Prelab Images - Axilla, Posterior Shoulder, & Arm

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Review the bony landmarks. (Play movie)

Plates N420 or TG2-03 and N421 or TG2-03 feature the scapula and have the acromion process, spine of scapula, supraspinatus and infraspinatus fossae, the borders, and the angles of the scapula labeled. The scapular notch is labeled as the suprascapular notch in plates N420 or TG2-03 and N421 or TG2-03. The clavicle is shown in plate N419. The head, neck (surgical and anatomical), bicipital groove (intertubercular sulcus), deltoid tuberosity, greater and lesser tubercles (and their crests), and the medial and lateral epicondyles are all parts of the humerus that can be seen in plate N420 or TG2-03. The radial groove of the humerus is in plate N421 or TG2-03. Plates N436 and N439 or TG2-04 show the olecranon, coronoid, and styloid processes of the ulna and the head, neck, tuberosity, and styloid process of the radius.

Step 2. With the arm abducted, remove the fat and lymph nodes from the axilla. (Play movie)

Plates N189 or TG4-08 and N184 or TG2-11 show the axillary vein. The axillary artery and its branches that will be dissected today are seen in N427 or TG2-15 and N429 or TG2-15. The brachial plexus is seen in N429 or TG2-15 and N430 or TG2-14. The lymph nodes of the mammary gland and upper limb can be reviewed in plate N184 or TG2-11. The pectoralis major can be seen forming the anterior axillary fold in plates N424 or TG2-12 and N181 or TG4-02 and the teres major and latissimus dorsi form the posterior axillary fold in plates N424 or TG2-07 and N181.

Step 3. Cut and remove the middle third of the clavicle. Cut the axillary vein lateral to its junction with cephalic vein and remove axillary vein and tributaries. (Play movie)

Plate N429 or TG2-15 shows the middle third of the clavicle removed and the axillary vein removed like you will need to do in lab (at this point in lab you will likely not be able to identify many of the features in this plate because they will be encased in fascia and covered by fat). Plates N32 or TG7-14 and TG7-15, N33, TG7-15 and N429 or TG2-15 show the brachial plexus emerging from between the anterior and middle scalene muscles (you may not be able to trace the brachial plexus this far back towards the spinal cord during lab). Plate N184 or TG2-53 shows the formation of the axillary vein from the brachial vein and basilic vein. The cross section on N435 shows these veins approaching each other, but does not show them uniting to form the axillary vein.

Step 4. Separate all brachial plexus nerves and axillary artery branches. (Play movie)

Plates N429 or TG2-15 and N430 or TG2-14 show the brachial plexus and branches you need to identify. The lateral pectoral nerve was identified in a previous lab and is fairly easy to trace back to the lateral cord. The musculocutaneous nerve and contribution of the lateral cord to the median nerve can be seen in plates N430, N473 and N474 or TG2-14 and TG2-15. Plate N474 or TG2-47TG2-17A,  and TG2-17B show the muscles innervated by the musculocutaneous nerve. The medial pectoral nerve can be traced from pectoralis minor to the medial cord (plate N429 or TG2-15). Moving distally on the medial cord you can identify the medial brachial cutaneous nerve (referred to as the medial cutaneous nerve of the arm), the medial antebrachial cutaneous nerve, the contribution to the median nerve from the medial cord, and the ulnar nerve (plate N430). Plates N475 and N476 follow the course of the median and ulnar nerves through the arm and show the muscles innervated by these nerves. Plate N429 or TG2-14 shows the axillary artery covering the posterior cord of the brachial plexus. The axillary nerve can be seen branching from the posterior cord (plate N430), traveling with the posterior circumflex humeral artery (plate N429 or TG2-14), and then projecting posteriorly through the quadrangular space to innervate teres minor and deltoid muscles (plate N443 or TG2-18) and the lateral skin of the arm (plate N481 or TG2-51). The radial nerve will emerge from the posterior cord (N430), and run in the radial groove on the posterior side of the humerus (N429 or TG2-20, N435). Plates N477 and N478 or TG2-50A follow the course of the radial nerve in the arm and forearm and identify the muscles innervated by the radial nerve. The upper subscapular nerve goes from the posterior cord of the brachial plexus (N430) to innervate the subscapularis muscle (N429 or TG2-15). The thoracodorsal nerve (middle subscapular) proceeds from the posterior cord of the brachial plexus to join the thoracodorsal artery (N427 or TG2-15, N426) and supply the latissimus dorsi (N426, N429 or TG2-07). The lower subscapular nerve exits the posterior cord of the brachial plexus (N447), runs briefly with the circumflex scapular artery (N447, N443 or TG2-08) and then proceeds to innervate teres major and subscapularis muscles (N440, N443 or TG2-08). Plate N189 or TG4-07 shows the tendon of pectoralis minor laying over the second part of the axillary artery (labeled 2 in plate N427 or TG2-15). Plate N429 or TG2-14 shows the relation of the cords to the axillary artery. Try to trace the brachial plexus as far back towards the scalene muscles of the neck as you can (as seen in plate N429 or TG2-15A). Plate N427 or TG2-15B shows a simplified schematic of the branches of the axillary artery and plate N429 or TG2-15A shows the branches of the axillary artery more similarly to the way you will see it in lab. The subscapularis muscle is shown in plate N426. Serratus anterior and the long thoracic nerve are seen in plate N185. The long thoracic nerve can also be seen in plates N429 or TG2-15 and N430. The lateral cutaneous branches of the intercostal nerves and the intercostobrachial nerve (T2) can be seen in plate N189 or TG4-08. The intercostobrachial nerve can often be confused with the medial brachial cutaneous nerve. The intercostobrachial nerve is also seen in plate N429 and its cutaneous distribution is shown in plate N481 or TG2-51.

