What is the term for the tough outer covering of the bone?

The tough outer covering of the bone is known as the periosteum. This membrane is critical for the protection of the bone, as it serves as a point of attachment for tendons and ligaments, and plays a role in bone growth and repair. The periosteum is rich in nerves and blood vessels, which help nourish the bone and aid in the healing process.

The endosteum, on the other hand, is a thin layer that lines the inner surface of the bone and is involved in bone growth and remodeling from the inside. Articular cartilage is a smooth tissue that covers the ends of bones at joint surfaces, facilitating movement and reducing friction. Bone marrow, which is found within the hollow spaces of bones, is responsible for the production of blood cells and is not related to the outer structure of the bone itself. Each of these options pertains to different aspects of bone structure and function, with the periosteum being specifically recognized as the protective outer layer.