ME.AfOIR OF CASIFElt. 
47 
pecially in birds of prey, all the bones wbieb can 
eoimnunicate with the chest or abdomen, are filled 
air, and I have demonstrated the foramina by 
which the air regularly enters and issues, with the 
■•espiration. The air which thus fills the ctivitios, 
tnust necessarily become lighter, as affected liy the 
temperature of the body, so that the weight of the 
ttnimals must thus become specifically less than that 
ef the air, thereby enabling them to fly will) much 
greater facility.” «■ 
He then remarks, that traces of these osseous air- 
t'ells are to be found in some other animals, and that 
there is an instance of it even in man, in the bony 
protuberance behind the ear, which is filled with air, 
received from the common air-passages ; and he 
tliaw's some conclusions respecting the use of the 
toarrow, the growth and reparation of bone, and the 
formation of callus, which are imjiortant in a phy- 
siological and pathologii’al point of view. 
This interesting subject he prosecuted with great 
^dour for a succession of years. As already stated, 
'6 immediately demonstrated tlie discovery to his 
***> and sent a memoir on the subject to the 
Flavian Society of Rotterdam ; and next year 
transmitted a paper to L’Academie des Science,!, 
'loh afterwards appeared in its Transactions — a 
proof, as the Professor remarks, lliat at this e[)och 
no one bad previously known this singular structure. 
tnost (Sula alia) will present one of tlie 
eauti.ul illustrations of this curious structure Eu. 
