THE DIGESTIVE TRACT. 



159 



THE PHARYNX. 



The pharynx consists essentially of a fibrous tunic, within which 

 lies the mucous membrane with the submucous tissue, while without 

 are arranged the fibres of the constrictor and other muscles ; three 

 coats, the mucous, the fibrous, and the muscular, are recognized, 

 therefore, as forming its walls. The histological differences distin- 

 guishing the upper, or respiratory, from the lower, or digestive, 

 portion of the sac depend largely upon variations within the mucosa, 

 especially as to the character of the epithelium. 



The upper, respiratory division of the pharynx is clothed with 

 stratified ciliated columnar epithelium containing numerous goblet- 

 cells, while the part situated below the level of the soft palate is cov- 

 ered with stratified squamous cells similar to those lining the oral 

 cavity. The tunica propria, or stroma of the mucosa, is formed 

 of a felt-work of fibrous bundles, together with a variable, in certain 

 parts large, quantity of elastic tissue. The subepithelial surface of 

 the mucosa, where covered by the squamous cells, is beset with 

 numerous small papillae ; these, however, are wanting beneath the 

 ciliated epithelium. 



Small mucous pharyngeal glands occur in many places ; they 

 are especially numerous in the deepest layers of the mucosa in the 

 immediate vicinity of the orifices of the Eustachian tubes, occurring 

 less frequently towards the lower part of the pharynx. The mucous 

 membrane contains a considerable quantity of adenoid tissue ar- 

 ranged as numerous lymph-follicles in the upper part of the cavity ; 1 

 these follicles closely resemble those found at the root of the tongue, 

 existing isolated or in groups. A conspicuous aggregation of such i 

 structures lies on the posterior wall of the pharynx between the j 

 openings of the Eustachian tubes, constituting the pharyngeal ( 

 tonsil, appropriately so named in view of the similarity of its struct- 

 ure to that of the palatine organs of like name. Some of the 

 mucous glands here also open into the central crypt. 



The submucous tissue unites the mucous membrane with the 

 fibrous coat, whose dense felt-work of fibro-elastic bundles forms a 

 structure frequently termed the pharyngeal aponeurosis. Its pos- 

 terior part is greatly thickened and forms the raphe to which the 

 constrictor muscles are attached. 



The muscular coat is formed of the striped fibres constituting the 

 constrictor and other muscles, with whose general arrangement the 

 disposition of the muscular tissue agrees. 



External to the muscular coat an irregular investment of areolar 

 tissue attaches the pharynx to the surrounding structures. 



The larger blood-vessels, lymphatics, and nerve-trunks take 



