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 most animals.

Human jawbone left
Human lower jaw viewed from the left

Arthropods

Bullant head detail
The mandibles of a bull ant

In arthropods, the jaws are chitinous and oppose laterally, and may consist of mandibles or chelicerae. These jaws are often composed of numerous mouthparts. Their function is fundamentally for food acquisition, conveyance to the mouth, and/or initial processing (mastication or chewing). Many mouthparts and associate structures (such as pedipalps) are modified legs.

Vertebrates

In most vertebrates, the jaws are bony or cartilaginous and oppose vertically, comprising an upper jaw and a lower jaw. The vertebrate jaw is derived from the most anterior two pharyngeal arches supporting the gills, and usually bears numerous teeth.

Fish

Pharyngeal jaws of moray eels
Moray eels have two sets of jaws: the oral jaws that capture prey and the pharyngeal jaws that advance into the mouth and move prey from the oral jaws to the esophagus for swallowing.

The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian. The two most anterior pharyngeal arches are thought to have become the jaw itself and the hyoid arch, respectively. The hyoid system suspends the jaw from the braincase of the skull, permitting great mobility of the jaws. While there is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed vertebrates (the Gnathostomes), which have seven arches, and primitive jawless vertebrates (the Agnatha), which have nine.

The original selective advantage offered by the jaw may not be related to feeding, but rather to increased respiration efficiency.[1] The jaws were used in the buccal pump (observable in modern fish and amphibians) that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the more familiar use of jaws (to humans), in feeding, was selected for and became a very important function in vertebrates. Many teleost fish have substantially modified jaws for suction feeding and jaw protrusion, resulting in highly complex jaws with dozens of bones involved.[2]

Amphibians, reptiles, and birds

The jaw in tetrapods is substantially simplified compared to fish. Most of the upper jaw bones (premaxilla, maxilla, jugal, quadratojugal, and quadrate) have been fused to the braincase, while the lower jaw bones (dentary, splenial, angular, surangular, and articular) have been fused together into a unit called the mandible. The jaw articulates via a hinge joint between the quadrate and articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones. Some species have jaw bones completely fused, while others may have joints allowing for mobility of the dentary, quadrate, or maxilla. The snake skull shows the greatest degree of cranial kinesis, which allows the snake to swallow large prey items.

Mammals

In mammals the jaws are made up of the mandible (lower jaw) and the maxilla (upper jaw). In the ape there is a reinforcement to the lower jaw bone called the simian shelf. In the evolution of the mammalian jaw, two of the bones of the jaw structure (the articular bone of the lower jaw, and quadrate) were reduced in size and incorporated into the ear, while many others have been fused together.[3] As a result, mammals show little or no cranial kinesis, and the mandible is attached to the temporal bone by the temporomandibular joints. Temporomandibular joint dysfunction is a common disorder of these joints, characterized by pain, clicking and limitation of mandibular movement.[4]

Sea urchins

Sea urchins possess unique jaws which display five-part symmetry, termed the Aristotle's lantern. Each unit of the jaw holds a single, perpetually growing tooth composed of crystalline calcium carbonate.

See also

References

  1. ^ Smith, M.M.; Coates, M.I. (2000). "10. Evolutionary origins of teeth and jaws: developmental models and phylogenetic patterns". In Teaford, Mark F.; Smith, Moya Meredith; Ferguson, Mark W.J. Development, function and evolution of teeth. Cambridge: Cambridge University Press. p. 145. ISBN 978-0-521-57011-4.
  2. ^ Britt, Robert Roy (28 November 2006). "Prehistoric Fish Had Most Powerful Jaws". Live Science.
  3. ^ Allin EF (December 1975). "Evolution of the mammalian middle ear". J. Morphol. 147 (4): 403–37. doi:10.1002/jmor.1051470404. PMID 1202224.
  4. ^ Wright, Edward F. (2010). Manual of temporomandibular disorders (2nd ed.). Ames, Iowa: Wiley-Blackwell. ISBN 978-0-8138-1324-0.

