THE TROCHLEAR 337 



rigemina bodies, by means of an inner set of fibers. The bond 

 of union between the cuneus and the pulvinar and lateral 

 geniculate bodies is by means of fibers, called the optic radiation. 

 The latter transmit visual impulses to the cortex. The inner 

 set of fibers in the optic tract pass to the superior quad- 

 rigeminal bodies, then* to the nuclei of the third, fourth, and 

 sixth nerves, at the same time receiving fibers from the cortical 

 centre (corticifugal tract) contained within the optic radiation. 

 Thus through the superior quadrigeminal bodies reflex paths 

 pass to the eye-muscle centres and in their turn are influenced 

 by the cortical centres through the corticifugal tract. 



The Oculomotor 



The oculomotor arises superficially from the crus anterior 

 to the pons, its deep origin being a gray nucleus in the floor 

 of the aqueduct of Sylvius. It runs to the outer side of the 

 posterior clinoid process, enters 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. The inferior divides 

 into three parts one for the inferior oblique, one to the inner, 

 and one to the lower rectus. The first supplies the motor root 

 of the lenticular ganglion. 



The Trochlear 



The trochlear nerve has an apparent origin laterad of the 

 frenulum veli, immediately behind the posterior quadrigeminal 

 body, 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 crus, enters the cavernous sinus, in whose 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 after crossing over the levator palpebne. It receives 

 sympathetic filaments in the sinus, and sends a recurrent 

 branch into the tentorium, 

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