A, The dura has been elevated from the floor of the middle fossa. Bone has been removed to expose the geniculate ganglion, the dura lining the internal acoustic meatus, the tensor tympani, some of the petrous carotid, and the superior semicircular canal. B, The bone of the petrous apex between the trigeminal nerve and the internal acoustic meatus has been removed to expose the side of the clivus. C, The exposure under the trigeminal nerve extends to the edge of the inferior petrosal sinus. D, The posterior fossa dura has been opened to expose the prepontine cistern, basilar artery, and abducens nerve. (Images courtesy of AL Rhoton, Jr.)