TRIFACIAL, OR TRIGEMIXAL SERVE. 641 



to be exquisitely sensitive. Longet and others have exposed the roots in animals imme- 

 diately after death, and have found that galvanization of the large root carefully insu- 

 lated produces no muscular contraction. All who have divided this root in living animals 

 must have recognized, not only that it is sensitive, but that its sensibility is far more acute 

 than that of any other nervous trunk in the body. It is much more satisfactory to divide 

 the nerve without etherizing the animal, as the evidence of pain is an important guide in 

 this delicate operation ; but, in using anaesthetics, we have never been able to bring an 

 animal under their influence so completely as to abolish the sensibility of the root itself. 

 For example, in cats that appear to be thoroughly etherized, as soon as the instrument 

 touches the nerve, there is more or less struggling. The large root of the fifth, then, is 

 an exclusively sensory nerve, and its sensibility is more acute than that of any other of 

 the cerebro-spinal nerves. 



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

 ately following section of the trifacial ; but there are interesting phenomena observed in 

 connection with the eye and the organs of taste. 



At the instant of division of the fifth, by the method just described, the eyeball is pro- 

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

 traction of the pupil was observed in the first operations of Magendie. The pupil, how- 

 ever, is usually restored to the normal condition in a few hours. Longet states that the 

 pupil is dilated by division of the fifth in dogs and cats. 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, as was shown by Magendie, even 

 after extirpation of both lachrymal glands. 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 influence of this nerve over the gen- 

 eral sensibility and the sense of taste in the tongue have been made by dividing the lin- 

 gual branch of the inferior maxillary 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 third or half of the tongue. It will be remembered, 

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

 tween the pterygoid muscles, and that section of this branch of the facial abolishes the 

 sense of taste in the anterior third or half 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 gustation. 



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

 phenomena of deglutition. In some recent researches upon the action of the sensitive 

 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 setion 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 :he velnm upon the corresponding 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 sensory nerve, conveying the impression from the velum palati to the 

 nerve-centres. This action probably takes place through filaments which pass from the 

 fifth to the mucous membrane through Meekel's ganglion. 



Itemols Efrcts of Division of the Tr( rac ial After the ordinary operation of divid- 

 ing the fifth nerve in the cranial cavity, the immediate loss of sensibility of the integu- 

 41 



