A dermatome is the area of cutaneous distribution of a single spinal nerve; there is considerable overlap between adjacent dermatomes.

The twelfth thoracic spinal nerves supply a band of skin around the thorax and anterior abdominal wall below the twelfth ribs, above the iliac crests laterally to the lower half of the region between the umbilicus and pubic crest anteriorly as far as the midline.  It typically lies above the inguinal ligament.