3?8 HANDBOOK OF PHYSIOLOGY. 



are somewhat more marked in the intervals between the sacculi. Toward 

 the lower end of the rectum they become more numerous, and at the 

 anus they form a strong band called the internal sphincter muscle. 



The mucous membrane of the large, like that of the small intestine, 

 is lined throughout by columnar epithelium, but, unlike it, is quite des- 

 titute of villi, and is not projected in the form of valvulce conniventes. 

 Its general microscopic structure resembles that of the small intestine: 

 and it is bounded below by the muscular is mucosw. 



The general arrangement of ganglia and nerve-fibres in the large 

 intestine resembles that in the small. 



Gland*. The glands with which the large intestine is provided are 

 of two kinds, (1) the tubular and (2) the lymphoid. 



(1.) The tubular glands, or glands of Lieberkfihn, resemble those 

 of the small intestine, but are somewhat larger and more numerous. 

 They also contain many goblet cells. 



(2.) Follicles of adenoid or lymphoid tissue are most numerous in 

 the caecum and vermiform appendix. They resemble in shape and 

 structure, almost exactly, the solitary glands of the small intestine. 

 Peyer's patches are not found in the large intestine. 



lleo-ccecal Valve. The ileo-caecal 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 inward 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. While the circular muscular fibres, however, of the 

 bowel at the junction of the ileum with the caecum are contained be- 

 tween the outer opposed surfaces of the folds of mucous membrane 

 which form the valve, the longitudinal muscular fibres and the peri- 

 toneum 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 inward 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 disappe,r 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 caecum. 

 That surface of each fold which looks toward the small intestine is 

 covered with villi, while that which looks to the caecum has none. 

 When the caecum is distended, the margin of the folds are stretched, 

 and thus are brought into firm apposition one with the other. 



