Part 103

Flower and Ruge describe the mammalian liver as being primarily divided by the umbilical fissure into two parts, the right and left lobes. Secondary fissures on either side may subdivide each of these primary lobes. On this basis we may recognize in the liver of the horse right lateral, right central, left central, and left lateral lobes. In the young foal these four lobes are distinctly recognizable. The two central lobes would correspond to the middle lobe of the foregoing description, and the right central lobe would be the equivalent of the quadrate lobe of man.

Footnote 100:

In the young foal the interlobular tissue is more abundant and the lobulation correspondingly distinct.

Footnote 101:

The hepatic veins may be recognized on section from the fact that they remain open, being connected closely with the parenchyma.

Footnote 102:

The ductless glands are organs which elaborate substances which pass directly into the veins or lymphatics, instead of being conveyed away by ducts. This process is termed internal secretion. The ductless glands include the lymph glands, which are described with the organs of circulation; the thyroid and thymus bodies, described usually with the respiratory organs; the adrenal or suprarenal bodies, described with the urinary organs; the pineal and pituitary bodies, described with the brain; and the spleen, described with the digestive system as a matter of convenience. The spleen is not, strictly speaking, a gland at all: it is not epithelial in origin or structure, but is mesenchymatous.

Footnote 103:

The student is strongly recommended to study the peritoneum of a foal or other small subject when the opportunity occurs, as in these the viscera are easily handled, and the course of the peritoneum can be followed without difficulty.

Footnote 104:

The passage is subject to a good deal of variation in caliber and is sometimes completely occluded.

Footnote 105:

In dissecting-room subjects (which are usually aged) the omentum often exhibits pathological changes, such as adhesions, rents, tumors, formation of twisted strands, etc.

Footnote 106:

The student will note here the difference between the structure and behavior of the brachydont (short-crowned) incisors of the ox and the hypsodont (long-crowned) type of the horse.

Footnote 107:

In popular language these are conveniently regarded as so many stomachs, and termed accordingly “first,” “second,” etc. Other names are in common use, _e. g._, paunch, honeycomb, manifold or manyplies, and rennet or true stomach.

Footnote 108:

It has been customary to term the sacs left and right respectively, but these do not represent the relations as they exist _in situ_ and as they are presented on frozen sections.

Footnote 109:

It is important to notice that the reticulum is separated from the pericardium by an interval of about 1 to 1½ inches (ca. 2 to 4 cm.) only, since foreign bodies which are often swallowed by cattle lodge in the reticulum, and not rarely (if sharp) perforate the reticulum and diaphragm.

Footnote 110:

The epiglottis in the pig seems to be constantly retrovelar. The pig frequently breathes through the mouth, and this is no doubt possible only when the soft palate is raised; it seems probable that it is also shortened.

Footnote 111:

The canines of the pig are “permanent pulp” teeth and therefore capable of continued growth, and are without roots in the strict sense.

Footnote 112:

It is usually stated that the cardiac end is funnel-shaped, but it is not so in formalin-hardened cadavers nor in frozen sections. The hiatus œsophagus is a long slit in the right crus of the diaphragm, and the terminal part of the œsophagus, which lies in it, is flattened transversely.

Footnote 113:

It will be noted that the fundus gland region does not extend up to the lesser curvature; here the cardiac mucosa joins the pyloric.

Footnote 114:

The description here given is based mainly on the appearance of the organ as hardened _in situ_, which differs radically from that of the soft organ, as is seen on comparison of the annexed figure (Fig. 321).

Footnote 115:

In the bulldog, which is very prognathic (“undershot”), the lower canines are opposite to or slightly in front of the plane of the upper incisors, and the upper canines are about opposite to the first lower cheek teeth. In the epignathic (“overshot”) dachshund the lower canines are under or slightly behind the upper ones.

Footnote 116:

Increase in number also occurs, the supernumerary teeth being at either end of the series.

