228 THE STORY OF BIRD-LIFE. 



closely-applied fingers form a sort of rod or 

 bar, continuous with the bones of the forearm. 

 Along this is found not a large, thin membrane 

 stretched between the wing and the body, as in 

 the bat, but a marvellously arranged series of stiff 

 feathers which w^e call quill-feathers. These 

 are so arranged that they let the wind pass 

 through the wing on the upstroke, but offer 

 an unyielding, sail-like surface on the down- 

 stroke, and thus make flight possible. You 

 will thus realise at once the great difference in 

 the mechanism by which flight is effected in the 

 pterodactyle and the bird, a difference so great 

 that we cannot well imagine the one form of 

 wing to have been derived from the other. 



The other claimant urged upon us as the most 

 probable ancestor, is the house that culminated 

 in the unwieldy dinosaur. That is to say, the 

 bird and the dinosaur both derive their origin in 

 all probability from the same stock. 



We rely for our evidence more particularly 

 upon the curious similarity of the hip-girdle and 

 the hind-limb, the similarity of these limbs in the 

 two forms being very striking : whilst the likeness 

 of the shoulder-girdle of each is scarcely less so. 



Let us compare the shoulder-girdle first. 



In the bird we have a long, curved, rod- 

 like bone, the scapula or blade-bone ; this rests 

 upon the ribs. One end is directed tailwards, 

 and is free ; the other, which is directed down- 

 wards and forwards, joins a second but often 

 shorter bone, the coracoid, as it is called. To 

 these is added the furcula or merry-thought; 

 the free ends of this are fixed by ligaments or 



