Yeah theres the sternal pectorals (your tits) and the clavicular pectorals (the one right under your collarbone)
Arnolds are basically shoulder presses but you start with a supinated grip at your chest, force your arms straight up while rotating to a pronated position. It's not good for the rotators I hear but whatever. I like how the anterior deltoids make my biceps bigger (gives a second bump on a bicep flex) and yeah it does great things for your chest.