If the bucket is too large, the patient abducts the stump, so as to lower the inner border and prevent pressure on the perineum; he carries the leg away from the side as he walks, and this is both unsightly and fatiguing. When an apparatus is completed, it is very easy to ascertain the site of the pressure on the ischium. The limb being put on, the ischium is fixed between the thumb and first finger, and it can then be ascertained whether it rests on the edge of the bucket or lies within it. This can be determined more exactly, if whilst the fingers which mark the position of the ischium are kept within the bucket, the patient is told to raise his stump. If the bucket is sufficiently narrow, it may be circular without the excavation for the perineum (Fig. 2). But this shape is unsatisfactory for another reason, because it results in a tendency for the limb to rotate inwards. At the moment when the artificial limb is coming in contact with the ground as it takes a step, the pelvis is oblique (the iliac spine of the sound side lying posterior to that of the amputated side). The sound limb as it executes its step is carried forwards, and the pelvis which was oblique in one direction now becomes oblique in the opposite direction. This movement is transmitted to the femur in the stump, so that the artificial limb turns inwards relatively to the stump. With each step this rotation becomes little by little more perceptible, and after a time the patient is obliged to correct it by turning the artificial limb with his hand. If, on the other hand, the front of the upper border of the bucket slopes downwards and inwards at an angle of about 45 degrees, when as a result of its weight the bucket turns inwards as the limb is swung, the base of the stump will come against a higher part of bucket; but when the pressure of the weight of the body returns, the stump, being forced into the bucket, will descend again along this slope, that is to say a passive external rotation of the artificial limb will be brought about, correcting at every step the tendency to internal rotation. [Illustration: AMPUTATIONS THROUGH THE THIGH FIG. 1. FIG. 2. FIG. 3. In the upright position the rami of the pubis and ischium, between which stretches the perineum, slope downwards and backwards at an angle of about 45° with the horizontal. The tuberosity of the ischium bounds the perineum posteriorly, and is its lowest point. The rami of the pubis and ischium, corresponding to the genito-crural fold, mark the boundary between the thigh and the perineum. These bones are unable to stand the pressure of an artificial limb.