondro-glossjs muscle, 1133 Chorda tympani nerve, 1246, 1298 Chordae tendineae, 979 WiUisii, 1475 Chorion, 1627 Choroid coat of eyeball, 15 11 structure of, 151 1 choroid proper, 151 1 lamina suprachoroidea, 1511 chorio - capillaris or tunica Ruyschiana, 1512 lamina vasculosa, 15 12 membrane of Bruch, or lamina basalis, 1512 tapetum, 151 2 Choroid plexus or plexuses — of lateral ventricle, 1405 of descending cornu of, 1409 blood-supply of, 1458 of fourth ventricle, 1380 blood-supply of, 1458 of third ventricle, 1405, 1415 blood-supply of, 1458 Choroidal fissure, 1409 development of, 1409 vein, 1455 Chromosomes, 1599 Chyli, receptaculum, 762 Cilia or eyelashes, 11 87 Ciliaris, orbicularis. 151 2 pars, retinae, 15 13 Ciliary body of eye, 15 12 ganglion, 11 56 branches of. 1157 summary of. 11 58* muscle, 15 1 3 nerves, long, 1156 short, 1 157 processes, 151 2 Cinerea, ala, 1378 Cinereum, tuber, 1424 Cingulum, 1395 Circle of Willis, 1343, 1454 Circular fissure of brain, 1384 sinus, 1478 Circulation, allantoic, 1642 course of, 971 placental, 1642 vitelline, 1641 Circulus major, 1516 minor, 151 6 Circumduction, 282 Circumferential lamellae, 6 Circumflex artery, anterior, 311 posterior, 312 external, 481 internal, 483 iliac artery, deep, 663 Circumflex iliac artery, superficial, of femoral, 479, 646 nerve, 316 Circumflexus palati muscle, 1252 Cisterna basahs, 1480 chyli, 762 magna, 1480 pontis, 1480 Clarke, Lockhart, intermedio-lateral, tract of, 1^22 posterior vesicular column of, 1322 Classification of bones, 7 of joints, 279 of movements, 281 Claudius, cells of, 1558 Claustrum, 14 14 Clava of medulla oblongata, 1350 Clavicle, 175 ossification of, 107 Clavi-pectoral fascia, 305 Cleft palate, varieties of, 104 Clefts, visceral, 1270 Clinoid process, anterior, 85 middle, 86 posterior, 83 Clitoris, 630 frenulum, 630 glans, 630 praeputium, 630 septum pectiniforme, 630 Clivus monticuli, 1368 of sphenoid, 83 Cloaca, 870 Cloacal fossa, 870 membrane, 870 Cloquet, fascia of, 461 Club-foot, tendons involved in, 565 Coaptation, 282 Coats of eyeball, 1507 Coccygeal body of Luschka, 862 Coccygeus muscle, 863 Coccyx, 36 ossification of, 3 7 Cochlea, 1550 canal of, 1550 lamina spiralis of, 1550 modiolus of, 1551 Cochleae, aqueductus, 1552 tuber, or promontory, 1539 Cochlear area, 75 artery, 1560 nerve, 1301, 1559 nucleus, lateral, 1491 ventral, 1491 Cochleariformis, processus, 78, 1539 Coeliac axis, 739 plexus, 736 Ccelom, 1622 Collieen, t, Collateral fissure, 1384 INDEX 1691 Colles, fascia of, 614 ligament of, 653 Colliculus seminalis, 855 Colon, ascending or right, 697 peritoneal relations of, 697 descending or left, 698 peritoneal relations of, 699 flexure of, hepatic, 697 splenic, 698 iliac, 699 peritoneal relations of, 699 pelvic, 859 peritoneal relations of, 859 transverse or middle, 698 peritoneal relations of, 698 taeniae of, 699 Columella nasi, 1196 Column, vertebral, 38 Columnae cameae, 977 Bertini, 818 rugarum, 898 Columns of Morgagni, 875 Comma tract of spinal cord, 1327 Comes nervi ischiadici, 433 mediani, 361 Commissures of brain — anterior, 1403 corpus callosum, 1400 Gudden, of, 1425 habenular, 1422 hippocampal, 1403 Meynert, of, 1430 middle or grey, 1416 posterior, 1423 Commissures of spinal cord — grey, 1317, 1322 white, 131 7, 1322 Communicating artery, anterior, 1450 posterior, 1449 Compact bone, 5 Complexus muscle, 292 Compressor sacculus laryngis muscle, 1291 Conarium, 1421 Concatenatae, glandulae, 1038 Concentric lamellae, 6 Concha, inferior, 109 middle, 95 superior, 95 Conchae, 1254 Condylar foramen, anterior, 60 joint, 2S0 Condylarthrosis, 280 Condyles, occipital, 59 third, 61 Cone-bipolar cells of retina, 1521 Cone of light, 1541 Cones of retina, 1523 Coni vasculosi of testis, 684 Conical cells of olf acton.- region, 1258 Conjoined tendon, 658 Conjunctiva, 1189 epithelium of, 1189 ocular, 1 1 89 palpebral, 1189 plica semilunaris of, 1190 Conniventes, valvulae, 788 Conoid ligament, 327 tubercle, 176 Constrictor isthmi faucium muscle, 1250 Constrictor muscle, inferior, 1264 middle, 1264 superior, 1265 nerve-supply of,. 1265 Conus arteriosus of heart, 975, 977 Conus medullaris of spinal cord, 1312 Convoluted tubule, distal, 819 proximal, 819 Cooper, fascia propria of, 464, 649, 671 ligamenta suspensoria of, 300 pubic ligament of, 461, 780 reflected tendon of, 658 tunica vasculosa of, 683 Copula, 165 Coraco-acromial ligament, 328 brachialis muscle, 335 clavicular ligament, 327 Coraco-humeral ligament, 344 Coracoid process, 182 Cordiform tendon of diaphragm, 759 Cords, vocal, false and true, 1284 Cornea of eyeball, 1508 nerve-supply of, 15 10 structure of, 1509 Corneal corpuscles, 15 10 Comeo-scleral junction, 1507 Comicula laryngis, 1280 Comu Ammonis, 1409 anterior, of spinal cord, 13 17 lateral, 13 18 posterior, 131 7 Comua of lateral ventricles, 1406 anterior, 1407 middle or descending, 1408 amygdaloid tubercle of, 1408 nucleus of, 1408 posterior, 1408 bulb of, 1408 calcar avis, 1408 hippocampus minor, 1408 Corona glandis, 648 radiata, 1401, 1414 Coronal section of skull, 149 Coronary arteries, of face, 1261 of heart, 958 ligaments of knee, ^^^ plexuses, 970 sinus, 986 1692 INDEX Coronary valve, 976 Coronoid fossa of humerus, 189 process of ulna, 197 Corpora albicantia, 1423 geniculata, 1420 mammillaria, 1423 peduncles of, 1423 quadrigemina, 1428 blood-supply of, 1456 brachium, inferior, 1429 superior, 1428 occipital fibres of, 1429 retinal fibres of, 1429 development of, 1430 structure of, 1429 Corpus albicans of ovary, 893 Corpus Arantii, 984 Corpus callosum, 1400 blood-supply of, 1457 corona radiata, 1401 destination of fibres of, 1401 forceps major, 1402 forceps minor, 1402 geniculate gyrus, 1401 genu, 1 401 peduncles of, 1401 radiatio corporis callosi, 1 401 rostrum, 1401 splenium, 1401 stria longitudinalis lateralis, 1401 mesialis, 1400 subcallosal gyrus, 1401 tapetum, 1401 Corpus den ta turn of cerebellum, 1373 fimbriatum, 885 geniculatum externum, 141 9 development of, 1420 internum, 1420 development of, 1421 Highmorianum, 683 luteum, 893 striatum, 1410 blood-supply of, 1457 connections of, 141 4 development of, 14 14 external capule of, 1414 internal capsule of , 141 3 extraventricular portion of, 1411 intraventricular portion of, 1410 relation of structures in region of, 1415 vein of, 1455 subthalamicum, 1421 trapezoides, of cerebellum, 1372 of pons Varolii, 1363 Corrugator supercilii muscle, 11 66 Corti, organ of, 1556 auditory of hair cells of, 1557 cells of Claudius, 1558 of Deiters, 1558 of Hensen, 1558 lamina reticularis, 1558 membrana tectoria, 1558 membrane of Corti, 1558 rods of, 1556 phalangeal processes of, 1557 tunnel of, 1556 Cortico-medullary arterial arches of kidney, 822 venous arches of kidney, 826 Costal cartilages, 46 Costo-clavicular ligament, 326 Costo-coracoid ligament, 305 membrane, 305 Cotunnius, nerve of, 1220, 1260 Cotyloid cavity, 226 ligament, 492 notch, 226 Cowper, glands of, 621 Coxae, OS, 220 Cranial cavity, dissection of, 1074 Cranial nerves — first, or olfactory. See Olfactory Bulb second, or optic. See Optic Nerve third, or oculo-motor, at base of skull, 1074 in outer wall of cavernous sinus, 1078 in orbit, 11 53 at sphenoidal fissure, 11 62 fibres of, course of, 1485 nucleus of, 1484 origin of, deep, 1484 superficial, 1341 summary of, 1485 fourth, trochlear, or pathetic, at base of skull, 1075 in outer wall of cavernous sinus, 1078 in orbit, 1153 at sphenoidal fissure, 1162 fibres of, course of, 1485 nucleus of, 1485 origin of, deep, 1485 superficial, 1341 summary of, i486 fifth, trigeminal, or trifacial, at base of skull, 1075 distribution of, 14B7 Gasserian ganglion, 1076 branches of, 1077 origin of, deep, i486 motor root, i486 INDEX 1693 Cranial nerves {continued) — fifth, origin of motor root, nuclei of i486, 1487 sensory root, i486 nuclei of, i486 superficial, 1341 summary of, 1487 sixth, or abducent, at base of- skull, 1075 in cavernous sinns, 1078 in orbit, 1153 at sphenoidal fissure, 1162 fibres of, course of, 1488 nucleus of, 1488 origin of, deep, 1488 superficial, 13 41 summary of, 1488 seventh, or facial, at base of skull, 1076 distribution of, 1489 in Fallopian aqueduct, 1297 after emerging from Fal- lopian aqueduct, 1 1 72 meatal portion of, 1297 cer\'ico-facial di\'ision of, 1174 fibres of, course of, 1488 geniculate ganglion, 1299 nucleus of, 1488 origin of, deep, 1489 superficial, 1341 pars intermedia of Wrisberg, 1299, 1489 sensory root of, 1299 summarj' of extracranial part of, 1 1 75 temporo-faciaj division of, "73 eighth, or auditory, at base of skull, 1076 cochlear division of, 1559 nervous chains of, 1 491 fibres of, course of, 1490 meatal portion of, 1300 origin of, deep, 1489 cochlear root, 1490 nuclei of, 1490 vestibular root, 1492 nuclei of, 1492 superficial, 1341 vestibular division, nervous chains of, 1494 ninth, or glosso-phaiyngeal, at base of skull, 1076 distribution of, 1496 extracranial portion of, 1223 branches of trunk, 1224 Cranial nerves {continued) — ninth, jugular ganglion of, 1223 petrous ganglion of, 1223 branches of, 1223 origin of, deep, 1495 superficial, 1341 summary- of, 1226 tenth, pneumogastric, or vagus, in abdomen, 786 at base of skull, 1076 cervical portion of, 1226 cardiac branches of, 1229 ganglion of root, 1226 branches of, 1226 of trunk, 1227 branches of, 1227 distribution of, 1497 inferior laryngeal branch of, 966, 1228, 1292 lingual branch of, 1227 origin of, deep, 1496 superficial, 1341 summary of, in neck, 1229 thoracic portion of left, 965 of right, 964 cardiac branches, 967, 968 pulmonary plexuses of, 967 eleventh, or spinal accessory, at base of skull, 1076 bulbar or accessory part of, 1229 distribution of, 1499 extracranial portion of, 1229 spinal part of, 1060, 1230 origin of, deep, 1498 superficial, 1341 summary of, 1231 twelfth, or hypoglossal, at base of skull, 1076 distribution of, 1500 extracranial portion of, 1231 branches of, 123 1 fibres of, course of, 1500 origin of, deep, 1500 superficial, 1341 summary of, 1232 Cranial nerves at base of brain, 1340 at base of skull, 1074 Cranio-cerebral topography, 1500 Cranio-facial angle, 149 Craniometrical terms, 157 Cranium, 56 development of, 159 Cremaster muscle, external, 656, 671 internal, 671 middle, 671 1 694 INDEX Cremasteric fascia, 656 reflex, 656 Crest, falciform, 75 incisor, loi of ilium, 220 infratemporal of sphenoid, 87 malar of sphenoid, 87 pubic, relations of structures at, 660 sphenoidal, 84 supramastoid, 70 of urethra, female, 899 male, 855 Cretinism, 159 Cretin skull, 159 Cribriform plate of ethmoid, 92 Cribrosa, lamina, 75 Crico-arytenoid joint, 1282 , muscle, lateral, 1288 posterior, 1288 Crico-thyroid joint, 1282 membrane, 1280 muscle, 1287 Cricoid cartilage, 1278 development of, 1279 Crista acustica, 1554 basilaris, 1555 galli, 92 terminalis, 975 vestibuli, 1549 Crucial ligaments of knee, 532 Cruciform ligament, 1305 transverse portion of, 1306 Crura cerebri, 1338 Crural (femoral) arch, deep, 460 superficial, 460 canal, 461 nerve, anterior, 470 ring, 461 sheath, 462 Crurale, septum, 461 Crureus muscle, 467 Crus cerebri, blood-supply of, 1456 crusta or pes, 1431, 1437 cortico - pontine fibres of, 1438 fronto - pontine strand of, 1438 tempore - pontine strand of, 1438 pyramidal fibres of, 1437 summary of, 1437 development of, 1437 lateral sulcus of, 143 1 nucleus of, 1432 oculo-motor sulcus of, 1431 posterior longitudinal bundle in. 1434 red nucleus of, 1432 structure j lernal, of, 1431 Crus cerebri, substantia nigra of, 143 1 superior cerebellar peduncle in 1433 summary of, 1435 tegmentum, 143 1 Cruscerebri, internal structure of,i 431 superior cerebellar peduncle in, 1433 nucleus of tegmentum, 1432 posterior longitudinal bundle in, 1434 red nucleus of, 1432 Crusta of crus cerebri, 1431, 1437 petrosa, 172 Cryptorchismus, 676 Cryptozygous skull, 132 Crypts of Lieberkiihn, 791 Cubo-cuneiform joint, 585 Cuboid bone, 263 Cubo-metatarsal joint, 587 Cucullaris muscle, 285 Culmen monticuli, 1368 Cuneate nucleus, accessory or ex' ternal, 1354 tubercle, 1350 Cuneatus, nucleus, 1354 Cuneiform bone of carpus, 202 of tarsus, 260 external, 262 internal, 260 middle, 261 Cuneiform cartilages, 1280 Cuneus of brain, 1391 Cup, palmar, 408 Cupola of cochlea, 1550 Cutaneous nerves of arm, internal, 313, 331, 340 lesser internal, 315, 331 of musculo-cutaneous, 332 of musculo-spiral, ex- ternal, 332 internal, 331, 343 of back, 283 of foot, 547 of forearm and hand, 348 of gluteal region, 424 of pectoral region, 298 of sacral plexus, perforating, 425 of scapular region, 319 of thigh, external, 449 internal, 449 middle, 449 of thorax, lateral, 298 of ulnar nerve, 332, 349 Cuvier, ducts of, loii Cystic duct, 710 structure of, 809 notch, 708 Cytoplasm, 894, 1597 INDEX i6q5 Dacryon, 133 Dartos, tunica, of scrotum, 650 Darwin, tubercle of, 1193 Deferens, vas, 668 development of, 686 structure of, 66g Decidua basilis, 1632, 1634 capsularis, 1632, 1634 reflexa, 1632 scrotina, 1632 vera, 1632, 1634 Deciduous membrane, 1632 Deiters, cells of, 1558 process of, 1320 nucleus of, 1492 Deltoid, 319 spine, 175 Demours, membrane of, 15 10 Dendrites, 1320 Dental arches, 168, 1238 artery — anterior, 1205 inferior, 1204 middle, 1205 posterior, 1205 canals, anterior and middle, 98 inferior, 118 posterior, 97 foramen, inferior, 118 nerves, inferior, 1209 superior, anterior, 1218 middle, 121 8 posteror, 12 18 papilla, 172 sac, 172 Dentate fissure, 1396 Dentated suture, 279 Dentatum, corpus, of cerebellum, 1373 Dentinal tubules, 172 Dentine, 172 Depressor alae nasi muscle, 1166 anguli oris muscle, 11 70 labii inferioris muscle, 11 70 Descemet, membrane of, 15 10 Descendens cervicis nerve, 1107 h^'poglossi nerve, 1107 Descent of testis, 671, 673 abnormal conditions of, 675 positions, 676 gubemaculum testis, 672 mesotestis, 671 metamorphoses of folds, 674 of processus vaginalis, 675 plica gubernatrix, 672 urogenital fold, 671 mesentery, 672 Descriptive terms, i Deutoplasm, 894 Development of arteries of lower limb, 568 Development of arteries of upper limb, 397 of cranium, 159 of diaphragm, 761 of external genital organs, 633 female, 634 male, 635 of eye, 1530 optic cup, 1532 stalk, 1534 vesicle, 1532 of face, 162 of heart, 991 mesocardial folds, 992 transformation of aortic bulb, 994 of auricular canal, 993 of single heart, 993 ventricle, 994 of hyoid bone, 165 of internal sexual organs, 685 genital ridge of, 685 indifferent organ of, 685 sex -cords of, 685 of limb bones, 591 of limb-buds, 591 of lymphatic system, 1016 jugular sacs, 1016 lymphatic vessels, 1017 structure of, ioi8 IjTnph glands, 1017 structure oi, 1019 sacs, 1016 retroperitoneal sacs, 1016 sciatica sacs, 10 17 metamorphosis of structures concerned in development of external genital organs, 636 of ovary, 687 egg-tubes of Pfliiger, 688 mesovarium, 688 rete-cords of, 6S7 summary of, 688 of principal arteries, 999 cervical arteries, 1002 primitive dorsal aortae, loco ventral aortae, 999 segmental arteries, 1000 subclavian arteries, 1002 summary of, 1003 vertebral arteries, 1003 visceral arch arteries, 1000 of principal veins, 1005 anterior cardinal veins, loio metamorphoses of, loio azj-gos veins, 1030 inferior vena cava, 1015 lumbar veins, 1015 posterior cardinal veins, lOII metamorphoses of, 1014 1696 INDEX Development of principal renal veins, 1015 subcardinal veins, 1012 metamorphoses of, 1014 suprarenal veins, 1015 umbilical or allantoic veins, 1008 summary of, 1009 vena portae, 1005 vitelline or omphalo-mes- enteric veins, 1005 