The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs is the visceral pleura. Only a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity.
The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm.
The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7).
The superior aspect of each pleural cavity extends approximately 2 to 3 cm above rib I and the costal cartilage into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately anterior to the esophagus. Major blood vessels and nerves pass in and out of the thorax at the superior thoracic aperture anteriorly and laterally to these structures.
An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axillary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7).
Each axillary inlet is formed by: the superior margin of the scapula posteriorly, the clavicle anteriorly, and the lateral margin of rib I medially.
The apex of each triangular inlet is directed laterally and is formed by the medial margin of the coracoid process, which extends anteriorly from the superior margin of the scapula.
The base of the axillary inlet’s triangular opening is the lateral margin of rib I.
Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over rib I.
Proximal parts of the brachial plexus also pass between the neck and upper limb by passing through the axillary inlet.
The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it (Fig. 3.8):
The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII.
The esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX.
The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII.
Numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm.
The breasts, consisting of mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9).
Vessels, lymphatics, and nerves associated with the breast are as follows:
Branches from the internal thoracic arteries and veins perforate the anterior chest wall on each side of the sternum to supply anterior aspects of the thoracic wall. Those branches associated mainly with the second to fourth intercostal spaces also supply the anteromedial parts of each breast.
Lymphatic vessels from the medial part of the breast accompany the perforating arteries and drain into the parasternal nodes on the deep surface of the thoracic wall.
Vessels and lymphatics associated with lateral parts of the breast emerge from or drain into the axillary region of the upper limb.
Lateral and anterior branches of the fourth to sixth intercostal nerves carry general sensation from the skin of the breast.
When working with patients, physicians use vertebral levels to determine the position of important anatomical structures within body regions.