Split One's Sides Meaning

(idiomatic) To laugh hysterically

Example: 1922, James Joyce, Ulysses Chapter 13
  Madcap Ciss with her golliwog curls. You had to laugh at her sometimes. For instance when she asked you would you have some more Chinese tea and jaspberry ram and when she drew the jugs too and the men's faces on her nails with red ink make you split your sides...