The terms radial and ulnar are derived from the radius and ulna
bones of the forearm. Loops which flow in the direction of the ulna
bone (toward the little finger) are called ulnar loops and those which
flow in the direction of the radius bone are called radial loops.
For test purposes, fingers of the right hand may be placed on the
corresponding print of the right hand appearing in figure 71, and it
will be noticed that the side of each finger which is nearer to the
thumb on the hand is also nearer to the thumb on the fingerprint card.
Place the fingers of the left hand on the corresponding prints of
the left hand shown in figure 71. It will be noticed that the
arrangement of the prints on the card is the reverse of the
arrangement of the fingers on the hand. The classification of loops
is based on the way the loops flow on the hand (not the card), so that
on the fingerprint card for the left hand, loops flowing toward the
thumb impression are ulnar, and loops flowing toward the little finger
impression are radial.