1 84 NORMAIv HISTOLOGY AND ORGANOGRAPHY. 



gastritis comes from excessive secretion of these 

 glands. The tissues of the submucosa are loosely 

 held together, and sections, therefore, may tear along 

 this layer. 



3. Muscular Coat. This consists of an inner cir- 

 cular and an outer longitudinal layer, although the 

 fibers of each often interlace. The longitudinal 

 layer is particularly strong, often thicker than the 

 circular. In the upper half many striated fibers are 

 present that are continuous with the pharyngeal 

 voluntary muscle. The control of these fibers en- 

 ables the dog to return food to the mouth that has 

 passed into the upper part of the esophagus. ' In the 

 lower half, only smooth muscle fibers are present. 

 The longitudinal layer passes on as the longitudinal 

 layer of the stomach and intestine, while the circular 

 becomes the diagonal fibers of the stomach and does 

 not pass to the intestine. Connective- tissue ele- 

 ments interlace and strengthen the whole muscu- 

 lature. Foods and liquids are carried along this 

 tube by peristaltic contraction of its muscles, and 

 in this way cattle and horses can take nourishment 

 without lifting their heads. 



4. Fibrous Coat. This consists of loose connec- 

 tive-tissue elements, mostly white fibrous, binding 

 the esophagus to adjacent structures. It is not 

 well defined and often difficult to demonstrate as a 

 distinct layer. 



STOMACH. 



The stomach varies greatly in form and position 

 according to physiological conditions. For de- 

 scriptive purposes it has two ends, cardiac and py- 



