What is the textual structure of original Pali versions of the suttas of the Majjhima Nikaya?

I am reading Majjhima Nikaya from the translation by Bhikkhu Nanamoli and Bhikkhu Bodhi. In this book, each sutta is divided into several numerical sections. Each section consists of one or a few paragraphs. Now Bhikkhu Bodhi writes in the Preface that the numerical sections were introduced by Ven. Nanamoli and are not found in the original Pali manuscripts. I wonder whether the paragraphs also are modern creations or are actually found in the Pali manuscripts. In the case of collections of verses like Dhammapada or Udana, it is easy to separate them in old palm-leaf manuscripts. But in case of prose treatises like Majjhima Nikaya or Digha Nikaya, how the paragraphs were separated traditionally?