Pelvic inlet

The superior circumference of the lesser pelvis forms the brim of the pelvis, the included space being called the superior aperture or pelvic inlet.

The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum.

The edge of the inlet is known as the pelvic brim. Occasionally, the terms are used interchangeably.

Boundaries
It is formed as follows:

Diameters
It has three principal diameters: antero-posterior, transverse, and oblique.