1. Birds and mammals have four chambered heart. Which are two atria and two ventricles.

2. The two atria are separated by inter-atrial septum and the two ventricles are separated by inter-ventricular septum.

3. Oxygenated blood received by the left atria passes to the left ventricle and Deoxygenated blood received by the right atria passes to the right ventricle without getting mixed

4. The blood is circulated to the body organs through the systemic circulation and to the lungs through Pulmonary circulation.

5. This shows that birds and mammals have two separate circulatory pathways which are Systemic and Pulmonary Pathway

Advantage of Double Circulation:

1. Deoxygenated and oxygenated blood remains separated and do not mix.