Just when anatomical researchers thought they knew the human body like the back of their hand, it went and surprised them again — this time, with a brand-new part of the jaw.

The subject of much speculation, the possible existence of a third layer in the masseter muscle — the most prominent of the masticatory muscles — has been alluded to in the odd historical text, with conflicting reports never quite pinning down its position.

But until last year, it was generally accepted to be bi-layered, consisting of a superficial and deep portion.

That is, until Swiss scientists, from the University of Basel, did a little digging.