THE CRANIAL NERVES 929 



which link the vestibule with the cerebellum, the nuclei of the motor 

 nerves of the eyeball and the motor cells of tha cord, the nucleus of 

 Deiters has an important relation to the co-ordination of those move- 

 ments mainly concerned in equilibration. Nothing is known of the 

 connections of the vestibular nerve with the cerebrum. Two promi- 

 nent symptoms may be associated with disease of the auditory nerve 

 (a) disturbance 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 connected 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 descending 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 (some- 

 times termed the descending root of the facial, vagus, and glosso-pharyn- 

 geal). It can be traced to the lower boundary of the spinal bulb. 

 Along the mesial border of the fasciculus solitarius are strung out the 

 somewhat scattered nerve-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 cells 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 soli- 

 tarius, 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 cesophageal 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 



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