Articles from The Science Of Fingerprints
Unidentified Latent Fingerprint File
How To Take Inked Fingerprints
The Identification Division Of The Fbi
Before pattern definition can be understood, it is necessary to
understand the meaning of a few technical terms used in fingerprint
The pattern area is the only part of the finger impression with
which we are concerned in regard to interpretation and classification.
It is present in all patterns, of course, but in many arches and
tented arches it is impossible to define. This is not important,
however, as the only patterns in which we need to define the pattern
area for classification purposes are loops and whorls. In these two
pattern types the pattern area may be defined as follows:
The pattern area is that part of a loop or whorl in which appear the
cores, deltas, and ridges with which we are concerned in classifying.
The pattern areas of loops and whorls are enclosed by type lines.
Type lines may be defined as the two innermost ridges which start
parallel, diverge, and surround or tend to surround the pattern area.
Figure 11 is a typical loop. Lines A and B, which have been emphasized
in this sketch, are the type lines, starting parallel, diverging at
the line C and surrounding the pattern area, which is emphasized in
figure 12 by eliminating all the ridges within the pattern area.
Figures 72 through 101 should be studied for the location of type
Type lines are not always two continuous ridges. In fact, they are
more often found to be broken. When there is a definite break in a
type line, the ridge immediatelyoutside of it is considered as its
continuation, as shown by the emphasized ridges in figure 13.
Sometimes type lines may be very short. Care must be exercised in
their location. Notice the right type line in figure 14.
When locating type lines it is necessary to keep in mind the
distinction between a divergence and a bifurcation (fig. 15).
A bifurcation is the forking or dividing of one line into two or more
A divergence is the spreading apart of two lines which have been
running parallel or nearly parallel.
According to the narrow meaning of the words in fingerprint parlance,
a single ridge may bifurcate, but it may not be said to diverge.
Therefore, with one exception, the two forks of a bifurcation may
never constitute type lines. The exception is when the forks run
parallel after bifurcating and then diverge. In such a case the two
forks become the two innermost ridges required by the definition. In
illustration 16, the ridges marked A--A are type lines even though
they proceed from a bifurcation. In figure 17, however, the ridges
A--A are not the type lines because the forks of the bifurcation do
not run parallel with each other. Instead, the ridges marked T are
the type lines.
Angles are never formed by a single ridge but by the abutting of one
ridge against another. Therefore, an angular formation cannot be used
as a type line. In figure 18, ridges A and B join at an angle. Ridge B
does not run parallel with ridge D; ridge A does not diverge. Ridges C
and D, therefore, are the type lines.
Focal points--Within the pattern areas of loops and whorls are
enclosed the focal points which are used to classify them. These
points are called delta and core.
The delta is that point on a ridge at or in front of and nearest the
center of the divergence of the type lines.
It may be:
- A bifurcation
- An abrupt ending ridge
- A dot
- A short ridge
- A meeting of two ridges
- A point on the first recurving ridge located nearest to
the center and in front of the divergence of the type lines.
The concept of the delta may perhaps be clarified by further
exposition. Webster furnishes the following definition: (1) Delta is
the name of the fourth letter of the Greek alphabet (equivalent to
the English D) from the Phoenician name for the corresponding letter.
The Greeks called the alluvial deposit at the mouth of the Nile, from
its shape, the Delta of the Nile. (2) A tract of land shaped like the
letter delta, especially when the land is alluvial, and enclosed
within two or more mouths of a river, as the Delta of the Ganges, of
the Nile, of the Mississippi (fig. 19).
When the use of the word delta in physical geography is fully
grasped, its fitness as applied in fingerprint work will become
evident. Rivers wear away their banks and carry them along in their
waters in the form of a fine sediment. As the rivers unite with seas
or lakes, the onward sweep of the water is lessened, and the sediment,
becoming comparatively still, sinks to the bottom where there is
formed a shoal which gradually grows, as more and more is
precipitated, until at length a portion of the shoal becomes higher
than the ordinary level of the stream. There is a similarity between
the use of the word delta in physical geography and in fingerprints.
The island formed in front of the diverging sides of the banks where
the stream empties at its mouth corresponds to the delta in
fingerprints, which is the first obstruction of any nature at the
point of divergence of the type lines in front of or nearest the
center of the divergence.
In figure 20, the dot marked delta is considered as the delta
because it is the first ridge or part of a ridge nearest the point of
divergence of the two type lines. If the dot were not present, point B
on ridge C, as shown in the figure, would be considered as the delta.
This would be equally true whether the ridges were connected with one
of the type lines, both type lines, or disconnected altogether. In
figure 20, with the dot as the delta, the first ridge count is ridge
C. If the dot were not present, point B on ridge C would be considered
as the delta and the first count would be ridge D. The lines X--X and
Y--Y are the type lines, not X--A and Y--Z.
In figures 21 to 24, the heavy lines A--A and B--B are type lines with
the delta at point D.
Figure 25 shows ridge A bifurcating from the lower type line inside
the pattern area. Bifurcations are also present within this pattern at
points B and C. The bifurcation at the point marked delta is the
only one which fulfills all conditions necessary for its location. It
should be understood that the diverging type lines must be present in
all delta formations and that wherever one of the formations mentioned
in the definition of a delta may be, it must be located midway between
two diverging type lines at or just in front of where they diverge in
order to satisfy the definition and qualify as a delta.
