Premaxillae

Premaxillae are paired bones at the anterior end of the upper jaw in most vertebrates. They form the frontmost portion of the maxilla and, in many species, bear the incisor teeth. In some reptiles and birds the premaxilla is a distinct bone at the tip of the upper jaw; in many mammals it is reduced or fused with the maxilla, contributing to the anterior margin of the upper dental arcade.

Anatomically, each premaxilla articulates with the nasal bone and the maxilla, and in some taxa with the vomer or other palatal bones. The tooth-bearing part is the alveolar process that supports the incisors. In humans, the premaxilla is small and typically fused to the maxilla; the incisor teeth develop in this region and the area is sometimes referred to as the incisive region of the maxilla.

Developmentally, the premaxilla forms intramembranously from neural crest cells derived from the first pharyngeal arch. Evolutionarily, the premaxilla is prominent in many early tetrapods, reptiles, and birds, where it remains a distinct bone at the jaw tip; in mammals it is often incorporated into the maxilla, with the incisor region remaining developmentally derived from the premaxillary segment.

Clinical and paleontological notes: The morphology of the premaxilla is routinely used in comparative anatomy and phylogenetic assessments, particularly in distinguishing relationships among birds, reptiles, and mammals. In humans, variation or anomalies in the premaxillary region can influence dental occlusion and palate formation during development.

Etymology: From Latin pre- 'before' and maxilla 'jawbone'.