To attach extension braces to the front of the leg piece the old and simple method adopted by Fouilloy may be used. It consists in attaching an elastic strap to the brace which passes over the shoulder on the side of the amputation (and which is fixed to the top of the thigh piece alongside of the other brace). The elastic strap ends in a bifurcated leather thong each branch of which (held in place by a loop of leather) descends obliquely alongside of the patella surface to be attached to the corresponding side of the leg in its upper third (Fig. 60). In Marks' method the braces end below in loops made of a leather thong (Fig. 61). These are held against the thigh piece by passing under leather bands; they reach as far down as the upper third on the inner and outer sides of the thigh (Figs. 62 to 65). To each of the loops, gliding on them by means of a pulley, is attached a leather strap which descends vertically to the upper third of the corresponding surface of the leg, being held in place by passing under a leather band. These two straps are attached to each other in front by a lace, which draws them towards the middle line, and in this way brings their line of action forwards. The tighter the lace is drawn the more powerful will be the extending force. [Illustration: FIG. 64. FIG. 65.] Instead of attaching the extension brace to the leg piece it may be made to pass under a pulley in the interior of the knee. What actually happens is that the thigh piece drops, owing to its weight, when the limb is swung free; this throws a strain on the brace which is transmitted to the leg piece by the following mechanism. The metal stop described on page 39 which limits extension of the knee during the period of weight bearing, is prolonged upwards and forwards beyond the hole through which the axis of the knee passes, this prolongation being furnished with two wooden pulleys (Fig. 69). The loops attached to the braces enter the front of the thigh piece, each by a separate opening, turn under the corresponding pulley and emerge again posteriorly (Figs. 66 to 68). [Illustration: Fig. 66. Fig. 67. Fig. 68.] This mode of attachment has the advantage that when the limb is swung the movement does not take place upon the shoulders--which easily become chafed by the ordinary suspenders--but upon the pulleys upon which the leather thongs work. The mechanism shown in figures 69 to 71 is interesting. When the metal lever moves around the axis of the knee joint, its lower end and the pulleys at the upper end travel in opposite directions: in flexion the pulleys move downwards and forwards, the lower end upwards and backwards; in extension they move in the opposite direction. Therefore when the limb is swung and the knee bends (Fig. 71), the thigh piece drops of its own weight, the braces tighten, raise the pulley and consequently make the lower end of the lever move downwards and forwards, thus extending the knee joint.