Anterior superior transcranial view of frontal sinus and dura mater. In this view, the five layers of the scalp are contained in the flap that has been reflected forward off the frontal bone. The deepest layer, the periosteum or pericranium is in view on the reflected flap. A portion of the frontal bone containing the bilateral frontal sinuses has been removed. This sinus is located between the outer and inner tables of the bone. Exposed is the outer, rough layer of the dura mater, the periosteal dura. This layer is largely fused with the inner smooth layer of dura mater, the meningeal dura, which faces the brain. (Image courtesy of AL Rhoton, Jr.)