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.
Sometimes type lines may be very short. 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).
A bifurcation is the forking or dividing of one line into two or more branches.
A divergence is the spreading apart of two lines which have been running parallel or nearly parallel.
According to the narrow meaning of the words in fingerprint parlance, a single ridge may bifurcate, but it may not be said to diverge. Therefore, with one exception, the two forks of a bifurcation may never constitute type lines. The exception is when the forks run parallel after bifurcating and the diverge. In such a case the two forks become the two innermost ridges required by the definition. In illustration 16, the ridges marked "A-A" are type lines even though they proceed from a bifurcation. In figure 17, however, the ridges A-A are not the type lines because the forks of the bifurcation do not run parallel with each other. Instead, the ridges marked "T" are the type lines.
Angles are nver formed by a single ridge but the abutting of one ridge against another. Therefore, an angular formation cannot be used as a type line. In figure 18, ridges A and B join at an angle. Ridge B does not run parallel with ridge D; ridge A does not diverge. Ridges C and D, therefore are the type lines.
