Genesis 32:32

(32) The sinew which shrank.—This translation has much authority in its favour, as the LXX. render the sinew that became numb, and the Vulgate the sinew that withered. More probably, however, it is the proper name for the large tendon which takes its origin from the spinal cord, and extends down the thigh unto the ankle. Technically it is called nervus ischiaticus, and by the Greeks was named tendo Achillis, because it reaches to the heel. Jewish commentators notice that this was the second special ordinance imposed upon the race of Abraham, circumcision having been enjoined upon them by God, while this grew out of an historical event in the life of their progenitor, to the reality of which it bears remarkable testimony.