PEDIGREES — THE FOUNDERS OF THE HOUSE. 225 



representing the stock from which the birds 

 arose. 



The first of these is that remarkable group of 

 extinct flying reptilia known as the pterodadyles, 

 the wing-fingered lizards, and there is certainly 

 much to be said, at first sight, for the probability 

 of an alliance with these. The structure of the 

 skull favours this view most. The power of 

 flight and the fact that the bones were pneu- 

 matic have also been urged as valid reasons 

 for this relationship. 



We may take the wing, I think, as the crucial 

 test, and upon the likeness of this to that of the 

 bird the whole claim must rest. To bring out 

 the full significance of this we will enlarge upon 

 our remarks in chapter IV., and endeavour to 

 show, by comparison, how the wings of the 

 pterodactyle, the bat, and the bird, are all 

 modifications of one common type — a five- 

 fingered hand. 



In the wings of all these it is the fingers, or 

 more exactly the hand, which have undergone 

 the greatest changes in this transformation into 

 the wing. 



In the pterodactyle all five fingers are re- 

 tained. The first four, however, are greatly 

 reduced in size. Three of them are provided 

 with small claws, and probably served to sus- 

 pend their possessor to some rock or tree during 

 rest, just as the bat to-day hooks himself up by 

 the tiny toes of his hind-feet. The fifth, or little, 

 finger was enormously developed, and served as 

 a support to a membrane formed by a drawing 

 out, so to speak, of the skin of the body. 

 P 



