develops from develops from endocardial cushion interventricular septum ventricular septum intermedium http://upload.wikimedia.org/wikipedia/commons/4/4d/Gray467.png SCTID:361468003 septum intermedium Wikipedia:Septum_intermedium Endocardial cushions project into the atrial canal, and, meeting in the middle line, unite to form the septum intermedium which divides the canal into two channels, the future right and left atrioventricular orifices[Gray's via WP]. UBERON:0004153 neural crest-derived structure