308 OUTLINES OF EVOLUTIONARY BIOLOGY 



FIG. 153. Outlines of Horses of different Geological Periods, showing their 

 Relative Sizes. (From Lull.) 



a, Praborohippus (Eocene) ; 6, Oroliippus (Eocene) ; c, Mesoliippus (Oligocene) ; d, Meryc- 

 liippus (Miocene); e, Pliohippus (Pliocene) i /, Equus (Receut). 



