COMPARATIVE ANATOMY AND EVOLUTION. 9 
sciences ; it is a mere description of nature. But it 
yields a far more accurate knowledge. In many cases 
it discloses, for the first time, the significance of organs, 
and gives to comparative anatomy the confirmation, 
and frequently the possibility of interpretation. The 
wing of a bird, in its individual parts, may be traced 
back without difficulty to B 
the anterior extremities of a 
reptile or a mammal. But 
the leg of a bird, as a com- 
plete organ does not har- 
monize with the leg of other 
vertebrata until the develop- 
ment of the bird in the egg 
reveals that the disposition 
of the segments and of the 
articulations is precisely the - 
same in both cases, and that 
the apparent anomaly is 
produced merely by the 
subsequent anchylosis of 
bones, which generally re- 
main separate. 
The complete leg of the 
bird (A) shows us at a, the 
femur, or thigh bone, and 
at 0, the tibia, or lower leg 
bone; but instead of the 
bones of the tarsus and me- 
tatarsus, the latter of which 
affords attachment to the Fic. x 
toes, we find only the long bone ¢, and at its lower 
