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The thoracic aorta (Fig. 4.1)
costal cartilage into superior epigastric and musculophrenic branches.
The ascending aorta arises from the aortic vestibule behind the
The thyrocervical trunk terminates as the inferior thyroid artery.
infundibulum of the right ventricle and the pulmonary trunk. It is con-
• 2nd part: the part of the artery that lies behind scalenus anterior. It
tinuous with the aortic arch. The arch lies posterior to the lower half of supply the breast. The internal thoracic artery divides behind the 6th
the manubrium and arches from front to back over the left main gives rise to the costocervical trunk (see Fig. 60.1).
bronchus. The descending thoracic aorta is continuous with the arch • 3rd part: the part of the artery that lies lateral to the lateral border of
and begins at the lower border of the body of T4. It initially lies slightly scalenus anterior. This part gives rise to the dorsal scapular artery.
to the left of the midline and then passes medially to gain access to the
abdomen by passing beneath the median arcuate ligament of the The great veins (Fig. 4.2)
diaphragm at the level of T12. From here it continues as the abdominal The brachiocephalic veins are formed by the confluence of the subcla-
aorta. vian and internal jugular veins behind the sternoclavicular joints. The
The branches of the ascending aorta are the: left brachiocephalic vein traverses diagonally behind the manubrium to
• Right and left coronary arteries. join the right brachiocephalic vein behind the 1st costal cartilage thus
The branches of the aortic arch are the: forming the superior vena cava. The superior vena cava receives only
• Brachiocephalic artery: arises from the arch behind the manubrium one tributaryathe azygos vein.
and courses upwards to bifurcate into right subclavian and right com-
mon carotid branches posterior to the right sternoclavicular joint. The azygos system of veins (Fig. 4.2)
• Left common carotid artery: see p. 133. • The azygos vein: commences as the union of the right subcostal vein
• Left subclavian artery. and one or more veins from the abdomen. It passes through the aortic
• Thyroidea ima artery. opening in the diaphragm, ascends on the posterior chest wall to the
The branches of the descending thoracic aorta include the: level of T4 and then arches over the right lung root to enter the superior
• Oesophageal, bronchial, mediastinal, posterior intercostal and sub- vena cava. It receives tributaries from the: lower eight posterior inter-
costal arteries. costal veins, right superior intercostal vein and hemiazygos veins.
• The hemiazygos vein: arises on the left side in the same manner as the
The subclavian arteries (see Fig. 60.1) azygos vein. It passes through the aortic opening in the diaphragm and
The subclavian arteries become the axillary arteries at the outer bor- up to the level of T9 from where it passes diagonally behind the aorta
der of the 1st rib. Each artery is divided into three parts by scalenus and thoracic duct to drain into the azygos vein at the level of T8. It
anterior: receives venous blood from the lower four left posterior intercostal
• 1st part: the part of the artery that lies medial to the medial border of veins.
scalenus anterior. It gives rise to three branches, the: vertebral artery • The accessory hemiazygos vein: drains blood from the middle poster-
(p. 135), thyrocervical trunk and internal thoracic (mammary) artery. ior intercostal veins (as well as some bronchial and mid-oesophageal
The latter artery courses on the posterior surface of the anterior chest veins). The accessory hemiazygos crosses to the right to drain into the
wall one fingerbreadth from the lateral border of the sternum. Along azygos vein at the level of T7.
its course it gives off anterior intercostal, thymic and perforating • The upper four left intercostal veins drain into the left brachio-
branches. The ‘perforators’ pass through the anterior chest wall to cephalic vein via the left superior intercostal vein.

The mediastinum IIbthe vessels of the thorax 13