Here is what the Kollel wrote in the Background to the Daf, Introduction to MASECHES PESACHIM:

>>There are two exceptionally short pages (Amudim) of Gemara in Pesachim (57b and 99a) due to the printers' addition of extensive Halachic summaries of the laws of the Korban Pesach (on 57b) and of the Korban Pesach Sheni (on 99a). The earliest printed, full edition of the Talmud (Venice, 1522) did not include these Halachic summaries. Instead, the remainder of the page after the end of chapter four (Daf 57b) and chapter nine (Daf 99a) was left blank, just as the remainder of the last page of every Maseches is left blank. Apparently, at the time of the Venice printing of the Talmud, "Pesach Rishon" and "Pesach Sheni" were still treated as distinct Masechtos, and it was deemed inappropriate to begin one on the same page that the other ended. At a later time these Halachic summaries were added as page-fillers. These Halachic summaries are based almost exclusively on the Rambam's rulings, with a small number of rulings culled from other Rishonim added in parentheses (which might be from a later date). It is not clear who authored these Halachic digests.<<

All the best

Kollel Iyun Hadaf