The FV viewed from the middle cranial fossa (a) and the extracranial view of the skull base (b). Panel (c) shows an example of the bilateral FV in the extracranial view of the skull base. The asterisks (*) in (a) and (b) indicate a bony process which probably hinders the approach of the structures passing through the FO. CC: carotid canal; FL: foramen lacerum; FO: foramen ovale; FS: foramen spinosum; FV: foramen of Vesalius.