big pipe bran pene ge en ae: ane sree fee Pires oe ae Ma ti Hates org dee ania A ye bap oe ee weir ee ely: doh bes titre dm TUBadienche meen ye bsha a ARNE ier rian Rs nalts vt as ¥ ne coe evens ie ne eles 7 Ponta Sac a a iieapemnaic ern ENR “ aa ahha * ae seh evita: ‘ POEs am we Soe ice ma atartt ewe ete ae tera ees uate = —— Sheet ae ‘tay set “ et ith rae ase vise a tek aed piesa bi AC tS tah at Dara ect 1 Ais Biss tf Ge cata ea d eis eh ie rere Rogie area 4 Peery eine Sihean esi SNS Rate lecannetnie ky 3 Sraba oe pa ce ae ini acon ve eee ea Pe Ss oer sb ten Sees CS i al er tees 4 ee eer tae Reece et Be pe = ela ee ras igre CIE ete ep toa ise Poorer keane ve oe ite. pl lye ee : ota pe gd eae ich G re (ine Pine pat 92 rica ip peg etal : Bicone pire Pati hina iabebenners Pus ides ng ee Peete St nian eat ee . Hie tae Meine fe ares ire tacts ee ee Bide copie Bisel id ies Lit ee ee Woy ee ea Ape oie eatin : iss ee. te Caries ML patie apeetnresy Pore ven Pa ies fo ieee es ee ioe sepia £o eee be te ae ae eles mates cane er nia Wess Pate otceee Seah geste Sete os mh ee hese oink ei pet aor ves melee ovgucet porn t eee aera Sa micuseress pacts ne eae zm = sles Selector Pai ist oe nai Riieaaseed eee as 3 pinlem eh nae Srna See oe pei chia el ee ee Pe Ce Bree ore as tt ae ee riorces Fee a pa iaee eee chi lecss Agree re rd : ee es Shere meet ae te CORNELL UNIVERSITY THE Flower Weterinary Library FOUNDED BY ROSWELL P. FLOWER for the use of the N. Y. STATE VETERINARY COLLEGE 1897 Cornell University Library SF 767.B81 iii 3 1924 021 941 830 vet Cornell University The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www. archive.org/details/cu31924021941830 A GUIDE TO THE DISSECTION OF THE DOG A GUIDE TO THE DISSECTION OF THE DOG BY O. CHARNOCK BRADLEY M.D., D.Sc., F.R.S.E., M.R.C.V.S. PRINCIPAL OF THE ROYAL (DICK) VETERINARY COLLEGE, EDINBURGH ; LECTURER ON COMPARATIVE ANATOMY, UNIVERSITY OF EDINBURGH WITH 69 ILLUSTRATIONS LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY AND CALCUTTA 1912 All rights reserved PREFACE Durine recent years the feeling that there was room for a book in English dealing with the anatomy of the dog has been steadily gaining ground. Doubt- less, in the opinion of many, the gap can be adequately filled only by a systematic treatise similar to the classic ‘ Anatomie des Hundes’ of Ellenberger and Baum. Until some such work makes its appearance, perhaps the present publication may serve as a temporary means of supplying the deficiency. For several reasons it was decided to introduce the subject of canine anatomy to the English reader in the form of short notes planned to aid him in his desire to obtain first-hand knowledge by dissection. Herein are given directions which experience has shown will help the student to display the various organs and structures in an orderly and profitable manner. The descriptions which follow are purposely given in the briefest possible form, in order that the dissection of the whole animal may be accomplished within a reasonable length of time. While primarily intended for the guidance of the student who proposes to join the ranks of a profession which already contains a fair number of special- ists whose work necessitates a close knowledge of the anatomy of the dog, it is hoped that these notes may be of some service to the student of comparative anatomy who wishes to gain an acquaintance with the structure of an easily obtained mammal. The nomenclature herein employed is that which may be called the Baden and Stuttgart modification of the B.N.A. of the human anatomist; and, if not perfect, is infinitely better than the nondescript nomenclature, crowded with synonyms, formerly found in works on comparative anatomy. My thanks are due to my colleague, Mr. W. M. Mitchell, M.R.C.VS., for assistance in many directions; and to the publishers for the cordial manner in which they have met my suggestions. O. CHARNOCK BRADLEY. EpinsurncH: June 1912. COLOURED ILLUSTRATIONS IN TEXT Dissection of the Pectoral Region Diagram of the Cranial Mesenteric Artery Coeliac Artery Portal Vein Medial Surface of fie Right Tang Medial Surface of the Left Lung Diagram of the Thoracic Duct : Diagram of Part of the Sympathetic Nemous System ‘ Diagram of the Urinary Organs of the Male Superficial Dissection of the Inside of the Thigh . Dissection of the Inside of the Thigh . Superficial Dissection of the Gluteal Region and Thigh Dissection of Gluteal Region and Lateral Aspect of the Thigh Deep Dissection of the Gluteal Region Diagram of the Arteries on the Dorsum of the Pes Diagram of the Nerves on the Dorsum of the Pes Dissection of the Lateral Aspect of the Leg ‘ i Dissection of Origin of Tibial and Common Peroneal Nerves Dissection of the Medial Aspect of the Leg Superficial Dissection of the Sole : Diagram of the Plantar Nerves of the Pes . Diagram of the Plantar Arteries of the Pes Diagram of the External Dliac and Hypogastric Aciaiien Superficial Dissection of the Shoulder and Neck . Dissection of the Shoulder Dissection of the Medial Aspect of ne eheuildey. die: eal Hei: Dissection of the Lateral Aspect of the Shoulder, Arm, and Forearm Dissection of the Arm . Dissection of the Medial Aspect of iis Hejeati Diagram of Nerves on the Dorsum of the Manus : Diagram of Nerves on the Volar Aspect of the Manus . Diagram of the Arteries on the Dorsum of the Manus . Diagram of the Volar Arteries of the Manus Dissection of the Side of the Neck and Thorax 100 101 111 117 119 121 125 127 131 133 138 139 140 147 ILLUSTRATIONS Superficial Dissection of the Face Dissection of the Tongue, Pharynx, etc. Dissection of the Larynx Dissection of the Larynx Dissection of the Orbit Dissection of the Orbit Arteries at the Base of the Brain PAGE 157 162 177 178 185 186 208 BLACK AND WHITE ILLUSTRATIONS IN TEXT Diagram of the Brachial Plexus Position of the Abdominal Viscera Extent of the Abdominal Muscles Transverse Section of the Abdomen Transverse Section through the Abdomen Transverse Section of the Abdomen Transverse Section of the Thorax Transverse Section of the Thorax Outline of the Spleen Outline of the Stomach Lateral Surface of the Right ae Lateral Surface of the Left Lung Diaphragmatic Surface of the Lungs . Outline of the Heart as seen from the Left . — Outline of the Heart as seen from the Right Diagram of the Branches of the Bronchi Outline of the Diaphragmatic Surface of the Liver Outline of the Visceral Surface of the Liver i Diagram of the Gall-bladder and its Associated Ducts Plexus of Lumbar and Sacral Nerves Tendons on the Dorsum of the Manus Transverse Section of the Spinal Cord Transverse Sections of the Spinal Cord at Different Levels : Lateral Surface of the Cerebral Hemisphere Dorsal View of the Cerebral Hemisphere Medial Surface of the Cerebral Hemisphere . Dissection to show the Floor of the Lateral Ventricle Lateral Aspect of Hind-brain and Mid-brain 113 132 204 204 212 213 214 216 220 DISSECTION OF THE DOG THE dissection of the dog is best begun with the animal lying on its back. If the subject is a female, the mammary glands should be examined as far as possible before any dissection is carried out. Mamma.—The mammary glands of the dog are eight to ten in number, arranged in a double row—often asymmetrical—along the ventral aspect of the thorax and abdomen. When ten glands are present, they can generally be designated as four thoracic, four abdominal, and two pubic. Though nipples are present in both sexes, mammary glands, as such, are seldom demonstrable in the male. Even in the female, except during the period of lactation, the mamme do not generally form very distinct projections. Each nipple (papilla mammz) is conical in form, covered with hairless skin, and pierced at its apex by numerous (eight to twelve) openings. Each small orifice leads to a milk canal (ductus lactiferus), which traverses the length of the teat from a milk sinus (sinus lactiferus) at its base. Dissection.—Make a longitudinal incision along the mid-ventral line from the middle of the neck to near the external genital parts, and a transverse incision from the medial aspect of one elbow to a corresponding point on the opposite limb. Two short and two long flaps of skin should now be reflected. In doing this, be careful to avoid removal of the mammary glands. On arriving at the base of the nipple, make a circular cut through the skin so as to leave the teat uninjured and attached to its gland. In turning outwards the flaps in the neck, avoid removal of the cutaneous muscle which here forms a thin layer of transverse fibres. If the mammary glands are not active the gland-tissue will be scanty and form merely a thin layer under the skin. Generally the thoracic glands are separate from each other, while those over the abdomen are continuous. The character of the glands is much more obvious during lactation, when they form a continuous, lobulated sheet stretching from the oral border of the pectoral muscles to the neighbourhood of the external genital parts. Dissection.—Remove the thoracic mammary glands and define the pectoral muscles. Then proceed with the dissection as in the male. B 2 DISSECTION OF THE DOG Dissection of the Male.—If the subject be a male, make an incision along the mid-ventral line from the middle of the neck to the prepuce. Then make a transverse incision from the medial aspect of one elbow to a similar point on the opposite limb. Turn back four flaps of skin. In doing so, an extensive but thin subcutaneous muscular sheet —m. cutaneus—will be exposed in the neck, where its fibres are transverse, and over the abdomen, where they are oblique. Define the pectoral muscles. In clearing the fascia from the pectoral muscles note small vessels and nerves (about six), which appear close to the mid-ventral line and proceed laterally over the surface of the muscles. These vessels are the perforating branches of the internal mammary artery. In the xiphoid region an artery and vein (branches of the cranial epigastric vessels) appear from under the border of the deep pectoral muscle, and run obliquely in caudo-lateral direction to supply the mammary region. These are larger in the female. M. PECTORALIS SUPERFICIALIS.—In the main the fibres of the superficial pectoral muscle run transversely to the long axis of the body. The origin of the muscle is from the first two segments of the sternum and from the septum between it and its fellow muscle, and its insertion—hidden as yet by the brachio-cephalic muscle—is to the line on the humerus running distalwards from the tuberculum majus. Crossing the superficial pectoral muscle close to its insertion, and lying in a narrow space bounded by this and the brachio-cephalic muscle, are two vessels : namely, a communicating branch from the cephalic vein to the external jugular vein, and the deltoid ramus of the thoraco-acromial artery. Dissection.—Reflect the superficial pectoral muscle by cutting across it close to its origin, and notice in doing so that the muscle increases in thickness towards its cranial border. Clean the surface of the deep pectoral muscle and dissect out the various structures lying in a triangular space at the root of the neck. In reflecting the superficial muscle observe its nerve of supply (from the brachial plexus) bending round the cranial border of the deep pectoral muscle, accompanied by the pectoral ramus of the thoraco-acromial artery and its satellite vein. M. PECTORALIS PROFUNDUS.—The deep pectoral muscle is much more extensive than the superficial member of the same group. Consequently, a considerable extent of it is visible before the superficial > nd is reflected. Its fibres are disposed with a varying degree of obliquity. "lhe most caudal fibres are the most oblique. The caudal border of the muscle is rendered some- what indefinite from the presence of a narrow band sometimes isolated, and always separable, from the rest. a DISSECTION OF THE DOG 3 The origin of the muscle is from the sternum from the level of the second costal cartilage to the xiphoid process. Its insertion is into the medial tubercle (tuberculum minus) of the humerus, and, by means of a thin tendon which crosses the origin of the biceps, to the lateral tubercle (tuberculum majus) y-——~v. jugularis externa _— m. brachio-cephalicus y --~ m™. sterno-cephalicus ----- m. pectoralis superficialis _ ye >.~-_——_— ; v7 n. medianus 7m, biceps brachii 7 eed | i A See et (in fk [ 1 1 \ | \ L —— X ! ™ is i ! n. ulnaris XN N 1 Ne m. triceps brachii \ | Sis \\ 1m. tensor fascie antibrachit ® %: \ \ +> \m. pectoralis profundus SSeS m. rectus abdominis Fic. 1.—Dissection of the pectoral region. also. The most caudal fibres of the muscle are connected with the cutaneous muscle of the abdomen. ; At the digs the neck is a triangular space of some moment on account of the structures contained therein. The lateral limit of the space is formed by the brachio-cephalic muscle. Medially the sterno-cephalic muscle forms its boundary ; while its base—caudal in position—lies at the edge of the pectoral muscles. Sy B2 4 DISSECTION OF THE DOG Within the space will be found the external jugular vein, the communicating branch from the cephalic vein, the omo-cervical arterial and venous trunks, and the nerves to the superficial pectoral and brachio-cephalic muscles. In the depths of the triangle is part of the brachial plexus of nerves. All these structures will be more fully exposed during the dissection of the axillary space. Dissection.—Reflect the deep pectoral muscle by cutting through it a short distance from its origin. This exposes the axillary space, the structures in which should be cleaned with great care. In reflecting the muscle, a lymph-gland (the axillary gland) will be found lying over the distal part of the teres major and between this and the pectoral muscle. Branches from the brachial plexus of nerves should also be noted bending round the axillary vessels to sink into and supply the deep pectoral muscle. AxittA.—The axillary space is bounded laterally by the scapula and the subscapular muscle, and medially by the chest-wall and the muscles clothing it. In the natural condition the space can scarcely be said to exist except as a narrow chink filled by areolar and fatty tissue ; but on dissection its medial and lateral walls are separated from each other and a definite space is produced. Dorsally the two walls meet at a very acute angle; ventrally, however, they diverge slightly, and the floor of the space is defined by the pectoral muscles. Cranially the axillary space communicates with the neck ; whereas caudally it is closed in by the latissimus dorsi and cutaneous muscles. The principal contents of the space are the axillary vessels and the brachial plexus of nerves. V. ET A. AXILLARIS.—The axillary vessels are among the structures first exposed on reflecting the deep pectoral muscle. The vein drains the blood from the limb, and joins the external jugular vein at the entrance to the chest, thus constituting one of the roots of the innominate vein. Its collateral tributaries are the lateral thoracic, subscapular and omo-cervical veins, and small vessels from the pectoral muscles. Occasionally the omo-cervical venous trunk joins the jugular direct. Of the tributaries the subscapular vein is by far the largest, its volume depending mainly upon the circumstance that it continues the cephalic vein. The axillary artery is a continuation of the subclavian artery. Com- mencing on a level with the first rib, it runs down the limb as far as the tendon of insertion of the teres major muscle. Most of its branches will be examined in connection with the scapular and arm regions, but two should now be noted as supplying the pectoral muscles and their neighbourhood. These are the thoraco-acromial and lateral thoracic arteries. A. THORACO-ACROMIALIS.—The thoraco-acromial artery soon divides into two branches, a ramus deltoideus and a ramus pectoralis. Both of these have DISSECTION OF THE DOG 5 been already noted in connection with the dissection of the pectoral muscles. Very commonly the deltoid ramus arises from the omo-cervical trunk. A. THORACALIS LATERALIS.—The lateral thoracic artery arises some little distance from the border of the first rib, supplies the pectoral muscles, runs along the deep face of the deep pectoral muscle in company with the nerve to the latissimus dorsi, and ends in the cutaneous muscle over the abdomen. TRUNCUS OMO-CERVICALIS.—The omo-cervical trunk is a branch of the subclavian artery. Arising within the first rib, it passes medial to the axillary artery and the brachial plexus to divide before long into the ascending cervical and transverse scapular arteries. The ascending cervical artery (a. cervicalis ascendens) runs for a distance on the medial surface of the brachio-cephalic muscle, and finally enters the substance of this muscle. The transverse scapular artery (a. transversa scapule) passes towards the cranial border of the subscapular muscle and divides into several branches, the main one of which accompanies the suprascapular nerve. N. purenicus.—The phrenic nerve will be found between the axillary vein and artery dorsal to the omo-cervical arterial trunk. It arises by three roots from the ventral divisions of the fifth, sixth, and seventh cervical nerves, and leaves the present dissection by entering the thorax. Later, it will be traced to the diaphragm to which it carries motor impulses. Dissection.—Cut across the axillary vessels, close to the first rib. This allows of a more complete inspection of the brachial plexus. PLEXUS BRACHIALIS.—The brachial plexus is a somewhat complex arrange- ment of nerves formed by branches from the last three cervical and the first two thoracic nerves. It is placed between the axillary vessels and the scalenus muscles. Its branches are: Nerve to the brachio-cephalic muscle, n. swprascapularis, n. subscapularis, n. musculo-cutaneus, n. axillaris, n. radialis, n. medianus, n. ulnaris, n. thoraco-dorsalis, nn. thoracales ventrales, and n. thoracalis longus. Most of these will be examined in the dissection of the limb; but the following points should be noted at the present moment. The ventral thoracic nerves (nn. thoracales ventrales) are mainly distributed to the pectoral muscles. One of them supplies the skin and cutaneous muscle on the side of the chest and abdomen. The thoraco-dorsal nerve (n. thoraco-dorsalis) supplies the latissimus dorsi muscle. If the subject is a male the external genital organs should next be dissected. PARTES GENITALES EXTERN#.—The male external genital parts consist of the scrotum, the penis, and the prepuce. The scrotum is a membranous bag with a double cavity in which the testes B 3 6 DISSECTION OF THE DOG ‘ are lodged. It lies between the thighs, and forms a rounded prominence crossed in a cranio-caudal direction (generally obliquely) by a shallow groove in which a faint line, the raphe scroti, may be detected. The skin of the scrotum is thin and provided with comparatively few hairs. Dissection.—Make an incision through the skin along the raphe of the scrotum, and expose the underlying tissues. nn, cervicales es co thor nn: n. thoracalis longus ~\ To m. brachio-cephalicus n. musculo-cutaneus n. thoraco-dorsalis n. suprascapularis \ ‘an. subscapulares \ “To m. pectoralis profundus ‘ . . n. axillaris nn. medianus et ulnaris ~~ n. radialis Fra. 2.—Diagram of the brachial plexus. The wall of the scrotum can be resolved into three layers. Of these the most superficial consists of skin. Under this is a fibrous tissue known as the tunica dartos, which, with its fellow of the other side, forms the median septum between the two scrotal cavities—the septum scroti. Removal, of the dartos exposes the third layer composed of a fascial tunic lined within by a serous membrane. The fascia is continuous with that covering the deep face of the transverse abdominal muscle, and is in the form of a pear-shaped sac the narrow end of which is connected with the superficial end of the inguinal canal. Along the dorsal side of the narrower part of the sac there is a muscular slip, the external cremaster muscle (m. cremaster externus), associated with the internal oblique muscle of the abdominal wall, on the one hand, and terminating, on the other hand, in an aponeurosis within the substance of the wall of the scrotum. : DISSECTION OF THE DOG 7 TUNICA VAGINALIS.—The tunica vaginalis is a serous membrane continuous, through the inguinal canal, with the peritoneum. Like other serous membranes it is composed of a parietal and a visceral part. The parietal portion lines the interior of the scrotum and is continuous with the visceral part in the caudo-dorsal region of the scrotal cavity. The visceral part of the tunic will be displayed after an examination of the testis and its surroundings has been made. Dissection.—Cut through the parietal tunica vaginalis with a pair of scissors, and examine the contents of the cavity of the scrotum. TESTIS. ET EPIDIDYMIS.—The testes are two oval organs, slightly flattened laterally (especially on the medial surface), each lodged in its own compartment of the scrotum. The long axis of each testis is oblique, and runs caudo-ventral. The two surfaces, medial and lateral, are smooth and convex, as is also the ventral border. The dorsal border and the two extremities are connected with the epididymis. ; The epididymis of the dog is relatively large. It consists of an elongated, laterally compressed mass formed by the tortuous windings of a long tube held together by dense connective tissue and covered by the tunica vaginalis. The body (corpus epididymidis), or main part of the structure, lies dorsal to the testis. The cranial and caudal ends, known respectively as the head (caput epididymidis) and the tai! (cauda epididymidis), are adherent to the extremities of the testis. The cauda is also firmly bound to the wall of the scrotum. From the cauda the ductus deferens takes origin. The duct runs cranialwards dorso-medial to the testis, at first somewhat convoluted but afterwards straighter, and passes into the inguinal canal. FUNICULUS SPERMATICUS.—The spermatic cord consists of the ductus deferens and certain blood vessels, nerves, and lymphatics. The vein within the cord is richly coiled and forms a prominent object, extending from the head of the epididymis into the inguinal canal. Partly buried within the venous mass is the internal spermatic artery (a. spermatica interna). The visceral part of the tunica vaginalis may now be followed. It is applied closely to the testis and epididymis, and dips in between these two organs to form a cavity, the sinus epididymidis, the entrance to which is lateral in position. Continued towards the inguinal canal, the tunic encloses the spermatic cord, from which and from the epididymis it is reflected as a mesentery containing fine nerve filaments. It will be observed that the deferent duct and the external spermatic artery are enclosed in a special sheath of the tunic which is an offset from the covering of the other constituents of the spermatic cord. Praputium.—the prepuce is a tubular sheath of integument enclosing the glans of the penis, and, in the retracted state of this organ, circumscribing a cavity which communicates with the surface by a slit-like orifice. The prepuce B4 8 : DISSECTION OF THE DOG consists of two layers : a double parietal layer, and a visceral layer intimately adherent to the glans penis. The superficial sheet of the parietal layer is composed of skin differing little from that of the neighbourhood. This should be reflected by making a longitudinal incision from the preputial orifice to the scrotum. Care must be taken to preserve the preputial muscle (m. pre- putialis) which, as a flattened band, springs from the abdominal aponeurosis in the xiphoid region, and runs immediately under the skin to form a loop round the orifice of the prepuce. If the deep sheet of the parietal layer be now slit open with a pair of scissors, its resemblance to mucous membrane will be manifest. The surface looking towards the penis is longitudinally folded and studded with irregular rows of flattened, rounded elevations caused by masses of lymphoid tissue. The membrane is directly continuous with the visceral layer of the prepuce, which extends over the glans penis to the urethral orifice where it meets the urethral mucous membrane. It should now be noted that the prepuce is supplied with blood by the external pudendal artery. Dissection.—The penis should now be freed from its surroundings as far as its root. In cleaning the organ, note the presence of a narrow, pale muscle, the retractor of the penis, running along its urethral surface from the anus to the vicinity of the glans. Preserve also the dorsal vessels and nerves which will be found on the opposite surface. Pewis.—The penis consists of a middle part (its body or corpus penis), a root (radix penis) attached to the arch formed by the two ischial bones, and a free extremity (glans penis) of considerable length. ; The term dorsum penis is applied to that aspect of the organ which is in contact with the abdominal wall; whereas the opposite aspect is called the urethral surface (facies urethralis). The body of the penis lies in the middle line, dorsal to the testes and crossed laterally by the ductus deferens. It is composed of three bodies running parallel to each other. The corpora cavernosa penis are two rods of erectile tissue surrounded end bound together by a dense fibrous envelope, the tunica albuginea [corporum cavernosorum], and separated from each other by a fibrous septum (septum penis). In the ischial region the two corpora diverge, each forming a crus penis which is attached to the border of the ischium. From about the middle of the penis, the corpora are continued onwards ag a bone, the os penis. This may be considered as formed by two narrow plates joined dorsally and diverging ventrally to enclose a groove in which the urethra lies. The caudal end of the bone is truncated. The cranial end is more pointed, and to it is appended a curved process composed of fibrous tissue of cartilage-like density. The third erectile body of the penis is the corpus cavernosum urethree, DISSECTION OF THE DOG 9 associated, as its name indicates, with the urethra, and lodged in a groove on the urethral surface of the penis. _ The two crura penis, forming the radix penis, are covered by the ischio- cavernous muscles. In the middle line, between the crura, the corpus caver- nosum urethre forms a double expansion, the bulbus urethre, also covered _ by a muscle, the M. bulbo-cavernosus. The glans penis of the dog is of considerable length. Thinnest about the middle, it expands into a swelling at each end. The caudal expansion known as the bulbus glandis is the larger, and is developed on the dorsal side of the os penis. From it the dorsal veins of the penis take origin. The smaller expansion of the glans forms the free extremity of the penis and is more cylindrical in form than the bulbus glandis. Its terminal part is pointed and has the urethral orifice at its apex. Running along the urethral surface of the glans is a feeble fold of prepuce known as the frenulum preputii. Vv. DORSALES PENIS.—The two dorsal veins of the penis arise in the erectile tissue of the bulbus glandis. Running along the dorsum of the penis to its root, they bend round the border of the ischia and form the main roots of the internal pudendal veins. AA. DORSALES PENIS.—The dorsal arteries of the penis lie lateral to the veins of the same name. Each forms the largest terminal branch of the internal pudendal artery of its own side, and, leaving the pelvis by curving round the border of the ischium, can be readily followed to the glans penis. NN. DORSALES PENIS.—The dorsal nerves of the penis, branches of the internal pudendal, accompany the dorsal vessels, each nerve lying lateral to the artery which it follows. Dissection.—Cut through the roots of the brachial plexus and clean up the ventral and lateral aspects of the thorax and abdomen. In doing this, first define the extent and attachments of the cutaneous muscle as far as the present dissection permits. Preserve the branches of the intercostal and lumbar vessels and nerves which appear about midway between the mid-dorsal and mid-ventral lines of the trunk. Observe that the branch from the third or fourth intercostal nerve is of good size and crosses the border of the latissimus dorsi muscle to reach the lateral aspect of the arm. It is connected with a ventral thoracic nerve from the brachial plexus. In removing the remains of the prepuce of the male, or the mamme of the female, take care not to destroy the external pudendal vessels and the external spermatic nerve which may be found embedded in an accumu- lation of fat in the inguinal region. The artery and vein can generally be traced to an anastomosis with branches from the cranial epigastric vessels. 10 DISSECTION OF THE DOG A group of lymph-glands will also be found in the inguinal region. Several vessels and nerves pierce the abdominal wall. Of these the circum- flex iliac vessels and the lateral cutaneous femoral nerve are the most conspicuous. They appear close to the angle of the ilium and are distri- buted in the cutaneous muscle of the abdomen and in the skin over the lateral proximal part of the thigh. A little cranial to the point of . appearance of the circumflex iliac vessels, the phrenico-abdominal artery pierces the oblique muscle of the abdomen. Branches of the ilio-inguinal and ilio-hypogastric nerves should also be noted and preserved. A. PUDENDA EXTERNA.—The external pudendal artery is generally a branch of the deep femoral, but it may arise from a common trunk from which springs the caudal epigastric artery as well. The origin of the vessel cannot be examined at present. Crossing the spermatic cord medially, the artery runs towards the umbilicus and supplies the inguinal lymph-glands, the prepuce, and the surrounding skin. In the female it is larger and furnishes blood to some of the mammary glands. ; N. SPERMATICUS EXTERNUS.—The external spermatic nerve is a part of the genito-femoral nerve. Appearing through the abdominal wall along with the external pudendal vessels, it crosses the spermatic cord and is expended in the external genital parts, or the mammary glands, and the skin of the inner part of the thigh. It is sometimes connected with the ilio-inguinal nerve. M. OBLIQUUS EXTERNUS ABDOMINIS.—The external oblique is the most superficial muscle of the abdominal wall. Its origin is by digitations from the ribs from the fifth or sixth to the last, and from the lumbo-dorsal fascia. The muscular fibres run in a caudo-ventral direction as far as the border of the straight abdominal muscle. Here they give place to an aponeurosis which . is attached to the linea alba. An important part of the aponeurosis stretches from the lateral angle of the ilium to the pubis near the symphysis. This constitutes the inguinal ligament of Powpart (ligamentum inguinale [Pouparti)), in association with which is the superficial opening of the inguinal canal. Opposite this opening the pectineus muscle takes part of its origin from the inguinal ligament. At the same pointa thin reflection of the aponeurosis to take part in the formation of the scrotum should be noticed. Medial to the inguinal canal,i.e.in the pubic region, the aponeurosis is thin and mixed with fibres from the other abdominal muscles. From the aponeurosis of the oblique muscle a thin, ill-defined sheet is reflected onto the medial aspect of the thigh. M. Lartissimus porsi.—As its name indicates, this is a very broad muscle covering the dorso-lateral part of the thorax. Its origin is from the lumbo- dorsal fascia, by means of which it is attached to the spinous processes of the last seven thoracic vertebre, and by fleshy strips from the last two or three ribs. Its insertion is by a flattened tendon into the crista tuberculi minoris of the DISSECTION OF THE DOG 11 humerus. The whole of the muscle cannot be conveniently examined at the present stage of the dissection. M. TRANSVERSUS COSTARUM.—This is a small, thin, irregularly triangular muscle placed over the union of the bony and cartilaginous segments of the first two or three ribs. Its origin is from the first rib, and its insertion, by means of a’thin and not very definitely bounded aponeurosis, is into the sternum from the third to the fifth or sixth costo-sternal joint. Dissection.— Until such time as the inguinal canal has been examined the abdominal wall should be dissected on one side only. Reflect the external oblique abdominal muscle after making two incisions. The first incision should be longitudinal and through the aponeurotic tendon of the muscle a short distance from the fleshy margin. The second incision must be transverse and through the fleshy part of the muscle about midway between the thigh and the last rib. Now turn the aponeu- rosis as far towards the middle line as possible. Note that, forming the medial boundary of the superficial opening of the inguinal canal, there is a stout band connected with the origin of the pectineus muscle. This is formed by a blending of the aponeuroses of the two oblique and the transverse abdominal muscles. Immediately cranial to this the external oblique aponeurosis can be reflected to the middle line (linea alba), but as the xiphoid region is approached the reflection becomes less and less complete owing to a fusion with the internal oblique aponeurosis. MM. OBLIQUUS INTERNUS ABDOMINIS.—Many of the fibres of the internal oblique muscle of the abdomen run in a cranio-ventral direction, but towards the region of the groin they become more and more transverse. The margin of the fleshy part of the muscle forms a sinuous curve, the most caudal part of which is superficial to the rectus muscle. The muscle has a dorsal attachment to the lumbo-dorsal fascia, the inguinal ligament, and the last two ribs. Ven- trally it is continued as an aponeurosis in which two layers can be demonstrated. The superficial layer assists the aponeurosis of the external oblique muscle in the formation of the superficial sheath of the rectus muscle, and thus reaches the linea alba. The fibres of the two aponeuroses become interwoven medial to an oblique line stretching from the middle line of the body near the pubis to about the middle of the breadth of the rectus muscle at the costal margin. The deep layer of the aponeurosis is incomplete and does not exist caudal to the umbilicus. As will be seen later, it blends with the aponeurosis of the transverse muscle of the abdomen to form the deep sheath of the rectus muscle. Dissection.—Make a longitudinal incision through the superficial sheath of the rectus muscle along a line a few millimetres within the lateral edge of the muscle. The incision should be made with care as the sheath is not very thick. Turn the sheath towards the middle line, and in 12 DISSECTION OF THE DOG doing so observe its firm attachment to the tendinous intersections of the underlying straight muscle. Cut across the fleshy part of the internal oblique muscle in the same manner as was done with the external oblique. Reflect the transverse muscle of the ribs. M. RECTUS ABDOMINIS.—The fibres of the straight muscle of the abdomen run parallel to the middle line of the body. Generally six tendinous inter- sections cross the muscle in an irregularly oblique manner. Of these one occurs on a level with the umbilicus; two are caudal, and three are cranial to this point. As has already been seen, the superficial sheath of the muscle is firmly adherent to the intersections. The cranial attachments of the rectus muscle are by means of a thin aponeu- rotic tendon (partly covered by the expanded insertion of the m. transversus costarum) from the cartilage of the first rib, and from the sternal end of the cartilages of the ribs from the second to the seventh. In addition fleshy slips leave the sternal ends of the eighth and ninth ribs. Caudally the muscle is attached to the border of the pubis. Dissection —Reflect the straight muscle by a transverse incision about the middle of its length, and thus expose the cranial and caudal epigastric vessels as well as certain intercostal and lumbar nerves and vessels. A, EPIGASTRICA CAUDALIS.—The caudal epigastric artery either arises in- dependently from the deep femoral artery, or it has an origin in common with the external pudendal. The artery lies on the deep face of the rectus muscle of the abdomen and runs in a cranial direction. It is accompanied by the caudal epigastric vein (v. epigastrica caudalis). A. ET V. EPIGASTRICA CRANIALIS.—The cranial epigastric vessels appear between the xiphoid process of the sternum and the ninth or tenth costal cartilages ; that is, not far from the middle line. They follow a slightly oblique direction on the deep surface of the rectus muscle. Superficial branches, piercing the muscle or crossing its medial border in the xiphoid region, have already been noticed. NeRvEs of THE ABDOMINAL WaLL.—Lying deep to the internal oblique and rectus muscles on the one hand, and superficial to the transverse muscle on the other, are branches of the last five thoracic and the first two lumbar nerves. The last four intercostal nerves are derived from the ventral primary divisions of the ninth, tenth, eleventh, and twelfth thoracic nerves. They appear from beneath the costal arch, cross the surface of the transverse muscle, and disappear under the rectus. The last thoracic nerve is similarly disposed. The ¢lio-hypogastric and ilio-inguinal nerves arise from the ventral primary divisions of the first two lumbar nerves. N. tlio-hypogastricus.—The ilio-hypogastric nerve divides into lateral and DISSECTION OF THE DOG 13 medial branches ; the former piercing the two oblique muscles to pass ventral- wards on the surface of the external oblique about midway between the last rib and the ilium. The medial branch is disposed between the internal oblique and the transverse muscles in the same manner as are the thoracic nerves. N. ilio-inguinalis—The ilio-inguinal nerve has a distribution very similar to that of the ilio-hypogastric. M. TRANSVERSUS ABDOMINIS.