Which bone type forms the ribs, breastbone, and skull?

• A. Cortical bone
• B. Flat bones
• C. Long bones
• D. Irregular bones

Answer: (B)

Understanding bone classification by shape helps explain why certain bones have their particular roles. Flat bones are thin, broad, and often curved, providing large, flat surfaces and a protective shield for underlying organs while also offering broad areas for muscle attachment. The ribs and sternum form a protective thoracic cage, and the bones of the skull create a protective case for the brain; all of these fit the description of flat bones. Their structure is efficient for shielding and for surface-area functions, and in the skull, flat bones typically have two outer layers of dense compact bone with cancellous bone in between. In contrast, long bones are elongated and light for movement, irregular bones have complex shapes, and cortical bone refers to the dense outer layer found in bone generally, not a shape category. So the ribs, breastbone, and skull are flat bones because of their broad, shield-like surfaces designed for protection and muscle attachment.