824 



THE NERVOUS SYSTEM 



it is considered to be the nerve of equilibration, and the connections noted above may be 

 considered the pathways by which it exercises this function. The fibres of the apparatus which 

 are represented in the spinal cord are supposed to convey impulses to the ventral horn (motor) 

 cells of the cord as far down as the lumbar region. 



The cochlear nerve, the auditory nerve proper, arises as the central processes of the bipolar 

 cells of the spiral ganglion of the cochlea. In the lateral periphery of the restiform body, just 

 before the latter enters the cerebellum, the nerve finds its two nuclei of termination, the ventral 

 nucleus and the dorsal nucleus (tuberculum acusticum, fig. 640). 



From the dorsal nucleus arise the acoustic medullary strice. These bundles pass around the 

 dorsal aspect of the restiform body and course just under the ependyma of the floor of the fourth 

 ventricle to the mid-line, where they suddenly turn downward into the substance of the meduUsa 

 and in doing so, cross to the opposite side and join the lemniscus. As the lemniscus becomes 

 separated higher up into a medial and lateral portion, these fibres course in the lateral lemniscul 

 and are distributed chiefly to the grey substance of the inferior quadrigeminate and media, 



Fin. 650. — Scheme showing Some of the Central Connections of the Acoustic Nerve. 



(In part after Edinger.) 



Inferior quadrigeminate body 

 -Nucleus of trochlear nerve 



Nucleus of lateral lemniscus 



Medial longitudinal fasciculus 



Lateral lemniscus 



Peduncle of superior olive 



Nucleus fastigii 



^Nucleus emboliformis 



Dentate nucleus 



_ Lateral nucleus of 



vestibular nerve 



Restiform body 



Dorsal nucleus of 



cochlear nerve 



^Ventral nucleus of 



cochlear nerve 

 .^•Cochlear nerve 



Vestibular nerve 



Superior olivary nucleus 



Trapezoid body 



geniculate body of that side. At the mid-line some of their fibres join the median longitudinal 

 fasciculus and by way of it are distributed to the nuclei of origin of other cranial nerves. In 

 frequent cases, the acoustic stria; course so deeply beneath the ependyma as not to be super- 

 ficially visible in the floor of the fourth ventricle. 



From the ventral nucleus of termination fibres arise which terminate about the cells of the 

 superior olivary nucleus of the same and opposite sides. The superior olive is a small accumu- 

 lation of grey substance which lies in the level of the inferior portion of the pons, and in line 

 with the much larger inferior olivary nucleus of the medulla. However, it is not analogous 

 to the latter in any sense. The two superior olives form links in the central acoustic chain. 

 From cells of the superior olivary nucleus of the same and opposite sides, fibres arise which pass 

 by way of the lateral lemniscus and terminate in the grey substance of the inferior quadri- 

 geminate body and in the medial geniculate body, thus associating these bodies with the ventral 

 nucleus of cochlear termination of the opposite side. From the medial geniculate body fibres 

 ari.se which pass to the cortex of the superior temporal gyrus. This path is supplemented by 

 fibres arising in the inferior quadrigeminate body, which likewise go to the temporal lobe. In 

 the lateral lemniscus .some of the acoustic fibres are interrupted by cells of the nucleus of the 

 lateral lemniscus. In cnjssing the mid-line, l)etween th(^ superior olives, the fibres from the two 

 sources form a more or less compact bundle, the corpus trapezoideum (trapezium). To this 

 are aflded fibres crossing between the nuclei trapeozidei, smaller masses of grey substance 

 juat ventral to the superior olives and jjrobably of the same significance. 



Also, some fibres arising in the nuclei of termination of the cochlear nerve pass to the in- 

 ferior quadrigeminate body of the same side. On the other hand, the connection with the medial 



