350 



THE DIGESTIVE SYSTEM 



in others, e.g., opossum, dog, pig, they are very abundant. Except 

 in man, the mucous alveoli contain demilunes. Esophageal glands 

 are the exception rather than the rule in mammals. The fact that they 

 are absent in all vegetable feeders but present in mixed feeders indicates 

 that they have a chemical rather than a mechanical function (Goetsch, 

 Amer. Jour. Anat., 10, 1, 1910). 



The Mucous Coat (Mucosa). The mucous coat of the esophagus 

 consists of a tunica propria or corium of areolar tissue which rests 

 upon a well-developed muscularis mucosse and is covered on its free 

 surface by stratified squamous epithelium. 



The muscularis mucosa? contains considerable bundles of smooth 



FIG. 327. PHOTOMICROGRAPH OF A LONGITUDINAL, SECTION THROUGH THE LOWER 

 THIRD OF THE HUMAN ESOPHAGUS, SHOWING A GROUP OF ESOPHAGEAL GLANDS. 



muscle whose general direction is a longitudinal one in its outer, and 

 circular in its inner portion. This layer forms the outermost stratum 

 of the mucous coat, and is penetrated by the ducts of the deep mucous 

 glands whose secreting acini lie in the submucosa. 



The inner portion of the tunica propria carries on its surface many 

 tall connective tissue papillae which project well into the epithelial coat 

 and which closely resemble the vascular papillae of the skin. 



The mid-portion of the corium is penetrated by the excretory ducts 

 of the mucous glands. These are at first lined by low columnar cells 

 which, as they approach the epithelial surface are changed into several 

 layers of flattened cells, which thus form a thin stratified lining, con- 

 tinuous with the superficial stratified squamous epithelium of the 

 esophageal mucosa. Many of these ducts possess small cystic dilata- 



