11. To form an idea of the signs or appearances of a luxation backwards, let us examine, for a moment, the natural situation of the olecranon, and the condyls of the humerus. As these eminences are easily felt under the skin, a knowledge and recollection of their situation will serve as a standard of comparison, to judge of the changes they experience in a luxation. When the fore-arm is extended, the olecranon is on a level with the internal condyl, and a little above the external one. In a state of flexion, it descends below this level, and is then farther below the internal than the external condyl. In either situation, it is nearer to the first than to the second, the radius separating it from the latter. 12. But, when a luxation has taken place, this apophysis, still remaining on a level with the two condyls, even although the fore-arm be half-bent, is oftentimes separated from the internal one, and driven towards the other: a preternatural protuberance announces this change of position of the olecranon. The coronoid apophysis, whose posterior surface glides in the large groove of the humerus, corresponds to this groove now only with its anterior surface: sometimes the olecranon cavity[21] receives its extremity. The radius passes backward over the small head of the humerus. At the fold of the arm, a transverse protuberance, more perceptible on the internal side, announces the presence of the displaced articular extremity of the os humeri. Over this extremity are reflected the biceps and the brachialis muscles in a state of violent distension. These muscles, greatly irritated by such distension, continue in a state of habitual contraction, in consequence of which, they keep the fore-arm half-bent. Nor can the anconeus muscle, which is necessarily relaxed, act so as to prevent this semiflection. Severe pains would be the consequence of attempts to extend the fore-arm; the limb is in a state of pronation; yet I find among the cases collected by Desault, several examples where supination existed; this state is explained by the relaxed condition of the pronator muscles. At the level of or opposite to the coronoid cavity is a depression or hollow manifesting the absence of the apophysis of that name. [21] That deep depression in the os humeri, which, in a natural state of the parts, receives the upper end of the olecranon process. TRANS. 13. Should chance give rise to a luxation forward, an anterior projection of the two bones of the forearm, and above all, of the coronoid eminence, a depression corresponding to the olecranon cavity, the extremity of the humerus carried backward and downward, the rigid extension of the fore-arm, a protuberance behind formed by the fractured olecranon (5), and severe pains, necessarily resulting from attempts to bend the limb, &c. would constitute the principal characteristic signs of the displacement.