Medical Definition of jaw
1: either of two complex cartilaginous or bony structures in most vertebrates that border the mouth, support the soft parts enclosing it, and usually bear teeth on their oral margin:a: an upper structure more or less firmly fused with the skull—called also , b: a lower structure that consists of a single bone or of completely fused bones and that is hinged, movable, and articulated by a pair of condyles with the temporal bone of either side—called also , ,
2: the parts constituting the walls of the mouth and serving to open and close it—usually used in plural
3: any of various organs of invertebrates that perform the function of the vertebrate jaws
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