Interior of dorsal half of heart from a human embryo of about thirty days. (Septum primum labeled at center top.)
|- style="text-align: center;" class="hiddenStructure"
| colspan="2" |
|- style="text-align: center; line-height: 1;" class="hiddenStructure"
| colspan="2" |
|- class="hiddenStructure"
|Latin
|colspan="2"|
|- class="hiddenStructure"
|[[List of subjects in Gray's Anatomy:135#Gray.27s_page_.23|Gray's]]
|colspan="2"|[subject #135 ]
|- class="hiddenStructure"
|System
|colspan="2"|
|- class="hiddenStructure"
|Carnegie stage
|colspan="2"|[13]
|- class="hiddenStructure"
|Days
|colspan="2"|
|- class="hiddenStructure"
|Precursor
|colspan="2"|
|- class="hiddenStructure"
|Gives rise to
|colspan="2"|atrial septum
|- class="hiddenStructure"
|MeSH
|colspan="2"|[]
|- class="hiddenStructure"
|Dorlands/Elsevier
|colspan="2"|[/]
|}
The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity.
