THE ILEO-C^CAL VALVE. 311 



large intestine are not known with any certainty, but 

 there is no reason to doubt that they resemble very nearly 

 those discharged by the glands of like structure in the 

 small intestine. 



The difficulty of determining the function of any single 

 set of the intestinal glands seems indeed almost insuper- 

 able, so many fluids being discharged together into the 

 intestine ; for all acting, probably, at once, produce a com- 

 bined effect upon the food, so that it is almost impossible 

 to discern the share of any one of them in digestion. 



Ileo-ccecal valve. The ileo-csecal valve is situate at the 

 place of junction of the small with the large intestine, and 

 guards against any reflux of the contents of the latter into 

 the ileum. It is composed of two semilunar folds of mucous 

 membrane. Each fold is formed by a doubling inwards of 

 the mucous membrane, and is strengthened on the outside 

 by some of the circular muscular fibres of the intestine, 

 which are contained between the outer surfaces of the two 

 layers of which each fold is composed. The inner surface 

 of the folds is smooth ; the mucous membrane of the ileum 

 being continuous with that of the caecum. 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 caecum is distended, the margins of 

 the folds are stretched, and thus are brought into firm 

 apposition one with the other. 



While the circular muscular fibres of the bowel 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 mus- 

 cular fibres and the peritoneum of the small and large 

 intestine respectively are continuous with each other, 

 without 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 longitudinal 



