What best describes the periosteum?

• A. A joint cavity filled with synovial fluid
• B. A dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles.
• C. A layer of cartilage on the ends of bones
• D. A muscle that covers bone

Answer: (B)

The periosteum is the dense fibrous membrane that covers almost the entire surface of a bone, except at the ends where articular cartilage sits. It has two layers: an outer fibrous layer that anchors to surrounding tissues and an inner cellular layer capable of forming bone. It also carries blood vessels and nerves to nourish the bone and contains cells involved in growth and repair. This description fits best because it highlights both the covering function and its role as a site of attachment for tendons and muscles. The other choices describe structures not part of the periosteum: a joint cavity with synovial fluid belongs to a joint, articular cartilage covers bone ends, and a muscle does not cover bone.