812 



THE ORGANS OF SPECIAL SENSE. 



structure with that lining the rest of the oral cavity. The mucous membrane 

 covering the tongue behind the foramen caecum and sulcus terminalis is thick and 

 freely movable over the subjacent parts. . It contains a large number of lymphoid 

 follicles, which together constitute what is sometimes termed the lingual tonsil. 

 Each follicle forms a rounded eminence, the centre of which is perforated by a 

 minute orifice leading into a funnel-shaped cavity or recess ; around this recess 

 are grouped numerous oval or rounded nodules of lymphoid tissue, each enveloped 

 by a capsule derived from the submucosa, while opening into the bottom of the 

 recesses are also seen the ducts of mucous glands. The mucous membrane on the 

 anterior part of the dorsum of the tongue is thin and intimately adherent to the 



EPIGLOTTIS. 



CIRCUM- 

 VALLATE 

 PAPILUE. 



FIG. 428. Upper surface of the tongue. 



muscular tissue, and covered with minute eminences, the papillce of the tongue. 

 It consists of a layer of connective tissue, the corium or mucosa, supporting 

 numerous papillae, and covered, as well as the papillae, with epithelium. 



The epithelium is of the scaly variety, like that of the epidermis. It covers the 

 free surface of the tongue, as may be easily demonstrated by maceration or boiling, 

 when it can be easily detached entire : it is much thinner than on the skin : the 

 intervals between the large papillae are not filled up by it, but each papilla has 

 a separate investment from root to summit. The deepest cells may sometimes be 

 detached as a separate layer, corresponding to the rete mucosum, but they never 

 contain coloring matter. 



