Figs. 1 and 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.
If the top of the bucket is narrower than the circumference of the top of the limb, measured below the ischium, it may be circular and still give support to the ischium, which will not slip into it. If the ischium does slip into the bucket, the result will be that it no longer serves as the support, the pressure coming instead upon the rami of the pubis and ischium and upon the perineum.
The constriction thus exerted upon the top of the stump may easily become insupportable. The correct solution of the problem is to cut down the upper border of the bucket opposite the perineum, letting it rise again posteriorly beneath the tuberosity of the ischium, and gain a good support there.
The same slope may be given to both edges of the bucket ([Fig. 5]). This obliquity in the posterior part serves no useful purpose: it is better on the contrary to lower the posterior border combining this semioblique fitting with a rise beneath the ischium and a depression under the perineum ([Fig. 6]).
These conditions are easily carried out in a wellmade wooden bucket, represented in [figures 8 and 9], in which it may further be seen that from the front it is convex outwards; from the side, convex forwards ([Fig. 9]). This form, which is that of some good American appliances, ought to be generally used.
The curve outwards, by drawing away the soft parts from it, frees the region of the ischium and allows the tuberosity of the ischium to press upon the bucket ([Fig. 8]).