DIGESTIVE SYSTEM. 



183 



site the eleventh dorsal vertebra. Two distinct 

 constrictions are present, one at the beginning and 

 one where it is crossed by the left bronchus. The 

 normal distention at these points is about four- 

 fifths inch. 



The wall of the esophagus may be divided into 

 four coats: mucous, submucous, muscular, and 

 fibrous. 



1. Mucous Layer. This layer is thrown into 

 many longitudinal folds and lined, as in the pharynx, 

 with stratified epithelium. The tunica propria is 

 well developed and may contain solitary lymph 

 nodes. Tubular glands resembling those of the 

 stomach are found in patches, particularly at the 

 extremities of the esophagus. They are entirely 

 confined to the mucosa and distinct from the mucous 

 glands found in the submucosa. Their function is 

 problematic. A muscularis mucosa is present in the 

 esophagus just external to the tunica propria, con- 

 sisting of longitudinally disposed smooth muscle 

 cells. This layer becomes more prominent in the 

 alimentary canal below the esophagus. 



2. Submucosa. This layer lies just external to 

 the muscularis mucosa and consists of loose con- 

 nective-tissue elements, blood and lymph vessels, 

 nerves and the bodies of mucous glands. These 

 glands are compound racemose and are particularly 

 abundant in the lower part of the esophagus. The 

 ducts pass through the muscular mucosa to open on 

 the epithelial surface. They secrete mucus for the 

 lubrication and protection of this surface. Not in- 

 frequently the morning vomit of mucus in chronic 



