Inside your body is a hard frame made of bones. It is called the skeleton. Your bones hold you up and give you your shape.

How many bones are in a grown-up's skeleton? There are 206. That is a lot of bones.

Bones also protect you. The bones of your skull protect your brain. Your ribs form a cage that protects your heart and lungs.

Look inside a bone. The outside is made of hard, dense bone. Inside that hard layer, many bones have a lighter, sponge-like tissue.

Some people think bones are dry sticks. But bones are living tissue. They are alive.

Many bones have soft bone marrow inside. The marrow makes most of your blood cells.

Bones have to meet somewhere. A joint is a place where two or more bones meet.

A baby's skull bones are not firmly joined at birth. This leaves soft spots on the head.

What if a bone breaks? Doctors use X-rays to see whether a bone is broken.

A cast or splint holds a broken bone still while it heals. Children's broken bones can heal well and heal quickly.

Animals have bones too. A giraffe has seven bones in its neck, the same number as a person. A bird's bones are hollow and light, which helps it fly.

Here is one more thing about living bones. Bones get stronger when you use them by being active.

Words to know

• skeleton: bone frame
• joint: where bones meet
• marrow: soft inside part
• cast: hard wrap