THE STOMACH. 83 



THE STOMACH AND INTESTINES. 



The stomach and intestines are lined with mucous membrane, i. e. f 

 a membrane containing glands which secrete mucus. 



The gastric and intestinal mucous membranes are constructed as 

 follows: 



1. The epithelial lining. 



2. The mucosa. 



3. The muscularis mucoscv. 



4. The submucosa. 



5. The muscular walls proper. 



6. The fibrous or peritoneal investment. 



In descriptive anatomy, the first four of the above are included in 

 the mucous coat. 



The epithelium of the inner surface of that portion of the alimen- 

 tary 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-ves- 

 sels.* 



The muscularis mucosse is a thin layer of involuntary muscular 

 fibre which separates the mucosa from the submucosa. 



The submucosa, composed of loose areolar tissue, serves to connect 

 the previous structures with the muscular coat proper, and contains 

 the larger trunks from which the capillaries of the mucosa either take 

 their origin, or into which they empty. An intricate plexus of lym- 

 phatics is also here situated. 



The muscular coat consists of strong bands, running in two or three 

 directions. The muscle plates are sustained by connective tissue. 



A peritoneal investment covers the organs, except at such points as 

 are occupied by the entrance and exit of blood-vessels, etc. 



THE STOMACH. 



The mucosa everywhere contains microscopical depressions, the gas- 

 tric tubules or peptic glands. These are concerned in the production 

 of the gastric juice, and in the absorption of fluids. 



* It is not always possible in mucous membranes to differentiate clearly be- 

 tween an epithelial lining and the mucosa; and in the stomach and intestine 

 they may be both included in the mucosa. 



