THE NERVOUS SYSTEM 115 



sixth or abducent all carry motor impulses to the mus- 

 cles which move the eyeball. Their function is, there- 

 fore, sufficiently indicated by their distribution. 



The fifth, or trifacial, resembles a spinal nerve in ris- 

 ing by a motor and a sensory root, only the sensory is 

 in front and the larger of the two. It is emphatically 

 the neuralgic nerve, so frequently does this painful af- 

 fection attack the sensory branches of this widely dis- 

 tributed nerve. Its synonym of trifacial is derived from 

 its splitting into three divisions and leaving the skull by 

 three openings. One division, the ophthalmic conveys 

 news from the mucous membrane and part of the skin 

 of the nose, the eyeball and lacrimal gland, forehead and 

 upper eyelid; the next, upper maxillary (jaw) is the 

 afferent nerve from the skin covering the upper jaw, 

 side of the nose, upper lip and lower lid and from the 

 teeth and gum of the upper jaw the tonsils .and nasal 

 and throat mucous membrane. The third division, in- 

 ferior maxillary, does the same work for the lower jaw 

 and its surroundings, including the tongue and salivary 

 inlands, the skin at the back of the ear running to the 

 top of the head, and takes all the efferent fibers which 

 are distributed to the muscles which move the lower jaw. 

 The nerve resembles a spinal nerve also in possessing 

 an enlargement called a ganglion on its afferent root in 

 which these fibers arise, the branches or roots of the 

 ganglion furnishing the connection with the brain. This 

 arrangement is identical with that of the spinal and 

 other cranial nerves which contain mixed fibers. 



The eleventh and twelfth, or hypoglossal, nerves con- 

 tain none but efferent (motor) fibers. The eleventh is 

 distributed to very important muscles of the neck and 

 back and is often connected with the surgical affection 

 called wry neck. 



