Oligodendroglial cells form the myelin sheaths of CNS axons and Schwann cells make the myelin of PNS axons. This is a photo of the myelin sheath in a peripheral nerve
Attribution:
Stephen C. Voron, M.D., Suzanne S. Stensaas, Ph.D. , Department of Neurobiology and Anatomy, University of Utah, School of Medicine, Salt Lake City, Utah 84132, http://library.med.utah.edu/kw/hyperbrain