What is cortical bone?

• A. The inner spongy bone
• B. The compact or dense bone found on the outer surfaces of bone
• C. Bone marrow
• D. Periosteum

Answer: (B)

Cortical bone is the dense, compact bone that forms the outer shell of most bones, giving them their strength and rigidity. It’s tightly packed with mineralized matrix and provides the load-bearing framework that resists bending. This outer, solid layer surrounds the inner spongy bone (cancellous bone), which is lighter and porous and houses trabeculae. Bone marrow sits inside the central cavities and within spaces of cancellous bone, while the periosteum is the fibrous membrane that covers the outer surface of bone (not the bone tissue itself).