Dragon anatomy- head study

A few types of dragon heads
Dragon lovers will probably recognise most of these.

EDIT:
For all the so called dragon-experts,the middle left one and the small middle were referenced by some pics you can find in the art gallery here [link] Although the left one i would guess was a D&D one i'm not sure,cause it was drawn by Eric Wadley or Jason Engle,i can't really remember but i'm guessing it represents a black D& D dragon.
Again,none of this was traced, i used the (unfortuantelly tiny) pic of the d&d one for ref. The history of the rest you can see in my first counter comment. This was a practice page,not grand work of art.