A pair of conjoined twin boys who were attached by their abdomens were successfully separated from one another during an operation this month.

The babies are recovering and getting more treatment at the First Affiliated Hospital of Guangxi Medical University, according to Huanqiu.com, which is affiliated with People’s Daily, the official newspaper of the Chinese Communist Party. They were born by cesarean section Nov. 8 at a local hospital in southeast China and underwent surgery on Dec. 19, although the successful procedure was announced only recently.

The delay before the procedure was to ensure that the babies would be able to handle the anesthesia and the trauma of an operation. The hospital also used that time to treat an infection and an ulcer the infants had at the spot on their stomachs where they were connected.

The medical staff separated the brothers’ abdominal walls, livers and other parts, Huanqiu.com reported. Then the doctors focused on the individual boys to repair their respective abdominal walls. The entire surgery took about four hours.

“They look very healthy,” the brothers’ father said after the surgery, according to the Daily Mail. “Now they’re separated, they would be able to do their own things in life in the future.”

Conjoined twins have also been known as Siamese twins, named for a famous pair of conjoined twins from Thailand, formerly called Siam, who were joined at the chest. Depictions of the rare medical phenomenon go back at least a few thousand years.

Twins like this develop when an embryo on partially separates into two and the babies develop connected to one another, the Mayo Clinic explained. If an embryo were to fully separate into two, that would create identical twins, while babies that develop from two separate eggs are called fraternal twins.

The chest, abdomen and pelvis are the most common places for conjoined twins to be attached, but they can also be connected at the spine or the head.

“Many conjoined twins die in the womb (stillborn) or die shortly after birth,” according to the Mayo Clinic. “Some surviving conjoined twins can be surgically separated. The success of surgery depends on where the twins are joined and how many and which organs are shared, as well as the experience and skill of the surgical team.”