Either of two bony structures that hold the teeth
and frame the mouth in humans and most vertebrates.
The upper jawbone, or maxilla, is fused
to the skull. The lower jawbone, or mandible,
is movable, having two ligament hinges,
one at each side of the temple near
the entrance to the ear. Powerful muscles, arising
from the temple on either side, attach to the mandible for movements needed
in chewing and biting; other muscles allow side-to-side and downward movement.
Displacement of the lower jaw from one or both of the temporomandibular
joints (located at the base of the skull) may be caused by a blow or by
yawning. The jaw is the most commonly dislocated jaw because it is very
unstable. Once dislocation has happened, it tends to recur.