Veterinary Gross Anatomy-II

Circle of willis

CIRCLE OF WILLIS (CIRCULUS ARTERIOSUS)

• From the superior face of the rete mirabile cerebri on either side a single vessel an emergent artery arises.
• It traverses the cavernous sinus penetrates the diaphragm sellae and divides into two primary branches at the base of the brain.
• The anterior primary branch passes forwards crosses the optic tract curves medially and divides into middle and anterior cerebral arteries.
• The middle cerebral artery passes laterally gains the sylvian fissure and divides to supply the lateral aspect of the cerebral hemisphere.
• The anterior cerebral artery passes in front of the optic chiasma gains the great longitudinal fissure and here it is connected to its fellow by a small anastomotic branch thus completing the anterior arc of the circle of Willis.
• It divides to supply the medial aspect of the cerebral hemisphere.
• A small internal ophthalmic artery detached by this vessel crosses the optic nerve and joins the external ophthalmic artery.
• The posterior primary branch passes backwards as the posterior cerebral artery inclines medially detaches the anterior cerebellar artery to the cerebellum and joins its fellow to form the basilar artery thus completing the posterior arc of the circle of Willis.
• This artery passes backwards in the central sulcus on the pons and joins the ventral spinal artery.
• During the course it detaches the posterior cerebellar artery, branches to the pons and medulla and chorioid branches to the chorioid plexus.
• The ventral spinal artery runs along the ventral median fissure of the spinal cord and is reinforced by branches from vertebral intercostal, sacral and coccygeal arteries.