170 



THE DIGESTIVE SYSTEM 



Fig. 107. — Diagram of a cross-section of the stomach of a dogfish {Sqimlvs acanth- 

 ias). This shows ruga-like folds of submucosa extending in toward the lumen. 

 The mucosa contains closely arranged simple tubular glands. A muscularis mucosa 

 separates these glands from the submucosa. The muscularis coat is represented by 

 a circular smooth muscle sheath and a thin longitudinal sheath. The adventitia is 

 dense and is associated with the mesentery. 



Fig. 108.— a cross-section of the stomach of a frog. The mucosa consists of 

 simple branched tubular glands whose basal secretory cells are serous in character and 

 acidophilic and the cells at the mouth of the gland appear to be mucous and 

 basophilic. There is a well-defined muscularis mucosa. The submucosa is thickest 

 in the region of the ruga-like extensions. The muscularis coat is represented by a 

 thick circular and a thin longitudinal sheath of smooth muscle. The adventitia is 

 a thin serosa. 



