540 CRANIAL NERVES. 



sinus, at the sphenoidal fissure, and in the cavity of the orbit, which will be now 

 described. 



In the cavernous sinus, the third, fourth, and ophthalmic division of the fifth, 

 are placed in the dura mater, forming the outer wall of the sinus in numerical 

 order, both from above downwards, and from within outwards. The sixth nerve 

 lies at the outer side of the internal carotid artery. As these nerves pass forwards 

 to the sphenoidal fissure, the third and fifth nerves become divided ; and the sixth 

 approaches the rest ; so that their relative position becomes considerably changed. 



In the sphenoidal fissure, the fourth, and the frontal and lachrymal divisions 

 of the ophthalmic, lie upon the same plane, the former being most internal, the 

 latter external ; and they enter the cavity of the orbit above the muscles. The 

 remaining nerves enter the orbit between the two heads of the External rectus. 

 The superior division of the third is the highest ; beneath this, the nasal branch 

 of the fifth ; then the inferior division of the third ; and the sixth lowest of all. 



In the orbit, the fourth, and the frontal and lachrymal divisions of the ophthalmic, 

 lie on the same plane immediately beneath the periosteum, the fourth nerve being 

 internal and resting on the Superior oblique, the frontal resting on the Levator 

 palpebrae, and the lachrymal on the External rectus. Next in order comes the 

 superior division of the third nerve lying immediately beneath the Superior rectus, 

 and then the nasal division of the fifth crossing the optic nerve from the outer to 

 the inner side of this cavity. Beneath these is found the optic nerve, surrounded 

 in front by the ciliary nerves, and having the lenticular ganglion on its outer 

 side, between it and the External rectus. Below the optic is the inferior division 

 of the third, and the sixth, which lies on the outer side of the cavity. 



FACIAL NERVE. 



The FACIAL NERVE, the portio dura of the seventh pair, is the motor nerve of 

 all the muscles of the face, the Platysma and Buccinator. It supplies also the 

 muscles of the external ear, the posterior belly of the Digastric and the Stylo-hyoid. 

 Through the chorda tympani it supplies the Lingualis ; by its tympanic branch, 

 the Stapedius and Laxator tympani; through the otic ganglion, the Tensor tympani ; 

 and through the connection of its trunk with the Yidian nerve, by the petrosal 

 nerves, it probably supplies the Levator palati and Azygos uvulae. It arises from 

 the lateral tract of the medulla oblongata, in the groove between the olivary and 

 restiform bodies. Its deep origin may be traced to the floor of the fourth ventricle, 

 where it is connected with the same nucleus as the sixth nerve. This nerve is 

 situated a little nearer to the middle line than the portio mollis, close to the lower 

 border of the pons Yarolii, from which some of its fibres are derived. 



Connected with this nerve, and lying between it and the portio mollis, is a small 

 fasciculus, the portio inter duram et mollem of Wrisberg. This accessory portion 

 arises from the lateral column of the cord. 



The nerve passes forwards and outwards upon the crus cerebelli, and enters the 



internal auditory meatus with 



Fig. 277. The Course and Connections of the Facial the auditory nerve. Within 



Nerve in the Temporal Bone. th(J meatus> the faeial nerve 



lies first to the inner side of 

 th auditory, and then in a 

 groove upon this nerve, and is 

 connected to it by one or two 



At the bottom of the mea- 

 tus, it enters the aquasductus 

 Fallopii, and follows the ser- 

 pentine course of that canal 

 through the petrous portion 



of the temporal bone, from its commencement at the internal meatus to its termina- 

 tion at the stylo-mastoid foramen. It is at first directed outwards towards the 



