HISTORY OF THE JLITOPTERNA 



503 



the species of ^Diadidphorus, animals 

 considerably taller than a sheep and of 

 heavier build. Their appearance was 

 not unUke that of a short-necked, horn- 

 less antelope, but with the feet of the 

 three-toed horses ! These feet were, 

 however, merely superficially like those 

 of the horses, differing in points of fun- 

 damental significance. In the horses, 

 the reduction of the digits was accom- 

 panied by a readjustment of the carpal 

 and tarsal articulations, so that, in 

 proportion as the median toe was en- 

 larged and the laterals reduced, the 

 weight was shifted more entirely upon 

 the former. This is the method of 

 digital reduction which Kowalevsky 

 called "adaptive" and is exemplified 

 in all existing artiodactyls and perisso- 

 dactyls and by none more perfectly 

 than by the monodactyl horses. In 

 "inadaptive reduction," the method 

 followed by ^Diadiaphorus and the 

 other genera of this family, there was 

 no readjustment, or a very imperfect 

 one, of the articulations, the lateral 

 digits, however small and rudimentary, 

 retaining the connections which they 

 had when they were of full size and 

 function. This distinction may seem 

 to be unimportant, but its signifi- 

 cance is shown by the fact that not 

 a single ungulate with inadaptively 

 reduced feet has survived to the present 

 time. 



XCal'i 



y 



"1 



sOo. 



Lcb 



^ 



M 



Fig. 250.— Left pes of tZ)ia- 

 diaphorus, from specimens 

 in Princeton University and 

 the American Museum. 

 Cal., calcaneum. As., as- 

 tragalus. N., navicular. 

 Cn. S, external cuneiform. 

 Cb., cuboid. 



