What does the periosteum cover on long bones?

The periosteum is a dense layer of connective tissue that serves as the protective outer covering of long bones. Its primary function is to provide a surface for muscle attachment and to house a network of blood vessels and nerves that nourish the bone. The periosteum covers the entire outer surface of long bones, ensuring that the bone is shielded from damage and infection.

The other options refer to different components or areas related to skeletal structure; however, they don't describe the specific role of the periosteum. Understanding that the periosteum encompasses the outer surface of long bones is crucial for recognizing its role in bone health and development, making this the correct response.