The sigmoid sinus is a dural venous sinus that lies deep within the human head, and just below the brain. It is actually a pair of two sinuses, right and left, that enable veins to spread from the middle of the head downwards. It is contiguous with the transverse sinus, which lies in the posterior part of the brain. This sinus starts just below the temporal bone and follows a convoluted course to the jugular foramen. At this point of its course the sinus meets with the internal jugular vein. This dual structure is in fact an extension of the transverse sinus. The transverse sinus varies in size just the same as the sigmoid one. As the tentorium reaches its end, the sigmoid receives the petrosal sinus, which is superior to it in terms of structure. The sigmoid sinus goes in an inferior manner through an S-shaped groove. This groove lies postero-medial to the mastoid. It is connected through the mastoid and the condylar messenger veins with the peri-cranial nerves.
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In Depth: Sigmoid sinus