Pectoralis minor muscle

The pectoralis minor is a fan-shaped muscle of the shoulder girdle.

Anatomy and innervation

It originates from the third to fifth ribs, and inserts on the coracoid process of the scapula.

Pectoralis minor muscle - ventral view

It is innervated by the medial and lateral pectoral nerves (C6-Th1), branches of the brachial plexus. The pectoralis minor is located under the pectoralis major, and both form the anterior wall of the axilla. The contracted muscle can be easily palpated there. It is also located close in relation to the brachial plexus and both the subclavian artery and vein, which all run between the muscle and the ribcage.

Lateral pectoral nerve - ventral view

Function

The pectoralis minor has two main functions. On one hand, it pulls the scapula anteriorly and inferiorly toward the ribs (abduction and depression respectively). This leads to a dorsomedial movement of the inferior angle of the scapula. This movement is both helpful when retracting the elevated arm and as well as moving the arm posteriorly behind the back. On the other hand, the pectoralis minor elevates the third to fifth ribs (given a fixed scapula) and expands the ribcage. By those means, it can also serve as an accessory muscle during inspiration.