I INTRODUCTION
possibilities in respect to the lower pair ; so, as anyone of the first group may be combined with any one of the second, there are 3 x 3, or nine possibilities in all. The practice of somewhat rolling the finger when printing from it, is necessary in order to impress enough of its surface to ensure that the points at which the boundaries of the pattern begin to diverge, shall be always included.
Plates are given of the principal varieties of patterns, having regard only to their more fundamental differences, and names are attached for the convenience of description ; specimens are also given of the outlines of the patterns in all the ten digits of eight different persons, taken at hazard, to afford a first idea of the character of the material to be dealt with. Another and less minute system of classification under three heads is then described, which is very useful for rough preliminary purposes, and of which frequent use is made further on. It is into Arches, Loops, and Whorls. In the Arches, there is no pattern strictly speaking, for there is no interspace ; the need • for it being avoided by a successive and regular broadening out of the ridges as they cross the bulb of the finger. In Loops, the interspace is filled with a system of ridges that bends back upon itself, and in which no one ridge turns through a complete circle. Whorls contain all cases in which at least one ridge turns through a complete circle, and they include certain double patterns which have a whorled appearance. The transitional cases are few ; they are fully described, pictured, and
