(Modified, from Fender, after Foerster) A dermatome is an area of skin supplied by the dorsal (sensory) root of a spinal nerve. The dermatomes were determined by plotting (a) the areas of vasodilation that resulted on stimulation of individual dorsal nerve roots, and (b) the areas of "remaining sensibility" after cutting three roots above and three roots below a given nerve root. The areas plotted represent the average finding for each dorsal root based on pain sensation. Areas determined for temperature sensation have similar limits, but those for touch are more extensive. Note that there is considerable overlapping of con- tiguous dermatomes; that is to say, each segmental nerve overlaps the territories of its neighbours. As a result, no anesthesia results unless two or more con- secutive dorsal roots have lost their functions. The 7th cervical dermatome (not depicted) begins lower on the upper arm than the 6th and includes most,