Which structure is the origin of the obturator externus muscle?

The obturator externus muscle originates from the obturator membrane and the adjacent bones of the pelvis, specifically the pubis and ischium. This origin provides the muscle with a stable anchor point from which it can exert its actions. The muscle's primary function is to externally rotate the thigh and stabilize the hip joint. The obturator membrane is a thin sheet covering the obturator foramen, and its association with surrounding bony structures contributes to the effective leverage during muscle contractions.

Understanding this anatomical origin aids in recognizing how the muscle is positioned in the pelvic region and influences its function during movement. The other listed options do not accurately describe the anatomical starting point of the obturator externus, as they either refer to neighboring muscles' origins or are inappropriate locations for the position of this particular muscle.