III.] HORSES. 75 



mains of these animals occur only in the superficial deposits, they 

 are met with abundantly in the Miocene and Pliocene deposits 

 of Europe and Asia, as well as in the United States; and it is 

 accordingly clear that the group was once widely distributed over 

 the northern hemisphere, whence its surviving members have 

 wandered southwards to Malaysia in the east and South America 

 in the west. 



Till introduced by the early Spanish settlers, horses, which are 

 now so abundant in the pampas, were totally un- H orses 

 known in South America in a living state, although 

 their fossilised remains occur commonly in the Pampean, as well 

 as in the somewhat older deposits of Parana, and Monte Hermoso. 

 They are, however, entirely unknown in the Santa Cruz beds. 

 Some of these fossil Argentine horses belong to the typical genus 

 Equus\ while others, on account of the simpler structure of their 

 molar teeth and the great length of the slits in the skull beneath 

 the nasal bones, are referred to a separate genus, under the name 

 of Hippidium. A third genus (Onohippidimn) is distinguished 

 from the latter by a large lachrymal depression in the bones of the 

 sides of the face, corresponding to the so-called larmier of the deer. 

 Fossil species of Equus occur in the Plistocene deposits of the 

 whole northern hemisphere, while those of the United States yield 

 remains of a genus (Pliohippus] nearly allied to the South American 

 Hippidium; and as both these genera are the descendants of 

 extinct forms whose remains occur in the older Tertiaries of the 

 same hemisphere, the extinct South American horses must likewise 

 be classed with the groups that have entered the country from the 

 north. Why these Plistocene South American Equida became 

 extinct in a country so admirably suited to their existence as 

 Argentina, is a question to which it is impossible to find a 

 satisfactory answer. With the horses we reach the last of the 

 Neogaeic representatives of the more typical ungulates, that is to 

 say the Artiodactyla and Perissodactyla ; and we pass on to the 

 other extinct subordinal groups, at least three of which, as already 

 said, are peculiar to it. 



From the preceding paragraphs it will be apparent that, if we 

 except the deer, horses, and the guanacos and their 

 allies, South America, so far as the Artiodactyla and 



