432 ANIMAL STUDIES 



fore feet and hind feet, but with the rudiment of the fourth 

 toe in the fore feet, of the same size in Mesohippus, smaller 

 in Miohippus. Also, the middle toe and hoof of the three 

 toes in each foot was distinctly larger than the others in 

 both MesoJiippus and MioMppus. Next came the Proto- 

 hippus, a horse about the size of a donkey, with three toes, 

 but with the two side toes on each foot reduced in size, and 

 probably no longer of use in walking. The middle toe and 

 hoof carried all the weight. Still later in the Tertiary era 



FIG. 253. Extinct four-toed horse (Eohippus) from the Eocene of Wyoming, 16 

 inches high. After W. D. MATTHEW, painting by C. R. KNIGHTI. 



lived the PlioMppus, an " almost complete horse." The side 

 toes of Plioliippus are reduced to mere rudiments or splints. 

 This animal differs from the present horse somewhat in 

 skull, shape of hoof, length of teeth, and other minor de- 

 tails. Lastly came the present horse, Equus, with the 

 splint bones or concealed rudiments of the side toes very 



