A long bone is a bone that has a shaft and 2 ends and is longer than it is wide. Long bones have a thick outside layer of compact bone and an inner medullary cavity containing bone marrow. The ends of a long bone contain spongy bone and an epiphyseal line. The epiphyseal line is a remnant of an area that contained hyaline cartilage that grew during childhood to lengthen the bone. All of the bones in the arms and legs, except the patella, and bones of the wrist, and ankle, are long bones.