VENOUS SYSTEM

1. It is collecting system formed by the uniting branches as smaller and then larger veins and venacava leading to the heart.
2. Blood from anterior part of the body is returned to heart by two (in general mammals) anterior venacavae (or precavals), while from the posterior part by single posterior venacava (or postcaval).
3. Human Heart receives blood only through two great veins: Superior vena cava from anterior part and inferior vena cava from posterior part.
4. Precaval is formed by the union of common' Jugular vein, subclavian vein, intercostal vein and anterior azygos vein.
5. The jugular veins as external and internal jugulars bring blood from head and neck. The right and left external jugulars are connected through jugular anastomosis. The subclavian vein brings blood from forelimbs and shoulder.
6. A pair of pulmonary veins come from lungs and open by a common pore into left auricle.
7. In posterior part the main vein is dorsal vein which leads to heart as postcaval. This is formed by the union of one renal vein from each kidney, one hepatic vein, gonadal veins and veins from hind limbs like sciatic and femoral veins.
8. As speciality the venous system forms portal system in some parts of the body.