Musar zu Bereschit 24:3

When Abraham made Eliezer swear that he would not take Isaac back to Charan, he made him swear by the organ on which circumcision had been performed, an organ that therefore had become dear to him, the symbol of the covenant with G–d (Genesis 24,3). Granted that there were good reasons then for the method employed by Abraham, why did Jacob request that Joseph, his son, perform the oath in the same manner by placing his hand on his father's organ (47,29)? Why did Joseph not mention the symbol of the oath that he made the brothers swear by when he in turn requested that the brothers swear they would take his remains with them when the time came for the redemption from Egypt (50,25)?