—As the name suggests, the fibres of the transverse muscle of the abdomen run, for the most part, in a direction at right angles to the long axis of the body. Towards the inguinal region, however, the fibres assume a caudo-ventral obliquity. The margin of the fleshy part of the muscle is mainly continued towards the middle line dorsal to the rectus muscle, but about midway between the umbilicus and the pubis the margin of the transverse overlaps the ventral surface of the straight muscle. The fibres of the transverse muscle arise from the extremities of the transverse processes of the lumbar vertebre, and from the medial surface of the last four or five ribs and their cartilages. The aponeurotic tendon which succeeds the fleshy part of the muscle, and by which it finds attachment to the linea alba, is blended with the deep layer of. the internal oblique aponeurosis cranial to the umbilicus. Thus it shares in the formation of the deep sheath of the rectus muscle. Caudal to the umbilicus the aponeurosis becomes thin, and, about midway between the umbilicus and the pubis, suddenly changes from the dorsal to the ventral side of the rectus. VAGINA M. RECTI ABDOMINIS.—The constitution of the sheath of the straight muscle can now be fully determined. The superficial or ventral layer of the sheath is mainly formed by the aponeuroses of the external and internal oblique muscles; but, in the inguinal region, to these is added the aponeurosis of the transverse muscle. The superficial layer, therefore, is complete and of considerable stoutness. The deep or dorsal layer of the sheath, on the contrary, is incomplete. Where the straight muscle lies over the costal cartilages no sheath interposes. From the region of the xiphoid process to a variable distance from the umbilicus the sheath is formed by the aponeurosis of the transverse muscle and the deeper layer of the aponeurosis of the internal oblique muscle. Caudal to this the transverse aponeurosis alone forms the sheath to a point about midway between the umbilicus and the pubis where, the aponeurosis passing ventral to the rectus, the deep sheath becomes deficient. Where the sheaths of the two recti muscles meet in the middle line a strong cord is formed. This is known as the linea alba, and stretches from the xiphoid process of the sternum to the symphysis pubis. Composed of interlacing and decussating fibres derived from the aponeuroses of the oblique and transverse muscles, it is broadest in the xiphoid region, gradually narrowing towards the pubis. At a point on the linea alba, generally about two-thirds of the distance from the pubis to the xiphoid, is a scar, the umbilicus, marking the point of attachment of the umbilical cord of embryonic life. 14 DISSECTION OF THE DOG CANALIS INGUINALIS.—The inguinal canal is a passage through the ab- dominal wall in which lies the spermatic cord of the male or the round ligament of the female. In the male, moreover, the testis descends into the scrotum by way of the canal. The canal is lined by a tubular connection between the peritoneum of the abdomen and the tunica vaginalis of the scrotum. In direction it is oblique ; its superficial extremity (annulus inguinalis subcutaneus) being caudal and medial to its deep extremity (annulus inguinalis abdominalis). The canal should be examined on that side of the abdomen where the muscles are yet intact. Introduce a probe or glass rod into the canal, and clean, in the first place, the subcutaneous ring. This is, speaking generally, an oval opening in the aponeurotic tendon of the external oblique muscle of the abdomen. The lateral boundary of the ring is formed by the stout part of the aponeurosis connected with the origin of the pectineus muscle. The medial boundary is formed by the combined aponeuroses of the external and internal oblique and the transverse muscles. The canal itself has a length of some 30 mm. and crosses the lateral border of the rectus muscle obliquely. Near the subcutaneous ring, it runs along the grooved surface of the inguinal ligament (Poupart’s ligament). The canal may be considered as possessing a ventral and a dorsal wall. The ventral wall throughout the whole of its extent is formed by the aponeurosis of the external oblique, and, throughout the greater part of its extent, by the fleshy part of the internal oblique muscle also. Close to the abdominal ring, some fibres of the transverse muscle may assist in the formation of this wall, but more com- monly the abdominal ring occurs solely in the fascia of the transverse muscle. The dorsal wall, close to the subcutaneous ring, is formed for a very short distance by the combined oblique and transverse aponeuroses. For the greater part the wall is constituted by the fascia of the transverse muscle covered internally by the peritoneum. In the female, the inguinal canal contains a funnel-shaped cavity continuous with that of the peritoneum. Outside its serous lining there is a considerable accumulation of fat. In intimate association with the inguinal canal are the external pudendal and caudal epigastric vessels. The external pudendal artery and vein cross the medial aspect of the spermatic cord at the subcutaneous ring. The caudal epigastric vessels also cross the medial side of the canal, but they do so obliquely and at a variable point in its length. Running for a distance parallel to the inguinal canal, and in its dorsal wall, is the external spermatic nerve. Dissection.—Open the abdominal cavity by making an incision along the whole length of the linea alba, and a transverse incision on each side through the transverse muscle and the peritoneum. This having been done, a fold of peritoneum will be discovered passing along the linea alba to the urinary bladder. In this fold there is frequently a considerable accumulation of fat. DISSECTION OF THE DOG 15 CAavVUM ABDOMINIS.—The bony boundaries of the abdominal cavity are incomplete. Dorsally, the lumbar and sacral vertebre with their transverse processes are covered by the thick muscles of the back. At the cranial end of the cavity some of the ribs and their cartilages form a girdle round the abdomen, while the pelvic bones serve the same purpose at the caudal end. Otherwise the lateral and ventral walls are formed by soft structures only. The ventral wall, much longer than the dorsal, slopes downwards from the pubes to the xiphoid process of the sternum, the steepness of the slope differing in different breeds. For descriptive purposes it is necessary to divide the general abdominal cavity into the pelvic cavity and the abdomen proper. The plane of separation is on a level with the promontory of the sacrum, the ilio-pectineal lines and the cranial border of pubes. It is, therefore, oblique to the long axis of the abdomen proper, inasmuch as it slopes caudalwards from the sacrum to the pubis. Though of questionable utility, the abdomen proper may be subdivided into nine regions by four imaginary planes—two transverse to the long axis of the body and two parallel to the median plane. One of the transverse planes cuts the abdomen on a level with the most caudal part of the twelfth rib. Thesecond transverse plane is parallel to the first and is taken on a level with the lateral angle of the ilium. Thus the abdomen is divided into three transverse zones which may be named subcostal, umbilical, and hypogastric. The two longitudinal planes of subdivision are parallel to the median plane of the body and are imagined as occurring on a level with the mid-point of the distance between the lateral angle of the ilium and the symphysis pubis. The longitudinal planes subdivide each transverse zone into three regions as follows : Subcostal zone. Epigastric region. {rp hypochondriac region. Left hypochondriac region. ee lumbar region. Umbilical region. Umbilical zone. ( Left lumbar region. ee iliac region. Hypogastric zone. Hypogastric region. ( Left iliac ‘region. ‘ CoNTENTS OF THE ABDOMEN PropeR.—The organs lodged within the abdomen are numerous and serve widely different physiological purposes. They may be tabulated as follows : Stomach. ; {sma intestine. (1) Alimentary organs. Large intestine. ‘| Liver. oe 16 DISSECTION OF THE DOG Fie. 3.—To show the position of the abdominal viscera in relation to the exterior. p.x., xiphoid process of sternum ; a.c., costal arch; y.f., gall-bladder; p., pylorus; h., liver; r.d., right kidney; c.t., transverse colon; 1, spleen; u., umbilicus; d., duodenum; o.d., right ovary; ic., cecum; 1.s., left kidney; o8., left ovary; c.d., descending colon; v.u., urinary bladder; u.t., uterus; p.r., prostate ; o.p., pubic bones. (This figure is reproduced by permission of Messrs. Bailliére, Tindall & Coz.) DISSECTION OF THE DOG —- ss (4S : BELA L5 LL Fic. 4.—To show the extent of the fleshy part of the abdominal muscles. p.x., xiphoid process of sternum a.c., costal arch; m.r.a., straight muscle of abdomen; mn.t.a., transverse muscle; m.o.e.a., external oblique muscle ; u., umbilicus; m.o.i.a., internal oblique muscle ; 0.p., pubic bones. (This figure is reproduced by permission of Messrs, Bailliére, Tindall & Coz.) 17 18 DISSECTION OF THE DOG ( Kidneys. Ureters. (2) Urinary organs. ( Bladder, oa duct and prostate in the ; male. iS) Bepredistive sreauk (crane uterine tube of Fallopius and uterus in the female. ( Spleen. (4) Ductless glands. { Adrenal glands. The abdominal aorta and its various (5) Arteries. ‘branches. The caudal vena cava and its tri- ( butaries. The portal vein and its ( tributaries. The commencement of the vena azygos. (6) Veins. (7) Lymph-glands and lymphatic vessels including the cisterna chyli and the commencement of the thoracic duct. (8) The abdominal part of the sympathetic nervous system. (9) The peritoneal lining of the cavity and investment of the organs contained therein. It is of the utmost importance to the surgeon that he should be familiar with the positions of the main abdominal organs in relation to each other and to the surface of the body. In the accompanying figures (figs. 3 and 4), the disposition of the muscles forming the wall of the abdomen, and the position of the underlying viscera, are indicated. Both diagrams are divided into equal squares in order that a ready comparison may be made. On first opening the abdomen only a few of the contained organs are brought to view. On turning aside the walls of the abdomen, indeed, little can be discovered but a double fat-laden membrane, the greater omentum (omentum majus), composed of four layers of peritoneum and containing, as will be explained later, a part of the peritoneal cavity called the omental bursa (bursa omentalis). On raising the omentum from the underlying coils of small intestine its connection with the greater curvature of the stomach, and its continuity with a peritoneal duplicature passing from the stomach to the spleen (ligamentum gastro-lienale), will be revealed. Projecting from under cover of the costal arch, the sharp ventral border of the liver will be visible. This border, it will be noticed, is deeply cut by fissures, in association with one of which the broad end of the gall-bladder can generally be seen. The ventral extremity of the spleen lies immediately caudal to the liver DISSECTION OF THE DOG 19 on the left side of the abdomen. Not infrequently the visible part of the spleen is more caudal in position and extends farther than usual towards the middle line. This depends partly upon the size of the spleen, but largely upon the amount of distension of the stomach. If the stomach is empty, possibly no part of it will be visible ; but when distended a considerable extent of the sac may protrude beyond the border of the liver. On turning the omentum over the ribs as far as possible, other organs will be exposed. Coils of small intestine occupy the greater part of the field of view ; but close to the pubis the urinary bladder may form a conspicuous object if it happens to contain much urine. Sometimes part of the descending colon can be detected ; and, if the subject be a female, part of the uterus may also be exposed. It will be observed that the interior of the abdominal wall, as well as the surface of the organs contained therein, issmooth and shiny. This is due to the presence of a serous membrane, the peritoneum, of which the greater omentum is a part. INTESTINUM TENUE.—The small intestine is a long, smooth tube, measuring about five times the length of the body ; and extending from the pylorus, in the epigastric region—where it is continuous with the stomach—to a point slightly caudal to the umbilicus and a short distance to the right of the median plane, where it ends by joining the cecum. The small intestine is divided into: (1) The duodenum ; (2) the jejunum (intestinum jejunum), and (3) the dlewm (intestinum ileum). The coils of the jejunum and ileum are freely movable, since they are suspended from the dorsal wall of the abdomen by a fold of peritoneum, known as the mesentery (mesenterium), by way of which the blood- vessels, 'nerves, and lymphatics gain access to the intestine. The duodenum is not so mobile, as will be seen at a later stage of the dissection. To expose this part of the alimentary tube, it may be necessary to turn the rest of the small intestine to the left. This having been done, a portion of the duodenum will be found running along the right side of the abdomen. A second part passes in the opposite direction and ends at an abrupt ventral flexure not far from the pylorus. A closer examination of the duodenum is better left until later. In association with the duodenum one of the two limbs of the pancreas will be observed. The terminal part of the ileum can generally be easily recognised as it travels cranialwards from somewhere near the pelvic inlet to its point of termination in the cecum. INTESTINUM cRASSUM.—lIn calibre the large intestine of the dog does not differ from the small intestine so much as it does in the other domesticated mammals. In length it falls very far short of the small intestine, measuring only about one-sixth of the length of the whole intestinal tube. For descriptive purposes, the large intestine is divided into the cecum, the colon, and the rectum os Gs 20 DISSECTION OF THE DOG INTESTINUM CaCUM.—The cecum is a short spiral or bent tube, the free blind end of which points towards the pelvis. There is considerable variation 1 - . - U m. longissimus dorst ! \ U m. ilio-costalis ; , Diaphragma * ' 1 ! Aorta 1 as m, latissimus dorsi. Vena cava caudalis mm. intercostales ' ' ' I 4 ' 1 ‘ 1 i y \ \ \ \ \ \ \ \ \ \ \ \ m. obliquus ' abdominis externus ; ct m. rectus abdominis Fic. 5.—Transverse section of the abdomen on a level with the eleventh thoracic vertebra. 7, 8, 9, 10, 11 = seventh, eighth, ninth, tenth, and eleventh ribs. in the length of this part of the intestine, and also in its form. It lies to the right of the median plane in the umbilical region. Coton.—The colon is divided into three parts: (1) The ascending colon (colon ascendens) leaves the caecum and runs cranialwards to the right of the median plane for a short distance and then turns to the left, thus forming the DISSECTION OF THE DOG 21 right colic flexure (flexura coli dextra) ; (2) the second part of the colon, the transverse colon (colon transversum), like the first, is generally very short. It crosses the median plane immediately cranial to the root of the mesentery, and, arriving on the left side of the abdomen, curves in a caudal direction at the left colic flexure (flexura coli sinistra) ; (3) the descending colon (colon descendens) Vena cava caudalis ' f ! Lymphoglandula ul m. longissimus dorsi \ s. m. wio-costalis. N m. obliquus abdominis internus m. obliquus abdominis externus- m. transversus abdominis - \ longus m. tibialis anterior--—-------------+-- = Fic. 30.—Dissection of inside of the thigh after removal of the gracilis muscle, and semimembranosus muscles. The artery lies in a passage or canal which is triangular in section. The medial wall of the canal is formed by the sartorius muscle; the cranio-lateral boundary is the medial vastus muscle, and the caudo-lateral wall is formed by the pectineus and adductor muscles. DISSECTION OF THE DOG 79 Small muscular branches arise from this part of the femoral artery, as do also the saphenous and articular arteries. V. FEMORALIS.—The femoral vein lies along the medial and aboral side of the femoral artery, and receives tributaries which are the satellites of the branches of the artery. N. sapHenvs.—The whole course of the saphenous nerve in the thigh is now exposed. A branch of the femoral nerve, it runs along the oral side of the femoral artery in the first part of its course, crossing the artery medially on a level with the border of the semimembranosus muscle, about which point it contributes a twig to accompany the articular branch of the femoral artery. A. GENU SUPREMA.—The articular branch of the femoral artery leaves the parent vessel as this disappears under the semimembranosus. It travels in a groove formed by the semimembranosus and medial vastus muscles, accompanied by a vein and a small branch of the saphenous nerve. Certain muscles are now exposed. These, enumerating them in order and beginning with the most oral, are: Medial vastus, pectineus, adductor, semimembranosus, and semitendinosus. M. vasTUS MEDIALIS.—The medial vastus is one of a group of three powerful muscles clothing the oral surface of the femur. Its origin, which cannot be properly examined until the adductor muscle has been reflected, is from the femur close to the head and from the proximal third of the medial lip of the linea aspera. The insertion is into the patella in common with the other muscles of the same group. M. pectinrus.—The pectineus muscle is rather narrow and rounded, and lies immediately aboral to the medial vastus. Its origin is blended with the attachment of the abdominal muscles, and extends from the ilio-pectineal eminence to the symphysis of the pubis. The insertion of the muscle is by means of a thin tendon to the distal part of the medial lip of the linea aspera, and along with the semimembranosus to the medial epicondyle of the femur. M. appuctTor FEMoRIS.—The adductor of the femur is a powerful muscle placed aboral to the pectineus. Its more distal part is covered by the semi- membranosus. The origin of the muscle is from the ventral surface of the pubis and ischium. It has a fleshy attachment to the whole of the linea aspera and a little of the popliteal space of the femur ; and a tendinous attachment, partly fused with the tendon of the pectineus, to the medial lip of the linea aspera. a5 5, ' M. semimEmMBranosus.—The semimembranosus muscle is long and thick, and partly hidden by the adductor. Two parallel parts can be readily separated towards the insertion of the muscle. -_ Their common origin is from the medial part of the sciatic tuber. ‘lhe oral portion is inserted into the medial epicondyle of the femur and the sesamoid bone in that neighbourhood. The aboral part is inserted into the articular margin of the tibia. 80 DISSECTION OF THE DOG M. SEMITENDINOSUS.—This is a long and fleshy muscle lying aboral and lateral to the semimembranosus, with an origin from the lateral part of the sciatic tuber; its insertion is by a strong tendon to the medial surface of the tibia and the anterior tibial crest in line with the insertion of the gracilis. Dissection.—Cut across the semimembranosus muscle about its middle, and reflect towards its origin and insertion. In turning upwards the proximal part look for the nerve to the muscle, as well as for that for the semitendinosus. The distal part of the femoral artery will be exposed as it lies in a triangular channel formed by the vastus medialis, adductor, and semi- membranosus muscles. In the depths of the groove formed by the semitendinosus, adductor, and biceps muscles the sciatic nerve will be found. This divides unequally into the tibial and common peroneal nerves. Now reflect the adductor and pectineus muscles by cutting them across not far from their origins. Thus will be revealed the branches of the obturator nerves supplying the adductor and pectineus, the deep femoral artery, the insertion of the ilio-psoas muscle, and the external obturator and quadratus femoris muscles. A. PROFUNDA FEMORIS.— —~-=— mM. vastus lateralis n. tschiadicus ~_ --- A+ ~~~ - m, adductor —- Mm, semimembranosus Phe a vast tas Sagi, a. femoralis n. tibialis ‘ m. semitendinosus -—~ a. femoris posterion, ~~ YY enn a - -—--——- mM. popliteus n. cutaneus sure medialis ~ —---————— - a, tibidlis anterior m. gastrocnemius caput mediale ~——F—--- RE n. peroneus profundus m, flexor digitorum ~—-~—-—m, tibialis anterior profundus = —~-~~-~-~___- m. extensor digitorum longus 2 ane m., extensor digilt quintt __ 1. peroneus superficialis Fic. 37.—Dissection of origin of tibial and common peroneal nerves. calf muscles are covered by the hamstring muscles, the fascia is not notably strong ; but in the distal half of the region it is thick, strong and tendinous, especially over the tendo-calcaneus [Achillis] (the combined tendons of gastrocnemius and plantaris muscles). In front of the tendon there is a thick tendinous cord inserted into the calcaneus. The small saphenous vein may be again examined and its termination noted. Examine the cutaneous nerves of the region. 94 DISSECTION OF THE DOG THE CUTANEOUS NERVES OF THE BACK OF THE LEG are derived from the saphenous, peroneal, and tibial nerves. The saphenous nerve supplies the medial aspect of the leg and pes. The lateral cutaneous of the calf (n. cutaneus sure lateralis) has been previously noted as arising either from the sciatic or from the peroneal nerve. It becomes superficial at the border of the biceps and supplies the skin of the posterior and lateral parts of the leg. N. CUTANEUS SURH MEDIALIS.—The medial cutaneous nerve of the calf is a branch of the tibial nerve, and arises a little distance before this nerve sinks between the two heads of the gastrocnemius muscle. Crossing the surface of the gastrocnemius slightly obliquely, along with a branch from the posterior femoral artery and the small saphenous vein, the nerve divides into two branches about the middle of the leg. These immediately pierce the deep fascia and become superficial. The posterior (plantar) branch runs along the lateral side of the tendo-calcaneus [Achillis] and supplies the skin about the tarsus. The anterior (dorsal) branch runs obliquely between the tendo-calcaneus and the deep flexor of the digits, is connected with the tibial nerve, and ends in the skin of the distal part of the leg, the tarsus and the metatarsus. A. sApHENA.—The origin of the saphenous artery from the femoral was noted in the dissection of the thigh. Crossing the surface of the gracilis and semitendinosus muscles subcutaneously, it arrives in the leg and immediately divides into anterior (dorsal) and posterior (plantar) branches. The anterior branch passes down the leg in association with the large saphenous vein and has been examined in connection with the dorsum of the pes. The posterior branch, much the larger, descends upon the deep flexors of the digit in a special compartment of the deep fascia which also contains the corresponding vein and the tibial nerve. A little proximal to the tarsus it supplies the lateral tarsal artery (a. tarsea lateralis) and is continued into the pes, where it will be followed subsequently. M. GastTrocnemius.—This powerful muscle arises by two heads. The lateral head takes origin from the lateral sesamoid and from the lateral border of the planum popliteum of the femur. The medial head arises from the medial sesamoid and the medial border of the planum poplitaum. The two heads soon join, and the common muscle thus formed gives place to a strong tendon about the middle of the leg. The insertion is into the tuber of the calcaneus. Dissection.—Cut across the gastrocnemius muscle just where its two heads are about to join. The process of reflecting the lateral head is made a little difficult by its close connection with the underlying plantaris muscle. M. priantaris.—The plantaris muscle arises in common with the lateral head of the gastrocnemius from the lateral sesamoid bone and the lateral lip of the planum poplitzum. In the distal third of the leg the fleshy belly of the DISSECTION OF THE DOG 95 muscle is replaced by a strong tendon closely associated with that of the gastrocnemius, the two together forming the so-called tendo-calcaneus of Achilles. At first the plantaris tendon is the deeper of the two; but, by m. sartorius 1 aN ‘XN ‘ \ / \ / \ SSHemess os m. gracilis a---- m. semitendinosus beside a, saphena S 1: oD —7-—7--- Mm. gastrocnemius iv 4 f \Y ~Rye - - ------- m. popliteus VA f> . n.saphenus®’ = WW \ SY -~-~------ m. plantaris SiS ee m. flexor hallucis longus mM, flexors = =—.—.— digitorum longus m. tibialis anterior. ___ a n. tibialis _n. plantaris lateralis n. plantaris medialis Fic. 38.—Dissection of the medial aspect of the leg. 96 DISSECTION OF THE DOG gradually passing on the medial side of the gastrocnemius tendon, it ultimately comes to be the more superficial. Two slips attach the plantaris tendon to the side of the tuber calcanei, from which point there is an apparent direct continuation of the tendon into the pes. This appearance, however, depends upon a modification of the short flexor of the digits (m. flexor digitorum brevis), which will receive consideration later. N. rrpratis.—The larger of the two terminal branches of the sciatic, the tibial nerve accompanies the peroneal nerve for a little distance, and then enters the gap between the two heads of the gastrocnemius muscle. Following the border of the plantaris muscle underneath the medial head of the gastro- cnemius, the nerve comes into relation with the posterior branch of the saphenous artery; and in the distal part of the leg it becomes associated with the deep flexor of the digits which it accompanies to the tarsus. The branches of the tibial nerve are as follows: (1) Medial cutancous nerve of the calf (n. cutaneus sure medialis), which has already been examined ; (2) branches (rami musculares), large and numerous, for the supply of all the muscles behind the tibia; (3) medial plantar nerve (n. plantaris medialis) ; (4) lateral plantar nerve (n. plantaris lateralis). The medial and lateral plantar nerves form the terminal branches of the tibial, and are distributed in the sole of the pes, where they will be examined at the proper time. Dissection.—Reflect the plantaris muscle and expose the deep muscles of the leg. These are three in number. The most lateral really consists of two muscles—m. flexor hallucis longus and m. flexor digitorum longus— but will be more conveniently referred to as the deep flexor of the digits. M. FLEXOR DIGITORUM PROFUNDUS.—The deep flexor of the digits arises from the head of the fibula and the proximal half of the border of this bone, from the lateral condyle of the tibia, from the proximal part of the posterior surface of the tibia, and from the interosseous membrane. The tendon of the m. flexor hallucis longus begins about the junction of the middle and distal thirds of the leg and passes down the groove formed by the calcaneus. The much smaller tendon of the m. flexor digitorum longus is more medial and passes down the groove on the medial malleolus, in which it is bound by an annular ligament. M. TIBIALIS POSTERIOR.—The posterior tibial muscle is very rudimentary. Arising from the head of the fibula under cover of the long flexor of the digits, its feeble tendon, following that of the long flexor, finally blends with the medial collateral ligament of the tarsus. M. popiitevs.—The popliteal muscle covers part of the flexor aspect of the articulation between the femur and tibia. Its origin is within the capsule of the joint from the lateral condyle of the femur (sesamoid). The fibres of the muscle spread out to find attachment to a triangular surface on the proximal posterior part of the tibia. DISSECTION OF THE DOG 97 A. POPLITEA.—The popliteal artery continues the femoral between the two heads of the gastrocnemius muscle, and insinuates itself between the popliteal muscle and the joint-capsule of the articulation between the femur and tibia. In order to follow the artery to its termination it is necessary to reflect the popliteal and long flexor muscles. This having been done, it will be found that the popliteal ends by dividing into the anterior and posterior tibial arteries. The latter is so small that, to all intents and purposes, the anterior tibial is the direct continuation of the parent vessel. A. TIBIALIS ANTERIOR.—The anterior tibial artery soon pierces the liga- mentous membrane between the tibia and fibula and thus gains the anterior tibial region, where its further course has been previously noted. THE SOLE OF THE PES.—Before any dissection is performed, five areas of modified skin should be noted. These are in the form of distinct, callous, hairless projections; one of them, the largest, lies in the hollow of the digits. Its form is that of a heart with the apex distal. The four smaller callosities lie over the joints between the second and third phalanges of the second, third, fourth, and fifth digits. The skin over the sole should now be removed and the structure and con- nections of the callosities determined. Each callosity consists of a fibro-fatty basis with which thick, horny, papillated skin is intimately connected. The callosities are joined to the sheaths of the flexor tendons by strong ligamentous bands. This is more particularly noticeable in connection with the large callosity, which also receives a bifurcating band from the tendon of the deep flexor muscle. MuscLES AND TENDONS OF THE SOLE.—The muscles and tendons of this part of the pes are arranged in the following layers : lst Layer.—M. flexor digitorum brevis, m. abductor digiti quinti. 2nd Layer.—Tendon of the m. flexor digitorum profundus, mm. lumbricales, m. quadratus plante. 3rd Layer —M. adductor digiti quinti, m. adductor digiti secundi, mm. interossel. 4th Layer —Tendon of m. peronzus longus. In the dissection of the most superficial layer an examination must be made of the sheaths of the flexor tendons. The sheaths assist the bones of the digits in the formation of osseo-membranous tubes in which the flexor tendons are contained. The dorsal wall of the tube is formed by the metatarsal sesa- moids and the phalanges; while the plantar portion of the tube is formed by the flexor sheaths which are attached to the margins of the above bones. The sheaths are not of uniform strength throughout. On a level with the sesamoid bones, and opposite the distal end of the first phalanx, a considerable accession H 98 DISSECTION OF THE DOG of transverse fibres contributes great strength to the sheaths. In cleaning the fascia from the surface of the short flexor of the digit, the medial plantar n, tibialis-----.4 m. tibialis posterior - - ~ - ~ 77m, abductor digitt quinti ""==-~~~ m, flexor digitorum brevis ae ee a ee — mm, accessorit mm, interossei -= - Slip from tendon of --m, flexor digitorum profundus to callosity Vie. 39.—Superficial dissection of the sole. nerve which runs along the medial border of the muscle must not be injured. M. FLEXOR DIGI- TORUM BREVIS.—This was mentioned in the dissection of the leg as forming the direct con- tinuation of the plan- taris muscle into the sole. Almost the whole of the muscular tissue of the short flexor has been replaced by ten- don. Continuous with the plantaris tendon at the tuber calcanei, the flattened tendinous band runs down the plantar aspect of the tarsus to the proximal part of the metatarsus, where it divides into two branches, each branch again dividing about the middle of the metatarsus. The initial part of the muscle is intimately connected with the fascia in the region of the tarsus. The four terminal ten- dons enter the flexor sheaths, divide into two slips which form a ring through which the deep flexor tendon passes, and end by becoming DISSECTION OF THE DOG 99 oe to the proximal part of the second phalanges of the second to fifth igits. M. ABDUCTOR DicITI QuINTI.—The abductor of the fifth digit is very rudi- mentary and somewhat variable. Two parts can be distinguished : (1) In the form of a tendinous band passing from the proximal part of the calcaneus to the base of the fifth metatarsal bone; (2) either with the same origin as the first part, or as an offshoot therefrom, as a feeble fleshy belly continued by a thin tendon to the first phalanx of the fifth digit. Dissection.—Cut across the short flexor close to its commencement ; cut its connections with the fascia and turn it downwards as far as possible. In performing this dissection care must be taken to preserve the two plantar nerves—terminal branches of the tibial nerve—and the plantar branch of the saphenous artery. M. FLEXOR DIGITORUM PROFUNDUS.—The strong tendon of the m. flexor hallucis longus runs along the groove on the calcaneus where it is bound down by a strong annular ligament, and is joined by the much smaller tendon of the m. flexor digitorum longus which has traversed a groove on the medial malleolus. The powerful deep flexor tendon so formed divides into four parts, one for each of the digits (second to fifth). Each tendon enters a flexor sheath, pierces the ring formed by a tendon of the short flexor, and is finally inserted into the terminal phalanx. MM. LumBricaLE3.—Three rather feeble lumbrical muscles arise from the plantar surface of the deep flexor tendon. Their thin tendons are traceable to the proximal end of the first phalanx of the third, fourth, and fifth digits. Occasionally small tendinous slips may join one or more of the tendons of the short flexor of the digits. M. QUADRATUS PLANT#.—The quadratus muscle is very small and thin, and arises from the distal extremity of the calcaneus and the lateral collateral ligament of the tarsus. Its fibres join the deep flexor tendon. N. trpratis.—The tibial nerve follows the tendon of the m. flexor hallucis longus to a level with the joint between the tibia and the talus, where it divides into the medial and lateral plantar nerves. The medial plantar nerve (n. plantaris medialis) is the smaller, and runs along the medial border of the m. flexor brevis to the middle of the metatarsus, where it ends in two branches. The more medial of the two is continued onwards as the n. digiti plantaris communis I. The more lateral branch crosses the plantar aspect of the short flexor muscle and divides into nn. meta- tarsei plantares II, IIZ, et IV, which join the common plantar digital nerves. The lateral plantar nerve (n. plantaris lateralis) is much larger. Placed between the superficial and deep flexor tendons, it disappears from view between the origins of the most lateral interosseous muscle and the adductor of the fifth H2 100 DISSECTION OF THE DOG n, tibtalis -~-~ n. plantaris : |-—_—_-—--- n. plantaris lateralis medialis ~~ n. digitalis --—— plantaris communis I nn. digitales plantares nn, metatarset Iil,alv plantares IT, === 4==ER- III, et IV Fic. 40.—Diagram of the plantar nerves of the pes. communes IT, digit. It cannot be followed satisfactorily until the deep muscles have been examined. Dissection Reflect the deep flexor tendon. M. ADDUCTOR DIGITI QUINTI.— The adductor of the fifth digit arises by a flattened tendon from the plantar surface of the tarsus. Crossing the sole somewhat obliquely, it dips in between the interosseous muscles of the fourth and fifth digits, and is inserted into the fifth metatarsal bone and the first phalanx of the fifth digit. M. ADDUCTOR DIGITI SECUNDI. —A smaller muscle than the pre- ceding, its origin is between that of the adductor of the fifth digit and the interosseous muscle of the second digit. Running distal- wards between the interosseous muscles of the second and the third digits, it is inserted into the first phalanx of the second digit. Mm. InTEROsSEI.—The inter- osseous muscles are four in number. Each takes origin from the tarsus and the proximal end of the metatarsal bones and divides into medial and lateral parts to be attached to the sesamoid bones. Dissection.—Reflect the ad- ductor muscles of the fifth and second digits and the interosseous muscle of the second digit. Follow the plantar ramus of the saphe- nous artery in the ligamen- tous tissue on the flexor aspect of the tarsus, and DISSECTION OF THE DOG 101 then between the in- terosseous muscle of the second digit and the adductor digiti quinti, until it joins the a. dorsalis pedis in the formation of the plantar arch. A. TARSEA MEDIALIS.— The plantar ramus of the saphenous artery is con- tinued, as the medial tarsal artery, along the medial side of the flexor aspect of the tarsus, and forms the arcus plantaris along with the dorsalis pedis artery. The medial tarsal artery then continues to the distal part of the metatarsus and di- vides into the second, third, and fourth plantar meta- tarsal arteries (aa. meta- tarsei plantares II, III, et IV), which join the com- mon plantar digital arteries. A. DORSALIS PEDIS.— The continuation of the anterior tibial artery appears deep in the sole between the second and third inter- osseous muscles and under cover of the origin of the m. adductor digiti quinti. Anastomosing with the plantar branch of the saphenous artery it forms the plantar arch (arcus plantaris), from which arise the second, third, and fourth common plantar digital ar- teries (aa. digitales plantares |} .-H----= a. saphena. Ramus plantaris é fi // sae Arcus plantaris aa, digitales plantares communes <> aa. metatarsee plantares j / J é Fic. 41.—Diagram of the plantar arteries of the pes. H 3 102 DISSECTION OF THE DOG communes II, III, et IV), which run between the second and third, third and fourth, and fourth and fifth metatarsal bones. N. PLANTARIS LATERALIS.—This, the larger of the two terminal branches of the tibial nerve, has been followed to its disappearance under the m. adductor digiti quinti. It will now be seen to end in several branches about the proximal third of the metatarsus. Some of these branches are distributed to the small muscles of the sole; three of them, the second, third, and fourth common plantar digital nerves (nn. digitales plantares communes II, TIT, et IV), follow the corresponding arteries of the same name. M. PERONZUS Lonaus.—The tendon of the long peroneal muscle has been followed as far as the lateral aspect of the tarsus. It can now be examined as it lies in the groove in the cuboid bone and crosses the plantar aspect of the tarsus to its insertion into the rudimentary first metatarsal bone (or, in its absence, into the second bone). The tendon is enclosed in a strong fibrous sheath which must be opened. ARTICULATIO GENU.—This joint is formed by the condyles and patellar sur- face of the femur, the patella, and the articular surface at the proximal end of the tibia. Although the adaption of the bony surfaces is indifferent, the joint, in virtue of the character and number of the ligaments in association therewith, is strongly constituted. Dissection.