of skull, 159 of teeth, 172 of testis, 686 rete cords of, 686 Wolffian duct of, 686 of valves of heart, 995 of veins, 1005 of lower limb, 569 of upper limb, 397 vitreous body, 1534 Diaphragm, 758 openings of, 760 ligaments of, 761 pelvic, 864 Diaphragma, oris, 11 31 sellae, 1475 Diaphragmatic plexus of nerves, 736 Diarthrosis, 280 Diencephalon, 1337, 1415 Digastric muscle, 11 29 nerve, 11 73 triangle, 11 01 contents of, 11 02 Digital arteries, palmar, 370 plantar, 564 fossa of peritoneum, 676 of tunica vaginalis, 681 Digiti, abductor minimi, of foot, 551 of hand, 379 extensor minimi, 384 flexor brevis minimi, of foot, 556 of hand, 380 opponens minimi, of foot, 556 of hand, 380 Digitorum, extensor brevis, 509 communis, 384 longus, 504 flexor brevis, 549 longus, 521 tendon of, 551 profunc'u5, 365 sublimis, 354 Dilator naris anterior, muscle, 1167 posterior, muscle, 1167 pupillae muscle, 1515 Diploe, 7 Diploic veins, 1473 Disc, germinal, 1614 Discs, intervertebral, 1038 Discus proligerus, 894 Dolichocephalic skull, 132, 158 Dorsalis linguae artery, 11 18 pedis artery, 510 nerve, 513 scapulae artery, 311 Dorsum ephippii of sphenoid, 83 sellae of sphenoid, 83 Dorsum ilii, 222 Douglas, pouch of, 879 recto-uterine folds of, 879 semilunar fold of, 660 Duct or ducts — Bartholin, of (sublingual), 11 36 bile, 806 common, 710 cystic, 710 ejaculatory, common, 852 galactophorous, 301 hepatic, 708 lymphatic, right, 1146 mesonephric, 830 Miillerian, 898 nasal, 1191 naso-lachrymal, 1 191 parotid, 1185 pronephric, 829 prostatic, 855 Rivini, of, great, 1136 segmental, 829 Steno or Stensen, of, 11 85 sublingual, 11 36 submaxillary, 11 34 thoracic, in abdomen, 762 in neck, 1145 in thorax, 1031 umbilical, 798 vitelline, 798 vitello-intestinal, 798 Walther, of, 1136 Wharton, of, 11 34 Wolffian, 811 Ductus arteriosi, ligamentum, 964 Ductus arteriosus, 997 cochlearis, 1555 Ductus communis choledochus, 710 endolymphaticus, 76, 1553 perilymphaticus, 78 reunions of Hensen, 1553 sacculi, 1553 thyro-glossus, 11 24 utriculi, 1552 utriculo-saccularis, 1552 venosus, 997 Duodeno-jejunal flexure, 695 Duodenum, 694, 731 first part of, 731 second part of, 731 third part of, 732 fourth part of, 732 Dura mater, of brain, 1470 blood-supply of, 1471 INDEX 1697 Dura mater, nerves of, 1473 processes of, 1473 sinuses of, 1475 structure of, 1471 of spinal cord, 1306 blood-supply of, 1308 nerves of, 1308 Duret, arteries of, 1450 Duvemey, glands of, 633 development of, 633 Dyad, 1606 Ear, development of, 1560 external, 1536 internal, 1548 middle, 1538 Earthy matter of bone, 4 Ebner, glands of. 1243 Eboris, membrana, 171 Ectopia cordis, 50 Efferentia, vasa, 684 Ejaculatory ducts, common, 852 development of, 872 structure of, 872 Elbow-joint, 398 Emboliformis, nucleus, 1373 Embryo, appendages of, 1624 formation of, 1618 Embryology, general, 1597 Eminentia arcuata, 75, 1550 articularis, 70 collateralis, 1409 teres, 13 78 Emissary veins, 1479 Enamel, 172 cells, 173 cuticle, 172 germ, common, 172 special, 172 organ, 172 prism, 173 Enarthrosis, 280 Encephalon, 1337 base of, 1337 arteries at base of, 1342 development of, 1458 flexures of primitive, 1458 meninges of, 1470 metamorphoses of secondary vesicles, 1460 rhombic lip of, 1460 of basal ganglia, 1466 of mesencephalon, 1462 of metencephalon, 1461 of telencephalon, 1463 of thalamencephalon, 1463 secondary cerebral vesicles, 1459 three primary cerebral vesicles, 1458 veins of, 1455 Endocardium, 988 Endognathion, 104 Endolymph of internal ear. 1552 Endolymphaticus, ductus, 76 Endoskeleton, i Endosteum, 11 Ensiform process, 47, 49 Entomion, 142 Ependyina, 1464 Ephippii, dorsum, of sphenoid, 83 Epicardium, 944, 988 Epicondyle, external, of humerus, 189 internal, of humerus, 189 Epicranial aponeurosis, 1069 Epididymis, 682 development of, 686 structure of, 683, 684 Epidural space, spinal, 1308 Epigastric artery, deep, 662 superficial, 479, 646 Epiglottis, 1275 frenum, 1276 functions of, 1292 Epi-hyal, 165 Epiotic centre of temporal bone, Si Epiphysis cerebri, 1421 Epiploicae, appendices, 699, 794 Epiploon, 716 Epipteric bone, 142, 155 Episternal bones, 51 Epi thalamus, 1421 Epitympanic recess and its pouches, 1545 Epoophoron, 884 development of, 883, 898 Equina, cauda, 13 14 Erector spinas muscle, 290 inner column, 292 middle column, 291 outer column, 290 Eruption of teeth, 1 70 Erythroblasts, 10 Ethmoid bone, 92 ossification of, 96 Ethmoidal arteries, 1260 canal, anterior, 68, 95 posterior, 68, 95 cells, 96 spine, 82 Ethmo-turbinals, 94 Eustachian groove, 147 orifice, 78 spine of sphenoid, 89 tube, 1274 development of, 1275 muscles connected with, 1275 valve, 976, 997 Exner, plexus of, 1443 Exoccipitals, 59 ExognathiDn, 104 Exomphalos, 680 107 1698 INDEX Exoskeleton, i Eye, 1506 chambers of, 1527 coats of, 1507 development of, 1530 equator of, 1506 meridian of, 1507 movements of, 1 151 muscles of, 11 47 Eyelashes, 11 87 Eyelids, 1187 development of, 11 90 structure of, 1187 Face, 56 arteries of, 11 78 development of, 162 landmarks of, 1163 muscles of, 1165 sensory nerves of, 1 1 76 Facial artery, cervical part of, 11 19 branches of , 11 19 facial part of, 11 78 branches of, 11 79 transverse, n8i nerve. See Cranial Nerves vein, 1 1 79 deep, 1206 transverse, 1181 Falciform crest, 75 ' process of Burns, 460 Fallopian tubes, 884 development of, 898 lymphatics of, 896 structure of, 895 Fallopius, aqueduct of, 75 Fallopius hiatus, 74 Falx cerebelli, 1474 cerebri, 1473 Fascia of Abernethy, 777 anal, 840 of anterior abdominal wall, deep, 643 superficial, 643 axillary, 300 of back, deep, 283 superficial, 283 bicipital or semilunar, 336 of brachial region, deep, 334 bucco-pharyn^eal, 1087 of Camper, 643 cervical, deep, 1085 clavi-pectoral, 305 of Cloquet, 461 ofCoUes, 614 of Cooper, propria, 649, 671 dentata of Tarinus, 1^96 of dorsum of foot, deep, 509 of forearm, deep, 351 gluteal, 425 deep, 426 Fascia of hand, back of, 390 interosseous, 394 iliaca, 764 infundibuliform, 665, 671 intercolumnar, 651 lata, 456 iliac lamina, 457 processes of, 458 pubic lamina, 457 of leg, deep, 497 lumbar, 765 masseteric, 1238 obturator, 837 of palm, superficial, 368 palmar, 369 parotid, 11 84 of pectoral region, 299 pelvic, parietal, 836 visceral, 838 perineal, deep, 619 pharyngeal, 1263 plantar, 545 propria of Cooper, 464 of pyriformis, 837 of scapular region, deep, 319 of Scarpa, 643 of Sibson, 937, 1146 spermatic, external, 651 internal, 649 middle, 656 subpubic, 619 superficial, of front of thigh, 452 temporal, 1074 transversalis, 665 triangular, 653 Fasciculus, arcuate, 1447 longitudinal, inferior, 1447 superior, 1447 occipito -frontal, 1447 perpendicular, 1447 retroflexus, 1447 solitarius, 1495 uncinate, 1447 Fastigii, nucleus, 1373 Fauces, 1249 pillars of, anterior, 1249 posterior, 1249 Femoral artery 477 first part, 478 second part, 478 branches of, 479 varieties of, 485 deep, 481 canal, 461 hernia, parts concerned in, 460 course of, 462 coverings of, 462 ligament of Hey, 460 opening, 472 ring, 461 sheath, 460 INDEX 1699 FemoraJ vein, 486 tributaries of, 486 varieties of, 488 external cutaneous, 455 internal cutaneous, 455 Femur, 232 female, 240 ossification of, 240 trigone of, 236 Fenestra ovalis, 1538 rotunda, 1539 Ferrein, pyramids of, 819 Ferruginea, substantia, 1378 Fibres, perforating, of Shaipey, 7 pjnamidal or motor, 141 3 thalamo- frontal, 141 3 thalamo-striate, 141 3 of Tomes, 172 Fibro-cartilages, interarticular, 281 acromio-clavicular, 327 of knee-joint, 534 in lower limb, 591 of radio-ulnar, inferior, 405 stemo-clavicular, 325 in upper limb, 411 Fibula, 250 ossification of, 253 Fibular artery, superior, 507 nerve, 445 Fillet, 1360 decussation of, 1359 lateral, 1367, 1436 mesial, 1367, 1435 Filum terminale of spinal cord, 1313 Fimbria, of brain, 1396, 1409 ovarian, 885 Fimbriae, 884 Fimbriata, plica, of tongue, 1241 Fimbriatum, corpus, 885 Fimbrio-dentate sulcus, 1396 Fissura palpebrarum, 1187 Fissure, auricular, 77 of Glaser, 72 petro-tympanic, 72 pterygo-maxillary, 144 sphenoidal, 88, 136 spheno-maxillarj-, 136, 143 sternal, 50 tympano-mastoid, 77 Fistula in ano, 614 umbilical urinary, 870 Flaccida, membrana, 1540 Flat bones, 7 Floccular fossa, 76, 82 Flocculus, 1 371 Flood's ligament, 345 Foetal circulation, 997 changes in, at birth, 999 peculiarities of, 996 Folds, neural, 161 8 Folium cacuminis, 1368 Follicles of Lieberkiihn, 791 FollicuU, liquor, 894 theca, 894 Fontana, canal of, 15 n spaces of, 15 10 FontaneUes, 155 sagittal, 65 Foot, arches of, 577 dorsum of, 509 as a whole, 274 Foramen or foramina — caecum of frontal bone, 67 carotico-clinoid, 86 carotid, 76, 148 condylar, anterior, 60, 14S dental, inferior, 118 of Huschke, 79, 82 infra-orbital, 97 jugular, 148, 1076 lacerum anterius, 88, 136 medium, 148, 152 orbitale, 88 posterius, 148, 154 of Luschka, 1380 of Magendie, 1380 magnum, 61, 148 stmctures passing through, 1076 malar, 104 mastoid, 73 mental, 116 of Monro, 141 7 obturator, 227 ' optic, 86 ovale, 86, 996 of capsule of shoulder-joint, 344 valve of, 996 palatine, accessory, external, 147 posterior, 147 posterior, 147 parietal, 63 pterygo-spinous, 89 quadratum of diaphragm, 760 rotundum, 86 sacro-sciatic, great, 904 compartments of, 429 small, 904 structures passing through, 430 of Scarpa, 102, 145 singulare, 75 spheno-palatine, 140, 144 sphenotic, 148 spinosum, 87 of Stensen, 102, 145 sternal, 50 stylo-mastoid, 77 supra-orbital, 134 supratrochlear, 189 thyroid, 227 lyoo INDEX Foramen or foramina [continued) — Vesalii, 86 of Winslow, 721, 802 Forearm, front of, 351 and hand, 348 back of, 382 Fore-gut, 798, 1623 Fore-kidney, 829 Formatio reticularis of medulla, 1352 alba, 1353 grisea, 1352 Fornicatus, gyrus, 1394 Fornix, anterior, of vagina, 889 posterior, of vagina, 889 of brain, 1402 development of, 1403 conjunctivae, 11 89 Fossa or fossae — of antihelix, 11 93 of base of skull, anterior, 150 middle, 151 posterior, 154 canine, 97 coronoid, 189 floccular, 76, 82 glenoid, 71 guttural, 147 of helix, 1 193 iliac, 223 incisor, 97 incudis, 1539 infraclavicular, 297 infraspinous, 178 intercondylar, 239 jugular, 76 lachrymal, 67 nasal, 137, 1254 navicularis, of male urethra, 857 of pudendum, 632 olecranon, 189 ovalis, 977 palatine, anterior, loi, 145 patellaris, 1529 peritoneal — digital, 676 duodenal, 721 duodeno-jejunal, 722 ileo-caecal, 722 ileo-colic, 722 inguinal, 676 intersigmoid, 722 para-duodenal, 722 peri-caecal, 722 retro-caecal, 722 retro-duodenal, 722 pituitary, 82 pterygoid, 88, 147 scaphoid, of auricle, 1193 of sphenoid, 89 spheno-maxillary, 144 supraspinous, 178 Fossa or fossae [continued) — supratonsillar, 1253 of Tarinus, 1339 temporal, 142 triangular, of auricle, 1193 trochlear, 67 vermiform, 58 zygomatic, 142 Fossula ovalis, 1538 rotunda, 1539 Fourchette, 632 Fovea centralis retinae, 15 18 structure of, 1524 elliptica, 1549 inferior, of fourth ventricle, 1377 spherica, 1549 superior, of fourth ventricle, 1378 Foveola of kidney, 821 Frenulum clitoridis, 630 Giacomini, 1396 labii, 1236 lingulae of cerebellum, 1368 veli of superior medullary velum, 1379, 1427 Frenum epiglottidis, 1276 linguag, 1237, 1241 praeputii, 647 Frontal artery, 1068, 1161 bone, 65 air sinuses of, 68 ala of, 67 nasal notch of, 67 orbital plates, 67 ossification of, 69 lobe of brain, 1385 nerve, 1154 vein, 1068 diploic, 1473 Fronto-pontine tract, 1413, 1444 Fronto-nasal process, 163 Fundiform ligament of Retzius, 501 Funiculus cuneatus, 1354 gracihs, 1353 Furcula, 1270 Furrow, nuchal, 1058 Furrows, palmar, 367 Fusca, lamina, 1508 Galactophorous ducts, 301 Galen, veins of, 1455 Gall-bladder, 709 development of, 809 structure of, 808 Gallinaginis, caput, 855 Ganglia, basal, 1466 Ganglion, aortico-renal, 736 Arnold, of, 121 1 basal, of Meynert, 1424 Bochdalek, of, 121 8 cervical, inferior, 1235 middle, 1235 INDEX 1701 Ganglion, cervical, superior, 1232 ciliary, 11 56 branches of, 1157 summary of, 1158 coccygeal, 862 diaphragmaticum, 758, 942 Gasserian, 1076 branches of, 1077 geniculate, of facial, 1299 branches of, 1299 habennlae, 1422 impar, 862 interpedunculare, 1440 jugular, 1223 Meckel, of, 12 19 mesenteric, inferior, 738 superior, 738 nodosum, 1226 otic, 121 1 petrous, 1223 phrenic, 736 Scarpa, of, 1300, 1558 semilunar, 736 spheno-palatine, 1219 spinal, 1325 spiral, 1559 splanchnic, 1035 stellatum, 1034 submaxillary, 1212 Valentin, of, 121 8 Wrisberg, of, 968 Ganglionic layer of retina, 1520 Gartner, duct or canal of, 883 Gasserian depression, 74 ganglion, 1076 branches of, 1077 Gastric sympathetic plexus, 736 Gastrocnemius, 518 Gastro-phrenic Ugament, 720 Gastrula, 1614 Gemellus, inferior, 430 superior, 429 Genial spines, 117 Geniculate bodies, 1420 ganghon, 1299 gyrus of corpus callosum, 1401 Genio-hyo-glossus muscle, 1131 Genio-hyoid muscle, 113 1 Genital cord, 685 eminence, 634, 635, 871 fold, 634, 871 ridge, 685 Genito-femoral nerve, 424, 770 Gerlach, valve of, 796 Germinal epithelium, 685 layers — structures derived from, 1617 summary of formation of, 1615 spot, 894 Germinal vesicle, 894 Giacomini, frenulum, 1396 Gimbemat's hgament, 434, 653 Ginglymus or hinge-joint, 280 Giraldes, organ of, 682 Girdle, pectoral, morphology of, 277 Glabella, 65, 133 Gladiolus, 47 Gland, Haversian, of hip-joint, 492 tarsal, 11 89 thymus, 945 thyroid, 1122 Glandis, corona, 648 Gland or glands — agminated, 791 axillary, 317 Bartholin, of, 633 Blandin, of, 1243 Bowman, of, 1257 bronchial, 1034 Brunner, of, 790 buccal, Ijanphatic, 11 83 mucous, 1 1 71 cardiac, of stomach, 783 carotid, 11 13 caval, 1034 ceruminous, 1537 cervical, deep, 1102 superficial, 1085 coccygeal, 862 coeliac, 742 concatenatae, 1062 Cowper, of, 621 Duvemey, of, 633 Ebner, of, 1243 femoral, deep, 455 superficial, 453 gastric, 783 lymphatic, 742 hepatic, 742 iliac, common, 777 external, 778 internal, 845 infraclavicular, 317 inguinal, 453 deep. 455 superficial, 453, 455 intercostal, anterior, 933 posterior, 1032 labial, 11 71 Littre, of, 858 of lower limb, summary of, 568 lumbar, 773 mastoid, 1073 mediastinal, anterior, 1032 posterior, 1034 superior, 1032 Meibomian, n88 mesenteric, 728 molar, 11 71 Moll, of, 1187 I702 INDEX Gland or glands [continued) — • of Montgomery, 300 Nuhn, of, 1243 occipital, 1063 odoriferae, 647 palatal, 1248 pancreatic, 742 parotid, lymphatic, 1183 salivary, 11 83 popliteal, 445 prelaryngeal, 1102 pretracheal, 1102 prostate, 853 pyloric, 784 sacral, 862 saphenous, 453 solitary, 791 splenic, 742 sternal, 933 submaxillary, lymphatic, iioi salivary, 1134 submental, iioi suprahyoid, iioi suprascapular, 1094 tibial, anterior, 509 tongue, of, 1243 Tyson, of, 647 of upper limb, 396 uterine, or utricular, 897 Weber, of, 1243 Glandula, of pars, socia parotidis, H84 Glandulae odoriferae, 647 Glans clitoridis, 630 penis, 648 Glaser, fissure of, 72, 1538 Gleno-humeral bands, 345 ligament, 345 Glenoid cavity, 180 fossa, 71 ligament, 345 Gliding joint, 280 movement, 282 Glisson, capsule of, 803 Globosus, nucleus, 1373 Globular processes, 162, 1240 Globus pallidus, 141 3 Glomerulus of kidney, 824 Glossary, 1668 Glosso-epiglottidean fold, 1276 Glosso-pharyngeal nerve. See Cranial Nerves Glottidis, rima, 1285 Glottis, false, 1284 respiratoria, 1285 vera, or true, 1285 vocalis, 1285 Gluteal artery, 430 lines, 222 nerve, inferior, 434 superior, 434 Gluteal region, 424 landmarks of, 424 vein, 432 Gluteus maximus, 426 medius, 428 minimus, 428 quartus, 429 Gnathic index of skull, 158 Gnathion, 133 Golgi, cells of, 1443 GoU, column of , 1315, 1326 Gomphosis, 172 Gonion, 142 Gowers, intermediate process of, 1322 tract of, 1330 Graafian follicles, 893 structure of, 893 Gracilis, adductor, muscle, 470 nucleus, 1353 Granular layer of Purkinje, 172 Granulosa, membrana, 894 Grey matter of spinal cord, varieties of, 1317 Groove, basilar, 59 bicipital, 186 carotid, 84 cavernous, 84 digastric, 72 infra-orbital, 98 nasal, of ethmoid, 93 neural, 161 8 nuchal, 283 olfactory, 82 optic, of sphenoid, 82 primitive, 161 4 pulmonary, of thorax, 53 radial, 195 sigmoid of temporal. 