What are the best stretches to improve leg flexibility?

My legs are already pretty flexible, i can do the splits this way:
http://upload.wikimedia.org/wikipedia/commons/9/9d/Splits_%282108057658%29.jpg

but not this way:
http://0.tqn.com/d/dance/1/0/n/2/-/-/split6.jpg

(pictures not of me)
so anyways i would like to be able to do the splits like that second picture.. what are some stretches that will help me achieve that?

please explain it with enough detail or maybe give a link to a website or picture because i dont want to hurt myself! thanks :)
 
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