Leg bone supports the pelvis though which is like a bowl for your lower belly...? Horse breaks a leg you have to put it down.^^Your spine is composed of bones, just as your skeleton is composed of bones =o)
I think it's bones in general.. because of the nelly part. I believe Nelly is being used as a horse name. They often put race horss down when they break a leg... but a leg bone doesn't hold up your stomach... your ribs would mostly be responsible for that.