 But Rabbi Yitzhak Alfasi explained [it as] that bone which holds fast all the [other] bones, while the "Kol Bo" has written Rashi's explanation under his name.Yet, the [book known as] "Sefer Mitzvot Gedolot" ("Hasemag") has written [under] the prohibitive command # 138, "Tarba de-Aqlivusta"