THE GLOSSOPHARYNGEAL. 555 



contains filaments derived from the lingual branch of the fifth pair, but 

 also at the base of the organ, throughout its posterior third, and in the 

 mucous membrane of the arches of the palate, which are supplied only 

 by the fibres of the glossopharyngeal. The difference between these two 

 regions is that while that supplied by the fifth pair possesses tactile 

 sensibility of a high grade in addition to that of taste, in the posterior 

 region the general sensibility is less acute than the special sensibility to 

 impressions of taste. The appreciation of savors is provided for by 

 both the lingual and glossopharyngeal nerves, each in its separate de- 

 partment of the oral cavity. The sense of taste accordingly, in the 

 experiments of Reid, was never completely abolished by division of 

 either one of these nerves. For its complete suspension, both of them 

 must be destroyed on both sides. The method adopted by Longet for 

 examining the condition of the taste in dogs, before and after division 

 of the glossopharyngeal nerves, was to place upon the base of the tongue 

 a few drops of a concentrated solution of colocynth. Although this 

 always produced in the animals, while in their natural condition, mani- 

 fest signs of disgust, it had no such effect, as a general rule, after sec- 

 tion of the glossopharyngeal nerves on both sides, 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 tongue it caused brisk movements of the jaws with all the in- 

 dications of a sense of repugnance. While in the anterior and more 

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

 appreciated, during the process of mastication, by the filaments of the 

 lingual nerve which are distributed there, the glossopharyngeal is the 

 nerve of taste for the posterior part of the organ. It is called into ac- 

 tivity after mastication is accomplished and at the moment when the 

 food is carried backward and compressed by the base of the tongue, the 

 pillars of the fauces^ and the walls of the pharynx. 



Connection with the Reflex Act of Deglutition. In the fauces and 

 pharynx, the glossopharyngeal nerve also possesses a peculiar sensibility 

 to certain impressions, which excite at once the muscles of the neigh- 

 boring parts and bring into play the complicated mechanism of degluti- 

 tion. This consists in drawing backward and upward the base of the ' 

 tongue, thus bringing the masticated food into and through the isthmus 

 of the fauces. The muscles of the pillars of the fauces (palato-glossal 

 and palato-pharj'iigeal) afterward contract and close the opening of the 

 isthmus, while the soft palate is drawn backward and extended across 

 the upper end of the pharynx, thus shutting off its communication with 

 the posterior nares ; and the contraction of the constrictor muscles of 

 the pharynx then forces its contents downward into the beginning of the 

 oesophagus. This process is an involuntary one. Both the contraction 

 of the special muscles, and their regular co-ordination in the necessary 

 series of successive movements, are actions which do not depend on the 

 exercise of the will, but which take place even in a state of unconscious- 

 ness under the stimulus supplied by contact of food or liquids with the 



