The Science of Fingerprints Part 10

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_Accidental_

Within the whorl group the subdivision type "accidental" is used for extension purposes only. In general cla.s.sification it is designated by the letter "W" and for extension purposes by the letter "X".

_The accidental whorl is a pattern consisting of a combination of two different types of pattern, with the exception of the plain arch, with two or more deltas; or a pattern which possesses some of the requirements for two or more different types; or a pattern which conforms to none of the definitions._ It may be a combination of loop and tented arch, loop and whorl, loop and central pocket loop, double loop and central pocket loop, or other such combinations. The plain arch is excluded as it is rather the absence of pattern than a pattern. Underneath every pattern there are ridges running from one side to the other, so that if it were not excluded every pattern but the plain arch would be an accidental whorl.

This subcla.s.sification also includes those exceedingly unusual patterns which may not be placed by definition into any other cla.s.ses.

Figures 269 to 271 are accidentals combining a loop with a tented arch. Figures 272 to 276 combine a loop and a plain whorl or central pocket loop. Figure 277 combines a loop and a double loop. Figure 278 combines a loop and a plain arch, so it is cla.s.sified as a loop.

Figure 279 combines a loop and a tented arch.

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Some whorls may be found which contain ridges conforming to more than one of the whorl subdivisions described. In such cases, the order of preference (if any practical distinction need be made) should be: (1) accidental, (2) double loop, (3) central pocket loop, (4) plain whorl.

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_Whorl tracing_

The technique of whorl tracing depends upon the establishment of the focal points--the deltas. Every whorl has two or more. When the deltas have been located, the ridge emanating from the lower side or point of the extreme left delta is traced until the point nearest or opposite the extreme right delta is reached. The number of ridges intervening between the tracing ridge and the right delta are then counted. If the ridge traced pa.s.ses inside of (above) the right delta, and three or more ridges intervene between the tracing ridge and the delta, the tracing is designated as an "inner"--I (fig. 280). If the ridge traced pa.s.ses outside (below) the right delta, and three or more ridges intervene between the tracing ridge and the right delta, the tracing is designated as an "outer"--O (fig. 281). All other tracings are designated as "meeting"--M (figs. 282 to 287).

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Tracing begins from the left delta. In no instance is a tracing to begin on a type line. In figure 288, tracing begins at the short ridge which is the left delta. It is true that inasmuch as the short ridge ends immediately the type line is next followed, but this is only because the type line is the next lower ridge. Its status as a type line is independent and has no bearing on the fact that it is being traced. This point is ill.u.s.trated further in figure 289. This pattern shows an inner tracing. It will be noted that the delta is at the point on the first recurve nearest to the center of the divergence of the type lines. It will be further noted that tracing begins at the point of delta on the left and continues toward the right, pa.s.sing inside of the right delta, with three ridges intervening between the tracing ridge and the right delta. This shows the tracing to be an inner tracing. If, in this case, the type line were traced (which would be the incorrect procedure), only two ridges would intervene between the tracing ridge and the right delta, resulting in an erroneous meeting tracing. Figure 290 is another example of the application of this rule. This ill.u.s.tration is also an inner whorl.

When the ridge traced ends abruptly, and it is determined that the ridge definitely ends, the tracing drops down to the point on the next lower ridge immediately beneath the point where the ridge above ends, continuing from there. Figure 291, therefore, is an outer whorl.

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In this connection it should be noted that the rule for dropping to the next lower line applies only when the ridge _definitely_ ends.

Short breaks in a ridge which may be due to improper inking, the presence of foreign matter on the ridges, enlarged pores, disease, or worn ridges should not be considered as definite ridge endings. The determination of what const.i.tutes a definite ending will depend, of course, upon the good judgment of the cla.s.sifier. When the question arises as to whether a break encountered in the ridge tracing is a definite ending, or whether there has been interference with a natural impression, the whole pattern should be examined to ascertain whether such breaks are general throughout the pattern. If they are found to be common, consideration should then be given to the possibility that the break is not a definite ridge ending. Appropriate reference tracing should be done in all such cases.

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Whenever the ridge traced bifurcates, the rule for tracing requires that the lower limb or branch proceeding from the bifurcation be followed. This is ill.u.s.trated in 292.

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Accidentals often possess three or more deltas. In tracing them only the extreme deltas are considered, the tracing beginning at the extreme left delta and proceeding toward the extreme right delta, as ill.u.s.trated in figure 293.

In a double loop or accidental the problem of where to stop tracing is sometimes presented. The rule is, _when the tracing pa.s.ses inside of the right delta, stop at the nearest point to the right delta on the upward trend_, as in figure 294. If no upward trend is present, continue tracing until a point opposite the right delta, or the delta itself, is reached (figs. 295 and 296).

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CHAPTER III

_Questionable Patterns_

No matter how definite fingerprint rules and pattern definitions are made, there will always be patterns concerning which there is doubt as to the cla.s.sification they should be given. The primary reason for this is the fact that probably no two fingerprints will ever appear which are exactly alike. Other reasons are differences in the degree of judgment and interpretation of the individual cla.s.sifying fingerprints, the difference in the amount of pressure used by the person taking the prints, and the amount or kind of ink used. Nothing can be done about faulty inking or pressure once the prints are taken.