EVOLUTION OK THE HORSE 24; 



the molar teeth is, too, ;i httle different from that of Eq-uus. Proto- 

 lii'ppus of the Xorth American I'hocene is also three-toed, but the 

 two additionally-developed toes are smaller than in ffipj^arion. 

 Otlier forms are dealt with below in connexion with the ancestry 

 of rerissixlactyles. It is a curious fact about Hi2}]}arion, which 

 is not now regarded as on the direct line of ei|uiue descent, that 

 the edges of the enamel plates of the molars may show a coni- 

 phcated folding very like that presented by that clearly terminal 

 form of rerisKodactyle Ufe, the gigantic Ulasmothcrinm. This is 

 indicative of high speciahsation, which ended in extinction. 



Ancestry of the Horses. — The Lophiodontidae and the 

 Palaeotheriidae are two of the most interesting extinct families 

 of Perissodactyles ; for among them we find what would appear 

 to be the ancestral forms of both the existing 'I'apirs and Horses. 

 The Ehinoceroses also would seem to be deri^-able from the 

 Palaeotheriidae. The very vagueness of the characters of these 

 creatures, considered from a classificatory point of ^'iew, has led to 

 much diversity in their placing. This though gratifying to the 

 e\'olutionist is tiresome to the writer who wishes to give a 

 methodical account of their various characters. It will be best 

 perhaps not to attempt an accurate placing or to reconcile con- 

 flicting opinion, but to give some saUent features of osteology 

 which lead to the belief in their relationship to existing groups of 

 Perissodactyles. A book upon the history of mammals would be 

 incomplete without some account of that well- ascertained series of 

 forms which seem to connect these primitive Perissodactyles with 

 the modern Horse. Eqtius, in fact, is not only the " show horse " 

 of the doctrine of evolution, but also the " stalking horse." 



In the Eocene of both Europe and America are met with a 

 number of forms from which we may start. Hyracotlicrium, 

 regarded on the one hand as the type of a sub-family of the 

 Eijuidae themselves, and on the other as a meml)er of the family 

 Lophiodontidae, was a small -sized animal, three feet or so in 

 length ; it possesses the complete Eutherian dentition with a slight 

 diastema. The orbits are not separated from the temporal fossa ; 

 the fore-limbs were four-toed, the hind three-toed, with moderately 

 long metapodia, especially on the hind-feet. The shoulder blade 



Soc. 1900, ]J. 379) in the cave whioli produced tlie remains of Glossothcriv m. A 

 piece of skin covered -vvitli Fox-red hair, possibly spotted with paler areas, is believed 

 to be a relic of OnoMppidnim. 



