980 



PHYSIOLOGY 



one ventricle. The right auricle receives venous blood from the 

 body by means of the vense cavse and forces it by its contraction into 

 the ventricle. From the ventricle the blood passes into the aorta, 

 whence it is carried partly by the pulmonary artery to the lungs, partly 

 by arteries to the different organs of the body. The blood which has 

 passed through the lungs and been arterialised flows through the 

 pulmonary veins to the left auricle, whence it passes into the ventricle 

 and mixes with the venous blood which is arriving from the right 

 auricle. The pulmonary circulation is thus merely a branch of the 

 general or systemic circulation. The bulbus aorta? in the frog is 



B 



C 



FIG. 367. Diagram of circulatory system in A, fish ; B, amphibian (frog) ; 



C, mammal. 



v, ventricle ; a, auricle ; K, gill capillaries ; A, aorta ; c, systemic 

 capillaries ; L, lung capillaries ; r, I, right and left auricles ; rV, IV, right 

 and left ventricles. 



divided into two parts by means of a spiral valve, by which a partial 

 separation of the blood coming from the right and left auricles is 

 effected, and the venous blood from the right auricle directed especially 

 into the pulmonary artery. 



In birds and mammals the heart has become entirely divided into 

 two halves, right and left, which have no communication with one 

 another except by way of the blood-vessels and capillaries. The 

 right heart receives the venous blood from all parts of the body and 

 sends it on to the right ventricle, whence it is forced into the lungs 

 along the pulmonary artery. In the lungs it takes up oxygen and 