—Clear away the remains of the muscles about the joint, but leave the tendons of origin of the popliteus muscle and the long extensor of the digits. Clean the surface of the joint-capsule and define the collateral ligaments. Capsula articularis—In describing the joint-capsule, it is convenient to consider it as divided into two parts: (1) The anterior part is roomy and attached to the condyles and about the margin of the patellar surface of the femur and along the articular edge of the tibia. The patella may be regarded as a bony island in this part of the capsule. On each side of the patella the capsule is thickened; the thickenings being connected with cartilaginous extensions of the bone. (2) The posterior portion of the capsule is much less roomy, and is attached about the articular margins of the femur and tibia. Both parts of the joint-capsule are adherent to the edges of the menisci between the femur and tibia, and are continuous with the collateral ligaments of the joint. It will be observed that the origins of the popliteus muscle and long extensor of the digits are within the capsule. Ligamentum patelle.—The patellar ligament is a, strong flattened band extending from the patella to the tuberosity of the tibia. A pad of fat is interposed between the ligament and the joint-capsule, and a small synovial DISSECTION OF THE DOG 103 bursa intervenes between the ligament and the smooth proximal part of the tibial tuberosity. The patellar ligament is, strictly speaking, the tendon of insertion of the quadriceps muscle of the thigh, and the patella is a sesamoid bone developed therein. Ligamentum collaterale tibiale—The medial collateral ligament passes from the condyle of the femur to just beyond the condyle of the tibia. The ligament is attached to the margin of the medial meniscus. Ligamentum collaterale fibulare—The lateral collateral ligament passes from the lateral condyle of the femur to the head of the fibula. Dissection.—Open the joint by making a transverse incision through the capsule just proximal to the patella and a longitudinal incision along each side of this bone. The patella with the patellar ligament may then be turned downwards. Observe the synovial fringes in the interior of the joint, and the cartilaginous extensions of the patella. Dissect away the posterior part of the capsule and examine the crucial ligaments and the menisci of cartilage interposed between the femur and the tibia. Lngamentum cruciatum anterius.—The anterior cruciate ligament passes obliquely from the anterior intercondyloid fossa of the tibia to the medial face of the lateral condyle of the femur. Ligamentum cruciatum posterius.—Not quite so strong as the anterior, the posterior cruciate ligament runs from the popliteal notch of the tibia to the lateral surface of the medial condyle of the femur. Menisci lateralis et medialis—The poor adaption of the femoral and tibial articular surfaces is partly compensated by the presence of two crescentic, cartilaginous pads of which the lateral is somewhat the larger. The convex edge of each meniscus is thick ; whereas the concave edge is thin and directed towards the intercondyloid eminence of the tibia. The convex border of the lateral meniscus is crossed obliquely by a deep groove for the reception of the tendon of origin of the popliteus muscle. Each meniscus is attached in front by ligamentous tissue to the anterior intercondyloid fossa of the tibia, and in addition there is a transverse ligament (lig. transversum genu) running from one meniscus to the other across the tibial attachment of the anterior cruciate ligament. Behind, the medial meniscus is attached to the posterior intercondyloid fossa of the tibia. The lateral meniscus has two posterior attachments ; one to the tibia just beyond the articular margin and lateral to the popliteal notch ; the other by a strong ligament which crosses the posterior cruciate ligament obliquely to end on the medial condyle of the femur. Dissection.—Now proceed to the examination of the joints between the nd 104 DISSECTION OF THE DOG tibia and fibula. All remains of the muscles will require to be cleaned away. There are two joints between the tibia and the fibula: a proximal tibio- fibular articulation (articulatio tibio-fibularis), and a distal tibio-fibular syndes- mosis (syndesmosis tibio-fibularis). Between these joints the znterosseous membrane of the ley (membrana interossea cruris) unites the two bones. Very commonly the distal third or more of the tibia and fibula are joined together by bone. Articulatio tibio-fibularis.—The tibio-fibular articulation is surrounded by a joint-capsule (capsula articularis). Syndesmosis tibio-fibularis.—The tibio-fibular syndesmosis is very strong and provided with an anterior and a posterior ligament (lig. malleoli lateralis anterius et lig. malleoli lateralis posterius) which bind the malleolus of the fibula to the distal end of the tibia. Dissection.—Remove all tendons, annular ligaments, and muscles from the tarsus, metatarsus, and digits. Articulatio talo-cruralis.—The talo-crural or ankle-joint, formed by the two bones of the leg and the talus, is a strong articulation provided with conspicuous ligaments. The jovnt-capsule (capsula articularis) is attached to the articular margins of the tibia, fibula, and talus. On the medial side of the joint the deltoid ligament (ligamentum deltoideum) arises from the medial malleolus, and, by diverging bundles, passes to the scaphoid, talus, and sustentaculum tali of the calcaneus. Laterally there are three ligaments running from the end of the fibula to the talus and calcaneus. The posterior talo-fibular Ligament (ligamentum talo-fibulare posterius), the most proximal of the three, joins the lateral aspect of the trochlea of the talus. The calcaneo- fibular ligament (ligamentum calcaneo-fibulare) is the strongest and best defined member of the group, and finds attachment to the lateral surface of the calcaneus. The anterior talo-fibular ligament (ligamentum talo-fibulare anterius) is very rudimentary and attached to the neck of the talus. Ligaments connected with the talus —A number of ligaments, some of them feeble, hold the talus in position. The posterior talocalcanean ligament (liga- mentum talo-calcaneum posterius) is rudimentary and is placed at the most proximal point of contact of the talus and calcaneus. A very poorly repre- sented lateral talo-calcanean ligament (ligamentum talo-calcaneum laterale) unites the lateral surfaces of the two bones. The medial talo-calcanean ligament (ligamentum talo-calcaneum mediale) is much stronger than the preceding, and is partly covered by the deltoid ligament. It runs from the tubercle on the medial surface of the talus to the sustentaculum tali. A dorsal tarsal ligament DISSECTION OF THE DOG 105 (ligamentum tarsi dorsale) joins the neck of the talus to the cuboid and third metatarsal bones. A small anterior talo-calcancan ligament (ligamentum talo-caleaneum anterius) will be found in the depths of the groove between the two bones with which it is associated. Dissection —Remove the talus. This is rendered difficult from the presence of a strong interosseous ligament. Ligamentum talo-calcaneum interosseum.—The talo-calcanean interosscous ligament passes between the two bones, and is attached to the grooves between their articular facets. Ligaments connected with the calcaneus.—Removal of the talus exposes both surfaces of the strong plantar calcanco-navicular ligament (ligamentum calcaneo- naviculare plantare), which passes from the sustentaculum tali to the navicular bone. Part of the cavity in which the head of the talus rests is formed by this ligament. The long plantar ligament (ligamentum plantare longum) is powerful and runs from the plantar surface of the calcaneus to the tubercle on the cuboid and on to the tubercle at the proximal end of the fifth metatarsal bone. Partly under cover of, and much shorter than, the preceding is the plantar calcaneo- cuboid liyament (ligamentum calcaneo-cuboideum plantare), which joins the calcaneus to the cuboid only. On the dorsal and lateral part of the joint between the calcaneus and cuboid is a short dorsal calcaneo-cuboid ligament (ligamentum calcaneo-cuboideum dorsale), which may be regarded as a thickening of the capsule of the joint. Ligaments connected with the navicular.—A short. dorsal cuboideo-navicular ligament (ligamentum cuboideo-naviculare dorsale) joins the cuboid and navicular on the dorsal aspect of the joint between the two bones. The navicular and lateral cuneiform bones are united by a small dorsal navicular- cuneiform ligament (ligamentum naviculari-cuneiforme dorsale), and a much stronger plantar ligament (ligamentum naviculari-cuneiforme plantare) joins the navicular and the medial cuneiform bones. The latter is continued to the first and second metatarsal bones. Dissection.—Remove the calcaneus and the plantar calcaneo-navicular and plantar navicular-cuneiform ligaments. The dissection exposes a short plantar cuboideo-navicular ligament (ligamentum cuboideo-naviculare plantare) uniting the plantar aspects of the navicular and cuboid bones. Articulationes tarso-metatarsee.—The metatarsal bones articulate with the cuboid and the three cuneiform bones, with which they are connected by dorsal, plantar, and interosseous ligaments. The dorsal ligaments are flattened bands of no great strength. The interosseous ligaments should be examined along with the interosseous tarsal ligaments. 106 DISSECTION OF THE DOG Dissection.—Separate the remaining bones of the tarsus in order to demonstrate the interosseous ligaments. Ligamenta tarsi interossea.—One of the interosseous ligaments—the talo- calcanean—has already been studied. Others will now be found joining the navicular to the cuboid, the cuboid to the lateral cuneiform, and the three cuneiform bones. Articulationes intermetatarsee.—Weak dorsal and plantar ligaments unite the bases of the metatarsal bones. The rigidity of the intermetatarsal joints depends upon strong interosseous ligaments. Articulationes metatarso-phalangee.—The metatarso-phalangeal joint is formed by four bones ; namely, the metatarsal bone, the first phalanx, and two sesamoid bones. The joint is enclosed by a capsule connected with the extensor tendons in front. On each side of the joint is a collateral ligament which joins the head of the metatarsal bone to the first phalanx and one of the sesamoid bones. The sesamoid bones are firmly united to each other by a strong interosseous ligament, and are further attached to the proximal part of the first phalanx by ligaments on each side of the joint as well as on its plantar aspect. Articulationes digitorum pedis.—The joints between the first and second, and second and third phalanges are provided with capsules and collateral ligaments. In addition, the joint between the second and third phalanges has two dorsal ligaments, which spring from the sides of the proximal end of the second phalanx and are attached to the proximal end of the third phalanx. Petvis.—The pelvis is a cavity bounded by the sacrum and the two hip bones, and differing in its contents dependent upon the sex. It is convenient to suppose that the subject being dissected is a male. The contents of the female pelvis will be considered later. The contents of the male pelvis may be tabulated as follows :— Rectum. ( Possibly a small part of the prostate. Viscera. Prostatic and membranous parts of the urethra. Deferent ducts. { Hypogastric vessels and their branches. { Middle sacral vessels. Pudendal nerve. Sacral plexus and its branches. - Obturator nerve. Sacral part of the sympathetic nervous system. Blood-vessels. Nerves. DISSECTION OF THE DOG 107 Before any dissection is effected, it is well to examine, as far as possible, the general disposition of the viscera and the arrangement of the peritoneum in the pelvis. At the inlet to the cavity the urinary bladder and part of the colon will be encountered. The urinary bladder is pear-shaped with its narrow end directed towards the pelvis. When entirely empty the bladder is small in size and firm to the touch. When distended with urine it projects for a variable distance towards the umbilicus, and is generally pushed more or less to one side by the neighbouring intestines. The peritoneal covering of the bladder is reflected from the organ in the form of three sheets. One of these (plica pubovesicalis) is ventral in position, triangular in form, extensive and thin. The other two are lateral in position (plice vesicales transverse), are also triangular, and contain the ureters. The two deferent ducts in their course from the abdominal ring of the inguinal canal lie dorsal to the neck, or narrow pelvic end, of the bladder. Each duct is contained in a fold of peritoneum, and the two ducts are united dorsal to the bladder by a triangular peritoneal fold with a free cranial base. Close to its termination each duct is crossed laterally by the ureter. The terminal part of the colon is dorsal to the bladder. The peritoneal investment is more extensive on the dorsal aspect of the bladder—where it is reflected onto the termination of the colon—than it is ventral to this organ. About the pelvic inlet the peritoneum generally covers a considerable accumulation of fat, on the removal of which the prostate is exposed. Dissection—Clean the muscles away from one hip bone. Liberate the root of the penis from the ischium. Cut along the symphysis of the ischia and pubes, and snip through the ilium immediately cranial to the acetabulum. This will isolate a piece of bone consisting of ischium, pubis, and part of the ilium. Remove this carefully. In doing so it will be necessary to cut through the origins of the levator ani, coccygeus and ischio-urethral muscles. Stumps of these should be left attached to the bone for examination at the proper time. Now clean the lateral surface of the pelvic organs, preserving the vessels and nerves and observing the arrangement of the peritoneum. M. coccyagEus.—The coccygeus muscle is the most lateral of a group contained within the pelvis. From their origin from the margin and medial aspect of the sciatic spine, the fibres of the muscle run towards the tail, diverging somewhat as they go, and are inserted into the transverse processes of the coccygeal vertebre from the second to the fifth. InrestInuM RECTUM.—The last part of the large intestine is a short and approximately straight tube continuing the colon through the pelvis and terminating at the anus. Externally the tube is even, and shows the course of longitudinal muscle fibres. Suspended from the mid-dorsal line by a narrow 108 DISSECTION OF THE DOG mesentery continuous with the mesocolon, the rectum has its dorsal surface covered by peritoneum to a level slightly caudal to the acetabulum. The line of peritoneal reflection slopes obliquely across the lateral face of the tube in such a manner that the ventral surface has scarcely anv peritoneal investment. The terminal opening of the intestine, the anus, is surrounded by thick skin provided with a somewhat scanty supply of short fine hairs. Close to the line of junction of skin and mucous membrane is a small opening on each side leading into a sac, from a hazel-nut to a walnut in size, known as the para-anal sinus (sinus para-analis). The sinus lies between the external sphincter muscle of the anus and the longitudinal muscle of the rectum, and has a lining membrane provided with glands which produce a thickish, strong-smelling secretion. M. LEVATOR ANI.—The levator muscle of the anus of the dog is relatively large but thin. Triangular in form, it lies over the lateral face of the rectum. Since it is medial to the coccygeus muscle, this has to be turned aside in order that the full extent of the levator may be exposed. The levator ani arises from the symphysis of the ischia and pubes, from the oral border of the pubis, and from the medial surface of the ilium. Some of its fibres blend with the sphincter ani, and some end on the first vertebra of the tail. M. SPHINCTER ANI EXTERNUS.—The external sphincter surrounds the anus as a ring. It consists of three portions more or less blended together, and is attached to the aponeurosis of the tail. The oral portion is poorly developed. The middle portion is connected with the m. bulbo-cavernosus, and the aboral portion with the retractor muscle of the penis. M. SPHINCTER ANI INTERNUS.—The internal sphincter muscle is merely a thickening of the circular muscle of the rectum. It should be noted here that the longitudinal muscular fibres of the rectum send a well-defined band to the ventral aspect of the first few coccygeal vertebra. VESICA URINARIA.— Although not a pelvic organ in the dog, it is convenient, because of its connections, to study the urinary bladder here rather than with the abdominal viscera. An ovoid sac with a strong muscular wall, the bladder is divided, for-descriptive purposes, into a main portion or body (corpus vesice) ; a blunt cranial end, the vertex (vertex vesice) ; and a narrow pelvic extremity, the neck (collum vesicz), continuous with the urethra. _ Ventrally the bladder lies on the abdominal wall, the great omentum sometimes intervening. Dorsally it is in contact partly with the colon, partly with coils of the small intestine. Dorsal to the neck are the deferent ducts. On each side the bladder is in relation to the small intestine and the ureter. Naturally the relations of the vertex of the bladder depend materially upon the amount of distension of the viscus. When the sac is moderately full it may touch the ileum. At all times the vertex is in contact with some part of the small intestine. DISSECTION OF THE DOG 109 Dissection.—Open the bladder by making an incision along the mid-ventral line from the vertex to the neck. The interior of the urinary bladder is lined by a mucous membrane of distinctly rugose character ; but towards the neck the ruge are generally less prominent than over the rest of the interior. In the dorsal part of the neck the openings of the ureters will be found, and if a probe be passed along a ureter, its oblique passage through the wall of the bladder can be demonstrated. The term trigone of the bladder (trigonum vesice) is applied to that triangular area whose angles are denoted by the openings of the ureters and urethra. Structure of the bladder—From a naked-eye examination it is evident that the wall of the urinary bladder is composed of the four layers customarily found in connection with hollow viscera of a like nature. A serous coat is derived from the peritoneum. A muscular tunic contains fibres running in different directions and arranged in rather ill-defined strata. The superficial stratum contains fibres mainly longitudinally disposed. A middle stratum has circular, and a deep stratum oblique and longitudinal fibres. The oblique and circular fibres form a sphincter vesice muscle at the neck of the bladder. A submucous tela unites the lining mucous membrane to the muscular tunic. ProstaTEe.—The prostate is a rounded, lobulated, yellowish mass completely surrounding the first part of the urethra, and imperfectly divided into two lateral lobes by a shallow median longitudinal groove. The surface is thinly covered by longitudinal muscular fibres continued from the bladder. Generally only a very small portion of the organ lies within the confines of the pelvis. The two deferent ducts insinuate themselves close together between the prostate and the neck of the bladder. URETHRA.—The male urethra is a tube concerned in the transmission of both urine and semen, and extends from the neck of the bladder to the free end of the penis. In the female it is much shorter and purely urinary in function. The tube is divisible into three portions : (1) Pars prostatica surrounded by the prostate ; (2) pars membranacea extending to the bony arch formed by the borders of the ischia ; (3) pars cavernosa within the corpus cavernosum urethre of the penis. ‘The pelvic portion (consisting of pars prostatica and pars membranacea} runs along the middle line immediately dorsal to the symphysis of the pelvis and ventral to the rectum. This portion of the urethra is surrounded by the urethral muscle (m. urethralis). A branch of the pudendal nerve destined for the prostate will be found running along the ventral face of the pars membranacea. If the pelvic portion of the urethra be opened by continuing the mid-ventral incision of the bladder backwards to the bony arch formed by the ischia, it will be evident that the lumen of the prostatic part is narrow, whereas that of the 110 DISSECTION OF THE DOG membraneous part is wider. On the dorsal wall of the prostatic part, moreover, an elongated ridge, the crista urethralis and colliculus seminalis, will be noticed ; and on each side of the ridge the opening of the ductus deferens and the numerous openings of the ducts of the prostate will be found. M. ISCHIO-CAVERNOSUS.—The ischio-cavernosus muscle is short and broad, and covers the crus penis. Its fibres arise from the dorsal aspect of the medial angle of the sciatic tuber, and are spread out over the expanded portion of the corpus cavernosum penis. M. BULBO-cAVERNOSUS.—The bulbo-cavernosus muscle of the dog is well developed. It consists mainly of transverse fibres covering the bulbus urethre, and is connected with the middle part of the sphincter muscle of the anus. M. RETRACTOR PENIS.—The long, pale retractor of the penis leaves the aboral part (possibly also the middle portion) of the sphincter ani, and runs along the urethral surface of the penis towards the glans. M. ISCHIO-URETHRALIS.—The ischio-urethral muscle is rather small, and springs from the dorsal aspect of the medial angle of the sciatic tuber. The fibres of the muscle pass to the symphysis of the ischium and are inserted into a fibrous ring through which pass the dorsal veins of the penis. M. URETHRALIS.—As has already been mentioned, the pelvic portion of the urethra is surrounded by a circular muscle, which can now be demonstrated as continuous with the bulbo-cavernosus muscle. A. uypocastTRics.—One of the terminal branches of the abdominal aorta, the hypogastric artery pursues an oblique caudo-lateral course across the brim of the pelvis. Between it and the middle sacral artery is a group of lymph-glands (lymphoglandule iliace). Scarcely has the hypogastric artery reached the pelvic cavity than it divides into two parts, which may be called, from their distribution, the one visceral, the other parietal. The artery crosses the ventral aspect of the common iliac vein obliquely. The ilio-psoas muscle lies on its lateral side, and ventrally it is separated from the terminal part of the colon by peritoneum only. A. UMBILICALIS.—The only collateral branch of the hypogastric is the umbilical artery, which proceeds towards the side of the vertex of the bladder in the lateral peritoneal fold connected with this viscus. A crantal vesical artery (a. vesicalis cranialis) arises from the umbilical, and supplies both the bladder and the prostate. A small branch, the a. deferentialis, follows the deferent duct for some distance. A, PUDENDA INTERNA.—The visceral part (pars visceralis) of the hypo- gastric artery consists solely of the internal pudendal artery, which travels at first alongside the rectum—from which it is separated by peritoneum— then across the lateral face of the coccygeus and levator ani muscles within the sciatic spine, to bend round the arch formed by the ischia, and, finally, to be continued as the dorsal artery of the penis. The following are the branches of the internal pudendal artery: (1) The DISSECTION OF THE DOG 111 umbilical artery (a. umbilicalis) very often arises from the visceral part of the hypogastric artery instead of from the main trunk ; (2) the middle hemor- rhoidal artery (a. hemorrhoidalis media) for the supply of the rectum and the region of the anus; (3) the perineal artery (a. perinei), a small branch ending in the perineum ; (4) arteries to the penis: (a) the dorsal artery of the penis (a. dorsalis penis) follows the dorsal vein and nerve along the dorsum of the penis to the glans ; (b) the deep artery of the penis (a. profunda penis) enters the corpus cavernosum penis; (c) the artery of the urethral bulb (a. bulbi urethra)—the largest of the three—sinks into the corpus cavernosum urethre. The parietal part (pars parietalis) of the hypogastric artery is larger than the visceral division of this vessel, and passes along the wall of the pelvis a. hypegastrica a. sacralis media a. tlio-lumbalis / a, gluleea cranialis 1 mS ul sole ee ee Das aR ee 4 ' i / L —_ Z —_——, age a _ a. caudalis lateralis Aorta _ Z f super ficeats oad ‘ BOE < a. glutwa caudatis a mesenterica caudalis--~~~" A; S we \ Sh : ee ay Ny q — - Fd / “ bg aa. lumbales hh oa 4 a. hemorrhoidals media . nt af / f \ Bis ot a. colica sinistra Z / / AX | ‘ i a. perinet / 7 sdalis * ‘ \ . ‘i a, hemorrhoidalis , ae a) Lae ; rs \- & Profundy penis cranialis ra 1 F ! 4 Ssh \ y . b, ore. aaa ‘ 7 e a. circumfleza ilium' Pi ; bi ; oo \ a. bulb urethre \ aa ; profunda F ey f 2 \ e a. dorsalis penis / ! ! \ \ a.iliaca externa | a \ ’ a. acferentialis ' i 4 ‘ \ \ 1 y . : \ a. pudenda interna ' ¥ * ( a. profunda femoris 1 Be hate sls ! a. vesicalis cranialis' | cs fey ‘ a. umbilicuiis 1 u. pudenda externa ’ a. epigastrica caudalis Fia, 42.—Diagram of the external iliac and hypogastric arteries. at a more dorsal level. Crossing first the medial face of the ilium and then the medial face of the piriformis and superficial gluteal muscles, it ends as the caudal gluteal artery previously examined in connection with the other deep gluteal structures. The vessels arising from the parietal part of the hypogastric artery are the following: (1) The ilio-lumbar artery (a. ilio-lumbalis) arises close to the origin of the pars parietalis, or even from the main stem of the hypogastric artery itself, and is expended in the psoas minor, ilio-psoas, sartorius, tensor .fascie latze and middle gluteal muscles; (2) arising at the oral border of the piriformis muscle, the cranial gluteal artery (a. gluteea cranialis) passes into the gluteal region along with the sciatic nerve; (3) branches are contributed to the internal obturator, levator ani, coccygeus and piriformis muscles (rami musculares) ; (4) the superficial lateral caudal artery (a. caudalis lateralis 112 DISSECTION OF THE DOG superficialis) has been noted before as supplying branches to the gluteal, gemelli, internal obturator, quadratus femoris, adductor, biceps, semitendinosus and semimembranosus muscles. V. uypogasTrica.—The hypogastric vein differs from the artery of the same name in not having distinct parietal and visceral parts. It has two main tributaries, viz. the caudal gluteal vein and a common vessel formed by the union of veins from the penis (dorsal and deep), the perineal vein, and the middle hemorrhoidal vein. The hypogastric vein thus formed lies lateral to, and midway between, the parietal and visceral parts of the artery. Its collateral tributaries are the cranial gluteal (often double), cranial vesical and ilio-lumbar veins corresponding to the arteries with the same names. N. puprenpvus.—The pudendal nerve is formed by roots from the first and second sacral nerves. These join on the medial side of the hypogastric vessels, and the nerve so produced accompanies the visceral part of the artery (internal pudendal artery). There is a close connection between the pudendal and posterior cutaneous femoral nerves. From the pudendal nerve the following branches take origin: (1) A branch running vertically in a ventral direction from the parent nerve close to its commencement, and supplying the urethra, prostate, and urinary bladder ; (2) mzddle hemorrhoidal nerve (n. heemorrhoidalis media) ; (3) perineal nerve (n. perinei) ; (4) dorsal nerve of the penis (n. dorsalis penis). The three last mentioned follow the arteries of the same name. From the dorsal nerve of the penis springs a twig, already noted, which follows the ventral face of the membranous urethra to the prostate. Dissection.—Remove the pelvic organs. Cut open the rectum longitudinally and observe the transverse folds of mucous membrane, which become longitudinal as the anus is approached. The lumen of the tube will be noted as greater than that of the colon. Cut open the para-anal sinus. Clear away the fat from that pelvic wall which is yet intact. By removal of the levator ani muscle, the internal obturator muscle will be exposed. Determine the constitution and branches of the sacral plexus. M. OBTURATOR INTERNUS.—The internal obturator muscle is thin, and lies on the ventral wall of the pelvis over the obturator foramen. Its origin is from the pubis and ischium as they form the margin of the foramen. The muscular fibres converge to a flat tendon which lies upon the gemelli muscles and is attached to the femur within the trochanteric fossa. NN. LUMBALES ET NN. SACRALES.—The seven lumbar and three sacral spinal nerves form a plexus which is simple at the commencement of the lumbar region, but becomes increasingly complicated towards the sacral DISSECTION OF THE DOG 113 region. The constitution of the nerves arising from the lumbar and sacral plexus may be summarised in this place. N. ilio-hypogastricus is formed by the first lumbar. N. ilio-inguinalis consists mainly of fibres derived from the second lumbar nerve, but has, in addition, a reinforcement from the first lumbar. N. genito-femoralis generally contains fibres from the third and fourth lumbar nerves, but occasionally those from the fourth are absent. N. cutaneus femoris lateralis is mainly formed by the fourth lumbar nerve, but it also receives a branch from the third. N. femoralis is constituted by the union of two main roots from the fifth and sixth lumbar nerves, with an occasional thin root from the fourth nerve in addition. fe 8a, . 7 n. cutaneus — 2K nn, lumbales femoris posterior 7 if 7 6 5 4 / n. pudendus / if, 5 . ‘ n. hemorrhoidalis n, ilio-inguinalis caudalis i : ; n. gluteus | 1 nN, genito- caudalis | n, obtura- femoralis \ 7 torius Sg n. cutaneus yi n, gluteus n. femoralis femoris n. ischiadicus cranialis lateralis Fic. 43.—Plexus of lumbar and sacral nerves. N. obturatorius results from the conjunction of three roots: namely, from the fourth, fifth, and sixth lumbar nerves. N. ischiadicus is formed by the fusion of large roots from the sixth and seventh lumbar nerves, and a smaller root from the first sacral nerve. N. gluteus cranialis receives its fibres from the same spinal nerves as does the sciatic nerve. N. gluteus caudalis contains fibres contributed by the first and second sacral nerves. N. pudendus has roots from the first, second, and third sacral nerves. N. cutaneus femoris posterior is formed by the second and third sacral nerves. N. hemorrhoidalis caudalis is composed of fibres derived from the first and second sacral nerves. With the exception of the obturator and caudal hemorrhoidal nerves, all the above have been examined. N. opruratorius.—The obturator nerve is of considerable size, and is formed by roots which join medial to the ilio-psoas muscle. The nerve crosses the medial surface of the ilium and enters the obturator foramen by insinuating 1 114 DISSECTION OF THE DOG itself betwéen the pubis and the internal obturator muscle. Entering the thigh, it lies between the pectineus and adductor muscles. N. HEMORRHOIDALIS CAUDALIS.—The caudal hemorrhoidal nerve supplies branches to the bladder and rectum. A. SACRA MEDIA.—The middle sacral artery arises from the end of the aorta in the angle formed by the two hypogastric arteries, and runs along the mid-ventral line of the sacrum into the tail. Pars ABDOMINALIS ET PELVINA SYSTEM SYMPATHICI.—The sympathetic system is continued from the thorax into the abdomen and onwards into the pelvis. The abdominal part is connected with a chain of seven lumbar ganglia which will be found deep down in the narrow chink between the two psoas minor muscles. The ganglia have the usual communications with the spinal nerves, and filaments arising from them take part in the formation of an aortic plexus. The various plexuses in connection with the abdominal viscera have already been examined. After the formation of the seventh lumbar ganglion, the sympathetic cord becomes markedly thinner. The sacral part is feebly developed and runs along the ventral surface of the sacrum immediately dorso-lateral to the middle sacral artery and vein. One or two small ganglia are present. Tue Femate Petvis.—The examination of the female pelvis follows the same lines as those laid down for the pelvis of the male. The first thing to be done is to make a general examination of the disposition of the pelvic organs so far as is possible before any dissection has been carried out. The pelvic inlet is occupied by the urinary bladder, the vagina, and a part of the colon. Thus the entrance to the female pelvis contains practically the same organs as are associated with the male cavity, with the addition of the vagina. The general form of the bladder agrees with that of the male organ, but there are no deferent ducts associated with its neck. As in the male, the peritoneum is reflected from its mid-ventral and lateral aspects onto the abdominal wall in the form of three membranous sheets. In the female, the peritoneum associated with the bladder does not extend into the pelvis but is reflected ventrally and laterally onto the abdominal wall about the brim of the pelvic inlet. From the dorsal side of the neck of the bladder peritoneum is continued to the vagina. The vagina occupies a position dorsal to the bladder and ventral to the termination of the colon. Lateral folds of peritoneum—ccntinuations of the broad ligament of the uterus—connect the vagina with the wall of the cavity. Dorsally the peritoneum is carried back for some distance into a pouch (the DISSECTION OF THE DOG 115 recto-uterine excavation of Douglas) which intervenes between the vagina and the colon, and in which the colon hangs by its short mesentery. Dissection.—Proceed as in the dissection of the male pelvis. INTESTINUM RECTUM.—The description as given for the male rectum applies also to the female. Ventrally, the rectum is related to the uro-genital sinus. The levator ani, and external and internal sphincter muscles, as well as the longitudinal muscular fibres of the rectum, have the same general disposition as in the male. VESICA URINARIA.—The description of the urinary bladder as given in connection with the male pelvis applies here, with the difference that there are no deferent ducts or prostate related with the neck, and the dorsal surface is in contact with the vagina. The presence of longitudinal muscular fibres continued from the neck of the bladder to the wall of the uro-genital sinus should be noted. Dissection.—Open the bladder and urethra by making an incision along the mid-ventral line. Uretura.—The female urethra is shorter than the corresponding canal of the male, and is purely urinary in function. Running ventral to the vagina it opens into the uro-genital sinus just beyond the margin of the ischium. ORGANA GENITALIA MULIEBRIA.—The reproductive organs of the female consist of the two ovaries with their associated uterine tubes of Fallopius, the uterus, the vagina, the uro-genital sinus, and the external genital parts. Of these the ovaries, uterine tubes, and uterus are abdominal in position. The ovaries and uterine tubes have been described earlier. Ursrvus.—The uterus consists of two long, tubular, divergent cornua (cornua uteri) and a short body (corpus uteri). The cornua are suspended in the sublumbar region by duplicatures of peritoneum known as the broad ligaments of the uterus (ligamenta lata uteri), and are connected with the cranial end, or fundus uteri, of the body. The pelvic extremity of the body is called the neck (cervix uteri) and is in continuity with the vagina. If the cornua be opened by a longitudinal incision, the longitudinally folded character of the mucous membrane lining the interior will be revealed. The cavity of the body of the uterus is small, and the part joining the vagina is much constricted to form the canal of the cervix (canalis cervicis uteri). The canal opens, on the one hand, into the body of the uterus by means of the internal orifice of the uterus (orificium internum uteri); while, on the other hand, it communicates with the vaginal cavity by the eaternal orifice of the uterus (orificium externum uteri). Vacrva.—The vagina is a long tube extending from the neck of the uterus 12 116 DISSECTION OF THE DOG to just beyond the margin of the ischium, where it is continuous with the uro-genital sinus. The interior should be exposed by making a longitudinal incision in the mid-ventral line. When this has been done, there will be no difficulty in determining the extent of the vagina, for its conspicuous longitudinal folds of mucous membrane cease abruptly at the junction of the vagina and the uro-genital sinus. The projection of the vaginal portion (portio vaginalis) of the cervix of the uterus into the vaginal cavity should be noticed. SINUS URO-GENITALIS.—The uro-genital sinus is a short tube with a com- paratively smooth interior. Just about the point of junction of the vagina and uro-genital sinus, the ventral wall of the latter is pierced by the eaternal opening of the urethra (orifictum urethre externum). PaRTES GENITALES EXTERN2%.—The external opening of the genital canal or vulva is in the form of a vertical slit with a rounded dorsal and a sharp ventral commissure. The margins of the opening are formed by prominent, rounded labia pudendi. Immediately within the ventral commissure is the clitoris, the homologue of the male penis. Muscles of the external genital parts.—The sphincter ani muscle is divisible into two parts, both more or less continuous with muscular fibres of the perineum. The oral part of the sphincter is continued almost completely towards the vulva as an ano-vulvar muscle. The aboral portion of the sphincter is only partially continuous with a perineal muscle also running to the vulva. The vulva is provided with a constrictor muscle connected with the two perineal slips just mentioned and consisting of external (aboral) and internal (oral) parts. A. Hypocastrica.—The hypogastric artery has the same origin and the same general disposition as has the corresponding vessel of the male. Naturally, however, there are certain differences dependent upon the differences in the organs of the two sexes. From the ramus visceralis (internal pudendal artery) springs a large branch from which the uterine and the cranial and caudal vesical arteries arise. The uterine artery (a. uterina) follows the body and cornua of the uterus. The cranial vesical artery (a. vesicalis cranialis) supplies the bladder mainly, but in addition sends twigs to the vagina. The caudal vesical artery (a. vesicalis caudalis) is mainly concerned in the nourishment of the vagina and the uro-genital sinus. The terminal branches of the internal pudendal artery are concerned in the supply of blood to the uro-genital sinus and the vulva. The ramus parietalis of the hypogastric artery comports itself as in the male. The rest of the dissection of the female pelvis proceeds on the lines given for the male. DISSECTION OF THE DOG 117 Dissection.