Chapter 4 The Skeletal System 143 one of the most frequently dislocated joints in the human body. Figure 4.19 summarizes the joints of the shoulder complex. The Arm The single bone of the upper arm is the humerus (Figure 4.20). The humerus is a large, strong bone, second in size only to the major bone of the to rotating. As a result, the glenohumeral joint allows motion in more directions than any other joint in the body. The glenohumeral joint, along with the bones and joints of the pectoral girdle, are 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 © Body Scientific International Figure 4.17 Anterior and posterior views of the shoulder girdle, ribs, and humerus. Clavicle Corocoid process Scapula Xiphoid process Body of sternum Anterior view Posterior view Humerus Head of humerus Spine of scapula Head of humerus Clavicle Acromion Acromioclavicular joint Spinous process of T1 Supraspinous fossa Sternoclavicular joint Manubrium 1st rib 7th rib 8th rib Costal cartilage 12th thoracic vertebrae Acromion © Body Scientific International Figure 4.18 Anterior and posterior views of the scapula. Acromion Acromion Suprascapular notch Glenoid cavity Lateral border Subscapular fossa Lateral angle Inferior angle Spine Supraspinous fossa Medial border Superior border Infraspinous fossa Coracoid process Superior angle Anterior view Posterior view Copyright Goodheart-Willcox Co., Inc.