Reflect the anterior thoracic wall, and locate major veins

Find these structures:

• • Superior vena cava

    • L. & R. brachiocephalic vv.

      • Internal jugular v.

      • Subclavian v.

1. Detach the serratus anterior m. from its proximal attachments to the ribs 1-8. Reflect the muscle superolaterally to expose the ribs and intercostal spaces.

Photo 1. Procedural: reflected serratus anterior m.

2. Detach the infrahyoid (strap) mm. from the posterior portion of the manubrium.

Photo 2. Procedural: detached sternocleidomastoid and infrahyoid mm.

3. Palpate the entire length of the clavicles. Remove any soft tissue on the anterior portions of the clavicles. Depress any contents deep to the clavicles to protect from damage.

Note: Make sure all soft tissue is removed from the clavicles before cutting. This will allow for a cleaner and more exact cut.

4. Cut through each clavicle with a small saw, just medial to the clavicular attachment of the trapezius m.

Photo 3. Procedural: clavicular cut

5. Free any clavicular attachments (subclavius mm. and costoclavicular ligaments) to the 1st ribs. This can be completed by blunt dissection and scissor cuts, if necessary. An important collection of neurovasculature and some muscle attachments are found just deep to the clavicle.

Photo 4. Procedural: protection of neurovasculature and muscle attachments.

6. Disarticulate the manubrium and the 1st ribs. This will involve chiseling or cutting (using a chisel or bone shears) through the synchondroses (cartilaginous joints) of the 1st ribs.

Photo 5. Procedural: disarticulation of the synchondroses of the 1st rib

7. Using scissors, cut the intercostal mm. in the intercostal space inferior to the 1st ribs, along the midaxillary line. Cut (using bone shears) the 2nd ribs along the midaxillary line. Continue cutting through intercostal mm. and ribs inferiorly to the 6th ribs.

Photo 6. Procedural: soft tissue and bone cuts

8. Lift the clavicles and manubrium anteriorly, and locate the internal thoracic aa. and vv. as they pass deep to the 1st ribs. Cut this vasculature at this level.

Photo 7. Procedural: internal thoracic vasculature cut

9. ‘Hinge’ (pull anteriorly) the cut portions of the anterior thorax to uncover deep structures. Anteriorly pull to remove the cut portions of the anterior thorax to uncover deep structures.

When pulling, this needs to be done forcibly to break ribs or tissues not completely cut in previous step. Care should be taken to not allow the sharp ends of cut bone to contact your skin.

10. Locate and clean the brachiocephalic vv., and follow to the formation of the superior vena cava. Follow the brachiocephalic vv. distally (superolaterally) to locate the internal jugular vv. and the subclavian vv.

Note: The junction of the internal jugular v. (IJV) and the subclavian v. is known as the venous angle. The venous angles receive lymphatics. The left venous angle receives the thoracic duct, a major lymphatic conduit. The right venous angle receives the right lymphatic duct. You will be asked to locate the thoracic duct in a later lab.

Photo 8. Venous angles, brachiocephalic v., & superior vena cava

Identify the pericardium, open the pericardium, and examine the great vessels and closely surrounding neurovasculature

Find these structures:

• Pericardium

  • Fibrous pericardium

  • Serous pericardium

    • Parietal layer

    • Pericardial cavity

    • Visceral layer (epicardium)

• Phrenic n.

• Internal thoracic a.

  • Pericardiacophrenic a.

• Superior vena cava

• Inferior vena cava

• Ascending aorta

11. Locate the pericardium. Identify the fibrous pericardium.

Note: The pericardium is comprised of a fibrous pericardium (externally) and a serous pericardium (internally). The serous pericardium has two parts: the parietal layer, which adheres to the fibrous pericardium to form the pericardial sac, and the visceral layer (aka the epicardium), which adheres to the surface of the heart. The space between the parietal and visceral layers is the pericardial cavity.

Photo 9. Pericardium

12. On each side of the pericardium, strip away the mediastinal pleura to reveal the phrenic n. and pericardiacophrenic a. & v.

Note: The pleurae are serous membrane sacs that surround and protect the lungs. The pleurae have regional specializations named for their locations. The portion of the pleura that is adjacent to the mediastinum is the mediastinal pleura.

