Anterior view of mandible, showing mandibular symphysis (red broken line)
Medial surface of the left half of the mandible, dis-articulated from the right side at the mandibular symphysis
|Anatomical terms of bone|
In human anatomy, the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis, or symphysis menti, or line of junction where the two lateral halves of the mandible fused at an early period of life. It is not a true symphysis as there is no cartilage between the two sides of the mandible.
This ridge 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.
When filter feeding, the baleen whales, of the suborder Mysticeti, can dynamically expand their oral cavity in order to accommodate enormous volumes of sea water. This is made possible thanks to its mandibular skull joints, especially the elastic mandibular symphysis which permits both dentaries to be rotated independently in two planes. This flexible jaw, which made the titanic body sizes of baleen whales possible, is not present in early whales and most likely evolved within Mysticeti.
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