146 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. This radial rotation is the familiar motion that enables the forearm and hand to rotate freely. Below the head and neck of the radius is the radial tuberosity, which is the attachment site for the biceps. The ulna is larger and stronger than the radius, and it articulates with the humerus at the humeroulnar joint (elbow). The ulna attaches to the wrist on the “little finger” side. Two processes are located at the proximal end of the ulna. The olecranon (oh-LEHK-ra-nahn) on the posterior side is the elbow. On the anterior side is the coronoid process, which is separated from the olecranon process by the trochlear notch. The ulnar tuberosity serves as an attachment site for part of the brachialis. The radius and ulna are connected along their entire lengths by an interosseus membrane. The two bones articulate at both ends, and these joints are known as the proximal and distal radioulnar joints. At the distal (lower) ends of both the radius and ulna are styloid processes that are easy to see and feel with your fingers. The distal end of the radius unites with several of the carpal bones of the wrist to form the radiocarpal joint (Figure 5.25). • Just below (distal to) the tubercles is the surgical neck, so named because it is the most frequently fractured portion of the humerus. • The mid-shaft of the humerus is marked by the radial groove, which underlies the radial nerve, and the deltoid tuberosity, to which the powerful deltoid muscle attaches. • At the distal end of the humerus are the prominent and readily palpable medial and lateral condyles. • Also at the distal end of the humerus and interior to the elbow joint are the trochlea on the medial side and the capitulum on the lateral side, both enabling free motion of the articulating ulna. • Just superior to the trochlea are the posterior olecranon fossa and the anterior coronoid fossa, which serve as sites of muscle attachments. As Figure 5.24 shows, the framework for the forearm consists of two bones—the radius and ulna. The radius is the bone that articulates with the wrist on the thumb side. The name radius comes from the ability of this bone to rotate “radially” around the ulna. Head of ulna Ulnar notch of radius Anterior view Posterior view Olecranon Articular facets Styloid process Radial tuberosity Radial notch of ulna Trochlear notch Interosseous borders Ulnar tuberosity Coronoid process Radius Ulna Interosseous membrane Styloid process Styloid process Neck of radius Head of radius Head of radius Neck of radius © Body Scientific International Figure 5.24 Anterior and posterior views of the radius and ulna.