The maxilla is a fusion of two bones along the palatal

Palate

The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...

 fissure that form the upper jaw

Jaw

The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

. This is similar to the mandible (lower jaw), which is also a fusion of two halves at the mental symphysis. Sometimes (e.g. in bony fish), the maxilla is called "upper maxilla," with the mandible being the "lower maxilla." Conversely, in bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s the upper jaw is often called "upper mandible."

Function

The alveolar process of the maxilla holds the upper teeth, and is referred to as the maxillary arch. The maxilla attaches laterally to the zygomatic bone

Zygomatic bone

The zygomatic bone is a paired bone of the human skull. It articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. The zygomatic is homologous to the jugal bone of other tetrapods...

s (cheek bones).

The maxilla assists in forming the boundaries of three cavities:

• the roof of the mouth
  Mouth
  The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
  
  
• the floor and lateral wall of the nasal antrum
• the wall of the orbit
  Orbit (anatomy)
  In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
  
  

The maxilla also enters into the formation of two fossae: the infratemporal

Infratemporal fossa

The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch.* anteriorly, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process...

 and pterygopalatine

Pterygopalatine fossa

The pterygopalatine fossa is a fossa in the skull. It is the indented area medial to the pterygomaxillary fissure leading into the sphenopalatine foramen.-Boundaries:It has the following boundaries:...

, and two fissures, the inferior orbital and pterygomaxillary.

Components

Each half of the fused maxilla consists of:

• The body of the maxilla
• Four processes
  • The zygomatic process
    Zygomatic process of maxilla
    The zygomatic process of the maxilla is a rough triangular eminence, situated at the angle of separation of the anterior, zygomatic, and orbital surfaces.* In front it forms part of the anterior surface....
    
    
  • The frontal process of maxilla
    Frontal process of maxilla
    The frontal process of the maxilla is a strong plate, which projects upward, medialward, and backward, by the side of the nose, forming part of its lateral boundary....
    
    
  • The alveolar process
  • The palatine process
• Infraorbital foramen
  Infraorbital foramen
  Above the canine fossa is the infraorbital foramen, the end of the infraorbital canal; it transmits the infraorbital artery, vein, and infraorbital nerve.-External links: *...
  
  
• The maxillary sinus
  Maxillary sinus
  The pyramid shaped maxillary sinus is the largest of the paranasal sinuses, and drains into the nose. It is present at birth as rudimentary air cells, and develops throughout childhood.-General characteristics:...
  
  

Articulations

The maxilla articulates with nine bones:

• two of the cranium: the frontal
  Frontal bone
  The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
  
   and ethmoid
• seven of the face
  Face
  The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...
  
  : the nasal
  Nasal bone
  The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
  
  , zygomatic
  Zygomatic bone
  The zygomatic bone is a paired bone of the human skull. It articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. The zygomatic is homologous to the jugal bone of other tetrapods...
  
  , lacrimal
  Lacrimal bone
  The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
  
  , inferior nasal concha, palatine
  Palatine bone
  The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...
  
  , vomer
  Vomer
  The vomer 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 maxillary bones.-Biology:...
  
  , and the adjacent fused maxillary bone.

Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate

Lateral pterygoid plate

The lateral pterygoid plate of the sphenoid is broad, thin, and everted; its lateral surface forms part of the medial wall of the infratemporal fossa, and gives attachment to the lateral pterygoid muscle; its medial surface forms part of the pterygoid fossa, and gives attachment to the medial...

 of the sphenoid

Sphenoid bone

The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

.

In other animals

In most vertebrates, the foremost part of the upper jaw, to which the incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

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

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

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

Osteichthyes

Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...

, amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s, and reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

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 nostril

Nostril

A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

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

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

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

Beak

The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...

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

Cartilaginous fish

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...

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

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

nous bar that is not homologous

Homology (biology)

Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

 with the bone found in other vertebrates.

See also

• Bone terminology
• Terms for anatomical location
• Ossification of maxilla
  Ossification of maxilla
  thumb|Figure 5: Anterior surface of maxilla at birth.thumb|Figure 6: Inferior surface of maxilla at birth.The maxilla is ossified in membrane. Mall 40 and Fawcett 41 maintain that it is ossified from two centers only, one for the maxilla proper and one for the premaxilla.These centers appear during...
  
  
• Hypostome
  Hypostome
  A hypostome , is a calcified harpoon-like structure near the mouth area of certain parasitic arthropods including ticks and mites , that allows them to anchor themselves firmly in place on a host mammal while sucking blood...
  
  
• Maxillofacial surgery