Pectoralis minor is a fan-shaped muscle in the front of the shoulder that secures the lateral angle of the scapula to the rib cage. Superficially, it is covered by the pectoralis major.
Origin – ribs 3-5. dissections show that it commonly attaches to the second rib and, occasionally attaches to the 6th rib.
Insertion – the medial aspect of the coracoid process of the scapula. This is usually a separate tendon from coracobrachialis and biceps femoris. Noted anomalies include a common tendon and an attachment to the greater tubercle of the humerus.
When the ribs are stabilized, pectoralis minor protracts and depresses the scapula. It stabilizes the pectoral girdle during downward movements like chopping wood or walking with a crutch. It synergizes with the pectoralis major, subclavius and latissimus dorsi in depressing the pectoral girdle.
When the pectoral girdle is stabilized, the pectoralis minor lifts the ribs for inhalation, especially during labored breathing. It synergizes with scalenes, serratus posterior superior and serratus anterior to lift the upper ribs and increase lung capacity.
The pectoralis minor and middle bellies of serratus anterior both connect the scapula with ribs 3-5. Both muscles have noted anomalies with attachments to ribs 2 and 6.
Pectoralis minor is invested in the costocoracoid membrane. This fascial structure forms a sheet that extends across the upper chest to also invest the subclavius. This membrane ties together the upper ribs, subclavius, pectoralis minor, clavicle, and coracoid process.
This membrane also covers the neurovascular bundle that feeds the upper extremity, making it an important part of Thoracic Outlet structures. you can read more about these structures in this post about Anatomy of Thoracic Outlet Syndrome.
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