Anterior Thorax & Neck LO 8

8.) Identify and detail the muscles of the anterior thorax: pectoralis major m., pectoralis minor m., and serratus anterior m.


Pectoralis major m.

  • Proximal attachments:
    • 2 heads:
      • Clavicular (clavicle)
      • Sternocostal (sternum and costal cartilages)
  • Distal attachment:
    • Shared tendon on crest of greater tubercle
    • Crosses the glenohumeral (shoulder) joint
  • Action(s):
    • Both heads contracting simultaneously:
      • Adduction & medial rotation of glenohumeral joint
    • Clavicular head independently:
      • Flexion of glenohumeral joint
    • Sternocostal head contracting independently
      • Extension of glenohumeral joint (from flexed position)

Action videos

  • Innervation:
    • Two nerves derived from the brachial plexus
      • Lateral pectoral n.
      • Medial pectoral n.
  • Dominant arterial supply:
    • Thoraco-acromial a. (branch of axillary a.) branches
  • Anatomical relationships:
    • Forms anterior wall of axilla
    • Forms inferior border of deltopectoral triangle/groove
    • Invested in pectoral fascia
      • Breast is located superficial to pectoral fascia
  • Clinical considerations:
    • Clavicular fractures
      • Can pull clavicular fractures with contraction, which may slow healing & damage deep structures
      • Important to immobilize area
    • Breast pathology & surgery
      • Due to the close anatomical relationship, pectoral fascia and muscle can be affected


Pectoralis minor m.

  • Proximal attachments: anterior ribs 3-5
  • Distal attachment: coracoid process of scapula
  • Actions
    • Stabilization of scapula to allow for efficient movements at other joints, specifically the glenohumeral joint
    • Protraction (moving the scapula anteriorly)
  • Innervation: medial pectoral n.
  • Dominant arterial supply: thoraco-acromial a. (branch of axillary a.) branches
  • Anatomical relationships:
    • Medial pectoral n. pierces the pectoralis minor m.
    • Important anatomical landmark locating branches of the axillary a. both in the lab, in imaging, and in surgeries
      • Subdivides the artery into 3 parts based on relationship to the muscle (medial, deep, or lateral to)
  • Clinical considerations:
    • Breast pathology & surgery
      • Due to the close anatomical relationship, pectoral fascia and muscle can be affected or resected


Serratus anterior m.

  • Proximal attachments: Ribs 1-8
  • Distal attachment: anterior surface of scapula
  • Actions:
    • Protraction of scapula
    • Upward rotation of glenoid fossa
      • Important for allowing full range of motion for the glenohumeral (shoulder) joint, particularly in abduction and flexion
    • Stabilization of scapula
  • Innervation: long thoracic n.
    • The placement of this nerve is unique in that it is superficial to the muscle
  • Anatomical relationships:
    • Forms the medial wall of the axilla
  • Clinical considerations:
    • With injury to the long thoracic n., the scapula may develop a wing-like appearance (‘winged scapula’)
      • The medial border of the scapula is displaced posteriorly and laterally in comparison to the uninjured side. This is particularly evident when the shoulder joint is flexed (as in pushing against a wall with the upper limb).
      • This affects scapular motion, but (more importantly) prevents full range of motion at the glenohumeral joint