PLATE 51 



ADAPTIVE REDUCTION OF TARSUS IN ANCHITHERIIN^E AND IN HIPPARION. 



DIAGRAMS SHOWING RELATIONS OF LATERAL TARSALS TO MEDIAN METATARSAL. 



All figures natural size. 



Figs. 1-3, 7-10 inner side of tarsus; Figs. 4-6, 11-14 outer side of tarsus. 



Middle Oligocene 7, 11 



Upper Oligocene 



S, 9, 12, 13 



Uppermost Oligocene 1, 4, 10, 14 



Middle Miocene 



Lower Pliocene 



3,6 



Mesohippus (J\I. bairdii, referred specimen, Am. Mus. 670). Cannon bone articu- 

 lates with ectocuneiform only, giving no support either to cuboid or internal 

 cuneiform. 



Miohippus (S, 12 M. gidleyi, referred specimen, Am. Mus. 705; 9, 13 M. equiceps, 

 referred specimen, Am. Mus. 7262). Cannon bone articulates with ectocunei- 

 form and cuboid but gives no support to inner cuneiform. 



Kalobatippus (1,4 A*, agatensis, type, Am. Mus. 14211; 10, 14 K. prcestans, type, Am. 

 Mus. 7269). Cannon bone articulates with ectocuneiform, cuboid, and inner 

 cuneiform, the two latter articulations narrow, oblique. 



Hypohippus (II. osborni, type, Am. Mus. 9407). Cannon bone articulates with 

 entocuneiform, cuboid, and inner cuneiform, the cuboid articulation somewhat 

 oblique. 



Hipparion (II. whitneyi, type, Am. Mus. 9S15). Cannon bone articulates with ecto- 

 cuneiform and cuboid but does not support inner cuneiform. 



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