FIFTH PAIR TRIFACIAL NERVES. 



493 



It resembles a spinal nerve in having its origin by two roots, 

 sensory and motor, and in having a ganglion on the sensory root. 

 It arises on the side of the pons Varolii ; and the sensory root, 

 which is the larger, may be traced to the restiform bodies and 

 lateral columns of the cord, the motor root having its deep origin 

 near the floor of the fourth ventricle. The nerve passes through 

 an opening in the dura mater, at the apex of the petrous temporal 

 bone, where the posterior root spreads out into a large ganglion, 

 the Gusserw.n, the anterior root passing beneath without any 

 connection. The Gasserian ganglion gives off the ophthalmic, 

 superior maxillary, and inferior maxillary branches. 



Fir,. 1S6. 



Right orbit opened to show the nerves of the eye. a a, Optic ; 6, Motor oculi ; c, Pathetic ; 

 d, Ophthalmic division of fifth pair ; d', Lachrymal ; d", Snpraorbital ; d'", Xasal ; e, Abdncens ; 

 '. Eectus externus muscle ; /, Orbital branch of superior maxillary nerve. 



The OPHTHALMIC NERVE, the smallest of the three divisions of 

 the trifacial nerve, passes forwards by the outer wall of the 

 cavernous sinus, in company with the third and sixth nerves, 

 enters the orbital fossa through the foramen lacerum orbitale, and 

 divides into three branches, the frontal, lachrymal, and nasal. 



The frontal or supraorbital -ner':^ is a large, flat branch, 

 placed on the internal wall of the optic fossa ; it ascends parallel 

 to the superior oblique muscle, passes through the supraorbital 

 foramen, and, after giving a branch to the upper eyelid, divides 



