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. [Illustration: 191] [Illustration: 192] [Illustration: 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 be construed as a circuit. An appendage connected at that point is considered to spoil the recurve on that side._ Figures 194 to 211 are typical examples of the plain whorl type. Figure 212 is, however, a loop, as the circuit is spoiled on one side by an appendage. [Illustration: 194] [Illustration: 195] [Illustration: 196] [Illustration: 197] [Illustration: 198] [Illustration: 199] [Illustration: 200] [Illustration: 201] [Illustration: 202] [Illustration: 203] [Illustration: 204] [Illustration: 205] [Illustration: 206] [Illustration: 207] [Illustration: 208] [Illustration: 209] [Illustration: 210] [Illustration: 211] [Illustration: 212] _Central pocket loop_ Within the whorl group, the subclassification type "central pocket loop" is used for extension purposes only. In general classification it is designated by the letter "W". Figures 213 to 236 are central pocket loops.