1. Muscle of the back Muscle are arranged in 2 layers:
Superficial layer: trapezius and latissimus dorsi
Deep layer: levator scapulae, rhomboidus minor and major
1. Trapezius
Origin:
The upper fibers arises from medial third of superior nuchal line & external occipital protuberance
The middle fibers arises from nuchal ligament & spinous process of C7
The lower fibers arises from spinous processes of all thoracic vertebrae and supraspinous ligament
Insertion:
The upper fibers pass downwards and forwards to be inserted to the posterior border of the lateral third of the clavicle

2. 2. The middle fibers pass transversly to the medial border of acromion and upper lip of the crest of spine of scapula
3. The lower fibers are inserted into rough tubercle on the crest of the spine of scapula
Nerve supply: spinal part of accessory nerve
Actions:
Upper fibers elevates the scapula
middle fibers retracts scapula;
Lower fibers together with the lower five digitations of serratus anterior rotate the scapula laterally as in raising the arm above the head

4. Latissimus dorsi Origin:
Tips of spinous processes of the lower 6 thoracic vertebrae and supraspinous ligament
thoracolumbar fascia,
Outer lip of iliac crest,
lower 3 or 4 ribs
Insertion: Floor of intertubercular groove of humerus
Nerve supply: Thoracodorsal nerve (C6, C7, C8)
Action: Extends, adducts, and medially rotates the arm as in swimming and raises body toward arms during climbing

7. Levator scapulae
Origin: from posterior tubercles of transverse processes of C1 to C4 vertebrae
Insertion: into the posterior aspect of the medial border of scapula from the superior angle to the root of spine
Nerve supply: from dorsal scapular nerve (C5)
Action: Elevates scapula and rotates it medially so the glenoid cavity looks downwards

8. Rhomboidus minor Rhomboidus major
Origin: ligamentum nuchae and spinous processes of C7 and T1
Insertion: posterior aspect of the medial margin of the scapula opposite its spine
Nerve supply: Dorsal scapular nerve (C4, C5)
Action: Retract scapula and rotates it medially to depress the glenoid cavity
Rhomboidus major
Origin: spinous processes of T2 to T4 vertebrae and supraspinous ligament
Insertion: posterior aspect of the medial border of scapula from level of spine to inferior angle
Nerve supply: Dorsal scapular nerve (C4, C5)
Action: the same as rhomboidus minor

11. Shoulder region 1. Deltoid muscle
Origin:
Anterior borders of lateral third of clavicle;
Lateral border of acromion
Lower lip of the crest of the spine of scapula
Insertion: Deltoid tuberosity of humerus
Nerve supply: Axillary nerve (C5, C6)
Action: 1. Anterior fibers: flexes and medially rotates the arm
2. Middle fibers: abducts the arm from 15 to 90 degrees
3. Posterior fibers: extends and laterally rotates the arm

13. Subacromial bursa: it is a large bursal sac that lies between the acromion and deltoid muscle superiorly and muscles on the upper surface of the capsule of shoulder joint inferiorly.
Coracoacromial arch: it is formed by the coracoid process, acromion, and coraco-acromial ligament. It is separated from the shoulder joint by subacromial bursa and tendons of supraspinatus, infraspinatus and subscapularis. It overhangs and protects the shoulder joint

14. 2. Supraspinatus
Origin: from the medial two-thirds of the supraspinous fossa
Insertion: fibres converge into a tendon which crosses above the shoulder joint and is attached to the highest facet of the greater tuberosity of the humerus.
Nerve supply: suprascapular nerve, C5 and 6.
Action: 1. initiates abduction of the arm from 0 to 15 degrees
2. it helps to stabilize the head of the humerus in the glenoid fossa during shoulder movements as one of the rotator cuff muscles.

