ess of the jaw at this level, render it the
weakest part of the arch. The fracture is usually due to direct
violence, such as a blow with the fist, the kick of a horse, or a fall
from a height. It is sometimes bilateral, the bone giving way at the
canine fossa on one side and just in front of the masseter on the
other; or both fractures may be at the canine fossae. The fracture is
usually oblique from above downwards and outwards, and is nearly
always rendered compound by tearing of the mucous membrane of the
mouth.

[Illustration: FIG. 254.--Multiple Fracture of Mandible.

(From Sir Patrick Heron Watson's collection.)]

When only one side is broken, the smaller fragment is usually
displaced outwards and forwards by the masseter and temporal muscles,
so that it overlaps the larger fragment. In bilateral fractures the
central loose segment is driven downwards and backwards towards the
hyoid bone by the force causing the fracture, and is held in this
position by the muscles attached to the chin, while both lateral
fragments are tilted outwards and forwards by the masseters and
temporals. The amount of displacement is best recognised by observing
the degree of irregularity in the line of the teeth. Abnormal mobility
and crepitus are readily elicited, and there is severe pain,
particularly if the inferior dental nerve is stretched or crushed. The
patient's attitude is characteristic; he supports the broken jaw with
his hands, and keeps it as steady as possible when he attempts to
speak or swallow. Saliva dribbles from the open mouth, and the speech
is indistinct.

In adults, the bone may be broken at the _symphysis_ as a result of
lateral compression of the jaw--for example, pressing together of the
angles. The general characters of the fracture are the same as those
of fracture of the body, but the displacement is inconsiderable.

Fractures of the _angle_ and through the _ramus_ are less common, and
are not attended with deformity, as the fragments are retained in
position by the masseter and internal pterygoid muscles. Fracture of
the _coronoid process_ is rare.

The _condyle_ is usually fractured just below the insertion of the
external pterygoid muscle (Fig. 254) by a fall on the chin or by a
severe blow on the side of the face. When the fracture is unilateral,
the broken condyle is tilted inwards and forwards by the external
pterygoid, and can be palpated from the mouth, while the rest of the
jaw is displaced _