i4 THE POCKET ANATOMY 



cavernous sinus near posterior clinoid process, lying above 

 and internal to 4th nerve. As it passes forwards to enter 

 orbit through sphenoidal fissure, the 4th nerve and frontal 

 branch of 5th cross externally and become superior to it. It 

 divides into two branches in the fissure, which enter orbit 

 between the heads of the external rectus, the nasal branch of 

 the 5th lying between the two ; whilst in cavernous sinus it 

 communicates with cavernous plexus. 



Distribution. Superior branch supplies superior rectus and 

 levator palpebrae superioris. Inferior divides into three, for 

 internal rectus, for inferior rectus, and for inferior oblique, 

 which latter gives off short or motor root to the lenticular 

 ganglion, through which the 3rd nerve supplies the ciliary 

 muscle and the sphincter fibres of the iris. 



Special function. Motor nerve of eyeball. 



4TH or TROCHLEAR. Origin Superficial : valve of Vieussens, 

 just behind corpora quadrigemina. Deep : floor of aqueduct 

 of Sylvius. 



Course. Winds round outer surface of crus cerebri and 

 pierces free border of tentorium ; passes forwards in outer 

 wall of cavernous sinus below 3rd, but enters orbit through 

 sphenoidal fissure above and internal to the other nerves and 

 external rectus. 



Distribution. Enters orbital surface of superior oblique. 



Special function. Motor nerve of superior oblique. 



5TH or TRIFACIAL. Origin Superficial : from the side of 

 the pons, by small motor and large sensory roots, the latter 

 having a ganglion on it. Deep : Sensory : (a) floor of 4th 

 ventricle ; (6) (ascending root), posterior horn of grey matter 

 of medulla, and upper part of cord. Motor: (a] floor of 4th 

 ventricle ; (b) (descending root), side of aqueduct of Sylvius. 



Course. The two roots pass forwards through oval opening 

 in dura mater near apex of petrous bone, the sensory root 

 entering the Gasserian ganglion, lodged on the apex of petrous 

 part of temporal bone. The motor root passes under ganglion 

 and is not connected with it, but goes through foramen ovale 

 uniting with the Inferior Maxillary division. 



The Gasserian ganglion : lodged in a depression (Meckel's 

 cave) near the apex of petrous part of temporal, gives off from 

 its anterior edge the ophthalmic, superior maxillary, and inferior 

 maxillary trunks. The two former are purely sensory ; the 

 last by joining small motor root becomes a mixed nerve. 



OPHTHALMIC or ist division of the 5th (sensory and smallest 

 branch) : courses along outer wall of cavernous sinus below 

 3rd and 4th nerves, to enter orbit through sphenoidal fissure. 



