ated to the interests of man that it will be well
briefly to set it before the reader. In the first stages of the
Tertiary period, in the age when we begin to trace the evolution of the
suck-giving animals above the lowly grade in which the kangaroos and
opossums belong, we find the ancestors of our mammalian series all
characterized by rather weakly organized limbs fitted, as were those of
their remoter kindred the marsupials, for tree climbing rather than for
moving over the surface of the ground. The fact is, that all the
creatures of this great clan acquired their properties of body in
arboreal life, and with such relatively small and light bodies as were
fitted for tree climbing. For this use the feet need to be
loose-jointed, and so the system of five toes, each terminating in a
sharp and strong nail or claw, became fixed in the inheritances. When,
gaining strength and coming to possess a more important place in the
world, these ancient tree-dwellers were able to occupy the ground which
of old had been possessed by the great reptiles, the limbs that had
served well for an arboreal life had to undergo many changes in order
to fit them for progression in the new realm.

If we watch the progress of a bear over the surface of the ground, we
readily perceive how lumbering is its gait and how poor the speed which
it attains. Its slow and shambling movement is due to the fact that it
has the tree-climbing foot, and is not well fitted for motion such as is
required in running. To attain anything like speed in this exercise it
is necessary to support the body on the tips of the toes. Every man who
has gained any skill in this art knows full well how incompetent he is
if he tries to run with rapidity in the flat-footed manner. The bear
cannot essay this method of progression on the toe-tips because its
loose-jointed feet cannot be made to support its heavy body. In this way
arose the necessity of developing a peculiar kind of foot when that part
had to serve for rapid locomotion. The experiments to this end have been
numerous and varied. Thus in the elephants, which retain the originally
numerous toes, the bones of these members are planted in an upright
position and tied together with such strong muscles and sinews, that the
foot parts have something like the solidity and strength of the upper
portions of the legs. In the single-hoofed or horse-like forms, and in
the cloven-footed animals, other series of experiments have b