Therefore the children of Israel eat not [of] the sinew which shrank,.... Which was contracted by the touch of the angel, and by which it was weakened and benumbed; or the sinew of the part that was out of joint, the sinew or tendon that keeps the thigh bone in the socket, together with the flesh that covered it, or the muscle in which it is; or that sinew, others, that contracts itself and gives motion to the thigh bone to work itself: of this the Israelites eat not:which [is] upon the hollow of the thigh; or the cap of it:unto this day; when Moses wrote this history:because he [the angel] touched the hollow of Jacob's thigh, in the sinew that shrank; and very superstitiously do they abstain from it unto this day: they have a whole chapter in one of their treatises in the Misnah , giving rules concerning it; where it is forbidden to eat of it, whether in the land of Israel or out of it; whether in common food or sacrifices, even in burnt offerings it was to be taken out; and whether in cattle of the house or of the field; and both in the right and left thigh, but not in fowls, because they have no hollow, and butchers are not to be trusted; and whoever eats of it to the quantity of an olive is to be beaten with forty stripes; and because the Jews are more ignorant of this nerve, as Mercer observes, therefore they abstain from all nerves in the posteriors of animals.
Leo of Modena says , of what beast soever they eat, they are very careful to take away all the fat and the sinew which shrunk: and hence it is, that in many places in Italy, and especially in Germany, they eat not at all of the hinder quarters of ox, lamb, or goat; because there is in those parts of the beast both very much fat, and also the forbidden sinew; and it asketh so much care to cleanse the parts of these, that there are few that are able to do it, or dare to undertake it.
Cholin. c. 7. sect. 1. 3. History of the Rites, Customs, &c. of the Jews, part 2. c. 7. sect. 3. p. 91. 92.