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

recurving ridge A would cross it. This is another figure showing a ridge which does not terminate on the side of the impression from which it entered but tends to do so, and, therefore, is considered as a loop.

 

Fig. 65

[Fig. 65]

 

In figure 66, we have a print which is similar in many respects to the one described in the preceding paragraph, but here the recurving ridge A continues and tends to terminate on the opposite side of the impression from which it entered. For this reason the pattern is not a loop, but a tented arch. The recurving ridge must touch or pass the imaginary line between delta and core and at least tend to pass out toward the side from which it entered, so that a ridge count of at least one can be obtained.

 

Fig. 66

[Fig. 66]

 

Figure 67 shows a ridge which enters on one side of the impression and, after flowing toward the center, turns or loops on itself and terminates on the same side from whence it entered. This pattern would be classified as a loop. This pattern should be distinguished from the pattern appearing in figure 139. Careful study of the pattern in figure 67 reveals that the core is located at C and the delta D. The imaginary line between these points will be crossed by the ridge forming a loop. In figure 139, the core is located on the recurve and an imaginary line between the delta and the core does not cross a looping ridge. Figure 139 is thus classified as a tented arch, as will be seen later.

 

Fig. 67

[Fig. 67]

 

Figure 68 shows at the center of the print a ridge which forms a pocket. It will be noticed that ridge A does not begin on the edge of the print, but this is of no significance. The ridge A within the pattern area recurves or loops, passing the imaginary line between the delta and the core, and tends to terminate toward the same side of the impression from whence it entered. This is a loop pattern possessing all of the requirements.

 

Fig. 68

[Fig. 68]

 

In figures 69 and 70, it will be observed that there is a ridge entering on one side of the pattern which recurves and then turns back on itself. These patterns are different from any others which have been shown in this respect but are classified as loops. In each of the patterns the core and delta are marked "C" and "D". The reader should trace the type lines in order to ascertain why the delta is located at point D, and then apply the delta rule.

 

Fig. 69

[Fig. 69]

 

Fig. 70

[Fig. 70]

 

Figure 71 is an example of loops as they appear on the rolled impression portion of a fingerprint card.

 

Fig. 71

[Fig. 71]

[Enlarge]

 

Ridge counting

The number of ridges intervening between the delta and the core is known as the ridge count. The technical employees of the Federal Bureau of Investigation count each ridge which crosses or touches an imaginary line drawn from the delta to the core. Neither delta nor core is counted. A red line upon the reticule of the fingerprint glass is used to insure absolute accuracy. In the event there is a bifurcation of a ridge exactly at the point where the imaginary line would be drawn, two ridges are counted. Where the line crosses an island, both sides are counted. Fragments and dots are counted as ridges only if they appear to be as thick and heavy as the other ridges in the immediate pattern. Variations in inking and pressure must, of course, be considered.

Figures 72 to 97 and figures 98 to 101 show various loop patterns. The reader should examine each one carefully in order to study the cores and deltas and to verify the count which has been placed below each pattern.

 

Figs. 72-77

Figs. 78-83

Figs. 84-89

Figs. 90-95

Figs. 96-101

[Figs. 72-101]

 

Figure 102 is a sketch reflecting the various types of ridges which the classifier will encounter when engaging in counting loop patterns.

 

Fig. 102

[Fig. 102]

 

In figure 103, the lighter lines are caused by the splitting or fraying of the ridges. Sometimes ingrained dirt will cause a similar condition between the ridges. These lines are not considered ridges and should not be counted.

 

Fig. 103

[Fig. 103]

 

In figure 104, the dot is not the delta because it is not as thick and heavy as the other ridges and might not be present if the finger were not perfectly inked and printed.

 

Fig. 104

[Fig. 104]

 

When the core is located on a spike which touches the inside of the innermost recurving ridge, the recurve is included in the ridge count only when the delta is located below a line drawn at right angles to the spike.

Figures 105 and 106 are examples of this rule.

 

Figs. 105-106

[Figs. 105-106]

 

If the delta is located in areas A, the recurving ridge is counted.

If the delta is located in areas B, the recurving ridge is not counted.

Radial and ulnar loops

The terms "radial" and "ulnar" are derived from the radius and ulna bones of the forearm. Loops which flow in the direction of the ulna bone (toward the little finger) are called ulnar loops and those which flow in the direction of the radius bone are called radial loops.

For test purposes, fingers of the right hand may be placed on the corresponding print of the right hand appearing in figure 71, and it will be noticed that the side of each finger which is nearer to the thumb on the hand is also nearer to the thumb on the fingerprint card. Place the fingers of the left hand on the corresponding prints of the left hand shown in figure 71. It will be noticed that the arrangement of the prints on the card is the reverse of the arrangement of the fingers on the hand. The classification of loops is based on the way the loops flow on the hand (not the card), so that on the fingerprint card for the left hand, loops flowing toward the thumb impression are ulnar, and loops flowing toward the little finger impression are radial.

The plain arch

In plain arches the ridges enter on one side of the impression and flow or tend to flow out the other with a rise or wave in the center. The plain arch is the most simple of all fingerprint patterns, and it is easily distinguished. Figures 107 to 118 are examples of the plain arch. It will be noted that there may be various ridge formations such as ending ridges, bifurcations, dots and islands involved in this type of pattern, but they all tend to follow the general ridge contour; i.e., they enter on one side, make a rise or wave in the center, and flow or tend to flow out the other side.

 

Figs. 107-110

Figs. 111-116

Figs. 117-118

[Figs. 107-118]

 

Figures 119 and 120 are examples of plain arches which approximate tented arches. Also, figure 121 is a plain arch approximating a tented arch as the rising ridge cannot be considered an upthrust because it is a continuous, and not an ending, ridge. (See following explanation of the tented arch.)

 

Figs. 119-121

[Figs. 119-121]

 

The tented arch

In the tented arch, most of the ridges enter upon one side of the impression and flow or tend to flow out upon the other side, as in the plain arch type; however, the ridge or ridges at the center do not. There are three types of tented arches: