THE ALIMENTARY CANAL. 239 



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 liga- 

 ment 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 \\ith 

 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. ioi,/"). 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 



