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Fig. 1.—Evolution of the horse. Stages passed through from the earhest four-toed Eohippus (upper left) to the three-toed Mesohippus (upper middle) to a form with the side toes reduced (Merychippus, upper right) to the small, clumsy, one-toed Equus scotti (lower left) to the modern horse (lower right).
Reproduced from photographs by W. E. Corbin of fos§ils found in successive layers of rocks and now preserved in the Museum at Amherst College.
