STOMACH. 



303 



The internal or mucous coat, is divided into right and left 

 portions. The latter is the cuticular portion, continuous with 

 the mucous membrane of the oesophagus, which it resembles in 

 structure and appearance; it is covered by a thick layer of 

 stratified epithelium. The line of demarcation between the two 

 portions is abrupt and dentated. The right portion, the villous, 

 or true digestive coat, is reddish in colour, soft, very vascular, 

 and velvety-looking. When examined with a lens, it appears 

 honey-combed, or covered by small shallow polygonal depressions 

 or alveoli, separated from each other by projecting intervals. 



FIG. 99. 



Internal aspect of Horse's Stomach, opened from below, a a, Cuticular mucous 

 membrane ; 6 6, Villous mucous membrane ; c c c, Line of demarcation between 

 the two portions ; d, Cardiac orifice ; e, Pyloric orifice and valve. 



Into these alveoli the gastric follicles open ; the latter lie in the 

 subepithelial tissue, perpendicular to the surface of the mem- 

 brane ; at the pyloric end some of these follicles terminate in 

 dilated sacs, or divide into two or more tubes. They consist of a 

 basement membrane, lined by columnar epithelium ; some of 

 them secrete gastric juice, others mucus ; the latter are lined 

 throughout with epithelium, while the gastric juice follicles have 

 their lower part filled with nucleated cells and granules. The 

 villous coat is also covered with numerous simple or lenticular 

 follicles. 



The mucous membrane, when the organ is empty, is thrown 

 into folds, or ruga 1 , which are very well seen in the villous por- 



