Stepwise Dissection of the Lateral Wall of the Right Cavernous Sinus. G, View showing the petrous carotid exposed lateral to V3 and below the greater petrosal nerve. Sometimes, no bone covers the terminal part of the petrous segment of the carotid in the floor of the middle fossa, as occurred in this case. The greater petrosal nerve courses about the petrous carotid, and a branch of the sympathetic plexus courses on the intracavernous carotid. H, View showing the petrous apex and roof of the internal acoustic canal removed to expose the facial nerve and anterior inferior cerebellar artery. The petrous carotid is exposed lateral to V3 and below the greater petrosal nerve. The greater petrosal nerve arises from the geniculate ganglion. I, View showing the trigeminal ganglion and posterior root removed, although the three divisions have been preserved. The petrous carotid becomes the intracavernous carotid after passing below the petrolingual ligament, which extends from the lingula of the sphenoid bone to the petrous apex. The abducens nerve passes lateral to the posterior vertical segment of the intracavernous carotid and medial to V1 to reach the superior orbital fissure. The inferolateral trunk arises from the horizontal segment of the intracavernous carotid and descends lateral to the abducens nerve. The intracavernous carotid has five parts, which are, from a posterior to anterior direction, the posterior vertical segment, posterior bend, horizontal segment, anterior bend, and anterior vertical segment. The anterior bend and anterior vertical segment are extremely short and correspond to the clinoidal segment. J, View showing a segment of the oculomotor nerve removed, with some of the material in the posterosuperior venous space evacuated to expose the origin of the meningohypophyseal trunk and its three most common branches: the inferior hypophyseal, dorsal meningeal artery, and tentorial arteries. K, View showing the posterosuperior and medial venous spaces evacuated to expose the inferolateral and meningohypophyseal trunks. The pituitary gland and the medial wall of the cavernous sinus are exposed between the intracavernous and supraclinoidal carotid. The abducens nerve passes below the petrosphenoid ligament (Gruber’s ligament) that forms the roof of Dorello’s canal and courses lateral to the posterior vertical segment of the intracavernous carotid and medial to the inferolateral trunk. (Images courtesy of AL Rhoton, Jr.)