Question

Two sets of muscles are attached to the front and back of the humerus respectively.
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Answer 1

The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus. The four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff. This cuff stabilizes the very mobile but inherently unstable glenohumeral joint.