[ 2o8 J 
late neceflity, in fuch lungs as thofe of birds, out of 
which the air can find a paffage into other cavities; 
for if the lungs were loofe in the cavity of the 
thorax , as is the cafe in all other animals, their 
cells could not be expanded, either by the depreffion 
of the diaphragm, or the elevation of the ribs ; 
lince the air ruthing in, to fill Op the vacuum in the 
cavity of the cheft, occafioned by thefe actions, 
would take theflraight road from the trachea through 
thofe pafTages ; and, of confequence, expand no part 
of the lungs which lay out of that line, whereby 
refpiration would be totally prevented ; it would be 
exactly the fame cafe, as when the lungs are fo 
much wounded, in other animals, as to allow of a 
free paffage for the air into the cavity of the 
thorax , &c. 
Of the Internal openings of the lungs. 
The openings in the lungs, by which they com- 
municate air to the other parts, are as follow : 
The membrane, or diaphragm above mentioned, 
is perforated in feveral places, with pretty large 
holes, which admit of a free paffage, between the 
cells of the lungs and the abdomen. A communi- 
cation which has frequently been noticed. 
To each of thefe perforations is joined a diftindt 
membranous bag, which is extremely thin and 
tranfparent; it receives the air, and being after- 
wards continued through the abdomen , gets attach- 
ments to many of thofe parts with which it comes 
in contadf. 
5 
There 
