Final answer:
The radius is situated on the lateral side of the forearm, running parallel to the medial ulna. Its proximal end includes the head that articulates with the elbow joint and proximal radioulnar joint. The radius is connected to the ulna by the interosseous membrane and ends distally at the wrist joint, where it articulates with carpal bones.
Step-by-step explanation:
The radius is located on the lateral (thumb) side of the forearm, running parallel to the ulna, which is positioned on the medial side. Proximally, at its upper end, the radius features a disc-shaped head that articulates with the capitulum of the humerus and the radial notch of the ulna, forming the proximal radioulnar joint. Just below the head is the neck of the radius, and further inferior on the medial side is the radial tuberosity, where certain muscles attach.
The connection between the radius and ulna is reinforced by the interosseous membrane along their respective interosseous borders. The distal end of the radius engages with two carpal bones to create the radiocarpal joint or wrist joint. The styloid process of the radius provides attachment for ligaments and is positioned more distally than the styloid process of the ulna, influencing the range of wrist motion.