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

The ninth thoracic spinal nerves supply a band of skin around the thorax and anterior abdominal wall over the ninth intercostal spaces posteriorly extending to the middle of the eighth intercostal spaces above and the tenth intercostal spaces below, to the lower half of the region between the xiphisternal joint and umbilicus anteriorly.