610 



CRANIAL NERVES. 



then passes between the two heads of the External Kectus, and is distributed 

 to that muscle on its ocular surface. 



The above-mentioned nerves, as well as the ophthalmic division of the fifth, 

 as they pass to the orbit, bear a certain relation to each other in the cavernous 

 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 of the outer wall of the sinus, in their 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 for- 

 wards to the sphenoidal fissure, the third and fifth nerves become divided into 

 branches, and the sixth approaches the rest ; so that their relative position be- 

 comes 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 of these ; beneath this lies 

 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 oph- 

 thalmic, 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 Palpebrse, 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 the orbit. 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 orbit. 



FACIAL NERVE. 



The Facial Nerve (portio dura of the seventh pair) is the motor nerve of all 

 the muscles of expression in the face, and of the Platysma and Buccinator. It 



supplies also the muscles of the 



Fig. 341. The Course and Connection of the Facial external ear, the posterior belly 

 Nerve, in the Temporal Bone- o f t ^ e Digastric, and the Stylo- 



hyoid. Through the chorda tvm- 

 pani it supplies the Lingualis; 

 by its tympanic branch, the Sta- 

 pedius and Laxator Tympani; 

 through the otic ganglion, the 

 Tensor Tympani; and through 

 the connection of its trunk with 

 the Vidian nerve, by the petrosal 

 nerves, it probably supplies the 



Levator Palati and Azygos TJvulas. 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 Varolii, from which some of its fibres are derived. 



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

 small fasciculus (jwrtio inter duram et mollem of Wrisberg, or portio intermedia). 

 This accessory portion arises from the lateral column of the cord. 



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



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