THE FORERUNNERS OF THE HORSE 263 



made at certain points of the chain, it seems 

 advisable to raise Professor Osborn's Anchi- 

 theriincB and Hyracotheriince to the rank of families, 

 so that the horse-line will be represented by the 

 three families EquidcB, AnchitheriidcB^ and Hyraco- 

 tkeriida;. 



Of these the Anchitheriidce will be character- 

 ised by the retention of functional lateral toes, by 

 the shortness of the crowns of the cheek-teeth and 

 their open valleys, unencumbered by cement, and 

 by incompleteness of the bony ring round the eye- 

 socket. The members of this family are of special 

 interest as indicating the passage from small marsh- 

 dwelling animals to types fitted for browsing in 

 forests ; these last passing in their turn into the 

 grazing and plain-dwelling Equidcs. Writing from 

 this point of view of the Miocene epoch in North 

 America, Professor Lull ^ remarks that — 



" This was a time of continental elevation and 

 great expansion of our western prairies and a con- 

 sequent diminution of the forest-clad areas. Many 

 mammals otherwise fitted for survival, such as the 

 titanotheres whose remains are very numerous in 

 the Oligocene beds, were unable to meet the new 

 conditions because of their very perfect adaptation 

 to softer herbage, and thus became extinct. This 

 was also true of certain horses, such as Hypohipptcs, 

 but the great majority were more plastic and in 



' Op. ciL, p. 177. 



