It is formed by the convergence of the inferior rami of the ischium and pubis on either side, below the pubic symphysis.

[1] The pubic arch is one of three notches (the one in front) that separate the eminences of the lower circumference of the true pelvis.

The subpubic angle is important in forensic anthropology, in determining the sex of someone from skeletal remains.

[1] Women have wider hips, and thus a greater subpubic angle, in order to allow for child birth.

This article incorporates text in the public domain from page 240 of the 20th edition of Gray's Anatomy (1918)