Fig. 42-17. Superior aspect of the base of the skull. The right
temporal bone (see fig. 42-19) has been removed, thereby
displaying the head of the mandible. The floor of the cranial
cavity presents three "steps"-the anterior, middle, and
posterior cranial fossae-separated by two ledges: (1) the lesser
wings of the sphenoid and (2) the upper border of the petrous
part of the temporal bone on each side. Click for high
resolution image.