—Remove the skin from the side of the neck, shoulder, and trunk. Preserve the cutaneous nerves, the largest of which are derived from the second, third, and fourth cervical spinal nerves. M. Curanrus.—On the removal of the skin from the neck, thorax, and abdomen, a muscular sheet, the cutaneous muscle, is revealed. This is divisible into two parts: (1) the cutaneous muscle of the face and neck, and (2) the cutaneous muscle of the thorax and abdomen. Glandwla parotis m, cleido-cervicalis fob : Glandula submacillaris \ : F i \ i \ : m, trapezius cervicalis ‘ 4 m, trapezius thoracalis ‘ m. latissimus dorsi ‘ , ‘ 1 ¥ iS mat j ry We , ae \ \ SS \ ’ mm. sterno-hyoideus et sterno-thyreoideus \ 1 \ L. , 1 \ \ , m, sterno-cephalicus , in v, fugularis externa q ‘ m. omo-transversartus bys ls > f “ m, deltotdeus ! m. pectoralis pro m, rectus abdominis f m. obliquus abdominis externus ~~sm, sterno-cephalicus oi Sm, triceps brachii. Caput longum sy? cephalica in. triceps brachii. Caput laterale “sm. brachialis Fic. 44.—Superficial dissection of the shoulder and neck. (1) M. cutaneus faciei et colli—In the neck the cutaneous muscle is arranged in two strata, the deeper of which consists of transverse fibres and extends from the’manubrium sterni to the larynx. The superficial stratum contains fibres which run obliquely ventro-orally, and is continued to the face. In the face itself there is a third, still deeper layer confined to the region of the chin, where it forms the submental muscle. (2) M. cutaneus abdominis et pectoris.—Covering the whole of the lateral 5 aspect of the abdomen and thorax caudal to the scapula is an extensive sheet 118 DISSECTION OF THE DOG of fibres running cranio-ventral in direction and converging upon the axilla, where a tendon connects the cutaneous with the deep pectoral muscle. Two muscles, the brachio-cephalic and the sterno-cephalic, are more or less blended, and together form a muscular sheet of no great thickness covering the lateral and ventral aspects of the neck. M. BRACHIO-CEPHALICUS.—The brachio-cephalic muscle is divisible into two parts, cleido-cervical and cleido-mastoid, joined together in the region of the shoulder joint and continued to the arm as a single muscle. The place of union of the two parts is marked by a transverse tendinous line, with which the vestige of the clavicle is associated. The cleido-cervical muscle is attached to the occipital bone and the cranial half of the ligamentum nuche. The cleido-mastoid muscle, covered by the sterno-cephalic muscle, is connected with the mastoid part of the temporal bone. It will be noted that the cleido-cervical and sterno-cephalic muscles in the lateral and dorsal parts of the neck are in the same plane and practically parts of the continuous thin muscular sheet; whereas the cleido-mastoid muscle is much thicker and in a deeper plane. The common aboral part of the brachio-cephalic muscle is inserted into the crista tuberculi majoris of the humerus. M. sTERNO-CEPHALICUS.—The sterno-cephalic muscle arises from the manubrium of the sternum, and is inserted into the mastoid part of the temporal bone. Its intimate connection with the cleido-cervical muscle has just been noted. M. tRapezius.—The trapezius muscle forms a thin irregularly triangular sheet over the scapular region, and consists of two parts—cervical and thoracic. The cervical trapezius arises from the ligamentum nuche caudal to the attachment of the cleido-cervical muscle. It is also attached to the spinous processes of the first two, three or four thoracic vertebree. The fibres of the muscle run in a caudal and ventral direction to be inserted into the spine of the scapula. The thoracic trapezius consists of fibres which run in a cranial and ventral direction. Their origin is from the spinous processes of the thoracic vertebre from the third or fourth to the ninth or tenth, and also from the lumbo-dorsal fascia. The insertion of the muscle is to the dorsal third or so of the spine of the scapula. Dissection.—Cut through the trapezius and cleido-cervical muscles close to their dorsal attachments, and turn them downwards. In doing so, note the presence of lymph-glands (lympho-glandule cervicales profunde) between the two muscles and under cover of the cleido-cervical and omo-transverse muscles. In the same neighbourhood, the superficial cervical branches of the transverse scapular vessels and the accessory DISSECTION OF THE DOG 119 nerve are to be found. The muscles exposed are the three rhomboids, the omo-transverse aud the latissimus dorsi. M. RHOMBOIDEUS CERVICALIS.—The cervical rhomboid takes origin from the ligamentum nuche as far towards the head as a level with the second or third cervical vertebra, and from the spinous processes of the first two or three thoracic vertebra. It is inserted into the medial face of the cranial angle of the scapula. m. rhomboideus m. serratus dorsalis ey feales \ sis ‘ a. subscapularis \ m, ilio-costalis dcetiombelious P 1 / m. splenius \ Ne m, longissimus dorsi thoracalis t if i . \ \ m. serratus ; ' / iB eee eee ye N dorsalis ' H / ee ee \ \ \ Oe ' 1 : / ; Sees \ \ VS oa \ Po i | ; \ a \ | Sai ac ‘i J - : 4 ee bo / oes ¢/ | i oe ae” eg’ : x oe ee eet y ‘ Mm ' \ * 5on- LA m, longus capitis se 5 / 7 ‘ i \'m. serratus ventralis fa ~ ~ ~~ im. supraspinatus “> m, infraspinatus a 7 é ea } yn Fe = i 4 StS Z i ra *s m. teres major | = ~~ “ ~~ xn, tom, deltoideus m, obliquus ‘ ; abdominis externus i i] i ¥ De mM. re ! ~~. : ve ee aa) | H rs a os hee m. triceps brachti ™. serratus i i ventralis ul / ™, pectorilis ,/ profundus , a. circumplexa humeri posterior Fic. 45.—Dissection of the shoulder after removal of the more superficial muscles. M. RHOMBOIDEUS CaPITIS.—This might reasonably be described as a part of the cervical rhomboid, since the two blend towards a common insertion. The muscle consists of a thin strip arising from the occipital bone. M. RHOMBOIDEUS THORACALIS.—The thoracic rhomboid is a very much shorter and feebler muscle than the cervical rhomboid. It arises from the spinous processes of the fourth to the sixth or seventh thoracic vertebra, and is attached to the scapula immediately caudal to the insertion of the cervical rhomboid. M. OMO-TRANSVERSARIUS.—The omo-transverse is a band-like muscle running from the wing of the atlas to the distal part of the spine of the scapula and the fascia over the deltoid. 120 DISSECTION OF THE DOG M. LATISSIMUS DoRSI.—The latissimus dorsi muscle has already been partly exposed in the dissection of the ventral aspect of the thorax and the axilla, and its insertion into the crista tuberculi minoris of the humerus has been examined. At the present stage of the dissection the origin of the muscle by a tendinous expanse from the lumbo-dorsal fascia, by means of which it is con- nected with the last seven thoracic and all the lumbar vertebrx, is to be examined. It will be found further that there is a fleshy origin from the last two ribs. N. accrssorius.—The accessory or eleventh cerebral nerve passes towards the shoulder ventral to the wing of the atlas, under cover of the brachio- cephalic muscle and between this and the omo-transverse. It then lies between the cervical part of the trapezius and the cervical part of the ventral serratus and supraspinous muscles, and finally disappears into the substance of the thoracic part of the trapezius. During the passage of the accessory nerve down the neck it is connected with the cervical nerves from the second to the fifth. Dissection.—Reflect the omo-transverse muscle. M. SERRATUS VENTRALIS.—During the dissection of the wall of the chest the thoracic part of the ventral serratus muscle was examined. The cervical portion of the muscle, arising from the transverse processes of the third, fourth, fifth, sixth, and seventh cervical vertebra, is now_exposed. Dissection. After noting the presence of a small communicating vein from the cephalic to the jugular on the surface of the brachio-cephalic muscle, the limb may be removed by cutting through the brachio-cephalic, rhomboid, latissimus dorsi, and ventral serratus muscles. Then the muscles, nerves and vessels on the deep face of the scapula and arm should be cleaned. M. suBscaPuLARIs.—The subscapular muscle is broad and fan-shaped and occupies the whole of the subscapular fossa of the scapula. Its fibres are separated into five or more portions by tendinous bands which converge towards the shoulder-joint. The origin of the muscle is from the subscapular fossa, and its insertion is into the tuberculum minus of the humerus. M. TerE3 Masor.—A powerful muscle placed immediately aboral to the foregoing, the origin of the teres major is from the axillary border of the scapula, the angle separating the axillary and vertebral borders of this bone, and the subscapular muscle. The insertion of the muscle is in common with that of the latissimus dorsi to the crista tuberculi minoris of the humerus. M. Biceps BRACHU.—The biceps muscle runs parallel to, and to the medial side of, the humerus. Arising from the coracoid process of the scapula, the strong tendon of origin is bound down in the intertubercular sulcus of the DISSECTION OF THE DOG 121 humerus by a transverse band of fascia and is surrounded by a synovial prolongation from the shoulder-joint. ; m. subscapularis. _ . m. supraspinatus, SS \ \ n. suprascapularis \ x aoe Mn. subscapulares m. pectoralis profundus Aa _-— ™. teres major _-- 2. thoraco-dorsalis _ 4. subscapularis n, musculo-cutaneus ~7 > —~~>-22-. _-— ™. latissimus dorsi aazillaris | | | JF WY------------------ n, radialis a __--— & profunda brachii m. brachio-cephalicus -—--- ee al weloesceme m, tensor fascice antibrachii n. musculo-cutaneus~ ~~~ ~~~ Xn ee = % enaris ae \ iat ee m. triceps brachii. Caput longum Begala Sse m. triceps brachti. Caput mediale m. biceps brachii - _-— «. collateralis ulnaris a. brachialis n. medianus -- ~~ a. collateralis radialis,---~~ prozimalis n. radialis superficialis---~ ~~ us m. extensor carpi radialis_---~ ae || a, ne m, flexor carpi radialis m. pronator teres —-~ . wan = ti(i‘éidéi PO Bee ee m, flexor digitorum sublimis a, radialis. q m., flexor digitorum profundus a, ulnaris Fie. 46.—Dissection of the medial aspect of the shoulder, arm, and forearm. The tendon of insertion of the biceps is double. The stronger part is attached to the tuberosity of the ulna; the weaker to the tuberosity of the radius. M. CoRACO-BRACHIALIS.—This is a small muscle lying in a depression 122 DISSECTION OF THE DOG bounded by the subscapular, teres major, and biceps muscles. It arises from the coracoid process by a long, narrow, flattened tendon which crosses the insertion of the subscapular muscle, and its insertion is into the crista tuberculi minoris, lateral to the common tendon of the teres major and latissimus dorsi muscles. M. TENSOR FASCLH ANTIBRACHII—The thin tensor of the fascia of the forearm lies mainly lateral to the latissimus dorsi from which it takes origin. The fibres of the muscle end on the olecranon of the ulna and in the fascia of the forearm. M. TRICEPS BRACHI.—The triangular gap between the scapula, humerus, and olecranon of the ulna is occupied by the powerful triceps muscle. Two of the heads—caput longum and caput mediale—can be dissected at this stage. The rest of the muscle must be left until the lateral aspect of the arm is examined. Caput longum.—The cleaning of the long head is facilitated by the reflection of the tensor fascize antibrachii. This head of the triceps is a thick, triangular muscle, springing from the distal two-thirds of the axillary border of the scapula, and ending in a strong tendon inserted into the olecranon. Caput mediale—Superficially the medial head of the triceps appears as an elongated muscle between the long head and the biceps, but a considerable amount of the muscle is hidden beneath the long head. The origin of the medial head is by one fleshy band from the crista tuberculi minoris, and by another from the neck of the humerus. A common tendon attaches the long and medial heads to the olecranon of the ulna, a synovial bursa intervening between the tendon and the bone. N. SUPRASCAPULARIS.—The large suprascapular nerve disappears into the interval between the oral border of the. subscapularis muscle and the supra- spinatus. After crossing the oral border of the scapula, branches are contributed to the supraspinous, infraspinous, teres minor, and deltoid muscles. NN. SUBSCAPULARES.—The subscapular nerves are small in size and three or four in number. They terminate in the subscapular and teres major muscles. N. AXILLARIS.—The axillary nerve is of large size, and enters the triangular space circumscribed by the subscapular, teres major, and coraco-brachial muscles. Then, passing between the long and medial heads of the triceps, it reaches the lateral aspect of the shoulder. Its branches supply the deltoid, teres major and minor, and infraspinous muscles. N. MUSCULO-CUTANEUS.—The musculo-cutaneous nerve passes distalwards between the axillary artery and the coraco-brachial muscle, and then accom- panies the brachial artery, lying oral to the vessel. The terminal part of the nerve runs between the radius and the biceps. Branches are given to the biceps, coraco-brachial, and brachial muscles. In the distal third of the arm a communicating branch joins the median nerve, and ashort distance distal to this the n. cutaneus antibrachii lateralis arises. DISSECTION OF THE DOG 123 N. MEDIANUS.—At its origin the median nerve is closely connected with the ulnar and radial nerves. All three accompany the axillary and brachial arteries as far as the origin of the deep artery of the arm where the radial nerve leaves the other two. The median and ulnar continue onwards in company with each other and the brachial artery as far as about the junction of the middle and distal thirds of the arm, where the ulnar parts company with the median nerve and the artery. The median nerve accompanies the artery into the forearm. N. RapraLis.—The radial nerve is generally the largest of the branches of the brachial plexus. As previously stated, it accompanies the median and ulnar nerves for some distance. At the distal border of the teres major the nerve sinks into the interval between the long and medial heads of the triceps. N. utnaRis.—The ulnar is as large as, or possibly larger than, the median nerve, by the side of which it runs as far as beyond the middle of the arm. Coursing, from this point, along the face of the medial head of the triceps, it passes into the forearm under cover of the antibrachial fascia. In the distal third of the arm the ulnar nerve contributes a palmar cutaneous branch (ramus cutaneus palmaris), which reaches the forearm by first running obliquely between the medial head of the triceps and the tensor of the anti- brachial fascia, and then across the medial face of the olecranon of the ulna. A. AXILLARIS.—The mode of origin and some of the branches of the axillary artery have been examined during the dissection of the axilla. The further course of the artery is first across the medial aspect of the shoulder-joint, and then over the coraco-brachial muscle and the tendon of insertion of the teres major. On a level with the distal border of the last-named muscle the axillary artery becomes the brachial. The only branch which belongs properly to the limb is the subscapular artery. A. SUBSCAPULARIS.—The subscapular artery is the largest branch of the axillary ; indeed it is larger than the continuation of the parent trunk, a circum- stance which has led to the conception that the axillary artery terminates at this point by bifurcation. The subscapular artery passes along the axillary border of the scapula between the subscapular and teres major muscles and on the medial face of the origin of the long head of the triceps. The full course of the vessel cannot be followed without reflection of the teres major; but this dissection had better be postponed for a. little. The following vessels are branches of the subscapular artery : (1) Branches (rami musculares) to the subscapular, teres major, trapezius, deltoid, supraspinous, and brachio-cephalic muscles. (2) A. circumflexa humert anterior —In many cases the anterior circumflex humeral artery arises directly from the axillary. Crossing the surface of the coraco-brachial (or teres major) muscle, the artery divides into two twigs, of 124 DISSECTION OF THE DOG which one disappears into the biceps muscle. The other travels towards the shoulder-joint, and finally anastomoses with the posterior circumflex artery. (3) A. circumflexa humeri posterior—The posterior circumflex humeral artery accompanies the axillary nerve round the back of the proximal part of the humerus. In the dissection of the lateral aspect of the shoulder it will be found under the deltoid muscle. (4) A. thoraco-dorsalis.—Arising close to the commencement of the sub- scapular artery, the thoraco-dorsal artery crosses the medial face of the teres major—to which it gives a branch or branches—and ends in the latissimus dorsi and cutaneous muscles and in the skin. ; (5) A. circumflexa scapule—tThe circumflex scapular artery is a small vessel which pierces the origin of the long head of the triceps and ramifies in the infraspinous muscle. From it springs the nutrient artery of the scapula. A. BRACHIALIS.—From its origin at the distal border of the teres major, the brachial artery runs distalwards in a groove formed by the biceps and the medial head of the triceps. Crossing the flexor aspect of the elbow-joint, it enters the forearm in company with the median nerve. The musculo-cutaneous nerve follows the oral, and the median nerve the aboral, border of the artery. The following branches leave the brachial artery while it is still in the arm : (1) A. profunda brachit—The deep artery of the arm leaves the brachial close to its origin, and, accompanied by the radial nerve, enters the chink between the long and medial heads of the triceps. (2) Ramus muscularis—A branch to the biceps leaves the brachial in the distal third of the arm. (3) A. collateralis ulnaris proximalis——The proximal ulnar collateral artery takes origin from the aboral side of the brachial almost opposite the artery to the biceps. Crossing the face of the medial head of the triceps in company with the palmar cutaneous ramus of the ulnar nerve, it is expended in the region of the elbow-joint and the ulnar aspect of the proximal half of the forearm. (4) A. collateralis radialis proximalis——The proximal radial collateral artery arises from the brachial about the same level as the origin of the ulnar collateral, but from the oral border of the parent vessel. After passing in succession over the communicating branch from the musculo-cutaneous to the median nerve, the medial face of the biceps, and the flexor aspect of the elbow, it reaches the forearm. (5) A. collateralis radialis distalis—The distal collateral radial artery leaves the brachial artery close to the elbow-joint. Running lateralwards, almost at right angles to the parent vessel, it lies between the biceps and the brachialis muscles on the one hand and the humerus on the other. The artery thus comes into relationship with the deep radial nerve, which it accompanies into the forearm. DISSECTION OF THE DOG 125 a Dissection.—Proceed to the examination of the outer aspect of the shoulder and arm. Remove the remains of the trapezius and omo-transverse muscles. Observe the termination of the subscapular artery and the m, infraspinatus ~~~ 2 ft gil m, teres major. + — ! \ a 4 | } m., triceps ( Caput longum—~ / | brachtt U Caput laterale~_ ies / eas me } atom os/m, deltoideus ~ : om, brachio-cephalicus [ | l= — — — — =m, brachialis ti Se eee v. cephalica | ¢ -—-——- n, radialis, Ramus superficialis } wed ; ari —-—-—-— m. extensor carpi radialis m. anconeus —~-~—~> 7 m. flexor carpi ulnaris -—* m, extensor carpt _ \ ulnaris ’ n. ulnaris, Ramus / cutaneus palmaris m, extensor digiti tertit et quarte n, ulnaris. Ramus dorsalis ae m. abductor ™* pollicis longus : Fic. 47.—Dissection of the lateral aspect of the shoulder, arm, and forearm. Com. — tendons of the common extensor of the digits; I, I, III, IV, and V = tendons of the extensors of the first, second, third, fourth, and fifth digits. 126 DISSECTION OF THE DOG commencement ofitscompanion vein. The artery appears at the axillary border of the scapula in the interval bounded by the teres major, infra- spinous, and long head of triceps muscles. Crossing the infraspinous muscle and the aponeurotic origin of the deltoid, it ends in the trapezius. M. supRASPINATUS.—The supraspinous muscle fills the whole of the supra- spinous fossa of the scapula from which it takes origin. In addition, some of its fibres arise from the subscapular muscle. Its insertion is into the greater tubercle of the humerus and into the insertion of the deep pectoral muscle. M. pe.rorpgvs.—Irregularly triangular in outline and placed in the angle formed by the spine of the scapula and the humerus, the deltoid muscle can be divided into two portions: (1) arising from the spine of the scapula by aponeurosis ; (2) taking origin from the acromion. The two parts blend into a common insertion to the deltoid tuberosity of the humerus. Veins of the arm.—The main veins of the arm begin as superficial veins in the forearm. V. MEDIANA CUBITI.—The median vein of the forearm divides, on a level with the tendon of insertion of the biceps, into a median basilic and a median cephalic. The median basilic vein (v. mediana basilica) crosses the medial face of the biceps and, receiving the ulnar vein or veins, becomes the basilic vein (v. basilica). This follows the brachial artery to the distal border of the teres major muscle, where it receives the deep humeral vein and becomes the axillary (v. axillaris). V. MEDIANA CEPHALICA.—The median cephalic vein runs in a groove formed by the brachio-cephalic and brachialis muscles, receives the radial vein, and becomes the cephalic vein (v. cephalica). After a short single course the cephalic vein becomes double. One of its parts, the original vein, travels along the groove between the superficial pectoral and deltoid muscles and finally joins the external jugular vein. The other part, generally the larger, follows the border of the deltoid, and disappears between the lateral and long heads of the triceps to join the subscapular vein. Before its disappearance a small twig leaves it to cross the brachio-cephalic muscle superficially and enter the external jugular vein. Dissection.—Reflect both parts of the deltoid muscle. This will expose the infraspinous and teres minor muscles, the origin of the lateral head of the triceps and the termination of the axillary nerve. The last named appears, along with the posterior circumflex vessels, from a triangular space bounded by the long and lateral heads of the triceps and the teres minor. M. inFrasprnatus.—The infraspinous muscle occupies the fossa of the same name. Its origin is from the whole extent of the fossa and in addition DISSECTION OF THE DOG 127 from the aponeurotic origin of the deltoid and from the long head of the triceps. On the lateral aspect of the shoulder-joint the muscle gives place to a flattened tendon which is attached to a ridge on the lateral face of the tuber- culum majus after having played over a smooth area covered by cartilage, a m. infraspinatus ----~--—---__ neers \ oe ‘ —--b--M, supraspinatus m. triceps brachti. Caput longum ce bliss m. teres minor pan - en nnwen- n. axillaris a. circumflera : / / humeri posterior : / Ber ae eee | See m. triceps brachii. | / Caput mediale a 4 ~--~4-L---m, brachialis a. profunda __— ee brachtt Of A ----- ----n, radialis Se m. biceps brachii ---}- ~------- n. radialis. Ramus profundus Paina ase n. radialis, Ramus superficialis SSR See m. extensor carpi radialis _ m, extensor digitorum communis m, anconceus ~ ees _m, extensor digiti quintt m. flexor carpi uUnens CHS sro SS= m, extensor carpi ulnaris Fic. 48.—Dissection of the arm after removal of the deltoid and the lateral head of the triceps muscle. synovial membrane further reducing the friction. Demonstrate this arrange- ment by cutting the tendon across close to its commencement, and turning back the two ends. This has the further advantage of showing a greater amount of the teres minor muscle. M. TERES MINOR.—The narrow, and somewhat rounded, teres minor lies 128 DISSECTION OF THE DOG along the aboral border of the infraspinous muscle. Its origin is from the distal third of the axillary border of the scapula and particularly from a rough elevation close to the glenoidal margin. The insertion is to the crista tuberculi majoris between the attachment of the infraspinous tendon and the origin of the lateral head of the triceps. M. TRICEPS BRACHII.—Two heads—caput longum and caput mediale—of the triceps have already been examined. It will be noticed that the long head is included in both the medial and lateral aspects of the arm. Caput laterale—The lateral head arises from the crista tuberculi majoris of the humerus under cover of the insertion of the deltoid. The main insertion of the head is into the olecranon of the ulna in common with the rest of the triceps. In addition there is a connection with the fascia of the forearm. Dissection.—Reflect the lateral head of the triceps. This will allow of an examination of the lateral part of the medial head which has origin close to the head of the humerus. The brachial and aconeus muscles and the radial nerve are also exposed. A branch of the deep artery of the arm accompanies the nerve and follows it into the forearm. M. BRACHIALIS.—The brachial muscle has its origin immediately medial to the insertion of the teres minor and the origin of the lateral head of the triceps. Running along the humerus in a spiral manner, the muscle crosses the flexor aspect of the elbow-joint and ends in two tendons which join the two tendons of the biceps. Thus it obtains insertion into both radius and ulna. M. aconzus.—The aconeus is a small muscle lying between the olecranon and the humerus. Its chief origin is from the lateral epicondyle ; but some fibres come from the lateral collateral ligament of the joint. The insertion of the aconeus is into the lateral face of the olecranon of the ulna. Some of the fibres, moreover, are inserted into the capsule of the elbow-joint. N. rapratis.—In the dissection of the medial aspect of the arm the radial nerve was observed to pass between the long and medial heads of the triceps. More of its course may now be examined. The nerve will be found at first between the two portions of the medial head of the triceps ; then between the medial head and the brachial muscle; and, lastly, between the lateral head and the brachial muscle. Here the nerve divides into deep and superficial branches, both of which proceed into the forearm. The superficial branch (ramus superficialis) of the radial nerve is subcutaneous and accompanies the radial vein. The deep branch (ramus profundus) follows the brachial muscle. Dissection Remove the skin from the forearm and the dorsum of the manus. In the superficial fascia blood-vessels and nerves should be discovered. DISSECTION OF THE DOG 129 V. MEDIANA cCUBITI—The median vein begins by draining the first digit. After crossing the medial aspect of the forearm it comes to occupy the groove between the extensor and flexor mass of muscles. The termina- tion of the vein on the flexor aspect of the elbow-joint has already been examined. V. RADIALIS.—The large radial vein commences as the dorsal veins of the second to the fifth digits. Just above the carpus a considerable augmentation of volume results from the reception of a large branch from the median vein. The radial vein now follows the anterior border of the forearm, and ends by assisting the median cephalic vein in the formation of the cephalic vein. Vv. ULNARES.—One or two small ulnar veins will be found over the posterior and medial part of the proximal third or so of the forearm. They may join the basilic vein. A. RADIALIS COLLATERALIS PROXIMALIS.—The proximal radial collateral artery, a branch of the brachial, enters the forearm by crossing the surface of the biceps muscle. A division into two branches takes place. The more lateral and larger of the two passes into the metacarpus and terminates as three common dorsal digital arteries (aa. digitales dorsales communes II, III, et IV) which lie in the grooves between the second and third, third and fourth, and fourth and fifth metacarpal bones. N. CUTANEUS ANTIBRACHII LATERALIS.—The lateral cutaneous nerve, a branch of the musculo-cutaneous, enters the foramen between the biceps and brachialis muscles, and then follows the median vein. N. RaDIsALis.—The superficial branch of the radial nerve travels down the forearm in company with the radial vein. About the level of the elbow it divides into medial and lateral branches. The medial branch, the smaller of the two, accompanies the communicating vein from the median to the radial vein and ends as the dorsal nerves of the first and second digits. The lateral branch crosses the extensor aspect of the carpus and terminates as dorsal nerves of the second, third, fourth, and fifth digits. Drerp Fascia.—The deep fascia of the forearm is strong and thick. It forms a sheath for all the muscles and passes between them as intermuscular septa. At the borders of the limb it is attached to the radius and ulna, and at the distal end of the radius forms an annular ligament by which the tendons of the extensor muscles are retained in place. Dissection —The deep fascia must be removed in order to allow of the examination of the anterior and lateral regions of the forearm and the dorsum of the manus. The annular ligament, however, must be left in position for the present. It is convenient to note here that the annular ligament has bony attach- ments at five places. The result is that four passages in which tendons are KE 130 DISSECTION OF THE DOG lodged are produced. The arrangement of the tendons may be summarised in the following manner : ULNAR. RADIAL. M. extensor pollicis longus et in- dicis proprius. M. extensor digiti tertii ct quarti. M. extensor digitorum communis. M. extensor carpi radialis. M. abductor pollicis longus. M. extensor digiti quinti. The muscles in front and on the lateral aspect of the forearm are arranged in two layers, superficial and deep. The superficial layer contains the mm. brachio-radialis, extensor carpi radialis, extensor digitorum communis, extensor digiti tertii et quarti, extensor digiti quinti, and extensor carpi ulnaris—in this order from the radial to the ulnar border of the forearm. M. BRACHIO-RADIALIS.—The brachio-radial muscle is very often exceed- ingly rudimentary or even absent, and lies immediately under the skin superficial to the radial extensor. The origin of the muscle is from the proximal part of the ridge above the lateral epicondyle of the humerus, and its insertion is into the medial border of the radius. M. EXTENSOR CARPI RADIALIS.—This, the most bulky muscle in front of the forearm, has origin partly from the lateral epicondyle of the humerus, but mainly from the ridge proximal to the eminence. The fleshy belly of the muscle lies lateral to the brachialis and is imperfectly divided into two layers. The superficial layer gives place to a flattened tendon which is inserted into the base of the second metacarpal bone (m. extensor carpi radialis longus). The deep part of the muscle, larger and longer than the preceding, is succeeded by a strong tendon which terminates at the base of the third metacarpal bone (m. extensor carpi radialis brevis). The two tendons are crossed obliquely in the distal third of the radius by the abductor pollicis longus, and are held down in a broad groove at the distal end of the radius by the annular ligament. M. EXTENSOR DIGITORUM COMMUNIS.—The common extensor muscle of the digits is lateral to the foregoing, with which it is intimately connected at its origin from the lateral epicondyle of the humerus and from the septum DISSECTION OF THE DOG 131 between the muscles. Four tendons leave the tapering end of the muscle, play through a groove at the distal end of the radius, and spread out on the dorsum of the manus. The tendons are finally inserted into the terminal phalanges of the second, third, fourth, and fifth digits. Le sees m. triceps brachtt a. brachialis.__ i brachialis prem Lan. medianus : woe AND N------- : , m., biceps brachti n, ulnaris m, pronator teres c _- @, interossea communis m. supinator ~— -~ ~~... al m. extensor carpi, --~~ ~~. m. flexor carpi ulnaris radialis IN mn m. flexor carpi radialis a, mediana-- ~~ ae ~.m. pronator quadratus in, flexor digitorum Saat sublimis Sea Oe are a, ulnaris ie ch <2 m. flexor digitorum = profundus a, radialis— ~- 47 m., flexor digitorum eee ees profundus. Caput radiale Fic. 49.—Dissection of the medial aspect of the forearm. Each tendon expands over the metacarpo-phalangeal articulation, with the capsule of which it is closely connected, and has a sesamoid bone over the proximal interphalangeal joint. In the neighbourhood of the joint between the metacarpal bone and the first phalanx, each tendon is joined by the tendon of one of the smaller extensors of the digit—extensor indicis proprius, extensor digiti tertii et quarti, and extensor digiti quinti. At the distal end of K2 132 DISSECTION OF THE DOG the first phalanx, each tendon is further jomed by the slender tendon of an interosseous muscle. The short extensor and interosseous tendons may blend before they unite with the common extensor tendons. : m. extensor carpi ulnaris~ — > m. extensor digiti quinti--— m. extensor digiti tertii et quarti 4t-—-m. extensor carpi radialis m, extensor digitorum_ communis q ——m. abductor pollicis longus m. extensor pollicis longus __ et indicts proprius Fic. 50,—Tendons on the dorsum of the manus, M. EXTENSOR DIGITI TERTIL ET QUARTI: M. EXTENSOR DIGITI QUINTI. —These two extensors of the digits arise as a common muscle from the lateral epicondyle of the humerus and the lateral collateral ligament of the elbow-joint. In the proxi- mal third of the forearm, the common mass divides into two fleshy bellies, of which that of the extensor of the third and fourth digits is the longer. The tendon in which the longer belly terminates divides as the carpus into two parts, which join those tendons of the com- mon extensor destined for the third and fourth digits. The very much stronger tendon of the ex- tensor of the fifth digit, in like manner, joins the common extensor _ slip belonging to that digit. M. EXTENSOR CARPI ULNARIS.—The ulnar ex- tensor of the carpus forms the extreme ulnar border of the forearm. A flat- tened and partly ten- dinous belly takes origin from the lateral epicon- dyle of the humerus, where it is closely asso- ciated with the anconeus. DISSECTION OF THE DOG The strong flattened tendon of the muscle is inserted into the base of the fifth metacarpal bone. An addi- tional connection of the tendon is with the annular ligament of the carpus and with a broad band of fascia crossing the pisiform bone. Between the band and the bone there is a synovial bursa. It should be noted that, unlike the tendons of the other extensors, the tendon of the ulnar extensor is not enclosed in a synovial sheath at the carpus. The deep layer of muscles in front of the forearm in- cludes the mm. extensor ‘pollicis longus et indicis proprius, abductor pollicis longus and supinator. The two first mentioned can be completely exposed by cut- ting that part of the annular ligament which binds down the tendons of the common extensor muscle of the digits. To expose the supinator muscle, it is necessary to reflect the radial extensor of the carpus and the common extensor of the digits. M. EXTENSOR POLLICIS LONGUS ET INDICIS PROPRIUS. —The extensor of the first and second digits is a small muscle lying under cover of the common extensor, with an origin from the middle third of the lateral border of the ulna. The small tendon n.radialis, | Ramus latcralis = nulmaris. ____ Ramus dorsalis nn. digitales 2 dorsales communesx== == II, 111, ek IV OS | ee ene n. radialis, Ramus medialis n. digitalis dorsalis =a medialis et lateralis digitt I si ats n, digitalis dorsalis medialis digitt II Fig, 51.—Diagram of nerves on the dorsum of the manus. K3 134 DISSECTION OF THE DOG of the muscle passes down that groove of the radius in which the common extensor tendons lie. In the metacarpal region it divides into two parts: one (inconstant) joins the first digit (m. extensor pollicis longus) ; the other fuses with that slip of the common extensor which goes to the second digit (m. extensor indicis proprius). M. ABDUCTOR POLLICIS LoNGUS.—The abductor of the first digit is distinctly semi-penniform. Its origin, partly under cover of the foregoing muscle, is from the middle two-fourths or more of the adjacent borders of the radius and ulna and the intervening interosseous membrane. The tendon runs along the medial border of the muscle, crosses obliquely over the tendon of the radial extensor, and ends on the base of the first metacarpal bone. A sesamoid bone is associated with the tendon at its insertion. M. svupinator.—The supinator muscle is small, flat, and irregularly triangular, and lies on the proximal fourth of the radius. Arising from the lateral epicondyle of the humerus and the lateral collateral ligament of the elbow-joint in association with the common origin of the extensors of the third, fourth, and fifth digits, the muscle is inserted into the anterior surface and medial border of the radius partly under the insertion of the pronator teres muscle. N. RADIALIS PROFUNDUS.—In the dissection of the arm it was seen that the radial nerve divided into deep and superficial branches. The deep radial nerve crosses the flexor aspect of the elbow-joint under cover of the radial extensor and supinator muscles. Inclining laterally, it then passes between the radius and the extensors of the third, fourth, and fifth digits to end in the ulnar extensor of the carpus. Dissection.— Before removing the skin from the palmar aspect of the manus, observe the presence of callosities similar in position and form to the five eminences encountered in the pelvic limb. In addition there is a sixth callosity present in a line with, but immediately distal to, the prominence caused by the pisiform bone. When the callosities have been examined the skin should be removed and the characters and connections of the fascia noted. Fascta.