Remove the skin of the upper limb down to the elbow.
Note the major cutaneous veins imbedded in the superficial fascia.
Locate the cephalic vein running between the pectoralis major and deltoid muscles.
On the medial arm, find the basilic vein.
Look in the cubital fossa for the median cubital vein.
Trace its connections with the cephalic and basilic veins.
Clean the superficial fascia away. Note how tough the deep fascia is here, and how it passes between major muscle groups to attach to the limb bones forming the intermuscular septa.
2. PECTORAL GROUP
Put the reflected pectoralis major muscle back in placeand note its origins.
Reflect it again and study the underlying pectoralis minor muscle.
Locate pectoralis minor's attachment to the coracoid process.
Find the pectoralis major crossing the long biceps tendon to insert on the lateral lip of the intertubercular groove.
Clean the pectoralis major tendon of insertion.
Between pectoralis major and minor you will find branches of the lateral and medial pectoral nerves (from the lateral and medial cords of the brachial plexus). Usually, the medial pectoral nerve supplies both pectoral muscles, while the lateral supplies only pectoralis major. You will also find branches of the thoracoacromial artery, a branch of the axillary artery that ramifies between the two pectoral muscles, sending branches to them and to the deltoids.
NOTE – the medial and lateral pectoral nerves are named for the cords of the brachial plexus that they are branching off of, not for their position in the body. Often, you will find the medial pectoral nerve in a more lateral position than the lateral pectoral nerve.
3. THE AXILLA
The fascia in the armpit, or axilla, is thick and extensive, and contains several important groups of lymph nodes clustered around the deep and superficial veins. Vessels and nerves of the forelimb pierce the cervical body wall layers as they cross the first rib, and draw out a fascial prolongation known as the axillary sheath. The lateral thoracic branch of the axillary artery runs down the rib cage near the origins of these lateral cutaneous nerves; its branches help to supply the breast.
Clear away the superficial fascia, superficial veins and lymph nodes, and cutaneous nerves, exposing the axillary sheath.
Open the sheath and identify the axillary artery and vein.
Sever the axillary vein below the subclavius muscle; reflect it together with its branches, and discard it.
Once the subclavian artery passes the first rib, it is renamed the axillary artery. The axillary artery gives rise to the following branches: superior thoracic, thoracoacromial, lateral thoracic, anterior and posterior humeral circumflex, and subscapular.
Remove part of the clavicle by making two cuts. The first cut with the saw is just medial to the trapezius insertion. The second cut is just lateral to the sternoclavicular joint.
Remove the middle piece of the clavicle together with the subclavius muscle, thus exposing the axillary artery and the trunks of the brachial plexus.
4. AXILLARY ARTERY
Note that the subclavian, axillary, and brachial artieries are all names for the same continuous structure. When the subclavian artery passes the lateral margin of the first rib, it is renamed the axillary artery. When the axillary artery passes the inferior border of teres major, it is renamed the brachial artery.
The first part of the axillary artery, running from the first rib to pectoralis minor, contains one branch, the superior thoracic artery.
The second part of the axillary artery, running behind pectoralis minor, contains two branches. The more medial branch is the thoracoacromial trunk. Find that branch near the lateral pectoral nerve. The lateral thoracic artery runs behind and lateral to pectoralis minor.
The third part of the axillary artery, lateral to pectoralis minor, contains three branches - the anterior and posterior humeral circumflex and the subscapular artery.
5. BRACHIAL PLEXUS
Identify the three cords of the brachial plexus, and confirm that all three posterior divisions join to form the posterior cord.
Trace the following branches of the anterior division:
musculocutaneous nerve as it runs into coracobrachialis
ulnar nerve as it runs along the medial side of the arm and forearm
median nerve as it runs down the middle of the arm and forearm
Identify the radial nerve running posterior to the axillary artery.
