Good thing I did!
They did not take an MRI. I guess they felt they didn't need to. They did, however, take more x-rays. The x-rays revealed a bone chip from an old injury but no current fracture. My foot is lined with deep red bruises running up and down and across the ankle. The doctor indicated that this is a sure sign of ligament damage.
They wanted to put me in a cast for a couple of weeks, but since I am driving to and from work, that won't do. Instead, they put me in what looks like a giant ski boot, to keep my foot in a neutral position and keep the ankle immobilized. I can bear weight on the ankle, since it is stable, but they want to limit lateral movement. I can remove the boot for driving and showering, but otherwise I should keep it on.
I also learned I had been using the crutch on the wrong side. Since I dispensed with the second crutch, I was using the one crutch on my right side. The doctor explained that I want to use the crutch on the side opposite the injury, that having it on the same side was causing me to put more weight on the ankle.
The doctor wanted to see me in two weeks. However, in two weeks I will be in Panamá. Thus, we are going to meet again next Thursday and then, if necessary, again when I return.
 A-ha! So I did chip my ankle a few years ago. I don't remember whether I kicked something or was hit by something, but I remember that the knobby part of my ankle was really sore and that I thought I could move something around inside. But I was ambulatory, so I felt no need to have it checked out.