Mandible

Mandibula

The mandible is the movable lower jaw bone of the skull, carrying the lower teeth and hinging on the temporal bones at each side.

At a glance

English: Mandible
Latin (TA2): Mandibula
System: Bone
Region: Head
Side: Single, on the midline
Muscles on it: Bucinator

About the mandible

The mandible is the bone of the lower jaw and the biggest and strongest bone of the face. It carries the lower teeth and lies below the maxilla. Apart from the tiny ossicles of the ear, it is the one bone of the skull that moves, hinging and gliding against each temporal bone at the temporomandibular joint. It starts as two halves that meet in the midline at the mandibular symphysis; these fuse during the first year, leaving a faint vertical ridge on the chin.

The bone has a curved horizontal body in front and a vertical ramus rising from each end, body and ramus meeting at the mandibular angle. On the outer face of the body, the chin forms the mental protuberance with a mental tubercle on each side, and a mental foramen opens below the second premolar for the mental nerve and vessels. The inner face carries the mental spines for genioglossus and geniohyoid, a pair of digastric fossae, and the mylohyoid line, with shallow hollows for the sublingual and submandibular glands above and below it. The upper or alveolar border holds the sockets for the teeth.

The ramus ends above in two processes separated by the mandibular notch: the flat, triangular coronoid process in front, for the temporalis, and the condylar process behind, a neck topped by the condyle that sits in the joint. The masseter covers most of the outer ramus and the medial pterygoid grips its inner side near the angle. In the middle of the inner face, the mandibular foramen leads into the mandibular canal, guarded by a small spine, the lingula, which anchors the sphenomandibular ligament.

The shape changes over life. At birth the angle is very open and the canal runs low; in the adult the ramus stands nearly upright; after tooth loss the alveolar bone is resorbed, so the canal and mental foramen come to lie near the upper border. Fractures are common in facial injury and are often paired with a second break on the other side; the condylar neck is a weak point. The jaw dislocates forward and downward, almost never backward.

Function and supply

Function: Opens and closes the mouth and moves the lower teeth against the upper ones in biting, chewing and speech.
Nerve supply: The inferior alveolar nerve, from the mandibular division of the trigeminal nerve, runs in the mandibular canal to the lower teeth and ends as the incisive nerve and the mental nerve, which supplies the lower lip.
Blood supply: The inferior alveolar artery accompanies the nerve through the canal; the facial artery may groove the lower border in front of the angle.

Parts of the mandible

Each number is marked on the model. Press one, here or on the model, to see it named in place.

Base of mandibleBasis mandibulaeThe thick, rounded lower edge of the body, below the tooth-bearing alveolar part. It can be traced under the skin along the jawline and gives attachment to the platysma and the deep cervical fascia.
Body of mandibleCorpus mandibulaeThe horseshoe-shaped horizontal part of the bone that curves round from one angle to the other and forms the chin in front. It has an outer and an inner surface, an upper alveolar border holding the teeth and a lower border, the base.
Digastric fossaFossa digastricaA shallow oval hollow on the inner face of the lower border, one each side close to the midline. The digastric muscle's front belly is anchored here, so the muscle can pull the jaw down and raise the hyoid.
GenionA midline craniometric point marking the tip of the mental spines, inside the chin. It is used as a reference when measuring the face and jaw on skulls and radiographs.
GnathionA measuring point at the lowest part of the chin in the midline, between the most forward and the lowest points of the mandible. Orthodontists and anthropologists use it to describe facial height and jaw position.
Inferior mental spineSpina mentalis inferiorThe lower of the small bony projections behind the chin on the lingual side. The geniohyoid muscle arises from it and runs back to the hyoid bone, helping to pull the hyoid forward during swallowing.
Mandibular dental archArcus dentalis mandibularisThe curved row of lower teeth held in the sockets of the alveolar part. It meets the upper arch when the jaws close, and its shape guides how the teeth bite and grind.
Mental foramenForamen mentaleA small opening on the outer face of the body, usually below the second premolar. The mental nerve and vessels leave the mandibular canal here to supply the skin of the chin and lower lip, which makes it a key site for dental nerve blocks.
Mental protuberanceProtuberantia mentalisThe triangular bony prominence at the front of the body in the midline that shapes the chin. Its lower corners rise into the mental tubercles on each side.
Mental tubercleTuberculum mentaleA small raised bump on each side of the lower part of the chin, at the lateral corners of the mental protuberance. Together with the protuberance it forms the bony framework felt as the point of the chin.
Mylohyoid lineLinea mylohyoideaA ridge running obliquely upwards and backwards along the inner surface of the body towards the third molar. The mylohyoid muscle, which forms the floor of the mouth, arises from it, and part of the superior constrictor of the pharynx and the pterygomandibular raphe attach near its back end.
Oblique line of mandibleLinea obliqua mandibulaeA faint ridge on the outer surface that runs from the mental tubercle up and back to the front border of the ramus. Depressor muscles of the lower lip and angle of the mouth arise from it, and the buccinator is attached along its upper part near the molars.
Sublingual fossaFovea sublingualisA smooth hollow inside the jaw above the front part of the mylohyoid line, one each side near the midline. It lodges the sublingual salivary gland.
Superior mental spineSpina mentalis superiorThe upper of the small projections behind the chin on the lingual side. The genioglossus, the main muscle that protrudes the tongue, takes origin from it.

Anthromica

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At a glance

About the mandible

Function and supply

Related structures

See the mandible where it really sits, with every layer of the body around it.