\ \ \ \\ \ \ ‘ \ S \ - \ \\ \ \\ A AX _ \ . — : _ SRN + ANN — NS ‘ ae . NR x \ . AN RA \ 1 CORNELL UNIVERSITY { MEDICAL LIBRARY { ITHACA DIVISICN. FROM SIMON HENRY GAGE, CLASS OF ei Cornell University Library Tena : DISSECTION OF THE DOG AS A BASIS FOR THE STUDY OF PHYSIOLOGY BY W. TL. HOWELL, A.B.,. PH.D, ASSOCIATE IN BIOLOGY, JOHNS HOPKINS UNIVERSITY, MEDICAL LIBRARY, STimson HO NEW YORK HENRY HOLT AND COMPANY 1888 Copyright, 1888, BY Henry Hott & Co. TABLE OF CONTENTS. INTRODUCTION. Method of killing and preparing the dog—Necessary dissecting instruments— Method of injecting and of making cannulas... . CHAPTER I. Muscles of the abdomen--The abdominal viscera—External and internal anatomy of the alimentary canal and connected organs—The urinary system—Female reproductive organs— Male reproductive organs—The diaphragm................. CHAPTER II. Muscles of the shoulder—Muscles of the arm..............+.05. CHAPTER III. The thoracic viscera—Dissection of the heart and great blood- vessels—Dissection of the mouth; of the nasal cavity; of the salivary glands; of the cartilages of the larynx............. CHAPTER IV. Injection of the blood-vessels—Dissection of the vascular system —Branches of the descending aorta; of the post-cava; of the portal system; of the pre-cava— Arteries of the anterior portion of the body. i. ssp. ccm untae stn oye teat eben ee CHAPTER V. Muscles of the thorax—Dissection of the neck; of the thoracic vagus; of the thoracic sympathetic; of the brachial plexus; of the muscles of the larynx... 66.06. cece cee eee cee CHAPTER VI. Dissection of the brain—Directions for the removal of the brain —External characters—Internal structure. .............ee00- CHAPTER VII. Dissection of the eye—Accessory organs of the eye—Muscles of the eyeball—Dissection of the eyeball...............-..0-005 PAGE 5 30 37 49 61 75 PREP AG.E. Ir is admitted beyond all question that even an elementary study of human physiology ought to be preceded by a more or less thorough dissection of some mammal. This little book, prepared originally for the author’s own class, is intended to give this necessary anatomical basis to those who have not the opportunity of dissecting the human body. With this purpose in view, attention has been directed to those organs which are the chief objects of physiological study, rather than to those which have mainly an ana- tomical interest. One chapter has been inserted treating of the anatomy of the muscles of the shoulder and arm, but the author does not think it advisable to require this of a class unless there is abundance of timeat the teacher’s disposal. The anatomy of these muscles is of no particular importance in general phy- siology, and even from the standpoint of comparative anatomy it has but little value owing to the incom- plete knowledge possessed with regard to muscle homologies among the mammalia. With reference to the muscles of the abdomen and the thorax the case is very different: these muscles play an important part in the performance of the respiratory movements, and their position and relations ought to be known by the student. Descriptions of these muscles, therefore, 6 PREFACE, have been inserted in connection with the chapters on the abdominal and thoracic viscera. The dog has been selected in preference to the rab- bit or the cat, the other animals usually employed for such purposes, for several reasons. In most respects its anatomy corresponds very closely to that of man ; the size of the blood-vessels and other organs is rela- tively large, and this is especially true of the thoracic viscera and the neck region, which can be dissected with more success by the beginner upon the dog than upon the rabbit or the cat; if small dogs are se- lected, they will be found to be of a convenient size for general laboratory use; finally, most of the usual physiological experiments and demonstrations are made upon the dog, and a knowledge of its anatomy will therefore prove particularly valuable to those who intend to make a special study of physiology. The directions for dissection have been divided into seven chapters, with the idea that a fresh dog would be used for each chapter with the exception of those upon the muscles of the shoulder and arm, the brain, and the eye, requiring therefore four dogs for the entire work, though a smaller number may be made to. answer. To obtain the most satisfactory results, how- ever, one must be careful not to attempt to dissect too much upon a single animal. When the student is at work upon the blood-vessels he should not be required to dissect at the same time the peripheral nervous system. A much better knowledge of the circulatory organs, especially of their relations to each other, will be obtained if they are dissected asa whole. After learning the anatomy of the blood-vessels the nerves can be dissected with greater success, and their rela- tions to the arteries and veins determined more easily. PREFACE, 7 The same remarks apply of course to other groups of organs. Fach chapter, therefore, with the exceptions named, has been arranged so as to include a number of regions or sets of organs which can be conveniently dissected upon one animal. If there is not sufficient time for a class to do the whole chapter, there is no obstacle in the way to prevent the teacher from select- ing the most important parts and omitting the others. In the use of terms denoting directions and relations it has been thought best to employ the usual nomen- clature rather than to adopt the more recent and more exact designations proposed by various authors. These latter are not as yet current in general anatomical literature or standard anatomies; indeed it remains to be seen which of those proposed will prove ‘“‘the fittest.” It did not seem wise, then, to burden the beginner with a discussion as to the use of terms, when in the great majority of cases the terms in ordinary use are suffi- ciently definite. The terms of direction made use of are: anterior, meaning toward the head; posterior, toward the tail ; dorsal and ventral, with the usual significance ; and right and left, inner and outer, with reference to the mid-line of the body. In the directions for dissecting and in the descrip- tive part of the text an effort has been made to avoid unnecessary minuteness in the instructions. To a per- son altogether ignorant of the methods of dissecting a written description cannot fully supply the place of an instructor ; it is necessary and indeed better for him to learn some things from experience. To students with some little experience in the art of dissection, or work- ing under the guidance of an instructor, it is a hin- drance rather than an advantage to attempt to describe just the direction and extent of each cut, the way in 8 PREFACE, which the instruments should be held, etc., or to point out all the numerous possible mistakes which may be made. It is better to leave something to the intelli- gence and discretion of the teacher or the pupil, if the dissecting is to prove a healthy discipline. It is but proper to say that the general idea of the arrangement of the directions for dissection was taken from the very excellent book on “ Practical Zoology” by Marshall and Hurst. I take pleasure also in expressing my thanks to my friend Mr. T. D. Coleman, Assistant in Physiology in this laboratory, for his kindness in helping me in the dissections and in the preparation of the diagrams. W. H. Howe... Jouns Hopkins University, BautTimore, Mo. INTRODUCTION. Tue following brief description of methods and instruments may contain some useful practical hints for those whose experience in such matters is limited. Method of Killing and Preparing the Dog.