Spongy bone is defined as?

• A. Dense outer bone
• B. Layer containing many small spaces inside compact bone
• C. The outer membrane
• D. A marrow type

Answer: (B)

Spongy bone, also known as cancellous bone, is the porous, lattice-like interior of bone made up of trabeculae. This structure creates many small spaces that lightens the bone and provides a framework to house bone marrow and blood vessels. That description fits best because spongy bone forms the inner, porous portion beneath the dense outer layer of compact bone. It is not the dense outer bone itself, nor the outer membrane, and it isn’t a type of marrow—though the spaces within it contain marrow.