Hi Pilou, do you mean you want to put a surface between those 2 curves? If so then you can use Loft to do that.

If you mean you want to build lines between 2 curves, there is not anything set up to do that automatically, you need to just draw the lines.

But you could try building a surface with Loft, then use Rhino to extract isoparms of the loft surface, that may help you for that particular case if you want some large quantity of those kinds of lines for some kind of special purpose.

- Michael