73 spinal, 283 spiral, 188 subcostal, 43 ulnar, of humerus, 1S9 Grooved suture, 280 Ground-bundle, anterior, 1329 lateral, 1331 Gubernaculum testis, O72 Gudden, commissure of, 1425 Gu6rin, sinus of, 858 valvule of, 858 Guide to digital arteries of hand, 367 to dissection of abdomen, 905 of brain, 1591 of ear, 1587 of eye, 1589 of head and neck, 1563 of lower limb, 392 of nasal cavities, 1585 of spinal cord, 1590 of thorax, 1046 of upper limb, 411 to gluteal artery, 432 INDEX 1703 Guide to palmar arch, deep, 367 superficial, 367 to removal of brain, 1 566 Gulae, plexus, 965 Gustatory cells, 1247 pore, 1247 Guthrie, muscle of, 617 Guttural fossa, 147 GjTus or g>'ri — angular, 1390 breves, 1393 callosal, 1394 cinguli, 1394 cuneus, 1391 dentatus, 1396 fomicatus, 1394 frontal ascending, 1385 inferior, 1386 pars basilaris, 1387 orbitalis, 1387 triangularis, 1387 speech centre of, 1387 middle, 1386 superior, 1386 geniculate, 1401 hippocampal, 1395 infracalcarine, 1391 lingualis, 1391 longus, 1393 marginal, 1388 occipito-temporal, 1393 orbital, anterior, 138S external, 1388 internal, 1387 posterior, 1388 parietal, ascending, 1389 inferior, 1389 superior, 1389 precentral, 1385 postcentral, 1389 postparietal, 1390 subcallosal, 1401 supracallosal, 1401 supramarginal, 1390 temporal, first, 1392 second, 1392 third, 1392 Habenula of pineal body, 1422 Habenulae, ganglion, 1422 trigonum, 1422 Hair-cells, 1554 Haller, vas aberrans of, 684 Hallucis, abductor, 549 adductor obliquus, 555 transversus, 555 arteria dorsalis, 512 magna or princeps, 565 extensor brevis, 510 proprius or longus, 504 flexor brevis, 555 Hallucis, flexor longus, 523 tendon of, 551 Ham, 440 Hamstring muscles, 437 Hamular process of lachrymal, 108 of sphenoid, 89 Hamulus of lamina spiralis, 1552 Hand, 175 as a whole, 216 Harmonic suture, 279 Hasner, valve of, 1192, 1255 Hassall, concentric corpuscles of, 946 Haversian canals, 5 gland of hip-joint, 492 of knee-joint, 537 system, 7 Head and neck, 1058 bones of, 56 of tibia, structures attached to 245 process, 1615 Heart, 970 apex of, 974 auricular portion of, 973 auricle, left, 980 right, 975 base of, 974 development of, 991 exterior of, 972 interior of, 975 structure of, 988 topography of, 970 of orifices of, 985 ventricular portion of, 973 ventricle, left, 981 right, 977 Heister, valves of, 809 Helicis major muscle, 1193 minor muscle, 1 193 Helicotrema, 1554 Helix, 1 192 Henle, band of, 660 cremaster muscle, internal, of. 671 hgament of, 658 tubule of, 819 Hensen, canahs or ductus reuniens of, 1553 cells of, 1558 Hensen's node, 1614, 1615 Hepatic artery, 741 canals, 805 cells, 805 duct, 708 flexure of colon, 697 lobule, 804 plexus, 736 veins, 805 Hepatis, pons, 706 sustentaculum, 697 Hernia, appendicular, 718 1704 INDEX Hernia, congenital, 679 diaphragmatic, 759, 761 femoral, 462 parts concerned in, 460 infantile, 680 inguinal — direct, internal, 678 oblique, external, 677 internal, 679 mesenteric, 717 meso-colic, 718 retro-peritoneal, 721 umbilical, 680 congenital, 680 Herophili, torcular, 59, 1475 Hesselbach, ligament of, 658 triangle of, 668 guide to, 642 Hey, femoral ligament of, 460 Hiatus, accessory, 75 Fallopii, 74 semilunaris, 1255 subarcuatus, 76 Highmore, antrum of, 102 corpus of, 683 Hilton, muscle of, 1291 white line of, 875 Hilton's law, 316 Hilum pulmonis, 949 Hind-gut, 798, 1623 Hind-kidney, 830 Hinge-joint, 280 Hip-joint, 488 movements of, 493 Hippocampal commissure, 1403 fissure, 1396 gyrus, 1399 Hippocampi, pes, 1409 taenia, 1405, 1409 Hippocampus major, 1409 minor, 1408 Holden's guide to great trochanter, 447 Homodjmamic, 3 Homogenetic, 3 Homologies, approximate, of bones of limbs, 277 Homology, 3 Horizontal section of skull, 149 Horner, muscles of, 1165 Houston, muscle of, 61 7 valves of, 874 Huguier, canal of, 72, 1538 Humeri, transversalis, artery, 320 Humerus, 184 anatomical neck of, 184 ossification of, 190 surgical neck of, 186 Hunter's canal, 475 Huschke, foramen of, 79, 82 vomerine cartilages of, 1199 Hyaloid artery, 1530 canal of eye, 1530 membrane, 1529 Hyaloplasm, 1597 Hydatids of Morgagni, in male, 682 Hydrocele, encysted, of spermatic cord, 676 Hymen, 631 development of, 632 Hyo-epiglottidean ligament, 1276 Hyo-glos^us muscle, 11 33 Hyoid arch, 165, 1272 bar, 163, 1272 bone, 121 development of, 165 ossification of , 123 Hypochordal bar, 55 Hypogastric sympathetic plexus, 738 zone, 690 subdivisions of, 690 Hypoglossal nerve. See Cranial Nerves Hypoglossi, trigonum, 1378 Hypophysis cerebri, 1079 Hypothalamus, 1423 Hypothalmi, pars mammillaris, 1423 pars optica, 1423 Hjrpothenar muscles, 379 Ileo-caecal fold, 722 valve, 797 Ileum, 695 peritoneal relations of, 695 Iliac arteries. See Arteries fossa, 223 left, contents of, 642 right, contents of, 642 veins. See Veins Ilii, dorsum, 222 Ilio-costalis muscle, 290 Ilio-hypogastric nerve, 425, 661, 769 Ilio-inguinal nerve, 449, 661, 770 Ilio-pectineal line, relation of struc- tures at pectineal portion of, 660 septum, 779 Ilio-psoas muscle, 465 Ilio-tibial band of fascia lata, 457 Ilium, 220 anterior superior spine of, 641 Impar, tuberculum, 1270 Incisor canal, loi crest, loi fossa, 97 teeth, 166 Incudis, fossa, 1539 Incus, 1543 Index, alveolar, 158 cephalic, 158 gnathic, 158 megjiseme, 158 INDEX 1705 Index, mesoseme, 158 microseme, 15S nasal, 158 orbital, 158 Indicis, abductor, muscle, 394 dorsalis, artery, 393 extensor, muscle, 388 radialis, artery, 381 Infracalcarine g>"rus, 1391 Infraglenoid ridge, 180 Infrahyoid muscles, 1102 region, 1106 Infra-orbital arter>', 1182, 1205 branches of, 1205 canal, 98, 136 foramen, 97 groove, 98 nerve, 1177, 121 7 branches of, 117 7, 1217 plexus, 1174 vein, 1 182 Infrapatellar pad of fat, 537 tendon, 470 Infraspinatus muscle, 320 Infraspinous fossa, 178 Infratemporal crest of sphenoid, 87 Infra trochlear nerve, 11 56 Infundibuliform sheath, 460 Infundibulum, 69, 94, 139 of Fallopian tube, 884 of heart, 975, 977 of kidney, 827 of lung, 952 of nasal fossa, 1254 of pituitary body, 1080 Inguinal canal, 666 position of, 642 fossae, 676 nerve, 449, 661, 770 Inion, 132 Innominatum, os, 220 Inscriptions or intersections of rectus abdominis muscle, 659 Insula of cerebral hemisphere. See Island of Reil Interarticular fibro-cartilages, 281 menisci, 281 Intercellular passages of liver, 806 Intercolumnar fibres, 651 Intercostal ner\es, 927, 103 1 spaces, 55 Intercosto-humeral nerve, 317, 331 Intercuneiform joints, 584 Interior of cranium, 149 Interlobar fissures of brain, 1382 calloso-marginaJ, 1383 circular or limiting, 1384 collateral, 1384 parieto-occipital, 1383 Rolandic, 1383 Sylvian, 1382 Interlobar notch of liver, 708 Interlobular plexuses of liver, 804 Intermaxillary' bone, 104 Intermediate septum, posterior, of spinal cord, 13 15 Intermetatarsal joints, 588 Interosseous artery, cinterior, of fore- arm, 361 common, of forearm, 360 posterior, of forearm, 361 membrane of forearm, 405 of leg, 577 muscles of foot, 556 dorsal, 557 plantar, 556 of h^d, 393 dorsal. 394 palmar, 394 nerve, posterior, of forearm, 358 Interparietal bone, 57, 61 Interpeduncular space, 1339 structures wthin, 1423 corpora albicantia vel mam- millaria, 1423 peduncles of, 1423 development of, 1424 infundibulum, 1080, 1424 locus perforatus posticus, .1439 pituitary body, 1079 tuber cinereum, 1424 Interpositum, velum, 1404 blood-supply of, 1458 Interspinales muscles, 294 Interstitial lamellae of bone, 6 Intertransversales muscles, 295 Intertubercular line, 689 plane, 689 Interventricular septum, 985 Intestinal canal, 694 blood-supply of, 725 development of, 724 Intestine, large, 695 structure of, 794 small, 694 structure of, 787 Inti:ajugular process, 61 Intralobular plexuses of liver, 804 Iris, 1515 arteries of, 1516 ciliary margin of, 151 5 muscles of, 15 15 nerves of, 15 16 pars iridica retinae, 15 15 pupil, 1515 pupillary margin of, 15 15 structure of, 15 15 uvea, 15 15 veins of, 1516 Irregular bones, 7 Ischio-rectal fossa, 612 x7o6 INDEX Ischio-rectal fossa, contents of, 613 diverticula of, 613 Ischium, 223 spine of, structures on back of, 434 tuberosity of, 224 Island of Reil, or insula, 1393 development of, 1396 gyri breves, 1393 gyrus longus, 1393 limen of, 1393 lobule precentral, 1393 postcentral, 1393 sulcus centralis, 1393 Isthmus faucium, 1249 pharyngeal, 1268 Iter a tertio ad quartum ventriculum, 1439 Iter chordae anterius, 72, 1538 posterius, 75, 1540 Ivory, 171 Jacobson, cartilages of, 11 99 organ of, 1262 development of, 1263 nerve of, 1224 Jejunum, 695 Joints, acromio-clavicular, 326 amphiarthrosis, 280 ankle, 569 arthrodia, 280 astragalo-calcaneal, 578 anterior, 579 posterior, 578 astragalo- navicular, 580 guide to, 543 atlanto-axial, 1301 atlanto-occipital, 1 303 calcaneo-cuboid, 582 guide to, 543 carpal, 406 first row, 406 second row, 407 carpo-metacarpal, 408 of thumb, 408 chondro-sternal, 1043 classification of, 279 condylarthrosis, 280 costo-central, 104 1 costo-chondral, 1043 costo-transverse. 1042 costo-vertebral, 1041 crico-arytenoid, 1282 crico-thyroid, 1282 cubo-cuneiform, 585 cubo-metatarsal, 587 diarthrosis, 280 elbow, 398 enarthrosis, 280 femoro-patellar, 540 of foot, 578 Joints, ginglymus, 280 gliding, 280 of hand, 406 hinge, 280 hip, 488 nerve-supply of, 493 interchondral, 1044 intercoccygeal, 900 intercuneiform, 584 intermetacarpal, 409 intermetatarsal, 588 interphalangeal (of foot 591 (of hand), 410 knee, 528 nerve-supply of, 538 lumbo-sacral, 899 metacarpo-phalangeal, 410 metatarso-phalangeal, 590 naviculo-cuboid, 583 naviculo-cuneiform, 584 of occipital bone, 1301 of pelvis, 899 pisiform, 406 pivot, 280 radio-carpal or wrist, 402 radio-ulnar, inferior, 404 intermediate, 405 superior, 404 of ribs, 1041 sacro-coccygeal, 900 sacro-iliac, 900 shoulder, 344 sternal, 1045 stemo-clavicular, 324 suture, 279 dentated, 279 false, 279 harmonic, 279 limbous, 279 serrated, 279 squamous, 279 true, 279 symphysis, 280 pubis, 903 synarthrosis, 279 synchondrosis, 279 syndesmosis, 280 tarsal, 578 tarso-metatarsal, 586 external, 587 internal, 58(> middle, 586 temporo-mandibular, 1214 tibio-fibular, inferior, 576 intermediat{^ 576 superior, 575 transverse carpal, 407 trochlearthrosis, 280 trochoides, 280 varieties of, 279 INDEX 1707 Joints of vertebral column, 1036 wrist, 402 Jugal point, 142 process of temporal, 70 Jugular foramen, 148 fossa of temporal, 76 notch of occipital, 61 process of occipital, 60 vein, anterior, 1083 external, 1084 development of, 1084 internal, 11 13 development of. 11 13 posterior, 1063 Jugum sphenoidale. 82 Karyokinesis, 1598 Karyoplasm, 1597 Kataphase, 1599 Kerkring, valves of. 788 Kidneys, 744 arteries of, 822 cortical part of, 819 development of, 829 early condition of, 829 hilum of, 748 medullary part of, 818 sinus of, 748, 818 structure of, 817 varieties of, 748 veins of, 826 Knee-joint, 528 arterial supply, 538 movements, 539 nerve-supply, 538 Kobelt, pars intermedia of, 633 parovarium of, 884 Krause, ulnar collateral nerve of, 3 16, 364 ventriculus terminalis of, 13 19 Labia majora, 628 development of, 630 minora, 629 development of, 630 Labial mucous glands, 1237 Labium t\-mpaiiicum, 1556 vestibulare, 1556 Labyrinth of ear, membranous, 1552 blood-supply of, 1559 osseous, 1548 of kidney, 819 Lachr\mal apparatus, 11 90 development of, 1191 artery, 1159 bones, 108 ossification of, 109 canaliculi, 1190 glcind, 1 146 nerve, 11 55 punctum, 1 187 Ladm-mal papilla, 11 87 sac, 1 1 90 structure of, 1 191 Lacrimalis, caruncula, 11 89 lacus, 1 1 87 Lacteals of small intestine, 728, 790 Lactiferous ducts, 301 Lacuna or lacunae — laterales, 1475 magna of Morgagni, 858 of Morgagni, S58 muscular, 779 vascular, 780 Lacunae of bone, 6 Lacunar region, 779 Lacus lacrimalis, 11 87 Lambda, 124 Lambdoid ligament, 501 Lamellae, circumferential or peri- pheral, 6 concentric, of bone, 6 interstitial, of bone, 6 pressure, 7 of femur, 240 tension, 7 of femur, 240 Lamina basalis, 1512 chorio-capillaris, 13 12 cribrosa of sclerotic, 1507 of internal auditory- meatus, 1551 of temporal bone, 75 dental, true, 173 elastic, anterior, of Bowman, 1509 posterior, of Descemet, 15 10 fusca, 1508 labio-dental, 172 reticularis, 1558 phalangeal process of. 1558 spiralis of cochlea, 1551 suprachoroidea, 151 1 terminalis of brain, 1424 vasculosa, 15 12 Lancisi, nerves of, 1401 Landmarks of abdominal wall, 639 of arm, 329 of back. 283 of scalp and neck, 1058 of thigh and popliteal space^ 435 of face, 1 1 63 of gluteal region, 424 of knee, 447 of leg, 496 of male perineum, 61 1 of side of neck, 1080 of sole of foot, 543 of front and inner side of thigh, 446 of front of wrist and palm, 367 1708 INDEX Langerhans, centro-acinar cells of, 810 islets of, 810 layer of, 1628 Laryngeal artery, inferior, 1 142 superior, 11 16 nerve, inferior or recurrent, 966, 1228, 1292 superior, 1227, 1292 external branch of, 1228, 1292 internal branch of, 1228, 1292 summary of, 1293 Larynx, aperture, superior, of, 1283 arteries of, 1293 cartilages of, 1275 arytenoid, 1279 comicula, 1280 cricoid, 1278 cuneiform, 1280 epiglottis, 1275 development of , 1294 glottidis, rima, 1285 glottis, 1285 interior of, 1283 ligaments of, 1 280 lymphatics of, 1293 mucous membrane of, 1286 muscles of, 1287 actions of, summary of, 1291 nerves of, 1292 pouch of, 1283 saccule of, 1283 sinus of, 1283 sinus pyriformis, 1283 structure of, 1275 veins of, 1293 ventricle of, 1283 vestibule of, 1283 vocal cords, false and true, 1284 Lateral sinus, 1476 course of, 1477 emissary veins of, 1479 guide to, 1501 Latham, circle of, 971 Latissimus dorsi muscle, 286 Law, Hilton's, 316 of ossification, 178, 190 Leg, the, 496 anterior aspect of, 503 external aspect of, 515 internal aspect of, 502 posterior aspect of, 517 Lemniscus, 1360 Lens, crystalline, 1528 capsule of, 1529 structure of, 1528 vesicle, 1532 Lenticular ganglion, 1156 branches of, 1157 summary of, 1158 Lenticularis, ansa, of optic thalamus, 1421 nucleus, 1412 blood-supply of, 1457 processus, of incus, 1543 Leptorhine skulls, 158 Lesser, triangle of, 1 1 30 Levator anguli scapulae muscle, 287 ani muscle, 862 palati muscle, 1251 Levatores costarum muscles, 296 longiores, 296 Lieberkiihn, crypts or follicles of, 791 Lienis, sustentaculum, 698, 720 Ligament or ligaments — accessory, of atlas and axis, 1 302 acromio-clavicular, 327 alar, of axis, 1305 of ankle-joint, 569 annular, 404 of ankle, anterior, 500 external, 498 internal, 499 of wrist, anterior, 376 posterior, 390 arcuate, of diaphragm, 761 of astragalo-calcaneal joint, an- terior, 579 posterior, 578 of astragalo-navicular joint, 580 atlanto-axial, 1302 atlan to-occipital, 1303 of auricle, 1 1 93 of bladder, false, 867 true, 867 of Bigelow, 489 of calcaneo-cuboid joint, 582 calcaneo-navicular, inferior, 580 central, of spinal cord, 13 13 check, of axis, 1 305 chondro-sternal, 1044 Colles, of, 653 common, anterior, of vertebrae, 1036 posterior, of vertebrae, 1037 conoid, 327 coraco-acromial, 328 coraco-clavicular, 327 coraco-humeral, 344 coronary, of knee, 535 costo-central, anterior, 1041 interarticular, 