I think Bruno is referring to the protrusion under the leading edge mid-length.
thos are called wing fences, and you find the on many "older" wing designs, including the 727. The design is just a little different.
See, wing fences prevent spanwise (root to tip) airflow commonly found on all wings.
Spanwise flow of air causes drag at the tip of the wing. Think of it as a "misplaced" winglet.
I think it also served another function on swept wings, but I can't seem to put my finger on it. Maybe it'll come to me. Meanwhile anyone is free to remind me.