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The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii)
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the
hard palate The hard palate is a thin horizontal bony plate made up of two bones of the facial skeleton, located in the roof of the mouth. The bones are the palatine process of the maxilla and the horizontal plate of palatine bone. The hard palate spans ...
in the front of the
mouth In animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an onto ...
. The two maxillary bones are fused at the intermaxillary suture, forming the anterior nasal spine. This is similar to the mandible (lower jaw), which is also a fusion of two mandibular bones at the mandibular symphysis. The mandible is the movable part of the jaw.


Structure

In humans, the maxilla consists of: * The body of the maxilla * Four processes ** the zygomatic process ** the frontal process of maxilla ** the alveolar process ** the palatine process * three surfaces – anterior, posterior, medial * the Infraorbital foramen * the maxillary sinus * the incisive foramen


Articulations

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 The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull The skull is a bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various ot ...
, and the adjacent fused maxilla. Sometimes it articulates with the orbital surface, and sometimes with the
lateral pterygoid plate The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite. Each process consists of a m ...
of the sphenoid.


Development

The maxilla is ossified in membrane. Mall and Fawcett maintain that it is ossified from ''two'' centers only, one for the maxilla proper and one for the premaxilla. These centers appear during the sixth week of prenatal development 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 development, 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.


Function

The alveolar process of the maxillae holds the upper teeth, and is referred to as the maxillary arch. Each maxilla attaches laterally to the zygomatic bones (cheek bones). Each maxilla assists in forming the boundaries of three cavities: * the roof of the
mouth In animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an onto ...
* the floor and lateral wall of the nasal cavity * the wall of the
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such ...
Each maxilla also enters into the formation of two fossae: the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. -When the tender bones of the upper jaw and lower nostril are severely or repetitively damaged, at any age the surrounding cartilage can begin to deteriorate just as it does after death.


Clinical significance

A maxilla fracture is a form of facial fracture. A maxilla fracture is often the result of facial trauma such as violence, falls or automobile accidents. Maxilla fractures are classified according to the Le Fort classification.


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
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth A tooth (plural, : teeth) is a hard, calcification, calcified structure found in the jaws (or mouths) of many vertebrates and used to Mastication, break down food. Some animal ...
s 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,
amphibian Amphibians are four-limbed and ectothermic vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic ma ...
s, and
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtle Turtles are an order of reptiles known as Testudines, ch ...
s, 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.
Bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, ...
s do not have a maxilla in the strict sense; the corresponding part of their beaks (mainly consisting of the premaxilla) is called "upper mandible". Cartilaginous fish, such as sharks, also lack a true maxilla. Their upper jaw is instead formed from a cartilaginous bar that is not homologous with the bone found in other vertebrates.


Additional images

File:Maxilla anterior.png, Skull. Maxilla shown in green. Maxilla - animation 02.gif, Skull. Maxilla shown in white.


See also

* Maxillofacial surgery * Maxillary crest


References


Further reading

* *


External links

* {{Authority control Bones of the head and neck Dental anatomy Irregular bones Human mouth anatomy