The diagram indicates the sternal angle of Louis.

The sternal angle is the angle formed between the manubrium of the sternum and the body of the sternum (manubriosternal junction), and is an important anatomical landmark. It marks the level of the 2^nd pair of costal cartilages which lies at the level of the intervertebral disc between thoracic vertebrae 4 and 5. This level represents several important anatomical features:

• Beginning and end of the aortic arch
• Bifurcation of the trachea
• Bifurcation of the pulmonary trunk
• Left recurrent laryngeal loops under arch of aorta
• Ligamentum arteriosum lies at this level
• Azygos vein drains into superior vena cava
• Cardiac plexus
• Thoracic duct empties into left subclavian vein

A helpful mnemonic for remembering the structures that lies at the level of the sternal angle is RATPLANT:

Rib (2^nd), Aortic arch, Trachea birfurcation, Pulmonary trunk bifurcation, Left recurrent laryngeal (and Ligamentum arteriosum), Azygos vein, Nerves – cardiac plexus, Thoracic duct

Learn about the sternal angle in this tutorial.