—The fascia at the back of the forearm may be divided into two layers. The more superficial of the two is the looser, and is continuous with the fascia of the arm. The deeper and denser layer is more limited to the forearm itself. It forms a tough investment for the muscles of the region, and sends septa between the individual members of the group. The fascia of the forearm is especially strong and tendinous in character close to the carpus. Here a band of it passes under the annular ligament (from the carpus to tendon of superficial flexor of the digits) and is partly attached to the medial border of the carpus and partly continued to the dorsal aspect of the manus. Over the DISSECTION OF THE DOG 135 projecting extremity of the pisiform bone it forms a transverse band associated with the tendon of the ulnar extensor. Between the fascia and the bone there is a synovial membrane, already mentioned. The fascia of the palmar aspect of the manus is connected intimately with the various callosities and with the annular bands of the flexor tendons. SUPERFICIAL VEINS OF THE PALM.—The proper digital veins unite with a venous arch at the distal part of the metacarpus. From the radial end of the arch there arises a large vessel which forms the root of the ulnar vein and one of the roots of the radial vein. At the ulnar extremity of the arch the superficial veins communicate with the deep vessels. As in front, so at the back of the forearm the muscles are arranged in two layers. The superficial layer contains four muscles which, enumerated from the medial towards the lateral side, are as follows: Mm. pronator teres, flexor carpi radialis, flexor digitorum sublimis, and flexor carpi ulnaris. Strictly speaking, however, the ulnar flexor has only one of its heads, and that the smaller, in the superficial layer. The humeral head of the muscle really forms an intermediate layer, and is to be sought for underneath the superficial flexor of the digits. M. PRONATOR TERES.—The round pronator is placed on the medial side of the elbow-joint, and, with the supinator muscle, circumscribes a triangular space the base of which is proximal. In the triangle are found the insertions of the brachial and biceps muscles, the median and deep radial nerves, and the brachial vessels. The pronator teres muscle has origin from the medial epicondyle of the humerus, and is inserted about the middle of the medial border of the radius superficial to the attachment of the supinator. M. FLEXOR CARPI RADIALIS.—The radial flexor of the carpus is a relatively small muscle arising from the medial epicondyle of the humerus between the pronator teres and the flexor digitorum profundus. About the middle of the forearm the muscle is succeeded by a thin rounded tendon which, after crossing the flexor aspect of the carpus, divides into two parts to be inserted into the bases of the second and third metacarpal bones. A reinforcing band leaves the middle of the medial border of the radius and joins the tendon of this muscle. M. FLEXOR DIGITORUM SUBLIMIS.—The superficial flexor of the digits is a large flattened muscle separated from the foregoing by a narrow strip of the deep flexor. Its origin is from the medial humeral epicondyle. In the distal part of the forearm a strong tendon passes over the flexor aspect of the carpus just medial to the pisiform bone. Arriving in the palmar region this divides into four parts, each of which, after splitting for the passage of the deep flexor tendon, finds insertion into the second phalanx of a digit. K4 136 DISSECTION OF THE DOG At the carpus three strong fibrous bands join the superficial flexor tendon. The first passes from the medial border of the carpus; the second is derived from the pisiform bone; and the third from the sesamoid at the medial side of the carpus connected with the tendon of the abductor pollicis longus. In the palm the flexor tendons are contained in flexor sheaths comparable to those of the pes. Slips to the callosities of the digits leave the tendons on a level with the metacarpo-phalangeal joint. Close to the carpus a separate tendinous and feebly muscular slip branches off from the lateral border of the flexor tendon of the fifth digit and ends in a transverse thickening of the flexor sheath opposite the metacarpo-phalangeal joint. M. FLEXOR CARPI ULNARIS.—This really consists of two separate muscles. The more superficial and the weaker head (caput ulnare) arises from the olecranon and is inserted into the pisiform bone by a thin flattened tendon which begins about the middle of the forearm. The deep, strong humeral head (caput humerale) lies mainly under cover of the flexor digitorum sublimis. It arises from the medial epicondyle of the humerus, and is inserted into the pisiform bone by a very short, strong tendon. The humeral head is anterior to the ulnar at its origin; but the ulnar head passes obliquely across the lateral surface of the humeral head, with the result that the small ulnar tendon is inserted into the pisiform in front of the stout humeral tendon. At their insertion a small synovial bursa intervenes between the two tendons. The deep layer of muscles consists of mm. flexor digitorum profundus and pronator quadratus. Dissection.—In order to follow the deep flexor tendons it is necessary to cut across the superficial flexor about the end of its fleshy belly. Liberate the tendon from its accessory slips derived from the carpus, and turn it downwards. At the carpus the superficial and deep flexor tendons are separated by a strong transverse band passing from the pisiform to the medial border of the carpus. This must be divided. Reflect the two heads of the flexor carpi ulnaris. M. FLEXOR DIGITORUM PROFUNDUS.—The deep flexor of the digits has three independent fleshy bellies. The largest, the humeral head, arises from the medial epicondyle of the humerus. The ulnar head—second in point of size—has origin from the proximal half of the ulna. The radial head is slender and springs from the middle two-fourths of the medial border of the radius. The tendons of the three heads join a short distance proximal to the carpus. The common tendon passes down the flexor side of the carpus, and, arriving in the palm, divides into four parts, each inserted into the terminal phalanx of a digit. DISSECTION OF THE DOG 137 A very small, variable muscular slip, sometimes difficult of demonstration, leaves the humeral head of the deep flexor in the distal third of the forearm and has been considered as homologous with the m. palmaris longus of man. Its very thin tendon soon divides into two parts which accompany the common tendon of the deep flexor into the palm, and terminate at the metacarpo- phalangeal joint by uniting with the superficial flexor tendons of the third and fourth digits. M. PRONATOR QUADRATUS.—The quadrate pronator muscle consists of transverse fibres crossing from the radius to the ulna and filling the inter- osseous space except at its ends. N. mepIanus.—The median nerve enters the forearm by passing between the pronator teres and the proximal end of the radius. It follows the humeral head of the deep flexor, and is related superficially to the flexor carpi radialis. In the distal half of the forearm the nerve occupies a groove formed by the humeral and radial heads of the deep flexor. Finally, crossing the flexor aspect of the carpus, between the tendons of the superficial and deep flexors, it ends as the volar metacarpal nerves (nn. metacarpei volares) of the first, second and third digits, which gain these by coursing between the first and second, second and third, and third and fourth metacarpal bones. The following arise from the median nerve: (1) A branch is contributed to the pronator teres just before the median passes under this muscle. (2) Under the pronator teres a large nerve arises for the supply of the radial flexor of the carpus, the superficial flexor of the digits, and the humeral head of the deep flexor. (3) A small branch accompanies the common interosseous artery for a short distance, and terminates in the pronator quadratus and radial head of the deep flexor of the digits. (4) A small branch supplies the muscular slip which has been thought homologous with the m. palmaris longus of man. N. utnaris.—The ulnar nerve gains the forearm by traversing the interval between the two heads of the flexor carpi ulnaris. It then travels towards the carpus on the deep flexor of the digits (numeral head) and under cover of the humeral head of the ulnar flexor of the carpus. Gaining the metacarpus by crossing the medial aspect of the pisiform bone, the ulnar nerve ends by dividing into a superficial and a deep branch. The branches of the nerve are as follows: (1) As the ulnar nerve is entering the forearm it gives off a bunch of branches to the flexor carpi ulnaris and the humeral and ulnar heads of the deep flexor of the digits. (2) A dorsal branch (ramus dorsalis) arises in the proximal third of the forearm, becomes superficial on the ulnar border of the limb just above the carpus, runs along the lateral border of the carpus and metacarpus, and ends over the fifth digit. (3) Terminal branches. Of these, the deep ramus (ramus profundus) disappears from view almost at once, and must, therefore, be followed later. The superficial branch (ramus superficialis) passes along the lateral border of 138 DISSECTION OF THE DOG n, medianus----~fP JF-- 7-777 n, ulnaris Sees, Ramus superficialis —---- Ramus profundus nn, melacarpet <== volares I, II, et III “~~~ n. digitalis volaris --- lateralis digiti V n. metacarpeus ~ volaris IV = nn, digitales ==svolares communes IL, III, e IV Fia. 52.—Diagram of nerves on the volar aspect of the manus. the flexor tendons and divides into two parts, of which one supplies the fifth digit, and the other follows the groove between the fourth and fifth metacarpal bones to join a part of the ramus profundus. A. MEDIANA.—The _bra- chial artery proceeds from the arm into the forearm by following the median nerve under the pronator teres, and so becomes the median artery. About the junction of the proximal and middle thirds of the forearm the median terminates by divid- ing into two vessels of unequal size—the radial and ulnar arteries. The collateral branches of the median artery are (1) articular to the elbow-joint ; (2) muscular to the flexors ; and (3) the common inter- osseous artery (a. interossea communis). The common interosseous artery leaves the median a short distance distal to the elbow-joint and soon divides into a dorsal and a volar branch. The dorsal inter- osseous artery (a. interossea dorsalis) at once pierces the interosseous membrane _be- tween the radius and the ulna, and thus gains the dorsal aspect of the forearm. Here it is continued distal- wards between the extensor carpi ulnaris and the exten- DISSECTION OF THE DOG 139 sor digiti quinti towards the carpus, where it assists the proximal col- lateral radial artery and the radial artery in the formation of the rete carpt dorsale. The volar interosseous artery (a. interossea vola- ris) is much larger than the dorsal artery of the same name, and follows the interosseous space under cover of the pro- nator quadratus muscle. Just above the carpus a moderately large branch is contributed to the rete carpi dorsale. In the re- gion of the carpus the artery comes into rela- tionship with the ulnar nerve, and medial to the pisiform bone it contri- butes a superficial branch which runs along the fifth digit. The continuation of the artery sinks into the deeper structures and will be followed later as the main contributor to the deep volar arch (arcus volaris profundus). A. RADIALIS. — The radial artery is much the ' smaller of the two ter- minal branches of the median. Following first the radial head of the deep flexor and then the medial border of the radius, it terminates just proximal to the carpus by a ; a. collateralis radialis : | ---b--- prozimalis, Ramus a, interossea.-. --i lateralis dorsalis 4 f | ) : L-—--a, radialis ~= 5200, digitales dorsales a communes aa, metacarpee dorsales. <5. RS » Fig. 53.—Diagram of the arteries on the dorsum of the manus. 140 DISSECTION OF THE DOG a a 2 a fy : | P4-4----a. ulnaris Le | ~-(---- a. tnterossea volaris _ arcs volaris profundus - aa. digitales volares <7 — communes Sea Fia. 54.—Diagram of the volar arteries of the manus. dividing into a dorsal and a volar branch. The former assists in the form- ation of the rete carpi dorsale; and the latter is concerned in the pro- duction of the deep volar arch. A. ULNARIS.—The ul- nar artery is so much larger than the radial that it might be regarded as the direct continuation of the median. It follows the median nerve along the medial border of the deep flexor, and crosses the flexor aspect of the carpus into the meta- carpus between the super- ficial and deep flexor tendons. Just above the carpus there is a slender communication between the ulnar and_ radial arteries. In the meta- carpus the ulnar artery contributes a common volar digital artery to the first digit ; and then ends about the middle of the metacarpus by dividing into common volar digitals for the second, third, and fourth digits (aa. digitales volares communes _ II, III, et IV). Each com- mon artery is joined by a communicating branch from the dorsal common digital artery, and then divides at the end of the metacarpus into two DISSECTION OF THE DOG 141 branches for the adjacent borders of neighbouring digits (aa. digitales volares proprie). MM. LUMBRICALES.—Three slender lumbrical muscles arise from the palmar aspect of the deep flexor tendon and lie between the tendinous slips belonging to second, third, fourth, and fifth digits. The middle muscle of the three is the best developed. Their fine tendons are inserted into the radial side of the proximal end of the first phalanx of the third, fourth, and fifth digits. Dissection.—Cut across the deep flexor tendon on a level with the carpus. This will allow of the dissection of the deep muscles, etc., of the palm. Mm. INTEROSSEI.—There are four fleshy and moderately large interosseous muscles lying over the second, third, fourth, and fifth metacarpal bones and in the grooves between them. They arise from the volar aspect of the distal row of the carpus and from the proximal end of the metacarpal bones. Each muscle divides into medial and lateral parts and is inserted to a pair of meta- carpal sesamoid bones. In addition tendinous cords are continued to the common extensor tendon. SHORT MUSCLES OF THE FIRST bDIGIT.—Three small, short muscles are connected with the first digit. The most medial, m. abductor pollicis brevis et opponens pollicis, is rudimentary and arises from the band which leaves the sesamoid bone at the medial side of the carpus to join the tendon of the super- ficial flexor. The abductor and opponens muscle is inserted into the distal part of the first metacarpal bone and the proximal phalanx of the first digit. M. flexor pollicis brevis is better developed than the foregoing, to the lateral side of which it lies, and arises from the volar aspect of the carpus. The muscle is inserted into the proximal phalanx of the first digit. The third short muscle of the pollex, m. adductor pollicis, is the largest of the three. Its origin is from the volar surface of the carpus between the foregoing and the interosseous muscle of the second digit, and its insertion is into the lateral face of the proximal phalanx of the first digit. M. apDUCTOR DIGITI sECUNDI.—The adductor muscle of the second digit is thin and narrow. Lying along the lateral border of the interosseous muscle of the second digit, it has origin from the volar face of the carpus, and is inserted into the first phalanx of the second digit. SHORT MUSCLES OF THE FIFTH DiGIT.—Four short muscles are connected with the fifth digit. One of these, the interosseous, has already been described. M. adductor digiti quintt arises from the flexor aspect of the carpus close to the origin of the adductor of the second digit. Crossing the interosseous muscles of the third and fourth digits obliquely, it gains the first phalanx of the fifth digit by sinking between the fourth and fifth interosseous muscles. M. abductor digitt quintet —The abductor is the largest of the three muscles now under consideration. It lies immediately under the skin on the lateral border of the carpus. The relatively thick fleshy belly arises from the pisiform 142 DISSECTION OF THE DOG bone and gives place to a thin tendon at the proximal part of the metacarpus. The insertion of the abductor is into the lateral aspect of the base of the first phalanx of the fifth digit, and into the lateral sesamoid bone. M. flexor digiti quinti brevis —The short flexor lies medial to the abductor, and has origin from the strong ligamentous band which joins the pisiform bone to the third and fourth metacarpals. Its slender tendon joins that of the abductor. Dissection.—The deep vessels and nerves of the palm must now be examined. The continuation of the ulnar artery runs under the ligamentous band which joins the pisiform to the third and fourth metacarpal bones, and then under the short flexor of the fifth digit. To follow it, it is necessary to reflect the adductors of the second and fifth digits as well as the interosseous muscle of the second digit. This dissection will also expose the continuation of the ulnar nerve. ARCUS VOLARIS PROFUNDUS.—The deep volar arch is formed under the short muscles of the digits in the proxima! third of the metacarpus, by the union of the continuation of the ulnar artery and the termination of the radial artery. The radial artery gains the arch by passing under the short muscles of the first digit. From the arch arise volar metacarpal arteries (aa. metacarpez volares IT, III, et IV) which run distalwards between the second and third, third and fourth, and fourth and fifth metacarpal bones. The third artery is the largest and most superficial. At the distal end of the metacarpus the volar metacarpal arteries are connected with the common dorsal digital arteries. RaMUS PROFUNDUS OF THE ULNAR NERVE.—The deep branch of the ulnar nerve follows the ulnar artery into the palm and is there related to the deep volar arch. Filaments are supplied to the deep muscles of the palm, and three common volar digital nerves (for the second, third, and fourth digits) are also furnished. The common volar nerves follow the arteries of the same name, and, at the distal end of the metacarpus, divide into the proper digital nerves (nn. digitale proprii) for the adjacent sides of neighbouring digits. Dissection.—It now only remains to examine the various joints of the limb. Remove the muscles and remains of fascia, etc., and begin the dissection of the articulations with the shoulder-joint. ARTICULATIO HUMERI.—The necessity for many or powerful ligaments in connection with the shoulder-joint is obviated by the numerous strong muscles closely surrounding the articulation. Indeed there is only a joint- capsule (capsula articularis) attached to the margin of the glenoid cavity of the DISSECTION OF THE DOG 143 scapula and to the head of the humerus. Strengthening bands leave the base of the coracoid process of the scapula and proceed to the tuberculum majus and tuberculum minus of the humerus. It will be noticed that a mem- branous ligament stretches from the acromion to the capsule. The capsule should be opened in order to allow investigation of the synovial membrane down the intertubercular sulcus in connection with the biceps tendon of origin. ARTICULATIO CUBITI.—The term ‘ elbow-joint,’ strictly speaking, includes three joints: the humero-radial articulation (articulatio humero-radialis), the humero-ulnar articulation (articulatio humero-ulnaris), and the proximal radio-ulnar articulation (articulatio radio-ulnaris proximalis). Capsula articularis—The joint-capsule, surrounding all three components of the elbow-joint, is strong in front where it is associated with the annular radial ligament, but weak and roomy behind where it is supported by the triceps and anconeus muscles. Ligamentum collaterale ulnare.—The ulnar collateral ligament springs from the medial epicondyle of the humerus and divides into two parts. One limb is attached to the border of the radius, while the other is connected with both radius and ulna. Ligamentum collaterale radiale—The radial collateral ligament leaves the lateral epicondyle of the humerus and, like the ulnar ligament, divides into two portions. One of these, the shorter and the stronger, ends on the lateral part of the head of the radius. The other, longer, weaker and more diffuse, joins the border of the ulna. Ligamentum annulare radii.—The radial annular ligament is essentially a thickening of the joint-capsule on the flexor aspect of the articulation. Attached to the lateral part of the head of the radius, it crosses over to unite with the tendons of insertion of the brachial and biceps muscles by which it is fixed to the ulna. From the middle of the ligament an offshoot, firmly adherent to the capsule, proceeds in a proximal direction to the humerus. Membrana interossea antibrachit—The interosseous membrane consists of short fibres passing between the two bones of the forearm. ARTICULATIO RADIO-ULNARIS DISTALIS.—The joint between the distal end of the radius and ulna is enclosed in a joint-capsule which consists mainly of ligamentous bands on the dorsal and volar aspects of the joint. ARTICULATIO RADIO-CARPEA.—Uniting the bones of the forearm to the 144 DISSECTION OF THE DOG proximal row of carpal bones are four ligaments which together close in the joint on all sides and form a capsule. Ligamentum radio-carpeum dorsale-——The dorsal radio-carpal ligament is thin and membranous, and passes from the dorsal aspect of the distal end of the radius to the cuneiform and scapho-lunar bones. Ligamentum radio-carpeuwm volare—The volar radio-carpal ligament, dis- posed similarly to the dorsal ligament, is thick and strong. In association with it there are two definite bands. One runs from the radius to the scapho-lunar bone: the other, very oblique in direction, unites the ulna to the scapho-lunar. Small bundles of fibres also end on the pisiform bone. Ligamentum collaterale carpi ulnare.—A not very well defined ulnar collateral ligament joins the ulna to the cuneiform. A few fibres may be continued to the fifth metacarpal bone. Ligamentum collaterale carpi radiale—Much better marked than the ulnar ligament, the radial collateral passes from the styloid process of the radius to the tubercle on the scapho-lunar. ARTICULATIO OSSIS PISIFORMIS.—The pisiform bone is held in position by five bands which connect it with (1) the ulna; (2) the scapho-lunar ; (3) the cuneiform (ligamentum piso-hamatum); (4) the fifth metacarpal bone (ligamentum piso-metacarpeum) ; and (5) the third and fourth metacarpal bones. LIGAMENTA INTERCARPEA.—The individual bones of the carpus are joined together by dorsal, volar, and interosseous intercarpal ligaments. The dorsal ligaments (ligamenta intercarpea dorsalia) are six in number. One joins the scapho-lunar and cuneiform, and three unite the members of the distal row of bones. Of the remaining two, one runs from the cuneiform to the unciform ; the other from the scapho-lunar to the trapezoid. The volar ligaments (ligamenta intercarpea volaria) are also six and have the same connections as the dorsal ligaments, except that the more medial of the two joining the two rows of bones passes from the scapho-lunar to the magnum and trapezoid. The interosseous ligaments (ligamenta intercarpea interossea) are concerned with the union of the different members of the same row of bones; that is, there are no interosseous ligaments running from one row to the other. ARTICULATIONES CARPO-METACARPE.—The four members of the distal row of carpal bones are joined to the bases of the five metacarpal bones by dorsal and volar ligaments. The remaining articulations of the manus are similar to the corresponding joints of the pes. Dissection.—Clean up the dorsal part of the chest wall and the lumbar DISSECTION OF THE DOG y 145 region. Note the cutaneous branches of the intercostal nerves and the vessels accompanying them. The two dorsal serratus muscles demand first attention. M. SERRATUS DORSALIS CRANIALIS.—The cranial dorsal serratus muscle springs by a broad, thin aponeurosis from the ligamentum nuche and the spinous processes of the first six or seven thoracic vertebre. The fibres run in a ventral and caudal direction to be inserted by digitations into the ribs from the second or third to the ninth or tenth. M. SERRATUS DORSALIS CAUDALIS.—The caudal dorsal serratus muscle arises from the dorso-lumbar fascia. Its fibres have the same direction as those of the internal oblique muscle of the abdomen, with which it appears to be continuous. The insertion of the muscle is into the last three ribs. Dissection.—Reflect the dorsal serratus muscles. M. LONGISSIMUS DORSI, ETC.—A powerful muscular mass lies in the groove formed by the transverse and spinous processes of the lumbar vertebre. On a level with the last rib the mass divides into three muscles : ilio-costalis, longissimus dorsi, and spinalis dorsi et cervicis. M. IL10-cosTauis.—The ilio-costal muscle leaves the common mass about the last rib, and has attachments by independent tendons to the ribs about their angles and the transverse processes of the last two or more cervical vertebre. Each tendon passes over one or two ribs before finding insertion. Slips from all the ribs except the first four or five join the muscle as it runs along the wall of the chest. M. LoNGissimus DoRsI.—The fibres of this powerful muscle arise from the ventral surface and crest of the ilium, and are attached to the transverse processes of the lumbar, thoracic, and last cervical vertebre, to the spinous processes of the lumbar and thoracic vertebre, and to the ribs. M. SEMISPINALIS DORSI ET CERVICIS cannot be completely examined at the present time. Dissection.—Remove the longissimus dorsi muscle. In doing so, observe the muscular branches of the dorsal rami of the intercostal and lumbar arteries. M. mvuytiripus.—A series of small muscles, larger in the lumbar than in the thoracic region, arise from the sacrum and the articular and transverse processes of the lumbar and thoracic vertebra, and are inserted into the spinous processes of these vertebrae. Each muscle passes over one spinous process before its insertion. M. suBMULTIFIDUS.—In the thoracic region it is customary to find yet shorter muscles underneath the multifidus. The bundles of the submultifidus muscle pass from the transverse process of a vertebra to the spinous process of the one immediately preceding it. 146 DISSECTION OF THE DOG Mm. LEVATORES CosTaRrUM.—The levators of the ribs are a series of small muscles arising from the transverse processes of the thoracic vertebre. The fibres of each muscle run in a caudal and ventral direction to be inserted into the cranial border of the rib succeeding the vertebra from which they have taken origin. Dissection.—The muscles of the tail should now be cleaned and examined. Mm. SACRO-COCCYGEUS DORSALES.—The dorsal sacro-coccygeal muscles are two in number, a medial and a lateral. The medial muscle arises from the spinous processes of the lumbar, sacral, and first coccygeal vertebre, and is inserted into the dorsal surface of the coccygeal vertebre. The lateral muscle springs from the articular processes of the last three lumbar and all the sacral vertebre, and from the transverse process of the first coccygeal vertebra. Rounded tendons pass over several vertebre and are inserted into the dorsal aspect of all the bones of the tail. M. SACRO-COCCYGEUS ACCESSORIUS.—The accessory sacro-coccygeal muscle may possibly represent the intertransverse muscles of other regions. It is a rounded muscle lateral in position to the preceding and with origin from the dorsal border of the ilium, the lateral border of the sacrum, and the transverse process of the first coceygeal vertebra. The insertion is into the side of the tail vertebra. M. coccyarus.—The coccygeal muscle has already been examined. MM. SACRO-COCCYGEUS VENTRALES.—As on the dorsal, so on the ventral side of the tail, there are medial and lateral muscles. The lateral ventral sacro-coccygeal muscle arises from the ventral face of the last lumbar vertebra, the sacrum, and the transverse processes of coccygeal vertebre. By long tendons the muscle is inserted into the ventral surface of the bones of the tail. The medial muscle springs from the ventral surface of the sacrum and the first coccygeal vertebra, and is inserted into the corresponding aspect of the tail vertebre. Dissection.—Reflect the skin from the ventral side of the neck and the mandibular region. Secure the previously detached manubrium of the sternum and the first costal cartilage, so as to keep the ventral cervical muscles on the stretch. Then clean up the external jugular vein on the side from which the limb has been removed. V. JUGULARIS EXTERNA.—The external jugular, much larger than the internal vessel of the same name, is the main vein of the neck. Formed at the aboral border of the submaxillary gland by the union of the external and internal DISSECTION OF THE DOG 147 maxillary veins, the external jugular crosses the surface of the sterno-cephalic muscle to assist the subclavian in the formation of the innominate vein. The following tributaries join the jugular at different points in its course : (1) Small veins from the skin; (2) a large and a small communicating branch from the cephalic vein of the arm; (3) the companion vein of the ascending cervical artery ; (4) the companion vein of the transverse scapular artery. m. splenius ! t I i : 58 ! m, biventer cervicis ! l Plexus brachialis t 1 I ' 1 ' m. completus n. thoracalis longus i) / / nets m. serratus dorsalis m., longissimus i} ' \ 1 \ 1 1 P 7 ! H / 7 capitis 1 ' / t m. serratus ventralis ' m. pectoralis profundus | ' ! ' | ! / ‘. / Yom. longissimus ! | ; 7 Be 1 cervicis Zi ! N. accessorius ———-— — ~>"~-. aa eae if é ) ' i se “ / ae 3 ' m. omo-transversarius -— ——— —— —-—-~ a J: i / H m. deido-mastoideus —-~— —-_.+_-__-~- ‘ ie e i / / ! / / : / / / # m. sterno-cephalicus - ~——-—— ye / \ / . , oe Ss / n, vagus et truncus ~« 7 7 , sympathicus ~~ ~—~~~~ / af ee { a, carotis — -—_____=> Tay, i f , 4% / v. jugularis interna ~-~ 7 z \ / i / », jugularis externa” ~~ ~~ ae \ if mm. sterno-hyoideus et — ~~~ ~~ 77, a ' sterno-thyreoideus see N ! i a, axillaris ~ # 7 i ! ' ‘ 7 / H : m. pectoralis superficialis yt | ! 7 [ m. transversus costarum” H i f 4 f ' | ' m. scalenus ! ! ! ' t t 1 f ' m. obliquus abdominis externus Fic. 55.—Dissection of the side of the neck and thorax. Very commonly the two Jast named unite to form an omo-cervical trunk which, in its turn, joins the jugular. . V. MAXILLARIS EXTERNA.—The external maxillary vein drains the blood from the face, the tongue, and the mandibular region. The main root is formed by the common facial vein which will be found in the groove between the masseter and digastric muscles. About the ventral border of the sub- maxillary gland the facial vein receives the common trunk formed by the union of the lingual and sublingual veins, and then changes its name to that of external maxillary vein. L2 148 DISSECTION OF THE DOG The lingual vein appears in the angle formed by the borders of the mylo- hyoid and digastric muscles, and is at once joined by a transverse vessel which passes across from one lingual vein to the other. . A group of lymph-glands (lympho-glandule submaxillares) are present about the point of junction of the facial vein and the common trunk of the lingual and sublingual veins. V. MAXILLARIS INTERNA.—The internal maxillary vein is formed under cover of the parotid gland, and is only visible, at the present stage of the dissection, as it runs along the aboral border of the submaxillary gland to unite with the external maxillary vein. Dissection Cut across the sterno-cephalic muscle a little distance from its sternal attachment and turn it aside. This will permit of the demon- stration of the common carotid artery, the internal jugular vein, the vagus and sympathetic nerves, as well as certain muscles. M. sTeRNo-HyorDEUS.—The sterno-hyoid muscles of opposite sides of the neck lie in contact with each other in the middle line. Each takes origin from the manubrium of the sternum and is inserted into the body of the hyoid bone. M. sTERNO-THYREOIDEUS.—In the region of the sternum the sterno-thyroid muscle is almost completely covered by the preceding ; but, owing to a diver- gence of the two sterno-thyroid muscles they are exposed more and more in their course to the larynx. The sterno-thyroid muscle has origin from the manubrium of the sternum and from the first costal cartilage, and is inserted into the aboral border of the thyroid cartilage about its middle. It should be noted that, a short distance from their origins, the above muscles are crossed transversely by a tendinous intersection ; and that at this line the two muscles of the same side of the neck are intimately connected with each other. The nerve supply of the sterno-hyoid and sterno-thyroid muscles is largely from the ventral division of the first cervical nerve ; but with this the descending branch of the hypoglossal nerve is blended. The composite nerve will be found along the lateral border of the muscles. V. JUGULARIS INTERNA.—The internal jugular vein is a vessel of small and variable size lying, in the main, lateral to the common carotid artery. Not only does the size of the vein vary in different animals, but the two vessels of the same animal are not necessarily of the same calibre. The origin of the internal jugular may be traced to the occipital and cerebral veins. Accompanying the common carotid artery, the vein is close to the trachea on the right side of the neck, and to the cesophagus on the left. It ends by joining either the innominate vein or the external jugular of its own side. The internal jugular receives the cranial and caudal thyroid, muscular, tracheal, and cesophageal veins. DISSECTION OF THE DOG 149 A. CAROTIS CoMMUNIS.—The two common carotid arteries leave the brachio- cephalic at no very great distance from each other. The right artery runs obliquely lateralwards across the ventral surface of the trachea, and then along the lateral face of this tube. The left artery has a similar relation to the trachea about the thoracic inlet, but in the neck it is in contact with the cesophagus. Each artery is in relation dorso-laterally with the combined trunk of the vagus and sympathetic nerves. On a level with the wing of the atlas the common carotid artery divides into external and internal carotid and occipital arteries. The collateral branches of the artery are: (1) The caudal thyroid artery (a. thyreoidea caudalis), a small vessel arising at the entrance to the chest and accompanying the recurrent nerve up the neck to end in the thyroid gland; (2) the cranial thyroid artery (a. thyreoidea cranialis), an artery of some size supplying the thyroid gland and contributing the ascending pharyngeal artery (a. pharyngea ascendens), muscular (rami musculares) and glandular (rami glandulares to the submaxillary gland) branches; (3) the laryngeal artery (a. laryngea), a small vessel ramifying in the larynx. N. vacus ET TRUNCUS SYMPATHICUS.—The thick nerve cord lying dorsal and lateral to the common carotid artery is formed on a level with the wing of the atlas by the union of the vagus nerve and the cervical cord of the sympathetic. These are bound together by strong connective tissue. N. RECURRENS.—The recurrent nerve, a branch of the vagus already encountered in the chest, follows the lateral aspect of the trachea and ends in the larynx. In the neck the nerve supplies branches to the trachea and ceso- phagus (rami tracheales et cesophagei). M. MyLo-HyoipEus.—Lying in the space between the two halves of the mandible, the mylo-hyoid is a flat, broad, thin muscle composed of transverse fibres arising from the mylo-hyoid line close to the alveolar border of the mandible. The fibres join a raphe in the middle line, as well as the symphysis of the mandible and the body of the hyoid bone. Dissection.—Turn the manubrium of the sternum, with the muscles attached thereto, as far as possible towards the head, and so expose the trachea and cesophagus. TracHEA.—The trachea is an almost cylindrical tube extending from the larynx to a point opposite the fourth rib, where it divides into the two bronchi. The lumen of the tube is not quite uniform on account of a certain amount of narrowing from the larynx to the thoracic entrance. Nor is the trachea abso- lutely in the middle line since there is some degree of inclination towards the right. At its commencement the windpipe is in contact dorsally with the cesophagus, but later this relation is exchanged for one with the longus colli muscle. The skeleton of the trachea consists of a variable number (thirty-five to forty) L3 150 DISSECTION OF THE DOG of incomplete rings of cartilage (cartilagines tracheales) joined together by membranous annular ligaments (ligamenta annularia). The interruption in the continuity of each ring is placed at the dorsal part of the tube, where transverse muscular fibres occur. The interior of the trachea is lined by a mucous membrane. ; (sorHacus.—The cesophagus is that part of the alimentary canal which intervenes between the pharynx and the stomach. For descriptive purposes it is divided into cervical, thoracic, and abdominal parts (pars cervicalis, pars thoracalis, et pars abdominalis). In the earlier dissections the thoracic and abdominal parts have been exposed and examined. The cervical part is at first in the middle line and immediately dorsal to the trachea, but an inclination towards the left soon becomes noticeable. At the entrance to the chest the cesophagus may be at a level even ventral to that of the trachea. GLANDULA THYREOIDEA.—One of the ductless glands, the thyroid consists of two lateral lobes connected ventral to the trachea by an isthmus of variable dimensions. Frequently the isthmus is absent; but when present, it connects the more caudal part of the two lateral lobes. Each lobe is elongated, with narrow oral and aboral extremities, and lies on the lateral face of the trachea immediately aboral to the larynx (over six or seven tracheal rings). The lateral surface of each lobe is covered by the sterno-cephalic muscle, and its ventral border is in contact with the sterno-thyroid muscle. In association with the thyroid gland are two or more small parathyroids. Dissection.