Cranial and caudal vena cava

Caudal Vena Cava: 

The caudal vena cava transports all the blood from caudal (inferior) to the diaphragm back to the right atrium of the heart. It begins where the two common iliac veins join in the caudal (inferior) abdominal region. In the thoracic cavity the phrenic nerve runs to the diaphragm along the caudal vena cava.

Cranial Vena Cava: The cranial (superior) vena cava transports all the blood from cranial (superior) to the diaphragm back to the right atrium of the heart. It begins where the two brachiocephalic veins join in the cranial (superior) thoracic region.