—The quickest and most merciful method of killing the dog is to chloroform him. For this purpose it is only necessary to have a tight box or metal can with a well-fitting cover. Inthe bottom of this box place a sponge saturated with chloroform, put in the dog and close the lid. After a short time the animal becomes quiet, but it should not be removed from the box until all respiratory movements have ceased. For convenience in dissecting the dog should then be tied down upon some form of dog-holder. Perhaps the simplest and most economical form, one which can be readily made and answers every purpose, is shown in I, Fig. 1. It consists of a board about 30 “inches long and 12 inches wide, supported upon two blocks, and having at one end a piece of bent iron, rod which can be fastened into the mouth, and serves to hold the head. On the sides of the board are six cleats by means of which the limbs.of the animal can be fastened in any desired position. With regard to the preservation of the animal, if the dogs are to be kept only a few days, or even a week, the simplest and least injurious method is to leave them on ice in an ice-box when they 10 INTRODUCTION. are not being dissected. A number of dogs can be kept in good condition in this way with but little expense, especially if it is possible to remove the intestines, or at least the large intestine and rec- tum, after the first day. This method of preserving the animal has the great advantage of not decolorizing any of the tissues, and furthermore prevents the sour odor which soon comes on after using preservative liquids. If it is not possible to make use of this method, and it is necessary to keep the animal for some time, recourse must be had to some of the usual preservative liquids. Immersing the dog in alcohol will keep it from decomposing, but leaves it in such a bad condition for dissecting that it is not to be recom- mended. Wickerscheimer’s liquid injected into the arteries after having previously washed out the blood with 0.6% sol. of NaCl is highly recommended, though my experience with it has been unsatisfactory. The formula for this liquid is as follows: Dissolve in 3 litres of boiling water 100 grms. of alum, 25 grms. of common salt, 12 grms. of potassium nitrate, 60 grms. of potassium carbonate, and 20 germs. of arsenious acid ; after cooling add 14 litres of glycerine and 4 litre of alcohol. A liquid which I have tried but few times, but which has given satisfaction, is made by mixing one part of glycerine with two parts of a 2% solution of corrosive sublimate, and adding to this mixture crystals of chloral hydrate in the proportion of 2 grms. of chloral to each 100 cc. of the liquid. This liquid keeps the animal pliant, does not destroy the color, and seems to bring out the nerves more distinctly. Necessary Dissecting Instruments —Each student should be provided with a small case of dissecting in- struments containing at least the following things: Fic. 1.—INSTRUMENTS. 12 INTRODUCTION. Two dissecting scalpels, one large and one small. Two dissecting forceps, one large with blunt ends, and one small with fine points for more delicate work. Two pairs of scissors, one with large blades for coarse work and one small pair for fine dissection. One seeker, an instrument of the form shown in II, Fig. 1. This will be found very useful in dissecting nerves, blood-vessels, etc., when by careful tearing with the seeker instead of cutting with the scalpel or scis- sors structures may be revealed which otherwise would be destroyed. Several weighted hooks of the kind shown in IV, Fig. 1. These consist simply of a strong hook to which is attached a cord about two feet in length, car- rying at its other end a lead weight. The most con- venient weight to use :s about 125 grammes, though it is well to have some lighter and some heavier than this. These weighted hooks are useful for holding back the skin, muscles, etc., while dissecting, and are much preferable to the ordinary chain-hooks sold with dissecting cases. In addition to these instruments there should be at hand for general use several artery-clamps or ‘‘serre- fines,” either of the form usually sold by instrument makers, or preferably like that shown in V, Fig. 1, hav- ing longer and narrower points; several aneurism needles of the form shown in ITI, Fig. 1, for passing ligature threads round blood-vessels, etc.; one or more pairs of strong bone forceps such as can be obtained from any instrument-maker ; a number of small sponges and a small saw. Cannulas and Injecting Syringe. The cannulas used in injecting can readily be made of any desired size from ordinary glass tubing. The steps in the pro- INTRODUCTION. 13 cess are represented in Fig. 1. The glass tubing is first held in the Bunsen flame until softened, and then pulled out gently to the form shown in A. After cooling a scratch is made with a file at the point indi- cated by the dotted line, the tube broken, and the end ground down obliquely to the form shown in B, upon a grindstone or a piece of ground glass. The narrow neck given to the cannula in this way is necessary in order to hold it firmly when tied in the blood-vessel. The two ends of the cannula should be slightly rounded by heating in the flame. If cannulas are needed for the smaller arteries, for ducts of the salivary gland, etc., the. glass tube after being softened in the flame is pulled out to the proper diameter and then this narrowed portion is treated as above. The requisite features of a good cannula, especially if it is to be used in experiments upon a living animal, are that the neck should be as short as possible, and not any narrower than is necessary to enable the cannula to be tied firmly in the vessel; and secondly, the lip of the cannula should not be made too oblique, not more so than