THE HIGHER ORGANISMS 



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to both systemic and pulmonary systems of vessels, that 

 of the systemic circulation returning to the right auricle, 

 that from the pulmonary to the left. Should both 

 of these auricles discharge the blood into the ventricle 

 without some provision for separating their contents, 





FIG. 54. Diagram of the heart and the branchial arches in mammals. A 

 dotted outline of the arches of the fish is drawn for ready comparison. The 

 auricles are represented in a posterior position, as in the preceding figures. 

 (Galloway.) 



much of the advantage gained by the auricular separa- 

 tion would be lost. The substance of the ventricle is, 

 however, peculiar in its sponginess, so that as the blood 

 enters the freshly aerated portion from the left auricle 

 is kept apart from the exhausted blood of the right 

 ventricle, and when the ventricular contraction takes 



