Normal skull. Coloured profile X-ray of the skull. The bones of the cranium are fused together to form a complete structure that protects the brain. Attached at the temporomandibular joint (TMJ) is the mandible, or jaw (lower right). Fillings (white) in the teeth can also be seen. The skull is supported by the vertebrae of the neck (bottom centre). At the front of the skull (right) the sinuses can be seen (dark hollows), which are air spaces lined with mucous membranes.