I cut one of the arms off...I cut it so that the stitching holding it to the body came with the arm, to help prevent it from unraveling.
Then I cut along the sleeve side seam starting form the shoulder and moving toward the cuff. I saved enough near the cuff to make a rolled turtle neck and a breast piece. I used another doggie clothing article to measure how far to cut. But you could measure your dog. It needs to open up just before his front legs.
Slide it on over his head! Its pretty fashionable don't you think?
I may crochet around the edges to finish it off and perhaps a little flap and button under the belly to help hold it in place. He wore it yesterday in his crate on our trip to Boston. Very comfy for sleeping in the car!
Kathy