Bones make up the skeleton. They are held together by ligaments, which are tough fibres. Muscles are wrapped around the bones. The muscles are attached to the bones by tendons. The muscles cause the bones to move around their joints.

Bones are not dead, but living materials. Their ends grow and the inside of the bone is the place where new blood cells are made. The soft inside of the bone, where the blood cells form, is called bone marrow.

Bones are made of calcium, and this is one reason it is important to have a diet that contains calcium, for example by drinking milk.