In
anatomy
Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
, the mandible, lower jaw or jawbone is the largest, strongest and lowest
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, ...
in the human
facial skeleton. It forms the lower
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 serv ...
and holds the lower
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...
in place. The mandible sits beneath the
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
. It is the only movable bone of the skull (discounting the
ossicles of the middle ear).
It is connected to the
temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex.
The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. ...
s by the
temporomandibular joint
In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral synovial articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...
s.
The bone is formed
in the fetus from a fusion of the left and right
mandibular prominence
The mandibular prominence is an embryological structure which gives rise to the lower portion of the face.
The mandible and lower lip derive from it. The mesenchymal cells within the mandibular prominence condense to form Meckel's cartilage.
It ...
s, 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.
[Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 59]
The word "mandible" derives from the Latin word ''mandibula'', "jawbone" (literally "one used for chewing"), from ''
mandere'' "to chew" and ''-bula'' (
instrumental
An instrumental is a recording normally without any vocals, although it might include some inarticulate vocals, such as shouted backup vocals in a big band setting. Through semantic widening, a broader sense of the word song may refer to inst ...
suffix).
Structure
Components
![Gray177](https://upload.wikimedia.org/wikipedia/commons/a/a3/Gray177.png)
The mandible consists of:
* The body, found at the front
* A ramus on the left and the right, the rami rise up from the body of the mandible and meet with the body at the
angle of the mandible __NOTOC__
The angle of the mandible (gonial angle) is located at the posterior border at the junction of the lower border of the ramus of the mandible.
The angle of the mandible, which may be either inverted or everted, is marked by rough, obliq ...
or the gonial angle.
Body
![Slide1oooo](https://upload.wikimedia.org/wikipedia/commons/7/70/Slide1oooo.JPG)
The body of the mandible is curved, and the front part gives structure to the
chin. It has two surfaces and two borders. From 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, which fuse at about one year of age.
This ridge divides below and encloses a triangular eminence, the
mental protuberance
The symphysis of the external surface of the mandible divides below and encloses a triangular eminence, the mental protuberance, the base of which is depressed in the center but raised on either side to form the ''mental tubercle
The mandibular s ...
(the chin), the base of which is depressed in the center but raised on both sides to form the
mental tubercle
The mandibular symphysis divides below and encloses a triangular eminence, the mental protuberance
The symphysis of the external surface of the mandible divides below and encloses a triangular eminence, the mental protuberance, the base of which ...
. Just above this, on both sides, the
mentalis
The mentalis muscle is a paired central muscle of the lower lip, situated at the tip of the chin. It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pouting muscle" due ...
muscles attach to a depression called the incisive fossa.
Below the second premolar tooth, on both sides, midway between the upper and lower borders of the body, are the
mental foramen
The mental foramen is one of two foramina (openings) located on the anterior surface of the mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels.
Structure
The ...
, for the passage of the mental vessels and nerve.
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
In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...
, the
depressor labii inferioris
The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle. It helps to lower the bottom lip.
Structure
The depressor labii inferioris muscle arises from the lateral surface of the mandible. This is below the mental for ...
and
depressor anguli oris
The depressor anguli oris muscle (triangularis muscle) is a facial muscle. It originates from the mandible and inserts into the angle of the mouth. It is associated with frowning, as it depresses the corner of the mouth.
Structure
The depres ...
, and the
platysma
The platysma muscle is a superficial muscle of the human neck that overlaps the sternocleidomastoid. It covers the anterior surface of the neck superficially. When it contracts, it produces a slight wrinkling of the neck, and a "bowstring" effec ...
(from below).
From the inside, the mandible appears concave. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the
genioglossus
The genioglossus is one of the paired extrinsic muscles of the tongue. The genioglossus is the major muscle responsible for protruding (or sticking out) the tongue.
Structure
Genioglossus is the fan-shaped extrinsic tongue muscle that forms the ma ...
. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the
geniohyoid
The geniohyoid muscle is a narrow muscle situated superior to the medial border of the mylohyoid muscle. It is named for its passage from the chin ("genio-" is a standard prefix for "chin") to the hyoid bone.
Structure
It arises from the inf ...
. In some cases, the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Above the mental spines, a median foramen and furrow are sometimes seen; they mark the line of union of the halves of the bone. Below the mental spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the
digastric
The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle belli ...
. Extending upward and backward on either side from the lower part of the symphysis is the
mylohyoid line
The mylohyoid line is a bony ridge on the internal surface of the mandible. It runs posterosuperiorly. It is the site of origin of the mylohyoid muscle, the superior pharyngeal constrictor muscle, and the pterygomandibular raphe.
