Maxilla

The maxilla (plural: maxillae /mækˈsɪliː/)[2] in animals is the upper fixed bone of the jaw formed from the fusion of two maxillary bones. The upper jaw includes the hard palate in the front of the mouth.[3][4] 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.

Maxilla
Gray189
Side view. Maxilla visible at bottom left, in green.
Gray190
Front view. Maxilla visible at center, in green.
Details
Precursor1st branchial arch[1]
Identifiers
MeSHD008437
TAA02.1.12.001
FMA9711
Anatomical terms of bone

Structure

Sobo 1909 100 - Palatine process of maxilla
Inferior surface of maxilla

In humans, the maxilla consists of:

Articulations

Each maxilla articulates with nine bones:

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

Development

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Figure 5: Anterior surface of maxilla at birth.
Gray162
Figure 6: Inferior surface of maxilla at birth.

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.[5][6]

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

FracLeftNasalBoneMark
Fracture of the left lacrimal / maxillary bone

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:

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

Maxilla fractures is a form of facial fracture caused by a 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 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.[7]

Birds 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.[7]

Additional images

Maxilla anterior

Skull. Maxilla shown in green.

See also

References

This article incorporates text in the public domain from page 157 of the 20th edition of Gray's Anatomy (1918)

  1. ^ hednk-023—Embryo Images at University of North Carolina
  2. ^ OED 2nd edition, 1989.
  3. ^ Merriam-Webster Online Dictionary.
  4. ^ Fehrenbach; Herring (2012). Illustrated Anatomy of the Head and Neck. Elsevier. p. 55. ISBN 978-1-4377-2419-6.
  5. ^ Mall, Franklin P. (1906). "On ossification centers in human embryos less than one hundred days old". American Journal of Anatomy. 5 (4): 433–458. doi:10.1002/aja.1000050403.
  6. ^ Fawcett, Edward (1911). "Some Notes on the Epiphyses of the Ribs". Journal of Anatomy and Physiology. 45 (Pt 2): 172–178. PMC 1288875. PMID 17232872.
  7. ^ a b Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 217–43. ISBN 0-03-910284-X.

Further reading

  • Sicher, Harry; Du Brul, E. Lloyd (1975). Oral Anatomy (6th ed.). St. Louis: Mosby. ISBN 0-8016-4604-9.
  • Worthington, Philip; Evans, John R., eds. (1994). Controversies in Oral & Maxillofacial Surgery. Saunders. ISBN 0-7216-3099-5.

External links

Agnathia

Agnathia (also termed hypognathous) is absence of a portion or the entirety of one or both jaws. It is a very rare condition.

Alveolar process

The alveolar process () (also called the alveolar bone) is the thickened ridge of bone that contains the tooth sockets (dental alveoli) on the jaw bones that hold teeth. In humans, the tooth-bearing bones are the maxilla and the mandible. The curved part of each alveolar process on the jaw is called the alveolar arch.

Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Cherubism

Cherubism is a rare genetic disorder that causes prominence in the lower portion in the face. The name is derived from the temporary chubby-cheeked resemblance to putti, often confused with cherubs, in Renaissance paintings.

Dasygnathoides

Dasygnathoides is an extinct genus of pseudosuchian from the Late Triassic (Carnian) Lossiemouth Sandstone of Scotland.

Frontal process of maxilla

The frontal process of maxilla is a strong plate, which projects upward, medialward, and backward from the maxilla, forming part of the lateral boundary of the nose.

Its lateral surface is smooth, continuous with the anterior surface of the body, and gives attachment to the quadratus labii superioris, the orbicularis oculi, and the medial palpebral ligament.

Its medial surface forms part of the lateral wall of the nasal cavity; at its upper part is a rough, uneven area, which articulates with the ethmoid, closing in the anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the posterior end of which articulates with the middle nasal concha, while the anterior part is termed the agger nasi; the crest forms the upper limit of the atrium of the middle meatus.

