The extensor digiti minimi muscle is a long, thin muscle of the forearm that arises from the humerus bone and inserts with the little finger’s extensor expansion. It serves to straighten the little or pinkie finger. Muscle extension occurs when the angle between the bones is increased - as when the forearm is aligned with the arm. An extensor, then, is any muscle serving to extend a bodily part (usually a limb) away from the body or when a digit is extended from its base.