Corpus: Anterior serratus muscle

The anterior serratus muscle is an external pectoral muscle that connects the ventral shoulder girdle to the trunk.

The anterior serratus muscle originates from the upper eight or nine ribs and attaches to the medial side of the scapula. It is composed of three distinct parts, each with specific functions that sometimes act antagonistically:

• Superior part: Originates from the 1st-2nd ribs and attaches to the superior angle of the scapula. This part of the muscle raises the shoulder, a movement known as elevation or cranial reduction of the scapula.
• Intermedial part: Originates from the 2nd-3rd ribs and extends to the medial edge of the scapula. This is the largest portion of the muscle and works with the superior part to pull the scapula forward (ventrally).
• Inferior part: Originates from the 4th-9th ribs and attaches to the medial border and inferior angle of the scapula. This part is often visible in athletes and is responsible for rotating the scapula laterally and enabling the elevation of the arm.

Together with the obliquus externus abdominis muscle, the anterior serratus muscle forms the Gerdy line.

The anterior serratus muscle forms the medial wall of the axilla. Its ventral portions are partially covered by the pectoralis minor muscle, while dorsally, it lies beneath the subscapularis muscle.

The muscle is innervated by the long thoracic nerve, originating from the supraclavicular part of the brachial plexus (C5-C7).

The anterior serratus muscle receives blood from several sources, including the muscular branches of the thoracodorsal artery, the superior thoracic artery, and the lateral thoracic artery.

The anterior serratus muscle plays a crucial role in fixing the scapula to the trunk and pulling it forward around the thorax. This action facilitates the rotation of the scapula, which is essential for the anteversion of the arm. The inferior part alone rotates the lower part of the scapula laterally, aiding in arm elevation, while the superior part helps lower the arm from an elevated position.

When the arm is stabilized, the anterior serratus acts as an auxiliary respiratory muscle, supporting inspiration. The muscle works in conjunction with the rhomboid muscles to fix the scapula to the thorax, with the rhomboid muscles acting synergistically despite their antagonistic pull direction.

The serratus anterior is also known as the "boxer's muscle" because it pulls the scapula forward during a punch, significantly increasing the arm's punching power.

Due to its distinctive shape, the anterior serratus muscle is easily visible under the skin of the lateral thoracic wall in well-trained individuals.

Paralysis of the anterior serratus muscle, often caused by damage to the long thoracic nerve, results in the inability to elevate the arm. Additionally, the scapula on the affected side may protrude in a wing-like shape, a condition known as scapula alata.