Massage & Bodywork

MARCH | APRIL 2022

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KNEAD TO KNOW New Muscle Layer Discovered on the Jaw Researchers at the University of Basel have discovered a previously overlooked section of the jaw muscles and described this layer in detail for the first time. The muscle is described as an additional, deeper layer in the masseter muscle, a prominent jaw muscle that is found in the rear part of the cheek and helps in chewing. The findings were published in Annals of Anatomy (https://doi.org/10.1016/j. aanat.2021.151879). The researchers recommend that the muscle be named musculus masseter pars coronidea, which means the coronoid part of the masseter, because the newly described layer of muscle is attached to the muscular (or "coronoid") process of the lower jaw. The team carried out a detailed anatomical study using computer tomographic scans. They analyzed stained tissue sections from deceased individuals and MRI data from a living person. "This deep section of the masseter muscle is clearly distinguishable from the two other layers in terms of its course and function," explains lead researcher Dr. Szilvia Mezey. The arrangement of the muscle fibers, she says, suggests that this layer is involved in the stabilization of the lower jaw. It also appears to be the only part of the masseter that can pull the lower jaw backward, or toward the ear. The structure of the masseter muscle has been debated in the past, but the descriptions were often contradictory and unconfirmed. "In view of these contradictory descriptions, we wanted to examine the structure of the masseter muscle again comprehensively," says study co-author Jens Christoph Türp. "Although it's generally assumed that anatomical research in the last 100 years has left no stone unturned, our finding is a bit like zoologists discovering a new species of vertebrate."

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