The skeletal system provides structure, protection, movement, and other essential functions for the body. It is composed of both cortical and cancellous bone tissue. There are four main types of bones: long bones in the limbs, short bones in the hands and feet, flat bones that protect organs, and irregularly shaped bones. Key bones include those of the skull, vertebral column, rib cage, shoulder girdle, pelvis, hands, feet, and long bones of the arms and legs. Bones develop through the process of ossification and continue changing throughout life.