belly, stomach
肚 centers on the abdomen as a physical container: the belly or stomach, especially in a bodily or anatomical sense.
肚 combines the flesh radical ⺼ (body part) with 土, which likely provides the sound ト. The character originally referred to the belly or stomach.
The flesh radical ⺼ shows this is a body part, and 土 looks like a cross-shaped container. Picture a belly as a container of earth, holding food like soil holds seeds.
For ト, imagine a toe poking a round belly: toe -> ト, and the belly jiggles.
in the heart