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In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: symphysis menti) or line of junction where the two lateral halves of the mandible typically fuse in the first year of life (6–9 months after birth). [1]
Since the mandible can go through a vast number of different movement paths, Posselt decided to start by studying the "border movements", a term he uses to denote the mandible's capacity for movement. Then he compared these with the habitual movements of the mandible. From the investigation, he concluded that:
The mandible hosts 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 ...
Insect mandibles are a pair of appendages near the insect's mouth, and the most anterior of the three pairs of oral appendages (the labrum is more anterior, but is a single fused structure). Their function is typically to grasp, crush, or cut the insect's food, or to defend against predators or rivals.
Humans have four types of teeth: incisors, canines, premolars, and molars, which each have a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food. The roots of teeth are embedded in the maxilla (upper jaw) or the mandible (lower jaw) and are covered by gums. Teeth are made of ...
Unlike other mouthparts, the labrum is a single, fused plate (though it originally was—and embryonically is—two structures). It is the upper-most of the mouthparts and located on the midline. It serves to hold food in place during chewing by the mandibles and thus can simply be described as an upper lip.
Growth of mandible depends on the normally developing condyles and the muscle function For example, trauma or infection that affect mastoid, middle ear or the joint will result in ankylosis of temporomandibular joint leading to mandibular micrognathia. [31] Macronagthia; Macronagthia is a condition of abnormally large jaws.
Strepsirrhines are also traditionally noted for their unfused mandibular symphysis (two halves of the lower jaw), [87] however, fusion of the mandibular symphysis was common in adapiforms, [92] notably Notharctus. [93] Also, several extinct giant lemurs exhibited a fused mandibular symphysis. [94]