The<unk>  of the developing heart gives rise to the trabeculated parts of the left and right ventricles.  In contrast, the smooth parts of the left and right ventricles originate from the embryological bulbus cordis.
The<unk>  becomes divided by a septum, the septum inferius or ventricular septum, which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow.
Its dorsal part increases more rapidly than its ventral portion, and fuses with the dorsal part of the septum intermedium.
For a time an interventricular foramen exists above its ventral portion, but this foramen is ultimately closed by the fusion of the aortic septum with the ventricular septum.
Primitive ventricle
Arachnoid mater
Cerebral aqueduct
Fourth ventricle
Olfactory foramina
Aortic arches
Prosencephalon
Growth cone