Information AboutJaw |
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The jaw is either of the two opposable structures forming, or near the entrance to, the Mouth . In most Vertebrate s, the jaws are Bony or Cartilaginous and oppose vertically, comprising an ''upper jaw'' and a ''lower jaw''. In Arthropod s, the jaws are Chitinous and oppose laterally, and may consist in ''mandibles'', ''chelicerae'', or, loosely, ''pedipalps''. Their function is fundamentally for food acquisition, conveyance to the mouth, and/or initial processing (''mastication'' or ''chewing''). The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it. In vertebrates, the lower jaw or ''mandible'' is the mobile component that articulates at its posterior processes, or ''rami'' (singular ''ramus''), with the temporal bones of the Skull on either side; the word ''jaw'' used in the singular typically refers to the lower jaw. The upper jaw or ''maxilla'' is more or less fixed with the skull and is composed of two bones, the ''maxillae'', fused intimately at the Median Line by a Suture ; incomplete closure of this suture and surrounding structures may be involved in the malformation known as Cleft Palate . The maxillary bones form parts of the roof of the mouth, the floor and sides of the Nasal Cavity , and the floor of the Orbit or ''eye socket''. The jaws typically accommodate the Teeth or form the bases for the attachment of a Beak . In Reptile s, the mandible is made up of five bones. In the evolution of Mammal s, four of these bones were reduced in size and incorporated into the ear. In their reduced form, they are known as the '' Malleus '' and '' Incus ''; along with the more ancient '' Stapes '', they are the '' Ossicles ''. This adaptation is advantageous, not only because a one-bone jaw is stronger, but also because the malleus and incus improve hearing. The term ''jaws'' is also used for articles resembling jaws in appearance or function, for example:
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