PERIPHERAL NERVES AND THE SYMPATHETIC SYSTEM 251 



II. The optic nerve is the nerve of sight. The fibres of 

 this nerve leave the brain by the optic tract. Their nearest 

 nuclei lie in the anterior corpus quadrigeminum and in the 

 lateral geniculate body. These parts are connected, on the 

 one hand, with the cerebral cortex by means of fibres of the 

 corona radiata and, on the other hand, with the more pos- 

 terior nuclei of the brain, especially the nuclei of the nerves 

 of the eye muscles. The optic tract passes over into the 

 chiasma, where a part of the fibres cross. Thence they pro- 

 ceed to the eye as the optic nerve. Because of this partial 

 crossing in the chiasma, the inner half of each retina is 

 innervated by fibres from the opposite side of the brain, while 

 the outer half receives fibres from the same side of the brain. 



III. The oculo-motor, IV. the pathetic (trochlear), and 

 VI. the abducent are the motor nerves for the external and 

 internal eye muscles (except the dilator of the pupil) and 

 the levator palpebrae superioris. The trochlear innervates 

 the superior oblique, the abducent the rectus externus, the 

 oculo-motor all the other eye muscles. 



V. The trigeminus contains : 



1. Sensory fibres for the whole head except the jaws and 

 ears, which are supplied by the glossopharyngeal and the 

 ramus auricularis vagi. 



2. Motor fibres for the muscles of mastication (temporal, 

 internal and external pterygoid, and masseter) ; also for the 

 tensor palati mollis, mylohyoid, the anterior belly of the 

 digastric, and the tensor tympani. 



3. Secretory fibres for the tear glands. 



The lingualis trigemini nerve contains secretory fibres (for the 

 submaxillary and sublingual glands) ; also vaso-dilators and fibres 

 for taste, which, however, originally leave the brain in company 

 with the facial and glossopharyngeal and through the corda tympani 

 reach the lingual. Besides these, the trigeminus contains vaso- 

 motor and secretory nerves fdr the sweat glands of the face, which, 

 however, are derived from the sympathetic. 



VII. The facial contains motor fibres for all the face 

 muscles, for the stylohyoid and the posterior belly of the 

 digastric, and for the stapedius muscles. It also contains 



