THE ALIMENTARY CANAL 



171 



of teleosts as pyloric ceca, small fiiiger-like pouches structurally 

 similar to the stomach. 



The Stumach of ^[inphibid. The mucosa consists of simple 

 branched tubular glands lined with simple columnar epithelium and 

 separated from each other by tunica ])r()])ria. The submucosa has 

 extensions forming folds into the lumen. There is in some s])ecies, 

 such as the frog (Fig. 108), a well-defined muscularis mucosa. The 

 muscularis coat has ])rominent circular muscle and a much thinner 

 longitudinal coat. 



The Stomach of Reptiles. — Submucosal folds are present here also. 

 The mucosa is composed of simple tubular glands lined with colum- 





Fig. 109. — Photograph through a ruga of the fundus of the dog's stomach. Note 

 the broad extension of the submucosa surmounted by the glandular mucosa. The 

 muscularis has a thick circular and thinner longitudinal coat. A muscularis mucosa 

 follows the outline of the glandular mucosa. 



nar epithelium. The superficial ei)itheliiim appears to be stratified 

 columnar in some forms and goblet cells may be nimierous. The 

 circular coat of the muscularis is prominent, but the longitudinal 

 coat is much narrower or represented by scattered bimdles. The 

 adventia is usually thin. 



The Mammalian Stomach.— The mucosa at the lower end of the 

 esophagus is marked by an abrujjt transition from a relati\ely 

 smooth surface and stratified squamous epithelium to the folded 

 and glandular mucosa of the stomach lined by simple columnar 

 epithelium. Below the mucosa the transition is more gradual, the 

 deep mucous glands of the esophagus often extending over into the 

 stomach. Folds in the stomach wall involving submucosa and 

 mucosa form ridges, or rugge, observed best in the empty stomach. 



