ON THE DEVELOPMENT OF DERMAL PAPILLAE AND EPIDERMAL RIDGES OF HUMAN SKIN

The formation of the primary dermal ledges, secondary dermal ledges, dermal papillae and epidermal ridges were observed with scanning electron microscope. The volar skin of 111 samples including embryos of 6th week to fetuses of 9th month were prepared. The distal phalanges and digites, palms and soles of freshly aborted embryos and fetuses were prepared by routine methods. Some of them were pretreated with ammonium thiocyanate to remove the epidermal layer for observation on the dermal surface. In the 6th week embryos, the body surface was covered by a layer of periderm. Each peridermal cell has many tiny microvilli and a large central vacuole projecting from the cell surface. In the third month fetuses, the primary dermal ledges and grooves gradually appeared, but the epidermal surface showed noepidermal ridges. The primary dermal ledges began.to divide into double parallel ledges,-the secondary dermal ledges in the 16th week fetuses. Concomitantly, a furrow was recognizable between the two related secondary dermal ledges. The dermal papillae first appeared in 19th week fetuses and then elevated gradually to form zigzag shape in 30th week. The epidermal ridges appeared simultaneously with the secondary dermal ledges in 4th to 5th month and the dermatoglyphic configurations were recognizable in 6th month fetuses. The embryogenesis and the relationship between the dermatoglyphic configuration on the skin surface and the dermal ledges and dermal papillae were discussed.