162 



Life and Letters of Francis Galton 



the great toes, it will be seen that the thumb is inward and the little 

 finger outward. [Finger-prints taken in this order from left to right are in 

 "natural order."] Inward and outward are respectively thumb-side and 

 little finger-side, but these terms are awkward when we have to use them 

 for the thumb and little finger themselves, and the same criticism applies to 

 the anatomical terms radial and ulnar when applied to those bones them- 

 selves*. 



Next Galton gives for the first time his explanation of the manner in 

 which the "core" of a pattern originates ; he held that it is due to the nail; 

 the ridges, instead of going straight across the bulb of the finger, are dis- 

 torted to cover the top of it; the space between the originally adjacent 

 parallel ridges Galton terms the "core." This core or interspace is filled up 



Arch 

 (side tfieuj) 



Arch 

 (front uieu) 



Interspace 

 (side uieu) 



Primary or Arch ; formation of Interspace. 



Loop 



Various Whorls 



Fig. 20. Cores in Interspace, showing " deltas." 



with an additional scroll work of ridges, which in themselves form the 

 pattern on which classification depends. When the scroll work of the core 

 consists of a series of ridges separated on the central portion of the bulb by 

 wider intervals than at the sides of the bulb, Galton in this memoir terms 

 it a "primary," but later he uses the term "arch." Next the "deltas" are 

 defined. These are the small "islands" at the points where the adjacent 

 parallel ridges begin to diverge to form the core. In a primary there are no 

 deltas, in a loop one and in a whorl usually two are discoverable. When 

 there are two deltas, the line joining them and its perpendicular bisector 

 serve as axes of reference ; when there is only a single delta, in a loop, Galton 



* Galton unfortunately transposed "inner" and "outer" in this memoir, calling the inside 

 of the thumb that "nearest to the rest of the hand" (p. 4). He corrected this error in his 

 Finger Prints (p. 70). 



