Pectoralis minor

Structure

Attachments

From the muscle's origin, the muscle's fibers pass superiorly and laterally, converging to form a flat tendon.

Origin

Pectoralis minor muscle arises from the upper margins and outer surfaces of the 3rd, 4th, and 5th ribs near their costal cartilages, and from the aponeuroses covering the intercostalis.

Insertion

Its tendon inserts onto the medial border and upper surface of the coracoid process of the scapula.

Innervation

The muscle receives motor innervation from the medial pectoral nerve.

Relations

Pectoralis minor muscle forms part of the anterior wall of the axilla. It is covered anteriorly (superficially) by the clavipectoral fascia. The medial pectoral nerve pierces the pectoralis minor and the clavipectoral fascia. In attaching to the coracoid process, the pectoralis minor forms a 'bridge' - structures passing into the upper limb from the thorax will pass directly underneath.

Axillary nodes are classified according to their positions relative to the pectoralis minor muscle. Level 1 are lateral, Level 2 are deep, Level 3 are medial. The pectoralis minor divides the axillary artery into three parts (in contrary sequence compared to the nodes) - first part medial, second part deep/posterior, third part lateral in relation to the pectoralis minor.

Variations

The origin is from the second, third and fourth or fifth ribs. The tendon of insertion may extend over the coracoid process to the greater tubercle. It may be split into several parts. Absence of this muscle is rare but happens with certain uncommon diseases, such as the Poland syndrome.