426 M E M O I R S 0/ the 
within its cavity, prelents itfelf to view, being furnifhed wfth fo 
many capillary veflel?, that when each of them is diflended with 
blood, it appears Ibmewhat like the Rete mirabile : This mem- 
brane is de-figned for admirable ufes, as fliall be prefently /laewn : 
I. By its very fine produ8ion clofing up the entrance to the laby- 
rinth, it hinders the pure and fubtile air that is lodged within its 
various cavities and meanders, from having at lead: a free commu- 
nication with that grofs air that is received thro' the aqueduct 
into the cavity of the Tympanum, i. This membrane gently 
warms the bony bafis of the labyrinth with the heat of the blood 
contained in the veffels, with which it is furniflied 5 and at the 
fame time cheriflies and preferves the motion of the air included 
in both the VeftibuU, and in all their winding canals, as alfo of 
that defecated Lympba impregnated with animal fpirits, where- 
with each fhoot of the ^ortio Mollis p^ th^^ ear is moiftcned. 
'". This membrane does alfo contain within its cavities air very 
much rarefied by the gentle heat of the blood in irs veflels, which 
being exceeding fine and plentifully impregnated with the ethereal 
matter, it is greatly fitted eafily to receive all the impreflions of 
fonorous objeds, and convey them quickly to the air, and to each 
branch of the Tortio Mollis, wherewith the infide of the labyrinth 
is furnifhed, as alfo to the Centrum Ovale of the brain 5 from 
what has been jull mentioned, it plainly follows that this mem- 
brane admirably contributes to the fenle of hearing 5 for being of 
a fine and curious texture, it gives both a free ingrefs and egrels 
to all the impreffions of lonorous bodies, which arc tranfmitted 
to it, as foon as they are communicated to the circumambient air, 
by the motion of that aethereal matter wherewith the air is im- 
pregnated, which pervades the innumerable fmall Foramina oi the 
external membrane of x}[\tTympamm^2iX\d, likewile by theinterpo- 
fition of the aqu^dudt 5 and according to Vieujjens every impret 
fion of found, by means of the air contained within the cavities 
of this membrane, as alfo of the circumambient external air, impreg- 
nated with asthereal matter, is in a moment conveyed into the 
labyrinth thro' its \Porta and Feneftray and from thence tranfimt- 
ted to the Centrum Ovale of the brain by means of the animal ipirits, 
where divers ideas of different fpecies and different denomina- 
tions are excited in the mind according to the diverfity of the 
impreffions of fonorous bodies 3 the truth of which is confirmed 
by experience^ for when the purulent matter of an impofthume 
within the Jpcphyfis Majloides, or within the Tympanum itlelf, 
has quite corroded this membrane, the fenfe of hearing is either 
much impaired or entirely loft : From what has been laid, it 
plainly 
