The whole thing consists of groups of four lines, with the second and fourth rhyming. But there would appear to be a couple of lines missing, before (or after):
He nearly supped a trough full of broth, says Mcgrath,
"He'll devour the tablecloth, if you don't hold him in."

I've looked all over the web, but haven't been able to find such a version. Anyone know anything about it?