DIGESTION. 



at the junction of the ileum with the caecum are contained between the 

 outer opposed surfaces of the folds of mucous membrane which form the 

 valve, the longitudinal muscular fibres and the peritoneum of the small 

 and large intestine respectively are continuous with each other, without 



FIG. 202. Horizontal section through a portion of the mucous membrane of the large intes- 

 tine, showing Lieberkiihn's glands in transverse section, a, lumen of gland lining of columnar 

 cells with c, goblet cells, 6, supporting connective tissue. Highly magnified. (V. D. Harris.; 



dipping in to follow the circular fibres and the mucous membrane. In 

 this manner, therefore, the folding inwards of these two last-named 

 structures is preserved, while on the other hand, by dividing the longitu- 

 dinal muscular fibres and the peritoneum, the valve can be made to dis- 

 appear, just as the constrictions between the sacculi of the large intestine 

 can be made to disappear by performing a similar operation. The inner 

 surface of the folds is smooth : the mucous membrane of the ileum being 

 continuous with that of the caacum. That surface of each fold which 

 looks towards the small intestine is covered with villi, while that which 

 looks to the caecum has none. When the caacum is distended, the 

 margins of the folds are stretched, and thus are brought into firm apposi- 

 tion one with the other. 



DIGESTION IN THE I 



After the food has been duly acted upon by the stomach, such as has 

 not been absorbed passes into the duodenum, and is there subjected to 

 the action of the secretions of the pancreas and liver which enter that 

 portion of the small intestine. Before considering the changes which 

 the food undergoes in consequence, attention should be directed to the 



