Paired, vertical vein of the posterior abdominal wall, adjacent and parallel to the vertebral column, posterior to the origin of the psoas major muscle (bodies of vertebrae and intervertebral disks from the twelfth thoracic to the fifth lumbar); it connects the common iliac (dorsal bone of the pelvis), iliolumbar, and lumbar veins in the paravertebral line, the right vein joining the right subcostal vein to form the azygos vein, the left vein uniting with the left subcostal (below the ribs); vein to form the hemiazygos vein (merger of the left ascending lumbar vein with the left subcostal vein).