The Science of Fingerprints by United States. Federal Bureau of Investigation (books to read in a lifetime txt) π
I. ARCH
a. Plain arch. b. Tented arch.
II. LOOP
a. Radial loop. b. Ulnar loop.
III. WHORL
a. Plain whorl. b. Central pocket loop. c. Double loop. d. Accidental whorl.
Illustrations 1 to 10 are examples of the various types of fingerprint patterns.
[Illustration: 1. Plain arch.]
[Illustration: 2. Tented arch.]
[Illustration: 3. Tented arch.]
[Illustration: 4. Loop.]
[Illustration: 5. Loop.]
[Illustration: 6. Central pocket loop.]
[Illustration: 7. Plain whorl.]
[Illustration: 8. Double loop.]
[Illustration: 9. Double loop.]
[Illustration: 10. Accidental.]
Interpretation
Before pattern definition can be understood, it is necessary
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Fig. 26
[Fig. 26]
β 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.
Fig. 27
[Fig. 27]
β 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. AβA and BβB 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.
Fig. 28
[Fig. 28]
β 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.
Fig. 29
[Fig. 29]
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.
Fig. 30
[Fig. 30]
In figure 31, AβA and BβB are the type lines, with the dot as the delta. The bifurcations cannot be considered as they do not open toward the core.
Fig. 31
[Fig. 31]
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 AβA 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, BβB.
Fig. 32
[Fig. 32]
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:
β The core is placed upon or within the innermost sufficient recurve.
β 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.
β 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.
β 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.
Figs. 33-34
Figs. 35-38
Fig. 39
[Figs. 33-39]
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.
Fig. 40
Figs. 41-44
Fig. 45
[Figs. 40-45]
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 XβX 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 XβX 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 XβX 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.
Fig. 46
Figs. 47-48
Fig. 49
[Figs. 46-49]
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.
Fig. 50
Figs. 51-52
[Figs. 50-52]
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.
Figs. 53-55
[Figs. 53-55]
The loop
In fingerprints, as well as in the usual application of the word "loop," there cannot be a loop unless there is a recurve or turning back on itself of one or more of the ridges. Other conditions have to be considered, however. A pattern must possess several requisites before it may be properly classified as a loop. This type of pattern is the most numerous of all and constitutes about 65 percent of all prints.
A loop is that type of fingerprint pattern in which one or more of the ridges enter on either side of the impression, recurve, touch or pass an imaginary line drawn from the delta to the core, and terminate or tend to terminate on or toward the same side of the impression from whence such ridge or ridges entered.
Essentials of a loopβ A sufficient recurve.
β A delta.
β A ridge count across a looping ridge.
A sufficient recurve may be defined as that part of a recurving ridge between the shoulders of a loop. It must be free of any appendages abutting upon the outside of the recurve at a right angle.
AppendagesβSome explanation is necessary of the importance attached to appendages. Much care must be exercised in interpreting appendages because they sometimes change the shape of the recurving ridge to which they are connected. For example, a loop with an appendage abutting upon its recurve between the shoulders and at right angles, as in illustration 56, will appear sometimes as in illustration 57 with the recurve totally destroyed. For further examples see figures 161 to 184.
Figs. 56-57
[Figs. 56-57]
The same is true of a whorl recurve, as in figures 58 and 59.
Figs. 58-59
[Figs. 58-59]
It is necessary, therefore, to consider and classify figures 56 and 58 as if they actually appeared as in figures 57 and 59.
In figure 60, there is a ridge marked "A" which enters on one side of the impression and, after recurving, passes an imaginary line drawn from the core C to delta D, and terminates on the same side of the impression from which it entered, marked "B", thus fulfilling all the conditions required in the definition of a loop. X and Y are the type lines. It will be noted in figure 61 that there is a ridge which enters on one side of the impression, recurves, and passes an imaginary line drawn from the delta to the core. It does not terminate on the side from which it entered but has a tendency to do so. In this case, all the requirements of the loop have been met, and consequently it is classified as such.
Fig. 60
[Fig. 60]
Fig. 61
[Fig. 61]
Figure 62 shows a ridge entering on one side of the impression, recurving, and passing beyond an imaginary line drawn from the delta to the core, although opposite from the pattern shown in figure 61. After passing the imaginary line, the recurving ridge does not terminate on the side of the impression from which it entered, but it has a tendency to do so, and the pattern is, therefore, a loop.
Fig. 62
[Fig. 62]
In figure 63, a ridge enters on one side of the impression and then recurves, containing two rods within it, each of which rises as high as the shoulder of the loop. From our study of cores, we know that the top of the rod more distant from the delta is the core, but the recurving ridge does not pass the imaginary line. For that reason the pattern is not classified as a loop, but is given the preferential classification of a tented arch due to the lack of one of the loop requisites. The proper location of the core and delta is of extreme importance, for an error in the location of either might cause this pattern to be classified as a loop.
Fig. 63
[Fig. 63]
Figure 64 reflects a similar condition.
Fig. 64
[Fig. 64]
In figure 65, there is a looping ridge A which enters on one side of the impression. The ridges B and C are the type lines. As determined by rules already stated, the location of the core and the location of the delta are shown, and if an imaginary line were placed on the core and delta, the
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