THE CENTRAL NERVOUS SYSTEM 825 



important relation to the co-ordination of those movements mainly 

 concerned in equilibration. Nothing is known of the connections 

 of the vestibular nerve with the cerebrum. Two prominent symp- 

 toms may be associated with disease of the auditory nerve (a) dis- 

 turbance or loss of hearing ; (b] loss or impairment of equilibration. 



The ninth or glosso-pharyngeal nerve comprises both sensory and 

 motor fibres sensory for the posterior third of the tongue and the 

 mucous membrane of the back of the mouth, motor for the middle 

 constrictor of the pharynx and the stylo-pharyngeus. It also 

 contains the nerves of taste for the posterior third of the tongue. 

 The efferent fibres arise from a nucleus (motor nucleus of the glosso- 

 pharyngeal} a little posterior to the facial nucleus. The afferent 

 fibres take origin from unipolar cells in ganglia of spinal type con- 

 nected with the nerve (ganglion petrosum and ganglion superius). 

 Entering the medulla oblongata, the central processes of these cells 

 bifurcate into ascending and descending branches. Their peripheral 

 processes pursue their course as the axons of sensory fibres to the 

 structures to which the nerve is distributed. The ascending 

 branches terminate in a nucleus (principal nucleus of the glosso- 

 pharyngeal} beneath the floor of the fourth ventricle. The descend- 

 ing branches, as well as similar branches from the pars intermedia 

 of the seventh nerve and from the afferent fibres of the vagus, form 

 a bundle called the fasciculus solitarius (sometimes termed the 

 descending root of the facial, vagus, and glosso-pharyngeal}. It can 

 be traced to the lower boundary of the spinal bulb. Along the 

 mesial border of the fasciculus solitarius are strung out the some- 

 what scattered n'erve-cells (descending nucleus of facial, vagus, and 

 glosso-pharyngeal}, around which the descending branches arborize. 

 At its upper end the grey matter of the fasciculus solitarius is con- 

 tinuous with the principal nuclei of the glosso-pharyngeal and vagus. 



The tenth nerve, or vagus, also contains both motor and sensory 

 fibres. The efferent fibres arise partly from the nucleus ambiguus 

 or ventral nucleus of the vagus, a collection of large nerve-cells 

 situated in the reticular formation, and extending from a point 

 a little below the facial nucleus to a point a little above the lower 

 limit of the medulla oblongata, where it becomes continuous with 

 the column of ceils from which the spinal fibres of the eleventh nerve 

 take origin. A second nucleus of origin for efferent vagus fibres is 

 constituted by the upper part of the dorsal accessory-vagus nucleus, 

 a collection of rather small cells extending from a little below the 

 lower margin of the pons to nearly the level of the first cervical nerve. 



The afferent fibres of the vagus arise from unipolar cells in ganglia 

 connected with the nerve (ganglion jugulare, ganglion nodosum). 

 In the medulla oblongata they bifurcate, like other fibres coming 

 off from the cells of ganglia of spinal type. The ascending branches, 

 which are short, terminate in the upper sensory or principal nucleus, 

 and the descending branches, which are long, in the cells of the 

 fasciculus solitarius, just as in the case of the glosso-pharyngeus. 



The motor fibres of the vagus are partly derived from the accessory, 

 whose internal branch joins the vagus not far from its origin. The 

 distribution of the nerve is more extensive than that of any other in 

 the body. The oesophagus receives both motor and sensory branches 

 from the oesophageal plexus. The pharyngeal branch of the vagus 

 is the chief motor nerve of the pharynx and soft palate (including 

 the tensor palati). The superior laryngeal branch is the nerve of 

 common sensation for the larynx above the vocal cords, and the 

 motor nerve of the crico-thyriod muscle. The inferior or recurrent 



