General Structure and Body of the Bone
The maxilla is one of the main paired bones of the facial skeleton. Anatomically, it consists of a central body (corpus maxillae) and four radiating processes.
The most important feature of the body is that it contains a spacious pneumatic cavity within—the maxillary sinus (sinus maxillaris), also known as the antrum of Highmore. The entrance to this cavity is called the maxillary hiatus (hiatus maxillaris), located on the nasal surface of the bone. On an intact skull, this wide opening is partially covered by neighboring bony structures, particularly the middle nasal concha.
Surfaces of the Maxillary Body
The body of the maxilla has four distinct surfaces, each contributing to important anatomical regions of the skull:
- Orbital surface (facies orbitalis) — forms the inferior wall (floor) of the orbit. It features the prominent infraorbital groove (sulcus infraorbitalis), which transitions into the infraorbital canal (canalis infraorbitalis). This canal opens onto the anterior facial surface via the infraorbital foramen (foramen infraorbitale), located above the canine fossa (fossa canina).
- Anterior surface (facies anterior) — bounded superiorly by the infraorbital margin (margo infraorbitalis). Medially, it transitions into the nasal notch (incisura nasalis), and inferiorly, at its anterior margin, projects as the anterior nasal spine (spina nasalis anterior).
- Infratemporal surface (facies infratemporalis) — dominated by the large maxillary tuberosity (tuber maxillae, or eminentia maxillae). This area presents alveolar foramina (foramina alveolaria) leading into alveolar canals (canales alveolares), through which vessels and nerves travel to the roots of the molars and premolars.
- Nasal surface (facies nasalis) — bounded anteriorly by the lacrimal groove (sulcus lacrimalis). In the center lies the maxillary hiatus leading into the maxillary sinus, and posteriorly runs the greater palatine groove (sulcus palatinus major), which, together with the corresponding groove of the palatine bone, forms the greater palatine canal.
Frontal and Zygomatic Processes
Four processes extend from the body. The first two project superiorly and laterally:
- Frontal process (processus frontalis). Its medial surface faces the nasal cavity, forming part of its lateral wall. Here lie the ethmoidal crest (crista ethmoidalis) and conchal crest (crista conchalis) for articulation with the ethmoid bone and inferior nasal concha, respectively. Its lateral surface faces the orbit, contributing to its medial wall. It features the anterior lacrimal crest (crista lacrimalis anterior) and the lacrimal margin (margo lacrimalis), which transitions into the lacrimal notch (incisura lacrimalis).
- Zygomatic process (processus zygomaticus). A relatively simple projection without intricate sub-structures. Its primary function is to articulate securely with the zygomatic bone.
Alveolar and Palatine Processes
The remaining two processes are directly related to the oral cavity and masticatory apparatus:
- Alveolar process (processus alveolaris). Participates in forming the alveolar arch (arcus alveolaris). It contains deep sockets—dental alveoli (alveoli dentales)—that anchor the roots of the teeth. These sockets are separated from one another by interalveolar septa (septa interalveolaria). For multi-rooted teeth (molars), interradicular septa (septa interradicularia) separate the individual root sockets. On the external surface of the process, the contours of the roots form visible alveolar yokes (juga alveolaria).
- Palatine process (processus palatinus). Forms the anterior two-thirds of the hard palate. On its nasal surface (facies nasalis), the nasal crest (crista nasalis) runs sagittally and terminates posteriorly in the posterior nasal spine (spina nasalis posterior). On its palatine surface (facies palatina), palatine spines (spinae palatinae) and palatine grooves (sulci palatini) are present. Anteriorly, incisive canals (canales incisivi) pass through the process, usually fusing to open at the incisive foramina (foramina incisiva). In some cases, the anterior segment exists as an independent structure—the incisive bone (os incisivum, or premaxilla). In such variants, the incisive suture (sutura incisiva) is clearly visible around the foramina.