Lab Manual - Pectoral Region, Posterior Shoulder & Breast
Upon completion of this session, the student will be able to:
- Describe the general gross features of the breast and its blood supply. (explanation)
- Describe the lymphatic drainage of the breast. (explanation)
- Identify the muscles of the pectoral region, their related fascia, nerve and regional blood supply, and general functions. (explanation)
- Describe the general features of the circulatory system. (explanation)
- Identify the posterior shoulder muscles and associated rotator cuff muscles. Give their general functions and nerve supply.
- Identify and demonstrate the regional blood supply of the posterior shoulder.
Readings and Modules:
- Prelab Learning Module and Prelab Images
- Moore's Clinically Oriented Anatomy: p. 98-106; 697-698; 704-712
1. Review the bony landmarks. (Play movie; View images: N 185, 419, 420, 421, TG 2-03A, 2-03B, 4-04)
Locate the following structures on the skeleton: crest of greater tubercle of the humerus; clavicle, suprasternal (jugular) notch, manubrium, sternal angle, body and xiphoid process of the sternum, coracoid process of the scapula.
Scapula and clavicle
2. Remove the skin from the chest wall as in Figure 2. (Play movie; View images: N 180, 182, 183, 184, 188, 189, 192, 257, 420, 427, 429, 430, TG 1-17, 2-10A, 2-10B, 2-11A, 2-11B, 2-12, 2-13, 2-15A, 2-15B, 4-02, 4-07, 4-11)
Remove the skin and subcutaneous tissue over the pectoral and anterior deltoid regions, down to about mid-brachium (Fig. 2).
The uppermost incision should directly overlie the clavicle. Make an encircling cut around the nipple and areola in the male, leaving them in place for future reference. Along the lateral margin of the sternum, identify anterior cutaneous branches of intercostal nerves. As you approach the anterior axillary line, use blunt dissection to find examples of lateral cutaneous branches of intercostal nerves in the superficial fascia running parallel to the ribs. Where do their anterior and posterior branches distribute? Identify several anterior branches of these nerves as they emerge along the anterior axillary line through the serratus anterior muscle. Observe serratus anterior arising from the anterolateral rib cage and passing backward to insert onto the vertebral border of the scapula.
Mammary gland. Incise through the nipple and areola with horizontal and vertical incisions. Is any pinkish glandular tissue visible? Normally no glandular elements are visible in the male. In the female, examine cut surfaces for lactiferous ducts and sinuses. Try to define a lobe. What are suspensory ligaments? Note attachments and location. Because of age and non-lactating condition of the gland, atrophy may be present and the internal structure hard to discern. It should be understood that in regard to female cadavers, nearly all of them, if not all, are elderly and postmenopausal and consequently many female structures influenced by female hormones will be difficult to demonstrate or identify throughout the body. Consider blood supply, nerve supply and lymphatic drainage. Note the position of the nipple in reference to the intercostal spaces.
Mammogram Breast cancer
3. Identify and reflect the pectoralis major muscle and identify its blood and nerve supply. (Play movie; View images: N 184, 188, 189, 420, 424, 427, 428, 429, 430, TG 2-12A, 2-12B, 2-13, 2-15A, 2-15B)
Clean the pectoralis major muscle and reflect it from its origins on the sternum and clavicle. (Caution: Do not cut deeply across the clavicular attachment in order to preserve the underlying nerves and vessels). Note pectoral (anterior axillary) lymph nodes deep to the lateral border of pectoralis major. Find the cephalic vein between adjacent borders of those muscles in the deltopectoral groove (or triangle). Follow the muscles to their insertions. Use blunt dissection to locate and identify the lateral pectoral nerve, medial pectoral nerve, pectoral branches of the thoracoacromial artery and vein as you clean. Why are lateral pectoral and medial pectoral nerves reversed from what you would expect?
Identify pectoralis minor muscle. Review its origin, course and insertion. Review the clavipectoral fascia.
Trace the lateral pectoral nerve, medial pectoral nerve, and branches of the thoracoacromial artery. Now trace the terminal part of the cephalic vein to the clavipectoral fascia. Where does the cephalic vein terminate?
4. Identify and reflect the pectoralis minor muscle, identify its blood and nerve supply and clavipectoral fascia. (Play movie; View images: N 184, 188, 189, 420, 424, 427, 428, 429, 430, TG 2-12, 2-15, 4-07)
Free the lateral border of the pectoralis major from the axillary fascia and reflect superiorly, taking care to preserve its vessels and nerves. Determine the manner of insertion of the sternocostal part. Next carefully reflect the pectoralis minor toward its insertion on the coracoid process. When this muscle is reflected the anterior wall of the axillary space has been removed. This space contains all of the neurovascular elements supplying the upper limb. They are for the most part embedded in fat and should not be dissected at this time; they will be considered later in the session on the axilla.
5. Reflect deltoid muscle from acromion and spine of scapula. (Play movie; View images: N 420, 421, 424, 425, 426, 427, 429, 430, TG 2-06A, 2-06B, 2-07, 2-08A, 2-08B, 2-09, 2-14, 2-15, 2-16A, 2-16B, 2-16C)
Remove the subcutaneous tissue from the dorsal surface of the deltoid and other scapular muscles.
Review the anatomy of the trapezius, latissimus dorsi, rhomboid and levator scapulae muscles.
