ANATOMY AND PHYSIOLOGY OF THE BRAIN 371 



the cavernous sinus, runs above the other nerves in 

 its outer wall, and divides into two branches, which 

 enter the orbit between the two heads of the external 

 rectus. It is joined in the sinus by sympathetic fila- 

 ments. The superior branch crosses the optic nerve 

 to supply the superior rectus and levator palpebrse 

 muscles. The inferior divides into three parts one 

 for the inferior oblique, one to the inner, and one to 

 the lower recti muscles. The first supplies the motor 

 root of the lenticular ganglion of the sympathetic 

 system. 



THE TROCHLEAR (FOURTH). The trochlear nerve 

 has an apparent origin from the upper side of the 

 valve of Vieussens, and a deep from the floor of the 

 aqueduct of Sylvius. The two nerves communicate 

 by a transverse band on the valve of Vieussens. The 

 nerve pierces the dura after crossing over the cms, 

 enters the cavernous sinus, in w T hose outer wall it lies 

 between the ophthalmic and third nerves, then crosses 

 the latter to enter the orbit through the sphenoidal 

 fissure above the external rectus, and enters the 

 superior oblique muscle. 



THE FIFTH NERVE (TRIFACIAL). The fifth or 

 trifacial is the largest of all the cranial nerves, and 

 arises by two roots, a motor and a sensor. The former 

 is small, and the latter has the Gasserian ganglion 

 upon it. Both arise from the side of the pons super- 

 ficially, the smaller root above the larger, some trans- 

 verse fibers of the pons separating the two. This 

 nerve conveys both motion and sensation. At the 

 apex of the petrous portion of the temporal the large 

 root forms the Gasserian ganglion; the smaller does 

 not join in the ganglion, but runs below it to join, 

 just below the foramen ovale, the lowest trunk pro- 

 ceeding from the ganglion. 



The Gasserian ganglion lies in a hollow near the apex 

 of the petrous portion of the temporal bone, the large 



