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== Circle of Willis  ==

== Circle of Willis  ==

[[Image:376px-Circle of Willis en.svg.png|thumb|right|150px|Generalised Structure of the Circle of Willis, Rhcastilhos, 2007, WikiMedia Commons]]

[[Image:376px-Circle of Willis en.svg.png|thumb|right|150px|Generalised Structure of the Circle of Willis, Rhcastilhos, 2007, WikiMedia Commons]]

Blood is supplied to the brain from a circle of arteries called the Circle of Willis (also called the ''cerebral arterial circle'' or ''arterial circle of Willis'') which lies ventrally to the hypothalamus where it forms a loose ring around the infundibular stalk. Although the appearance of the circle of Willis is fairly constant amongst mammals, the sources of blood supply to the circle and the direction of flow around the circle are very species specific. Blood is supplied to the brain by the ''internal carotid artery'' in dogs and horses whilst in other domestic species the main blood supply is from branches of the ''maxillary artery''.  The Circle of Willis is made up of the following arteries;  

Blood is supplied to the brain from a ventral arterial supply in all species, from a circle of arteries called the Circle of Willis (also called the ''cerebral arterial circle'' or ''arterial circle of Willis'') which lies ventrally to the hypothalamus where it forms a loose ring around the infundibular stalk. Although the appearance of the circle of Willis is fairly constant amongst mammals, the sources of blood supply to the circle and the direction of flow around the circle are very species specific. Blood is supplied to the brain by the ''internal carotid artery'' in dogs and horses whilst in other domestic species the main blood supply is from branches of the ''maxillary artery''.  The Circle of Willis is made up of the following arteries;  

*Left and right inferior cerebral arteries  

*Left and right inferior cerebral arteries