The Anterior Vena Cava (Fig. )

The anterior vena cava (V. cava cranialis) returns to the heart the blood from the head, neck, thoracic limbs, and the greater part of the thoracic wall. It is formed at the ventral part of the thoracic inlet by the confluence of the two jugular and two brachial veins. Its origin is attached to the first pair of ribs. It passes backward in the anterior mediastinum, at first median and ventral to the common carotid trunk, then deviates to the right of the anterior aorta, and opens into the right atrium opposite to the third rib. The demarcation between vein and atrium is not very distinct. It contains no valves except at the mouths of its radicles. Its length is about five to six inches (ca. 12 to 15 cm.) and its caliber about two inches (ca. 5 cm.) in a subject of medium size. Its right face is crossed by the right phrenic nerve, and on the left it is related to the anterior aorta and brachiocephalic artery. It receives, in addition to small pericardial and mediastinal veins, the following tributaries:

1. The internal thoracic vein (V. thoracica interna) is a satellite of the artery of that name. It opens into the anterior vena cava at the first rib.

2. The vertebral vein (V. vertebralis) corresponds to the homonymous artery. On the right side it terminates either in front of the deep cervical vein or by a short common trunk with it. On the left side it almost always unites with the deep cervical and vertebral vein to form a common trunk.

3. The deep or superior cervical vein (V. cervicalis profunda) corresponds to the artery. On the right side it leaves the artery at the first intercostal space, crosses the right face of the trachea and opens into the vena cava; it may form a common trunk with the dorsal or vertebral. On the left side there is nearly always a common trunk for all three.

4. The dorsal vein (V. costo-cervicalis) corresponds to the artery. On the right side it leaves the artery on entering the thorax, crosses the right face of the trachea, and opens into the vena cava in front of the deep cervical or by a common trunk with it. On the left side it almost always joins the deep cervical and vertebral to form a short common trunk which crosses the left face of the intrathoracic part of the brachial artery opposite the second rib and opens into the anterior vena cava.

The Vena Azygos

The vena azygos (Fig. ) is an unpaired vessel which arises at the level of the first lumbar vertebra by radicles coming from the psoas and the crura of the diaphragm; it is connected with the first lumbar vein. It passes forward along the right side of the bodies of the thoracic vertebræ, in contact usually with the thoracic duct, which separates the vein from the aorta. At the seventh vertebra it leaves the spine, curves downward and forward over the right side of the thoracic duct, trachea, and œsophagus, and opens into the right atrium opposite the third intercostal space. Its tributaries are:

1. The last fourteen intercostal veins (Vv. intercostales) of the right side. On the left side the last four to seven intercostal veins usually empty into the vena hemiazygos. This vessel runs on the left side of the aorta from the fourteenth to the eleventh thoracic vertebra, passes between the aorta and the spine, and joins the vena azygos. In its absence its tributaries join the vena azygos.

2. The œsophageal vein (V. œsophagea), satellite of the œsophageal artery, joins the vena azygos as it inclines downward.

3. The bronchial vein (Vena bronchialis) unites with the preceding to form a short common trunk (Ellenberger-Baum), or empties into the great coronary vein (Chauveau).