Pectoral Region Anatomy PDF

1) Pectoralis major muscle Origin; Clavicular head; from anterior surface of medial ½ of clavicle Strernocostal head; from anterior surface of sternum, front of the upper 6 costal cartilages and aponeurosis of external abdominal oblique muscle Insertion; by a bilaminar tendon into the l...

1) Pectoralis major muscle Origin; Clavicular head; from anterior surface of medial ½ of clavicle Strernocostal head; from anterior surface of sternum, front of the upper 6 costal cartilages and aponeurosis of external abdominal oblique muscle Insertion; by a bilaminar tendon into the lateral lip of bicipital (inter-tubercular) groove of humerus (the lower border is twisted to form the “anterior axillary fold”) Nerve supply; medial and lateral pectoral nerves Action: Clavicular head; flexion, adduction and medial rotation of arm Sternocostal head; extends the flexed arm + adduction and medial rotation of arm (acting in swimming, rowing and climbing with latissimus dorsi muscle) Whole muscle; adduction and medial rotation of arm 2) Pectoralis minor muscle Origin; from anterior surfaces of 3rd, 4th and 5th ribs close to their costal cartilages Insertion; into medial border and upper surface of coracoid process of scapula Nerve supply; medial pectoral nerve Action: a) Protraction and depression of shoulder girdle b) Downward rotation of scapula c) Helps in deep inspiration by raising the ribs when scapula is fixed  Coracoid process of scapula Pectoralis minor muscle Medial pectoral nerve 3 4 5 3) Subclavius muscle Origin; from upper surface of 1st costo-chondral junction Insertion; into the groove in the middle 1/3 of inferior surface of clavicle Nerve supply; nerve to subclavius (C5) Action: it steadies clavicle during excessive movements of shoulder girdle Subclavius Site; strong sheet of deep fascia that occupies the interval between subclavius muscle above and pectoralis minor muscle below, deep to the upper part of pectoralis major muscle Attachment; Above; it splits to enclose subclavius muscle, then gets attached to inferior surface of clavicle Below; it splits to enclose pectoralis minor muscle, then continues downwards to form “suspensory ligament of axilla”, which fuses with axillary fascia Medially; attaches to 1st and 2nd costal cartilages Laterally; attaches to coracoid process of scapula, where it blends with the coraco-clavicular ligament Coraco-clavicular ligament Clavi-pectoral fascia Suspensory ligament of axilla [N.B.] The fascia from the clavicle to the floor of axilla is called “axillary fascial septum”, which includes; 1) Fascia enclosing subclavius muscle 2) Clavipectoral fascia 3) Fascia enclosing pectoralis minor muscle 4) Suspensory ligament of axilla Axillary fascial septum  Subclavius muscle Acromiothoracic artery and cephalic vein Clavi-pectoral fascia Lateral pectoral nerve Pectoralis minor muscle Pectoralis major muscle Suspensory ligament of axilla Axillary fascia at base of axilla Structures piercing clavipectoral fascia: 1) Cephalic vein 2) Lateral pectoral nerve 3) Acromiothoracic artery 4) Lymph vessels from infraclavicular lymph nodes to apical axillary lymph nodes Acromion process Acromiothoracic Cephalic vein artery Lateral pectoral nerve Clavi-pectoral fascia Infra-clavicular lymph nodes 1) Pectoralis major muscle 2) Pectoralis minor muscle 3) Subclavius muscle 4) Serratus anterior muscle Serratus anterior muscle Origin; it arises by 8 digitations from outer surfaces of the upper 8 ribs, midway between their angles and costal cartilages (1st digitation arises from the 1st and 2nd ribs as well as the fibrous arch between these 2 ribs) Insertion; into ventral surface of medial border of scapula 1st digitation inserts in the superior angle 2nd and 3rd digitations fan out to insert into the whole length of the medial border Lower 5 digitations insert into the inferior angle Nerve supply; nerve to serratus anterior (long thoracic nerve) from C5, 6 and 7 (descends on outer surface of the muscle in the mid-axillary line) Action: Whole muscle;  Powerful protraction of scapula as in boxing  Fixation of scapula to chest wall as in pushing against resistance  Helps in deep inspiration by elevation of ribs when scapula is fixed (accessory muscle of inspiration) Lower 5 digitations (with upper and lower fibers of trapezius); rotate scapula upwards as in raising arm above the head in abduction from 90-180° Applied anatomy: injury of long thoracic nerve (as during operation of radical mastectomy) causes paralysis of serratus anterior muscle, so the medial border and inferior angle of scapula are no more in contact with chest wall, and when the patient pushes against resistance they move backwards causing “winging of scapula”