The pectoralis minor (french: muscle petit pectoral) - named from its being the smaller of the two muscles which arise from the front of the chest - is a fan- shaped or triangular sheet, with its inner edge divided into three teeth.

 

Origin

  • The upper borders and outer surfaces of the third, fourth, and fifth ribs near their anterior extremities ;
  • the fascia covering the intercostal muscles in the spaces between these ribs.

Insertion

  • The upper surface of the coracoid process of the scapula ;
  • the upper part of the tendon of the coraco-brachialis along its inner border.

Structure


Its origin is by aponeurotic slips, which, after becoming fleshy, converge upwards, outwards, and somewhat backwards, upon the flattened tendon, which is attached chiefly to the coracoid process, but blends for an inch or more below that process with the origin of the coraco-brachial.

Nerve-supply


From the inner cord of the brachial plexus (through the eighth cervical nerve) by the internal anterior thoracic, which enters its deep surface learthe upper border, the nerve subsequently piercing the muscle to send filaments to the pectoralis major.

Action

Its action is to draw downwards and forwards the scapula, depressing at the same time the point of the shoulder. Taking its fixed point from the coracoid process, it draws upwards and outwards the ribs to which it is attached, and also helps in forced inspiration. Its connection with the tendon of the coraco-brachial will enable it to act slightly as a flexor and adductor of the humerus.

Relations

Superficially, the pectoralis major ; deeply, the external intercostal muscles ; and, near its insertion, the axillary vessels and brachial nerves.

Variations


The origin may extend upwards as far as the second, or downwards to he sixth rib, and it may receive additions from the pectoralis major. It is occasionally altogether absent. Its insertion may be continued over the coracoid process to the capsule of the shoulder joint, the greater tuberosity of the humerus, or the clavicle.

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