CRANIAL NERVES. 107 



root, which then divides into an anterior and posterior branch, the former 

 of which is distributed to the muscles of mastication, viz. : temporal, mas- 

 seter, internal and external pterygoid muscles. 



Properties. It is the most acutely sensitive nerve in the body, and 

 endows all the parts to which it is distributed with general sensibility. 



Irritation of the large root, or any of its branches, will give rise to 

 marked evidence of pain ; the various forms of neuralgia of the head and 

 face being occasioned by compression, disease, or exposure of some of its 

 terminal branches. 



Division of the large root within the cranium is followed at once by a 

 complete abolition of all sensibility in the head and face, but is not attended 

 by any loss of motion. The integument, mucous membranes and .the eye 

 may be lacerated, cut or bruised, without the animal exhibiting any evidence 

 of pain. At the same time the lachrymal secretion is diminished, the pupil 

 becomes contracted, the eyeball is protruded, and the sensibility of the 

 tongue is abolished. 



The reflex movements of deglutition are also somewhat impaired ; the 

 impression of the food being unable to reach and excite the nerve centre in 

 the medulla oblongata. 



Galvanization of the small root produces movements of the muscles of 

 mastication ; section of the root causes paralysis of these muscles, and the 

 jaw is drawn to the opposite side, by the action of the opposing muscles. 



Influence upon the Special Senses. After division of the large root 

 within the cranium, a disturbance in the nutrition of the special senses 

 sooner or later manifests itself. 



Sight. In the course of twenty-four hours the eye becomes very vascular 

 and inflamed, the cornea becomes opaque and ulcerates, the humors are 

 discharged, and the eye is totally destroyed. 



Smell, The nasal mucous membrane swells up, becomes fungous, and 

 is liable to bleed on the slightest irritation. The mucus is increased in 

 amount, so as to obstruct the nasal passages ; the sense of smell is finally 

 abolished. 



Hearing. At times the hearing is impaired, from disorders of nutrition 

 in the middle ear and external auditory meatus. 



Alteration in the nutrition of the special senses is not marked if the sec- 

 tion is made posterior to the ganglion of Gasser, and to the anastomosing 

 filaments of the sympathetic which join the nerve at this point; but if the 

 ganglion be divided, these effects are very noticeable, due to the section of 

 the sympathetic filaments. 



