Animation of a flight through cancellous bone. Cancellous bone, also called spongy or trabecular bone, is formed of thin interlinking struts called trabeculae. This gives it a low density and a large surface area. The spaces are often filled with bone marrow, and are the sites of blood cell production. Cancellous bone is generally found within the ends of long bones, contrasting with the harder and more structural cortical (or compact) bone, which typically forms the hard outer surfaces. Clip made from K003/6204, which has a transparent alpha channel background.