272 



THE ORGANS 



so-called columncB rectales. A change in the character of the mucous 

 membrane begins at the upper end of the columnae rectales. Here 

 the simple columnar epithelium of the gut passes over into a stratified 

 squamous epithehum, beneath which is a papillated stroma. The 

 glands continue for a short distance beyond the change in the 

 epithelium, but soon completely disappear. At the anus there is a 

 transition from mucous membrane to skin similar to that described 

 as occurring at the margin of the lips (page 225). 







gl 



Fig. 175. — ^lucous Membrane of Human Rectum, a, Superficial epithelium, com- 

 posed almost wholly of mucous cells, the columnar cells lying between them being so 

 compressed as to appear as thin dark lines; gl, lumen of gland of Lieberkuhn. X60. 

 (Prenant.) 



2. The submucosa is similar in structure to that of the large 

 intestine. 



The muscularis of the rectum differs from that of the large intes- 

 tine in that the longitudinal layer is continuous and thick. 



The serous coat is absent in the lower part of the rectum, being 

 replaced by a fibrous connective-tissue layer, which connects the rec- 

 tum with the surrounding structures. 



The Peritoneum, Mesentery, and Omentum 



The peritoneum (see also p. 169) is a serous membrane which lines 

 the walls of the abdomen (parietal peritoneum) and is reflected over 

 the contained viscera (visceral peritoneum). It consists of two 