Note: The phrenic n. and pericardiacophrenic vasculature are often adhered to the lateral portion of the pericardium, anchored under a layer of mediastinal pleura. If this is the case, use blunt dissection to carefully separate the vasculature from the fibrous pericardium.

Photo 10. Phrenic n. and pericardiacophrenic a. & v.

13. Open the pericardium by making a vertical midline incision (with scissors) through the fibrous pericardium from the diaphragm to the arch of the aorta.

Note: The parietal layer of the serous pericardium adheres to the fibrous pericardium, and also is cut in the step above.

Photo 11. Procedural: midline incision of pericardium

14. Make a second incision, from the apex of the heart to the right border along the diaphragmatic surface. Additionally, note where the fibrous pericardium covers the bases of the great vessels. To better see the great vessels, reflect the fibrous pericardium laterally in this location as well.

Photo 12. Procedural: inferior incision of the pericardium

15. Identify the great vessels: superior vena cava, inferior vena cava, pulmonary trunk, and ascending aorta.

Photo 13. Superior vena cava, ascending aorta, and pulmonary trunk

Locate the superior mediastinum, and identify contents

Find these structures:

• Superior vena cava

• Ascending aorta

• Arch of aorta (aortic arch)

  • Brachiocephalic trunk

  • L. common carotid a.

  • L. subclavian a.

• Ligamentum arteriosum

• Pulmonary trunk

  • L. & R. pulmonary aa..

Note: The mediastinum is a space medial to the lungs, inferior to the plane of the first ribs, superior to the diaphragm, anterior to the vertebral column, and posterior to the sternum. The superior mediastinum is the portion of the mediastinum above the plane formed from the sternal angle and the intervertebral disc of T4/T5. The superior mediastinum contains the arch of the aorta (and branches), ligamentum arteriosum, the distal (superior portion) of the superior vena cava (and brachiocephalic vv.), thoracic duct, vagus nn. (CNs X), phrenic nn., thymus gland, and portions of the trachea and esophagus.

16. Following the ascending aorta superiorly, locate the arch of aorta and its three branches: brachiocephalic trunk, L. common carotid a., and L. subclavian a.

Photo 14. Aortic arch, brachiocephalic trunk, L. common carotid, and L. subclavian a.

24. Cut the L. brachiocephalic v. at its midpoint. Reflect both ends of the L. brachiocephalic v. (and their tributaries) laterally to further expose the arch of the aorta and its branches.

Note: The arch of the aorta (aortic arch) connects the ascending aorta to the descending aorta. Typically, three branches - brachiocephalic trunk, L. common carotid a., & L. subclavian a. - originate from the arch of the aorta to supply blood to the head, neck, upper limbs, and thorax.

Photo 15. Arch of aorta and branches

18. Locate the ligamentum arteriosum. This structure connects the inferior surface of the aortic arch to the origin of the L. pulmonary a. and is the remnant of the fetal ductus arteriosus.

Note: Lifting the aortic arch superiorly yields the clearest view of the ligamentum arteriosum.

Photo 16. Ligamentum arteriosum

Examine the structures of the root of the neck

Note: The root of the neck (RON) is the nexus between the neck, thorax, and upper limbs. The RON is the proximal attachment site for many neck muscles and transmits important neurovasculature (common carotid aa., jugular vv., subclavian aa. & vv., vagus nn., trunks of the brachial plexus).

Find these structures:

• • Subclavian v.

  • Anterior scalene m.

  • Subclavian a.

  • Phrenic n.

LEFT SIDE of donor

19. Gently clean the fascia from the L. brachiocephalic v. at its division into left IJV and subclavian v.

Note: Be careful not to damage the thoracic duct, which joins venous return in the vicinity of the left venous angle.

Photo 17. Thoracic duct & left venous angle

20. Reflect the distal portion of the L. brachiocephalic v. (along with the origins of the IJV and subclavian v.) laterally (beyond the first rib) to expose the vicinity of the proximal portion of the L. subclavian a.

21. Locate and carefully clean the anterior scalene m. Be sure to not remove the phrenic n. on the anterior scalene m.

Note: The (anterior, middle, posterior) scalene muscles may either act to weakly flex the neck, or serve as accessory muscles of respiration (by slightly elevating the first two ribs, thus expanding the volume of the thoracic cavity). The anterior and middle scalene mm. attach to the first rib, and the posterior scalene m. attaches to the second rib.

