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The arch of the aorta (aortic arch), the curved continuation of the ascending aorta (Figs. 1.65A and 1.67; see Table 1.5), begins posterior to the 2nd right sternocostal (SC) joint at the level of the sternal angle. It arches superiorly, posteriorly and to the left, and then inferiorly. The arch ascends anterior to the right pulmonary artery and the bifurcation of the trachea, reaching its apex at the left side of the trachea and esophagus as it passes over the root of the left lung. The arch descends posterior to the left root of the lung beside the T4 vertebra. The arch ends by becoming the thoracic (descending) aorta posterior to the 2nd left sternocostal joint.

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The ascending aorta, approximately 2.5 cm in diameter, begins at the aortic orifi ce. Its only branches are the coronary arteries, arising from the aortic sinuses (Fig. 1.55B). The ascending aorta is intrapericardial (Figs. 1.66A & B); for this reason, and because it lies inferior to the transverse thoracic plane, it is considered a content of the middle mediastinum (part of inferior mediastinum).

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ABDOMINAL AORTA Most arteries supplying the posterior abdominal wall arise from the abdominal aorta (Fig. 2.98A; Table 2.15). The subcostal arteries arise from the thoracic aorta and distribute inferior to the 12th rib. The abdominal aorta is approximately 13 cm in length. It begins at the aortic hiatus in the diaphragm at the level of the T12 vertebra and ends at the level of the L4 vertebra by dividing into the right and left common iliac arteries. The abdominal aorta may be represented on the anterior abdominal wall by a band (approximately 2 cm wide) extending from a median point, approximately 2.5 cm superior to the transpyloric plane to a point slightly (2–3 cm) inferior to and to the left of the umbilicus at the level of the supracristal plane (plane of the highest points of the iliac crests) (Fig. 2.98B). In children and lean adults, the lower abdominal aorta is suffi ciently close to the anterior abdominal wall that its pulsations may be detected or apparent when the wall is relaxed (see the blue box “Pulsations of Aorta and Abdominal Aortic Aneurysm” on p. 319).

The common iliac arteries diverge and run inferolaterally, following the medial border of the psoas muscles to the pelvic brim. Here each common iliac artery divides into the internal and external iliac arteries. The internal iliac artery enters the pelvis. (Its course and branches are described in Chapter 3.) The external iliac artery follows the iliopsoas muscle. Just before leaving the abdomen, the external iliac artery gives rise to the inferior epigastric and deep circumfl ex iliac arteries, which supply the anterolateral abdominal wall.

Branches of the Abdominal Aorta. The branches of the descending (thoracic and abdominal) aorta may be described as arising and coursing in three “vascular planes” and can be classifi ed as being visceral or parietal and paired or unpaired (Fig. 2.98A & C; Table 2.15). Paired parietal branches of the aorta serve the diaphragm and posterior abdominal wall. The median sacral artery, an unpaired parietal branch, may be said to occupy a fourth (posterior) plane because it arises from the posterior aspect of the aorta just proximal to its bifurcation. Although markedly smaller, it could also be considered a midline “continuation” of the aorta, in which case its lateral branches, the small lumbar arteries and lateral sacral branches, would also be included as part of the paired parietal branches.