Periosteum is best described as what?

• A. Fibrous sheath surrounding the bone
• B. The cartilage layer at joint surfaces
• C. The hollow center of bone
• D. The inner marrow cavity

Answer: (A)

Periosteum is a dense fibrous membrane that covers the outer surface of bones (except where articular cartilage is present at joints). It has an outer fibrous layer and an inner cellular layer rich in osteogenic cells, which makes it essential for protection, nourishment via blood vessels, and as an attachment site for tendons and ligaments. The inner cellular layer also enables bone growth in diameter and repair. The cartilage layer at joint surfaces is articular cartilage, not periosteum; the hollow center of bone is the medullary (marrow) cavity, not the periosteum.