Doctors in India operating on a two-year-old child who was born with four arms and four legs say that the surgery is going well.
Lakshmi Tatma is joined at the pelvis to what is, in effect, a headless, undeveloped twin.
A team of surgeons in the southern city of Bangalore is working in shifts to separate Lakshmi's spinal column and kidney from that of her twin.
It is hoped the procedure will allow her to survive beyond adolescence.
"It has been so far so good," hospital spokesman Siva Rudrayya told reporters.
"She is responding well, although there were a lot of complications. Doctors believe she has an 80% chance of survival," he said.
The doctor leading the operation, Sharan Patil, told the BBC's World Today programme that his team is prepared for 40 hours of continuous surgery.
"However if everything goes smoothly it will finish much quicker," he said.
Dr Patil said he heard about "this little girl in the state of Bihar that she needed particular help and I did reach out and went to this small village near the border with Nepal.
"It was appalling to find her with an infected sore and suffering from continuous fever without any medical help."
Dr Patil added that the girl's parents were eager for the operation to be performed.
"The villagers and some of the relations were not so keen about going ahead with the surgery but the parents are looking to the future and they were very, very keen and motivated to have medical intervention," he said.
The child has been hailed by some in her village in the northern state of Bihar as the reincarnation of the multi-limbed Hindu goddess of wealth, Lakshmi.
Conjoined twins are rare, occurring in about one in every 200,000 births.
They originate from a single fertilised egg, so they are always identical and of the same sex.
The overall survival rate of conjoined twins is somewhere between 5% and 25%.
Historical records over the past 500 years detail about 600 surviving sets of conjoined twins - more than 70% of which have been female twins.