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62-463: In jawed vertebrates , the mandible (from the Latin mandibula , 'for chewing'), lower jaw , or jawbone is a bone that makes up the lower – and typically more mobile – component of the mouth (the upper jaw being known as the maxilla ). The jawbone is the skull 's only movable, posable bone, sharing joints with the cranium's temporal bones . The mandible hosts

124-405: A stomach , and paired appendages (pectoral and pelvic fins, arms, legs, wings, etc.). Other traits are elastin , a horizontal semicircular canal of the inner ear, myelin sheaths of neurons , and an adaptive immune system which has discrete lymphoid organs ( spleen and thymus ), and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in

186-628: A branch of Placoderms was most likely the ancestor of present-day gnathostomes. A 419-million-year-old fossil of a placoderm named Entelognathus had a bony skeleton and anatomical details associated with cartilaginous and bony fish, demonstrating that the absence of a bony skeleton in Chondrichthyes is a derived trait. The fossil findings of primitive bony fishes such as Guiyu oneiros and Psarolepis , which lived contemporaneously with Entelognathus and had pelvic girdles more in common with placoderms than with other bony fish, show that it

248-524: A condition of shock in humans, e.g. when someone's mouth suddenly hangs agape in response to something. The exaggerated visual gag of a jaw dropping to the floor was a trademark of American animation director Tex Avery , who would often employ it when the Big Bad Wolf spies a sexually attractive woman. Gobstoppers , a type of hard candy, are known in North America as jawbreakers due to

310-446: A condition which can offset facial symmetry and cause posterior crossbite . The mandibular alveolar process can become resorbed when completely edentulous in the mandibular arch (occasionally noted also in partially edentulous cases). This resorption can occur to such an extent that the mental foramen is virtually on the superior border of the mandible, instead of opening on the anterior surface, changing its relative position. However,

372-470: A deceased person's age. Dental remains of Nazi leader Adolf Hitler , including part of a mandible with teeth, were the solitary physical evidence used to confirm his death in 1945. In the Hebrew Bible and Christian Old Testament Book of Judges , Samson used a donkey's jawbone to kill a thousand Philistines . As early as 1900, the phrase jaw-dropping was used as an adjective to describe

434-427: A depression called the incisive foramen . Vertically midway on either side of the body, below the second premolar tooth, is the mental foramen , through which the mental nerve and blood vessels pass. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus. Attached to this is the masseter muscle ( related to mastication ),

496-405: A doubled mandibular canal via radiograph. The mandible forms the lower jaw and holds the lower teeth in place. It articulates with the left and right temporal bones at the temporomandibular joints. The condyloid process, the superior (upper) and posterior projection from the ramus, makes the temporomandibular joint with the temporal bone. The coronoid process, superior and anterior projection from

558-605: A partial mandibulectomy which caused a conspicuous deformity. In his fight against cancer, American film critic Roger Ebert had a partial mandibulectomy in 2006, in addition to later surgeries. Jawed vertebrate Gnathostomata ( / ˌ n æ θ oʊ ˈ s t ɒ m ə t ə / ; from Ancient Greek : γνάθος ( gnathos ) 'jaw' + στόμα ( stoma ) 'mouth') are the jawed vertebrates . Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. Most gnathostomes have retained ancestral traits like true teeth ,

620-463: A technique using a syringe and cocaine which was performed successfully by 1885. One fifth of facial injuries involve a mandibular fracture. Mandibular fractures are often accompanied by a 'twin fracture' on the opposite side. There is no universally accepted treatment protocol, as there is no consensus on the choice of techniques in a particular anatomical shape of mandibular fracture clinic. A common treatment involves attachment of metal plates to

682-419: Is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylohyoid vessels and nerve. Behind this groove is a rough surface, for the insertion of the medial pterygoid muscle . The mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli , with small openings for nerves. On arriving at

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744-410: Is a quadrilateral, sheet-like muscle. It is thinner than the middle and inferior constrictor muscles. The sites of origin of the muscles collectively are the pterygoid hamulus (and occasionally the adjoining posterior margin of the medial pterygoid plate ) anteriorly, (the posterior margin of) the pterygomandibular raphe , the posterior extremity of the mylohyoid line of mandible , and (negligibly)

