English: Process of endochondral ossification. Long bones are first formed as cartilage template and then ossification occurs at the center of the cartilaginous bone anlagen, which is called the “primary ossification center.” After a secondary ossification center is formed, the cartilage between primary and secondary ossifications, which is called the growth plate, grows rapidly and is then replaced by bone after invasion of blood vessels into the cartilage. (Left) CCN2 gene was cloned as a hypertrophic chondrocyte specific gene 24 (hcs24). Its gene product promotes proliferation and differentiation of chondrocytes, osteoblasts, and vascular endothelial cells