From Realsoft3D Wiki

Select an edge of the loop you want to select, hold down shift key and hit Loop. Your loop will be selected. Here a screenshot:


Extend this selection on the neighbours with holding down ctrl - button and click again loop.


now imagine you want to add a another line for getting the lips more smooth at a certain place. Just select again an edge where this extra line shall go through and hold down shift and control key and then hit loop again:


and add now the line with split E (split selected edge) leaving the number of splits at 1 and hit accept. Now just hit add and the line will be added.