1042 costo-clavicular, 326 costo-colic, 698, 720 costo-transverse, middle, 1043 posterior, 1043 superior, 1043 cotyloid, 492 crico-thyroid membrane, 1280 capsular, 1T98 crucial, 532 INDEX 1709 Ligament or ligaments {continued) — cruciform, 1305 of cu bo-cuneiform joint, 585 of cubo-metatarsal joint, 587 discs, interv^ertebral, 1038 of elbow, 398 femoral, of Hey, 460 Flood's, 345 gastro-phrenic, 720 Gimbemat, of, 653 glenoid, 345 gleno-humeral, 345 Henle, of. 658 Hesselbach, of, 658 of hip-joint, 488 hyo-epiglottidean, 1276 ilio-femoral, 4S9 ilio-lumbar, 900 ilio-trochanteric, 490 incus, of, 1544 interclavicular, 326 of intercuneiform joints, 584 of intermetatarsal joints, 588 internal brachial of Struthers, .335 mterosseous, of forearm, 405 inferior, of leg, 576 membrane of leg, 577 of interphalangeal joints (of hand), 410 (of foot), 591 interspinous, of vertebrae, 1040 intertransverse, of vertebrae, 1040 ischio-capsular, 490 of knee-joint, 528 accessory, 535 of laminae of vertebrae, 1039 larynx, of, 1280 lieno-phrenic, 720 Ueno-renal, 720 Uyer, of, 718 coronary, 719 falciform, 718 lateral, 719 posterior, 719 round, 719 suspensory, 718 triangular, 719 lumbo-sacral, lateral, 900 malleus, of, 1540 metacarpo-phalangeal, 410 metatarso-phalangeal, 590 of naviculo-cuboid joint, 583 of naviculo-cuneiform joint, 584 oblique, of forearm, 405 occipito-axial, 1304 odontoid, of axis, lateral, 1 305 middle, 1305 orbicular, 404 palpebral, 11 88 patellar, lateral, 531 Ligament or ligaments {continued) — pelvic, transverse, 619 perineal, transverse, 619 phreno-colic, 6g8, 720 phreno-splenic, 720 plantar, long, 582 short, 582 Poupart, of, 651 pterjgo-mandibular, io88 pterygo-spinous, 1088 pubic, 903 of Cooper, 461, 780 pubo-femoral, 490 pubo-prostatic, 839 radiate, 1041 radio-ulnar, superior and in- ferior, 404 rhomboid, 326 sacro-coccygeal, 900 sacro-iliac, 901 sacro-sciatic, great, 901 small, 902 Schlemm's, 345 of shoulder-joint, 344 spheno-mandibular, 12 14 spino-glenoid, 328 spiral, of cochlea, 1555 spleen, of, 720 spring, 580 stapes, annular of, 1544 stellate, 1041 stemo-clavicular, 324 stemo-pericardial, 944 stylo-hyoid, 11 34 stylo-mandibular, 1215 subpubic, 903 suprascapular (transverse), 328 supraspinous, of vertebrae, 1040 suspensory, of axis, 1 305 of eye (Lockwood's), 1151 of lens, 1530 of penis, 647 tarsad, 1165, 1188 of tairso-metatarsal joints, ex- ternal, 587 internal. 586 middle, 586 temporo-mandibular, 1214 teres, 491 th>TO-arytenoid, 1281 thyro-epiglottidean, 1275 th\TO-hyoid membrane, 1280 of tibio-fibular joint, inferior, 576 superior, 575 transverse, of atlais, 1302 transverse, deep (of hand), 409 superficial (of hand), 368 transverse, of hip-joint, 492 transverse, humeral, 345 of knee-joint, 535 of leg, 576 I7IO INDEX Ligament or ligaments {continued) — transverse, metacarpal, 409 metatarsal, 589 trapezoid, 327 triangular, of urethra, 619 of uterus, broad, 880 round, 881 vaginal, of hand, 375 of vertebrae, 1036 of wrist-joint, 402 Y-shaped, of Bigelow, 489 Zinn of, 1150 Ligamentum or ligamenta — alaria, 537 arcuatum, 903 externum, 761 internum, 761 brevia (of hand), 376 ductiis arteriosi, 964 vehosi, 999 latum pulmonis, 937 longa (of hand), 376 mucosum, 537 nuchae, 286, 106 1 patellae, 470, 528 pectinatum iridis, 1510 posticum VVinslowii, 529 subflava, 1039 suspensoria of Cooper, 300 teres, 491 JLigula of fourth ventricle, 1378 Limb, lower, 424 bones of, 220 divisions of, 220 guide to dissection of, 592 summary of veins of, 566 upper, 283 bones of, 1 75 divisions of, 1 75 guide to dissection of, 41 1 Limbic lobe of brain, 1394 Limbous suture, 279 Limbus laminae spiralis, 1556 sphenoidalis, 82 Vieussenii, 993 Linea alba, 639 aspera of femur, 236 splendens, 13 11 Lineae semilunares, 640 transversae, 640 Lingual artery, 1117 branches of, 11 18 nerve, 12 10 branches of, 1211 veins, 11 18 Lingula of cerebellum, 1368 of mandible, 118 sphenoidalis, 84 Lips, 1237 Liquor folliculi, 894 Lisfranc's ligament. 587 Lisfranc's operation, 587 tubercle, 44 Lissauer, tract of , 1327 Lith(?tomy, lateral, structures avoided in, 628 divided in, 627 Littr6, glands of, 858 Liver, 702 borders of, 708 cells of, 805 component parts of, 702 Liver, connections of, 702 development of, 807 duct of, 708 early life, in, 710 excretory apparatus of, 708 fissures or fossae of — caval, 708 cystic, 705 portal, 706 transverse, 706 umbilical, 706 venosal, 707 impressio cardica, 704 colica, 706 duodenalis, 706 gastrica, 705 renalis, 706 suprarenahs, 708 lijjaments of, 718 lobes of — caudate, 706 left, 705 quadrate, 705 right, 705 Spigel's, 707 tuber papillare of, 706 lobules of, 804 notches of — cystic, 708 interlobar, 708 umbilical, 708 oesophageal groove of, 707 outline of, summary of, 702 peritoneal relations of, 70S position of, 702 surfaces of, 703 structure of, 803 topography of, 702 tuber omentale, 705 uncovered area of right lobeof, 708 Lobes and lobules of cerebral hemi- spheres. See Cerebral Hemi- spheres of cerebellum. See Cerebellum Lobuli testis, 683 Lockwood, superior tendon of, 1 149 suspensory ligament of, 1151 Locus caeruleus, 1378 perforatus anticus, 1340 blood-supply of, 1456 INDEX 1711 Locus perforatus posticus, 1439 blood-supply of, 1456 Longbones, 7 Longissimus dorsi muscle, 291 Longitudinal fissure, great, 1344 sinus, inferior, 1475 superior, 1475 emissary veins of, 1479 Lowenthal, anterior marginal bundle of, 1329 Lower, tubercle of, 977 Lucidum, septum, 1403 Lumbar aponeurosis, 765 posterior lamina of, 289 plexus, 768 vertebrae, 25 Lumbo-sacral cord, 771 Lumbrical muscles (of hand), 376 (of foot), 553 Lvtschka, cartilage of, 1282 coccygeal gland of, 862 stemo-pericardial ligaments of, 944 Lung-buds, 954 Lungs, 946 cervical part of, 11 46 development of, 954 in foetus, 955 root of, 951 structure of, 95 1 Lunulae of aortic valves, 984 Lutea, macula, 151 8 Luteum, corpus, 893 Luys, nucleus of, 1421 Lymphatic glands- aortic, 757 anticubital, 335 axillary, 317 bronchial, 1034 buccal, 1 1 83 caval, 1034 cervical, deep, 1102 superficial, 1085 colic, 731 femoral, deep, 455 superficial, 453 ileo-colic, 729 ihac, common, 777 external, 778 internal, 845 infraclavicular, 317 inguinal, 452 deep, 455 superficial, 452 intercostal, anterior, 933 posterior, 1032 intestine, of large, 731 of small, 728 jugular, right and left trunk, Lymphatic glands [continued) — of lower limb, summar\' of, 568 lateral aortic, 757 lingual, 1 1 19 lumbar, lateral, 774 median, 773 maxillary, internal, 1206 mediastinal, anterior, 1032 posterior, 1034 superior, 1032 mesenteric, 728 meso-colic, 731 occipital, 1063 parotid, 11 83 popliteal, 445 pre-aortic, 757 pretracheal, 1127 pubic, 453 rectal, 877 retro-aortic, 758 retro-pharyngeal, 1270 saphenous, 453 sternal, 933 stomach, of, 785 submental, 1105 submaxillary, iioi thoracic, 957 tibial, anterior, 509 thyroid, inferior, 11 29 of upper limb, 396 system, development of, 1016 trunk, axillary, 317 vessels of — abdominal wall, deep, 664 superficial, 646 anal canal, 877 auricle, 11 95 bladder, 868 colon, ascending, 729 descending, 731 iliac, 731 pelvic, 731 transverse, 729 face, deep, 1183 superficial, 1182 Fallopian tube, 896 gluteal region, 435 gall-bladder, 809 heart, 988 intercostal spaces, 930 intestine, large, 731 small, 728 kidney, 826 larynx, 1293 liver, 806 lower limb, 567 lungs. 954 nasal fossa, 1261 nose, 1 1 96 oesophagus, 1022 I7I2 INDEX Lymphatic glands {continued) — ■ ovary, 894 penis, deep, 649 superficial, 648 pericardium, 945 perineum, female, 638 male, deep, 625 superficial, 625 pharynx, 1269 pia mater, 1311 pleura, 939 rectum, 877 scrotum, 650 spinal cord, 1334 stomach, 785 testis, 683 tongue, 1246 tonsils, 1254 upper limb, deep, 396 superficial, 395 ureter, 827 urethra, female, 899 male, 858 uterus, 897 vagina, 898 vesiculae seminales, 872 Lymphatics, axillary, 301 epicondylar, internal, 335 infraclavicular, 302 internal mammary, 302 of mamma, 301 of scalp, frontal region, 1074 subareolar, 301 Lyra, 1403, 1446 McBurney, point of, 642 Macewen's triangle, 72 Macula acustica sacculi, 1553 utricuU, 1552. 1553 lutea, 1 51 8 structure of, 1524 Magendie, foramen of, 1380 Malar artery, 1182 bone, 104 ossification of, 107 marginal process of, 106 Malleolar folds of malleus, 1540 Malleolus, external, 250 internal, 247 Malleus, 1542 Malpighian corpuscles of kidney, 824 of spleen, 814 pyramids of kidney, 818 Mamma, 300 development of, 303 lymphatics of, 302 nerves of, 302 structure of, 302 vessels of, 301 Mammae, accessory, 302 Mammary artery, external, 311 Mammary artery, internal, cervical part, 1 142 thoracic part, 931 Mammillary process, 25 Mandible, 115 Mandibular arch, 163, 1272 Mantle of brain, 1393 Manubrium sterni, 47 Marginal bundle, anterior, of Lowen- thal, 1329 posterior, of Lissauer, 1327 Marrow, 10 Marshall, oblique vein of, 987 vestigial fold of, 944 Martrnotti, cells of, 1443 Masseter muscle, 1199 Masseteric fascia, 1238 nerve, 1207 Mastication, muscles of, 1199 Mastoid antrum, 73, 1546, 1547 cells, 73 foramen, 73 portion of temporal, 72 Mater, dura, cranial, 1470 spinal, 1306 pia, cranial, 14 81 spinal, 1 310 Maturation of ovum, 1608 Maxillary air-sinus, 102 artery, external, 1178 internal, 1202 first part of, 1203 branches of, 1203 second part of, 1 205 branches of, 1205 third part of, 1205 branches of, 1207 bone, inferior, 115 • ossification of, 119 superior, 97 ossification of, 103 nerve, inferior, 1077, 1207 anterior division of, 1207 posterior division of, 1209 summary of, 1214 superior, 1077, 121 7 branches of, 1158, 1217 summary of, 1221 process of mandibular arch, 1272 processes, 163 vein, internal, 1206 Maxillo-turbinal, 109 Meatus auditorius externus, 1536 bloodvessels of, 1537 lymphatics of, 1537 nerves of, 1537 auditor}', external, 78 internal, 75 inferior, 139 INDEX 1713 Meatus, middle, 95, 139 superior, 95, 139 urinaxius, female, 631, 890 male, 6og, 854 Meatus of nasal fossae, 1254 inferior, 1255 middle, 1254 atrium of, 1255 bulla ethmoidalis of, 1255 hiatus semilunaris of, 1255 vestibule of, 1255 superior, 1254 Meckel, cartilage of, 163, 1272 cave of, 1076 diverticulum of, 695, 799 ganglion of, 1219 branches of, 1220 summary' of, 1221 Median artery, 361 nerve, 340, 365 inner root of, 315 outer root of, 315 branches of, 365 in hand, 372 digital branches of, 372 summary of, 373 Vein, 332 deep, 332 basilic vein, 332 cephalic vein, 332 Mediastinal space, 939 Mediastinum, anterior, 940 middle, 941 posterior, 941 superior, 940 testis, 683 thoracis, 939 Medulla, 10 Medulla oblongata, 1345 oblongata, anterior area of, 1347 lateral area of, 1348 posterior area of, 1350 arcuate fibres of, superficial, 1359 deep, 1359 nucleus of, 1355 blood-supply of. 1456 central canal of, 1360 clava of, 1350 closed or lower part of, 1 346 cuneate nucleus of, external, 1354 accessory, 1354 tubercle, 1350 decussation, motor, 1348 of pyramids, 1348 sensory, 1359 development of, 1361 fillets, 1360 Medulla oblongata {continued) — formatio reticularis, 1352 alba, 1353 grisea, 1352 funiculus cuneatus, 1350 gracilis, 1350 Rolando, of, 1350 longitudinal bundle, pos- terior. 1358 nucleus cuneatus, 1350 graciUs, 1350 oUvary body of. 1348 nucleus, 1354 dorsal accessory, 1355 infenor. 1354 mesial, 1355 open or upper part of, 1346 pyramid of, 1347 decussation of, 1348 pyramidal tract, crossed, 1348 direct. 1348 raphe of, 1360 relation of chief nerve- fasciculi of spinal cord to, 1361 restiform body of, 1357 structure, internal, of, 1351 substantia gelatinosa of Ro- lando of, 1353 tubercle of Rolando of, 1350 white matter of, 1356 Medullaris, conns, 1312 stria, 1416 Medullary artery of femur, 484 of fibula, 526 of humerus. 339 of radius and ulna, 361 of tibia, 525 laminae of lenticular nucleus, 1412 membrane, 11 nerve of tibia, 443 ■ rays of kidney, 822 summary of, 822 spaces, 7 Medulla spinalis, 13 12 Megacephahc skulls, 157 Megaseme, 158 Meibomian glands. 1 1 88 Meissner, plexus of, 787, 793 Membrana eboris, 171 flaccida, 1540 granulosa, 894 nictitans, 11 90 pupillaris, 151 7 sacciformis, 405 tectoria, 1558 tympani, 1540 secondary. 1542 108 1 714 INDEX Membrane of Reissner, 1555 Meningeal artery, middle, 1203, 1471 guides to divisions of, 1502 small, 1204, 1 47 1 Meninges of encephalon, 1470 of spinal cord, 1306 Menisci, interarticular, and marginal, 281 Mental artery, 1 1 82 foramen, 116 point, 133 protuberance, 116 tubercle, 116 Mercier, bar of, 866 Meridian of eyeball, 1507 Mesaticephalic skulls, 132, 158 Mesencephalon, 1337, 1427 Mesenteric glands, 728 hernia, 717 holes, 717 plexus, inferior, 738 superior, 738 Mesentery, definition of, 711 primitive ventral, 724 . dorsal, 724 proper, 717 ventral gastro-duodenal, 724 Mesethmoid, 93 Meso-appendrx, 697, 717 : Mesocardium, 992 Mesocephalic skulls, 157 Meso-colon, pelvic, 718, 859 transverse, 718 Mesoderm, formation of, 1615 somatic, 1620 splanchnic, 1620 Mesogastrium, 724, 802 Mesognathion, 104 Mesognathous skulls, 134, 158 Mesometrium, 887 Meso-nephron, 748 Meso-nephros, 829 Mesorchium, 671, 688 Mesorhine skulls, 158 • Mesosalpinx, 881 Mesoseme, 158 Mesosternum, 49 Mesovarium, 688, 881 Metacarpal bone, first, 209 second, 209 third, 210 fourth, 211 fifth, 211 Metacarpus, 208 ossification of, 214 as a whole, 213 Metanephric blastema, 83b Meta-nephros, 830 Metaphase, 1599 Metasternum, 49 . , Metatarsal artery, 512 bone, first, 266 second, 266 third, 267 fourth, 268 fifth, 269 Metatarsus, 265 ossification of, 272 as a whole, 271 Metathalamus, 1419 Metencephalon, 1337 Metopic suture, 125 Metopism, 69 Meynert, commissure of, 1430 Microcephalic skulls, 157 Microseme, 158 Mid-gut, 798, 1623 Mid-kidney, 829 Milk teeth, 169 Mitosis, 1598 Mitral cells, 1448 orifice, 980 position of, 985 valve, 982 Moderator band of heart, 978 Modiolus, 1 55 1 spiral canal of, 1 551, 1559 Molar teeth, 168 Molecular layer, of cerebellum, 1375 inner, of retina, 152 1 outer, of retina, 1522 Moll, glands of, 11 87 Monro, foramina of, 1417 point of, 642 sulcus of, 1 416 Mons Veneris, 628 Montgomery, glands of, 300 Morbus caeruleus, 999 Morgagni, anal valves of, 876 columns of, 875 hydatids of, 682 lacunae of, 858 sinus of, 1265 Morphology, 3 of pectoral girdle, 277 Morula, 161 2 Moss-fibres of Cajal, 1376 Mouth, 1236 development of, 1239 stomodajum, 1239 bucco - pharyngeal mem- brane, 1239 globular process, 1240 labial ridge, 1240 maxillary process of first visceral arch, 1240 primitive oral cavity, 1240 vestibule of, 123O Movements, angular, 282 circumduction, 282 INDEX 1715 Movements, coaptation, 282 gliding, 282 pronation, 406 of ribs, 1045 rotation, 282 supination, 406 of temporo - mandibular joint, 1216 of vertebral column, 1040 Muliebres, testes, 894 Miiller, ducts of, 830, 898 fibres of, in retina, 1523 Multifidus spinae muscle, 294 Muscles — abductor hallucis, 549 indicis, 394 minimi digiti (of foot), 551 (of hand), 379 ossis metatarsi quinti, 551 pollicis, 377 accelerator urinae, 616 accessorius ad ilio-costalem, 290 adductor brevis, 471 gracilis, 470 longus, 471 magnus, 471 minimus, 472 obliquus hallucis, 555 pollicis, 378 transversus haUucis, 555 pollicis, 378 anconeus, 386 arytaeno-epiglottideus, 1290 arytenoid, 1290 attoUens auriculam, 1072 attrahens auriculam, 1072 auricle of, extrinsic, 1072 intrinsic, 1193 biceps femoris (flexor cruris), 437 flexor cubiti, 336 biventer cervicis, 293 brachialis anticus, 337 brachio-radialis, 383 bulbo-cavemosus, of female, 637 of male, 616 buccinator, 1169 cervicahs ascendens, 290 . cihar>', 1513 circumflexuspalati, 1252 coccygeus, 863 complexus, 292 compressor sacculus laryngis, 1291 naris, 1 166 urethrae, of female, 637 of male, 617 venae dorsalis penis, 616 constrictor, inferior, of pharynx, T264 Muscles [continued) — constrictor, isthmi faucium, 1250 middle, of pharynx, 1264 superior, of pharynx, 1263 urethrae, of female, 637 of male, 61 7 coraco-brachiahs, 335 corrugator cutis ani, 612 supercilii, 11 66 cremcister, 656 crico-arjrtenoid, lateral, 1288 posterior, 1288 crico-thyroid, 1287 crureus, 467 cucullaris, 285 I deltoid, 319 depressor aJae nasi, 1166 anguli oris, n 70 labii inferioris, 1 1 70 detrusor urinae, 865 diaphragm, 758 central tendon of, 759 development of, 761 foramina of, 760 digastric, 1129 dilator naris anterior, 1167 posterior, 1167 ejaculator urinae, 616 erector cKtoridis, 637 penis, 615 spinae, 290 inner column, 292 middle column, 291 outer column, 290 extensor bre\'is digitorum, 509 hallucis, 510 pollicis, 388 carpi radialis brevior, 383 longior, 3 S3 ulnaris, 386 communis digitorum, 384 indicis, 388 longus digitorum, 504 hallucis, 504 poUicis, 388 minimi digiti, 384 ossis metacarpi pollicis, 388 primi intemodii • pollicis. 