NEW SCIENCE OF PALEONTOLOGY 



The terminal phalanx, or coffin-bone, has a shallow 

 median bone in front, as in many species of this group 

 in the later tertiary. The fourth digit exceeds the 

 second in size, and the second is much the shortest of 

 all. Its metacarpal bone is considerably curved out- 

 ward. In the hind-foot of this genus there are but 

 three digits. The fourth metatarsal is much larger 

 than the second. 



" The larger number of equine mammals now known 

 from the tertiary deposits of this country, and their 

 regular distributions through the subdivisions of this 

 formation, afford a good opportunity to ascertain the 

 probable descent of the modern horse. The Ameri- 

 can representative of the latter is the extinct Equus 

 fraternus (Leidy), a species almost, if not wholly, 

 identical with the Old World Equus caballus (Lin- 

 naeus), to which our recent horse belongs. Huxley 

 has traced successfully the later genealogy of the horse 

 through European extinct forms, but the line in Amer- 

 ica was probably a more direct one, and the record is 

 more complete. Taking, then, as the extreme of a 

 series, Orohippus agilis (Marsh), from the eocene, and 

 Equus fraternus (Leidy), from the quaternary, interme- 

 diate forms may be intercalated with considerable cer- 

 tainty from thirty or more well-marked species that 

 lived in the intervening periods. The natural line of 

 descent would seem to be through the following genera : 

 Orohippus, of the eocene; Miohippus and Anchithe- 

 rium, of the miocene; Anchippus, Hipparion, Proto- 

 hippus, Pliohippus, of the pliocene ; and Equus , quater- 

 nary and recent. 



" The most marked changes undergone by the suc- 



109 



