Corpus: Pectoralis minor muscle

The pectoralis minor muscle is a thin, triangular muscle located on the upper part of the bony thorax, directly beneath the pectoralis major muscle. It is one of the outer pectoral muscles that connect the ventral shoulder girdle to the trunk.

The pectoralis minor muscle originates from the upper edges or ventral surfaces of the third, fourth, and fifth ribs, as well as the aponeuroses covering the intercostal spaces between them. The muscle fibers extend cranially and laterally, converging to form a flat tendon that attaches to the medial edge and cranial surface of the coracoid process of the scapula.

The pectoralis minor muscle is innervated by the medial pectoral nerve (C8-Th1) and the lateral pectoral nerve (C5-C7) from the brachial plexus.

Arterial blood is supplied to the pectoralis minor muscle by muscular branches of the superior thoracic artery and the pectoral branch of the thoracoacromial artery. Venous blood is drained through the pectoral veins into the subclavian vein.

The pectoralis minor muscle functions to pull the scapula obliquely downward, moving it caudally, medially, and ventrally. When the arms are fixed, such as when propped up, the pectoralis minor acts as an auxiliary respiratory muscle, aiding in breathing along with the pectoralis major muscle.