PLATE 39 



REDUCTION OF CARPUS IN MIOCENE EQUID^E. 



DIAGRAMS SHOWING RELATIONS OF CARPAL BONES TO MEDIAN METATARSAL, AND PROGRESSIVE REDUCTION OF THE VESTIGIAL 



FIFTH DIGIT. 



All figures one-half natural size. 



1- 3 Outer side of carpus 



8-10 " " " " 



15-17 " " " " 



4- 7 Inner " " " 



H_14. " « « " 



18-20 " " " " 



Middle Oligocene 15, 18 Mesohippus (M. bairdii, referred specimen, Am. Mus. 9777). Unciform facet on Mtc. 



Ill vertical, giving ulna no support on cannon bone. Fifth digit a short splint. 

 Upper Oligocene 16, 19 Miohippus (M. gidleyi, referred specimen, Am. Mus. 1195). Unciform facet slightly 



oblique. 



Uppermost Oligocene 17, 20 Kalobatippus (K. agatensis, type, Am. Mus. 14211). Unciform facet somewhat 



oblique; trapezium more lateral in position. 

 Middle Miocene 8, 11 Hypohippus (H. osborni, type, Am. Mus. 9407). Unciform facet on Mtc. V greatly 



reduced; Mtc. II giving some support to magnum. 

 Middle Miocene 9, 10, 12, 13, 14 Parahippus (9, 13 P. pawhiensis atavus, type, 1 Am. Mus. 14233; 10, 12 P. tyleri, 



referred specimen, Am. Mus. 13767; 14 Parahippus, Am. Mus. 14182). Unciform 



facet on Mtc. Ill oblique, fifth metacarpal a very short splint or nodule, trapezium 



lateral in this and following genera. 

 " " 2, 6 Merychippus (2 M. isoncsus primus, referred specimen, Am. Mus. 14179; 6 M. copla- 



cidus, type, Am. Mus. 9397). Unciform facet on cannon bone oblique, fifth 



metacarpal a small nodular rudiment. 

 Lower Pliocene 1, 4, 5 Hipparion (1, 4 H. whitneyi Gidley, type, Am. Mus. 9815; 5 H. gracile, drawing from 



Gaudry's figure). Unciform facet on cannon bone more horizontal, Mtc. V a 



small nodule, magnum facet on Mtc. II oblique or in some species reduced and 



vertical, a condition that might lead to trapezoid acquiring a footing upon the 



cannon bone. 



Lower Pliocene 3, 7 Pliohippus ? spec, referred specimen, Am. Mus. 10690. Unciform facet on Mtc. 



Ill more horizontal, fifth metacarpal a vestigial nodule. 



1 See also parts of type skeleton, Am. Mus. 14233, Plate 38. 



300 



