6 8 FINGER PRINTS
CHAP.
ducts exist within the interspace, as are to be found in adjacent areas of equal size, whose mouths require to be supported and connected. This is effected by the interpolation of an independent system of ridges arranged in loops (Fig. 8, 3 ; also Plate 5, Fig. 9, a, f ), or in scrolls (Fig. 8, 4 ; also Fig. 9) g, h), and this interpolated system forms the "pattern." Now the existence of an interspace implies the divergence of two previously adjacent ridges (Fig. 8, 2), in order to embrace it. Just in front of the place where the divergence begins, and before the sweep of the pattern is reached, there are usually one or more very short cross-ridges. Their effect is to complete the enclosure of the minute triangular plot in question. Where there is a plot on both sides -of the finger, the line that connects them (Fig. 8, 4) serves as a base line whereby the pattern may be oriented, and the position of any point roughly charted. Where there is 'a plot on only one side of the finger (Fig. 8, 3), the pattern has almost necessarily an axis, which serves for orientation, and the pattern can still be charted, though on a different principle, by dropping a perpendicular from the plot on to the axis, in the way there shown.
These plots form corner-stones to my system of outlining and subsequent classification ; it is therefore extremely important that a sufficient area of the finger should be printed to include them. This can always be done by slightly rolling the finger (p. 39), the result being, in the language of map-makers, a cylindrical projection of the finger (see Plate 5, Fig.
