274 FACULTIES OF BIRDS. 
cavity common to the chest and abdomen; while 
the great office of decarbonization of the blood is 
securely performed, advantage is taken to let the air 
into all the cavities, even into those of the bones. 
“The weight of the body being a necessary con- 
comitant of muscular strength, we see why birds, 
by reason of their lightness, as well as by the con- 
formation of their skeleton, walk badly. And, on 
the other hand, in observing how this lightness is 
adapted for flight, it is remarkable how small an ad- 
dition to their body will prevent them rising on the 
wing. If the griffin-vulture be frightened after his 
repast, he must disgorge before he flies; and the 
condor, in the same circumstances, is taken by the 
Indians, like a quadruped, by throwing the lasso 
over it. It is interesting to notice the relations of 
great functions in the animal economy: birds are 
Oviparous, because they never could have risen on 
the wing had they been viviparous ; if the full stom- 
ach of a carnivorous bird retard its flight, we per- 
ceiyg that it could not have carried its young. The 
light body, the quill-feathers, the bill, and the laying 
of eggs, are all necessarily connected. 
‘** As every one must have observed, the breast- 
bone of birds extends the whole length of the body ; 
and owing to this extension, a lesser degree of mo- 
tion suffices to respiration; so that a greater surface, 
necessary for the lodgment and attachment of the 
muscles of the wings, is obtained, while that surface 
is less disturbed by the action of breathing, and is 
more steady. Another peculiarity of the skeleton 
of the bird is the consolidation of the vertebre of 
the back; a proof, if any were now necessary, that 
the whole system of bones conforms to that of the 
extremities, the firmer texture of the bones of the 
trunk being a part of the provision for the attach- 
ment of the muscles of the wings. The ostrich and 
cassowary, which are rather runners than fliers, 
have the spine loose. 
