New muscle layer discovered on the human jaw

The team described an additional, deeper layer in the masseter muscle, a prominent jaw muscle which is found in the rear part of the cheek and helps in chewing.

The newly discovered muscle layer (red) runs from the back of the cheekbone to the anterior muscular process of the lower jaw. The masseter muscle thus not only consists of a superficial (S) and a deep (D) part, but also has a deeper layer (C = coronoid), which has now been described for the first time. (Illustration: Jens C. Türp, UZB)

Researchers from Switzerland have discovered a new layer of muscle on our jaw. The team described an additional, deeper layer in the masseter muscle, a prominent jaw muscle which is found in the rear part of the cheek and helps in chewing.

Their findings were published recently in the journal Annals of Anatomy. They recommend that the muscle be named Musculus masseter pars coronidea, which means the coronoid part of the masseter.

The team carried out a detailed anatomical study using computer tomographic scans. They analysed stained tissue sections from deceased individuals and MRI data from a living person.

Lead author Dr. Szilvia Mezey from the Department of Biomedicine at the University of Basel explained in an email to indianexpress.com: “We have been looking to clarify the architecture of the masseter muscle not only from the point of view of an anatomist but also approached it from the angle of dentists specialised in orofacial pain. This new approach allowed us to locate and describe a part of the muscle that has been simply overlooked or not specified in enough detail by former authors.”

When asked what the role of this muscle was, she added that it can at the moment only be deduced from its architecture. “It is likely to be involved in retracting the lower jaw back towards the ear and stabilising the temporomandibular joint, for example, while chewing,” she says. The team has planned to conduct a detailed analysis of the function of the muscle to validate the theory deduced from the architecture.

“Most people think of human anatomy as science where everything has been fully described for decades. However, there are still many areas of the human body where more detailed descriptions are needed, especially in view of modern medical treatments allowing for more specific and focused interventions,” adds Dr. Mezey.

So does this mean our textbooks need revisions? “Anatomy textbooks are regularly revised with new editions following the results of the latest research in all areas of anatomy, not only on the macroscopic level but also including histology and embryology,” she concludes.

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