Blood circulation was discovered by William harvey. In case of vertebrates, blood circulation is of closed type, which can be grouped into two categories :
(a) Single circulation (b) Double circulation

# Double circulation in mammals can be divided into three parts :
(1) Cardiac circulation : The amount of blood present in the heart. Its value is 7%.
(2) Pulmonary or lesser circulation : The amount of blood present in the surrounding of lungs and pulmonary blood vessels. Its value is 9%.
(3) Systemic or greater circulation : The amount of blood which circulates in the rest part of the body. Its value is 84%. It can be divided into three parts –
Arterial circulation – 15%
Capillary circulation – 5%
Venous circulation – 64%