bone

the hard connective tissue that, with CARTILAGE , forms the SKELETON . Bone has a matrix of COLLAGEN fibres with bone salts (crystalline calcium phosphate or hydroxyapatite, in which are the bone cells, OSTEOBLASTS and OSTEOCYTES ). The bone cells from the matrix. There are two types of bone: compact or dense, forming the shafts of long bones, and spongy or cancellous, which occurs on the inside and at the ends of long bones and also forms the short bones. Compact bone is a hard tube covered by the periosteum (a membrane) and enclosing the BONE MARROW and contains very fine canals (see HAVERSIAN CANALS ) around which the bone is structured in circular plates. See also SKULL .