204 HUMAN PHYSIOLOGY. 



vestibular nerves at their origin, is followed by a loss of the power of coordina- 

 tion and equilibration. 



Functions. The cochlear nerve presides over the sense of hearing. It 

 carries to the brain the nerve impulses produced by the impact of atmospheric 

 vibrations on the ear, and which give rise to the sensation of sound. The 

 vestibular nerve carries nerve impulses to the brain, which excite certain 

 reflex adaptive movements by which the equilibrium of the body is maintained. 



Ninth Nerve. Glossopharyngeal. 



Origin. From nerve-cells in the ganglia situated on the trunk of the nerve 

 near the medulla oblongata viz., the petrosal ganglion and the jugular 

 ganglion. From these cells a single branch emerges, which soon divides into 

 two branches, one of which passes centrally, the other peripherally. The 

 centrally directed branches enter the medulla oblongata, where they terminate 

 around nerve-cells. The peripherally directed branches collectively form the 

 two main divisions from which the nerve takes its name. 



The glossopharyngeal also contains efferent nerve-fibers, which have their 

 origin in nerve-cells beneath the floor of the fourth ventricle. 



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

 receiving near the jugular ganglion fibers from the facial and pneumogastric 

 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 sensor nerve, but its sensibility is not so acute as 

 that of the trigeminal. Irritation of the trunk after its exit from the cranium 

 produces contraction of the muscles of the palate and pharynx, owing to the 

 presence of motor fibers. 



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). 



Function. Governs the sensibility of the pharynx, presides partly over 

 the sense of taste, and controls reflex movements of deglutition and vomiting. 



