FOURTH PAIE. 



595 



In the orbit, the fourth nerve inclines inwards above the muscles, and 

 enters finally the upper oblique muscle at its orbital surface. 



While in its fibrous canal in the outer wall of the sinus, the fourth nerve is joined 

 by filaments of the sympathetic, and not unfrequently is blended with the ophthalmic 



Fig. 403. VIEW FROM ABOVE OP THE MOTOR NERVES 

 OF THE EYEBALL AND ITS MUSCLES (after Hirsch- 

 feld and Leveille, altered). 



Fig. 403. 



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 

 iris, zona ciliaris, and choroid coat, with the ciliary 

 nerves. 



, the upper part of the internal carotid artery 

 emerging from the cavernous sinus ; 6, the superior 

 oblique muscle ; &', its anterior part passing through 

 the pulley ; c, the levator palpebrse superioris ; d, 

 the superior rectus ; e, the internal rectus ; /, the 

 external rectus; /', its upper tendon turned down ; 

 gr, the inferior rectus j h, insertion of the inferior 

 oblique muscle. 



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

 of the optic nerve entering the eyeball ; III, the 

 common oculo-motor ; IV, the fourth or trochlear 

 nerve ; V, the greater root of the trigeminus ; V, 

 the smaller or motor root ; VI, the abducent nerve ; 

 1, the upper division of the third nerve separating 

 from the lower and giving twigs to the levator palpe- 

 brse and superior rectus ; 2, the branches of the 

 lower division supplying the internal and inferior 

 recti muscles ; 3, the long branch of the same nerve 

 proceeding forward to the inferior oblique muscle, 

 and close to the number 3, the short thick branch 

 to the ciliary ganglion : this ganglion is also shown, 



receiving from behind the slender twig from the nasal nerve, which has been cut short, 

 and giving forwards 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 distribution of the trochlear nerve to the 

 upper surface of the superior oblique muscle ; 6, the abducent nerve passing into the 

 external rectus. 



division of the fifth. Bidder states that three or more small filaments of this nerve 

 extend in the tentorium as far as the lateral sinus ; and has figured one as joining the 

 sympathetic on the carotid artery. (Neurologische Beobachtungen, Von F. H. Bidder. 

 Dorpat, 1836.) 



FIFTH PAIR OF NERVES. 



The fifth, or trifacial nerve (nerv. trigeminus), the largest cranial nerve, 

 is analogous to the spinal nerves, in respect that it consists of a motor and 

 a sensory part, and that the sensory fibres pass through a ganglion while 

 the motor do not. Its sensory division, which is much the larger, imparts 

 common sensibility to the face and the fore part of the head, as well as to 

 the eye, the nose, the ear, and the mouth ; and endows the fore part of 

 the tongue with the powers of both touch and taste. The motor root 

 supplies chiefly the muscles of mastication. 



