Ans: (a) Sphenoid sinusRef: Dhingra's ENT 6th ed. /138* Spheno ethmoidal recess is situmated above the superior turbine. Sphenoid sinus opens into is* Sphenoid sinus. It has an anterior part & posterior part.Anterior Part: roof related to the olfactory tract, optic chiasma, frontal lobe while the lateral wall is related to optic nerve internal carotid artery & maxillary nerve.Posterior Part: Roorf is related to the pituitary gland in the sella tucica while each lateral wall is related to cavernous sinus, internal carotid artery and CN 3rd and all division of 5th nerve