760 



THE THEORY OF TRANSFORMATIONS 



[CH. 



Ungulates, the group which includes the rhinoceros, the tapir, 

 and the horse. 



Let us begin by choosing as our type the skull of Hyrachyiis 

 agrarius, Cope, from the Middle Eocene of North America, as 



Fig. ,39.3. The pelves of Archaeopteryx and of Apatornis, with three 

 transitional types interpolated between them. 



figured by Osborn in his Monograph of the Extinct Rhino- 

 ceroses* (Fig. 394). 



The many other forms of primitive rhinoceros described in 

 the monograph differ from Hyrachyus in various details — in the 

 characters of the teeth, sometimes in the number of the toes, and 

 BO forth ; and they also differ very considerably in the general 



* Mem. Amer. Mus. of Nat. Hist, i, iii, 1898. 



