What exercises train the side bicep.

I always thought, that having moderately big biceps and huge triceps is enough, but after I saw this guy yesterday, I realized I have something seriously missing in my arm developement.

It's the side bicep, the one that separates the main bicep with the tricep or branchialis. This side bicep I think is very important cause it gives a large bicep look when looking at the arms from the front. Don't you agree?

What exercises train this part. I heared, hammer curls, but what else, and how are hammer curls properly performed?

Thanks bros.