14. They occur, in general, in two ways, being the result, sometimes of the action of external bodies, immediately applied, and at other times of the same action, operating by way of a counter-stroke. The occasional percussion of a body on the fore-arm, furnishes an example of the first mode of fracture. This is much more frequent, in general, than the other, which usually arises from a fall on the wrist; but, in such a case, as it is the large lower end of the radius that forms the principal point of articulation with the hand, that bone alone sustains almost all the force of the stroke, and is very generally the exclusive seat of the fracture. § III. OF THE SIGNS OR APPEARANCES. It is in general difficult to be mistaken with respect to the signs which characterize fractures of the fore-arm. A mobility of the limb where it was before inflexible; a crepitation almost always easily perceived; a depression, sometimes evident, at the place of division; a protuberance sometimes formed under the skin by the fragments; pain produced by the motion of the part; a crack sometimes heard by the patient, at the moment of the accident; an inability to perform the motions of pronation and supination; the almost constant semi-flexion of the fore-arm; such, together with the phenomena common to all fractures, are those which essentially characterize this, and which must generally remove all doubts which the swelling of the limb may temporarily create respecting its existence. 6. There is a circumstance, however, where a fracture near to the joint of the wrist, may give rise to appearances similar to a luxation of that part. In both cases, indeed, a convexity behind, and a depression before, or the reverse, are perceived, and are the effect of a displacement of the fragments. But the styloid apophysis being carefully examined, will always determine, according as it is found above or below the deformity, from which of the two causes the deformity arises. Besides, a greater mobility in one than in the other affection, and a crepitation, will guard the practitioner from an error, into which I saw a surgeon fall in the presence of Desault, whom he called on to consult, in the case of a child six years old, which laboured under a supposed luxation. § IV. OF DISPLACEMENT. 7. Most of the phenomena which accompany fractures of the fore-arm (5), are evidently the result of a displacement of the fragments; a displacement, not, in general, very perceptible in the longitudinal direction of the bones, because the muscular action, tending to produce it in that direction, is not very powerful. When it does occur in this way, it is most frequently the immediate effect of the stroke that produced the fracture.