What is the name of the membrane that lines the medullary cavity?

The membrane that lines the medullary cavity of long bones is called the endosteum. This thin layer is crucial for bone growth, repair, and remodeling, as it contains osteoblasts and osteoclasts, which are responsible for the formation and resorption of bone tissue. The endosteum also lines the inner surfaces of the bone, including the trabecular (spongy) bone and the medullary cavity, where bone marrow is located.

In contrast, the periosteum is a connective tissue membrane that covers the outer surface of the bone, providing attachment points for tendons and ligaments. Epimysium and perimysium are layers of connective tissue associated with skeletal muscle; epimysium surrounds the entire muscle, while perimysium surrounds individual fascicles within the muscle. Thus, these terms are related to muscle anatomy and not to the structure of bone or the medullary cavity.