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).