266 THE STRUCTURAL EVIDENCE OF EVOLUTION. 



if they present any ordinal characters resembling those of the 

 Artiodactyla, they are equally shared by certain extinct Perisso- 

 dactyla. 



From the hints above furnished, we may regard the succession 

 of modifications of foot-structure to be nearly as follows : 



Ruminantia. Rhinocerus. Equus. Elephas. 



I I.I 



Omnivora. Palseotherium. Hyracotherium.* 



/ 

 Symborodoa. Palseosyops. Uintatherium. 



\ / / 



* BathmodoD. 



\ / 



* 

 VI. THE ANCESTRAL TYPE OF MAMMALIA EDUCABILIA. 



I trust that I have made it suflBciently obvious that the primi- 

 tive genera of this division of mammals must have been Buno- 

 donts with pentadactyle plantigrade feet. It therefore follows that 

 Elephas was not the descendant of Eohasileus nor Bathmodon in 

 a direct line, but from some common ancestor with tubercular 

 teeth, through Ifasfodon. We may anticipate the discovery of 

 such a genus, and believe that it will not be widely removed from 

 the Eocene Hyopsodus, or perhaps Achcenodon. This will, then, 

 be the primitive ungulate. 



But it will be more than this ; it can not be far removed from 

 the primitive carnivore and the primitive quadrumane. The Car- 

 nivora are all modified bunodonts, and the lower forms ( Ursus 

 Procyon, e. g.) are pentadactyle and plantigrade. As to the 

 Quadrumana, man himself is a pentadactyle plantigrade buno- 

 dont. This view has been already expressed, as follows: "The 

 type of Tomitherium, already described, evidently stands between 

 lemurine monkeys and such small allies of Pdlceotlieriidm with 

 conic tubercular teeth {Oligotomus, Orotlierium,\ etc.), and which 

 abound in the Eocenes of Wyoming. . . . The dentition of the 

 two types is, indeed, but little different in the Quadrumanous and 



* This was called Hipposyus in the original essay — a name which really applies 

 to a different type. (Ed. 1886.) 



f Both these are names for Pliolophus, a close allay of Ilyracotherium. (Ed. 

 1886.) 



