The bullet probably hit the Union soldier as he was fleeing. It may have struck his cartridge box first, which sent it tumbling through the muscle of his right buttock, broke his right leg and buried itself sideways in his thigh bone just below the hip.

His buddies probably carried him as they retreated before the storm of Rebel gun and cannon fire. At the field hospital, the harried surgeons probably took a look at him and moved on to those less seriously wounded.

After he died, he was laid in a shallow pit with a dead comrade and the sawed-off arms and legs of as many as 11 more soldiers cut down at the Civil War’s Second Battle of Bull Run, in August 1862.

On Wednesday the National Park Service is scheduled to announce that archaeologists have found the “limb pit” where the two soldiers and the amputated arms and legs were buried.

The discovery, on the battlefield just north of Manassas, Va., is extraordinary, experts said.

Nothing like it has been found before, and a century and a half after the battle, when a Park Service archaeologist examined the fallen Yankee’s thigh bone, the bullet was still stuck in it.

“As an archaeologist … it’s exciting,” said Brandon Bies, who brought the bone out of the pit. “As a human being, lifting the leg of an American soldier and holding the bone with the bullet that killed him, it’s an emotional experience.”

Scientifically, it’s “one in a million,” he said. “But for that soldier, it wasn’t a good one in a million. It was the end of his life.”

The two soldiers — referred to as Burial 1, with the embedded bullet, and Burial 2 — were placed side by side in the pit. The severed limbs were carefully arranged next to them, like broken tree branches, according to a photograph from the dig.

Burial 1 probably went in first, because Burial 2 was partially on top of him.

The hole was about a foot deep, and over the years farm plows had carried off the skull of one man and part of the skull of the other.

Anthropologists from the Smithsonian Institution have studied the injuries suffered by the two soldiers and examined the cut marks on the severed limbs made by the surgeons’ saws. There were nine severed legs and two arms in all.

The identities of the soldiers are not known, and their fates were probably a mystery for their families, painful and enduring.

But scientific tests and circumstantial evidence show they were probably Northerners.

The bullet in the leg of Burial 1 was fired from an imported British Enfield rifle musket then commonly used by Confederates, said Bies, now the superintendent of the Manassas National Battlefield Park.

The Burial 1 soldier, who was probably in his 20s, stood about 5 feet 7 inches tall. No clothing was found with him.

The man in Burial 2 was laid to rest in his Union coat — its four eagle-imprinted buttons were found in the pit with him.

He was probably in his 30s, and only about 5-foot-5.

He had been wounded by one large ball that smashed his upper right arm, a smaller one that hit him in the groin and a smaller one that struck near his right shin. Several of the rounds were found in the ground near him.

The Second Battle of Bull Run was at that point the largest battle ever in the Western Hemisphere, Bies said, and involved almost 125,000 combatants. Roughly 1,700 Union soldiers and 1,200 Confederates were killed, and a combined total of more than 14,000 were wounded.

The two soldiers will be the first burials in the new section of Arlington National Cemetery when it opens this summer. Their coffins will be built with wood from a downed tree taken from the battlefield.

The Park Service said it is still deciding what to do with the limbs.