UNIT 2
Friction ridge skin
Two cornerstones to the use of fingerprints as a mean of personal identification are the permanence (persistency or durability) and the uniqueness of friction ridge skin.
friction ridge skin morphogenesis - the biological development of form
The Volar areas of the skin (palm, finger and sole areas of the epidermis) are known to display a series of friction ridges taking various forms and shapes.
The skin is divided into 2 layers.
The outer layer epidermis is a stratified epithelium of 5 sublayers. (bottom to top)
stratum germinativum (basal generating layer)
stratum spinosum (spinous layer)
stratum granulosum (granular layer)
stratum lucidum (transitional hyalin layer)
stratum corneum (horny cornified layer)
The layer under the epidermis is called the dermis, it is 15 to 40 times thicker than the epidermis.
The permanency of the friction ridge pattern is largely due to this generative process, whereby the cells constituting of the epidermis (and thus its shape) are produced on the inner protected basal layer just above the dermis.
Morphogenesis of the friction ridge skin
The morphogenesis of the friction ridge starts during the first weeks of gestation.
The hand starts to develop from 5 to 6 weeks EGA (estimated gestational age). The first fingers appear at 6 to 7 weeks along with the appearance of volar pads on the palm. Volar pads are temporary swellings of mesenchymal tissue under the epidermis.
It is between weeks 11 and 20 that the major development of friction ridge occurs. The volar pads provide the bedding for that development.
At around 10 weeks EGA, cells on the basal layer start to proliferate (reproduce rapidly). The location of the initial proliferations seems coincident with sweat gland development, but it could also be associated with the arrangement of superficial dermal nerves (Merkel cell clusters and Meissner corpuscles) that orchestrates the spacing and general arrangement of the papillary ridges (Dell and Munger 1986). These cells, each associated with a sweat gland, multiply rapidly and fuse into ridges called “ledges” (Hale 1952). These ridges, called primary dermal ridges, are still immature and will start to mature by developing downward within the dermis. Individual dermal ridges are not yet differentiated on the areas surrounding these focal areas; rather, the dermis presents a primordial crepe-like appearance (Figure 1.3). The latter is predictive of the basic orientation of the ridge structure to be manifested there later (Okajima and NewellMorris 1988).
Prior to ridge development, the embryonic epidermal surface — the periderm — is three or four cell layers thick and smooth on its outer surface (Figure 1.3).
note
Volar pads appear on each finger at 7 to 8 weeks and remain clearly visible till 10 weeks, when the growth of the hand overtakes the pads, rendering them not visible by 16 weeks EGA. This is described as the ‘regression’ stage of the volar pads.
but it could also be associated with the arrangement of superficial dermal nerves (Merkel cell clusters and Meissner corpuscles) organized in an approximately two-dimensional hexagonal grid that orchestrates the spacing and general arrangement of the papillary ridges (Dell and Munger 1986).
Biological basis of fingerprints
The skin is divided into 2 layers.
The outer layer epidermis is a stratified epithelium of 5 sublayers. (bottom to top)
stratum germinativum (basal generating layer)
stratum spinosum (spinous layer)
stratum granulosum (granular layer)
stratum lucidum (transitional hyalin layer)
stratum corneum (horny cornified layer)
The layer under the epidermis is called the dermis, it is 15 to 40 times thicker than the epidermis.
The permanency of the friction ridge pattern is largely due to this generative process, whereby the cells constituting of the epidermis (and thus its shape) are produced on the inner protected basal layer just above the dermis.
Formation of ridges
Primary dermal ridge development
The hand starts to develop from 5 to 6 weeks EGA. The first fingers appear around 6 to 7 weeks. At that time, volar pads appear on the palm (interdigital pads first, followed by thenar and hypothenar pads). They appear on each finger at 7 to 8 weeks. These pads remain clearly visible until 10 weeks, when the growth of the hand overtakes the pads, rendering them not visible by week 16 EGA. It is between weeks 11 and 20 that the major development of friction ridge skin occurs.
At around 10 weeks EGA, cells on the basal layer start to proliferate. The location of the initial proliferations seems coincident with sweat gland development. These cells, each associated with a sweat gland, multiply rapidly and fuse into ridges called “ledges”. These ridges, called primary dermal ridges, are still immature and will start to mature by developing downward within the dermis.
The permanence of friction ridge pattern is largely due to the generative process where the cells constituting of the epidermis are produced on the inner protected basal layer just above the dermis
Volar pads
Volar pads are temporary swellings of mesenchymal tissue under the epidermis.
They appear at 6-8 weeks EGA and remain clearly visible till 10 weeks EGA, when the growth of the hand overtakes rendering them invisible by week 16. This is described as the “regression” stage of volar pads.
