os longum - in vertebrate animals: a long cylindrical marrow-containing bone of a limbbone, os - rigid connective tissue that makes up the skeleton of vertebrates endosteum - vascular membrane that lines the inner surface of long bones epiphysis - the end of a long bone; initially separated from the main bone by a layer of cartilage that eventually ossifies so the parts become fused metaphysis - the growing part of a long bone between the diaphysis and the epiphysis |