The maxillary sinuses
are the largest of the paranasal sinuses. These large pyramidal cavities occupy the bodies of the maxillae. The apex of the maxillary sinus extends toward and often into the zygomatic bone. The base of the maxillary sinus forms the inferior part of the lateral wall of the nasal cavity. The roof of the maxillary sinus is formed by the floor of the orbit. The floor of the maxillary sinus is formed by the alveolar part of the maxilla. The roots of the maxillary teeth, particularly the first two molars, often produce conical elevations in the floor of the maxillary sinus. Each sinus drains by an opening, the maxillary ostium, into the middle meatus of the nasal cavity via the semilunar hiatus. Because of the superior location of this opening, it is impossible for the sinus to drain when the head is erect until the sinus is full. The arterial supply of the maxillary sinus is mainly from superior alveolar branches of the maxillary artery; however, branches of the greater palatine artery supply the floor. Innervation of the maxillary sinus is from the anterior, middle, and posterior superior alveolar nerves branches of CN V2.