1-158-745 - Oxford Science Archive/Heritage Images

Evolution of the horse, c1920. Diagram of seven stages in the development of hind and forelimbs: 1,1A Eohippus; 2,2A Orohippus; 3,3A Mesohippus; 4,4A Hypohippus; 5,5A Merychippus; 6,6A Hipparion; 7,7A modern horse. Over time the toes shorten and disappear.