From your pictures, I am unconvinced its a bone or fossil.
At best, it looks to me like a fossil of some busted up bone that has been covered with some encrustation. (I don't favor this explanation.)
I am not seeing any structural symmetry that would be expected of a skull (if more than 1/2 of it were present).
Volcanic racks can have bubbles in them. The bubbles and their distribution do not look very biological to me, but there are some bones that could have that pattern (in that case I would expect it to be a small fragment of a larger bone.
More information would help:
- Where was it found geographically.
- What do you know about the geologic history of the area?
I have found some weird and interesting looking rocks that are not fossils, but are caused by biological activity (like carbonate marine worm holes/tunnels).
I have also found some volcanic rocks in weird shapes. I found one in Hawaii which was the last flow of an eruption. A nearby palm tree fell over into it and let the impression of the budding top of the tree (somewhat like a pineapple).
Rocks can get weird shapes for weird reasons.