Which structure forms around the bone during intramembranous ossification?

• A. Endosteum.
• B. Periosteum.
• C. Articular capsule.
• D. Synovial membrane.

Answer: (B)

Periosteum forms around the developing bone in intramembranous ossification. In this process, bone tissue differentiates directly from mesenchyme, without a cartilage model. As the bone matrix begins to ossify, the surrounding mesenchymal tissue becomes the periosteum, a protective outer layer that also houses cells capable of contributing to bone growth in thickness and repair. The inner lining of bone, the endosteum, sits on internal surfaces like the medullary cavity and is not the outer covering formed during this process. Joint-related structures such as the articular capsule and synovial membrane are unrelated to the bone’s formation here.