mbrella, being forced
through the orbit, the nasal cavities, or the pharynx. These injuries
will be referred to in describing fractures of the anterior fossa.

The majority of basal fractures result from such accidents as a fall
from a height, the patient landing on the vertex or on the side of the
head, or from a heavy object falling on the head. The violence is
therefore indirect in so far as the bone breaks at a point other than
the seat of impact.

In other cases the base is broken by the patient falling from a height
and landing on his feet or buttocks, the force being transmitted
through the spine to the occiput, and the bone giving way around the
foramen magnum. Sometimes the condyle of the lower jaw is driven
through the base of the skull by a blow or fall on the chin, and
fissures radiate into the base from the glenoid cavity. It is usual to
describe these also as fractures by indirect violence, but as the
skull gives way at the point where it is struck, these are really
fractures by direct violence. Von Bergmann, Bruns, and Messerer have
done much to elucidate the mechanism of basal fractures.

In the consideration of the mode of production of basal fractures by
indirect violence, the irregular shape of the cavity, the varying
strength and thickness of its different parts, and the existence of
the foramina through the bone are to be borne in mind. The force
acting on the skull tends to increase one diameter of the cavity, and
to diminish the opposite diameter. The resulting fracture, therefore,
is due to bursting of the skull, and tends to take place at the part
which has least elasticity--that is, at the base. It has been found
that the site and direction of basal fractures bear a fairly constant
relation to the direction of the force by which they are produced.
When, for example, the skull is compressed from side to side, the line
of fracture through the base is usually transverse, and it may
implicate one or both sides (Fig. 191). On the other hand, when the
pressure is antero-posterior, the fracture tends to be longitudinal;
and when oblique, it tends to be diagonal.

[Illustration: FIG. 191.--Transverse Fracture through Middle Fossa of
Base of Skull.]

Fractures of the base usually take the form of a single fissure, or a
series of fissures, which, as a rule, run through the foramina in
their track. Small portions of bone are sometimes completely
separated. It is common for a fissure through the base