Which bone is dense and forms the outer layer of bones?

• A. Cortical bone
• B. Woven bone
• C. Trabecular bone
• D. Cancellous bone

Answer: (A)

Dense, outer bone is cortical bone. It forms the protective shell around most bones and is tightly packed, giving it high strength with relatively low porosity. This compact, outer layer is what you feel as the hard surface of a bone and is organized into osteons (concentric lamellae around a central vessel) that maximize structural strength along the bone’s length. In contrast, the inner portion of bone is trabecular (cancellous) bone, which is spongy and porous, providing lightness and housing bone marrow. Woven bone is an immature form with disorganized collagen that's later replaced by the organized lamellar structure of cortical and trabecular bone.