The first 10 amendments to the Constitution are referred to as the “Bill of Rights” Article 4 is most defiantly a part of the Bill of Rights. How can you have written these two statements simulatenously without your head exploding? ;)
Article 4, the one you cited, is not an Amendment to the Constitution. It is Article 4 of the Constitution.
Each article of the constitution is called an amendment! Article 4 is the 4th Amendment. Haven’t you ever read the Constitution?
http://www.nara.gov/exhall/charters/billrights/billrights.html