![]() The heart tube is located ventral (anterior) to the pharyngeal pouches, a series of structures that give rise to the head and neck components ( Fig. The developing heart forms within the pharyngeal mesoderm, in the region that develops into the neck, and migrates into the thorax over time. The descending thoracic aorta gives rise to the posterior intercostal arteries at each vertebral level, which connect to the corresponding anterior intercostal arteries. The internal thoracic arteries (mammary arteries) proceed directly inferiorly along the ipsilateral side of the sternum, and connect with the anterior intercostal arteries. The vertebral arteries arise from the superior aspect of the subclavian artery and proceed superiorly toward the head. ![]() The subclavian arteries give rise to two important branches at their proximal end. The third branch is the left subclavian artery, which proceeds superiorly for a short distance before making a sharp turn leftward to continue directly toward the left arm. The second branch of the aortic arch is the left common carotid artery, which proceeds superiorly and slightly leftward, toward the left side of the neck. The right subclavian artery proceeds directly rightward toward the right arm, while the right common carotid artery proceeds superiorly and slightly rightward, toward the right side of the neck. The first branch is the brachiocephalic artery, which courses rightward and superiorly for a short distance before dividing into the right subclavian artery and right common carotid artery. The transverse aortic arch most commonly gives rise to three branches. Isthmus-the junction of the transverse and descending aorta. ![]() The arterial duct, extending from the origin of the left pulmonary artery, inserts into the aortic ![]() It then turns downward to continue as the descending thoracic aorta just leftward and anterior to the spine. The ascending aorta continues as the transverse arch, which courses almost directly posterior, and only slightly leftward, abutting the left side of the trachea, and coursing over the left mainstem bronchus ( Fig. Because the ventricular outflow tracts cross each other, the aortic valve is to the right of the pulmonary valve. The normal aorta extends superiorly from the center of the heart, posterior to the pulmonary trunk ( Fig. ![]()
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