THE THIRD OR OCULOMOTOR NERVE 



979 



Infratrochlear 

 nerve. 



THE TRIED OR OCULOMOTOR NERVE (N. OCULOMOTORIUS) 



(Figs. 729, 730). 







The third or oculomotor nerve supplies all the muscles of the orbit except the 

 Superior oblique and External rectus; it also supplies, through its connection 

 with the ciliary ganglion, the Sphincter muscle of the iris and the Ciliary muscle. 

 It is a rather large nerve, of cylindric form and firm texture. 



Its apparent origin is from the oculomotor groove along the ventromesal border 

 of the crus. The deep origin may be traced through the substantia nigra, red 

 nucbus, and tegmentum of the crus to a nucleus situated on either side of the 

 median line beneath the floor of the aqueduct. The nucleus of the oculomotor 

 nerve also receives fibres from the abducent nerve of the opposite side. The 

 nucleus of the oculomotor nerve, considered from a physiological standpoint, 

 can be subdivided into several 

 smaller groups of cells, each group 

 controlling a particular muscle (see 

 p. 902). 



On emerging from the brain, the 

 nerve is invested with a sheath of 

 pia,and enclosed in a prolongation 

 from the arachnoid. It passes 

 between superior cerebellar and 

 posterior cerebral arteries, and then 

 pierces the dura in front of and 

 external to the posterior clinoid 

 process, passing between the two 

 processes from the free and attached 

 borders of the tentorium, which 

 are prolonged forward to be con- 

 nected with the anterior and poste- 

 rior clinoid processes of the sphe- 

 noid bone. It passes along the 

 outer wall of the cavernous sinus 

 (Figs. 505 and 506); above the other 

 orbital nerves, receiving in its course 

 one or two filaments from the 

 cavernous plexus of the sympa- 

 thetic, and a communicating branch 

 from the first division of the tri- 

 geminal nerve. It then divides into 

 two branches, which enter the orbit 

 through the sphenoidal fissure, be- 

 tween the two heads of the External 

 rectus muscle (Fig. 729). On 

 passing through the fissure, the nerve is placed below the trochlear nerve and 

 the frontal and lacrimal branches of the ophthalmic nerve, while the nasal nerve is 

 placed between its two divisions (Fig. 738). 



The superior division (ramus superior) (Fig. 730), the smaller, passes inward 

 over the optic nerve, and supplies the Superior rectus and Levator palpebrae 

 muscles. The inferior division (ramus inferior) (Fig. 730), the larger, divides 

 into three branches. One passes beneath the optic nerve to the Internal rectus; 

 another, to the Inferior rectus; and the third, the longest of the three, passes 

 forward between the Inferior and External recti to the Inferior oblique. From 



Motor root. / \^ Recurrent filament 

 Sensory root, to dura mater. 



FIG. 729. Nerves of the orbit, seen from above. 



