premaxilla

The premaxilla, or premaxillary bone, is the most anterior portion of the upper jaw in most vertebrates. It lies in front of the maxilla and typically bears the incisor teeth. In many tetrapods the premaxilla is a distinct bone; in mammals, including humans, it remains a small, wedge-shaped element at the front of the upper jaw and helps form the anterior margin of the maxilla as well as part of the floor of the nasal cavity and the anterior portion of the hard palate.

Development and variation: The premaxilla develops from neural crest cells in the first pharyngeal arch. The relative size, shape, and degree of fusion with the maxilla vary among taxa. In birds and many reptiles it forms a sizable, often tooth-bearing region that contributes substantially to the beak or snout, while in many mammals it remains a discrete front portion of the upper jaw.

Function and anatomy: The premaxilla commonly houses or supports the anterior teeth and contributes to the architecture of the face by participating in the nasal floor and the front part of the palate. Its articulation with the maxilla and with nasal bones helps define the boundary between the oral and nasal cavities.

Evolution and paleontology: In fossil skulls the premaxilla is a key element for identifying species and understanding jaw evolution. Its morphology can reflect shifts in dentition, feeding strategy, and facial structure across vertebrates, from beaked birds to tusked extinct mammals.