Pectoralis minor muscle (26)
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The pectoralis minor muscle is a small triangular muscle found deep to the pectoralis major in the anterior aspect of the thorax.
This muscle originates from three fleshy bellies that insert into the superior border and anterior surface of the third, fourth and fifth ribs. The muscle fibers converge superolaterally to insert into the inferomedial aspect of the coracoid process, of the scapula, where the tendon of the pectoralis minor intermingles and fuses with the tendon of the coracobrachialis muscle.
The pectoralis minor lies immediately anterior and covers some of the structures of the axillary region, the axillary artery and vein and some of the components of the brachial plexus. In fact, the pectoralis minor muscle is the landmark that divides the axillary artery into its three components: proximal (between the first rib and the medial border of the pectoralis minor). middle (deep to the pectoralis minor), and distal (between the lateral border of the pectoralis major and the inferior border of the teres major muscle). Thus defined the pectoralis major forms part of the anterior wall of the axilla.
In conjunction with other muscles, the pectoralis minor helps to maintain the scapular and shoulder joint in position. If the scapula is fixed, the pectoralis major assists to elevate the anterior thoracic wall during forced inhalation. The pectoralis minor also works as a depressor of the scapula and shoulder joint, abducts the scapula, and rotates the scapula.
The pectoralis minor is innervated by the medial pectoral nerve (C8.T1), a branch of the brachial plexus. Some of the fibers of the medial pectoral nerve perforate the pectoralis minor to provide nerve supply to a portion of the pectoralis major. The pectoralis minor is one of the 17 muscles that attach to the scapula.
Sources:
1. “Gray’s Anatomy” Henry Gray, 1918
2. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
3. "Gray's Anatomy" 42nd British Ed. Churchill Livingstone 2021
4. “An Illustrated Atlas of the Skeletal Muscles” Bowden, B. 4th Ed. Morton Publishing. 2015
5. "Trail Guide to The Body" 4th. Ed. Biel, A. Books of Discovery. 2010