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The atrial chambers are divided by two septa. The first to form is the septum primum, which grows down to fuse with the endocardial cushions. The diagram shows a lateral view of the septum. In the SEM, it is viewed from above. 
                     Species: Mouse 
                     Day Gestation: 14 
             Approx. Human Age: 8 weeks 
                                   View: 
                 Atrial Septation
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