C, Lateral view of the parasellar area and the oculomotor triangle. The temporal lobe has been elevated to expose the oculomotor and trochlear nerves as they enter the roof of the cavernous sinus. The oculomotor triangle is the triangular patch of dura through which the oculomotor nerve enters the roof of the cavernous sinus. The optic tract passes backward on the medial side of the uncus. D, Enlarged view of the clinoidal, oculomotor, supratrochlear, and infratrochlear cavernous sinus triangles. The optic strut is exposed in the anterior part of the clinoidal triangle, the clinoid segment is exposed in the midportion and the roof of the cavernous sinus is exposed in the posterior part. The upper margin of the clinoid segment is surrounded by the upper dural ring, which is formed by the dura extending medially from the upper surface of the anterior clinoid. The lower margin of the clinoid segment is defined by the lower dural ring, which is formed by the dura extending medially from the lower margin of the anterior clinoid. The dura on the lower margin of the anterior clinoid, referred to as the carotidoculomotor membrane, separates the lower surface of the anterior clinoid from the upper surface of the oculomotor nerve and extends medially to form the lower dural ring. The posterior bend of the internal carotid artery and the origin of the meningohypophyseal trunk, which gives rise to the tentorial and dorsal meningeal arteries, are exposed in the infratrochlear triangle. The abducens nerve passes through Dorello’s canal and between the lateral surface of the intracavernous carotid and the medial side of the ophthalmic nerve. The inferolateral trunk arises from the horizontal segment of the intracavernous carotid and passes above the abducens nerve. E, Lateral view of cavernous sinus. F, View, through the sphenoid sinus, of the medial side of the cavernous sinus. The optic nerve is exposed at the upper margin of the clinoidal triangle and above the optic strut. On the sphenoid sinus side of the specimen, the optic canal is seen above the opticocarotid recess, which leads into the optic strut. The clinoid segment rests against the posterior aspect of the optic strut in both views. In the lateral view, the superior orbital fissure through which the ophthalmic, trochlear, abducens nerves pass is seen below the optic strut. In the view through the sphenoid sinus, the medial edge of the superior orbital fissure produces a wide rounded prominence below the optic strut, and the maxillary nerve produces a prominence in the lower part of the sphenoid sinus just distal to the foramen rotundum. The lateral wing of the sphenoid sinus extends laterally under the maxillary nerve into the medial part of the floor of the middle fossa. Opening the middle fossa floor in the anteromedial and anterolateral triangles exposes the sphenoid sinus. G, Posterior view of the inferolateral triangle. The medial edge of the inferolateral triangle extends between the dural entrances of the IVth and VIth nerves. The inferior limb extends from the VIth nerve to where the first vein lateral to Meckel’s cave joins the superior petrosal sinus and the superior limb extends from that vein to the dural entrance of the IVth nerve. The ostium of Meckel’s cave is located within the inferolateral triangle. H, Posterior view of the inferomedial triangles. The medial limb of the inferomedial triangle extends from the posterior clinoid to the dural entrance to the abducens nerve. The lateral limb extends between the dural entrances of the IVth and VIth nerves and the superior limb extends from the IVth nerve to the posterior clinoid. On the right side, there is an abnormal projection of the posterior clinoid process, which extends below the oculomotor nerve toward the petrous apex. (Images courtesy of AL Rhoton, Jr.)