What do veterinarians do with the dead pets?

Our veterinarian cremates animals that they have put down by charging a fee. I believe they give you the option to bury your pet if you choose and they probably have a special box to prevent contamination or something. I'm not quite sure about that though. I do feel the irresponsibility of the vet who dumped those animals should have his license taken away for good. That is just really sad on so many levels that he would do that