A parietal foramen is an opening in the skull for the parietal emissary vein, which drains into the superior sagittal sinus. Occasionally, a small branch of the occipital artery can also pass through it. Each foramen is located at the back part of the parietal bone, close to the upper or sagittal border. It is not always present, and its size varies considerably. Parietal foramina are most commonly bilaterally symmetrical, with the same number on each side, although they may exist as a single foramen found on only one of the parietal bones.