ATRIUM 



VCNTHICL£ 

 SINUS VCNOSUS 



FIG. 119. FISH 



RIGHT ATRIUM 



LEFT ATRIUM 

 SINUS ySNOSUS 

 VENTRICLE 



FIG. 120. AM PH IB I A ft 



RIGHT ATRIUM 



LEFT ATRIUM 



RIGHT VENTRICLE 



LEFT VENTRICLE 



FIG. 121. REPTILE 



RIGHT ATRIUM 



LEFT A TRIUM 



RIGHT VENTRICLE 



LEFT VENTRICLE 



FIG. 122. BIRD 



Figs. 119, 120, 121, 122. — A series of vertebrate hearts and diagrams to show the 

 paths of the blood. The reptilian heart represented in Fig. 121 is that of a lizard; 

 in many other reptiles the wall separating the ventricles is complete. Note the pro- 

 gressive steps in the organization of parts of the heart to provide for the propulsion 

 of the blood to, and the reception of blood from, the lungs. 



