No, it's not just a tiny organ pouch that requires surgery when it begins to hurt; an appendix is also additional material at the end of a book or paper.
You would think that the appendix at the end of a book came after appendix the body part, wouldn't you? After all, our bodies have been around a lot longer than books have. But you'd be wrong. The name for the organ, also known as vermiform appendix, came into use later, no doubt because it is something attached — as its Latin root is translated — to the intestines just as an appendix is attached to the end of a book.