CRANIAL NERVES. 2OI 



Distribution. The efferent fibers, known collectively as the small root, 

 emerge from the side of the pons Varolii, pass forward beneath the ganglion 

 of Gasser, beyond which they enter the inferior maxillary 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 mylo- 

 hyoid 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 dis- 

 charged, 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 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, endows 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 Nerve. 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 in 



