THE TONGUE. 609 



or tip, thin and narrow, is directed forwards against the inner surface of the 

 lower incisor teeth. The under surface of the tongue is connected with the 

 lower jaw by the Genio-hyo-glossi muscles ; from its sides, the mucous mem- 

 brane is reflected to the inner surface of the gums ; and, in front, a distinct fold 

 of that membrane, the frsenum linguae, is formed beneath its under surface. 



The tip of the tongue, part of its under surface, its sides, and dorsum, are free. 



The dorsum of the tongue is convex, marked along the middle line by a raphe, 

 which divides it into two symmetrical halves ; and this raphe terminates behind, 

 about half an inch frota the base of the organ, a little in front of a deep mucous 

 follicle, the foramen csecum. The anterior two-thirds of this surface are rough, 

 and covered with papilla? ; the posterior third is more smooth, and covered by the 

 projecting orifices of numerous muciparous glands. 



The mucous membrane invests the entire extent of the free surface of the 

 tongue. On the under surface of the organ it is thin and smooth, and may be 

 traced on either side of the fraenum, through the ducts of the submaxillary glands ; 

 and between the sides of the tongue and the lower jaw, through the ducts of the 

 sublingual glands. On being traced over the borders of the organ, it gradually 

 assumes its papillary character. 



The mucous membrane of the tongue consists of structures analogous to those 

 of the skin, namely, a cutis or corium, supporting numerous papillse, and covered, 

 as well as the papillae, with epithelium. 



The cutis is tough, but thinner and less dense than in most parts of the skin, 

 and is composed of similar tissue. It contains the ramifications of the numerous 

 vessels and nerves from which the papilla? are supplied, and affords insertion to 

 all the intrinsic muscular fibres of the organ. 



The papilla of the tongue are thickly distributed over the whole of its upper 

 surface, giving to it its characteristic roughness. They are more prominent than 

 those of the skin, which is chiefly due to their not being concealed under the 

 epithelium, but from their standing out prominently from the surface like the villi 

 of the intestine. The principal varieties are the papillae maximae (circumvallatae), 

 papillae mediae (fungiformes), and papillae minimae (conicae and filiformes). 



The papillse maximse (circumvallatae) are of large size, and vary from eight to 

 ten in number. They are situated at the back part of the dorsum of the tongue, 

 near its base, forming a row on each side, which, running backwards and inwards, 

 meet in the middle line, like the two lines of the letter A inverted. Each papilla 

 consists of a central flattened projection of mucous membrane, circular in form, 

 from ^ to ^2 of an inch wide, attached to the bottom of a cup-shaped depression 

 of the mucous membrane ; the exposed part being covered with numerous small 

 papilla?. The cup-shaped, depression forms a kind of fossa round the papilla, 

 having a circular margin of about the same elevation, covered with smaller papillae. 

 The fissure corresponding to the papilla, where the two lines of the circumvallate 

 papillae meet, is so large and deep, that the name/oramen csecum has been applied 

 to it. In the smaller papillae, the fissure exists only on one side. 



The papillse medise (fungiformes), more numerous than the preceding, are 

 scattered irregularly and sparingly over the dorsum of the tongue, but are found 

 chiefly at its sides and apex. They are easily recognized, among the other papillae, 

 by their large size, rounded eminences, and deep red color. They are narrow at 

 their attachment to the tongue, but broad and rounded at their free extremities, 

 and covered with secondary papillae. Their epithelium investment is very thin. 



The papillse minimse (conicae et filiformes) cover the anterior two-thirds of the 

 dorsum of the tongue. They are very minute, more or less conical or filiform in 

 shape, and arranged in lines corresponding in direction with the two rows of the 

 papillae circumvallatas, excepting at the apex of the organ, where their direction 

 is transverse. The filiform papillae are of a whitish tint, owing to the thickness 

 and density of their epithelium; they are covered with numerous secondary 

 papillae, are firmer and more elastic than the papillae of mucous membrane 

 generally, and often inclose minute hairs. 

 39 



