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Origin Third to fifth ribs, near their costal cartilages Insertion Medial border and superior surface of the coracoid process of the scapula Artery Pectoral branch of the thoracoacromial trunk Nerve Medial pectoral nerve (C8, T1) Actions Stabilizes the scapula by drawing it inferiorly and anteriorly against the thoracic wall, raises ribs in inspiration Latin Musculus pectoralis minor | ||
The pectoralis minor (/ˌpɛktəˈreɪlᵻs ˈmaɪnər/) is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body.
Contents
Structure
It arises from the upper margins and outer surfaces of the third, fourth, and fifth ribs, near their cartilages and from the aponeuroses covering the intercostalis.
The fibers pass superior and lateral and converge to form a flat tendon, which is inserted into the medial border and upper surface of the coracoid process of the scapula.
Relations
The pectoralis minor muscle 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.
Function
The pectoralis minor depresses the point of the shoulder, drawing the scapula inferior, towards the thorax, and throwing its inferior angle posteriorly.