Fingerprint. Macrophotograph of the index finger of a young male human showing details of skin ridges in the outer cornified (keratinised) epidermis. These minute ridges form distinctive patterns, each pattern (fingerprint) is unique to an individual. The tiny depressions on the surface of the skin are sweat glands (exocrine gland). The glands lie as coiled tubular structures in the dermis of the skin, straightening out into a long duct which rises through the epidermis to the skin surface. The secretion of sweat, mostly sodium chloride, is carried to the surface through this duct. Sweating is a method for controlling body temperature.