A group of scientists announced that they had managed to isolate a body part that had never been described before. This is a deep muscle layer located in the masticatory muscle, the lower jaw lift muscle, which is necessary for chewing. The masticatory muscle is the most important masticatory muscle. Its main function is to raise the lower jaw relative to the jawbone and exert chewing force. It also plays a small role in the elongation of the lower jaw and in lateral movements, and plays a secondary role in the aesthetics of the face.
Modern anatomy textbooks describe the masticatory muscle with two layers: deep and superficial. Nevertheless, several historical texts also mention the possible existence of a third layer. However, these works are very contradictory in relation to her position.
In a recent study, a team of specialists from the University of Basel (Switzerland) conducted an anatomical study to clarify the presence and morphological characteristics of this famous third layer, other than the masticatory muscle.
For this work, the results of which are published in the journal Annals of Anatomy, the authors dissected a dozen human heads preserved in formaldehyde. They also performed CT scans of sixteen corpses and examined the MRI of a living person.
The muscle for pulling the jaw back
At the end of their analysis, the authors of this work emphasize that they have indeed discovered a third deep layer, anatomically distinct from the masticatory muscle. According to the study, it runs from the medial surface of the zygomatic process of the temporal bone to the root and posterior edge of the coronal process (triangular protrusion on the lower jaw).
“This deep area of the masticatory muscle is clearly different from the other two layers in terms of stroke and function,” says Sylvia Mezey, lead author of the study. Judging by the location of the muscle fibers, the muscle layer probably helps to stabilize the lower jaw by “lifting and retracting” the coronal process. This muscle layer is actually the only part of the masticatory muscle capable of pulling the jaw back.
“Although it is generally assumed that anatomical studies over the past hundred years have not overlooked anything, our discovery is somewhat reminiscent of the discovery by zoologists of a new species of vertebrates,” emphasizes Jens Christoph Turp, co-author of this work.
To facilitate discussion of this recently described part of the masticatory muscle, the authors propose to name it M. masseter pars coronoidea (the coronoid part of the masticatory muscle). Its discovery may help doctors better perform surgical operations in this area of the jaw and better treat diseases associated with the joint connecting the jaw to the skull.