What is the hollow part of a bone that contains bone marrow called?

• A. Medullary cavities
• B. Endosteum
• C. Periosteum
• D. Cortex

Answer: (A)

The hollow center of a bone that houses bone marrow is the medullary cavity. In long bones, this space runs through the shaft and is where marrow resides—red marrow for blood cell production in younger individuals, often replaced by yellow marrow (fat) in many adults. The cavity is lined by a delicate membrane called the endosteum, while the bone’s outer surface is covered by the periosteum and the dense outer layer is the cortex. So, when asking for the hollow part that contains marrow, the term medullary cavity (medullary cavities when referring to multiple bones) is the best fit.