Resorption of the unmineralized proximal part of Meckel's cartilage in the rat. A light and electron microscopic study.

The resorption of the unmineralized proximal part of Meckel's cartilage in the rat has been investigated by light microscopy and transmission electron microscopy. In the new-born animal an independent resorption area differentiates at the level of the open end of the incisor root and resorption progresses towards the proximal end of Meckel's cartilage. The process of remodelling differs from the usual process of endochondral ossification taking place in the distal part of the cartilage rod. First the perichondrium is affected, where macrophage- and fibroblast-like cells appear to degrade the unmineralized cartilage matrix. The chondrocytes in the center of the cartilage are undergoing degeneration. Finally, giant cells resembling macrophages attack the degenerating chondrocytes. Such giant cells seem to contribute to the digestion of cellular components of the cartilage rod. Thus, Meckel's cartilage provides a suitable model for studying cartilage breakdown under non-ossifying conditions.