will facilitate its introduction into the vessel. Three of these cannulas will be required in the injection of the blood-vessels as described in Chapter IV., one for the aorta and two for the venz cave. As these must all be of large size they can easily be made. With reference to the syringe, the best form un- doubtedly is the usual brass injection syringe provided with several brass cannulas and a stop-cock ; it can be obtained from any of the instrument-makers. These syringes, however, are very expensive, and those who cannot afford to buy them will find the common white-metal syringes with double leather piston a 14 INTRODUCTION. cheap and serviceable substitute. These latter can be obtained from Whitall, Tatum & Co. of Philadelphia, of different sizes and at very small cost. The best size to use for the dog is one holding six or eight ounces. Before using this syringe the piston must be left in water for some time to swell, otherwise it will not work tight in the barrel; though if left too long in: the water the trouble will be in the other direction. The method of using the syringe in injecting is de- scribed in Chapter IV. CHAPTER L MUSCLES OF THE ABDOMEN AND AB DOMINAL VISCERA. MUSCLES OF THE ABDOMEN. Make a median tnctston through the skin and fat extending from the meddle of the sternum to the sym physts pubis; at the two ends of this make lateral in czstons on each side, and reflect the flaps of skin to- gether with the subjacent fat. The muscular portion of the abdominal wall wll be exposed. I. The Linea Alba is the white line extending along the ventral mid-line of the abdomen; it is formed by the fusion of the tendons of the muscles of the two sides. 2. The External Oblique Muscle arises by fleshy slips from the posterior ribs, from the fourth to the thirteenth, and in part from the fascia below the thirteenth rib; the fibres pass obliquely inward and posteriorly, and end in a broad, thin aponeurosis lying along the middle of the abdominal wall and fusing with its fellow of the opposite side. Make an inctston through the aponeurosts at tts Junc- tion with the muscle fibres, and reflect the muscle out- ward, separating ut carefully from the muscles beneath, 16 MUSCLES OF THE ABDOMEN 3. The Internal Oblique Muscle arises from the crest of the ilium, from Poupart’s ligament, and from the aponeurosis of the transversalis muscle anterior to the ilium; its fibres pass obliquely inward and anteriorly to end in a thin aponeurosis which meets its fellow in the mid-line, and lies immediately below that of the external oblique, the two being separated with some difficulty. 4. The Rectus Abdominis Muscle is a_ straight band of fibres arising anteriorly from the sternum and the cartilaginous portions of the posterior ribs, and inserted at the symphysis pubis. Several zigzag lines of fibrous tissue pass transversely across the band of fibres in their course, making it in reality a poly- gastric muscle. 5. The Transversalis Abdominis arises by fleshy slips from the under surface of the posterior ribs and from the region of the lumbar vertebre; the fibres pass transversely inward, and end in a thin aponeurosis lying beneath the rectus abdominis, Dissect off very carefully the rectus abdomints and the transversalts,; a thin membrane, the peritoneum, well be exposed covering over the abdominal organs. THE ABDOMINAL VISCERA. After removal of the peritoneum the abdominal viscera are exposed in situ. The intestines are con- cealed by a special fold af the peritoneum, che reat omentunz, which hangs down from the stomach. The omentum is loaded with fat, and if held up against the light it will be found to be penetrated by a num- ber of minute holes. : AND ABDOMINAL VISCERA. 17 A, THE ALIMENTARY CANAL. I. The Gsophagus. The posterior end of the cesophagus as it enters the stomach can be seen by pressing aside the lobes of the liver; it penetrates the diaphragm below the middle. 2. The Stomach may be studied in situ by lift- ing up the lobes of the liver so as to expose it fully. When empty it lies obliquely in the body, having a marked bend at the posterior end; when filled it lies more transversely. a. THE Funpus. The left or cardiac end of the stomach is much dilated; the enlarged portion which lies to the left of the entrance of the cesophagus is the fundus. b. Tue Great Curvature is the line from the fundus along the posterior margin of the stomach to the beginning of the intestines. c. THE SMALL CurRvaTurRE is the line from the opening of the cesophagus along the anterior margin of the stomach to the beginning of the intestine. d. Tue Pytorus is the opening of the stomach into the intestines. The position of the pylorus is marked externally by a shallow constriction. This region of the stomach is spoken of as the pyloric end as dis- tinguished from the cardiac end in the neighborhood of the oesophagus. 3. The Intestines. a. THe Duopenvm is the first portion of the small intestine. It begins at the pylorus, bends suddenly to the posterior for several inches, and then forward again for some distance, making a U-shaped loop, which continues directly into the remainder of the small intestine. The glandular organ lying in the 18 MUSCLES OF THE ABDOMEN curvature of the duodenum is the pancreas; its at- tachments must not be disturbed. b. Tue Savy InreEstTINE is several feet in length, and forms a very much convoluted tube which is at- tached to the dorsal wall of the body by a membrane, the mesentery. Starting from the duodenum, follow the small intestine to its ending in the large intestine. c. THe Mesentery is a double layer of the peri- toneum which is reflected from the dorsal wall of the abdomen, and encloses the stomach and _ intestines. Blood-vessels, nerves, and lymphatics pass to the in- testines between its two layers. d. THe C-cum is seen at the point where the small intestine passes into the large; it isa coiled diverticu- lum of the intestine two or more inches in length. e. THe LarGe INTESTINE commences at the ceecum. The first portion is known as the colox , it passes an- teriorly for a short distance as the ascend7ng colon, then transversely, the ¢ransverse colon, and finally posteriorly as the descending colon, which is continued directly into f. Tue Rectum. This is the terminal portion of the large intestine ; it les within the pelvis, and opens to the exterior through the anus. g. Pever’s Patcnes. At intervals along the lower portion of the small intestine, on the border oppo- site the attachment of the mesentery, a number of small oval bodies will be seen, the Peyer’s patches. They are masses of lymphoid tissue imbedded in the intestinal wall. h. Lympu Granps. Enclosed within the layers of the mesentery will be found a number of lymph glands, flattened oval bodies varying in size. Where the AND ABDOMINAL VISCERA. 