LIFE PLANS. 263 



1. Equu$, late Pliocene. Common horse, feet reduced to central series 



of bones (middle finger and toe), a pair of "splints" to rep- 

 resent second and fourth digits. 



2. Pliohip'pus, middle Pliocene. Smaller, central digital series more 



slender; splints more elongated; crown of upper molars 

 shorter, and crescentic areas simpler. 



3. Protohip'pus, early Pliocene. Size of Ass; central digital series 



still more slender; splints terminated by dangling hooflets; 

 ulna long as arm, but slender; fibula rudimentary; crowns of 

 molars much shorter. 



4. Miohip'pus, of late Miocene. Size of sheep ; three functional toes 



before and three behind ; small splint of fifth digit, before ; 

 ulna distinct, long as radius, but very slender at lower end ; 

 fibula co-ossified with tibia at lower end ; molar crowns de- 

 cidedly short; enamel folds much simpler than in horse. 



5. Jfao&q/ptu, of oldest Miocene. Size of sheep ; three functional 



toes before and three behind, but more nearly equal than in 

 Miohippus ; large splint of fifth digit, before ; radius and ulna 

 distinct, and also tibia and fibula. 



6. Orohip'pus, of middle Eocene, of Wyoming and Utah. Size of 



fox ; four functional toes before and three behind ; ulna com- 

 plete and distinct from radius ; tibia and fibula also distinct ; 

 molar crowns exceedingly short ; enamel pattern simple. 



7. Eohip'pus, of oldest Eocene, of New Mexico. Size of fox ; four 



functional toes before and three behind ; rudiments of outer 

 or fifth toe behind, and hence, probably, of first digit before ; 

 hoofs mere thick, broad and blunt claws; molars less spe- 

 cialized than in Orohippus, without cement. 



The affinities, gradations, and successions thus indicated are 

 facts of observation ; they depend on no theory of organic 

 history. They simply show that each type of the past pos- 

 sessed characters which related it to organisms yet future. 

 There was retrospect ; there was anticipation. The past was 

 bound to the present; the present, to the future. History 

 was a constant unfolding of that which was contained in the 

 past. Progress was a perpetual fulfillment of prophecy. 



