THE UNGULATA, OK HOOFED ANIMALS. 127 



of evolution,' may truly be applied to the whole 

 order. All the animals of the present age have be- 

 come what they are, but in scarcely any other case 

 is the process of becoming so obvious, or the transi- 

 tion more perfect : the transition, that is, from the 

 less specialised dentition of the Omnivora to the 

 peculiar jaw of our horses and ruminants, the 

 disappearance of the toes of the five-fingered 

 primary-hoofed animals down to our two-toed 

 ruminants and one-toed horse. 



The basis of the correct classification has long 

 since been given by Owen, who divided all the 

 Hoofed animals into odd-hoofed and pair-hoofed. 

 It is not the number of toes that is the characteris- 

 tic feature, but the distribution of the weight of 

 the body upon the outer parts of the legs, or, what 

 is the same thing, the relation of the lengthened 

 axis of the leg to the middle toe. The Odd-hoofed 

 animals (Perissodactyld) are those with either five, 

 four, or one toe, but where the lengthening of the 

 axis of the upper and lower arm, and upper and 

 lower leg, passes through the middle toe, whereby 

 the middle toe has to bear the main weight even 

 where we have a three, four, or five-toed animal. 

 And Paired-hoofed animals (Artiodactyla) are those 

 where the axis passes between the middle and the 



