16 



THE HOESE 



first digit (pollex or hallux) has only been found in some 

 extremely ancient and primitive forms. 



It will not be necessary to enter into any descrip- 

 tion of the remaining anatomical characters by which 

 these two groups are distinguished, although, as before 

 said, they are very marked, and pervade almost every 

 portion of their organisation. The differential cha- 

 racters of the feet can be readily appreciated, even by 

 those who have little anatomical knowledge, and suffice 

 to show the fundamental distinction between them. 



Having now eliminated from consideration all 

 mammals but ungulates, and all ungulates but perisso- 

 dactyles, we may henceforth confine our attention solely 

 to this group, as it is the one which contains the horse 

 and all its nearest relatives, and we must first endeavour 

 to trace its history back in geological time as far as our 

 available records will take us. 



It is now well known that mammals existed far 

 back into the secondary or mesozoic age, as far back as 

 the Rhsetic or uppermost beds of the Triassic system ; 

 but these had none of the characters of ungulates. 

 They were all very small in size, and apparently more 

 nearly allied to the Marsupialia and Insectivora than to 

 any other existing orders. Until quite recently not a 

 trace of any mammal had been found in any of the 

 strata attributed to the great Cretaceous epoch. The 

 blank has, however, been partially filled up by the dis- 



