Answer:
vestigial valves and free tissue attached to the septum primum
Explanation:
During the ninth week of the embryo's life, it is possible to observe thinned regions in the right venous valve that further evolve as perforations. These 'vestigial valves' can be observed in the right atrium of adult hearths. Moreover, in an embryo of 25-mm, the free border of the septum primum contains a portion of free tissue that it has been proposed to be vestigial, which may be found in structurally abnormal adult hearts.
