Keyhole opening in left anterolateral skull. For orientation, anterior is toward the upper right corner of the image; inferior is toward the upper left corner. An opening was made at the level of the orbital plate of the frontal bone revealing two compartments. Dura mater covering the frontal lobe is located above the orbital plate in the anterior cranial fossa. Below this plate, in the orbit, is the periorbita, the periosteal lining of the bones of the orbit. (Image courtesy of AL Rhoton, Jr.)