Identifying the radius in the human forelimb skeleton

Steps:

• Examine the diagram of the forelimb bones, focusing on the forearm region between elbow and wrist.
• Recall that the forearm has two parallel bones: the radius (lateral, thumb side) and ulna (medial, pinky side).
• Distinguish the radius as the straighter, more mobile bone that rotates around the ulna during forearm supination/pronation.
• Compare diagram labels or positions to match the lateral forearm bone.

Why B is correct:

• B corresponds to the lateral forearm bone, defined anatomically as the radius, which articulates with the humerus at the elbow and thumb-side carpals at the wrist.

Why the others are wrong:

• A is the humerus, the single upper arm bone proximal to the forearm.
• C is the ulna, the medial forearm bone that forms the elbow's hinge joint.
• D is a wrist bone (carpal), located distal to the forearm.

Final answer: B