Final answer:
The radius articulates with the capitulum of the humerus, as the capitulum is a structure on the distal humerus specifically designed to form an elbow joint with the head of the radius.
Step-by-step explanation:
The anatomical structure that articulates with the capitulum of the humerus is the radius. The capitulum is a knob-like structure located on the anterior surface of the distal humerus. The distal end of the humerus features two main articulation areas: the trochlea, which articulates with the ulna, and the capitulum, which articulates with the head of the radius. This configuration forms part of the elbow joint and allows for the range of motion necessary for various arm movements. Therefore, the correct answer from the provided options is the radius (1).