The Conjoined Twins Before Trishna and Krishna

Updated at 10:10 p.m. ET for news of the surgery's conclusion

(Nov. 16) -- Back in the mid-19th century, two brothers named Chang and Eng Bunker captured the world's attention because of a small, 4-inch ligament connecting them at the chest. They were born in Siam in 1811, and thus came the term "Siamese twins."

Despite the immense fame and fortune they ultimately achieved, they frequently argued and wished to be separated. At the time physicians determined any such procedure would be too great a risk.

The latest set of conjoined twins, 2-year-old sisters Trishna and Krishna, also faced great risks. The girls, who were rescued nearly two years ago from a Bangladesh orphanage by the Children First Foundation, were connected at the back of the head, a condition medically known as craniopagus twins.

Given a 25 percent chance of surviving the procedure without brain damage, the sisters are doing "very well" after the surgery, according to doctors quoted by the Associated Press.

Unlike Chang and Eng, who had no choice but to stay connected, Trishna and Krishna had no choice but to be separated. When Krishna arrived at Melbourne's Royal Children's Hospital she was dying of heart failure caused by the uneven blood circulation she shared with her sister. In order to save her, doctors began surgical procedures more than a year ago leading up to this week's physical separation.

Neurosurgeon Wirginia Maixner and her team was determined to make the separation a success -- for both girls. There's never been a thought about sacrificing one for the other. "We considered both these girls have equal importance to life," Maixner told an Australian news site, "and we either could save both girls and we would not risk one child for the other."

Risky as it sounds, Trishna and Krishna aren't the only twins to brave such odds in recent years. In 2003, surgeons successfully operated on Egyptian brothers Ahmed and Mohamed Ibrahim in Dallas, the year before Filipino twins Carl and Clarence Aguirre survived their trip to New York for the procedure.

In both cases, the boys were close in age to Trishna and Krishna. Not quite 3 years of age, their brains are still developing and they aren't fully aware of their situation. Another set of craniopagus twins that attempted separation, also in 2003, didn't have the same good fortune. Iranian sisters Ladan and Laleh Bijani were 29 when they decided they wanted to see the world with a bit more privacy. Fully aware of the risks, they braved the operation, but died in the midst of it.

Separation surgeries have become relatively common since 1950, with roughly 75% resulting in one or both siblings surviving. But even without separation, life hasn't always proved as cruel as it may seem for those forever together. Here's a look at a few cases of conjoined twins who either rejected a separation or never wished for one:

Yvonne and Yvette McCarther -- Born in 1949 and connected at the head (they just missed the boom in separations), the sisters lived for 43 years in complete harmony. Confidence, humor and perseverance helped them live remarkable lives, touring the country as gospel music singers. They spent their final days enrolled in a community college, dying shortly before graduation. Degrees were awarded posthumously at their funeral.

Mary and Margaret Gibb -- Known as America's Siamese Twins, the Gibb sisters were born in 1912, joined at the base of the spine. They enjoyed a successful career in vaudeville, traveling the world and seeing places they may never had without their unique connection. In 1928 a doctor had offered to separate them, but the sisters declined. They lived happily together for 54 years.

Lucio and Simplicio Godino -- Like the Gibb sisters, the Godinos were joined at the base of the spine and also found success in vaudeville. Born in 1908, they lived to be 28. "We accept the inevitable and make the best of it, convinced that united we stand, divided we fall," they once said. "And we have no desire to fall."

Millie-Christine McKoy -- Also connected at the lower spine, African-American twins Millie-Christine (they chose to be called one hyphenated name) were born into slavery in 1851. They escaped that life and made a career of singing, dancing and playing the piano and guitar on stage. By the time they retired, it's believed they had earned more than $250,000.

The Spider Sisters -- The now 39-year-old Ganga and Jamuna Mondal of India share three legs and four arms and have earned a living performing since they were children. A recent Discovery Channel documentary involved an American doctor who believed he could separate them. They opted to stay together. Ganga explained: "The way God made us is the way we will live." Ganga and Jamuna's outlook is inspiring, but for Trishna and Krishna, the way God made them cannot be the way they will live. Here's hoping the way neurosurgeons make them will.