AU'DITORY, or EIGHTH, NERVE. Ac cording to the older nomenclature, the portio mollis of the seventh pair. The nerve connected with the special sense of hearing. The ap parent origin of this nerve is from the ventro lateral surface of the medulla immediately be hind the transverse fibres of the ports. Of the two distinct bundles of fibres that can be dis tinguished in it. one (the cochlear division) passes to the outer side of the restiform body, or inferior peduncle of the cerebellum, while the other (the vestibular division) passes to the inner side of the restiform body. The fibres terminate in three nuclei. Of these, two are situated in the gray matter of the fourth ven tricle, and are known respectively, from their positions, as the median nucleus and the lateral nucleus of the eighth nerve. The third, or ac cessory nucleus, is a group of cells just ventral to the restiform body at the point of convergence of the two roots. The fibres of the cochlear division of the nerve are the axones of cells situated in the spiral ganglion, or ganglion of Corti ; these cells are bipolar, and their peripheral termination is, in Corti's organ, situated within the bony cochlea, the ends of the fibres of the cochlear division mainly in the lateral nucleus.
The fibres of the vestibular division of the nerve are the axones of cells situated in Scapa's ganglion of the internal ear; these cells are also bipolar, their peripheral terminations being among the hair-cells of the crista and macula aeustiea in the vestibule and semi - circular canals; the ends of the fibres of the vestibular division arc mainly in the median and acces sory nuclei. Py means of neura, whose cell bodies are situated in these nuclei, auditory im pressions are transmitted to higher centres.
The auditory nerve leaves the cranial cavity, in company with the facial nerve, by means of the internal meatus. At the bottom of the meatus the two divisions of the nerve separate, the vestibular branch passing to the vestibule and semi-circular canals, the cochlear branch passing to the cochlea. Within the meatus the auditory nerve is connected by one or two fila ments with the facial. See EAR.