Lastly, about the time of
man's coming on the earth, appears his faithful servant, the horse, in
which those little side hoofs have disappeared, leaving only two
little "splint" bones to mark the place where these side hoofs belong.
Thus, step by step, our horses' feet were built up; while these parts
were changing, the other parts of the animals were also slowly
altering. They were at first smaller than our horses,--some of them
not as large as an ordinary Newfoundland dog; others as small as
foxes.
[Illustration: FIG. 11. DEVELOPMENT OF HORSES'S FOOT.]
As if to remind us of his old shape, our horses now and then, but
rarely, have, in place of the little splint bones above the hoof, two
smaller hoofs, just like the foot of _Miohippus_. Sometimes these are
about the size of a silver dollar, on the part that receives the shoe
when horses are shod.
In this way, by slow-made changes, the early mammals pass into the
higher. Out of one original part are made limbs as different as the
feet of the horse, the wing of a bat, the paddle of a whale, and the
hand of man. So with all the parts of the body the forms change to
meet the different uses to which they are put.
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