Study of these data indicates that the quadruped pelvis retains many things in common through all the orders especially in being a roughly rectangular structure lying chiefly horizontally, with a poorly developed false pelvis, straight ischia and a long symphysis pubis; the angle of the true conjugate is greater than in man and may be up to 80°. The long pubic synostosis changes the relation of the true and diagonal conjugate, but the former is no indicator of pelvic capacity, since in lower mammals the promontory of the sacrum lies anterior to the symphysis; the vertical diameter is a better measure of pelvic size and form. Sacral movement seems greater in lower animals especially in youth. The shape of the pelvic inlet is triangular in the lowest forms, the posterior base of this becoming wide as one ascends in a zoological line; the concavity of the ilia also increases so that the higher the animal the more curved are the lateral borders. In quadrupeds the anteroposterior diameter is greater than the lateral; the reverse is true in man. The long straight-sided quadruped pelvis is retained because of the direction of the forces from the legs, which is as much or more upon the anterior or pubic arch as upon the sacroiliac junction. In the semiupright position of the monkey the force is directed backward and downward upon the sacrum, this aiming to widen the pelvis by forcing the ilia apart. The effect of the upward force from the femora is to throw the pelvis upward and anteriorly by directing the line of action through the acetabula more toward the ventral surface. The sacroiliac ligaments hold the ilia firmly, their alæ being spread outward by the force from above. Elevation of the pubes shortens their symphysis and the true conjugate. By these changes the birth canal is shorter, entirely bony, with the upper inlet on the same plane, and promontory and symphysis are near enough the same level to be met at the same time by the engaging head. In these pelves the anteroposterior diameter is still long and superior rotation is not necessary.