Need some help....

Hi, I've been doing a lot of dumbell/body weight/band, work. Push ups ect, and it is going really well. However I want to know if there are any good exercises, limited to that equipment which I could use to work on: A) My back and b) my shoulders. And just out of curiosity inbetween your back where the two big bones (shoulder blades?) stick out, why do some people have more of an 'incline' or a 'dent' than others? I mean can you increase the size of the muscle over your spine and if so how?

Thank you.
Tim
Btw, anybody know of a website/picture which shows you the human body, like where all the bones, muscle are ect.
 
shoulders
shoulder presses
lateral raises
bent over raises

back
bent over dumbbell rows
shrugs
dumbbell pullovers

body map:
 
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