19 cecum joins the intestine there is a collection of these glands known as the Pancreas Assellz. B. INTERNAL ANATOMY OF THE ALIMENTARY CANAL AND APPENDICULAR ORGANS. Ligature the stomach about one inch to the left of the pylorus, and at the esophagus. Remove the stomach from the body, cutting through its walls just beyond the ligatures, open rt along the great curvature, wash with water and examine. 1. The Stomach. The walls of the stomach con- sist of an outer layer of peritoneum, a middle layer of muscle which is thicker at the pyloric end than elsewhere, and an internal layer of mucous membrane. The last layer is connected to the mus- cular wall by sub-mucous areolar tissue, and can easily be pulled or dissected away. The mucous mem- brane is thrown into numerous folds which are es- pecially marked in the cardiac region. Cut out a prece of the small intestine, selecting a portion which contatns one or more Peyer's patches, open along the line of the mesentery, wash thoroughly and examine. 2. The Small Intestine. The walls of the small intestine are composed of the same layers as those of the stomach. The mucous membrane is not thrown into foids, but is raised into a number of minute pro- cesses which can be seen better with a magnifying- glass. These processes are set closely together like the pile of velvet; they are known as the V2ddz. Examine the appearance of a Peyer's patch when seen from the inside. 20 MUSCLES OF THE ABDOMEN 3. The Cecum. Cut out the cecum together with the adjotning por- trons of the small and large intestine, lay open, and wash with water, The boundary line between the small and the large intestine is marked by a circular thickening of the mucous membrane—representing the 2/eo-colic valve. On one side the mucous membrane of the small intestine is shaggy with villi; on the other, the colon, the membrane is smooth. The mucous mem- brane of the caecum is thickly studded with small lympb follicles. 4. The Colon. The mucous membrane is smooth throughout, showing no villi, but in some places it is thrown into irregular folds or ruge. 5. The Pancreas lies in the loop of the duo- denum ; it is an elongated glandular body of pinkish color, 6. The Pancreatic Ducts. In the dog there are two main ducts; one, the smaller, opens into the duodenum about an inch beyond the pylorus, close to or in connection with the bile duct; the other, larger duct opens into the duodenum about 1 or 13 inches lower down. (The close attachment of the pancreas to the duodenum conceals these ducts. They can be demonstrated most easily by tearing away care- fully the pancreas from the duodenal wall with a blunt-pointed instrument, commencing at the pylorus. The ducts are tougher than the loose connective tissue attaching the rest of the pancreas, and can be ex- posed easily in this way.) 7. The Spleen is an elongated, flattened, dark- red body lying to the left of the stomach, and con- nected to it by a fold of the peritoneum, the gastro- AND ABDOMINAL VISCERA. 21 splenic omentum. It is wider at the upper end; the blood-vessels enter it along the line of attachment of the omentum. 8. The Liver. The anterior surface is convex, and fits against the arched diaphragm to which it is at- tached by a median fold of peritoneum, the sasfen- sory liganent. The organ is relatively large in the dog, and, as in other mammals, may be divided into two principal lobes, the right and the left. Each of these is again subdivided into smaller lobes, the left into two and the right into four, the homologies of which are not properly known. They may be named as follows: a. THe Lerr Centrat Lose lies against the left half of the diaphragm. b. THe Lerr Laterat Lopsg, the largest lobe of the liver, lies between the left central and the cardiac end of the stomach. c. THe Ricur CenTRAL Lose lies against the right half of the diaphragm; it has a deep groove on its under surface for the reception of the gall-bladder. d. THe Ricut LaTerat Lose is just posterior to the right central. e. THE CaupaTE Losg, posterior to the last, les to the right of and dorsal to the pyloric end of the stom- ach, extending backward to the right kidney. f. Tue SpiceLtian Loses, the smallest lobe of the liver, projects into the small curvature of the stomach ; it lies dorsal to a fold of the peritoneum connect- ing the liver to the stomach, the /epato-gastrec omentnii2. g. THE GALL-BLADDER is a large, thin-walled oval sac imbedded in the right central lobe. h. THe Brie-puct has the arrangement shown in 22 MUSCLES OF THE ABDOMEN Fig. 2, It opens into the duodenum about an inch below the pylorus. The duct leading directly from the gall-bladder is known as the cys/ec duct. In the dog it is very short. L. CENTRAL L. LATERAL - L. LATERAL SPIGELIAN CAUDATE AND R LATERAL Fic, 2. DIAGRAM OF THE BILE-DUCT AND ITS BRANCHES, C. THE URINARY SYSTEM. Remove the liver, spleen, and intestines from the abdomen, taking care not to disturb the reproductive or the urinary organs. Ln renoving the liver it will prove most conventent to double-ligature the large enferwor cava above and below the liver, and cut be- tween the ligatures. Ln removing the tntestines double- ligature the rectum as near the anus as possible, and cut between the ligatures. I. The Kidneys are a pair of dark-red oval bodies lying against the dorsal wall of the abdomen, outside of the peritoneum. Each is usually im- bedded in fat. If this is carefully removed, the Az/us will be exposed as a notch on the inner border where the blood-vessels and ureter enter the kidney. AND ABDOMINAL VISCERA. 23 2. Adrenal Bodies—one on each side. They lie in- ternal to the upper portion of the kidney, and are surrounded by fat. Each is an elongated, yellowish body about # in. in length. 3. The Ureter emerges from the hilus of the kidney, passes backward and inward to reach the under surface of the bladder, into which it opens, well down toward the neck. Make an opening in the ureter about an inch from the bladder, and through this opening pass a bristle or probe into the bladder. Notice that the ureter runs obliquely in the wall of the bladder some distance before it reaches the in- terior. 4. The Bladder is a thin-walled muscular sac which when filled with urine projects some distance above the symphysis pubis. Cut open the bladder and remove any urine that may be present with a sponge. Determine the position of the opening of the ureters internally. From each a white thickening of the mucous membrane passes downward to the urethra, inclosing a triangular area, the ¢rzgone. 5. The Urethra, the duct of the bladder arises from the lowest portion of the bladder. Its further course will be seen in the dissection of the repro- ductive system. 