The choanae are the oval-shaped openings between the nasal cavities and the nasopharynx (Fig. 8.241). Unlike the nares, which have flexible borders of cartilage and soft tissues, the choanae are rigid openings completely surrounded by bone, and their margins are formed: inferiorly by the posterior border of the horizontal plate of the palatine bone, laterally by the posterior margin of the medial plate of the pterygoid process, and medially by the posterior border of the vomer.