Long, hard, dense bones made of connective tissue that provide strength, structure, and mobility (such as the femur or thigh bone). A long bone is a bone that has a shaft and 2 ends. There are also bones in the fingers that are classified as "long bones" even though they are short in length. This is due to the shape of the bones, not the actual size. Long bones contain yellow bone marrow and red bone marrow (which produces blood cells).