

THE AUDITORY. 551 



paralysis. Various explanations are given to account for these phe- 

 nomena. By some writers they are referred exclusively to the motor 

 properties of the chorda tympani. If the fibres of this nerve which 

 accompany the branches of the lingual in their peripheral distribution 

 have an influence upon the circulation and secretion in the tongue 

 similar to that which they exert in the submaxillary gland, it is plain 

 that when these actions are depressed by section of the chorda tym- 

 pani, the sense of taste may be diminished in the corresponding parts 

 as an indirect result of its paralysis. Others, on the contrary, attri- 

 bute this effect to sensitive fibres in the chorda tympani, which convey 

 the impressions of sapid substances directly from without inward, and 

 which, of course, cease their action when the nerve is divided. The 

 indications obtained by experiment on this point are as yet too obscure 

 to allow of a decisive opinion. The precise manner in which the chorda 

 tympani takes a share in the exercise of the sense of taste is more or 

 less a matter of uncertainty. But there is no question that its paralysis 

 interferes, to an appreciable degree, with this sense; and an alteration 

 of the taste, accompanying facial paralysis upon the same side, is a 

 symptom which fixes the location of the nervous lesion at some point 

 inside the stylomastoid foramen. 



Eighth Pair, The Auditory. 



On the posterior surface of the medulla oblongata, a little behind the 

 widest part of the fourth ventricle, a number of white striations run 

 from the neighborhood of the median line, transversely outward, toward 

 the posterior edge of the peduncles of the cerebellum. These striations, 

 which are sometimes exceedingly distinct, represent the commencement 

 of the roots of the auditory nerve. The nucleus from which they 

 originate is a mass of gray substance situated directly beneath them, 

 containing nerve cells of various form and size, some of which belong 

 to the smaller variety, while some of them, according to Dean, are 

 among the largest of those met with in the nervous system. The gray 

 matter of the nucleus, at its lateral portion, extends outward and upward 

 toward the white substance of the cerebellum, with which it is connected 

 by numerous bundles of radiating fibres. 



The fibres originating from this ganglion partly run directly outward 

 in a superficial course, forming the white striations visible at this point, 

 and, uniting with each other, curve round the posterior border of the 

 peduncles of the cerebellum to reach the lateral surface of the medulla 

 at the lower edge of the pons Varolii. Some of them follow a deeper 

 course, passing obliquely through the substance of the medulla outward 

 and downward to the same point. These fibres, united with each other, 

 form the posterior root of the auditory nerve. 



The anterior root consists of fibres which are traced backward from 

 their point of emergence, partly to the floor of the fourth ventricle, but 

 also in. great measure, according to Clarke, Dean, and Henle, into the 

 white substance of the cerebellum, where they mingle with fibres coming 



