Artist illustration of the connective tissue associated with a peripheral nerve. Nerves are composed of nerve fascicles (individual fascicles eventually become branches of the nerve). The entire nerve (all of the fascicles) are enveloped by connective tissue called epineurium. Individual fascicles are delineated by connective tissue called perineurium. Layers of flattened mesodermal cells, called perineural epithelium (epithelioid) cells, line the perineurium and offer a protective barrier. Connective tissue inside perineural epithelium is called endoneurium. It surrounds neurolemmocytes. Axons are either myelinated or non-myelinated (not shown). The latter are ensheathed (by the dozens) by individual neurolemmocytes, in series. Individual myelinated axons are enveloped by a series of myelin internodes, each formed by a single neurolemmocyte.