6. The Internal Structure of the Kidneys. Remove one from the body and slice it open along ats long diameter, preferably a little to one side of the ma-line. Each kidney has externally a fibrous investment which can be peeled off easily with the forceps. The proper substance of the kidney is divided into a cor- tical and a medullary layer. 24 MUSCLES OF THE ABDOMEN a. THE CorticaL Susstance forms the external layer. It is of a darker color, and somewhat mottled owing to the presence of the J/al/pighzan bodtes. b. THe MeEpuLtary Susstance forms the internal layer. It is of a lighter color, and striated owing to the peculiar arrangement of the uriniferous tubules and blood-vessels. The uriniferous tubules are united into a number of groups, each of a pyramidal form, and known as the Alalpighian prramtzds. c. Tue Sinus. The medullary substance encloses a cavity, the sinus, which is a continuation inward of the hilus. It is filled with connective tissue, blood- vessels, and the greatly expanded ureter, which here is known as the pe/v7s. The expanded pelvis breaks up into a number of smaller divisions, cadzces, each of which clasps the apex of a pyramid. With a little dis- section this arrangement of the pelvis may be demon- strated. D. THE DIAPHRAGM. The diaphragm is the muscular septum between the abdomen and the thorax, and can now be examined from the abdominal side. It is a dome-shaped parti- tion, partly muscular, partly membranous. 1. The Central Tendon lies at the top of the dome. It is a thin membrane passing into muscular substance at all points of its circumference. 2. The Muscular Substance has three origins: a. Posteriorly from the bodies of several of the lumbar vertebrze by two thick muscular slips or crura, b. From the ensiform cartilage. c. From the cartilages of the posterior ribs. AND ABDOMINAL VISCERA, 25 From these points the muscular substance passes up along the walls of the thorax for some distance, and then bends inward somewhat abruptly to end in the central tendon. £. FEMALE REPRODUCTIVE ORGANS. Lf dissected upon a new dog, open the abdomen as in the dessection of the abdominal viscera, and remove the stomach, tntestines and liver. Then cut through the skin and muscles above the pubts symphysts so as to ex- pose this and the ramt running from zt above and below for a short distance. Cut through the sym- physts with bone forceps, and the ramt above and below the obturator foramen at a distance of about one-half inch on cach side of the symphyses. Remove carefully the preces of bone thus rsolated. 1. The Ovaries. Me poe = [ a ~ ; a o XILR.C, XII, RAMUS COMMUNICANS, |, LUMBAR GANGLION, BRANCHES TO ABDOMINAL ee ORGANS. Fic, 6.—D1AGRAM OF THE VAGUS AND SYMPATHETIC NERVES AND SOLA PLEXUS/ DISSECTION OF THE NECK. 69 this nerve curves round the sub-clavian artery, and then continues forward into the neck as described. After giving off other branches to the lungs, the vagus descends along the oesophagus, and finally divides into two branches, one of which passes to the dorsal side of the cesophagus, and is there joined by a similar branch from the right vague ; the other division passes to the ventral side of the oesophagus, where it joins the similar ventral branch of the right vagus. The two new trunks thus formed can be traced to the stomach ; each ends in a plexus of nerve-fibres, which are distributed to the stomach and make connections also with the solar plexus of the coeliac ganglia. 18. The Thoracic Sympathetic Trunk. From the inferior cervical ganglion two branches pass to the large 1st thoracic ganglion, one above and one below the sub-clavian artery, forming a ring known as the “annulus of Vreussens.” From this annulus one or more small branches may be given off toward the heart to join the cardiac plexus. The ist thoracic ganglion is very large, and besides its connections with the inferior cervical gives off the following branches: a. A large branch, the vercebral, passing forward to join with the two lower cervical spinal nerves. 4 A branch tothe 1st thoracic spinal nerve. ¢. A’branch to the 2d thoracic spinal. ad A branch to the 3d thoracic spinal, and sometimes, e, a branch to the 4th thoracic spinal. From the 1st thoracic ganglion the sympathetic trunk continues backward along the spinal column, andat intervals shows ganglionic swellings, usually one for each rib after the 3d or 4th; but this is sometimes irregular. From each ganglion a branch passes to the 7° DISSECTION OF THE NECK corresponding spinal nerve. These branches of com- munication are known as the raved communicantes. In the posterior portion of the thorax, just after giving off a ramus communicans to the 12th or the 13th thoracic spinal nerve, the sympathetic sends off a large branch to the inner side, known as the splanchnic nerve, This nerve passes through the diaphragm and (in the dog) ends in a ganglionic enlargement, the Splanchnic ganglion. From this ganglion small branches can be traced inward and forward, ending in a larger nerve-mass, the celzac ganglion, which lies just posterior to the coeliac axis and on the ventral aspect of the aorta. There is a similar arrangement on the other side, the two coeliac ganglia being connected with each other by cross-branches and sending very numerous fine branches to the surrounding abdominal organs, which form what is called the solar plexus. The solar plexus, as before mentioned, is connected with the terminal plexuses of the vagi. After giving off the splanchnic the sympathetic may have one more ganglion in the thorax, from which a ramus communicans is given to the 13th thoracic spinal nerve, and a small branch, the sva// splanchuze, which joins the splanchnic ganglion. It then passes through the diaphragm and continues as the abdomi- nal sympathetic, which also has ganglionic enlargements as in the thorax. From these ganglia branches arise which form plexuses, similar to the solar plexus, for the abdominal and pelvic organs. The two sympa- thetic trunks finally unite at the posterior end of the sacrum in an unpaired ganglion lying in the mid-line. 19. The Brachial Plexus in the dog is formed from the 6th, 7th and 8th cervical spinal nerves and the 1st thoracic spinal nerve, and usually receives a small DISSECTION OF THE NECK. 71 branch from the 2d thoracic spinal nerve. Shortly after emerging from the vertebral canal these nerves branch to form a complicated plexus, represented in Fig. 7, from which branches are given off to the arm, fore-arm, shoulder, etc. The plexus should be dissected upon the side the least injured by previous dissection ; in this case probably the right side. Cut TO CLAVO-DELTOID VI SUPRA-SCAPULAR " ES SUB-SCAPULAR MUSCULO-CUTANEOUS CIRCUMFLEX Vill So MUSCULO-SPIRAL I SS MEDIAN aX Zo U Sa. LNAR R oF Ue oy, & TERES MAJOR I TA NEOus Fic. 7.