Obturator Externus is a fan-shaped muscle being located above and lateral to the pectineus.  It’s not a muscle of adductor compartment but its here due to its close relationship with the structures of the adductor compartment of the thigh.

Origin

It originates from the outer surface of the anterior half of the obturator membrane and adjoining anterior and inferior margins of the obturator foramen.

Insertion

The fibres converge backwards and laterally to create a tendon, which spirals upward over the inferior and posterior surfaces of the neck of femur to be fit in the trochanteric fossa of greater trochanter of the femur.

Nerve Supply

By the posterior section of the obturator nerve.

Actions

It’s the lateral rotator of the thigh.