THE RECTUM. 401 



the same name found in the small intestine. As we approach 

 the rectum an increase in their length becomes apparent. 



In the vermiform appendix we find the collection of solitary 

 lymph-follicles so closely placed that the space left between 

 adjoining glands does not equal in diameter that of these struc- 

 tures themselves. 



The longitudinal layer of the muscle-coat is quite thin be- 

 tween the taenise coli, or flat longitudinal bands of the large 

 intestine. These bands themselves represent thickened layers 

 of the musculosa. It appears that the circular fibres are espe- 

 cially developed in the portions between the sacculi of the 

 csecum and colon. 



The blood-vessels are arranged after the same plan as in the 

 small intestine. In the submucosa are contained large trunks, 

 running parallel to the surface. Capillaries arise from these, 

 and ascend almost vertically between the crypts of Lieberkiihn, 

 the capillary network surrounding those structures being only 

 moderately developed. 



As regards the lymphatics, they have a distribution similar 

 in all essential respects to that found in the small intestine. 



The nerves likewise imitate in their structure and arrange- 

 ment those encountered in the small intestine. Meissner's 

 plexus appears to be provided with comparatively large gan- 

 glia and relatively small component cells. The plexus of 

 Auerbach also attains conspicuous development in the large 

 intestine. 



THE RECTUM. 



The internal sphincter ani represents a thickening of the 

 circular layer of the muscle-coat. In its upper portion the 

 rectal mucous membrane is like the same structure of the large 

 intestine. Lower down we find the columnar epithelium grad- 

 ually replaced by stratified pavement-epithelium. 



The follicles of Lieberkiihn are large and long. Finally, 

 the mucous membrane gradually passes into the ordinary in- 

 tegument surrounding the anal orifice. 



The blood-vessels, lymphatics, and nerves resemble in their 

 distribution those of the colon, and are devoid of characteristic 

 peculiarities. 



26 



