The system of major venous sinuses lies within folds of the dura. The central cerebral veins drain into the great cerebral vein (Galen) which joins the inferior sagittal sinus to form the straight sinus in the center of the tentorium. The straight sinus converges at the occiput with the superior sagittal sinus and the transverse sinuses. The venous drainage passes from the transverse sinuses in the outer edges of the tentorium to the sigmoid sinuses. The superior petrosal sinuses from the cavernous sinuses empty into the junction of transverse and sigmoid sinuses. The sigmoid sinuses curve down through the posterior fossas to the internal jugular veins at the base of the skull. The cavernous sinuses also receive the spheno-parietal sinus drainage and also empty along the inferior petrosal sinus directly into the internal jugulars.
The surface cerebral veins drain directly into the major sinuses as well as into two major veins, the great anastomotic vein (of Trolard) and the small anastomotic vein (Labbe). These veins are avoided when making dural incisions.
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