Surrounding each muscle fiber (cell) is a delicate external lamina composed primarily of reticular fibers. This external lamina is produced by the muscle fiber and, when observed through the light microscope, cannot be distinguished from the cell membrane of the muscle fiber, the sarcolemma. The prefix sarco- refers to muscle and is used to rename some structures found in muscle cells. The endomysium, a delicate network of loose connective tissue with numerous reticular fibers, surrounds each muscle fiber outside the external lamina. A bundle of muscle fibers with their endomysium is surrounded by another heavier connective tissue layer called the perimysium. Each bundle ensheathed by perimysium is a muscle fasciculus.