Dominant Drainage Pathways of Different Parts of the Central Lobe. A, B, and C are respectively the upper, middle, and lower thirds of the precentral gyrus, and D, E, and F are the upper, middle, and lower thirds of the postcentral gyrus. Parts A, B, and D drain to the superior sagittal sinus in 100% of the hemispheres. Parts C and F drain predominantly to the sphenoparietal and transverse sinuses with a slightly higher proportion of the precentral gyrus draining to the sphenoparietal and the postcentral gyrus to the transverse sinus. In some hemispheres the lower third drained to the superior sagittal sinus due to the presence of a large vein of Trolard that drained predominantly upwards. The most common location of the vein of Trolard was along the territory drained by the postcentral vein. In 10% of the hemispheres, area E drained to the transverse sinus due to the presence of larger than average parietosylvian veins. (Image courtesy of AL Rhoton, Jr.)