The Loop
In fingerprints, as well as in the usual application of the word
loop, there cannot be a loop unless there is a recurve or turning
back on itself of one or more of the ridges. Other conditions have to
be considered, however. A pattern must possess several requisites
before it may be properly classified as a loop. This type of pattern
is the most numerous of all and constitutes about 65 percent of all
prints.
A loop is that type of fingerprint pattern in which one or more of
the ridges enter on either side of the impression, recurve, touch or
pass an imaginary line drawn from the delta to the core, and terminate
or tend to terminate on or toward the same side of the impression from
whence such ridge or ridges entered.