Structure
The ...
, which gives origin to the
mylohyoid muscle
The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth. It is named after its two attachments near the molar teeth. It forms the fl ...
; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the
constrictor pharyngis superior
The superior pharyngeal constrictor muscle is a muscle in the pharynx. It is the highest located muscle of the three pharyngeal constrictors. The muscle is a quadrilateral muscle, thinner and paler than the inferior pharyngeal constrictor muscle ...
, and to the
pterygomandibular raphe
The pterygomandibular raphe (pterygomandibular ligament) is a ligamentous band of the buccopharyngeal fascia. It is attached superiorly to the pterygoid hamulus of the medial pterygoid plate, and inferiorly to the posterior end of the mylohyoi ...
. Above the anterior part of this line is a smooth triangular area against which the
sublingual gland rests, and below the hinder part, an oval fossa for the
submandibular gland.
Borders
*The superior or alveolar border, wider behind than in front, is hollowed into cavities, for the reception of the teeth; these cavities are sixteen in number and vary in depth and size according to the teeth which they contain. To the outer lip of the superior border, on either side, the
buccinator
The buccinator () is a thin quadrilateral muscle occupying the interval between the maxilla and the mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity.Illustrated Anatomy of the Head ...
is attached as far forward as the first molar tooth.
*The inferior border is rounded, longer than the superior, and thicker in front than behind; at the point where it joins the lower border of the ramus a shallow groove; for the
facial artery
The facial artery (external maxillary artery in older texts) is a branch of the external carotid artery that supplies structures of the superficial face.
Structure
The facial artery arises in the carotid triangle from the external carotid arte ...
, may be present.
Ramus
![BodyParts3D FJ6399 Mandible](https://upload.wikimedia.org/wikipedia/commons/6/6b/BodyParts3D_FJ6399_Mandible.stl)
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 the whole of its extent to the masseter muscle.
On the inside at the center there is an oblique
mandibular foramen
The mandibular foramen is an opening on the internal surface of the ramus of the mandible. It allows for divisions of the mandibular nerve and blood vessels to pass through.
Structure
The mandibular foramen is an opening on the internal surfa ...
, 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
The lingula of the mandible is a prominent bony ridge on the medial side of the mandible. It is next to the mandibular foramen. It gives attachment to the sphenomandibular ligament.
Structure
The lingula of the mandible is a prominent bony ri ...
, which gives attachment to the
sphenomandibular ligament
The sphenomandibular ligament (internal lateral ligament) is one of the three ligaments of the temporomandibular joint. It is situated medially to - and generally separate from - the articular capsule of the joint. Superiorly, it is attached to the ...
; at its lower and back part 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 medial pterygoid muscle (or internal pterygoid muscle), is a thick, quadrilateral muscle of the face. It is supplied by the mandibular branch of the trigeminal nerve (V). It is important in mastication (chewing).
Structure
The medial ptery ...
. 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 and communicates with them by small openings. On arriving at the
incisor teeth
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, wher ...
, 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 the teeth.
Borders
*The lower border of the ramus is thick, straight, and continuous with the inferior border of the body of the bone. At its junction with the posterior border is the angle of the mandible, which may be either inverted or everted and is marked by rough, oblique ridges on each side, for the attachment of the masseter laterally, and the
medial pterygoid muscle
The medial pterygoid muscle (or internal pterygoid muscle), is a thick, quadrilateral muscle of the face. It is supplied by the mandibular branch of the trigeminal nerve (V). It is important in mastication (chewing).
Structure
The medial ptery ...
medially; the
stylomandibular ligament is attached to the angle between these muscles. The anterior border is thin above, thicker below, and continuous with the oblique line.
*The region where the lower border meets the posterior border is the angle of the mandible, often called the gonial angle.
*The posterior border is thick, smooth, rounded, and covered by the
parotid gland
The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the ma ...
. The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the
mandibular notch.
Processes
*The
coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size.
*The
condyloid process
The condyloid process or condylar process is the process on the human and other mammalian species' mandibles that ends in a condyle, the mandibular condyle. It is thicker than the coronoid process of the mandible and consists of two portions: the ...
is thicker than the coronoid, and consists of two portions: the mandibular condyle, and the constricted portion which supports it, the neck. The condyle is the most superior part of the mandible and is part of the
temporomandibular joint
In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral synovial articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...
.
