The human skeleton is made of bones. Bones support the body, give shape to the body and protect the inside organs of the body like heart, lungs. About 206 bones make up the skeleton of the average adult. The outer part of the bone is tough and very hard.
The inside of a bone is filled with a soft material known as marrow. It is in the marrow that the manufacture of blood cells takes place.
The outside of the bone is covered with a fibrous sheath which is well supplied with blood vessels. There are different types of bones, each designed to perform in different ways. Long bones forming the limbs provide strength to support the bones that make up the structure of the body.
Small bones found at the wrist and ankles are squatter to allow a variety of movement.