Evourios or tiie iiol'.^i-: i.\ .\.\ri in-: 23 



always picstMit in llic caiiici- stages, hul pro'^i-cssively smallci-. is now 

 liciicrally absent cntirclw I'lic crowns of the teeth an* inucli lonj^er, and 

 of the two liah'-sepa rated inner cohnnns on tlie uppei- molars, one has 

 disappearcMl. the other has incicased in size and changed in foiin. 

 The skull has lengthened and the animal is much larger. 



It is well represented among the fossil horses by the skeleton and 

 skulls of Kquiis scotti already noticed and by skulls, jaws and teeth of 

 other speci(»s from vai'ious localities. 



Fig. 13. Eqnuii. Pleistocene. Tpper teeth, one-half natural *<i/e. Very lonj^- 

 t'ro\\'ned teeth, heavily eemented 



136. Hippidium, Onohippidium. Pleistocene. South America. 

 The feet are hke those of Equus, except that they are short and stout. 

 The teeth are like those of PUohippns, from which it is supposed to be 

 descended. The skull is large and long with very long slender nasal 

 bones. A cast of the skeleton of Hippidhim presented by the Museo 

 Xacional of Buenos Ayres, Argentine Republic, is on exhibition, also a 

 skull cast of Onohippidium. 



CONCLUSIONS 



THESE are the principal stages in the evolution of the modern 

 horse from the httle four-toed Eohippus. Intermediate between 

 them are numerous minor stages, the earher species of each genus 

 being more primitive, the later species more advanced. The series of 

 upper molar teeth shown in Figs. 19-20 show no wide differences from 

 one stage to the next. But between most of them several intermediate 

 species are known. This gradual change is seen not merely in one or a 

 few selected parts, but in every bone, every tooth, every portion of the 

 skeleton. Elsewhere in the hall may be found similar although less com- 

 plete series leading up from animals very close to Eohippus into the 

 modern tapir and rhinoceros. The conclusion is unavoidable that horse, 

 rhinoceros and tapir, three races widely different to-day, are derived 

 through progressive changes from a common ancestral type. NeAV specie-^- 

 ma}' have appeared suddenh', but the race in its !)roader lines is the 

 product of gradual evolution, and diverse races may be traced back to a 

 more ancient common stock. ^ 



-Scientific criticisms of "Darwinism" are concerned with the way in which new species have ap- 

 peared, whether by infinitesimal gradations or by finite " mutations," appreciable although usually small 

 steps. The broader lines of evolution are not affected by these criticisms. 



