XI THE CRANIAL NERVES 517 



The eighth pair are the auditory nerves. The auditory 

 is, as we have seen (p. 392), divided into the cochlear 

 and vestibular nerve. (See later, p. 52.3). 



The ninth pair, or glossopharyngeal nerves, are 

 mixed nerves ; each being, partly, a nerve of taste, and 

 supplying the hind-part of the mucous membrane of the 

 tongue, and, partly, a motor nerve for the pharyngeal 

 muscles. 



The tenth pair is the two pneumogastric nerves, 

 often called the vagus. These very important nerves, 

 and the next pair, are the only cranial nerves which are 

 distributed to regions of the body remote from the head. 

 The pneumogastric supplies the larynx, the lungs, the 

 liver, and the stomach, and branches of it are connected 

 with the heart. 



The eleventh pair again, called spinal accessory, 

 differ widely from all the rest, in arising, in part, from the 

 sides of the spinal cord, between the anterior and posterior 

 roots of the cervical nerves. They run up, gathering fibres 

 as they go, to the medulla oblongata, and then leave the 

 skull by the same aperture as the pneumogastric and 

 glossopharyngeal. They are purely motor nerves, supply- 

 ing certain muscles of the neck, while the pneumogastric 

 is mainly sensory, or at least afferent. 



The ticelfthpair, or hypoglossal nerves, are the motor 

 nerves which supply the muscles of the tongue. 



Of these nerves, the two foremost pairs do not properly 

 deserve that name, but are, as we have said, really 

 processes of the brain. The olfactory pair are prolonga- 

 tions of the cerebral hemispheres ; the optic pair, of the 

 walls of the third ventricle. 



The optic nerve from each eye meets its fellow nerve 

 from the other eye at the base of the brain below the 

 third ventricle. Here they cross each other in what is 

 called the optic chiasma (covered by the pituitary 

 body P in Fig 160) and are continued on backwards, 



