A round figure, structure or part.
- c. block — see ring block.
- ciliary arterial c. — formed from the anterior ciliary arteries; lies within the ciliary muscle.
- iridial arterial c. — formed from the posterior long ciliary arteries and supplying blood to the iris.
- iridial vascular c. — a ring of vessels formed by the anterior ciliary arteries; provide fine branches to the iris and ciliary body.
- c. of safety — see flight distance.
- c. system — see breathing circuit.
- c. 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.
- c. of Willis — anastomotic loop of vessels near the base of the brain. See cerebral arterial circle.
