Conjoined twins who were attached at the head were successfully separated after more than 20 hours of surgery at Montefiore.

Anias and Jadon McDonald, of Illinois, were born 13 months ago conjoined at the head and brain. The surgery was the twins' fourth and final marathon operation after several prior surgeries.

Scientists say one out of 2.5 million births result in conjoined twins. The twins were met with a team of 40 professionals during the course of their visit at Montefiore.

Dr. James Goodrich, a lead doctor on the team, successfully performed separation surgery on one other pair of twins in 2004. 

The children's parents say the decision to have them separated was a difficult one, but it's one they had to make to try to give their kids as normal and healthy a life as possible.

The boys' mother, Nicole McDonald, posted an update on her Facebook page Friday evening from the hospital that said, "It's time for the next chapter of our lives." She added she is ready to fight alongside her baby boys as they begin their recovery process.

McDonald says Anias's brain was affected during the surgery, which could cause some complications with his mobility.

Studies have shown that 80 percent of twins joined at the head die from medical problems by the age of 2 if they are not separated.