Anterior superior transcranial view of ethmoid sinuses 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 has been removed to expose 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. Anteriorly, near the midline, bone of the floor of the anterior cranial fossa has been removed to expose the roof of the ethmoid sinuses, which border medially with the nasal cavity, and laterally with the orbit. (Image courtesy of AL Rhoton, Jr.)