This is a dissection of the right parasellar area with the dura mater removed to show structures on the lateral wall of the cavernous sinus and floor of the middle cranial fossa. Note the superior-to-inferior relationship of the oculomotor, trochlear, ophthalmic, and maxillary nerves (OTOM) as they converge on the superior orbital fissure. Venous blood within the cavernous sinus obscures the cavernous segment of the internal carotid artery. Near the petrous apex the trigeminal nerve expands at the trigeminal (semilunar) ganglion from which arises its three divisions. The ophthalmic nerve courses through the superior orbital fissure, the maxillary nerve courses through the foramen rotundum, and the mandibular nerve courses through foramen ovale. The middle meningeal artery is shown emerging from the foramen spinosum. The greater superficial petrosal nerve emerges from a hiatus in the petrosal bone and courses anteromedially deep to the trigeminal nerve towards the foramen lacerum where it joins the deep petrosal nerve. (Image courtesy of AL Rhoton, Jr.)