The structure indicated is the arch of the aorta.

The aorta arises from the left ventricle of the heart and supplies the body with oxygenated blood. The aorta can be divided into thoracic and abdominal parts (the thoracic aorta pierces the diaphragm to enter the abdominal cavity, becoming the abdominal aorta). The thoracic aorta consists of:

• Ascending aorta
• Aortic arch
• Descending (thoracic) aorta

The aortic arch lies in the superior mediastinum and begins and ends at the level of the angle of Louis (sternal angle) which lies at the level of the intervertebral disc between T4/T5.

The arch of the aorta gives rise to three branches:

1. Brachiocephalic trunk
2. Left common carotid
3. Left subclavian artery

You can remember the branches of the aortic arch using the mnemonic ABC’S – Aorta – Brachiocephalic trunk, Common carotid (left), Subclavian (left).

Learn more about the great vessels in this tutorial