Spongy bone development continues outward from the ossification center as matrix is secreted, osteoblasts will differentiate to osteocytes which will be housed in lacunae. Growth outward is facilitated because mesenchymal cells at the outer regions still give rise to bone stem cells until ossification id complete. In the development of long bones, many ossification centers develop and contribute to faster growth. The blood supply to inner cartilaginous shaft increases which stimulates the production of osteoblasts which accelerates the process of bone formation. This is the primary ossification center from which bone grows and forms a thin layer of bone at the periphery.
Osteoclasts invade the newly formed spongy bone and carve out a marrow cavity.
The length of a bone is increased at a secondary ossification center. At about birth, blood vessels penetrate the epiphysis and from a secondary center of ossification. Bone formation here is similar to that which occurs in the primary center of ossification, but the bony remains spongy. This cartilage covers the end of the bone and forms the articular cartilage. Deeper from the end between the epiphysis and diaphysis, some cartilage remains to form the epiphyseal plate.