CIRCULATION 



291 



EXTRA-CARDIAC FACTORS MAINTAINING CIRCULATION 



In considering the flow of blood through the vessels due to 

 the distribution of pressure in arteries and veins, it must be 

 remembered that the central pump or heart is not the only 

 factor maintaining it (fig. 133). 



The thorax in the movements of respiration is a suction 



INTRACRANIAL CIRCULATION 



PULMONARY CIRCULATION 



ABDOMINAL CIRCULATION 



CIRCULATION IN LIMBS 



FIG. 133. Scheme of the Circulation, modified from Hill, to illustrate the influ- 

 ence of the various extra-Cardiac Factors which maintain the Flow of Blood. 



pump of considerable power, which draws blood into the heart 

 during inspiration. While the auricles may be regarded as 

 the cisterns of the heart, the abdominal blood vessels are 

 the great blood reservoir, and the diaphragm contracting in 

 inspiration presses the blood from this reservoir up into the 

 thorax and heart. When, in intermittent muscular exercise, 

 the abdominal muscles are tightened and the respiratory move- 



