At 12:45 p.m. Saturday, conjoined twins Jade and Erin Buckles lay like an open book, connected only by a stretch of skin deep inside the incision made to divide them. Above it lay their hearts, livers, diaphragms -- once attached, all now separate. As two surgeons made the final cuts, working toward each other, the shared tissue narrowed to an hourglass of white against a dark-blue field of sterile towels.

Then it was gone.

In the future, one girl should be able to run and get her sister and show her a surprise. They should be able to turn their backs in anger. They will have secrets. They will lead their own lives.

The separation of Jade and Erin Buckles, performed Saturday at Children's Hospital in the District, was a testament to how much human beings can endure, and how much they can achieve. It was a rebirth for the nearly 4-month-old Woodbridge twins, and a triumph for the surgical team of two dozen people who made the girls' independent lives possible.

The procedure lasted about six hours, four shorter than the chief surgeon expected, and transpired without a major complication. But like all complex operations, it held small surprises and more than a moment of hazard.

The separation does not ensure the health -- or even the survival -- of either twin. They were critically ill, though stable, yesterday in the hospital's intensive care unit. They face the usual risks after major surgery -- infection, bleeding, respiratory failure, blood clots, wound breakdown -- as well as the particular problems arising from the massive reconstruction of their chests and abdomens.

Nevertheless, when the day ended, the operating team felt nothing short of joy.

As Jade, the second twin to be finished, was readied to be taken from the operating room to the intensive care unit, Kurt Newman, the hospital's chief of surgery -- who had overseen the operation but did not perform it -- spoke to the group working on her.

"Did I tell you you're about the finest team I've ever worked with?" he said. "I'm proud of every single one of you."

Operating Room 3 burst into applause, each person clapping for the others.

Here is an account of the operation from inside the surgical suite. The action was viewed directly and also watched on a television monitor, which carried video from a camera worn on the heads of two surgeons.

Picking an Approach

At every idle moment during the past week, Gary E. Hartman's mind wandered back to the question of what he would face when the skin connecting Jade and Erin from mid-chest to mid-abdomen was finally cut open and folded back.

Would the hearts, which appeared to be separate on the imaging scans but which beat in perfect unison, be connected in an unexpected way? What problem should he address first? Should he turn immediately to the liver, the huge organ that composed most of their shared anatomy? How hard would it be to work deep in the crevasse that would form as he cut them apart? How should he apportion the babies' shared skin so each would have enough to cover the gaping wound that would be left?

The leader of the surgical team, Hartman, 56, had separated three other sets of conjoined twins. He went over the impending operation in his mind the way ski racers take themselves through a course, imagining every gate and turn. He envisioned three approaches. But Friday, he admitted that until the moment of surgery, there was no way to know which approach would be right.

"We're going to pick it as we do it," he said.

That night, he, his wife, Susan, and their daughter, Emi, 5, went to dinner at a Chinese restaurant on Connecticut Avenue NW with another couple. It's a Friday night tradition, and Hartman wanted to keep his personal run-up to the operation as normal as possible.

His surgical partner, Navy Capt. Stephen Morrow, arrived at Children's Hospital shortly before 7 a.m., already having worked an hour.

Morrow is one of two pediatric surgeons at the National Naval Medical Center in Bethesda. He and his partner are also responsible for patients at Walter Reed Army Medical Center in the District. The other physician was out of town, so by 6 a.m., Morrow had gone on rounds for their patients at Walter Reed. He checked on five babies they had operated on, and a newborn admitted the night before. That last baby had an intestinal narrowing, pyloric stenosis, that can be fixed with a 45-minute operation.

"The trouble is, they can't eat until you fix them," Morrow said as he waited in scrubs outside the twins' operating room as they were prepared for surgery. "So I'll have to do that whenever I get done here."

The operation did not begin until more than two hours after the babies arrived in the surgical suite.

A team of four anesthesiologists -- Ramesh Patel and Barbara O'Neill, assisted by Yewande Johnson and Phil Ludmer -- put them to sleep. The twins were outfitted with monitoring devices from head (temperature probes up their noses, tubes into their stomachs) to foot (intravenous lines on the forefoot, pulse oximeters around a toe).

A catheter was inserted into a major vein in the arm of each baby so large volumes of blood and fluids could be delivered rapidly, if necessary. Other catheters were put into arteries to provide a precise measure of blood pressure. Still others were put in their bladders to measure urine output. Electrocardiogram leads were patched onto shoulders and legs. Arms were taped and strapped onto boards, and each girl was given a cap made of heat-retaining foil.

