5. The os femoris may be fractured indifferently at any point between its condyls and its neck. But the part where this accident most frequently occurs, is about the centre of the curve of the bone, where most of the motions and shocks impressed on it by external violence expend their force. 6. Whatever may be the seat of the fracture, its direction is sometimes transverse, but most frequently oblique, a variety which does not affect the real nature of the disease, but which possesses, as to its consequences, a very important influence. As in other affections of the kind, so here, the bone is sometimes affected alone, and, at other times, to a fracture simple or complicated by means of splinters, is added an injury done to the surrounding soft parts. Hence result compound fractures, differently varied, according to the nature of the parts affected, and to the extent and other circumstances of these affections. But, as Petit observes, this bone is less frequently shattered or crushed into several pieces, than those that are more superficially situated. 7. Extraneous causes are known to render falls more frequent in man than in other animals, and to multiply in him the fractures of the lower extremities, by multiplying the action of external bodies on these extremities. This action may be exerted on the os femoris in two modes. Sometimes only passive, it merely offers a resistance to the power which puts the bone in motion; thus, in a fall, the os femoris, being pressed between the ground which resists, and the weight of the body that bears on it, bends beyond the extent of its flexibility or pliancy, and finally gives way. At other times the influence of external bodies is actively and directly exerted in this accident: thus a stone, or a piece of timber, falling on the thigh, fractures the bone, in consequence of communicating to it a degree of motion greater than its power of resistance. 8. In common, the first mode of division is by a true counter-stroke, similar to that which fractures the clavicle, the ribs, &c. In the second mode, the fracture is always direct. The middle part of the bone is generally broken in a counter-stroke: wherever the direct stroke is received, that is the place of the fracture which it produces; the division, most frequently oblique in the first case, is sometimes perpendicular or transverse in the second. From a counter-stroke result most commonly simple fractures, while compound ones are usually owing to a direct stroke. § III. OF THE SIGNS AND THE DISPLACEMENT.