568 



NERVOUS SYSTEM. 



FIG. 218.-Limtte of cutaneous distri- Volving Other parts, but all 

 button of sensory nerves to the 

 face, head and neck (Beclard). 



also, are given off two or three branches which pass to the submaxillary 



ganglion. 



3. The inferior dental nerve, the largest of the three, passes in the sub- 



stance of the inferior maxillary bone, beneath the teeth, to the mental fora- 



men, where it emerges upon the face. The most 

 important sensory branches are those which sup- 

 ply the pulps of the teeth and the branches upon 

 the face. The nerve, emerging upon the face 

 by the mental foramen, called the mental nerve, 

 supplies the integument of the chin and the 

 lower part of the face and the lower lip. It also 

 sends certain filaments to the mucous membrane 

 of the mouth. 



Properties and Uses of the Trifacial. The 

 trifacial is the great sensory nerve of the face 

 and of the mucous membranes lining the cavi- 

 ties about the head. It is impossible to stimu- 

 late this nerve at its origin without seriously in- 



observations with 



regard to the properties of the large root go to 

 show that it is an exclusively sensory nerve and 

 that its sensibility is very acute as compared with 



n f>, Ar TIPVVPC Tf waa rlivirl^rl in fno cranial r>av 



omer Bives. it was ai\mea in me cranial cav- 



if v V\r Mavn M899 '9^\ Tfnrlora /1893\ anrl Ma 

 ir J "J Mayo (ISxJ/S- 6), V OQera (IS/^j ana Ma- 



c 3 a?^e r rves branches f the cervi " endie (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 was divided. The operative proced- 

 ure employed by Magendie has been followed by other physiologists, particu- 

 larly Bernard, who made a number of important observations on the immedi- 

 ate and remote effects of section of the nerve. The section is usually made 

 through the ganglion of Gasser. The operation is difficult on account of 

 the danger of wounding large blood-vessels. When this operation is per- 

 formed without accident, the cornea and the integument and mucous mem- 

 brane upon that side of the head are instantaneously deprived of sensibility 

 and may be pricked, lacerated or burned, without the slightest evidence of 

 pain on the part of the animal. Almost always the small root of the fifth 

 is divided as well as the large root, and the muscles of mastication are para- 

 lyzed upon one side ; but with this exception, there is no paralysis of motion, 

 sensation alone being destroyed upon one side. 



Immediate -Effects of Division of the Trifacial. This nerve has never 

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

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

 operated upon and found to be exquisitely sensitive. Physiologists have ex- 

 posed the roots in animals immediately after death, and have found that 



n 



of the inferior maxillary divis- 



ion; 4, distribution of the ante- 



rior branches of the cervical 

 nerves; 5,5, distribution of the 



