The maxilla (plural: ''maxillae'' ) in

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, wi ...

is the upper fixed (not fixed in

Neopterygii Neopterygii (from Greek νέος ''neos'' 'new' and πτέρυξ ''pteryx'' 'fin') is a subclass of ray-finned fish (Actinopterygii). Neopterygii includes the Holostei and the Teleostei, of which the latter comprise the vast majority of extant ...

)

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, an ...

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 th ...

in the front of the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

. The two maxillary bones are fused at the intermaxillary suture, forming the

anterior nasal spine The anterior nasal spine, or anterior nasal spine of maxilla, is a bony projection in the skull that serves as a cephalometric landmark. The anterior nasal spine is the projection formed by the fusion of the two maxillary bones at the intermaxill ...

. This is similar to the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

(lower jaw), which is also a fusion of two mandibular bones at the

mandibular symphysis In human anatomy, the facial skeleton of the skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more p ...

. The mandible is the movable part of the jaw.

Structure

Sobo 1909 100 - Palatine process of maxilla

In humans, the maxilla consists of: * The body of the maxilla * Four

processes A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

** the

zygomatic process The zygomatic processes are three processes (protrusions) from other bones of the skull which each articulate with the zygomatic bone. The three processes are: * Zygomatic process of frontal bone from the frontal bone * Zygomatic process of maxi ...

** the frontal process of maxilla ** the

alveolar process The alveolar process () or alveolar bone is the thickened ridge of bone that contains the tooth sockets on the jaw bones (in humans, the maxilla and the mandible). The structures are covered by gums as part of the oral cavity. The synonymous te ...

** the palatine process * three surfaces – anterior, posterior, medial * the

Infraorbital foramen In human anatomy, the infraorbital foramen is one of two small holes in the skull's upper jawbone ( maxillary bone), located below the eye socket and to the left and right of the nose. Both holes are used for blood vessels and nerves. In anatomic ...

* the

maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Nathaniel Highmore (surgeon), Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.Human Anatomy, Jacobs, Elsevier, 2008, ...

* the

incisive foramen In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood ves ...

Articulations

Each maxilla articulates with nine bones: * two of the

cranium The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, ...

: the frontal and

ethmoid The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...

* seven of the

face The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may aff ...

: the

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...

, zygomatic, lacrimal,

inferior nasal concha The inferior nasal concha (inferior turbinated bone or inferior turbinal/turbinate) is one of the three paired nasal conchae in the nose. It extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, cu ...

palatine A palatine or palatinus (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman times.

vomer The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxil ...

, and the adjacent fused maxilla. Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate 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 Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...

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

of the maxillae holds the upper teeth, and is referred to as the maxillary arch. Each maxilla attaches laterally to the

zygomatic bone In the human skull, the zygomatic bone (from grc, ζῠγόν, zugón, yoke), also called cheekbone or malar bone, is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is ...

s (cheek bones). Each maxilla assists in forming the boundaries of three cavities: * the roof of the

* the floor and lateral wall of the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...

* 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 a ...

Each maxilla also enters into the formation of two fossae: the infratemporal and pterygopalatine, and two fissures, the

inferior orbital The inferior orbital fissure is formed by the sphenoid bone and the maxilla. It is located posteriorly along the boundary of the floor and lateral wall of the orbit. It transmits a number of structures, including: * the zygomatic branch of the ...

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 Facial trauma, also called maxillofacial trauma, is any physical trauma to the face. Facial trauma can involve soft tissue injuries such as burns, lacerations and bruises, or fractures of the facial bones such as nasal fractures and fractu ...

. A maxilla fracture is often the result of facial trauma such as

violence Violence is the use of physical force so as to injure, abuse, damage, or destroy. Other definitions are also used, such as the World Health Organization's definition of violence as "the intentional use of physical force or power, threatened ...

falls Falls may refer to: Places * Waterfalls or rapids * Falls, North Carolina, USA * Falls, West Virginia, USA Other uses * The ropes or wires, fed through davits, that are used to secure and lower a ship's lifeboats. * Falls (surname) * The sepa ...

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 present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, w ...

s are attached in mammals consists of a separate pair of bones, the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

e. These fuse with the maxilla proper to form the bone found in humans, and some other mammals. In

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartila ...

, 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

nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called t ...

s. 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 vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s do not have a maxilla in the strict sense; the corresponding part of their

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for fo ...

s (mainly consisting of the premaxilla) is called "upper mandible".

Cartilaginous fish Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

, such as sharks, also lack a true maxilla. Their upper jaw is instead formed from a

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...

bar that is not

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

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.

References

External links

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