—Remove the skin from the ear and the parotid region. Clean up the auricular nerves, vessels, and muscles. AURIS EXTERNA.—Before commencing the dissection of the muscles of the external ear, it is necessary to have some knowledge of the cartilages to which they are attached. The cartilages of the external ear are three in number—conchal, scutiform, and annular. The conchal cartilage or auricula is the largest, and forms the projecting, conspicuous part of the ear. Its form varies greatly with the breed of the dog ; but, generally speaking, it may be said to have a funnel-like or trumpet-shaped outline. The wide free part of the cartilage has two borders— cranial and caudal—meeting at the tip of the ear. At the base of the cranial border is an irregular projection known as the helix. At the lateral part of the narrow, basal portion of the cartilage is a curved, plate-like projection, the tragus ; and immediately caudal to this an irregular process, the anti-tragus. The scutiform cartilage is in the form of a plate of irregular outline, and lies on the temporal muscle oral to the base of the conchal cartilage. The annular cartilage, as its name implies, is ring-like in form, and is adherent to the margin of the external acoustic meatus of the temporal bone. DISSECTION OF THE DOG 151 M. scUTULARIS.—Medial and oral to the base of the ear is a thin sheet of muscle, the scutular muscle, divisible into two portions: (1) the m. fronto- scutularis, springing from the zygomatic process of the frontal bone and from the orbital band ; (2) the m. interscutularis, thinner than the preceding and continuous with the corresponding muscle of the other ear. The two muscles are inserted into the scutiform cartilage. Mm. auriculares anteriores —There are three auricular muscles lying mainly to the nasal side of the base of the ear. The uppermost (most dorsal) continues the fronto-scutularis from the scutiform cartilage to a fold of skin at the base of the oral border of the conchal cartilage. The middle muscle of the group is very short, and connects the scutiform and conchal cartilages. The lowest (most ventral) muscle has a broad tendinous origin from the fronto-scutularis, sometimes also from the zygomatic muscle, and is inserted into the antitragus. M. AURICULARIS INFERIOR.—The inferior auricular muscle is narrow and long, and lies over the parotid and submaxillary glands. Arising from the fascia over the region of the larynx, its insertion is into the conchal cartilage close to that of the lowest anterior auricular muscle. MM. AURICULARES POSTERIORES.—Three muscles fall within this group. One of them is the long levator; the others are the long and short abductors. The long levator rises from the mid-dorsal line of the neck, and is inserted into both conchal and scutiform cartilages. The long levator is aboral to the interscutular muscle and in the same plane, and the two muscles are more or less continuous. Dissection.—Reflect the scutular and long levator muscles. MM. AURICULARES SUPERIORES.—The superior group of muscles contains a short and a middle levator. The short levator arises from the scutiform cartilage and passes to the conchal cartilage. The middle levator lies under cover of the interscutular and long levator muscles, and takes origin from the sagittal crest. The muscle divides into two parts, and its fibres are partly inserted into the conchal and partly into the scutiform cartilage. The long abductor muscle arises from the ligamentum nuche, and is inserted into the lateral aspect of the conchal cartilage. Dissection.—Reflect the middle levator and long abductor muscles. The short abductor takes origin from the occipital bone, and passes to the medial side of the base of the conchal cartilage. Mm. ‘AURICULARES PROFUNDI.—The deep auricular muscles consist of two rotators—long and short—placed underneath the scutiform cartilage and running from this to the conchal cartilage. M. rracicus.—The tragicus muscle is divided into two parts—lateral and medial. L4 152 DISSECTION OF THE DOG M. tragicus lateralis springs from the border of the mandible between the condyloid and angular processes. M. tragicus medialis joins the tragus to the base of the conchal cartilage. M. HELIcIs joins helix and antitragus. M. TRANSVERSUS AURICUL®.—The transverse muscle is a band of fibres lying on the conchal cartilage close to the insertion of the long levator. M. ANTITRAGICUS consists of a few fibres placed immediately aboral to the attachment of the inferior auricular muscle, and runs from the tragus to the antitragus. A. AURICULARIS POSTERIOR.—The main artery of the external ear is the posterior auricular, a branch of the external carotid. Commencing on a level with the hyoid bone, this artery runs to the base of the ear underneath the parotid gland, and is distributed to the aboral and medial portions of the ear. A. AURICULARIS ANTERIOR.—The anterior auricular artery is a branch of the superficial temporal from which it is derived on a level with the zygoma. The vessel ramifies over the oral and medial parts of the external ear. N. AURICULARIS POSTERIOR.—The posterior auricular nerve leaves the seventh cerebral nerve under the parotid gland and divides into branches which follow those of the posterior auricular artery. N. AURICULARIS INTERNUS.—Also a branch of the seventh cerebral nerve, the internal auricular pierces the deep lateral part of the conchal cartilage in the interior of which it is distributed. The temporal division of the auriculo-palpebral branch of the seventh nerve supplies the oral part of the ear. The auricular branch of the second cervical nerve is distributed over the lateral and aboral part of the ear ; and the occipital branch of the first cervical nerve spreads out over the medial surface. M. occrriratis.—Although not belonging to the ear, the occipital muscle may be examined at this stage of the dissection. The muscle is a narrow, thin band running longitudinally from the superior nuchal line of the occipital bone and the sagittal crest of the parietal into the fascia which is blended with the periosteum of the frontal bone. The muscles of the dorsal part of the neck must now be examined. M. spLenius.—The splenius muscle is triangular, with its apex caudal and its base at the occipital bone. The origin of the muscle extends as far caudal as the fifth or sixth thoracic spinous process, and is continued along the middle dorsal line throughout the cervical region. At first the origin is aponeurotic, but from the first or second thoracic spine onwards it is fleshy. The insertion of the muscle is into the occipital bone and mastoid part of the temporal bone. About the level of the atlas the fibres of the splenius are closely connected ' with the tendon of the longissimus capitis muscle. DISSECTION OF THE DOG 153 M. LONGISSIMUS CERVICIS.—This muscle is immediately ventral to the splenius, and intimately connected with the longissimus dorsi. With an origin from the transverse processes of the first five or six thoracic vertebra, its insertion is into the transverse processes of the last four or five cervical vertebree. Dissection.—Reflect the splenius by cutting through the entire length of its origin. Observe the branches of the cervical nerves. Then reflect the longissimus cervicis by a transverse incision about the middle of the muscle. M. LONGISSIMUS CAPITIS ET ATLANTIS.—These two muscles are readily separated, but are better considered together. The longissimus capitis muscle arises from the transverse processes of three or four thoracic vertebre and from the last three or four cervical articular processes. By union with the splenius the muscle obtains an insertion into the mastoid part of the temporal bone. The longissimus atlantis is a very much smaller muscle than the preceding, and passes from the third, fourth, fifth, and sixth cervical articular processes to the wing of the atlas. M. sEMISPINALIS CAPiITIs.—Dorsal and medial to the preceding in position, the semispinalis muscle of the head consists of two parts—m. biventer cervicis and m. complexus. The former is readily distinguished by the presence of four oblique tendinous intersections. This muscle arises from the spinous processes of the second to the fourth or fifth, and from the transverse processes of the fourth, fifth, and sixth thoracic vertebre, as well as from the ligamentum nuche. The complexus muscle has its origin from the transverse processes of the first two or three thoracic vertebre, and from the articular processes of the last five cervical vertebre. The two parts of the semispinalis muscle may or may not join about the level of the atlas. In any case they are inserted into the occipital bone. Two branches of the second cervical nerve are associated with the biventer cervicis muscle. A large branch pierces the muscle close to its insertion and proceeds to the ear. A much smaller nerve either pierces the muscle close to the middle line, or appears between the muscle and the ligamentum nuche, and ramifies in the skin medial to the base of the ear. Dissection—Cut across the complexus muscle on a level with the joint between the atlas and the epistropheus. Free the biventer cervicis muscle from its origin and turn it towards the head. In reflecting these two muscles the large dorsal primary divisions of the cervical nerves will be observed between the complexus and multifidus muscles. M. SEMISPINALIS DORSI ET CERVICIS.—This muscle, as has previously been noted, is continuous with the longissimus dorsi. It receives a bundle of 154 DISSECTION OF THE DOG fibres from the first thoracic vertebra, and is attached to the articular and spinous processes of the last six cervical vertebree. ‘ M. MULTIFIDUS CERVICIS.—The multifidus of the neck is a continuation of the already examined multifidus muscle of the back, but is much better developed. In position lateral to the semispinalis and underneath the com- plexus, the muscle consists of four or five bundles which run from the articular processes of the last four or five cervical vertebra to the spinous processes of the second, third, fourth, and fifth vertebre of the neck. The dorsal divisions of the cervical nerves appear at the lateral border of the muscle and lie on its superficial surface. MM. INTER-TRANSVERSARII.—The intertransverse muscles of the neck are double, with the ventral primary divisions of the cervical nerves passing between their dorsal and ventral portions. LigaMENTUM NucH#.—The ligament of the nape of the neck is in the form of a flattened, elastic cord extending from the spinous process of the epi- stropheus to the tip of the spinous process of the first thoracic vertebra, where it is continuous with the supraspinous ligament. By careful examination, the dissector can satisfy himself that the ligament consists of right and left halves. Immediately behind the occipital bone there is a group of muscles, the straight and oblique muscles of the head, which connects the atlas and epi- stropheus to the skull. The occipital nerve (a branch of the second cervical nerve) and branches of the occipital vessels cross the muscles superficially. M. RECIUS CAPITIS DORSALIS MAJOR.—The larger dorsal straight muscle of the head is flat and in contact with its fellow of the opposite side. With an origin from the spinous process and possibly also from the adjacent part of the caudal articular process of the epistropheus or second cervical vertebra, its insertion is into the occipital bone immediately ventral to the insertion of the semispinalis capitis. A separable part of the muscle (m. rectus capitis dorsalis medius) arises from the oral extremity of the spinous process of the second cervical vertebra. Dissection.—Reflect the rectus capitis dorsalis major muscle. M. RECTUS CAPITIS DORSALIS MINOR.—This is a small muscle passing from the oral border of the dorsal arch of the atlas to the occipital bone. M. OBLIQUUS CAPITIS CAUDALIS.—Of the two oblique muscles of the head the more caudal is the larger. A powerful muscle springing from the whole of the spinous process of the epistropheus, its fibres run obliquely oral and lateral to be inserted into the wing of the atlas. M. OBLIQUUS CAPITIS CRANIALIS.—Smaller than the preceding, this muscle arises from the oral and lateral border of the wing of the atlas, runs obliquely orally and medially, and is inserted into the mastoid process of the temporal bone. DISSECTION OF THE DOG 155 Dissection—Reflect the longissimus capitis et atlantis muscles. Remove the caudal oblique muscle of the head and the intertransverse muscles in order to show the vertebral vessels and the second cervical nerve. A. VERTEBRALIS.—The vertebral artery is a branch of the subclavian. After leaving the chest, the artery enters the interval between the longus colli and scalenus muscles and gains the transverse foramen of the sixth cervical vertebra. After traversing the foramina in the transverse processes of the cervical vertebra from the sixth to the first, a union is effected under the wing of the atlas with a branch of the occipital artery. The dissection of the face should be commenced by an examination of the external parts of the eye. PaLPEBR#.—The eyelids, using the term in the more usual sense, are two in number: upper (palpebra superior) and lower (palpebra inferior); but to these may be added a much less obvious third eyelid (palpebra tertia). The upper and lower eyelids may be described as membranous curtains arranged for the protection of the eye. The upper lid is the larger and the more movable, and is provided with a special muscle, the m. levator palpebree. superioris, by which it is raised. Each lid has an outer surface (facies anterior palpebre) covered with hair-bearing skin, and an inner surface (facies posterior palpebre) applied to the eyeball and rendered smooth by the conjunctiva, a membrane continued from the lid over the front part of the eyeball. The free borders of the lids (limbi palpebrales) bound the palpebral fissure (rima palpebrarum), which is in the form of a narrow slit when the lids are closed, but assumes an elliptical outline when the eye is open. The free border of the upper eyelid carries a row of long and strong hairs. The two lids are joined at the lateral and medial commissures (commissure palpebrarum lateralis et medialis). Both are acute, and in the neighbourhood of the medial commissure the eyelids circumscribe a space (lacus lacrimalis) in which is a rounded body, the lachrymal caruncle (caruncula lacrimalis). On the margins of the lids near the medial commissure are the small puncta lacrimalia, upper and lower, leading into the lachrymal ducts (ductus lacrimales), by which the tears are drained from the eye. , Each eyelid contains a framework of fibrous tissue, the tarsus, much better developed in the upper than in the lower lid. A sphincter muscle (m. orbicu- laris oculi) is associated with the eyelids, and can be exposed by the removal of the skin over them. In addition, the upper lid and the region of the eyebrow -contain muscular fibres which corrugate the eyebrow (m. corrugator supercilii). The third eyelid consists of a pigmented semilunar fold of conjunctiva, the membrana nictitans, easily demonstrated near the medial commissure, and a 156 DISSECTION OF THE DOG piece of cartilage (cartilago palpebre tertize) which will be examined along with the other contents of the orbit. Dissection.—Remove the skin from the face and proceed to examine the underlying muscles. The nerves and vessels of the face must be carefully preserved. M. zycomaticus.—A narrow, band-like muscle arising from the scutiform cartilage of the ear, the zygomatic crosses the face obliquely and is inserted at the angle of the mouth. M. risorrus.—The risorius muscle is merely that portion of the cutaneous muscle of the face which lies in the region of the angle of the mouth and is inserted close to the termination of the zygomatic muscle. M. QUADRATUS LABII SUPERIORIS.—Covering the side of the nose, the quadrate muscle is divisible into three parts: (1) M. nasolabialis, with fibres arising from the maxillary and frontal bones in the neighbourhood of the medial commissure of the eye, and from the frontal fascia, to end in the substance of the upper lip; (2) m. malaris, thin and connected with the foregoing at its origin, where it blends also with the orbicular muscle of the eye, and confused with the buccinator muscle at its insertion; (3) m. levator labit swperioris proprius, with an origin from the maxillary bone in the region of the infra- orbital foramen, and an insertion about the nostril. M. caninus.—Ventral to the proper levator of the upper lip in position, the canine muscle arises close to the infraorbital foramen and from the canine fossa of the maxillary bone. Its insertion is into the upper lip. M. succinaTorR.—The buccinator muscle consists of two strata: (1) The more superficial stratum contains fibres running obliquely from the alveolar border of the maxilla to the lateral face of the mandible ; (2) the deeper fibres run obliquely downwards and forwards from the maxilla on a level with the last two or three cheek-teeth to the lateral face of the mandible. M. ORBICULARIS ORIS.—A sphincter muscle contained in the lips, the orbicular muscle of the mouth, provides a means by which the lips are approximated and the entrance to the mouth is closed. MM. INCISIVI LABII SUPERIORIS ET INFERIORIS.—The upper and lower incisive muscles are best demonstrated by removing the mucous membrane from the inside of the lips. In dissecting the upper incisive muscle of each side a large branch of the infraorbital nerve is exposed. The muscles consist of bundles of fibres passing into the lips from the incisive bone and the mandible on a level with the second and third incisor and the canine teeth. : M. massETER.—The masseter muscle is powerful and lies over the mandible ventral to the zygomatic arch. A complete examination should be postponed. GLANDULA PAROTIS.—The parotid gland of the dog is relatively small. DISSECTION OF THE DOG 157 Irregularly triangular in outline, with a base notched and embracing the auricle and an apex overlying the submaxillary gland, it is lodged in a depression bounded by the base of the external ear, the masseter muscle, and the wing of the atlas. The lateral surface of the gland is covered by the cutaneous and inferior auricular muscles ; while its deep or medial surface covers the facial nerve, the internal maxillary vein, the base of the external ear, part of the digastric muscle, and part of the submaxillary gland. The great auritular vein runs along its aboral border. m. zygomat tcus ‘ / / n. auriculo-palpebralis. Ramus zygomaticus 1 n. lacrimalis , \ n. frontalis ‘ N m. orbicularis oculi . n. zygomaticus f v, mazillaris interna 1 : t / n. buccalis dorsalis / a. et v. facialis' Ductus parotideus f n. buccalis ventralis’ Lympho-glandule v ' ' t t ' I f / vy. macxillaris externa , Ramus colli Fig. 56.—Superficial dissection of the face. Commencing at the oral border and close to the apex of the gland, and formed by the union of a number of smaller ducts, the parotid duct (ductus parotideus [Stenonis] ) crosses the surface of the masseter muscle, pierces the cheek, and opens into the mouth on a level with the third maxillary premolar tooth. The nerves of the face are derived from two sources: namely, the fifth and the seventh cerebral nerves. NERVUS FACIALIS.—The facial, or seventh cerebral nerve acquires a super- ficial position by emerging between the border of the mandible and the parotid 158 DISSECTION OF THE DOG gland. The following are its superficial branches: (1) The auriculo-palpebrat nerve (n. auriculo-palpebralis), which divides into a temporal ramus (ramus temporalis), supplying the front part of the ear, and a zygomatic ramus (ramus zygomaticus). The latter crosses the zygomatic arch, furnishes twigs to both eyelids, and ends on the side of the nose, where it arrives by curving round.the medial side of the eye. (2) The dorsal buccal nerve (n. buccalis dorsalis) crosses the surface of the masseter muscle and ends in the upper lip; while (3) the ventral buccal nerve (n. buccalis ventralis) follows the ventral border of the muscle and ends in the lower lip. A considerable amount of intercommunica- tion takes place between branches of the two buccal nerves. (4) The smallest superficial branch of the facial nerve—the cervical branch (ramus colli)—pierces the parotid gland and joins the superficial cervical branch of the second spinal nerve. N. rriceminus.—The trigeminal, or fifth cerebral nerve, has not long left the brain before it divides into three parts—the ophthalmic, maxillary, and mandibular nerves—all of which supply branches which should be sought at this stage of the dissection. N. ophthalmicus.—Two branches of the ophthalmic nerve become superficial about the eye: (1) The frontal nerve (n. frontalis) leaves the orbit by bending round the orbital band—a fibrous cord stretching from the zygomatic to the frontal bone—and is expended in the upper eyelid and its neighbourhood, where it assists in the formation of the anterior auricular plexus; (2) the infratrochlear nerve (n. infratrochlearis) appears medial to the eye. N. maxillaris—The maxillary nerve furnishes four branches—two small and two large—to the face: (1) The lachrymal nerve (n. lacrimalis) leaves the orbit lateral to the point of exit of the frontal nerve, and plays a part in the formation of the anterior auricular plexus ; (2) the zygomatic nerve (n. zygoma- ticus) is quite small, emerges from the orbit close to the lateral commissure of the eyelids and ends mainly in the lower eyelid ; (3) the two large infraorbital nerves (nn. infraorbitales) leave the foramen of that name and spread out in the substance of the upper lip and nose. They will receive further attention at a later stage. N. mandibularis——The mandibular nerve contributes three branches to the face: (1) The superficial temporal nerve (n. temporalis superficialis) bends round the border of the mandible and divides into auricular and temporal branches ; (2) the mental nerve (n. mentalis) leaves the foramen of the same name and supplies the lower lip; (3) the buccinator nerve (n. buccinatorius) becomes visible at the oral border of the masseter muscle and ends in the cheek and lower lip, some of its branches joining the plexus formed by the buccal nerves derived from the seventh cerebral nerve. A. FactaLis.—The facial artery will be found in a groove bounded by the masseter and digastric muscles. Its branches are the inferior labial artery (a. labialis inferior), the angular artery of the mouth (a. angularis oris), and the DISSECTION OF THE DOG 159 superior labial artery (a. labialis superior), which ramify in the parts indicated by their names. A. INFRAORBITALIS.—The infraorbital artery leaves the homonymous foramen along with the large nerves of the same name, and terminates in dorsal nasal (a. nasi dorsalis) and lateral nasal (a. nasi lateralis) branches. A. TRANSVERSA FACIEI.—The transverse facial artery, a branch of the superficial temporal, is generally a very small vessel which crosses the surface of the masseter muscle. ; V. FACIALIS ET V. MAXILLARIS EXTERNA.—The facial vein is formed by the union of the angular vein of the eye and the dorsal nasal vein. Running down the face, it receives the superior labial, reflex, buccinator, and inferior labial veins, and becomes the external maxillary vein on a level with the inferior border of the mandible. Instead of joining the facial vein directly, the buccinator may unite with the inferior labial. The external maxillary vein will be found in the groove between the mas- seter and digastric muscles. It runs backwards ventral to the submaxillary gland, and ends by uniting with the internal maxillary vein to form the external jugular. The main collateral tributaries of the external maxillary vein are the deep facial and the lingual. The former appears at the oral border of the masseter muscle. The lingual vein joins the external maxillary just before this flows into the jugular. A transverse vessel, on a level with the body of the hyoid bone, forms a link between the lingual veins of the two sides of the head. Dissection.—The parotid gland must now be removed with great care. When this has been done, the origin of those branches of the facial nerve which have recently been examined in connection with the face will be exposed. M. MaAssETER.—The powerful masseter muscle completely fills the con- siderable depression ventral to the zygomatic arch. Very tendinous in structure, its origin is from the whole of the ventral border and the immediately adjacent medial surface of the zygomatic processes of the zygomatic and temporal bones. On account of a difference in the direction of its fibres at different depths, the muscle may be divided into three imperfectly separated strata. The most superficial fibres are caudo-ventral in direction; the middle stratum has practically vertical fibres ; and in the deepest stratum their direction is ventral and oral. The masseter muscle is inserted into the whole of the fossa on the lateral surface of the mandible, the ridges bounding the fossa, the angular process, and a ridge continued in an oral direction from this process. In the dissection of the masseter muscle care must be exercised to preserve its nerve of supply—the masseteric nerve (n. massetericus)—a branch of the mandibular nerve, which reaches the muscle by way of the mandibular notch, and is most easily found between the middle and deep strata of the muscle. Dissection.—The temporal muscle is covered by a strong temporal fascia 160 DISSECTION OF THE DOG attached to the margins of the temporal fossa, and particularly thick at its attachment to the zygomatic arch. Make an incision along the border of the arch, and turn the fascia upwards. In doing this, some fibres of the muscle which arise from the deep face-of the fascia will have to be divided. The fascia should be removed completely. The superficia] temporal vessels will be exposed in the process. With bone forceps snip through the zygomatic arch close to the mandibular articulation, and at its other end as close as possible to the orbit. The piece of bone, with the remains of the masseter muscle attached thereto, must be removed. M. TEMPORALIS.—The powerful temporal muscle, mixed with much ten- dinous tissue, arises from the whole of the temporal fossa, which it fills completely. In addition to the bony origin, some fibres spring from the orbital band and the temporal fascia. The insertion of the muscle into the coronoid process of the mandible is rendered somewhat indefinite by confusion with the masseter. A. TEMPORALIS SUPERFICIALIS.—The superficial temporal artery is one of the two terminal branches of the external carotid. Crossing the aboral end of the zygomatic process of the temporal bone, it pierces the temporal fascia and runs towards the frontal bone approximately parallel to the zygomatic arch and in close relationship with the temporal muscle. Terminal twigs supply the frontal region and both eyelids. The collateral branches of the artery are as follows: (1) Transverse facial artery (a. transversa faciei), a small vessel already encountered on the surface of the masseter muscle; (2) antertor auricular artery (a. auricularis anterior), leaving the parent vessel as this crosses the zygomatic arch, and terminating in the muscles and skin over the medial and oral parts of the external ear; (3) in addition, there are small branches which end in the parotid gland, the masseter and other muscles, and the skin. V. TEMPORALIS SUPERFICIALIS.—The superficial temporal vein is arranged in conformity with the artery. Dissection.—The following dissection must be performed on one side of the head only. With a saw or bone-forceps separate the coronoid process from the rest of the mandible, and then cut through the bone on a level with the first premolar tooth. Liberate the insertion of the digastric muscle from the bone, and carefully pass the knife through the muscles, etc., attached to the medial surface of the mandible, keeping the edge of the knife as close to the bone as possible. Disarticulate the mandibular joint, bearing in mind the close relationship which exists between the joint and the internal maxillary artery. Remove the piece of mandible which the foregoing operations have isolated. This dissection involves the partial destruction of the pterygoid muscles and DISSECTION OF THE DOG 161 the inferior alveolar vessels and nerve ; but the dissector will have an opportunity later of examining these on the other side of the head. Note the presence of the mylo-hyoid nerve—a branch of the mandibular nerve—and the sublingual vessels. Now turn the mylo-hyoid muscle downwards as far as possible. GLANDULA SUBMAXILLARIS.—The submaxillary gland is a rounded, yellow- ish object, placed between the digastric muscle and the wing of the atlas on a level slightly deeper than that of the parotid gland. While being the least distinctly lobulated of all the salivary glands, the submaxillary, in consequence of a strong fibrous capsule, is the most definite in form. _ In contact with the lateral surface of the gland are the narrow, ventral end of the parotid, the inferior auricular and cutaneous muscles, the cervical branch of the facial nerve, and the superficial branch of the second spinal nerve. This surface, moreover, is not infrequently traversed by a shallow groove in which the internal maxillary vein is lodged. The medial surface is moulded upon the sterno-cephalic and digastric muscles. The submaxillary duct (ductus submaxillaris [Whartoni]) leaves the medial surface of the gland and crosses the surface of the digastric muscle under cover of the sublingual gland. Then, accompanying the larger sublingual duct over the stylo-glossal muscle, it finally opens into the mouth on a poorly marked elevation—the sublingual caruncle (caruncula sublingualis)—by the side of the frenulum of the tongue. GLANDULA SUBLINGUALIS.—The sublingual gland is elongated, narrow, reddish in hue, and stretches from the submaxillary gland, with which it is in intimate contact, to about the level of the third premolar tooth. Two parts are readily distinguished : (1) a larger, thicker aboral portion; and (2) a much smaller, thin and narrow, oral part. The aboral portion (gl. sublingualis grandicanalaris) lies between the digastric, pterygoid, and masseter muscles and a part of the mandible. Its duct (ductus sublingualis major) runs along the surface of the stylo-glossal muscle, in company with and somewhat dorsal to the submaxillary duct, in common with which it opens into the mouth. The feebly developed oral portion of the sublingual gland (gl. sublingualis parvicanalaris) lies between the mylo-hyoid muscle and the mucous membrane of the mouth, and is occasionally slightly overlapped by the aboral portion, from which it can only be distinguished by its slightly paler colour. The lingual nerve crosses the lateral surface of this part of the sublingual gland obliquely. There are several (eight to twelve) smaller sublingual ducts (ductus sublinguales minores). Dissection Remove the submaxillary and sublingual glands and clean the muscles, vessels, and nerves on the side of the tongue, pharynx, and larynx. M 162 DISSECTION OF THE DOG M. picasrricus.—Inasmuch as this muscle has only one fleshy belly in the dog, the name ‘ digastric’ is apt to mislead. The strong muscle arises from the jugular process of the occipital bone, and is inserted into the medial surface and ventral border of the mandible. M. styLo-nyorpEus.—A thin and narrow fleshy slip crosses the surface of the digastric muscle. This is the stylo-hyoid muscle, which has an attenuated J-~~—- a. carotis externa -- a. occipitalis --~ a. carotis interna —. a. carotis communis a, lingualis Be bs 3 ae -.n. laryngeus cranialis m. genio-glossus“ | -* \ 5 Seae- m. thyreo-pharyngeus m. genio-hyoideus © oe a-. M. crico-pharyngeus ae a e a. thyreoidea ae os, “>--*" cranialis m. mylo-hyoideus Tractus olfactortus.._------ _-7 a. cerebri anterior Stria lateralis ----- - a. cerebri media Trigonum olfactorium-~ ~ n. opticus- -—P-+- a “ ~ a&. chorioidca Lobus piriformis _ Tuber cinereum ~ a@. communicans posterior Corpus mamillare |----—- a. cerebri posterior KD ie iar aay gar n, oculo-motoriu. n. trochlearts - ¥~ ~~~ 7~ a, cerebelli anterior Pons --- n. abducens _--- n. facialis _--- n. acusticus -- ~ Cerebellum ~~~ a. basilaris wee ee ee | LS ee a. auditiva interna - a. cerebelli posterior n. vagus -7~ ~~. n. accessorius n. hypoglossus «~~~ ‘ Medulla oblongata - ~~ Fig. 64,—Arteries at the base of the brain, point the artery contributes a posterior communicating branch (a. communicans posterior) to the posterior cerebral artery, and then immediately ends by dividing into the middle and anterior cerebral arteries. The middle cerebral artery (a. cerebri media) gains the Sylvian fissure, and spreads out over almost the whole of the lateral surface of the cerebral hemi- sphere. A small choroidal artery (a. chorioidea) leaves the middle cerebral close to its commencement, and follows the optic tract to end in the choroid plexus of the lateral ventricle. The anterior cerebral artery (a. cerebri anterior) passes dorsal to the optic nerve, and converging upon the median plane, either fuses with its fellow artery of the other side of the brain, or is joined to this by a transverse anterior com- municating artery (a. communicans anterior). The anterior cerebral artery ramifies over the medial surface of the hemisphere. DISSECTION OF THE DOG 209 CIRCULUS ARTERIOSUS [WILLISI].—The anastomoses, mentioned above, result in the production of the arterial circle of Willis, which lies in the depressed area in front of the pons. Anteriorly the circle is formed by the direct or indirect (by the anterior communicating artery) union of the anterior cerebral arteries. Laterally the posterior communicating arteries link the anterior to the posterior part of the circle, which is completed behind by the two terminal branches of the basilar artery. Dissection.—Remove the membranes and vessels from the base of the brain. This must be done with the utmost care in order to avoid injury to the brain tissue generally, but especially to prevent tearing away the roots of the several cerebral nerves. The relation of the pia mater to the nerve roots is so intimate that it is probably safest to cut the membrane with scissors around each root. It is well to preface the detailed examination of the brain by a cursory inspection of certain structures at its base. The ventral aspect of the medulla oblongata is divided into two latera halves by a median longitudinal fissure (fissura mediana ventralis) continuous with the ventral fissure of the spinal cord and bounded on each side by a pro- minent white strand, the pyramid (pyramis), which disappears under the pons. The median fissure terminates abruptly at the foramen cecum, a blind depres- sion close to the pons. Lateral to the pyramid, and separated from it by a shallow groove, is the oval facial tubercle (tuberculum faciale). Immediately oral to this is a transverse prominence, the corpus trapezoidewm. The prominent pons forms a convex elevation, and is continued laterally into the cerebellum. The broad rounded cerebral peduncles appear oral to the pons and, diverging somewhat, disappear into the cerebral hemispheres. Consequent upon their divergence, a depressed area, the interpeduncular fossa (fossa interpeduncularis) is produced. The oral boundaries of the fossa are formed by the optic tracts —white cords appearing at the edge of the pyriform lobe of the cerebrum— and the optic chiasma produced by the union of the two tracts. The aboral part of the fossa is formed mainly by the posterior perforated substance (sub- stantia perforata posterior), which derives its name from the presence in it of numerous small openings by which blood-vessels reach the deeper brain tissue. The oral portion of the fossa is occupied by the mammillary body and the tuber cinereum. The mammillary body (corpus mamillare) is a prominent white object, frequently showing indications of its double nature, connected with the two columns of the fornix. A grey elevation of somewhat less promin- ence intervenes between the mammillary body and the optic chiasma. This, the tuber cinereum, is connected by means of a hollow stalk, the infundibulum, with the hypophysis, which, as a rule, is left behind in the removal of the brain from the cranium. On a level with the interpeduncular fossa, the cerebral hemisphere is raised P 210 DISSECTION OF THE DOG into a pyriform lobe. A small oral continuation of the lobe is separated from the main mass by a deep transverse depression in which the middle cerebral artery lies. Oral to the depression is the olfactory lobe (lobus olfactorius), consisting of the olfactory bulb (bulbus olfactorius) from which arises a flattened white band, the olfactory tract (tractus olfactorius). At its posterior extremity the tract divides into medial and lateral strie ; the former disappearing into the fissure between the two hemispheres; the lateral coursing, as a white band, across the surface of the oral prolongation of the pyriform lobe, and finally disappearing in the prominent part of this lobe. Between the two stria is a grey eminence, the olfactory tubercle (tuberculum olfactorium), the greater part of which is pitted with holes and thus constitutes the anterior perforated substance (substantia perforata anterior). NERVI CEREBRALES.— Twelve cerebral nerves arise from each half of the brain. These are either named numerically or are given names signifying their function or distribution : First cerebral nerve . i : Nervus olfactorius. Second ,, f, ; ; . os opticus. Third a ‘i : : . , oculomotorius. Fourth ,, na ; ; : ., trochlearis. Fifth Pe sa . . ; , trigeminus. Sixth ie i ‘ : : ,, abducens. Seventh _,, 4 F : : » facialis. Eighth ,, 3. Oe : é . _ acusticus. Ninth 8 we % F : . glossopharyngeus. Tenth a fs ‘ : : » vagus. Eleventh ., PA ‘ : ; 5, accessorius. Twelfth ,, m8 : .. hypoglossus. Each cerebral nerve is connected with cells in the interior of the brain, from which it can be traced to some definite point on the exterior where it has what is generally called its ‘superficial origin.’ The superficial origins of the various nerves should now be determined. N. otracrorius.—Numerous small olfactory nerves leave the olfactory. bulb and immediately enter the foramina of the ethmoid bone. They are generally left behind when the brain is removed. N. opticus.—The optic nerve is a large round cord leaving the optic chiasma. N. ocuLomorortus.