388 proprius hallucis, 504 secundi intemodii pollicis, 388 flexor accessorius (of foot), 553 brevis digitorum, 549 hallucis, 5^-, minimi digiti (of foot), 556 (of hand), 380 pollicis, 378 carpi radialis, 352 ulnaris, 2^;^ I7I6 INDEX Muscles {continued) — flexor longus digitorum, 521 tendon of, 551 hallucis, 523 tendon of, 551 poUicis, 366 profundus digitorum, 365 sublimis digitorum, 354 frontalis, 1068 gastrocnemius, 518 gemellus, inferior, 430 superior, 429 genio-hyo-glossus, 1131 , genio-hyoid, 1131 gluteus maximus, 426 medius, 428 minimus, 428 quartus, 429 gracilis, 470 Guthrie, of, 617 hamstring, 437 Horner, of, 1165 Houston, of, 617 hyo-glossus, 1133 hypothenar, 379 iliacus, 766 minor, 7^7 ilio-capsularis, 767 ilio-costalis, 290 ilio-psoas, 465, 766 infrahyoid, 1102 infraspinatus, 320 intercostal, external, 926 internal, 927 interosseous (of foot), 556 (of hand), 393 primus volaris, 378 interspinales, 294 intertransversales, 295 ischio-cavemosus, of male, 615 of female, 637 larynx, of, 1287 summary of actions of, 1291 latissimus dorsi, 286 levator anguli oris, 11 68 scapulae, 287 ani, 862 glandulae thyroidea^ 11 22 labii inf erioris, 1 1 70 superioris, 11 68 alaeque nasi, 1 166 menti, 11 70 palati, 1 25 1 palpebral superioris, 1147 prostata;, 863 levatores costarum, 296 longiores, 296 urethrae, 617 longissimus dorsi, 291 longus colli, 1294 lumbricales (of foot), 553 Muscles {continued) — lumbricales (of hand), 376 masseter, 1199 mastication, of, 1199 multifidus spinae, 294 mylo-hyoid, 1130 obliqui, of eye, 1150 obliquus externus abdominis, 65a internus abdominis, 654 inferior, of eye, 1150 superior, of eye, 1150 obturator externus, 473 internus, 429 occipitalis, 1068 occipito-frontalis, 1068 omo-hyoid, 1102 posterior belly of, 320 opponens minimi digiti (of foot), 556 (of hand), 380 pollicis, 377 orbicularis oris, 1 1 70 palpebrarum, 11 65 palato-glossus, 1250 pharyngeus, 1250 palmaris brevis, 368 longus, 352 pectineus, 465 pectorahs major, 303 minor, 306 perinsei transversus, profundus, 617 superficialis, 615 peroneus .brevis, 517 longus, 515 tertius, 505 plantar is, 520 platysma, 1082 popliteus, 521 prevertebral, 1294 pronator quadratus, 366 radii teres, 351 psoas magnus, 766 parvus, 766 pterygoid, external, 1200 internal, 1202 pubo-vesical, 865 pyramidalis abdominis, 659 nasi, 1 166 pyriformis, 429, 864 quadratus femoris, 430 lumborum, 767 menti, 11 70 quadriceps extensor femoris 466 recto-coccygei, 875 rectus abdominis, 658 sheath of, 659 capitis lateralis, 1294 anticus major, 1294 minor, 1294 femoris, 466 INDEX 1717 Muscles {continued)— rectus, external, of eye, 1 149 inferior, of eye, 1149 rectus, internal, of e%e, 1148 superior, of eye, 1147 respiration, of, 1045 rhomboideus major, 287 minor, 287 Retrahens auriculam, 1072 rider's muscle, 473 risorius of Santorini, 1168 rotatores spinae, 294 salpingo-pharyngeus, 1275 j sartorius, 464 scalenus anticus, 11 36 medius, 11 36 posticus, 1 138 scansorius, 429 semimembranosus, 438 semispinalis colli, 294 dorsi, 294 semitendinosus, 437 serratus magnus, 318 posticus, inferior, 2S8 superior, 288 soft palate, of, 1250 soleus, 519 sphincter ani extemus, 612 intemus, 875 pupillae, 1 51 5 vaginae, 637 vesicae, 865 spinalis dorsi, 292 splenius. 289 capitis, 290 colli, 290 stapedius, 1545 stemalis, 304 stemo-cleido-mastoid, 1088 posterior border of, 1061 stemo-hyoid, 1103 stemo-thyroid, 1103 stylo-glossus, 1 1 33 stylo-hyoid, 1130 stylo-pharyngeus, 1221 subanconeus, 342 §ubclavius, 306 subcostal, 1035 subcrureus, 469 subscapularis, 323 supinator radii brevis, 386 longus. 383 supraspinatus, 320 temporal, 1074, 1200 tensor fasciae femoris, 464 palati, 1252 tarsi, 1 165 tympani, 1544 teres major, 321 minor, 321 thenar, 377 Muscles {continued) — thyro-arj-tenoid, 1289 thyro-hyoid, 1103 tibialis anticus, 504 • posticus, 522 tongue, of, intrinsic, 1244 lingualis inferior, 1245 superficialis, 1244 transversus, 1245 verticalis, 1243 trachelo-mastoid, 292 transversalis abdominis, 656 cervicis, 292 pedis. 555 transversus nuchas, 1061 trapezius, 285 in neck, 1061 triangularis menti, 1 1 70 stemi, 933 triceps extensor cubiti. 342 trochlearis, of eye, 1 150 tympanum, of, 1544 vastus extemus, 467 intemus, 468 Wilson, of, 61 7 Wood's muscle, 551 zygomaticus major, 1168 minor, 11 68 Musculi papiUares, 977 pectinati, 975 Mnsculus accessorius ad ilio - cos- talem, 290 of foot. 553 antitragicus, 1194 helicis major, 1 194 minor, 1194 incisivus, inferior, 11 71 superior, 11 71 naso-labialis, 11 71 obUquus of auricle, 1194 snspensorius duodeni, 732 tragicus, 11 94 transversus of auricle, 1194 Musculo - cutaneous nerve of arm, 315. 340 of leg. 503 summary- of, 504 Musculo-spiral nerve, 316, 342 branches of. 343 Myelencephalon. 1337. 1345 Myeloplaxes of Robin, 10 Myentericus. plexus, 787. 793 Mylo-hyoid muscle. 11 30 Myocardium. 988 structure of, 991 M3nrtifonnes, caxunculae, 632 Myrtiform fossa, 97 Nabothi. ovula, 897 Nares, anterior. 140 posterior, 140 I7I8 INDEX Nasal artery, 1181 bones, 107 • ossification of, 108 cartilages, 1197 duct, 1191 development of, 1191 Nasal fossae, 137 arteries of, 1260 development of, 1261 floor of, 1256 lymphatics of, 1261 meatus of, 1254 mesial nasal process, 1262 mucous membrane of, 1256 nasal capsule, 1262 nerves of, 1259 regions of, 1256 roof of, 1256 wall of, inner, 1256 outer, 1254 index, 158 point, 133 process, lateral, 162 mesial, 162 spine, anterior, 97, loi posterior, 11 1 vein, transverse, 1181 Nasion, 133 Nasmyth's membrane, 172 Naso-palatine artery, 1260 canal, loi Naso-pharynx, 1268 Natal cleft, 424 Nates of corpora quadrigemina, 1428 Natis, fold of, 424 Navicular bone (of foot), 258 Navicularis, fossa, 857 Neck of humerus, anatomical, 184 surgical, 186 landmarks of, 1080 side of, 1080 Nelaton's line, 447 NeopalliuR^, ' 1 464 Nerves — abdominal wall, of, 645, 661 abducent. See Cranial Nerves anterior femoral, 470 interosseous, 365 Arnold, of, 1073, 1226 auditory. See Cranial Nerves auricle, of, 1195 auricular, great, 1059 branches of, 1059, 1178 posterior, 1073, 1173 branches of, 1073, 11 73 auriculo-temporaJ, 1070, 1209 branches of, 1070, 1209 Bell, external respiratory, of, 1098 brachial plexus, 312, 1096 infraclavicular branches of, 314 Nerves {continued) — brachial supraclavicular branches of, 313, 1098 plexus, branches of inner cord, 315 outer cord, 314 posterior cord, 315 buccal, long, 11 77, 1208 plexus, 1 1 75 short, 1 169 calcaneo-plantar nerve, 528, 548 Casserius, perforating nerve of, 315 cervical plexus, 1091 branches of, deep, 1093 superficial, ascend- ing, 1092 descending, 1061, 1093 cervical spinal, posterior primary divisions of, 1066 superficial, 1060, 1093 transverse, 1060 chorda tympani, 1246, 1298 circumflex, 316 coccygeal, 845 Cotunnius, of, 1260 crural, anterior, 771 cutaneous, of back, 283 of foot, 547 of forearm and hand, 348 of gluteal region, 424 internal, of arm, 315, 331, 340 lesser, of arm, 315, 331 of pectoral region, anterior, 298 lateral, 298 perforating, of sacral plexus, 425 of scapular region, 319 of thigh, external, 449 internal, 449 middle, 449 dental, inferior, 1209 branches of, 12 10 superior, anterior, 1218 middle, 121 8 posterior, 1218 descendens cervicis, 1107 hypoglossi, 11 07 digastric, 11 73 dorsal, last, 661 of penis, 627 dorsalis pedis, 513 dorso-lumbar, 768 eighth cranial. See Cranial Nerves eleventh cranial. See Cranial Nerves external respiratory of Bell, 313 INDEX 1719 Nerves {continued) — face, of, motor, 11 72 sensory, 11 76 facial. See Cranial Nerves fibular, 445 first cranial, 1258, 1482 fourth cranial. See Cranial Nerves fifth cranial. See Cranial Nerves genito-femoral, 770 •crural (femoral) branch of, 450 glosso-pharyngeal. See Cranial Nerves *■ gluteal, inferior, 434, 847 r gluteal, superior, 434, 847 hemorrhoidal or perineal branch of fourth sacral, 611, 849 inferior, 612, 626 hypogastric, of ilio-hypogastric, 645 hypoglossal . See Cranial Nerves ilio-hypogastric, 661, 769 iliac branch of, 425 ilio-inguinal, 449, 661, 770 infra-orbital, 11 77 branches of, 1177, 1217 inguinal, 449, 661, 770 intercostal, 927, 103 1 branches of, 929 lower five, 661 intercosto-humeral, 317, 331 Krause, ulnar collateral nerve of, 316, 364 laryngeal, inferior or recurrent, 966, 1228, 1292 left in thorax, 966 summary of, 1293 superior, 1227, 1292 external branch of, 1228, 1292 internal branch of, 1228, 1292 summary of, 1293 lingual, of fifth, 1210, 1246 of glosso-pharyngeal, 1246 of pneumogastric, 1227 lumbo-sacral cord, 771 masseteric, 1207 maxillary, inferior, 1077, 1207 anterior division of, 1207 branches of, 1207 posterior division of, 1209 branches of, 1209 recurrent meningeal branch of, 1077 motor root of, 1207 sensory root of, 1207 summary of, 12 14 maxillarj', superior, 1077, 1217 branches of. 1158, 1217 Nerves {continued) — maxillary, in infra-orbital canal, 1217 in spheno - maxillary fossa, 1217 recurrent meningeal, branch of, 1077 summary of, 1221 median, 340, 365 inner root of, 315 outer root of, 315 in hand, 372 digital branches of. 372 palmar cutaneous of, 349 median, summary of, 373 medullary, of tibia, 443 mental, 11 77 musculo-cutaneous, of arm, 315, 340 cutaneous branch of, 332 musculo-cutaneous, of leg, 503 summary of, 504 musculo-spiral, 316, 342 branches of, 343 cutaneous, external, 332 internal, 332, 344 mylo-hyoid, 1210 nasal, in cranial cavity, 1074 in orbit, 1155 in nasal fossa, 11 56 infratrochlear branch of, 1176 nasal branches of, 1259 terminal branch of, 11 77 nasal infe»ior, 1221, 1259 superior, 1220, 1259 naso-palatine, 1220, 1260 ninth cranial. See Cranial Nerves obturator, 450, 474, 771 accessor^', 475, 771 geniculate branch of, 474 internus muscle, to, 434, 847 occipital, great, 1059 least, 1059 small, 1059 oculo - motor. See Cranial Nerves olfactory, 1258, 1482 ophthalmic, 1077 optic. See Oplx Nerve orbital, of superior maxillary, 1158 pars intermedia of Wrisberg, 1076, 1299 patellar plexus, 450 perineal, 626 superficial, 626 deep, 627 of fourth sacral, 611, 849 peroneal, 445 1720 INDEX Nerves {continued) — peroneal, deep, 509 petrosal, deep, great, 1234 small, 1548 superficial, external, 1078, 1298 great, 1078, 1297 small, 1078, 1224 1548 summary of, 1 300 pharyngeal, 1227 plexus, 1227 branches of, 1227 phrenic, in neck, 1093 in thorax, 942 plantar, 558 external, 560 summary of, 561 internal, 558 summary of, 559 pneumogastric. See Cranial Nerves popliteal, external, 445, 848 branches of, 445 internal, 443, 848 branches of, 443 to popliteus, 445 posterior interosseous, 358 pudendal, long, of Soemmering, 436, 627 pudic, 625, 848 to quadratus femoris, 435 radial, 350, 357 palmar cutaneous of, 349 rami communicantes, abdominal, 761 cervical, 1107 thoracic, 103 1 ramus communicans fibularis, 445 tibialis, 443 rhomboids, to, 313, 1098 sacral, 845 saphenous, external or short, 518 internal or long, 450 I sciatic-, great, 439, 848 branches of, 439 guide to, 439 small, 436, 848 branches of, 436 recurrent branches of, 425 scrotal, long, 627, 650 second cranial. See Optic Nerve seventh cranial. See Cranial Nerves sixth cranial. See Cranial Nerves Soemmeiing, long pudendal of, 436, 627 Nerves {continued) — spinal accessory. See Cranial Nerves posterior primary divisions of, 296 splanchnic, 1035 pelvic, 847 stylo-hyoid, 11 73 subclavius muscle, to, 314, 1098 subcostal, 661, 773 iliac branch of, 425 . suboccipital, posterior primary division of, 1066 anterior primary division of, 1091 subsartorial plexus, 452 subscapular, 315 supra-acromial, 298, 319 supraclavicular, 298 supra-orbital, 1067 suprascapular, 314, 321, 1098 suprasternal, 298 supratrochlear, 1067 sural, 445 sympathetic, gangliated cord of in abdomen, 761 in neck, 1232 constitution of, 1235 cardiac accelerator fibres, 1236 dilator pupillae fibres, 1235 ganglia of — , cervical, inferior, 1235 branches of, 1235 middle, 1235 branches of, 1235 superior, 1232 branches of, 1232 in pelvis, 862 in thorax, 1034 ganglion impar of, 862 plexuses^ — cardiac, 968 carotid, 1234 cavernous, 1079, 1234 epigastric, 734 hypogastric, 738 pelvic, 840 solar, 734 temporal, deep, 1207 temporo-malar, 1070, 1158 tenth cranial. See Cranial Nerves third cranial. See Cranial Nerves thoracic, anterior, external, 314 internal, 315 posterior, 13 13 thyro-hyoi4, 1108 tibial, 443 anterior, 509 posterior, 527 INDEX 1721 Nerves {continued) — tibial, posterior, fibular branch of, 527 twelfth cranial. See Cranial Nerves tongue of, 1246 trifacial or trigeminal. See Cranial Nerves . trochlear. See Cranial Nerves tympanic, 1224 thyro-hyoid, 1108 trigeminal, 1075 ulnar. 315, 364 branches of, 364 collateral of Krause, 316, 364 cutaneous of, 332, 349 ulnar, dorsal branch of, 350 in hand, 374 deep division, 374 superficial division, 374 palmar cutaneous, 349 summary of, 374 vagus. See Pneumogastric, under Nerves Vidian, 12 19 formation of , 1219 of Wrisberg, 315, 331 Nerve-plexuses, annular, of eye, 1510 aortic, 738 brachial, 1096 buccal, 1 1 75 cardiac, deep, 968 superficial, 968 carotid, 1234 cavernous, 1234 cervical, 1091 coeliac, 736 coronary, 970 diaphragmatic, 736 epigastric, 734 gastric, 736 gulae, 965 hepatic, 736 hypogastric, 738 intra-epithelial, of eye, 1510 lumbar, 768 Meissner, of, 787, 793 mesenteric, inferior, 738 superior, 738 myentericus, of Auerbach, 787, 793 ovarian, 738 pelvic, 840 pharyngeal, 1227 phrenic, 736 pudic, 847 renal, 738 sacral, 846 sacro-coccygeal, 849 sciatic, 847 Nerve-plexuses, solar, 734 spermatic, 738 splenic, 736 subepithelial, of eye, 15 10 suprarenal, 736 tympanic, 1548 vertebral, 1235 Nerve-roots of spinal nerves, anterior, 1322 posterior, 1322 Nervous system, 1306 cephalic ganglia, 1469 cerebro-spinal, 1306 development of, 1468 peripheral, 1468 neural crests, 1468 spinal ganglia, 1468 sympathetic, 1306 ganglia, 1470 Neural folds. r6i8 tube, 161 8 Neurenteric canal, 161 8 Neuroglia of spinal cord, 1320, 1335 gUa-cells of, 1320 neuroglial fibres of, 1322 Neuron, 1320 Nictitans, membrana, 1190 Nidus avis of cerebellum, 1371 Nipple avis of cerebellum, 1371 Nipple, 300 Nomenclature, anatomical, 1647 Norma basilaris, 145 frontalis et facialis, 132 lateralis, 140 occipitalis, 131 verticalis, 132 Nose, 1196 apertures, of, 1198 arteries of, 11 96 cartilages of, 1197 cms laterale, 11 98 mediale, 1198 Huschke, of, 1199 Jacobson, of, 1199 lateral, lower, 1 198 upper, 1 197 minor, 1198 septum, of, 1 199 sesamoid, 1198 vomerine, 1199 development of, itco lymphatics of, 1 1 > 6 nerves of, 1196 Notch, great scapular, 1 79 jugal, 61 lachrymal, of superior maxilla, 99 popliteal, 243 pterygoid, 88 spheno-palatine, 114 supra-orbital. 