Ravana is a giant figure in Indian mythology. He is often called the "Demon-King of Lanka", traditionally associated with the modern nation and island of Sri Lanka. Taking the evil genius theme, Indian story tellers created a persona who is said to have been as smart and strong as ten men. This is why he is often portayed with ten heads and twenty arms.
This wooden statue is representative of South Indian portrayals of Ravana. But, if you count the heads, there are only nine. The Indian artist elected to sacrifice the literal notion of ten heads in favor of symmetry, with a central head evenly flanked by four others. Originally there were twenty arms. (The text is from a UPenn exhibit display plaque.)
Perhaps the South Indian Artist just couldn't count.