No pattern-no problem...
The muskrat has been fleshed and tanned, right?
Turn it inside out and sew the bottom together along the legs and tail seams, don't forget to sew shut the front leg holes too...
Cut the neck along the circumference, except the back half and then turn it to where the fur side is out again...
The head will fold over like a flap now because of the weight of the head and the back of the neck has became the hinge...
You can make loops for the back of you want to, but it would look cooler if you tucked it under your sash/belt and had it peeking over the belt...