Why are thighs important?

I know it sounds like a silly or weird question, but I'm serious. >Genesis 24:2 >------------ >One day Abraham said to his oldest servant, the man in charge of his household, “Take an oath by putting your hand under my **thigh**. >Genesis 47:29 >------------- >As the time of his death drew near, Jacob called for his son Joseph and said to him, “Please do me this favor. Put your hand under my **thigh** and swear that you will treat me with unfailing love by honoring this last request: Do not bury me in Egypt. >Leviticus 7:33 >-------------- >The right **thigh** must always be given to the priest who offers the blood and the fat of the peace offering. >Revelation 19:16 >---------------- >On his robe at his **thigh** was written this title: King of all kings and Lord of all >lords. Why is the thigh important?