326 HUMAN PHYSIOLOGY 



series of delicate finger-like processes, the villi. The tissue 

 of the villi and that between the Lieberkiihn's follicles is 

 chiefly lymphoid, and in certain places this lymphoid 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 (Brunner's glands). 



The Large Intestine is about 2 metres in length. The 

 small intestine enters it at one side, and the opening is 

 guarded by a fold of mucous membrane which forms the 

 ileo-csecal valve. Above the opening of the small intestine 

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

 appendix ( F.), a narrow tube with an abundance of lymph 

 tissue in its wall. Below the opening of the small intestine 

 is the colon (Col.\ which, after passing up the right side 

 across the abdomen and down the left side, takes an S-like 

 bend to end in the rectum (R.), which, passing forward, 

 suddenly turns down and opens at the anus. The sudden 

 bend is of importance in retaining the contents of the rec- 

 tum. 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 muscular coat of the colon 

 differs from that of the rest of the alimentary canal, in that 

 the longitudinal fibres are arranged in three bands. 



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 mammals, the fibrous tissue supporting the liver cuts 



