NUCLEI OF VESTIBULAR NERVE 



823 



the rootlets of the vagus or glosso-pharyngeus, as the case may be. The vagus is thought to 

 receive more efferent fibres from the nucleus ambiguus than does the glosso-pharyngeus, and 

 Cunningham notes that it may be questioned whether the latter nerve contains any motor 

 fibres at all, there being paths by which the fibres of its motor branch (to the stylo-pharyngeus 

 muscle) might enter it other than direct from motor nuclei. 



The vesLibular and cochlear nerves are usually considered as one nerve and together are 

 designated as the acoustic or eighth cranial nerve. While both are purely sensory, are similar 

 in development and course together, they are distinct as to function and their nuclei of termina- 

 tion differ. They are here described as separate cranial nerves. The two nerves approach the 

 brain stem together and enter it at the lateral aspect of the junction of medulla oblongata and 

 pons. 



The vestibular nerve arises as the central processes of the bipolar cells of the vestibular 

 ganglion, and passes into the brain-stem on the ventro-mesial side of the restiform body to find 

 its nucleus of termination (nucleus vestibularis) in the floor of the fourth ventricle. This 

 nucleus occupies a triangular area of considerable extent (area acustica, fig. 640), and is usually 

 subdivided into a lateral nucleus (Deiters'), a medial nucleus (Schwalbe's), a superior nucleus 

 (Bechterew's), and an inferior nucleus (nucleus spinalis). The latter is a downward pro- 

 longation of the general nucleus vestibularis which accompanies the desceriding or spinal root 

 of the nerve. 



Fig. 649. — Transverse Section op Medulla at Inferior Border of Pons. 



Medial longitudinal fasciculus 

 Nucleus of medial 

 eminence 

 Acoustic medullary 

 ^ . stria 



Lateral nucleus of ves- 

 tibular nerve 



Descending root of ves- 

 tibular nerve 

 _Dorsal root of coch- 

 lear nerve 

 Restiform body 



Dorsal nucleus 

 of cochlear 

 nerve 



% /o? 



Ventral nucleus 

 cochlear 



nerve 



Spinal tract of 

 trigeminus / 

 Nucleus of spinal / 

 tract of trigem- 

 inus 



Lemniscus— - 





^f/ "ff \ \ VV.^ Cochlear nerve 



L.'^ "Vestibular nerve 



•* '^ Root filum of glosso-pharyngeus 



' ^^H!L - Cerebello-olivary fibres 



i'^'-i.jti Thalamo-ohvary tract , 



'^J^ ~'\'< H **< .:^k-^hL^ i^^ - Nucleus of inf 



enor olive 

 External arcuate fibres 



Pyramid 



Nucleus arcuatus 



From the cells of the lateral and inferior nuclei axones are given off which form paths to 

 the lateral funiculus of the spinal cord (vestibulo-spinal fasciculus, fig. 619) and to its anterior 

 marginal fasciculus (ventral vestibulo-spinal tract). From both the lateral nucleus and the 

 superior nucleus a special path is given off which passes upward and terminates in the roof 

 nucleus of the cerebellum (nucleus fastigii) of the opposite side and in the nucleus dentatus and 

 the cortex of the vermis. Also, fibres arising in the nuclei fastigii are said to terminate in the 

 lateral (Deiters') nucleus in addition to those which probably descend into the anterior 

 marginal fasciculus of the spinal cord. From the medial and also from the superior nucleus 

 fibres pass to the medial longitudinal fasciculus of both sides, and are distributed to the 

 nucleus of the abducens of the same side and to the nuclei of the trochlear and oculo- 

 motor nerves of the opposite side and of the masticator nerve of the same and opposite sides. 

 From the lateral and medial nuclei, and probably from all, fibres arise which cross the mid- 

 line to enter the lemniscus and ascend to the cerebrum (lateral portion of the thalamus) on 

 the opposite side. The lateral (Deiters') nucleus is said to contribute more fibres to the 

 medial longitudinal fasciculus than does a nucleus of any other cranial nerve. If any of these 

 fibres descend the cord, they must do so in its anterior marginal fasciculus. 



The inferior nucleus is accompanied by the descending or spinal root of the vestibular nerve, 

 which begins to assemble in the nuclei above. This root is composed of both caudal branches 

 of' the entering fibres of the nerve and chiefly of fibres arising from the cells of its nuclei. 

 Thus for the vestibular nerve it corresponds in every way to the solitary tract for the vagus, 

 and to the spinal tract of the trigeminus. Such of its fibres as descend into the spinal cord 

 most probably do so in the lateral vestibulo-spinal fasciculus. 



Many of the anatomical details of the central connections of the vestibular nerve have not 

 yet been determined with exactness. In addition to whatever other functions it may have, 



