Figure 1. Cellular response of condylar cartilage during natural growth (Sprague-Dawley rats at 56 days of age). The progression of cellular response generated by natural growth is well-reflected by the zone-like packing of chondrocytes, from the superficial layer downward, consecutively being (A) the articular zone, (R) the resting zone, (P) the proliferative zone, (H) the hypertrophic zone, and (E) the erosive zone. The thickness of cartilage is of substantial proportion to that of the bony tissue underneath, indicating the dominance of chondrogenesis with moderate transition into osteogenesis (H&E, Bar = 10 µm).