—The oculomotor nerve has origin from the cerebral peduncle about the middle of its length and towards its medial border. N. TROCHLEARIS.—Since the origin of the trochlear nerve is from the anterior medullary velum, it cannot be demonstrated at present. The nerve itself, however, will be found curving round the lateral border of the cerebral peduncle, in the interval between this and the cerebrum and cerebellum. The trochlear is the smallest of the cerebral nerves. ~ DISSECTION OF THE DOG 211 = N. TRicEMiINvus.—The trigeminal is the largest of the cerebral nerves and arises by two roots from the lateral part of the pons. Of the roots, the larger (portio major) is sensory in function; while the much smaller medial root (portio minor) is motor. N. appucens.—The abducent nerve has its origin from the most anterior part of the groove forming the lateral limit of the pyramid of the medulla oblongata. N. FACIALIS ET N. acusticus.—The facial and acoustic nerves arise together from the lateral extremity of the corpus trapezoideum. The facial is the more medial, and slightly the smaller. N. GLOSSOPHARYNGEUS, N. VAGUS, ET N. ACCESSORIUS.—From the lateral border of the ventral surface of the medulla, a series of nerve rootlets take origin. These join to form the glosso-pharyngeal, vagus, and accessory nerves. The accessory nerve, in addition to its medullary roots, contains fibres derived from the cervical part of the spinal cord. The spinal roots of the accessory unite as a single cord, which enters the cranium by the foramen magnum and joins the medullary roots to form the complete nerve. N. Hypociossus.—The hypoglossal nerve arises by several rootlets from the aboral portion of the groove lateral to the pyramid. Dissection—As a preliminary to the examination of the surface of the cerebral hemispheres, they must be carefully denuded of the covering formed by the pia and arachnoid. Since the whole of their surface cannot be examined without the separation of the two hemispheres from each other, it is well to procure two brains. One of these should be left intact; while the cerebellum, medulla oblongata, and pons of the other should be separated from the cerebrum by a transverse in- cision made just in front of the pons. The two hemispheres of this specimen may now be isolated by an incision in the plane of the great longitudinal fissure. HEMISPH=RIA CEREBRI.—The two cerebral hemispheres form the greater part of the bulk of the brain. Each is flattened laterally in a certain degree, and so possesses two surfaces—lateral and medial. The lateral surface, for the main part convex, is applied to the walls of the cranium. The medial surface, on the contrary, is flattened, and much of it faces the corresponding surface of the opposite hemisphere; but the more aboral portion, faintly concave, joins the rest at an angle and is separated from the cerebellum by the tentorium only. If, in the intact specimen, the hemispheres are separated as far as possible by opening the longitudinal fissure between them, it will be found that they are connected by a broad commissural band, the corpus callosum. It will be observed, moreover, that the width of the commissure is not as great as Pe 212 DISSECTION OF THE DOG the length of the hemisphere; i.e. the corpus callosum does not reach the frontal and occipital poles of the hemisphere. The surface of the hemisphere is sculptured by lines, known as fissures — (fissure) and sulci, which separate winding ridges referred to generally as convoluttons (gyri). Lateral surface.—A fissure of great fundamental importance—the rhinal fissure (fissura rhinalis)—separates the olfactory and pyriform lobes from the rest of the lateral surface. That part which is dorsal to the rhinal fissure is covered with convolutions, rising tier above tier, and arranged in a curved manner about a short straight fissure of considerable depth, the lateral cerebral fissure of Sylvius (fissura cerebri lateralis [Sylvii]). The Sylvian fissure occurs S. cructatus Ss. suprasylvius ' / A ( t s. lateralis s. coronalts . / ; S. orbilalis . Bulbus olfactorius~ cl 7 Ree - aes Tractus olfactorius Pissura rhinalis ‘s. postsylvius Fissura cerebrit lateralis [Sylvit] Fie. 65.—Lateral surface of the cerebral hemisphere. on a level with that transverse depression which crosses the pyriform lobe. In the depths of the fissure, and in the natural condition hidden from sight, are several short convolutions composing the insula. Bent round the Sylvian fissure is a convolution bounded on the other side by a sharply curved ectosylvian sulcus (sulcus ectosylvius). More dorsal in position is a sulcus comprised in reality of two parts, though in the majority of specimens its double character is not apparent. The oral segment is one of the deepest of the several cerebral sulci, and is known as the suprasylvian sulcus (s. suprasylvius). Continuous with this, and united to it at an angle, is the post-sylvian sulcus (s. postsylvius). The area between the suprasylvian sulcus and the dorsal margin of the hemisphere is cut by the lateral sulcus (s. lateralis) generally, but not always, continuous anteriorly with the coronal sulcus (s. coronalis). The coronal can be distinguished from the lateral sulcus by its greater distance from the margin of the hemisphere. Small sulci of DISSECTION OF THE DOG 213 little moment—ectolateral and post-lateral—indent the surface of the hemisphere in the neighbourhood of the occipital pole. Consequent upon the lateral inclination of the coronal sulcus, an area of cerebral cortex, roughly quadri- lateral in form, is isolated. In this area is the cruciate sulcus (s. cruciatus) which crosses the border of the hemisphere and is continued onto its medial surface. In the oral part of the lateral surface is the long, curved orbital sulcus (8. orbitalis), one end of which lies close to the cruciate sulcus, while the other joins the rhinal fissure. Medial surface.—-The cruciate sulcus is prolonged, as has been said, to the medial surface of the hemisphere, where it is very generally continuous with the intercalary sulcus (s. intercalaris), so named because of its inter- position between the cruciate sulcus on the one hand and the calcarine sulcus on the other. i allie The calcarine sulcus (sulcus calcarinus), one of the most im- portant of the cerebral grooves, forms an angle with the inter- calary sulcus with which it is continuous, and is confined to that part of the medial surface in contact with the tentorium of the cerebellum. Between the margin of the hemisphere and the inter- calary and calcarine sulci are one or two secondary grooves of no ! sawostlareralts great depth and inconstant in He RlneaeS disposition. The medial surface Fic. 66.—Dorsal view of the cerebral hemisphere. of the hemisphere oral to the cruciate sulcus is also indented by a number of grooves of no great moment. A fissure of fundamental importance—the hippocampal fissure (fissura hippocampi)—forms the medial boundary of the pyriform lobe. -— Bulbus olfactorius -s. orbitalis _- 8. cruciatus eee eee —s. coronalis | _ s. lateralis s. ectosylvius ._ Ss. postsylvius — — Ss Dissection.—Part of one cerebral hemisphere should be removed to a level with the corpus callosum. This must be done by making a suc- cession of slices in planes parallel to that of the corpus. The specimen in which the two hemispheres have been separated by a longitudinal incision, is of service in acting as a guide to the direction and depth to which the slices should be removed. As soon as the corpus callosum can be plainly seen, it is well to remove the remains of the convolution 214 DISSECTION OF THE DOG immediately dorsal to it by tearing rather than cutting. This is necessary because the lateral ventricle, a cavity roofed over by the corpus callosum, projects above the level of the medial part of the body. There is, therefore, danger of opening the ventricle if the slicing process is continued. When sufficient of one hemisphere has been removed the other should be treated in the same way. In the process of this dissection some features of the inner structure of the cerebrum will be revealed. The depth of some of the sulci will be demonstrated, and the fact that the convolutions are composed of an outer rind of grey matter enclosing a core of white matter will be dis- closed. As the sections become deeper the white cores of the convolutions s, intercalaris s. suprasplenialis , S$. cruciatus , S$. post- _ calcarina Bulbus ~ olfactorius \ E Corpus callosum f ick i Fornix LFissura rhinalis Fic. 67.—Medial surface of the cerebral hemisphere. become confluent. Finally a large island of white matter occupies the central part of the section of each hemisphere, and is connected by the corpus callosum with a similar island in the other hemisphere. The study of the corpus callosum is best carried out by an examination of the hemi-sected brain in conjunction with that of the specimen just dissected. Corpus cALLosum.—The corpus callosum is a broad transverse band mainly concerned in connecting the two hemispheres with each other. It will be noted that it is not co-extensive with the hemisphere, but that it coincides roughly with the middle two-fourths of the length of that structure. The dorsal surface of the corpus callosum is flat or has a slight convexity. Numerous transverse lines (striae transverse) denote that the body is mainly composed of commissural fibres. In addition, faint longitudinal markings, equivalent to the striz longitudinales of the human brain, may be detected. DISSECTION OF THE DOG 215 The ventral surface forms the roof of the lateral ventricles, and in the median plane is connected with the septum pellucidum, a partition separating the cavities of the two ventricles. The lateral boundaries of the corpus callosum are lost in the white substance of the hemispheres. The main part of the corpus callosum is known as the truncus corporis callosi. Its aboral end is thickened and forms the splenium corporis callosi. On examination of the sagittal median section of the brain, the oral end of the body will be seen to make an abrupt bend. This is the genu corporis callosi, from which is a recurved, tapering (in section) rostrum corporis callosi connected in its turn with the lamina terminalis. Dissection.—It is now necessary to expose the interior of the lateral ven- tricles. Make a longitudinal incision through the corpus callosum about three or four mm. from the middle line. Then remove that part of the body which is lateral to the incision by tearing it away with either forceps or the end of the handle of the scalpel. When both ventricles have been opened in this manner a narrow strip of the corpus callosum will be left undisturbed. From the main part of the ventricle so exposed two cornua proceed. One of these is anterior in position and can be followed to its termination without difficulty. The other (inferior) cornu must be followed by the piecemeal removal of portions of the hemisphere. Previous to doing this, however, it will be well to note that the cornu is at first directed in a lateral, backward and ventral direction. Later its course is medialwards and forwards. A proper understanding of the lateral ventricle and its boundaries will be facilitated by dissection from the medial side. To do this, remove the corpus callosum and the immediately adjacent part of the hemisphere from the hemi-sected brain. Though the anterior cornu may be com- pletely investigated in this specimen, it is better to do no more than expose the first part of the inferior cornu. VENTRICULUS LATERALIS.—The lateral ventricle represents the cavity of the vesicle from which the cerebral hemisphere originally developed, and is in communication with the third ventricle by way of the interventricular Joramen of Monro (foramen interventriculare [Monroi]), a small opening imme- diately beneath the fornix. Generally the cavity of the ventricle is not spacious, since its roof and floor are mostly in contact. For descriptive purposes the lateral ventricle is divided into three parts— a central part, an anterior cornu, and an inferior cornu. The central part (pars centralis) has a roof formed by the corpus callosum, and a medial wall, by which it is separated from the other ventricle, consisting of the septum pellucidum and the fornix. There is no lateral wall, because the roof and floor meet and thus form the lateral boundary. oe The floor of the central part of the ventricle is formed by several important 216 DISSECTION OF THE DOG objects. Of these the most anterior is a pear-shaped grey eminence, the caudate nucleus (nucleus caudatus), the narrow end of which is continued into the inferior cornu. Along the medial border of the caudate nucleus runs a vascular fringe, the choroid plexus (plexus chorioideus ventriculi lateralis). The appearance of the plexus might lead to the assumption that it is actually within the ventricle. It is, however, excluded from the cavity by a thin =. aN ——Stria terminalis Corpus geniculatum ee laterale a Corpus geniculatum~ mediale = ~s Thalamus ~~ Corpus pineale +x Corpora quadrigemina Fig. 68.—Dissection to show the floor of the lateral ventricle and the dorsal part of the mid-brain. cellular investment, the ependyma, continuous with that lining the whole of the interior of the ventricle. Parallel to, and partially covered by, the choroid plexus, is the edge of the fornix and its backward prolongation, the fimbria hippocampi. The last named is a white hem appended to the greyer, rounded, ridge-like eminence, the hippocampus, with the mention of which the list of components of the floor is completed. The anterior cornu (cornu anterius) of the ventricle is, strictly speaking, a mere extension of the central part beyond the level of the foramen of Monro. DISSECTION OF THE DOG 217 It inclines in a ventral direction and, in the dog, ends blindly about the level of the tuberculum olfactorium. In many mammals the cornu is continuous with the cavity of the olfactory bulb. The inferior cornu (cornu inferius) is a tapering curved prolongation of the ventricle traceable into the pyriform lobe, where it ends on a level with the point at which the optic tract makes its appearance on the surface of the brain. The cornu contains the tail of the caudate nucleus (cauda nuclei caudati) reduced to a narrow grey ridge, and the diminished continuations of the choroid plexus, fimbria, and hippocampus. SEPTUM PELLUCIDUM.—A thin medial partition separates the anterior part of the pars centralis of the two ventricles, and fills in the triangular gap between the corpus callosum and the fornix. This is the septum pellucidum, in reality composed of two thin lamine with a narrow chink-like cavity intervening. Dissectton.—The fornix must now be exposed as completely as the present stage of the dissection permits. Cut across the remains of the corpus callosum about the genu, and remove it from this point to the splenium. Its connection with the septum pellucidum is necessarily destroyed in the proceeding. The hemi-sected brain affords much assistance in the study of the fornix, which there appears as a curved white band, ventral to the corpus callosum. Fornix.—The fornix consists of two bands of longitudinal fibres pursuing an arched course and intimately connected with each other at one place. The united bands constitute the body of the fornix (corpus fornicis) and are related to the corpus callosum and the septum pellucidum. At each end of the body the two constituent parts of the fornix separate. At the anterior end the separation is not very great and results in the production of the columne fornicis, two rounded white cords which curve ventralwards in front of the foramen of Monro. Continuing to the base of the brain the columns form the prominent mammillary body, the double character of which is thus ex- plained. From the posterior end of the body of the fornix arise two crura fornicis. These, widely diverging, are at first connected with the corpus callosum. Soon they form the white hem—fimbria hippocampi—adherent to the hippocampus; and, as such, are continued down the inferior cornu of the lateral ventricle. Some fibres of the crus fornicis are spread out as a white layer (alveus) on the surface of the hippocampus. Dissection.—Cut across the fornix about the point where the crura are . . leaving the body. Now, with the utmost care, remove the isolated aboral part of the hemispheres; i.e. the hippocampus and adjacent part of the wall of the inferior cornu of the ventricle. 218 DISSECTION OF THE DOG This is a convenient opportunity to study the association of the hippo- campal fissure of the exterior with the hippocampus in the interior. It will be observed that the two coincide in position; indeed, the fissure causes the elevation of the hippocampus. Between the hippocampal fissure and the fimbria hippocampi is a narrow, somewhat corrugated strip, the fascia dentata hippocampi. TELA CHORIOIDEA VENTRICULI TERTI.—The choroid tela of the third ventricle is a triangular double fold of pia mater containing a layer of arachnoid and some blood-vessels. It is interposed between the fornix and part of the hippocampus on the one side and the thalami on the other. The apex of the triangle lies at the foramen of Monro. Each of its sides is bounded by the choroid plexus of the central part of the lateral ventricle. At its base the tela divides into its two component sheets of pia mater continuous with the pia covering the surface of the brain generally. The cleft into which the choroid tela and the choroid plexuses of the inferior cornua of the lateral ventricles are insinuated, is known as the transverse cerebral fissure (fissura transversa cerebri). Dissection.—Seize the apex of the choroid tela with forceps and strip it from the surface of the thalami upon which it lies. As this is done the cleft-like third ventricle will be exposed. THaLamus.—The thalamus is an oval mass of grey matter separated from the caudate nucleus by an oblique groove containing a narrow white band, the stria terminalis. The dorsal surface of the thalamus is convex in the main and bounded medially by a prominent border formed by a longitudinal ridge, white in colour, known as the medullary stria (stria medullaris). The anterior end of the stria appears to join one of the columns of the fornix, while pos- teriorly it is apparently connected with the pineal body. The medial surfaces of the two thalami are flattened and form the lateral walls of the narrow third ventricle. Crossing the ventricle and uniting the two thalami is a thick, rounded grey bridge of tissue, the intermediate mass (massa intermedia). The lateral and ventral surfaces of the thalamus cannot be demonstrated at present, as they are in connection with other parts of the brain. The lateral surface is in contact with a band of white matter known as the internal capsule. The ventral surface rests on the dorsal or tegmental part of the cerebral peduncle (the hypothalamus). CoRPUS PINEALE.—In the middle line where the posterior part of the two thalami are in contact, the small and inconspicuous pineal body will be found. The base of the body contains one of the recesses of the third ventricle. VENTRICULUS TERTIUS.—The third ventricle is the narrow space between the two thalami. The choroid tela forms the roof of the ventricle, while its floor corresponds to the tuber cinereum, mammillary body and the posterior perforated substance. Anteriorly the cavity is bounded by the terminal lamina, DISSECTION OF THE DOG 219 the columns of the fornix, and the anterior commissure. The ventricle com- municates with the lateral ventricles through the foramen of Monro, and posteriorly an aditus (aditus ad aqueductum cerebri) gives access to the aqueduct of Sylvius. The regularity of the contour of the cavity is broken by several recesses. Among these is the recess of the infundibulum (recessus infundibuli) extending into the hypophysis. The optic recess (recessus opticus) is just dorsal to the optic chiasma. In the base of the pineal body is a small pineal recess (recessus pinealis), and above it a much more extensive swprapineal recess (recessus suprapinealis). CoMMISSURA ANTERIOR.—The anterior commissure is a transverse band of fibres readily demonstrated in the hemi-sected brain. If such a specimen be examined, the commissure will be seen in section as a small oval white object, immediately in front of the columns of the fornix. In the specimen from which the structures overlying the thalami have been removed, a glimpse of the commissure may be obtained between the slightly divergent columns of the fornix. CoMMISSURA POSTERIOR. — The posterior commissure consists of a narrow white strand crossing the brain transversely at the base of the pineal body. It is best demonstrated in a median longitudinal section. Dissection.—This is a convenient time at which to make a complete ex- amination of the mid-brain. Strip the membranes from the corpora quadrigemina, aboral to the thalami in position, and from the adjacent parts of the cerebellum. Be careful to preserve the small trochlear nerve to be found deep down in the depression between the cerebellum and the corpora quadrigemina. MESENCEPHALON.—The mid-brain is the short and narrow segment joining the pons and cerebellum on the one hand with the cerebrum on the other. It has a dorsal part formed by the corpora quadrigemina, and a larger ventral portion consisting of the peduncles of the cerebrum. In the intact brain the corpora quadrigemina are completely hidden by the cerebral hemisphere. Running through the mid-brain is a passage, the aqueduct of Sylvius (aqueduc- tus cerebri [Sylvii]), which connects the third and fourth ventricles. CoRPORA QUADRIGEMINA.—These are four rounded elevations lying between the thalami and cerebellum and arranged in two pairs. The anterior eleva- tions (colliculi anteriores) are somewhat more clearly defined, and are closer together than the posterior colliculi. These latter are separated from each other by a wide and shallow groove, from which a thin thread-like frenulum veli runs into the anterior medullary velum. The two colliculi of the same side are separated by a narrow but not very deep transverse groove. Laterally each colliculus is continued by a brachium. The brachium of the anterior colliculus (brachium quadrigeminum anterius) is scarcely demonstrable, 220 DISSECTION OF THE DOG since it becomes buried immediately on leaving the colliculus. The brachium of the posterior colliculus (brachium quadrigeminum posterius), on the contrary, is easily traced as a rounded ridge-like eminence, running in a ventral and nasal direction to disappear under an oval white eminence, the medial geniculate body. CoRPORA GENICULATA.—The geniculate bodies, medial and lateral, are intimately connected with the thalamus and the corpora quadrigemina. The lateral geniculate body (corpus geniculatum laterale) is closely applied to the Corpora quadrigemina % _ Cerebellum Py Corpus geniculatum mediale Tractus peduncularis transversus’ i ; \ f Pyramis ! D, y A, iL U ' Pedunculus cerebri ; Pons a ! . n. trochlearis Corpus trapezoideum Fic. 69.—Lateral aspect of hind-brain and mid-brain. posterior part of the thalamus, and from it the optic tract appears to arise. The medial geniculate body (corpus geniculatum mediale) is an oval eminence between the optic tract and the brachium of the posterior colliculus. TRACTUS OpTIcUS.—The optic tract, in the form of a white band, curves obliquely round the lateral part of the cerebral peduncle. To the naked eye it appears to commence in the lateral and medial geniculate bodies. Micro- scopically, however, its fibres are connected with the lateral geniculate body, the anterior colliculus and the thalamus. PEDUNCULI CEREBRI.—Forming the ventral part of the mid-brain, each cerebral peduncle is divisible into two portions—the tegmentum and the basis pedunculi. Of these, the basis pedunculi is the smaller and the more ventral. The superficial distinction between the two parts is indicated by two grooves. The lateral groove (sulcus lateralis) is visible when the mid-brain is viewed from the side, and runs from the pons to the medial geniculate body. The extent of the basis pedunculi in a medial direction is marked by a groove from which the roots of the oculomotor nerve take origin—the sulcus nervi oculomotorit. DISSECTION OF THE DOG 221 “a An indistinct narrow ridge of fibres winds round the cerebral peduncle beginning at the brachium of the anterior colliculus and ending vaguely about the mammillary body. This is the fransverse peduncular fasciculus (fasciculus peduncularis transversus [Guddeni]). Dissection.—Cut across the mid-brain, making the section through the anterior colliculus but not so far forwards as to injure the geniculate bodies. An examination of the cut surface of the mid-brain reveals the aqueduct of Sylvius, which places the third and fourth ventricles in communication with each other. In general the outline of the aqueduct is lozenge-shaped, and around it is a mass of grey nerve matter. The differentiation of the tegmentum and basis pedunculi can readily be made by an observation of the position of the two grooves already noted on the surface. In addition, a stratum of nerve tissue of somewhat different colour lies between the two structures. Dissection.—By a median incision separate the two halves of what remains of the cerebrum. Of one half, make a series of horizontal sections about two or three mm. thick. The other half should be cut into slices by vertical transverse incisions. In making these sections it is well to use a broad-bladed knife or a razor. CoRPUS STRIATUM, ETC.—The so-called basal ganglia of the cerebral hemi- sphere consist of masses of grey matter separated by intervening strata of white matter. The ganglia are the caudate and lentiform nuclei of the corpus striatum, the claustrum, and the amygdaloid nucleus. Nucieus caupatus.—A partial examination of the caudate nucleus was made after the lateral ventricle had been opened. The nucleus consists of a mass of grey matter of curved pear-shaped form. ‘The head (caput nuclei caudati) is thick and forms a projection in the anterior cornu of the ventricle. From the head the nucleus tapers somewhat rapidly to a tail (cauda nuclei caudati), which follows the inferior cornu of the ventricle to end in the amyg- daloid nucleus (nucleus amygdale) in the roof of the extremity of the cornu. From what has previously been seen and from the sections now under examina- tion, it is manifest that two surfaces of the caudate nucleus may be described. A free ventricular surface is covered by the ependyma of the lateral ventricle. A deeper surface is embedded in the substance of the cerebral hemisphere, and is mainly in contact with the internal capsule. NUCLEUS LENTIFORMIS.—The lentiform nucleus is an irregularly lens- shaped mass of grey matter placed lateral to the caudate nucleus and the thalamus. Smaller than the caudate nucleus, it is connected with this by strands of grey matter which cross the intervening white stratum. In addition the 222 DISSECTION OF THE DOG two nuclei are connected with each other and with the grey matter of the surface of the hemisphere at the olfactory tubercle. CLAUSTRUM.—The claustrum is a very thin layer of grey matter lateral to the corpus striatum and very nearly co-extensive with the insula, i.e. the convolutions hidden in the Sylvian fissure. CApSULA INTERNA—The term internal capsule is applied to the white matter separating the caudate nucleus and the thalamus on the one side from the lentiform nucleus on the other. The continuity of the capsule is much interfered with anteriorly by the grey strands crossing from one nucleus to the other. In horizontal sections the capsule is bent opposite the stria termi- nalis at what is known as the knee of the internal capsule (genu capsule interne). The limb in front of the genu may be designated the frontal part (pars frontalis capsule interne), and the limb behind the genu the occipital part of the capsule (pars occipitalis capsule interne). The internal capsule is of great importance since it contains fibres derived from or passing to various parts of the cerebral cortex. The divergence of the fibres dorsal to the capsule is referred to as the corona radiata. CAPSULA EXTERNA.—The term external capsule is applied to the layer of white matter between the lentiform nucleus and the claustrum. RHOMBENCEPHALON.—Attention must now be directed to the hind-brain composed of the medulla oblongata, the pons, and the cerebellum. MEDULLA OBLONGATA.—An arbitrary limit to the spinal cord is made on a level with the foramen magnum; but when the brain and cord have been removed from the body, it is difficult to say exactly where the cord ends and the medulla oblongata begins. The medulla extends as far in a nasal direction as the pons. At first it has the same general form as the spinal cord; but soon it becomes dorso-ventrally flattened and expanded laterally. The increase in width is associated with the opening out of the central canal (continued from the spinal cord) into the fourth ventricle. The bilateral character of the medulla oblongata is made manifest on the surface by the presence of ventral and dorsal median fissures continuous with the like land-marks of the spinal cord. While the ventral median fissure (fissura mediana ventralis) can be traced as far as the pons, where it terminates abruptly at the foramen cecum, it is not of uniform depth throughout. About the aboral end of the medulla oblongata numerous fibres pass from one side to the other (the decussation of the pyramids) and cause the fissure to be very shallow at this point. The dorsal median fissure (fissura mediana dorsalis) is not so extensive. It is continued only to the extremity of the fourth ventricle, where it apparently widens out in conformity with the lateral divergence of the two halves of the dorsal portion of the medulla oblongata. Along each side of the ventral median fissure is a very definite strand of nerve fibres known as the pyramid of the medulla oblongata (pyramis [me- dulle oblongate]). Followed towards the cerebrum, the pyramid disappears DISSECTION OF THE DOG 223 under the pons. Research has shown that the fibres composing the pyramid are derived from nerve cells in the grey matter of that part of the cerebral cortex which lies in the neighbourhood of the cruciate sulcus. From their origin these fibres, which are motor in function, pass by way of the corona radiata and internal capsule into the basis of the cerebral peduncle and so through the pons into the pyramid of the medulla oblongata. Close to the foramen magnum the fibres cross over from one side to the other (decussation of the pyramids) and travel along the crossed pyramidal tract of the opposite side of the cord. Lateral to the pyramid is a groove, of no great depth, from which the rootlets of the abducent and hypoglossal nerves arise. The groove separates the pyramid from an elevation known as the facial tubercle (tuberculum faciale). In an adult dog the tubercle is not very conspicuous, because its surface is crossed by the external arcuate fibres (fibre arcuate externe) which traverse the lateral border of the medulla oblongata obliquely. Behind the facial tubercle the medulla oblongata resembles the lateral part of the spinal cord, and to the naked eye it appears as if the lateral columns of the cord were merely prolonged into the medulla. This appearance is, however, contrary to fact. The lateral column of the cord contains fibres not present in a similar position in the medulla, e.g. the crossed pyramidal tract. On each side of the dorsal median fissure is a very narrow strand of fibres forming the funiculus gracilis, which deviates from the middle line when the end of the fourth ventricle is reached and expands slightly to form the clava. Lateral to the gracile funicle is the much wider funiculus cuneatus. This also diverges laterally on reaching the ventricle and forms the eminence called the tuberculum cinereum. The gracile and cuneate funicles form the direct continuation of the dorsal column of the spinal cord. The clava and tuberculum cinereum contain collections of nerve cells (nucleus funiculi gracilis et nucleus funiculi cuneati) in association with which the fibres of the dorsal column of the cord end. A third band of white matter lies lateral to the funiculus cuneatus. This is known as the funiculus of Rolando because it is produced by the substantia gelationosa [Rolandi] of the cord coming towards the surface when the medulla oblongata is reached. A superficial naked-eye examination of the medulla oblongata leads to the conclusion—an erroneous one—that the three funicles just mentioned are continued forwards as the restiform body (corpus restiforme), a thick strand which, after forming a floor for the lateral prolongation of the fourth ventricle, turns abruptly dorsalwards and enters the cerebellum. It will be observed that the external arcuate fibres enter largely into the formation of the restiform body. Pons.—The pons is a transverse prominence between the medulla oblongata and the cerebral peduncles. Its ventral surface is convex from side to side 224 DISSECTION OF THE DOG with a very shallow antero-posterior groove in the middle line. The dorsal surface assists in the formation of the floor of the fourth ventricle, and will be examined later. On each side the pons is continued into the cerebellum as the brachium pontis. A superficial examination of the pons suffices to show that it is composed largely of transverse fibres. The greater part of these are superficial to the pyramids. Some, however, cross the dorsal aspect of the pyramids, and, since they are more caudal than the superficial fibres, form an elongated transverse area, the trapezoid body (corpus trapezoideum) on the surface of the brain. From the lateral part of this body the facial and acoustic nerves have their superficial origin. Dissection.—The course of the pyramids should be followed through the pons. This can be done by making a longitudinal incision across the middle of the pons, and a similar incision just medial to the origin of the trigeminal nerve. Now, with a pair of forceps, tear away the superficial transverse fibres of the pons until the pyramid is exposed. The con- tinuity of the pyramid with the basis pedunculi can thus be demonstrated. CEREBELLUM.—The cerebellum, a transversely elongated, rounded mass, forms the dorsal and more bulky part of the hind-brain. For descriptive purposes three parts may be distinguished, namely, a central vermis and two hemispheres. The vermis is the most prominent part of the organ, and projects beyond the level of the hemispheres as a rounded ridge, more sharply defined in its caudal and ventral parts than elsewhere. The hemisphere, lateral in position, is narrow anteriorly but rapidly widens. A small lateral appendage is conspicuous when the brain has been removed from the cranium, and is received into a depression in the temporal bone when the parts are in their natural position. It is with the hemisphere that the restiform body, the brachium pontis, and the brachium conjunctivum are connected ; that is to say, access to the vermis is only obtained by way of the hemisphere. The restiform body and the brachium pontis have been mentioned in connection with the medulla oblongata and pons respectively. At the present stage of the dissection the brachium conjunctivum cannot be seen in its entirety, but a glimpse of it is obtained between the brachium pontis and_ the posterior colliculus of the corpora quadrigemina. The surface of the cerebellum is beset with narrow ridges or folia separated by fissures. Deeper fissures cut the cerebellum into lobes, the disposition of which can be more easily studied in sections, as will be done presently. It should be observed, however, that the most lateral part of each hemisphere is separated from the rest by a fissure running in a sagittal direction. The portion so defined is composed of the paraflocculus and flocculus. The para- flocculus consists of two rows of folia from the more ventral of which projects the petrous lobule (lobulus petrosus), so named from its location in a fossa of DISSECTION OF THE DOG 225 the petrous portion of the temporal bone. Into the depths of the fissure between the paraflocculus and the rest of the hemisphere the brachium pontis can be followed. Between the paraflocculus and the origins of the facial and acoustic nerves is the flocculus, a small collection of folia separated from the paraflocculus by a fissure of considerable depth. Dissection.—Make a median sagittal section through the vermis of the cerebellum and the two medullary vela—thin membranes forming the roof of the fourth ventricle. By separating the two halves of the cere- bellum a view of the floor of the ventricle may be obtained. The cut surface of the vermis should be examined and the arrangement of the lobes and fissures noted. ARBOR VIT#.—A sagittal section of the vermis of the cerebellum reveals in a very striking manner the peculiar arrangement of grey and white matter. The grey matter forms a continuous layer on the surface of the organ. The white matter within, as a consequence of the presence of numerous fissures, presents a tree-like appearance in sections, and therefore goes by the name of arbor vite. From the central mass of white matter various branches radiate. Of these, two are conspicuously large and form the core of the two largest lobes of the cerebellum separated from each other by the deepest of the cerebellar fissures. BRACHIUM CONJUNCTIVUM.—Two of the connections of the cerebellum, viz. the restiform body and the brachium pontis, have previously been examined. Up to the present, however, the third connection—the brachium conjunctivum— could not be examined in its whole length. If the two halves of the cerebellum be separated as much as possible the brachium will be seen connected with the hemisphere immediately within the brachium pontis. Followed towards the mid-brain, each brachium runs in a slightly medial direction to disappear ‘under the posterior colliculus of the corpora quadrigemina. MEDULLARY VELA.—Ventral to the cerebellum, and connected round the ends of the vermis with the white matter of this organ, are two thin mem- branes which form the roof of the fourth ventricle. The anterior medullary velum (velum medullare anterius) is a triangular membrane filling the space between the two brachia conjunctiva. The base of the triangle bends round the end of the vermis and is continuous with its white core. The posterior medullary velum (velum medullare posterius) is somewhat more complicated. Its cerebellar attachment stretches from the median plane —-where it has a connection similar to that of the anterior velum—to the floc- culus. The velum soon loses its nervous elements and gives place to a very thin translucent membrane composed of pia mater lined internally with ependyma. This completes the posterior part of the roof of the fourth ventricle and is attached to the margins of the cavity. VENTRICULUS QUARTUS.