Fig. 99.—Section of the Ileocolic Valve.
Fig. 98.—a, ileum; b, ascending colon; c, cæcum; d, position of ileocolic valve.
Fig. 99.—a, cæcum; b, colon; c, ileum; d, longitudinal muscle layer; e, transverse muscle layer; f, mucosa; g, ileocolic valve (opened, as when material is passing into the colon).
At the bottom of the cæcum on its inner surface is seen a collection of solitary glands forming one of the agminated glands of Peyer, or Peyer’s patches. The mucous membrane is without villi. It presents a few considerable elevations, probably solitary glands.
The rectum is the terminal portion of the large intestine lying in the median line close to the dorsal body wall, from which it is suspended by the short mesorectum. Its structure is like that of the colon. It opens externally at the anus. The entire large intestine has a length about one-half that of the animal. At each side of the anus are two large secreting sacs, the anal sacs or glands, each about a centimeter in diameter. These open into the anus one or two millimeters from its caudal boundary.
Muscles of the Rectum and Anus.—Owing to the close interrelation of the muscles of the rectum and anus with those of the urogenital organs, all these muscles will be [described] together at the end of the description of the urogenital system.
7. The Liver, Pancreas, and Spleen.
—The Liver. Hepar.—The liver ([Figs. 100] and [101]) is a large red-brown organ occupying the cranial part of the abdominal cavity. It is closely applied to the caudal surface of the diaphragm and extends thence ventrad of the stomach so as to conceal all but its pyloric end. Owing to the position of the stomach the larger mass of the liver is on the right side and it extends somewhat further caudad on this side.
The liver is divided by the dorsoventral suspensory ligament into the right and left lobes, and each half is again divided into lobes. On the left is a small left median (b) and a larger left lateral lobe (a). The left lateral (a) extends caudad with a thin edge which covers the greater part of the ventral surface of the stomach. On the right there is a large right median (or cystic) lobe (c, c′). Its cranial surface is dome-shaped and fitted against the right two-thirds of the caudal surface of the diaphragm. Its ventral edge is thin, its dorsal edge thick, and its caudal surface marked by a deep dorsoventral cleft in which lies the gall-bladder ([Fig. 101], f). Dorsad and caudad of the cystic lobe is the right lateral lobe (d, d′), which is deeply cleft. Its elongated caudal division (d′) extends in a point to the caudal end of the right kidney and is adapted to the medial half of its ventral surface. Its smaller and more compact cranial division (d) ends ventrally in a thin edge. It lies between the caudal division (d′) and the cystic lobe (c), and its dorsal surface is adapted to the suprarenal body. The caudate or Spigelian lobe ([Fig. 101], e) is an elongated, triangular, pyramidal lobe. It lies in the omental sac and partly closes the foramen epiploicum (foramen of Winslow). At its base it is connected with the caudal division of the right lateral lobe (d′).