circle /cir·cle/ (ser´k'l) a round structure or part.
circle of Willis
circle of Willis
cerebral arterial circle c. of Willis.
Berry's circles charts with circles on them for testing stereoscopic vision.
defensive circle the coexistence of two conditions which tend to have an antagonistic or inhibiting effect on each other.
circle of Haller a circle of arteries in the sclera at the site of the entrance of the optic nerve.
Minsky's circles a series of circles used for the graphic recording of eye lesions.
circle of Willis the anastomotic loop of vessels near the base of the brain.
circle of Wil·lis (w l s)n. A roughly circular anastomosis that is located at the base of the brain and formed by the anterior communicating artery, the two anterior cerebral, the two internal carotid, the two posterior communicating, and the two posterior cerebral arteries. |
circle of Willis
Etymology: Thomas Willis, English physician, 1621-1675
a vascular network at the base of the brain formed by the interconnection of the middle cerebral, anterior cerebral, posterior cerebral, basilar, anterior communicating, and posterior communicating arteries.
circle
a round figure, structure or part.
circle block
see ring block.
ciliary arterial circle
formed from the anterior ciliary arteries; lies within the ciliary muscle.
iridial arterial circle
formed from the posterior long ciliary arteries and supplying blood to the iris.
iridial vascular circle
a ring of vessels formed by the anterior ciliary arteries; provide fine branches to the iris and ciliary body.
circle of safety
see flight distance.
circle system
see breathing circuit.
circle test
walking a horse in a small circle, first one direction then the other, is used in a neurological examination to detect ataxia and abnormalities in proprioception.
circle of Willis
anastomotic loop of vessels near the base of the brain. See cerebral arterial circle.
circle of Willis
An arterial ring surrounding the optic chiasma and hypothalamus. It is formed anteriorly by the anterior cerebral arteries which are linked by the anterior communicating artery; posteriorly, by the division of the basilar artery into the posterior cerebral arteries and, laterally the latter are united by the posterior communicating arteries to the internal carotid arteries. An aneurysm in one part of the circle of Willis may compress the optic chiasma, resulting in a visual field loss. As the terminal branches of the internal carotid arteries are called the middle cerebral arteries, the circle of Willis is sometimes considered to be formed laterally by the latter (Fig. C11). See internal carotid artery; preretinal haemorrhage; heteronymous hemianopia.
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Fig. C11 Diagram showing the circle of Willis and the optic chiasma
circle of Willis
circulus arteriosus cerebri Anatomy A conduit of anastomosed arteries that encircle the optic chiasm and hypophysial region at the base of the brain, consisting of parts of each internal carotid, anterior, middle, and
posterior cerebral arteries, and anterior and posterior communicating arteries. See Berry aneurysm.
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