Deltoid muscle. Carefully remove the investing fascia from the posterior half of the deltoid muscle revealing its origin, insertion, and posterior border. Note the heavy fasciculation and the differences between the central (multipennate) and posterior (parallel) fibers.
Reflect the muscle by cutting its origin from the spine of the scapula and lateral border of the acromion and reflect it as far laterally as possible. Leave the anterior portion of the muscle intact. Carefully probe in the underlying fat and connective tissue to locate the axillary nerve and the posterior circumflex humeral artery and vein emerging from the quadrangular space to enter the deltoid. The major trunks of these vessels and nerve appear on the medial side of the neck of the humerus and encircle the humerus dorsally in a lateral direction, radiating branches into the deltoid muscle. Note that the arteries and veins distribute to all the muscles in the area. In your dissection, clean until you find the major trunks lying on the dorsum of the humerus. Trace all branches.
Supraspinatus muscle. Removal of the insertion of the trapezius muscle from the spine of the scapula and the acromion (leaving it attached to the clavicle) will expose the supraspinatus muscle. Clear any additional fat and loose connective tissue from the muscle. Note that its muscular fascia spans from the spine to the superior border of the scapula and is of greater density medially. Does the muscle use this fascia as an origin? Trace the muscle laterally toward its insertion. Note that it passes deep to the acromion process.
6. Saw off acromion and reflect the supraspinatus muscle. (Play movie; View images: N 421, 423, 425, 426, 427, TG 2-03, 2-06, 2-08, 2-09, 2-42)
Reflect the acromion process forward by cutting through the junction of the spine and acromion with a saw. As you reflect the acromion process, look for a bursa between it and the supraspinatus muscle (subacromial bursa). Does it continue laterally deep to the deltoid muscle (subdeltoid bursa)? Significance? Trace the muscle to its insertion on the humerus. Palpate the greater tubercle. Remove the muscular fascia and then reflect the muscle from the supraspintous fossa beginning at the medial margin of the fossa. Scoop the muscle out, scraping it from its bony attachments. To how much of the supraspinous fossa does it attach? As you reflect the muscle note the suprascapular artery, vein and nerve entering the deep side of the muscle. Locate the scapular notch. How are the suprascapular artery,vein, and nerve related to the scapular notch? Do not completely reflect this muscle to its insertion, as it combines with the capsule of the shoulder joint before it inserts into the greater tubercle of the humerus.
7. Reflect infraspinatus from the medial border of scapula toward shoulder and find nerves and vessels beneath. (Play movie; View images: N 33, 426, 429, 430, TG 2-08, 2-14, 2-15, 7-17)
Infraspinatus muscle. Observe the muscular fascia, which attaches to the spine and borders of the scapula and forms a compartment for the muscle. Remove this fascia and determine if it was part of the origin of the infraspinatus. Define the boundaries of the muscle. Reflect the muscle from the infraspinous fossa from medial to lateral as with the supraspinatus. How much of the fossa is used for muscle origin? As you reflect the muscle identify the suprascapular nerve, artery and vein as they enter the deep surface of the muscle and supply it. Trace the nerve, artery, and vein from the supraspinous to the infraspinous fossa through the notch of the neck of the scapula. Does the artery terminate in the infraspinatus muscle? Reflect the muscle only as far laterally as the lateral border of the scapula. Palpate the point of the insertion into the greater tubercle of the humerus.
8. Dissect the teres minor and major muscles. (Play movie; View images: N 421, 424, 426, 427, 429, TG 2-06, 2-07, 2-08, 2-09, 2-15A, 2-15B)
Teres minor muscle. Remove the muscular fascia and locate its origin. Is the muscle separate or fused with the lateral border of the infraspinatus muscle? Note the fascial septum between these adjacent muscles. Trace the insertion of the teres minor to the greater tubercle of the humerus, but do not reflect the muscle. Note the sequence of insertions of the three muscles to the greater tubercle. Examine individual facets of insertion on the greater tubercle of the humerus on a skeleton. Carefully clean along the lateral border of the muscle near its insertion and note the nerve to the teres minor from the axillary nerve and the accompanying branches of the posterior circumflex humeral vessels. The supraspinatus, infraspinatus, teres minor, and subscapularis (to be seen later) muscles make up the rotator cuff. What is the significance of this designation?
Teres major muscle. Remove the muscular fascia and locate the origin of the muscle from the inferior angle and the lower third of the lateral border of the scapula. Trace the muscle laterally until it joins the latissimus dorsi. Note that the two muscles travel together and are adherent as they pass to the anterior side of the humerus. Do not trace to their insertions at this time. Remove, carefully, the large masses of fat and connective tissue found in this area. As you trace the teres major laterally you will run into the long head of the triceps brachii overlying it on its dorsal side.
Updated: 15 Sept 2011
Clean the long head of triceps as it continues upward to attach to the infraglenoid tubercle of the scapula. This muscle forms a boundary between two spaces along the lateral border of the scapula: the triangular space and the quadrangular space. What are the boundaries of the quadrangular space? What does it transmit? Find the circumflex scapular artery in the triangular space and trace its branches and its course into the infraspinatous fossa. Is there an open anastomosis between it and the suprascapular artery? What does it supply? Does it anastomose with the suprascapular artery? What is the significance of this anastomosis? Review the arteries that you have dissected that supply the scapular region. The nerve to teres major will be identified in a later dissection. Consider the actions of the posterior shoulder muscles, concentrating on functional groups.
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