In a cross contour drawing the line go across the form. This is different than a contour drawing where the form is just outlined. Cross contour studies can help the artists and viewer understand the volume of the form. Cross contour lines "wrap" around the form almost like the wrappings on the proverbial mummy or an object wrapped with string.
Vincent Van Gogh, Pollard Birches ink on paper
Careful variations in the cross contour lines can yield effective volume and detail of surface form.
In some cross contour drawings the wrapping line is broken or interrupted. This can be an effective way of showing light and shadow as in this drawing.