Pectoralis Minor Muscle Anatomy

The pectoralis minor presents as a triangular muscle situated in the anterior thoracic wall, deep to the more prominent pectoralis major muscle. Its distinctive triangular shape contributes to its efficient mechanical function.

The pectoralis minor serves as a crucial landmark in the axillary region, forming important relationships with neurovascular structures. Together with the coracoid process, it creates a significant anatomical bridge under which the axillary vessels and brachial plexus travel. This relationship becomes particularly relevant in cases of thoracic outlet syndrome, where compression of these structures may occur.

Pectoralis Minor Muscle Anatomy

The muscle originates from the anterior surfaces of ribs 3, 4, and 5, with attachments near their respective costal cartilages, forming the broader base of the triangle. The muscle fibers converge superolaterally to insert into the medial border and superior surface of the coracoid process of the scapula, creating the apex of the triangle.

The pectoralis minor muscle receives its primary innervation from the medial pectoral nerve, derived from the medial cord of the brachial plexus. This nerve typically contains fibers from spinal segments C8 and T1. The medial pectoral nerve often pierces the pectoralis minor before supplying it, creating an intimate relationship between the nerve and muscle that surgeons must consider during procedures in this region.

Additionally, the lateral pectoral nerve, though primarily supplying the pectoralis major, may contribute some innervation to the pectoralis minor through communicating branches. This dual innervation pattern provides some redundancy in the neural control of this important stabilizing muscle.

See Also: Brachial Plexus Anatomy Overview

The arterial supply of the pectoralis minor demonstrates a rich network primarily derived from the thoracoacromial artery, a branch of the second part of the axillary artery. The thoracoacromial artery divides into several branches, with the pectoral branch being the primary supplier to the pectoralis minor. This vessel typically courses along the muscle’s superior border, providing numerous penetrating branches throughout its substance.

Secondary blood supply comes from the lateral thoracic artery, another branch of the axillary artery, which provides additional perfusion to the muscle’s lateral portions. The intercostal arteries, particularly from the third through fifth intercostal spaces, also contribute to the muscle’s blood supply at its costal attachments. The venous drainage pattern closely follows the arterial supply, with most blood returning via the thoracoacromial and lateral thoracic veins, which ultimately drain into the axillary vein. Additional drainage occurs through the internal thoracic veins via small perforating vessels that accompany the anterior intercostal arteries.

The muscle performs several essential functions in shoulder girdle mechanics. When the ribs are fixed, it acts to stabilize the scapula against the thoracic wall and assists in drawing the scapula anteriorly and inferiorly. This action is particularly evident during forward reaching movements. Conversely, when the scapula is fixed, the pectoralis minor can elevate the ribs, contributing to forced inspiration, making it an accessory muscle of respiration.

References & More

1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice – https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-5230-9
2. Clinically Oriented Anatomy – https://shop.lww.com/Moore-Clinically-Oriented-Anatomy/p/9781496347213
3. Baig MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Pectoral Muscles. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed