Conjoined twins separated after 13-hour surgery (PICTURES)

(CBS) Twins are famously close. But Joshua and Jacob Spates aren't quite as close as they used to be, now that surgeons in Memphis have successfully separated the conjoined twins.

Medical miracle? Conjoined twins separated in Memphis

The boys, born in Memphis on Jan. 24, were separated on August 29 in a grueling, 13-hour operation at Le Bonheur Children's Hospital, according to a written statement released by the hospital.

Joshua and Jacob were so-called pygopagus twins, a particularly rare form of conjoined twins in which the bodies are joined back to back at the pelvis and lower spine. The boys shared a rectum, muscles, and nerves but have their own hearts, heads, and limbs.

The boys remain in the hospital's pediatric intensive care unit, where they're recuperating from surgery and being treated for a variety of medical problems.

But if they're not out of the woods yet, they've already beaten the odds. Conjoined twins occur only about once in every 200,000 live births and up to 60 percent are stillborn, according to the website of the University of Maryland Medical Center. What's more, conjoined twins who survive long enough to be surgically separated are three times more likely to be girls, according to the American Pediatric Surgical Association.