In the tractate Eruvin ( 5a), the Gemara discusses a case where the Korah is less than 10 Tefachim from the ground ... so how do you fix it? The Gemara says you have to dig down until the height from the area you dig up to the Korah is 10 Tefachim, or handsbreadths. Rav Yosef says the length of the ditch only has to be 4 Tefachim and Abaye says 4 Amos. The Gemara conjectures that Rav Yosef holds like Rav Ami who says that a distance inward of 4 Tefachim is considered important enough to maintain the status of a Mavoy, or alleyway.The case of Rav Ami is the basis for the illustration in Rashi.The Gemara continues by outlining a case of a Mavoy that has a breach on the side toward its top.לימא בדרבי אמי ורבי אסי קמיפלגי, דאיתמר, מבוי שנפרץ מצידו כלפי ראשו, איתמר משמיה דרבי אמי ורבי אסי, אם יש שם פס ארבעה מתיר בפירצה עד עשר, ואם לאו, פחות משלשה מתיר, שלשה אינו מתיר, לרב יוסף אית ליה דרבי אמי, לאביי לית ליה דרבי אמי.The Gemara suggests: Let us say that these Amora’im disagree with regard to the ruling of Rav Ami and Rav Asi. As it was stated: If the side wall of a Mavoy was breached toward its entrance, what is the Halacha? It was stated in the name of Rav Ami and Rav Asi: If an upright board (Pas) 4 Tefachim wide remains of the original wall, the Korah or Lechi at the entrance to the Mavoy renders it permitted to carry in the Mavoy even if there is a breach of up to 10 Amos wide. And if not, the following distinction applies: If the breach is less than 3 Tefachim, it is permitted to carry in the Mavoy, (based on the principle of Lavud, which means that such a small gap is considered Halachically insignificant). If the breach is 3 or more Tefachim, it is not permitted to carry. The Gemara proposes that Rav Yosef holds like Rav Ami, and Abaye does not hold like Rav Ami.רש״ישנפרץ מצידו אחד - מן הכתלים שבצד ארכו:כלפי ראשו - סמוך לקורה הימנה ולפנים:אם יש שם פס ד׳ - אם נשתייר מן הכותל או עשה פס ד׳ במקום הפרצה סמוך לקורה:The picture illustrates the above comments of Rashi. We see a Mavoy that is breached toward its top (Klapei Rosho), and there is a Korah that extends the width of the alleyway on the very top. There is a “Pas” (or the remnant of the wall) toward the top right which is 4 Tefachim into the “Pirtzah” next to the “Korah.” Problem: The word “Pas” here is situated in the wrong place, (opposite the “Pirtzah”). Also, there is too much space between the Korah and the Pas. See picture below (Peirush Chai) which shows the Pas joined together with the Korah at a right angle.This is the case of Rav Ami of the broken wall. (Peirush Chai)The wall portion that says “4” is either a “Pas” (upright board) or what remains of the original wall. It is attached to the “Rosh.” This diagram and all the other modern diagrams such as in Artscroll (commentary section) and the Oz Vehadar edition all have the remaining wall area (or the Pas) situated under the Korah. There is no space between the Korah and the side wall. The key in the Rashi is where it says דכיון דישהכשר אורך מבוי מן הקורה עד הפירצה . This indicates that there is no gap.Piryo B’Ito also shows the Pas extending to being underneath the Korah “MiTachas L’Korah.”Manuscripts: I checked seven manuscripts of Rashi on Eruvin. All had a diagram preceded by the word “Kazeh.” Below are a few examples. Conclusion: A diagram was drawn by Rashi, who included the word “Kazeh.” Over time, it was represented in different ways. The diagram in the Vilna Shas thus canonized two obvious errors that were introduced since Rashi’s time.