434 M E M O IR S of the 
fi-iuts it, as long as the mufcles of the internal ear are at reft 5 
but on the contrary, when either of its mufcles is contrafled, it 
opens italirtle: The fecond aperture, which is almoft round, 
VieuJJens calls the jfanua Labyrinthi^ becaufe it gives admiffion 
into the Imall and nearly round cavity, which leads to the laby- 
rinth i for this cavity communicates not only with the extremity 
of the lemi-oval fpiral du6t of the Cochlea^ but likewife with 
the Concha^ by a linall chink in its bads, and conlequently with 
the femi-circular du(^ls hereafter to be defcribed; x\\t J^nna is 
covered and clofed up with a very thin fmall membrane, which, 
by its curious texture, gives an eafy admiflion into the labyrinth 
to the ethereal matrer, charged with the impreffions of fonorous 
bodies : Behind the Janua LahyrintJoi is a fmall cavity, by Vi- 
euffens called the Veftibulum primum, and becaufe it leads to the 
Cochlea and Concha^ by '2)u Verney^ the Veftibulum Labyrinthi j 
io that the three lemicircular du6is of the labyrinth, together 
with the Cochlea are, as it were, its two apartments ieparated 
from each other by the Concha^ and yet at the fame time commu- 
nicating together by means thereof^ and therefore Vieuffens calls 
it the Veftibulum Secundum of the labyrinth : That very fine 
membrane, which doles up the jfanua Labyrinthi, expands it- 
felf into its Veftibulum ^rimum^ covers all its internal fuperficies, 
and confequently clofes externally the fmall chink in the balls of 
the Concha^ together with the extremity of the Cochlea j lb that 
it adheres to theie very fine nervous membranes which cover the 
internal parts of the Cochlea-, and Concha^ and by their means 
communicates with the 'Portio Mollis of the ear. 
The Veftibulum Secundum^ which is the fame with the Concha 
of ancient anatomifts, is much larger than the Veftibulum Tri- 
f?jum^ its cavity, which is nearly round, is about two lines in di- 
ameter 5 ib that in adults it may contain about two grains of wheat, 
when divided into three or four parts, as Vieujffens tried feveral 
times; in it are obferved nine apertures, viz. two fmall, and 
almoft imperceptible Foramina^ which receive two fmall branches 
of the Portio Jllcllis of the ear j again, there is a pretty long 
chink in its bafis, and Ibmewhat winding ^ and an oval aperture 
in that fide, which regards the cavity of the Tympanum, called 
by ancient anatomifts Feneftra Ovalis 5 and laftly, the mouths of 
the three femi-circular duds, which are only five in number 5 for 
the fuperior lemi-circular du(^, in that place where it regards the 
poftenor parts of the head, is lb united with the inferior lemi- 
circular du(51-, as that both open by one common aperture into the 
interior parts of the Concha-^ for which reafon Vieujjhis calls it, 
as 
