rautamiekka 
To be fair, it could be argued only a whole skull not covered by the head would count, those being the 1st 3 below.
And it could be argued broken skull & open skull should be aliased.
pony skull -> skull
horse skull -> skull
cow skull -> skull
broken skull -> skull
open skull -> skull
exposed skull -> skull
horse skull -> skull
cow skull -> skull
broken skull -> skull
open skull -> skull
exposed skull -> skull
