UNQULATA. 341 



bunodonts, like their existing representatives, had a simple 

 stomach and did not chew the cud ; and it seems likely that the 

 powers of rumination were only acquired by the more specialized 

 artiodactyls in the latter half of the Tertiary period. 



The existing pigs and peccaries, or Suidae, are the least- 

 altered descendants of the primitive Artiodactyla. They are 

 all bunodont animals, with the canine teeth more or less 

 well-developed. Their carpal and tarsal bones, their meta- 

 carpals and metatarsals are never completely fused together, 

 and rarely indeed exhibit any tendency to fusion; while the 

 ulna and fibula are always complete and separate from the 

 radius and tibia. Fragmentary remains of genera of this type 

 can already be recognized among the fossils of the Lower 

 Eocene both in Europe and North America ; and the fully- 

 differentiated characteristic artiodactyl astragalus is known 

 from deposits of this remote period in France (Rheims), 

 Wyoming, and New Mexico. The earliest forms are note- 

 worthy on account of the upper molars being more or less 

 quadrate in shape and considerably wider than the lower 

 molars a condition persistent among the ruminants through- 

 out the course of their evolution, but not observed among 

 the later and true pigs, in which the upper and lower molars 

 are almost equally narrow. As the series of Suidse and their 

 allies are traced upwards, the molars sometimes exhibit phases 

 of development curiously parallel with those to be noticed 

 among the Proboscidea. Listriodon, from the Middle Miocene 

 of Europe, exhibits lophodont teeth remarkably similar to 

 those of JJinotherium ; the molars of many pigs are miniatures 

 of the corresponding teeth of Mastodon ; while the hinder-most 

 true molar of the existing wart-hog (Phacochcerus) of Africa is 

 in structure not unlike the molar of Elephas. It is also to be 

 observed that, except in such persistent old types as the 

 peccaries, the canines become transformed into tusks of per- 

 sistent growth. 



Homacodon (fig. 196). Small animals not larger than rabbits. The 

 brain-case is moderately large, with a sharp sagittal crest ; the orbital 

 cavity is not separated by bone from the temporal fossa. The dentition 

 seems to have been complete, i.e., comprising the usual 44 teeth. The 