From the posterior cord find the axillary nerve and the nerves to the latissimus group (upper subscapular, thoracodorsal, and lower subscapular nerves).
6. FLEXORS OF THE ARM
Anatomically the word “arm” is restricted to the upper limb between the shoulder and elbow. There are only four muscles in the arm: one in the extensor compartment, the triceps brachii, and three in the flexor compartment, the biceps brachii, coracobrachialis, and brachialis.
Separate the three flexors, biceps brachii, coracobrachialis, and brachialis and compare their origins.
Locate the musculocutaneous nerve where it originates from the brachial plexus and follow it distally into the coracobrachialis muscle.
Expose the tendon of the long head of the biceps in the intertubercular groove, noting its synovial sheath. The origin itself from the supraglenoid tubercle will be seen when the shoulder joint is dissected.
Follow the path of the short head of the biceps to the coracoid process.
Pull up the biceps brachii muscle to reveal some of the muscular branches of the musculocutaneous nerve. If possible, locate its emerging cutaneous portion (the lateral cutaneous nerve of the forearm) above the elbow on the lateral surface of the arm.
With the biceps brachii pulled up, observe the deeper brachialis muscle.
The insertions of both biceps brachii and brachialis cannot be seen until some dissection has been done in the forearm.
The musculocutaneous nerve innervates biceps brachii, coracobrachialis, and brachialis and ends in a cutaneous nerve - hence its name.
Follow the brachial artery into the flexor compartment of the arm.
Locate the profundabrachii (deep artery of the arm) and collateralbranches of this artery.
NOTE - Sometimes the brachial artery divides into radial and ulnar arteries within the flexor compartment of the arm. More commonly, this division occurs in the forearm.
The profunda brachii artery passes back to supply the posterior (extensor) compartment of the arm and joins the radial nerve to run along the spiral groove of the humerus. The profunda brachii artery ends in a couple of radial collateral arteries.
7. LATISSIMUS GROUP
Follow the latissimusdorsi from its broad origin on the back to its narrow tendon of insertion on the floor of the intertubercular groove of the humerus (deep to the pectoralis major).
You will find the tendon of teres major inserting on the medial lip of the intertubercular groove of the humerus.
Locate the subscapularis muscle originating from the ventral surface of the scapula.
Follow subscapularis to its insertion on the lesser tubercle of the humerus proximal to latissimus dorsi and teres major.
You will also be able to examine the triceps brachii running from the humerus and scapula to the olecranon process of the dorsal elbow. An important opening called the quadrangular space is formed by the inferior margin of the teres minor, the shaft of the humerus, the superior margin of teres major and the lateral margin of the long head of the triceps. The axillary nerve and posterior humeral circumflex artery pass through this space. Just below the quadrangular space sits the triangular interval formed by the inferior margin of the teres major, the humerus, and the long head of triceps. The radial nerve and deep brachial artery pass through this interval. Nerves and vessels can be injured in these spaces.
8. DELTOID GROUP
The motor nerve for the deltoid group is the axillary nerve; one of the two terminal branches of the posterior cord of the brachial plexus.
Turn your cadaver over so that it is prone and you can work on the back of the shoulder.
Place your thumb on your clavicle, wrapping the palm of your hand around the ball of your shoulder, and put your fingers on the spine of your scapula -- you have delineated the origins of the deltoid muscle.
Carefully transect the deltoid along its origins on the cadaver so that you can expose the axillary nerve.
Underneath the deltoid muscle, note the bursa that lubricates the motion of the deltoid over the humerus and supraspinatus muscle.
Follow the axillary nerve around the back of the neck of the humerus as it passes through the quadrangular space.
Locate the teres minor muscle stretching from the scapula to the greater tubercle of the humerus. Like the deltoid, the teres minor is innervated by the axillary nerve.
Find the posterior humeral circumflex artery accompanying the axillary nerve. It is the major artery to the deltoid.
