Fresh revelations in anatomy: New layer of muscle discovered on the jaw

In a revelation that could redefine certain aspects of anatomical studies as we know it, scientists have now discovered humans have a new layer of muscles behind the cheeks that stabilise the lower jaw.

Until now, the consensus was that the masseter muscle at the back of the cheeks consists of two layers — one superficial and one deep — but new findings indicate that is an additional third, even deeper layer.

The masseter is a thick, somewhat quadrilateral muscle found at the back of the mouth of mammals and its most notable function is to elevate the mandible, thus moving the jaw and helping in chewing. The action of this muscle is prominently felt when one presses the teeth together.

The new study, published in the Annals of Anatomy journal earlier this month, indicates an additional layer of muscles in the masseter, which stabilises the lower jaw and is possibly the only part that can pull the lower jaw back toward the ear.

“The masseter muscle is considered to be bilayered, consisting of a superficial and a deep part,” the introductory text to the study reads.

“However, a few historical texts mention the possible existence of a third layer as well, but they are extremely inconsistent as to its position. Here we performed an anatomical study to clarify the presence and morphological characteristics of a distinct third layer of the masseter muscle,” it says.

Detailing the results of the study, the text reads, “An anatomically distinct, deep third layer of the masseter muscle was consistently demonstrated, running from the medial surface of the zygomatic process of the temporal bone to the root and posterior margin of the coronoid process.”

More distinctly, the study notes that the aforementioned text is the first detailed description of this part of the masseter muscle. The scientists, in conclusion, recommended the name M masseter pars coronoidea (coronoid part of the masseter) to refer to this newly discovered layer on the jaw.