Expansion
Third makes carotid, fourth makes arch and subclavian, sixth makes pulmonary and ductus
Expansion
- Arch 1 - largely regresses; contributes to the maxillary artery
- Arch 2 - largely regresses; contributes to the stapedial artery
- Arch 3 - common carotid and proximal internal carotid
- Arch 4 - left: the arch of the aorta; right: the proximal right subclavian artery
- Arch 5 - never forms properly, or regresses
- Arch 6 - pulmonary arteries; on the left the distal part persists as the ductus arteriosus
This asymmetry is the explanation for the recurrent laryngeal nerves. Each nerve hooks under the sixth arch artery. On the right that artery regresses, so the nerve rises to the fourth arch derivative, the subclavian artery. On the left the sixth arch persists as the ductus, so the nerve is held down at the aortic arch.