When there is a choice between two or more possible deltas, the
following rules govern:
-The delta may not be located at a bifurcation which does
not open toward the core.
In figure 26, the bifurcation at E is closer to the core than the
bifurcation at D. However, E is not immediately in front of the
divergence of the type lines and it does not open toward the core.
A--A and B--B are the only possible type lines in this sketch and it
follows, therefore, that the bifurcation at D must be called the
delta. The first ridge count would be ridge C.
- When there is a choice between a bifurcation and another
type of delta, the bifurcation is selected.
A problem of this type is shown in figure 27. The dot, A, and the
bifurcation are equally close to the divergence of the type lines, but
the bifurcation is selected as the delta. The ridges marked T are
the type lines.
- When there are two or more possible deltas which conform
to the definition, the one nearest the core is chosen.
Prints are sometimes found wherein a single ridge enters the pattern
area with two or more bifurcations opening toward the core. Figure 28
is an example of this. Ridge A enters the pattern area and bifurcates
at points X and D. The bifurcation at D, which is the closer to the
core, is the delta and conforms to the rule for deltas. A--A and B--B
are the type lines. A bifurcation which does not conform to the
definition should not be considered as a delta irrespective of its
distance from the core.
- The delta may not be located in the middle of a ridge
running between the type lines toward the core, but at the
nearer end only.
The location of the delta in this case depends entirely upon the point
of origin of the ridge running between the type lines toward the core.
If the ridge is entirely within the pattern area, the delta is located
at the end nearer the point of divergence of the type lines. Figure 29
is an example of this kind.
If the ridge enters the pattern area from a point below the divergence
of the type lines, however, the delta must be located at the end
nearer the core. Ridge A in figure 30 is of this type.
In figure 31, A--A and B--B are the type lines, with the dot as the
delta. The bifurcations cannot be considered as they do not open
toward the core.
In figure 32, the dot cannot be the delta because line D cannot be
considered as a type line. It does not run parallel to type line A--A
at any point. The same reason prevents line E from being a type line.
The end of ridge E is the only possible delta as it is a point on the
ridge nearest to the center of divergence of the type lines. The other
type line is, of course, B--B.
The delta is the point from which to start in ridge counting. In the
loop type pattern the ridges intervening between the delta and the
core are counted. The core is the second of the two focal points.
The core, as the name implies, is the approximate center of the
finger impression. It will be necessary to concern ourselves with the
core of the loop type only. The following rules govern the selection
of the core of a loop:
- The core is placed upon or within the innermost
- When the innermost sufficient recurve contains no ending
ridge or rod rising as high as the shoulders of the loop,
the core is placed on the shoulder of the loop farther from
- When the innermost sufficient recurve contains an uneven
number of rods rising as high as the shoulders, the core is
placed upon the end of the center rod whether it touches the
looping ridge or not.
- When the innermost sufficient recurve contains an even
number of rods rising as high as the shoulders, the core is
placed upon the end of the farther one of the two center
rods, the two center rods being treated as though they were
connected by a recurving ridge.
The shoulders of a loop are the points at which the recurving ridge
definitely turns inward or curves.
Figures 33 to 38 reflect the focal points of a series of loops. In
figure 39, there are two rods, but the rod marked A does not rise as
high as the shoulder line X, so the core is at B.
Figures 40 to 45 illustrate the rule that a recurve must have no
appendage abutting upon it at a right angle between the shoulders and
on the outside. If such an appendage is present between the shoulders
of a loop, that loop is considered spoiled and the next loop outside
will be considered to locate the core. In each of the figures, the
point C indicates the core. Appendages will be further explained in
the section concerning loops.
Figures 46 to 48 reflect interlocking loops at the center, while
figure 49 has two loops side by side at the center. In all these cases
the two loops are considered as one. In figure 46, when the shoulder
line X--X is drawn it is found to cross exactly at the point of
intersection of the two loops. The two loops are considered one, with
one rod, the core being placed at C. In figure 47, the shoulder line
X--X is above the point of intersection of the two loops. The two are
considered as one, with two rods, the core being at C. In figure 48,
the shoulder line X--X is below the point of intersection of the
loops. Again the two are treated as one, with two rods, the core being
placed at C. In figure 49, the two are treated as one, with two rods,
the core being placed at C.
In figure 50, the delta is formed by a bifurcation which is not
connected with either of the type lines. The first ridge count in this
instance is ridge C. If the bifurcation were not present, the delta
would be a point on ridge C and the first ridge count would be ridge
D. In figure 51, the ridge which bifurcates is connected with the
lower type line. The delta in this would be located on the
bifurcation as designated and the first ridge count would be ridge C.
Figure 52 reflects the same type of delta shown in the previous figure
in that the ridge is bifurcating from a type line and then bifurcates
again to form the delta.
A white space must intervene between the delta and the first ridge
count. If no such interval exists, the first ridge must be
disregarded. In figures 53 and 54, the first ridge beyond the delta is
counted. In figure 55, it is not counted because there is no interval
between it and the delta. Notice that the ridge running from the delta
toward the core is in a straight line between them. If it were not, of
course, an interval would intervene as in figures 53 and 54.
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