Fig. 3-3. Spinal and peripheral nerve distributions. Of the two sensory fibers of spinal nerve A, one joins peripheral nerve X and the other joins Y. A plexus allows both fibers to enter spinal nerve A. Two fibers of spinal nerve B also join the two peripheral nerves. Thus, the areas (dermatomes) supplied by the two spinal nerves differ from those supplied by the two peripheral nerves, as is shown in the subdivided rectangle. Overlap is omitted. Click for high resolution image.