g 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 a