Fingerprint Ulnar Radial Loops
The Loops of a fingerprint constitute between 60 and 70 per cent of the patterns encountered. In a loop pattern, one or more of the ridges enters on either side of the impression, recurves, touches or crosses the line of the glass running from the delta to the core, and terminates or tends to terminate on or in the direction of the side where the ridge or ridges entered. There is one delta. On the right you will see a loop pattern. You will notice that it has one delta (shown in the blue box) and a core (shown in the red box). By definition the existence of a core and one delta makes this pattern a loop.
Loops are classified not only by the fact that they have one delta and one core but also by something called a ridge count. Loops are two kinds, ‘radial’ and ‘ulnar’, named after the radius and ulna, the two bones in the forearm. The radius joins the hand on the same side as the thumb, and the ulna on the same side as the little finger.
The distinction between Ulnar and Radial loops depends on which hand the loop is found on. In the image at left the core pattern area (noted in red) tends to come in from the left and go back out the left. Hold your left hand up to the screen and note that your little finger is on the left, which is the direction that the pattern tends to come in from and go back out to. Since this is towards your little finger, and by virtue of that towards your Ulnar bone in your arm, this makes the loop an Ulnar loop.
Obviously to make the distinction between these two types of loops you have to know on which hand they appear because if a loop pattern is an Ulnar loop on the right hand, then by default it will be a Radial loop if found on the left hand.
Radial loops are not very common. Most of the time if you find a radial loop on a person it will usually be on the index fingers.
Now, if you were to place your right hand up to the screen and make the same comparison you would find that the pattern area now tends to come in and go out towards your thumb. It so happens that the radial bone in your arm is on your thumb side so now this loop would be considered a radial loop.