The Science of Fingerprints | Page 4

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CHAPTER II
Types of Patterns and Their Interpretation
Types of patterns
Fingerprints may be resolved into three large general groups of patterns, each group bearing the same general characteristics or family resemblance. The patterns may be further divided into sub-groups by means of the smaller differences existing between the patterns in the same general group. These divisions are as follows:
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 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.
[Illustration: 11]
[Illustration: 12]
[Illustration: 13]
[Illustration: 14]
[Illustration: 15]
[Illustration: 16]
[Illustration: 17]
[Illustration: 18]
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 immediately outside 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,