For some time now my dog rex has had these patches on his elbows. They are black and rough and there is no hair there. My mom thinks there just from how he lays but I've never seen that on another dog. Does anyone know what they could be? When he got his vaccinations on August 6th the vet looked him over and never said anything about them, but I will be going back in September so he can get his booster(since its his first time getting vaccs) and I will be able to ask the doctor then. Maybe I'm being crazy. I'd appreciate any comments.