Footnote 117:

The valve does not seem to be efficient, since experience shows that rectal injections can be made to pass beyond it. This may be partly due also to the fact that the terminal part of the ileum runs horizontally forward, and the ileo-cæcal orifice faces into the beginning of the colon.

Footnote 118:

Ellenberger and Baum state that the cæcum may reach a length of 20 cm. in very large dogs.

Footnote 119:

When the stomach is very full, it pushes the left portion of the colon over to the right, producing an acute angle in place of a transverse branch. The terminal part of the colon is thus oblique in direction.

Footnote 120:

An external nose (Nasus externus), such as exists in man, forming a projection distinctly marked off from the rest of the face, does not exist in the domesticated animals.

Footnote 121:

The septal cartilage is to be regarded as an unossified part of the mesethmoid. It will be noted that the line of demarcation between the bone and the cartilage is irregular and varies with age; extensive ossification for calcification) of the cartilage is commonly found in old animals. The process often results in the formation of calcareous islands in the cartilage.

Footnote 122:

In the ordinary position of the head and neck, and while the parts are at rest, about half of the larynx lies between the branches of the mandible; when the head and neck are extended, proportionately more of the larynx lies behind a plane through the posterior borders of the rami. It is here described in the position it occupies when the head and neck are extended.

Footnote 123:

The term glottis is commonly used to designate the interval between the vocal bands and arytenoid cartilages or the structures that inclose that space.

Footnote 124:

In so-called œdema glottidis this loose submucous tissue becomes infiltrated with fluid, in some cases causing occlusion of the vestibule.

Footnote 125:

The arrangement of the muscles should be noted, since the space inclosed by the divergence of the sterno-cephalici and the convergence of the omo-hyoidei is the area of election for the operation of tracheotomy.

Footnote 126:

The student should bear in mind that these terms are employed simply as a matter of convenience in description; all the parts, though differently named, form a continuous whole.

Footnote 127:

The apertures do not exist in the fœtus, and are sometimes absent in the adult subject. Some of them may be produced in dissection by the necessary disturbance of the parts. Clinicians state that a serous exudate formed in one pleural sac usually passes through to the other side in the horse.

Footnote 128:

A correct idea of the natural form and size of the lung cannot be obtained from a specimen in this state. The lungs should be hardened _in situ_ for this purpose.

Footnote 129:

Some authors consider each lung to be divided into anterior and posterior lobes by the cardiac notch, so that the right lung would have three lobes and the left lung two lobes.

Footnote 130:

In fœtal lung the lobulation is much more distinct. Pigmentation of the lung is sometimes seen in horses, and in such cases the pigment is deposited mainly in the interlobular tissue, thus mapping out the lobules.

Footnote 131:

It must not be inferred from the necessarily brief account here given that the two sets of vessels are quite distinct. On the contrary, competent observers state that numerous small branches of the bronchial arteries anastomose with pulmonary vessels. Part of the blood conveyed to the lungs by the bronchial arteries is returned by the pulmonary veins. In the horse bronchial veins are absent or inconstant.

Footnote 132:

The cervical part of the gland is very variable. The thoracic lobe of one side may have no cervical continuation; the other lobe may then give off a single prolongation which bifurcates. The thoracic part in the new-born foal occupies most of the space which is later taken up by the apices of the lungs. Its two lobes are in contact, and its deep surface is molded on the anterior part of the pericardium and the large vessels.

Footnote 133:

It is therefore often termed the precardiac lobe.

Footnote 134:

The arrangement here is one of the most striking features of the pig’s larynx. The short, thick middle hyo-epiglottic ligament and the anterior part of the thyro-hyoid membrane are inelastic, while the posterior part of the membrane is thin and elastic and allows the epiglottis to be separated by a considerable interval from the thyroid cartilage. Moreover, the borders of the epiglottis are connected with the thyroid cornua of the hyoid bone by lateral hyo-epiglottic ligaments.

