336 DISiSECTION OF THE EABBIT. 



B. Internal Structure of the Alimentary Canal. 



1. The stomach. 



Slit up the stomach along its posterior surface : wash out 

 its contents, and examine it under water. 



The wall of the stomach consists of an outer 

 peritoneal investment; a middle muscular layer, 

 thickened at the pyloric end ; and an inner layer of 

 mucous membrane, which is raised into irregular 

 longitudinal folds. The pyloric orifice is narrowed 

 by a prominent muscular rim. 



2. The small intestine. 



Gut out a small piece from the toall, and examine its inner 

 surface under water. 



The villi are minute tag-like processes of the 

 mucous membrane, covering its surface, and giving 

 it a velvety appearance. 



Peyer's patches present a honeycombed appear- 

 ance, the depressions being occupied by smooth 

 convex lymph-follicles, and bordered by villi. 



3. The caecum. 



Bemove the cmcum from the body, cutting across the small 

 intestine and the colon about an inch from it. Take the 

 ccBCum to the sink, and slit it open longitudinally : wash out 

 its contents thoroughly, and examine under water. 



The inner surface is papillose, and raised along 

 the Une of the external constriction into a prominent 

 spiral fold, a quarter of an inch or more in width. 

 The opening from the saeculus rotundus is small and 

 circular ; that into the colon is much larger. 



Cut the vermiform appendix across to see the thickness 

 of its wall ; and slit it open to examine its inner surface, 

 lohich is similar to that of Peyer's patches, but with smaller 

 follicles. 



