50 NEEYOTJS SYSTEM A!NT> GEKEKAL SENSATION. 



which these nerves are distributed are occasioned by impres- 

 sions made upon the optic nerve ; as such motions cease when 

 the trunk of that nerve is divided. 



[ 100. The fourth pair consist of motory fibrils. They 

 take a long course, and are distributed to the superior oblique 

 muscles, to which they are especially destined. 



[ 101. The sixth pair are likewise motory nerves. Their 

 distribution is restricted to the external straight muscles of 

 the eye-ball. The function of these nerves has been proved, 

 both by experiments and pathological observations. 



[ 102. The fifth pair resemble in their origin, structure, 

 and distribution, compound spinal nerves. Their anterior 

 roots are distributed exclusively to the muscles of mastication. 

 The posterior roots impart sensation to the integuments of the 

 forehead, temples, eyelids, nose, mouth, the greater part of 

 the ear, the conjunctiva, the mucous membrane of the nasal 

 fossae, a great part of the mouth, pharynx, upper surface of 

 the tongue, teeth, and gums. These great nerves divide into 

 three branches, 1st, the opthalmic (5) passes into the orbit, en- 

 dows the eye with sensibility, and comes out beneath the eye- 

 brow, to be distributed on the forehead and temples ; 2nd, 

 the superior maxillary (5) traverses a canal beneath the orbit, 

 and distributes leashes of filaments to the skin of the cheeks, 

 nose, and upper lip; 3rd, the inferior maxillary (5") is distri- 

 buted to the tongue, pharynx, tonsils, mouth, teeth, gums, chin 

 and lips. 



[ 103. The Facial Nerve (fig. 19, d, fig. 20, /) is the 

 true motory nerve of the muscles of the face, and enables the 

 countenance to reflect the varied emotions of the mind. This 

 nerve does not impart sensation, that function being performed 

 by the branches of the fifth pair. Beneath the origin of the 

 facial nerve is seen the divided trunk of the acoustic, or audi- 

 tory nerve. 



[ 104. The Glosso-pharyngeal Nerve (9) is distributed to 

 the tongue and pharynx : its function is not so clear as that of 

 the preceding nerves. By some it is regarded as the special 

 nerve of taste ; by others as a moto-sensitive nerve, as it con- 

 tains motory and sensitive fibrils. 



[ 105. The Pneumo-gastric Nerve (10) is distributed to 

 the larynx, air passages, lungs, heart, esophagus, and stomach. 

 It sends branches, likewise, to the plexuses which surround the 



