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- 

 ceive 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 vertebrae 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. 



