Figure 1: Bromodeoxyuridine (BrdU) incorporation into developing articular cartilage. Mid-sagittal paraffin wax sections through the proximo-distal axis of the knee joint of M. domestica showing the effect of BrdU incorporation on articular cartilage growth 1 month post-injection. [A, B] Comparative fluorescence and phase contrast images [A, B, respectively] showing the distribution of BrdU in the distal femoral condylar cartilage. BrdU is incorporated into a small number of surface zone cells (arrows) and into a relatively greater proportion of underlying transitional zone cells.