THE ALIMENTARY CANAL 353 



serous connective tissue which is covered by mesothelium. The serous 

 coat supports the larger blood and lymphatic vessels and nerve trunks 

 which supply the organ. 



The Muscular Coat. The muscular coat of the stomach consists in 

 general of two layers of smooth muscle fibers a thin outer longitudinal, 

 and a much thicker inner circular and oblique layer. The regular cir- 

 cular arrangement of these fibers is much distorted by the peculiar 

 dilatation and partial rotation to which the stomach is subjected in the 

 course of its development, and as a result of this change obliquely placed 

 fibers form a considerable portion of the muscular coat. 



The oblique fibers are most numerous toward the cardiac end of the 

 stomach, where they form a third muscular layer, the innermost portion 

 of the muscular coat. The longitudinal fibers are most abundant toward 

 the cardiac and pyloric orifices and along the lesser curvature; in the 

 fundus and mid-region of the stomach they form only a very thin layer. 

 The circular fibers form the thickest of the three muscular layers and 

 are nearly equally distributed in all portions, except that at the cardiac 

 and pyloric orifices they become much thickened to form the sphincter 

 muscles. The pyloric sphincter is especially well developed. 



The layers of the muscular coat of the stomach are united by thin 

 septa of connective tissue; that between the longitudinal and circular 

 layers contains the myenteric nerve plexus and the larger blood-vessels 

 which supply this coat. 



The Submucosa. The submucosa consists of loose areolar tissue 

 which supports the blood-vessels, lymphatics, and the submucous nerve 

 plexus, all of which distribute their branches to the mucous membrane. 

 In no portion of the stomach does this coat contain glands. 



The Mucous Coat. The muscularis mucosaB forms a thin but com- 

 plete layer from one end of the stomach to the other, and marks the 

 outer boundary of the mucous membrane. It usually consists of two 

 thin layers, an inner circular and an outer longitudinal. Here and 

 there muscle fibers extend from the muscularis mucosaB into the corium 

 between the gastric glands. 



The surface of the mucosa is clothed with tall columnar epithelium, 

 and the whole membrane is thrown into wavy folds, an arrangement 

 which is permitted by the very loose meshes of the submucous areolar 

 coat. The corium of the mucosa is closely packed with tubular secreting 

 glands, which open on the surface by wide-mouthed, crypt-like ducts 

 or foveolae, and arc embedded in a fine fibroreticular tissue containing 

 many lymphocytes. 



