The Pulmonary Veins

The pulmonary veins return the arterial blood from the lungs to the left auricle of the heart. They are four in number, two for each lung. The pulmonary differ from other veins in several respects:

1. They carry arterial instead of venous blood.
2. They are destitute of valves
3. They are only slightly larger that arteries they accompany
4. They accompany those vessels singly

They commence in a capillary network upon the walls of the air cells, where they are continuous with the capillary ramifications of the pulmonary artery, and uniting together, from one vessel for each lobule. These vessels uniting successively, from a single trunk for each lobe, three for the right and two for the left lung. The vein from the middle lobe of the right lung generally unite with that from the upper lobe, forming two trunks on each side, which open separately into the left auricle. Occasionally they remain separate; there are then three veins on the right side. Not infrequently the two left pulmonary veins terminate by a common opening.

Within the lung, the branches of the pulmonary artery are in front, the veins behind, and the bronchi between the two.

At the root of the lung, the veins are in front, the artery in the middle, and the bronchus behind.

Within the pericardium, their anterior surface is invested by the serous layer of the membrane. The right pulmonary veins pass behind the right auricle and ascending aorta and superior vena cava; the left pass in front of the thoracic aorta with the left pulmonary artery.