Papillary lines can be found on the insides of your hands and on the bottoms of your feet and toes. These are the lines you see on your fingertips, for example. The purpose of papillary lines is that we have more grip. Suppose you don't have a papillary line on your fingers, so your fingers are completely smooth, the chance that we let our glass of water slide out of our hands is a lot bigger. In the 18th century it was discovered that you can also recognize someone with fingerprints, so in addition to grip, our lines on the fingers are also a means of identification. The combination of all your fingerprints is unique and no one else has it, not even identical twins have the same fingerprints.