178 



MICROSCOPIC ANATOMY OF THE ORGANS. 



The outer muscle layer (the constrictors of the pharynx) 

 consists of striated muscle. 



C. (ESOPHAGUS. 



In the wall of the oesophagus can be distinguished : mucosa, 

 submucosa, muscularis, and tunica adventitia. 



The mucosa is similar in structure to that of the mouth 

 cavity. It possesses, however, a thin layer not found in the 

 oral mucous membrane, the so-called muscularis mucosce. This 

 lies at the edge of the tunica propria, between it and the sub- 

 mucosa, and consists of longitudinally disposed smooth muscle 

 cells. Only in the lower half of the oesophagus is it a 

 complete layer. 



FIG. 133. 



Epithelium 



Blood-vessel 



Mucosa 



Submucosa 



Muscularis 



i-ctiun uf the oesophagus of a dog. X 25. 



The submucosa consists of firm connective tissue containing 

 blood-vessels, nerves, and mucous glands. The latter do not 

 differ from the mucous glands of the mouth cavity. They 

 occur throughout the entire length of the oesophagus. The 

 ducts pass through the muscularis mucosse, and are lined for 

 a short distance from their mouths with stratified cuboidal 

 epithelium. Under the muscularis mucosse there is usually a 

 considerable dilatation of the lumina of the ducts. In the 



