I just want to know, if the traps has 4 parts what part of the traps is the 4th? I only know is the upper, middle and lower, and what exercise that I need to do for the part that I did not know?

Thanks! I appreciate it..

Do prone cobras. Lay on your stomach arm as outstretched in front of you with palms facing down. Lift your torso up with your head and arms coming up off the ground. Either use light dumbbells (10lbs) and rotate your arms in a jumping Jack fashion not allowing your palms to touch the ground