66 1722 INDEX Notch, suprascapular, 179 Notochord, 53, 16 19 Nuchae, ligamentum, 286, 1061 Nuchal furrow, 1058 groove, 283 Nuck, canal of, 881 Nucleus or nuclei — ambiguus, 1495 amygdaloid, 1414 arcuate, 1355 auditory, cochlear, lateral, 1490 ventral, 1491 dorsal or principal, 1492 external, 1492 internal, or of descend- ing root, 1492 Bechterew, of, 1493 caudatus, 141 1 cuneate, accessory or external, 1354 cuneatus, 1354 Deiters, of, 1492 emboliformis, 1373 fastigii, 1373 globosus, 1373 gracilis, 1353 lateralis, 1356 lenticularis, 1411, 1412 globus pallidus of, 141 3 medullary laminae of, 1412 putamen of, 1412 oculo-motor, 1439 olivary, accessory, dorsal, 1354 mesial, 1354 inferior, 1355 pontis, 1362 red, of tegmentum, 1432 of trigeminal nerve, 1365 of mesencephalic root of, 1439 motor of, 1365 sensory of, 1365 trochlear, 1439 Nuhn, glands of, 1243 Nymphae, 629 Obelion, 124 Obex, 1378 Obliquus capitis inferior muscle, 1064 superior muscle, 1064 externus abdominis muscle, 650 internus abdominis muscle, 654 inferior muscle of eyeball, 1150 : . superior muscle of eyeball, 1150 musculus of auricle, 1194 Oblongata, medulla, 1345 Obturator artery, 488 abnormal or aberrant, 462 canal, 904 externus muscle, 473 Obturator fascia, 837 foramen, 227 internus muscle, 429, 864 nerve to, 434 membrane, 904 nerve, 450, 474 accessory, 475 vein, 488 Occipital artery, first part of, 1 120 second part of, 1062 third part of, 1062 bone, 57 ossification of, 61 glands, 1063 lobe of brain, 1390 nerve, great, 1059 least, 1059 small, 1059 point, 132 sinus, 1477 guide to, 1501 sulcus, lateral, 1391 transverse, 139 1 triangle, 1091 veins, 1063 Occipito-axial ligaments, 1304 Occipito-temporal gyrus, 1393 Ocular appendages, 11 87 Oculi, tendo, 11 88 Oculo - motor nerve. See Cranial Nerves Odontoblasts, 171 Odontoid process of axis, 17 Odoriferae, glandulae, 647 (Esophagus, cervical part of, 11 29 development of, 1023 lymphatics of, 1022 structure of, 1022 thoracic part of, 1021 Olecranon rete, 363 Olfactorium, trigonum, 1397 Olfactory areas, development of, 1261 bulb, 1397 structure of, 1448 hairs, 1258 lobe, 1397 development of, 1397 lobules of, 1397 mucous membrane, 1257 nerves, course and distribution of, 1258 origin of, 1482 organ, development of, 1398 primitive nasal fossae, 1261 region of nasal fossa, 1256 sulcus of frontal lobe, 1 3S7 tract, 1397 Olivary body, 1348 eminence, 82 nuclei, 1354 peduncle, 1354 INDEX 1723 Omentale, tuber, of liver, 705 Omental tuberosity- of pancreas, 734 Omentum, gastro-colic, 690, 716 gastro-hepatic, 716 gastro-splenic, 701, 717 great, 690, 716 small, 716 Omo-hyoid muscle, 11 02 posterior bellj' of, 320 Oocyte, primary, 1606 Oogenesis, 1604 Opening, femoral, 472 saphenous, 458 Openings into orbit, 136 Opercula insulae, 1394 Ophryon, 133 Ophthalmic artery, 1159 ganglion, 1156 branches of, 11 57 summary of, 1158 nerve, 1077 branches of, 1 154 summary of, 1 158 veins, 1161 Opisthion, 148 Opisthotic centre, 81 Optic chiasma or commissure, 1424 cup, 1532 disc of retina, 15 19 foramen, 86 nerve in cranial ca\'itj', 1424 course of, 1483 development of, 1530 in orbit, 1152 origin of, deep, 1425 superficial, 1483 radiation. 1427, 1446 stalk. 1532, 1534 thalami, 14 17 blood-supply of, 1456 connections of, 1420 development of, 1421 nuclei of, 1420 structure of, 1420 tract, 1425 roots of, 1425 inner or commissural, 1427 , outer or visual, 1425 summary of fibres of, 1427 vesicle, prii..arj', 1458, 1532 secondary, or optic cup, 1532 Opticus, poms, of retina, 1519 Ora serrata of retina, 1518 structure of, 1525 Orbicularis ciliaris muscle, 1512 oris muscle, 11 70 palpebrarum muscle, 1165 processus of incus, 1543 Orbit, 1 1 46 contents of, 11 46 fascia of, 1151 muscles of, 1147 nerves in, 1152 ciliary ganglion, 1156 nerves, long, 1156 short, 1 157 fourth cranial, 1153 frontal, 11 54 lachrymal, 11 55 nasal, 1155 optic, 1 152 orbital, 1158 sixth cranial, 1153 supra -orbital, 11 54 supratrochlear, 1154 temporo-malar, 1158 third cranial, 1153 periosteum of, 11 46 Orbital index, 158 nerve, 1158, 1217 malar branch of, 11 77 temporal branch of, 1070, 1177 sulcus, 1387 Orbito-sphenoids, 84 Orbits, 134 openings into, 136 Orthognathous skuUs, 134, 158 Os calcis, 256 ossification of, 258 centrale, 208 coxse, 220 ossification of, 227 mnominatum, 220 ossification of, 227 japonicum, 107 magnum, 205 planum of ethmoid, 94 pubis, 225 spine of, 226 tincae, 886 trigonum, 256, 264 unguis, 108 uteri externum. 886 internum, 888 Ossification, 8 centres of, 8 in cartilage, 9 in membrane, 8 law of, 1 78 Osteoblasts, 10 Osteoclasts, 9 Osteogenetic fibres, 8 layer, 9 Otic ganglion, 1211 branches of, 12 12 Otoconia, 1553 Otoliths, 1551 Ovarian plexus, 738 1724 INDEX Ovary, 88i abnormal positions of, 884 descent of, 883 development of, 687 ligament of, 883 structure and development of, 892 suspensory, of, 883 poles of, 882 structure of, 892 Oviduct, 884 Ovulation, 1607 Ovum, 894, 1603 fertilization of, 1610 maturation of, 1608 Oxyntic cells, 783 Pacchionian bodies, 1481 depressions, 64 Pacinian bodies of foot, 559 of hand, 373 Palate bones, no ossification of, 114 soft, 1248 glands of, 1250 muscles of, 1250 nerves of, 1252 relation of component parts of, 1252 Palatine arterj'^, descending, 1205, 1260 branch of ascending pharyngeal, 1121 canal, posterior, 112 accessory, external, 112 posterior, 112 fossa, anterior, loi, 145 foramen, accessory, external, 147 posterior, 147 posterior, 147 Palatine nerves, 1221 Palato-glossus muscle, 1250 Palato-maxillary canal, 112 Palato-pharyngeus muscle, 1250 Pallidus, globus, 1413 Pallium of brain, 1393 Palmar arch, deep, 380 branches of, 381 superficial, 370 summary of, 382 bursa, great, 374 cup, 408 fascia, 369 furrows, 367 interosseous arteries, 381 veins, deep, 382 Palmaris brevis muscle, 368 longus muscle, 352 Palmatae, plicae, 888 Palpebrae, 1187 Palpebral arteries, external, 1182 Palpebral arteries, internal, 1181 ligaments, 11 88 veins, 1182 Palpebrarum, fissura, 11 87 tendo, 1 188 Pampiniform plexus, 670 Pancreas, 732 connections, position, and rela- tions of, 732 development of, 812 lymphatics of, 812 structure of 809 Pancreatic duct, 811 accessor^', 8u Papilla, bile, 789 lacrimalis, 1187 Papillae of tongue, 1242 Paracentral lobule, 1388 Paradidymis, 682 Paraflocculus, 1462 Parametrium, 887 Pararectal fossa, 836 Parathyroids, 11 25 Paravesical fossa, 836 Paravesicular fossa, 836 Parietal bones, 62 ossification of, 65 foramen, 63 lobe of brain, 1388 Parieto-occipital fissure of brain, 1383 Paroophoron, 884 development of, 687, 883 Parotid gland, 11 83 development of, 11 86 duct, 1 1 85 lymphatic glands, 1183 Parotidis, glandula socia, 11 84 Parovarium, 884 Pars basilaris of frontal lobe, 1387 ciliaris retinae, 1513 intermedia of Kobelt, 633 of Wrisberg, 1299, 1489 iridica retinae, 1515 membranacea septi of heart, 985 orbitalis of frontal lobe, 1387 triangularis of frontal lobe, 1387 Patella, 241 ossification of, 242 Patellaris, fossa, 1529 Patellar plexus of nerves, 450 Pathetic (trochlear) nerve. See Cranial Nerves Pavilion of Fallopian tube, 885 Pecquet, cistern of. See Recepta- culum Chyli Pectineus muscle, 4b5 Pectiniforme, septum, of clitoris, 630 of penis, 868 Pectoral girdle, morphology of, 277 region, 297 Pectoralis major muscle, 303 INDEX 1725 Pectoralis minor muscle, 306 Pelvic fascia, in female, visceral, 879 in male, parietal, 836 visceral, 838 girdle, 220 Pelvis, 228, 833 axes of, 231 of child, 232 contents of, 834 diameter, conjugate, 230 transverse, 230 false, 228 female, 878 peritoneum of, 879 viscera, position of, 878 inclination of, 230 of kidney, 826 male, 834 peritoneum of, 834 viscera, position of, 834 sexual differences of, 231 true, 228 Penis, 647 angle of, 858 composition of, 648 corpora cavernosa, 868 corpus spongiosum, 869 bulb of, 869 coverings of, 647 cms, 618 fascial sheath of, 647 glans, 648 praeputium, 647 structure of, 868 Perforaculum, 1602 Perforating arteries of profunda femoris, 484 fibres of Sharpey, 7 Pericardium, 942 development of, 945 sinus, transverse, of, 944 structure of, 945 Perichoroidal lymph-space, 1508 Peridental membrane, 172 Periglottis, 1276 Perilymph of internal ear, 1552 Perilymphaticus, ductus, 78 Perineal body, 636 fascia, deep, 619 fold, 871 pouch, 614 triangle, deep, 618 Perineum, female, 628 male, 611 central tendinous point of, 618 Periosteum, 9 Periotic cartilaginous capsules, 160 Perisclerotic lymph-space, 1151, 1508 Peritontum, 710 Peritoneum, course of, transverse, 713.715 vertical, 711 development of, 725, 8oi folds of, 711 ligaments, 718 mesenteries, 717 omenta, 716 fossa, digital, of, 676 fossae, pelvic, of, 836 in foetus, 1644, 1645 pelvic, in female, 879 in male, 834 plicae of, on anterior abdominal wall, 676 pouches of, on anterior ab- dominal wall, 721 primitive, of testis, 674 sac, great, of, 720 small, of, 720 structure of, 725 Permanent teeth, 170 Peroneal artery, 5 26 anterior, 509, 526 posterior, 527 varieties of, 527 bone, 250 groove, 251, 264 nerve, 445 deep, 509 spine, 258 Peroneus brevis muscle, 517 longus muscle, 515 tertius muscle, 505 Pes accessor ius, 1409 anserinus, 11 73 cms cerebri, of, 1431, 1437 hippocampi, 1409 Petit, canal of, 1530 triangle of, 286, 654 guide to, 642 Petrosal nerves- — deep, great, 1234 small, 1548 superficial, external, 1078, 1298 great, 1078, 1297 small, 1078, 1224, 1548 summary of, 1299 sinus, inferior, 1478 superior, 1478 Petro-squamous sinus, 1479 Petro-tympanic fissure, 72 Petrous ganglion of glosso-phar>-n- geal, 1223 Peyer, patches of, 791 Pfliiger, egg-tubes of, 687, 688 Phalanges of foot, 271 muscular attachments of, 271 ossification of, 272 1726 INDEX Phalanges of hand, 213 muscular attachments of, 215 ossification of, 216 Pharyngeal aponearosis, 1266 artery, ascending 1121 branches of, 11 21 bursa, 1269 isthmus, 1268 nerve, 1220 pouches, 1270 developTient of, 1270 metamorphoses of, 1270 of first, 1270 second pouch, 1270 third pouch, 1270 fourth pouch, 1270 tuberculum impar, 1270 furcula, 1270 sinus arcuatus, 1270 recess, lateral, 1269 tonsil, 1269 tubercle, 59 Pharyngo-epiglottidean folds, 1276 Pharynx, 1263 blood-supply of, 1269 development of, 1270 lymphatics of, 1269 miucous membrane of, 1267 muscles, constrictor, of, 1264 relations of. 1263 Phenozygous skulls, 132 Philtrum, 1164, 1237 Pia mater, cranial, 1481 structure of, 1482 spinal, 1 3 10 blood-supply of, 131 1 lymphatics of, 131 1 nerves of, 1311 structure of, 1311 Pigmentary layer of retina, 1523 Pineal body, 1421 development of, 1422 habenula, peduncle, or stalk of, 1422 stria medullaris vel pinealis, 1422 structure of, 1422 Pisiform bone, 203 Pituitary body, 1079 development of, 1080 structure of, 1080 fossa, 82 membrane, 1256 Pivot joint, 280 Placenta, 1635 circulation of, 1642 Plagiocephalus, 159 Plantar artery, external, 562 varieties of, 565 internal, 561 varieties of, 565 Plantar branch of dorsalis pedis, 5G5 fascia, 545 muscles, 549 nerve, external, 560 summary of, 561 internal, 558 summary of, 559 triangle, 556 Plantaris muscle, 520 Platycnemism, 249 Platyrhine skulls, 158 Platysma muscle, 1082 Pleura, 935 Pleurae, blood-supply of, 939 development of, 939 lymphatics of, 939 reflections of, 936 lines of, 937 Plexus, subsartorial, 452 Plica epigastrica, 676 hypogastrica, 676 semilunaris of conjunctiva, 1190 sublingualis, 1135, 1237 urachi, 676 ureterica, 866 Plicae palmatae, 888 villosae, 783 Pneumogastric nerve. See Cranial Nerves Pocularis, sinus, 855 Point, auricular, 140 central tendinous, of perineum, 618 jugal, 142 Polar bodies, 1608 extrusion of, 1608 PoUicis, abductor, 377 adductor obliquus, 378 transversus, 378 dorsales, arteriae, 393 extensor brevis (extensor primi intemodii), 388 longus (extensor secundi internodii), 388 ossis metacarpi, 388 flexor brevis, 378 longus, 366 opponens, 377 princeps, arteria, 380 Pomum Adami, 1277 Pons hepatis, 706 Tarini, 1440 Varolii, 1338, 1362 blood-supply of, 1456 cor])us trapezoide$ of, i^'63 nuclei of, 1365 ascending root of fifth nerve, 1365 facial nerve, 1365 sixth nerve, 1365 INDEX 1727 Pons Varolii, nuclei of, olivary, su- perior, 1365 posterior longitudinal bundle in, 1365 structure of, 1362 Pontis, cistema, 1480 nucleus, 1 362 Popliteal artery, 440 branches of, 442 varieties of, 443 nerve, external, 445 branches of, 445 internal, 443 branches of, 443 notch, 243 space, 435, 440 boundaries of, 440 contents of, 440 vein, 443 Popliteus muscle, 521 nerve to, 445 Portae, vena, 742 branches of, in liver, 804 sinus, of, 743 Portal canals, 804 fissure, 706 structures at, 706 sinus, 743 vein, 742 Porus opticas, 1519 Postcentral sulcus of brain, 1389 Posticum, tuber, 1370 Post-sphenoid, 91, 160 Poupart, ligament of, 460, 651 Praecuneus of brain, 1 390 Praeputium clitoridis, 630 penis, 647 Precentral sulcus of brain, 1385 Prechordal cartilages and plate, 160 Preglenoid tubercle, 71 Pre-interparietal bone, 155 Prelarj-ngeal lymphatic glands, 1127 PremaxiUa, 103 Presphenoid, 91, 160 Presternum, 47 Pretracheal lymphatic glands, 11 27 Prevertebral muscles, 1294 Process, accessory, of lumbar verte- bra, 26 acromion, 182 basilar, 59 clinoid, anterior, 85 middle, 86 posterior, S3 coracoid, 182 coronoid, of mandible, 118 of ulna, 197 ensiform, 47, 49 external auditory, 79 iron to-nasal, 162 Process, globular, 163 hamular, of sphenoid, 89 intrajugular, 61 jugal, of temporal bone, 70 jugular, 60 lateral aasal, 162 marginal, of malar, 106 maxillary, 163 of first or mandibular arch, 1272 mesial nasal, 162 muscular, of arytenoid cartilage, 1279 nasal, of frontal, 67 orbital, of malar, 104 paramastoid, 61 postglenoid, 70 styloid, of temporal bone, 79 supracondylar, 188 uncinate, of ethmoid, 96 vaginal, of sphenoid, 84 of temporal bone, 79 vocal, of arytenoid cartilage, 1279 xiphoid, 47, 49 Processus cochleariformis, 78, 1539 dentatus, 17 reticularis of spinal cord, 1318 tubarius, 89 vaginalis, 675 abnormal conditions of, 676 Proctodaeum, 871, 87S Profunda artery of brachial, superior, 338 inferior, 339 of ulnar, 370 femoris artery. 481 vein, 487 Prognathous skulls, 134, 158 Proligerus, discus, 894 Pronation, 406 Pronator quadratus muscle, 366 radii teres muscle, 351 Pronephros, 829 Pronucleus, female, 1605 male, 1610 Pro-otic centre, 61 Prosencephalon, 1337 Prostate gland, 853 blood-supply of, 873 development of, 873 lymphatics of, 873 structure of, 872 Prostatic fissure, 853 sinus, 855 Prussak, pouch of, 1546 Psalterium, 1403, 1446 Psoas magnus muscle, 766 parvus muscle, 766 sheath, 764 Pterion. 126 1728 INDEX Pterotic centre, 8t Pterygoid bones, 92 canal, 89 fossa, 88, 147 muscle, external, 1200 internal, 1202 notch, 88 plate of sphenoid, external, 89 internal, 89 plexus of veins, 1206 processes, 88 tubercle of sphenoid, 89 Pterygo-mandibular ligament, 1088 Pterygo-maxillary fissure, 144 region, 1199 Pterygo-palatine artery, 1206 bar, 164 canal, 84, 113 Pterygo-spinpus foramen, 89 ligament, 1088 Pubic angle, 226 crest, 226 relation of structures at, 660 spine, 226 Pubis, OS, 225 Pudendal nerve, long, of Soemmering, 436, 627 Pudendum, 628 frenulum, 632 rima, 629 vestibule of, 632 Pudic artery, inferior external, 481 internal, 433 guide to second part, 434 superior external, 479 Pulmonary alveoli, 952 groove of thorax, 53 orifice of heart, 978 position of, 985 valve of heart, 980 Pulp cavity, 171 dental, 171 Pulvinar of epiglottis, 1276 of optic thalamus, 1419 Punctum lacrimale, 1187 Pupil. 