The obturator foramen is indicated in this diagram.

The obturator foramen lies inferior to the acetabulum of the pelvis and is an opening between the ischium and pubic bones. It is covered almost entirely by the obturator membrane. A small gap is left between the superior margin of the obturator membrane and the pelvic bone above, known as the obturator canal, which allows a few vessels and nerves to pass out from the pelvic cavity to communicate with the lower limb. There are three structures which pass through the obturator canal:

1. Obturator artery
2. Obturator vein
3. Obturator nerve

Learn more about the anatomy of the pelvic bones in this tutorial