348 HEAD AND NECK 



Anterior to the foramen caecum and sulcus terminalis the 

 mucous membrane which covers the dorsum, sides, and tip 

 of the oral part of the tongue is studded with papillae of 

 different kinds. As these are individually visible to the naked 

 eye the mucous membrane presents a very characteristic 

 appearance. Further, a median groove or sulcus extends back- 

 wards from the tip of the tongue to the foramen caecum, and 

 divides the anterior two-thirds of the dorsum into two halves. 



On the inferior surface of the tongue the mucous mem- 

 brane is smooth and comparatively thin. In the median 

 plane it forms \hefrenulum lingua, which has been studied 

 at an earlier stage. On each side of the median line the 

 deep lingual vein may be noticed, in the living subject, extend- 

 ing forwards towards the tip. To the lateral side of the vein, 

 and, therefore, somewhat nearer the border of the tongue, is a 

 delicate and feebly marked ridge of mucous membrane, from 

 the free border of which a row of fringe-like processes or 

 fimbriae project. It is termed the plica fimbriata ; as it extends 

 forwards, towards the tip of the tongue, it inclines towards 

 the median plane. On the side of the tongue, immediately 

 anterior to the lingual attachment of the glosso -palatine 

 arches, five short vertical fissures in the mucous membrane, 

 separated by intervening folds, may be noticed. The folds are 

 called \hz papilla foliattz. They are the representatives of leaf- 

 like folds of the mucous membrane which are much more 

 highly developed in certain of the lower animals (hare and 

 rabbit), and which are specially concerned in receiving the 

 impressions of taste. 



Papillae Linguales. The papillae are of four kinds, and 

 differ in size, shape, and in the position they occupy on 

 the surface of the tongue. They are termed the vallate, 

 the fungiform, the conical, and the filiform. 



Papillce Vallata. The vallate papillae (O.T. circumvallate), 

 seven to twelve in number, are the largest, and are placed 

 immediately anterior to the sulcus terminalis, in two rows 

 which diverge from each other in an antero-lateral direction, 

 like the two limbs of the letter V. The foramen caecum 

 lies immediately posterior to the median vallate papilla, which 

 forms the apex of the V. In form, a vallate papilla is 

 broad and somewhat cylindrical, slightly narrower at its 

 attached end than at its free extremity, and it is sunk in a pit. 

 It is thus surrounded by a deep trench, the outer wall of 



