348 THE DIGESTIVE SYSTEM 



There is no muscularis mucosas in the mucous membrane of the 

 pharynx; its place is taken by a layer of connective tissue which is 

 exceedingly rich in longitudinal elastic fibers. This layer lies imme- 

 diately upon the muscular coat, into which processes of fibro-elastic tissue 

 extend between the muscular bundles; hence this fibro-elastic layer also 

 serves as a submucosa. 



The superficial layer of the corium contains diffuse collections of 

 lymphoid tissue and occasional small lymph nodules. 



The muscular coat of the pharynx is formed by its constrictor 

 muscles. Their striated fibers mostly pursue an oblique course. Where 

 these muscles are not immediately attached to the periosteum of the 

 vertebrae, the pharynx is invested with an outer coat of areolar con- 

 nective tissue by which it is loosely united to adjacent organs. 



ESOPHAGUS 



The esophagus or gullet is a short tube about 25 centimeters (10 

 inches) in length, connecting the pharynx with the cardia of the 

 stomach. Its wall contains the usual four coats: (1) the outer fibrous; 

 (2) muscular; (3) submucous; and (4) mucous (fig. 327). 



The Outer Fibrous Coat. The outer fibrous coat envelops the 

 wall of the esophagus and unites it to the adjacent organs. It consists 

 of loose fibrous tissue, and contains the blood and lymphatic vessels 

 and nerve trunks which supply the three inner coats. It is not in- 

 vested by a serous layer. 



The Muscular Goat. The muscular coat contains an outer longi- 

 tudinal and an inner circular layer of muscle fibers, which are sep- 

 arated by a narrow septum of loose fibrous tissue. In the upper third 

 of the esophagus the muscle is of the striated variety, in the middle 

 third it is mixed, in the lower third it is generally smooth. The distri- 

 bution of the muscle in the lower third is subject to great individual 

 variation, and occasionally striated fibers are often found all the way 

 down to the diaphragmatic opening. 



The fibrous septum between the muscular layers contains the larger 

 blood-vessels and the myenteric nerve plexus. 



The Submucous Coat. The submucous coat forms a layer of 

 areolar connective tissue which firmly unites the muscular and the 

 mucous coats. It contains those blood and lymphatic vessels, together 

 with the submucous nerve plexus, whose branches supply the mucous 

 membrane. It also contains a considerable number of tubulo-acinar 



