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Floor of the Cranial Cavity Showing Circulus Arteriosus and Dural Venous Sinuses
This is a specimen of the floor of the cranial cavity showing the arteries forming the circulus arteriosus (arterial circle of Willis) (colored red) and a few dural venous sinuses (colored blue)
The following structures are identified:
- Anterior cerebral artery
- Posterior communicating artery
- Basilar artery
- Posterior cerebral artery
- Straight sinus
- Superior petrosal sinus
- Transverse sinus
Circulus arteriosus (Circle of Willis):
The Circle of Willis is a circulatory anastomosis of the major arteries supplying the cerebrum. It is formed at the base of the brain by the flowing arteries:
Anteriorly, by the anterior communicating and the anterior cerebral arteries
Posteriorly, by the basilar artery dividing into two posterior cerebral arteries
Laterally on each side, by the posterior communicating artery connecting the internal carotid artery with the posterior cerebral artery.
Dural venous sinuses:
The dural venous sinuses are spaces between the endosteal and meningeal layers of the duramater. They contain venous blood that are drained from the central nervous system, face and scalp. There are no valves in the sinuses or in the veins that are connected to the sinuses. The vast majority of the venous blood in the sinus drains from the cranium via the internal jugular vein
Anterior cerebral artery:
The anterior cerebral artery is a smaller terminal branch of the internal carotid artery. The artery supplies most of the medial surface of the cerebrum.
It also supplies:
A narrow strip of superolalateral surface of cerebral cortex adjoining the superomedial border upto the parito-occipital sulcus
Medial part of the orbital surface of the frontal lobe.
Posterior communicating artery :
The posterior communicating artery is a branch of the internal carotid artery. It runs backward and anaotomoses with the proximal part of the posterior cerebral artery.
Basilar artery :
The basilar artery is formed by the union of two vertebral arteries at the lower part of the pons. It takes part in the formation of “Circle of Willis” and supplies the brain. The artery ascends in the basilar sulcus on the ventral surface of the pons. It terminates at the upper border of the pons by dividing into right and left posterior cerebral arteries. Anterior inferior cerebellar, pontine branches, labyrinthine, and superior cerebellar arteries are the other branches of the basilar artery.
Posterior cerebral artery :
The posterior cerebral arteries are the terminal branches of the basilar artery. They are given off at the upper border of pons and participate in the formation of “Circle of Willis”
Straight sinus :
The straight sinus is formed by the union of the great cerebral vein and inferior sagittal sinus. It runs posteriorly in the junction between the falx cerebelli and tentorium cerebelli to become continuous with one of the transverse sinuses (most commonly the left).
Superior petrosal sinus :
The superior petrosal sinuses are paired sinuses that are located at the edge of the tentorium cerebelli, i.e., on the ridge of petrous part of the temporal bone. They drain into the transverse sinuses.
Transverse sinus:
The transverse sinuses are paired sinuses that extend laterally from the confluence of sinuses in the tentorium cerebelli. The transverse sinuses travel ventrally to become the sigmoid sinuses of each side. The sigmoid sinuses bend into an S-shaped curve and continue into the internal jugular vein through the jugular foramen.
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