closer to your shaft is the inner penis your pc muscle is under your balls if you do alot of pc's like me you have a big lump there when you get hard. the lump has gotten bigger and bigger as i have been pcing so it is not the inner penis because the inner dosent change size.
Yes I know all about the anatomy. I've been doing PC exercises for three years, so I think I know what I'm talking about. That "lump" is your internal penis. It's bigger now because you have better circulation because of PC exercises. It is not the PC muscle itself. If you press that lump with your thumb you should be able to feel your urethra. If it were your PC muscle it wouldn't automatically get hard when you are erect because it is a voluntary muscle. You have to flex it, it does not flex on its own. It gets hard from the bloodflow during an erection because it is the inner penis.