Fig. 24. Substantia propria of bulbar conjunctiva, showing myelinated (MN) and unmyelinated (UN) nerve fibers. In both fibers, axons (A) are wrapped with Schwann's cells (SC) that have a basement membrane (bm). However, the axons are single and have a myelin sheath (ms) in the former; they are multiple and have no myelin sheath in the latter. nf, neurofilament; nt, neurotubule; m, mitochondria. (× 20,800). Inset. Higher power of a portion (arrow) of the myelin sheath, showing the lamellar structure. (× 40,000)