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 the 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 Vater 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 Peyer’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 (¢) 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 
