Which bone forms the forearm on the thumb side?

Which bone forms the forearm on the thumb side?

• A. Ulna
• B. Humerus
• C. Radius
• D. Phalanges

Answer: (C)

The radius is the bone that forms the forearm on the thumb side. In the usual anatomical position, the forearm is oriented so the thumb side is the lateral side, making the radius the lateral bone and the ulna the medial bone. The radius runs from the elbow to the wrist along the thumb side and enables forearm rotation around the ulna (pronation and supination). At the wrist, its distal end articulates with the carpal bones (scaphoid and lunate), forming the wrist near the thumb. The other bones—ulna is on the little-finger side, humerus is the upper arm bone, and phalanges are the finger bones.

The radius is the bone that forms the forearm on the thumb side. In the usual anatomical position, the forearm is oriented so the thumb side is the lateral side, making the radius the lateral bone and the ulna the medial bone. The radius runs from the elbow to the wrist along the thumb side and enables forearm rotation around the ulna (pronation and supination). At the wrist, its distal end articulates with the carpal bones (scaphoid and lunate), forming the wrist near the thumb. The other bones—ulna is on the little-finger side, humerus is the upper arm bone, and phalanges are the finger bones.