*The mandibular notch, separating the two processes, is a deep semilunar depression and is crossed by the
masseteric vessels and nerve.
Foramina
The mandible has two main holes (
), found on both its right and left sides:
*The mandibular foramen, is above the mandibular angle in the middle of each ramus.
*The mental foramen sits on either side of the mental protuberance (chin) on the body of mandible, usually inferior to the
apices of the mandibular first and second premolars. As mandibular growth proceeds in young children, the mental foramen alters in direction of its opening from anterior to posterosuperior. The mental foramen allows the entrance of the mental nerve and blood vessels into the mandibular canal.
Nerves
![Panoramicfilm](https://upload.wikimedia.org/wikipedia/commons/4/4d/Panoramicfilm.JPG)
The
inferior alveolar nerve
The inferior alveolar nerve (IAN) (also the inferior dental nerve) is a branch of the mandibular nerve, which is itself the third branch of the trigeminal nerve. The inferior alveolar nerves supply sensation to the lower teeth.
Structure
The in ...
, a branch of the
mandibular nerve, (a major division of the
trigeminal nerve
In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chew ...
), enters the mandibular foramen and runs forward in the mandibular canal, supplying sensation to the teeth. At the mental foramen, the nerve divides into two terminal branches: incisive and mental nerves. The incisive nerve runs forward in the mandible and supplies the anterior teeth. The mental nerve exits the mental foramen and supplies sensation to the lower lip.
Variation
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 inferior alveolar nerve may be present, in which case a second mandibular foramen, more inferiorly placed, exists and can be detected by noting a doubled mandibular canal on a radiograph.
Development
The mandible forms as a bone (
ossifies) over time from a left and right piece of
cartilage, called
Meckel's cartilage
In humans, the cartilaginous bar of the mandibular arch is formed by what are known as Meckel's cartilages (right and left) also known as Meckelian cartilages; above this the incus and malleus are developed. Meckel's cartilage arises from the fir ...
.
These cartilages form the cartilaginous bar of the
mandibular arch
The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arche ...
. Near the head, they are connected with the ear capsules, and they meet at the lower end at the mandibular symphysis, a fusion point between the two bones, by
mesodermal
The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Embry ...
tissue. They run forward immediately below the condyles and then, bending downward, lie in a groove near the lower border of the bone; in front of the
canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened howeve ...
they incline upward to the symphysis. From the proximal end of each cartilage the
malleus
The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations f ...
and
incus
The ''incus'' (plural incudes) or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmit ...
, two of the bones of the middle ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the
sphenomandibular ligament
The sphenomandibular ligament (internal lateral ligament) is one of the three ligaments of the temporomandibular joint. It is situated medially to - and generally separate from - the articular capsule of the joint. Superiorly, it is attached to the ...
.
Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind 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 the incisor teeth is surrounded and invaded by the
dermal bone
A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including much of the skull, jaws, gill covers, shoulder girdle and fin spines rays ( le ...
(also known as the membrane bone). Somewhat later, accessory nuclei of cartilage make their appearance:
*a wedge-shaped nucleus in the condyloid process and extending downward through the ramus;
*a small strip along the anterior border of the coronoid process;
*smaller nuclei in the front part of both alveolar walls and along the front of the lower border of the bone.
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
The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular
The suprangular or surangular is a jaw bone found in most land ver ...
center''), is formed in the human mandible by an ingrowth from the main mass of the bone.
At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first year.
File:Gray178.png, Figure 3: Mandible of human embryo 24 mm. long. Outer aspect.
File:Gray179.png, Figure 4: Mandible of human embryo 24 mm. long. Inner aspect.
File:Gray180.png, Figure 5: Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled.
File:Gray181.png, Figure 5: Mandible of human embryo 95 mm. long. Inner aspect. Nuclei of cartilage stippled.
Aging
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
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone t ...
, 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 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 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, 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
The mylohyoid line is a bony ridge on the internal surface of the mandible. It runs posterosuperiorly. It is the site of origin of the mylohyoid muscle, the superior pharyngeal constrictor muscle, and the pterygomandibular raphe.
Structure
The ...
; 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°.
In 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.
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, the angle measures about 140°, and the neck of the condyle is more or less bent backward.
File:Gray182.png, Newborn
File:Gray183.png, Childhood
File:Gray184.png, Adult
File:Gray185.png, Old age
Function
![gray383](https://upload.wikimedia.org/wikipedia/commons/0/06/Gray383.png)
The mandible forms the lower jaw and holds the lower teeth in place. It articulates with the left and right
temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex.
