The development of the epidermal ridges

Abstract

Normal and abnormal dermatoglyphic figures have been extensively investigated, but little is known of the factors involved in the development of epidermal ridges and subsequent pattern formation. A series of tissue sections from fetuses of various ages were prepared for comparative light and electron microscopy. The sections for study by light microscopy were stained with borax toluidine blue and the others, after fixation in glutaraldehyde osmic acid, with uranyl acetate/lead citrate. These preparations show the early development of epidermal layers, involving thickening, accumulation of glycogen, linking of desmosomes in prickle cells, down growth of the basal layer to form glandular folds, and the final ridge formation by 12-16 wk of fetal age. Once ridges are established, it is difficult to explain the formation of patterns. The position of volar pads is important, for loops and whorls occur on their surfaces with triradii between them or at their edges. Stresses produced by skin growth and subsidence of volar pads could be detected by the tightly packed epidermal cells, which might then grow along parallel pressure lines. The parallel lines could later be transformed into patterns by the lines following points of minimal concavity on the external surfaces. (Ridler - Shenley)