"We sat on it for a year," Dr. Hack said in an interview. "We thought that this thing is so large, it had to have been seen and recorded by someone. But we found that nobody had described this muscle originating in this particular area."

The muscle exists in identical form on each side of the face. It extends from a bony outgrowth behind the eye socket down to the lower jaw, the researchers said. The tissue, which varies in size among individuals, is about one and a half inches long, three-quarters of an inch wide, and half an inch deep, they said.

A paper detailing the anatomical description of the muscle has been accepted for publication in a peer-reviewed specialty dental journal, Cranio: The Journal of Craniomandibular Practice, he said. The researchers are also scheduled to present their findings on Tuesday in Baltimore at the annual meeting of the American Association for the Advancement of Science.

Dr. Daniel O. Graney, who heads the anatomy program at the University of Washington Medical School at Seattle, said he was skeptical of the claim of finding a new facial muscle, but would reserve final judgment until he saw data on the find.

"Gross anatomy has been around for a long time and we are pretty familiar with most of the body," said Dr. Graney, an associate professor of biological structure. "In terms of finding something spectacularly different, it's hard to believe."