Right lateral superior view of middle cranial fossa. The cerebrum has been removed to expose the dural covered cranial floor. Through this, several structures can be observed. A remnant of the tentorium cerebelli remains attached to the anterior clinoid process and along the superior border of the petrous portion of the temporal bone, which houses the superior petrosal sinus. This sinus drains the orbit and cavernous sinus to the transverse sinus. The petrous bone forms the posterior wall of the middle fossa. Medial to the anterior clinoid process the internal carotid artery emerges out of the dura intracranially and adjacent to the optic nerve, which enters the optic canal. The oculomotor nerve is observed leaving the midbrain-pontine junction and penetrating dura to enter the lateral wall of the cavernous sinus enroute to the orbit via the superior orbital fissure. The trochlear nerve, the smallest of the cranial nerves, arises from the dorsal surface of the midbrain (the only cranial nerve to exit from the dorsal surface of the brainstem). It has the longest intracranial length of any of the cranial nerves. It penetrates the dura near the posterior clinoid process and enters the lateral wall of the cavernous sinus before passing through the superior orbital fissure to the orbit where it supplies motor innervation to the superior oblique muscle. The cut stump of the trigeminal nerve can be seen where it crosses the apex of the petrous bone to enter a split of dura (Meckel's cave) and expands as the trigeminal (Gasserian) ganglion. Its maxillary division can be seen entering the foramen rotundum and its mandibular division entering the foramen ovale. (Image courtesy of AL Rhoton, Jr.)