ITCZ
From
Douglas Jetliners by Guy Norris & Mark Wagner.
The wing also featured "vortilons", small chord-wise fences on the lower wing surface that improved control at high angles of attack up to 30 degrees. In most attitudes, the vortilons were aft of the area where the airflow "stagnated," so they had little effect. However, when the aircraft was in a potentially dangerous, nose-up attitude, the vortilons poked past the stagnation point and triggered vortices. The vortices extend over the upper wing surface and limited the span-wise flow, thereby preserving lift on the outboard wing sections, so the inner wing would stall first. In a swept wing design, this makes the nose pitch sharply down, enabling the crew to recover control quickly. The vortilons also reduced the downwash from the wing on the tail, which helped crews recover from potential deep stalls.
I like the explanation given by one of the sim instructors, with years of DC9 time from TAA. During development the wing didn't develop as much lift as expected and some sprog aerodynamicist suggested that the lack of pylons for #2 & #3 probably allowed too much span-wise airflow, so that tacked on pseudo pylons, and, Bob's your uncle.
Remember, Google's your friend. "dc9 vortilons" = 5 pages of hits. 
