Radius

(ra'-de-us). In biology: (a) spoke bone, the outer of the two bones of the anti brachium or anterior limb of a vertebrate; see A/uscles, Table of; (b) one of the veins of an insect's wing; (c) a ray of the first order, of the shaft of a feather (used in the plural); (d) one of the radiating threads of a spider's web; (e) a bifurcated piece, of which there are five, in the oral skeleton of an echinoderm. I. In geometry, the line drawn from the center of a circle to its circumference. 2. One of the cartilaginous rods supporting the fins in fishes. 3. See Ray . Radii auricula res, lines projected on the cranium at right angles to a line pa ing through the auricular points. R. ciliares, the ciliary proce es. R. fix us, in craniometry, aline connecting the inion and the hormion. R. front is, wrinkles of the forehead. R. lent is. lines radiating from the poles of the crystalline lens. R. medulla res, bundles of receiving tubules of the kidney, beginning in one tubule at the apices of the papillae, dividing dichotomously, and extending nearly to the cortical surface.