Peripheral nerves, light micrograph. Cross-section of a peripheral nerve showing myelinated axons. Myelin forms sheaths (brown or black) enclosing the central axon. As an electrical insulator myelin facilitates rapid conduction of impulses along the axon. The nerves shown are supported by connective tissue (green) called perineurium. Paraffin section, osmium/fast green stain. Magnification: x220 when width printed at 10cm.