Most of the blood bypasses the liver sinusoids through a shunt labeled the ductus venosus. Anatomically, the entrance of the caudal vena cava is closer to the foramen ovale then to the atrioventricular opening. Most of the blood then proceeds to the left atrium through the foramen ovale. Fetal blood leaves the left ventricle by way of the aorta, the first branch of the aorta is the coronary artery which supplies the heart with very rich blood. The second branch off the aorta, the brachiocephalic trunk, leads to the carotid arteries which head towards the brain to provide very oxygen rich blood to brain.
Blood returning to the heart from the head and front legs does so through the cranial vena cava.
Anatomically, the cranial VC is located closer to the right atrioventricular opening. The blood then exits the heart through the pulmonary trunk. However, because the fetal lungs are still undeveloped and not yet filled with air they offer great resistance. Instead the oxygen poor blood bypasses the lungs and enters the aorta through the ductus arteriosus, where it mixes with the oxygen rich blood. It is interesting to note that the anatomical relation of the ductus arteriosus is below the exits for the coronary arteries and brachiocephalic trunk.