ix.]' PALEONTOLOGY AND EVOLUTION. 197 



Another series of closely affiliated forms, though the 

 evidence they afford is perhaps less complete than that 

 of the Equine series, is presented to us by the Dicho- 

 bune of the Eocene epoch, the Cainotherium of the 

 Miocene, and the Tragulida, or so-called " Musk-deer," 

 of the present day. 



The Tragulidce have no incisors in the upper jaw, and 

 only six grinding-teeth on each side of each jaw ; while 

 the canine is moved up to the outer incisor, and there is 

 a diastema, in the lower jaw. There are four complete 

 toes on the hind foot, but the middle metatarsals usually 

 become, sooner or later, ankylosed into a cannon bone. 

 The navicular and the cuboid unite, and the distal end 

 of the fibula is ankylosed with the tibia. 



In Cainotherium and Dichobune the upper incisors are 

 fully developed. There are seven grinders ; the teeth 

 form a continuous series without a diastema. The meta- 

 tarsals, the navicular and cuboid, and the distal end of 

 the fibula, remain free. In the Cainotherium, also, the 

 second metacarpal is developed, but is much shorter than 

 the third, while the fifth is absent or rudimentary. In 

 this respect it resembles Anoplotherium secundarium. 

 This circumstance, and the peculiar pattern of the upper 

 molars in Cainotherium, lead me to hesitate in considering 

 it as the actual ancestor of the modern Tragulidce. If 

 Dichobune has a four-toed fore foot (though I am inclined 

 to suspect that it resembles Cainotherium) , it will be a 

 better representative of the oldest forms of the Traguline 

 series; but Dichobune occurs in the Middle Eocene, 

 and is, in fact, the oldest known artiodactyle mammal. 

 Where, then, must we look for its five-toed ancestor ? 



If we follow down other lines of recent and tertiary 

 Ungulata, the same question presents itself. The Pigs 

 are traceable back through the Miocene epoch to the 

 Upper Eocene, where they appear in the two well-marked 



