Muscles of the upper limb are found in the pectoral region, shoulder, upper arm, anterior and posterior compartments of the forearm, and in the hand. In this first video, we will cover muscles of the pectoral region.
The pectoral region is on the anterior chest wall and has four muscles that move the arm – pectoralis major and minor, serratus anterior, and the subclavius.
Pectoralis major is the most superficial of these pectoral muscles and has two heads – a smaller clavicular head and a larger sternalcostal head. The clavicular head originates from the clavicle, while the sternal head originates from the sternum, as well as the superior six costal cartilages and the aponeurosis of the external oblique muscle. Both heads insert into the humerus at the lateral lip of the bicipital groove of humerus.
The pectoralis major adducts and medially rotates the arm. The sternalcostal head is the prime mover of the pushup. It causes extension of the arm at the shoulder. Meanwhile, the clavicular head causes flexion of the arm at the shoulder.
Pectoralis minor is underneath pectoralis major. It originates from the 3rd to 5th ribs and inserts into the coracoid process, which is part of the scapula. The pectoralis minor pulls the scapula in against the thoracic wall, stabilizing it.
Also anchoring the scapula to the ribcage is the serratus anterior. The serratus anterior is found along your sides, sitting atop your ribs with its branches originating from ribs 18 or from ribs 19. Two branches usually arise from the second rib, so there is one more branch than the number of ribs from which the branches originate. The serratus anterior attaches to the costal, or ribfacing, surface of the scapula’s medial border.
The serratus anterior can be divided into three parts based on post of insertion superior, intermediate, and inferior. This muscle holds your scapula against your ribcage. It also pulls your scapula forward and around the ribcage, for example when you throw a punch. By allowing your scapula to rotate past 90 degree abduction, it allows you to raise your arm over 90 degrees.
Finally, we come to the subclavius, which runs horizontally underneath the clavicle. It originates from the junction of the first rib and its costal cartilage, inserts into the inferior surface of the clavicle, and serves to anchors the clavicle and moves it down and forward. Also, in the event of a broken clavicle, it protects the underlying brachial plexus, which is responsible for both cutaneous and muscular innervation of the upper limb.

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