The complex arrangement of the thoracic viscera and their important topographic relationships are perhaps best revealed, understood, and retained when expressed in terms of some relatively stable or fixed skeletal reference point, e.g., a numbered vertebra. If the reference object is visible and/or palpable on the body’s surface, so much the better. The sternal angle (of Louis), a slight bony ridge or depression on the upper chest wall, corresponding to the manubriosternal joint, is such a landmark. It is useful, because it indicates on the body’s surface the anterior projection of an imaginary horizontal plane at which many important mediastinal structures begin, end, or change direction.
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