THE CRANIAL NERVES 289 



Eighth Nerve (Auditory). 



Origin. This is a nerve of special sense. Its apparent 

 origin is by two roots one from the groove between the 

 olivary and restiform bodies at the lower border of the pons, 

 the other coming around the upper end of the restiform 

 body to join the first in the groove. The deep origin of the 

 two roots is different. That of the median root is the dor- 

 sal auditory nucleus in the floor of the fourth ventricle; 

 that of the lateral root is mainly from the ventral auditory 

 nucleus in front of the restiform body between the two 

 roots. 



Course and Distribution. Crossing the posterior border 

 of the middle peduncle of the cerebellum, it enters the in- 

 ternal auditory meatus in company with the facial nerve and 

 the nerve of Wrisberg. At the bottom of the meatus it re- 

 ceives fibers from the seventh, and divides into branches 

 which pass to the cochlea, semi-circular canals and vestibule. 



Function. This nerve receives and conveys to the brain, 

 impressions produced by sound waves; it is the nerve of 

 hearing and is in all probability not sensible to stimulation 

 in any other way. 



Ninth Nerve (Glosso-pharyngeal). 



Origin. The apparent origin of this nerve is from the 

 upper part of the medulla in the groove between the olivary 

 and restiform bodies. Its deep origin is in the lower part of 

 the floor of the fourth ventricle above the nucleus of the 

 tenth. 



Course and Distribution. Leaving the skull by the jugu- 

 lar foramen, it passes forward between the internal jugu- 

 lar vein and the internal carotid artery, descends in front of 

 the latter to the lower border of the stylo-pharyngeus where 

 it curves inward, runs beneath the hyoglossus, and is distrib- 



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