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An electron microscopic study of mesenchyme during development of interdigital spaces in man

Cell movements and degenerations occur normally during embryogenesis and have received particular attention during development of limbs in the chick. The present investigation suggests that similar phenomena occur during formation of interdigital spaces in man. Upper limb buds were dissected from a human embryo (CR 15.5 mm, age estimated at 6 weeks postfertilization), fixed in phosphate buffered glutaraldehyde, and prepared for electron microscopy. Mesenchymal cells in developing interdigital zones appeared to be undergoing either mitosis or necrosis. Macrophagy of necrotic mesenchymal cells, which begins distad in the appendage bud, contributes to the final formation of an interdigital space.