Pectorals (Pecs) Muscle Anatomy

Location & Overview

The pectoral muscle group consists of pectoralis major and pectoralis minor. This muscle group is often referred to as the “pecs”. Pectoralis major is the larger superficial muscle of the anterior chest wall, while pectoralis minor is the smaller triangular muscle that lies deep to it. Together, they form a superficial and deep pectoral pair in the anterior thoracic and anterior axillary regions.^[1,2]

Pectoralis major is a broad, fan-shaped muscle that covers much of the upper anterior thorax. Its inferior border forms the anterior axillary fold, which is the rounded muscular fold at the front of the armpit. Laterally, it lies near the deltoid at the deltopectoral groove, and the cephalic vein runs in this region.^[1,2]

Pectoralis minor lies deep to pectoralis major and contributes to the anterior wall of the axilla. It runs from the upper ribs to the coracoid process of the scapula. Because of this position, it is closely related to the axillary vessels, brachial plexus, and clavipectoral fascia.^[1,2]

Pectoralis minor is also a useful landmark for the axillary artery. The axillary artery is described in three parts according to its relationship with pectoralis minor. This makes the muscle important not only as a scapular muscle but also as a regional landmark in the axilla.^[1,2]

Anatomical variation can affect the pectoral muscles. Poland syndrome may include absence of the sternocostal part of pectoralis major and absence of pectoralis minor. This is a congenital anomaly rather than the normal arrangement of the group, but it is useful context when considering pectoral muscle anatomy.^[1,2]

Origin & Insertion

Pectoralis major and pectoralis minor have different attachment patterns because they act on different bones. Pectoralis major connects the anterior thoracic wall to the humerus, while pectoralis minor connects the upper ribs to the scapula. This explains why pectoralis major acts mainly at the shoulder joint and pectoralis minor acts mainly on the scapula.^[1,2]

Pectoralis Major Origin & Insertion

Pectoralis major has a broad origin from the anterior chest wall. Its clavicular head arises from the anterior surface of the medial half of the clavicle. Its sternocostal head arises from the anterior sternum and the superior six costal cartilages, and it also receives fibers from the aponeurosis of the external oblique. An aponeurosis is a broad, sheet-like tendon.^[1,2]

The distal tendon of pectoralis major inserts on the lateral lip of the bicipital groove of the humerus, also called the lateral lip of the intertubercular sulcus. The tendon is layered and the fibers twist as they converge, so fibers from different parts of the muscle reach the humerus in an organized arrangement.^[1,2]

Detailed anatomical descriptions differ slightly in how they divide the proximal attachments of pectoralis major. The costal cartilage attachments may be described as extending from the first to seventh costal cartilages, with the first and seventh often absent, or summarized as the superior six costal cartilages. These descriptions support the same main pattern: a broad anterior thoracic origin converging to the humerus.^[1,2]

Haladaj et al. (2019) reported typical pectoralis major structure in 63.75% of 80 cadaveric specimens. A separate clavicular portion was the most frequent variation, and fusion between the clavicular portion of pectoralis major and deltoid was reported in 5% of specimens.^[3]

Pectoralis Minor Origin & Insertion

Pectoralis minor arises from ribs 3-5 and the fascia over the intercostal spaces. Its fibers pass superiorly and laterally to insert on the coracoid process of the scapula. The coracoid process is the hook-like bony projection on the anterior scapula that also provides attachment for several other shoulder-region structures.^[1,2]

The costal attachments of pectoralis minor can vary. Some sources describe origins that may involve the second to fifth ribs, third to fifth ribs, second to fourth ribs, or third to fourth ribs, and costal attachment variation is common.^[1,2]

Asghar et al. (2021), in a systematic review and meta-analysis of 25 studies and 4146 shoulders, estimated anomalous or ectopic pectoralis minor insertion at 19.27%. This means the tendon may extend beyond the coracoid process in a notable minority of shoulders, but the standard anatomical insertion remains the coracoid process.^[4]

Action & Function

Pectoralis major acts mainly on the humerus at the shoulder joint. Its main humeral actions are adduction, which draws the arm toward the body, and medial rotation, which turns the humerus inward. These actions are especially important when the arm moves against resistance.^[1,2]

The actions of pectoralis major depend on which fibers are active and on the starting position of the arm. The clavicular head flexes the humerus. The sternocostal head extends the humerus from a flexed shoulder position, so it should not be described as a general shoulder extensor in every arm position.^[1,2]

Pectoralis minor acts mainly on the scapula. It depresses and protracts the scapula and helps stabilize the scapula against the thoracic wall. In this context, depression means drawing the shoulder blade downward, while protraction means drawing it forward around the rib cage.^[1,2]

Pectoralis minor may also assist rib elevation during deep or forced inspiration when the pectoral girdle is fixed or elevated. The pectoral muscles should not be treated as major muscles of quiet breathing; they are generally electromyographically quiet during normal inspiration and active during forced inspiration.^[1,2]

Innervation

The pectoral muscles are supplied by the medial and lateral pectoral nerves, which are branches of the brachial plexus. The brachial plexus is the nerve network that supplies the upper limb and shoulder region.^[1,2]

Pectoralis major receives both lateral and medial pectoral nerve supply. The clavicular fibers are associated mainly with C5-C6 ventral rami, while the sternocostal fibers are associated mainly with C7-C8-T1 ventral rami. In practical terms, pectoralis major is supplied by the lateral pectoral nerve and medial pectoral nerve, with root values commonly summarized as C5-C7 for the lateral pectoral nerve and C8-T1 for the medial pectoral nerve.^[1,2]

Pectoralis minor is supplied primarily by the medial pectoral nerve, usually described with C8-T1 roots. It may also receive a variable contribution from the lateral pectoral nerve.^[1,2]

Some lateral pectoral nerve fibers can reach pectoralis minor through a communicating branch to the medial pectoral nerve. Boers, Bleys, and Schellekens (2022) found the lateral pectoral nerve, medial pectoral nerve, and ansa pectoralis in all seven cadavers examined. This supports surgical-anatomy variation in nerve course, but the sample size is too small for broad prevalence estimates.^[5]

Blood Supply

Pectoralis major is supplied mainly by the pectoral branch of the thoracoacromial artery. The thoracoacromial artery arises from the second part of the axillary artery and gives off pectoral, deltoid, clavicular, and acromial branches. Smaller secondary vessels may also come from neighboring thoracic arterial branches, but the pectoral branch of the thoracoacromial artery is the key named arterial supply.^[6,7]

Pectoralis minor is also supplied primarily by the pectoral branch of the thoracoacromial artery. Additional supply may come from nearby thoracic arterial branches, including the superior thoracic and lateral thoracic arteries, but the pectoral branch remains the main named arterial supply shared by the pectoral muscle pair.^[8,9]

The arterial pattern matches the topography of the group: pectoralis major and pectoralis minor are both in the anterior thoracic and axillary region, close to the axillary artery and its branches.^[1]