480 THE NERVOUS SYSTEM. 
medulla than the vago-glosso-pharyngeal nucleus of termination. Kolliker states 
that it can be traced downwards as low as the level of the decussation of the 
fillet, and upwards as high as the place of entrance of the cochlear root of the 
auditory nerve. From its dorsal aspect the axons of the cells proceed, and in the 
first instance they pass backwards towards the floor of thé fourth ventricle; then, 
bending suddenly outwards and forwards, they join the afferent roots of the vagus 
and glosso-pharyngeal nerves, and emerge from the brain in company with these. 
Auditory Nerve (nervus acusticus).—This is a large nerve which joins the brain 
at the lower border of the pons Varolii and on the ventral aspect of the restiform 
body. It is an afferent nerve, and its fibres spring from bipolar ganghonic cells 
either within or in the immediate neighbourhood of the labyrinth or internal ear 
(see section dealing with the organs of sense). Reaching the brain the auditory 
nerve divides into two parts, viz. the nervus cochlearis and the nervus vestibularis, 
which present totally different connexions and apparently exercise absolutely 
distinct functions. In their further course these two divisions deviate from each 
other so as to embrace the restiform body—the vestibular part entering the pons 
on the inner or mesial aspect of the restiform body, whilst the cochlear part 
sweeps round its outer surface. Special nuclei of termination require to be 
studied in connexion with each part of the nerve. 
The cochlear nerve is composed of finer fibres than the vestibular nerve, 
and these acquire their medullary sheaths at a later period. It is the true nerve 
of hearing, and its fibres end in a ganglion which hes in intimate relation to the 
restiform body, and which may be described as consisting of two parts. Of these 
one, called the tuberculum acusticum or the lateral cochlear nucleus, is a pyriform 
mass which is placed on 
the outer aspect of the 
restiform body — between 
it and the flocculus fof 
a the cerebellum. The 
oni second part, termed the 
a ventral cochlear nucleus, 
ee does not extend so low 
down as the tuberculum 
BEerREING acusticum. It isa wedge- 
ogee shaped nuclear mass which 
is placed on the ventral 
aspect of the restiform 
body in the interval be- 
tween the cochlear and 
vestibular divisions of the 
auditory nerve, after they 
have separated from each 
other. The fibres of the 
cochlear nerve enter these 
twogangliaandend around 
the cells in terminal arbor- 
isations, which are finer, 
closer, and more intricate 
than those met with in 
any other nerve nucleus 
in the brain. 
The vestibular nerve 
enters the brain at a 
Fic. 357.—CENTRAL CONNEXIONS oF THE CocHEEAR anp Vestisutar Slightly higher level than 
Divisions OF THE AUDITORY NERVE, the cochlear nerve and on 
(Diagram founded on drawings by Edinger and Ferrier and Turner.) AW a eiseral aspec + of the 
ventral cochlear nucleus. It forces its way backwards through the pons between 
the restiform body, which lies on its outer side, and the spinal root of the 
DORSAL PART 
Conpy 
S S TRAPEZOIDE® 
my § 
Vy, ‘2 
ENTRAL paRT OF PO 
