Fish bone. Coloured scanning electron micrograph (SEM) of a caudal (tail) fin bone from a fish. Bone tissue can be either cortical (compact) or cancellous. Cortical bone usually makes up the exterior of the bone, while cancellous bone is found in the interior. Cancellous bone is characterised by a honeycomb arrangement, comprising a network of trabeculae. These structures provide support and strength to the bone. The spaces within this tissue contain bone marrow (not seen), a blood forming substance.