806-474: Is composed of a cartilagenous structure homologous with Meckel's cartilage. This also remains a significant element of the jaw in some primitive bony fish, such as sturgeons . In reptiles , Meckel's cartilage ossifies into the (multiple) bones of the lower jaw, while mammals of the Cretaceous (145–66 Mya) had both Meckel's cartilage and a mandible. In lobe-finned fishes and the early fossil tetrapods ,

868-427: Is divided into four parts according to its four distincts origins: a pterygopharyngeal, buccopharyngeal, mylopharyngeal, and a glossopharyngeal part. The muscle inserts onto the pharyngeal raphe , and pharyngeal spine . It is innervated by pharyngeal branch of the vagus nerve via the pharyngeal plexus . It acts to convey a bolus down towards the esophagus, facilitating swallowing. The superior constrictor muscle

930-438: Is formed in the human mandible by an ingrowth from the main mass of the bone. At birth, the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth , imperfectly partitioned off from one another. The mandibular canal is of large size and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth. The angle

992-467: Is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process is of comparatively large size, and projects above the level of the condyle. After birth, the two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but more especially behind

1054-460: Is provided primarily by the pharyngeal branch of the ascending pharyngeal artery , and the tonsilar branch of the facial artery . The interval between the upper border of the muscle and the base of the skull is closed by the pharyngeal aponeurosis , and is known as the sinus of Morgagni . There is an interval between superior pharyngeal constrictor and middle pharyngeal constrictor, this space contains glossopharyngeal nerve, lingual nerve and

1116-406: Is that jaws are homologous to the gill arches . In jawless fishes a series of gills opened behind the mouth, and these gills became supported by cartilaginous elements. The first set of these elements surrounded the mouth to form the jaw. The upper portion of the second embryonic arch supporting the gill became the hyomandibular bone of jawed fish, which supports the skull and therefore links

1178-409: Is the skull's largest and strongest bone. In old age, the bone can become greatly reduced in volume where there is a loss of teeth, and consequent resorption of the alveolar process and interalveolar septa. Consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is closer to the alveolar border. The ramus is oblique in direction,

1240-569: The Andy Gump deformity after the comic book character , whose design apparently lacks a jaw; proposed reconstruction methods include implanting synthetic material , potentially involving 3D printing . Bone loss (as in osteoporosis ) can be mitigated in the jawbone via bone grafting , which is sometimes performed to support dental implants (replacing teeth individually or in groups ). Mandibular prosthetics date back to ancient Egypt and China , but significant advancements were made in

1302-411: The depressor labii inferioris and depressor anguli oris (which support the mouth ), and the platysma (extending down over much of the neck ). From the inside, the mandible appears concave. On either side of the lower symphysis is the mental spine (which can be faint or fused into one), to which the genioglossus (the inferior muscle of the tongue ) attaches; the geniohyoid muscle attaches to

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1364-403: The facial skeleton , the mandible tends to deform in old age; it is also subject to fracturing . Surgery allows for the removal of jawbone fragments (or its entirety) as well as regenerative methods. Additionally, the bone is of great forensic significance. In humans , the mandible is the largest and lowest bone in the facial skeleton . It is the only movable bone of the skull (discounting

1426-413: The incisor teeth , it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. In the posterior two-thirds of the bone the canal is situated nearer the internal surface of the mandible; and in the anterior third, nearer its external surface. It contains the inferior alveolar vessels and nerve, from which branches are distributed to

1488-468: The malleus and the incus of the middle ear. In recent human evolution , both the oral cavity and jaws have shrunk in correspondence with the Neolithic-era shift from hunter-gatherer lifestyles towards agriculture and settlement, dated to c.  10,000 BCE . This has led to orthodontic malocclusions . The mandible forms as a bone (ossifies) from Meckel's cartilage, which forms

1550-408: The sister taxon of Gnathostomata. Jaw development in vertebrates is likely a product of the supporting gill arches. This development would help push water into the mouth by the movement of the jaw, so that it would pass over the gills for gas exchange. The repetitive use of the newly formed jaw bones would eventually lead to the ability to bite in some gnathostomes. Newer research suggests that

