594 



THE DIGESTIVE TRACT. 



muscle-layers, is capable of producing very large folds, which 

 are arranged longitudinally from the cardia to the pylorus, and 

 are least marked in the latter situation. When the stomach 

 is empty, the folds of the mucosa completely occlude the 

 cavity. The covering surface epithelium of the stomach is indis- 

 tinctly stratified; the innermost flat, horny layer and the col- 

 umnar layer are well marked, while the middle layers of cuboidal 

 epithelia are often wanting. The difficulty of obtaining for 

 examination the unchanged gastric mucosa of man is, perhaps, the 

 reason why the presence of flat, horny epithelia has been over- 

 looked. The columnar epithelium gradually loses its character, 



FIG. 251. OESOPHAGUS OF A RABBIT. TRANSVERSE SECTION. 



E, horny layer; R, rete mucosum ; C, layer of columnar epithelia; M, loose connective 

 tissue, with injected blood-vessels ; T, circular layer of striped muscles, with the adjacent 

 oblique and longitudinal layers, L, L l . Magnified 150 diameters. 



and is transformed into the cuboidal epithelium of the gastric 

 glands. 



The majority of the gastric glands are of the simple tubular 

 variety, though it often happens that two or more tubules empty 

 into a common tube of larger caliber, opening at the inner surface 

 of the mucosa. In the stomach of man, in the middle portions of 

 the mucosa, branching tubular glands are said to occur (Kolliker). 



