Meaning of a phrase?

Hi
Do you know the meaning of "the bottom split out of his stomach..." In this extract of O'connor's novel?
"...The boy sensed that this was the heart of his great-uncle's madness, this hunger, and what he was secretly afraid of was that it might be passed down, might be hidden
in the blood and might strike some day in him and then he would be tornby hunger like the old man, the bottom split out of his stomach so that nothing would heal or fill it but the bread of life.
He tried when possible to pass over these thoughts, to keep his vision located on an even level, to see no more than what was in front of his face and to let his eyes stop at the surface of that.”
Thank you