I260 HUMAN ANATOMY. 



nucleus of Bechterew. The small mass corresponds with the lateral vestibular nucleus (nuc. 

 lateralis ii. vestibularis] or nucleus of Deiters. The fibres of the descending root end around the 

 neurones within the spinal nucleus in a manner similar to that in which the constituents of the 

 spinal root of the trigeminus terminate in relation with the neurones within the substantia 

 gelatinosa, whilst those of the ascending vestibular root end around the cells within the remain- 

 ing vestibular nuclei. 



Although much uncertainty and conflict of opinion exist as to the details of the secondary 

 paths by which the impulses carried by the vestibular fibres are distributed, it may be accepted 

 as established that fibres pass from the nuclei of reception : {«) to the cerebellum (chiefly to the 

 roof nucleus of the opposite side and, possibly, also to the nuclei globosus and emboliformis) 

 as constituents of the nucleo-cerebellar tract, by which the impulses of equilibration are carried 

 to the great coordinating centres, {b) as arcuate fibres ventro-medially into the tegmentum of the 

 pons, cross the mid-line and bend upward or downward to pass to other levels, some fibres, 

 however, remaining on the same side. From the character of the impulses it is probable that 

 only relatively few vestibular fibres join the median fillet to ascend to the optic thalamus. Other 

 connections of the nuclei include: (r) commissural fibres between Bechterew's nucleus of the 

 two sides, {d ) fibres to the abducent nucleus, [e) crossed and uncrossed fibres from Deiters' 

 nucleus to the posterior longitudinal fasciculus and (/) fibres from the same nucleus to the 

 spinal cord. » 



It must be understood that by no means all of the neurones of Deiters' nucleus are con- 

 cerned in transmitting afferent impulses to the cerebellum, for, as a matter of fact, many are 

 links in the path by which the cerebellar cells exercise coordinating influences over the root- 

 cells of the spinal nerves. Starting in the cerebellum, such efferent impulses are carried by 

 efferent fibres which descend through the median part of the inferior cerebellar peduncle and 

 probably end around certain of the cells within Deiters' nucleus. From these cells, in turn, 

 originate the fibres of the vestibulo-spinal tract, which, after tr.iversing the medulla, enter the 

 antero-lateral column of the cord and end in relation with the motor root-cells. A shorter and 

 more direct path for vestibular reflexes is probably formed by the collaterals of the vestibular 

 fibres that end around the spinal neurones of Deiters' nucleus. It must not be forgotten that 

 Deiters' nucleus is the origin for important contributions to the posterior longitudinal fasciculus 

 (page my), by which the vestibular impulses impress the nuclei of the motor and, perhaps to a 

 limited degree, also those of the sensory nerves. 



Practical Considerations. — The auditory nerve is rarely the seat of primary 

 disease. It is most frequently affected consecutively to disease of the middle and in 

 ternal ears. It is sometimes, though seldom, paralyzed in fractures of the base of the 

 skull. Operations on this nerve have been performed for relief from persistent 

 and annoying tinnitus. 



THE GLOSSO-PHARYNGEAL NERVE. 



The ninth or glosso-pharyngeal nerve (n. glossopharyngeus) is a mixed nerve, 

 containing motor and sensory fibres, the latter including those transmitting the 

 impulses of the special sense of taste. The motor element is quite small and sup- 

 plies only the stylo-pharyngeus muscle and secretory fibres to the parotid gland, 

 while the sensory fibres are distributed to the mucous membrane of the middle ear, 

 fauces, tongue and pharynx. 



The Nuclei of the Glosso-Pharyngeal, Vagus and Accessory Nerves. — 

 In the description of the medulla (page 1073) attention was called to the presence of  

 nuclei common to a greater or less extent to the series of lower lateral nerves including 

 the seventh, nmth, tenth and vagal part of the eleventh, which, with the exception of 

 the last named, are mixed nerves. The motor fibres of these nerves differ from those 

 of the series of median motor nerves — the third, fourth, sixth and twelfth — (a) in the 

 more lateral situation and less compact grouping of their cells of origin and {b) in 

 the less direct course they follow to reach the surface of the brain. To avoid repeti- 

 tion, the general arrangement and characteristics of the nuclei related to the glosso- 

 pharyngeal, vagus, and accessory part of the eleventh nerve will be here described. 



The Motor Nuclei. — The groups of neurones related to the efferent 

 fibres proceeding from what has been collectively called the vagal complex, 

 embrace the nucleus ambiguus, regarded as a somatic nucleus, and the nucleus 

 dorsalis. which, since it gives origin to fibres supplying involuntary muscle, is 

 considered, in principle at least, as equivalent to a splanchnic or sympathetic 

 component. The dorsal nucleus is mixed, being partly motor and partly sensory, 



