The maxilla is the upper jaw. In mammals it is tightly fused to the skull, but in fish and reptiles it is usually not. In snakes, for example, the maxilla is able to move relative to the rest of the skull, and the jaws can separate entirely to swallow prey.
Maxilla Media
Inferior surface of maxilla
Anterior surface of maxilla at birth
Inferior surface of maxilla at birth
Fracture of the left lacrimal / maxillary bone
Skull. Maxilla shown in green.