Note: The anterior scalene m. is an important anatomical landmark for understanding the neurovasculature of the root of the neck. There are four classic anatomical relationships to understand:

• 1. the anterior scalene m. is sandwiched between the subclavian v. (anterior) and subclavian a. (posterior),

  2. the anterior scalene m. establishes the borders for the divisions of the subclavian a.,

  3. the anterior scalene m. is immediately posterior to (and closely associated with) the phrenic n. as the phrenic n. descends the neck and the root of the neck, and

  4. the anterior scalene m. is separated from the middle scalene m. by the roots (ventral primary rami of spinal nn.) and trunks of the brachial plexus and subclavian a..

Photo 18. Anterior scalene m.

22. Follow the phrenic n. inferiorly into the superior mediastinum.

Note: The phrenic n. (C3,4,5) descends from the cervical plexus through the root of the neck (just anterior to, and upon the anterior scalene m.) before entering the thorax between the subclavian a. & v. The phrenic n. is efferent (motor) and afferent (sensory) to the diaphragm and afferent (sensory) to the pericardium and diaphragmatic pleura.  

Photo 19. Phrenic n. (lungs removed)

RIGHT SIDE of donor

23. Laterally reflect the R. subclavian v. from the right venous angle to beyond the lateral edge of the 1st rib, and clean the connective tissue to reveal the anterior scalene m., the R. subclavian a., and the 1st rib.

Note: The subclavian a. is conceptually divided into three parts, with respect to the vessel’s relationship to the anterior scalene m. The first part of the subclavian a. is found medial to the anterior scalene, the second part of the subclavian a. is posterior to the anterior scalene, and the third part is lateral to the anterior scalene. The second and third parts of the subclavian a. will be dissected in a later lab.

Anterior scalene m.:

Photo 20. Right subclavian a.

Note: The first part of the subclavian a. typically hosts three major branches:

• vertebral a.,

• thyrocervical trunk,

• internal thoracic a. (supplies anterior thoracic & abdominal walls & the diaphragm).

Photo 21. Subclavian a., 1st part

Trace the vagus nerves (CN X) from the neck to the thorax, and locate vagus branches

Find these structures:

• R. & L. vagus nn. (CNs X)

• R. & L. recurrent laryngeal n.

24. Locate the vagus n. in the carotid sheath. Follow the vagus nn. to locate the recurrent laryngeal nn.

Note: The vagus n. (CN X) is the major parasympathetic conduit to the thorax and abdomen, and is the major innervation to muscles of the larynx and pharynx, and aspects of the head.

Note: The R. and L. vagus nn. take different routes into the thorax. Both nerves descend the neck within the carotid sheaths, and cross anteriorly over the subclavian aa., deep to the first ribs. The R. vagus n. then sends a major branch (the R. recurrent laryngeal n.) inferiorly and then posteriorly around the R. subclavian a., lateral to the trachea, on a course for the larynx. The L. vagus n. sends the L. recurrent laryngeal n. inferiorly and then posteriorly around the concavity of the arch of the aorta, lateral to the trachea, also on a course for the larynx.  

Photo 22. Recurrent laryngeal nn.

Identify intercostal mm. and neurovasculature

Find these structures:

• External intercostal mm.

• Internal intercostal mm.

• Innermost intercostal mm.

• Internal thoracic a.

  • • Anterior intercostal brs.

    • Musculophrenic a.

    • Superior epigastric a.

• • Intercostal neurovascular bundle (VAN: vein, artery, nerve)

    • Intercostal aa., anastomoses of the following:

      • Anterior intercostal br. (internal thoracic a.)

      • Posterior intercostal aa. (aorta; seen in later dissection)

    • Intercostal vv.

      • Anterior intercostal vv. (internal thoracic v.)

      • Posterior intercostal vv. (seen in later dissection)

    • Intercostal nn. (VPR of T1-11)

25. Return the anterior thoracic wall to anatomical position (i.e. ‘un-hinge’). Beginning at the cut mid-axillary line, identify the external intercostal mm. in several intercostal spaces.

