Complex sentence: Furthermore, only the jurisdiction of the Supreme Court was explicitly defined in Article III of the U.S. Constitution, and since the lower federal courts were created by Congress (as per the Judiciary Act of 1789), their jurisdiction had to be defined by Congress.
Split into simpler sentences: Furthermore, only the jurisdiction of the Supreme Court was explicitly defined in Article III of the U.S. Constitution. Since the lower federal courts were created by Congress with the Judiciary Act of 1789, their jurisdiction had to be defined by Congress.