This foot is mounted on the leg at an angle of 45° beyond the right angle, with an interposed rubber cylinder, which allows of the diminution of the angle to 25° or 30° but no further. It is important that flexion to a right angle should not be possible. In fact, a slight degree of equinus is essential in order to secure the locking of the knee in extension, exactly as with the fixed foot (compare figures 73, 74 and 75 with figure 72), and as on the shoe there is always a heel which makes us walk normally in slight equinus, the two feet will be similar in appearance, the slight movement of the artificial foot being sufficient to allow a rolling movement of the sole upon the ground (Figs. 77 to 86). [Illustration: FIG. 76.] [Illustration: FIG. 76A.] The figures 76 and 76A show the simplest and best known mechanism. On the upper surface of the foot two cavities are hollowed, one in front and one behind the bolt of the ankle joint, in each of these is placed a cylinder of rubber; the posterior cylinder is about twice as thick as the anterior. Above them the leg piece is fixed, it ends in front in a short instep which lies within the cavity hollowed out in the foot. The foot is attached to the leg piece by a bolt made as follows: a steel tube fitting into two corresponding grooves in the leg and foot, is attached to the leg by being prolonged upward into a vertical rod, which is secured by a nut inside the leg piece. Upon the steel tube moves a brass rod shaped like an inverted U, the two ends of which pass through the foot and fasten beneath it by two nuts (Fig. 82). Raising the point of the foot further compresses the anterior piece of rubber, lowering it relieves the pressure upon this piece and compresses the posterior piece. But the tension and the size of the pieces of rubber are such that they are under slight compression in the position of rest, the foot being in 30° of equinus. So that this foot is never loose. When pressure is made on the point of the foot it may come to within 15° or 20° of a right angle, but it returns to its angle of 30° as soon as the pressure ceases. [Illustration: Figs. 77 to 81. Contact of the sole with the ground in normal walking. Heel first then toe, with progressive dorsiflexion of the ankle joint. Compare with the contact of the artificial foot in figures 82 to 86.] With boots on, with heels of 2·5 centimetres the two feet are in the same position when the soles are flat on the ground. The forepart of the foot (representing the toes and the anterior part of the metatarsals) is kept in this position (Fig. 76) in slight extension by a piece of rubber, compression of which allows an increase of extension of 15° to 20°.