Which layer is the outermost portion that adheres to the cranial vault and serves as the periosteum of the skull?

• A. Meningeal layer
• B. Subdural space
• C. Epidural space
• D. Periosteal layer of dura mater

Answer: (D)

The outermost layer that stays attached to the skull and acts as its periosteum is the periosteal layer of the dura mater. The dura mater has two layers: an outer periosteal layer that hugs the inner surface of the skull and a deeper inner layer that covers the brain and forms folds like the falx cerebri. The periosteal layer is continuous with the cranial periosteum at sutures, so it effectively serves as the periosteum for the skull bones. The other spaces mentioned (epidural and subdural) are potential spaces that relate to between skull and dura or dura and arachnoid, not to the outermost covering itself.