Part 136

FIG. 320.—ILEO-CÆCAL OPENING AND ADJACENT PART OF CÆCUM AND COLON OF PIG.

a, Mucous membrane of colon; b, mucous membrane of cæcum; c, Peyer’s patch; d, ileo-cæcal opening; e, end of ileum; f, folds (frenula) of ileum. (After P. Schumann.) ]

THE STOMACH

The =stomach= is large and pyriform. Its average capacity is about 1½ to 2 gallons (ca. 5.7 to 8 liters). When full it extends backward to the last left intercostal space laterally and the umbilicus ventrally. The left portion is large and rounded, while the right portion (Pars pylorica) is small, and bends sharply upward to join the small intestine. The parietal surface is related to the liver, gall-bladder, and diaphragm. The visceral surface is related to the intestine, the mesentery, and the pancreas. The great curvature is related to the diaphragm, spleen, and abdominal floor. The pyloric end lies on the right lateral lobe of the liver. The left extremity presents a flattened conical blind pouch, the =diverticulum ventriculi=, the apex of which projects backward. The œsophagus joins the stomach very obliquely, almost in the median plane, and about three or four inches (ca. 8 to 10 cm.) below the twelfth thoracic vertebra. The cardiac opening is slit-like and is bounded above and to the left by a fold which contains a thickening of the internal oblique layer of the muscular coat. The opening into the diverticulum is situated above and a little to the left of the cardia; it is transversely oval, and is bounded (except externally) by a thick fold which contains spirally arranged muscular fibers. The mucous membrane may be divided into four regions. Over a quadrilateral area around the cardia (about one inch on the right and two or three inches on the left side of the orifice) it is œsophageal in character, and presents a number of folds. A sharp line of demarcation separates this from the rest of the mucous membrane, which is soft and glandular. The second or cardiac gland region is pale gray in color and thin (ca. 0.5 to 1 mm.); it extends about to the middle of the stomach. The third or fundus gland region is readily distinguished by its thickness (ca. 3 mm.) and its brownish-red mottled appearance. The fourth or pyloric region is pale, thinner than the preceding, and presents a number of irregular folds. At the pylorus there is a remarkable ridge which projects from the wall of the lesser curvature and diminishes considerably the size of the orifice. It is about an inch and a half (ca. 3 to 4 cm.) long and nearly half an inch (ca. 1 cm.) high. Sometimes it is grooved; in other cases it has the form of a rounded eminence attached by a pedicle to the wall. Fibers from the circular muscular coat extend into it.

FIG. 321.—LIVER OF PIG, SOFT SPECIMEN SKETCHED WITH LOBES DRAWN APART. ]

THE INTESTINE

The =small intestine= is 50 to 65 feet (ca. 15 to 20 m.) long. The mesentery of about the first two feet (ca. 60 cm.) is two to two and a half inches (ca. 5 to 6 cm.) long; this part may be termed duodenum. The remainder (Jejuno-ileum) has a mesentery about six to eight inches (ca. 15 to 20 cm.) long, which is thick and contains a quantity of fat, and numerous large lymph glands at its root; the root is attached in the sublumbar region behind the stomach and blends here with the mesentery of the large intestine. The small intestine is arranged in close coils and lies mainly on the left side and floor of the abdomen, from the stomach to the pelvis; some coils, however, lie against the right flank. The opening of the =bile-duct= is about one or two inches (ca. 2.5 to 5 cm.) from the pylorus, and that of the =pancreatic duct= about four or five inches (ca. 10 to 15 cm.) beyond it. =Peyer’s patches= and =solitary glands= are numerous and very distinct; the patches are usually band-like and prominent; the solitary glands form projecting nodules marked by crypts.

FIG. 322.—LIVER OF PIG, VISCERAL SURFACE.

Photograph of specimen hardened in situ. ]

The =large intestine= is about 15 feet (ca. 4 to 5 meters) in length, and is for the most part much wider than the small intestine; it is connected by a mesentery with the dorsal abdominal wall between the kidneys. The =cæcum= is cylindrical, about 8 to 12 inches (ca. 20 to 30 cm.) long, and 3 to 4 inches (ca. 8 to 10 cm.) wide. It lies against the upper part of the right flank, its blind end reaching to within about two inches (ca. 5 cm.) of the pelvic inlet. The ileum joins the cæcum obliquely and projects somewhat into its lumen. The =colon= has at first about the same caliber as the cæcum, but becomes gradually smaller. Most of it is arranged in three close, double spiral coils in the mesentery, in relation chiefly to the right flank externally, and to the small intestine behind and to the left. On emerging from this spiral labyrinth, it passes forward to the stomach and pancreas and then turns backward; this terminal part is narrow, median in position, and closely attached by a short mesentery to the sublumbar region. The =rectum= is usually surrounded by a quantity of fat. The cæcum has three longitudinal muscular bands and three rows of sacculations, which are continued a short distance on the colon. The spiral colon has two bands and two series of sacculations, which, however, gradually disappear in the centrifugal part.