—DIAGRAM OF THE BRACHIAL PLEXUS OF THE Doc. carefully through the muscles on the side of the verte- bral column where the neck and thorax meet until some of the nerves are exposed, and then from this trace out the other members of the plexus. In order to expose the plexus fully one must take great care not to cut small branches, and must dissect slowly. The following are the chief terminal branches of the plexus. From which of the spinal nerves they are derived can be seen from the figure, although the arrangement of the plexus varies somewhat in different individuals. a. Branch distributed chiefly to the clavo-deltoid, 72 DISSECTION OF THE NECK. b. Supra-scAPULAR NERVE to muscles on the dorsal side of the scapula. c. SUB-SCAPULAR NERVE to muscles on the ventral side of the scapula. d. MuscuLo-cuTaNnEous NERVE supplies the biceps and may be traced finally to the elbow, where it breaks up into fibres distributed to the skin of the elbow and fore-arm. e. CIRCUMFLEX NeRvE sends some branches to the teres major and the sub-scapular muscles, and then passes dorsally between the insertion of the teres major and the triceps, giving off branches to the triceps and the anterior deltoid muscles. f. MuscuLo-spIRaL Nerve passes obliquely round the humerus to the dorsal side to reach the radial side of the fore-arm,where it divides into two branches, the radial and posterior inter-osseus nerves. It supplies the muscles and skin of the back of the arm, and in the fore-arm is distributed to the muscles and the digits of the radial side. g. THE Mepran NERVE. h. THe Utnar Nerve. These two nerves arise together from the 8th cervical and 1st thoracic nerve ; they pass to the fore-arm and hand, to which they are distributed. i. A branch to the teres major and latissimus dorsi muscles, k. Tue InteraLt Cutaneous Nerve. Besides giv- ing some branches to the pectoral muscles this is dis- tributed to the skin on the inner side of the arm. 20. The Intrinsic Muscles of the Larnyx. To dissect these muscles tt ts better to remove the larynx and cpiglottis entirely from. the body. Cut DISSECTION OF THE NECK, 73 through the trachea below the larynx and through the pharynx above the hyotd bone; in taking out the larynx dissect wt free from the esophagus, whith adheres to its dorsal side. The intrinsic laryngeal muscles form six patrs, and with the cxception of the arytenotd muscles correspond very well to those of human anatomy. The ellustrations tn the text-book of human anatomy may therefore be consulted tf necessary. a. THe Crico-THyroip MuscLeis a short triangular muscle arising from the ventral and lateral faces of the cricoid, and is inserted into the posterior border of the thyroid and its posterior cornu. b. THE PosTERIOR CRICO-ARYTENOID MUSCLE arises from the flattened dorsal surface of the cricoid, and is inserted into the arytenoid cartilages, the fibres passing obliquely forward and outward. c. THe Lateral CRIcO-ARYTENOID is concealed by the wing of the thyroid. Cut through the posterior horn of the thyroid where it joins the cricoid and lift up the wing of the thyroid. The muscle is seen as a band of fibres arising from the lateral surface of the cricoid, and passing obliquely toward the dorsal side to be inserted into the arytenoid. d. Tue Tuyro-aRvTENOID MUSCLE is anterior to the last, the fibres having somewhat the same general direction. It consists of two nearly separate muscular bands which arise from the internal face of the ventral portion of the thyroid and pass dorsally to be inserted into the arytenoid. e. THE ARYTENO-EPIGLOTTIDEAN lies anterior to the last and nearly parallel with it. It arises from the arytenoid cartilage and passes ventrally and forward to endin the aryteno-epiglottidean fold. The muscles 74 DISSECTION OF THE NECK. of the two sides at their origin are connected by a cross-slip of muscular fibres. f. THe AryTENoID Muscie. The fleshy portion arises from the arytenoid cartilage just anterior to the insertion of the posterior crico-arytenoid, and is in- serted into the inner angle of the arytenoid of the opposite side. CHAPTER VI, DISSECTION OF THE BRAIN. The brain should be removed tmmediately after kill- zng the dog, and placed tn alcohol for a week or longer before dissecting. To prevent flattening wrap the brain zm raw cotton before placing rt in the alcohol. Lo remove the brain, first skin the head, and cut off the muscles attached to the skull especially in the occipr- talregion. Thenwitha small hand-saw carefully saw through the bone in a horizontal plane round the skull so as totsolate the cap of the skull. Werth alittle care this can be done without tearing the brain at all. Re- move the cap and with bone forceps chip off as much of the sides of the skull as ts necessary to fully uncover the brain. Take out the brain by lifting it up care- Sully from ether end, and cutting the nerves that come off from the ventral surface. Cut the nerves so as to leave as much of a stump as possible adhering to the brain. Ln addition to the brain hardened in alcohol tt will be conventent to harden twoother brains in Miiller's or 76 DISSECTION OF THE BRAIN, Lrlickes* liquid for a month or more, then wash them well 1 water and keep in 80% alcohol. One should be divided longitudinally by a cut through the great longr- tudinal fissure and the corpus callosum, and the other should be divided into a series of cross-sections, each about 1 in. thick, from the antertor to the pos- tertor cnd of the bratn. After having dissected an alcohol brain according to the following directions the study of these cross and longitudinal sections will prove very tnstructive tn giving the proper relations of the atffercnt parts to one another. A. THE BRAIN MEMBRANES. 1. The Dura Mater will be exposed in removing the brain. It is the tough membrane lining the inside of the skull. It projects in between the lobes of the cerebrum as a vertical fold, the falx cerebrz, and as a transverse fold, the ¢entorzuim, between the cerebrum and cerebellum. 2. The Pia Mater is a much thinner membrane, closely investing the brain; it is very vascular, since the blood-vessels supplying the brain are carried in it. * The composition of these liquids is as follows: MULLER’S LIQUID. WaAleP oak tn: e000 ce tee eee aes 100 parts Potassium bichromate..........-....- 2 parts Sodium sulphate... 1... ... cece ee ee ees I part. ERLICKI’S LIQUID. ; Water ics nincianest i saraneaaiobe: Ke I0O parts, Potassium bichromate..............6. 