An electron microscopic study of the premineralizing zone of the condylar cartilage of the mouse mandible.

The mandibular condylar cartilage of young ICR mice was used for ultrastructural studies with special emphasis on the cells and matrix in the premineralizing zone. It became evident that cytodifferentiation of chondroblasts was accompanied by deposition of intracellular lakes of glycogen, followed within the premineralizing hypertrophic chondrocytes by a gradual reduction in the glycogen content of the lakes and its replacement by lipid-like droplets. The premineralizing condylar cartilage, like that of other cartilage involved in mineralization, showed numerous matrix vesicles (Types I and II) unassociated with appreciable amounts of collagen.