'Hollow' in the Bible

and he seeth that he is not able for him, and he cometh against the hollow of his thigh, and the hollow of Jacob's thigh is disjointed in his wrestling with him;

therefore the sons of Israel do not eat the sinew which shrank, which is on the hollow of the thigh, unto this day, because He came against the hollow of Jacob's thigh, against the sinew which shrank.