The cleido-mastoid generally arises from the basi-occipital, and the pectoralis major is connected with the latissimus dorsi.
The chief muscular mass, arising from the sternum in the shape of a U, is the pectoralis muscle; its fibres converge into a strong tendon, which is inserted upon the greater tubercle and upper crest of the humerus, which it depresses and slightly rotates forwards during the downstroke.
From the outer tuberculum extends the large crista superior (insertion of pectoralis major and of deltoideus major muscles).
Muscles developed arm depressors, pectoralis major, latissimus dorsi and teres major.
Dumbbell bench press: The dumbbell bench press works the pectoralis major.