I PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



of the bulb of the digit without making any backward turn or twist. 

 The pattern is a loop when the ridges make a single backward turn 

 lint no twist. The pattern is a whorl when the ridges make at least 

 one complete circle, or what mariners consider in reference to the 

 compass a " complete circuit ". Another characteristic serves as an 

 infallible guide to the differentiation of the arch, the loop and the 

 whorl. On examining the fingers beyond the last joint, it is found 

 that the ridges nearest the joint are more or less transverse. On 

 passing to the tip of the bulb, the ridges are found to be arched. 

 Two ridges are taken as the boundary line of the pattern, the top- 

 most transverse ridge and the lowest arch. 



At the angles of divergence of the lowest arch and topmost 

 transverse ridge there is a triangular plot made by a line which 

 crosses the mouths of these angles. This triangular plot is called a 

 delta, and by the enumeration of the deltas a pattern can be classified. 

 An arch has no delta. A loop has one delta. A whorl has two 

 deltas. The importance of rolling the finger here becomes apparent. 

 The deltas are often at the margin of the pattern, and if the finger is 

 dabbed down without rolling, the deltas may be missed altogether. 

 They must be included if present, if absent their absence must be 

 beyond doubt. 



Proceeding then on this plan, taking care to note the presence or 

 absence of deltas, the finger-prints can be classified into one of three 

 large divisions Arch, Loop, Whorl. This appears simple in theory, but 

 in practice much difficulty is met with in the shape of ambiguous 

 patterns, for arches shade off into loops and loops into whorls, and 

 there is, so to speak, a debatable ground between arch and loop and 

 again between loop and whorl. 



Careful examination with a lens is often necessary before the con- 

 tour of the pattern can be exactly determined. Often the core of the 

 pattern forms a guide to classification. Once all are classified they 

 can be arranged in various tables according to percentages, and in 

 those which are to be discussed to-day Gallon's system of tabulation 

 has been strictly followed. 



