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Abstract
The ultrastructure of the human optic nerve was studied by electron microscopy. All neuroectodermal components are separated from the niesodermal components by a pial-glial interface. No nonmyelinated axons were seen, save for isolated single axons which probably represent myelinated axons cut within nodes of Ranvier. Myelination appears consistent with a hypothesis of spiral wrapping. Redundant myelin sheathing of one axon may superficially laminate onto another. The principal glial types are fibrous with a ribosome poor cytoplasm, and a ribosome rich variety with few cytoplasmic fibrils. The latter seems to best meet oligodendroglial characters; and the former, those of fibrous astrocytes. However, intermediate types are also seen. Nonmyelinated fibers are seen ending in the connective tissue around the central retinal artery, and their synaptic vesicles often possess dense granules.