( 888 ) 
fluous Moifture is contain’d in them for we may reafona* 
bly fuppofe, as in all other Cavities of the Body, there are 
certain Glands for feparating proper Liquors convenient 
for the ufes dehgn’d ; fo here there feems to be a ne- 
cefTity for feparating a certain quantity of Moifture, 
fit to lubrifie the Mufcles of the OfTicles, and facilitate 
their Motion; as alfo to preferve the Memhrana Tjm 
fmi from becoming too dry. This drynefs of the 
Memhrana Tympani, and the thicknefs of the Liquor 
feparated by thefe Glands, is often the caufe of a Deaf- 
neis in Human Subjedls ; efpecially thofe that are ad- 
vanc’d in Age. This cellulous Strudure of the Cavitas 
Tympmiy (eems to be very proper for receiving of the 
fuperfluous Humidity ; and thefe Communications are 
requifite for conveying it from one Cellule to another, till 
it is emptyed into the ReceptacuJum Commune the Aque- 
duct, whereof hereafter. 
This firft or cellulous Cavity is two Inches broad, and 
reaches from the Crena Tympani to the foramen Ovale^ 
or entry into the Fefttbulumy which is (hut by the 
Stapes, The fecond Part of this Cavity is more fuper- 
ficial (Fig^ II. fr), in form not unlike a Pear, from a 
narrow beginning becoming broader and more fuperfi- 
cial, terminating Semicircularly, fmooth in the Bottom, 
and having feveral incurvated Lines running acrofs it ; 
it reaches much farther than the Veflibulum, being one 
Inch five Lines from before to behind, and one Inch 
tranfverfiy where broadefi:. What fuperfluous Moi- 
flure it contains is difeharg’d into the fore«named A- 
quedu6l. 
Befide the above-mentioned ufes for thefe two Ca- 
vities, viz» to receive and dilcharge the fuperfluous 
Moifture; they are alfo moft beneficial and afiifiing 
to the Hearing ; for, no fooner is the external Air mo- 
dulated, and thc^ Memh^m Tympani mov’d thereby, 
than 
