The radius and ulna are long bones that make up the forearm, extending from the elbow to the wrist. In the anatomical position, the radius is found in the lateral forearm, while the ulna is found in the medial forearm.

The radius and ulna are the two long, parallel bones of the forearm. In the anatomical position, the ulna is situated medially, or closer to the body, whereas the radius is positioned laterally. As such, structures on the medial side of the forearm are often referred to as “ulnar,” while those on the lateral side are described as “radial.”

The radius is opposite your ulna, on the lateral (thumb) side of your forearm. Your radius rotates over your ulna when you stretch your arm straight out in front of you with your palms facing down. They’re more parallel to each other when you hold your arms straight out with your palms face up.

In an anatomical presentation (when the hands are extended and the palm is facing the viewer) the radius is lateral and the ulna is medial. They are inverse in measures, resulting from the position of the head: the radius is small proximally (head) and large distally, while the ulna is large proximally and small distally (head).

The radius and ulna are the two long bones in the forearm. The radius is the bone on the thumb side, closer to the body, while the ulna is on the same side as the pinkie. These two bones rely on each other for support.