I258 CLASS MAMMALIA. 



from this same prolific stock. From this Condylarthrous suborder 

 we have abundant evidence that the two existing suborders of the 

 Artiodactyla and Perissodactyla, now so sharply distinguished, have 

 both taken their origin ; and perhaps the Hyracoidea may also 

 trace their derivation from this group. Another extinct Eocene 

 suborder of Ungulates, comprising the Coryphodons of Europe and 

 America, and the huge and uncouth Dinocerata of the United 

 States, tends to show a connection between the Perissodactyla and 

 Proboscidea, which till recently were referred to distinct orders. 



All living Ungulates, as we shall subsequently mention, are dis- 

 tinguished by the total absence of clavicles, but in the remarkable 

 Tyfiotheriuni, of the Pleistocene of South America, these bones were 

 retained. In its dentition, moreover, that genus shows features 

 now peculiar to the Rodents ; and by its help, together with the 

 evidence afforded by an Eocene group known as the Tillodonts, 

 we can dimly see how the Rodents may have been connected with 

 the ancestors of both the Ungulates and the Carnivores. 



Having seen from these brief notices how intimate appears to 

 have been the relationship between the chief terrestrial orders of 

 Mammals in the Lower Eocene, we may glance at the evidence 

 afforded by the Mammals of the Eocene as to the connection 

 between some of the families of these orders. Among the Car- 

 nivora, no two families are better distinguished than the Dogs, or 

 CanidcE, with their triangular upper molars and digitigrade feet, 

 and the Bears, or Ursidoe, in which the upper molars are rhom- 

 boidal and the feet are plantigrade. In the Eocene, however, we 

 have Aififlhicyon, with the teeth of a Dog and the limbs of a Bear ; 

 and in the later Tertiary the Bear-like Hycznarctus, of which the 

 dentition retains many Dog-like features. So perfect, indeed, is 

 the transition between Dogs and Bears, that it seems convenient to 

 include both groups in a single family. Again, in another direction, 

 the Dogs of the Eocene seem to pass imperceptibly into the Civets 

 ( Viverridce) through Cynodictis ; while it is almost impossible to 

 distinguish the Civets from the Hyaenas on the one hand, and the 

 Cats (Felidce) on the other. Still more remarkable is the apparent 

 connection in the Eocene of the Civets with the Weasels (Mus- 

 telidcz), since these two families are widely sundered at the pres- 

 ent day. 



Turning to the Ungulates, at the present day the Artiodactylate 

 suborder can be readily divided into four sections — viz., the Pigs, 

 or Suina ; the Camels, or Tylopoda ; the Chevrotains, or Tragulina ; 

 and the Cattle and Deer, or Pecora. When, however, we go back 

 to the early Tertiary, we find a complete transition from the Suina 

 to the Pecora ; while it is almost impossible to distinguish Deer 

 from Chevrotains ; and the early Camels exhibit signs of close 



