950 THE NERVOUS SYSTEM 



the vestibular and the cochlear are separate; they are separate at their entrance 

 into the lateral aspect of the medulla oblongata; and their central connections, 

 peripheral distributions and functions are different. 



The vestibular nerve arises as processes of the cells of the vestibular ganglion 

 (ganglion of Scarpa), situated upon and blended within the nerve at the bottom 

 of the internal auditory meatus. Unlike the ordinary spinal ganglion, to which 

 it corresponds, the cells of the vestibular ganglion retain an embryonal, "bipolar," 

 form. The central processes course v/ith the cochlear nerve in the internal 

 auditory meatus medialward, caudad and slightly downward, inferior to the 

 accompanjdng facial and glosso-palatine nerves, and, arching ventrally around 

 the restiform body, they enter the medulla at the inferior border of the pons, lat- 

 eral to the glosso-palatine and facial and medial to the entrance of the cochlear 

 nerve. They find their nucleus of termination spread in the floor of the fourth 

 ventricle and grouped as the median, the lateral (Deiters'), the superior, and the 

 nucleus of the spinal root of the vestibular nerve. In the internal auditory mea- 

 tus, the vestibular nerve is connected by two small filaments of fibres with the 

 glosso-palatine nerve. These are either visceral motor fibres for the vessels of the 

 domain of the vestibular or are aberrant fibres which course only temporarily 

 with the vestibular and return to the glosso-palatine. 



The peripheral processes of the cells of the vestibular ganglion terminate in the 

 specialised or neuro-epithelium comprising the maculce in the sacculus and the 

 utriculus and the cristas in the ampullae of the three semicircular canals. Thus 

 there are five terminal branches of the nerve. None of its fibres terminates in the 

 cochlea. The vestibular ganglion has a lobar form, one lobe giving rise to a 

 superior utriculo -ampullar division which divides into three terminal branches; the 

 other giving a sacculo-ampullar division which gives two terminals. 



The superior or utriculo -ampullar branch divides into the following terminal 

 branches: — 



(1) The utricular branch passes through the superior macula cribrosa of the vestibule 

 and terminates in the macula acustica of the utriculus. 



(2) Accompanying the utricular branch through the superior macula cribrosa is a branch, 

 the superior ampullar, to the crista acustica of the ampulla of the superior semicircular canal, 

 and — 



(3) A similar branch, the lateral ampullar, to the ampulla of the lateral semicircular canal. 



The inferior or sacculo-ampullar branch accompanies the cochlear nerve a 

 short distance further than the superior, and divides into — 



(4) A branch, the posterior ampullar, which passes through the foramen singulare and the 

 inferior macula cribrosa and terminates in the ampulla of the posterior semicircular canal, and — 



(5) A branch, the saccular, which passes through the middle macula cribrosa and terminates 

 in the macula acustica of the sacculus. 



The central connections of the vestibular nerve are described in detail on pages 823, 824. 

 Its' large nucleus of termination, spread through the area acustica in the floor of the fourth 

 ventricle, and divided into four sub-nuclei, is associated with the nuclei fastigii, globosus, and 

 emboliformis of the cerebellum, with the nuclei of the eye-moving nerves, with the spinal cord, 

 and probably with the cerebral cortex. 



THE COCHLEAR OR AUDITORY NERVE 



The fibres of the cochlear nerve are distributed to the organ of Corti in the 

 cochlea, and so are considered as comprising the auditory nerve proper. They 

 arise from the long, coiled spiral ganglion of the cochlea, the cells of which, like 

 those of the vestibular ganglion, are bipolar. The peripheral processes of these 

 cells arc shorter than those of the vestibular ganglion. They terminate about the 

 auditory or hair-cells of the organ of C 'orti and thus collect impulses aroused by 

 stimuli alTectiug these cells. The central processes of the ganglion cells continue 

 through tiie modiohir (;amil and the tractus spiralis foraminosus of the cochlea, 

 and theiH'C, joining the vestibular nerve through the internal auditory meatus, 

 accompanying the facial jicrve and internal auditory artery, they course medial- 

 ward and downward, ap[)roach and enclasp the restiform body (fig. 6G5) and 

 enter the lateral aspect of brain-stem to terminate in their dorsal and ventral 

 nuclei. A description of these nuclei and tiie further central connections of the 

 cochlea with the superior olive, the nuclei of the eye-moving nerves, the inferior 

 quadrigeminate bodies, the medial genicnilate bodies, and with tlie cerebellum 

 and temj)oral lobes of the cerebral hemisj)her('S is given on pages 824, 839. 



