Palm. Magnified section of palm, historical artwork. The external ridged surface is the cuticle, with the thin layer of skin below this known as the rete mucosum, or epidermis. Deeper in is the living layer, known as the dermis, consisting of the papillary layer and the corium. The papillary layer shown consists of five secondary papillae, which are in turn composed of primary papillae (white). The corium is dark fading to light, indicating decreasing vascularity (blood supply). Deeper still is the subcutaneous fatty layer (yellow, bottom). From 'The Nerves of the Human Body', London 1839.