Deformed Silkie Chicken Skull

Deformed Silkie chicken skull. The top of the skulls vault (common in silkies) did not close over. This allowed the brain to be exposed resulting in the chicken to be vulnerable to injury and neurological issues. 
This chicken was displaying multiple neurological issues and was euthanased. 
Furthermore the colour of this skull is a natural mutation known as fibromelanosis that causes melanin hyperpigmentation colouring the bones and tissue black. 
This bird in particular wasn't overly hyperpigmented as they do tend to vary.