part of part of anatomical conduit atrial septum primum foramen primum EMAPA:17012 Opening in the septum primum between the two atria of the embryonic heart[TMD]. UBERON:0009149 EHDAA2:0001826 Wikipedia:Primary_interatrial_foramen VHOG:0001470 The tetrapod clade develops a complete atrial septum and loses the fifth aortic arch altogether. [ISBN:978-0030223693 Liem KF, Bemis WE, Walker WF, Grande L, Functional Anatomy of the Vertebrates: An Evolutionary Perspective (2001) p.620]; [about heart development] In the various tetrapod classes ontogenetic events essentially recapitulate the phylogenetic stages.[well established][VHOG] SCTID:308852002 ostium primum UMLS:C1517292 interatrial foramen primum primary interatrial foramen NCIT:C34178 First of the two openings to perforate the septum primum between the two atria of the embryonic heart. [TFD][VHOG]