Here, two types of drawings are intermixed in one, to create an odd effect. One type of drawing is the flat etching. Such is the embroidery on clothings or wallpaper patterns. This type of drawing is used on the dragon's neck, body, tail, wings. The other type of drawing, is depiction of real 3D object using primarily technique of shading. This type of drawing is used to create the box in the center, the dragon's legs, and the crystals. Escher skillfully mixes the two to create a very odd effect that makes the viewer become aware of the interpretation process. (via)