The upper border articulates with the frontal bone and the anterior with the nasal; the posterior border is thick, and hollowed into a groove, which is continuous below with the lacrimal groove on the nasal surface of the body: by the articulation of the medial margin of the groove with the anterior border of the lacrimal a corresponding groove on the lacrimal is brought into continuity, and together they form the lacrimal fossa for the lodgement of the lacrimal sac.

The lateral margin of the groove is named the anterior lacrimal crest, and is continuous below with the orbital margin; at its junction with the orbital surface is a small tubercle, the lacrimal tubercle, which serves as a guide to the position of the lacrimal sac.

Fukuisaurus

Fukuisaurus (meaning "Fukui lizard") is a genus of herbivorous dinosaur from the Early Cretaceous. It was an ornithopod which lived in what is now Japan.

Remains of Fukuisaurus were discovered in 1989, in the Kitadani formation in Katsuyama, Fukui Prefecture, in rocks from the Kitadani Formation, dating to the Barremian. The type species, Fukuisaurus tetoriensis, was described in 2003 by Yoshitsugu Kobayashi and Yoichi Azuma. The genus name refers to Fukui; the specific name to the geological Tetori Group. The type specimens or cotypes are FPDM-V-40-1, a right maxilla, and FPDM-V-40-2, a right jugal. Further elements of a skull and a right sternal plate had been recovered. Since 2003 much more extensive finds have been made and much of the skeleton is now known.

Fukuisaurus is a relatively small species. In 2010 Gregory S. Paul estimated the length at 4.5 meters, the weight at four hundred kilograms. Being a bipedal, optionally quadrupedal, animal, it was similar in general build to Iguanodon, Ouranosaurus and Altirhinus. According to the describers Fukuisaurus was exceptional in that its skull was not kinetic: the tooth-bearing maxilla would be so strongly fused to the vomer that a sideways chewing motion would have been impossible.

A cladistic analysis showed that Fukuisaurus was a basal member of the Hadrosauroidea, less derived than Altirhinus.

High-arched palate

A high-arched palate (also termed high-vaulted palate) is where the palate is unusually high and narrow. It is usually a developmental feature that may occur in isolation or in association with a number of conditions. It may also be an acquired condition caused by chronic thumb-sucking. A high-arched palate may result in a narrowed airway and sleep disordered breathing.Example conditions which may be associated with a high-arched palate include:

Crouzon syndrome

Down syndrome

Apert syndrome

Ehlers-Danlos Syndrome

Treacher Collins syndrome

Marfan syndrome

Incontinentia pigmenti

Allergic rhinitis

Infraorbital canal

The infraorbital canal is a canal found at the base of the orbit that opens on to the maxilla. It is continuous with the infraorbital groove and opens onto the maxilla at the infraorbital foramen. The infraorbital nerve and infraorbital artery travel through the canal.

Mandible

The mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human face. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone of the skull (discounting the ossicles of the middle ear).The bone is formed in the fetus from a fusion of the left and right mandibular prominences, and the point where these sides join, the mandibular symphysis, is still visible as a faint ridge in the midline. Like other symphyses in the body, this is a midline articulation where the bones are joined by fibrocartilage, but this articulation fuses together in early childhood.The word "mandible" derives from the Latin word mandibula, "jawbone" (literally "one used for chewing"), from mandere "to chew" and -bula (instrumental suffix).

Maxilla (arthropod mouthpart)

In arthropods, the maxillae (singular maxilla) are paired structures present on the head as mouthparts in members of the clade Mandibulata, used for tasting and manipulating food. Embryologically, the maxillae are derived from the 4th and 5th segment of the head and the maxillary palps; segmented appendages extending from the base of the maxilla represent the former leg of those respective segments. In most cases, two pairs of maxillae are present and in different arthropod groups the two pairs of maxillae have been variously modified. In crustaceans, the first pair are called maxillulae (singular maxillula).

Modified coxae at the base of the pedipalps in spiders are also called "maxillae", although they are not homologous with mandibulate maxillae.