Try to find its anastomosis with the anterior humeral circumflex artery. Both anterior and posterior humeral circumflex arteries are branches of the axillary artery.
The deltoid is the most powerful abductor of the humerus. It works against a great mechanical disadvantage; you might compare it to attempting to move a door by pulling on a doorknob affixed near the hinges. Its power is augmented by its multipennatestructure, which permits the maximum number of fibers to pull on a given insertion.
9. ROTATOR CUFF
Three short muscles - supraspinatus, infraspinatus and teres minor - originate from the dorsal surface of the scapula and run laterally to insert on the greater tubercle of the humerus. Teres minor is a member of the deltoid group, and receives its innervation via the axillary nerve. Supraspinatus and infraspinatus are innervated by the suprascapular nerve. The fourth rotator cuff muscle, subscapularis, runs from the ventral surface of the scapula to the lesser tubercle of the humerus. Subscapularis is innervated by the upper and lower subscapular nerves. These four muscles form a muscular cuff around the head of the humerus. They act to rotate the humerus in various directions, stabilize the joint and prevent dislocation of the shoulder joint under tension.
You have already examined subscapularis and teresminor. When you reflected the deltoid, you exposed the insertions of supraspinatus, infraspinatus and teres minor, on the posterior surface of the greater tuberosity.
Underneath the deltoid, locate the posterior aspect of greater tubercle of the humerus. The muscles attach here. The most inferior insertion is that of teres minor. The one above teres minor is infraspinatus, and the most superior is supraspinatus.
Trace supraspinatus from its insertion, then under the coracoacromial arch , and back to its origin in the supraspinatus fossa of the scapula.
Verify that it is directly in contact with the loose fibrous capsule of the joint, and partly fuses with it.
While the deltoid is a very powerful abductor of the humerus, the supraspinatus is needed to overcome the initial mechanical disadvantage that the deltoid suffers at the beginning of this motion.
Follow infraspinatus back to its origin on the scapula. It adjoins teres minor, which it assists in rotating the humerus laterally
Two parallel vessels, the transverse cervical and suprascapular arteries, supply the dorsal aspect of the scapula.
Locate the origins of the suprascapular and transverse cervical arteries from the thyrocervical trunk of the subclavian artery.
Follow them as they run back over the shoulder.
Find the branches of the transverse cervical artery to the rhomboids and levator scapulae muscles.
Trace the suprascapularartery to the supraspinatus and infraspinatus muscles.
The transverse cervical, suprascapular, and subscapular arteries anastomose freely around the scapula. This chain of anastomoses can supply blood to the limb if the axillary artery is occluded distal to their origins.
10. EXTENSORS OF THE ARM
The extensor compartment of the arm contains only one major muscle, triceps brachii, along with a small slip of the triceps muscle called anconeus. Do not worry about anconeus in your dissection. The RADIAL nerve providesthe innervation to ALL the muscles in this compartment.
Identify the three origins of triceps brachii.
Note that the radial and axillarynerves enter the extensor compartment around lower and upper edges of teres major, respectively.
Trace the radial nerve (motor to triceps and all the distal extensors in the forelimb) and profunda brachii artery along the spiral groove between lateral and medial heads of triceps.
Transect and reflect the lateral head of the triceps as you follow the underlying structures.
The superficial veins of the arm are large and prominent thus they are commonly used to draw blood or inject a solution. The median cubital vein in the cubital fossa is the most commonly used. Due to the close positions of the brachial artery and medial nerve care most be taken when accessing this vein.
2. Axillary nerve injuries
Due to the proximity of the axillary nerve to the surgical neck and head of the humerus it can be damaged in both fractures of the surgical neck and inferior dislocations of the glenohumeral joint. Injury to the axillary nerve impairs the deltoid and teres minor muscles and sensory innervation to the upper lateral portion of the arm. To test deltoid function the arm is abducted against resistance starting from a position of ~ 15 degrees of abduction.