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In the ostrich, no air gets into the os humeri ; 
but it enters every other part, as defcribed above, in 
very large quantities. In the common fowl, no 
air appears to enter any bone but the os humeri. 
The wood-cock has none either in the firftbone of 
the wing, or in the thigh-bones. On the other 
hand, in the pelican, the air pafies on to the ulna 
and radius , and into thofe bones which anfwer to 
the carpus and metacarpus of quadrupeds. 
Thus then, the abdomen , the cells furrounding 
the pericardium , the lower and fore part of the 
neck, the axilla , the cellular membrane under the 
pedtoral mufcles, &c. all communicate with the 
lungs, and are capable of being filled with air; and 
again, from thofe cells the Jlernum, ribs, ’vertebra of the 
back and loins, bones of the pelvis, oJJ'a burner or urn, 
and ojfa femorum , can, in many birds, be furnifhed 
with air. 
This fupply, of the bones with air, is not wholly 
by means of the lungs ; for the cells of the bones of 
the head, in fome birds, are filled with it, of which 
the owl is a remarkable inftance. In this bird, the 
diploe between the two plates of the fcull is cellular, 
and admits a confiderable quantity of air, which is 
furnifhed by the Euftachian tube. 
Some authors confidered the diploe , in the cranium 
of a bird, as a continuation of the mamillary pro- 
cefs * ; and have looked upon it as a circumftance 
peculiar to tinging birds ; but this is not the cafe. 
'* The only thing fimilar to this communication, in birds, of 
the cells of bones with the external air, is that of the internal, 
ear of quadrupeds, by the Euftachian tube. 
3 
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