In mammals, the recurrent laryngeal nerve (RLN) loops around the ligamentum arteriosum on the left side and around the subclavian artery on the right side. It is generally considered that such an asymmetric arrangement of the right and left RLN is brought about by a transformation of the aortic arches at an early stage of embryonic development. We have dissected rough-toothed dolphins and Pacific white-sided dolphins in this study. In both species, the right RLN hooked around the costocervical trunk, while the left RLN hooked around the ligamentum arteriosum. The external carotid artery, the internal carotid artery, the subclavian artery, and the costocervical trunk arose radially from the brachiocephalic trunk on the right side. The left costocervical trunk arose directly from the aortic arch. The right and left subclavian arteries ran ventral to the subclavian vein and the vagus nerve, in a similar manner to the secondary subclavian arteries in birds. These findings suggest that the replacement of the primary (or dorsal) subclavian artery by the secondary (or ventral) subclavian artery might occur at a certain embryonic stage in dolphins as well.