15. 3. Infraspinatus Origin: from the medial two-thirds of the fossa
Insertion: Its fibres converge to a tendon which passes behind the shoulder joint to be attached to the middle facet on greater tuberosity of humerus.
Nerve supply: suprascapular nerve, C5 and 6.
Action:
1. lateral rotator of the arm.
2. it helps to stabilize the head of the humerus in the glenoid fossa during shoulder movements as one of the rotator cuff muscles.
N.B. rotator cuff muscles are: supraspinatus, infraspinatus, subscapularis and teres minor

16. 4. Teres minor 5. Teres major
Origin: from the upper two-thirds of a flattened strip on posterior surface of scapula adjoining its lateral border,
Insertion: to the lowest facet of the greater tuberosity of the humerus.
Nerve supply: Axillary nerve (C5, C6)
Action: Laterally rotate the arm
5. Teres major
Origin: from the lower third of a strip on the posterior surface of the scapula adjoining its lateral border
Insertion: to the medial lip of the intertubercular sulcus of the humerus.
Nerve supply: Lower subscapular nerve (C5, C6)
Action: Adducts and medially rotates the arm

18. 6. Subscapularis
Origin: from medial two thirds of the subscapular fossa of the scapula
Insertion: into the lesser tubercle of humerus
Nerve supply: Upper and lower subscapular nerves (C5, C6)
Action: Medially rotates and adduct arm and helps hold humeral head in glenoid cavity
Subscapular bursa:
it is prolongation of the synovial membrane of shoulder joint through a gap in the upper anterior part of capsule.
It extends between subscapularis muscle and the medial part of the capsule, front of the neck of scapula and root of coracoid process.
facilitates movement of subscapularis over these parts.

20. I- Quadrangular space:
Intermuscular Spaces
I- Quadrangular space:
1. Boundaries: as follows:
Above: the subscapularis and capsule of the shoulder joint,
Below: the teres major muscle,
Medially: the long head of the triceps and
Laterally: the surgical neck of the humerus.
2. Contents: The axillary nerve and the posterior circumflex humeral vessels pass backward through this space.

21. II- The upper triangular space:
1. Boundaries: as follows:
above by subscapularis anteriorly, teres minor posteriorly,
below by teres major, and
laterally by the long head of triceps.
2. Contents: The circumflex scapular artery

22. III- The lower triangular space:
1. Boundaries:
above by subscapularis anteriorly and teres major posteriorly
medially by the long head of triceps
laterally by the humerus.
2. Contents: The radial nerve and the profunda brachii vessels

24. The suprascapular nerve:
Beginning: from the upper trunk of the brachial plexus (C5 and 6) in the posterior triangle in the neck.
Course: It runs downward and laterally and passes beneath the suprascapular ligament, which bridges the suprascapular notch, to reach the supraspinous fossa.
Distribution: It supplies the supraspinatus and infraspinatus muscles and the shoulder joint.

25. Axillary Nerve
Beginning: The axillary nerve arises from the posterior cord of the brachial plexus (C5 and 6) in the axilla.
Course: It passes backward and enters the quadrangular space with the posterior circumflex humeral artery. it comes into close relationship with the surgical neck of the humerus. It terminates by dividing into anterior and posterior branches
Branches
1. An articular branch to the shoulder joint
2. An anterior terminal branch supplies the deltoid and the skin that covers its lower part.
3. A posterior terminal branch, which gives off a branch to the teres minor muscle and a few branches to the deltoid, then emerges from the posterior border of the deltoid as the upper lateral cutaneous nerve of the arm

26. Diagram of circumflex arteries and axillary nerve
Axillary artery
Anterior circumflex humeral artery
Posterior circumflex humeral artery
Axillary nerve
Articular branch
T.S. of humerus
Branch to teres minor
Cutaneous branches

27. Anastomosis around the scapula
Three arteries share in the anastomosis:
Deep branch of transverse cervical artery: arises from thyrocervical trunk from the first part of subclavian artery. It descends along the medial border of scapula and gives branches to both surfaces of scapula
Suprascapular artery: arises from the thyrocervical trunk that originates from the first part of subclavian artery. It passes over suprascapular ligament giving branches to supraspinatus, then it descends through the spinoglenoid notch to end by ramifying in infraspinatus
Subscapular artery arises from the 3rd part of axillary artery. It descends along the lower border of subscapularis giving branches as the circumflex scapular artery which anastomosis with the branches of the previous arteries
This anastomosis is important as if a ligature is applied to the artery between the 1st part of subclavian and 3rd part of axillary, collaterals of anastomosis open and establish sufficient arterial supply for the upper limb.