Development of femoral head to the rat from calcification to ossification

The development of the epiphysis of the femoral head from calcification to ossification was investigated in 50 rats of Wistar strain from an age of 10 to 63 days using radiography and histology. The first deposition of calcium in the cartilage appeared in the central portion of the epiphysis at an age of about 21 days. The region of calcification gradually expanded toward the periphery and after about 3 weeks it occupied the entire epiphysis except for the periphery. After completion of calcification ossification began in the lateral part of the epiphysis at the earliest at an age of 6 weeks. The onset of ossification was characterized by disintegration of hypertrophied cartilage cells and formation of bone trabeculae accompanied by vascular invasion from the lateral side.