Figure 2. Histological specimens stained with H-E of central area of the mandibular condylar cartilage (A1 to D1) and photomicrographs of immunoreactivity for type II (A2 to D2) and type X collagen (A3 to D3) antibody in the central area of the mandibular condylar cartilage. (A) Control group, (B) Whole-day group, (C) Light-period group, and (D) Dark-period group. F, fibrous layer; P, proliferative cell layer; T, transitional layer; M, mature cell layer; H, hypertrophic cell layer. Scale bar = 200 µm.