THE ANCESTRY OF THE HORSE 169 
the toes were not the only changes that were 
required to transform the progeny of the Hy- 
racothere into a horse. These are the most 
evident ; but the increased complexity in the 
structure of the teeth was quite as important. 
HIPPOTHERIUM EQUUS EXCELSUS EQUUS CABALLUS: LINN 
{SONESUM. COPE LEJDY “DOMESTIC HORSE 
of the Horse. 
The teeth of gnawing animals have often been 
compared to a chisel which is made of a steel 
plate with soft iron backing, and the teeth of 
a horse, or of other grass-eating animals, are 
simply an elaboration of this idea. The hard 
