46 THE STRUCTURE AND LIFE OF BIRDS cnap, 
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 §. 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 pterodacty!’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. 
