In the first case there is a true _counter-stroke_, the ordinary effect, either of a severe blow on the point of the shoulder, which is the most common occurrence; or, as happens less frequently, of a fall on the arm when it is extended for the purpose of guarding the body from the force of the accident. Under these circumstances, being pressed between the sternum, which makes resistance, and the body which acts on its extremity, the clavicle is bent in that direction which is most natural to it; but, not being sufficiently flexible, it gives way generally in the place where its curvature is the greatest. Thus the ribs are broken, when the sternum, by being violently driven backward, forces them to bend in the centre beyond their natural flexibility. In the second case, the fracture occurs at the spot where the stroke is given. Here the momentum or quantity of force applied on the bone, surpassing the solidity which the bone possesses, its continuity is necessarily destroyed. 4. But in whatever way the fracture is produced, it is either oblique or transverse, single or double, in the middle or towards the extremities of the bone, simple or compound. An oblique fracture is most frequently the effect of a _counter-stroke_; a transverse fracture is the more common result of the immediate action of external bodies; a counter-stroke seldom produces any thing but a simple fracture; while compound fractures are generally owing to a direct stroke. The one produces a solution of continuity in the middle of the bone, or thereabout; because in that part the curvature is most considerable. The other is almost always the cause of this solution, when it occurs at the extremities. To the latter alone, is a double division to be attributed. The reason of these differences is already so plain, that it would be a waste of time to dwell on an explanation of them. § III. OF THE SIGNS. 5. The several phenomena that attend a fracture of the clavicle, taken together, leave in general but little doubt as to its existence, particularly when the fracture is oblique. As is the case in most other instances of the kind, so here, an acute pain is felt at the instant of the stroke; sometimes a cracking of the bone is distinctly heard by the person injured; on every occasion, it becomes suddenly impracticable to perform circular or rotatory motions with the arm; motions from before backwards can still be executed, but are difficult and painful, and, as I have already observed (1), the individual injured is reduced to the class of animals destitute of clavicles.