Section 32. Five Aortic Arches Are Generally Stated to Appear

altogether in the fowl, but not simultaneously. The first two, the mandibular and the hyoid vascular arches, early disappear, and are not comparable to any in the frog. The third is the first branchial arch, and, like the corresponding arch in the frog, forms the carotid artery; the second branchial is the aortic arch; and what has hitherto been regarded as the third (the fifth arch, i.e.) the pulmonary artery. A transitory arch, it is now known, however, appears between the second branchial and the last, and it is therefore the fourth branchial arch which is the pulmonary, just as it is in the frog.