REDWOOD CITY, Calif. – Jurors in Scott Peterson’s murder trial winced and glanced away yesterday as they looked at photos of Laci Peterson’s badly decomposed body cast in larger-than-life images on a white wall screen.

Her corpse was missing the head, neck, forearms, and part of her left leg, and her rib cage and other bones speckled with barnacles were exposed.

Dr. Brian Peterson, the forensic pathologist who performed the autopsy, said two of Laci’s ribs were fractured, but he could not say whether the injuries came before or after her death. Brian Peterson isn’t related to Laci or Scott Peterson.

“The only internal organ that was present was the uterus,” Dr. Peterson told jurors. “I was limited by the fact there was so much of the body absent.”

Dr. Peterson said he examined the remains for any signs that her extremities had been physically cut off, but could find nothing conclusive.

“For example, if a joint were taken apart with a knife or a saw, that would oftentimes leave marks on the bone. There were no such marks,” Dr. Peterson said.

He said the tides and currents in San Francisco Bay, or fish eating away at her flesh, could have caused the body to tear apart. He explained in detail how autopsies are performed by cutting open the chest and head and removing the organs.

“In this case, there was no brain to examine because the head was missing. There was no heart or lungs to examine because the chest was empty,” he said.

He said he could tell the woman had been pregnant by the size of her uterus, which had expanded to about 10 inches. It normally is the size of a golf ball, he said.

Dr. Peterson said the top of the uterus was open and there were no signs of a cesarean section.

“I determined the baby had exited through the top of the uterus,” he said.

Prosecutors are trying to prove that Mr. Peterson killed his eight-months pregnant wife on or around December 24, 2002, then dumped her weighted body into the bay.

The remains of Laci Peterson and her fetus washed up in April 2003 not far from the Berkeley Marina, where Scott Peterson says he launched his boat that Christmas Eve morning for a solo fishing trip.

Defense lawyers maintain that someone else abducted and killed Laci as she walked the couple’s dog around the neighborhood after Mr. Peterson had left for his fishing trip. They claim the baby was born alive and killed later.

Prosecutors maintain the fetus was expelled from Laci’s decaying corpse.

Earlier, prosecutors used an expert to attempt to show Mr. Peterson lied about a crucial element in the case when he told police he used cement mix to repair his driveway.

Prosecutors claim Mr. Peterson used the cement to make five anchors, one of which was found in his boat. The others, which they allege he used to sink his wife’s body in the bay, have not been discovered. Mr. Peterson told police he made only one anchor and used the rest of a 90-pound bag of cement to repair his driveway. Jurors have also heard Mr. Peterson tell the same story to his dead wife’s brother, Brent Rocha, on a wiretapped telephone call.

However, a prosecution witness testified the concrete samples taken by police from Mr. Peterson’s driveway did not match the concrete in the anchor discovered on the boat. Robert O’Neill, president of Micro-Chem Laboratories, which analyzed the concrete, said the material from the driveway was inconsistent with the material in the anchor.

“This is a different mix,” Mr. O’Neill told jurors. On cross-examination, defense lawyer Mark Geragos vigorously attacked Mr. O’Neill’s findings, noting that the only difference in the two concrete mixtures was that the sample taken from the driveway contained large gravel-like chunks. All other components in both mixtures were identical, Mr. Geragos said.

Mr. O’Neill acknowledged Mr. Geragos’s assessment was correct but insisted the two concrete samples were from different mixes.

Mr. Geragos said Mr. Peterson poured the cement mix onto the driveway where the larger rocks already were and that’s when the two mixed together.

Mr. O’Neill disagreed. “The larger rocks were obviously mixed in with the material,” he said. It’s a key part of the prosecution case and could be powerful if it proves that Mr. Peterson lied about where the remainder of the cement mix was used, legal experts said.