7. It follows from what has been said respecting the different states of the articulation, during its various motions (4), that the clavicle is not equally liable to be luxated in every direction. Inclining naturally backward, but a very slight degree of motion in that direction is necessary, to effect a luxation forward. To produce a luxation backward or inward, it is necessary, on the other hand, that the humeral extremity of the bone should make a sweep at least three times the extent of that required in the preceding case. Besides, motions in this direction are accompanied with pain, particularly if they be made by force. Luxation downward is prevented, on the one hand, by the cartilage of the first rib, which presents to the bone an insurmountable barrier. On the other hand, to produce this kind of luxation, it would be necessary for the external extremity of the clavicle to be forced upwards, an occurrence very seldom occasioned by falls. Luxation upward, or over the superior edge of the sternum, must be the effect of a stroke, which, by depressing the point of the shoulder, and forcing it at the same time forward, presses the sternal extremity against the internal and superior part of the capsule, which, being thus lacerated, suffers a luxation to take place. But such a derangement of the articulating surfaces is very rarely produced by falls. Whence it follows, that of the different kinds of luxation of the clavicle, that in a downward direction is altogether impracticable. Those backward and upward, though possible, occur but rarely in practice; while that in a forward direction, on the contrary, is not an unfrequent accident. This tends to confirm the observations of practitioners, and particularly of Desault, whose immense collection on the subject furnishes examples of the last kind of luxation only. 8. In these luxations, there is for the most part, a rupture of the capsular ligament, and an escape of the bone through the opening. But sometimes the ligament is only preternaturally distended, and then the luxation is incomplete. § III. OF THE SIGNS.