The brain case on the top of the skull is made from thin flat bones. They are locked together in joints that do not let them move. These bones form a hard protective layer over the soft brain material inside. If the bones were thicker they would make the skull heavier and it would be then more difficult to move.

The backbone is made from small irregular shaped bones called vertebrae. They have irregular shapes which fit neatly into one another. This gives the whole backbone strength. The reason why there are many small bones in the backbone rather than one long one is that the column of smaller bones is flexible. It allows the body to bend. In addition to the irregular shape the vertebrae have an oval solid portion which provides support for the whole back. Each vertebra has a hole in it through which the spinal cord runs and they have a projection above the hole which helps to protect the cord. You can feel these projections if you rub your fingers down the back of your neck.

Each end of a body muscle is attached to a bone. One end is attached to a bone that does not move when the muscle pulls. This bone is like the foundation for the muscle. The other end is attached to a bone which does move when the muscle pulls. For example, the shoulder blade is a large, flat bone. It provides a large foundation or support for some of the muscles which move the upper arm.

Not only the size and the shape of the bone is related to the bone's task in the body but the structure of the bone is also related to its task. This is perhaps best seen in a leg bone. A leg bone has to provide support for almost all the weight of the body and has to be light enough to move easily so a person can walk and run. The bone is made strong by having a structure like a tube. The walls of the tube are made from compact bone. This material is strong but light in weight. The inside of the bony tube is filled with yellow marrow this is lighter in weight than solid bone and so makes the bone easier to move. The ends of the bone have to be large so they make strong joints with other bones to allow for both movement and support. If the large ends were also solid they would make the bone heavy so the bone has many cavities like a sponge in it to make it lighter.

By looking at a bone you can work out what it does in the body.