The belly, in Psalms 16:4, signifies the interior understanding.

In Genesis 25:23, it signifies conception of interior and exterior good. (Arcana Coelestia 3293)

In Isaiah 46:3, the belly signifies from the beginning of the church. (Arcana Coelestia 4918[2], 5550)

The belly signifies people who are being regenerated, and people who have been regenerated. (Apocalypse Explained 710[3])

(References: Apocalypse Explained 622)