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the five pairs of spinal nerves rising in the lumbar region of the vertebral column. They become increasingly large the more caudal their origin and pass laterally and downward under the cover of the psoas major or between its fasciculi and form part of the lumbar plexus. The lumbar sympathetic ganglia follow no fixed pattern, and fusions of adjacent ganglia are common. When occurring separately, lumbar ganglia lie on the corresponding vertebra or the intervertebral disk caudally. The ganglion of the second lumbar segment is the largest and the most constant.