M, The trigeminal nerve has been reflected forward to expose the opening into the lateral wing of the sphenoid sinus. The vidian nerve, formed by the union of the greater and deep petrosal nerves, courses forward in the vidian canal to reach the pterygopalatine fossa. N, Enlarged view of the petrolingual and petrosphenoid ligaments. The petrosphenoid ligament extends from the lower part of the lateral margin of the dorsum sellae above the abducens nerve to the petrous apex. The lower margin of the posterior wall of the cavernous sinus is located at the lower margin of Dorello’s canal. Anteriorly, the lower margin of the cavernous sinus is located at the level that the internal carotid artery exits the area below the petrolingual ligament and enters the posterior part of the cavernous sinus. O, The exposure has been extended down to the infratemporal and pterygopalatine fossae. The infratemporal fossa contains branches of the mandibular nerve and maxillary artery, the pterygoid muscles, and the pterygoid venous plexus. The maxillary nerve passes through the foramen rotundum to enter the pterygopalatine fossa. P, Enlarged view. The pterygopalatine fossa is located between the posterior maxillary wall and the pterygoid process. The vidian nerve penetrates the upper part of the pterygoid process and the area below the foramen rotundum to enter pterygopalatine fossa. The maxillary nerve gives rise to zygomatic, infraorbital, and posterosuperior alveolar nerves, and branches and rami to the pterygopalatine ganglion. (Images courtesy of AL Rhoton, Jr.)