Part 139

The =small intestine= has an average length of about thirteen feet (ca. 4 meters). It occupies most of the abdominal cavity behind the liver and stomach. The duodenum begins at the portal fissure and passes backward and upward, at first on the visceral surface of the liver, then in contact with the right flank. Near the pelvis it turns inward and sharply forward, passes along the inner border of the left kidney, and joins the jejunum to the left of the root of the mesentery. The mesoduodenum is given off from the common mesentery; it is a relatively wide fold, except at the terminal part. Here there are two short folds, one of which joins the mesocolon; the other passes on to the terminal part of the colon. The first part of the mesoduodenum contains the right branch of the pancreas. Its root is blended with the mesocolon to form a common mesentery. The remainder of the small intestine forms numerous coils, and is attached by a wide mesentery to the sublumbar region. The =pancreatic= and =bile-ducts= open into the duodenum about two or three inches (ca. 5 to 8 cm.) from the pylorus; the =accessory pancreatic duct= opens an inch or two (ca. 2.5 to 5 cm.) further back. The mucous membrane has very long villi. The duodenal (Brunner’s) glands occur only near the pylorus. Peyer’s patches are numerous (about twenty in young subjects), and begin in the duodenum. They are usually elliptical in outline, but the last one is band-like, reaches to the end of the ileum and is four to sixteen inches (ca. 10 to 40 cm.) long in young dogs (Ellenberger). There is an ileo-cæcal valve. The muscular coat is relatively thick.

FIG. 336.—DEEP DISSECTION OF ABDOMINAL VISCERA OF DOG (FEMALE).

BL, Bladder; B, body; C, C′, cornua of uterus; O, O′, ovaries; L. K., left kidney. The concealed part of the colon is indicated by dotted lines. (From photograph of formalin-hardened subject.) ]

The =large intestine= is two to two and a half feet (ca. 60 to 75 cm.) long. Its caliber is about the same as that of the small intestine, and it has neither longitudinal bands nor sacculations.

The =cæcum= is about three or four inches (ca. 8 to 10 cm.) long, and is twisted in a spiral fashion. The twist is maintained by the peritoneum, which attaches it to the ileum. It is situated usually against the middle of the upper part of the right flank, below the duodenum and the right branch of the pancreas.

The =colon= is attached to the sublumbar region by a mesentery, the mesocolon. It presents three parts, which correspond to the ascending, transverse, and descending colon of man. The first or right part (Colon ascendens) is very short. It begins at the junction of the ileum and cæcum, and passes forward along the inner surface of the duodenum and the right branch of the pancreas till it reaches the pyloric part of the stomach; here it turns inward and crosses the median plane, forming the transverse part (Colon transversum). The third or left part (Colon descendens) passes backward in the sublumbar region along the inner border or ventral surface of the left kidney; then inclines toward the median plane and joins the rectum. The caliber of the colon is about the same throughout. It has no bands nor sacculations.

FIG. 337.—CÆCUM OF DOG.

1, Ileum; 2, cæcum; 3, colon. (From Leisering’s Atlas.) ]

FIG. 338.—TERMINATION OF ILEUM OF DOG.

a, Colon; b, cæcum; c, ileum; d, ileo-cæcal opening; e, circular depression around end of ileum. (After P. Schumann.) ]

The mucous membrane of the cæcum contains numerous solitary glands; they are found also in the first part of the colon.

The =rectum= is almost completely covered with peritoneum, the line of peritoneal reflection being under the second or third coccygeal vertebra. At the junction of the rectum and anus the mucous membrane has a stratified, squamous epithelium, and contains the =anal glands=. A small opening on either side leads into two lateral =anal sacs= (Sinus paranales); these are usually about the size of a hazelnut, and contain a dirty gray, fatty substance, which has a peculiar and very unpleasant odor. The skin which lines these pouches contains coil glands. Further back the skin contains large sebaceous glands and peculiar =circumanal glands=.

The retractor ani muscle is extensive. It arises from the shaft of the ilium, the pubis, and the symphysis pelvis, and passes upward and backward to end on the first coccygeal vertebræ and the sphincter ani externus. The retractors, together with the coccygei, form a sort of pelvic diaphragm, analogous to that of man.

THE LIVER

The liver is relatively large, weighing usually about 5 per cent. of the body-weight. It is divided into six or seven =lobes= by fissures which converge at the portal fissure. When the gland is examined in the soft condition, all the lobes are visible on the visceral surface, but usually only four on the parietal surface.

The =left lateral lobe= is the largest, and is oval in outline. The =left central lobe= is much smaller and is prismatic. The =right central lobe= is second in size, and presents a somewhat tongue-shaped quadrate lobe, marked off by the deep fissure in which the gall-bladder lies. The =right lateral lobe= is third in size, and is oval in outline. On its visceral surface is the large =caudate lobe=; this consists of two parts—on the right, the caudate process; on the left, the papillary process or lobe, both often being subdivided by fissures.

FIG. 339.—LIVER OF DOG.

Soft specimen sketched with lobes drawn apart. ]

FIG. 340.—LIVER OF DOG, VISCERAL SURFACE; HARDENED in situ.

Left central lobe, gall-bladder, and great part of right central lobe not visible. ]

When hardened in situ (with the stomach full), the gland presents the following characters:

The visceral surface is marked by a somewhat oblique ridge (corresponding to the lesser curvature of the stomach), which separates two deep cavities. The depression to the left of the ridge is occupied by the body and fundus of the stomach. The depression on the right is smaller, and is occupied by the pyloric part of the stomach, the origin of the duodenum, and the right branch of the pancreas. The gall-bladder is not visible.

When the stomach is empty and contracted, the visceral surface of the liver is strikingly different. There is then a shallow impression for the left part of the stomach on the left lobe, and a large convex area, related to the small intestine and a mass of omentum. The pyloric and duodenal impressions are not much changed. The gall-bladder is visible.

The portal fissure is very deep and might well be termed a fossa. It is bounded on the right (externally) by the caudate process, on the left (internally) by the papillary process or lobe, which is directed ventrally. The hepatic artery enters at the dorsal end and the portal vein centrally, while the bile-duct leaves at the ventral part. The left central lobe is not visible, and the right central one is largely concealed.

The parietal surface is extremely convex, being adapted to the diaphragm and the adjacent part of the ventral wall of the abdomen. On it all the lobes except the papillary are completely or partially visible. The gall-bladder is visible in the fissure between the quadrate and chief portions of the right central lobe.

The dorsal border presents a renal impression on its right portion. The posterior vena cava passes downward and forward at first in a deep groove on the caudate lobe, then largely embedded in the parietal surface of the right lateral lobe; it receives two large hepatic veins just before piercing the diaphragm.

The œsophageal notch is large, and is occupied on the right by the thick margin of the hiatus œsophageus. The left border is opposite to the ninth and tenth ribs; it is thin and is marked by numerous indentations. The caudate process extends usually a little beyond the last right rib, between the right kidney and the right branch of the pancreas. The ventral border lies on the ventral abdominal wall a variable distance behind the xiphoid cartilage.

FIG. 341.—SPLEEN OF DOG, VISCERAL SURFACE.