THE CRANIAL NERVES 



649 



4. The trochlear nerve arises in the trochlear nucleus which is 

 situated in the central gray matter below the floor of the aqueduct just 

 posteriorly to the lateral subnucleus of the oculomotor nerve. These 

 fibers pass horizontally backward and emerge behind the posterior 

 corpora quadrigemina, where they cross in the anterior medullary 

 velum. It is a motor nerve supplying fibers to the superior oblique 

 muscle of the eyeball. The action which this muscle gives rise to, 

 simultaneously with the muscle attached to the opposite eyeball, is not 

 under the control of the will. 



5. The trigeminus nerve originates from two roots, a small anterior 

 or portio minor, and a large posterior or portio major. The former is 

 motor and the latter sensory in its function. Its motor root arises 

 in part from a small nucleus in the pons and partly from ganglion 



Accessory 



N. opht 



ly ^i^\ Principal 

 ^i>^ i motor 

 -jT^y^ji^j nucleus 



Descending 

 spinal root 



N. max. sup. N. max. inf. 



Fig. 322. — Nuclei of Origin op the Fifth Cranial Nerve. 



after Van Gehuchten.) 



(From Poirier and Charpy, 



cells situated in the region of the corpora, laterally to the aqueduct 

 of Sylvius. Its musculomotor fibers are distributed peripherally 

 through the ramus masticatorius to the different muscles of mastica- 

 tion, as well as to the muscles of deglutition, inclusive of the muse, 

 mylohyoid eus, the tensor veli palatini and muse, azygos uvulae. It also 

 contains secretomotor fibers for the lacrimal gland and sweat-glands, 

 and vasomotor fibers for the tongue and face. The latter, of course, 

 are of sympathetic origin and use the path of this nerve merely as a 

 highway to reach distal parts. 



This nerve is of importance chiefly on account of its sensory power, 

 because it conveys the sensations of touch, pain and temperature from 

 the skin of the face, the adjoining region of the scalp, the mucous 

 membrane lining the nasal and oral cavities, and from the teeth and 



