350 MANUAL OF ZOOLOGY SECT. 



two chambers, right and left, by a partition. Into the right 

 auricle the sinus venosus drives the venous blood from the 

 great veins ; into the left open the pulmonary veins, bring- 

 ing the oxygenated blood from the lungs. Both the auricles 

 open into the ventricle, the cavity of which is partly divided 

 by a septum. From the ventricle are given off the main 

 arteries (systemic arteries) which branch throughout all parts 

 of the body, and the pulmonary arteries, which pass direct 

 to the lungs. By various arrangements of the parts which 

 need not be described at present, the venous blood from 

 the right auricle is mainly guided into the pulmonary 

 arteries, and passes to the lungs to obtain oxygen and part 

 with its carbon dioxide ; while the arterial blood is mainly 

 guided to the systemic arteries. A certain degree of mixing, 

 however of the venous and arterial currents takes place as 

 they pass through the ventricle. 



In the Rabbit this mixing of the arterial and venous 

 currents is entirely prevented, owing to the ventricle being 

 completely divided into two chambers right and left. 

 There is no distinct sinus venosus. The right auricle 

 opens into the right ventricle and fills it with venous 

 blood from the great veins. From the right auricle the 

 blood is driven through a pulmonary artery to the lungs. 

 From the lungs the oxygenated blood is returned by means 

 of the pulmonary veins to the left auricle ; from the left 

 auricle it enters the left ventricle, and from the latter is 

 driven out through the system of systemic arteries to all 

 parts of the body. There are thus two distinct currents of 

 blood constantly passing simultaneously through the heart, 

 but entirely cut off from one another, viz., a venous current 

 on the right side and an arterial on the left. The blood of 

 the Rabbit has a much higher temperature than that of the 

 Dog-fish or Lizard, 



