The biceps brachii act distally to flex the elbow, but they also act proximally relative to their attachments to the scapula. The coracobrachialis also aids in the flexion and adduction of the humerus.īiceps brachii – Many people are surprised to learn the most recognizable “arm” muscles, those that flex the elbow, are also considered part of the shoulder musculature. This results in the depression of the point of the shoulder and brings the scapula close to the posterior thoracic ribs.Ĭoracobrachialis – The coracobrachialis is another small, low-force-producing muscle that attaches proximally at the anterior point of the coracoid process (lateral to the pectoralis minor) and distally to the medial surface of the humerus on the opposite side of the bone from the deltoid tuberosity. When contracting, by virtue of its connection to the coracoid process, the muscle tilts the scapula forward to a small degree. The pectoralis minor is a small and not especially strong muscle. It lies underneath the pectoralis major and runs to the superior and medial side of the coracoid process of the scapula, its distal attachment. Pectoralis minor – The pectoralis minor attaches proximally to the upper and outer aspect of the third, fourth, and fifth ribs.
In a relaxed posture, the muscle is important in keeping the head of the humerus in its seat in the glenoid fossa of the scapula.
The muscle is also important in humeral flexion and internal rotation of the humerus. The primary action driven by the pectoralis major is humeral adduction - i.e., movement of the arm toward center. Both segments also have minor tendinous connections to the ribs near their major proximal attachments. The sternal segment (pars sternalis) represents the bulk of the muscle, attaching proximally along the lateral border of the sternum.
This clavicular segment is superior and represents a smaller massed segment. The clavicular portion (pars clavicularis) attaches proximally to the inferior and medial half of the clavicle. The pectoralis major is a segmented muscle with the segments sharing a common distal attachment to the lip of the bicipital groove of the humerus. Pectoralis major – The pectoralis major, a large and important muscle of the shoulder joint, is likely one of the two most recognized muscles in the body (the biceps brachii being the other). Figure 1: The anterior muscles of the shoulder, including the pectoralis major, the underlying pectoralis minor, and the coracobrachialis, largely underlying the biceps brachii.
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