40 THE MAMMALIA. 



In America, two forms of perfect Solipedes were evolved : 

 Fliohippus — which, like Ilipparion^ was about the size of a 

 donkey — and our modern horse. As the toes can be traced step 

 by step in their modifications, so we can also follow the specialisa- 

 tion of the teeth. This, though very curious, has not kept pace 

 with the extraordinary modification of the toes. The modern 

 horse still possesses 40 teeth, but the first pre-molar, which was a 

 good " working tooth " in Eocene and Miocene species, is in all 

 modern horses rudimentary, functionless, and early lost. The 

 canines also have greatly diminished in size and are rarely present 

 in the mare, so that practically a very large number of adult 

 horses have eight teeth less than their predecessors. 



No fossil Solipede was larger than the horse of modern limes. 

 In this respect, the horse forms rather an exception among the 

 land Mammalia, showing that it is now probably at the highest 

 point of perfection of which the species is capable. The anthro- 

 morphic apes and the genus Equus are amongst the few land 

 Mammalia which can show no extinct members of their order 

 excelling them in size. Man belongs to an order which has not 

 yet degenerated. What his " expectations of life," as a species, 

 may be, can be guessed from the fate of other species. Histori- 

 cally speaking, his endurance may be very long ; geologically 

 speaking, it will probably be brief. 



The Perissodactyls (odd-toed, hoofed animals) survive in a 

 more fragmentary form than perhaps any other sub-order of 

 Mammals. Of the seven principal families of Perissodactyls, 

 three alone survive, and one only has not degenerated in size 

 {Equus.) Of the genus Tapiridae, one family alone — the tapirs — 

 survive. They were represented by an enormous amount of 

 forms, ranging from the Eocene downwards, and varying from the 

 size of a hare to that of a rhinoceros. The rhinoceros is a heavy 

 animal of conservative type, which has managed to exist from 

 Miocene times, and is represented, even in the Eocene, by allied 

 genera, differing chiefly from the existing rhinoceros in possessing 

 no nasal-horns. The most highly specialised form of rhinoceros 

 {R. Tichorrinus, the celebrated woolly rhinoceros), which had the 

 nasal septum completely ossified to support the horns, died out 

 sooner than the less specialised forms. As is well known, it was 



