Muscles of the Pectoral Region

The following muscles of the pectoral region allow for movement of the upper limbs:

  1. Pectoralis Major - lies superior to pectoralis minor

    • This muscle has two heads with different points of origin:

      • It’s clavicular head originates from the anterior surface of the medial clavicle

      • It’s sternocostal head originates from the anterior surface of the sternum, the six superior costal cartilages and the aponeurosis of the external oblique muscle

    • Both these heads attach to the intertubercular sulcus of the humerus

    • This muscle acts to adduct and medially rotate the upper limb while also moving the scapula anteroinferiorly. Separately, its clavicular head also aids the flexion of the upper limbs.

    • This muscle is innervated by the medial and lateral pectoral nerves.

  2. Pectoralis Minor - lies inferior to pectoralis major

    • This muscle originates from the third to fifth ribs and attaches into the coracoid process of the scapula.

    • This muscle functions to stabilize the scapula by moving it in an anteroinferior direction.

    • This muscle is innervated by the medial pectoral nerve.

  3. Serratus Anterior

    • This muscle originates from the lateral aspects of ribs 1-8 in a serrated manner and attaches to the costal surface of the medial border of the scapula.

    • This muscle acts to hold the scapula against the ribcage and to rotate it such that the arm can be raised more than 90 degrees.

    • This muscle is innervated by the long thoracic nerve.

  4. Subclavius

    • This muscle originates from the junction of the first rib and its costal cartilage and attaches to the inferior surface of the middle third of the clavicle.

    • This muscle acts to hold the clavicle in place as well as depressing it.

    • This muscle is innervated by the nerve to subclavius.

Clinical Notes:

  1. A winged scapula occurs with the long thoracic nerve is injured therefore causing paralysis of the serratus anterior muscle. A wing scapula is when the medial border of the scapula is able to move in a lateral and posterior direction, away from the thorax. This also makes abduction of the arm horizontally difficult as paralysis of the serratus anterior muscle means that it is not able to act to rotate the scapula.