340 ANIMAL LIFE PAST AND PRESENT. 



all the birds of the Secondary epoch were provided 

 with teeth, while in some Pterodactyles those organs 

 were wanting as shown in Fig. 45. The most ready 

 means of distinguishing a Pterodactyle from a bird is, 

 however, to be found in the structure of the fore-limb. 

 Thus it will be seen from Fig. 43 that the " hand " of a 

 Pterodactyle carries three fingers furnished with claws, 

 and a fourth extremely elongated finger which has no 

 terminal claw, and supports the membranous wings. 

 It is on the whole probable that this elongated finger 

 corresponds to the little finger of the human hand, the 

 thumb being probably represented by the small splint- 

 like bone seen at the wrist in the figure; and in any 

 case the finger in question is the outermost one, whether 

 it correspond to the ring-finger or the little finger of 

 the human hand. Now in the wing of a bird, on the 

 contrary, neither of the bones corresponding to the 

 fingers are greatly elongated, while the longest of these 

 modified fingers is the one representing the index or 

 fore-finger of the human hand, and is, therefore, the 

 very opposite of the elongated finger of the Flying 

 Dragons. This essential difference between the struc- 

 ture of the wing of a Pterodactyle and that of a bird 

 is of such radical importance as to indicate that the 

 Flying Dragons could not possibly have been the 

 ancestors of birds ; which, as we have mentioned in the 

 preceding chapter, were more probably descended from 

 those extraordinary reptiles known as Dinosaurs. 



The shield-like bone seen in Fig. 43, lying in the 

 middle of the chest in front of the back-bone, corre- 



