The sigmoid sinuses are large venous channels located within the skull. They are part of the dural venous sinuses, which collect blood from the brain and drain it into the internal jugular veins. The sigmoid sinuses are shaped like an "S" and run along the posterior part of the skull, helping to transport deoxygenated blood away from the brain. These sinuses play a crucial role in the brain's venous drainage system. They receive blood from various sources, including the transverse sinuses and the cavernous sinuses, and ultimately lead to the internal jugular vein, ensuring proper circulation and pressure regulation within the cranial cavity.