PLATE 4 
EXPLANATION OF FIGURES 
7 Internal bundles of the right atrium of the human heart, posterior view. 
The vena cavae have been opened through their posterior walls. The inferior 
vena cava is spread widely open. The endocardium has been removed. 
8 Internal bundles of left atrium of the human heart, posterior view. The 
posterior wall of the atrium has been cut and widely opened. The endocardium 
has been removed. 
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