INTESTINAL DIGESTION. 233 



The mucous lining of the large intestine is continuous 

 anteriorly with that of the ileum, posteriorly with the common 

 integument. It is thin, more or less coated with mucus, 

 scantier in glands than in the small intestine, but the ori- 

 fices of the Lieberkuehnian crypts are more apparent, owing 

 to the surface here being destitute of villi. Saccular recesses, 

 more or less capacious, exist in the membrane lining the large 

 intestine. The difference in degree of vascularity gives rise 

 to difference in the colour of the mucous coat in various por- 

 tions of the gut: thus, that lining the caecum is generally 

 more deeply coloured than that of the colon, whilst the rectal 

 mucous membrane is more vascular, and hence redder than 

 the colic or ccecal one. 



At the termination of the ileum is the ileo-colic or 

 ileo-ccecal valve, which is constituted of two folds of mucous 

 membrane, almost parallel to each other, and horizontal, leav- 

 ing between them an elliptical orifice when partially drawn 

 asunder. The folds consist of the circular fibres of the intes- 

 tine, lined on the inner or ileac side by the villous membrane 

 of the small, whilst on the csecal and colic side they are 

 covered by the mucous membrane proper to the large intes- 

 tine. It is worthy of notice, that though muscular fibre? 

 partly enter into the construction of the valve, its e9> 

 ciency is explicable on purely mechanical grounds, as proved 

 by the fact, that it is competent in the dead body. 



The anus is the outlet of the intestine, which is perfectly 

 closed, except during the evacuation of feculent matters, and 

 is made perceptible externally by the elevation of the tail, 

 being situated in a space bounded superiorly by the sacrum 

 and coccyx, laterally by the ischial tuberosities, and inferiorly 

 by the urethra in the male and vulva in the female. 



It is lined within by the mucous membrane of the rectum, 

 which is loose and of a marked red colour. Its external 



