GLOSSO-PHARYNGEAL NERVE. 459 



by the corner of the mouth, and in mastication the food has partly 

 a tendency to escape by the same opening, and partly accumulates, 

 on the affected side, between the gums and the cheek, owing to the 

 paralysis of the buccinator muscle, which receives its motor fila- 

 ments from the facial nerve. Thus, the action of all the superficial 

 facial muscles is suspended, the expression of the face is destroyed, 

 and the movements of the lips and the prehension of the food 

 seriously interfered with. 



Though the facial, however, be essentially a motor nerve, yet its 

 principal branches distributed to the face have a certain degree of 

 sensibility ; that is, when these branches are irritated in the middle 

 of their course, the animal immediately gives evidence of a painful 

 sensation. Longet has shown, by an extremely ingenious mode 

 of experiment, 1 that this sensibility of the branches of the facial 

 does not depend on any sensitive fibres of their own, but upon 

 those which they derive from inosculation with the fifth pair. He 

 exposes, for example, the facial nerve in the dog, and, irritating its 

 principal branches one after the other, at each application of the 

 irritant there are evident signs of pain. He then divides the facial 

 nerve at its point of exit from the stylo-mastoid foramen, and 

 finds that, after this operation, the sensibility of its branches still 

 remains. The fibres, accordingly, upon which this sensibility 

 depends, do not pass out with the trunk of the nerve, but are 

 derived from some other source. The experimenter, then, upon 

 another animal, divides the fifth pair within the skull, leaving the 

 facial untouched; and afterward, on irritating as before the ex- 

 posed branches of the latter nerve, he finds that its sensibility has 

 entirely disappeared. It is by filaments, accordingly, derived from 

 the fifth pair, that a certain degree of sensibility is communicated 

 to the branches of the facial. 



These facts account for the peculiar circumstance that, in cases 

 of tic douloureux, the spasmodic pain sometimes follows exactly 

 the course of the facial nerve, viz : from behind the ear forward 

 upon the side of the face ; and yet the section of this nerve does not 

 put an end to the neuralgia, but only causes paralysis of the facial 

 muscles. 



GLOSSO-PHARYNGEAL. This nerve originates from the lateral 

 portion of the medulla oblongata, passes outward, and enters the 



1 Traite de Physiologie, vol. ii. pp. 354-357. 



