The circulatory system is the transport system of the body,it transports various substances from tissues to tissues .Besides ,it maintains the chemical composition and physical environment of the body fluids ,essential for the metabolic reactions on which the life wheels on smoothly .Moreover , in certain animals such as birds and mammals ,it also it also maintains a body temperature to a constant level. The circulatory system of vertebrates , including mammal fall under two categories , blood vascular system and  lymphatic system .These are distinguishable on the basis of the circulatory or transporting medium; it is blood in the blood vascular system and lymph in the lymphatic system .However , the remarkable fact about the circulatory system of mammals is that it is of closed type i.e., the circulatory medium flows in vessels; even the lymph does not flow in open spaces within the body. 1.BLOOD VASCULAR SYSTEM ;The blood vascular system of the rabbit or any other mammal ,like that of other vertebrates , consists of the rabbit of higher muscular and highly contractile heart ,blood vessels,pervading every part of the body and blood vessels due to the pumping action of the heart . HEART The heart of the rabbit and other mammals, including man ,lies in the mediastinal space between the lungs ,inclined slightly to the left,.It is somewhat pear -shaped with broad -base ,lying toward the trachea ,and a narrow apex ,lying toward the diaph ragm .The heart is covered by the pericardium which is composed of two thin membranes between which is present a lymph like fluid called pericardial fluid .This fluid ensures free movement of the heart and absorbs shocks which oterwise may hurt the heart . External Structure ; The heart is extenally distinguishable into a broad anterior part called atrial or auricular part and a poterior narrow part called ventricular part .These two parts are demarcated by a transverse shallow groove like coronary sulcus which is placed far forward ,making the auricular part smaller than the ventricular part .The auricular part consists of the right and left auricles .Like wise , the ventri cular is also divided into the right and left auricles .Likewise , the ventricular part is also divided into the left and right ventricles by a logitudinal sulcus which starts from the base of the ventricular part , almost medially and extends backward obliquely toward the right not reaching the apex and therefore the left ventricle is large than the right ventricle . The sinus venosus and trunkus arteriosus are not found in the heart of the rabbit or any other mammal .The sinus venosus is merged into the right auricle and is represanted only by the sinu - auricular node[sanode] . Likewise , the trunkus arteriosus is completely merged in the left ventricle .The right auricle recieves venous or deoxygeneted blood from all parts of the body , except lungs by two superior vena cavae [anteroir vaena cavae or precavals ] and an inferior vena cava [= posterior vena cavae or postcaval ], whereas the left auricles recieves ithe oxygeneted blood from lung by two pulmanary veins The aorotid arches arise from the ventricles ; the pulmonary aorta arises from the right ventricle and the caratico- systemic aorta from the left ventricle .The pulmonary aorta and caratico -systemic aorta are joined by a liga ment called ligamentum arteriosus . The blood supply of the heart is maintain by acoronary artery and a coronery vein .