Mature bones are made up of three types of tissue: compact tissue (the hard outer portion of most bones); cancellous tissue (spongy tissue inside the bones that contains bone marrow, which makes blood cells); and subchondral tissue (smooth bone tissue of the joints). A layer of cartilage covers subchondral tissue to cushion the movement of joints.
Bones support and protect internal organs, act as levers and braces for muscles to produce movement, and produce and store blood cells in the bone marrow.