SECT. IX. PHYSIOLOGY. 87 
vessels, readily explains the formation of the 
sinuses of Valsalva. 
ecru. The French physiologists have had long 
disquisitions on the unequal capacities of the 
cavities of the heart, but they do not séem to 
have arrived at any thing certain on the subject. 
Senac’s idea that the right ventricle is not so 
completely emptied by its systole as the left, 
appears plausible; for as both cavities transmit 
the same quantity of blood, it is reasonable to 
‘suppose that a residue of it should be left in the 
right ventricle after it has contracted. Some have 
alleged that the size of the right ventricle is 
affected after death by the contraction of veins 
propelling the blood into it. 
ccm. When the two ventricles of the heart 
contract, its apex strikes against the fifth and 
sixth ribs; this percussion may generally be felt 
externally, but lying on the right side, or deep 
inspiration, renders it either obscure or imper- 
ceptible. During infancy, the pulsations of the 
heart rise as high as a hundred and twenty in 
the minute, in old age they sink as low as sixty. 
cctv. The expansion and contraction of the 
cavities of the heart are audible externally, either 
by the application of one ear opposite the region 
of the heart, or still better by the stethoscope 
invented by Laennec. “ In a well-proportioned 
