Dictionary.net

A surface situated obliquely to the p. of the horizon; one of the elementary mechanical powers.

"The sciatic spines," says Lusk, "divide the pelvic cavity into two unequal sections. In the larger, anterior section, the lateral walls slope toward the symphysis and arch of the pubes, while posteriorly the walls slope in the direction of the sacrum and coccyx. The declivities in front of the spines are termed the anterior inclined ps of the pelvis, over which rotation of the occiput takes place in the mechanism of normal labor. Behind the spines the lateral slopes are known as the posterior inclined ps.".

A plane inclined at a greater or less angle to the horizon. It is reckoned a mechanical power, because a weight can be raised along it by agents who would be unable to lift the weight directly.