Where should I place the commas in this paragraph?

When the muskrat went under the bridge I moved so I could face downstream comfortably. He reappeared and I had a good look at him. He was eight inches long in the body and another six in the tail.Muskrat tails are black and scaled flattened not horizontally like beavers' tails but vertically like a belt stood on edge. In the winter, muskrats' tails sometimes freeze solid and the animals chew off the frozen parts up to about an inch of the body......