Every time you walk, settle into a chair, or hug your child,
you're using your bones, muscles, and joints. Without these
important body parts, we wouldn't be able to stand, walk, run,
or even sit. Bones and What They Do From our head to our toes,
bones provide support for our bodies and help form our shape.
The skull protects the brain and forms the shape of our face.
The spinal cord, a pathway for messages between the brain and
the body, is protected by the backbone, or spinal column. The
ribs form a cage that shelters the heart, lungs, liver, and
spleen, and the pelvis helps protect the bladder, intestines,
and in women, the reproductive organs. Although they're very
light, bones are strong enough to support our entire weight. The
human skeleton has 206 bones, which begin to develop before
birth. When the skeleton first forms, it is made of flexible
cartilage, but within a few weeks it begins the process of
ossification. Ossification is when the cartilage is replaced by
hard deposits of calcium phosphate an