Begin this journey with the cadaver face-up, or in a supine position. By reflecting the skin of the anterior thoracic wall, you can see the thickness of the superficial fascia. You should also be able to see the extent of the pectoralis major. Examine its attachments. This muscle forms the anterior wall of the armpit or axilla. Note the anterior head of the deltoid. Its distal attachment is very close to the distal attachment of the pectoralis major.

Reflect the pectoralis major laterally and find the pectoralis minor. You will probably see the medial pectoral nerve coursing through the pectoralis minor on its way to the pectoralis major. You should also be able to see the lateral pectoral nerve on the pectoralis minor's medial edge (without passing through the pectoralis minor) heading directly to the pectoralis major.

Question: Why are these two nerves seemingly backwards in relationship to their names?

Hint: The nerves are named for their origin, from the brachial plexus.

If you look on the lateral side of the thoracic wall, you'll see the saw-like border of the serratus anterior muscle. You won't be able to see its scapular attachment until we turn the cadaver over into the prone position.

Running perpendicular to the fiber direction of the serratus anterior, about at the mid-axillary line, you should be able to identify the motor nerve supply to the serratus, the long thoracic nerve.

With the upper extremity abducted, find the more posteriorly placed latissimus dorsi. This muscle forms the posterior wall of the axilla or armpit.

If you hold the latissimus away from the thoracic wall, you should be able to see its motor nerve supply, the thoracodorsal nerve. Even though we have not identified the teres major from a posterior approach, see if you can find this muscle from an anterior approach. Identify its motor nerve supply, the lower subscapular nerve.

If you look deep and posterior in the axilla, medial to the teres major, you should be able to see the subscapularis and its motor nerve supply the upper subscapular nerve.

Turn the cadaver face-down, into a prone position so you can find the posterior muscles and nerves of the shoulder. Figure 10-1.

First, on the inferior part of the back, identify the broad superficial latissimus dorsi muscle. If this muscle has been cut, reflect it superior and laterally and see if you can find its motor nerve supply, the thoracodorsal nerve.

Near the superior border of the latissimus you should be able to see the teres major muscle.

Now if you move your observation to the superior aspect of the back, we can see the bilateral trapezoid shaped trapezius. Note its extensive vertebral and scapular attachments.

Reflect the muscle superior and lateral. On the back side of this muscle, running in a longitudinal direction, you should be able to see the motor nerve supply to the trapezius, cranial nerve XI or the spinal accessory nerve.

Deep to the trapezius, observe the two horizontal bilateral rhomboid muscles. The rhomboid major lies inferior to the smaller rhomboid minor.

Slightly superior and lateral to the rhomboids, arising from the superior scapular angle, we can see the levator scapulae. Looking deep to both of these muscles, and with a little luck, you can now identify the motor nerve supply to both of these muscles, the dorsal scapular nerve.

If you reflect the rhomboids and gently lift the scapula up, you can see or feel the serratus anterior. It runs from the medial border of the scapula laterally towards its insertion on the upper eight ribs.

Let's now focus on the shoulder itself. Clearly visible and coming off the acromion process is the middle head of the deltoid.

Moving more posterior, observe the posterior head of the deltoid as it arises from the inferior edge of the scapular spine. This muscle should be detached from its scapular origin and reflected laterally.

Now you should be able to see the axillary nerve as it enters the deep surface of this muscle. With this muscle reflected you can also see the posterior three "rotator" cuff muscles. Starting superiorly and moving inferior from the lateral edge of the shoulder, observe the supraspinatus, infraspinatus and the teres minor. Note how all three of these muscles insert on the greater tubercle of the humerus.

Laterally reflect the cut outside half of the supraspinatus. Observe the motor nerve supply to the supra and infraspinatus, the suprascapular nerve, as it courses through the suprascapular notch.

Once again identify the teres major, inferior and medial to the teres minor and superior to the latissimus dorsi.