How come when i sit down i can put my leg behind my head, but i cant do the splits?

i really dont get it. you know what i mean, i can bring my leg riight over my head, but i cant do the splits? :S am i flexible, but not flexible enough?How come when i sit down i can put my leg behind my head, but i cant do the splits?
because you use different muscles entirely for both actionsHow come when i sit down i can put my leg behind my head, but i cant do the splits?
I've always had the same issue...can put both legs behind my head even (still at age 34) but yet have never in my life been able to do the splits. I think its got something to do with totally extended the legs.
well im sure that you do the ';splits'; in bed
bcoz u'll end up in hospital??