Posteriorly, the roof of each cavity slopes inferiorly to the choana and is formed by: the anterior surface of the sphenoid bone, the ala of the vomer and adjacent sphenoidal process of the palatine bone, and the vaginal process of the medial plate of the pterygoid process.
Underlying the mucosa, the roof is perforated superiorly by openings in the cribriform plate, and anterior to these openings by a separate foramen for the anterior ethmoidal nerve and vessels.