Fig. 34 Nerve fiber layer near the optic nerve head. Longitudinally sectioned axons of ganglion cells are on top, and transversely sectioned nerve fibers are below them (Ax), each enveloped in their axolemma. Some fibers are separated by Müller cell processes (M). There are transversely sectioned neurotubules (nt) and mitochondria in the nerve fibers. The plasma membranes between these fibers are separated from one another by the usual 20-nm intercellular space. er, smooth endoplasmic reticulum. Arrowheads point to mitochondria. Open arrow indicates clumps of glycogen granules in the Müller cells (original magnification ×18,500; courtesy of Dr. Takeo Iwamoto).