A dermatome is an area of the skin that is supplied by only one posterior root and its ganglion. Compared with the relatively regular arrangement of the dermatomes on the trunk, the situation in the limbs appears to be unclear at first sight. However, the arrangement of the dermatomes becomes understandable once the growth of the limbs is taken into consideration. If the pre-axial margin from the thorax is followed along the limbs towards the periphery and back to the thorax along the postaxial margin, a regular sequence of dermatomes can be seen from C4 to T2 through C8 and T1 for the arm, and from L1 to S2 through L5 and S1 for the lower limb.