308 THE EVOLUTION OF MAN. 



bony parts of the limbs are also formed at first from soft 

 undifferentiated cell-groups of the skin-fibrous layer. These 

 afterwards change into cartilage, and from these the per- 

 manent bones originate by a tertiary process. 184 



The development of the muscles, or the active organs of 

 locomotion, is, as yet, of much less interest than that of the 

 skeleton, or the passive instruments of motion. The Com- 

 parative Anatomy of these is, indeed, of much higher im- 

 portance than their Embryology. But as very little attention 

 has, as yet, been paid to the Comparative Anatomy and 

 Ontogeny of the muscular system, we have only very 

 general ideas of its Phylogeny also. The muscular system 

 as a whole has developed in the most intimate reciprocal 

 correlation with the bone system. 185 



