Irregular bones are composed of which material?

• A. Dense compact bone
• B. Hyaline cartilage
• C. Compact bone only
• D. Primarily spongy bone covered with a thin layer of compact bone

Answer: (D)

Irregular bones have a porous internal structure formed by cancellous (spongy) bone, with a thin outer shell of compact bone. This design provides strength and support while keeping the bone lighter, and it also creates spaces for marrow within the trabecular network. Examples like vertebrae show this pattern clearly: a mostly spongy interior surrounded by a thin compact bone layer. Hyaline cartilage isn’t bone tissue, and compact bone alone would miss the porous interior that irregular bones rely on. So the description of primarily spongy bone covered with a thin layer of compact bone best fits irregular bones.