1515 Pupillaris, membrana, 151 7 Parkin je, cells, of, 1375 fibres of, 990 granular layer of, 1 72 Putamen of lenticular nucleus, 141 2 Pylori, antrum, 693 sphincter, 782, 786 Pyloric valve, 786 Pylorus, 693, 786 position of, 694 Pyramidal tract, direct, 1328, 1348 crossed, 1327 Pyramids, Ferrein, of, 822 Malpighi, of, 818 Pyramids, medulla oblongata, of, 1347 decussation of, 1348 Pyriformis muscle, 429, 864 sinus of larynx, 1283 Quadrangular muscular space of arm, 323 Quadrate lobule of brain, 1390 lobe of liver, 705 Quadratus femoris muscle, 430 nerve to, 435 men ti muscle, 1 1 70 Quadriceps extensor femoris, 466 Quadrigemina, corpora, 1428 lower pair of, 1428 structure of, 1429 , upper pair of, 1428 structure of, 1430 Radial artery, 356 first part of, 356 branches of, 356 second part of, 391 branches of, 392 third part of, 380 branches of, 380 varieties in hand, 382 nerve, 350, 357 vein, 334 Radiata, corona, 14 14 Radiatio corporis callosi, 1401 Radiation, optic, 1427, 1446 Radius, 191 grooves of, 195 ossification of, 196 Ramus communicans fibularis nerve, 445 tibialis nerve, 443 Ranineartery, 1118, 1246 Rathke, pouch of, 92 Rauber's layer, 161 2 Rays, medullary, of kidney, 822 Receptaculum chyli, 762 Recess, infundibular, of third ven- tricle, 1416, 1417 lateral, of fourth ventricle, 1380 optic, of third ventricle, 1416 pineal, of third ventricle, 141 7 spheno-ethmoidal, 84 Recessus cochleae, 1549 utriculi, 1549, 1552 Rectal pits, 874 Recti muscles of eyeball, 114 7 Recto-coccygei muscles, 875 Recto-uterine folds, 879 pouch, 879 Recto-vesical pouch, 836 Rectum, female, 890 male, 860 blood-supply of, 875 development of, 877 INDEX 1729 Rectum, lymphatics of, 877 peritoneal relatious of, 835 structure of, 873 valves of, 874 Rectus abdominis muscle, 658 sheath of, 659 capitis anticus major muscle, 1294 minor muscle, 1 294 posticus major muscle, 1064 minor muscle, 1064 lateralis muscle, 1294 femoris muscle, 466 Recurrent laryngeal nerve, 966, 1228, 1292 Red nucleus of the tegmentum, 1432 Reduction-division, 1606 Refracting media of eyeball, 1527 Reid, base line of, 1504 Reil, island of, 1393 development of, 1396 Reissner, membrane of, 1555 Relation of muscles at back of upper end of femur, 494 along linea aspera, 495 on front of body of os pubis, 494 Renal sympathetic plexus, 738 Respiratory apparatus, development of, 954 Restiform body, 1351, 1357 arcuate fibres, 1358 cerebeUo-olivary fibres, 1358 cerebellar tract, direct, 1358 Rete, acromial, 324 olecranon, 363 testis, 684 Rete-cords, 686 Reticularis, processus, of spinal cord, 1318 Retina, 1517 arteria centralis retinae, 1525 cone-granules, 1523 fibre- baskets of, 1524 fovea centralis, 151 8 macula lutea, 1518 nerve-cells of , 1526 ora serrata, 15 18 porus opticus, 15 19 rod-granules, 1522 structure of, 1519 bacillary layer, 1523 ganglionic layer, 1320 granular layer, inner, 1521 outer, 1522 molecular layer, inner, 152 1 outer, 1522 nuclear layer, inner, 1521 outer, 1522 optic layer, 1520 pigmentary layer, 1523 Retina, structure of, plexiform layer, inner, 1521 outer, 1522 rods and cones layer,. 1523 sustentacular fi^bres of, 1523 veins of, 1526 Retrahens auriculam muscle, 1072 Retro-pharyngeal space, 1087 Retro-pubic pad of fat, 836 Retzius, fundiform ligament of, 501 Rhinencephalon, 1400 Rhinion, 133 Rhombencephalon, 1337, 1345 Rhombic lip, 1460 Rhomboideus major muscle, 287 minor muscle, 287 Rhomboids, nerve to, 3 1 3 Rib, first, 43 second, 45 tenth, 45 ele\enth, 45 twelfth, 45 Ribs, 41 development of, 56 ossification of, 46 Rider's bone, 473 muscles, 473 Rima glottidis, 1285 oris, 1236 pudendi, 629 Ring, abdominal, external, 653 guide to, 641 internal, -665 guide to. 642 crural, 461 crural or femoral, 461 guide to, 641 Risorius muscle, 1168 Rivinus, great duct of, 1 1 36 notch of, 1538 Robin, myeloplaxes of, 10 Rod-bipolar cells of retina, 1521 Rods of retina, 1523 Rolandic angle, 1504 line, 1504 Rolando, fissure of, 1383 guide to, 1504 funiculus of, 1350 substantia gelatinosa of, 135J tubercle of, 1351 Rosenmiiller, fossa of, 1269 organ of, 884 Rostrum, 84 Rotation, 282 Rotatores spins muscles, 294 Rotula, 241 Rotunda, fenestra, 1539 fossula, 1539 Rugarum, columnae, of vagina, 898 Ruyschiana, tunica, 1512 109 1 73° INDEX Sac, lachrymal, iigo development of, 1191 Sacciformis, membrana, 405 Saccule of internal ear, 1553 laryngeal, 1283 Sacculus endolymphaticus, 1553 Saccus reuniens, 973, 995 Sacral canal, 35 plexus, 846 Sacro-uterine folds, 879 Sacro-vertebral angle, 38 Sacrum, 30 ossification of, 36 Sagittal fontanelle, 65 line, 1378 Salpingo-pharyngeus muscle, 1250, 1275 Santorini, cartilages of, 1 280 duct of, 811 fissures of, 1536 Saphenous artery, external, 442 internal, 484 nerve, external or short, 518 internal or long, 450 opening, 458 guide to, 641 vein, anterior, 455 external or short, 514 internal or long, 455 guide to, 456 posterior, 455 Sartorius muscle, 464 Scala media, 1554 tympani, 1554 vestibuli, 1554 Scalene tubercle or spine, 44 Scalenus anticus muscle, 11 36 medius muscle, 1136 posticus muscle, 11 38 Scansorius muscle, 429 Scaphocephalus, 158 Scaphoid bone of carpus, 201 of tarsus, 258 fossa of sphenoid, 89 Scapula, 178 ossification of, 184 Scapular artery, posterior, 287, 1143 notch, great, 179 region, 319 Scarpa, fascia of, 643 foramina of, 102, 145 ganglion of, 1300 triangle of, 475 Schindylesis, 131, 280 Schlemm, canal of, 15 11 ligament of, 345 Schneiderian membrane, 1256 Sciatic artery, 432 extra-pelvic branchos of, 432 nerve, great, 439 Sciatic nerve, great, branches of, 439 guide to, 439 small, 436 branches of, 436 recurrent branches of, 425 notch, great, 227 small, 224, 227 vein, 433 Sclerotic coat of eyeball, 1507 blood-supply of, 1508 nerve-supply of, 1508 structure of, 1508 Scrobiculus cordis, 639 Scrotum, 649 arteries of, 650 development of, 635 lymphatics of, 650 nerves of, 650 septum, 650 -structures forming wall, 649 Segmental tubes of Wolf&an body, 829 Segmental type, 3 Segmentation cavity, 1613 of ovum, 161 1 Sella turcica of sphenoid, 82 dorsum of, 83 Sellae, diaphragma, 1475 Semicircular canals, membranous, 1553 structure of, 1553 osseous, 1550 Semicircularis, taenia, 14 15 Semilunar bone, 202 fascia of biceps, 336 ganglion, 736 Semilunaris, hiatus, 1255 Semimembranosus muscle, 438 Seminales, vesiculae, 852 blood-supply of, 872 development of, 872 structure of, 871 Seminiferous tubules, 683 Semispinalis colli muscle, 294 dorsi muscle, 294 Semitendinosus muscle, 437 Sensory nerves of face, 1 1 76 Septa, intermuscular, of brachial region, 334 of foot, 547 of leg, 498 of thigh, 458 Septula renum, 818 Septum, femorale, 461 lucidum, 1403 orbitale, 11 88 pectiniforme of clitoris, 630 of penis, 868 posticum of spinal cord, 13 10 primum, 993 INDEX 1731 leptum, secundum, 993 trans versum, 1644 Jerrata.ora, of retina 151^ ierratus magnus muscle, 31b posticus inferior muscle 28» superior muscle. 2b» Sertoli, cells of. 684, 686 Sesamoid bones of foot, 272 of hand. 216 Sexual eminence, 634, 872 Sharpey, perforatmg fibres of. 7 Sheath, axillary, 312 crural, 460 fe noral, 460 infundibuliform, 460 of flexor tendons of hand. 375 Short bones, 7 Shoulder-girdle. I75 Shoulder-joint, 344 , ^^^^ Shrapnell. membrane of, 154° Sibson, fasciaof. 1146 Sigmoid cavity of radius I95 ^ great, of ulna, 198 small, of uhia, 198 groove of temporal, 73 Sinus arcuatus, 1270 basilar. I479 cavernous. 1478 circular, 1478 circularis iridis, 1511 coronary. 986 Guerin. of, 858 laryngeal. 1283 lateral, 1476 guide to, ijO'^ longitudinal, inferior, 1475 superior. i475 guide to, 1501 Morgagni, of. 1265 occipital. 1477 _ petrosal, inferior, 1478 superior, 1478 petro-squamous, 1479 pocularis, 855 portal. 743 prostatic, 855 pyriformis. 1283 spheno-parietal, 1478 straight. 1476 transverse, 1479 tympani. 1539 venosus. 992 sclerse. 1511 Sinusoids. 1005 Sinus, annularis, 1005 tarsi, 277 uro-genital. 635 Skeleton, i visceral arch, I59. 161 SkuU. anterior region of, 132 at birth, 155 Skull, brachycephalic, 132, 158 of cretin. I59 deformities of, 15° development of, I59 doUchocephalic, 132, i5» of female, 156 horizontal section of, I49 ^ inferior region of, 145 internal base of . 15° lateral region of . 14° leptorhine, 158 longitudinal arc of. i5» megacephalic, 157 mesaticephaUc, 132, i5» mesocephalic, I57 mesognathous, 134. i5» mesorhine, 158 microcephalic, 157 orthognathous, 158 platyrhine, 158 posterior region of, 131 prognathous, 134. ^5° racial pecuUarities of, 156 sagittal section of, 149 superior region of, 132 as a whole, 123 Smegma praeputii, 647 Snufi-box, anatomical, 308 loemmering, long pudendal nerve of, 436. 627 Solar plexus, 734 Sole of foot, 543 , landmarks of, 543 Soleus muscle, 519 Sohtarius, fasciculus. I495 Somites, mesodermic. 1619 Speech-centre. 1387 Spermatic artery-. 754 terminal part of. 670 varieties of, 754 cord, 668 coverings of. 671 fascia, external, 651, 671 internal, 649. 671 middle. 656, 671 plexus of nerves, 738 of veins. 754 Spermatoblasts, 1602 Spermatogenic cells, i6oi Spermatogenesis. 1602 Spermatozoa. 1603 Spheno-ethmoidal recess, 90. 1254 Spheno-mandibular Ugament 1214 Spheno-maxillary fissure, 136, 143 ^ fossa, 144 Spheno-palatine artery-. 1206, 1260 1 foramen, 140. 144 ' ganglion. 12 19 branches of. 1220 roots of, 1 2 19 nerves, 12 17 1732 INDEX Spheno-palatine notch, 114 Spheno-parietal sinus, 1478 Sphenoidal air sinuses, 90 crest, 84 fissure, 88, 136 structures passing through, 1162 process of palate bone, 113 turbinate or spongy bone, 90 Sphenoid bone, 82 ossification of, 91 Sphenotic foramen, 148, 152 Sphenotics, 91 Sphincter ani externus muscle, 612 intemus muscle, 875 pupillae muscle, 15 15 pylori muscle, 782, 786 vaginae muscle, 637 vesicae muscle, 865 Spigel, lobe of, 707 tuber papillare of, 706 Spinal accessory nerve. See Cranial Nerves canal, 40 arteries of, 13 31 cord, 1306 arteries of, 1332 central canal of, 13 19 characters, external, of, 1 3 12 distinguishing, in differ- ent regions, 1320 columns of, 13 14 commissures of, 1317, 1322 conus meduUaris of, 1312 development of , 1334 ependymal zone, 1335 marginal zone, 1335 metamorphoses of pri- mitive spinal cord, 1336 lumen of neural tube, 1336 myelospongium, 1334 neural fold, 1334 groove, 1334 plate, 1334 tube, 1334 neuroglia, 1335 glia or spider cells, 1335 neuroblasts, 1335 axons of cells, 13 35 dorsal or posterior roots, 1323 enlargements of, 1312 filum terminale of, 13 13 fissures of, 13 14 furrow, posterior interme- diate of, 1 315 grey matter of, 131 7 Spinal cord, grey matter of, cells di, 1320, 1322 substantia gelatinosa oi Rolando, 1317, 1322 Gowers, intermediate pro- cess of, 1 31 8 ground-bundle, anterior, of, 1329 lateral, of, 1331 ligament, central, of, 13 13 ligamenta denticulata of, 1311 lymphatics of, 1334 marginal bundle, anterior, of, 1329 marginal bundle, posterior, of, 1327 meninges of , 1306 arachnoid, 1309 dura mater, 1306 pia mater, 13 10 nerve-cells of, 1320 of anteriorcornu, 1321 Clarke's column, 1322 intermedio-lateral cell- column, 1321 posterior vesicular cell- column, 1322 Stilling, dorsal nucleus of, 1322 nerve-fibres of, course of, 1323 processus reticularis of, 1 3 1 8 structure of, internal, 13 17 minute, 1320 tracts of. See Tracts veins of, 1333 ventral or white commis- sure, 1323 white matter of, 1319, 1323 ganglia, 1315, 1325 groove, 283 nerves, 13 15 divisions, primary, of, 13 16 groups of, 1 3 15 origin of, 13 15 relation of vertebrae to, 1316 posterior primary divisions of, 1066 roots of, 13 15 Spinalis dorsi muscle, 292 Spindle, 1599 Spine, genial, 117 iliac, anterior and posterior, 220, 222 nasal, anterior, 97, loi of frontal, 67 posterior, iii palatal, iii peroneal, 258 INDEX 1733 Spine, of tibia, 244 Spino-thalamic fibres, 1330 Spino-umbilical lines, 640 Spiral ganglion, 1559 groove of humerus, 188 line of femur, 236 Spireme, 1599 Splanchnic ganglion, 1035 nerves, thoracic, 1035 pelvic, 862 Spleen, component parts, connec- tions, and position of, 699 accessory, 701 development of, 815 ligaments of, 720 lymphatics of, 815 nerves of, 815 peritoneal relations of, 701 structure of, 813 Splendens, linea, 1311 Splenic dulness, area of, 702 flexure of colon, 698 sympathetic plexus, 736 Splenium of corpus callosum, 1401 Splenius muscle, 289 capitis, 290 coUi, 290 Spongy bone, inferior, 109 middle, 95 superior, 95 Spring ligament, 580 tubercle of navicular, 259 Stage of irruption in ossification, 9 Stapedius muscle, 1545 nerve to, 1 298 Stapes, 1543 Stellatum, ganglion, 1034 Steno or Stensen, duct of, 11 85 canal of, loi foramina of , 102, 145 Stephanion, 142 Sternal angle, 48 fissure, 50 foramen, 50 Sternalis muscle, 304 Stemebrae, 47 Sterno-cleido-mastoid muscle, 1088 posterior border of, 1061 Stemo-hyoid muscle, 11 03 Stemo-pericardial ligaments of Luschka, 944 Stemo-thyroid muscle, 1103 Sternum, 47 development of, 56 ossification of, 50 Stilling, canal of, 1530 dorsal nucleus of, 1322 Stomach, component parts, connec- tions, and position of, 691 curvatures of, 692 blood-supply of, 785 Stomach, development of, 798 divisions of, 693 gastro-phrenic ligament of, 720 lymphatics of, 785 Meckel's diverticulum of, 799 nerves of, 786 orifices of, 692 peritoneal relations of, 694 structure of, 781 topography of, 693 trigone or uncovered area of, 694 U-loop, 800 Stomatodaeum, 798 Stomodaeum, 1239 Straight sinus, 1476 Stratum intermedium, 1512 Striae acusticae, 1377 Stria longitudinalis lateralis, 1401 mesialis, 1400 medullaris vel pinealis, 1422 Striatum, corpus, 1410 Structure of bone, 5 of a vertebra, 12 Structures derived from germinal layers, 161 7 in middle line of neck, 1081. 1 104 Stylo-glossus muscle, 11 33 Stylo-hyal, 82 Stylo-hyoid muscle, 1 1 30 ligament, 11 34 nerve, 1173 Styloid process of fibula, 250 of radius, 193 of third metacarpal bone, 210 of temporal bone, 79 of ulna, 200 Stylo-mandibular ligament, 1088, 1215 Stylo-mastoid foramen, 77 Stylo-pharyngeus muscle, 1221 Subanconeus muscle, 342 Subarachnoid space of brain, 1480 of spinal cord, 1309 Subarcuatus, hiatus, 76 Subcallosal gyrus, 1401 Subclavian artery-, 11 38 left, first part of, in neck, 1140 in thorax, 961 right, first part of, 1138 second part of, 1140 third part of, 1095 groove, 176 triangle, 1094 vein, 1096, 1 144 Subclavius muscle, 306 nerve to, 314, 1098 Subcostal groove, 43 line, 689 1734 INDEX Subcostal nerve, iliac branch of, 425 plane, 689 zone, 690 subdivisions of, 690 Subcrureus muscle, 469 Subdural space of brain, 1471 of spinal cord, 1309 Subflava, ligamenta, 1039 Subiculum, 1395 Sublingual artery, 11 18 ducts, 1 1 36 gland, 1 135 development of, 11 36 ducts of, 1 1 36 structure of, 11 36 Submaxillary duct, 11 34 gland, 1 1 34 development of, 11 35 duct of, 1 134 structure of, 11 35 ganglion, 12 12 branches of, 121 3 roots of, 1 2 1 3 lymphatic glands, 11 01 triangle, 11 00 contents of, iioi Submental glands, 11 01 triangle, 1105 Subnasal point, 133 Suboccipital nerve, anterior primary division of, 1091 posterior primary division of, 1066 region, 1064 muscles of, 1064 triangle, 1065 venous plexus, 1066 Subperitoneal areolar tissue or fat, 676 Subsartorial plexus, 452 Subscapular artery, 311 nerves, 315 Subscapularis muscle, 323 Substantia ferruginea, 1378 gelatinosa of Rolando, 1317, 1353 nigra, 1438 propria of cornea, 1509 Subthalamic tegmental region, 1421 Subthalamicum, corpus, 1421 Sulcus — callosal, 1395 centralis insulae, 1393 fimbrio-dentate, 1396 frontal, inferior, 1385 superior, 1385 intraparietal, 1389 laminaj spiralis, 1556 lateral, of crus cerebri, 143 1 occipital, lateral, 1391 transverse, 1391 occipito-temporal, 1392 Sulcus {continued) — oculo-motor, of crus cerebri, 1431 olfactorius, 100 olfactory, 1387 orbital, 1387 postcentral, 1389 postero-lateral, of spinal cord» 1315 precentral, 1385 sclerae, 1507 temporal, 1392 terminalis of right auricle, 973 of tongue, 1 241 triradiate, 1387 tympanicus, 79, 1538 valleculae, 1338 Supination, 406 Supinator radii brevis muscle, 386 radii longus muscle, 383 ridge of ulna, 200 Supra-acromial nerve, 298, 319 Supracallosal gyrus, 1401 Supraclavicular nerve, 298 triangle, 1094 Supracondylar process of humerus* 188 Suprahyoid glands, 11 01 region, 1104, 1129 Supramastoid crest of temporal, 70 Suprameatal triangle, 72 Supra-occipital bone, 57 Supra-orbital artery, 1067, 1160 foramen, 134 nerve, 1067, 11 54 notch, 66 vein, 1068 Suprapatellar pad of fat, 542 tendon, 469 Suprarenal capsules, 749 development of, 81 7 lymphatics of, 817 structure of, 816 plexus, 736 Suprascapular artery, 320, 1096, 1145 branches of, 321 nerve, 314, 321, 1098 notch, 179 vein, 1096, 1 1 45 Supraspinatus muscle, 320 Supraspinous fossa of scapula, 1 78 Suprasternal nerve, 298 space, 1086 Supratrochlear foramen of humerus, 189 nerve, 1067, 1154 Sural nerves, 445 Suspensoria, ligamenta, of Cooper, 300 Suspensory ligament of axis, 1305 of lens, 1530 of penie, 647 INDEX 1735 Sustentacular fibres of retina, 1523 Sustentaculum hepatis, 720 lienis, 720 tali, 258 Sutures, 279 coronal, 124 dentated, 279 false, 279 fronto-ethmoidal. 