—The fourth ventricle represents the cavity of Q 226 DISSECTION OF THE DOG the original vesicle from which the hind-brain developed. Consequently it is in communication with the central canal of the spinal cord at the one end and with the cavities of the rest of the brain at the other. The opening of the central canal into the ventricle has already been commented upon. If the anterior medullary velum be raised the communication with the aqueduct of Sylvius—and through this with the third ventricle—will be revealed. In outline the cavity is rhomboidal ; hence the name fossa rhomboidea as applied to its floor. From the narrow caudal part—calamus scriptorius—it widens to the level of the place where the restiform bodies turn up into the cerebellum. Here’ the transverse diameter is materially increased by the presence of lateral recesses (recessus laterales), which curve round the caudal aspect of the restiform bodies. In front of the recesses, the ventricle narrows to the entrance of the aqueduct of Sylvius. The roof or dorsal wall of the ventricle is formed by the two medullary vela and the thin pial continuation of the posterior velum. Seen in sagittal section, the roof is somewhat tent-like, being continued into a recess, the fastigium, between the vermis attachments of the two vela. Theroof, moreover, is rendered irregular on a level with the lateral recesses by an invagina- tion produced by the choroid plexus (plexus chorioideus ventriculi quarti). That part of the plexus which is related to the recesses can readily be seen in the intact brain as a vascular tuft occupying an angular depression formed by the cerebellum and medulla oblongata. The membranous roof is defective. at the extremity of the lateral recess, where a small irregular opening, the lateral aperture (apertura lateralis ven- triculi quarti), places the cavity of the ventricle in communication with the subarachnoid space. The floor of the ventricle is formed by the medulla and pons. Divided into two lateral halves by a median longitudinal groove, the floor is further sub- divided into areas. A longitudinal limiting groove (sulcus limitans) forms the lateral boundary of an elongated and narrow medial area. The limiting groove is quite shallow, but deepens a little at two places known as the anterior and posterior fovee. A prominent medial eminence (eminentia medialis) occurs about the middle of the length of the strip demarcated by the median and limiting grooves. A triangular area, the hypoglossal trigone (trigonum nervi hypoglossi) intervenes between the posterior fovea and the median groove, while lateral to it is the grey ala cinerea. An elevated acoustic areca (area acustica) forms a conspicuous object lateral to the limiting sulcus and opposite the recess of the ventricle. Dissection.—lt is now necessary to remove the remains of the muscles attached to the vertebral column, the ribs, the pelvis, and the occipital DISSECTION OF THE DOG 227 bone, in order that the ligaments connected with these parts of the skeleton may be examined. The bodies of adjacent vertebre are connected by discs of fibro-cartilage (fibrocartilagines intervertebrales). If two vertebre be separated from each other, it will readily be seen that the connecting cartilage is composed of a peripheral fibrous portion (annulus fibrosus) and a much softer central part (nucleus pulposus). Assisting in the firm union of the vertebre are two longitudinal bands. The ventral longitudinal ligament (lig. longitudinale ventrale) is attached along the ventral aspect of the vertebral bodies from the sacrum to about the fifth thoracic vertebra, where it materially diminishes in volume. The dorsal ligament (lig. longitudinale dorsale) is more sharply defined. Running along the ventral wall of the vertebral canal from the sacrum to the dens of the epistropheus, it has the form of a band of unequal width. At each intervertebral fibro-cartilage the ligament widens somewhat, to become narrow again on a level with the vertebral body. Yellow ligaments (ligamenta flava) bridge the narrow gap between neigh- bouring vertebral arches. In the thoracic region these ligaments are narrow, but are considerably wider in the cervical region. The joint-cavities between contiguous articular processes of the vertebrae are enclosed by joint-capsules (capsule articulares) with the customary attachment around the articular surfaces, and possessed of the usual synovial lining. Forming the bond of union between the vertebral spinous processes are the supraspinal and interspinal ligaments. The supraspinal ligament (lig. supraspinale) is a strong cord-like object attached to the summits of the pro- cesses from the sacrum to about the first thoracic vertebra, where it is continuous with the ligament of the nape. The interspinal lgaments (ligg. interspinalia) fill the intervals between the spinous processes, and are confined to the thoracic and lumbar regions. In the lumbar region ¢ntertransverse ligaments (ligg. intertransversaria) connect the transverse processes. ARTICULATIO ATLANTO-OCCIPITALIS.—The articulation between the atlas and the condyles of the occipital bone has a cavity continuous with that between the. atlas and the epistropheus, and is enclosed by a joint-capsule (capsula articularis) on each side. An extensive ventral atlanto-occipital membrane (membrana atlanto-occipitalis ventralis), disposed on the ventral side of the joint, closes in the interval between the atlas and the occipital bone ; while a dorsal membrane (membrana atlanto-occipitalis dorsalis), also extensive but rather stronger than the ventral membrane, bridges the space on the dorsal aspect of the articulation. The union of the two bones is finally effected by the presence of a lateral atlantal ligament (lig. laterale atlantis) on each side. This is connected with the joint-capsule, and runs from the edge of the atlas to the jugular process of the occipital bone. Q2 228 DISSECTION OF THE DOG ARTICULATIO ATLANTO-EPISTROPHICA.—The joint cavity of the atlanto- epistrophic articulation, continuous as previously stated with that of the foregoing joint, is enclosed by the customary joint-capsule. Intimately connected therewith, and passing between the arches of the atlas and epistro- pheus, is a tectorial membrane (membrana tectoria), from which an interspinal ligament (ligamentum interspinale) may be separated with difficulty. Asso- ciated with the dens of the epistropheus are alar and transverse ligaments. The former (ligamenta alaria) spring from the tip of the dens, and diverging proceed forwards to be attached within the occipital condyles. The transverse ligament (lig. transversum dentis), along with the atlas, forms a ring within which the dens rotates. ARTICULATIONES COSTO-VERTEBRALES.—Since a rib is in contact by its head with the bodies of two vertebre, and by its tubercle with the transverse process of the more caudal of the two vertebre, it follows that there are two joints between a typical rib and the vertebral column. The capitular articulation (articulatio capituli) possesses two joint-cavities, corresponding to the two vertebral bodies with which the head of the rib is in contact, and separated from each other by an interarticular ligament to which the two joint-capsules are attached. The interarticular ligament (lig. capituli coste interarticulare) springs from the depression on the head of the rib, and passes to the middle plane of the body where it is continuous with the same ligament of the corresponding joint of the other side of the body. Broad at its attachment to the head of the rib, the ligament narrows as it lies under cover of the dorsal longitudinal ligament of the vertebral column. There is a slight connection between the ligament and the intervertebral fibro-cartilage. On the ventral aspect of the joint is the radiate ligament (lig. capituli coste radiatum) with fibres extending, in a radiating fashion, from the neck of the rib to the bodies of the vertebre and the interposed intervertebral fibro-cartilage. The costo-transverse articulation (articulatio costo-transversaria) between the tubercle of the rib and the transverse process of the vertebra, is provided with the customary joint-capsule. In addition there are a dorsal ligament and the ligament of the neck. The former (lig. costo-transversaria dorsale) passes from the vertebral transverse process to a point on the rib immediately lateral to the tubercle. The ligament of the neck (lig. colli coste) runs between the vertebra and the dorsal aspect of the neck of the rib. ARTICULATIO SACRO-ILIACA.—The slightly moveable articulation between the sacrum and the ilium is provided with a very short joint-capsule. Ligaments disposed in the vicinity of the joint all tend to restrict its range of movement. DISSECTION OF THE DOG 229 The ventral sacro-tiliac ligament (lig. sacro-iliacum ventrale) consists of short fibres joining the sacrum and ilium, and lies, as its name indicates, ventral to the joint. Short and long sacro-iliac ligaments (lig. sacro-iliacum dorsale breve et lig. sacro-iliacum dorsale longum) connect the ilium with the spinous processes and the lateral border of the sacrum respectively. At some distance from the sacro-iliac joint, but conveniently considered in this place, is the sacro-tuberous ligament (lig. sacro-tuberosum), which stretches in the form of a stout cord from the edge of the sacrum to the sciatic tuber of the ischium. SYMPHYSIS PELVIS.—The two pubes and the two ischia join in the median plane at the symphysis of the pelvis. Occasionally in old animals the union becomes bony. A few transverse fibres, crossing the ventral aspect of the symphysis, constitute the arcuate ligament (lig. arcuatum). ORGANON AUDITUS.—It now remains for the dissector to complete the dissection of the organ of hearing by an examination of the internal ear and the cavity of the tympanum. To do this with any degree of satisfaction, it is necessary to have several specimens, so that sections across some of them may be made with a fine saw, while one at least is examined after piece-meal removal of parts of the bone. Prior to commencing the dissection of the internal ear and the cavity of the tympanum, it would be well that the student have some general idea of the auditory apparatus as a whole. The organ of hearing is naturally divided into three parts: an external ear or auricle (auricula), a middle ear or cavity of the tympanum, and an internal ear. An examination of the cartilages of the external ear and the muscles concerned in the production of their movements was conducted at an earlier stage of the dissection. The canal circumscribed by the external ear is known as the external acoustic meatus (meatus acusticus externus) and is partially bounded by the temporal bone. The meatus ter- minates at the membrane of the tympanum (membrana tympani), by which its cavity is separated from that of the tympanum. The cavity of the tympanum, or middle ear, is a space within the temporal bone connected with the interior of the pharynx by the auditory tube of Eustachius (tuba auditiva [Eustachii]). Crossing the cavity from the membrane of the tympanum to its inner-wall is a chain of three auditory ossicles by way of which vibrations of the tympanic membrane are transmitted to the internal ear. The air-containing cavity of the osseous bulla of the temporal bone is in free communication with the tympanic cavity. The internal ear consists of a series of spaces and canals within the tem- poral bone, to which is given the collective name of osseous labyrinth (labyrinthus 230 DISSECTION OF THE DOG osseus), containing membranous sacs and tubes—the membranous labyrinth (labyrinthus membranaceus). The central space of the osseous labyrinth, the vestibule (vestibulum), in the dried skull communicates with the cavity of the tympanum by an oval opening, the fenestra of the vestibule (fenestra vestibuli). In the fresh state and in the living animal the fenestra is occluded by the base of the stapes, one of the auditory ossicles. In the posterior part of the vesti- bule are fine openings leading into the three semicircular canals (canales semi- circulares ossei), while in the lower and anterior part of the cavity is an opening into the spiral canal of the cochlea. The cochlea itself resembles the shell of a snail,.and consists essentially of the spiral canal wound round a central column of bone designated the modiolus. The spiral canal ends blindly at the apex of the cochlea, where it forms the cwpola (cupula). Into the canal a spiral lamina of bone (lamina spiralis ossea) projects for some distance from its inner (modiolar) wall; thus the canal is partially divided into two com- partments ; one of which, the scala vestibult, communicates with the vestibule, the other, the scala tympani, in the macerated bone opening by a small rounded aperture—the fenestra of the cochlea (fenestra cochlea)—into the cavity of the tympanum. In the fresh condition the fenestra is closed by a membrane. The membranous labyrinth consists of the saccule, the utricle, three semicircular ducts and the cochlear duct. The saccwle (sacculus) and the utricle (utriculus) are lodged in the vestibule, and are placed in indirect communication with each other by means of the endolymphatic duct (ductus endolymphaticus). The semicircular ducts (ductus semicirculares) occupy the three bony semicircular canals and are in communication with the utricle. The cochlear duct (ductus cochlearis) is attached, on the one side to the outer wall of the spiral canal of the cochlea, and on the other to the edge of the bony spiral lamina. At the base of the cochlea the duct is connected with the saccule by a narrow uniting duct (ductus reuniens). The blind apical termination of the duct does not quite reach the cupola of the cochlea, thus allowing a communication between the scala vestibuli and the scala tympani. Dissection.—As previously stated, it is scarcely possible to make a com- plete dissection of the ear on one specimen only. In order to examine the cavity of the tympanum the lower part of the osseous bulla should be removed bit by bit, a ring of bone being left round the external acoustic meatus. In order to demonstrate the tympanic: membrane properly, it is necessary to remove the cartilages of the auricle. It will be observed that the cavities of the tympanum and of the osseous bulla communicate with each other by a wide opening bounded by the serrated edge of a thin plate of bone. CAVUM TYMPANI.—The tympanic cavity is a narrow, air-containing chamber between the internal ear and the end of the external acoustic meatus. Its outer wall is formed almost entirely by the thin, translucent tympanic DISSECTION OF THE DOG 231 membrane (membrana tympani). On the inner wall, which separates the cavity from the labyrinth of the internal ear, is a well-marked projection, the promontory (promontorium), above and slightly in front of which is the fenestra of the vestibule. Below the promontory is the fenestra of the cochlea. Leading from the anterior part of the tympanic cavity is the narrow opening of the auditory tube of Eustachius. Dissection.—Snip all round the outer wall of the tympanum, so that it may be removed. In the process an irregular space, the epitympanic recess (recessus epitympanicus), containing the incus and the head of the malleus, will be revealed in connection with the roof of the tympanic cavity. OssicULA AUDITUS.—The auditory ossicles are three in number, namely, the malleus, the incus, and the stapes. The malleus is the outermost and the largest of the three bones. It consists of a large upper part or head (capitulum mallei), below which is a neck (collum mallei), and a manubrium (manubrium mallei) and two processes. The head carries an articular surface for contact with the incus. The manubrium is attached to the tympanic membrane, as is also the lateral process (processus lateralis). The anterior process (processus anterior) is extremely slender, and is attached by ligament to the wall of the tympanic cavity. The incus bears some resemblance to a human bicuspid tooth, and possesses a body and two crura. The body (corpus incudis) carries a saddle-shaped surface for articulation with the head of the malleus. The short crus (crus breve) is movably connected with the wall of the tympanum; while the long crus (crus longum) articulates with the head of the stapes. The stapes, a stirrup-shaped bone, consists of a head (capitulum stapedis), two crura (crus anterius et crus posterius), and a base. The base (basis stapedis) is in the form of an oval plate lodged in, and so connected with the margin of the fenestra vestibuli that some amount of movement can take place. MUSCULI OSSICULORUM AUDITUS.—Connected with the auditory ossicles are two small muscles. The tensor muscle of the tympanum (m. tensor tympani) is short and conical, with an origin from a depression just anterior to the epitympanic recess. A slender tendon connects the muscle with the manubrium of the malleus close to its root. The stapedius muscle (m. stapedius) is inserted into the head of the stapes. CANALIS FACIALIS.—The dissector should open up the whole length of the facial canal, beginning at the stylomastoid foramen and working toward the internal acoustic meatus. He will then find that the canal curves round the base of the cochlea and the posterior part of the internal wall of the tympanum. INDEX ABDOMEN, 15 Arteries: Caudal thyroid, 149 Accessory pancreatic duct (of Santorini), 39 Central, of retina, 188 Cerebro-spinal, 168 Choroidal, 208 Circumflex scapular, 124 Ceeliac, 39 Acoustic area (of fourth ventricle), 226 Aditus of aqueduct of Sylvius, 219 Aggregated lymph-nodules of Peyer, 27 Ala cimerea, 226 Amygdaloid nucleus, 221 Annular cartilage, 150 Anterior commissure, 219 fovea, 226 medullary velum, 225 perforated substance, 210 Aortic semilunar valves, 54 Appendix of laryngeal ventricle, 179 Aqueduct of Sylvius, 219, 221 Aqueous humour of eyeball, 189, 193 Arachnoid, 202, 206 Arbor vite, 225 Arrangement of cardiac orifices, 57 Arterial circle of Willis, 209 ARTERIES : Angular, of mouth, 158 Anterior auricular, 160 bronchial, 30 cerebellar, 207 cerebral, 208 circumflex humeral, 123 communicating, 208 femoral, 77, 80 mediastinal, 30, 42 tibial, 92, 97 Aorta, 54, 59, 72 Artery of urethral bulb, 111 Articular artery (from femoral), 79 Ascending cervical, 5, 56 pharyngeal, 149 Axillary, 4, 123 Basilar, 207 Brachial, 124 Brachio-cephalic, 54 Bronchial, 61 Buccinator, 182 Caudal epigastric, 12 gluteal, 85 mesenteric, 26 Common carotid, 55, 149, 163 interosseous, 138 Condyloid, 168 Costo-cervical trunk, 55 Cranial epigastric, 12, 30 gluteal, 85, 111 hemorrhoidal, 26 mesenteric, 25 thyroid, 149 vesical, 110, 116 Deep artery of arm, 124 penis, 111 cervical, 55 circumflex iliac, 73 femoral, 80 volar arch, 139, 142 Deferential, 110 Distal radial collateral, 124 Dorsal arteries of penis, 9, 111 digital, 88, 129 interosseous, 138 metatarsal, 92 nasal, 159 Dorsalis pedis, 92, 101 Ethmoidal, 188 External carotid, 164 iliac, 75 maxillary, 164 pudendal, 10 Facial, 158 Femoral, 77 Frontal, 188 Gastro-duodenal, 40 -lienal, 40 Greater palatine, 183 Hepatic, 40 Hyaloid, 192 Hypogastric, 110, 116 Tleo-czeco-colic, 25 Tlio-lumbar, 111 Q 3 234 INDEX Arteries : Inferior alveolar, 165 Arteries: Right colic, 25 labial, 158 coronary, 51 Infraorbital, 159, 182 gastric, 40 Intercostal, 29, 61, 62 gastro-epiploic, 40 Internal auditory, 207 subclavian, 55 carotid, 168, 197, 208 Saphenous, 77, 80, 94 mammary, 30, 41, 56 Spheno-palatine, 183 maxillary, 165, 182 Splenic, 40 pudendal, 110 Stylo-mastoid, 164 spermatic, 73 Sublingual, 164 Intestinal, 25 Subscapular, 123 Lachrymal, 187 Superficial lateral caudal, 111 Laryngeal, 149 temporal, 160 Lateral circumflex femoral, 77, 80 Superior labial, 159 nasal, 159 Supreme intercostal, 55 tarsal, 94 Thoraco-acromial, 4 thoracic, 5 -dorsal, 124 Left colic, 26 Thymic, 42 coronary, 51 Transverse cervical, 28, 56 gastric, 40 facial, 159, 160 gastro-epiploic, 40 scapular, 5, 56 subclavian, 54, 55 Ulnar, 140 Lesser palatine, 182 Umbilical, 110, 111 Lingual, 164 Uterine, 116 Lumbar, 73 Vertebral, 55, 155 Medial tarsal, 101 Volar digital, 140 Median, 138 interosseous, 139 Mental, 165 metacarpal, 142 Middle cerebral, 208 ARTICULATIONS: colic, 25 Atlanto-epistrophic, 228 hemorrhoidal, 111 -occipital, 227 meningeal, 165, 198 Carpo-metacarpal, 144 sacral, 114 Costo-vertebral, 228 Musculo-phrenic, 30 Digital, 106 Occipital, 168 Elbow-joint, 143 Esophageal, 61 Hip-joint, 86 Omo-cervical trunk, 5, 56 Humero-radial, 143 Ophthalmic, 182, 187 -ulnar, 143 Pancreatico-duodenal, 40 Intermetatarsal, 106 Pericardiaco-phrenic, 30, 41 Intersternal synchondroses, 35 Perineal, 111 Knee-joint, 102 Phrenic, 72 Laryngeal, 180 Phrenico-abdominal, 72 Mandibular, 193 Plantar arch, 101 Metatarso-phalangeal, 106 digital, 101 Pisiform, 144 metatarsal, 101 Radio-carpal, 143 Popliteal, 97 -ulnar, 143 Posterior auricular, 164 Sacro-iliac, 228 cerebellar, 207 Shoulder-joint, 142 cerebral, 207 Sterno-costal, 35 ciliary, 188 Symphysis of the pelvis, 229 circumflex humeral, 124 Talo-crural, 104 communicating, 208 Tarso-metatarsal, 105 deep temporal, 165 Tibio-fibular, 104 femoral, 8i Vertebral, 227 meningeal, 168 Ary-epiglottic folds, 176 Proper digital, 88 Arytenoid cartilages, 175 Proximal radial collateral, 124, 129 Auditive tube of Eustachius, 174, 229 ulnar collateral, 124 Auditory ossicles, 231 Radial, 139 Auricles of heart, 49 Renal, 73 Axilla, 4 INDEX 235 Basis PEDUNCULI, 220 Bicuspid valve, 54 Brachia of quadrigeminal bodies, 219 Brachium conjunctivum, 224. 225 pontis, 224 Brain, 206 Bronchi, 157 Caoum, 20 Calamus scriptorius, 226 Canines, 171 Capsule of lens, 193 Cartilages of the nose, 198 Cauda equina, 203 Caudate nucleus, 216, 221 Cavity of the nose, 199 Central canal, 205 grey matter, 205 Cerebellum, 224 Cerebral hemispheres, 211 peduncles, 206, 209, 219, 220 Cervical enlargement (of spinal cord), 202 Chambers of the eye, 193 Cheeks, 170 Chord tendinex, 53 Choroid, 190 Choroid plexus, 216, 226 tela, 218 Ciliary body, 190 processes, 190 zonule, 192 Cisterna chyli, 74 Claustrum, 222 Clava, 223 Clitoris, 116 Cochlea, 230 Cochlear duct, 230 Colon, 20 Columne fornicis, 217 Columns of spinal cord, 205 Common bile-duct, 36 Conchal cartilage, 150 Conical papille, 172 Conjunctiva, 155 Conus arteriosus, 52 medullaris, 202 Cornea, 190 Corniculate cartilage, 175 Corona radiata, 222 Coronary sulcus, 49 Corpora quadrigemina, 219 Corpus callosum, 211, 214 striatum, 221 trapezoideum, 209, 224 Cricoid cartilage, 175 Crossed pyramidal tract, 223 Crura fornicis, 217 Crystalline lens, 192 Cuneiform cartilages, 176 Cupola, 230 Cystic duct, 36 Decussation of the Pyramids, 223 Deferent duct, 7 Diaphragma sellz, 196 Ductus reuniens, 230 Duodeno-jejunal flexure, 38 recess, 25 Duodenum, 19, 38 Dura mater, 194, 201 Ear, 150, 229 Endocardium, 51 Endolymphatic duct, 230 Ependyma, 216 Epicardium, 47 Epididymis, 7 Epiglottic vallecula, 173, 176 Epiglottis, 175 Epiploic foramen of Winslow, 24 External acoustic meatus, 229 arcuate fibres, 223 capsule, 222 ear, 150 Eyeball, 188 Eyelids, 155 Facrab canal, 231 tubercle, 209, 223 Falx cerebri, 195 Fascia of forearm, 129, 134 leg, 89 Fasciculus cuneatus, 205, 206 gracilis, 205, 206 Fastigium, 226 Female genital organs, 67, 115 Femoral triangle, 77 Fenestra cochlez, 230 vestibuli, 230 Filiform papille, 172 Filum terminale, 202 Fimbria hippocampi, 216, 217 Fissures of medulla oblongata, 222 Flocculus, 225 Foliate papilla, 173 Foramen cecum, 209, 222 Fornix, 217 Fossa ovalis, 52 rhomboidea, 226 Fourth ventricle, 225 Frenulum of the lip, 170 tongue, 172 Frenulum veli, 219 Frontal sinus, 200 Fungiform papille, 173 Funicles of spinal cord, 205 Funiculus cuneatus, 223 gracilis, 223 of Rolando, 223 236 GALL-BLADDER, 36, 64 GANGLIA: Caudal mesenteric, 26 Ciliary, 187 Coeliac, 66 Cranial cervical, 167 mesenteric, 25, 66 First thoracic, 61 Gasserian, 197 Jugular, 166 Nodose, 166 Otic, 184 Spheno-palatine, 183 Spinal, 203 Gelatinous substance of Rolando, 205 Geniculate bodies, 220 Glosso-epiglottic fold, 173 -palatine arch, 169 Glottis, 176 Greater omentum, 18, 23 Grey commissures (of spinal cord), 205 Grooves of spinal cord, 203 Harper’s Gland, 188 Hard palate, 171 Heart, 48 Hepatic ducts, 65 Hilus of kidney, 70 Hind-brain, 222 Hippocampal fissure, 213 Hippocampus, 216 Hyaloid canal, 192 fossa, 192 membrane, 190, 192 Hypoglossal trigone, 226 Hypothalamus, 218 InEvum, 19 Incisor papilla, 172 Incisors, 171 Incus, 231 Inguinal canal, 14 Tnsula, 212 Inter-arytenoid cartilage, 175 Interior of the duodenum, 67 intestines, 27 kidney, 70 Intermediate mass, 218 Internal capsule, 218, 222 Interpeduncular fossa, 206, 209 Interventricular foramen of Monro, 215 Tris, 191 Isthmus faucium, 170 JEJUNUM, 19 Kipneys, 69 INDEX LacHRYMAL caruncle, 155 ducts, 155 gland, 185 Lamina chorio-capillaris, 190 fusca, 190 terminalis, 215 vasculosa, 190 Large intestine, 19 Laryngeal prominence, 175 Larynx, 174 Lateral aperture (of fourth ventricle), 226 groove (of mid-brain), 220 recess (of fourth ventricle), 226 ventricle, 215 Left atrium of heart, 53 ventricle of heart, 54 Lentiform nucleus, 221 Lesser omentum, 23 LIGAMENTS : Alar, 228 Arcuate, 229 Broad (of uterus), 68 Calcaneo-cuboid, 105 -fibular, 104 -navicular, 105 Collaterals of carpus, 144 Crico-thyroid, 175, 177 Cruciate, 103 Cuboideo-navicular, 105 Deltoid, 104 Denticulate, 202 Dorsal atlanto-occipital membrane, 194, 227 costo-transverse, 228 longitudinal, 227 tarsal, 104 Fibular collateral, 103 Gastro-lienal, 18 Hyo-thyroid, 175, 177 Inguinal (of Poupart), 10 Interarticular, 228 Intercarpal, 144 Internal proper sternal, 35 Interosseous membrane (of forearm), 143 (of the leg), 104 tarsal, 106 Interspinal, 227, 228 Intertransverse, 227 Lateral atlantal, 227 Ligament of neck of rib, 228 Ligamenta flava, 227 Ligamentum nuche, 154 Long plantar, 105 sacro-iliac, 229 Navicular-cuneiform, 105 Patellar, 102 Pectinate of iris, 191 Pisiform, 144 Plantar, 105 Pulmonary, 34 Radial annular, 143 collateral, 143, 144 Radiate, 228 Ligaments: Radiate sterno-costal, 35 Radio-carpal, 144 Round (of hip), 86 (of uterus), 68 Sacro-tuberous, 229 Short sacro-iliac, 229 Supraspinal, 227 Suspensory of lens, 192 Talo-calcanean, 104, 105 -fibular, 104 Tectorial membrane, 228 Temporo-mandibular, 193 Thyro-epiglottic, 180 Tibial collateral, 103 Transverse (of dens), 228 (of hip-joint), 86 Triangular (of liver), 65 Ulnar collateral, 143, 144 Ventral atlanto-occipital membrane, 227 longitudinal, 227 sacro-iliac, 229 Ventricular, 180 Vocal, 179 Limiting sulcus, 226 Linea alba, 13 Lingual papille, 172 septum, 173 Lips, 170 Liver, 35 Lobes of liver, 63 Longitudinal fissure (of brain), 206 groove (of heart), 50 Lumbar enlargement (of spinal cord), 202 Lungs, 42 Lymph-glands, 4, 10, 25, 27, 48, 73, 83, 110, MALE external genital parts, 5 Malleus, 231 Mammary glands, 1 Mammillary body, 206, 209 Maxillary sinus, 200 Meatus nasi, 199 Medial eminence (of fourth ventricle), 226 Median fissure (of spinal cord), 203 longitudinal fissure (of medulla), 209 septum (of spinal cord), 205 Mediastinal septum, 31, 34 Medulla oblongata, 206, 222 Medullary striz, 218 vela, 225 Membrana nictitans, 155, 188 tympani, 229, 230 Membranous iabyrinth, 230 Menisci, 103 Mesentery, 19, 23 Mesocolon, 23 Mesometrium, 68 Mesosalpinx, 68 Mesovarium, 68 Mid-brain, 219 INDEX 237 Modiolus, 230 Molars, 171 Mouth, 169 MUSCLEs : Abductor of the fifth digit, 99, 141 pollex, 134, 141 Adductor of the femur, 79 fifth digit, 100, 141 pollex, 141 second digit, 100, 141 Anconeus, 128 Ano-vulvar, 116 Anterior tibial, 89 Antitragicus, 152 Arytenoid, 178 Auricular, 151 Biceps brachii, 120 femoris, 82 Biventer cervicis, 153 Brachialis, 128 Brachio-cephalic, 118 -radial, 130 Buccinator, 156 Bulbo-cavernous, 9, 110 Canine, 156 Capsularis, 86 Cerato-hyoid, 166 Ciliary, 190 Cleido-cervical, 118 -mastoid, 118 Coccygeus, 107, 146 Common extensor of the digits, 89, 130 Complexus, 153 Coraco-brachial, 121 Corrugator of eyebrow, 155 Crico-pharyngeus, 166 -thyroid, 177 Cutaneous, 117 Deep flexor of the digits, 96, 99, 136 gluteal, 83 pectoral, 2 Deltoid, 126 Diaphragm, 71 Digastric, 162 Dorsal crico-arytenoid, 178 serratus, 145 straight (of the head), 154 Extensor of the fifth digit, 90 Extensors of third, fourth and fifth digits, 132 External cremaster, 6 oblique abdominal, 10 obturator, 82 pterygoid, 182 Gastrocnemius, 94 Gemelli, 83 Genio-glossal, 162 -hyoid, 163 Gracilis, 77 Helicis, 152 Hyo-epiglottic, 180 -glossal, 163 -pharyngeus, 166 148 238 Muscles: Iliacus, 74 Tlio-costalis, 145 -psoas, 74, 80 Incisive, 156 Inferior oblique (of eye), 187 Infraspinous, 126 Intercostal, 29 Intermediate vastus, 86 Internal oblique abdominal, 11 obturator, 85, 112 pterygoid, 181 Interosseous, 100, 141 Intertransverse, 154 Ischio-cavernous, 110 -urethral, 110 Jugulo-hyoid, 166 Lateral crico-arytenoid, 179 straight muscle of the head, 181 vastus, 83 Latissimus dorsi, 10, 120 Levator ani, 108 of soft palate, 165 of the upper eyelid, 155, 186 lip, 156 Levators of the ribs, 146 Lingual, 173 Long abductor of the pollex, 134 extensor of the digits, 89 : hallux, 91 pollex, 133 flexor of the digits, 96 hallux, 96 Longissimus capitis et atlantis, 153 cervicis, 153 dorsi, 145 Long peroneal, 90, 102 Longus capitis, 181 colli, 181 Lumbrical, 99, 141 Malar, 156 Masseter, 156, 159 Medial vastus, 79 Middle gluteal, 83 Multifidus, 145, 154 Mylo-hyoid, 149 Naso-labial, 156 Oblique muscles of the head, 154 Occipital, 152 Omo-transverse, 119 Opponens pollicis, 141 Papillary (of heart), 53 Pectinate (of heart), 51 Pectineus, 79 Pharyngo-palatine, 166 Piriformis, 83 Plantaris, 94 Popliteal, 96 Posterior tibial, 96 Preputial, 8 Pronator quadratus, 137 teres, 135 INDEX Muscles : Proper extensor of the second digit, 133 Psoas major, 74 minor, 74 Pterygo-pharyngeus, 166 Quadrate of upper lip, 156 Quadratus femoris, 82 lumborum, 74 plantz, 99 Quadriceps femoris, 86 Radial extensor of the carpus, 130 flexor of the carpus, 135 Rectus femoris, 86 Retractor (of eye), 187 of the penis, 110 Rhomboid, 119 Risorius, 156 Sacro-coccygeal, 146 Sartorius, 77 Scalenus, 28 Scutular, 151 Semimembranosus, 79 Semispinalis capitis, 153 dorsi et cervicis, 145, 153 Semitendinosus, 80 Short extensor of the digits, 91 flexor of the digits, 98 fifth digit, 142 pollex, 141 peroneal, 90 Sphincter of the anus, 108 eyelids, 155 lips, 156 pupil, 191 vulva, 116 Splenius, 152 Stapedius, 231 Sterno-cephalic, 118 -hyoid, 148 -thyroid, 148 Straight abdominal, 12, 13 muscles of the eye, 187 Stylo-glossal, 162 -hyoid, 162 -pharyngeus, 166 Submultifidus, 145 Subscapular, 120 Superficial flexor of the digits, 135 gluteal, 82 pectoral, 2 Superior oblique (of eye), 186 Supinator, 134 Supraspinous, 126 Temporal, 160 Tensor fascie late, 82 of the fascia of the forearm, 122 soft palate, 165 tympani, 231 Teres major, 120 minor, 127 Thyro-hyoid, 163 -pharyngeus, 166 Muscles: Tragicus, 151 Transverse abdominal, 13 costal, 11 thoracic, 31 Trapezius, 118 Triceps, 122, 128 Ulnar extensor of the carpus, 132 flexor of the carpus, 136 Urethral, 109, 110 Uvule, 169 Ventral serratus, 28, 120 straight muscle of the head, 181 Ventricular, 179 Vocal, 179 Zygomatic, 156 Myocardium, 57 NASO-LACHRYMAL duct, 200 -palatine duct, 200 NERVES : Abdominal part of the sympathetic, 114 Abducent, 187, 211 Accessory, 120, 167, 211 Acoustic, 211 Ansa subclavia, 62 Anterior auricular, 152 Auriculo-palpebral, 158 Axillary, 5, 122 Brachial plexus, 5 Buccinator, 158, 184 Cardiac plexus, 56 Caudal gluteal, 85, 113 hemorrhoidal, 113, 114 mesenteric plexus, 26 Cerebral, 196, 210 Common peroneal, 91 Cranial gluteal, 85, 113 mesenteric plexus, 25 Deep peroneal, 89, 92 radial, 134 temporal, 165, 184 Dental, 183 Dorsal buccal, 158 digital, 89 metatarsal, 92 nerves of penis, 9, 112 cesophageal trunk, 58, 66 External nasal, 183 spermatic, 10, 75 Facial, 157, 211 Femoral, 75, 81, 113 Frontal, 158, 185 Genito-femoral, 75, 113 Glosso-pharyngeal, 166, 211 Greater palatine, 183 splanchnic, 71 superficial petrosal, 198 Hypoglossal, 163, 167, 211 Ilio-hypogastric, 12, 75, 113 -inguinal, 13, 75, 113 Inferior alveolar, 184 INDEX Nerves: Infraorbital, 158, 183 Infratrochlear, 158, 186 Intercostal, 12, 29, 63 Internal auricular, 152 Lachrymal, 158, 183 Lateral cutaneous femoral, 75, 85, 113 (of calf), 94 (of forearm), 122 plantar, 96, 99, 102 Lesser palatine, 183 splanchnic, 71 Lingual, 163, 184 Long thoracic, 5, 28 Lumbar, 112 Mandibular, 158, 184 Masseteric, 159, 184 Maxillary, 158, 183 Medial cutaneous (of calf), 94, 96 dorsal cutaneous, 88 plantar, 96, 99 Median, 5, 123, 137 Mental, 158 Middle hemorrhoidal, 112 Musculo-cutaneous, 5, 112 Mylo-hyoid, 184 Naso-ciliary, 186 Obturator, 80, 113 Oculo-motor, 187, 210 Olfactory, 210 Ophthalmic, 158, 185 Optic, 187, 210 Pelvic part of the sympathetic, 114 Perineal, 112 Phrenic, 5, 47 Plantar digital, 99, 102 metatarsal, 99 Posterior auricular, 152 cutaneous femoral, 82, 113 nasal, 183 Pudendal, 112, 113 Pulmonary plexus, 56 Radial, 5, 123, 128, 129 Recurrent, 59, 149 Sacral, 112 Saphenous, 77, 79, 94 Sciatic, 84, 113 Short ciliary, 187 Spheno-palatine, 183 Spinal, 202 Subscapular, 5, 122 Superficial peroneal, 88, 92 temporal, 158, 184 Superior labial, 183 laryngeal, 167 Suprascapular, 5, 122 Sympathetic trunk, 149 Thoracic part of the sympathetic, 61 Thoraco-dorsal, 5 Tibial, 96, 99 Trigeminal, 158, 211 Trochlear, 185, 210 239 240 Nerves : Ulnar, 5, 123, 137, 142 Vagus, 58, 149, 166, 211 Ventral buccal, 158 cesophageal trunk, 58, 65 thoracic, 5 Vidian, 198 Volar digital, 142 metacarpal, 137 Zygomatic, 158, 183 OcULO-MOTOR groove, 220 Csophagus, 59, 150 Olfactory bulb, 210 lobe, 210 tract, 210 tubercle, 210 Omental bursa, 18, 24 Optic chiasma, 206, 209 papilla, 191 recess, 219 tracts, 209, 220 Ora serrata, 191 Orbiculus ciliaris, 190 Orbit, 184 Orbital band, 184 Osseous labyrinth, 229 Ostium arteriosum (of heart), 53, 54 venosum (of heart), 53 Ovarian bursa, 68 Ovary, 68 Pancreas, 38 Pancreatic duct (of Wirsung), 39 Paraflocculus, 224 Parotid duct, 157 gland, 156 Pelvis (female), 114 (male), 106 of kidney, 70 Penis, 8 Pericardium, 31, 47 Perichoroidal lymph-space, 189 Periorbita, 184 Peritoneum, 22, 65 Petrous lobule, 224 Pharyngo-palatine arch, 169 Pharynx, 173 Philtrum, 170 Pia mater, 202, 207 Pineal body, 218 recess, 219 ma Pleura, 31 Pons, 206, 223 Porta of liver, 65 Posterior commissure, 219 fovea, 226 medullary velum, 225 perforated substance, 209 Premolars, 171 Prepuce, 7 Promontory, 231 INDEX Prostate, 109 Pubo-vesical fold, 107 Pulmonary ligament, 34 semilunar valves, 53 Puncta lacrimalia, 155 Pylorus, 38 Pyramid, 209, 222 Pyriform lobe, 210 sinus, 176 Recess of the Infundibulum, 219 Recto-uterine excavation, 68 Rectum, 107, 115 Restiform body, 223 Retina, 191 Rhinal fissure, 212 Right atrium (of heart), 51 ventricle (of heart), 52 Rima cornealis, 189 Root of lung, 46 SAccULE, 230 Salivary papilla, 170 Scala tympani, 230 vestibuli, 230 Sclera, 189 Scrotum, 5 Scutiform cartilage, 150 Sections of spinal cord, 205 Semicircular canals, 230 ducts, 230 Semilunar valves, 56 Septum of the nose, 198 pellucidum, 215, 217 ventriculorum, 52 Sheath of straight abdominal muscle, 13 Sinuses of dura mater, 194, 197 Small intestine, 19 Soft palate, 168 Sole of the pes, 97 Solitary lymph-nodules, 27 Spermatic cord, 7 Spinal cord, 202 Spiral lamina, 230 Spleen, 36 Stapes, 231 Stomach, 37 Stria terminalis, 218 Structure of the bladder, 109 intestines, 27 cesophagus, 59 stomach, 66 wall of heart, 57 Subarachnoid cisterns, 207 space, 202, 207 Subdural cavity, 194, 201 Sublingual caruncle, 161 ducts, 161 gland, 161 Submazxillary duct, 161 gland, 161 INDEX 24] Sulci of brain, 212 Veins: Cranial vesical, 112 Suprapineal recess, 219 Deep circumflex iliac, 73 Suprarenal glands, 70 ‘ facial, 159 Supratonsillar fossa, 169 Dorsal digital, 87 metatarsal, 87 TaPetum, 190 veins of penis, 9 Tarsus (of eyelid), 155 External iliac, 76 Teeth, 170 jugular, 146 Tegmentum, 220 maxillary, 147, 159 Tentorium cerebelli, 196 Facial, 159 Terminal crest (of heart), 52 Femoral, 79 groove (of heart), 52 Great saphenous, 77 Testis, 7 Hepatic, 74 Thalamus, 218 Hypogastric, 112 Third ventricle, 218 Tlio-lumbar, 112 Thoracic duct, 61, 74 Inferior labial, 159 Thorax, 31 Innominate, 48 Thymus, 42 Intercostal, 29, 62 Thyroid cartilage, 175 Internal jugular, 148, 168 gland, 150 mammary, 42, 148 Tongue, 172 Lingual, 159 Tonsil (palatine), 169 Lumbar, 73 Tonsillar sinus, 169 Median basilic, 126 Trabecule carne, 52 cephalic, 126 Trachea, 57, 149 (of forearm), 129 Transverse cerebral fissure, 206 Middle hemorrhoidal, 112 peduncular fasciculus, 221 Occipital sinus, 194 sinus of pericardium, 48 of heart, 51 vesical folds, 107 penis, 112 Tricuspid valve, 53 Phrenic, 74 Tuber cinereum, 206, 209 Phrenico-abdominal, 73 Tubercle of Lower, 52 Perineal, 112 Tunica vaginalis, 7 Petrosal sinuses, 197 Tympanic cavity, 230 Portal, 40 Radial, 129 Umpizicvs, 13 Reflex, 159 Ureter, 70 Renal, 73 Urethra, 109, 115 Sagittal sinus, 194 Urinary bladder, 108, 115 Small saphenous, 87 Uro-genital sinus, 116 Spermatic, 73 Uterine tube, 68 Spinal, 20 Uterus, 67, 115 Superficial temporal, 160 Utricle, 230 Superior labial, 159 Transverse sinuses, 194 Vaatna, 115 Ulnar, 129 Vallate papille, 173 Vena azygos, 48, 62, 74 Valve of the colon, 27 Ventricle of larynx, 176, 179 vena cava, 52 Ventricular folds, 176 VEINS: Vestibule of the ear, 230 Axillary, 4, 126 larynx, 176 Basilar plexus, 197 a nose, 200 Basilic, 126 Villi, 27 Buccinator, 159 Vitreous body, 191 Cephalic, 126 Vocal folds, 176 Caudal epigastric, 12 Vomero-nasal cartilage, 200 gluteal, 112 organ, 200 vena cava, 48, 73 Vulva, 116 Cavernous sinus, 197 . . Common iliac, 73 WHITE commissure (of spinal cord), 205 anial epigastric, 12 : . duteal. 112 ZONULAR spaces, 192 vena cava, 48 Zygomatic gland, 182 PRINTED BY SPOTTISWOODE AND CO. LTD., COLCHESTER LONDON AND ETON Be ties teat ae es fs pers iar tr Ciesek LED ean hehe "a aceite OA a ieee at rs es fia in ef iti et mr i i, Bid peri gate ie cated eee aD Bel Bee: eee eta Dahesh ater ata et ia te plone ea oe er openct oy = Seecaenth no enet th — Suis = See ee Soe eee ce ce merece tent cee Se oe od, Catt 4 bla rate Siihtasiel (i by, Shee Halas Lay a ian tes oe? SHY hities as the 7 ie Tita tains one eatin tn Abe la Poon pacer eens jure viaep uty Vewtysunver ein ae o Seon rm are RUA’ by che me Ld a) i ahi eee cy ern! Lateef tones a laninasiie a Males cin ot ti rie i ih