THE HEAD AND NECK 1 241 



The Tongue. 



The tongue is a muscular and very sensitive organ, covered by 

 the buccal mucous membrane, and situated on the floor of the 

 mouth. It is concerned in the sense of taste, mastication, deglu- 

 tition, and speech, and it consists of a root or base, a body, and 

 a tip. The root is attached to the hyoid bone. The tip is the 

 anterior free extremity, which, in the quiescent state, hes behind 

 the upper incisor teeth. The body presents an upper surface or 

 dorsmn, an imder surface, and two lateral borders, right and 

 left. The dorsiun is convex from before backwards, and pre- 

 sents over its anterior two-thirds a median depression or raphe, 

 on either side of which the surface is convex from side to side. 

 This raphe terminates posteriorly in the foramen ccecum. In this 

 region the dorsum presents a V-shaped groove, known as the 

 stdctts terminalis. The point of the V is at the foramen caecum, 

 and the two limbs pass outwards and forwards to the sides of the 

 tongue, where the anterior pillars of the fauces are connected with 

 it. The sulcus terminalis marks the union of the two portions, 

 anterior and posterior, from which the tongue is developed. The 

 portion behind it, representing one-third, is the basal, lymphoid, 

 or pharyngeal portion. It occupies the buccal portion of the 

 pharynx, and overhangs the epiglottis. The portion in front of 

 the sulcus terminalis, representing two-thirds, is known as the 

 buccal or papillary portion. 



Mucous Membrane. — ^The mucous membrane covering the basal 

 or pharyngeal portion of the tongue is destitute of proper papillae, 

 but is freely provided with lymphoid follicles similar to those of 

 the tonsils, and with mucous glands. The follicles are ranged upon 

 the walls of crypts, the mouths of which open upon the surface. 

 The mucous membrane in this region forms the glosso-epiglottidean 

 fold, or frenum epiglottidis, which is mesiaUy placed. On either 

 side of this fold, between it and each pharyngo-epiglottidean 

 fold, there is a pouch or depression, called the vallecula. 

 In front of the sulcus terminalis the mucous membrane of the 

 dorsum, borders, and tip of the tongue is freely covered by 

 characteristic papillae, which, being visible to the naked eye, impart 

 to this part its distinctive appearance. These papillae bear secon- 

 dary papillae, which, however, are concealed by the epithelial 

 covering. The mucous membrane on the under surface of the 

 tongue in the median line forms, near the tip, a vertical fold, called 

 the frenum linguce. A little external to the frenum, on either side, 

 is an indistinct fringed fold, called the plica fimbriata. The two 

 plicae converge as they pass forwards towards the tip, and inside 

 each the outline of the ranine vein may be visible. On either side 

 of the tongue, in the region of the limbs of the sulcus terminals, 

 the mucous membrane presents a few ridges which represent the 

 "papilla foliata of such animals as the rabbit. 