130 fronto-lachrymal, 130 fronto-malar, 127, 129 fronto-maxillaiA', 127 fron to-parietal, 124 fronto-squamosal, 126 grooveJ, 280 harmonic, 279 intermaxillary', 127 interparietal or sagittal, 124 lachrymo-ethmoidal, 130 lachrymo-maxillary, 130 limbous, 279 malo-maxillary, 127 metopic, or frontal, 69, 125 occipito-mastoid, 124 occipito-parietal, 123 orbital, 129 orbital -palato-ethmoid, 1 29 orbito-malo-maxillary-, 129 orbito-palato-maxillary, 129 orbito-spheno-frontal, 129 palato-maxillary, 128 parieto-mastoid, 125 parieto-squamosal, 125 petro-squamosal, 128 premaxillary, 128 pterygo-maxillary, 128 schindylesis, 131, 280 serrated, 279 special, 121 spheno-frontal, 126 spheno-malar, 129 spheno-parietal, 126 spheno-squamosal, 127 squamo-mastoid, 128 squamous, 279 Sylvian border of sphenoid, 85 fossa, 1464 line, 1503 point, 1382 guide to, 1503 vein, deep, 1456 superficial, 1455 Sylvius, aqueduct of, 1439 development of, 1439 grey matter of, 1439 nerve-nuclei related to, 1439 fissure of, 1382 development of, 1464 hmbs of, 1383 Sjrmpathetic gangliated cord and plexuses. See Nerves Symphysis, 280 Synarthrosis, 279 Synchondrosis, 279 Symcitium, 1629 Syndesmosis, 280 Synovia, 281 Synovial membrane, 281 of tar siomT ligament, of female, 636 of male, 619 muscular space of arm, 323 Triangularis menti muscle, 1 1 70 Triceps extensor cubiti muscle, 342 Tricuspid orifice, 976, 979 position of, 985 valve, 979 Trifacial or trigeminal nerve. See Cranial Nerves Trigone, external, of bladder, 851 internal, of bladder, 866 Trigonocephalus, 159 Trigonum acusticum, 1378 femoris, 236 habenulae, 1422 hypoglossi, 1378 olfactorium, 1397 OS, 256, 264 vagi, 1378 ventriculi of lateral ventricle, 1409 Triradiate sulcus, 1387 Trochanter, great, 234 small, 234 Trochlea of humerus, 189 Trochlear fossa, 67 nerve. See Cranial Nerves Trochlearthrosis, 280 Trochoides, 280 Troltsch, pouches of, 1546 True vertebrae, 11 Tubarius, processus, 89 Tube, Eustachian, 1274 development of, 1275 muscles connected with 1275 Tuber calcis, 256 cinereum, 1424 cochleae, 1539 ischii, 224 omentale, 705 posticum, 1370 valvulae, 1370 Tubercle, adductor, of femur, 236 amygdaloid, 1408 carotid, 20 Chassaignac's, 20 Darwin's, 1193 lachrymal, 100 Lisfranc's, 44 malar, 105 mental, 116 pharyngeal, 59 preglenoid, 71 pterygoid of sphenoid, 89 radial, 195 scalene, 44 Tuberculum impar, 1270 Tuberosity, great, of humerus, 186 Tuberosity, small, of humerus, 186 of malar, 104 omental, of pancreas, 734 of palate, 112 of superior maxilla, 97 Turbinate bones, inferior, 109 ossification of, no sphenoidal, 90 process, inferior, of ethmoid, 95 superior, of ethmoid, 95 Tubules, seminiferous, 683 uriniferous, 819 Tunica albuginea, 683 dartos, 650 * vaginalis, 681 vasculoaa of Cooper, 683 Tiirck, column of, 1328 Tympani, membrana, 1540 secondary, 1542 sinus, 1539 tegmen, 1539 Tympanic annulus, 80 artery, 1203 attic, 73, 1545 canaliculus, 77 nerve, 1224 plate of temporal, 79 ' plexus of nerves, 1548 sulcus, 79 Tympanicus, sulcus, 1538 Tympano-hyal, 82 Tympano-mastoid fissure, 77 Tympanum, 1538 arteries of, 1547 mucous membrane of, 1545 muscles of, 1544 nerves of, 1548 ossicles of, 1542 development of, 1543 ligaments of, 1544 movements of, 1545 T5rpe, segmental, 3 Tyson, glands of, 647 Ulna, 197 coronoid process of, 197 olecranon process of, 197 ossification of, 200 Ulnar artery, 358 first part of, 358 branches of, 360 second part of, 364 third part of, 3 70 branches of, 370 varieties of, 363 in hand, 382 collateral nerve of Krause, 316, 364 nerve, 315, 364 branches of, 364 INDEX 1739 Ulnar nerve, dorsal branch of, 350 in hand, 374 nerve, summary of, 374 vein, anterior, 334 posterior, 334 U-loop, 800 Umbilical cord, 1630 duct, 798 notch of liver, 708 urinary fistula, 163 1 zone of abdomen, 690 subdiviiions of, 690 Umbilicus, 640, 1630 Umbo, 1541 Unciform bone, 2o5 Uncinate process of pancreas, 733 Uncus of brain, 1395 Unguis, OS, 108 Upper limb, bones of, 175 divisions of, 1 75 guide to dissection of, 411 Urachus, 870 Ureter, in abdomen, 826 in pelvis, 849 development of, 829 structure of, 826 Urethra, female, 890 development of, 899 lymphatics of, 899 male, 854 bulb of, 618, 869 development of, 870 ligament, triangular, of, 619 lymphatics of, 858 membranous part of, 856 prostatic part of, 854 spongy part of, 856 Urinarius, meatus, female, 631, 890 male, 647, 854 Uriniferous tubules, 819 structure of, 821 summary- of, 821 Uro-genital fold, 830 Uro-genital sinus, 830, 870 Utaro-vesical folds, 879 pouch, 879 Uterus, 885 anteflexion of 887 anteversion of, 887 birth, at, 889 body of, 886 cavity of, 888 broad ligament of, 880 cervix of, 886 ca\-ity of, 888 development of, 8g8 fundus of, 885 gravid. 1633 isthmus of, 886 lymphatics of, 897 position of, 887 Uterus, relations, general, of, 887 peritoneal, of, 887 structure of, 896 varieties of, 889, 899 Uterus masculinus, 855 Utricle of internal ear, 1552 of male urethra, 855 Uvea of iris, 15 15 Uvula of cerebellum, 1370 of soft palate, 1248 vesicae, 866 Vagi, trigonum, 1378 Vagina, 889 arteries of, 898 development of, 898 fornix of, 889 lymphatics of, 898 orifice, external, of, 631 structure of, 897 Vaginal ligaments, 375 Vaginale, ligamentum, 675 Vaginalis, processus, 675 Vagus (pneumogastric) nerve. See Cranial Ner\'es Valentin, ganglion of, 12 18 Vallecula of cerebellum, 1369 Sylvii, 1382 of tongue, 1 24 1 Valsalva, sinuses of, 984 Valve or valves — anal, 875 aortic, 983 bicuspid, 982 Gerlach, of, 796 ' Guerin, 858 Hasner, of, 1192 Heister, 809 Houston, of, 874 ileo-caecal or ileo-colic, 797 mitral, 982 pulmonary, 980 pyloric, 786 rectal, 874 tricuspid, 979 Tulpius, of, 797 Vieussens, of, 1379 Valvulae conniventes, 788 tuber, 1370 Valvule, Guerin, of, 858 Varieties of joints, 279 Varolii, pons, 1362 blood-supply of, 1456 Vas aberrans, of Haller, 684 deferens, 668 ampulla of, 852 development of, 686 pelvic portion of, 852 structure of, 669 Vasa efferentia of testis, 684 recta, false, of kidney, 823 I740 INDEX Vasa rec^, true, of kidney, 824 Vasculosi, coni, 684 Vastus externus muscle, 467 internus muscle, 468 Vater, ampulla of, 710 Veins — anal, 876 angular, 11 79 dorsal arch of foot, 514 auditory, internal, 1560 auricle, of, 1195 auricular, posterior, 1073, 1121 axillary, 312 azygos, left, lower, in abdomen, 762 in thorax, 1029 upper, 1030 right, in abdomen, 762 in thorax, 1028 transverse, 1030 basilar, 1456 basilic, 334 median, 332 bronchial, 1025 capsular, of liver, 804 cardiac or coronary, 985, 987 cardinal, loio central, of liver, 805 cephalic, 334 median, 332 cerebellar, 1456 cerebral, 1455 cervical, deep, 11 45 transverse, 109G, 1145 choroidal, 1455 clitoris, dorsal, of, 638 coronary sinus, 986 corpus striatum, of, 1405, 1455 cystic, 742 deferential, 670 development of, 1005, 1010 diploic, 1473 emissary, 1479 epigastric, deep, 663 superficial, 646 superior, 663 extraspinal, anterior, 1333 facial, common, 11 20 deep, 1206 superficial, on face, 1179 in neck, 11 20 transverse, 1181 femoral, 486 tributaries of, 486 varieties of, 488 cutaneous, external, 455 internal, 455 frontal, 1068 diploic, 1473 Galen, of, 1405, 1455 ' gastric, 739 Veins {continued) — gastro-epiploic, left, 741 right, 742 gluteal, 432 hemorrhoidal, inferior, 625, 876 middle, 876 superior, 876 plexus, external, 876 internal, 876 hepatic, 805 iliac, circumflex, deep, 664 common, 776 development of, 776 external, 778 development of, 779 internal, 844 development of, 845 infra-orbital, 1182 innominate, 955 intercostal, 930, 1027 collateral, 930, 1027 superior, 1028 intralobular, of liver, 805 intraspinal, anterior longi- tudinal, 1333 posterior longitudinal, 1333 iris, of, 1516 jugular, anterior, 1083 external, 1084 internal, 11 13 posterior, 1084 mastoid emissary tribu- tary of, 1479 primitive, loio labyrinth, of, 1560 larynx, of, 1293 lingual, 1 1 18 dorsal, 11 19 of lower limb, summary of, 566 lumbar, 773 ascending, 772 mammary, internal, 933 Marshall, oblique, of, 987 maxillary, internal, 1206 median, 332 deep, 332 meningeal, 1472 mental, 1182 mesenteric, inferior, 730 superior, 728 nasal fossa, of, 1261 transverse, 11 81 obturator, 488 occipital plexus, 1063 occipital emissary tribu- tary of, 1479 parietal emissary tribu- tary of, 1479 occipital diploic, 1473 omphalo-mesenteric, 1005 ophthalmic, 1161 INDEX 1 741 Veins {continued) — ovarian, 890 plexus, 890 of palm, 372 deep, 382 palpebral, 1182 pampiniform plexus, 670 pancreatico-duodenal, 742 parumbilical. 719 penis, dorsal, of, 647 pharynx, of, 1269 phrenic, inferior, 752 plexus, dorsal of hand, 350 palmar, 351 popliteal, 443 portal, 742, 804 profunda femoris, 487 pterygoid plexus, 1206 pudic, internal, 625 pulmonary, 953, 964 pyloric, 742 radial, 334 ranine, 11 18 renal, 753 retina, of, 1526 saphenous, anterior, 455 external or short, 514 internal or long, 455 guide to, 456 posterior, 455 sciatic, 433 sclerotic, of, 1508 spermatic, 754 spinal column, of, 1332 dorsal plexus, 1332 cord, of. 1333 splenic, 741 subcardinal, 1012 subclavian, 1096, 1144 subcostal, 773 sublobular of liver, 805 suboccipital plexus, 1066 posterior condylar emis- sary, tributary of, 1479 superficijil, of sole of foot, 548 supra-orbital, 1068 suprarenal, 752 suprascapular, 1096, 1145 Sylvian, deep, 1456 superficial, 1455 temporal, superficicd, 1072 deep, 1206 temporo-maxillary vein, 11 85 thyroid, 1123 tonsils, of, 1254 tympani, membrana, of, 1541 tympanum, of, 1547 ulnar, anterior, 334 posterior, 334 umbilical, 1008 Veins {continued) — uterine, 891 vaginal, 892 of Uver, 804 vertebral, 1144 anterior, 11 45 vitelline, 1005 VeU, frenulum, 1427 Velum interpositum, 1404 arteries of, 1458 veins of, 1405 medullary, inferior, 1379 superior, 1379 pendulum palati, 1248 Vena cava, inferior, 755 development of, 757, 1015 tributaries of, 756 superior, 956 development of, 957 lOII magna Galeni, 1405, 1455 portae, 742 development of, 744, 1005 sinus of, 743 tributaries of, sources of, 743. 744 summary of, 744 within the liver, 804 salvatella, 351 Venae advehentes, 1008 basis vertebrae, 1333 comites, brachial, 340 palmar, 372 radial, 357 tibial, anterior, 506 posterior, 525 ulnar, 364 minimae cordis, 976, 987 rectae of kidney, 825 revehentes, 1008 stellatae of kidney, 825 Thebesii, 987 vorticosae, 15 12 Ventricle or ventricles — fifth, 1404 development of, 1404 fourth, 1376 choroid plexuses of , 1380 development of, 1380 floor of, 1377 summary of, 1377 roof of, 1 3 78 summary of, 1379 lateral, 1405 choroid plexuses of, 1405, 1409 comua of, 1406. 1408 development of, 1409 septum lucidum, 1403 third, 14 15 174* INDEX Ventricle or ventricles [continued) — third, choroia plexuses of, 1405, 1415 development of, 141 7 floor of, 14 16 recesses of, 141 6, 1417 roof of, 1 4 15 summary of, 14 15 larynx, of, 1283 Ventriculus terminalis of Krause, 1319 Vermiform appendix, 696 mesentery of, 697 positions of, 697 structure of, 796 fossa, 58 process of cerebellum, 1367 Vermis of cerebellum — inferior; 1370 nodule of, 1371 pyramid of, 1370 tuber posticum vel valvulae of, 1370 uvula of, 1370 superior, 1368 central lobule of, 1368 clivus monticuli, 1368 culmen, 1368 folium cacuminis, 1368 lingula, 1368 Vertebra, atlas, 14 ossification of, 29 axis, 17 ossification of, 29 cervical, 12 sixth, 20 classification of, 1 1 component parts of, 1 1 false, II, 30 lumbar, 25 fifth, 27 ossification of true, 27 prominens, 19 thoracic, 20 peculiar, 23 Vertebral aponeurosis, 289 arteries, at base of brain, 1342 artery, development of, 1142 first part of, 1141 second part of, 1 141 third part of, 1065 fourth part of, 1451 bow, 55 column, II, 38 development of, 54 sympathetic plexus, 1235 vein, 1 1 44 anterior, 11 45 Vertex of skull, 132 Verumontanum, 855 Vesalii, foramen, 86 Vesicae, uvula, 866 Vesicles, cerebral, 1458, 1459 Vesicula prostatica, 855 Vesiculae seminales, 852 blood-supply of, 872 development of, 872 lymphatics of, 872 structure of, 871 Vespertilionis, alae, 880 Vestibular area, inferior, 75 superior, 75 artery, 1560 nerve, 1300, 1558 Vestibule of internal ear, 1548 of middle meatus, of nasal fossa 1255 of mouth, 1236 of pudendum, 631 Vestigial fold of Marshall, 944 Vibrissas of nostrils, 11 96 Vicq d'Azyr, bundle of , 1402, 1423 Vidian artery, 1206, 1260 canal, 89 nerve, 1219 Vieussenii, ansa, 1235 limbus, 993 Vieussens, valve of , 1379 Villi of small intestine, 789 Villosae, plicae, of stomach, 783 Villous coat of small intestine, 788 Vincula accessoria tendinum, 376 Visceral arches, 1271 clefts, 1270 Visual centre, higher, 1427 centres, lower, 1427 Visual purple or rhodopsin, 1523 Vitelline duct, 695 membrane, 894 Vitello-intestinal duct, 695 Vitellus, 894 Vitreous body, 1529 Vocal cords, false and true, 1284 process of arytenoid cartilage, 1279 Volar artery, superficial, 357 Volkmann's canals, 6 Vomer, 114 ossification of, 115 Vorticosae, venae, 1512 Vulva, 633 Waldeyer, paroophoron of, 884 Weber, glands of , 1243 Wharton, duct of, 1134 Wharton's jelly, 163 1 White line of Hilton, 875 of pelvic fascia, 838 matter of spinal cord, 1319 Willis, circle of , 1343, 1454 parts within, 1455 INDEX 1743 Willisii, chordae, 1475 Wilson, muscles of, 617 Winslow, foramen of, 721, 802 posterior ligament of, 529 Wirsung, duct of, 81 1 Wolffian body, 684, 829 duct, 686, 829 tubules, 829 Wood's muscle, 551 Wormian bones, 155 Wrisberg, cartilages of, 1280 ganglion of, 968 nerve of, 315, 331 pars intermedia of , 1299, 1489 Xiphistemum, 47, 49 Xiphoid process, 47, 49 Yolk, 894 Yolk-sac, 1627 Yolk-staik, 1627 Zinn, hgamentof, 1150 zonula of, 1530 Zona arcuata, 1555 orbicularis, 489 pectinata, 1555 pellucida, 1603 radiata, 894 Zonula ciliaris, 1530 Zinn, of, 1530 Zygomatic fossa, 142 Zygomaticus major muscle, 1168 minor muscle, 11 68 Zygoma, 70 THE END BaHiiire, Tindall fr* Ccx, 8, Henrietta Street, Cowent Gmrden, London, 19u7 A 0 QM Buchanan, Alexander MacGregor 23 Manual of anatomy B83 1916 BioMed PLEASE DO NOT REMOVE CARDS OR aiPS FROM THIS POCKET UNIVERSITY OF TORONTO LIBRARY