ht is less distorted than that
of the parts lying outside the perpendicular. The light and the plate
remaining constant, the amount of distortion varies directly with the
distance between the object and the plate.

To ensure accuracy in the diagnosis of fracture by the X-rays, it is
necessary to take two views of the limb--one in the sagittal and the
other in the coronal plane. By the use of the fluorescent screen, the
best positions from which to obtain a clear impression of the fracture
may be determined before the radiograms are taken. Stereoscopic
radiograms may be of special value in demonstrating the details of a
fracture that is otherwise doubtful.

Imperfect technique and faulty interpretation of the pictures obtained
lead to certain fallacies. In young subjects, for example, epiphysial
lines may be mistaken for fractures, or the ossifying centres of
epiphyses for separated fragments of bone. The os trigonum tarsi has
been mistaken for a fracture of the talus. In the vicinity of joints
the bones may be crossed by pale bands, due to the rays traversing the
cavity of the joint. In this way fracture of the olecranon or of the
clavicle may be simulated. The neck of the femur may appear to be
fractured if a foreshortened view is taken.

It is possible, on the other hand, to overlook a fracture--for
example, if there is no displacement, or if the line of fracture is
crossed by the shadow of an adjacent bone. In deeply placed bones such
as those about the hip, or in bones related to dense, solid
viscera--for example, ribs, sternum, or dorsal vertebrae--it is
sometimes difficult to obtain conclusive evidence of fracture in a
radiogram.

It is to be borne in mind also, and especially from the medico-legal
point of view, that, as early callus does not cast a deep shadow in a
radiogram, the appearance of fracture may persist after union has
taken place. The earliest shadow of callus appears in from fourteen to
twenty-one days, and can hardly be relied upon till the fourth or
sixth week. The disturbed perspective produced by divergence of the
rays may cause the fragments of a fracture to appear displaced,
although in reality they are in good position. If the limb and the
plate are not parallel, the bones may appear to be distorted, and
errors in diagnosis may in this way arise. In this relation it should
be mentioned that perfect apposition of the fragments and anatomically
accurate restoration of the outline of the bo