CA, CD

CВ, СЕ, Radii of Circle. lines proceeding from a center; a ray; especially, a line drawn from the center to the periphery E of a circle or sphere; also, the measure of the semidiameter._ 2. In an at. and zool., the outer one of the two bones of the forearm, or corresponding part of the fore leg; the bone on the thumb side of the forearm, extending from the humerus to the carpus, and bearing upon its distal end the manus or hand: so called from its revolving, somewhat like a spoke, about the ulna, as in man and other mammals whose fore limb exhibits the motions called pronation and supination. In most animals, however, the radius is motionle , being fixed in a state of pronation, when it appears as the inner rather than the outer of the two bones, or as by far the larger bone, of the forearm, the ulna being often much reduced. In man the radius is as long as the ulna without the olecranon, and somewhat stouter, especially in its distal parts. It presents a small, circular, cupped and button-like head, for articulation with the capitulum of the humerus and le er sigmoid cavity of the ulna, following which is a constriction termed the neck, and next to this a tubercle for the insertion of the biceps muscle. The shaft enlarges from above downward, and is of somewhat prismatic form, with the sharpest edge of the prism presenting toward the ulna. The lower end has two large articular facets for articulation with the scaphoid and lunar bones (forming the radio carpal articulation, or wrist-joint), a lateral facet for the radio-ulnar articulation, and a stout projection called the styloid proce , for the insertion of the supinator long us muscle. The radius is pronated by the pronator radii teres and pronator quadratus, and supinated by the supinator long us and supinator brevis, a isted by the biceps. Quite a similar form and disposition of the radius characterize various mammals which use their fore paws like hands, as monkeys, mice, squirrels, opo ums, etc. The radius of others, as the horse and ox, is more different, and a ociated with a much reduced and ankylosed ulna. In birds the radius is so peculiarly articulated with the humerus that it slides lengthwise back and forth upon the ulna in the opening and closing of the wing, pronation and supination being absent in this cla of animals. See pronation and supination, and cuts under carpus, Ca tarrhina, Equidæ, forearm, ox, pinion, Plesiosaur us, and solidungulate. 3. In ichth., a bone of the pectoral arch, wrongly identified by some naturalists with the radius of higher vertebrates. The one so called by Cuvier is the hyper coracoid, and that of Owen is the hypo coracoid.-4. In entom., a vein of the wing of some insects, extending from the pterostigma to the tip of the wing.-5. [ cap.] In conch., a genus of Ovulidæ. R. volra is the shuttle-shell or weaver-shell.-6. pl. In ornith., the barbs of the main shaft of a feather; the rays of the first order of the rachis.-7. In arachnology, one of the radiating lines of a geometrical spider's web, which are connected by radix a single spiral line.-8. In echinoderms, one of the five radial pieces of the dentary apparatus of a sea-urchin, being an arched rod-like piece articulated at its base with the inner extremity of each rotula, running more or le nearly parallel with the rotula, and ending in a free bifurcated extremity. Also called the compa of the lantern of Aristotle (which see, under lan tern ). See also cut B under lantern.-9. pl. Specifically, in Cirriped i a, the lateral parts of the shell, as distinguished from the paries, when they overlap: when overlapped by others, they are called alæ.-10. In bot., a ray, as of a composite flower, etc.-11. The movable limb or arm of a sextant; also, a similar feature in any other instrument for measuring angles.12. In fort., a line drawn from the center of the polygon to the end of the outer side. - Auricular radii. See auricular. Geometrical radius of a cog-wheel, the radius of the pitch-circle of the wheel, in contradistinction to its real radius, which is that of the circle formed by the crests of the teeth. - Oblique line of the radius. See oblique. - Fronator radii quadratus. See pronator quadratus, under pronator. - Pronator radii teres. See pronator. - Proportional radii, in a system of gears, or in a set of gears of the same pitch, radii proportioned in length to the number of teeth in the respective wheels. The proportional radii of any two geared wheels, when taken together, are equal to the line connecting the centers of the wheels, which line is the basis of computation in determining them. Also called primitive radii.- Radii acce orii, the barbs of the aftershaft or hypo rachis of a feather.-Raastronomicus. dius Same as radiometer, 1. Radius of concavity. Same as radius of curva ture. Radius of curva ture, the radius of the circle of curvature - that is, of the osculating circle at any point of a curve. In the cut, AHBC is the primitive curve (in this A K C case an ellipse); KHJ, the circle of curvature, oscu- G lating the primitive curve at H; T, the of curvature; TH, the radius of curvature; GFTED, the locus of centers of curvature, or the evolute. The radius of curvature wrap ping itself upon the evo lute gives the primitive F D T IMG:content-1557.png:[blocks in formation] Radius of Curvature. curve. Radius of di ipation. See di ipation.-Radius of explosion. See mine 2, 2 (b).-Radius of gyration, in mech., the distance from the axis to a point such that, if the whole ma of a body were concentrated into it, the moment of inertia would remain unchanged. If the axis is a principal axis, this radius becomes a prin See cipal radius of gyration. Radius of rupture. dius of curvature. Radius of torsion, the element mine2, 2 (b). - Radius of the evolute. as ra of the arc of a curve divided by the angle of torsion. Radius vector (pl. radii vectores ), the length of the line joining a variable point to a fixed origin: in astronomy the origin is taken at the sun or other central body. See vector. Real radius. See geometrical radius.