My body’s framework

I have a skeleton inside of me. That’s what my bones are called. If I
had no bones, I wouldn’t be able to stand or bend or run or play. I’d be
floppy like a rag doll.

I have bones of many shapes and sizes. Leg bones are long. Toe bones are
short. Rib bones are rounded. Some bones in my head are flat. The bones
in my spine look a little like the spools that hold thread.

Some bones, like those in the top of my head, can’t move. Others, like
those in my legs, fit together so that they do move. That’s why I can
bend and move so well.

My bones are hard. But they are not so hard on the inside as they are on
the outside. Inside, the bone cells are not so tightly packed together
and there are many tiny holes between the cells.

Some bones, like those in my legs, are hollow like tubes. Inside the
hollow is bone marrow. Marrow is made up of tissue, fat, tiny veins and
arteries, and cells that make new blood cells for my body.

Every day new cells are added to my bones, and my bones become longer
and larger.