OF EVOLUTION. 63 



lacks full confirmation that the embryo horse is 

 polydactyl. These are important facts bearing 

 upon the developmental history of the animal. 



The cameline animals, especially those of the 

 New World, present a connecting series or chain 

 almost as complete as that which has been estab- 

 lished for the horse. The existing animals of this 

 group, in common with other ruminants, have 

 the bones of the middle-foot (the metapodials) 

 united into a single " cannon-bone," as in the deer, 

 but they differ strikingly from all other mem- 

 bers of the broad group which they represent 

 in possessing a pair of incisor teeth in the upper 

 jaw. By some naturalists the absence of superior 

 cutting teeth in the ruminants has been supposed 

 to stand in direct connection with the develop- 

 ment of horns, but just in what manner has not 

 been definitely determined. It is, however, an 

 interesting circumstance, that the cameline forms, 

 almost alone among ruminants, are entirely des- 

 titute of horns, while they possess the peculiar 

 dental character above referred to. 



