If your dog becomes lethargic and does not want to eat or drink then I would suggest taking him to the vet and have him x-rayed. Usually the vet will tell you to give him soft food and Pedialite to drink and watch for the bone to come out in his feces.
Small pieces of bones most likely will not cause any damage to your dog. If you are concerned, you can try to give him a little bit of canned food to help coat the stomach and move through faster.