CRANIAL NERVES. 95 



Deep Origin. From the gray matter of the medulla oblongata. 



Distribution. The nerve then passes into the orbit through the sphe- 

 noidal fissure, and is distributed to the external rectus muscle. Receives 

 filaments from the cervical portion of the sympathetic, through the carotid 

 plexus and spheno-palatine ganglion. 



Properties. When irritated, the external rectus muscle is thrown into 

 convulsive movements, and the eyeball is turned outward. When divided 

 or paralyzed, this muscle is paralyzed ; motion of the eyeball outward past 

 the median line is impossible, and the homonymous diplopia increases as 

 the object is moved outward past this line. The images are upon the same 

 plane and parallel. Internal strabismus results because of the unopposed 

 action of the internal rectus. 



Function. To turn the eyeball outward. 



5th Pair. Trifacial. Trigeminal. 



Apparent Origin. By two roots from the side of the pons Varolii. 



Deep Origin. The deep origin of the two roots is the upper part of 

 the floor and anterior wall of the 4th ventricle, by three bundles of fila- 

 ments, one of which anastomoses with the auditory nerve ; another passes 

 to the lateral tract of the medulla ; while a third, grayish in color, goes to 

 the restiform bodies, and may be traced to the point of the calamus scrip- 

 torius. 



Filaments of origin have been traced to the "trigeminal sensory nucleus," 

 located on a level with the point of exit of the nerve, and to the posterior 

 gray horns of the cord, as low down as the middle of the neck. 



Distribution. The large root of the nerve passes obliquely upward 

 and forward to the ganglion of Gasser, which receives filaments of com- 

 munication from the carotid plexus of the sympathetic. It then divides into 

 three branches. 



1. Ophthalmic branch, which receives communicating filaments from 

 the sympathetic, and sends sensitive fibres to all the motor nerves of the 

 eyeball. It is distributed to the ciliary ganglion, lachrymal gland, sac and 

 caruncle, conjunctiva, integument of the upper eyelid, forehead, side of 

 head and nose, anterior portion of the scalp, ciliary muscle and iris. 



2. Superior maxillary branch, sends branches to the spheno-palatine 

 ganglion, integument of the temple and lower eyelid, side of forehead, 

 nose, cheek and upper lip, teeth of the upper jaw, and alveolar processes. 



3. Inferior maxillary branch, which, after receiving in its course fila- 

 ments from the small root and from the facial, is distributed to the sub- 



