480 THE NERVOUS SYSTEM. 



its galvanization followed by contraction of the upper part of the 

 pharynx, this effect was probably due to reflex action, since the nerve 

 was still in connection with the medulla oblongata. This conclusion 

 is rendered certain by the investigations of Reid,* who found that 

 irritation of the glossopharyngeal nerve produced movements of the 

 throat and lower part of the face ; but these movements were also pro- 

 duced, after the nerve had been divided, by irritation of its cranial 

 extremity. Its sensibility, however, appears to be of a low grade, 

 as compared with that of the trigerniiial nerve. While some ob- 

 servers (Reid) found its irritation, outside the jugular foramen, give 

 rise to indications of pain, others (Panizza) have failed to elicit by 

 this means any signs of sensibility whatever ; and others still (Longet) 

 speak of them in an uncertain manner. This variation in the observed 

 results is sufficient to show the inferior capacity of the glossopharyngeal 

 nerve for painful impressions ; since no experimenter has ever doubted 

 the acute sensibility of the fifth pair. 



But notwithstanding the comparative deficiency of this nerve and 

 the parts to which it is distributed, in ordinary sensibility, it serves 

 to transmit impressions of a special character, which are connected 

 with two different but associated functions, namely : 1. The sense of 

 taste, and, 2. The act of deglutition. 



Connection with the Sense of Taste. The sensation of taste exists 

 not only in the anterior portion of the tongue supplied from the lingual 

 "branch of the fifth pair, but also at the base of the organ, throughout 

 its posterior third, and in the arches of the palate, supplied by fibres 

 of the glossopharyngeal. But while the region supplied by the fifth 

 pair possesses also a tactile sensibility of high grade, in the posterior 

 region the general sensibility is much inferior to that of taste. The 

 method adopted by Longet for examining the sense of taste in dogs 

 was to place on the base of the tongue a few drops of a concentrated 

 solution of colocynth. Although this always produced, in the natural 

 condition of the animal, manifest signs of disgust, it had no such effect, 

 as a rule, after section of the glossopharyngeal nerves, provided the 

 solution were applied only to the posterior part of the tongue and the 

 pharynx ; while if even a minute quantity came in contact with the 

 tip or edges of the organ it caused brisk movements of the jaws 

 with all the indications of repugnance. In the anterior and more 

 movable parts of the tongue, accordingly, the sensations of taste are 

 appreciated, during mastication, by the filaments of the lingual nerve. 

 The glossopharyngeal, on the other hand, is the nerve of taste for the 

 posterior part of the organ ; and is called into activity after mastica- 

 tion is accomplished, when the food is carried backward for deglutition 

 and compressed by the base of the tongue, the pillars of the fauces, 

 and the walls of the pharynx. 



* Todd's Cyclopaedia of Anatomy and Physiology. Article, Glossopharyngeal 

 Nerve. 



