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 difiiculty, to 

 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 ti.e 

 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 ^, 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 



Fig. I. 



toes, we find only the long bone c, and at its lower 



