156 



STUDIES IN PHYSIOLOGY 



being carried on side by side as in the higher vertebrates, 

 are arranged, so to speak, one behind the other, or tandem, 

 and the blood is driven successively through the gill and 

 systemic capillaries by the contraction of a single ventricle. 

 Circulation in the Frog. In the frog's heart there are three 

 chambers, namely, two auricles, and a single ventricle. The 



Art 



rtery tos/ght lung - . X/ * 

 ar?as/</ri ~---; 



ft/gfrt auric/e 



Artery ton'ht or/n>^ 



flight lung 



Artery to left 

 'Jung and stin 



Artery tp left arm 

 teftaur/c/e 

 ' Mentric/e 



-/.efttvny 

 --Dorsa/aorto 



--.~Arterits to 



A/d/ieys 



Mcf/ieys 



FIG. 61. Arteries in the Circulation of the Frog. 



left auricle, as is the case in the human heart, receives the 

 blood that has taken up oxygen in the lungs, while to 

 the right auricle comes the blood from the other organs of 

 the body. Both these auricles send the blood they receive 

 into the single ventricle, and so the oxygenated blood is 

 mixed more or less with blood that has been deprived of 

 oxygen during its course through the body. By a compli- 

 cated system of valves, however, the blood that has the 



