46 THE STRUCTURE AND LIFE OF BIRDS chap. 



projecting from the wrist, and which may be a remnant 

 of the first metacarpal or only a sesamoid bone [see Fig. 

 17 (1)]. The wing is a great sheet of membrane sup- 

 ported by this ulnar finger, which was of enormous, 

 length, and also by the leg and tail. Thus, whereas 

 two fingers united help in the formation of the bird's 

 wing, only one forms part of the pterodactyl's, for the 

 other three are little clawed appendages of no use in 

 flight. Whether these fingers in the bird be Nos. 3 and 

 4, or 2 and 3 makes little difference. There are two, 

 not one only, and there is no sign that the smaller one 

 is likely to disappear, and the larger one being No. 2 

 or 3 does not correspond to the pterodactyl's ulnar 

 finger which is No. 4 or 5. The two together form a 

 short stout bone that contrasts forcibly with the ptero- 

 dactyl's finger of which the one striking characteristic 

 is its length. Besides the question of fingers the whole 

 build of the pterodactyl's wing is different. It gets 

 its expanse from its great membrane. The bird ob- 

 tains from its feathers its spread of canvas, while the 

 pterodactyl has no feathers at all. Its wing, formed by 

 a membrane stretched from the arm to the leg and to 

 the tail, was more like a bat's wing than a bird's. But 

 here again there is an important difference. All the 

 bat's digits except the thumb help to support the wing, 

 in the pterodactyl only this one ulnar finger. 



We must, therefore, look for other evidence of the 

 kinship of pterodactyls to birds. Take the head first. 

 The pterodactyl had a large brain case and, for a 

 reptile, an extraordinarily high forehead. The orbits 

 of his eyes were large. The bones of his skull were 

 light and became fused together at an early age. 



