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Side view. Maxilla visible at bottom left, in green.
Front view. Maxilla visible at center, in yellow.
|Precursor||1st branchial arch|
|Anatomical terms of bone|
The maxillae (plural: maxillae //) consist of upper palate of mouth or maxilla or two halves that are fused at the intermaxillary suture to form the upper jaw. This is similar to the mandible (lower jaw), which is also a fusion of two halves at the mandibular symphysis.
Each half of the fused maxillae consists of:
- The body of the maxilla
- Four processes
- Infraorbital foramen
- The maxillary sinus
Each maxilla articulates with nine bones:
- two of the cranium: the frontal and ethmoid
- seven of the face: the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, vomer, and the adjacent fused maxilla.
These centers appear during the sixth week of fetal life and unite in the beginning of the third month, but the suture between the two portions persists on the palate until nearly middle life. Mall states that the frontal process is developed from both centers.
The maxillary sinus appears as a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does not reach its full size until after the second dentition.
The maxilla was formerly described as ossifying from six centers, viz.,
- one, the orbitonasal, forms that portion of the body of the bone which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and the lateral wall of the nasal cavity;
- a second, the zygomatic, gives origin to the portion which lies lateral to the infraorbital canal, including the zygomatic process;
- from a third, the palatine, is developed the palatine process posterior to the incisive canal together with the adjoining part of the nasal wall;
- a fourth, the premaxillary, forms the incisive bone which carries the incisor teeth and corresponds to the premaxilla of the lower vertebrates;
- a fifth, the nasal, gives rise to the frontal process and the portion above the canine tooth;
- and a sixth, the infravomerine, lies between the palatine and premaxillary centers and beneath the vomer; this center, together with the corresponding center of the opposite bone, separates the incisive canals from each other.
Changes by age
At birth the transverse and antero-posterior diameters of the bone are each greater than the vertical.
The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit.
The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest, owing to the development of the alveolar process and the increase in size of the sinus.
Each maxilla assists in forming the boundaries of three cavities:
In other animals
Sometimes (e.g. in bony fish), the maxilla is called "upper maxilla," with the mandible being the "lower maxilla." Conversely, in birds the upper jaw is often called "upper mandible."
In most vertebrates, the foremost part of the upper jaw, to which the incisors are attached in mammals consists of a separate pair of bones, the premaxillae. These fuse with the maxilla proper to form the bone found in humans, and some other mammals. In bony fish, amphibians, and reptiles, both maxilla and premaxilla are relatively plate-like bones, forming only the sides of the upper jaw, and part of the face, with the premaxilla also forming the lower boundary of the nostrils. However, in mammals, the bones have curved inward, creating the palatine process and thereby also forming part of the roof of the mouth.
Skull from below. Maxilla shown in green. (Mandible is not shown.)
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This article uses anatomical terminology; for an overview, see anatomical terminology.
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