The skeletal system consists of bones, cartilage, and joints that work together to support the body, protect organs, allow for movement, store minerals, and produce blood cells. Bones are made of living cells, protein fibers, and calcium deposits. They are surrounded by periosteum and contain Haversian canals that hold blood vessels and nerves. Bone marrow is found inside bones. Cartilage is softer than bone but still provides structure. Ossification replaces cartilage with bone over time. Ligaments connect bones at joints, which can be immovable, slightly movable, or freely movable depending on their type of movement.