Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. This forms a primary ossification center. Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity.

What happens ossification center?

An ossification center is a point where ossification of the cartilage begins. The first step in ossification is that the cartilage cells at this point enlarge and arrange themselves in rows. The matrix in which they are imbedded increases in quantity, so that the cells become further separated from each other.

What are the four steps of ossification?

Intramembranous Ossification Intramembranous ossification follows four steps. (a) Mesenchymal cells group into clusters, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form.