24 parts. Copper sulphate: s....o2.c5 sar cease $ part. The brains should be immersed in a relatively large quantity of these liquids, and during the first week of the hardening the liquid should be changed either every day or every second day. The Erlicki's liquid acts more quickly and is probably the better one of the two to use. DISSECTION OF THE BRAIN. Tf B. EXTERNAL CHARACTERS OF THE BRAIN, 1. The Dorsal Surface of the Brain. a. THE CEREBRAL HEMISPHERES occupy the greater portion of the dorsal surface. They show a number of well-marked fissures and convolutions (sulci and gyri). The two hemispheresare connected by a broad white commissure, the corpus callosum, which may be seen by gently separating the two hemispheres and tearing or cutting away the pia mater which stretches across from one to the other. The corpus lies well toward the ventral surface of the hemispheres. b. THe Otractory Loses are a pair of large flat tened triangular lobes projecting from the ventral sur- face of the brain, but visible in a dorsal view. c. THE Corpora QuUADRIGEMINA may be exposed by pressing apart the cerebellum and the cerebrum, and tearing away the intervening pia mater. They consist of two pairs of rounded elevations, of which the pos- terior pair are the larger. d. THe CrereseLLum. The whole surface is marked with narrow folds which run both in a transverse and a longitudinal direction. They are seen better if the pia mater is stripped off. The cerebellum is divided into a large median lobe, the verzs, in which the folds run transversely, and two lateral lobes or hez- spheres in which the folds have a general longitudinal direction. On the outer and under sides of the hemi- spheres the loose floccular lobes will be seen if the brain: has been carefully removed. With a parr of forceps tear away carefully the pra mater beneath and posterior to the cerebellum to bring znto view the medulla oblongata. e. THE Meputita Ostoncata lies beneath and 78 DISSECTION OF THE BRAIN. posterior to the cerebellum, and posteriorly passes into the spinal cord. Anteriorly the medulla widens out to form the fourth ventricle, which lies immediately under the cerebellum. This lozenge-shaped or oval cavity is covered over anteriorly by a thin sheet of nervous mat- ter, the valve of Vieussens or the anterior medullary velum, easily seen, by pressing backward the cerebel- lum, as a thin membrane running from the posterior border of the corpora quadrigemina over the anterior part of the fourth ventricle. Posteriorly the fourth ventricle is roofed in by a similar membrane lying immediately under the cerebellum and probably re- moved in exposing the ventricle, the Aosterzor medul- Lary velum. f. Floor oF THE FourrH VENTRicLE. About the middle are seen two transverse bands of fibres—medu/- lary or auditory strie—the origin of the auditory nerve. The posterior end of the ventricle where the lateral walls converge is known as the calamus scrip- tor7us. g. Fascicut1 oF THE MEDULLA OsLoNGATA. Pos- terior to the calamus scriptorius the dorsal surface of the medulla shows a median fissure continuous with the posterior median fissure of the cord. On each side of this les a rounded eminence, the /asezcalus gracil’s (posterior pyramid). Just exterior to this on each side is the small /fasceculus cuncatus. If these two fasciculi are followed forward they run into a rounded eminence on each side, forming the lateral boundary of the fourth ventricle, the restzfornz bodes, and these followed anteriorly are seen to pass up into the cerebellum, forming the posterzor peduncles of the cerebellum, making a connection between the cere- bellum and cord. DISSECTION OF THE BRAIN. 79 2. The Ventral Surface of the Brain. a. THE CEREBRAL HEMISPHERES meet in front, but diverge posteriorly. The vertical fissure separating the hemispheres (on the dorsal side) is continued around for some distance on the ventral surface. Note the large olfactory lobes lying along the ventral surface. b. THe Optic Cutasma. Lying at the end of the fis- sure is a transverse band of nerve-fibres, the chiasma. The oftzc nerves arise from it anteriorly, and poste- riorly it passes backward and outward, forming the optic tracts, which finally end in the corpora quadri- gemina. By carefully lifting up the side of the cere- bral hemisphere each tract may be followed as it passes over the optic thalamus, in which some of the fibres end, until it reaches the corpora quadrigemina. c. THE Lamina CINEREA is exposed by turning back the optic chiasma. As will be seen later, it forms the anterior wall of the third ventricle. If gently torn, the third ventricle will be exposed. d. THE INFUNDIBULUM lies immediately behind the chiasma. It isa median prolongation of the ventral surface of the brain: at its apex is the petuztary body. The infundibulum is hollow within, the cavity being a prolongation of the third ventricle. e. THE Corpora ALBICANTIA are two small white eminences posterior to the infundibulum. f. THe Crura CEREBRI are the two eminences lying outside of and posterior to the corpora albicantia. They pass forward and upward into the cerebral hemispheres, diverging from each other; they form: the connection between the cerebral hemispheres and the medulla. (To expose them clearly the pia mater must be cleaned off, taking care not to injure the cranial nerves. ) 80 DISSECTION OF THE BRAIN. g. THE Pons Varo. is the large band of trans- verse fibres lying back of the crura cerebri. It con- sists of transverse commissural fibres connecting the two sides of the cerebellum. Followed up toward the dorsal side it will be seen to pass into the cere- bellum on each side, forming the mzddle peduncles of the cerebellum. h. Corpus TRAPEZOIDEUM, a band of similar trans- verse fibres lying posterior to the pons, and inter- rupted in the mid-line by the azterzor pyramzds. i. Tue ANTERIOR Pyramips, the two bands of longitudinal fibres lying on the ventral surface of the medulla and ending (apparently) anteriorly in the pons. ‘The anterior median fissure also ends at the pons. 3. The Roots of the Twelve Cranial Nerves. a. Tue Otractory or IJ. cranial nerves arise from the under side of the olfactory lobes; most probably they were torn off in removing the brain. b. THE Optic or II. cranial nerves arise from the anterior border of the optic chiasma. c. THe OcuLo-moror or III. cranial nerves arise in the space between the two crura cerebri. d. Tue Patueticus or IV. cranial nerve is very small, and on the ventral surface appears in the space between the cerebral hemisphere and the crus cerebi on each side. The real origin is from the valve of Vieusscens on the dorsal side of the brain. It may be followed back easily to this point. e. THE TRIGEMINAL or V. cranial nerve is very large, and arises from the sides of the pons by two roots. The smaller, inner one is the motor root; the larger, outer one the sensory root. f. Tur Apspucens or VI. cranial nerve is small, and DISSECTION OF THE BRAIN. 