The abdominal portion of the sympathetic trunk is situated in front of the vertebral column, along the medial margin of the Psoas major. It consists usually of four lumbar ganglia, connected together by interganglionic cords. It is continuous above with the thoracic portion beneath the medial lumbocostal arch, and below with the pelvic portion behind the common iliac artery. The ganglia are of small size, and placed much nearer the median line than are the thoracic ganglia. Gray rami communicantes pass from all the ganglia to the lumbar spinal nerves. The first and second, and sometimes the third, lumbar nerves send white rami communicantes to the corresponding ganglia. The rami communicantes are of considerable length, and accompany the lumbar arteries around the sides of the bodies of the vertebrae, passing beneath the fibrous arches from which some of the fibers of the Psoas major arise.