1612-601: The variable lymphocyte receptor gene. It is now assumed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins . Until recently these ancestors, known as antiarchs , were thought to have lacked pectoral or pelvic fins. In addition to this, some placoderms (extinct fish with bony plates) were shown to have a third pair of paired appendages, that had been modified to claspers in males and basal plates in females—a pattern not seen in any other vertebrate group. The Osteostraci (bony armored jawless fish) are generally considered

1674-436: The adult, the alveolar and subdental portions of the body are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°, also the adult condyle is higher than the coronoid process and the sigmoid notch becomes deeper. The adult mandible

1736-445: The angle measures about 140°, and the neck of the condyle is more or less bent backward. The posterior of the mandible is notoriously resistant to the full effects of local anesthesia . The IAN provides sensory innervation to much of the mandible and its teeth, making it a target of block anesthesia . Injecting the nerve is challenging due to the amount of surrounding soft tissue . American surgeon William Stewart Halsted developed

1798-409: The bone homologous to the mandible of mammals is merely the largest of several bones in the lower jaw. In such animals, it is referred to as the dentary bone or os dentale , and forms the body of the outer surface of the jaw. It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower angular bone and a suprangular bone just above it. The inner surface of

1860-428: The cartilaginous bar of the mandibular arch and, dorsally, parts of the middle ear. The two sides of the jawbone are inferiorly fused at the mandibular symphysis (the chin) during the first year of life. The cartilage of the ramus is replaced by fibrous tissue, which persists to form the sphenomandibular ligament . Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind

1922-438: The chief part of the body lies above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the mylohyoid line ; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°. The fibrocartilage of the mandibular symphysis fuses together in early childhood. In

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1984-486: The deep remodelling of the vertebrate skull that must have taken place as early jaws evolved. The ancestor of all jawed vertebrates have gone through two rounds of whole genome duplication. The first happened before the gnathostome and cyclostome split, and appears to have been an autopolyploidy event (happened within the same species). The second occurred after the split, and was an allopolyploidy event (the result of hybridization between two lineages). The customary view

2046-444: The dentary, articular, and angular bones remain, while in living amphibians , the dentary is accompanied only by the prearticular, and, in salamanders , one of the coronoids. The lower jaw of reptiles has only a single coronoid and splenial, but retains all the other primitive bones except the prearticular and the periosteum. In birds, the various bones have fused into a single structure. In mammals, most have disappeared, leaving only

2108-481: The early vertebrate jaw has been described as "a crucial innovation" and "perhaps the most profound and radical evolutionary step in the vertebrate history". Fish without jaws had more difficulty surviving than fish with jaws, and most jawless fish became extinct during the Triassic period. However studies of the cyclostomes , the jawless hagfishes and lampreys that did survive, have yielded little insight into

2170-532: The fracture to assist in healing. The mandible may be dislocated anteriorly (to the front) and inferiorly (downwards) but very rarely posteriorly (backwards). The articular disk of the temporomandibular joint prevents the mandible from moving posteriorly, making the condylar neck particularly vulnerable to fractures. Further, various jawbone damage can cause temporomandibular joint dysfunction , with symptoms including pain and inflammation . The jawbone can also become deviated in mandibular lateral displacement ,

2232-503: The fracturing risk they impose on teeth. Owing in part to the forensic evidence of Hitler's death being limited to his dental remains (including a jawbone fragment broken and burnt around the alveolar process), some fringe accounts (bolstered by the Soviet Union , which captured Berlin in 1945) allege that Hitler faked his death (ostensibly along with Eva Braun ). In later decades, American real-estate businessman Fred Trump had

2294-427: The incisor teeth becomes ossified and incorporated with this part of the mandible. About the sixth week of fetal life, intramembranous ossification takes place in the membrane covering the outer surface of the ventral end of Meckel's cartilage, and each half of the bone is formed from a single center which appears, near the mental foramen. By the tenth week, the portion of Meckel's cartilage which lies below and behind

2356-414: The incisor teeth is surrounded and invaded by the dermal bone (also known as the membrane bone). Somewhat later, accessory nuclei of cartilage make their appearance, as These accessory nuclei possess no separate ossific centers but are invaded by the surrounding dermal bone and undergo absorption. The inner alveolar border, usually described as arising from a separate ossific center ( splenial center ),

