1 66 THE ARCTOG^IC REALM. [CHAP. 



American Eocene, is, however, the proximate ancestor of the 

 horse-family (Equid<z)\ and we have thus evidence that the fore- 

 runners of both the horses and tapirs were widely spread over the 

 whole of northern Arctogaea. Hyracotherium, it may be observed, 

 had the typical forty-four teeth characteristic of the earlier euther- 

 ians, and four toes to the front, and three to the hind feet; but in 

 the still earlier Phenacodus, which seems to be the ultimate 

 ancestor of the horses, each foot was furnished with five complete 

 toes. As other instances of the community between the early 

 Tertiary mammalian fauna of the northern halves of the two 

 hemispheres, we may cite the genus Pachynolophus of the middle 

 and upper Eocene of Europe and the Bridger Eocene of the United 

 States, which connects Hyracotherium with the under-mentioned 

 horse-like animals ; and also Hyrachyus, typically from the 

 Bridger, but probably occurring in the French phosphorites ; the 

 latter being more nearly related to the rhinoceroses. 



FlG. 36. LEFT UPPER CHEEK-TEETH OF Palceotheri 



Passing by several less important genera confined to one or 

 the other hemispheres, we come to the family Pal&otheriidce, 

 which is an ill-defined one including forms connecting the pre- 

 ceding with the undoubted Equidce. Here the typical Oligocene 

 genus Pal&otheriuni) which includes large tapir-like animals with 

 three toes to each foot, is exclusively European. The same is the 

 case with the contemporary Anchilophus, represented by smaller 

 forms with more decidedly horse-like affinities; but with the 

 Miocene and upper Oligocene Anchitherium, used in its wider 

 sense, we once more come to a genus common to Western and 

 Eastern Arctogaea. In this genus the jaws are provided with the 

 typical forty-four teeth; but the last lower molar has generally lost 

 the third lobe found in the preceding forms ; the fifth metacarpal 

 bone being still represented by a splint. In the small A. 



