Pelvic brim
The pelvic brim is the edge of the pelvic inlet. It is an approximately Mickey Mouse head-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis.
The pelvic brim is obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum.
The oblique plane passing approximately through the pelvic brim divides the internal part of the pelvis into the false or greater pelvis and the true or lesser pelvis. The false pelvis, which is above that plane, is sometimes considered to be a part of the abdominal cavity, rather than a part of the pelvic cavity. In this case, the pelvic cavity coincides with the true pelvis, which is below the above-mentioned plane.
