In case you've come across this (above) graphic anywhere on the Internet and freaked out because you didn't/did have that muscle, then calm down!
This 'missing muscle' phenomenon is a part of a 'Proof of Evolution' video shared by Vox, highlighting the changes our bodies have gone through because of evolution.
It's pretty incredible and oddly fascinating, take a look:
[facebook ]https://www.facebook.com/Vox/videos/494982027356071/[/facebook]
Amazing, right?