The skin is marked by three types of surface irregularities: The tension lines, flexure lines and papillary ridges.
Form a network of linear furrows which divided the surface into polygonal or lozenge shaped areas . These lines to some extent correspond to variations in the pattern of fibers in the dermis.
These are commonly known as skin creases or skin joints. They are certain permanent lines along which the skin folds during habitual movements of the joints. As the folding of skin normally occurs during flexion, they are known as flexure lines.
The skin along these lines is thin and firmly bound to the deep fascia. The lines are prominent opposite the flexure of the joints, particularly on the palms, soles and digits.
These are also known as friction ridges. They are confined to palms and soles along with the digits. They form narrow ridges separated by fine parallel grooves, arranged in curved arrays. They correspond to patterns of dermal papillae. The major patterns in the human fingerprints include loops, whorls and arches. These patterns and many other minor features are determined genetically by multifactorial inheritance.