 

Step 5. Review teres minor & major musculature

Review triangular and quadrangular spaces


Step 6. Open the arm compartments. (Play movie)

The medial and lateral intermuscular septa can be seen in plate N435. These septa divide the arm into anterior, posterior, and neurovascular components, which can be identified in plate N435 as well. Plate N420 or TG2-06 shows the insertion of the coracobrachialis and deltoid on the humerus. The intermuscular septae can also be seen in plate N429, but are not labeled. The biceps brachii and its long head, short head, and the bicipital aponeurosis can be seen in plate N431 or TG2-17 and the biceps insertion on radial tuberosity can be seen in N431 or TG2-17. The coracobrachialis can be seen in plates N431 or TG2-17 and N474. The brachialis muscle can be seen in plates N431 or TG2-17 and 473 or TG2-47. The musculocutaneous nerve can be seen innervating the biceps, brachialis, and coracobrachialis muscles in plate N474 or TG2-47. Plates N429 or TG2-17 and N435 show the brachial artery, brachial veins, and median nerve in the neurovascular compartment of the arm. Plates N473 or TG2-48, TG2-49, and TG2-50 and N475 trace the median nerve into the cubital fossa. Plates N473 or TG2-48, TG2-49, and TG2-50 and N476 show the course of the ulnar nerve in the arm and forearm. Plate N435 shows the ulnar nerve drifting away from the neurovascular compartment as it approaches the medial epicondyle. The medial antebrachial cutaneous nerve (of the forearm) can be seen moving superficially in plate N435 and emerging from the deep investing fascia to innervate the skin in plates N479 or TG2-02 and 480. The radial nerve can be seen in plate N426 on the tendon of latissimus dorsi just before it enters the radial groove of the humerus. Trace the radial nerve to the back of the humerus (N477 or TG2-50) and while doing so try to make the radial nerve identifiable from the posterior side of the cadaver because later in this lab you will need to flip the cadaver over to further trace the radial nerve. The brachial veins are labeled in plates N429 or TG2-53 and N435 and are seen joining the basilic vein in plate N184 (unlabeled). Plate N434 or TG2-19 shows a good schematic of the brachial artery in the arm. Plates N431 or TG2-17 and N433 or TG2-17 show the brachial artery and median nerve passing through the cubital fossa. The brachial artery is seen dividing in plate N434 or TG2-19 and the median nerve is seen continuing into the forearm in plates N473 or TG2-48 and N475. Plate N477 (TG2-50 may also help) shows the radial nerve in between the brachialis and brachioradialis muscles near the cubital fossa where you need to find it. Plate N479 or TG2-02 shows the median cubital vein in the superficial fascia overlying the cubital fossa. Plates N420 or TG2-06 and N421 or TG2-06 show the origin and insertion of the arm muscles discussed in step 4.

Step 7. Cut the lateral head of the triceps obliquely in the direction of the radial groove to expose the radial nerve and deep brachial artery. (Play movie)

First, try to locate the radial nerve by searching between the long and lateral head of the triceps, inferior to the quadrangular space (plate N432 or TG2-18). Take care not to damage the nerve during this step. Plate N432 or TG2-18 identifies the long, lateral and medial heads of the triceps muscle. Insert a probe between the triceps and the radial nerve and cut through the triceps while using the probe to protect the nerve. The cut should follow the radial groove (N421 or TG2-03) and the result will look similar to plate N432 or TG2-18 (bottom picture). Branches of the radial nerve in the arm can be seen in plates N432 or TG2-18 and N477 or TG2-50. Plate N473 or TG2-24 shows the radial nerve appearing anteriorly. Plates N477 and N478 or TG2-50 show the radial nerve and all of its braches in the arm and forearm. The deep brachial artery is shown coming from the brachial artery in plate N434 or TG2-19 and running with the radial nerve in plate N432 or TG2-18. Plate N421 or TG2-06 shows the origins and insertion of the triceps brachii. Plates N432 or TG2-18, N473 or TG2-49, and N476 or TG2-30 illustrate the ulnar nerve running behind the medial epicondyle. Plates N432 or TG2-18 and N434 or TG2-50 label the anconeus muscle. Finally, plate N444 or TG2-19 shows that the superior ulnar collateral artery runs with the ulnar nerve in the arm.

 

Updated: 24 Oct 2011