The skeletal system consists of 206 bones and other structures that provide structure, support, protection, movement, mineral storage, and blood cell formation. Bones are classified based on their shape as long bones, short bones, flat bones, irregular bones, or sesamoid bones. Long bones are typically longer than wide with heads at both ends. Short bones are generally cube-shaped while flat bones are thin and curved. Irregular bones have irregular shapes that do not fit other categories. Sesamoid bones are small bones that form in tendons.