Which of the following muscles attaches onto both the scapula and the radius?

The biceps brachii is the correct answer because it has two origins, one of which is from the scapula and the other from the coracoid process of the scapula. It plays a vital role in both shoulder and elbow movements, as it acts on both joints. The distal attachment of the biceps brachii is at the radial tuberosity on the radius, highlighting its connection to the forearm.

In contrast, the trapezius primarily facilitates movements of the scapula and does not attach to the radius. The levator scapula is involved in elevating the scapula but also does not have an attachment to the radius. The pectoralis major is attached to the clavicule and sternum and connects to the humerus, but it does not attach directly to the radius or the scapula. Thus, the specific attachment points of the biceps brachii to both the scapula and the radius make it unique among the options provided.