As the last step, they were draped. All but the "surgical field" was covered in sterile cotton towels. Bulging under the bright overhead lights were the mounds formed by two "tissue expanders" -- balloon-like devices, inserted six weeks earlier, that slowly inflated with water to stretch and force the infants to grow more skin, which would help the surgeons close the gaping, post-separation hole.

Plastic surgeon Michael Boyajian, using a sterile felt-tip pen, drew a blue-ink line on the skin to mark the incision.

"Ready to start?" Hartman asked the anesthesiologists behind a curtain of blue paper at the head of the operating table. They answered yes.

At 10:29 a.m., Boyajian made the cut. His assistant, Georgetown plastic surgery resident Mark Venturi, helped as they opened the skin and removed the expanders, which came out like two polished crystal balls. The surgeons put a few stitches in the edge of the abundant skin, slightly yellow from the iodine solution used to disinfect it, and tacked it down to pieces of cloth to hold it back. When the fascia, the underlying layer of tissue covering the abdominal and chest cavities, was fully visible, they stepped aside. It was 10:44.

Hartman and Morrow moved to the head of the table, flanked by their own assistants, pediatric surgery fellows Danielle Walsh and Patricia Lange. The four cut quickly and methodically through the fascia, using a Bovie, an instrument that coagulates blood vessels with heat as it cuts. An assistant held a suction catheter near the instrument's tip, vacuuming up the thin plume of smoke it made. Tiny blood vessels, like a mass of wrecked spider webs, covered the tissue.

The doctors worked from abdomen to chest, crossing the diaphragm that formed a partition between the two cavities. As a small hole opened into the chest, they could see the movement of organs.

An edge of lung, smooth and tawny, slid in and out rhythmically from under the cut edge of the fascia. The pericardium -- a shared sac holding both twins' hearts -- squirmed. In a minute, it, too, was opened, exposing the girls' purple, glistening, frantically beating hearts.

The hearts looked just as they did in a plaster model made in preparation for the operation. Erin's lay horizontal, its tip outstretched and pointing at her sister's, like the finger of Jehovah in Michelangelo's Sistine Chapel painting. The surgeons let them lie and returned to the abdomen. They gently felt the stomachs and removed and traced the length of the intestines, assuring themselves that the girls didn't share any of those organs.

"Are Frank and Greg here?" Hartman asked, referring to Children Hospital's two heart surgeons, who were standing by. He wanted to ask what sort of protection, perhaps a wet piece of gauze, he should put over the hearts as the team worked on the liver.

Gregory DiRusso stepped up on a footstool so he could peer over Hartman's shoulder.

"Is there any advantage to dividing it now?" he asked.

They conferred and decided it would be best to check the hearts for connections -- and to cut those connections -- before moving on to the potentially bloody and risky liver division.

DiRusso and his colleague, Frank Midgley, moved to the head of the table. Their gloved fingers slid along the wet, squirming surfaces of the hearts, probing every contour. They found a connection -- a band of tissue a little thicker than a pencil lead. As they put padded pieces of thread around it, allowing them to hold it for cutting, something unexpected happened.

For the first time, Erin's and Jade's hearts did not beat in unison.

"The heart rate and the EKGs just separated," Craig Sable, a cardiologist monitoring the hearts, said in amazement. "It's definitely different from before you did that."

When the surgeons took the pressure off the connection, the hearts returned to lockstep.

For months, the doctors had worried they might find something unexpected inside the pericardium. Almost all chest-joined twins have some heart connection. The CAT and MRI scans of the twins never showed the hearts to be 100 percent separate, though no obviously shared structures could be seen.

Now, the team had found something never before described in the annals of conjoined twins -- a heart bridge that also functioned as an electrical circuit, capable of letting one baby's heart set the pace of the other.

It was clear, however, that each heart was perfectly capable of setting its own rhythm (though electronic pacemakers were at the ready, just in case). The team paused a moment to remark on the surprises of surgery. Then they cut the connection and moved on.

The heart surgeons stepped away. DiRusso walked over to where Sable was examining the EKG strip that demonstrated the existence of a new cardiac anomaly.

"That's cool," he said. "You going to write it up?"

It was 11:51 a.m. Hartman and Morrow had turned to the liver, down the middle of which lay another surprise.

Before the operation, Hartman joked with one doctor that it would be nice if the liver had a dotted line directing him where to cut, but he expected no such luck. Now, he was looking at a long white line -- the remnant of something called the falciform ligament -- running in the plane where the girls livers had fused during fetal development.

