Mandible

Mandible
Sperm whale mandible

In vertebrates, the mandible, lower jaw or jawbone is a bone forming the skull with the cranium.

In lobe-finned fishes and the early fossil tetrapods, 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, 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 bone just above it. The inner surface of the jaw is lined by a prearticular bone, while the articular bone 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.[1]

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 teleosts, only the dentary, articular, and angular bones remain, while in living amphibians, the dentary is accompanied only by the prearticular, and, in salamanders, 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.[1]

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 bones, 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 therapsids, 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 and the incus of the middle ear.[1]

Finally, the cartilagenous fish, such as sharks, 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.[1]

References

  1. ^ a b c d Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 244–247. ISBN 0-03-910284-X. 

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  • mandible — (n.) late 14c., jaw, jawbone, from M.Fr. mandible and directly from L.L. mandibula jaw, from L. mandere to chew, from PIE root *mendh to chew (Cf. Gk. mastax the mouth, that with which one chews; morsel, that which is chewed, masasthai to chew,… …   Etymology dictionary

  • Mandible — Man di*ble, n. [L. mandibula, mandibulum, fr. mandere to chew. Cf. {Manger}.] 1. (Anat.) The bone, or principal bone, of the lower jaw; the inferior maxilla; also applied to either the upper or the lower jaw in the beak of birds. [1913 Webster] 2 …   The Collaborative International Dictionary of English

  • mandible — ► NOUN 1) the lower jawbone. 2) either of the upper and lower parts of a bird s beak. 3) either half of the crushing organ in an insect s mouthparts. ORIGIN from Latin mandere to chew …   English terms dictionary

  • mandible — [man′də bəl] n. [OFr < LL mandibula < mandibulum, a jaw < L mandere, to chew < IE base * menth , to chew > MOUTH] the jaw; specif., a) the lower jaw of a vertebrate: see SKULL b) either of a pair of biting jaws of an insect or… …   English World dictionary

  • Mandible — The mandible is the bone of the lower jaw. The joint where the mandible meets the upper jaw at the temporal bone is called the temporomandibular joint. * * * A U shaped bone (in superior view), forming the lower jaw, articulating by its upturned… …   Medical dictionary

  • mandible — Most anterodorsally situated of gnathal appendages; one, of a pair, of heavily calcified jaws; the teeth. [Hobbs and Jass, 1988]. On of the heavily calcified jaws lying anterior to (beneath, in ventral view) the other mouth parts but visible in… …   Crustacea glossary

  • mandible — UK [ˈmændɪb(ə)l] / US noun [countable] Word forms mandible : singular mandible plural mandibles medical the lower jaw of a person, animal, or fish a) the top or bottom part of a bird s beak b) either of the two parts of an insect s mouth that it… …   English dictionary

  • mandible — [[t]mæ̱ndɪb(ə)l[/t]] mandibles 1) N COUNT A mandible is the bone in the lower jaw of a person or animal. [TECHNICAL] Syn: jawbone 2) N COUNT: usu pl An insect s mandibles are the two parts of its mouth which it uses for biting, similar to an… …   English dictionary

  • mandible —   n. lower jaw; either part of bird s beak or insect s mouth parts.    ♦ mandibular, a.    ♦ mandibulate, a. having mandible …   Dictionary of difficult words

  • mandible — n. 1 the jaw, esp. the lower jaw in mammals and fishes. 2 the upper or lower part of a bird s beak. 3 either half of the crushing organ in an arthropod s mouth parts. Derivatives: mandibular adj. mandibulate adj. Etymology: ME f. OF mandible or… …   Useful english dictionary

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