Tosefta zu Chullin 7:9

The [prohibition against eating] the sciatic nerve applies to mixed-breeds, [and] applies to two thighs -- the left thigh and the right thigh. Rabbi Yehuda says, it only applies to one, and logic dictates that it is the right [thigh]. This is the general rule: Whatever has a "spoon of the thigh" (Gen. 32:33), [the prohibition against eating] the sciatic nerve apply to it. Whatever does not have a "spoon of the thigh," [the prohibition against eating] the sciatic nerve does not apply to it. It applies to a fetus, and its fats are forbidden, the words of Rabbi Meir. Rabbi Yehuda says, it does not apply to a fetus. And its fats are permitted, the words of Rabbi Eliezer. And the Sages say, *they are trusted with respect to it (*i.e., butchers are trusted to have removed the sciatic nerve (see Hul. 7:1)) and with respect to [having removed the forbidden] fats. One who sends a cut-up thigh to his friend is required to remove the sciatic nerve [before sending it]. [One who sends a] whole [thigh] does not need to remove the sciatic nerve from it. One who buys a cut-up thigh from the butcher does not need to remove the sciatic nerve from it [since the butcher is trusted to have already removed it], but [one who buys] a whole [thigh] needs to remove the sciatic nerve from it. One who sells a cut-up thigh to an idolater does not need to remove the sciatic nerve from it, as long he does not sell it in front of another Jew, because he (i.e., the other Jew) may come back and buy it from him (i.e., from the idolater, in the belief that the sciatic nerve had been removed). And on account of two things, they said, "We do not sell carrion or tereifah meat to an idolater": (1) because he may return and feed it to a Jew; [and] (2) another thing, is that we are not permitted to cause someone to be mistaken about what he is eating (i.e., the idolater would assume that Jews do not sell carrion or tereifahs and would come to be deceived, cf. Hul. 94a:5). And on account of two things, they said, "A Jew may not say to an idolater, 'Buy meat for me'": On account of [the idolater potentially being sold] carrion-flesh or tereifah. And one other thing: On account of force (i.e., the idolater taking the meat by force rather than paying for it (Hul. 94a:20-94b:1)).