Amazing and cool desktop wallpaper: “3D Scary Skull Abstract Shapes” only for free. The skull is a bony structure that forms the head in vertebrates. It supports the structures of the face and provides a protective cavity for the brain. The skull is composed of two parts: the cranium and the mandible. In humans, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone.