The nucleus ambiguus is the special visceral efferent nucleus for CN IX (glossopharyngeal nerve) and CN X (vagus nerve) that resides in the rostral lateral medulla just dorsal to the inferior olivary nucleus. It supplies motor fibers to the palate and pharynx and mediates the efferent arm of autonomic vagal output, increasing parasympathetic tone in the heart and gut. The name “nucleus ambiguus” refers to the fact that the nucleus is notoriously difficult to locate on dissection or imaging, and its location varies substantially across different species.