266 THE HORSE AND ITS RELATIVES 



distinguished by the presence of a large preorbital 

 pit in the skull. 



Akin to Hypohippus, which was at one time 

 regarded as inseparable from the Old World genus, 

 is the European Anchitheriu77t, typically repre- 

 sented by A . aurelianense (rom the Middle Miocene 

 freshwater beds of Sansan, in Gers, France, and 

 other equivalent continental formations, which was 

 known to science long before the discovery of 

 the allied American forms. Anckitherium was 

 an animal of the approximate size of a sheep, 

 and, in addition to its broad, short-crowned cheek- 

 teeth, is specially characterised by the rudiment 

 of the pit, or " mark," in the centre of the 

 summits of the crowns of the incisor teeth, which, 

 as we have seen, attains such a large development 

 in the modern horse and its relatives. In Ancki- 

 therium the pits were, however, developed only 

 in the permanent incisors. The lateral toes in 

 each foot are considerably smaller than the central 

 one, but probably touched the ground in walking. 

 Another feature is that the ulna in the fore-limb 

 and the fibula in the hind one form complete 

 although slender bones, which are, however, seve- 

 rally united with the radius and tibia. In the 

 horse they are represented only by their upper 

 extremities. In many respects Anckitherium and 

 its relatives approximate to the well-known PalcBO- 

 tkeriuni, of the European Oligocene, and the two 



