Final answer:
The pelvic inlet is formed by the superior margin of the pubic symphysis, pectineal lines of the pubis, arcuate lines of the ilium, and the sacral promontory. This anatomical feature separates the true pelvis from the false pelvis, and its shape is wider in females to accommodate childbirth.
Step-by-step explanation:
The structures that form the pelvic inlet, which is also known as the pelvic brim, include the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory. The pelvic inlet defines the boundary between the greater pelvis (false pelvis) and the lesser pelvis (true pelvis). The true pelvis contains the bladder and other pelvic organs, while the false pelvis contains portions of the intestines. The shape of the pelvic inlet is different between males and females, with the female pelvis being typically wider to accommodate childbirth, featuring a round or oval shape, greater subpubic angle, and a larger pelvic outlet.