THE EQUID^E, OR HORSES. 



213 



line begins in the Early Eocene with, the Eoliippus 

 of the size of a fox, which possessed, in addition to 

 the four well-developed toes of the fore-foot, the 

 remnants of a fifth. According to a remark of 

 Marsh's, this animal, in foot and dentition, al- 

 ready shows unmistakably that with it commenced 

 the branching off of the progenitors of the horse 



d 



rA 



nr m 



FIG. 38. Foot of the Fossil Horses of North America. 

 a, Orohippus ; 6, Mesohippus ; c, Miohippus ; d, Protohippus ; e, Equus. 



from the other Odd-hoofed animals : * in the next 

 higher division of the Eocene, another genus 

 (Orohippus, Fig. 38) makes its appearance, replacing 

 Eoliippus , and showing a greater though still dis- 

 tant resemblance to the equine type. The rudi- 

 mentary first digit of the fore-foot has disappeared, 



and the last premolar has gone over to the molar 

 20 



