I used to work in a place where two of my colleagues (one of them my supervisor) used to interrupt each other a lot, often degenerating to heated, unproductive

I used to work in a place where two of my colleagues (one of them my supervisor) used to interrupt each other a lot, often degenerating to heated, unproductive arguments. I started using a whiteboard for all our meetings. For whatever issue we were discussing, I would first write it down. I then proceeded to function as a moderator. Whenever one of my colleagues wanted to interrupt, I made sure to keep him/her at bay by pointing out that I wanted to let other colleague finish first. Whenever one of them would drift away from the main issue, I would point out to the topic on the whiteboard and emphasize that we needed to keep the conversation focused on that issue. It worked wonders. In general, I've noticed that having a "meeting leader" that keeps the meeting on track with the agenda and functions as a moderator really improves the quality of the meetings and even makes them shorter.