The great Swiss mathematician Ludwig Schläfli (1814-1895) left after his death more than three hundred and fifty notebooks. They include mathematical studies and new results, as well as works about classical mathematical texts and a priori more surprising fields like modern European languages, as well as classical and oriental languages, theology and philosophy. Those notebooks were bequeathed to the Swiss National Library where they are still preserved today. Among them, one finds archival fonds No 254, namely two notebooks where Schläfli presents his analysis of Euclid's Elements. Those abundantly illustrated and annotated notebooks show their author's attraction to geometry and how meticulous a copyist he was. Many indices suggest that they go back to Schläfli's youth, when he started his theology studies at the University of Bern. This thesis presents an historical introduction and a critical edition of the two notebooks No 254.