The Science of Fingerprints by United States. Federal Bureau of Investigation (books to read in a lifetime txt) 📕

ridge count.

 

Figs. 136-137

[Figs. 136-137]

 

In figure 138, the reader will note the similarity to the figures 136 and 137. The only difference is that in this figure the type lines are running parallel from the right. It will be noted from these three patterns that the spaces between the type lines at their divergence show nothing which could be considered as delta formations except the looping ridges. Such patterns are classified as tented arches because the ridge count necessary for a loop is lacking.

 

Fig. 138

[Fig. 138]

 

Figure 139 is an example of a tented arch. In this pattern, if the looping ridge approached the vertical it could possibly be a one-count loop. Once studied, however, the pattern presents no real difficulty. There are no ridges intervening between the delta, which is formed by a bifurcation, and the core. It will be noted that the core, in this case, is at the center of the recurve, unlike those loops which are broadside to the delta and in which the core is placed upon the shoulder. This pattern has a recurve and a separate delta, but it still lacks the ridge count necessary to make it a loop.

 

Fig. 139

[Fig. 139]

 

Figures 140 and 141 are examples of tented arches. These two figures are similar in many ways. Each of these prints has three abrupt ending ridges but lacks a recurve; however, in figure 141 a delta is present in addition to the three abrupt ending ridges. This condition does not exist in figure 140, where the lower ending ridge is the delta.

 

Figs. 140-141

[Figs. 140-141]

 

When interpreting a pattern consisting of two ending ridges and a delta but lacking a recurve, do not confuse the ridge count of the tented arch with that of the ridge count for the loop. The ridge count of the tented arch is merely a convention of fingerprinting, a fiction designed to facilitate a scientific classification of tented arches, and has no connection with a loop. To obtain a true ridge count there must be a looping ridge which is crossed freely by an imaginary line drawn between the delta and the core. The ridge count referred to as such in connection with the tented arches possessing ending ridges and no recurve is obtained by imagining that the ending ridges are joined by a recurve only for the purpose of locating the core and obtaining a ridge count. If this point is secure in the mind of the classifier, little difficulty will be encountered.

Figures 140 and 141, then, are tented arches because they have two of the characteristics of a loop, delta and ridge count, but lack the third, the recurve.

Figure 142 is a loop formation connected with the delta but having no ridge count across a looping ridge. By drawing an imaginary line from the core, which is at the top of the rod in the center of the pattern, to the delta, it will be noted that there is no recurving ridge passing between this rod and the delta; and, therefore, no ridge count can result. This pattern is classified as a tented arch. There must be a white space between the delta and the first ridge counted, or it may not be counted. Figure 143 is also a tented arch because no ridge count across a looping ridge can be obtained, the bifurcations being connected to each other and to the loop in a straight line between delta and core. The looping ridge is not crossed freely. No white space intervenes between the delta and the loop. These patterns are tented arches because they possess two of the characteristics of a loop, a delta and a recurve, but lack the third, a ridge count across a looping ridge.

 

Figs. 142-143

[Figs. 142-143]

 

Figure 144 is a tented arch combining two of the types. There is an angle formed by ridge a abutting upon ridge b. There are also the elements of the type approaching a loop, as it has a delta and ridge count but lacks a recurve.

 

Fig. 144

[Fig. 144]

 

Figures 145 to 148 are tented arches because of the angles formed by the abutting ridges at the center of the patterns.

 

Figs. 145-146

Figs. 147-148

[Figs. 145-148]

 

Figure 149 is a tented arch because of the upthrust present at the center of the pattern. The presence of the slightest upthrust at the center of the impression is enough to make a pattern a tented arch.

 

Fig. 149

[Fig. 149]

 

An upthrust must be an ending ridge. If continuous as in figure 150, no angle being present, the pattern is classified as a plain arch.

 

Fig. 150

[Fig. 150]

 

Figures 151 to 153 are plain arches. Figure 154 is a tented arch.

 

Figs. 151-152

Figs. 153-154

[Figs. 151-154]

 

Figure 155 is a plain arch because it is readily seen that the apparent upthrust A is a continuation of the curving ridge B. Figure 156 is a tented arch because ridge A is an independent upthrust, and not a continuation of ridge B.

 

Figs. 155-156

[Figs. 155-156]

 

Figures 157 and 158 are plain arches. Figure 158 cannot be said to be a looping ridge, because by definition a loop must pass out or tend to pass out upon the side from which it entered. This apparent loop passes out upon the opposite side and cannot be said to tend to flow out upon the same side.

 

Figs. 157-158

[Figs. 157-158]

 

In figures 159 and 160, there are ending ridges rising at about the same degree from the horizontal plane.

