What is the outer covering of the bone called?

• A. Endosteum
• B. Cortex
• C. Periosteum
• D. Medullary cavity

Answer: (C)

The outer covering of a bone is the periosteum. It’s a tough, vascular membrane that envelops the bone’s exterior surface (except where articular cartilage covers joints). The periosteum has an outer fibrous layer that protects and anchors tendons and ligaments, and an inner cellular layer that contains osteoblasts and other progenitor cells essential for growth and repair. It also brings in blood vessels and nerves, with fibers (Sharpey's fibers) anchoring into the underlying cortical bone. By contrast, the cortex refers to the dense outer bone tissue beneath the periosteum, the endosteum lines internal surfaces such as the medullary cavity, and the medullary cavity is the hollow interior of long bones that houses marrow.