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 
oer: 7. Cy AS GR 
eS PET BS sa20 Gass ioe ~ 
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 
