THE TONGUE. 



1573 



Nerves. The tensor palati is supplied by the mandibular division of the fifth 

 pair, the other muscles by the pharyngeal plexus. The mucous membrane of the 

 hard palate is supplied by the anterior palatine nerve and terminal branches of the 

 naso-palatine. That of the soft palate is supplied by the other palatine nerves 

 and by branches from the glosso-pharyngeal. 



THE TONGUE. 



The tongue is a median muscular organ attached to the floor of the mouth, 

 the symphysis of the jaw, and the body and both horns of the hyoid, covered with 

 mucous membrane, which when the mouth is closed it practically fills (Fig. 1339). 

 The root is the attached portion, extending from the hyoid to the symphysis, com- 

 posed of the genio-glossi and the hyo-glossi muscles. The tip is the free anterior 

 end, flat both above and below when extended, and surrounded by mucous mem- 

 brane. Behind this the tongue is a solid mass. The dorsum in its anterior two- 

 thirds is convex from side to side, and rests against the hard and soft palates ; the 

 posterior third, nearly vertical, looks backward, forming the front wall of the pharynx 

 when the mouth is closed. There is a median groove in the upper part of this pos- 

 terior third, continued for a little distance onto the top, in which the uvula rests. 

 This hind portion is so broad that the edges of the tongue reach quite to the sides 



FIG. 1332 



FIG. 1333. 



Floor of the mouth and pharynx of an embryo of 7.5 

 mm. (From a reconstruction.) cop., copula; P., furcula; 

 /., anlage of the body of the tongue; Ti., tuberculum 

 impar; l-III, branchial arches. 



Plica 

 mediana 



Plica 

 sublingualis t 



Plica-l 

 fimbriata i 



Fibres of- 

 genio-glossus 



Under surface of tongue of new-born child. 

 (Gegtnbawr.) 



of the pharynx. In the anterior two-thirds the edges of the tongue are prominent, 

 overhanging the sides. 



Development shows that the tongue has a double origin. The body arises 

 from a paired anlage near the midline in the anterior part of the mouth, while the 

 root develops from a median elevation, the copula, and the adjoining portions of the 

 second visceral arches. The tuberculum impar of His plays probably only a sub- 

 ordinate role. The thyro-glossal duct comes to the surface at the junction of these 

 two parts, which, in the infant, are still separated by the sulcus terminalis. 



The mucous membrane of the lateral and inferior surface is thin and smooth 

 with small papillae at the tip. In the middle it forms a fold, the frenum, running 

 from near the tip to the floor of the mouth. In infancy this is occasionally so 

 short as to restrain the tip of the tongue from the motions necessary for nursing. 

 Often it is hardly visible. The plica fimbriata and the plica sublingualis are two 

 folds on either side of the front part of the under surface, of which the former with 

 ragged edges is the outer, the longer, and the larger. Both are distinct in the infant 

 and (especially the latter) lost or poorly marked later. The plicae fimbriatae bound 

 a triangular space which Gegenbaur considers a rudiment of the under-tongue of some 

 mammals. The mucous membrane of the dorsum is divisible into two wholly differ- 

 ent regions : the one comprising the anterior two-thirds, the other the posterior ver- 

 tical third. The line of separation, or sulcus terminalis, is, however, not transverse, 

 but, starting at the side from the anterior pillar of the fauces, runs backward and 

 inward to meet its fellow. This is not usually visible in the adult ; but its place is 



