FOOD AND DIGESTION 341 



tissue is massed in nodules which are either placed singly or 

 grouped together in the lower part of the small intestine to 

 form Peyer's patches. In the first part of the small intestine 

 the upper part of the duodenum (D. ) the submucous layer 

 is full of small branching glands lined by an enzyme-secreting 

 epithelium (Brunners glands). 



The Large Intestine. The small intestine enters it .at one 

 side, and the opening is guarded by a fold of mucous membrane 

 which forms the ileo-caecal valve. Above the opening of the 

 small intestine a csecal pouch exists, and at the top of this is the 

 vermiform appendix (V.),& narrow tube with an abundance of 

 lymph tissue in its wall. This is specially well developed 

 in the rabbit. Below the opening of the small intestine is 

 the colon (Col.). This ends in the rectum (E.), which opens at 

 the anus. The last part of the rectum is surrounded by a 

 strong band of muscle the internal sphincter ani by which 

 it is compressed. The whole large intestine is covered by 

 columnar epithelium, and is studded with Lieberkiihn's follicles, 

 in which the epithelium is chiefly mucus-secreting in type. 

 There are no villi. 



The caecum and colon in the horse (fig. 152) are enormously 

 developed, holding about 120 litres, or seven times as much as 

 the stomach. The colon is divided into the double colon, which 

 is of immense size and complexity, and the single colon, which 

 is smaller and simpler, and which ends in the rectum. 



The large intestine of ruminants is much smaller per unit of 

 weight of the animal than that of the horse. In the ox, its 

 capacity is less than 40 litres. 



In all animals it is the small intestine which presents the 

 greatest extent of surface for absorption. 



Into the duodenum, the bile duct and the duct of the 

 pancreas open. The bile duct is formed by the union of the 

 ducts from the lobes of the liver. Upon its course is a diver- 

 ticulum, the gall bladder. The Liver (Li.) is a large solid- 

 looking organ, formed originally as a double outgrowth from 

 the alimentary canal. These outgrowths branch, and again 

 branch, and between them the blood coming from the mother 

 to the foetus flows in a number of capillary channels. Later, 

 when the alimentary canal has developed, the blood from it 

 is streamed between the liver tubules. In man and other 



