This model represents the 6 classical aortic arches. They are paired and surround the esophagus and trachea. All of these arches are not present at the same time, and they are of different sizes than represented on the model.   

Normally the first 2 arches atrophy and disappear. They are not important for cardiovascular development but remnants of them do contribute to the maxillary and stapedal arteries in the head. We will remove them from the model.

First two arches atrophy and disappear

Here you can see the model with the first 2 arches removed.  

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The 3rd arches form the common carotid arteries and proximal segments of the internal carotid artery. We will leave them attached at their base at the aortic sac.  

3rd arches

3rd arches attached at the aortic sac

The segment of the dorsal aorta between the 3rd and 4th arches is called the carotid duct. It also atrophies and disappears, and we will remove it from the model.

Cartoid duct

The right 4th arch forms the proximal segment of the right subclavian artery.  

Proximal segment of the right subclavian artery

The left 4th arch forms the definitive aortic arch.  

Definitive aortic arch

The 5th arches are present in reptiles but not in mammals, and are not important for this demonstration. They will be removed from the model.  

5th arches

The 6th arches are sometimes referred to as the caudal or pulmonary arches to avoid the inappropriate use of "6th arch" in mammals where 5 arches are the norm.  

Caudal or pulmonary arches

The proximal segment of the left caudal arch forms the pulmonary trunk and the distal segment forms the muscular ductus arteriosus.

Pulmonary trunk

Muscular ductus arteriosus

The proximal segment of the right caudal arch forms the proximal right pulmonary artery and the distal segment atrophies.

Proximal right pulmonary artery

Distal segment atrophies

The left and right pulmonary arteries grow distally as branches from the proximal left and right caudal arches.

Left and right pulmonary arteries

The 7th intersegmental arteries arise from the dorsal aorta caudal to the last arch and supply blood to the forelimbs cranial to the first rib.

7th intersegmental arteries

The paired 7th intersegmentals are pulled forward along the wall of the aorta (yellow arrow) by tension produced between the cranially-developing forelimbs and 1st rib and the caudal expansion of the growing heart ("caudal descent of the heart").

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The right 4th arch separates from the aorta after the right 7th intersegmental arrives and the two arterial segments form the right subclavian artery. The left 7th intersegmental stops partway down on the arch and remains as the left subclavian branch from the left 4th arch.

Right 4th arch	Right 7th intersegmental
Left 7th intersegmental	Left 4th arch

All that the surgeon needs to be familiar with and to recognize during a corrective procedure are the left and right 4th arches, the caudal arches, and the intersegmentals, as shown here.

4th arches, caudal arches, intersegmentals

In the normal mammal, all of the mature aortic arch structures lie on the left side of the esophagus and trachea (birds normally have a right aortic arch).

Mature aortic arch structures (mammal)