TERTIARY FOSSILS. 97 



For example, the elephant, with its short meta- 

 tarsus, is a low form compared with the horse, in 

 which the heel is raised so much above the ground. 

 This is a progress of characters which could be 

 shown in many other families. It is a progress 

 which may be generally described as passing from 

 the phocal form of the hind extremities, through 

 the plantigrade, and ascending to its ultimatum 

 in the digitigrade. Now this progress is coinci- 

 dent with the distribution of the various lines of 

 animals in physical geography, for while the first 

 are marine, the second are generally found in con- 

 nexion Avith shores, rivers, and low grounds, and 

 the last (always the smallest) with the more 

 varied surface of the interior. When we find, 

 then, animals of the second kind most conspicuous 

 in this period, we have actual phenomena re- 

 markably in accordance with the scheme of de- 

 velopment. We look in, as it were, upon the 

 world, or at least, its chief zoological province, at 

 the time when the lines had attained to the terres- 

 trial mammal forms fitted for fluviatile and jungle 

 life, and ere from these had yet sprung the whole 

 of the smaller but more highly organized deni- 

 zens of natm-e's common. 



Our critic, having now run over the whole series 

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