What provides the outer protective layer of long bones, aiding in muscle attachment?

The periosteum is a dense layer of connective tissue that envelops the bones except at the surfaces of the joints. It serves multiple essential functions, including providing an outer protective layer for long bones. This tough outer covering not only safeguards the bone from injury but also serves as an attachment point for muscles, tendons, and ligaments, which is crucial for facilitating movement and stability.

Additionally, the periosteum plays a vital role in the growth and repair of bones due to its rich supply of blood vessels and nerve fibers. It contains osteoblasts, which are cells important for bone formation. These qualities make the periosteum integral to both the structural integrity and functional aspects of long bones.

Other structures mentioned also have specific roles: articular cartilage covers joint surfaces to reduce friction, the marrow cavity is involved in the production of blood cells, and the endosteum lines the inner surfaces of the bone. However, none of these components provide the same protective outer layer or muscle attachment capabilities as the periosteum.