546 On the Effect of Impacts and Strains [July, 
their great speed). Among ungulates they are very imperfect in 
the Proboscidea. The orders mention- 2 
ed all have elastic pads on the under 
sides of their feet or toes. The same is 
true of the lowest types of both the Av- 
tiodactyla and Perissodactyla, the hip- 
popotami and rhinoceroses. In the 
Ruminantia the trochlee are well de- 
veloped. (figure 10) with one ex- 
Fic. 5. Fic. 6. Fic. 8. Fic. 7. 
Fic. 5.—Distal extremity of tibia of Amblyctonus sinosus Cope. Fic. 6,—Distal 
extremity of tibia of Oxyena morsitan$ Cope. Both flesh-eaters and two-thirds nat- 
ural size. From Report Expl. and Surv. W. of 1ooth Mer., G. M. Wheeler, rv, Pt. 11. 
Fic. 7.— End of tibia and astragalus of Archelurus debilis. Fic. 8.— Femur of 
Nimravus gomphodus. Carnivora, one-third natural size. Mus. Cope. 
,.ception, and that is the distal metacarpal and metatarsal keels 
of the Camelide (figure 9). These animals confirm the probability 
of the keels being the effect of long-continued shocks, for they 
ate the only Ruminants which have elastic pads on the inferior 
sides of their digits. 
That these processes may be displacements due to shocks long; 
continued, is rendered probable by the structure of the bones 
themselves. (1) They project mostly in the direction of gravity. 
Constant jarring on the lower extremity of a hollow cylinder 
with soft (medullary) contents, and flexible end walls would 
tend to a decurvature of both inferior and superior adjacent end 
walls. If the side walls are wide and resistant, the projection 
will be median, and will be prolonged in the direction of the 
