Radius (anatomy)
The radius is one of two long bones in the forearm, running from the elbow to the wrist on the thumb side. It works in tandem with the ulna to enable the remarkable motion of pronation and supination—the twisting that lets your palm face up or down.
The radius is shorter and thinner than its partner, yet bears significant mechanical load during gripping and lifting. Its head articulates with the upper arm bone at the elbow, while its expanded distal end forms the primary wrist joint with the carpals. A fibrous membrane connects it to the ulna, creating a stable yet flexible structure.
Named from the Latin for "ray"—evoking how it radiates from the center of the forearm—the radius is a favorite subject for anatomical illustration and has fascinated craftspeople and theorists alike for centuries. Its unique geometry reflects millions of years of evolutionary refinement for primate dexterity.