Above and to the left aspect of the pericardial sac, identify the left vagus nerve. Just inferior to the arch of the aorta, the left vagus nerve gives several branches. The largest branch is the left recurrent laryngeal nerve [below the probe]. Beneath the arch of the aorta, the left recurrent laryngeal nerve passes laterally and posteriorly to the ligamentum arteriosum, and continues superiorly to innervate the larynx. The other branches of the left vagus nerve are cardiac branches [held by the probe].