The pectoralis major is the most superficial muscle in the pectoral region. It is large and fan-shaped and is composed of a sternal head and a clavicular head. It is active in deep or forced inspiration, but not expiration.
The superior and inferior fibres of the pectoralis major attach to the crest of the greater tubercle of the humerus. The superior fibres are more anterior and caudal on the ridge, whereas the posterior fibres twist in on themselves and are more posterior and cranial than the superior fibres.
Test the pectoralis major
The two heads of the muscle can be tested separately:
- The head of the pectoralis major clavicle can be assessed by transverse adduction of the arm at the glenohumeral joint against resistance, during which it can be seen and palpated.
- The sternocostal head of pectoralis major can be tested by adduction of the arm and the glenohumeral joint against resistance, during which it can be seen and palpated.