Angle of Louis
This is a palpable ridge at the upper part of the sternum where the manubrium and body of the sternum articulate. It is the point from which costal cartilages can be counted (the first rib is difficult to feel as it is largely buried beneath the clavicles) and is also the level of the disc between T4 vertebra and T5 vertebra vertebrae.
Although not exactly at T4, both the angle of Louis and the T4 vertebral body are used as approximate landmarks for the bifurcation of the trachea and concavity of the aortic arch. These seems accurate in about 40-50% of a series of 51 patients.