Pectoralis minor muscle

The pectoralis minor is a thin, triangular muscle located in the anterior thoracic wall, lying deep to the pectoralis major muscle. Despite its smaller size, it serves as an important scapular stabiliser and a key anatomical landmark in the axilla.

Attachments

1. Origin

• Anterior surfaces of ribs 3 to 5 near their costal cartilages

2. Insertion

• Medial border and superior surface of the coracoid process of the scapula

Innervation

• Via the medial pectoral nerve (C8, T1). The nerve pierces the muscle before supplying it, and ends up further supplying the pectoralis major muscle.

Blood Supply

• Pectoral branch of the thoracoacromial artery

• Contributions from the lateral thoracic artery

Functions

• Stabilises the scapula by drawing it anteriorly and inferiorly against the thoracic wall

• Assists in protraction and downward rotation of the scapula

• Acts as an accessory muscle of respiration, elevating ribs during forced inspiration when the scapula is fixed

Anatomical Relations

• Divides the axillary artery into three parts (proximal, posterior, distal)

• Lies anterior to important neurovascular structures, including: axillary artery and vein, and the cords of the brachial plexus.

Clinical Relevance

• Pectoralis minor syndrome: Compression of neurovascular structures beneath the muscle, contributing to thoracic outlet syndrome

• Important landmark in axillary surgery and regional anaesthesia