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the 12 pairs of spinal nerves emerging from the spinal cord at the level of the thorax, including 11 intercostal nerves and one subcostal nerve. They are distributed mainly to the walls of the thorax and the abdomen. The thoracic nerves do not enter a plexus but follow independent courses, making them different from other spinal nerves. The first two intercostal nerves innervate the upper limb and the thorax; the next four supply only the thorax; and the lower five supply the walls of the thorax and the abdomen. Each subcostal thoracic nerve innervates the abdominal wall and the skin of a buttock. See also autonomic nervous system.