He is a very handsome boy!!!!! I have a skinny boy too! Harley will eat and he just wont gain any weight. I took him in for some testing and vet said he was just fine. They took blood and urine and told me to knock it off!! LOL!! I was really worried he was not getting enough to eat. Since we have more than one dog I would even seperate them to see how much he would eat. I thought if the bag of food said he needed 1/2 cup then he should eat that much food.
So as long as he is eating and drinking ok I don't think it's a problem. I can feel Harley's hips and spine too. You can also take him in for some testing just to make sure everything is ok.