Skull. Coloured X-ray of a side view of a healthy skull. The bones of the cranium (centre) are fused together to form a solid structure that encloses and protects the brain. At bottom right is the jaw (mandible), embedded in which are the teeth. Above the jaw is the nose. The dark spaces around the nose are the paranasal sinuses (air-filled spaces). The sinuses decrease the weight of the front of the skull, aid in warming and humidifying inhaled air, and increase the resonance of the voice. One of the eye orbits (sockets) is seen above the nose.