Temporalis insertion

or...The superior temporal line.

That is that elegant curve sweeping up to the left from the outside corner of the eye. It marks where the temporalis muscle is attached to the skull...you can feel it work if you put your finger on your temple and make chewing motions.
Like most people in the First World today, mine are pretty weedy, this guy's were so strong that they have caused those little crenelations of bone along the line.
Although he was probably younger than me when he died, the biting surfaces of my molars are almost un-worn, his have worn away all the enamel.
A hard old life when your bread was full of grit.