SENSES OF SMELL, TASTE, HUNGER AND THIRST 



749 



number of taste buds. Sometimes as many as one hundred of these 

 may be congregated in the depression encircling a single papilla. It 

 is to be noted especially that they are well protected against the ordi- 

 nary mechanical stimuli which arise in consequence of the movements 

 of the tongue 



The Innervation of the Taste Buds. In accordance with their wide 

 distribution, it cannot surprise us to find that their innervation can 

 only be accomplished with the help of several nerves. Those directly 

 involved are the lingual nerve, a branch of the inferior maxillary 

 division of the trigeminus, and the glossopharyngeal and vagus nerves. 

 The first innervates the anterior region of the tongue, or about two- 

 thirds of the entire organ; the second the posterior part and root of 

 the tongue as well as the adjoining soft parts, and the third the epi- 



Gasseri&n Ganglion 



FIG. 374. DIAGRAM SHOWING ORIGIN AND COURSE OF THE NERVE FIBERS OF TASTE. 



glottis and mucosa of the larynx proper. It is to be noted, however, 

 that the fibers allotted to the lingual nerve, pursue a double course, i.e., 

 while some of them remain within the system of the trigeminus, others 

 leave it to enter that of the chorda tympani. The latter, in turn, 

 either continue in this system of the seventh cranial nerve (portio 

 intermedia Wrisbergii) or pass over to the glossopharyngeal nerve. 

 It seems certain, however, that the fibers originally allotted to the 

 glossopharyngeus and vagus nerves, pursue a straight course to their 

 respective nuclei in the medulla. 



The function of the glossopharyngeus is, of course, quite evident, 

 because cutting this nerve leads to a loss of the sensations of taste 

 in the region innervated by it and eventually to a complete atrophy of 

 the corresponding taste buds. The fact that the chorda tympani 

 takes part in the conduction of taste-impulses, may be evinced at any 

 time by stimulating this nerve as it traverses the tympanic cavity. 

 The usual effect of this procedure is a metallic or sour taste, but some 



