New observations on the development of the embryonic chick femur: cartilage calcification before resorption.

The use of calcium-specific histochemical techniques and electron microprobe analysis allowed us to detect the earliest calcium deposits and thus to define the successive events of osteoid and cartilage calcification during the development of the femur among chick embryos from 7 to 14 days. Contrary to the results already published on the embryonic development of the avian limb diaphyseal cartilage, our study shows that: calcium (ionized or precipitated) is detected very early in femur embryonic development; as early as 8 days, precipitation of insoluble calcium salts occurs in hypertrophied chondrocytes cytoplasm; calcification of hypertrophied cartilage matrix begins during cartilage resorption at 10 days.