230 



THE CRANIAL NERVES. 



Speedily becoming firm and round, the nerve is directed from the interpeduncular 

 space forwards, as well as somewhat outwards, between the posterior cerebral and 

 superior cerebellar arteries to the outer side of the posterior clinoid process, a little 

 anterior to which it penetrates the layer of dura mater forming the outer boundary 

 of the cavernous sinus. Contained within this membrane, it continues its course 



Fig. 148. PLAN OF THE THIRD NERVE, 



WITH THE CILIARY GANGLION. 



(G. D. T.) 



The ganglion is seen to be attached 

 by its short root to the nerve of the 

 inferior oblique muscle ; LR, its long, 

 and SR, its sympathetic root. 



forwards to the inner end of the sphenoidal fissure, and there divides into two parts, 

 upper and lower, which enter the orbit between the heads of the external rectus 

 muscle, and are separated from each other by the nasal branch of the ophthalmic 

 nerve. As the third nerve lies in the outer wall of the cavernous sinus, it is con- 

 nected by slender filaments with the cavernous plexus of the sympathetic, and it 

 receives also a small branch from the ophthalmic division of the fifth nerve. 



The upper, the smaller part, is directed inwards over the optic nerve to the 



Fig. 149. VIEW FROM ABOVE OF THE MOTOR NKRVKS OF THE EYEBALL 

 AND ITS MUSCLES (after Hirschfeld and Leveille, altered). (Allen 

 Thomson. ) 



The ophthalmic division of the fifth pair has been cut short ; the 

 attachment of the muscles round the optic nerve has been opened up, 

 and the three upper muscles turned towards the inner side, their 

 anterior parts being removed ; a part of the optic nerve is cut away to 

 show the inferior rectus ; and a part of the sclerotic coat and cornea is 

 dissected off showing the ins, ciliary muscle, and choroid coat, with 

 the ciliary nerves. 



, upper part of the internal carotid artery emerging from the 

 cavernous sinus ; b, superior oblique muscle ; b' t its anterior part 

 passing through the pulley ; c, levator palpebrse superioris ; d, superior 

 rectus ; e, internal rectus ; f, external rectus ; f, its upper tendon 

 turned down ; g, inferior rectus ; h, insertion of inferior oblique 

 muscle. 



II, optic commissure ; II', part of the optic nerve entering the 

 eyeball ; III, common oculomotor ; IV, trochlear nerve ; V, large root 

 of fifth ; V, small or motor root ; VI, abducent nerve ; ] , upper 

 division of third nerve, giving twigs to the levator palpebrse and 

 superior rectus ; 2, branches of lower division supplying the internal 

 and inferior recti muscles ; 3, the long branch of the same nerve pro- 

 ceeding forwards to the inferior oblique muscle, and close to the 

 number 3, the short root of the ciliary ganglion : this ganglion is also 

 shown, receiving from behind its long root, which has been cut short, 

 and giving forward some of its ciliary nerves, which pierce the sclerotic 

 coat ; 3', marks the termination of some of these nerves in the ciliary 

 muscle and iris after having passed between the sclerotic and choroid 

 coats ; 4, the trochlear nerve entering the upper surface of the superior 

 oblique muscle ; 6, the abducent nerve passing into the external rectus. 



superior rectus muscle of the eye and the elevator of the eyelid, to both of which 

 muscles it furnishes branches. 



The lower and larger portion of the nerve divides into three branches ; of these 

 one reaches the inner rectus ; another the lower rectus ; and the third, the longest 

 of the three, runs onwards between the lower and the outer rectus, and terminates 

 below the ball of the eye in the inferior oblique muscle. The last-mentioned branch 

 is connected with the lower part of the ciliary ganglion by a short thick offset 

 (short root of the ganglion), and gives one or two filaments to the lower rectus 

 muscle. 



