224 HUMAN PHYSIOLOGY. 



the ganglion of Gasser, beyond which they enter the inferior max- 

 illary division. After a short course most of these fibers leave the 

 common trunk and are distributed to the muscles of mastication, 

 viz. : the temporal, the masseter, the internal and external pterygoid 

 muscles. Other fibers are distributed to the mylohyoid muscle, the 

 tensor palati and the tensor tympani muscles. 



Properties. Stimulation of the small root produces convulsive 

 movements of the muscles of mastication ; section of the root causes 

 paralysis of these muscles, after which the jaw is drawn to the 

 opposite side by the action of the opposing muscles. 



The Influence of the Trigeminal on 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 nu- 

 trition in the middle ear and external auditory meatus. 



Alteration in the nutrition of the special senses is not marked 

 if the section is made posterior to the ganglion of Gasser and to the 

 anastomosing filaments of the sympathetic, which join the' nerves at 

 this point ; but if the ganglion be divided, these effects are very 

 noticeable, owing to the section of the sympathetic filaments. 



Function. The trigeminal nerve, through its afferent fibers, en- 

 dows all the parts of the head and face to which it is distributed 

 with sensibility ; through its efferent fibers it gives motion to the 

 muscles of mastication, and to the tensor muscle of the palate and 

 the tensor of the tympanic membrane ; through anastomosing fibers 

 from the sympathetic it influences the nutrition of the special senses. 



Seventh Pair. Portio Dura. Facial Nerve. 



Origin. From a large nucleus of nerve-cells situated in the gray 

 matter beneath the upper half of the floor of the fourth ventricle. 



Distribution. From this origin the nerve emerges from the lower 

 border of the pons. It then passes into the internal auditory meatus 



