This is a very low magnification image of a portion of a large peripheral nerve cut transversely. In this preparation, the myelin sheaths were not well fixed and the membrane lipids were extracted. The small spots at the center of some of the circles are the residual portions of the axons. The extracellular epineurium (e) is the thicker, outer, more lightly stained region, which helps provide resistance to mechanical stress. The perineurium (p) is the inner, more darkly stained cellular layer that surrounds the entire nerve, preserves the ionic environment and protects against penetration of pathogens. Larger strands of endoneurium, containing blood vessels, subdivide the nerve and provide support to the axons.