Footnote 135:

The kidneys are soft, plastic organs, and hence an accurate knowledge of their form can be gained only from a study of specimens which have been hardened _in situ_. The description here given is based on this method. For this purpose subjects should be hardened in the standing position to avoid artefacts.

Footnote 136:

The most instructive sections are those made in the horizontal and transverse planes, through the pelvis in each case.

Footnote 137:

The fœtal kidney is divided by furrows into a number of polygonal areas, each of which is the base of a pyramidal lobe or renculus. These furrows usually disappear before or soon after birth in the foal, although traces of them are sometimes seen in the adult.

Footnote 138:

In the kidney of the horse the renal columns dip in between the pyramids very superficially as compared with the arrangement in the human kidney. Breuer states that the pyramids are 40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct.

Footnote 139:

The crest is the result of fusion of the papillæ or apices of the pyramids in the embryo.

Footnote 140:

This is commonly termed the fundus by veterinarians, but is not the homologue of the fundus of the human bladder.

Footnote 141:

This would correspond to the fundus vesicæ of man.

Footnote 142:

From the standpoint of comparative anatomy the term “adrenal” seems decidedly preferable to “suprarenal.”

Footnote 143:

This is a remnant of the gubernaculum testis of the fœtus.

Footnote 144:

The tunica vaginalis is not a part of the scrotum in the strict or narrow sense of that term, but is included here on practical grounds.

Footnote 145:

Sometimes one vesicula or both are very large in the gelding. The writer has seen four cases in the dissecting room, three of which were bilateral, the other unilateral. The vesicula resembled the urinary bladder in appearance and contained about a quart of thick, amber-colored secretion.

Footnote 146:

It has been customary to divide the pelvic part of the urethra into prostatic and membranous parts. These terms apply well in human anatomy, but have no special value in comparative anatomy. In the horse a prostatic part hardly exists, unless we assume that it and the neck of the bladder together are only about an inch in length. There is no membranous part in the sense in which that term is used in regard to man.

Footnote 147:

The statement often made that it acts as a sphincter of the bladder is a hypothesis of doubtful plausibility. In material hardened _in situ_, in which the internal urethral orifice is tightly closed, the urethral muscle apparently takes no part in the closure.

Footnote 148:

This is clinically important, since enlargement of the prostate may interfere with micturition.

Footnote 149:

These terms apply properly only when the adjacent viscera are removed and the ovaries are actually “suspended” by the broad ligaments. When the ovary is in its natural position, the surfaces are dorsal and ventral, the former corresponding to the “external” surface if the free border is directed outward, to the “internal” if the free edge is medial.

Footnote 150:

The Fallopian tubes may be regarded, both in structure and morphology, as prolongations of the uterus (McMurrich).

Footnote 151:

The arrangement is the only exception to the general rule that the serous cavities are closed. In this case the mucous membrane of the fimbriated extremity is continuous with the adjacent peritoneum, a persistence of the embryonic relations of the Müllerian duct.

Footnote 152:

In formalin-hardened subjects there is frequently a pronounced ring-like constriction at the beginning of the vulva.

Footnote 153:

The term vulva is used here in the sense in which it is understood generally by English and French veterinarians. In the German works it is applied only to the labia and other structures around the external orifice of the urogenital sinus, while the sinus itself is termed the vestibule of the vagina (Vestibulum vaginæ).

Footnote 154:

Lesbre states that the cornua may attain a length of 45 to 50 cm.

Footnote 155:

The pericardium is described before the heart since it must be examined first in the laboratory.

Footnote 156:

This is termed the tubercle of Lower in human anatomy and the tuberculum intervenosum by German veterinary anatomists.

Footnote 157:

These vessels will be described later in their systematic order.

Footnote 158:

The relation to the guttural pouch is not constant. In some cases—especially when the head and neck are extended—the artery lies behind the pouch. The backward extension of the latter is variable.

