Correlative biochemical and morphological studies of myelination in human ontogenesis. I. Myelination of the spinal cord.

Biochemical, light and electron microscopic observations in six human fetuses between the 16th and 34th weeks of gestation and five infants, 1 day to 3 years old, are presented. The results indicate that myelination of the human spinal cord started before the 16th week of gestation, as a considerable amount of myelin is isolated at this time biochemically, and occasionally axons with loose myelin coils are observed in the electron microscope. It is also stressed that morphological studies are insufficient to evaluate the completion time of the myelination process, as it can be shown biochemically that qualitative myelin maturation takes a long time.