816 



THE NERVOUS SYSTEM. 



and (d) trapezium of the pons. The first-mentioned origin, however, gives most 

 of the fibres (see Fig. 488). The auditory nerve passes forward across the pos- 

 terior border of the middle peduncle of the cerebellum, in company with the 

 facial nerve, from which it is partially separated by a small artery (auditory). 

 It then enters the internal auditory meatus, with the facial nerve in a groove 

 along its upper and fore part. At the bottom of the meatus it receives one or 

 two filaments from the facial nerve, and then divides into two branches, cochlear 

 and vestibular. The auditory nerve is soft in texture (hence the name portio 

 mollis), and is destitute of neurilemma. The distribution of the auditory nerve 

 in the internal ear will be found described along with the anatomy of that organ 

 in a subsequent page. 



Surgical Anatomy. The auditory 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, or it may be 

 bruised or 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 arise from loud explosions from dynamite, etc. , prob- 

 ably 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. 



Ninth Pair (Figs. 490, 491, 492). 



The Ninth or G-losso-pharyngeal Nerve is distributed, as its name implies, to 

 the tongue and pharynx, being the nerve of sensation to the mucous membrane 

 of the pharynx, fauces, and tonsil, and a special nerve of taste to all the parts of 

 the tongue to which it is distributed. Its superficial origin is by three or four 

 filaments closely connected together, from the upper part of the medulla oblon- 

 gata, in the groove between the olivary and the restiform body. 



Its deep origin may be traced through the fasciculi which lie betAveen the 

 lateral and posterior areas of the medulla to a nucleus of gray matter in the 

 lower part of the floor of the fourth ventricle, beneath the inferior fovea, above 

 the nucleus of the pneumogastric. From its superficial origin it passes outward 

 across the flocculus, and leaves the skull at the central part of the jugular fora- 

 men, in a separate sheath of the dura mater, external to and in front of the 

 pneumogastric and spinal accessory nerves (Fig. 386). In its passage through 

 the jugular foramen it grooves the lower border of the petrous portion of the 

 temporal bone, and at its exit from the skull passes forward between the jugular 

 vein and internal carotid artery, and descends in front of the latter vessel, and be- 

 neath the styloid process and the muscles connected with it, to the lower border of 

 the Stylo-pharyngeus. The nerve now curves inward, forming an arch on the side 



of the neck, and lying upon the Stylo-pharyngeus 

 and Middle constrictor of the pharynx, above the 

 superior laryngeal nerve. It then passes beneath 

 the Hyoglossus, and is finally distributed to the mu- 

 cous membrane of the fauces and base of the tongue, 

 and the mucous glands of the mouth and tonsil. 



In passing through the jugular foramen the nerve 

 >,,^^ presents, in succession, two gangliform enlarge- 



Spinal accessory. W ', ,^ -.& n i ,, - 



V%V a ments. The superior, the smaller, is called the jug- 

 c. ***?** ular ganglion ; the inferior and larger, the petrous 

 FIG. 490. 9th,ioth,andiithneryes, ganglion, or the gant//it>n nf Andefteh. 



their origin, ganglia, and communica- ' Vp^ superior> Qr jugular,' ganglion is situated ill the 



u-pper part of the groove in which the nerve is lodged 



during its passage through the jugular foramen. It is of very small size, and 

 involves only the lower part of the trunk of the nerve. It is usually regarded 

 as a segmentation from the lower ganglion. 



^Jugular ganglion. 

 Petrous ganglion, 

 tympanic br. 



