Drawing Undulations

From Draw like da Vinci, p. 47: This shows how to draw foreshortened curves. Looking along a line of hills, they overlap one another as they recede in the distance. Da Vinci's relief maps show hills and valleys that fold like fabric. The ropey muscles of the upper arm overlap in a foreshortened view, in a similar way to a tree's twisting branches when they are foreshortened.