THE MOUTH AND PHARYNX 149 



THE MOUTH AND PHARYNX 



The mottth cavity is lined by a mucous membrane, consisting^ 

 of a stratified squamous epithelium and a connective tissue layer 

 below it. The connective tissue layer possesses minute papillae 

 resembling those of the skin. Numerous mucous glands open 

 into the oral cavity, as well as the salivary glands. 



The tongue, which is composed chiefly of striated muscle, ex- 

 hibits on its upper surface very large papillae. These papillaa are 

 of three sorts: (1) Filiform, or conical; (2) fungiform, or those 

 having a constricted base, and (3) circumvallate, which are only 

 eight or ten in number, arranged like an inverted V, at the back 

 of the tongue. The last variety are large, fungiform, and sur- 

 rounded by a depression, outside of which is a wall -like elevation. 

 Taste -buds are flask -shaped collections of epithelial cells, special- 

 ized for the perception of taste, and supposed to be connected with 

 nerve-fibers. .They occur at the sides of the circumvallate papillae 

 and elsewhere on the tongue. They are most easily studied in 

 sections of the papillae foliata? of the rabbit, w r hich are symmetrical, 

 oval areas, marked with parallel ridges, at the back of the tongue. 

 There is an abundance of lymphoid tissue at the back of the tongue, 

 either diffused or occurring as distinct spherical lymph -follicles. 



The tonsils are large collections of lymphoid tissue, containing 

 numerous denser spherical masses, lympli- follicles. Stratified squa- 

 mous epithelium covers the free surface of the tonsils and lines 

 certain blind depressions into the tonsils (crypts). The epithelium 

 is more or less infiltrated with lymphoid cells, which enter it from 

 the underlying tissue. The attached surface of the tonsil is covered 

 by a connective tissue capsule, which forms an adventitia. 



The so-called salivary corpuscles are lymphoid cells which have 

 escaped and become mixed with the saliva. 



The structure of the pharynx is nearly like that of the mouth. 

 Only the lower division, however, is lined with stratified squamous 

 epithelium. The portion above the level of the soft palate is cov- 

 ered with stratified columnar epithelium, which is also ciliated, 

 indicating its connection with the respiratory tract. The mucous 

 membrane of the pharynx also contains mucous glands and lym- 

 phoid tissue. A mass of lymphoid tissue occupying a position in 

 the upper part between the Eustachian tubes is called the pharyn- 

 geal tonsil of Luschka. 



