124 THE ALIMENTARY SYSTEM, 



vicinity of the tonsils ; after exposure to the saliva with its 

 low specific gravity they become swollen and granular. 



The Pharynx. 



The walls of the pharynx consist of three layers, mucous 

 membrane, a fibrous coat, and a muscular layer. The upper 

 part of the pharynx, above the palate, belongs to the respira- 

 tory tract and is lined with ciliated epithelium ; the lower 

 part belongs to the alimentary tract and is lined with squamous 

 epithelium. 



The mucous membrane of the pharynx is continuous with 

 that of the adjacent cavities, and consists of three layers, 

 epithelium, tunica propria, and submucosa, and contains 

 mucous glands and lymphoid tissue. 



The epithelial lining in the upper or respiratory portion of 

 the pharynx consists of stratified ciliated epithelium, con- 

 tinuous with that of the nasal fossae and Eustachian tubes ; 

 in the lower or alimentary portion it consists of stratified 

 squamous cells. 



The tunica propria is a well-marked fibrous membrane, 

 which in the lower part of the pharynx has papillae projecting 

 among the squamous epithelium. 



The submueosa is a layer of areolar tissue connecting the 

 mucosa with the fibrous and muscular tissues beneath, and 

 containing numerous small racemose mucous glands and nod- 

 ules of lymphoid tissue. 



The lymphoid nodules often have crypts, like those of the 

 tonsils. There is a special collection of lymphoid tissue on 

 the posterior surface of the pharynx between the Eustachian 

 tubes, called the pharyngeal tonsil. 



The fibrous coat, or pharyngeal aponeurosis, is a firm fibrous 

 membrane lying underneath the mucous membrane, thicker 

 above, and becoming thinner below. Posteriorly it is thick- 

 ened to form the median raphe. 



The muscular layer, beneath the fibrous, is a sheet of volun- 

 tary muscle made up by the three constrictors and other 

 muscles of the pharynx. 



The soft palate consists of a thin layer of the voluntary 

 palate muscles with fibrous aponeu roses, lined on each side by 



