radius

/ray"dee euhs/, n., pl. radii /-dee uy'/, radiuses.
1. a straight line extending from the center of a circle or sphere to the circumference or surface: The radius of a circle is half the diameter.
2. the length of such a line.
3. any radial or radiating part.
4. a circular area having an extent determined by the length of the radius from a given or specified central point: every house within a radius of 50 miles.
5. a field or range of operation or influence.
6. extent of possible operation, travel, etc., as under a single supply of fuel: the flying radius of an airplane.
7. Anat. the bone of the forearm on the thumb side. Cf. ulna (def. 1). See diag. under skeleton.
8. Zool. a corresponding bone in the forelimb of other vertebrates.
9. Mach. Now Rare. the throw of an eccentric wheel or cam.
10. a rounded corner or edge on a machined or cast piece of metal.
11. Entomol. one of the principal longitudinal veins in the anterior portion of the wing of an insect.
[1590-1600; < L: staff, rod, spoke, beam, orig., RAY1]

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bone
 in anatomy, the outer of the two bones of the forearm when viewed with the palm facing forward. All land vertebrates have this bone. In humans it is shorter than the other bone of the forearm, the ulna.

      The head of the radius is disk-shaped; its upper concave surface articulates with the humerus (upper arm bone) above, and the side surface articulates with the ulna. On the upper part of the shaft is a rough projection, the radial tuberosity, which receives the biceps (biceps muscle) tendon. A ridge, the interosseous border, extends the length of the shaft and provides attachment for the interosseous membrane connecting the radius and the ulna. The projection on the lower end of the radius, the styloid process, may be felt on the outside of the wrist where it joins the hand. The inside surface of this process presents the U-shaped ulnar notch in which the ulna articulates. Here the radius moves around and crosses the ulna as the hand is turned to cause the palm to face backward (pronation).

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Universalium. 2010.

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