er part of each limb. Twenty-eight small
bones are found in the hand, while twenty-seven are present in the foot.

=How the Bones may be Injured.=--In the young some of the entire bones
and parts of many others are soft like gristle. For this reason, the
bones of the young seldom get broken, but they are easily bent and
pressed out of their natural shape. On this account you should hold the
body erect in sitting and walking. Bending over the table or desk day
after day is not only likely to cause round shoulders, but is sure to
squeeze up the lungs and other organs so they cannot do their best work.

Sitting at a table or desk, so that one shoulder is higher than the
other or carrying books at the side, so that they rest on the hip may
cause a curve sidewise in the backbone. Tight clothing about the waist
presses the ribs out of shape and hurts the other organs within the
body.

[Illustration: FIG. 82.--How the bones are held together. A piece has
been cut out of the tough ligament to show the cup of the hip bone
into which the head of the thigh bone fits.]

=Caring for Broken Bones.=--When a bone of the arm or leg is broken, the
muscles tend to make the ends shove over each other. The broken ends are
sometimes sharp, and if the limb is bent, these may tear through the
flesh. This may be prevented by binding a board firmly on opposite sides
of the limb across the broken part. This will hold the bones in place
until the surgeon comes and will also allow the patient to be moved.

The surgeon will set the broken bones by bringing the ends together
and holding them in place by sheets of wood or metal firmly held by a
bandage. In a few days the membrane around the bone begins to grow new
bone to join the broken parts.

=How the Bones are joined together.=--The two general classes of
joints are the _movable_ and _immovable_. Except the lower jaw, the
bones of the skull are so tightly joined together that there is no
motion between them. The bones of the wrist and back have but little
movement. The freest motion is at the shoulder joint, where the round
head of one bone fits into the shallow cup of another. This is called
a _ball and socket joint_. Such a joint is found also at the hip. At
the elbow and knee the bones move back and forth like a hinge and
these are named _hinge joints_.

=Working Parts of a Joint.=--The ends of the bones are covered with a
thin layer of gristle. The bones are held in place by several str