988 ` The Perissodactyla. [Nov, 
seen in the Amblypoda. This may have had something to d 
with the extinction of the Oreodontidz. (Ege 
The cause of this rotation of the first on the second rows o 
carpal and tarsal bones may be now referred to. Mammals, et 
cept those which are completely plantigrade (as the bear), tum 
the toes out in walking! In the Ungulata, the toes of te 
posterior foot are more strongly turned outwards than those of 
the anterior foot. In the digitigrade Carnivora, which represent 
the highest type of the Unguiculata, the movement is reverses, 
the anterior toes being turned outwards more than the posterior. 
As the foot is descending towards the ground, it is, with | 
distal part of the leg, rotated from within outwards. The 
tation of the foot is promptly arrested at the moment of 
contact with the ground, and the effect of this arrest is to f! 
duce a torsion of the leg, and a pressure from within outwat 
of the proximal or moving element of each articulation, a? 
the distal or fixed element. Thus a constant torsion strain 4 
within outwards has been exerted by the first row of carga q 
and tarsal bones, on the second row, and thus has iar 
believe, the gradual transition from the linear arrangem 
those bones of the Condylarthra to their alternation eee 
Diplarthra. The advance of diplarthrism is in direct ratio al 
advance of digitigradism, for the greater the length of the ‘| 
the greater is the elasticity of the leg, and the greats Ki 
torsion. This is especially true of the posterior leg, yee q 
_ prominent heel; and thus is explained the fact that dip! Pe 
appears in that foot before it does in the fore foot, aS in the aq 
_boscidia. (Plate XXIX. A 
To the same ASH torsion is. to be ascribed the aut ie 
tension of the radius and tibia over the first row of vrticulatod 
the almost exclusion of the ulna and fibula from the ee 
This reasoning when applied to the Unguiculate a 
fied by other circumstances. In the Carnivora the 
the body does not rest on the ungues as in the Unten . 
_ the pads of connective tissue beneath the digits. a 
on the application of the foot to the ground the rigid" 
the carpal and tarsal articulations do not present tH ie y 
sistance seen in the Ungulata, but yield more of eget per 
-Familiar exception to this rule is seen in some horses; but et ae 
` _ Out, and the tapir, which represents the horse’s ancestors, turns the 2° i 
