1881.] , Origin of the Foot Structures of the Ungulates. 271 
the Eocene genera, the slender median digit could not have sus-~ 
tained the weight on a hinge, without great risk of dislocation. 
This explanation it can be said, applies only to the posterior foot. 
The posterior foot has, however, led the way in the evolution of 
Ungulata, and the fore foot may have followed in accordance 
with the law of antero-posterior symmetry in growth. A curi- 
ously malformed deer from Mendocino county, Cal., throws some 
Fic. 4. 
Fic, 3. 
Fic, 3.—Right posterior foot of Protohippus sejt 
one-half natural size. From Repor S. Geol. 
S 
uctus Cope, from Colorado, about 
Surv. Terrs. F. V. Hayd : 
ight posterior foot of Poébrotherium labiatum Cope, from Colorado, 
Fie. 4.-—Righ 
three-fifths nat. size. From Hayden’s Report, Iv, Pl. Cxv. 
light on this subject. It has apparently a single functional digit 
on each foot. Examination shows that the posterior foot is 
_ bidigital, but that the phalanges are fused; while the anterior 
foot is perissodactyle, all the digits but the third being rudimen- 
