The structure of the skeleton
Our skeleton provides a framework for our body. It supports the body's weight and holds things in place, but is also very flexible. Nearly all of the skeleton's bones are connected to one another by joints, cartilage, ligaments or muscles. The bones have an active internal metabolism. Chemical reactions take place inside them, making them able to adjust to the different loads put on them and to renew themselves when needed.
Bones have different shapes depending on what job they do. Some offer protection, like the skull or the iliac crest (one on either side of the pelvis). Others mainly serve to make movement possible. One example is the ball-shaped end of the upper arm bone (humerus) in the shoulder joint.
The various structures depend on what the bone needs to do. Protective bones, like the skull (cranium) or breastbone (sternum), tend to be flat pieces of bone. The bones in our arms and legs are largely made up of tubular bones that are strong but quite light.