BALTIMORE, SEPT. 12 -- Siamese twins born joined at the head and surgically separated a week ago returned to the operating room for irrigation of scalp wounds, officials at Johns Hopkins Hospital said today.

The 7-month-old West German twins underwent operations late Friday. And they remained in critical but stable condition and in artificially induced comas, hospital spokeswoman Joanne Rogers said.

Their conditions, including the comas induced to suppress brain function, have remained essentially unchanged since their 22-hour separation surgery last weekend.

"They did go back in. It was a preventative measure to irrigate scalp wounds to prevent infection," she said.

The twins, Benjamin and Patrick Binder, were born joined at the back of the head. They shared skull bone and a major vein but their brains were separate.

The twins were separated in an operation that began at 7:15 a.m. last Saturday and ended at 5:15 a.m. Sunday.

Benjamin Binder was left without enough skin to cover the back of his head and experienced brain swelling. Doctors covered his head with a fabric mesh until they were able to stretch the skin on his head gradually with the use of silicon implants. Friday, Benjamin's skin was finally found to be elastic enough so that doctors were able to stretch it over the spot where he had been joined to his brother.

Rogers said the swelling in the infant's brain also had diminished.

"They are still critical but stable. And there is no brain swelling," she said.

Doctors are expected to begin weaning the twins from medication they have been on since their initial surgery at Hopkins.

"They hope to wake them up from their coma today or tomorrow," Rogers said. "That will be a gradual process that will take several days."

Until the twins are out of their comas, doctors will not be able to determine what, if any, brain damage they suffered as a result of surgery.