144 Introduction to Anatomy & Physiology The ulna is larger and stronger than the radius, and it articulates with the humerus at the humeroulnar (hyoo-mer-oh-UHL-ner) joint at the elbow. The ulna attaches to the wrist on the “little finger” side. The bony projection at the upper end of the ulna, called the olecranon (oh-LEHK-ra-nahn) process, is what people refer to as the elbow. The radius and ulna are connected along their entire lengths by an interosseus (in-ter-AHS-ee-us) membrane. The two bones articulate at both ends, and these joints are known as the proximal and distal radioulnar (ray-dee-oh-UHL-nar) joints. upper leg. The upper end of the humerus forms a rounded head, which, as mentioned, articulates with the glenoid fossa of the scapula to form the glenohumeral joint. As Figure 4.21 shows, the framework for the forearm consists of two bones—the radius (RAY-dee-us) and ulna (UHL-nuh). 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 “radially” rotate around the ulna. This radial rotation is the familiar motion that enables the forearm and hand to rotate freely. Articulating Bones of the Shoulder Complex Joint Notched Bone Joining Bone or Region acromioclavicular joint acromion of the scapula clavicle sternoclavicular joint sternum clavicle scapulothoracic joint scapula thorax glenohumeral joint glenoid fossa of the scapula humerus Figure 4.19 Goodheart-Willcox Publisher © Body Scientific International Figure 4.20 Anterior and posterior views of the humerus. Anterior view Posterior view Head Surgical neck Lateral epicondyle Greater tubercle Greater tubercle Anatomical neck Lesser tubercle Intertubercular sulcus Deltoid tuberosity Deltoid tuberosity Coronoid fossa Radial fossa Lateral epicondyle Trochlea Capitulum Medial epicondyle Medial supracondylar ridge Radial groove Lateral supracondylar ridge Olecranon fossa Copyright Goodheart-Willcox Co., Inc.