The systemic veins may be arranged into three groups: (1) The veins of the heart. (2) The veins of the upper extremities, head, neck, and thorax, which end in the superior vena cava. (3) The veins of the lower extremities, abdomen, and pelvis, which end in the inferior vena cava.
The pulmonary veins return the arterialized blood from the lungs to the left atrium of the heart. They are four in number, two from each lung, and are destitute of valves. The commence in a capillary net-work upon the walls of the air sacs, where they are continuous with the capillary ramifications of the pulmonary […]