526 NERVOUS SYSTEM 



the lower part of the face and the lower lip. It also sends certain fila- 

 ments to the mucous membrane of the mouth. 



Properties and Uses of the Trifacial. The trif acial is the great sen- 

 sory nerve of the face and of the mucous membranes lining the cavities 

 about the head. It is impossible to stimulate this nerve at its origin 

 without seriously involving other parts; but observations in regard to 

 the properties of the large root go to show that it is an exclusively sen- 

 sory nerve, and that its sensibility is very acute as compared with other 

 nerves. It was divided in the cranial cavity by Mayo (1822-1823), 

 Fodera (1823) and Magendie (1824). Magendie divided the nerve at 

 its root by introducing a small cutting stylet through the skull. He 

 succeeded in keeping the animals alive for several days or weeks and 

 noted in his experiments immediate loss of sensibility in the face on 

 the side on which the nerve had been divided. When this operation 

 is performed without accident, the cornea and the integument and 

 mucous membrane on that side of the head are deprived of sensibility 

 and may be pricked, lacerated or burned without any evidence of pain. 

 Almost always the small root of the fifth is divided as well as the large 

 root, and the muscles of mastication are paralyzed on one side ; but 

 with this exception, there is no paralysis of motion, sensation alone being 

 destroyed. 



Immediate Effects of Division of the Trifacial. This nerve has not 

 been exposed in the cranial cavity in living animals ; but its branches on 

 the face and the lingual branch of the inferior maxillary division have 

 been operated on and found to be exquisitely sensitive. Physiologists 

 have exposed the roots in animals immediately after death and have 

 found that stimulation of the large root carefully insulated produces no 

 muscular contraction. All who have divided this root in living animals 

 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. 



So far as audition and olfaction are concerned, there are no special 

 effects immediately following section of the trifacial ; but there are cer- 

 tain important 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. The pupil, however, usually is 

 restored to the normal condition in a few hours. After division of the 

 nerve, the lachrymal secretion is diminished, but this is not the cause of 

 the subsequent inflammation, for the eyes are not inflamed, even after 

 extirpation of both lachrymal glands. 



Another of the immediate effects of complete division of the fifth 

 nerve is loss of general sensibility in the tongue. Most experiments 



