Only
the hairless parts of the body ---- the inner surfaces of the hands
and the soles of the feet ---- are covered with patterns formed by
raised ridges of skin known as friction or papillary ridges. The
study of fingerprints, or dactyloscopy, forms only one privileged
section of the wider of lophoscopy: dactyloscopy is the more widely
used section in practice even though prints from the soles of the
feet are as characteristic as fingerprints, they are less often used
for identification purposes due to their low rate of occurrence. The
patterns formed by the papillary ridges are important since they are
already formed in the foetus by the fourth month of pregnancy and
they do not change until death. These patterns cannot be altered,
except by accident, mutilation, or very serious skin desease, as
they are formed in deep layers of the dermis.
The skin consists of two main layers: the outer skin or
epidermis, and the inner or true skin, known the dermis. The
epidermis is constantly being worn away and replaced by new skin
generated by the upper layer of the dermis - a papillary layer
(stratum mucosum) which is the source of the ridges known as
'papillary ridges'. The sweat glands, located in the dermis,
discharge sweat at the skin surface through sweat pores found at the
top of the ridges.
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Structure
of skin showing friction ridges and pores connected to sweat
glands
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Such pore holes are critical to the production of
latent prints since sweat reaches the surface of the hand and
efficiently coats the tops of the fingerprint ridges with
sweat. Sweat glands serve as small chemical reservoirs and
contain a variety of water-soluble chemical compounds, produced or
stored by the body. The dermal layer of the skin also contains the
nerves of touch which terminate at the underside of the epidermis.
The epidermis contains no nerves but does contain nerve endings.
Fingerprint patterns are not formed at the surface of the skin but
are determined by the arrangement of various elements, such as sweat
glands, nerves, and blood vessels found below the surface of the
skin. Sebaceous glands and hair follicles are found in the dermal
layer of other skin surfaces but are absent in friction skin.
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Cross
section of a friction ridge
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Should the top layer of skin suffer any injury, the ridges grow back
after healing in the exact pattern they had before. Therefore,
superficial cuts or abrasions alter fingerprint characteristics only
temporarily. If the injury reaches deep into the dermis and destroys
the dermal papillae, then growth of new epidermal cells is impaired
and a permanent scar is created.
Fingerprint detail is unique and individual for a given finger, even
if two fingerprints may be similar, as is the case with identical
twins, since the detail in a fingerprint is formed in an accidental
manner during gestation. Wilder and Wentworth followed by Cummins
and Midlo were pioneers in the study of ridge morphology and gave
numerous indications on the formation of papillary ridges. From the
third month of foetal life, bumps or points develop at variable
rates on the tactile surfaces, with each point containing a pore.
These fuse together as lines to give the papillae. The general
pattern is influenced by heredity, but this is not the case for
papillary minutiae as these are the result of stress and variable
pressure on the tactile surfaces when the points fuse into lines.
The ridge characteristics that make fingerprints unique are known as
minutiae, Galton points, characteristic points or points of
identification.
Page Design © Ian Hunter.
Content © Christopher J
Lennard BSc(hons), PhD and Trevor Patterson Det. Sen Sgt New South
Wales Police Service. |
