Pulmonary vein pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the lung hilum. Behind the pulmonary artery is the bronchus. The right main pulmonary veins (contains oxygenated blood) pass behind the right atrium and superior vena cava; the left in front of the descending thoracic aorta. Occasionally the three lobar veins on the right side remain separate, and not infrequently the two left lobar veins end by a common opening into the left atrium. Therefore, the number of pulmonary veins opening into the left atrium can vary between
Azygos vein its left-side equivalent. This terminology is only accurate in some species, such as the human, dog and cat. Ruminants (such as sheep and cows) have paired azygos veins. Azygos vein The azygos vein is a vein running up the side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superior vena cava and inferior vena cava and can provide an alternative path for blood to the right atrium when either of the venae cavae is blocked. The azygos vein transports deoxygenated blood from the posterior walls of the thorax and abdomen into