Regina and Renata Salinas Fierros lay in side-by-side beds for the first time in their 10-month-old lives Thursday after doctors separated and rebuilt the twins' bodies in a marathon surgery.

"To see the girls today beginning to wake up and move and respond is great excitement for us all," lead surgeon Dr. James Stein said at a news conference.

While Renata was the sleepier of the pair, Regina moved an arm, doctors reported.

"She was the feistier of the two," said Dr. William McIlvaine.

The girls were born facing each other, conjoined from the lower chest to the pelvis. They were fused in several places, including the liver and genitals. They shared a large intestine, and Regina was born with one kidney.

The operation began at 6 a.m. Wednesday, and the reconstructive surgery ended about 4 a.m. Thursday, two hours earlier than doctors had anticipated.

Doctors made an incision at the breastbone and then divided the internal organs.

Late Wednesday, the young twins spent their first moments apart, when one was wheeled to another room so plastic surgeons could begin the reconstruction work.

Regina and Renata's type of fusion occurs in only about 10 percent of cases.

The twins were born in Los Angeles on Aug. 2 to Mexican parents who were visiting relatives in the United States. The girls' mother, 23-year-old Sonia, said she didn't realize she was carrying conjoined twins until she was hospitalized with an infection.

The couple extended their tourist visas so the twins could receive medical care.