Types of fingerprints
We find chance fingerprints at a crime scene. They are of 3 types →
visible prints/ patent prints
they are visible to the naked eye
produced when coloured contaminants are present on the finger or palm and he touches any surface
Eg → blood prints, ink prints, paint prints, etc.
these do not require any kind of developmental processes, rather they are simply photographed and sent for analysis
plastic prints
formed when the fingers or palm come in contact with a plastic body or surface such as soap, butter, clay, freshly painted surface
they do not require any kind of developmental processes, rather they are simply photographed and sent for analysis
latent prints
these are not visible to the naked eye
these are hidden or concealed impressions left on various objects
the papillary ridges of friction skin have numerous sweat pores which secrete sweat and oily matter
due to this sweat, whenever fingers or palm come in contact with any surface they leave an invisible impression
in order to make them visible they are treated with physical or chemical methods.
Fingerprint pattern
Plain arch → a pattern in which the ridges enter on one side of the pattern then flow towards the other side with a rise at the centre.
Tented arch → a fingerprint pattern where majority of the ridges from an arch and one or more ridges at the centre shape a tent in the outline giving an angle of 90 degree or less, or one with an upward crust having an angle of 45° or more.
Radial loop → it has a downward or slanting of ridges towards the direction of the thumb or the radial bone either to the right or left hand.
Ulnar loop → it has a downward slop or slanting of ridges towards the direction of the little finger or the ulnar bone either to the right or left hand
plain whorl → this pattern consists of two deltas and in which at least one ridge makes a turn through one complete circuit of 360°
two types → elongated or oval whorl, spiral or circular whorl
Central pocket loop → this pattern posses 2 delta with one or more ridges forming a complete circuit which may be oval, spiral, circular or any variant of a circle.
Double loop → it consists of 2 separate and distinct loop formations with 2 sets of cores and 2 deltas.
Lateral pocket loop → it is formed by 2 loops flowing in the same direction. The pocket is formed by downward bending on one side of the ridge of other loop before they recurve.
twinned loop → in this one loop is resting upon or encircling the other and the ridges containing the point of core have their exit towards different deltas.
accidental loop → it consists of a combination of 2 different patterns
combination of a loop and any whorl
it can not be the combination of an arch with other pattern
Ridge characteristics (minutiae)
Bifurcation → a single ridge which splits into 2 ridges forming a y-shape structure.
Trifurcation → a friction ridge that splits into 3 friction ridges.
Double bifurcation → in this one of the bifurcated ridges bifurcates.
Ridge cross → it is a point where 2 ridges cross each other forming an X formation.
Spur/ Hook → a friction ridge which recurves and ends abruptly
fragment → an independent ridge of relatively small length
Enclosure → a ridge that bifurcates and then converges to form an eye like shape.
lake/ island → a ridge that forms a lake like structure, smaller than the enclosure.
Plain and rolled finger prints
Ridge counting
It is the process of counting the ridges that touch or cross an imaginary line drawn between the core and the delta.
Procedure/Rules of ridge counting
locate the delta and core
draw an imaginary line between core and delta
count all ridges which touch or cross the imaginary line drawn between the core and the delta
incipient ridges, puckering, dissociated and creases are not counted
fragments and dot ridges are counted
do not include core and delta
Ridge tracing
The process of tracing the ridges intervening between
Rules/ Procedure of ridge tracing
look for the left delta and trace towards the front of the right delta
when the ridge is bifurcated always follow the lower branch until tracing is completed
determine whether the tracing ridge flows inside, outside or meet the right delta.
*insert diagram *
The hand starts to develop from 5 to 6 weeks EGA. The first fingers appear around 6 to 7 weeks. At that time, volar pads appear on the palm (interdigital pads first, followed by thenar and hypothenar pads). Volar pads are transient swellings of mesenchymal tissue under the epidermis on the volar surfaces of the fetus. Volar pads appear on each finger at 7 to 8 weeks. These pads remain clearly visible until 10 weeks, when the growth of the hand overtakes the pads, rendering them not visible by week 16 EGA. This phenomenon is often described as the “regression” stage of the volar pads. It is between weeks 11 and 20 that the major development of friction ridge skin occurs. The volar pads provide the bedding for that development.
At around 10 weeks EGA, cells on the basal layer start to proliferate. Prior to ridge development, the embryonic epidermal surface — the periderm — is three or four cell layers thick and smooth on its outer surface. The location of the initial proliferations seems coincident with sweat gland development, but it could also be associated with the arrangement of superficial dermal nerves (Merkel cell clusters and Meissner corpuscles) organized in an approximately two-dimensional hexagonal grid that orchestrates the spacing and general arrangement of the papillary ridges (Dell and Munger 1986). These cells, each associated with a sweat gland, multiply rapidly and fuse into ridges called “ledges” (Hale 1952). These ridges, called primary dermal ridges, are still immature and will start to mature by developing downward within the dermis. Individual dermal ridges are not yet differentiated on the areas surrounding these focal areas; rather, the dermis presents a primordial crepe-like appearance. The latter is predictive of the basic orientation of the ridge structure to be manifested there later (Okajima and Newell- Morris 1988).