Final answer:
The strong fibrous membrane that lines the medullary cavity is called the endosteum, important for bone growth, repair, and remodeling.
Step-by-step explanation:
The strong fibrous membrane that lines the medullary cavity of a bone is called the endosteum. This delicate lining plays a crucial role in bone growth, repair, and remodeling. While the periosteum covers the outer surface of the bone, containing blood vessels and nerves that nourish compact bone, the endosteum specifically lines the inner surface of the medullary cavity.
Additionally, it is important not to confuse this with the layers protecting the central nervous system, such as the pia mater, which is a different thin fibrous membrane covering the outer surface of the CNS.