XI PALEONTOLOGY AND EVOLUTION 359 



mals, the reduction and specialisation of parts in 

 the Anckitherium remain great. 



Is it not probable then, that, just as in the 

 Miocene epoch, we find an ancestral equine form 

 less modified than Equus, so, if we go back 

 to the Eocene epoch, we shall find some quadruped 

 related to the Anchithcrium, as Hipparion is re- 

 lated to Equus, and consequently departing less 

 from the average form ? 



I think that this desideratum is very nearly, if 

 not quite, supplied by PlagiolopJius, remains of 

 which occur abundantly in some parts of the 

 Upper and Middle Eocene formations. The 

 patterns of the grinding-teeth of Plagiolophus are 

 similar to those of Anchitherium, and their crowns 

 are as thinly covered with cement; but the 

 grinders diminish in size forwards, and the last 

 lower molar has a large hind lobe, convex outwards 

 and concave inwards, as in Palwotherium. The 

 ulna is complete and much larger than in any of 

 the Eqiiidm, while it is more slender than in most 

 of the true Palccotheria ; it is fixedly united, but 

 not ankylosed, with the radius. There are three 

 toes in the fore limb, the outer ones being slender, 

 but less attenuated than in the Equidm. The 

 femur is more like that of the Palccotheria than 

 that of the horse, and has only a small depression 

 above its outer condyle in the place of the great 

 fossa which is so obvious in the Equidcc. The fibula 

 is distinct, but very slender, and its distal end is 



