THE ALIMENTARY CANAL. 237 



is an ovoid space in the wall of the duodenum. The space 

 is encroached upon by numerous folds of the walls. The 

 common bile-duct and the pancreatic duct open into it, the 

 former extending; from tb.c bottom of the ampulla nearly to its 

 mouth, and the latter extending from the bottom about half-way 

 to the mouth. Two centimeters caudoventrad of the opening 

 of the ampulla of Vatcr is the opening of the accessory pan- 

 creatic duct. It can usually be demonstrated only by passing- 

 a bristle into the duodenum through an opening in the duct. 



The jejunum is the part of the small intestine following the 

 duodenum. It is not separated from the part of the small 

 intestine following it by any sharp line. In man it constitutes 

 two-fifths of the small intestine exclusive of the duodenum, and 

 is characterized by its emptiness after death and by the absence 

 from it of rc}xr's agminated glands (Peyer's patches). 



The ileum is the portion of the small intestine between the 

 jejunum and colon. It lies suspended by its mesentery in 

 numerous folds in the caudal part of the abdominal cavity, 

 separated from the ventral abdominal wall only by the great 

 omentum. It is of nearly uniform diameter, but its caudal por- 

 tion is thinner- walled than its cranial portion. Its walls have 

 a microscopic structure like that of the duodenum and jejunum. 

 On its inner surface and on the inner surface of the jejunum are 

 seen close-set villi, but these become rather sparser toward the 

 caudal end of the ileum and disappear about one centimeter 

 from the opening into the colon. Among the villi of the 

 caudal end of the ileum are numerous rounded elongations free 

 from villi. These are the solitary follicles or solitary glands 

 (lymphatic) of the intestine. These glands when aggregated 

 together form the agminated glands or patches of Peyer. The 

 ileum passes at the caudal end into the colon, the opening 

 being guarded by the ileocolic valve (Fig. 99). This is formed 

 by a marked projection of the mucosa (/) and transverse 

 muscle layer {e) of the ileum into the colon. Its surface is 

 free from villi. 



6. The Large Intestine. Intestinum crassum. — ■ The 

 large intestine is divided into colon and rectum. The colon 

 or first part of the large intestine lies against the dorsal body 



