Pectoralis minor muscle

At a glance

English

Pectoralis minor muscle

Latin (TA2)

Musculus pectoralis minor

System

Muscle

Region

Trunk

Side

Paired, left and right

Inserts on

The fifth rib and fourth rib

About the pectoralis minor muscle

Pectoralis minor lies on the front of the upper chest, hidden under pectoralis major and wrapped in the clavipectoral fascia. Small as it is, it is one of the most useful landmarks of the axilla, because it crosses directly in front of the main vessels and nerves on their way from the neck and chest into the arm.

The muscle arises by three fleshy slips from the third to fifth ribs, close to where they join their cartilages, and also from the fascia over the intercostal muscles there. The slips converge upward and outward into a short, flat tendon that attaches to the scapula's coracoid process, along its inner edge and upper face. The origin varies, sometimes taking in the second or sixth rib, and occasionally the tendon continues over the coracoid towards the shoulder joint.

Pulling on the coracoid, the muscle draws the scapula forward and downward against the chest wall and tilts its lower angle backward, so it helps to lower the point of the shoulder and to protract the scapula, for example in pushing. When the shoulder is fixed, it can lift the third to fifth ribs and so act as an accessory muscle of forced inspiration, as seen in breathless patients who brace their arms. It is supplied by the medial pectoral nerve, which pierces it on the way to pectoralis major, with help from the lateral pectoral nerve, and receives blood from the pectoral branch of the thoracoacromial artery and from the lateral and superior thoracic arteries.

Surgeons and anatomists use this muscle to split the axillary artery into three sections: the first lies medial to it, the second behind it, the third lateral to it. Surgeons also use it to grade the axillary lymph nodes into levels lateral, deep and medial to the muscle. A short, tight pectoralis minor tilts the scapula forward and can narrow the space beneath it, compressing the nerves and vessels in one form of thoracic outlet syndrome. It is missing in Poland syndrome.

Attachments, action and supply

Origin

Third to fifth ribs, on their upper edges and outer faces close to the costal cartilages.

Insertion

Coracoid process of the scapula, on its inner edge and upper face.

Action

Draws the scapula forward and downward against the chest wall; with the scapula fixed, raises the ribs in forced inspiration.

Nerve supply

Medial pectoral nerve (C8, T1), with fibres from the lateral pectoral nerve.

Blood supply

Pectoral branch of the thoracoacromial artery, and the lateral and superior thoracic arteries.