SKIN STRUCTURE
and
FINGERPRINTS
SKIN STRUCTURE
SKIN STRUCTURE
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The uppermost layer of the skin structure is the
epidermis, which itself contains several layers:
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the basal cell layer, which is the deepest layer of
the epidermis. Here cells divide to produce new skin
cells, which move towards the skin surface, pushed
upward by the dividing cells below them.
the spinous cell layer,
the granular cell layer, and
the stratum corneum which is the top layer of the
epidermis that we see from the outside. These cells
are dead, contain a lot of keratin and are arranged in
overlapping layers that make them tough and
waterproof.
SKIN STRUCTURE
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The dermis contains a variable amount of fat,
collagen and elastin fibres which provide
strength and flexibility to the skin.
Blood vessels supply nutrients and remove any
waste products. They also help maintain body
temperature by dilating and narrowing.
Nerves in the dermis detect heat, cold, pain,
pressure and touch and relay this information to
the brain.
SKIN STRUCTURE
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A sebaceous gland opens into each hair follicle
and produces sebum, a lubricant for the hair
and skin that helps repel water, damaging
chemicals and microorganisms.
Sweat glands occur on all skin areas — each
person has more than 2 million.
Sweat moves to the skin’s surface via the sweat
duct, and evaporation of this water from the
skin has a cooling effect on the body.
SKIN STRUCTURE
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The papillary layer is the dermal layer
responsible for fingerprints.
FINGERPRINTS
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What Are they?
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They are the marks left behind
when someone touches an object.
Fingerprints can be:
an impression left in something soft, such as putty,
wet paint
 a print left by a hand covered in blood, dirt, paint, etc
 an invisible deposit left by the secretions from the
skin (oils and perspiration from tiny pores. These
types of prints are called latent prints.
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FINGERPRINT PATTERNS
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The three main patterns of fingerprints are the
- ARCH
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- LOOP
- WHORL
To help identify a fingerprint as one of these patterns,
you look for delta points. These are triangular
shapes that form where two patterns meet.
Arch Patterns
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Arches are patterns that run from one side of the
finger to the other with out making any backwards
turns, so an arch actually has no delta.
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A plain arch:
 appears like waves tending
to flow through the print
A tented arch:
 Has an upward ridge that
gives the pattern a spine
Loop Patterns
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Loops are the most common print. Where a ridge
makes a backwards turn a loop is formed.
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Radial and Ulnar Loops:
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Double Loop:
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These loops slope downwards
toward the thumb (radial) or
little finger (ulnar)
Has two clear intertwined loops,
with two deltas and two cores
Pocked Loop:
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This is like the loop, but with a small
circle at the turning point
Core
Delta
Whorl Patterns
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25-35% of patterns encountered are whorls. In a whorl,
ridges make a complete turn (a circuit). Any pattern that
contains 2 or more deltas will be a whorl.
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Plain whorl
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Tends to lead to a complete circuit
Central Pocket whorl
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Consists of one re-curving
ridge, or an obstructions at
right angles to the line of flow
Composite or Mixed Patterns
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Composite patterns consist of a mixture of patterns, and
may have three or more deltas.
 They are usually combinations of loops and whorls,
and can also include tented arches.
 Some composite patterns are called ‘accidentals’ as the
ridges are too irregular in outline to be grouped.
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Composite fingerprint patterns
are not common.
Fingerprint Identification
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Even with pattern classification, it would be
impossible to declare two fingerprints to be from
the same finger if you were relying purely on
matching patterns…..
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The pattern is important, but it is the actual
characteristics of the print, ie. the little variations that
occur in the ridge patterns, that enable prints to be
matched.
Fingerprint Identification (cont’d):
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The procedure involves:
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Fingerprint pattern is determined
Detection of minutiae (specific and identifiable ridge
patterns)
Comparison of the relative positions of the minutiae
points with a reference print (usually an inked
impression of the suspect’s print)
Ridge Characteristics
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There are three basic ridge characteristics:
- The ridge ending
- The bifurcation
- The dot and the island
dot
island
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Ridge characteristics are called minutiae
Basic and composite ridge characteristics (minutiae)
Minutiae
Example
Minutiae
ridge ending
bridge
bifurcation
double bifurcation
dot
trifurcation
island (short
ridge)
opposed bifurcations
lake (enclosure)
ridge crossing
hook (spur)
opposed
bifurcation/ridge
ending
Example
Try to identify am many minutiae as you can on these
fingerprints