Interpretation



Before pattern definition can be understood, it is necessary to

understand the meaning of a few technical terms used in fingerprint

work.



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

lines.





















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

branches.



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

sufficient recurve.



- 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

the delta.



- 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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