Dissector Answers - Pectoral Region, Posterior Shoulder & Breast

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Describe the general gross features of the breast and its blood supply.
  2. Describe the lymphatic drainage of the breast.
  3. Identify the muscles of the pectoral region, their related fascia, nerve and regional blood supply, and general functions.
  4. Describe the general features of the circulatory system.

Learning Objectives and Explanations:

1. Describe the general gross features of the breast and its blood supply. (W&B 107-110, N 182A, 182B, TG 2-10A, 2-10B, 2-11A)
The mammary gland is a modified sweat gland. It is entirely contained within subcutaneous tissue. The most important internal gross features are glandular, namely secretory glands, lactiferous ducts, and lactiferous sinuses. (It is the glandular nature of the breast that makes it a common site for the development of cancer.) Externally, an important feature is the nipple, which is surrounded by the areola. Each of the approximately 20 lactiferous sinuses have an individual opening on the nipple.

A breast's arterial supply is derived from branches of the internal thoracic artery (including anterior intercostals), the lateral thoracic artery, the thoracoacromial artery, and posterior intercostal arteries. Venous drainage follows arterial supply, primarily draining into the axillary vein, but also draining some blood into the internal thoracic vein.
2. Describe the lymphatic drainage of the breast. (W&B 109, N 184, image, TG 2-11B)
Lymph passes from the nipple, areola, and lobules to the subareolar lymphatic plexus. From there: Lymphatic vessels in the skin of the breast drain into the axillary, inferior deep cervical, infraclavicular, and parasternal lymph nodes.

Lymph from the axillary lymph nodes subsequently drains into the subclavian lymph trunk. Lymph from parasternal nodes enters the bronchomediastinal trunk.
3. Identify the muscles of the pectoral region, their related fascia, nerve and blood supply, and general functions. (W&B 111-113, N 188, 189, TG 2-12A, 2-12B)
Muscle Origin Insertion Action Innervation Artery Notes
pectoralis major medial 1/2 of the clavicle, manubrium & body of sternum, costal cartilages of ribs 2-6, sometimes from the rectus sheath of the upper abdominal wall crest of the greater tubercle of the humerus flexes and adducts the arm, medially rotates the arm medial and lateral pectoral nerves (C5-T1) pectoral branch of the thoracoacromial trunk the deep fascia on its anterior surface should not be fused to the fascia of the mammary gland - if it is, this is an important clinical sign indicating breast disease
pectoralis minor ribs 3-5 coracoid process of the scapula draws the scapula forward, medialward, and downward medial pectoral nerve (C8, T1) pectoral branch of the thoracoacromial trunk branches of medial pectoral nerve usually pierce pectoralis minor to reach the pectoralis major muscle
serratus anterior ribs 1-8 or 9 medial border of the scapula on its costal (deep) surface it draws the scapula forward; the inferior fibers rotate the scapula superiorly long thoracic nerve (from ventral rami C5-C7) lateral thoracic a.

a lesion of long thoracic nerve will cause winging of the scapula (i.e., the medial border of the scapula falls away from the posterior chest wall and looks like an angel's wing) (Latin, serratus = to saw)

4. Describe the general features of the circulatory system. (W&B 17-24)
The human circulatory system actually contains two complete "circuits". The right side of the heart receives deoxygenated blood from the body and pumps it to the pulmonary circuit (i.e., the lungs). The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body.

The general order of vessels, beginning with the aorta, is artery, arteriole, capillary, venule, vein, then back into the heart. There are exceptions - the hepatic portal system is the major one you will deal with soon. In gross anatomy, you will only be concerned with structures that are visible without a microscope, i.e. arteries and veins.
Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Sternum - The Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls - The Mammae (Breasts) - The Lymphatics of the Upper Extremity - Surface Anatomy of the Thorax - Surface Markings of the Thorax


Questions and Answers:

7. From where do the lateral cutaneous branches (anterior and posterior) of intercostal nerves arise and to where do they distribute?
The lateral cutaneous branches of a typical intercostal nerve arise lateral to the angles of the ribs, divide into anterior and posterior branches, and supply the skin of the thoracic and abdominal walls. (W&B 108, N 188, 189, TG TG4-02, TG4-11)
8. Is any pinkish mammary glandular tissue visible?
It is likely that your cadaver does not have any appreciable mammary tissue. Most of the cadavers are elderly.
9. What are suspensory ligaments of the mammary glands?
The suspensory ligaments are fibrous condensations of the connective tissue stroma which are prominent in the superior part of the mammary gland. These help support the lobules of the gland and attach it to the dermis of the overlying skin. (N 182A, 182B, TG 2-10A, 2-10B)
10. Consider blood supply, nerve supply, and lymphatic drainage of the breasts.
Blood: A breast's arterial supply is derived from branches of the internal thoracic artery (including anterior intercostals), the lateral thoracic artery, the thoracoacromial artery, and posterior intercostal arteries. Venous drainage follows arterial supply, primarily draining into the axillary vein, but also draining some blood into the internal thoracic vein.

Nerves: The skin of the breast is innervated by anterior and lateral cutaneous branches of the 2nd through 6th intercostal nerves. For example, the area around the nipple and areola is innervated via the T4 spinal nerve.

Lymphatic drainage (W&B 109, N 184, TG 2-11B, image): Lymph passes from the nipple, areola, and lobules to the subareolar lymphatic plexus. From there: Lymphatic vessels in the skin of the breast drain into the axillary, inferior deep cervical, infraclavicular, and parasternal lymph nodes.

Lymph from the axillary lymph nodes subsequently drains into the subclavian lymph trunk. Lymph from parasternal nodes enters the bronchomediastinal trunk.
11. Why are lateral pectoral and medial pectoral nerves reversed (with respect to their names and relative locations) from what you would expect?
Both of these nerves supply the pectoralis major. The "medial" and "lateral" designations of these two nerves refers to the cords of the brachial plexus from which they are derived. (Do not worry about this now, but it will haunt you later!) They are not topographic designations. (To remember which is which, think about the Medial pectoral nerve being a Major nerve which supplies both the pectoralis Major and the pectoralis Minor. The Lateral nerve is a Little nerve, and only innervates pectoralis major.) (N 430, TG 2-12B, 2-13)
12. Where does the cephalic vein terminate?
The cephalic vein passes between the deltoid and pectoralis major muscles and empties into the termination of the axillary vein. (Latin/Greek, cephalicus/kephalikos = head) (N 424, TG 2-12A, 2-02A)