428 The American Naturalist. [May, 
With the assumption of the digitigrade position however, — 
the plantar pad was reduced, the foot became more elongated, 
and the strain became more localized. In this position of the _ 
foot the weight of the body falls upon the phalanges, which 
are now bent at a considerable angle upon the metapodials, 
and an especial strain is produced by the flexor tendons where a 
they pass over the distal ends of the metapodials. In a foot of — 
this type therefore, do we find a considerable advance in the 
development of the median keel and lateral grooves of the 
metapodials? Those of the third digit are most advanced for — 
the reason that the strain is more concentrated and localized — 
FIGURE 2.—Modern Tapir. Posterior or plantar surface of the hind foot. 
at this point. In none of the metapodials however, do the 
lateral grooves and keel extend more than half-way around 
the articular ends, nor does the keel rise but little above the 
lateral boundaries of the grooves. This is well shown in such 
forms as the tapir, rhinoceros, Hyracotherium and nearly 
the Eocene Perissodactyla. While the foot remained in the 
digitigrade position, the median keel of the metapodials made 
little or no impression upon the lower edge of the articular 
surface of the proximal phalanx, for the reason that the main 
flexure of the foot was between the first phalanges and the 
