THE DEEP CONNEXIONS OF THE CEEEBEAL NERVES. 605 



When the nervus vestibularis, as it traverses the brain, reaches the medial aspect 

 of the dorsal portion of the restiform body, its fibres bifurcate to form ascending 



jand descending tracts. The latter pass vertically downwards in separate bundles 

 and form the descending tract of the vestibular nerve (Figs. 498, p. 565; 495, 

 p. 561; and 530, p. 597). This proceeds through the inferior part of the 



. pons into the medulla oblongata, in which it may be traced as far as the level of 

 the decussation of the medial lemniscus. Associated with the descending tract 



'there is a column of gray matter, with nerve-cells strewn sparsely throughout it. 

 This is the nucleus of the descending tract, and the fibres end in fine arborisa- 

 tions around these nerve-cells. 



Some of the ascending fibres of the vestibular nerve end in the nucleus lateralis. 

 This nucleus is composed of a number of large and conspicuous multipolar 

 nerve-cells, 



Nucleus fastigi 

 Vermis Cerebell , 



which are scat- 

 tered amidst the 

 bundles of the 

 vestibular 

 nerve. As it is Anterior 



j j Cransvers' 



traced upwards temporal 



Vestibular fibre 



passing Co vermis 



Insula 



into the pons 

 the nucleus 

 gradually in- 

 clines back- 

 wards, and final- 

 ly it occupies a 

 place in the 

 side wall of 

 the fourth ven- 

 tricle. It attains 

 its greatest de- 

 velopment at 

 the level of the 

 emerging part of 

 the facial nerve 

 and this upper 

 part is some - 

 times termed 

 the nucleus 



gyr 



AUDITORY 

 RADIATION 



LEMNISCUS__ 



LATERALIS" 



Nucleus 

 lemniscus 

 lateralis \ 



Nucleus emboliformis 

 Ngcleus 

 de ntatus 

 ebelli 



Corpus 

 qeniculatum 



mediate 



Vestibular Fibre 



en<jng in 



lateral cerebellar 

 cortex 



-Dorsal cochlear nucleus 

 / f., Ventral cochlear nucleus 



Cochlea 



Principal 

 Vestibular nucleus 



MEDULLA OBLONCATA 

 Corpus trapejoideum 



FIG. 535. CENTRAL CONNEXIONS OF THE COCHLEAR AND VESTIBULAR 

 DIVISIONS OF THE ACOUSTIC NERVE. 



Vestibular fibres green. Cochlear fibres yellow. 



superior. 



Other ascending fibres pass without interruption into the cerebellum to 

 terminate in the cortex of the vermis and hemisphere. In their course many of 

 these fibres pass through the nucleus fastigii, and many writers describe them as 

 terminating in this nucleus ; but according to Eamon y Cajal they merely traverse 

 it on their way to the cerebellar cortex. 



From the large-celled nucleus lateralis best known as Deiters' nucleus a, strand 

 of fibres passes medially to reach the medial longitudinal fasciculus, of which it 

 forms one of the most important constituent elements. Some of these fibres pass 

 upwards to the nuclei of the oculomotor, trochlear, and abducens nerves ; others 

 downwards, probably to the nucleus of the accessory nerve, which are concerned 

 in regulating the movements of the eyes and the head respectively, because 

 they need to be thus closely linked to the receptive nucleus of the nerve 

 (vestibular), which is concerned with the appreciation of movements of the head 

 and the position of the body in space. Other fibres arise from the lateral 

 nucleus and pass directly to the spinal medulla without passing through the 

 medial longitudinal bundle; they form the fasciculus vestibulospinaris, which 

 passes downwards in the funiculus anterior and distributes fibres to the various 

 motor nuclei in the anterior column of the spinal medulla (Fig. 524, p. 590, and 

 Fig. 473, p. 534). 



The nucleus superior (Bechterew's nucleus) likewise emits a group of fibres 



