<p>Separate sections were treated with collagen I, collagen II, collagen X, and osteocalcin primary antibodies and corresponding secondary biotinylated IgG. The signals were developed with 3,3′-diaminobenzidine and photographed on an Axioskop 2 Zeiss microscope. Five sections from four discs were used at each time point. Arrows showing hypertrophy chondrocytes.</p