This is a right lateral view looking down into the posterior cranial fossa following an anterior transpetrosal approach (reflection of the temporal lobe, reflection of the tentorium cerebelli, and partial resection of the petrous bone). The brainstem has been removed for clarity of the field. From this perspective, the trigeminal nerve can be seen crossing over the petrous bone and expanding into the trigeminal ganglion. The greater superficial petrosal nerve is shown emerging through a hiatus in the petrous bone to reach the middle cranial fossa. It courses deep to the trigeminal nerve towards the foramen lacerum where it is joined by the deep petrosal nerve (a branch from the internal carotid sympathetic nerve plexus) to form the nerve of the pterygoid canal or Vidian nerve. The ipsilateral superior petrosal sinus is shown at the cut edge of the tentorium cerebelli and the contralateral inferior petrosal sinus is visible along the petroclival groove. (Image courtesy of AL Rhoton, Jr.)