External links

Anilingus

Anilingus (from the Latin anus + -lingus, from lingere, "to lick", variantly spelled "analingus",) is the oral and anal sex act in which a person stimulates the anus of another by using the mouth, including lips, tongue, or teeth. It is also called anal–oral contact and anal–oral sex; colloquial names include rimming and rim job. It may be performed by and on persons of any sexual orientation for pleasure or as a form of erotic humiliation. Health risks include fecal–oral transmission.

CFB Moose Jaw

Canadian Forces Base Moose Jaw (IATA: YMJ, ICAO: CYMJ), also known as 15 Wing Moose Jaw, is a Canadian Forces base located 4 nautical miles (7.4 km; 4.6 mi) south of Moose Jaw, Saskatchewan. It is operated as an air force base by the Royal Canadian Air Force and is home to Royal Canadian Air Force Pilot training and 431 Squadron, aka Snowbirds.

The base's airfield is named after Air vice-marshal Clifford McEwen and is one of only three military aerodromes in Canada to be named after an individual, Valcartier (W/C J.H.L. (Joe) Lecomte) Heliport and Cold Lake/Group Captain R.W. McNair Airport being the others.

The airport is classified as an airport of entry by Nav Canada and is staffed by the Canada Border Services Agency (CBSA). The customs service is restricted to 15 Wing – Moose Jaw aircraft only.

Canine tooth

In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, fangs, or (in the case of those of the upper jaw) eye teeth, are relatively long, pointed teeth. However, they can appear more flattened, causing them to resemble incisors and leading them to be called incisiform. They developed and are used primarily for firmly holding food in order to tear it apart, and occasionally as weapons. They are often the largest teeth in a mammal's mouth. Individuals of most species that develop them normally have four, two in the upper jaw and two in the lower, separated within each jaw by incisors; humans and dogs are examples. In most species, canines are the anterior-most teeth in the maxillary bone.

The four canines in humans are the two maxillary canines and the two mandibular canines.

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.

Chin

The chin or the mental region is the area of the face below the lower lip and including the mandibular prominence. It is formed by the lower front of the mandible.

Dislocation of jaw

Dislocations occur when two bones that originally met at the joint detach. Dislocations should not be confused with Subluxation. Subluxation is when the joint is still partially attached to the bone.When a person has a dislocated jaw it is difficult to open and close the mouth. Dislocation can occur following a series of events if the jaw locks while open or unable to close. If the jaw is dislocated, it may cause an extreme headache or inability to concentrate. When the muscle's alignment is out of sync, a pain will occur due to unwanted rotation of the jaw.If the pain remains constant, it may require surgery to realign the jaw. Depending on the severity of the jaw's dislocation, pain relief such as paracetamol may assist to alleviate the initial chronic pain. If the pain relief is taken for an extended period of time, it may negatively affect the person while talking, eating, drinking, etc.

Elasmobranchii

Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including the sharks (superorder Selachii) and the rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

The earliest elasmobranch fossils came from the Devonian and many surviving orders date back to the Cretaceous, or even earlier. Many species became extinct during the Permian and there was a burst of adaptive radiation during the Jurassic.

Jew's harp

The Jew's harp, also known as the jaw harp, mouth harp, Ozark harp or juice harp, is a lamellophone instrument, consisting of a flexible metal or bamboo tongue or reed attached to a frame. The tongue/reed is placed in the performer's mouth and plucked with the finger to produce a note. Each instrument produces one pitch only, with its multiples (overtones), though different sized instruments provide different pitches. There is no standard pitch.

Jew's harps may be categorized as idioglot or heteroglot (whether or not the frame and the tine are one piece), by the shape of the frame (rod or plaque), by the number of tines, and whether the tines are plucked, joint-tapped, or string-pulled.

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).

Mandibular fracture

Mandibular fracture, also known as fracture of the jaw, is a break through the mandibular bone. In about 60% of cases the break occurs in two places. It may result in a decreased ability to fully open the mouth. Often the teeth will not feel properly aligned or there may be bleeding of the gums. Mandibular fractures occur most commonly among males in their 30s.Mandibular fractures are typically the result of trauma. This can include a fall onto the chin or a hit from the side. Rarely they may be due to osteonecrosis or tumors in the bone. The most common area of fracture is at the condyle (36%), body (21%), angle (20%) and symphysis (14%). While a diagnosis can occasionally be made with plain X-ray, modern CT scans are more accurate.Immediate surgery is not necessarily required. Occasionally people may go home and follow up for surgery in the next few days. A number of surgical techniques may be used including maxillomandibular fixation and open reduction internal fixation (ORIF). People are often put on antibiotics such as penicillin for a brief period of time. The evidence to support this practice; however, is poor.

