A new muscle layer has been discovered in our lower jaw, which plays an important role in chewing. Scientists have dissected 12 heads of human beings donated to the laboratory to discover the missing body part.

  • A new layer of muscle in the lower jaw has been discovered
  • It is an extra muscle layer found in the masseter muscles. This muscle sits at the back of the cheeks and aids in chewing.
  • Scientists have called the new layer M. Masseter pars Coronoidea. You can feel it by pressing your thumb against your back while chewing. 

Scientists continue to be amazed by the human body, according to a recent discovery of a hidden layer of muscle under the lower jaw.

Researchers at University of Basel (Switzerland) discovered an additional layer of muscle in the masseter muscles. It sits behind the cheeks, and is crucial in chewing.

The original masseter muscle had one part superficially and one deeper. However, scientists discovered an extra layer after dissecting human heads that were donated for the laboratory.

The new layer, which scientists have named M. masseter pars coronoidea (coronoid part of the masseter), can be felt by pressing your hand against the back of your jaw while you chew.

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Researchers at the University of Basel in Switzerland found an additional muscle layer (c) in the masseter muscle, which sits on the back of your cheeks and plays a major role in helping us chew

The University of Basel, Switzerland discovered an extra muscle layer (c), which is located on your back and helps you chew.

Dr Szilvia Mezey from the Department of Biomedicine at the University of Basel, said in a statement: ‘This deep section of the masseter muscle is clearly distinguishable from the two other layers in terms of its course and function.

She says that the arrangement of muscle fibers suggests that the layer responsible for stabilizing the lower jaw is this one.

It also appears to be the only part of the masseter that can pull the lower jaw backwards – that is, toward the ear.

Mezey started this project with twelve human head samples, which she and her colleagues donated to the laboratory. They were then preserved in formaldehyde.

The masseter muscle was previously described as having one superficial and one deep part, but an additional, even deeper layer (c) was found after scientists dissected human heads donated to the lab

After scientists removed human heads from their donors, they discovered a deeper, more substantial layer to the masseter muscles (c).

A portion of the superficial masseter had to be removed in order to expose the deep masseter, which was also taken out.

‘At this point, the attachment of the temporal muscle onto the coronoid process also became clearly visible, marking the correct depth for locating the attachment of the third, deepest layer of the masseter, the pars coronoideus,’ reads the study published in the journal Annals of Anatomy.

‘The coronoid part of the masseter was identified by its diagonally-running fibers, which lie underneath the deep masseter, originate posteriorly from the temporal side of the zygomatic arch, and run diagonally-anteriorly towards the coronoid process of the mandible.’

This deep section of the masseter muscle (c) is clearly distinguishable from the two other layers in terms of its course and function

The deep masseter muscle section (c) can be clearly distinguished from the other two layers by its function and course.

Although earlier studies suggested that there might be a third muscle at the end of the masseter’s life, scientists divided the area in two layers, as they were unable to agree on an appropriate standard.

Although research suggests a third layer of skin, most works place it in the jaws at different locations, deeming them ‘extremely inconsistent’.

Professor Jens Christoph Türp from the University Center for Dental Medicine Basel, said in a statement: ‘In view of these contradictory descriptions, we wanted to examine the structure of the masseter muscle again comprehensively.

‘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.’