THE STRUCTURE OF THE BRAIN STEM m 



corpus trapezoides or trapezium. After making connections with the si 

 olivary body and a special nucleus, they join the superficial set of fibrefa 

 run up in the tegmentum to the inferior corpora quadrigemina, forming the 

 lateral fillet. 



The vestibular nerve (Fig. 194) also has two nuclei of termination the 

 median nucleus with small cells, and the lateral or Deiters' nucleus with large 

 cells. Some fibres pass also to the nuckus of Bechterew, which is in close 

 relation with the roof nuclei of the cerebellum. The descending fibres end 



TO VERMIS 



TO HEMISPHERE 



FIBRES OF 

 VESTIBULAR 

 ROOT 



NERVE 

 ENDINGS 

 IN MACULXE 

 8.AMPULL/E 



FIG. 194. Plan of the course and connections of the fibres forming the vestibular 



root 'of the auditory nerve. (SCHA.FER.) 



r, restif orm body ; v, descending root of fifth nerve ; p, cells of principal nucleus 

 of vestibular root ; d, fibres of descending vestibular root ; nd, a cell of the descend- 

 ing vestibular nucleus; D, cells of nucleus of Deiters; B, cells of nucleus of Bech- 

 terew; nt, cells of nucleus tecti (fastigii) of the cere bellum ; plb, fibres of posterior 

 longitudinal bundle. No attempt has been made in this diagram to represent the 

 actual positions of the several nuclei. Thus a large part of Deiters' nucleus lies 

 dorsal to and in the immediate vicinity of the restiform body. 



chiefly in the median nucleus, while the ascending fibres end^in Deiters' 

 nucleus. From the latter a distinct band of fibres passes up to the cere- 

 bellum, forming the median division of the restiform body, while other fibres 

 run across to the tegmentum of the opposite side, where they take part in the 

 formation of the posterior longitudinal bundle. 



In a section through the fourth ventricle through the middle of the pons, 

 a group of large cells is seen in the position occupied by the nucleus of the 

 hypoglossal below. These cells give rise to the fibres of the sixth nerve. 

 Another group is seen lying laterally and more deeply, evidently belonging to 

 the lateral horn system. This is the nucleus of the seventh or facial nerve, 

 the fibres of which pass dorsally and anteriorly, looping round the sixth 

 nerve-nucleus, before issuing as the root of the seventh nerve. 



In the upper part of the pons we find the fifth nerve (Fig. 195) with its 

 two roots. The fibres of the sensory root derived from the cells of the 