Maxilla

The maxilla (plural: maxillae ) 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. 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.

Moose Jaw

Moose Jaw is the fourth largest city in Saskatchewan, Canada. Lying on the Moose Jaw River in the south-central part of the province, it is situated on the Trans-Canada Highway, 77 km (48 mi) west of Regina. Residents of Moose Jaw are known as Moose Javians. The city is surrounded by the Rural Municipality of Moose Jaw No. 161.

Moose Jaw is an industrial centre and important railway junction for the area's agricultural produce. CFB Moose Jaw is a NATO flight training school, and is home to the Snowbirds, Canada's military aerobatic air show flight demonstration team. Moose Jaw also has a casino and geothermal spa.

Moose Jaw Warriors

The Moose Jaw Warriors are a major junior ice hockey team in the Western Hockey League based out of Moose Jaw, Saskatchewan. The team plays its home games at Mosaic Place. The franchise moved to Moose Jaw from Winnipeg after the 1983–84 season, where they were known as the Winnipeg Warriors. The Warriors played in the Moose Jaw Civic Centre also known as "The Crushed Can" for 26 seasons, before moving to Mosaic Place in the city centre. The team has never won the WHL championship.

Muscles of mastication

There are four classical muscles of mastication. During mastication, three muscles of mastication (musculi masticatorii) are responsible for adduction of the jaw, and one (the lateral pterygoid) helps to abduct it. All four move the jaw laterally. Other muscles, usually associated with the hyoid, such as the mylohyoid muscle, are responsible for opening the jaw in addition to the lateral pterygoid.

Open-jaw ticket

An open-jaw ticket is an airline return ticket where the destination and/or the origin are not the same in both directions.

Prognathism

Prognathism is a positional relationship of the mandible or maxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull. In general dentistry, oral and maxillofacial surgery, and orthodontics, this is assessed clinically or radiographically (cephalometrics). The word prognathism derives from Greek πρό (pro, meaning "forward") and γνάθος (gnáthos, "jaw"). One or more types of prognathism can result in the common condition of malocclusion, in which an individual's top teeth and lower teeth do not align properly.

Rural Municipality of Moose Jaw No. 161

Moose Jaw No. 161 is a rural municipality in the Canadian province of Saskatchewan, located in the southern part of the province west of Regina in SARM Division No. 2. It surrounds the independently governed city of Moose Jaw, which is located just southwest of its centre.

Synapsid

Synapsids (Greek, 'fused arch'), synonymous with theropsids (Greek, 'beast-face') [not to be confused with Therapsida (Greek, 'beast-arch'), which are subordinate to Synapsida], are a group of animals that includes mammals and every animal more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids; more advanced mammal-like ones, therapsids. The non-mammalian members are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of the later amniotes; the other is the sauropsids, a group that includes modern reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period.

Synapsids were the largest terrestrial vertebrates in the Permian period, 299 to 251 million years ago, although some of the larger pareiasaurs at the end of Permian could match them in size. As with other groups then extant, their numbers and variety were severely reduced by the Permian–Triassic extinction. By the time of the extinction at the end of Permian, all the older forms of synapsids (known as pelycosaurs) were already gone, having been replaced by the more advanced therapsids. Though the dicynodonts and Eutheriodontia, the latter consisting of Eutherocephalia (Therocephalia) and Epicynodontia (Cynodontia), continued into the Triassic period as the only known surviving therapsids, archosaurs became the largest and most numerous land vertebrates in the course of this period. The recently discovered Lisowicia bojani was the size of an elephant. The cynodont group Probainognathia, which includes Mammaliaformes, were the only synapsids who outlasted the Triassic. After the Cretaceous–Paleogene extinction event, the synapsids (in the form of mammals) again became the largest land animals as well as becoming the largest marine animals.

Vise

A vise (American English) or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever.

Head
Neck
Trunk
Limbs
Other
Maxilla
Zygomatic
Palatine
Mandible
Nose
Other

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