122 ANIMALS OF THE PAST 



bones left by the animals of a million yester- 

 days. Thus we find that certain characters 

 distinguish the bone of a mammal from that 

 of a bird, a reptile, or a fish, and these in turn 

 from one another, and this constitutes the 

 A B C of comparative anatomy. And, in a 

 like manner, the bones of the various divisions 

 of these main groups have to a greater or less 

 extent their own distinguishing characteristics, 

 so that by first comparing the bones of extinct 

 animals with those of creatures that are now 

 living we are enabled to recognize their nearest 

 existing relative, and then by comparing them 

 with one another we learn the relations they 

 bore in the ancient world. But it must be 

 borne in mind that some of the early beasts 

 were so very different from those of to-day 

 that until pretty much their entire structure 

 was known there was nothing with which to 

 compare odd bones. Had but a single incom- 

 plete specimen of Triceratops come to light 

 we should be very much in the dark concern- 

 ing him ; and although remains of some thirty 

 individuals have been discovered, these have 

 been so imperfect that we are very far from 



