One capsule, two ligaments, viz. the interclavicular and costo-clavicular ligaments,[5] and the anterior portion of the sterno-cleido-mastoideus muscle, strengthen the connexion of these two surfaces, and tend, on one hand, to prevent their luxation, while, on the other, this luxation is favoured and facilitated by the following circumstances: 1st, the disproportion between the dimensions of the two articulating surfaces; 2dly, the mobility of the joint; and 3dly, by this joint’s constituting a kind of centre for the motions of the arm. [5] I find in English books of anatomy no appropriate names for these two ligaments. I am therefore obliged to translate the French terms for them literally. The anatomist will have no difficulty in recollecting their situation. TRANS. 3. On the humeral side, an elliptical surface, slightly convex, and inclined downwards, is immediately joined to a corresponding surface of the acromion, elliptical also, a little concave and directed upwards. Hence two kinds of inclined plains, which would be very liable to dislocations, by sliding easily over each other, were they not firmly secured by a capsule, by accessory fibres, by the intersection of those of the deltoid and trapezius muscles, and, above all, by two ligaments, the rhomboid and the conoid.[6] [6] I do not recollect any terms in English works of anatomy equivalent to these. TRANS. Having laid down these preliminary considerations, let us proceed to examine, in particular, each kind of luxation to which the clavicle is subject. LUXATION OF THE STERNAL EXTREMITY. § II. OF THE CAUSES AND DIFFERENT KINDS OF DISPLACEMENT. 4. The sternal articulation of the clavicle experiences different changes, according to the different movements of this bone. If these movements be in a backward direction, the articulating surface is turned forward, straining the anterior part of the capsule, the corresponding ligament, and the extremity of the sterno-cleido-mastoideus muscle. If, on the other hand, they be in a forward direction, the posterior ligament, and the adjacent portion of the capsule are overstretched. In motions directed upwards, the costo-clavicular ligament, and the external and inferior part of the capsule, and in those directed downwards, the inter-clavicular ligament, and the internal portion of the capsule, experience a similar degree of tension.