THE DIGESTIVE SYSTEM 



227 



The Esophagus 



The esophagus is that portion of the alimentary canal which extends 

 from the pharynx to the stomach. It is nearly ten inches in length and is 

 the narrowest part of the digestive tract. From the pharynx it passes 

 just beneath the backbone through the mediastinum and diaphragm 

 to the cardiac region of the stomach. 



The wall of the esophagus consists of the four layers characteristic 

 of the digestive tract, tunica mucosa, tunica submucosa, tunica muscularis, 



MUCOSA 



> i-»SUBMUCOSA 



MUSCULARIS MUCOSAE 

 MUCOUS GLAND 



CIRCULAR MUSCLES 



,_ '(^LONGITUDINAL 

 i,'' MUSCLES 



^ADVENTITIA 



VAGUS NERVE 



Fig. 214. — The esophagus as seen in cross section. A is a section of the entire 

 esophagus. J5 is a small portion much enlarged. The layers of tissue characteristic of 

 the entire alimentary canal are found in the esophagus. (Redrawn after Braus.) 



and tunica adventitia ; but the serous layer which covers the stomach and 

 intestine is wanting in the esophagus, since the body-cavity Uned by the 

 serosa does not extend into the neck. The tunica mucosa includes not 

 only the stratified squamous epithelium which lines the esophagus, but 

 also a connective-tissue tunica propria and a muscularis mucosae, a thin 

 layer of longitudinal muscle fibers. The muscular coat of the esophagus 

 consists of striped fibers in the upper third, while those of the lower two- 

 thirds are smooth. (Fig. 214) 



