A dermatome is the area of cutaneous distribution of a single spinal nerve; there is considerable overlap between adjacent dermatomes.  Spinal nerves C4-T2 are distributed to the upper limb.

The second thoracic spinal nerves supply a band of skin around the thorax over the second intercostal spaces extending to the middle of the first intercostal spaces above and the third intercostal spaces below, as well as skin of the axilla and medial aspects of the arms.