The Science of Fingerprints
Double loop and central pocket loop
Figure 267 is a plain whorl. It is not classified as a double loop as one side of one loop forms the side of the other. Figure 268 is a plain loop. It is not a double loop because all of the recurves of the loop on the right are spoiled by appendages.
Within the whorl group the subdivision type "accidental" is used for extension purposes only. In general classification 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.
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 classified as a loop. Figure 279 combines a loop and a tented arch.
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.
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 passes 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 passes 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).