318 DIGESTIOX. 



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 with each other. 



While the circular muscular fibres of the bowel at the 

 junction of the ileum with the esecum 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 

 muscular fibres and the peritoneum, the valve can be made 

 to disappear, just as the constrictions between the sacculi 

 of the large intestine can be made to disappear by per- 

 forming a similar operation. 



The Pancreas, and its Secretion. 



The pancreas is situated within the curve formed by the 

 duodenum ; and its main duct opens into that part of the 

 intestine, either through a small opening or through a duct 

 common to itself and to the liver. The pancreas, in its 

 minute anatomy, closely resembles the salivary glands ; 

 and the fluid elaborated by it appears almost identical with 

 saliva. When obtained pure, in all the different animals 

 in which it has been hitherto examined, it has been found 

 colourless, transparent, and slightly viscid. It is alkaline 

 when fresh, and contains a peculiar animal matter named 

 pancreatin and certain salts, both of which are very similar 

 to those found in saliva. In pancreatic secretion, however, 

 there is no sulpho-cyanogen. Pancreatin is a substance 

 coagulable by heat, and in many other respects very 



