Piriform aperture

The anterior nasal aperture (piriform or pyriform aperture) is a heart- or pear-shaped opening it the skull. Its long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral nasal cartilage and alar cartilages of the nose. It is bounded above by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxilla; and below by the same borders, where they curve medialward to join each other at the anterior nasal spine.