8 arises from the ventral surface of the medulla back of the pons, g. Tue Faciat or VII. cranial nerve arises from the outer side of the anterior border of the corpus trape- zoideum behind the origin of the trigeminal. h. Toe Avupirory or VIII. cranial nerve arises just outside of and behind the facial nerve. It is larger than the facial. 1. THE GLOSSOPHARYNGEAL AND THE Vacus, the IX. and the X. cranial nerves, arise together by a num- ber of slender roots from the side of the medulla behind and to the outer side of the origin of the auditory nerve. j. THe Spinat Accessory or XI. cranial nerve arises by a number of roots from the side of the cord and medulla, extending forward as far as the origin of the vagus nerve. k. Toe Hypoctossau or XII. cranial nerve arises from the ventral surface of the medulla close to the mid-line and just outside of the anterior pyramids, C. THE INTERNAL STRUCTURE OF THE BRAIN. 1, The Cerebral Hemispheres (/ore-brain or pros- encephalon). With a razor kept wet with alcohol take off hort- zontal slices of the cerebral hemispheres, cutting care- Sully until the corpus callosum ts reached. a. Note the structure of the cerebral hemispheres: the outer cortzcal layer of gray. matter folded into the interior at the sulci, and the inner or medullary por- tion of white matter—nerve-fibres. b. Notice the direction of the fibres of the corpus callosum, running transversely from one hemisphere to the other. 82 DISSECTION OF THE BRAIN. Remove carefully with forceps and knife the corpus callosum until the lateral ventricles are exposed, taking care not to injure the fornix, which les tmmediately beneath, c. THe LaTERAL VENTRICLES, one on each side, fully exposed after complete removal of the corpus callosum. In each three chambers or horns may be distinguished; the an¢erzor cornu, a narrow slit run- ning forward and separated from the anterior cornu of the other side by a vertical partition—the septum luctduim ; the descending cornu, situated posteriorly and curving downward and outward; the posterzor cornu, situated at the most posterior end of the ven- tricle, a small diverticulum running backward, very inconspicuous in the dog. d. THe Septum Lucipum is the vertical partition lying between the anterior cornua of the two ventricles. It contains within its walls a small cavity, the so- called 5th ventricle, not formed by the closing in of the embryonic medullary tube like the other true ventricles of the brain. e. THE Corpus STrIatTuM is the oval mass _pro- jecting into each anterior cornu from the side of the cerebral hemisphere. Only a part of the corpus striatum is seen in the dissection; the remainder is concealed in the walls of the hemisphere. It is originally an outgrowth from the floor of the vesicle of the cerebral hemispheres, and contains two nuclei of gray matter in its interior—the xucleus caudatius, con- tained within the part which projects into the ven- tricle, and the zzcleus lentrcularizs, contained within the part buried in the avall of the hemisphere. Lay open the descending cornu on one side by care- fully cutting away the sides of the cerebral hemisphere. DISSECTION OF THE BRAIN. 83 Note its extensive course, sweeping around downward and forward to the bottom of the temporal lobe of the hemisphere. f. Tue Hippocampus Major is the prominent con- vex ridge lying along the floor of the descending cornu. THe Fornix. The postertor pillar of the fornix is the narrow band of white fibres lying along the anterior border of the hippocampus major. The pos- terior pillars on each side followed forward meet just at the posterior edge of the septum lucidum, and unite for a short distance to form the dody of the fornix; then bending downward they diverge again, forming the azterzor pillars of the fornix, which run toward the base of the brain. Cut away the outer wall of the anterior cornu on the same side on whith the wall of the posterior cornu was removed. h. THe ForamMen oF Monro, one on each side, is the slit-like opening underneath the body and anterior pillar of the fornix. It leads into the 3d ventricle, and is the passage of communication between the 3d and the lateral ventricles. Zo expose the 3d ventricle lift up carefully the pos- terior pillars of the fornix where they converge and tear them away with the forceps Remove in the same way the portion of the corpus callosum still left be- tween the posterwor pillars of the fornix and forming the roof of the 3d ventricle. Properly speaking, the &rpus callosum does not form the roof of the 3d ventricle. The true roof of the ventricle is a portion of the pia mater known as the velum interpositum which lies immediately be- neath the corpus callosum. The velum interpositum 84 DISSECTION OF THE BRAIN. gets into the interior through the great transverse fissure of the brain between the cerebrum and cere- -bellum. At the anterior end of the ventricle it con- tinues on through the foramen of Monro on each side into the lateral ventricles, forming the chorozd plexuses. Each choroid plexus is a thin vascular fold of membrane which passes backward into the descend- ing horn of the lateral ventricle upon the hippocampus major. If the corpus callosum is removed with suffi- cient care these relations of the pia mater can easily be demonstrated upon the dog’s brain. i. THE 3D VENTRICLE is seen as a narrow slit begin- ning just back of the anterior pillars of the fornix, and extending posteriorly as far as the corpora quadrigemina. While narrow from side to side, it is quite deep. 2, The Optic Thalami (thalamencephalon) are the two oval masses forming the sides of the 3d ventricle. a. THE PINEAL GLAND is connected by a stalk to the upper and posterior end of the 3d ventricle. It was originally a diverticulum from this ventricle. b. THE CoMMISSURES OF THE 3D VENTRICLE. The Afzddle Commussure is very large, but delicate and easily broken. It passes across the middle of the ventricle between the optic thalami. The Fosterzor Comimoessure is at the extreme pos- terior end of the 3d ventricle, lying beneath the stalk of the pineal gland; It is anarrow band of white fibres. The Anterior Commissure lies at the extreme ante- rior end of the 3d ventricle, just where the anterior pillars begin to diverge from each other. By cutting the body of the fornix open vertically this commis- sure can be brought into full view. It isa narrow band of white fibres. DISSECTION OF THE BRAIN. 85 Cutting through the middle commissure, the 3d ventricle can be seen to pass downward and forward toward the base of the brain, ending finally in the in- fundibulum. This can be seen best in a median longi- tudinal section of the brain. Posteriorly the 3d ven- tricle passes into the agueduct of Sylvzus just beneath the posterior commissure.