94 THE NERVOUS SYSTEM 



with the pharyngeal branch of the vagus to form the pharyngeal 

 plexus (p. 96). They supply sensory fibres to the mucous 

 membrane of the pharynx and inhibitory fibres to the con- 

 strictor muscles. 



The few motor fibres in the glosso-pharyngeal nerve supply 

 the stylo-pharyngeus, which aids in the elevation of the thyreoid 

 cartilage during the act of deglutition. It is possible that the 

 motor fibres supplied to the tensor veli palatini by the otic 

 ganglion (p. 70) are ultimately derived from the glosso- 

 pharyngeal through the tympanic plexus (vide supra). 



The glosso-pharyngeal nerve is never affected alone. The 

 motor nucleus is involved in bulbar paralysis (p. 108) and the 

 trunk of the nerve may be involved in syphilitic meningitis in 

 the posterior cranial fossa, but, in both cases, the tenth and 

 the eleventh nerves are also affected, owing to the close rela- 

 tionship which exists between the three nerves, as regards both 

 their nuclei and their intra-cranial course (Figs. 35 and 47). 



The Vagus or Tenth Cerebral Nerve possesses both motor 

 and sensory fibres. The motor fibres arise from the nucleus 

 ambiguus, an elongated column of grey matter which extends 

 downwards through the medulla oblongata and becomes con- 

 tinuous with the anterior column of grey matter in the spinal 

 medulla (Fig. 47). 



The sensory fibres end partly in the nucleus of the tractns 

 solitarius and partly in the nucleus dorsalis, which lies in the 

 dorsal part of the medulla oblongata immediately under the 

 lower part of the floor of the fourth ventricle (Fig. 47). 



The emerging fibres of the vagus pass forwards through the 

 medulla oblongata and appear in the groove between the olive 

 and the restiform body, immediately below the rootlets of the 

 glosso-pharyngeal nerve (Fig. 8). 



Together with the latter and the accessory nerve, the vagus 

 leaves the skull through the jugular foramen and, in this part 

 of its course, it exhibits an enlargement, which is termed the 

 jugular ganglion. 



