Gray’s Anatomy is the gospel of human musculature. But even the gospel, apparently, can err. Last February, Gary Hack, a research dentist at the University of Maryland in Baltimore, announced that he and his colleague Gwendolyn Dunn had found a new muscle in the face. Hack stumbled onto the structure while working on a cadaver so altered by previous dissections that he was forced to cut into the face from the front--instead of the usual side approach. Cutting from that unconventional angle exposed an unfamiliar muscle connecting the lower jawbone, the mandible, to the sphenoid bone behind the base of the eye socket. Hack named the muscle sphenomandibularis. He suspects that it stabilizes the jaw during chewing rather than actually moving the jaw.
Researchers in Brazil and France, however, who claim to have come across the structure before, say it’s not a new muscle at all--just a part of the larger temporalis muscle, which clenches the jaw. To prove his case, Hack must show that sphenomandibularis has its own nerve and blood supply, connects at both ends to the skeletal structure, and has a distinct function. Hack says he and his colleagues are well on their way to establishing all these things. But even if the muscle proves to be part of a previously identified one, says Hack, it will be a new part. There is no description whatsoever of this muscular entity in Gray’s Anatomy or any of 15 other anatomy textbooks, he says.