Understanding the stages of friction skin growth during fetal development is of utmost importance to the friction ridge identification specialist. The task of explaining friction skin persistency and uniqueness would be a difficult one to say the least without this knowledge.
Scientific research has provided us with reasons as to why fingerprints are persistent and unique - the main premises of fingerprint identification.
The embryonic skin at 4 to 5 weeks consists of a single layer of surface ectoderm (later to form the epidermis) overlying the mesenchyme (connective tissue derived from mesoderm and forms the connective tissue in the dermis).
The layer of surface ectodermal cells proliferate and form a layer of squamous (flattened) epithelium, the periderm, and a basal germinative layer. The cells of the periderm continually undergo keratinization (maturization process) and desquamation (process of cells sloughing off) and are replaced by cells arising from the basal layer.
The basal germinative layer of the epidermis becomes the stratum germinativum, which produces new cells that are displaced into the layers superficial to it. At 8 weeks, the epidermis has the thickness of three or four cells. Even at this early stage the epidermis is strongly constructed. The surface membranes of adjacent cells, which are smooth at this time, lie against one another but at some points on these adjoining cell walls are junctions. At these junctions are structures called desmosomes. As the skin develops, these desmosomes grow larger and the cell junctions become wavy lines and the cell walls interdigitate.
Development of Volar Pads
Embryology research has shown that the development of epidermal ridges are preceded by the formation of volar pads (swelling of mesenchymal tissue) that first appear as elevations on the palm around 6.5 weeks postfertilization, followed by the five digits about one week later.
Volar pads exhibit rapid growth between 6.5 and 10.5 weeks. Initially the pads appear evenly rounded, however, by the 9th week, the pads begin to vary in both position and shape.
There have been numerous studies on volar pad development and its influence on friction ridge path configuration and pattern formation. Studies have shown that there is a direct correlation between the location, shape and size of volar pads and friction ridge patterns. The shape of the volar pad can be the result of genetics or external physical influences or a combination of both. Similarities in overall pattern design can be seen quite often in siblings - especially identical twins. This is apparently the result of similar genetic encoding responsible for volar pad development. Since identical twins have the same DNA, if they have different overall friction ridge patterns (ie.loop v. whorl) it is believed to be caused by external pressures and stresses (differential growth) which have altered the volar pad shape during fetal development.
In 1929, Harold Cummins published a paper "The Topographic History of the Volar Pads In The Human Embryo". In his paper he describes how the growth of epidermal (friction) ridges is dependant on "two major development circumstances, namely, variations in the histology of different regions and differential growth incident to the production of irregular reliefs of the volar surfaces".
He goes on to say...
"The various configurations are not determined by self-limited mechanism within the skin. The skin possesses the capacity to form ridges, but the alignments of these ridges are as responsive to stresses in growth as are the alignments of sand to sweeping by wind or wave."
In other words, friction ridge patterns are not just the result of genetic factors but also random physical stresses and tensions.
Friction Skin Growth....continued next page.
Friction Skin Growth