THE LIVER

FIG. 323.—LIVER OF PIG, PARIETAL SURFACE.

Photograph of specimen hardened in situ. ]

The liver is relatively large, its average weight being about 4 to 4½ pounds (ca. 2 kg.). It is thick and very strongly curved. It is divided by three deep interlobar incisures into four principal =lobes=—=right lateral=, =right central=, =left central=, =left lateral=; the last of these is usually considerably the largest. On the upper part of the right lateral lobe is the =caudate lobe= and its process. That part of the right central lobe which lies below the portal fissure and to the left of the gall-bladder and cystic duct is homologous with the quadrate lobe of man. The parietal surface is extremely convex, its most anterior part reaching to a plane through the lower part of the sixth or seventh intercostal space. The visceral surface is deeply concave; most of it is related to the stomach, for which there is a correspondingly large and deep gastric impression. There is a duodenal impression on the upper part of the right lateral lobe, but no renal impression, as the right kidney does not touch the liver. The fossa for the gall-bladder is mainly on the right central lobe, but also in part on the adjacent surface of the left central lobe. The posterior vena cava enters the dorsal border of the caudate lobe and soon becomes entirely embedded in the gland substance, emerging only at its passage through the diaphragm. The œsophageal notch is large and is occupied mainly by the large right crus of the diaphragm. The right lateral border extends backward to the upper part of the twelfth intercostal space or thirteenth rib. The left lateral border is opposite the eighth rib and intercostal space. The ventral border extends backward about as far as the umbilicus.

There are no lateral ligaments and the falciform ligament disappears early.

The =gall-bladder= is attached in the fossa vesicæ felleæ on the right central lobe, at a considerable distance from the ventral border. The cystic duct joins the hepatic duct at an acute angle immediately after the emergence of the latter from the portal fissure. The =bile-duct= (Ductus choledochus) opens at the papilla duodeni about one or two inches (ca. 2.5 to 5 cm.) from the pylorus.

FIG. 324.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, LEFT SIDE.

D, Costal line of diaphragm; U, ureter; V. S., vesicula seminalis; B. g., bulbo-urethral gland; P, penis. ]

FIG. 325.—PROJECTION OF VISCERA OF PIG ON BODY-WALL, RIGHT SIDE.

D, Costal attachment of diaphragm; O, ovary. ]

Owing to the large amount of interlobular tissue, the =lobules= are mapped out sharply; they are polyhedral in form and are 1 to 2.5 mm. in diameter. For the same reason the gland tissue is much less friable than that of the other animals, from which it is easily distinguished.

THE PANCREAS

The =pancreas= is elongated, and is situated transversely on the dorsal abdominal wall, with its right extremity on the ventral surface of the right kidney, and the left end touching the dorsal end of the spleen and the left kidney. The right portion has two lobes; the posterior lobe bends around the great mesenteric artery and the portal vein; the anterior one is pointed, extends downward and forward about in the median plane, and is attached to the portal fissure and the duodenum. The left portion is prismatic and rests mainly on the left sac of the stomach, its left extremity being included between the left kidney and the dorsal end of the spleen. The pancreatic =duct= passes from the anterior lobe directly through the duodenal wall, opening about five or six inches (ca. 12.5 to 15 cm.) from the pylorus. The interlobular tissue usually contains a good deal of fat.

THE SPLEEN

The =spleen= is long and narrow. Its long axis is nearly dorso-ventral in direction, and is slightly curved to conform to the left part of the greater curvature of the stomach. The dorsal end lies under the vertebral ends of the last three ribs. The ventral end is smaller, reaches to the ventral abdominal wall, and lies against the left lobe of the liver. The visceral surface has a longitudinal ridge on which the hilus is situated; this divides the surface into nearly equal gastric and intestinal areas. The spleen is attached so loosely to the stomach that it may be regarded as being intercalated in the great omentum. In large subjects it may reach a length of 15 to 18 inches (ca. 38 to 45 cm.) and a width of 3 to 4 inches (ca. 8 to 10 cm.).

DIGESTIVE SYSTEM OF THE DOG

THE MOUTH

The size and form of the mouth vary greatly in different breeds, the cavity being in some long and narrow, in others short and wide. The =rima oris= is very extensive, so that the labial commissure is opposite the third or fourth cheek tooth. The =lips= are thin and mobile, and present numerous tactile hairs. The upper lip has a small, central, bare area which forms part of the muzzle, and is marked by a central groove, the philtrum, or (as in the bulldog) a fissure, giving the appearance of harelip. The lateral borders of the lower lip are flaccid and denticulated. The mucous membrane is usually pigmented and forms distinct frena labiorum. The labial glands are small and scanty.