208 THE STORY OF BIRD-LIFE. 



tinctly bird-like ia type. Nevertheless matiy of 

 these bird-like characters undoubtedly bespeak a 

 reptilian origin. 



In many points Archceopteryx and the embryo 

 or nestlings of modern birds exactly agree, and 

 both point to a more generalized ancestral type. 

 The two most important of these differences are 

 concerned with the skeleton of the wing and leg. 



We have reason to believe that both these 

 limbs possessed at one time five digits a-piece. 

 Gradually two of them vanished from the wing, 

 and at least one from the foot. In the adults 

 of modern birds the three bones of the middle- 

 hand, called the metacarpals, are all so completely 

 blended as to give the impression that they have 

 all been cast, as it were, in a single mould, whilst 

 the three bones that go to form the middle bones 

 of the foot, or metatarsals, are welded into a 

 single solid shaft, without betraying the slight- 

 est indication that they ever were distinct. In 

 the young bird, however, this shaft is traversed 

 by three fine seams suggesting that originally 

 there were three separate bones. In the still 

 younger bird or embryo, not only do we find 

 these bones actually sejDarate, but we get evidence 

 of there having been as many &sfive digits, as in 

 the reptilian foot. The fourth exists in many 

 living and fossil birds as the hallux or hind-toes. 

 No bird, living or extinct, is known in which the 

 fifth toe is present. The fifth toe of the Dorking 

 fowl is simply a double hallux or hind-toe. 



In the wing, as in the foot, in the young bird 

 the three metacarpals, so completely welded in 

 the adult, are distinctly traceable as separate 