 

Figs. 159-160

[Figs. 159-160]

 

Figure 159, however, is a plain arch, while 160 is a tented arch. This differentiation is necessary because, if the first pattern were printed crookedly upon the fingerprint card so that the ending ridge was nearer the horizontal plane, there would be no way to ascertain the true horizontal plane of the pattern (if the fissure of the finger did not appear). In other words, there would be no means of knowing that there was sufficient rise to be called an upthrust, so that it is safe to classify the print as a plain arch only. In figure 160, however, no matter how it is printed, the presence of a sufficient rise could always be ascertained because of the space intervening between the ending ridge and the ridge immediately beneath it, so that it is safe to classify such a pattern as a tented arch. The test is, if the ridges on both sides of the ending ridge follow its direction or flow trend, the print may be classified as a plain arch. If, however, the ridges on only one side follow its direction, the print is a tented arch.

An upthrust, then, must not only be an ending ridge rising at a sufficient degree from the horizontal plane, but there must also be a space between the ending ridge and the ridge immediately beneath it. This, however, is not necessary for a short upthrust or spike, or any upthrust which rises perpendicularly.

In connection with the proper classification to be assigned to those borderline loop-tented arch cases where an appendage or spike is thrusting out from the recurve, it is necessary to remember that an appendage or a spike abutting upon a recurve at right angles in the space between the shoulders of a loop on the outside is considered to spoil the recurve.

If the appending ridge flows off the looping ridge smoothly in such a way that it forms a bifurcation and not an abutment of two ridges at a right angle, the recurve is considered as remaining intact. The test is to trace the looping ridge toward the appendage, and if, when it is reached, the tracing may be continued as readily upon the appendage as upon the looping ridge, with no sudden, sharp change of direction, the recurve is sufficient. Figures 161 to 184 should be studied with this in mind.

 

Figs. 161-163

Figs. 164-175

Figs. 176-181

Figs. 182-184

[Figs. 161-184]

 

Figures 185 to 190 show additional examples of tented arches.

 

Figs. 185-186

Figs. 187-190

[Figs. 185-190]

 

The reason that figure 185 is given the classification of a tented arch is because of the presence of all the loop requirements with the exception of one, which is the recurve. In this pattern appear three ending ridges. The lowest ending ridge provides the delta, and the other two by the convention explained previously, provide the ridge count. It is a tented arch, then, of the type approaching the loop, with two of the characteristics, but lacking the third, a recurve. Figures 186 and 187 are tented arches of the same type. A close examination of these prints will reveal that when the imaginary line is drawn between delta and core no ridge count across a looping ridge can be obtained. It must be remembered that the core of a loop may not be placed below the shoulder line. Lacking one of the three characteristics of a loop, these patterns must be classified as tented arches. When figure 188 is examined, it will be noticed that the recurve is spoiled by the appendage abutting upon it between the shoulders at a right angle, so it must also be classified with the tented arches. In figure 189, the only possible delta must be placed upon the looping ridge, thus preventing a ridge count although delta and recurve are present. Figure 190 is assigned the classification of a tented arch. One of the requirements of a loop type is that the ridge enters on one side, recurves, and makes its exit on the side from which it entered. This, of course, makes it necessary that the ridge pass between the delta and the core. It will be noted from this figure that although this ridge passes between the delta and the core, it does not show any tendency to make its exit on the side from which it entered, and therefore the loop classification is precluded, and it is a tented arch.

The whorl

The patterns to which numerical values are assigned in deriving the "primary" in the extension of the Henry System of fingerprint classification used by the Federal Bureau of Investigation are the whorl-type patterns, which occur in about 30 percent of all fingerprints.

The whorl is that type of pattern in which at least two deltas are present with a recurve in front in each. Figures 191 to 193 reflect the minimum requirements for the whorl.

 

Figs. 191-193

[Figs. 191-193]

 

It is important to note that the above definition is very general; however, this pattern may be subdivided for extension purposes in large groups where whorls are predominant. Even though this extension may be used, all types of whorls are grouped together under the general classification of "Whorl" and are designated by the letter "W".

The aforementioned subdivisions are as follows: The Plain Whorl, The Central Pocket Loop, The Double Loop, and The Accidental.

The plain whorl

The "plain whorl" consists of the simplest form of whorl construction and is the most common of the whorl subdivisions. It is designated by the symbol "W" for both general classification and extension purposes.

The plain whorl has two deltas and at least one ridge making a complete circuit, which may be spiral, oval, circular, or any variant of a circle. An imaginary line drawn between the two deltas must touch or cross at least one of the recurving ridges within the inner pattern area. A recurving ridge, however, which has an appendage connected with it in the line of flow cannot