Origin :

Serratus Anterior  is composed of three group of fibers.      

1st group- The most superior serration, which attaches anteriorly to the first (and sometimes the second) rib, connects posteriorly to the superior angle of the scapula. This bundle of fibers lies nearly parallel to the underlying ribs.

2nd group- The next 2 serrations attach anteriorly to nearly half the length of the second and third ribs to form a flat sheet of nearly parallel fibers, which attach posteriorly to the length of the vertebral border of the scapula. These fibers angle across ribs at around 45.

3rd group- The last inferior five or six serrations attach anteriorly to the next five or six ribs (rib 4 to rib 8 or 9). This third group is the strongest part of the muscle and forms a quarter-circle fan, which converges posteriorly on the inferior angle of the scapula.

The digitations which attach to the lower ribs interdigitate anteriorly with the external abdominals.

Innervation
SA is supplied by long thoracic nerve or nerve of bell from the anterior rami of the c5,c6,c7.

Action :

Serratus anterior moves scapula upward, laterally and forward. Serratus anterior supports flexion and abduction of the arm by stabilizing scapula and by contributing upward rotation. SA is not active during initial

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