A small ligament attached to the superior surface of the pulmonary trunk and the inferior surface of the aortic arch. It is a nonfunctional vestige of the ductus arteriosus, and is formed within three weeks of birth. The ligamentum arteriosum is closely related to the left recurrent laryngeal nerve, a branch of the left vagus nerve. After splitting from the left vagus nerve, the left recurrent laryngeal loops around the aortic arch posterior to the ligamentum arteriosum, after which it ascends to the larynx[WP]. [ http://en.wikipedia.org/wiki/Ligamentum_arteriosum ]