Footnote 159:

By some authors the term facial is applied to the artery only after it turns around the lower border of the jaw.

Footnote 160:

The artery is conveniently placed at its inflection for taking the pulse, since it is superficial and lies directly on the bone.

Footnote 161:

This vessel appears to represent both the supraorbital and frontal of man.

Footnote 162:

The term axillary is often applied to the artery from the first rib to the point of origin of the subscapular branch.

Footnote 163:

The pulse can be taken where the artery lies on the lateral ligament, since the pectoral muscle is thin here.

Footnote 164:

This vessel is also termed the A. metacarpea volaris superficialis or the palmar metacarpal artery.

Footnote 165:

In the great majority of subjects this vessel and some of its branches are the seat of more or less extensive verminous aneurysm, produced by the Sclerostomum armatum. In the author’s experience an entirely normal specimen is quite exceptional in adult horses.

Footnote 166:

The left branch is a descriptive convention rather than a reality, since the arteries of the small intestines spring from the mesenteric trunk either directly or by short common stems with an adjacent vessel.

Footnote 167:

The obliteration in the adult extends a variable distance from the vesical end toward the origin, but usually involves only a small part.

Footnote 168:

Most of the veins are depicted in the illustrations of the section on the arteries, to which reference is to be made.

Footnote 169:

Chauveau says “the bronchial veins, which ramify on the bronchi like the arteries of which they are satellites, open into the great coronary vein very near its mouth, after having united to form a single vessel, which sometimes opens directly into the atrium.” Ellenberger and Baum state that the bronchial and œsophageal veins open into the vena azygos separately or by a common trunk. Martin describes a short broncho-œsophageal trunk, but the vein which he figures as the bronchial does not come from the lungs, but is a small mediastinal vessel. The author finds such a vessel entering the terminal part of the œsophageal vein, but no distinct bronchial vein in the horse.

Footnote 170:

M’Fadyean records a case in which the vein lay on the deep face of the omo-hyoideus with the carotid artery.

Footnote 171:

The venous angle formed by this junction indicates the position of the thyroid gland.

Footnote 172:

These are termed by Chauveau and M’Fadyean the subsphenoidal confluents.

Footnote 173:

The place and mode of termination is quite variable. It may disappear from the surface of the thigh at any point above the distal third. In some cases it passes through the anterior part of the gracilis instead of dipping in between that muscle and the sartorius.

Footnote 174:

This often joins the posterior femoral or the popliteal vein.

Footnote 175:

The term chyle is often applied to the lymph carried by the efferent vessels of the intestine when it contains products of digestion, and these vessels may be designated as lacteals or chyle vessels.

Footnote 176:

The lymph vessels of these organs appear to vary considerably in their mode of termination, and the arrangement needs further study. Some ducts from the stomach, liver, and spleen open directly into the cistern.

Footnote 177:

Abscess here can be reached readily by an incision between the vein and the omo-hyoideus.

Footnote 178:

It is, of course, only the pericardium which comes in contact with the wall, but it is customary as a matter of convenience to speak of the relation of the heart as though it were direct.

Footnote 179:

Only the most important differential features of the arrangement of the vessels as compared with those of the horse will be considered.

Footnote 180:

The homologies of the vessels of the lower parts of the limbs are still uncertain. The account given here is mainly based on the views of Sussdorf and Baum.

Footnote 181:

It is difficult to make the arrangement of these vessels clear in a brief textual description, but a reference to the schematic figure will explain the main facts.

Footnote 182:

Most of the differences in the veins of the ox are correlated with those of the arteries of which they are satellites and will not be described. The account here given consists chiefly of those differential features which could not be deduced from a knowledge of the arteries.

Footnote 183:

The upper series is continuous with the posterior mediastinal (œsophageal) glands and the lower or tracheal glands with the bronchial. Hence we might well designate the mediastinal glands as œsophageal (anterior and posterior) and tracheo-bronchial.

