COMPARATIVE ANATOMY AND EVOLUTION. 



9 



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 com- 

 parative anatomy the confirmation, and frequently the pos- 

 sibility of interpretation. The ^ ^ 

 wing of a bird, in its individ- 

 ual parts, may be traced back 

 without difficulty to the an- 

 terior extremities of a rep- 

 tile or a mammal. But the 

 leg of a bird, as a complete 

 organ does not harmonize 

 with the leg of other verte- 

 brata until the development 

 of the bird in the t.%% reveals 

 that the disposition of the 

 segments and of the articula- 

 tions is precisely the same 

 in both cases, and that the 

 apparent anomaly is pro- 

 duced merely by the subse- 

 quent anchylosis of bones, 

 which generally remain sep- 

 arate. 



The complete leg of the 

 bird (A) shows us at a, the 

 femur, or thigh bone, and 

 at 6, the tibia, or lower leg 

 bone; but instead of the 



bones of the tarsus and metatarsus, the latter of which 

 affords attachment to the toes, we find only the long bone 

 c, and at its lower extremity a small bone supporting the 



