Serratus anterior muscle

The serratus anterior is a muscle that originates on the surface of the upper eight or nine ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula.

Human anatomy

Origin

Serratus anterior normally originates by nine or ten slips from either the first to ninth ribs or the first to eight ribs. Because two slips usually arise from the second rib, the number of slips is greater than the number of ribs from which they originate.

Insertion

The muscle is inserted along the medial border of the scapula between the superior and inferior angles. The muscle is divided into three named parts depending on their points of insertions: the superior part is inserted near the superior angle; the intermediate part is inserted along the medial border; and the inferior part is inserted near the inferior angle.

Function

All three parts described above pull the scapula forward around the thorax, which is essential for anteversion of the arm. As such, the muscle is an antagonist to the rhomboids. However, when the inferior and superior parts act together, they keep the scapula pressed against the thorax together with the rhomboids and therefore these parts also act as synergists to the rhomboids. The inferior part can pull the lower end of the scapula laterally and forward and thus rotates the scapula to make elevation of the arm possible. ...
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