Figure 24-2. A, Scheme of the main connections of the azygos, caval, and vertebral systems of veins. Connections of the azygos and hemiazygos veins with the posterior intercostal veins also occur. B, The main veins of the thorax. An interrupted blue line indicates the course of a left superior vena cava (a rare anomaly) on its way to the coronary sinus. Click for high resolution image.