Scientists recently uncovered a part of the body that had never been described before: a deep layer of muscle in the masseter, which raises the lower jaw and is critical for chewing.
Modern anatomy textbooks describe the masseter muscle as having two layers, one deep and one superficial. "However, a few historical texts mention the possible existence of a third layer as well, but they are extremely inconsistent as to its position," the study authors wrote in a new report, published on Dec. 2 in the online edition of the journal Annals of Anatomy. So the team decided to check whether the prominent jaw muscle might have a hidden, super-deep layer, as the historical texts suggest. To do so, they dissected 12 human cadaver heads that had been preserved in formaldehyde; they also took CT scans of 16 "fresh" cadavers and reviewed an MRI scan from a living subject, according to the report. Through these examinations, they identified an "anatomically distinct" third layer of the masseter muscle. This deep, deep layer runs from the zygomatic process — a bony projection that forms part of the "cheek bones" and can be felt just in front of the ear — to the coronoid process — a triangular projection on the lower jawbone. Read more...
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