Story at a glance

  • Researchers at the University of Basel in Switzerland found a previously overlooked section of the masseter muscle.
  • The newly discovered layer runs from the back of the cheekbone to the anterior muscular process of the lower jaw.
  • The layer is the third on the body’s most prominent jaw muscle .

Researchers at the University of Basel in Switzerland in partnership with the University Center for Dental Medicine in Basel are the first to find and describe in detail a new layer of the masseter muscle, one of the main muscles humans use to chew, in a new study.

The masseter muscle can be easily seen when a person is eating, chewing gum or clenching their jaw for any other reason, and starts from the lower part of the skull and stretches to the lower jaw. 

Anatomy textbooks usually describe the masseter as having two layers “a superficial and a deep part,” according to the study. 


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But the research team, led by Szilvia Mezey from the Department of Biomedicine at the University of Basel and Professor Jens Christoph Türp from the University Center for Dental Medicine Basel, have found an even deeper layer. 

In the study, published in the scientific journal Annals of Anatomy, the pair proposes the newly found layer be named “Musculus masseter pars coronidea” or the coronoid section of the masseter, since the new layer is connected to a small triangular section of the lower jaw called the coronoid process. 

“This deep section of the masseter muscle is clearly distinguishable from the two other layers in terms of its course and function,” said Mezey in a statement. 

Researchers believe that due to arrangement of the layer’s muscle fibers it is used to stabilize the lower jaw and work to pull the lower jaw backward. 

There are other studies from the early 2000s that report the masseter having three layers, but previous researchers ended up just dividing the superficial part of the muscle into two sections and agree with previous descriptions on the deeper section, according to a statement. 

“In view of these contradictory descriptions, we wanted to examine the structure of the masseter muscle again comprehensively,” said 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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Published on Dec 20, 2021