Unique muscle layer chanced on on the jaw

The newly chanced on muscle layer (red) runs from the lend a hand of the cheekbone to the anterior muscular route of of the lower jaw. The masseter muscle thus not finest features a superficial (S) and a deep (D) section, nonetheless also has a deeper layer (C = coronoid), which has now been described for the first time. (Illustration: Jens C. Türp, UZB)

Human anatomy soundless has a couple of surprises in store for us: researchers on the University of Basel maintain chanced on a previously overpassed a part of our jaw muscle mass and described this accretion intimately for the first time.

The masseter muscle is basically the most prominent of the jaw muscle mass. Whereas you happen to space your fingers on the lend a hand of your cheeks and press your enamel collectively, you’ll truly feel the muscle tighten. Anatomy textbooks on the total describe the masseter as consisting of 1 superficial and one deep section.

Now, researchers led by Dr. Szilvia Mezey from the Division of Biomedicine on the University of Basel and Professor Jens Christoph Türp from the University Center for Dental Treatment Basel (UZB) maintain described the come of the masseter muscle as consisting of an further third, even deeper layer. In the scientific journal Annals of Anatomy, they imply that this accretion be given the title Musculus masseter pars coronidea – in a whole lot of phrases, the coronoid a part of the masseter – since the newly described layer of muscle is related to the muscular (or “coronoid”) route of of the lower jaw.

The anatomical stumble on used to be basically based totally on detailed examination of formalin-mounted jaw musculature, pc tomographic scans and the evaluation of stained tissue sections from deceased members who had donated their bodies to science. This used to be apart from MRI recordsdata from a dwelling particular person.

 As if a unusual animal species had been chanced on

“This deep a part of the masseter muscle is clearly distinguishable from the two a whole lot of layers in phrases of its route and characteristic,” explains Mezey. The affiliation of the muscle fibers, she says, means that this accretion is inquisitive in regards to the stabilization of the lower jaw. It also looks to be the excellent section of the masseter that might perchance perchance well pull the lower jaw backwards – that is, toward the ear.

A stumble on at historical anatomy reviews and textbooks unearths that the come of the masseter muscle has already raised questions previously. In a old edition of Gray’s Anatomy, from the yr 1995, the editors also describe the masseter muscle as having three layers, although the cited reviews had been basically based totally on the jaw musculature of a whole lot of species and partly contradicted one another.

Assorted particular particular person reviews from the early 2000s also reported three layers, nonetheless they divided the superficial a part of the masseter into two layers and agreed with well-liked works of their description of the deeper part.

“In seek for of those contradictory descriptions, we wanted to see the come of the masseter muscle again comprehensively ,” says Türp. “Even though it’s on the total assumed that anatomical analysis in the final 100 years has left no stone unturned, our finding is a exiguous cherish zoologists discovering a unusual species of vertebrate.”

Fashioned newsletter

Szilvia Mezey, Magdalena Müller-Gerbl, Mireille Toranelli, Jens Christoph Türp

The human masseter muscle revisited: first description of its coronoid section.

Annals of Anatomy (2021), doi: 10.1016/j.aanat.2021.151879

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