l] OF THE EQUIDAE 7 



Three years ago the American Museum set on foot under the 

 direction of Prof. Henry Fairfield Osborn a special exploration 

 into the fossil history of the horse. " The object was to connect 

 all the links between the Lower Eocene five-toed, and Lower 

 Pleistocene one-toed horses and to ascertain the relations of 

 the latter to the horses, asses, and zebras of Eurasia and Africa. 

 The first great result obtained is the proof of the multiple 

 nature of horse evolution during the American Oligocene and 

 Miocene. Instead of a single series as formerly supposed there 

 are five, one leading to Neohipparion the most specialized 

 antelope-like horse which has ever been found, a second of inter- 

 mediate form probably leading through Protohippus to Equus 

 as Leidy and Marsh supposed, a third leading to the Upper 

 Miocene Hypohijjpus, a persistently primitive probably forest or 

 swamp-living horse with short crown teeth adapted to browsing 

 rather than grazing, and three spreading toes ; this horse has 

 recently been found in China also. A fourth and fifth line of 

 Oligocene-Miocene horses became early extinct. This poly- 

 phjdetic or multiple law," says Prof Osborn \ "is quite in 

 harmony with the multiple origin of the historic and recent 

 races of horses as recently established by Ridgeway and Ewart. 

 The Pliocene horse of America still requires further exploration 

 before we can positively affirm either that all the links to Equus 

 are complete, or that America is indubitably the source of this 

 genus. The Lower Pleistocene of America exhibits a great 

 variety of races ranging in size from horses far more diminutive 

 than the smallest Shetland to those exceeding the very largest 

 modern draught breeds. Yet all these races became extinct, 

 not surviving into the human period, as was the case in South 

 America. The relation of these North American races to 

 those of South America and of Asia and Africa is again a 

 subject requiring further investigation in which it is necessary 

 to exercise the most extreme accuracy." 



In the recent Equidae each foot consists of a single complex 

 digit, but digits ii. and iv. are complete in the embryo and also 

 survive though degraded in the adult, and there is a callosity 



1 "Evolution of the Horse," a paper read before the British Association 

 (Section D), Tuesday, Aug. 23, 1904 (Nature, 22 Sep. 1904, p. 520). 



