ZBrush for Digital 3-D Printing - ZBrush Creature Design: Creating Dynamic Concept Imagery for Film and Games - page 733

6. To add a sense of skin stretching across those bones, use the Standard brush. Dial down the draw size
and stroke across the tarsal bone forms. This will start to create a series of raised ridges crossing the tarsal
bones, which can be resolved into skin. Step up to a higher subdivision level and continue to sketch in
raised wrinkles. These will read like tissue skin over the larger bony forms ( Figure 11-40 ) .
Figure 11-40: Smaller standard brush strokes across the bony forms help suggest wrinkled skin.