It is necessary that the inner line of flow be fixed artificially. The inner line of flow is determined by drawing an imaginary line between the inner delta and the center of the innermost recurve or looping ridge.
In the central pocket loop, one or more of the simple recurves of the plain loop type usually recurve a second time to form a pocket within the loop. The second recurve, however, need not be a continuation of—or even connected with—the first. It may be an independent ridge.
If no second recurve is present, an obstruction at right angles to the inner line of flow is acceptable in lieu of it. An obstruction may be either curved or straight. A dot, of course, may not be considered an obstruction.
The definition does not require a recurve to cross the line of flow at right angles. The angle test needs to be applied to obstructions only.
The recurve or obstruction of the central pocket loop, as that of the plain whorl, must be free of any appendage connected to it at the point crossed by the line of flow and on the delta side. An appendage at that point is considered to spoil the recurve or obstruction.
Figures 237 and 238 are also central pocket loops despite the appendages connected to the recurves, because they are not connected at the point crossed by the line of flow.
[Figs. 237-238]
Figure 239, although possessing a recurve, is classified as a loop because the second delta is located on the only recurving ridge.