Pectoral Region

On the skeleton provided note the following bony landmarks and then palpate the corresponding points on the cadaver:
 

1. the sternum 

2. the suprasternal notch

3. the infrasternal notch

4. the xiphoid process of the sternum

5. the sternal angle (of Louis)

The sternal angle is formed by the junction of the manubrium and body of the sternum. This site is the location of the attachment of the costal cartilages of the second pair of ribs.

Identify the (6) clavicle on the skeleton, and palpate it on the cadaver. Note that it extends from the suprasternal notch to the tip of the shoulder. The tip of the shoulder is formed by the (7)acromion process of the scapula.

Become familiar with the following lines of reference used to delineate the surface anatomy of the pectoral and axillary region:

1. mid-sternal line

2. mid-clavicular line

3. anterior axillary line

4. posterior axillary line

5. mid-axillary line

Identify the anterior axillary fold and the posterior axillary fold. The anterior axillary fold is formed by the underlying pectoral muscles; the posterior axillary fold is formed by the latissimus dorsi muscle.

Reflection of skin

1. Make a mid-sternal incision from the suprasternal notch to the infrasternal angle.

2. Make another incision from the suprasternal notch along the clavicle to the tip of the shoulder. Later in the dissection you can extend this incision down the arm to a point just above the elbow.

3. Make an incision from the infrasternal notch as far laterally as the mid-axillary line. Now reflect the flap of skin outlined by the incisions 1, 2 and 3.

Remove the breast along with the flap of skin.

Cutaneous nerves and blood vessels emerging near the sternum will not be dissected. However, ask your instructor about the origin of the anterior cutaneous nerves . The perforating arterial branches originate from the internal thoracic artery, an artery to be dissected in a subsequent dissection.

Dissection of the Pectoral Region

Identify the pectoralis major muscle. The thin fascia which covers the muscle is, as you may have guessed, named the pectoral fascia. The pectoralis major originates from the sternum, the costal cartilages of the first seven ribs and from the medial part of the clavicle.

Note that the muscle has a dual origin (Netter, 399), a (1) sternocostal head and a (2)clavicular head. Also note the manner in which the tendon of the muscle twists as it passes to its insertion into the humerus.

Delineate the deltopectoral groove and expose the cephalic vein within the groove (4) between the deltoid muscle and (3) the pectoral muscle.

Clean the pectoralis major, divide it in the middle and reflect the two halves medially and laterally. (7) You have now uncovered the pectoralis minor muscle(8) (Netter, 403).

Between the clavicle and the pectoralis minor muscle identify the thin clavipectoral fascia. This fascia attaches to the clavicle, invests the small subclavius muscle, splits to invest the pectoralis minor, and then continues, to blend with the axillary fascia (Netter, 403). The clavipectoral fascia between the pectoralis minor and the clavicle is pierced by the cephalic vein, the thoracoacromial artery and vein, and the lateral pectoral nerve.

Note that the pectoralis minor muscle is a key structure in the axillary region. The axillary artery is divided into three parts with respect to the pectoralis minor muscle. From the first part, proximal to the muscle arises one blood vessel, the supreme thoracic artery, a small artery which supplies the first one or two intercostal spaces. From the second part of the axillary artery, deep to the pectoralis minor muscle, arise two arteries, the thoracoacromial trunk and the lateral thoracic arteries (Netter, 402a). The third portion of the axillary artery, distal to pectoralis minor, gives rise to the subscapular artery and the anterior and posterior humeral circumflex arteries.

Identify the serratus anterior muscle and its motor nerve, the long thoracic nerve (Netter, 404). Note the digitations of the serratus anterior muscle.

You may be able to identify the intercostobrachial nerve emerging from the second intercostal space. It is a cutaneous nerve. If it is not immediately obvious, do not spend all day looking for it.

Review Questions 

1. What is the angle of Louis?

2. What ribs articulate at the sternal angle?

3. What reference line lies vertically mid-way between the anterior and posterior axillary folds?

4. What nerves enter the superficial fascia at the mid-axillary line?

5. What nerves enter the superficial fascia at the lateral borders of the sternum?

6. What name is given to ventral primary rami which pass between the ribs from the intervertebral foramina to the sternum?

7. What is the function of the intercostal nerves in addition to giving origin to cutaneous nerves?

8. What vessels accompany the intercostal nerves?

9. What is the usual position of the nipple with respect to the thoracic wall?

10. What are the boundaries of the deltopectoral triangle.

11. What structure lies within the deltopectoral groove?

12. What fascia covers the pectoralis major?

13. What fascia passes from the clavicle to invest the pectoralis minor?

14. Why is the lateral pectoral nerve so named, when it appears to lie medial to the medial pectoral nerve?

15. What is the blood supply to the pectoral muscles?

16. What structures pierce the clavipectoral fascia?

17. What are the anatomical sites to which lymph from the breast may flow?

18. What is the axillary tail of the breast? Why is this important to know?

Answers: 

1. The sternal angle; formed by the junction of the manubrium and body of the sternum.

2. The second pair of ribs, by their costal cartilages.

3. Mid-axillary line.

4. The lateral cutaneous branches of the ventral primary rami.

5. The anterior cutaneous branches of the ventral primary rami.

6. Intercostal nerves

7. They innervate the intercostal muscles

8. The intercostal arteries and veins. Most of these arteries come from the aorta.

9. In the fourth intercostal space

10. Medial border of deltoid, lateral border of pectoralis major, and the inferior border of the clavicle

11. Cephalic vein

12. Pectoral fascia

13. Clavipectoral fascia

14. The lateral pectoral nerve is so named because it arises from the lateral cord of the brachial plexus; it is not named according to its position.

15. Pectoral branches of the thoracoacromial trunk.

16. Cephalic vein, thoracoacromial artery and vein, pectoral nerves

17. To axillary nodes along the internal thoracic artery, to lymphatics of the opposite breast, and even to abdominal viscera

18. The axillary tail is the normal breast tissue which extends into the axilla. This tissue can be mistaken for a tumor