Pectoralis major muscle
The pectoralis major is a paired, superficial muscle located on the anterior surface of the thoracic cage. If you’re a gym lover, you’ll hear these muscles also being referred to as the pecs muscles. The pectoralis major has a broad origin, based on which it is divided into three parts: clavicular part, sternocostal part and abdominal part. All three parts converge laterally and insert onto the greater tubercle of humerus.
The main function of this chest muscle as a whole is the adduction and internal rotation of the arm on the shoulder joint. Acting independently, the clavicular part helps to flex the extended arm up to 90°, while the sternocostal part facilitates the extension of the flexed arm by pulling it downwards.
|Origin||Clavicular part: anterior surface of medial half of clavicle
Sternocostal part: anterior surface of sternum, Costal cartilages of ribs 1-6
Abdominal part: Anterior layer of rectus sheath
|Insertion||Crest of greater tubercle of humerus|
|Action||Shoulder joint: Arm adduction, Arm internal rotation, Arm flexion (clavicular head), arm extension (sternocostal head);
Scapulothoracic joint: Draws scapula anteroinferiorly
|Innervation||Lateral and medial pectoral nerves (C5-T1)|
|Blood supply||Pectoral branches of thoracoacromial artery, perforating branches of internal thoracic artery|
In this article, we will discuss the anatomy and function of the pectoralis major muscle.
Origin and insertion
The pectoralis major muscle is a fan-shaped muscle that consists of three parts that originate from three different sites:
- The clavicular part originates from the anterior surface of the medial half of the clavicle.
- The sternocostal part originates from the anterior surface of sternum and the anterior aspects of the costal cartilages of ribs 1-6.
- The smallest, abdominal part originates from the anterior layer of the rectus sheath.
The muscle fibers from all three parts run laterally, converging towards the proximal humerus. They give off a broad tendon that inserts along the crest of the greater tubercle of humerus.
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The pectoralis major muscle is a broad superficial muscle found superficially in the anterior chest wall. In males, it is covered by the deep layer of fascia, subcutaneous tissue and the adjacent skin. In females, it is covered by the breast. The deep surface of the muscle covers the pectoralis minor and serratus anterior muscles and the anterior surface of the upper six ribs.
The triangular depression between the pectoralis major muscle, deltoid muscle and clavicle is called infraclavicular fossa (Mohrenheim’s fossa) which serves as an important landmark in the surgical procedures on the subclavian artery.
To expand your knowledge check out our article about the main muscles of the thorax check out our other articles, videos, quizzes and labeled diagrams.
The pectoralis major muscle is innervated by the lateral and medial pectoral nerves (root value C5-T1), which stem from the brachial plexus.
When the arm is the anatomical position, the pectoralis major acts as a strong adductor and internal rotator of the humerus at the shoulder joint. Acting independently, the clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane. The sternocostal portion of the muscle can produce the antagonistic movement and extend the humerus back to the anatomical position.
Acting together with the of latissimus dorsi muscle, the pectoralis major muscle pulls the trunk forwards or upwards when its humeral attachment is fixed. This action is important in activities such as climbing. When acting from the humeral attachment, the pectoralis major muscle also facilitates the act of inspiration. This is particularly important during forced breathing in physical distress.
Poland syndrome is an embryonic malformation of the thoracic wall, which is accompanied by a defect of the pectoralis major muscle in combination with other malformations of the upper extremities (e.g. malformations of the fingers). The muscle can be partly or completely missing. Depending on the degree of severity, the adduction and internal rotation of the shoulder joint are more or less difficult to perform (for example, the crossing of the raised arms). In addition, affected patients have visibly distorted breasts due to the aplasia of the pectoralis major muscle, which is why a plastic-surgical reconstruction can be used therapeutically.