1. [TA] In anatomy, a ring-shaped structure or group of structures, as formed by anastomosing arteries or veins, or by connected (communicating) nerves, 2. A line or process with every point approximately equidistant from the center. SYN: circulus [TA]. [L. circulus]
- cerebral arterial c. [TA] the roughly pentagonally shaped c. of vessels on the ventral aspect of the brain in the area of the optic chiasm, hypothalamus, and interpeduncular fossa; formed, sequentially and in anterior to posterior direction, by the anterior communicating artery, the two anterior cerebral, the two internal carotid, the two posterior communicating, and the two posterior cerebral arteries. SYN: circulus arteriosus cerebri [TA], arterial c. of cerebrum, c. of Willis.
- closed c. a circuit for administration of an inhalation anesthetic in which there is complete rebreathing with carbon dioxide absorption.
- defensive c. obsolete term for the addition of a secondary affection that limits or arrests the progress of the primary affection, as thought to occur when pneumothorax supervenes on pulmonary tuberculosis, the former having a therapeutic effect on the latter.
- Huguier c. anastomosis around the isthmus of the uterus (junction of the cervix with the body) between the right and left uterine arteries.
- least confusion c. in the configuration of rays emerging from a spherocylindrical lens system, the place where diverging rays of the lens first forming a line image are balanced by converging rays of the second lens.
- major arterial c. of iris an arterial c. at the ciliary border of the iris. SYN: circulus arteriosus iridis major [TA], major circulus arteriosus of iris [TA], greater arterial c. of iris.
- minor arterial c. of iris an arterial c. near the pupillary margin of the iris. SYN: circulus arteriosus iridis minor [TA], minor circulus arteriosus of iris [TA], lesser arterial c. of iris.
- Pagenstecher c. in the case of a freely movable abdominal tumor, the mass is moved throughout its entire range, its position at intervals being marked on the abdominal wall; when these points are joined, a c. is formed, the center of which marks the point of attachment of the tumor.
- Ridley c. SYN: circular sinus (1).
- rolling c. a mechanism for the replication of circular DNA.
- semi- closed c. a circuit for administration of an inhalation anesthetic in which partial rebreathing with carbon dioxide absorption is combined with loss from the circuit of a portion of respired gases through valves.
- vascular c. 1. the c. around the mouth formed by the inferior and superior labial arteries; 2. SYN: areolar venous plexus.
- vascular c. of optic nerve [TA] a network of branches of the short ciliary arteries on the sclera around the point of entrance of the optic nerve. SYN: circulus vasculosus nervi optici [TA], circulus arteriosus halleri, circulus zinnii, Haller c. (1), Zinn corona, Zinn vascular c..
- vicious c. the mutually augmenting action of two independent diseases or phenomena, or of a primary and secondary affection;
- Vieth-Müller c. a geometric c. passing through the optical centers of two eyes by which points adjacent to the point of fixation, both lying on the c., theoretically fall on corresponding retinal points.
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cir·cle 'sər-kəl n
1 a) a closed plane curve every point of which is equidistant from a fixed point within the curve
b) the plane surface bounded by such a curve
2) something (as an anatomical part) in the form of a circle or section of a circle <an arterial \circle> see CIRCLE OF WILLIS
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cir·cle (surґkəl) [L. circulus] a round figure, structure, or part. See also anulus and ring.Medical dictionary. 2011.