Two-year-old Mohamed Ibrahim sat upright for the first time Monday -- eight days after being separated from his twin brother.

Mohamed, now breathing on his own, is the more active and alert twin, said Dr. James Thomas, chief of critical care services at Children's Medical Center Dallas (search).

His brother Ahmed should be taken off his ventilator late Monday or Tuesday. Both have shown what doctors called "dramatic improvement" since their surgery.

Neurosurgeons separated the intricate connection of blood vessels running between the brains of the conjoined Egyptian twins (searchin a 34-hour operation.

"The two boys are different in many ways, including their responses to complex neurological surgery," Thomas said. "Each is recovering in his own way."

The hospital said the twins are showing more motion in their arms and legs, and improved response to verbal cues from the family and medical team.

Thomas said he is cautiously optimistic that doctors will not have to place Mohamed back on a ventilator. Both continue to run low-grade fevers, but don't appear to have infections.

"These boys are still at a critical stage in their recoveries and therefore are kept in an environment that minimizes stimulation," Thomas said. "Their visitors are limited to the immediate family, their Egyptian nurses and the medical team only."

The twins, born in Egypt on June 2, 2001, were separated Oct. 12.

Thomas said Ahmed has not had any repeat of a seizure he suffered Friday night. A lumbar drain (searchwas removed Sunday after CT scans showed no accumulation of spinal fluid. Mohamed's lumbar drain remains in place.

Also Monday, doctors in New York successfully completed the first of at least three operations on 18-month-old conjoined twins from the Philippines.

Carl and Clarence Aguirre are joined at the top of their heads and share a major vein that drains blood from the brain to the heart. Monday's operation was to stretch the twins' skin so there will be enough to cover their heads when they are separated.

"We were mainly looking at crossover between the blood vessels," said Dr. James Goodrich, who led a team of 20 in the 5-hour operation. "We did not find much, and that's a very good sign. ... There were no surprises."