Pectoralis minor

The pectoralis minor (/ˌpɛktəˈreɪlɪs ˈmaɪnər/) is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body.

Pectoralis minor
Pectoralis minor (shown in red).
Pectoralis minor muscle (shown in red). The bone shown in blue is the shoulder blade.
Details
OriginThird to fifth ribs, near the costochondral junction
InsertionMedial border and superior surface of the coracoid process of the scapula
ArteryPectoral branch of the thoracoacromial trunk
NerveMedial pectoral nerve (C8)
ActionsStabilizes the scapula by drawing it inferiorly and anteriorly against the thoracic wall, raises ribs in inspiration
Identifiers
LatinMusculus pectoralis minor
TA98A04.4.01.006
TA22305
FMA13109
Anatomical terms of muscle

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.[1]

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
An individual with an axillary arch as well as sternalis muscle and an accessory abdominal portion of the pectoralis major.

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 superior, towards the thorax, and throwing its inferior angle posteriorly.

Additional images
  • Position of pectoralis minor muscle (shown in red).
  • Right pectoralis minor muscle. Deep dissection.

References

This article incorporates text in the public domain from page 438 of the 20th edition of Gray's Anatomy (1918)

  1. http://www.teachmeanatomy.com/muscles-of-the-pectoral-region/%5B%5D
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