Pectoralis minor
Musculus pectoralis minor
Also known as: pec minor
A small, triangular muscle deep to pectoralis major, running from ribs 3–5 to the coracoid process. It stabilises the scapula by pulling it down and forward against the chest wall.
Overview
Pectoralis minor arises from the outer surfaces of ribs 3–5 near their costal cartilages and ascends to the medial border and upper surface of the coracoid process. It lies entirely deep to pectoralis major, within the clavipectoral fascia.
It protracts and depresses the scapula and rotates it downward, holding it against the thoracic wall. With the scapula fixed, it raises ribs 3–5 in forced inspiration. Its main importance is as an anatomical landmark. It divides the axillary artery into three parts: the 1st part lies proximal to it (one branch), the 2nd behind it (two branches) and the 3rd distal to it (three branches). It also divides the axillary lymph nodes into levels I–III for breast cancer surgery. It is supplied by the medial pectoral nerve (C8–T1), which pierces it, with help from the lateral pectoral nerve.
Anatomy
- Origin
Outer surfaces of ribs 3–5, near the costal cartilages.
- Insertion
Medial border and superior surface of the coracoid process of the scapula.
- Action
Depresses, protracts and downwardly rotates the scapula; raises ribs 3–5 in forced inspiration.
- Innervation
Medial pectoral nerve (and lateral pectoral nerve).
- Nerve roots
C8–T1 (C5–T1 including lateral pectoral contributions)
- Arterial supply
Pectoral branch of the thoraco-acromial trunk; lateral thoracic and superior thoracic arteries.
- Relations
Crosses the axillary artery (dividing it into three parts) and the cords of the brachial plexus. Forms part of the anterior wall of the axilla.
Function
- Stabilises the scapula against the thoracic wall (depression, protraction)
- Accessory muscle of inspiration when the scapula is fixed
Clinical significance
Axillary lymph node levels
In breast cancer surgery, nodes are staged relative to pectoralis minor. Level I nodes lie lateral (inferior) to it, level II deep to it, and level III medial (superior) to it, below the clavicle.
Pectoralis minor syndrome
A tight pectoralis minor (from posture or overhead athletics) can compress the brachial plexus and axillary vessels beneath it. It is a form of neurogenic thoracic outlet syndrome.
Mnemonics
Axillary artery branches
"Screw The Lawyer Save A Patient": Superior thoracic (1st part); Thoraco-acromial and Lateral thoracic (2nd part); Subscapular, Anterior and Posterior circumflex humeral (3rd part).
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.