Which membrane lines the marrow cavity?

The membrane that lines the marrow cavity is known as the endosteum. This thin layer of connective tissue plays a vital role in bone health and regeneration. It is composed of a layer of osteoprogenitor cells and osteoclasts, which are essential for bone remodeling and repairing processes. Being in direct contact with the bone marrow, the endosteum serves as a crucial site for the activity of these cells, contributing to the maintenance and growth of the bone.

In contrast, the periosteum covers the outer surface of bones and is responsible for the attachment of tendons and ligaments, providing a protective layer and serving as a conduit for blood vessels and nerves. The crest refers to a prominent ridge along a bone, while the medullary membrane is not a commonly recognized term in relation to bone anatomy. Thus, the endosteum's specific role in lining the marrow cavity makes it the correct answer.