1. Muscles
Pectoralis Major
Description: large, fan-shaped muscle covering upper chest. Covered by pectoral fascia (thin lamina of deep fascia)
Origin: sternal end of clavicle, sternum, cartilage of ribs 1 – 6 and aponeurosis of external oblique muscle
Insertion: fibres converge to insert into greater tubercle of humerus
Action: Powerful adductor and medial rotator of arm
Relations:
- Anterior: pectoralis minor
- Posterior:
Nerve supply: from brachial plexus via lateral and medial pectoral nerves
Pectoralis Minor
Description: small triangular muscle
Origin: anterior surface of ribs 3 – 5
Insertion: coracoid process of scapula
Action: assists in protraction of scapula
Relations:
- Anterior:
- Posterior: pectoralis major
Nerve supply: medial and lateral pectoral nerves (C6 – C8)
Serratus Anterior
Description: fan-shaped muscle, forms medial wall of axilla
Origin: arises as series of digitations from upper 8 ribs.
Insertion: entire anterior surface of vertebral border of scapula
Action: “boxer’s muscle” – protracts scapula, rotating inferior angle laterally and upward, elongating the upper limb
Relations:
- Anterior:
- Posterior: pectoralis major
Nerve supply: long thoracic nerve C5 – C7 roots of the brachial plexus
Subclavius
Description: small cylindrical muscle
Origin: costal cartilage of rib 1
Insertion: subclavian groove on inferior surface of clavicle
Action: helps stablise and depress pectoral girdle
Relations:
Nerve supply: nerve to subclavius (C5 and C6)
Trapezius
Description: large flat muscle, most superficial
Origin: anterior surface of ribs 3 – 5
Insertion: fibres converge to insert into greater tubercle of humerus
Action: Powerful adductor and medial rotator of arm
Relations:
- Anterior: pectoralis minor
- Posterior:
Nerve supply: accessory nerve (CNXI), C3 and C4
Levator scapulae
Description: strap-like muscle, floor of the posterial traingle
Origin: transverse processes C1 – C4
Insertion: medial border of scapula, superior to spine
Action: Powerful adductor and medial rotator of arm
Relations:
Nerve supply: from cervical plexus – cervical spinal nerves and dorsal scapular nerve (C3 – C5)
Rhomboids Major and Minor
Description: two rectangular muscles
Origin:
- Minor: spins process of C7 and T1
- Major: spinous process of T2 – T5
Insertion: medial border of scapula
Action: retracts scapula together with middle fibres of trapezius
Relations:
- Anterior:
- Posterior: trapezius
Nerve supply: Dorsal scapular nerve (C4 and C5)
Latissimus dorsi
Description: broad, flat, triangular muscles of lower back. Covered by trapezius superiorly. Contributes to posterior wall of axilla. Lateral border of latissimus dorsi forms a boundary of the lumbar triangle.
Origin: indirect attachment via lumbodorsal fascia into spines of lower six thoracic vertebrae, lumbar vertebrae, lower 3 – 4 ribs and iliac crest
Insertion: spirals around teres major, inserts in floor of intertubcular sulcus of humerus
Action: primer mover of shoulder joint extension, powerful arm adductor, medially rotates arm at shoulder, depresses scapula
Relations:
Nerve supply: Thoracodorsal nerve (C6 – C8)
2. Joints
Sternoclavicular joint
Description: synovial joint between bulbous medial end of clavicle, superolateral part of manubrium and first costal cartilage
Nerve supply: medial supraclavicular nerves C3 and C4 from cervical plexus
Acromioclavicular joint
Description: synovial joint between lateral end of clavicle and medial border of the acromion.
Nerve supply: suprascapular nerve C5 and C6 from brachial plexus