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 plain arch is the most simple of all fingerprint patterns, and it
is easily distinguished. Figures 107 to 118 are examples of the plain
arch. It will be noted that there may be various ridge formations such
as ending ridges, bifurcations, dots and islands involved in this type
of pattern, but they all tend to follow the general ridge contour;
i.e., they enter on one side, make a rise or wave in the center, and
flow or tend to flow out the other side.
Figures 119 and 120 are examples of plain arches which approximate
tented arches. Also, figure 121 is a plain arch approximating a tented
arch as the rising ridge cannot be considered an upthrust because it
is a continuous, and not an ending, ridge. (See following explanation
of the tented arch.)