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The clavicle and parts of the thoracic cage provide prominent surface landmarks. Directional terms are used to help orient the reader to the thorax. The cutaneous innervation of the anterior portion of the thoracic wall is from lateral and anterior cutaneous nerves via ventral rami, forming a segmental dermatomal pattern.
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Palpable bony landmarks and reference lines are important to use for anatomic orientation as well as a guide to locate deep structures. You should become familiar with the following structures of the anterior portion of the thoracic wall (Figure 2-1A; Table 2-1):
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- Clavicles. Course transversely along the superior portion of the chest wall from the manubrium to the acromion of the scapula and, therefore, are easily palpable. However, the clavicle, overly rib 1, which makes rib 1 impalpable.
- Jugular notch of the sternum. Located between the medial ends of the clavicles.
- Sternal angle (of Louis). Articulation between the manubrium and sternal body. The sternal angle serves as the location for the articulation of rib 2 with the sternum at the T4–T5 vertebral level. The sternal angle is often visible and palpable and serves as an important surface landmark for several underlying structures.
- Xiphoid process. An inferior pointed projection of the sternal body. The xiphoid process lies at the level of the T9 vertebral body.
- Costal margins. Formed by costal cartilages 7–10.
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The following imaginary vertical lines provide anatomic and clinical descriptions for orientation (Figure 2-1A):
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- Midsternal line. Dropped through the center of the sternum. It is a component of the median plane.
- Midclavicular line. Dropped through the middle of the clavicle, just medial to the nipple.
- Anterior axillary line. Dropped through the anterior axillary fold formed by the pectoralis major muscle.
- Midaxillary line. Dropped through the middle of the axilla, along the lateral border of the thoracic wall. The midaxillary line is bounded by the anterior axillary fold (pectoralis ...