Chondroblasts produce cartilage in the shape of mature bone. Blood vessels surround and penetrate the perichondrium, becoming the periosteum. Osteoprogenitor cells in periosteum become osteocytes and make calcified cartilage. Calcified cartilage is turned into bone, starting in a region of the diaphysis called the primary ossification center. Bone development moves outward from the primary ossification center.
Osteoclasts break down the middle of the diaphysis, forming the medullary cavity.
Cartilage Ossification - endochondral ossification changes cartilage into bone 4.