Supraorbital canal

In some species (Ruminants, Pigs), the supra-orbital duct (Canalis supraorbitalis), that can be multiple, replaces the supra-orbital foramen (Foramen supraorbitale) allowing vessels and nerves to pass through the thickness of the frontal bone from the orbit to the external surface of the frontal bone, opening into the deep longitudinal supra-orbital groove (Sulcus supraorbitalis).