Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 145 Arm The single bone of the upper arm is the humerus (Figure 5.23). The humerus is a large, strong bone, second in size only to the major bone of the upper leg. The upper end of the humerus forms a rounded head that articulates with the glenoid fossa of the scapula to form the glenohumeral joint. The humerus includes a number of bony landmarks: • The anatomical neck is a slightly indented line that mostly circles the humeral head. • The greater and lesser tubercles are bulbous projections that are lateral to the humeral head and are separated by a prominent indentation called the intertubercular sulcus. glenoid fossa, in addition to rotating. As a result, the glenohumeral joint allows motion in more directions than any other joint in the body. The glenohumeral joint and the bones and joints of the shoulder girdle are collectively referred to as the shoulder complex. Together these joints provide the significant range of motion present in a healthy shoulder. This large degree of mobility, however, comes at the cost of instability: the shoulder is one of the most frequently dislocated joints in the human body. Figure 5.22 summarizes the joints of the shoulder complex. 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 (shoulder) joint glenoid fossa of the scapula humerus Figure 5.22 Goodheart-Willcox Publisher 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 © Body Scientific International Figure 5.23 Anterior and posterior views of the humerus.