as is the case in
perching, the tendons of this muscle are stretched over the knee and
ankle joints, thus pulling the digits together, and causing them of
their own accord to grasp the perch more or less tightly. When a bird
wishes to unloose its hold, it simply rises on its feet and relaxes the
tendons.

All birds by no means possess this particular muscle, but all the
perchers have some muscular arrangement in the legs and toes that
practically answers the same purpose. If you will bend your wrist
backward as far as you can, you will observe that your fingers will
have a tendency to curve slightly forward. This is caused by the
stretching of the tendons over the convex part of your bent wrist
joints.

The typical bird has four digits, three in front and one reaching
backward. The hind toe is called the hallux, and corresponds to the
thumb of the human hand, so that in grasping an object it can be made
to meet any of the other toes. But many birds are not provided with a
quartet of digits. The ostrich has only two, the inner and hinder toes
being wanting. However, this great fowl does not experience any lack,
for its feet are almost solid like hoofs, and quite flat, and hence are
especially adapted for traveling across the sandy desert.

No bird has ever been found with more than four toes; and four seem to
be ample for all purposes. A fifth toe for a bird would be as useless
as a fifth wheel on a wagon. Quite a number of species have only three
toes, most of them among the walkers and waders, and none, I believe,
among the true perchers. Take the plovers and sanderlings, for
example, which spend most of their time, when not on the wing, in
running about on the ground, especially along the seashore or the banks
of streams and lakes, and seldom, if ever, sit on a perch--in their
case a fourth toe would be worse than a superfluous appendage; it would
be an encumbrance, dragging along in the mud and mire. In these
species it is the hind toe that is lacking, their three digits all
being in front, where they are of the greatest service. There is
another class of birds that have hind toes, though very much reduced
because their owners do not perch, but scuttle about on the beach.
This class includes the little spotted sandpipers which you often see
running or flying along the shores of a river or lake.

Curious to tell, several species of woodpeckers are tridactyl--that is,
three-toed--and still more curious