ITS ANCESTOES AND EELATIONR. 43 



and species and far more restricted than formerly in 

 geographical distribution. When we consider how 

 extremely imperfect our knowledge of the former 

 inhabitants of the earth must necessarily be, com- 

 pared with that of those now existing, it is remark- 

 able that we have already evidence enough to show 

 that, at any period we may select since the Middle 

 Eocene time, Perissodactyles were far more abun- 

 dant, varied, and widely distributed than they are 

 at present. This is the more interesting, as it is in 

 marked contrast with what we know of the history 

 of the other great division, the Artiodactyles, the 

 latest modification of which, especially the hollow- 

 horned ruminants or Bovidw (antelopes, sheep, or 

 oxen), are now the dominating members of the great 

 Ungulate order, widespread in geographical range, 

 rich in generic and specific variation, and numerous 

 in individuals. 



Of the three existing families of Perissodactyles, 

 the least modified are, compared to their former 

 abundance, in the most decadent state, while the 

 most recently formed, and greatly modified, and 

 most progressive group was until very recently 

 bravely holding its own, in at least one region of its 

 former extensive range. On the great plains of the 

 African continent, zebras and quaggas roamed in 

 countless herds within the memory of living man, 



