Further branchial arch artery development

The branchial arch arteries undergo a number of changes during development which are not detailed in the main menu. These include:

• after formation of the arch arteries and the aorticopulmonary septum, the aortic sac, the most distal part of the truncus arteriosus in continuity with the ventral aorta, divides up to form the vessels that will become after birth the:
  • brachiocephalic trunk
  • proximal section of the aortic arch
• the great vessles, in conjuction with the heart, shift relatively caudally due to elongation and folding of the embryo; consequently, the recurrent laryngeal nerves which supply the sixth branchial arch, are encroached upon. Therefore, by birth the nerve courses around the vessels which have traversed its path. This varies beween sides:
  • on the left, the nerve is pulled inferiorly by the sixth aortic arch artery; this becomes the ductus arteriosus. After birth, the left recurrent laryngeal nerve can be seen to course around the ligamentum arteriosusm.
  • on the right, the fifth and sixth arch arteries regress and so the nerve is pulled inferiorly by the fourth arch artery. After birth, the right recurrent laryngeal nerve hooks around the right subclavian artery.
• the section of the dorsal aortae between the third and fourth arches degenerates after birth
• the right dorsal aorta regresses from its junction with the seventh intersegmental artery
• the fourth aortic arch on the right combines with the right dorsal aorta and the seventh intersegmental artery to form the right subclavian artery