Footnote 184:

When enlarged, as is often the case in tuberculosis, this gland frequently causes difficulty in swallowing and in rumination and produces chronic or recurrent bloating.

Footnote 185:

The relative weight is subject to wide variation. It is large in hunting dogs and such as are trained for speed or worked.

Footnote 186:

Limitations of space and the purpose of this work preclude consideration of the finer structure of the nervous system, for which ample literature is available.

Footnote 187:

The description given here is intended to present the chief facts in regard to the brain as they may be studied in the dissecting room. The vessels and membranes which must be examined first have been described.

Footnote 188:

Unless care is used in removing the brain the infundibulum is likely to be torn and the pituitary body left in the cranium. In this case there is a small opening which communicates with the third ventricle.

Footnote 189:

The fossa corresponds in position to the locus perforatus anticus of the human brain, but is not pierced by numerous openings for vessels in the horse.

Footnote 190:

The decussation varies superficially in different specimens. In some there is a distinct superficial crossing of fibers so that the median fissure is practically effaced at this point.

Footnote 191:

In the new nomenclature the term lamina quadrigemina is applied to the dorsal mass of the mid-brain, and the four eminences which it bears are the corpora quadrigemina.

Footnote 192:

In man a distinct superior brachium connects the superior pair with the lateral geniculate body, but in the domesticated animals the union with the optic thalamus is too direct to allow of any definite arm being recognized.

Footnote 193:

On a strictly embryological basis the optic part of the hypothalamus, comprising the anterior part of the third ventricle and the structures associated with it, belong to the telencephalon, but will be considered here as a matter of convenience.

Footnote 194:

This backward projection of the thalamus is equivalent to the pulvinar and lateral geniculate body of man, which are not superficially divided in the domestic animals.

Footnote 195:

In order to study the configuration of the hemisphere it should be separated from its fellow by median section and from the brain stem by cutting across the mid-brain. Material for this purpose should be hardened _in situ_.

Footnote 196:

Termed by Lesbre the parietal fissure and by M’Fadyean the great oblique fissure.

Footnote 197:

Just above this point is a lobe which is homologous with the insula of man. When the overhanging gyri which partly conceal it—forming the operculum—are removed, there are disclosed several short, deeply placed gyri (Gyri breves).

Footnote 198:

By some authors this is regarded as the homologue of the cruciate fissure of the dog, but it seems likely that the latter is represented by a short and inconstant sulcus situated further forward.

Footnote 199:

From the morphological point of view other structures should be included, but in descriptive anatomy it is usual to limit the application of the term to the parts enumerated above.

Footnote 200:

It is generally believed that these constitute an olfactory path.

Footnote 201:

It is hardly possible to get an accurate idea of the shape of the ventricle except by studying a cast of it. The size of the ventricles varies in different subjects, and it is not rare to find more or less disparity between the two ventricles of the same brain.

Footnote 202:

The term arose from the striated appearance of the mass in sections cut in certain planes, the gray matter being cut up into strands by tracts of white fibers.

Footnote 203:

Although this nerve springs directly from the ganglion, it contains motor as well as sensory fibers.

Footnote 204:

This ganglion appears to be equivalent to the jugular or superior and petrous ganglia of man.

Footnote 205:

In some cases the left vagus passes back below the junction of the jugular veins and the termination of the left brachial vein. It then runs backward and somewhat dorsally across the left face of the anterior vena cava to reach its usual position.

Footnote 206:

The nerve lies here about a finger’s breadth above the thyroid gland. If, however, the gland is enlarged it may come in contact with the nerve. The same is true in regard to the relation to the anterior cervical lymph glands.

Footnote 207:

In order to examine the plexus and the origins of its chief branches conveniently and with as little disturbance of relation as possible, the subject should be suspended in imitation of the natural position and the fore limb abducted as much as is necessary.

Footnote 208: