One of the bones of the skull that does not have a sinus is the frontal bone.
The frontal bone is located at the front of the skull, forming the forehead and the upper part of the eye sockets. Unlike some other skull bones, the frontal bone, while it does contribute to the overall structure and protective function of the skull, doesn’t contain any air-filled spaces known as sinuses. The sinuses that are commonly found in other skull bones, such as the maxilla or sphenoid, play roles in reducing weight within the skull, warming and humidifying air, and even enhancing resonance in speech. Therefore, when considering the frontal bone in relation to sinuses, it stands out as a unique case in the anatomy of the skull.