Not sure how correct this is, but it'll have to suffice for explaining...
The biceps (green) goes in under the delta/shoulder muscle. I think there's a smaller muscle on the lower outside of the biceps (blue), and it meets with the muscle which bends funnily into the lower arm (pink), and the blob of that one covers a few muscles which come out from under it. The biceps is 2 muscles btw, and and is sometimes show because they're a bit displaced. On the back of the leg there's a biceps too (biceps femoris) and it kinda splits up and goes on each side of the back of the knee, making the hole. Maybe you can feel its two tendons on the back of the knee and lower upper leg.
The shoulder muscle is the same as the 'breast' muscle. It kind of shoots radially and turning into it. I marked this with a darker magenta string. Often you get a little hole there (intersection of biceps, delta and breast) of you do the hulking 'hulk' pose.
The upper leg has a few easy muscles to remember. The 'drop' muscle on the inside, and under is a diagonal string muscle. Inside towards the croth theres a lot of little strings, and I don't know the exact details of those, other than the ones which are relevant to stretching panty cloth of course... The hip bone might show (yellow).
The neck would be a bit strange. The Trapezius (back of neck, I think we call it the 'cloak' muscle) would probably wrap behind the back and up to the back of the head. The 'nod' muscle would somehow merge with it.
