What part of the skin causes the skin surface have ridges on the tips of the fingers and toes?

The ridges on the surface of the skin, especially on the fingertips and toes, are caused by the dermal papillae—small, finger-like projections of the dermis (the inner layer of the skin) that push upward into the epidermis. These dermal papillae create unique patterns of friction ridges, which appear as the visible lines and whorls we see on the skin surface.