In his book Krayti Uflayti (65:16), Rav Yonatan Eibeschitz tells a story of a renowned and learned butcher an expert at nikur, removing the sciatic nerve as required by the halacha. This butcher announced one day that the nerve customarily removed was the wrong one. Rav Yonatan comments, “I investigated the matter thoroughly and found that the nerve which he claimed was the correct one is found only in male animals and not females. I then showed him the Smag (Sefer Mitzvot HaGadol), who writes that the prohibition of eating the sciatic nerve applies to both male and female.”
Rav Yonatan’s conclusion, however, is perplexing. For it is clear from the final line of the Smag that it is referring to the obligation of people – both male and female – to follow this law. It is not discussing the gender of the animals at all!
Various possibilities have been offered to resolve this difficulty. One approach posits that Rav Yonatan meant the Behag (Ba’al Halachot Gedolot), not the Smag. In fact, the Behag does write that the sciatic nerve is present in both males and females.
Another approach points to one of the early copies of the Krayti Uflayti, which was printed during the lifetime of Rav Eibeschitz, and in which there is a correction in his handwriting. It replaces the letters samech mem gimmel (an acronym for Sefer Mitzvot HaGadol) with the letters samech hey nun, which is an acronym for seder hanikur (the procedure for nikur). In fact, when the Tur describes the procedure for nikur (Yoreh Deah 65), he mentions removing the sciatic nerve in both males and females.
An objection, however, has been raised to both of these approaches. When the Behag and the Tur mention males and females, it is possible that they are referring to nicknames for different nerves (along the lines of today’s male and female electrical connectors), rather than to the gender of the animals themselves.
A different refutation of the butcher can be found in Rashi (Chullin 90a, s.v. hane’echalin). He mentions that the prohibition of eating the sciatic nerve applies to a sin offering (korban chatat); we know that only female animals may be used for sin offerings. This is not a conclusive proof, though, as it is possible that Rashi is referring to a communal sin offering (chatat ha-tzibbur). This offering is always of a male animal. Thus the question as to whether the butcher’s claim could have been correct remains an open one.