Which layer of the dura mater separates in some areas to form dural folds and venous sinuses?

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

Answer: (A)

The inner, or meningeal, layer of the dura mater is the one that separates from the outer periosteal layer in places. When this separation occurs, it forms inward folds (such as the falx cerebri and tentorium cerebelli) that help partition the brain. Within these folds, venous channels called dural venous sinuses develop. So the layer responsible for forming both the dural folds and the venous sinuses is the meningeal layer of the dura mater. The arachnoid mater is a separate membrane beneath the dura, and the subdural space is only a potential space between layers, not the structure that forms the folds and sinuses.