I think you're talking about the corpus spongiosum or the bulbourethral artery...?? Tbh I'm not that crystal on penis anatomy, even though I should be!
Someone correct me if I'm wrong, but I think intensive training of the PC muscle (kegels) will make that part of your dick thicker.
I know from my own experience, that when I actually do kegel continuously for 2-3 days (yes it doesn't take more than that to feel the effect), my PC muscle feels strong, and that part of my dick is thick and defined. It feels kind of like my dick is made of 3 seperate
cylinders, which are put together to form one big pipe
Although I'm not sure if only kegels contribute to make that exact part bigger... I know that clamped kegels have done wonders for me on that part, although a very consistent kegel routine is required to make it more than temporary (In my experience).
I agree it does look very healthy and muscular. The interesting thing is that even very big guys with apparently strong erect cocks, don't always have that muscular definition.. so that makes me wonder if there's something else going on.
Also genetics obviously play a part
