Pectoral Muscles

Axilla

• It is a narrow space between the chest wall and the pectoral limb containing a large amount of loose connective tissue.
• This space is crossed by the large vessels and the nerves intended to supply the muscles of the pectoral limb.
• It corresponds to the armpit of the man.
• In resting condition, this space can scarcely exist, except perhaps to a small extent at its lower part: but it is clearly observed when the limb is abducted.

Pectoral muscles

• These muscles form a thick mass, which occupy the space between the lower part of the chest wall and the medial face of the shoulder and arm. They are divisible into two layers – superficial and deep. The superficial layer is again divisible into anterior and posterior muscles.
• Superficial Pectoral (Pectoralis superficialis)
  • Anterior superficial pectoral
    • This is thicker and smaller of the two layers of the superficial pectoral, extending from the manubrium sterni to the antero-ventral part of the arm.
    • Orgin: The ventro-lateral aspects of the anterior part of the sternum.
    • Insertion: In common with the brachiocephalicus, to the anterior edge of the humerus.
    • Action: To adduct the limb and draw it forwards.
  • Posterior superficial pectoral
    • This is closely blended with the preceding muscle and extending from the ventro-lateral aspect of the sternum to the medial side of the forearm.
    • Origin: The ventral and lateral aspects of the anterior part of the sternum behind the origin of the preceding muscle.
    • Insertion: To the crest of the humerus and fascia of the forearm.
    • Action: To adduct the limb and to tense the fascia of the forearm.
• Deep Pectoral (Pectoralis profundus)
  • It is a large, fleshy muscle extending from the level of xiphoid cartilage forwards and upwards to the level of the shoulder joint.
  • Origin: The ventral surface of the sternum and tunica abdominalis.
  • Insertion: Medial tuberosity of the humerus.
  • Action: To adduct and retract the limb.
  • Blood supply: External thoracic artery.
  • Nerve supply: Pectoral nerves.