THE STOMACH AND INTESTINES 151 



THE STOMACH AND INTESTINES 



The stomach and intestines are lined with mucous membrane^ 

 i.e., a membrane containing epithelial cells, usually of the columnar 

 variety, which secrete mucus. 



The gastric and intestinal walls are constructed as follows: 



1. The epithelial lining. 



2. The mucosa. 



3. The muscularis mucosce. 



4. The submucosa. 



5. The muscular walls proper. 



6. The fibrous or peritoneal investment. 



In descriptive anatomy, the first three of the above are included 

 in the mucous coat. 



The epithelium of the inner surface of that portion of the 

 alimentary tract under consideration is of the columnar variety. 

 Variations occur in the deeper layers, which will be referred to 

 later on. 



The mucosa, with its epithelial covering, is thrown into coarse 

 folds, rugce or valve -like reduplications, which greatly increase the 

 extent of surface. It contains the principal glands and capillary 

 blood-vessels. The epithelial lining is usually considered as a part 

 of the mucosa. 



The muscularis mucosas is a thin layer of involuntary muscular 

 fiber, which separates the mucosa from the submucosa. Some of 

 the cells run in a longitudinal and others in a circular direction. 



The submucosa, composed of loose areolar tissue, serves to con- 

 nect the previous structures with the muscular coat proper, and 

 contains the larger trunks from which the capillaries of the mucosa 

 take their origin, or into which they empty. An intricate plexus 

 of lymphatics is also situated here. 



The muscular coat consists of strong bands, running chiefly in 

 two directions, corresponding to an inner circular and an outer 

 longitudinal layer. Near the cardiac end there is an imperfectly 

 developed oblique layer. The muscle -plates are sustained by con- 

 nective tissue. 



A peritoneal investment covers the organs, except at such points 

 as are occupied by the entrance and exit of blood-vessels and lym- 

 phatics through the mesenteries, with a few exceptions. 



