The superior and inferior regions of the bony pelvis are separated by a series of landmarks that indicate a boundary known as the pelvic brim (pelvic inlet). These landmarks are the sacral promontory, the of each ilium, and along the superior edges of each pubic bone, and the pubic symphysis.

Arcuate lines

Explanation:

Arcuate lines of the iliums often described as the fine rounded border on the iliums internal surface, it runs through the articular surface of ilium to the lateral end of pectineal line, it occupies the same position with the intermediate part of pelvic brim.

It is part of pelvic bones, which is associated with iliac fossa and iliacus muscle, often considered to be inferior to the other two.

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