18 



To-day the " even-toed/' or artiodactyla, greatly predominate. 

 The distinction between these two sub-orders, differentiated at 

 the base of the Eocene, really rests, not upon the number 

 of toes in each foot, but upon the position of the axis of 

 the limb, which in the older perissodactjl types was central, the 

 weight of the body resting on the longer and larger middle, or 

 third, toe or finger, whether there were two or four others present 

 fully developed or not. In these " odd-toes," or mesaxonia, as 

 Marsh prefers to term them, the first and fifth toes were the first 

 to lose touch of ground, to dwindle gradually away and become 

 finally absorbed. In the next stage the second and fourth toes 

 were similarly affected, as in the case of the modern horse, the 

 North American Indian's "beast with one finger nail," adapted 

 for rapid " tip-toe " progression on hardest ground. 



In the "even-toes,^' or ai'tiodactyl type, on the contrary, the 

 axis of the limb was shifted from the central toe to the space 

 between the third and fourth toes, which thus became equally 

 developed in the cloven foot. As the weight of the body was 

 thrown more on them they both increased in size and strength, 

 also at the expense of the two outsiders, which, therefore, 

 dwindled away until at last they became lost entirely in the 

 various stages of structural modification, which resulted in the 

 numerous forms of ada.ption from slow, flat-footed locomotion on 

 swampy soil, to dainty, swift, " tiptoe " progression on hard 

 ground. In other words, the mesaxonia have one big toe in the 

 centre of the foot, while the paraxonia, better off, have two 

 equally divided. 



'J'he structure of the extinct Dinocerata throws much light on 

 the interesting question of the coming into being of the great 

 group of hoofed quadrupeds which have played, and may still 

 continue to play, so far as the even-toed paraxonian line is 

 concerned, such an important part in the economy of nature. 

 The discovery of so many varied and well-defined forms of 

 ungulates and other mammalia in the Eocene deposits necessarily 

 antedates the first appearance of the class upon earth. Unfor- 

 tunately, the land areas or shores of the extensive Cretaceous 

 oceans in America have not yet been developed, but a group of 

 small-brained, hornless, flat-footed ungulates, with five fully- 

 developed toes on each foot, the axis being central, probably 

 existed at that epoch. 



The proto-ungulata, or "' first hoofs," Marsh considers to be 

 directly represented to-day by the existing coney [Ryrax) of 

 Scripture, which must not be confounded with the rabbit, though 



