The mandible, or lower jaw, is the largest and strongest bone of the face. It develops from the first pharyngeal arch. It has a horseshoe-shaped body which lodges the teeth, and a pair of rami which project upwards from the posterior ends of the body and provide attachment to muscles.
Each half of the body has outer and inner surfaces, and upper and lower borders.
The outer surface presents the following features.
(1) The sumphysis menti is the line at which the right and left halves of the bone meet each other. It is marked by a faint ridge.
(2) The mental protuberance [mentum = chin) is a median triangular projecting area in the lower part of the midline. The inferolateral angles of the protuberance form the mental tubercles.
(3) The mental foramen lies below the interval between the premolar teeth.
(4) The oblique line is the continuation of the sharp anterior border of the ramus of the mandible. It runs downwards and forwards towards the mental tubercle.
(5) The incisive fossa is a depression that lies just below the incisor teeth.
The inner surface presents the following features.
(1) The mylohyoid line is a prominent ridge that runs obliquely downwards and forwards from below the third molar tooth to the median area below the genial tubercles.
(2) Below the mylohyoid line the surface is slightly hollowed out to form the submandibular fossa. which lodges the submandibular gland.
(3) Above the mylohyoid line there is the sublingual fossa in which the sublingual gland lies.
(4) The posterior surface of the symphysis menti is marked by four small elevations called the superior and inferior genial tubercles.
(5) The mylohyoid groove (present on the ramus) extends on to the body below the posterior end of the mylohyoid line.
The upper or alveolar border bears sockets for the teeth.
The lower border of the mandible is also called the base. Near the midline the base shows an oval depression called the digastric fossa.
The Body
Each half of the body has outer and inner surfaces, and upper and lower borders.
The outer surface presents the following features.
(1) The sumphysis menti is the line at which the right and left halves of the bone meet each other. It is marked by a faint ridge.
(2) The mental protuberance [mentum = chin) is a median triangular projecting area in the lower part of the midline. The inferolateral angles of the protuberance form the mental tubercles.
(3) The mental foramen lies below the interval between the premolar teeth.
(4) The oblique line is the continuation of the sharp anterior border of the ramus of the mandible. It runs downwards and forwards towards the mental tubercle.
(5) The incisive fossa is a depression that lies just below the incisor teeth.
The inner surface presents the following features.
(1) The mylohyoid line is a prominent ridge that runs obliquely downwards and forwards from below the third molar tooth to the median area below the genial tubercles.
(2) Below the mylohyoid line the surface is slightly hollowed out to form the submandibular fossa. which lodges the submandibular gland.
(3) Above the mylohyoid line there is the sublingual fossa in which the sublingual gland lies.
(4) The posterior surface of the symphysis menti is marked by four small elevations called the superior and inferior genial tubercles.
(5) The mylohyoid groove (present on the ramus) extends on to the body below the posterior end of the mylohyoid line.
The upper or alveolar border bears sockets for the teeth.
The lower border of the mandible is also called the base. Near the midline the base shows an oval depression called the digastric fossa.
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