40 Anatomy of the Nervous System 



nucleus, and immediately under the floor of the fourth 

 ventricle, lies a small-celled nucleus of roughly triangular form 

 in cross section, the chief vestibular nucleus {dorsal vestibular 

 nucleus, nucleus dorsalis seu medialis nervi vestibuli, nucleus 

 triangularis) .'^ This large nucleus extends all the way from 

 a point a little behind the entrance of the V nerve root to 

 the level of the anterior part of the hypoglossal nucleus 

 (Pis. VIII.-X.). 



Some of the ascending vestibular fibres do not end in 

 any of these nuclei but run directly into the cerebellum, 

 where they end in the roof nuclei and in certain parts of the 

 cortex (PL X.). 



Fortuyn also saw vestibular fibres entering the ventral 

 cochlear nucleus in the rat. 



Secondary fibres from the nuclei of Deiters and Bechterew 

 join the direct fibres to the cerebellum and end with them in 

 that structure. 



Other fibres arising in these nuclei pass medially to enter 

 an important longitudinal correlation tract on either the same 

 or the opposite side (PL X.). This tract is the medial longi- 

 tudinal bundle, which lies in the angle between the raphe 

 and the gray matter of the ventricular floor. Through this 

 tract, the vestibular impulses are conveyed to various motor 

 centres, particularly the eye-muscle nuclei, the ascending tract 

 of Deiters (tractus Deiters ascendens) forming a definite group 

 of fibres in the lateral part of the bundle in the midbrain. 



Yet other fibres from Deiters' nucleus form a diffuse tract 

 in the reticular formation, which runs down to the spinal 

 cord, conveying impulses to the spinal motor neurons. This 

 is the vestibulospinal tract {fasciculus vestibulo-spinalis, tractus 

 Deiters descendens). Its fibres pass obliquely between the 



^The term triangular nucleus has also been applied to the cuneate 

 nucleus. 



The chief vestibular nucleus contains several centres and receives 

 vestibular fibres only in its lateral part (F"use). 



