idges
and should not be counted.

In figure 104, the dot is not the delta because it is not as thick and
heavy as the other ridges and might not be present if the finger were
not perfectly inked and printed.

When the core is located on a spike which touches the inside of the
innermost recurving ridge, the recurve is included in the ridge count
only when the delta is located below a line drawn at right angles to
the spike.

Figures 105 and 106 are examples of this rule.

If the delta is located in areas A, the recurving ridge is counted.

If the delta is located in areas B, the recurving ridge is not
counted.

[Illustration: 102]

LOOP
25 RIDGE COUNTS

1. SHORT RIDGE
2. }
3. } BIFURCATION
4. }
5. } BIFURCATION
6. RIDGE
7. ENDING RIDGE
8. }
9. } BIFURCATION
10. RIDGE
11. ENDING RIDGE
12. RIDGE
13. SHORT RIDGE
14. }
15. } BIFURCATION
16. }
17. } ISLAND
18. }
19. } BIFURCATION
20. ENDING RIDGE
21. DOT
22. RIDGE
23. }
24. } ISLAND
25. ENDING RIDGE

[Illustration: 103]

[Illustration: 104]

[Illustration: 105]

[Illustration: 106]

_Radial and ulnar loops_

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._

_The plain arch_

_In plain arches the ridges enter on one side of the impression and
flow or tend to flow out the other with a rise or wave in the center._
The pla