TRIFACIAL NERVE. 569 



stimulation of the large root carefully insulated produces no muscular con- 

 traction. All who have divided this root in living animals must have recog- 

 nized, not only that it is sensitive, but that its sensibility is far more acute 

 than that of any other nervous trunk in the body. 



As far as audition and olfaction are concerned, there are no special effects 

 immediately following section of the trifacial ; but there are certain impor- 

 tant phenomena observed in connection with the eye and the organs of 

 taste. 



At the instant of division of the fifth, the eyeball is protruded and the 

 pupil becomes strongly contracted. This occurs in rabbits, and the contrac- 

 tion of the pupil was observed in the first operations of Magendie. The 

 pupil, however, usually is restored to the normal condition in a few hours. 

 After division of the nerve the lachrymal secretion becomes very much less 

 in quantity ; but this is not the cause of the subsequent inflammation, for 

 the eyes are not inflamed, even after extirpation of both lachrymal glands 

 (Magendie). The movements of the eyeball are not affected by division of 

 the fifth. 



Another of the immediate effects of complete division of the fifth nerve 

 is loss of general sensibility in the tongue. Most experiments upon the influ- 

 ence of this nerve over the general sensibility and the sense of taste in the 

 tongue have been made by dividing the lingual branch of the inferior maxil- 

 lary division. When this branch is irritated, there are evidences of intense 

 pain. When it is divided, the general sensibility and the sense of taste are 

 destroyed in the anterior portion of the tongue. It will be remembered, 

 however, that the chorda tympani joins the lingual branch of the fifth as it 

 passes between the pterygoid muscles, and that section of this branch of the 

 facial abolishes the sense of taste in the anterior two-thirds of the tongue. 

 If the gustatory properties of the lingual branch of the fifth be derived from 

 the chorda tympani, lesions of the fifth not involving this nerve would be 

 followed by loss of general sensibility, but the taste would be unaffected. 

 This has been shown to be the fact, by cases of paralysis of general sensibility 

 of the tongue without loss of taste in the human subject, which will be dis- 

 cussed more fully in connection with the physiology of gustation. 



Among the immediate effects of section of the fifth, is an interference 

 with the reflex phenomena of deglutition. In a series of observations upon 

 the action of the sensory nerves in deglutition, by Waller and Prevost, it 

 was found that after section of the fifth upon both sides, it was impossible 

 to excite movements of deglutition by stimulating the mucous membrane of 

 the velum palati. After section of the superior laryngeal branches of the 

 pneumogastrics, no movements of deglutition followed stimulation of the 

 mucous membrane of the top of the larynx. In these experiments, when the 

 fifth was divided upon one side, stimulation of the velum upon the corre- 

 sponding side had no effect, while movements of deglutition were produced 

 by irritating the velum upon the sound side. These experiments show that 

 the fifth nerve is important in the reflex phenomena of deglutition, as a sen- 

 sory nerve, conveying the impression from the velum palati to the nerve-cen- 



