Ans: a (Glossopharyngeal nerve) Ref: Chaurasia 4th ed pg 223 fig. 14.18, pg 225The structures passing between the superior constrictor and the base of skull (sinus of morgagni):A-L-A-auditory tubelevator veli palateascending palatine artery"Auditory tube is about 3.6 cm long and is divided into an outer bony part which is 12 mm long and an inner cartilagenous part which is 24 mm long.The levator veli palati is attatched to its inferior surface. Ascending palatine artery is a branch of facial artery"Also note:Structures passing through the superior orbital fissureupper part:middle part:R/c meningeal branch of the ophthalmic artery lacrimal nerve frontal nerve superior ophthalmic vein trochlear nerve lower part:inferior ophthalmic veinoculomotor nerve naso ciliary nerve abducent nerveThe structures passing between superior and middle constrictors-stylopharyngeusglossopharyngeal nerveBetween middle and inferior constrictors:internal laryngeal nerve-Superior laryngeal vesselsBetween lower border of inferior constrictor and esophagusRecurrent laryngeal nerveInferior laryngeal vessels