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Figure 11.44 Development of the inferior vena cava, azygos vein, and superior vena cava. A. Seventh week. The anastomosis lies between the subcardinals, supracardinals, sacrocardinals, and anterior cardinals. B. The venous system at birth showing the three components of the inferior vena cava.

sacrocardinal segment of the inferior vena cava. When the renal segment of the inferior vena cava connects with the hepatic segment, which is derived from the right vitelline vein, the inferior vena cava, consisting of hepatic, renal, and sacrocardinal segments, is complete.

With obliteration of the major portion of the posterior cardinal veins, the supracardinal veins assume a greater role in draining the body wall. The 4th to 11th right intercostal veins empty into the right supracardinal vein, which together with a portion of the posterior cardinal vein forms the azygos vein (Fig. 11.44). On the left the 4th to 7th intercostal veins enter into the left supracardinal vein, and the left supracardinal vein, then known as the hemiazygos vein, empties into the azygos vein (Fig. 11.44B).

CLINICAL CORRELATES Venous System Defects

The complicated development of the vena cava accounts for the fact that deviations from the normal pattern are common.

Hepatic segment inferior vena c—

Sacrocardinal segment inferior vena cava

Hepatic Vein

Azygos vein

Hepatic segment

Renal segment'

Sacrocardinal segment

Persistent Left Sacrocardinal Vein

Superior vena cava

Renal segment inferior vena cava

Azygos vein

Hepatic segment

Sacrocardinal segment inferior vena cava

—Persistent left sacrocardinal vein

Renal segment'

Sacrocardinal segment

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