The prohibition of eating the sinew of kosher animals's thigh

Beresheet 32:32 (33) Therefore Benai Yisrael eat not [of] the sinew which shrank, which [is] upon the hollow of the thigh, unto this day: because he touched the hollow of Ya'akov (יעקב)'s thigh in the sinew that shrank.

The prohibition of eating the sinew of kosher animal's thigh ("gid ha nasheh")

The two primary tissues are forbidden in the hindquarter:

• The Inner sinew - the Sciatic nerve - which branches out from the rear of the spinal column and runs down the inner side of the kosher animal's leg, is forbidden by the Torah.

• The outer sinew - the common peroneal nerve - which runs across the thigh on the outer side of the kosher animal's leg, is forbidden by the sages (chullin 91a)

Every last trace of these nerves must be removed, and the fat covering the sciatic nerve which look like strings and certain other veins are removed.

The pertinent halachot regarding this prohibition are found in Shulchan Aruch Yoreh De'ah 65