Which type of bone constitutes the outer portion and contains osteons?

• A. Compact
• B. Spongy
• C. Cancellous
• D. Trabecular

Answer: (A)

The outer portion of most bones is compact bone, also called cortical bone. Its defining feature is the osteon (Haversian system), a cylindrical unit with a central Haversian canal that houses blood vessels and nerves, surrounded by concentric lamellae that hold osteocytes in lacunae connected by canaliculi. This dense, highly organized structure gives compact bone its strength and limited porosity, ideal for withstanding loads along the bone’s axis. In contrast, spongy bone is found inside bones and at the ends of long bones; it’s made of a lattice of trabeculae and lacks osteons, providing lighter weight and spaces for marrow. Therefore, the outer portion that contains osteons is compact bone.