Chapter 6: Thorax

THORACIC CAVITY AND ANTERIOR THORACIC WALL

While performing the thoracic cavity dissection, you will be following many of the structures of the neck as they enter through the superior thoracic aperture. Of particular importance is observing the course of the vagus, phrenic, and recurrent laryngeal nerves. The thorax is composed of three enclosed cavities, the mediastinum for the heart, and two plural cavities, one for each lung. As these cavities are enclosed, they depend on movement and reorientation for their drainage. Infections and inflammation, as well as inactivity, can cause a build-up of fluid within these areas.

1. Place the cadaver in the supine position.

2. If not already done, reflect the pectoralis major, pectoralis minor, and serratus anterior from their costal attachments, and reflect the rectus abdominis muscle inferiorly.

3. Open the thoracic cavity using a bone saw by cutting along the lateral, axillary margin of the thoracic cage and through the clavicle mid-shaft. Then cut the soft tissue along the inferior costal angle, including reflecting the diaphragm, to remove the anterior thoracic cage, which you will use to identify the structures in the steps below.

4. On the external surface of the anterior thorax, identify the external intercostal muscle between the ribs and note the orientation of its fibers (Figure 6.1).

1. Turn the chest plate over to identify the endothoracic fascia and the internal intercostal muscle just deep to the external intercostal muscle and observe that its fibers run perpendicular to the fibers of the external intercostal muscle. Note that the internal intercostal muscle is the only muscle of the intercostal group to fill the intercostal space fully anteriorly to the sternum (Figure 6.2 ).

1. On the lateral boundaries of the anterior thoracic wall, identify the innermost intercostal muscle.

2. Identify the transversus thoracis muscle on the inferior portion of the internal anterior thoracic wall as it attaches to the body of the sternum and xiphoid process.

3. On the internal surface inferior to each rib, identify the anterior intercostal vein, anterior intercostal artery, and intercostal nerve in that order from superior to inferior (Figure 6.3).

1. Trace the anterior intercostal artery anteriorly to the internal thoracic artery and its accompanying internal thoracic vein coursing down and up the lateral margin of the sternum. The internal thoracic artery branches from the subclavian artery, and the internal thoracic vein drains into the brachiocephalic vein behind the first rib.

2. The pleura is the connective tissue layer that surrounds the ...