Which tissue lines the medullary cavity and inner bone surfaces?

• A. Periosteum lines the medullary cavity
• B. Articular cartilage lines the joint surfaces
• C. Endosteum lines the medullary cavity and inner bone surfaces
• D. Periosteum lines the outer surface

Answer: (C)

Endosteum is the lining of internal bone surfaces, including the medullary (marrow) cavity and the inner surfaces of cortical and trabecular bone. This thin membrane contains osteogenic (bone-forming) cells that can become osteoblasts or osteoclasts as needed, supporting bone growth, remodeling, and repair from the inside. Periosteum, by contrast, covers the outer surface of bone, while articular cartilage lines joint surfaces to reduce friction. So the tissue that lines the medullary cavity and the inner bone surfaces is the endosteum.