Pectoralis major has two heads one arising from the clavicle, the second from the sternum and costal cartilages.
Each of these two heads can act independently, the clavicular head to flex and the sternocostal head to extend the glenohumeral joint. Together they medially rotate and adduct the humerus.
Innervation is from the lateral (C5,6,7) and medial pectoral nerves (C8, T1). It is therefore the only upper limb muscle to be supplied by all 5 segments of the brachial plexus.
It inserts into the lateral lip of the intertubercular groove (remember the lady between two majors).
Surgically the pectoralis minor muscle is used to divide the axillary lymph nodes into different levels.
Pectoralis minor is surrounded by the pectoral fascia.
Poland syndrome is a congenital absence of both pectoralis major and minor. It is associated with breast hypoplasia and absent rib segments.
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