Note: The external intercostal muscle fibers run inferomedially from the rib above to the rib below. Think ‘putting your hands in your front pants pockets’ - the muscle fibers run the same direction.

External intercostal mm.:

26. Notice the transition from muscle fibers to external intercostal membranes as you move anteriorly and towards the sternum.

Photo 23. External intercostal mm. and membranes

27. In several intercostal spaces, carefully remove the external intercostal mm. and membranes to expose the internal intercostal mm. Start medially (close to the sternum), and remove the white and fibrous external intercostal membranes. These membranes are easily distinguishable from the deep internal intercostal mm. fibers.

Note: The internal intercostal m. fibers run perpendicular to the external intercostal m. fibers.

Internal intercostal mm.:

28. Hinge the anterior thoracic wall to get a clear view of the inner surface of the anterior thoracic wall. Uncover the innermost intercostal mm. by removing investing fascia. These are the deepest of the intercostal mm., and these muscle fibers run in the same direction as the internal intercostal mm. The intercostal neurovasculature runs between the internal intercostal and innermost intercostal mm. The transversus thoracis mm. are also visible in this view. Remove any remaining investing fascia. These mm. are not located exclusively in the intercostal spaces. The proximal attachment for these mm. are the inferior sternum, and the fibers radiate superolaterally to ribs and costal cartilages.

Note: The transversus thoracis mm. attaches the inferior portion of the sternum and the sternal ends of ribs 4-6 to the costal cartilages and inferior borders of ribs 2-6. When activated, these muscles pull ribs inferiorly to decrease the volume of the thoracic cavity. To best visualize the length of the internal thoracic vasculature, you must reflect the transversus thoracis mm. from the sternum.

Innermost intercostal mm.:

Photo 25. Innermost intercostal and transversus thoracis mm.

29. Locate the internal thoracic aa. and vv. They were cut to allow the anterior thoracic wall to be reflected.

Photo 26. Internal thoracic a. and v.

30. Locate anterior intercostal branches of the internal thoracic aa. for the first 5-6 intercostal spaces (there are 2 branches per intercostal space). These branches anastomose with posterior intercostal aa. (from the superior intercostal aa. and the thoracic aorta) to supply blood to the thoracic wall. Follow one or two branches laterally to locate the intercostal neurovascular bundle. Innermost intercostal mm. must be removed to follow the neurovasculature laterally.

Note: Intercostal neurovascular bundles consist of a vein, artery, and nerve (vein nearest to the rib). The arteries are supplied anteriorly via anterior branches of the internal thoracic arteries (intercostal spaces 1-6) or the musculophrenic aa. (intercostal spaces 7-9), and posteriorly by posterior intercostal aa., which arise from either the superior intercostal aa. (intercostal spaces 1 & 2), or the thoracic aorta (intercostal spaces 3-11). The anterior and posterior intercostal vv. veins are similarly arranged. Anterior intercostal vv. drain into the internal thoracic vv., whereas posterior intercostal vv. drain into either the brachiocephalic vv. (intercostal space 1), superior intercostal vv. (typically for intercostal spaces 2-3, sometimes 4), or the azygos system (typically for intercostal spaces 4-11). All of the intercostal nn. are ventral primary rami of thoracic spinal nn. 1-11.

Photo 27. Intercostal neurovasculature

Note: There are two intercostal neurovascular bundles: larger superior bundles, and smaller inferior bundles. The superior bundles are easier to locate, as they lie in the costal groove of the inferior border of ribs.

Note: A useful mnemonic to remember the order of the superior neurovascular bundle is VAN: vein is superior, artery is intermediate, and nerve is inferior. The order is opposite for the inferior bundle: NAV, with the vein lying nearest to the rib below.

31. Follow each internal thoracic a. and v. inferiorly. Cut the transversus thoracis mm. from their attachments to the sternum, and reflect laterally. Expose the internal thoracic aa. and their points of bifurcation into the superior epigastric aa. and musculophrenic aa. around the sixth intercostal space.

Note: The superior epigastric a. is the direct continuation of the internal thoracic a. The musculophrenic a. is the lateral terminal branch.

Photo 28. Superior epigastric a. and musculophrenic a.