Maxillary hypoplasia

Maxillary hypoplasia is an underdevelopment of the maxillary bones, which produces midfacial retrusion and creates the illusion of protuberance (jutting forward) of the lower jaw. It is associated with Crouzon syndrome, Angelman syndrome, as well as fetal alcohol syndrome. It can also be associated with Cleft lip and cleft palate. Some people could develop it due to poor dental extractions.

Mucogingival junction

A mucogingival junction is an anatomical feature found on the intraoral mucosa. The mucosa of the cheeks and floor of the mouth are freely moveable and fragile, whereas the mucosa around the teeth and on the palate are firm and keratinized. Where the two tissue types meet is known as a mucogingival junction.

There are three mucogingival junctions: on the facial of the maxilla and on both the facial and lingual of the mandible. The palatal gingiva of the maxilla is continuous with the tissue of the palate, which is bound down to the palatal bones. Because the palate is devoid of freely moveable alveolar mucosa, there is no mucogingival junction.

Nanningosaurus

Nanningosaurus is a genus of hadrosaurid dinosaur from the upper Late Cretaceous of the Nalong Basin, Guangxi, China.

The type and only species is Nanningosaurus dashiensis, named and described by Mo Jinyou, Zhao Zhongru, Wamg Wei and Xu Xing in 2007. The generic name refers to the city of Nanning, located close to the excavation site. The specific name is derived from the Pinyin da-shi, "great stone", the name of the village where the discovery was made.Nanningosaurus is based on holotype NHMG8142, an incomplete skeleton including skull, arm, leg and pelvis remains found in 1991, together with the holotype of Qingxiusaurus. The discoveries were in 1998 reported in the scientific literature. The paratype is NHJM8143, a right maxilla.In 2010, Gregory S. Paul estimated the body length of Nanningosaurus at 7.5 metres, its weight at 2.5 tonnes. No autapomorphies were given but a unique combination of diagnostic characteristics includes a high and sharp ascending branch of the maxilla, a short rear branch of the maxilla, relatively few tooth positions (twenty-seven in the maxilla), a transversely wide lower quadrate with a weak paraquadratic notch, a gracile upper arm, and an ischium that at the lower end of its rear edge curves towards its expanded tip.Mo et al. (2007), who described the specimen, performed a phylogenetic analysis that suggests Nanningosaurus was a basal lambeosaurine, although they stressed the support for this was tentative. This animal was the first hadrosaurid named from southern China.

Palatine process of maxilla

In human anatomy of the mouth, the palatine process of maxilla (palatal process), is a thick, horizontal process of the maxilla. It forms the anterior three quarters of the hard palate, the horizontal plate of the palatine bone making up the rest.

Panorpida

Panorpida or Mecopterida is a proposed superorder of Endopterygota. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is also supported by recent molecular data.

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 and usually termed as the incisive bone. Other terms used for this structure include premaxillary bone or os premaxillare, and intermaxillary bone or os intermaxillare.

Spider anatomy

The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata (sections or segments), eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.

Spiders also have several adaptations that distinguish them from other arachnids. All spiders are capable of producing silk of various types, which many species use to build webs to ensnare prey. Most spiders possess venom, which is injected into prey (or defensively, when the spider feels threatened) through the fangs of the chelicerae. Male spiders have specialized pedipalps that are used to transfer sperm to the female during mating. Many species of spiders exhibit a great deal of sexual dimorphism.

Zygomatic process

Each Zygomatic process is the part of a bone which articulates with the zygomatic bone. The three processes are:

Zygomatic process of frontal bone from the frontal bone

Zygomatic process of maxilla from the maxilla (malar process)

Zygomatic process of temporal bone from the temporal boneThe term zygomatic derives from the Greek Ζυγόμα zygoma meaning "yoke". The zygomatic process is occasionally referred to as the zygoma, but this term usually refers to the zygomatic bone or occasionally the zygomatic arch.

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