The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. ...
s at the temporomandibular joints.
*Condyloid process, superior (upper) and posterior projection from the ramus, which makes the temporomandibular joint with the temporal bone
*Coronoid process, superior and anterior projection from the ramus. This provides attachment to the
temporal muscle
In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomat ...
.
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 teeth primarily for chewing food. These teeth also often have wide and sometimes deep grooves on the surfaces.
Clinical significance
Fracture
![Mandbular fractures](https://upload.wikimedia.org/wikipedia/commons/3/37/Mandbular_fractures.png)
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 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
The articular disk of the temporomandibular joint is a thin, oval plate made of non-vascular fibrous connective tissue located between the mandible's condyloid process and the cranium's mandibular fossa.
Its ''upper surface'' is concavo-convex fr ...
prevents the mandible from moving posteriorly, making the condylar neck particularly vulnerable to fractures.
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, 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 leaves the inferior alveolar nerve without its bony protection, although it is still covered by soft tissue.
Forensic medicine
When remains of humans are found, the mandible is one of the common findings, sometimes the only bone found. Skilled experts can estimate the age of the human upon death because the mandible changes over a person's life.
Other vertebrates
In
lobe-finned fish
Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...
es and the early fossil
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s, 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
The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular
The articular bone ...
bone just above it. The inner surface of the jaw is lined by a ''prearticular'' bone, while the
articular bone
The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals.
Anatomy
In most vertebrates, the articular bone is connected to two ...
forms the articulation with the skull proper. Finally 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 as well.
This complex primitive pattern has, however, been simplified to various degrees in the great majority of vertebrates, as bones have either fused or vanished entirely. In
teleost
Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...
s, only the dentary, articular, and
angular bones remain, while in living
amphibians, the dentary is accompanied only by the prearticular, and, in
salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s, 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.
[
While, in birds, these various bones have fused into a single structure, in mammals most of them have disappeared, leaving an enlarged dentary as the only remaining bone in the lower jaw – the mandible. As a result of this, the primitive jaw articulation, between the articular and ]quadrate bone
The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids.
In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper pa ...
s, has been lost, and replaced with an entirely new articulation between the mandible and the temporal bone. An intermediate stage can be seen in some therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s, in which both points of articulation are present. Aside from the dentary, only few other bones of the primitive lower jaw remain in mammals; the former articular and quadrate bones survive as the malleus
The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations f ...
and the incus
The ''incus'' (plural incudes) or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmit ...
of the middle ear.[
Finally, the cartilaginous fish, such as ]shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s, do not have any of the bones found in the lower jaw of other vertebrates. Instead, their lower jaw is composed of a cartilagenous structure homologous with the Meckel's cartilage of other groups. This also remains a significant element of the jaw in some primitive bony fish, such as sturgeons.[
]
Society and culture
* In the Book of Judges
The Book of Judges (, ') is the seventh book of the Hebrew Bible and the Christian Old Testament. In the narrative of the Hebrew Bible, it covers the time between the conquest described in the Book of Joshua and the establishment of a kingdom ...
, Samson
Samson (; , '' he, Šīmšōn, label= none'', "man of the sun") was the last of the judges of the ancient Israelites mentioned in the Book of Judges (chapters 13 to 16) and one of the last leaders who "judged" Israel before the institution o ...
used a donkey's jawbone to kill a thousand Philistines
The Philistines ( he, פְּלִשְׁתִּים, Pəlīštīm; Koine Greek (LXX): Φυλιστιείμ, romanized: ''Phulistieím'') were an ancient people who lived on the south coast of Canaan from the 12th century BC until 604 BC, whe ...
.
*Dental remains of Adolf Hitler
Adolf Hitler (; 20 April 188930 April 1945) was an Austrian-born German politician who was dictator of Nazi Germany, Germany from 1933 until Death of Adolf Hitler, his death in 1945. Adolf Hitler's rise to power, He rose to power as the le ...
including part of a mandible with teeth were the solitary physical evidence used to confirm his death in 1945. The Soviet account published in 1968 describes and photographically depicts the jawbone as being broken off at the alveolar process.
Additional images
File:Mandible.jpg, Lateral view
File:Processus_alveolaris.png, Alveolar process
See also
* Bone terminology
* Oral and maxillofacial surgery
* Simian shelf The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles.
Humans a ...
* Terms for anatomical location
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
References
External links
*
{{Authority control
Vertebrate anatomy
Parts of a bird beak
Facial bones