144: NEKVOTJS SYSTEM. 



The observations upon the division of the fifth pair in 

 the cranial cavity, made by Fodera, Mayo, Magendie, Ber- 

 nard, and others, are most interesting in connection with the 

 functions of its sensitive branches, and will be referred to in 

 detail in treating of the properties of the large root. In ad- 

 dition to the loss of sensibility following section of the entire 

 nerve, Bernard has noted carefully the effects of division of 

 the small root, which cannot be avoided in the operation. 

 In rabbits, the paralysis of the muscles of mastication upon 

 one side, and the consequent action of the muscles upon the 

 unaffected side only, produce, a few days after the opera- 

 tion, a remarkable change in the appearance of the incisor 

 teeth. As the teeth in these animals are gradually worn 

 away in mastication and reproduced, the lower jaw being 

 deviated by the action of the muscles of the sound side, the 

 upper incisor of one side and the lower incisor of the other 

 touch each other but slightly and the teeth are worn uneven- 

 ly. This makes the line of contact between the four incisors, 

 when the jaws are closed, oblique instead of horizontal. 1 "We 

 have often divided the fifth pair in the cranial cavity in rab- 

 bits, by the method employed by Magendie and Bernard, 

 and have repeatedly verified these observations. 



There is little left to say with regard to the functions of 

 the motor root of the fifth nerve, in addition to our descrip- 

 tion of the action of the muscles of mastication, contained in 

 the volume on digestion, 8 except as regards the action of the 

 filaments sent to the muscles of the velum palati. In deg- 

 lutition, the muscles of mastication are indirectly involved. 

 This act cannot be well performed unless the mouth be 

 closed by these muscles. When the food is brought in con- 

 tact with the velum palati, muscles are brought into action 

 which render this membrane tense, so that the opening is 

 adapted to the size of the alimentary bolus. These muscles 



1 BERNARD, Lemons sur la physiologic et la pathologic du systeme 

 Paris, 1858, tome ii., p. 100. 



4 See vol. ii., Digestion, p. 147, et seq. 



