THE CENTRAL NERVOUS SYSTEM 723 



results in a grotesque contortion. The mouth appears like a diagonal 

 slit in the face, its angle being drawn up on the sound side, and the 

 patient cannot bring the lips sufficiently close together to be able to 

 blow out a candle or to whistle. Liquids escape from the mouth, 

 and food collects between the paralyzed buccinator and the teeth. 

 The labial consonants are not properly pronounced. Taste may be 

 lost in the anterior two-thirds of the tongue when the nerve is injured 

 between the entrance of the gustatory fibres from the trigeminus 

 and their exit by the chorda tympani, but not when the lesion is in 

 the nucleus of origin, or anywhere above it. Hearing is sometimes 

 impaired because the auditory and facial nerves, lying close together 

 for part of their course, are apt to suffer together, but perhaps also 

 because the stapedius muscle is supplied by the seventh. 



The eighth or auditory nerve arises from the medulla oblongata 

 by two roots (a dorsal and a ventral), one of which passes in on each 

 side of the restiform body. The auditory nucleus in the floor of the 

 fourth ventricle consists of two parts, a lateral, or outer, and a median, 

 or inner, nucleus. The lateral nucleus we have already recognised, 

 under the name of the nucleus of Deiters, as a possible origin of the 

 antero-lateral descending tract. It is also a nucleus of reception for 

 some of the fibres of the ventral auditory root, the axons of which, 

 and especially their collaterals, form synapses with some of its cells. 

 The median auditory nucleus is also a nucleus of reception for the 

 ventral root. Through the nucleus of Deiters the ventral root is 

 connected with the cerebellum. At the junction of the dorsal and 

 ventral roots on the ventral surface of the restiform body lies a swell- 

 ing, the accessory nucleus, into which, and into another smaller swell- 

 ing, the tuberculum acusticum, the fibres of the dorsal root pass, and 

 with whose cells they come into contact by their end arborizations. 

 The nerve-cells of the accessory nucleus and the acoustic tubercle, 

 therefore, constitute the nucleus of reception for the dorsal root-fibres. 

 The cells of origin, both of the dorsal and of the ventral root, are 

 situated in the internal ear, the former in the ganglion spirale, or 

 ganglion of Corti, which is embedded in the bony spiral of the cochlea, 

 the latter in the ganglion vestibulare, which lies in the vestibule. These 

 cells seem to correspond to the ganglion cells on the posterior root of a 

 spinal nerve, but, unlike them, they remain, even in mammals, bipolar 

 throughout life. Their central processes form the axons of the auditory 

 nerve. Their peripheral processes are distributed in the case of the 

 dorsal root to the organ of Corti, in the case of the ventral root to 

 the semicircular canals and the vestibule. For this reason the dorsal 

 root is often called the cochlear division, and the ventral root the 

 vestibular division of the auditory nerve. And it is believed that 

 the cochlear and vestibular roots are physiologically as well as 

 anatomically distinct. For, as we shall see (p. 732), it is extremely- 

 probable that the cochlea subserves the function of hearing, the 

 semicircular canals and vestibule the function of equilibration. We 

 must assume, from clinical and experimental data, that the dorsal 

 root is connected through its nuclei with the first, or first and second 

 temporo-sphenoidal convolutions on the opposite side. The strice 



46 2 



