1004 



THE NERVE SYSTEM 



(6) The superior ampullar branch, accompanying the utricular branch, to end 

 in the crista acustica of the ampulla of the superior semicircular canal. 



(c) The lateral ampullar, to the ampulla of the lateral semicircular canal. 



The lower or sacculoampullar branch is somewhat longer and divides into: 



(a) The posterior ampullar, passing through the foramen singulare and the 

 inferior macula cribrosa to end in the ampulla of the posterior semicircular canal. 



(6) The saccular branch, passing through the middle macula cribrosa to end in 

 the macula acustica of the sacculus. 



FIG. 742. Distribution of the acoustic nerve. (Semidiagrammatic.) (Testut.) 



Applied Anatomy. The acoustic nerve is frequently injured, together with the facial nerve, 

 in fractures of the middle fossa of the base of the skull implicating the internal auditory meatus. 

 The nerve may be either torn across, producing permanent deafness, it may be bruised, or it may 

 be pressed upon by extravasated blood or inflammatory exudation, when the deafness will in all 

 probability be temporary. The nerve may also be injured by violent blows on the head without 

 fracture, and deafness may follow loud explosions of dynamite, etc., probably from some lesion 

 of this nerve, which is more liable to be injured than the other cranial nerves on account of its 

 structure. The test that the nerve is destroyed and that the deafness is not due to some lesion 

 of the auditory apparatus is obtained by placing a vibrating tuning-fork on the head. The 

 vibrations will be heard in cases where the auditory apparatus is at fault, but not in cases of 

 destruction of the auditory nerve. 



Tinnitus aurium is commonly present in cases of ear disease. The sounds are variable in 

 intensity and nature buzzing, hissing, whistling, rushing, bell-ringing, and so forth. In the 

 insane, tinnitus is associated with delusions and hallucinations of hearing, and may be due to 

 nothing more than impacted cerumen in the meatus. 



THE NINTH OR GLOSSOPHARYNGEAL NERVE (N. GLOSSOPHARYNGEUS) 



(Figs. 743, 744). 



The ninth or glossopharyngeal nerve is distributed, as its name implies, to the 

 tongue and pharynx, being the nerve of ordinary sensation to the mucous mem- 

 brane of the pharynx, fauces, and tonsil; and the nerve of taste to all parts of 

 the tongue to which it is distributed. 