2418-458: The jaw is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper. A set of three narrow coronoid bones lie above the prearticular bone. As the name implies, the majority of the teeth are attached to the dentary, but there are commonly also teeth on the coronoid bones, and sometimes on the prearticular. Most vertebrates exhibit a simpler scheme, as bones have either fused or vanished. In teleosts , only

2480-682: The jaw to the cranium. The hyomandibula is a set of bones found in the hyoid region in most fishes. It usually plays a role in suspending the jaws or the operculum in the case of teleosts . While potentially older Ordovician records are known, the oldest unambigious evidence of jawed vertebrates are Qianodus and Fanjingshania from the early Silurian ( Aeronian ) of Guizhou , China around 439 million years ago, which are placed as acanthodian -grade stem -chondrichthyans. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Superior pharyngeal constrictor muscle The muscle

2542-432: The jawbone is known as a mandibulectomy . The removal of a small portion is known as partial mandibulectomy and a larger portion segmental mandibulectomy . This can be performed to remove a tumor, circumvent cancer in nearby areas, and/or in response to infection, osteonecrosis , or injury. The removed portion can be replaced with metal plating or bone from elsewhere in the body. Oral muscles tend to work differently after

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2604-419: The jawless craniates Agnatha .   † Placodermi    [REDACTED]    Acanthodians , incl. Chondrichthyes (cartilaginous fishes) [REDACTED]    Actinopterygii    [REDACTED]    Amphibia    [REDACTED]    Sauria    [REDACTED]    Mammalia    [REDACTED] The appearance of

2666-562: The joint of the jawbone enables actions such speech and yawning , while playing a more subtle role in activities such as kissing and breathing . The mandible of vertebrates evolved from Meckel's cartilage , left and right segments of cartilage which supported the anterior branchial arch in early fish . Fish jaws surface in species of the large arthrodire genus Dunkleosteus ( fl.  382–358 million years ago ), which crushed prey with their quickly articulating mouths. The lower jaw of cartilaginous fish , such as sharks ,

2728-421: The late 19th century with new techniques for attaching prosthetics to a depreciated jawbone as well as bone grafting. In 2010, the first successful face transplant was conducted on a Spanish farmer after a self-inflicted gun accident ; this included the replacement of the entire mandible. The mandible can provide forensic evidence because its form changes over a person's life, and this can be used to determine

2790-461: The lower teeth (their depth delineated by the alveolar process ). Many muscles attach to the bone, which also hosts nerves (some connecting to the teeth) and blood vessels . Amongst other functions, the jawbone is essential for chewing food. Owing to the Neolithic advent of agriculture ( c.  10,000 BCE ), human jaws evolved to be smaller . Although it is the strongest bone of

2852-445: The lower mental spine. Above the mental spine, a median foramen and furrow can line the symphysis. Below the mental spine is an oval depression (the digastric fossa of the mandible ) where the digastric muscle attaches. Extending backward and upward on either side from the lower symphysis is a ridge called the mylohyoid line , where the mylohyoid muscle attaches; a small part of the superior pharyngeal constrictor muscle attaches to

2914-451: The mandible and supplies the anterior teeth. The mental nerve exits the mental foramen and supplies sensation to the chin and lower lip. Males generally have squarer, stronger, and larger mandibles than females. The mental protuberance is more pronounced in males but can be visualized and palpated in females. Rarely, a bifid IAN may be present, resulting in a second and more inferiorly placed mandibular foramen. This can be detected by noting

2976-399: The mandible. As a result, there is only articulation between the mandible and temporal bones, as opposed to articulation between articular and quadrate bones . An intermediate stage can be seen in some therapsids , in which both points of articulation are present. Aside from the dentary, only few other bones of the lower jaw remain in mammals; the former articular and quadrate bones survive as

3038-411: The mental foramen, to provide space for the three additional teeth developed in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles; but, the alveolar portion is the deeper of the two, and, consequently,

3100-503: The more inferior body of the mandible is not affected and remains thick and rounded. With age and tooth loss, the alveolar process is absorbed so that the mandibular canal becomes nearer the superior border. Sometimes with excessive alveolar process absorption, the mandibular canal disappears entirely and deprives the IAN of its bony protection, although soft tissue continues to guard the nerve. The surgical removal ( resection ) of all or part of

3162-405: The origin of teeth along with, or soon after, the evolution of jaws. Late Ordovician -aged microfossils of what have been identified as scales of either acanthodians or "shark-like fishes", may mark Gnathostomata's first appearance in the fossil record. Undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian , and become abundant by

