432 MEMOIRS of the 
diflecling human lubje£ls, that both the external and internal 
membranes of the Tympanum^ nay, and fon^times the greater 
portion of its mufcle was wanting, thefe parts having been cor- 
rupted, nay entirely wafted by the fharp purulent matter of an 
impofthume, either in the Cellula of the ^pophyfis Maftoides 
or in the cavity of the tympanum itfelf ; and yet in all the lub- 
jefts, wherein one or both ears had an impofthume, the fenfe of 
hearing was not entirely loft in the ear affedted, as he learned 
from the perlbns themfelves while alive . 
VieuJJefis upon weighing attentively, whether both mufcles of 
the internal ear moved voluntarily or not, was of opinion, that 
they are put into motion, partly by the will, partly by imprel- 
fions received from Ibnorouv"? bodies, without the knowledge, and 
ibmetimes againft the will of the foul j {o that they move partly 
voluntarily and partly involuntarily ; and m reality it is very proba- 
ble that, by the fame aft of the will, by which we are determined 
to hear any thing eafily and diftindtly, the animal fpirits are alio 
determined to flow towards thefe mufcles, in order to promote 
their motion, by which means the perception of a found is 
rendered more expeditious and diftinft ^ yet ftill the motion of 
the mufcles of the internal ear cannot be faid to be merely volun- 
tary, fince every one by his own experience may be convinced, 
they often move contrary to his inclination : And the cafe being 
fo, there is no other extrinfic caufe to determine the mufcles of 
the internal ear to motion, than the asthereal matter, charged 
with the impreflions of for^orous bodies 5 and that fuch a caufe 
excites them to motion in the following manner, Vieuffens thinks 
is very probable ; when the ^ethereal matter arrives at the exter- 
nal membrane of the ^lympcinum^ in repeated vibrations, which 
are ibmetimes quicker and ibmetimes ilower, it is almoft entirely 
conveyed into its cavity, and both then, and when it pervades its 
pores, it ftrikes that membrane, and protrudes it towards the in- 
ternal parts of the head ; upon which it drives the extremity of 
the handle of the Malleus^ conne6kd to it, from the Meatus 
^mlitorius towards the cavity of the 'Tympanum^ and elevates it, 
and at the fame time deprefle«s its head, together with the IncuSy 
faftened thereto ; whilft the head of the Malleus and the Incus 
are thus deprcfled, they draw towards them the two tendons of 
the monogaftric mufcle of the internal ear, extend the whole mufl 
c\^y and difpofe it in iuch a manner as to acquire an elafticity 
fitted to promote its contraction ; but fmce the vibrations of the 
air impregnated with the jethereal matter, tho' they follow quick 
upon eacii other, are always diftinguiihable by certain fmall in- 
tervals 
