110 HUMAN PHYSIOLOGY. 



Deep Origin. By two roots from the floor of the 4th ventricle, each 

 root consisting of a number of gray filaments, some of which decussate in 

 the median line; the external root has a gangliform enlargement contain- 

 ing fusiform nerve cells. 



Distribution. The two roots wind around the restiform bodies and 

 enter the internal auditory meatus, and divide into an anterior branch 

 distributed to the cochlea, and a posterior branch distributed to the vesti- 

 bule and semicircular canals. 



Properties. They are soft in consistence, grayish in color, consisting 

 of axis cylinders with a medullary sheath only; they are not sensible to 

 ordinary impressions, but convey the impression of sound. 



Function. Governs the sense of hearing. Receives and conducts to 

 the brain the impression of sound, which gives rise to the sensations of 

 hearing. 



gth Pair. Glosso-pharyngeal. 



Apparent Origin. Partly from the medulla oblongata and the inferior 

 peduncles of the cerebellum. 



Deep Origin. From the lower portion of the gray substance in the 

 floor of the 4th ventricle. 



This nerve has two ganglia ; the jugular ganglion includes only a por- 

 tion of the root filaments ; the ganglion of Andersch includes all the fibres 

 of the trunk. 



Distribution. The trunk of the nerve passes downward and forward, 

 receiving near the ganglion of Andersch fibres from the facial and pneu- 

 mogastric nerves. It divides into two large branches, one of which is 

 distributed to the base of the tongue, the other to the pharynx. In its 

 course it sends filaments to the otic ganglion ; a tympanic branch which 

 gives sensibility to the mucous membrane of the fenestra rotunda, fenestra 

 ovalis, and Eustachian tube; lingual branches to the base of the tongue; 

 palatal branches to the soft palate, uvula and tonsils ; pharyngeal branches 

 to the mucous membrane of the pharynx. 



Properties. Irritation of the roots at their origin calls forth evidences 

 of pain ; it is, therefore, a sensory nerve, but its sensibility is not so acute 

 as that of the trifacial. Irritation of the trunk after its exit from the 

 cranium produces contraction of the muscles of the palate and pharynx, 

 due to the presence of anastomosing motor fibres. 



Division of the nerve abolishes sensibility in the structures to which it is 

 distributed, and impairs the sense of taste in the posterior third of the 

 tongue (see Sense of Taste). 



