The anatomy of the extrinsic chest muscles is more complicated than the first glance suggests. They originate on the front of the axial skeleton and insert on the upper extremity. Generally speaking, they protract the scapula and draw the humerus toward the midline.
This arrangement gets a little more complicated with the pectoralis major. The clavicular head allows us to flex the humerus while protracting the scapula. For example, we might do this when opening a door, shaking hands, or reaching into the back of a low cabinet.
Notably, the scapula gets trapped by pectoralis major but is the insertion point for pectoralis minor and serratus anterior. Likewise, the clavicle is the origin of clavicular pec but the insertion of the subclavius. Also, it is trapped by serratus anterior and pectoralis minor.
Something interesting and less complicated happens when we take pectoralis major out of the picture.
The deep extrinsic chest muscles are pectoralis minor, serratus anterior, and subclavius. They all originate on ribs and insert on the shoulder girdle.
When you look at the lateral view, it is easy to see how these muscles are not about moving the arm but mobilizing and stabilizing the platform on which the arm performs, the shoulder girdle. The two fan-shaped muscles, pectoralis minor and serratus anterior, grasp the scapula’s corners. Accordingly, they tilt the scapula while protracting it. Subclavius acts as an assistant to protract the clavicle on which tethers the scapula.
Here are the individual posts, which detail the anomy of each extrinsic chest muscle.
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Tony Preston has a practice in Atlanta, Georgia, where he sees clients. He has written materials and instructed classes since the mid-90s. This includes anatomy, trigger points, cranial, and neuromuscular.
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