Answer
The boundary between the epidermis and dermis is histologically conspicuous and usually wavy. The upward waves are fingerlike extensions of the dermis called dermal papillae (see fig. 6.3), and the downward epidermal waves between the papillae are called epidermal ridges. The dermal and epidermal boundaries thus interlock like corrugated cardboard, an arrangement that resists slippage of the epidermis across the dermis.
Work Step by Step
Figure 6.3;Also "The Dermis" Page 180