222 



COMPAKATIVB PHYSIOLOGY, 



THE ACTION OF THE MAMMALIAN HEART. 



What takes place may be thus very briefly stated : The 

 right auricle contracting squeezes the blood through the au- 

 ricular-ventricular opening into the right ventricle, never quite 



Superior Vena 

 ' CaTa. 



Capillaries of the 

 Head, etc. 



Pulmonary Ca- 

 , pillaries. 



\]\rain Arterial 

 Trunk. 



Fig. 194. — Diagram of tlie circulation. The arrows indicate the course of the blood. 

 Thongh the pulmonary, the lower and the upper parts of the. systemic circulation 

 are represented so as to show the distinctness of each, it will be also apparent that 

 they are not independent, Eelative size of different parts of the system is only 

 very generally indicated. 



emptying itself probably; immediately after the right ventricle 

 contracts, by which its valves are brought into sudden tension 

 and opposition, thus preventing reflux into the auricle ; while 

 the blood within it takes the path of least resistance, and the 