"I may be wrong," Hartman said. "There may be a dotted line."

They cut down onto the ligament with a device called a harmonic scalpel. It was not a knife, but an alligator-jawed instrument that took bites of tissue, sealing blood vessels with sound waves as it went. The ligament proved only briefly useful as a guide. A truer route was plotted with ultrasound pictures periodically made by radiologist Dorothy Bulas, who had stepped to the table.

It was a long, slow, nerve-wracking trip through the organ as the surgeons worked to avoid the large blood vessels coursing through it. The scalpel made a whump-whump-whump sound as it cut.

At 12:24 p.m., Hartman announced to a round of applause that the girls now had two livers. The surgeons sealed the cut surfaces of the organ with an argon laser. They then sprayed them with thrombin, a protein that promotes clotting, using a small atomizer.

"A little perfume. Perfume for the girls," Hartman said.

The surgeons made the final cuts of the diaphragm, then of the skin. There were now two separate babies. Their yawning abdominal wounds, packed with wet gauze, were loosely stitched closed. At 1:11 p.m., Jade was taken to a nearby operating room, where the surgery on her was completed. It was the first time the sisters had been outside each other's presence.

As the surgeons rescrubbed for the next phase of the operation, Erin lay alone on her back in the spotlight. It was a weird and oddly peaceful scene. Her liver looked for all the world like a cut pomegranate, moist, red and mottled from the laser burns. Her heart beat with supreme confidence, moving in and out of her chest like a pink tongue.

Over the next two hours, parallel problems were confronted and solved by Hartman and Morrow, assisted by the wandering plastic surgeon, Boyajian. They closed the pericardial sacs of each girl, using white, finely woven Gore-Tex. Before finishing, Hartman gently pushed the tip of Erin's heart down several times, asking the anesthesiologists if the maneuver had any effect on her blood pressure or pulse. It didn't. Convinced it was safe, he sewed down the final edge of the pericardial patch, redirecting the tip of the heart ever so slightly. He didn't have to build an elaborate tent over it, as he had thought he might.

The girls were fused to each other where each should have had a sternum -- the breastbone. Once they were separated, the right and left edges of their open chests were formed by the ends of their ribs, which normally would have been connected to a breastbone.

The surgeons didn't try to bring the ribs together. Instead, they covered the "defect" with a sheet of material that looked like a miniature Pegboard, sewing the sides to the ribs, and the bottom to the diaphragm. Scar tissue will grow into the holes, and the board itself will be absorbed by the body, leaving behind a fibrous mat that will offer at least some protection.

Finally, and with effort and luck, the skin was closed. There was enough for each girl. In fact, there was enough for each girl to get her own, custom mock bellybutton.

"That looks so beautiful," Hartman said, looking at Danielle Walsh's navel handiwork, the last task of the day.

"Time?" she asked.

"Last stitch in and it's 3:45," he answered. A few minutes later, he stepped away from the table, saying, "Love our team, love our team, love our team."

As it happened, Jade, whom everyone expected to be the easier operation and the first completed, was harder and the second one done. Morrow wiped down the skin of her closed incision at 4:03 p.m. Before she left the operating room, however, the oxygen levels in her blood fell to worrying, though not dangerous, levels. For nearly an hour, Patel and Ludmer suctioned her lungs, ordered and studied X-rays and stabilized her for transport.

"These little babies have so little reserve," Kurt Newman, chief of surgery, said as he waited for an elevator to follow Jade upstairs to the ICU. "It doesn't take much to dip a wing."

There, as Morrow waited for parents Melissa and Kevin Buckles to see their daughters separate for the first time, he rubbed his forehead and said casually to a nurse, "I can't believe I still have a pyloric stenosis to do."

When the couple arrived, the nurses and doctors were still working on Jade. The parents would see her in a minute. They went first to Erin's bed. They looked down at her, their eyes brimming with worried and grateful tears.

A medical team moves Jade Buckles from the operating table after she was successfully separated from her conjoined twin, Erin, at Children's Hospital.The medical team separates conjoined twins Jade and Erin Buckles. "We're going to pick it as we do it," Gary Hartman said of his team's approach.Melissa and Kevin Buckles embrace after seeing their daughters Jade and Erin for the first time since the girls were separated.Melissa Buckles cries as she prepares to hand off her twin daughters for their surgery at Children's Hospital.

Jade and Erin Buckles touch each other's hands as the girls are anesthesized before surgery. Nurse Diane Maria and physicians Mark Venturi and Michael Boyajian, right, watch a monitor during surgery on the conjoined twins at Children's Hospital.