bone

noun

The hard calcareous substance that makes up the skeleton of teleosteans, i.e., 'bony fishes'. Differs in structure from the cartilage of elasmobranch, which may, however, also be hardened through deposition of calcium, also the hard connective tissue consisting of cells (osteoblasts, osteocytes) in a mixture of collagen fibres and hardened by calcium and phosphate salts( calcium hydroxapatite), serving to support the body. The cells are lost eventually leaving cavities and the bone is termed cellular, typical of Dipnoi, Crossopterygii Chondrostei, primitive Teleostei, e.g. Cyprinidae, Siluridae, Salmonidae, Anguillidae, and some advanced Teleostei, e.g. Perca, Gadus. Another form of bone is termed osteoid and lacks the ramifications seen in cellular bone. After the osteocytes disintegrate, the spaces they leave are filled with matrix and the bone is known as acellular, e.g. in Cyclopterus, Mola. Bone is strong and rigid in contrast to cartilage.