THE TONGUE 



43 1 



posteriorly from the tip of the tongue to the foramen caecum, 

 and divides the anterior two-thirds of the dorsum into two 

 halves. 



On the under surface of the tongue the mucous mem- 

 brane is smooth and comparatively thin. In the median 

 plane it forms thefrenu/um lingua, which has been studied 

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

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

 tending anteriorly towards the tip. To the lateral side of this, 



Tip of tongue, 

 turned up 



Deep lingual vein 



Orifice of. 

 submaxillary duct 



Frenulum linguae 

 Plica fimbriata 



Plica sublingualis 



FlG. 169. The Sublingual Region in the interior of the mouth. 



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

 delicate and feebly marked fold 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 

 anteriorly, 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. These are 

 \\\e papillce foliatce. 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), 



