e
upper arm and the front of the forearm and the hand, their tendons
passing over the convexities of the elbow and wrist, while the flexors
occupy the opposite sides, and their tendons run up into the
concavities of the joints. There are several powerful pectoral muscles
which run out from the shoulder and breast, and operate upon the upper
end of the humerus, and with these the wing is lifted and the strokes
are made during flight.

Another mechanical contrivance deserves attention. An extremely
elastic cord reaches over from the shoulder to the wrist joint,
supporting a fold of skin that occupies the deep angle of the elbow,
and that is covered with short, fluffy feathers. When the bird is
flying, this cord is stretched and forms the front edge of that section
of the wing. But, now, suppose the wing is closed, will not this cord
make a cumbersome fold, flapping loosely in the angle of the elbow?
Such would, indeed, be the case, did not its extreme elasticity enable
it to contract to the proper length, so as to keep the wing's border
straight and smooth.

Without the feathers the wing would be useless as an instrument of
flight. The shorter plumes that shield the bases of the long quill
feathers are called the coverts, which are found on both the upper and
under surfaces of the wing. They are divided into several sets,
according to the position they occupy, and are called the "primary
coverts" (because they overlie the bases of the primaries), the
"greater coverts," the "middle coverts," and the "lesser coverts."
Forming a vast expansion of the bony and fleshy framework are the
quills, or flight-feathers, called collectively the "remiges." These
plumes mainly determine the contour of the wing, and constitute a thin,
elastic surface for striking the air--one that is sufficiently
resilient to give the proper rebound and yet firm enough to support the
bird's weight. The longest quills are those that grow on the hand or
outer extremity of the wing and are known as the primaries. What are
called the secondaries are attached to the ulna of the forearm, while
the tertiaries occupy the humerus and are next to the body. All these
feathers are so placed relatively that the stiff outer vane of each
quill overlaps the more flexible inner vane of its successor, like the
leaves of certain kinds of fans, thus presenting an unbroken surface to
the air. As to the structure of these plumes, they combine firmness,
lightness