[The development of the digital flexion creases in humans]

Human embryos, ranging from 10 to approximately 150-200 mm crown-rump length, were examined in order to study the formation of flexion creases on the fingers. These creases were found to be formed in two stages. They appear first during the 2nd month of development as shallow trenches between the tactile elevations. At the end of the 3rd month the skin of the creases does not take part in the formation of dermal and epidermal ridges. By that time the fine structure of the flexion creases becomes discernible. These embryological observations, together with the findings from anthropological, genetic and clinical studies, rather point to genetic than to purely mechanical factors as the cause of flexion creases on human fingers.