in North America of rare Extinct Vertebrates. 219 



for swiftness. In the Pliocene and existing Equines (horse, 

 ass, zebra) the phalanges of the second and fourth have ceased 

 to be developed, and their metapodials (ib. fig. 8, ii & iv) 

 are reduced to the farrier's " splint-bones ;" growth has been 

 concentrated on the third digit. With this simplified form of 

 foot speed is maximized and escape from enemies best assured. 

 The safetj of no antecedent Perissodactyle was so provided 

 for. The strategy of Equines is retreat rather than combat ; if 

 driven to defence, the single hoof on the hind foot is launched 

 out at the assailant. 



As a general rule, it may be remarked that no Eocene 

 hoofed mammal bears weapons ; the canines are small when 

 recognizable, so small in some as to have suggested to their 

 discoverer the name " Anoplotheriumj^ or weaponless. Par- 

 tial elevations of the outer table of the skull, analogous to the 

 nasal pair in an old Miocene hornless Rhinoceros* ^ are deve- 

 loped in pairs on other parts of the skull, even on the mandi- 

 ble {Dinoceras e. g.). It is most probable that these large 

 and low obtuse prominences, like the pair in Acerotherium 

 pleurocerosj Duv., and the median one in Camelopardalis, were 

 covered with hairy or callous tegument, not capped wath horn : 

 they cannot be cited as "weapons." One of these singu- 

 lar mammals, the Dinoceras viirabile of Marsh, from the 

 " Eocene of Wyoming," offers the exceptional instance of 

 a pair of upper canines descending, like those of Machairodus 

 and TrichechuSj outside and beyond the lower border of the 

 mandible. 



But the character which is exceptional in the oldest Tertiary 

 Ungulates becomes the rule in the newest ones and in existing 

 species. The Rhinoceroses, e. ,7., have their mesial horns, the 

 Ruminants their parial ones, the Boars their horn-like tusks ; 

 and this better-weaponed condition of herbivorous objects of 

 prey seems to be correlated with concomitant increase in 

 number, size, and force of their carnivorous enemies. 



At the Eocene period Carnivores appear to have been but 

 few and not large. The Hycenodon of Hordwell and of the 

 Eocene sup^rieure du Gard, the Pterodon and Cynodon of the 

 Lignites of Debruge, the Arctocyon of the Eocene infdrieure 

 a la V^re, the Galethylax of the Paris Gyps, the Rhagathe- 

 rium of the Eocene of Mauremont did not acquire the size of 

 a panther. The species of Amphicyon and Hyoinarctos make 

 their appearance at the Miocene period, but are mostly inferior 



* '* C'est du Rhinoceros minutus, G. Cuv., qu'il faut rapprocher un rhino- 

 ceros du Bourbonnais que M. JDuvernoy supposait avoh* deux cornes 

 placees I'une a cote du iiez et I'autre de I'autre cote" (Ossein. Foss., ed. 

 posthum., 8vo). 



15* 



