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 ab- 

 sent 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 pro- 



. ,.- -ii ^is.* a* pria or corium of areolar 



tissue which rests upon a 

 -c. M. well-developed muscularis 

 mucosffi and is covered on 

 its free surface by strati- 

 fied squamous epithelium. 

 The muscularis mu- 

 cosa3 contains consider- 

 able bundles of smooth 

 muscles whose general di- 

 rection is a longitudinal 

 one in its outer, and cir- 

 cular in its inner portion. 

 This la}*er forms the 

 outermost stratum of the 

 mucous coat, and is pene- 

 trated by the ducts of the 

 deep mucous glands 

 whose secreting acini lie 

 in the submucosa. 



The inner portion of 

 the tunica propria car- 



FIG. 327. TRANSVERSE SECTION OF HUMAN 

 ESOPHAGUS THROUGH LOWER THIRD. 



Z,, lumen; F., fibrous tunic; C. A/., circular muscle 

 layer; L. M., longitudinal muscle layer; G., mucous 

 glands in 'submucosa (S.)} L.N., lymph nodule; 

 M. M., muscularis mucosse; T. P., tunica propria; 

 E., stratified squamous epithelium; B. V., blood 

 vessels. (Adapted from Merkel.) 



ries 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, continuous with 

 the superficial stratified squamous epithelium of the esophageal mucosa. 