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3224-428: The outside, the mandible is marked in the midline by a faint ridge, indicating the mandibular symphysis , the line of junction of the two halves of the mandible. This ridge divides below and encloses a triangular eminence, the mental protuberance (the chin), the base of which is depressed in the center but raised on both sides to form the mental tubercle . Just above this, on both sides, the mentalis muscles attach to

3286-440: The posterior ridge, near the alveolar margin . Above the anterior ridge, the sublingual gland rests against a smooth triangular area, and below the posterior ridge, the submandibular gland rests in an oval depression. The ramus of the human mandible has four sides, two surfaces, four borders, and two processes. On the outside, the ramus is flat and marked by oblique ridges at its lower part. It gives attachment throughout nearly

3348-668: The procedure, requiring therapy to relearn operations such as eating and speaking. During recovery, a feeding tube is utilized, and sometimes a tracheotomy is also performed to maintain respiration in case of swollen muscles. In a technique illustrated in the 19th century, the flesh of the face is incised along the inferior of the mandible and peeled upward for the bone's removal. Complications can involve difficulties with free flap transfer and airway management. Additional side effects include pain, infection, numbness, and (rarely, fatal) bleeding. Even successful surgeries can result in deformity , with an extreme version being referred to as

3410-526: The ramus. This provides attachment to the temporal muscle . Teeth sit in the upper part of the body of the mandible. The frontmost part of teeth is more narrow and holds front teeth. The back part holds wider and flatter (albeit grooved) teeth primarily for chewing food. The word mandible derives from the Latin word mandibula 'jawbone' (literally, 'used for chewing'), from mandere 'to chew' and -bula ( instrumental suffix). In addition to mastication,

3472-431: The side of the tongue. Four parts of the muscle are distinguished according to the origin: The muscle's fibres extend posterior-ward from its origin to form the midline pharyngeal raphe which then attaches onto the pharyngeal tubercle (of the basilar part of the occipital bone ). The superior pharyngeal constrictor muscle receives motor innervation from the pharyngeal plexus of vagus nerve . Arterial supply

3534-470: The start of the Devonian . Gnathostomata is traditionally a infraphylum , broken into three top-level groupings: Chondrichthyes , or the cartilaginous fish; Placodermi , an extinct grade of armored fish; and Teleostomi , which includes the familiar classes of bony fish , birds , mammals , reptiles , and amphibians . Some classification systems have used the term Amphirhina . It is a sister group of

3596-520: The stylopharyngeus muscle. The superior fibers arch beneath the levator veli palatini muscle and the Eustachian tube . Constriction of the muscle constricts the superior portion of the pharynx . As soon as the bolus of food is received in the pharynx, the elevator muscles relax, the pharynx descends, and the constrictors contract upon the bolus, conveying it downward into the esophagus . [REDACTED] This article incorporates text in

3658-504: The teeth. The mandible has two main holes ( foramina ), found on both its left and right sides: The inferior alveolar nerve (IAN), a branch of the mandibular nerve (itself a major division of the cranium's trigeminal nerve ), enters the mandibular foramen and runs forward in the mandibular canal, supplying sensation to the gums and teeth. Before passing through the mental foramen, the nerve divides into two terminal branches: incisive and mental nerves. The incisive nerve runs forward in

3720-399: The vibrating ossicles of the middle ear ). It is connected to the skull's temporal bones by the temporomandibular joints . In addition to simply opening and closing, the jawbone can articulate side to side as well as forward and back. The mandible consists of: The body of the mandible is curved, and the front part gives structure to the chin . It has two surfaces and two borders. From

3782-411: The whole of its extent to the masseter muscle. On the inside at the center there is an oblique mandibular foramen , for the entrance of the inferior alveolar vessels and nerve . The margin of this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula of the mandible , which gives attachment to the sphenomandibular ligament ; at its lower and back part

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3844-458: Was a relative rather than a direct ancestor of the extant gnathostomes. It also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes. Fossil findings of juvenile placoderms, which had true teeth that grew on the surface of the jawbone and had no roots, making them impossible to replace or regrow as they broke or wore down as they grew older, proves the common ancestor of all gnathostomes had teeth and place

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