Which term describes the hard outer layer of bone?

• A. Endosteum
• B. Periosteum
• C. Cortical bone
• D. Cancellous bone

Answer: (C)

The outer hard layer of bone is cortical bone, also known as compact bone. This dense tissue forms the tough shell around the bone, providing most of its strength and stiffness to resist bending and load. It is organized into tightly packed mineralized layers around central Haversian canals, which carry blood vessels and nerves. In contrast, the lining inside the bone is the endosteum, the membrane covering internal surfaces; the periosteum covers the outer surface of bone and contains cells important for growth and repair; cancellous bone is the lighter, porous, spongy interior found inside bones.